User's Manual

NASCAR TPMS - User Manual V1.doc
Page 5 of 6
1.2 Functional description
The wheel electronics are mounted on the wheel and measure tire pressure, temperature and wheel electronic
status. The measured data is sent from the wheel via a transmit stage in the wheel electronics. A system with
relatively seldom-measured data transfer is adequate for tire pressure monitoring provided it features the
additional option of detecting sudden pressure loss. This enables the electronics in the wheel to be designed
for minimal power draw and thus maximize battery life.
All wheel electronics have a unique ID code that is forwarded along with data at each transfer. The HF transfer
occurs in the 433MHz range, referred to as the ISM range. The trigger functionality is achieved by the use of a
125kHz LF channel.
The control unit calls up the wheel electronics via the trigger transmitters when power is supplied to the MDE.
When a pressure loss > 0.2 bar on the previously sent pressure value is detected, the wheel electronics switch
immediately to fast-send mode. In this situation, the wheel electronics measure and send every 0.8 seconds.
The TPMS system measures and transfers considerably more data than is necessary to ensure reliable basic
function. It can therefore use a data transfer path this is not assigned for the error-free transfer of each
individual data protocol. Using the trigger function, an implausible and/or non-received data message can be
requested again from the corresponding wheel electronics.
The data sent by the wheel electronics is received via the digital antennae and is subsequently decoded. The
decoded data is transferred onwards to the MDE unit via a digital interface (LIN interface). The MDE unit
evaluates the received data and forwards the information to the driver information system as required. This
provides the driver with information on the necessary tire pressure or tension adjustments.
The main functional characteristics of the control unit are:
- A central warning algorithm and an algorithm for the wheel manager.
- The vehicle-specific connection for the power supply system and manufacturer-specific operation and
display philosophy.
The essential feature of wheel management is the self-learning system with automatic individual wheel
detection and the detection of the corresponding installed positions (wheel position detection). Due to fast
triggering of the wheel electronics when active, the system can detect a flat tire far in advance to the start of a
journey.