IMPROVEMENT OF A TRANSMISSION COMPONENT FOR A DRY OPERATING CONTINUOUS SPEED VARIATOR WITH PUSHING LINKS AND A TRAPEZOIDAL CORE.

Abstract

Organe de transmission pour variateur de vitesse à maillons transversaux poussants, fonctionnant à sec, disposés autour d'une âme sans fin (2) formée d'une courroie trapézoïdale à flancs obliques (5) en contact avec les faces intérieures (10) des étriers (1) ou des étriers fermés (15) formant les maillons dont les faces obliques extérieures (11) sont en contact avec les flasques des poulies de transmission. Application au domaine de la variation continue de vitesse pour automobiles et machines industrielles.

Description

The present invention relates to the field of continuously variable speed transmissions by relative displacement of pulley flanges operating by dry mechanical adhesion, the power transmission element being a flexible link, formed of an endless strip, carrying transversely rigid elements called links. This certificate of addition relates to the main application FR 2 625 783, filed on January 11, 1988, under the title "Transmission unit for continuous speed variator with pushing transverse links and flexible core, operating by dry friction." The prior art displayed in the said application may be supplemented by patents such as DE 2,557,724 by HEYNAU, describing conjugate contact surfaces between links to ensure transverse holding between them, FR 2,540,953 by RNUR and CPIO describing centering pins and conjugate holes to ensure transverse support between riders characterized by their contact surface with a strap forming the flexible core, EP 0.073.962 from NISSAN MOTOR presenting riders formed of alternating blocks at 1800 equipped alternately with pins and holes, US 4.433.965 from HATTORI and US 4.610.648 from MIRANTI relating to flexible cores made of flat belts carrying links made of filled polymers or composites possibly reinforced with short fibers. All these patents essentially concern a flexible transmission link whose core is a flat strip, band, or layer of metal strips. All the devices described in these documents prove, in use, to be extremely unstable in the straight section of the path between pulleys, where the thrust is exerted by reciprocal contact between the aligned links. This situation was already known at the time of filing the main application, in which a particular provision, described in Figure 7 and the subject of claim 22, sought to remedy such instability. In practice, however, it is observed that even the coincidence between the fictitious primitive line of the pushing links and the neutral fiber of the endless core is insufficient to ensure the stability of the device when significantly higher powers are to be transmitted. The objective of the invention covered by this additional certificate is to provide variants of the transmission element for a continuously variable speed drive, which is the subject of the main application, enabling increased performance and addressing instability issues. These variants relate to the definition of the endless web, the contact area between said endless web and the pushing links, and the design of the latter. A much more effective damping solution is possible using an endless web made of a standard-sized V-belt. Due to the geometric shape of such a V-belt, the contact between the pushing links and the endless web occurs through surfaces free from relative movement, resulting in better stress distribution and consequently reducing heat generation during operation. The invention consists of a transmission element for a continuously variable speed drive, with transverse links pushing according to one of claims 1, 8 to 12 or 15 to 22 of the main application, characterized in that the endless core is a trapezoidal belt with oblique flanks in contact with the inner faces of the stirrup-shaped links surrounding said trapezoidal belt, their outer oblique faces forming the surface which comes into contact with the flanges of the transmission pulleys. The invention will be better understood upon reading the description accompanying the drawings, in which Figure 1 is a side view of the assembly showing a few links aligned on the flexible core; - figure 2 is a cross-section of the transmission between two links, cutting the flexible core; - Figure 3 represents a variant with made-up links closed stirrups surrounding the flexible core seen in section right, in view 3a, in its free state, in view 3b, in place. Figure 1 shows, in lateral view, the assembly of several transversely rigid links, which, to clearly identify their role, will be referred to hereafter as stirrups. The stirrups (1) are mounted aligned with the endless web (2), shown here in its straight path between the two pulleys of a transmission with a variable ratio achieved by changing the radius of contact. Power transmission occurs primarily through the reciprocal support of the stirrups (1) by their parallel faces (3). Their oblique faces (4) are symmetrically exposed, as shown, to allow winding, over a variable radius, upon contact with the pulley flanges. The parallel face (3) and the oblique face (4) are joined progressively. The stirrup (1) is made of high modulus polymer materials as described in the main application. Figure 2 is a perpendicular section of the transmission unit, taken through a cross-section of the endless web (2), which is a V-belt. This V-belt has oblique flanks (5), either bare (in the type known as bare-flared belts) or covered with a fabric wrapping (in the type known as wrapped belts), intended for contact with the stirrups. The outer surface (6) is represented by the larger base of the section. The reinforcing element (7) consists of a high-modulus material, most commonly textile, embedded in an elastomeric base (8) to which it is intimately bonded by physicochemical means, as well as to the transverse compression-resistant elements extending to the small base (9) of the section. This reinforcing element (7) constitutes the neutral fiber of the V-belt. In this application, the belt, when wound around the pulleys, is in contact along all of its oblique sides (5) with the inner faces (10) of each stirrup. When passing over the pulleys, each stirrup (1), on the other hand, is in contact via its outer oblique faces (11) with the flanges of said pulleys, the angle of which is not necessarily the same as that of the inner faces (10). Lateral harpoons (12) are provided on the stirrup (1), on either side of the outer surface (6) of the endless web (2). Their spacing is adapted to the elasticity of the V-belt so that the stirrup (1) can be forcibly engaged over it during assembly. After assembly, the very small surface area of ​​the lateral harpoons (12) prevents the stirrups from falling in the straight section of the transmission, particularly in the return strand where the pushing links of the stirrups (1) are not necessarily in contact with each other, their parallel faces being in contact. Experience has shown that a coating (6a) with a low coefficient of friction is suitable for the outer surface (6). This coating (6a), with a low coefficient of friction, is advantageously made of a very high molecular weight polyethylene film or polytetrafluoride, for example. The centering pin (13) and recess (14) guidance devices provided in the main patent remain fully compatible with contact by the inner faces (10) of the stirrup against the oblique sides (5) of the endless web. Furthermore, it appears that the contact pressure on the inner faces (10) of the stirrup (1) and the oblique flanks (5) of the endless web (2) is exerted, with very rapid stress variations, during the transition from the straight position to the position wound on the pulley. In contrast, this contact pressure is exerted between two surfaces that remain in permanent contact, unlike the use of a conventional V-belt, where each point only periodically comes into contact with the pulley flanges. The fictitious primitive lines of the stirrups (1) coinciding in the region of the neutral fiber of the endless core (2) represented by the reinforcing element (7), no gap between constituent materials is required for operation. Micrometric displacements can occur in the area of ​​the lateral harpoons (12) and the outer surface (6) because one of the surfaces—the stack of stirrups (1)—is made of solids of constant thickness, whose parallel faces separate from each other during winding, and the other is the endless core polymer (2), whose length varies, outside the neutral axis, between a straight position and a winding. For this reason, the coating (6a), with a low coefficient of friction, was deemed necessary, but must retain a deformability compatible with the belt's flexing. Below the neutral fiber, in the area of ​​the elements resisting transverse compression, the tapered shape of the oblique faces (4) on the stirrups (1) reduces the contact area between them and the endless web (2) to a fraction of the elastically deformable surface in bending of the belt. During the bending, the stirrups (1) come together and therefore participate in the volumetric compression of this part of the endless web (2) located between the neutral fiber, at the level of the reinforcing element (7) and the small base (9) of the section. Consequently, using a belt of standardized dimensions for industrial or automotive applications as the endless web (2) of the transmission element for a variable speed drive, and capable of withstanding significantly higher stresses than those typically encountered in its use, allows for the transmission of much greater power. This results in surface stresses considerably higher than those observed in prior art designs; experience shows that the power transmitted can be divided into two parts: one-third due to the tension exerted by the V-belt, and two-thirds due to the reciprocal support of the pushing links. The stresses are thus much more evenly distributed over the entire surface, primarily in compression along the oblique flanks (5) of the endless web (2), without relative movement. However, pressures of the same order of magnitude, because they are the consequence of it, are exerted in a similar way on the external oblique faces (11) of the stirrup (1), pressed by their support on the flanges of the pulleys. The risks of high alternating stresses in the area (E) of the rounded bottom of the stirrup (1), studied by the finite element method, as described in the main application, are, in the application which is the subject of this certificate of addition, considerably reduced due to the use of an endless web (2) in the form of a trapezoidal belt. This is why the powers transmitted by the transmission element thus produced can be all the higher. Figure 3 represents a variant, still in perpendicular section, of a stirrup further minimizing the risks of alternating fatigue under the effect of stresses. Instead of being engaged over the endless web (2) by forcing harpoons against the cladding (6a), the closed stirrup (15) is equipped with a tab (16), hinged by a hinge (17) which allows it to be closed over the endless web (2), preferably fitted with the cladding (6a) on its outer surface (6). View 3a shows the free state of a closed stirrup (15) and view 3b the state in place on the endless web (2). The tab (16) is closed after assembly and, for example, clipped in place by the irreversibility of the shapes, resting on its end by a rim (18). Preferably, however, cavities (19) on the body of the closed stirrup (15) and corresponding bosses (20) are provided on the tab (16). Other arrangements are possible, such as positioning the cavities (19) on the tab (16), with the corresponding bosses (20) then being supported by the body of the closed stirrup (15), or positioning one cavity (19) and one boss (20) on the tab (16), with the body of the closed stirrup (15) then supporting the corresponding boss (20) and the other cavity (19). After assembly, the external shapes of the stirrup (1) remain symmetrical to allow for indifferent orientation of said stirrups during assembly. Thus, the closed stirrup (15) constitutes a beam resisting compression through its external oblique faces (11) under better conditions, noting that its small base, where the critical zone (E) is located, is of reduced thickness compared to the thickness between parallel faces, due to the presence of the oblique faces. The composite belt thus formed can be used as a wide V-belt with external transverse compression reinforcements. A preferred manufacturing method for the transmission component according to the invention involves the prior manufacturing of the stirrups or closed stirrups equipped with their hinged tongue by mass production molding of a composite material made of short fiber reinforced polymer. In parallel, the trapezoidal belt constituting the endless core is preferentially constructed by superimposing, around a mandrel for making a reinforcing element embedded in a base made of polymeric composition. This belt is intimately bonded, by physicochemical adhesion, to the reinforcing element, made of yarn or twisted material with a high modulus, preferably textile, as well as to the compression-resistant elements extending from the neutral fiber of the endless, trapezoidal core formed by the reinforcing element. The portion of the V-belt containing the compression-resistant elements is made by stacking layers of cords coated with a polymeric composition or by stacking sheets of polymeric composition reinforced with short, oriented fibers, ensuring the transverse rigidity required for the V-belt. The coating, a material with a low coefficient of friction such as very high molecular weight polyethylene or polytetrafluoride of ethylene, is intimately bonded, by physico-chemical adhesion to the large base of the V-belt, during vulcanization, for example. A suitable guiding method ensures the mounting of either type of stirrup onto the wrapped or unwrapped V-belt. In the case of closed stirrups, the closing of the tabs is optionally followed by welded seams of the two alignments of conjugate bosses, for example by ultrasonic welding, cyanoacrylate bonding, or any other similar process. The number of stirrups mounted on the endless web of given length is controlled, in order to ensure a toleranced play with minimum and maximum, said play being absorbed during the ovalization of the transmission element between two winding radii and two straight portions. The dry-operating transmission unit, according to the invention, has significantly increased power transmission capabilities in a compact form compared to those of the V-belt which constitutes its endless core, practically tripling its performance. The invention provides manufacturers of variable speed drives with the possibility of creating high-performance flexible links without requiring delicate techniques or complex new technologies, using components whose manufacturing processes are proven and require only limited tooling regardless of the initial lengths of the transmission elements to be produced.

