Abstract
Improvement in fuel economy and emission reduction is the major challenge for automotive industry today. Friction reduction is one of the ways to improve the overall powertrain efficiency and thus fuel economy. In manual transmission one of the sources of friction is churning of lubricant oil. This churning loss is influenced primarily by the viscosity of lubricant, oil immersion depth of gears and transmission RPM. There is an increasing trend for reduction of viscosity to reduce churning losses however limit is imposed by the durability requirement of transmission components. This paper analyses the effect of three lubricants on churning loss and efficiency in a 5 speed manual transmission. All the three lubricants met the minimum durability criteria. Mechanical loss test was conducted at no load to quantify the churning loss in the transmission at different RPM. In present study we found a good correlation between mechanical loss test results and viscosity of lubricant oil. Efficiency was also measured for input torque and input RPM range covered under MODIFIED INDIAN DRIVING CYCLE (MIDC). Efficiency test results did not correlate well with viscosity. To understand the mismatch between viscosity and efficiency test results, an alternate method was developed where behavior of lubricant under load was studied by measuring mechanical loss of transmission. In this method, preload of differential taper roller bearings was increased and mechanical loss measurements were performed at different RPM range with different lubricants. The results obtained thus explained the opposite behavior of mechanical loss and efficiency with respect to lubricant viscosity. This new method can be employed in case where efficiency measurement is not possible or for screening of lubricants from multiple samples based on traction coefficient. However this method can only be used in transmission having taper roller bearing. Finally overall effect on FE is simulated in the software for three lubricants and thus test conditions used allowed a clear distinction between the lubricants tested.