EP2412979B1 - Pressure pump with suction nut - Google Patents

Description

The invention relates to a positive displacement pump with an adjustment for their specific delivery volume. The pump comprises at least two rotatably mounted conveying wheels, which are in a conveying engagement with each other to promote a working fluid under pressure increase from a low pressure side of the pump to a high pressure side of the pump in a rotary drive of at least one of the conveyor wheels. The invention further relates to a pump comprising the system for the supply of an aggregate with a working or lubricating fluid. In preferred uses, the pump is used to supply an internal combustion engine with lubricating oil, i. H. it forms with this use the lubricating oil pump of the engine. The specific delivery volume is understood to mean the delivery volume of the pump [delivery volume / rotational speed] which is related to the rotational speed of one of the delivery wheels.

Positive displacement pumps are known in which one of the conveying wheels arranged in a pump chamber is displaceable along its axis of rotation and relative to the other of the conveying wheels for adjusting the volume flow. For this purpose, a piston is arranged on an end face of the feed wheel, which is displaceable together with the feed wheel and forms a sealing gap with an enclosure for the piston circumference. On the side facing away from the impeller of the piston, a control chamber is arranged, in which a means for generating a sliding movement of the piston is arranged.

In this arrangement, there is often the problem that in the pump chamber located pressure fluid flows through the sealing gap in the control chamber. This leakage of the sealing gap can lead to more or less large problems in the control of the pump.

The DE 10 2008 025 346 A1 describes a control oil pump with a control piston and two meshing gears. By an axial displacement of the control piston, the degree of overlap of the two gears changes, which allows the control oil pump to change the flow rate of the oil. For example, at high speeds of a cold engine, it is necessary to minimize the flow of oil. However, since even with a minimum overlap of the gears still a high volume flow of the oil may be present, a the control piston radially circumferential recess is incorporated, which is referred to as a bypass groove, with a minimum overlap of the gears a short circuit between the suction and pressure chamber on.

It is an object of the invention to provide a positive displacement pump, in particular a gear pump or external gear pump, which is even better controllable.

The object is achieved by the displacement pump according to claim 1. Advantageous further developments emerge from the dependent claims, the description and the figures.

The invention is based on a positive displacement pump, in particular a gear pump or external gear pump.

The pump comprises a pump chamber and a control chamber, which are separated from each other by a displaceable piston. In the pump chamber, a first impeller and a second impeller are arranged, wherein the impellers are preferably gears and are engaged with each other. In particular, the gears mesh at a combing point, d. H. Teeth of the gears mesh there. The gears may have an involute or cycloidal or other tooth shape known to those skilled in the art. The piston is preferably axially, d. H. slidable along the axis of rotation of one of the conveyor wheels, in particular of the feed wheel, which is displaceable together with the piston. It is possible that only a first delivery wheel and a second delivery wheel are arranged in the pump chamber, whereby in particular only a single combing point is formed. Alternatively, however, embodiments are possible in which in addition to the first impeller and the second impeller in the pump chamber, a third impeller is arranged, which is either with the first impeller or with the second impeller in engagement, whereby the third impeller with the first or the second impeller can form a further Kämmstelle.

The pump chamber comprises a suction chamber on a suction side and on a pressure side a pressure chamber, which are separated from each other by means of the intermeshing conveyor wheels. In the suction chamber opens a feed opening, can be supplied by the fluid to be delivered from outside the pump chamber into the pump chamber. In the pressure chamber opens a discharge opening, by means of the fluid to be pumped from the pump chamber z. B. on the lubrication points of an aggregate, in particular motor is eligible. During delivery operation, the pressure in the suction chamber is lower than in the pressure chamber. Each engagement of interlocking conveyor edges, a suction chamber and a pressure chamber can be formed.

In embodiments with only a first impeller and a second impeller they can interlock, with only a suction chamber and only one pressure chamber is formed. In embodiments with a first, second and third impeller they can interlock at two points, so that each engagement a suction chamber and a pressure chamber is formed. For example, the first impeller may be engaged with the second impeller and the second impeller may be with the third impeller. The two pressure chambers can be fluidly separated or connected. The same can apply to the two suction chambers. The advantage of connected suction chambers or pressure chambers is that the flow rate for a fluid guidance system can be increased, in particular doubled. The advantage of separate suction chambers and / or pressure chambers is that with a single pump several, in particular two fluid circuits, which can be separated from each other or connected to each other, can be supplied. The peripheral portion of the feed wheel, which is in engagement with the two other feed wheels, can open in the circumferential direction between the engagement points in a suction chamber and in a pressure chamber. This conveyor wheel may in particular have two of these sections. The suction chamber located on one side may be separated from the pressure chamber located on the same side, z. Example by means of a wall which wraps around the second conveyor wheel over part of the circumference and forms a sealing gap with this part of the circumference. As a result, fluid can be conveyed from the suction chamber with a first volume flow to the pressure chamber located on the other side and with a second volume flow to the pressure chamber located on the same side.

