Stop/Start System Description and Operation
Table 1: Autostop Enable Ambient
and Engine Coolant Temperature Table
The Stop/Start System is used to improve fuel efficiency in
stop/start driving. The vehicle automatically shuts down the engine
in appropriate conditions at a traffic light, for example,
resulting in zero tail pipe emissions and saving fuel which
otherwise is used idling the engine when stationary. The engine
instantly restarts when the driver is ready to move away.
As soon as the driver prepares to move away (depress the clutch
pedal), the engine starts quietly and almost instantly; it only
takes the system around 0.3 s to start the engine. The process is
near unnoticeable, and happens before gear selection is
completed.
To support the increased number of engine starts, the starter
motor is upgraded with a high performance electric motor and a
stronger pinion engagement mechanism with reduced noise levels.
Along with the upgraded starter motor, advanced battery
technology is required to ensure the vehicles battery can handle
the frequent charge and discharge cycles common with stop/start
operation. There is an intelligent battery sensor connected to the
battery which continually monitors the battery charge and healthy
state. The engine control module (ECM) uses this information from
the intelligent battery sensor to determine if the battery charge
and health is sufficient for an Stop/Start condition.
The Stop/Start system can reduce fuel consumption and carbon
dioxide (CO2) emissions by up to 5% in mixed driving conditions. In
an urban environment and in heavy traffic with frequent stops the
savings may increase to as much as 10%.
There are also sophisticated controls in place to help ensure
the Stop/Start System does not compromise the needs of either the
driver or vehicle. For the engine to shutdown, the vehicle must be
below 3 km/h (5 MPH), the manual transmission in neutral and the
clutch pedal fully released. To restart, the driver simply
depresses the clutch pedal and the enhanced starter motor engages
the engine, ready for when first gear is selected. When the engine
has been shut down by the Stop/Start System, the tachometer needle
will rest at the Autostop indicator icon (500 RPM point) indicating
the engine has been shut down by the Stop/Start System.
To ensure neither the needs of the driver or vehicle are
compromised the engine will not shut down in the following
circumstances:
| • |
Ambient and coolant
temperature correlation does not match specified values.
|
| • |
Ambient temperature is less
than -10°C (14°F) |
| • |
Battery temperature is less
than 0°C (32°F) or greater than 55°C (131°F)
|
| • |
Driver seat belt is not
fastened and the drivers door is not fully closed |
| • |
Clutch or accelerator pedal is
pressed |
| • |
HVAC system demand is
high |
| • |
HVAC defrost has been
selected |
Likewise the engine will automatically restart if:
| • |
Driver door opened and driver
seat belt unbuckled |
| • |
Vehicle speed increases
|
| • |
Brake booster vacuum has been
reduced |
| • |
Engine coolant temperature is
greater than 125°C (257°F) |
| • |
Economy mode turned OFF by
driver |
| • |
Autostop time exceeded 5
min |
When the Stop/Start System has shut down the engine, and the
ambient temperature is below 15°C (59°F), the ECM will
activate the Stop/Start auxiliary relay which controls the electric
engine coolant pump motor to continually circulate the engine
coolant through the engine while the engine is off. This is to
ensure the engine and passenger compartment temperature is
maintained while off. Once the Stop/Start System has restarted the
engine, the ECM will turn off the electric coolant pump motor, thus
allowing the engines internal coolant pump to circulate the engine
coolant. The Stop/Start System is automatically activated each time
the ignition switch is turned on, although there is an ECO Switch
on the instrument panel to disable the system, if the driver so
desires.
Autostop Criteria
The ECM will send an Autostop state message to the body control
module (BCM) and shut down the engine when all of the following
criteria is met. The BCM will transmit the Autostop state message
to the instrument cluster which will display the Autostop indicator
in the tachometer display.
| • |
Vehicle speed during drive
cycle was greater than 3 km/h (2 MPH) |
| • |
Ambient and engine coolant
temperature correlation meets specified values. |
| • |
Hood switch status is
closed |
| • |
Driver door status is
closed |
| • |
Driver seat belt status is
buckled |
| • |
Brake booster vacuum is
greater than 45 kPa (7 PSI) |
| • |
Clutch switch is fully
released |
| • |
Transmission neutral position
switch indicates neutral |
| • |
Vehicle speed is less than 5
km/h (3 MPH) |
| • |
Engine speed is below 1 500
RPM |
| • |
Engine coolant temperature is
less than 120°C (248°F) |
| • |
No A/C compressor request from
HVAC (A/C or Defrost modes) |
| • |
Battery voltage greater than
12 V |
| • |
Battery state of charge
greater than 75% (changes with state of health) |
| • |
Diesel particulate filter
regeneration is not active |
Autostop Enable Ambient and Engine Coolant Temperature
Table
Ambient Temperature
|
Coolant Temperature
|
Autostop Enable
|
less than -10°C (14°F)
|
max
|
No
|
-10°C (14°F)
|
60°C (140°F)
|
Yes
|
0°C (32°F)
|
50°C (122°F)
|
Yes
|
6°C (43°F)
|
40°C (104°F)
|
Yes
|
12°C (54°F)
|
30°C (86°F)
|
Yes
|
20°C (68°F)
|
18°C (64°F)
|
Yes
|
30°C (86°F)
|
18°C (64°F)
|
Yes
|
30°C (86°F)
|
18°C (64°F)
|
Yes
|
|
| |
Autostart Criteria
The ECM will send an Autostart state message to the BCM. If all
of the following conditions are true the ECM and BCM will restart
the vehicle.
