Abstract:Hydraulic fluctuation can directly affect the opening and closing characteristics of electrichydraulic type variable valve system and indirectly affect the status data of cylinder gas. The pressure fluctuation and the systematical evaluation parameters were establised based on the working process of electrohydraulic variable valve system for DK4A diesel engine, and the influence of oil pressure from 2.5 to 4.5 MPa on the pressure fluctuation in variable valve system of diesel engine was analyzed by the evaluation parameters. The results show that with the increasing of oil pressure, the characteristic parameters of pressure fluctuation phases(α1α8) are appeared in advance, and the peak pressure of p1 and p2 are increased. The pressure difference and the pressure mutation rate of pressure fluctuation range(β1,β2,β4)are increased, and the pressure mutation rate of range β5 is increased first with latter decreased change. The average value of pressure fluctuation, the fluctuation rate and the fluctuation variance of range β3 are increased. The average value of pressure fluctuation is almost constant with slight change of fluctuation range, and the variance value is increased slowly in the range of β6.