Drive belt with cross-member and endless stack for continuously variable transmission

Abstract

The invention relates to a cross-member for a drive belt of a pulley-type continuously variable transmission, said drive belt comprising a row of cross-members mounted on a stack of a plurality of mutually nested rings. The transverse member is provided with a trapezoidal base (13) having two contact surfaces (37), between the ridges (39) of which there is a groove (38). According to the invention, the uppermost ridge (39-b) and the lowermost ridge (39-a) of the contact surface (37) lie in the same plane (VTP) and have substantially the same width as the ridges (39) lie between the grooves (38) thereof.

Description

Technical Field

[0001] The invention relates to a transverse member or component intended to be part of a drive belt for a continuously variable transmission having two pulleys and a drive belt. Background Art

[0002] This type of drive belt is known from European Patent Publication WO 2015 / 097293 A1 and comprises a row of metal cross-members mounted together on at least one stack of a plurality of interlocking continuous metal strips (i.e., flat, thin rings) and along the circumference of the at least one stack. Each cross-member defines at least one slot for accommodating and restraining a corresponding portion of the circumference of the at least one annular stack while allowing the cross-member to move, i.e., slide along its circumference. This particular type of drive belt is known as a push belt or push belt.

[0003] In the following description, the terms axial, radial, and circumferential are used when the belt is positioned in a circular pattern outside the transmission. Furthermore, the thickness of the cross member is defined along the circumference of the belt, the height along the radial direction, and the width along the axial direction.

[0004] Known cross members all include a base, a middle portion, and a top portion. The middle portion of the cross member extends radially between the base and top portions, while the one or more grooves are defined between the base and top portions of the cross member, located to one side of the middle portion. At the one or more grooves, the radially outward-facing surface of the cross member base contacts and radially supports the ring stack. Hereinafter, this specific surface is referred to as the bearing surface.

[0005] In a row of transverse members of a drive belt, at least a portion of a front body surface (oriented in the general direction of belt rotation in the transmission) of a transverse member abuts at least a portion of a rear body surface (oriented in the opposite direction) of a corresponding front transverse member in the row, while at least a portion of a rear body surface of a transverse member abuts at least a portion of a front body surface of a corresponding rear transverse member. At least one of the front and rear body surfaces of the transverse member, for example the front body surface, includes an axially extending convexly curved surface portion. The curved surface portion divides the front body surface into a radially outer surface portion and a radially inner surface portion, the two portions being angled relative to each other. The abutting transverse members of the drive belt can tilt relative to each other while maintaining mutual contact at the curved surface portion, which is hereinafter referred to as a tilted edge, but is also known in the art as a rocking edge. The tilted edge allows the transverse member row of the drive belt to follow the local curvature of the loop stack imposed by the pulleys.

[0006] The cross member also has a protrusion, i.e., a spike, protruding from its front main surface, and a cavity, i.e., a hole recessed into its rear main surface. In a row of cross members for a drive belt, the protrusion of the rear cross member is at least partially located within the cavity of the front cross member. This prevents or at least limits relative displacement of adjacent cross members in a plane perpendicular to the circumference of the drive belt. Typically, the protrusion and cavity have similar overall shapes, for example, roughly cylindrical with a slight taper (i.e., cone). The protrusion is slightly smaller than the cavity, such that, in the drive belt, there is a gap between the inner periphery of the cavity of the front cross member and the outer periphery of the protrusion of the rear cross member when inserted (particularly fully inserted) into the cavity of the front cross member. Therefore, when the cavity and protrusion are roughly cylindrical, the outer diameter of the protrusion is smaller than the inner diameter of the cavity. Regarding the latter, it should be noted that since the cavity and protrusion are typically slightly tapered (i.e., conical), the diameters of the cavity and protrusion are compared at equidistant points perpendicular to the rear and front main surfaces of the cross member, respectively.

[0007] The portion of the circumferential surface of a transverse member extending between its front and rear body surfaces is intended to come into (frictional) contact with the pulleys by clamping between two tapered disks on each pulley. These pulley-disc-engaging portions of the transverse member's circumferential surface are located on both axial sides and are referred to as the (pulley) contact surfaces. These contact surfaces of the transverse members are angled relative to one another, defined as the nominal value, the so-called belt angle, which is the average value of these angles for all transverse members of the drive belt.

[0008] Frictional contact between the transverse members and the contact surfaces of the pulley sheaves enables force transfer between them, thus enabling the drive belt to transmit drive torque and rotational motion from one pulley to the other. Furthermore, due to the conical shape of the pulley sheaves, the transverse members also experience a radially outward component of the clamping force applied to each pulley. This radial component places the drive belt, and in particular its loop stack, under tension and causes the corresponding portion of the drive belt located between the pulley sheaves of each pulley to displace in mutually opposite radial directions between its minimum and maximum radial positions. The relative radial positions of the drive belt at the two pulleys determine the speed (and torque) ratio transmitted between the pulleys.

