Adjustable, single-stroke vane pump, method for operating a vane pump, system for generating a pressure medium flow and steering system

Abstract

The invention relates to an adjustable, single-stroke vane pump (1) for generating a pressure medium flow for a consumer (2), comprising a pump housing (3) in which an adjustable cam ring (4) is inserted and comprising a rotor (5) and a drive shaft (6) which are rotatable within the cam ring (4). The rotor (5) carries vanes (7) which form working chambers (8) between the rotor (5) and the cam ring (4). A suction connection (9) and a pressure connection (10) for a pressure medium are formed between the rotor (5) and the cam ring (4). Furthermore, an adjusting device (17) is provided for changing the eccentricity of the cam ring (4) relative to the rotor (5). The adjusting device (17) is designed such that an adjustment of the eccentricity of the cam ring (4) is possible at least between a positive and a zero eccentricity.With a positive eccentricity, the cam ring (4) is shifted from a zero eccentricity in a positive direction such that, upon rotation of the rotor (5) in a first direction of rotation (18), the pressure medium flows into the working chambers (8) through the suction port (9) and flows out through the pressure port (10). With a zero eccentricity, no pressure medium is delivered to the consumer (2) upon rotation of the rotor (5). The drive shaft (6) is designed and configured for drive by an output shaft (105) of a vehicle transmission (4).