The conveyor wheels are - relative to the respective axes of rotation - the combing point in the opposite direction of a particular cylindrical wall of the pump chamber wrapped over part of its circumference. In particular, the outer diameter of the gears form a sealing gap with the walls, which partially wrap around the gears. For a promotion, the conveyor wheels are rotatable at its combing point in the direction of the suction chamber. The flowing in the suction space in the tooth spaces of the conveyor wheels fluid is taken in the tooth gaps and along the wrap around the pressure side, in particular in the Promoted pressure chamber. The engagement of the conveyor wheels at the Kämmstelle prevents the backflow of the fluid. As a result, on the suction side, in particular in the suction chamber, a negative pressure and on the pressure side, an overpressure, in particular based on the ambient pressure.

One of the conveyor wheels via a drive device, such. B. one or the engine to be lubricated or its crankshaft rotates and takes in this case the other of the conveyor wheels. Preferably, the driving impeller is axially fixed in the pump. The driven by the driving conveyor wheel conveyor wheel can be moved along its axis of rotation, in particular shifted back and forth. If present, the entrained feed wheel can take another impeller, which is preferably arranged axially fixed in the pump. In such an embodiment with a first, second and third feed wheel, the feed wheel is preferably displaceable, with the other two conveyor wheels, such as. B. the first and third conveyor wheels in engagement. At maximum axial coverage of the displaceable feed wheel with the or the other conveyor wheels, the pump can promote the maximum flow. The volumetric flow can be reduced by displacing one delivery wheel relative to the other or the other so that the axial coverage decreases. With minimal overlap of the conveyor wheels, the pump can promote its minimum flow. By shifting at least one of the conveyor wheels of the volume or flow rate of the pump is adjustable. The displaceable feed wheel is axially fixedly connected to the piston. A displacement of the piston causes a displacement of the feed wheel. The control chamber has a preferably cylindrical wall, in which the preferably also cylindrical piston is slidably received longitudinally. The outer circumference of the piston forms a sealing gap with the inner circumference of the control chamber. The sealing gap is dimensioned so that the piston is axially displaceable. Although the sealing gap seals the pump chamber substantially from the control chamber, but due to the required longitudinal displacement of the piston a certain clearance between the piston and wall is required, which allows a certain leakage of the sealing gap. This leakage allows the fluid to flow from the pump chamber, in particular from the pressure range, in the direction of the control chamber.

In the control chamber, a means is arranged, which can cause a displacement force for the piston. For example, this means may be a spring, a motor or generally an actuator. Preferably, this agent is a fluid, such as. As oil, which has a particular varying pressure, which is preferably less than the pressure of the fluid to be delivered, in particular oil on the pressure side and greater than the pressure of the fluid to be delivered on the suction side.

For the regulation of the volume flow, it may be undesirable for fluid to flow from the pump chamber to the control chamber, as this could disturb a precise regulation of the pump.

The pump according to the invention therefore has a device with which the fluid flowing out of the pump chamber in the direction of the control chamber can be discharged, preferably towards the suction side. As a result, despite a certain leakage of the sealing gap between piston and piston guide or piston guide wall, no fluid can flow out of the pump chamber into the control chamber, since it is removed or removed from the sealing gap before the control chamber is reached. Preferably, the fluid flowing in the direction of the control chamber is guided or discharged to or to the suction side of the pump. For this purpose, preferably prevails in the device, a pressure which is lower than the pressure of the fluid on the pressure side of the pump chamber and preferably also lower than the pressure of the fluid in the control chamber. For example, the suction side meets the requirements for low pressure. In particular, the suction side of the pump is fluidic, d. H. Fluidführbar or hydraulically connected to the device. As a result, the fluid to be discharged can be sucked onto or to the suction side. Preferably, the device comprises a channel which is arranged in the region in which the piston forms the sealing gap with the piston guide surrounding the piston, in particular the wall of the control chamber. The channel could basically be arranged in the wall of the control chamber. Preferably, the channel is arranged in the piston between the pump and control chamber. It is generally preferred that the channel is open towards the sealing gap.

