INTRODUCTION

Wildhaber [1926] and Novikov [1956] have proposed helical gears based on generation by circular arc rack-cutters. The difference between the two inventions is that the gear tooth surfaces of Wildhaber gears are in line contact and the gear tooth surfaces of Novikov gears are in point contact. Figures 17.1.1 and 17.1.2 show the first and second versions of Novikov gears with one and two zones of meshing, respectively.

Point contact in Novikov gears has been achieved by application of two mismatched rack-cutters for generation of the pinion and the gear, respectively. The principle of mismatching of generating surfaces had already been applied for generation of spiral bevel gears and hypoid gears for localization of bearing contact before Novikov's invention was proposed. However, Novikov was the first who (i) applied mismatched tool surfaces for generation of helical gears, and (ii) achieved reduction of contact stresses due to small difference of curvatures of generating and generated tooth surfaces.

There are two weak points in Novikov design:

1. (i) The function of transmission errors of a misaligned gear drive is a discontinuous linear one, and the transfer of meshing between neighboring teeth is accompanied by high acceleration that causes a high level of vibration and noise [Litvin & Lu, 1995].

2. (ii) Bending stresses of Novikov gears, especially of the first design, are of large magnitude.

The manufacturing of Wildhaber–Novikov gears is based on application of two mating hobs that are conjugated to the respective mismatched rack-cutters.