An insight into throttle mapping

The torque map is probably the single most important reference map used in Formula 1 engine management. It is the fingerprint of an engine and of critical importance for engine engineers to help optimise the on track engine performance.

“In its simplest form, the engine torque map is a theoretical model of the engine. It represents the torque output of the engine for a given engine throttle position and engine speed. In this respect it appears outwardly similar to a driver torque pedal map, the only change being the look-up against engine throttle position instead of the driver’s pedal. However, in reality, the differences are far more complex and wide reaching. From this map, you know for any given speed or throttle position that you should produce a certain amount of engine torque,” says Renault Sport F1 engine engineer David Lamb. “We then use that reference map to ensure the engine is behaving as it should out on the circuit. We measure the actual engine torque with an on-car sensor, and when you overlay this with the value predicted by the torque map, you shouldn’t notice any large differences. If you have a hesitation or a drivability issue, you will see it clearly because the measured torque will not match the reference torque."

The torque map doesn’t change much over the course of a weekend, or between races. “Under the new technical directive, issued between the German and Hungarian Grands Prix, you can’t really change the maps that much over a weekend or between races. It’s like a fingerprint of the engine. There will be subtle differences between the teams due their respective air boxes and exhausts, which will slightly change the form of the map. Prior to this directive, we would change the torque map freely to suit the climatic conditions. For example, the engines will produce nearly 10% less torque at Sao Paulo than they will this weekend in Korea due to Sao Paulo’s high altitude. By changing the torque map to the prevailing conditions the engine response will feel the same to the driver across the season. Nowadays we have to request this torque map change from the FIA, and fully justify our reasoning.”

As well as ensuring the engine behaves as it should, the map is also used to improve the driveability of the car for the driver. “When the driver lifts off the pedal the engine can be either fired in four cylinders or fully cut, depending on the level of overrun support he requires,” explains David. “When the driver goes back on the pedal from full ignition cut, you need to inject more fuel than usual to ‘wet’ the engine. Inject too little or too much and you will have a torque deficit from target, which can cause a hesitation and a loss of lap time. The initial torque demand will generally be met with only four cylinders, as you’d rather save a bit of fuel and have four cylinders firing strongly using a more open throttle than have eight coming into life rather weakly with a relatively closed throttle.

"When the torque demand exceeds that which can be met with just four cylinders, the remaining cylinders need to be fired. These will also require ‘wetting’. At this point you also have to close the throttles at a rate which coincides with the final four coming back into life – this is the tricky bit! Get it right and the driver should feel nothing across the transition, just a change in engine pitch. In all cases, the torque map is used in conjunction with other settings to govern both the fuelling requirements and throttle position."

The engine torque map is used for a multitude of other processes, such as the pit limiter, rev limiter and downshift control. “The engine torque map is without doubt one of the most important calibrations in the SECU. It really is the reference point. When the driver lifts of the pedal, it’s the engine torque map that decides by how much we close the throttles. When he goes back on power, it’s the engine torque map that stipulates to what point they open. It all works off that map.”