JP4938603B2 - Pulley for continuously variable transmission and continuously variable transmission - Google Patents

Description

  The present invention relates to a continuously variable transmission pulley and a continuously variable transmission, and more particularly to a continuously variable transmission pulley and a continuously variable transmission having excellent wear resistance.

  As shown in FIG. 6 (a), a conventional vehicle belt type continuously variable transmission has an input pulley 1, an output pulley 2, and endlessly formed metal wound around the input pulley 1 and the output pulley 2. A belt provided with a belt 3 made of metal is generally used. The input pulley 1 or the output pulley 2 transmits the rotational torque of the input pulley 1 to the output pulley 2 via the belt 3 while controlling the winding diameter of the belt 3 to change the gear ratio.

  Specifically, as shown in FIG. 6 (b) (enlarged view of portion A in FIG. 6 (a)), the belt 3 includes two endless steel bands 3a and 3a juxtaposed, and the two bands 3a. , 3a, a plurality of square-shaped blocks (metal elements) 3b are fitted along the circumferential direction of the band. Further, the input pulley 1 and the output pulley 2 wound around the belt 3 include two nested conical sheaves 2A and 2B as shown in FIG. 6C (the figure is a sectional view of the output pulley 2). I have. The above-described control of the winding diameter of the belt 3 is performed by moving two conical sheaves along the rotation axis of the pulley. At this time, the conical circumferential surfaces (sheave surfaces) of the sheaves 2A and 2B that are in frictional contact with the edge of the belt 3 slide along the edge of the belt 3 as the belt 3 rotates and the winding diameter of the belt 3 is controlled. It becomes the moving surface 2a. The tension of the belt 3 wound around the pulleys 1 and 2 is high, and the belt 3 itself is made of steel, so that the sliding surfaces of the pulleys 1 and 2 are easily worn.

  Therefore, in order to maintain the durability of the continuously variable transmission pulley and the continuously variable transmission, it is desirable to suppress wear of the sliding surface of the pulley. In view of such a problem, for example, a pulley for a belt type continuously variable transmission in which the surface hardness of a base material including a sliding surface is Hv750 or more by carburizing or carbonitriding (carburizing and nitriding). Has been proposed (see Patent Document 1).

JP 2000-8121 A

  However, the pulley described in Patent Document 1 can improve the wear resistance by making the surface hardness a predetermined hardness by carburizing or carbonitriding, but as described above, the continuously variable transmission Since a high surface pressure repeatedly acts on the sliding surface of the pulley for use, there is a risk that not only mere abrasive wear but also wear due to cracks due to surface fatigue may occur. Furthermore, the sliding surface of the pulley for the continuously variable transmission has a risk that the surface hardness decreases due to sliding heat generation, and wear due to the fatigue cracks may be promoted. As a result, there is a case where the wear of the sliding surface cannot be sufficiently reduced with a pulley in which the surface hardness of the pulley is simply made hard.

  The present invention has been made in view of the above-described problems, and its object is to suppress fatigue cracks on the sliding surface of the pulley due to repeated load from the belt and sliding heat generation with the belt. Another object of the present invention is to provide a continuously variable transmission pulley and a continuously variable transmission that can improve the wear resistance of a sliding surface.

  In order to solve the above problems, the inventors have intensively studied. As a result, in order to suppress wear on the sliding surface of the pulley, the occurrence of cracks due to fatigue is suppressed, and even when cracks occur. Therefore, it was considered important to suppress the progress of the cracks. Therefore, the inventors suppress the occurrence of cracks by setting the surface hardness of the sliding surface to a predetermined surface hardness, and even if cracks occur, the structure in the vicinity of the surface The inventors obtained new knowledge that the development of cracks can be suppressed by using residual austenite and applying residual compressive stress to predetermined locations.

  The present invention is based on the above-described new knowledge, and the pulley for continuously variable transmission according to the present invention has at least a sliding surface wound around a metal belt and sliding on the metal belt. A continuously variable transmission pulley using a material selected from chrome steel or chrome molybdenum steel defined in JIS G 4053 as a material steel, wherein the continuously variable transmission pulley includes the sliding surface. Surface hardness of Hv800 or more, at least a residual compressive stress of 1200 MPa or more is applied to the surface layer including the sliding surface, and the remaining austenite is 15 to 20 μm or more in the depth direction from the sliding surface. Residual austenite layer having 40% by volume, and internal residual in which a residual compressive stress of 300 MPa or less is applied to at least 30 μm or more in the depth direction from the sliding surface It is characterized by comprising a reduced stress portion, at least.

