Engine on energy management, function - GF54.10-P-1060FQ
MODEL 218
Function requirements, general
- Signal "engine running" set
The CDI control unit (N3/9) (with diesel engine) or the ME-SFI control unit (N3/10) (with gasoline engine) sends the "engine running" signal via the chassis CAN (CAN E) (up to 28.02.2013) or chassis CAN 1 (CAN E1) (as of 01.03.2013), 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)
- Power supply function sequence via additional battery (G1/7) (as of 01.09.2014 vehicles without engine 642 and without CODE 494 (USA version))
Function sequence for voltage provision
The voltage provision function comprises the following subfunctions:
- Determine charge state of battery function sequence
- Charge on-board electrical system battery function sequence
- Function sequence for alternator regulation (alternator management)
Determine charge state of battery function sequence
The state of the on-board electrical system battery is recorded by the battery sensor (B95). The battery sensor 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, 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 battery 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 fast 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.
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. The alternator management contains lowering charging voltage and the regenerative (energy management) braking option in the engine's decel mode. 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%.
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 = 14.39 V. This external starting aid or workshop mode is not canceled until the speed is v > 0 km/h.
Voltage provision
Quick charging:
- Voltage up to U = 15 V
- Once after circuit 50 ON (engine start)
- Optimized charging of on-board electrical system battery, incl. during short trips
- Duration t = 20 s to 1 h
- Quick charging ends when charge of on-board electrical system battery is at 80%
- No quick charging when the on-board electrical system battery is too warm
Transition to alternator management:
- Quick charging ended
- Stable engine operation
- Temperature of on-board electrical system battery TBatt > 15 °C (up to 31.05.2012), TBatt > 10 °C (as of 01.06.2012)
- Outside temperature TOutside > 15 °C (up to 31.05.2012), TOutside T> 10 °C (as of 01.06.2012)
- Charge level of the on-board electrical system battery > 70%
Temperature-based charging:
- Temperature of on-board electrical system battery TBatt < 15 °C
- Outside temperature TOutside < 15 °C
- Quick charging ended, alternator management not possible
- Voltage range U = 13.5 to 15 V
- Linear charging characteristic
Alternator management:
- Voltage U = 12.6 V (up to 31.05.2012), U = 12.7 V (as of 01.06.2012), for some light functions U = 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 = 14.3 V
Transition to charging in deceleration mode:
- Stable engine operation
- CDI control unit or ME [ME-SFI] control unit detects deceleration mode
Charging in deceleration mode:
- Voltage up to U = 15 V
- Activated by CDI control unit or ME [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):
- Takes place in the CDI control unit or ME-SFI [ME] 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 CDI control unit or the ME-SFI control unit communicates with the alternator via the drivetrain LIN (LIN C1) and evaluates the alternator operating rate. The CDI control unit or the ME-SFI control unit subsequently sends information about the alternator operating rate via the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013), front SAM control unit and interior CAN to the rear SAM control unit. The state of the on-board electrical system battery is recorded by the battery sensor. The battery sensor sends corresponding parameters of the on-board electrical system battery via on-board electrical system 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 via the interior CAN, front SAM control unit and chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013) to the CDI control unit or to the ME-SFI control unit. The CDI control unit or 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 CDI control unit or the ME-SFI control unit then requests the calculated specified voltage (excitation voltage) of the alternator via the drivetrain LIN at the alternator; the alternator then sets this voltage. In addition, the CDI control unit or ME-SFI 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. 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 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, 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.
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 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
- Engine speed
- Consumer reduction shutoff stage
- State of on-board electrical system battery
- Engine start
The CDI control unit or the ME-SFI control unit communicates with the alternator via the drivetrain LIN and evaluates the alternator operating rate. The CDI control unit or the ME-SFI control unit subsequently sends information about the alternator operating rate via the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013), front SAM control unit and interior CAN to the rear SAM control unit.
The state of the on-board electrical system battery, the voltage and the current are recorded by the battery sensor. The battery sensor sends corresponding parameters of the on-board electrical system battery via on-board electrical system LIN to the rear SAM control unit. 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 and chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013) to the CDI control unit or 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
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.
The consumer reduction function is activated when the on-board electrical system voltage falls 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. The rear SAM control unit sends the request to reduce power or to shut down consumers via the interior CAN to the to the relevant control units which are connected to the interior CAN and via interior CAN, front SAM control unit and chassis CAN 1 to the steering column tube module control unit (N80).
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 shutoff sequence is shown as of 01.06.2012 in the table below.
| Shutoff step | Shutoff stage | Consumers with reduced or no power | Responsible control unit | Maximum current in A |
|---|---|---|---|---|
| 1 | 1 | Heating level 6, passenger side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 2 | 2 | Heating level 5, driver side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 3 | 3 | Heating level 4, passenger side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 4 | 4 | Heating level 3, driver side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 5 | 5 | Heating level 2, passenger side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 6 | 6 | Heating level 1, driver side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 7 | 7 | Seat heater level 3 (with code (873) Seat heater for left and right front seats) | Rear SAM control unit with fuse and relay module (N10/2) | 13.2 |
| 8 | 8 | Seat heater level 2 (with code (873) Seat heater for left and right front seats) | 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 |
| 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 | Rear SAM control unit with fuse and relay module (N10/2) | 30.0 |
| 13 | 13 | Rear blower (with code (581) Comfort automatic air conditioning) P = 50 % | Automatic climate control and operating unit (N22/7) | 5.5 |
| 14 | 14 | Blower in front P = 50% | Automatic climate control and operating unit (N22/7) | 16.0 |
| 15 | 15 | Fan P = 50% | Automatic climate control and operating unit (N22/7) | 31.0 |
| 16 | 16 | Circuit 15R relay (1) (N10/2kB) | Rear SAM control unit with fuse and relay module (N10/2) | 6 |
| 17 | 18 | Seat heater stage 1 (with code (873) Seat heater for left and right front seats) | Rear SAM control unit with fuse and relay module (N10/2) | 3.3 |
The shutoff sequence is shown up to 31.05.2012 in the table below.
