GF54.10-P-1060LE Engine on Energy Management, Function
GF54.10-P-1060LE Engine On Energy Management, Function
General function requirements
^ Circuit 61 ON
The circuit status of circuit 61 is made available on the chassis CAN (CAN E) by the CDI control unit (N3/9) (with diesel engine) or by the ME-SFI [ME] control unit (N3/10) (with gasoline engine) and forwarded by the central gateway control unit (N93) to the front SAM control unit with fuse and relay module (N10/1) via the interior CAN (CAN B).
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).
Depending on the rpm- and temperature-dependent power output of the alternator (G2) or the DC/DC converter control unit (N83/1) (on model 221.095/195) and if a large number of consumers are in operation at the same time, overload situations can arise which must 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.
Depending on the engine mounted in the vehicle, either the CDI control unit or the ME-SFI [ME] control unit is installed. The term "engine control unit" is used below to refer to both control unit types.
"Engine on" energy management comprises the following subfunctions:
^ Voltage provision function sequence
^ Dynamic idle speed control function sequence
^ Consumer reduction function sequence
Voltage provision function sequence
The voltage provision function comprises the following subfunctions:
^ Determine charge state of battery function sequence
^ Function sequence on-board electrical system battery for charging (without model 221.095/195)
^ Function sequence on-board electrical system battery for charging (model 221.095/195)
^ Alternator regulation function sequence
Determine charge state of battery function sequence
The state of the on-board electrical system battery is continuously 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 front SAM control unit reads in the calculated data from the battery sensor via on-board electrical system LIN (LIN B7), also measures the voltages at circuit 30 and circuit 30g and calculates the specified voltage of the alternator or of the DC/DC converter control unit (on model 221.095/195) that is required to provided the requested energy.
With the engine switched off (circuit 61 OFF), the charge level of the on-board electrical system battery is determined by means of current integration with forward projection of the current charge.
Function sequence for on-board electrical system battery charging (without model 221.095/195)
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 quick 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 can take from t= 20 s to 1 h.
Following this, a temperature-dependent characteristic or the alternator management function is used. 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 circuit 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
- Quick charging ends when charge of on-board electrical system battery is at 80%
- No quick 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 > Batt 15 °C
- Outside temperature T > 15 °C Outside
- Charge level of the on-board electrical system battery > 70%
- No trailer operation
Temperature-based charging:
- Fast charging ended, alternator management not possible
- Voltage of U = 13.5 V (in summer) to 15 V (in winter)
- Linear charging characteristic
Alternator management:
- Voltage U = 12.6 V, for some lighting 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
- Engine control unit detects deceleration mode
Charging in deceleration mode:
- Voltage up to U = 15 V
- Activated by engine control unit
- On-board electrical system battery charged when "free" energy is available
Function sequence on-board electrical system battery for charging (model 221.095/195)
The on-board electrical system battery is charged primarily using energy from the high-voltage on-board electrical system. For this purpose, the energy stored in the high-voltage battery (A100g1) is fed from the DC/DC converter control unit to the 12 V on-board electrical system (up to approx. I = 100 A). If the energy provided by the DC/DC converter control unit cannot cover the power requirement, the alternator is activated as an auxiliary power source.
Alternator regulation function sequence
Alternator regulation (alternator management):
- Takes place in the engine 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 (approx. h = 2000 m and higher), catalytic converter heating)
The alternator regulation controls the power output of the alternator. The front SAM control unit reads in the on-board electrical system battery parameters provided by the battery sensor via the on-board electrical system LIN, calculates the specified alternator voltage required to provide the energy requested by consumers and makes these requests available on the interior CAN.
The central gateway control unit forwards these via the chassis CAN to the engine control unit, which evaluates the data in consideration of further input factors (e.g. air conditioning ON), calculates the optimum specified voltage for the alternator and sends a corresponding signal via the drivetrain LIN (LIN C1) to the alternator. In addition, the engine 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.
On model 221.095/195, the request for the specified voltage is sent by the engine control unit to the DC/DC converter control unit via the drive train sensor CAN (CAN I).
The engine control unit compares the alternator's specified voltage values with the alternator's output voltage values in order to determine the energy state of the on-board electrical system. This comparison is termed power management.
The energy state is sent as a voltage value via the chassis CAN to the central gateway control unit and from there forwarded via the interior CAN to the front SAM control unit.
The front 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 values sent out cyclically by the front SAM control unit via the chassis CAN is used by the power management in the engine 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 front 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 in the engine control unit 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 set higher when the load from consumers is high. 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 calculation of dynamic idle speed control in the engine control unit:
- 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 engine control unit and this value is made available via the chassis CAN.
The central gateway control unit forwards this via the interior CAN to the front SAM control unit.
Data on the state, voltage and current of the on-board electrical system battery is placed on the on-board electrical system LIN by the battery sensor for the front SAM control unit. The front SAM control unit reads in and evaluates all relevant data and calculates the required alternator current.
On model 221.095/195, the necessary current from the DC/DC converter control unit is calculated.
The maximum excitation current is calculated using the prevailing excitation current and the operating rate of the alternator. The maximum alternator current at various idle speeds is determined based on the maximum excitation current. The front SAM control unit makes corresponding requests available via the interior CAN.
The front SAM control unit forwards these via the central gateway control unit and via the chassis CAN to the engine control unit, which then increases 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 convenience functions.
This avoids a negative charge balance 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 first consumer's power consumption is reduced 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.
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 front SAM control unit sends the request for power reduction or shutoff of consumers to the corresponding control units via the interior CAN.
The shutoff sequence is shown in the following table.
Steps 1-25:
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 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 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 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:
- 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 on-board electrical system voltage remains stable at a value of U = 11.8 V for t ≥ 10 s or the circuit status changes from circuit 15R to circuit 15C, the front SAM control unit ends the on-board electrical system emergency mode function.
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.
