Driving mechanism for a pump

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a drive mechanism for a pump, more specifically to a variable drive mechanism for a hydraulic pump.

2. Description of Related Art

From the prior art variable displacement pumps are known, wherein the displacement volume and the volume flow are mechanically adjustable. Vane-cell pumps and piston pumps are suited for adjustment in this way. These pumps only deliver a required amount of fluid, with adjustment being effected within the pump. It is, however, a disadvantageous effect that movable parts must be adjusted mechanically whereby accuracy is impaired, that orifices reducing the efficiency are used for volume flow control, and that the rotational speed is limited more narrowly than in the case of fixed displacement pumps.

In order to remedy these problems, polyphase machines are employed as a drive mechanism for a pump in the prior art, the input voltage and input frequency of which are variable by means of a frequency converter. The frequency converter may be physically separate from the polyphase machine or coupled to it by screw connection. Direct AC converters may be employed as frequency converters, whereby the motor winding is switched to different outer conductor voltages. It is, however, a drawback that the output frequency may only be adjusted in large steps, and that only frequencies below the mains frequency are possible.

These drawbacks are are eliminated in a frequency converter including an intermediary circuit. In such a link converter, the mains voltage is rectified to a direct voltage, smoothed, and applied to a DC-AC converter. At the output of the DC-AC converter, an alternating current having a different voltage and a different frequency is then available, which will then arrive in the polyphase machine. Polyphase machines preferred for economic reasons are the widely spread three-phase asynchronous machines. Such a motor features availability of a multiplicity of types and the fact that it does not require any startup aids.

Due to eddy currents and magnetic reversals in the magnetic material and due to the effect of the electrical current in the coil resistances of the above mentioned polyphase machines, heat is produced which limits the useful performance. In order to dissipate this heat, surface cooling is typically employed in the three-phase asynchronous machine, whereby ventilator losses are additionally incurred.

A fan-type air cooling which reduces the temperature at the surface is shown in FIG.

1

. Herein a rotor

102

and the stator coil

101

on which heat is produced are located inside a housing

106

. On the housing

106

, radiator fins

105

are provided which expose the generated heat to air on a large surface. A fan

103

increases the flow velocity of the intake air and guides it past protection caps

104

across the radiator fins

105

where the air may adsorb the generated heat.

Inasmuch as the cooling medium used is a gas and is sufficiently available in the environment, surface cooling is an economically favorable manner of proceeding if cooling may take place independently of engine speed, the amount of heat to be dissipated does not exceed a certain limit, and air cleanness and humidity suffice specific minimum requirements.

At the frequency converter, too, energy is generated which cannot be transferred to the pump. Generatory energy is re-supplied into the mains in the case of very large drive mechanisms upwards of approximately 30 kW. In the case of drive mechanisms in the medium or lower performance range, a braking resistance is inserted in the intermediary circuit whenever the intermediary circuit voltage exceeds a particular value. At this braking resistance, the conversion of excessive energy into heat, which is transferred from the housing to the surrounding air, takes place.

SUMMARY OF THE INVENTION

It is the object of the present invention to optimise and efficiently execute cooling of a drive mechanism for a pump including a drive motor, wherein high compactness of the device is to be ensured.

Moreover in the present invention, the efficiency of a standard asynchronous motor is to be enhanced, and a large quantity of heat is to be dissipated from the standard asynchronous motor.

It is furthermore desired to reduce the airborne noise emission of a combination of drive motor and pump.

This object is attained through a drive mechanism for a pump including a drive motor in accordance with claim

1

. Herein a frequency converter for actuation of a drive motor is mounted on a heat dissipator cooled by the hydraulic fluid to be conveyed by the pump. Thus, in the absence of an additional cooling medium, the temperature of the frequency converter may be reduced and its operation be designed to be more effective.

In a preferred manner, the heat dissipator is located at the suction port of the pump in order for the pressure and the volume flow at the pressure port of the pump to be at the desired values.

Even though more intense cooling of the drive motor might be desired or required, it is favorable to arrange this drive motor inside the heat dissipator in such a way that maximum enveloping flow takes place. In this way, the heat transfer from the drive motor to the pressure liquid thus also used as a cooling liquid may be optimised.