| Shutoff step | Shutoff stage | Consumers with reduced or no power | Responsible control unit | Maximum current in A |
|---|---|---|---|---|
| 1 | 1 | Heating level 6, passenger side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 2 | 2 | Heating level 5, driver side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 3 | 3 | Heating level 4, passenger side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 4 | 4 | Heating level 3, driver side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 5 | 5 | Heating level 2, passenger side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 6 | 6 | Heating level 1, driver side heat boosting (with engine 642.8, 651.9) | Automatic climate control and operating unit (N22/7) | 18.5 |
| 7 | 7 | Rear blower (with code (581) Comfort automatic air conditioning) P = 50 % | Automatic climate control and operating unit (N22/7) | 5.5 |
| 8 | 8 | Blower in front P = 50% | Automatic climate control and operating unit (N22/7) | 16.0 |
| 9 | 9 | Fan P = 50% | Automatic climate control and operating unit (N22/7) | 31.0 |
| 10 | 11 | Circuit 15R relay (1) (N10/2kB) | Rear SAM control unit with fuse and relay module (N10/2) | 6 |
| 11 | 12 | Seat ventilation (with code (401) | Front comfort seats, incl. seat heating and seat ventilation) Rear SAM control unit with fuse and relay module (N10/2) | 2.2 |
| 13 | 13 | Seat heater level 3 (with code (873) Seat heater for left and right front seats) | Rear SAM control unit with fuse and relay module (N10/2) | 13.2 |
| 14 | 14 | Rear window heater | Rear SAM control unit with fuse and relay module (N10/2) | 30.0 |
| 15 | 15 | Wiper park heater | Front SAM control unit with fuse and relay module (N10/1) | 15 |
| 16 | 16 | Seat heater level 2 (with code (873) Seat heater for left and right front seats) | Rear SAM control unit with fuse and relay module (N10/2) | 13.2 |
| 17 | 17 | Seat heater stage 1 (with code (873) Seat heater for left and right front seats) | Rear SAM control unit with fuse and relay module (N10/2) | 3.3 |
| 18 | 18 | Steering wheel heater (with code (443) Steering wheel heater) | Steering wheel heater control unit (N25/7) | 8.0 |
| 19 | 20 | Mirror heater | Left front door control unit (N69/1) and right front door control unit (N69/2) | 3.5 |
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 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.
In addition to consumer reduction the following consumers are switched off:
- Multicontour seat pneumatic pump (M40) (with code (409) Left/right front multicontour seats)
- Active multicontour seat pneumatic pump (M40/1) (with code (432) Active multicontour seat)
- Left front active multicontour seat control unit (N32/19) (with code (432) Active multicontour seat)
- Right front active multicontour seat control unit (N32/22) (with code (432) Active multicontour seat)
- AIRmatic control unit (N51/3) (with code (489) AIRmatic (air suspension with continuous variable damping) or code (488) Steel/air suspension)
- TLC control unit (N121) (with code (881) Remote trunk closing (RTC))
- Liftgate control unit (N121/1) (on model 218.9)
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 circuit 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:
- Idle speed increase
- Consumer reduction
Power supply function sequence via additional battery (as of 01.09.2014 vehicles without engine 642 and without CODE 494 (USA version))
To be able to engage transmission position "P" with a discharged on-board electrical system battery, the electronic ignition lock control unit (N73) is also supplied with power through the additional battery. The capacity of the additional battery is 1.2 Ah.
The power supply function over the additional battery encompasses the following subfunctions:
- Determine function sequence of status of additional battery
- Function sequence of charge additional battery
Determine function sequence of status of additional battery
The front SAM control unit performs battery state recognition immediately after the engine is started, and sends the result via the interior CAN to the rear SAM control unit. This provides information on the availability of the additional battery's electrical output. 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 the battery state recognition, the voltage of the additional battery is also checked after each engine start. To perform this check, charging must be stopped for t = 20 ms. The check is performed every t = 5 s. The battery state recognition can also be started using a diagnosis tester.
If voltage is not applied to the additional battery or if it is discharged or defective, the fault message "Backup battery fault" is shown in the multifunction display (A1p13) of the instrument cluster (A1). The rear SAM control unit transmits the data required for this to the IC via the interior CAN.
Function sequence of charge additional battery
The additional battery is permanently charged after battery state recognition when the engine is running. The additional battery is charged via the front SAM control unit. Charging is only interrupted for as long as it takes to run the battery state recognition. The charging current is limited by means of a resistor to P = 15 W. A diode prevents the additional battery from feeding back into the on-board electrical system.
| Electrical function schematic for alternator management | PE54.10-P-2064-97XAA |
| Electrical function schematic for dynamic idle speed increase | PE54.10-P-2063-97XAA |
| Electrical function schematic for comfort function shutoff | PE54.10-P-2076-97XAA |
| Overview of energy management system components | GF54.10-P-9990FQ |