A component level laboratory test methodology development for validating transmission bush 2020-01-1409
In the era of fierce competition, launching a defect free product on time would be the key to success. In modern automobile, the transmission system is designed with utmost care in order to transfer the maximum power from engine to driveline smoothly and efficiently. Optimized design of all the transmission components is necessary in order to meet the power requirement with the least possible weight. Transmission bush failure was observed in one of the transmissions during complete system level testing. Bushes are generally press fitted on the main shaft and counter shaft on which the needle roller bearing is mounted. In some cases, the free axial movement of the gear is restricted by the hub or shaft itself. But in other cases, due to assembly constraints, the bush itself is flanged to restrict the axial free play of the gear. When the respective gear is not in engaged condition, the bush does not get any axial thrust. Once the gear is engaged, due to the axial thrust caused by the helical gear, the bush experiences a certain amount of axial thrust. This axial thrust was suspected to be the reason of failure. A component level test set up maintaining the boundary condition was made and axial load was applied on the bush using hydraulic actuator. The failure mode was simulated consistently, and design modifications were carried out. Modified designs were also tested using the newly derived test methodology and the modified design with the required durability life was adopted for implementation. The complete system level durability test was again performed with the modified bush and no failure was reported thereafter. The component level test methodology helped to test number of design iterations and number of samples within a stipulated time and cost. This methodology can be used in all future projects as a part of front-loading support before performing complete system level test.