ECO Start/Stop Function Engine Management, Function - GF07.10-D-1042TSA

Engine 651 in model 907 with code MJ8 (ECO start/stop function) 

Block diagram 

The ECO start/stop function is subdivided into the engine-side and the on-board network side scope. The "Engine management, start/stop function" subfunction is examined from the point of view of the engine management.

Function requirements for engine management, start/stop function, general points 

• Engine running.
• No overvoltage or undervoltage
• Outside temperature in the range -10 to 40 °C
• Speed of 8 km/h exceeded once during forward travel
• Engine hood closed
• System diagnosis complete and fault-free
• No Crash event occurred in the driving cycle

Engine management start-stop function, general 

For a stationary vehicle, the ECO start/stop function switches the engine off automatically and starts it again, as soon as the driver wishes to drive off. The fuel consumption and thus the exhaust emissions are reduced by cutting out the engine with the vehicle at a standstill.

The CDI control unit (N3/28) continuously performs a system diagnosis and assesses the system conditions for the ECO start/stop function.

It is still possible to stop and start the engine on request by the driver in the conventional way.

All of the systems participating in the ECO start/stop function constantly check their status and send this to the powertrain control unit (N127) and via the drive CAN (CAN C) to the CDI control unit.

The SAM control unit (N10) checks the function of all the components involved and sends the status via the interior CAN (CAN B), electronic ignition lock (EZS) control unit (N73/8), suspension FlexRay (Flex E), powertrain control unit, and via the drive CAN to the CDI control unit. If the function requirements are fulfilled, the driver is notified of the ECO start/stop function readiness by the "ECO" symbol in the instrument cluster (A1).

Engine management Start-Stop function, function sequence 

The ECO start/stop function consists of the following partial functions:

• Function sequence for automatic engine stop
• Function sequence for automatic engine start
• Function sequence for forced engine start (a start dictated by the system)

Function sequence for automatic engine stop 

The engine is switched off by the CDI control unit if all of the following function requirements are fulfilled:

• Vehicle speed = 0 km/h (for an automatic transmission)
• Vehicle speed ≤ 8 km/h (for a manual transmission)
• Coolant temperature between 60 °C and 115 °C
• Transmission oil temperature between 10 °C and 120 °C
• Engine RPM in specified value range
• Gear range "D" or "N" (for a automatic transmission)
• Transmission in neutral (for a manual transmission)
• Accelerator not operated
• Service brake actuated up to vehicle stillstand (for an automatic transmission).
• Service brake actuated (for a manual transmission)
• Adequate vacuum in the brake booster
• Engine hood closed
• No crash signal
• Steering wheel angular velocity in the specified value range
• Condition of the on-board electrical system OK
• Driver door closed
• Driver seat belt applied
• Interior temperature regulated

The CDI control unit reads in the following signals for fulfilling the function requirements:

• Coolant temperature sensor, coolant temperature
• Crankshaft position sensor, engine speed
• Accelerator pedal module, accelerator pedal operation via the powertrain control unit and drive CAN
• Position sensor for transmission neutral position (for manual transmission) via the powertrain control unit and drive CAN
• Clutch travel sensor (manual transmission with code MJ8 (ECO start/stop function)) via the powertrain control unit and drive CAN
• Instrument cluster, vehicle speed via user interface CAN (CAN-HMI), electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN
• Supplemental Restraint System control unit (SRS), direct crash signal
• Supplemental Restraint System control unit (SRS) via user interface CAN, EZS control unit, chassis FlexRay, powertrain control unit and drive train CAN:
  • Indirect crash signal
  • Status of driver seat belt
• Control and operating unit for automatic climate control, air conditioning status via the interior CAN, EZS control unit, suspension FlexRay, powertrain control unit, and via the drive CAN:
  • Engine stop prohibition
  • Engine start request
• EZS control unit, chassis FlexRay, powertrain control unit and drive train CAN
• Signal that engine hood is closed
• ESP® control unit via suspension FlexRay, powertrain control unit, and drive CAN:
  • Brake vacuum sensor
  • Brake actuation
  • Wheel speed
  • Engine start request
  • Engine stop release
  • Engine stop prohibition
• Parking system control unit (with code JB6 (Parking Package with 360° camera)), engine torque request (increase or decrease) via suspension FlexRay, powertrain control unit, and drive CAN
• Steering column tube module (MRM) control unit, steering wheel angle, and steering wheel angular velocity via suspension FlexRay, powertrain control unit, and drive CAN
• Duel system control unit, fuel pressure via the drive train CAN
• Fully integrated transmission control (VGS) electric controller unit (N15/11) (with code G42 (7G-TRONIC PLUS)), drive range status via drive CAN

After an automatic engine stop a maximum of three automatic engine stops are permitted without exceeding the speed threshold of 8 km/h.

After the fourth engine start, the vehicle must exceed a speed of 8 km/h for the engine to be stopped again.

Upon opening the engine hood in automatic engine stop, the ECO start/stop function is switched off and all indicator symbols in the instrument cluster light up. The engine must be restarted using the start/stop button (S2/2).

Function sequence for automatic engine start 

With a manual transmission, the engine is automatically started upon actuating the acceleration or clutch pedal. For an A/T the engine is automatically started upon releasing the brake or actuating the accelerator pedal.

The CDI control unit actuates the circuit 50 starter relay (F152kC) with a ground signal. The power contact of the relay closes and the solenoid switch of the starter is supplied to "circuit 50" with voltage from "circuit 30".

Via the drive CAN, the fuel pump control unit receives the "fuel specified pressure" signal from the CDI control unit and actuates the fuel pump with the fill level sensor (M3/6) accordingly.

• Vehicle speed > 2 km/h in forward travel and immediately upon recognition of rolling backwards (for an automatic transmission)
• Vehicle speed > 8 km/h in forward travel and for reverse travel (for a manual transmission)
• System or communication error of the following systems:
  • Presence of driver
  • Steering
  • On-board electrical system
  • Brake and management systems
  • Accelerator pedal
  • Transmission
  • Starter
  • Motor

Function sequence for forced engine start (a start dictated by the system) 

The forced engine start subfunction is available as a protection function. Here, the engine is force started autonomously (without any action taken by the driver) by the CDI control unit if one of the following function requirements occurs:

• on-board network status required
• Coolant temperature >115 °C
• Exceeding the engine stop period of a maximum 3 min
• Air conditioning system requires engine running (e.g. windows fogged up).
• Vacuum at brake booster not in the specified range (residual pressure in brake booster falls below -200 mbar)
• Driver presence recognition (driver seat belt or driver's door is opened).
• Change of the steering wheel angle by more than 8°

A maneuvering process is recognized for an engaged reverse gear and the ECO start/stop function is deactivated. If the engine is stopped it is force started by the system and the engine stop function is suppressed if it is running.

The ECO start/stop function is subsequently activated again for an engaged forward gear and for exceeding a vehicle speed 15 km/h.

The engine is also started if the driver door is opened, the driver seat belt buckle is opened or the ECO start/stop function is switched off via the ECO start/stop function button.

Electrical function schematic for engine management, ECO start/stop function	PE07.10-D-2724-97TSA
Overview of system components for common rail diesel injection (CDI)	GF07.16-D-9997TSA