Patent Publication Number: US-9841020-B2

Title: Hydraulic feed device and hydraulic system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Patent application 10 2012 210 899.8 filed Jun. 26, 2012, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a hydraulic feed device, in particular an oil feed device, preferably for an internal combustion engine, with the features of the preamble of the claim  1 . The invention further relates to a hydraulic system provided with such a hydraulic feed device, preferably for an internal combustion engine, in particular of a motor vehicle. 
     BACKGROUND 
     From DE 10 2010 041 550 A1, a hydraulic feed device is known which has a pendulum-slide cell pump in which an internal rotor is drivingly connected to an external rotor via pendulum slides. Furthermore, the known hydraulic feed device is provided with a hydraulic positioning device for changing eccentricity between internal rotor and external rotor, which has a positioning element for adjusting the eccentricity. Furthermore, the positioning element is preloaded by means of a spring device for setting a maximum eccentricity. 
     In the case of a pendulum-slide cell pump, the feed rate, besides the speed, is also determined through the eccentricity between the internal rotor and the external rotor. The greater the eccentricity, the higher the feed rate is. In contrast, if the internal rotor and the external rotor are arranged concentrically, the feed rate is reduced to the value “0”, regardless of the speed. 
     Such hydraulic feed devices can be used in motor vehicles so as to drive a hydraulic working means, preferably oil, in a hydraulic system of the vehicle. Of particular interest are combined hydraulic systems comprising at least two different hydraulic circuits that are assigned to different functions. For example, a primary circuit for actuating a hydraulically actuatable clutch can be coupled with a secondary circuit for supplying lubrication points with oil. The different hydraulic circuits have different requirements in terms of the necessary hydraulic pressure. While lubricating oil supply only needs a constant, comparatively low oil pressure, a clutch may require a varying oil pressure. For example, for shifting the clutch, the oil pressure can be temporarily raised to a high level. 
     For reducing costs it is desirable to use only a single common hydraulic feed device in such a combined hydraulic system so as to provide both hydraulic circuits with the required hydraulic pressure, wherein the different pressure requirements are to be considered. For this purpose it is principally possible to equip the hydraulic system with a comparatively complex arrangement of control and regulating valves in order to be able to implement the desired hydraulic pressures in both hydraulic circuits. However, the costs for this are comparatively high. 
     SUMMARY 
     The present invention is concerned with the problem of providing for a hydraulic system of the above-described kind an improved embodiment that is characterized by a comparatively simple structure. Moreover, high functional reliability and/or operational reliability are aimed at. 
     This problem is solved according to the invention by the subject matter of the independent claim. Advantageous embodiments are subject matter of the dependent claims. 
     The invention is based on the general idea to equip the hydraulic positioning device with a first pressure adjusting chamber and a second pressure adjusting chamber for displacing the positioning element against the preload direction of the spring device, wherein the first pressure adjusting chamber is hydraulically connected in an uncontrolled manner to the pressure side of the pendulum-slide cell pump while the second pressure adjusting chamber is hydraulically connected to the pressure side of the pendulum-slide cell pump and is controlled via a control valve. Through this construction, the first pressure adjusting chamber acts as a pressure limiter. If the pressure on the pressure side of the pendulum-slide exceeds a predetermined pressure, the pressure correlating therewith effects in the first pressure adjusting chamber an adjustment of the positioning element against the preload direction of the spring device, thus in the direction of reduced eccentricity. By reducing the eccentricity, the feed rate and thus in particular the pressure generation of the pendulum-slide cell pump is reduced accordingly, by which means the desired effect as a pressure limiter is implemented. Furthermore, the first pressure adjusting chamber functions independent of the second pressure adjusting chamber so that even in the event of a failure of the control valve, the pressure limiting function is still maintained. To this extent, using two separate pressure adjusting chambers, one of which is coupled permanently and uncontrolled to the pressure side of the pendulum-slide cell pump, enables a functionally reliable operation, even in the case that the control valve fails. To this extent, a fail-safe principle can be implemented. 
