Outstanding safety and well-balanced ride comfort combined with impressive driving dynamics on dry, wet as well as wintry roads, plus superlative skills off the beaten track are some of the key strengths of the third-generation M-Class with permanent all-wheel drive. The premium SUV also makes its mark with new chassis developments and innovative dynamic handling control systems designed to increase both driving pleasure and active safety in winter.
The optional ON&OFFROAD package for the new M-Class uses six different driving modes to optimise driving dynamics and handling safety by providing the optimum drive control needed to cope with the wide spectrum of operating conditions encountered both on and off the road. Drivers have the choice of an automatic mode, two specially programmed off-road modes as well as three on-road modes – “Winter”, “Sport” and “Towing”.
The specific driving modes for all-wheel drive resolve a conflict of objectives that has previously hampered further development of 4MATIC and the 4ETS electronic traction system as well as ESP® and acceleration skid control (ASR). To take an example: on off-road tracks or snow-covered roads, it is important that the control systems respond very gently due to the low friction coefficients, but this makes a sporty set-up virtually impossible. Conversely, a sporty basic setup impairs performance abilities in off-road terrain and snow. In the past, excellent compromises were always found which worked brilliantly under all conditions. The new ON&OFFROAD package with its specific driving modes, however, enables driving dynamics and handling safety to be optimised almost as far as is physically possible under all operating conditions by maximising networking between the individual control systems.
In terms of “hardware”, the ON&OFFROAD package comprises an underguard, a two-stage transfer case with low-range ratio, an inter-axle differential lock and enhanced AIRMATIC functionality that allows a maximum ground clearance of 285 millimetres and a fording depth of 600 millimetres.
Winter driving mode: more fun, more safety
The driving mode is chosen using a rotary control on the centre console. To ensure the selected driving mode – in this case “Winter” – is clearly indicated, a special snowflake graphic appears in the instrument cluster, while the COMAND screen shows the M-Class in a wintry, snow-covered landscape.
The ON&OFFROAD package’s winter driving mode optimises handling on roads affected by snow, ice or freezing rain and when using snow chains, and offers drivers added safety with its well-defined, predictable reactions. The extensive fine-tuning work carried out focused on further increasing longitudinal traction, at the same time as improving lateral dynamics and handling safety. The development team was able to implement these specifications to impressive effect using targeted control mechanisms in the drivetrain:
- When pulling away with or without the steering turned, the inter-axle lock in the centre differential is triggered earlier in order to increase traction and reduce understeer when accelerating briskly. In parallel to this, the 7G-TRONIC PLUS switches to the “gentler” ECO mode and automatically engages 2nd gear when pulling away to avoid high wheel slip. Finally, a flatter response curve gives the driver more sensitive control over the accelerator pedal.
- Maintaining a locking torque that has been set in the centre differential for longer improves handling stability and helps the driver by making the self-steering characteristics more definite.
- Higher ASR slip thresholds when driving in a straight line result in high traction levels as well as safe operation with snow chains with outstanding tractive power.
- ASR slip thresholds lowered when cornering in order to ensure stable handling characteristics at all times as far as is physically possible.
ACTIVE CURVE SYSTEM for safe fun in the snow at its very best
When the ON&OFFROAD package is combined with the ACTIVE CURVE SYSTEM (ACS), a specially programmed winter set-up guarantees dynamic driving pleasure while giving the driver excellent control over the vehicle for a high degree of handling safety. ACS uses active anti-roll bars at the front and rear axles to compensate for the roll angle of the body through bends, increasing agility and driving pleasure in the process. At the same time, the system is capable of giving the M-Class greater traction, especially in wintry road conditions with low grip levels.
The ACTIVE CURVE SYSTEM “Snow mode” features two control strategies. Firstly, many of the parameters needed for driving on wintry roads are already incorporated into the basic functions, i.e. when the ON&OFFROAD package’s Automatic driving mode is activated. This means that the system’s reactions to the driver’s steering inputs will be less dynamic on slippery surfaces. External influencing factors, such as fluctuating friction coefficients on roads that are partially covered in ice or snow, are balanced out faster though. Thanks to this control strategy, the M-Class becomes far more docile, even if the vehicle switches between moderate oversteer and understeer.
Secondly, the system control for the winter driving mode includes a special control algorithm. In just the same way as the shaped skis thrill alpine skiers by closely following the desired line even through turns with a tight radius, the M-Class handles in tight bends in this mode. This control strategy produces increased traction on snow-covered road surfaces by dynamic displacement of the wheel loads. If the driver turns into a tighter bend while travelling at a constant speed or accelerating, the wheel load and, as a result, the traction will be increased at the front wheel on the outside of the bend. Doing so minimises the understeer that is otherwise typical in this driving situation. If the driver then reduces the steering angle when exiting from the bend while travelling at a constant speed or accelerating, the load at the rear wheel on the outside of the bend will be raised instead. This has the effect of increasing lateral support at the rear axle, so that the vehicle’s handling is stabilised in the same way as when entering the bend. This time though, it is the tendency to oversteer that is countered.
M-Class sets benchmarks in the world of SUVs
The third generation of the Mercedes-Benz M-Class excels above all with its outstandingly efficient use of energy. On average, the fleet consumes 25 percent less fuel than the predecessor models. The ML 250 BlueTEC 4MATIC is the fuel efficiency champion, consuming just 6.0 l per 100 km on the NEDC driving cycle (158 g CO2/km) and capable of covering up to 1500 kilometres on a single tank of fuel. Other key strengths of the premium SUV with permanent all-wheel drive include outstanding safety and well-balanced ride comfort combined with impressive driving dynamics both on the road and off the beaten track. A distinctive body design and a versatile interior that is highly conducive to its occupants' wellbeing further enhance the M-Class driving experience.
Source: Daimler AG
Copyright © 2011, Mercedes-Benz-Blog. All rights reserved.