JP2011502214A - Ring component of transmission belt and manufacturing method therefor - Google Patents

Abstract

  The present invention relates to a method for producing an endless metal ring (32) for a transmission belt (1) suitable for power transmission in a continuously variable transmission, wherein the ring (32) is contained in an atmosphere containing at least ammonia gas. In a method having a step of nitriding or surface hardening at a high temperature (IX), after the step of surface hardening (IX) is completed, the ring (32) is subjected to another or post-treatment step (IX-A) of the manufacturing method. In VIII) in a hot reducing atmosphere.

Description

  The present invention relates to a manufacturing method for an endless thin flexible metal strip, which is used for a power transmission between two conventionally known continuously variable transmissions or CVT adjustable pulleys used in automobiles. It is usually built into the transmission belt. The invention further relates to the product obtained by said method.

  Such a band, at least for use in a transmission belt, is also referred to as a transmission belt ring component. Such transmission belt and ring components are generally known, for example from EP 1403551. In this known type of transmission belt, commonly referred to as a push belt, a large number of such rings are incorporated in at least one, but usually two, stacked, ie, radially overlapped sets. . Known push belts further comprise a number of transverse metal elements slidably attached to such a set of bands. In the use of push belts, conventional rings are manufactured from maraging steel, and this type of steel, in particular, has the relatively advantageous possibility of welding and plastically deforming materials with high tensile strength properties; Combined with excellent resistance to wear and bending and / or tensile stress fatigue, at least after a suitable heat treatment of the ring.

  Previously known rings are provided with sufficient hardness of the core material to achieve good tensile, yield, and bending strength properties combined with a high resistance to metal fatigue, the ring core being a ring material In a substantially harder and thus wear-resistant outer surface layer. The maximum thickness provided in the hard surface layer limits internal ring stress and provides sufficient elasticity to the ring to provide resistance to longitudinal bending and fatigue failure. Of course, this latter feature is particularly important in the application of ring transmission belts. This is because the ring is subjected to many loads and bending cycles during the service life of the ring. In order to achieve the desired material properties, the known production methods include two heat treatments: ring aging, ie bulk precipitation hardening, and surface hardening, in particular nitriding, usually gas soft nitriding. The steps of a general manufacturing method for such belts, at least belt ring parts, have been used by the applicant for decades and are well known in the art, for example European patent applications This is described in Japanese Patent Publication No. 1055738.

  A problem with known ring manufacturing methods is that an iron-nitride layer may be formed on the ring surface during gas soft nitriding, which is referred to as a compound layer and affects the surface hardness and ductility. . As a result, the mechanical properties of the nitrided ring component are not as uniform as desired, and the ring surface layer may become too brittle locally for proper use in a push belt.

  The thickness of such compound layers is not only significantly dependent on the composition of the maraging steel alloy, but also on the gas soft nitriding process environment, such as process temperature, time, and atmosphere, ie the composition of the nitriding gas. . However, this layer tends to form more quickly and more extensively. Because of the efficiency of nitriding, for example, when processing time is shortened by increasing the processing temperature and / or (gas) nitriding potential (determined by individual ammonia and hydrogen gas concentrations). This is because the environment is optimized.

  The object of the present invention is to achieve the desired mechanical properties for the ring component of the push belt without any special restrictions on the nitriding environment of the ring in order to avoid the formation of the compound layer. That is.

  According to the invention, this object is achieved with the specific means indicated in the characterizing part of claim 1. According to this claim, after the nitriding step, another post-treatment step is performed, in which the ring is essentially free of ammonia and oxidation, preferably mainly nitrogen, preferably Is heat-treated in a reducing atmosphere containing several (for example, 15) vol% hydrogen. During such post-treatment, the iron-nitride dissolves and the compound layer is effectively removed from the ring surface. The presence of hydrogen significantly accelerates this process of removing the compound. Such ring post-treatment can be provided such that it takes a relatively short time compared to the time typically or at least conventionally required for nitriding and aging of the ring. However, the temperature should preferably have conditions similar to the temperature conditions of the previous nitridation step, having values in the range of 400-500 ° C.

  In the case of such conditions of the ring manufacturing method, in particular ring nitridation can be performed efficiently in terms of time and cost, and at least it is not necessary to avoid the formation of an iron-nitride compound layer, this iron-nitride The compound layer is eventually removed later in the post-ring treatment.

  According to the present invention, the post-treatment can be set so that bulk precipitation hardening of the ring material, ie aging, occurs simultaneously. In practice, according to the present invention, if appropriate processing conditions are applied in such post-processing, aging can be completed during said post-processing, and a conventional aging step before nitriding is performed. Preferably it can be skipped. In this ring manufacturing method, the known ring heat treatment sequence by aging prior to nitriding is effectively reversed so that nitriding first and then aging. This avoids the so-called overaging of the ring in the post-processing that can occur in conventional manufacturing methods.

  The basic principle of the present invention will now be described based on the embodiments shown in the drawings.