     The pressure in the second pressure adjusting chamber can be regulated by means of the control valve. Hereby, the second pressure adjusting chamber can be used for adjusting the pressure on the pressure side of the pendulum-slide cell pump. Since both pressure adjusting chambers drive the positioning element in the same direction, namely against the preload direction of the spring device, the adjustable driving forces generated in the second pressure adjusting chamber are added to the non-adjustable, permanently acting driving forces which act in the first pressure adjusting chamber. 
     In particular, according to a preferred embodiment, the first and the second pressure adjusting chambers can be designed in such a manner that in the case that in both pressure adjusting chambers there is a pressure below a predetermined maximum pressure, they are able to displace the positioning element against the spring force of the spring device for reducing the eccentricity. Thus, as long as the pressure on the pressure side of the pendulum-slide cell pump does not exceed the predetermined maximum pressure, the feed rate or pressure generation of the pendulum-slide cell pump can be varied, in particular reduced, by correspondingly activating the control valve. 
     According to another advantageous embodiment, the first pressure adjusting chamber can be designed in such a manner that even in the case that the second pressure adjusting chamber is unpressurized, the first pressure adjusting chamber displaces the positioning element against the spring force of the spring device for reducing the eccentricity as soon as the pressure prevailing on the pressure side of the pendulum-slide cell pump exceeds a predetermined maximum pressure. For example, the second pressure adjusting chamber can be connected via the control valve to an unpressurized hydraulic reservoir. Even in this case, the first pressure chamber ensures that a predetermined maximum pressure on the pressure side of the pendulum-slide cell pump is not exceeded so that the first pressure adjusting chamber can act as a pressure limiter completely independent of the second pressure adjusting chamber. 
     The spring device can be arranged within the positioning device in a counter-pressure chamber that is permanently hydraulically connected, thus uncontrolled, to a suction side of the pendulum-slide cell pump. In this manner, the maximum pressure to be monitored can be specified in a comparatively accurate absolute manner by appropriately designing the first pressure adjusting chamber and the spring device. 
     According to an advantageous embodiment of the invention, the control valve can be configured as a proportional valve. A proportional valve quasi enables any intermediate positions between an open position and a closed position. While in the open position the second pressure adjusting chamber is fluidically connected to the pressure side of the pendulum-slide cell pump, this connection is blocked in the closed position. The proportional valve now enables any desired intermediate positions in order to transmit the pressure of the pressure side of the pendulum-slide cell pump in a more or less throttled manner to the second pressure adjusting chamber. It is therefore possible in the second pressure adjusting chamber to set virtually any pressures that are within a pressure interval that is limited toward the lower limit by the pressure on the suction side of the pendulum-slide cell pump, and is limited toward the upper limit by the pressure on the pressure side of the pendulum-slide cell pump. 
     According to another advantageous embodiment, the control valve can be configured as a 3-port/2-way directional control valve, the first port of which is hydraulically connected to the pressure side of the pendulum-slide cell pump, the second port of which is hydraulically connected to the second pressure adjusting chamber, and the third port of which is hydraulically connected to a relatively unpressurized, in particular atmospheric hydraulic reservoir. Thus, in a first end position (open position), the control valve can couple the first port to the second port so that the pressure side of the pendulum-slide cell pump is connected to the second pressure adjusting chamber. However, in a second end position (closed position), the second port is connected to the third port so that the second pressure adjusting chamber is connected to the hydraulic reservoir. Through the configuration of the 3-port/2-way directional control valve as a proportional valve, virtually any intermediate positions can be implemented between the two end positions so that the pressure in the second pressure adjusting chamber can be adjusted as desired between the pressure on the pressure side and the pressure in the hydraulic reservoir. In the unpressurized or atmospheric hydraulic reservoir, there is ambient pressure, thus atmospheric pressure, for example. 
