OVERSPEED DETECTOR FOR VEHICLE CONTROL SYSTEM
SUMMARY:
The function of the overspeed and motion detector is to allow the vehicle to proceed if its speed is below the authorized speed limit and to envoke irrevocable emergency stopping if the vehicle exceeds the limit or if any circuit in the overspeed and motion detector fails.
The Overspeed detection apparatus described here comprising a pair of high pass filters having inputs governed by actual vehicle speed signals and the outputs of the respective filters in accordance with the actual speed limit inputs. The frequency of the inputs must be above the frequency of the high pass filters.an oscillator generating and check signal having a frequency higher than the frequency of the high pass filters is provided as a checking means. There is also a a switching means for alternately applying the check frequency to the inputs. The two states of operation are defined by either both filters deliver outputs contemporaneously or the case in which one of the filters at a time is delivering an output.

A speed sensor generates a signal indicative of actual vehicle speed in accordance with signals from a tachometer (produces electrical pulses at a rate proportional to the speed of a notched wheel or gear) . the motion detector circuit checks the integrity of the speed sensor. After the vehicle has stopped at a station, the same circuit must show no motion for a period of time before the doors are allowed to open. the speed sensor pulses are proportional to the speed of the vehicle. These pulses after amplification and shaping are fed through a high-pass filter . the speed limit signals received from the demodulator decides the cutoff frequency of the filter. the speed sensor pulses do not pass through the filter If the vehicle is not overspeed.

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