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System Overview Of Automobile Electric Power Steering
Electric Power Steering system, EPS (Electric Power Steering, abbreviation) is a kind of rely on motor directly provide auxiliary torque of the Power Steering system, with the traditional HPS Hydraulic Power Steering system (Hydraulic Power Steering) compared to, EPS system has many advantages. EPS is mainly composed of torque sensor, speed sensor, motor, deceleration body and electronic control unit (ECU), etc.
Development history of the development process of the car, the steering system has experienced four stages of development:
From the initial mechanical Steering system (Manual Steering, "MS") for the development of Hydraulic Power Steering system (Hydraulic Power Steering, referred to as "HPS"), then the electronically controlled Hydraulic Power Steering system (company Hydraulic Power Steering, the EHPS) and Electric Power Steering system (Electric Power Steering, hereinafter referred to as EPS).
Mechanical steering system of automobile assembly, in the car parking and driving at low speed when the driver's steering load is too heavy, in order to solve this problem, the United States GM company pioneered in the 1950 s adopted the hydraulic power steering system on the car. However, hydraulic power steering system is unable to take into account the vehicle at low speed when the steering portability and high-speed stability, so in 1983, Japan Koyo company launched have speed induction function of electronically controlled hydraulic power steering system. This new type of steering system can provide decreased gradually with the increase of speed, steering, but complex, high cost, and cannot be overcome hydraulic system itself has many shortcomings, is a kind of between the hydraulic power steering and the transition between the electric power steering. In 1988, Japan Suzuki company first in the small car Cervo equipped with Koyo company research and development of steering power type electric power steering system; In 1990, the Japanese Honda company also adopted the independent research and development on the NSX sports cars of the rack power type electric power steering system, from then on, unveiled on auto electric power steering applications history.
Type and advantages and disadvantages of our common power steering are mechanical hydraulic booster, electronic hydraulic power and electric power.
The mechanical hydraulic booster
Mechanical and hydraulic power is our one of the most common dynamical method, it was born in 1902, by the British Frederick w. Lanchester invention, and the earliest application is delayed for half a century later, the commercialization of the Chrysler 1951 mature hydraulic steering system is applied in the Imperial line disappears. Because the technology is mature and reliable, and low cost, has been widely spread.
Mechanical hydraulic booster system main component of hydraulic pump, tubing, pressure fluid control valve, V belt, storage tanks, etc. This power is part of the engine power output into hydraulic pump pressure, auxiliary force on steering system, so that the tires.
The electronic hydraulic pressure boost
Due to mechanical hydraulic power consumption need sharp engine power, so people on the basis of mechanical hydraulic booster was improved, developed a more save energy consumption of electronic hydraulic power steering system. The system of the steering pump is no longer directly driven by the engine, but by the motor to drive, and on the basis of before equipped with the electric control system, make to the size of the auxiliary power is not only related to the steering Angle, also related to the speed. Mechanical structure increased hydraulic reaction equipment and flow distributing valve, the new electronic control system including the speed sensor, electromagnetic valve, steering ECU, etc.
Electric power
EPS is the abbreviation of English for Electric Power Steering, Electric Power Steering system. Electric power steering system is the development direction of automobile steering system. The system provided by the electric power machine direct steering, eliminating the hydraulic power steering system required for the power steering pumps, hoses, hydraulic oil, conveyor belt and pulley mounted on the engine, save energy, and protect the environment. In addition, also has the easy, flexible assembly and under various conditions can provide steering characteristics. It is with these advantages, electric power steering system as a new steering technology, will challenge the everyone is very familiar with, have the hydraulic steering system with more than 50 years history.
Driver in manipulation of the steering wheel steering, steering and steering wheel torque sensor detects the size of the torque, the voltage signal to the electronic control unit, the electronic control unit according to detect torque of the torque sensor voltage signals, the rotation direction and speed, etc., to the motor controller issued a directive, the motor output corresponding size and direction of the steering torque, thus generating auxiliary power. Cars don't turn, the electronic control unit is not issuing commands to the motor controller, motor does not work.
Advantage advantages compared with traditional hydraulic power steering system, electric power steering system has the following advantages:
1, only when the steering motor to provide power, can significantly reduce fuel consumption
Traditional hydraulic power steering system with the engine drives the steering pump, no matter to or not to consume power engine parts. And electric power steering system is powered by a motor in the steering, not to not waste energy. Therefore, the electric power steering system can reduce fuel consumption of the vehicle.
Compared with hydraulic power steering system test shows that, when not to electric power steering can reduce fuel consumption by 2.5%; In turn, can be reduced by 5.5%.
2, steering size can be adjusted by the software, to be able to take into account the steering portability and low speed when high speed steering stability, back is good performance.
The traditional hydraulic power steering system provided by the steering size can change with the increase of speed. Although this makes the vehicle at low speed have good steering portability, but in high speed steering wheel is too light, have turned to "FaPiao" phenomenon, the driver without significant sense of "road", reduce the stability of vehicle at high speed and the driver's sense of security.
