TOOTHED BELT DRIVE WITH VARYING TOOTH PITCH

Abstract

Toothed belt drive with a toothed belt and at least two toothed pulleys, wherein the toothed belt has at least one drive side provided with a toothed profile, the toothed belt wraps around the toothed pulleys over a partial area of their circumference and the teeth of the toothed belt meshingly engage in the tooth gaps of the toothed pulleys, wherein at least one of the toothings on the belt or pulley is formed as a series of tooth pitches varying along the circumference, wherein the individual tooth pitches are designed to vary by up to a maximum of 5% relative to the mean tooth pitch on the belt or pulley, and the absolute deviation of a varied tooth pitch from the mean tooth pitch on the belt or pulley is limited by the backlash of the toothing,
wherein the backlash E.sub.S results from the difference of the width e.sub.S of the tooth gaps of the respective toothed pulley and the width e.sub.R of the teeth of the toothed belt in the middle of the tooth height of the teeth of the toothed belt.

Claims

1.-9. (canceled)

10. A toothed belt drive comprising a toothed belt and at least two toothed pulleys, wherein the toothed belt has at least one drive side provided with a toothed profile, wherein the toothed belt wraps around the toothed pulleys over a partial area of their circumference and teeth of the toothed belt meshingly engage in tooth gaps of the at least two toothed pulleys; wherein at least one of toothings on the toothed belt or at least one pulley of the at least two toothed pulleys is formed as a series of tooth pitches varying along the circumference; wherein individual tooth pitches are designed to vary by up to a maximum of 5% relative to a mean tooth pitch on the toothed belt or the at least one pulley of the at least two toothed pulleys, and wherein an absolute deviation of a varying tooth pitch from the mean tooth pitch on the is limited by backlash of the toothing; and, wherein the backlash results from the difference of the width eS of the tooth gaps of the respective toothed pulley and width eR of teeth of the toothed belt in the middle of a tooth height of the teeth of the toothed belt.

11. The toothed belt drive as claimed in claim 10, in which the varying tooth pitch on the toothed belt or the at least one pulley of the at least two toothed pulleys is formed periodically or according to a predetermined pattern.

12. The toothed belt drive as claimed in claim 10, wherein the varying tooth pitch on the toothed belt or the at least one pulley of the at least two toothed pulleys is formed in a positive or a negative direction relative to the mean pitch.

13. The toothed belt drive as claimed in claim 10, wherein the toothed belt or the at least one pulley of the at least two toothed pulleys is designed with a varying tooth pitch and the respective other part is designed with a regular tooth pitch.

14. The toothed belt drive as claimed in claim 10, wherein the toothed belt and the at least one pulley of the at least two toothed pulleys are designed with a varying tooth pitch.

15. The toothed belt drive as claimed in claim 10, wherein the varying pitch is arranged in such a way that a lowest possible level in tooth meshing order (TMO) results.

16. The toothed belt drive as claimed in claim 15, wherein levels of orders adjacent to the tooth meshing order (TMO) resulting from the specific arrangement of the varying tooth pitches do not exceed the a lowest possible level in tooth meshing order (TMO).

17. An electric power steering gear for a motor vehicle comprising the toothed belt drive as claimed in claim 13.

18. A mold for producing a toothed belt for the toothed belt drive as claimed in claim 13, wherein the mold is designed in such way that the toothing of the mold that forms the belt teeth is formed with a series of varying tooth pitches which, in the belt circumferential direction formed in longitudinal or subsequent operation, are designed to vary by up to a maximum of 5% relative to a mean tooth pitch of the belt (nominal pitch) at the height of the effective cord line running through a cord center, a mesh pitch that results in subsequent operation at the height of a pulley tip circle, and a pitch at mean tooth height, wherein an absolute deviation of these varying tooth pitches is limited by absolute backlash, wherein the absolute backlash is defined as a difference of width, resulting in subsequent operation, of a tooth gap of the pulley and the width of the engaging belt tooth in the middle of the tooth height.

