Pump exhibiting an adjustable delivery volume

Abstract

A pump which exhibits an adjustable delivery volume, the pump including (a) a pump housing comprising a delivery chamber; (b) a delivery rotor which can be rotated about a rotary axis within the delivery chamber, for delivering the fluid; (c) an adjusting device, including: (c1) an adjusting member which can be adjusted in the pump housing in order to adjust the delivery volume of the pump; (c2) a first setting chamber for generating a first setting pressure for adjusting the adjusting member; (c3) and a second setting chamber for generating a second setting pressure for adjusting the adjusting member; (d) a fluidically operable valve for adjusting the setting pressure of the first setting chamber; (e) and an electromagnetic valve, comprising: a pressure port for a setting fluid which is diverted from the high-pressure side; and a relief port for the setting fluid.

Claims

1. A pump which exhibits an adjustable delivery volume, the pump comprising: (a) a pump housing comprising 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; (b) a delivery rotor which can be rotated about a rotary axis within the delivery chamber, for delivering the fluid; (c) an adjusting device, comprising: (c1) an adjusting member which can be adjusted back and forth in the pump housing in a setting direction and a restoring direction in order to adjust the delivery volume of the pump; (c2) a first setting chamber for generating a first setting pressure for adjusting the adjusting member in the setting direction; (c3) and a second setting chamber for generating a second setting pressure for adjusting the adjusting member in the setting direction; (d) a restoring device, arranged in the pump housing, for generating a restoring force which acts on the adjusting member in the restoring direction; (e) a fluidically operable valve for adjusting the setting pressure of the first setting chamber, the fluidically operable valve comprising: a pressure port for a setting fluid which is diverted from the fluid of the high-pressure side; a working port, connected to the first setting chamber, for the setting fluid; and a relief port for the setting fluid; (f) and an electromagnetic valve, comprising: a pressure port for a setting fluid which is diverted from the high-pressure side; and a relief port for the setting fluid, (g) wherein the electromagnetic valve comprises a working port for the setting fluid, which is connected to the second setting chamber, in order to adjust the setting pressure of the second setting chamber.

2. The pump according to claim 1, wherein the relief port of the fluidically operable valve and/or the relief port of the electromagnetic valve is/are connected to the low-pressure side of the pump, at a point downstream of a reservoir for the fluid.

3. The pump according to claim 1, wherein the fluidically operable valve comprises: a valve space; a control piston which can be moved back and forth within the valve space between a first piston position and a second piston position; a tensing device for generating a tensing force which acts on the control piston in the direction of one of the piston positions; and a control chamber for generating a control force which acts on the control piston counter to the tensing force of the tensing device; and the control chamber comprises an inlet, which is permanently attached to the high-pressure side of the pump, for a control fluid.

4. The pump according to claim 3, wherein the tensing device of the fluidically operable valve exerts a tensing force which is greater than a control force which occurs when the electromagnetic valve is properly and/or actively functioning.

5. The pump according to claim 3, wherein the control piston comprises at least a first annular portion, which separates the pressure port and the working port from each other in one piston position and separates the working port and the relief port from each other in another piston position, and a second annular portion which comprises at least one passage opening and is arranged axially between the pressure port and the first annular portion.

6. The pump according to claim 5, wherein one axial end of the control piston comprises a first axial protrusion for arranging the tensing device, and another axial end of the control piston comprises a second axial protrusion for forming an abutment.

7. The pump according to claim 5, wherein at least the first annular portion is formed as a solid body.

8. The pump according to claim 5, wherein the annular portions differ from each other in their diameter.

9. The pump according to claim 3, wherein the pressure port of the fluidically operable valve also forms the inlet into the control chamber of the fluidically operable valve.

10. The pump according to claim 1, wherein the fluidically operable valve comprises a housing which comprises at least two regions which differ from each other in their inner diameter.

11. The pump according to claim 1, wherein the electromagnetic valve comprises: a valve space; a control piston which can be moved back and forth within the valve space between a first piston position and a second piston position; a tensing device for generating a tensing force which acts on the control piston in the direction of one of the piston positions; and an electromagnetic device for generating an electromagnetic force which acts on the control piston counter to the tensing force of the tensing device; and the electromagnetic device comprises a port for connecting to an external controller.