It is a figure which shows schematically the conventional continuous variable transmission provided with the power transmission belt which has a ring component. It is a perspective view which shows a part of belt. FIG. 2 shows a part of a conventional method for manufacturing a metal ring part of a belt. It is a figure which shows a part of manufacturing method by this invention. It is a figure which shows a part of manufacturing method by this invention.

  FIG. 1 shows the central portion of a conventional continuously variable transmission or CVT commonly used in vehicle drivelines between the engine and wheels. The transmission has two pulleys 1, 2 each provided with two conical pulley disks 4, 5, with a generally V-shaped pulley groove formed between the two pulleys, Disc 4 can move axially along pulley shafts 6, 7 to which pulley discs are attached. The transmission belt 3 is wound around the pulleys 1 and 2 and transmits the rotational motion ω and the torque T from one pulley 1 and 2 to the other pulley 2 and 1.

The transmission also has an actuating means for applying an axial clamping force _Fax toward the other pulley disk 5 to at least one disk 4 so that the belt 3 is interposed between the pulley disks. It can be tightened. Also, the transmission speed ratio is determined thereby, and this speed ratio is defined as the ratio between the rotational speed of the driven pulley 2 and the rotational speed of the drive pulley 1.

A part of a known drive belt 3 is shown in detail in FIG. The belt 3 has endless pulling means 31. In this particular example, the endless pulling means 31 consists of two sets of flat or strip-like flexible metal rings 32. The belt 3 further has a large number of plate-like transverse elements 33, which are in contact with the tension means 31 and are held by the tension means. Element 33 receives the force F _ax the tightening, the input torque T _in is added to the so-called driving pulley 1, friction between the disks 4, 5 and the belt 3 rotates the driving pulley 1, this rotation is similar Is transmitted to a so-called driven pulley 2 via a transmission belt 3 that rotates in a straight line.

  During operation in CVT, the belt, particularly the ring component 32, is subject to periodically changing tensile and bending stresses, ie fatigue loads. Normally, the resistance to fatigue or fatigue strength of the ring part 32 determines the functional life of the transmission belt 3 at a given torque T transmitted by this ring. Therefore, it has been conventionally desired to develop a method for manufacturing a transmission belt in order to achieve the necessary ring fatigue strength while suppressing material and manufacturing costs.

  FIG. 3 shows the relevant parts of the conventional manufacturing method of the ring part 32 of the transmission belt, which has been carried out since the initial manufacture of the transmission belt, in which the separate steps are indicated by Roman numerals. . In a first step I, a sheet of base material 11 is bent into a cylindrical shape and the sheet ends 12 that are abutted against each other are welded in a second step II to form a tube 13. In the third step III, the tube 13 is annealed. Thereafter, in a fourth step IV, the tube 13 is cut into a number of rings 14 which are then rolled in step V to give a final product of 0.1-0.2 mm, usually about 185 μm. It is stretched to the required thickness. After rotation, the wheel 14 is usually referred to as the ring 32.

  Ring 32 is further annealed in step VI to eliminate internal stresses that occur during rolling (step V). Thereafter, in a seventh step VII, the ring 32 is calibrated, i.e. the ring is mounted around two rotating rollers and stretched to a predetermined circumferential length. In this seventh step VII, an internal stress distribution is also applied to the ring 32. Thereafter, the ring 32 is heat treated in two separate steps. That is, aging or bulk precipitation hardening is performed in the eighth step VIII, and nitriding or surface hardening is performed in the ninth step IX. In addition, in particular, such heat treatment heats the ring 32 in an industrial oven or furnace containing a controlled gas atmosphere, which is typically nitrogen and other gases for ring aging, i.e., 5 vol%. Of hydrogen gas, and nitrogen and ammonia for nitriding the ring. Both heat treatments are typically performed at 400-500 ° C., for about 45-120 minutes, depending on the base material for the ring 32 (maraging steel alloy composition) and the mechanical properties desired for the ring 32. be able to.

  Finally, the set 31 of rings 32 processed in this way is stacked in a radial manner, ie, nested, with a number of rings 32 selected according to purpose, as further shown in FIG. Is formed. In order to obtain the required number of rings 32 suitable for forming one set 31, the circumferential length of the ring 32 (or other suitable parameter such as diameter) is measured in the tenth step X, In the last shown eleventh step XI, the set 31 of rings 32 is assembled by telescoping the required number of appropriately sized rings 32 together.

  In the nitridation process (9th step IX in FIG. 3), ammonia molecules present in the oven atmosphere dissolve at the surface of the ring 32, thereby forming nitrogen atoms, which nitrogen atoms are formed in the steel of the ring 32. Absorbed (ie diffuses) into the matrix. Thereby, additional hardness in the surface layer of the ring 32 is formed by the nitrogen gap and nitrogen-containing precipitates. Inevitably, however, some of the nitrogen atoms thus formed already react with the iron atoms of the maraging steel on the surface of the ring 32 to locally form an iron-nitride layer called a compound layer. To do. Depending on the time, temperature, and process atmosphere settings of the nitridation step IX, these iron-nitrides may be formed smaller or larger. As a result, the mechanical properties of the ring 32 are not as uniform as desired, and the surface layer of the ring may become too brittle locally for proper use in the transmission belt 3. It is therefore mainly preferred to prevent the formation of such compound layers by optimizing the ring nitridation process settings in this regard. However, in doing so, the efficiency of the ring nitriding step IX is usually adversely affected.

