The basic performance of the steering system of the car is to ensure that the vehicle has better steering stability when turning the steering wheel under any working conditions. With the continuous development of automotive electronics and the integration of automotive systems, automotive steering systems from the traditional Hydraulic Power Steering System (HPS), Electronically Controlled Hydraulic Power Steering Systern (ECHPS) Developed to the Electro-Hydraulic Power Steering System (EHPS). In recent years, Steer-ing-By-Wire (SBW) has also become a research hotspot abroad. SBW is a type of X-By-Wire. The full name of X-By-Wire is "a safety-related fault-tolerant system without mechanical and hydraulic backup systems." "X" indicates any safety related operations, including steering, braking, and so on.
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1 Structure and basic principle of automotive remote control steering system
1.1 Structure of the vehicle's remote control steering system
The vehicle's remote control steering system consists of three main parts: steering wheel assembly, steering actuator and main controller (ECU), as well as auxiliary systems such as fail-safe systems and power supplies.
The steering wheel assembly includes a steering wheel, a steering wheel angle sensor, a torque sensor, and a steering wheel returning positive torque motor. The main function of the steering wheel assembly is to convert the driver's steering intention (by measuring the steering wheel angle) into a digital signal and transmit it to the main controller; at the same time, accept the torque signal from the main controller to generate the steering wheel return torque to provide Give the driver the corresponding road feeling information. The steering execution assembly includes a front wheel angle sensor, a steering execution motor, a steering motor controller, and a front wheel steering assembly. The function of the steering execution assembly is to accept the command of the main controller and control the steering wheel rotation by the steering motor controller to realize the steering intention of the driver.
The main controller analyzes and processes the collected signals, determines the motion state of the vehicle, sends commands to the steering wheel and the steering motor, and controls the operation of the two motors to ensure an ideal vehicle response under various working conditions. Reduce the driver's compensation task for the steering characteristics of the car as the vehicle speed changes, reducing the burden on the driver. At the same time, the controller can also recognize the driver's operation command and determine whether the driver's steering operation is reasonable in the current state. When the car is in an unstable state or the driver gives a wrong command, the steer-by-wire system will shield the driver from the wrong steering operation and automatically perform stable control to restore the car to a stable state as soon as possible.
The fail-safe system is an important module of the line-controlled steering system. It includes a series of monitoring and implementation algorithms to deal with different fault forms and fault levels in order to maximize the normal driving of the car. As one of the most widely used vehicles, the safety of automobiles is the first factor to be considered and the basis of all research. Therefore, the automatic detection and automatic processing of faults is one of the most important components of the line-controlled steering system. It uses rigorous fault detection and processing logic to maximize vehicle safety.
The power system is responsible for the power supply of the controller, the two actuator motors, and other vehicle appliances. The maximum power of the front wheel corner execution motor is 500-800W. Plus the other electronic equipment on the car, the burden of the power supply is quite high. heavy. Therefore, to ensure that the grid works stably under heavy load, the performance of the power supply is very important.
1.2 Introduction to the principle of automotive remote control steering system
The car steering system is the key component that determines the active safety of the car. The traditional car steering system is a mechanical system. The steering motion of the car is realized by the driver steering the steering wheel and transmitted to the steering wheel through the steering gear and a series of rods. . The car-steering steering system eliminates the mechanical connection between the steering wheel and the steering wheel, completely deflects by electric energy, and gets rid of the various limitations of the traditional steering system. It can not only freely design the force transmission characteristics of the steering of the car, but also design the steering of the car. The angular transmission characteristic brings unlimited space to the design of the steering characteristics of the car, and is a major innovation of the steering system of the automobile.
The working principle of the car remote steering system. The sensor is used to detect the driver's steering data, then the signal is transmitted to the ECU on the vehicle via the data bus, and the feedback command is obtained from the steering control system; the steering control system also obtains the driver's steering command from the steering mechanism and the steering system. Get the wheel condition to direct the movement of the entire steering system. The steering system controls the wheel to turn to the desired angle and feeds the wheel's corner and turning torque back to the rest of the system, such as the steering mechanism, to give the driver a sense of road. The road feel can vary depending on the situation. Controlled by the steering control system.
1.3 Characteristics of automotive remote control steering system
(1) Improve vehicle safety performance. The mechanical connection such as the steering column is removed, completely avoiding the damage of the steering column to the driver in the crash accident; the intelligent ECU judges whether the driver's operation is reasonable according to the driving state of the car, and makes corresponding adjustments; when the car is at the limit In the working condition, the car can be automatically controlled stably.
(2) Improve driving characteristics and enhance maneuverability. Based on the vehicle speed, traction control and other relevant parameters, the steering ratio (the ratio of the steering wheel angle to the wheel angle) is constantly changing. At low speeds, the steering ratio is low, which can reduce the angle of steering of the steering wheel when turning or stopping; The steering ratio becomes larger and better straight running conditions are obtained.
(3) Improve the driver's sense of the road. Since there is no mechanical connection between the steering wheel and the steering wheel, the driver's "road feel" is generated by simulation. The information that best reflects the actual driving state of the vehicle and the road surface condition can be extracted from the signal as a control variable of the steering wheel returning positive torque, so that the steering wheel only provides useful information to the driver, thereby providing a more realistic "road" for the driver. sense".
(4) Enhance car comfort. Due to the elimination of the mechanical structural connection, the unevenness of the ground and the imbalance of the steering wheel are not transmitted to the steering shaft, thereby reducing the driver's fatigue; the driver's leg movement space and the space of the vehicle chassis are significantly increased.
