Steer by wire is one of the most significant new technologies that Lexus has ever introduced. Officially known as One Motion Grip, this world-first technology replaces the traditional mechanical connection between the steering wheel and steering rack with an electrical connection. The aim is to actually enhance the connection between car and driver. But how is that possible? We look at how such a counter-intuitive approach can actually work.
How does 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.
How is steer by wire different from traditional steering?
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 manoeuvres 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.
What are the advantages of altering the steering gear ratio?
The steering gear ratio can be optimised to suit the vehicle’s speed: geared down for low-speed manoeuvres and geared up for medium- to high-speed driving. As chief engineer Takashi Watanabe explains: “Our vision is to use electrification technology as a means to enhance basic vehicle performance, so that we can continue to pursue driving pleasure for all future generations.”
In this respect, constant modifying of the steering gear ratio allows the One Motion Grip system to deliver steering that is perfectly tuned for each circumstance, from removing the requirement for hand-over-hand operation when parking to enhancing straight-line stability on motorways.
Removing the physical link between road and steering wheel naturally shields the driver from unnecessary vibrations from the tyres and brakes, however the precise computational judgment of the One Motion Grip system ensures that it doesn’t provide an anaesthetised experience but continues to deliver confidence-inspiring levels of driving feedback.
Why does One Motion Grip come with a steering yoke?
One Motion Grip has been tuned to require just 150 degrees of steering wheel rotation between straight ahead and full lock. This eliminates the need for any hand-over-hand movements, meaning the driver can turn the steering from full lock to full lock without fully crossing their arms or even needing to move their hands from a ten-to-two position.
As the top quarter of a traditional steering wheel would therefore be redundant, Lexus adopted a butterfly-style yoke design with input from takumi drivers. Not only does this shape encourage proper hand positioning for optimal vehicle control but it creates a more open view of the instrument binnacle and road ahead. Lexus designers took advantage of this to set the instruments higher and further away than would be possible with a conventional steering wheel, minimising the need for the driver to adjust their sightline.
Is steer by wire safe?
Absolutely. Rest assured that Lexus would not include this technology if it wasn’t safe or even advantageous. Lexus engineers have ensured the system provides feel and feedback at all times, maintaining a strong connection between driver and car. There is also fail-safe provision of processors and an emergency power supply in the unlikely event that the system loses its principal power supply.