Sliding constant velocity universal joint

Abstract

This reduces the induced thrust of the double-offset constant velocity universal joint during vehicle startup. [Solution] In the double-offset sliding constant-velocity universal joint 1, the curvature center O1 of the outer spherical portion 13 and the curvature center O2 of the inner spherical portion 15 of the cage 5 are offset by an equidistant distance F on the opposite side of the joint center O in the axial direction. This distance F (cage offset amount) and the pitch circle diameter PCD of the multiple balls 4 are used. BALL F / PCD ratio BALL This value should be between 0.05 and less than 0.07. This shifts the operating angle at which induced thrust begins to occur towards higher angles, thereby reducing induced thrust in the low operating angle range.

Description

[Technical Field]

[0001] This invention relates to a sliding constant velocity universal joint. [Background technology]

[0002] Constant velocity universal joints, which are applied to automobile drive shafts and propeller shafts, are broadly classified into two types: sliding joints that allow both angular displacement and relative axial movement between the two shafts, and fixed joints that allow angular displacement between the two shafts but do not allow relative axial movement between the two shafts.

[0003] Known sliding constant velocity universal joints include double offset type universal joints (DOJ) that use balls as rolling elements to transmit rotational torque, and tripod type universal joints (TJ) that use rollers as rolling elements. For example, Patent Document 1 below shows a double offset type universal joint that is lighter and more compact by increasing the number of balls from 6 to 8. Furthermore, Patent Document 2 below shows a double offset type universal joint that increases the maximum operating angle to 30° or more while also being lighter and more compact.

[0004] Double offset constant velocity universal joints have advantages over tripod type constant velocity universal joints, such as less circumferential play, superior responsiveness, and lower manufacturing costs. However, they also have disadvantages, such as high sliding resistance, which easily transmits vehicle vibrations, especially engine vibrations during idling. Therefore, various measures to counter idling vibrations have been considered for double offset constant velocity universal joints. For example, Patent Document 3 below describes a technique for absorbing idling vibrations by creating a gap between the outer surface of the inner ring and the inner surface of the cage. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-73129 [Patent Document 2] Japanese Patent Publication No. 2007-85488 [Patent Document 3] Japanese Patent Publication No. 2013-231518 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, as vehicle ride comfort improves, the NVH (Noise, Vibration, Harshness) characteristics required of constant velocity universal joints are also becoming more stringent. Due to its structure, double offset constant velocity universal joints inevitably experience sliding contact between components. Therefore, even with measures such as those shown in Patent Document 3, it is difficult to reduce the sliding resistance to the same level as tripod-type sliding constant velocity universal joints, where components primarily contact each other by rolling. This sliding resistance problem, particularly the idling vibration problem, has become a bottleneck, and in recent years, the application range of double offset constant velocity universal joints has been almost entirely limited to parts that are less susceptible to engine vibration (for example, rear drive shafts).

[0007] Incidentally, in recent years, vehicle electrification has progressed, and the number of electric vehicles (EVs) that run solely on the power of an electric motor, and hybrid vehicles (HEVs) that run on the power of both an electric motor and an engine, is increasing. Because electric motors have superior responsiveness compared to engines, constant velocity universal joints that transmit power from electric motors also require low circumferential play and excellent responsiveness. Furthermore, since EVs do not generate engine vibrations, and in HEVs the engine is basically stopped when the vehicle is stopped (idling), these vehicles do not experience the idling vibration problem, which is the main reason why the application of double offset type constant velocity universal joints is limited. From these perspectives, in EVs and HEVs, the adoption of double offset type sliding constant velocity universal joints with low circumferential play and excellent responsiveness is being considered as a sliding type constant velocity universal joint installed in power transmission systems such as drive shafts and propeller shafts.

