1. Field of the Invention
The invention relates to a method for modifying friction clutch engagement characteristics to compensate for clutch wear.
2. Background of the Invention
In a typical powertrain system for road vehicles, such as light-duty trucks and heavy-duty trucks, torque is delivered from the vehicle engine to the torque input side of a multiple-ratio transmission through a friction clutch that is under the control of the vehicle operator. Torque is transmitted from a torque output portion of the transmission through a transmission mainshaft, a driveshaft and a differential-and-axle assembly to vehicle traction wheels. A vehicle operator may change the overall speed ratio of the powertrain by selectively engaging and disengaging clutch elements or brake elements in the transmission as the transmission drive ratio is upshifted and downshifted. To effect an upshift or a downshift, the operator typically will open the friction clutch by relieving a clutch apply spring force to separate an engine driven clutch friction disk and a torque output clutch friction disk. When torque delivery is interrupted in this fashion, ratio changes can occur in the transmission under zero torque conditions.
When the clutch is applied following a ratio upshift or downshift, a power flow path through the clutch is reestablished following a clutch slipping mode. In order to maintain optimum shift quality, a desired calibrated relationship of clutch torque and clutch engagement angle must be maintained during the clutch engagement interval. Although a correct functional relationship of clutch torque and clutch engagement angle can be precalibrated initially, clutch wear, which will inevitably take place due to numerous clutch engagements and disengagements, will result in a change in the functional relationship of clutch torque and engagement angle. Shift quality then may deteriorate and clutch control system failures may occur because of excessive wear. This deterioration of clutch performance due to wear also will affect vehicle launch from a standing start as the vehicle operator engages the clutch friction disks.
Currently, this clutch friction disk wear problem is dealt with by scheduling periodic time-consuming servicing of the vehicle, which results in an increase in overall operating costs and unproductive down-time for the vehicle.