| With the increased pace of life, people's concept of time is also growing, making high-speed become a needs. Besides, as the rapid development of China's automobile industry, the continuing improvement of automotive technology, the appearance of more and more highway and improvement of road condition, the need of high-speed gradually be met. However, following with the high-speed is a sharp increasing in the rate of traffic accidents. Through investigation and analysis of traffic accidents, handling and stability problems induce an important factor in traffic accidents. And hence the handling and stability problem acquire high concern in high-speed security. Especially with the development trend of higher speed of vehicles, the more and more intensive traffic, non-professional driver, vehicle handling and stability design is particularly important.To be one of the systems controlled directly by the driver to ensure the behavior of the automotive, the steering system plays a vital role in handling and stability. Vehicle power steering system is a key component of the car. It has a direct relationship with vehicle safety and comfort, and the quality of its performance directly affects people's evaluation to cars. Hydraulic power steering system is the first to be introduced in the power steering system. Undergoing 60 years'development, hydraulic power steering system technology becomes relatively more mature than other power steering system. And it has its own advantages: respond sensitively, manipulate lightly, track with high precision, be able to absorb road shock. The other a more important advantage is that even if the power system goes into failure, the mechanical steering system comes to work as emergency steering system.In steering design process, there always be existing a contradiction in"light"and"spirit". And it's a focus to coordinate the relationship between the two. In the hydraulic power steering system, the coordination of these two main characteristics embodied in the steering pump and valve characteristics. The steering pump characteristic reflects the relationship the pump flux changes with the engine speed. This characteristic shows the power system assist torque in different rotating speed. When the car is idling, it needs maximum assist torque due to tire encounter the maximum resistance torque. With the enhancement of engine speed, pump flow decreases; when the is running at high speed, taking the needs of the driver road feel into account, the flow the pump can provide is minimal, and the flow stay at the nearly same flow when the speed increasing. Steering valve characteristic refers to the relationship the assist torque acting with the steering torque the driver throw to steering wheel. This feature reflects the assist torque the steering system needs in the different steering wheel torque in order to meet the light requirements and road feel.The valve's pre-open space, short circumferential length of the incision, axial effective length, short axial length of the incision, the valve mandrel radius and the number of groove is the main factors that affect the characteristics of the rotary valve. These parameters mainly affect the assisting character in the common area and the maximum angle area, but have little effect on non-sensitive areas. In addition, the affects on the characteristics of the valve will increase with the increasing of the pump flow.Focus of this paper is to study the hydraulic power steering system on vehicle handling and stability, so, this paper established the steering system dynamic model based on Simulink in the third chapter and the vehicle model based Carsim. As the steering system in Carsim is relatively simple, this article will shield the steering system and join the model based on Simulink established in the third chapter. And finally complete the vehicle model. In order to ensure the accuracy of the model, this paper making use of steady-state circular test and snake test of national standards in the automotive industry, compare the test data and the corresponding dynamic tests data in Carsim. The results show that the model'validity. Through the preparatory work done in the previous three chapters, the paper has built an accurate vehicle model and discussed the influence the structural parameters of the rotary valve doing to the valve characteristics. In the fifth chapter, this paper carried out dynamic tests to the vehicle model with different valve characteristics first. And then according to Pro.K.H.Guo's assessment ideas based on total variance analysis, analyze the influence of the structural parameters of the rotary valve doing to vehicle handling and stability. |
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