WO1998025029A1

WO1998025029A1 - Motor pump unit

Info

Publication number: WO1998025029A1
Application number: PCT/DK1997/000551
Authority: WO
Inventors: Jørn Holger KLAUSEN; Ingvard Mosby Madsen; Peter FRØSLEV
Original assignee: Danfoss A/S
Priority date: 1996-12-03
Filing date: 1997-12-02
Publication date: 1998-06-11
Also published as: KR100391007B1; AU5187398A; EP0943056B1; ATE247777T1; DE69724271T2; EP0943056A1; KR20000057358A; DE69724271D1

Abstract

Motor pump unit in which the pump comprises a first rotating or orbiting displacement element, which performs a relative movement in relation to a second displacement element. The motor is an electric motor driving the pump directly by means of a common shaft, which extends through a common flange containing the bearing of the shaft, the common flange forming the basis of connection of the motor and the pump. This enables a compact construction of the motor pump unit, demanding no means for connection of motor and pump. The efficiency of the motor pump unit is thus increased. The weight of the motor pump unit can become so low that the unit will be particularly suited for fitting in a portable high pressure cleaner. The motor pump unit can also be used as fuel pump in an oil burner.

Description

Motor pump unit

The invention concerns a motor pump unit comprising a rotary electric motor driving a pump. The pump comprises a first rotating or orbiting displacement element, which performs a relative movement in relation to a second displacement element. The displacement elements are arranged between a first and a second side plate, of which at least one comprises commutation channels with connections to an inlet and a pressure outlet, respectively.

It is commonly known to drive gear wheel pumps from electric motors. Motor and pump each have their own shaft, and the shafts are connected with each other. Both motor and pump have end flanges. The connection of a motor and a pump is difficult, as the rotation axis of the two shafts must be adapted. This can be difficult in practice, so the connection is made by means of a flexi- ble element, whose deflection provides balancing of inaccuracies. The connection of rotating shafts implies, even at small obliquities, an unfavourable loading of bearings, and large energy losses occur in both connection and bearings.

Pumps used for oil burners are often driven by e.g. electric motors, which drive both an oil pump and a fan supplying air. The motor is provided with a shaft extending outwards at either end of the rotor of the motor. One end of the shaft is connected with the pump shaft, while the other end of the shaft drives the fan. Pump and fan get the same rotation speed, with no opportunity of individual regulation.

From US 5,040,950 is known a portable high pressure cleaner, in which a quickly rotating motor drives a high- pressure pump through a reduction gear, the pump being a gear wheel pump comprising two gear wheels rotating on individual axes, by which the intermeshing teeth of the gear wheels pump water from an inlet to a high-pressure outlet.

The use of a reduction gear has a negative influence on the efficiency of the high-pressure cleaner, and the gear requires lubrication by a lubricant, e.g. oil. Thus, there is a risk that lubricant penetrates to the inside of the pump and gets mixed with water, which has a detrimental effect on the environment. When disposing of a worn-out high-pressure cleaner, it must be drained of oil, in order not to cause pollution. Gear and lubricant also contribute to an increase of the weight of the high- pressure cleaner, which is a disadvantage, if it has to be portable. At the same time, the use of a gear influences the price of the high-pressure cleaner.

It is the purpose of the invention to suggest a motor- pump unit with a high efficiency and a low weight, which can be used and disposed of without detrimental environmental effects.

This task can be solved with a motor-pump unit as described in the introduction, in that the electric motor drives the pump directly by means of a common shaft extending through a common flange, which has a common bearing for the shaft of the motor pump unit, the common bearing controlling the placing of the shaft and the common flange in relation to both motor and pump.

This will solve all known problems of connection motor and pump, as both motor and pump are aligned by the common flange, securing a very exact control of the pump in relation to the motor during fitting, and the perfect assembling causes a minimum load on shaft and bearings, as the deflection of the shaft is very small.

A possible application of the motor pump unit is a fuel pump for an oil burner. The separation of fan and pump involves the opportunity of independent regulation. Further, an optimum dimensioning of the motor of the pump in relation to the actual requirement is possible, and at the same time, a fan having its own motor can be opti- mised.

Another possible application of the motor pump unit is a high pressure cleaner, which can be made without using a gear between motor and pump. This increases the effi- ciency, and the motor pump unit can work without needing oil. The weight of the motor pump unit can become so low that the unit can be particularly suited for use in a portable high pressure cleaner.

