Engine Stop Start System

The Engine Stop Start (ESS) system automatically stops and starts the engine when certain conditions are met to improve fuel economy and lower Carbon Dioxide (CO2) emissions.

The primary input for an automatic transmission vehicle to gain an autostop is zero vehicle speed with the brake pedal depressed, while the primary input to autostarting is release of the brake pedal. Many secondary inputs determine if it is acceptable to autostop and autostart. A number of devices on the vehicle are added or improved to support the ESS function.

• Automatic Transmission 

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  • New thermal management system for maintaining optimum operating temperature
  • Vehicle launch control coordination with engine and brake system
  • The Transmission Control Module (TCM) receives pseudo drive neutral gear (D6) requests during ESS events. The D6 neutral gear will be needed if the TCM resets due to deep voltage drops during engine cranking. The driveline should be closed because tclutchtch is normally opened. The ESS system waits for confirmation of the neutral gear engagement from the TCM prior to performing the ESS start event. The confirmation D6 neutral signal broadcasts on the Controller Area Network (CAN)-C bus.
• Batteries - Supplemental Battery and Cranking Battery 

  - During cranking, both batteries work together to provide a starter load. During a stop/start event, the two batteries work separately:

  • The smaller supplemental battery supports the vehicle ignition off electrical load.
  • The larger cranking battery supports the start events.
• Body Control Module (BCM) 

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  • A modified BCM for communications and starter control.
• Door Ajar Switch 

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  • The driver door ajar switch for ESS vehicles has two diagnostic resistors installed in the latch assembly circuit. This resistor allows the BCM to detect an open or shorted condition in the circuit.
• Dual Battery Control and Power Relay  -
  • The Dual Battery Control Relay (DBCR) and Power Control Relay (PCR) are placed in between the cranking battery and supplemental battery.
  • For automatic cranking, the dual battery relay will close when the controller receives ESS indications that the vehicle will be starting soon. This will cause the power control relay to open the contact.
  • The DBCR will be closed for a calibrated time or until the engine Revolutions Per Minute (RPM) reach a calibrated limit. Once either of these calibrated limits are reached, the DBCR will open again causing the PCR to close the contact.
• Engine 

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  • Lubrication system and wear components to manage increased stop and start frequency.
  • In order to protect the engine against damage caused by inadvertently sparking a cylinder following a rollback condition due to an ESS event, the Powertrain Control Module (PCM) effectively turns off the fuel and spark drivers below a calibrated Revolution Per Minute (RPM) limit.
  • A Bi-directional crank sensor is used to remember the stop engine position for faster restarts.
• ESS Disable Switch located on the Integrated Center Stack (ICS) 

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  • A hard switch is located in the center stack switch bank.
    NOTE:

    When the ESS system is deactivated (OFF) the LED in the button will be illuminated.

  • The ESS switch generates a signal that is transmitted to the BCM.
• Engine Mounts 

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  • Optimized for Noise, Vibration, Harshness (NVH) given increased engine stop and start frequency.
• Electronic Stability Controls (ESC) 

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  • Provides brake controls using Hill Start Assist (HSA) during autostart and transmission engagement transition to prevent vehicle movement while in an autostop condition during the transition from brake pedal to accelerator pedal. Brakes to be released commensurate with torque request and torque capacity
  • Ensure module compatibility with cranking during HSA function (voltage drop, etc.)
  • For non HSA vehicles, the brake hold feature prevents the vehicle from lurching forward during a restart when the vehicle is on a grade. The ESC holds the brake pressure when the system has determined that the vehicle is at a stand still. Once the vehicle engine is running and the accelerator pedal has been applied, the pressure is released. The brake pressure is then ramped out as quickly as possible.
  NOTE:

  When the ESC system is deactivated (OFF) the Light Emitting Diode (LED) light in the button will be illuminated.

• Flywheel / Drive Plate 

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  • Revised ring gear with chamfered, hardened gear teeth to improve starter pinion engagement and reduced gear tooth wear
• Generator 

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  • Higher output alternator to provide greater charging capacity immediately following autostarts. The generator slowly ramps up its duty cycle enough as to prevent flickering of the cluster lights and to allow for working vehicle driveability.
  • No requirement for voltage regulation on ESS systems.
• Hood Switch 

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  • The hood switch diagnostics compares the state of two hood open switches. In the event that there is disagreement between the states of the two switches, the logic concludes that one of the switches has failed. Because this type of diagnostic cannot determine which switch as failed (and therefore the true state of the hood), it is assumed that the vehicle is in an unsafe state for ESS and the limp home actions will be taken.
  • The secondary hood switch is wired to the PCM.
• Heating Ventilation and Air Conditioning (HVAC) Control Unit and Controls 

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  • Added control features to provide interior climate management.
  • Fan speed control adjusted during autostop.
  • Autostop inhibit and autostart request based on combination of interior temperature, sun loading and variation from temperature set point and/or ambient temperature. This may inhibit some autostops or reduce autostop duration.
• Intelligent Battery Sensor (IBS)  - The IBS is responsible for measuring the state-of-charge. It will also predict voltage and capacity (ah) for future crank events. The IBS is also responsible for measuring battery temperature and alternator voltage current.
• Instrument Panel Cluster (IPC) 

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  • Revised instrument cluster with stop-start specific graphics and IPC messaging.
• PCM: 
  • Circuit board population for added inputs and outputs.
  • Stop-start coordinator added to manage all autostop and autostart activity.
  • Impact on torque, security, On Board Diagnostics (OBD) and end of line diagnostics.
• Radio 

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  • Added stop-start specific messaging and menu selections.
• Starter (High Durability): 
  • Enhanced starter with increased life brushes, needle bearings, pre-loaded pinion gear spring and other changes to enhance longevity and improve NVH
  • Starter power increased to compensate for brush losses and to increase cranking speed
  • A Dual Battery Control and Power Relay Control is required to achieve minimum system voltage drop requirements of critical modules and devices and autostop duration and frequency objectives. It is located on a bracket attached to the lower front of the engine, below the Air Conditioning (A/C) compressor.

