An Electromechanical Valve Drive Incorporating a Nonlinear Mechanical Transformer 2003-01-0036
In traditional internal combustion engines, a camshaft acts on the valve stems to open and close the valves. Valve timing is fixed relative to piston position. On the other hand, if a valve is flexibly controlled by a variable valve actuation (VVA) system, we can achieve significant improvements in fuel efficiency, engine performance, emissions, etc. One of the most advanced variable valve actuation systems is the VVA operated by an electromechanical actuator without a camshaft, the so-called bi-positional electromechanical valve drive (BPVD). Existing BPVD's characteristically use a spring to provide the required mechanical power for operating a valve. The use of a spring provides many benefits to the design of the system, but it also results in difficult design challenges. The large holding force against the spring at the ends of the stroke virtually dictates the use of a normal-force electromagnetic actuator, which, from a servomechanical point of view, is not good compared to a shear-force bi-directional electromagnetic actuator. And, the large holding force generates a large jerk at the beginning and the end of a stroke and makes it difficult to achieve a soft valve landing. A new electromechanical valve drive (EMVD) design is proposed, which incorporates a nonlinear mechanical transformer and a shear-force electromagnetic actuator, which eliminates the large jerk and allows improved control under disturbances with acceptable average and peak electric power. This design is modeled, analyzed, and simulated.