the vehicle by carefully selecting the
engine mounting system. The mount-
ing system for the Volvo 850 has
been designed on the following
grounds:
- The two main engine mounts
(hydromounts) are located at the node
for the vibrations. This means on a
line through the centre of gravity for
the powertrain.
- By using soft support at the front
of the engine, the engine is kept in
balance while the main mounts do not
carry bending loads.
- By using two nonlinear reaction
rods, extreme loads from the drive
shafts are taken care of.
When designing the engine mount-
ing system great attention was taken
to the engine vibration characteristics.
The engine mounting consists of a
two-way insulation system, where
two main hydromounts, one support
mount and the lower torque reaction
rod are mounted to a rubber insulated
subframe (figure 20). This gives an
excellent insulation of engine vibra-
tions.
The main mounts and the torque
reaction rods are located in positions
with low displacement amplitude of
vibration. The dynamic stiffness of the
mounts is low to give a good vibra-
tion isolation for small displacement
amplitudes. Large displacement am-
plitudes from the chassis are damped
by the hydraulic system of the hydro-
mounts, which is essential for a good
ride comfort.
Due to the engine vibration char-
acteristics, the displacement am-
plitude of vibration is larger in the po-
sition where the support mount is
located. Therefore it has progressive
characteristics with a low initial dy-
namic stiffness .
The main purpose of the torque re-
action rods is to restrict the engine
motions due to the torque of the en-
gine. Their characteristics are softly
progressive with a low initial stiffness.
Engine vibration levels
The firing order of the B5254F is
1-2-4-5-3, with even firing interval of
144 crank degrees.
Both theory and practical ex-
perience show that there are primarily
two vibration characteristics which
must be considered when installing
the engine in a car. The engine is ex-
cited by a first order of rotating inertia
couple with magnitude
From the principal vibration pattern
due to these excitations, it is possible
to minimize the disturbance input to