The Battery, Starting, and Charging systems operate in conjunction with one another, and must be tested as a complete system. For correct operation of starting/charging systems, all components used in these 3 systems must perform within proper specifications. When attempting to diagnose any of these systems, it is important that you keep their interdependency in mind.

The diagnostic procedures used in each of these sections include the most basic conventional diagnostic methods, to the more sophisticated OBD built into the PCM. Use of an induction-type milliampere ammeter, volt/ohmmeter, battery charger, carbon pile rheostat (load tester), and 12-volt test lamp may be required.

Certain starting system components are monitored by the PCM and may produce a Diagnostic Trouble Code (DTC).

How does the

ESS system function 

- simple overview:

• ESS shuts the engine off when the vehicle stops
• The vehicle has to be stopped for a pre-set time before the engine is switched off
• Then, it restarts when the driver releases the brake to move the vehicle
• The system senses brake pedal position and vehicle speed to determine that the vehicle is moving
• Powertrain calibration makes the decision when to shut off the engine and when to restart the engine again
• The ESS function is transparent to the driver
• When the engine stops, a smaller secondary battery keeps accessory features powered, like the fan, wipers, headlights, audio system, etc.
• A Dual Battery Control and Power Relay Control are used to smooth out voltage dips when the starter cranks the engine

Primary Autostop Enablers  - Brake pedal depressed (automatic transmission).

Secondary Autostop Enablers  - Vehicle speed, coolant temperature, hood closed, doors closed, driver's seat belt latched, interior climate and settings, battery state and energy demand, steering wheel angle, steering wheel torque, ambient temperature, time and speed since last autostop, transfer case position, and ESC status, No stop-start related faults present.

Autostop Events 

• Autostop state broadcast on CAN bus.
• Cluster telltale illuminates.
• Engine shutdown begins.

As the engine slows it passes through three phases:

• Fuel and spark restart permissible.
• Restart prohibited.
• Restart permitted, based on start system employed.

Autostart requests are evaluated throughout the autostop event.

When in autostop: 

• Instrument cluster stop/start telltale remains illuminated.
• IPC displays the autostop state message.
• Body controller starter relay is energized providing the engine controller with direct starter control.

Vehicle Function: 

• Consumer electronics continue to function in a normal manner.
• HVAC fan speed and other setting adjusted to maximize cabin comfort and autostop duration (based on climate control settings and conditions).
• Electric Power Steering (EPS) maintained during autostop, possibly with reduced maximum assist.

System Requested Autostarts: 

• Battery State.
• Brake Vacuum.
• Climate control stress.
• Vehicle speed.
• Steering wheel angle or torque.
• Transmission selector position.

ESS Disable (while autostopped) 

• Vehicle systems monitored that may disable stop-start (requiring a key restart if in autostop) include: hood opened, occupant sensing indicating driver not present, unsafe gear shift position for autostart and critical system faults.

Autostart Decision: 

• All autostart enablers present.
• Brake pedal released or shifter place in reverse (automatic transmissions).
• Throttle pedal depressed.

Autostart Events: 

• Autostart state broadcasts on the CAN bus.
• IPC ESS telltale illumination cancelled.
• IPC display changed to previous IPC message (outside temp and compass, etc).
• Hill Assist requested.
• Starter relay commanded to initiate cranking.
• Engine achieves idle speed.

Launch Events: 

• Automatic transmission clutches engaged.
• Hill assist released.
• Climate control returned to pre-autostop conditions.
• ESS Ready state broadcast on the CAN bus.
• Embedded IPC stop-start message indicating "Stop/Start Ready".

IPC Pop Up Messages Displayed on the EVIC 

- IPC message states Stop/Start Autostop Active 

• No Chime.
• Normal Use.
• Pop-up maintained for 5 seconds.
• Displays with green hard telltale.

Stop/Start To Restart Press 

• Single Chime.
• Pop up maintained for 5 seconds.

Stop/Start Restart Required Fault Detected 

• Single chime.
• Malfunction Indicator Lamp (MIL) or ESS system fault preventing safe state confirmation during autostop.

IPC Pop Up Messages Displayed within IPC "Ring" menu 

Stop/Start Ready 

• ESS conditions met to enable engine stop.

Stop/Start Off 

• ESS turned off by the customer at the switch.

Stop/Start Not Ready 

• ESS conditions are not met to enable engine stop (ex: HVAC settings, engine temperature, etc).

Stop/Start Not Ready Steering Wheel Turned 

• ESS condition not met with steering wheel turned past calibrated angle.