A METHOD FOR THE PRODUCTION OF A TRANSVERSE ELEMENT FOR A DRIVE BELT AND A TRANSVERSE ELEMENT OBTAINED THEREWITH

The present invention relates to the method for the production of a transverse element for a drive belt according to the preamble of claim 1 hereinafter, and to the transverse element obtained therewith. Such a drive belt is generally used for the transmission of a driving power between two shafts in a drive line, the drive belt being passed around two or more rotating pulleys and being clamped between them. A generally known use of such a transmission is the continuously variable transmission for 2-wheeled motor vehicles such as scooters . The drive belt and transmission are known per se and were disclosed in, for example, the US patent with publication number 4,612,005 back in 1986.

The known drive belt comprises a more or less continuous series of discrete transverse elements and an endless, i.e. self-contained, tension element, which can be composed of a single substantially ribbon-shaped ring or of two or more of such rings, which are then concentrically stacked. The tension element is retained in the radial or vertical direction and in the axial or transverse direction in a central opening of the transverse elements . The transverse elements and the tension element can be movable relative to each other or fixed in the longitudinal or peripheral direction of the tension element. In the first-mentioned design of the drive belt, said drive belt will transmit the driving power between the pulleys largely under the influence of pressure forces exerted between the transverse elements, the tension element guiding the transverse elements in the desired path, while in the second case tensile forces in the tension element are responsible for this, the transverse elements providing the transmission of power between the pulleys and the tension element.

Each transverse element is provided with two main faces oriented in the peripheral direction of the drive belt, and with two side faces placed at an acute angle to each other, which side faces extend on either side of the transverse element between the main faces and are intended for frictional contact with the transmission pulleys. The transverse element is provided with an opening situated centrally in the transverse element, through which opening the tension element is guided. The opening is bounded in the radial direction and in the axial direction by respective parts of the transverse element, namely radially outwards by a top transverse beam, radially inwards by a bottom transverse beam, and in the individual axial direction by a respective strut. One of the two struts in this case is provided with a full cut, which thus extends between a respective side face and the opening of the transverse element and between the front and rear face thereof . This means that as part of the assembly of the drive belt the transverse beams can be moved away from each other, or bent, and the tension element can be accommodated in the opening of the transverse element . In this case a thinning of the other strut, for example, of a transverse beam acts as an elastic hinge.

The known cut will always be formed with a certain radial dimension or height, at any rate with the manufacturing means conventionally available for that purpose, such as the integral forming of transverse element and cut, for example by means of die cutting or injection molding, or the subsequent making of a cut in the transverse element that has been preformed as a whole, for example mechanically, thermally or chemically, in other words, the parts of the transverse element lying directly below and directly above the cut in practice will not - or at any rate will not as a matter of course - be in contact with each other. This means that the mutual retention of the tension element and the transverse element in the drive belt is not

optimal. For example, if the tension element is made of steel, in particular a high-alloy maraging steel, said tension element can in principle be provided with an advantageously low height, for example of less than 0.25 millimeter, preferably around and close to 0.18 millimeter. In that case even a relatively low height of the cut of, for example, 0.10 millimeter, i.e. of around and close to half the height of the tension element, cannot be ignored, because the tension element could force open such a cut during operation of drive belt, so that the latter can be damaged.

The abovementioned patent publication does provide additional closing means for fixing against each other the abovementioned parts of the transverse element lying above and below the cut, but such means will complicate the assembly of the drive belt and increase its production costs .

The object of the present invention is to provide a transverse element and a method for the production thereof that renders the use of the abovementioned additional closing means unnecessary. In the new transverse element the abovementioned parts lying on either side of the cut are preferably automatically forced against each other with some closing force. The envisaged object is achieved according to the invention by using the combination of measures from the characterizing portion of claim 1. According to the invention, the transverse element is produced in an injection molding process, in which the respective parts of the cut strut lying below and above the cut are separated from each other by the dam of the injection mold, which dam also defines the opening of the transverse element and in this case, viewed from said cut strut in the direction of the non-cut strut is at any rate effectively tapered. Because the material of the non-cut strut during its solidification can shows a greater shrinkage on the axial side of the opening than on the opposite axial side near the respective side face of the transverse element, the two

transverse beams at least have the tendency to move towards each other, and the ultimate height of the cut in the end product can advantageously be smaller or even equal to zero. In the latter case the method according to the invention has the additional advantage that in the end product the parts of the cut strut lying below and above the cut are pressed against each other, with the result that the radial dimension or height of the opening is determined clearly and accurately.

