Academia.eduAcademia.edu

Figure 3 – uploaded by Francesco Castellani

See full PDFdownloadDownload figure
Fig. 4. Example of Characteristic Curve The classic test, for extracting the features of a shock absorber, is based on submitting a sinusoidal motion with fixed amplitude to the system and then measuring the force transmitted by the damper to the structure. The synchronized data of force, displacement and velocity are collected, in order to generate the two characteristic graphs in output from the analysis, which are the force-displacement and force-velocity diagrams (Figure 4).

Figure 4 Example of Characteristic Curve The classic test, for extracting the features of a shock absorber, is based on submitting a sinusoidal motion with fixed amplitude to the system and then measuring the force transmitted by the damper to the structure. The synchronized data of force, displacement and velocity are collected, in order to generate the two characteristic graphs in output from the analysis, which are the force-displacement and force-velocity diagrams (Figure 4).

Related Figures (15)

Fig. 1. The evolution of cavitation cavitation” when it involves the entire compressed chamber. Finally, it is called “complete cavitation’, when it involves also the chamber which is in compression phase [12]. Although the phenomenon is highly investigated in volumetric compression machines, scientific iterature regarding shock absorbers is at its early stages. For this reason, this work has the objective to evaluate the beginning and the evolution of phenomenon, when the shock absorber is subject to variations in pressure and temperature. Further objective is to understand how the variation of these parameters affects the overall performances.
Fig. 1. The evolution of cavitation cavitation” when it involves the entire compressed chamber. Finally, it is called “complete cavitation’, when it involves also the chamber which is in compression phase [12]. Although the phenomenon is highly investigated in volumetric compression machines, scientific iterature regarding shock absorbers is at its early stages. For this reason, this work has the objective to evaluate the beginning and the evolution of phenomenon, when the shock absorber is subject to variations in pressure and temperature. Further objective is to understand how the variation of these parameters affects the overall performances.
Fig. 2. The test bench and a detail of its road crank The Department of Engineering at the University of Perugia provides an instrumental set, for capturing the test data. The test bench (Figure 2) is constituted by a static solid structure and by a road crank actuated by an electrical motor. This stresses the shock absorber with sinusoidal displacement at variable frequency from | to 6 Hz.
Fig. 2. The test bench and a detail of its road crank The Department of Engineering at the University of Perugia provides an instrumental set, for capturing the test data. The test bench (Figure 2) is constituted by a static solid structure and by a road crank actuated by an electrical motor. This stresses the shock absorber with sinusoidal displacement at variable frequency from | to 6 Hz.
Fig. 3. Render of the transparent monotube shock absorber The central element of the experimental set up is the transparent monotube shock absorber (Figure 3), with a separate compensation chamber, where a floating piston separates oil from nitrogen.
Fig. 3. Render of the transparent monotube shock absorber The central element of the experimental set up is the transparent monotube shock absorber (Figure 3), with a separate compensation chamber, where a floating piston separates oil from nitrogen.
24 tests are carried out by varying the relative pressure among predetermined values [0 - 0.2 - 0.5 - 1 MPa] and changing the stress of the frequency bank from | to 6 Hz, by 1Hz steps. The temperature is kept constant and equal to 20°C. The working fluid is never replaced; it has a SAE 5W viscosity and the settings of the valves are unchanged for all the tests. Starting from the highest frequency, the output data from the test are processed through a Matlab script, reconstructing the Characteristic Curve (Figure 5). Apparently, the cavitation phenomenon occurs only for relative pressure near to zero bar. Yet, analysing further through optical acquisitions, it is possible to verify that the phenomenon is clearly present in many tests. For example, at 0.5 MPa pressure, an incipient cavitation is observed (Fig. 6).
24 tests are carried out by varying the relative pressure among predetermined values [0 - 0.2 - 0.5 - 1 MPa] and changing the stress of the frequency bank from | to 6 Hz, by 1Hz steps. The temperature is kept constant and equal to 20°C. The working fluid is never replaced; it has a SAE 5W viscosity and the settings of the valves are unchanged for all the tests. Starting from the highest frequency, the output data from the test are processed through a Matlab script, reconstructing the Characteristic Curve (Figure 5). Apparently, the cavitation phenomenon occurs only for relative pressure near to zero bar. Yet, analysing further through optical acquisitions, it is possible to verify that the phenomenon is clearly present in many tests. For example, at 0.5 MPa pressure, an incipient cavitation is observed (Fig. 6).
