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

MODEL 207.3/4 as of model year 2014 

Function requirements, general 

IMPORTANT The CDI control unit (N3/9) (with diesel engine) or the ME-SFI [ME] control unit (N3/10) (with gasoline engine) sends the "Engine running" or "Drivetrain operational" signal via chassis CAN 1 (CAN E1), front SAM control unit with fuse and relay module (N10/1) and interior CAN (CAN B) to the rear SAM control unit with fuse and relay module (N10/2).

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 the variable power output of the alternator (G2) and 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 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 may result that could impair the engine's starting capability. 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 comprises the following subfunctions:

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 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 of the on-board electrical system battery. This value can be used to determine the acid density of the on-board electrical system battery. This, along with the battery capacity, is then used to compute the charge stored in the on-board electrical system battery. The rear SAM control unit reads the computed data from the battery sensor via the on-board electrical system LIN (LIN B7), while also measuring the voltages at circuit 30 and circuit 30g, and computes the alternator voltage required to provide the energy requested by consumers.

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 optimum manner. Depending on various factors, the specified voltage is determined using the alternator management or using the temperature-dependent charging characteristic incl. 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, a temperature-dependent characteristic or the alternator management function (T batt > 10°C) is used.

The alternator management contains lowering charging voltage (U = 12.7 V) and the regenerative (energy management) 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 or the workshop mode. At the same time, the alternator voltage is increased constantly to U = 14.3 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 Pulse Graph>
G10081753Courtesy 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 rear SAM control unit reads-in the on-board electrical system battery parameters as provided by the battery sensor over the on-board electrical system LIN and calculates the required alternator specified voltage. The rear SAM control unit then sends this value via the interior CAN, front SAM control unit and chassis CAN 1 to the CDI control unit or the ME-SFI [ME] control unit. 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 control unit then requests the calculated specified voltage via the drivetrain LIN (LIN C1) at the alternator; the alternator then sets this voltage. 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. A continuous comparison of these two values and the corresponding corrections are designated as energy management. The CDI control unit or the ME-SFI control unit sends information about the alternator operating rate to the rear SAM control unit via chassis CAN 1, the front SAM control unit and interior CAN. 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 power management function in the CDI control unit or in the ME-SFI control unit adopts the alternator specified voltage values for the rear SAM control unit as a guideline value only because certain vehicle conditions (e.g. engine comfort, idle stability, engine start and 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 rear SAM control and that of the energy management into account.

IMPORTANT If a fault is found in the battery sensor, 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. 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 and information about the alternator operating rate to the rear SAM control unit via chassis CAN 1, the front SAM control unit and interior CAN.

Information on condition, voltage and current of the on-board electrical system battery is recorded by the battery sensor. The battery sensor sends this information to the rear SAM control unit via the on-board electrical system LIN.

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. Corresponding information is read in by the CDI control unit or the ME-SFI control unit via the drivetrain LIN. The maximum possible excitation current is used to calculate the maximum possible alternator current at different idle speeds. The rear SAM control unit sends corresponding requests via the interior CAN, front SAM 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 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.

The function for cutting back comfort functions 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 rear SAM control unit sends the request for power reduction or shutoff via the interior CAN to the corresponding control units. The shutoff sequence is shown in the table below.

Shutoff step Shutoff stage Power-reduced or deactivated function Executing control unit Maximum current in A
1 1 Heating level 6, heat boosting (with engine 642.8, 651.9), passenger side Automatic climate control and operating unit (N22/7) 18.5
2 2 Heating level 5, heat boosting (with engine 642.8, 651.9), driver side Automatic climate control and operating unit (N22/7) 18.5
3 3 Heating level 4, heat boosting (with engine 642.8, 651.9), passenger side Automatic climate control and operating unit (N22/7) 18.5
4 4 Heating level 3, heat boosting (with engine 642.8, 651.9), driver side Automatic climate control and operating unit (N22/7) 18.5
5 5 Heating level 2, heat boosting (with engine 642.8, 651.9), passenger side Automatic climate control and operating unit (N22/7) 18.5
6 6 Heating level 1, heat boosting (with engine 642.8, 651.9), driver side Automatic climate 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 CODE 873 (Seat heater for left and right heated front seat)) Rear SAM control unit with fuse and relay module (N10/2) 13.2
8 8 Seat heater stage 2 (with CODE 401 (Front comfort seats, incl. seat heating and seat ventilation) or CODE 873 (Seat heater for left and right heated front seat)) Rear SAM control unit with fuse and relay module (N10/2) 13.2
9 9 Wiper park heater Front SAM control unit with fuse and relay module (N10/1) 15.0
10 10 Mirror heater Left front door control unit (N69/1) and right front door control unit (N69/2) 3.5
11 12 Rear window heater Rear SAM control unit with fuse and relay module (N10/2) 30.0
12 14 Blower P = 50 % Automatic climate control and operating unit (N22/7) 16.0
13 15 Fan P = 50% Automatic climate control and operating unit (N22/7) 31.0
14 16 Circuit 15R relay (1) (N10/2kB) Rear SAM control unit with fuse and relay module (N10/2) 6.0
15 18 Seat heater stage 1 (with CODE 401 (Front comfort seats, incl. seat heating and seat ventilation) or CODE 873 (Seat heater for left and right heated front seat)) Rear SAM control unit with fuse and relay module (N10/2) 3.3

When the on-board electrical system voltage has been stabilized to a value above U = 12.2 V, consumer reduction 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 rear 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 rear 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. As soon as the on-board electrical system voltage has stabilized to a value of U = 11.8 V for t ≥ 10 s or a change in status from circuit 15R to circuit 15C has occurred, the rear SAM control unit ends the on-board electrical system emergency mode function.

The triggered functions are returned in the specified sequence:

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