When the steering wheel vanishes
How “steer-by-wire” is set to transform the car of the future.
The non-too distant vision of driverless cars sounds promising: You get in your car, start it up – then sit back and let it drive you to work. Even rush-hour gridlock could become a thing of the past because autonomous vehicles make traffic flows easier to manage and control, resulting in reduced congestion. And time on the road could be spent usefully – reading a newspaper, checking emails, or maybe even eating breakfast in a space more reminiscent of a lounge than a classic five-seater.
Among the technologies helping turn this vision into a reality are “steer-by-wire” systems. These are steering systems with no mechanical link between steering wheel and wheels. Steering commands are transmitted electronically, like in airplanes. When the car of the future switches to autopilot on longer drives, the lack of mechanical components in the steer-by-wire system means the steering wheel can be moved out of the way until it is needed again, providing additional space the driver can use for other things. For this scenario thyssenkrupp’s developers have already designed a stowable steering wheel.
Steer-by-wire systems are the next generation of today’s electric power assisted steering systems, in which the driver’s steering movements are supported by an electric motor. This has lots of advantages: Firstly these steering systems are more energy-efficient than the hydraulic steering systems they succeeded, because the motor is only activated when the driver actually needs it to help with steering. Compared with conventional hydraulic steering systems, in which oil pressure has to be maintained permanently, electric steering systems save up to half a liter of fuel for every one hundred kilometers driven. Advantage number two is driving safety. Electric steering systems are a prerequisite for driver assistance systems such as park assist, lane assist and distance warning systems.
Above all steer-by-wire will change vehicle architectures. The elimination of mechanical components means OEMs will have greater flexibility when designing the car interior. Theoretically you can now steer the car from anywhere inside the vehicle. Also there’s no need for different versions for left- and right-hand drive. A further positive effect is that with no mechanical link to the road, the vehicle interior is acoustically “sealed off”. Vibrations and noise are no longer transmitted straight into the cockpit. Elaborate sound-proofing measures are no longer needed.
On the other hand, the lack of direct contact with the road means some steering feel is lost. That’s one of the biggest challenges for thyssenkrupp’s chassis engineers. They have to find the perfect combination of software and hardware to provide a completely authentic driving feel. Key to this is the feedback actuator, which simulates the feedback from the road and transmits it to the steering wheel for the driver. That’s safety-relevant because – unlike simulations on a games console – steering has to feel completely authentic at all times. Otherwise the driver loses the feel for different driving situations.
Actually safety is always the number-one priority in the development of steer-by-wire systems. It’s essential that the car can still be maneuvered safely even if the electronic data transfer is interrupted or there is a partial system failure. So a belt-and-suspenders approach is called for.
That’s why thyssenkrupp’s steering specialists are working on secondary systems within the steering system, such as integrating a second steering motor. If one of the motors fails, the other ensures that steering is still possible. They are also developing fallback solutions outside the steering system. For example, the drive and brake systems of an electric car can be used to steer the front wheels by varying the amount of power or braking force applied to the individual wheels; in this way they can take over the steering function in an emergency and ensure the vehicle can be maneuvered safely.
thyssenkrupp has already tested steer-by-wire systems on prototype vehicles. The steering experts are now working with customers to develop the technology to production maturity. Until then we will (still) have our hand on the steering wheel.