length BMW 750IL 1998 E38 Level Control System Manual

45
Level Control Systems
Air Springs
An identifying feature of the E65/E66 air spring is the internally guided air bellows. Internally
guided means that the bellows is guided in an aluminum casing. The bellows is support-
ed on this casing. This prevents the compression forces from weighing heavily on the bel-
lows.
This process allows the bellows to be manufactured from a thin, flexible diaphragm which
can react to minimal shocks and in this way provide a more comfortable suspension.
The diaphragm is composed of only one fabric layer embedded in rubber. The fibers with-
in the fabric run longitudinally along the spring strut. The bellows is therefore known as an
axial air bellows.
The bottom end of the air spring strut is enclosed
in a bellows in order to protect the diaphragm
against the mechanical effects of fouling (sand, dirt
etc.). The lower end of the bellows incorporates
small holes for pressure compensation in the
space between the roll piston and bellows. The
action of the bellows rolling in this space produces
pressure differences.
The bellows together with the roll piston contains
a volume of air that is sufficient for optimum sus-
pension.
A residual pressure holding valve on the air spring
strut prevents it from being depressurized. The air
spring strut remains under pressure in the event of
a loss of pressure in the system. The residual
pressure is 3.25 +/- 0.75 bar. This ensures that
the bellows is not damaged when the car is still
being moved.
The residual pressure holding valve is secured with
Loctite and must NOTbe removed.
The air spring strut is initially filled at the manufac-
turer to 10 bar. This pressure is reduced to 3.5 bar
when the spring strut is to be stored. Under this
pressure, the strut is extended to maximum
length.
The connection of the air spring struts to the air
supply unit (distributor block) is located on the left
of the luggage compartment under the flap on
which the wheel nut wrench is mounted.