The channel can be arranged between the end faces of the piston, in particular approximately in the middle. Preferably, the sealing gap extends from the channel in the direction Pump chamber and control chamber. The channel can be formed by a groove or a groove in the piston or the wall surrounding the piston.

The channel extends at least partially preferably completely, or annularly over the circumference of the sealing gap. If the channel is arranged only partially over the circumference, it may preferably be located at a circumferential position, which is in the region of the pressure side of the pump chamber.

The channel may be connected to the suction side or another region, in particular fluidly, which has a lower pressure than the pressure side and / or the control chamber. In particular, in the channel, a fluid guide section open, which leads to the suction side or the side with the lower pressure, in particular into the pump chamber and / or the suction side or the suction chamber with the channel, in particular fluidly connects. The fluid guide section preferably also opens into the suction side or the suction chamber. The fluid guide section may be open or closed towards the sealing gap. Furthermore, the fluid guide section may extend approximately parallel or at least in the direction of the axis of rotation of the axially displaceable gear.

The pressure for the fluid in the control chamber is preferably removed on the high pressure side of or after the pump. Basically, this pressure could be removed at the pressure chamber of the pump chamber. The pressure is preferably taken off at a point on the pressure side at which the fluid pressure corresponds as closely as possible to the fluid pressure of a consumer to be supplied by the pump with the fluid. If the consumer is, for example, the engine, in particular the reciprocating engine of a motor vehicle, then the fluid pressure is preferably the pressure of the so-called main gallery, ie. H. the channel from which branch the channels for the individual lubrication points for the crankshaft and / or the camshaft. Preferably, the piston forms a displaceable wall for the control chamber, wherein the control chamber can be acted upon with the gallery pressure.

In particular, a valve, in particular a 3/2-way valve is arranged in the fluid guide section between the gallery and the control chamber, with which the control chamber optionally fluid leading to the gallery or a reservoir is connectable. Optionally, a valve with the same functions as a 3/2-way valve may be used, but with an additional switching position in which the valve is in a blocking position, ie an inflow of the fluid into the control chamber and an outflow of the fluid from the control chamber is locked. Example is a 4/3-way valve.

In preferred embodiments, the displacement of the piston may be at least supported by a spring element. The spring can z. B. be arranged so that they in case of failure of the scheme, such. B. the control valve, the pump by moving the piston and the displaceable feed wheel in a position for maximum flow.

The pump may further comprise a further piston which is arranged on the side opposite the piston for the control chamber side of the feed wheel. In the following, the piston for the control chamber is referred to as a control piston and the opposite piston as a pressure piston. The pressure piston, control piston and delivery wheel can be displaced as a unit. The pressure piston can sealingly abut against a wall surrounding it, in particular pressure chamber wall and form a sealing gap. In principle, alternatively or additionally, the pressure piston can have a device with which fluid flowing out of the pump chamber in the direction of the pressure chamber can be discharged. The explanations for the design of the fluid-removing device for the control piston also apply accordingly to the pressure piston.

A groove may be provided on the circumference of the pressure piston, which is provided as an alternative or in addition to the fluid discharge device. The groove is positioned so that it connects the pressure chamber with the suction chamber with minimal overlap of the conveyor wheels or with a minimum volume flow of the pump. As a result, the groove, which can also be referred to as a short-circuit groove, act in the manner of a bypass, which further regulates the pump with minimal flow to be pumped by passing fluid from the pressure chamber via the groove back into the suction chamber. The groove can open in the position for the minimum flow to the non-displaceable, ie, for example, to the first impeller out. At positions of the plunger out of position for minimal flow, the groove can be sealed by the wall surrounding the pressure piston, in particular with respect to the pressure chamber and the suction chamber.

The pressure piston preferably has a cross section which is not rotationally symmetrical. In particular, the pressure piston has a circular cross-section with a circular recess which does not extend from the edge of the circular cross-section towards the center, however, to the center. The cross-sectional area, in particular the area of the end face of the pressure piston, is smaller than the cross-sectional area of the control piston. The pressure piston may be motor or spring-loaded. Preferably, the pressure piston is pressurized with a fluid, in particular with an oil, which is removed in particularly preferred embodiments on the pressure side of or after the pump. Again, it is preferable to remove the pressure from the gallery or main gallery of the engine. In general, a fluid guide section may be provided for the decrease in pressure, which opens into the pressure and / or control chamber.

