The paper presents the results of the hydropneumatic suspension strut researches on indicator test stand. The front hydropneumatic suspension strut for Citroen BX and C5 was researched. The aim of this investigation was to determine the damping characteristics (points of force for maximum linear velocity). The stroke and rotary velocities were selected on indicator test stand. For that extortion parameters force versus displacement and force versus velocity diagrams were determined. The damping characteristics were determined too

Andrzej Wieczorek

Piotr Folęga

Rafał Burdzik

Łukasz Konieczny

English

Journal of Measurements in Engineering

  © VIRBROENGINEERING. ISSN PRINT 2335-2124, ISSN ONLINE 2424-4635, KAUNAS, LITHUANIA 155 
24. Determination of the damping characteristics of hydro 
pneumatic suspension strut 
Łukasz Konieczny1, Rafał Burdzik2, Piotr Folęga3, Andrzej Wieczorek4 
1, 2, 3Silesian University of Technology, Faculty of Transport, Gliwice, Poland 
4Silesian University of Technology, Faculty of Mining and Geology, Gliwice, Poland 
1Corresponding author 
E-mail: 1lukasz.konieczny@polsl.pl, 2rafal.burdzik@polsl.pl, 3piotr.folega@polsl.pl, 
4andrzej.n.wieczorek@polsl.pl 
(Received 2 September 2013; accepted 7 September 2013) 
Abstract. The paper presents the results of the hydropneumatic suspension strut researches on 
indicator test stand. The front hydropneumatic suspension strut for Citroen BX and C5 was 
researched. The aim of this investigation was to determine the damping characteristics (points of 
force for maximum linear velocity). The stroke and rotary velocities were selected on indicator 
test stand. For that extortion parameters force versus displacement and force versus velocity 
diagrams were determined. The damping characteristics were determined too. 
Keywords: hydro pneumatic suspension strut, damping characteristic, vibration diagnostics. 
1. Introduction 
The technical condition of the shock can be examined on indicator shock absorber test stand. 
Such an examination can plot the work graph of the shock absorber (force versus displacement) 
as well as the velocity graph (force versus linear velocity) and determine damping characteristics 
[1, 2, 4, 5]. Determination of the damping characteristics can be achieved in two ways (the basis 
of designated force-displacement diagram at a constant stroke and variable angular velocity or the 
angular velocity is constant and the value of the stroke is changed). The damping characteristic is 
determined assuming a value for the maximum damping piston velocity (separately compression 
and decompression). The implementation of the designation of the characteristics of those two 
methods may lead to some discrepancies in the designated characteristics [6]. 
Determining of damping characteristic of hydropneumatic strut is carried out in conjunction 
with a gas spring (the gas spring is part of hydraulic cylinder). Suspension vibration is causing 
changes in the volume of gas separated from the liquid susceptible membrane. The fluid flows 
through the gland – central hole and hole around overshadowed disc springs – play the role of 
shock absorber in hydropneumatic strut. The disc springs play the role of bump valves in shock 
absorber. Dimensions of central hole and holes around and disc spring characteristic determine 
the characteristics of hydropneumatic strut.  
  
Fig. 1. View of hydropneumatic strut and damper [9] 
2. Test stand and measurement system 
The indicator test stand used in researches has been depicted in Fig. 2 [3, 7, 8]. 
24. DETERMINATION OF THE DAMPING CHARACTERISTICS OF HYDRO PNEUMATIC SUSPENSION STRUT.  
ŁUKASZ KONIECZNY, RAFAŁ BURDZIK, PIOTR FOLĘGA, ANDRZEJ WIECZOREK 
156 JOURNAL OF MEASUREMENTS IN ENGINEERING. SEPTEMBER 2013, VOLUME 1, ISSUE 3  
 
Fig. 2. View of laboratory indicator test stand (Citroen BX and C5 strut) 
Determining of damping characteristic of hydropneumatic strut is carried out in conjunction 
with a gas spring, so it is necessary pressurizing of fluid in hyropneumatic strut. For this purpose 
single section hand pump shown on Fig. 3 was used. 
 
Fig. 3. View of single section hand pump 
24. DETERMINATION OF THE DAMPING CHARACTERISTICS OF HYDRO PNEUMATIC SUSPENSION STRUT.  
ŁUKASZ KONIECZNY, RAFAŁ BURDZIK, PIOTR FOLĘGA, ANDRZEJ WIECZOREK 
 © VIRBROENGINEERING. ISSN PRINT 2335-2124, ISSN ONLINE 2424-4635, KAUNAS, LITHUANIA 157 
The measurement system used in the test is shown in Fig. 4. The force sensor CL 16 and 
displacement transducer PTx-200 were used to perform the measurement of force and 
displacement. The analyzer SigLab 20-22 was used for recording signals.  
 
