VS - Electrical Systems From Stop-Start to Hybridization

A linear relationship exists between battery Open Circuit Voltage and battery State Of Charge, this characteristic is therefore used to determine an absolute SoC value by a simple voltagemeasurement. To do so, the vehicle has to switch to a “deep sleep mode” to limit as much as possible the quiescent current from all control units and reach a quasi-

Open-Circuit Voltage at battery level, this operation can only be performed when the vehicle is parked.

The calculation of SoC can be further refined by correcting the SoC with the battery self-discharge rate and vehicle quiescent consumption during long parking periods.

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Tracking the balancing of current that flows in the battery does not provide an absolue SOC value. Therefore, a reset for calibration of absolute state-of-charge is needed. The Open-Circuit Voltage is used as a reference to determine the State of Charge.

V

The SoC can be determined by measuring the Open Circuit Voltage

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Open Circuit Voltage - OCV (V)

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100 90

80

70

60

50

40 30

State Of Charge (%)

Stop-Start status versus State Of Charge

If the energy-balance between consumption and recharge phases permits to maintain a sufficient State Of Charge, the automated-Stop is enabled. When the energy management system detects that the Depth of Discharge is too high it automatically restarts the engine and disables the Stop mode so that the alternator re-energizes the board-net and recharges the battery.

The following graph illustrates how Stop-Start is managed according to the State Of Charge level. During Stop phase the SoC drops according to the energy consumption level.

OK

DISABLED

ENABLED

DISABLED ENABLED

Stop-Start status

Automated FORCED re-crank

START

STOP

START

STOP

STOP

ENGINE START

Battery SoC

+

SoC Temp.(*)

SoC

Max. Depth of Discharge

Vehicle startup and drive Engine heat-up and SoC recovery

Vehicle in urban traffic

The battery SoC can vary down to a relative deep discharge

SoC is too low, it must be recovered to secure the coming cranking demand

(*) The Stop-Start function is enabled according to numerous parameters, the battery State of Charge and the engine working temperature being at the heart of the strategy.

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