Heat pump type air conditioning system for automotive vehicle

This is a division of application Ser. No. 08/970,806, filed Nov. 14, 1997 now U.S. Pat. No. 6,125,643.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to improvements in a heat pump type air conditioning system for an automotive vehicle in which a passenger compartment is heated and refrigerated under the action of engine coolant and refrigerant, and more particularly to the improvements to solve various problems encountered in conventional similar heat pump type air conditioning systems so as to offer the heat pump type air conditioning system suitable for practical use.

2. Description of the Prior Art

Hitherto, heat pump type air conditioning systems have been developed for automotive vehicles. Such air conditioning systems carry out both refrigeration and heating for a passenger compartment under cycle operations using a refrigerant. The air conditioning systems include a sub-condenser or interior heat exchanger disposed inside the passenger compartment, in which high temperature and pressure refrigerant from a compressor is introduced into the sub-condenser so as to be used as a heat source for heating the passenger compartment. A main condenser or exterior heat exchanger is disposed outside the passenger compartment. Additionally, a four-way valve is provided to change over flow of the refrigerant from the sub-condenser to the main condenser and vise versa to accomplish a changeover between a refrigeration operation and a heating operation of the air conditioning system. More specifically, the refrigerant discharged from the compressor is introduced to the main condenser during the refrigeration operation, whereas the refrigerant is directly introduced to the sub-condenser through a bypass passage which is formed bypassing the main condenser.

Such heat pump type air conditioning systems have been recently mounted on a part of high quality cars and so-called one box-type cars having a relatively large space, in which they a so-called dual air conditioning type including a front unit for air-conditioning a front region (for example, a front seat part) of the passenger compartment and a rear unit for air-conditioning a rear region (for example, a rear seat part) of the passenger compartment. Accordingly, the front and rear regions of the passenger compartment can be independently air-conditioned so as to achieve a comfortable air conditioning for the passenger compartment. Such air conditioning systems operate as follows: During the heating operation of the air conditioning system, the front unit uses engine coolant as a heat source while the rear unit uses as a heat source a high temperature and pressure refrigerant which is compressed by the compressor. Such air conditioning systems are arranged to pump up heat from the low temperature outside air in the circulating process or refrigeration cycle of the refrigerant and uses it to heat the passenger compartment.

Such air conditioning systems encounter with problems in case of carrying out the heating operation of the passenger compartment of the automotive vehicle. For example, when the temperature of the outside air is low, for example, in the morning in winter, the temperature of the engine coolant is low at the engine starting, and the temperature rise of the refrigerant is not sharp. Consequently, it is difficult to put the air conditioning system into such a state as to blow warm air into the passenger compartment simultaneously with the starting of operation of the air conditioning system, so that the air conditioning system is low in quick or instant heating ability and is low in heating performance. Particularly in the one-box type cars which provided with a diesel engine and are large in space of the passenger compartment, the rate of temperature rise of the engine coolant is low as compared with automotive vehicles provided with a usual gasoline engine while it is required to heat the large space, and therefore there is such a tendency as to be low in quick heating ability and heating performance for the passenger compartment. In view of this, a heat pump type air conditioning system of the following type has now been proposed: The refrigerant is heated under the action of heat of the coolant for a driving system in an electric vehicle thereby to be increased in enthalpy and becoming high in temperature. Accordingly, the thus heated refrigerant exhibits a high heating ability of the air conditioning system. Such a heat pump type air conditioning system is disclosed in Japanese Patent Provisional Publication No. 7-101227.

Thus, the various heat pump type air conditioning systems and improvements therefor have been developed and proposed.

However, the above-discussed heat pump type air conditioning systems have encountered a variety of drawbacks which will be discussed below. That is, it is usual to carry out an on-off control of the compressor by making an on-off control of a magnetic clutch (disposed between the compressor and an engine) in accordance with the discharge pressure of the compressor in order to protect the compressor from its breakage when the discharge pressure of the compressor excessively rises. The discharge pressure of the compressor is detected by a pressure sensor. However, in case of protecting the compressor only under the on-off control of the compressor, shock (impact) and noise are generated with the on-off control (for example, the on-off action of the magnetic clutch) of the compressor. It will be understood that the on-off actions of the magnetic clutch correspond respectively to a connection and a disconnection between the compressor and the engine. These connection and disconnection tend to readily be transmitted as shock to the driver, thereby lowering the drivability of the vehicle.

Further, in order to cause the heat pump type air conditioning systems to exhibit a high heating performance, it is required to recover the refrigerant accumulated in the exterior heat exchanger to the compressor thereby using a large amount of the refrigerant for the heating operation of the air conditioning system. In this regard, the above-discussed air conditioning systems of the dual air conditioning type mounted on the one box-type cars and the like have a relatively large volume condenser and a relatively long piping, so that a considerable time is required to recover the refrigerant. Additionally, for example in case of accomplishing the refrigeration and heating operations of only the rear unit, the refrigerant becomes unnecessary for the front unit. Accordingly, if the refrigerant (for the front unit) accumulated in the evaporator and the like are recovered, a large amount of the liquid state refrigerant is supplied to the compressor, thereby causing the fears of compressing the liquid state refrigerant, and of cleaning the inside of the compressor with the liquid state refrigerant. This degrades the reliability of the compressor itself.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved heat pump type air conditioning system for an automotive vehicle, by which drawbacks encountered in conventional heat pump type air conditioning systems can be effectively overcome.

