Pump comprising an adjusting device and a control valve for adjusting the delivery volume of the pump

Abstract

A pump including a port connecting a suction of the pump to a reservoir of a fluid; region an adjusting device for adjusting the delivery volume of the pump; a control valve, including a relief port, a control piston, and a tensing device which acts on the control piston; and an additional control device for generating a control force which acts on the control piston, counter to the tensing device, wherein the relief port is connected to the suction region by bypassing the reservoir.

Claims

1. A pump which exhibits an adjustable delivery volume, the pump comprising: (a) a pump housing, comprising: a pump port for connecting the pump to a reservoir of a fluid to be delivered; a delivery chamber which comprises a delivery chamber inlet on a low-pressure side of the pump, and a delivery chamber outlet on a high-pressure side of the pump, for a fluid; and a suction region extending from the pump port up to at least the delivery chamber inlet on the low-pressure side; (b) a delivery member which can be moved within the delivery chamber for delivering the fluid from the low-pressure side to the high-pressure side; (c) an adjusting device for adjusting the delivery volume of the pump; (d) a control valve, arranged outside the suction region, comprising: (d1) a pressure port for a setting fluid which is diverted from the fluid of the high-pressure side; (d2) a working port for the setting fluid, which is connected to the adjusting device; (d3) a relief port for the setting fluid; (d4) a valve space, and a control piston which can be moved back and forth within the valve space between a first piston position and a second piston position; (d5) and a tensing device for generating a tensing force which acts on the control piston in the direction of the second piston positions; (e) and an additional control device for generating a control force which acts on the control piston, counter to the tensing force of the tensing device, (f) wherein the control valve: (f1) connects the working port to the pressure port when the control piston is in the first piston position and (f2) separates the working port from the pressure port and connects the working port to the relief port when the control piston is in the second piston position, so the setting fluid can flow off into the valve space via the working port and from the valve space into the suction region via the relief port; (g) wherein the relief port is connected to the suction region by bypassing the reservoir; (h) wherein the relief port is connected to the suction region by a relief channel, and the relief channel feeds into the suction region at or downstream of the pump port; (i) wherein the valve space comprises a tensing chamber for the tensing device; and (j) wherein the relief port feeds into the tensing chamber such that the tensing chamber is connected to the suction region of the pump housing in any state of the control valve.

2. The pump according to claim 1, wherein the control valve is arranged in or on the pump housing, and the relief channel extends from the relief port up to and into the suction region in and/or on the pump housing.

3. The pump according to claim 1, wherein: the pump housing comprises a housing structure, which surrounds the delivery chamber, and a housing cover which is connected to the housing structure; the housing cover together with the housing structure forms a joining gap extending around the delivery chamber; and the relief port is connected to the suction region by means of a relief channel which extends in and/or on the housing cover and/or in the joining gap.

4. The pump according to claim 1, wherein: the pump housing comprises a housing structure, which surrounds the delivery chamber, and a housing cover which is connected to the housing structure; the housing cover together with the housing structure forms a joining gap extending around the delivery chamber; the valve space of the control valve extends in the movement direction of the control piston up to and into or through the joining gap; and the housing cover seals the valve space.

5. The pump according to claim 1, wherein the additional control device is connected to an external controller, and is configured to modulate the magnitude of the tensing force in accordance with control signals of the external controller.

6. The pump according to claim 1, wherein the control valve comprises: a control chamber comprising an inlet for a control fluid for generating the control force by way of a control fluid pressure which acts on the control piston within the control chamber; and a modulating valve, which is arranged in a flow path of the control fluid, for changing the control fluid pressure acting in the control chamber, wherein the control fluid is diverted on the high-pressure side of the pump from the fluid delivered by the pump.