Driver Enabled Conditions that will enable Autostart:
| • |
Transmission in neutral,
clutch partially or fully depressed |
| • |
If transmission is in gear,
clutch must be fully depressed in order for Autostart |
System Enabled Conditions that will enable Autostart as long as
transmission is not in gear
| • |
Brake booster vacuum is less
than 40 kPa (7 PSI) |
| • |
Vehicle speed is greater than
10 km/h (4 MPH) |
| • |
HVAC inside air temperature
changes than 3°C (5°F) (with HVAC Automatic) |
| • |
A/C compressor request from
HVAC (A/C or Defrost modes) |
| • |
Battery voltage less than 11
V, |
| • |
Battery state of charge is
less than 73% (changes with state of health) |
| • |
Diesel particulate filter
regeneration is requested |
| • |
Economy mode turned OFF
|
| • |
Driver door status changes to
open and driver seat belt status changes to unbuckled. |
| • |
Hood switch status changes to
open |
| • |
Autostop time exceeded 5
min |
If the crank time exceeds 2 s, a manual ignition switch restart
will be necessary.
System Components
Engine Control Module (ECM)
The engine control module (ECM) monitors the inputs from the engine
coolant temperature (ECT) sensor, vehicle speed sensor (VSS), hood
ajar switch, brake booster vacuum sensor, the clutch pedal position
sensor, the manual transmission neutral position switch and engine
speed to determine Autostart and Autostop conditions. The ECM also
controls the auxiliary coolant pump motor.
Engine Coolant Temperature sensor
The ECT sensor is used to determine engine operating temperature.
Intake Air Temperature Sensor
The ECM uses this sensor to monitor ambient air temperature. If too
cold, the Autostop will not occur.
Inside air temperature sensor
The HVAC control module monitors the passenger compartment
temperature sensor to determine the temperature inside the
passenger compartment. The HVAC control module sends this
temperature reading to the ECM on the data communication circuit.
The ECM uses this temperature values to determine if a restart is
requires based on the temperature inside the passenger compartment.
Vehicle speed sensor
The vehicle speed sensor is used to determine vehicle speed. If
vehicle speed is detected above a calculated value during an
Autostop condition, the ECM will start the engine.
Hood Ajar Switch
If the hood switch is in the open position, the vehicle will not
Autostop. If the hood is opened during Autostop, the vehicle will
automatically restart.
Brake Booster Vacuum Sensor
The ECM monitors vacuum in order to ensure proper power assist for
the brake pedal. If the ECM determines vacuum is too low, it will
restart the engine.
Clutch Pedal Position Sensor
The ECM monitors the clutch pedal position sensor for partial and
fully depressed conditions. A partially depressed clutch pedal will
cause the ECM to restart the engine during an Autostop condition if
the transmission is in the Neutral position If the transmission is
determined to be in gear, the ECM will not restart the engine until
the clutch pedal is fully depressed.
Neutral Position Switch
The manual transmission neutral position switch is used to
determine if the transmission is in gear. The ECM will not allow
Autostop until the clutch is engaged, the transmission is in the
neutral position and then the clutch is fully disengaged.
Coolant Pump Motor
The ECM will turn on the auxiliary coolant pump motor during
Autostop to maintain engine operating temperature and also maintain
HVAC temperature. Once the engine is running, the ECM will turn off
the coolant pump motor.
Body Control Module (BCM)
The body control module (BCM) monitors the ECO switch in order to
enable or disable the system. It is also the master of the low
speed communication bus and transfers the appropriate messages to
the instrument cluster and the HVAC.
Intelligent Battery Sensor
The BCM monitors the intelligent battery sensor for battery state
of current, state of health, and battery charge via the data
communication bus. If the battery is determined to be in poor state
of health or having a low charge, the BCM will not allow the ECM to
Autostop.
ECO Switch
The ECO switch can disable the Autostart system if desired.
DC to DC Converter
The DC to DC converter monitors battery voltage during Autostop and
will maintain operating voltage to the radio, instrument cluster
and instrument panel displays. Battery voltage will drop slightly
during Autostop and the DC to DC converter will maintain a constant
voltage to ensure proper operation of the driver informational
displays.
Driver Door Switch
The BCM monitors the driver door switch at all times. The BCM will
not allow Autostop if the door is ajar and will Autostart if the
driver door is opened and the seat belt unbuckled during Autostop.
Driver Seat Belt Switch
The BCM monitors the driver seat belt switch at all times. The BCM
will Autostart if the seat belt is unbuckled and the driver door
opened during Autostop.
Instrument Cluster
In order to differentiate between a normal engine shut down (engine
speed 0 RPM) and when the engine has been shut down by the
Stop/Start System, the tachometer needle will rest at the Autostop
indicator icon (500 RPM point) indicating the engine has been shut
down by the Stop/Start System. Once the engine is restarted, or the
ECO button has disengaged Autostop, the tachometer will function
normally.
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