Claims

DEMANDS 1. Transmission component for a continuously variable speed drive, with transverse links pushing along one of the claims 1, 8 to 12 or 15 to 22 of the application patent FR 2 625 783, characterized in that the soul without end (2) is a trapezoidal belt with oblique flanks (5) in contact with the inner faces (10) of the links in stirrup-shaped (1) or (15), surrounding said belt trapezoidal, their oblique outer faces (11) forming the surface that comes into contact with the flanges of the transmission pulleys.

2. Transmission component for continuously variable speed drive according to claim 1, characterized in that the soul without end (2) is formed by a trapezoidal belt with flanks oblique (5), wrapped.

3. Transmission component for continuously variable speed drive according to claim 1, characterized in that the soul without end (2) is formed by a trapezoidal belt with flanks oblique (5), bare.

4. Transmission element according to any one of claims 1 to 3 characterized in that the endless soul (2) is endowed, on its outer surface (6), of a coating (6a) low coefficient of friction, on which the links stirrup-shaped (1) or (15) come to rest, during the straight trajectory in the return strand.

5. Transmission element according to claim 1, characterized in that the guidance device of the stirrup-shaped links (1) or (15) are secured to the times by the existence of centering pins (13) and recesses (14) located near the lateral harpoons (12) or cavities (19) and by the alignment of the inner faces (10) supported on the oblique sides (5) of the web without end (2) consisting of a trapezoidal belt.

6. Transmission component for continuously variable speed drive according to any one of claims 1 to 4, characterized in that that the stirrup-shaped links are made of closed stirrups (15), comprising a tongue (16), coming to enclose the soul without end (2) by the commitment in the cavities (19) of the conjugate bosses (20).

7. Transmission component for continuously variable speed drive according to claim 6, characterized in that the final closure of each of the closed stirrups (15) is secured by welding or bonding in the cavities (19) of the combined bosses (20).