[PowderfaceTr.]

It was already said that most
drivers prefer the ignition cut
method for torque reduction in a
traction control system. Cutting
the spark means there is better
feedback for the driver and he or she
gets a better feel for what the car is
doing. This provides confidence and
repeatability. We therefore need to
configure the ECU to cut the spark to
reduce the torque. This might seem
like a simple thing to do, but we
must be careful. For example if we
start to cut one cylinder per engine
cycle straight away there will be a
very steep loss in torque, resulting in
a less than favourable situation for
the driver. It is therefore necessary
to start more gradually and cut one
cylinder every 3rd cycle and then
increase the severity if more torque
reduction is needed. Using this
method requires a lot of work on
generating the matrix for the cylinder
cut as the table needs to be very
large to control the torque reduction
adequately. Pictured is an example of
a table used for pit lane speed limit
and although this one is quite large,
it is far too small for traction control.
There is, however, a solution that
makes life easier, and that is to use a
randomiser for the ignition cut. This
uses predefined parameters and
smooths out the torque reduction.
Once the torque reduction
method is set, it is time to look at
some of the other parameters. As a
reminder, the following parameters
all influence the traction control.
If we look at for example the
User Multiplier, it is useful to give
the driver a bit of control over the
severity of the traction control.
The same switch is also used to
set the maximum allowed slip so
it is necessary to be careful when
configuring this value. Some of the
other parameters can then be seen
on the left hand side. Do we want
to control it is the spin or slip of the
wheels. How much slip is there and
how fast is the slip building up?


Looking at some data for a
specific corner, we see the traction
control is set to 4 and the torque
reduction is limited to 34.9 per cent –
this setting appears to suit fairly well,
at least it inspires confidence as the
driver keeps his foot flat and slides
the car around. We could probably do
a bit more to smooth out the torque
reduction as the rpm does fluctuate a
bit due to the ignition cut.
On the next lap the driver tries
a less intrusive setting, but as the
assistance is reduced the confidence
is lost and the driver interferes and
goes out of the throttle. We also
see much more action in the slip
percentage (Orange line at the
bottom) indicating excessive slip. This
is clearly an effect of less maximum
torque reduction indicated by the
pink TCS_trq channel.
No doubt the driver’s feedback
will be that setting three is probably
not appropriate for the current level
of grip, but setting 4 might be a bit
too intrusive so there might be a
happy medium between the two.
It is then necessary to adjust some
parameters to create the traction
control settings that are likely to
work. In order to do so it’s a good
practice to set up a simulation. There
are two elements needed for this;
a good analysis tools package and
the calculation method used in the
ECU to determine the level of torque
reduction. The way to do this will be
different depending on software and
hardware, in Pi Toolbox the lookup
table function allows us to generate
two dimensional maps in excel which
directly replicate what is used in the
ECU calibration tool so the simulation
becomes relatively easy. Pictured
are sample screenshots of simulated
torque values versus the current ones
which make it easy to predict the
behaviour on track.
In theses instances we have
reduced the user torque limit to 30.9
per cent so we can see the effect
this will have on the TCS torque.
Additionally the simulation shows
the level of cut produced by the
traction control strategy.