Mathematical modelling of excavator productivity taking into account the parameters of the adsorbed vapour layer in the tribo-connections of an axial-piston pump
DOI:
https://doi.org/10.33216/1998-7927-2025-295-9-31-41Keywords:
excavator hydraulic drive, axial piston pump, adsorbed surfactant layer, wear, volumetric efficiency, productivityAbstract
The performance of crawler hydraulic excavators largely depends on the efficiency of the hydraulic system, primarily on the volumetric capacity of the axial piston pump that supplies the working equipment. During prolonged operation, the mating surfaces of the pump tribopair (cylinder block – distribution washer, piston – cylinder) are subject to wear, which leads to an increase in internal leaks and a gradual decrease in volumetric efficiency and, as a result, machine productivity. Modern hydraulic fluids for construction equipment contain anti-wear additives based on surfactants (SAS), which are physically adsorbed on microscopic irregularities of metal surfaces and form a thin protective film.
This adsorbed film partially compensates for surface roughness, increases the actual contact area, reduces local contact stresses at the base of irregularities and thus slows down wear. However, the thickness of this film is not constant: it decreases during the operation of the excavator due to a reduction in the concentration of SAS under the influence of mechanical loads and temperature. To compensate for this phenomenon, in the practice of operating hydraulically driven machines, the working fluid is periodically replaced as planned, thus restoring the concentration of SAS to its initial level. The article proposes a refined mathematical model in which the thickness of the SAS film is described by an exponential law. At the same time, the restoration of the properties of the hydraulic fluid over a fixed time interval is taken into account by introducing the function of changing the thickness of the surfactant film into the expression for calculating the effective tribological clearance associated with the model of leakage changes in the pumping unit of an axial piston pump. On this basis, the dependence of the change in the volumetric efficiency of the pump on the operating time of the excavator and the frequency of hydraulic fluid replacement is determined.
On this basis, the dependence of the volumetric efficiency of the pump on its operating time was obtained and, ultimately, the dependence of the excavator's performance on its operating time, taking into account the frequency of replacement of the hydraulic fluid in the hydraulic drive.
The model is parameterised for a CAT 320 class hydraulic excavator with a bucket volume of 0.75 m³ (two pumps with a capacity of 215 l/min, working pressure up to 35 MPa) and can be used to justify the choice of hydraulic fluids and maintenance intervals for hydraulic drives in construction and road machinery.
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