Clutch slave cylinder unit and clutch having the same

Abstract

The invention relates to a clutch slave cylinder unit (1) for actuating a clutch in a powertrain of a motor vehicle, wherein the clutch slave cylinder unit (1) comprises a cylinder (2) and a piston (6) which can be positioned relative to each other therein, wherein the piston and the cylinder form a fluid chamber (9) which can be loaded with a hydraulic fluid to actuate the clutch, wherein the clutch slave cylinder unit (1) comprises a pressure compensation device (12) which causes pressure to be discharged from the fluid chamber (9) when a defined maximum pressure and / or maximum stroke is exceeded. The invention also relates to a clutch having the clutch slave cylinder unit (1).

Description

Technical Field

[0001] The present invention relates to a clutch slave cylinder unit (also commonly referred to as CSC-concentric slave cylinder), which is used to actuate a clutch in a powertrain of a motor vehicle, wherein the clutch slave cylinder unit comprises a cylinder and a piston which can be positioned relative to each other therein, the piston and the cylinder forming a fluid chamber, the fluid chamber being loadable with a hydraulic fluid to actuate the clutch. The present invention also relates to a clutch for a powertrain of a motor vehicle having the clutch slave cylinder unit. Background Art

[0002] Clutch slave cylinder units which are connected to a clutch master cylinder unit via a (hydraulic) line system are known from the prior art. The clutch slave cylinder unit has a piston which can be positioned relative to one another in a cylinder and which closes a fluid chamber in a fluid-tight manner. The fluid chamber of the clutch slave cylinder unit is connected to the fluid chamber of the clutch master cylinder unit via a hydraulic line, so that by a defined stroke of the master piston a defined volume of hydraulic fluid is moved into the fluid chamber of the clutch slave cylinder unit and a defined stroke is caused there, which is used to actuate a clutch which is operatively connected to the clutch slave cylinder unit. It is also mentioned whether the usual CSC application in the field of CRS (clutch release system) is volume-controlled for dry clutches or wet clutches. The significant advantage of such a volume-controlled application is that, based on the functional principle (movement of a defined volume on the system side), overshoot hardly occurs.

[0003] In certain situations, volume-controlled actuation of the clutch slave cylinder unit is undesirable, and an advantageous alternative is to directly load the clutch slave cylinder unit with hydraulic fluid, for example in a wet clutch or a hybrid clutch, by means of a pump. In the case of such loading, the clutch slave cylinder unit is controlled by the pump via a pressure, against which the reaction force of the wet clutch acting on the clutch slave cylinder unit on the clutch side reacts.

[0004] A problem with pressure-controlled clutch slave cylinder units is that pressure overshoots can occur in certain operating states. The consequence of this overshoot is a relative movement of the piston and cylinder of the clutch slave cylinder unit that exceeds the desired and permitted stroke of the clutch slave cylinder unit. In this case, an unconventional actuation of the clutch or even an undefined guidance of the piston in the cylinder can occur, with the consequence of tilting and / or jamming of the piston and / or damage or destruction of the piston-cylinder seal, which can lead to a system failure in the worst case. Summary of the invention

[0005] The object of the present invention is to avoid or at least reduce the disadvantages of the prior art and to prevent unconventional relative movements of the cylinder and the piston of the clutch slave cylinder unit, in particular during pressure-controlled actuation.

[0006] The object of the invention is achieved in such a clutch slave cylinder unit in that the clutch slave cylinder unit has a pressure compensation device which causes pressure to be discharged from the fluid chamber when a defined maximum pressure (in the fluid chamber) and / or a maximum stroke (of the piston-cylinder unit) is exceeded. The object is also achieved by a clutch for a drive train of a motor vehicle having a clutch slave cylinder unit according to the invention.

[0007] The invention advantageously enables pressure-controlled actuation of a clutch or reduces the risk of overshoot and erroneous actuation in volume-controlled clutches and clutch actuation systems, since excessive actuation pressures, for example due to overshoot, which can occur in particular within the scope of rapid control of the unit, can be automatically and from a defined upper limit without requiring relatively complex open-loop or closed-loop control technology solutions for this purpose. The system is particularly robust, reliable and easy to manufacture.

