JP2014101984A - Constant velocity universal joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a frictional resistance of a slide contact part between a torque transmitting member and an inner joint member and between the torque transmitting member and an outer joint member in a constant velocity universal joint in which the torque transmitting member is placed between the inner joint member and the outer joint member.SOLUTION: A constant velocity universal joint of this invention comprises an outer joint member 20 having a hole 24 of a hexagonal shape of a sectional plane perpendicular to a rotating axis and an inner wall surface 26 of the hole 24 being a flat plane in parallel with a rotating axis P-P; an inner joint member 10 stored in the hole 24 of the outer joint member 20 with its outer peripheral surface 16 being spherical plane; and a plurality of torque transmitting members 30 placed between the inner wall surface 26 of the outer joint member 20 and the outer peripheral surface 16 of the inner joint member 10. Material constituting a surface of the torque transmitting member 30 of which part is contacted with the inner joint member 10 or the outer joint member 20 is metal with yield strength of 100 MPa or more and a low frictional coefficient against either the inner joint member 10 or the outer joint member 20 or both of them.

Description

  The present invention relates to a constant velocity universal joint.

  Constant velocity universal joints are roughly classified into a fixed type capable of only angular displacement and a sliding type capable of angular displacement and axial displacement (plunging), and is appropriately used depending on the application. For example, in the case of an automobile drive shaft, a fixed type constant velocity universal joint is used on the wheel side (outboard), and a sliding type constant velocity universal joint is used on the differential gear side (inboard).

  A tripod type constant velocity universal joint is known as an example of a sliding type constant velocity universal joint. However, the tripod type constant velocity universal joint has a large number of parts, the outer diameter of the joint is large relative to the diameter of the shaft coupled to the inner joint member, and the shape of the inner wall surface of the outer joint member is complicated. Has a problem. In order to solve these problems, Patent Document 1 proposes a constant velocity universal joint that consists of two parts, an inner joint member and an outer joint member, with a significantly reduced number of parts compared to the tripod type constant velocity universal joint. Has been. The constant velocity universal joint includes an inner joint member and an outer joint member, and the inner joint member is accommodated inside the outer joint member. The inner wall surface of the outer joint member has a regular hexagonal shape when viewed in a cross section perpendicular to the rotation axis, and is a flat surface parallel to the rotation axis when viewed in a cross section including the rotation axis. The inner joint member has a convex spherical outer peripheral surface corresponding to each flat surface constituting the inner wall surface of the outer joint member. Because of this structure, axial displacement and angular displacement (bending) are possible between the inner joint member and the outer joint member, but relative movement in the circumferential direction is prevented, and therefore torque transmission Is possible.

  However, in the thing of patent document 1, the convex spherical outer peripheral surface of an inner joint member and the flat surface of the inner wall surface of an outer joint member contact. Therefore, the contact part of both becomes a point contact. Therefore, the surface pressure of the contact portion becomes very high, and the contact portion is easily damaged. In order to eliminate such a problem, Patent Document 2 proposes that a torque transmission member be separately provided between the inner joint member and the outer joint member. Thereby, although the number of parts increases compared with the thing of patent document 1, the surface pressure of a contact part falls and a joint lifetime improves.

JP-A-5-172152 Japanese Patent Laid-Open No. 7-190081

  In the constant velocity universal joint of Patent Document 2, the surface pressure of the contact portion is lower than that of Patent Document 1 by interposing a torque transmission member between the inner joint member and the outer joint member. Because of the sliding contact, the sliding resistance when the joint rotates at the operating angle is still larger than that of the rolling contact. In particular, in the case of a constant velocity universal joint used for an automobile drive shaft or propeller shaft, it is necessary to reduce slide resistance from the viewpoint of improving the durability of the joint and NVH characteristics.

  The present invention relates to a constant velocity universal joint of the type described in Patent Document 2 described above, which is neither a tripod type nor a type using a ball, and between the torque transmission member and the inner joint member and between the torque transmission member and the outer side. It aims at reducing the frictional resistance of the sliding contact part between joint members.