7. The pump according to claim 1, wherein: the control piston comprises a first piston surface and a second piston surface; a first control chamber comprising: a first control port for a control fluid for generating a first control force by way of a first control fluid pressure which acts on the first piston surface, counter to the tensing force, within the first control chamber and a second control chamber comprising a second control port for a control fluid for generating a second control force by way of a second control fluid pressure which acts on the second piston surface, counter to the tensing force, within the second control chamber; and the additional control device comprises a modulating valve for changing the first control fluid pressure and/or the second control fluid pressure.

8. The pump according to claim 7, wherein the first control fluid and/or the second control fluid is diverted on the high-pressure side of the pump from the fluid delivered by the pump.

9. The pump according to claim 7, wherein the modulating valve is embodied separately from the pump housing and is arranged separately from the pump housing in a delivery cycle of the pump.

10. The pump according to claim 7, wherein the control fluid is diverted on the high-pressure side at a point downstream of a filter for cleaning the fluid.

11. The pump according to claim 1, wherein: the adjusting device comprises an adjusting member, which is assigned to the delivery member, and a setting pressure chamber; the setting pressure chamber is connected to the working port of the control valve; the setting fluid can be applied to the adjusting member in the setting pressure chamber in a setting direction in which it can move; and the adjusting device also comprises a spring device which exerts a spring force, counter to the pressure of the setting fluid, on the adjusting member.

12. The pump according to claim 1, wherein: the pump is a rotary pump, and the delivery member is a delivery rotor which can be rotated about a rotary axis within the delivery chamber; the adjusting device comprises: an adjusting member which surrounds the delivery rotor or is arranged on an end-facing side of the delivery rotor and can be moved back and forth within the pump housing for the purpose of adjusting the delivery volume, and a setting pressure chamber which is connected to the working port of the control valve; and the setting fluid can be applied to the adjusting member in the setting pressure chamber in a setting direction in which it can move.

13. The pump according to claim 1, wherein the pump is driven in accordance with the speed of an assembly to be supplied with the fluid by the pump and is driven by the assembly in a fixed rotational speed relationship to the assembly.

14. The pump according to claim 1, wherein the fluid is a lubricating oil, and the pump is a lubricating oil pump in a lubricating oil delivery cycle of a combustion engine, and is used to supply the combustion engine with the lubricating oil.

15. The pump according to claim 1, wherein the fluid is a lubricating oil, and the pump is a lubricating oil pump in a lubricating oil delivery cycle of a drive motor of a motor vehicle, and is used to supply the drive motor with the lubricating oil.

16. The pump according to claim 1, wherein the additional control device is connected to a controller of an assembly to be supplied with the fluid by the pump, and is configured to modulate the magnitude of the tensing force in accordance with control signals of the external controller.

17. The pump according to claim 1, wherein the delivery member is a delivery rotor which can be rotated about a rotational axis within the delivery chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Example embodiments of the invention are described below on the basis of figures. Features disclosed by the example embodiments, each individually and in any combination of features, advantageously develop the subject-matter of the claims and the embodiments described above and also the subject-matter of the aspects. There is shown:

(2) FIG. 1 a pump which can be adjusted in terms of its delivery volume and which comprises a control valve and a relief channel of a first example embodiment, in an isometric representation;

(3) FIG. 2 the pump in a plan view;

(4) FIG. 3 a delivery cycle which comprises the pump, in a schematic representation;

(5) FIG. 4 the control valve in a longitudinal section;

(6) FIG. 5 a region of the pump which comprises the control valve, in a plan view; and

(7) FIG. 6 the pump comprising the control valve and a relief channel of a second example embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a pump in a vane cell design by way of example. The pump comprises a pump housing comprising a housing structure 1 and a cover 2. The housing structure 1 accommodates and/or mounts components of the pump such that they can be moved. The housing structure 1 is open on an axial end-facing side, thus facilitating the arrangement of components of the pump in or on the housing structure 1. The cover 2 can be fitted to the housing structure 1 and, when fitted, seals the housing structure 1 on the end-facing side in question. The housing structure 1 and the cover 2 comprise joining surfaces 1a and 2a which axially face each other and which are axially pressed against each other when the cover 2 is attached to the housing structure 1, such that an internal space of the pump housing 1, 2 is circumferentially sealed off.

