Method for checking the adjustment accuracy of a clutch in a stationary state of an electric or hybrid vehicle

Abstract

A method for checking the adjustment accuracy of a clutch (7, 8) when an electric or hybrid vehicle is stationary, wherein the electric or hybrid vehicle has at least one electric motor (2) and wherein the clutch (7, 8) to be checked is arranged in the force flow between the electric motor (2) and a shaft (5, 6) that can be kept stationary, the method comprising at least the following steps: - keeping the shaft (5, 6) stationary, - setting a defined desired torque at the clutch (7, 8) to be checked, - continuously accelerating the electric motor (2) until the clutch (7, 8) slips for the first time, - comparing the torque achieved at the electric motor (2) with the desired torque set at the clutch (7, 8), or - the method comprising at least the following steps: - keeping the shaft (5, 6) stationary, - accelerating the electric motor (2) to a defined speed, - setting a defined desired torque at the clutch (7, 8) to be checked, - comparing the torque of the electric motor (2) required to maintain a constant speed with the desired torque set at the clutch (7, 8).

Description

Technical Field

[0001] The invention relates to a method for checking the adjustment accuracy of a clutch in a stationary state of an electric or hybrid vehicle, wherein the electric or hybrid vehicle has at least one electric machine and wherein the clutch to be checked is arranged in the force flow between the electric machine and a stationary shaft. Background Art

[0002] Clutches of various types are an essential component in automotive engineering. To ensure their precise function, specifically, high torque accuracy and thus high driving comfort, it is essential to know all of their parameters as accurately as possible throughout the clutch's lifecycle. Multi-plate clutches (friction clutches) are particularly frequently used in modern automotive engineering. For example, multi-plate clutches can be used to transmit torque between the vehicle's drivetrain and transmission. Furthermore, multi-plate clutches can be used, for example, to implement torque vectoring units on at least one axle of the vehicle. Multi-plate clutches, or clutches in general, are typically driven electromechanically, with the torque that the clutch can transmit being calculated from the position of the actuator. If effects occur during the clutch's service life that were not accounted for in this torque calculation—for example, changes in the friction coefficient due to water ingress into the lubricant of a wet clutch or contamination, wear, or temperature effects—these can lead to significant deviations between the desired torque (desired torque) that the clutch should transmit and the torque that the clutch actually transmits (actual torque). This can result in deviations that do not meet the clutch's requirements or even lead to safety-critical conditions. Summary of the Invention

[0003] The object of the present invention is to provide an improved method for checking the adjustment accuracy of a clutch when an electric or hybrid vehicle is stationary.

[0004] This need can be met by a method for checking the control accuracy of a clutch when an electric or hybrid vehicle is stationary, wherein the electric or hybrid vehicle has at least one electric motor and the clutch to be checked is arranged in the force flow between the electric motor and a shaft that can be held stationary, the method comprising at least the following steps: holding the shaft stationary, setting a defined desired torque at the clutch to be checked, continuously accelerating the electric motor until the clutch first slips, and comparing the torque achieved at the electric motor with the desired torque set at the clutch, or the method comprising at least the following steps: holding the shaft stationary, accelerating the electric motor to a defined speed, setting a defined desired torque at the clutch to be checked, and comparing the torque of the electric motor required to maintain a constant speed with the desired torque set at the clutch. Advantageous embodiments of the invention are described in the dependent claims.

[0005] The method according to the present invention for checking the adjustment accuracy of a clutch is used in an electric or hybrid vehicle and is performed while the vehicle is stationary. An electric or hybrid vehicle in which the method according to the present invention can be used has at least one electric motor. The clutch to be checked is arranged in the force flow between the electric motor and a shaft that can be held stationary, i.e., fixed.

[0006] In this context, a clutch is understood to mean a single clutch, for example a multi-plate clutch.

[0007] In this context, an electric or hybrid vehicle at a standstill is understood to mean an electric or hybrid vehicle that is stationary and not moving.

[0008] The method according to the invention can be performed "statically" or "dynamically".

[0009] The "static" variant of the method according to the invention comprises at least the following steps:

[0010] Keep the shaft fixed,

[0011] Set a defined desired torque on the clutch to be checked,

[0012] Continue to accelerate the motor until the clutch slips for the first time.

[0013] The achieved torque of the electric machine is compared with the desired torque predefined at the clutch.

[0014] The "dynamic" variant of the method according to the invention comprises at least the following steps:

[0015] Keep the shaft fixed,

[0016] Accelerate the motor to the specified speed.

[0017] Set a defined desired torque on the clutch to be checked,

[0018] The torque of the electric machine required to maintain a constant rotational speed is compared with the desired torque set at the clutch.

