Alternative controls in Steer-by-Wire vehicles: Will the joystick replace the steering wheel?

Innovative Steer-by-Wire technologies open completely new possibilities for the design of vehicle interiors and the development of innovative control concepts: Because Steer-by-Wire systems replace the conventional mechanical steering system with an electronic control system, there are degrees of freedom with which the interior can be designed to be more innovative and ergonomic. thyssenkrupp Steering sees great potential in this area: engineers are researching alternatives to the steering wheel as we know it today. Rotary wheel or joystick: Thomas Maier, Test Engineer Vehicle Dynamics & Testing at thyssenkrupp Steering, has developed three different concepts and compared them in tests.

“In addition to the many possibilities and advantages in terms of traffic and accident safety as well as the driving experience, Steer-by-Wire technology also offers the possibility of alternative input devices instead of the classic steering wheel,” explains Thomas Maier. Especially with regard to autonomous driving, the question arises as to what role the steering wheel will play in the future. One thing is clear: the higher the level of automation, the less the driver has to operate the steering wheel and can focus on other tasks. In highly automated vehicles in particular, the steering wheel could be replaced by alternative control elements that enable a more flexible interior design. As part of a larger study, Thomas Maier has developed and refined various concepts and tested them in road tests.

Three new operating concepts as an alternative to the steering wheel

Based on extensive experience from previous projects at thyssenkrupp Steering in Eschen (Principality of Liechtenstein) and with a view to the most complete possible integration into the vehicle environment, the engineer developed a total of three concepts.

•  Micro wheel: The micro wheel consists of a turntable as a base and a knob that can be rotated on the turntable and operated with just three fingers. Similar control elements are already being produced by various suppliers for people with physical disabilities, but they are quite simple and therefore not intended for the masses.

• Finger wheel: The inspiration for the finger wheel was, on the one hand, the classic remote control used in remote-controlled model cars and, on the other, the fact that similar controls are already used to operate infotainment systems, such as BMW's “iDrive”. The finger wheel concept is particularly compact and can be integrated most smoothly into the vehicle environment.

• Joystick: The joystick concept is a further development of tests carried out as part of a master's thesis at thyssenkrupp Steering. The joystick is aligned vertically so that it is controlled by a rotational movement of the forearm via the wrist.

The different concepts were integrated into one of the research vehicles of the steering specialists from Liechtenstein. “In order to evaluate the steering behavior of the various devices in terms of controllability, fatigue, sensitivity and user-friendliness, various driving maneuvers were defined, which were performed and subjectively evaluated by a professional test driver from thyssenkrupp Steering,” reveals Thomas Maier. In order to better analyze the different areas, the maneuvers were divided into driving situations with different dynamics.

Test drives with different dynamics identify strengths and weaknesses of the concepts

The test drives with low dynamics primarily involved everyday maneuvers at low speeds. For example, precisely following a marked line on a winding road at 20 km/h.

The test drives with medium dynamics involved driving maneuvers with a moderate degree of difficulty at higher speeds. For example, driving along a handling course without reaching the limits of driving dynamics.

The set-up for the tests with high dynamics included demanding driving maneuvers at higher speeds, such as double lane change maneuvers at high speeds.

Selected signals were measured, recorded and evaluated for all maneuvers. “In order to be able to classify the test results accurately, all maneuvers were performed with the normal steering wheel in addition to the three steering wheel alternatives,” reports Thomas Maier. “Starting from this basic reference, the respective performances were rated from significantly worse to significantly better, each with three sub-levels.” The analysis of the data painted a clear picture.

Micro wheel performs worst

“The micro wheel performed worst overall in the comparison,” reveals Thomas Maier. “In terms of controllability, it showed disadvantages compared to the other devices in all tests, especially on the handling course and the double track change maneuver. The angle-dependent rotary knob position had the greatest influence on the poorer results, as it does not produce a homogeneous and easily unpredictable movement sequence.” Nevertheless, the micro wheel - like the other devices - also showed advantages over the conventional steering wheel when it came to parking maneuvers. The micro wheel also performed quite well in terms of muscular fatigue in the driver's arm and showed advantages over the other concepts in terms of sensitivity. However, due to its size alone, the concept can only be integrated into the vehicle environment to a limited extent, and it also lags behind the other two devices in terms of ergonomics and intuitiveness, as Thomas Maier notes.

Finger wheel user-friendly but too sensitive

The finger wheel showed significantly better results here. “The concept is very intuitive and user-friendly and can be best integrated into the existing environment,” says Thomas Maier. In terms of basic controllability, the finger wheel did not show any significant impairments in driving maneuvers with low and medium dynamics, only reversing was more difficult compared to the conventional finger wheel.

The joystick scores with maximum controllability

The joystick achieved the best results in terms of controllability, especially during highly dynamic maneuvers. Thomas Maier: “The high vehicle response to steering inputs, especially at low speeds, was also evident with the joystick due to the very high virtual transmission ratio, although the higher torque counteracts this somewhat.” Thomas Maier found that the joystick showed the strongest signs of fatigue in the arm across all tests. Another shortcoming: in terms of integration into the interior environment, the joystick is the most difficult to integrate due to its size and orientation.

Optimization potential for further tests

“The current state of development still shows limitations in terms of comfort at low speeds and controllability during highly dynamic evasive maneuvers, which require further investigation,” says Thomas Maier, summarizing the results.

The developer also sees potential in terms of operating sensitivity and fatigue. “The results regarding fatigue indicate that higher steering torques would be possible for both the finger wheel and the micro wheel, which would also counteract sensitivity at low speeds and possibly also enable more control in the area of the double lane change maneuver. On the other hand, the basic torque of the joystick could be lowered to reduce fatigue.”

Another effective way to reduce sensitivity at all speeds could be to significantly increase damping at high steering input speeds. This should reduce the high steering wheel angular velocities and also lead to more controllable behavior during evasive maneuvers.

Further tests and adjustments are already underway, particularly with regard to the sensitivity of the individual concepts. New functions and control concepts for the finger wheel and joystick are also being tested in order to overcome the difficulties identified.

Cooperation with car manufacturers

Extensive prototype vehicle set-ups are planned together with car manufacturers (OEMs) in order to further develop the innovative concepts for alternative control elements and promote their possible applications. Through close cooperation with OEMs, practical solutions are to be developed that will significantly improve driving comfort and functionality in future vehicles.

Regardless of which concept the future belongs to, thyssenkrupp Steering will play a decisive role in the controls of the future.