Slidable constant velocity universal joint and wheel drive device comprising the same

Abstract

To reduce an induction thrust of a double offset type slidable constant velocity universal joint, to make it suitable for use in a power transmission system of a vehicle (EV or HEV) with an electric motor as a drive source.SOLUTION: In a double offset type slidable constant velocity universal joint 1 that is provided in a power transmission system of a vehicle with an electric motor as a drive source, an axial gap (pocket gap) δ1 is formed between a pocket 12 of a holder 5 and a ball 4, and an axial gap δ2 of 0.6 mm or more is formed between a spherical part 15 of an inner surface of the holder 5 and a spherical outer peripheral surface 8 of an inside joint member 3.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a sliding type constant velocity universal joint and a wheel drive device including the same. [Background technology]

[0002] Constant velocity universal joints applied to automobile drive shafts and propeller shafts can be broadly divided into sliding types, which allow both angular displacement and relative axial movement between two shafts, and fixed types, which 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 (DOJ) that use balls as rolling elements for transmitting rotational torque, and tripod constant velocity universal joints (TJ) that use rollers as rolling elements. For example, the following Patent Document 1 shows a double offset constant velocity universal joint that is lightweight and compact by increasing the number of balls from six to eight. Also, the following Patent Document 2 shows a double offset constant velocity universal joint that has a maximum operating angle of 30° or more and is further lightweight and compact.

[0004] A double offset constant velocity universal joint has the advantages of less circumferential backlash, better response, and lower manufacturing costs than a tripod constant velocity universal joint, but has the disadvantage of greater sliding resistance and greater transmission of vehicle vibrations, particularly engine vibrations during idling. Therefore, various measures against idling vibrations have been considered for double offset constant velocity universal joints. For example, Patent Document 3 below shows 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-73129 [Patent Document 2] JP 2007-85488 A [Patent Document 3] JP 2013-231518 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, as improvements in vehicle ride comfort progress, the NVH (Noise, Vibration, Harshness) characteristics required of constant velocity universal joints are becoming more stringent. Because double offset constant velocity universal joints are structurally unable to avoid the occurrence of sliding contact between parts, even if measures such as those shown in Patent Document 3 are taken, it is difficult to reduce the sliding resistance to the same level as tripod-type sliding constant velocity universal joints in which parts mainly come into contact with each other by rolling. Such problems of sliding resistance, particularly idling vibration, have become a bottleneck, and in recent years, the application range of double offset constant velocity universal joints has been limited to areas that are less susceptible to engine vibration (for example, rear drive shafts).

[0007] Meanwhile, in recent years, the electrification of vehicles has progressed, and electric vehicles (hereinafter referred to as EVs) that run only on the power of electric motors and hybrid vehicles (hereinafter referred to as HEVs) that run on the power of electric motors and engines are on the rise. Electric motors have better response than engines, so constant velocity joints that transmit the power of electric motors are also required to have less circumferential backlash and better response. In addition, since there is no engine vibration in EVs and the engine is basically stopped in HEVs while the vehicle is not moving (during idling), these vehicles do not have the problem of idling vibration, which is the main factor limiting the application of double offset type constant velocity joints. From the above perspective, the adoption of double offset types that have less circumferential backlash and have better response is being considered as sliding type constant velocity joints to be provided in the power transmission systems of drive shafts, propeller shafts, etc. in 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 friction between internal parts when rotating through an operating angle. This induced thrust resonates with the vehicle body and can cause various vibration problems such as swaying and muffled noise when starting off. Such problems are particularly noticeable in EVs and HEVs, which are quiet. Therefore, if the induced thrust can be reduced, there is a possibility that double offset type constant velocity universal joints can be used suitably 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. [Means for solving the problem]

[0010] As described above, the induced thrust is an axial load generated due to the frictional force between the internal parts of the sliding type constant velocity universal joint. Specifically, as shown in FIG. 12, the resultant force of the axial resistance Qx caused by the frictional force of the contact portion between the track groove 101a of the outer joint member 101 and the ball 102, and the axial resistance Hx caused by the frictional force of the contact portion between the outer spherical surface 103a of the cage 103 and the cylindrical inner peripheral surface 101b of the outer joint member 101 becomes the induced thrust. FIG. 13 shows the result of the induced thrust Fx (=Qx+Hx) of a double offset type constant velocity universal joint having eight balls, which was obtained by mechanical analysis. As shown in the figure, it was thought that in the double offset type constant velocity universal joint, the induced thrust of the order component of the same number as the number of balls (8 in the figure) is mainly generated.

