BELT FOR A BELT DRIVE DEVICE

Abstract: A belt (6) for a belt drive device is composed of a plurality of metal elements (10) arranged on a pair of carriers (30). The elements consist of two or more different thickness. The mixing ratio is the thinner element to the thickest element is less than fifty percent, and the elements are arranged at random.

Description: The present invention relates to a belt for a belt drive device, and more particularly to a belt for a continuously variable belt-drive transmission for a motor vehicle. A known continuously variable belt-drive transmission disclosed in United States Patent No. 4,338081 comprises an endless belt running over a drive pulley and a driven pulley. Each pulley comprises a movable conical disc which is axially moved by a fluid operated servo device so as to vary the running diameter of the belt on the pulleys in dependence on driving conditions. The belt comprises a plurality of metal elements adjacently arranged in the longitudinal direction of the belt, and a pair of endless carriers inserted in opposed slits of each element. When the belt enters or leaves the pulleys, the alignment of the elements is distorted, causing misalignment of elements. Such deviations of elements generate noises. One of the causes of the noises is that the elements strike against the pulleys. Another is that when inclination of an element to the adjacent element changes, elements bump against each other, or a gap between the adjacent elements is increased or decreased as a result of the change of the inclination so that air in the gap vibrates and oil splashes. For example, in the case of a belt which is composed of elements each having a thickness of 2.2 mm and has a length of 589 mm, the frequency of noise is in a range between 2 and 10 kHz. The noise corresponds to frequency of elements at a time when passing a certain point in the course of the belt. For example, when the speed of the belt in 5 m/sec, and the thickness of the elements is 2.2 mm, the frequency is 5000/2.2 = 2272.72. Namely, the most commonly heard noise is 2.27 kHz. Namely, when elements have the same thickness, timing of the elements passing the certain point is constant so that sound pressure level (S.P.L.) becomes high. The sound pressure level can be decreased by changing the timing. The change of the timing can be achieved by giving a variety to the thickness of elements in a belt. Accordingly, a noise reducing V-belt having elements in the form of blocks supported on a band member, the blocks having uneven pitch, has been proposed in Japanese Patent Laid Open 61-270535 to reduce the noise. However, the prior art does not disclose differences of the thicknesses of the elements nor the combinations thereof. Laid Open Japanese patent 61-290258 discloses a V-belt which aims to reduce the S.P.L., of noise generated during operation by using several different kinds of V-block elements arranged irregularly on the band. The kinds of V-block differ in that they have shoulder parts of different shapes. The present invention seeks to provide a belt for a continuously variable transmission for quiet operation without any loss of durability. According to the present invention there is provided a belt for a continuously variable transmission, comprising: a plurality of metal elements arranged on carrying means, characterised in that the elements are of at least two kinds, one kind being distinguished from the other by a difference in the maximum thickness of the element; and, the elements being arranged substantially at random to attenuate the noise generated by the belt during use. From a production managing point of view, it is preferable to manufacture only a minimal number of kinds of element. Furthermore, in order to decrease the distortion of the belt and to prevent the carrier from excessive bending when the elements are unstable, elements are preferably formed as thin as possible provided that the strength of the element can be maintained. Accordingly it is desirable that the difference between thicknesses is small. To achieve these objects the thickness of the elements may be adjusted by attaching a sheet to the element. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Figure 1a is an elevational view of a continuously variable transmission; Figure 1b is a schematic cross section of the transmission of Figure 1a; Figure 2 is an elevational view of an element of a belt according to the present invention; Fig. 3 is a sectional view of the elements; Fig. 4 is a graph showing peak sound pressure levels in relation to mixing ratios when two kinds of elements are mixed; Fig. 5 is a graph showing a range of mixing of elements effective for reducing noises; Fig. 6 is an elevational view of an element of a belt of another embodiment; Fig. 7 is a sectional view of the elements of Fig. 6; Fig. 8 is a partially cut-away side elevational view of the element of Fig. 6; and Fig. 9 is a partially cut-away side elevational view of a modification of the element of the second embodiment. Referring to Figures 1a, 1b and 2, a continuously variable transmission 1 in which a belt according to the present invention is illustrated, has an input shaft 2 and an output shaft 4 provided in parallel with the input shaft 2. A drive pulley 3 and a driven pulley 5 are mounted on shafts 2 and 4 respectively. A fixed conical disc 3a of the drive pulley 3 is integral with input shaft 2 and an axially movable conical disc 3b is axially slidably mounted on the input shaft 2. A conical face of the fixed conical disc 3a confronts a conical face of the movable conical disc 3b thereby forming a groove there-between. A fixed conical disc 5a of the driven pulley 5 is formed on the output shaft 4 opposite a movable conical disc 5b. Conical faces of the respective discs 5a and 5b form a groove. A belt 6 engages the drive pulley 3 and the driven pulley 5. The belt 6 comprises a plurality of metal elements 10 adjacently arranged in the longitudinal direction of the belt. Each element has a body portion 12, a head portion 14, a pillar portion 13 at the center and a pair of horizontal slits at both sides thereof, between the body portion 12 and head portion 14. A pair of metal carriers 30 are inserted in the slits. As shown in Fig. 3, the thickness of the body portion 12 becomes smaller toward the bottom end, thereby forming an inclination 12a under a pitch line. Thus, the elements 10 can pass around the pulleys. The body portion 12 has shoulders 18 at the lateral sides and the head portion 14 has ears 19 at lower side portions, each corresponding to the shoulder 18. Each shoulder 18 and ear 19 are arranged so as to engage with the carriers 30. A recess 20 is formed on each side of the pillar portion 13 so as to prevent the carrier 30 from rubbing the pillar portion 13. A recess 21 is formed on the bottom of the body portion 12 thereby balancing the distribution of pushing force exerted on the elements 10. The carrier 30 comprises laminated layers of flexible thin strips so that bending stress which occurs when the carrier 30 passes over the pulley having a small effective radius, is decreased. Each element 10 has a projection 16 on its one side and a dimple 15 on the other side. The projection 16 of one element 10 engages with the dimple 15 of the adjacent element with a small gap there-between and all elements are arranged side by side. The belt 6 is thus assembled. In order to determine the difference between thicknesses of elements 10, mixing ratios and distribution of elements appropriate for reducing noises, an experiment was carried out using two kinds of elements E₁ and E₂ distributed at random. The elements E₁ and E₂ have different thicknesses t₁ and t₂ each of which is a value at a maximum thickness portion of the element. The following table shows whether the reduction of noises was detected by human senses in two examples. Thickness t₁ of the elements E₁ in both examples was 2.2 mm, which is the thickness of a conventional element. Thicknesses t₂ in example I and II are 2.1 mm and 2.0 mm, respectively. The percentage of the elements E₂ ranges from 10 to 50% of the total number of elements. A ratio r of difference of thicknesses between elements E₁ and E₂ can be obtained from r = (t₁ - t₂)/t₁. Peak values of sound pressure level (SPL) of frequencies of various combinations of elements are calculated by fast Fourier transform and shown by lines a to e in Fig. 4. Points on lines a and b indicate percentages and levels which were actually experimented as described in the table, and lines c to e are based solely on calculations. The limit of the peak SPL for sufficiently reducing the noises is - 3.5 dB. The noise decreases as the ratio r of thickness difference increases. Accordingly, the ratio r of thickness difference of the elements E₁ and E₂ must be larger than approximate 0.05 and the percentage of the second element E₂ must be more than 10%. When the ratio 4 exceeds 0.3 or the percentage of the second element exceeds 50%, the effect of noise reduction becomes substantially constant. It was found that the noise is not decreased at all if the two kinds of elements are alternately arranged compared with a belt comprising a single kind of element. Thus, the elements must be arranged at random in accordance with the table of random numbers. When the belt comprises three or more kinds of elements, it can be determined whether the noise of the belt is sufficiently decreased by the following calculations. Supposing that among n kinds of elements E₁ to E n , the most thick elements E₁ has a largest percentage in number (i.e. is the most numerous), and the ratio r of difference of thickness ti of a certain element E i to the thickness t₁ of the most thick element is