  The present invention solves the problem by forming at least a portion of the surface of the torque transmission member that contacts the inner joint member or the outer joint member with a metal having a low coefficient of friction with respect to the inner joint member and / or the outer joint member. . That is, the constant velocity universal joint of the present invention includes an outer joint member having a hexagonal hole in a cross section perpendicular to the rotation axis, and an inner wall surface of the hole being a flat surface parallel to the rotation axis, and is accommodated in the hole. An inner joint member having a spherical outer peripheral surface, and a plurality of torque transmission members interposed between the inner wall surface of the outer joint member and the outer peripheral surface of the inner joint member, and the torque Of the surface of the transmission member, the portion that comes into contact with the inner joint member or the outer joint member is made of a metal having a yield strength of 100 MPa or more and a low friction coefficient with respect to the inner joint member or the outer joint member or both. It is.

  For the sake of simplicity, “inner joint member or outer joint member or both” will hereinafter be referred to as “inner joint member and / or outer joint member”. The torque transmission member has two surfaces, a side in contact with the inner joint member and a side in contact with the outer joint member. And when it says "an inner joint member and an outer joint member", those both surfaces are object, and when it says "an inner joint member or an outer joint member", it means that either one side is object.

Any metal may be used as long as it has a low coefficient of friction with respect to the inner joint member and / or the outer joint member. For example, it is a copper alloy, preferably brass, more preferably high-strength brass, and specific examples thereof include high-strength brass casting type 1 CAC301 (old symbol HBsC1) (JIS H 5120: 97). The friction coefficient of these metal materials is sufficiently lower than that of carbon steel usually used for the inner joint member and the outer joint member.
In addition to forming only the surface of the torque transmission member with such a metal material, the entire torque transmission member may be formed with such a metal material. Moreover, it is good also as a multilayered structure made into two or more layers from the surface of a torque transmission member toward a core part.

  Further, the contact between the torque transmission member and the inner joint member and between the torque transmission member and the outer joint member is preferably in the category of elastic deformation, and for this purpose, the metal material constituting the torque transmission member is 100 MPa or more. It shall have yield strength or yield strength (stress at the point where plastic deformation begins, ie yield point). Although the stress acting on the torque transmission member varies depending on the input torque of the constant velocity universal joint and the design of the internal parts, for example, assuming use as a drive shaft, if there is no yield strength of 100 MPa or higher, The torque transmission member may be deformed when a high operating angle is taken.

According to the present invention, the surface of the torque transmission member is made of a metal having a low coefficient of friction with respect to the inner joint member and / or the outer joint member, so that the torque is transmitted between the inner joint member and the torque transmission member and between the outer joint member and the torque transmission. The frictional force with the member is reduced, which is advantageous in terms of vibration characteristics.
In addition, since the conventional constant velocity universal joint has a high surface pressure, it is necessary to form a hardened layer by heat treatment at least at the contact portion. According to the present invention, since the surface pressure is low, no heat treatment is performed. However, as long as it has the required yield strength, the heat treatment can be omitted.

It is a front view of the constant velocity universal joint which shows the Example of this invention. It is a longitudinal cross-sectional view of the state where the maximum operating angle of the constant velocity universal joint shown in FIG. 1 is taken. It is a front view of the inner joint member of the constant velocity universal joint shown in FIG. It is a perspective view of the inner side coupling member of the constant velocity universal joint shown in FIG. (A) is sectional drawing of a torque transmission member, (B) is a side view, (C) is an expanded sectional schematic diagram of an outer surface. It is sectional drawing of a torque transmission member. (A) is sectional drawing of a torque transmission member, (B) is a side view. (A) is sectional drawing of a torque transmission member, (B) is a side view. It is a diagram which shows a time-dependent change of a friction coefficient. (A), (B), (C) is a side view of a torque transmission member. It is a schematic diagram of the surface which provided the micro recessed part (dimple).

Embodiments of the present invention will be described below with reference to the accompanying drawings.
Here, FIG. 1 is a view of the constant velocity universal joint in a state where the operating angle is 0 as viewed from the opening end face side of the outer joint member. FIG. 2 shows a longitudinal section of the constant velocity universal joint taken at the maximum operating angle θmax along the line II-II in FIG. The symbol O in FIG. 2 represents the joint center, and the symbol PP represents a rotation axis of the outer joint member, that is, a line perpendicular to the paper surface of FIG.

