Hydraulic actuation system, method for controlling the hydraulic actuation system and drive train with the actuation system

Abstract

Hydraulic actuation system (10) for a vehicle, - with a slave cylinder (11) for actuating a clutch device (4), wherein the slave cylinder (11) has an annular housing (12) and an axially movable annular piston (12) which delimit a pressure chamber (14) which can be filled with an operating medium; - with a pump (20) for generating an actuating volume flow (103) for the slave cylinder (11), which is fluidly connected to the slave cylinder (11) on a pressure side (23) via a pressure line (19); - with a pressure control valve (21) connected in parallel to the pump (20) for limiting an actuating pressure on the pressure side (23); wherein a flow path on the pressure side (23) from the pump (20) to the pressure chamber (13) is designed to be vent-free, characterized in that the annular housing (12) is accommodated in a housing section (16), wherein an intermediate space (17) surrounding the axis of rotation (100) is formed radially between the annular housing (12) and the housing section (16), which intermediate space is fluidically connected, on the one hand, to the pressure chamber (14) via at least one fluid opening (15) formed on the annular housing (12) and, on the other hand, to the pressure line (19) via a pressure connection (18) formed on the housing section (16).

Description

[0001] The invention relates to a hydraulic actuation system for a vehicle having the features of the preamble of claim 1. Furthermore, the invention relates to a method for controlling the hydraulic actuation system and a drive train with the actuation system.

[0002] Concentric slave cylinders (CSC) are typically used in both hybrid and purely electric vehicle drive systems. These serve, for example, to separate the electric motor from the combustion engine or to change gears. Such slave cylinders essentially consist of an annular housing and an annular piston that can be axially displaced within the annular housing. The annular piston is operatively connected to a clutch in such a way that the clutch is actuated, in particular engaged. A hydraulic actuation system according to the preamble of claim 1 is known from DE 10 2016 115 300 A1.

[0003] It is an object of the present invention to propose a hydraulic actuation system which is characterized by a simple and cost-effective design.

[0004] This object is achieved by a hydraulic actuation system having the features of claim 1, a method having the features of claim 8, and a drive train having the features of claim 9. Preferred or advantageous embodiments of the invention emerge from the subclaims, the following description, and the accompanying figures.

[0005] The subject matter of the invention is a hydraulic actuation system designed and / or suitable for a vehicle. In particular, the hydraulic actuation system serves to actuate at least one clutch device of an electric or hybrid drive train of the vehicle.

[0006] For this purpose, the actuation system comprises a slave cylinder, which is designed and / or suitable for actuating the clutch device. In particular, the slave cylinder serves to transmit an actuation force to the clutch device in order to open or close the clutch device. The clutch device can be designed as a friction clutch, preferably a friction-disk clutch, or a positive-locking clutch, preferably a dog clutch. The slave cylinder is preferably designed as a concentric slave cylinder, also known as a "concentric slave cylinder (CSC)". In particular, the concentric slave cylinder is designed as a central releaser.

[0007] For this purpose, the slave cylinder essentially comprises an annular housing and an annular piston that is axially movable within the annular housing. The annular piston and the annular housing are preferably arranged coaxially and / or concentrically with respect to the rotational axis. The annular housing preferably has a central through-opening, in particular a bore, through which at least one shaft can be passed when the actuating cylinder is installed. The rotational axis is preferably defined by a rotational axis of the shaft. The annular piston is preferably rotationally symmetrical with respect to the rotational axis.

[0008] The annular housing and the annular piston define a pressure chamber that can be filled with an operating medium. The annular housing has an annular chamber that surrounds the axis of rotation, and the annular piston is accommodated in the annular chamber of the annular housing so that it can move axially with respect to the axis of rotation. The annular chamber is delimited axially with respect to the axis of rotation by the annular piston, so that the pressure chamber is formed between the annular piston and the annular housing. In particular, the annular chamber is open on one side in the axial direction delimited by the annular piston and closed in an axially opposite direction. The operating medium is preferably a hydraulic fluid, specifically hydraulic oil. When the slave cylinder is actuated, an actuating pressure is hydraulically generated by the actuating system, so that an actuating force resulting from the actuating pressure is transferred to the annular piston, which is disengaged axially.

[0009] For this purpose, the actuation system comprises a pump which is designed and / or suitable for generating an actuation volume flow for the slave cylinder, wherein the pump is connected to the slave cylinder on a pressure side via a pressure line. In particular, the pump serves to build up and maintain the actuation pressure on the pressure side or in the pressure chamber of the slave cylinder. In particular, the pump is designed as an electrically operated pump. This means that the pump can be driven by a separate electric motor. Preferably, the fluid pump is connected to a fluid source on a suction side via a suction line.

