Toothed belt drive

Abstract

Toothed belt drive having one toothed belt and at least two, preferably helically geared, toothed pulleys, wherein the toothed belt wraps the toothed pulleys over a part-region of the circumference of the latter and the teeth of the toothed belt mesh in the tooth gaps of the toothed pulleys, wherein the air gap E.sub.S or E.sub.S(mk) that relates to the nominal pitch P and results from the difference between the width es of the tooth gaps of the respective toothed pulley and the width e.sub.R of the teeth of the toothed belt is configured at the mean height of the teeth, depending on the tooth count z.sub.R of the toothed pulleys and on the tooth count z of the toothed pulleys, or on the tooth counts z.sub.k of the smaller toothed pulley and on z.sub.g of the larger toothed pulley, respectively.

Claims

1. A toothed belt drive comprising: a toothed belt having a plurality of teeth and at least one drive side provided with a first toothed profile; at least two toothed pulleys each having a circumference and defining tooth gaps; said toothed pulleys each having a second toothed profile that is complementary to said first toothed profile; said toothed belt being configured to wrap said at least two toothed pulleys over a part-region of the circumference of each of said at least two toothed pulleys; said teeth of said toothed belt being configured to mesh in said tooth gaps of said at least two toothed pulleys; wherein an air gap (E.sub.S) that relates to a nominal pitch (P) and results from a difference between a width (e.sub.S) of the tooth gaps of the respective one of said at least two toothed pulleys and a width (e.sub.R) of said teeth of said toothed belt at a mean height of said teeth, depending on a tooth count (z.sub.R) of said toothed belt and on a tooth count (z) of said respective one of said at least two toothed pulleys, is configured such that $\begin{array}{cc}{E}_S=e_S-e_R=\left[C_S+\frac{0.004.Math.z}{z_R-z}\right].Math.P& \end{array}$ wherein (C.sub.S) is predefined as a constant for a standard backlash in the case of toothed belt drives in a range of
0.06C.sub.S0.08.

2. The toothed belt drive of claim 1, wherein one of said at least two toothed pulleys has a pitch circle diameter of (d)45 mm.

3. The toothed belt drive of claim 1, wherein one of said at least two toothed pulleys has a tooth count between 20 and 60.

4. The toothed belt drive of claim 1, wherein said at least two toothed pulleys are helically geared.

5. A toothed belt drive comprising: a toothed belt having a plurality of teeth and at least one drive side provided with a first toothed profile; at least two toothed pulleys each having a circumference and defining tooth gaps; said at least two toothed pulleys each having a second toothed profile that is complementary to said first toothed profile; said toothed belt being configured to wrap said at least two toothed pulleys over a part-region of the circumference of each of said at least two toothed pulleys; said teeth of said toothed belt being configured to mesh in said tooth gaps of said at least two toothed pulleys; wherein said at least two toothed pulleys have dissimilar diameters and include a smaller toothed pulley and a larger toothed pulley; and, at said smaller toothed pulley an air gap (E.sub.S(mk)) that relates to a nominal pitch (P) and results from a difference between a width (e.sub.Smk) of said tooth gaps of said smaller toothed pulley and a width (e.sub.R) of said teeth of said toothed belt at a mean height of said teeth, depending on a tooth count (z.sub.R) of said toothed belt and on a tooth count (z.sub.k) of said smaller toothed pulley and on (z.sub.g) of said larger toothed pulley, is configured such that: $\begin{array}{cc}{E}_{S\left(\mathrm{mk}\right)}=e_{\mathrm{Smk}}-e_R=\left[C_S+\frac{0.004.Math.z}{z_R-z_k}+\left(\frac{z_g}{z_k}-1\right).Math.\frac{C_{\mathrm{mk}}.Math.2.Math.u}{P.Math.z_g-2u}\right].Math.P& \end{array}$ wherein (C.sub.S) is predefined in a range of
0.06C.sub.S0.08 and (C.sub.mk) is predefined as a modified constant for said air gap in the case of toothed belt drives in a range of
1.00C.sub.mk2.00.

6. The toothed belt drive of claim 5, wherein said smaller toothed pulley has a pitch circle diameter of (d)45 mm.

7. The toothed belt drive of claim 5, wherein said smaller toothed pulley has a tooth count between 20 and 60.

8. The toothed belt drive of claim 5, wherein said at least two toothed pulleys are helically geared.

9. A toothed pulley for use in a toothed belt drive having a toothed belt provided with a first toothed profile including teeth, the toothed pulley comprising: a toothed pulley body having a circumference and teeth defining tooth gaps therebetween; said toothed pulley body having a second toothed profile that is complementary to the first toothed profile; said toothed pulley body being configured to have the toothed belt wrapped over a part-region of the circumference of said toothed pulley body; said toothed gaps being configured to have the teeth of the toothed belt mesh therein; and, wherein a backlash of said toothed pulley body is configured such that an air gap (E.sub.S) that relates to a nominal pitch (P) and results from a difference between a width (e.sub.S) of the tooth gaps of said toothed pulley body and a width (e.sub.R) of the teeth of the toothed belt at a mean height of said teeth, depending on a tooth count (z.sub.R) of the toothed belt and on a tooth count (z) of said toothed pulley body, is configured such that $\begin{array}{cc}{E}_S=e_S-e_R=\left[C_S+\frac{0.004.Math.z}{z_R-z}\right].Math.P& \end{array}$ wherein (C.sub.S) is predefined as a constant for a standard backlash in the case of toothed belt drives in a range of
0.06C.sub.S0.08.

