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Engine On Energy Management, Function - GF54.10-P-1060GR

MODEL 166 up to model year 2016 

Function requirements, general 

IMPORTANT The CDI control unit (N3/9) (diesel engine) or the ME-SFI [ME] control unit (N3/10) (gasoline engine) sends the "Engine running" or "Drivetrain operational" status via chassis CAN 1 (CAN E1), the electronic ignition lock control unit (N73) and interior CAN (CAN B) to the SAM control unit (N10).

Engine on energy management, general 

Engine on energy management ensures the stability of the on-board electrical system as well as an even charge balance in the on-board electrical system battery (G1).

Given that the power output of the alternator (G2) is dependent on engine speed and temperature, plus the fact that many consumers are used simultaneously, overload situations can arise that need to be buffered by the on-board electrical system battery. If such a situation lasts for an extended period or if the charging capacity of the on-board electrical system battery is low, a negative charge balance may result that impairs the starting capability of the engine. In situations where the on-board electrical system is overloaded for prolonged periods, engine on energy management works to increase the power output of the alternator or to switch off comfort-related electrical consumers in order to balance the charge/discharge ratio of the on-board electrical system battery.

Energy management for driving encompasses the following subfunctions:

Function sequence for voltage provision 

The voltage provision function sequence encompasses the following:

Function sequence for determination of charge level of on-board electrical system battery 

The state of the on-board electrical system battery is recorded by the battery sensor (B95). This calculates corresponding parameters by means of voltage, current and temperature measurements on the on-board electrical system battery. The charge level of the on-board electrical system battery is the ratio of the current charge to the maximum storable charge. The basis for determining the charge level is the calculation of the internal resistance of the on-board electrical system battery.

Charge on-board electrical system battery function sequence 

Charging of the on-board electrical system battery requires that the specified voltage be determined. The specified voltage is the voltage that must be present at the terminals of the on-board electrical system battery in order to charge the on-board electrical system battery in an optimal manner. Depending on various factors, the specified voltage is determined using the alternator management or using the temperature-dependent charging characteristic including the quick charge function. After the engine is started, quick charging is performed first at high voltage until the charge level of the on-board electrical system battery is recognized as being sufficient.

IMPORTANT The rapid charging occurs with a charging voltage of U = 15 V and can last from t = 20 s to 1 h.

After this, the system changes over to temperature-guided charging or alternator management (as of T > 15 °C (up to 30.06.2012) or T > 10 °C (as of 01.07.2012)). Alternator management includes lowering of the charging voltage (to U = 12.6 V (up to 30.06.2012) or U = 12.7 V (as of 01.07.2012)) and the possibility of regenerative braking (energy recovery) when the engine is in deceleration mode.

When the alternator management is active, one of the front doors is open and the ground speed is v = 0 km/h, the alternator management changes to the jump start mode or the workshop mode. The alternator voltage is raised here constantly to U = 13.9 V. This external starting aid or workshop mode is not canceled until the speed is v > 0 km/h. An emergency shutoff is activated when driving down long hills in order to avoid overcharging of the on-board electrical system battery resulting from long periods of deceleration fuel shutoff. This emergency shutoff deactivates regenerative braking (energy recovery) in cases of high voltage combined with low power consumption.

If the on-board electrical system battery is fully charged (for example after driving in the cold or long downhill travel), the voltage is lowered further to return the battery to its optimum charge level of 80 %.

Fig 1: On-Board Electrical System Battery Voltage Graph
G10076685Courtesy of MERCEDES-BENZ USA

Quick charging:

Temperature-based charging:

Transition to alternator management:

Alternator management:

Transition to charging in deceleration mode:

Charging in deceleration mode:

Function sequence for alternator regulation (alternator management) 

Alternator regulation (alternator management):

The alternator control actuates the alternator's power output. The SAM control unit reads in the on-board electrical system battery parameters as provided by the battery sensor via battery sensor LIN (LIN B15) and calculates the required alternator specified voltage. The SAM control unit then sends this value via the interior CAN, electronic ignition lock control unit and chassis CAN 1 to the CDI control unit or to the ME-SFI control unit. The CDI control unit or the ME-SFI control unit evaluates this value taking additional input factors (e.g. air conditioning ON) into consideration and calculates the optimum specified voltage for the alternator. The CDI control unit or the ME-SFI [ME] control unit then calculates the alternator specified voltage over the drivetrain LIN (LIN C1) to the alternator, which then sets it. In addition, the CDI control unit or ME-SFI [ME] control unit checks the input factors for plausibility in order to rule out any overcharging or faulty charging of the on-board electrical system battery.

