Patent ID: 8276724

Claim:
A power transmission system for a vehicle changing power transmission state by electric control in which an input shaft and an output shaft coaxially disposed in a main housing is configured such that power is connected/disconnected by a main clutch, the power transmission system for a vehicle comprising: a ball ramp that has an apply plate which axially moves freely to apply axial pressing force to the main clutch and is restricted in rotation with respect to one of the input shaft and the output shaft and a cam which is disposed adjacent to the apply plate with balls therebetween; a pilot clutch that is made of a non-magnetic material and disposed to restrict rotation of a cam of the ball ramp with respect to the other one of the input shaft and the output shaft which is not restricted in rotation with the apply plate, by axial pressing force; a magnetic coil that has a ring shape perpendicular to an axial direction and is fixed in a core member, the core member has a cross section which covers a surface of the magnetic coil facing the pilot clutch and the core member is open to an opposite side and is fixed in the main housing; an armature that is disposed to be axially movable toward the pilot clutch when being attracted by a magnetic force of the magnetic coil; and an apply cylinder that is disposed to be axially movable to transmit axial movement force of the armature to the pilot clutch, wherein the core member and the armature have surfaces facing each other, which have partial slopes.