Method for controlling a friction clutch

Abstract

The invention relates to a method for controlling a pressure-dependent actuated friction clutch (17) for a motor vehicle drivetrain, wherein, to close the friction clutch (17), an actuating system (1) applies a system pressure (p) to a slave cylinder (6) controlled between a lower and an upper pressure limit, and a slave cylinder piston (20) is moved along an actuating path (x) to actuate an actuating mechanism (21) of the friction clutch (17), the system pressure (p) is maintained between the lower and upper pressure limits when the friction clutch (17) is closed, and is released to open the friction clutch (17). To check the functionality of the friction clutch (17) and its actuation, a pressure-displacement characteristic curve of the system pressure (p) is recorded over the actuating path (x) during a movement of the slave cylinder piston (20) and compared with a predetermined target characteristic curve.

Description

[0001] The invention relates to a method for controlling a pressure-dependent actuated friction clutch for a drive train of a motor vehicle, wherein, to close the friction clutch, an actuating system applies a system pressure to a slave cylinder controlled between a lower pressure limit and a pressure upper limit, and a slave cylinder piston is moved along an actuating path to actuate an actuating mechanism of the friction clutch, the system pressure is maintained between the lower pressure limit and the pressure upper limit when the friction clutch is closed, and is released to open the friction clutch.

[0002] Devices for actuating a clutch, such as a friction clutch and optionally a parking lock, are known from German patent applications DE 10, 2020 111 970 A1, DE 10 2020 125 334 A1, and DE 10 2021 106 660 A1. An actuating system with a slave cylinder is operated by means of a method stored, for example, in a control unit. A fluid, for example, a hydraulic fluid such as oil, along with the necessary connecting and piping elements, is compressed to a system pressure, thereby axially displacing a slave cylinder piston along an actuating path. The slave cylinder piston acts on an actuating mechanism of the friction clutch and closes it under system pressure.The friction clutch is actuated in a simple and therefore quick pressure-controlled manner. This means that when the system pressure is set between a lower and upper pressure limit, the friction clutch is assumed to be engaged without checking the actuation path. The state of the friction clutch – closed or open – can be verified, for example, by the torque transmission of the friction clutch, the differential speed between the input and output parts, and / or similar parameters.

[0003] The object of the invention is to further develop a method for actuating a friction clutch. In particular, the object of the invention is to be able to detect damage or wear of the friction clutch and / or the actuating system that actuates it.

[0004] The problem is solved by the subject matter of claim 1. The dependent claims describe advantageous embodiments of the subject matter of claim 1.

[0005] The proposed method serves to control a pressure-dependent friction clutch for the drivetrain of a motor vehicle. The drivetrain can be conventionally configured as an internal combustion engine and a downstream transmission with the friction clutch between the engine and the transmission. Preferably, the drivetrain is hybrid or purely electric, with the friction clutch acting as a disconnect clutch between two electric motors or as a separator clutch between a drive unit consisting of an internal combustion engine and an electric motor and another electric motor.The friction clutch is preferably designed for wet operation, wherein a lamellar pack consisting of alternating friction and counter-plates on the input and output sides is axially loaded against a stop by an actuating mechanism, for example, comprising an actuating lever or pot, so that with increasing axial load, a frictional connection is established between the friction and counter-plates by means of the actuating mechanism, thus closing the friction clutch. The actuating mechanism is part of an actuation system, wherein the friction clutch is actuated by pressure control.This means that under system pressure, a slave cylinder piston exerts an axial load on the actuating mechanism, closing the friction clutch. This continues until the system pressure is released, at which point the slave cylinder piston, preloaded by a spring that engages when the friction clutch closes, returns to its pressureless zero position, opening the friction clutch. The system pressure is generated by a pump, which delivers the system pressure to the slave cylinder via a pressure line or similar connection. The system pressure is preferably measured by a pressure sensor located in the pressure line.