Another object of the present invention is to provide an improved heat pump type air conditioning system for an automotive vehicle, which effectively improves drivability of the vehicle while being effectively protected from being damaged, and additionally high in reliability and low in production cost.

A further object of the present invention is to provide an improved heat pump type air conditioning system for an automotive vehicle, which is high in reliability for a compressor itself and for recovery of a refrigerant.

A still further object of the present invention is to provide an improved heat pump type air conditioning system for an automotive vehicle, which includes a refrigerant recovery system by which a large amount of refrigerant can be effectively recovered for a short time, thereby ensuring a high heating performance of the air conditioning system.

An aspect of the present invention resides in a heat pump type air conditioning system (A) for an automotive vehicle. The heat type air conditioning system comprises a first unit (

10

) including a heater core (

11

) through which an engine coolant of an engine flows, and a first heat exchanger (

12

) which forms part of a refrigeration cycle including a compressor (

1

) and a first condenser (

3

), a refrigerant circulating in the refrigeration cycle. A second unit (

20

) is provided including a second condenser (

21

) and a second heat exchanger (

22

) which are fluidly connected in parallel with the first heat exchanger (

12

). A valve (V

2

) is fluidly connected in series with the second condenser (

21

) and disposed such that a part of the refrigerant is introduced through the valve into the second condenser (

21

) and said second heat exchanger (

22

). A sub-heat exchanger (

30

) is disposed outside the first and second units and fluidly connected in series with the second heat exchanger (

22

), the refrigerant flowing from the second heat exchanger (

22

) being introduced into the sub-heat exchanger to be heated by a part of the engine coolant, the refrigerant discharged from the sub-heat exchanger being returned to the compressor. An electromagnetic clutch (

40

) is provided such that the compressor (

1

) is drivably connectable with the engine therethrough, the electromagnetic clutch being engaged to establish a driving connection between the compressor so as to operate the compressor and disengaged to cut the driving connection so as to make the compressor inoperative. A control device (C) is operatively connected to the electromagnetic clutch (

40

) for controlling the electromagnetic clutch to be disengageable in accordance with a temperature within the air conditioning system (A).

According to this aspect, by virtue of the fact that the electromagnetic clutch is controlled to be disengageable in accordance with the temperature within said air conditioning system, the time cycle of the on-off (engaging and disengaging) actions of the electromagnetic clutch is prolonged thereby reducing the frequency of changeover from the connecting state (between the engine and the compressor) to the disconnecting state (between the engine and the compressor) and vice versa. This improves the drivability of the automotive vehicle on which the air conditioning system is mounted. Additionally, the reduced frequency of the changeover minimizes a pressure variation in the air conditioning system while contributing to protecting the air conditioning system itself.

Another aspect of the present invention resides in a heat pump type air conditioning system for an automotive vehicle. The heat pump type air conditioning system comprises a first unit (

110

) including a heater core (

111

) through which an engine coolant of an engine flows, and a first evaporator (

112

) which forms part of a first refrigeration cycle including a first condenser (

103

), a first liquid tank (

104

a

) and a first expansion valve (

105

a

) which are fluidly connected in series with each other, the first refrigeration cycle being supplied with a refrigerant discharged from a compressor (

101

) driven by the engine through a first valve (V

11

), the compressor being fluidly connected in series with the first evaporator (

112

). A second unit (

120

) includes a second condenser (

121

) and a second evaporator (

122

) which is fluidly connected in series with the second condenser (

121

) through a second liquid tank (

104

b

) and a second expansion valve (

105

b

), the second condenser (

121

), and the second evaporator (

122

) being fluidly connected in series with the compressor (

101

) and forming part of a second refrigeration cycle which is supplied with a part of the refrigerant discharged from the compressor (

101

) through a second valve (V

12

). A refrigerant recovery line (R

1

) is fluidly connected in series with the first condenser (

103

) to introduce the refrigerant discharged from the first condenser (

103

) into the second refrigeration cycle during a heating operation of the air conditioning system (A).

According to this aspect, by virtue of the refrigerant recovery line for introducing the refrigerant discharged from the first condenser to the second refrigeration cycle during the heating operation of the air conditioning system, the refrigerant to be recovered is returned to the compressor through the second refrigeration cycle, so that the refrigerant is put into its evaporated state and therefore there are no fear of compressing a liquid in the compressor, of arising flowing-out of oil, and of causing rinsing action with the refrigerant. As a result, the compressor

1

can normally operate without lowing the reliability thereof.

