Sliding type constant velocity universal joint and method for manufacturing same

Abstract

This method includes performing gentle injection processing (shot blasting) on at least one surface among a cylindrical inner peripheral surface 6 of an outer joint member 2 of a double offset type constant velocity universal joint 1, a surface of a track groove 7 of the outer joint member 2, a spherical outer peripheral surface 8 of an inner joint member 3, a surface of a track groove 9 of the inner joint member 3, a spherical surface part 13 of an outer peripheral surface of a cage 5, and a spherical surface part 15 of an inner peripheral surface of the cage 5 such that a forged surface, a rolled surface or a machined surface remains at a bottom part 22 of a valley part of a roughness curve.

Description

Sliding constant velocity universal joint and manufacturing method thereof

[0001] The present invention relates to a sliding type constant velocity universal joint and a method for manufacturing the same.

[0002] Constant velocity universal joints used in automobile drive shafts and propeller shafts can be broadly divided into sliding types that allow both angular displacement and relative axial movement between two shafts, and fixed types that allow angular displacement between two shafts but do not allow relative axial movement between the two shafts.

[0003] Known sliding type constant velocity universal joints include double offset constant velocity universal joints (DOJs) that use balls as rolling elements for transmitting rotational torque, and tripod constant velocity universal joints (TJs) that use rollers as rolling elements. For example, Patent Document 1 listed below discloses a double offset constant velocity universal joint that is lightweight and compact by increasing the number of balls from six to eight. Patent Document 2 listed below also discloses a double offset constant velocity universal joint that has a maximum operating angle of 30° or more and is even lighter and more compact.

[0004] Compared to tripod-type constant velocity universal joints, double offset-type constant velocity universal joints have the advantages of less circumferential backlash, better responsiveness, and lower manufacturing costs, but they have the disadvantage of greater sliding resistance and greater susceptibility to vehicle vibrations, particularly engine vibrations during idling. Therefore, various countermeasures for idling vibrations have been studied for double offset-type constant velocity universal joints. For example, Patent Document 3 listed below discloses a technology for absorbing idling vibrations by providing a gap between the outer peripheral surface of the inner ring and the inner peripheral surface of the cage.

[0005] Japanese Patent Laid-Open No. 10-73129 Japanese Patent Laid-Open No. 2007-85488 Japanese Patent Laid-Open No. 2013-231518

[0006] However, as vehicle ride comfort continues to improve, the NVH (Noise, Vibration, Harshness) characteristics required of constant velocity universal joints are becoming more stringent. Because double offset constant velocity universal joints inevitably experience sliding contact between their components due to their structure, even if measures such as those shown in Patent Document 3 are implemented, it is difficult to reduce the sliding resistance to the same level as tripod-type sliding constant velocity universal joints, in which the components primarily contact each other by rolling. This sliding resistance problem, particularly the problem of idling vibration, has become a bottleneck, and in recent years the application range of double offset constant velocity universal joints has been largely limited to locations that are less susceptible to engine vibration (e.g., rear drive shafts).

[0007] In recent years, the electrification of vehicles has progressed, with an increase in electric vehicles (hereinafter referred to as EVs) that run solely on the power of electric motors and hybrid vehicles (hereinafter referred to as HEVs) that run on the power of both electric motors and engines. Because electric motors have superior responsiveness compared to engines, constant velocity universal joints that transmit the power of electric motors are also required to have low circumferential backlash and excellent responsiveness. Furthermore, since EVs do not generate engine vibrations and HEVs essentially stop their engines while the vehicle is stopped (idling), these vehicles do not experience the problem of idling vibration, which is the main factor limiting the application of double offset constant velocity universal joints. From these perspectives, the adoption of double offset sliding constant velocity universal joints, which have low circumferential backlash and excellent responsiveness, is being considered for use in EVs and HEVs as sliding constant velocity universal joints for power transmission systems such as drive shafts and propeller shafts.

[0008] On the other hand, in a sliding-type constant velocity universal joint, an axial load (induced thrust) is generated due to frictional forces between internal parts when rotating through a working angle. This induced thrust resonates with the vehicle body, which can cause various vibration problems such as swaying and muffled noise when starting. Such problems are particularly noticeable in EVs and HEVs, which are known for their quietness. Therefore, if the induced thrust can be reduced, double-offset constant velocity universal joints may be suitable for use in EVs and HEVs.

