Civil Engineering Reference
In-Depth Information
a necessary step to meet the expectation of both trends, increasing efficiency and
increasing functionality.
With the help of a calculation example using conversion formulae, the statement
and the potential for efficiency enhancement are confirmed. Using a battery supply
of 14 V and an ECU with an idle-current of approximately 100 mA implies 1.4 W
per ECU in idle state. The conversion formula says that 100 W electrical load are
current to 0.1 l of fuel per 100 km, where 1 l fuel raises the emission of 2.5 kg of car-
bon dioxide. Thus, an additional ECU would raise 3.5 g CO
2
emissions per 100 km
even when it is in idle state and is waiting for a functioning request and its actors are
not active. The statistical department of the German government gives an average
of 11,500 driven km per car for the year 2008. As a consequence of this, an addi-
tional ECU would result in an additional emission of about 400 g of CO
2
per year.
Regarding electric vehicles, the motivation lies in a more efficient power con-
sumption, which is essential to bring up today's kilometre range of electric vehicles.
How is it possible to face these two none-harmonizing trends?
The fact is that many ECUs are responsible for functions that are not used very fre-
quently. A back-view camera, for example, is not in use when the car is driving on the
highway for hours. Other examples are seat ECUs, door ECUs or sun-roof ECUs. If
these ECUs are connected to the CAN bus, the bus communication holds these ECUs
in permanent awake state even though the communication is not relevant for these
ECUs. A solution must be found to set unused ECUs to a sleep mode and to reactivate
them only in case of use. This working principle is named as partial networking.
Figure
2.48
shows the potential of a CAN bus with partial networking. None-
used functions result in sleeping of the corresponding ECU. In case of a functional
request, the corresponding ECU is woken up. This can happen without any notice of
the driver. The real-time requirements are fulfilled in such a way that the driver may
not notice that a function is completely disabled due to its sleeping ECU.
Back to the above example calculating the impact of electrical power consump-
tion on CO
2
emissions and considering an average of 12 ECUs which can be used
for partial networking this would bring a potential of 17 W saving electrical power.
This would result in approximately 0.42 g CO
2
per km and in 5 g CO
2
per year. Even
high-saving potentials of more than a gram for partial networking are presented in
the past. Considering penalties of up to 95 euro for exceeding emission boundaries
forced by the government, a partial networking ECU can result in up to 3.33 euro
savings. Even 17 W brings some effect on the range of electric vehicles.
In the following, several variants of setting particular ECUs to sleep and reawake
them are described.
2.5.2
Realization Methods
2.5.2.1
Variant 1: Disconnecting the Supply Voltage
By disconnecting the supply voltage, ECUs can be turned off completely. This kind
of separated working availability of ECUs already exists in the car. ECUs, which
