McLaren Super Sports Car Has Seven-Speed DCT
A glimpse of the future potential of dual clutch transmissions in ultra high performance applications is provided by the sophisticated seven-speed gearbox and advanced control system fitted to the latest on-road sports car from McLaren Automotive, the passenger car division of the organization famous for its successful Grand Prix team and earlier road cars such as the F1 and the McLaren Mercedes SLR.
Though the new MP4 12C is a mid-engine, two-seater coupé incorporating all the latest Formula One know-how, it is not a direct successor to the limited-run, grand prix-inspired 1993 F1, nor a competitor to the Bugatti Veyron, both of which are in the million-dollar bracket.
Instead, the new McLaren is priced at around £150,000 ($225,000), and is designed to compete against familiar top-end sports cars such as the Porsche 911 Turbo, Ferrari 458 Italia, and Lamborghini Gallardo. In contrast to these models, however, 12C is fully composite in its construction, as McLaren achieved a breakthrough in volume production techniques for its highly-rigid carbon fiber tub, dubbed MonoCell by the company. This helps give the V-8 powered coupé a dry weight of under 1300 kg – substantially less than that of its competitors.
In the typically obsessive McLaren fashion, however, almost none of the 12C's components are off-the-shelf items, as might be expected for a car that is to be built at a rate of just 1,000 a year. Company engineers consistently refuse to make any compromises in component specifications or performance, so everything has been developed in-house or in collaboration with a select group of trusted suppliers. McLaren is tight-lipped about these relationships, but a report in Autocar magazine suggests that the flat-plane crank V-8 engine was co-developed with Ricardo. An earlier report in the same publication stating that the dual clutch transmission owes its origins to Italy’s Graziano is, however, contradicted by Richard Farquhar, McLaren Automotive’s Powertrain Manager, in the company’s launch material for the model:
"McLaren was offered proprietary dual clutch transmissions but none was right for our concept. The dimensions and packaging would have been compromised by the layout and positioning of the masses in every case," states Farquhar "Our Seamless Shift Gearbox (SSG) is a twin layshaft design with two small diameter wet clutches placed side by side, rather than concentrically."
"As a result we have built a seven speed gearbox that is 150-200 millimeters shorter than a conventional single layshaft six or seven speed box. This, in turn, allowed us to bring the mass of the transmission as far forward as possible in relation to the rear axle, thereby benefitting not only the concentration of weight nearer the centre of the 12C, but also allowing the central part of the diffuser to ramp up earlier for better downforce," he concludes.
In particular, explains Farquhar, the compact twin layshaft design helped minimize mass behind the rear axle, improving vehicle handling by focusing mass towards the center and reducing the polar moment of inertia, as well as improving rear crash performance. In further pursuit of the ultimate in handling dynamics and to keep the center of gravity as low as possible, the close spacing of the input and output shafts in the gearbox allows the whole power train to be set lower in the chassis.
As befits its Seamless Shift name, the transmission is controlled for maximum smoothness as well as peak performance by McLaren’s own electronic system, with the control box and the weight-saving aluminum wiring harness also McLaren's own design. The system offers multiple programs ranging from a highly-focused track mode to sport and normal for road use, and a fully automatic setting for times when driver involvement is not required.Additional modes include Launch Control for race-style starts and Winter, where all electronic functions are automatically set to suit low-grip conditions.
In terms of shift strategy McLaren says the SSG "... takes the driver’s own inputs and uses them to directly control the engine’s torque and speed to deliver performance, economy or comfort as requested." A key aspect of the shift strategy stressed by McLaren engineers is the Pre-Cog function. They liken this to the first press of the shutter button on a camera, an action which focuses the camera and sets the exposure, but which does not take a picture. On the 12C, the first-stage pull on the shift paddle sends a signal to the transmission to preselect the next ratio. The second-stage movement is the one that actually executes the gearshift, in a matter of milliseconds. The benefit, says the company, is even faster shifting once the command is given.
Even the method of gearshift actuation mirrors the experience of the grand prix car. The fingertip shift paddles operated by the driver are in fact a single die cast aluminum rocker, pivoted in the center of the steering wheel axis and turning with the wheel when the driver applies lock. A pull on the right-hand paddle – or a push on the left one – triggers an upshift; downshifts are prompted by a pull on the left or a push on the right. The two different actuation stages – Pre-Cog and the shift confirmation – are accompanied by a defined click from the paddle that can be felt and heard by the driver.
Seamless Shifting
The strength of the impulse felt by the driver during shifts can be adjusted by another unique McLaren feature, the rotary powertrain control switch on the dashboard Active Dynamics Panel. Rotating the P knob changes throttle response, gearbox strategy, shift times, and the feel of the gear change; a coaxial "manual" button controls the manual operation of the transmission. Three positions are offered: normal, sport, and track. An accompanying rotary switch – H, for handling – performs a parallel adjustment of chassis-related functions, allowing the driver to select the most suitable combinations of suspension and roll stiffness, steering weight, and stability control intervention. A similar concentric "aero" button deploys the airbrake to a 15-degree angle so as to increase aerodynamic downforce.
The advantage of the two separate controls for power train and handling is that the driver can set each independently of the other, said Louis Baldanza, McLaren Automotive’s Product Manager for 12C.
"Spirited driving on rough B-roads for example can be enjoyed with 'P' in 'sport' and 'H' in 'normal,' giving great throttle response and sharp gearshifts, but with a smooth ride. On arriving at a circuit, the owner can then simply switch to 'track' for both 'P' and 'H,' depress 'Manual' and 'Aero' for full control of the gearshifts and maximum downforce from the Airbrake," he concluded.
Given that the 3.8 liter, twin-turbo engine produces close to 600 hp and 600 Nm of torque, McLaren’s target of CO2 emissions of "... well below 300 g/km" would seem a major challenge, even taking into account the vehicle’s unusually light weight. "I am particularly satisfied by the environmental performance," says Farquhar. "With the 12C we are leading the way in the sports car market with a smaller capacity pressure-charged engine: not only will we deliver class-leading power output but the 12C engine will consume considerably less fuel than its competitors. Our target on emissions is 300 g/km of CO2, but we won’t rest until we get below that. "I am convinced we have created the blueprint for the way forward for engine technology in the sports car market," he insists.
To date, few people apart from McLaren staff and the company's F1 stars Jenson Button and Lewis Hamilton have driven the 12C. Yet its on-paper specification is extremely impressive, with many key aspects of its performance edge attributed to its innovative dual clutch transmission and the advanced electronic systems that control it.
With minimal torque loss, there is none of the lurch, hesitation, or unpredictability that characterize traditional automated-manual transmission systems, says the company: "The character of the transmission will engage even experienced drivers with its responsiveness and its contribution to the whole dynamic package," it insists. This could well prove to be an understatement – and the landmark McLaren could quickly become a high-speed advertisement for the benefits of advanced dual clutch transmission systems.
| McLaren MP4 12C Specifications | |
|---|---|
| Engine | 3.8 liter twin-turbo V-8 |
| Transmission | 7-speed wet clutch DCT |
| Target max power | 600 hp at 7000 rpm |
| Target peak torque | 600 Nm at 3000 rpm |
| Target CO2 emissions | <300 g/km |
| Performance | Not disclosed |
| Price | Approx $225,000-265,000 |
| Availability | Early 2011 |
Story Filed: 5/03/2010
By Tony Lewin, managing editor DCTfacts.com