Coupling Crankshafts On An Opposed-Piston Engine With A Geartrain On Both Sides

The subject matter relates to an opposed-piston engine that incorporates a pair of gear trains, or other coupling mechanisms, located on both ends of the pair of crankshafts driven by reciprocating pistons within the cylinders of the engine.

Inventor: John Kessler

Disclosure Numbers: D461

Date of This Draft: 06/22/2016

Prepared by: Joel F. Lemke

ABSTRACT

The subject matter relates to an opposed-piston engine that incorporates a pair of gear trains, or other coupling mechanisms, located on both ends of the pair of crankshafts driven by reciprocating pistons within the cylinders of the engine.

BACKGROUND

Multiple solutions to coupling the crankshafts on an opposed piston engine have been suggested, and pursued.  Most consist of some mechanism, such as a gear train, in a particular axial position that transmits torque from one crank to another to ensure accurate phasing between them.  FIG. 1 shows a portion of an Achates Power† opposed-piston engine with three cylinders, a pair of crankshafts and a five gear train connecting the pair of crankshafts on one side of the engine. This configuration would be applicable to any opposed-piston engine with one or more cylinders. However, when the engine gets very long, such as with more than six cylinders, the crankshaft torsional compliance may result in a detrimental phase error for the pistons farthest from the coupling mechanism.  On high speed racing engines, a double-ended gear train is sometimes applied to minimize camshaft dynamic behavior.  On opposed-piston engines with a long profile, due to a large number of cylinders, two separate crankshaft coupling mechanisms can be employed, located on opposite sides of the crankshafts, to offset possible phasing errors between pistons.

DESCRIPTION

The following description outlines a layout wherein there are 2 separate crankshaft-coupling mechanisms and some of the concepts for how this layout could be practically implemented.

In an opposed-piston two-stroke engine with two crankshafts where two separate coupling mechanisms are situated on opposite sides of the crankshafts, a “standard” gear train, with the power takeoff, would still be designed to handle the majority of the engine loads.  The second coupling mechanisms, at the other end (free end) of the crankshafts, could be designed in multiple configurations.

It could be a repeat of the “standard” gear train with the same number of gears, (three and three or five and five etc.).   Or, it could be a proportional number of gears such as five for the “standard” and three for the secondary or three for the “standard” and five for the secondary.  However, whatever proportion of gears  used must keep the odd number relationship for compatible crankshaft rotation.

Other possibilities for the secondary gear train could use a different number of teeth from the primary gear train to provide unique auxiliary speed opportunities, and de-tune tooth mesh frequency generated resonances while still being designed to handle the full crank coupling torques.

Still another configuration for the secondary gear train could be a smaller gear set that is designed only to handle enough torque to minimize timing variations.  This could be accomplished by attaching to the crank via a quill shaft, or some other torsional compliance within the system.

The secondary coupling mechanism could also be a different torque transmission mechanism such as an external belt.  This belt configuration could be as simple as looping a single serpentine belt around pulleys on both cranks that would provide some benefit to crank coupling torques.  Other possibilities for the secondary coupling mechanism might be the use of tie bars between the upper and lower cranks or even a simple cogged belt assembly.

Regardless of the configuration used for the secondary crankshaft coupling mechanism, the benefits realized would be:

Lower variation in injection timing relative to actual minimum volume for the “free end” cylinders, and lower torsional activity of the coupling mechanism system.

D461 Fig 1