Fuel injector and fuel injection system

申请号 US10321429 申请日 2002-12-18 公开(公告)号 US06719224B2 公开(公告)日 2004-04-13
申请人 Shigeiku Enomoto; Moriyasu Goto; Tetsuo Morita; Masaaki Kato; Hisaharu Takeuchi; 发明人 Shigeiku Enomoto; Moriyasu Goto; Tetsuo Morita; Masaaki Kato; Hisaharu Takeuchi;
摘要 A fuel supply system has a pump, a common rail, and injectors. Pressurized fuel is stored in the common rail. The common rail distributes the fuel to the injectors. A liquid fuel and a liquefied gas fuel such as dimethyl ether and a liquefied petroleum gas may be used as a fuel. In each injector, a valve element is actuated directly by an electromagnetic actuator. The injector has a low pressure chamber for decreasing a biasing force which acts on the valve element in a valve closing direction. The valve element can be divided for replacement. The injector has means for suppressing the bounce of the valve element. A hydraulic unit which utilizes the fuel suppresses the bounce of the valve element. The fuel supply system is connected to a refrigerating cycle. The fuel leaking from the fuel supply system is cooled and again liquefied by the refrigerating cycle.
权利要求

What is claimed is:1. A fuel injector comprising:an elongated valve element;a spring for urging the valve element in a valve closing direction; andan electromagnetic actuator having an armature integral with an end portion of the valve element and adapted to be attracted to a stator against the biasing force of the spring when a coil is energized, wherein:an oil pressure damper chamber is formed between an end face of the armature and an end face of the stator;one of the end face of the armature and the end face of the stator is generally flat;the other one of the end face of the armature and the end face of the stator includes an annular protuberance, which axially protrudes from the rest of the other one of the end face of the armature and the end face of the stator and radially inwardly defines the oil pressure damper chamber; andat least one cutout portion is formed in the annular protuberance to extend through a wall of the annular protuberance in a direction generally perpendicular to an axial direction of the valve element.2. The fuel injector according to claim 1, further comprising a casing member which receives the valve element therein, wherein the valve element forms a large-diameter portion as a spring retaining portion at an intermediate position thereof, and the spring is disposed between the spring retaining portion and one end face of the casing member.3. The fuel injector according to claim 2, further comprising a member which defines an armature chamber which receives the armature therein, wherein the oil pressure damper chamber is formed on one side of the armature and an armature moving space for allowing the armature to move away from the stator and drawing out the valve element is formed on the other side of the armature.4. The fuel injector according to claim 1, wherein the fuel injector is supplied with a liquefied gas fuel and injects the supplied liquefied gas fuel from a nozzle hole in response to an opening operation of the valve element.5. The fuel injector according to claim 1, wherein the other one of the end face of the armature and the end face of the stator is generally flat except the annular protuberance.6. The fuel injector according to claim 1, wherein the annular protuberance extends along an outer peripheral edge of the other one of the end face of the armature and the end face of the stator.7. The fuel injector according to claim 1, wherein the annular protuberance radially communicate between the oil pressure damper chamber and a space located radially outward of the annular protuberance when the one of the end face of the armature and the end face of the stator is engaged with the annular protuberance of the other one of the end face of the armature and the end face of the stator.8. A fuel injector comprising:an elongated valve element;a spring for urging the valve element in a valve closing direction;an electromagnetic actuator having an armature integral with an end portion of the valve element and adapted to be attracted to a stator against the biasing force of the spring when a coil is energized, wherein an oil pressure damper chamber is formed between an end face of the armature and an end face of the stator;a casing member which receives the valve element therein, wherein the valve element forms a large-diameter portion as a spring retaining portion at an intermediate position thereof, and the spring is disposed between the spring retaining portion and one end face of the casing member;a spring retaining member constituted by a plurality of split pieces mounted on the large-diameter portion of the valve element; anda shim member mounted on the large-diameter portion of the valve element, the shim member being placed on a spring retaining face side of the spring retaining member and adapted to unite and fix the plural pieces of the spring retaining member.9. The fuel injector according to claim 8, wherein the oil pressure damper chamber is defined by a recess, the recess enclosed by a stepped portion being formed in at least one of the end face of the armature and the end face of the stator which are opposed to each other.10. The fuel injector according to claim 9, wherein the stepped portion provides a cutout portion, the armature comes into abutment against the stator through contact of the stepped portion, when the armature is attracted to the stator.

说明书全文

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Applications No. 2001-307355 filed on Oct. 3, 2001, No. 2001-308495 filed on Oct. 4, 2001, No. 2001-317688 filed on Oct. 16, 2001, No. 2001-384772 filed on Dec. 18, 2001 and No. 2002-14338 filed on Jan. 23, 2002 the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel injection system and a fuel injector in an internal combustion engine (hereinafter referred to simply as engine).

2. Related Art

For example, in the case of a common rail type fuel injection system applied to a diesel engine, there usually is employed a fuel injector having a two- or three-way solenoid valve. In connection with such a fuel injector, for example the technique disclosed in JP-A-9-42106 is well known. According to this technique, fuel of a high pressure is introduced into a pressure control chamber provided on an opposite-to-nozzle holes side of a valve element, and the valve element is actuated by allowing the high-pressure fuel present in the pressure control chamber to leak to a low pressure side at every fuel injection. However, in the case of the fuel injector disclosed in the above publication, there occurs leakage of the high-pressure fuel from the pressure control chamber at every fuel injection. There also is a problem that the number of components increases and the structure becomes complicated.

Recently there has been an increasing demand for reducing the cost of the fuel injector. To meet this demand, that is, for reducing the number of components which constitute the fuel injector, a study is being made about a direct-acting type fuel injector in which a valve element is actuated directly by an electromagnetic drive unit.

On the other hand, as an alternative to gas oil and taking the volatilizability, ignitability and combustibility of fuel or emission into account, there recently has been studied the use of liquefied gas fuels such as dimethyl ether (DME) and liquefied petroleum gas (LPG) with a cetane number improving additive incorporated therein. LPG as referred to herein means a liquefied petroleum gas with a cetane number improver incorporated therein unless otherwise specified. In case of using a liquefied gas fuel, the fuel is apt to vaporize because of a low boiling point and the amount of fuel leaking from the fuel injector tends to increase. Therefore, it becomes necessary to provide a recovery system for recovering fuel leaking from the fuel injector. For example, as is disclosed in JP-A-11-22590, it is necessary to provide a purge tank for the recovery of vaporized liquefied gas fuel and a compression pump for compressing and liquefying a gaseous liquefied gas fuel recovered into the purge tank. As a result, there arises the problem that the cost of the fuel injection system concerned increases. To solve this problem, as noted above, it is proposed to use, for example, such a direct acting type fuel injector

100

as shown in FIG.

10

and thereby decrease the amount of fuel leaking from the fuel injector

100

.

In the fuel injector

100

shown in

FIG. 10

, a valve element

101

extends vertically in the figure and an armature

102

is integrally provided at an upper end of the valve element

101

by laser welding for example. Holes

103

a

and

104

a

are formed in a casing

103

and a valve body

104

, respectively, and the valve element

101

is received into the holes

103

a

and

104

a

. A stator

105

is disposed in opposition to the armature

102

. When a coil

106

is energized and the armature

102

is thereby attracted to the stator

105

, the valve element

101

lifts upward in

FIG. 10

against the biasing force of a spring

107

, whereby nozzle holes

108

are opened and high-pressure fuel fed from a common rail system is injected from the nozzle holes

108

. In such a fuel injector

100

as shown in

FIG. 10

, the number of components is small and hence it is possible to attain the reduction of cost. Moreover, in the fuel injector

100

shown in

FIG. 10

, it is possible to decrease the amount of leaking fuel and therefore it becomes unnecessary to use a purge tank for the recovery of leaking fuel and a compression pump.

However, in the fuel injector

100

shown in

FIG. 10

, since the valve element

101

is actuated directly by an electromagnetic drive unit, it is necessary for the electromagnetic drive unit to actuate the valve member

101

against a force developed by an oil pressure acting on the valve element

101

. Accordingly, for enhancing the injection pressure of fuel injected from the fuel injector

100

, it is necessary to increase the size of the electromagnetic drive unit and thereby increase the driving force. However, the space ensured in an engine mounting portion is limited and therefore the size of the electromagnetic drive unit and that of the fuel injector

100

are limited. As a result, a maximum fuel injection pressure of about 30 MPa is a limit at present and a further increase of pressure is difficult.

For example, in connection with a common rail type fuel injection system for a diesel engine, there is known such a fuel injector as is disclosed in JP-A-10-18934. On the other hand, as a direct-acting type fuel injector there is proposed one illustrated in FIG.

16

. In the same figure, components equal to those illustrated in

FIG. 10

are identified by like reference numerals.

In an engine mounted on a vehicle, fuel injectors are replaced at every about 100,000 km running. In this case, for attaining the reduction of cost, it is proposed to remove a retaining nut

110

of a fuel injector

100

and replace only a nozzle portion

104

located at the tip of the injector. However, an armature

102

is fixed to a valve element

101

and the diameter of the armature

102

is usually larger than that of a hole

103

a

. This is for obtaining a satisfactory electromagnetic performance. Therefore, at the time of replacement of the nozzle portion

104

, not only the removal of the retaining nut

110

, but also a disassembling work for an electromagnetic solenoid portion

111

is required, resulting in that the maintainability is deteriorated. Thus, an improvement is desired.

FIG. 28

shows a fuel injector

100

in the related art. When a valve element

101

is opened, the valve member moves until abutment against a valve opening stopper

112

. At this time, the valve element

101

bounces as a reaction of its abutment against the stopper

112

. In many cases, for example the layout of intake/exhaust valves in an engine head portion requires the valve element

101

to be long, with the result that the valve member becomes heavy. Particularly, in the case of such a liquefied gas fuel as DME, the bounce of the valve element

101

becomes large. Such a bounce of the valve element

101

obstructs an accurate adjustment of fuel quantity.

In a fuel injector

100

shown in

FIG. 33

, when a valve element

101

opens, it strikes against a stopper

111

and bounces. Due to this bouncing during valve opening, an injection quantity Q becomes wavy relative to a pulse width T, thus making injection control difficult.

Further, when a coil

106

is de-energized, with loss in attraction of an armature

102

by a stator

105

, and the valve element

101

closes with the biasing force of a spring

107

, the valve element

101

strikes against a sheet portion of a nozzle body

104

and causes bouncing. Due to this bouncing in valve closing, there occurs re-injection (secondary injection) after the end of injection, thus resulting in deterioration of the injection characteristic.