The recess of the pressure piston may preferably have a distance from the center of the cross section, which corresponds to the difference between the distance of the axes of the first and second delivery wheel and the outer diameter of the first delivery wheel.

Preferably, the fluid of the control chamber and in particular also the pressure chamber from the same fluid delivery system as the fluid of the pump chamber or pump chamber and control chamber optionally also the pressure chamber are fluidly connected to each other.

The invention further relates to a system for supplying an aggregate, preferably a piston internal combustion engine, with a working fluid or lubricating fluid, the system comprising the positive displacement pump and the unit.

Figur 1

eine Prinzipskizze einer erfindungsgemäßen Verdrängerpumpe in einer Anordnung mit einem maximalen Volumenstrom,

Figur 2

die Skizze aus Figur 1 mit einem minimalen Volumenstrom,

Figur 3

eine Regeleinheit für die Vorrichtung aus den Figuren 1 und 2,

Figur 4

die Regeleinheit aus Figur 3, in der die Wirkung der Einrichtung zur Abführung des Fluids dargestellt ist,

Figur 5

eine Prinzipskizze einer weiteren Ausführungsform einer erfindungsgemäßen Verdrängerpumpe in einer Seitenansicht und einer Draufsicht,

Figur 6

ein Schaltbild mit einer Regelung umfassend ein 3/2-Wegeventil, und

Figur 7

ein Schaltbild mit einer Regelung umfassend ein 4/3-Wegeventil.

The invention has been described with reference to several embodiments. In the following, a particularly preferred embodiment will be described with reference to figures. The features disclosed in this case further advantageously form the invention, in particular also with the features described above. Show it:

FIG. 1

a schematic diagram of a positive displacement pump according to the invention in an arrangement with a maximum flow rate,

FIG. 2

the sketch FIG. 1 with a minimum volume flow,

FIG. 3

a control unit for the device of the Figures 1 and 2 .

FIG. 4

the control unit off FIG. 3 in which the effect of the device for discharging the fluid is shown,

FIG. 5

a schematic diagram of another embodiment of a positive displacement pump according to the invention in a side view and a plan view,

FIG. 6

a circuit diagram with a control comprising a 3/2-way valve, and

FIG. 7

a circuit diagram with a control comprising a 4/3-way valve.

The Figures 1 and 2 show an external gear pump with a first gear 7 and a second gear 6. The first gear 7 is driven by a drive such. B. the crankshaft of a motor driven (not shown). Since the first gear 7 is in a meshing engagement with the second gear 6, the second gear 6 is taken away from the rotational movement of the first gear 7. First and second gear 6, 7 rotate in opposite directions of rotation, so that at their Kämmstelle roll their Wälzkreisdurchmesser each other.

The first gear 7 is axially bordered on both end sides by a wall of the housing 15, which form a sealing gap with the housing 15. The first gear 7 is looped over part of the circumference of a wall of the housing 15. The outer diameter of the first gear 7 and the outer surfaces of the tooth tips form a sealing gap with the housing 15.

The second gear 6 is also looped over part of its circumference by the housing 15, whereby the outer diameter of the second gear 6, in particular the outer surfaces of its tooth tips form a sealing gap with the housing 15. The second gear 6 is rotatably mounted on a shaft which connects a control piston 3 and a pressure piston 13 with a defined distance from each other, which is approximately the width of the second gear 6 plus the thicknesses of the sealing gaps, which the end faces of the second gear 6 with the Control piston 3 and the pressure piston 13 form corresponds.

The housing 15 and the pistons 3, 13 form a pump chamber 1. Below the combing point of the two gears 6, 7, a suction chamber is formed in the pump chamber and above the combing a pressure chamber. The pump has connections for a supply of lubricating oil to the suction chamber and for a discharge of the lubricating oil from the pressure chamber in the direction of the engine.

The control piston 3 has a circular cross-section and is slidably received in a control chamber 2. The outer circumference of the cylindrical control piston 3 forms a sealing gap 8 with the correspondingly cylindrical inner circumference of the control chamber 2. The diameter of the control piston 3 corresponds approximately to the outer diameter of the second gear 6.

