## 4 Results from the Test
### Temperature Characteristics  
The recorded temperature allowed us to assess the rate of heating of the shock absorbers during the entire test cycle. The temperature measurement was carried out for new shock absorbers and after durability tests at the MTS stand. This measurement was not performed for shock absorbers removed from trailers used by customers. The first to be tested were new shock absorbers and those dismantled from semi-trailers on which durability tests were carried out. The temperature change recorded when determining the dynamic characteristics was relatively small; hence, the authors decided not to perform this type of measurement for shock absorbers from trailers used by customers. Figure 15 shows the result of temperature measurement over time for the tested shock absorbers.  
In all cases of the tested shock absorbers, an increase in temperature was observed as the frequency of their operation and the duration of continuous operation increased. For new shock absorbers and those after durability tests, the temperature varied in the range of 23-45 \({}^{\circ}\)C. At the beginning and end of the dynamic test, the shock absorber operating speed was set to 0.2 (m/s). The value of the temperature increase in the first and second case for this speed was similar and amounted to 1-2 \({}^{\circ}\)C. Even though the value of the temperature increase for the same shock absorber operating speed is the same, a reduction in the maximum force value was observed when stretching and compressing the shock absorber. Table 4 shows the difference in the average value of the maximum force obtained during stretching (compression) at the beginning of the dynamic test and after the shock absorber temperature increased to approximately 35 \({}^{\circ}\)C.  
Based on the obtained test results, it can be concluded that as the temperature increases, the efficiency of the shock absorber decreases by decreasing the maximum force generated during its operation. For the tested shock absorbers, the decrease in this force was between 2 and 9%, depending on the type of semi-trailer from which the shock absorber came. It should be noted that manufacturers of shock absorbers used in commercial trailers are aware of the increase in shock absorber temperature during their operation and allow shock  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Stretching** & **Compressing** \\ \hline M4 & 5\% & 9\% \\ SL & 3\% & 9\% \\ New & 6\% & 8\% \\ Customers & 2\% & 7\% \\ \hline \hline \end{tabular}
\end{table}
Table 4: Summary of the difference in the average maximum force value at the beginning and end of the dynamic test.  
Figure 15: Results of temperature measurement during dynamic tests of shock absorbers: (**A**) shock absorbers dismantled from an M4 semi-trailer, (**B**) shock absorbers dismantled from an SL semi-trailer, (**C**) new shock absorbers.  
absorber operation up to 110 \({}^{\circ}\)C as normal operating conditions. Above this temperature, it is recommended to introduce an additional cooling system. It should be noted that such high temperatures should not occur under operating conditions. Temperatures above 100 \({}^{\circ}\)C can be achieved during very high dynamics of shock absorber operation, i.e., during durability tests on stands intended for this purpose [33] and tests carried out on test tracks [34].