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

Abstract

In a double-offset sliding constant velocity universal joint (1) provided in a power transmission system of a vehicle using an electric motor as a drive source, an axial gap (groove gap) ([delta] 1) is formed between a ball (4) and a groove (12) of a retainer (5). An axial gap (delta 2) of 0.6 mm or more is formed between the spherical surface portion (15) of the inner peripheral surface of the retainer (5) and the spherical outer peripheral surface (8) of the inner joint member (3).

Description

Technical Field

[0001] The present invention relates to a sliding constant velocity universal joint and a wheel drive device having the sliding constant velocity universal joint. Background Technology

[0002] Constant velocity universal couplings used in the drive shafts and transmission shafts of motor vehicles are generally divided into two types: sliding type, which allows both angular displacement and axial relative movement between the two shafts, and fixed type, which allows angular displacement between the two shafts but does not allow axial relative movement between the two shafts.

[0003] As sliding constant velocity universal joints, known types include double-offset constant velocity universal joints (DOJ) that use balls as rolling elements to transmit rotational torque, and three-ball-pin constant velocity universal joints (TJ) that use rollers as rolling elements. For example, Patent Document 1 below shows a double-offset constant velocity universal joint that achieves lightweight compactness by increasing the number of balls from 6 to 8. Furthermore, Patent Document 2 below shows a double-offset constant velocity universal joint that achieves further lightweight compactness by increasing the maximum operating angle height to 30° or more.

[0004] Compared to three-ball-pin type constant velocity universal joints, double-offset type constant velocity universal joints have advantages such as less circumferential wobble, excellent responsiveness, and low manufacturing cost. On the other hand, they have disadvantages such as high sliding resistance and easy transmission of vehicle vibrations, especially engine vibrations at idle. Therefore, various idle vibration countermeasures have been studied in double-offset type constant velocity universal joints. For example, Patent Document 3 below shows a technique for absorbing idle vibration by setting a gap between the outer circumferential surface of the inner ring and the inner circumferential surface of the retainer.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 10-73129

[0008] Patent Document 2: Japanese Patent Application Publication No. 2007-85488

[0009] Patent Document 3: Japanese Patent Application Publication No. 2013-231518 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, with improvements in vehicle ride comfort, the NVH (Noise, Vibration, Harshness) characteristics required for constant velocity joints have become more stringent. Double-offset constant velocity joints inherently cannot avoid sliding contact between components. Therefore, even with countermeasures as described in Patent Document 3, it is difficult to reduce sliding resistance to the same level as that of a three-ball-pin sliding constant velocity joint where components primarily roll against each other. This problem of sliding resistance, particularly idling vibration, has become a bottleneck. In recent years, the application of double-offset constant velocity joints has been largely limited to areas less susceptible to engine vibration (e.g., rear drive shafts).

[0012] However, in recent years, with the continuous development of vehicle electrification, the number of electric vehicles (hereinafter referred to as EVs) that operate solely on the power of electric motors and hybrid electric vehicles (hereinafter referred to as HEVs) that operate on the power of both electric motors and engines has been increasing. Electric motors offer superior responsiveness compared to engines; therefore, constant velocity joints (CV joints) that transmit power from electric motors are required to have minimal circumferential wobble and excellent responsiveness. Furthermore, EVs do not generate engine vibration, and in HEVs, the engine is essentially stopped during idling; therefore, the idling vibration problem, which is the main reason limiting the application of double-offset CV joints, is not present in these vehicles. Based on these considerations, a double-offset type CV joint with minimal circumferential wobble and excellent responsiveness has been investigated for use as a sliding CV joint in power transmission systems such as drive shafts and transmission shafts in EVs and HEVs.

[0013] On the other hand, in sliding constant velocity universal joints, axial loads (induced thrust) are generated due to friction between internal components when rotating at an operating angle. Because this induced thrust resonates with the vehicle body, it can sometimes cause various vibration problems such as lateral swaying and roaring noises during start-up. Such problems are particularly pronounced in EVs and HEVs, which are known for their quiet operation. Therefore, if the induced thrust can be reduced, it may be possible to appropriately use double-offset constant velocity universal joints in EVs and HEVs.

[0014] Therefore, the object of the present invention is to reduce the induced thrust of the double-offset constant velocity universal joint, so as to make it suitable for use in the power transmission system of vehicles (EV, HEV) driven by electric motors.