  However, according to the present invention, it is not necessary to prevent the compound layer from being formed in the ring nitriding step IX. This is because it has been found that such a layer can be easily removed later in another post-processing step IX-A. This additional post-processing step is performed after step IX of nitriding the ring is completed, as schematically shown in FIG. With this design of the ring manufacturing method, in particular the nitriding step IX can be carried out efficiently in terms of time and cost, and at least it is not necessary to avoid the formation of an iron-nitride compound layer in the ring 32. The nitride compound layer is eventually removed later in the post-treatment step IX-A.

  In such a post-treatment step IX-A, the ring 32 is in a reducing atmosphere consisting essentially of ammonia and oxygen and preferably consisting mainly of nitrogen, more preferably nitrogen containing several vol% hydrogen. To 400-500 ° C. In this later heat treatment step IX-A, the iron-nitride is decomposed and the compound layer formed during nitridation is thus effectively and suitably removed from the ring surface. In the presence of hydrogen gas, this compound removal can be significantly accelerated. According to the present invention, the hydrogen concentration is preferably 5-15 vol%, more preferably about 10 vol% of the processing atmosphere.

  According to the present invention, the post-treatment of the ring 32 for removing the compound layer can be suitably set so that bulk precipitation hardening of the ring material, that is, aging occurs simultaneously. In practice, if conventional aging step VIII process settings are applied in the post-treatment, the bulk precipitation hardening of the ring material can be completely completed during the post-treatment. Thus, a preferred efficient and effective form for practicing the present invention in the overall ring manufacturing process is simply to reverse the order of conventionally used aging and nitriding ring heat treatments, i.e., conventional The conventional aging step VIII is performed after the ring nitriding step IX is completed. In this ring manufacturing method, the ring aging step VIII serves as a post-treatment according to the invention, ie to remove from the ring surface the compound layer formed during ring nitridation. This ring manufacturing method according to the present invention is illustrated in FIG. In this case, the post-processing does not require any additional steps with respect to the conventional ring manufacturing method as shown in FIG. Furthermore, the so-called overaging of the ring 32 and the consequent reduction in core hardness, which can occur when the post-processing is added as an additional step to such a conventional ring manufacturing method, is avoided.

  The invention is now further defined along a series of claims, apart from the foregoing description, also related to all the details in the claims and discussed directly from which the person skilled in the art derives directly and clearly. And all details and aspects of

  1, 2 pulley, 4, 5 pulley disk, 6, 7 pulley shaft, 11 sheet of base material, 12 sheet end, 13 pipe, 14 wheels, 31 endless tension means, 32 ring, 33 transverse element

Claims (10)

  A method of manufacturing an endless metal ring (32) for a transmission belt (1) suitable for power transmission in a continuously variable transmission, wherein the ring (32) is heated at high temperature in an atmosphere containing at least ammonia gas. In a method having a step (IX) of nitriding or surface hardening with a ring, after completion of the surface hardening step (IX), the ring (32) is subjected to another or post-treatment step (IX-A; VIII of the manufacturing method). ) In a high-temperature reducing atmosphere, a method for producing an endless metal ring for a transmission belt suitable for power transmission in a continuously variable transmission.   Such a step (IX, IX-A; VIII) is carried out immediately in succession, possibly in one chamber of an industrial furnace, by pumping in the reducing atmosphere after surface hardening is completed. The method according to claim 1, wherein the method is performed by blowing a nitriding atmosphere from.   The method according to claim 1 or 2, wherein the reducing atmosphere mainly comprises nitrogen gas.   The method of claim 3, wherein the reducing atmosphere further contains hydrogen gas.   The method according to claim 4, wherein hydrogen gas is 5 to 15 vol%, preferably 9 to 11 vol%, of the reducing atmosphere.   The method according to any one of claims 1 to 5, wherein, in a post-treatment step (IX-A; VIII), the reducing atmosphere is maintained at a temperature of 400 to 500C.   The method according to any one of claims 1 to 6, wherein the post-treatment step (IX-A; VIII) is performed for 45 to 120 minutes.   A method for producing an endless metal ring (32), preferably according to any one of claims 1 to 7, wherein the ring (32) is at a high temperature in an atmosphere containing at least ammonia gas. Aging or bulk hardening at a temperature (IX) and a step (VIII) of aging or bulk precipitation hardening the ring (32) at an elevated temperature in an atmosphere consisting primarily of nitrogen. A method of manufacturing an endless metal ring, characterized in that one step (VIII) is performed after the nitriding step (IX) is completed.   9. A method according to any one of claims 1 to 8, wherein the ring (32) is formed from maraging steel.   Endless metal ring (32) part for a transmission belt (1) suitable for power transmission in a continuously variable transmission, manufactured in the manufacturing method according to any one of the preceding claims.

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