Damage matching criterion for development of accelerated duty cycle from road load data, and achieving right duty cycle to determine gear and bearing durability.
To be published on October 11, 2019 by SAE International in United States
Event: International Conference on Advances in Design, Materials, Manufacturing and Surface Engineering for Mobility
While designing the transmission, designer needs to have a duty cycle which is a set of load cases against which he wants to confirm the durability of the same. This is done through data acquisition by running a vehicle on various terrains and converting those data points to a concise set of load cases which we term as duty cycle. This is required because data acquired has millions of data points giving value of torque and RPM at every millisecond which cannot be directly used to assess the fatigue durability of gears and bearings. Converting these millions of road load data points into fewer number of load cases is always a challenge. For a transmission designer, it is being a major hurdle to determine as what is the scientific way of converting these millions of data points into a concise duty cycle. The road load data is taken for few hundred or few thousand kilometres covering enough types of terrains on which vehicle is expected to run. But the methods available with todays engineers does not establish the relation between duration of collected road load data and expected transmission life and duration of test rig. The designer does not know whether the millions of data points are being represented correctly in the fewer load cases while evaluating the durability of the gears and bearing in the transmission or any geared drive for that matter. The calculation of equivalent load of the data points from road load data which is a torque, RPM and duration can be moved along SN curve to convert given torque and RPM to higher torque and rpm. This is the easiest way which many engineers are following using a binning method. However, calculation of equivalent load by binning method does not confirm that the cumulative damage due to the number of load cases in a bin is equal to the damage by a condensed equivalent load. The method developed at Romax is unique and confirms that the damage caused due millions of data point of a road load data for gear contact, gear bending and bearing damage (roller and ball both) for all gear and bearing in a system is equal to the damage caused by condensed duty cycle. This is done in one single analysis run. Moreover, the one can develop a test duty cycle for same damage with specified single torque or RPM or specified duration to develop accelerated duty cycle.