Transfer Case: Description and Operation

17. AWD TRANSFER SYSTEM





Outline
This is the electronically controlled Multi-Plate Transfer (MP-T) type AWD transfer system, originally designed for SUBARU, consisting of a transfer hydraulic pressure control unit incorporating a vehicle speed sensor, control unit, and duty solenoid and a transfer clutch (hydraulic multi-plate clutch).
The control unit stores optimum transfer clutch torque data for a variety of driving conditions. When actual driving conditions (vehicle speed, detected by various sensors, the control unit from the memory. It then controls the operation of the transfer throttle opening, gear range, wheel slip, etc.) are deselects a duty ratio most suitable to the given condition clutch by means of the hydraulic pressure which controls the duty solenoid and provides optimum rear torque distribution.
Various sensors and the control unit also serve as gear shift control, lock-up control and Hydra pressure control.
The AWD transfer unit is housed in the extension case together with the bearing, rear drive shaft, etc.





Transfer Clutch (Multi-Plate Clutch)
The transfer unit consists of a hydraulic multi-plate clutch and a transfer hydraulic control system incorporating a duty solenoid valve. It is housed in the extension case together with the bearings, rear drive shaft, etc.
The transmission control unit has duty ratios memorized in advance according to running conditions. In order to obtain the optimum transfer torque for the running condition, the oil pressure that is applied to the drive plates and driven plates is controlled by applying oil pressure to the transfer piston from the transfer oil pressure control device including the duty solenoid.
Also, the transfer clutch drum and rear drive shaft are joined to each other by welding. The rear drive shaft has drilled oil passages for transfer clutch control and also for lubrication of extension bushing and ball bearing in it.





Transfer Oil Pressure Control Device
The transfer valve body is bolted to the side of the extension case through two gaskets and one separate plate.
Operating oil for the transfer valve body is routed to the extension case through a pipe connecting the discharge circuit of the oil pump on the front of the transmission case to the rear of the case. It is then delivered to the oil pressure circuit provided in the plane on which the transfer valve body is mounted.
This line pressure is reduced to a fixed level by the pilot valve, and becomes the initial pressure of the duty solenoid C. Line pressure is also delivered to the transfer control valve where it is regulated by duty pressure variations to control the oil pressure so that optimum rear torque distribution is obtained according to running conditions.