An Efficient Lift Control Technique in Electro-hydraulic Camless Valvetrain Using Variable Speed Hydraulic Pump 2011-01-0940

Significant improvement in fuel consumption, torque delivery and emission could be achieved through flexible control of the valve timings, duration and lift. In most existing electro-hydraulic variable valve actuation systems, the desired valve lift within every engine cycle is achieved by accurately controlling of the solenoid-valve opening interval; however, due to slow response time, precision control of these valves is difficult particularly during higher engine speeds. In this paper a new lift control strategy is proposed based on the hydraulic supply pressure and flow control. In this method, in order to control the peak valve lift, the hydraulic pump speed is precisely controlled using a two-input gearbox mechanism. This eliminates the need for precision control of the solenoid valves opening interval within every cycle. To achieve a smooth control signal, it is worthwhile to control the maximum valve lift within few engine cycles rather than every cycle; therefore, instead of using the governing non-linear differential equations of the mechanism, a novel average model of the system is developed based on energy conservation equations. A non-linear sliding mode controller (SMC) is also designed based on the developed average model and the boundary layer method is used to eliminate the chattering problem. The performance of the proposed controller is then examined through some simulations. Moreover, the new lift control technique is implemented experimentally by reconfiguration of the existing electro-hydraulic valve system prototype and empirical results are then compared with those obtained from the simulations.