Take the driver away from the steering wheel and allow passengers to do other things and there’s a risk they might get motion sickness as they’re more likely to feel the effects of the vehicle’s movements.
In current cars, everyone sits in a uniform direction, making it less likely that occupants will feel the constant pitching backwards and forwards through acceleration and braking and the rolling and tilting as they travel around corners, not to mention the impact of variable road surfaces.
But in the future vehicle cabins could look very different. Occupants could be facing backwards, reading, working or even sleeping as autonomous technology takes control of our cars and we’re afforded more time to relax. But to do that, and to maintain passenger comfort regardless of what is happening on the road, chassis technologies need to become smarter.
Active chassis systems have already been produced for high-end vehicles, technologies that can react to the bumps and dents in roads to improve ride quality, but companies are now developing fully active systems that can almost entirely eliminate the effects of vehicle body movement.
Tier One supplier ZF is among those developing the technology. The company’s head of development for active dampers, Thomas Kutsche, says: “By the time the autopilot takes over, all passengers want to be completely relaxed and unaware of the vehicle’s movement, regardless of what is happening on the road. Fully active chassis systems can help fulfil this requirement.”
ZF’s approach uses a force path different from conventional solutions. Instead of spring-mounted adjustment, it uses the piston rod of the damper and an integrated electric motor pump to regulate the chassis more dynamically.
Forget potholes
The electric pump is key to the system; the unit features integrated electronics and works as a bidirectional actuator on each wheel – it can create forces in both upward and downward directions.
This could improve control over all low-frequency car body movement. When cornering, for example, the two inner wheels could be retracted and the outer ones extended, enabling the car to remain virtually horizontal.
“The system requires one pump per wheel and enables cars to actively raise and lower each wheel, virtually eliminating the impact on occupants of even major road unevenness and potholes. It is also effective against pitching forward and back as well as rolling or tilting around corners, for example,” says Kutsche.
ZF isn’t the only firm to see the benefits of active chassis control technology in autonomous vehicles. Tenneco is developing systems that will help improve ride quality too, and it sees another benefit, especially as these technologies will need to be run on 48V rather than traditional 12V electrical systems.
Miguel Dhaens, Tenneco’s advanced engineering manager, says: “The biggest advantage is the ability to more easily transfer energy flows to and from the active suspension. In a hydraulic damper you have a fixed relation between compression and rebound; in an active damper you can electronically adjust compression and rebound independently and create in-cabin refinement.
“But in the compression phase, the system allows kinetic energy to be harvested and converted into electrical energy. The energy that is harvested can be stored and used at a next event when the system is activated, therefore having a better energy balance.”
Bumpy road ahead?
There are challenges that still need to be addressed, particularly in processing the data and the speed at which systems can react to it.
“The maximum allowable latency depends on vehicle speed and the response time of various systems to initiate the vehicle’s longitudinal, lateral or vertical actuators,” says Dhaens.
For example, sometimes it might be better to avoid an object by swerving around it rather than the chassis trying to adapt to it.
Actively lifting wheels gives another dimension in avoiding shallow objects on the road or adapting to the road’s layout and increasing the ride comfort.
In the future the mechanical aspects of the systems could also be linked to forward-facing sensors – cameras and lidar, for example – to bring a predictive aspect to the technology. But what is certain is that these technologies will be needed if autonomous vehicles are to reach their full potential.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.