Plunging-type constant velocity universal joint and wheel driving device provided with same

Abstract

In a double-offset-type plunging-type constant velocity universal joint 1 provided in a power transmission system of a vehicle using an electric motor as a drive source, an axial clearance (pocket clearance) δ1 is formed between a pocket 12 of a holder 5 and a ball 4, and an axial clearance δ2 of 0.6 mm or more is formed between a spherical surface part 15 of an inner peripheral surface of the holder 5 and a spherical outer peripheral surface 8 of an inner joint member 3.

Description

Sliding constant velocity universal joint and wheel drive device equipped with same

[0001] The present invention relates to a sliding type constant velocity universal joint and a wheel drive device including 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 types, which have low circumferential backlash and excellent responsiveness, is being considered for use in sliding-type constant velocity universal joints for drive shafts, propeller shafts, and other power transmission systems of EVs and HEVs.

[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. 12 , the induced thrust is the result of the axial resistance Qx resulting from the frictional forces at the contact points between the track grooves 101 a 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 103 a of the cage 103 and the cylindrical inner peripheral surface 101 b of the outer joint member 101. FIG. 13 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 14 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 14 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 so on, 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. 12 ). 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 15 and 16. Figure 15 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 is 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 16, 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 14). When induced thrust of various order components is 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 perspective, the inventors of the present invention have considered the possibility of suppressing each order component of induced thrust by equalizing the axial load generated in each phase of a double-offset constant velocity universal joint. Specifically, they adopted a structure in which (1) an axial gap is provided between the cage pockets and the balls, and (2) an axial gap is provided at the fitting portion between the cage and the inner joint member. These structures have conventionally been adopted to counter idling vibration, and therefore are not necessary for EVs and HEVs, which do not suffer from idling vibration problems. However, through their verification, the inventors have found that each order component of induced thrust can be reduced by providing axial clearance between the balls and the cage pockets and between the cage and the inner joint member as described above. This is thought to be because the imbalance in axial load caused by variations in frictional force among the phases is absorbed by the axial clearances (1) and (2) described above, thereby equalizing the axial load in each phase.

[0015] In light of the above, the present invention provides a sliding type constant velocity universal joint which is provided in a power transmission system of a vehicle driven by an electric motor, 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; an outer peripheral surface formed with spherical portions which come into sliding contact with the cylindrical inner peripheral surface of the outer joint member; an inner peripheral surface formed with spherical portions which come into sliding contact with the spherical outer peripheral surface of the inner joint member; and a cage having a plurality of pockets which hold the plurality of balls, wherein axial gaps are formed between the pockets of the cage and the balls, and an axial gap of 0.6 mm or more is formed between the spherical portions of the inner peripheral surface of the cage and the spherical outer peripheral surface of the inner joint member.

[0016] As described above, the sliding-type constant velocity universal joint according to the present invention is characterized by adopting a structure that has been conventionally used as a countermeasure against idling vibration in EVs and HEVs (particularly EVs driven only by electric motors) that do not suffer from the problem of idling vibration. Specifically, by forming an axial gap between the pockets of the cage and the balls, and by providing an axial gap at the fitting portion between the cage and the inner joint member, it is possible to reduce each order component of the induced thrust. Note that if the axial gap between the spherical portion of the inner peripheral surface of the cage and the spherical outer peripheral surface of the inner joint member is too small, it will not be possible to sufficiently absorb the unbalance in the axial load at the contact portions of each phase. Therefore, this axial gap is set to be 0.6 mm or more.

[0017] If the axial gap between the spherical portion of the inner peripheral surface of the cage and the spherical outer peripheral surface of the inner joint member is excessively large, the balance of the internal components is lost and the torque loss rate increases. Therefore, it is preferable that this axial gap be 1.5 mm or less.

[0018] For example, by making the radius of curvature of the spherical portion of the inner peripheral surface of the cage larger than the radius of curvature of the spherical outer peripheral surface of the inner joint member, an axial gap can be provided at the fitting portion between the cage and the inner joint member.

