Mechanics and FEM estimation of gaps generated in star-ring active contacts of ORBIT motor during operation

We estimate deformations or gaps occurring at all the ideally form-closed contacts, that separate the chambers, in epitrochoid (cycloidal class) generated star-ring gears of ORBIT® motors. The direct measurement of these deformations and gaps is not an easy task as the contact positions are inaccessible for installing any measuring device. Therefore, we target the accurate theoretical estimation of these deformations and gaps for any pressure or torque load. The problem poses statically indeterminate, as there are multiple contacts. We use FEM in Ansys® environment to model the problem and its solution. We develop the model to its final stage with gradual improvement in assessing more accurate and realistic boundary conditions as well as loading patterns. We make an elaborate presentation of this process in this investigation report. Interestingly, in ORBIT motor momentary occurrence of gap at the transition active contact, i.e., the contact separating the two adjacent chambers with one in high pressure and the other in low pressure, is unavoidable. This occurs for a substantial period of a power cycle and sometimes in both transition contacts, that separate the overall high pressure zone and the low pressure zone. The inter-chamber leakages through these gaps are partially responsible for lowering the volumetric efficiency. The present investigation is limited to establishing a method of estimating deformation and gaps at the active contacts of such units. Our proposed method can be used for any such unit of any geometric design data and kinematic model.