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Old 10-08-2009, 07:14 AM
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Powertrain: pure McLaren

The McLaren MP4-12C is powered by a twin-turbocharged, 3.8 litre 90° V8 engine – the ‘M838T’. This marks the start of a new era in ‘core’ segment sports cars – smaller capacity, lighter weight, higher efficiency and more economical power units. The engine has the highest specific power output in its segment which, when allied to its low weight carbon composite chassis, delivers exemplary power- and torque-to-weight ratios.

’M838T’ is a unique McLaren power unit, developed specifically for the 12C. It is compact, lightweight, very stiff, and offers an uncompromising combination of very high performance and good driveability, with excellent economy and CO2 emission values.

Taking power and emissions in combination (measured by its horsepower to CO2 ratio), the 12C delivers its power at greater efficiency than any other car on the market with an internal combustion engine, including hybrids.

‘M838T’ features dual variable valve timing and produces around 600bhp and 600Nm of torque. A dry sump and flat plane crankshaft allow the engine to be placed extremely low in the chassis thereby lowering the centre of gravity and improving handling responses. It also features composite cam covers and intake manifolds, which reduce weight and heat transmission into the charge air, as well as Nikasil-coated aluminium liners for further weight reduction.

The McLaren engine revs to 8,500rpm, has quick transient throttle response and delivers its abundant torque throughout the rev range. A staggering 80 per cent of torque is available at below 2,000rpm, ensuring great driveability and no need to floor the throttle to deliver performance.

And it delivers a great soundtrack to highlight the engine’s performance, flexibility and driveability. The sound of the engine has been thoroughly engineered through exhaust manifold design and tuning of the exhaust and intake systems to deliver a unique engine note.

The high level exhaust pipes exit through a mixing box, rather than a conventional and heavy silencer box. All parts of the exhaust system up to the mixing box feature sandwich layer heat-shielding that helps reduce heat from the engine bay. In just an 18mm gap, exhaust gas temperatures reduce from 900°C to 300°C.

The engine drives the rear wheels through two wet clutches and a McLaren-developed seven speed Seamless Shift dual clutch gearbox (SSG).

The Seamless Shift technology offers variable programmes ranging from ‘normal’ for road use and ‘sport’ for quicker changes still, right up to a lightning quick high performance mode. In addition an ‘automatic’ mode, ‘launch control’ and ‘winter’ modes can be selected, the latter changing all electronic functions to suit low friction conditions and delivering maximum driver aid and support. There is no traditional manual transmission offered; the two pedal layout offered further scope to create a narrow, and therefore light, car.

The 12C’s SSG is a development on the automated and sequential manual gearboxes with paddle shifts that proliferate in the car market today. The character of the transmission will engage even experienced drivers with its responsiveness and its contribution to the whole dynamic package.

With minimal torque loss, there is none of the lurch, hesitation or unpredictability that characterise traditional automated-manual transmission systems.

Design of the SSG system was driven by a demanding mechanical package that not only reduced weight and improved dynamic control for the entire vehicle, but also delivered driver benefits.

It is lightweight and compact in design and positioned in exactly the best location. The input shaft lies very close to the output shaft to help position the entire powertrain low in the vehicle. Twin secondary shafts ensure any rear axle weight overhang is minimised and rear crash performance is uncompromised. The bespoke SSG is further complemented by an entirely new control system.

This obsessive attention to detail comes as second nature to McLaren, but is not just there to satisfy the engineers’ passions. McLaren’s designers have also engineered the system to work seamlessly with the driver.

The system reduces weight and benefits packaging targets, but also ensures that driving programmes and shift strategies take 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.

Gears are changed using a Formula 1 style rocker shift that pivots in the centre of the steering wheel. It is actuated on either side of the steering wheel (pulling right changes up, pulling left down).

As with the McLaren Formula 1 car, a shift can be actuated either by pulling or by pushing on the rocker. The rocker moves with the steering wheel, rather than being mounted on the steering column, so that if a gearchange is needed while lock is being applied the driver does not have to fumble around to change gear.

The rocker itself incorporates an innovative feature created by McLaren engineers called Pre-Cog. The name stands for pre-cognition, literally ‘foreknowledge’. The rocker on the 12C has two positions with a slightly different haptic (or feel) for each. The driver applies first pressure to the rocker and it informs the gearbox to get ready to swap ratios, thereby saving time – latency – between the message being sent and the gearbox being primed to act. The second pressure confirms that the gear should be changed and the torque handover is completed in milliseconds.

“What Pre-Cog actually does is initiate the shift process by priming the clutch and torque handover – it takes significant time out of the process,” explained Dick Glover, Technical Director McLaren Automotive.

“It’s a little bit like the first pressure on a camera shutter button. There’s no requirement for the driver to use it but it is more satisfying and engaging if you do. The SSG also promotes seamless shifting in which the driver doesn’t have to reduce engine power at all – rather than the gearshift slowing you down, it actually speeds the car up by recovering the energy of the crank spinning as it drops engine speed,” he said.

In practice the latency of the shift is virtually zero, the actual gear change time is very fast and the level of impulse can be varied according to the gearbox mode. Considering that McLaren was the first Formula 1 team to introduce seamless shift gearchanges into motor racing, it was a natural step to develop such a bespoke transmission to its sports car project.


Chassis: Proactive control

The suspension for the McLaren MP4-12C breaks new ground, offering hitherto unseen levels of roll control and grip (an almost flat cornering attitude, depending on the programme selected).

Although such track-like responses would normally imply a rock-hard ride, the 12C delivers compliance and ride comfort more akin to an executive saloon car. The mix of occupant cosseting and sporting potential is truly unique. The 12C offers the driver both class-leading ride comfort and class-leading performance.

The whole chassis package produces not only a unique relationship between ride and handling, but also astonishing lateral grip and outstanding traction. The 12C is poised and balanced whether negotiating high or low speed corners, during direction changes, under heavy or light braking and on tightening or opening corners.

The trick behind blending such opposing objectives lies in the innovative Proactive Chassis Control system, uncompromised geometry, and weight distribution.

The suspension is based on double wishbones with coil springs. The dampers are interconnected hydraulically and provide adaptive responses depending on both road conditions and driver preference.

The Proactive system features adjustable roll control which replaces the mechanical anti-roll bars that have been a standard feature of road cars since time immemorial. It allows the car to maintain precise roll control under heavy cornering while decoupling the suspension in a straight line for excellent wheel articulation and compliance.

There are three suspension modes that are selected on the Active Dynamics Panel. As with the powertrain adjustment, there is a ‘normal’, a ‘sport’ mode and a high performance mode which adjusts numerous parameters in the system.

Not only is the Proactive suspension a unique application that delivers absolute benefits to driver and passenger, but it is also another example of McLaren’s drive to achieve all-round performance goals from core engineering targets.

For example, the unique blend of a compliant ride with ultra-sharp handling also delivers ownership benefits as it protects suspension bushes from wear and tear, with McLaren’s research suggesting a potential for up to ten times more mileage than on some competitor cars. Also, the hydraulic pump that supports the dampers is the same pump that supports the electro-hydraulic steering system. Why use two pumps when one - small and lightweight - pump will do?

The powertrain packaging also contributes to the 12C’s handling prowess.

The engine is mounted low down in order to lower the centre of gravity while the radiators are rear-mounted and reduce weight by saving on long piping to and from the engine (and the fluids they would hold). The value of rear-mounted radiators is key to the 12C’s handling and balance. The more weight that can be concentrated within the wheelbase and towards the centre of gravity, the lower the polar moment of inertia, thereby improving corner turn in.
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