The pump may comprise an inner, externally toothed gear wheel, which rotates around a first centre, where the first gear wheel co-operates with a second outer, internally toothed gear wheel, which rotates around a second centre. Thus the invention can be made with a gerotor pump, which is suited for rotation at high speed.

The common flange may comprise a first bore for admission of the common shaft and a second concentric bore for admission of the common bearing. Thus, the placing of the shaft is determined by means of the bearing in relation to the common flange. The bearing may be a ball bearing, but roller or needle bearings can also be used. Further, slide bearings in the shape of a bushing can be used. The common flange can be made with a recess for admission of one of the side plates of the pump. Thus, the placing of the side plate is determined by the common flange.

The common bearing of the shaft can also be formed in the common flange. Thus, the bore of the flange can be used as bearing, and the flange can be made of a suitable bearing material.

By means of a common shaft, the common bearing can secure optimum positioning of the first, inner, externally toothed gear wheel of the pump. An optimum placing of the inner gear wheel will reduce frictional losses and the risk of jamming.

The common bearing can also secure optimum positioning of the common flange, which guides the placing of the channel discs and the outer ring of the pump, which again secure the positioning of the second, outer, internally toothed gear wheel of the pump. This gives an optimum placing of the outer gear wheel of the pump, and together with the optimum placing of the inner gear wheel, this produces an ideal gear wheel pump.

The gear wheels of the pump can be arranged between side plates comprising commutation channels with connection to the inlet and the pressure outlet, respectively, which side plates are made of ceramics with an addition of wear and friction reducing materials. Thus the side plates can contribute to reducing the frictional losses of the pump. A long life can also be obtained.

Advantageously, the gear wheels of the pump can be made of a powder, which is sintered together, to which powder are added materials with corrosion, wear and friction reducing properties. This implies that the gear wheels can be produced so accurately that jamming is avoided and the intermeshing of the inner and outer gear wheels can take place with very small frictional losses.

The common flange can form the basis of the stator of the electric motor, and at the same time the common flange forms the basis of a connection flange. Thus, motor and pump are assembled with common bolts, extending from the stator of the motor, through the common flange and fi- nally through the connection flange of the motor.

The common flange may comprise a number of channels creating a connection between commutation channels of the side plates and an inlet and/or an outlet, whose connec- tion branch (es) is/are inserted in the common flange.

Thus, connection to the pump can be made via the common flange, which forms the basis of at least one connection branch.

The common flange can comprise means for flow regulation with connection to the channels of the common flange. Thus, the common flange can form the basis of one or more valves .

Advantageously, the channels of the common flange can be provided with at least one heating element. Thus, an oil preheater can be built into the motor pump unit, which will be advantageous for oil burner applications.

The channels of the common flange can be connected with a filter, which is fitted in the common flange. Thus, the medium of the pump can be filtered before entering the pump.

The flange of the motor pump unit can comprise means for ventilating the pump. Thus the pump can be ventilated, which may be necessary in connection with the first start of the pump.

The connection flange can form a connection between an inlet and at least one of the channel discs, and also between at least one of the channel discs and the pressure outlet of the motor pump unit. Thus, the motor pump unit can be connected e.g. to an oil tank or a water supply, and the outlet can be connected to a nozzle in an oil burner, or to a hose, which forms connection to the handle of a high pressure cleaner. The connection flange can be made with valves for regulation of pressure or flow.

The motor pump unit can have a connection flange, which creates a connection between an inlet and at least one of the channel discs, and between at least one of the channel discs and the pressure outlet of the motor pump unit.

Advantageously, the connection flange surrounds the pump, and between connection flange and pump there is a chamber, which is connected with the inlet or the outlet of the pump. Thus, any leakages from the motor will be caught, and the pump can be made without an O-ring seal- ing.

The motor pump unit can comprise a pressure regulation valve. This secures a constant pressure level on the outlet of the motor pump unit.

The pressure regulation valve can be made with a by-pass connection, which returns medium to the low pressure side of the pump, when the fixed pressure level has been reached. The pressure regulation valve can be made with a setting element for setting of the desired pressure level . The motor pump unit may also comprise a flow regulation valve. Thus, the motor pump unit can set the outlet pressure in relation to a flow value, e.g. 5 1 per min- ute. If the motor pump unit is used for a high pressure cleaner, a connected flow restriction will automatically receive the pressure, which is built up by the fixed flow over the restriction.

