Detailed explanation of the structure of the steer-by-wire system

The steer-by-wire system is an automotive electronic technology related to safety. By eliminating the hard connection between the front wheel and the steering wheel, an electrical signal is generated when the steering wheel is turned. The signal is transmitted to the steering drive motor, and the motor drives the steering mechanism to steer. The steer-by-wire system provides a variable steering ratio, allowing the driver to achieve a larger steering ratio by switching between different driving modes. It helps to reduce costs and improve production efficiency. Compared with the traditional electric power steering system, the steer-by-wire system reduces the number and complexity of parts and simplifies the entire structure, thereby saving manufacturing time and cost, which has significant advantages for mass production. The steer-by-wire technology can provide a smoother driving experience by eliminating the hard connection between the wheel and the steering wheel. On uneven roads, the system can reduce the vibration and pulling of the wheel, making driving safer and more comfortable. The steer-by-wire system improves the vehicle's handling flexibility, especially in narrow spaces. Through the precise control of the steering wheel by the electronic control unit, the system can adapt to different driving environments and driving styles and provide stable maneuverability.

We organize this system based on different information sources.

Part 1

Tesla's steer-by-wire system

1) Front steering system

2) Rear steering system

Physical picture

Based on the description in the patent, we can see that it is basically consistent with the finished product of this system.

Tesla's steer-by-wire system includes a steering wheel torque feedback actuator assembly, a front wheel steering actuator assembly, a power supply assembly, a vehicle communication network, and a dedicated communication system to improve system reliability through regional isolation of redundant components. The system may also include a differential gearbox road wheel actuator to allow absolute position of the road wheel, and a position sensor assembly, which includes a magnetic sensor and an inductive sensor.

This means there are four controllers here, two Primary/Secondary Steering Feedback Acuator controllers 21A and 21B for the steering wheels, and Primary/Secondary Road Wheel Acuator controllers at the execution level.

For CyberTruck, the use of wire-controlled steering and rear-wheel steering technology makes the vehicle more flexible and stable at low and high speeds. At low speeds, the rear wheels can rotate up to 10 degrees in the opposite direction, improving the vehicle's maneuverability in narrow spaces, especially making it easier to turn in parking lots. At high speeds, fine-tuning of the rear wheels provides more stable movement, making the vehicle change between lanes more smoothly and the overall driving feel more comfortable.

At present, Tesla will officially deliver the first batch of mass-produced models in Q1 2024.

Part 2

Design Challenges

This has been explained in the previous article "The Zhineng Report: Development Trends in Automotive Wire-Controlled Steering Technology".

Steer-by-wire technology also faces some challenges. Its highly integrated electronic technology and advanced sensor technology increase the difficulty of R&D and production, resulting in relatively high production costs. The system is highly dependent on power and electronic components. Once a failure occurs, the steering system may fail. At the Shanghai Auto Show, I took the time to visit Nexteer's booth to see the development of domestic steer-by-wire technology. Overall, Tier 1 suppliers focus on R&D reserves. Domestic automakers need Tesla to take the lead in this regard.