[0009] Regarding the belt angle, WO 2015 / 097293 A1 teaches how to design a transverse member so that the belt angle exceeds the so-called pulley angle, defined by the tapered discs of the input pulley of a transmission. This pulley is directly connected to the engine or electric motor, meaning its rotational speed is the same as or at least proportional to that of the engine or electric motor. This difference between the belt angle and the pulley angle advantageously increases the coefficient of friction between the drive belt and the input pulley, thereby increasing the maximum drive torque that can be transmitted by the transmission for a given pulley clamping force. Specifically, according to WO 2015 / 097293 A1, the belt angle exceeds the pulley angle by at least 0.2 degrees and at most 1.2 degrees.

[0010] Another known design method for increasing the coefficient of friction between a drive belt and a pulley is described in JP2000179626A and EP3835618A1. Both patents teach that the protrusion of the drive belt cross-member is offset radially inward relative to its cavity. As a result, the (virtual) center axis of the roughly cylindrical or conical protrusion is located radially inside the (virtual) center axis of the correspondingly shaped cavity. Therefore, in the design of this cross-member, the above-mentioned gap of the protrusion in the drive belt cavity is smaller on the lower side of the protrusion than on its upper side. In fact, according to EP3835618A1, this gap can be completely eliminated, meaning that it extends radially inward, that is, the bottom side of the protrusion basically coincides with the bottom side of the cavity, or even lies radially inward thereof.

[0011] Due to this offset between its protrusions and recesses, the transverse member, even when running in a straight path between the pulleys, will tilt backward (or at least have a tendency to tilt backward) in the belt row because the protrusions are forced into the (higher) recesses. As a result, the transverse member enters between the pulley sheaves in this backward tilted direction, which can advantageously increase the friction between it and the pulleys in the tangential direction.

[0012] A plurality of substantially equidistant grooves are provided on the otherwise flat contact surface, extending between and substantially perpendicular to the front and rear main body surfaces of the cross member. These grooves serve to contain and / or drain transmission oil from the contact surface when the higher contact portion located between the grooves comes into (frictional) contact with the pulley. Numerous design variations of this macroscopic surface structure of the contact surface have been proposed in the art (e.g., see WO 2013 / 000493 A1, JP 2011075089 A1, JP 20100236663 A1, EP 2119939 A1, JP 2007303520 A1, and EP 0994275 A1). For each such design variation, several design variables apply, such as the groove pitch (i.e., measured center-to-center between adjacent grooves in a virtual tangent plane to the contact surface), the groove depth (i.e., measured perpendicular to the tangent plane), and the contact ratio (calculated by subtracting the groove width—measured along the tangent plane to the contact surface—from the groove pitch, divided by the groove pitch). It is therefore not clear at all what specific shape of the contact surface (ie what surface structure) is preferred in practice. Summary of the Invention

[0013] Taking into account the partially divergent, incomplete and / or even conflicting teachings of the above-mentioned prior art, the present invention aims to provide a detailed shape of the contact surface so as to achieve an optimal balance between the manufacturability of the transverse member, the running performance of the drive belt and its lifespan, thereby consolidating the known technical insights.

[0014] According to the present invention, the grooved contact surface of the crossmember is provided with flat or at most slightly convex curved sections at both its upper and lower ends. At the upper end, the contact surface transitions to the load-bearing surface via a convex curved transition surface; at the lower end, the contact surface transitions to the bottom surface of the crossmember base portion via a convex curved transition surface. These flat or slightly convex curved sections coincide with virtual tangent planes of the respective contact surfaces, thereby forming a contact area with the pulley sheaves at their maximum spacing along the height of the crossmember. This maximum spacing helps ensure stable contact between the crossmember and the pulley sheaves, and in particular prevents radial rotation of the crossmember relative to the pulley sheaves, which would otherwise adversely reduce friction.

[0015] Preferably, the upper and lower ends of the respective contact surfaces extend in the height direction over a distance that is substantially the same as the distance that the contact portion of the contact surface extends between a pair of adjacent grooves. Otherwise, i.e., if these ends are too short, there is a risk that, after stone tumbling of the transverse member during manufacturing, the convexly curved transition surface will transition directly into the uppermost or lowermost groove of the contact surface. Stone tumbling is typically used to round off and remove burrs from the edges of transverse members after they have been cut, particularly by punching from a substrate.

[0016] Preferably, the upper and lower end portions and the contact portions of the corresponding contact surfaces are slightly convexly curved, with a radius of curvature of not less than 1 mm, preferably not more than 10 mm. As a result, during the initial so-called running-in phase of the transmission, the wear rate of the contact surfaces is relatively high due to the limited initial contact surface area with the pulley discs, thereby enabling the transverse member to quickly and optimally engage the pulleys, in particular, to form a precise angular engagement with the pulley discs.

