An insight into pedal mapping

Pedal maps are one of the main factors which allow to match an engine's feel to a driver's requirements. David Lamb, the Renault engine engineer for Williams F1 gives an insight into what they are and how they can be tuned.

David Lamb, Renault Sport F1 engine engineer for Williams F1 Team expands: “There are essentially two types of pedal map. There’s a conventional one dimensional pedal map, which is basically a representation of a driver’s throttle against the pedal input that is passed across to the engine controller. You can use this to quickly change the feel of the engine to the driver, but it is slightly obsolete now; you might have found it in the sport ten years ago. Some road cars now feature a ‘sporty’ pedal map of exactly this style, with the initial engine response feeling more aggressive to give the impression of it being racier.

“Now when we talk about pedal maps we talk about the torque pedal map, which is a two dimensional map against engine speed and throttle pedal position. For a given pedal position and a given engine speed, you generate an engine torque demand from the driver. It is this demand that gets fed to the engine side of the ECU to deliver the required amount of torque.”

While the role of pedal maps is to ensure the driver has the power he requires, they can also be used to give the driver a bit of help.

“With driver torque pedal maps, you can have different philosophies. You can have a constant torque map, where regardless of the engine speed you receive the same torque demand for a given throttle pedal position. However, this offers no wheel spin assistance, which can be incorporated with a constant power style pedal map.

“For example, say you’re at 50% pedal on the throttle and at 15,000 RPM, you might get around 200Nm of torque. If you get a bit of wheelspin and the engine speed increases to 16,000 RPM, the torque at the wheels will be reduced as this is a constant power pedal map – power being the product of torque and engine speed. It’s not traction control as it isn’t controlling to a wheel slip target, but instead an open-loop method to try and help wheelspin control. It can be of real benefit when the tyres are worn out.”

The maximum amount of torque engine engineers are proportionally allowed to remove as a function of engine speed is limited by the FIA so, as always, getting the right balance to help the driver and stay on the right side of the law is a juggling act.

David expands, “You can have an area of constant torque on a pedal map followed by a region of ‘constant power’ decay afterwards. Your torque pedal map could therefore be a mix of this and a constant torque map, depending on the preference of your driver and your car.”

But it isn’t just in the use of the pedal that mapping is important. It is also when the driver is off-throttle that is of almost equal importance.

“The zero percent line is when the driver is completely off the pedal. It is this line that sets the amount of over-run push. This is when the engine continues to turn and produce torque, albeit still slightly negative, under braking. Getting this correct is essential as we use it to reduce rear locking under braking. It’s another open-loop system, this time pseudo anti-lock, so as the tyres wear out the driver will tend to increase the amount of push during the course of a stint.

“The downsides are that the heat rejection to water and oil will go up, so fluid temperatures will increase, and you’ll also use more fuel to achieve this. It’s quite a pronounced effect: if you plan to use maximum push for the whole race you could end up adding another two kilos to the starting race fuel load.”

This weekend, the starting point for the pedal maps will be the maps from the last race in Singapore.

“We will start this weekend with the pedal maps from Singapore. Tyre wear was pretty high last time out so we increased our anti wheelspin gradient. We’ll start with that as a baseline, so that the engine feels the same to the drivers as the last time they drove it, and we’ll adapt that over the weekend, gradually shaping it to how the circuit evolves and the driver’s feedback.”