     According to an advantageous embodiment, the control valve can comprise an electric actuator that can be activated by means of electrical control signals. By means of such an actuator, the control valve can be activated relatively precisely according to the respective pressure requirements. In particular when using a proportional valve, the desired pressures in the second pressure adjusting chamber can be adjusted comparatively accurately in this manner. 
     According to another advantageous embodiment, the positioning element can be formed by a stator in which the rotor is rotatably arranged and which is pivotably adjustable about a pivot axis extending parallel and eccentric to the rotational axis of the internal rotor in a housing of the positioning device, wherein the rotational axis of the internal rotor is arranged stationarily or locally fixed with regard to the housing. For example, a shaft extending coaxial to the rotational axis of the internal rotor can be fastened to the housing so that the internal rotor is rotatably mounted on this shaft. Alternatively, this shaft can also be rotatably mounted on the housing, wherein in this case, the internal rotor is arranged rotationally fixed on this shaft. The configuration of the positioning element as a stator in which the external rotor is mounted to be pivotable relative to the internal rotor and eccentric to the rotational axis of the internal rotor results in an extremely compact construction for the positioning device. 
     Due to this construction, the positioning device is structurally integrated in the pendulum-slide cell pump since the stator of the pendulum-slide cell pump, on the one hand, mounts the external rotor of the pendulum-slide cell pump and, on the other, forms the positioning element of the positioning device. 
     According to an advantageous refinement, the first pressure adjusting chamber can be arranged proximal to the pivot axis in the housing. Hereby, the pressure forces that can be generated in the first pressure adjusting chamber have a comparatively short lever arm for driving the positioning element/stator. Thus, comparatively high maximum pressures can be implemented which can be reduced by means of the first pressure adjusting chamber. 
     Additionally or alternatively, the second pressure adjusting chamber can be arranged distal to the pivot axis in the housing. Through this measure, the pressure forces that can be generated in the second pressure adjusting chamber have a comparatively long lever arm for driving the positioning element. Thus, even lower pressure forces can also be utilized for generating significant actuating forces for adjusting the positioning element/stator. 
     Additionally or alternatively, the spring device can be arranged distal to the pivot axis in the housing. Through this measure, the spring device too has a comparatively long lever arm. However, through this, a comparatively great spring travel for the spring device is implemented at the same time so that, for example, sufficient installation space can be implemented for a linear spring characteristic. 
     According to another advantageous refinement, the first pressure adjusting chamber can be directly bounded by a first inner wall portion of the housing and a first outer wall portion of the stator. Additionally or alternatively, it can be provided that the second pressure adjusting chamber is directly bounded by a second inner wall portion of the housing and a second outer wall portion of the stator. This measure results in a structure for the hydraulic feed device which can be implemented in a particularly simple manner and in which the positioning device is integrated in the housing of the pendulum-slide cell pump. 
     In another advantageous embodiment, the spring device can comprise at least one compression spring, for example a helical compression spring, via which the stator is supported by the housing. This too facilitates a compact embodiment that can be implemented in a simple manner. 
     A hydraulic system according to the invention that is preferably used in a motor vehicle comprises a primary hydraulic circuit, a secondary hydraulic circuit and a hydraulic feed device of the above-described kind for hydraulic medium supply to the two hydraulic circuits. If the hydraulic system has only one of these two circuits, accordingly, only a single hydraulic feed device is provided. The primary circuit, for example, has variable hydraulic pressure needs wherein, in particular temporarily, comparatively high pressures can also be required. In contrast to this, the secondary circuit can have comparatively constant hydraulic pressure needs on a comparatively low pressure level. For example, the primary circuit can serve for controlling a clutch while the secondary circuit can serve for cooling and/or lubricating the clutch and/or a transmission and/or an internal combustion engine and/or other components of the vehicle. Through suitably actuating the control valve, the pressure that is provided on the pressure side by the pendulum-side cell pump can be varied via the second pressure adjusting chamber, for example, to temporarily provide high pressure. By means of the second pressure adjusting chamber it can be ensured that the predetermined maximum pressure is not exceeded in the primary circuit or in the secondary circuit. 