[0015] Solution for solving the problem

[0016] As mentioned above, the induced thrust is an axial load generated by the friction between the internal components of a sliding constant velocity universal joint. Specifically, such as Figure 12As shown, the resultant force of the axial resistance Qx caused by the friction between the raceway groove 101a of the outer coupling member 101 and the contact portion of the ball 102, and the axial resistance Hx caused by the friction between the outer spherical surface 103a of the retainer 103 and the cylindrical inner circumferential surface 101b of the outer coupling member 101, becomes the induced thrust. Figure 13 The figure shows the result of induced thrust Fx (=Qx+Hx) of a double-offset constant velocity universal joint with 8 balls, obtained through mechanism analysis. As shown in the figure, in the double-offset constant velocity universal joint, it is assumed that the induced thrust mainly produces a number of frequency components that are the same as the number of balls (8 in this figure).

[0017] On the other hand, Figure 14 The results show the actual induced thrust of a double-offset constant velocity universal joint with eight balls. In this test, assuming the vehicle starts, while a torque of 900 Nm is input to the outer coupling member of the constant velocity universal joint at a speed of 150 rpm, the working angle is changed from 0° to 12° at a rate of 10.7° / min, and the axial load (induced thrust) applied to the outer coupling member is measured. Figure 14 The X-axis represents the frequency of vibration generated in the constant velocity universal joint, the Y-axis represents the operating angle of the constant velocity universal joint, and the Z-axis represents the magnitude of the axial load (induced thrust) applied to the outer coupling component. The peak at 2.5 Hz in the figure represents the first component of the induced thrust (the vibration component generated once per revolution of the constant velocity universal joint), the peak at 5 Hz represents the second component, the peak at 7.5 Hz represents the third component, and so on, up to the peak at 20 Hz represents the eighth component. Based on the actual measurement results shown in the figure, the induced thrust not only produces the eighth component but also several other components, confirming that the first component appears particularly significantly.

[0018] As described above, the cause of the various induced thrusts is considered as follows. As mentioned above, the induced thrust Fx is the resultant force of the axial resistance Qx between the ball and the outer coupling member and the axial resistance Hx between the retainer and the outer coupling member (refer to...). Figure 12 Additionally, the axial resistances Qx and Hx are the resultant forces of the loads generated in each phase. It should be noted that "each phase" refers to the phase of each ball and the raceway groove in contact with the ball in the outer coupling component (in the case of an 8-ball double-offset constant velocity universal coupling, phases 1 to 8); and the phase of each spherical part between the raceway grooves of the outer coupling component and the cylindrical part between the grooves of the retainer in contact with the outer coupling component (in the case of an 8-ball double-offset constant velocity universal coupling, phases 1 to 8).

[0019] Here, in Figure 15 , 16 The diagram shows the mechanical analysis results of the axial load and its resultant force (Qx) applied to the raceway grooves of each phase of the outer coupling member in a double-offset constant velocity universal coupling with eight balls. Figure 15 The diagram shows the axial components of the raceway loads in each phase and their resultant force in an ideal state where all components are of uniform size and all phases have uniform surface characteristics. In this case, the axial loads (refer to the dashed lines) in the raceways of all phases become uniform, and their resultant force becomes a regular shape (refer to the solid lines) strongly exhibiting a specific order component (eighth order component in the example). However, in reality, due to deviations in the dimensions of each component, deviations in the surface characteristics of the contact areas, etc., the contact state of the internal components becomes non-uniform. Therefore, as... Figure 16 As shown, the axial loads generated in the orbit at each phase deviate (refer to the dashed lines), and their resultant force becomes irregular in shape (refer to the solid lines). As a result, the induced thrust (Fx=Qx+Hx) produces various orders of magnitude components containing a first-order component (refer to...). Figure 14 If induced thrust of various degrees is generated in this way, there will be more resonance points with the vehicle body, which will increase the likelihood of noise and vibration problems.

[0020] Based on the above viewpoints, the inventors believe that by homogenizing the axial load generated in each phase of the double-offset constant velocity universal joint, it is possible to suppress the number of components of induced thrust. Specifically, the following structure is adopted: (1) an axial clearance is provided between the groove of the retainer and the ball, and (2) an axial clearance is provided at the fitting portion between the retainer and the inner coupling member. The above structure has been used as a countermeasure against idling vibration in the past, and therefore does not need to be adopted in EVs and HEVs that do not have idling vibration problems. However, according to the verification of the inventors, by providing axial clearances between the ball and the groove of the retainer, and between the retainer and the inner coupling member as described above, it is possible to reduce the number of components of induced thrust. This is believed to be because the imbalance of axial load caused by the deviation of friction force in each phase is absorbed by the axial clearances in (1) and (2) above, thereby homogenizing the axial load at each phase.