The necessary difference in local solidification shrinkage is attributed to the fact that in the injection molding process according to the invention the material in the area around said side face solidifies earlier than that in the area around the opening. Although it is true that the abovementioned difference in solidification shrinkage is small in absolute terms, the mutual movement, or the mutual rotation, of the transverse beams of the transverse element has still been found sufficient to achieve the desired effect. Moreover, the local solidification shrinkage according to the invention is controlled or adjusted by the choice and/or the design of the transverse element. In particular, the axial dimension or width of the opening of the transverse element must be selected so as to be sufficiently large for this purpose, so that the abovementioned slight mutual rotation of the transverse beams will lead to a considerable mutual movement of the ends thereof. The present invention is suitable particularly for the production of transverse elements of a material with a solidification shrinkage in the region of 0.4% to 4%, and in particular around 0.6%. The invention is also suitable in particular for the production of transverse elements of a polymer material or plastic, more particularly a thermoplastic, such as a polyamide with or without glass, carbon or aramid fiber reinforcement .

According to the invention, such a solidification

shrinkage desired for forcing the cut to close can be reinforced, or at any rate optimized, by using one or more of, and preferably all of, the following measures in the design of the transverse element. First, the smallest axial dimension or width of the non-cut axial boundary of the opening in the transverse element or strut is preferably at least twice as great as the largest radial dimension or height of the opening. The smallest width of the non-cut strut preferably has a value in the region of 2 to 10 times the greatest height of the opening, and more particularly the abovementioned smallest width is equal to 5 times said greatest height.

Secondly, the smallest radial dimension or height of the top radial boundary of the opening in the transverse element or top transverse beam is preferably twice as great as the greatest height of the opening. In particular, the lowest height of the top transverse beam has a value in the region of 2 to 10 times the greatest height of the opening, and more particularly the last-mentioned smallest height is five times said greatest height.

Thirdly, the smallest radial dimension or height of the bottom radial boundary of the opening in the transverse element or bottom transverse beam is preferably at least twice as great as the greatest height of the opening. In particular, the smallest height of the bottom transverse beam has a value in the region of 2 to 10 times the greatest height of the opening, and more particularly the last-mentioned smallest height is equal to 5 times said greatest height .

Fourthly, the axial boundary of the opening in the transverse element on the side of the non-cut strut, i.e. a side face thereof facing the opening, is preferably formed by an at least partially, and preferably fully, concavely curved face. This concave boundary face butts up here to the radial boundary faces of the opening, namely the underside of the top

transverse beam and the upper side of the bottom transverse beam, it being desirable to provide a convexly curved transitional face between the concave boundary face and the radial boundary faces. The present invention also relates to the transverse element that is obtained by the present method.

The invention will now be explained in greater detail with reference to the exemplary embodiments illustrated in the appended figures.

Figure 1 represents a diagrammatically shown cross section of the known transmission provided with two pulleys and a drive belt.

Figure 2 shows diagrammatically an isometric view of a section of the known drive belt provided with transverse elements and a tension element .

Figure 3 illustrates diagrammatically the manufacturing process according to the invention.

Figure 4 shows a front view and a cross section of a first example of the transverse element according to the invention.

Figure 5 shows the front view of the first example of the transverse element according to the invention of figure 4 in greater detail . Figure 6 shows a front view of a second example of the transverse element according to the invention.

