GB1144567A - Improvements in and relating to servo motors for vehicle brake systems - Google Patents

Abstract

1,144,567. Brake servomotors; valves. GIRLING Ltd. 29 March, 1966 [30 March, 1965], No. 13345/65. Headings F2F and F2V. A control valve, particularly for a brake servomotor in which reaction or " feel " is applied to the control valve directly by a diaphragm 27 through the action of a deformable deflecting plate 28 such as is described in Specification 1,144,566, may be either manually or hydraulically operated, and comprises a valve seat member 58 including a pair of relatively stationary valve seats 60, 62 respectively circumscribing one and both of two passages in the member 58, and a common valve closure member 84 which is fitted to the deflector plate 28 such that, on deformation of the plate 28, it tilts correspondingly so as to pivot about one of the valve seats and thereby open the passage circumscribed by the other valve seat. In order that the plate 28 should deform in the desired manner, a dished plate 94 is secured on the output rod 92 of the servomotor, which as shown is of the vacuum suspended type, and presents an annular bead 96 at a position radially inward of the centre of pressure of the diaphragm 27 so that when the valve is operated, as shown by movement of a pedaloperated rod 80 acting on a block 74 to push in a stem 50 which carries the head 58, the inner portion of the deflector plate, which is composed of flexibly joined segments, initially moves forward, causing deformation of the deflector plate 28 and hence pivoting of the closure member 84 about the seat 62 to open air passage 106, circumscribed by seat 60, allowing atmospheric air to pass via a filter 78 and passages 75, 102 to passages 104 arranged in a ring between the seats 60 and 62 and hence to the power chamber 24 of the servomotor, but, as pressure builds up in the chamber 24, the deformation of the deflector plate is progressively reduced until the lap position shown (in which it is flat), is reached, a reaction force then being exerted on the stem 50 which is proportioned in accordance with the relative radii of the bead 96 and the centre of pressure of the diaphragm 27. On relaxation of the force applied to move the stem 50 inwardly, deformation of the deflector plate 28 in the opposite direction occurs, causing the closure member 84 to pivot about the seat 60 and open the passages 104 via openings 42 left between the segments of the deflector plate to the vacuum chamber 22, thus restoring the vacuum suspended condition. When the brake is fully released a thickened portion 26 of the diaphragm rests on a reentrant portion of the servomotor casing. The casing is formed of two portions 12, 14 between which the outer periphery of the diaphragm 27 is clamped, the inner periphery of the diaphragm being engaged in a groove in the head 58. Return springs 95 and 98 are provided, and the arrangement is such that on failure of the vacuum supply the head 100 of an extension 88 of the output shaft 92 can be engaged directly by the thrust block 74.