A study of influence of shaft misalignment and hob design on tooth contact of worm gear for MDPS

: The gear contact pattern is an important indicator of whether the contact between the gear teeth is stable, the load distribution is acceptable, and edge contact does not occur. Due to the anti-backlash design of the MDPS(motor-driven power steering) speed reducer, the center distance between the worm and the worm wheel continuously varies during driving. Therefore, the contact pattern varies according to the center distance. The contact pattern also varies according to the oversize and the thread number of the hob. This paper examines the variation of the contact pattern of the worm gear for MDPS according to a center distance error, hob oversize, and the thread number of the hob. The surface separation topology based on differential geometry was used to examine the contact pattern, and finite element analysis was used for crosschecking.