Method of determining at least one shift parameter of a vehicle transmission

1. A method for determining at least one shift parameter of a vehicle transmission, the vehicle transmission comprising a first clutching device and a first speed ratio; a second clutching device and a second speed ratio; an input; and an output, wherein the input and the output of the vehicle transmission are connectable by engaging the first clutching device or the second clutching device, the method comprising:

performing a shift by disengaging the first clutching device and/or engaging the second clutching device, wherein the first clutching device stops transferring torque through the vehicle transmission at a first time point, wherein the second clutching device starts transferring torque through the vehicle transmission at a second time point;

determining the at least one shift parameter at the first time point and/or at the second time point;

determining an amount of torque at the input of the vehicle transmission at the first time point and/or the second time point, wherein the at least one shift parameter is a first pressure-torque relationship determined at the first time point and/or a second pressure-torque relationship determined at the second time point, wherein the first pressure-torque relationship is stored in a first look up table and the second pressure-torque relationship is stored in a second look-up table, wherein the at least one shift parameter is a second friction coefficient μ2 of the second clutching device, wherein the second friction coefficient μ2 is based on the second pressure-torque relationship and geometry of the second clutching device and/or wherein the shift parameter is a first friction coefficient μ1 of the first clutching device, wherein the first friction coefficient μ1 is based on the first pressure-torque relationship and geometry of the first clutching device; and

determining the first friction coefficient μ 1 and/or the second friction coefficient μ 2 and comparing the first friction coefficient μ 1 and/or the second friction coefficient μ 2 with a predetermined threshold.

2. The method according to claim 1 , further comprising:

determining a rotational speed of a second input of the second clutching device;

determining a rotational speed of a second output of the second clutching device;

determining a second slip speed of the second clutching device while performing the shift, wherein the second slip speed is a difference between the rotational speed of the second input and the second output;

determining whether the second slip speed falls below or exceeds a second predetermined threshold, the second time point being the time point when the second slip speed falls below or exceeds the second predetermined threshold; and

determining the at least one shift parameter when the second slip speed falls below or exceeds the second predetermined threshold.

3. The method according to claim 1 , further comprising:

determining a rotational speed of a first input of the first clutching device;

determining a rotational speed of a first output of the first clutching device;

determining a first slip speed of the first clutching device while performing the shift, wherein the first slip speed is a difference between the rotational speed of the first input and the first output;

determining whether the first slip speed falls below or exceeds a predetermined threshold, the first time point being the time point when the first slip speed falls below or exceeds a first predetermined threshold; and

determining the at least one shift parameter when the first slip speed falls below or exceeds the first predetermined threshold.

4. The method according to claim 1 , wherein a pressure inside the first clutching device and/or a pressure inside the second clutching device are/is determined at the first time point and/or the second time point.

5. The method of claim 4 , wherein the pressure is determined

by measuring the pressure in the corresponding clutching device by a pressure sensor or

by using a pressure set point of the corresponding clutching device.

6. The method according to claim 1 , wherein a corresponding friction coefficient μ i is determined using the following equation:

μ i =τ i /[( p i −p i,kiss ) R i N i A i ],

where τ i is the amount of torque determined at the corresponding time point, p i is an engagement pressure of the corresponding clutching device, p i,kiss is a relief pressure of the corresponding clutching device, R i is a friction plate radius, A i is a friction plate area, and N i is a number of friction plates of the corresponding clutching device.

7. The method according to claim 6 , comprising:

performing the shift by disengaging the first clutching device and/or engaging the second clutching device;

determining, when performing the shift, the torque and the engagement pressure inside the first clutching device; and

decreasing the pressure inside the first clutching device to a first pressure-level at which the first clutching device stops transferring torque through the transmission, wherein the first pressure-level is based on the pressure-torque relationship of the first look up table determined in a previous shift.

8. The method according to claim 1 , comprising:

performing the shift by disengaging the first clutching device and/or engaging the second clutching device;

determining, when performing the shift, the torque and the pressure inside the second clutching device; and

increasing the pressure inside the second clutching device to a second pressure-level at which the second clutching device starts transferring torque through the transmission, wherein the second pressure-level is based on the pressure-torque relationship of the second look up table determined in a previous shift.

9. The method of claim 8 , wherein the pressure inside the second clutching device is increased to the second pressure-level by executing a feedforward control procedure and/or

after the pressure inside the second clutching device has been increased to the second pressure-level, the pressure inside the second clutching device is further increased by executing a feedback control procedure using the pressure inside the second clutching device as a control variable, a second slip speed as a process variable and a reference slip speed profile as a process variable.

10. The method according to claim 1 , further comprising:

outputting an alert if the first friction coefficient μ 1 and/or the second friction coefficient μ 2 fall below or exceed the predetermined threshold.

11. The method according to claim 1 , wherein the first clutching device and/or the second clutching device are hydraulic clutching devices.

12. The method according to claim 11 , wherein a hydraulic pressure inside the first clutching device and/or a hydraulic pressure inside the second clutching device are/is determined at the first time point and/or the second time point.

13. The method according to claim 11 , wherein the first clutching device is emptied using a predetermined first pressure profile and/or the second clutching device is filled using a predetermined second pressure profile.

14. A transmission controller for controlling the vehicle transmission, wherein the transmission controller is configured to carry out the method according to claim 1 .