  According to the present invention, by setting the surface hardness of the sliding surface to Vickers hardness Hv800 or higher, not only the abrasive wear can be suppressed, but also the occurrence of initial cracks on the surface of the sliding surface can be suppressed. In addition, the surface hardness of the sliding surface is preferably higher, but since an extreme improvement in hardness leads to an increase in cost, surface treatment in consideration of the cost is required.

  Further, since the pulley for continuously variable transmission of the present invention is provided with a residual compressive stress of at least 1200 MPa on the surface layer including the sliding surface, the residual compressive stress can suppress the occurrence and progress of cracks. it can. That is, when the residual compressive stress is smaller than the above range, the effect of suppressing the crack growth cannot be sufficiently exhibited. The higher the residual compressive stress, the better. However, in consideration of productivity such as manufacturing cost, for example, the upper limit value of the residual compressive stress is more preferably 1800 MPa or less.

  The surface layer to which the residual compressive stress of 1200 MPa or more is applied is not particularly limited as long as the internal residual compressive stress portion can be secured, but the depth from the sliding surface is not limited. In order to obtain a retained austenite layer containing 15 to 40% by volume of retained austenite in a portion of 20 μm or more, the thickness of the surface layer is preferably at least less than 20 μm.

  Further, the continuously variable transmission pulley includes a retained austenite layer having a residual austenite of 15 to 40% by volume in a depth direction of 20 μm or more from the sliding surface. Processing-induced transformation of retained austenite occurs, and new martensite (fresh martensite) is generated, which promotes work hardening. Further, since martensite is continuously generated from the retained austenite, softening due to tempering due to sliding heat generation with the belt can be suppressed. From the viewpoint of manufacturing, the retained austenite layer is more preferably 100 μm or less in the depth direction from the sliding surface.

  As described above, the occurrence and progress of the initial crack on the sliding surface is suppressed by the residual stress in the above range, and the sliding surface generates sliding heat by contact with the belt, and the residual compressive stress is released. Even if it is a case, by providing the retained austenite at the position where the crack propagates (at least 20 μm or more in the depth direction from the sliding surface), it is possible to expect the processing-induced transformation of the retained austenite. Progress can be suppressed. That is, when it deviates from the said position, the progress of a crack cannot be suppressed more effectively. In addition, when the retained austenite is less than 15% by volume, it is not possible to sufficiently expect the effect of suppressing crack propagation due to the processing-induced transformation. Furthermore, it is difficult to build a structure with a proportion of retained austenite higher than 40% by volume, and the production cost increases to obtain such a steel structure, and the retained austenite is a soft structure. Decrease in hardness is inevitable.

  Note that the above-mentioned “working-induced transformation” means that the crystal lattice of retained austenite is expanded and contracted to martensite, and when the stress of the structure acts by the working-induced transformation, the structure of the austenite depends on the characteristics of the austenite. Although the portion having す る deforms for a moment, it immediately changes to hard martensite (rather than austenite), and the strength of the deformed portion can be increased.

  Further, by providing an internal residual compressive stress portion to which a residual compressive stress of 300 MPa or less is applied at least 30 μm or more from the sliding surface, it is possible to ensure the impact resistance characteristics of the entire pulley. That is, when it is larger than the residual compressive stress, the impact resistance of the entire pulley may be lowered.

  The pulley for the continuously variable transmission is selected from a high-concentration carburizing process, a carburizing / nitrogenizing process (carbonitriding process), shot blasting, lapping, cavitation shot, etc. after processing the steel material into a pulley shape. It can be obtained by combining two or more treatments and applying the treatment to the sliding surface.

  As a material used in the pulley for continuously variable transmission according to the present invention, it is necessary to select a steel material whose hardness can be increased by carburizing, and chromium steel defined in JIS G 4053, which has been widely used conventionally, Alternatively, chromium molybdenum steel should be used. In addition, chrome steel and chrome molybdenum steel mean steel described by the symbols SCr and SCM in the standard. Such a material is excellent in carburizing properties, and a pulley having a surface hardness increased easily by the above-described treatment can be produced.

