While it will likely take another decade for self-driving cars to become ubiquitous, the automotive industry is already busy testing solutions that will best fit future cars. On the road to becoming driverless, one major element is steering. Replacing humans, their perception, senses and reactions by machine takes a lot of effort, but in fact, the technology to relieve drivers of their duties has already been around for a while.
The biggest challenge is to prove that a system is safe under any circumstances, says László Naszádos, E/E Hardware department leader at ThyssenKrupp Presta Hungary Kft. There are a myriad of systems that work well in 99% of the cases. The big deal here is to cover the remaining 0.5-1%. Manufacturers can’t afford to launch a car that is only mostly safe – there can be no circumstances under which it fails. Finding those unusual situations and exceptions that can cause a problem is not always easy. Sun glare may blind cameras or sensors, just as they do humans. To prepare driverless systems, engineers make multiple calculations. They must do much more analysis, make calculations well beyond the error margin and create conditions under which they can test it all.
To test how their systems work, ThyssenKrupp engineers buy mass-produced production vehicles and install their own systems. The transformation is fairly simple: They set up cameras, sensors and a computer in the car. “Obviously, we choose a model that already has our steering system so that they can co-operate with the electronics we are to test. The emphasis is always on safety: We have to be able to provide sufficient backup,” Naszádos says.
“Autonomous cars are made up of two parts: the ‘head’ and the lower parts. The head can see, hear, sense what is going on and makes decision based on the information. We deal with the lower parts that execute these decisions,” Naszádos said. “We develop ever more steering systems that are suitable for use in autonomous cars – at every level of them,” he adds.
The company already has many autonomous features integrated in its partners’ cars. Among these are lane departure warning systems, lane keeping assistant, parking assistant and cruise control. Yet the pace of market launch of any development is set by car makers. “The technology for our steer-by-wire system was available ten years ago,” Naszádos says. “Their launch may not have been [financially] viable at that time,” he added. Although these developments will first appear only in luxury models, they will soon trickle down to economy cars. When first introduced, ABS, for example, used to be an extra. Now, carmakers are required by law to install it in every model, Naszádos points out.
ThyssenKrupp’s systems can be found in Mercedes and BMW and several Chinese manufacturers’ models. The number of brands is about to expand soon, but since negotiations are ongoing, Naszádos could not reveal which makers will next incorporate the company’s steering system in their models. “Ten years ago, we were considered newcomers in the market. It was not until 2010 when production started and clients’ trust began to increase,” the engineer says.
The company is known for developing electric power-assisted steering systems for all vehicle classes. These offer greater energy efficiency than conventional hydraulic steering and, depending on the vehicle, can reduce fuel consumption by up to 0.3 liters of fuel per hundred kilometers. This technology is also a prerequisite for a variety of driver assist systems such as wind compensation, park assist, lane assist and partial or fully automated driving. In the case of autonomous cars, it can provide essential access for the control of the steering system. Building upon this, the company has developed a steer-by-wire system where the steering wheel and the shaft are no longer connected physically. Steering wheel commands are transmitted electronically from a control unit to an electric motor that performs the steering operation without a back-up mechanical system.
Steering is the driver’s main line of communication with the car. Any distortion in the guidance channel makes every other perception more difficult to comprehend. The demise of mechanical control systems requires the use of electromechanical actuators and human-machine interfaces such as pedal and steering feel emulators.
Automakers have started to replace hydraulic assist with a computer-controlled electric motors due to the latter system’s energy/fuel-saving properties. Eliminating an engine-driven hydraulic pump increases gas mileage. The main advantage of electric systems – be it electric power or steer-by- wire – over hydraulics is their simpler structure and more efficient operation. Hydraulic servo-assisted steering absorbs energy constantly to operate the oil pump. E-steering systems will only use energy during steering and when the electric engine needs assistance. Steer-by-wire is not to be confused with electric power steering. It is rather one step in that direction.
In 10-15 years’ time, all cars will likely run on a steer-by-wire system. Traditional components such as the steering column, intermediate shafts, pumps, hoses, belts, coolers and vacuum servos and master cylinders will be eliminated from the vehicle. The E/E Hardware Department is responsible for the development of the Electronic Control Unit. The team is working on the design and verification of the electronic circuits, sensors and motors. Together with the system and software developers they form the functionality and functional safety of the steering systems.