On the opposite side of the control piston 3 of the second gear 6 is a pressure piston 13 which is arranged along the axis of rotation of the second gear 6 slidably in a pressure chamber 9. The outer circumference of the pressure piston 13 forms with the wall of the pressure chamber 9 a sealing gap 17. The pressure piston 13 is cylindrical over most of its circumference and has an outer diameter which corresponds approximately to the outer diameter of the second gear 6. Furthermore, the pressure piston 13 has a part-cylindrical recess 14 with a radius which corresponds approximately to the radius of the outer diameter of the first gear 7, wherein the recess 14 extends from the peripheral side to the central axis of the piston 13. The distance of the recess 14 from the central axis of the pressure piston 13 or the axis of rotation of the second gear 6 is approximately the distance between the axes of rotation of the first and second gear 6, 7 minus the radius of the outer diameter of the first gear 7. The recess 14 allows in the FIGS. 3 and 4 separately shown unit of pressure piston 13, second gear 6 and control piston 3 from the in FIG. 1 shown maximum conveying position, in which the first and second gear 6, 7 are in complete axial overlap, in an in FIG. 2 to move shown minimum conveying position, in which the first and second gear 6, 7 only partially overlap axially. The recess 14 forms with the in FIG. 2 shown position a sealing gap with the outer diameter or the outer surfaces of the tooth tips of the first gear. 7

The pressure piston 13 has, in particular at its cylindrical outer diameter, a groove 18, which can also be referred to as a short-circuit groove or bypass channel. The groove 18 extends in the circumferential direction of the cylindrical portion of the pressure piston 13. The groove 18 is, as in the Figures 1 and 2 can be seen, circumferentially from the wall, which forms the sealing gap 17 with the pressure piston 13, sealed. On both sides of the groove 18, the cylindrical outer diameter of the pressure piston 13 forms a sealing gap 17 with the wall. The wall is formed by the housing 15. The groove 18 opens to the recess 14 through openings 19d, 19s. The openings 19d, 19s are arranged so that one of these openings 19d can be displaced into the pressure space and the other of the openings 19s into the suction space. The openings 19 d, 19 s are sealed in most of the conveying positions, in particular in the maximum conveying position of the second gear 6 of the piston 13 of the leading wall of the housing 15 ( FIG. 1 ). In the position of the second gear 6 for a minimum volume flow of the pressure piston 13 is shifted so far that the groove 18, in particular their openings 19 d, 19 s from the seal with the housing 15, whereby the openings 19 d, 19 s to the first gear open out. One of the openings 19d opens into the pressure chamber, the other of the openings 19s opens into the suction chamber. As a result, in the position of the pump for a minimum volume flow, fluid can flow back from the pressure chamber via the groove 18 into the suction chamber. Thus, the volume flow delivered by the pump can be lowered even further.

The pressure piston 13 and the control piston 3 have discharge pockets 16 at their end faces facing the second gear wheel 6, which provide better pressure distribution in the oil during the delivery operation.

The pressure chamber 9 is preferably permanently subjected to a pressure corresponding to the pressure from the main gallery of the engine. For this purpose, the main gallery of the engine is fluid-conducting connected to a feeder 10 and the pressure chamber 9. The fluid or oil contained in the pressure chamber 9 exerts a force on the pressure piston 13 which depends on the end face of the pressure piston 13 facing the pressure chamber 9. Preferably, the pressure chamber 9 is permanently acted upon by the pressure from the main gallery of the engine.

The control chamber 2 is also acted upon by a pressure, preferably the pressure from the main gallery of the engine. Through the supply 11, the amount of fluid contained in the control chamber or the pressure can be varied. Through the supply 11 of the control chamber 2 fluid supplied or fluid can be removed. The fluid supply and discharge can be controlled by a valve 12, which has 3 connections and 2 switching positions in the example shown, which is why it can be referred to as a 3/2-way valve. Via the valve 12, the control chamber 2 is fluid leading to the main gallery ( Fig. 1 ) or connectable to a storage container ( Fig. 2 ).

When the pressure chamber 9 and the control chamber 2 are each acted upon by the pressure of the main gallery, shifts the in FIG. 3 shown unit in the in FIG. 1 shown position, since the control chamber 2 indicative end face of the control piston 3 is greater than the pressure chamber 9 indicative end face of the pressure piston 13, whereby the fluid of the control chamber 2 has a greater force on the in FIG. 3 If the valve 12 is switched so that the control chamber 2, instead of the main gallery with a reservoir, as generally preferred the oil pan fluidly connected, the permanently applied pressure of the pressure chamber 9 the in FIG. 3 shown unit in the in FIG. 2 move shown position, wherein the oil contained in the control chamber 2 is guided into the reservoir.