[0011] Meanwhile, Fig. 14 shows the results of measuring the actual induced thrust of an eight-ball double offset constant velocity universal joint. In this test, assuming the start of a vehicle, 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 deg to 12 deg at a rate of 10.7 deg / min, and the axial load (induced thrust) applied to the outer joint member was measured. The X-axis in Fig. 14 shows the frequency of vibration generated in the constant velocity universal joint, the Y-axis shows the working angle of the constant velocity universal joint, and the Z-axis shows the magnitude of the axial load (induced thrust) applied to the outer joint member. The peak that appears at 2.5 Hz in the figure is the first-order component of the induced thrust (the vibration component that occurs once per rotation of the constant velocity universal joint), the peak that appears at 5 Hz is the second-order component, the peak that appears at 7.5 Hz is the third-order component, and the peak that appears at 20 Hz is the eighth-order component. From the actual measurement results shown in the figure, it can be seen that the induced thrust not only has an 8th-order component, but also many other order components, with the 1st-order component being particularly prominent.

[0012] As described above, the causes of the occurrence of induced thrusts of various orders are considered 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 the resultant forces of the loads occurring in each phase. Note that "each phase" refers to the phases of each ball and each track groove in contact with it (first to eighth phases in the case of an eight-ball double offset type constant velocity universal joint) at the contact portion between the track grooves of the outer joint member and the balls, and refers to the phases 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 it (first to eighth phases in the case of an eight-ball double offset type constant velocity universal joint).

[0013] Here, in an eight-ball double offset type constant velocity universal joint, the mechanical analysis results of the axial load applied to the track grooves of each phase of the outer joint member and its resultant force (Qx) are shown in Figs. 15 and 16. Fig. 15 shows the axial components of the track loads of each phase and their resultant force in an ideal state in which all parts have uniform dimensions and the surface properties of all phases are uniform. In this case, the axial loads (see dotted line) in the tracks of all phases become uniform, and these resultant forces have a regular shape in which a specific order component (the 8th order component in the illustrated example) is strongly expressed (see solid line). However, in reality, the contact state of the internal parts becomes non-uniform due to the variation in the dimensions of each part and the variation in the surface properties of the contact parts. Therefore, as shown in Fig. 16, the axial loads generated in the tracks of each phase vary (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 occurs in this way, the number of resonance points with the car body increases, and the possibility of causing noise and vibration problems increases.

[0014] From the above viewpoint, the inventors of the present invention considered that each order component of the induced thrust could be suppressed by equalizing the axial load generated in each phase of the double offset type constant velocity universal joint. Specifically, a structure was adopted in which (1) an axial gap was provided between the pocket of the cage and the ball, and (2) an axial gap was provided at the fitting portion between the cage and the inner joint member. These structures were conventionally adopted as measures against idling vibration, and therefore do not need to be adopted in EVs and HEVs, which do not have the problem of idling vibration. However, the inventors of the present invention verified that each order component of the induced thrust could be reduced by providing axial play between the ball and the pocket of the cage, and between the cage and the inner joint member, as described above. This is believed to be because the unbalance of the axial load generated by the variation in frictional force in each phase was absorbed by the axial play of (1) and (2) above, which equalized the axial load in each phase.

[0015] From the above, the present invention provides a sliding type constant velocity universal joint 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 circumferential surface; an inner joint member having a plurality of linear track grooves formed on a spherical outer circumferential surface; 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 circumferential surface formed with a spherical portion which comes into sliding contact with the cylindrical inner circumferential surface of the outer joint member; an inner circumferential surface formed with a spherical portion which comes into sliding contact with the spherical outer circumferential surface of the inner joint member; and a cage having a plurality of pockets which hold the plurality of balls, An axial gap is formed between the pocket of the cage and the ball, The present invention provides a sliding type constant velocity universal joint in which 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.

