Case Study: Effect of Core Hardness on Impact Strength of the Crown Wheel

Crown wheel can experience severe impact load when there is sudden drop in clutch pedal during vehicle operation. The higher core hardness at the pitch circle diameter of the gear teeth could drastically reduce the impact energy absorption characteristic of the material resulting in very fine micro crack on the teeth surface. The optimum core hardness range is very much necessary in order to improve the material impact energy absorption characteristic and subsequent balance between the impact & fatigue strength of the gear. The Brugger sample method is used to select the best core hardness range that exhibits optimum impact energy. The Brugger specimens with various core hardness bands, starts from 30 HRC to 45HRC, are prepared and tested for impact energy absorption capacity. The raw material with appropriate jominy value is used to prepare the specimen. Based on the Brugger test result, the optimum core hardness band is selected. The current gear-set with optimized core hardness are tested for gear set fatigue & impact shock load. The modified gear-sets with optimum core hardness show no significant variance in fatigue life compared to earlier, but exhibit enhanced impact strength.