On the other hand, in many cases, the valve element

101

is required to be long for example due to the layout of intake/exhaust valves in an engine head, resulting in that the valve element

101

becomes heavy and there occurs markedly such bouncing as referred to above.

Particularly in the case of such liquefied gas fuels as LPG and DME, since their viscosities are low, not only the bouncing of the valve element

101

becomes large, but also the time taken until damping of the bounding becomes long and the aforesaid inconvenience occurs markedly.

A leak fuel recovery system is disclosed, for example, in JP-A-11-22590. An outline thereof will now be given with reference to FIG.

35

. In the same figure, fuel stored in a fuel tank

550

is discharged from a low pressure pump

551

and is compressed to a high pressure by means of a high pressure pump

552

, then is fed to a common rail

553

. Connected to the common rail

553

are fuel injectors

554

in a number corresponding to the number of engine cylinders.

Fuel leaking from the high pressure pump

552

and fuel injectors

554

is once recovered into a fuel recovery tank (purge tank)

555

, then is liquefied by a fuel compressor

556

and is returned to the fuel tank

550

.

In the construction of

FIG. 35

it is necessary to provide a leak fuel recovery system comprising the fuel recovery tank

555

and the fuel compressor

556

, thus giving rise to the problem that the construction becomes complicated and the cost increases.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved fuel injector.

It is another object of the present invention to provide a fuel injector having a compact construction and capable of handling high pressure fuel.

It is a further object of the present invention to provide a fuel injector improved in maintainability.

It is a still further object of the present invention to provide a fuel injector wherein the bouncing of a valve member is suppressed.

It is a still further object of the present invention to provide a liquefied gas fuel supply system having a high utility.

In one aspect of the present invention there is provided a fuel injector which is provided with an oil pressure reducing means. The oil pressure reducing means reduces an oil pressure acting in a nozzle hole closing direction which oil pressure is included in an oil pressure acting on a valve element. Since the oil pressure acting on a valve element in the nozzle hole closing direction is reduced, the force required for an electromagnetic drive unit to actuate the valve element decreases. Consequently, even when the valve element is actuated directly by the electromagnetic drive unit, the pressure of fuel fed to the fuel injection system concerned can be increased while retaining the constitution of the electromagnetic drive unit for example. Thus, even when the valve element is actuated directly by the electromagnetic drive unit, the pressure of injected fuel can be further increased without an increase in size of the constitution.

The above fuel injector according to the present invention is what is called an actuator direct acting type fuel injector wherein an armature is attracted to a stator upon energization of a coil and consequently a valve element integral with the armature moves to open the nozzle hole. In this construction, the valve element is provided in a divided manner into a rod portion and a valve portion, which are connected together through a connecting member. According to this construction, when the armature is attracted to the stator upon energization of the coil, the valve portion moves together with the rod portion to open or close the nozzle hole. With the rod portion, the valve portion and the connecting member connected to one another, the rod portion is accommodated in a first casing and the valve portion is accommodated in a second casing.

According to the above construction, if the first and second casings are disassembled and the connecting member is disconnected, it becomes possible to remove only the valve portion exclusive of the rod portion. Therefore, when the valve portion is to be replaced after a long-term use of the fuel injector, the replacing work efficiency is improved. As a result, it is possible to realize a construction superior in maintainability of an actuator direct acting type fuel injector.

In the above construction, when the coil is energized, the armature is attracted to the stator against the biasing force of a spring and the valve element moves to its closing position. In this case, since an oil pressure damper chamber is provided between an end face of the armature and that of the stator, the bouncing of the armature and valve element is suppressed when the valve opens by virtue of a damper effect. Therefore, it is possible to keep the fuel injection quantity under control.

According to the present invention, when an electric actuator (e.g., an electromagnetic solenoid or a piezo-electric actuator) causes an armature (driver) to displace in the valve opening direction, fuel having an accumulated pressure is injected from a nozzle. As a result of this injection, the pressure decreases on the nozzle side rather than in a throttle portion and the pressure in a second chamber becomes lower than that in a first chamber. Since the second chamber lower in pressure lies on the side (in the valve opening direction) opposite to the nozzle, a pressure receiving portion is urged to the opposite-to-nozzle side (in the valve opening direction) by virtue of a differential pressure. With this urging force based on the differential pressure, the bouncing of the valve element when opened is suppressed. When the electric actuator causes the armature to displace in the valve closing direction, the injection of fuel is stopped. Once the fuel injection is stopped, the flow of injected fuel is cut off suddenly, so that the pressure on the nozzle side rather than in the throttle portion increases to a higher level than the pressure of accumulated pressure fuel and the pressure in the second chamber becomes higher than that in the first chamber. At this time, the first chamber which is low in pressure lies on the nozzle side (in the valve closing direction), so that the pressure receiving portion is urged to the nozzle side (in the valve closing direction) by virtue of a differential pressure. With this urging force induced by the differential pressure, the bouncing of the valve element when closing is suppressed. Since the bouncing in valve opening and closing is thus suppressed, the injection characteristic is improved. Even in the case where the valve element is long and heavy, it is possible to improve the injection characteristic because the occurrence of bounce is suppressed by the differential pressure.

Further, even where the fuel viscosity is low as in such a liquefied gas fuel as LPG or DME, since the occurrence of bounce is suppressed by the differential pressure, it is possible to improve the injection characteristic.

According to a further feature of the present invention, fuel having an accumulated pressure is injected from the nozzle upon displacement of the armature in the valve opening direction by the electric actuator. With this fuel injection, the fuel flows from the first chamber to the second chamber formed on the side (in the valve opening direction) opposite to the nozzle through a passage formed along the side face of the armature. As a result of this fuel flow in the valve opening direction, the armature undergoes a force advancing toward the side (in the valve opening direction) opposite to the nozzle, whereby the bouncing of the valve body in valve opening is suppressed. When the electric actuator causes the armature to displace in the valve closing direction, the injection of fuel is stopped. Once the fuel injection is stopped, the flow of the injected fuel is cut off suddenly, so that the pressure on the nozzle side rather than in the throttle portion rises to a higher level than that of the accumulated pressure fuel which is fed and the pressure in the second chamber becomes higher than that in the first chamber. As a result, the fuel flows from the second chamber which is high in pressure to the first chamber located on the nozzle side (in the valve closing direction) through the passage formed along the side face of the armature. With this fuel flow in the valve closing direction, the armature undergoes a force advancing toward the nozzle side (in the valve closing direction), so that the bouncing of the valve element when closing is suppressed.

In another aspect of the present invention there is provided a fuel supply system for the supply of a liquefied gas fuel, in which a liquefied gas fuel stored in a fuel tank is fed through fuel piping to a fuel injection system.

In this system there is provided an air conditioner which is provided with at least an expansion valve, an evaporator, and a condenser, and a liquefied gas fuel stored in the fuel tank is fed as refrigerant to the air conditioner. Further, the liquefied gas fuel leaking from the fuel injection system is introduced into the air conditioner.

The liquefied gas fuel introduced into the air conditioner is mixed as refrigerant into the liquefied gas fuel which is circulating through the air conditioner, then flows downstream.

According to the above construction, the liquefied gas fuel leaking from, for example, a high pressure pump and a fuel injector both constituting the fuel injection system is subjected to a liquefying process in the air conditioner (condenser) and is returned to the fuel tank through the air conditioner. Thus, there is not required any additional construction as the fuel recovery system. Additionally, the condenser in the air conditioner plays the role of recovering the leak fuel in addition to its inherent role of liquefying the refrigerant (liquefied gas fuel) and thus the condenser can be used in common. As a result, it is possible to simplify the construction of the fuel supply system and reduce the cost thereof.

BREIF DESCRIPTION OF DRAWINGS

Features and advantages of embodiments will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings:

FIG. 1

is a partial sectional view of an injector according to a first embodiment of the present invention;

FIG. 2

is a block diagram of a fuel injection system according to the first embodiment of the present invention;

FIG. 3

is a sectional view showing an assembled state of components which constitute the injector according to the first embodiment of the present invention;

FIG. 4

is a partial sectional view of the injector according to the first embodiment of the present invention;

FIG. 5

is a partial sectional view of an injector according to a third embodiment of the present invention;

FIG. 6

is a sectional view of an injector according to a fourth embodiment of the present invention;

FIG. 7

is a sectional view of an injector according to a fifth embodiment of the present invention;

FIG. 8

is a partial sectional view of the injector according to the fifth embodiment of the present invention;

FIG. 9

is a partial sectional view of the injector according to the fifth embodiment of the present invention;

FIG. 10

is a sectional view of an injector according to a related art;

FIG. 11

is a sectional view of an injector according to a sixth embodiment of the present invention;

FIG. 12

is a perspective view of components of the injector according to the sixth embodiment of the present invention;

FIG. 13

is a partial sectional view of the injector according to the sixth embodiment of the present invention;

FIG. 14

is a partial sectional view of the injector according to the sixth embodiment of the present invention;

FIG. 15

is a partial sectional view of the injector according to a seventh embodiment of the present invention;

FIG. 16

is a sectional view of an injector according to a related art;

FIG. 17

is a sectional view of an injector according to an eighth embodiment of the present invention;

FIG. 18

is a partial sectional view of the injector according to the eighth embodiment of the present invention;

FIG. 19

is a plan view of components of the injector according to the eighth embodiment of the present invention;

FIG. 20

is a sectional view showing a disassembled state of components of the injector according to the eighth embodiment of the present invention;

FIG. 21

is a partial sectional view of the injector according to the eighth embodiment of the present invention;

FIG. 22

is a time chart showing the operation of the injector according to the eighth embodiment of the present invention;

FIG. 23

is a graph showing an injection quantity characteristic of the injector according to the eighth embodiment of the present invention;

FIG. 24

is a sectional view showing a disassembled state of the injector according to the eighth embodiment of the present invention;

FIG. 25

is a sectional view showing a disassembled state of the injector according to the eighth embodiment of the present invention;

FIG. 26

is a sectional view showing a disassembled state of an injector according to a ninth embodiment of the present invention;

FIG. 27

is a sectional view showing a disassembled state of an injector according to a tenth embodiment of the present invention;

FIG. 28

is a sectional view of an injector according to a related art;

FIG. 29

is a sectional view of an injector according to an eleventh embodiment of the present invention;

FIG. 30

is a time chart showing the operation of the injector according to the eleventh embodiment of the present invention;

FIG. 31

is a graph showing an injection quantity characteristic of the injector according to the eleventh embodiment of the present invention;

FIG. 32

is a sectional view of an injector according to a twelfth embodiment of the present invention;

FIG. 33

is a sectional view of an injector according to a related art;

FIG. 34

is a block diagram showing a fuel injection system and an air conditioner both according to a thirteenth embodiment of the present invention; and

FIG. 35

is a block diagram of a system according to a related art.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Plural embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.