  As shown in FIGS. 1 and 2, the constant velocity universal joint includes an inner joint member 10, an outer joint member 20, and a torque transmission member 30 as main components. The inner joint member 10 is located inside the outer joint member 20, and a plurality of torque transmission members 30 are interposed therebetween.

  The inner joint member 10 has an axial through hole 12 at the shaft center, and a serration hole 14 is formed in the through hole 12 (see FIG. 4). Then, the serration shaft of the shaft 18 is inserted into the serration hole 14 so as to be coupled to transmit torque. As is well known, it is also possible to employ a spline or other uneven coupling instead of serration.

A plurality of inner torque transmission surfaces 16 are formed on the outer peripheral surface of the inner joint member 10. In the case of FIGS. 1, 3, and 4, there are a total of six inner torque transmission surfaces 16 (a) to 16 (c). Each inner torque transmission surface 16 has a convex spherical shape. When viewed in a cross section including the rotation axis of the inner joint member 10, that is, in a longitudinal section (see FIG. 2), the inner torque transmission surface 16 is an arc having the joint center O as the center of curvature. Therefore, the center of curvature of the inner torque transmission surface 16 is on the rotation axis. Further, when viewed in a cross section (see FIG. 3), it is an arc having a radius r centered on one of the points C (a) to C (c) arranged at equal intervals on the pitch circle PC. The pitch circle PC is a circle centered on the joint center O on the joint center plane (a plane including the joint center O and perpendicular to the rotation axis), and its radius r ₀ is determined by the use conditions (particularly load conditions) of the joint. .

  More specifically, the pair of inner torque transmission surfaces 16 (a) facing each other across the point C (a) is an arc having the center of curvature at the point C (a) and at the same time the point C (a). It is also part of the spherical surface at the center. Similarly, the pair of inner torque transmission surfaces 16 (b) facing each other across the point C (b) are arcs having the center of curvature at the point C (b) and at the same time spherical surfaces having the center at the point C (b). Is part of. Further, the pair of inner torque transmission surfaces 16 (c) facing each other across the point C (c) is a circular arc having the center of curvature at the point C (c) and at the same time a spherical surface having the center at the point C (c). It is a part. Thus, the inner torque transmission surface 16 is composed of three sets each having a common center of curvature (C (a), C (b) or C (c)).

  Two inner torque transmission surfaces 16 adjacent to each other in the circumferential direction face each other with large-diameter end edges to form ridge lines. Referring to FIG. 3, a ridge formed by the inner torque transmission surface 16 (b) and the inner torque transmission surface 16 (c) (a line segment formed at the intersection of two adjacent surfaces is shown at the bottom of the figure. Or a half straight line) appears as a straight line running in the vertical direction in the figure, and is formed by the inner torque transmission surface 16 (a) and the inner torque transmission surface 16 (b) at a position advanced 120 degrees counterclockwise therefrom. There is a ridge formed by the inner torque transmission surface 16 (c) and the inner torque transmission surface 16 (a) at a position advanced 120 degrees counterclockwise therefrom. In this way, the three sets of inner torque transmission surfaces 16 (b) (c), 16 (a) (b), 16 (c) (a) each form a ridge. A portion between the ridges on the outer periphery of the inner joint member 10 can be formed into an arbitrary shape after taking the strength of the inner joint member 10 and processing into consideration.

  As shown in FIGS. 1 and 2, the outer joint member 20 includes a cup-shaped mouth portion 22 and a stem portion 28 extending from the bottom of the mouth portion 22, and other serration shafts formed on the stem portion 28. A shaft (not shown) is coupled to be able to transmit torque. Here, it is also possible to adopt a spline or other uneven coupling instead of serration.