     According to an advantageous embodiment, a control device can be provided for generating control signals which correlate with a hydraulic pressure demand of the primary circuit, wherein the control device is coupled to the control valve in such a manner that the control device actuates the control valve by means of the control signals. In this manner, the feed rate or the feed pressure of the pendulum-slide cell pump can be adapted to the actual demand of the primary circuit. 
     In an advantageous refinement, the control device can be coupled with a pressure sensor system that measures the hydraulic pressure provided by the hydraulic feed device. In this manner, a closed loop control can be created so as to be able to adjust or control the desired hydraulic pressure demand as accurately as possible. 
     In another advantageous embodiment, the secondary circuit can be connected to the hydraulic feed device via a volume flow control valve. The volume flow control valve enables adjusting a predetermined volume flow in the secondary circuit, independent of the pressure on the pressure side of the pendulum-slide cell pump. 
     For a use according to the invention of a hydraulic system of the above-described kind, the hydraulic system can serve for supply of a vehicle transmission, wherein the primary circuit of the hydraulic system supplies a hydraulic actuating device for actuating a clutch of the transmission with oil on a relatively high pressure level, while the secondary circuit of the hydraulic system supplies the lubrication points of the transmission with oil on a relatively low pressure level. The adjectives “high” and “low” are to be understood in relation to one another so that the high pressure level lies above the low pressure level. 
     A vehicle transmission according to the invention is provided with a hydraulic system of the above-described kind. 
     Further important features and advantages of the invention arise from the sub-claims, from the drawings, and from the associated description of the figures based on the drawings. 
     It is to be understood that the above-mentioned features and the features still to be explained hereinafter are usable not only in the respective mentioned combination but also in other combinations or alone without departing from the context of the present invention. 
     Preferred exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein identical reference numbers refer to identical, or similar, or functionally identical components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the figures, schematically, 
         FIG. 1  shows a sectional view of a hydraulic feed device, 
         FIGS. 2 and 3  show circuit-diagram-like schematic diagrams of a hydraulic system in different operating states. 
     
    
    
     DETAILED DESCRIPTION 
     According to  FIG. 1 , a hydraulic feed device  1 , which preferably can be an oil feed device, comprises a pendulum-slide cell pump  2  and a hydraulic positioning device  3 . The pendulum-slide cell pump  2  comprises an internal rotor  4 , an external rotor  5  and a stator  6 . The external rotor  5  is rotatably mounted in the stator  6 . Furthermore, the external rotor  5  is drivingly connected to the internal rotor  4  via a plurality of pendulum slides  7 . Furthermore, the internal rotor  4  is arranged concentric to a shaft  8  that extends coaxial to a rotational axis  9 . The rotational axis  9  and/or the shaft  8  are arranged fixed or stationary with regard to a housing  10  of the device  1 . Here, the shaft  8  can be fastened to the housing  10 , wherein in this case, the internal rotor  4  is mounted rotatably on the shaft  8 . As an alternative, the internal rotor  4  can also be connected to the shaft  8  in a rotationally fixed manner; in this case, the shaft  8  is mounted rotatably in the housing  10 . In both cases, the rotational axis  9  is stationary or fixed with regard to the housing  10 . However, it is preferred that the shaft  8  is rotatably mounted in the housing  10 , by which means it is in particular possible to use the shaft  8  as drive shaft for driving the internal rotor  4 . However, another embodiment is principally also conceivable. For example, the external rotor  5  and the stator  6  can interact like an electric motor, for which purpose suitable electromagnetic coils, which are not shown here, can be arranged on the stator  6 , while permanent magnets (likewise not shown) can be arranged on the external rotor  5 . 