[0010] Furthermore, the actuation system has a pressure control valve connected in parallel to the pump, which is designed and / or suitable for limiting an actuation pressure on the pressure side. In particular, the pressure control valve is designed to control the fluid flow on the pressure side depending on the actuation pressure on the pressure side. Preferably, the pressure control valve is closed until the actuation pressure is reached and maintained, and is opened when it is exceeded and the actuation pressure is reduced. In particular, the pump and the pressure control valve are part of a Smart Hydraulic Actuator (SHA). For this purpose, the pressure control valve can be connected to a branching point of the pressure line on the slave cylinder side.

[0011] Within the scope of the invention, it is proposed that a flow path on the pressure side from the pump to the pressure chamber is designed to be vent-free, in particular vent-valve-free. In particular, vent-free means that the hydraulic actuation system on the pressure side between the pump and the slave cylinder has no venting function for the targeted venting of the hydraulic path and / or no venting of the slave cylinder is carried out. Preferably, no vent valve is provided on the pressure side, in particular downstream of the pump and / or upstream of the pressure control valve, via which the hydraulic actuation system could be vented. In particular, the flow path runs from the pump via the pressure line to the pressure chamber and optionally to the pressure control valve, wherein the actuation volume flow generated by the pump is conveyed or can be conveyed along the flow path.Although, depending on the installation position, air on the pressure side can, in principle, escape at least partially via the parallel pressure control valve, the pressure control valve is not a vent valve. Furthermore, the slave cylinder does not have a venting function.

[0012] The invention is based on the idea that a so-called "Smart Hydraulic Actuator (SHA)" with a pump for actuating the clutch device is increasingly being used in electrified powertrains. This has the advantage of providing a virtually "infinite" displacement volume to actuate the slave cylinder. With such an actuation solution, it has previously been assumed that additional venting of the slave cylinder is required to ensure its proper function. This requires an additional vent valve and, above all, an additional venting procedure, which increases the complexity and cost of the hydraulic actuation system.

[0013] The invention is based on the finding that while air trapped in the hydraulic actuation system influences the release time, this influence is negligible above a certain pump flow rate. Furthermore, it has been demonstrated that the trapped air does not affect the achievement of the target pressure on the pressure side, since the actuation pressure required to actuate the slave cylinder is maintained at a constant pressure level via the pressure control valve. Thus, a hydraulic actuation system is proposed that is fully functional without a venting function and is thus characterized by a simple and cost-effective design.

[0014] In a specific implementation, the pump is dimensioned such that, based on the actuation volume flow, any air cushion on the pressure side is compensated and / or can be compensated within a specified actuation time. Particularly preferably, the pump is designed to provide an actuation volume flow which, regardless of any air volume, generates the actuation pressure within an actuation time of less than 1 second, preferably less than 0.5, in particular less than 0.1 seconds. Put simply, the actuation volume flow is selected to be large enough, depending on the hydraulic actuation system, that the actuation pressure is generated and / or can be generated within the actuation time, at least when the pressure chamber of the slave cylinder is completely filled with air.In other words, the annular piston can disengage at approximately the same speed in a completely emptied pressure chamber as in a completely vented pressure chamber. Thus, a vent-free actuation system is proposed that can be reliably actuated within a specified actuation time, even if air is present.

[0015] In a specific development, it is provided that the pump is designed to provide a minimum volume flow of at least 3 l / min to generate the actuation pressure. In particular, the disengagement time of the slave cylinder is essentially constant due to the minimum volume flow of at least 3 l / min, regardless of its filling level with air or operating medium. This means that the actuation time is less than 1 second, preferably less than 0.5 seconds, in particular less than 0.1 second, from an actuation volume flow of at least 3 l / min. In particular, the fluid pump is designed to generate and / or maintain a constant volume flow of at least 3 l / min upon actuation of the slave cylinder.Alternatively or optionally additionally, it is provided that the fluid pump is designed to generate and / or maintain a volume flow of more than 3 l / min, preferably more than 10 l / min, especially more than 15 l / min, at least during actuation. The invention is based on the finding that, starting at an actuation volume flow of > 3 l / min, no significant difference in the release time can be measured between a pressure chamber of the slave cylinder completely filled with air and a pressure chamber of the slave cylinder completely filled with operating medium.