(9) FIG. 2 shows the pump in a plan view onto the open housing structure 1. The cover 2 has been removed, such that functional components of the pump can be seen.

(10) The housing structure 1 surrounds a delivery chamber 5 in which a delivery member 10 is arranged such that it can be rotated about a rotational axis Rio. The housing structure 1 comprises a pump port 3 which is used as an inlet, and a pump port 8 which is used as an outlet, for a fluid to be delivered, for example engine lubricating oil. The pump port 3 on the low-pressure side is used to connect the pump to a reservoir for the fluid, and the pump port 8 on the high-pressure side is used to connect to an assembly to be supplied with the fluid. The delivery chamber 5 comprises a low-pressure side and a high-pressure side. When the delivery member 10 is rotary-driven in the rotational direction indicated, i.e. clockwise, fluid flows through the pump port 3 into the pump housing 1, 2 and through a delivery chamber inlet 6 on the low-pressure side in the pump housing 1, 2, into the delivery chamber 5, and is expelled at an increased pressure through the delivery chamber outlet 7 on the high-pressure side of the pump and discharged via the pump port 8. A suction region 4 is formed on the low-pressure side of the pump housing 1, 2, wherein the fluid delivered by the pump flows through the suction region 4 on its flow path from the pump port 3 to the delivery chamber inlet 6. Due to the design of the pump 100, the suction region 4 extends up to and into the delivery chamber 5 and also comprises the region of the delivery chamber 5 in which the delivery cells increase in size when the delivery member 10 is rotated. A high-pressure region of the pump housing 1, 2 which adjoins the suction region 4 on the flow path comprises the region of the delivery chamber 5 in which the delivery cells decrease in size and extends from this partial region of the delivery chamber 5 up to and including the pump port 8 via the delivery chamber outlet 7.

(11) The delivery member 10 is a delivery rotorin the example, an impellercomprising a rotor structure 11, which is central with respect to the rotational axis Rio, and vanes 12 which are arranged in a distribution over the circumference of the rotor structure 11. The vanes 12 are guided, such that they can be shifted in a sliding manner in the radial direction or at least substantially in the radial direction, in slots in the rotor structure 11 which are open towards the outer circumference of the rotor structure 11.

(12) The outer circumference of the delivery member 10 is surrounded by an adjusting member 20 which is, by way of example, shaped as an adjusting ring. When the delivery member 10 is rotary-driven, its vanes 12 slide over an inner circumferential surface of the adjusting member 20. The rotational axis R.sub.10 of the delivery member 10 is arranged eccentrically with respect to a parallel axis of the adjusting member 20 which is central in relation to the inner circumferential surface, such that delivery cells formed by the delivery member 10 and the adjusting member 20 increase in size on the low-pressure side of the delivery chamber 5 and decrease in size again on the high-pressure side in the rotational direction when the delivery member 10 is rotated. Because the delivery cells increase and decrease in size periodically with the rotational speed of the delivery member 10 in this way, the fluid is delivered from the low-pressure side to the high-pressure side, where it is delivered at an increased pressure through the delivery chamber outlet 7 and then through the pump port 8.

(13) The volume of fluid delivered by each revolution of the delivery member 10, the so-called specific delivery volume, can be adjusted. If the fluid is a liquid and thus a good approximation of an incompressible fluid, the absolute delivery volume is directly proportional to the rotational speed of the delivery member 10. In the case of compressible fluids, for example air, the relationship between the delivered amount and the rotational speed may not be linear, but the absolute delivered amount and/or mass likewise increases with the rotational speed.