A further aspect of the present invention resides in a heat pump type air conditioning system for an automotive vehicle. The heat pump type air conditioning system comprises a compressor (

206

), an exterior condenser (

207

) disposed outside a passenger compartment of the vehicle, an interior condenser (

205

) disposed inside the passenger compartment, a pressure-reducing device (

209

), and an interior evaporator disposed inside the passenger compartment which are connected in series with each other through a refrigerant piping (

212

). A bypass passage (

213

) is formed bypassing the exterior condenser to allow the refrigerant discharged from the compressor (

206

) to be introduced to the interior condenser (

205

) bypassing the exterior condenser (

207

). A flow passage change-over device (

220

) is provided to introduce the refrigerant discharged from the compressor (

206

) to the exterior condenser (

207

) during a refrigeration operation of the air conditioning system and to the bypass passage (

213

) during a heating operation of the air conditioning system. A refrigerant recovery passage (

230

) is provided such that the refrigerant stayed in the exterior condenser (

207

) is returned therethrough to a suction side of the compressor (

206

), the refrigerant recovery passage (

230

) being located to connect the outlet side of the exterior condenser (

207

) and the suction side of the compressor (

206

). A valve (

231

) is disposed in the refrigerant recovery passage (

230

) to be opened to allow the refrigerant to flow through the refrigerant recovery passage and to be closed to prevent the refrigerant from flowing through the refrigerant recovery passage.

According to this aspect, the refrigerant can be recovered in its liquid state from the outlet of the exterior condenser during the heating operation of the air conditioning system. Accordingly, a large amount of the refrigerant can be recovered for a short time without causing a reverse flow of the refrigerant to the exterior condenser. The amount of the refrigerant within the heating cycle can be always maintained at a suitable level during the heating operation of the air conditioning system. This solves the problems of lowering the heating performance due to the heating operation under a refrigerant-shortage condition and of lowering a lubricating ability, thereby improving the performance and reliability of the air conditioning system.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, same reference numerals (characters) designate same elements and parts throughout all figures, in which:

FIG. 1

is a diagrammatic view of a first embodiment of a heat pump type air conditioning system according to the present invention;

FIG. 2

is a graph showing relative relationships between the temperature of intake air in a rear unit and the discharge pressure of a compressor in the air conditioning system of

FIG. 1

;

FIG. 3

is a diagrammatic view of a modified example of the first embodiment heat pump type air conditioning system of

FIG. 1

;

FIG. 4

is a diagrammatic view of a second embodiment of the heat pump type air conditioning system according to the present invention;

FIG. 5

is a diagrammatic view of a third embodiment of the heat pump type air conditioning system according to the present invention;

FIG. 6

is a diagrammatic view of a modified example of the third embodiment heat pump type air conditioning system of

FIG. 4

;

FIG. 7

is a diagrammatic view of another modified example of the third embodiment heat pump type air conditioning system of

FIG. 5

; and

FIG. 8

is a diagrammatic view of a further modified example of the third embodiment heat pump type air conditioning system of

FIG. 5

; and

FIG. 9

is a schematic illustration of a main condenser forming part of the heat pump type air conditioning system of FIG.

5

.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to

FIGS. 1

to

3

, a first embodiment of a heat pump type air conditioning system for an automotive vehicle is illustrated by the reference character A. The air conditioning system A of this embodiment comprises front or first unit

10

and a rear or second unit

20

. The front unit

10

is arranged to condition air which is selectively drawn from the inside and the outside of a passenger compartment (not shown) of the automotive vehicle under the action of a fan (not shown) and to blow the conditioned air toward a front seat for vehicle passenger. The rear unit

20

is arranged to condition air which is selectively drawn from the inside and outside of the passenger compartment under the action of a fan and to blow out the conditioned air toward a rear seat for vehicle passenger. Accordingly, this air conditioning system A is called a dual air conditioning system.

The front unit

10

includes a casing

10

a

defining thereinside an air flow passage

10

f

in which air flows in a direction (air flow direction) indicated by an arrow F

1

. A heater core

11

and a first heat exchanger

12

are disposed in the air flow passage

10

f

and located respectively at the downstream and upstream sides relative to the air flow direction F

1

. The heater core

11

is arranged such that engine coolant (hot water) heated by an engine

2

is circulated therethrough. More specifically, the front unit

10

includes an intake unit (not identified), a cooling unit (not identified) and a heater unit (not identified) which are disposed in the order mentioned in the air flow direction in the casing

10

a

though not clearly shown. The intake unit includes an intake door (not shown) and the above-mentioned fan. The cooling unit includes the first heat exchanger

12

. The heat unit includes an air mixing door (not shown) and the heater core

11

. The air mixing door is disposed in front of the heater core

11

and arranged to control the ratio in flow amount between hot air passing through the heater core

11

and cool air bypassing the heater core

11

thereby to prepare air having a predetermined temperature in a region downstream of the heater core

11

, and arranged to prevent air from passing through the heater core

11

Additionally, a variety of vents (air blow openings) are formed at the downstream side of the heater core

11

of the heater unit so as to blow the air (having been controlled in temperature) prepared upon mixing the hot air and the cool air toward the front seat inside the passenger compartment, though not shown.