[0021] Based on the above, the present invention provides a sliding constant velocity universal joint, comprising: an outer coupling member having multiple straight raceway grooves formed on its cylindrical inner circumferential surface; an inner coupling member having multiple straight raceway grooves formed on its spherical outer circumferential surface; a plurality of balls disposed between the raceway grooves of the outer coupling member and the raceway grooves of the inner coupling member; and a retainer having an outer circumferential surface having a spherical portion that slides in contact with the cylindrical inner circumferential surface of the outer coupling member, an inner circumferential surface having a spherical portion that slides in contact with the spherical outer circumferential surface of the inner coupling member, and a plurality of grooves for retaining the plurality of balls. The sliding constant velocity universal joint is disposed in the power transmission system of a vehicle driven by an electric motor.

[0022] An axial gap is formed between the groove of the retainer and the ball.

[0023] An axial clearance of 0.6 mm or more is formed between the spherical part of the inner circumferential surface of the retainer and the spherical outer circumferential surface of the inner coupling member.

[0024] Thus, the sliding constant velocity universal joint according to the present invention is characterized by employing a conventional structure as a countermeasure against idling vibration in EVs and HEVs (especially EVs driven only by electric motors) that do not produce idling vibration problems. Specifically, by forming an axial clearance between the groove and the ball of the retainer, and by providing an axial clearance at the fitting portion of the retainer and the inner coupling member, the number of components that induce thrust can be reduced. It should be noted that if the axial clearance between the spherical part of the inner circumferential surface of the retainer and the spherical outer circumferential surface of the inner coupling member is too small, the imbalance of axial load at the contact portion of each phase cannot be adequately absorbed; therefore, the axial clearance is 0.6 mm or more.

[0025] If the axial clearance between the spherical part of the inner circumferential surface of the retainer and the spherical outer circumferential surface of the inner coupling component is too large, the balance of the internal components will be disrupted and the torque loss rate will increase. Therefore, the axial clearance is preferably less than 1.5 mm.

[0026] For example, by making the radius of curvature of the spherical part of the inner circumferential surface of the retainer greater than the radius of curvature of the spherical outer circumferential surface of the inner coupling member, an axial clearance can be provided at the mating part of the retainer and the inner coupling member.

[0027] Alternatively, by having a cylindrical surface parallel to the axis on the inner circumferential surface of the retainer, and spherical surfaces provided on both axial sides of the cylindrical surface and smoothly continuous with the cylindrical surface, an axial clearance can be provided at the fitting portion of the retainer and the inner coupling component.

[0028] When the surfaces of the raceway grooves of the outer coupling component and the cylindrical inner circumferential surface and the raceway grooves of the inner coupling component are forged surfaces, the roughness of these surfaces increases, thus making it easier for the deviation of the axial load in each phase to increase. In this case, as described above, it is particularly effective to provide axial clearances between the grooves of the balls and the retainer, and between the retainer and the inner coupling component, to absorb the deviation of the axial load in each phase.

[0029] The aforementioned sliding constant velocity universal joint can be appropriately assembled into a wheel drive system that uses an electric motor as its drive source. Specifically, a wheel drive system 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 aforementioned sliding constant velocity universal joint.

[0030] Invention Effects

[0031] As described above, according to the present invention, the induced thrust of the double-offset sliding constant velocity universal joint, which has less sway and excellent responsiveness, can be reduced, and therefore it can be appropriately used in the power transmission system of EV and HEV. Attached Figure Description

[0032] Figure 1 This is an axial sectional view of a double-offset sliding constant velocity universal joint according to an embodiment of the present invention.

[0033] Figure 2 yes Figure 1 A cross-sectional view of the sliding constant velocity universal joint in the orthogonal direction of the shaft.

[0034] Figure 3 yes Figure 1 Enlarged sectional view of the inner coupling components and retainer of the sliding constant velocity universal coupling.

[0035] Figure 4 yes Figure 3 Enlarged view of part C.