(14) The specific delivery volume depends on the eccentricity, i.e. the distance between the central axis of the adjusting member 20 and the rotational axis R.sub.10 of the delivery member 10. In order to be able to change this axial distance, the adjusting member 20 is arranged such that it can be moved within the pump housing 1, 2by way of example, pivoted about a pivot axis R.sub.20. In variations, a modified adjusting member can also be arranged such that it can be linearly moved within the pump housing 1, 2. For adjusting the specific delivery volume and/or eccentricity, it is preferably able to move transverse to the rotational axis R.sub.10 of the delivery member 10. It would in principle also be conceivable for it to be axially adjustable, thus enabling an axial width of the delivery cells to be adjusted.

(15) A pivot bearing region of the adjusting member 20 is denoted by 21. The pivot bearing is embodied as a slide bearing, in that the pivot bearing region 21 of the adjusting member 20 is in direct sliding contact with a co-operating surface of the housing 1.

(16) For the purpose of adjusting in a setting directionin the example embodiment, the pivoting directiona setting fluid pressure which acts in a setting direction is applied to the adjusting member 20. A restoring force acts in the opposite setting direction, counter to this setting pressure. The restoring force is generated by a spring device comprising one or more mechanical spring membersin the example embodiment, a single spring member 25. The spring member 25 is embodied and arranged as a helical pressure spring. For the purpose of applying pressure using the setting fluid, the side of the adjusting member 20 which lies opposite as viewed from the pivot axis R.sub.20 across the rotational axis R.sub.10 of the delivery member 10 comprises an acting region 22 of the adjusting member 20 which functionally acts as an adjusting piston and which is formed integrally with an annular portion of the adjusting member 20. On one side of the acting region 22 of the adjusting member 20, a setting pressure chamber K is formed in the pump housing 1, 2, into which the setting fluid can be introduced in order to exert a setting force, which acts in the setting direction, on the acting region 22 of the adjusting member 20 and via the latter on the adjusting member 20. The restoring force likewise, by way of example, acts directly on the acting region 22 of the adjusting member 20.

(17) The setting pressure chamber K is fed with the setting fluid delivered by the pump, in order to apply the setting fluid pressure to the adjusting member 20 in the setting direction, against the force of the spring member 25. The setting direction is selected such that the eccentricity between the delivery member 10 and the adjusting member 20 and thus the specific delivery volume of the pump decreases in size when the adjusting member 20 is moved in the setting direction.

(18) The adjusting member 20 together with the housing 1 forms a sealing gap which separates the setting pressure chamber K from the low-pressure region in the setting direction. A sealing element 24 is arranged in the sealing gap in order to better seal off the sealing gap. The sealing element 24 is arranged in a receptacle of the adjusting member 20.

(19) In relation to controlling or regulating the delivery volume by applying the control fluid pressure as described, reference is made to DE 10 2011 086 175 B3, which is incorporated by reference in this respect and also with respect to other details of the functionality of the pump of the example embodiment.

(20) The pump comprises a control valve 30 for influencing the setting pressure which prevails in the setting pressure chamber K. The control valve 30 is an integral constituent part of the pump 100, in that the pump housing 1, 2 also forms the housing of the control valve 30. The pump, including the control valve 30, can be fitted as a unit. The delivery and adjusting components, such as in particular the delivery member 10 and the adjusting member 20, and the control valve 30 are combined by means of the common pump housing 1, 2 to form a fitted unit.

(21) A relief channel 35 connects the control valve 30 directly to the suction region 4. The relief channel 35 extends in the pump housing 1, 2 directly from the control valve 30 all the way to the suction region 4. It feeds into a valve space 31 of the control valve 30, formed by the pump housing 1, 2, at one end and into the suction region 4 at the other end. In the example embodiment shown, the relief channel 35 is formed in the joining surface 1a of the housing structure 1, and the cover 2when fittedseals off the relief channel 35 in a fluid seal.

