GB391890A - Improvements relating to electric trolley bus brakes - Google Patents

Abstract

391,890. Vehicle brakes. SMITHSON, J. G., Oakdale, Alvechurch, Worcestershire. Nov. 25, 1931, No. 32659. [Class 103 (i).] In electrically-propelled road vehicles provided with fluid-pressure brakes for the driven and non-driven wheels and also with electric regenerative or rheostatic braking, the fluidpressure brakes for the driven wheels are automatically cut out when the electric braking exceeds a predetermined value, in order to prevent skidding of the wheels. The brakes for the non-driven wheels may be applied automatically when the electric braking exceeds a given value. In one arrangement, a pedal controls a main valve for admitting compressed air to the fluid-pressure brake system and a rheostat controlling the electric braking. The air supply to the rear wheel brakes is controlled also by the valve device shown in Fig. 2, comprising supply and exhaust valves l, m actuated by a solenoid d in the electric braking circuit through a lever n. Normally the valve l is opened as shown, by the spring p. Pipes s, t, u are connected respectively to the main valve, the rear wheel brake cylinders, and the atmosphere. In braking, the pedal first cuts out resistance in the rheostat and then opens the main valve so that the non- driven front wheel fluid-pressure brakes are applied as well as the electric braking ; if, however, the braking current is above a certain value the solenoid d is actuated to permit the valve l to close and to open the exhaust valve m so that the fluid-pressure brakes for the rear wheels are not applied. When the electric braking current falls to a value sufficient to permit the spring p to overcome the magnetic force on the solenoid core, the valve l is opened to supply the rear brake cylinders until the pressure therein acting upon the piston q is sufficient to restore equilibrium with the valves l, m both closed. Fig. 3 shows an arrangement in which the main valve may be controlled either directly or by the electric braking current. The pipes w, x are connected respectively to the main reservoir and to atmosphere and the pipe y directly to the front wheel brakes and to the supply pipe s of the valve device, Fig. 2, for the rear wheel brakes. The first movement of the pedal a applies the electric brake under the control of the rheostat i and if the braking current is small, the fluid-pressure brakes will not be applied. If, however, the braking current in the solenoid d<1> is sufficient to overcome the spring p<1> the valve l<1> is opened and the front wheel brake cylinders are supplied thereby ; the same current in the solenoid d, Fig. 2, however, closes the valve l so that the rear wheel brakes are not applied. When the pressure in the front wheel brake cylinders acting on the piston q<1> reaches a value dependent upon the braking current the parts of the device shown in Fig. 2 assume a position of equilibrium in which the valves l<1>, m<1> are both closed. Fall of the current causes the valve m<1> to open to reduce the braking pressure correspondingly. By sufficient movement of the pedal the lever n<1> may be actuated directly to admit compressed air to the brake system.