1998 BMW 740I Owners Manual

184n
Deceleration sensors continuously
monitor the physical forces acting upon
the vehicle. In a severe frontal collision,
the gas generators of the driver's airbag
and the front passenger airbag are ig-
nited. However, the passenger-side air-
bag is only triggered if an additional
sensor has recognized that the passen-
ger seat is occupied.
In the event of a severe side impact, the
head protection and side airbags in the
front and/or rear
* are triggered.
390de319
The airbags located under the marked
covers inflate and unfold in a matter of a
few milliseconds. In this process they
tear through the rated breaking points
of the upholstered covers or press them
out.
Because the inflation process must be
virtually instantaneous, it is necessarily
accompanied by a certain amount of ig-
nition and inflation noise. The gas which
the system employs to inflate the airbag
is not dangerous, and the associated
smoke is quickly dissipated.
The entire process is completed within
fractions of a second.On vehicles with automatic transmis-
sion Adaptive Transmission Control
(ATC) uses a number of factors to cal-
culate the maximally efficient gear. In
this process it monitors your personal
driving style, the situation in which you
are driving, the condition of the road
and the traffic conditions.
ATC recognizes your personal driving
style from the positions and movements
of the gas pedal, declaration when
braking and lateral acceleration through
curves. Four shift characteristics – from
comfort-oriented to performance-ori-
ented – are available for selection by
ATC.
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ATC
Airbags ATC

185n
RepairsIndexOverview Controls Car care Technology Data
In order to take driving conditions into
account, ATC registers corners and
both uphill and downhill gradients. For
example, if you maintain speed through
a curve, the transmission does not up-
shift.
On uphill gradients, it shifts only when
the engine speed increases in order to
make more efficient use of power re-
serves. On downhill gradients ATC
downshifts when the speed of the vehi-
cles increases causing the driver to
step on the brakes.
With respect to road conditions, ATC
monitors the friction between the tires
and the road. The system responds to
slippery road surfaces (snow and ice)
by activating the winter program.
Second gear is used when moving
away from a standstill, upshifts occur
sooner, and on descents downshifting
does not occur in spite of the applica-
tion of brakes. This enables you to
"feel" the road as you drive and pro-
duces greater dynamic stability. If the
friction between the tires and the road
is adequate, the normal system is again
activated. The system also leaves the
winter program when you shift from
drive position "D" to "S," "3" or "2," or if
the ASC+T/DSC
* is deactivated.By recognizing traffic conditions, ATC
can retain maximum driving comfort.
For instance, the system recognizes
stop-and-go traffic and then proceeds
only in second gear until it encounters
higher starting loads.
Of course the selector lever can still be
used to select specific gear ratios. Per-
formance-oriented driving is enabled by
shifting from drive position "D" to "S,"
"3" or "2." Positions "3" and "2" each
limit upshifts to the next gear. Position
"2" is best for driving on steep mountain
slopes with a heavy load.Precision sensors monitor the number
of revolutions of the wheels. When
equipped with DSC, they also monitor
steering angle, lateral acceleration,
brake pressure and the movement of
the vehicle around its vertical axis.
If differences in the wheel speeds oc-
cur, the system counteracts the danger
of wheelspin by reducing torque. If nec-
essary, the system also responds with
additional applications of the brakes at
the rear wheels.
If the system detects an instability in the
vehicle's condition, the braking action
can also be directed to the front wheels
by the DSC in order to stabilize the ve-
hicle.
You may need some time to become
accustomed to this system intervention.
However, it helps provide optimum pro-
pulsive force and driving stability.
The braking intervention may be ac-
companied by a certain degree of
noise.
ATC ASC+T/DSC
*

