Steer-by-wire Introduction
The concept of ‘smart vehicles’ has been floated several times in recent years in the automotive industry. Every automotive designer has their own definition of this concept, with most of the focus on automating processes to get a faster response. This also includes replacing mechanical connections and linkages with electronic signals, coupled with sensors and actuators as well. The steer-by-wire system is part of this set of innovative features.
Working of a Steer-by-wire system:
As you may have accurately guessed, a steer-by-wire system essentially replaces the mechanical linkages between the steering wheel and steering rack, i.e., the steering column, with electronic connections instead. The steering wheel position sensor measures the extent to which the driver wants to steer the car and sends this data to the control unit, which in turn sends out commands to the steering actuator to execute the turn.
Source: https://www.researchgate.net/publication/318595731_Adaptive_Global_Fast_Sliding_Mode_Control_for_Steer-by-Wire_System_Road_Vehicles#fullTextFileContent
Advantages of using a Steer-by-wire system:
One of the obvious advantages of the steer-by-wire system is the reduction in weight due to the decreased number of mechanical components. Additionally, this kind of design reduces overall wear and tear and helps improve maintenance ability.
It also allows for more flexible design options, as there is no restriction on placing the steering wheel in a particular location. Furthermore, there is no need of designing separate versions of the steering system for left-hand and right-hand-drive vehicles. This also results in a better acoustic design for the vehicle cockpit, as vibrations and noise aren’t transmitted directly.
Fail-safes for Steer-by-wire:
As in any x-by-wire system, even a steer-by-wire system needs some redundant mechanisms that can take over in case of failure. Many a time, an additional steering motor is added to the setup, which can take charge in case the first motor stops receiving signals. Another interesting solution is to control the amount of driving force being sent to the front wheels, which will create a steering effect.
Design optimizations and improvements made possible by Steer-by-wire:
There can be an improvement in the way the driver gets steering feedback while turning the vehicle. In a conventional steering system, the steering ‘feel’ is restricted by the mechanics of the steering system.
However, with no physical connections restricting the steering feedback in the steer-by-wire system, there is a lot of scope for improvement and optimization.
This includes introducing new degrees of freedom in configuring the steering feel, and the time required to tune this feel can also be shortened using software-based tools for optimizing the steering feel.
One can also optimize the steering feel by using road feedback. A normal steer-by-wire system will not transmit any bumps back to the steering wheel, but some automotive designers try to use this feedback to improve how the steering wheel feels while driving on a bumpy road.
A big advantage of this kind of design is that the amplitude of road feedback can be easily controlled, thus enabling automakers to adapt the intensity of feedback to the selected driving mode. (For example, these road bumps will be suppressed in ‘comfort’ mode.)
The virtual steering ratio is another design modification aided by the steer-by-wire system. Since there is no mechanical linkage present, the only limits to the steering are set by the tuning of vehicle response and the chassis.
The steering ratio (the ratio of the number of degrees the steering wheel turns to the number of degrees the wheel(s) turn as a result) can be varied to simulate extreme rack configurations as well, which will improve maneuverability and controllability of the vehicle.
Furthermore, a virtual steering ratio can also be used to apply a steering angle offset. This helps in improving the stability of the vehicle in terms of steering.
This may be achieved by using a steering stability controller (correcting the yaw rate of the vehicle to follow a pre-set model) or a steering stability assistant (using a superimposed steering angle to stabilize the vehicle based on the driver’s input).
Both are active safety features that can enhance the stability of the vehicle while being nearly imperceptible. They can respond faster than a human in case of unnatural deviation from the road and help in mitigating the effect of steering instability.
Steer By Wire Controls Development at Dorleco:
Thus, a steer-by-wire system can help in improving the response of the vehicle, while also allowing for design modifications and optimizations that would not be otherwise possible in a conventional steering system.
It also allows for better vehicle design in terms of noise and vibration-damping, flexibility in deciding the location of the steering wheel, and less wear-and-tear of other physical components.
At Dorleco, we work on developing control algorithms and delivering controls software for steer-by-wire functions in hybrid and electric vehicles.
