Automobile electric power steering system

1. Overview of automobile electric power steering system

Power Steering System Electric (EPS) is a new power steering system, which has been developed as a new technology, which has been used as a new technology, which has a good development prospect. The basic working principle of the system is:the torque sensor and speed sensor are applied to the steering wheel of the steering wheel torque and the vehicle current speed (back to normal when the microprocessor according to the built-in control strategy and algorithm, calculate the ideal power torque, then converted into the corresponding current, drive motor according to the current operation; the motor torque and the driving torque of the transmission to mechanical steering system, and the driver's steering torque, to overcome the steering resistance torque, realize the vehicle's final turn. EPS to make up for the shortcomings of HPS and EHPS, has the advantages of energy-saving, environmental protection, high efficiency, security and so on, is the future of power steering system of development direction. At present, the device on the front axle load in below 900 kg in small cars.

2. Characteristics of electric power steering system

With the development of automobile electronic technology, the requirements for automobile design and the level of control of the vehicle are becoming higher and higher, especially for the automobile energy saving and environmental protection characteristics of higher requirements. The traditional hydraulic power steering system (HPS) has become more and more obvious, which can not fully meet the needs of the times. The electric power steering system (EPS) will be the latest power electronic technology and high performance motor control technology applied to the vehicle steering system, can significantly improve the static and dynamic performance of the vehicle, and effectively improve the driver's portability and safety, but also more energy saving and environmental protection. For pure electric vehicles, the use of EPS is an inevitable choice, because it itself is not an internal combustion engine, power steering system power source only from the motor, so the power steering system of pure electric vehicles can only be EPS or EHPS, generally speaking, designers are tend to choose EPS. Therefore, the future of the steering system, electric power steering system will become the mainstream of the power steering system, the system for development and research into more and more car companies and research institutions focus. Compared with other power steering systems, the system has outstanding advantages:(1) more energy saving and environmental protection. EPS because there is no hydraulic device, is a typical "on-demand" (on-demand) system, that is, only when the steering system to work, while the vehicle is not running or straight running without the energy, so that will consume less energy. Therefore, compared with the hydraulic power system, in a variety of driving conditions can be energy saving 80% to 90%. In the case of non steering, vehicle fuel consumption with EPS will be reduced by 2.5%; in the use of steering, it will be reduced by 5.5%. At the same time, due to the low temperature at 40, EPS can also work well, and the traditional hydraulic system to wait until the hydraulic oil preheating to work properly, because the EPS does not start with such a preheating process, so it saves energy. At the same time, there is no leakage of liquid oil in the traditional hydraulic power steering system, which also avoids the environmental pollution, and complies with the requirements of environmental protection. (2) the effect is better. EPS can be aimed at various operating conditions of the vehicle, through the optimization of the power curve, make the power more accurate, more ideal power effect. In addition, damping control can be used to reduce the disturbance caused by the uneven road surface, and to protect the steering wheel when the vehicle is running at low speed, and to improve the steering stability of the vehicle at high speed. (3) the weight is greatly reduced. Compared with EPS, the structure of HPS is more simple, the number of parts is reduced greatly, so the weight is reduced greatly, and the arrangement is more convenient, and the noise is reduced. (4) security is better. Compared with HPS, when the EPS fails, the system can immediately cut off the power transmission of the motor and the transmission mechanism through the electromagnetic clutch, and quickly turn into the pure mechanical steering condition. In addition, due to the direct by the motor to provide power, so the EPS is independent of the vehicle's drive system, as long as the electric vehicle DC-DC does not occur, even when the vehicle does not start or other failures can provide help. (5) production and development cycle is shorter. EPS's previous research and development time is longer, but once the design is completed, it can be modified by the corresponding procedures, rapid implementation and specific models, and thus can greatly reduce the development time for different models. (6) improving the return characteristics of the steering system. At a certain speed, when the driver turns the steering wheel angle, the vehicle itself has the ability to return the vehicle to the direction of the vehicle, which is determined by the inherent structure of the vehicle. The EPS system can be used to control the normal process, and the software is used to adjust the design parameters to get the best performance of the vehicle. And in the traditional hydraulic control system, the vehicle design once completed, its back is the characteristics can not be changed, otherwise it is necessary to transform the chassis of the mechanical structure, it is difficult to achieve. (7) EPS efficiency is generally higher than HPS, the use of a wide range of vehicles, especially for electric vehicles. But for now, the domestic research is mainly based on the introduction of foreign technology. For EPS system, the key technology research, such as ECU, sensor, control technology, etc., compared with foreign advanced technology has a big gap.

3. Application development trend of electric power steering system

EPS application development, on the one hand, need to consider the future development trend of key components such as a variety of sensors, power supply, MCU, automotive power system, etc., on the other hand, need to consider the future development trend of the practical application system including the lateral acceleration and yaw rate and other factors. From the point of view of the development of key components:(1), the sensor is currently the direction of miniaturization, integration, greater work temperature range. Sensor is an important part of EPS, EPS sensor including torque sensor, vehicle speed sensor, angle sensor, etc., the main contact resistance shift sensor, non-contact photoelectric sensor and a new type of switched reluctance sensor. The early EPS torque sensor for the contact sensor, this sensor is easy to produce due to friction and wear. Non contact torque sensor, which uses magnetic, optical and sensing technology, effectively avoids this problem and is the trend of future application. With the improvement of people's safety, comfort and handling stability, the single function sensor can not meet the needs of a variety of performance, while the use of multiple sensors will inevitably lead to increased costs, while there are security risks,