14.1 INTRODUCTION

Cycloidal gears (Chapter 13) and involute gears (Chapters 10, 11, 14, 15, and 16) have different areas of application. This chapter covers involute gears with parallel axes, whose design is based on the assumption that the gear tooth surfaces are in instantaneous contact along a line (line contact) in the case of aligned gear drives. Although the influence of errors of alignment should be considered in the study of the real meshing (see Chapters 15, 16, and 17), in this chapter we consider a preliminary study limited to the theoretical study of meshing. This allows the reader to focus initially on the theoretical study of involute gears. However, we have to emphasize that the modern design of helical gear drives is directed at observation of localized bearing contact (obtained by tooth surfaces being in point contact instead of line contact), simulation of meshing of misaligned gear drives, and stress analysis (see Chapters 15, 16, and 17). The nomenclature used in this chapter is presented in Section 14.10.

14.2 GENERAL CONSIDERATIONS

Helical gears that transform rotation between parallel axes in opposite directions are in external meshing and are provided with screw tooth surfaces of opposite directions.

The axodes of nonstandard gears are two cylinders of radii r _{o 1} and r _{o 2} related as

These cylinders are called the operating pitch cylinders as well. Henceforth, we differentiate standard and nonstandard helical gears. The operating pitch cylinders (the axodes) coincide with the pitch cylinders in...