  Further, as a material used in the pulley for continuously variable transmission according to the present invention, at least one of Si, Mn, and Mo contained in chromium steel or chromium molybdenum steel defined in JIS G 4053 is further increased. Steels containing components in a range that satisfies at least one of the following conditions (a) to (c) can also be used. (A) Si: exceeding 0.35% by mass and 1.0% by mass or less, (b) Mn: exceeding the upper limit of the content of Mn defined in the JIS standard in the selected material, And 1.5 mass% or less, (c) Mo: It exceeds the upper limit of content of Mo prescribed | regulated by the said JIS specification in the selected material, and is 0.8 mass% or less. According to the present invention, the wear resistance of the sliding surface can be further improved by increasing the amount of at least one of the elements (a) to (c) as compared with the steel specified in JIS G 4053. it can.

  That is, Si is useful for improving the temper softening resistance, and exceeds the upper limit of 0.35 mass% of the Si content defined in the JIS standard (JIS G 4053) in the selected material. Tempering softening resistance can be further improved. However, if it is more than 1.0% by mass, the toughness of the material may be reduced.

  Mn is useful for ensuring the hardenability of the material, and by adding the Mn content exceeding the upper limit of the Mn content defined in the JIS standard (JIS G 4053) in the selected material, Hardenability can be improved. However, when it is more than 1.5% by mass, there is a risk of causing grain boundary oxidation.

  Mo is useful for securing the hardenability of the material in the same manner as Mn. The Mo is contained in the selected material in excess of the upper limit of the Mo content specified in the JIS standard (JIS G 4053). Thus, the hardenability can be further improved. However, when it is more than 0.8% by mass, the workability of the material may be reduced.

  Note that the lower limit of Mn and Mo exceeds the upper limit of the content of contained elements (Mn, Mo) defined in JIS standard (JIS G 4053), according to the JIS standard depending on the selected material. This is because the upper limit value of the content of the specified contained elements is different. For example, when the selected material is SCM420, the upper limit value of the Mo content in SCM420 defined in JIS standard (JIS G 4053) is 0.25% by mass. “Exceeding the upper limit of the Mo content defined by the JIS standard in the selected material” means “exceeding 0.25 mass%” in this case.

  Moreover, as steel of the material used in the pulley for continuously variable transmission according to the present invention, an element in a range satisfying at least one of the following conditions (d) to (g) is additionally added. As a result, the wear resistance of the sliding surface can be further improved. (D) Nb: 0.005-0.2 mass%, (e) Ti: 0.005-0.2 mass%, (f) Ni: 0.05-3.0 mass%, (g) B: It is 0.0005-0.005 mass%.

  That is, Nb forms Nb (C, N) and is useful for preventing crystal grain coarsening of the material. When the amount is less than 0.005% by mass, this effect cannot be expected. Moreover, even if it is more than 0.2 mass%, the effect will be saturated and the effect beyond it cannot be anticipated.

  Ti forms Ti (C, N) and is useful for preventing coarsening of crystal grains of the material. When the amount is less than 0.005% by mass, it is difficult to obtain this effect. Moreover, even if it is more than 0.2 mass%, the effect will be saturated and the effect beyond it cannot be anticipated.

  Ni is useful for ensuring the hardenability of the material, and when less than 0.05% by mass, this effect cannot be expected. Moreover, when more than 3.0 mass%, a raise of hardness will be caused and the workability of material will be reduced.

  B is useful for ensuring the hardenability of the material and is useful for improving the grain boundary strength. When the content is less than 0.0005% by mass, this effect cannot be expected. Moreover, even if it is more than 0.005 mass%, the said effect will be saturated and the effect beyond it cannot be anticipated.

  As described above, Nb, Ti, Ni, and B can be obtained by including them in the material, so that useful properties can be obtained. Can do.

  Furthermore, the continuously variable transmission according to the present invention includes the pulley described above in one or both of the input pulley and the output pulley, and includes at least a metal belt wound around the input pulley and the output pulley. . By using such a pulley, the wear resistance of the pulley can be improved.

