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

Model 205, 253 

Function requirements in general 

IMPORTANT Model 205, 253 (except 253.99)

The CDI control unit (N3/9) (diesel engine) or the ME-SFI control unit (N3/10) (gasoline engine) sends the signal "Engine running" via drive train CAN (CAN C1), drivetrain control unit (N127), chassis FlexRay (Flex E), electronic ignition lock control unit (N73) and interior CAN (CAN B) to the front SAM control unit (N10/6).

IMPORTANT The drivetrain control unit sends the "Drivetrain operational" signal over the suspension FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit.

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).

If lots of electrical consumers are operated simultaneously, overload situations may occur, which have to then be buffered by the on-board electrical system battery. If such an overload situation lasts for an extended period or if the charging capacity of the on-board electrical system battery is low, a negative charge/discharge ratio could arise. In such an instance, the mobility and the stable supply of all electrical consumers can no longer be assured.

Engine ON energy management increases during on-board electrical system overload

The energy management also reduces the comfort consumers to enable an equalized charge balance for the on-board electrical system battery to be achieved.

Energy management for driving encompasses the following subfunctions:

IMPORTANT Model 205.012/013/047/053/147/212/213/247/253, 253.311/353/354/911/953/954

To enable the "P" selector lever position to be engaged even when the on-board electrical system is overloaded, the electronic ignition lock control unit is also powered through the auxiliary battery of the ECO start/stop function (G1/13).

IMPORTANT Model 205 with transmission 722, 725

Model 253 with transmission 725

Model 253.99

To enable selector lever position "P" to also be engaged when the on-board electrical system is overloaded, the electronic ignition lock control unit is also supplied with voltage through the park pawl capacitor (C8).

Voltage provision 

The voltage provision function comprises the following subfunctions:

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).

The battery sensor 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. This is based on the calculation of the internal resistance. This, along with the battery capacity, is then used to compute the charge stored in the on-board electrical system battery. The front SAM control unit reads in the battery sensor data via the battery sensor LIN (LIN B15) and also measures the voltages at circuit 30 and circuit 30g (model 205 up to 31.05.2018, model 253 (except model 253.99) up to 31.05.2019) and/or circuit 30t (model 205 as of 01.06.2018, model 253 (except model 253.99) as of 01.06.2019, model 253.99).

The front SAM control unit uses the data to calculate the measure required to meet the given energy requirement:

Charge on-board electrical system battery 

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 optimum manner. Depending on different factors, the specified voltage is determined based on the following influencing variables:

After an engine start (except model 253.99) rapid charging initially takes place (except code U98 (LITHIUM ION STARTER BATTERY (LISB))) at a high voltage (U = 15 V), until a charge level for the on-board electrical system battery of 80 % is detected.

IMPORTANT Model 205, 253

except code U98 (LITHIUM-ION STARTER BATTERY (LISB)) Rapid charging occurs with a charging voltage of 15 V and can last from 20 s to 1 h. It is only following this step that a temperature-dependent characteristic or alternator management (except code B01 (48V technology)) is used.

The alternator management (except code B01 (48V technology) and except model 253.99) includes lowering the charging voltage to 12.8 V and a recuperation option in engine overrun mode. When the alternator management is active, one of the front doors is open and the vehicle speed is 0 km/h, the alternator management changes to the jump start mode. At the same time, the alternator voltage is increased constantly to 14.3 V. This jump-start is only canceled when the vehicle speed is greater than 0 km/h.

Hybrid vehicle: 

The on-board electrical system battery is charged using energy from the high-voltage on-board electrical system. To this end, the energy stored in the high-voltage battery (A100g1) is fed by the power electronics control unit to the 12 V on-board electrical system. On model 205.012/212 up to 01.03.2018, the alternator is also switched-in, if the energy provided by the power electronics control unit does not meet the given energy requirements.