  The mouth portion 22 of the outer joint member 20 has a hole 24 opened at one end, and the inner wall surface of the hole 24 is seen in a cross section perpendicular to the rotation axis PP of the outer joint member 20 as can be seen from FIG. Thus, it is a regular polygon shape (regular hexagon in the illustrated example). Each surface 26 constituting the inner wall surface of the hole 24 is a flat surface parallel to the rotation axis PP of the outer joint member 20. The surface 26 is referred to as an outer torque transmission surface with respect to the inner torque transmission surface 16 described above. The outer torque transmission surface 26 may be literally flat (straight) as viewed in a cross section perpendicular to the rotation axis PP of the outer joint member 20, or may be an arc with a large curvature radius. In this case, the outer torque transmission surface 26 is a partial cylindrical surface parallel to the rotation axis PP.

  As shown in FIG. 2, the outer torque transmission surface 26 is formed with circumferential grooves for mounting the clips 25 at two positions in the axial direction. In FIG. 1, the groove is indicated by a broken line, and the clip 25 is omitted. Here, the outline of the clip 25 is also a regular hexagon and is divided at one place in the circumferential direction so that it can be attached and detached using elastic deformation. FIG. 1 shows a state where the clip 25 is removed. The clip 25 plays a role of defining a sliding range of the torque transmitting member 30 described later.

  The inner torque transmission surface 16 and the outer torque transmission surface 26 form a pair, and there are six pairs in the illustrated example. Each pair of inner torque transmission surface 16 and outer torque transmission surface 26 face each other and form a wedge space 36 therebetween. The torque transmission member 30 interposed between the inner joint member 10 and the outer joint member 20 is disposed in the wedge space 36. The torque transmission member 30 illustrated in FIG. 5 has a substantially circular button shape (see FIG. 5B). A surface that contacts the inner joint member 10 is referred to as an inner surface 32, and a surface that contacts the outer joint member 20 is referred to as an outer surface 34. The inner side surface 32 has a concave spherical shape, and comes into spherical contact with the convex spherical inner torque transmission surface 16 of the inner joint member 10. In FIGS. 1 and 2, the radii of curvature of both are shown as being the same, but they are not necessarily the same. For example, the radius of curvature of the inner surface 32 of the torque transmitting member 30 is set to that of the inner torque transmitting surface 16. It may be smaller than the radius of curvature. Further, the centers of curvature of both may be appropriately offset.

  The outer surface 34 of the torque transmission member 30 is in contact with the flat outer torque transmission surface 26 of the outer joint member 20. In FIG. 1, for the sake of simplicity, the outer torque transmission surface 34 is shown as if it were a flat surface. FIG. 5A shows an example in which the outer surface 34 is a convex spherical surface, and the symbol SR represents the radius of curvature of the convex spherical surface of the outer surface 34. In this case, since the contact relationship between the outer surface 34 and the outer torque transmission surface 26 is a point contact, a gap that opens in a wedge shape toward the outer periphery is formed. Therefore, the surrounding lubricant can be drawn in and the lubricant can be supplied to the contact portion.

  The surface pressure increases as the radius of curvature SR of the convex spherical surface of the outer surface 34 decreases. Therefore, it is necessary to form a gap that opens in a wedge shape toward the outer periphery while preventing the surface pressure from becoming too high. In addition, since the distance between two opposing surfaces of the outer torque transmission surface 26 of the outer joint member 20 corresponds to the diameter of a circle inscribed in the inner wall surface of the regular hexagon, the curvature is more than half of the distance between the two surfaces. If the radius SR is decreased, there is a possibility that relative rotation between the inner joint member 10 and the outer joint member 20 is permitted. However, this does not achieve the basic function of the constant velocity universal joint of torque transmission. From this point of view, the curvature radius SR of the convex spherical surface of the outer surface 34 is the two opposing surfaces of the outer torque transmission surface 26 of the outer joint member 20, specifically, points C (a) and C (b ) Or C (c), and is preferably larger than half of the distance between two opposing surfaces of the pair of outer torque transmission surfaces 26 (a), 26 (b) or 26 (c) facing each other. Preferably, it is 5 times or more the half of the distance between the two surfaces.

