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The Dynamic Q5

Min Reading Time
Tags: Safety, AutonomousDriving
ZF's new active damping system, sMOTION, takes driving comfort, dynamics and safety to a whole new level. That's a huge plus when it comes to highly automated driving.
Martin Westerhoff, July 31, 2018
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Martin Westerhoff studied technology journalism and writes about vehicles and technologies since then. He has a soft spot for motorsports and racing cars.
Long plastic sleepers are stuck to the asphalt like oversized Band-Aids. They are there for one reason and one reason only: to wreak as much havoc as possible on any car that crosses them. Unperturbed, the driver steers his SUV onto this special shake and vibration track. One of the passengers in the back clutches the handle above the window as the SUV crosses the bumps at full speed. But from inside the car, they're barely noticeable. “Impressive!” he gasps, releasing his grip.

Active equals safer and more comfortable

Active equals safer and more comfortable

Sven Greger, the man behind the wheel, chuckles with satisfaction. He's a ZF research engineer who works on the basic development of our semi-active and active chassis components. Greger is used to passengers – many of them buyers or other research engineers from international automotive manufacturers – reacting this way on the proving ground. “Our sMOTION fully active chassis system introduces new degrees of freedom to counteract vehicle body movement,” he says, “We can give each wheel its own active countermovement to prevent driving situations from exciting the car body.” But along with greater comfort, sMOTION significantly improves dynamics and safety compared to current systems. Used in conjunction with cameras, the chassis system can identify the road condition, for example by anticipating bumps or potholes, and change its settings accordingly.
sMOTION can actively pull up or push down the wheels.
Dr. Christoph Elbers, Vice President Car Chassis Technology Development

A damping system has to deal with a lot of situations. Uneven tracks inevitably lead to direct impact, which is cushioned by the suspension. If a wheel rolls over an obstacle, it lifts, compressing a spring between the steering knuckle and the car body. Then the spring decompresses. The damper's job is to attenuate the resulting vibration as quickly as possible. Aside from direct impact, vehicles have to contend with motive forces, braking forces and centrifugal forces. These forces associated with driving dynamics can prompt the car body to move in the direction of three spatial axes (see diagram below). The challenge lies in the fact that different driving situations each demand a specific damping force. Minimizing body movement on curves requires high damping force. Driving over slightly uneven surfaces only requires a little. And safe contact between the tires and the ground requires moderate damping force. “A conventional damper can only ever reach a compromise between sporty and comfortable, albeit a good compromise,” says Dr. Christoph Elbers, Vice President Car Chassis Technology Development at ZF.

When vehicle dynamics trigger movement, sMOTION kicks in

The evolution of the CDC damping system

The evolution of the CDC damping system

ZF's semi-active Continuous Damping Control (CDC) system solved the problem of these conflicting objectives decades ago. Our semi-active damping system went into volume production for passenger cars in 1997. Using the signals from two wheel and body sensors for each spatial axis, plus additional information such as vehicle speed, lateral acceleration and steering angle stored in a control unit, the system continuously monitors driving conditions and calculates the optimum damping force for each wheel. The damper has either one or two electronically controlled solenoid valves that can change the oil flow in milliseconds to adjust the damping hardness. ZF chassis expert Dr. Elbers explains: “sMOTION takes things a step further. Using the basic design of our tried-and-tested CDC, we developed a damper that can actively pull up or push down the wheel.”
Until now, vehicle body excitation was tolerated or even desirable to a certain degree so as to give drivers perceptible feedback on conditions. But in highly automated or autonomous vehicles, all the occupants become passengers. And in that scenario, every vibration, impact, roll or pitch simply stops people from reading or working. This causes dispositions known as motion sickness, making these activities impossible,” says Dr. Elbers. “This effect is amplified by innovative seat arrangements in which driver and passengers may no longer have a view in the direction of travel.” A remedy can only be found in an active chassis. sMOTION is a ZF solution for the future that is already improving driving comfort today. Practically undisturbed by the driving process, passengers can spend their travel time working or relaxing.

Powerful actuators for a smooth ride

Powerful actuators for a smooth ride

sMOTION can actively adjust movements occurring at a frequency of up to five Hertz – the equivalent of 0.2 seconds of vibration. In the test vehicle, this is carried out by a powerful actuator on each wheel, which is triggered by the control software. Depending on the E/E architecture of the passenger car manufacturer, the control unit's commands can also be networked with other by-wire systems. In such a system network, chassis control can act even more efficiently. "By-wire systems offer better vehicle control, shorter stopping distances, more steering flexibility, higher driving stability at high speeds and increased driving comfort," explains Dr. Elbers.
13.6 hp
corresponds to the total power
of all four 2.5-kilowatt actuators in the sMOTION test vehicle.

Today, ZF is one of the leading suppliers of by-wire technologies. The interaction of brake-by-wire, steer-by-wire and sMOTION enables passenger cars to master the dynamic driving forces of longitudinal, transverse and vertical dynamics even better than one of the systems alone could. In this way, software can be used in sporty applications to adjust the vehicle's properties in terms of driving physics, to increase safety or to significantly heighten comfort in highly automated or autonomous vehicles. With its technology, ZF can thus ensure that all occupants feel so comfortable while traveling that no one will reach for a handhold anymore, even when the road gets bumpy.
sMOTION GTD 2022

In a nutshell: Thanks to the fully-active sMOTION damping system, driving becomes not only more comfortable but also more dynamic and safer. The challenge: different driving situations each demand a specific damping force. Minimizing body movement in curves requires a high damping force, for example. However, driving over slightly uneven surfaces requires only a little. And maintaining safe contact between the tires and the ground requires a moderate damping force. Used in conjunction with cameras, the chassis system can identify the road conditions by anticipating bumps or potholes, for example, and change its settings accordingly. Thus sMOTION also contributes to highly automated driving.