3 Series E90 320i (N43) SAL
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Battery status - battery charge too low
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Air conditioning requirements - cooling
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Partial vacuum in brakes not low enough
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Vehicle starting to roll.
Special features of switch-off inhibiting and switch-on prompting
Battery status and onboard power supply
The battery status is a key factor influencing whether switch-off inhibiting and/or switch-on
prompting are set. The battery status is calculated in the APM (Advanced Power
Management). This function is integrated into the engine management (see energy
management) and has been specifically extended for the Auto Start Stop function.
The aim is to permit reliable starting of the combustion engine after a defined parked
period, in terms of the onboard power supply. Before the combustion engine is switched off,
a reliable prediction of the minimum usable, absolute residual capacity and the minimum
voltage level in a subsequent hot start is made. The APM calculates the condition of the
electrical onboard power supply based on the battery status.
If the battery's charge condition falls into the red zone after the engine has been switched
off by the Auto Start Stop function, the Auto Start Stop function starts the engine.
Air conditioning requirements (heating operation / air conditioning operation)
If the coolant temperature is well below the target outlet temperature (heating-up mode),
this is treated as a switch-off inhibitor. In the heating-up mode, the electric auxiliary water
pump (N47) and electric main water pump (N43) are activated upon an ASSF engine stop.
This is prompted by the heating and air conditioning control unit via the bus system.
In the event of an ASSF engine stop, climatic comfort may be reduced (formation of
humidity/odours) because the air conditioning compressor is not running and consequently
delivers no cooling output.
If the evaporator temperature rises above a threshold value during the ASSF engine stop
when the air-conditioning system is switched on, this is treated as a switch-on prompt and
the engine starts automatically.
If the condensation sensor measures a value that suggests condensation will occur, with
the automatic air conditioning switched on the Auto Start Stop function is suppressed
(switch-off inhibiting). If this occurs during an ASSF engine stop, a switch-on prompt is
issued.
Insufficient braking pressure
To ensure that there is always sufficient braking force (including when the engine is
switched off), the partial vacuum in the brake servo must always be monitored. If
necessary, the engine is started automatically as soon as the partial vacuum falls below
500 hPa during an ASSF engine stop.
Steering assistance
The engine will not be switched off for as long as the steering wheel is being turned.
Steering assistance is always assured. Only when the Auto Start Stop function ceases to
identify any movement of the steering wheel via the steering column switch centre can the
engine be switched off. This information is provided via the bus system.
Safety requirements
SI Auto Start Stop function E81 E87 E90 E91 E92 E93 R56
BMW AG - TIS
25.01.2013 03:01
Issue status (12/2007) Valid only until next DVD is issued
Copyright
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