Design diversity of HEVs with example vehicles from HEV competitions Page: 10 of 12
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the grid. In this way, the engine is used as little as possible.
In one of its passive energy management strategies, the
vehicle can engage the engine during higher-speed operation
and during high power demands. As the batteries are
depleted, the engine is engaged more and more frequently,
until it is used for all power requirements. This blending of
the ZEV and HEV modes is more sophisticated than other
(typically series HEV) approaches that use a particular battery
SOC setpoint to engage the engine for increased range.
This unique parallel HEV design has an advantage over a
series HEV with similarly sized components because there is
no need for a generator in a parallel design. In addition, for
highway driving, the engine efficiency can be as high or
higher than a series HEV because a parallel design does not
experience the efficiency losses associated with converting
power from an engine into electrical power, then back to
mechanical power.
(3) University of Tennessee - Unlike the Maryland HEV
design that load-levels the engine during hard accelerations
and transients, the Tennessee design uses the electric motor
essentially for power-peaking the undersized engine. The
engine is the same 1.0-L engine model used in the Maryland
design, but it has been modified for use with natural gas. The
electric motor is a 32-kW brushless DC that is used during
high power demands that the engine cannot fully handle. The
electric motor engages for only 2-3 seconds during the
beginning of the acceleration events, providing 20-30 kW of
power. The (gasoline equivalent) fuel economy results were
slightly worse than stock, with 9.8 km/L (23 mpg) compared
to the stock rate of 12.3 km/L (29 mpg), however, the
emissions rates were lower than the California ultra-low
emissions vehicle (ULEV) rates.
The amount of energy depleted during the accelerations is
small and is almost completely resupplied during regenerative
braking. One novel feature used by Tennessee and a few
other schools: the engine does not use an alternator, but draws
power from a DC/DC converter off the main battery pack to
supply an undersized 12-V accessory battery.
(4) Western Washington University- The energy
management strategy of this vehicle is similar to that of the
UC Davis vehicle. This HEV is classified as a parallel,
charge-sustaining, ZEV-capable, vehicle with significant
electrical energy storage. A modified stock engine was used
with a 32-kW electric motor. The accelerator pedal gives
input to both the engine throttle and the motor controller. A
simple control mechanism engages the engine when the
batteries can not provide enough power to match the level
associated with the pedal position. The engine is quickly
started at a particular level of pedal depression; further
depression gradually opens the throttle. When the batteries
are charged, the vehicle can be driven normally without
depressing the accelerator pedal far enough to engage the
engine. But as the battery SOC drops, the accelerator pedal is
depressed more to achieve the desired power until eventually,
when the batteries are dead, the engine works full time to
power the vehicle.
This control strategy, though robust, is not as
sophisticated as a fully active computer control that provides
optimal use of the hybrid components. Most HEV designs
were controlled using a simple control; these vehicles wereoperated successfully, but had limited success in
demonstrating high vehicle efficiency.
.()_ California State University. Chico - This charge-
sustaining, series, ZEV-capable HEV with significant
electrical energy storage capacity had an enormous 31-kWh
nickel-metal-hydride battery pack and a powerful 150-kW
(200-hp) electric motor. This HEV uses the thermostat power
control strategy.
The vehicle achieved a SOC corrected 13.8-km/L
(32.4-mpg) result on the FTP test (a stock Saturn gets 12.3
km/L). Not only is the fuel efficiency impressive, but this
vehicle has an estimated 240-km ZEV range and the power to
accelerate significantly faster than the stock Saturn.
(6) University of West Virginia - This vehicle, like that
designed by the CSU Chico team, is a dual-mode HEV with
an on/off engine control strategy. However, this team took a
very direct, relatively low-cost approach that produced very
good results in 1994. This series, charge-sustaining,
ZEV-capable HEV, with significant battery storage capacity,
used a relatively inexpensive 44-kW DC-type electric motor
that does not have regenerative braking capabilities. The
batteries were typical lead-acid type. In spite of the low-tech
approach, the vehicle achieved a ZEV efficiency of 5.97
mi/kWh (a result on the order of advanced-production EVs)
and 20.4 km/L (48.1 mpg) SOC-corrected fuel economy. The
engine/generator was a 16.4-kW (22-hp) 0.6-L Kawasaki
2-cylinder coupled to a Fisher alternator. The engine was
operated at high-output for efficiency and produced slightly
more charge than was used during the FTP emissions and fuel
economy test. The high charge rate allowed the engine to be
off during one third of the entire test cycle.
DESIGN SPACE - The designs of the participating
vehicles in the HEV competitions can be shown within the
design space cube shown in Figure 2. With these plots we can
look at ZEV capability and range, estimated
charge-sustainability, underpowered designs, the various HEV
types, and overall design trends.a)
w
m)35 _ - Range Extender
3p .5 Dual-Mode
- - * aoo
f Saturn
e Fod
15 2
.' Fueled Engine-Electric
10
150 18 32 54 72 90 108 126
Engine Power [IWI
Figure 9: Engine and Battery Sizing by . lass144
Engine and Battery Sizing by Class - Figure 9 includes
the battery energy vs. engine power axes of the cube (a top
view). Boxed regions show the classic HEV types. Notice
that, as a whole, the amount of battery storage was reasonably.1.
8
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Duoba, M.; Larsen, R. & LeBlanc, N. Design diversity of HEVs with example vehicles from HEV competitions, article, December 31, 1996; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc687488/m1/10/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.