Wheel electronics

In all wheels, wheel electronics systems are installed in the wheel drop center. The wheel electronics systems are bolted onto the filling valves (made of metal). All wheel electronics systems are common parts. The valid operating temperature lies between -40 °Celsius and +125 °Celsius. The wheel electronics monitor the actual temperature in the tire. If the temperature is greater than approx. 115 °Celsius, the RDC switches into a mode with restricted functionality. Under certain circumstances, a hardware shutdown takes place. When stationary, the wheel electronics perform a cyclical roll identification process in order to identify a starting process. During the starting process, a measuring cycle lasting for 3 seconds is observed. While the vehicle is being driven, a repeated and cyclical roll identification process is performed to confirm and to end driving operations with a measuring cycle lasting for 60 seconds.

At regular intervals (every 3 seconds), the wheel electronics measure the tire pressure and the temperature in the wheel electronics. These measured data are transmitted to the RDC control unit automatically in a regular transmission (every 30 seconds) from the tire to the RDC control unit. In the event of a pressure change greater than 0.2 bar within two consecutive pressure measurements or fast tire pressure loss, the wheel electronics switch immediately into a rapid transmission mode. In this case, the wheel electronics measure and transmit measuring data from the tires at short intervals (1 second). Every set of wheel electronics is equipped with its own Identification Feature (ID) to enable it to be identified by the RDC control unit. This Identification Feature is transmitted together with every data transfer.

Fig 1: Identifying Wheel Electronics

Courtesy of BMW OF NORTH AMERICA, INC.

The wheel electronics are supplied with power by a lithium ion battery. The service life is designed for approx. 10 years. To avoid any unnecessary load on the state of charge of the battery, the wheel electronics operate in 5 different operating conditions. In which operating condition (mode) a set of wheel electronics perform a measurement or transmit a radio signal depends upon:

• Tire pressure
• Tire air temperature