[0027] figure 1 Shows the central part of an existing continuously variable transmission or CVT commonly used in a drive train between the engine and the drive wheels of a motor vehicle. The transmission includes two pulleys 1, 2, and each pulley 1, 2 is provided with two conical pulley discs 4, 5, and a substantially V-shaped groove is defined in the two conical pulley discs Between 4 and 5, one of the two conical pulley disks 4, 5 can be axially along the corresponding pulley shaft 6, 7 (the disk 4 is arranged on the pulley shaft 6, 7) To move. The transmission belt 3 surrounds the pulleys 1 and 2 to transmit the rotational movement ω and the accompanying torque T from one pulley 1, 2 to the other pulley 2, 1. The transmission usually also includes a starting device that applies a clamping force Fax directed to the axial direction of the corresponding other pulley disk 5 on the at least one disk 4, so that the belt 3 is clamped on the disk 4, the disk Between 5. And, the transmission (speed) ratio between the rotation speed of the driven pulley 2 and the rotation speed of the drive pulley 1 is determined thereby.
[0028] An example of an existing transmission belt 3 is figure 2 As shown in detail in its cross-sectional view, the belt 3 includes two ring groups 31, each of which includes a group (in this example) of six thin and flat (ie, ribbon-shaped) flexible steel 环件32. The belt 3 also includes a plurality of plate-shaped steel transverse elements 33 which are held together by the ring groups 31 respectively located in corresponding recesses of the transverse elements 33. The transverse element 33 bears the clamping force Fax, so that when the input torque Tin is applied to the so-called drive pulley 1, the friction between the disks 4, 5 and the belt 3 causes the rotation of the drive pulley 1 to pass through the same rotating The transmission belt 3 is transferred to a so-called driven pulley 2.
[0029] During the operation of the CVT, the transmission belt 3 and especially its steel ring 32 are subjected to periodically varying tensile and bending stresses (ie, fatigue loads). Generally, the metal fatigue resistance (that is, the fatigue strength of the ring 32) thus determines the functional life of the transmission belt 3 under the condition that a given torque T is transmitted by the transmission belt 3. Therefore, in the development of transmission belt manufacturing methods, the long-term overall goal is to achieve the required fatigue strength of the ring with the minimum combined material and processing costs.
[0030] image 3 The current relevant part of the existing overall manufacturing method of the transmission belt 3 (ie, the manufacturing of the steel ring 32 assembly of the transmission belt 3) is shown, wherein the individual processing steps are indicated by Roman numerals.
[0031] In the first processing step I, a thin sheet or plate of the base material with a thickness generally ranging from 0.4mm to 0.5mm is bent into a cylindrical shape, and the joined plate ends 12 are welded together in the second processing step II to form Open, hollow cylinder or tube 13. In the third processing step III, the tube 13 is annealed. Thereafter, in the fourth processing step IV, the tube 13 is cut into a plurality of annular rings 14, which are then rolled up in the fifth processing step V to be elongated while being The thickness is reduced to a value of 0.150-0.200 mm, usually to about 185 microns. After being rolled, the ring 14 is generally referred to as a steel ring 32. The steel ring 32 is then subjected to another, ring annealing processing step VI, to eliminate the previous coil by restoring annealing and recrystallization of the ring material at a temperature much higher than 600 degrees Celsius (for example, about 800 degrees Celsius) The work hardening effect of the manufacturing process (that is, the fifth step V). Thereafter, in the seventh processing step VII, the steel rings 32 are aligned, that is, they are installed around two rotating rollers and stretched to a predetermined circumferential length by forcing the rollers apart. In this seventh processing step VII, the internal stress distribution is also applied to the steel ring 32.
[0032] Thereafter, the steel ring 32 is heat-treated in two processing steps (ie, precipitation hardening or aging treatment in the eighth processing step VIII and gas nitrocarburizing in the ninth processing step IX). In particular, these two types of heat treatments involve heating the steel ring 32 in an industrial furnace or furnace containing a controlled gas protective atmosphere, which generally includes nitrogen and some (e.g., volume) for the aging treatment. The percentage is about 5%) hydrogen, and for gas nitrocarburizing usually includes nitrogen, hydrogen, and ammonia. According to the base material of the steel ring 32 (that is, the alloy composition of martensitic steel) and the desired mechanical properties of the steel ring 32, both of these heat treatments are usually performed in the temperature range of 400 degrees Celsius to 500 degrees Celsius. And each lasts about 45 minutes to more than 120 minutes. Regarding the latter, it should be noted that in general, the target is that the core hardness value is 520HV1.0 or more, the surface hardness value is 875HV0.1 or more, and the surface nitride layer, or nitrogen diffusion zone, has a thickness range of 19-37μm.
