Electronic Tire Pressure Control
As of November, 2003, all passenger cars, vans and off-road vehicles in the USA, must be equipped with tyre pressure-supervision systems. Insufficient tyre pressure is a security risk (bursting of the tyre is possible)
and increases the fuel consumption. Also the service life of the tyres can be increased if the approved tyre pressure is maintained. It becomes interesting when a continuous supervision of the tyre pressure is coupled
to the safety installations of the vehicle. An automatic maximum speed limitation in the event of pressure loss, particularly with emergency wheel systems would be exemplary.
Let us consider first of all, the indirect measuring systems. They use the sensors which nearly every car already has, namely, the ABS equipment. Their frequencies are compared with each other and then calculated from the deviation in the pressure difference. The system accuracy, in the meantime, has been
increased to approx. 0.2 bar. Only a steady pressure loss, which can occur, e.g., with very long controlling intervals, is not registered.
In the case of electronic tyre pressure supervision, tyre valve, battery, pressure sensor and transmitter in the wheel rim, (mostly near to the valve) form a unit. Additionally, there is also another temperature sensor
which provides for the switching off of the system when the wheel rim reaches very high temperatures, e.g., through braking,. Each transmitter, either in the wheel arch (see above figure) or the wheel-RPM sensor
aerial, sends a signal with its identity number and a data-record. These sensors are sufficient, by the way, also for the spare tyre, if this is equipped with a transmitter. To spare the Lithium batteries, substantially far
more measurements are taken, in normal operation, than are transmitted. Only when the wheel is in motion are the values transferred. Moreover, the transmission frequency only increases if the tyre pressure drops.
Thus a service life of approx. 7 years for the battery (newer systems up to 10 years) is achieved nowadays. The batteries cannot be separately exchanged.
Should a certain pressure loss be exceeded, the driver receives a warning when switching on the ignition. Both a slow puncture and a sudden pressure loss are indicated during the trip. The momentary tyre pressure
can also be called up from the memory and be stored. A change of the tyre pressure during the trip is only possible with a central connection of the tyre valves through the wheel hub (off-road vehicles and trucks).
Winter tyres on their wheel rims must also be equipped with suitable units. The new identity numbers must be reported to the controlling system. For this, a visit to the garage is necessary. This is also valid when
exchanging two of the wheels. Otherwise, the dropping tyre pressure is indicated falsely, e.g., the rear left tyre instead of the front left tyre. 06/09