The key technology of steering by wire

With the development of automotive bus technology, there are many kinds of bus standards, which will be used in the future to have some bus standards and protocols with high speed and real time transmission characteristics. There are TTP, Bytef-light and FlexRay standards for this kind of bus. TTP (time triggered protocol) is a communication protocol used in distributed real-time control system is complete, can support a variety of fault tolerant strategy, with recovery and integration of the node; BMW, Byte-light can be used in the communication network of automobile wire control system, which can meet the needs of some high priority messages to ensure the time triggered determine the delay requirements, and can meet the needs of some news event, need to interrupt processing requirements; and other car manufacturers now plans to adopt FlexRay, which is a kind of network communication system is especially suitable for the next generation of cars should be used, with fault tolerance function and message transmission time is determined, which can meet the high-speed communication vehicle control system request. BMW, Daimler-Chryler, Motorola and Philips jointly developed the FlexRay standard, GM company, Boseh company and Volkswagen company also joined the joint development association, now has 7 core members, working together in the development of automotive distributed control system of the high speed bus standard. The physical layer standard before the FlexRay standard has been developed by Philips, the communication protocol is being developed. The introduction of the standard not only improves the consistency and reliability of information transmission, but also simplifies the process of information development and use, and reduces the cost. From now on, because FlexRay is based on time and event triggered protocol, it is better than TTP. The SBW system based on bus technology turns the traditional mechanical steering system into the electrical system which is connected with the high speed fault tolerant communication bus, and realizes the automation, intelligence, network and information of the system.

Steer by wire system structure

The SBW system consists of steering wheel, front wheel steering module module, the main controller (ECU) and automatic anti fault system.

1 steering wheel module

The steering wheel module comprises a steering wheel assembly, a steering wheel angle sensor, a torque sensor, a steering wheel torque motor. Its main function is to turn to the driver's intention (as measured by the steering wheel angle) is converted into digital signal and transmitted to the main controller and main controller to the steering wheel aligning torque motor control signals sent from the steering wheel aligning torque, to provide information to the driver the road.

2 front wheel steering module

The front wheel steering module comprises a front wheel rotation angle sensor, a steering actuator motor, a motor controller and a front wheel steering assembly. Its function is to measure the front wheel angle signal feedback to the main controller, and accept the command of the main controller to control the steering wheel to complete the required front wheel angle, to achieve the driver's steering intention.

3 main controller

The main controller of the collected signal analysis and processing, to determine the motor state, to the steering wheel back to the positive torque motor and steering motor to send commands to control the two motor coordination. The master controller can also identify the driver's operation instructions, and determine whether the steering operation is reasonable in the current state. When the car is in non steady state or the driver sends the wrong order, the front wheel steering by wire system will automatically control or driver error steering operation screen, in a reasonable manner of vehicle automated driving the car back to the steady state as soon as possible.

4 automatic control system

Automatic fault protection system is an important module of steer by wire system, it includes a series of monitoring and implementation of algorithm, make corresponding treatment according to the fault types and fault of different grade, in order to keep the car's normal driving maximum. Steer by wire technology used in fault detection and processing logic, to maximize the vehicle safety performance.

The working principle of the steer by wire system

The working process: from the steering wheel sensor and various vehicle current state information to the electronic control system, using computer to control the operation of the information, and then issued a directive on the vehicle steering system, the steering of vehicle. At the same time, the information given by the steering resistance sensor in the wheel steering subsystem is also electronically controlled.

The performance characteristics of the system two, steer by wire

The steering wheel and the steering wheel is no mechanical connection between the system, is open, by bus transmission the necessary information, so the system also called flexible steering system. Has the following performance characteristics:

The flexible steering system can eliminate the steering interference problem, which provides a significant precondition for the realization of multi function automatic control, as well as the system integration of the vehicle dynamic control system and the vehicle ride comfort control system.

On a front wheel drive car, steering shaft rigid space need to be considered in the installation of the engine, the steering shaft must be based on the car is driving on the left or right driving engine mounted near the design personnel must coordinate various arrangement of parts. The flexible steering removes the rigid mechanical connection between the various functional modules of the original steering system, which greatly facilitates the general layout of the system.

Comfort is improved. In the rigid steering system, uneven pavement and the steering wheel is not balanced, can turn back to figure 1 steer by wire system schematic diagram of working principle of Tutu 2 steering shaft system, and the system is not flexible.