Experimental Evaluation of Rotary Engine Timing Gear Loads

The function of the timing gear of a rotary engine is to control the angular velocity of the rotor in relation to that of the crankshaft. The only load on the gear consists of the friction load due to the rotor seals, the torsional motion of the rotor and any torque developed on the rotor caused by uneven pressure distribution across the rotor flank. In the design of the gear and attachments an estimate of the loads must be made. In the case of an aircraft engine, knowing the actual loads and designing accordingly would result in the most weight effective configuration.

A specially instrumented stationary gear of a Deere 0.6 7 liter SCORE III rotary engine was used to measure the peak torque during test stand operation. The results of the test confirm that rotor friction and torsional motion (due to drive line dynamics) produce the prime gear load below 70% design speed. At the higher engine speeds, a sub-system resonance of the rotor contributes significantly to the total load on the gear.

The results of this test, together with the results of three earlier tests conducted on stationary gears are used to establish a design guide. This design guide relates the stationary gear load to crankshaft mean torque and engine displacement.