Since a higher pressure prevails in the pump chamber 1, in particular in the suction chamber, than in the control chamber 2, oil is pressed out of the pump chamber 1 via the sealing gap 8 in the direction of the control chamber 2. This leakage oil can be harmful to the control of the pump. Therefore, according to the invention, a channel 8 open towards the sealing gap is introduced into the control piston 3. The channel 4 is arranged so that there is a respective sealing gap between it and the end faces of the control piston 3. In particular, the channel 4 may be arranged approximately centrally between the two end faces. The channel 4 extends annularly over the particular entire circumference of the cylindrical control piston third

The channel 4 is connected by means of a fluid guide section 5 with the pump chamber 1, in particular with the suction chamber or the suction side. By means of the channel 4, the leakage oil flowing over the sealing gap 8 is intercepted and via the fluid guide section 5 guided into the pump chamber 1. The in FIG. 3 shown fluid guide portion 5 extends approximately parallel to the axis of rotation of the second gear 6 and is open to the sealing gap 8. How out FIG. 3 In the discharge pocket 16, which is arranged in particular in the suction region, a relatively constant pressure prevails, ie that pressure fluctuations exerted on the fluid by the toothing of the rotating delivery wheel 6 are less pronounced or reduced.

In FIG. 5 a further embodiment of the invention is shown. The pump includes, in addition to the first gear 7 and the second gear 6, a third gear 27. The second gear 6 is engaged with both the first gear 7 and the third gear 27 in meshing engagement. As best in the side view of the FIG. 5 can be seen, a suction chamber and a pressure chamber is formed at each Kämmstelle, which are separated by means of the Kämmstelle of each other, ie lying opposite. There, where the teeth of the gears 6, 7, 27 run into the Kämmstelle is a pressure chamber; There, where they leak from the combing point, a suction chamber. Furthermore, a pressure chamber is arranged next to the suction chamber, which are separated from each other without a comb, such. B. by means of a wall which forms a sealing gap with the circumference of the gear 6.

From a suction chamber fluid from the meshing gears 6, 27; 6, 7 are conveyed both to the opposite pressure chamber and to the adjoining pressure chamber. For example, fluid from the suction chamber, which opens to the meshing point of the second and third gear 6, 27, with a partial flow via the third gear 27 to the opposite pressure chamber, which opens to the meshing point of the gears 6, 27, and with another Partial flow via the second gear 6 to the adjacent pressure chamber, which opens to the meshing point of the first and second gear 6, 7 promoted. The same principle is applicable to the fluid of the suction chamber, which opens to the meshing of the gears 6, 7, applicable, ie there is a partial flow through the first gear 7 to the opening to the meshing of the gears 6, 7, opposite pressure chamber and a Partial flow via the second gear 6 to the opening to the meshing point of the gears 6, 27, adjacent pressure chamber promoted.

The first gear 7 and the third gear 27 may be substantially axially fixedly received in the housing, while the second gear 6 is axially displaceable relative to the first and third gear 7, 27, as in the plan view FIG. 5 indicated by the arrow direction. For the execution FIG. 5 , in particular for the design of the control piston 3 including channel 4 and pressure piston 13 including groove 18 is on the description of the FIGS. 1 to 4 directed. However, the pressure piston 13 is opposite to in the FIGS. 1 to 4 changed execution shown. By the additional third gear 27, the pressure piston 13 has two mutually opposite recesses, which like the recess 14 from the FIGS. 3 and 4 are designed. The pressure piston 13 has a recess 14 for the first gear 7 and on the circumference opposite a further second recess for the third gear 27. The grooves 18 open with their openings 19 in the position for the minimum flow in the juxtaposed suction and pressure chambers. For example, fluid can be removed from the pressure chamber opening onto the combing point 6, 7 via the groove 18 to the suction space opening onto the combing point 6, 27. Fluid from the pressure chamber opening into the combing point 6, 27 can be removed via a further groove 18 into the suction space opening onto the combing point 6, 7. By returning the fluid of the pressure chambers, the flow rate of the pump can be reduced.