For the heat dissipator any tubular shape is well suited inasmuch as in this way the number of dead zones is minimised, and at the same time a uniform enveloping flow around the drive motor may take place in the heat dissipator. Moreover it is thereby also possible to favorably solve problems with respect to sealing of the heat dissipator.

When using a standard asynchronous motor, the A and B flanges may be fastened on both sides of the tubular main portion of the heat dissipator, so that the drive mechanism according to the present invention may be used on already existing drive motors in a simple manner. Preferably seals are introduced between between the cyclindrical portion of the motor and the respective flanges in order to isolate the inside of the motor from the cavity of the heat dissipator.

When the electrical connection between the drive motor and the frequency converter is routed through a flange lid, an impairment of the cable for electrical actuation of the drive motor due to the hydraulic flow in the heat dissipator is avoided.

A fan may be provided on a drive motor fan shaft externally of the heat dissipator in order to cause movement of air around the heat dissipator. Hereby the temperature of the pressure liquid supplied to the pump is reduced.

The port leading to the tank and the port leading to the pump are preferably located outside the mechanical connection between the flanges and the flange lids. Due to such an arrangement, mechanically stable installation of the drive motor into the heat dissipator is made possible, and a rapid movement of pressure liquid through the heat dissipator is equally permitted.

In order to avoid rectilinear, preferred flow paths in the heat dissipator, the ports in another embodiment of the present invention are offset with respect to the output shaft of the drive motor, i.e., they are formed in different relative positions on the flange lids. Uniform flow through all ranges of the heat dissipator is hereby achieved.

High compactness of the drive mechanism according to the present invention is ensured in the present invention through the fact that the front face-side lid of the drive motor is concurrently used as the sealing cover for the pump.

Preferably a fluid conduit connecting the space adjacent the drive motor with the suction port of the pump extends in the front face-side lid. Hereby an arrangement of conduits externally of the drive mechanism is avoided, and operational safety is enhanced.

In a preferred embodiment, the space adjacent the drive motor is the cavity in the heat dissipator, whereby a space-saving arrangement of pump, drive motor and frequency converter at concurrent efficient cooling of motor and frequency converter is made possible.

It is furthermore an advantage that the pump is an axial piston pump, and support means are provided at the front face-side lid as an abutment for the axial pistons. As a result of these support means, vibrations of the pump may be minimised because a design of the support means becomes possible which is conceived with a view to the mechanical properties only.

Radially outside of the support means, a housing comprised of sound-insulating material and fastened to the front face-side lid may be provided. As this housing is mechanically connected at only one end portion with the support means, preferably insulated against structure-borne noise, the acoustic emission of the pump is reduced.

In another preferred embodiment, the opposite end portions of the drive motor are secured to the heat dissipator through flange lids of flexible material. Such a structure further contributes to increased sound attenuation of the drive mechanism.

Further developments in accordance with the invention constitute the subject matters of the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall now be described in detail by referring to the annexed drawings, wherein:

FIG. 1

represents a sectional view of a conventional three-phase asynchronous machine with surface cooling.

FIG. 2

is a schematic representation of a drive mechanism according to the invention and a driven pump when incorporated into a hydraulic circuit.

FIG. 3

shows a sectional view of the drive mechanism for a pump according to the present invention.

FIG. 4

shows the lateral view of the drive mechanism according to the invention of

FIG. 3

when viewed from the left side.

FIG. 5

represents a second embodiment of the drive mechanism according to the invention.

FIG. 6

shows a third embodiment of the drive mechanism according to the invention.

FIG. 7

shows a fourth embodiment of the drive mechanism according to the invention.

FIG. 8

shows a fifth embodiment of the present invention.

FIG. 9

shows a sixth embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

At the outset, the relevant portion of a hydraulic system including a drive mechanism according to the present invention is explained by referring to FIG.

2

.

Inside a heat dissipator

40

a drive motor

20

is provided, the output shaft

24

of which is connected to the drive shaft

12

of a hydraulic pump

10

. Moreover on the heat dissipator

40

a frequency converter

30

is located which provides a desired voltage and frequency at the drive motor

20

through a cable

46

a.

