The hybrid ECU also signals the engine ECU to provide
“spark and fuel” to the engine. The engine ECU electrically
energizes the engine’s fuel pumps, electronic fuel injectors,
and ignition coils while the motor-generator spins the crank-
shaft until the engine “fires” and runs on its own power.
Battery Pack Charging Mode
After driving a few miles in the all-electric mode, the
HV battery pack becomes partially discharged. When the
hybrid ECU detects the lower voltage (about 70% dis-
charge), it starts the internal combustion engine to propel
the vehicle and recharge the HV battery pack. Refer to
Figure 38-4D. The engine crankshaft spins the motor-
generator, which in turn sends electricity to the power
control module and battery pack.
Hybrid System Voltages
Most hybrids use two voltage systems: a high-
voltage (HV) system for the electric drive system and a
12-volt system for most of the vehicle’s conventional
electrical/electronic components. Both systems are wired
separately but interface through the ECUs and the power
control module.
The hybrid high-voltage system typically operates
on voltages that range from around 250 volts up to 650
volts ac or dc. The large conductors and electrical/elec-
tronic components in the high-voltage system permit
thousands of amps of current to be fed through the elec-
tric drive system. This is enough energy to power several
small homes.
698 Section 5 Electrical Systems
Figure 38-4. Study the basic modes of hybrid operation carefully. A—In the all-electric mode, the battery pack provides the energy
to propel the vehicle. B—The motor assist 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, cur-
rent flow out of the motor-generator recharges the battery pack. D—In the battery recharging mode, the motor-generator is locked
to the crankshaft or transaxle gears to spin and act as a generator to recharge the battery pack.
A
C
B
D