[0036] Figure 5 yes Figure 3 An enlarged view of part D.

[0037] Figure 6 It is shown Figure 3 A cross-sectional view of an example of the specifications of the mating part of the inner coupling component and the retainer.

[0038] Figure 7 It is shown Figure 3 A cross-sectional view of another example of the specifications of the mating part of the inner coupling component and the retainer.

[0039] Figure 8This is a graph showing the measurement results of the induced thrust in the embodiment (axial clearance δ2=1mm).

[0040] Figure 9 The figure shows the measurement results of the induced thrust of the comparative example (axial clearance δ2=0.5mm).

[0041] Figure 10 This is a graph showing the change in torque loss rate when the axial clearance δ2 is different.

[0042] Figure 11 It is equipped with Figure 1 A top view of an electric vehicle (EV) with a constant velocity universal joint.

[0043] Figure 12 This is a cross-sectional view showing the portion of a double-offset constant velocity universal joint that is subjected to axial load when rotating with a working angle.

[0044] Figure 13 This is a diagram showing the analytical results of the induced thrust of a double-offset constant velocity universal joint.

[0045] Figure 14 This is a graph showing the measured results of the induced thrust of a double-offset constant velocity universal joint.

[0046] Figure 15 This is a diagram showing the analytical results of the axial load applied to the raceway groove of the outer coupling component (the case where the axial load applied to the raceway groove of each phase is uniform).

[0047] Figure 16 This is a diagram showing the analytical results of the axial load applied to the raceway groove of the outer coupling component (the case where the axial load applied to the raceway groove of each phase is uneven). Detailed Implementation

[0048] The following describes in detail the embodiments of the sliding constant velocity universal joint involved in the present invention based on the accompanying drawings.

[0049] Figure 11 An electric vehicle (EV) is shown that operates solely using the power of an electric motor. This EV has a wheel drive unit 61 driving the front side of the front wheels 51 and a wheel drive unit 62 driving the rear side of the rear wheels 52. Each wheel drive unit 61, 62 has a drive unit 63 including an electric motor and a drive shaft 64 serving as a power transmission system for transmitting the driving force of the electric motor to the front wheel 51 or the rear wheel 52. In the example shown, the drive unit 63 of the front wheel drive unit 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 unit 62 is connected to the left and right rear wheels 52 via the left and right drive shafts 64.

[0050] Each drive shaft 64 includes, for example, a sliding constant velocity universal joint 1 disposed on the inner side (drive unit 63 side), a fixed constant velocity universal joint 65 disposed on the outer side (wheel 51, 52 side), and an intermediate shaft 66 connecting the two constant velocity universal joints 1 and 65. The sliding constant velocity universal joint 1 is a double-offset type constant velocity universal joint according to an embodiment of the present invention. The structure of this sliding constant velocity universal joint 1 will be described in detail below.

[0051] like Figure 1 as well as Figure 2 As shown, the sliding constant velocity universal joint 1 of this embodiment includes: one axial end ( Figure 1 The coupling consists of a cup-shaped outer coupling member 2 (open at the left end), an inner coupling member 3 disposed on the inner circumference of the outer coupling member 2, a plurality of balls 4, and a retainer 5 holding the plurality of balls 4. An internal component 10, including the inner coupling member 3, the balls 4, and the retainer 5, is axially displaceable and accommodated within the inner circumference of the outer coupling member 2. An intermediate shaft 66 (see reference 11) is engaged in the shaft hole 11 of the inner coupling member 3 via a spline fit. Figure 11 The end of ). It should be noted that in the following description, Figure 1 The axial direction of the outer coupling component 2 and the inner coupling component 3, with the working angle at 0° as shown, is called the "axial direction". Figure 1 The bottom side of the outer coupling component 2 in the axial direction with the working angle at 0° as shown (as shown) Figure 1 The right side of the coupling is called the "inner side of the coupling". Figure 1 The opening side of the outer coupling member 2 in the axial direction with the working angle at 0° as shown (as shown) Figure 1 The left side of the coupling is called the "coupling opening side".

[0052] On the cylindrical inner circumferential surface 6 of the outer coupling member 2, straight raceway grooves 7 extending axially are formed at equal intervals in multiple locations along the circumference. On the spherical outer circumferential surface 8 of the inner coupling member 3, straight raceway grooves 9 extending axially are formed at equal intervals in multiple locations along the circumference. The balls 4 are arranged one by one between the raceway grooves 7 of the outer coupling member 2 and the raceway grooves 9 of the inner coupling member 3, which are opposite each other in the radial direction, to transmit rotational torque between the two coupling members 2 and 3.

