Hydraulic power transmission joint

A hydraulic power transmission joint for transmitting torque in response to a rotational-speed difference between input and output shafts capable of relative rotations, said joint comprising:

• a cam housing interposed between said input and output shafts and coupled to one of said shafts, said cam housing being provided with a cam face having two or more raised portions formed on its internal side;
• a rotor coupled to the other of said shafts and rotatably housed in said cam housing, said rotor having a plurality of axially extending plunger chambers;
• a plurality of plungers each reciprocatively accommodated in each of said plurality of plunger chambers under a pressing force of a return spring, said plurality of plungers being operated by said cam face upon said relative rotations of said two shafts;
• an intake/discharge hole formed in said rotor and leading to said plurality of plunger chambers;
• a rotary valve being in rotatable sliding contact with an end face of said rotor, said rotary valve being positioned relative to said rotor in a predetermined relationship, said rotary valve having on its surface a plurality of intake ports and a plurality of discharge ports acting respectively as intake valves and discharge valves depending on a positional relationship relative to said intake/discharge hole;
• an orifice generating a flow resistance as a result of flow of oil discharged by the operation of said plungers;
• and
• a torque characteristic shifting mechanism for changing over torque transmission characteristics in a stepwise manner depending on a rotational-speed difference between said two shafts;
• said torque characteristic shifting mechanism including:
• an accommodation hole formed outside of said discharge ports of said rotary valve;
• a weight member received in said accommodation hole rockably around a center of rotation by the action of a centrifugal force;
• a drain hole for allowing a communication between said accommodation hole and said discharge ports;
• a ball located under said weight member for blocking said drain hole, said ball serving to open said drain hole when said weight member rocks by a centrifugal force;
• and
• a spring for urging the end portion of said weight member opposite to said center of rotation, said spring setting a predetermined rotational-speed difference as a torque characteristic changeover point.