Clutch with dual pistons and springs

Claim 1

A friction clutch comprising a plurality of frictional clutch plates adapted for being pressed together in an operative position and released in an inoperative position, a piston including first and second relatively displaceable members, a first spring means coupling the clutch plates and the first said displaceable member, means defining a chamber adjacent said piston and into which pressure fluid can be introduced to produce a rise in pressure in said chamber to displace said piston, means providing for advance displacement of the second member of the piston relative to the first member thereof by the pressure of the fluid in the chamber, said second member of the piston being provided with a passageway which is positioned to provide a discharge path for pressure fluid from said chamber after said second member has undergone a given magnitude of relative displacement after initiation of supply of pressure fluid to said chamber, said passageway being initially blocked by said first member of the piston whereby the full pressure of said pressure fluid is initially applied to the piston, the rate of increase of said pressure in the chamber then diminishing upon opening of the passageway after said second member has undergone said given magnitude of relative displacement, and a second spring means acting on the second displaceable member to resist displacement thereof and having a strength different from that of the first spring means to cause the second displaceable member to contact the clutch plates in the advance displacement thereof for reversing the inequality of displacement of the first and second members after said discharge path has been established to cause the passageway to again become blocked and the discharge path closed so that the pressure in the chamber rises abruptly to the full pressure of said pressure fluid and the clutch plates are forceably pressed together by both the first and second members.