Patent GB-461906-A (GB)
Title: Brake control system for vehicles
IPC: B60T8/32
Filed: 1935-08-31
Abstract: 461,906. Vehicle brakes. COMPAGNIE INTERNATIONALE DES FREINS AUTOMATIQUES SOC. ANON. Aug. 31, 1935, Nos. 24392 and 24393. Convention dates, Aug. 31, 1934 and Aug. 5, 1935. [Class 103 (i)] A braking system for vehicles comprises two control members, one being acted upon by a force which depends on the vehicle speed and the other by a force proportional to the pressure of the brake elements on the wheels the members acting to determine the braking pressure and the control system of the one member being such that the relation between the force applied to this member and the speed follows a non-linear law which corresponds to the curve of maximum permissible braking pressure for varying speeds. The system shown in Fig. 1 comprises magnets 8, 9 controlling supply and exhaust valves 7, 6 for the cylinder 2 the piston 2a of which applies the brakes. The speed control device comprises a magnet 13 in the circuit of a dynamo 18 driven from a wheel axle and acting in opposition to a piston 12 subject to the braking pressure, on a switch arm 15. Springs 19, 20 prevent the device from operating below a given braking pressure and speed. Normally with the main switch in position D both magnets 8, 9 are energized so that the valves 6, 7 are held respectively open and closed and the cylinder 2 is exhausted. In position 0, magnet 8 is de-energized, and magnet 9 being insufficient to hold open valve 6, this valve closes, and valve 7 also remains closed. In position F both magnets are de-energized and valve 7 opens to supply the cylinder 2 from the reservoir 4 and apply the brakes. The pressure of the piston 2<a> is transmitted through the pipe 10 to the piston 12. When the brake pressure on the piston 12 reaches a value corresponding to the force of the magnet 13 due to the speed the switch arm 15 closes through contacts 16 the circuit of the magnet 9 thus cutting off the supply to the cylinder 2 and as the speed falls the circuit of magnet 8 is also completed by the switch member 17 thus opening the valve 6 to reduce the braking pressure to the corresponding value. In order that the force exerted by the magnet may correspond to the maximum permissible braking pressure at varying speed, the magnetic circuit of the magnet may have a certain saturation, or the dynamo may be of the compound type with the series winding acting in the same or opposite direction to the shunt winding. In order that the braking pressure may also be reduced as the brake shoes become heated a resistance of for example iron, the resistance of which varies with the temperature and which is embedded in a mass may be included in the circuit of the magnet 13. In the modification shown in Fig. 2, the piston 31 is subject to the pressure in chamber 23 connected to the brake cylinder and to that of the magnet 28 acting against a spring 32. The current in the magnet is due to that of a battery 33 opposed by that of a dynamo 34 driven by an axle of the vehicle. Normally, the switch 35 being in the position shown, the magnet is energized, and a rocking lever 30 on the rod 29 of the magnet holds the supply valve 22 closed, and the exhaust valve 25 open. Movement of the switch 35 by increasing the resistance permits the valve 22 to apply the brake until the cylinder pressure on the piston 31 recloses it so that assuming the voltage of the dynamo not to have varied a predetermined pressure is established in the cylinder for each position of the switch. As the speed falls, however, the current in the magnet increases, and the exhaust valve 25 is opened to reduce the cylinder pressure. The magnet 28 may instead have two windings in the battery and dynamo circuit respectively and acting in opposition. The braking pressure may in addition be caused to vary with the weight of the vehicle either by causing the magnetic field of the dynamo or a resistance in the circuit of the magnet to vary with the weight as by the yielding of the suspension springs of the vehicle.