Function Sequence For Dynamic Idle Speed Control

Dynamic idle speed control sets the engine's idle speed such that no current needs to be drawn from the battery when the vehicle is idling. The idle speed is increased for a higher consumer load. Idle speed increase is done in a preventive manner. The system adopts 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
• Battery voltage
• Battery current
• Engine speed
• Consumer reduction shutoff step
• State of battery
• Engine start

ECM transmits the "Engine running" signal and information on alternator utilization via CAN communication to BCM. Information regarding the condition, voltage, and current of the battery is recorded by the battery sensor which transmits this via LIN communication to BCM. BCM receives and evaluates all relevant information and calculates the required alternator current.

The maximum possible excitation current is calculated from the current excitation current and the alternator utilization. Corresponding information is received by ECM via LIN communicaiton.The maximum possible excitation current is used to calculate the maximum possible alternator current at different idle speeds.

BCM transmits corresponding requests via CAN communication to ECM, which then raises the idle speed accordingly.

The idle speed is reversed under the following circumstances:

• Alternator malfunction
• Simultaneous occurrence of the following conditions:
  • Consumer reduction not active
  • Consumer load no longer high