Steer-by-wire

The Steer-by-Wire technology offers numerous opportunities for ADAS, autonomous drive and even steering functions we haven’t yet invented. It also has favourable impact on design, production and safety. But there is a great concern that the loss of the mechanical link will also make a drop in the joy and quality of driving, making the car to be something of a damp squib. That would be terrible sacrifice. The Sentient Steer-by-Wire technology was born in urge to explore any drawbacks and how to counteract them, but also to make use of the advantages for steering feel and driving experience. The soul of the car.

Torsion bar free

First some words on the mechanical conditions for steering feel. The steering feel quality is not only dependent on software and tuning, but of course also depending on the mechanical basis. The feedback motor is directly coupled to the steering shaft with the steering wheel in the other end, without a torsion bar. The mechanical quality is thus very high, i. e. in practice free from play and friction. This results in a high degree of steering sophistication for on-centre feel and precision and the possibility to give sporty feedback, without compliance feel, that is superior to not only Steer-by-Wire solutions with torsion bar and a reduction gear, but even typically better than traditional EPS with a mechanical link.

Base Feel & Variable Ratio

The base steering feel consists of the following software elements; lateral acceleration feedback, both on-centre and off-centre, damping, friction, tyre feel and active return. The tuning in these elements are very fast and straight forward compared to traditional tuning of assist or boost curve. And this is a real advantage, because with sbw you will also tune variable gear ratio, both for vehicle speed and rack travel.

In low velocities the driver can reach full road wheel angles but for higher speeds the gearing is not possible. For instance, you can use a constant yaw rate as philosophy, that means that a certain steering wheel angle shall generate specific yaw rate for all vehicle speeds. This approach is also used in the aircraft industry. For lower speeds it is not possible to reach higher yaw rates and instead a constant gearing will be used that allows the driver to reach full road wheel angles.

Limit Handling Feel

Understeer in an old car, when the front wheels start to lose grip, the torque in the steering wheel progressively drops thanks to the receding pneumatic trail in the tyre contact patch. It is honest feedback to the driver that car starts to understeer and the feedback elegantly matches the vehicle state intuitively, i. e. less feedback equals to less response. Unfortunately, this feedback can be more or less lost in many modern cars with EPS. In the Steer-by-Wire car this feedback is recreated to replicate the torque reduction perceived in a good hydraulic gear.

Steering feel during oversteer have had same attention to tuning. And this combination is the foundation for a trustworthy and engaging on limit feedback, that we have been perfecting for 3 winter seasons in the north of Sweden.

Road Feel

Road disturbances are of course fully suppressed with Steer-by-Wire and adverse phenomena such as pulling and torque steer are eliminated. While that feels perfectly comfortable to drive it can also generate concerns about the steering feel being too numb, silent, or even dead. Many would say it lacks road feel. Good road feel has been described as running over a coin and by the feel in the steering wheel you can tell if it is heads or tails. Some believe that the loss of road feel is a drawback you must accept with Steer-by-Wire, since there is no mechanical link to transmit the information. That is of course not true, since the information can be picked up and transmitted to the steering wheel by other means. The way we have solved this allow for wanted road feedback and at the same time being inherently free from adverse side effects.

Vehicle Response Augmentation

Steer-by-Wire can also improve vehicle response. We have developed functions for quite spirited or extreme driving conditions. There are many rational reasons to say that this is totally unnecessary. People don’t drive like that or at least they shouldn’t. It is enough if the car is safe, it doesn’t have to make you smile in extremely rare driving. All true. But if you are among those lucky few, maybe a motor journalist that get the chance to explore an exclusive car on a track, then it should definitely be beautiful to drive as well. If you think this makes sense, then Vehicle Response Augmentation makes all the sense. Ok, it probably makes the car a little bit safer to handle as well. But mostly more beautiful to drive.