[0008] On the other hand, in a sliding constant velocity universal joint, an axial load (induced thrust) is generated due to frictional force between internal parts when the joint rotates at an operating angle. Specifically, as shown in Figure 5, the resultant force of the axial resistance Qx caused by the frictional force at the contact point 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 at the contact point between the outer spherical surface 103a of the cage 103 and the cylindrical inner circumferential surface 101b of the outer joint member 101 is the induced thrust.

[0009] Figure 6 shows the results of a mechanism analysis of the induced thrust Fx (=Qx+Hx) generated when a double-offset constant velocity universal joint with eight balls rotates at its operating angle. With the constant velocity universal joint at its operating angle, the phase angle at which the balls are positioned on the opening side of the outermost joint member is 0 degrees, and the phase angle at which they are positioned on the inner side of the outermost joint member is 180 degrees. As shown in the figure, the double-offset constant velocity universal joint generates an induced thrust of the same order as the number of balls n (8th order in the illustrated example) due to its structure. This nth-order induced thrust resonates with the vehicle body, potentially causing various vibration problems such as lateral swaying and booming noise during acceleration. These problems are particularly pronounced in EVs and HEVs, which are known for their quiet operation. Therefore, if the induced thrust during vehicle acceleration can be reduced, the double-offset constant velocity universal joint may be suitable for use in EVs and HEVs.

[0010] Therefore, the present invention aims to reduce the induced thrust of a double-offset constant velocity universal joint during vehicle starting, making it suitable for use in the power transmission system of vehicles (EVs and HEVs) driven by electric motors. [Means for solving the problem]

[0011] The inventors investigated the relationship between the magnitude of the nth-order component of the induced thrust generated in a double-offset constant velocity universal joint and the axial offset amount of the curvature centers of the outer and inner spherical surfaces of the cage relative to the joint center (hereinafter referred to as "cage offset amount"). Specifically, the relationship between the cage offset amount F and the ball's pitch circle diameter (PCD) was investigated. BALLF / PCD ratio BALL A double offset type constant velocity universal joint (conventional product) with a cage offset of 0.08, and a joint with a cage offset amount smaller than the conventional product (specifically, F / PCD BALL For each of the double-offset constant velocity universal joints (improved version) with a value of 0.06, the nth-order induced thrust component was analyzed when the operating angle was changed. The analysis conditions assumed the starting phase, where resonance between the nth-order induced thrust and the vehicle body is a problem, and the rotational speed was 150 min⁻¹. -1 The torque was set to 900 Nm.

[0012] Figure 7 shows the analysis results for the conventional product, and Figure 8 shows the analysis results for the improved product. In both the conventional and improved products, the induced thrust increases as the operating angle increases. In the conventional product, induced thrust begins to occur when the operating angle exceeds 2°, and at an operating angle of 5°, the induced thrust exceeds 10N, a level that could be problematic in vehicles. In contrast, in the improved product, induced thrust hardly occurs until the operating angle is around 3°, and even at an operating angle of 5°, the induced thrust is less than 10N. Thus, the improved product, with its smaller cage offset, shifts the operating angle at which induced thrust begins to occur to a higher angle compared to the conventional product, resulting in smaller induced thrust in the low operating angle range of 5° or less. This is thought to be because the smaller the cage offset, the larger the operating angle at which contact load between the inner surface of the outer joint member and the outer surface of the cage begins to occur (see Figure 9).

[0013] Based on the above findings, the present invention provides a sliding constant velocity universal joint comprising: an outer joint member having a plurality of linear track grooves formed on its cylindrical inner circumferential surface; an inner joint member having a plurality of linear track grooves formed on its spherical outer circumferential surface; a plurality of balls disposed between the track grooves of the outer joint member and the track grooves of the inner joint member; and a cage having an outer spherical surface portion that slides against the cylindrical inner circumferential surface of the outer joint member and an inner spherical surface portion that slides against the spherical outer circumferential surface of the inner joint member, wherein the center of curvature of the outer spherical surface portion and the center of curvature of the inner spherical surface portion of the cage are offset by an equal distance (F) on the opposite side of the joint center in the axial direction, The ratio (F / PCD BALL ) of the distance (F) to the pitch circle diameter (PCD BALL ) of the plurality of balls is 0.05 or more and less than 0.07, to provide a sliding constant velocity joint.