[0009] Therefore, an object of the present invention is to reduce the induced thrust of a double offset type constant velocity universal joint so that it can be suitably used in the power transmission system of a vehicle (EV or HEV) that uses an electric motor as a drive source.

[0010] As described above, induced thrust is an axial load generated due to frictional forces between the internal components of a sliding-type constant velocity universal joint. Specifically, as shown in FIG. 9 , the induced thrust is the result of the axial resistance Qx resulting from the frictional forces at the contact points between the track grooves 101a of the outer joint member 101 and the balls 102, and the axial resistance Hx resulting from the frictional forces at the contact points between the outer spherical surface 103a of the cage 103 and the cylindrical inner peripheral surface 101b of the outer joint member 101. FIG. 10 shows the results of mechanical analysis of the induced thrust Fx (= Qx + Hx) in a double offset constant velocity universal joint having eight balls. As shown in the figure, it was previously believed that a double offset constant velocity universal joint would mainly generate induced thrust of order components equal in number to the number of balls (eight in the figure).

[0011] Meanwhile, Figure 11 shows the results of measuring the actual induced thrust of an eight-ball double-offset constant velocity universal joint. In this test, simulating a vehicle starting situation, a torque of 900 Nm was input to the outer joint member of the constant velocity universal joint at a rotation speed of 150 rpm, while the working angle was changed from 0° to 12° at a rate of 10.7° / min. The axial load (induced thrust) applied to the outer joint member was measured. The X axis in Figure 11 represents the frequency of vibration generated in the constant velocity universal joint, the Y axis represents the working angle of the constant velocity universal joint, and the Z axis represents the magnitude of the axial load (induced thrust) applied to the outer joint member. The peak appearing at 2.5 Hz in the figure is the first-order component of the induced thrust (a vibration component that occurs once per rotation of the constant velocity universal joint), the peak appearing at 5 Hz is the second-order component, the peak appearing at 7.5 Hz is the third-order component, ..., and the peak appearing at 20 Hz is the eighth-order component. From the actual measurement results shown in the figure, it can be confirmed that the induced thrust not only has an eighth-order component, but also many other order components, with the first-order component appearing particularly prominently.

[0012] As described above, the causes of the generation of induced thrusts of various orders are thought to be as follows: As described above, the induced thrust Fx is the resultant force of the axial resistance Qx between the balls and the outer joint member and the axial resistance Hx between the cage and the outer joint member (see FIG. 9 ). The axial resistances Qx and Hx are each the resultant force of the loads generated in each phase. Note that "each phase" refers to the phase of each ball and each track groove in contact with it (first to eighth phases in the case of an eight-ball double offset constant velocity universal joint) at the contact portion between the track grooves of the outer joint member and the balls, and to the phase of each spherical portion between the track grooves of the outer joint member and each column portion between the pockets of the cage in contact with them (first to eighth phases in the case of an eight-ball double offset constant velocity universal joint).

[0013] Here, the results of a mechanical analysis of the axial loads applied to the track grooves of each phase of the outer joint member and their resultant force (Qx) in an eight-ball double-offset constant velocity universal joint are shown in Figures 12 and 13. Figure 12 shows the axial components of the track loads of each phase and their resultant force in an ideal state where all components have uniform dimensions and uniform surface properties in all phases. In this case, the axial loads (see dotted line) in the tracks of all phases are uniform, and the resultant force has a regular shape (see solid line) with a strong presence of a specific order component (eighth order component in the illustrated example). However, in reality, the contact state of the internal parts becomes non-uniform due to variations in the dimensions of each part and variations in the surface properties of the contact areas. Therefore, as shown in Figure 13, variations occur in the axial loads generated in the tracks of each phase (see dotted line), and the resultant force has an irregular shape (see solid line). As a result, the induced thrust (Fx = Qx + Hx) generates various order components, including the first order component (see Figure 11). When various order components of induced thrust are generated in this way, the number of resonance points with the vehicle body increases, increasing the possibility of causing noise and vibration problems.

[0014] From the above viewpoints, the inventors have considered that it may be possible to suppress each order component of induced thrust by equalizing the axial load generated at the contact portion of each phase of a double offset constant velocity universal joint. Specifically, since it is well known that the roughness of the contact surface affects the frictional force when the contact portion between parts is boundary lubricated, they considered that suppressing the variation in surface roughness between phases would be effective in equalizing the axial load (i.e., frictional force) at the contact portion of each phase.

