Method and system for controlling a transfer case clutch to avoid wheel slip

A method for controlling, with the aid of a digital computer, a clutch that driveably connects an input and an output with varying degrees of clutch engagement, the clutch operating in a vehicle driveline that includes an engine controlled by throttle position, the method comprising the steps of:

• inputting to and executing in the computer a computer readable program code algorithm for operating the clutch partially engaged;
• providing the computer with a data base including at least a first desired clutch engagement that varies with the current throttle position and vehicle speed, and a second desired clutch engagement that varies with a current throttle rate and a current vehicle speed;
• providing a signal in the computer representing the current throttle position, and vehicle speed;
• repetitively determining in the computer at frequent intervals during execution of the algorithm the current throttle rate, the first desired clutch engagement corresponding to the current throttle position and vehicle speed, and the second desired clutch engagement corresponding to the current throttle rate and vehicle speed;
• issuing from the computer a command clutch duty cycle signal representing the greater of the first desired clutch engagement and the second desired clutch engagement;
• and
• changing the degree of clutch engagement in response to the command signal.

In a transfer case, driveably connected to an engine controlled by throttle, a system for controlling a clutch that driveably connects the first output and second output with varying degrees of clutch engagement, comprising:

• means for operating the clutch partially engaged;
• means for determining a current throttle position, throttle rate and vehicle speed;
• means for determining a first desired clutch engagement corresponding to the current throttle position and the current vehicle speed;
• means for determining a second desired clutch engagement corresponding to the current throttle rate and the current vehicle speed;
• means for producing a command clutch duty cycle signal representing the greater of the first desired clutch engagement and the second desired clutch engagement, whereby the degree of clutch engagement is changed in response to the command signal.