[0019] Alternatively, the inner peripheral surface of the retainer may have a cylindrical surface parallel to the axis and the spherical portions provided on both axial sides of the cylindrical surface and smoothly continuing from the cylindrical surface, thereby making it possible to provide an axial gap at the mating portion between the retainer and the inner joint member.

[0020] When the track groove surfaces and the cylindrical inner peripheral surface of the outer joint member and the track groove surfaces of the inner joint member are forged surfaces, the roughness of these surfaces increases, which tends to increase the variation in the axial load for each phase. In this case, it is particularly effective to provide axial gaps between the balls and the cage pockets and between the cage and the inner joint member, as described above, to absorb the variation in the axial load for each phase.

[0021] The sliding type constant velocity universal joint can be suitably incorporated into a wheel drive device 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.

[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] 3 is an axial sectional view of a double offset sliding type constant velocity universal joint according to one embodiment of the present invention. FIG. 3 is an axial sectional view of the sliding type constant velocity universal joint of FIG. 1 in a direction perpendicular to the axis. FIG. 4 is an enlarged sectional view of an inner joint member and a cage of the sliding type constant velocity universal joint of FIG. 1. FIG. 5 is an enlarged view of part C of FIG. 3. FIG. 6 is an enlarged view of part D of FIG. 3. FIG. 6 is a sectional view showing an example of the specifications of the fitting portion between the inner joint member and the cage of FIG. 3. FIG. 7 is a sectional view showing another example of the specifications of the fitting portion between the inner joint member and the cage of FIG. 3. FIG. 7 is a diagram showing the measurement results of induced thrust in an example (axial clearance δ2 = 1 mm). FIG. 8 is a diagram showing the measurement results of induced thrust in a comparative example (axial clearance δ2 = 0.5 mm). FIG. 9 is a diagram showing the change in torque loss rate when the axial clearance δ2 is changed. FIG. 10 is a plan view of an electric vehicle (EV) equipped with the constant velocity universal joint of FIG. 1. FIG. 11 is a sectional view showing a portion to which an axial load is applied when the double offset type constant velocity universal joint rotates at an operating angle. FIG. 12 is a diagram showing the analysis results of induced thrust in a double offset type constant velocity universal joint. Fig. 1 is a diagram showing the results of measurements of induced thrust in a double offset constant velocity universal joint. Fig. 2 is a diagram showing the results of analysis of the axial load applied to the track grooves of the outer joint member (when the axial load applied to the track grooves of each phase is uniform). Fig. 3 is a diagram showing the results of analysis of the axial load applied to the track grooves of the outer joint member (when the axial load applied to the track grooves of each phase is 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] 11 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. 11 ) is coupled by spline fitting to an axial hole 11 of the inner joint member 3. In the following description, when the operating angle is 0° as shown in FIG. 1 , the axial direction of the outer joint member 2 and the inner joint member 3 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 part of the inner surface of the pocket 12 (surfaces facing each other in the axial direction) 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 part of the inner surface of the pocket 12 of the cage original form become ground surfaces, and the other areas become pocket punched surfaces or turned surfaces.

[0034] 3, an axial gap (hereinafter referred to as "pocket gap δ1") is provided between the wall surface of the pocket 12 of the cage 5 and the ball 4. If the axial dimension of the pocket 12 of the cage 5 is Lc and the ball diameter of the ball 4 is Db, then the pocket gap δ1 is expressed as δ1 = Lc - Db.

[0035] The pocket gap δ1 is preferably set to 0.001 to 0.05 mm. Even a small amount of pocket gap δ1 can be effective. If the pocket gap δ1 is greater than 0.05 mm, the amount of deviation of the balls 4 from the plane bisecting the working angle increases, which may lead to a decrease in the constant velocity and durability of the sliding type constant velocity universal joint 1.

[0036] 4 and 5 , an axial gap δ2 is provided between the spherical portions 15 on the inner peripheral surface of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3. The axial gap δ2 is the amount of relative axial movement of the inner joint member 3 with respect to the cage 5, from a position where the spherical outer peripheral surface 8 of the inner joint member 3 abuts against the spherical portions 15 on the inner peripheral surface of the cage 5 when the inner joint member 3 is moved in one axial direction with respect to the cage 5, to a position where the spherical outer peripheral surface 8 of the inner joint member 3 abuts against the spherical portions 15 on the inner peripheral surface of the cage 5 when the inner joint member 3 is moved in the other axial direction with respect to the cage 5.