[0015] Therefore, the present invention provides a method for manufacturing a sliding type constant velocity universal joint including an outer joint member having a plurality of linear track grooves formed on a cylindrical inner peripheral surface thereof, an inner joint member having a plurality of linear track grooves formed on a spherical outer peripheral surface thereof, a plurality of balls arranged between the track grooves of the outer joint member and the track grooves of the inner joint member, and a cage having an outer peripheral surface formed with a spherical portion which comes into sliding contact with the cylindrical inner peripheral surface of the outer joint member and an inner peripheral surface formed with a spherical portion which comes into sliding contact with the spherical outer peripheral surface of the inner joint member, and holding the plurality of balls, the method comprising the steps of: forming at least one surface of the cylindrical inner peripheral surface of the outer joint member, the surface of the track grooves of the outer joint member, the spherical outer peripheral surface of the inner joint member, the surface of the track grooves of the inner joint member, the spherical portion of the outer peripheral surface of the cage, and the spherical portion of the inner peripheral surface of the cage by forging, rolling, or machining; and a step of subjecting the surface to blasting so that a forged surface, a rolled surface or a machined surface remains at the bottom of the valleys of the roughness curve of the surface.

[0016] The present invention also provides a sliding type constant velocity universal joint including an outer joint member having a plurality of linear track grooves formed on a cylindrical inner peripheral surface thereof, an inner joint member having a plurality of linear track grooves formed on a spherical outer peripheral surface thereof, a plurality of balls arranged between the track grooves of the outer joint member and the track grooves of the inner joint member, and a cage having an outer peripheral surface formed with a spherical portion in sliding contact with the cylindrical inner peripheral surface of the outer joint member and an inner peripheral surface formed with a spherical portion in sliding contact with the spherical outer peripheral surface of the inner joint member, and holding the plurality of balls, The present invention provides a sliding type constant velocity universal joint, wherein the peaks of the roughness curve of at least one of the cylindrical inner peripheral surface of the outer joint member, the surface of the track groove of the outer joint member, the spherical outer peripheral surface of the inner joint member, the surface of the track groove of the inner joint member, the spherical portion of the outer peripheral surface of the cage, and the spherical portion of the inner peripheral surface of the cage are jet-blasted surfaces, and the bottoms of the valleys of the roughness curve of the above surfaces are either forged surfaces, rolled surfaces, or machined surfaces.

[0017] In this way, in the present invention, the contact surfaces between the components are subjected to blasting (e.g., shot blasting). This blasting does not actively form new recesses (valleys), but is gentle blasting that leaves the processed surface (forged surface, rolled surface, or machined surface) before blasting at the bottom of the valleys in the roughness curve of the contact surface. By performing this gentle blasting, the peaks in the roughness curve of the contact surface are removed or crushed by the blasting, thereby reducing the surface roughness. This suppresses variations in the surface properties between phases and equalizes the axial load generated at the contact points of each phase, thereby reducing each order component of the induced thrust.

[0018] The roughness parameter Rsk of the surface subjected to the gentle blasting is preferably a negative value, and the roughness parameter Rp of the surface subjected to the gentle blasting is preferably 2 or less.

[0019] For example, the track groove surfaces and cylindrical inner peripheral surfaces of outer joint members and the track groove surfaces of inner joint members are often formed by forging from the viewpoint of manufacturing costs. Such forged surfaces have a high surface roughness, which tends to result in large variations in axial load for each phase. Therefore, when the surface of the base material is a forged surface, it is particularly preferable to suppress variations in roughness by performing the above-described gentle blasting. In this case, the bottoms of the valleys in the roughness curve of the blasted surface are the forged surface.

[0020] The sliding type constant velocity universal joint can be suitably incorporated into the power transmission system of a vehicle using an electric motor as a drive source. Specifically, a wheel drive device can be obtained that includes an electric motor, wheels, and a power transmission system that transmits the driving force of the electric motor to the wheels via the sliding type constant velocity universal joint.

[0021] The blasting may be, for example, shot blasting, or may be performed using an elastic medium at least partly made of an elastomer.

[0022] As described above, according to the present invention, it is possible to reduce the induced thrust of a double offset sliding constant velocity universal joint which has little backlash and excellent responsiveness, and therefore this can be suitably used in the power transmission systems of EVs and HEVs.