[0016] Thus, the sliding type constant velocity universal joint according to the present invention is characterized by adopting a structure that has been conventionally adopted as a measure against idling vibration in EVs and HEVs (particularly EVs driven only by electric motors) that do not have 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, each order component of the induced thrust can be reduced. 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, the unbalance of the axial load at the contact portion of each phase cannot be sufficiently absorbed, so this axial gap is set to be 0.6 mm or more.

[0017] If the axial gap between the spherical portion of the inner surface of the cage and the spherical outer 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 surface of the retainer has 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 surfaces, so that an axial gap can be provided at the fitting 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 pockets of the cage and between the cage and the inner joint member as described above in order to absorb the variation in the axial load for each phase.

[0021] The above-mentioned 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 above-mentioned sliding type constant velocity universal joint. Effect of the Invention

[0022] As described above, according to the present invention, it is possible to reduce the induced thrust of a double offset sliding type 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. [Brief description of the drawings]

[0023] [Figure 1] 1 is an axial cross-sectional view of a double offset type sliding type constant velocity universal joint according to one embodiment of the present invention. FIG. [Diagram 2] 2 is a cross-sectional view of the sliding type constant velocity universal joint of FIG. 1 taken in a direction perpendicular to the axis. [Diagram 3] 2 is an enlarged sectional view of an inner joint member and a cage of the sliding type constant velocity universal joint of FIG. 1. [Figure 4] FIG. 4 is an enlarged view of part C in FIG. [Diagram 5] FIG. 4 is an enlarged view of part D in FIG. [Figure 6] FIG. 4 is a cross-sectional view showing an example of the specifications of a fitting portion between the inner joint member and the cage in FIG. 3. [Figure 7] 4 is a sectional view showing another example of the specifications of the fitting portion between the inner joint member and the cage in FIG. 3. FIG. [Figure 8] FIG. 13 is a diagram showing the measurement results of induced thrust in an embodiment (axial gap δ2=1 mm). [Figure 9] FIG. 13 is a diagram showing the measurement results of induced thrust in a comparative example (axial gap δ2=0.5 mm). [Figure 10] FIG. 13 is a diagram showing a change in torque loss rate when the axial clearance δ2 is changed. [Figure 11] FIG. 2 is a plan view of an electric vehicle (EV) on which the constant velocity universal joint of FIG. 1 is mounted. [Figure 12] 4 is a cross-sectional view showing a portion to which an axial load is applied when a double offset type constant velocity universal joint rotates at an operating angle. FIG. [Figure 13] FIG. 11 is a diagram showing the analysis results of induced thrust in a double offset type constant velocity universal joint. [Figure 14] FIG. 13 is a diagram showing the results of measuring induced thrust in a double offset type constant velocity universal joint. [Figure 15] FIG. 11 is a diagram showing an analysis result of an axial load applied to a track groove of an outer joint member (when the axial load applied to the track groove of each phase is uniform). [Figure 16] FIG. 11 is a diagram showing an analysis result of an axial load applied to a track groove of an outer joint member (when the axial load applied to the track groove of each phase is non-uniform). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 only on the power of an electric motor. This electric vehicle has a front wheel drive device 61 that drives the front wheels 51, and a rear wheel drive device 62 that drives the rear wheels 52. Each wheel drive device 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 the rear wheels 52. In the illustrated example, the drive unit 63 of the front wheel drive device 61 is connected to the left and right front wheels 51 via the left and right drive shafts 64, and the drive unit 63 of the rear wheel drive device 62 is connected to the left and right rear wheels 52 via the 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 type 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] As shown in Figs. 1 and 2, the sliding type constant velocity universal joint 1 of this embodiment includes a cup-shaped outer joint member 2 with one axial end (left end in Fig. 1) open, an inner joint member 3 arranged on the inner periphery of the outer joint member 2, a plurality of balls 4, and a retainer 5 for holding the plurality of balls 4. An internal part 10 consisting of the inner joint member 3, the balls 4, and the retainer 5 is accommodated on the inner periphery of the outer joint member 2 so as to be displaceable in the axial direction. An end of an intermediate shaft 66 (see Fig. 11) is coupled to an axial hole 11 of the inner joint member 3 by spline fitting. In the following description, the axial direction of the outer joint member 2 and the inner joint member 3 in a state of an operating angle of 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 inner 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-extending linear track grooves 7 are formed at multiple locations in the circumferential direction at equal intervals on the cylindrical inner peripheral surface 6 of the outer joint member 2. Axial-extending linear track grooves 9 are formed at multiple locations in the circumferential direction at equal intervals 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 face each other 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 cage 5 has an outer circumferential surface formed with a spherical portion 13 that slides against the cylindrical inner circumferential surface 6 of the outer joint member 2, and tapered surfaces 14 provided on both axial sides of the spherical portion 13. The cage 5 has an inner circumferential surface formed with a spherical portion 15 that slides against the spherical outer circumferential 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 present invention is not limited to this, and 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 the opposite axial side 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 and 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 inner side 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 side 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 bisecting plane of the operating angle at any 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. Note that, 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 disposed 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 disposed 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, the original outer joint member is molded. In the turning process, the outer circumferential surface of the original outer joint member is turned. In the rolling process, a male spline is 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 through 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 circumference of the original form of the inner joint member. In the heat treatment process, the original form of the inner joint member is subjected to heat treatment (e.g., carburizing, quenching, and tempering). In the grinding process, the spherical outer circumferential surface (area excluding the track grooves) of the original form of the inner joint member 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 roughly cylindrical cage original is formed by die-molding. In the turning process, the inner and outer peripheral surfaces of the cage original are turned. In the pocket punching process, the cage original is punched in the radial direction to form pockets 12. In the heat treatment process, the cage original is heat-treated (for example, carburized, quenched, and tempered). 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 are ground. When manufactured according to 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 5 become ground surfaces, and the other areas become pocket punched surfaces or turned surfaces.

