The plastic gears of car door lock device are prone to fracture in the region of pitch line

so the structural strength should be checked.The gear pair model is created in CAXA

and then the distributing feature on stress and strain of the gear pair in one contact cycle is studied in Ansys12.0.Some conclusionsare summarized finally: Both the contact stress and the nodal displacement would come up to the maximum when the gear pair mesh at the pitch point;The maximum stress is less than the limited contact strength of the gear pair;The large difference on the contact strength between two adjacent meshing positions illustrates that there is an exchange in contaction between single tooth and twos teeth;To the plastic gear

when the meshing type is single tooth meshing moving from tooth tip to pitch point

the maximum contact strength tends to lower.Theoretical reference is provided for the gear of the car door lock device.