By Kalwinder KaurJan 11 2013
For automated vehicles, real-time measurement of tire pressure is possible via the sensing device located in the tire. This sensing device sends information to a display system to alert the driver to a change in the pressure of all four tires. A complete tire pressure monitoring system includes a pressure sensor, a signal processor, a temperature sensor, and a transmitter.
A simple description of a tire pressure monitoring system involves illuminating a warning light in cabin components to a vehicle system when tire pressure is low or if the temperature to the tires is excessive. In some vehicle systems, the tire pressure sensor is located on the rim opposite the valve stem.
Road vehicle tires are affected by many factors and it is important that operational adjustment parameters such as tire pressure and temperature are monitored to ensure the safety of a moving vehicle. Parameters, such as tire width and tire deflection are also monitored regularly to support tire performance.
There is a number of tire pressure sensors incorporated into road vehicles by car manufacturers. One such sensor is a piezoresistive pressure sensor, which is mounted onto the wheel of a car. This sensor works by detecting the degree of air pressure in a vehicle tire.
Tyre Pressure System - Operation
During operation, as the wheel rotates in a relative position to the axle, the sensor activates and transmits a signal to a display system – a process possible via the use of a circular antenna, which is also fixed to the wheel. There is also an antenna mounted on the brake caliper along with a signal decoder and both antennas then act as an interface system for carrying a sensor signal about the tire pressure.
With the majority of tire pressure monitoring systems, a sensor is mounted onto the top of a valve stem which then transmits a radio frequency (RF) signal. This is an easy method to remember in that if the vehicle tire is deflated, the RF changes accordingly.
The pathway to this tire pressure monitoring system involves the sensor picking up a change in tire pressure and then transmitting an RF signal to a receiver mounted under the dashboard in the cabin unit to a vehicle. In the event of a tire pressure drop below 25 psi (172 KPa), the receiver highlights this message by illuminating the warning light. For many tire pressure monitoring systems, the pressure sensing system is not activated and in full operation until the vehicle is moving at a speed of 25 mph (40 Km/h). The receiver to the monitoring system is typically connected to a data link connector under the dashboard.
The pressure sensor that makes up the tire pressure monitoring system is attached to a valve stem and is battery powered. The structure to this sensor includes a retention nut attached to the valve stem located to the outer part of a wheel rim. A grommet is also used to seal the join between the nut and the wheel rim.
Johnson Controls, specialists in the automotive industry, have recently developed a next-generation direct measuring tire pressure monitoring system with an additional aim to reduce CO2 emissions.
Valve Stem
The main purpose of the valve stem is to behave as an RF antenna, with the tire pressure module being the receiving unit. During movement of a vehicle, the sensor transmits an RF signal to the tire pressure module (i.e., the receiver, typically located in the right-hand C pillar to a vehicle) in 60-second intervals.
The module receiving the RF data on tire pressure and compares this measurement data to the low tire pressure limits. A discrepancy in the measurement data results in this module transmitting a voltage signal via data links to the message center, which is followed by a warning message to the driver.
Sources and Further Reading
- Nwagboso C.O. (1993). Automotive Sensory Systems. India, New Dehli: Thomas Press (India) Ltd.
- Knowles D. (2011). Automotive Suspension & Steering System: Classroom Manual. USA, New York: Delmar, Cengage Learning.
- Vehicle Tyre Pressure Monitoring - Sensorland
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