JP6890595B2 - A transverse element having a nanocrystal surface layer for a drive belt for a continuously variable transmission, and a method for manufacturing the transverse element. - Google Patents

Description

The present invention relates to both a transverse element of the form described in the superordinate concept of claim 1 and a method of manufacturing the transverse element. Such types of transverse elements are used as components of drive belts for continuously variable transmissions, especially for use in automobiles such as passenger cars. The drive belt consists of a row of such transverse elements arranged concentrically with each other or continuously arranged along the perimeter of at least one set of metal rings stacked on top of each other. Typically, the cross member is provided with, or at least defined, one recess for each set of rings on the drive belt. For each crossing member, a circumferential portion of such a ring set is housed in the recess.

In the transmission, a drive belt is used to transmit the driving force between the two shafts. In this case, the drive belt is passed around two rotatable pulleys, each cooperating with one of such transmission shafts, through which a V-shape extending in the circumferential direction of the pulley. Two conical discs are provided to define the groove, and the drive belt is housed in the V-shaped groove. By coordinatingly changing the axial distance between each disc of the two pulleys, the radius of the drive belt in each pulley, and thus the rotation speed ratio between the transmission shafts, is changed while maintaining the tension state of the drive belt. Can be made to. Such transmissions and drive belts are widely known to those of skill in the art and are described, for example, in European Patent Application Publication No. 1243812.

The transmission of the driving force between each pulley and the drive belt is performed by friction, and each side surface of the transverse element, that is, the axial surface of the transverse element is provided with a contact surface for contacting the pulley disc. ing. The contact surfaces of the transverse elements are oriented between the conical discs of each pulley so as to form an angle approximately matching the angle of the V-shaped groove defined by these conical discs. Typically, the contact surface is provided with a region located below, such as a groove or hole that receives lubricating oil and / or cooling fluid. Lubricating oils and / or cooling fluids are typically applied to known transmissions and are pushed out between the (relatively upper) portion of the contact surface and the pulley disc that are in physical frictional contact during operation of the transmission.

In the following, the vertical upward direction is defined in relation to the transverse element so as to correspond to the divergence direction of the contact surface of the transverse element, the thickness direction of the transverse element is defined as the circumferential direction of the ring set, and the width direction is , Are oriented at right angles to both the height direction and the thickness direction.

The known transverse element is further provided with two main body surfaces. That is, it is a front side surface and a rear side surface, and these surfaces extend substantially parallel to each other and form a right angle with respect to the thickness direction. The recess of the transverse element extends between these two main body surfaces. The bottom surface of the recess is defined by the support surface of the transverse element that supports the ring set in the drive belt and at least partially on the laterally oriented side of the transverse element that defines the side wall of the recess. Adjacent to each other via a concavely curved transition surface.

In automotive use, at least the transverse elements of the drive belt are made of metal, typically steel, to cope with the forces generated during the operation of the drive belt. In particular, the transverse element is made of steel containing 0.6 to 1.2% by weight of carbon, and the transverse element can be cut from such a basic material and then quench hardened. After such quench hardening, the transverse elements are preferably deburred by a (stone) tumbling process to remove burrs from the cutting edges of the transverse elements, as well as compressive residual stresses on the surface layer of the transverse elements. Is also given. Such compressive residual stress reduces the tensile stress level during operation and suppresses surface defects, i.e. the initiation and / or growth of microcracks due to fatigue. However, further improvement in fatigue strength of transverse elements is still desired by those skilled in the art. This, on the one hand, can improve the service life of the transmission as a whole, and on the other hand, the driving force desired to be transmitted by the transmission can be improved and / or the transmission can be miniaturized.

According to the present invention, the fatigue strength of the transverse element can be improved by providing the so-called nanocrystal surface layer at the position of the transition surface of the transverse element. Such nanocrystal surface layers are metal crystals, i.e., relatively thin layers that form an outer surface with particularly small particles. It has been found that such features delay the onset of fatigue fracture at the transition surface, i.e., occur only at fairly high stress levels and / or after more stress cycles have occurred. This can be explained by the situation where the stone applied in the stone tumbling process is generally too large to easily get inside the recesses of the transverse element. That is, these stones do not reach the transition plane, that is, do not collide with the transition plane, so that the local compressive residual stress level, and thus the resistance to fatigue crack initiation, is lower than the other surface portions of the transverse element.

