| The brake performance of automobiles is critical to the people's driving safety. The third auxiliary braking system is often applied because the braking performance of a vehicle is more important especially when driving downhill in mountainous and hilly areas. Hydrodynamic retarder is widely used in this field because of its unique advantage and superior performance.The hydrodynamic retarder is not a driving component. Instead, it is an auxiliary equipment working under the brake operating process of hydrodynamic coupling. An automobile equipped with a hydrodynamic retarder is bound to have a greatly improved braking performance, a reduced failure rate, and lower maintenance and operating costs. The presence of hydrodynamic retarders in automobiles satisfies the expectation of the safety, comfort, and efficiency of automobiles.The hydrodynamic retarder, like the engine and transmission, will become an indispensable part of vehicles in the future, due to the rapid growth of the automobile industry in China.The development and application of hydrodynamic retarders will benefit China environmentally, economically, and socially.A hydrodynamic retarder mainly consists of a working wheel, tank, cooling system, and control system. When fluid is pumped into the working chamber, the rotor blade, along with the working fluid, constantly rotates by means of the working medium. The high-speed liquid impacts the stator blade, causing hydraulic losses, and thus resulting in braking torque. The size of the braking torque directly affects the capacity of vehicle deceleration. Eight different models of structural parameters of the hydrodynamic retarder are developed in this thesis. In order to determine the optimal model for a hydrodynamic retarder, computational fluid dynamics (CFD) is applied to optimize the structural parameters, and thus produce maximum torque size. On that basis, the dynamic fluid-pumping process of hydrodynamic retarder is analyzed. The summary of main research mainly in the following two aspects: 1. Optimization on different structural parameters of hydrodynamic retardersThe three-dimensional models of hydrodynamic retarders is established based on different parameters, which include cavity shape, number of blades, blade tilting angle, and fluid inlet and outlet.Under different rotating speeds and with the fluid completely filled, obtain numerical results of the entire working process for each hydrodynamic retarder model, and then analyze different simulation results on velocity and pressure fields. Curves for models of hydrodynamic retarders under different rotation rates are drawn. Based on calculation and simulation results, the structural parameters of an optimal hydrodynamic retarder are as follows: elliptic cavity shape, 35 stator blades,37 rotor blades, and 45°blade tilt angle.2. Simulation analysis of the dynamic characteristics of hydrodynamic retarderThe dynamical liquid-pumping process of hydrodynamic retarder is simulated under various unstable conditions. Then analyze the relationship between the liquid filling-rate,the pressure,and the velocity of liquid inlet and outlet. Then determine the amount of liquid to be filled per unit time under a variety of assumptions. Finally, by using time as x-coordinate, torque size as y-coordinate,and liquid filling-rate as intermediate variable, draw different curves and analyze the dynamical characteristics of hydrodynamic retarder under unstable conditions. According to calculation and simulation results,as the liquid filling-rate increases, time increases gradually. The process is fairly fast in the beginning, and then becomes slower as it continues. The dynamic response time of the entire procedure takes about 1.83seconds.
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