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Engine on energy management, function - GF54.10-P-1060RF

Model 205, 253 

Function requirements, general 

IMPORTANT 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), powertrain 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).

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. If an on-board electrical system overload persists, the engine ON energy management boosts the power output of the alternator (G2) or the energy transfer from the high voltage on-board electrical system through the power electronics control unit (N129/1) (model 205.012/047/147/212/247). 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:

Function sequence for voltage provision 

The voltage provision function comprises the following subfunctions:

Function sequence for determining charge level 

The condition of the on-board electrical system battery is recorded by the battery sensor (B95) (except CODE U98 (LITHIUM ION STARTER BATTERY (LISB))) or by the electronic circuit in the on-board electrical system battery (with CODE U98 (LITHIUM ION STARTER BATTERY (LISB))).

The battery sensor or the electronic circuit in the on-board electrical system battery calculates corresponding parameters on the 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 data from the battery sensor or the electronic circuit in the on-board electrical system battery over the battery sensor LIN (LIN B15) and also measures the voltages on circuit 30 and circuit 30g and calculates the specified voltage of the alternator required for providing the requested energy or the required energy transfer from the high-voltage on-board electrical system over the power electronics control unit.

Function sequence for charging 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 the various factors involved, the specified voltage is determined on the basis of the alternator management or the energy transfer required from the high-voltage on-board electrical system over the power electronics control unit or based on the temperature-dependent charging characteristics incl. rapid charging function (except CODE U98 (LITHIUM ION STARTER BATTERY (LISB))). After starting the engine, rapid charging at high voltage is conducted (except CODE U98 (LITHIUM ION STARTER BATTERY (LISB))), until a sufficiently high charge level on the on-board electrical system battery is detected.

The on-board electrical system battery in model 205.012/047/147/212/247 is mainly 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. If the energy made available by the power electronics control unit does not meet the existing energy requirements, the alternator will be switched on for support.

IMPORTANT Model 205 except code U98 (LITHIUM-IONEN-STARTERBATTERIE (LISB)) The rapid charging occurs with a charging voltage of U = 15 V and can last from t = 20 s to 1 h. Only following this, a temperature-dependent characteristic or the alternator management function is used.

IMPORTANT The alternator management includes lowering the charging voltage (U = 12.7 V) and the regenerative braking option in the engine's decel 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. At the same time, the alternator voltage is increased constantly to U = 14.3 V. This jump-start is only canceled when the vehicle 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 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%.

Fig 1: On-Board Electrical System Battery Voltage Versus Time Graph
G10133627Courtesy of MERCEDES-BENZ USA

Voltage provision 

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

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 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 over 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, powertrain 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 or by the electronics in the on-board electrical system battery. The battery sensor or the electronic circuit in the on-board electrical system battery sends corresponding parameters of the on-board electrical system battery to the front SAM control unit over the battery sensor LIN. 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, powertrain 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 205.012/047/147/212/247

The CDI control unit or the ME-SFI [ME] control unit sends the specified alternator voltage over the drive train CAN, powertrain 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. The actual specified voltage of the alternator is therefore obtained by taking both the specified voltages sent by the front SAM control and that of the energy management into account.

IMPORTANT If a fault is found in the battery sensor or in the electronics circuit of the on-board electrical system battery, the energy management 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. 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, powertrain 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 is recorded by the battery sensor or by the electronics circuit in the on-board electrical system battery. The battery sensor or the electronic circuit in the on-board electrical system battery sends corresponding parameters of the on-board electrical system battery to the front SAM control unit over the battery sensor LIN. The front SAM control unit evaluates all relevant information and computes the energy required. If the energy required is more than what the alternator can supply, idle speed increase takes effect. 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, powertrain 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 205.012/047/147/212/247

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

The idle speed increase is reversed under the following circumstances:

Function sequence for consumer reduction (deactivation of convenience 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 required electrical power to stabilize the on-board electrical system voltage is available again.

IMPORTANT Detailed information on evaluation of alternator operating rate is available in the section "Alternator regulation".

When the on-board electrical system voltage drops to less than U = 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 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 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. t = 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 reducing output or shutoff of consumers via to the control units that are connected to interior CAN and to the CDI control unit or the ME-SFI control unit via interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN.

The "De-icing" shut-off sequence (t ≤ 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 (engine 626, 651) Climate control unit (N22/1)
2 2 PTC 2nd branch, heat boosting (engine 626, 651) Climate control unit (N22/1)
3 3 PTC 3rd branch, heat boosting (engine 626, 651) Climate control unit (N22/1)
4 4 PTC 4th branch, heat boosting (engine 626, 651) Climate control unit (N22/1)
5 5 PTC 5th branch, heat boosting (engine 626, 651) Climate control unit (N22/1)
6 6 PTC 6th branch, heat boosting (engine 626, 651) Climate 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 unit (N22/1)
10 11 Blower in front P = 50% Climate control unit (N22/1)
11 12 Fan P = 50% CDI control unit (N3/9) (diesel engine) or ME-SFI 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 (engine 626, 651) Climate control unit (N22/1)
2 2 PTC 2nd branch, heat boosting (engine 626, 651) Climate control unit (N22/1)
3 3 PTC 3rd branch, heat boosting (engine 626, 651) Climate control unit (N22/1)
4 4 PTC 4th branch, heat boosting (engine 626, 651) Climate control unit (N22/1)
5 5 PTC 5th branch, heat boosting (engine 626, 651) Climate control unit (N22/1)
6 6 PTC 6th branch, heat boosting (engine 626, 651) Climate 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 unit (N22/1)
13 16 Blower in front P = 50% Climate control unit (N22/1)
14 17 Fan P = 50% CDI control unit (N3/9) (diesel engine) or ME-SFI 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)

When the on-board electrical system voltage has been stabilized to a value above U = 13.5 V or when the permissible discharge current is undershot, reducing output or shutoff of consumers is revoked in the reverse order with a waiting time between each of t = 1s.

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 U = 10.6 V for t ≥ 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 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 front SAM control unit ends the on-board electrical system emergency mode function. The power reduction or consumer shutoff is canceled.

Function sequence for power supply over additional battery for ECO start/stop function (model 205.012/047/147/212/247) or over park pawl capacitor (transmission 722, 725) 

To enable the selector lever position "P" to still be engaged even when the on-board electrical system is overloaded, the electronic ignition lock control unit is also powered through the additional battery for the ECO start/stop function (model 205.012/047/147/212/247) or through the park pawl capacitor (transmission 722, 725).

  Electrical function schematic for alternator management   PE54.10-P-2064-97FBA
  Electrical function schematic for dynamic idle speed increase   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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