Description

The invention relates to an adjustable, single-stroke vane pump for generating a pressure medium flow for a consumer according to the preamble of claim 1.The invention further relates to a method for operating an adjustable, single-stroke vane pump for generating a pressure medium flow for a consumer.The invention further relates to a computer program product.The invention also relates to a system for generating a pressurized medium flow for a consumer.The invention also relates to a steering system of a vehicle.Pumps are known from the prior art which have one or more rotors for conveying a fluid; these can be, inter alia, rotary displacement pumps (rotary piston pumps, rotary piston pumps, gear pumps, rotary slide pumps, vane pumps), radial piston pumps or centrifugal pumps.From the prior art, in particular unidirectionally operated pumps are known, i.e. pumps which convey a pressure medium in only one direction of rotation and thus generate a flow of pressure medium in a conveying direction / flow direction for a consumer. However, bidirectionally operable pumps are also known which permit a reversal of the direction of rotation so that a pressure medium can be conveyed in two directions. The known pumps which can be operated bidirectionally and are used in practice generally use the pump principle "gear pump" or "axial piston pump".Conventional vane cell pumps generally convey hydraulic fluid in only one rotational direction of the rotor of the vane cell pump.Vane cell pumps can be designed both as constant pumps, i.e. with a constant geometric delivery volume, or with an adjustable delivery volume, i.e. with a variable geometric delivery volume, so that the delivered volume of the pressure medium can be adjusted between a maximum delivery quantity and a minimum delivery quantity. Both vane cell pumps with a constant geometric delivery volume and vane cell pumps with a variable geometric delivery volume can have a cam ring which in the first case is not adjustable and in the second case is adjustable, as shown below. Adjustable cam rings are sufficiently known from the prior art.The term "geometric delivery volume" is generally used to denote the volume of the vane pump delivered per revolution. In adjustable vane cell pumps, the geometric delivery volume depends on the eccentricity between the rotor and the cam ring and thus on the size of the working chambers or cells.Vane cell pumps with an adjustable delivery volume, which are frequently also referred to as variable displacement pumps, are usually constructed as follows. In a pump housing, a cam ring or a stroke contour ring and a rotatably mounted rotor are substantially arranged. The rotor has radial slots in which vanes are arranged so as to be radially displaceable and positively guided by the slots. During operation of the vane pump, the vanes thus slide with their outer ends in contact with the inner wall of the cam ring and thereby bring about the delivery of a pressure medium or a hydraulic fluid (e.g. a pressure oil). In contrast to pumps with a constant delivery volume (constant pumps), pumps with a variable delivery volume can avoid an overproduction of hydraulic fluid resulting, in particular at high rotational speeds, which hydraulic fluid has to be partially compensated, for example, by a bypass circulation in the case of constant pumps. Therefore, in the case of constant pumps in the higher speed range, mechanically unusable energy is consumed by the bypass circulation, which corresponds to an unnecessary loss of heat or energy. For regulating the delivery volume, in particular for reducing the delivery volume as the rotational speed of the rotor increases, the eccentricity of the cam ring with respect to the rotor is changed, in particular reduced. For this purpose, a conventional vane cell pump has a regulating device (e.g. a flow control valve) with two outputs, which can act on a left or a right pressure chamber via control channels with a portion of the hydraulic fluid conveyed in each case. The pressure chambers act from the left and right respectively on the outer surface of the cam ring and thus bring about the desired change in the eccentricity of the cam ring with respect to the rotor.A vane cell pump of the type mentioned at the beginning is known, for example, from DE 10 2004 060 082 A1.A vane pump of this type is also known from DE 10 2014 105 613 A1, for which purpose reference is made in particular to FIGS. 1 to 3 of this document for illustrating a structure of a conventional vane pump.Regarding the further prior art, reference is also made to DE 10 2014 115 159 A1.The control of the geometric displacement volume of the vane pump takes place, as illustrated above, by a hydraulic adjustment of the stroke or the eccentricity between the cam ring and the rotor. In addition, a restoring spring is frequently also used in order to load the cam ring with a compressive force which presses the cam ring in a direction or in a position which corresponds to the maximum delivery volume. This is intended to ensure that the cam ring, in the absence of hydraulic loading, is located in a position in which the geometric delivery volume is at a maximum. Conventional vane cell pumps can usually not be brought to a so-called zero eccentricity, in which the central axes of the cam ring and of the rotor run coaxially, since in this position, the adjustment control is no longer given due to the lack of pressure medium flow or the lack of pressure of the pressure medium flow and the zero eccentricity can therefore no longer be cancelled in a pressure-dependent manner with the aid of a flow control valve.DE 10 2015 107 543 A1 discloses a vane cell pump for delivering a fluid for a consumer of a steering system, which pump is intended to be reversible in its direction of rotation and in which it is not intended to provide a control valve for regulating a volume flow of the vane cell pump. However, a vane cell pump with a constant geometric delivery volume is essentially described here. A vane pump with a variable geometric delivery volume is additionally mentioned, but is not shown or described in more detail.DE 10 2014 221 447 A1 discloses a vane cell pump for an automatic transmission for motor vehicles. The cam ring is pivotable about a pivot bearing relative to the pump housing and the rotor, so that a variable delivery volume results. With maximum eccentricity of the cam ring with respect to the rotor axis, a maximum delivery volume results, while with a non-eccentric relative position of cam ring and rotor, the delivery volume is equal to zero. Intermediate positions and thus different delivery volumes should be possible between these two extreme positions, i.e. minimum and maximum eccentricity.DE 103 37 653 A1 discloses a vane cell pump for a steering system for motor vehicles. It is disclosed that the volume flow can be adjusted continuously, wherein in the neutral middle position (zero eccentricity) with zero delivery only the friction of the pump has to be overcome. This is intended to result in a low-loss standby mode. The use of the vane cell pump in conjunction with a drive by an electric motor or the motor of the vehicle is disclosed.The object of the present invention is to further develop an adjustable, single-stroke vane pump for generating a pressure medium flow for a consumer, in particular to expand its possible uses.This object is achieved by an adjustable, single-stroke vane pump according to claim 1.The present invention is further based on the object of creating a method for operating an adjustable, single-stroke vane pump for generating a pressure medium flow for a consumer, by means of which the possible uses of the vane pump are extended.This object is achieved by a method according to claim 17.The present invention further relates to the object of providing an advantageous computer program product for a vane cell pump or for operating a vane cell pump.This object is achieved by claim 25.The present invention is also based on the object of making available an advantageous system for generating a pressurized medium flow for a consumer.This object is achieved by a system according to claim 26.The present invention is further based on the object of providing a steering system for a vehicle which is supplied with pressure medium in a particularly advantageous manner, in particular simply, safely and in an energy-saving manner.This object is achieved by a steering system according to claim 29.The adjustable single-stroke vane pump according to the invention serves for generating or conveying a pressure medium flow for a consumer. The vane cell pump has a pump housing in which an adjustable cam ring is inserted. The vane pump further includes a rotor and a drive shaft rotatable within the cam ring. The rotor carries vanes which form working chambers between the rotor and the cam ring. Between the rotor and the cam ring, a suction connection and a pressure connection for a pressure medium are formed. Furthermore, an adjusting device is provided for changing the eccentricity of the cam ring relative to the rotor. According to the invention, it is provided that the adjusting device is designed in such a way that an adjustment of the eccentricity of the cam ring is possible at least between a positive eccentricity and a zero eccentricity, wherein in the case of the positive eccentricity the cam ring is displaced from the zero eccentricity in a positive direction in such a way that in the case of a rotation of the rotor in a first direction of rotation the pressure medium flows into the working chambers through the suction connection and flows out through the pressure connection. According to the invention, it is provided that, in the case of the zero eccentricity, no delivery of pressure medium to the consumer takes place during a rotation of the rotor. Furthermore, it is provided according to the invention that the drive shaft is designed and configured for driving by an output shaft of a vehicle transmission.The vane cell pump according to the invention can be used in applications which cannot be realized with a conventional adjustable vane cell pump. As a result, the vane cell pump according to the invention can be used particularly advantageously as a power steering pump or as an emergency power steering pump.By actively adjusting the cam ring position relative to the rotor to a zero eccentricity, during the operation of the vane pump or in advance the delivery characteristic can be set such that the vane pump can be operated in a state in which no delivery takes place.If no active adjustment takes place, the vane pump preferably delivers a constant volume flow which is dependent on the rotational speed in such a way as is known from the prior art, in particular in vane pumps in which a flow control valve is used.The vane cell pump according to the invention can have a cam ring which can be actively adjusted independently of the rotational speed and / or the rotational direction of the rotor and / or a stop for the cam ring which can be actively adjusted independently of the rotational speed and / or the rotational direction of the rotor for variable adjustment of the stroke of the vane cell pump up to zero delivery (zero eccentricity). This can take place during the operation of the vane pump or at a standstill.In this way, in particular the following operating mode can be realized. By actively adjusting the cam ring to zero eccentricity with respect to the rotor, the delivery of the vane pump can be avoided and the energy consumption reduced, independently of the direction of rotation and the rotational speed, since no pressure medium is delivered as a result. As a result, additional components, such as clutches, for shutting down the unit can be avoided.The possibility provided according to the invention of setting a zero eccentricity of the cam ring relative to the rotor makes it possible in a particularly advantageous manner to have the vane cell pump driven by the output shaft of the vehicle transmission.The output shaft of the vehicle transmission may be stationary or may rotate in an opposite direction when the vehicle is not moving forward but backward. This, if the output shaft of the vehicle transmission is used to drive the input shaft of the rotor or the rotor, respectively, would result in the rotor rotating in a second rotational direction opposite the first rotational direction. The volume flow would thus be transported in the opposite direction, i.e. flow out from the working chambers through the suction connection. By setting a zero eccentricity when the rotor rotates in the second rotational direction, this can be avoided.Alternatively, a freewheel could also be used, so that the rotor does not rotate in the second rotational direction.The invention makes it possible to set a zero eccentricity of the cam ring relative to the rotor as required when the rotor rotates in the first rotational