GB884880A - A system of automatically controlling road vehicles - Google Patents

Abstract

884,880. Automatic speed-control systems. GENERAL MOTORS CORPORATION. April 25, 1960 [May 6, 1959], No. 14380/60. Class 38 (4). A system for automatically controlling a road vehicle 12 comprises a generator 14 for developing a command signal voltage, a generator 18 for developing a vehicle speed signal voltage, and two separate conductors 16, 20 in the road connected respectively to the generators. Apparatus on the vehicle is arranged to develop signal pulses corresponding in frequency to the frequencies of the command and speed signal voltages, and to correlate these pulses to produce an output voltage corresponding to the difference between them, a speed control device on the vehicle being adjusted in response to the output voltage. The generator 14 develops a carrier wave keyed or modulated at a frequency corresponding to the command speed, the generator 18 producing an unmodulated carrier wave. The conductor 20 is of criss-cross configuration to afford alternate zones of high and low signal intensities, a winding 24 having a signal voltage induced in it representing the vehicle speed. This signal voltage is transferred through a demodulating circuit 26 to an amplifier 28, differentiator 30, and clipperamplifier 32 producing peaked pulses corresponding in frequency to road speed. These peaked pulses are delivered to counting circuits 34, 36. Signal energy from cable 16 induces in winding 40 a command signal voltage which is applied to demodulator 42 producing squarewave pulses which are increased by amplifier 44 before being impressed on counting circuit 34. An amplifier inverter 46 ensures that the command signal delivered to counting circuit 36 is out of phase with respect to the command signal applied to the circuit 34. A summing circuit 60 adds the outputs from each counting circuit, the combined output voltage being applied to integrator 62 producing a D.C. voltage which is amplified and applied to throttle servo 66, so altering the throttle setting that the road speed is related to the command speed. The counting circuits each comprise a capacitor which is charged by the peaked wave pulses during the off-periods of the square-wave pulses, the charge being erased and the counting circuit reset before any net voltage is developed across the capacitor when the frequencies of the two pulses are equal. If the road speed tends to exceed the command speed, more than one of the peaked wave pulses occur during the interval in which the command signal is off, and the net voltage developed across the capacitor will change the output of a transistor connected to the summing circuit, Fig. 3 (not shown). The throttle opening is then reduced until the vehicle speed corresponds to the command speed. In another arrangement, the throttle setting is adjusted towards a datum value when the road speed either exceeds or is less than the command speed. A stop relay 68 responds when there is a loss of command signal voltage to render the amplifier 64 inoperative and to close the throttle.