12. The pump according to claim 11, wherein the tensing device of the electromagnetic valve is provided for setting a piston position in which the second setting chamber is connected to the relief port of the electromagnetic device.

13. The pump according to claim 1, wherein the pump is arranged in a fluid cycle, and a filter for cleaning the fluid delivered by the pump is arranged in the fluid cycle at a point downstream of the pump, and the setting fluid for at least one of the setting chambers and/or the control fluid for the fluidically operable valve is/are diverted at a point downstream of the filter.

14. The pump according to claim 1, wherein the relief port of the fluidically operable valve and/or the relief port of the electromagnetic valve is/are connected to a suction region of the pump housing at a point downstream of a reservoir for the fluid.

15. The pump according to claim 4, wherein the control piston comprises at least a first annular portion, which separates the pressure port and the working port from each other in one piston position and separates the working port and the relief port from each other in another piston position, and a second annular portion which comprises at least one passage opening and is arranged axially between the pressure port and the first annular portion.

16. The pump according to claim 6, wherein at least the first annular portion is formed as a solid body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An example embodiment of the invention is described below on the basis of figures. Features disclosed by the example embodiment, 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 an adjusting member and multiple setting chambers for applying pressurised setting fluid to the adjusting member;

(3) FIG. 2 the pump together with assigned valves for adjusting the delivery volume and delivery characteristics of the pump; and

(4) FIG. 3 one of the assigned valves, in a longitudinal section.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows a pump 1 in a vane cell design by way of example. The pump 1 comprises a pump housing comprising a housing structure 2 and a cover. The housing structure 2 accommodates and/or mounts components of the pump 1 such that they can be moved. The housing structure 2 is open on an axial end-facing side, thus facilitating the arrangement of components of the pump in or on the housing structure 2. The cover can be fitted to the housing structure 2 and, when fitted, seals the housing structure 2 on the end-facing side in question. The cover has been removed in FIG. 1, such that functional components of the pump can be seen in the plan view onto the open housing structure 2 shown.

(6) The housing structure 2 surrounds a delivery chamber 5 in which a delivery rotor 10 is arranged such that it can be rotated about a rotary axis R.sub.10. The pump housing comprises a housing inlet on a low-pressure side for connecting the pump 1 to a reservoir R, and a housing outlet on a high-pressure side for discharging a fluid to be delivered, for example engine lubricating oil, 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 rotor 10 is rotary-driven in the rotational direction indicated, i.e. anticlockwise, fluid flows through the housing inlet into the pump housing and through a delivery chamber inlet 4 on the low-pressure side in the pump housing, into the delivery chamber 5, and is expelled at an increased pressure through a delivery chamber outlet 6 on the high-pressure side of the pump and discharged via the housing outlet. A suction region is formed on the low-pressure side of the pump housing, wherein the fluid delivered by the pump flows through the suction region on its flow path from the housing inlet to the delivery chamber inlet 4. The suction region 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 rotor 10 is rotated. A high-pressure region of the pump housing which adjoins the suction region 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 housing outlet via the delivery chamber outlet 6.

(7) The delivery rotor 10 is an impeller comprising a rotor structure 11, which is central with respect to the rotary axis R.sub.10, 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. The vanes 12 are supported on the radially inner side on a supporting structure 13 which can be moved transverse to the rotary axis R.sub.10.

(8) The outer circumference of the delivery rotor 10 is surrounded by an adjusting member 20 which is, by way of example, shaped as an adjusting ring. When the delivery rotor 10 is rotary-driven, its vanes 12 slide over an inner circumferential surface of the adjusting member 20. The rotary axis R.sub.10 of the delivery rotor 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 rotor 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 rotor 10 is rotated. Because the delivery cells increase and decrease in size periodically with the rotational speed of the delivery rotor 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 6 and then through the housing outlet.

(9) The volume of fluid delivered by each revolution of the delivery rotor 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 rotor 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.

(10) The specific delivery volume depends on the eccentricity, i.e. the distance between the central axis of the adjusting member 20 and the rotary axis R.sub.10 of the delivery rotor 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 housingby 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. For adjusting the specific delivery volume and/or eccentricity, it is preferably able to move transverse to the rotary axis R.sub.10 of the delivery rotor 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.

