GB673940A - Improvements in or relating to theft alarm systems for automobiles - Google Patents

Abstract

673,940. Burglar and like alarms. GRAY, A. R. Sept. 15, 1948. No. 24185/48. Class 118 (i). [Also in Group XIX] A theft alarm for road vehicles comprises a mileage counter adapted tc close alarm contacts upon a predetermined distance being travel led by the vehicle after setting the de vice. A mileage cylinder 11 is slidably carried on a square shaft 12 and its toothed rim 13 is urged out of contact with a gear train 14, 15, 16, 17 by a spring 26. An annular cam surface 20 gradually rises from the rear face of the toothed rim 13 and ends in an abrupt radial step 22. An arm 31 is adapted to engage the cam surface 20 when the cylinder 11 is rotated and move the cylinder so that rim 13 engages the gear wheel 14, spring 34 (acting on the arm 31) being stronger than spring 26. By depressing knob 33 against spring 34 the arm 31 is moved back to allow cylinder 11 to be freely rotated by knob 29 which is set to a chosen mileage by the aid of a scale on plate 70 as in Fig. 5 (not shown). On releasing knob 33 the arm 31 presses on cam 20 to move cylinder 11 into engagement with the gear train and when the vehicle is subsequently moved the cylinder 11 is slowly rotated by a cable drive 18 which may be coupled to the speedometer cable as in Fig. 3 (not shown). When the end 22 of the cam 20 passes the arm 31 the cylinder 11 suddenly moves axially under pressure of spring 26 and disengages rim 13 from the gear train, at the same time bridging alarm contacts 40, 41, by a conductive insert 23 in an insulator portion 24 of the cylinder 11. Contacts 40, 41 close circuits from the vehicle battery to a solenoid Fig. 4 (not shown) which interrupts the ignition circuit and to audible and visible alarms and via a bimetallic thermal flashing device. The device will operate if the vehicle is towed without the engine running, and may be set for a very short distance so that the alarm is given almost immediately the vehicle is moved. Sufficient space is provided between the step 22 and commencement of the cam 20 to allow the cylinder 11 to be set at an "off" position in which the insert 23 is clear of contacts 40, 41 but the rim 13 is not pressed into engagement with the gear train. A reset button for restoration of the ignition circuit is also provided on panel 70 and the device is mounted in a lockable compartment on the dashboard or other convenient position.