Advantageously, the pump comprises an overflow valve, which connects the pressure outlet of the pump with its inlet, if the outlet pressure of the pump exceeds a fixed value. Thus, a by-pass connection can be established during short flow interruptions. Motor and pump will continue rotating and a quick reestablishment of the flow is possible, which is expedient in high pressure cleaner applications.

The motor pump unit may comprise a pressure switch, which disconnects the electrical connection to the motor, if an upper limit pressure is exceeded. This provides a security function, which starts working before the motor pump unit or the environment are damaged.

The motor can be provided with a thermal switch, which disconnects the electrical connection to the motor, if the thermal switch exceeds a fixed temperature. This protects the motor against damages, which may occur on overheating of the motor windings.

If the motor pump unit is used for a high pressure cleaner, it is advantageous for the motor to be a highspeed electric motor, which drives the pump directly. Thus, even a small pump can obtain a sufficient displace- ment for high pressure cleaning. The speed of the electric motor can be controlled by a frequency converter. Thus the pressure or the displacement of the pump can be regulated by means of the fre- quency converter. Measured values of pressure, flow and temperature can be used for regulation of the frequency converter. An operation panel can be equipped with means for setting of desired pressure, flow or temperature.

The electric motor can be a series motor, in which the current first passes a stator winding, and then a rotor winding via a commutator. Thus a cheap and well-known motor can be used.

Alternatively, the invention can be made with a synchronous motor. This is a motor with a permanently magnetic rotor, and, if operated with high-frequency AC, the motor has a fixed relation between speed and frequency.

In another alternative embodiment the electric motor can be an asynchronous motor. This is a simple and cheap motor, whose torque is automatically adapted to the actual requirement.

The invention can also be made with a reluctance motor. This motor is particularly suited for high speed, by which the motor is supplied from a frequency converter.

The common flange can have a bore from the motor side for adoption of a sealing element. Thus, it can be obtained that the medium lubricates the common bearing, which is advantageous, if the medium is oil. The sealing element can be made of a flexible material, e.g. rubber, and have the shape of a lip sealing, which bears on the common shaft. The pump can have means for sealing, to prevent medium from getting in touch with the bearings of the motor pump unit. If the medium is water, or any other medium, which can damage the bearing, it is advantageous to prevent medium from getting to the bearing. Means for sealing can be embedded in a ring-shaped recess, arranged concentrically around the shaft in the inner gear wheel or in the opposite side plate, where a resilient element presses a wearing ring against the opposite surface. This gives a simple and cheap sealing of the pump.

In the following the invention is explained on the basis of the drawings, showing:

Fig. 1 a possible embodiment of the invention

Fig. 2 an enlarged section of a possible sealing arrangement

Fig. 3 a second possible embodiment of the invention Fig. 4 a third possible embodiment of the invention

Fig. 5 a section through the embodiment shown in fig. 4

Fig. 6 a fourth possible embodiment of the invention

Fig. 1 shows a motor-pump unit 1, comprising an electric motor 2 and a pump unit 3, in which the motor 2 is connected with the pump 3 by means of a shaft 4. Between the electric motor 2 and the pump unit 3 there is a common flange 5, which contains a common bearing 6. The pump unit consists of two channel discs 7 and 8, between which there is an inner, externally toothed gear wheel 9, which is connected with the shaft 4 by means of a driver 10. The inner gear wheel 9 co-operates with an outer, internally toothed gear wheel 11, which rotates freely in a spacing ring 12. A connection flange 13 contains an inlet 15 and an outlet 14, which are connected with the gear wheel set through the channel disc 8. The pump unit 3 is sealed by means of a number of O-rings 16. Further, the shaft 4 is supported by a bearing 19.

The motor pump unit as shown in fig. 1 is extremely easy to produce, as during assembling the motor shaft and the bearing 6 control the placing of the common flange 5, which forms the basis of the channel discs 7 and 8, which again guide the spacing ring 12. At the same time, the shaft 4 is guiding the inner gear wheel 9. This gives a pump, which is easy to assemble, and which can work very precisely.

