全可变气门技术对二冲程缸内制动性能的影响

Influence of Fully Variable Valve Technology on Two-Stroke In-Cylinder Brake Performance

利用自主研制的全可变液压气门机构(FHVVS)开展由主制动和副制动组成的二冲程缸内制动技术的仿真研究.通过GT-Power搭建了6缸柴油机仿真计算模型,分析了排气制动升程开启时刻与最大升程对主制动性能的影响,讨论了排气门早关对副制动性能的影响,确定了配气凸轮和FHVVS的主要设计参数.通过气门运动规律试验台架,对研制的FHVVS气门升程进行了试验测量,结果表明:FHVVS实现了一个工作循环内进/排气门单次开启与两次开启之间的快速平稳转换.根据实测气门运动规律,对二冲程缸内制动性能进行了模拟,可知,与原机制动方式相比,二冲程制动大幅度提高了低转速工况的有效制动转矩T_(tqb),使转速为1100r/min时的有效制动转矩T_(tqb)提高了57.1%;二冲程制动明显降低了高转速工况的最大缸内压力,在转速为2100r/min时最大缸内压力降低了28.2%.

A two-stroke in-cylinder brake technology consisting of main brake and auxiliary brake was studied by using a self-developed fully hydraulic variable valve system(FHVVS).A simulation model of a six-cylinder diesel engine was established with GT-Power.The influence of exhaust brake lift opening timing and maximum lift on main brake performance was analyzed,and the influence of exhaust valve early closing on auxiliary brake performance was discussed.The main design parameters of valve cam and FHVVS were determined.The intake and exhaust valve lifts of the FHVVS were measured on a test bench.The results show that a fast and smooth switching between single and twice opening of the intake and exhaust valves in a working cycle can be realized with the FHVVS.The performance of two-stroke in-cylinder brake was simulated based on the measured valve lift curve.It is found that the two-stroke brake greatly improves the brake power at low speed,the brake torque is 57.1%higher than that of original in-cylinder brake at the speed of 1100r/min.Two-stroke brake significantly reduces the maximum in-cylinder pressure at high speed,and the maximum in-cylinder pressure is 28.2%lower than that of original brake at the speed of 2100r/min.