Abstract
The friction at the contact surfaces of a vehicle body vibration damper, which are moved relatively to each other, influences its transmission behavior at the start of movement (breakaway force) as well as with excitation signals of higher velocity and thus has an impact on the comfort properties of the damper. According to Vibracoustic (Die wichtigsten Kriterien für deutsche Autofahrer beim Autokauf, Springer Fachmedien Wiesbaden GmbH, Wiesbaden, 2019), for most German drivers (63%) comfort (in addition to brand and appearance) before driving dynamics (53%) and environmental compatibility (48%) is the most important criteria when evaluating a new car, which explains the importance of this vehicle characteristics. Furthermore, the friction is present with any relative movement of the damper and is, therefore, relevant for the design of the damper and the associated vertical dynamics. The friction is generally determined in the fully assembled state of the damper, including oil filling and gas pressure at a very low movement velocity to eliminate the influence of the damping force. This measurement method allows no or only inadequate statements about the friction behavior at, e.g. more dynamic excitation scenarios. As a result, the aim should be to characterize the friction properties without the influence of hydraulic damping at the start of movement or reversal of movement, as well as at higher movement velocities. Another goal is to evaluate the influence of the internal pressure of the damper on its friction behavior. The test damper used here is a commercially available monotube damper that has been modified in accordance with the requirements for these tests. The results shown below can be used as starting variables for further investigations for the targeted optimization of the friction properties and thus for the improvement of driving comfort. The reduction in damper friction promises an increase in comfort due to the improved decoupling of the vehicle body from the road excitation. Furthermore, the data obtained enable the level of detail of simulation models to be increased and serve as a basis for comparing different friction pairings and contact surfaces in the damper. For the substitution of coatings (chrome-free piston rods → environmental protection) or tube materials (aluminum matrix composites → lightweight construction) as well as for changes in the surface structure and roughness, the results enable an evaluation of the friction properties compared to conventional dampers and the adjustment of the friction pairings in the sense of the best possible functionality.
Highlights
The transmission path for roadway-induced vibrations from the wheel-roadway contact to the vehicle body and the passenger is largely defined by the stiffness, masses and1 3 Vol.:(0123456789)Automotive and Engine Technology (2020) 5:79–90 this reason, road and chassis-induced noise and vibrations are even more clearly the focus of NVH3 optimization in this type of vehicle
The test bench used for the experiments is a hydropulse test bench from the manufacturer Inova consisting of a conventional hydraulic system, which parameters are designed for testing a wide range of different vehicle body vibration dampers
As part of the investigations presented here, the friction properties of a commercially available monotube damper were characterized in various theoretical excitation scenarios
Summary
The transmission path for roadway-induced vibrations from the wheel-roadway contact to the vehicle body and the passenger is largely defined by the stiffness, masses and. The monotube damper (Fig. 1) creates friction on the separating piston, which isolates the oil-filled working area from the gas-filled compensation area. As part of the transmission path (Fig. 2), this results in a slight change in the transmission behavior or a stiffening of the system compared to the consideration of purely hydraulic forces, which can have a negative influence on certain vibration and noise phenomena in different frequency ranges. This property gives rise to the above-mentioned influence on the NVH behavior of the vehicle, which tends to be adversely affected by the increase of stiffness and possible stick–slip effects, towards higher frequencies. It can be seen that the friction in the damper primarily affects driving comfort
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