[0014] As described above, by making the cage offset amount (distance F) smaller than that of the conventional product, the operating angle at which the n-th component of the induced thrust begins to occur is shifted to the high angle side, and the induced thrust in the low operating angle range where it is often used can be reduced. Therefore, at the time of starting the vehicle, vibration caused by the induced thrust of the sliding constant velocity joint can be suppressed.

[0015] In the above sliding constant velocity joint, it is preferable to set the cage offset amount F so that the induced thrust generated under the conditions of a rotational speed of 150 min -1 and a torque of 900 Nm is 10 N or less in the operating angle range of 5° or less.

[0016] In the above sliding constant velocity joint, at least one of the track grooves, cylindrical inner peripheral surfaces of the outer joint member, and the track grooves of the inner joint member can be a forged surface.

[0017] The number of balls of the above sliding constant velocity joint can be, for example, 8.

[0018] The above sliding constant velocity joint can be suitably mounted on a vehicle having an electric motor as a drive source. Specifically, a wheel drive device including an electric motor, a wheel, and a power transmission system that transmits the driving force of the electric motor to the wheel via the above sliding constant velocity joint can be obtained.

Advantages of the Invention

[0019] As described above, according to the present invention, since the induced thrust of the double offset type constant velocity joint at the time of starting the vehicle can be reduced, it can be suitably used for the power transmission system of an EV or HEV.

Brief Description of the Drawings

[0020] [Figure 1] It is a plan view of an electric vehicle (EV). [Figure 2] It is an axial cross-sectional view of a sliding constant velocity joint (double offset constant velocity joint) according to an embodiment of the present invention. [Figure 3] It is a cross-sectional view in a direction orthogonal to the axis of the sliding constant velocity joint of FIG. 2. [Figure 4] It is a front view schematically showing a measuring device for induced thrust. [Figure 5] It is a cross-sectional view showing a part where an axial load is applied when the double offset constant velocity joint rotates at an operating angle. [Figure 6] It is a diagram showing an analysis result of the induced thrust of a double offset constant velocity joint. [Figure 7] It is a diagram showing an analysis result of the induced thrust for each operating angle of a double offset constant velocity joint according to a conventional product. [Figure 8] It is a diagram showing an analysis result of the induced thrust for each operating angle of a double offset constant velocity joint according to an improved product. [Figure 9] It is a diagram showing an analysis result of the contact load between the outer joint member and the cage in a conventional product and an improved product.

Mode for Carrying Out the Invention

[0021] An embodiment of the sliding constant velocity joint according to the present invention will be described in detail below based on the drawings.

[0022] Figure 1 shows an electric vehicle (EV) that runs solely on the power of an electric motor. This electric vehicle has a front wheel drive system 61 that drives the front wheels 51 and a rear wheel drive system 62 that drives the rear wheels 52. Each wheel drive system 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 system 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 system 62 is connected to the left and right rear wheels 52 via the left and right drive shafts 64.

[0023] Each drive shaft 64 has a sliding constant velocity universal joint 1 provided on the inboard side (drive unit 63 side), a fixed constant velocity universal joint 65 provided on the outboard side (wheel 51, 52 side), and an intermediate shaft 66 connecting both constant velocity universal joints 1 and 65. As this sliding constant velocity universal joint 1, a double offset type constant velocity universal joint according to one embodiment of the present invention is applied. The configuration of this sliding constant velocity universal joint 1 will be described in detail below.