[0017] Preferably, each groove is defined by a concavely curved groove bottom and flanked by convexly curved groove edges, which align with one of the upper and lower ends of the corresponding contact portion or contact surface. This curved groove profile facilitates manufacturing, particularly in blanking processes for cutting transverse members from strip material. Furthermore, the convex design of the groove edges ensures that the contact ratio of the contact surface advantageously increases rapidly after the aforementioned run-in phase of belt operation, thereby minimizing further wear of the contact surface during extended belt operation (assuming the contact ratio after run-in wear is sufficiently high). Ideally, in this latter regard, the radius of curvature of the groove bottom and groove edges is approximately one order of magnitude smaller than the radius of curvature of the aforementioned contact portion of the contact surface, with a value ranging from 0.03 to 0.1 mm, preferably approximately 0.05 mm.

[0018] To minimize wear on the contact surface, the groove depth can be relatively small, specifically, only 25 to 50 microns, preferably approximately 30 microns. This shallow groove profile facilitates manufacturing, particularly during the blanking process. Combined with the aforementioned preferred curvature radii of the groove base and edges, and the preferred contact portion extension of 0.1 to 0.2 mm, the preferred groove depth allows for a relatively small groove spacing of 0.15 to 0.35 mm, preferably approximately 0.25 mm. For reference, the total height of the contact surface from its upper end to its lower end is in the millimeter range, typically approximately 7 mm, meaning that a total of approximately 28 grooves are present on the contact surface.

[0019] The preferred dimensions of the groove contact surface are such that the initial contact ratio is between 0.4 and 0.6, and the contact ratio after run-in wear is greater than 0.65, preferably about 0.75. This relatively small initial contact ratio enables the desired rapid run-in of the drive belt, while the relatively large contact ratio after run-in wear minimizes further wear of the contact surface during extended operation of the drive belt while ensuring adequate transmission oil drainage.

[0020] As another independent aspect, the present invention relates to a tapered structure that can be applied to the middle part of the transverse member in the height direction, which tapered structure is known in the prior art EP2325523A1. Through this known tapered structure, the width of the middle part gradually increases from the bottom to the top of the transverse member. As a result, the height and weight of the transverse member can be effectively reduced. The known design relies on the fact that the pulley disc is tapered, making it possible for the middle part of the transverse member to gradually become thinner in the radial direction without reducing the space available for accommodating the ring stack between the pulley disc and the middle part. According to EP2325523A1, optimally, the cone angle of the middle part of the transverse member (i.e., the angle defined by its side) is the same as the belt angle, which in turn corresponds to the angle defined between the pulley discs of the pulley (i.e., the pulley angle). In traditional transmission designs, the pulley angle and the belt angle are approximately 22°, but in practice a value of 18° is also used.

[0021] According to the present invention, a hidden flaw in this known crossmember design has recently been discovered. Specifically, during belt assembly, the ring stack is inserted axially into the grooves of the crossmember. If the stack is inadvertently inserted too far, it can impact the sides of the center section. Given the tapered shape of the center section, this impact is disadvantageously concentrated at the top corners of the stack, making it more susceptible to damage. Indeed, the greater the tapered angle of the center section, the less axial clearance is available at the top corners of the stack, especially compared to the axial clearance at the bottom corners, and the greater the risk of damaging contact between the crossmember and the stack in the belt assembly. This risk and damage have previously gone unnoticed because it does not directly affect the operation of the belt in the transmission. However, it could lead to premature belt failure, particularly fatigue failure of the outermost rings of the stack, which was previously attributed to other causes.

[0022] The present invention seeks to strike a balance between minimizing the mass of the cross-member (by setting the taper angle in the middle of the cross-member equal to the pulley angle) and minimizing the risk of ring stack damage in the drive belt assembly (by setting the taper angle in the middle of the cross-member to zero). According to the present invention, this goal is achieved by setting the taper angle in the range of 50% to 90% of the pulley angle, which in conventional transmission designs corresponds to a range of 11° to 20°. More preferably, the taper angle is set in the range of 14° to 18° (i.e., approximately 60% to approximately 80% of the pulley angle), with 17° (i.e., approximately 75% of the pulley angle) being a typical optimal value.

[0023] It is noteworthy that JPH0483941A discloses a cross-member and annular stack, whose rotation angle is limited between the axial alignment position of the cross-member relative to the annular stack and the maximum rotation position of the cross-member relative to the annular stack. In order to ensure that the annular stack maintains linear contact with the side surfaces of the middle portion of the cross-member in the axial direction, the middle portion is tapered, and its side surfaces are angled relative to each other, the angle being twice the rotation angle. In conventional designs of existing drive belts, the rotation angle is approximately 1° to 2°, so the corresponding taper angle of the middle portion of the cross-member is approximately 2° to 4° (i.e., less than 20% of the belt angle). Obviously, the rotation angle is determined by the gap between the cross-member and the annular stack in the radial direction and the total width of the annular stack in the axial direction. In any case, the latter known taper angle of the middle portion of the cross-member is much smaller than the taper angle according to the present invention.