By means of the shaft 4 the motor 2 drives first the inner gear wheel 9, and by means of the inner gear wheel 9 also the outer gear wheel 11 to perform a rotary movement. However, there is a displacement of the rotation centres of the inner gear wheel 9 and the outer gear wheel 11. Thus, a gerotor pump occurs, which is commu- tated by means of channels in the channel discs 7 and 8. The electric motor 2 is a high-speed motor, which drives the gerotor pump at a speed of up to 24,000 r.p.m. This gives a very large displacement capacity with a very small pump. The pump is able to supply 8 to 10 1 per minute at a pressure of more than 60 bar, which makes the motor pump unit particularly suited for a high pressure cleaner. Advantageously, the channel discs 7 and 8 are made of ceramics, and plane ground on the side surfaces. Together with the collector ring 18 and the resilient elements 17, this provides an efficient and cheap sealing, which protects the rotating shaft against liquid leakage.

Fig. 2, showing an enlarged section of part of fig. 1, shows a possible embodiment of a sealing between working chambers of the gear wheel set and the driving shaft. In both sides of the inner gear wheel 9 there are circumferential grooves comprising a first resilient element 17, which can be an 0-ring. On this element 17, a collector ring 18 is yieldingly fixed, and pressed against the surrounding channel discs 7 and 8.

Fig. 3 shows an alternative embodiment of the invention, in which common reference numbers have been maintained. Fig. 3 deviates in that the bearing 19 is omitted, so that the shaft 4 is only supported by the common bearing 6. Besides, fig. 3 shows an alternative connection flange 21 with an inlet 15 and an outlet 14. The inlet 15 of the flange 21 is connected with a surrounding chamber 22, which surrounds the whole pump unit. The surrounding chamber is sealed towards the surroundings by means of 0- rings 16. This saves O-rings in the pump unit itself, as any leakage between the channel disc 7 or 8 and the spacing ring 12 will end in the chamber 22, from which there is a direct access to the suction connection. Thus, the demand for planeness of the ceramic channel discs 7 and 8 is reduced. The surrounding chamber 22 also offers the opportunity of cooling the pump unit.

Fig. 4 shows a section through an alternative embodiment of a liquid pump according to the invention. The liquid pump shown in fig. 4 is particularly suited for media with lubricating properties, e.g. oil.

The motor pump unit 1 comprises an electric motor 2 and a pump 3 driven by the motor. The electric motor comprises a stator 25 and a rotor 26. The rotor is fixed on a shaft 4, which is embedded rotatably in a bearing 27. The bearing 27 is fixed on the stator 26 by means of bolts 28, which pass through both the stator 25, the common flange 5 and a connection flange 23. Further, the motor is provided with a fan 29 for cooling of the motor. The bolts 28 are arranged in bushings 30 at the passage between the stator 25 and the common flange 5, where the bushings create a positioning between the flange 5 and the stator 25.

A sealing element 24, which, in the embodiment shown, has the shape of a ring, is fitted around a shaft 4 between the rotor 26 and a ball bearing 6. The sealing element 24 is arranged in a first bore in the flange 5 and bearingly retained against the bottom of the bore by means of a locking ring 31. The ball bearing 6 is also fitted around the shaft 4. The ball bearing 6 is arranged in a second bore in the flange 5 and retained in relation to the shaft 4 by means of locking rings 32.

A first side plate 7 is also fitted around the shaft 4. The side plate 7 is arranged in a third bore in the flange 5. An outer ring 12 is bearingly arranged on the side plate 7 and forms a stationary element in the pump. The outer ring 12 is retained in relation to the side plate 7 by means of a pin 33. A second side plate 8 is bearingly arranged on the outer ring 12. An outer gear wheel 11 is arranged between the first side plate 7 and the second side plate 8 inside the outer ring 12. The gear wheel 11 rotates freely inside the outer ring 12. An inner gear wheel 9 is arranged between the first side plate 7 and the second side plate 8 inside the outer gear wheel 11. The inner gear wheel 9 is retained on the shaft 4 by means of a spring 10.

As mentioned, the ball bearing 6 is fitted in a second bore in the flange 5, and the ball bearing 6 forms the basis of the side plate 7 in the pump. The side plate 7 forms the basis of the outer ring 12 and the gear wheel 11. As the ball bearing 6 is fitted in the second bore, the ball bearing 6 is guided in relation to the flange 5, and as the side plate 7, the outer ring 12 and the gear wheel 11 are fitted in relation to the ball bearing 6, these elements are also guided in relation to the flange

5. The ball bearing 6 also forms the basis of the shaft 4 in the flange 5. Thus the shaft 4 guides the inner gear wheel 9 in relation to the outer gear wheel 11.

