The transmissions used in Formula One do not require the use of a clutch during gear changes, and as such, drivers only use a clutch during the start of the race and when leaving a pit stop. Despite this infrequent use, they are still an important contributor to a car’s performance, not least because a poor start can ruin a race result.
Carbon-carbon clutches have been the norm in Formula One since the mid-1980s, providing high levels of bite and heat resistance coupled with low inertia. Before regulations dictated a minimum crankshaft height, there was a drive by clutch manufacturers towards ever-smaller diameter clutch discs. The smaller the clutch, the lower the engine could be placed, and thus centre of gravity would also be lowered.
These clutches, some as little as 87 mm in diameter, still contained the same amount of material as a larger clutch, to absorb the thermal load on launch, but putting them in a smaller package reduced inertia. These days, most Formula One clutches are about 97 mm in diameter and feature four carbon friction discs, housed in a titanium basket. The assembly must be robust enough to survive the forces exerted by a 750 bhp engine while also remaining dimensionally stable when rotating at 18,000 rpm.
Clutch release is controlled by an hydraulic release bearing, the movement of which is actuated by a high-pressure electro-hydraulic servo controlled by signals from the ECU, which in turn are interpreted from driver inputs to a steering wheel paddle. With launch control systems now banned, drivers are responsible for controlling the clutch on launch. A Formula One car has a narrow power band, and getting the balance between bogging down off the start and lighting up the tyres is a fine one. Drivers therefore need a clutch that provides a consistent biting point, both at the start line and when leaving the pits after a stop.
To achieve this consistency, clutch manufacturers invest considerable research time into ensuring that the interfaces between the clutch discs and the clutch basket and pressure plates are optimised. For example, if there is any degree of friction between the clutch drive plates and the arms of the clutch basket, the point at which the clutch bites can vary. Other factors such as the ratio between clutch paddle movement and the movement of the release bearing also need to be considered, with mechanical systems within the clutch helping to ‘soften’ the initial bite as the clutch is released.
There will be a number of new regulation changes in 2014 that directly and indirectly affect the design of transmissions. The most important is a change from seven to eight gears, in order to account for the reduction in maximum engine revs from 18,000 to 15,000. The number of forward gear ratios will also be increased from seven to eight, the benefits of which will be offset by restrictions on gear ratios.
At the start of the season, each team must nominate a set of ratios for the entire season – a considerable challenge given the wildly differing nature of tracks. If a team picks an unsuitable set though, they have the chance to change their ratios once within the season. The demands placed on the transmission by the new turbocharged engines and energy recovery systems will also be considerable. The power units will produce more torque than the current high-revving V8s, which will have to be accounted for in the gearbox and clutch designs.
Written by Lawrence Butcher