FIG. 2

shows an outline of a fuel injection system according to a first embodiment of the present invention. The fuel injection system of this embodiment is a common rail type fuel injection system in a diesel engine which uses DME as fuel.

DME stored in a fuel tank

1

is fed to a high pressure pump

2

by means of a low pressure pump (not shown). The DME fed to the high pressure pump

2

is pressurized by the same pump and then is fed to a common rail

3

. In the common rail

3

is stored DME which has been accumulated at an injection pressure (50-80 MPa). Fuel injectors

10

in a number corresponding to the number of engine cylinders are connected to the common rail

3

. The fuel injectors

10

are operated in accordance with drive signals provided from an ECU

4

.

The fuel injectors

10

are each provided with a casing

11

and a valve body

12

. The casing

11

and the valve body

12

are integrally clamped with a retaining nut

14

through a distance piece

13

. The casing

11

and the valve body

12

are formed with coaxial holes

11

a

and

12

a

, respectively, into which a valve element

20

is received. The valve element

20

is formed as an axially extending rod, having two slide portions

21

and

22

. Plural nozzle holes

15

are formed in a tip portion of the valve body

12

. A valve seat portion

16

is provided on an inlet side of the nozzle holes

15

of the valve body

12

. An abutment portion

23

capable of sitting on the valve seat portion

16

is provided at a tip of the valve element

20

. When the abutment portion

23

sits on the valve seat portion

16

, the flow of DME is shut off to stop the injection of fuel from the nozzle holes

15

. On the other hand, when the abutment portion

23

leaves the valve seat portion

16

, the flow of DME is allowed and is injected from the nozzle holes

15

.

The valve element

20

has a large-diameter portion

24

at a position corresponding to the distance piece

13

which is an intermediate portion. In the large-diameter portion

24

are disposed a spring retainer

25

and a shim

26

. A spring

27

is disposed between an inner wall of the casing

11

and the shim

26

, whereby the valve element

20

is urged downward in

FIG. 2

, i.e., in a nozzle hole closing direction.

As shown in

FIG. 3

, the spring retainer

25

is constructed of two dividable pieces, while the shim

26

is formed by a ring-like plate. As shown in

FIG. 4

, the spring retainer

25

is mounted in a sandwich relation to the large-diameter portion

24

of the valve element

20

, followed by mounting of the shim

26

. As a result, the spring retainer

25

is clamped radially inwards by the shim

26

and is fixed to the valve element

20

. The shim

26

fulfills a spring force adjusting function. That is, the biasing force of the spring

27

can be adjusted by adjusting the plate thickness of the shim

26

.

As shown in

FIG. 2

, an inlet port member

18

is attached to the casing

11

through a gasket

17

. The inlet port member

18

is connected to the common rail

3

and the high pressure DME is introduced from the common rail

3

into the holes

11

a

and

12

a

through the inlet port member

18

. A filter

19

for removing foreign matters contained in DME is press-fitted into the inlet port member

18

.

An electromagnetic drive unit

30

is installed in the casing

11

on the side opposite to the valve body. The electromagnetic drive unit

30

has an armature

31

, a stator

32

, and a coil

33

. The armature

31

is fixed to an end portion of the valve element

20

on the side opposite to the nozzle holes integrally with the valve member. The stator

32

is disposed in opposition to the armature

31

. The coil

33

is disposed on an outer periphery side of the stator

32

. The coil

33

, when supplied with electric power from ECU

4

, generates a magnetic field. With the magnetic field generated by the coil

33

, a magnetic attraction is developed between the stator

32

and the armature

31

. In this embodiment, the valve element

20

is attracted in the nozzle hole opening direction by virtue of the magnetic attraction induced between the armature

31

and the stator

32

in the electromagnetic drive unit

30

and is actuated directly by the electromagnetic drive unit

30

. That is, the fuel injector

10

of this embodiment is a direct acting type fuel injector. A shim

34

is disposed between the stator

32

and the casing

11

. A cap housing

35

clamps and fixes the stator

32

to the casing

11

through the shim

34

. On an inner periphery side of the stator

32

is formed an armature chamber in which the armature

31

is accommodated movably.

In mounting the electromagnetic drive unit

30

and the spring

27

, the valve element

20

and the armature

31

which are integral with each other are inserted into the holes

11

a

and

12

a

as deep as possible downward in FIG.

2

. In this state, the shim

26

and the spring

27

are mounted to the valve element

20

and the bisplit spring retainer

25

mounted in a bisplit state to the large-diameter portion

24

of the valve element

20

. With the spring retainer

25

thus connected, the shim

26

is fitted thereon to fix the spring retainer. Thereafter, the distance piece

13

and the valve body

12

are fixed to the casing by means of the retaining nut

14

. Further, the stator

32

and the shim

34

are fixed to an end portion of the casing

11

on the side opposite to the valve body by means of the cap housing

35

, whereby the electromagnetic drive unit

30

is mounted to the casing

11

.

In connection with mounting the electromagnetic drive unit

30

and spring

27

in accordance with the above procedure, an inside diameter d1 of the shim

26

is set larger than an outside diameter d2 of the large-diameter portion

24

of the valve element

20

, as shown in

FIGS. 3 and 4

. For example, d1 is 4.1 mm and d2 is 4.0 mm. Therefore, the shim

26

can be fitted onto the large-diameter portion

24

from the opposite-to-armature side of the valve element

20

. Further, in the armature chamber

36

, as shown in

FIG. 2

, a sufficient distance LZ is ensured between an end face of the armature

31

on the casing

11

side and an end face of the casing

11

on the armature

31

side is ensured, whereby the valve element

20

can be easily inserted downward in FIG.

2

and the spring

27

and other components can be mounted easily.

The armature chamber

36

with the armature

31

received therein is in communication with the hole

11

a

through a passage

37

, whereby DME of a high pressure is introduced into the armature chamber

36

through the hole

11

a

. As shown in

FIG. 1

, a hole

20

a

is formed on the valve element

20

on the side opposite to the nozzle holes. A rod member

28

is provided on an inner periphery side of the hole

20

a

so as to be slidable with respect to an inner wall of the hole

20

a

. An oil pressure reducing means is constituted by both hole

20

a

and rod member

28

. A space formed between the hole

20

a

and the rod member

28

, i.e., a space formed in the hole

20

a

on the nozzle holes

15

side rather than on the rod member

28

side, serves as a low pressure chamber

29

. The rod member

28

is formed with a communication hole

281

and one end thereof is in communication with the low pressure chamber

29

, while the opposite end thereof is in communication with the fuel tank

1

shown in

FIG. 2

which lies on the low pressure side.

Therefore, the internal pressure of the low pressure chamber

29

is almost equal (about 0.6 MPa) to that of the fuel tank

1

. An O-ring

38

is installed between the rod member

28

and the stator

32

to prevent leakage of DME to the exterior from the armature chamber

36

.

Since the inside diameter of the hole

20

a

and the outside diameter of the rod member

28

are almost equal to each other, the inner wall of the hole

20

a

and an outer wall of the rod member

28

slide with respect to each other. The rod member

28

is fixed to the stator

32

by press-fitting for example. Accordingly, when the armature

31

and the valve element

20

integral with each other reciprocate axially, the rod member

28

, as well as the armature

31

and the valve element

20

, reciprocate relatively with respect to each other, so that the volume of the low pressure chamber

29

changes.

The inside diameter of the hole

20

a

and the outside diameter of the rod member

28

are assumed to be d3, while the outside diameter of the valve element

20

and the inside diameter of the valve seat portion

16

of the valve body

12

opposed to the abutment portion

23

are assumed to be d4. If d3 and d4 are set equal to each other like, for example, d3=1.8 mm and d4=1.8 mm, the oil pressure based on the high pressure DME acting on the valve element

20

becomes balanced. Further, the force induced by the oil pressure of DME acting on the valve element

20

decreases by an amount corresponding to the area of an end face

29

a

of the low pressure chamber

29

located on the nozzle holes

15

side. Thus, it is possible to improve the pressure of DME injected from the fuel injector

10

. For example, with d3=d4=1.8 mm, even when the pressure of DME is about 80 MPa, it is possible to actuate the valve element

20

without changing the constitution and output force of the electromagnetic drive unit

30

and the shapes of components.

it is possible to actuate the valve element

20

without changing the constitution and output force of the electromagnetic drive unit

30

and the shapes of components.

A small amount of DME present in the armature chamber

36

leaks out to the low pressure chamber

29

through the clearance between the hole

20

a

and the rod member

28

. However, the flow rate of DME leaking out to the low pressure chamber

29

in this embodiment is extremely small in comparison with that in the fuel injector disclosed for example in JP-A-9-42106 in which high pressure fuel present in the pressure control chamber is allowed to leak to the low pressure side at every fuel injection. Therefore, the DME leaking to the low pressure chamber

29

can be recovered directly into the fuel tank

1

.

Next, the following description is provided about the operation of the fuel injector

10

according to the first embodiment.

When electric power is fed from the ECU

4

to the coil

33

, a magnetic attraction is developed between the armature

31

and the stator

32

by a magnetic field created in the coil

33

. When the magnetic attraction developed between the armature

31

and the stator

32

becomes larger than the sum of both the biasing force of the spring

27

and the force based on the pressure in the holes

11

a

and

12

a

and acting on the valve element

20

in the nozzle holes closing direction, the armature

31

and the valve member

20

integral with the armature lift upward in FIG.

2

. As a result, abutment portion leaves the valve seat portion

16

and the injection of fuel from the nozzle holes

15

is started.

When the supply of electric power to the coil

33

is stopped, the magnetic attraction between the stator

32

and the armature

31

vanishes. Consequently, the valve element

20

move downward in

FIG. 2

with both the biasing force of the spring

27

and the force based on the pressure of DME and acting on the valve element

20

in the nozzle holes closing direction. As a result, the abutment portion

23

sits on the valve seat portion

16

and the injection of fuel from the nozzles holes

15

is stopped.

According to the fuel injector

10

of the first embodiment, as described above, the low pressure chamber

29

is formed in an end portion of the valve element

20

on the side opposite to the nozzle holes, whereby the force acting on the valve element

20

in the nozzle holes closing direction can be diminished. Further, by equalizing d3 to d4, it is possible to balance the pressure of DME acting on the valve element

20

, and hence it is possible to decrease the force for actuating the valve element

20

in the nozzle holes opening direction. Accordingly, the pressure of DME injected can be made high without an increase in drive force of the electromagnetic drive unit

30

and without an increase in size of the constitution of the same drive unit.

