Rhombic Drive for Stirling Engine

Four connecting rods are arranged as the sides of a rhombus are connected with journals at the vertices. Two opposite journals can rotate around two fixed axes. The other two vertices move along a straight line. If piston rods and pistons are attached coaxially to those two vertices, a rhombic drive can be created in which two pistons move in the same barrel. This arrangement can be used to create a Stirling engine.