Patent ID: 6675695
Filing Date: 2004-01-13
Classification: B60T

Abstract:
A pneumatic servomotor for an assisted braking of a motor vehicle having a rigid casing with a transverse partition wall located therein that is movable in an airtight manner between a front chamber and a rear chamber, said front chamber being connected to receive a first pressure corresponding to an engine negative pressure while said rear chamber is selectively connected to said first pressure and a second pressure corresponding to atmospheric pressure; a piston integral with said partition wall that moves with said partition wall, and a control rod that selective moves inside said piston as a function of an axial input force, said control rod exerting an input force in the forward direction against a return force applied to said control rod by a return spring; said control rod being biased towards either an intermediate actuation position or an end actuation position as a function of a rate of speed at which an input force is applied to said control rod; a plunger that is connected to said control rod with a front part located inside said piston, and a three-way valve, including at least an annular seat borne by a rear section of said plunger, said three-way valve varying the second pressure within said rear chamber by connecting said front chamber with said rear chamber when said control rod is in a rest position and gradually connecting said rear chamber with said second pressure in response to an actuation force being applied to said control rod; said plunger having a finger that is slidingly fitted on a front end thereof, said finger when said control rod is in said end actuation position being biased by the plunger into contact with a reaction disk that is integral with said piston, said finger transmitting a reaction force corresponding to an operational force that urges the wall toward the front chamber to the plunger and to the control rod; and a unidirectional clutch device with a coaxial sleeve that slides on said plunger, and axial-locking means that locks said sleeve in an end front axial position such that a front end annular bearing surface of said sleeve locks the finger, independently of said plunger and of said control rod; characterised in that said unidirectional clutch device includes damping means, said damping means being made of an elastomeric material and interposed between a stop-forming transverse intermediate face of said plunger defined by transverse annular front face carried by a shoulder-forming rear section of said plunger and an opposite transverse face of said sleeve, said damping means permitting a noiseless return of said sleeve to its rear rest position once said input force terminates and said locking means no longer lock said sleeve, said sleeve having a tubular shape, with an inner diameter that corresponds to a diameter of a front section of said plunger, and in that said opposite transverse face of said sleeve is formed by said annular rear face of said sleeve whereas a rear face of said rear section bears said rear annular seat of said three-way valve, said elastomeric damping means comprise a ring-type joint that is retained on said annular front face of said shoulder-forming rear section of said plunger, said ring-type joint at least having a rear annular section and a lip-forming truncated-cone-shaped front section with a taper of said truncated-cone-shaped front section being directed backwards therefrom that engages said sleeve to decelerate the speed of said sleeve in returning to a position of rest prior to said sleeve actually bearing against said rear annular section.