Chapter 22 Hybrid Drive Systems 421
Idle Stop Mode
In idle stop mode, the engine automatically shuts off
when the vehicle comes to a full stop and restarts when the
vehicle reaches a predetermined speed or when the HV
battery pack has partially discharged. This prevents wasted
energy and exhaust emissions during idling or when the
engine is not needed.
Regenerative Braking Mode
Regenerative braking mode is an electric brake system
that works in conjunction with the conventional hydraulic
brakes. During the regenerative braking mode, the motor-
generator serves as an alternator or AC current generator to
send high current through the hybrid power cables, to the
power control module, and into the battery pack. Look at
Figure 22-4C.
When the brakes are applied, the brake pedal sensor
sends a signal to the hybrid ECU, prompting the motor-
generator to function as a generator. With moderate brake
pedal pressure, the conventional hydraulic brakes do not
apply the friction pads into the spinning brake armatures.
Instead, the motor-generator places a drag on the rotating
tires, wheels, and drive train, slowing the vehicle.
When the brake pedal is pressed harder for quicker
stops, the brake pedal sensor signals the computer system to
apply the conventional hydraulic brakes to stop the vehicle
more quickly. The front hydraulic friction brakes are only
applied in quick stops or panic stops. By reducing the use
of the hydraulic friction brakes, the hybrid can recapture
and conserve energy normally lost to the atmosphere as
wasted heat energy and brake dust.
If the hybrid is braked carefully, almost all of the
kinetic energy stored in the weight of the moving vehicle
is recaptured as electrical energy. This normally lost kinetic
Figure 22-4. Study the basic modes of hybrid operation. A—In all-electric mode, the battery provides the energy to propel the vehicle.
B—In motor assist mode, the internal combustion engine and motor-generator propel the vehicle. This mode is often used during
rapid acceleration. C—In the regenerative braking mode, the motor-generator acts as an electric generator that places a drag on the
drive train to help slow the vehicle. At the same time, current fl ow out of the motor-generator recharges the battery pack. D—In the
battery recharging mode, the motor-generator armature is locked to the crankshaft or transaxle gears to spin and act as a generator
to recharge the battery pack.
Motor-Generator
Propels Vehicle
A
C
B
D
DC Battery
Pack Power Out
Power Control Module
Converts DC to AC
Engine
Off
AC Voltage
No Fuel
Being
Used
Hybrid
ECU
Engine
ECU
Power Control Module
Converts AC to DC
Engine
Off
Hybrid
ECU
Engine
ECU
No Fuel
Consumption
Motor-Generator
Resists Wheel and Tire
Rotation to Slow Vehicle
Hydraulic Brakes
Not Applied
Battery Pack
Recharges
AC Voltage
Motor-Generator
Helps Propel Vehicle
Power Control Module
Converts DC to AC
DC Out
Fuel Fed
to Engine
Engine
Running
Battery Pack Energy
Helping Propel the
Vehicle
DC Voltage
Power Control Module
Converts AC to DC
Engine
Running
Fuel Being
Consumed
Motor-Generator
Driven by Engine
Battery Pack
Recharges
AC Voltage DC Voltage
Previous Page Next Page