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
a plurality of arms extending radially outward from the outer hub to the outer rim;
wherein the radially outermost ends of proximate pairs of arms in the plurality of arms are arcuately spaced apart according to a pitch sequence describing a pseudo-random pattern of relative spacings, and wherein the selected 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.
2. The pulley of claim 1 , wherein the pitch sequence reduces the rotational symmetry of the pulley about the axis of rotation of the pulley in comparison to that which would be present if there was no variation in arcuate spacing.
3. The pulley of claim 2 , wherein the pitch sequence is repeated within the circumference of the outer rim.
4. The pulley of claim 1 , wherein the pitch sequence eliminates the rotational symmetry of the pulley about the axis of rotation of the pulley.
5. The pulley of claim 4 , wherein the arms of the plurality of arms are sheet-like ribs.
6. The pulley of claim 5 , wherein at least the outer hub, outer rim, and plurality of arms are a thermoplastic, a molded thermosetting plastic, or a plastic composite.
7. The pulley of claim 4 , wherein the plurality of arms consists of thirty two arms, and the pitch sequence is X n ={9, 10, 11, 12, 10, 11, 12, 13, 12, 11, 10, 9, 11, 12, 13, 10, 10, 13, 12, 11, 9, 10, 11, 12, 13 12, 11, 10, 12, 11, 10, 9}, where n is an integer 1 through 32 representing, in order, first through thirty second possible proximate pairs of arms.
8. The pulley of claim 1 , further comprising a second plurality of arms extending radially outward from the outer hub to the outer rim, wherein the radially outermost ends of proximate pairs of arms in the second plurality of arms are arcuately spaced apart according to a pitch sequence describing a pseudo-random pattern of relative spacings.
9. The pulley of claim 8 , wherein the pitch sequence of the first plurality of arms and the pitch sequence of the second plurality of arms are the same pitch sequence, and wherein the radially outermost ends of proximate pairs of arms between the first and second pluralities of arms are angularly offset by an angular spacing.
10. The pulley of claim 9 , wherein the first plurality of arms consists of thirty two arms, the second plurality of arms consists of thirty two arms, and the pitch sequence is X n ={9, 10, 11, 12, 10, 11, 12, 13, 12, 11, 10, 9, 11, 12, 13, 10, 10, 13, 12, 11, 9, 10, 11, 12, 13 12, 11, 10, 12, 11, 10, 9}, where n is an integer 1 through 32 representing, in order, first through thirty second possible proximate pairs of arms.
11. The pulley of claim 1 , wherein the selected 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.
12. A method of constructing a low noise pulley comprising the steps of:
constructing a hub, including an outer hub, and an outer rim;
constructing a plurality of arms radiating outward from the outer hub to the outer rim;
selecting a pitch sequence describing a pseudo-random pattern of relative spacings between proximate pairs of arms wherein the selected 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; and
arcuately spacing the radially outermost ends of the plurality of arms about the outer rim of the pulley in accordance with the selected pitch sequence.
13. The method of claim 12 , wherein the selected pitch sequence reduces the rotational symmetry of the pulley about the axis of rotation of the pulley in comparison to that which would be present if there was no variation in arcuate spacing.
14. The method of claim 12 , wherein the selected pitch sequence is repeated within the circumference of the outer rim.
15. The method of claim 12 , wherein the selected pitch sequence eliminates the rotational symmetry of the pulley about the axis of rotation of the pulley.
16. The method of claim 15 , wherein the plurality of arms consists of thirty two arms, and the selected pitch sequence is X n ={9, 10, 11, 12, 10, 11, 12, 13, 12, 11, 10, 9, 11, 12, 13, 10, 10, 13, 12, 11, 9, 10, 11, 12, 13 12, 11, 10, 12, 11, 10, 9}, where n is an integer 1 through 32 representing, in order, first through thirty second possible proximate pairs of arms.
17. The method of claim 12 , wherein the selected 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.
18. 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 outermost ends of proximate pairs of arms in the first and second pluralities of arms are, respectively, arcuately spaced apart about the outer rim according to a pitch sequence describing a pseudo-random pattern of relative spacings the selected pitch sequence includes at least three successive relative spacings, the selected 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; and
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.
19. The pulley of claim 18 , wherein the arms of the first plurality of arms are arcuately spaced apart according to the pitch sequence; and the arms of the second plurality of arms are arcuately spaced apart according to the same pitch sequence.
20. The pulley of claim 19 , wherein the first plurality of arms connect the outer hub to the outer rim predominantly on a first side of the lateral midline of the pulley, and wherein the second plurality of arms connect the outer hub to the outer rim predominantly on an opposite side of the lateral midline of the pulley.
21. The pulley of claim 20 , wherein the arms of the first and second pluralities of arms are sheet-like ribs.
22. The pulley of claim 19 , wherein the first plurality of arms consists of thirty two arms, the second plurality of arms consists of thirty two arms, and the pitch sequence is X n ={9, 10, 11, 12, 10, 11, 12, 13, 12, 11, 10, 9, 11, 12, 13, 10, 10, 13, 12, 11, 9, 10, 11, 12, 13 12, 11, 10, 12, 11, 10, 9}, where n is an integer 1 through 32 representing, in order, first through thirty second possible proximate pairs of arms.
23. The pulley of claim 18 , wherein the selected 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.