     The external rotor  5  has a longitudinal centre axis  11  which, in the state of the  FIG. 1 , is arranged eccentric to the rotational axis  9 , which is arranged concentric to the internal rotor  4  and, accordingly, has an eccentricity  12 . In such a pendulum-slide cell pump  2 , the amount of this eccentricity  12  determines the feed rate or the achievable pressure on a pressure side  13  of the pendulum-slide cell pump  2 . The greater the eccentricity  12 , the higher the achievable pressure. 
     With the aid of the hydraulic positioning device  3 , it is now possible to adjust, thus change, the eccentricity  12  between the internal rotor  4  and the external rotor  5  so as to be able to vary or adjust on the pressure side  13  the pressure that can be generated with the aid of the pendulum-slide cell pump  2 . For this purpose, the positioning device  3  comprises a positioning element  14  with the aid of which the relative position between external rotor  5  and internal rotor  4  can be changed. In detail, the position of the external rotor  5  relative to the housing  10  can be changed with the aid of the positioning element  14 . Since with regard to the housing  10 , the internal rotor  4  is arranged stationarily via the shaft  8 , changing the relative position between the external rotor  5  and the housing  10  results in a change of the relative position between the external rotor  5  and the internal rotor  4 , by which means the eccentricity  12  changes. 
     In the preferred embodiment illustrated in  FIG. 1 , the positioning element  14  is substantially formed by the stator  6  of the pendulum-slide cell pump  2 . By changing the relative position of the stator  6  in the housing  10 , the external rotor  5  mounted therein is inevitably also displaced relative to the housing  10 . The stator  6  and/or the positioning element  14  are mounted on the housing  10  so as to be pivotably adjustable about a pivot axis  15 . The pivot axis  15  extends parallel and eccentric to the rotational axis  9  of the internal rotor  4 . 
     The positioning device  3  also comprises a first pressure adjusting chamber  16  and a second pressure adjusting chamber  17 . Both pressure adjusting chambers  16 ,  17  serve for displacing the positioning element  14 . In  FIG. 1 , a first chamber region  18 , in which the first pressure adjusting chamber  16  is formed, is indicated by an ellipse. Furthermore, a second chamber region  19 , in which the second pressure adjusting chamber  17  is formed, is indicated in  FIG. 1  by a further ellipse. The positioning device  3  further comprises a spring device  20  which is supported one the one side on the housing  10  and on the other side on the stator  6  thereby preloading the stator  6  into a position in which a maximum eccentricity  12  is given. 
     In the example shown in  FIG. 1 , the spring device  20  generates a compressive force. Furthermore, the spring device  20  is exemplary implemented here with a helical compression spring  21 . 
     The first pressure adjusting chamber  16  is hydraulically connected to the pressure side  13  of the pendulum-slide cell pump  2  in a permanent and uncontrolled manner. Furthermore, the first pressure adjusting chamber  16  is arranged such that the pressure forces prevailing therein drive the positioning element  14  against a spring force  22  which is indicated in  FIG. 1  by an arrow. The second pressure adjusting chamber  17  is also hydraulically connected to the pressure side  13  of the pendulum-slide cell pump  2 ; however, this hydraulic connection is controlled by means of a control valve  23  that is illustrated in the  FIGS. 2 and 3 . Here too, the arrangement of the second pressure adjusting chamber  17  takes place such that the pressure prevailing therein counteracts the spring force  22  of the spring device  20 . 