[0023] FIG. 1 is an axial sectional view of a double offset sliding type constant velocity universal joint according to one embodiment of the present invention. FIG. 2 is an axial sectional view of the sliding type constant velocity universal joint of FIG. 1. FIG. 3 is an enlarged sectional view of the surface of a track groove before blasting (shot blasting). FIG. 4 is an enlarged sectional view of the surface of a track groove after blasting (shot blasting). FIG. 5 is a plan view of an electric vehicle (EV) equipped with the constant velocity universal joint of FIG. 1. FIG. 6 is a roughness curve (left), load curve (center), and amplitude distribution curve (right) of the surface of the track groove of an outer joint member before blasting. FIG. 7 is a roughness curve (left), load curve (center), and amplitude distribution curve (right) of the surface of the track groove of an outer joint member after blasting. FIG. 8 is a graph showing measurement results of induced thrust in a double offset constant velocity universal joint. FIG. 9 is a sectional view showing a portion where an axial load is applied when a double offset constant velocity universal joint rotates at a working angle. FIG. 11 is a diagram showing analysis results of induced thrust in a double offset constant velocity universal joint. FIG. 12 is a diagram showing actual measurement results of induced thrust in a double offset constant velocity universal joint. 1A and 1B are diagrams illustrating analysis results of axial loads applied to track grooves of an outer joint member (when the axial loads applied to the track grooves of each phase are uniform); and 1C are diagrams illustrating analysis results of axial loads applied to track grooves of an outer joint member (when the axial loads applied to the track grooves of each phase are non-uniform).

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a sliding type constant velocity universal joint according to the present invention will be described in detail below with reference to the drawings.

[0025] 5 shows an electric vehicle (EV) that runs solely on the power of an electric motor. This electric vehicle has a front wheel drive unit 61 that drives the front wheels 51 and a rear wheel drive unit 62 that drives the rear wheels 52. Each wheel drive unit 61, 62 has a drive unit 63 including an electric motor and a drive shaft 64 as a power transmission system that transmits the driving force of the electric motor to the front wheels 51 or rear wheels 52. In the illustrated example, the drive unit 63 of the front wheel drive unit 61 is connected to the left and right front wheels 51 via left and right drive shafts 64, and the drive unit 63 of the rear wheel drive unit 62 is connected to the left and right rear wheels 52 via left and right drive shafts 64.

[0026] Each drive shaft 64 has, for example, a sliding type constant velocity universal joint 1 provided on the inboard side (drive unit 63 side), a fixed type constant velocity universal joint 65 provided on the outboard side (wheels 51, 52 side), and an intermediate shaft 66 connecting both constant velocity universal joints 1, 65. A double offset constant velocity universal joint according to one embodiment of the present invention is applied as this sliding type constant velocity universal joint 1. The configuration of this sliding type constant velocity universal joint 1 will be described in detail below.

[0027] 1 and 2 , a sliding type constant velocity universal joint 1 of this embodiment includes a cup-shaped outer joint member 2 having one open axial end (the left end in FIG. 1 ), an inner joint member 3 disposed on the inner periphery of the outer joint member 2, a plurality of balls 4, and a cage 5 for holding the plurality of balls 4. An internal part 10 consisting of the inner joint member 3, the balls 4, and the cage 5 is housed on the inner periphery of the outer joint member 2 so as to be axially displaceable. An end of an intermediate shaft 66 (see FIG. 5 ) is coupled by spline fitting to an axial hole 11 of the inner joint member 3. In the following description, the axial direction of the outer joint member 2 and the inner joint member 3 in a state where the operating angle is 0° as shown in FIG. 1 is referred to as the "axial direction," the bottom side of the outer joint member 2 (right side in FIG. 1 ) in the axial direction is referred to as the "joint deep side," and the opening side of the outer joint member 2 (left side in FIG. 1 ) is referred to as the "joint opening side."

[0028] Axial-direction extending linear track grooves 7 are formed at equal intervals in a plurality of positions in the circumferential direction on the cylindrical inner peripheral surface 6 of the outer joint member 2. Axial-direction extending linear track grooves 9 are formed at equal intervals in a plurality of positions in the circumferential direction on the spherical outer peripheral surface 8 of the inner joint member 3. One ball 4 is disposed between each of the track grooves 7 of the outer joint member 2 and the track groove 9 of the inner joint member 3, which are opposed in the radial direction, to transmit rotational torque between the two joint members 2, 3.