2 Main technical development of automotive remote control steering system
The realization of the automotive remote steering system has the following key technologies to be solved.
2.1 Stability, reliability and safety of the wire-controlled steering system
An important factor in the current popularity of wire-steering steering systems is their reliability. It is not yet possible to strike a good balance between reliability and cost. The world's major research institutions are conducting joint research on this issue, and believe that this issue can be resolved reasonably. The implementation of the loader's remote steering system must address the following issues:
(1) At present, electronic components have not yet reached the level of reliability of mechanical components. How to ensure that after the failure of electronic components, the system can still achieve its most basic steering function, that is, how to ensure stable, reliable and safe operation of the electronic steering system. Very important, this is also the most prominent problem of the electronic steering system at present;
(2) Since there is no direct mechanical connection between the steering wheel and the steering wheel, how to provide the driver with a suitable road feel so that the driver can feel the condition of the road and the position of the steering wheel, thereby adjusting the steering accordingly. Torque is one of the key technologies;
(3) In order to ensure the driving safety of the vehicle, that is, as long as the vehicle is in operation, it should ensure that the steering system can function;
(4) How to realize the steering wheel steering lap, steering sensitivity and road feeling can be adjusted by software.
Stability, reliability and safety of the steer-by-wire system For traditional mechanical systems, the safety and reliability of the system can be achieved through careful design. However, the steer-by-wire system relies completely on the mechanical connection between the steering wheel and the steering wheel. Electronic and electrical components come to work. At present, electronic components have not yet reached the level of reliability of mechanical components. How to ensure that after the failure of electronic components, the system can still achieve its most basic steering function, that is, how to ensure the stable, reliable and safe operation of the wire-controlled steering system is very important. of. This is also the key technology that the wire-steering steering system needs to solve most. To solve this problem, some foreign automobile companies have adopted system redundancy and fault tolerance technology.
2.2 The problem of simulating "road feeling" in the wire-controlled steering system
How to generate a sense of road that allows the driver to sense the actual driving state of the car and the road surface condition is one of the problems that must be solved to realize the wire-steering steering system. This involves motor vibration control technology that simulates road feel.
There is always a contradiction between light and spirit in the steering system of automobiles. For this reason, the steering gear is often designed as a variable transmission ratio, which is mainly based on the small angle of the steering wheel and light when the steering wheel is at a large angle. However, the scope of the spirit is only in the vicinity of the middle position of the steering wheel, it is only meaningful for high-speed driving, and the transmission ratio cannot be changed with the vehicle speed, so this method cannot fundamentally solve this contradiction. In addition, the steering force and the road feeling are also mutually constrained. The small steering force means that the steering is light and can reduce the driver's physical exertion; however, if the steering force is too small, there is a lack of road feeling. Because the traditional hydraulic power steering can't adjust and control the power in real time, the relationship between the coordinated steering force and the road feel is difficult. Especially when the car is driving at a high speed, it will still provide a large boost, which makes the driver lack the sense of road and even feels the car drifting. , thus affecting the stability of handling. Since the steer-by-wire system is powered by the motor, the motor has the effect of spring damping, which can reduce the impact of the uneven road surface on the steering wheel and the vibration caused by the wheel imbalance, thus reducing the driver's "road feeling". . The motor vibration control technology using analog road sense can effectively solve this problem.
2.3 Power supply problem of the line-controlled steering system
The steer-by-wire system cannot be implemented under the traditional ECU power supply system. In the future, the vehicle will adopt power supply technology, and the power supply problem of the automotive electronic accessories will be satisfactorily resolved.
2.4 Sensor accuracy and cost issues
The sensor is one of the most important devices in a steer-by-wire system. Multiple steering sensors are required to participate in the on-line steering system. The function of these sensors is to detect the magnitude and direction of the torque or angle of the steering wheel and steering motor in real time and convert this information into electrical signals for transmission to the electronic controller. The electronic controller performs analysis and calculation according to the control model according to the signal of the steering sensor and the signal of the vehicle guiding unit, and then sends the information to the steering wheel motor and the two steering motors.
The accuracy of the sensor determines the performance reliability of the entire wire-steering steering system. Accelerating the development of researching reliable and inexpensive sensors is important, and the high price is also a reason why wire-controlled steering systems are difficult to promote.
3 Application prospects
From the level of the overall technical development of China's loader industry, there is still a long way to go before the large-scale application of loader-steering steering technology, but the adoption of this technology will definitely bring about a qualitative leap in the technical level of China's loader industry.
Auxiliary driving system and driverless driving are emerging hot research fields. The best way to realize intelligent steering of vehicles is to adopt the wire-steering steering system. Therefore, the development of the wire-controlled steering system also provides a good research for the development of autonomous vehicles. The platform itself has a good application prospect. The transfer of the steer-by-wire system from the automotive industry to the engineering vehicle is an inevitable trend in the development of engineering vehicles. Although domestic and foreign manufacturers have just begun to pay attention to this problem, we believe that the steer-by-wire system will inevitably be in construction vehicles with its unique advantages. Get a wide range of applications.
4 Conclusion
In summary, the automotive line-controlled steering technology in order to obtain the best car steering performance, improve the car's handling, stability and safety, so that the car has a certain degree of intelligence. The development of automotive wire-steering technology represents the future direction of automotive steering technology and will dominate the automotive steering field. China's research on wire-steering technology is still blank and cannot be compared with foreign countries. Starting from the existing conditions in China, in-depth and meticulous research on the system will have far-reaching significance for expanding the application of electric drive technology, accelerating the electronic development of domestically produced vehicles and providing support for future smart car driving technology.
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