In this first embodiment there is adopted a direct acting method wherein the valve element

20

is actuated directly by the electromagnetic drive unit

30

, for example in comparison with a fuel injector wherein a valve member is actuated by controlling the oil pressure in a pressure control chamber, it is possible to greatly diminish the amount of DME discharged from the fuel injector

10

to the low pressure side. The adoption of the direct acting method is further advantageous in that the leakage of fuel can be diminished even when a high pressure liquefied gas fuel, e.g., DME, is used as fuel as in this first embodiment.

A description will be given below of a fuel injector according to a second embodiment of the present invention.

This second embodiment is a modification of the first embodiment and the construction of a fuel injector

10

according to this second embodiment is the same as that in the first embodiment. In the second embodiment the relation between d3 and d4 is different from that in the first embodiment, which relation is set as d3<d4. With d3<d4, the force based on the pressure of DME and acting on the valve element

20

is imbalanced and becomes larger in the nozzle holes closing direction. More specifically, for d4=1.8 mm, d3 is set smaller in accordance with the maximum pressure of DME which is injected. By the setting, the period from the time when the supply of electric power to the coil

33

is stopped until the abutment portion

23

sits on the valve seat portion

16

is shortened and the response characteristic of the valve element

20

in valve closing is improved.

The value of d3 can be calculated in accordance with both d4 and maximum injection pressure of DME. For example, if the maximum injection pressure of DME is 80 MPa, then for d4=1.8 mm, the value of d3 is set in the range from 1.4 to 1.6 mm. By the setting, when the pressure of DME fed to the fuel injector

10

is 80 MPa, the force based on the pressure of DME and acting on the valve member corresponds, for example in the conventional fuel injector

100

shown in

FIG. 10

, to the force which acts on the valve member

101

when the pressure of DME is in the range from about 15 to 30 MPa.

According to this second embodiment, the force acting on the valve element

20

can be decreased even when the pressure of DME is improved. Besides, the spring

27

is disposed between the large-diameter portion

24

of the valve element

20

and an end face of the casing

11

, for example in comparison with the spring

107

in the conventional fuel injector

100

shown in

FIG. 10

, the spring

27

used in this embodiment is disposed apart from the stator

32

, thus permitting easy insertion of the rod member

28

into the stator

32

. Therefore, it is easy to change the inside diameter of the hole

20

a

and the outside diameter of the rod member

28

and hence the value of d3 can be changed easily.

A fuel injector according to a third embodiment of the present invention is shown in

FIG. 5

, in which components substantially common to the first embodiment are identified by like reference numerals, and explanations thereof will here be omitted.

In a fuel injector

40

according to this third embodiment, as shown in

FIG. 5

, a small-diameter portion

42

is formed at an end portion of a valve element

41

on the side opposite to nozzle holes. The small-diameter portion

42

is integral with the valve element

41

and extends to the opposite-to-nozzle-holes side of the valve element. A hole

43

a

is formed in a stator

43

and the small-diameter portion

42

can slide and reciprocate on an inner periphery side of the hole

43

a

. The hole

43

a

is in communication with a fuel tank

1

which corresponds to a low pressure side. According to this construction, a pressure equal to the internal pressure of the fuel tank

1

acts on an end face of the small-diameter portion

42

and also on the hole

43

a

as is the case with the low pressure chamber

29

in the first embodiment. An outside diameter of the small-diameter portion

42

and an inside diameter of the hole

43

a

, which are indicated at d5, are set so as to meet the relationship of d5≦d4 like d3 in the second embodiment. The amount of DME leaking out from the clearance between the small-diameter portion

42

and the hole

43

a

is very small, so that the leaking fuel is recovered directly into the fuel tank

1

.

In this third embodiment, the pressure of DME acting on the valve element

41

in the valve closing direction can be reduced as in the first embodiment, thus making it possible to diminish the force required for actuating the valve element

41

.

A fuel injector according to a fourth embodiment of the present invention is shown in

FIG. 6

, in which components substantially common to the first embodiment are identified by like reference numerals, and explanations thereof will here be omitted.

In a fuel injector

50

according to this fourth embodiment, as shown in

FIG. 6

, an armature

52

fixed to an end portion of a valve element

51

on the side opposite to nozzle holes is formed in the shape of a flat plate. A stator

53

is provided in opposition to the armature

52

. A shim

54

is disposed between the stator

53

and a casing

11

. A cap housing

55

clamps and fixes the stator

53

to the casing

11

in a sandwiching relation to the shim

54

. The valve element

51

is provided with a slide portion

511

. The slide portion

511

is slidable with respect to an inner wall of a hole

12

a

formed in a valve body

12

.

At an end portion of the valve element

51

on the side opposite to nozzle holes there is formed a small-diameter portion

512

integrally with the valve element

51

. The small-diameter portion

512

can slide and reciprocate along an inner periphery side of a hole

53

a

formed in the stator

53

. The hole

53

a

is in communication with a fuel tank

1

which corresponds to a low pressure side. According to this construction, a pressure equal to the internal pressure of the fuel tank

1

acts on the hole

53

a

and also on an end face of the small-diameter portion

512

. An inside diameter of the hole

53

a

and an outside diameter of the small-diameter portion

512

, which are indicated at d7, are set so as to meet the relationship of d7≦d4 like d3 in the first or the second embodiment. The amount of fuel leaking out from the clearance between the small-diameter portion

512

and the hole

53

a

is very small, so that the leaking DME is recovered directly into the fuel tank

1

.

In this fourth embodiment, the valve element

51

slides with respect to the valve body

12

or the stator

53

at two portions of slide portion

511

and small-diameter portion

512

. In comparison with the first embodiment wherein the valve member slides at three portions of slide portion

21

, slide portion

22

, and hole

20

a

, the management of coaxiality of components can be done easily in this fourth embodiment.

A fifth embodiment of the present invention is shown in FIG.

7

.

In a fuel injector

60

according to this fifth embodiment, a valve element is constructed of a valve rod portion

71

and a valve needle portion

72

, which are connected together by a connecting portion

73

. The connecting portion

73

has a spherical ball

731

and a fixing member

732

. A valve body

62

is fixed to one end portion of a casing

61

and an electromagnetic unit

80

is fixed to an opposite end portion of the casing. A hole

62

a

is formed in the valve body

62

and a slide portion

74

and a slide portion

74

formed on the valve needle portion

72

is slidable with respect to an inner wall of the hole

62

a

. Plural nozzle holes

63

are formed in a tip end portion of the valve body

62

. A valve seat portion

64

is provided on an inlet side of the nozzle holes

63

of the valve body

62

. An abutment portion

75

capable of sitting on the valve seat portion

74

is provided at a tip of the valve needle portion

72

. When the abutment portion

75

sits on the valve seat portion

64

, the flow of DME is cut off to stop the injection of DME from the nozzle holes

63

. On the other hand, when the abutment portion

75

leaves the valve seat portion

64

, the flow of DME is started and DME is injected from the nozzle holes

63

.

An electromagnetic drive unit

80

is installed on the casing on the side opposite to the valve body. The electromagnetic drive unit

80

has an armature

81

, a stator

82

, a coil

83

, and a cap housing

84

. The armature

81

is formed integrally with the valve rod portion

71

on the side opposite to the nozzle holes. The stator

82

is disposed in opposition to the armature

81

. The coil

83

is disposed on an outer periphery side of the stator

82

. The coil

83

, when supplied with electric power from ECU

4

, generates a magnetic field. With the magnetic field thus generated by the coil

83

, there occurs a magnetic attraction between the stator

82

and the armature

81

. By energizing the coil

83

, the valve rod portion

71

and the valve needle portion

72

as valve components are actuated directly by the electromagnetic drive unit

80

. A cap housing

84

is provided in a surrounding relation to an outer periphery side of the coil

83

and forms a magnetic circuit in cooperation with both armature

81

and stator

82

. The stator

82

and the casing

61

are fixed with a retaining nut

65

through a shim

85

.

DME of a high pressure fed from a common rail

3

flows into an intake port

821

formed in the stator

82

. The DME having thus entered the intake port

821

then flows through flow passages

822

and

823

formed eccentrically with respect the central axis of the stator

82

, further through a flow passage

811

formed in the armature

81

and a flow passage

851

formed in the shim

85

, and is fed to the tip end portion of the valve body

62

.

A small-diameter portion

76

is formed at an end of the valve rod portion

71

on the side opposite to nozzle holes.

The small-diameter portion

76

is formed integrally with the valve rod portion

71

and extends to the side opposite to nozzle holes. A hole

82

a

is formed in the stator

82

and the small-diameter portion

76

can slide and reciprocate along an inner periphery side of the hole

82

a

. The hole

82

a

is in communication with a fuel tank

1

which corresponds to a low pressure side. According to this construction, a pressure equal to the internal pressure of the fuel tank

1

acts on the hole

82

a

and also on an end face

76

a

of the small-diameter portion

76

. If an outside diameter of the small-diameter portion

76

and an inside diameter of the hole

82

a

are assumed to be d9 and an inside diameter of the valve seat portion

64

in the valve body

62

and an outside diameter of the abutment portion

75

in the valve needle portion

72

are assumed to be d10, there exists a relationship of d9≦d10 as in the first and second embodiments. Since the amount of DME leaking out from the clearance between the small-diameter portion

76

and the hole

82

a

is very small, the leaking fuel is recovered directly into the fuel tank

1

.

A detailed description will be given below about the valve element used in the fuel injector

60

of this embodiment.

As shown in

FIG. 8

, the valve element has a valve rod portion

71

and a valve needle portion

72

, which are connected together by a connecting portion

73

. An end face of the valve rod portion

71

on the valve needle portion

72

side and an end face of the valve needle portion

72

on the valve rod portion

71

side are each formed in a centrally recessed conical shape and a ball

731

is held within the recessed space. The valve rod portion

71

and the valve needle portion

72

are formed with projecting portions

711

and

721

, respectively, which project radially outwards, and a fixing member

732

is engaged with the projecting portions

711

and

712

. At both axial ends of the fixing member

732

are formed a pair of retaining portions

732

a

, which are engaged with the projecting portions

711

and

712

of the valve rod portion

71

and the valve needle portion

72

, respectively.

The fixing member

732

is formed of a metallic material such as steel and has a generally C-shaped section obtained by removing a part of a cylinder as shown in FIG.

