DIY Traction Control

[Jorgen Karlsson]

Hi,

Lets assume that you have a turbo car with no catalytic converter.

I think that we want to keep the boost as high as possible even when TC is
doing its job, this would require us to alternate between cutting sparc and
fuel.

Cutting spark will limit power and send raw fuel out into the exhaust
manifold where it will ignite, this will cause very high exhaust
temperatures and lots of exhaust energy that drives ther turbine.

Cutting fuel will limit power and will not provide any energy that drives
the turbine.

Changing spark timing would be nice as it can act like something between a
cut spark and a normal combustion. It will provide some power and a bit more
exhaust energy to drive the turbine. But lets stay away from that for now.


If we want to do this right we need to know: if the clutch is released, real
vehicle speed, driven wheel speed, Boost, throttle and exhaust temperature.

The exhast temperature tell us if we can cut spark without melting the
manifold or the turbine.

The throttle position can be used to tell the system what boost level we
want to keep when the TC is working.

The boost tell us if we need can cut fuel without letting the boost drop to
much or if we need to dump some fuel to keep the turbo spinning.


Example.
Car:
Honda civic FWD, manual, 1.8l, turbo, no cat, lots of power.
Maximum boost 1.2bar gauge, maximum exhast temperature 1800oF.
We want to optimize this car for streetracing on low profile tires, this
mean that we can let the exhaust gas temperature get as high as 1800oF and
that we will have our share of traction problems.

We want to keep the boost above 1.0bar if the EGT permits.

A two step rev limiter will simplify the starting procedure a lot on a FWD
dragrace car and that function is best built into the TC box too but we'll
ignore that for now.

The TC is not activated until the clutch is released and this occurs when
the speed is high enough to keep the engine above 5k. Because of the TC the
throttle is floored until we reach the finish line.

The front wheels lose traction at once and are spinning 70% faster then we
want them too, EGT=1300, BOOST=0.5. This tell us that we want to cut lots of
power, we want more boost and the EGT is very safe. We try cutting 40% power
by running this sequence:
no spark, fire, no spark, fire, fire.

After a few cycls of this we find:

30% wheel spin, Boost 0.8bar, EGT 1350(probably sensor lag.)
Need to decrease power a bit, Boost still to low, EGT still safe.

We don't want to cut one spark after an other because we pay our own turbos
and are forced to run this sequence (40% of total power):
no spark, fire, no spark, fire, no fuel.

After a few cycls of this we find:

5% wheel spin, Boost 0.9bar, EGT 1400.
Need to increase power a bit, Boost still to low, EGT still safe.
We jump back to the 60% power sequence:
no spark, fire, no spark, fire, fire.

After a few cycls of this we find:

15% wheel spin, Boost 1.1bar, EGT 1450
Power is ok, Boost higher then needed, EGT still safe.
We modify the 60% power sequence:
no spark, fire, no fuel, fire, fire.

After a few cycls of this we find:

15% wheel spin, Boost 1.2bar, EGT 1500
Power is ok, Boost high enough to open the wastegate, EGT still safe.
We modify the 60% power sequence again to limit exhaust energy:
no fuel, fire, no fuel, fire, fire.


Depending on the amount of wheel spin compared with the current engine
output we decide the amount of power we want to try next time. The way we
decrease the power is decided by the boost level unless the exhaust
temperature is to high.

Power to high>cut more cylinders.

Power to low> cut less cylinders.

Low boost> cut more spark and less fuel.

High boost> cut less spark and more fuel.

High EGT> cut less spark and more fuel.


The software pick the right power level depending on wheel spin and the
right sequence depending on boost and EGT.
Sequences suitable for a four cylinder engine:

80% Power
spark, fire, fire, fire, fire
fuel, fire, fire, fire, fire

60% Power
spark, fire, spark, fire, fire
spark, fire, fuel, fire, fire
fuel, fire, fuel, fire, fire

40% Power
spark, fire, spark, fire, fuel
spark, fire, fuel , fire, fuel
fuel, fire, fuel, fire, fuel

20% Power
spark, fire, spark, fuel, fuel
spark, fire, fuel, fuel, fuel
fuel, fire, fuel, fuel, fuel


This system would only need an rpm input to allow it to double as 2 step
revlimiter, launch control, flatshift, ALS and ALS cooldown idle control.
All of them very cool functions.

Comments are welcome!


Jorgen Karlsson
Gothenburg, Sweden.


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