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Alternative Fuels for Transportation
Launching
Decelerating/braking
M
T
B
E
F
P
G
D
M
T
B
E
F
P
G
D
Accelerating
Battery charging during driving
M
T
B
E
F
P
G
D
M
T
B
E
F
P
G
D
Normal driving
Battery charging
M
T
B
E
F
P
G
D
M
T
B
E
F
P
G
D
B: Battery
E: Engine
F: Fuel tank
G: Generator
M: Motor
P: Power converter
T: Transmission
D: Differential
Electrical link
Hydraulic link
Mechanical link
Figure 12.6
Engine-heavy series–parallel hybrid operating modes.
Figure 12.7 shows a relatively motor-heavy, series–parallel hybrid system,
in which there are six operating modes. For launching, the battery solely
feeds the electric motor to propel the vehicle while the engine is in the off
mode. For both accelerating and normal driving, both the engine and electric motor work together to propel the vehicle. The key difference is that the
electrical energy used for accelerating comes from both the generator and
battery whereas that for normal driving it comes solely from the generator
driven by the engine. Notice that a planetary gear is usually employed to
split up the engine output, hence to propel the vehicle and to drive the generator. During decelerating or braking, the electric motor acts as a generator
to charge the battery via the power converter. Also, at light load, the engine