  According to the pulley for continuously variable transmission according to the present invention, the wear resistance of the sliding surface is reduced by suppressing fatigue cracks on the sliding surface of the pulley due to repeated load from the belt and sliding heat generation with the belt. Can be improved.

Hereinafter, the present invention will be described by way of examples.
Example 1
<Test body>
As shown in FIG. 3, chromium molybdenum steel (JIS standard: SCM420) was prepared and machined into the shape of the pulley for continuously variable transmission shown in FIG. 6 (c). Next, the pulley is put into a heating furnace, held at 900 ° C. for 7 hours, then held at 850 ° C. for 1 hour, then oil-quenched at 130 ° C., tempered at 160 ° C. for 1 hour, and carburized. Processed. Then, a shot peening treatment was performed on the sliding surface, a residual compressive stress was applied to the surface, and a test body having residual austenite in the internal tissue layer was manufactured.

  Specifically, as shown in FIG. 1, the sliding surface 2a has a surface hardness of Vickers hardness Hv992 (Hv800 or higher) and a sliding surface having a residual stress of 1390 MPa (1200 MPa or higher). A surface layer 21 including the surface 2a, a retained austenite layer 22 having 22.6% by volume (15-40% by volume) of retained austenite at a depth of 20 to 30 μm from the sliding surface 2a, and a depth from the sliding surface. A test body (pulley for continuously variable transmission) including at least an internal residual compressive stress portion 23 to which a residual compressive stress of 239 MPa (300 MPa or lower) was applied to a portion of 30 μm or more in the vertical direction was manufactured. Here, the residual compressive stress of the specimen is measured by an X-ray residual stress measuring device, and the ratio of the structure of residual austenite is measured by observing a cross section along the depth direction with a microscope. confirmed.

  2 shows the depth from the sliding surface 2a of the test body and the internal residual stress distribution at the depth, and the manufactured test body has a surface layer including the sliding surface (region A in FIG. 2). ) Is applied with a residual compressive stress of 1200 MPa or more, and a residual compressive stress of 300 MPa or less is applied to the internal residual compressive stress portion (region B in FIG. 2), which is a portion 30 μm in the depth direction from the sliding surface. Will be.

<Abrasion test>
The continuously variable transmission equipped with the manufactured specimen (pulley for continuously variable transmission) was attached to a device that can arbitrarily change the input torque, and a wear test was conducted. Torque and sheave input to the primary pulley (input pulley) under the condition (γmax) where the belt winding position is fixed on the underdrive side where the gear ratio, which is considered to be the most severe as the operating environment condition of the pulley, is maximum. The friction test was performed with the belt narrow pressure applied in an overloaded state.

  Specifically, the amount of wear on the sheave surface (sliding surface) after 17 hours of operation in an environment where the input torque Tin = 300 Nm, the input rotation speed Nin = 3400 rpm to the primary pulley, the gear ratio γmax is fixed, and the oil temperature is 150 ° C. (Abrasion depth) was measured. These results are shown in FIG.

  The “carbon concentration (%)” shown in FIG. 4 indicates the value (mass%) of the carbon concentration contained in the sliding surface, and the “surface hardness (Hv)” indicates the Vickers hardness of the sliding surface. “Residual σ (MPa)” is the value of residual compressive stress, “surface” is the residual compressive stress on the sliding surface, and “30 μm” is 30 μm in the depth direction from the sliding surface. The value of the residual compressive stress of this part is shown. Furthermore, “post-SP residual γ (%)” indicates the ratio (volume%) of the retained austenite structure in the portion of 20 μm to 30 μm in the depth direction from the sliding surface.

(Examples 2 to 10)
In the same manner as in Example 1, test bodies of Examples 2 to 10 were manufactured. Example 2 differs from Example 1 in the processing conditions of shot peening, and Examples 3 to 10 differ from Example 1 in that a steel material shown in FIG. 3 is used. In addition, Examples 2 to 10 are common to Example 1, as shown in FIG. 4, the surface hardness of the sliding surface is Vickers hardness Hv800 or more, and the sliding surface is 1200 MPa or more. A surface layer including a sliding surface to which residual stress is applied, a residual austenite layer having 15 to 40% by volume of residual austenite in a portion of 20 μm to 30 μm in the depth direction from the sliding surface, and a depth direction from the sliding surface. The test piece (pulley for continuously variable transmission) was manufactured so as to include an internal residual compressive stress portion provided with a residual compressive stress of 300 MPa or less in a portion of 30 μm or more. And the abrasion test was done on these test bodies on the same conditions as Example 1. These results are shown in FIG.