9

. The fixing member

732

can be fitted on the connection of the valve rod portion

71

, valve needle portion

72

and ball

731

radially from the outside and can be removed from the connection. Further, the fixing member

732

is formed with plural slits

732

b

to make the overall axial length changeable.

The reason why the plural slits

732

b

are formed in the fixing member

732

and the fixing member

732

is made capable of expansion and contraction axially is as follows.

The fuel injector

60

is usually replaced when a running distance of a vehicle with a diesel engine mounted thereon reaches a predetermined distance (about 100,000 km). Taking the cost of replacement of the fuel injector

60

into account, it is desirable to replace only the casing

61

, valve body

62

and valve needle portion

72

which are high in the frequency of wear or loss. In this embodiment wherein the valve rod portion

71

and the valve needle portion

72

are constituted as separate portions, there occur variations in size of both portions. Consequently, there is a fear that the lift quantity of the valve rod portion

71

and the valve needle portion

72

as constituents of the valve element, i.e., the spacing between the armature

81

and the stator

82

, may vary after the replacement of parts. Thus, it is necessary that the spacing between the armature

81

and the stator

82

be adjusted by changing the size of the ball

731

, and it is desirable that the fixing member

732

expand or contract according to the size of the ball

731

. For this reason the fixing member

732

is constituted so as to be capable of expansion and contraction.

In this fifth embodiment the ball

731

is interposed between the valve rod portion

71

and the valve needle portion

72

, so even when the valve rod portion

71

or the valve needle portion

72

tilts due to a machining error for example, it is possible to connect the valve rod portion

71

and the valve needle portion

72

with each other while accepting the tilt by the ball

731

. Thus, a high machining accuracy is not required of the valve rod portion

71

or the valve needle portion

72

and hence it is possible to reduce the number of machining steps and the machining cost.

In the above plural embodiments DME is used as fuel introduced into the respective fuel injectors. In the present invention, however, there also may be used as fuel another liquefied gas fuel such as LPG or an ordinary liquid fuel such as gas oil or gasoline. Also as to the fuel injection system, it is not limited to the common rail type.

Next, a sixth embodiment of the present invention will be described. In this embodiment the present invention is applied to a fuel injector for a vehicular diesel engine wherein a liquefied gas such as DME or LPG is used as fuel.

The fuel injector according to this embodiment is what is called a direct acting type fuel injector wherein a valve element is directly operated by means of an electromagnetic solenoid (actuator).

FIG. 11

illustrates a sectional structure of the fuel injector and a construction around the same injector. The fuel injector, indicated at

230

, is actuated in accordance with a drive signal provided from ECU

4

.

The construction of the fuel injector

230

will now be described in detail. A casing

231

and a valve body

232

constitute a first casing member and a second casing member respectively, which are rendered integral with each other by tightening a retaining nut

233

. Coaxial holes

231

a

and

232

a

are formed in the casing

231

and

232

, respectively, and a rod (rod portion)

234

and a valve (valve portion)

235

, which constitute a valve element, are received into the holes

231

a

and

232

a

. A slide portion

234

a

of the rod

234

is in contact with an inner wall of the hole

231

a

, while a slide portion

235

a

of the valve

235

is in contact with an inner wall of the hole

232

a

, the rod

234

and the valve

235

being slidable vertically in the figure. A space adjusting shim (shim member)

236

is interposed between the rod

234

and the valve

235

, and in this state these components are connected together by means of a fixing member

237

which serves as a connecting member. The valve member construction comprising the rod

234

, valve

235

, shim

236

, and fixing member

237

is a characteristic portion of this embodiment and the details thereof will be described later.

Plural nozzle holes

232

b

are formed in a tip portion of the valve

232

. The nozzle holes

232

b

close when a tip of the valve

235

comes into abutment against the valve body

232

and open when the tip of the valve

235

leaves the valve body

232

.

In an electromagnetic solenoid section, an armature

239

is fixed to an upper end in the figure of the rod

234

and a first stator

240

is provided in opposition to the armature

239

. A second stator

242

is attached to the first stator

240

through an insert member

241

which is formed of a non-magnetic material such as SUS304. These components are rendered integral in an oil-tight manner by such means as laser welding. A coil

243

is mounted on an outer periphery of the first stator

240

. Further, a spring

244

is received in the first stator

240

and the valve element comprising the rod

234

and the valve

235

is urged to the valve closing side (lower side in the figure).

A plate

245

is disposed between the second stator

242

and the casing

231

and in this state a cap housing

246

is mounted to the casing

231

. The plate

45

also functions as a valve stopper and the lift quantity of the rod

234

(valve

235

) is restricted by abutment of an upper surface of the slide portion

234

a

of the rod

234

against the plate

245

.

An inlet port member

248

is attached to the casing

231

in a sandwiching relation to a gasket

247

. Fuel of a high pressure is introduced from a common rail into the holes

231

a

and

232

a

through the inlet port member

248

. A bar filter

249

for preventing the entry of foreign matters is press-fitted and fixed into the inlet port member

248

.

The hole

231

a

is in communication with an armature chamber

251

through a communication passage

250

. Therefore, the high pressure fuel acts on the rod

234

and the valve

235

at any position and it is possible to prevent the leakage of fuel from high to low position in the associated slide portion.

In the fuel injector

230

of the above construction, when the coil

243

is de-energized, the valve element (rod

234

and valve

235

) is held in its closed position with the biasing force of the spring

244

. At this time, the nozzles holes

232

b

close and the fuel injection by the fuel injector

230

is stopped. When the coil

243

is energized, the armature

239

is attracted to the first stator

240

and the valve element (rod

234

and valve

235

) moves to the valve opening side (upward in the figure) against the biasing force of the spring

244

, whereby the nozzle holes

232

b

are opened to effect fuel injection.

A detailed description will be given below about a characteristic construction of the valve element.

FIG. 12

is a sectional view showing the connection between the rod

234

and the valve

235

on a larger scale and

FIG. 13

is a perspective view showing the construction of the fixing member

237

.

As shown in

FIG. 12

, a lower end face of the rod

234

and an upper end face of the valve

235

are both flat faces and the shim

236

, which is in the shape of a flat plate, is interposed between both flat end faces. The rod

234

and the valve

235

are formed with outwardly projecting flange portions

234

b

and

235

b

, respectively, and the fixing member

237

is mounted so as to engage the flange portions

234

b

and

235

b

. That is, the fixing member

237

as a pair of upper and lower engaging portions

237

a.

As shown in

FIG. 13

, the fixing member

237

is formed of a metallic material such as iron or steel and is in a C-shape in plan obtained by removing a part of a cylinder. The fixing member

237

can be fitted on the connection of the rod

234

, valve

235

and shim

236

from the outside and can be removed. In the fixing member

237

are formed plural slits (expanding/contracting portions)

237

b

so as to make the axial length of the fixing member changeable.

The reason why the fixing member

237

is given the expanding/contracting function by the slits

237

b

will be set forth below.

Generally, the fuel injector

230

is replaced at every predetermined running distance of the vehicle concerned (at every about 100,000 km), and from the standpoint of cost it is only the nozzle portion (valve body

232

and valve

235

) that is replaced. In this case, according to the above construction wherein the valve element is divided into rod

234

and valve

235

, there occur variations in size of those components and this is presumed to be a cause of a change in valve lift quantity (an air gap quantity between the armature and the stator) after the replacement of parts. Thus, there arises the necessity of changing the thickness of the shim

236

to adjust the spacing, and the fixing member

237

is given a function of expansion and contraction so that it can cope with a change in thickness of the shim

236

.

More specifically, in

FIG. 14

which shows the connection of rod

234

and valve

235

in a disassembled manner, if the distance between an lower end face of the casing

231

and that of the rod

234

is assumed to be L1 and the distance between an upper end face of the valve body

232

and that of the valve

235

is assumed to be L2, the distance L1 is measured in an abutted state of the rod

234

against the plate

245

. Likewise, for (new) valve body

232

and valve

235

after replacement, the distance L2 is measured in an abutted state of the tip of the valve

235

against the sheet portion of the valve body

232

. Then, a required thickness of the shim

236

is determined from the distances L1 and L2.

In replacing the nozzle portion (valve body

232

and valve

235

), the retaining nut

233

is released and the valve body

232

is removed. Further, the fixing member

237

is removed and the valve

235

is removed from the rod

234

. Now, the removal of the used nozzle portion (valve body

232

and valve

235

) is completed. Then, the distances L1 and L2 shown in

FIG. 14

are measured in the manner described above and a shim

236

matching the measured values is provided, thereafter, a new nozzle portion (valve body

232

and valve

235

) is mounted. The mounting may be done in reverse procedure from the dismounting procedure.

According to this embodiment described above in detail there are obtained the following effects.

When the valve portion is to be replaced after a long-term use of the fuel injector

230

, the efficiency of the replacing work is improved. As a result, in the actuator direct acting type fuel injector

230

, there can be realized a construction superior in maintainability.

Since the shim

236

is interposed between the rod

234

and the valve

235

and these components are interconnected by the fixing member

237

having an expanding/contracting function, even if the thickness of the shim

236

is changed, it is possible to cope with the change.

Since the rod

234

, valve

235

and shim

236

are abutted and connected together at respective flat faces, even if the central axes of the rod

234

and valve

235

are slightly deviated due to a machining error for example, the rod

234

and the valve

235

can be connected together while accepting (absorbing) the deviation.

Since the fuel injector

230

described above is of an actuator direct acting type construction, there is little leakage of fuel and the fuel injector can be embodied suitably as a fuel injector for a liquefied gas fuel.

A seventh embodiment of the present invention will now be described.

FIG. 15

is a sectional view showing a connection between a rod

234

and a valve

235

on a larger scale. In the construction illustrated in

FIG. 15

, a lower end face of the rod

234

and an upper end face of the valve

235

are in the shape of a centrally recessed cone, with a spherical ball

261

as a shim being interposed therebetween. By changing the size (diameter) of the ball

261

there is adjusted a valve lift quantity (air gap quantity between an armature and a stator). In this case, even if the connection between the rod

234

and the valve

235

tilts slightly due to a machining error for example, the rod

234

and the valve

235

can be connected together while accepting the tilt.

Although in the above embodiments the present invention is embodied as fuel injectors for the injection of a liquefied gas fuel such as DME or LPG, the present invention may also be applied to fuel injectors which inject other fuels. For example, the invention may be embodied as a fuel injector for the injection of gas oil or gasoline. Also in this case it is possible to realize a construction superior in maintainability.

