The chassis and suspension: Refined sportiness for the sports tourer

Oct 3, 2011
  • Chassis and suspension: new four-link rear axle, sporty ESP® tuning
  • Steering: new electric power steering with assistance functions
  • Brakes: electric parking brake improves overall package
"Fascinatingly agile" is the assessment of all test drivers who have put the
new B-Class through its paces to date. Three factors are instrumental to the substantially enhanced dynamic performance in comparison to its predecessor, which does not come at the cost of any compromises on comfort: the lowered centre of gravity, the new four-link rear axle and the upgraded ESP® Electronic Stability Programme.
On the four-link rear axle, the arising forces are absorbed by three control arms and one trailing arm per wheel. This means that longitudinal and lateral dynamics are virtually independent of one another. Wheel carriers and spring links consist of aluminium, in order to reduce the unsprung masses.
Mercedes-Benz is deploying the latest ESP® generation – ESP®9 – in the
B-Class for the first time. Torque Vectoring Brake helps to counter the tendency towards oversteering during fast cornering. Specific steering impulses (see below) assist the driver. The engineers' overall aim has been to provide gentle intervention by the ESP®system which will always afford the B-Class's occupants protection, without detracting from the pleasures of driving: experienced motorists can drive very speedily, while less experienced drivers with a less well-rounded driving style will be receive a timely reminder of the physical limits involved in driving.
Steering: mechanical with electric assistance
The electromechanical steering of the B-Class has been redesigned. The electric motor of the servo assistance system is now located directly on the steering gear as a dual pinion EPS system. The steering system makes an important contribution to the vehicle's overall efficiency, as the steering assist function only requires energy when steering actually takes place. A Direct-Steer system is available in combination with the sports package. Locating the EPS system here results in a noticeably more direct steering ratio over the turning angle with the aid of the variable ratio. This enhances the vehicle's handling and agility substantially. The electric power steering also enables various steering assistance functions which are activated by the ESP®control unit. These include
  • Countersteering in case of oversteering
  • Corrective steering when braking on road surfaces offering different levels of grip (split-fraction braking)
  • Mitigating the extent to which the front-wheel drive influences the steering
  • Compensating crosswind and road gradients
  • The electric power steering also makes Active Park Assist possible.
With a turning circle of eleven metres in diameter, the B-Class is particularly agile.
On all engine variants, the B-Class comes with disc brakes on all wheels. The callipers on the rear axle and the brake boosters are made of aluminium. For the first time in the compact class, the HOLD function which is familiar from the larger model series has been adopted into the B-Class: when stopping, for example at traffic lights, the driver merely has to press the brake pedal slightly more firmly and the brake will remain engaged until he moves off again. The brake is released automatically when the driver steps on the accelerator. On versions with manual transmission, the Hill Hold function automatically prevents the vehicle from rolling back unintentionally when starting on a slope.
Mercedes-Benz is equipping the B-Class for the first time with an electric parking brake, which operates by means of actuator motors acting on the
callipers of the rear axle. The parking brake is activated via a button under the light switch on the left of the dashboard. This creates additional space in the centre console, as the handbrake lever is no longer required. When the button is pressed at speeds of over four km/h, the parking brake acts as an emergency brake, activating all four wheel brakes via the ESP®'s hydraulic unit.
In conjunction with the automatic transmission, the parking brake offers a particularly convenient mode of functioning: when the driver accelerates sufficiently after fastening his seat belt, the parking brake is released automatically.
The much improved driving dynamics of the new B-Class are based on a four-link rear axle and a McPherson strut front axle.
Mercedes-Benz B-Class, chassis