Patent GB-299804-A (GB)
Title: Improvement in brake mechanism
IPC: B60T13/24
Filed: 1928-10-26
Abstract: 299,804. Bragg, C. S., and Kliesrath, V. W. Nov. 1, 1927, [Convention date]. Fluid-pressure.-Control valve mechanism for fluid-pressure brake apparatus comprises a higher pressure valve subject on one face to the variable pressure in the brake cylinder and closed by a spring against the pressure of the source of higher pressure acting on the other face and a lower pressure valve subject to the opposing pressures in the brake cylinder and of the lower pressure source in such a manner that the pressure required to operate both valves gives an indication of the pressure applied by the brake piston. The system shown is one in which vacuum normally subsists on both sides of the piston, atmospheric air or other higher pressure fluid being admitted on one side to apply the brakes. A member 10 secured to the piston 3 forms a chamber 11 which is in permanent communication with the higher pressure source, the atmosphere as shown, by the piston rod 5 and passage 8. The higher pressure valve 14 seats on the member 10. The lower pressure valve 16 which seats on the valve 14 in a chamber 17 formed within this valve is mounted on the sliding rod 20 to which the operating pedal &c. is connected. The rear piston chamber is connected by apertures 13 to the chamber 11<a> of the valve 14 and bv passage 18 to the forward chamber of the valve 16, the rear chamber 17 of which is open at all times by the hollow valve rod 20 and apertures 23 to the forward piston chamber. This chamber is connected to the suction pipe of the vehicle engine by the pipe 24 and normally, as the valve 16 is open the rear piston chamber is also evacuated through the passages 18, 13. The valve 14 is normally seated by a spring 15 the pressure of which is just sufficient to overcome the maximum fiuid pressure difference normally acting on the valve. When the valve rod 20 is pulled to the left to apply the brakes the valve 16 is seated and the valve 14 is opened to admit air through the rod 5 to the rear piston chamber and as the pressure in this chamber and therefore also on the rear face of the valves 14, 16 increases, the pressure that the operator must exert to hold the valves respectively opened and closed increases and indicates to him the pressure acting on the piston 3. If the forward movement of the rod 20 ceases, the piston movement continues until the valve 14 is reseated thus relieving the operator of the pressure of the valve spring 15 while holding the brakes applied. When releasing the brakes the movement of the rod 20 is assisted by the suction acting on the valve 16. Fig. 6 shows a modified construction in which the higher pressure valve 114 is provided with a seat engaging part 114b of smaller diameter, controlling ports 112a between the piston rod 105 and the rear piston chamber. A sliding fit between the valve member 114 and the piston member 110 is obtained by a gasket 114<c>. The chamber 111 is permanently connected to the passage in the piston rod by passages 110<a>. The suction valve 116 seats on a ring 119 secured to the valve 114. In a further construction the higher pressure valve proper is carried by a flexible diaphragm upon which the fluid pressure acts, this diaphragm being secured at its outer edge to the part 110. The cylinder 1 may he connected by pipes to other cylinders not provided with valves for operating brakes on the same or other vehicles. The valve mechanism may be arranged exteriorly of the cylinder being preferably connected between the pedal and the brake mechanism as described in Specification 292,153.