Fuel economy of multigrade gear lubricants

Abstract

The paper discusses the setup of a light duty axle efficiency test in evaluating gear lubricants for their fuel economy performance. Data collected with an internal reference oil highlight the repeatability of the test in different axles. Comparisons between single grade SAE 90 to multigrade gear lubricants were made under a variety of pinion torques and speeds to simulate highway and city driving conditions. A discussion of lubricant rheology and its importance to maintaining film strength for adequate bearing and gear lubrication for optimum torque efficiency and axle temperature is provided.

Axle gear oils: Tribological characterization under full film lubrication

“…These are examples of the continuously tightening legislation with which the automotive industry has to deal. At the same time, consumers demand for increased performance and engine horse-power has increased 34% in the last decade [1,2,3,4,5,6]. To match these contradicting requirements a huge pressure is put on vehicle efficiency at all levels.…”

“…To match these contradicting requirements a huge pressure is put on vehicle efficiency at all levels. The efforts from automotive manufacturers resulted in improved aerodynamics, more fuel efficient high torque engines operating at lower rpm, energy saving gearboxes and smaller axles with lower ratios [1,2,6,7].…”

“…Axle transmissions have low torque efficiency, typically between 95% and 97%, depending on the type of vehicle and on the applied torque and speed, and they are subjected to several energy loss mechanisms: load dependent losses generated by gears and rolling bearings that are related to the transmitted torque input and load-independent losses or churning losses generated by gears, rolling bearings and seals that are related to the input speed and lubricant properties [1,2,3,9]. To minimize the torque loss in the axle transmission, car manufactures act simultaneously on load depend and load independent losses, through design and material modifications as well as through improvements in lubrication, which try to minimize friction and wear on the moving parts.…”