(Comparative Examples 1-4)
A test body was manufactured in the same manner as in Example 1. The comparative examples 1 to 3 differ from the first embodiment in that the carburizing process conditions and the shot peening process conditions are changed. Specifically, in Comparative Examples 1 to 3, the residual compressive stress of the surface layer including the sliding surface is less than 1200 MPa, the internal residual compressive stress of the part of 30 μm or more exceeds 300 MPa, and the residual austenite of the part of 20 μm or more. This is different from Example 1 in that the amount is less than 15 volume%. Further, the comparative example 4 is different from the example 1 in that shot peening was not performed. Specifically, Comparative Example 4 is different from Example 1 in that the surface hardness of the sliding surface is less than Hv800 and the residual compressive stress of the surface layer is less than 1200 MPa. And the abrasion test was done with respect to the test body of Comparative Examples 1-4 on the same conditions as Example 1. FIG. These results are shown in FIG.

(Result 1 and Discussion 1)
The wear amounts of Examples 1 to 10 were all 10 μm or less, but the wear amounts of Comparative Examples 1 to 4 were all over 10 μm.
In Comparative Examples 1 to 3, even when the surface hardness of the sliding surface is Hv 800 or more, when cracks occurred on the sliding surface due to repeated load from the belt and sliding heat generation with the belt, Since the value of the residual compressive stress of the surface layer is lower than those of 1 to 10, it is considered that cracks are likely to progress. Further, when cracks further progress in the depth direction from the sliding surface, Comparative Examples 1 to 3 have a smaller proportion of the structure of retained austenite in the retained austenite layer than Examples 1 to 10, It is considered that the effect due to the processing-induced transformation is hardly exhibited. As a result, in Comparative Examples 1 to 3, it is considered that wear due to fatigue cracks occurs more easily than in Examples 1 to 10, and the value of the wear amount is increased.

  In addition, since Comparative Example 4 does not perform shot peening, the surface hardness and the residual stress on the surface are lower than those in Examples 1 to 10, so that it is easy to wear abrasively and further cracks on the sliding surface. It is thought that the occurrence of cracks and the development of cracks are easy. As a result, it is considered that the value of the wear amount in Comparative Example 4 was larger than that in Examples 1-10.

  As shown in FIGS. 3 and 4, the specimens of Examples 6 and 9 contain nickel that satisfies the range of 0.05 to 3.0% by mass, and the specimen of Example 7 is 0. The specimen of Example 8 contains niobium that satisfies the range of 0.005 to 0.2% by mass, and the specimen of Example 8 contains titanium that satisfies the range of 0.005 to 0.2% by mass. The test body contains boron that satisfies the range of 0.0005 to 0.005 mass%. Even when an element is further added within the above range, it is considered that the wear resistance of the sliding surface is ensured as shown in FIG.

(Examples 11 to 13)
A test body was manufactured in the same manner as in Example 1. The difference from Example 1 is that carburizing and nitriding treatment (carbonitriding treatment) is performed instead of carburizing treatment. Specifically, the pulley was put into a heating furnace and held at 950 ° C. for 6 hours, then held at 850 ° C. for 4 hours, and then oil-quenched at 60 ° C., followed by tempering at 160 ° C. for 1 hour, Carburizing and nitriding treatment was performed. Then, under the same conditions as in Example 1, the sliding surface was subjected to shot peening treatment, a test body having residual compressive stress and residual austenite on the surface was manufactured, and an abrasion test was performed. The result is shown in FIG. In addition, in order to evaluate the carburizing and nitriding treatment, in addition to the carbon concentration, the nitrogen concentration in the sliding surface is also shown.

