Vehicle drive system having first and second operating modes and method of operating same

摘要

A drive system for a vehicle having a set of front wheels and a set of rear wheels drivable from a source of power includes a transfer case having first and second operating states, a front drive mechanism having corresponding first and second operating states and a control system which can be actuated to change the operating mode of the vehicle drive system between a two-wheel drive mode and a four-wheel drive mode by changing the operating states of the transfer case and the drive assembly in proper sequence. The transfer case includes a conventional interaxle differential to permit general vehicle operation in the four-wheel drive mode. The transfer case also includes a chain and sprocket assembly which can be selectively engaged to control the transfer of drive torque to the front wheels. The engagement of the chain and sprocket assembly is controlled by a shiftable clutch collar within the transfer case. The front drive mechanism includes a front axle differential which interconnects a pair of shaft assemblies. One of the shaft assemblies includes an axle shaft having inner and outer sections which are selectively coupled by a second shiftable clutch collar. Both of the clutch collars are shifted by means of vacuum motors which are interconnected to shift the clutch collars in the proper sequence. Actuation of the vacuum motors is under operator control through a vacuum switch. In changing from the two-wheel drive mode to the four-wheel drive mode, the front axle vacuum motor is first actuated to couple the inner and outer sections of the axle shaft, and then the transfer case vacuum motor is actuated to transfer drive torque to the front wheels through the chain and sprocket assembly. The order is reversed in changing from the four-wheel drive mode to the two-wheel drive mode.