【作者】 袁哲；

【导师】 马文星；

【作者基本信息】 吉林大学 ， 机械设计及理论， 2013， 博士

【摘要】 近些年来，运输的高速化和重型化对车辆的制动性能提出了更高的要求。传统的行车制动器已经不能满足长时间频繁制动的需要，重型车急需装备一种辅助制动系统。液力缓速器具备了制动平稳、高速制动能力强、体积小及噪声小等优点，因此在这一领域获得了广泛应用。液力缓速器通过作用于传动系统而减轻车辆制动系统的负荷，使车辆均匀减速，提高了车辆制动系统的可靠性和安全性。通过减少车辆行驶中的制动次数，延长了制动器和轮胎的使用寿命，体现出液力缓速器具有较高的经济性。通过减少频繁的启、制动，安装了液力缓速器的车辆可提高乘客的舒适性。但液力缓速器在工作过程中，油温会不断升高，如果冷却系统不能达到很好的散热效果，产生的热量不能被及时释放，就可能导致工作油变质、部分机件损坏、密封件失效漏油等，这些都会导致缓速器制动性能下降和行车制动器可靠性降低。本文以杭州前进齿轮箱集团股份有限公司“重型及特种车辆自动变速技术研究(7-2010-008)”为依托，针对液力缓速器工作腔内部及板翅式换热器内部的流体流动与换热特性进行了CFD数值计算和试验研究。主要研究内容有如下几方面：1.液力缓速器的热流耦合研究基于热流耦合的数值模拟理论，以R295型闭式液力缓速器与D438型开式液力缓速器作为研究对象，对其在不同转速和不同充液率工况进行了流动传热的数值计算。通过对转子转速为1500r/min，液力缓速器工作腔内温度场及流场分布趋势的分析、研究，了解了液力缓速器在全充液和部分充液工况下的内部流动规律与温度场情况。通过对工作腔内流动特性及温度场规律形成原因的深入分析，对液力缓速器的工作机理有了更加全面、透彻的了解，进而便于对液力缓速器进行优化设计。接着，在忽略温度对工作油物理性质影响的情况下，对R295型闭式液力缓速器与D438型开式液力缓速器，在不同转速且全充液工况下的制动转矩进行了数值计算，得到二者的制动转矩与转速关系曲线。在此基础上，以相同制动转矩为基点，对经过循环圆相似放大的481mm开式液力缓速器与循环圆直径仍为295mm的闭式液力缓速器在不同转速且全充液、相同转速且不同充液率的工况分别进行了数值计算，得到二者的制动转矩与转速、制动转矩与充液率关系曲线。通过开式与闭式液力缓速器的对比分析，进一步了解了两种类型液力缓速器各自的优点和不足，为重型车液力缓速器的选型提供了一定的理论依据，也为换热器的选型提供了前提条件。2.液力缓速器的换热器数值分析通过对开式与闭式液力缓速器温度对比，得知闭式液力缓速器的温度较高，因此重点介绍了为R295型闭式液力缓速器进行的换热器选型。首先，对为R295型闭式液力缓速器选择的板翅式换热器的冷却性能进行了分析。为板翅式换热器的芯体选择平直型和锯齿型两种不同的翅片类型，由于计算条件有限，对两种翅片类型的换热器模型进行了简化，选取周期模型作为计算区域。在进行边界条件与相关参数设置后，对两种不同翅片类型的板翅式换热器进行了CFD数值计算。数值计算结果表明，锯齿型翅片换热器的散热效果要好于平直型翅片换热器，平直型翅片的板翅式换热器不能满足R295型闭式液力缓速器对散热的需求，但锯齿型翅片则满足要求。通过对选择的锯齿型板翅式换热器的压降核算，证明其压降值在合理的范围内，符合使用要求。在此基础上，研究了锯齿型板翅式换热器的工作油进口速度对温度分布的影响，得知随着工作油进口速度的增加，工作油的质量流量也随之增加，沿流动方向的温度降低速度较慢。3.工作油温度对制动性能影响的研究由于不同温度下，液力缓速器内的液力传动油具有不同的物理性质，会对液力缓速器的制动性能造成一定影响。因此，对工作油温度对液力缓速器制动性能的影响进行了分析。首先对液力缓速器内工作油温度随工况及充液率的变化规律进行研究，得知随着转速的增加，工作腔内工作油温度升高；在相同转速下，随着充液率的增加，工作油的温度也随之升高。在此基础上，在考虑温度对工作油物理性质影响的条件下，研究了不同工况与不同充液率下液力缓速器的制动特性。通过分析，得知随着转速的增加，液力缓速器的制动转矩变大，油温升高，与忽略油温影响的情况相比较，制动性能变差；而在转速相同的情况下，随着充液率的增加，液力缓速器制动转矩值增大，工作油温度随之升高，与忽略油温影响的情况相比较，制动性能仍然变差。4.液力缓速器热平衡试验研究对循环圆直径为438mm的开式液力缓速器进行了热平衡试验研究。通过台架试验，测量得到在不同转速且全充液工况下的开式液力缓速器进油口与出油口处工作油的温度。将通过台架试验测量的液力缓速器出口油温与CFD数值计算所得结果进行对比，二者所得结果基本吻合，也由此证明了利用流动传热计算方法的正确性和可靠性。更多还原

【Abstract】 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.更多还原