[0053] The retainer 5 is provided with a plurality of grooves 12, each groove 12 holding a ball 4. A spherical portion 13, which slides with the cylindrical inner circumferential surface 6 of the outer coupling member 2, and conical surfaces 14 are provided on both axial sides of the spherical portion 13 are formed on the outer peripheral surface of the retainer 5. A spherical portion 15, which slides with the spherical outer circumferential surface 8 of the inner coupling member 3, is formed on the inner peripheral surface of the retainer 5. In this embodiment, as... Figure 2 The diagram shows a case where the number of raceway grooves 7 and 9, balls 4, and grooves 12 is 8, but it is not limited to this; for example, the number of them could also be set to 6.

[0054] The center of curvature O1 of the spherical part 13 on the outer circumference of retainer 5 and the center of curvature O2 of the spherical part 15 on the inner circumference (i.e., the center of curvature of the spherical outer circumference 8 of the inner coupling member 3) are offset by an equal distance F relative to the coupling center O (the intersection of the plane passing through the center of all the balls 4 and the axis of the two coupling members 2 and 3) on opposite sides of the axial direction (refer to...). Figure 1 In the example shown, the center of curvature O1 of the spherical portion 13 of the outer peripheral surface of the retainer 5 is offset towards the inside of the coupling relative to the coupling center O, and the center of curvature O2 of the spherical portion 15 of the inner peripheral surface of the retainer 5 is offset towards the coupling opening relative to the coupling center O. Therefore, when an operating angle is applied between the outer coupling member 2 and the inner coupling member 3, the balls 4 held in the groove 12 of the retainer 5 remain within the bisecting plane of that operating angle at any given angle, thus ensuring constant velocity between the outer coupling member 2 and the inner coupling member 3. Furthermore, the balls 4 held in the retainer 5 roll on the raceway groove 7 of the outer coupling member 2, allowing the inner component 10 to move freely axially relative to the outer coupling member 2. It should be noted that, conversely, the curvature center O1 of the spherical part 13 of the outer peripheral surface of the retainer 5 can be positioned on the opening side of the coupling, and the curvature center O2 of the spherical part 15 of the inner peripheral surface of the retainer 5 can be positioned on the inner side of the coupling.

[0055] The outer coupling component 2 is manufactured through forging, turning, rolling, heat treatment, and grinding processes. In the forging process, a die forms the prototype of the outer coupling component. In the turning process, the outer peripheral surface of the prototype is turned. In the rolling process, an external spline is formed on the shaft portion of the prototype. In the heat treatment process, the prototype is heat-treated (e.g., high-frequency quenching and tempering). In the grinding process, the outer peripheral surface of the prototype is ground. When manufactured in this manner, the cylindrical inner peripheral surface 6 and the raceway groove 7 of the outer coupling component 2 become forged surfaces.

[0056] The inner coupling component 3 is manufactured through forging, turning, broaching, heat treatment, and grinding processes. In the forging process, a die forms a generally cylindrical prototype of the inner coupling component. In the turning process, the inner and outer circumferential surfaces of the prototype are turned. In the broaching process, an internal spline is formed on the inner circumference of the prototype. In the heat treatment process, the prototype is heat-treated (e.g., carburizing, quenching, and tempering). In the grinding process, the spherical outer circumferential surface (excluding the raceway groove) of the prototype is ground. If manufactured in this manner, the spherical outer circumferential surface 8 of the inner coupling component 3 becomes the grinding surface, the raceway groove 9 becomes the forging surface, and the inner circumferential surface (internal spline) becomes the cutting surface.

[0057] The retainer 5 is manufactured through a forging process, a turning process, a groove punching process, a heat treatment process, and a grinding process. In the forging process, a die forms a generally cylindrical retainer prototype. In the turning process, the inner and outer circumferential surfaces of the retainer prototype are turned. In the groove punching process, the retainer prototype is punched radially to form a groove 12. In the heat treatment process, the retainer prototype is heat-treated (e.g., carburizing, quenching, and tempering). In the grinding process, the spherical portion 13 of the outer circumferential surface of the retainer prototype, the spherical portion 15 of the inner circumferential surface, and a portion of the inner surface of the groove 12 (faces facing each other axially) are ground. If manufactured in this manner, the spherical portion 13 of the outer circumferential surface of the retainer 5, the spherical portion 15 of the inner circumferential surface, and a portion of the inner surface of the groove 12 become the ground surfaces, while other areas become the groove punching surfaces or turning surfaces.