Vehicle with code B01 (48V technology):

The on-board electrical system battery is charged using energy from the 48 V on-board electrical system. To this end, the energy stored in the 48 V on-board electrical system is fed by the DC/DC converter control unit to the 12-V on-board electrical system. The front SAM control unit sends information on the on-board electrical system capacity utilization over the interior CAN to the DC/DC converter control unit.

Model 253.99: 

The on-board electrical system battery is charged using energy from the high-voltage on-board electrical system. To this end, the energy stored in the high-voltage battery is fed by the DC/DC converter control unit into the 12 V on-board electrical system.

IMPORTANT Model 205, 253 (except 253.99)

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 recuperation. This emergency shutoff deactivates regenerative braking in cases of high voltage combined with low power consumption. If the on-board electrical system battery becomes 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%.

G15021994Courtesy of MERCEDES-BENZ USA

Voltage provision 

Rapid charging (except CODE U98 (LITHIUM ION STARTER BATTERY (LISB))): 

Temperature-based charging: 

Transition to alternator management (except code B01 (48V technology) and except model 253.99): 

Alternator management (except code B01 (48V technology) and except model 253.99): 

Transition to charging in overrun mode (except model 253.99): 

Charging in overrun mode (except model 253.99): 

Alternator regulation (except code B01 (48V technology) and except model 253.99) 

Alternator regulation (alternator management):

The alternator control actuates the alternator's power output. The CDI control unit or the ME-SFI control unit communicates with the alternator via the drive train LIN (LIN C1) and evaluates the alternator operating rate. The CDI control unit or the ME-SFI [ME] control unit sends information on alternator capacity over the drive train CAN, drivetrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit.

The state of the on-board electrical system battery is recorded by the battery sensor. The battery sensor sends corresponding parameters for the on-board electrical system battery over the battery sensor-LIN to the front SAM control unit. The front SAM control unit evaluates all of the relevant information and calculates the specified voltage required for the alternator. The front SAM control unit then sends this value to the CDI control unit or the ME-SFI control unit via interior CAN, electronic ignition lock control unit, chassis FlexRay, drivetrain control unit and drive train CAN. The CDI control unit or the ME-SFI [ME] control unit evaluates this, taking additional input factors (e.g. A/C ON) into consideration, and calculates the ideal specified voltage for the alternator. The CDI control unit or the ME-SFI [ME] control unit then calculates the alternator specified voltage via drive train LIN 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.

IMPORTANT Model 205.012/013/047/053/147/212/213/247/253, 253.311/353/354/911/953/954

The CDI control unit or the ME-SFI [ME] control unit sends the specified alternator voltage over the drive train CAN, drivetrain control unit and hybrid CAN (CAN L) to the power electronics control unit.

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. As soon as it becomes apparent that the on-board electrical system voltage is not high enough, the power management is gradually reduced. The alternator can then make its full output available.

The energy management in the CDI control unit or in the ME-SFI [ME] control unit adopts the alternator specified voltage values for the front SAM control unit as a guideline value only, because certain vehicle conditions, e.g. engine comfort, idle stability, engine start, irregular engine operation have to be taken into consideration. Therefore, the actual specified voltage of the alternator is obtained from the alternator specified voltages sent by the front SAM control unit, superimposed by power management corrections.

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

Dynamic idle speed control (except code B01 (48V technology) and except model 253.99) 

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. Idle speed increase is performed 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 communicates with the alternator via the drive train LIN and evaluates the alternator operating rate.

The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal and information on alternator capacity via drive train CAN, drivetrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the front SAM control unit.

The state, voltage and current of the on-board electrical system battery are detected by the battery sensor. The battery sensor sends corresponding parameters for the on-board electrical system battery over the battery sensor-LIN to the front SAM control unit. The front SAM control unit evaluates all relevant information and computes the energy required. If the energy requirement cannot be covered by the alternator management, the idle speed is increased. The maximum possible excitation current is calculated from the current excitation current and the alternator utilization. The maximum possible excitation current is used to calculate the maximum possible alternator current at different idle speeds. The front SAM control unit sends corresponding requests over the interior CAN, electronic ignition lock control unit, chassis FlexRay, drivetrain control unit and drive train CAN to the CDI control unit or the ME-SFI [ME] control unit, which then raises the idle speed accordingly.