The rotational speed of the pump, and consequently the torque thereof, may thus be adjusted by suitably controlling the frequency converter

30

.

Through a first conduit portion

51

the heat dissipator

40

is connected with a tank

50

through which a pressure medium, which may be oil, water, or some other fluid to be conveyed by the pump, is supplied. The tank

50

may be replaced with any hydraulic system supplying pressure liquid.

The pressure liquid from the heat dissipator

40

arrives via a second conduit portion

52

at the suction port

11

of the pump

10

through which the desired variation of the volume flow and pressure of the pressure liquid is performed.

As an alternative it is, however, also possible to directly connect the tank

50

to the suction port

11

of the pump

10

and to provide the heat dissipator

40

only downstream from a pressure port

13

of the pump

10

. In this case, the heat dissipator

40

must be of a pressure-resistant design.

In the following, the structural component comprised of heat dissipator

40

, drive motor

20

, and frequency converter

30

shall be described in more detail by referring to FIG.

3

.

The drive motor

20

located in the heat dissipator

40

and preferably having the form of a standard asynchronous motor comprises a central cyclindrical portion

21

on which radiator fins are provided. At the two front surface sides of this cyclindrical portion

21

, an A flange

22

and a B flange

23

, respectively, are provided which close the front surface sides. The cyclindrical portion

21

, the A flange

22

and the B flange

23

are known from the prior art. Thus the use of conventional standard asynchronous motors in the present invention is made possible, with the fan designated by reference numeral

103

in

FIG. 1

having to be removed in FIG.

3

.

In order to prevent the entrance of pressure liquid into the space between rotor and stator coil in the drive motor

20

, peripheral seals

44

,

45

are formed at the joints between the cyclindrical portion

21

and the A flange

22

and B flange

23

, respectively.

In the first embodiment as shown in

FIG. 3

, the heat dissipator

40

includes a tubular portion

42

wherein the tube may have a circular cross-sectional shape as shown in

FIG. 4

, or any other angular, oval or ellipsoid shape. It is, however, necessary to ensure the inner diameter of the tubular portion

42

to be larger than the outer diameter of the cyclindrical portion

21

from the drive motor

20

including the radiator fins mounted there, so that the pressure liquid may cool the entire outer periphery of the drive motor

20

.

At the axial end portions of the tubular portion

42

there are, as is shown in

FIG. 3

, flange lids

47

a,

47

b

sealed against the tubular portion

42

and the A and B flanges (

22

,

23

). At the flange lid

47

b

an inlet port

48

is arranged through which the pressure liquid enters into a cavity

43

of the heat dissipator

40

formed by the tubular portion

42

and the flange lids

47

a,

47

b.

Moreover a cable connector

46

is provided in the flange lid

47

b,

whereby electrical connection between the drive motor

20

and a connection cable

46

a

to the frequency converter

30

is established. An outlet port

49

guiding the pressure liquid from the cavity

43

of the heat dissipator

40

is arranged at the flange lid

47

a.

In addition there is a circular opening

49

a,

the function of which is described below, in the flange lid

47

a.

When the drive motor

20

is to be mounted in the heat dissipator

40

, initially the B flange

23

of the drive motor

20

is fastened to the flange lid

47

b

in such a manner as to enable establishing an electrical connection to the frequency converter

30

via the cable connector

46

a.

Then the tubular portion

42

is fastened to the flange lid

47

a

in a fluid-tight manner. Subsequently a cyclindrical projection

27

is inserted at the A flange

22

of the drive motor

20

in the circular opening

49

a

in the flange lid

47

a

and sealed against it, with the flange lid

47

b

at the same time being set on the tubular portion

42

and sealed against it. As a result, the motor shaft

24

of the drive motor

20

protrudes from the heat dissipator

40

on the side of the flange lid

47

a

and may be connected with the pump drive shaft

12

in accordance with FIG.

2

. As an alternative it is, however, also possible to arrange the heat dissipator

40

and the pump

10

at a greater distance than is shown in FIG.

2

.

The frequency converter

30

is located on the periphery of the tubular portion

42

of the heat dissipator

40

while contacting the outer peripheral surface at portion

42

with a surface as large as possible.

