The mechanism of induction of stresses and deformations in plastic cycloidal gears used in gerotor pumps has been analysed using the finite element method and the ABAQUS program. It has been found that the gear system remains under the influence of the mechanical load resulting from the torque on the pump shaft and the hydraulic load resulting from the activity of pressure in the intertooth displacement chambers. It has also been discovered that the intertooth forces and stresses are formed only in the part of the gear that can be referred to as 'active'. In the other part of the gear, forces and stresses do not occur, and the part can be referred to as 'passive'. Another finding of the research is that gear deformations occur such that the teeth of the external gear are deformed and moved in the direction of the active part of the mesh, and the teeth of the internal gear in the direction of the passive part. Thus, radial and axial intertooth clearances are formed, which result in internal leakages in the pump, as well as in lower working pressure and efficiency of the machine. A way of determining the load range for plastic gears used in gerotor pumps has been specified. It has also been observed that the loading of the pump should not result in reduced stresses s z higher than compressive stresses s c equal to the plasticity limit Re of the plastic, that is, s z ( s c 5 Re. At the same time, the radial clearance h r and the axial clearance h a should not exceed the extreme values h r max and h a max assumed for a particular size of gerotor pump, that is, h r , h r max and h a , h a max .

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Cycloidal gears make up the main working unit of hydraulic gerotor machines. In the article, a question of a more efficient application of plastics in building the gears is discussed. The discussion is based on a numerical strain analysis which was done by means of the finite elements method. The stress and deformation values in the operating cycloidal gears were specified. The numerical analysis was carried out in two stages in order to determine the optimum gear tooth profile. The profile depends on the tooth height and on the tooth correction coefficient. At the first stage, the optimum tooth height coefficient was calculated. Having determined the optimum value , the analysis was continued, and at the second stage, the optimum correction coefficient v for the gears at an earlier selected constant value was defined. The analysis results were useful in selecting parameters for determining the geometrical characteristics of the cycloidal gears. The parameters were then used in defining the most suitable tooth profile for the hydraulic machine featuring the cycloidal gears.

The working unit of the hydraulic gerotor machine is a system of cycloidal gears. In the paper, ways of increasing the load-carrying capacity of the plastic cycloidal gears have been presented. The objective has been achieved through of structural and material modifications. The modifications were introduced while making the numerical models of the cycloidal gear system. The fundamental feature of the modifications is the combination of a plastic and a steel core in the design of the cycloidal gear system. While examining the system, the influence of the plastic-steel combination on the stress and deformation distributions in the operation of the cycloidal gears was verified. The numerical analysis was conducted using the finite elements method. The results of the analysis show that the introduction of the modifications strengthens the cycloidal gear system. Therefore, the conclusion that a system can work in the fluid power gerotor machines dedicated to operating at higher working pressure p seems justified. A result of the analysis is a presentation of solutions which will enable the strengthening and a higher load-carrying capacity of the gear system. Another finding of the research was determination of the maximum value of working pressure p at which the hydraulic gerotor machines with the modified cycloidal gears can operate.