Assistor for reducing stepping force

Claim 1

An assistor comprising: an assistor casing; a push rod disposed in said casing and being freely movable in the axial direction thereof, said push rod having an outside end and an inside end, said outside end being connected to a clutch pedal; a piston disposed within said casing and connected to the inside end of said push rod, said piston dividing said casing into first and second chambers, said first chamber freely communicating with the atmosphere; a first rubber diaphragm securely attached around a peripheral edge of said piston, and having an outer peripheral edge securely fixed to said casing; change-over valve means for switching said second chamber from communication with the atmosphere to communication with a negative pressure source and vice-versa, said change-over valve means including a poppet valve connecting said negative pressure source to said second chamber and a second rubber diaphragm operatively connected to said poppet valve for sealing said second chamber from communication with the atmosphere; and a negative-pressure setting spring and and thus said piston being operatively interlocked with said change-over valve means such that upon the movement of said push rod toward said change-over valve means, said negative pressure source is communicated with said second chamber and the atmosphere is sealed off therefrom.