[0019] Preferably, the method is applied to a clutch that is part of a clutch system having at least two clutches, wherein each clutch of the clutch system is checked for its adjustment accuracy with the aid of the method according to the invention, and wherein during the checking of one clutch of the clutch system, at least one other clutch is completely disengaged.

[0020] Disengagement of the clutch is understood to mean complete disconnection of the clutch.

[0021] The method according to the present invention uses precise torque and speed information from the electric motor to check the control accuracy of the clutch. A defined clutch target torque is predefined via the clutch drive and compared with the torque of the electric motor (taking into account the transmission ratio and efficiency). This allows deviations in control accuracy to be identified and appropriate corrective measures to be taken in the software (motor control). Furthermore, changes in the coefficient of friction can be determined, making it possible to detect the ingress of water into the lubricant (oil) of a wet clutch, as this results in a specific change in the coefficient of friction curve.

[0022] In other words, the method according to the present invention makes it possible to check the control accuracy of a clutch using an electric drive without requiring additional components. The method according to the present invention improves clutch control accuracy and enables the detection of faults, particularly water ingress into a lubricant such as oil in a wet clutch. This increases vehicle safety, reduces complaints, and improves vehicle performance through high clutch control accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be described below by way of example with reference to the accompanying drawings.

[0024] Figure 1 A schematic diagram shows a configuration for applying the method according to the invention.

[0025] Figure 2 A schematic diagram of an electric motor vehicle axle with a “torque vectoring” unit is shown.

[0026] Figure 3 Shown in accordance with Figure 2 Schematic flow chart of the method according to the invention using a “torque vectoring” unit of an electric motor vehicle axle as an example. DETAILED DESCRIPTION

[0027] The method according to the invention for checking the adjustment accuracy of a clutch 7, 8 is used in an electric or hybrid vehicle and is performed when the vehicle is stationary. An electric or hybrid vehicle in which the method can be used has at least one electric machine 2, a clutch 7, 8 and a shaft 5, 6 ( Figure 1 ).

[0028] exist Figure 2 The "torque vector control" system 1 is schematically shown in FIG. Figure 2 The method according to the invention is explained using the example of a "torque vectoring" system 1 shown in FIG. However, the method can in principle be used in all systems in which torque can be transmitted via clutches 7, 8 to fixed shafts 5, 6 by means of an electric machine 2. Figure 1 ).

[0029] Therefore, a prerequisite for carrying out the method according to the invention is a drive arrangement in which a drive can be driven by the electric motor 2 as a drive device via the clutch 7 , 8 to be tested to the fixed shaft 5 , 6 .

[0030] exist Figure 2 The "torque vectoring" system 1 shown in FIG. 1 comprises an electric machine 2, which is operatively connected to a motor vehicle axle 4 of an electric or hybrid motor vehicle via a reduction gear 3. The motor vehicle axle 4 can be, for example, the front axle or rear axle of the motor vehicle and has two side shafts 5, 6, namely a first side shaft 5 and a second side shaft 6, each of which is connected to at least one wheel of the motor vehicle.

[0031] A clutch is provided between the reducer 3 and the corresponding sideshaft 5, 6, namely a first clutch 7 between the reducer 3 and the first sideshaft 5 and a second clutch 8 between the reducer 3 and the second sideshaft 6. The two clutches 7, 8 are designed as multi-plate clutches. The first sideshaft 5 and the second sideshaft 6 can both be fixed independently of each other via the service brakes of the vehicle. Therefore, the first sideshaft 5 and the second sideshaft 6 are designed to be fixed. The fixing usually takes place automatically, that is, without the need for intervention by the vehicle driver ( Figure 2 ).

[0032] In order to further illustrate the method, only one of the two clutches 7, 8 of the "torque vectoring" system 1, namely the first clutch 7, is checked. Figure 3 ). The clutch to be checked is therefore the first clutch 7. The second clutch 8 is checked by a similar application of the method adapted for the second clutch 8.

[0033] The method for checking the adjustment accuracy of the first clutch 7 and / or the second clutch 8 can be carried out in two different variants, namely a first variant (“static” variant) and a second variant (“dynamic” variant).

[0034] In a first "static" variant of the method, when the vehicle is parked, the service brake of the first side shaft 5 is automatically actuated, thereby securing the first side shaft. At the same time, the second clutch 8 (the clutch not to be checked) is completely disengaged. The first clutch 7 (the clutch to be checked) is then set to a defined desired torque. In order to determine the torque of the motor 2 until the first slip of the first clutch 7, the torque of the motor 2 is subsequently increased continuously. The torque determined is compared with the desired torque of the first clutch 7, taking into account the transmission ratio and losses of the reducer 3. In this way, deviations ( Figure 2 , Figure 3 ).