Figure 1 shows very diagrammatically in cross section the known continuously variable transmission 1 with two pulleys 2, 3 and a drive belt 10. The known drive belt 10 comprises a more or less continuous series of discrete transverse elements 12 and, at least in the present exemplary embodiment, a single annular tension element 11. A section of the known drive belt 10 is shown in greater detail in figure 2. Each transverse element 12 is provided with two main faces 14 (only the front face 14 of which is visible in figure 2) oriented in mutually opposite peripheral directions of the drive belt 10 and with two side faces 15 (only the left side face 15 of which is

visible in figure 2) placed at an acute angle to each other, extending on either side of the transverse element 12 between the main faces 14 thereof and intended for the frictional contact with the transmission pulleys 2, 3.

The transverse elements 12 are provided with a central opening 13 , through which the tension element 11 is guided, which opening 13 is bounded by respective parts of the transverse element 12 , namely radially outwards by a top transverse beam 16, radially inwards by a bottom transverse beam 17, and in the individual axial directions by a respective strut, i.e. a left- hand and a right-hand strut 18 and 19 respectively. The mutual freedom of movement of the tension element 11 and the transverse elements 12 is limited in the radial and in the axial directions to a clearance provided between them. In the present exemplary embodiment the transverse elements 12, on the contrary, are freely movable in the peripheral direction of the tension element 11 relative thereto. Both the abovementioned opening 13 and the tension element 11 are provided with a substantially rectangular periphery with a radial dimension or height that is clearly lower than an axial dimension or width thereof. More particularly, the height of the tension element 11 and/or of the opening 13 is equal to 1 % to 10 %, preferably 2 to 3 % of the width thereof .

In order to be able to assemble the drive belt 10, i.e. in order to be able to place the tension element 11 in the opening 13 of the transverse elements 12, one of the two struts 18, 19 of the transverse elements 12, here the left-hand strut 18, is provided with a cut 20. The cut 20 extends here between the left-hand side face 15 and the opening 13, on the one hand, and the two main faces 14 of the transverse element 12, on the other hand. By means of this provision, the two transverse beams 16 and 17 can be moved away from each other, or bent, and the transverse element 12 can then be slid over the tension element 11, in which case the

latter will then ultimately be situated in the opening 13. It is usual here for the tension element 11 to be made of a tension proof material, such as steel or fiber material, and the transverse elements 12 of a fiber reinforced or other plastic.

It is pointed out that, although in the appended figures the left-hand strut 18 of the transverse element 12 is provided with the cut in each case, the transverse elements 12 in the drive belt 10 are preferably accommodated alternately in mirror image fashion for the sake of symmetry, i.e. in the drive belt 10 the cut 20 is preferably provided alternately in the left-hand strut 18 and the right-hand strut 19 of the successive transverse elements 12. In addition, the transverse elements 12 in practice will generally also be provided with a projection (not shown here) and with a complementary depression (not shown either) , in such a way that in the drive belt the projection of a first transverse element 12 is accommodated at least partially in the depression of a second, i.e. adjacent, transverse element 12.

Although it cannot be seen on the scale of figure 2, the cut 20 has a certain non-negligible radial dimension or height. In other words, the parts of the transverse element 12 situated below and above the cut 20 respectively, here the top transverse beam 16 and the left-hand strut 18, in reality do not automatically rest against each other, which can adversely affect the functioning of the known transverse element 12 , or of the known drive belt 10. According to the present invention, the transverse element 12 can be improved in the abovementioned respect in an advantageously simple manner by adapting the design or the shaping thereof and the manufacturing process to each other. More specifically, the invention relates to an injection molding process, in which the transverse element 12 is produced integrally, in other words in one piece.

In the known injection molding process a molding template or injection mold 50, generally made of metal