Fig. 6. Images acquisition of the test, 6Hz, 0.5 MPa
Fig. 6. Images acquisition of the test, 6Hz, 0.5 MPa
Only at a gas pressure of 1 MPa, bubbles are not observed. Decreasing the frequency of the stress, cavitation occurs only for low values of pressure.
Only at a gas pressure of 1 MPa, bubbles are not observed. Decreasing the frequency of the stress, cavitation occurs only for low values of pressure.
Fig. 8. Images acquisition of the test, 6Hz, OMPa Fig. 7. Images acquisition of the test, 6Hz, 0.2MPa
Fig. 8. Images acquisition of the test, 6Hz, OMPa Fig. 7. Images acquisition of the test, 6Hz, 0.2MPa
At 0.2 MPa pressure, an evolved cavitation arises (Figure 7); at 0 MPa, a complete cavitation is observed (Figure 8).
At 0.2 MPa pressure, an evolved cavitation arises (Figure 7); at 0 MPa, a complete cavitation is observed (Figure 8).
Fig. 10. Summary grid of an optical evaluation main chamber is caused. Maintaining a constant temperature, the stress frequency and the pressure are varied, in order to generate a general map of the onset of the cavitation and its evolution. Through the map of Figure 10, one can argue that the most challenging testing ground is the regime of low pressure — high frequency stress.
Fig. 10. Summary grid of an optical evaluation main chamber is caused. Maintaining a constant temperature, the stress frequency and the pressure are varied, in order to generate a general map of the onset of the cavitation and its evolution. Through the map of Figure 10, one can argue that the most challenging testing ground is the regime of low pressure — high frequency stress.
Fig. 11. Video acquisitions of piston, stressed 6 Hz, gas pressure 0.5 MPa, during the variation of the temperature From the grid (Figure 10) produced by the first analysis of the data made through the video capture, it is evident that the effect of temperature on the cavitation is the opposite of what one could expect. Evaluating the test carried out at [6 Hz, P = 0.5 MPa] of Figure 11, it arises that, in the captured frames at a temperature of T = 20 °C, the cavitation occurs in the incipient phase. As the temperature increases, it fades and ceases to exist.
Fig. 11. Video acquisitions of piston, stressed 6 Hz, gas pressure 0.5 MPa, during the variation of the temperature From the grid (Figure 10) produced by the first analysis of the data made through the video capture, it is evident that the effect of temperature on the cavitation is the opposite of what one could expect. Evaluating the test carried out at [6 Hz, P = 0.5 MPa] of Figure 11, it arises that, in the captured frames at a temperature of T = 20 °C, the cavitation occurs in the incipient phase. As the temperature increases, it fades and ceases to exist.
Fig. 12. Characteristic Curve, 6Hz, 0.5MPa, [20-30-40-50 °C]
Fig. 12. Characteristic Curve, 6Hz, 0.5MPa, [20-30-40-50 °C]
Fig. 13. Characteristic Curve, 5Hz, OMPa, [20-30-40-50 °C] The situation changes when, at the start of the test, a complete cavitation phase is present (orange colour of Figure 10). In this condition, during the variation of the temperature, the cavitation phenomena decreases, as arises from _ the Characteristic curve (Figure 13).
Fig. 13. Characteristic Curve, 5Hz, OMPa, [20-30-40-50 °C] The situation changes when, at the start of the test, a complete cavitation phase is present (orange colour of Figure 10). In this condition, during the variation of the temperature, the cavitation phenomena decreases, as arises from _ the Characteristic curve (Figure 13).
Fig. 14. Variation the performance of the shock absorber It is possible to summarize this trend through a plot, illustrating the variation of the performances of the shock absorber. They are expressed in Joules, and in Figure 14 they are shown as function of the pressure and of the stress of the frequency bench.
Fig. 14. Variation the performance of the shock absorber It is possible to summarize this trend through a plot, illustrating the variation of the performances of the shock absorber. They are expressed in Joules, and in Figure 14 they are shown as function of the pressure and of the stress of the frequency bench.
It is possible to summarize this trend through the plot of Figure 16, illustrating the variation of the performances of the shock absorber. They are expressed in Joules, and they are shown as function of the temperature, for fixed values of frequency bench stress and pressure.
It is possible to summarize this trend through the plot of Figure 16, illustrating the variation of the performances of the shock absorber. They are expressed in Joules, and they are shown as function of the temperature, for fixed values of frequency bench stress and pressure.
Related topics:
EngineeringMechanical EngineeringMaterials ScienceHydraulic systems and structuresShock Absorber Design
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved