METHOD FOR CONTROLLING A CLUTCH UNIT

Abstract

A method for controlling a clutch unit for a drive train of a motor vehicle, wherein the clutch unit comprises a wet-running friction clutch for controllably transmitting torque from an input element to an output element of the clutch unit, wherein the clutch unit comprises oil for cooling the friction clutch, wherein heat inputs which contribute to heating the oil of the clutch unit are calculated, heat outflows which contribute to cooling the oil of the clutch unit are calculated and, as a function of the heat inputs and heat outflows, a maximum admissible clutch torque is calculated, and wherein the current clutch torque of the friction clutch is limited to the maximum admissible clutch torque.

Claims

1. A method for controlling a clutch unit for a drive train of a motor vehicle, wherein the clutch unit comprises a wet-running friction clutch for controllably transmitting torque from an input element to an output element of the clutch unit, wherein the clutch unit comprises oil for cooling the friction clutch, wherein heat inputs which contribute to heating the oil of the clutch unit are calculated, heat outflows which contribute to cooling the oil of the clutch unit are calculated and, as a function of the heat inputs and heat outflows, a maximum admissible clutch torque is calculated, and in that the current clutch torque of the friction clutch is limited to the maximum admissible clutch torque.

2. The method as claimed in claim 1, wherein calculation of the heat inputs which contribute to heating the oil of the clutch unit comprises torque-dependent heat inputs which comprise the current torque of the drive train on the output element side and/or comprises rotational speed-dependent heat inputs which comprise the current rotational speed of the drive train on the output element side.

3. The method as claimed in claim 1, wherein calculation of the heat outflows which contribute to cooling the oil of the clutch unit comprises heat outflows to adjacent components and/or heat outflows to the ambient air.

4. The method as claimed in claim 1, wherein, as a function of the heat inputs and the heat outflows, a limiting clutch torque is calculated, such that on application of the limiting clutch torque to the friction clutch the oil of the clutch unit is no further heated.

5. The method as claimed in claim 1, wherein, as a function of the heat inputs and the heat outflows, a current temperature of the oil of the clutch unit is calculated.

6. The method as claimed in claim 1, wherein the maximum admissible clutch torque is calculated as a function of the limiting clutch torque and/or as a function of the current temperature of the oil of the clutch unit.

7. The method as claimed in claim 1, wherein the maximum admissible clutch torque is calculated by interpolation between the limiting clutch torque and a maximum clutch torque, wherein the interpolation factor is dependent on the current temperature of the oil of the clutch unit.

8. The method as claimed in claim 1, wherein the current torque of the drive train on the output element side, which is used for calculating the heat inputs, is calculated from the current clutch torque.

9. The method as claimed in claim 1, wherein the output element of the clutch unit is a propeller shaft or is connected for rotation to a propeller shaft and torque is controllably transmissible to a secondary axle of the motor vehicle by the clutch unit.

10. The method as claimed in claim 1, further including providing a torque transmission arrangement with an input element, an output element, a clutch unit and a control device, wherein the clutch unit comprises at least one wet-running friction clutch for controllably transmitting torque from the input element to the output element, as well as a casing which contains the friction clutch and oil for cooling the friction clutch.

Description

DRAWINGS

[0027] The drawing described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure.

[0028] FIG. 1 is a schematic representation of a method according to the invention for controlling a clutch unit for a drive train of a motor vehicle.

DESCRIPTION OF THE INVENTION

[0029] FIG. 1 is a diagrammatic representation of a sequence of a method according to the invention for controlling a clutch unit for a drive train of a motor vehicle.

[0030] The clutch unit controlled by this method comprises an oil-cooled friction clutch for variably transmitting torque from an input element to an output element of the clutch unit. The output element of the clutch unit is here connected for rotation to a propeller shaft, such that torque is controllably variably transmissible to a rear axle of the motor vehicle by the clutch unit.

[0031] According to the method, in a step 1, heat inputs which contribute to heating the oil of the clutch unit are firstly calculated. The calculation comprises determining torque-dependent heat inputs as substep 1.1 of step 1 taking account of heat inputs from the current torque of the drive train on the output element side 7. The calculation furthermore takes account of rotational speed-dependent heat inputs, 1.2, making use of the current rotational speed of the drive train on the output element side 8 as the input variable.

[0032] In a step 2, which may proceed in parallel to step 1, heat outflows which contribute to cooling the oil of the clutch unit are calculated. Calculation of the heat outflows 2 which contribute to cooling the oil of the clutch unit comprises taking account of the heat outflows to adjacent components 2.1 and taking account of the heat outflows to the ambient air 2.2. Input variables for calculating the heat outflows are therefore the ambient air temperature 9, and possibly the component temperature of adjacent components 10.

[0033] As a function of the heat inputs 1 and the heat outflows 2, a current temperature of the oil of the clutch unit is calculated in step 6.

[0034] A conclusion as to the current thermal load 11 can be drawn from the current temperature of the oil 6.

[0035] A limiting clutch torque is additionally calculated as a function of the heat inputs 1 and heat outflows 2 in step 5, wherein the limiting clutch torque indicates that clutch torque at which the oil of the clutch unit is no further heated. The sum of the heat flows is therefore equal to zero at the limiting clutch torque.

[0036] As a function of the limiting clutch torque 5 and as a function of the current temperature of the oil of the clutch unit 6 or the thermal load 11 determined therefrom, a maximum admissible clutch torque is calculated in a step 3.

[0037] The maximum admissible clutch torque 3 is in particular calculated by interpolation between the calculated limiting clutch torque 5 and a maximum clutch torque, wherein the interpolation factor is dependent on the current temperature of the oil of the clutch unit 6 or the thermal load 11 determined therefrom.

[0038] The maximum admissible clutch torque 3 is therefore calculated as a function of the heat inputs 1 and the heat outflows 2.

[0039] In ongoing operation, the current clutch torque of the friction clutch, i.e. the torque actually applied to the friction clutch, is then limited, step 4, to the maximum admissible clutch torque determined thereby.

[0040] The current torque of the drive train on the output element side 7, which is used for calculating the heat inputs 1, is calculated in step 12 from the current, now limited, clutch torque of step 4.

LIST OF REFERENCE NUMERALS

[0041] 1 Calculation of heat inputs [0042] 1.1 Torque-dependent heat inputs [0043] 1.2 Rotational speed-dependent heat inputs [0044] 2 Calculation of heat outflows [0045] 2.1 Heat outflows to adjacent components [0046] 2.2 Heat outflows to the ambient air [0047] 3 Calculation of maximum admissible clutch torque [0048] 4 Limitation of current clutch torque [0049] 5 Calculation of limiting clutch torque [0050] 6 Calculation of current temperature of the oil of the clutch unit [0051] 7 Current torque of the drive train on the output element side [0052] 8 Current rotational speed of the drive train on the output element side [0053] 9 Ambient air temperature [0054] 10 Component temperature of adjacent components [0055] 11 Calculation of current thermal load [0056] 12 Calculation of the current torque of the drive train on the output element side