Analysis and characterization of the friction of vehicle body vibration dampers

摘要

The friction at the contact surfaces of a vehicle body vibration damper, which are moved relatively to each other, influencesits transmission behavior at the start of movement (breakaway force) as well as with excitation signals of higher velocityand thus has an impact on the comfort properties of the damper. According to Vibracoustic (Die wichtigsten Kriterien fürdeutsche 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 thedamper 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. Thismeasurement method allows no or only inadequate statements about the friction behavior at, e.g. more dynamic excitationscenarios. As a result, the aim should be to characterize the friction properties without the influence of hydraulic dampingat the start of movement or reversal of movement, as well as at higher movement velocities. Another goal is to evaluate theinfluence of the internal pressure of the damper on its friction behavior. The test damper used here is a commercially availablemonotube damper that has been modified in accordance with the requirements for these tests. The results shown belowcan be used as starting variables for further investigations for the targeted optimization of the friction properties and thus forthe improvement of driving comfort. The reduction in damper friction promises an increase in comfort due to the improveddecoupling of the vehicle body from the road excitation. Furthermore, the data obtained enable the level of detail of simulationmodels 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 matrixcomposites → lightweight construction) as well as for changes in the surface structure and roughness, the results enable anevaluation of the friction properties compared to conventional dampers and the adjustment of the friction pairings in thesense of the best possible functionality.