The rear unit

20

includes a casing

20

a

defining thereinside an air flow passage

20

f

in which air flows in a direction (air flow direction) indicated by an arrows F

2

. A second condenser

21

and a second heat exchanger

22

are disposed in the air flow passage

20

f

and located respectively at the downstream and upstream sides relative to the air flow direction F

2

. More specifically, the rear unit

20

includes an intake unit (not identified), a cooling unit (not identified) and a heater unit (not identified) which are disposed in the order mentioned in the air flow direction in the air flow passage

21

similarly to the front unit

10

, though not clearly shown. The intake unit includes an intake door (not shown) and the above-mentioned fan. The cooling unit includes the second heat exchanger

22

. The heater unit includes an air mixing door (not shown) and the second condenser

21

. The air mixing door is disposed in front of the second condenser

21

and arranged to control a ratio in flow amount between hot air passing through the second condenser

21

and cool air bypassing the second condenser

21

thereby to prepare air having a predetermined temperature in a region downstream of the second condenser

21

, and arranged to prevent air from passing through the second condenser

21

. Additionally, a variety of vents (air blow openings) are formed at the downstream side of the second condenser

21

of the heater unit so as to blow air (having been controlled in temperature) prepared upon mixing the hot air and the cool toward the rear seat inside the passenger compartment, though not shown.

In this embodiment, the air conditioning system A includes a first refrigeration cycle or circuit and a second refrigeration cycle or circuit. The first refrigeration cycle is constituted of a compressor

21

, a first condenser

3

, a liquid tank

4

a

, a first valve V

1

, a first expansion valve

5

a

, and the first heat exchanger

12

(in the front unit

10

) which are connected to each other through a piping or lines for a refrigerant. The second refrigeration cycle is constituted of a second valve V

2

, the second condenser

21

(in the rear unit

20

), a liquid tank

4

b

, a second expansion valve

5

b

, the second heat exchanger

22

(in the rear unit

20

), and a sub-heat exchanger

30

which are fluidly connected to each other through a piping or lines for the refrigerant and in parallel with the first heat exchanger

12

. A changeover in flow of the refrigerant between the first and second refrigeration cycles is carried out under combination of the opening and closing actions of the first valve V

1

and the second valve V

2

.

In order to realize a refrigeration operation and a heating operation of the air conditioning system A in the same cycle, a bypass circuit or passage

3

B is provided to allow the refrigerant discharged from the compressor

1

to bypass the first condenser

3

. A four-way valve

7

is provided to cause flow of the refrigerant discharged from the compressor

1

to be changed over from the first condenser

3

to the bypass circuit

3

B and vice versa. In other words, under the action of the four-way valve

7

, the refrigerant from the compressor

1

is introduced to the bypass circuit

3

B during a heating operation of the air conditioning system A while to the first condenser

3

during a refrigeration operation of the air conditioning system A.

The four-way valve

7

includes a hermetically sealed casing which is formed with one inlet port Pi and three outlet ports Po. A sliding member S is sidably disposed in the casing and arranged to establish communication between selected two of the three outlet ports Po, so that one outlet port Po other than the selected two outlet ports Po is brought into communication with the inlet port Pi. The inlet port Pi of the four-way valve

7

is in communication with the discharge side of the compressor

1

, while the three outlet ports Po of the four-way valve

7

are respectively in communication with the inlet of the first condenser

3

, the suction side of the compressor

1

(through a refrigerant return circuit or passage R), and the outlet of the first condenser

3

(through the bypass circuit

3

B).

The four-way valve

7

is used for effecting the return circuit R. This return circuit R functions to once return a large amount of the refrigerant staying in the first condenser

3

and the like to the compressor

1

in case that the engine coolant cannot be immediately used as a heat source for heating the passenger compartment because the temperature of outside air is low at starting of the heating operation of the air conditioning system A. This enables a large amount of the refrigerant to be used to attain a high performance heating.

Regarding the front unit

10

, during the heating operation of the air conditioning system A, the refrigerant discharged from the compressor

1

flows through the four-way valve

7

, the bypass circuit

3

B for the first condenser

3

, the liquid tank

4

a

, the first valve V

1

, the expansion valve

5

a

, and the first heat exchanger

12

in the order mentioned and then returns to the compressor

1

. During the refrigeration operation of the air conditioning system A, the refrigerant discharged from the compressor

1

flows through the four-way valve

7

, the first condenser

3

, the liquid tank

4

a

, the first valve V

1

, the expansion valve

5

a

, and the first heat exchanger

12

in the order mentioned and then returns to the compressor

1

.

The heater core

11

is arranged to be supplied with an engine coolant flown from the engine

2

by opening a hot water cock or valve

11

a

in a hot water circuit or passage W.

Regarding the rear unit

20

, both during the refrigeration and heating operations of the air conditioning system A, the refrigerant discharged from the liquid tank

4

a

flows through the second valve V

2

, the second condenser

21

, the liquid tank

4

b

, the second expansion valve

5

b

, the second heat exchanger

22

, and the sub-heat exchanger

30

in the order mentioned and returns to the compressor

1

.

The sub-heat exchanger

30

is disposed outside the air flow passages

10

f

,

20

f

of the front and rear units

10

,

20

. The engine coolant from the engine

2

is introduced into the sub-heat exchanger

30

by opening a hot water cock or valve

11

b

in the hot water circuit W, in which a heat exchange is made between the engine coolant and the refrigerant flowing through the sub-heat exchanger

30

. In other words, the refrigerant flowing through the sub-heat exchanger

30

is heated by the engine coolant, so that the refrigerant makes its isoentropic change. The refrigerant having make its isoentropic change is returned to the compressor

1

thereby causing the air conditioning system A to exhibit a higher heating performance.