[0037] Specific specifications for providing the axial gap δ2 will be described with reference to FIG. 6 . In this specification, the radius of curvature Rc of the spherical portion 15 of the inner peripheral surface of the cage 5 is larger than the radius of curvature Ri of the spherical outer peripheral surface 8 of the inner joint member 3, and the center of curvature of the radius of curvature Rc is offset in the radial direction with respect to the axis of the cage 5. The radial gap between the spherical outer peripheral surface 8 of the inner joint member 3 and the spherical portion 15 of the inner peripheral surface of the cage 5 is smallest at the outermost diameter portion (the axial center) of the spherical portion 15 of the cage 5 and gradually increases from there toward both sides in the axial direction. The radial gap between the outermost diameter portion of the spherical portion 15 of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3 is substantially zero, but a small radial gap is provided to allow relative movement between them. As a result, the axial gap δ2 that allows relative axial movement between the cage 5 and the inner joint member 3 is provided.

[0038] Figure 7 shows another specification for providing the axial gap δ2. In this specification, the spherical outer peripheral surface 8 of the inner joint member 3 is formed by a single spherical surface with a curvature radius Ri, as in Figure 6. Meanwhile, a cylindrical portion 16 parallel to the axis of the cage 5 is formed on the inner peripheral surface of the cage 5, and spherical portions 15 with a curvature radius Rc are smoothly connected to both axial ends of the cylindrical portion 16. The curvature radius Rc of the spherical portion 15 on the inner peripheral surface of the cage 5 and the curvature radius Ri of the spherical outer peripheral surface 8 of the inner joint member 3 are substantially Rc≈Ri, although there is a small spherical gap for sliding guide. In this specification, the spherical outer peripheral surface 8 of the inner joint member 3 is slidably guided in the axial direction by the cylindrical portion 16 on the inner peripheral surface of the cage 5, allowing the inner joint member 3 to move axially relative to the cage 5 by the axial dimension S of the cylindrical portion 16. That is, the axial dimension S of the cylindrical portion 16 becomes the axial gap δ2 between the cage 5 and the inner joint member 3.

[0039] When the sliding-type constant velocity universal joint 1 has an operating angle, a rotational driving force from the electric motor is input to the outer joint member 2, and 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, an axial pocket gap δ1 is provided between the wall surface of the pocket 12 of the cage 5 and the balls 4, and an axial gap δ2 is 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. The pocket gap δ1 and the axial gap δ2 absorb variations in the axial load in each phase, thereby uniforming the axial load in each phase, and therefore each order component of the induced thrust can be suppressed.

[0040] Figure 8 shows the measurement results of the induced thrust generated in the sliding type constant velocity universal joint 1 (Example) with an axial clearance δ2 of 1 mm. The measurement conditions were the same as those of the test in Figure 14. Specifically, the axial load (induced thrust) applied to the outer joint member was measured when the working angle was changed from 0 deg to 12 deg at 10.7 deg / min while a torque of 900 Nm was input at a rotation speed of 150 rpm. As described above, it can be confirmed that by providing the axial clearance δ2 between the cage 5 and the inner joint member 3, the magnitude of each order component of the induced thrust is reduced compared to the measurement results when the axial clearance δ2 was set to substantially zero (see Figure 14).

[0041] On the other hand, Figure 9 shows the measurement results of the induced thrust generated in the sliding type constant velocity universal joint 1 (comparative example) in which the axial clearance δ2 is 0.5 mm. The measurement conditions are the same as those of the test in Figure 14. In this case, compared to the measurement results in which the axial clearance δ2 is substantially 0 (see Figure 14), the magnitude of each order component of the induced thrust is slightly smaller. However, compared to the measurement results in which the axial clearance δ2 is 1 mm (see Figure 8), each order component of the induced thrust (especially the first order component) is larger, and the effect of reducing the induced thrust cannot be said to be sufficient. From these results, the axial clearance δ2 should be 0.6 mm or more.

