GF54.10-P-1060FL Engine on Energy Management, Function
GF54.10-P-1060FL Engine On Energy Management, Function
Function requirements, general
^ Circuit 61 ON
The CDI control unit (N3/9) (with diesel engine) or ME-SFI control unit (N3/10) (with gasoline engine) makes available the circuit status of circuit 61 via the chassis CAN (CAN E). The front SAM control unit with fuse and relay module (N10/1) forwards this via the 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 a balanced charge/discharge ratio in the on-board electrical system battery (G1).
Given that the power output of the alternator (G2) is dependent on engine speed and temperature, plus 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 a 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 vehicle's starting capability.
In those 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.
Engine on energy management comprises the following subfunctions:
^ Voltage provision function sequence
^ Dynamic idle speed control function sequence
^ Consumer reduction function sequence
^ Function sequence for power supply via additional battery (G1/7) (with transmission 722.9)
Voltage provision function sequence
The voltage provision function comprises the following subfunctions:
^ Determine charge state of battery function sequence
^ Charge on-board electrical system battery function sequence
^ Alternator regulation function sequence
Determine charge state of battery function sequence
The state of the on-board electrical system battery is monitored by the battery sensor (B95).
This uses various voltage, current and temperature measurements to compute parameters that serve as the basis for energy management. 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.
When the engine is switched off (circuit 61 Off) the charge level of the on-board electrical system battery is determined by means of current integration by the extrapolation of the current charge.
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 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, fast charging is performed first at high voltage until the charge level of the on-board electrical system battery is recognized as being sufficient.
Fast charging is done with a charging voltage of U = 15 V and may take from 20 s to 1 h.
After this a changeover is made to a temperature-dependent characteristic or the generator management (as of T > 15 °C). The generator management contains the lowering of the charging voltage (U = 12.6 V) and the possibility of regenerative braking in the decel mode of the engine.
Special considerations as of 1.6.10:
If the generator management is active, one of the front doors is open and the vehicle speed is v = 0 km/h the generator management changes into the jump start or workshop mode. In the process the generator voltage rises to a constant U = 13.9 V. This jump start or workshop mode is first canceled when the vehicle speed is v > 0 km/h.
A safety cutout 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 protective cutout 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%.
The following graph shows the shows the various phases of voltage provision.
Fast charging:
- Voltage up to U = 15 V
- Once after engine start
- Optimized charging of on-board electrical system battery, incl. during short trips
- Duration t = 20 s to 1 h
- Fast charging ends when charge of on-board electrical system battery is at 80%
- No fast charging during trailer operation (with code (550) Trailer hitch and when on-board electrical system battery is too hot)
Transition to alternator management:
- Fast charging ended
- Stable engine operation
- Temperature of on-board electrical system battery T > 15 °C Batt
- Outside temperature T > 15 °C Outside
- Charge level of the on-board electrical system battery > 70%
- No trailer operation
Alternator management:
- Voltage U = 12.6 V, with some exterior lamp 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
Temperature-based charging:
- Temperature of on-board electrical system battery T Batt < 15 °C
- Outside temperature T outside < 15 °C
- Fast charging ended, alternator management not possible
- Voltage range U = 13.5 to 15 V
- Linear charging characteristic
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
Alternator regulation function sequence
Alternator regulation (alternator management):
- Takes place in the CDI control unit or ME-SFI [ME] control unit
- Sets the specified voltage of the on-board power supply 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 regulation controls the power output of the alternator. The rear SAM control unit reads in the parameters provided by the battery sensor via the on-board electrical system LIN and calculates the generator specified voltage required to provide the energy requested.
The corresponding requests are made available via the interior CAN.
The front SAM control unit forwards these via the chassis CAN to the CDI control unit or ME-SFI [ME] control unit, which evaluates the data in consideration of further input factors (e.g. air conditioning ON), computes the optimum specified voltage for the alternator and sends a corresponding signal via the drivetrain LIN (LIN C1) to the alternator. 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 [ME] control unit compares the alternator's specified voltage values with the alternator's output values in order to get a picture of the energy state of the on-board electrical system. This comparison is termed power management. The energy state is sent as a value via the chassis CAN to the front SAM control unit and from there forwarded via the interior CAN to the rear SAM control unit.
The rear SAM control unit evaluates this feedback accordingly. If the on-board electrical system voltage is found to be too low, power management is deactivated in steps to allow the alternator to provide its full power output.