calculated, as follows: r = (t₁ - t i )/t₁ A minimum ratio r m is the smallest value of r and is the ratio between the most thick element E₁ and the subordinate element E₂. Percentage P i of the element E i is then calculated as follows. P i = a i /A × 100 where A is the total number of the elements E₁ to E n and a i is the number of a certain element E i . The total percentage P T is the sum of the percentages P₂ to P n (P T = P₂ + ... Pn = (A - a₁)/A × 100). A hatched area in Fig. 5 shows a range where noise is decreased in relation to the minimum difference ratio r m and the total P T . A borderline in Fig. 5, connecting points indicated by P T = 22, r m = 0.05 and P T = 10, r m = 0.3, is a line connecting percentages of each ratios on a noise-reduction limit line in Fig. 4. The above-described conditions for reducing noises of the belt of the present embodiment can be summarized as below: a) Two or more kinds of elements E₁ to E n are distributed at random. b) The minimum ratio r m of the difference of thicknesses of elements is in the range of 0.05 and 0.5. c) The percentage P T of elements excluding the elements E₁ is in the range of 10 to 50%. d) When the minimum ratio r m is between 0.05 and 0.3, the minimum percentage P T is 22% at the ratio 0.05 and linearly decreases to 10% at the ratio 0.3. Figs. 6 to 9 show another embodiment of the present invention. Same numerals as those in Figs. 1 to 3 designate same parts. In the present embodiment, elements of equal thickness are used. However, in order to increase the thickness of an element, an adjustment sheet 31 is attached to the element in accordance with the combination of thickness. The shape of the sheet is similar to the element 10 in elevation as shown by a dotted line in Fig. 6. The size is slightly smaller than the element 10 so as not to rub the pulleys or carriers. Referring to Fig. 8, each adjustment sheet 31 has an opening 31b in which the projection 16 of the element 10 is engaged. The adjustment sheet 31 is fixed to the element 10 by a pair of pawls 31a which are engaged to recesses 20 of the element 10. Alternately, a pair of pawls 31c may be provided to engage recesses 21 at the bottom of the element 10 as shown in Fig. 9. Thus, the thickness t of the element 10 referred to in the previous embodiment corresponds to a sum of thicknesses of the element 10 and the adjustment sheet 31 in the present embodiment. In order to provide a belt with elements in three or more different thicknesses, several kinds of adjustment sheets may be used. Further, two or more sheets of equal thickness may be attached to an element. Although the number of the most thick element E₁ is larger than the remainder in the embodiments, it is possible to set the number of another element than the most thick element to a maximum value.

Claims: 1. A belt (6) for a continuously variable transmission (1), comprising: a plurality of metal elements (10) arranged on carrying means (30), characterised in that the elements (10) are of at least two kinds, one kind being distinguished from the other by a difference in the maximum thickness of the element; and, the elements being arranged substantially at random to attenuate the noise generated by the belt during use. 2. A belt as claimed in claim 1 wherein one kind of element is more numerous than any one of the other kind of elements. 3. A belt as claimed in claim 1 or claim 2 wherein there are at least three kinds of element and the most numerous kind of element accounts for at least fifty percent of the elements in the belt. 4. A belt as claimed in any preceding claim wherein at least one element (10) has a sheet (31) attached to the element to adjust the thickness of the element (10). 5. A belt as claimed in any one of the preceding claims wherein the minimum ratio (rm) of difference (t1 - ti) of the thickness (t1) of the most numerous kind of element (E1), having the greatest thickness (t1) and any one of the other kinds of element (Ei) having the thickness (ti), to the greatest maximum thickness (t1) is in the range between 0.05 and 0.5, that is to say 0.05 ≦ rm = t1 - ti t1 ≦ 0.5 6. A belt according to any one of the preceding claims wherein the percentage (Pt) of the kinds of element (Ei) other than the most numerous kind (E1) is in the range of 10 to 50. 7. A belt according to claim 5 wherein the percentage (Pt) is inversely proportional to the minimum ratio (rm) between the values rm = 0.05 and rm = 0.3 and, Pt is substantially 22% when rm = 0.05 and Pt is substantially 10% when rm = 0.3. 8. A continuously variable transmission (1) having a drive pulley (3) and a driven pulley (5), coupled by a belt (6) as claimed in any one of the preceding claims.

Inventors: IDE, TOHRU, SATOH, MITSUGU
Applicants: FUJI JUKOGYO KABUSHIKI KAISHA, VAN DOORNE'S TRANSMISSIE B.V.
Application year: 1988
Main classification: F16G5
IPC codes: F16G5