【作者】 董颖；

【导师】 何仁； 罗福强；

【作者基本信息】 江苏大学 ， 车辆工程， 2007， 博士

【摘要】 利用发动机对车辆进行制动,得到的制动功率稳定,长时间工作时不受温度变化的影响,并且可以消除发动机过冷,在一定程度上减轻汽车的制动系统发热、制动效率降低及汽车跑偏,因此在汽车的制动过程中得到广泛的应用。国内对发动机的制动能力利用水平多年来一直停留在发动机排气辅助制动(排气缓速器)的应用水平,制动功率较小,制动效果较差,不能满足大部分情况下的辅助制动要求。近年来国外出现了通过改变发动机配气正时增加制动功率的发动机制动技术,使发动机的制动功率增大,可以达到甚至超过发动机的输出功率,并且可以实现发动机制动功率的分级输出。针对国内在对发动机的制动能力利用开发方面缺乏成熟的理论指导,本文通过对发动机的制动工作过程以及制动能力的深层次利用进行研究,为开发具有自主知识产权并且性能优良的发动机缓速器提供技术指导和理论支持。首先介绍了现有的利用发动机进行制动的技术,简要分析了各种发动机制动技术的制动能力与其制动工作过程的关系,在此基础上通过对发动机制动工作过程的研究,分析了在每个发动机冲程中增加制动功率的方法以及对整个工作过程的影响,提出了几种增加发动机制动功率的方法。结合目前发动机配气技术的最新研究成果,提出实现发动机最大制动能力的理想发动机制动工作过程,并给出了发动机制动能力利用系数的概念,以评价不同发动机制动方式对发动机最大制动能力的利用水平。其次建立了发动机拖动、发动机排气缓速器、发动机减压缓速器、发动机泄漏缓速器以及发动机泄漏缓速器与发动机排气缓速器联合工作时的数学模型,通过数值计算的方法模拟分析了结构参数和运行参数的变化对各种发动机缓速器工作性能的影响,并通过实验的方法对数学模型进行了验证,实验结果与模拟计算结果比较吻合,验证了数学模型的准确性,计算方法和结论可用于发动机缓速器的结构设计和性能研究。利用高次多项式函数对发动机减压缓速器的减压凸轮进行了设计,设计结果表明,通过合理选择各项参数,在基本段包角很小的情况下用高次多项式函数进行减压凸轮的设计完全可以满足配气机构以及减压缓速器的性能要求。最后分析了发动机缓速器工作时对汽车制动稳定性的影响,提出调整主制动系统的制动力分配系数可以提高发动机缓速器与主制动系统联合工作时的制动稳定性。在发动机制动功率较大而且可以分级输出的情况下研究了汽车的下坡能力,结果表明,单独使用发动机减压缓速器,可以使汽车在各种坡道上以稳定的车速行驶。利用模糊控制的方法实现了发动机减压缓速器的自动控制,模拟计算结果表明模糊控制系统能够对发动机减压缓速器进行自动控制,并且制动过程比较柔和,具有工程实用价值。更多还原

【Abstract】 Engine is widely used as an auxiliary brake system in automobile deceleration process, at this time it is working as a retarder, it can provide a steady braking power and it’s working temperature will keep constant for a very long time. Engine retarder makes the engine temperature not too lower than the engine’s working temperature, and the braking power of engine retarder is distributed by differential, so the safety performance is enhanced. In china, the research level of engine retarder is still on the engine brake and the exhaust brake, the braking power is small and it can not fit the most of brake requirement. Recently, there is another engine retarder technology abroad, it changes the valve timing of the engine dragging process, which makes the braking power of engine retarder closely to the rated output, or even bigger than it. Furthermore, it can give the different braking power at the same engine speed. As there is lack of mature theory about the development of the engine’s retard ability, this paper investigates the working process and the braking power development of engine retarder, gives a support in both theory and technology to develop high performance engine retarder.Firstly, the existing engine retarder technology is introduced; the relationship between the braking power and the working process in different engine retarder type is briefly analyzed. Based on above analysis, by the working process research when engine working as a retarder, the method to increase the braking power in every engine stroke and the effect of this method to the whole working process are analyzed, some methods to increase the engine braking power are concluded. Combined with the latest results of the variable valve actuation, a brand new ideal working process of engine retarder to get the largest braking power of the engine is put forward. A new concept of "engine braking power utilizing coefficient" to evaluate the utilizing level of the different engine retarder types to the largest braking power of the engine is put forward.Secondly, the mathematical model of the engine brake, engine exhaust brake, compression release engine retarder, engine bleed retarder, engine bleed retarder compound with the engine exhaust brake are set up. Through the mathematical calculation methods the performances of every kind engine retarder with the different structure parameters and different running parameters are simulated. The computer simulation results are fit with the experiments results. The computation methods and the results can be used to design the structure and analyze the performance of the engine retarder.The cam profile of the compression release engine retarder is designed by high-order polynomial functions. The calculation results show that, by properly choosing the parameters, the high-order polynomial is fit for the decompression cam profile, even the angles of basic segment are small. The performance of the decompression cam meets the requirement of the valve train and the compression release engine retarder.Finally, the vehicle braking stability is analyzed when engine retarder is working, a method that by adding the braking forces distribution ratio between the front and rear brake to improve the braking stability of vehicle is put forward when the engine retarder is co-working with the main brake system. The ability of vehicle going downhill is analyzed when engine retarder can offer a classification and big braking power. It shows that with the compression release engine retarder, vehicles can run at a steady economical speed on all slopes. An auto control of compression release engine retarder is designed by fuzzy control. The simulation shows that the designed control system can make the automobile run at a relatively steady speed, and during the process, the acceleration varies slightly, the designed control system is suitable for engineering practice.更多还原