Overview
This document contains the following information:
General
Idle speed control (except hybrid vehicles, electric vehicles)
Reduction in on-board electrical system load
Automatic circuit disconnection
General
If a large number of electrical consumers are operated simultaneously, overload situations can occur which have to be buffered by the 12 V on-board electrical system battery alone. If such an overload situation lasts for an extended period or if the charging capacity of the 12 V on-board electrical system battery is low, a negative charge/discharge ratio could arise. In this case, the mobility of the vehicle and the stable supply of all electrical consumers can no longer be assured. To counteract a voltage drop, the energy management system starts functions which can stabilize the on-board electrical system voltage.
The energy management calculates the energy required based on the charge level of the 12 V on-board electrical system battery. If the energy requirement, for example, cannot be covered by the alternator management, the idle speed is increased and the load on the on-board electrical system is reduced by disabling comfort functions.
Idle speed control (except hybrid vehicles, electric vehicles)
The idle speed control function increases the idle speed of the combustion engine as a consequence of a high load on the on-board electrical system. The idle speed increase causes a higher power output at the alternator. In idle mode, electrical energy may then not have to be drawn from the 12 V on-board electrical system battery. The idle speed is increased as a preventive measure. In other words, the system does not respond to a lack of electrical energy. The combustion engine control unit regulates the idle speed according to the requirements of the energy management system.
The following factors are used for idle speed control calculations:
Voltage, 12 V on-board electrical system battery
Current, 12 V on-board electrical system battery
Condition, 12 V on-board electrical system battery
Alternator excitation current
Alternator operating rate
Engine speed
Consumer reduction shutoff stage
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 combustion engine control unit and the alternator communicate with each other via the alternator interface.
The idle speed increase is reversed under the following circumstances:
Generator faulty
On-board electrical system voltage was stabilized
Vehicles with 48 V technology:
The electrical energy required to charge the 12 V on-board electrical system battery is provided by the 48 V battery. Depending on the state of charge of the 48 V battery, the power output of the starter-alternator can also be increased by the idle speed control.
Reduction in on-board electrical system load
The energy management system reduces the on-board electrical system load by disabling comfort functions if the required electrical energy cannot be provided.
If the on-board electrical system voltage drops relatively quickly, then the power consumption of as many consumers as possible is limited or deactivated within a short period.
The energy management then terminates the functions exerting a load on the on-board electrical system:
If the on-board electrical system voltage has stabilized at a specific value.
If the circuit status has changed downwards from circuit 15R.
Consumer reduction is then canceled.
Automatic circuit disconnection
The energy management system switches from circuit 15 ON to circuit 15R ON if no control activities are detected within 30 min with the combustion engine switched off. All consumers that are supplied with voltage in the case of circuit 15 ON are switched off. If the voltage then drops to a defined value, the energy management system starts consumer reduction.
Function schematics | |||
Dynamic idle speed increase, function schematic | Model 118Model 167 except code B01 (48V technology) except code ME05 (Hybrid drive 85 kW-94 kW variant (incl. plug-in))Model 177, 247 except code ME08 (Hybrid drive 75-84 kW VARIANT (INCLUDING PLUGIN))Model 213 as of model year 2021 except code B01 (48V technology) except code ME05 (Hybrid drive 85 kW-94 kW variant (incl. plug-in)) except code ME08 (Hybrid drive 75-84 kW VARIANT (INCLUDING PLUGIN))Model 238, 257, 290 as of model year 2021 except code B01 (48V technology) | ||
Subsystems | |||
Evaluate battery charge level, basic function | |||
Charge battery while driving, basic function | |||
Reduce consumers, basic function | |||
Control units | |||
Combustion engine control unit, basic function | Model all (CAR) | ||
Basic function of signal acquisition and actuation module | Model 118, 177, 247 | ||
Basic function of signal acquisition and actuation module at front | Model 167, 293 | ||
Components | |||
On-board electrical system battery, basic function |