Comfort electronics Active suspension sMotion from ZF reduces travel sickness

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With the active chassis system sMotion, ZF aims to resolve an old conflict of objectives in the design of car chassis, ensuring stability and dynamics on one hand and comfort on the other. The system precisely adjusts the damping force to the respective driving situation; furthermore, the dampers can initiate rapid individual vertical movements, actively lifting the vehicle to ensure optimal road holding.

In car chassis, it has always been about combining excellent dynamic properties with the best comfort. For this, ZF has developed its active chassis system sMotion. "Our fully active chassis system sMotion can almost completely prevent the movements of the vehicle body in certain driving situations," explains Dr. Peter Holdmann, a board member at ZF and also responsible for the Chassis Solutions division. This includes the pitching and rolling, which were previously inevitable side effects of dynamic steering, braking, and acceleration maneuvers, and intensified the more weight a vehicle carried.

The new Porsche models Panamera and Taycan already use part of the ZF system for implementing the Porsche Active Ride air suspension chassis – specifically, the technology group's damper and valve technology.

Damping system CDC as a basis

The active chassis system is based on the adaptive ZF damping system Continuous Damping Control (CDC) with two external valves that independently control the compression and rebound of the damper. This way, the damping hardness is optimally adjusted to the respective driving situation, which is already a great gain in terms of driving comfort and dynamics. sMotion goes a step further: with the system, a high-performance pump can pump oil into and out of the damper, actively moving the suspension via the piston rod. This allows the electronic control to individually neutralize the effects of road surface irregularities on each wheel. It is also able to compensate for or even counteract the wheel height during cornering—for example, during acceleration and braking.

Active vertical movement of the wheels

This effect is especially enormous during dynamic driving maneuvers: In a sharp steering movement to the right, a conventionally damped vehicle would "lean" on the left side. In a car equipped with sMotion, this type of vertical movement of the vehicle body is avoided. The vehicle can even adjust the cornering angle to the speed and display a "helicopter mode" when braking and accelerating. This makes the vehicle appear almost nimble in its driving behavior.

Two figures illustrate the system's performance: within half a second, the active dampers can "raise" a vehicle by eight centimeters. In this manner, the control electronics, also developed by ZF, can keep a three-ton car almost level on the road at a cornering force of up to 1 g.

Motion sickness: Minimizing causes

This individual wheel-active body control, which does without stabilizers, has significant potential in terms of comfort. If vertical movements of the vehicle body are prevented, motion sickness also becomes a thing of the past. It mainly affects passengers who focus on other activities while driving today: "Our system prevents the so-called motion sickness, which mainly affects passengers who read or watch movies during the journey," explains Thomas Kutsche, Vice President Engineering Productline Suspension at ZF. The calming of the vehicle body can be further enhanced, especially when information about road irregularities is known and the system precisely compensates for them. As automated and autonomous driving continues to increase in practice, this chassis feature becomes increasingly valuable for all vehicle occupants.

Portfolio addition

With sMotion, the supplier expands its portfolio for the steering, brake, and chassis of passenger cars. With all these electronically controlled actuators, ZF can influence the complete longitudinal, lateral, and vertical dynamics of vehicles as a software-controlled overall system. The combination of these technologies will lead to networked chassis systems in the future, which can be holistically coordinated with the ZF software cubiX. (se)