Research On Water Hydraulic Retarder System And Its Intelligent Control Strategy

Hydraulic retarder has the advantages of high braking torque, brake softly, low noise, small volume, light quality and so on. So its popularization in the field of domestic automobile auxiliary brake is imperative in the future. And water hydraulic retarder which takes the engine coolant as the working medium have gradually attracted attention of the industry. It shares the same medium with the engine cooling system. Compared with traditional oil retarder, water hydraulic retarder has more compact structure, lighter quality, higher braking torque, its cost of use and maintenance is also greatly reduced, and the car’s driving safety is higher.For the study of key technology about water hydraulic retarder, the emphasis is whether its braking performance meets the requirement. While the hardware and software design quality of electric control system will directly affect its braking performance. During the use of water hydraulic retarder, not only stable and reliable braking torque but also rapid response is required. But the braking torque and the filling ratio are not just a simple proportional relationship, so its control process becomes quite complicated. And the key of the research is how to choose effective control strategy of water hydraulic retarder in software design, so as to achieve good dynamic response and steady state properties. In view of the problem, a series of studies are carried out, and the key research contents and conclusions include the following aspects:(1) The advantages and disadvantages of different auxiliary braking are firstly compared. Then the structure, working principle, advantages and disadvantages of water hydraulic retarder are analyzed. Finally this paper introduces the overseas and domestic research status about water hydraulic retarder in detail, and also gives the theoretical and practical significance of the research project.(2) The basic theories related with hydraulic retarder are elaborated. Based on the relevant research results of existing hydraulic components, which include hydraulic torque converter, hydraulic coupling, etc. According to the function and structure characteristics of designed water hydraulic retarder, this paper establishes the similar mathematical model of water hydraulic retarder which meets the research requirement, and makes the conclusion that the braking torque is approximatively proportional to the filling ratio.(3) The characteristic of the retarder system model and the control requirements in two modes of vehicle downhill at a constant speed and the foot operate intelligently are analyzed in detail. Then the method of parameter self-tuning fuzzy control is applied in the electric control system of retarder, so the static and dynamic characteristics of the system are both ensured in the control process, and the specific structure of the controller are eventually designed.(4) In order to analyze the results of water hydraulic retarder control simulation later, the evaluation indicators of braking performance are firstly established. In the aspect of vehicle dynamics analysis, this paper eventually establishes the whole vehicle braking dynamic model and sub-models after analyzing the situation of vehicle’s downhill braking. For two-axle vehicles of rear wheel drive, this paper also studies the distribution of braking force between front and rear wheels after installing water hydraulic retarder on the vehicle to ensure the braking security.(5) In the module of Matlab/Simulink, the simulation model of the vehicle braking is established. And after inputting related structural parameters of a certain type of vehicle and water hydraulic retarder, the control system simulation analysis of water hydraulic retarder is carried out. The simulation curve of speed, braking deceleration, filling ratio and so on under different control strategies are obtained after simulation. The result of simulation shows the difference between the designed intelligent controller and the normal fuzzy controller. In the control of settled gradient constant speed downhill brake, the speed steady state error coming to plus or minus 0.05% can reduce about 67% of time, and the maximum overshoot volume can reduce about 1.3%, and the peak time can reduce about 50%. It is concluded that the system becomes more stable, and its response speed is faster. In the control of foot intelligent brake, at the initial brake speed of 80km/h, when it is an emergency brake, the brake time can reduce about 29%, and the brake distance can reduce about 40%. When it is a slow brake, the brake time can reduce about 24%, and the brake distance can reduce about 36%. As mentioned above, the good control performance of designed intelligent controller is verified.