10. The toothed pulley of claim 9, wherein the toothed belt drive is of an electric steering gear.

11. An electric power steering gear for motor vehicles comprising: a toothed belt drive including a toothed belt having a plurality of teeth and at least one drive side provided with a first toothed profile; said toothed belt drive further including at least two toothed pulleys each having a circumference and defining tooth gaps; said toothed pulleys each having a second toothed profile that is complementary to said first toothed profile; said toothed belt being configured to wrap said at least two toothed pulleys over a part-region of the circumference of each of said at least two toothed pulleys; said teeth of said toothed belt being configured to mesh in said tooth gaps of said at least two toothed pulleys; wherein an air gap (E.sub.S) that relates to a nominal pitch (P) and results from a difference between a width (e.sub.S) of the tooth gaps of the respective one of said at least two toothed pulleys and a width (e.sub.R) of said teeth of said toothed belt at a mean height of said teeth, depending on a tooth count (z.sub.R) of said toothed belt and on a tooth count (z) of said respective one of said at least two toothed pulleys, is configured such that $\begin{array}{cc}{E}_S=e_S-e_R=\left[C_S+\frac{0.004.Math.z}{z_R-z}\right].Math.P& \end{array}$ wherein (C.sub.S) is predefined as a constant for a standard backlash in the case of toothed belt drives in a range of
0.06C.sub.S0.08.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 shows a helically geared toothed belt drive with a high reduction gear ratio, in the form of a diagram;

(3) FIG. 2 shows the meshing conditions prevalent between a toothed belt and a toothed pulley in the configuration according to an embodiment of the invention;

(4) FIG. 3 shows the meshing conditions prevalent between the toothed belt and a small toothed pulley in the configuration according to an embodiment of the invention;

(5) FIG. 4 shows a variates diagram for the tooth play/the backlash configured according to the invention, plotted over the tooth count; and,

(6) FIG. 5 shows a diagram of the reduction in noise achievable in quantitative terms in the case of a configuration of a belt drive according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(7) FIG. 1 shows a helically-geared toothed belt drive 1 with a high reduction gear ratio, having one toothed belt 2, one large toothed pulley 3 as the drive output pulley, and one small toothed pulley 4 as the drive input 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 the toothed pulleys over a part-region of their circumference, and the teeth of the toothed belt mesh in the tooth gaps of the toothed pulleys. The same applies in an analogous manner to the large toothed pulley 3.

(8) FIG. 2 in an enlarged illustration shows the meshing conditions prevalent between the toothed belt 2 and the toothed pulley 4 in the configuration according to a first embodiment. Illustrated here are the parameters e.sub.S, that is, the gap width of the toothed pulley, and e.sub.R, that is, the toothed width of the belt, and the cord center 6, that is, the central plane of the reinforcement elements that are vulcanized into the toothed belt, also referred to as the effective cord line.

(9) This cord center or effective cord line 6 is to be found again in FIG. 3 which shows the meshing conditions prevalent in a configuration according to a second embodiment. To be seen here is also the gap width of the modified small toothed pulley e.sub.Smk which is illustrated here for highlighting the configuration according to the invention for toothed drive with a comparatively high gear ratio as compared to the gap width of the toothed pulley e.sub.S from FIG. 2. It can be clearly seen in this illustration that the backlash E.sub.S(mk)=e.sub.Smke.sub.R for the comparatively small toothed wheel in the configuration according to the second embodiment (smaller toothed wheel, higher gear ratio, dissimilar tooth counts and diameters) is in this case larger than the backlash E.sub.S=e.sub.Se.sub.R in the configuration as per the first embodiment, the latter being directed substantially toward the configuration of comparatively large toothed wheels.

(10) The respective backlash, also referred to as tooth play or, internationally, as backlash, is established by the radius 8 of the mean tooth height, herein relating to the nominal pitch P of the toothed pulley and the toothed belt.

(11) The effective line spacing u which as a parameter is to be found again in the formula associated with the subject matter of the second embodiment is also illustrated in FIG. 3. The effective line spacing u describes the difference between the crown circle radius 7 of the (herein smaller) toothed pulley 4 and the radius of the cord center 6 in the wrap arc.

