Michel engine

Although the forces in a cam engine are often greater and the frictional losses are high, they can also allow the use of larger bearing surfaces than a conventional crankshaft.

Before the development of high performance bearing materials,[note 3] the cam and swashplate engines appeared to offer some advantages.

In the first Michel engines, the cam had two surfaces, a main surface on which the pistons worked when running and another ring inside this that gave a desmodromic action to constrain the piston position during engine startup.

It is described in two early German sources,[6][7] but although mentioned in the 1928 NACA report,[3] it appears to have been superseded by then.

At this time, the maximum speed that a piston and its rings could travel within a cylinder was limited by state of design and lubrication techniques to maintain a good seal and avoid seizure.

[8] A 1,000 bhp Michel marine engine, intended for submarines,[note 6] was quoted as weighing 42,000 kg, compared to 128,000 kg for a comparable four-stroke diesel engine of similar speed and power.

[note 7] In the 1930s, Michel abandoned the cam engine idea and used conventional crankshafts, although requiring three of them, one per cylinder.

[note 8] The engine was now much smaller, lighter and had a greater specific power, both by weight and by volume.

Rather than the typical geared drive, as used by the Jumo, there was a triangular coupling rod frame, driven by an overhung crank on the end of each crankshaft.

The frame also drove the fuel injection pump, mounted in the top vee between the cylinders.

This was of unorthodox design: a rectangular pumping chamber formed on the triangular coupling frame.

A claimed advantage was the lack of a cylinder head gasket, which was a reliability problem for early diesels at this time.

Possibly it was successful, but simply its unusual nature led to it being ignored during World War II in favour of concentrating on more established designs.