direction and a pressure medium flow generated by the vane pump is not required (standby operation).The zero eccentricity of the cam ring relative to the rotor can be adjusted in particular when a flow of pressure medium from the vane pump according to the invention to the consumer is not required, e.g. because no steering movement is to take place or takes place or because the consumer is supplied with pressure medium by another pump, in particular a pump driven by a vehicle engine, in particular by an internal combustion engine, e.g. a main steering pump.The adjusting device according to the invention can correspondingly adjust the positive eccentricity of the cam ring depending on the demand of the consumer, in particular in order to support another pump, e.g. a main steering pump, or in order to take over the supply of the consumer alone, wherein in this case the eccentricity of the cam ring can preferably be adjusted such that, on the one hand, an adequate pressure medium flow is available for the respective driving situation, but, on the other hand, an unnecessarily large pressure medium flow to the consumer is avoided.According to the invention, it is provided that the drive shaft or the rotor of the vane cell pump is driven by the output shaft or an output shaft of the vehicle transmission, i.e. that the drive shaft is correspondingly designed and configured to be connected to the output shaft of the vehicle transmission or driven by it.The vane cell pump according to the invention is suitable in particular in combination with a main steering pump.The main steering pump can preferably be driven by a vehicle engine of a vehicle. In this case, it can be provided that the main steering pump provides the pressurized medium flow for a vehicle steering system of the vehicle when the vehicle engine, in particular an internal combustion engine, is switched on or running. The main steering pump can be driven in a conventional manner by the vehicle engine, in particular an output shaft of the vehicle engine or a V-belt driven by the vehicle engine. In addition, the use of the vane cell pump according to the invention can be provided, in particular as a power steering pump or as an emergency power steering pump which is driven by the output shaft of the vehicle transmission. This allows the vehicle engine to be turned off when the vehicle does not need to be accelerated or driven. The flow of pressurized medium for supplying the vehicle steering is provided in this case or when the vehicle engine is switched off or is not running, then by the vane pump according to the invention, preferably in an embodiment as a power steering pump or as an emergency power steering pump. The output shaft of the vehicle transmission drives the drive shaft or the rotor of the vane pump according to the invention, which in turn provides the flow of pressurized medium for the vehicle steering system. That is, when the vehicle engine is off and the vehicle transmission is rotating, pressurized fluid flow may be provided to the vehicle steering. This allows energy to be saved without the vehicle steering being impaired. Such a method or a deactivation of the vehicle engine is particularly appropriate at a higher speed of the vehicle, in particular when the vehicle rolls or "sails" without driving, i.e. when the drive motor is deactivated during the journey, and in particular when the vehicle is travelling straight ahead, in which only small steering movements are necessary in any case.According to the invention, a control device can be provided and configured which controls the adjusting device in such a way that the zero eccentricity of the cam ring relative to the rotor can be adjusted independently of the direction of rotation and a rotational speed of the rotor.Such a setting may be advantageous in particular when the rotor is at a standstill and / or when the rotor rotates in the first rotational direction, but a pressure medium flow generated by the vane pump is not required, and / or when the rotor rotates in a second rotational direction which is opposite to the first rotational direction.Because the vane cell pump according to the invention has a control device which controls the actuating device in such a way that the actuating device sets the zero eccentricity of the cam ring relative to the rotor when the rotor is stationary and / or when the rotor rotates in a second direction of rotation, the vane cell pump according to the invention can be used and operated more universally compared with the previously known vane cell pumps.The possibility of setting the zero eccentricity even when the rotor is rotated in the first rotational direction makes it possible to save energy if the flow of pressurized medium is not required or the consumer is otherwise supplied with pressurized medium.The vane cell pump can prevent "reverse" delivery in the event of a change in the rotational direction (from the first rotational direction to the second rotational direction), which is not desired for many applications.The solution according to the invention also prevents undesired pressure pulsations.According to the invention, it can be provided that the control device controls the adjusting device in such a way that, when a vehicle is at a standstill and / or when a vehicle is moving forward, if a pressure medium flow generated by the vane pump is not required, and / or when a vehicle is moving backward, in which the vane pump is installed, the adjusting device adjusts the zero eccentricity of the cam ring relative to the rotor.It has been found that if the vane cell pump according to the invention is installed in a vehicle and is driven by the output shaft of the vehicle transmission, it is particularly advantageous if the control device controls the adjusting device in such a way that, when the vehicle is stationary and / or when the vehicle is travelling backwards, the zero eccentricity of the cam ring relative to the rotor is set.Even when the vehicle is travelling forwards, the setting of the zero eccentricity can be advantageous if the pressure medium flow is not required, since energy can thereby be saved.The vane cell pump according to the invention can be used in applications which could not be realized with a conventional adjustable vane cell pump. Among other things, the vane cell pump according to the invention can also be adjusted in applications such as a hydraulic transmission as a power steering pump and / or as an emergency power steering pump. For the aforementioned applications, the vane cell pump according to the invention is particularly suitable. However, the use of the vane cell pump according to the invention is not limited to the examples mentioned above.The solution according to the invention makes it possible that during the operation of the vane pump or in advance the delivery characteristic is set in such a way that different operating modes can be realized which cannot be realized with the vane pumps known from the prior art. This is illustrated in more detail below, also with reference to the method according to the invention.Depending on the setting of the control or regulation, the delivery characteristic of the vane cell pump according to the invention can be set independently of the operating mode of the drive unit during installation or during the operation of a system, in particular a steering system, in which the vane cell pump is integrated.According to the invention, it can be provided that the vane pump, in particular the pump housing and / or the rotor and / or the drive shaft and / or the cam ring, are designed or arranged in such a way that the adjusting device can set a positive and a zero eccentricity and optionally even a negative eccentricity, as is illustrated in more detail below, relative to the rotor.In a manner known in principle, an outer ring can be inserted into the pump housing. In principle, the pump housing of the vane pump can assume the function of an outer ring (also referred to as an intermediate ring). The design of an outer ring has, however, proved to be expedient for series production. In this embodiment, the cam ring is located within the outer ring.In a manner which is in principle likewise known, it can be provided that the rotor has slots in which the vanes which form the working chambers are arranged displaceably. For this purpose, a rear-vane fluid pressure is used in a known manner, which substantially acts on the ends of the vanes guided in the slots of the rotor.With regard to possible advantageous configurations of the vane cell pump, reference is hereby made to DE 10 2005 043 253 B4.The pump housing can be closable with the aid of a cover, so that the cam ring is bounded on one end side by the cover and on the other end side by the pump housing. It can also be provided here that an end plate is arranged at the end face between the cam ring and the pump housing. Alternatively or additionally, it can also be provided that a cover-side control plate is arranged on the end face between the cam ring and the cover. The working chambers can thus be bounded in the axial direction of the rotor by the cover or the cover-side control plate or the pump housing or the end plate. The cover or the cover-side control plate and / or the end plate or the pump housing can have suction or pressure ribs in a known manner, which can serve to allow pressure medium to flow into or out of the suction connection or the pressure connection.Within the scope of the invention, when an outer ring is inserted into the pump housing, this is to be understood as an inner wall of the pump housing, insofar as features relate to this. Furthermore, if features relate to the pump housing or the cover, the control plate or the end plate can be understood as part of the cover or pump housing, insofar as features relate thereto.The pressure medium is preferably a hydraulic fluid, for example a pressure oil.With regard to further advantageous configurations, reference is also made to DE 10 2015 115 587 A1.According to the invention, it can be provided that the adjusting device is designed in such a way that an active adjustment of the eccentricity of the cam ring relative to the rotor is possible independently of and / or in addition to a volume flow-dependent regulation.It has proven to be particularly advantageous if the adjusting device is designed such that an active adjustment of the eccentricity of the cam ring relative to the rotor is possible independently of a volume flow-dependent regulation, i.e. independently of the pressure of the pressure medium. As a result, a suitable delivery characteristic can be set. In particular, if necessary, the cam ring can be set to a zero eccentricity relative to the rotor, so that no conveyance takes place. Depending on the driving situations, in particular depending on whether a vehicle is driving backward or stationary, a suitable position of the cam ring relative to the rotor can be set or this position can be influenced by the active actuator, which can be controlled independently of the volume flow.In addition to the active adjustment of the eccentricity, a volume flow-dependent regulation can also be provided, for example using a flow control valve.According to the invention, it can furthermore be provided that the adjusting device for adjusting the eccentricity of the cam ring relative to the rotor has at least one active actuator which acts indirectly or directly on the cam ring and which can be controlled independently of the pressure of the pressure medium.It has been found to be particularly suitable if the adjusting device has at least one active adjusting element which can be controlled independently of the pressure of the pressure medium. The eccentricity, in particular also a zero eccentricity, can thus be adjusted as required. In addition to a conventional adjustment or regulation of the cam ring, which is optionally, but preferably provided, as a function of the pressure of the pressure medium or of the pressure medium flow, the active actuator enables an independent regulation or control of the cam ring as a function of freely selectable parameters.According to the invention, it can be provided that the adjusting device for adjusting the eccentricity of the cam ring relative to the rotor has the at least one active actuator and additionally a flow control valve, which influences the eccentricity of the cam ring as a function of a volume of the pressure medium flow from the pressure connection to the consumer.This solution has proven to be advantageous in order to realize, in addition to an adjustment with the aid of the active actuator, an adjustment as a function of a volume flow of the pressure medium, i.e. an adjustment as a function of the pressure of the pressure medium.According to the invention, it can alternatively also be provided that the adjusting device for adjusting the eccentricity of the cam ring relative to the rotor has the