| Based on a certain type of heavy-duty diesel engine,a fully hydraulic variable valve system(FHVVS)suitable for bottom-mounted camshaft diesel engine is introduced in this paper.FHVVS can achieve continuous variations in maximum valve lift,valve opening duration and the timing of valve closing.FHVVS adopts the composite transmission form of mechanical-hydraulic,and adopts hydraulic plunger control mechanism to change the amount of discharged oil,FHVVS is simple in structure,reliable in operation and low in cost.The research and work on the FHVVS system based on a certain type of heavy-duty diesel engine is as follows:(1)Based on the guiding principle of good versatility,reliable structure,small overall size and easy processing and installation,the overall layout idea of the fully hydraulic variable valve system of a certain type of heavy-duty diesel engine(bottommounted camshaft)was determined,and the overall layout scheme was completed.The design of the case,hydraulic plunger and control mechanism,hydraulic piston,accumulator,inlet check valve and other components were completed;the functions,structure and working principle of each component were introduced.(2)The complete hydraulic and dynamic simulation model of the FHVVS based on a certain type of heavy duty diesel engine was established by AMESim software.The model is divided into control system,cam driving system,hydraulic piston and valve system and hydraulic pipeline transmission system.The model is used to simulate and verify the function of the FHVVS.The predicted intake valve motion and pressure fluctuation under different engine speeds and different DC motor angles were provided by the simulation,which also provided key parameters and reference values for the redesign of the FHVVS.According to the pressure fluctuation of the high-pressure system obtained by simulation,the force and deformation of the key component case were simulated and analyzed.(3)The processing and assembly work of the FHVVS prototype was completed;the motored test bench was built,and it was driven by the motor directly towing the camshaft to operate the FHVVS,the hydraulic pumping station lubrication system was used to provide the hydraulic oil required for the FHVVS and the lubricating oil required for the diesel engine.A test data acquisition system was built,and the laser displacement sensor was used to collect the valve lift displacement signal,CDM signals and TDC signals were collected to assist in processing the valve lift displacement signal.(4)The intake valve motion measurement test of FHVVS for a certain type of heavy-duty diesel engine was completed,and the valve lift of the engine under different DC motor angles and different engine speeds was measured.The test results show that the valve lift of the FHVVS,the valve opening duration and the valve timing are continuously variable within a certain range,and the function of the FHVVS is initially verified.(5)The simulation model was calibrated and verified based on the results of the experimental measurements.The motion characteristics of the FHVVS are studied by AMESim simulation software.The AMESim model is used to simulate the hydraulic fluctuations of the plunger chamber and the hydraulic piston chamber under different engine speeds and different DC motor angles.The effects of engine speed and DC motor angle on the amplitude and period of hydraulic fluctuation are analyzed.(6)The valve opening process is analyzed according to the plunger chamber pressure and the piston chamber pressure,and the valve opening process is divided into four stages:valve opening section,valve rising section,valve falling section and valve seating section;FHVVS is a mechanical-hydraulic composite transmission system.The higher the engine speed,the greater the internal hydraulic fluctuations.Therefore,the performance of the FHVVS engine at high speed is analyzed.The results show that the FHVVS works normally at the highest engine speed,and there is no phenomenon such as valve lift distortion. |
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