The CDI control unit or the ME-SFI control unit compares the optimum specified voltage for the alternator with the actual alternator power and is thus able to determine the energy state of the on-board electrical system. The continuous comparison of these two values and the corresponding corrections are designated as power management. The CDI control unit or the ME-SFI control unit sends information about the alternator operating rate via chassis CAN 1, the electronic ignition lock control unit and interior CAN to the SAM control unit.

As soon as it becomes apparent that the on-board electrical system voltage is too low, the power management function is gradually reduced. The alternator can then make its full output available.

The power management function in the CDI control unit or in the ME-SFI [ME] control unit adopts the alternator specified voltage values of the SAM control unit as guideline values only, because certain vehicle conditions, e.g. engine comfort, idle stability, engine start, irregular engine operation also have to be taken into consideration. The actual specified voltage of the alternator therefore results from the overlay of the power management function and the alternator specified voltage sent by the SAM control unit.

IMPORTANT If a fault is found in the battery sensor, the energy management function switches to a fixed voltage of U = 14.3 V. This behavior can also be activated using a diagnosis service in order to check the alternator, for example.

Function sequence for dynamic idle speed control 

Dynamic idle speed control sets the engine's idle speed such that no current needs to be drawn from the on-board electrical system battery when the vehicle is idling. The idle speed is increased for a higher consumer load. The idle speed is increased as a preventive measure. In other words, the system does not respond to a lack of electrical energy, but rather sets the required idle speed based on the present load.

The following factors are used for dynamic idle speed control computations:

The CDI control unit or the ME-SFI control unit sends the "Engine running" signal via chassis CAN 1, the electronic ignition lock control unit and interior CAN to the SAM control unit.

Information on condition, voltage and current is recorded by the battery sensor and it sends this over the battery sensor-LIN to the SAM control unit.

The rear SAM control unit reads and evaluates all relevant information and computes the required alternator current.

The maximum possible excitation current is calculated from the current excitation current and the alternator utilization. The maximum excitation current is used to calculate the maximum possible alternator current at different idle speeds.

The SAM control unit sends corresponding requests over the interior CAN, electronic ignition lock control unit and chassis CAN 1 to the CDI control unit or the ME-SFI [ME] control unit, which then raises the idle speed accordingly.

The idle speed is reversed under the following circumstances:

Function sequence for consumer reduction (deactivation of comfort functions) 

If the alternator can no longer provide the required electrical power, the load on the on-board electrical system is reduced by cutting back comfort functions. This serves to avoid any significantly negative charge balance for the on-board electrical system battery. This in turn retains the engine's starting capability. The comfort functions are reactivated when the alternator is again able to provide the required electrical power to stabilize the on-board electrical system voltage.

The function is activated when the on-board electrical system voltage drops below U = 12.2 V. The first consumer's power consumption is reduced at t = 20 s following engine start. If the cutback conditions remain unchanged, the power consumption of one further consumer will be reduced every following second.

IMPORTANT Consumer reduction in case of PRE-SAFE® deployment:

The front left reversible emergency tensioning retractor (A76) and the front right reversible emergency tensioning retractor (A76/1) have very high starting and operating currents. The power consumption of some high power consumers is therefore reduced or the consumers shut off altogether as quickly as possible for approx. t = 2s when the reversible emergency tensioning retractors are triggered in order to reduce the load on the on-board electrical system.

The SAM control unit sends corresponding requests via the interior CAN or via the interior CAN, electronic ignition lock control unit and chassis CAN 1 to the corresponding control units.

The shutoff sequence is shown in the table below.

