| 摘要 |
1,204,266. Automatic speed control. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. Jan.29, 1969 [Feb. 7, 1968], No. 6106/68. Heading G3R. [Also in Division F2] In a wheeled vehicle the braking or tractive effort is reduced upon the occurrence of wheel slide or spin, respectively, due to loss of adhesion the control system being arranged so that the effort is reapplied slightly before full adhesion is regained. A first embodiment controls only the braking effort. An A.C. tachometer generator coupled to a braked axle applies a frequency proportional to wheel speed at terminals 1, 2. This is converted by a Schmitt trigger 5 and diode pump 11-14 to a D.C. voltage X proportional to the speed. The voltage X is applied through a differentiating capacitor 30 to an amplifier 31 which thus delivers an output at 32 dependent on the deceleration of the wheel. When this deceleration exceeds a value pre-set by a potentiometer 40, transistors 36, 37 are triggered to energize an electromagnetic valve 38 to reduce the hydraulic brake pressure. When transistor 37 becomes conducting a transistor 22 is cut off. This greatly increases the time constant of the circuit around capacitor 30 so that it can no longer follow the variation of voltage X but instead discharges (chain line Y of Fig.1) at a constant rate set by a rheostat 25. The amplifier 31 thus continues to receive a constant deceleration signal sufficiently large to maintain the transistor 37 inconduction and hold off the brake. With the braking reduced the wheel begins to accelerate again (point B Fig.1) towards the vehicle speed Z. At a time D the voltage X once again becomes equal to the voltage Y on the capacitor 30 and thereafter capacitor 30 begins to recharge. The input to amplifier 31 is thus reversed (indicating acceleration) and transistor 37 is cut off to restore the braking. In a second embodiment Fig.3 (not shown) parts of the circuit of Fig.2 are repeated to respond to negative values so that tractive effort is reduced if wheel acceleration becomes excessive. In a modification Fig.4 (not shown) the voltage Y on the capacitor 30 is directly compared with the speed voltage X by a differential amplifier 65. This is arranged to restore the braking or tractive effort when X and Y are equal. Means may be provided to restore braking after a predetermined time protecting against failure of the system and to prevent operation of the system at very low speeds e.g. during shunting of railway vehicles. |
