Developing Next Generation Axle Fluids, Part III: Laboratory CAFE Simulation Test as a Key Fluid Development Tool 2003-01-3235

The regulatory drive for emission reductions, increased fuel costs, and likely increases in Corporate Average Fuel Economy (CAFE) requirements have made fuel efficiency a key issue for North American vehicle manufacturers and marketers. At the same time the popularity of sport utility vehicles and light trucks has made it more difficult to achieve CAFE objectives. In order to accommodate both public vehicle preference and government mandated CAFE requirements automobile manufacturers are seeking all available means to increase fuel economy through advanced system design, engineered materials, and improved lubricant technology.

Axle lubricants can have a significant impact on fuel economy; moreover, axle lubricants can be tailored to deliver maximum operating efficiency over either specific or wide ranges of operating conditions. With the proper lubricant technology, improvements can be realized under both the normal city-highway driving conditions typically associated with passenger cars and under more highly loaded conditions often encountered in light truck operation.

Historically, axle lubricants have been assessed for energy efficiency in a variety of full scale vehicle methods including over-the-road fleets, track testing and chassis dynamometers [1, 2, 3, 4]. Although real world in nature, these methods are subject to many variables which are difficult to control and thus obtaining accurate and repeatable efficiency estimates can be problematic. In order to increase the level of confidence in axle efficiency measurements, a full-scale light duty axle test was developed which appears to be an accurate predictor for the Federal Test Procedure 75 (FTP-75) cycle used for new vehicle qualification by the USA Environmental Protection Agency [5]. This method simulates the FTP-75 cycle by performing a series of steady-state speed-load conditions on a laboratory axle stand without axle sump temperature control. The test was developed using specific speed/load conditions from the actual FTP-75 testing. Data taken at each speed-load condition are used to determine a weighted efficiency value for each lubricant tested. Test repeatability and sensitivity have been explored using axle lubricants with known performance in the FTP test cycle.