ES350075A1 - Fluid Pressure Servomotor of the Vacuum-Suspended Type, adapted for Superatmospheric Pressure Operation - Google Patents

Abstract

In a fluid pressure servomotor of the vacuumsuspended type for braking systems a housing, consisting of a front shell 10 and a rear shell 12 joined together by a twist lock connection 14, houses at least one plastics pressure differential responsive movable wall 22 reciprocally mounted within the housing and a valve device located within a tubular portion 28 of the movable wall 22 projects outwardly through an opening in the housing, the valve device being operatively connected to an operator-actuated push rod 113 adapted to communicate the interior of the tubular portion to the control chamber side of the movable wall upon actuation of the push rod, the servomotor having means for preventing the interior of the tubular portion from communicating to atmosphere and establishing communication to a source of superatmospheric pressure air via connection 120 an a hollow portion 108 of the push rod. In operation, when the brake pedal is depressed a reaction plunger 72 moves inwardly under the action of the three-part push rod assembly 108, 110 and 113 to close the gap between a head 74 of the plunger and a deformable disc 30. At the same time a valve flange 76 on the movable wall 22 closes off vacuum suspension of the chambers on either side of the wall 22 and a diaphragm 18. Further inward motion of the brake pedal causes further inward motion of the reaction plunger 72 to remove the valve seat, formed on the rear face of reaction plunger 72, from the valve face 86 of the poppet valve to communicate the chamber to the radial passage 166 through the tubular portion 28 to allow super-atmospheric air from a reservoir 122 to create an immediate pressure differential across the wall 22 and the diaphragm 18 to project the force transmitting rod 36 forwardly and pressurize a master cylinder 40 to apply the vehicle brakes 46. Fig. 3 shows an alternative embodiment wherein a cup-shaped structure 152 is secured to the servomotor housing 12b and is connected via a fitting 154 to the source of super-atmospheric pressure air. In this case the push rod 158 is not formed with a hollow connection and a standard valve arrangement 72b is utilized. The push rod 158 is located in the end of the cup-shaped housing 152 through a sealing plate 160 which is arranged to be held between a plate 162 and an inwardly-turned flange 164 of the housing 152 to permit radial movement of the sealing plate 160 to accommodate arcuate action of the push rod 158.