BMW I01 Product Information page 76

I01￿High-voltage￿Components
4.￿Electrical￿Machine￿Electronics
Activation￿of￿the￿electrical￿vacuum￿pump
The￿electrical￿machine￿electronics￿provides￿the￿hardware￿for￿the￿evaluation￿of￿the￿signals￿of￿the
brake￿vacuum￿sensor￿and￿for￿the￿activation￿of￿the￿electrical￿vacuum￿pump.￿The￿function￿logic￿for
the￿activation￿of￿the￿electrical￿vacuum￿pump￿is￿located￿not￿in￿the￿EME￿control￿unit,￿but￿in￿the￿DSC
control￿unit.￿The￿EME￿and￿DSC￿control￿unit￿exchange￿sensor￿signals￿and￿the￿switch-on￿request￿for￿the
electrical￿vacuum￿pump￿via￿bus￿signals￿at￿the￿PT-CAN￿and￿PT-CAN2.
The￿brake￿vacuum￿sensor￿is￿mainly￿known￿from￿conventionally￿driven￿vehicles￿with￿automatic￿engine
start-stop￿function.￿Similar￿to￿those￿vehicles,￿it￿is￿also￿installed￿in￿the￿I01￿at￿the￿housing￿of￿the￿brake
servo.
The￿sensor￿is￿supplied￿with￿voltage￿from￿the￿electrical￿machine￿electronics￿and￿returns￿a￿voltage
signal￿depending￿on￿the￿vacuum￿in￿the￿brake￿servo.￿This￿analog￿sensor￿signal￿is￿converted￿by￿the￿EME
control￿unit￿to￿the￿actual￿brake￿vacuum￿and￿sent￿as￿a￿bus￿signal￿to￿the￿DSC￿control￿unit.
The￿DSC￿control￿unit￿evaluates￿the￿brake￿vacuum￿signal,￿includes￿dynamic￿handling￿characteristics
(e.g.￿the￿driving￿speed)￿and￿the￿accelerator￿pedal￿actuation￿and￿determines￿whether￿the￿electrical
vacuum￿pump￿should￿be￿switched￿on.￿The￿function￿logic￿in￿the￿DSC￿control￿unit￿also￿takes￿into
consideration￿a￿hysteresis￿so￿that￿the￿electrical￿vacuum￿pump￿is￿not￿constantly￿switched￿on￿and￿off.
Instead,￿it￿remains￿switched￿on￿until￿a￿requested￿minimum￿level￿of￿the￿brake￿vacuum￿is￿reached.￿The
DSC￿control￿unit￿sends￿back￿the￿switch-on￿request￿from￿the￿electrical￿vacuum￿pump￿as￿a￿bus￿signal￿to
the￿EME￿control￿unit.
The￿electrical￿machine￿electronics￿contains￿an￿output￿stage￿(semiconductor￿relay),￿with￿whose￿help
the￿voltage￿supply￿of￿the￿electrical￿vacuum￿pump￿can￿be￿switched￿on￿and￿off.￿Upon￿request￿the
output￿voltage￿of￿the￿DC/DC￿converter￿can￿be￿shifted￿through￿directly￿to￿the￿electrical￿vacuum￿pump.
Switch-on￿currents￿of￿up￿to￿30 A￿can￿occur￿in￿the￿process.￿The￿current￿level￿is￿restricted￿electronically
to￿protect￿the￿output￿stage￿and￿the￿line.￿There￿is￿no￿control￿of￿the￿power￿or￿engine￿speed￿for￿the
electrical￿vacuum￿pump￿–￿it￿is￿simply￿switched￿on￿and￿off.
A￿malfunction￿of￿the￿electrical￿vacuum￿pump￿is￿identified￿using￿a￿brake￿vacuum￿sensor￿by￿means￿of
the￿no￿longer￿available￿vacuum.￿At￿least￿the￿legally￿prescribed￿deceleration￿(increased￿brake￿pedal
force)￿is￿available.￿The￿DSC￿will￿realize￿a￿type￿of￿hydraulic￿brake-servo￿assistance,￿i.e.￿depending￿on
the￿driver￿pressure￿a￿hydraulically￿reinforced￿circuit￿pressure￿is￿generated.
Advantage:￿Lower￿brake￿pedal￿force￿also￿in￿this￿fault￿scenario
Disadvantage:￿Modified￿brake￿pedal￿response.
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