at least one active actuator and no flow control valve, which influences the eccentricity of the cam ring as a function of a volume of the pressure medium flow from the pressure connection to the consumer.It has proven advantageous for certain applications if no flow control valve is provided in addition to the at least one active actuator, i.e. if the eccentricity of the cam ring is not influenced by a flow control valve. In this case, it can be provided that an adjustment of the cam ring by the active actuator is optionally carried out in such a way that a speed of the vehicle and / or other parameters are taken into account. It can also be provided that, controlled by the control device for adjusting the eccentricity by the active actuator, a volume flow of the pressure medium flow and / or directly or indirectly the rotational speed of the rotor and / or of the drive shaft is taken into account.It is advantageous if the at least one active actuator is fixedly connected to the cam ring in such a way that the active actuator can change the eccentricity of the cam ring relative to the rotor in a positive direction and a negative direction, in particular can set both a positive and a zero eccentricity of the cam ring.It has proven to be advantageous if the at least one active control element, in particular if exactly one active control element is provided, is connected to the cam ring in a fixed or non-detachable or rigid manner, preferably in such a way that the connection can only be canceled if joining means (connecting means) or components are destroyed or damaged. This allows the active actuator to both push and push the cam ring so that the actuator can move the cam ring to the desired position. The active control element can preferably be a regulating pin which is preferably fixedly or rigidly connected to the cam ring.According to the invention, it can furthermore be provided that the adjusting device has two adjusting members, wherein an adjusting member is connected to the cam ring in such a way that the cam ring is displaceable in a positive direction for changing the eccentricity and an adjusting member is connected to the cam ring in such a way that the cam ring is displaceable in a negative direction for changing the eccentricity.A design of the adjusting device with two adjusting elements can make it possible for the cam ring to be displaceable particularly uniformly and reliably relative to the rotor. It can be provided that one actuator displaces the cam ring in a positive direction and the other actuator displaces the cam ring in a negative direction. A fixed connection between the control element and the cam ring is not necessary in this case. Alternatively, it can also be provided that each of the control elements both pulls and pushes or presses, for which purpose a fixed or rigid or non-detachable connection is then preferably provided between the control element and the cam ring.It is advantageous if the adjusting device has two active adjusting members which are suitable for applying opposing forces to the cam ring, or the adjusting device has an active adjusting member and a passive, non-controllable adjusting member, preferably a spring, which are suitable for applying opposing forces to the cam ring.It has been found to be particularly suitable if the adjusting device has two active adjusting members which can apply opposite forces to the cam ring, so that the cam ring can be adjusted to the desired eccentricity with respect to the rotor. The control elements can be fixedly connected to the cam ring or not fixedly connected to the cam ring as required, for example by only touching the cam ring.For controlling the eccentricity of the cam ring, it can also be provided that the adjusting device has only one active actuator and additionally a passive actuator, the effect of which on the cam ring cannot be actively controlled. The passive actuator can be, for example, an elastic element or preferably a spring. The selective or as required adjustment of the eccentricity of the cam ring relative to the rotor is effected by the active actuator, which applies a force corresponding to the desired adjustment of the cam ring, which force presses against the force of the passive actuator, does not apply a force or applies a force that acts in the same direction as the passive actuator. The passive actuator has the advantage that it can preferably be dimensioned such that the passive actuator displaces the cam ring from zero eccentricity when the active actuator does not apply force. Preferably, the passive actuator forces the cam ring in a positive direction from zero eccentricity.According to the invention, it can furthermore be provided that the at least one actuating device is a mechanical and / or electrical and / or electromechanical and / or hydraulic and / or pneumatic actuating element that can be controlled independently of the pressure of the hydraulic fluid.A configuration of the actuator as a pneumatic and / or mechanical and / or electrical and / or electromechanical actuator has proven to be particularly suitable for most applications.The at least one active actuator is preferably designed as a mechanical and / or electromechanical and / or as a hydraulic and / or as a pneumatic actuator.The adjustment of the eccentricity is preferably effected by means of an active mechanical and / or electrical and / or electromechanical actuator in that the actuator acts directly on the cam ring.The adjustment can be made active on one side, preferably with an electromechanical actuator, or active on both sides, preferably with two electromechanical actuators, which apply forces acting in opposite directions to the cam ring.The adjustment of the eccentricity can also take place via a passive actuator, as described above, and an active actuator, which can preferably be controlled electromechanically or mechanically or electrically.According to the invention, it can furthermore be provided that the adjusting device is configured to adjust the position of a stop against which the cam ring strikes when the latter has reached one of its end positions, wherein the adjusting device additionally has a passive adjusting element, preferably a spring, which acts on the cam ring in such a way that the cam ring is loaded with a compressive force in the direction of the stop.The adjustment of the position of a stop against which the cam ring strikes when the latter has reached one of its end positions, for example a maximum positive eccentricity or a zero eccentricity, has proven to be suitable for limiting the maximum geometric conveying volume or defining an end position. In this case, a passive actuator, preferably an elastic element or a spring, can additionally preferably be provided, which loads the cam ring with a compressive force in the direction of the stop.It can furthermore be provided that the adjusting device has a stop which limits the maximum positive eccentricity and a stop which defines the zero eccentricity or, as shown below, limits a maximum negative eccentricity, wherein at least one of the stops, preferably both stops, can be adjustable.The stops can also be an outer ring, insofar as an outer ring is provided, the inner wall of which has a corresponding configuration, so that it acts as a stop. The stop can, however, also be a stop element which is independent of the outer ring or the pump inner wall and is preferably fixedly connected to the outer ring or the pump housing. The stop can also be designed as an active actuator or be connected to an active actuator in such a way that the stop can be adjusted. This can be a mechanical and / or electrical and / or electromechanical and / or hydraulic and / or pneumatic actuator or a corresponding stop.The stop can be part of the adjusting device.According to the invention, it can furthermore be provided that the actuating device for changing the eccentricity of the cam ring relative to the rotor has a first pressure chamber between an outer side of the cam ring and an inner wall of the pump housing, wherein a pressure in the first pressure chamber acts on the cam ring with a compressive force in order to press the cam ring in a positive direction and / or that the actuating device has a second pressure chamber between an outer side of the cam ring and an inner wall of the pump housing, wherein a pressure in the second pressure chamber acts on the cam ring with a compressive force in order to press the cam ring in a negative direction.A control of the cam ring with the aid of a first pressure chamber and a second pressure chamber is sufficiently known from the prior art, among other things from the documents mentioned with respect to the prior art. The two pressure chambers are supplied with the pressure medium, wherein the pressure in the first and in the second pressure chamber is preferably controlled by a flow control valve, which preferably has a high-pressure chamber and a low-pressure chamber. Such a control or regulation is fundamentally known. The first pressure chamber is preferably fluidically separated from the second pressure chamber between the outer side of the cam ring and the inner wall of the pump housing or of an outer ring (in this respect present) by a sealing means.Within the scope of the invention, it can preferably be provided that the adjusting device has a first pressure chamber and a second pressure chamber, which are pressurized in a known manner for controlling or regulating the eccentricity of the cam ring, wherein this is a volume flow-dependent or speed-dependent control or the control is dependent on the pressure of the delivered pressure medium, i.e. is not independent thereof. In addition, at least one active control element is preferably provided, which can be controlled independently of the pressure of the pressure medium or the rotational speed of the drive shaft of the vane pump or of the output shaft of the vehicle transmission.The solution according to the invention is not limited to the provision of a first pressure chamber and / or a second pressure chamber which are fluidically connected to the pressure medium which the vane pump delivers for consumption. The first and / or the second pressure chamber can also be dispensed with within the scope of the invention. Furthermore, the first pressure chamber and / or the second pressure chamber can also be controlled with another pressure medium independently of the pressure medium which the vane pump delivers to the consumer.According to the invention, it can furthermore be provided that the actuating device has a superposition device in order to superimpose the pressure in the first pressure chamber and / or the second pressure chamber.In one embodiment of the invention, it can be provided that the pressure in the first pressure chamber and / or in the second pressure chamber or the hydraulic control thereof is superimposed as required by a superposition device in order to achieve a specific adjustment of the eccentricity of the cam ring or an adjustment deviating from the usual control, in particular a displacement of the cam ring, which is independent of the pressure of the pressure medium or of the rotational speed of the drive shaft of the vane pump or of the output shaft of the vehicle transmission or which overlays the pressure. The superposition device can be configured, for example, to increase the pressure in one of the pressure chambers and / or to decrease it in the other pressure chamber, for example by adjusting the flow control valve by an active actuator or two oppositely acting active actuators or an active actuator and a passive actuator which generate opposing forces. It can be provided, for example, that the superposition device acts on a piston of the flow control valve and adjusts its position.According to the invention, it can furthermore be provided that the vane pump is designed as a power steering pump and / or as an emergency power steering pump and / or the consumer is a vehicle steering system, in particular a steering cylinder, of a vehicle.For such an application, the vane cell pump according to the invention has proven to be particularly suitable. However, the vane pump is not limited to this use.The vane cell pump according to the invention is particularly suitable for generating a pressure medium flow for a vehicle steering system.In one embodiment of the invention, it can furthermore be provided that the adjusting device is designed in such a way that an adjustment of the eccentricity of the cam ring relative to the rotor between the positive eccentricity and a negative eccentricity is possible, wherein in the case of the negative eccentricity the cam ring is displaced from the zero eccentricity in a negative direction opposite the positive direction.Because the setting of the eccentricity of the cam ring relative to the rotor is possible not only within a positive eccentricity, as before, but also within a negative