Description

[0021] The invention will be explained in more detail on the basis of an exemplary embodiment. In the figures:

[0022] FIG. 1 shows a basic representation of the belt drive according to the invention,

[0023] FIG. 2 shows the meshing conditions between the toothed belt and toothed pulley with a pitch variation on the toothed belt in an enlarged view,

[0024] FIG. 3 shows the backlash as play or the difference in the gap between two adjacent toothed pulley teeth and a belt tooth at half the tooth height of the belt in an enlarged view,

[0025] FIG. 4 shows a diagram with a spectral comparison of sound power levels in the tooth meshing order (TMO) and secondary orders with reduction of the level of the tooth meshing order by a series of varying pitches compared with a regular pitch,

[0026] FIG. 5 shows a diagram with spectral comparison of sound power levels in the tooth meshing order (TMO) and secondary orders with reduction of the level of the tooth meshing order and limitation of the secondary order level to the level of the tooth meshing order by another, improved series of varied pitches compared with a regular pitch.

[0027] FIG. 1 shows a helically-geared toothed belt drive 1 with a toothed belt 2, a large toothed pulley 3 as the driven pulley and a small toothed pulley 4 as the drive pulley. The toothed belt 2, by way of the drive side thereof that is provided with a toothed profile, runs onto the small toothed pulley 4 in the run-in region 5. The small toothed pulley 4 has a toothed profile that is complementary to the toothed profile of the belt, wherein the toothed belt wraps around the toothed pulleys over a partial area of their circumference, and the teeth of the toothed belt meshingly engage in the tooth gaps of the toothed pulleys. The same correspondingly applies to the large toothed pulley 3.

[0028] FIG. 2 shows the meshing conditions between the toothed belt 2 (solid line) and toothed pulley 4 (thin line) in the embodiment according to the invention as claimed in claim 1 in an enlarged view, with the toothed pulley 4 being configured with a regular pitch P4, while the toothed belt 2 is configured with a varying pitch P2. Shown are the regular pitch angle on the toothed pulley 4 corresponding to the nominal pitch P on the cord center 6 and two pitch angles on the toothed belt 2 that vary in comparison. For the sake of better clarity, the nominal pitch P on the cord center is not shown in this figure. At each radial level, whether at the cord center, the tip circle of the toothed pulley or the middle of the tooth height, the respective meshing pitches (or arc lengths) of the toothed pulley 4 and toothed belt 2 are thus different from one another.

[0029] FIG. 3 shows the absolute backlash, also referred to as play. This is the difference of the width of a tooth gap eS of the pulley 4 and the width of the meshing belt tooth eR in the middle of the tooth height.

[0030] If the noise of a toothed drive is subjected to an order analysis, the energy content of the noise is considered via an order, in the case of toothed belt drives via an order that is formed from a frequency spectrum that is calculated using a Fast Fourier Transform (FFT). An order spectrum can be mapped with an FFT, from which the level or the amplitude of each order can be determined with certain concurrent calculations/filters. This occurs with the frequency of the meshing engagement, the tooth meshing order, as well as with a number of secondary orders. This gives the diagrams shown in FIGS. 4 and 5, which show the amplitude of the sound power level of a belt drive with toothed pulley and toothed belt in spectral orders.

[0031] FIG. 4 shows a diagram which shows the amplitude of the sound power level of a belt drive with regular pitches on the toothed pulley and toothed belt from the prior art compared with a belt drive according to the invention in spectral orders. Here, the level of the tooth meshing order (TMO) is reduced to a fraction by a series according to the invention of varying pitches on the toothed belt, although the levels of a plurality of secondary orders exceed the level of the tooth meshing order (IMO).

[0032] FIG. 5 shows a diagram which in turn shows the amplitude of the sound power level of a belt drive with regular pitches on the toothed pulley and toothed belt from the prior art compared with a belt drive according to the invention in spectral orders. Here, although the level of the tooth meshing order (TMO) is reduced by another series according to the invention of varying pitches on the toothed belt, the levels of all secondary orders do not exceed that of the tooth meshing order (IMO).

LIST OF REFERENCE SIGNS

Part of the Description

[0033] 1 Toothed belt drive [0034] 2 Toothed belt [0035] 3 Toothed pulley (driven pulley) [0036] 4 Toothed pulley (drive pulley) [0037] 5 Run-in region [0038] 6 Cord center [0039] e.sub.S Width of a tooth gap [0040] e.sub.R Width of the meshing belt tooth in the middle of the tooth height [0041] P Nominal pitch [0042] P2 Varying pitch of the toothed belt 2 [0043] P4 Regular pitch of the toothed pulley 4