• The McLaren P1: Pushing the envelope

    • McLaren P1
    • McLaren electric motor battery
    • McLaren's SA-born marketing chief Greg Levine
    • Characteristic McLaren nostril slits guide hot, tumbling exit air sideways, but allow a precisely channeled blast of cool air through to the intake snorkel. Right: cutaway shows drivetrain component layout of electric motor and battery (green), petrol engine (pink) and transmission (orange).
    • McLaren front view
    • McLaren button detail
    • E-drive team leader Richard Hopkirk explains electro-boost
    • Chief designer Dan Parry-Williams
    • Cutaway showing the drivetrain
    • Jekyll or Hyde? Pushbutton control for electro-boost, ride characteristics and drive mode. (Right) Aero balance is maintained by active elements front and rear.
    Date:13 July 2013 Tags:

    Attempting to build the ultimate modern supercar around a breakthrough go-fast technology that exists nowhere but in your mind could be considered questionable. But McLaren went and did it anyway. By Anthony Doman

    MacLaren P1
    Powertrain: Longitudinal mid-engine, RWD with integrated lightweight electric motor
    Engine: V8 twin-turbo, 3 799 cm3, 550 kW
    Electric motor: 133 kW
    Transmission: 7-speed SSG
    Body: Carbon fibre monocage
    Suspension: RaceActive chassis control
    Weight: 1 395 kg
    0-200 km/h: <7 seconds
    Top speed: 350 km/h (limited)
    Price: R11,5 million (approx)

    The brief: stunning looks, racer performance, planet-friendly electric drive. The problem: nobody knows how to do it. And besides, it doesn’t exist.

    McLaren Automotive has provided an unprecedentedly detailed look into the process of developing a supercar by putting its new roadgoing flagship P1 under the microscope in an intensive, extended briefing at its technology centre at Woking in Surrey, south of the English capital. Tech media spent one and a half days immersed in the minutiae of the car in P1 – The Workshop. Under the stewardship of chief designer Dan Parry Williams, team leaders in the P1 project revealed insider details of a car that represents not only a homage to a formidable high-performance heritage, but also a breakthrough in technology. At the same time, it is the flagbearer for a new direction in motor racing.

    Transformer action toys on the tables told a story about where the design team were at when they began throwing around ideas a little over two years ago. “In general, there was something in the air about a kind of Transformer car, maybe. That was where we started: a car that would actually transform itself from one thing into another,” says Parry-Williams. It had to be about more than top speed and acceleration. Even the company’s previous car, the 12C, is “beyond the capability of most public roads”, he says.

    Essentially, the new car had to be beautiful, without compromising performance. It had to be comfortable for road driving, but have massive downforce so that it could be as fast on a track as a GT car. Finally, it had to have electric drive that raised the bar in terms of performance.

    Transformer
    “The first challenge was how to turn a road car into a race car,” says Parry-Williams. “We needed to get 200 per cent stiffer in heave, or vertical mode, and lower by 50 to 55 mm. In other words, completely change the suspension. “We didn’t want to do this with a truck and a team of technicians – we wanted to do this with a button.” Except they had no idea how to do it.

    Track cars ride very low, for best aerodynamics, and they need plenty of downforce with rock-hard suspensions. “You have to make them very stiff so as not to bury them into the ground at high speed,” says vehicle dynamics specialist Paul Burnham. That’s completely opposite to a road car, which needs good ground clearance and a soft ride.

    Using the 12C’s hydraulic system as a basis, the P1 adds new circuits that provide complete, independent control of ride height and heave stiffness – at the touch of a button. This changes the amount of fluid in the circuits, and the pressure in those circuits and that controls the stiffness through the use of gas accumulators. The suspension geometry is completely new, to cater for the radical change in operating conditions.

    The force
    Downforce is a prerequisite for a successful race car. Simply slapping a big wing on the rear would achieve the 600-kg target McLaren had set (more than a GT racer’s) – at the cost of horrendous drag, to say nothing of horrendous looks. Moreover, because the downforce varies as the square of the speed (double the speed and you get four times the downforce), by the time you reach top speed, there is too much of it.

