Study On The Valve Variable Movement Characteristics Of Diesel Hydraulic Valve Mechanism

When the traditional vehicle engine is in working condition,the intake valve and exhaust valve only need to be opened once in a working cycle.However,with the continuous development and improvement of vehicle engine technology,in some cases,it is urgent for the engine to open the valve twice or even several times in a working cycle,and to realize the smooth switching between the single opening mode and the double opening(or multiple opening)mode with the change of engine operating conditions.This topic takes the hydraulic valve mechanism which is independently developed to match a six cylinder diesel engine as the research object,and studies the valve lift under different engine operating conditions.The main work are as follows:Firstly,the structure and working principle of the hydraulic valve mechanism are introduced.The key component of the hydraulic valve mechanism is the rotary valve which rotates synchronously with the camshaft.The closing time of the intake valve and the conversion between single opening and multiple opening of the intake and exhaust valves can be controlled by adjusting the oil drain time.It can make valve seat smoothly by controlling valve seat velocity through the valve seat buffer mechanism.Secondly,the reverse towing test bench is built and the valve lift of the engine at 1200 r/min is measured.By calculating the angle-area value of 40 working cycles,the maximum fluctuation rate of angle-area value is only 0.35%,which indicates that the hydraulic valve mechanism can run smoothly.By measuring the valve lift under different intake and drain phase angles,it is verified that the hydraulic valve mechanism can realize the continuous change of the maximum valve lift,opening duration and valve timing.Thirdly,based on the AMESim simulation software,a simulation model of the hydraulic valve mechanism is built.The hydraulic valve mechanism simulation model is divided into five parts:cam-hydraulic tappet module,hydraulic piston-valve module,low-pressure system module,rotary valve drain area control module,and piston throttle area control module.Through the simulation calculation of the intake and exhaust valve lift at 1200 r/min,and the comparison with the previous test results,the accuracy of the simulation model is verified.Fourthly,a new valve lift and cam profile are designed.Based on the relevant parameters of the original valve lift,the main lift of the intake and exhaust valves is redesigned,and on this basis,the secondary intake lift,the exhaust reflux lift and the compression braking lift are added innovatively.The minimum clearance between the valve and the piston is calculated,and the result shows that the valve and piston will not collide with the newly designed valve lift.Through the transmission relationship between the valve and the cam in the overhead camshaft,the cam lift is obtained by the reverse thrust of the valve lift,and the curvature radius of the cam is calculated.Fifthly,according to the newly designed valve lift,the valve lift under different engine conditions is simulated.In order to make the main lift of exhaust valve close before TDC in exhaust braking mode,the lift of exhaust valve under the action of different diameter orifices is simulated and calculated.According to the results,two parallel orifices with diameter of 1.8mm are selected as the most suitable orifices.At the same time,the variation trend of tappet chamber pressure,piston chamber pressure and valve acceleration at 1600 r/min is compared.It is found that the pressure fluctuation of piston chamber has a great influence on the valve acceleration,which makes the valve acceleration fluctuate periodically with the same frequency in the whole process.The seating velocity of intake and exhaust valves is calculated.The results show that the seating velocity of intake and exhaust valves is reasonable,and the hydraulic valve mechanism can make the valve seat smoothly.Finally,the valve lift under different working conditions is measured by using the reverse drag test bench.The results show that the hydraulic valve mechanism can realize single opening and multiple opening of the valve,and the opening lift under different working conditions meets the design goal.