[0058] like Figure 3 As shown, an axial gap (hereinafter referred to as "groove gap δ1") is provided between the wall of the groove 12 of the retainer 5 and the ball 4. When the axial dimension of the groove 12 of the retainer 5 is set as Lc and the diameter of the ball 4 is set as Db, the groove gap δ1 is represented by δ1=Lc-Db.

[0059] The groove clearance δ1 is preferably set to 0.001~0.05mm. A slight adjustment to the groove clearance δ1 is sufficient to achieve the desired effect. Furthermore, if the groove clearance δ1 is greater than 0.05mm, the deviation of the ball 4 from the bisecting plane of the working angle increases, potentially leading to a decrease in the constant velocity and durability of the sliding constant velocity universal coupling 1.

[0060] like Figure 4 and Figure 5As shown in the magnified view, an axial clearance δ2 is provided between the spherical part 15 of the inner circumferential surface of the retainer 5 and the spherical outer circumferential surface 8 of the inner coupling member 3. The axial clearance δ2 is the amount of relative axial movement of the inner coupling member 3 relative to the retainer 5, from the position where the spherical outer circumferential surface 8 of the inner coupling member 3 abuts against the spherical part 15 of the inner circumferential surface of the retainer 5 by moving the inner coupling member 3 axially to one side relative to the retainer 5, to the position where the spherical outer circumferential surface 8 of the inner coupling member 3 abuts against the spherical part 15 of the inner circumferential surface of the retainer 5 by moving the inner coupling member 3 axially to the other side relative to the retainer 5, to the position where the spherical outer circumferential surface 8 of the inner coupling member 3 abuts against the spherical part 15 of the inner circumferential surface of the retainer 5.

[0061] use Figure 6 The specific specifications for setting the aforementioned axial clearance δ2 are explained. In this specification, the radius of curvature Rc of the spherical portion 15 of the inner circumferential surface of the retainer 5 is greater than the radius of curvature Ri of the spherical outer circumferential surface 8 of the inner coupling member 3, and the center of curvature of the radius of curvature Rc is offset radially relative to the axis of the retainer 5. The radial clearance between the spherical outer circumferential surface 8 of the inner coupling member 3 and the spherical portion 15 of the inner circumferential surface of the retainer 5 is smallest at the outermost diameter portion (axial center) of the spherical portion 15 of the retainer 5, and gradually increases towards both axial sides from this point. The radial clearance between the outermost diameter portion of the spherical portion 15 of the retainer 5 and the spherical outer circumferential surface 8 of the inner coupling member 3 is substantially 0, but a small radial clearance is provided to allow relative movement between the two. Thus, an axial clearance δ2 is provided between the retainer 5 and the inner coupling member 3 to allow relative axial movement between the two.

[0062] Figure 7 Another specification for setting the axial clearance δ2 is shown. In this specification, the spherical outer circumferential surface 8 of the inner coupling member 3 and... Figure 6 Similarly, it is formed by a single spherical surface with a radius of curvature Ri. On the other hand, a cylindrical portion 16 parallel to the axis of the retainer 5 is formed on the inner circumferential surface of the retainer 5, and spherical portions 15 with a radius of curvature Rc are smoothly connected to both ends of the cylindrical portion 16 in the axial direction. Regarding the radius of curvature Rc of the spherical portion 15 of the inner circumferential surface of the retainer 5 and the radius of curvature Ri of the spherical outer circumferential surface 8 of the inner coupling member 3, there is a small spherical gap for sliding guidance, but in fact Rc≈Ri. In this specification, the spherical outer circumferential surface 8 of the inner coupling member 3 is axially slidably guided by the cylindrical portion 16 of the inner circumferential surface of the retainer 5, thereby allowing the inner coupling member 3 to move the axial dimension S of the cylindrical portion 16 relative to the retainer 5 in the axial direction. That is, the axial dimension S of the cylindrical portion 16 becomes the axial gap δ2 between the retainer 5 and the inner coupling member 3.

