Estimating the Lifetime of Gear Lubricants

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The main goal of this paper is to present methods on how to take oil degradation into account in reliability modeling. Therefore mineral oil based gear lubricant was artificially aged in an oven and reliability data was gathered from exemplary selected tests. For testing the aged oil, three tests were selected: two simple test benches (Brugger test apparatus and a four-ball roller test) and a gear test bench. To include oil aging into the transmission’s system reliability, two possibilities were considered: - as a machine component and - the lubricant and its deterioration as an influence on component life. The gathered reliability data from the test results were used to derive statistical life models according to the proposed possibilities. The presented work leads to a more realistic reliability model of transmissions which considers the influence of oil degradation besides mechanical and electronic failure modes. Nowadays, the prediction of a system’s reliability is the main goal in order to minimize warranty costs, meet quality standards and ensure the customer’s satisfaction. If a transmission itself is considered as a mechanical system, you first need to know the failure behavior of the system’s elements [Ref 1]. A common method to describe the failure behavior of mechanical machine components is to use a Weibull distribution for every single element as well as for the complete mechanical system. The lifetime of mechanical machine components such as gears, bearings and shafts can be calculated, for example, by means of a damage accumulation hypothesis [Ref 2, 3, 4]. The transmission lifetime is also affected by sophisticated lubricants. Oil lubricants are complex chemical products and not easy to describe in terms of their failure behavior.

Keywords: RAMS 2010 Proceedings - Product Reliability - Reliability Model