Fig. 4. Scheme of measurement system 
3. Results of research 
For the purpose of determining the damping characteristics of the hydropneumatic column it 
is important that the pressure of fluid for vehicle static load is known. Hydropneumatic suspension 
is a kind of adaptive suspension which keeps constant clearance independent of the static load. 
Determining of damping characteristic on indicator test stand for Citroen BX and C5 strut was 
made for 50 mm stroke and changeable angular velocity. The pressure of fluid in strut was 
corresponding to empty car. In this examination was plotted the work graph (force versus 
displacement) as well as the velocity graph (force versus linear velocity) and damping 
characteristics were determined (value of force for the maximum piston velocity, separately for 
compression and decompression) – Fig. 5. 
 
Fig. 5. Determining of damping characteristic  
Damping characteristic for Citroen BX is presented in Fig. 5 and for Citroen C5 is presented 
in Fig. 6.  
The damping characteristics for Citroen BX and Citroen C5 struts are similar. Since the 
suspension is “soft” (used gas spring with constant mass of gas) so the damping forces are not as 
24. DETERMINATION OF THE DAMPING CHARACTERISTICS OF HYDRO PNEUMATIC SUSPENSION STRUT.  
ŁUKASZ KONIECZNY, RAFAŁ BURDZIK, PIOTR FOLĘGA, ANDRZEJ WIECZOREK 
158 JOURNAL OF MEASUREMENTS IN ENGINEERING. SEPTEMBER 2013, VOLUME 1, ISSUE 3  
large as in case of mechanical suspension with coli spring and hydraulic shock absorber. The 
characteristics are nonlinear and unsymmetric.  
a) 
 
b) 
Fig. 6. Damping characteristic: a) Citroen BX strut, b) Citroen C5 strut 
4. Conclusions 
There are many differences between damping characteristic for hydraulic shock absorber and 
hydopneumatic strut. Damping characteristic of hydropneumatic strut is carried out in conjunction 
with a gas spring, so it is necessary to perform pressurizing of fluid in hyropneumatic strut. The 
research must be repeated for different values of static pressure (static load of vehicle). The force 
sensor of test stand must allow measurement of static force and the dynamic changes in the forcing.  
Nowadays, when hydropneumatic and active suspensions are more commonly used, it is 
necessary to develop new universal methods for testing all kinds of suspensions. The comparison 
of measurement methods for determining damping characteristics of classic, hydropneumatic and 
active suspensions can be a first step to develop universal methods.  
References 
[1] Burdzik R., Gardulski J., Konieczny Ł. Methodology for determining the damping forces of the 
hydropneumatic strut on t indicator test stand. Przegląd Mechaniczny, Vol. 2, 2007, p. 38-40, (in 
Polish). 
[2] Dixon J. C. The Shock Absorber Handbook. Society of Automotive Engineers Inc., Warrendale, PA, 
1999.  
[3] Gardulski J., Warczek J. Investigation on force in frictional kinematic pairs to assess their influence 
on shock absorber characteristic. Transport Problems, Vol. 3, Issue 1, 2008, p. 19-24. 
[4] Konieczny Ł., Gardulski J. Application of simulation researches in diagnostic's of vehicle 
hydropneumatic suspension. Transport Problems, Vol. 2, Issue 1, 2007, p. 13-21.  
[5] Konieczny Ł. Determination of the damping characteristics of hydropneumatic strut taking into 
account the chosen parameters. Zeszyty Naukowe Politechniki Śląskiej, Transport, Vol. 69, 2010, 
p. 85-89, (in Polish). 
[6] Konieczny Ł., Burdzik R., Warczek J. Determinations of shock absorber damping characteristics 
taking stroke value into consideration account. Diagnostyka, Vol. 3, 2010, p. 51-54. 
[7] Konieczny Ł. The use of nonlinear effects in the vibro-acoustic diagnosis of hydropneumatic 
suspension. Zesz. Nauk. Pśl. Nr. 1862, Transp., Vol. 74, 2012, (in Polish). 
[8] Konieczny Ł. Identification of damping characteristic of hydropneumatic strut for example front 
column Citroen C5. WibroTech 2012, XVI Scientific Conference of Vibroacoustics and 
Vibroengineering, XI Polish Seminar Vibroacoustics in Technical Systems, Kraków, 2012, (in Polish). 
[9] Potocki W. Citroen BX. Publishing House Komunikacji i Łączności, (in Polish). 


Determination of the damping characteristics of hydro pneumatic suspension strut

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