User's Manual

bf1systems IRTPTMS V3 System Description
bf1systems IRTPTMS V3 System Description V1_01
1_01
Page 6 of 15
RD096 110124
5.2 Functional Description
The wheel electronic is mounted on the wheel rim and measures tyre 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 tyre 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 125 kHz 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 measured pressure value is detected, the wheel electronics switch immediately
to fast-transmit mode. In this situation, the wheel electronics measure and transmit every 0.8 seconds.
The IRTPTMS 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 antenna 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 tyre pressure or temperature.
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.
6 Warning Algorithm
The system monitors a nominal pressure, which is set automatically when the tyre speed exceeds 30kph, and a fixed set
minimum warning pressure. The higher value in each case is used to generate the deflation warning.
6.1 Warning Limit “Minimum pressure”
At this warning limit, a check is made against the minimum warning pressure Abs
Pressure
Minimum, which is programmed
into the system as a fixed value.
The corresponding warning bit is set, if the measured pressure lies below this threshold twice in succession.
6.2 Warning Limit “Nominal pressure minus relative deviation” (Nominal Pressure – 25%)
This warning limit is calculated from the nominal pressure less a relative deviation of 25% of the nominal pressure. The
nominal pressure is specified by the driver. An accuracy reserve of 0.1 Bar is added to the warning limit.
The corresponding warning bit is set if the measured pressure lies below this threshold twice in succession.