Experience Innovation – Steer-by-wire system in the new Lexus RZ

The Lexus RZ is an all-electric SUV that impresses with its innovative technology and modern equipment. As an innovative and pioneering vehicle, the RZ is the first car in Lexus' brand history to feature a fully autonomous electric drive.

One of the most remarkable innovations in this vehicle is the new steer-by-wire steering system. In contrast to conventional mechanical or hydraulic steering systems, this electronic steering system replaces the direct connection between the steering wheel and the wheels with electronic signals. Does the new steering system have a future or is it a victim of over-engineering?

Photo provided by Lexus Europe

Although the «Steer-by-Wire» System isn’t exactly new on the car market as several manufacturers already worked with it for rear-wheel-steering and Infinity had launched a Steer-by-Wire option for their Q50 sedan in 2013 (with a regular steering column as a backup in case of failure, they later discontinued to offer the non-connected steering variant due to uncertain reasons), Lexus and Toyota are the first to hit the market, fully convinced that their system will do the job as it should be, without any steering column mounted in their cars.

The boldly designed RZ is an outstanding car. It’s safe to say, whether you like its looks or not, that the RZ isn’t an ordinary car at all. It is not only in the design of the car that Lexus is breaking new ground, as the Japanese luxury car brand is also venturing into new territory with the technology used.

Steer by Wire is one of the most significant new technologies ever introduced by Lexus. Officially called One Motion Grip, this world first replaces the steering column, the conventional mechanical connection between the steering wheel and steering rack with an electrical connection. The aim is to improve the connection between car and driver. But how could this be possible? Let’s take a look at how such a counter-intuitive approach could potentially work out.

How does the new One Motion Grip work?

One Motion Grip provides no mechanical link between the steering wheel and steering rack, so information between these two essential elements is transferred electronically, or ‘by wire’.

Specifically, this means that movement from the steering wheel is sensed by a Steering Torque Actuator located at the end of the steering column (see image below). Information is sent to a Steering Control Actuator, which translates it into mechanical movement within the steering rack. Additional data about the road surface is gathered from the tyres and relayed to the control actuator to further enhance and modify its reactions.

A fixed mechanical connection between the steering wheel and steering rack creates a fixed steering gear ratio. In other words, this means that the steering movement inputted by the driver in a traditional steering set-up will always deliver the same degree of movement through the steering rack. While the level of power assistance can be altered depending on circumstances, the speed of the steering and the amount of turns it takes to go from lock-to-lock remains constant.

By removing this physical connection and its associated constraints, the One Motion Grip steer by wire system can freely alter the steering gear ratio to best suit the prevailing road conditions. During slow-speed maneuvers it can even be configured to allow the driver to turn the steering wheel from lock-to-lock without removing their hands from a fixed position on the wheel.

Illustration provided by Lexus Europe

Let’s have a seat

The Tazuna cockpit concept ensures that the most important driving-related controls are located in the immediate vicinity of the driver. The less important, less frequently used controls are now accessible via the central touchscreen. For more intuitive operation, some hardware buttons have been retained on the central display. These include the controls for switching the audio functions on and off and for the air conditioning. Another example of simple, intuitive operation in line with the Tazuna concept are the sensor buttons on the steering wheel. They were first introduced in the new Lexus NX and can be assigned to preferred functions such as driving mode selection, navigation and audio. When the driver touches the respective button, its shape and function are shown on the head-up display so that they do not have to look at the steering wheel to find the right button.

Photos provided by Lexus Europe

Driving experience:

By removing the physical connection between the road and the steering wheel, the driver is specifically shielded from vibrations from the road, tires and brakes. However, the intentionally precise calculation of the One Motion Grip system ensures that it does not lead to a numbing experience but continues to provide a confidence-inspiring level of driving feel.