[0029] The cage 5 is provided with a plurality of pockets 12, and each pocket 12 holds one ball 4. The outer peripheral surface of the cage 5 is formed with a spherical portion 13 that slides against the cylindrical inner peripheral surface 6 of the outer joint member 2, and tapered surfaces 14 that are provided on both axial sides of the spherical portion 13. The inner peripheral surface of the cage 5 is formed with a spherical portion 15 that slides against the spherical outer peripheral surface 8 of the inner joint member 3. In this embodiment, as shown in Fig. 2, the number of track grooves 7, 9, balls 4, and pockets 12 is eight, but the number of these may be six, for example.

[0030] The center of curvature O1 of the spherical portion 13 on the outer peripheral surface of the cage 5 and the center of curvature O2 of the spherical portion 15 on the inner peripheral surface (i.e., the center of curvature of the spherical outer peripheral surface 8 of the inner joint member 3) are offset by an equal distance F on opposite axial sides from the joint center O (the intersection of a plane passing through the centers of all the balls 4 and the axes of both joint members 2, 3) (see FIG. 1 ). In the illustrated example, the center of curvature O1 of the spherical portion 13 on the outer peripheral surface of the cage 5 is offset toward the back of the joint from the joint center O, and the center of curvature O2 of the spherical portion 15 on the inner peripheral surface of the cage 5 is offset toward the joint opening from the joint center O. As a result, when an operating angle is applied between the outer joint member 2 and the inner joint member 3, the balls 4 held in the pockets 12 of the cage 5 are always maintained within the plane bisecting the operating angle regardless of the operating angle, thereby ensuring uniform velocity between the outer joint member 2 and the inner joint member 3. Furthermore, the balls 4 held by the cage 5 roll on the track grooves 7 of the outer joint member 2, thereby allowing the internal part 10 to move axially relative to the outer joint member 2. Conversely to the above, the center of curvature O1 of the spherical portion 13 on the outer peripheral surface of the cage 5 may be located on the joint opening side, and the center of curvature O2 of the spherical portion 15 on the inner peripheral surface of the cage 5 may be located on the joint inner side.

[0031] The outer joint member 2 is manufactured through a forging process, a turning process, a rolling process, a heat treatment process, and a grinding process. In the forging process, an original outer joint member is formed by die-molding. In the turning process, the outer circumferential surface of the original outer joint member is turned. In the rolling process, male splines are formed on the shaft portion of the original outer joint member. In the heat treatment process, the original outer joint member is subjected to heat treatment (e.g., induction hardening and tempering). In the grinding process, the outer circumferential surface of the original outer joint member is ground. When manufactured according to these procedures, the cylindrical inner circumferential surface 6 and the track grooves 7 of the outer joint member 2 become forged surfaces.

[0032] The inner joint member 3 is manufactured through a forging process, a turning process, a broaching process, a heat treatment process, and a grinding process. In the forging process, a substantially cylindrical original form of the inner joint member is molded. In the turning process, the inner and outer circumferential surfaces of the original form of the inner joint member are turned. In the broaching process, a female spline is formed on the inner periphery of the original form of the inner joint member. In the heat treatment process, the original form of the inner joint member is heat treated (for example, carburized, quenched, and tempered). In the grinding process, the spherical outer circumferential surface of the original form of the inner joint member (regions excluding the track grooves) is ground. When manufactured through these procedures, the spherical outer circumferential surface 8 of the inner joint member 3 becomes a ground surface, the track grooves 9 become a forged surface, and the inner circumferential surface (female spline) becomes a machined surface.

[0033] The cage 5 is manufactured through a forging process, a turning process, a pocket punching process, a heat treatment process, and a grinding process. In the forging process, a substantially cylindrical cage original form is formed by die-molding. In the turning process, the inner and outer peripheral surfaces of the cage original form are turned. In the pocket punching process, the cage original form is punched in the radial direction to form the pockets 12. In the heat treatment process, the cage original form is subjected to heat treatment (e.g., carburizing, quenching, and tempering). In the grinding process, the spherical portion 13 on the outer peripheral surface, the spherical portion 15 on the inner peripheral surface, and the inner surfaces of the pockets 12 of the cage original form are ground. When manufactured using this procedure, the spherical portion 13 on the outer peripheral surface, the spherical portion 15 on the inner peripheral surface, and the inner surfaces of the pockets 12 of the cage 5 become ground surfaces, and the other areas become pocket punched surfaces or turned surfaces.