The compressor

1

is drivably connected to the engine

2

through an electromagnetic clutch

40

. The electromagnetic clutch

40

makes its on-off actions under its on-off control. More specifically, the electromagnetic clutch

40

is switched ON to be engaged thereby to transmit a rotational power from the engine

2

to the compressor

1

, while switched OFF to be disengaged thereby to prevent the rotational power from the engine

2

from being transmitted to the compressor

1

. The on-off control of the electromagnetic clutch

40

is made in accordance with a temperature (intake air temperature) of air taken into the air flow passage

20

f

of the rear unit

20

. More specifically, a temperature sensor SE

1

is disposed in the air flow passage

20

f

in the intake unit of the rear unit

20

in order to detect the intake air temperature. A signal (representative of the intake air temperature) is transmitted from temperature sensor SE

1

to a control unit C. The control unit C makes the on-off control of the electromagnetic clutch

40

in accordance with the signal from temperature sensor SE

1

. In other words, when the temperature sensor SE

1

detects that the intake air temperature in the rear unit

20

is not lower than a predetermined level (for example, 30° C.), the control unit C controls the electromagnetic valve

40

to be switched OFF to be disengaged. When the electromagnetic valve

40

is disengaged, the compressor

1

is switched OFF to stop its compression action. When the electromagnetic valve

40

is engaged upon being switched ON, the compressor is switched ON to make its compression action. Thus, an on-off control of the compressor

1

is accomplished in accordance with the intake air temperature in the rear unit

20

.

According to experiments, as shown in

FIG. 2

, it has been revealed that a proportional relationship exists between the intake air temperature (° C.) in the rear unit

2

and the discharge pressure (kg/cm

2

) of the compressor though such a relationship is slightly changed according to engine speed (the revolution speed) of the engine

2

. In

FIG. 2

, three relationships respectively obtained at engine speeds of 800 rpm, 1500 rpm and 3000 rpm are shown. A “Compressor-Off Region” indicated in

FIG. 2

represents a region where the compressor

1

is switched OFF to stop the compression action of the compressor

1

. This means that the same effect can be obtained by accomplishing the on-off control of the compressor

1

in accordance with the discharge pressure of the compressor

1

and in accordance with the intake air temperature in the rear unit

20

.

Here, in case that the on-off control of the compressor

1

is accomplished in accordance with the intake air temperature in the rear unit

20

, a response in control is lower than that in case that the on-off control of the compressor

1

is accomplished in accordance with the discharge pressure of the compressor

1

. However, a time cycle of the on-off (engaging and disengaging) actions of the electromagnetic clutch

40

is prolonged thereby reducing a frequency of changeover from a connecting state (between the engine

2

and the compressor

1

) to a disconnecting state (between the engine

2

and the compressor

1

) and vice versa. This improves a drivability of the automotive vehicle on which the air conditioning system A is mounted. Additionally, the reduced frequency of the changeover reduces a pressure variation in the air conditioning system A and therefore is desirable from the view point of protecting air conditioning system A itself.

Therefore, in this embodiment, operation of the air compressor

1

is stopped to stop the heating operation in the rear unit

20

when the intake air temperature in the rear unit

20

reaches the predetermined level.

Next, manner of operation of the thus arranged first embodiment heat pump type air conditioning system A will be discussed hereinafter.

Initial Stage of Heating Operation

When the temperature of the outside air (air outside the vehicle) is low (for example, about −10° C. to about +5° C.) so that the engine coolant has a lower temperature at the starting of the heating operation of the air conditioning system A, it is difficult to use the engine coolant for heating the passenger compartment, employing the heater core

11

. At such a time, the refrigerant has been staying inside the first condenser

3

and the like, and therefore a large amount of the refrigerant does not exist in the compressor

1

. In case of accomplishing heating for the front and rear seats under this condition, a setting is made as follows: The first and second valves V

1

, V

2

are opened; and the four-way valve

7

is in the state shown in FIG.

1

.

When the compressor

1

is switched ON to be operated under this condition, the refrigerant which has been staying mainly in the first condenser

3

and the like is introduced into the suction side of the compressor

1

through the four-way valve

7

and the refrigerant return circuit R so as to be recovered. As a result, a large amount of the refrigerant is discharged from the compressor

1

. The high temperature and pressure refrigerant discharged from the compressor

1

flows through the four-way valve

7

, the bypass circuit

3

B, the liquid tank

4

a

, the first valve V

1

, the expansion valve

5

a

and the first heat exchanger

12

in the order mentioned.

