GB970305A - Improvements relating to the testing of vehicle tyre pressures - Google Patents

Abstract

970, 305. Measuring pressure electrically; indicating apparatus. N. LAING. Dec. 29, 1960 [Dec. 29, 1959], No. 44614/60. Headings G1J, G1L and G1W. Apparatus for determining the internal pressure of a tyre 1 comprises means for determining a value dependent on the load on the tyre, means for determining a value dependent on the contact area between the tyre 1 and a base 2 and means for determining the pressure from these values. In one embodiment, Fig. 1, the load is measured by means of a displaceable base 2 connected through a lever 6 piston 9, piston 13 transfer lever 14 and transfer rod 21. The contact area is determined by the fluid displaced from within an elastic pad 25. This displacement operates a piston 28 to displace rod 21. Displacements of rod 21 due to load and contact area measurements are transmitted to a pivoted operating lever 15 to move a displaceable rack 17 to actuate a pointer 20. A dial may be provided, Fig. 7, which is divided into four quadrants and has lines 56, 57 to indicate the highest and lowest permissible pressures for each tyre. Alternatively the contact area value may be determined by a pad of hollow units, Fig. 2, between a resilient layer 44 and a solid base 46. In another embodiment, Fig. 5, the base comprises two condenser plates 32, 33 with a layer of resilient dielectric 34 between them. When a tyre 49 (Fig. 6) is located on the base, the dielectric is compressed and the capacitance increased by an amount approximately proportional to the area of contact, measured by the potential across the plates 32, 33 with constant current. The load is measured at 35 by a piezocrystal 35 or differential transformers 54, and the two signals are combined in a wattmeter-type instrument 40.