(22) FIG. 3 schematically shows a fluid delivery cycle containing the pump 100. The pump 100 delivers fluid from a reservoir 98 to an assembly M to be supplied with the fluid, for example lubricating oil to an internal combustion engine, for driving a motor vehicle, which forms the assembly M. Once it has flowed through the assembly M, the fluidrelieved of pressureflows back into the reservoir 98. On the low-pressure side, the pump 100 delivers the fluid from the reservoir 98, through a feed conduit 99, the pump port 3 and the suction region 4 of the pump housing 1, 2, into the delivery chamber 5 (FIG. 2), from which it is expelled at an increased pressure. On the high-pressure side, a main flow 101 is delivered to the assembly M by the pump 100. A smaller portion is diverted from the main flow 101 and guided, as a setting fluid, to a pressure port P of the control valve 30. The pressure port P is correspondingly connected to the main flow 101 via a secondary flow conduit. The control valve 30 is connected to the adjusting device of the pump 100 via a working port A. The adjusting device comprises the setting pressure chamber K (FIG. 2) and the schematically indicated adjusting member 20. The adjusting device can comprise another setting pressure chamber or, as applicable, multiple other setting pressure chambers in which the setting fluid or a different setting fluid acts on the adjusting member 20. In FIG. 3, the adjusting member 20 also stands for the other components of the adjusting device, such as for example the setting pressure chamber K, the spring member 25 and optionally one or more other setting pressure chambers.

(23) The control valve 30 also comprises a relief port S for the setting fluid. The relief port S is directly connected to the suction region 4 via the relief channel 35. The reservoir 98 is bypassed. No fluid flows to the reservoir 98 through the relief port S, and no fluid flows from the reservoir 98 to the control valve 30 through the relief port S. There is therefore no fluid communication between the relief port S and the reservoir 98. The pressurised setting fluid is fed back into the suction region 4 energy-efficiently via the relief port S. Setting fluid which is fed back for relieving pressure on the adjusting member 20 does not first have to be suctioned again from the reservoir 98 by the pump 100. The setting fluid, which is fed back via a short path, exhibits a higher pressure than the fluid situated in the reservoir and contains less air. Both these factors help to improve the effectiveness of the pump 100.

(24) The control valve 30 comprises a valve space 31, whichas already mentionedis formed by the pump housing 1, 2, and a control piston 32 which can be moved within the valve space 31. The control piston 32 can be moved back and forth within the valve space 31 between a first piston position and a second piston position. In FIG. 3, the control piston 32 assumes an intermediate position between the first piston position and second piston position. In the intermediate position shown, the control piston 32 separates the pressure port P from both the working port A and the relief port S. If the working port A is connected to the setting pressure chamber K (FIG. 2), then the control valve 30 blocks the setting pressure chamber K when the control piston 32 is in the intermediate position, such that aside from unavoidable leakage losses, the setting pressure which prevails in the setting pressure chamber K remains constant.

(25) If the control piston 32 is moved from the intermediate position into the first piston position, i.e. to the left in FIG. 3, the pressure port P is connected to the working port A, such that the setting fluid reaches the adjusting device, and the setting pressurei.e. a pressure of the high-pressure side of the pump 100is applied to the adjusting member 20, wherein the adjusting device is designed such that an increase in the setting pressure reduces the specific delivery volume of the pump 100.

(26) If the control piston 32 is moved from the intermediate position into the second piston position, i.e. to the right in FIG. 3, the working port A is initially separated from the pressure port P and subsequently, when the second piston position has been reached, connected to the relief port S and the relief channel 35. When the control piston 32 is in the second piston position, the setting fluid can flow off into the valve space 31 via the working port A and from the valve space 31 into the suction region 4 via the relief port S. When the control valve 30 is in this state, with the control piston 32 in the second piston position, the setting pressure chamber K (FIG. 2) and/or optionally a different setting pressure chamber of the adjusting device is pressurised to the comparatively lower pressure of the suction region 4, thus achieving an effective relief of pressure on the adjusting member 20.

(27) The control valve 30 comprises a tensing device 33 which exerts a tensing force, which acts in the direction of the second piston position, on the control piston 32. The tensing device 33 is, by way of example, a helical pressure spring which is arranged in a tensing chamber 34 of the valve space 31 and acts on an axial end-facing side of the control piston 32. The relief port S feeds into the tensing chamber 34.

