GB1134173A - Abnormal pressure indicator for pneumatic tyres - Google Patents

Abstract

1,134,173. Visible signalling circuits. L.B. SAFETY DEVICES Inc. 9 Feb., 1966 [18 Feb., 1965], No. 5613/66. Heading G4F. [Also in Divisions G1 and H3] Low type pressure on a moving vehicle produces unbalance vibrations which are detected by electromagnetic transducers, one for each wheel, mounted on a stationary part of a respective brake housing, Fig. 1 (not shown). Each transducer 10 (Fig. 2) comprises fixed permanent magnets 28, 30 and a movable magnet 34 suspended by mutual repulsion between them. The magnets are within a coil 36 contained in a housing secured to the brake housing plate and axle assembly. Vibration of a wheel produces relative reciprocating movement of the magnet 34 and a voltage output from the coil 36. The output voltage from each transducer is fed to a respective silicon controlled rectifier switch 64 (Fig. 5) whereby if the amplitude of vibration and hence the voltage is sufficient the rectifier will conduct. A pulsed voltage is produced by a conventional multivibrator 71, or by a unijunction transistor oscillator, Fig. 6, not shown, from the vehicle battery, which produces a flashing light from a warning lamp 20 (one lamp for each wheel) when its associated S.C.R. switch conducts, indicating low pressure in a particular wheel. In an alternative arrangement. Fig. 7 (not shown), the transducer voltage when sufficiently high causes a transistor switch (92) to conduct, causing a current of increasing amplitude to flow from the battery through a transformer primary. A resulting secondary voltage is rectified and charges a capacitor (94). When the capacitor voltage is high enough a neon lamp is ignited. When the current stops increasing the lamp is extinguished, and the flashing rate is a function of the vibration frequency of the transducer 10. The sensitivity of the-apparatus is adjustable so that the lamps are extinguished under normal tyre pressure and speed conditions. Since vibrations due to wheel unbalance, and not attributable to tyre pressure abnormalities, are also detectable and will actuate the warning lamps, the sensitivity adjustment is made after the wheel has been balanced.