From the beginning of the birth of the car, the steering wheel has always been the communication window between the driver and the car, through the mechanical device, connecting the steering lever and the steering wheel to achieve the driver's control intention. However, after the millennium, with the empowerment and blessing of science and technology, electronic control gradually replaced the design of mechanical connections, such as electronic handbrakes, electronic shift paddles, etc. Today, on the eve of the era of high-end autonomous driving, the steering system is also beginning to tend to be electronically controlled by the system, which we call "steer-by-wire".
Wire-controlled steering is not new, and fighter jets have long been used
Earlier fighters were also operated by hydraulic or pull-wire and tie-rod mechanical connections, but a large number of mechanical pipelines were scattered throughout the fuselage, which not only increased the design difficulty and weight of the aircraft, but also reduced the transmission sensitivity. At the same time, fighter pilots will often do more than a few G maneuvers, at this time the control lever requires a lot of physical exertion, which is not a good thing for combat flight. So NASA's "steer-by-wire" technology for aerospace began to enter the vision of engineers, and one of the first devices to use on-line steering was the famous F-16 fighter.
In addition, steer-by-wire technology is also used in large special vehicles, such as those with hundreds of tons of self-propelled minecarts, or large vehicles carrying equipment such as intercontinental missiles/launch vehicles. Due to the large size of the body and the special wheel layout, steer-by-wire has become a lower-cost, but also more efficient option.
Back to our family car field today, from the original pure mechanical steering system, through mechanical hydraulic power steering (HPS), electro hydraulic power steering (EHPS), to now has been widely used electric power steering (EPS), the steering system towards more sensitive operation, The direction of more reliable structures and lower power consumption is constantly evolving.
Compared with EPS, the biggest difference between steer-by-wire is the cancellation of the physical connection between the steering wheel and the steering wheel, its steering torque is completely dependent on the down steering actuator to output, and the direction and size of the down steering actuator output force depends on the control signal given by the control algorithm, which means that the steering is completely determined by the control algorithm. The algorithm can perform the input signal of the steering wheel through clutch coupling, or it can be decoupled to achieve independent steering away from the steering wheel according to the steering requirements of automatic driving.
In the era of autonomous driving, steer-by-wire may become a trend
Through the above example, we can find that if the steer-wire is applied on a family car, then there will be the following advantages:
1. The advantage of wire steering is that there is no hard connection between the steering wheel and the steering machine, and only a small part of the road surface vibration is transmitted to the steering wheel, which is highly comfortable;
2. Omit the space occupied by the mechanical structure of the vehicle's front cabin, giving the designer more space to use;
3. There is no mechanical steering pipe column, which greatly improves the safety of the crew compartment after the collision of the vehicle;
4. The steering wheel angle and steering torque can be independently adjusted by the ECU to adapt to the requirements of different types of drivers for "feel".
But these don't make it a "must- have" for autonomous driving. As we all know, the realization of the real automatic driving function requires the tacit cooperation of the three levels of "front-end perception layer", "central decision-making layer" and "bottom execution layer".
The "front perceptual layer" includes cameras, millimeter-wave radar and lidar and other sensing devices responsible for capturing information, and the "central decision-making layer" gives command signals to route planning, driving control, etc. through algorithms, and transmits to the wheels, throttle, steering and braking of the "bottom execution layer" to complete a series of vehicle control actions.
In the whole execution process, the "chassis execution layer" has higher requirements for execution accuracy and faster response to demand. However, the traditional EPS is limited by many factors such as installation space, force transmission characteristics, and angle transmission characteristics, and cannot be freely designed. Therefore, the steer-by-wire steering system that can be "completely detached" from the driver to achieve steering control is very suitable for the needs of automatic driving, and this feature greatly improves the probability that steer-by-wire will become a "must-have" for automatic driving.
Currently, the vehicles we are testing equipped with conventional steering systems, below L3 level autonomous driving, the steering wheel needs to be ready to take over at any time.
Imagine that in the future era of steer-by-wire, in the mode of automatic driving, after the electronic control takes over, the decoupled steering wheel can be completely contracted, providing more intelligent space for the car.
70 years of exploration for a better future
Although steer-by-wire is beginning to be noticed by more and more car companies, the application in passenger cars is not smooth. As early as the 1950s, TRW and Germany's Kasselmann and others proposed the concept of vehicle-by-wire steering, but because the steering system was very mature at that time and subject to cost, this idea did not land.
It was not until 1990 that Mercedes-Benz resumed the research on front-wheel steer-by-wire and applied the steer-by-wire system it developed to the concept car F200 in 1996.
At the 71st Geneva International Automobile Exhibition in 2001, the concept car FILO designed and developed by Bertone in Italy also adopted a steer-by-wire system, which eliminated the steering wheel and used a joystick for steering operation.
While European and American companies are making efforts, Japanese companies have also shown their talent for "technical houses". At the 2018 Beijing Auto Show, JTEKT showed off a steer-by-wire demonstration machine, which earned enough eyeballs; at the same time, the steer-by-wire steering system developed by Japan's Koyaba and Nissan is also the only steer-by-wire system currently used in mass-produced models.
The first car company to eat crabs was Infiniti. Infiniti for this set of steer-by-wire preparation of a full 3 independent ECU driving computer, the vehicle must be at least ECU issued the same instructions to complete the steering, if a sudden failure, the other two ECU can ensure normal steering, but if the three ECU issued instructions are all different, at this time the steering-by-wire can not work properly, Infiniti for this to prepare a backup mechanical steering, ECU failure after the system will immediately engage the clutch, restore the mechanical steering connection.
Looking back at the domestic market, Great Wall Motors announced the "Coffee Intelligent 2.0 Smart Wire Control Chassis" in 2021, which is a technology platform built with the goal of L4 level and above automatic driving, which was first released at the 8th Great Wall Motor Science and Technology Festival in June this year, and plans to achieve mass production in 2023.
On December 1, the first meeting of the Steer By Wire (SBW) working group of the China Automobile Research Institute announced that Jidu, Weilai and Geely have officially become the joint lead units for the development of steer-by-wire technology and standardization research, and will lead the formulation of relevant national standards for steer-by-wire. At the same time, Jidu Automobile also regards "steer-by-wire" as one of its core competitiveness, and actively deploys the self-research work of steer-by-wire.
Bang reviews
Teacher Bang learned that as a new next-generation steering technology, the research and development of relevant technologies and regulations for wire steering are also being carried out simultaneously. At present, foreign countries have relaxed the relevant regulatory restrictions on the on-wire steering and allowing the on-wire steering for mass production. In January 2022, China's steering standard (GB 17675-2021) will also lift restrictions on the coupling of steering system steering wheels and wheel objects. At that time, under the leadership of car companies such as Jidu, Weilai and Geely, the development and standardization of wire steering technology will be further improved, and China's unmanned autonomous driving technology will also usher in a new chapter.