In this PhD thesis we studied the influential parameters with respect to the operation of an orbital hydraulic motor, the main function of which is the conversion of hydraulic energy into mechanical work. The total efficiency, which depends on the volumetric and hydraulic-mechanical efficiency, was selected as the main criterion for the above-mentioned conversion of energy. Oil and water test rigs were developed and built for the two different working fluids. Research activities were split into two parts. In the first part, we tried to change the design parameters and reduce the internal leakage, which would lead to an increase of the volumetric efficiency of the hydraulic motor. In the second part, we focused on the contact engineering and tribological improvements, which could lead to better hydraulic-mechanical characteristics. The result shows that the design parameters of the hydraulic motor play a very important role. The total efficiency increased up to 5\,\% when the hole size in the valve plate was changed. The result of a basic hydraulic test shows that the labyrinth sealing with the corresponding annular grooves can significantly reduce the internal leakage. Within the tribological tests we investigated the influence of surface roughness, surface hardness, load, and lubricant on the coefficient of friction, wear loss and wear coefficient in two contacts, i.e., (1) steel/steel and (2) DLC/steel. Considering the coefficient of friction and the wear loss, very promising tribological behaviour was observed for the SS/DLC in water. The result of the tribological test gave us the motivation for further investigations related to the DLC coating, deployed on the outer floating ring of the hydraulic motor. The maximum total efficiency of the modified hydraulic motor was 23\,\%. A combination of DLC, steel and water represents a promising solution for environmental sensitive applications, where oil should be replaced by water.
|