Next, an eighth embodiment will now be described.

FIG. 17

illustrates a sectional structure of a fuel injector according to this embodiment and a construction around the fuel injector.

A detailed description will now be given about the construction of the fuel injector. A casing

331

and a valve body

332

constitute a dividable casing member. Both are rendered integral with each other by tightening a retaining nut

333

. A part (a lower end portion in the figure) of the casing

331

is constituted in a divided form as a distance piece

334

. Coaxial holes

331

a

and

332

a

are formed in the casing

331

and the valve body

332

, respectively, and an elongated valve element

335

is received therein. The valve element

335

has slide portions

335

a

and

335

b

at two upper and lower positions in the figure. Plural nozzle holes

332

b

are formed in a tip portion of the valve body

332

. When a tip of the valve element

335

comes into abutment against the valve body

332

, the nozzle holes

332

b

close, while when the tip of the valve element

335

leaves the valve body

332

, the nozzle holes

332

b

open.

A large-diameter portion

335

c

is formed at an intermediate position of the valve element

335

(a position corresponding to the distance piece

334

) and a spring retainer

336

and a shim (shim member)

337

are disposed so as to be put on the large-diameter portion

335

c

. A spring

338

is provided between an inner wall of the casing

331

and the shim

337

and the valve element

335

is urged to the valve closing side (downward in the figure) constantly by the spring

338

.

As shown in

FIG. 20

, the spring retainer

336

is constituted by bisectable halves (pieces) and the shim

337

is constituted by a ring plate. As shown in

FIG. 21

, the spring retainer

336

is mounted to the large-diameter portion

335

c

in a sandwiching relation to the valve element

335

, followed by further mounting of the shim

337

to fix the spring retainer

336

. The shim

337

fulfills a spring force adjusting function. That is, the biasing force of the spring

338

is adjusted by changing the plate thickness of the shim

337

.

Referring back to

FIG. 17

, an inlet port member

348

is attached to the casing

331

in a sandwiching relation to a gasket

347

and fuel of a high pressure is introduced from a common rail into the holes

331

a

and

332

a

through the inlet port member

348

. A bar filter for preventing the entry of foreign matters is press-fitted and fixed into the inlet port member

348

.

On the other hand, according to the construction of an electromagnetic solenoid section, an armature

339

is fixed to an upper end in the figure of the valve element

335

and a stator

340

is provided in opposition to the armature

339

.

A coil

341

is disposed on an outer periphery of the stator

340

. A shim

342

is disposed between the stator

340

and the casing

331

and in this state a cap housing

343

is mounted to the casing

331

.

An armature chamber

351

for receiving the armature

339

therein is in communication with the hole

331

a

through a communication passage

350

and a liquefied gas fuel of a high pressure is introduced into the armature chamber

351

. Therefore, the high pressure fuel acts on the valve element

335

at any position and thus it is possible to eliminate the leakage of fuel such that the fuel leaks out from high to low pressure position in the slide portion of the valve element.

The space between the armature

339

and the stator

340

serves as an oil pressure damper chamber

344

, the construction of which will now be described with reference to FIG.

18

. In the same figure, out of an end face of the stator

340

and that of the armature

339

, the former is formed flat. On the other hand, on an outer edge portion of the end face of the armature

339

is formed annular protuberance

339

a

, which corresponds to a stepped portion, with a recess being defined so as to be surrounded by the protuberance

339

a

. The protuberance

339

a

also plays the role of a stopper when the armature moves. When the valve element

335

opens, an open position thereof is defined by the position at which the protuberance

339

a

of the armature

339

abuts the stator

340

.

FIG. 19

is a plan view of the armature

339

as seen from above. As shown in the same figure, cutout portions are formed in the protuberance

339

a

at one or more positions (two positions in the figure).

The larger the volume change rate of the oil pressure damper chamber

344

relative to the valve lift quantity (stroke), the more outstanding the effect as an oil pressure damper. In other words, in the construction of

FIG. 18

, the smaller the height LX of the protuberance

339

a

, the more outstanding the effect as an oil pressure damper. However, if the height LX of the protuberance

339

a

is too small, it is difficult to attain a high machining accuracy.

In this embodiment the height LX is set at 0.1-0.3 mm as an example. A lift quantity (distance LY in the figure) of the valve element

335

is adjusted by the shim

342

disposed between the stator

340

and the casing

331

.

In the fuel injector

330

of the above construction, when the coil

341

is de-energized, the valve element

335

is held in its closed position with the biasing force of the spring

338

. At this time, the nozzle holes

332

b

are closed to stop the injection of fuel by the fuel injector

330

. When the coil

341

is energized, the armature

339

is attracted to the stator

340

and the valve element

335

moves to its open side (upper side in the figure) against the biasing force of the spring

338

. The valve element

335

lifts until abutment of the protuberance

339

a

of the armature

339

against the stator

340

, so that the nozzle holes

332

b

open to effect the injection of fuel.

With lift of the valve element

335

, the spacing (distance LY) between the protuberance

339

a

of the armature

339

and the stator

340

becomes shorter and the volume of the oil pressure damper chamber

344

becomes smaller. The fuel present within the oil pressure damper chamber

344

flows out through the spacing (distance LY) between the protuberance

339

a

and the stator

340

, which spacing, however, becomes narrower with lift of the valve element

335

and acts as an oil pressure damper. When the valve opening of the fuel injector

330

is completed, the oil pressure chamber

344

is shut off from the exterior by contact of the protuberance

339

a

with the stator

340

.

When the fuel injector

330

closes, the valve element

335

returns to its closed position with the biasing force of the spring

338

upon de-energization of the coil

341

. At this time, the liquefied gas fuel is introduced between the armature

339

and the stator

340

through the cutout portions

339

b

, whereby the disengagement between the armature

339

and the stator

340

is done quickly. Consequently, the closing motion of the valve element

335

is assisted and the valve element

335

closes quickly.

FIG. 22

is a time chart showing a lift behavior of the valve element relative to a drive signal for the fuel injector

30

and

FIG. 23

illustrates an injection quantity characteristic of the fuel injector

330

. In both figures, the related art is indicated with dotted lines for comparison purpose.

In

FIG. 22

, after turning ON of a drive signal which is inputted to the fuel injector

330

from ECU

4

, the lift of the valve element

335

is started and the valve opening motion is ended upon abutment of the protuberance

339

a

of the armature

339

against the stator

340

. Thereafter, the fuel injector

330

is held in its open condition. In this case, the bouncing of the valve element

335

upon arrival of the valve element

335

at its opening position (upon abutment of the protuberance

339

a

against the stator

340

) is diminished. After opening of the valve element

335

and upon turning OFF of a drive signal, the fuel injector

330

closes.

In

FIG. 23

, the pulse width plotted along the axis of abscissa represents an elapsed time from the start of valve opening. In this embodiment, unlike the related art, there is obtained a characteristic such that the injection quantity increases monotonously with an increase of the pulse width. Thus, it is seen that a satisfactory injection characteristic (metering characteristic) can be achieved.

Next, a description will be given of a mounting procedure for the fuel injector

330

, especially a mounting procedure for the spring

338

, with reference to

FIGS. 24 and 25

. First, the electromagnetic solenoid section and the inlet port member

348

are mounted to the casing

331

.

The valve element

335

integral with the armature is also mounted.

As shown in

FIG. 24

, an integral combination of the valve element

335

and the armature

339

is brought down insofar as possible and in this state the spring

338

and the shim

337

are fitted on the valve element

335

, then two bisplit spring retainer halves

336

are mounted on the large-diameter portion

335

c

. Then, as shown in

FIG. 25

, with the two spring retainer halves

336

coupled together, the shim

337

is fitted to fix the spring retainer

336

. Thereafter, the distance piece

334

and the valve body

332

are fixed with the retaining nut

333

, whereby the mounting of the fuel injector

330

is completed.

In the above mounting work, the diameter d1 of the shim

337

is set larger than the outside diameter d2 of the large-diameter-portion

335

c

of the valve element

335

. For example, d1 is 4.1 m and d2 is 4.0 mm. Therefore, the shim

337

can be inserted from the lower side of the valve element

335

. Further, as shown in

FIG. 17

, the distance LZ (armature moving space) between a lower end face of the armature

339

and the casing

331

in the armature chamber

351

is ensured sufficiently, whereby the valve element

335

can be brought down as shown in the figure, thus permitting easy mounting of the spring

338

, etc.

According to this embodiment described above in detail there are obtained the following effects.

Since the oil pressure damper chamber

344

is provided between the armature

339

and the stator

340

, the bouncing of the valve element

335

and that of the armature

339

in valve opening are suppressed by virtue of a damper effect. Consequently, the fuel injection quantity can be kept under control.

Since the cutout portions

339

b

are formed in the protuberance

339

a

of the armature

339

, disengagement between the armature

339

and the stator

340

is done quickly when the valve element

335

returns to its closed position after valve opening. Accordingly, the fuel injector

330

operates in a satisfactory manner.

Since the spring

338

is disposed at an intermediate position of the valve element

335

, it is not necessary for the spring to be interposed between the armature and the stator as in the construction of FIG.

28

. Consequently, it is possible to realize an advantageous construction including the oil pressure damper chamber

344

. As to the construction of the spring retainer portion, since the spring retainer

336

comprising plural split pieces is used, it is easy to effect mounting of the spring retainer

336

. Further, the spring force can be adjusted by adjusting the thickness of the shim

337

.

Since the fuel injector

330

described above adopts an actuator direct acting type construction, the leakage of fuel is diminished and the fuel injector thus embodied is suitable as a fuel injector for a liquefied gas fuel. Further, since a liquefied gas fuel is low in viscosity, the use thereof causes a serious problem of valve element bouncing, but this problem can be solved by the above construction of the fuel injector

330

.

A ninth embodiment will now be described. In this ninth embodiment, as shown in

FIG. 26

, an end face of an armature

339

is formed flat and an annular protuberance

361

is formed on an end face of a stator

340

. In this case, the protuberance

361

corresponds to a stepped portion and an oil pressure damper chamber

344

is formed by a recess which is surrounded with the protuberance

361

.

Next, a tenth embodiment will be described. In this tenth embodiment, as shown in

FIG. 27

, a stator

340

is provided with a stepped portion

362

instead of protuberance

361

. In

FIG. 27

the machining of the stator

340

for forming an oil pressure damper chamber

344

is easier than in FIG.

26

. At a position near the protuberance

361

or near the stepped portion

362

the stator

340

may be divided in two vertically in the figure. In this case, the machining of the protuberance

361

or the stepped portion

362

becomes still easier. Stepped portions (or protuberances) may be formed at end faces of both armature and stator to define an oil pressure damper chamber.