(11) 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 structure 2.

(12) For the purpose of adjusting in a setting direction Vin the example embodiment, the pivoting directiona setting pressure of a setting fluid is applied to the adjusting member 20. A restoring force acts in the opposite directionthe restoring directioncounter to the fluidic setting pressure. The restoring force is generated by a spring device 25 comprising one or more mechanical spring membersin the example embodiment, a single spring member. The spring member 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 rotary axis R.sub.10 of the delivery rotor 10 comprises an acting region 22 of the adjusting member 20 which functionally acts as an adjusting piston. On one side of the acting region 22 of the adjusting member 20, a first setting chamber K.sub.1 is formed in the pump housing, into which the setting fluid can be introduced in order to exert a first setting force, which acts in the setting direction V, on the acting region 22 of the adjusting member 20 and thus on the adjusting member 20. The restoring force of the spring device 25 likewise, by way of example, acts directly on the acting region 22 of the adjusting member 20.

(13) The first setting chamber K.sub.1 is fed with the setting fluid delivered by the pump 1, in order to apply the first setting pressure to the adjusting member 20 in the setting direction V, against the force of the spring device 25. The setting direction V is selected such that the eccentricity between the delivery rotor 10 and the adjusting member 20 and thus the specific delivery volume of the pump 1 decreases in size when the adjusting member 20 is moved in the setting direction V.

(14) The adjusting member 20 together with the housing structure 2 forms a sealing gap which separates the first setting chamber K.sub.1 from the low-pressure region in the setting direction V. 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.

(15) A second setting chamber K.sub.2 is formed in the pump housing, into which a pressurised setting fluid can likewise be introduced in order to be able to exert another, second setting pressure on the adjusting member 20 in the second setting chamber K.sub.2. The setting chambers K.sub.1 and K.sub.2 are formed adjacently in the circumferential direction on an outer circumference of the adjusting member 20 and are sealed off from each other by means of another sealing element. In the two setting chambers K.sub.1 and K.sub.2, the respective setting fluid acts directly on the adjusting member 20. Instead of applying pressure directly, it would be possible in modified embodiments to arrange for the pressure to be applied to the adjusting member 20 indirectly using two or more setting pistons, wherein the first setting pressure would act on at least one such setting piston and the second setting pressure would act on at least one other setting piston. The adjusting device can comprise another setting chamber, or as applicable multiple other setting chambers, in which a setting fluid acts on the adjusting member 20 directly or instead indirectly via a setting piston in each case.

(16) The first setting pressure which prevails in the first setting chamber K.sub.1 and the second setting pressure which prevails in the second setting chamber K.sub.2 can be altered by applying the respective setting fluid to the setting chambers K.sub.1 and K.sub.2, respectively, via an assigned valve. Setting fluid is applied to one of the setting chambers K.sub.1 and K.sub.2 via a fluidic valve, while setting fluid is applied to the other of the setting chambers K.sub.1 and K.sub.2 via an electromagnetic valve. In the example embodiment, the fluidic valve is assigned to the first setting chamber K.sub.1, and the electromagnetic valve is assigned to the second setting chamber K.sub.2.

(17) FIG. 2 shows a fluid delivery cycle containing the pump 1. The pump 1 is shown schematically, as are the other components of the fluid cycle. As can be seen from FIG. 1, the pump 1 thus includes the adjusting device comprising the adjusting member 20, the spring device 25 and the setting chambers K.sub.1 and K.sub.2. In preferred embodiments, the fluidic valve 30 is also an integral constituent part of the pump housing, in that the fluidic valve 30 is arranged in or on the pump housing. The electromagnetic valve 40 is also regarded as forming part of the pump 1, although the electromagnetic valve 40 can be arranged slightly away from the pump housing. Arranging it externally in relation to the pump housing can in particular be advantageous when the electrical insulation of a feed conduit for electrical energy and/or control signals causes problems in the immediate environment of the pump housing.

