Abstract: A system is provided for indicating excessive wear of brake linings. The system is usable on vehicles such as automobiles, cars, trucks and busses as well as aircraft or other applications where it is desirable to detect excessive wear of brake linings during operation thereof. The system includes an acoustical signal generating device having an air inlet normally closed by the brake lining. When the lining wears away to a minimum safe thickness, the inlet is opened and ambient air flows into the generator to produce an acoustical signal. An acoustical receiver is positioned in spaced operative relation to the brake system and responds to the acoustical signal to provide a warning indication on the dashboard, for example, of the vehicle so that the operator of the vehicle will be alerted to the worn brake condition.

Abstract: A method and apparatus are provided for monitoring tire pressure for motor vehicles, or the like, in which coded sound signals emitted from a wheel-mounted sound signal generator are detected and processed. The coded signal from the generator serves to distinguish the sound signal from background noise. The output of the generator is comprised of at least two coherent frequencies that beat acoustically with one another to produce an amplitude modulated sound signal that is then detected by a transducer which converts the sound signals into the electrical signals. The electrical signals are then fed through the processing circuitry including a detector which extracts the modulation envelope and applies it to an audio band-pass filter. The filter accepts the envelope within a predetermined frequency range, eliminating all signals which are not within the designed band pass. A second detector converts the audio signal to a DC level and feeds it to a threshold comparator.

Abstract: A pressure-responsive signalling valve for use on pneumatic tires is adapted to generate a highly efficient acoustical signal whenever the pressure within the tire falls outside of a predetermined range. The emitted signal is detected by means of an acoustical receiver which, in turn, is coupled to an alarm typically in the form of a warning light or audio device conveniently located within the vehicle to alert the driver. The acoustical valve employs a rolling or flat seal disc diaphragm and a flat sealing arrangement providing a positive sealing action, minimal friction, low hysteresis and extremely precise pressure response characteristics.

Abstract: Excessively high or low tire pressure is detected automatically with a warning signal generated for the operator. A device is attached to each wheel and includes a spring-loaded piston mounted for reciprocation in a cylinder formed in the device. The cylinder is provided with a porting arrangement which opens only at certain pressure limits. When the ports are opened a sonic or ultrasonic signal is generated and detected by sensors located in proximity to each wheel. The signals detected by the sensors are processed and utilized to actuate a warning signal that provides a visual and/or audio output for the operator. Means are provided for discriminating between background noise and the generated signal as well as to discriminate as to the location of the affected tire. In a modification of the invention, a reserve chamber is integrated into the body of the wheel and is adapted to replenish automatically air lost from the tire.

Abstract: A gas-actuated sound signal generator is provided to produce a simple, reliable sound signal of predetermined frequency, or combination of frequencies. The signal generator is intended for use primarily with a tire pressure sensing system on a vehicle as a means for transmitting the occurrence of a low tire pressure condition from a wheel to a microphone mounted in fixed position to the vehicle and connected via processing circuitry to an alarm near the operator. The device is operated upon the release of a small amount of air from the tire if the tire pressure drops, for example, below a preset limit. The air released from the tire flows into the signal generator and is converted into a sound signal for detection by the microphone. The signal generator is comprised of a cavity block, a shim and a cover. The block contains an entrance feed through which air is admitted as from the tire and a cavity spaced from the entrance feed.

Abstract: Excessively high or low tire pressure is detected automatically with a warning signal generated for the operator. A device is attached to each wheel and includes a spring-loaded piston mounted for reciprocation in a cylinder formed in the device. The cylinder is provided with a porting arrangement which opens only at certain pressure limits. When the ports are opened a sonic or ultrasonic signal is generated and detected by sensors located in proximity to each wheel. The signals detected by the sensors are processed and utilized to actuate a warning signal that provides a visual and/or audio output for the operator. Means are provided for discriminating between background noise and the generated signal as well as to discriminate as to the location of the affected tire. In a modification of the invention, a reserve chamber is integrated into the body of the wheel and is adapted to replenish automatically air lost from the tire.