Test Methodology with Shock Loads and Fatigue Limit of Press Fitted Gears on Shaft 2013-01-2794

In case of new generation of commercial vehicles, three shaft transmissions are designed with press fitted gears on counter shaft. It allows user to save the cost of transmission manufacturing by considerable amount. In case of heavy commercial vehicles, which are being used in abusive conditions such as mining and off-road applications, it becomes absolutely necessary to ensure that the gears press fit should withstand the continuous loads and impact loads. There are design guidelines available to ensure proper fit and torque carrying capacity between the mating parts. Still, there are gear slippage, shaft and gear breakage failures in the field. In this scenario, there is a need to develop bench test procedure which will capture such failures in the prototype stage.

Looking at the failures in the field, it is necessary to capture all above hidden failures in design validation phase. So, the test methodology is developed in house based on road load data acquisition on mines and off road applications with abusive test conditions. All captured data analyzed and converted into suitable test cycle for simulating the hidden failures on test bench. It includes all spikes of torque, impact of load and frequency of the loads that are experienced at press fit location.

The test procedure presented in this paper focuses on generating relationship between designed press fit joint factor of safety and its fatigue limit for failure (cycles to failure). After collecting road load data, it was analyzed and found that with 2 times of rated torque, the press fit joint slippage was simulated at highly accelerated level. This was later devised in a test norm for press fit joint undergoing tipper and other offroad application. This test is also useful for testing the gears strength in static mode capacity of gears under impact and jerky loads.