[0006] To engage the friction clutch, the pump pressurizes the slave cylinder with the system pressure, which is controlled between a lower and upper pressure limit. This moves the slave cylinder piston along an actuation path, acting on the friction clutch's actuating mechanism. With the friction clutch engaged, the system pressure is maintained between the lower and upper pressure limits. If necessary, the pump will replenish the system pressure if it falls below the lower limit. To disengage the friction clutch, the system pressure is released, for example, by venting the fluid, compressed to the system pressure, into a pressureless sump via a switching valve.

[0007] For example, the actuation system can include a bidirectional pump that supplies at least one vehicle component, in particular the friction clutch, with a fluid for lubrication and cooling in one direction of rotation. When a system pressure is requested or when the existing system pressure drops below the lower pressure limit, the pump reverses its direction of rotation and adjusts the system pressure between the lower and upper pressure limits before reversing its direction of rotation to supply the at least one vehicle component. To open the friction clutch, the system pressure is released, for example, by opening a switching valve located between the slave cylinder and a pressureless sump.To maintain the system pressure at the slave cylinder in an improved manner, a check valve can be arranged between the pump and the slave cylinder, preferably in a section of the system shortly before the slave cylinder, with the switching valve interposed.

[0008] According to an advantageous embodiment of the drive train for implementing the proposed method, the actuating system can, by means of the system pressure, engage a parking lock in addition to the friction clutch via a further slave cylinder, wherein a switching valve is arranged between the slave cylinders. The parking lock can be designed to be displacement-controlled, wherein the system pressure is controlled, for example, by means of the switching valve separating the two slave cylinders, depending on the displacement of the slave cylinder piston actuating the parking lock. The slave cylinder actuating the parking lock can be equipped with a displacement sensor for this purpose.

[0009] To monitor the function of the actuation system, and preferably the function of the friction clutch, over its service life, a pressure-displacement characteristic curve of the system pressure is recorded during a movement of the slave cylinder piston across the actuation stroke and compared with a predefined target characteristic curve. The resulting gradients of the recorded pressure and system pressure across the actuation stroke allow the characteristics of the actuation system and the friction clutch to be determined, and appropriate measures to be taken if necessary. For this purpose, the actuation stroke of the slave cylinder piston and / or the actuation mechanism is continuously monitored. A displacement sensor can be used for this purpose.

[0010] It is taken into account that the continuously recorded pressure-displacement characteristic curve may deviate from the target curve due to factors such as wear, temperature changes, service life, manufacturing tolerances, and / or similar influences. Therefore, only a pressure-displacement characteristic curve exceeding the range-specific parameters is interpreted as a malfunction of the actuation system or the friction clutch when compared to the target curve. The target characteristic curve can be continuously adapted to current operating conditions of the drivetrain, such as its aging, climate, and / or similar factors.

[0011] For example, a comparison of the currently recorded pressure-displacement characteristic with the target characteristic can be determined in at least one section of the actuation path in the form of its slope.

[0012] Preferably, the behavior of the friction clutch is tested and subsequently fault-assessed during clutch engagement. For example, during clutch engagement, as the system pressure increases over the actuation stroke, faulty clutch stiffness can be inferred if the slope of the pressure-displacement characteristic curve deviates significantly from the target stiffness curve. Alternatively or additionally, the shape of the pressure-displacement characteristic curve can be evaluated alongside the stiffness to gain detailed insights into the friction clutch's malfunction, such as stiffness loss, material cracks, fractures of the clutch assembly, deformations, settling processes, and / or similar issues of the actuating components and / or stops, damage to the friction plate assembly, and / or the like.

[0013] For example, a pressure-displacement characteristic curve that is flatter than the target characteristic curve can indicate a faulty stiffness of the friction clutch.

[0014] However, when the friction clutch is opening, the behavior of the actuating system can be checked. For example, if the pressure-displacement characteristic is flatter than the target characteristic, or if its behavior over the actuating travel is unusual, a faulty return movement of the actuating system can be inferred. For example, friction, insufficient preload on the return spring, or a broken spring may cause the slave cylinder to return slowly, the switching valve to the sump may be blocked or malfunctioning, and / or other factors may be responsible for the slowed return of the slave cylinder piston and the kinematically coupled actuating mechanism. A pressure-displacement characteristic that is significantly steeper than the target characteristic may, for example, indicate that the fluid contains air.