[0024] As shown in Figures 2 and 3, the sliding constant velocity universal joint 1 of this embodiment comprises a cup-shaped outer joint member 2 with an open end in the axial direction (the left end in Figure 2), an inner joint member 3 arranged on the inner circumference of the outer joint member 2, a plurality of balls 4, and a cage 5 that holds the plurality of balls 4. The internal components 10, consisting of the inner joint member 3, the balls 4, and the cage 5, are housed on the inner circumference of the outer joint member 2 so as to be axially displaceable. The end of the intermediate shaft 66 (see Figure 1) is connected to the axial hole 11 of the inner joint member 3 by spline fitting. In the following description, in the state with an operating angle of 0° as shown in Figure 2, 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 Figure 2) in the axial direction is referred to as the "rear joint side," and the opening side of the outer joint member 2 (left side in Figure 2) is referred to as the "opening joint side."

[0025] The cylindrical inner surface 6 of the outer joint member 2 has linear track grooves 7 extending in the axial direction formed at equal intervals at multiple locations in the circumferential direction. The spherical outer surface 8 of the inner joint member 3 has linear track grooves 9 extending in the axial direction formed at equal intervals at multiple locations in the circumferential direction. One ball 4 is placed between the track grooves 7 of the radially opposing outer joint member 2 and the track grooves 9 of the radially opposing inner joint member 3, and transmits rotational torque between the two joint members 2 and 3.

[0026] The cage 5 is substantially cylindrical, with pockets 12 formed at equal intervals at multiple locations in the circumferential direction. Each pocket 12 holds one ball 4. The outer circumferential surface of the cage 5 has an outer 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 outer spherical portion 13. The inner circumferential surface of the cage 5 has an inner spherical portion 15 that contacts the spherical outer circumferential surface 8 of the inner joint member 3. In this embodiment, the number of track grooves 7, 9, balls 4, and pockets 12 is shown as 8, but it is not limited to this, and for example, these numbers may be 6.

[0027] At least one of the track groove 7 of the outer joint member 2, the cylindrical inner circumferential surface 6 of the outer joint member 2, and the track groove 9 of the inner joint member 3 is a forged surface. In this embodiment, the track groove 7 of the outer joint member 2, the cylindrical inner circumferential surface 6, and the track groove 9 of the inner joint member 3 are all forged surfaces. The spherical outer circumferential surface 8 of the inner joint member 3, the outer spherical portion 13 and inner spherical portion 15 of the cage 5, and the inner circumferential surface of the pocket 12 are, for example, ground surfaces.

[0028] The center of curvature O1 of the outer spherical surface portion 13 of the cage 5 and the center of curvature O2 of the inner spherical surface portion 15 (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 (hereinafter referred to as the "cage offset amount F") in the axial direction opposite to the joint center O (the intersection of the plane passing through the centers of all the balls 4 and the axial centers of both joint members 2 and 3), that is, with respect to the axial center of the pocket 12 (see Fig. 2). In the illustrated example, the center of curvature O1 of the outer spherical surface portion 13 of the cage 5 is offset to the back side of the joint with respect to the joint center O, and the center of curvature O2 of the inner spherical surface portion 15 of the cage 5 is offset to the opening side of the joint with respect to the joint center O.

[0029] Thereby, when an operating angle is imparted between the outer joint member 2 and the inner joint member 3, the ball 4 held in the pocket 12 of the cage 5 is always maintained in the bisecting plane of the operating angle at any operating angle, whereby the constant velocity property between the outer joint member 2 and the inner joint member 3 is ensured. Further, when the ball 4 held in the cage 5 rolls on the track groove 7 of the outer joint member 2, the internal component 10 is axially movable with respect to the outer joint member 2. Incidentally, conversely, the center of curvature O1 of the outer spherical surface portion 13 of the cage 5 may be arranged on the opening side of the joint, and the center of curvature O2 of the inner spherical surface portion 15 of the cage 5 may be arranged on the back side of the joint.