When the valve element

335

opens in the construction of

FIGS. 26 and 27

, its open position is defined by the position at which an end face of the armature

339

abuts the protuberance

361

or the stepped portion

362

. In this case, it is preferable that a cutout portion be formed in at least one position of the protuberance

361

or the stepped portion

362

.

Although in the above embodiments the protuberance

339

a

of the armature

339

or the protuberance

361

or the stepped portion

362

of the stator

340

functions as a stopper, there may be provided a separate stopper member. That is, it is not always necessary to adopt the construction wherein the armature

339

side and the stator

340

side are in contact with each other. There may be adopted another construction insofar as there is obtained an oil pressure damping function during movement of the valve element

335

.

Although in the above embodiments a sufficient distance LZ (armature moving space) between the lower end face of the armature

339

and the casing

331

is ensured so that the valve element

335

can be brought down in the armature chamber

351

, this point is not essential to accomplishing the present invention. There may be adopted a construction wherein the distance LZ (armature moving space) is small. In this case, however, for improving the mountability of the spring

338

disposed at an intermediate position of the valve element

335

, it is preferable to for example shallow the spring receiving portion of the casing

331

which portion is for receiving the spring

338

therein (extend the length of the distance piece

334

upward in FIG.

17

).

Although in the above embodiments the present invention is embodied as fuel injectors for the injection of liquefied gas fuels such as DME and LPG, the invention may be embodied as a fuel injector for the injection of any other fuel, e.g., gas oil or gasoline. Also in this case it is possible to keep the fuel injection quantity under control.

Next, an eleventh embodiment will be described. In this embodiment, a nozzle side (valve closing direction) and an opposite-to-nozzle side (valve opening direction) are assumed to be a lower side and an upper side, respectively, but these are for the convenience of explanation and are different from those in actual mounting.

FIG. 29

illustrates a sectional structure of a fuel injector

401

and a construction around the fuel injector.

The construction of the fuel injector

401

will be described below in detail.

A casing of the fuel injector

401

is constituted by a coupled combination of a body

406

and a nozzle body

407

, which are rendered integral with each other by tightening a retaining nut

408

. Coaxial through holes

409

and

410

are formed in the body

406

and the nozzle body

407

, respectively, with an elongated valve element

411

being received into the through holes

409

and

410

.

The valve element

411

is adapted to slide vertically through the through holes

409

and

410

and has slide portions

412

and

413

at two upper and lower positions respectively. Plural nozzle holes

414

are formed at a tip portion of the nozzle body

407

. When a tip of the valve element

411

comes into abutment against (sits on) the nozzle body

407

, the nozzle holes

414

close, while when the tip of the valve element

411

leaves (disengages from) the nozzle body

407

, the nozzle holes

414

open.

A compression coil spring

415

is disposed at an upper end portion of the valve element

411

. The valve element

411

is urged downward constantly with a restoring force of the spring

415

.

A fuel hole

416

is formed on an upper side of the valve element

411

and fuel fed from an inlet

417

flows through a passage formed within the body

416

, a first chamber

420

formed just under an armature

418

, a throttle portion

421

defined by a clearance between the armature

418

and a surrounding component, further through a second chamber

422

formed just above the armature

418

, and is introduced into the fuel hole

416

located centrally of the armature

418

.

The throttle portion

421

is defined by a clearance between a side face of the armature

418

and a lower inner core

434

which constitutes a lower portion of a stator

423

. The clearance is set at a value in the range from 60 to 300 &mgr;m in terms of a radial size.

In an intermediate position of the valve element

411

is formed a branch hole

426

for conducting fuel conducted from the fuel hole

416

into a fuel passage

425

which is formed between the through hole

409

of the body

406

and the valve element

411

. The fuel thus introduced into the fuel passage

425

is then conducted to the nozzle holes

414

side through a nozzle chamber

427

formed between the through hole

410

of the nozzle body

407

and the valve element

411

.

Next, the inlet

417

will be described below.

The inlet

417

is mounted to the body

406

in a sandwiching relation to a gasket

430

and serves as an inlet for a common rail

3

. A bar filter

431

for preventing the entry of foreign matters is press-fitted and fixed into the inlet

417

.

Next, reference will be made below to an electromagnetic solenoid valve

432

.

An armature

418

in the electromagnetic solenoid

432

is fixed to the upper portion of the valve element

411

by press-fitting for example, and a stator

423

is disposed in opposition to the armature

418

. Thus, there is constituted what is called a plunger type solenoid.

The stator

423

is made up of an upper inner core

433

having an attraction face, a lower inner core

434

located sideways of the armature

418

and having a pole face, and a ring-like middle inner core

435

sandwiched between the upper inner core

433

and the lower inner core

434

.

The upper inner core

433

and the lower inner core

434

are formed of a soft magnetic material because they serve as magnetic paths of the electromagnetic solenoid

432

. On the other hand, the middle inner core

435

is formed of a non-magnetic material to block the passage of a magnetic flux.

The upper inner core

433

, the lower inner core

434

, and the middle inner core

435

are stacked and in this stacked state they are integrally fixed by a bonding means such as laser welding to constitute the stator

423

.

A coil

436

for generating a magnetic force to let the armature

418

be attracted to the stator

423

is disposed on an outer periphery of the stator

423

and is fixedly molded with resin together with connecting terminals

438

within a solenoid housing

437

.

A stopper

440

is disposed between the stator

423

and the body

406

. The stopper

440

not only functions to determine a fully open position of the valve element

411

but also functions as a shim for adjusting the spacing (i.e., a final gap) between the armature

418

and the stator

423

.

The following description is now provided about the operation and effect of the fuel injector

401

in this embodiment.

FIG. 30

is a time chart showing pressure behaviors of the lower first chamber

420

and the upper second chamber

422

. In the same figure, valve lift and injection rate in this embodiment are indicated with solid lines and those in the related art are indicated with broken lines.

FIG. 31

is a T-Q characteristic diagram showing an injection quantity (Q) relative to pulse width T.

Upon turning ON of a drive signal provided from ECU

4

to energize the coil

436

, the armature

418

is attracted to the stator

423

and the valve element

418

lifts upward against the biasing force of the spring

415

. When the valve element

411

abuts the stopper

440

, the valve opening motion is over and subsequently the valve element is held in the open condition. As the valve element

411

rises, its tip leaves (disengages from) the nozzle body

407

and the nozzle holes

414

open, allowing liquid fuel to be injected through the nozzle holes.

In the fuel injector

100

of the related art shown in

FIG. 33

, the valve element

101

and the stopper

111

strike against each other at the time of valve opening, resulting in that there occurs bouncing of the valve element

101

several times as indicated with broken lines in FIG.

30

. The injection rate is influenced by the bouncing and deteriorates. Further, as indicated with a broken line in

FIG. 31

, the injection rate Q is wavy relative to the pulse width T and thus it is impossible to effect a stable injection control.

In the fuel injector

401

of this embodiment, as compared with the above related art, when the injection of fuel is started, the internal pressure of the nozzle chamber

427

and that of the second chamber

422

(an upper surface of the armature

418

) which is in communication with the nozzle chamber

427

decrease. At this time, the internal pressure of the first chamber

420

(a lower surface of the armature

418

) changes little because the propagation thereof is prevented by the throttle portion

421

formed sideways of the armature

418

. Consequently, an oil pressure difference acts up and down of the armature

418

and the armature (corresponding to the pressure receiving portion) is urged upward (in the valve opening direction) due to the oil pressure difference. With the urging force induced by the pressure difference, the bounce of the valve element

411

in valve opening is suppressed.

At the time of fuel injection, the fuel flows out of the first chamber

420

(below the armature

418

), then flows through the passage (throttle portion

421

) formed sideways of the armature

418

, and further flows toward the overlying second chamber

422

(above the armature

418

). With this upward flow of the fuel, the armature

418

is given an upward force (in the valve opening direction). Also by this action the bounce of the valve element

411

is prevented.

Upon turning OFF of the drive signal provided from ECU

4

to de-energize the coil

436

, there no longer is any attractive force for the armature

418

by the stator

423

and the valve element

411

is displaced downward with the biasing force of the spring

415

. When the valve element

411

abuts the sheet of the valve body

407

, the valve closing operation is over and thereafter the closed state of the valve is maintained. When the valve element

411

moves down and the tip thereof comes into abutment against (sits on) the nozzle body

407

, the nozzle holes

414

close to stop the injection of fuel.

In the conventional fuel injector

100

shown in

FIG. 33

, due to collision of the valve element

101

with the nozzle body

104

at the time of valve opening there occurs bouncing of the valve element

101

several times as indicated with a broken line in FIG.

30

. As a result, there occurs a secondary injection after closing of the valve.

In the fuel injector

401

of this embodiment, as compared with the above related art, when the injection of fuel is stopped, the flow of injected fuel is cut off suddenly, so that the internal pressure of the nozzle chamber

427

and that of the second chamber

422

(the upper surface of the armature

418

) which is in communication with the nozzle chamber

427

increase. At this time, the internal pressure of the first chamber

420

(the lower surface of the armature

418

) changes little because the propagation thereof is prevented by the throttle portion

412

formed sideways of the armature

418

. Consequently, an oil pressure difference acts up and down of the armature

418

and the armature is urged downward (in the valve closing direction) due to the oil pressure difference. With the urging force induced by the pressure difference, the bounce of the valve element

411

in valve closing is suppressed.

When the nozzle holes

414

are cut off and the internal pressure of the second chamber

422

rises, fuel flows out of the second chamber

422

(above the armature

418

), then flow through the passage (throttle portion

421

) formed sideways of the armature

418

, and further flows toward the first chamber

420

(below the armature

418

). With this downward flow of the fuel, the armature

418

is given a downward force (in the valve closing direction). Thus, also by this action the bounce of the valve element

411

in valve closing is suppressed.

On the other hand, since the fuel injector

401

described above adopts a direct acting type construction wherein the valve element

411

is actuated directly with the electromagnetic solenoid

432

, there is little leakage of fuel and thus the fuel injector

401

is suitable as a fuel injector for a liquefied gas fuel.

Besides, even when the valve element

411

is long and heavy as in this embodiment, it is possible to improve the injection characteristic because the occurrence of bouncing of the valve element

411

is suppressed.

Further, in the case where the viscosity of fuel is low like such a liquefied gas fuel as LPG or DME, there arises a serious problem caused by bouncing of the valve element

411

, but according to this embodiment it is possible to suppress the bounce of the valve element even in case of a low fuel viscosity.

