Oliff & Berridge
Hydraulic pressure control device for clutch for controlling drive torque distribution in four wheel drive device
 The hydraulic pressure for operating the two wheel drive/four wheel drive switchover clutch in the part-time type four wheel drive device or the central differential lock-up clutch in the full-time type four wheel drive device is produced by a combination of a pressure regulation valve and two switchover valves to be selectable among several substantially different pressure levels so that the four wheel drive device can be quickly switched over between the complete four wheel operation and the complete two wheel operation, including one or more intermediate half clutched incomplete four wheel operation. 
Toyota Jidosha Kabushiki Kaisha
B Y
B60K Y10T
inventional additional
Nobuyuki Koujiro Shinya Yasuo
Kato Kuramochi Nakamura Houjo