The limitations of the stone tumbling process, in principle, relate to all interface of the recess, but here the highest tensile stress levels occur during operation and should be given the most attention in said transition planes.

Thus, a drive belt with a defined transverse element can, on the one hand, have a relatively long operating (fatigue) period of use and, on the other hand, transfer more power between the pulleys while maintaining that period of use. It has the advantage of being able to.

Particularly good results are obtained with crystal or particle size in the nanocrystal surface layer at the transition plane that fits within a (virtual) sphere with a diameter of 0.1 micrometer. Particle sizes less than 0.1 μm, such as about 50 nm, are usually two orders of magnitude smaller (ie, 1/100) than the particle size across the nanocrystal surface layer or in another (surface) portion of the transverse element. .. The most suitable thickness range for the nanocrystal surface layer at the transition plane of the transverse element is 1-10 μm.

In a more detailed aspect of the transverse element according to the present invention, the nanocrystal surface layer is provided not only on the transition surface of the transverse element but also on the support surface of the transverse element. This support surface is not really prone to fatigue crack initiation, but is extremely significantly loaded by continuous frictional contact with the ring set. According to the present invention, not only the local resistance to the initiation of fatigue cracks but also the resistance to wear is preferably improved by the presence of the nanocrystal surface layer.

It is noted to those skilled in the art that such nanocrystal surface layers can be formed on steel products of various compositions by mechanical plastic deformation. In the context of the present disclosure, it is possible to enter the interior of the transverse element recess and reach the transition surface of the transverse element, deforming only the thin surface layer and leaving the other surface portion of the transverse element untouched. A plastic deformation process that can be provided must be provided. According to the present invention, such a known shot peening process can be appropriately configured for this purpose. In addition, another possible plastic deformation process uses a fluid or gas (including plasma) as the medium to achieve the deformation required to form the nanocrystal surface layer. For example, an ultrasound-based process or a laser-based process.

Here, the above-mentioned principles and features of the novel transverse element and its proposed manufacturing method will be further described by way of example with reference to the accompanying drawings.

FIG. 5 is a diagram schematically showing an example of a widely known continuously variable transmission provided with two pulleys and a drive belt. It is a figure which shows schematic the cross section of the known drive belt which incorporated a transverse element and a ring set. It is a figure which shows schematic the metal crystal structure including the nanocrystal surface layer. It is an enlarged view which shows the actual cross section of the transverse element which clearly shows the crystal structure of the transverse element including a nanocrystal surface layer. It is a figure schematically showing the process for providing a transverse element with a nanocrystal surface layer.

FIG. 1 shows the center of a known continuously variable transmission or CVT that is typically applied between the engine and the drive wheels of the vehicle in the power transmission path of the vehicle. The transmission includes two pulleys 1 and 2, each of which is provided with a pair of conical pulley discs 4 and 5 attached to a pulley shaft 6 or 7. A pulley groove extending in the circumferential direction of a substantially V shape is defined between the pulley discs 4 and 5. At least one of the pulley discs 4 of each pair of pulley discs 4 and 5, that is, each of the pulleys 1 and 2, is axially movable along the pulley shafts 6 and 7 of the pulley discs 1 and 2. The drive belt 3 is wound around the pulleys 1 and 2 in order to transmit the rotational movement and the torque accompanying the rotational movement between the pulley shafts 6 and 7, and is located in the pulley groove of the pulley.

The transmission generally also has an operating means for applying a clamping force directed in the axial direction to the pulley disc 4 which is movable in the axial direction of each of the pulleys 1 and 2 during operation. This clamping force is directed toward the other pulley disc 5 of the pulleys 1 and 2, whereby the drive belt 3 is clamped between the discs 4 and 5 of the pulleys 1 and 2. These clamping forces not only define the frictional force between the drive belt 3 and each of the pulleys 1 and 2, but also the radial direction of the drive belt 3 at each of the pulleys 1 and 2 between the pulley discs 4 and 5 of the pulley. The position R is also specified. This radial position R determines the gear ratio between the pulley shafts 6 and 7 of the pulley.