Electric power steering system provides convenient adjustment of size by software. At low speeds, the electric power steering system can provide larger steering, provide the vehicle's steering portability; As speed increases, the electric power steering system to provide the steering can be gradually decreases, and turn to when the driver required to provide force will gradually increase, so the driver can feel obvious sense of "road", enhances the stability of the vehicle.
Electric power steering system can also exert certain additional back to positive torque and damping torque, making low speed when the steering wheel back to the middle position accurately, and can inhibit the high-speed rotating is steering wheel oscillation and overshoot in the process, both the return-to-center performance at high and low speed vehicles.
3, compact structure, light quality, good production line assembly, easy to maintenance
Cancelled the electric power steering system hydraulic steering oil pump, oil cylinder, hydraulic pipeline and oil tank, and the motor and deceleration institutions can make a whole, and the steering column and steering makes the entire steering system structure is compact, light quality, good on the production line of assembling, save time, easy to maintenance.
4, through the program setup, easy to match with different models, electric power steering system can shorten the cycle of production and development.
Because the electric power steering system has many advantages above, thus obtained is more and more widely used in recent years.
Electric power steering system is on the basis of the mechanical steering system, install the motor and deceleration mechanism, torque Angle sensor, speed sensor and the electronic control unit (ECU) for ECU.
Edit this section the characteristics of hydraulic power steering system has been developed for more than half a century, the technology has been quite mature. But with the development of the auto microelectronics technology, constantly improve to automobile energy saving and environmental protection requirement, the system of energy consumption and pollution to the environment may cause the inherent shortage is more and more obvious, can't completely meet the requirements of times development.
Electric power steering system will be the latest power electronic technology and high performance motor control technology applied in automobile steering system, can significantly improve vehicle dynamic performance and static performance, enhance the driver's driving comfort and safety, reduce environmental pollution, etc. Once the system is put forward, therefore, is brought to the attention of many big car companies, and carry on research and development, the future of the steering system of electric power steering steering system will become mainstream, compared with the other steering system, the system highlights the advantage embodies in:
A, reduce the fuel consumption.
Engine to drive the hydraulic pump hydraulic power steering system, make the hydraulic oil flow ceaselessly, wasted energy. Instead of electric power steering system (EPS) only need to operation need motor provides energy, this energy can come from battery, also can come from the engine. Moreover, energy consumption is associated with the steering and the current speed of steering wheel. When the steering wheel does not turn, the motor doesn't work, need to start work under the influence of the motor in the control module and output the corresponding size and direction of the torque to produce power-assist steering torque, and the system output maximum steering torque, when the car spin with the change of the vehicle speed, output torque is also follow changes. The system realize the "on-demand power", is the real "on-demand power type" (on demand) system. Car when starting a cold winter, the traditional hydraulic system response is slow, until after the hydraulic oil preheating can work normally. Because the electric power steering system design is not dependent on the engine and there is no hydraulic oil tube, is not sensitive to cold weather, the system can work even when to 40 ℃, so provides quick cold start. Because the system does not start at the time of preheat, save the energy. Hydraulic pump is not used, to avoid the engine of parasitic energy loss, improve the fuel economy, and is equipped with electric power steering system of the vehicle and is equipped with hydraulic power steering system of vehicle contrast experiment shows that under the condition of not to, is equipped with electric power steering system of vehicle fuel consumption by 2.5%, in use to case, the fuel consumption was reduced by 5.5%.
Second, strengthened to follow.
In the electric power steering system, electric power machine attached directly to the steering mechanism can make the energy directly to the turning of the wheel. The system USES inertial shock absorber effect, make the reversal of the wheel and steering wheel shimmy water reducing greatly. So steering system's ability to resist disturbance greatly enhanced compared with the hydraulic power steering system, rotating torque generated by motor, without turning hysteresis effect of hydraulic power system, enhance the follow performance of steering wheel to the steering wheel.
3, improve the steering characteristics are back.
Until today, the development of the power steering system performance has reached the limit, the return-to-center characteristics of a electric power steering system has changed all that. When the driver to rotate the steering wheel Angle to loosen, the system can automatically adjust back to the middle of the wheel. The system also can let the engineers use software within the maximum adjustment to get the best design parameters are features. From low speed to high speed, and can get a bunch of return-to-center performance curve. Through flexible software programming and easy to get motor in various speed and torque under different shape features, the torque characteristics makes the system can significantly improve the steering ability, provides the steering is back to match the vehicle dynamic performance camera features. In the traditional hydraulic control system, to improve the features to be transformed mechanical structure of the chassis, it is difficult to implement.
Fourth, improve the steering stability.
Through to the car at high speed oversteering method to test stability characteristics of car. By using this method, high speed (100 km/h) of a car's on the corner of the excessive force it roll, in a short time since the return is in the process, the adoption of microcomputer control, makes the motor has higher stability and the driver feel more comfortable.