eccentricity, the vane pump according to the invention can be used even more universally. The cam ring can be displaced from a positive eccentricity beyond the zero eccentricity into a negative eccentricity. The vane cell pump according to the invention thus makes it possible in this embodiment for the cam ring, starting from a positive eccentricity, to be able to be displaced in a negative direction or in a negative eccentricity to such an extent that the cam ring is moved beyond the zero eccentricity in a direction in which the cam ring has a negative eccentricity with respect to the rotor.By adjusting the eccentricity from positive to negative eccentricity in the event of a change in the rotational direction of the rotor, the conveying direction of the vane pump can be maintained.Within the scope of the invention, it is preferably provided that in the event of a change in the rotational direction, i.e. when the rotor rotates in a second rotational direction, a zero eccentricity is set, i.e. no pressure medium is conveyed. As already explained, this prevents the pressure medium from being conveyed backwards, i.e. the pressure medium flows through the pressure connection into the working chambers and flows out through the suction connection. However, in one embodiment of the invention, it is alternatively also possible that, when the rotor rotates in the second rotational direction, a negative eccentricity of the cam ring relative to the rotor is set. Thus, pressure medium continues to be sucked into the working chambers through the suction connection or flows out of the working chambers through the pressure connection. The connected load, preferably a vehicle steering system, can thus continue to be supplied with pressure medium. This can be advantageous in order to provide a pressurized medium flow, in particular for a vehicle steering system, even when the vehicle is moved backward, i.e. the rotor rotates by the output shaft in the second direction of rotation (opposite to the first direction of rotation that results when the vehicle is travelling forward).As explained above, this is in particular an alternative to a zero eccentricity being set when the rotor rotates in a second rotational direction. The setting of a zero eccentricity will be sufficient in most applications and can be realized more cost-effectively than the design of a vane pump in such a way that a negative eccentricity can also be set. In particular, if the vane cell pump is designed as a power steering pump and / or as an emergency power steering pump and a vehicle steering is supplied with pressure medium primarily by a main steering pump which is driven by a vehicle engine, a zero eccentricity will generally be sufficient during a reverse travel, i.e. in the case of a changed rotational direction of the rotor, since in this driving situation the vehicle engine, in particular an internal combustion engine, typically operates or runs and the main steering pump is thus driven.The present invention also relates to a method for operating an adjustable, single-stroke vane pump for generating a pressure medium flow for a consumer. The vane cell pump operated with the method according to the invention has a pump housing in which an adjustable cam ring is inserted. The vane pump further includes a rotor and a drive shaft rotatable within the cam ring, the rotor supporting vanes forming working chambers between the rotor and the cam ring.Between the rotor and the cam ring, a suction connection and a pressure connection for a pressure medium are formed. An adjusting device is also provided for changing the eccentricity of the cam ring relative to the rotor.The method according to the invention provides that the adjusting device enables an adjustment of the eccentricity of the cam ring between a positive eccentricity and at least one zero eccentricity, wherein, for adjusting the positive eccentricity, the cam ring is displaced from the zero eccentricity in a positive direction, wherein, in the case of a positive eccentricity and a rotation of the rotor in a first rotational direction, pressure medium flows in through the suction connection into the working chamber and flows out through the pressure connection. According to the invention, when adjusting the eccentricity of the cam ring to a zero eccentricity, it is provided that no pressure medium is conveyed to the consumer. Furthermore, it is provided that the drive shaft is driven by an output shaft of a vehicle transmissionThe method according to the invention enables operating modes and applications which could not be depicted in this way in the case of vane cell pumps according to the prior art.According to the invention, it can be provided that the adjusting device adjusts the zero eccentricity of the cam ring relative to the rotor independently of the direction of rotation and a rotational speed of the rotor.According to the invention, it can be provided that the adjusting device sets the zero eccentricity of the cam ring relative to the rotor when the rotor is at a standstill and / or when the rotor rotates in the first rotational direction, but a flow of pressurized medium is not required, and / or when the rotor rotates in a second rotational direction, which is opposite to the first rotational direction.The vane cell pump can be placed in a state or operated in a state in which no delivery takes place.It is advantageous if the adjusting device is controlled in such a way that, in the event of standstill and / or in the event of forward travel of a vehicle, if a pressure medium flow generated by the vane pump is not required, and / or in the event of rearward travel of a vehicle in which the vane pump is installed, the adjusting device adjusts the zero eccentricity of the cam ring relative to the rotor.According to the invention, it can be provided that the adjusting device enables an adjustment of the eccentricity of the cam ring relative to the rotor between the positive eccentricity and a negative eccentricity, wherein, in order to set a negative eccentricity, the cam ring is displaced from the zero eccentricity in a negative direction opposite to the positive direction.In one configuration of the method according to the invention, it can be provided that the vane cell pump is configured and designed so that a negative eccentricity of the cam ring relative to the rotor can also be set. For setting a negative eccentricity of the cam ring, the cam ring is displaced in a negative direction opposite to the positive direction starting from the zero eccentricity.As a result of the possibility of setting a negative eccentricity, if the direction of rotation of the rotor changes or the rotor rotates in a second direction of rotation, an adjustment of the cam ring relative to the rotor to a negative eccentricity can also take place alternatively to a zero eccentricity. This allows a further operating mode to be set.By adjusting the eccentricity from positive to negative eccentricity (or vice versa), the conveying direction of the vane pump can be maintained during a change in the direction of rotation of the rotor.The vane cell pump according to the invention or the method according to the invention enables variable setting of the stroke of the vane cell pump, optionally up to a negative stroke direction or a negative eccentricity during operation of the vane cell pump or at standstill.It is advantageous if, within the scope of the method according to the invention, it is provided that the adjusting device for adjusting the eccentricity of the cam ring relative to the rotor has at least one active adjusting element which acts indirectly or directly on the cam ring and which is controlled independently of the pressure of the pressure medium.According to the invention, it can furthermore be provided that the adjusting device has two active adjusting members which are suitable for applying opposing forces to the cam ring, or the adjusting device has an active adjusting member and a passive, non-controllable adjusting member, preferably a spring, which are suitable for applying opposing forces to the cam ring.According to the invention, it can furthermore be provided within the scope of the method for operating the vane pump that the actuating device has a first pressure chamber between an outer side of the cam ring and an inner wall of the pump housing, wherein the first pressure chamber is acted upon by a compressive force in order to press the cam ring in a positive direction and / or that the actuating device has a second pressure chamber between an outer side of the cam ring and an inner wall of the pump housing, wherein the second pressure chamber is acted upon by a compressive force in order to press the cam ring in a negative direction.According to the invention, it can furthermore be provided that the vane pump is designed as a power steering pump and / or as an emergency power steering pump and / or the consumer is a vehicle steering system of a vehicle.The present invention also relates to a computer program product having program code means for carrying out a method according to one of Claims 17 to 24 or a method having the method features described above when the program is executed on a control device of a vane pump according to one of Claims 1 to 16.It is particularly advantageous if the computer program product is configured such that the control device controls the actuating device as a function of driving situations of a vehicle or takes it into account. Preferably, the vane cell pump according to the invention, in particular in an embodiment as a power steering pump and / or as an emergency power steering pump, is switched on when the vehicle engine is switched off. Furthermore, the setting of a zero eccentricity can be provided when the output shaft of the vehicle transmission, which drives the drive shaft or the rotor of the vane pump, is stationary or does not rotate. The setting of a zero eccentricity or also of a negative eccentricity can furthermore be provided when the rotor rotates in the second rotational direction or when the vehicle in which the vane pump is installed moves backwards.It is preferably provided within the scope of the invention that the vane cell pump according to the invention is switched off when the internal combustion engine drives the main steering pump. It can be advantageous here if brief overlaps are provided, in particular in the operating situation in which the internal combustion engine is switched off and the pressure medium supply to the consumer, in particular to the steering gear, is then taken over by the power steering pump or emergency power steering pump (and vice versa).It is preferably provided that, apart from short-term overlaps when one of the pumps is switched off and when the other pump is switched on, no simultaneous delivery is provided. In principle, however, it would also be conceivable for both pumps to simultaneously convey pressure medium. A deactivation of the vane cell pump according to the invention, if it is used in addition to a main steering pump and the vane cell pump according to the invention is driven by an output shaft of a vehicle transmission, can be achieved independently of the rotational speed of the output shaft or the rotational speed of the rotor / of the drive shaft of the vane cell pump in that the actuating device, controlled by the control device, sets a zero eccentricity of the cam ring relative to the rotor. As a result, the pressure medium flow which the vane pump according to the invention delivers can be switched on and off quickly as required. The vane cell pump according to the invention can thus be switched on or switched off in each case depending on whether the vehicle engine is switched on or switched off, by setting the zero eccentricity or by displacing the cam ring relative to the rotor in such a way that the axis of rotation of the rotor and the axis of rotation of the cam ring are not arranged or run coaxially.The solution according to the invention thus makes it possible not only when the output shaft is stationary or the rotor does not rotate or when the rotor rotates in the second rotational direction to set a zero delivery or a zero eccentricity of the vane pump according to the invention, but in a wide variety of operating states. The energy consumption of the pump can thus be reduced to a minimum. The control device and at least one active control element are particularly suitable for this purpose.The solution according to the invention is not limited to the fact that a zero eccentricity is set only when the rotor is at a standstill and / or when the rotor rotates in a second rotational direction.The invention also relates to a system for generating a pressurized medium flow for a consumer, having a vane pump according to one of Claims 1 to 16 or a vane pump which is operated according to one of Claims 17 to 24, for delivering a pressurized medium for the at least