Third Generation

This model was made of steel. It was a 0.6 liter displacement.  The elliptic bearings were replaced with gears. Another change was that the cylinder pairs were reoriented to the parallel. The planetary crankshaft had a stroke of 80 mm.  If this had been a running engine, its power would be about 35 kilowatts.  Viewing ports were cut into the cylinder walls to observe the internal motion.  In this generation, the cylinders were parallel and coupled with channel stock at either end.  The throttles were attached to the channel stock.  Throttles moved axially with the rotation of a spiral cam.  The crankshafts were supported with planetary gears.

The first two figures below show details of the planetary crankshaft.  The 40 mm spur gear is engaged with a fixed 80 mm ring gear.  This can be seen in the right side of the second figure.  The interesting and very useful part of this design is the motion that results from turning the 40 mm gear.  In that figure, if the 40 mm  gear moves clockwise around the inside of the 80 mm ring, it will complete two counterclockwise revolutions before returning to its starting point.  But after returning to its starting point, the net effect on the 40 mm gear is that it rotated one revolution counterclockwise.  Animations show this motion.   The center of the 40 mm gear moves in a 40 mm circle.  The YankeeDiesel uses this motion for its planetary crankshaft.

The real advantage of this motion is taken when a crankpin is offset on the 40 mm gear.  That offset can cancels the circular motion and results in reciprocating motion.  Since the spur gear has a net of one revolution for a complete cycle, the crankpin has reciprocating motion and rotating motion.

The reciprocating motion is obtained if the offset is one quarter the diameter of the ring gear.  The plane of the reciprocating motion will be orientated with the engaged tooth and the offset crankpin.