[0034] Of the surfaces of the components (outer joint member 2, inner joint member 3, and cage 5) of the sliding type constant velocity universal joint 1 prepared by the above procedure, excluding the balls 4, the contact surfaces that come into contact with other components are subjected to blasting. Specifically, blasting is performed on at least one surface of the cylindrical inner circumferential surface 6 of the outer joint member 2, the surfaces of the track grooves 7 of the outer joint member 2, the spherical outer circumferential surface 8 of the inner joint member 3, the surfaces of the track grooves 9 of the inner joint member 3, the spherical portion 13 on the outer circumferential surface of the cage 5, and the spherical portion 15 on the inner circumferential surface of the cage 5. The blasting is a processing method in which particles (media) of several μm to several mm in size are sprayed by compressed air or mechanical centrifugal force and collided with the processed surface. In this embodiment, shot blasting is performed on the surfaces of the track grooves 7 of the outer joint member 2 by spraying media.

[0035] Before shot blasting, the surface of the track groove 7 is a forged surface, and as shown in FIG. 3, numerous minute irregularities are formed. By spraying media onto this forged surface, the peaks of the roughness curve are crushed or removed, as shown in FIG. 4. This shot blasting does not actively form recesses in the forged surface, but rather removes only the peaks of the roughness curve, leaving the bottoms of the valleys unformed. After such gentle shot blasting, the surface of the track groove 7 has peaks 21 of the roughness curve processed by shot blasting (blast-processed surface), while the bottoms 22 of the valleys of the roughness curve are not subjected to shot blasting and remain as the forged surface.

[0036] When shot blasting is performed using conventional metal media, the peaks of the surface roughness curve are removed while the valleys are deepened, making it difficult to obtain the surface texture shown in Figure 4. Therefore, for example, by using elastic media, at least a portion of which is made of elastomer, it is possible to perform gentle shot blasting that removes only the peaks of the peaks of the roughness curve as described above. For example, particles made of abrasives bonded with elastomer can be used as elastic media. In addition to changing the media material as described above, the gentle shot blasting described above can also be performed by changing the size and spray speed of the media.

[0037] The surface (surface of the track groove 7) that has been subjected to the above-described gentle shot blasting satisfies at least one of the following: Rsk is a negative value, and Rp is 2 or less. In addition to the above conditions, it is desirable to satisfy at least one of Ra being 1.5 or less, preferably 0.6 or less, and Rz being 10 or less, preferably 6 or less. In this embodiment, the surface of the track groove 7 satisfies all of the above conditions. It is not necessary to set lower limits for the above surface roughness parameters, but, for example, the lower limit for Rsk is -3, the lower limit for Rp is 0.5, the lower limit for Ra is 0.2, and the lower limit for Rz is 1.0.

[0038] Note that Rsk, Rp, Ra, and Rz are the skewness, maximum peak height, arithmetic mean height, and maximum height of the roughness curve over the reference length as specified in JIS B 0601-2013, respectively. Rsk is positive when the amplitude distribution curve has many peaks relative to the mean line of the roughness curve, and negative when it has many valleys. Measurement of these parameters is performed at the contact point between each part, over a range of 4 mm in total, consisting of five sections of 0.8 mm reference length along the axial direction.

[0039] When torque is input from the electric motor to the outer joint member 2 while the sliding-type constant velocity universal joint 1 has an operating angle, the torque is transmitted to the inner joint member 3 via the cage 5 and the balls 4. At this time, axial sliding resistance occurs at the contact portions between the components, causing an axial load (induced thrust) to be generated in the outer joint member 2. However, the axial load is not uniform in each phase and varies due to variations in the dimensions and surface properties of the components. In this embodiment, as described above, the surface of the track grooves 7 of the outer joint member 2 is subjected to gentle shot blasting, thereby reducing the surface roughness of this surface and suppressing variations in the surface properties among the phases. This uniformizes the axial load generated at the contact portions between the track grooves 7 and the balls 4 in each phase, thereby reducing each order component of the induced thrust.

[0040] The present invention is not limited to the above-described embodiment. Other embodiments of the present invention will be described below, but redundant description of the same points as those in the above-described embodiment will be omitted.