FIG. 6 shows a circuit diagram with a 3/2-way valve 12 and one of the pumps described herein. In the FIGS. 6 and 7 the unit of pressure piston 13, second gear 6 and control piston 3 is shown as a sliding wall, which is acted upon by a spring which is arranged in the control chamber 2 and acts as a compression spring, with a force. The spring pushes the unit 13, 6, 3 in the absence of an external force in the position for a maximum flow ( FIG. 1 ). In the in FIG. 6 shown switching position, in addition to the spring force, the unit 13, 6, 3 pressed into the position for the maximum flow, on the one hand because of the spring force and on the other hand because of the opposite the pressure piston 13 enlarged cross-sectional area of the control piston 3. The pressure chamber 9 is via the feeder 10 with subjected to the same pressure as the control chamber 2. By z. B. electrical and / or magnetic actuation of the valve 12, this is brought against the pressure of a return spring in its second switching position, whereby the fluid of the control chamber 2 in the reservoir, such. B. an oil pan is returned. Since the force of the spring in the control chamber 2 is less than that through the pressure permanently applied to the pressure chamber 9 pressure, the unit 13, 6, 3 in the in FIG. 2 moved position shown for minimum flow.

FIG. 7 shows a circuit diagram with a 4/3-way valve 22 and one of the pumps described herein. At the in FIG. 7 shown first switching position of the valve 22, the unit 13, 6, 3 is moved to a position for a maximum flow, due to the force of the arranged in the control chamber 2 spring and the fluid pressure in the control chamber 2. The pressure chamber 9 is depressurized. The fluid of the pressure chamber 9 is guided into the reservoir. In the second switching position, the terminals of the valve 22 are blocked, so that the unit 13, 6, 3 z. B. can be blocked in an intermediate position between the positions for a maximum and minimum flow. In the third position of the 4/3-way valve 22, the unit 13, 6, 3 in the in FIG. 2 shown pressed position, since the force of the spring is less than the force exerted by the pressure in the chamber 9 to the unit 13, 6, 3 compressive force. The fluid from the control chamber 2 is guided into the reservoir.

Claims (10)

1. A displacement pump, in particular a gear pump, comprising a pump chamber (1) and a regulating chamber (2) which are separated from each other by means of a piston (3), characterised in that the pump has a device (4, 5) with which fluid flowing from the pump chamber (1) towards the regulating chamber (2) can be drained onto a suction side of the pump, wherein the device has: a channel (4) which is disposed in the region in which the piston (3) forms a sealing gap (8) with a piston guide which surrounds the piston (3); and a fluid-guiding section (5), wherein the channel (4), which extends over the circumference of the sealing gap (8), is open towards the sealing gap (8), and the fluid-guiding section (5) leads into the channel (4) and leads to the suction side.
2. The displacement pump of the preceding claim, wherein the piston (3) comprises the channel (4).
3. The displacement pump of any one of the preceding two claims, wherein the sealing gap (8) extends from the channel (4) towards the pump chamber (1) and the regulating chamber (2).
4. The displacement pump of any one of the preceding claims, wherein the fluid-guiding section (5) leads into the pump chamber (1).
5. The displacement pump of any one of the preceding claims, wherein the piston (3) forms a shiftable and/or translationally movable wall for the regulating chamber (2), wherein the regulating chamber (2) can be loaded with a pressure.
6. The displacement pump of any one of the preceding claims, wherein a valve (12), in particular a 3/2 directional regulating valve or a 4/3 directional regulating valve, is disposed in a fluid-guiding section to the regulating chamber (2) and can optionally load the regulating chamber (2) with a pressure, relieve it of a pressure or connect it to a reservoir in a fluid-guiding manner.
7. The displacement pump of any one of the preceding claims, wherein shifting and/or translationally moving the piston (3) is at least supported by a spring element.
8. The displacement pump of any one of the preceding claims, further comprising a displacement wheel (6) with which fluid can be displaced from a suction side to a pressure side of the pump and which is coupled to the piston (3) such that an axial shift of the piston (3) causes an axial shift of the displacement wheel.
9. The displacement pump of the preceding claim, wherein the displacement wheel (6) is a second displacement wheel (6) which is in engagement with at least one other displacement wheel (7, 27).
10. A system for supplying an assembly, preferably a piston combustion engine, with a working fluid or a lubricating fluid, wherein the system comprises the displacement pump of any one of the preceding claims.

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