Patent GB-814552-A (GB)
Title: Improvements in or relating to devices for receiving and repeating optical signals on automotive vehicles
IPC: B60Q1/50
Filed: 1956-07-18
Abstract: 814,552. Visible signalling between vehicles. CIBIE, L. July 18, 1956 [July 26, 1955], No. 22285/56. Class 118 (2). [Also in Group XXXVII] An arrangement for detecting in a first vehicle the approach of an overtaking vehicle comprises a heat-sensitive switch controlling an electrically operated warning device in the first vehicle and responsive to the heat content of the headlamps of the overtaking vehicle. In all of the described embodiments the closing (or opening) of the normally open (or closed) switch contacts is controlled by a pair of heat-sensitive elements one of which passes through the focal point of a reflectoi mounted at the rear of the first vehicle and the other of which is outside the focal plane so that (in the absence of radiation from an overtaking vehicle and which would be concentrated at the focus) the effects of changes in ambient radiation are neutralized. Fig. 1 shows one embodiment in which the moving contact 3 is carried by a plate 2 pivotally mounted at 4 and constrained to be normally separated from the fixed contact 8 by means of two thermally extensible wires, one of which, 5, passes through the focal point F of a parabolic mirror mounted at the rear of the first vehicle whilst the other, 6, is outside the focal plane so that when light from the head-lamp 11 of an overtaking vehicle is incident on the mirror the resulting heating effect at the focal point being greater than that in the neighbourhood of wire 6 causes wire 5 to extend and allows wire 6 to effect closure of the contacts thus causing a warning lamp 10 to be switched on. Radiation from directions other than along the axis of the parabolic mirror, e.g. ambient radiations which are not concentrated at the focal point, are equally effective on both wires and the switch is not operated. In a second embodiment (Fig. 2) the contacts 14, 16 are carried by respective strips 13, 15 of magnetic material the permeability of which varies with temperature, strip 13, which passes through the focal point of the mirror, being normally held by the attraction of an electromagnet 12 to keep the contacts apart in the absence of heating caused by radiation from an overtaking vehicle. When light from such a vehicle is incident on the mirror the reduction in permeability of strip 13 due to the consequent heating allows it to spring back and so close the contacts, changes in ambient radiation being neutralized since a similar effect is produced on both contact carrying strips. In a further embodiment each contact is carried by a thermally extensible wire one of which passes through the focus of the parabolic mirror and each of which is tensioned by a spring, both springs acting in opposite directions (Fig. 3, not shown). Fig. 4 shows another embodiment in which the moving contact 30 is carried by a blade 29 passing through the focus of the mirror, a further blade 27 being welded to blade 29 and the space between filled by heat-insulating material (e.g. glass wool). The external faces of both blades are blackened so that most of the radiation received along the axis of the mirror is connected into heat which then causes the contacts to close since blade 29 expands more than blade 27, ambient radiation, as before, producing equal and opposite effect on both blades. The blades 27, 29 may be replaced by a sheet of thermally insulating material both faces of which are blackened and one face of which passes through the focus. In a further embodiment (Fig. 5) the moving contact 36 is carried by a pair of blades 34, 37, the latter (which passes through the focus F5 of the mirror) being secured to a fixed piece 35a to which blade 34 is secured by means of a leaf spring 35. Both blades are made of metal having the same thermal coefficient of expansion and to improve the thermal efficiency of the arrangement the surface of the blades may be blackened. In operation the expansion of blade 37 due to radiation received along the mirror axis allows the contacts 36, 38 to close since blade 34 being outside the mirror focus receives less radiation and consequently expands to a lesser extent. In similar manner to the other embodiments ambient radiation is ineffective to produce closure of the contacts. In all embodiments the mirrors may be replaced by lenses disposed on the opposite side of the heat-sensitive elements to that shown.