Patent GB-425988-A (GB)
Title: Improvements in safety switches for motor vehicles, operable on collision or overturning
IPC: H01H35/14
Filed: 1933-09-21
Abstract: 425,988. Automatic circuit-breakers; gravity and inertia switches. HIRST, J. A., Northgate Works, Chester, and LINWOOD, C., 190, West George Street, Glasgow. Sept. 21, 1933, No. 26045. [Class 38 (v)] [See also Group XXVI] An apparatus for minimizing the risk of fire in road vehicles and aircraft comprises a gravity or inertia switch operable on collision or overturning, connected in the releasing circuit of a circuit-breaker, which when released disconnects the battery, opens the field circuit of the dynamo, and earths the magneto. One general arrangement is shown in Fig. 3, and one embodiment of circuit-breaker and inertia switch is shown in Fig. 7. The circuit-breaker comprises an arm A pivoted at a<1> and held in the latched position shown by a spring-controlled catch F. The arm A carries a contact bridge B which normally connects the battery K to the consuming devices O, such as lights and starter, a second contact bridge C which normally completes the field circuit of the dynamo M, and a third bridge which, on release, earths the magneto N. A plunger f<3> attached to the catch F co-operates with a trip coil f<4> which is connected at one end to the battery K through bridge B. The other end of the coil f<4> is connected to one terminal of a normally open liquid type inertia switch J and to one terminal of a normally open solid type inertia switch J<2>, the other terminals of the inertia switches being connected to earth through a switch H. The coil f<4> is also connected to one terminal of a push button switch H<2>, the other terminal of which is connected to earth. On collision or overturning, one or both of the inertia switches operates to complete the circuit of coil f<4> to release the catch F and allow the switch arm A to move to disconnect the battery, open the field circuit of the dynamo and earth the magneto. The switch A is reset after the inertia switches have been reset, by means of a lever G on the dashboard acting through a Bowden wire g<1> on a lever g<2> which engages a lug on the switch arm A. If it is desired to reset the switch A without opening the flame-proof casing to reset the inertia switches, the switch H is opened. The inertia switches are then only connected to earth through an indicator lamp h<1> which does not carry sufficient current to operate the coil f<4>. The switch A may be opened at any time, such as when parking the vehicle, by closing the switch H<2> to complete the circuit of the coil f<4>. The switch H<2> is connected by a pivoted lever h<2> to the switch H so that operation of the switch H<2> closes the switch H if this has been opened to disconnect the inertia switch temporarily. Any attempt then to close the switch A by means of the lever G, results in the immediate energization of the coil f<4> and again reminds the driver that the inertia switches have not been reset. The solid type inertia switch J<2> comprises a contact bridge urged into the contacting position by a spring, (not shown), and held in the open position by a metal ball j<4> which is displaced by impact but not by tilting to allow the switch to close. The liquid type gravity and inertia switch J is shown in Fig. 7 and comprises a metal casing having at its lower end a metal plug 30 containing a quantity of mercury j<1>. The other pole of the switch is an insulated metal contact j<3>. Mounted beneath the upper contact j<3> is an insulating member 35 forming a narrow annular space 37 which permits contact to be made on considerable impact or tilting, but prevents accidental contact. Splashing of the mercury is accommodated in a recess 38. In a modification, Fig. 5, (not shown), the switch A is held closed by an energized electromagnet, the circuit of which is broken by the operation of the inertia switches. In a modification, the switch H operates to cut out the mercury switch only, so that in the case of aircraft, the switch A will not be released when banking. Specification 361,377 is referred to.