Tham khảo tài liệu 'gear noise and vibration episode 1 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 40 Chapter 4 However normal reasonably accurate teeth do not have sudden changes of loading along a line of contact. In general the load rises smoothly as tip relief or end helix relief reduces and then should stay constant over a large section of the length of line of contact. If we split a line of contact into 30 slices we would not expect more than about 20 of the maximum load variation from one slice to a neighbour Fig. . As neighbouring slices have similar loads and deflections the shear buttressing effects should be small and with smooth load increases or decreases the shear force effects on either side of a slice should roughly cancel out except for the end slice where in any case the necessary chamfer will alter local stiffness. The result of these practical effects is that for most tooth contact lines buttressing effects are small and the thin slice model is much more accurate than might be expected. One time that buttressing effects are significant is when one gear is much wider than the other and no end relief has been given. This condition of course tends to cause rapid failures at the sharp comer because of stress concentration effects and because lubrication is impossible at a sharp comer. Differing gear widths tends to occur with small pinions which have been cut directly into a shaft to give minimum diameter. Another area where buttressing is important occurs with high helix angle gears which are too narrow to have end relief where one end of the tooth flank is less supported due to the angle of the end of the tooth. Even in this case the extra stiffness of one tooth end may largely compensate for the lower stiffness of the mating tooth end to give roughly constant mesh stiffness. However the local root stresses will be much higher with the unsupported tooth end. Tooth shape assumptions A perfectly general program would take a series of pinion tooth flanks with completely arbitrary flank shapes including corrections and errors and with .
