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Tire pressure monitoring with Siemens VDO Tire Guard

Siemens Tire GuardFrankfurt - Two-thirds of all tire failures are preceded by a gradual loss of pressure. The "Tire Guard" monitoring system presented by Siemens VDO Automotive AG at the 59th Frankfurt Motor Show warns the driver in such cases.

During an inspection of more than 140,000 motor vehicles as part of the "Tire Check 2000", the German Road Safety Council discovered that 37 percent of all cars in-spected had faults with their tires. 15 percent had insufficient pressure. Since poorly inflated tires have to perform more flexing work, the rubber heats up more. Excessive thermal load, however, is one of the possible reasons for the sudden seperation of the tire tread from the carcass. The environment also suffers as a result of low tire pres-sure: The rolling resistance and thus the fuel consumption both increase. With the "Tire Guard" monitoring system developed by Siemens VDO it is possible to detect changes in tire pressure and to warn the driver in advance. Since two-thirds of all total tire failures are preceded by a gradual drop in pressure, this system makes a major contribution to increased road safety.

Siemens VDO Tire Guard is based on a direct measurement of the air pressure in the tire. The advantage of this high-precision method: Very small changes in the air pres-sure can be detected, irrespective of road condition, vehicle load, degree of wear or temperature of the tire. Furthermore the signal is always available, even when the ve-hicle is parked.

The actual pressure measurement is performed with a micromechanical sensor, a sili-con-based vacuum measuring cell. The deformation of the diaphragm occurring under different air pressures can be measured using piezoresistive sensors and processed electronically.

There are, however, more comfortable places for a sensor than in the tire. At a vehicle speed of 250 km/h, the sensor is exposed to 1,000 times the force of gravity. Further-more, it is exposed to the vibrations caused by the unevenness of the road, almost completely without support. In order to allow the electronics in the sensor to survive under these conditions, it is embedded in a vibration-absorbing compound in the plas-tic housing. The housing is screwed into the bed of the wheel with the valve nut. On aluminium wheels, the low weight of the sensor unit of only 35 grams (including the valve) can be compensated by a corresponding casting form.

The measurement values obtained by the sensor are transmitted at a frequency of approx. 433 MHz (Europe) or 315 MHz (USA) by radio to the controller. The com-pany's many years of experience with radio-based products guarantees a very reliable link between the sensors and the central controller.

In the event of a drop in pressure, a display in the cockpit or an acoustic alarm signal warns the driver. The electronics used in the Siemens VDO system know which tire is losing air. A continuous display of the air pressure in each individual tire is also possi-ble.

Tire Guard helps automobile manufacturers to comply with the legislation in the field of tire pressure monitoring to be expected in the future. In the USA the TREAD (Trans-portation, Recall, Enhancement, Accountability and Documentation) Act due to come into force in 2003 prescribes that all newly registered vehicles have to be equipped with an air pressure warning system.




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