I have been following this discussion fairly well but the "Reverse

Rotation"

in the chart threw me. Could we have an explanation ?

I believe that the chart is showing the envelope of peak amplitudes of tooth loading vs. crankshaft speed. During one rotor revolution, some teeth may see loads on one face, while other teeth see loads on the opposite face. The "normal rotation" curve shows the load on the highest loaded tooth that is loaded on one face, while the "opposite normal rotation" curve shows the load on the highest loaded tooth (necessarily a different tooth) that is loaded on the opposite face. It is also quite likely that different teeth experience the highest load under different conditions of speed, load, acceleration, etc. Moving the load around different teeth helps the gear's fatigue life. All of this implies that for a constant crank velocity, the rotor velocity is not quite constant -- sometimes it tries to lead the crank, sometimes it tries to lag the crank. The reasons for this non-sinusoidal oscilliatory motion may include friction, resonance, combustion non-uniformity through the chamber, resultant force vector from the pressure-area terms on each face, engine acceleration or deceleration, manufacturing tolerances, .....

Curtiss Wright/Deere/RPI rotors used hard attachments of the gear to the rotor, a system that worked well under most conditions. When failures began to occur as engine output was increased, the system was simply strengthened. This may have led to heavier and costlier structures than the Mazda approach which is to reduce the stiffness of the system, thus reducing stresses. It seems from the curves that Mazda has found that too soft is not as good as "just soft enough," hence the change from 9 pins (softer) to 12 pins (stiffer). It's also interesting that the 12 pin solution has higher loads at most speeds that are in the automotive operating range for a 13B engine. It kind of suggests that the change in rotor gear attachment was developed to facilitate the production of the higher speed Renesis engine. It also suggests that if one is going to operate below 8000 rpm, the nine pin rotor is adequate if not superior.

Jonathan Lauter
Rotary Power Marine Corporation
516-656-5685
www.rotarypowermarine.com

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