186n
Radio reception BMW Active Seat
*
AM provides substantially longer recep-
tion ranges than FM. AM broadcast sig-
nals, propagated at ground level in the
form of surface waves, are also re-
flected from the ionosphere as atmo-
spheric waves.
Frequency-modulation (FM) provides
substantially better sound quality than
AM. However, because FM transmis-
sions rely on line-of-sight broadcast
waves, their effective reception range is
limited.360de062
Although numerous factors combine to
impose inherent limitations on the re-
ception quality available from mobile ra-
dios, specially designed systems can
be employed to minimize their effects:
With radio stations which broadcast
over multiple frequencies, the "Radio
Data System" (RDS) ensures that the
frequency with the best reception qual-
ity will automatically be selected.
The Diversity Antenna system employs
several FM antennas integrated within
the rear window to provide three sepa-
rate sources for receiving broadcast
waves. An integral processor automati-
cally selects the antenna with the best
FM reception quality at any given time.
Because the ongoing antenna selection
process is completed within millisec-
onds, it remains inaudible to the radio
listener.The Active Seat is an advanced devel-
opment in BMW seats. These seats are
engineered with orthopedic consider-
ations so that you will be less fatigued
during longer trips and sitting for long
periods without moving. The seat is no
longer a passive link between the road,
the running gear, and the driver. In-
stead, by means of an active modifica-
tion to the seat's surface, the seat
causes weight transfers which are slight
and imperceptible. The basic seating
position is not changed by this.
In the seat's upholstery, beneath the
surface of the seat, there is a cushion of
fluid on the left and right. The fluid is
slowly circulated back and forth be-
tween the cushions by means of a
pump.
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RepairsIndexOverview Controls Car care Technology Data
BMW Active Seat
*
Safety belt tensioner DSP sound system
*
This causes a movement of the spinal
column which is barely detectable, to-
gether with an improvement in the flow
of blood to the intervertebral disks and
the muscle structure in the area of the
spinal column.
The passengers do not suffer as much
from muscle tension, back pain in the
lumbar region or symptoms of fatigue.
As a result, the Active Seat represents a
significant contribution to driving com-
fort and driving safety.
The safety belt tensioner responds to
collisions by tightening the belts to en-
sure that occupants remain firmly posi-
tioned in their seats. A gas-pressure
system retracts the buckle assembly to
tension the shoulder and lap belts
within fractions of a second. This re-
duces the tendency to slide under the
lap belt.
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The DSP Professional premium sound
system features a special amplifier
combined with Digital Sound Process-
ing (DSP) and integrated speakers to
surround you with crisp, true-to-life
sound reproduction.
The speaker system's subwoofers,
woofers, midrange speakers and tweet-
ers furnish you with an impressively full-
bodied listening experience. The indi-
vidual components are oriented so as
to produce the aural sensation that you
would experience facing the stage in a
concert hall. The system also automati-
cally adjusts the bass and treble set-
tings to compensate for changes in vol-
ume and vehicle speed.390de109

188n
Rearview mirror with automatic dimmerThe interior rearview mirror with auto-
matic dimming feature reduces glare
from following traffic by adapting the in-
tensity of the reflected images to corre-
spond to levels of light registered by the
unit's sensors. The mirror reverts to its
undimmed setting as soon as the light
source disappears. One of these sen-
sors is mounted on the front of the mir-
ror housing and is designed to monitor
light levels in the area immediately for-
ward of the vehicle. The second sensor
is integrated within the mirror's glass.
The electronic control system operates
by comparing the respective levels of
luminous intensity in front of and behind
the car. The difference provides the ba-
sic parameter used to modulate an
electrical current and induce chemical
changes in a semisolid layer incorpo-
rated in the lens. 390de113
The semisolid reacts chemically to this
electrical current, thus providing infi-
nitely-variable dimming of the mirror
(electrochromic technology).
As a result, it is no longer necessary to
dim the mirror manually, and the driver
can maintain full concentration on traf-
fic.

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RepairsIndexOverview Controls Car care Technology Data
Tire Pressure Control (RDC)
*
The Tire Pressure Control system as-
sumes the task of regular tire pressure
checks for you. Tire pressures are mon-
itored at all four wheels, even when the
vehicle is moving.
Behind the valve stem in every wheel,
there is an electronic chip which is de-
signed for severe-duty applications and
long service life. It contains a pressure
sensor, a transmitter and a battery. The
pressure is measured in extremely short
time intervals and then transmitted by a
radio signal. If an irregularity is de-
tected, the transmission rate is in-
creased.380de673
Near every wheel, there are antennas in
the body which receive the signals from
all four wheels. A central electronics
system evaluates the quadruple signals
which it receives and forwards any
changes.
The RDC provides an important contri-
bution to driving safety.

190n
Xenon lamps
*
The xenon lamps light up the side and
front areas of the vehicle with signifi-
cantly more brightness and uniformity
than the traditional halogen lamp.
In a xenon lamp,
an electric arc re-
places the filament in order to generate
intense illumination. A gas mixture in a
quartz piston with metal vapor is ignited
by a high electric voltage. The arc that
is generated is then sustained by a
lower voltage. When the lamp is turned
on there is a brief period of high inten-
sity. Maximum brightness is attained in
approx. 15 seconds.
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Xenon lamps
provide significantly-im-
proved visibility, especially during ad-
verse weather conditions and driving
situations (driving at night in heavy rain
or through road repair areas where
there are no lanemarkers, for instance).
Vehicles with xenon lamps are
equipped with automatic-dynamic
headlamp range control. As a result, the
highway is always optimally lighted, re-
gardless of load conditions, and drivers
in oncoming traffic are not blinded.
Xenon lamps make a significant contri-
bution to highway safety since other
highway users, bicyclists and motorcy-
clists in the right lane, and pedestrians
are more easily detected.

191n
RepairsIndexOverview Controls Car care Technology Data
Water and dirt repellent windshield
*
With this windshield (not released at
this time), a specially-smoothed surface
causes water drops to bead up and run
off, thus carrying particles of dirt with
them.
Traditional windshields, even when they
are in new condition, have a microscop-
ically "rough" surface (1). The surface of
the water and dirt repelling windshield
is smoothed with a clear transparent
fluid.
Depending on the cleanliness of the
windshield, the water beads up and
runs off at approx. 40 mph (60 km/h) as
a result of the air flow (2). The coating
has no negative effect on vision through
the windshield because it is completely
transparent.390de337
Additional benefits:
>Clear vision in adverse weather con-
ditions, resulting in enhanced driving
safety
>Less glare when driving in the rain at
night.