A fuel injector

451

according to a twelfth embodiment of the present invention will now be described with reference to

FIG. 32

which illustrates a sectional structure of the fuel injector

451

. A description will be given below about a principal portion different from the previous eleventh embodiment. In this twelfth embodiment the same reference numerals as in the eleventh embodiment represent the same functional components as in the eleventh embodiment.

In this twelfth embodiment, disc

441

(corresponding to the pressure receiving portion) which undergoes a differential pressure is provided at an upper end of a valve element

411

which extends upward beyond the armature

418

, and a first chamber

420

is formed below the disc

441

, while a second chamber

422

is formed above the disc

441

. Further, a throttle portion

421

is defined by a clearance between the disc

441

and a component (body

406

).

Also with this arrangement it is possible to obtain the same effects as in the eleventh embodiment. The disc

441

which undergoes a differential pressure need not be positioned above the armature

418

, nor need be the disc

441

in the shape of a disc.

Although the fuel injectors

401

and

451

of the above eleventh and twelfth embodiments are for the injection of a liquefied fuel such as DME or LPG, the present invention is also applicable to fuel injectors which inject other fuels. For example, the present invention may be applied to a fuel injector for the injection of gas oil or gasoline while preventing the occurrence of bouncing of a valve element used therein.

Although in the above embodiments there is used the electromagnetic solenoid

432

as an example of an electric actuator, there may be used another electric actuator such as a piezoelectric actuator comprising a large number of stacked piezoelectric elements.

Further, a passage resistance means for increasing the passage resistance of fuel may be provided in the throttle portion

421

so that the force of fuel flowing through the throttle portion

421

is greatly exerted on the valve element

411

.

A thirteenth embodiment of the present invention will now be described. In this embodiment there are provided a fuel supply system for the injection and supply of a liquefied gas fuel such as DME or LPG to a diesel engine and also provided an air conditioner.

In

FIG. 34

, a liquefied gas fuel such as DME or LPG is stored in a liquid state within a fuel tank

510

. The internal pressure of the fuel tank

510

is equal to a saturated vapor pressure of the liquefied gas fuel. In case of using DME as a liquefied gas fuel, a saturated vapor pressure of DME is about 0.6 MPa at room temperature, for example, 25° C. A low pressure pump

511

is disposed within the fuel tank

510

. With the low pressure pump

511

, the liquefied gas fuel is fed in a pressurized state to a predetermined feed pressure (3 MPa or so) to a high pressure pump

513

through a pipe

512

.

The internal pressure of the fuel tank

510

is equal to a saturated vapor pressure of the liquefied gas fuel, and when the temperature of the liquefied gas fuel locally rises only slightly or the pressure thereof locally drops only slightly within the fuel tank

510

, there occur bubbles (vapor). In such a case, by disposing the low pressure pump

511

within the fuel tank

510

, the formation of bubbles caused by a pressure drop in a path extending from the fuel tank

510

to the low pressure pump

511

and a deficient suction of the low pressure pump

511

are prevented. At the same time, a temperature difference between the fuel tank

510

and the low pressure pump

511

becomes smaller, whereby the formation of bubbles caused by the temperature difference and the resulting deficient suction of the low pressure pump

511

are prevented.

The high pressure pump

513

compresses the liquefied gas fuel to a high pressure (35 MPa or so) corresponding to the injection pressure and feeds the thus-compressed high pressure fuel to a common rail

515

through a pipe

514

. The liquefied gas fuel leaking from a slide portion or a seal portion of the high pressure pump

513

passes through a pipe

516

and is recovered into a fuel recovery tank

517

. The common rail

515

and the fuel recovery tank

517

are connected together through a pipe

518

, with a pressure limiting valve

519

being disposed at an intermediate position of the pipe

518

. In this case, surplus fuel is recovered into the fuel recovery tank

517

through the pressure limiting valve

519

lest the fuel pressure within the common rail

515

should exceed a predetermined level (35 MPa or so).

Fuel injectors

520

in a number corresponding to the number of engine cylinders are connected to the common rail

514

, and as the fuel injectors

520

are actuated, the high pressure fuel stored in the common rail

515

is fed by injection to the diesel engine. The fuel injectors

520

are each constructed of an electromagnetic control valve

520

a

which intermits the supply of the high pressure fuel from the common rail

515

and an injection nozzle

520

b

which causes a valve element to move with operation of the electromagnetic control valve

520

a

and allows the fuel to be injected from a nozzle tip. The operation of each fuel injector is controlled by means of a microcomputer (not shown). The liquefied gas fuel leaking for example from a valve element slide portion of each fuel injector

520

passes through a pipe

521

and is recovered into the fuel recovery tank

517

.

The following description is now provided about the air conditioner. The fuel which has been pressurized to about 3 MPa into a liquefied state by means of the low pressure pump

511

passes through a pipe

531

and is fed to an expansion valve

532

. An air conditioner control valve

533

is installed at an intermediate position of the pipe

531

, whereby the air conditioner is controlled ON and OFF. For example, when an air conditioner switch is turned ON by a vehicle occupant, the air conditioner control valve

533

is opened to permit the passage of the liquefied gas fuel flowing from the fuel tank

510

toward the expansion valve

532

. Upon turning OFF of the air conditioner switch, the air conditioner control valve

533

is closed to inhibit the passage of the liquefied gas fuel flowing from the fuel tank

510

toward the expansion valve

532

.

In the expansion valve

532

, the liquefied gas fuel which is in a liquefied state is expanded rapidly into mist of a low temperature and low pressure and the misty fuel flows to an evaporator

535

through a pipe

534

. In the evaporator

535

, a latent heat necessary for evaporation is removed from the ambient air through evaporator fins, whereby the ambient air is cooled. At this time, a blower motor

536

is operated and the air present within the vehicle compartment is cooled thereby. The liquefied gas fuel evaporated in the evaporator

535

passes through a pipe

537

and is fed to the fuel recovery tank

517

.

A pressure bulb

538

is attached to the pipe

537

and the degree of opening of the expansion valve

532

is adjusted in accordance with the fuel temperature detected by the pressure bulb

538

. More specifically, the degree of opening of the expansion valve

532

becomes large when the fuel temperature is high, while it becomes small when the fuel temperature is low.

The liquefied gas fuel which has been recovered in a gaseous state into the fuel recovery tank

517

flows through a pipe

539

into a compressor

540

, in which it is sucked and compressed. The liquefied gas fuel having been increased in both temperature and pressure in the compressor

540

passes through a pipe

541

and flows into a condenser

542

. Then, in the condenser

542

, the liquefied gas fuel is cooled with an engine cleaning fan and is liquefied while being removed its condensation latent heat. The fuel thus liquefied flows into a receiver tank

544

, in which it is separated into gas and liquid. Then, only the liquid passes through a pipe

545

and is fed into the fuel tank

510

.

At an intermediate position of the pipe

545

is provided a check valve

546

, which permits only the flow of fuel advancing from the receiver tank

544

(condenser

542

side) toward the fuel tank

510

. Therefore, for example when the engine is OFF, a reverse flow of the liquefied gas fuel from the interior of the fuel tank

510

to the receiver tank

544

is prevented.

According to the above construction shown in

FIG. 34

, in the common rail type fuel injection system, the liquefied gas fuel leaking from the high pressure pump

513

, common rail

515

and fuel injectors

520

is once recovered into the fuel recovery tank

517

and is thereafter liquefied by means of the compressor

540

and the condenser

542

, then is returned to the fuel tank

510

. In this case, the compressor

540

and the condenser

542

not only plays its inherent role of liquefying the refrigerant (liquefied gas fuel) but also fulfills the role of recovering the leakage fuel. Thus, the sharing of the compressor

540

and the condenser

542

can be achieved.

Since in this embodiment the fuel injection system and the air conditioner share the compressor

540

, the operation of the compressor

540

is kept ON during operation of the engine, but the operation of the air conditioner is turned ON or OFF arbitrarily by the air conditioner control valve

533

. At this time, also in the case where the air conditioner control valve

533

is closed to turn OFF the air conditioner, the foregoing leakage fuel is separately liquefied by the compressor

540

and the condenser

542

.

According to this embodiment described above in detail there are obtained the following effects.

Unlike the related art, since the compressor

540

and the condenser

542

are shared by the common rail type fuel injection system and the air conditioner, it is not necessary to use a fuel compressor dedicated to the recovery of fuel. As a result, it is possible to simplify the construction as a fuel supply system and reduce the cost. Of course, also as to the vehicle which carries this system thereon, the cost thereof can be reduced.

Since there is adopted a construction wherein a liquefied gas fuel is stored in a liquid state within the fuel tank

510

and is fed in the liquid state to the expansion valve

532

in the air conditioner, it is possible to feed the liquefied gas fuel in the liquid state to the expansion valve

532

from just after the start of the engine. That is, although the refrigerant (liquefied gas fuel) usually vaporizes while the engine is OFF, it is no longer required to wait for liquefaction of the refrigerant just after the start of the engine. Consequently, a vehicle compartment cooling effect can be obtained so much earlier.

Further, since the low pressure pump

511

is disposed within the fuel tank

510

, a pressure drop in the path from the fuel tank

510

to the low pressure pump

511

, the formation of bubbles due to a temperature difference between the fuel tank

510

and the low pressure pump

511

, and a consequent deficiency in suction of the low pressure pump

511

, can be prevented.

The position for the discharge of leakage fuel from the fuel injection system to the air conditioner side is not limited to the position between the evaporator

535

and the compressor

540

. It may be changed as desired if it is possible to carry out the liquefying process for the leakage fuel and if the construction adopted permits the leakage fuel to be discharged upstream of the condenser

542

.

Although in this embodiment the compressor

540

is essential to the air conditioner, it is also possible to accomplish the air conditioner without using the compressor

540

. Particularly, in case of using a liquefied gas fuel as refrigerant, the liquefaction of the liquefied gas fuel can be done by only cooling and condensation in the condenser

542

and thus an air conditioner is constituted.

It is also possible to embody this system without using the fuel recovery tank

517

. In this case, the fuel leaking from the fuel injection system may be discharged directly into a pipe (e.g., the pipe

539

) laid within the air conditioner.

Although the fuel injection system in this embodiment is a common rail type fuel injection system, there may be used another type of a fuel injection system. For example, there may be adopted a construction wherein the liquefied gas fuel is pressurized high and is then fed to each fuel injector, using a distribution type fuel injection pump, without using a common rail.

Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the present invention as defined in the appended claims.

QQ群二维码
意见反馈