[0024] As a separate and independent aspect, the present invention also aims to optimize the overall design of a continuously variable transmission. This particular aspect of the invention is based on the inventors' novel insight that known design features, with respect to the friction increases they each achieve between the drive belt and pulleys, are not actually complementary. That is, the friction increase achieved by applying a known difference in belt and pulley angles cannot be further increased by applying a known offset between the protrusion and cavity (or vice versa).

[0025] According to the invention, the projections of the drive belt cross-members are still preferably offset radially inwards relative to their cavities in a known manner, however, the optimal difference between the belt angle and the pulley angle is less than 0.4 degrees, more preferably between 0.02 degrees and 0.2 degrees. By applying such a small difference between the belt angle and the pulley angle, the (maximum) contact pressure between the drive belt and the pulley, as well as their wear during operation, are both low, while by applying a known offset between the projections and the cavities, a high coefficient of friction between the two can still be achieved.

[0026] More specifically, according to the present invention, the offset between the projection of the transverse member and the cavity is optimally defined such that the bottom side of the projection substantially coincides with the bottom side of the cavity, at least within a tolerance of 10 microns or less between the transverse members of the drive belt. Thus, for a generally cylindrical drive belt, the offset is preferably approximately half the difference between the outer diameter of the projection and the inner diameter of the cavity. However, in the context of the present invention, a practical range for this offset is 40% to 80% of the difference between the diameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Below, the continuously variable transmission and the related transmission belt design according to the present invention are further and more detailedly described by means of exemplary embodiments and with reference to the accompanying drawings, in which:

[0028] - Figure 1 A schematic perspective view of a continuously variable transmission having a drive belt running on two pulleys is provided;

[0029] - Figure 2 A schematic cross-sectional view of a known drive belt oriented in its circumferential direction is provided;

[0030] - Figure 3 A schematic widthwise view of a cross member of a known drive belt is provided;

[0031] - Figure 4 yes Figure 2 An enlarged view of the detail of the cross member shown in;

[0032] - Figure 5 Schematically shows the Figure 4 the same details of the cross-member shown, but designed in accordance with said further aspect of the invention;

[0033] - Figure 6 Provided Figure 5 Detailed enlargement of the image;

[0034] - Figure 7 yes Figure 2 Another enlarged detail of the cross member shown;

[0035] - Figure 8 Schematically shows the Figure 7 The same details of the drive belt as shown in , but only the cross members are shown;

[0036] - Figure 9 yes Figure 2 Another enlarged detail of the cross member shown;

[0037] - Figure 10 Schematically shows the Figure 9 A cross section of the straight track portion of the drive belt of the cross member shown;

[0038] - Figure 11 Schematically shows Figure 9 The frictional contact between the drive belt including the cross member and the pulleys shown in FIG.

[0039] It is particularly important to note that these drawings are schematic and, in particular, not drawn to scale. DETAILED DESCRIPTION

[0040] Figure 1 A continuously variable transmission is shown schematically, for example, as a transmission for use between a prime mover and its drive wheels in a motor vehicle. The known continuously variable transmission is generally designated by reference numeral 1. The continuously variable transmission 1 comprises two adjustable pulleys 2, 3 and a closed-loop drive belt 6 which is wound around the pulleys 2, 3. The pulleys 2, 3 are each equipped with a pulley shaft 4 and two pulley discs 7, 8, wherein the first pulley disc 7 is fixed to the pulley shaft 4 of the respective pulley 2, 3, and the second pulley disc 8 is axially movable relative to the pulley shaft 4 while being rotationally fixed to the pulley shaft 4. During operation of the transmission 1, the drive belt 6 is clamped between the respective pulley discs 7, 8 at each pulley 2, 3 with a running radius Rr. By moving the pulley discs 7, 8 of the pulleys 2, 3 closer to or further away from each other, the running radius Rr can be varied, thereby varying the speed ratio of the transmission.

[0041] In the general design currently shown, the drive belt 6 comprises two sets of continuous belts or rings 5 stacked radially on top of each other (see Figure 2 ), which is hereinafter referred to as ring pile 9 ( Figure 1 Only one of them is shown in FIG. 1 ). The transverse members 10 of the drive belt 6 are arranged on the ring stack 9 in a substantially continuous row along its entire circumference. Figure 1 Only a portion of the cross member 10 is shown separately.

