Using Transmission Data to Isolate Individual Losses in Coastdown Road Load Coefficients

Area of Science:

• Automotive Engineering
• Environmental Science
• Mechanical Engineering

Background:

• The U.S. Environmental Protection Agency (EPA) continuously assesses advanced automotive technologies for regulatory compliance.
• Accurate measurement of transmission efficiency is crucial for evaluating vehicle performance and emissions.

Purpose of the Study:

• To develop a method for estimating and isolating transmission and drivetrain losses from vehicle coastdown data.
• To enable more accurate analysis of aerodynamic and rolling resistance for fleet-wide efficiency evaluations.

Main Methods:

• Benchmarking multiple transmissions using a modified coastdown test to measure transmission output drag.
• Representing transmission drag data as a second-order polynomial expression (F₀ + F₁V + F₂V²).
• Analyzing EPA's published vehicle coastdown and dynamometer coefficients to identify relationships among coefficients.

Main Results:

• Transmission drag data can be predictably represented by a second-order expression.
• Relationships observed among transmission coefficients were also present in vehicle coefficients.
• Vehicle coefficients can directly estimate and remove transmission/drivetrain losses from coastdown data.

Conclusions:

• A novel method allows for the accurate estimation of transmission and drivetrain losses using existing vehicle test data.
• Eliminating these losses enables more precise quantification of aerodynamic and rolling resistance.
• This approach facilitates independent evaluation of efficiency improvements across vehicle fleets without detailed vehicle-specific data.