Engine On Energy Management, Function - GF54.10-D-1060TSA

Model 907

Function requirements, general

"Engine running" signal set.

The CDI control unit or the ME-SFI control unit sends the "Engine running" signal via the powertrain CAN (CAN C), the powertrain control unit (N127), the suspension FlexRay (Flex E), the electronic ignition lock (EZS) control unit (N73/8) and the interior CAN (CAN B) to the SAM control unit (N10).

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 balance could arise. In this case, a stable supply to all electrical consumers is no longer ensured.

Engine ON energy management sets the alternator voltage so that the on-board electrical system battery is optimally charged for the corresponding application. 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). It also powers down the comfort consumers to enable the on-board electrical system battery to achieve an even charge balance.

Engine ON energy management encompasses the following subfunctions:

Function sequence for battery charge management
Function sequence for dynamic load shutoff
Function sequence for dynamic idle speed increase

Function sequence for battery charge management

The battery charge management is the most complex module in the engine ON energy management system. In order to optimally charge the on-board electrical system battery for the corresponding application, various voltage levels are calculated that serve as specifications for the alternator. The battery charge management system can use different modes and switch between these modes to ensure optimum charging under changing conditions.

The voltage levels calculated in these modes consist of a maximum and minimum voltage level that the alternator must not exceed or drop below. There are also two specified voltages that the CDI control unit or the ME-SFI control unit must comply with where possible. The CDI control unit or the ME-SFI control unit has control over the alternator and at its own discretion may deviate from the specified voltages. It switches automatically between two specified voltages if electrical energy can be generated efficiently, e. g. if the engine is in overrun mode.

Battery charge management encompasses the following subfunctions:

Rapid charging
Temperature-based charging/normal charging
Alternator management
Service mode

Rapid charging

After the engine is started, rapid charging is performed first at high voltage until the charge level of the on-board electrical system battery is recognized as being sufficient.

Rapid charging is done with a charging voltage of 15 V at the alternator and can last up to 1 h. Only after this will a temperature-dependent characteristic or the alternator management function 1 be used.

Rapid charging is ended when one of the following cases occurs:

On-board electrical system battery sufficiently charged (state of charge above 80 %)
On-board electrical system battery too warm
Trailer connected
Rapid charging active for more than 1 h after engine start

Rapid charging is prevented from ending if the automatic start/stop is still requesting it, i.e. until the relay diagnoses are complete.

Temperature-based charging/normal charging

Temperature-based charging is the default mode that is always used if a higher-order mode cannot or cannot yet be used due to some conditions not being met. In the case of lead-acid on-board electrical system batteries, a full charge is usually aimed for, with the charging voltage being the optimum for the prevailing battery temperature.

The switch to temperature-based charging is directly dependent on and related to the rapid charging process. Recuperation is also possible in this mode.

To adapt the charging voltage to a specific on-board electrical system battery, a linear function is provided which is dependent on the on-board electrical system battery temperature; this function calculates the charging voltage. The target charging voltage at 0 °C is taken as the starting point

Alternator management

The aim of alternator management is to charge the on-board electrical system battery as efficiently as possible. For this purpose, the charging voltage of the on-board electrical system battery is lowered to the minimum level at which continuous operation is still possible. In addition, a battery state of charge of 80 % to 90 % is aimed for. Firstly, the power consumption of the consumers and consequently the load on the belt drive is reduced. Secondly this creates potential for a possible charging stroke which can be supplied to the on-board electrical system battery through recuperation. This charge can be obtained solely from the vehicle's kinetic energy.

Activation of alternator management:

In many cases, a low charging voltage is not effective, e. g. when the on-board electrical system battery is cold or when high-power consumers are active. In order for the charging voltage to be lowered, a comparatively large number of conditions need to be met:

Sufficient state of charge of on-board electrical system battery
Sufficient temperature of on-board electrical system battery
No trailer hitched
Rapid charging completed
Automatic start/stop permits the charging voltage to be lowered.
State of charge of on-board electrical system battery has been ≥ 80 % once since terminal 15R was activated
Vehicle driven once with driver's door and front passenger door closed
The vehicle has covered a total distance of at least 3 km.
Consumer shutoff stage not active
Air conditioning permits the charging voltage to be lowered.
ESP® permits the charging voltage to be lowered.
DISTRONIC permits the charging voltage to be lowered.