A filter holder 34 is shown between the inlet 15 and the gear wheels 9, 11 of the pump. This filter holder 34 is arranged between the second side plate 8 and a cover 23. The filter holder 34 is provided with a sleeve, which supports a mechanical filter 35.

Sealings 16, being O-rings in the embodiment shown, are arranged between the first side plate 7 and the flange 5 and form the sealing of an outlet from the pump. Another sealing 16, in the embodiment shown also an O-ring, is arranged between the cover 23 and the flange 5 and forms the sealing of the inlet 15 in the cover 23. The cover 23 is fixed to the flange 5 by means of the bolts 28. An additional sealing 16, in the embodiment shown also an 0- ring, is arranged between the cover 23 and the filter 35, and seals so that the medium, in the embodiment shown fuel, must pass the filter 35 before being led to the gear wheel 11 and the gear wheel 9.

Fig. 5 is a section through the oil pump at right angles to the section shown in fig. 1. The section shows various elements, which could not be seen in fig. 4.

A ventilation plug 36 is fitted in a first threaded hole in the flange 5. A sealing 37 is formed by arranging an O-ring between the ventilation plug 36 and the bottom of the first threaded hole. A regulation screw 38 is fixed in a second threaded hole in the flange 5. A sealing 39, in the embodiment shown an O-ring, is arranged between the flange 5 and the regulation screw 38. The regulation screw 38 comprises a spring element 40, in the embodiment shown a helical spring, a spring guide 41, forming the bearing of the spring element 40, and also of a regulation cone 42, which forms a regulation element.

A pressure controlled valve 43 is fixed in a third threaded hole in the flange 5, which valve only opens after exceeding a fixed first pressure level, and closes as soon as a second fixed pressure level has been reached. A sealing 44, in the embodiment shown an O-ring, is arranged between the flange 5 and valve 43. The valve 43 comprises a diaphragm 45, which bears on a spring retainer 46. A spring element 47, in the embodiment shown a helical spring, bears on the spring retainer 46 and is bearingly retained on the spring retainer 41 by means of a jacket 48.

Fig. 6 is a section through a fourth possible embodiment of the invention. In the embodiment shown the common flange 49 forms the bearing 50 of the shaft 4. The flange 49 replaces both the ball bearing 6 and the first side plate 7. Thus the shaft 4 is embedded in the flange 5 and the gear wheel 11 and the gear wheel 9 of the pump bear direct on an outer surface of the flange 5. In the embodiment shown, the bore, through which the shaft ex- tends, is preferably provided with a coating or a bushing (not shown), which is made of a bearing material. Alternatively, the flange 5 is made of a material, which is a suitable bearing material for the shaft 4.

The embodiments shown in both fig. 4, fig. 5 and fig. 6 involve the advantage that a ball bearing 6, slide bear- ings 50 or other ways of using the flange 5 as bearing for the shaft 4, and the fixing of the pump elements 7,

9, 11, 12 and 8 around the shaft cause that the pump elements are completely positioned in relation to the common shaft 4 of motor and pump.

In the above, the invention is described with reference to special embodiments of a motor pump unit according to the invention. However, many other embodiments of the invention are also possible.

Claims

Patent Claims

1. Motor pump unit comprising a rotary electric motor driving a pump, which pump comprises a first rotating or orbiting displacement element, which performs a relative movement in relation to a second displacement element, the displacement elements being arranged between a first and a second side plate, of which at least one comprises commutation channels with connections to an inlet and a pressure outlet, respectively, characterised in that the electric motor (2) drives the pump (3) directly by means of a common shaft (4) extending through a common flange (5, 49), which has a common bearing (6) for the shaft (4) of the motor pump unit (1), the common flange (5, 49) forming the basis of the connection of motor (2) and pump (3), and the common bearing (6) guiding the placing of the shaft (4) and the common flange (5, 49) in relation to both motor (2) and pump (3) .

2. Motor pump unit according to claim 1, characterised in that the pump (3) comprises a first inner, externally toothed gear wheel (9), which rotates around a first centre, where the first gear wheel co-operates with a second outer, internally toothed gear wheel (11), which rotates around a second centre.

