GB1505804A - Method and apparatus for measuring air pressure in pneumatic tyres - Google Patents

Abstract

1505804 Measuring tyre pressures electrically CONSOLIDATED FREIGHTWAYS Inc 2 March 1976 08302/76 Heading G1N The pressure inside a pneumatic tyre 22, Fig. 3, is monitored by a transducer 20 located internally, comprising a coil on a toroidal, magnetostrictive core forming part of the tuning circuit of an oscillator which receives its power and transmits the measuring signal by inductive couplings. The power supply is derived from an RF oscillator contained in a box 34, Fig. 2, connected to a primary transmitting antenna 36 consisting of a flat coil in the roadway. The RF field produced is picked up by receiving antenna 38 forming part of the pressure sensor unit 21, and rectified to provide power for an oscillator whose frequency is determined by the inductance of element 20, which is varied by the internal tyre pressure acting through a diaphragm 70 on the toroidal core. The electronic components are formed on a semi-conductor wafer surrounded by antenna 38. The measuring signal is fed to secondary transmitting antenna 26 and picked up by receiving antenna 28 consisting of a second flat coil in the roadway, with its axis at 90 degrees to that of antenna 36. After passing through filters the measuring signal is fed to display devices 32. The pressure sensor unit 21 may be bonded to the inner wall of tyre 22, as shown in Fig. 3, embedded in the tyre casing Fig. 8 (not shown), incorporated into a repair plug inserted into the tyre side wall Fig. 7 (not shown), or formed as a freely rotatable sphere inside the tyre Fig. 9 (not shown). The antennae 28, 36 may be segmented and duplicated laterally to facilitate distinguishing between signals from multiple wheel assemblies, and each tyre may produce a coded identification signal. Power for the sensor unit 21 may alternatively be derived from the EMF induced in receiving antenna 38 during rotation as it cuts the flux of a magnet attached to the vehicle, especially for use with radial tyres with metal belts. The receiving antenna 28 may also be attached to the vehicle, and the signals from each tyre may be fed sequentially to display devices 32.