373
Hybrid Vehicles
electric motor work together to propel the front axle, while the rear electric
motor also drives the rear axle. Notice that this operating mode involves
three propulsion devices (one engine and two electric motors) to simultaneously propel the vehicle. During normal driving with battery charging, the
engine output is split up to propel the front axle and to drive the front generator to charge the battery. The corresponding device to mechanically couple
the engine, front electric motor/generator and front axle altogether is usually
based on a planetary gear. During cruising, the battery delivers electrical
energy to the front electric motor only to drive the front axle whereas both
the engine and rear electric motor are off. During decelerating or braking,
both the front generator and rear electric motor (which works as a generator)
serve to simultaneously charge the battery. A unique feature of this dualaxle system is the capability of axle balancing. In case the front wheels slip,
the front generator absorbs the change of engine output power; through the
battery, this power difference is then used to feed the rear motor to drive the
rear wheels.
Figure 12.9 shows another dual-axle complex hybrid system, where the
front-wheel axle is driven by an electric motor and the rear-wheel axle is
propelled by a hybrid drivetrain. Focusing on vehicle propulsion, there are
six operating modes. For launching, the battery delivers electrical energy
only to the front electric motor that in turn drives the front axle of the vehicle
whereas both the engine and rear electric motor are off. Once the vehicle
moves forward, the battery also delivers electrical energy to the rear electric
motor that functions to quickly rise up the engine speed, thus cranking the
engine. For accelerating, the front electric motor drives the front axle while
both the engine and rear electric motor work together to propel the rear axle.
So, there are three propulsion devices (one engine and two electric motors)
simultaneously propelling the vehicle. During normal driving, the engine
works alone to propel the rear axle of the vehicle. During decelerating or
braking, both the front motor (which acts as a generator) and rear generator serve to simultaneously charge the battery. For battery charging during
driving, the engine output is split up to propel the rear axle and to drive the
rear generator to charge the battery.
12.4.5 iSg System Operation
In conventional automobiles, the starter motor and generator are separately
coupled with the engine as shown in Figure 12.10, hence providing high starting torque for cold cranking and generating electricity for battery charging,
respectively. This arrangement takes the advantage of simplicity, but suffers
from poor utilization of both machines and hence results in heavy weight
and bulky size. In order to incorporate both functions in a single unit, the
development of ISG systems is accelerating (Walker et al. 2004). As shown in
Figure 12.11, the ISG system serves both cold cranking and battery charging,
while eliminating the use of transmission belts and flywheels. Essentially,
Hybrid Vehicles
electric motor work together to propel the front axle, while the rear electric
motor also drives the rear axle. Notice that this operating mode involves
three propulsion devices (one engine and two electric motors) to simultaneously propel the vehicle. During normal driving with battery charging, the
engine output is split up to propel the front axle and to drive the front generator to charge the battery. The corresponding device to mechanically couple
the engine, front electric motor/generator and front axle altogether is usually
based on a planetary gear. During cruising, the battery delivers electrical
energy to the front electric motor only to drive the front axle whereas both
the engine and rear electric motor are off. During decelerating or braking,
both the front generator and rear electric motor (which works as a generator)
serve to simultaneously charge the battery. A unique feature of this dualaxle system is the capability of axle balancing. In case the front wheels slip,
the front generator absorbs the change of engine output power; through the
battery, this power difference is then used to feed the rear motor to drive the
rear wheels.
Figure 12.9 shows another dual-axle complex hybrid system, where the
front-wheel axle is driven by an electric motor and the rear-wheel axle is
propelled by a hybrid drivetrain. Focusing on vehicle propulsion, there are
six operating modes. For launching, the battery delivers electrical energy
only to the front electric motor that in turn drives the front axle of the vehicle
whereas both the engine and rear electric motor are off. Once the vehicle
moves forward, the battery also delivers electrical energy to the rear electric
motor that functions to quickly rise up the engine speed, thus cranking the
engine. For accelerating, the front electric motor drives the front axle while
both the engine and rear electric motor work together to propel the rear axle.
So, there are three propulsion devices (one engine and two electric motors)
simultaneously propelling the vehicle. During normal driving, the engine
works alone to propel the rear axle of the vehicle. During decelerating or
braking, both the front motor (which acts as a generator) and rear generator serve to simultaneously charge the battery. For battery charging during
driving, the engine output is split up to propel the rear axle and to drive the
rear generator to charge the battery.
12.4.5 iSg System Operation
In conventional automobiles, the starter motor and generator are separately
coupled with the engine as shown in Figure 12.10, hence providing high starting torque for cold cranking and generating electricity for battery charging,
respectively. This arrangement takes the advantage of simplicity, but suffers
from poor utilization of both machines and hence results in heavy weight
and bulky size. In order to incorporate both functions in a single unit, the
development of ISG systems is accelerating (Walker et al. 2004). As shown in
Figure 12.11, the ISG system serves both cold cranking and battery charging,
while eliminating the use of transmission belts and flywheels. Essentially,