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9 janvier 2012 1 09 /01 /janvier /2012 21:00

I found an interesting article on Ricardo's website related to the MP4-12C engine. Link to the pdf were the article copied below has been published.

OPR33In some ways the M838T is a classic design, a 90 degree V8 with a flat-plane crank and four valves per cylinder. But despite that superficial orthodoxy and despite its extraordinary robustness, there is nothing ordinary about the specification of the new McLaren V8: in fact, it is cutting edge in almost every respect. The engine has the lowest CO2 emissions in its class – just 279 g/km – and meets both EU5 and ULEV2 emissions standards. Power output is a thrilling 600 PS at 7500 rev/min, matched by 600 Nm torque at 3000 rev/min. Thanks to clever fundamental design the compact cylinder block has an exceptionally low mass: not only are the main and lower bedplate crankcases sand cast in aluminium alloy, but so are the top-hung, wet cylinder liners, a feature which saves an additional 4 kg compared to conventional cast iron liners. Careful targeting of the sand cores helps keep the weight down too, and the finished assembly comes in at just 36 kg. The flat-plane crankshaft allows a smaller counterweight radius and, combined with the short stroke, this allows a low block height of just 201 mm and a crank-to-ground centre line height – important for road-holding – of only 121 mm. Dry-sump lubrication also allows low positioning of the engine in the chassis and this helps create the lowest possible centre of gravity for the MP4-12C. 

So-called picture-frame sealing eliminates T-joints in the crankcase assembly and thus the risk of oil leaks, while high levels of feature integration (as opposed to separate components and covers) not only reduces component count and weight, but also the likelihood of faults such as coolant leaks.

Ricardo’s analysis tools played a crucial role in designing a high-quality and robust engine, and their use in the development of the cylinder block is a particularly good example. “We did encounter some difficulties and we are quite open about that,” admits Yates. What is important, though, is how those inevitable hurdles were identified and quickly overcome. Early on in the development phase there were some instances of liner cracking, for example, but by looking closely at the clearances, the support and how the liner was loaded and clamped, these problems were quickly eradicated.

Pumping losses (the energy expended pumping air into and around an engine) are a major source of wasted energy and increased fuel consumption. In the new V8, Ricardo isolated crankcase bays one and four from two and three and also isolated the timing chain case from the crankcase bays. This prevents the transfer or, literally, the pumping, of air between the bays and through internal passages: this significantly improves both power and fuel consumption at high speeds.

Top end design

The cylinder head is one of the most important assemblies in any engine, and its design makes a particularly important contribution to the performance, emissions and fuel consumption characteristics. In this case, each of the two cylinder heads has double overhead camshafts, each camshaft being fitted with its own phaser. Like the block, the cylinder heads are optimized for weight, single-piece plastic cam covers giving a net weight saving of 2.3 kg and an aluminium rocker carrier and thin-wall spark plug tube saving a further 2.5 kg.

The narrow included valve angle reduces the width (and weight) of the head and an integrated housing for the variable valve timing gear enables compact oilways and minimises the overall length of the heads. Again, from the perspective of quality and robustness, single-plane oil sealing rules out oil leaks.

Needless to say, the head design is minutely optimized to maximise performance and minimise fuel consumption and CO2 emissions. Exhaust valve size is maximised to avoid gas flow restriction and to increase the available turbine energy. Intake ports are designed to provide excellent gas flow while retaining good tumble characteristics for efficient fuel-air mixing. The high flow rate reduces pumping losses and the tumble helps low-speed combustion as well as improving fuel economy at high speed. The quadruple cam phasers improve response, torque, power and fuel economy throughout the engine speed range.

The valvetrain features end-pivoted finger followers and a single ‘beehive’ design of valve spring, the low mass and high stiffness of which provides accurate valve control at high speed while keeping forces – and thus frictional losses – to a minimum. The cam profiles were also designed to improve these characteristics, with the use of VALDYN at the design stage helping eliminate any risk of loss of contact with the camshaft, spring surge or valve bounce.

The head casting went through a number of development phases after analysis of the first version revealed the potential for excessive temperatures in the exhaust bridge. Thermo-mechanical finite element analysis made it possible to evolve the design of the cooling passages and head gasket shaping to optimize the targeting and velocity of coolant jets, as well as making components easier to manufacture.

Cooling: critical for efficiency

Temperature control is critical to engine efficiency, and for this reason the V8 has a three-plate electrical thermostat which allows higher running temperatures during normal driving and ensures operating temperature is reached very quickly. The three-plate thermostat is effectively three-way or with three valves, so the unit can graduate cooling, something that is especially important during warm-up or during part load. It offsets the huge thermal changes between an engine capable of idling at a few hundred revs producing minimal power and maximum power of 600 PS at 7500 rev/min.

On that note, even the idle speed of the V8 was scrutinised and reduced to 600 rev/min from its initial target of 850. “The idle speed was important and driving that down was something we found we could do,” says Yates. “It benefits CO2 emissions and also the noise characteristic of the engine.”

Clearly, the sound quality of a supercar engine is crucial and a considerable amount of work was carried out to get the balance just right both inside and out. Because turbochargers significantly mute the wave form of intake noise, a sound transmission system incorporating a resonator was included to pipe sound to the cabin. The design of the exhaust system also took into account sound quality as well as efficiency. Like the cam covers, the entire inlet manifold is also moulded in plastic, reducing weight at the top of the engine to lower the centre of gravity.

The test regime was thorough and unforgiving. Five thousand hours of basic testing on seven dynamometers running in shifts served to check and validate every aspect of the new engine – from performance and emissions to mechanical durability testing of individual components. The work included thermal shock testing – the engine temperature rising to 116 Celsius at full power then being ‘crashed’ back to 20 Celsius using chilled coolant – a brutal process repeated hundreds of times to verify fatigue performance as well as severely checking the sealing of joints and components.

A further 3000 hours simulating the famous Nürburgring Nordschleife race circuit using real data logged during track testing there gave the equivalent of 73,000 km on-track driving. At the same time, major component and system-level testing was being carried out elsewhere on rigs in a combined test plan between Ricardo, McLaren and their suppliers. Final vehicle testing comprised more than 1,000,000 km on a mixture of road and track at Nardò, Idiada and the Nordschleife. The final stage prior to production was the building of 95 ‘made like production’ prototypes using production sequences and tools.

At the end of all of this, and just 18 months from the start of the collaboration with Ricardo, a unique new engine was born, possessing spectacular performance and emissions and easily meeting the high-level goals set by McLaren based on the exacting expectations of its very discerning customer base. The MP4-12C that it powers defines a completely new segment within the premium sports car market. To build a brand new car is a challenge; to build a brand new high-performance sports car that is ground-breaking, efficient, high-quality, lightweight, practical, dynamic, safe, comfortable, and visually arresting is a greater challenge still. McLaren – with help from Ricardo and other highly innovative supply chain partners – looks to have achieved this in considerable style.

And for Ricardo employees and investors, the new High Performance Assembly Facility also provides a proven approach for taking high performance, Ricardo-developed products into production applying world-class quality principles and practices within a lowvolume setting. As such, the facility is both a model factory and a business template that will be of keen interest to many potential customers seeking to add a halo, high-quality, performance product to their model line-up.

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