Environmental Engineering Reference
In-Depth Information
Motor Show, the semi-encapsulated motorcycle has a 160 hp (119 kW) Yamaha
engine plus 5-speed gearbox, including radiator, exhaust, brake, battery, fuel tank
and suspension all packaged within a single 22
00
wheel. The system is cited as being
an autonomous motor unit, or independent wheel drive.
2.5 Hydraulic post-transmission hybrid
Architecting a post-transmission hybrid with hydraulic M/G is probably the most
sound engineering approach. Not only will a hydraulic motor have the necessary
torque and power density, but will also offer dramatic launch and acceleration
performance.
2.5.1 Launch assist
Figure 2.34 illustrates the concept of hydraulic propulsion in which a hydraulic
motor-pump (M/P) is connected at the transmission output shaft. Hydraulic fluid
flow is managed at a valve head within the M/P and includes a reservoir located
beneath the chassis at the vehicle's rear axle. A comparison of hydraulic to electric
drives is given in Reference 21. In this reference the author points out that power
densities of the hydraulic systems will be higher than that of the electric systems
because hydraulic pressures can be increased to achieve more performance.
Hydraulic system pressures of 5,000 psi (350 bar) are containable and provide M/P
performance at levels of 0.5 kW/kg. Working pressures and speeds of, for example,
an axial piston pump have not increased much beyond 350 bar due to issues with
noise and vibration. A relative comparison of hydraulic versus electric systems is
shown in Figure 2.34.
10
Hydraulic (swach plate, bent axis pumps)
1
Electric machines
Automotive starter: 0.3 kW/kg
Hybrid S/A(8 kW): 0.5 kW/kg
Hybrid M/G (50 kW): 1.2 kW/kg
0.1
0 50 100 150 200 250 300 350
Nominal power (kW)
Figure 2.34 Specific power density (kW/kg) of hydraulics versus electric systems
