The Experimental Research On Hydraulic Power Steering System Of Car And The Analysis Of On-center Handling Performance

In the driving processes, steering is a basic motion of the car. The driver changes the car's driving direction by controlling the steering wheel. Steering system is a necessary part in modern cars which consists of several transmission components and connects to the chassis, suspension and wheels. Toward the whole vehicle's dynamics system,the steering system is the input part of the car's turning motion and it's characteristic has a direct influence to the automotive handling stability and driving security.With the development of the freeway and the increasing of the vehicle's speed, the turning road feel of the high-speed driving car gets more and more attentions.Every driver wants to receive a safty and comfortable feel from the car, especially in high-speed conditiones, so the researches of on-center handling performance become very important both in theory and reality."the strategy of car adapting driver"also incarnates the vehicle's design idea of active security.As we know,vehicle's handling stability depends on three elements that are driver, vehicle and road. Considering the physiologic, gender, age and so on, the driver is the most difficult part to change in the"driver-vehicle-road"closed-loop system,so"the strategy of car adapting driver"is the essential method to solve the vehicle's handling stability problem.The main works in this paper are as following:1. Have built a testrig for measuring the parameter characteristic of hydraulic power steering system and completed a lot of experimental research about the steering system's relational characteristic;2. On the basis of the steering system characteristic experiments, have built a precise vehicle steering system dynamic model in Adams/Car and completed some experimental verifications of the whole vehicle model;3. Analyzing the relationship between steering system's characteristic parameters and on-center handling performance of a car. This paper interprets how these factors affect the performance of on-center handling characteristic on the basis of the steering system dynamic model. At last it gives some useful advices about how to improve the performance of on-center handling of a car. These parameters consist of steering ratio, stiffness, dry friction, and hydraulic power characteristics. The main conclusions are as following:The detail of the research works and conclusions are as following:1. Surrounding the exploitation and the experimental researches of hydraulic power steering system testrig we have mostly carried out several works hereinafter:(1)Have introduced the main exploitation thoughts, designing blue print of the hydraulic power steering system testrig and have done some research works on the major functionits of the testrig;(2)Have introduced the three main subsystems composing the hydraulic power steering system testrig and dedigned hardware accessing mode which includes the constituent and installation of the actual measurement part; the disign of the supporting part, wheel vertical force loading system, wheel aligning torque loading system, wheel fixing device; measuring system of steering wheel's angle and torque, measuring system of wheel's angle and torque and measuring system of oil pressure in hydraulic power piston.(3)By the experimentations, we get the hydraulic power steering system's characteristics such as steering ratio, stiffness, dry friction, and hydraulic power characteristics, and prepare some reliable basic datas for modelings, analyses and researches.2. In Adams/Car built a hydraulic power steering system dynamics model, modified the steering system template of the Adams/Car and added the hydraulic power steering system characteristics that we got from the experimens into the template. After that carried out some simulations, such as slalom, constant turning and on-center handling, to validate the model. The results showed that the model we have built is correct.3. Have introduced the objective evaluation indices of the on-center handling performances and the meaning, calculation method of each index in detail.Have analysed the effects of the steering ratio, stiffness, dry friction, and hydraulic power characteristics to the whole vehicle on-center handling performances.The conclusions we have gotten are as following:(1)Steering ratio has a serious influence on on-center handling performances. It has a great influence in the steering sensitivity. With the steering ratio decreasing, the steering sensitivity is increasing. At the low speed, we can make steering ratio small in order to alleviate the drivers'burden. However, in high speed we should make it larger to alarm the drivers. If the hydraulic powering characteristic is constant, bigger the steering ratio is, littler the steering effort is. Therefore, we can better the road feel if we can make the steering ratio littler in high speed. So we can arrive at the conclusion that the steering ratio which is variable can improve both the steering sensitivity and the road feel. That is also to say that electric powering steering is in prospect in future.(2)The steering system's stiffness has a serious influence on on-center handling performances and affects the dynamic response characteristics and understeer characteristic of the vehicle's turning motion. Reducing the steering system's stiffness can increase automotive understeer characteristics, but might reduce automotive steering sensitivity at the same time, so the vehicle's turning motion becomes slowly and the steering wheel becomes slowness. Therefore, although the steering system's stiffness plays a very important part in the automotive understeer characteristic, but usually in the design process of vehicle we don't go in for such flexibility.(3)The dry friction of the steering system can influence on-center road feel in high speed severely. The dry friction effects the steering torque mostly, but can hardly does the lateral acceleration and the steering sensitivity. Reducing the dry friction can reduce the steering wheel's torque but the lateral acceleration and steering sensitivity don't change. In the design process of vehicle, the dry friction of the steering system should be reduced as well as possible to enhance the "Signal-to-Noise Ratio",on the other hand we can add a hydraulic retarder which has a relationship with the speed to reduce the transmission of the road impact.(4)The quality of hydraulic powering can have a serious compact on the on-center handling and stability .While the Hydraulic powering are working on, Steering effort will decrease obviously and road feel turns to be worse, but not does acceleration. The traditional hydraulic powering steering characteristic was constant to vehicle velocity. If we enlarge the hydraulic power to alleviate the driver's burden, the driver would lose the road feel in high speed. As long as we can utilize Hydraulic Electric Powering Steering (HEPS)or Electric Powering Steering (EPS), we could improve the quality of steering effort in high speed observably, for powering steering characteristic can be variable with the vehicle speed.