  As described above, the curvature radius SR of the convex spherical surface of the outer side surface 34 is inevitably larger than half of the distance between two opposing surfaces of the outer torque transmitting surface 26 of the outer joint member 20, so that the inner torque is inevitably increased. The radius of curvature of the transmission surface 16 is larger. Therefore, the angular displacement between the inner joint member 10 and the outer joint member 20 is performed at the spherical contact portion between the inner torque transmission surface and the torque transmission member. Therefore, the sharing of allowing the angular displacement of the joint between the inner joint member 10 and the torque transmission member 30 and allowing the axial displacement of the joint between the outer joint member 20 and the torque transmission member 30 is established, Uneven wear due to the uneven contact of the torque transmitting member 30 can be prevented, and the slide resistance can be reduced.

  On the other hand, the curvature radius SR of the convex spherical surface of the outer surface 34 is set so that the contact circle generated under the maximum load does not protrude from the outer periphery of the torque transmission member 30, in other words, the contact circle is larger than the outer diameter of the torque transmission member 30. (The contact circle means the shape of the contact surface. In the field of rolling bearings, the contact surface between the ball bearing raceway and the ball is an ellipse. However, when the outer surface 34 of the torque transmitting member 30 is a convex spherical surface, the shape of the contact surface with the flat outer torque transmitting surface 26 is a circle, which is referred to as a contact circle). To illustrate specific conditions for such setting, SR / r0 <350. Here, SR represents the radius of curvature of the convex spherical surface, and r0 represents the radius of the pitch circle PC on which the centers of curvature C (a) to C (c) of the inner torque transmission surface 16 of the inner joint member 10 are arranged.

  FIG. 5C shows a method for measuring the height H of the convex spherical outer surface 34 of the torque transmitting member 30. A circle indicated by an imaginary line represents a roundness that smoothly connects the outer peripheral surface and the outer surface 34 of the torque transmission member 30. An intersection point 38 between this circle and the tangent line of the outer surface 34 is obtained, and the distance from the intersection point 38 to the vertex of the outer surface 34 is defined as a height H. In this case, the height H also means the height of the opening of the plow that opens in a wedge shape toward the outer periphery of the torque transmission member 30. In the case of grease lubrication, the opening height of this gap is 20 to 300 μm, preferably 40 to 80 μm.

  FIG. 6 shows an example in which the outer side surface 34 of the torque transmitting member 30 is a convex cylindrical surface. In the same figure, the code | symbol R represents the curvature radius of the outer surface 34 of convex cylindrical surface shape. In this case, since the contact relationship between the convex cylindrical outer surface 34 and the flat outer torque transmission surface 26 is a line contact, the surrounding lubricant is drawn in and the lubricant is sufficiently supplied to the contact portion. In that respect, the same effects as those in the case of the point contact described above can be obtained.

  The convex spherical surface and the convex cylindrical surface mentioned above as examples of the convex curved surface are both a part of the rotating body and are symmetrical, but it is not always necessary to have such a symmetrical shape. Moreover, it can also be set as what is called a crowning shape. In short, as long as a clearance that opens in a wedge shape toward the outer periphery of the torque transmission member 30 can be formed between the outer surface 34 of the torque transmission member 30 and the outer torque transmission surface 26 of the outer joint member 20, it is arbitrary. It can be made into the shape. The outer shape of the torque transmission member 30 is not limited to a circle, but may be a polygon, a rectangle, or any other shape. In this sense, a button shape does not specify any external shape.

  The inner joint member 10, the outer joint member 20, and the torque transmission member 30 are all formed of a metal material such as steel. The inner torque transmission surface 16 of the inner joint member 10 and the outer torque transmission surface 26 of the outer joint member 20 are preferably subjected to induction hardening or other surface hardening treatment to improve wear resistance. When the joint rotates with the operating angle taken, the torque transmission member 30 slides on the outer torque transmission surface 26 in the direction of the rotation axis PP of the outer joint member 20. At this time, slip occurs between the outer torque transmission surface 26 and the torque transmission member 30. Therefore, by providing a hardened layer by surface hardening treatment at least in a region where the torque transmitting member 30 slides in the outer torque transmitting surface 26, in addition to suppressing wear of the outer torque transmitting surface 26, the outer joint member 20 Torsional strength can be ensured.