[0015] The branches of the pressure-displacement characteristic curve of the closing and opening friction clutch naturally exhibit hysteresis. It follows that the width of this hysteresis can also be used for fault analysis. Furthermore, the continuous analysis of the pressure-displacement characteristic curve can, in addition to monitoring for malfunctions of the friction clutch and the actuation system, also contribute to the development of these components throughout their service life.

[0016] Depending on the detected malfunction and the degree of error, an entry in an error memory, a driver warning, emergency operation of the vehicle and / or deactivation of the vehicle may be initiated.

[0017] The invention is described in relation to the invention described in the Fig. 1 and Fig. The embodiment shown in section 2 is explained in more detail below. These show: Fig. 1 a schematic representation of an actuation system for actuating a friction clutch and a parking lock and Fig. 2 a diagram to illustrate the pressure-displacement characteristic of the actuation system of the Fig. 1 compared to a target characteristic curve.

[0018] The Fig. Figure 1 shows a schematic diagram of the actuating system 1, designed as a hydraulic system, for actuating the friction clutch 17, by means of which the method according to the invention can be carried out, for example. The actuating system 1 includes the pump 2, designed, for example, as a gear pump, which is connected on one side to the coolant line 3 to provide a speed-controlled volume flow of fluid, such as hydraulic fluid. The coolant line 3 supplies fluid, such as oil, to at least one first component 4, designed, for example, as a heat exchanger, the friction clutch 17 for its cooling, and / or the like. The fluid 7 is supplied to this component 4 for the purpose of cooling or lubrication. On the other side, the pump 2 is connected to the pressure line 5. The pressure line 5 serves to supply the slave cylinders 6, 8, the parking lock 9, and the friction clutch 17.The switching valve 10, such as a two-way switching valve, is provided for the selective actuation of the slave cylinders 6, 8.

[0019] Pump 2 is designed as an electrically driven reversible pump to supply fluid 7 in a first direction of rotation to coolant line 3 and in a second direction of rotation to pressure line 5. Pump 2 is driven by electric motor 11, which is controlled by control unit 15. Pump 2, electric motor 11, and power electronics 12 together form an electric pump actuator. Pressure sensor 14 is located in pressure line 5 and is connected to control unit 15 and, via control unit 15, to a higher-level control unit that manages the entire actuation system.

[0020] The switching valve 23, such as a two-way switching valve, serves to reduce pressure in the pressure line 5 and thus to open the friction clutch 17, connecting the slave cylinder 6 to the sump 13.

[0021] The system pressure p in the pressure line is detected by means of the pressure signals from the pressure sensor 14.

[0022] When a system pressure p is applied to the slave cylinder piston 20 of the slave cylinder 6, the slave cylinder piston 20 moves from its depicted zero position along the actuation path x and moves the actuating mechanism 21 to close the friction clutch 17, so that a frictional connection is formed between the input part 18 and the output part 19 of the friction clutch 17. The actuation path x is monitored by the displacement sensor 22, whose displacement signals are acquired and evaluated by the control unit 15. To open the friction clutch 17, the switching valve 23 is opened and the fluid 7 is discharged into the unpressurized sump 13 as the system pressure p is released, whereby the slave cylinder piston 20 is returned to its zero position by means of a return spring (not shown).

[0023] In the control unit 15, pressure-displacement characteristic curves are formed from the detected displacement and pressure signals of the displacement sensor 22 and the pressure sensor 14, particularly during actuation processes of the friction clutch 17, and compared with a target characteristic curve.

[0024] The Fig. Diagram 24 shows a plurality of pressure-displacement characteristic curves 25, determined from the signals of the displacement sensor 22 and the pressure sensor 14 under different operating conditions, which are arranged within the given tolerances around the target characteristic curve 26. The sub-branches 27 are assigned to a closing process and the sub-branches 28 to an opening process of the friction clutch 17 and exhibit the hysteresis 29.