The alternator's specified voltage value sent out cyclically by the rear SAM control unit via the chassis CAN is used by the power management in the CDI control unit or ME-SFI [ME] control unit only as a guideline value, since it also has to take certain vehicle states into consideration, including engine comfort, idle stability, engine start, rough engine operation. 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 alternator management into account.
If a fault is found in the battery sensor, the on-board power supply 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.
Dynamic idle speed control function sequence
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. A higher idle speed is adjusted for a high consumer load. Idle speed increase is done in a preventive manner. 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 engine rpm is calculated by the CDI control unit or by the ME- SFI control unit and the corresponding value made available via the chassis CAN.
The front SAM control unit forwards this via the interior CAN to the rear SAM control unit.
Data on the state, voltage and current of the on-board electrical system battery are placed on the on-board electrical system LIN for the rear SAM control unit. The rear SAM control unit reads and evaluates all relevant data and computes the required alternator current.
The maximum excitation current is calculated based on the current excitation current and the alternator's capacity utilization. The maximum alternator current at various idle speeds is determined based on the maximum excitation current. The rear SAM control unit makes corresponding requests available via the interior CAN.
The front SAM control unit forwards these via the chassis CAN to the CDI control unit or ME-SFI [ME] control unit, which then raises the idle speed accordingly.
The increase in idle speed will be set back under the following conditions:
- 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
Consumer reduction function sequence
The consumer reduction function is activated as soon as the alternator is no longer able to provide the requested electrical output. The on-board electrical load is reduced by cutting back comfort functions.
This avoids a negative charge/discharge ratio and ensures that starting ability is preserved.
The consumer reduction function is canceled when the alternator is again able to provide the requested electrical output to stabilize the on-board electrical system voltage.
The consumer reduction function is activated when the on-board electrical system voltage falls below U = 12.2 V. The power consumption of the first consumer is reduced t = 20 s after engine start. If the cutback conditions remain unchanged, the power consumption of one further consumer will be reduced every following second.
Consumer reduction in case of PRE-SAFE deployment: The left front reversible emergency tensioning retractor (A76) and the right front reversible emergency tensioning retractor (A76/1) have very high starting and operation 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 following table.
Steps 1-19:
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 onboard power supply 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 on-board power supply management uses all options available through dynamic power management to enforce a positive charge/discharge ratio.
If the on-board electrical system voltage drops below U = 10.6 V for t ≥ 10s, 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:
- 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:
- KDS [trunk lid control control unit] (N121) (on model 212.0 with code (881) Remove trunk closing (HDFS))
- Liftgate control unit (N121/1) (on model 212.2)
- Multicontour seat pneumatic pump (M40) (with code (409) Left/right front multicontour seats)
- Pneumatic pump for dynamic multicontour seat (M40/1) (with code (432) Left and right dynamic multicontour seat)
- Left front dynamic multicontour seat control unit (N32/19) and right front dynamic multicontour seat control unit (N32/22) (with code (432) Left and right dynamic multicontour seat)
- AIRmatic control unit (N51/3) (with code (489) AIRMATIC (air suspension with continuously adjustable damping) or with code (488) Steel/air suspension)
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 rear SAM control unit ends the function onboard electrical system emergency running.
The triggered functions are returned in the specified sequence:
- The idle speed increase is set back.
- Power can again be supplied to the consumers that were shut off.
Power supply via additional battery function sequence (with transmission 722.9)
In order to be able to also engage selector lever position "P" when the on-board electrical system has failed, the electronic ignition lock control unit (N73) is also supplied with voltage via the additional battery.
The capacity of the additional battery is 1.2 Ah.
The function of power supply via additional battery is comprised of 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
In order to be able to generate information about the availability of electrical power from the additional battery, a simple battery state recognition for the additional battery is integrated in the front SAM control unit. This is carried out immediately after the engine has been started.
If the engine is switched off while carrying out the battery state recognition, the front SAM control unit interrupts the battery state recognition and rejects the results from the previous measurement In addition to battery state recognition, the voltage of the additional battery is continuously checked. 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 by means of diagnosis tester.
If there is no voltage at the additional battery or if this is discharged or defective, the fault message "Backup battery fault" is displayed in the multifunction display of the IC. 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 while battery state recognition is being performed. The charging current is limited to P = 15 W by a resistance. A diode prevents the additional battery from feeding back into the onboard electrical system.