  The constant velocity universal joint is used by filling the space between the inner joint member 10 and the outer joint member 20 with a lubricant such as grease. Then, boots are attached to prevent the lubricant from leaking and to prevent water and other foreign substances from entering. Such boots for constant velocity universal joints are well known, and thus detailed description thereof is omitted.

  In the above-described configuration, the inner joint member 10 and the outer joint member 20 are capable of angular displacement, axial variation, and displacement in which both are combined. The angular displacement is a relative motion of the inner joint member 10 and the outer joint member 20 that are bent around the joint center O in the longitudinal section (see FIG. 2). The axial displacement is a relative movement in which the inner joint member 20 moves in the direction of the rotation axis PP of the outer joint member 10.

  Since the outer surface 34 of the torque transmission member 30 can slide along the outer torque transmission surface 26 in the axial direction of the outer joint member 20, the constant velocity universal joint can also be plunge. The plunging amount corresponds to the distance between the pair of clips 25 indicated by symbol A in FIG. That is, when the torque transmission member 30 abuts on the clip 25, further axial movement is prevented. If the distance A between the clips 25 is reduced and both sides of the torque transmitting member 30 in the axial direction are restricted by the clips 25, it can be used as a fixed type constant velocity universal joint that does not allow plunging.

  When the joint rotates with the operating angle θ taken as shown in FIG. 2, the inner torque transmission surface 16 of the inner joint member 10 and the outer torque transmission surface 26 of the outer joint member 20 via the torque transmission member 30. Torque is transmitted between the two. The torque transmission member 30 during torque transmission reciprocates in the direction of the rotation axis PP of the outer universal joint 20 with a constant stroke corresponding to the operating angle. Due to the friction that occurs, a force that rotates (rotates) the torque transmission member 30 about its center line acts. The rotation of the torque transmitting member 30 does not cause a problem such as the progression of uneven wear due to uneven contact, and also advantageously works to draw in the lubricant.

  Since the inner surface 32 of the torque transmission member 30 and the inner torque transmission surface 16 are in spherical contact, the surface pressure at the contact portion is not high. The outer surface 34 and the outer torque transmission surface 26 of the torque transmission member 30 are in point contact or line contact. However, as described above, the surface pressure is not so high by appropriately setting the radius of curvature of the outer surface 34. In addition, a gap that opens in a wedge shape toward the outer periphery of the torque transmission member 30 can be formed. Abundant lubricant is supplied to the sliding contact portion by the drawing action of the lubricant by the gap formed in this way. Therefore, it is possible to suppress the wear at the sliding contact portion, to achieve the long life of the constant velocity universal joint and to reduce the torque. In addition, generation of vibrations and abnormal noise can be prevented, and NVH characteristics when mounted on a vehicle can be improved.

  Next, the material of the torque transmission member 30 will be described. Examples of general materials for the torque transmission member 30 include steel, brass, aluminum alloy, and the like. However, as a material constituting at least the surface of the torque transmission member 30, the inner joint member 10 and / or the outer joint member 20 may be used. Use metal with low coefficient of friction. Further, from the viewpoint of preventing wear, it is preferable that the metal constituting at least the surface of the torque transmission member 30 is different from the inner joint member 10 and / or the outer joint member 20 and avoids “toggle”.

  As an example of such a metal material, the already exemplified brass can be cited. The main components (mass%) of the high strength brass casting type 1 CAC301 are Al: 0.5 to 1.5, Fe: 0.5 to 1.5, Mn: 0.1 to 1.5, Zn: 33. 0 to 42.0, the balance is Cu. In the case of the high-strength brass casting type 1 CAC301, the yield strength is about 400 MPa. When the yield strength is 400 MPa, if the maximum contact surface pressure of Hertz contact is 667 MPa or less obtained by dividing the yield strength by 0.6, plastic deformation does not occur macroscopically. Furthermore, as means for improving the yield strength of the contact surface layer, for example, an ECAP (Equal Channel Angular Pressing) method can be cited. The ECAP method is a plastic processing method in which relatively large materials can be uniformly and plastically deformed to refine the crystal grain size from submicron to nanometric range, and the cross-sectional shape of the material is the same before and after processing. Is a feature. For example, ECAP can be applied to a rod-shaped material before the torque transmission member is processed into a final button shape.