Under starting of the engine

1

, the engine coolant whose temperature having been raised to some extent flows into the heater core

11

; however, the engine coolant at this time is not sufficiently raised in temperature, and therefore it is not desirable to use the engine coolant to heat the passenger compartment. Accordingly, in such a condition, it is preferable that the hot water cock

11

a

is closed to prevent the engine coolant from flowing into the heater core

11

or that air in the air flow passage

10

f

cannot flow through the heater core

11

under the action of the intake door, in which the hot water cock

11

b

is opened so as to allow the engine coolant to flow through the sub-heat exchanger

30

. By this, air introduced from the intake unit into the inside of the front unit

10

is brought into contact with the first heat exchanger

12

in which the high temperature and pressure refrigerant flows, in which heat exchange is made between the air and the refrigerant. Thereafter, the air flows to the downstream side of the air flow passage

10

f

and blown through the vents to the passenger compartment.

Concerning the rear unit

20

, the flow of the high temperature and pressure refrigerant which is bifurcated after flowing out of the liquid tank

4

a

enters the second condenser

21

through the second valve V

2

. Here, heat exchange is made between the refrigerant and the air flowing through the air flow passage

20

f

of the rear unit

20

, so that the air to be supplied to the passenger compartment is heated. Thereafter, the refrigerant is condensed and to become medium in temperature and high in pressure, and is subjected to an adiabatic expansion in the second expansion valve

5

b

, so that the refrigerant becomes further low in temperature and low in pressure. Then, the refrigerant flows into the second heat exchanger

22

which functions as an evaporator. Here, heat exchange is made between the refrigerant and the air flowing through the air flow passage

20

f

of the rear unit

20

, in which the refrigerant evaporates after cooling air and then becomes low in temperature and in pressure to flow into the sub-heat exchanger

30

. Accordingly, the air to be supplied to the passenger compartment is first dehumidified and refrigerated by the second heat exchanger

22

, and therefore heated by the second condenser

21

.

It is preferable that a door (not shown) is disposed in front of the second heat exchanger

22

to prevent the air from passing through the second heat exchanger

22

during the heating operation of the air conditioning system A since it is not desirable that the air is cooled by the second heat exchanger

22

during the heating operation.

The low temperature and pressure refrigerant flowing through the sub-heat exchanger

30

takes in the heat of the engine coolant and rises in temperature to make its isotropic change. The refrigerant having made its isotropic change is returned to the compressor

1

to be again compressed, so that the temperature of the refrigerant discharged from the compressor

1

rises. In this case, the refrigerant to be returned to the compressor

1

is heated in the second heat exchanger

22

by the air and additionally heated in the sub-heat exchanger

30

by the engine coolant, so that a so-called two-stage heating is made to the refrigerant. This causes the air conditioning system A to exhibit a high heating performance while improving an instant or quick heating characteristics for the passenger compartment. Besides, when the thus heated refrigerant is again compressed by the compressor

1

, a temperature rise of the refrigerant is further promoted. When the thus heated refrigerant circulates to again reach the first and second heat exchangers

12

,

22

, the refrigerant is again heated here to obtain a further high temperature thereby causing the air conditioning system A to exhibit a further high heating performance so that high temperature air is blown into the passenger compartment. This tendency is amplified with a time lapse, thus greatly improving the instant or quick heating characteristics of the air conditioning system A.

When the temperature of the engine coolant has risen in the course of the above operation of the air conditioning system A, the heating ability of the sub-heat exchanger

30

is increased while the heating ability of the heater core

11

is increased in connection with the front unit

10

, so that considerable high temperature air is blown into the passenger compartment under the combination effect of the increased heating abilities of the sub-heat exchanger and the heater core

11

.

Concerning the rear unit

20

, the heating ability of the second condenser

21

is increased, and therefore considerably high temperature air is blown into the passenger compartment. It will be understood that the door which has been closed in front of the second heat exchanger

22

is allowed to be opened when the heating ability of the second condenser

21

is increased as discussed above, thereby making it possible to accomplish a so-called dehumidifying heating in which dehumidified air is heated. This defogs a window glass near the rear seat, thereby securing a safety driving of the vehicle.

During Stable Heating Operation

When the temperature of the engine coolant rises to some extent so that the temperature within the passenger compartment rises to some extent, the hot water cock

11

b

is closed thereby preventing the engine coolant from flowing into the sub-heat exchanger

30

. This prevents the refrigerant from being unnecessarily heated thereby to accomplish a normal heating operation of the air conditioning system A.

In this embodiment, when the intake air temperature within the rear unit

20

becomes a level not lower than the predetermined temperature, the temperature sensor SE

1

detects the temperature level and provides the signal representative of the temperature level to the control unit C. The control unit C causes the electromagnetic clutch

40

to be switched OFF or disengaged, thereby stopping the compression action of the compressor

1

. In contrast, when the intake air temperature within the rear unit

20

lowers to a level lower than the predetermined level, the compression action of the compressor

1

is again made. Thus, the on-off control of the compressor

1

is accomplished in accordance with the temperature of the air flowing through the air flow passage

20

f

in the rear unit

20

. Since the on-off control of the compressor

1

is accomplished in accordance with the intake air temperature in the rear unit

20

, a response in control may be lower than that in case that the on-off control of the compressor

1

is accomplished in accordance with the discharge pressure of the compressor

1

. However, the time cycle of the on-off (engaging and disengaging) actions of the electromagnetic clutch

40

is prolonged thereby reducing the frequency of changeover from the connecting state (between the engine

2

and the compressor

1

) to the disconnecting state (between the engine

2

and the compressor

1

) and vice versa. This improves a drivability of the automotive vehicle on which the air conditioning system A is mounted. Additionally, the reduced frequency of the changeover minimizes a pressure variation in the air conditioning system A while contributing to protecting the air conditioning system A itself.

