无凸轮电液可变气门机构动态特性试验

A camless electric-hydraulic variable valve actuator(EHVVA) test system was designed and developed. Operating characteristics of the EHVVA were investigated experimentally under four different engine speeds of 2 500，2 000，1 500 and 1 000 r/min，respectively. Unlike the cam derived valve mechanism，the EHVVA characteristic is less influenced by the engine speed while possesses relatively higher fullness coefficient. Moreover，the peak acceleration for the EHVVA is lower than that for the cam derived cases under high engine speed conditions，indicating a smaller reciprocating force of inertia. Evolution of oil pressure within the plunger cavity can be divided into three distinct stages，i.e.，the oil pressure set up stage，the oil pressure hold stage and the oil pressure unload stage. As the engine speed increases，increasingly higher driven oil pressure is needed to achieve better valve opening responsiveness. In the meantime，the reduced control signal pulse width finally results in the operating condition transition from full response state transform into insufficient response state. The research result of the cycle-to-cycle variation characteristics show that the variation coefficients for the maximum oil pressure，the maximum valve lift and the time-area value of the valve opening are all less than 4%.