one consumer.In the system, it is advantageous if the consumer is a vehicle steering system of a vehicle. In this case, the system is provided with a main steering pump driven by a vehicle engine for supplying the vehicle steering system with pressure medium. The drive shaft of the vane cell pump is driven by an output shaft of a vehicle transmission.The vane cell pump is preferably designed as a power steering pump and / or as an emergency power steering pump in order to supply the vehicle steering system with pressure medium when the vehicle engine is switched off.The system according to the invention makes it possible in a particularly advantageous manner to save energy and nevertheless to ensure the steering capability of the vehicle steering system. In particular in the driving situations already described, it can advantageously be provided that the vehicle engine is switched off or switched off, as a result of which the main steering pump is then also no longer operated, the function of which can then be taken over, however, by the auxiliary steering pump or the emergency auxiliary steering pump (if the vehicle engine fails unintentionally), which is driven by the output shaft of the vehicle transmission.The system according to the invention is also suitable in particular for ensuring that even in the event of a failure of the vehicle engine, the vehicle steering system is still supplied with a pressurized medium flow.The present invention also relates to a steering system of a vehicle having a vehicle steering system and a main steering pump for generating a pressurized medium flow for the vehicle steering system and additionally to a system according to Claim 27 or a vane pump according to one of Claims 1 to 16 or a vane pump which is operated according to one of Claims 17 to 24.Features which have been described in connection with one of the subject matters of the invention, namely given by the vane cell pump according to the invention, that the computer program product, the system according to the invention for generating a pressure medium flow, the method according to the invention for operating a vane cell pump or the steering system according to the invention, can also be advantageously implemented for the other subject matters of the invention. Likewise, advantages which have been mentioned in connection with one of the subject matters of the invention can also be understood to relate to the other subject matters of the invention.In addition, it should be pointed out that terms such as "comprising", "having" or "having" do not exclude other features or steps. Further, terms such as "a" or "the" that indicate a singular number of steps or features do not exclude a plurality of features or steps - and vice versa.In a heuristic embodiment of the invention, however, it can also be provided that the features introduced in the invention with the terms "comprising", "having" or "with" are listed in the end. Accordingly, one or more enumerations of features within the scope of the invention may be considered as completed, for example considered for each claim. The invention can consist, for example, exclusively of the features mentioned in claim 1.It should be noted that terms such as "first" or "second", etc. are used primarily for reasons of distinguishability of respective device or method features and are not necessarily intended to indicate that features are mutually related or are related to one another.Exemplary embodiments of the invention are described in more detail below with reference to the drawings.It shows: FIG. 1 shows a schematic illustration of a vane cell pump according to the invention; FIG. 2 shows an active actuator of an adjusting device in a first exemplary embodiment; FIG. 3 shows an active actuator of an adjusting device in a second exemplary embodiment; FIG. 4 shows a schematic illustration of an operating mode of the vane cell pump according to the invention; FIG. 5 shows a schematic illustration of a further operating mode of the vane cell pump according to the invention at zero eccentricity; FIG. 6 is a schematic illustration of an embodiment of the adjusting device for adjusting the eccentricity of the cam ring; FIG. 7 is a schematic illustration of a further embodiment of the adjusting device for adjusting the eccentricity of the cam ring; FIG. 8 is a schematic illustration of a further embodiment of the adjusting device with a superposition device in order to adjust the eccentricity of the cam ring; FIG. 9 is a schematic illustration of a further embodiment of the adjusting device for adjusting the eccentricity of the cam ring with two active adjusting members; FIG. 10 is a schematic illustration of a further embodiment of the adjusting device for adjusting the eccentricity of the cam ring; FIG. 11 is a block diagram of a steering system having a vane pump for delivering the fluid to a consumer; and FIG. 12 shows a schematic illustration of a steering system of a vehicle having a main steering pump driven by a vehicle engine and a vane pump according to the invention, which is driven by a vehicle transmission.Adjustable, single-stroke vane cell pumps 1 for generating a pressure medium flow for a consumer 2 are sufficiently known from the prior art, for which purpose reference is also made, for example, to DE 10 2005 040 702 A1 and DE 10 2005 043 253 B4.Only the features essential for the invention are therefore illustrated in more detail below.As can be seen from FIG. 1, the vane cell pump 1 according to the invention has a pump housing 3. In a manner not shown in more detail, an outer ring can be inserted in the pump housing 3.An adjustable cam ring 4 is inserted into the pump housing 3.The pump housing 3 offers sufficient installation space for the displacement of the cam ring 4 between a positive eccentricity and a zero eccentricity or optionally also a negative eccentricity or between a positive stroke and a zero stroke or optionally also a negative stroke, as is illustrated in more detail below.The cam ring 4 is adjustable or displaceable within a preferably elliptical space of the pump housing 3.Within the cam ring 4 or in the cam ring 4, a rotor 5 is rotatably mounted via a drive shaft 6. Between the rotor 5 and the cam ring 4 there are formed working chambers 8 delimited by vanes 7. The vanes 7 are supported by the rotor 5 or are movably arranged in slots of the rotor 5, so that the vanes 7 can be advanced and retracted in the slots of the rotor 5. For this purpose, a rear-wing fluid pressure is preferably used in a manner known in principle.The drive shaft 6 can also be referred to as the axis of rotation.The drive shaft 6 or the axis of rotation is positionally fixed with respect to the pump housing 3.Between the rotor 5 and the cam ring 4 a suction connection 9 and a pressure connection 10 for a pressure medium are formed. In FIG. 1, the suction connection 9 is shown as a suction region and the pressure connection 10 as a pressure region.FIG. 1 also shows lines 11 which lead to the consumer 2 or to a pressure medium reservoir 12, for example a tank with the pressure medium.In the exemplary embodiment, a line 11 leads from the pressure medium reservoir 12 to the suction connection 9.FIG. 1 also shows a passive actuator 13, which is preferably a spring. Furthermore, an active actuator 14 is illustrated in FIG. 1. The passive control element 13 and the active control element 14 each act in the opposite direction on the cam ring 4 in order to adjust its eccentricity with respect to the rotor 5 or the drive shaft or rotational axis 6.A possible adjustment of the eccentricity of the cam ring 4 with respect to the rotor 5 is designated by the stroke 15 in FIG. 1 by way of example. The stroke 15 can be positive or even zero (zero eccentricity), depending on the position of the active actuator 14 according to FIG. 1, The stroke 15 can also be negative, if the setting of a negative eccentricity is also provided in a particular embodiment.In FIG. 1, a sealing point 16 is furthermore exemplarily shown, which ensures a seal between the pump housing 3 and the active control element 14.The adjustment of the active control element 14 is symbolized in FIG. 1 by a double arrow.According to the invention, an adjusting device 17 is provided which is designed in such a way that an adjustment of the eccentricity of the cam ring 4 is possible at least between a positive eccentricity and a zero eccentricity. In the case of a positive eccentricity, the cam ring 4 is displaced from a zero eccentricity in a positive direction in such a way that, in the case of a rotation of the rotor 5 in a first rotational direction 18, the pressure medium flows into the working chambers 8 through the suction connection 9 and flows out through the pressure connection 10.Zero eccentricity is to be understood as meaning that the central axes or the rotational axes of the cam ring 4 and of the rotor 5 are arranged coaxially with respect to one another.In the illustration according to FIG. 1, the cam ring 4 is displaced in a positive direction. The rotor 5 rotates in the first direction of rotation 18, so that pressure medium flows into the suction connection 9, which pressure medium originates from the pressure medium reservoir 12 in the exemplary embodiment. The pressure medium flows out of the pressure connection 10 again or is conveyed to the consumer 2.Depending on the direction of rotation of the drive shaft 6, the rotor 5 of the vane cell pump 1 rotates in the first direction of rotation 18 or an opposite second direction of rotation 19.In the exemplary embodiment, a control device 20 is provided, which can control the adjusting device 17, in particular the active actuator 14, on the basis of various parameters in such a way that a desired eccentricity of the cam ring 4 relative to the rotor 5 or else a zero eccentricity can be set. The control device 20 can also set a negative eccentricity if necessary if the vane cell pump 1 according to the invention is provided for this purpose or is configured for this purpose.In the exemplary embodiment, it is provided that, when the rotor 5 is at a standstill and / or when the rotor 5 rotates in a second rotational direction 19 which is opposite the first rotational direction 18, the adjusting device 17 adjusts the zero eccentricity of the cam ring 4 relative to the rotor 5.Furthermore, a zero eccentricity of the cam ring 4 relative to the rotor 5 can be adjusted as required if a pressure medium flow generated by the vane pump 1 is not required (standby operation).The control device 20 is only shown in principle in FIG. 1.The adjusting device 17 for adjusting the eccentricity of the cam ring 4 relative to the rotor 5 has at least one active adjusting element 14, which acts on the cam ring 4 and which can be controlled independently of the pressure of the pressure medium.The at least one active control element 14 can be fixedly connected to the cam ring 4 in such a way that the control element 14 can change the eccentricity of the cam ring 4 relative to the rotor 5 in a positive direction and a negative direction and can set both a positive eccentricity and a zero eccentricity and optionally a negative eccentricity.FIG. 6 shows an exemplary embodiment in which the adjusting device 17 has an active adjusting element 14, which is rigidly or fixedly connected on one side to the cam ring 4 in order to adjust the latter by pulling and pushing or pressing.A possible stroke 15 is symbolized in FIG. 6 by the double arrow.The adjusting device 17 can also have two adjusting members, wherein one adjusting member is connected to the cam ring 4 in such a way that the cam ring 4 can be adjusted, in particular displaced, in a positive direction for changing the eccentricity, and one adjusting member is connected to the cam ring 4 in such a way that the cam ring 4 can be adjusted, in particular displaced, in a negative direction for changing the eccentricity. For this purpose, the actuating device 17 can preferably have two active actuating elements 14 or an active actuating element 14 and a passive actuating element 13.An embodiment of the adjusting device 17 with two active adjusting members 14 is illustrated in FIG. 9. The two active control elements 14 are suitable and arranged to apply opposing forces to the cam ring 4. The active actuators 14 may or may not be fixedly connected to the cam ring 4.FIG. 10 shows an embodiment in which the adjusting device 17 has an active adjusting member 14 and a passive, non-controllable adjusting member 13, preferably a spring, which are likewise arranged and suitable for applying opposing forces to the cam ring 4.The control device 20 can correspondingly control the adjusting device 17 or the active adjusting elements 14 in order to perform a desired setting.In the exemplary embodiment, the adjusting device 17 can be configured to adjust the position of a stop 21, against which the cam ring 4 strikes when the latter has reached one