During Refrigeration Operation

In order to accomplish refrigeration for both the front and rear seats, the first and second valves V

1

, V

2

are opened, and the sliding member S of the four-way valve

7

is moved. Under this state, when the compressor

1

is operated to make its compression action, the refrigerant discharged from the compressor

1

flows through the four-way valve

7

, the first condenser

3

, the liquid tank

4

a

, the first valve V

1

, the first expansion valve

5

a

, and the first heat exchanger

12

in the order mentioned, in the first refrigeration cycle. The flow of the refrigerant is bifurcated at the downstream side of the liquid tank

4

a

, so that the refrigerant flows through the second valve V

2

, the second condenser

21

, the second expansion valve

5

b

, the second heat exchanger

22

, and the sub-heat exchanger

30

in the order mentioned.

By this, the air introduced into the air flow passage

10

f

in the front unit

10

is subjected to heat exchange at the first heat exchanger

12

which functions as an evaporator, in which the heat exchange is made between the air and the low temperature and pressure refrigerant flowing through the heat exchanger

12

thereby to provide dehumidified low temperature air. This air is distributed to the side of the heater core

11

and the side of a bypass passage (not shown) bypassing the heater core

11

under the action of the air mixing door, thereby preparing cool air and hot air. The cool air and the hot air are mixed or not mixed to obtain air having a predetermined temperature. The air having the predetermined temperature is blown through the vents into the passenger compartment.

Concerning the rear unit

20

, the refrigerant which has been lowered in pressure by the second expansion valve

5

b

flows into the second heat exchanger

22

. The air refrigerated by the second heat exchanger

22

is distributed to the side of the second condenser

21

and to the side of a bypass passage (not shown) bypassing the second condenser

21

under the action of the air mixing door, thereby preparing cool air and hot air. The cool air and the hot air are mixed or not mixed to prepare air having a predetermined temperature. The air having the predetermined temperature is blown through the vents into the passenger compartment.

The refrigerant discharged from the second heat exchanger

22

flows into the sub-heat exchanger

30

; however, the refrigerant is returned at this state to the compressor

1

since the hot water cock

11

b

is closed to prevent the engine coolant from flowing into the sub-heat exchanger

30

.

In order to accomplish refrigeration only for the front seat, the second valve V

2

is closed In order to accomplish refrigeration only for the rear seat, the first valve V

1

is closed.

While only an example of the first embodiment has been shown and described, variations thereto will occur to those skilled in the art within the scope of the present inventive concepts which are delineated by the claims. For example, while the four-way valve

7

and the refrigerant return circuit R have been shown and described as being provided to return the refrigerant staying in the refrigerant circuit to the compressor

1

, it will be understood that the air conditioning system A may be operated without returning the staying refrigerant to the compressor

1

, in which the four-way valve

7

is replaced with open-and-close valves V

3

, V

4

which are respectively disposed in the inlet of the first condenser

3

and the bypass circuit

3

B as shown in FIG.

3

.

According to the first embodiment air conditioning system A, by virtue of the fact that the electromagnetic clutch is controlled to be disengageable in accordance with the temperature within said air conditioning system, the time cycle of the on-off (engaging and disengaging) actions of the electromagnetic clutch is prolonged thereby reducing the frequency of changeover from the connecting state (between the engine and the compressor) to the disconnecting state (between the engine and the compressor) and vice versa. This improves the drivabilty of the automotive vehicle on which the air conditioning system is mounted. Additionally, the reduced frequency of the changeover minimizes a pressure variation in the air conditioning system while contributing to protecting the air conditioning system itself.

FIG. 4

illustrates a second embodiment of the heat pump type air conditioning system A for an automotive vehicle, similar to the first embodiment air conditioning system. The air conditioning system A of this embodiment comprises front or first unit

110

and a rear or second unit

120

. The front unit

110

is arranged to condition air which is selectively drawn from the inside and the outside of a passenger compartment (not shown) of the automotive vehicle under the action of a fan (not shown) and to blow the conditioned air toward a front seat for vehicle passenger. The rear unit

120

is arranged to condition air which is selectively drawn from the inside and outside of the passenger compartment under the action of a fan and to blow out the conditioned air toward a rear seat for vehicle passenger. Accordingly, this air conditioning system A is called a dual air conditioning system.