[0034] 3, an axial gap (hereinafter, this axial gap will be referred to as "pocket gap δ1") is provided between the wall surface of pocket 12 of cage 5 and ball 4. If the axial dimension of pocket 12 of cage 5 is Lc and the ball diameter of ball 4 is Db, then 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 larger than 0.05 mm, the amount of deviation of the ball 4 from the bisecting plane of 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 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 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 portion 15 on the inner peripheral surface of the cage 5 by moving the inner joint member 3 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 portion 15 on the inner peripheral surface of the cage 5 by moving the inner joint member 3 in the other axial direction with respect to the cage 5.

[0037] A specific specification for providing the axial clearance 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 clearance between the spherical outer peripheral surface 8 of the inner joint member 3 and the spherical portion 15 of the inner joint member 5 is smallest at the outermost diameter portion (the center in the axial direction) of the spherical portion 15 of the cage 5, and gradually increases from there toward both sides in the axial direction. The radial clearance 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 clearance is provided to allow the relative movement between them. As a result, an axial clearance δ2 is provided between the cage 5 and the inner joint member 3 to allow the relative axial movement between them.

[0038] FIG. 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 of a single spherical surface with a curvature radius Ri, as in FIG. 6. On the other hand, 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 slight 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, so that the inner joint member 3 can move in the axial direction by the axial dimension S of the cylindrical portion 16 relative to the cage 5. 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 rotational driving force from the electric motor is input to the outer joint member 2 while the sliding type constant velocity 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, an axial load (induced thrust) is generated in the outer joint member 2 due to axial sliding resistance at the contact portion between each part. However, the axial load in each phase is not uniform and varies due to variations in the dimensions and surface properties of each part. 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 of 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 the variations in the axial load in each phase, thereby making the axial load in each phase uniform, and therefore each order component of the induced thrust can be suppressed.

[0040] Fig. 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 Fig. 14, and 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 inputting a torque of 900 Nm at a rotation speed of 150 rpm. In this way, 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 smaller than the measurement result when the axial clearance δ2 is substantially zero (see Fig. 14).

