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Throttle Mapping on DBW cars

In modern cars, there is no longer a “throttle cable” linking the throttle pedal to the throttle bodies. Now we have a throttle pedal that is a sensor/input to the ECU, and the ECU controls the throttle bodies. This is known as “drive by wire”. This has a number of advantages. One of the biggest is that the ECU is no longer reacting to throttle changes and trying to respond to this with changes in fueling, it now knows this is happening and can make changes to fueling in sync with the throttle changes. Another major benefit is that we can easily alter the “sensitivity” of the throttle pedal, and the mapping of throttle pedal to throttle body, or throttle pedal to target torque, depending on the ECU’s control structure.

With the ability to alter the “effect” of throttle position and throttle change on the drivability of the car, we open up a new world of parameter tuning. A system that is more responsive with smaller throttle changes will “feel” more “sporty” or “more powerful”. Often, this is accomplished by a non-linear throttle mapping, where 10% at the throttle pedal could be interpreted as 20% by the maps in the ECU, 20% as 40%, etc. This will make the engine feel more powerful to the driver, but 100% will still need to be 100%, so the actual power of the engine has not changed. The downside to this (especially as we search for the “what is too much” point) is the decreased fine throttle control.

If we look at fine throttle control, it may be of an advantage to make certain areas of the throttle less responsive. This is especially true in conditions were available torque may exceed available grip, and thus the driver will need to modulate the throttle in order to not spin the tires. On cars with traction control, they may or may not do this well enough to be “better” than driver control. In either case, traction control can be rough on the drivetrain in many applications, as the torque cut can be drastic and hammer the components. (Much like ABS can be helpful, but still not as good as a good driver.) On cars that do not have these features (traction control specifically for this discussion), the throttle mapping allowing for better control and thus less wheel spin will help with vehicle balance via tire temperature, and thus also tire wear.

This mapping will of course be very driver specific, and within the constraints of most of the ECU’s, adding resolution/linearity in some areas might mean giving up some of that in others. That compromise is what is needed to be adjusted to fit the car, driver, and track.

The driver being a large part, but the chassis being a key player too. A good example of that interaction between driver/car/throttle is corner exit. How (and how quickly) that torque change is requested might provide wheel spin in some cases, but might also provide the initial torque bump to help lock the differential more in other cases. The interaction between the driver and the differential, especially in a more conventional limited slip differential like a Salisbury, is controlled by the throttle pedal.