Method and control unit for controlling a friction clutch between an internal combustion engine and a change speed transmission

1. A method for controlling a friction clutch between an internal combustion engine and a change speed transmission, which comprises the steps of:

forming a measure of an average coupling torque;

forming a variable for controlling the friction clutch in dependence on a set point value, the set point value lying between the average coupling torque and periodically occurring peak values being an upper limit of a torque to be transferred by the friction clutch; and

controlling the friction clutch such that a slip of the friction clutch with reduced power transmission being permitted in a case of the periodically occurring peak values of the torque occurring.

2. The method according to claim 1 , which further comprises:

logically combining the average coupling torque with a first correction value to form the set point value for a maximum coupling torque to be transmitted given the average coupling torque.

3. The method according to claim 2 , wherein outside a predetermined range of a rotational speed of the internal combustion engine in which the logical combination with the first correction value takes place, logically combining the average coupling torque with a second correction value to form a further set point value at which periodically occurring peak values of the coupling torque are also transmitted.

4. The method according to claim 2 , which further comprises:

forming a measure of an actually transmitted torque from operating parameters of at least one of the internal combustion engine, the friction clutch and the change speed transmission; and

forming at least one of the set point value and the variable in dependence on the measure.

5. The method according to claim 4 , which further comprises using a first rotational speed on a primary side of the friction clutch and a second rotational speed on a secondary side of the friction clutch as the operating parameters.

6. The method according to claim 5 , which further comprises:

forming an integral of a difference between the first and second rotational speeds resulting in a integral value; and

forming the measure in dependence on the integral value.

7. The method according to claim 6 , which further comprises:

comparing the integral value with an anticipated value for the integral; and

changing the variable such that the friction clutch transmits more torque if the integral is higher than the anticipated value, and transmits less torque if the integral is lower than the anticipated value.

8. A control system for controlling a friction clutch between an internal combustion engine and a change speed transmission, the control system comprising:

a control unit programmed to:

form a measure of an average coupling torque;

form a variable for controlling the friction clutch in dependence on a set point value, the set point value lying between the average coupling torque and periodically occurring peak values as an upper limit of a torque to be transferred by the friction clutch; and

controlling the friction clutch such that a slip of the friction clutch with reduced power transmission being permitted in a case of the periodically occurring peak values of the torque occurring.

9. The control system according to claim 8 , wherein said control unit is programmed to:

logically combine the average coupling torque with a first correction value to form the set point value for a maximum coupling torque to be transmitted given the average coupling torque.

10. The control system according to claim 9 , wherein outside a predetermined range of a rotational speed of the internal combustion engine in which the logical combination with the first correction value takes place, said control unit is programmed to logically combine the average coupling torque with a second correction value to form a further set point value at which periodically occurring peak values of the coupling torque are also transmitted.

11. The control system according to claim 9 , wherein said control unit is programmed to:

form a measure of an actually transmitted torque from operating parameters of at least one of the internal combustion engine, the friction clutch and the change speed transmission; and

form at least one of the set point value and the variable in dependence on the measure.

12. The control system according to claim 11 , wherein said control unit is programmed to use a first rotational speed on a primary side of the friction clutch and a second rotational speed on a secondary side of the friction clutch as the operating parameters.

13. The control system according to claim 12 , wherein said control unit is programmed to:

form an integral of a difference between the first and second rotational speeds resulting in a integral value; and

form the measure in dependence on the integral value.

14. The control system according to claim 13 , wherein said control unit is programmed to:

compare the integral value with an anticipated value for the integral; and

change the variable such that the friction clutch transmits more torque if the integral is higher than the anticipated value, and transmits less torque if the integral is lower than the anticipated value.