(28) A first control pressure chamber 36 comprising a first chamber port X and a second control pressure chamber 37 comprising a second chamber port Y are formed in the valve space 31. A control pressure of a control fluid can be applied to the control piston 32 in each of the control pressure chambers 36 and 37. The respective control fluid acts on a first piston surface (36a) of the control piston 32, which in the example embodiment is embodied as a stepped piston, in the control pressure chamber 36 and on a second piston surface (37a) of the control piston 32 in the control pressure chamber 37. The respective control fluid exerts a first control force on the control piston 32 in the control pressure chamber 36 and a second control force on the control piston 32 in the control pressure chamber 37 in accordance with the control pressures and piston surfaces. The control valve 30 is embodied such that the first control force and second control force each act counter to the tensing force of the tensing device 33.

(29) At its chamber port X, the control pressure chamber 36 is permanently connected to the main flow 101, delivered by the pump 100, via a secondary flow conduit which diverts from the main flow 101. The fluid delivered by the pump is thus also used as a control fluid, wherein a control pressure which permanently prevails in the control pressure chamber 36 during pump operations depends on the pressure of the high-pressure side of the pump 100 and for example at least substantially corresponds to the pressure at the diversion point.

(30) In order to be able to apply control fluid to the second control pressure chamber 37, the control fluid for this chamber 37 is also diverted from the main flow 101. The control fluid diverted from the main flow 101 to the control pressure chamber 37 is guided to the chamber port Y via another secondary flow conduit, but not directly. A modulating valve 40 is arranged in this secondary flow conduit. The chamber port Y can be optionally connected to the main flow 101, or instead to the suction region 4 via a feedback conduit 45, by means of the modulating valve 40. The control valve 30 and the modulating valve 40 are thus configured for permanently applying a first control pressure to the control piston 32, counter to the tensing force of the tensing device 33, in the first control pressure chamber 36 and enabling a second control pressure, which likewise acts counter to the tensing force, and thus an additional control force to be optionally connected up or cut off, up or down to the pressure of the suction region 4.

(31) The modulating valve 40 can be configured to switch back and forth only between the two switched states mentioned. It can also be configured to assume one or more middle switched states between the two extreme switched states, in order to be able to vary the additional control force in multiple increments. The modulating valve 40 can also be configured to continuously vary the control pressure in the second control pressure chamber 37 and thus the additional control force.

(32) The control pressures prevailing in the control pressure chambers 36 and 37 which achieve an equilibrium between the forces acting on the control piston 32on the one hand, the tensing force of the tensing device 33 and on the other hand, the control forces generated by the control fluidcan be specifically modulated by means of the modulating valve 40. The equilibrium pressure of the fluid delivered by the pump 100 which is achieved when the forces are in equilibrium can be modulated correspondingly and the delivery characteristic curve of the pump 100the delivery pressure over the rotational speed of the pumpthus varied. An upper limit for the delivery pressure can in particular be adjusted, for example optionally set to one of at least two different pressure levels.

(33) For relieving pressure on the second control pressure chamber 37, the control fluid is channelled back to the pump 100 in a feedback conduit 45 by bypassing the reservoir 98, preferably directly into the suction region 4 of the pump housing 1, 2 as in the example embodiment. In a modification, the feedback conduit 45 can instead also be guided back to the low-pressure side of the pump 100, likewise by bypassing the reservoir 98, to a connecting point downstream of the reservoir 98 and upstream of the pump port 3. The statements made with respect to the setting fluid correspondingly apply to feeding the control fluid back by bypassing the reservoir 98. Although the control fluid for relieving pressure is fed back in the preferred embodiments by bypassing the reservoir 98, conventional arrangements in which the control fluid for relieving pressure is fed back to the reservoir 98 are not to be excluded.