Thus the frequency converter

30

is cooled by a flow of liquid from the inlet port

48

to the outlet port

49

. Cooling of the entire outer peripheral surface of the drive motor

20

is also effected simultaneously with the aid of this flow of liquid.

In order to provide a uniform heat exchange in the entire cavity

43

of the heat dissipator

40

, baffles

41

may be provided in the preferred embodiment of the invention between the inner peripheral wall at the tubular portion

42

and the outer peripheral wall of the cyclindrical portion

21

of the drive motor

20

including the radiator fins, as is schematically shown in FIG.

3

.

In the second embodiment of the present invention as shown in

FIG. 5

, the inlet port

48

′ and the outlet port

49

′ are offset with respect to each other in the radial direction of the tubular portion

42

. Hereby both a uniform enveloping flow around the drive motor

20

and furthermore a sufficient heat exchange of the pressure liquid with the frequency converter

30

may be provided in the cavity

43

in the absence of any baffles.

In accordance with the third embodiment of the present invention as shown in

FIG. 6

, a fan shaft

25

″ of the drive motor having a fan

26

″ fastened to it may extend through the flange lid at which the inlet port

48

″ is provided. This fan

26

″ brings about air circulation around the heat dissipator independently of rotational speed, whereby the outer wall of the heat dissipator

40

is cooled. As a result, the temperature of the pressure liquid entering the pump

10

is lowered. The fan

26

″ is preferably lined with an air-permeable protective cap

29

″ in order to prevent injury hazard while the fan

26

″ rotates. The cable

46

″ must in this case be arranged externally of the fan

26

″.

FIG. 7

shows a fourth embodiment of the present invention having a modified heat dissipator construction. The flange lids of the first embodiment are here incorporated into the heat dissipator

240

. In order to allow for mounting of the drive motor

220

which may here also be a standard asynchronous motor, an insertion flange

228

having a greater outer diameter than the cyclindrical portion

221

of the drive motor

220

is fastened at the B flange

223

of the drive motor

220

. In this insertion flange

228

, the corresponding port for the cable

246

towards the frequency converter

230

is provided. Accordingly, during installation it is only necessary to insert the drive motor

220

in the circular opening

49

a

and mount the insertion flange

228

at the B flange

223

. As a result, the number of joints on the heat dissipator

240

requiring to be sealed is reduced.

The embodiments shown in

FIGS. 2

to

7

share the circumstance that the pressure liquid to be pumped cools both the frequency converter and the drive motor. Forced air cooling is thus implemented which is advantageous in comparison with fan-type air cooling in conventional asynchronous machines in terms of both cooling effect and effectivity, inasmuch as the pressure liquid is, in any case, pressurised through the pump. A further enhanced effectivity is made possible by the additional fan cooling in according with the third embodiment shown in FIG.

6

.

It is an additional advantage in the embodiments of

FIGS. 2

to

7

that axial forces transmitted by the pump to the drive motor are attenuated by the pressure liquid in the vicinity of the drive motor. Here an attenuation of airborne noise emission by an additional 6 dB may be achieved.

Cooling in the drive mechanisms for pumps in accordance with

FIGS. 2

to

5

and

FIG. 7

moreover takes place independently of environmental air. Thus efficient cooling is also possible in a case where the air is highly polluted or humid, whereby the drive motor including a fan would be attacked.

The most basic exploitation of the inventive concept of the present invention is, however, shown in

FIG. 8

representing the fifth embodiment. In the fifth embodiment, a frequency converter

330

is located on a conduit portion

351

connecting a hydraulic source with a pump. The amount of heat produced in the frequency converter is transferred to the liquid flowing in conduit portion

351

. Cooling of the drive motor may in this embodiment be effected in a conventional manner via surface cooling utilising a fan.

In

FIG. 9

, a further development of the second embodiment is shown as a sixth embodiment of the present invention. The sixth embodiment differs from the second embodiment in that an A flange

122

is provided as a front face-side lid of the drive motor, which forms the sealing cover of a pump

110

at the same time.

