Racing Transmissions

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As you flip the paddles of your road car you are benefitting from years of Formula 1 development
Transferring power from engine to road is one of the areas where your road car may seem more sophisticated than a current Formula 1 car. Sequential boxes with F1-style paddle shifts are common, but while many road cars have a `robotised manual’ in which a computer selects gears, the FIA requires that drivers still pull a lever.
Inside, the basic mechanism of a racing gearbox is little different to a manual road car: pairs of cogs selected by forks sliding on selector rails, though the cogs are engaged by ‘dogs’ — crude but tough. Instead of the manual H-pattern shift, which allows any gear to be selected from neutral, sequential boxes use a rotating drum in the same plane as the shafts to swap gears. Grooves machined into this drum accept a pin on each selector fork, and because the grooves veer left and right, they also slide the fork back and forth as the barrel rotates. Once first and second are done with, that groove runs straight as the barrel turns further and the 3-4 groove slides that fork between those ratios. And so on. Turning the barrel can be by a mechanical lever or by electric, pneumatic or hydraulic actuators triggered with the paddle.
An F1 box is semi-automatic in that the ECU controls clutch movement and matches engine speed for perfect engagement. This means the driver can keep his foot flat on the throttle during upshifts or on the brake while the computer blips the flyby-wire throttle for downchanges, taking a few hundredths of a second, and only operates the clutch (with his finger) at the start. As shifts get lightning fast, the momentum lost while the clutch is disengaged has become crucial. In the 1980s Porsche developed its double-clutch box, where the next gear is pre-engaged and selected by switching clutches. But that brings extra weight and is banned in F1 and the Le Mans Series; today’s race box goes part-way down this route with double selectors so the next gear is ready to go, making shifts essentially seamless.
Ratios are closely spaced to keep the V8 engine spinning at 15-18,000rpm, where the immense torque is reasonably constant. All six or seven ratios can be rapidly changed for different circuits, with much time on simulators going into the final choice, and each gearset will only be raced once, though the rules say that the box itself must last four races. Which is tough, as at Monaco F1 cars don’t stay in one gear for more than a second over two hours. To avoid a car stalling on the track after a spin, an anti-stall function is mandatory, automatically dipping the clutch if the revs drop below a set limit. Despite the 750bhp it must handle, an F1 clutch, which uses carbon to carbon plates, is remarkably small — only 100mm across.
To help centralise mass, the gears sit ahead of the diff. This means a longer wheelbase, unless you use a transverse box as Lola sports cars do, which also makes changing ratios easier. But the long, lean F1 greyhounds retain inline gears to benefit wing airflow. Because an F1 engine lies so low the final drive has to be stepped up through bevel gears to drive the hydraulically-controlled limited-slip differential. Although this responds to traction and yaw inputs to help ‘steer’ the car in a bend, this response has to be set in the pits and can’t be altered on the track if conditions change. It’s one area where your car may be cleverer than Jenson’s, with traction and stability control, an active diff and adaptive damping — all functions which F1 helped to stimulate.
F1 rules require a reverse gear, a lightweight ‘add on’ which won’t take much use, which is also engaged hydraulically, yet another load on the complex electro-hydraulic system. Until recently hydraulics problems have often sidelined an otherwise healthy car. It’s the complexity of integrating this with the electronic and mechanical elements that led small teams such as Virgin, HRT and Lotus to buy in the Xtrac box and control systems for their debut year, though Virgin specified a unique gearcase to mount its own suspension design. For 2011 HRT will use a Williams gearbox and hydraulics, which also means sharing rear suspension geometry. Lotus Racing, on the other hand, will employ Red Bull’s technology within its own gearcase, giving it freedom over rear geometry.
Magnesium, aluminium, titanium and carbon fibre have all been used for the highly stressed gearcase, which apart from suspension loads also has to resist high temperatures and remain oil-tight, hence its advanced ceramic seals and bearings. Yet, helped by the power downshift to 2.4-litre engines, today’s gearboxes are 25 per cent lighter than five years ago.
The optional reappearance of KERS adds packaging complications. Intrinsic weight is not the problem (minimum car weight rises for 2011) but as cars are built underweight and tweaked for weight distribution using ballast, this concentration of mass reduces the options. Whether using a flywheel or a motor/generator and batteries, KERS is bulky and awkward to package, especially as the refuelling ban means the larger fuel tank uses space where you might want your KERS. It’s this space clash that has caused Williams to drop its sizeable flywheel/motor system (currently being used on Porsche’s GT3 racers) for a more compact and flexible battery alternative.
While batteries will be placed as low as possible, the drive motor can mount anywhere along the driveline, even at the rear of the diff. But to keep mass central and avoid aero interference on the way to the rear wing it makes sense to place the motor at one end or the other of the crankshaft. Honda recently released details of its unraced 2009 system, which employed a motor/generator geared sideways off the front of the crank to sit alongside the tank, with its control unit in the sidepod and batteries low in the nose. It remains to be seen whether other teams have drawn similar conclusions. But the Honda installation reveals another complication: the sudden power switches are so intense that both motor and black box have to be liquid-cooled.
Outside F1, KERS technology is less restricted. Zytec (which shares technology with McLaren) ran a competitive hybrid LMP car in the ALMS, and recently tested a Honda Super GT with a motor in the transaxle. The 2011 edition of Lola’s hugely successful LMP1 coupe is designed to accept hybrid power, while the incoming Le Mans regs allow such systems on front or rear axles, so we may see 4WD cars at La Sarthe. This constant technology crossover confirms the old truth — racing does improve the breed.
With thanks to the Lola Design Office for their consultation. For more information on Lola click on to www.lola-group.com

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