Research On Transmission Case Tolerance And Its Impacts On The Gear Meshing Characteristics

As an important part of automotive power system, the performances of transmission directly affect the overall performances of the car. The previous studies about transmission performances were based on the ideal assembly model without tolerance. The paper established the mathematical model of transmission case tolerances and obtained the relations between the transmission case tolerances and axis deviations. This paper also analyzed the impacts of axis deviations on the gear meshing characteristics.Firstly, the mathematical model of transmission case tolerances was established by homogeneous transformation matrix method. The main steps included: Firstly, established the coordinate systems at the ideal positions and the actual positions of the important geometric features and used the homogeneous transformation matrixes to connect these coordinate systems. Secondly, represented the transmission case tolerances as inequality constraints based on the tolerance definitions. Thirdly, developed the mathematical model of the axis deviations by the definitions. In addition, the gearbox case axis deviations calculation software was developed by MATLAB GUI.Secondly, the contact model of helical gear with axis deviations was established based on tooth contact analysis(TCA). Then the impacts of the axis deviations on the meshing path and transmission gear ratio were studied by this contact model. The results showed that the stagger angle and the intersection angle would lead to edge contact, while the gear ratio would occur periodic jumps. And the impact of the stagger angle on the gear ratio was larger than the intersection angle.Thirdly, the finite model of helical gear with axis deviations was established by the ANSYS APDL commend. Then the impacts of axis deviations on the gear meshing stress were studied. The results showed that the deviation of center distance had a certain critical value, the contact stress and bending stress would rise sharply when the deviation of center distance exceeded the critical value. And the stagger angle and the intersection angle had little effect on the bending stress, but would increase the contact stress.Finally, the actual deviations of the gearbox case was measure by the coordinate measuring instrument. Through comparing measurement results and calculation results, tolerance mathematical model was verified. And the sensitivities of axis deviations on the transmission case tolerances were studied. The paper also analyzed the differences of the two tolerancing ways on the axis deviations and gear characteristics.