Patent ID: 8490768

Claim:
A multi-plate clutch system, comprising: a clutch outer connected to an input member; a clutch inner connected to an output member; a plurality of driving friction plates engaged with the clutch outer in such a way as to be movable in an axial direction and to be unrotatable relative to the clutch outer; a plurality of driven friction plates interleaved with the driving friction plates, said plurality of driven friction plates being engaged with the clutch inner in such a way as to be movable in the axial direction and to be unrotatable relative to the clutch inner; a pressure plate movable in the axial direction in order to cause the driving friction plates and the driven friction plates to frictionally engage with each other by bringing the driving friction plates and the driven friction plates into pressure contact with each other; a clutch spring for biasing the pressure plate in a direction in which the pressure plate brings the driving friction plates and the driven friction plates into pressure contact with each other; and an assist mechanism configured to increase a pressure-contact force of the pressure plate when acceleration torque is changed, wherein the clutch inner is movable in the axial direction of the output member and the pressure plate is a member different from the clutch inner, and the clutch inner and the pressure plate are connected together to be unrotatable relative to each other and to be capable of being separated from each other in the axial direction in such a way that, when the assist mechanism increases the pressure-contact force of the pressure plate, the pressure plate is moved in a direction to bring the driving friction plates and the driven friction plates into pressure contact with each other while the clutch inner is moved relative to the pressure plate in the same direction in such a way as to be detached from the pressure plate, wherein: the clutch inner includes an engagement cylinder part engaging the driven friction plates with an outer periphery of the engagement cylinder part thereof; an insertion cylinder part coaxially inserted in the engagement cylinder part is provided to the pressure plate; a plurality of groove forming projecting parts in which spline grooves are respectively formed are provided to one of an inner periphery of the engagement cylinder part and an outer periphery of the insertion cylinder part; and a plurality of spline projecting parts engaged with the respective spline grooves are provided to the other of the inner periphery of the engagement cylinder part and the outer periphery of the insertion cylinder part.