[0030] In a double-offset constant velocity joint, it is necessary to rotate the cage 5 in conjunction with a change in the operating angle so that the ball 4 held in the cage 5 is always arranged in the bisecting plane of the operating angle. At this time, if the cage offset amount F is too small, it becomes difficult for the cage 5 to rotate smoothly in conjunction with a change in the operating angle, and thus the operation of the constant velocity joint becomes unstable. Therefore, in a conventional double-offset constant velocity joint, in order to stabilize the operation, the cage offset amount F is set to be relatively large. Specifically, the ratio F / PCD BALL (see Fig. 3) of the cage offset amount F to the pitch circle diameter PCD of the plurality of balls 4 BALL is set within the range of 0.07 to 0.11.

[0031] In contrast, the constant velocity universal joint 1 of this embodiment has a smaller cage offset amount F than conventional products. Specifically, the cage offset amount F and the pitch circle diameter PCD of the multiple balls 4 BALL F / PCD ratio BALL This is less than 0.07. As a result, compared to conventional products, the operating angle at which induced thrust begins to occur is larger, and the induced thrust in the operating angle range of 5° or less is 10N or less (see Figure 8). On the other hand, in order to ensure the operability of the constant velocity universal joint 1, F / PCD BALL It is set to 0.05 or higher.

[0032] When installed in a vehicle, the operating angle of the sliding constant velocity universal joint 1 is often set to approximately 4-5°. The operating angle of a constant velocity universal joint refers to the operating angle generated in each constant velocity universal joint of the drive shaft when the steering is set to the straight position in a vehicle with one occupant on a horizontal, flat road surface. In this case, when the vehicle starts moving, the sliding constant velocity universal joint 1 is used at an operating angle of 5° or less. Therefore, as described above, by suppressing the induced thrust in the operating angle range of 5° or less to 10N or less, vibrations caused by resonance between the induced thrust of the sliding constant velocity universal joint 1 and the vehicle body are reduced when the vehicle starts moving. For this reason, the sliding constant velocity universal joint 1 described above can be suitably used in electric vehicles (EVs) which have excellent quietness.

[0033] The actual measurement of the induced thrust of the sliding constant velocity universal joint 1 is performed using the apparatus shown in Figure 4. This figure shows a part of the power circulation type testing machine used to measure the induced thrust force and slide resistance force. In this figure, the double offset type constant velocity universal joint of this embodiment is positioned on side A (hereinafter referred to as the "A-side joint"), and a paired fixed type constant velocity universal joint (for example, a Zepper-type constant velocity universal joint) is positioned on side B (hereinafter referred to as the "B-side joint"). The inner joint member of the A-side joint and the inner joint member of the B-side joint are connected via an intermediate shaft, and a predetermined operating angle θ is applied to both joints. In addition, the outer joint member of the A-side joint is connected to a load cell, and the outer joint member of the B-side joint is connected to a hydraulic servo.

[0034] During induced thrust measurement, a load torque at a predetermined rotational speed is applied to the B-side coupling. This load torque is transmitted from the B-side coupling to the A-side coupling via the intermediate shaft, causing the A-side coupling to rotate at a speed equal to the input rotational speed. At this time, induced thrust is generated inside the A-side coupling, and this induced thrust is detected by a load cell via the outer coupling member of the A-side coupling.

[0035] For example, with the above device, the rotation speed is 150 min⁻¹. -1 The load torque is set to 900 N·m, and the device is swept at a constant oscillation speed from 0° to 12° with an operating angle θ. The effective value (mean square rms of the result of Fourier transform of the axial load data) of the nth-order component (the 8th-order component in this embodiment) obtained by frequency analysis of the measured data is acquired as the induced thrust.

[0036] The present invention is not limited to the embodiments described above. Other embodiments of the present invention will be described below, but redundant explanations of points similar to those in the embodiments described above will be omitted.

