Chapter 30 Engine Starting Systems 511
When the key is released, the relay opens. This stops
the solenoid current to disengage the starting motor.
ECM-Controlled 12-Volt Starting Circuit
An ECM-controlled starting circuit automati-
cally energizes and de-energizes the 12-volt starting
motor as soon as engine sensors detect fuel combus-
tion and the resulting rapid increase in crankshaft
rpms (speed sensor signal). The engine control mod-
ule and body control module operate the 12-volt
starting circuit automatically.
If a driver accidently holds the start key or start
button too long, newer hybrids protect the starter
pinion gear from damage caused by excessive speed.
Most late-model starting systems are programmed
to open the circuit between the ignition switch and
the starter solenoid whenever the engine is running.
This prevents the driver from accidentally engaging
the starting motor and grinding its pinion gear into
the fl ywheel gear when the fl ywheel gear is spin-
ning at high speeds.
Hybrid Starting Systems
Early-model hybrids used a 12-volt starting sys-
tem and a separate high-voltage propulsion system.
Since this design added weight and complexity to
the vehicle, most late-model hybrids use the motor-
generator to crank the engine for starting.
A late-model hybrid starting system includes the
following components:
• Motor-generator—The motor-generator serves
as a high-torque motor for rotating the engine
crankshaft.
• HV power cables—Three HV power cables
connect the HV power control module to the
motor-generator. Two HV power cables con-
nect the HV battery to the HV power control
module.
• Hybrid control module—The hybrid con-
trol module detects a need to start or stop the
engine.
• HV power control module—The HV power
control module converts dc into three-phase
ac for the motor-generator. If the vehicle does
not have a separate hybrid control module, the
HV power control module determines when
the engine should be started and sends three-
phase ac to operate the motor-generator for
engine startup.
• Engine control module (ECM)—The engine
control module activates the fuel and ignition
systems so the engine will start and run.
The motor-generator armature (rotor) can be
attached directly to the engine crankshaft. Refer to
Figure 30-17. The motor-generator can also be con-
nected to the engine through the transmission or
transaxle. In this arrangement, the HV power con-
trol module and the hybrid control module must
lock the torque converter clutch and the transmis-
sion motor-generator clutch so the motor-generator
can spin the engine crankshaft for starting.
Motor-generators easily spin the engine crank-
shaft. Many hybrid starting systems are very quiet
when engaged. When driving, it is diffi cult to tell
when the HV starting system fi res up the engine.
Armature Starter coil
Figure 30-17. In many hybrid designs, the motor-generator
rotor is mounted directly onto the engine crankshaft fl ange. If
three-phase current is fed to the stator coils by the HV power
control module, the rotor magnets, armature, and crankshaft
will be spun easily until the engine fi res. (Honda)