Based on the self-developed variable-mode valve actuation system,a combined simulation of the valve actuation system and the engine used was carried out to study their coupling operation characteristics,which pro-vides a theoretical proof for vehicle application.The results show that there is a strong coupling relationship be-tween the in-cylinder pressure and the valve operation,especially in the exhaust valve operation stage near top dead center(TDC)and below the engine speed of 2 300 r/min.The higher the engine speed is,the greater the valve dynamic lift loses,and the higher the maximum cylinder pressure is.While their change degree is gradually re-duced at engine speed over 2 300 r/min.Adding a transitional lift on the exhaust brake cam after TDC can eliminate the exhaust valve recoil,and further improve contradiction relationship between the braking power and the maxi-mum in-cylinder pressure.Compared with the ideal four-stroke brake,braking power of the two-stroke brake is ob-viously increased,and the maximum in-cylinder pressure is obviously reduced.The actual two-stroke braking power is increased by 35.94％,45.61％and 27.54％,and the maximum in-cylinder pressure decreased by 45.42％,27.20％and 7.35％at 1 600,1 900 and 2 400 r/min,respectively.
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