- 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.
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.
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.
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.
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.
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
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.
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.