New BMW M6 Convertible in Depth

Press Release

Page 1: Short Version
Page 2: Design
Page 3: Drivetrain
Page 4: Chassis
Page 5: Safety
Page 6: Equipment
Page 7: Specifications

• Powered by 2005 and 2006 International Engine of the Year winner

• The most advanced BMW production car engine ever

• Formula 1-inspired technology and manufacturing processes

• Engine ECU makes 200 million calculations per second

• 5.0-litre V10 engine powered recent world land speed record holder

• World’s first production seven-speed sequential manual gearbox

With its origins in BMW’s recent 10-cylinder Formula One programme, the heart of the new BMW M6 Convertible offers enthusiasts one of the most advanced engines currently on sale. It has ‘the best engine in the world’ having been awarded the coveted International Engine of the Year title for the second successive year – a first in the history of the awards.

Delivering an intoxicating blend of refined power, tractability and economy, not to mention a thrilling exhaust note, the 5.0-litre V10 unit offers the performance of a supercar for use everyday. The 4,999cc engine was the first high revving V10 engine to appear in a BMW production car, making its debut in the BMW M5 in April 2005 followed by the M6 Coupé in September. Producing 507hp at 7,750rpm, but with a maximum engine speed of 8,250rpm, the new M6 Convertible provides all the performance of an M car but with the added benefit of wind-in-the-hair motoring.

Such an accomplished set of statistics are underscored by the car’s real world driveability. A peak torque figure of 520 Newton metres at 6,100rpm is important but the engine also serves up 390Nm of torque at just 1,500rpm for real world-pulling power. This figure is made all the more impressive with the knowledge that this is a naturally-aspirated powerplant without any supercharger or turbocharger to boost output.

At full power the pistons of the high-revving naturally aspirated engine cover 20 metres a second. By comparison the pistons in a modern day Formula One engine move at 25 metres per second at 18,000rpm. Only a minor difference in speed but, while the F1 engine only has to travel 500 miles or so before a complete rebuild, the M6 Convertible’s powerplant has to last a lifetime.

Cast at the BMW light alloy foundry in Landshut, the same place as the BMW’s F1 engines, the M6 Convertible powerplant is inspired by the pinnacle of motorsport. Each of the ten cylinders has its own throttle butterfly and the new V10 engine is the first series production V-engine to feature a bedplate design for the crankcase.

Brains behind the brawn

The performance of BMW’s V10 engine would not be possible without the world’s fastest engine management system (MS S65). It can perform over 200 million individual calculations per second – a record for a regular production car engine. Compared to the award-wining E46 M3 engine, an MS S65 system is eight times faster and has ten times as much memory capacity.

Made up of more than 1,000 individual components, including a 32-bit processor, the M6 Convertible’s ‘brain’ co-ordinates all engine and gearbox functions using several subservient control units. Furthermore, it is not a component that has been bought in from outside. BMW created all the hardware and software of the MS S65 in-house and this ease of integration is one of the reasons for the engine’s outstanding performance and emissions data.

When operating, the MS S65 receives over 50 input signals and calculates the optimum ignition point, ideal cylinder charge and injection quantity for each individual cylinder on each individual combustion cycle. The unit also calculates the optimum camshaft angle and the ideal position for each of the ten individually controlled throttle butterflies.

The system manages other ancillary functions:

• the electronic throttle control valve is co-ordinated by a potentiometer on the accelerator pedal

• idle speed control and emissions control for the optimum in torque and power output

• on-board diagnosis for use by BMW service engineers

• new and innovative ionic current technology to manage engine ‘knock’, misfiring and combustion ‘misses’

• ‘Power’ button beside the gear lever allows a 400hp or 507hp engine programme to be selected. The M6 Convertible always starts in P400 mode - the engine is programmed to deliver ‘only’ 400hp. Pressing the Power button brings in the full 507hp. The 507hp setting can be pre-selected in MDrive Manager within iDrive and activated immediately from the MDrive button on the steering wheel, along with other bespoke selections. (See later in this section)

Bi-VANOS

All BMW petrol engines have been fitted with a variant of VANOS, BMW’s variable camshaft timing system since the M52 engine appeared in the 1994 E36 3 Series and the E34 5 Series of the same year. The latest incarnation fitted to the M6 Convertible ensures the optimum charge cycle to deliver the best balance of performance and economy.

