Page 305 - Gear Technology Solutions

21.4 Generating Principle of a Cross-Axes Helical Gear Pair

The relationship between generating rack and the two mating helical gears
which mesh under a cross-axis angle is shown in Figure 3. The two gear rota-
tions as well as the generating rack movement are in three different planes.
The graphic in Figure 3 makes it evident, that the common contact location be-
tween pinion and gear in each shift position of the rack can only be a single
point.

Figure 3: Generating rack between pinion and gear

21.5 Influence of Center Distance Changes

Figure 4 shows in 4 steps the changes to the contact location and contact
normal vectors in order to explain the physics behind the center distance sen-
sitivity of crosses axes helical gears. The initial pair of normal vectors is drawn
for example in the pitch point. The center distance change moves the normal
vector of the upper gear to location 2. Rotation 3 is required to eliminate the
backlash which was caused by the center distance change. The new contact-
ing point of both gears will neither be in position 1 nor will it be in position 3. A
new contacting point with a normal vector pair will result from the interaction of

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