Low noise pulley
View Patent ↗Low-noise pulleys and methods of constructing low-noise pulleys are disclosed. In a first aspect, first and second pluralities of arms extending radially outward from the outer hub to the outer rim are angularly offset from each other about the axis of rotation to eliminate symmetry across the lateral midline of the pulley. In a second aspect, the radially outermost ends of a plurality of arms are arcuately spaced apart according to a pitch sequence describing a pseudo-random pattern of relative spacings so as to reduce or eliminate rotational symmetry of the pulley. In a third aspect, features of the first and second aspects are combined, and in one embodiment, first and second pluralities of arms are, respectively, approximately oppositely canted so as to vary the arcuate spacings of the laterally outermost ends of the arms.
1. A pulley for an endless belt drive system, the pulley comprising:
a hub including an outer hub;
an outer rim; and
first and second pluralities of arms extending radially outward from the outer hub to the outer rim, the first and second pluralities being equal in number, wherein the radially and laterally outermost ends of the arms of the first and second pluralities of arms are, respectively, arcuately spaced apart about the outer rim;
wherein the arms of the second plurality of arms are angularly offset from the arms of the first plurality of arms about the axis of rotation of the pulley; wherein the arms of the first plurality of arms are canted with respect to a lateral midline of the pulley, and the arms of the second plurality of arms are approximately oppositely canted with respect to the lateral midline; wherein the arms of the first plurality of arms alternate with the arms of the second plurality of arms about the axis of rotation of the pulley; and wherein the radially and laterally outermost ends of the arms of the first and second pluralities of arms are, respectively, arcuately spaced apart according to a pitch sequence describing a pseudo-random pattern of relative spacings.
2. The pulley of claim 1 , wherein V shapes are defined by the radially and laterally outermost ends of proximate pairs of arms between the first and second pluralities of arms, and the vertices of proximate V shapes are both offset with respect to the axis of rotation and disposed on opposite sides of the lateral midline of the pulley.
3. The pulley of claim 2 , wherein the lateral ends of the arms of the first plurality of arms are joined to the proximate lateral ends of the arms of the second plurality of arms.
4. The pulley of claim 1 , wherein the radially and laterally outermost ends of proximate pairs of arms of the first plurality of arms are arcuately spaced apart according to the pitch sequence, and the radially and laterally outermost ends of proximate pairs of arms of the second plurality of arms are arcuately spaced apart according to the same pitch sequence.
5. The pulley of claim 4 , wherein the first plurality of arms consists of sixteen arms, the second plurality of arms consists of sixteen arms, and the pitch sequence is X n ={9, 10, 11, 12, 10, 11, 12, 13, 12, 11, 10, 9, 11, 12, 13, 10}, where n is an integer 1 through 16 representing, in order, first through sixteenth possible proximate pairs of arms.
6. The pulley of claim 1 , wherein the pitch sequence is repeated within the circumference of the outer rim.
7. The pulley of claim 1 , wherein the pitch sequence eliminates the rotational symmetry of the pulley about the axis of rotation of the pulley.
8. The pulley of claim 1 , wherein the pitch sequence includes at least three successive relative spacings, and the three successive relative spacings differ from each other by at least four percent of the smallest relative spacing.
9. The pulley of claim 8 , wherein the pitch sequence includes at least four successive relative spacings, and the difference between a maximum and minimum relative spacing of the four successive relative spacings is at least sixteen percent of the average relative spacing of the four successive relative spacings.
10. The pulley of claim 9 , wherein within any portion of the pitch sequence representing one fifth of the circumference of the outer rim, the average spacing of the relative spacings is within five percent of that of any other sequence of relative spacings present about the circumference of the outer rim.
11. A method of constructing a low-noise pulley comprising the steps of:
constructing a hub, including an outer hub, and an outer rim;
constructing first and second pluralities of arms connecting the outer hub to the outer rim, the first and second pluralities being equal in number, wherein the radially and laterally outermost ends of the arms of the first and second pluralities of arms are, respectively, arcuately spaced apart about the outer rim;
angularly offsetting the arms of the second plurality of arms from the arms of the first plurality of arms about the axis of rotation to eliminate lateral symmetry across a lateral midline of the pulley;
angularly canting the arms of the first plurality of arms with respect to the lateral midline, as well as approximately oppositely angularly canting the arms of the second plurality of arms with respect to the lateral midline, wherein the arms of the first plurality of arms alternate with the arms of the second plurality of arms about the axis of rotation of the pulley; and
arcuately spacing apart the radially and laterally outermost ends of the arms of the first plurality of arms according to a pitch sequence describing a pseudo-random pattern of relative spacings, and arcuately spacing apart the radially and laterally outermost ends of the arms of the second plurality of arms according to the same or another pitch sequence describing a pseudo-random pattern of relative spacings.
12. The method of claim 11 , wherein V shapes are defined by the radially and laterally outermost ends of proximate pairs of arms between the first and second pluralities of arms, and the vertices of proximate V shapes are both offset with respect to the axis of rotation and disposed on opposite sides of the lateral midline of the pulley.
13. The method of claim 12 , further comprising the step of joining the lateral ends of the arms of the first plurality of arms to the proximate lateral ends of the arms of the second plurality of arms.
14. The method of claim 11 , wherein the radially and laterally outermost ends of proximate pairs of arms of the first plurality of arms are arcuately spaced apart according to the pitch sequence, and the radially and laterally outermost ends of proximate pairs of arms of the second plurality of arms are arcuately spaced apart according to the same pitch sequence.
15. The method of claim 11 , wherein the pitch sequence includes at least three successive relative spacings, and the three successive relative spacings differ from each other by at least four percent of the smallest relative spacing.
16. The method of claim 15 , wherein the pitch sequence includes at least four successive relative spacings, and the difference between a maximum and minimum relative spacing of the four successive relative spacings is at least sixteen percent of the average relative spacing of the four successive relative spacings.
17. The method of claim 16 , wherein within any portion of the pitch sequence representing one fifth of the circumference of the outer rim, the average spacing of the relative spacings is within five percent of that of any other sequence of relative spacings present about the circumference of the outer rim.
18. The method of claim 11 , wherein the first plurality of arms consists of sixteen arms, the second plurality of arms consists of sixteen arms, and the pitch sequence is X n ={9, 10, 11, 12, 10, 11, 12, 13, 12, 11, 10, 9, 11, 12, 13, 10}, where n is an integer 1 through 16 representing, in order, first through sixteenth possible proximate pairs of arms.
19. The method of claim 11 , wherein the pitch sequence is repeated within the circumference of the outer rim.
20. The method of claim 11 , wherein the pitch sequence eliminates the rotational symmetry of the pulley about the axis of rotation of the pulley.