GB1375185A - - Google Patents

Abstract

1375185 Pneumatic tyre under-inflation indicating systems J K BOUCHER 29 Aug 1972 [1 June 1971] 18495/71 Heading B7C [Also in Divisions H1 and H3] A system for indicating when the pressure in the tyre of a vehicle wheel falls below a predetermined minimum value comprises an arcuate length 10 of electrically conducting material extending through, or substantially through, 360 degrees and housed in a sleeve 12 of a dielectric material, and a pair of arms 29 each consisting of a length 30 of electrically conducting material housed in a sleeve 32 of a dielectric material, the length 10 being mounted in use to be rotatable with the wheel but being electrically isolated from the wheel when the tyre pressure is above the minimum value, and the arms 29 being mounted on a non-rotatable part of the vehicle such that they are electrostatically screened from one another and be adjacent diametrically opposed regions of the length 10 to be capacity coupled with the regions in order that an electric signal fed to a first of the arms can be transmitted to the second, the system being such that, in use, when the tyre pressure falls to the minimum value the path of the signal from the first arm is altered in such manner that a warning device is actuated. In the embodiment shown in Figs. 1 and 2, the ends of the sleeve 12 are joined by a plastics plug 16 to form a ring and the ring is mounted on a flange 8 provided on the inboard side of the wheel, one end of the length 10 is connected by a wire 18 to earth via a switch (not shown, see Division H1) responsive to the tyre pressure and mounted on a plate 22 on the wheel rim, the arms 29 are mounted on the non-rotatable back plate 26 of the wheel hub, a 20-30 kHz oscillator is connected via a wire 38 to the length 30 of a first of the arms 29, and the length 30 of the second arm is connected by a wire 40 to a warning circuit (see also Division H3) powered by the vehicle battery and including a D.C. amplifier and a warning device in the form of a lamp and/or an audio oscillator. In use, the switch is open when the tyre pressure is above the minimum value so that the signal is transmitted from the first to the second arm and is received by the D.C. amplifier which is biased off by the signal to prevent energization of the warning device, and the switch closes when the tyre pressure falls to the minimum value such that transmission of the signal to the second arm is prevented and the D.C. amplifier is caused to energize the warning device. The sheathing 12, 32 may be made of plastics and the cores 10, 30 may be made of braided copper wire.