| The continuous variability of maximum valve lift,opening duration and valve timing can be attained by using fully hydraulic variable valve system(FHVVS)in gasoline engine,which is one of the newest progress of variable valve timing technology development.The maximum valve lift and opening duration of FHVVS can be continuous variable on a wide range,thus can implement internal EGR,variable and effective compression ratio by the way valve closed early or late inlet valve shut to control the air intake.In a word,the fully variable hydraulic valve system is an effective means to realize the low energy consumption and low pollution of the engine,and thus has important theoretical significance and use value.A test bench to measure the valve movement characteristics of FHVVS was built up,in which the valve-seating characteristics,multi-cylinder engine uniformity and valve lift cyclic variations were especially measured.The main works and results are as follows:(1)The structure layout and working principle of FHVVS were introduced.The FHVVS is mainly composed of the inlet CAM,hydraulic lifter components,the shells,electronic control transmission parts and gear transmission parts and so on,these parts constitute the FHVVS valve drive mechanism,valve control mechanism and valve seating buffer mechanism.The intake valves are opened by hydraulic oil which is driven by the cam.The drain time of the system was control by a control valve mechanism.The valve seating-velocity is controlled by a valve seating buffer mechanism.Thus,FHVVS has characteristics of fast response speed,reliable operation and low cost.(2)Experimental prototype and motored experiment bench were introduced.Choose BJ486EQ gasoline engine as test prototype,FHVVS was installed on the cylinder cover,the width and length direction were not more than the original size of cylinder head,and maximum keep the generality and compactness of the whole structure.The motored experiment bench simulate the actual running state of valve-train,including hydraulic lubrication system and valve train system.The valve lift was measured with a laser displacement sensor.The motored experiment bench can real-time collecting CAM shaft Angle signals,hydraulic pressure signals,laser displacement signals,etc.(3)The valve seating process and characteristics of FHVVS system was discussed in this paper,especially the valve-seating velocity,the rebound height and impact noise of the intake valve with hydraulic piston cone-top throttling and side throttle hole of valve-seating buffer mechanism were analyzed.The test results show that the valve-seating velocity,the rebound height and impact noise can be significantly reduced in the valve-seating buffer mechanism with the hydraulic piston side throttle hole.The FHVVS can give steadily opening and seating.(4)The FHVVS is composed of two shells,applied in a four-cylinder engine.The characteristics of FHVVS is that the first cylinder and the second cylinder shared a control valve mechanism,which is installed in the front shell;the third cylinder and the forth cylinder shared a control valve mechanism,which is installed in the rear shell.Due to machining error,hydraulic energy loss,the valve lift for each cylinder is different.Thus mainly uneven valve lift for the FHVVS exist in the first/second cylinder and third/forth cylinder,in two cylinders of the share a shell,in two valves of the same cylinder.Therefore,each valve lift was measured on motored experiment bench carrying FHVVS,studying the valve lift uniformity of the multi-cylinder engine.(5)The valve lift cyclic variations for FHVVS was studied,analyzing the influence factors of cyclic variation,and did relevant test.Measuring the small valve lift(H=2 mm)of eight valves under different speed,calculating the average of eight valve lift,the cyclic variations of maximum valve lift and time-area value.And drawing distribution diagram of the valve lift curve and maximum valve lift,analyzing the law to improve the valve lift cyclic variations. |
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