The adjustment of the camshaft timing relative to the crankshaft is variable and controlled by the MS S65 control unit. Bi-VANOS allows for an adjustment in angle of the intake camshaft by up to 66° while the outlet camshaft varies by a maximum of 37° relative to the crankshaft. These angle adjustments are made as a function of the accelerator position and engine load. In practice, this means increased performance, an improved torque curve, optimal response to driver inputs, lower fuel consumption and fewer emissions.

For example, with the accelerator depressed and the car at low speed the Bi-VANOS system increases valve overlap thereby boosting internal gas recirculation. This reduces the chance of some of the fuel not igniting in the cylinder and lowers fuel consumption. Despite being a high performance car, the M6 Convertible records 18.6mpg on the combined cycle.

A clean exhaust and sound

Although the intake system contributes significantly to the performance of the V10 M6 engine, the importance of the exhaust cannot be underestimated. Two stainless steel five-into-one, equal length, tubular manifolds carry the exhaust gases from the engine. To achieve exact diameters, the seamless pipes have been formed from the inside using hydroforming - a high water pressure forming technique using pressures up to 800 bar to create a pipe wall thickness of just 0.8mm.

This exhaust construction process saves weight and allows for optimum engine breathing. The detailed construction and layout of the exhaust system virtually eliminates back pressure. As a result of the thin-walled exhaust manifolds, the catalysts heat up and reach their optimum operating temperature more quickly, even after a cold start.

To meet European EU4 and American LEV2 standards two trimetal-coated catalytic converters are fitted in each of the two exhausts to clean the exiting gases. The BMW M6 Convertible posts CO2 emissions figure of 366g/km. The gases leave the exhaust system through four prominent tail pipes, a BMW M trademark, that give the M6 Convertible its distinctive deep throated growl.

Lightweight engine technology

It is not just the exhaust gas manifold where weight reduction has taken place. Every gram of unnecessary mass has been removed to deliver a V10 engine that weighs the same as a V8.

• The very stiff and finely-balanced crankshaft weighs just 21.8kgs and is made of forged, high tensile steel carried in six bearings for strength.

• Each piston is made of high temperature resistant aluminium alloy with an iron coating and weighs 481.7g (including gudgeon pins and piston rings).

• Each fracture-split connecting rod is made of high strength 70MnVS4 steel and weighs 623g (including the bearing shells).

The V10’s two aluminium cylinder heads are produced at the BMW light alloy foundry in Landshut, alongside BMW Formula One engines. Each features integrated air ducts (important for rapid catalytic converter warm-up) and four valves per cylinder, with valves actuated by spherical tappets with hydraulic valve play compensation. The tappet diameter has been reduced to 28mm and each one weighs only 31g.

Ten individual throttle valves

Pioneered in motor sport, each of the ten cylinders has its own throttle butterfly. The highlights of such an arrangement are:

• All throttle valves are electronically-controlled.

• Two contact-less Hall potentiometers determine the position of the throttle pedal 200 times per second.

• The engine management system reacts in just 120 milliseconds and causes two activators to adjust the ten throttle valves.

• The V10 engine uses ten flow-optimised intake trumpets to breathe air from two intake plenums. Both the plenums and trumpets are made of a lightweight compound containing 30 per cent fibreglass.

High g-force lubrication

Under hard cornering the new M6 Convertible has the potential of generating more than 1g of lateral g-force. Under extreme braking, negative acceleration of up to 1.3g can be reached. Under such extreme conditions, it is critically important that engine oil continues to lubricate the two cylinder heads and the crankcase. The engineers have therefore equipped the M6 with a quasi-dry sump system and a ‘traverse’ force regulated supply.

When lateral acceleration exceeds 0.6g oil is forced to the outer cylinder head. The traverse oil supply system, incorporating two electrically operated duo-centric pumps, collects the oil and transports it to the main oil sump. A lateral g-sensor also transmits signals to the pumps to determine the exact volume of oil required at the sump. Using two oil reservoirs – a smaller one in front of the cross member and a larger one behind – the quasi-dry sump oil system ensures that the crankcase is never short of oil regardless of the g forces.

World’s first seven-speed Sequential Manual Gearbox

BMW was the first manufacturer in the world to offer a seven-speed sequential manual gearbox with Drivelogic. The seven-speed sequential M gearbox (SMG III) has been designed specifically for the rigours of the high revving 5.0-litre V10 engine – it is capable of handling torque of up to 550Nm and engine speeds of up to 8,500rpm.