    They needed an active system to create a suitably efficient aerodynamic road car that could stick to the road like a racer. And then there was also the little matter of cooling 900 horsepower and an E-drive system.

    “We had to have low drag and a car that looked good. The starting point was trying to fit the wing between the car’s rear haunches,” explains Simon Lacey, who moved from heading aerodynamics in McLaren’s racing division to the P1 programme. The narrower wing lost downforce, which had to be found by adding camber via using a two-element rear wing. “(That) was great for me because it meant I could wheel out all the wing design tools from Formula 1,” he says. The only unique change is that this wing does need to go back into its low drag position, so it retracts into the bodywork. “We can cut drag by 30-35 per cent when you back the wing off,” he says.

    The rear downforce has to be balanced with force from the front end. Using a race car’s front splitter was out of the question because of considerations such as pedestrian safety and intake vents for cooling.

    “Essentially we followed the same thought process as with the rear wing: if you can’t do it with size, do it with curvature,” he says. The solution was a wing section into the floor just in front of the front wheels.

    “In the same manner that we had the active rear wing to generate rear downforce, we had to have something in the front of the car so that when the wing was backed off we were still close to the balance we were trying to achieve. We have added these flaps just on the trailing edge section of the wing to spool the air coming off it, so when we are either backing the rear wing off or under heavy braking, we can spin off a bit of front downforce, not make the car quite so grabby.”

    It cuts through the air with minimal disruption. “You can see the car is incredibly small already, but the air that we leave behind is smaller still… we tried to design a car that every packet of air coming towards it does one job, and one job only, and then we get rid of it.” An example of that is the characteristic McLaren “nostrils” on the bonnet of the car, the exits for the central cooler. Hot, turbulent, tumbling air coming out of it is spaced specifically to allow a pocket of cool undisturbed air to come up the windscreen and to drop just inside the correct width for the engine air intake on the roof.

    All about E
    As experienced as they were in aerodynamics and suspension, so inexperienced were McLaren in road-car hybrid systems. “I don’t know whether it’s smart or dumb to take on something like this, but we’ve done it,” says Parry-Williams.

    Off-the-shelf systems just were not up to the job. “We would have been able to reduce CO2, but it would definitely have made the car go slower,” he says. “We also wanted surprising EV performance, but a realistic engine range, as I’ve mentioned before… and there’s no doubt that it puts a grin on your face.”

    They needed to design and build the highest-performance system of this kind ever. One of those they enlisted was E-drive team leader Richard Hopkirk, who spent eight years in racing powertrains – specifically Formula 1’s KERS (Kinetic Energy Recovery System) electro-boost. His previous job, in fact, was managing KERS tactics for F1 driver Lewis Hamilton.

    Hopkirk says the simplest way to think of an E-drive system is as an instant energy buffer, able to move energy from engine to wheels and back. “And you can do that instantly, which gives us quite a few neat tricks you can play with the system: it practically eliminates turbo lag, can be used in gearshifts to pull the engine speed down when you’re changing gear, to blip the throttle during downshifts, and in traction control to give you a faster response and to improve your lap time. The car’s brain is adjusting the e-motor torque 200 times a second and it does that continuously.”

    Adding an E-drive boost can be done automatically or by pressing the IPAS (Instant Power Assist System) button on the steering wheel.

    “In auto boost, we have shaped the combined torque curve to what we think is the best performance for most tracks and most around town use. It’s nice and progressive at the midrange, but flaring out to peak power at the top end and the key point to note is that at the bottom end, 1 000 r/min, the torque is 500 N.m. That is almost as much as the 12 C flat out, which is 600 N.m. So that is really serious pull from this powertrain.”

    When the driver wants full control, activating IPAS gives maximum acceleration, like F1 drivers use KERS. The big difference: F1 drivers are limited by regulations to just 7 seconds a lap. IPAS is available on a continuous basis.

