The gear pair meshing process of the straight conjugate internal gear pump is analyzed

by using tangent polar coordinate method

based on the meshing angle function

the formulation for calculating trapping volume are deduced

and it is affirmed through UG modeling measurement. Then

by using MATLAB programming

the effect of the gear basic parameters on trapping oil characteristic of NBX3pump is analyzed

got the following conclusions:the bigger addendum circle radius of internal gear

tooth profile half-angle

arc tooth thichness of pitch circle angle and smaller addendum circle radius of straight gear is useful to decreasing the adverse effect of trapping oil phenomenon.