[0008] Advantageous embodiments are claimed hereinafter and are explained below.

[0009] One embodiment of the invention is characterized in that the maximum pressure is greater than or equal to the pressure required for conventional actuation of the clutch, which can also be referred to as the operating pressure, or the maximum stroke is greater than or equal to the stroke required for conventional actuation of the clutch, which can also be referred to as the operating stroke. In normal operation of the clutch slave cylinder unit, the pressure in the fluid chamber is always below the maximum pressure, so that reliable actuation of the clutch is ensured. By correspondingly defining the maximum pressure with a corresponding "safety distance" from the operating pressure, the system can be set very robustly or very finely responsively.

[0010] According to another embodiment, the cylinder of the clutch slave cylinder unit has a cylinder wall, and the piston and the cylinder wall are sealed relative to each other by means of at least one sealing section. The sealing section preferably shields the pressure compensation device from the pressure acting in the fluid chamber when the piston is in the normal operating position, so that the pressure compensation device is only exposed to the hydraulic fluid and its pressure in the event of overpressure, which results in a particularly robust and durable unit.

[0011] It is particularly advantageous if, according to an embodiment, an opening is formed and arranged in the cylinder wall such that, when the stroke required for conventional clutch actuation is exceeded, hydraulic fluid can escape from the fluid chamber. This allows a pressure compensation device that is particularly simple to design, robust and reliable. In particular, such a pressure compensation device allows a response based not only on exceeding a maximum pressure but also on exceeding a maximum stroke and allows the hydraulic fluid to be discharged from the fluid chamber.

[0012] In particular, the opening in the form of at least one groove is formed in the cylinder wall. When the piston is positioned in the maximum stroke, the opening fluidically connects its high-pressure side with its low-pressure side, so that the hydraulic fluid can flow out very easily and over a short path. In addition, such a groove can be easily produced and simultaneously forms a complete flow path from the high-pressure side to the low-pressure side, so that the formation of a separate line can be dispensed with and the device according to the invention can be easily and robustly constructed.

[0013] The groove can extend in particular in the axial direction of the clutch slave cylinder unit, and thus in the direction of movement of the piston in the cylinder. This results in a particularly precise response behavior of the unit, together with a rapid and brief discharge of the hydraulic fluid from the fluid chamber.

[0014] It is particularly advantageous if a plurality of openings are formed in the cylinder wall, which are distributed in the circumferential direction. This ensures that the piston in the cylinder is guided reliably and in a defined manner even when the operating pressure is exceeded and the pressure compensation device responds and the piston is in a maximum stroke position outside its normal position. Furthermore, a uniform pressure drop occurs with respect to the longitudinal axis of the unit according to the invention and the piston geometry, so that tilting of the piston in the cylinder is avoided, which is particularly advantageous for the piston guide and the piston seal.

[0015] According to another embodiment of the clutch, the clutch is designed as a wet clutch or a hybrid clutch. The clutch slave cylinder unit can be arranged in a wet chamber of the clutch or can be fluidically connected to the wet chamber of the clutch in an advantageous manner. In addition, the opening can fluidically connect the fluid chamber of the unit according to the invention and the wet chamber of the clutch to each other when the piston is positioned in the maximum stroke. This allows a particularly simple design of the hydraulic system of the clutch, since, on the one hand, separate hydraulic circuits do not need to be formed for the clutch and, on the other hand, for the piston slave cylinder unit, and separate measures do not need to be taken for intercepting the hydraulic fluid that is discharged from the fluid chamber due to pressure overshoot.

