378
Alternative Fuels for Transportation
ω = (1 + ρ ω
) − ρω ,
d
e
g
N
ρ =
s
,
N r
where T d is the driveline torque, T m is the motor torque, T e is the engine torque,
ω d is the driveline speed, ω e is the engine speed, ω g is the generator speed, ρ
is the planetary gear ratio, N S is the number of sun gear teeth, and N r is the
number of ring gear teeth. By controlling the power taken by the generator
and then feeding back into the motor, ω e can be maintained constant when ω d
is varying. Hence, a continuously variable ratio between engine speed and
wheel speed can be achieved.
The advantages of this ECVT propulsion system are summarized below:
• Because of the absence of clutches, torque converters or shifting
gears, it can significantly improve the transmission efficiency and
reduce the overall size, hence increasing both the energy efficiency
and power density. Also, since it is mechanically simple, it offers
high reliability.
• In the presence of a continuously variable ratio between engine speed
and wheel speed, the engine can always operate at its most energyefficient or optimal operation line (OOL) as shown in Figure 12.14,
hence resulting in a considerable reduction of fuel consumption.
• The system can fully enable the idle stop feature (the engine is completely shut down when the vehicle is stopped) and the electric
launch feature (the motor provides all necessary torque required to
put the vehicle in motion). These two features are particularly essential to improve the energy efficiency of the full hybrid.
• The system can fully enable regenerative braking when the vehicle
is slowing or downhill coasting, and full-throttle acceleration where
both the engine and electric motor operate simultaneously to provide the required power demand.
The key disadvantage of all available ECVT propulsion systems is the reliance on planetary gearing. This planetary gear is a mechanical device in
which transmission loss, gear noise, and regular lubrication are inevitable. In
recent years, active researches are being conducted, aiming to get rid of this
mechanical planetary gear while retaining ECVT propulsion.
Rather than using a planetary gear, the combination of two concentrically arranged machines can realize the power split for the full hybrid.
Figure 12.15 shows the system concept in which the two machines are
mechanically coupled and electrically connected (Eriksson and Sadarangani
2002; Hoeijmakers and Ferreira 2006). The first machine is a double-rotor
Alternative Fuels for Transportation
ω = (1 + ρ ω
) − ρω ,
d
e
g
N
ρ =
s
,
N r
where T d is the driveline torque, T m is the motor torque, T e is the engine torque,
ω d is the driveline speed, ω e is the engine speed, ω g is the generator speed, ρ
is the planetary gear ratio, N S is the number of sun gear teeth, and N r is the
number of ring gear teeth. By controlling the power taken by the generator
and then feeding back into the motor, ω e can be maintained constant when ω d
is varying. Hence, a continuously variable ratio between engine speed and
wheel speed can be achieved.
The advantages of this ECVT propulsion system are summarized below:
• Because of the absence of clutches, torque converters or shifting
gears, it can significantly improve the transmission efficiency and
reduce the overall size, hence increasing both the energy efficiency
and power density. Also, since it is mechanically simple, it offers
high reliability.
• In the presence of a continuously variable ratio between engine speed
and wheel speed, the engine can always operate at its most energyefficient or optimal operation line (OOL) as shown in Figure 12.14,
hence resulting in a considerable reduction of fuel consumption.
• The system can fully enable the idle stop feature (the engine is completely shut down when the vehicle is stopped) and the electric
launch feature (the motor provides all necessary torque required to
put the vehicle in motion). These two features are particularly essential to improve the energy efficiency of the full hybrid.
• The system can fully enable regenerative braking when the vehicle
is slowing or downhill coasting, and full-throttle acceleration where
both the engine and electric motor operate simultaneously to provide the required power demand.
The key disadvantage of all available ECVT propulsion systems is the reliance on planetary gearing. This planetary gear is a mechanical device in
which transmission loss, gear noise, and regular lubrication are inevitable. In
recent years, active researches are being conducted, aiming to get rid of this
mechanical planetary gear while retaining ECVT propulsion.
Rather than using a planetary gear, the combination of two concentrically arranged machines can realize the power split for the full hybrid.
Figure 12.15 shows the system concept in which the two machines are
mechanically coupled and electrically connected (Eriksson and Sadarangani
2002; Hoeijmakers and Ferreira 2006). The first machine is a double-rotor