(18) The pump 1 delivers fluid, for example lubricating oil, from a reservoir R to an assembly M to be supplied with the fluid, for example an internal combustion engine for driving a motor vehicle, which forms the assembly M. An assembly M which is formed by an internal combustion engine and is to be supplied with the fluid can drive the pump 1, as illustrated in FIG. 2, such that the delivery rotor 10 is rotary-driven in a fixed rotational speed relationship with an output shaft of the assembly M. On the low-pressure side, the pump 1 delivers the fluid from the reservoir R through a feed conduit, the housing inlet and the suction region of the pump housing, into the delivery chamber 5 (FIG. 1), from which it is expelled at an increased pressure. On the high-pressure side, a main flow 50 which is delivered by the pump 1 is delivered to the assembly M via a filter 48. Once it has flowed through the assembly M, the fluidrelieved of pressureflows back into the reservoir R.

(19) A smaller portion is diverted from the main flow 50 and guided, as a setting fluid, to a pressure port P of the fluidic valve 30. The pressure port P is correspondingly connected to the main flow 50 via a secondary flow conduit. The fluidic valve 30 is connected to the first setting chamber K.sub.1 (FIG. 1) via a working port A. In FIG. 2, the adjusting member 20 also stands for the other components of the adjusting device, such as for example the spring member 25 and the setting chambers K.sub.1, K.sub.2 and optionally one or more other setting chambers.

(20) The fluidic valve 30 also comprises a relief port S for the setting fluid. The relief port S is directly connected to the suction region of the pump housing via a relief channel 35. The reservoir R is bypassed. The relief channel 35 preferably extends in or on the pump housing directly from the fluidic valve 30 all the way to the suction region of the pump housing. No fluid flows directly to the reservoir R through the relief port S, and no fluid flows from the reservoir R to the fluidic valve 30 through the relief port S. There is therefore no direct fluid communication between the relief port S and the reservoir R. The pressurised setting fluid is fed back into the suction region of the pump housing 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 R by the pump 1. The setting fluid, which is fed back via a short path, exhibits a higher pressure than the fluid situated in the reservoir R and contains less air. Both these factors help to improve the effectiveness of the pump 1.

(21) Although relieving pressure into the suction region of the pump housing provides a whole series of advantages over relieving pressure into the reservoir R, the fluidic valve 30 can be relieved of pressure towards the reservoir R via its relief port S in modified embodiments.

(22) The fluidic valve 30 is operated using a control fluid which is also diverted from the high-pressure side of the pump 1 and which is guided to a control port C of the fluidic valve 30.

(23) The electromagnetic valve 40 can be a proportional valve using which the setting pressure in the second setting chamber K.sub.2 (FIG. 1) 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 and therefore piston positions. In the example embodiment, the electromagnetic valve 40 is such a switching valve and connects the second setting chamber K.sub.2 to the high-pressure side of the pump 1 in a first switched state and separates it from the high-pressure side of the pump 1 and instead connects it to the low-pressure side of the pump 1 via a feedback conduit 45, by bypassing the reservoir R, in a second switched state. The second setting chamber K.sub.2 is therefore connected to the high-pressure side of the pump 1 when the electromagnetic valve 40 is in the first switched state, and to the low-pressure side of the pump 1 when the electromagnetic valve 40 is in the second switched state. If the electromagnetic valve 40 assumes the first switched state, the setting pressures in the setting chambers K.sub.1 and K.sub.2 jointly act on the adjusting member 20. If the electromagnetic valve 40 assumes the second switched state, the setting pressure only then acts on the adjusting member 20 in the first setting chamber K.sub.1, while the comparatively low pressure of the suction region of the pump housing prevails in the second setting chamber K.sub.2. This first setting pressure has to be corresponding higher in order to move the adjusting member 20 in the setting direction V, against the restoring tensing force of the spring device 25.

(24) It also holds for the electromagnetic valve 40 that while the relief port S of the electromagnetic valve 40 is preferably connected directly to the suction region of the pump housing, alternatively relieving the pressure on the electromagnetic valve 40 into the reservoir R is not however to be excluded.

(25) The electromagnetic 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 electromagnetic valve 40 in order to modulate the delivery pressure of the pump 1. The modulation resides in the fact that by means of the electromagnetic valve 40, it is possible to alter the size of the delivery pressure at which the specific delivery volume of the pump 1 is reduced by adjusting the adjusting member 20.

