Engine On Energy Management, Function - GF54.10-P-1060RR
Model 190
Function requirements, general
- Signal "engine running" set
The ME-SFI control unit (N3/10) sends the "engine running" signal via the drive train CAN (CAN C1), powertrain control unit (N127), 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). 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 engine's starting capability and the stable supply of all electrical consumers can no longer be assured. In situations where the on-board electrical system is overloaded for prolonged periods, the engine ON energy management increases the power output of the alternator (G2). 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
- Function sequence for dynamic idle speed control
- Function sequence for consumer reduction (deactivation of convenience functions)
Function sequence for voltage provision
The voltage provision function comprises the following subfunctions:
- Determine charge state of battery function sequence
- Function sequence for charging on-board electrical system battery
- Function sequence for alternator regulation (alternator management)
Determine charge state of battery function sequence
The state of the on-board electrical system battery is determined by the electronics integrated in the on-board electrical system battery. The electronics in the on-board electrical system battery calculate corresponding parameters by means of voltage, current and temperature measurements at 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, 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 in the data from the electronics in the on-board electrical system battery via the battery sensor LIN (LIN B15), while also measuring the voltages at circuit 30 and circuit 30g, and computes the alternator specified voltage required to provide the energy requested by consumers.
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 various factors, the specified voltage is determined using the alternator management or using the temperature-dependent charging characteristic.
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, the charging voltage is lowered accordingly (e.g. after driving in the cold or long downhill travel) in order to return the battery to its optimum charge level of 80 %.
A distinction is made between the following types of battery charging:
- Temperature-based charging
- Alternator management
- Charging in deceleration mode
Temperature-based charging:
- No alternator management possible
- Voltage range U = 13.6 to 14.4 V
- Linear charging characteristic
Transition to alternator management:
- Stable engine operation
- Temperature of on-board electrical system battery Tbatt > 0°C
- Outside temperature TOutside > 0°C
- Charge level of the on-board electrical system battery > 70%
Alternator management:
- Voltage U = 12.8 to 13.5 V
- Charge level of the on-board electrical system battery 80%
- Reduced consumer power consumption
- With air conditioning ON and high blower setting U = 13.5 V
Transition to charging in deceleration mode:
- Stable engine operation
- ME-SFI [ME] control unit detects deceleration mode
Charging in deceleration mode:
- Voltage up to U = 15 V
- Activated by ME-SFI control unit
- On-board electrical system battery charged when "free" energy is available
Function sequence for alternator regulation (alternator management)
Alternator regulation (alternator management):
- Occurs in ME-SFI control unit.
- Sets the specified voltage of the energy management.
- Switches to regenerative braking voltage in deceleration mode.
- Sets a lower voltage in exceptional cases (e.g. stall prevention, cold start at high altitude, catalytic converter heating).
The alternator control actuates the alternator's power output. The ME-SFI control unit communicates with the alternator via drivetrain LIN (LIN C1) and evaluates the alternator operating rate. The ME-SFI control unit then sends information about the operating rate of the alternator to the rear SAM control unit via the drive train CAN, powertrain control unit, chassis CAN 1, the front SAM control unit and interior CAN.
The state of the on-board electrical system battery is acquired by the integrated electronics. The electronics in the on-board electrical system battery send corresponding parameters of the on-board electrical system battery via the battery sensor LIN to the rear SAM control unit. The rear SAM control unit evaluates all relevant information and calculates the specified voltage required for the alternator. The rear SAM control unit then sends this value to the ME-SFI control unit via the interior CAN, front SAM control unit, chassis CAN 1, powertrain control unit and engine CAN (CAN C). The ME-SFI 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 ME-SFI control unit then requests the calculated specified voltage (excitation voltage) via the drivetrain LIN at the alternator; the alternator then sets this voltage. The ME-SFI [ME] control unit also checks the input factors for plausibility in order to rule out any overcharging or faulty charging of the on-board electrical system battery.
The ME-SFI [ME] control unit compares the optimum values for alternator's specified voltage with the alternator's actual output values in order to get a picture of 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 onboard 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 ME-SFI control unit adopts the alternator specified voltage values for the rear SAM control unit as guideline values 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 overlaying the specified voltage determined by the power management function with the alternator specified voltage sent by the rear SAM control unit.
If a fault is found at the electronics in the on-board electrical system battery, the energy management switches to a fixed voltage of U = 14.4 V that must not be exceeded.