     Designing the two pressure adjusting chambers  16 ,  17  is advantageously carried out such that in the case that a pressure prevailing in both pressure adjusting chambers  16 ,  17  lies below a predetermined maximum pressure, the two pressure adjusting chambers  16 ,  17  displace the positioning element  14  against the spring force  22  for reducing the eccentricity  12 . Furthermore, the first pressure adjusting chamber  16  is advantageously designed such that in the case that the second pressure adjusting chamber  17  is quasi unpressurized, it displaces the positioning element  14  against the spring force  22  of the spring device  20  for reducing the eccentricity as soon as the pressure prevailing on the pressure side  13  exceeds the predetermined maximum pressure. In other words, as soon as the pressure on the pressure side  13  exceeds the predetermined maximum pressure, the pressure forces thereby generated in the first pressure adjusting chamber  16  are sufficient for displacing the positioning element  14  against the spring device  20  for reducing the eccentricity  12 . In contrast, if the pressure on the pressure side  13  is below the maximum pressure, the pressure forces generated in the first pressure adjusting chamber  16  are not sufficient to displace the positioning element  14  against the spring device  20 . However, in the case of pressures on the pressure side  13  below the maximum pressure, displacing the positioning element  14  against the spring device  20  is still possible if in addition a corresponding pressure is built up in the second pressure adjusting chamber  17  via the control valve  23 . Thus, with the aid of the first pressure adjusting chamber  16 , the function of a pressure limiter can be implemented while with the aide of the second pressure adjusting chamber  17 , the function of a pressure adjusting device can be implemented. 
     In the example of the  FIG. 1 , the spring device  20  is arranged in a counter pressure chamber  24  which is permanently, thus uncontrolled, hydraulically coupled to a suction side  25  of the pendulum-slide cell pump  2 . 
     In the embodiment shown in  FIG. 1 , the first pressure adjusting chamber  16  is arranged proximal to the pivot axis  15  in the housing  10 . In contrast, the second pressure adjusting chamber  17  and the spring device  20  and/or the counter pressure chamber  24  are arranged distal to the pivot axis  15  in the housing  10 . Furthermore, in the embodiment shown here it is provided that the first pressure adjusting chamber  16  is directly bounded by a first inner wall portion  26  of the housing  10  and a first outer wall portion  27  of the stator  6 . Furthermore, the second pressure adjusting chamber  17  is directly bounded by a second inner wall portion  28  of the housing  10  and a second outer wall portion  29  of the stator  6 . The compression spring  21  used for implementing the spring device  20  supports the stator  6  via the housing  10 . 
     According to the  FIGS. 2 and 3 , a hydraulic system  30 , as it can be implemented, for example, in a motor vehicle, comprises a primary hydraulic circuit  31  and secondary hydraulic circuit  32  which are jointly connected to a hydraulic feed device  1  of the above-described kind. The primary circuit  31  can be used, for example, for shifting a clutch. The primary circuit  31  is characterized by a variable hydraulic pressure demand, wherein in particular for shifting the clutch, a comparatively high hydraulic pressure is temporarily needed. In contrast to this, the secondary circuit  32  is characterized by a substantially constant hydraulic pressure demand which ranges on a comparatively low pressure level. For example, the secondary circuit can be a cooling and/or lubricating oil circuit. The hydraulic system  30  is also equipped with a control device  33  which is suitably connected to the control units  45  and  46 , respectively, of the two circuits  31 ,  32  of the hydraulic system  30 , and to the control valve  23 . Furthermore, the control device  33  is coupled to a pressure sensor system  34 , by means of which the hydraulic pressure provided on the pressure side by the hydraulic feed device  1  can be measured. Moreover, the secondary circuit  32  is connected to the hydraulic feed device  1  via a volume flow control valve  35 . The example shown is a controllable volume flow control valve  35  that can be actuated or activated by means of the control device  33 . The sensor system  34  and also the volume flow control valve  35  are situated in a hydraulic periphery  47  of the hydraulic system  30 . 
     Depending on the hydraulic pressure demand of the primary circuit  31 , the control device  33  can generate control signals correlating with said demand so as to be able to suitably activate the control valve  23  and to implement the desired hydraulic pressure demand. Via the sensor system  34 , pressure control can be implemented. 
