In order to efficiently predict and investigate a vehicle’s vertical dynamics, it
is necessary to consider the suspension component properties holistically.
Although the effects of suspension stiffness and damping characteristics on
vertical dynamics are widely understood, the impact of suspension friction in
various driving scenarios has rarely been studied in both simulation and road
tests for several decades.
The present study addresses this issue by performing driving tests using a
special device that allows a modification of the shock absorber or damper
friction, and thus the suspension friction to be modified independently of other
suspension parameters. Initially, its correct functioning is verified on a shock
absorber test rig. A calibration and application routine is established in order
to assign definite additional friction forces at high reproducibility
levels.
The device is equipped in a medium-class passenger vehicle, which is driven on
various irregular road sections as well as over single obstacles. For all tested
road sections, a linear decrease of ride comfort in terms of specific relevant
vertical objective values is found by increasing the friction force. This
emphasizes a definite link between suspension friction and vertical vehicle body
vibration, resulting in a negative impact on vertical ride comfort. However, the
longitudinal vehicle body vibration is not significantly affected.
The relevance of friction in terms of transmitting the energy associated with
road unevenness to the chassis in the frequency range of the chassis’ natural
frequency is found to be remarkably high on smooth roads, and still considerably
high on bumpy roads. The chassis and wheel resonance frequencies are
significantly friction-dependent due to the damper’s slip or stick states. The
results obtained from smooth road tests demonstrate the practical relevance of
accurately considering friction for the given suspension type in terms of
vertical ride comfort prediction.