[0042] The transverse member 10 is movable relative to the ring stack 9, at least along its circumference. Torque can thus be transmitted between the pulleys 2, 3 by friction between the pulleys 2, 3 and the transverse member 10, as well as by the transverse members 10 pressing against each other and pushing forward along the circumference of the ring stack 9 in the direction of rotation of the pulleys 2, 3. The transverse member 10 and the ring stack 9 (and the rings 5 of the ring stack 9) of the drive belt 6 are typically made of (high-grade) steel. This particular type of transmission 1 and its general operating principle are well known per se.

[0043] Figure 2 Schematically shows a cross section of a known drive belt 6 in the length or circumference direction C, ie perpendicular to the axial direction A and radial direction R of the drive belt 6. Thus, Figure 2 , a cross section of a ring stack 9 is shown, together with a front view of one cross member 10 of the drive belt 6. Each of the ring stacks 9 consists of five individual flat, thin and flexible annular rings 5, which are stacked concentrically with respect to one another in the radial direction R, i.e. nested within one another, to form the respective ring stack 9. In practice, a ring stack 9 typically contains more than five annular rings 5, i.e. typically up to twelve or more.

[0044] Figure 2 Also shown is a cross member 10, which comprises, radially outwardly, a base portion 13 having a generally regular trapezoidal shape, a relatively narrow middle portion 14, and a generally triangular top portion 15. The middle portion 14 is located in the center of the cross member, so that a groove 33 provided on either side thereof is located between the base portion 13 and the top portion 15, and a respective one of the two ring stacks 9 is received in the groove 33. A radially outward bearing surface 42 of the base portion 13 of the cross member 10 supports the radial inner side of the respective ring stack 9 at each groove 33.

[0045] The front main surface of the cross member 10 is indicated by reference numeral 11, and the rear main surface of the cross member 10 is indicated by reference numeral 12. In the drive belt 6, at least a portion of the front surface 11 of the cross member 10 abuts at least a portion of the rear surface 12 of the corresponding front cross member 10, and at least a portion of the rear surface 12 of the cross member 10 abuts at least a portion of the front surface 11 of the corresponding rear cross member 10.

[0046] The cross member 10 receives the clamping force applied between the disks 7, 8 of each pulley 2, 3 via its contact surfaces 37, which are provided on each axial side of the cross member 10. These contact surfaces 37 are offset radially outwards from one another so as to form an acute angle between them, which is indicated as belt angle φ and is very close to the belt angle θ formed between the pulley disks 7, 8 of the pulleys 2, 3 (see FIG. Figure 1 ).

[0047] The cross-members 10 are provided with protrusions 40 projecting from their front surfaces 11 and corresponding cavities 41 on their rear surfaces 12. In the drive belt 6, the protrusions 40 of the rear cross-member 10 are at least partially located within the cavities 41 of the front cross-member 10, thereby preventing relative displacement of successive cross-members 10 in a plane perpendicular to the circumferential direction C of the drive belt 6, or at least limiting such displacement to play or clearance between the protrusions 40 and cavities 41 in the respective directions within said plane. In the figures, the protrusions 40 and cavities 41 are generally cylindrical, but other shapes for protrusions 40 and cavities 41 are also known. Specifically, they are typically designed to have a slight taper, i.e., a conical shape, in the art.

[0048] At the front surface 11 of the cross member 10, an inclined edge 18 is defined. The inclined edge 18 is represented by a convexly curved region of the front surface 11, said region dividing said front surface 11 into two parts in the radial direction R, said two parts being at an angle to each other, so that the cross member 10 tapers below the inclined edge 18 (i.e. radially inwards), as shown in FIG. Figure 3 As shown, the figure schematically shows Figure 2 Side view of the middle cross member 10. An important function of the inclined edge 18 is to provide mutual pushing contact between the consecutive cross members 10 when they are in a slightly rotated (i.e., tilted relative to each other) position at the pulleys 2, 3. Specifically, when the leading cross member 10 of a pair of consecutive cross members 10 enters between the two pulley sheaves 7, 8 of the pulleys 2, 3, it rotates relative to the trailing cross member 10 of the pair of consecutive cross members 10 that has not yet entered the pulley 2, while its rear surface 12 remains in contact with the inclined edge 18 on the front surface 11 of the trailing cross member 10. In the figures, the inclined edge 18 is located at the base 13 of the cross member 10, but it is also known to position the inclined edge 18 at least partially in the middle portion 4 of the cross member 10.

[0049] For the sake of completeness, it should be noted that alternative general designs for drive belts of the type currently under consideration are known in the art, for example from International Patent Publication WO 2018 / 210456 A1. This latter alternative drive belt design comprises only a single annular stack located within a single central opening in each cross-member. This central opening is directed radially outwards of the drive belt and is therefore defined by the base of the cross-member and two cylindrical portions, each extending radially outwards from a respective side of the base. In addition, the cross-members of this latter drive belt are provided with the aforementioned protrusion-recess pairs—either at a single location in the centre of the base or in two cylindrical portions, one in each portion—as well as the aforementioned contact surfaces 37 located axially on either side of the cross-member.

