Environmental Engineering Reference
In-Depth Information
However, with fluid power, the mass of system components such as reservoir,
lines, fittings and fluid is generally more than doubled. In the Airbus 320, for
example, the hydraulic components in one system weigh 200 kg while the plumbing,
fittings and pressure containment mass adds an additional 240 kg. In total, the
redundant hydraulic system weighs some 560 kg. In an electric system operating at
high voltage, the dominant mass will be contributed by the M/Gs themselves and very
minimal contribution will come fromwiring harness, connectors and cable shielding.
The hydraulic launch assist hybrid is an excellent example of hydraulic M/Ps
applied to the propeller shaft of a truck or SUV. During decelerations, the hydraulic
launch assist accumulator is charged by a hydraulic pump driven by, and directly
connected to, the vehicle's propeller shaft. Then, on subsequent acceleration, the
accumulator hydraulic pressure is discharged through the same M/P operating as a
motor, thereby adding propulsion power during acceleration. Such systems operate
at 350-420 bar and require substantial containment structure around the accumu-
lator and M/P.
2.5.2 Hydraulic-electric post-transmission
There are proponents of hydraulic energy storage in an electric drive system. The
concept is sound, and reminiscent of flywheel systems, but most likely not eco-
nomical. In order to deplete/replenish, the hydraulic storage and electric M/G
connected to a hydraulic M/P is necessary, as illustrated in Figure 2.35 according to
Reference 22. The hydraulic system described in this section has been called an off-
grid power boost, or mechanical capacitor, by its inventor, Steven Bloxham.
Supervisory
controller
E-steer
M/G
FD
ICE
XM
M/G
High pressure
accumulator
Low pressure
accumulator
M/P
Figure 2.35 Hydraulic-electric post-transmission hybrid
In Figure 2.35 the presence of two energy conversions sets an upper bound on
system efficiency at approximately 76% each way, or 58% turnaround, assuming
the following reasonable component efficiencies. Efficiency of the hydraulic M/P
is taken at 90% and electric M/G at 92%. A 58% turnaround efficiency is less than
