6
Principles
The suspension system
As ÓsupportingÓ components of the
suspension system, the suspension elements
form the connection between the wheel
suspension and the bodywork. This system is
complemented by the spring action of the
tyres and vehicle seats.
The suspension elements include steel
springs, gas/air and rubber/elastomers or
combinations of the above.
Steel spring suspensions have become well
established in passenger vehicles. Steel
springs are available in a wide variety of
designs, of which the coil spring has become
the most widespread.
Air suspension, which has been used for
many years in heavy goods vehicles, is
Þnding increasing application in passenger
vehicles due to its system-related
advantages.
242_047
In the case of the passenger vehicle we can
differentiate between
sprung masses
(body
with drive train and parts of the running gear)
and
unsprung masses
(the wheels, brakes
and parts of the running gear and the axle
shafts).
As a result of the suspension system, the
vehicle forms an oscillatory unit with a
natural frequency of the bodywork
determined by the sprung masses and the
matching of the suspension system (see
ÓVibrationÓ chapter).
Sprung mass
Unsprung mass Suspension element
Suspension element
49
At an air spring pressure of >3.5 bar, the valve
body lifts against the resilience of both valve
springs and opens valve seats 1 and 2. The air
spring pressure then passes to the air dryer
via the throttle and non-return valve 3. Once it
has passed through the air dryer, the air ßows
through the valve seat of the pressure
limiting valve and the discharge Þlter into the
ambient air.
The signiÞcant drop in pressure downstream
from the throttle results in the uptake of the
relative air humidity whereby the moisture
uptake of the Òwaste airÓ is increased. Pneumatic discharge valve
The pneumatic discharge valve performs two
tasks:
¥ It is a residual pressure retaining device
¥ and a pressure limitation device
A predeÞned minimum pressure (>3.5 bar) is
necessary to prevent damage to the air
springs (U-bellows).
The residual pressure retaining device
ensures that the pressure in the air
suspension system does not fall below
3.5 bar during de-pressurisation (except in
the case of leaks upstream from the
pneumatic discharge valve).
242_037 Discharge valve N11Pneumatic discharge valve (cover)
Valve bodyPressure limiting valve
Valve seat 1
Valve seat 2
Discharge Þlter Vent pipeNon-return valve 3
Air dryer Throttle