One Motion Grip has been tuned to require just 170 degrees of steering wheel rotation between straight wheels to full lock. This eliminates the need for any hand-over-hand movements. As the wheels do not turn the same radius during various different speeds, the new steering system needs some practice. During maneuvering and slower speeds, the wheels turn quicker which can turn your parking job into a whole new experience. While driving through the Portuguese hilly landscape, I noticed that I often turned the steering wheel too much in slow and tight bends and therefore steered too hard and had to correct the angle. The longer the drive went on, the more smoothly I was able to control the car. The steering requires practice. Lexus therefore decided to install the steer-by-wire system only in conjunction with the yoke steering wheel in order to make it visually clear to the driver that they are dealing with different technology here. Otherwise, the steer-by-wire system feels very intuitive above 50kph.

A short delay is noticeable when the steering angle is corrected abruptly. This is hardly noticeable when parking, but I miss a more direct connection to the road when driving ambitiously on winding country roads.

personal opinion on the steer-by-wire system:

Advantages:

• Without the mechanical connection, there is greater design freedom and space in the interior. The steering wheel can be made more ergonomic and it is possible to conceal or modify the steering wheel if required.

• If necessary, the system can make automatic corrections or intervene in emergency situations to improve control. It is also less susceptible to mechanical wear parts, which can increase reliability.

• The steer-by-wire system enables the integration of additional assistance functions, such as automatic lane keeping or adaptive steering, which adapts to the driving situation.

• The system has a second power circuit to prevent steering failures in any case.

Disadvantages:

• Lexus claims that the steer-by-wire system enables finer control of steering movements. Electronic control allows the steering reactions to be adapted to the driving situation, resulting in more precise and responsive steering as an overall advantage. I personally take this opinion as a negative point due to potential function override. I suspect less engagement and precision. Under certain circumstances, the steering system could steer the vehicle autonomously without the driver being able to intervene. (my horror scenario)

• The electronic control system is technically complex and can increase maintenance and repair costs. If the system fails, repairs are often more expensive than with conventional steering systems.

• Some drivers find the feel and feedback of conventional mechanical steering safer and more familiar. The lack of a direct connection can influence the driving experience and affect confidence in the technology.

• In the event of power failures or electronic faults, there is a risk that the steering system will fail or function to a limited extent. Although modern systems have redundant safety mechanisms, dependence on electronics remains a risk.

• As steer-by-wire systems are still relatively new, there are different legal regulations and approval processes around the world that could restrict their spread.

Lexus RZ550e premiere:

The RZ550e F SPORT is equipped with Interactive Manual Drive (M-button on the center console), a first for Lexus, which allows the driver to interact more with the vehicle and control the power output via paddle shifters, similar to a dual clutch gearbox with padels. Actuation is accompanied by real-time feedback via the accelerator pedal as well as corresponding sounds and visual effects, creating an even closer connection between driver and machine.

The system is programmed with the characteristics of a virtual eight-speed gearbox. The virtual torque of the power source is calculated based on the accelerator pedal position and speed and then multiplied by the transmission ratio of the selected virtual gear. To further enhance the driving experience, the Lexus imitates engine sounds. The system works with a rev limiter to give the driver a better sense of the timing of gear changes and the associated changes in vehicle state.

On the instrument display, the gearshift recommendation shows the vehicle status, helping the driver to select the optimum shift timing also known from the Hyundai Ioniq 5 N.

To summarize, I conclude that the fascinating steer-by-wire steering system works better than I expected. However, I am very skeptical about this technology because, especially as artificial intelligence advances, a car could, in the worst case, start to drive itself without a driver being able to control it at all. From my point of view, I also maintain that car manufacturers generally trust drivers less to safely steer and drive a car. On the other hand, it’s great to see that some are still experimenting with new technology.

What’s the verdict?

The steer-by-wire steering system in the Lexus RZ450e and RZ550e offers a few advantages, particularly in terms of driving comfort and innovative assistance functions. However, the challenges and potential risks should not be ignored. With advancing technology and increasing acceptance, these systems could play an even greater role in automotive engineering in the future, whereby safety and reliability must always take center stage. I personally liked the Steer-by-wire system better that I would have expected.

To end this review I'd like to thank Lexus Switzerland for the invite to Faro. It has been an interesting trip to the beautiful Algarve region in southern Portugal.

Phots & review by RPM | Robin P.M.