BMW G12 2015 Technical Training Manual page 68

G12￿Voltage￿Supply￿and￿Bus￿Systems
3.￿Voltage￿Supply
3.2.12.￿PCU￿with￿vehicle￿electrical￿system￿assistance￿measure
On￿vehicles￿with￿the￿equipment￿Electric￿Active￿Roll￿Stabilization,￿energy￿is￿supplied￿by￿the￿auxiliary
battery￿in￿the￿engine￿compartment.
Modern￿vehicles￿have￿a￿high￿energy￿consumption￿due￿to￿the￿many￿electrical￿consumers.￿As￿a￿result,
there￿is￿a￿high￿demand￿on￿the￿battery￿particularly￿in￿phases￿in￿which￿the￿combustion￿engine￿is￿not
running￿and￿the￿alternator￿supplies￿no￿energy￿(e.g.￿engine￿start-stop￿phases).
In￿order￿to￿protect￿the￿battery,￿a￿DC/DC￿converter￿is￿installed￿in￿the￿Power￿Control￿Unit￿(PCU)￿and￿an
auxiliary￿battery￿is￿installed￿in￿the￿engine￿compartment.
The￿preconditions￿for￿the￿direction￿of￿the￿energy￿management￿are￿calculated￿from￿the￿use￿of￿the
vehicle.￿When￿the￿engine￿is￿running￿the￿auxiliary￿battery￿is￿charged￿from￿the￿conventional￿vehicle
electrical￿system.￿During￿the￿phases￿in￿which￿the￿combustion￿engine￿is￿not￿running,￿e.g.￿automatic
engine￿start-stop￿function,￿the￿conventional￿vehicle￿electrical￿system￿is￿supplied￿by￿the￿auxiliary
battery.
The￿Power￿Control￿Unit￿(PCU)￿is￿connected￿to￿the￿PT-CAN2￿and￿a￿DC/DC￿converter￿with￿a￿power
of￿500 W.
3.2.13.￿24￿V￿Electronic￿Power￿Steering
The￿higher￿weight￿8-cylinder￿engine￿in￿the￿G12￿results￿in￿a￿higher￿front￿axle￿load.￿This￿increases￿the
effort￿that￿is￿required￿by￿the￿power￿steering￿servo.￿Due￿to￿these￿high￿currents,￿it￿is￿necessary
to￿increase￿the￿voltage￿supply￿of￿the￿EPS￿to￿24 V.
An￿auxiliary￿battery,￿separating￿element￿and￿a￿charging￿unit￿for￿the￿auxiliary￿battery￿are￿required￿for
this.￿These￿components￿are￿installed￿in￿the￿luggage￿compartment￿of￿the￿G12.
The￿charging￿unit￿monitors￿the￿state￿of￿charge￿and￿charges￿the￿auxiliary￿battery￿using￿a￿DC/DC
converter.￿It￿monitors￿a￿line￿shield￿of￿the￿24￿V￿line￿and￿various￿other￿conditions.￿The￿charging￿unit￿also
switches￿the￿relay￿in￿the￿separating￿element,￿which￿integrates￿the￿auxiliary￿battery￿in￿the￿circuit.￿The
EPS￿is￿supplied￿with￿24￿V￿only￿once￿this￿relay￿has￿been￿switched￿on.￿The￿EPS￿can￿also￿be￿operated
with￿12 V￿in￿the￿event￿of￿a￿fault.
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