DOI: 10.5061/dryad.2bvq83bnj
title: Hybrid-electric passenger car energy utilization and emissions: Relationships for real-world driving conditions that account for road grade

description: Past research showed on-road emissions patterns unique to hybrid electric
 vehicles (HEVs), indicating the need to account for them in emissions
 models as projected HEV sales increase over the coming decades. This work
 defines and characterizes a variable that quantifies HEV operating
 behavior to inform future development of new HEV emissions models based on
 current knowledge of conventional vehicle (CV) emissions patterns.
 Instantaneous hybridization factor (IHF), was quantified using on-road
 data collected from a 2010 Toyota Camry HEV. IHF is the ratio of electric
 system power to total system power and accounts for energy storage in the
 high voltage battery (IHF ranges from −1 to +1). Relationships between IHF
 and vehicle specific power (VSP), road type and road grade were examined.
 Negative VSP resulted in regenerative braking operation
 (IHF = −0.01 to −1) 90% of the time. IHF identified the
 VSP range where HEV operation was highly variable
 (VSP = −1 to 8 kW/ton) when driving at speeds
 below the ICE-off threshold (42 mph). VSP and IHF together account for
 76–86% of the variability in HEV CO2 emissions in this study. CO2 model
 results using VSP computed with the measured real-world road grade
 (R2 = 0.86) gave improved fits over the no-grade VSP
 model (R2 = 0.69). This study establishes one framework
 for calculating the instantaneous HEV power split, confirms the need to
 include road grade in VSP for accurate modeling of vehicle emissions, and
 identified the need for significant improvements in on-board diagnostic
 (OBD) scantool measurement requirements for HEVs in three areas: (1)
 temporal resolution (sub-second to capture transient events such as ICE
 restarts); (2) simultaneous data logging capability for multiple
 controller area networks (i.e., engine and HEV parameters together); and
 (3) improved data precision.
description: On-board
 emissions and vehicle operating data were collected by the UVM
 Transportation Air Quality Laboratory during real-world driving of one HEV
 and one CV, on a 50 km (32 mi) route over a variety of roadways in
 Chittenden County, Vermont using the custom Total On- board Tailpipe
 Emissions Measurement System (TOTEMS). Both vehicles were model year 2010
 Toyota Camry of similar driving performance, but different engine size,
 vehicle weight (due to HEV battery pack) and transmission type.  The
 dataset includes records of time-aligned 1Hz data, including emission
 rates (# or mass per sec) of criteria, air toxics and particle number (PN)
 and associated engine and hybrid system operating parameters.  Detailed
 lists of the parameters collected and data collection protocols are
 available in published UVM Transportation Research Center research reports
 (Holmén et al. 2014).  Sampling conditions for a total of 28 CV and 33 HEV
 sampling runs were conducted over an 18-month period under ambient
 temperatures ranging between -13 and 35 °C.  Road grade on the driving
 route was measured independently at sub-meter resolution and varied
 between -13.2 to +11.5%.
description: The "Data Dictionary" EXCEL file summarizes the
 contents of the database, with units for each parameter and descriptions
 of all acronyms.  The UVM TRC Research
 Report, Holmén et al. 2014, is linked below via
 URL to U.S. Department of Transportation National Transportation Library
 where PDF of the report may be found if the UVM Transporation Research
 Center website is not available
 (https://www.uvm.edu/cems/trc/trc-research-reports).