Design and Control of a Partially 3D Printed Valve Actuator for a Free Piston Engine

The use of electronically controlled valves allows a high degree of flexibility in the operation of internal combustion engines. Due to the mechanical decoupling from the crankshaft, it is possible to operate four-stroke free-piston engines. The valve timing can be controlled using a rotary-electric-drive for each camshaft or directly for each valve using a linear-electric-actuator. By using electric linear actuators, a camshaft can be dispensed with and a new degree of freedom in the design of the valve lift curve is created. However, there is the problem of controllability. It must be possible to open and close a valve with a stroke of up to 4mm in a highly dynamic manner without touching the pistons. Another problem is that the valves are located in the combustion chamber of the internal combustion engine and are therefore exposed to high thermal stress. Due to the heating of the valve, part of the heat is also transferred to the mover, which could cause the permanent magnets used to lose their magnetic properties without extensive cooling.Under these circumstances, it should be investigated whether it is possible to develop an electric linear machine from many standard components and to operate it as a valve actuator. A linear-acting reluctance machine was developed and tested. The linear machine was designed using an FEM model. Another special feature of the actuator is that the stator was made of standard sheet metal. The possibilities of 3D printing were used for the implementation. Only the mover had to be made individually. The developed linear machine was controlled in two different ways. The test resulted in a smooth trajectory with the cascade control and a very fast trajectory with the on-off control structure.