of its end positions, for example the maximum positive eccentricity or the zero eccentricity. This is illustrated by way of example in FIG. 7. As is likewise shown in FIG. 7, the adjusting device 17 can optionally additionally have a passive actuator 13, preferably a spring, which acts directly on the cam ring 4 in such a way that the cam ring 4 is loaded with a compressive force in the direction of the stop 21.The adjusting device 17 can have a first pressure chamber 22 between an outer side of the cam ring 4 and an inner wall of the pump housing 3 in order to change the eccentricity of the cam ring 4 relative to the rotor 5. A pressure in the first pressure chamber 22 can thereby apply a compressive force to the cam ring 4 in order to press the cam ring 4 in a positive direction. Alternatively or preferably additionally, the adjusting device 17 can furthermore have a second pressure chamber 23 between an outer side of the cam ring 4 and an inner wall of the pump housing 3. The pressure in the second pressure chamber 23 can act in such a way that the cam ring 4 is acted upon by a compressive force in order to press the cam ring 4 in a negative direction.The pressure chambers 22, 23 can be regulated in a manner known in principle by the pressure medium or the pressure of the pressure medium which is to be conveyed from the pressure medium reservoir 12 to a consumer 2. For this purpose, a flow control valve, not shown in detail, can be provided in a known manner.Within the scope of the exemplary embodiment, the use of a flow control valve can be provided. However, it can also be provided within the scope of the exemplary embodiment that no flow control valve is used or the vane cell pump 1 does not have a flow control valve or no flow control valve is provided for the method according to the invention.It should be noted that the configuration of the vane cell pump 1 with a first pressure chamber 22 and a second pressure chamber 23 is optional for all exemplary embodiments. A first pressure chamber 22 and a second pressure chamber 23 can also be dispensed with within the scope of the invention, wherein the configuration of a first pressure chamber 22 and a second pressure chamber 23 can be suitable, in particular for adjusting the cam ring 4 within a positive eccentricity or, if appropriate, within a negative eccentricity, in order to vary the geometric working volume in the case of the positive eccentricity or the negative eccentricity, in particular depending on the rotational speed of the rotor 5. In FIG. 1, the first pressure chamber 22 and the second pressure chamber 23 are shown only by way of example, wherein the representations of seals and hydraulic connections have been omitted. Their arrangement and design are known from the prior art. It should be noted that the pressure chambers 22, 23 are also optional in the exemplary embodiment of FIG. 1. The design or presence of pressure chambers 22, 23 depends on whether a speed-dependent control is provided in addition to the control with the aid of the actuating device 17 or whether the pressure chambers 22, 23 are to be used within the scope of the actuating device 17.FIG. 8 shows an embodiment with pressure chambers 22, 23. Thus, the pressure chambers 22, 23 can be used for adjusting the eccentricity of the cam ring 4 between a positive eccentricity and a zero eccentricity or also a negative eccentricity. In the exemplary embodiment according to FIG. 8, the superposition device 24 has an active actuator 14 and a passive actuator 13, for example a spring, in order to superpose the pressure in the pressure chambers 22, 23 with the aid of said active actuator. The superposition device 24 can also have only one active actuator 14 or also two active actuators 14.In all exemplary embodiments, it can preferably be provided that the at least one active actuator 14 is a mechanical and / or electrical and / or electromechanical and / or hydraulic and / or pneumatic actuator that can be controlled independently of the pressure of the pressure medium or can be controlled accordingly.FIG. 2 shows, by way of example, a configuration of an active actuator 14 in an electromechanical configuration or with an electromechanical control.FIG. 3 shows an example of an active actuator 14 in an embodiment as a pneumatic or hydraulic actuator or with a pneumatic or hydraulic control.The exemplary embodiment also serves to disclose a method for operating an adjustable, single-stroke vane pump 1 for generating a pressure medium flow for a consumer 2.The pressure medium is preferably a hydraulic fluid, in particular a pressure oil.With regard to the method for operating an adjustable, single-stroke vane pump 1 and also with regard to the computer program product, reference is also made to the above and the following explanations.FIG. 4 shows an operating mode or a configuration of the vane cell pump 1, which makes it possible to shift the cam ring 4 relative to the rotor 5 into a negative eccentricity. Such a displacement may be provided when the rotational direction of the rotor 5 changes. By a displacement into a negative eccentricity, it can be achieved that despite a changed direction of rotation of the rotor 5, the conveying direction of the vane cell pump 1 does not change, that is to say that pressure medium continues to flow into the working chambers 8 via the suction connection 9 and flows out through the pressure connection 10. As already explained above, such a configuration or such an operating mode is optional. As a rule, it will be provided that a zero eccentricity is set during a rotation of the rotor 5 in the second rotational direction 19, that is to say that no conveying takes place. Alternatively, however, it is also possible that, if the vane cell pump 1 is designed accordingly, a negative eccentricity is set so that pressure medium continues to be pumped.The middle image in FIG. 4 shows a rotation of the rotor 5 in the first rotational direction 18. When the rotational direction changes, that is, when the rotor 5 rotates in the second rotational direction 19 (right image), the cam ring 4 assumes a position with a negative eccentricity. The delivery direction of the vane cell pump has thus been maintained, i.e. the suction and delivery (see the arrows in FIG. 4 ) is unchanged.FIG. 5 shows an operating mode of the vane cell pump 1, in which no delivery takes place. The cam ring 4 is set to a zero eccentricity. The vane cell pump 1 can be operated in this state without the delivery of the pressure medium taking place, regardless of the rotational direction 18, 19 in which the rotor 5 of the vane cell pump 1 rotates.A zero eccentricity of the type shown in FIG. 5 is set under the control of the control device 20, by the setting device 17, preferably when the rotor 5 is at a standstill and / or when the rotor 5 rotates in a second rotational direction 19. However, a zero eccentricity can also be set when the rotor 5 rotates in the first rotational direction 18, or a zero eccentricity can be set independently of the rotational direction and / or the rotational speed of the rotor 5, in particular when it is desired that the vane pump 1 according to the invention does not convey any pressure medium and thus energy is correspondingly saved.FIG. 11 shows, in a first embodiment, a steering system 100 for a motor vehicle, in particular for a passenger car or a commercial vehicle. The steering system 100 can comprise, in a manner not shown in more detail, a steering wheel to be actuated by the driver, which steering wheel acts on a vehicle wheel via a steering gear via a steering column and adjusts the vehicle wheel in accordance with the driver's intention. The steering system 100 comprises the vane cell pump 1 according to the invention, which generates a pressurized medium flow or a hydraulic pressure for a consumer 2.The consumer 2 can be an actuating cylinder which typically has two separate chambers which are each connected to a pressure control valve via hydraulic lines. The hydraulic pressure or the pressure medium flow generated by the vane pump 1 can be supplied to the pressure regulating valve.FIG. 12 shows a particularly advantageous system 200 for generating a pressurized medium flow for a consumer 2, having a vane cell pump 1 according to the invention or a vane cell pump 1, which is operated according to the method according to the invention, for delivering a pressurized medium for the at least one consumer 2. The system 200 has a main steering pump 102 for supplying the vehicle steering 101 with pressure medium. The main steering pump 102 is driven by a vehicle engine 103. The vehicle engine 103 is preferably an internal combustion engine. The vehicle can preferably be a vehicle in which an internal combustion engine is used for the drive, or else a vehicle which has both an internal combustion engine and an electric motor, in particular a so-called hybrid vehicle. In the exemplary embodiment according to FIG. 12, the drive shaft 6 of the vane cell pump 1, which is part of the system 200, is driven by an output shaft 105, which in turn is driven by a vehicle transmission 104 or is part of the vehicle transmission 104. The vehicle transmission 104 is driven or accelerated by the vehicle engine 103. When the vehicle is coasting (or coasting) and the engine is off, the vehicle transmission 104 continues to be driven or travels with the vehicle wheels.The vehicle engine 103 and the vehicle transmission 104 are not part of the system 200.In the exemplary embodiment according to FIG. 12, the vane cell pump 1 is designed as a power steering pump and / or as an emergency power steering pump in order to supply the vehicle steering 101 with pressure medium when the vehicle engine 103 is switched off or is not running or when the vehicle engine has failed.In the exemplary embodiment according to FIG. 12, it can preferably be provided that the control device 20 sets a zero eccentricity when the output shaft 105 or the rotor 5 is stationary and / or that a zero eccentricity of the cam ring 4 relative to the rotor 5 is set when the rotor 5 rotates in the second direction of rotation 19, which is in particular the case when the vehicle is moving backwards. Alternatively, during a reverse travel of the vehicle, i.e. when the rotor 5 rotates in the second rotational direction 19, a negative eccentricity can also be set, so that a delivery, preferably a delivery of pressure medium or hydraulic fluid, continues to take place from the pressure medium reservoir (tank) to the consumer 2, in particular a vehicle steering system 101 or an adjusting cylinder / steering cylinder of the vehicle steering system 101.In the exemplary embodiment according to FIG. 12, it is preferably provided that the zero eccentricity is set when the rotor 5 rotates in the first rotational direction 18, but the vehicle steering system 101 does not require a flow of pressurized medium from the vane cell pump 1 according to the invention, for example because a supply by the main steering pump 102 takes place sufficiently and / or because the vehicle steering system 101 does not require pressurized medium.In the exemplary embodiment according to FIG. 12, it is preferably provided that the main steering pump 102 and the vane cell pump 1 according to the invention are not operated simultaneously, but a short-term overlap can be provided when one of the pumps 1, 102 is switched off, so that continuous supply of the vehicle steering 101 is ensured.The exemplary embodiment according to FIG. 12 also serves to disclose a steering system 100 in a second configuration. The steering system 100 has a vehicle steering system 101, a main steering pump 102 for generating a pressurized medium flow for the vehicle steering system 101 and additionally a vane pump 1 according to the invention and / or the system 200.An advantageous motor vehicle can have the steering system 100, in particular according to FIG. 12, and additionally a vehicle engine 103 and a vehicle transmission 104, wherein the vehicle engine 103 drives the main steering pump 102 and the vehicle transmission 104 or an output shaft 105 of the vehicle transmission 104 drives the drive shaft 6 or the rotor 5 of the vane cell pump 1 according to the invention.List of reference numbers:1 Vane pump 2 Consumer 3 Pump housing 4 Cam ring 5 Rotor 6 Drive shaft 7 Vane 8 Working chamber 9 Suction connection 10 Pressure connection 11 Line 12 Pressure medium reservoir 13 Passive actuator 14 Active actuator 15 Stroke 16 Sealing point 17 Actuating device 18 First direction of rotation 19 Second direction of rotation 20 Control device 21 Stop 22 First pressure chamber 23 Second pressure chamber 24 Superposition device 100 Steering system 101 Vehicle steering system 102 Main steering pump 103 Vehicle motor 104 Vehicle transmission 105 Output shaft 200 System for generating a flow of pressure mediumReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2004 060 082 A1