FIG. 2 shows in more detail an example of a known drive belt 3 in a cross section facing the circumferential direction. The drive belt 3 incorporates an endless tension element 31 in the form of two sets of flat, thin, or ribbon-shaped, flexible metal rings 44. The drive belt 3 further has a plurality of transverse elements 32 attached to the tension element 31 along the circumferential direction of the tension element. In this special example, each ring set 31 is housed in each recess 33 defined by the transverse element 32 on each side of the transverse element 32, i.e. on each axial plane of the central portion 35 of the transverse element 32. ing. The recess 33 of the transverse element is located between the inner portion 34 and the outer portion 36 of the transverse element 32 when viewed in the radial direction with respect to the entire drive belt 3. The bottom surface of the recess 33 is defined by the support surface 41 of the inner portion 34 of the transverse element 32, and the side wall of the recess 33 is defined by the side surface 43 of the central portion 35 of the transverse element 32.

On the axial surface of the inner portion 34 of the transverse element, the transverse element 32 is provided with a contact surface 37 for frictional contact with the pulley discs 4 and 5. The contact surfaces 37 of each transverse element 32 are oriented with each other so as to form an angle Φ that substantially matches the angle of the V-shaped pulley groove. Therefore, when the transverse element 32 receives the clamping force and thereby the input torque is applied to the so-called drive pulley 1, the friction between the discs 4 and 5 and the belt 3 causes the rotation of the drive pulley 1 as well. The transmission is performed so as to be transmitted to the so-called driven pulley 2 via the rotating drive belt 3 or vice versa.

During operation in the CVT, the transverse element 32 component of the drive belt 3 is intermittently clamped between each pair of pulley discs 4 and 5 of the pulleys 1 and 2. Such an intermittent clamp apparently results in intermittent compression of the inner portion 34 of the transverse element 32, where similarly and / or the contact surfaces 37 on each side of the transverse element make a predetermined angle. A changing tensile stress is generated by the formation and orientation and by the contact of the drive belt 3 with the adjacent transverse element 32. The changing tensile stress (also) occurs in the transition region between the inner portion 34 and the central portion 35 of the transverse element 32. As a result, it has been observed that fatigue cracks typically start from the concavely curved transition surface 42 that is provided between the support surface 41 and the side surface 43 and connects them. According to the present invention, the onset of such fatigue cracks can be avoided, or at least delayed, by providing a so-called nanocrystal surface layer NSL at the location of the transition surface 42 of the transverse element 32.

FIG. 3 shows currently desired particles having smaller size particles Gs near the outer surface of the workpiece 50 as compared to the particles Gb located towards the more bulk material of the workpiece 50. The crystal structure is shown schematically. Smaller size particles Gs on the surface define the nanocrystal surface layer NSL.

In FIG. 4, such a nanocrystal surface layer NSL is further shown by a photograph taken by a scanning electron microscope (SEM). The smallest particles in the nanocrystal surface layer NSL are smaller than 1/100 of the largest particles Gb in the bulk material of the workpiece 50. In particular, in FIG. 4, the nanocrystal surface layer NSL has a thickness of about 5 μm, and the particle size of the nanocrystal surface layer NSL is about 50 nm on average. On the other hand, in the bulk material of the transverse element 32, the width of the crystal particles is 2 to 20 μm in any direction. The above numerical values are usually preferable in the content of the present disclosure, that is, for applying to the position of the transition surface 42 on the transverse element 32 of the drive belt 3.

The nanocrystal surface layer NSL can be applied to the transverse element 32 by a shot peening process. This process is schematically shown in FIG. In the shot peening process, small particles 60, such as tiny glass beads, are conveyed and discharged from one or more nozzles 61 at a predetermined speed, for example by an air stream. The nozzle 61 is shaped and oriented such that the granules 60 collide with a desired surface portion of the transverse element 32, i.e., at least the concavely curved transition surface 42 of the transverse element. Such collisions of the shot peening granules 60 cause minimal plastic deformation in the surface layer of the transverse element 32, resulting in local miniaturization of the crystal structure of the transverse element 32.

