Cat & Mouse Internal-Combustion Engines

Also known as Scissors or Pursuing-Piston engines

Updated: 24 July 2008

This gallery is in course of arrangement
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The engines on this page have vanes that approach and recede from each as they go round, the changes in the volume between them allowing the usual compression, expansion, etc. They used to be on The Rotary Piston engines page but have now been given their very own page as they are conceptually rather different.

Similar engines that have "cylindrical" pistons moving toroidal cylinders also have their own page: toroidal engines. These have now been moved to their own pages in the interest of faster downloads.

See the Unusual IC Engines page for a full list of engine types.

Please ignore the #-numbers, this is just a filing system that attempts to keep all this organised.


Left: The Kauertz engine: 1967.

Originator: Eugen Kauertz (German)

This is a fine example of the scissors or pursuing-piston type of rotary engine, which has resurfaced many times. The primary vane or piston rotates at a steady speed, while the secondary vane rotates at a varying speed, opening and closing the spaces between them.

From Popular Science, Jan 1967

Left: The Kauertz engine: 1967.

This shows how the gear and crank mechanism moves one vane with respect to another as the whole assembly rotates. I think the central sun gear is fixed to the casing.

From Popular Science, Jan 1967

One objection to the Kauertz engine is the high inertial loadings on the vanes as they accelerate and decelerate; these are transmitted to rather flimsy-looking linkages. And there seems likely to be sealing issues, as with all rotary engines.


Left: The Virmel engine: 1966.

Originators: Virginia and Melvin Rolfsmeyer (Nebraska, USA)

The Virmel engine is very similiar to the Kauertz, but both sets of vanes stop and start, driven by a sun-and-planet system driving two cranks. Rotary IC engine patents frequently speak of the Kauertz-Virmel type of engine.

Yes, it's a pretty rubbish picture. It is, however, the only one I have been able to find so far.

From Science & Mechanics, Oct 1966

Left: The Virmel engine: 1966.

The internals. On the left are the two piston vanes, pulled apart axially. On the right, the cranks and connecting rods that move the piston vanes; the shape at the top is a hand, giving the scale.

From Science & Mechanics, Oct 1966.

As with the Kauertz engine, there looks to be high inertial loadings on the piston vanes as they accelerate and decelerate; once again these forces are transmitted to flimsy-looking linkages.

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