[0042] Furthermore, if the axial clearance δ2 is too large, the internal backlash of the sliding type constant velocity universal joint 1 becomes excessive, causing the internal balance to be disrupted and the torque loss rate to increase. For example, Fig. 10 shows the analysis results of the torque loss rate when the rotation speed is 1200 rpm, the working angle is 8 degrees (common angle), and the input torque is 300 N m, assuming high-speed driving. As shown in the figure, when the axial clearance δ2 is 2 mm (white circles), the torque loss rate is larger than when the axial clearance δ2 is 1 mm (black circles). From the above results, it is not necessarily the case that the larger the axial clearance δ2, the better, and it is preferable to set it to, for example, 1.5 mm or less.

[0043] 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.

[0044] Of the sliding type constant velocity universal joint 1, components other than the balls 4 (the outer joint member 2, the inner joint member 3, and the cage 5) may be subjected to surface treatment. Specifically, surface treatment such as manganese phosphate treatment or shot blasting may be applied to at least one 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.

[0045] The surface that has been subjected to the above surface treatment satisfies at least one of the following: Rsk is a negative value, and Rp is not more than 2. In addition to the above conditions, it is desirable to satisfy at least one of the following: Ra is not more than 1.5, preferably not more than 0.6, and Rz is not more than 10, preferably not more than 6.

[0046] 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.

[0047] Although 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, they may be finished by cutting or grinding after heat treatment (quenching). Furthermore, the outer peripheral surface and the inner peripheral surface of the cage 5 are generally ground to reduce manufacturing costs, but they may be finished by cutting or rolling after heat treatment (quenching).

[0048] Furthermore, the double offset sliding constant velocity universal joint of the present invention can be applied not only to electric vehicles (EVs) that run solely on the driving force of an electric motor, but also to the power transmission system of hybrid vehicles (HEVs) that run on the power of both an electric motor and an engine.

[0049] 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 16 Cylindrical portion 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 δ1 Axial clearance between the pocket and the ball (pocket clearance) δ2 Axial clearance between the cage and the inner joint member

Claims

1. A sliding type constant velocity universal joint which is provided in a power transmission system of a vehicle driven by an electric motor, comprising: an outer joint member having a plurality of straight track grooves formed on its cylindrical inner peripheral surface; an inner joint member having a plurality of straight track grooves formed on its spherical outer peripheral surface; a plurality of balls arranged between the track grooves of said outer joint member and the track grooves of said inner joint member; an outer peripheral surface formed with a spherical portion which comes into sliding contact with the cylindrical inner peripheral surface of said outer joint member, an inner peripheral surface formed with a spherical portion which comes into sliding contact with the spherical outer peripheral surface of said inner joint member, and a cage having a plurality of pockets which hold said plurality of balls, wherein axial gaps are formed between the pockets of said cage and the balls, and an axial gap of 0.6 mm or more is formed between the spherical portion of the inner peripheral surface of the cage and the spherical outer peripheral surface of the inner joint member.

2. A sliding type constant velocity universal joint as set forth in claim 1, wherein the axial gap between the spherical portion of the inner peripheral surface of the cage and the spherical outer peripheral surface of the inner joint member is 1.5 mm or less.

3. A sliding type constant velocity universal joint as set forth in claim 1, wherein the radius of curvature of the spherical portion of the inner peripheral surface of the cage is larger than the radius of curvature of the spherical outer peripheral surface of the inner joint member.

4. A sliding type constant velocity universal joint as described in claim 1, wherein the inner surface of the retainer has a cylindrical surface parallel to the axis and spherical portions provided on both axial sides of the cylindrical surface and smoothly continuing with the cylindrical surfaces.

5. A sliding type constant velocity universal joint according to claim 1, wherein the surface of the track groove and the cylindrical inner peripheral surface of the outer joint member, and the surface of the track groove of the inner joint member are forged surfaces.

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

7. 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.

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