Gearing with a ZK worm and an involute helical gear is used in the motor drive system of automotive continuous variable valve lift (CVVL) because of production cost. Since the geared system does not satisfy the meshing condition, transmission error (TE) and teeth interference (TI) are inevitable. This paper introduces a method for reducing TE and eliminating TI. Transmission error function is derived mathematically and used in checking TI. The first prototype for an automobile shows a lot of NVH problem, which is simply combined by coinciding with the helix/lead angles of two gears at the pitch point. By an optimal process with alternating the pressure and helix angles of worm gear system, an prototype of CVVL worm drive of which NVH problem is acceptably solved is designed.

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