Design and Optimisation of Internal Components for a Reciprocating Compressor Powering a Camless Valvetrain

Abstract: Freevalve AB develops camless valvetrains for internal combustion engines using pneumatic and hydraulic systems. An air compressor is used to generate pressure in the pneumatic system. To further increase efficiency of the Freevalve system, a new compressor tailored to its purpose, is being developed in house. This thesis is part of the development of this compressor, which is a reciprocating piston compressor. The piston and connecting rod are the two main components developed within the frames of the thesis. A dynamic model is set up for load case and crankshaft balancing analysis. Prototypes of pistons and connecting rods for the compressor were designed and manufactured with the objective of providing a stable testing platform for the complete Freevalve system. The components were then further analysed with topology optimisation to further improve the system. The prototype features a piston made from aluminium 7075-T6 and a connecting rod and piston pin made from 17-4 PH hardened stainless steel. The total prototype assembly mass is 926 grams, including the crankshaft. For the topology optimisation, two alternatives for the piston were designed, one to be machined in 7075-T6, and the other to be printed in AlSi10Mg using Direct Metal Laser Sintering (DMLS). The machined piston does not have the possibility to follow the optimisation results perfectly. However with the better mechanical properties of the 7075-T6 alloy, the final mass of the two pistons differs only by 4 grams. The final mass of the optimised assembly is 741 grams. As a result, the imbalanced inertial force is lowered by 28%.