(34) The modulating valve 40 is an electromagnetic valve. It can be a proportional valve using which the control pressure in the control pressure chamber 37 can be continuously adjusted. It can in particular however also be a manifold switching valve which can be switched between two, three or as applicable even more switched states. In the example embodiment, the modulating valve 40 is such a switching valve and connects the control pressure chamber 37 to the high-pressure side of the pumpin the example embodiment, the main flow 101in a first switched state and separates it from the high-pressure side of the pump and instead connects it to the pump 100 via the feedback conduit 45, by bypassing the reservoir 98, in a second switched state. The control pressure chamber 37 is therefore connected to the high-pressure side of the pump 100 when the modulating valve 40 is in the first switched state, and to the low-pressure side of the pump 100 when the modulating valve 40 is in the second switched state. If the modulating valve 40 assumes the first switched state, the control pressures in the control pressure chambers 36 and 37 jointly act on the control piston 32 in the direction of the first piston position, counter to the tensing force of the tensing device 33. If the modulating valve 40 assumes the second switched state, the control pressure only then effectively acts on the control piston 32 in the first control pressure chamber 36. This control pressure has to be corresponding higher in order to move the control piston 32 into the first piston position, against the restoring tensing force of the tensing device 33. When the first piston position has been assumed, the pressure port P is connected to the working port A, such that the setting pressure of the setting fluidin this case, the pressure of the high-pressure side of the pump 100acts on the adjusting member 20 and thus in the direction of reducing the delivery volume of the pump.

(35) The modulating valve 40 comprises a signal port 41 at which it is connected to an external controller. If the assembly M is a drive motor of a vehicle, an engine controller can in particular form the external controller. Such engine controllers are typically formed as characteristic-curve controllers or characteristic-map controllers. In an engine characteristic-map controller, the requirements of the drive motor can be stored in an electronic memory of the controller in a characteristic map of different engine variables, for example a temperature and/or rotational speed of the engine and/or a lubricating oil pressure at a critical point in the engine and/or the load state of the engine and so forth. On the basis of corresponding measured variables and the stored characteristic map, the external controller forms the output signal using which it actuates the modulating valve 40 in order to modulate the delivery pressure of the pump 100 which is sufficient to move the control piston 32 into the first piston position.

(36) FIG. 4 shows the control valve 30 in a longitudinal section. The ports A, P and S for the setting fluid and the ports X and Y for the control fluid, together with the end portions of the feed and drainage channels extending within the pump housing 1, 2, can be seen. The shape of the control piston 32, in order to obtain a stepped piston comprising a first piston surface (36a) to which the control fluid is applied in the control pressure chamber 36 and a second piston surface (37a) to which fluid is applied in the control pressure chamber 37, can likewise be seen.

(37) The valve space 31 is formed primarily in the housing structure 1, as an axial blind bore by way of example. It is open in the direction of the cover 2 at one of the two end faces of the control piston 32. The cover 2 seals the valve space 31 at the open end. The tensing chamber 34 is formed in the end region of the valve space 31 which is sealed by the cover 2, such that the control piston 32 and then the tensing device 33 can be inserted through the opening, into the valve space 31. Once the cover 2 has been fitted, the tensing device 33 is axially supported on it.

(38) The relief channel 35 feeds into the tensing chamber 34, such that the tensing chamber 34 is connected to the suction region 4 of the pump housing 1, 2 in any state of the control valve 30, i.e. irrespective of the position of the control piston 32.

(39) FIG. 5 shows the immediate vicinity of the control valve 30 in a plan view onto the joining surface 1a of the housing structure 1. The cover 2 has been removed, such that there is a clear view into the valve space 31. The control piston 32 has been inserted, and the tensing device 33 has likewise been positioned. It is then merely necessary to attach the cover 2 to the housing structure 1 in order to complete the pump as such, including the integrated control valve 30 for arranging in a delivery cycle.

