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NAVC Hybrid Transit Bus Certification
Workgroup
The
primary goal of the NAVC Hybrid Transit Bus Certification project
was to develop a comprehensive protocol for the testing and certification
of heavy-duty hybrid-electric vehicles engines. The Hybrid Transit
Bus Certification Workgroup comprises government and industry stakeholders
working collaboratively to determine the best course of action.
The general consensus among participants in the Workgroup was that
short-term certification testing to help early market penetration
should remain engine based and the responsibility of the engine
manufacturers. A sunset date of 2004 was selected due to new emissions
standards scheduled to go into effect at that time, and the need
to re-evaluate the WorkgroupÕs recommendations in light of technology
advancement expected by then.
To
help build consensus on an appropriate cycle for short-term hybrid
engine certification, the NAVC workgroup turned to the Special Test
Procedures provisions in the Code of Federal Regulations (CFR).
In brief, the EPA had granted permission to Navistar in 1998 to
use a special test procedure in certifying the T444E engine, which
had been designed for the "light heavy-duty" market, for use in
a limited number of "heavy heavy-duty" hybrid transit buses. In
making its request to EPA, Navistar indicated that the quasi-steady
state ISO 8178-4 D-2 5-Mode Test Cycle (D-2) was more representative
of actual engine operation in the hybrid-electric bus than the transient
FTP cycle. Furthermore, Navistar showed that the engine could meet
the urban bus emission standards on the D-2 cycle. EPA approved
NavistarÕs request to use the D-2 cycle and on-highway deterioration
factors, but limited it to one model year only and required that
the engine be properly labeled for hybrid use only.
The
NAVC Hybrid Transit Bus Certification Workgroup set out to analyze
in-use hybrid engine data in order to determine the most representative
existing engine cycle for certifying hybrid engines. The conclusion
of this analysis is that, while it does not appear that the D-2
cycle is representative of the hybrid application, the use of a
steady-state cycle appears acceptable. The Workgroup gathered hybrid
engine operating data collected during actual bus operation to compare
to various established test cycles. Comparison of the in-use hybrid
engine operation data to the FTP test cycle shows conclusively that
the hybrid engines have substantially less aggressive transient
behavior than the FTP. Furthermore, hybrid engines will be more
closely characterized by steady-state operation than by an aggressive
test schedule such as the FTP.
Continued
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