(26) The electromagnetic valve 40 comprises a valve piston, a solenoid 46 coupled to the valve piston and operable in response to signals received via signal port 41, and a spring means 43 exerting a spring force onto the valve piston counter to a force the solenoid 46 does exert onto the valve piston in response to the signals received via signal port 41.

(27) FIG. 3 shows the fluidic valve 30 in a longitudinal section. The ports A, P and S for the setting fluid and the port C for the control fluid can be seen. The fluidic valve 30 is an integral constituent part of the pump 1, in that the pump housing also forms the housing of the fluidic valve 30. The pump 1, including the fluidic valve 30, can be fitted as a unit. The delivery and adjusting components, such as in particular the delivery rotor 10 and the adjusting member 20, and the fluidic valve 30 are combined by means of the common pump housing to form a fitted unit.

(28) The valve space 31 is formed in the housing structure 2, as an axial blind bore by way of example. It is open at one of the two end faces of the control piston 32. A sealing part 37 seals the valve space 31 at the open end. A tensing chamber 34, in which the tensing device 33 acts on the control piston 32, is formed in an axial end region of the valve space 31.

(29) The relief channel 35 (FIG. 2) feeds into the tensing chamber 34, such that the tensing chamber 34 is connected to the suction region of the pump housing in any state of the fluidic valve 30, i.e. irrespective of the position of the control piston 32. In FIG. 3, the relief channel extends perpendicular to a shifting axis of the control piston 32, out of the tensing chamber 34. Alternatively or additionally, the relief channel can extend obliquely, in parallel or in an extension of the shifting axis of the control piston 32, out of the tensing chamber 34.

(30) 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 has assumed the second piston position. In the second piston position, the working port A is connected to the relief port S. The setting fluid can flow into the valve space 31 via the working port A and flow off from the valve space 31 into the suction region of the pump housing via the relief port S. When the fluidic valve 30 is in this state and the control piston 32 is in the second piston position, the first setting chamber K.sub.1 is pressurised to the comparatively low pressure of the suction region, thus effectively relieving pressure on the adjusting member 20.

(31) If the control piston 32 is moved from the second piston position into the first piston position, i.e. to the right in FIG. 3, the pressure port P is connected to the working port A, and via the working port A to the first setting chamber K.sub.1, such that the setting pressurea pressure of the high-pressure side of the pump 1is applied to the adjusting member 20, wherein the adjusting device is configured such that an increase in the setting pressure causes a reduction in the specific delivery volume of the pump 1.

(32) The control port C, indicated at the fluidic valve 30 in the schematic in FIG. 2, can be combined with the pressure port P, as can be seen in FIG. 3. Correspondingly, the pressure port P can also simultaneously form the control port C. A control chamber 36 which is formed in the valve space 31 and in which the fluidic control force is applied to the control piston 32, counter to the tensing force of the tensing device 33, also forms a connecting chamber for the ports P and A when the control piston 32 is in the first piston position.

(33) The inlet C of the fluidic valve 30 is permanently attached to the high-pressure side of the pump 1. A control pressure and therefore a control force against the tensing device 33 permanently acts on the control piston 32 while the pump 1 is in operation. The tensing device 33 of the fluidic valve 30 is biased. It permanently exerts, on the control piston 32, a tensing force which acts against the control force and is greater than a maximum control force, acting on the control piston 32, which occurs when the electromagnetic valve 40 is properly functioning and actively actuated. A properly functioning and active electromagnetic valve 40 regulates the pump 1 during operations, via the second setting chamber K.sub.2, in such a way as to result in a maximum control force acting on the control piston 32 which is smaller than the tensing force of the tensing device 33 of the fluidic valve 30 and therefore smaller than the control force necessary for switching the first switching position and therefore the first piston position. In operational states in which the electromagnetic valve 40 is active and functioning properly, the fluidic valve 30 is always switched to its second switching position and therefore the second piston position, since the electromagnetic valve 40 regulates the pump 1 to a maximum delivery output which results in a control force acting on the control piston 32 of the fluidic valve 30 which is smaller than the counteractive tensing force of the tensing device 33. The control force acting on the control piston 32 of the fluidic valve 30 which results from the maximum delivery output is not sufficient to switch the fluidic valve 30 from the second switched state to the first switched state or to shift the control piston 32 from the second piston position to the first piston position.