[0016] In one specific implementation, the pressure control valve is designed as a pressure-controlled directional control valve that can be controlled and / or switched by the pressure on the pressure side of the pump. In other words, a valve position of the pressure control valve depends on the pressure prevailing on the pressure side of the fluid pump. For this purpose, fluid is preferably pumped by the fluid pump into the pressure chamber or the intermediate chamber until the target pressure set on the pressure control valve is reached. The pressure control valve can be switchable between a blocking position and an open position, with pressure building up in the blocking position and pressure reducing in the open position on the pressure side. Preferably, the pressure control valve is automatically switched from the blocking position to an open position when the specified target pressure or the actuating pressure is reached. In particular, the pressure control valve is designed as a 2 / 2-way valve.Alternatively, the pressure control valve can also have more than two ports and / or more than two switching positions. This provides a hydraulic actuation system in which a virtually "infinite" displacement is available to actuate the slave cylinder. By using a pressure-controlled pressure control valve, any air trapped on the pressure side does not affect the achievement of the target pressure, thus ensuring operational reliability even if the venting is omitted.

[0017] In a specific implementation, it is provided that the pressure control valve is connectable to the fluid source and / or another hydraulic circuit, at least briefly, to reduce excess pressure on the pressure side. In particular, when the actuating pressure is reached, the pressure control valve is switched from the blocked position to the open position in order to discharge an excess quantity of operating medium. In the simplest case, the excess quantity of operating medium can be returned directly to the fluid source. Alternatively, however, the excess quantity of operating medium can be supplied to another hydraulic circuit as required via the pressure control valve. In principle, the additional hydraulic circuit serves to cool and / or lubricate a transmission and / or at least one drive motor of the drive train. Alternatively, or optionally in addition, the additional hydraulic circuit serves to actuate a parking lock, another clutch device or the like.The fluid source can be a sump, a tank, a reservoir, or the like. Thus, an actuation system is proposed that is characterized by a particularly efficient and demand-based supply of operating fluid.

[0018] In a design development, the actuation system is provided with a check valve that blocks in the direction of the pump and is arranged in series between the pump and the slave cylinder to maintain the actuation pressure. In simple terms, the check valve allows flow in only one direction, from the pump to the slave cylinder. When the slave cylinder is actuated, the actuation volume flow is generated, with volume being pumped into the pressure chamber until the actuation pressure is reached and the annular piston is disengaged. The check valve ensures that the actuation pressure, particularly in the disengaged end position of the annular piston, is kept constant even when the pump is at a standstill.Specifically, a drop in actuation pressure due to leakage can be compensated for by the pump, so that the actuation pressure applied to the slave cylinder is kept constant by the pressure control valve. Thus, an actuation system is proposed that is characterized by efficient operation and a cost-effective design.

[0019] According to the invention, the annular housing is accommodated in a housing section, wherein an intermediate space is formed radially between the annular housing and the housing section, which intermediate space runs around the axis of rotation and is fluidically connected to the pressure chamber via at least or exactly one fluid opening formed in the annular housing and to the pressure line via a pressure connection formed in the housing section. In particular, the flow path is formed or co-formed by the pressure connection opening, the intermediate space and the at least one fluid opening. In other words, the pressure chamber can be supplied with fluid from the pump via the pressure connection opening, the intermediate space and the at least one fluid opening. In principle, the annular housing can have exactly one fluid opening, which can be arranged at any position viewed in the circumferential direction.Alternatively, however, the annular housing can also have a plurality of fluid openings which are distributed in the circumferential direction and / or evenly spaced from one another. The at least one fluid opening can be arranged on a radial outer side of the annular housing and / or open radially into the pressure chamber or the intermediate space. For this purpose, the fluid opening can be formed by a bore or the like made radially in the annular housing. The pressure connection can be arranged on a radial outer side of the housing section and / or open radially into the intermediate space. For this purpose, the pressure connection can be formed or co-formed by a bore or the like made radially in the housing section. Particularly preferably, the pressure line is directly connected to the pressure connection. The housing section can be formed by a clutch housing, a transmission housing or a motor housing.Preferably, the intermediate space is bounded in the radial direction by an inner circumference of the housing section and an outer circumference of the annular housing. Thus, a slave cylinder is proposed that can be easily connected to the pressure line. Furthermore, the radially outer intermediate space creates a compensation chamber for at least partial compensation of the operating medium and / or air.

