Abstract: A piston and cylinder machine, e.g. an engine or pump, in which the cylinder rotates about a first axis from which the cylinder is spaced, and the piston rotates about a second axis inclined to the first with the result that during the rotation, the piston reciprocates relative to the cylinder. Gas flow is controlled by a rotary valve which communicates with the cylinder and which rotates about an axis parallel to or coincident with the first axis. The piston is maintained in position relative to the cylinder by restraining means in the form, for example, of flat abutment surfaces provided between the piston and a spherically-surfaced piston ring thereon so as to limit lateral movement of the piston ring relative to the piston.

Abstract: A piston and cylinder machine of the kind in which there is a wobble mechanism for reciprocating the piston in the cylinder or an arrangement in which a piston assembly and a cylinder assembly rotate about respective inclined axes so that such rotation is accompanied by relative reciprocation of the piston and cylinder, is provided with a piston having a part which has a surface exposed inside the cylinder to define at least a part of one end of a chamber therein and which, to provide sealing of the chamber, has a peripheral surface forming a sphere. Improved torque transmitting or reacting means for maintaining the correct relative orientation of the piston and cylinder are provided.