[0035] In the "dynamic" second variant of the method, when the vehicle is parked, the service brake of the first side shaft 5 is automatically actuated, thereby securing the first side shaft. At the same time, the second clutch 8 (not the clutch to be checked) is completely disengaged. The motor 2 is then adjusted to a defined speed, which causes a differential in the first clutch 7. The first clutch 7 is then driven towards a defined desired torque. The torque to be expended by the motor 2 in order to keep the defined speed constant is compared with the defined desired torque of the first clutch 7, taking into account the transmission ratio and losses of the reducer 3. Deviations can be determined from the comparison. Via the second variant of the method, the clutch characteristic ( Figure 2 , Figure 3 ).

[0036] From the deviations determined by means of the first and / or second variants of the method, it is possible to estimate at different operating points of the first clutch 7 what causes errors in the control accuracy of the first clutch 7 (e.g. wear, contamination of the lubricant by abrasive particles or water ingress). The torque comparison is performed on the software side via the motor control of the electric motor 2. The software reacts accordingly to the result of the comparison and, for example, adapts the clutch parameters of the first clutch 7 to the "new" situation or outputs a fault message ( Figure 2 , Figure 3 ) However, the comparison can also be performed on the software side via another control unit installed in the motor vehicle, such as an inverter control unit, an actuator control unit, etc.

[0037] The desired torque at the first clutch 7 is set via the actuator unit of the first clutch 7. The actuator unit can be designed, for example, electrically, electromechanically, pneumatically or hydraulically.

[0038] In particular, the detection of water ingress into the lubricant (here, for example, oil) in the wet clutches 7, 8 should be noted. Water in the oil leads to a clear and specific change in the friction coefficient and the friction coefficient variation curve of the clutches 7, 8 with respect to the differential. If the behavior of the clutches 7, 8 (to be checked) in the event of water ingress is known, the method according to the invention can identify the change in the friction coefficient caused by water and also the amount of water in the oil can be estimated. If water ingress has been detected, remedial measures can be taken in order to prevent danger or complaints to the motor vehicle driver and to re-establish the required adjustment accuracy of the clutch system. On the software side, remediation can be achieved by adapting the saved clutch characteristic curves of the clutches 7, 8 to the changed friction coefficient. On the hardware side, one possible remedial measure is an oil change. Another remedial measure concerns the ingress of water. Figure 2 The system shown in FIG. 1 can selectively introduce clutch energy into the respective clutches 7, 8 when the vehicle is parked with the service brake closed. This results in heating of the oil and thus evaporation of the water in the oil. The hot, humid air escapes through the vehicle's ventilator and, after the oil has cooled, is drawn in again as cooler air with a lower water content, thereby reducing the water content in the oil without requiring a stop at the plant. Figure 2 , Figure 3 ).

[0039] Reference Signs List

[0040] 1. "Torque Vectoring" System

[0041] 2 motors

[0042] 3 reducer

[0043] 4 motor vehicle axles

[0044] 5First side axis

[0045] 6 Second side axis

[0046] 7First clutch

[0047] 8 Second clutch

Claims

1. A method for checking the adjustment accuracy of a clutch (7, 8) when an electric or hybrid vehicle is stationary, wherein the electric or hybrid vehicle has at least one electric motor (2) and wherein the clutch (7, 8) to be checked is arranged in the force flow between the electric motor (2) and a shaft (5, 6) that can be held stationary, the method comprising at least the following steps: - keep the shafts (5, 6) stationary, - setting a defined desired torque at the clutch (7, 8) to be checked, - continuously accelerating the motor (2) until the clutch (7, 8) slips for the first time, - comparing the torque achieved at the electric motor (2) with a desired torque preset at the clutch (7, 8), Or the method at least comprises the following steps: - keep the shafts (5, 6) stationary, - accelerating the motor (2) to a defined speed, - setting a defined desired torque at the clutch (7, 8) to be checked, - comparing the torque of the electric machine (2) required to maintain a constant rotational speed with the desired torque set at the clutch (7, 8).

2. The method according to claim 1, characterized in that The clutch (7, 8) is part of a clutch system having at least two clutches (7, 8), wherein each clutch (7, 8) of the clutch system is checked for its adjustment accuracy by means of the method according to claim 1, wherein during the checking of one clutch (7, 8) of the clutch system, at least one other clutch (7, 8) is completely disengaged.

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