The paper presents issues related to the operation of hydraulic shock absorbers. The primary objective was to determine the influence of temperature and the technical condition on the damping properties of a twin-tube hydraulic shock absorber. Three units (one new and two used) of the same type of a shock absorber were used for testing. During the tests, the shock absorber was subjected to sinusoidal excitation at fixed values of frequency and displacement amplitudes. There are few low-temperature tests of shock absorbers available in the literature; thus, great emphasis was placed on this aspect of the study. The characteristics of the shock absorbers were determined from a temperature of −30 °C until a steady-state temperature was reached at a given excitation. The resistance force at this temperature is about 2.5 times higher than at 20 °C. The study shows that such high forces can lead to the failure of shock absorber components (especially the valves). The amount of energy dissipated in a single operating cycle of a shock absorber decreases non-linearly with the increase of the temperature. Understanding the temperature dependence of the shock absorber in combination with the cooling curve allows for the steady-state temperature to be estimated at a given excitation. The study also shows that the installation of used shock absorbers in vehicles is not acceptable. Although there are no external signs of wear, their characteristics can differ significantly from those of new shock absorbers.

In this study are presented the results of the simulation tests of the friction pairs occurring between the spring leaves while considering a condition of the mating surfaces and an impact of the velocity of their mutual dislocation on the values of the friction coefficients. It has been proposed a methodology in respect of a determination of the coefficients of the static and kinetic friction. Two kinds of the specimens have been prepared for the tests, which have been cut out from a spring leaf of the prototype spring – they have created the model friction pairs. The condition of the specimen surface and their selected mechanical properties have been evaluated. During the experimental tests have been considered: four sliding velocities, four variants of the surface conditions and two values of the normal load. The tests of the friction pairs have been performed at the laboratory stand for measuring the friction force. The results of the tests have been presented in a form of the time courses of friction force, graphs and tabular summaries of the friction coefficients. It has been conducted a comparative analysis of the results in order to determine an influence of the test results on the values of the determined friction coefficients. The proposed research conditions are approximate to the typical operating conditions of the road vehicles.

This article presents a simulation study of the suspension system in a vehicle that weighs approximately 12 tons (class N2). The authors have tested the influence of experimentally determined values of friction coefficients on the energy dissipated in the multi-leaf spring. The study was carried out using finite element analysis with LS-DYNA software. A nonlinear vibration model of the complete spring was developed, including the variable friction forces between the leafs. The model takes into account the sprung and unsprung mass of the chassis. Numerical tests were carried out using three different coefficients of friction (determined experimentally) for a selected speed of the car. Random realizations of the road micro-profile (type A, B, C) recommended by ISO 8608 were used. The results of the tests were presented in the form of acceleration curves in the vertical direction, comparative plots of daily vibration exposure A(8) and vibration transmission coefficient (T), and the distributions of RMS acceleration in frequency of one-third octave bands. This data was used to assess the quality of the vibration isolation system between the front suspension of the vehicle and the driver’s seat.

The article deals with investigations of a prototype single and double multi-leaf spring composed of a four-leaf main spring and a double-leaf supporting spring subjected to the cyclic loads. A methodology of a measurement conducted during experimental tests and a set of research instruments used in the stand research allow evaluation of the effects of friction and the accompanying heat stress of the leaf spring in the quasi real operating conditions. The role of clearances and friction in operation of this type of construction as well as analytical, numerical, and bench testing methods used in the research on the effect of energy dissipation due to friction on operation of the leaf spring are discussed. Dynamic elastic characteristics with hysteresis loops and identification of leaf cooperation areas are presented for the single and double multi-leaf springs tested under different conditions.