| 摘要 |
An electromagnetic actuator is provided at the outer periphery of and out of contact with a casing of a transmission joint for transmitting torque between two shafts. The electromagnetic actuator produces an electromagnetic field within the joint main body when an exciting current is supplied to a solenoid coil of the actuator. A movable magnetic ring is provided in the casing so as to be movable in the axial direction. The ring is moved in the axial direction by receiving an electromagnetic force induced by the field produced by the electromagnetic actuator. A relief valve connected to the ring is moved over an orifice of a pump, and a spring biasing the relief valve is compressed due to such movement, thereby establishing a relief pressure. When a rotational difference, created by the tires of the vehicle, occurs between the shafts of the joint, and an oil pressure of the pump rises while the joint is in a locked state in which the relief valve closes the orifice, the relief valve is opened, thereby limiting torque transmission to a predetermined value based on the relief pressure. Further, by opening a free valve also associated with the pump, the torque transmitting function of the pump rendered inoperative and a free state (2WD) occurs in which there is no torque transmission. A detecting coil is provided in parallel with the solenoid coil. After the solenoid coil is driven, the current value is changed. A change in magnetic flux according to a magnetic resistance in association with the movement of the movable magnetic ring occurs in the detecting coil. The position of the movable magnetic ring is discriminated from a voltage which is generated in the detecting coil in this instance.
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