GB260967A - Improvements in power actuators or servomotors - Google Patents

Abstract

260,967. Bragg, C. S., and Kliesrath, V. W. Nov. 5, 1925, [Convention date]. Pneumatic relays.-A vacuum servomotor described as operating a brake has a vacuum maintained on both sides of the piston and is connected to the suction pipe by reduced passages of less cross-sectional area than the air or other pressure pipes. A check valve is arranged in the suction pipe connection. The servomotor 1 is connected by a pipe 62 to the intake manifold of an internal-combustion engine, the spring-controlled brake lever 88 being connected to a central valve shaft 20. The piston 3 has valve chambers 11, 12 with oppositely disposed valve seats 13, 14, 15, 16 respectively, and with ports 34, 36 communicating with opposite sides of the piston. A central suction chamber 17 is provided between the chambers 11, 12. The piston rod 5 has an aperture 31 in a cap 8 which permits air to pass to ports 24<a> in the valve shaft, and rod 5<a> has air apertures 31<a>. Conical valves 40 - - 43 . preferably of moulded rubber, which engage and are pressed towards the seats 13 - - 16 by spring washers, are mounted between collars on the shaft 20 which has a central partition 23. The left-hand end of shaft 20 is connected to suction pipe 62. An adjustable collar 21 and the collars 41<a>, 42<a> are so set as to hold the valves 41, 42 slightly off their seats in the end position of the piston, Fig. 3, so as to ensure the presence of a vacuum on both sides of the piston. After the brake has been operated, the slight opening thus provided prevents the delivery of air to the intake manifold of the engine in such quantity as to interfere with the running of the engine. A check valve 65 is arranged on the manifold connection to prevent the throttle 64 affecting the servomotor. On operating the lever 88, valve 42 is closed and valve 41 opened, and air is freely supplied to the right-hand side of the piston to effect its movement. When the operator stops, the piston continues its motion and brings the valves 41, 42 to their slightly-open position. When the brake lever is released and is moved back. wards by the spring 89, the piston is returned by the load on the brake without the admission of air to the left of the piston. When the operator removes his foot from the lever 88, the valveshaft moves faster than the piston, closes valves 41, 53 and opens valve 40 thereby admitting air to return the piston and brake to the off position. The valves again take up the position shown in Fig. 3. Lost motion between the collar 25 on the valve shaft 20 and the cap 8 and collar 26 on rod 5 enables the operator to add his physical force to that of the servomotor, or to operate the brake directly in case of failure of power. In a modification, a valve-like element similar to valve 40 is always closed so that air is never admitted to the left-hand side of the piston. Tn this construction the collar 21 is dispensed with, and the collar and the end of the shaft 20 engage the cap 8 when both inner valves are slightly open. Specification 226,514 is referred to.