     The control valve  23  in the embodiments shown here is a proportional valve. Furthermore, the control valve  23  is a 3-port/2-way directional control valve. The control valve  23  thus has a first port  36  that is hydraulically connected to the pressure side  13  of the pendulum-slide cell pump  2 . Furthermore, a second port  37  of the control valve  23  is hydraulically connected to the second pressure adjusting chamber  17 . A third port  38  of the control valve  23  is hydraulically connected to a hydraulic reservoir  39  that is comparatively unpressurized or has ambient pressure. A suction line  40  runs from the hydraulic reservoir  39  to the suction side  25  of the pendulum-slide cell pump  2 . Furthermore, a return line  41  of the primary circuit  31  and the secondary circuit  32  runs back to the reservoir  39 . A hydraulic medium filter  42  can be arranged in the suction line  40 . 
     The control valve  23  has an electric actuator  43  by which means it can be activated via the control device  33  with the aid of electrical control signals. 
     In the state of the  FIG. 2 , the primary circuit  31  does not need high oil pressure. This state according to  FIG. 2  also corresponds to the fail-safe state that is adopted by the hydraulic feed device  1  in the event of a power outage. For example, for this purpose, the control valve  23  is preloaded by means of a return spring  44  into the end position shown in  FIG. 2 , which end position corresponds to a closed position. By means of the actuator  43 , the control valve  23  can be displaced against the return force of the return spring  44  into the other end position shown in  FIG. 3 , which other end position corresponds to an open position. 
     In the state of the  FIG. 2 , the second port  37  in the control valve  23  is connected to the third port  38  so that finally the second pressure adjusting chamber  17  is connected to the reservoir  39 . In this closed position, the first port  36  is advantageously blocked so as to avoid leakage through the control valve  23 . In this closed position, the second pressure adjusting chamber  17  thus is separated from the pressure side  13 . If the pressure on the pressure side  13  remains below the maximum pressure, the spring force  22  is predominant so that the maximum eccentricity  12  is set. If, in contrast, the pressure on the pressure side  13  in this state becomes higher than the maximum pressure, the pressure forces prevailing in the pressure adjusting chamber  16  become greater than the spring force  22 , by which means the positioning element  14  is displaced, resulting in a decrease of the eccentricity  12 . Consequently, the feed rate of the pendulum-slide cell pump  2  is reduced correspondingly as a result of which the pressure that can be generated therewith decreases correspondingly. 
     In the state of  FIG. 3 , the control valve  23  is in its open position in which the first port  36  is connected to the second port  37  while the third port  38  can be blocked. As a result, the pressure side  13  of the pendulum-slide cell pump  2  is connected to the second pressure adjusting chamber  17 . Thus, pressure forces are also generated in the second pressure adjusting chamber  17 , which pressure forces act against the spring device  20  and add to the pressure forces prevailing in the first pressure adjusting chamber  16 . Overall, the spring force  22  of the spring device  20  can be overcome in this manner so that also in this case, displacing the positioning element  14  for reducing the eccentricity  12  and thus for reducing the pressure build-up on the pressure side  13  can be actively effected by means of the control device  33 . A reduced feed rate or a reduced oil pressure is required in particular in such cases in which the primary circuit  31  does not need increased oil pressure for shifting the clutch. However, if the primary circuit  31  needs increased oil pressure temporarily or for a short time, the actuator  43  can be actuated via the control device  33  in such a manner that, for example, the end position shown in  FIG. 2  is set for a short time and as a result, the maximum eccentricity  12  is set, as long as the pressure on the pressure side  13  does not exceed the maximum pressure. 
     Also, if the pressure on the pressure side  13  in the state shown in  FIG. 3  exceeds the maximum pressure, a positioning movement driven by the first pressure adjusting chamber  16  takes place for the positioning element  14  resulting in a reduction of the eccentricity  12  so that the pressure limitation can also be ensured in this state. 
     It is clear that by means of the proportional valve  23  principally any intermediate positions between the two end positions shown in the  FIGS. 2 and 3  can be set so that basically any pressure between the pressure of the pressure side  13  and the pressure of the pressure side  25  or the reservoir  39  can be set.