Patent GB-1386600-A (GB)
Title: Road vehicles
IPC: B60Q1/44
Filed: 1971-11-15
Abstract: 1386600 Signalling systems; signalling apparatus on vehicles UNITED KINGDOM ATOMIC ENERGY AUTHORITY 14 Feb 1973 [15 Nov 1971] 53002/71 Headings G4F and G4Q A road vehicle having stop-lights includes means responsive to a stop signal given by another vehicle ahead, to operate the stop lights. In one embodiment (not shown) the vehicle has a short-range, directional radio-transmitter which emits a short duration signal when the brake pedal is depressed, and a directional receiver mounted to receive a similar signal from another vehicle ahead. The signal received causes a parallel switch in the brake circuit to close, thereby operating the brake lights. A luminous or audible warning may be given inside the vehicle when the brake lights are so operated. Sensitivity of the receiver may vary with vehicle speed. The radio apparatus may be replaced by ultra-sonic apparatus or infra-red apparatus, or inductive electromagnetic apparatus. In a second embodiment (as shown) the vehicle has forward-mounted red-sensitive and green-sensitive detectors 1, 2 (Fig. 1) connected to amplifiers 3, 4 whose gains are set according to an acceptable colour balance. Differentiating circuits of equal value receive the amplifier outputs; changes in the respective colours give rise to transients across R1 or R2, and a differential amplifier 5 compares the voltages of the transients to produce an output when the red-light voltage is the larger. Diode D1 ensures that a fall in green light level does not produce such an output. The output from the amplifier 5 passes through an AND-gate 7 and delay 8 to a circuit 9 which operates the brakelights. By use of the two detectors, lighting of the brake lights of a vehicle ahead causes operation of the brake lights of the vehicle in question. This arrangement is stated to operate well in the dark or moderate daylight, but for use in normal daylight, a circuit which prevents brake light operation if an increase in red light is not accompanied by a change of colour balance in favour of the red is needed. In the latter case (Fig. 2) red and green light signals pass through logarithmic amplifiers to differentiating circuits which input to a differential amplifier 17. The inputs cancel if the strength of the incident light changes without any change in colour balance. The output from amplifier 17 is connected, as indicated, to the second input of the AND-gate 7 (Fig. 1) so that the latter is not enabled in the circumstance just mentioned. In order to prevent inhibition of the correct operation of the circuit of Fig. 1 at night, in the instance that all lights in the field of view are red, artificial background light is supplied at 18, 19 (Fig. 2). The delay 8 and differential amplifier 6 (Fig. 1) operate to prevent a brake signal being propagated indefinitely back along a line of vehicles all fitted with the apparatus if no driver, other than the first, actually applies the brakes. The delay 8 delays the output to the circuit 9 for an interval after receipt of the signal from the vehicle ahead, while amplifier 6 generates a signal which extinguishes the brake light without delay. A repeater in circuit 9 keeps the brake lights on, once operated, until switched off by amplifier 6. Moreover, an overriding timing circuit 10 ensures the repeater does not hold the brake lights on for more than 0À5 to 1À0 second. When a driver actually applies the brakes, the lights remain on for the duration of application. The differentiating circuits will reject very slow light changes, but where a more critical discernment of the source of change is necessary (i.e. to reject changes not associated with a brake light filament lamp), networks responsive to selected signal rise-times can be used.