IMPORTANT Model 205.012/013/047/053/147/212/213/247/253, 253.311/353/354/911/953/954

The CDI control unit or the ME-SFI [ME] control unit sends the specified alternator voltage over the drive train CAN, drivetrain control unit and hybrid CAN to the power electronics control unit.

The idle speed increase is reversed under the following circumstances:

Consumer reduction (deactivation of comfort functions) 

If the alternator (except code B01 (48V technology) and except model 253.99) or DC/DC converter control unit (with code B01 (48V technology) or model 253.99) can no longer provide the required electrical output, the on-board electrical system load is reduced by shifting down from 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 required electrical power to stabilize the on-board electrical system voltage is available again.

IMPORTANT Detailed information on evaluation of alternator operating rate can be found in the information "Alternator regulation".

When the on-board electrical system voltage drops to less than 12.2 V (except code U98 (LITHIUM-ION STARTER BATTERY (LISB))) or when the maximum discharge current is reached (with code U98 (LITHIUM-ION STARTER BATTERY (LISB))), the consumer reduction is activated. The first consumer's power consumption is reduced 20 s after engine start. If the cutback conditions remain unchanged, the power consumption of one further consumer will be reduced every following second.

IMPORTANT Model 205, 253

with code 299 (PRE-SAFE® system)

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. 2 s when the reversible emergency tensioning retractors are triggered in order to reduce the load on the on-board electrical system.

The front SAM control unit sends the request for power output limitation or to shutoff consumptions over the interior CAN to the corresponding control units that are connected to the interior CAN and over the interior CAN, electronic ignition lock control unit, suspension FlexRay, drivetrain control unit and the drive CAN to the CDI control unit or to the ME-SFI [ME] control unit.

The "De-icing" shut-off sequence (≤ 10 min) is included in the following table. A switch is then made to the "Comfort" shut-off sequence.

Sequence Shutoff stage Power-reduced or deactivated function Responsible control unit
1 1 PTC 1st branch, heat boosting (diesel engine) Climate control control unit (N22/1)
2 2 PTC 2nd branch, heat boosting (diesel engine) Climate control control unit (N22/1)
3 3 PTC 3rd branch, heat boosting (diesel engine) Climate control control unit (N22/1)
4 4 PTC 4th branch, heat boosting (diesel engine) Climate control control unit (N22/1)
5 5 PTC 5th branch, heat boosting (diesel engine) Climate control control unit (N22/1)
6 6 PTC 6th branch, heat boosting (diesel engine) Climate control control unit (N22/1)
7 7 Seat heater stage 3 (with CODE 401 (Seat climate control for driver and front passenger) or CODE 873 (Seat heater for driver and front passenger)) Rear SAM control unit (N10/8)
8 8 Seat heater stage 2 (with CODE 401 (Seat climate control for driver and front passenger) or CODE 873 (Seat heater for driver and front passenger)) Rear SAM control unit (N10/8)
9 10 Rear blower P = 50 % (with CODE 581 (Automatic air conditioning)) Climate control control unit (N22/1)
10 11 Blower in front P = 50% Climate control control unit (N22/1)
11 12 Fan P = 50% CDI control unit (N3/9) (diesel engine) or ME-SFI [ME] control unit (N3/10) (gasoline engine)
12 13 Trunk socket, cigarette lighter (with CODE 301 (Smoker package)) Front SAM control unit (N10/6)
13 14 Mirror heater Left front door control unit (N69/1) and right front door control unit (N69/2)
14 15 Spray nozzle hose heater (with CODE 875 (Heated windshield washer system)) Front SAM control unit (N10/6)
15 17 Rear window heater Rear SAM control unit (N10/8)
16 20 Seat heater stage 1 (with code 401 (Seat climate control for driver and front passenger) or code 873 (Seat heater for driver and front passenger)) Rear SAM control unit (N10/8)
17 20 Seat ventilation (with CODE 401 (Seat climate control for driver and front passenger)) Rear SAM control unit (N10/8)

The shutoff sequence "Comfort" is shown in the table below.