[0041] On the other hand, Fig. 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 Fig. 14. In this case, compared to the measurement results in which the axial clearance δ2 is substantially 0 (see Fig. 14), the magnitude of each order component of the induced thrust is slightly smaller, but compared to the measurement results in which the axial clearance δ2 is 1 mm (see Fig. 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 the above results, the axial clearance δ2 is set to 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 lost and increasing the torque loss rate. 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 deg (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 circle), the torque loss rate is larger than when the axial clearance δ2 is 1 mm (black circle). From the above results, it is not necessarily true 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 embodiment. Other embodiments of the present invention will be described below, but redundant description of the same points as the above embodiment will be omitted.

[0044] In the above-described sliding type constant velocity universal joint 1, the components other than the balls 4 (the outer joint member 2, the inner joint member 3, and the cage 5) may be subjected to a surface treatment. Specifically, 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 of the outer circumferential surface of the cage 5, and the spherical portion 15 of the inner circumferential surface of the cage 5 may be subjected to a surface treatment such as manganese phosphate treatment or shot blasting.

[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 greater than 2. In addition to the above conditions, it is desirable to satisfy at least one of the following: Ra is not greater than 1.5, preferably not greater than 0.6, and Rz is not greater than 10, preferably not greater than 6.

[0046] Rsk, Rp, Ra, and Rz are respectively the skewness, maximum peak height, arithmetic mean height, and maximum height of the roughness curve of the reference length specified in JIS B 0601-2013. Rsk is a positive value when there are many peaks in the amplitude distribution curve relative to the average line of the roughness curve, and a negative value when there are many valleys. Measurement of these parameters is performed at the contact position between each part, over a range of 4 mm in total, consisting of 5 sections of 0.8 mm × 0.8 mm reference length along the axial direction.

[0047] In addition, 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 finished by forging as described above in order to reduce manufacturing costs, but may be finished by cutting or grinding after heat treatment (hardening). In addition, the outer peripheral surface and the inner peripheral surface of the cage 5 are generally finished by grinding as described above, but may be finished by cutting or rolling after heat treatment (hardening).

[0048] Furthermore, the double offset type sliding constant velocity universal joint of the present invention can be applied not only to electric vehicles (EVs) that run only 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 an electric motor and an engine. [Explanation of symbols]

[0049] 1. Sliding 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 surface 7 Track groove 8 Spherical outer surface 9 Track groove 10 Internal parts 12 Pockets 13 Spherical part 14 Tapered surface 15 Spherical part 16 Cylindrical section 51 Front wheel 52 Rear wheel 61, 62 Wheel drive unit 63 Drive unit 64 Drive shaft (power transmission system) 65 Fixed constant velocity joint 66 Intermediate shaft O Joint center O1 Center of curvature of the spherical part of the outer periphery of the cage O2 Center of curvature of the spherical part of the inner circumference of the 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 pocket and ball (pocket clearance) δ2 Axial clearance between the cage and the inner joint member

Claims

1. A sliding type constant velocity universal joint 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 circumferential surface; an inner joint member having a plurality of linear track grooves formed on a spherical outer circumferential surface; 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 joint member having a spherical portion which comes into sliding contact with the cylindrical inner circumferential surface of the outer joint member, an inner joint member having a spherical portion which comes into sliding contact with the spherical outer circumferential surface of the inner joint member, and a cage having a plurality of pockets which hold the plurality of balls, An axial gap is formed between the pocket of the cage and the ball, A sliding type constant velocity universal joint, in which 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. 2. The sliding type constant velocity universal joint according to claim 1, wherein the axial gap between the spherical portion of the inner circumferential surface of the cage and the spherical outer circumferential surface of the inner joint member is 1.5 mm or less.

3. 2. The sliding type constant velocity universal joint according to claim 1, wherein a radius of curvature of a spherical portion of an inner peripheral surface of said cage is larger than a radius of curvature of a spherical outer peripheral surface of said inner joint member.

4. 2. 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 a spherical portion provided on both axial sides of the cylindrical surface and smoothly continuing with the cylindrical surface.

5. 2. The sliding type constant velocity universal joint according to claim 1, wherein a surface of said track grooves and said cylindrical inner circumferential surface of said outer joint member, and a surface of said track grooves of said inner joint member are forged surfaces.

6. 2. The sliding type constant velocity universal joint according to claim 1, which is provided 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; wheels; and the power transmission system that transmits the driving force of the electric motor to the wheels via the sliding type constant velocity universal joint according to claim 1.

Images