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

3
Contents
Principles
Vehicle suspension.................................................................. 4
The suspension system .......................................................... 6
Vibration ................................................................................... 8
Characteristic values of springs .......................................... 12
Conventional running gear without self-levelling ............ 14
The self-study programme is not intended as a workshop manual.
The self-study programme will provide you with
information on design and functions.
New
NoteImportant:
Note
Page
For maintenance and repairs please refer to the current
technical literature.
Principles of air suspension
Self-levelling air suspension ............................................... 16
Characteristic values of air spring ...................................... 21
Vibration damping................................................................. 23
Shock absorbers (vibration dampers) ................................ 25
PDC shock absorbers ........................................................... 33
System overview ................................................................... 38
Air springs .............................................................................. 40
Air supply unit ........................................................................ 42
Diagram of pneumatic system ............................................. 43
Compressor ........................................................................... 44
Air dryer ................................................................................. 47
Discharge valve N111 ........................................................... 48
Valve for suspension struts N150 and N151....................... 51
Self-levelling suspension sender G84 ................................ 52
Self-levelling suspension control unit J197 ....................... 54
Self-levelling suspension warning lamps K134 ................ 55
Function diagram ................................................................... 56
Interfaces................................................................................ 57
The control concept .............................................................. 58
Other features of the control concept ................................ 60
Self-levelling suspension, A6

12
00

Characteristic values of
springs
Characteristic curve/spring rate of springs
We can obtain the characteristic curve of a
spring by producing a forces/travel diagram.
The spring rate is the ratio between the
effective force and the spring travel. The unit
of measurement for the spring rate is N/mm.
It informs us whether a spring is hard or soft.
If the spring rate remains the same
throughout the entire spring travel, the spring
has a linear characteristic curve.
A soft spring has a ßat characteristic curve
while a hard spring has a steep curve.
A coil spring is harder due to:
¥ a greater wire diameter
¥ a smaller spring diameter
¥ a lower number of coils
Principles
242_018
If the spring rate becomes greater as the
spring travel increases, the spring has a
progressive characteristic curve.
Coil springs with a progressive characteristic
curve can be recognised as follows:
a) uneven coil pitch
b) conical coil shape
c) conical wire diameter
d) combination of two spring elements
(example, see next page)
242_019
Spring travel s
Resilience F
Linear characteristic curve
Hard spring
Progressive characteristic
curve
a
b
c Linear characteristic curve
Soft spring

31
0,52 0,260
-0,26-0,52
0,52 0,260
-0,26-0,52
0,52 0,260
-0,26-0,52
The force/stroke diagrams thus obtained can
be converted into force/velocity diagrams (f-v
diagrams).
These characteristic curves show the
relationship between the damping force and
the piston speed, thereby indicating the
shock absorber characteristics.
We differentiate between linear, progressive
and decreasing characteristic curves. Damping force
The damping force depends upon the oil
volume to be displaced (surface of the
damping valve), the ßow resistance of the
damper valves, the speed of the damper
piston and the viscosity of the damping oil.
The damping force is determined with the aid
of a test machine. At a constant speed, this
machine produces various rebound and
compression strokes thereby producing
differing rebound and compression speeds in
the damper.
242_066
F-v diagram characteristic curve progressions (speed constant for all strokes)
decreasing
progressive
linear
Traction
force
Compression
force
Traction
force
Compression
force
Traction
force
Compression
force
v in m/s
v in m/s
v in m/s 25 mm
50 mm
75 mm
100 mm
Stroke

43
Diagram of pneumatic
system
1 Suction Þlter
2 Compressor with motor V66
3 Non-return valve 1
4 Air dryer
5 Non-return valve 2
6 Non-return valve 3
7 Throttle
8 Discharge Þlter
9 Pneumatic discharge valve
123
465
7
9
11
10 Discharge valve N11
11 Valve for suspension strut HL N150
12 Valve for suspension strut HL N151
13 Rear left air spring
14 Rear right air spring
from the relay for
compressor J403from control unit
J197
10
1213242_034
from control unit J197
14
8

46
Self-levelling suspension, A6
Discharge/lowering
The air spring valves N150 and N151 and
discharge valve N111 open during
compression. The air spring pressure ßows to
the pneumatic discharge valve and out of the
system from there via the air dryer and the
pressure limiting valve (see description of
pneumatic discharge valve).
242_056 Pneumatic discharge valve
with pressure limiting valve
Diagram of pneumatic system, discharge
11
12
107
64
9
8
4 Air dryer
6 Non-return valve 3
7 Throttle
8 Discharge Þlter
9 Pneumatic
discharge valve
10 N111
11 N150
12 N151
from control unit J197from control unit J197
242_059

50
Self-levelling suspension, A6
The pressure limiting function protects the
system against inadmissible high pressure
e.g. when the compressor fails to switch off
due to a defective relay contact or defective
control unit.
242_035
242_017
Diagram of pneumatic system, pressure limiting function
12
9
8
1 Suction Þlter
2 Compressor
8 Discharge Þlter
9 Pneumatic discharge
valve
from relay J 403
In such cases, the pressure limiting valve
opens against the resilience from approx.
13.5 bar upwards, and the pressure is
discharged via the discharge Þlter.
Pressure limiting valve
Discharge Þlter
from control unit J197
from control unit J197

52
Self-levelling suspension, A6
Self-levelling
suspension sender G84
The vehicle level is detected by the self-
levelling system G84 sender (level
sensor).
A contact-free angle sensor is used to
determine the spring compression
between the rear axle and the bodywork
with the aid of the connecting link
kinematics unit.
The connection of the connecting link
kinematics unit (see Þgures 242_044 and
242_045) is designed to largely
compensate for one-sided compression.
This connection allows self-levelling to
operate using only one level sensor.
The self-levelling system in the Audi A6
is not able to compensate for different
levels on the left and right-hand sides
(e.g. due to one-sided loads).
Pin assignment for level sensor G84
J197 Self-levelling suspension
control unit Pin
1 Earth (from J197)
2 Vacant
3 Vacant
4 Analogue signal output,
voltage signal
5 5 Volt voltage signal
(from J197)
6 Vacant
242_044 Self-levelling suspension sender G84
Connecting link
Axle cross member
Connection to the torsion beam axle assembly in the front
wheel drive version
Bracket (attached to chassis)
Connecting link Self-levelling suspension sender G84
Bracket
Anti-roll bar
Connection for quattro drive with double-wishbone axle
242_045
Sub-frame
The angle sensor operates according to the
Hall principle. Evaluation electronics
integrated into the sensor convert the signal
of the Hall IC into a voltage signal
proportional to the angle (see diagram).

56
Self-levelling suspension, A6
M
+ -+ -+ -
31
1234
Functional diagram
C11 Condenser
G84 Self-levelling suspension sender
J197 Self-levelling suspension control unit
J403 Relay for self-levelling suspension
compressor
K134 Self-levelling suspension warning
lamp
N11 Discharge valve
N150 Rear left strut valve
N151 Rear right strut valve
S Fuse
V66 Compressor motor
T. 30T. 15T. 30
242_001 S SJ403
V66
N111 N150 N151 K134
J197
G84
= Input signal
= Output signal
= Positive
= Earth
= bi-directional
1 Diagnostic interface
2 Driving speed signal
3 Door contact signal
4 Terminal 50 signal
C11