(34) The control force acting on the control piston 32, and the tensing force of the tensing device 33 of the fluidic valve 30, do not solely determine the switching position of the fluidic valve 30 when the electromagnetic valve 40 is properly and actively functioning. The control force acting on the control piston 32, and the tensing device 33, imbue the fluidic valve 30 with a fail-safe feature if the electromagnetic valve 40 fails. The control force acting on the control piston 32, and the tensing device 33, are used as a back-up for applying pressure to the adjusting member 20 in case the electromagnetic valve 40 or the assigned control device fails due to a defect, for example because a cable breaks or an electrical plug connection becomes detached, or when the electromagnetic valve 40 is deactivated in particular operational states. The fluidic valve 30, in particular the tensing device 33, is configured such that if the electromagnetic valve 40 fails or is deactivated, the delivery volume of the pump 1 is adjusted from a maximum towards a minimum only once a pump output pressure has been reached which is greater than a maximum pump output pressure which is set when the electromagnetic valve 40 is properly and actively functioning, and smaller than a pump output pressure which would result in damage to at least one component. The fluidic valve 30 and the first setting chamber K.sub.1 are used to protectively regulate the pump 1 down, when the electromagnetic valve 40 fails because it is defect or deactivated.

(35) The control piston 32 comprises a first annular portion 51 and a second annular portion 52 which are axially spaced from each other. The first annular portion 51 fluidically separates the control chamber 36 and the tensing chamber 34 from each other. In the second piston position, the first annular portion 51 separates the pressure port P and the working port A from each other and connects the relief port S to the working port A. In the first piston position, the first annular portion 51 separates the working port A and the relief port S from each other and connects the pressure port P to the working port A. The first annular portion 51 comprises a single sealing surface which is embodied to be continuous and therefore uninterrupted in the circumferential direction and axially. The sealing surface of the first annular portion 51 abuts the housing structure 2, forming a seal. It exhibits a constant diameter. The first annular portion 51 is formed as a solid body and is therefore not embodied to be hollow.

(36) The second annular portion 52 is arranged in the control chamber 36. The second annular portion 52 is arranged axially between the pressure port P and/or inlet C and the first annular portion 51. The second annular portion 52 comprises axial passage openings 53 which fluidically connect the pressure port P and the inlet C to the first annular portion 51. The passage holes 53 therefore connect a control surface of the first annular portion 51 to the pressure port P and the inlet C. The passage holes 53 are embodied as bores. The first annular portion 51 exhibits a diameter which is smaller than the diameter of the second annular portion 52, thus making it possible to ensure that the control piston 32 is correctly fitted. It is in principle conceivable for the first annular portion 51 to exhibit a diameter which is greater than the diameter of the second annular portion 52. The inner diameter of the housing of the fluidic valve 30 is correspondingly embodied to be stepped. The housing of the fluidic valve 30 comprises two regions which differ from each other in their inner diameter. The diameter of the annular portions 51, 52 respectively abuts the inner diameter of the housing. In order to form the housing of the fluidic valve 30, the housing structure 2 comprises a stepped bore. The housing structure 2 forms the housing of the fluidic valve 30.

(37) For arranging the tensing device 33, the control piston 32 comprises a first axial protrusion 54 on which the tensing device 33, in particular the helical spring, is arranged or fitted. The first axial protrusion 54 forms a spring seating. The tensing device 33, in particular the helical spring, surrounds the first axial protrusion 54. The first axial protrusion 54 extends from the first annular portion 51 axially into the tensing chamber 34. The tensing device 33, in particular the helical spring, is supported at one end on the first annular portion 51.

(38) In order to form an abutment for the second piston position, a second axial end of the control piston 32 comprises a second axial protrusion 55. The second axial protrusion 55 forms an abutment in the second piston position in which the pressure port P and the working port A are separated from each other. In the second piston position, the second axial protrusion 55 abuts a counter abutment. The counter abutment is formed by the sealing part 37. The second axial protrusion 55 extends from the second annular portion 52 axially towards the sealing part 37. The axial protrusions 54, 55 exhibit a diameter which is respectively smaller than the diameters of the annular portions 51, 52.