The front unit

110

includes a casing

110

a

defining thereinside an air flow passage

110

f

in which air flows in a direction (air flow direction) indicated by arrows F

1

. A heater core

111

and a first heat exchanger

112

are disposed in the air flow passage

111

f

and located respectively at the downstream and upstream sides relative to the air flow direction F. The heater core

111

is arranged such that engine coolant (hot water) heated by an engine

102

is circulated therethrough. More specifically, the front unit

110

includes an intake unit (not identified), a cooling unit (not identified) and a heater unit (not identified) which are disposed in the order mentioned in the air flow direction in the casing

110

a

though not clearly shown. The intake unit includes an intake door (not shown) and the above-mentioned fan. The cooling unit includes the first heat exchanger

112

. The heat unit includes an air mixing door (not shown) and the heater core

111

. The air mixing door is disposed in front of the heater core

112

and arranged to control the ratio in flow amount between hot air passing through the heater core

111

and cool air bypassing the heater core

111

thereby to prepare air having a predetermined temperature in a region downstream of the heater core

111

, and arranged to prevent air from passing through the heater core

111

. Additionally, a variety of vents (air blow openings) are formed at the downstream side of the heater core

111

of the heater unit so as to blow the air (having been controlled in temperature) prepared upon mixing the hot air and the cool air toward the front seat inside the passenger compartment, though not shown.

The rear unit

120

includes a casing

120

a

defining thereinside an air flow passage

120

f

in which air flows in a direction (air flow direction) indicated by arrows F

2

. A second condenser

121

and a second evaporator

122

are disposed in the air flow passage

120

f

and located respectively at the downstream and upstream sides relative to the air flow direction F

2

. More specifically, the rear unit

120

includes an intake unit (not identified), a cooling unit (not identified) and a heater unit (not identified) which are disposed in the order mentioned in the air flow direction in the air flow passage

120

f

similarly to the front unit

110

, though not clearly shown. The intake unit includes an intake door (not shown) and the above-mentioned fan. The cooling unit includes the second evaporator

122

. The heater unit includes an air mixing door (not shown) and the second condenser

121

. The air mixing door is disposed in front of the second condenser

121

and arranged to control a ratio in flow amount between hot air passing through the sub-condenser and cool air bypassing the second condenser

121

thereby to prepare air having a predetermined temperature in a region downstream of the second condenser

121

, and arranged to prevent air from passing through the second condenser

121

. Additionally, a variety of vents (air blow openings) are formed at the downstream side of the second condenser

121

of the heater unit so as to blow air (having been controlled in temperature) prepared upon mixing the hot air and the cool toward the rear seat inside the passenger compartment, though not shown.

In this embodiment, the air conditioning system A includes a first refrigeration cycle or circuit (not identified) and a second refrigeration cycle or circuit (not identified). The first refrigeration cycle includes a compressor

101

, a first valve V

11

, a first condenser

103

, a first liquid tank

104

a

, a first expansion valve

105

a

, and the first evaporator

112

which are connected in series with each other in the order mentioned through a piping or lines for refrigerant. The second refrigeration cycle includes a second valve V

12

, the second condenser

121

, a second liquid tank

104

b

, a second expansion valve

105

b

, the second evaporator

122

, and a sub-heat exchanger

130

which are connected in series with each other in the order mentioned through a piping or lines for the refrigerant. A changeover operation in flow of the refrigerant between the first and second refrigeration cycles is carried out under the combination of the opening and closing actions of the first valve V

11

and the second valve V

12

. Additionally, a refrigeration operation and a heating operation of the air conditioning system A can be realized in the same cycle.

In this embodiment, a refrigerant recovery circuit or line R

1

is provided to introduce the refrigerant discharged from the first condenser

103

into the second refrigerant cycle. Specifically, the refrigerant recovery line R is arranged to return the refrigerant discharged from the first condenser

103

into the second liquid tank

104

b

. More specifically, the refrigerant recovery line R

1

includes a line or passage P through which the outlet of the first condenser

103

and the outlet of the second condenser

121

are fluidly connected with each other. A third valve V

13

and a one-way valve

140

are disposed in the passage P. The third valve V

13

is opened during the heating operation of the air conditioning system A. The one-way valve

140

is arranged to direct flow of the refrigerant from the first condenser

103

to the second evaporator

122

. Accordingly, at the starting of the heating operation of the air conditioning system A, the refrigerant stayed in the first condenser

103

is returned to the second refrigeration cycle thereby accomplishing a high performance heating operation of the air conditioning system A upon using a large amount of the refrigerant.

The heating operation can be accomplished with the front unit

110

. In case of the heating operation with the front unit

110

, the refrigerant discharged from the compressor

1

flows through the first valve V

11

, the first condenser

103

, the first liquid tank

104

a

, the first expansion valve

5

a

and the first evaporator

112

in the order mentioned and then returns to the compressor

1

. This flow of the refrigerant is the same as that during the refrigeration operation of the air conditioning system A. During the normal heating operation of the air conditioning system A, a hot water cock or valve

111

a

in a hot water circuit W is opened to allow engine coolant (relatively high in temperature) flowing out of the engine

102

to be introduced into the heater core

111

. The heater core

111

functions to heat the air which has been cooled by the first evaporator

112

. It will be understood that the engine coolant of the engine

102

circulates through the hot water circuit W.

During the refrigeration and heating operations of the air conditioning system A, concerning the rear unit

120

, the refrigerant whose flow has been bifurcated from the first refrigeration cycle upon opening of the second valve V

12

flows through the second condenser

121

, the second liquid tank

104

b

, the second expansion valve