and provided with a mold cavity 51 whose shape at least approximately corresponds to the product to be injection molded, here the transverse element 12, is used. Such an injection mold 50 is shown in cross section in figure 3. The injection mold 50, or its mold cavity 51, is filled with the desired material, which is introduced under pressure to it in a liquid state, in other words in a non-polymerized and/or sufficiently heated state. In the injection molding process according to the present invention the transverse element 12 is formed integrally, for which purpose the opening 13 and the cut 20 of the transverse element are achieved by means of a dam 52 in/of the injection mold 50 shaped substantially corresponding thereto. Such a dam 52 in a general sense is also sometimes referred to as an insert. On account of the stiffness and strength required of it, said dam 52 must, of course, be provided with certain minimum dimensions, with the result that the radial dimension or height equal to zero - or at least less than 0.1 mm - desired for the cut 20 apparently cannot be achieved. However, during the solidification or hardening of the material of the transverse element 12 shrinkage occurs in it, which solidification shrinkage according to the present invention can be used to such advantage that the cut 20 is closed by it. According to the invention, the solidification shrinkage of the material of the non-cut strut 19 (in this case the right-hand strut) on the side of the opening 13 in this case must be sufficiently greater on the side of the respective side face 15 (in this case the right-hand side face), which is achieved by the fact that the material on the side of the abovementioned side face 15 solidifies earlier than it does on the side of the opening 13.

In order to accommodate the abovementioned effect, according to the invention at least the dam 52 must preferably uniformly, but at least effectively taper from the cut strut 18 in the direction of the non-cut

strut 19. A width dimension DB of the dam 52 at the position of the cut 20 of the transverse element 12 to be formed in this case preferably has a value in the region of 0.3 to 0.5 mm. More particularly, the substantially radially oriented boundary faces 23, 24 of the opening 13, namely the underside 23 of the top transverse beam 16 and the upper side 24 of the bottom transverse beam 17, are oriented at a slight angle a. of a few degrees to each other. Said angle α preferably has a value in the region of 1 to 5 degrees and is preferably equal to 3 degrees . According to the invention, the abovementioned parameters in conjunction with the axial dimension or width B13 of the opening 13 must preferably comply with the equation: 513=-^-, tan(αr) so that the parts of the cut strut 18 lying below and above the cut respectively are advantageously pressed against each other with a certain closing force and the radial dimension or height of the opening 13 is advantageously determined clearly and accurately at least in the end product. Furthermore, in this particular case the abovementioned radially oriented boundary faces 23, 24 of the opening 13 will advantageously ultimately automatically lie parallel in the end product.

In the form of the transverse element 12 defined by the injection mold 50 the parts 15a, 15b of the left- hand side face 15 lying below and above the cut 20 respectively {see figure 4) can be corrected by the rotation of the top transverse beam 16 relative to the bottom transverse beam 17 that occurs when the transverse element is removed from the injection mold cavity 51, in such a way that in the process the abovementioned parts 15a, 15b ultimately lie in line with each other. For this purpose, the corresponding wall parts 53a, 53b of the injection mold 50 are placed at an acute angle, which is at least equal to 180 degrees of arc minus the earlier mentioned angle α.

According to the present invention, the design of the transverse element 12 furthermore preferably complies with at least one of the characteristics discussed below with reference to figure 4. Figure 4 here shows diagrammaticalIy an enlarged detail in front view of a first example of a molded transverse element 12 according to the present invention, and also a cross section A-A thereof. Just as in the known transverse element 12 of figure 2 , this transverse element 12 according to the invention is also provided with the central opening 13, which is bounded radially outwards by the top transverse beam 16, radially inwards by the bottom transverse beam 17 and in the individual axial directions by respective struts, i.e. left-hand and right-hand struts 18 and 19 respectively. The left-hand strut 18 is provided here with the abovementioned cut 20.

The left-hand strut 18 is provided with the cut 20, which in this example merges into an opening 21 gradually widening in the radial or vertical direction, i.e. more or less V-shaped, between the cut 20 and the respective, i.e. left-hand, side face 15 of the transverse element 12. This means that in the assembly of the drive belt 10 the transverse element 12 can be relatively easily fitted on the tension element 11, the transverse element 12 at the position of the opening 21 being pressed against an axially directed side face of the tension element 11 and the cut 20 being opened. In order to prevent damage to the transverse element 11 and/or the tension element 12, the V-ahape of the opening must be at most 45 degrees of arc, and preferably 20 to 30 degrees of arc.

It can be seen in the cross section A-A that the transverse element 12, in particular, the bottom transverse beam 17 thereof, tapers radially inwards, in order to enable mutual rotation of two adjacent transverse elements 12.

