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Chassis: High degree of comfort on long journeys paired with driving pleasure

Nov 28, 2018
Stuttgart

At least as agile as its predecessor while even more comfortable – that was the development brief handed to the suspension specialists for the new B-Class. The suspension with active damping control (optional equipment) enables the driver to choose the preferred damping characteristics.

The front axle of the new B‑Class features a McPherson design. Wheel control is taken care of by one transverse control arm below the wheel centre, the McPherson strut and one tie rod. The transverse control arm in the new B-Class is a forged aluminium component. This reduces both weight and unsprung masses. The steering knuckles are made of cast aluminium.

The powerful versions of the new B-Class as well as all models with adjustable damping have a complex 4-link rear suspension. This is also installed in vehicles with mid-range engines and larger wheels. The three transverse arms and one trailing arm at each rear wheel are configured for maximum driving stability, comfort and longitudinal/lateral dynamics. The rear axle is mounted on a subframe isolated from the bodyshell by rubber bushings so that fewer vibrations are transferred from the suspension to the body.

The versions with the entry-level engine variants come with a twist-beam rear axle in the basic configuration. Its U-section rotates in a targeted manner in one-sided compression and rebound, and acts as a stabiliser bar. The torsion-beam rear axle is secured to the body with two bearings and uses the same attachment points to the body-in-white as the multi-link axle's trailing arm. Single-tube shock absorbers and separate coil springs are used for both the four-link and the twist-beam rear axle.

Three suspension variants: choice of setups

As standard the new B-Class is equipped with a comfort suspension with steel springs and DYNAMIC SELECT. The spring travel with 80/100 millimetre (jounce/rebound) on the front axle and 100/100 millimetre on the rear axle are among the longest in this vehicle class and a sign of the excellent driving comfort. The B-Class has more attenuation reserve than the A-Class on account of the larger luggage compartment.

The lowered comfort suspension (15 millimetres) has specially configured springs and dampers for more sporty characteristics.

The suspension with active damping control has also been lowered by 15 mm and enables the driver to choose the preferred damping characteristics. A valve in each of the four shock absorbers is electronically actuated to control the oil flow. The damping characteristics are changed by regulation of the oil flow. The gear ratio spread between the Sport and Comfort programmes is larger than in the previous Mercedes-Benz compact car generation. The Comfort programme comes into its own especially when travelling at low speeds, for example on a cobblestone road.

Several sensors constantly monitor the suspension status, driving situation and driving style of the driver, and adjust the damping at each wheel. Information is also added by the engine, transmission, braking system, steering and driving assistance systems. The damping is specifically stiffened during acceleration, braking or steering manoeuvres to reduce pitching and body roll, and to improve wheel loads and the ground contact of the tyres. When applying the adaptive adjustable damping to the B-Class, its higher seating position in comparison to the A-Class as well as the vehicle's rolling behaviour were taken into consideration.

Steering: also supports automated driving

The gearing of the electro-mechanical rack-and-pinion steering is located behind the wheel centre, and servo assistance is speed-sensitive as standard. With 16.8:1, the gear ratio in keeping with the vehicle segment is somewhat more indirect than in the A-Class (where it is 14.6:1 or 15.4:1 depending on the suspension, all figures for centre position).

The B-Class features Steer Assist in conjunction with the driver assistance package. The driver's steering movements to stabilise the vehicle are assisted by additional steering torque generated by the electric servo unit.

In combination with Active Distance Assist DISTRONIC, transverse control takes place with Active Steer Assist to add active lane-keeping to the intelligent cruise control.

Brakes: ADAPTIVE BRAKE as standard

The new B-Class has a hydraulic dual-circuit braking system in X-configuration with the brake control function ADAPTIVE BRAKE as standard. The electric parking brake is standard equipment. The rear axle features a combined floating brake calliper with an electric parking brake function.

ADAPTIVE BRAKE puts technology from the top-of-the-line model Mercedes-Benz models into the B-Class. Thanks to electronic control, the hydraulic dual-circuit braking system allows assistance functions that improve safety and comfort. This includes priming of the braking system in critical situations: if the driver's foot moves abruptly from the accelerator to the brake pedal before an emergency stop, the braking system increases the pressure in the brake lines and brings the pads into contact with the brake discs so that maximum braking power is available as soon as the driver hits the brake pedal. This priming of the brakes allows the system to assist the standard Brake Assist.

ADAPTIVE BRAKE also brings safety benefits in wet conditions. The system briefly applies the brake pads at regular intervals to wipe the film of water from the brake discs, ensuring that the brakes are able to perform at their peak. This automatic brake drying function is always activated when the windscreen wiper of the B-Class has been switched on for a certain time, and the finely metered braking impulses go unnoticed by the driver but ensure optimal braking power even in wet driving conditions.

After braking to a standstill, briefly pressing the brake pedal a little further is all that is required to activate the HOLD function. The car is then held by the brakes, even if the driver's foot is taken off the brake pedal. In this way ADAPTIVE BRAKE prevents unintentional moving-off at traffic lights or in stop-and-go traffic, or rolling backwards on uphill gradients. The HOLD function is deactivated automatically when the car moves off.

Wheels: Larger dimensions for more attractive looks and more ride comfort

The range of wheels and tyres begins at 16 inches. It comprises steel wheels in size 16 and 17 inches and light-alloy wheels in size 16 to 19 inches. In comparison to the preceding model series, the outside diameter of the tyres has been increased from 645 mm to 660 mm. Apart from a more attractive look, this also offers smoother ride comfort.

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