[0025] If, for example, the friction clutch 17 experiences reduced stiffness due to material fatigue or a material crack, the pressure-displacement characteristic curve 30 is significantly flatter compared to the target characteristic curve 26 and also to the mean of the other pressure-displacement characteristic curves 25, so that with appropriate analysis a malfunction of the friction clutch 17 can be detected and appropriate measures such as an entry in a fault memory, a driver warning, emergency operation or a shutdown of the vehicle can be initiated. Reference symbol list 1 Actuation system 2 pumps 3 Coolant line 4 components 5 Pressure line 6 slave cylinders 7 Fluid 8 slave cylinders 9 Parking restrictions 10 switching valve 11 Electric motor 12 Power Electronics 13 Swamp 14 Pressure sensor 15 Control unit 17 Friction clutch 18 Entrance section 19 Initial section 20 slave cylinder pistons 21 Actuation mechanism 22 Position sensor 23 Switching valve 24 Diagram 25 Pressure-Displacement Characteristic Curve 26 Target characteristic curve 27 sub-branch 28 partial branch 29 Hysteresis 30 Pressure-Displacement Characteristic Curve p System pressure x Actuation path QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10, 2020 111 970 A1

[0002] DE 10 2020 125 334 A1

[0002] DE 10 2021 106 660 A1

[0002]

Claims

[1] Method for controlling a pressure-dependent actuated friction clutch (17) for a drive train of a motor vehicle, wherein, to close the friction clutch (17), an actuating system (1) applies a system pressure (p) to a slave cylinder (6) controlled between a lower pressure limit and a pressure upper limit, and a slave cylinder piston (20) is moved along an actuating path (x) to actuate an actuating mechanism (21) of the friction clutch (17), the system pressure (p) is maintained between the lower pressure limit and the pressure upper limit when the friction clutch (17) is closed, and is released to open the friction clutch (17), characterized by , that during a displacement of the slave cylinder piston (20) a pressure-displacement characteristic curve (25, 30) of the system pressure (p) over the actuation distance (x) is recorded and compared with a predetermined target characteristic curve (26). [2] Method according to claim 1, characterized by, that in the comparison a pressure-displacement characteristic curve (30) that goes beyond a range-specific behavior is interpreted as a malfunction. [3] Method according to claim 1 or 2, characterized by , that in at least one path area of ​​the actuation path (x) the slopes of the pressure-displacement characteristic curve (25, 30) and the target characteristic curve (26) are compared. [4] Method according to any one of claims 1 to 3, characterized by , that when the friction clutch (17) closes, the behavior of the friction clutch (17) is checked. [5] Method according to claim 4, characterized by , that if the pressure-displacement characteristic curve (30) is flatter than the target characteristic curve (26), it is concluded that the friction clutch (17) has a faulty stiffness. [6] Method according to any one of claims 1 to 5, characterized by , that when the friction clutch (17) opens, the behavior of the actuating system (1) is checked. [7] Method according to claim 6, characterized by, that if the pressure-displacement characteristic curve is flatter than the target characteristic curve (26), it is concluded that the actuating mechanism (21) has a faulty return movement. [8] Method according to any one of claims 2 to 7, characterized by , that if a malfunction is detected, depending on the degree of error, an entry will be made in an error memory, a driver warning will be issued, an emergency operation of the vehicle and / or a shutdown of the vehicle will be initiated. [9] Method according to any one of claims 1 to 8, characterized by, that the actuating system (1) comprises a bidirectional pump (2) which supplies at least one component (4), in particular the friction clutch (17), with a fluid in one direction of rotation and changes the direction of rotation when a system pressure (p) is requested or when the existing system pressure (p) falls below the lower pressure limit and adjusts the system pressure (p) between the lower pressure limit and the upper pressure limit, wherein a switching valve (23) arranged between the slave cylinder (6) and a pressureless sump (13) is opened to relieve the system pressure (p). [10] Method according to claim 9, characterized by , that the actuating system (1) switches a parking lock (9) by means of the system pressure (p) next to the friction clutch (17) by means of a further slave cylinder (8), wherein a switching valve (10) is arranged between the slave cylinders (6, 8).

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