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DEVELOPMENT Tires and Wheels
2.2 Direct Measurement Systems
Byte 1 Synchronisation 1111 1111
Byte 2 Synchronization 1111 1110
Byte 3 Identifier MSB
Byte 4 Identifier
Byte 5 Identifier
Byte 6 Identifier LSB
Byte 7 Druck / Pressure
Byte 8 Temperatur / temperature
Byte 9 Batterie-Restlebensdauer /
Battery power indicator
Byte 10 Status
Byte 11 CRC MSB
Byte 12 CRC LSB
Termination-Bit „0˝
Within this context, the measurement cycles
are defined depending on of the vehicle
movement. Longer measurement cycles
are possible if the vehicle is station-
Table 1: Data telegram of
the wheel electronics
Table 2: Comparison of indirect measuring TPMS with the three Beru versions
Functional features ABS supported TSS generation 2 TSS generation 2 TSS generation 3
series systems without trigger with trigger without trigger
Pressure measurement
in four wheels
– + + +
Temperature measurement
in four wheels
– + + +
Alarm for tire defect
Soft alarm (low sub-
+ + + +
standard pressure)
Hard warning (sub-
– + + +
standard pressure 25 %)
Alarm for even loss of
– + + +
pressure in all wheels – + + +
Alarm issued with position
Automatic learning
of new wheels
– – + +
(e. g. winter wheels)
Automatic learning
– +* + +
of new wheel positions
Rapid diagnosis of
– +* + +
the components
Target pressure transfer
for changes in pressure
+ + + +
due to driver actions
Pressure display menu
with measurement
+ + + +
values and position
Immediate availability
of the pressure values
– – + +
before start of driving
Satidfies NHTSA
minimum alarm
thresholds and
– +** + +**
response time – + + +
*With user invention; **when parked, the control unit must be powered via terminal 30
ary; the cycles are then cut appropriately
if the vehicle is in motion and may even
be measured in seconds if significant
changes in the pressure are identified
over time – i.e. if there is a tire defect or
the tire is being inflated. The tire electronics
autonomously recognizes vehicle
movement using a roll switch.
An alternative is a needs-based triggering
of the measurement via the reverse
channel to the wheel electronics. The trigger
transmitters required for this are installed
in the wheel arches.
In addition to the clocking of measurement
procedures, the trigger transmitters
enable the wheel positions to be learned in
a simple manner. The frequency band of
around 125 kHz used for the trigger channel
ensures that the range of the transmitted
trigger signal remains low due to the small
antenna structure in a ratio to the wavelength,
which permits reliable control of
the individual wheel electronics. Neighbouring
wheels remain unaffected, thus
enabling clear identification.
Therefore, in a comparison of the direct
and indirect measurement systems, Table
2, Beru recognizes the clear advantages of
the direct measurement system. This was
also the basis for the decision in 1995 to develop
a TPMS on this technological basis.
3 Functional Components
The functional components in the solution
that Beru developed as an example of a
modern tire pressure monitoring system
include the wheel electronics, (digital) antenna,
trigger transmitter and control unit.
Depending on the application, user interfaces
and displays are also necessary. The
summary of the individual elements is presented
in the schematic diagram shown in
Figure 1.
3.1 The Wheel Electronics
The wheel electronics unit represents the
core component. This unit, which is fitted
to the valve on the inside of the wheel, Figure
2, must be able to cope with extreme
ambient conditions. It must be capable of
withstanding temperatures of between
–40°C and + 120 °C – in bursts even as high
as + 150 °C – with acceleration values of up
to 2,000 g.
The form of the housing in contact with
the valve connection is by means of a
moulded spherical surface and, as such, it
can be fitted to nearly all known rim types
with only one design, Figure 3.
The unit is encapsulated to protect it
against the penetration of water and to
provide resistance to chemical residue in
the tires. A Teflon filter, patented by Beru,
beneath a “chimney”, Figure 4, guarantees
the required permeability for the interior
pressure to the sensor element.
The wheel electronics consist of three in-
4 ATZ 2/2005 Jahrgang 107