[0063] When the aforementioned sliding constant velocity universal coupling 1 has its working angle, if the rotational driving force from the electric motor inputs torque to the outer coupling member 2, the torque is transmitted to the inner coupling member 3 via the retainer 5 and the balls 4. At this time, axial sliding resistance is generated at the contact points between the components, thereby generating an axial load (induced thrust) on the outer coupling member 2. However, due to the deviations in the size and surface properties of the components, the axial load at each phase is uneven, resulting in deviation. In this embodiment, as described above, an axial groove gap δ1 is provided between the wall surface of the groove 12 of the retainer 5 and the axial direction of the balls 4, and an axial gap δ2 is provided between the spherical part 15 of the inner circumferential surface of the retainer 5 and the spherical outer circumferential surface 8 of the inner coupling member 3. By utilizing the groove gap δ1 and the axial gap δ2 to absorb the deviation of the axial load at each phase, the axial load at each phase is homogenized, thereby suppressing the various components of the induced thrust.

[0064] exist Figure 8 The results of measuring the induced thrust generated by a sliding constant velocity universal coupling 1 (example) with an axial clearance δ2 of 1 mm are shown. Measurement conditions and... Figure 14 The experiment was similar; specifically, the axial load (induced thrust) applied to the outer coupling member was measured while a torque of 900 Nm was input at 150 rpm and the working angle was varied from 0 to 12 degrees at a rate of 10.7 degrees / min. In this way, by setting an axial clearance δ2 between the retainer 5 and the inner coupling member 3, the results were compared with those obtained when the axial clearance δ2 was substantially zero (see...). Figure 14 Compared to the previous method, it can be confirmed that the magnitudes of the various components that induce thrust are smaller.

[0065] On the other hand, Figure 9 The results of measuring the induced thrust generated by a sliding constant velocity universal coupling 1 (comparative example) with an axial clearance δ2 of 0.5 mm are shown. Measurement conditions are the same as... Figure 14 The experiment was the same. In this case, the results were the same as those obtained when the axial clearance δ2 was substantially zero (see reference). Figure 14 Compared to the previous results, the magnitudes of the various components of the induced thrust are slightly smaller, but still comparable to the results measured when the axial clearance δ2 is 1 mm (see reference). Figure 8 Compared to the previous method, the components of induced thrust (especially the primary component) are larger, indicating that the reduction effect of induced thrust is not sufficient. Based on the above results, the axial clearance δ2 is greater than 0.6 mm.

[0066] Furthermore, if the axial clearance δ2 is too large, the internal wobble of the sliding constant velocity universal coupling 1 becomes excessive, thereby disrupting the internal balance and increasing the torque loss rate. For example, in Figure 10The figure shows the analytical results of torque loss rate when the operating angle is set to 8 degrees (usual angle) and the input torque is set to 300 N·m at a speed of 1200 rpm during high-speed driving. As shown in the figure, the torque loss rate is greater when the axial clearance δ2 is 2 mm (white circle) compared to when the axial clearance δ2 is 1 mm (black circle). Based on the above results, a larger axial clearance δ2 is not necessarily better; it is preferable to set it to, for example, 1.5 mm or less.

[0067] This invention is not limited to the embodiments described above. Other embodiments of the invention will be described below, but points identical to those described above will be omitted from the description.

[0068] Surface treatment can also be applied to the components other than the ball bearing 4 in the aforementioned sliding constant velocity universal coupling 1 (outer coupling component 2, inner coupling component 3, retainer 5). Specifically, surface treatments such as manganese phosphate treatment and shot peening can be applied to at least one of the following surfaces: the cylindrical inner circumferential surface 6 of the outer coupling component 2, the raceway groove 7 of the outer coupling component 2, the spherical outer circumferential surface 8 of the inner coupling component 3, the raceway groove 9 of the inner coupling component 3, the spherical part 13 of the outer circumferential surface of the retainer 5, and the spherical part 15 of the inner circumferential surface of the retainer 5.

[0069] The surface treated as described above satisfies at least one of Rsk being negative and Rp being 2 or less. In addition to the above conditions, it is desirable that Ra is 1.5 or less, preferably 0.6 or less, and Rz is 10 or less, preferably 6 or less.