[0033] Finally, a plurality of steel rings 32 processed in this way are radially stacked (ie nested) to form a ring group 31, as further described in image 3 In the last (that is, the eleventh) processing step XI drawn. Obviously, the steel ring members 32 of the ring group 31 must be appropriately sized, for example, they must be slightly different in circumferential length so that the steel ring members 32 can fit around each other. The steel ring 32 of the ring group 31 obtained for this purpose is usually selected from many known steel rings 32 with different circumferential lengths in the previous (that is, tenth) processing step X.
[0034] When the steel ring member 32 thus processed was tested by tensile strength test, the fracture surface showed a ductile fracture portion DP and two brittle fracture portions BP extending from the nitride layer NL toward the side surface of the ring member 32. Figure 4 A typical imaging example including the fracture surface of the steel ring 32 shows the different textures of the ductile fracture part DP and the two brittle fracture parts BP and indicates the range of the nitride layer NL, but the nitride layer is in Figure 4 Difficult to distinguish. The range or layer thickness of the brittle fracture portion BP is directly related to the range or thickness of the nitrided layer NL, at least given a certain composition of the ring base material of the steel ring. Figure 5 The figure of gives an example of this association, which relates the measured brittle fracture layer thickness BP to a specific value of the nitride layer thickness NL. Figure 5 The graph of is used as a predetermined reference graph (or linear equation) in the mass production of the steel ring 32, which can be advantageously relied upon to check the nitride layer thickness NL of one of the (random) samples through a simple tensile strength test.
[0035] Image 6 The figure relates to another material property of the steel ring 32, that is, the measured hardness H of the steel ring 32 when the Vickers hardness is 100 grams force ([HV0.1]). This performance is for two different substrates MAT1, MAT2 are plotted as a function of the distance x (micrometers) from the outer surface. In both cases, namely for both MAT1 and MAT2, the steel ring 32 has a nitride layer NL, and the nitride layer NL extends 28 microns inwardly from the outer surface of the steel ring 32. The steel ring 32 made of these two substrates MAT1 and MAT2 undergoes tensile strength tests, resulting in the brittle fracture layer thickness BP1 in the first substrate MAT1 being 20 microns and the brittle fracture layer in the second substrate MAT2 The thickness BP2 is 16 microns. For the sake of completeness, it should be noted that Figure 5 The figure has been changed from above about Image 6 The steel ring 32 made of the first substrate MAT1 is obtained.
[0036] Such as Image 6 As shown, for the two substrates MAT1 and MAT2, the range of brittle fracture BP is related to the hardness H of the steel ring 32 of 750HV0.1 or higher. In fact, if the hardness H of the steel ring 32 is kept below the limit value of 750HV0.1, the fracture surface of the steel ring 32 produced by the tensile strength test does not show the brittle fracture BP at all. Based on this later observation, it is currently believed that by making the steel ring 32 have a surface hardness H of less than 750HV0.1, the toughness of the steel ring 32 is the best in terms of the fatigue strength of the steel ring 32 alone. Good. However, for the actual use of the steel ring 32 as a part of the ring group 31 of the transmission belt 3, the range of the brittle fracture BP may reach about 10 microns, because below this value, the fatigue strength of the steel ring 32 Any improvement of is relatively small, such as Figure 7 Shown. When the 10 micron boundary value of the BP thickness of the brittle fracture is used as Figure 5 The boundary value of the thickness of the nitride layer NL is about 18 microns. Furthermore, the 18 micrometer boundary value of the nitride layer NL can be related to a certain level of compressive residual stress. In the latter aspect, Figure 8 The graph provides the residual stress RS measured on the outer surface layer of the steel ring 32 as a function of the thickness of the nitride layer NL of the steel ring 32.
[0037] Such as Figure 8 As shown, the boundary value of the negative (ie compressed) residual stress RS at the surface of the steel ring 32 of about 650 MPa is applicable to the boundary nitride layer thickness NL of 18 microns. In addition, the above-mentioned preferable lower limit of the residual stress RS of -600 MPa corresponds to the nitride layer thickness NL of 16 microns. Finally, it should be noted that the lower limit of the nitride layer thickness of 10 microns corresponds to the residual stress RS of about -350Mpa.
[0038] In addition to all the contents of the foregoing specification and all the details of the drawings, the present disclosure also relates to and includes all the features of the claims. The parenthesized reference signs in the claims do not limit their scope, but merely serve as non-binding examples of corresponding features. The features of the claims can be individually applied to the specified product or the specified process according to the specific situation, but a combination of two or more of these features can also be applied therein.
[0039] The present invention represented by the present disclosure is not limited to the embodiments and/or examples explicitly set forth herein, but also includes its modifications, improvements and practical applications, especially those modifications, improvements and practical applications within the capabilities of professionals in the field.