[0020] In a specific embodiment, the pressure connection is arranged essentially on the upper side of the housing section in the intended installation position of the slave cylinder. In particular, the pressure connection can be arranged between a 9 o'clock position and a 3 o'clock position, preferably between an 11 o'clock position and a 1 o'clock position, specifically in a 12 o'clock position, with respect to the rotational axis. The radial connection of the pressure line on the upper side of the annular housing thus ensures that the annular space does not form the highest point of the actuation system, thereby ensuring at least partial or complete filling of the pressure space with fluid.

[0021] Another object of the invention relates to a method for controlling a hydraulic actuation system, as already described above, in which an actuation volume flow for generating an actuation pressure on the pressure side is conveyed from the pump to the pressure chamber along a flow path, wherein the flow path is not vented. In particular, a constant actuation volume flow of at least 3 l / min is provided by the pump. Preferably, the actuation pressure prevailing on the pressure side is limited by the pressure control valve. For this purpose, the pressure control valve is switched from the blocked position to the open position when a target pressure is reached. Particularly preferably, the slave cylinder is actuated when the actuation pressure is reached. For example, the clutch device can be selectively opened or closed when the slave cylinder is actuated.

[0022] Another subject of the invention relates to a drive train for a vehicle, with at least or exactly one drive motor, with at least or exactly one clutch device and with the hydraulic actuation system as already described above. It can be provided that the electric drive motor forms the only traction motor for the vehicle. Alternatively, the vehicle has further traction motors, for example further electric drive motors and / or an internal combustion engine for generating the drive torque. The electric drive motor can be assigned to a single driven wheel of the vehicle and / or be designed as a single-wheel drive. Alternatively, the electric drive motor is assigned to two driven wheels, preferably a common axle, and / or is designed as one electric axle.In other embodiments, the electric drive machine can also be assigned to all driven wheels and / or wheels of the vehicle and / or be designed as an all-wheel drive.

[0023] The clutch device is designed to decouple the drive engine in certain driving situations and / or to disconnect a drive torque path, wherein the hydraulic actuation system, in particular the slave cylinder, is designed and / or suitable for actuating the clutch device. In particular, the clutch device is designed as a separating clutch, which is designed to disconnect the drive torque path downstream of the drive engine. This allows the drive engine to rotate without any drive torque being transferred to the driven wheels.

[0024] Further features, advantages, and effects of the invention will become apparent from the following description of preferred embodiments of the invention. These show: Fig. 1 a schematic representation of a drive train as an embodiment of the invention, Fig. 2 a schematic representation of a hydraulic actuation system for actuating a clutch device; Fig. 3 a diagram with characteristic curves of the actuation time over the actuation volume flow of a slave cylinder according to Fig. 2.

[0025] Fig. 1 shows a drive train 1 for a vehicle, wherein the drive train 1 comprises a drive motor 2 and a further drive motor 3, which is drive-coupled and / or can be coupled via a clutch device 4. The drive motor 2 and the further drive motor 3 can each be designed as an electric machine. Alternatively, the drive motor 2 can also be designed as an internal combustion engine.

[0026] The clutch device 4 is designed as a separating clutch, also called a K0 clutch, for interrupting the drive torque between the two drive motors 2, 3. When the clutch device 4 is closed, a shaft 5, e.g., a crankshaft, of the drive motor 2 is rotationally fixedly coupled to another shaft 6, e.g., a rotor shaft, of the other drive motor 3. When the clutch device 4 is open, they are rotatable relative to each other. For example, the clutch device 4 can be designed as a claw clutch or a multi-disk clutch.

[0027] The drive train 1 also has a transmission device 7, which is connected on the input side to the drive motor 2 or the additional drive motor 3 and on the output side to a differential 8. A torque generated by the drive motor 2 and / or the additional drive motor 3 is transmitted or translated via the transmission device 7 to the differential 8 and thus to the driven wheels 9 of the vehicle. For example, the transmission device 7 can be designed as a dual-clutch transmission.

[0028] Fig. Figure 2 shows a hydraulic actuation system 10, which is designed and / or suitable for actuating the clutch device 4. The actuation system 10 has a concentric slave cylinder 11, abbreviated to CSC, which is arranged or can be arranged coaxially and / or concentrically to the shaft 5 and / or the further shaft 6. The slave cylinder 11 serves to actuate the clutch device 4, wherein the slave cylinder 4 is coupled for movement to an actuating element of the clutch device for this purpose.