3. Motor pump unit according to claim 1 or 2, character- ised in that the common flange (5, 49) comprises a first bore for admission of the common shaft (4) and a second concentric bore for admission of the common bearing (6) .

4. Motor pump unit according to one of the claims 1 to 3, characterised in that the common flange (5, 49) has a recess for admission of one of the side plates

(7, 8) of the pump (3) .

5. Motor pump unit according to one of the claims 1 to 4, characterised in that the common bearing (50) of the shaft (4) is formed in the common flange (49) .

6. Motor pump unit according to one of the claims 1 to 5, characterised in that by means of a common shaft (4), the common bearing (6) secures optimum positioning of the first, inner, externally toothed gear wheel (9) of the pump.

7. Motor pump unit according to one of the claims 1 to 6, characterised in that the common bearing (6) also secures optimum positioning of the common flange (5, 49) , which guides the placing of the channel discs (7, 8) and the outer ring (12) of the pump, which again secure the positioning of the second, outer, internally toothed gear wheel (11) of the pump.

8. Motor pump unit according to one of the claims 1 to 7, characterised in that the common flange (5, 49) forms the basis of the stator (25) of the electric motor, and at the same time the common flange (5, 49) forms the basis of a connection flange (13, 21) .

9. Motor pump unit according to one of the claims 1 to 7, characterised in that the common flange (5, 49) comprises a number of channels creating a connection between the commutation channels of the side plates and an inlet (15) and/or an outlet (14), whose connection branch (es) is/are inserted in the common flange (5) .

10. Motor pump unit according to claim 9, characterised in that the common flange (5) comprises means for flow regulation (43) with connection to the channels of the common flange (5) .

11. Motor pump unit according to claim 9, characterised in that the channels of the common flange (5) are provided with at least one heating element.

12. Motor pump unit according to claim 9, characterised in that the channels of the common flange (5, 49) are connected with a filter fitted in the common flange (5, 49) .

13. Motor pump unit according to claim 9, characterised in that the common flange (5, 49) comprises means (36) for ventilating the pump.

14. Motor pump unit according to one of the claims 1 to 13, characterised in that the motor pump unit has a connection flange (13, 21, 23), which forms a connection between an inlet (15) and at least one of the channel discs (7, 8), and also between at least one of the channel discs (7, 8) and the pressure outlet (14) of the motor pump unit.

15. Motor pump unit according to claim 14, characterised in that the connection flange (21, 23) surrounds the pump (3), and between connection flange (21, 23) and pump (3) there is a chamber (22), which is connected with the inlet (15) or the outlet (14) of the pump (3) .

16. Motor pump unit according to one of the claims 14 to 15, characterised in that the motor pump unit com- prises a pressure regulation valve (43) .

17. Motor pump unit according to one of the claims 14 to

16, characterised in that the motor pump unit com- prises a flow regulation valve (38) .

18. Motor pump unit according to one of the claims 14 to

17, characterised in that the pump (3) comprises an overflow valve, which connects the pressure outlet (14) of the pump with its inlet (15), if the outlet pressure of the pump (3) exceeds a fixed value.

19. Motor pump unit according to one of the claims 14 to

18, characterised in that the motor pump unit com- prises a pressure switch, which disconnects the electrical connection to the motor (2), if an upper limit pressure is exceeded.

20. Motor pump unit according to one of the claims 14 to 19, characterised in that the motor (2) is provided with a thermal switch, which disconnects the electrical connection to the motor (2) , if the thermal switch exceeds a fixed temperature.

21. Motor pump unit according to one of the claims 1 to 20, characterised in that the motor (2) is a highspeed electric motor driving the pump (3) directly.

22. Motor pump unit according to one of the claims 1 to 21, characterised in that the speed of the electric motor (2) is controlled by a frequency converter.

23. Motor pump unit according to one of the claims 1 to 22, characterised in that the common flange (5, 49) has a bore from the motor side for admission of a sealing element (24).

24. Motor pump unit according to one of the claims 1 to 23, characterised in that the pump (3) has means for sealing (17, 18), to prevent medium from getting to the bearings (6, 19) of the motor pump unit, which means for sealing (17, 18) are embedded in a ring- shaped recess, arranged concentrically around the shaft (4) in the inner gear wheel (9) or in the oppo- site side plate (7, 8), where a resilient element

(17) presses a wearing ring (18) against the opposite surface .