  Further, since the torque transmission member 30 is a component that slides with respect to the inner joint member 10 and the outer joint member 20, the Young's modulus (longitudinal elastic modulus) is desirably 35 GPa or more. If the Young's modulus is less than 35 GPa, it may be deformed when a large frictional force is applied to the sliding portion. As is well known, the Young's modulus is the vertical stress (stress generated in the direction perpendicular to the cross section) and longitudinal strain (ratio between the axial deformation and the original length when a load is applied in the axial direction of the material). A ratio.

  The entire torque transmission member 30 may be formed of a metal having a low coefficient of friction with respect to the inner joint member 10 and / or the outer joint member 20, or only the surface that slides with respect to the inner joint member 10 or the outer joint member 20. May be formed of a metal having a low coefficient of friction with respect to the inner joint member 10 and / or the outer joint member 20. Further, all or a part of such a surface may be formed of a metal having a low coefficient of friction with respect to the inner joint member 10 and / or the outer joint member 20. For example, a part of the torque transmission member 30 may be formed of a metal having a low coefficient of friction with respect to the inner joint member 10 and / or the outer joint member 20, and a portion not involved in the sliding may be another, for example, an inexpensive metal. .

  When only the surface of the torque transmission member 30 is made of such a metal, as an example, there is a method of covering the surface of the base material of the torque transmission member 30 with the metal. Specific means for coating include plating, thermal spraying, chemical vapor deposition, physical vapor deposition and the like. Examples of plating include nickel (alloy) plating and chromium (alloy) plating. Examples of metals used for thermal spraying include metals such as nickel alloys and nickel-chromium alloys, and non-metals such as chromium oxide and chromium carbide.

  Alternatively, there is a method of combining different materials. Examples of combinations are shown in FIGS. 7, only the surface (surface) that contacts the inner joint member 10 and the outer joint member 20 is formed of a metal having a low coefficient of friction with respect to the inner joint member 10 and / or the outer joint member 20, and the inside is different from that. This is an example of an inexpensive metal such as a carbon steel SC for mechanical structure or a rolled steel SS for general structure. Specifically, an inner surface 32 that contacts the inner torque transmission surface 16 of the inner joint member 10 and a surface 34 that contacts the outer torque transmission surface 20 of the outer joint member 20 are provided on the inner joint member 10 and the outer joint member 20. A metal layer 38a having a low coefficient of friction is provided on the surface. Therefore, the torque transmission member 30 of FIG. 7 has a three-layer cross section. FIG. 8 shows that only the center of the torque transmitting member 30 is made of a metal 38b having a low coefficient of friction with respect to the inner joint member 10 and / or the outer joint member 20, and the surroundings are other inexpensive metals such as carbon for machine structure. This is an example of steel SC or general structural rolled steel SS. The torque transmission member shown in FIGS. 7 and 8 can be manufactured by machining or forging.

  Using a Sabang friction and wear tester, the friction was measured, and a test for confirming the change with time was performed (see FIG. 9). The test form is a one-way slide in which a flat sample is pressed against the top of a rotating ring. The material of the sample is a high-strength brass casting type 1 CAC301 (Example) and a non-tempered carbon steel for mechanical structure S30C (Comparative Example). The ring was made of high carbon chrome bearing steel SUJ2 and subjected to standard heat treatment (quenching and tempering) of the rolling bearing. As a lubricating method, a viscosity grade VG2 lubricating oil (Mobil Velocity Oil No. 3 (VG2)) was immersed in a felt pad at room temperature and pressed against the lower part of the ring. The surface roughness (JIS B 0601: 2001) was 0.3 μmRa for the sample and 0.02 μmRa for the sliding surface (cylindrical surface) of the ring. The rotation direction of the ring was made parallel to the surface roughness of the sample. The maximum contact surface pressure was 125 MPa, the rotational peripheral speed of the ring was 3.8 m / s, and the test time was 10 min (sliding distance 2260 m). The displacement of the sample was detected by a strain cage, and the dynamic friction coefficient was calculated.

