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The accelerator pedal

According to the regulations the accelerator pedal is, “The only means by which the driver may control acceleration torque to the driven wheels.” 

No longer is the pedal simply a means of directly moving the throttles on the engine, as the rules now state that the driver demands torque from the pedal, with the ECU decoupling the traditional relationship between the pedal and throttle with a map. Such maps are now restricted to tyre type, so just three maps are allowed for wet weather, intermediate and dry tyres. Previously, different maps could be selected for the race start and other race situations. The regulations also enforce other restrictions on the pedal, for example no detents or other means can be used to aid the driver in holding a specific position, such as holding revs steady at the race start.

In terms of the foot pedal itself, the part has evolved tremendously over the years, from being a simple metal rod and footplate to operate a Bowden cable to a bespoke carbon fibre moulding operating as a fly-by-wire control. Accelerator pedals are not as mechanically loaded as brake pedals, so their design is far simpler, and this is further aided by fly-by-wire needing sensors rather than a cable. Due to the lighter load on the pedal it is commonly made from carbon fibre, although fabricated titanium or machined aluminium have also been used. 

The pedal is often mounted to a bracket common with the brake pedal and heel rest, which bolts into the monocoque floor, there being different mounting points for different sized drivers. Pivoting at its base on a bearing, the pedal is a simple lever, the driver’s foot modulating the pedal via a footplate. As a driver tends to left-foot brake and no longer slips their foot between accelerator and brake, the footplate can be bounded by side plates to prevent the foot flipping off the pedal. Some teams have these as simple bonded-on sections of carbon fibre; others mould the plate itself into a dished shape in which the foot sits. Abrasive tape is bonded to the footplate to allow the driver’s foot to grip rather than slide over the pedal. Equally key is the spring used to resist the driver’s foot, and these will be tailored to suit the driver’s preference for stiffness and travel. Even with an exotic carbon fibre pedal, a simple bolt and lock nut is still used as a stop to pedal travel.

Detecting the pedal travel has equally evolved since fly-by-wire was introduced. Initially, linear or rotary since sensors between the chassis and pedal were used and, owing to the critical nature of the sensor, these were doubled or even tripled up for redundancy. In recent years, for simpler packaging the linear sensors have been replaced with non-contact sensors, such as Hall effect or induction types, the sensors being built into the pivoting plate and the target magnet being embedded into the base of the pedal. As the teams cautiously start to take up these new sensors, the pedal may use two or more different sensor types for redundancy.

Accelerator pedal-related retirements are rare, but in qualifying for the 2012 US Grand Prix, Jenson Button suffered a complete loss of drive due to a pedal failure. It seems the electronics were the problem, and he was unable to complete the session. This serves to highlight how critical such an apparently simple part can be.

Fig. 1 - Carbon fibre throttle pedals are now common, but can use different sensor technology

Written by Craig Scarborough

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