(12) Overall, for an operation that is as noiseless as possible, the backlash of each toothed pulley is thus fundamentally aligned by way of two partially opposing effects, on account of which the production state of the toothed belt is also taken into account. This takes place in that a type of standard rule takes into account the tooth count of the belt and the shape of the latter on a drum as a result of the production process of the belt, as well as the tooth count of the respective pulley. As has already been illustrated above, this configuration according to the invention is particularly suitable for the configuration of low-noise belt drives when the toothed pulleys either have relatively large and approximately identical diameters, or differ only slightly in terms of the diameter and the tooth count. The decisive factor in terms of noise is the unimpeded meshing at the crown circle of the toothed pulley such that the meshing pitch at the crown circle is indeed significant.

(13) Assuming that production variances in the production of the toothed belt add up in the pitch of the toothed belt, the effect that the backlash can be smaller the fewer teeth there are in a wheel would result. This contrasts with the further effect that the curvature of the belt in the wrapping of the pulley wheel modifies the truly decisive meshing pitch at the crown circle such that the air gap should accordingly be larger the fewer teeth there are in the wheel.

(14) Accordingly, the configuration according to the second embodiment is provided, on account of which an additional modification which takes into account the difference in curvature between the small and the large toothed pulley is present for the smaller of the two pulleys. The curvature that is vulcanized/frozen by the mold drum and is thus predefined is thus already present in the production of the toothed belt, while two further curvatures that differ from the former are created in operation and in the wrapping on the toothed pulleys.

(15) The influence of these three dissimilar curvatures per the second embodiment is represented by the tooth counts of the small and the large toothed pulley, and by the tooth count of the belt for the influence by way of the production of the latter on account of the term carried over from the first embodiment which applies to be standard backlash and to both pulleys. Surprisingly, by way of the configuration of the invention disclosed with respect to the first and second embodiments, a particularly low-noise configuration of a toothed belt drive is attained even with toothed belts produced in a standard manner.

(16) FIG. 4 shows the abovementioned opposing effects in a respective variates diagram. The tooth play/the backlash herein is plotted over the tooth count. The solid lines represent the variates range which results within the limits predefined by the constant C.sub.S in the case of a configuration of the backlash according to the first embodiment. The chain-dotted lines represent the variates range which results with the constants C.sub.S and C.sub.mk in the case of a corresponding configuration according to the second embodiment.

(17) The difference between the individual configurations as per the first and second embodiments can also be very well highlighted by way of FIG. 4. The design point, or the variates pair 10, respectively, shows the configuration of the backlash in the case of a toothed pulley of a comparatively large diameter/higher tooth count as per the first embodiment, wherein the generation of noise when meshing has been successfully reduced here.

(18) However, if a toothed pulley of a smaller diameter/lower tooth count according to the configuration according to the first embodiment were to be configured, the design point/variate pair 11 (less backlash) would result. However, the generation of noise when meshing in the smaller wheel could not be reduced in the case of this constellation. This is only possible once a design according to a configuration as is disclosed with respect to the second embodiment is performed. By way of such a configuration an air gap according to the variates pair/design point 12 (larger backlash) is achieved. A significant reduction in noise is thus achieved.

(19) FIG. 5 shows the attainable reduction in noise in the case of a configuration of a belt drive according to the invention as per FIG. 1 also in a purely quantitative manner. Various toothed belts which had already been subjected to a prior noise test under normal conditions, thus tested using commonplace toothed pulleys from the prior art, were provided for the investigation. These prior tests led to the tested toothed belts being grouped in various quality classes in relation to the emission of noise, specifically in a 1st quality class, in a 2nd quality class, and a wastage class.

(20) These belts were then tested again in terms of the emission of noise, but this time in a belt drive in which the respective smaller toothed pulleys were configured according to the invention, the backlash thereof having been modified specifically according to the second embodiment.

(21) The graph in FIG. 5 shows the improvement in terms of the emission of noise that has been achieved on account thereof. This resulted in a reduction in the impact noise by up to 5.2 dB.

(22) Such a serious reduction in noise under normal criteria corresponds to the spacing in the noise behavior between 1st quality and wastage. Accordingly, belts which with a view to the noise behavior thereof were previously to be classified as wastage, by way of the configuration of a toothed belt drive/toothed pulley according to the invention can again be reclassified to such an extent that the belts in terms of the emission of noise can still be used as quality products. This clearly shows that the configuration of a toothed belt drive according to the invention, or of the toothed pulleys thereof and the backlash of the latter causes a significant improvement in the emission of noise of toothed belt drives even in the case of standardized toothed belts.

(23) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

LIST OF REFERENCE SIGNS

Part of the Specification

(24) 1 Toothed belt drive 2 Toothed belt 3 Toothed pulley (output drive pulley) 4 Toothed pulley (input drive pulley) 5 Run-in region 6 Radius of the cord center 7 Crown circle radius of the sprocket (small toothed pulley) 8 Radius of mean tooth height 9 Root circle radius of the sprocket (small toothed pulley) 10 Pair of variates/design point for backlash 11 Pair of variates/design point for backlash 12 Pair of variates/design point for backlash