[0029] The slave cylinder 11 has an annular housing 12 and an annular piston 13 accommodated in the annular housing 12, which is axially movable relative to the annular housing 11 with respect to a rotational axis 100 of the shaft 5 or the further shaft 6 between an engaged and a disengaged end position 101, 102. The annular housing 12 and the annular piston 13 are arranged coaxially and concentrically with respect to the rotational axis 100.

[0030] In certain driving modes where no drive energy is required, such as coasting, the slave cylinder 11 is actuated to open the clutch device 4. Shaft 5 and the further shaft 6 are thus drive-technically separated from each other, so that no energy is transferred to the wheels 9 and the vehicle continues to roll without actively consuming energy from the battery.

[0031] The annular piston 13 rests radially within the annular housing 12, sealing the pressure chamber 14 axially, so that a pressure chamber 14 is axially delimited or sealed by the annular piston 13. The slave cylinder 11 is hydraulically actuated, wherein the pressure chamber 11 is filled with a hydraulic operating medium, e.g., hydraulic oil, in an operating state. For this purpose, the annular housing 12 has at least one fluid opening 15 on a radial outer side, through which the pressure chamber 14 is supplied with the operating medium.

[0032] The actuation system 10 has a housing section 16 in which the annular housing 12 is at least partially accommodated. An intermediate space 17 is formed radially between the annular housing 12 and the housing section 16, which space 17 surrounds the axis of rotation 100 and is fluidly connected to a pressure line 19 via a pressure connection 18. The pressure connection 18 is arranged essentially on an upper side of the housing section 16, in particular between a 9 o'clock position and a 3 o'clock position. The fluid opening 15 connects the pressure chamber 14 to the intermediate space 17, wherein the fluid opening 15 can in principle be arranged at any location in the circumferential direction. For example, the housing section 16 is designed as a housing of the drive motor 2, the further drive motor 3, or the transmission 7.

[0033] The hydraulic actuation system 10 has a Smart Hydraulic Actuator (SHA), which essentially comprises a pump 20, a pressure control valve 21, and a check valve 22. The pump 20 is fluidly connected to the slave cylinder 11 on a pressure side 23 via the pressure line 19. The pump 20 generates an actuation volume flow 103, which flows along a flow path from the pump 20 via the pressure line 19 and the intermediate space 17 into the pressure chamber 14, thereby increasing the pressure in the pressure chamber 14 and applying an actuation force to the annular piston 13. For this purpose, the pump 20 is connected to a fluid source 26 on a suction side 24 via a suction line 25. For example, the fluid source 26 can be an oil sump.

[0034] The check valve 22 is connected on the pressure side 23 in series with the pump 20 in the pressure line 19, whereby the check valve 22 permits flow toward the slave cylinder 11 and prevents flow toward the pump 20. The check valve 22 serves to maintain the actuating pressure in the slave cylinder 11 when the pump 20 is at a standstill.

[0035] The pressure control valve 21 is connected on the pressure side 23 in parallel to the pump 20, wherein the pressure control valve 21 limits the actuating pressure. For this purpose, the pressure control valve 21 can be switched at least between a blocking position and an open position depending on the actuating pressure on the pressure side 23, wherein a pressure build-up takes place in the blocking position and a pressure reduction takes place in the open position. When the slave cylinder 11 is actuated, the pump 20 delivers the operating medium into the pressure chamber 14 until a predetermined target pressure is reached, wherein the pressure control valve 21 switches at least briefly to the open position upon reaching the target pressure in order to maintain the actuating pressure at a constant pressure level. For this purpose, the pressure control valve 21 can be designed as a pressure-controlled directional control valve, e.g., a 2 / 2-way valve. In principle, the excess amount of operating medium can be fed via the pressure control valve 21 directly to the fluid source 26, as in Fig. 2. Alternatively, the excess amount of operating medium can also be supplied elsewhere, e.g., for cooling and / or lubricating the drive motor 2 and / or the additional drive motor 3 and / or the transmission 7.

[0036] The pump 20 thus provides a virtually "infinite" displacement volume to actuate the slave cylinder 11 and, if necessary, to cool and / or lubricate the drive components. Typically, a vent valve is integrated into the pressure line 19 on the pressure side and / or a venting function is integrated into the slave cylinder 11 to vent any air trapped in the actuation system 10, particularly in the pressure chamber 14. This increases the complexity and cost of the actuation system 10.

[0037] The pump 20 should therefore be dimensioned such that the flow path on the pressure side 23 from the pump 20 to the pressure chamber 14 can be designed without venting, i.e., without a vent valve. For this purpose, the actuating volume flow provided by the pump 20 is so high that any air volume present on the pressure side 23, in particular in the pressure chamber 14, is compressed or compensated within a specified actuation time of, for example, less than 0.2 seconds.