Sequence Shutoff stage Consumers with reduced or no power Responsible control unit Maximum Currentin A
1 1 Heating level 6, heat boosting (engine 642.8, 651.9), passenger side (83 %) Automatic climate control control and operating unit (N22/7) 18.5
2 2 Heating level 5, heat boosting (engine 642.8, 651.9), driver side Automatic climate control control and operating unit (N22/7) 18.5
3 3 Heating level 4, heat boosting (engine 642.8, 651.9), passenger side Automatic climate control control and operating unit (N22/7) 18.5
4 4 Heating level 3, heat boosting (engine 642.8, 651.9), driver side Automatic climate control control and operating unit (N22/7) 18.5
5 5 Heating level 2, heat boosting (engine 642.8, 651.9), passenger side Automatic climate control control and operating unit (N22/7) 18.5
6 6 Heating level 1, heat boosting (engine 642.8, 651.9), driver side Automatic climate control control and operating unit (N22/7) 18.5
7 7 Seat heater stage 3 (with CODE 401 (Front comfort seats, incl. seat heating and seat ventilation) or with CODE 873 (Seat heater for left and right front seat)) Driver seat control unit (N32/1) and front passenger seat control unit (N32/2) 13.2
8 8 Seat heater stage 2 (with CODE 401 (Front comfort seats, incl. seat heating and seat ventilation) or with CODE 873 (Seat heater for left and right front seat)) Driver seat control unit (N32/1) and front passenger seat control unit (N32/2) 13.2
9 9 Wiper park heater Automatic climate control control and operating unit (N22/7) 15.0
10 10 Mirror heater Left front door control unit (N69/1) and right front door control unit (N69/2) 3.5
11 11 Steering wheel heater (with CODE 443 (Steering wheel heater)) Steering column tube module control unit (N80) 8.0
12 12 Rear window heater Automatic climate control control and operating unit (N22/7) 30.0
13 13 Rear blower (with CODE 581 (Comfort automatic air conditioning)) P = 50 % Automatic climate control control and operating unit (N22/7) 5.5
14 14 Blower in front P = 50% Automatic climate control control and operating unit (N22/7) 16.0
15 15 Fan P = 50% Automatic climate control control and operating unit (N22/7) 31.0
16 16 Sockets SAM control unit (N10) 6.0 - 8.0
17 18 Seat heater stage 1 (with CODE 401 (Front comfort seats, incl. seat heating and seat ventilation) or with CODE 873 (Seat heater for left and right front seat)) Driver seat control unit (N32/1) and front passenger seat control unit (N32/2) 3.3

When the on-board electrical system voltage has been stabilized to a value above U = 12.2 V, the comfort functions are switched on again in reverse order with a waiting time in each case of t = 1 s.

The on-board electrical system emergency mode represents a special case of consumer reduction. This is activated by the energy management if the on-board electrical system battery remains below a defined voltage threshold for a certain period of time.

The energy management uses all options available through dynamic power management to enforce a positive charge balance.

If the on-board electrical system voltage drops below U = 10.6 V for t ≥ 10 s, the SAM control unit activates the on-board electrical system emergency mode function.

The following functions are then activated:

Unlike normal consumer reduction, power reduction or consumer shutoff is done with a cycle time of t = 200 ms.

In addition to consumer reduction the following consumers are switched off:

As soon as the on-board electrical system voltage has stabilized for t ≥ 10 s at a value of U = 11.8 V or a change in circuit status from circuit 15R to circuit 15C has occurred, the SAM control unit ends the on-board electrical system emergency mode function.

The switched off or power reduced consumers are switched on again.

Function sequence for power supply over additional battery (except code B03 (ECO start/stop function)) or additional battery for ECO start/stop function (with CODE B03 ECO start/stop function)) 

To allow selector lever position "P" to be engaged even when the on-board electrical system is overloaded, the electronic ignition lock control unit is also supplied with power from the additional battery or the ECO start/stop function additional battery.

The capacity of the additional battery is 1.2 Ah, that of the additional battery for the ECO start/stop function is 12 Ah.

The power supply function over the additional battery encompasses the following subfunctions:

Determine function sequence of status of additional battery 

The SAM control unit runs a battery state recognition immediately after the engine is started. This provides information about the electrical power of the additional battery. If the engine is switched off during the battery state recognition, the SAM control unit switches this off and discards the previous results. In addition to battery state recognition, the voltage of the additional battery is continuously checked. To perform this check, charging must be stopped for t = 20 ms. The check is performed every t = 5 s.

IMPORTANT Battery state recognition can be started using the diagnostic tester. If voltage is not applied to the additional battery or if the additional battery is discharged or defective, the fault message "Backup battery fault" is shown in the multifunction display (A1p13) of the instrument cluster (A1). The SAM control unit transmits the data required for this to the instrument cluster over the interior CAN.

Function sequence of charge additional battery 

The additional battery is charged as required after battery state recognition when the engine is running. Charging of the additional battery is controlled by the SAM control unit.

  Electrical function schematic for alternator management   PE54.10-P-2064-97NAA
  Electrical function schematic for dynamic idle speed increase   PE54.10-P-2063-97NAA
  Electrical function schematic for comfort function shutoff   PE54.10-P-2076-97NAA
  Overview of energy management system components   GF54.10-P-9990GR 
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