Abstract: A four-wheel drive vehicle has an engine clutch for transmitting the output of an engine to a transmission having two driving ranges, main drive wheels operatively connected to an output shaft of the transmission, auxiliary drive wheels, and a transfer clutch for transmitting the output of the transmission to the auxiliary drive wheels. A control system is provided with a first detector for detecting whether the engine clutch is in partial engagement state or entire engagement state and for producing a clutch condition signal representing a clutch condition, and a second detector for producing a driving condition signal. The control system responds to the clutch condition signal and to the driving condition signal for controlling torque capacity of the transfer clutch so as to cause the transfer to slip clutch in dependency on the clutch condition.

Abstract: A four-wheel drive vehicle has an engine clutch for transmitting the output of an engine to a transmission, main drive wheels operatively connected to an output shaft of the transmission, auxiliary drive wheels, and a transfer clutch for transmitting the output of the transmission to the auxiliary drive wheels. A control system is provided with a calculator for producing a deceleration signal representing deceleration of the vehicle. A control unit is provided to respond to the deceleration signal for controlling the torque capacity of the transfer clutch so as to increase the torque capacity with increase of the deceleration.

Abstract: A four-wheel drive vehicle has an main clutch for transmitting the output of an engine to a transmission, main drive wheels operatively connected to an output shaft of the transmission, auxiliary drive wheels, and a transfer clutch for transmitting the output of the transmission to the auxiliary drive wheels. A control system is provided with a detector for detecting whether the main clutch is in partial engagement state or entire engagement state and for producing a clutch condition signal representing a clutch condition. The control system responds to the clutch condition signal for controlling torque capacity of the transfer clutch so as to slip the transfer clutch.

Abstract: An air breather structure for oil seals in an automatic transmission having a final reduction device and an automatic transmission device. Each oil seal comprises a pair of sealing members with a space therebetween. A differential case for the final reduction device and an automatic transmission case are coupled at ends thereof interposing a gasket. Two rotating shafts extend across the gasket for transmitting an output of the automatic transmission to front and rear wheels of a vehicle for four-wheel driving. The oil seals are provided around the rotating shafts respectively. Both of the oil seals are located in the automatic transmission case and the space of each oil seal is communicated with the atmosphere through passages including cavities provided in both cases and an opening formed in the gasket and a hole formed in an upper portion of the differential case.