GB450697A - Improvements in servo brake mechanism for motor vehicles - Google Patents

Abstract

450,697. Fluid - pressure brakes. JOHNSON, M. E., 134, Ealing Road, Wembley, Middlesex. Feb. 18, 1935, Nos. 5213 and 31545. [Class 103 (i)] In a control valve for servo-brake mechanism comprising an annular space around a reduced portion between a pair of pistons providing communication between the atmosphere port and the servomotor port, a shoulder or taper is provided connecting one piston to the reduced portion whereby the passage through the annular space is gradually restricted and finally shut off as the valve moves to open the port connected to the power source. In Fig. 2, the servomotor port h<1> is normally connected to the atmosphere port i<1> through the annular space c<4> between the two pistons c<5>, c<6> sliding in the casing c<1>. When the valve is moved to apply the brake, a shoulder x of slightly less diameter than the pistons enters the passage c<4> to provide a restricted passage for the inlet of air through the port i<1> as the port g<1> leading to a source of suction begins to be uncovered. With continued movement of the valve the port i<1> is closed by the piston c<5> and the port g<1> is further opened. The intermediate position of the valve in which a restricted entry of air is permitted when the suction port is partly open permits effective graduation of application and release of the braking pressure. The valve may be used in the arrangement shown in Fig. 1, for a vehicle in which the casing c<1> is connected to the pedal a by a member d to which also is attached one end of the bellows e, the other end of which is connected to a lever f, pivoted at f<1>. Lever f is connected also by rod b<1> to the valve c and to the brakes. Depression of the pedal operates the valve to apply the brakes by the bellows and may also apply the brakes mechanically by engagement of a stop v, Fig. 2, on the valve with the casing c<1>. In Fig. 7, the two pistons c', c<8> are connected by a tapered part r and the piston c' has a conical part q which normally closes the suction port g<1>. As shown, the valve is operated by hydraulic pressure acting on a piston k through pipe l against the action of a spring j. When the valve is moved the port g<1> is connected to the servomotor port h<1> and the passage to the atmosphere port i is gradually restricted by the part r and finally closed by the entry of the piston c<7> into the right hand part of the casing. Fig. 6 shows a system in which the valve c<1> shown in Fig. 7, operated by hydraulic pressure produced by a master cylinder n controls servomotors e which apply brake shoes by wedges p, the shoes being applied also by hydraulic cylinders o. The servomotors may however operate separate brake shoes or brakes upon other wheels for example on a trailer vehicle. The valves shown in Figs. 2 and 7 may be modified for operation, by hydraulic pressure and by pullrods respectively. The servomotors may be operated by fluid under pressure instead of suction.