Clutch engaging motor with automatic exhaust valve

Claim 1

In a hydraulically actuated clutch mechanism having a clutch drum and a hydraulic piston slidably disposed in said clutch drum and having a head wall member forming with an inner wall member of the clutch drum a hydraulic fluid chamber therebetween, friction clutch means, and spring means urging said piston to return toward its clutch-release position, said piston being adapted to engage with said friction clutch means against said spring means when hydraulic pressure is applied thereto, and being disengaged therefrom when hydraulic pressure is released therefrom by means of the return spring means, the combination therewith of a check valve device disposed in one of said members at an outer part thereof with respect to the rotational axis of the clutch drum and comprising, a passageway including a check valve seat for discharging hydraulic fluid unidirectionally out of said chamber, another spring means, and a check valve biased by said another spring means toward said valve seat and adapted to sealingly engage said valve seat thereby interrupting the fluid flow through said passageway when said piston is in clutch engagement position, said check valve having a projection protruding into said chamber when the check valve is seated and adapted to abut against one of said wall members and be actuated thereby to open the passageway whenever said piston returns to its release position at which said head wall member closely approaches said inner wall member.