[0016] It is also mentioned that according to the present invention, in order to prevent damage caused by overshoot, an axially extending groove is proposed. In the maximum stroke position of the piston that exceeds the operating stroke, pressure compensation can be achieved via this. By introducing a radially distributed outlet groove or multiple outlet grooves for the hydraulic medium in the housing, the pressure overshoot can be reduced via the groove without exceeding the maximum permissible stroke of the CSC. In normal CSC operation, the operating stroke is reached accordingly. If an overshoot now occurs in the pressure, the piston is further actuated by means of its seal through the pressure increase and passes over the radially arranged outlet groove. If the outlet groove is passed, a pressure drop can occur in the fluid chamber, and the piston is thus not further actuated. As a result, the piston cannot exceed its maximum stroke. For wet dual clutches, especially in hybrid modules, the present invention now makes it possible to control the CSC in a pressure-controlled manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention is explained in more detail below with reference to the accompanying drawings, in which different embodiments are shown. The accompanying drawings show:

[0018] Figure 1 A longitudinal section through the clutch slave cylinder according to the invention is shown in a first operating state;

[0019] Figure 2 A longitudinal section showing the clutch slave cylinder according to the invention in a second operating state; and

[0020] Figure 3 The longitudinal section through the clutch slave cylinder according to the invention is shown in a third operating state. DETAILED DESCRIPTION

[0021] The drawings are only schematic and are only useful for understanding the invention. Identical elements are provided with the same reference numerals.

[0022] Features of individual exemplary embodiments can also be implemented in different exemplary embodiments. Features can therefore be substituted for one another.

[0023] Figure 1 The clutch slave cylinder unit 1 according to the invention is shown in longitudinal section. The clutch slave cylinder unit has a cylinder 2, which has a cylinder bottom 3 and a cylinder wall 4. A piston 6 is arranged in a cylinder chamber 5 surrounded by the cylinder bottom 3 and the cylinder wall 4, and the piston can be relatively positioned in the direction of the longitudinal axis 7 of the clutch slave cylinder unit 1.

[0024] The piston 6 is sealed against the cylinder wall 4 by means of a piston seal 8, so that a fluid chamber 9 sealed by the piston 6 and the piston seal 8 is formed in the cylinder 2. The fluid chamber is connected to a fluid pump not shown in the figure via a fluid channel 10, so that the fluid chamber 9 can be loaded with hydraulic fluid by means of the fluid pump, or hydraulic fluid can be pumped out of the fluid chamber 9 by means of the fluid pump. An operating arm 11 is provided at the end of the piston 6 facing away from the fluid chamber 9, and a clutch not shown in the figure can be indirectly or directly operated via the operating arm.

[0025] In the cylinder wall 4, a plurality of openings 12 are formed in the form of grooves 12, of which only one groove 12 is shown in each case for a better understanding of the drawing. The grooves 12 are distributed uniformly on the cylinder wall in the circumferential direction and, as will be seen from the following description of the other figures, are used to bring about a pressure discharge from the fluid chamber 9 when a defined maximum pressure in the fluid chamber 9 and / or a defined maximum stroke of the piston 6 in the cylinder 2 is exceeded, in the present exemplary embodiment in that the hydraulic fluid can flow out of the fluid chamber 9 via the grooves 12.

[0026] Figure 1The exemplary embodiment of the clutch slave cylinder unit 1 is shown in a non-pressure-loaded state. Here, the piston 6 is in its minimum stroke position 17 relative to the cylinder 2 and the piston seal 8 bears sealingly against the cylinder wall 4 over its entire circumference. In this functional position, the fluid chamber 9 forms a closed, pressure-tight system which is open only to the hydraulic pump via the fluid channel 10. In this functional state, the clutch is in a non-actuated state.

[0027] Figure 2 Show Figure 1 The clutch slave cylinder unit 1 is in the second functional position, in which the fluid chamber 9 is loaded with hydraulic fluid by means of a hydraulic pump. Due to the pressure loading, the piston 6 is in its operating position or operating stroke 15, which represents a position defined for conventional clutch actuation. In this position, the piston seal 8 rests sealingly against the cylinder wall 4 as before, so that the hydraulic pressure present in the fluid chamber 9 is transmitted to the clutch via the actuating arm 11 and actuates the clutch. The force that reacts against the pressure in the fluid chamber 9 is the reset force of the clutch.