In the design of the transverse element 12 shown in figure 4 a number of further measures are taken, as a

result of which the top transverse beam 16 and the top transverse beam 17 have the tendency to move towards each other, or to rotate, and the cut 19 is automatically forced to close, at any rate in so far as the transverse element 12 concerned has been produced by means of the abovementioned injection molding process .

In accordance with a first measure according to the invention, the smallest axial dimension or width B19 of the non-cut strut 19 is preferably at least twice as great as the greatest radial dimension or height H13 of the opening 13. In particular, the abovementioned smallest width B19 has a value in the region of 2 to 10 times the greatest height H13 of the opening 13, and more particularly the abovementioned smallest width B19 is equal to 5 times said greatest height H13. Moreover, said greatest height H13 of the opening 13 in the design the transverse element 12 shown here corresponds to the radial dimension of the two struts 18, 19. In accordance with a second measure according to the invention, the smallest radial dimension or height H16 of the top transverse beam 16 is preferably at least twice as great as the greatest height H13 of the opening 13. In particular, the abovementioned smallest height H16 has a value in the region of 2 to 10 times the greatest height H13 of the opening 13, and more particularly the abovementioned smallest height H16 is equal to 5 times said greatest height H13.

In accordance with a third measure according to the invention, the smallest radial dimension or height H17 of the bottom transverse beam 17 is preferably at least twice as great as the greatest height H13 of the opening 13. In particular, the last-mentioned lowest height H17 has a value in the region of 2 to 10 times the greatest height H13 of the opening 13, and more particularly the last-mentioned lowest height H17 is equal to 5 times said greatest height H13.

In accordance with a fourth measure according to the invention, the axial boundary 22 of the opening 13

in the transverse element 12 on the side of the non-cut strut 19, i.e. the side face 22 thereof facing the opening, is preferably formed by an at least partially, and preferably fully, concavely curved face 22. This concave boundary face 22 here abuts the abovementioned underside 23 of the top transverse beam 16, on the one hand, and the upper side 24 of the bottom transverse beam 17, on the other hand. According to the invention, the concave boundary face 22 is preferably provided with a radius of curvature having a value in the region of 0.25 mm to 1.5 mm.

Figure 5 shows a detail of figure 4 again, on the basis of which the preferred design of the transverse element 12 according to the present invention for achieving the envisaged material shrinkage is defined in an alternative manner. In accordance with the invention, the diameter D13 of a first imaginary circle touching the abovementioned axial side face 22 and the abovementioned radially oriented boundary faces 23, 24 of the opening 13 must be at least half the value of the diameter D12 of a second imaginary circle extending within the periphery of the transverse element 12 up to an edge thereof, the center point of which second imaginary circle coincides with the center point of the first imaginary circle. In particular, the diameter D13 of the first imaginary circle has a value in the region of 0.1 to 0.5 times the diameter D12 of the second imaginary circle and, more particularly, is equal to 0.2 times said diameter D12. Figure 6 shows an enlarged detail in front view of a second example of a transverse element 12 shaped according to the present invention. Said second example is distinguished from the first example of figure 4 in that the top transverse beam 16 is provided with a smaller axial dimension or width and a smaller radial dimension or height. In particular, through the abovementioned smaller width thereof, the top transverse beam 16 in the transmission will not come into frictional contact with the transmission pulleys 2,

3 and as a result of this the non-cut, right-hand strut 19 will be subjected to considerably less load. This means that the shape of this right-hand strut 19 can be adapted in the optimum manner for the solidification shrinkage envisaged for it in accordance with the present invention and for its function as an elastic hinge during the assembly of the drive belt 10.

Finally, according to the invention, in the injection molding process it is advantageous for the transverse element 12 to be injected from a position which, viewed in the axial direction is away from the non-cut strut, in the present case the right-hand strut 19 has been removed, preferably from the axial center of one of the transverse beams 16, 17. Such injection supports solidification shrinkage envisaged by the invention, or the local differences envisaged for it.