[0070] It should be noted that Rsk, Rp, Ra, and Rz represent the skewness, maximum peak height, arithmetic mean height, and maximum height of the roughness curve along the reference length specified in JIS B 0601-2013, respectively. Rsk is positive relative to the mean line of the roughness curve when there are many peaks in the amplitude distribution curve and negative when there are many valleys. These parameters are measured at the contact points between components, within a total range of 4 mm, defined by a 0.8 mm × 5 interval along the axial reference length.

[0071] In addition, to reduce manufacturing costs, the raceway groove 7 of the outer coupling component 2 and the cylindrical inner circumferential surface 6, as well as the raceway groove 9 of the inner coupling component 3, are usually forged and precision machined as described above. However, they can also be precision machined by machining or grinding after heat treatment (quenching). Furthermore, the outer and inner circumferential surfaces of the retainer 5 are usually ground and precision machined as described above. However, they can also be precision machined by machining or rolling after heat treatment (quenching).

[0072] Furthermore, the double-biased sliding constant velocity universal joint involved in this invention is not limited to electric vehicles (EVs) that only use electric motors for propulsion, but can also be applied to the power transmission system of hybrid electric vehicles (HEVs) that use both electric motors and engines for propulsion.

[0073] Explanation of reference numerals in the attached figures

[0074] 1: Sliding constant velocity universal joint (double offset constant velocity universal joint)

[0075] 2: Outer coupling components

[0076] 3: Inner coupling components

[0077] 4: Ball bearing

[0078] 5: Retainer

[0079] 6: Cylindrical inner circumference

[0080] 7: Raceway groove

[0081] 8: Spherical outer circumference

[0082] 9: Raceway groove

[0083] 10: Internal components

[0084] 12: Groove

[0085] 13: spherical face

[0086] 14: Conical surface

[0087] 15: spherical face

[0088] 16: Cylindrical section

[0089] 51: Front wheel

[0090] 52: Rear wheel

[0091] 61, 62: Wheel drive system

[0092] 63: Drive Unit

[0093] 64: Drive shaft (power transmission system)

[0094] 65: Fixed constant velocity universal joint

[0095] 66: Intermediate shaft

[0096] O: Coupling center

[0097] O1: Center of curvature of the spherical part of the outer periphery of the retainer.

[0098] O2: The center of curvature of the spherical part of the inner circumference of the retainer.

[0099] Fx: Induced thrust

[0100] Qx: Axial resistance between the outer coupling component and the balls

[0101] Hx: Axial resistance between the outer coupling component and the retainer

[0102] δ1: Axial clearance between the groove and the ball (groove clearance)

[0103] δ2: Axial clearance between the retainer and the inner coupling component.

Claims

1. A sliding type constant velocity universal joint comprising: an outer joint member in which a plurality of linear grooves are formed in a cylindrical inner peripheral surface; an inner joint member in which a plurality of linear grooves are formed in a spherical outer peripheral surface; a plurality of balls disposed between the grooves of the outer joint member and the grooves of the inner joint member; and a retainer having an outer peripheral surface in which a spherical surface portion that is in sliding contact with the cylindrical inner peripheral surface of the outer joint member is formed, an inner peripheral surface in which a spherical surface portion that is in sliding contact with the spherical outer peripheral surface of the inner joint member is formed, and a plurality of grooves that retain the plurality of balls, wherein the sliding type constant velocity universal joint is provided in a power transmission system of a vehicle that is driven by an electric motor, wherein an axial gap is formed between the grooves of the retainer and the balls, and wherein an axial gap of 0.6 mm or more is formed between the spherical surface portion of the inner peripheral surface of the retainer and the spherical outer peripheral surface of the inner joint member.

2. The sliding type constant velocity universal joint according to claim 1, wherein the axial gap between the spherical surface portion of the inner peripheral surface of the retainer and the spherical outer peripheral surface of the inner joint member is 1.5 mm or less.

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

4. The sliding type constant velocity universal joint according to claim 1, wherein the inner peripheral surface of the retainer has a cylindrical surface that is parallel to an axis and the spherical surface portion that is provided on both axial sides of the cylindrical surface and is smoothly continuous with the cylindrical surface.

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

6. The sliding type constant velocity universal joint according to claim 1, wherein the sliding type constant velocity universal joint is provided in a power transmission system of a vehicle that is driven by only the electric motor.

7. A wheel drive device, wherein the wheel drive device comprises: the electric motor; a wheel; and the power transmission system that transmits a driving force of the electric motor to the wheel via the sliding type constant velocity universal joint according to claim 1. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Images