What is a steer-by-wire system? A brief analysis of steer-by-wire technology

Steering-By-Wire

Cybertruck uses wire-controlled rotation to replace the traditional mechanical rotation method of vehicles, making the control more perfect, which is also a necessary step towards high-end intelligent driving.

What is a steer-by-wire system? Simply put, steer-by-wire completely eliminates the physical connection between the steering wheel and the wheels, and uses electrical signals to control the steering of the wheels. The steer-by-wire system not only has all the advantages of a traditional mechanical steering system, but can also optimize the angle transfer characteristics, which is difficult for a mechanical system to achieve.

The steer-by-wire system is not a new technology. Various OEMs have developed this technology a long time ago, including Toyota, Volkswagen, Great Wall, BYD, Weilai, etc., as well as the world-renowned Tier 1 Bosch, Continental, and ZF, are all developing and implementing steer-by-wire. However, the only one that has truly put it into mass production is Tesla's Cybertruck.

Therefore, Cybertruck's subsequent performance is of great market guidance significance. At the same time, this technology is also the core technology of the "sliding chassis", so its subsequent batch status is very meaningful for reference.

Although the steer-by-wire technology can eliminate the original bulkier transmission mechanism and make the vehicle lighter (light means low cost and long battery life) and lower cost compared to traditional technology, electrification is controlled by signals. Once a problem occurs, the consequences will be very serious. Therefore, when this technology was first used on aircraft, a double redundant design was adopted for double insurance.

The steer-by-wire technology is currently widely used in vehicles, mainly in rear-wheel drive, and rarely in front-wheel drive. The main reason is that this technology cannot have any problems, and the failure of electrical signals can be caused by many factors, such as battery power failure, signal delay and loss, etc.

In order to prevent the battery from suddenly running out of power, Cybertruck not only uses a 48V battery system to power the motor on the left side of the picture below, but also connects to high-voltage power. In addition, there are 2 backup batteries to ensure that the battery is not out of power, which is also a dual redundancy design.

Cybertruck's steer-by-wire system uses two motors, each of which can produce about 50-60% of its maximum torque in low-speed parking situations. If one fails, there is still one motor available to provide redundancy. The same motor (only one) is used to drive the rear steering system, which can give the driver a sense of simulated feedback. This feedback is very important. Without this feedback, the driver is less able to perceive the steering of the wheels. It also transmits data from the tires and the ground to the analysis unit to give a better driving experience. For example, when you are steering, it can keep the grip of the tires and the ground in the best condition.

Since electrical signals replace traditional mechanical control, the effectiveness and timeliness of signal transmission are very important. Cybertruc uses Ethernet communication instead of traditional CAN communication. It has a Gigabit Ethernet system to move data, which can meet high-speed communication. The data network delay is only half a millisecond, which is very suitable for turn signals. It also provides sufficient bandwidth to allow various controllers to communicate in real time.

Compared with CAN communication, Ethernet has a higher bandwidth. The whole vehicle can share a daisy chain. The POE technology can realize direct power supply of the Ethernet interface without a separate low-voltage power supply, which can greatly reduce the cost of wiring harness. This technology will also be rapidly commercialized and implemented with the rapid commercialization of in-vehicle Ethernet and future intelligent driving.

Summarize:

Although steer-by-wire technology is not a very advanced technology, it is used in large quantities on vehicles. At least Lexus encountered many problems when it tried it out. This technology directly cancels the traditional sensor mechanical control through electrical signals. Although it is inexpensive and can give drivers a better driving experience, the most basic requirement of a vehicle is safety. There are many levels of failure factors of electrical signals. Promoting technological progress requires market verification and time. If the technology is very stable in the future, the integrated technology of the "electric skateboard" will also go a step further.