The McLaren MP4-12C’s Sequential Shift Gearbox (SSG) is not only the lightest and most compact in its class, but it also sets new standards for the refinement and durability of a dual clutch transmission, according to supplier Oerlikon Graziano.
McLaren chose a dual clutch transmission (DCT) because it could combine smoothness and refinement with the potential for very rapid gearshifting and little or no torque interruption during acceleration.
“McLaren has a very clear understanding of its brand and of the type of cars that it should make. This is reflected in the technologies and innovations that are chosen for their powertrains,” explains Paolo Mantelli, head of automotive transmissions at Oerlikon Graziano. “As well as being immensely fast and dynamically capable, the cars must be comfortable, refined, efficient and a pleasure to drive every day. We worked closely with McLaren Automotive’s engineers to develop a new transmission that would help them meet these targets.”
The new transmission had to be as small as possible to allow the engine to be mounted close to the rear axle line, maximising passenger space. A three shaft architecture was chosen because it helps to minimise gearbox length.
All eight ratios use Oerlikon Graziano’s high-performance synchronisers, further optimised to allow substantially faster changes without compromising durability. In addition the transmission features a 'pre-cog' facility where light pressure on the gearchange paddle by the driver causes the transmission to engage the next gear and prepare the clutch. Full pressure on the paddle completes the gearchange in a fraction of the normal time.
“We wanted to achieve genuinely fast, smooth shifting without any of the ‘tricks’ that can be employed to make a DCT feel fast,” says Mike Everitt, MD of Vocis, a specialist in dual clutch control systems.
“The secret is to get the very best out of the whole control system with a highly-optimised interaction between the software and the hardware," Everitt says. "This ensures that the responses are not just quick and accurate but are also consistent and progressive. That means rigorous attention to the fluid dynamics and to the design and calibration of the control algorithms.”
The McLaren's dynamic performance - its ability in acceleration, braking and cornering - gave the transmission designers a tough task to ensure reliability. “At 1g, the oil will be at 45 degrees to the horizontal. The McLaren can significantly exceed 1g both cornering and accelerating and substantially exceed it under braking,” says Oerlikon Graziano’s dual clutch transmission programme manager Alberto Noto. Specialist test techniques allowed the team to improve the management of oil flow in the transmission, aiding durability while also minimising the weight of the gearbox.
The new transmission is manufactured at Oerlikon Graziano’s plant in Luserna, Italy, using a combination of precision automation and traditional craft skills, withcomprehensive end-of-line testing using custom-built automated systems.
Oerlikon Graziano has also recently started production of transmissions for the Lamborghini Aventador and Aston Martin Vantage S, each one using a different technology carefully matched to the character and technical requirements of the vehicle.
