oil level AUDI A6 ALLROAD 1999 C5 / 2.G Pneumatic Suspension System

27
Single pipe gas-pressure shock absorber
With the single pipe gas-pressure shock
absorber, the working chamber and the oil
reservoir are located in a single cylinder.
Volumetric changes caused by the piston rod
and the temperature changes in the oil are
compensated by another gas chamber which
is separated from the working cylinder by a
dividing piston. The level of pressure in the
gas chamber is approx. 25 - 30 bar and must
be able to sustain the damping forces during
compression.
The damping valves for compression and
rebound are integrated into the piston.
Comparison of single/dual pipe gas-pressure shock absorbers
Dual pipe gas-pressure shock
absorberSingle pipe gas-pressure shock
absorber
Valve function The tendency towards cavitation
is reduced by the gas pressure in
the oil reservoirMinimal tendency towards
cavitation thanks to high gas
pressure and separation of oil and
gas
Characteristic
curvesAny, due to separate valves for
compression and reboundDependant on the gas pressure
during compression
Short damping
strokesGood Better
Friction Low Higher due to seal under pressure
Design Greater diameter Longer due to gas chamber in the
cylinder
Installation
positionApproximately vertical Any
Weight Heavier Lighter
242_082
Piston with damping
valves
Dividing piston
Gas chamber
Damper valves

40
The air springs
The installation of the air springs on the front-
wheel drive and the quattro drive is the same
as in the steel spring version. This allowed the
use of the axle design from the production
running gear with few modiÞcations.
In the front wheel drive version the piston is
conical in shape to allow sufÞcient clearance
for the spring movement between the
bellows and the piston.
In the quattro drive the air springs are
combined coaxially with the dampers to
act as a suspension strut.
Self-levelling suspension, A6
242_043
quattro drive
Coaxial arrangement of air springs/PDC damper
242_042
Front-wheel drive
Separate arrangement of air springs/PDC damper
Air springs may not be moved while
at atmospheric pressure since the
U-bellows cannot uncoil on the piston
and would be damaged.
In a vehicle with depressurised air
springs, the corresponding air springs
must be Þlled with the aid of the
diagnostic tester (see Workshop
Manual) before raising or lowering
the vehicle.

44
Self-levelling suspension, A6
The compressor
The compressed air is generated by means of
a single stage piston compressor with
integrated air dryer. In order to avoid oil
contamination of the U-bellows and the dryer
cartridge, the compressor is a so-called dry
running compressor.
Permanently lubricated bearings and a PTFE
(polytetraßuoroethylene) piston ring ensure a
long service life.The discharge valve N111 and the pneumatic
discharge valve are integrated into the dryer
cartridge housing.
In order to protect the compressor from
overheating, it switches off at excess
temperatures (see Overheating protection
chapter, page 61).
Discharge valve N11Pneumatic discharge valve
with pressure limiting valve
Non-return valve 3Air dryer
Non-return valve 1
PTFE piston ring
Suction Þlter
Discharge Þlter
Pressure connector
242_013
Non-return valve 2