[0041] In the above embodiment, the track grooves 7 of the outer joint member 2 are subjected to gentle blasting (shot blasting). However, instead of or in addition to this, the gentle blasting may be applied to one or more locations among the cylindrical inner peripheral surface 6 of the outer joint member 2, the spherical outer peripheral surface 8 of the inner joint member 3, the surfaces of the track grooves 9 of the inner joint member 3, the spherical portions 13 on the outer peripheral surface of the cage 5, and the spherical portions 15 on the inner peripheral surface of the cage 5. For example, when the gentle blasting is applied to the spherical outer peripheral surface 8 of the inner joint member 3, the spherical portions 13 on the outer peripheral surface of the cage 5, and the spherical portions 15 on the inner peripheral surface, the peaks of the peaks in the roughness curves of these surfaces become blasted surfaces, and the bottoms of the valleys become machined surfaces, specifically, ground surfaces. Furthermore, when the gentle blasting is applied to the surfaces of the track grooves 9 of the inner joint member 3, the peaks of the peaks in the roughness curves of this surface become blasted surfaces, and the bottoms of the valleys become forged surfaces.

[0042] Furthermore, the track grooves 7 and the cylindrical inner peripheral surface 6 of the outer joint member 2 and the track grooves 9 of the inner joint member 3 are generally forged to reduce manufacturing costs, but they may also be finished by cutting or grinding after heat treatment (quenching). When these surfaces are subjected to the above-mentioned gentle blasting, the peaks of the peaks in the roughness curves of these surfaces become blasted surfaces, and the bottoms of the valleys become machined surfaces (cut surfaces or grinding surfaces). Furthermore, the outer peripheral surface and the inner peripheral surface of the cage 5 are generally ground to a finish, but they may also be finished by cutting or rolling after heat treatment (quenching). When these surfaces are subjected to the above-mentioned gentle blasting, the peaks of the peaks in the roughness curves of these surfaces become blasted surfaces, and the bottoms of the valleys become machined surfaces or rolled surfaces.

[0043] In the above-described sliding type constant velocity universal joint 1, the axial dimension of the pocket 12 of the cage 5 may be made larger than the diameter of the ball 4, thereby providing an axial gap between the wall surface of the pocket 12 and the ball 4. This axial gap can be set, for example, within the range of 0.001 to 0.05 mm. Alternatively, the axial dimension of the pocket 12 of the cage 5 may be made smaller than the diameter of the ball 4, thereby bringing the wall surface of the pocket 12 into contact with the ball 4 via a negative gap (interference).

[0044] Furthermore, an axial gap may be provided between the spherical portion 15 on the inner peripheral surface of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3. In this case, the cage 5 and the inner joint member 3 are able to move axially relative to each other, and the maximum amount of relative axial movement between them at this time is the axial gap. This axial gap can be set, for example, within a range of 0.6 to 1.5 mm. Alternatively, the axial gap between the cage 5 and the inner joint member 3 may be set to substantially zero. For example, the centers of curvature of the spherical portion 15 on the inner peripheral surface of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3 may be aligned, and their radii of curvature may be made approximately the same. In this case, a slight radial gap is formed between the spherical portion 15 on the inner peripheral surface of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3 to allow relative movement therebetween, but the amount of relative axial movement between them is substantially zero.

[0045] Furthermore, the double offset sliding type constant velocity universal joint of the present invention is not limited to electric vehicles (EVs) that run solely on the driving force of an electric motor, but can also be applied to hybrid vehicles (HEVs) that run on the power of an electric motor and an engine, and to the power transmission systems of vehicles that run solely on the power of the engine.

[0046] A comparative example in which no shot blasting was performed on the surface (forged surface) of the track grooves 7 of the outer joint member 2 of the constant velocity universal joint 1 described above and an example in which gentle shot blasting was performed using elastic media were prepared, and the surface roughness and induced thrust of each were measured. Fig. 6 shows the roughness curve, load curve, and amplitude distribution curve of the track groove surface of the outer joint member of the comparative example. Fig. 7 shows the roughness curve, load curve, and amplitude distribution curve of the track groove surface of the outer joint member of the example. As can be seen from these figures, the track groove surface of the example in which shot blasting was performed has a smaller roughness than the track groove surface of the comparative example in which shot blasting was not performed, and in particular, the peaks of the roughness curve are smaller (Rsk is a negative value).

[0047] Figure 8 shows the measurement results of induced thrust for the example and comparative example. The measurement conditions were the same as those for the test in Figure 11. Specifically, the axial load (induced thrust) applied to the outer joint member was measured when the working angle was changed from 0 degrees to 12 degrees at 10.7 degrees / min while a torque of 900 Nm was input at a rotation speed of 150 rpm. As can be seen from this figure, the example in which the track grooves of the outer joint member were subjected to gentle shot blasting had a reduced induced thrust, particularly at a relatively large working angle (7 degrees or more), compared to the comparative example in which the track grooves were not subjected to shot blasting.