In alternator management mode, the voltage position fluctuates between 15 V in overrun mode (recuperation) and a minimum that can be increased when the following exceptions arise:

Halogen exterior lights switched on
Windshield wiper switched on
The air conditioning system requests an increase.
ESP® requests an increase.
DISTRONIC requests an increase.

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 overrun mode fuel shutoff. In cases of high voltage with low power consumption or if the temperature of the on-board electrical system battery is too high, the emergency shutoff deactivates recuperation.

Service mode

For some development and service applications, it is necessary to be able to set a defined voltage at the alternator output, e. g. to check the alternator or the control loop. In service mode, the alternator voltage is steadily increased to 14.3 V, even if there is a fault in the battery sensor (B95). No recuperation takes place. The service mode is switched on via the diagnostic system.

Function sequence for dynamic load shutoff

If the output required by the consumers exceeds the power generated by the alternator, electrical energy is drawn from the on-board electrical system battery. As long as the voltage level is high enough to enable stable operation of all consumers, and it is anticipated that the on-board electrical system battery is capable of cold-starting, this can be tolerated. At the same time, however, excessively rapid aging of the on-board electrical system battery needs to be avoided.

To safeguard all these issues, the dynamic load shutoff reduces the consumer load gradually by successively shutting off certain consumers. Once the on-board electrical system has reached a stable and functional state again, the consumers can be successively switched back on again.

The dynamic load shutoff intervenes when the following conditions are met:

Engine running and alternator is supplying power.
Voltage of the on-board electrical system battery drops below a predefined threshold.
Calculated demand current exceeds power generated by the alternator.

The following conditions must be met in order to shut off consumers:

The calculated demand current drops below a predefined limit minus a hysteresis.
Filtered voltage of the on-board electrical system battery exceeds a predefined threshold.
Alternator utilization is less than 70 %

Function sequence for dynamic idle speed increase

The current generated by the alternator is dependent on the engine speed and excitation current, but at idle speed the alternator can only deliver a fraction of its maximum power. An overload of the on-board electrical system at idle speed can be averted by increasing the idle speed under certain conditions.

Two thresholds or three engine speeds are available that can be set: idle speed, engine speed of increase stage 1 and engine speed of increase stage 2.

The engine speeds are not specified at this point, but must be adopted by the CDI control unit or the ME-SFI control unit. The engine speeds are only used for selecting a specific alternator current from the alternator characteristics map. Only then is the prevailing demand current calculated. Individual large consumers, such as the windshield heater, may request additional demand. This is already factored into the corrected demand current, even if no current is flowing yet.

Two current values are formulated as thresholds that, if exceeded, generate a request to increase engine speed.

These current values are determined in two ways:

They are transmitted directly by the CDI control unit or the ME-SFI control unit via the powertrain CAN, powertrain control unit, suspension FlexRay and electronic ignition lock (EZS) control unit to the interior CAN.
They are calculated from an alternator characteristics map. In this case, a specific characteristics map is selected and the corresponding current thresholds are determined based on the alternator excitation current. The available alternator characteristics maps are documented in the CAN signal description.

If the corrected demand current exceeds one of the two thresholds, the appropriate increase is requested immediately.

The thresholds also apply when canceling the increase stages when they are undershot by the demand current plus a hysteresis of 10 A. A debounce time must also be observed before the increase stage is actually canceled.

Lowering of the increase stage may be prevented if consumer shutoff is still active at the same time.

If the battery sensor is not available because it reports a fault or the battery sensor LIN (LIN B15) has failed, increase stage 2 is requested permanently.

Electrical function schematic for alternator management	Model 907 with engine 642, 651	PE54.10-D-2064-97TSA
Electrical function schematic for alternator management	Model 907 with engine 274	PE54.10-D-2064-97TSB
Overview of energy management system components		GF54.10-D-9990TSA