Sequence Shutoff stage Power-reduced or deactivated function Responsible control unit
1 1 PTC 1st branch, heat boosting (diesel engine) Climate control control unit (N22/1)
2 2 PTC 2nd branch, heat boosting (diesel engine) Climate control control unit (N22/1)
3 3 PTC 3rd branch, heat boosting (diesel engine) Climate control control unit (N22/1)
4 4 PTC 4th branch, heat boosting (diesel engine) Climate control control unit (N22/1)
5 5 PTC 5th branch, heat boosting (diesel engine) Climate control control unit (N22/1)
6 6 PTC 6th branch, heat boosting (diesel engine) Climate control control unit (N22/1)
7 9 Spray nozzle hose heater (with CODE 875 (Heated windshield washer system)) Front SAM control unit (N10/6)
8 10 Mirror heater Left front door control unit (N69/1) and right front door control unit (N69/2)
9 11 Seat heater stage 3 (with CODE 401 (Seat climate control for driver and front passenger) or CODE 873 (Seat heater for driver and front passenger)) Rear SAM control unit (N10/8)
10 12 Rear window heater Rear SAM control unit (N10/8)
11 14 Seat heater stage 2 (with CODE 401 (Seat climate control for driver and front passenger) or CODE 873 (Seat heater for driver and front passenger)) Rear SAM control unit (N10/8)
12 15 Rear blower P = 50 % (with CODE 581 (Automatic air conditioning)) Climate control control unit (N22/1)
13 16 Blower in front P = 50% Climate control control unit (N22/1)
14 17 Fan P = 50% CDI control unit (N3/9) (diesel engine) or ME-SFI [ME] control unit (N3/10) (gasoline engine)
15 18 Trunk socket, cigarette lighter (with CODE 301 (Smoker package)) Front SAM control unit (N10/6)
16 20 Seat heater stage 1 (with code 401 (Seat climate control for driver and front passenger) or code 873 (Seat heater for driver and front passenger)) Rear SAM control unit (N10/8)
17 20 Seat ventilation (with CODE 401 (Seat climate control for driver and front passenger)) Rear SAM control unit (N10/8)

If the on-board electrical system voltage has been stabilized to a value above 13.5 V, or if the permissible discharge current has been undershot, then the power output limitation or deactivation of consumers occurs in reverse order with a waiting time of 1s each time.

The on-board electrical system emergency mode represents a special case of consumer reduction. This is activated by the energy management in the front SAM control unit if the voltage of 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 10.6 V for longer than 10 s, the front SAM control unit activates the on-board electrical system emergency mode function.

This causes the activation of the following engine on energy management functions:

Unlike reducing the number of consumers, limiting the power output of or switching off consumers occurs with a cycle time of 200 ms.

As soon as the on-board electrical system voltage has stabilized to a value of 11.8 V for 10 s or a change in circuit status from circuit 15R to circuit 15C has occurred, the front SAM control unit ends the on-board electrical system emergency mode function. Consumer output limitation or deactivation is canceled.

  Electrical function schematic for alternator management Model 205, 253 (except 253.99) except code B01 (48V technology) PE54.10-P-2064-97FBA
  Electrical function schematic for dynamic idle speed increase Model 205, 253 (except 253.99) except code B01 (48V technology) PE54.10-P-2063-97FBA
  Electrical function schematic for comfort function shutoff   PE54.10-P-2076-97FBA
  Overview of energy management system components   GF54.10-P-9990RF 
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