(40) In the first example embodiment, the relief channel 35 is formed completely on the housing structure 1. The relief channel 35 extends in the joining surface 1a as a channel which is open in the direction of the cover 2 and sealed off by the cover 2 when the latter is fitted. In a modification, the relief channel 35 can instead also be formed in the joining surface 2a of the cover 2, where it exhibits the same profile as the relief channel 35 formed on the housing structure 1 in the first example embodiment. Such a modification is indicated in FIG. 4. Only an end portion of the relief channel 35 near the control valve 30 can be seen in FIG. 4. The end portion extends in the joining surface 2a of the cover 2 and not, as illustrated in FIGS. 2 and 5 for the first example embodiment, in the joining surface 1a of the housing structure 1.

(41) FIG. 6 shows a pump 100 which differs from the pump 100 described above only in that the relief channel, which connects the relief port S of the control valve 30 to the suction region 4 of the pump housing 1, 2, is formed completely in the cover 2. While the relief channel 35 of the first example embodiment is formed in the joining surface 1a of the housing structure 1 or, in the modification indicated in FIG. 4, in the joining surface 2a of the cover 2 and is therefore not ultimately completed until the housing structure 1 and the cover 2 are joined, the relief channel of the second example embodimentwhich, because of this difference, is referred to as the relief channel 39extends within the cover 2. The relief channel 39 can in particular comprise a linear main channel portion which overlaps in one end region with the control valve 30 and in another end region with the suction region 4 and is connected to the valve space 31 of the control valve 30 and to the suction region 4 via short channel portions which are each formed in the cover 2 and divert or deviate from the main channel portion. An advantage of the relief channel 35 of the first example embodiment is its ease of manufacture, while an advantage of the relief channel 39 of the second example embodiment is its simplicity with respect to sealing off the internal space of the pump housing 1, 2.

(42) In the example embodiments, the pressure port P of the control valve 30 is connected to the high-pressure side of the pump 100 within the pump housing 1, 2. The setting fluid is diverted while still in the high-pressure region of the pump housing 1, 2 and is guided to the pressure port P. The connection between the working port A and the setting pressure chamber K and/or optionally a different setting pressure chamber of the adjusting device expediently likewise extends within the pump housing 1, 2. Since the relief port S is likewise connected to the suction region 4 within the pump housing 1, 2 via the relief channel 35 or 39 which extends completely within the pump housing 1, 2, a maximum degree of integration is achieved with regard to the setting fluid. Fitting the pump is simplified, since no additional feed and/or drainage conduits have to be provided for the setting fluid andif arranged in a delivery cycleconnected. On the other hand, it would however be conceivable to divert the setting fluid from the main flow 101 at a point upstream of the pump housing 1, 2, i.e. upstream of the pump port 8 (FIG. 3). In such modifications, the setting fluid is advantageously diverted at a point upstream of a filter arranged downstream of the pump, and before a first assembly to be supplied with the fluid, in order to guide fluid which is cleaned in the filter to the control valve 30.

(43) The modulating valve 40 can advantageously be arranged separately from the pump housing 1, 2. Arranging it away from the pump housing 1, 2 is in particular advantageous when the modulating valve 40 is formed as an electromagnetic valve. If the modulating valve 40 is arranged away from the pump 100, then conduits leading to the modulating valve 40 for supplying power and/or transmitting control signals do not have to be screened or do not have to be as elaborately screened against the fluid to be delivered by the pump 100. This does, however, require that on the other side, the feed conduits for the control fluid first have to also be connected to the pump housing 1, 2. Since the flow cross-sections of the modulating valve 40 are typically smaller than the flow cross-sections of the control valve 30, it is particularly advantageous in relation to the control fluid if it is diverted only after it has been cleaned in a filter, in order to avoid the risk of the narrow valve cross-sections becoming blocked.

(44) With regard to FIGS. 1 and 6, it may be noted merely for the sake of completeness that the pump 100 in the example embodiments is a constituent part of a pump unit which also comprises a vacuum pump in addition to the pump 100, and the pump 100 together with the vacuum pump forms a fitted unit. This is however extraneous to the invention.