    “Now you’ve got two challenges: the first is maintaining battery charge, so you don’t run out of power, and the second one is keeping the system cool. The system maintains charge – it recharges really aggressively in race mode. Then we control that torque curve so that down the straight you use just the right amount, so that for most tracks you are going to be truly charge sustaining.”

    The electric motor produces similar performance to “let’s say, the upper end of the VW Golf range. This thing’s nippy; you can cruise silently around town, nipping into gaps in traffic. You can even take it on a motorway… it feels like a proper car to drive.”

    To improve overall system performance it’s been made as light as possible. The charger off-board, unusual for a plug-in vehicle, and because the battery is built into the carbon fibre monocage it doesn’t need a separate case. Higher than normal system voltage keeps the conductor size down. “We have put the e-motor on the input shaft of the gearbox and run it faster. That means you can super-high performance and torque, but for less weight.”

    And CO2 emissions are less than 200 grams a kilometre. The Bugatti Veyron gets 600 g/km.

    The power
    Uncomfortably close to the driver’s rear end, exhaust gas streaming into the turbo at 980 degrees was just one of the many challenges facing the team trying to package what is essentially two different powerplants in the P1’s “shrinkwrap” design. But that knowledge is also part of the driving experience.

    “We had to keep the exhaust system light (but) we are dealing with tremendous temperatures in the rear,” says Paul (Arkesdon). “We looked at the F1 teams and how their systems worked, and we started to explore exotic metals such as Inconel and gold, both of which are employed on our exhaust system here. The biggest challenge is that it has to meet legislation – it has to be road-legal. We also set ourselves an internal target: this is a track car, it has to sound exciting.”

    The driver experience also played a part in the design of the air induction system. It uses a roof snorkel, reminiscent of the original McLaren road car, the F1. But this element is incorporated in the monocage to avoid superfluous features on the outside, “We had to tune the induction system for the driver to be able to feel the air. We’ve tuned the whole system for NVH, while still being very lightweight.”

    The engine itself is a complete rework of the 12C’s twin-turbo V8. Everything from fuel pump to pistons has been redesigned and the new turbos are bespoke to McLaren. Of the patent-pending cylinder heads, he says, “Two years ago, a number of industry heads said that we were never going to be able to design this head. We have actually bettered what we set out to do.” The cylinder block has been redesigned to make it compatible with the electric drive and has also been made internally stiffer. The transmission is basically that of the 12C, but with better cooling, the ability to marry electric drive and the capacity for much higher torque loading.

    Allan Paterson, from battery supplier Johnson Matthey, says the target set was the highest power density battery system in a road vehicle – “a system that can discharge itself twice in a 7-minute Nordschleife lap and still last the lifetime of the car is no mean feat”.

    A huge amount of engineering, much of it to refine the liquid cooling system’s complex system of baffles and channels to equalise the cooling fluid flow rate, went into the design.

    What they ended up with is six modules, each containing 54 lithiumion cells for a total of 324 cells producing 555 volts. Out of its total weight of 92 kilograms, the cells weigh 68 kilograms. That’s far better than traditional battery packs for hybrids, in which the battery portion weighs about half the total. Battery chemistry has created power densities an order of magnitude higher than conventional hybrid systems, with an active balancing system that is able to shuttle energy around between the cells in the pack.

    “In terms of numbers, it’s more about continuous steady state power, and that’s about 135 kW. In terms of instant peak power, that’s about 180 kW for a few seconds. EV-only range is at least 10 km; the pack is rated just under 5 kWh.”

    The electric motor itself, created in-house from scratch within 2½ years, develops 120 kW and weighs about 40 kg with its associated controller electronics. That is the highest performance to weight ratio of any automotive electric motor available today.

    Overall, they achieved what they set out to do. It’s a hugely impressive technological achievement. To listen to chief test driver Chris Godwin, it’s pretty decent to drive, too. The ultimate supercar, though? Dry and understated, Parry- Williams conceded that “the best the world has ever seen” was all very well… “until the next one comes along”.



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