[0050] In a common design of the cross member 10, the contact surface 37 is provided with a plurality of substantially equidistant grooves 38 on an otherwise flat surface, e.g. Figure 4 Shown is an enlarged view of one axial side of the base portion 13 of the cross member 10 , but with the central portion of the contact surface 37 between the cut-off lines CL omitted.

[0051] In the embodiment shown, each groove 38 is defined by a concavely curved bottom with convexly curved groove edges on either side thereof that are aligned with ridges 39 of the contact surface 37. These ridges 39 all lie in a common virtual tangent plane VTP so that these portions 39 will come into common contact with the pulley sheaves 7, 8 during operation of the drive belt 6 in the transmission 1. The grooves 38 serve to direct transmission fluid away from this contact.

[0052] Convexly curved transition surfaces 44 are provided at both ends of the contact surface 37 in the height direction, between the contact surface 37 and the bearing surface 42 , and between the contact surface 37 and the bottom surface 45 of the base 13 of the cross member 10 .

[0053] A relatively narrow ridge 39-a is provided between the transition surface 44 at the lower end of the contact surface 37 and the lowermost groove 38-a of the contact surface 37. The lowermost ridge 39-a allows the contact surface 37 to have a greater extension in the height direction between its lowermost ridge 39-a and the uppermost ridge 39-b.

[0054] However, according to the present invention, an improvement can be achieved by increasing the width of the lowermost ridge 39-a, as shown in FIG. Figure 5 As shown, three pairs of adjacent dashed lines represent the widths of the corresponding ridges 39-a, 39-b, 39-c between the corresponding adjacent grooves 38 or between the corresponding adjacent grooves 38 and the transition surface 44. Preferably, the width of the lowermost ridge 39-a of the contact surface 37 is substantially the same as the width of the uppermost ridge 39-b thereof. More preferably, as Figure 5 As shown, all ridges 39, 39-a, 39-b, 39-c of the contact surface 37 have substantially the same width.

[0055] Furthermore, according to the present invention, Figure 6 A further enlarged view of the contact surface 37 is schematically shown in FIG. , wherein the ridge 39 preferably has a minimum convex curvature. The curvature radius R39 of the ridge 39 is preferably between 1 and 10 mm, and more preferably at least one order of magnitude greater than the curvature radius R38b of the concave curved groove bottom and / or the curvature radius R38e of the convex curved groove edge. Figure 6As further shown, at least initially, i.e. before the drive belt 6 is running in the transmission 1, the width W39 of the ridge 39 (measured between the convexly curved edges of two adjacent grooves 38 in the common virtual tangent plane VTP) is approximately 45% of the groove pitch GP (measured from center to center between two adjacent grooves 38 in the common virtual tangent plane VTP).

[0056] Figure 2 Another aspect of the common design of the cross member 10 shown is the tapering of its middle portion 14, so that the width of the middle portion gradually increases from the base 13 to the top 15 of the cross member 10. In other words, the axial side surfaces 43 of the middle portion diverge radially outward and form a cone angle β therebetween. According to EP2325523-A1, the cone angle β ideally corresponds to the pulley angle θ and therefore also to the belt angle φ. In conventional transmission designs, these pulley angles, belt angles, and cone angles are all approximately 22 degrees (e.g., 22°±1°). This known design relies on the fact that the pulley sheaves 7, 8 are conical, so that the middle portion 14 of the cross member 10 can gradually narrow without reducing the space available to accommodate the ring stack 9 between the pulley sheaves 7, 8 and the middle portion 14.

[0057] However, according to the present invention, Figure 7 As shown, when the ring stack 9 is inserted axially into the groove 33 of the cross member 10 to assemble the drive belt 6, there is a risk that the ring stack 9 (especially its top corner 9C) will hit the side 43 of the middle part 14 of one or more cross members 10 and cause damage. When the cone angle β of the middle part 14 is large, the axial clearance available between the ring stack 9 and the middle part 14 is smaller than when the cone angle β is small ( Figure 7 : dashed line 43' versus solid line 43), the risk of such harmful impact is higher. Therefore, according to the present invention, by reducing the cone angle β of the middle portion 14 compared to the prior art, in particular by setting the cone angle β to 17°±1°, the assembly process of the drive belt 6 can be simplified.

[0058] Another advantage of reducing the cone angle β of the middle portion 14 is that its side faces 43 are oriented at a less acute angle or a greater angle relative to the bearing surface 42 of the base 13. Figure 8 As shown, this means that the curvature of the concave portion of the curved transition 46 between the side 43 and the corresponding bearing surface 42 of the base 13 can be advantageously reduced without increasing the size of the groove 33a formed in the base portion 1 by the transition 46 as part of the groove 33. Alternatively, the size of the groove 33a can be reduced when a conventional curvature of the transition 46 is adopted. In either case, the mechanical strength, and in particular the fatigue strength, of the cross member 10 is improved.

