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place using the driver information system
without positional allocation.
4.2 Trigger System
If positional allocation is required in addition
to the wheel electronics, the trigger system
is the best technical solution compared
to the other systems currently on offer.
The added number of components provides
fast and reliable detection of the
wheel positions. The transmitter is controlled
by the central control unit. A trigger
signal causes the allocated wheel electronics
to record a new pressure and temperature
measurement value and to transmit it
as a radio telegram encoded as requested
information.
Allocation to the wheel position is possible
very quickly due to the correlation between
a radio data set registered (marked)
in the central receiver and the trigger request.
The trigger-controlled system provides
the pressure information even before
the driver sets off.
In this system, the target values for the
tire pressures can be specified for each axle
by control unit programming and can also
be derived directly from the set pressures
using a calibration modulator.
A visual indication is given in the display,
which highlights the positional information,
Figure 5.
4.2 Trigger System
4.3 Compact System
Figure 6 shows the components of the actual
TSS.
The latest development continues to reduce
the number of system components.
The Beru compact system (TSS 3rd generation)
will consist only of a central receiver
unit with an integrated control unit function
and four wheel electronic systems.
Positional allocation takes place on
the basis of the rotary direction signal,
which the wheel electronic systems provide
in the radio data, relating the information
on the direction in which the vehicle
is moving, in combination with the
axle-specific separation from the fitted
wheel electronic systems to a comparison
of the various RF reception levels.
This is achieved by the installation of the
central receiver unit at the front or rear of
the vehicle in order to provoke these differences
in the RF level. Definition of the
target value for tire pressure takes place
as described above. A monitor displays
the warning and the positional information.
5 Integration in the Vehicle
Figure 5: Display in the Beru-TSS as used in the Audi A6 showing the
pressure and temperature values in the individual tires
ATZ 2/2005 Jahrgang 107
System integration in the vehicle is divided
into two areas. On the one hand, the best
positions for the hardware in terms of tech-
nical and design aspects must be defined,
and on the other hand the system must be
coupled to the vehicle wiring.
5.1 Installation Space
The potential installation spaces are surveyed
in terms of their radio frequency reception
characteristics in order to identify
the best possible position for installing the
receiver antenna. The most favourable position
is usually in the underbody, in the
bumpers or in the wheel arch. However, if
the vehicle manufacturer so wishes, the antenna
can also be installed in the vehicle interior.
The system is fundamentally designed
so that the reception of the RF signal can also
be guaranteed if the tires provide considerable
attenuation. Additional damping by
environmental influences (snow, rain) is also
considered in the system design.
5.2 Networking
Another factor of the system integration is
the connection of the system to the vehiclespecific
wiring. In most applications, the
control unit is operated in the existing comfort
CAN.
The components of the tire pressure
monitoring system all have a self-diagnosis
capability. The specific manufacturer’s diagnosis
services provide the required diagnosis
information.
The vehicle bus also deals with the operation
and display of the pressure information.
5.3 Technical Specifications
Statutory requirements, for example the
NHTSA initiative and the demands voiced
by vehicle manufacturers, define the
framework for alarm thresholds and response
times.
5.4 Special Features of the
Beru TSS
In addition to the tire pressure, the Beru
Tire Safety System also evaluates the tire
temperature. This is based on the general
gas law. This temperature compensation
means that the alarm threshold can be
aligned with the tire pressure.
A message is issued if the alarm threshold
was exceeded on two successive samples.
Given a typical transmission interval
of one minute, this means that detection
takes no longer than two minutes. If there
are high changes in pressure, the wheel
electronics transmit signals in cycles of
merely a second. In these cases, the detection
period is only two seconds.
In addition to tire defects with rapid loss
of pressure, the system also detects a gradual
loss of pressure – for example due to dif-
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