5, provide flexible steering.
Electric power steering system of the steering force from the motor. Through the software programming and hardware control, available to cover the entire speed variable steering force. Variable power shift depending on the size of the steering torque and speed. Whether parking, low speed or high speed, it can provide reliable, controllable good sense, and easier to yard operation.
For traditional hydraulic system, variable steering torque is very difficult to achieve and the cost is very high, in order to get the variable steering torque, must add an additional controller and other hardware. But in the electric power steering system, variable steering torque are usually written to the control module, can be obtained through the rewrite of the software, and the required fee is very small.
Six, adopting "green energy", to meet the requirements of modern cars.
Electric power steering system application "of" the cleanest power as an energy source, completely banned the hydraulic equipment, there is no leakage of liquid oil in the hydraulic power steering system problems, can say the system is complied with the era of "green" trend. The system because it has no hydraulic oil, no hoses, pumps and seals, avoid the pollution. Tubing and hydraulic steering system use polymer recycling, not easy to damage to the environment.
Seven, system structure is simple, takes up the space is little, convenient layout, superior performance.
Because the system has a good modular design, so don't need to redesign a different system, testing, processing, etc., not only save the cost, also for the design of different system offers great flexibility, and easier to assembly production line. Because there is no oil pump, tubing, and the pulley on the engine, allows engineers to design the system have more leeway, and the system control module, can design together and gear rack or separate design, very high space utilization ratio of engine parts. Saves the system installed on the engine belt pulley and the oil pump, set aside the space can be used to install other parts. Many consumers when buying a car is very concerned about the maintenance of vehicles. Cars with electric power steering system without oil pump, no hose connection, can reduce many worries. In fact, the traditional hydraulic steering system, hydraulic pressure oil pump and hose accidents accounted for 53% of the entire system failure, such as hose leakage and oil pump oil leak.
Eight, assembly production line.
Hydraulic system of electric power steering system has no need of pump, tubing, flow control valves, storage tanks and other components, the number of parts is greatly reduced, reducing the workload of assembly, save the assembly time, improve the assembly efficiency.
Electric power steering system since the mid - 1980 - s since the early put forward, as the development direction of automobile steering system, will replace the existing mechanical steering system, hydraulic power steering system and electric control hydraulic steering system.
Working principle of electric power steering system are as follows: first, the torque sensor to measure the pilot control torque on the steering wheel, the speed sensor to measure the current driving speed of vehicles, the then pass these two signal to ECU; ECU according to the built-in control strategy, calculates the ideal goal of steering torque, instruction for motor into current; Then, motor power torque by the retarding mechanism of amplification effect on the mechanical steering system, and the driver's manipulation of the moment overcomes the steering resistance moment together, realize the steering of the vehicle.
Edit this section of the key technologies of electric power steering system key technology mainly includes two aspects of hardware and software.
Mainly related to sensor, motor and ECU hardware technology. Sensor is the source of the whole system, and its accuracy and reliability is very important. Motor is the actuator of the system, its performance is good or bad determines the performance of the system. ECU is the operation center of the whole system, so the performance and reliability of the ECU is crucial.
Software technology mainly includes the control strategy and fault diagnosis and protection of two parts. Motor control strategy is used to determine the current goals and track the current, make the motor output corresponding torque. Fault diagnosis and protection procedures used for the operation of the monitoring system, and alarm when necessary and some protection measures for its implementation.
The working process of the electric power steering system (EPS) as a substitute for traditional hydraulic system products has entered into automobile manufacturing field. In contrast to the previous forecast, EPS is not only suitable for small cars, and some medium-sized cars are suitable for 12 v electric system installation. EPS system contains the following components: the torque sensor, the detection of steering wheel movement and the movement of vehicle; Electronic control unit, according to the torque sensor for signal of the size of the computing power; Electronic control unit (ECU) for motors, according to the torque output values formation; Produced by a reduction gear, and improve the motor power, and transmits it to the steering gear.
Other vehicle system control algorithm input information is provided by the car CAN bus (for example, the steering Angle and vehicle speed, etc.). Motor driver also need other information, such as motor rotor position sensor (motor) and current (current sensor. Motor is controlled by four mosfets. Large with micro controller is not direct driving MOSFET gate capacitance, so need to using interfaces in the form of driver IC. For security reasons, the complete machine control system monitoring must be carried out. The motor control system integration on the PCB, usually contains a relay, the relay can be used as the main switch, in the case of a detected fault, disconnect the electrical and electronic control unit.
Micro control unit (mu C) must be EPS control system with dc motor. Micro control unit according to the steering wheel torque sensor with the required torque information, forming a current control loop. In order to improve the safety level of system, the micro control unit shall have a board oscillator, so even in the case of external oscillator failure, can guarantee that the performance of the micro control unit, at the same time should also have on watchdog. Of infineon XC886 integrat