Research On Hydrodynamic Retarder And Its Control System Of Heavy Truck

In order to guarantee the running safety, the heavy vehicles are equipped with auxiliarybrakes besides of service brakes. The two most common auxiliary brakes are hydrodynamicretarder and eddy current retarder. Compared with eddy current retarders, the hydrodynamicretarders have a high braking efficiency per unit mass and without thermal fade, sohydrodynamic retarders are commonly adopted as auxiliary brakes of heavy vehicles inforeign countries. However, applications of auxiliary brakes in domestic are inclined to eddycurrent retarders because of product price and related policies, the research on hydrodynamicretarders fall behind obviously as a result. With the implementation of related laws andstandards of auxiliary brakes of heavy vehicles in China, overseas famous manufacturers forhydrodynamic retarders race to control domestic market of auxiliary brakes of heavyvehicles. Therefore, it is necessary to make systematic study on hydrodynamic retarder indepth and develop hydrodynamic retarder products with China’s independent intellectualproperty. In this thesis, the systematic study of hydrodynamic retarders was carried out interms of the structure, hydraulic control system, performance prediction method as well asdownhill-retarding performance. The main work and conclusions are listed as follows:1. Structure Design and Analysis of Hydrodynamic RetarderConsidered the power driveline structure of heavy trucks and own characteristics ofhydrodynamic retarders fully, the design requirement of hydrodynamic retarder wasdetermined according to force equilibrium equations during downhill-running and stipulationof downhill-retarding performance in international and national standards, that is the brakingtorque has to be more than772N.m when the rotor speed equals to1064r/min. Analyzed theadvantages and disadvantages of open-type and closed-type hydrodynamic retarder in detail,an open-type hydrodynamic retarder was designed. The torus diameter of rotor and stator are358mm and360mm respectively.2. Hydraulic Control System Design and Analysis of Hydrodynamic RetarderThe characteristics of hydraulic control system of VOITH, ZF and ALLISON hydrodynamic retarder were analyzed in detail, on the basis, a hydraulic control systemwhich is suited to the open-type hydrodynamic retarder was designed according to controlrequirements. The control system can accomplish oil-charge and oil-discharge rapidly, andadjust charging ratio of working chamber continuously in line with retarding demands.Working principle of hydraulic control system was illustrated, and pressure flowcharacteristics, flow continuity equation and spool dynamic equilibrium equations of valveswere analyzed minutely.3. Performance Prediction of Hydrodynamic RetarderThe performance prediction process of hydrodynamic retarder was given, the channelmodel and mesh model were established, the control equations which is used to describe thegas-liquid two-phase flow inside hydrodynamic retarder were determined and the boundaryconditions and fluid properties were appointed. On the base, the control equations werediscretized by finite volume method and the discrete equations were solved by SIMPLEalgorithm.The velocity distribution that from CFD calculation was solved by Eulerian equation,then the braking torque under different rotor speeds and charging ratios were obtained. Theresults show that the braking torque of hydrodynamic retarder is a quadratic function of rotorspeed and a linear function of charging ratio. At last, the mathematical expression thatdescribes how the braking torque response to rotor speed and charging ratio’s variation wasobtained by the least square surface fitting method.The outlet pressure distribution that from CFD calculation was solved by area-weightedaverage algorithm, then the outlet pressure values under different rotor speeds and chargingratios were obtained. The results show that the outlet pressure of hydrodynamic retarder is aquadratic function of rotor speed and a linear function of charging ratio. At last, themathematical expression that describes how the outlet pressure response to rotor speed andcharging ratio’s variation was obtained by the least square surface fitting method.4. Downhill-retarding Performance Calculation and Analysis of HydrodynamicRetarderThe hydromechatronics simulation model of downhill-retarding performance of hydrodynamic retarder was established, and the downhill-retarding performance under fixedslope and variable slope was calculated. The retarding work process was analyzed in detailand the influence of gears and set speeds on retarding performance was compared. Theresults show that, when gear is fixed, the higher the set speed is, the shorter the time forvehicles to stable on the set speed is, when the set speed remains constant, the higher thegear is, the longer the time for vehicles to stable on the set speed is. The downhill-retardingperformance of hydrodynamic retarder designed was evaluated by such three indexes asmaximum dynamic difference, speed overshoot and displacement coefficient under stablespeed. The results shows that the hydrodynamic retarder designed has a gooddownhill-retarding performance.