[0048] DESCRIPTION OF SYMBOLS 1 Sliding type constant velocity universal joint (double offset type constant velocity universal joint) 2 Outer joint member 3 Inner joint member 4 Ball 5 Cage 6 Cylindrical inner peripheral surface 7 Track groove 8 Spherical outer peripheral surface 9 Track groove 10 Internal part 12 Pocket 13 Spherical portion 14 Tapered surface 15 Spherical portion 21 Crest 22 Bottom 51 Front wheel 52 Rear wheel 61, 62 Wheel drive device 63 Drive unit 64 Drive shaft (power transmission system) 65 Fixed type constant velocity universal joint 66 Intermediate shaft O Joint center O1 Center of curvature of spherical portion of outer peripheral surface of cage O2 Center of curvature of spherical portion of inner peripheral surface of cage Fx Induced thrust Qx Axial resistance between outer joint member and ball Hx Axial resistance between outer joint member and cage

Claims

1. A sliding type constant velocity universal joint comprising: an outer joint member having a plurality of linear track grooves formed on a cylindrical inner peripheral surface; an inner joint member having a plurality of linear track grooves formed on a spherical outer peripheral surface; a plurality of balls arranged between the track grooves of the outer joint member and the track grooves of the inner joint member; and a cage having an outer peripheral surface formed with a spherical portion that comes into sliding contact with the cylindrical inner peripheral surface of the outer joint member, and an inner peripheral surface formed with a spherical portion that comes into sliding contact with the spherical outer peripheral surface of the inner joint member, and holding the plurality of balls, a peak of a roughness curve of at least one of the cylindrical inner peripheral surface of the outer joint member, the surface of a track groove of the outer joint member, the spherical outer peripheral surface of the inner joint member, the surface of a track groove of the inner joint member, the spherical portion of the outer peripheral surface of the cage, and the spherical portion of the inner peripheral surface of the cage is a jet-blasted surface, and a bottom of a valley of the roughness curve of the said surface is any one of a forged surface, a rolled surface, or a machined surface.

2. A sliding type constant velocity universal joint according to claim 1, wherein the surface roughness parameter Rsk is a negative value.

3. A sliding type constant velocity universal joint according to claim 1, wherein the surface roughness parameter Rp is 2 or less.

4. A sliding type constant velocity universal joint according to claim 1, wherein the bottom of the valley of the surface roughness curve is a forged surface.

5. The sliding type constant velocity universal joint according to claim 1, which is provided in the power transmission system of a vehicle using an electric motor as a drive source.

6. A wheel drive device comprising the electric motor, a wheel, and the power transmission system that transmits the driving force of the electric motor to the wheel via the sliding type constant velocity universal joint according to claim 1.

7. A manufacturing method of a sliding type constant velocity universal joint comprising an outer joint member having a plurality of linear track grooves formed on a cylindrical inner peripheral surface thereof, an inner joint member having a plurality of linear track grooves formed on a spherical outer peripheral surface thereof, a plurality of balls arranged between the track grooves of the outer joint member and the track grooves of the inner joint member, and a cage having an outer peripheral surface formed with a spherical portion which comes into sliding contact with the cylindrical inner peripheral surface of the outer joint member and an inner peripheral surface formed with a spherical portion which comes into sliding contact with the spherical outer peripheral surface of the inner joint member, and holding the plurality of balls, comprising the steps of: forming at least one surface of the cylindrical inner peripheral surface of the outer joint member, the surface of the track grooves of the outer joint member, the spherical outer peripheral surface of the inner joint member, the surface of the track grooves of the inner joint member, the spherical portion of the outer peripheral surface of the cage, and the spherical portion of the inner peripheral surface of the cage by forging, rolling or machining; and a step of subjecting said surface to blasting so that a forged surface, a rolled surface or a machined surface remains at the bottom of the valleys of the roughness curve of said surface.

8. A method for manufacturing a sliding type constant velocity universal joint according to claim 7, wherein the blasting process is shot blasting.

9. A method for manufacturing a sliding type constant velocity universal joint according to claim 7, wherein said blasting is carried out using elastic media at least partly formed of an elastomer.

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