12 V Starting and Charging
5-13
Enhanced Starter Motor
Operation (KL9)
The Engine Stop/Start system in GM vehicles
automatically turns off the engine when the vehicle
comes to a stop under certain driving conditions, and
can quickly restart the engine in about 0.3 seconds
when commanded to do so.
In order to smoothly restart the engine as quickly as
possible while managing the greater number of engine
starts, the Stop/Start system uses an enhanced starter
motor that operates differently from a conventional
starter motor. It has a high performance electric motor
and a stronger pinion engagement mechanism than a
conventional starter. It also has independent control of
the pinion and motor.
The enhanced starter motor continues using the typical
pinion engagement mechanism with a starter solenoid
that drives the pinion gear to engage or disengage the
flywheel of the engine. When engaged, the starter
motor can rotate the engine flywheel and, in turn, the
crankshaft.
On the enhanced starter of a Stop/Start system the
operation is done in two separate functions inside the
solenoid, Starter Motor and Pinion Actuator. Each
function controlled individually by the ECM. There are
two separate relays to control the two separate parts of
the enhanced solenoid:
•
KR27 Starter Motor Relay
•
KR27C Starter Pinion Actuator Relay
The two individually-controlled relays allow for smooth
engagement of the pinion gear into the flywheel with
minimum noise and wear.
When the vehicle is coming to a stop, just before the
engine stops rotating (at approximately 50 RPM) during
stop/start operation, the ECM energizes the Starter
Pinion Solenoid Actuator Relay to easily push the
pinion gear into the flywheel gear without gear clash.
(Fig. 8) When the engine stops rotating during Stop/
Start operation (Auto Stop mode), the starter pinion
gear is fully engaged, ready for the starter motor to
become energized to quickly start the engine again.
A secondary need for the starter pinion to be driven into
the flywheel gear before the engine stops rotating is to
address quickly changing demands on the engine. For
example, when a driver is slowing nearly to a stop
—
and the Stop/Start system is preparing for Auto Stop
mode
—
but suddenly decides to release the brake and
accelerate
In this situation, the engine has already stopped
rotating, or nearly so. A conventional starter cannot
restart the engine until the engine has completely
stopped. However, with the enhanced starter, the
starter pinion gear is fully engaged and ready to begin
rotating the engine even before it fully stops turning.
Otherwise, the engine would actually have to stop
rotating before the pinion can engage smoothly to begin
a restart.
To prevent a lag in engine operation, the ECM uses
predictive speed matching of the flywheel gear speed
and the pinion gear speed to engage the pinion gear
into the flywheel gear without gear clash before the
engine fully stops. By predicting how long it takes the
starter motor to spin up using an algorithm, the pinion
gear speed can be matched to the flywheel gear speed.
The result is an almost instant restart that is possible at
extremely low engine speeds.
Circuit Description
Keyless Start
When the Ignition mode switch is placed in the crank
position, a discrete signal is supplied to the body
control module (BCM) notifying it that the ignition is in
the crank position. The BCM then sends a serial data
message to the engine control module (ECM) that
crank has been requested. The ECM then verifies that
the clutch is fully depressed or the automatic
transmission is in Park/Neutral. If it is, the ECM then
supplies 12 V to the control circuit of the starter relay.
When this occurs, battery positive voltage is supplied
through the switch side of the crank relay to the S
terminal of the starter solenoid.
Key Start
When the ignition switch is placed in the Start position,
a discrete signal is supplied to the body control module
(BCM) notifying it that the ignition is in the Start
position. The BCM then sends a message to the engine
control module (ECM) notifying it that CRANK has been
requested. The ECM verifies that the transmission is in
Park or Neutral. If it is, the ECM then supplies 12 V to
the control circuit of the crank relay. When this occurs,
battery positive voltage is supplied through the switch
side of the crank relay to the S terminal of the starter
solenoid.
2021 - Silverado 4500HD, 5500HD, and 6500HD Electrical Body Builder Manual