But why seven-speed? Smaller steps between each gear reduce the dips in torque and power as each higher gear is selected. The transmission, with its short overall transmission ratio, matches the torque to the power output and ultimately translates it into optimum forward thrust.

The seven-speed SMG system is a true manual gearbox but with the gear changes managed by a super-fast electronic programme. Gears can be changed using the gear lever – forward to change down, backwards to change up – or by using the paddles behind the steering wheel. The SMG system efficiently matches engine speed, even in the case of full throttle upchanges. Offering all the benefits of a manual gearbox, such as engine braking and lower fuel consumption, the SMG system means there isn’t the energy-sapping torque converter of an automatic.

How it works

The gears in an SMG system are shifted electro-hydraulically using shift-by-wire technology – a product of the aerospace industry. This latest incarnation of an SMG system has the hydraulic unit and actuators integrated into the gearbox casing. When a change is required, the control unit actuates magnetic valves controlling the system’s hydraulics.

The hydraulic oil, operating under 90 bar pressure, flows via a magnetic valve into the clutch master cylinder to open the clutch. Then, using solenoid valves, four hydraulic cylinders in the actuator are switched, affecting the gear change process by means of four rods. When down-shifting the transmission double de-clutches automatically, including a blip of the throttle so the gears mesh perfectly.

To put this technology in perspective, the new seven-speed SMG III is 20 per cent quicker than the previous SMG II system that saw service on E46 M3 models. That’s a gear change in just 50 milliseconds – much faster than a talented driver using a normal manual gearbox who would take ten times as long.

The optimum change point is identified in the M6 Convertible using the rev band in the Head-up Display. When the rev band flashes, the optimum gear change can be achieved.

Drivelogic

An essential feature of the new seven-speed SMG system is Drivelogic, which offers 11 gear change options determined by the driver with a push of a button. Each programme offers a different speed of change. The higher the programme selected the shorter the shift time. These programmes are chosen using the Drivelogic button beside the gear lever. Alternatively the MDrive Manager function (see below) can be used to select a gear change speed as a part of the one-touch MDrive button function activated by a switch on the multi-function steering wheel.

Launch control

The concept of the sequential manual gearbox has its origins in motor sport. It is not surprising, though maybe a little indulgent, that a launch control function is included. The system is honed to ensure that the rear wheels transmit the maximum power to the road without spinning excessively. In other words, it provides the optimum straight-line acceleration.

To activate launch control:

• switch off the DSC traction control fully

• select the ‘S6’ manual gear change mode with the Drivelogic button next to the gear lever

• push and hold the centre gear lever forward while applying full throttle with the accelerator pedal

• when the optimum engine speed for take-off is reached (4,200rpm), release the gear lever and allow the SMG system to take over

• the accelerator pedal must be kept fully depressed for the M6 to accelerate as quickly as possible with the gearbox continuing to up-shift on the way to the car’s maximum speed. If the accelerator pedal is released, even by a fraction, the launch control function is cancelled

Launch control is not a function for use on public roads.

MDrive Manager for even more control

The MDrive Manager provides one car with two or more personalities - an automotive Jekyll and Hyde. Activated by the MDrive button on the steering wheel, the driver can select very different personalities for their M6 Convertible. The system can be set up in the MDrive Manager section of iDrive. From there a number of individual performance functions of the car can be pre-selected and then activated via the MDrive button.

• Engine output. Three stages are offered P400, P500 or P500 Sport.

• Gear change speed. SMG Drivelogic offers one of six manual programmes or five automatic shift modes

• Three stages of traction control: DSC active, MDynamic Mode engaged (enabling greater degrees of controllable wheel slip) or DSC deactivated.

• Ride comfort. The Electronic Damper Control can be set to Normal, Comfort or Sport damper settings.

• Head-up Display preference. Normal or M specific display mode can be chosen.

MDrive Manager allows a comfortable day-to-day GT to metamorphosise at the touch of a button into a raw sports car. For example, the driver of an M6 Convertible could go from gentle cruising to a car set to P500 programmed for power, the SMG set at the fastest shift setting, DSC selected to MDynamic Mode, damper control on ‘Sport’ and the Head-up Display on the M mode, all at the touch of one button.