The new EQS SUV: the suspension

Apr 19, 2022
Stuttgart

The chassis of the new EQS SUV comprises a four-link axle at the front and an independent multi-link suspension at the rear. The AIRMATIC air suspension with continuously adjustable damping ADS+ is standard equipment. To increase ground clearance, the vehicle level can be raised by up to 25 millimetres. In addition to the DYNAMIC SELECT modes ECO, COMFORT, SPORT and INDIVIDUAL, the EQS SUV also features OFFROAD, a further mode for off-road driving. It can be used with or without ESP®. Also standard is rear-axle steering with a steering angle of up to 4.5 degrees for great manoeuvrability in town and agility over land.

The standard-fit AIRMATIC air suspension responds particularly sensitively. It combines air suspension bellows with adaptive ADS+ dampers whose characteristics can be varied at each individual wheel fully automatically, in both the compression and rebound stages. While driving, a sophisticated sensor system and algorithms set the dampers according to the quality of the road to ensure that, for example, driving over a bump with just one wheel is not transmitted to the entire axle and the interior. Spring and damper are combined in one strut on the front axle, but separate on the rear axle.

This level control is part of AIRMATIC. It keeps the ground clearance constant irrespective of the vehicle load, but also makes changes when needed. To increase ground clearance, the vehicle level can be raised by up to 25 millimetres. This is possible up to a speed of 80 km/h. The body can be raised by 25 mm at the touch of a button below 60 km/h, above 70 km/h it is automatically lowered back to normal level. Furthermore, in the COMFORT and SPORT modes, the body is automatically lowered by 10 and 15 mm, respectively, at speeds above 110 km/h to reduce drag and increase driving stability. If the vehicle drops below 80 km/h, the body level returns to the initial position.

Manoeuvrable: both axles can do the steering

The standard rear-axle steering with a steering angle of up to 4.5 degrees contributes to the manoeuvrable and dynamic impression of the EQS. Alternatively, the rear wheels can even turn in by up to 10 degrees. This allows a turning circle of 11.0 instead of 11.9 metres, which corresponds to the turning circle of many lower mid-range models. The variant with the large steering angle can still be activated after delivery via an upgrade over the air (OTA). The respective rear-axle angles and trajectories are shown in the driving mode menu on the central display.

The interaction between the front-axle and rear axle-steering is configured to ensure agile responsiveness in urban and country traffic with little steering effort. At the same time, it also achieves a very high level of stability. This results in e.g. small side-slip angles and a high level of yaw suppression. At high speeds, the focus is more on stability, though without compromising precision and responsiveness. This added value is achieved by the integrated actuation of steering and brakes (ESP®), and considerably improves driving safety as a result.

The operating principle of the rear-axle steering in detail: An electric motor drives a spindle at the rear axle via a drive belt. This makes axial adjustments to the spindle. Depending on the speed (below/above 50 km/h) and the steering angle, the rear wheels turn in the same or the opposite direction as the front wheels (same direction or counter-direction). In simplified terms, this results in greater agility and a smaller turning circle by counter-steering and more stability with same-direction steering. The environmental data of the vehicle sensors (radar, camera, ultrasonic) are used to adapt the maximum angle to the relevant situation. The system switches from counter-direction to same-direction steering at more than 50 km/h.

DYNAMIC SELECT: with OFFROAD driving mode

The driver can change the characteristics of the drive, ESP®, suspension and steering using DYNAMIC SELECT. In addition to ECO, COMFORT, SPORT and INDIVIDUAL, the 4MATIC versions of the EQS SUV feature OFFROAD, a further mode for off-road driving. Overall, the accelerator pedal curve is much flatter there. The vehicle level is raised by 25 mm. At speeds above 80 km/h, the vehicle lowers to normal level. If the speed falls below 50 km/h, the vehicle is raised again. Two versions of the OFFROAD driving mode with and without ESP® can be selected:

In the OFFROAD driving mode with activated ESP®, little slip is permitted on the potentially spinning wheels. In this way, significantly fewer tracks are left behind on a wet meadow, for example. This is achieved through torque balancing between eATS and ESP®. The pressure in the control system thus matches the torque at the wheel exactly. When articulated in the terrain, a kind of pre-filling takes place. This means that the unloaded wheel is already supplied with pressure in the wheel brake during the rebound phase in order to prevent it from spinning.

The aim of the OFFROAD driving mode with ESP® OFF is to allow sufficient slip, but still make the vehicle safe and easy to control. A lot of wheel slip, for example, is helpful to have enough propulsion on sand - the vehicle burrows forward. The control thresholds of the ASR traction control system are significantly widened here. Even in potentially critical situations, such as turning around on a dune, when the momentum is not enough to reach the top, the driver always has full torque available. Power is sufficiently available from the eATS.

The off-road ABS works with significantly more slip. The slip is reduced via the steering angle so that the vehicle remains steerable. Downhill Speed Regulation (DRS) is now realised via the iBooster and not via a hydraulic unit (ESP®) as the models with combustion engine. As a result, DRS now controls much more quietly and even more smoothly.

The default setting is the COMFORT driving mode. The selection is acknowledged by acoustic and visual feedback. The desired driving mode is shown as the status and depicted on the central display.

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