In addition to the concavely curved transition surface 42, the support surface 41 may also be treated, ie shot peened, if appropriate. However, other surface portions of the transverse element 32, such as the front main body surface and the back main body surface and its (pulley) contact surface 37, are preferably such other as a result of a known deburring process. It is left untreated by such a shot peening process to avoid (further) increasing the compressive residual stress near the surface portion of the. Further according to the present invention, such a shot peening process is known to prevent the nanocrystal surface layer NSL from being removed by crystal growth and recrystallization in the austenitic heat treatment that is part of quench hardening. It is performed after the quench hardening process of.

The present invention relates to and includes all features of the claims, in addition to all the preceding description and all the details of the accompanying drawings. The reference numerals in parentheses in the claims do not limit the scope of the claims, but rather are described as non-binding examples of each feature. The features described in the claims may be applied separately within the product or method of delivery, but may also be applied to any combination of two or more of these features.

The invention represented by this disclosure is not limited to embodiments and / or examples expressly referred to herein, in particular, modifications, amendments, improvements, and modifications of the invention achieved by those skilled in the art. It also includes actual usage examples.

Claims (6)

A transverse element (32) for the drive belt (3), wherein the drive belt has an endless tension element (31) and said to transmit driving force between two pulleys (1, 2). It has a plurality of crossing elements (32) slidably provided on the tension element (31), and the crossing element (32) is made of steel and is a part of the tension element (31). The recess (33) has at least one recess (33) for receiving the support surface (33) located radially inside the tension element (31), especially in the drive belt (3). 41) and the side surface (43) of the drive belt (3) located opposite to the axial surface of the tension element (31), and between the support surface (41) and the side surface (43). At the transverse element (32), which is provided and which connects them, is defined by at least a partially concavely curved transition surface (42).
Nanocrystal microstructures are provided at the location of the concavely curved portion of the transition surface (42) and the location of the support surface (41) of the surface layer of the transverse element (32).
The drive belt (3 ) is characterized in that the transverse element (32) is provided with a nanocrystal surface layer (NSL) only at both the transition surface (42) and the support surface (41). ) For the transverse element (32). The particle size of the metal crystal of the crossing element (32) in the nanocrystal surface layer (NSL) is 0.1 micrometer at the maximum, and the metal of the crossing element (32) in the nanocrystal surface layer (NSL). the average particle size of the crystals, the nanocrystal surface layer 2 orders of magnitude smaller than the average particle size of outer metal crystals (NSL), according to claim 1 transverse elements according (32). The transverse element (32) according to claim 2 , wherein the thickness of the nanocrystal surface layer (NSL) is 1 to 10 micrometers. A method of manufacturing a transverse element (32) for a drive belt (3), wherein the drive belt is an endless tension element (1) for transmitting driving force between two pulleys (1, 2). It has a plurality of crossing elements (32) slidably provided on the tension element (31), and the crossing element (32) is made of steel and the tension element (31) is formed. ), The recess (33) is located radially inside the tension element (31), especially in the drive belt (3). Support surface (41), side surface (43) of the drive belt (3) facing the axial surface of the tension element (31), and the support surface (41) and the side surface (43). In a method of manufacturing a transverse element (32), which is provided between and connected to, and is defined by at least a partially concavely curved transition surface (42).
The cross-sectional element (32) is subjected to plastic deformation of only the surface layer at the location of the concavely curved portion of the transition surface (42) and the location of the support surface (41), whereby the surface layer is subjected to plastic deformation. Provided with nanocrystal microstructure ,
For the drive belt (3), the transverse element (32) is subjected to plastic deformation of only its surface layer only at both the transition surface (42) and the support surface (41). A method of manufacturing the transverse element (32) of the above. The particle size of the metal crystal of the transverse element (32) in the nanocrystal surface layer (NSL) provided with the nanocrystal microstructure is 0.1 micrometer at the maximum, and the nanocrystal surface layer (NSL) has a maximum particle size of 0.1 micrometer. The transverse element (32) according to claim 4 , wherein the average particle size of the metal crystal of the transverse element (32) is two orders of magnitude smaller than the average particle size of the metal crystal outside the nanocrystal surface layer (NSL). how to. The method for manufacturing a transverse element (32) according to claim 5 , wherein the thickness of the nanocrystal surface layer (NSL) is 1 to 10 micrometers.

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