In such a structure, the pump

110

preferably is an axial piston pump. More precisely, the A flange

122

comprises a cyclindrical projection

127

on which components of the pump

110

are fastened. These components are, e.g., support means

114

for an adjustable or non-adjustable axial abutment

115

of the axial pistons and a housing

116

. The support means

114

comprise elongated portions

114

a

in parallel with the axial pistons and portions

114

b

offset at an angle and arranged opposite the cyclindrical projection

127

, which are contacted by the abutment

115

of the axial pistons.

The housing

116

ist preferably cup-shaped and encloses the support means

114

without contacting them in the position in which it is attached on the cyclindrical projection

127

. Leakage oil may thus be contained by the housing

116

, and noise may be attenuated. In order to improve insulation against structure-borne noise and vibrations, the housing is manufactured of mineral casting material (reaction resin forming material) which is also massively utilised in the prior art owing to its excellent shaping properties and its low weight.

Between the cyclindrical projection

127

and the housing

116

, structure-borne noise insulating material (not represented) is preferably installed.

The twofold function of the A flange

122

with respect to attaching hydraulic and electrical components is, however, not the only advantage of the A flange. The hydraulic connection between the cavity of the tubular portion

42

and the axial pistons may also be achieved with the aid of the A flange

122

. To this end, the outlet port

149

communicating with the suction port

111

of the pump

110

through a fluid conduit in the A flange is located in the A flange

122

in a radial direction thereof. In contrast, the outlet port

49

″ emerges axially in the second embodiment of FIG.

5

.

The pressure port

113

of the pump

110

radially emerges from the cyclindrical projection

127

, so that the pressure fluid may be supplied along short conduit lengths, and thus at lower energy losses.

In the sixth embodiment, the outlet port

149

may be offset with respect to the inlet port

48

in relation to the output shaft of the drive motor as is shown in

FIG. 9

, or may be arranged at any other position at the circumference of the A flange

122

depending on the desired fluid conduction in the heat dissipator

40

. The position of the pressure port

113

on the outer periphery of the cyclindrical projection

127

depends on the desired location of withdrawing the pressure fluid.

Moreover the frequency converter

30

may be provided not at the heat dissipator but on a conduit leading away from the pressure port

113

of the pump

110

.

The sixth embodiment thus provides a drive mechanism for a pump wherein the fluid conduits are shortened and the suction conduit towards the suction port of the pump is not visible from the outside. This enhances compactness of the overall device.

In conclusion, it may be stated that the principle of the sixth embodiment, in particular the formation of a front face-side lid for the drive motor as a sealing cover for the pump, may be combined with the particular features of the preceding embodiments.

In the first to third and fifth and sixth embodiments, structure-borne noise and vibrations of the drive motor may be insulated better if the flange lids are fabricated of a sound-insulating material such as, e.g., rubber or plastic. A plastic material preferably used is polyurethane.

The advantages of the sound-insulating material are particularly conspicuous in the sixth embodiment inasmuch as, owing to the integral formation of drive motor and pump

110

, the amplitude of the vibrations generated by the drive motor is raised. Flange lids

147

a,

147

b

of sound-insulating material thus enable low-noise operation despite a compact construction.

Thanks to the present invention in accordance with

FIGS. 1

to

9

it is, however, possible to achieve a further advantage cooling conduits containing a flow a cooling water are provided in the cavity designated by reference numeral

43

in FIG.

3

and designated as conduit portion

351

in FIG.

8

. This advantage resides in the fact that in a device presenting the subject matter of the present invention such as, e.g., a plastic casting machine, a separate oil cooler need not be provided.

The present invention thus relates to a drive mechanism for a pump implemented by means of a drive motor, the rotational speed and torque of which are influenced by a frequency converter. The frequency converter is arranged on a heat dissipator confining a flow of pressure liquid guided to the pump. Herein it is advantageous to also arrange the drive motor inside the said heat dissipator, for this makes it possible to perform intense forced air cooling of a pump-drive motor system without the necessity of an additional cooling liquid. The drive motor preferably has a central arrangement inside a tubular heat dissipator and is exposed to the pressure liquid over its entire circumference. Baffles or offset connecting sleeves allow for uniform flow through the entire heat dissipator.