Study On Heat-flow Coupling And Heat Transfer System Of Hydrodynamic Retarder Of Heavy Vehicle

With the development of high-speed and heavy-duty of vehicle in recent years, thehigher requirement of vehicle’s braking performance is needed. For longtime frequentbraking of the heavy vehicle, the conventional service braking can not meet the needs anymore. A kind of auxiliary braking system is needed in this context. The hydrodynamicretarder is widely used in this field because of its advantages, such as smooth braking, strongbraking capacity in high speed, small volume and low noise. The hydrodynamic retarder actson transmission system in order to alleviate the load of braking system and make the vehicledecelerate uniformly, so it can improve reliability and security of the braking system.Through decreasing the number of braking while the vehicle is in motion, the hydrodynamicretarder is able to extend the life of brake and tires. From this, it shows that thehydrodynamic retarder is more economical. Through decreasing frequently starting andbraking, the vehicle with hydrodynamic retarder will make passengers feel more comfortable.The oil temperature will increase continually in the working process of hydrodynamicretarder. If cooling system does not have good heat dissipation effect and the heat can not bereleased in time, it may result in deterioration of working oil, damage of some machineryparts, failure of sealing element, oil leakage and so on. All these reasons will result in thedecline of braking performance of the hydrodynamic retarder and lead to the decline ofreliability of service brake.This thesis is supported by “Study on automatic transmission technology of heavyvehicle and special vehicle (7-2010-008)” of Hangzhou advance gearbox group co., LTD.The thesis aims at the flow and heat transfer characteristics of working chamber of the hydrodynamic retarder and the plate-fin heat exchanger. The main contents are listed asfollows.1. Study on heat-flow coupling of hydrodynamic retarderR295closed-type hydrodynamic retarder and D438open-type hydrodynamic retarderare taken as the study objects and based on numerical simulation theory of heat-flowcoupling, the numerical calculation on flow and heat transfer of two-type hydrodynamicretarders are carried out in the condition of different rotating speeds and differentliquid-filled ratios. Through analyzing and studying on temperature field and flow field inthe working chamber of hydrodynamic retarders when the rotating speed of rotor is1500rpm, the internal flow rule and temperature field of hydrodynamic retarders are known in thecondition of all filling liquid and partial filling liquid. Through analyzing on the cause ofcharacteristics of flow and temperature field, the working principle of hydrodynamicretarders will be understood more roundly and deeply. It is good for optimization design ofhydrodynamic retarder. And then, in condition of ignoring the influence of the temperatureon the physical properties of working oil, the braking moment of R295closed-type andD438open-type hydrodynamic retarders are calculated in the condition of different rotatingspeed and all filling liquid. Through simulating and analyzing, the relation between thebraking moment and rotating speed is gotten. On this basis, based on the same brakingmoment, the open-type hydrodynamic retarder of effective diameter481mm and theclosed-type hydrodynamic retarder of effective diameter295mm in the conditions ofdifferent rotating speed and all filling liquid, same rotating speed and different filling ratesare separately calculated. Through simulating, the relation curves between the brakingmoment and rotating speed, and the relation curves between the braking moment and fillingrates are gotten. Through comparing and analyzing on the open-type and closed-typehydrodynamic retarders, the advantages and disadvantages of two-type hydrodynamicretarders are understood deeply. Through the above analysis, it provides some theoreticalbasis and prerequisites for the selection of hydrodynamic retarder of heavy vehicle. At thesame time, it also provides prerequisites for selecting the heat exchanger. 2. Simulation analysis of heat exchanger for hydrodynamic retarderThrough comparing the temperature of the open-type and closed-type hydrodynamicretarders, we know that the temperature of closed-type hydrodynamic retarder is higher.Therefore, this part focuses on selecting heat exchanger for R295closed-type hydrodynamicretarder. First of all, the cooling capacity of plate-fin heat exchanger for R295closed-typehydrodynamic retarder is analyzed. Two different fin types of straight fin and serrated fin arechosen as the core of plate-fin heat exchanger. The heat exchanger models of two-type finsare simplified, and cycle models are chosen as calculation region because of limit calculationcondition. After boundary conditions and relevant parameters are set, the plate-fin heatexchangers of two-type fins are simulated. The results show that the heat dissipation effect ofserrated fin is better than straight fin. The plate-fin heat exchangers of straight fin can notmeet heat dissipation of R295closed-type hydrodynamic retarder requirements, but serratedfin can meet its standards. Through checking the pressure of the plate-fin heat exchangers ofserrated fin, it shows that the pressure is in a rational range and it is in line with therequirements. On this basis, the inlet velocity of working oil that is on the influence of thetemperature distribution is studied. With the increase of inlet velocity of working oil, themass flow of working oil increases at the same time and the rate of temperature declinesmore slowly along the flow direction.3. Study on the influence of working oil temperature on the braking performanceThe hydrodynamic drive oil in hydrodynamic retarder has different physical propertiesin different temperatures, so it will influence on the braking performance. This part studieson the influence of working oil temperature on the braking performance of hydrodynamicretarders. First, the changing rules of temperature of the working oil with the variation ofworking conditions and filling rates in hydrodynamic retarder are studied. With the increaseof the rotating speed, the temperature of working oil in working chamber increases. With theincrease of the filling rates in the same rotating speed, the temperature of working oilincreases. On this basis, in condition of considering the influence of the temperature on thephysical properties of working oil, the braking characteristics of hydrodynamic retarderswith different working conditions and different filling rates are studied. With the increase ofthe rotating speed, the braking moment and the oil temperature both increase. Compared with ignoring the influence of the oil temperature, the braking performance gets worse. Withthe increase of the filling rates in the same rotating speed, the braking moment and thetemperature of working oil both increase. Compared with ignoring the influence of the oiltemperature, the braking performance still gets worse.4. Thermal balance test research of hydrodynamic retarderThermal balance test of open-type hydrodynamic retarder with the effective diameter of438mm is studied. Through bench test, the temperatures of working oil in the oil inlet and oiloutlet of open-type hydrodynamic retarder in the condition of different rotating speeds andall filling liquid are gotten. Through comparing the experimental results and the CFDsimulation results, it is found out that they are agreed approximately with each other. Fromthis, the accuracy and reliability of computational method of flow and heat transfer isvalidated.