Improvements relating to vehicle warning devices

摘要

987,214. Locating conductive and magnetic bodies. ELECTRIC & MUSICAL INDUSTRIES Ltd. June 30, 1961 [July 5, 1960], No. 23395/60. Heading G1N. [Also in Divisions G4 and H4] In a system for warning a vehicle of the presence of another vehicle ahead (or behind) in the same traffic lane 1-2, two signal paths are provided extending along the traffic lane in the form of transmission lines or, as shown, series of transformer coupled coils M r , M r+1 &c. N r , N r+1 &c. A transmitter on a vehicle injects a signal into the coil M r , M r+1 &c. over which it is located, the signal travelling along the M signal path until it reaches another vehicle in the lane which couples the two paths. The signal is thereby returned along the N path to a receiver on the first vehicle and actuates an indicator. In the direction of traffic flow 3 there is a voltage step up between successive M coils and a voltage step down between successive N coils, thus discriminating between signals from a vehicle ahead and from a vehicle behind. However by reversing these step-up and down arrangements following vehicles may be detected in lieu of vehicles ahead. By choosing appropriate transformation ratios of the coil coupling transformers the amplitude of a received signal may be proportional to the distance between the two vehicles. To cancel the signal produced in a vehicle receiver due to the path coupling effected by the vehicle itself a bucking signal may be provided. Preferably, however, a 30 degreees phase shift is produced between successive coils in the signal paths and the receiver is made phase sensitive thereby also to indicate the distance between the vehicles in question. The M and N sets of coils are arranged at right angles to each other to prevent direct coupling between them. The N coils may be in the road surface and the M coils beside the road so that adjustments between them may be made. When transmission lines are used in lieu of the coils a directional coupler effect can be obtained to discriminate against a following vehicle.