Basics
Maximum Chain Speed V max =R v
Minimum Chain Speed V min = r v
Chordal Rise
Figure 2.13 The Height of Engagement
Therefore, even when the sprockets rotate at the same speed, the chain speed is not steady according to a ratio of the sprocket radius (with chordal action). Chordal action is based on the number of teeth in the sprockets:
Ratio of speed change = (V max – V min ) / V max = 1 – cos (180˚/N)
Figure 2.14 shows the result. In addition to the number of teeth, if the shaft center distance is a common multiple of the chain pitch, chordal action is small. On the other hand, if shaft center distance is a multiple of chain pitch + 0.5 pitch, chordal action increases. Manufacturing and alignment errors can also impact chordal action. In a flat-belt power transmission machine, if the thickness and bending elas- ticity of the belt are regular, there is no chordal action. But in toothed-belt sys- tems, chordal action occurs by circle and chord, the same as chains. Generally this effect is less than 0.6 percent, but when combined with the deflection of the pulley center and errors of belt pitch or pulley pitch, it can amount to 2 to 3 percent.
V max – V min V max
Number of Teeth in Sprocket
Figure 2.14 Speed Variation Versus the Number of Sprocket Teeth
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