  FIG. 9 shows the change over time in the friction coefficient. In the example, the friction coefficient was obviously smaller from the beginning than in the comparative example. The coefficient of friction at the end of the test was about 0.002 in the example, and about 0.025 in the comparative example (about 12.5 times). From this result, it can be said that the embodiment has a small frictional resistance, and therefore the sliding heat generation is reduced.

  Further, by providing the torque transmission member 30 with a lubricant holding mechanism, it is possible to promote lubrication of the contact portion, prevent wear and damage, and reduce frictional force. FIG. 10 shows an example of a lubricant holding mechanism 40 in the form of a groove 42. Although the number of the grooves 42 is arbitrary, FIG. 10 (A) shows an example of one line and FIG. 10 (B) shows an example of two orthogonal lines. Of course, it is also possible to set it as a radial groove | channel of 3 or more. In addition to the groove 42, a lubricant reservoir 44 may be provided. FIG. 10C shows an example in which a lubricant reservoir 44 is provided at the intersection of the orthogonal grooves 42. The lubricant holding mechanism 40 shown in FIG. 10 is an example in the case of being provided on the outer side surface 34 that contacts the outer joint member 20 of the torque transmission member 30, but is provided on the inner side surface 32 that contacts the inner joint member 10. Alternatively, it may be provided on both sides.

  FIG. 11 shows an example of the lubricant holding mechanism 40 in the form of a minute dimple 46. As shown in the figure, the lubricant is held in the micro dents 46 by randomly forming innumerable micro dents 46 having a depth of several tens of microns. The micro dent 46 can be formed by barrel processing, shot blasting, shot peening or the like.

  The constant velocity universal joint of the present invention can be used not only for a drive shaft and a propeller shaft in an automobile drive system, but also for an automobile steering shaft. Furthermore, it can be widely used not only for automobiles but also for power transmission systems of various industrial machines.

DESCRIPTION OF SYMBOLS 10 Inner joint member 12 Through-hole 14 Serration hole 16 Inner torque transmission surface 18 Shaft 20 Outer joint member 22 Mouse part 24 Hole 25 Clip 26 Outer torque transmission surface 28 Stem part 30 Torque transmission member 32 Inner side 34 Outer side 36 Wedge space 38a , 38b Low friction metal 40 Lubricant holding mechanism 42 Groove 44 Small dent (dimple)
46 Lubricant pool

Claims (9)

An outer joint member in which a cross section perpendicular to the rotation axis has a hexagonal hole, and an inner wall surface of the hole is a flat surface parallel to the rotation axis;
An inner joint member housed in the hole and having an outer peripheral surface of a convex spherical shape;
A plurality of torque transmission members interposed between the inner wall surface of the outer joint member and the outer peripheral surface of the inner joint member, and the inner joint member or the outer side of the surfaces of the torque transmission member A constant velocity universal joint in which a material constituting a portion in contact with the joint member is a metal having a yield strength of 100 MPa or more and a low friction coefficient with respect to the inner joint member or the outer joint member or both.   The constant velocity universal joint according to claim 1, wherein the torque transmission member is covered with the metal.   The constant velocity universal joint according to claim 1 or 2, wherein the torque transmission member has a multilayer structure and the outermost layer is the metal.   4. The constant velocity universal joint according to claim 1, wherein the central portion and the periphery of the torque transmission member are made of different materials, and the material of the central portion is the metal.   The constant velocity universal joint according to any one of claims 1 to 4, wherein the metal is a copper alloy.   The constant velocity universal joint according to claim 1, further comprising a lubricant holding mechanism on a surface of the torque transmission member.   The constant velocity universal joint according to claim 6, wherein the lubricant holding mechanism is on a surface of the torque transmission member that contacts the inner joint member.   The constant velocity universal joint according to claim 6, wherein the lubricant holding mechanism is on a surface of the torque transmission member that contacts the outer joint member.   The constant velocity universal joint according to claim 6, 7 or 8, wherein a lubricant reservoir is provided in addition to the lubricant holding mechanism.

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