[0037] The track groove 7 and cylindrical inner surface 6 of the outer joint member 2, and the track groove 9 of the inner joint member 3 are generally forged to reduce manufacturing costs, but they may also be finished by cutting or grinding after heat treatment (quenching). Similarly, the outer and inner surfaces of the cage 5 are generally ground to finish as described above, but they may also be finished by cutting or rolling after heat treatment (quenching).

[0038] In the above-described sliding constant velocity universal joint 1, the axial width of the pocket 12 of the cage 5 may be made larger than the diameter of the ball 4 to provide an axial gap (pocket gap) between the wall surface of the pocket 12 and the ball 4. This axial gap can be set, for example, within the range of 0 to 0.05 mm. Alternatively, the axial dimension of the pocket 12 of the cage 5 may be made smaller than the diameter of the ball 4 to bring the wall surface of the pocket 12 and the ball 4 into contact via a negative gap (compression allowance).

[0039] Furthermore, the inner circumferential surface of the cage 5 and the spherical outer circumferential surface 8 of the inner joint member 3 may be made relatively axially movable. This relative axial movement (axial gap) can be set, for example, within the range of 0.6 to 1.5 mm. Alternatively, the relative axial movement between the cage 5 and the inner joint member 3 may be made substantially zero. For example, the centers of curvature of the inner spherical surface 15 of the cage 5 and the spherical outer circumferential surface 8 of the inner joint member 3 may be made to coincide, and their radii of curvature may be made substantially the same. In this case, a small radial gap is formed between the inner spherical surface 15 of the cage 5 and the spherical outer circumferential surface 8 of the inner joint member 3 to allow relative movement between them, but the relative axial movement between them is almost zero.

[0040] Furthermore, the double-offset sliding constant velocity universal joint according to the present invention is not limited to electric vehicles (EVs) that use only an electric motor as a power source, but can also be applied to the power transmission systems of hybrid electric vehicles (HEVs) that use both an electric motor and an engine as power sources, and vehicles that use only an engine as a power source. [Explanation of symbols]

[0041] 1. Sliding constant velocity universal joint (double offset type constant velocity universal joint) 2. Outer joint member 3. Inner joint member 4 balls 5 cages 7, 9 Track grooves 10 Internal parts 13. Outer spherical portion of the cage 15. Inner spherical portion of the cage F Cage offset amount O joint center Center of curvature of the outer spherical portion of the O1 cage Center of curvature of the inner spherical surface of the O2 cage PCD BALL Ball pitch circle diameter

Claims

1. An outer joint member having multiple straight track grooves formed on its cylindrical inner surface, An inner joint member having multiple straight track grooves formed on its spherical outer surface, A plurality of balls are arranged between the track groove of the outer joint member and the track groove of the inner joint member, The device comprises an outer spherical surface portion that slides against the cylindrical inner surface of the outer joint member, and an inner spherical surface portion that slides against the spherical outer surface of the inner joint member, and a cage that holds the plurality of balls, In a sliding constant velocity universal joint in which the center of curvature of the outer spherical portion and the center of curvature of the inner spherical portion of the cage are offset by an equal distance (F) on the opposite side of the joint center in the axial direction, The distance (F) and the pitch circle diameter (PCD) of the plurality of balls ＢＡＬＬ ) ratio (F / PCD ＢＡＬＬ A sliding constant velocity universal joint in which the coefficient of force is 0.05 or more and less than 0.

07.

2. In the operating angle range of 5° or less, rotational speed 150 min －１ The sliding constant velocity universal joint according to claim 1, wherein the induced thrust generated under the condition of a torque of 900 Nm is 10 N or less.

3. The sliding constant velocity universal joint according to claim 1, wherein at least one of the track groove of the outer joint member, the cylindrical inner circumferential surface, and the track groove of the inner joint member is a forged surface.

4. The sliding constant velocity universal joint according to claim 1, wherein the number of balls is eight.

5. A sliding constant velocity universal joint according to claim 1, which is mounted on a vehicle driven by an electric motor.

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