Patent GB-967926-A (GB)
Title: Improvements in and relating to speed control systems
IPC: B61L3/22
Filed: 1963-07-23
Abstract: 967, 926. Automatic speed control. GENERAL SIGNAL CORPORATION. July 23, 1963 [Sept. 14, 1962], No. 29110/63. Heading G3R. A signal is communicated to a vehicle over a track, the frequency of the signal being proportional to the desired speed of the vehicle. The output frequency of an oscillator is manually variable for setting the speed, a carrier frequency being modulated by the output of the oscillator and applied to the rails of the track through a transmitter. The reference signal is received on the vehicle through inductance coils and is first amplified and demodulated, and then applied to a lowpass filter which rejects all but the oscillator frequency. The output of the filter is amplified, and is passed to a trigger circuit for converting the signal into a series of square waves whose frequency is the same as that of the input signal. The square-wave output is amplified and differentiated to produce a series of alternate positive and negative pulses applied to a one-shot multivibrator the output of which is a series of equal energy negative voltage pulses, one pulse being produced for each cycle of the oscillator. The series of equal energy pulses are applied to an averaging circuit to provide a D.C. signal over line 30, the magnitude of the voltage of this signal being proportional to the desired vehicle speed. The amplified square wave output is further applied through averaging and trigger circuits to an indicating relay which is energized when a variable frequency signal is being picked-up by the inductance coils on the vehicle. An axle-driven frequency generator produces a sinusoidal output signal whose frequency is proportional to the actual vehicle speed, the amplified sine wave being applied to a trigger shaping circuit for conversion into a series of square wave pulses which are differentiated to provide a train of alternate positive and negative pulses. The positive-going pulses are applied to a reset one-shot multivibrator, the output of which appears as a series of narrow positive-going pulses over line 43 to the base of transistor Q12. One pulse is generated by the reset one-shot multivibrator for each cycle output from the axle-driven generator. A ramp generator circuit comprising transistor Q13 provides a series of ramp voltage pulses for comparison with the voltage on line 30. When transistor Q12 is cut off, capacitor 44 is charged through diode 45, transistor Q13 and resistor 46. Each time a pulse is applied along line 43, transistor Q12 conducts and capacitor 44 is short-circuited. A series of ramp voltage pulses appears at the collector of transistor Q13, the maximum magnitude of which depends upon the time between pulses on the line 43, the magnitude of the ramp pulses being inversely proportional to the actual speed of the vehicle. When the vehicle is over-speed, diode 48 will not conduct. However, if the vehicle is under-speed the magnitude of the ramp pulses exceeds the voltage on line' 30 and the diode 48 conducts to apply a series of clamped ramp pulses to a differentiating circuit 49, 50, resulting in a series of negative pulses appearing at the collector of transistor Q14. These pulses are amplified and differentiated for application to the base of transistor Q16B. Pulses from the reset one-shot multivibrator associated with the axledriven generator are differentiated and applied through line 58 to the base of transistor Q16A in advance of those applied to the transistor Q16B. If the vehicle is over-speed no pulses are applied to transistor Q16B so that relay TVOS is energized, whilst, when differentiated under-speed pulses are applied to the base of transistor Q16B, the relay is de-energized. The relay TVOS controls the throttle-setting of the vehicle to restore the actual speed to the desired value. In addition the brakes of the vehicle may be appliedto decrease the speed when necessary. When the vehicle is not in motion, a negative biasing voltage is applied over wire 58 to the base of transistor Q16A to ensure that the relay TVOS is de-energized.