[0059] In particular, according to the present invention, the concave transition structure 46 between the corresponding side surface 43 and the corresponding bearing surface 42 has a compound curvature, consisting of at least two adjacent concave segments R1 and R2, wherein the first concave segment R1 connects to the side surface 43, the second concave segment R2 forms the bottom of the groove 33a, and at least one convex segment R3 connects to the bearing surface 42. To minimize the size of the groove 33a, the radii of curvature of the first concave segment R1 and the radii of curvature of the convex segment R3 are relatively small. To maximize the strength of the base 13, the radius of curvature of the second concave segment R2 is relatively large, specifically 2 to 2.5 times the radius of curvature of the first concave segment R1. The radius of curvature of the convex segment R3 is preferably 0.5 to 1 times the radius of curvature of the first concave segment R1. The spans of the first and second concave segments R1 and R2 are preferably 45° to 90°, respectively, for a combined span of 120° to 160°. In terms of absolute values, the radius of curvature of the first concave section R1 is preferably 0.4 to 0.5 mm, while the radius of curvature of the second concave section R2 is preferably 0.8 to 1 mm.

[0060] Another aspect of the common design of the cross member 10 is that its protrusion 40 is located below the cavity 41, i.e. radially inward, as shown in FIG. Figure 9 The upper portion (i.e., radially outer portion) of the middle cross member 10 is shown in an enlarged schematic diagram. Specifically, an offset CLO is applied radially inwardly between the (virtual) center axis CA40 of the generally cylindrical protrusion 40 and the (virtual) center axis CA41 of the generally cylindrical cavity 41. By this design measure, the cross member 10 is pushed into a rearwardly tilted position in the straight path portion of the drive belt 6 between the pulleys 3 and 4, as shown in FIG. Figure 10 As shown in . Therefore, the cross member enters the pulley in this backward tilted direction, which significantly increases the friction between the drive belt 6 and the pulleys 3, 4. In addition, through this known design measure, the noise generated by the drive belt 6 running in the transmission 1 can be significantly reduced.

[0061] According to another known design of the cross member 10, the contact surface 37 thereof is oriented at a belt angle φ which is greater than the pulley angle θ, as shown in FIG. Figure 11 In particular, the belt angle φ is 0.2 to 1.2 degrees greater than the pulley angle θ. Similarly, the friction between the drive belt 6 and the pulleys 3 and 4 is significantly increased by the latter design.

[0062] However, according to the present invention, the friction increases achieved by these two known design measures are not complementary. Furthermore, according to the present invention, an improvement is achieved by applying a relatively small difference of less than 0.4 degrees between the belt angle φ and the pulley angle θ, and by applying a relatively large offset CLO between the protrusion 40 and the cavity 41, preferably such that the bottom surface 40a of the protrusion 40 (i.e., the radially innermost portion 40a) and the bottom surface 41a of the cavity 41 (i.e., the radially innermost portion 41a) substantially coincide with each other, at least on average, between the transverse members 10 of the drive belt 6. This relatively large offset CLO achieves the known advantages of high belt / pulley friction and low belt running noise, while the relatively small belt / pulley angle difference contributes to reduced wear during operation, thereby extending the service life of the drive belt 6.

[0063] The present disclosure, in addition to all the details of the preceding description and drawings, also relates to and encompasses all the features of the appended claims. Parenthetical references in the claims do not limit their scope but are provided merely as non-binding examples of the respective features. A feature of the claims may be applied individually to a given product or process, as the case may be, but any combination of two or more of such features may also be applied.

[0064] The invention represented by this disclosure is not limited to the embodiments and / or examples explicitly mentioned herein, but also encompasses modifications, adaptations, and practical applications that are possible for those skilled in the art.

Claims

1. A transmission belt (6) for a continuously variable transmission (1), the continuously variable transmission having two adjustable pulleys (2, 3) and the transmission belt (6), the transmission belt (6) comprising: A ring stack (9), comprising a plurality of mutually nested rings (5); and a plurality of transverse members (10) arranged on the ring stack (9), each of the transverse members defining a groove (33) for accommodating the ring stack (9); the groove (33) being delimited on its radial outer edge by a top portion (15) of the transverse member (10), and on its axial side by a middle portion (14) of the transverse member (10), the middle portion having a side surface (43) generally axially facing the groove (33), and the groove (33) being delimited on its radial inner edge by a base portion (13) of the transverse member (10); the base portion having a bearing surface (42) generally radially outwardly facing the groove (33), a bottom surface (45) generally facing radially inwardly, and a contact surface (45) generally facing axially. A surface (37), and corresponding convex transition surfaces (44) respectively arranged at both ends of the contact surface (37) and between the contact surface (37) and the bearing surface (42) or between the contact surface (37) and the bottom surface (45), a plurality of grooves (38) are arranged on the contact surface (37), and the grooves are separated by ridges (39) of the contact surface (37), characterized in that the two outermost ridges (39-a, 39-b) of the contact surface (37) are directly connected to the corresponding convex transition surfaces (44), and all the ridges (39) of the contact surface (37), including the outermost ridges (39-a, 39-b), together define a common virtual tangent plane (VTP) for frictional contact with the pulleys (2, 3).

