Vehicle four-wheel drive apparatus

A vehicle four-wheel drive apparatus comprising:

• a transfer for transmitting a portion of driving force that is output from a drive source to auxiliary drive wheels;
• a propeller shaft that is interposed between the transfer and the auxiliary drive wheels for transmitting a power from the transfer to the auxiliary drive wheels;
• a first connection/disconnection mechanism that is provided in the transfer for selectively connecting or disconnecting the power transmitted to the propeller shaft via the transfer;
• a second connection/disconnection mechanism that is provided between a downstream side of the propeller shaft and the auxiliary drive wheels for selectively connecting or disconnecting the power between the propeller shaft and the auxiliary drive wheels,
• a first thrust force amplification mechanism for switching a connection/disconnection state of the first connection/disconnection mechanism;
• a first control clutch;
• a first actuator;
• a second thrust force amplification mechanism for switching connection/disconnection state of the second connection/disconnection mechanism;
• a second control clutch;
• and
• a second actuator,
• wherein each of the first connection/disconnection mechanism and the second connection/disconnection mechanism has a switching member, the switching member is configured to be movable in an axial direction of a rotation axis so as to obtain a first position at which a power input shaft and a power output shaft that are rotatable around the rotation axis respectively are connected and a second position at which the power input shaft and the power output shaft that are rotatable around the rotation axis respectively are disconnected,
• wherein each of the first thrust force amplification mechanism and the second thrust force amplification mechanism is configured to have a pair of rotary members that is rotatable around the rotation axis, the pair of rotary members is configured to be axially separated by being rotated relative to each other, and one of the pair of rotary members causes the switching member of each connection/disconnection mechanism to move in one direction of the rotation axis,
• wherein a first rotation suppression torque is able to be added to the other one of the pair of rotary members by the first control clutch through the first actuator,
• wherein a second rotation suppression torque is able to be added to the other one of the pair of rotary members by the second control clutch through the second actuator,
• wherein one of the pair of rotary members of each of the first thrust force amplification mechanism and the second thrust force amplification mechanism is connected to a rotary member whose rotating speed is increased in proportion to a vehicle speed in a non-rotatable relatively manner respectively, and
• wherein at least one of the first connection/disconnection mechanism and the second connection/disconnection mechanism is provided with a synchronization mechanism for synchronizing the rotations of the power input shaft and the power output shaft.