METHOD AND APPARATUS FOR ESTIMATING CLUTCH FRICTION COEFFICIENT

1 . A method for determining an estimate transmissibility of a clutch in a vehicle powertrain, comprising:

cutting off fuel supply of an engine driving a first side of the clutch;

setting a clutch pressure between a first side and a second side of the clutch to a positive value at which there is a non-zero difference between an angular accelerations at the first side and the second side of the clutch; and

deriving said estimated transmissibility from a deviation between said non-zero acceleration difference and a second angular acceleration caused by a drag torque of the engine.

2 . The method of claim 1 , wherein the cutting, the setting, and the deriving are carried out while the vehicle is coasting.

3 . The method of claim 2 ,

wherein in the setting, the clutch pressure is gradually reduced to a value at which said non-zero difference is negligibly small but non-zero, and

wherein the deriving, the estimated transmissibility is derived assuming the angular acceleration difference to be zero.

4 . The method of claim 1 , wherein in the setting, the clutch pressure is gradually increased.

5 . The method of claim 4 , wherein the clutch is gradually increased from substantially zero to a pressure at which the difference between angular accelerations at the first side and the second side of the clutch becomes substantially zero.

6 . The method of claim 4 ,

wherein in the deriving, an expected rotation speed of the clutch side is calculated based on an earlier estimated value of the transmissibility and the engine drag moment, and

wherein an updated value of the transmissibility is obtained as a function of said expected rotation speed and an actual rotation speed of the clutch side.

7 . The method of claim 4 , wherein the clutch is placed between the engine and a gearbox of the powertrain and the gradual increase of the clutch pressure is carried out while upshifting the gearbox.

8 . The method of claim 1 , wherein the drag torque of the engine is assumed to be a predetermined function of the engine temperature.

9 . An apparatus for shifting gears in a vehicle powertrain, comprising:

an engine;

a gearbox;

a clutch configured to selectively couple said gearbox to said engine; and

an actuator configured to operate the clutch in which a pressure applied to the clutch during a synchronization of as first side and a second side of the clutch is controlled depending on an estimated transmissibility of the clutch; and

a controller configured to determine the estimated transmissibility of the clutch, the controller configured to:

cut off fuel supply of the engine driving a first side of the clutch;

set a clutch pressure between a first side and a second side of the clutch to a positive value at which there is a non-zero difference between angular accelerations at the first side and the second side of the clutch; and

derive said estimated transmissibility from a deviation between said angular acceleration difference and an angular acceleration caused by a drag torque of the engine.

10 . The apparatus of claim 9 , wherein the pressure applied to the clutch is increased if a decrease of the transmissibility is detected, and/or the pressure applied to the clutch is decreased if an increase of the transmissibility is detected.

11 . The method of claim 9 , wherein a duration of the shifting process is increased if a decrease of the transmissibility is detected.

12 . A vehicle powertrain, comprising:

an engine;

a gearbox;

a clutch configured to selectively couple said gearbox to said engine;

an actuator configured to operate the clutch;

a sensor configured to detect a difference between an angular acceleration at a first side and a second side of the clutch; and

a controller configured to:

generate a control parameter to the actuator;

estimate an estimated transmissibility of the clutch from a deviation between said difference and an angular acceleration caused by a drag torque of the engine.

13 . The vehicle powertrain of claim 12 , wherein the controller is further configured to vary control parameters output to the actuator from one gear shifting process to another depending on the estimated transmissibility.

14 . The apparatus of claim 9 , wherein the pressure applied to the clutch is increased if the pressure applied to the clutch is decreased if an increase of the transmissibility is detected.