Environmental Engineering Reference
In-Depth Information
into the driveline. Clutch C1 is a disconnect clutch that is actuated when the engine
load is not desirable, such as during electric-only propulsion and during regen-
erative braking when engine compression braking is not needed. Clutch C2 is the
main drive clutch, designed for smooth engagement/disengagement and having
mechanical damper mechanisms integral to the clutch disc. Clutch C2 is actuated
during engine and electric motor assisted launch and acceleration, grade climbing
and descent, and for prolonged cruise.
Energy storage in the switchable series-parallel hybrid is shown as a battery pack,
but this could be an advanced battery for high cycle life, an ultra-capacitor alone as
used in the Nissan Condor Super-Capacitor truck, or in combination. The Toyota
Group switchable series-parallel hybrid uses an ultra-capacitor for transient energy
storage. The rationale for ultra-capacitor storage is that energy is stored in the same
form that it is being used - as electrons. That is, the same electricity that propels the
vehicle is stored as accumulated charge in the unit's double layer capacitance. There is
no electrochemical conversion to rob turnaround efficiency. Electrostatically stored
charge is released during electric-only launch and replenished during regenerative
braking. More will be said of ultra-capacitor energy storage in Chapter 10. The real
benefit of these cyclable energy storage devices is their high efficiency. For ultra-
capacitors the charge, discharge and turnaround efficiency under constant current
conditions is given by their RC time constant and the pulse dwell time,
T
:
!
;
!
1
2
T
;
1
1
þ
2
T
h
chg
¼
1
2
T
h
dchg
¼
h
ta
¼
ð
2
:
1
Þ
1
þ
2
T
The Hino company now has 300 such urban route buses equipped with the
switchable series-parallel hybrid propulsion system and claims a fuel economy
improvement of 80% over a conventional diesel bus.
Toyota Motor Company (TMC) has developed an experimental low fuel con-
sumption vehicle dubbed the ES
3
[11] (Figure 2.6). The TMC ES
3
achieved a fuel
consumption of 2.13 L/100 km on the Japan 10-15 mode. The ES
3
propulsion
system is derived from its sister vehicle, the European Yaris, which employs a 1.4 L,
I4, TDI engine. Equipped with common rail injection, variable ratio turbo and a
compact CVT, the ES
3
is seen as a pioneering vehicle in low fuel consumption
clean diesel technology. The key to low fuel consumption is the energy regenerator
hybrid technology depicted in Figure 2.6. The ES
3
powertrain is conventional in all
respects except for the electric M/G integrated into the CVT in a post-transmission
parallel hybrid architecture. No specifics are given for the ultra-capacitor rating
other than it is high voltage.
Low fuel consumption is achieved through idle-stop powertrain control and
in part from a regenerative brake system that is augmented by a high voltage ultra-
capacitor energy storage module. Vehicle braking energy is recuperated by the M/G
regenerator and fed to the energy storage module. From there the recovered energy is
used in part for warm restart of the engine and in part to sustain vehicle loads on the
low voltage power network. A dc/dc converter is used to regulate the variable voltage