[0012] DE 10 2014 105 613 A1

[0013] DE 10 2014 115 159 A1

[0014] DE 10 2015 107 543 A1

[0016] DE 10 2014 221 447 A1

[0017] DE 103 37 653 A1

[0018] DE 10 2005 043 253 B4 [0059, 0140]DE 10 2015 115 587 A1

[0063] DE 10 2005 040 702 A1

[0140]

Claims

Adjustable, single-stroke vane cell pump (1) for generating a pressure medium flow for a consumer (2), having a pump housing (3) in which an adjustable cam ring (4) is inserted, having a rotor (5) and a drive shaft (6) which are rotatable within the cam ring (4), wherein the rotor (5) carries vanes (7) which form working chambers (8) between the rotor (5) and the cam ring (4), and wherein a suction connection (9) and a pressure connection (10) for a pressure medium are formed between the rotor (5) and the cam ring (4), and having an actuating device (17) for changing the eccentricity of the cam ring (4) relative to the rotor (5), characterized in that, the drive shaft (6) being designed and configured for driving by an output shaft (105) of a vehicle transmission (104), and the actuating device (17) being designed such that an adjustment of the eccentricity of the cam ring (4) is possible at least between a positive eccentricity and a zero eccentricity, wherein in the case of the positive eccentricity the cam ring (4) is displaced from the zero eccentricity in a positive direction such that, in the case of a rotation of the rotor (5) in a first rotational direction (18), the pressure medium flows through the suction connection (9) into the working chambers (8) and flows out through the pressure connection (10), and wherein, in the case of the zero eccentricity, no delivery of the pressure medium to the consumer (2) takes place in the case of a rotation of the rotor (5).Vane cell pump according to Claim 1, characterized in that a control device (20) is provided and configured which controls the actuating device (17) in such a way that the zero eccentricity of the cam ring (4) relative to the rotor (5) can be adjusted independently of the direction of rotation and a rotational speed of the rotor (5).Vane cell pump according to Claim 2, characterized in that the control device (20) controls the actuating device (17) in such a way that, when a vehicle is at a standstill and / or when a vehicle is moving forwards, if a pressure medium flow generated by the vane cell pump (1) is not required, and / or when a vehicle in which the vane cell pump (1) is installed is moving backwards, the actuating device (17) sets the zero eccentricity of the cam ring (4) relative to the rotor (5).Vane cell pump according to Claim 1, 2 or 3, characterized in that the actuating device (17) is designed in such a way that an active adjustment of the eccentricity of the cam ring (4) relative to the rotor (5) is possible independently of and / or in addition to a volume-flow-dependent regulation.Vane cell pump according to one of Claims 1 to 4, characterized in that the actuating device (17) has, for setting the eccentricity of the cam ring (4) relative to the rotor (5), at least one active actuating element (14) which acts indirectly or directly on the cam ring (4) and which can be controlled independently of the pressure of the pressure medium.Vane cell pump according to Claim 5, characterized in that the actuating device (17) for adjusting the eccentricity of the cam ring (4) relative to the rotor (5) has the at least one active actuating element (14) and additionally a flow control valve which influences the eccentricity of the cam ring (4) as a function of a volume of the flow of pressure medium from the pressure connection (10) to the consumer (2).Vane cell pump according to Claim 5, characterized in that the actuating device (17) for adjusting the eccentricity of the cam ring (4) relative to the rotor (5) has the at least one active actuating element (14) and no flow control valve which influences the eccentricity of the cam ring (4) as a function of a volume of the flow of pressure medium from the pressure connection (10) to the consumer (2).Vane cell pump according to Claim 5, 6 or 7, characterized in that the at least one active actuating element (14) is fixedly connected to the cam ring (4) in such a way that the active actuating element (14) can change the eccentricity of the cam ring (4) relative to the rotor (5).Vane cell pump according to one of Claims 1 to 8, characterized in that the actuating device (17) has two actuating elements (13, 14), wherein one actuating element (13, 14) is connected to the cam ring (4) in such a way that the cam ring (4) can be displaced in a positive direction relative to the rotor (5) in order to change the eccentricity, and one actuating element (13, 14) is connected to the cam ring (4) in such a way that the cam ring (4) can be displaced in a negative direction in order to change the eccentricity.Vane cell pump according to Claim 9, characterized in that the actuating device (17) has two active actuating elements (14) which are suitable for applying opposing forces to the cam ring (4), or the actuating device (17) has an active actuating element (14) and a passive, non-controllable actuating element (13), preferably a spring, which are suitable for applying opposing forces to the cam ring (4).Vane cell pump according to one of Claims 5 to 8, characterized in that the at least one active actuating element (14) is a mechanical and / or electrical and / or electromechanical and / or hydraulic and / or pneumatic actuating element which can be controlled independently of the pressure of the pressure medium.Vane cell pump according to one of Claims 1 to 11, characterized in that the actuating device (17) is designed to adjust the position of a stop (21) against which the cam ring (4) strikes when the latter has reached one of its two end positions, wherein the actuating device (17) additionally has a passive actuating element (13), preferably a spring, which acts on the cam ring (4) in such a way that the cam ring (4) is loaded with a compressive force in the direction of the stop (21).Vane cell pump according to one of Claims 1 to 12, characterized in that the actuating device (17) for changing the eccentricity of the cam ring (4) relative to the rotor (5) has a first pressure chamber (22) between an outer side of the cam ring (4) and an inner wall of the pump housing (3), a pressure in the first pressure chamber (22) acting on the cam ring (4) with a compressive force in order to press the cam ring (4) in a positive direction, and / or in that the actuating device (17) has a second pressure chamber (23) between an outer side of the cam ring (4) and an inner wall of the pump housing (3), a pressure in the second pressure chamber (23) acting on the cam ring (4) with a compressive force in order to press the cam ring (4) in a negative direction.Vane cell pump according to Claim 13, characterized in that the actuating device (17) has a superposition device (24) in order to superpose the pressure in the first pressure chamber (22) and / or the second pressure chamber (23).Vane cell pump according to one of Claims 1 to 14, characterized in that the vane cell pump (1) is designed as a power steering pump and / or as an emergency power steering pump and / or the consumer (2) is a vehicle steering system (101) of a vehicle.Vane cell pump according to one of Claims 1 to 15, characterized in that the actuating device (17) is designed in such a way that an adjustment of the eccentricity of the cam ring (4) relative to the rotor (5) between the positive eccentricity and a negative eccentricity is possible, wherein, in the case of the negative eccentricity, the cam ring (4) is displaced from the zero eccentricity in a negative direction which is opposite the positive direction.Method for operating an adjustable, single-stroke vane cell pump (1) for generating a pressure medium flow for a consumer (2), having a pump housing (3) in which an adjustable cam ring (4) is inserted, having a rotor (5) and a drive shaft (6) which are rotatable within the cam ring (4), wherein the rotor (5) carries vanes (7) which form working chambers (8) between the rotor (5) and the cam ring (4), and wherein a suction connection (9) and a pressure connection (10) for a pressure medium are formed between the rotor (5) and the cam ring (4), and having an adjusting device (17) for changing the eccentricity of the cam ring (4) relative to the rotor (5), characterized in that, the drive shaft (6) being driven by an output shaft (105) of a vehicle transmission (104) and the adjusting device (17) enabling an adjustment of the eccentricity of the cam ring (4) at least between a positive eccentricity and a zero eccentricity, wherein, in order to adjust the positive eccentricity, the cam ring (4) is displaced from the zero eccentricity in a positive direction, wherein, in the case of a positive eccentricity and a rotation of the rotor (5) in a first rotational direction (18), pressure medium flows in through the suction connection (9) into the working chamber (8) and flows out through the pressure connection (10), and wherein, in the case of an adjustment of the eccentricity of the cam ring (4) to a zero eccentricity, no pressure medium is conveyed to the consumer (2).Method according to claim 17, characterised in that the adjusting device (17) adjusts the zero eccentricity of the cam ring (4) relative to the rotor (5) independently of the direction of rotation and a rotational speed of the rotor (5).Method according to Claim 18, characterized in that the actuating device (17) is controlled in such a way that, in the case of standstill and / or in the case of forward travel of a vehicle, when a pressure medium flow generated by the vane pump (1) is not required, and / or in the case of rearward travel of a vehicle into which the vane pump is installed, the actuating device (17) sets the zero eccentricity of the cam ring (4) relative to the rotor (5).Method according to one of Claims 17 to 19, characterized in that the actuating device (17) has, for setting the eccentricity of the cam ring (4) relative to the rotor (5), at least one active actuating element (14) which acts indirectly or directly on the cam ring (4) and which is controlled independently of the pressure of the pressure medium and / or the rotational speed of the drive shaft (6).Method according to claim 20, characterised in that the adjusting device (17) has two active adjusting members (14) which are suitable for applying opposing forces to the cam ring (4), or the adjusting device (17) has an active adjusting member (14) and a passive, non-controllable adjusting member (14), preferably a spring, which are suitable for applying opposing forces to the cam ring (4).Method according to one of Claims 17 to 21, characterized in that the actuating device (17) has a first pressure chamber (22) between an outer side of the cam ring (4) and an inner wall of the pump housing (3), wherein the first pressure chamber (22) is acted upon by a compressive force in order to press the cam ring (4) in a positive direction, and / or in that the actuating device (17) has a second pressure chamber (23) between an outer side of the cam ring (4) and an inner wall of the pump housing (3), wherein the second pressure chamber (23) is acted upon by a compressive force in order to press the cam ring (4) in a negative direction.Method according to one of Claims 17 to 22, characterized in that the vane cell pump (1) is designed as a power steering pump and / or as an emergency power steering pump and / or the consumer (2) is a vehicle steering system (101) of a vehicle.Method according to one of Claims 17 to 23, characterized in that the actuating device (17) enables an adjustment of the eccentricity of the cam ring (4) relative to the rotor (5) between the positive eccentricity and a negative eccentricity, wherein, in order to set a negative eccentricity, the cam ring (4) is displaced from the zero eccentricity in a negative direction opposite the positive direction.Computer program product having program code means for carrying out a method according to one of Claims 17 to 24 when the program is executed on a control device (20) of a vane pump (1) according to one of Claims 1 to 16.System (200) for generating a pressure medium flow for a consumer (2), comprising a vane pump (1) according to one of Claims 1 to 16 or a vane pump (1) which is operated according to one of Claims 17 to 24, for conveying a pressure medium for the at least one consumer (2).System (200) according to Claim 26, characterized in that the consumer (2) is a vehicle steering system (101) of a vehicle, and wherein a main steering pump (102), which is driven by a vehicle engine (103), is provided for supplying the vehicle steering system (101) with pressure medium, and wherein the drive shaft (6) of the vane pump (1) is driven by an output shaft (105) of a vehicle transmission (104).System (200) according to Claim 27, characterized in that the vane cell pump (1) is designed as a power steering pump and / or as an emergency power steering pump in order to supply the vehicle steering system (101) with pressure medium when the vehicle engine (103) is switched off.Steering system (100) of a vehicle having a vehicle steering system (101) and a main steering pump (102) for generating a pressurized medium flow for the vehicle steering system (101) and additionally having a system (200) according to Claim 27 or having a vane pump (1) according to one of Claims 1 to 16 or having a vane pump (1) which is operated according to one of Claims 17 to 24.

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