A new ductile cast iron flywheel integrated with a gear and its manufacturing process were developed to reduce the manufacturing steps and costs compared with a conventional flywheel around which a steel ring gear is fit.
In this process, the ring gear teeth around a spheroidal graphite cast iron flywheel are formed directly in a net shape and free from any defects using the hot form-rolling method, followed by the thermomechanical treatment with controlled cooling in a short time. To obtain the strength and properties required for the flywheel gear, the matrix structure of martensite and pearlite in the gear teeth is made at the tooth face and the tooth bottom, respectively, by controlling the cooling rate after the hot form-rolling operation. The developed thermomechanical treatment gear is superior to that made by the conventional hobbing and heat treatment with respect to accuracy, strength and anti-wear property. The developed gear showed no problem in the endurance test using a practical engine.
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