[0038] Fig.Figure 3 shows a diagram in which the actuation time in seconds (ordinate) is plotted against the actuation flow rate in l / min (abscissa). The characteristic curves 104, 105 describe the actuation time as a function of the actuation flow rate for slave cylinders 10 filled with different amounts of air. For example, characteristic curve 104 describes the curve "CSC completely empty = plenty of air" and characteristic curve 105 describes the curve "CSC completely full = no air." As can be seen from the diagram, from an actuation flow rate of approximately > 3 l / min, no significant difference in the actuation times can be seen between the two characteristic curves 104, 105. This means that from an actuation flow rate of 3 l / min, a slave cylinder 10 completely filled with air disengages just as quickly as a completely vented slave cylinder 10.Thus, a vent-free actuation system 10 is proposed, which enables a cost-effective and uncomplicated design and flow path. List of reference symbols 1 drivetrain 2 drive machine 3 additional drive machines 4 Coupling device 5 Wave 6 more waves 7 gearboxes 8 Differential 9 wheels 10 Actuation system 11 slave cylinder 12 ring housings 13 ring pistons 14 Printing room 15 Fluid opening 16 Housing section 17 gap 18 Pressure connection 19 Pressure line 20 pump 21 Pressure control valve 22 Check valve 23 printed pages 24 Suction side 25 Suction line 26 Fluid source 100 axis of rotation 101 engaged end position 102 disengaged end position 103 Actuation volume flow 104 characteristic curve 105 characteristic curve

Claims

[1] Hydraulic actuation system (10) for a vehicle, - with a slave cylinder (11) for actuating a clutch device (4), wherein the slave cylinder (11) has an annular housing (12) and an axially movable annular piston (12) which delimit a pressure chamber (14) which can be filled with an operating medium; - with a pump (20) for generating an actuating volume flow (103) for the slave cylinder (11), which is fluidly connected to the slave cylinder (11) on a pressure side (23) via a pressure line (19); - with a pressure control valve (21) connected in parallel to the pump (20) for limiting an actuating pressure on the pressure side (23); wherein a flow path on the pressure side (23) from the pump (20) to the pressure chamber (13) is designed to be vent-free, characterized byin that the annular housing (12) is accommodated in a housing section (16), wherein an intermediate space (17) is formed radially between the annular housing (12) and the housing section (16) which surrounds the axis of rotation (100) and which is fluidically connected on the one hand to the pressure chamber (14) via at least one fluid opening (15) formed on the annular housing (12) and on the other hand to the pressure line (19) via a pressure connection (18) formed on the housing section (16). [2] Hydraulic actuation system (10) according to claim 1, characterized by that the pump (20) is dimensioned such that, based on the actuating volume flow (102), any air volume on the pressure side (23) is compensated within a specified actuation time. [3] Hydraulic actuation system (10) according to claim 2, characterized bythat the pump (20) is designed to provide a minimum actuating volume flow (102) of at least 3 l / min to generate the actuating pressure. [4] Hydraulic actuation system (10) according to one of the preceding claims, characterized by that the pressure control valve (21) is designed as a pressure-controlled directional control valve which can be controlled and / or switched by the pressure on the pressure side (23) of the pump (20). [5] Hydraulic actuation system (10) according to one of the preceding claims, characterized by that the pressure control valve (21) can be connected at least briefly to a fluid source (26) and / or a further hydraulic circuit in order to reduce an overpressure on the pressure side (23). [6] Hydraulic actuation system (10) according to one of the preceding claims, characterized bythat a check valve (22) blocking in the direction of the pump (20) is arranged in series between the pump (20) and the slave cylinder (11) to maintain the actuating pressure. [7] Hydraulic actuation system (10) according to one of the preceding claims, characterized by that the pressure connection (18) is arranged in a proper installation position essentially on an upper side of the housing section (16). [8] A method for controlling a hydraulic actuation system (10) according to any one of the preceding claims, in which: - an actuating volume flow (103) for generating an actuating pressure on the pressure side (23) is conveyed from the pump (20) to the pressure chamber (14) along a flow path, wherein the flow path is not vented. [9] Drive train (1) for a vehicle, with at least one drive motor (2, 3) for generating a drive torque and with a clutch device (4) for interrupting the drive torque, characterized by a hydraulic actuation system (10) according to one of the preceding claims.

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