(Comparative Examples 5-7)
A test body was manufactured in the same manner as in Example 1. The difference from Example 1 is that the carburizing and nitriding treatment was performed by changing to the carburizing treatment, and the shot peening treatment conditions were changed. Comparative Examples 5 to 7 include sliding surfaces. The residual compressive stress of the surface layer is 1200 MPa or less, the internal residual compressive stress is applied to a portion of 30 μm or more greater than 300 MPa, and the residual austenite of the portion of 20 μm or more is less than 15% by volume. And the abrasion test was done with the same conditions as Example 1 with respect to the test body of Comparative Examples 5-7. The result is shown in FIG.

(Result 2 and discussion 2)
The wear amounts of Examples 11 to 13 were all 10 μm or less, but the wear amounts of Comparative Examples 5 to 7 were all over 10 μm. In the same manner as described above, Comparative Examples 5 to 7 have a lower residual compressive stress in the surface layer than Examples 11 to 13 and a small proportion of retained austenite in the retained austenite layer, so that the effect of processing-induced transformation is exhibited. Probably not. As a result, in Comparative Examples 5 to 7, wear due to fatigue cracks was more likely to occur than in Examples 11 to 13, and the value of the amount of wear was considered to have increased.

  As mentioned above, although the embodiment of the present invention has been described in detail, the specific configuration is not limited to this embodiment, and even if there is a design change within a scope not departing from the gist of the present invention, they are not limited to the present invention. Is included.

The schematic diagram which showed the cross section containing the sliding surface of the pulley (test body) for continuously variable transmission which concerns on Example 1. FIG. The schematic diagram which showed the depth from the sliding surface of the pulley for continuously variable transmissions which concerns on Example 1, and the internal residual stress distribution in this depth. The table | surface which showed the composition of the pulley for continuously variable transmissions of Examples 1-10 and Comparative Examples 1-4. The figure which showed the result of the characteristic and abrasion test of Examples 1-10 and Comparative Examples 1-4. The figure which showed the characteristic of Examples 11-13 and Comparative Examples 5-7, and the result of the abrasion test. It is a principal part schematic diagram of the conventional continuously variable transmission, (a) is a principal part perspective view of a continuously variable transmission, (b) is the elements on larger scale of the A section of (a), (c) is The schematic cross section of an output pulley.

Explanation of symbols

  1: input pulley, 2: output pulley, 2A, 2B: sheave, 2a: sliding surface, 3: belt, 21: surface layer, 22: residual austenite layer, 23: internal residual compressive stress part

Claims (4)

A material selected from chrome steel or chrome molybdenum steel defined in JIS G 4053 is used as a material steel, at least part of which is wound around a metal belt and having at least a sliding surface that slides on the metal belt. A pulley for a continuously variable transmission,
The continuously variable transmission pulley is:
A surface layer including the sliding surface, the surface hardness of the sliding surface is Hv800 or more, and a residual compressive stress of at least 1200 MPa is applied;
A retained austenite layer having a depth of 15 to 40% by volume of retained austenite in a portion deeper in the depth direction than the surface layer and in a portion of 20 to 30 μm in the depth direction from the sliding surface;
A pulley for continuously variable transmission, comprising at least an internal residual compressive stress portion to which a residual compressive stress of 300 MPa or less is applied to a portion of at least 30 μm or more in the depth direction from the sliding surface. In the pulley for continuously variable transmission according to claim 1, the amount of Si, Mn, and Mo contained in the steel of the material is further increased, and at least one of the following conditions (a) to (c) is satisfied. A pulley for a continuously variable transmission, characterized by using steel containing components.
(A) Si: more than 0.35% by mass and 1.0% by mass or less (b) Mn: exceeding the upper limit of the Mn content defined in the JIS standard in the selected material, and 1.5% by mass or less (c) Mo: exceeding the upper limit of the Mo content specified by the JIS standard in the selected material and 0.8% by mass or less In the pulley for continuously variable transmission according to claim 1 or 2, Nb, Ti, Ni, B is further added to the steel used as a material, and at least one of the following conditions (d) to (g) is satisfied: A pulley for a continuously variable transmission, characterized by using steel to which elements in a satisfactory range are added as a material.
(D) Nb: 0.005 to 0.2% by mass
(E) Ti: 0.005 to 0.2% by mass
(F) Ni: 0.05-3.0 mass%
(G) B: 0.0005 to 0.005 mass%   A continuously variable transmission comprising the continuously variable transmission pulley according to any one of claims 1 to 3.

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