Think of a solid block cylinder shaped (acting as the block of a standard engine) with say 5 6 holes bored out through its length in a circular pattern, with an additional tube down the centre (similar to the magazine of a revolver gun).
Each of the outer tubes would act as cylinders, and the
central tube as the hub as well as the inlet and exhaust ports. Within each cylinder there would be two pistons one on each side. Attached to each outer end of the pistons would be a roller mechanism (replacing the con-rods).
At the outer edges of the main block would be rotated sine shaped cylinders / blocks i.e. one end has been shaped to go up and down if something is rotated around its central point.
Sorry to bore or confuse you so far, but its a bit difficult to explain.
The idea being that the main block rotates with the outer sine shaped block remaining stationary, the roller mechanism on the pistons is pushed against the sin shaped block thus as the main block is rotated the pistons are pushed in and out creating reciprocating motion.
To replace the valves of a standard engine - the central hub would be fixed, so as the main block is rotated around it this would line up two holes say as each of the pistons are being pulled outwards thus replicating the induction stroke of a standard engine. As the main block is rotated more, the holes are no longer aligned and the compression stroke begins (the pistons being pushed in by the incline of the sin shaped block) at x degrees after TDC of the sine wave, the mixture is ignited throwing the pistons outwards against the decline of the sine block, thus providing power to rotate the main block (and ultimately the output shaft) with the momentum the pistons are then pushed in again (pushed against the incline of the sine block), at the same time the exhaust hole are lined up on the central hub and the gases are expelled, only to repeat the cycle again.
The sine wave on the outer block could be repeated X number of times so that X number of cycles could occur on one rotation of the main block. Also each cylinder would be firing (with 6 cylinders - 360 / 6 -) 60 degrees after each other creating a very smooth torque curve.
Variable compression could be incorporated by altering the height of each sine wave (for example the exhaust stroke could compressed completely to expel all the gases by making that sine crest slightly higher than the others) or by moving the outer blocks in our out. Also variable valve timing could be incorporated by turning the inlet / outlet hub slightly.
The number of moving parts would be drastically reduced and the RPM could be considerably higher, it would also be far more compact, although cooling could be difficult unless a turbine was incorporated and cooling fins on the main block.
Sorry it a bit long winded, but I hope you can understand the basic concept.