Until recently reserved for science fiction cars, such as the unforgettable K2000 series Kit of the 1980s, the handlebar – whose main interest is to allow easier reading of the instruments – has recently made its first appearance in a real car, in this case the Tesla Model S Plaid. Strangely, in this case, the “yoke”, as the American electric car manufacturer called it, was not associated with an innovative steering system, which allowed the passage to demonstrate by the absurd that this interface could only be really practical with, at least, a variable gear ratio.
Indeed, the characteristic of a handlebar is to offer only one mode of grip, in this case with the position of the hands said at 9:15. Which supposes being able to face all driving situations with very limited range of motion. To achieve this goal, Lexus and Toyota engineers have developed a steer-by-wire steering system called One Motion Grip, which will soon be offered on the Lexus RZ450e and Toyota Bz4x. No mechanical connection between the handlebars and the wheels here, just an electric machine behind the handlebars acting as an angle sensor and force feedback, and an electric motor operating the rack bar. This system in particular makes it possible to obtain a continuously variable gear ratio proportional to the speed, in order to be very direct to promote agility at low speed, very gear down to guarantee rock-solid stability above. In all cases, the maximum steering angle of the handlebar is 300°, that is 150° on each side.
In practice, the operation of this system called One Motion Grip is very convincing in everyday situations. For example, it greatly facilitates the task of the driver when maneuvering by reducing the amplitude of the movements to be provided, you just have to be careful not to steer shorter than necessary in this context. On the contrary, the increased gear ratio allows very fluid changes of trajectory on the highway. The system developed by Toyota/Lexus also makes it possible to filter out the unpleasant vibrations which could be generated by an uneven surface, and to automatically compensate for deviations in trajectory which could be caused by a crosswind. The reactions of the system are however more difficult to predict in dynamic driving, when the speed varies rapidly, or in an emergency situation which provokes a reaction of reflex trajectory correction on the part of the driver, a reaction which can sometimes be exaggerated at low speed when steering is very direct.
Toyota/Lexus’ One Motion Grip isn’t the first steer-by-wire system offered on a production car. Infiniti, Nissan’s luxury brand, had already offered one on the Q50 in 2014. This device also suffered from sometimes too rapid variations in the steering ratio depending on the speed. Braking in support could, for example, cause a destabilizing tightening of the trajectory not desired by the driver. In addition, the Infiniti system retained a classic steering wheel in order to be able to return to a fixed ratio, obtained via a mechanical steering column which was only there to drive the rack in the event of failure of the electrical system. For the Toyota/Lexus One Motion Grip system, the redundancy provided to compensate for a possible breakdown is both electrical and electronic, with in particular a battery and a backup computer. Even in default mode, it will therefore still be a steer-by-wire type system.
