BRAKE BOOSTER WITH ALTERNATE ACTIVATION BY ROTARY ELECTRIC MOTOR

摘要

A vacuum booster for a vehicle brake system provides a working pressure valve seat (141) on a translating valve member (140) axially movable with respect to the air valve body (102), the latter being an input member for operation input to the booster. A rotary electric motor (106) has an output shaft coupled through rotary to linear motion conversion apparatus to move the translating valve member with its working pressure valve seat relative to the air valve body. The motion conversion apparatus preferably includes a screw (148) on the output shaft of the rotary electric motor, an axial nut (150) engaged with the screw for axial movement with rotation of the screw and a radial drive pin (152) engaging the nut with the translating valve member for mutual axial motion. This drive arrangement provides much greater mechanical force than a linear solenoid; and this allows a more straightforward design of the valve arrangement, particularly the use of a high friction seal such as a simple "O"-ring (144) in a groove. In further contrast to a linear solenoid, it further provides positive control of the working pressure valve seat position, mechanical advantage in the motion conversion apparatus and an extended range of travel with constant force throughout the range.