2. The transmission belt (6) according to claim 1, characterized in that The width of the outermost ridges (39-a, 39-b) of the contact surface (37) of each transverse member (10) of the drive belt (6) is equal to the width of the other ridges (39), said width being measured between two consecutive grooves (38) in the contact surface (37).

3. The transmission belt (6) according to claim 2, characterized in that - the width of the outermost ridges (39-a, 39-b) and the ridge (39) is between 0.1 and 0.2 mm, and, The width of the groove (38) measured between two consecutive ridges (39) has a value between 0.4 and 0.6 times the width of the outermost ridges (39-a, 39-b) and the ridge (39).

4. Drive belt (6) according to the preceding claim, characterized in that The outermost ridges (39-a, 39-b) and the ridge (39) of each cross member (10) of the drive belt (6) are provided with convex curved profiles, each having a radius of curvature between 1 and 10 mm, and together defining the virtual tangent plane (VTP).

5. Drive belt (6) according to the preceding claim, characterized in that - the base (13) of each transverse member (10) of the drive belt (6) has two contact surfaces (37) oriented substantially in opposite axial directions to one another and defining a belt angle (φ) therebetween, and, - The central portion (14) of each transverse member (10) of the drive belt (6) has two side surfaces (43) oriented substantially in opposite axial directions and defining a cone angle (β) having a value between 50% and 90% of the belt angle (φ).

6. The transmission belt (6) according to claim 5, characterized in that - said cone angle (β) has a value between 60% and 80% of said belt angle (φ), and preferably 75% of said belt angle (φ), or, - the cone angle (β) has a value between 14 and 18 degrees, and preferably 17 degrees, wherein the strip angle (φ) is approximately 22 degrees.

7. The transmission belt (6) according to claim 5 or 6, characterized in that A curved transition structure (46) is present between at least one of the two side surfaces (43) of the middle portion (14) of each cross member (10) of the drive belt (6) and the load-bearing surface (42) of the base portion (13) of the cross member; the curved transition structure has a concavely curved first portion connected to the corresponding side surface (43), a convexly curved third portion connected to the corresponding load-bearing surface (42), and a concavely curved second portion connected to both the first portion and the third portion, the concavely curved second portion forming the radially inward bottom of the curved transition structure (46), and the concave curvature radius R2 of the second portion is greater than the concave curvature radius R1 of the first portion and the convex curvature radius R3 of the third portion, preferably at least 2 to 2.5 times the concave curvature radius R1 of the first portion, more preferably between 0.4 and 0.5 mm.

8. A continuously variable transmission (1) with two adjustable pulleys (2, 3) and a drive belt (6) according to any one of the preceding claims, wherein each adjustable pulley comprises two pulley discs (7, 8) defining a pulley angle (θ) between them, characterized in that Each cross member (10) of the drive belt (6) is provided with a protrusion (40) on its front side (11) and a cavity (41) on its back side (12), the protrusion (40) being located below the top (15), i.e., being located radially more inwards than the cavity (41) located in the top (15) of the cross member (10), and the average value of the belt angle (φ) of the cross member (10) of the drive belt (6) is at least 0.02 degrees and at most 0.4 degrees greater than the pulley angle (θ) of at least one of the two pulleys (2; 3), preferably not more than 0.2 degrees.

9. The continuously variable transmission (1) according to claim 8, characterized in that The size of the protrusion (40) of the corresponding transverse member (10) is slightly smaller than the cavity (41) of the corresponding transverse member (10), so that the bottom surface (40a) of the protrusion (40) in the radial direction substantially coincides with the bottom surface (41a) of the cavity (41).

10. The continuously variable transmission (1) according to claim 8 or 9, characterized in that The protrusion (40) and the cavity (41) of the corresponding transverse member (10) are roughly cylindrical, wherein the diameter of the protrusion (40) is smaller than the diameter of the cavity (41), and the position of the central axis (CA40) of the protrusion (40) on the top (15) of the corresponding transverse member (10) is lower than the position of the central axis (CA40) of the cavity (41) on the top (15) of the corresponding transverse member (10), and the magnitude of the lowering is 40% to 80% of the difference between the diameters of the protrusion (40) and the cavity (41), preferably 50%±5% of the difference in the diameters.

Images