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 and thus the power output of the alternator 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:
- Alternator excitation current
- Alternator operating rate
- On-board electrical system battery voltage
- On-board electrical system battery current
- State of on-board electrical system battery
- Engine speed
- Consumer reduction shutoff stage
- Engine start
The ME-SFI control unit communicates with the alternator via the drivetrain LIN and evaluates the operating rate of the alternator. The ME-SFI control unit then sends information about the operating rate of the alternator to the rear SAM control unit via the drive train CAN, powertrain control unit, chassis CAN 1, the front SAM control unit and interior CAN.
The state, voltage and current of the on-board electrical system battery are acquired by the electronics in the on-board electrical system battery. The electronics in the on-board electrical system battery send corresponding parameters of the on-board electrical system battery to the rear SAM control unit via the battery sensor LIN. The rear 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 rear SAM control unit sends corresponding requests via the interior CAN, front SAM control unit, chassis CAN 1, powertrain control unit and engine CAN to the ME-SFI control unit, which increases the idle speed accordingly.
The idle speed increase is reversed under the following circumstances:
- Engine off or alternator defective
- Simultaneous occurrence of the following conditions:
- Consumer reduction not active
- On-board electrical system emergency mode not active
- Consumer load no longer high
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.
Detailed information on evaluation of alternator operating rate can be found in the "Alternator regulation (alternator management)" section.
If the permissible discharge current of the on-board electrical system battery is exceeded, the consumer reduction function 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. The rear SAM control unit sends the request to reduce power or to shut down consumers via the interior CAN to the corresponding control units that are connected to the interior CAN, and via the interior CAN, front SAM control unit and chassis CAN 1 to the powertrain control unit.
Model 190
with CODE 299 (PRE-SAFE® system)
The left reversible emergency tensioning retractor (A76) and the 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 shutoff sequence is shown in the table below.
| Sequence | Shutoff step | Power-reduced or deactivated function | Responsible control unit | Maximum current in A |
|---|---|---|---|---|
| 1 | 7 | Seat heater stage 3 (with CODE 873 (Seat heater for driver and front passenger)) | Rear SAM control unit with fuse and relay module (N10/2) | 13.2 |
| 2 | 8 | Seat heater stage 2 (with CODE 873 (Seat heater for driver and front passenger)) | Rear SAM control unit with fuse and relay module (N10/2) | 13.2 |
| 3 | 10 | Mirror heater | Left door control unit (N69/1) and right door control unit (N69/2) | 3.5 |
| 4 | 12 | Rear window heater | Rear SAM control unit with fuse and relay module (N10/2) | 30.0 |
| 5 | 14 | Blower P = 50 % | Climate control control unit (N22/1) | 16.0 |
| 6 | 15 | Fan P = 50% | Powertrain control unit (N127) | 31.0 |
| 7 | 16 | Circuit 15R relay (1) (N10/2kB) | Rear SAM control unit with fuse and relay module (N10/2) | 6.0 |
| 8 | 18 | Seat heater stage 1 (with CODE 873 (Seat heater for driver and front passenger)) | Rear SAM control unit with fuse and relay module (N10/2) | 3.3 |
When the discharge current then drops below the permissible level again, the consumer reduction function is canceled in the reverse order with a waiting time of t = 5 s in each case.
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 limit value defined for the discharge current of the onboard electrical system battery is exceeded for a certain period. The energy management uses all options available through dynamic power management to enforce a positive charge balance.
If the discharge current of the on-board electrical system battery is too high, the rear SAM control unit activates the on-board electrical system emergency mode function.
This causes the activation of the following energy management functions:
- Idle speed increase
- Deactivation of alternator management
- Consumer reduction with shutoff of short-term consumers
Unlike consumer reduction, power reduction or consumer shutoff is done with a cycle time of t = 200 ms. As soon as the stability of the on-board electrical system has been restored or the circuit status has changed from circuit 15R to circuit 15C, the rear SAM control unit ends the on-board electrical system emergency mode function.
The triggered functions are returned in the specified sequence:
- Idle speed increase
- Consumer reduction
| Electrical function schematic for alternator management | PE54.10-P-2064-97HBA | ||
| Electrical function schematic for dynamic idle speed increase | PE54.10-P-2063-97HBA | ||
| Electrical function schematic for comfort function shutoff | PE54.10-P-2076-97HBA | ||
| Overview of energy management system components | GF54.10-P-9990RR |