Abstract: According to the definition and description of error in the gear precision standard， an equivalent definition of assembly errors and machining errors was proposed for the gear dynamic analysis. A gear parametric model with assembly errors and machining errors was established by Pro/E secondary development. Then the gear finite element model was created based on dynamic contact mechanics and explicit dynamic finite element method. Finally， its dynamic simulation was conducted using the large deformation explicit dynamics software ANSYS/LSDYNA， thus the the calculation for gear contact stress on tooth contact was available to consider the effects of assembly errors and machining errors. Results showed that the larger all kinds of random errors are， the greater the impact of the gear contact stress are. Of all kinds of random errors， the effects of gear machining error and misalignment error on the plane of action are the most obvious， while the misalignment error on the vertical plane of action exerts the least effect on the gear contact stress. The most significant fluctuation of tooth contact stresses appears when the assembly errors and machining errors both exist.

Key words: spur gear, assembly errors, machining errors, parametric, contactimpact, dynamic simulation, contact stress