A new electromagnetic valve actuator

In conventional internal combustion engines, engine valve displacements are fixed relative to crankshaft position. If these valves are actuated as a variable function of crankshaft angle, significant improvements in fuel economy can be achieved. Existing electromagnetically actuated variable-valve-timing (WT) systems characteristically use springs to provide the large inertial power to move the engine valves. However, the large spring forces generated when the valve is being closed or opened make it difficult to hold the valve without using a normal-force electromagnetic actuator. With normal-force electromagnetic actuators, it is difficult for the valve to engage its seat at a low velocity. Furthermore, from a control systems perspective, these unidirectional normal-force actuators pose difficult design challenges when compared to bi-directional shear-force actuators, as the former have nonuniform force constants. In this paper, we propose a novel electromagnetic valve drive (EMVD) system, and discuss the design and construction of the experimental apparatus, power electronics and controllers for the EMVD. This EMVD comprises an electric motor that is coupled to an engine valve-spring system with a nonlinear mechanical transformer. Simulation results show significant advantages of this EMVD over previously designed actuation systems.