In-Situ Measurement of Holistic Powertrain Efficiency in Vehicles 2018-01-0324
Conventional methods for determining automotive powertrain efficiency include (1) component-level testing, such as engine dynamometer, transmission stand or axle stand testing, (2) simulations based on component level test data and (3) vehicle-level testing, such as chassis dynamometer or on-road testing. This paper focuses on vehicle-level testing to show where energy is lost throughout a complete vehicle powertrain. This approach captures all physical effects of a vehicle driving in real-world conditions, including torque converter lockup strategies, transmission shifting, engine control strategies and inherent mechanical efficiency of the components. A modern rear-wheel drive light duty pickup truck was instrumented and tested on a chassis dynamometer. Power was measured at the engine crankshaft output, the rear driveshaft and at the dynamometer. Additionally, fuel flow rate was measured along with a chemical analysis of the fuel for lower heating value to give an estimate of chemical energy available to the engine. Power at each measurement location was summed over three regulated drive cycles (FTP-75, HwFET and US06), yielding total energy and efficiency for a given drive cycle. An advanced signal acquisition and processing scheme, previously developed at SwRI, captured engine torque in the crank-angle domain in-situ. The results are validated by comparing calculated transmission efficiency against results from steady-state bench testing. The technique not only calculates component-level efficiencies on a vehicle under real-world driving conditions, but more importantly describes how the individual components integrate with the vehicle and perform at a system level. A thorough description of the technique along with real data is presented.