[0028] Figure 3 Show Figure 1 and 2 The clutch slave cylinder unit 1 is shown in the figure in the case of a pressure overshoot, in which the pressure in the fluid chamber 9 exceeds the normal pressure for actuating the clutch and reaches a defined maximum pressure. Due to the high pressure in the fluid chamber 9, the piston 6 has continued to be squeezed out of the cylinder chamber 5 to the position of the maximum stroke 16. At this point, the piston 6 has moved so far that the piston seal 8 is positioned on the groove 12. In the area of ​​the groove 12, the piston seal no longer rests sealingly on the cylinder wall 4. Hydraulic fluid at maximum pressure can leak out of the fluid chamber 9 via the groove 12, causing a pressure drop in the fluid chamber 9 as soon as the piston seal moves past the groove 12 and loses its sealing effect. This immediate pressure drop in the fluid chamber 9 occurs in a particularly advantageous manner, so that the piston 6 can move without exceeding the maximum pressure at the moment of the pressure drop. Figure 3 , and reliably avoids overloading or incorrect actuation of the clutch. Figure 3 It is also indicated by arrow 17 that the hydraulic fluid is conducted via groove 12 into outlet channel 13 , which is advantageously connected to a wet chamber of the clutch (not shown in the figure).

[0029] Reference numerals list

[0030] 1 Clutch slave cylinder unit

[0031] 2 cylinders

[0032] 3 Cylinder bottom

[0033] 4 Cylinder wall

[0034] 5 Cylinder Room

[0035] 6 Piston

[0036] 7 longitudinal axis, axial direction

[0037] 8 Piston seal

[0038] 9 Fluid chamber

[0039] 10 Fluid Channel

[0040] 11 Manipulator Arm

[0041] 12 Opening, slot

[0042] 13 Exhaust channel

[0043] 14 Minimum stroke

[0044] 15 operating strokes

[0045] 16 Maximum stroke

[0046] 17 Arrow pointing in the direction of flow

Claims

1. A clutch slave cylinder unit (1) for operating a clutch in a powertrain of a motor vehicle, wherein the clutch slave cylinder unit (1) comprises a cylinder (2) and a piston (6) which can be positioned relative to each other therein, wherein the piston and the cylinder form a fluid chamber (9), wherein the fluid chamber can be loaded with a hydraulic fluid to operate the clutch, and wherein: The clutch slave cylinder unit (1) has a pressure compensation device (12), which causes pressure to be discharged from the fluid chamber (9) when a limited maximum pressure and / or maximum stroke (16) is exceeded. The pressure compensation device is formed and arranged with an opening (12) in the form of at least one groove in the cylinder wall (4), so that when the maximum pressure and / or maximum stroke is exceeded, the hydraulic fluid can escape from the fluid chamber (9) through the groove-shaped opening using a discharge channel between the inner side of the cylinder wall and the outer wall of the piston.

2. The clutch slave cylinder unit (1) according to claim 1, characterized in that: The maximum pressure is greater than or equal to the pressure required for conventional clutch operation, or the maximum stroke (16) is greater than or equal to the stroke (15) required for conventional clutch operation.

3. The clutch slave cylinder unit (1) according to claim 1, characterized in that: The piston (6) and the cylinder wall (4) are sealed relative to one another by means of a sealing section (8).

4. The clutch slave cylinder unit (1) according to claim 1, characterized in that: The opening fluidically connects the high-pressure side of the piston (6) with its low-pressure side when the piston (6) is positioned in the maximum stroke.

5. The clutch slave cylinder unit (1) according to any one of claims 1 to 4, characterized in that: The opening (12) or the groove (12) extends in the axial direction (7) of the clutch slave cylinder unit (1).

6. The clutch slave cylinder unit (1) according to any one of claims 1 to 4, characterized in that: A plurality of openings (12) are formed in the cylinder wall (4), and are distributed in the circumferential direction.

7. A clutch for a drive train of a motor vehicle, comprising a clutch slave cylinder unit (1) according to any one of the preceding claims.

8. The clutch according to claim 7, characterized in that: The clutch is designed as a wet clutch or a mixed clutch, and the clutch slave cylinder unit (1) is arranged in a wet chamber of the clutch and / or is fluidically connected to the wet chamber of the clutch.

9. The clutch according to claim 7 or 8, characterized in that: When the piston (6) is positioned in the maximum stroke, the opening (12) fluidically connects the fluid chamber (9) to the wet chamber of the clutch.

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