By December 12, 2013 Read More →

New BMW M models designed to excel both on the road and at the track

BMW M4 Coupe_frontOne of the primary objectives in the development of the BMW M3 Sedan and BMW M4 Coupe was to ensure the new cars offered impressive race track capability. In order to provide steering precision, on-the-limit adjustability, agility and driving feeling together with unbeatable traction and outstanding directional stability with the significantly increased performance capability of the new BMW M3 Sedan and new BMW M4 Coupe, the axles of the outgoing BMW M3 have been redesigned with painstaking attention to detail. Low weight and a high level of rigidity for the axle systems are essential ingredients in ensuring the cars provide an ultra-dynamic driving experience. In the double-joint spring strut front axle alone, the use of a lightweight aluminium construction for components such as control arms, wheel carriers and axle subframes saves five kilograms over a conventional steel design. Play-free ball joints and elastomer bearings developed specially for the BMW M3 Sedan and BMW M4 Coupe ensure an optimum and direct transfer of forces both laterally and longitudinally.

An aluminium stiffening plate, CFRP front strut brace and additional bolted joints between the axle subframe and the body structure all help to increase the rigidity of the front end. Also lighter than the construction in the outgoing BMW M3 is the new five-link rear axle. All the control arms and wheel carriers are manufactured using forged aluminium, which reduces the unsprung masses of the wheel-locating components by around three kilograms compared with the previous model generation. The rigid connection between the rear axle subframe and the body – without the use of elastic rubber elements – is borrowed from motorsport and serves to further improve wheel location and therefore directional stability.

The development of the tyres for the cars was incorporated into the construction process for the axles from the outset. For high-performance sports cars like the BMW M3 Sedan and BMW M4 Coupe, in particular, steering feel and precision are the foremost considerations in the development of tyres for the front axle, alongside lateral stability and braking forces. At the rear axle, meanwhile, traction, lateral stability and directional stability take centre stage. For this reason, both cars will leave the factory on low-weight 18-inch forged wheels (front axle: 9 J x 18, rear axle: 10 J x 18) with mixed-size tyres (front axle: 255 mm, rear axle: 275 mm). 19-inch tyres are available as an option. The specially developed forged wheels make a significant contribution to the reduction in the cars’ unsprung masses and, in turn, to the optimisation of dynamic qualities and efficiency.

In order to ensure optimum operating temperatures in everyday use, on short journeys around town and out on the race track, the BMW M GmbH engineers have developed an extremely effective cooling system. For example, alongside the two ultradynamic turbocharger units, the air intake system of the six-cylinder engine also includes an indirect intercooler, maximising charge pressure and engine output. As well as a main radiator, the track-ready cooling concept also comprises a water cooler repositioned to the side for the high- and lowtemperature water circuits, and the engine and transmission oil (if the M Double Clutch Transmission is specified).

The engine’s power is transferred to the road via a standard six-speed manual gearbox with robust double-plate clutch. This unit is considerably more compact than its predecessor and 12 kilograms lighter. As a means of increasing shift comfort, the manual gearbox uses innovative new carbon friction linings in its synchroniser rings. Dry sump lubrication provides an efficient supply of oil to all parts of the engine. The gearbox blips the throttle on downshifts – previously a feature reserved for the M Double Clutch Transmission. This engagement speed control function improves the smoothness of the transmission, helps to enhance stability and was originally developed by motor sport engineers.

The optional seven-speed M Double Clutch Transmission with Drivelogic prompts the new high-revving turbocharged engine into emotionally impressive feats. As well as changing gear automatically, in manual mode the transmission enables ultra-fast gear changes with no interruption in the flow of power. The integrated Launch Control function ensures optimum sprinting performance off the line, producing acceleration figures that would be out of range with the manual gearbox. The Smokey Burnout function allows the driver to indulge in a degree of rear wheel spin while the car is moving at low speeds. Stability Clutch Control opens the clutch when the car is understeering to bring it back into line. And M DCT also includes functions like the Drivelogic modes that can be selected by the driver to give the BMW M3 and BMW M4 more comfortable, more economy-focused or even sportier characteristics. The additional seventh gear over the manual gearbox allows longer gear ratios – and delivers the efficiency gains you would expect as a result.

The properties of the extremely light yet impressively durable material CFRP have allowed the engineers to follow a fundamentally new approach in the manufacture of the drive shaft. Made from CFRP, this component feeds the engine’s torque from the gearbox to the rear differential and works under extremely heavy loads – especially in high-performance vehicles. Among the other components that add fresh polish to the dynamic repertoire of the BMW M3 Sedan and BMW M4 Coupe are the hollow lightweight output shafts of the rear differential and the Active M Differential, which uses an electronically controlled multi-plate limited-slip differential to optimise traction and directional stability. The multi-plate limited-slip differential works with extremely high precision and speed. Its control unit links up with the DSC (Dynamic Stability Control) system and also takes into account the position of the accelerator pedal, the rotational speed of the wheels and the car’s yaw rate.

Every driving situation is therefore precisely analysed and an impending loss of traction on one side of the car identified at an early stage. The degree of lock – which may be anywhere between 0 and 100 per cent – is adjusted as required within a fraction of a second, enabling wheel spin to be prevented on slippery surfaces, in instances where the right and left rear wheel have widely differing friction coefficients, in tight bends and when changing direction with particular vigour. Optimising traction in this way also provides unbeatable driving stability in challenging conditions and allows impressively dynamic acceleration out of corners. While DSC intervenes as required to counteract understeer and oversteer, M Dynamic Mode allows greater wheel slip and therefore easy drifting. Owners with a taste for sporty and dynamic driving will appreciate this breadth to the cars’ handling, although DSC will still step in if the car ventures over the limits – unless it is switched off completely. Whichever setting the driver chooses, he or she remains responsible for the car’s stability.

 

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