Sliding constant-velocity universal joint

Abstract

In a double offset type sliding constant velocity universal joint 1, the curvature center O1 of the outer peripheral spherical surface section 13 of a cage 5 and the curvature center O2 of the inner peripheral spherical surface part 15 are offset by an equal distance F to opposite sides in the axial direction with respect to the joint center O. The ratio F / PCDBALL of the distance F (cage offset amount) to the pitch circle diameter PCDBALL of a plurality of balls 4 is 0.05 or more and less than 0.07. As a result, the operation angle at which the induced thrust starts to be generated is shifted to the high angle side, and the induced thrust in the low operation angle region can be reduced.

Description

Sliding constant velocity universal joint

[0001] The present invention relates to a sliding type constant velocity universal joint.

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

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

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

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

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

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

[0008] On the other hand, in a sliding-type constant velocity universal joint, an axial load (induced thrust) is generated due to the frictional force between internal parts when rotating through an operating angle. Specifically, as shown in Fig. 5 , the resultant force of the axial resistance Qx caused by the frictional force at the contact portion between the track grooves 101a of the outer joint member 101 and the balls 102 and the axial resistance Hx caused by the frictional force at the contact portion between the outer spherical surface 103a of the cage 103 and the cylindrical inner circumferential surface 101b of the outer joint member 101 becomes the induced thrust.

[0009] FIG. 6 shows the results of mechanical analysis of the induced thrust Fx (= Qx + Hx) generated when a double offset constant velocity universal joint having eight balls rotates at a working angle. When the constant velocity universal joint is at a working angle, the phase angle at which the balls are positioned closest to the opening of the outer joint member is 0°, and the phase angle at which the balls are positioned closest to the innermost end of the outer joint member is 180°. As shown in the figure, a double offset constant velocity universal joint generates an induced thrust of the same order as the number n of balls (eighth order in the illustrated example). This nth-order induced thrust resonates with the vehicle body, potentially causing various vibration problems, such as rolling and muffled noise, during start-up. These problems are particularly pronounced in quieter electric vehicles (EVs) and hybrid electric vehicles (HEVs). Therefore, if the induced thrust during start-up can be reduced, double offset constant velocity universal joints may be suitable for use in EVs and HEVs.

[0010] Therefore, the present invention aims to reduce the induced thrust of a double offset type constant velocity universal joint when the vehicle starts, making it suitable for use in the power transmission system of vehicles (EVs and HEVs) that use electric motors as their drive source.

[0011] The inventors have verified the relationship between the magnitude of the nth-order component of the induced thrust generated in a double offset type constant velocity universal joint and the axial offset of the center of curvature of the outer spherical surface portion of the cage and the center of curvature of the inner spherical surface portion 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 pitch circle diameter PCD of the ball ＢＡＬＬ Ratio of F / PCD ＢＡＬＬ The double offset type constant velocity universal joint (conventional product) has a cage offset of 0.08, and the cage offset amount is smaller than that of the conventional product (specifically, F / PCD ＢＡＬＬ The analysis was performed on the double offset constant velocity universal joint (improved model) with a working angle of 0.06, and the nth order induced thrust component was analyzed when the working angle was changed. The analysis conditions were assumed to be the time when the nth order induced thrust and the resonance with the vehicle body become a problem, and the rotation speed was 150 min. －１ The torque was set to 900 Nm.

[0012] The analysis results for the conventional product are shown in Figure 7, and the analysis results for the improved product are shown in Figure 8. For both the conventional product and the improved product, the induced thrust increased as the operating angle increased. With the conventional product, induced thrust began to occur when the operating angle exceeded 2°, and at an operating angle of 5°, the induced thrust exceeded 10 N, a level that could potentially cause problems in a vehicle. In contrast, with the improved product, almost no induced thrust occurred until the operating angle reached approximately 3°, and even at an operating angle of 5°, the induced thrust was below 10 N. As such, with the improved product, which has a small cage offset, the operating angle at which induced thrust begins to occur shifts higher than with the conventional product, and the induced thrust is smaller at low operating angles of 5° or less. This is thought to be because the smaller the cage offset, the larger the operating angle at which contact load begins to occur between the inner circumferential surface of the outer joint member and the outer circumferential surface of the cage (see Figure 9).

[0013] Based on the above findings, the present invention provides a sliding type constant velocity universal joint comprising: an outer joint member having a plurality of linear track grooves formed on a cylindrical inner peripheral surface thereof; an inner joint member having a plurality of linear track grooves formed on a spherical outer peripheral surface thereof; a plurality of balls arranged between the track grooves of the outer joint member and the track grooves of the inner joint member; and a cage having an outer peripheral spherical portion in sliding contact with the cylindrical inner peripheral surface of the outer joint member and an inner peripheral spherical portion in sliding contact with the spherical outer peripheral surface of the inner joint member, and holding the plurality of balls, wherein the center of curvature of the outer peripheral spherical portion and the center of curvature of the inner peripheral spherical portion of the cage are offset by an equal distance (F) on opposite sides in the axial direction from the joint center, ＢＡＬＬ ) and the ratio (F / PCD ＢＡＬＬ ) is 0.05 or more and less than 0.07.

[0014] As described above, by making the cage offset amount (distance F) smaller than that of conventional products, the operating angle at which the nth-order component of induced thrust begins to occur can be shifted to the higher angle side, thereby reducing induced thrust in the low operating angle range that is often used. As a result, vibrations caused by induced thrust in the sliding type constant velocity universal joint can be suppressed when the vehicle starts moving.

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

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

[0017] The number of balls in the sliding type constant velocity universal joint may be, for example, eight.

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

[0019] As described above, according to the present invention, the induced thrust of a double offset constant velocity universal joint can be reduced when a vehicle starts moving, and therefore this can be suitably used in the power transmission system of an EV or HEV.

[0020] FIG. 3 is a plan view of an electric vehicle (EV). FIG. 4 is an axial cross-sectional view of a sliding type constant velocity universal joint (double offset constant velocity universal joint) according to one embodiment of the present invention. FIG. 5 is a cross-sectional view orthogonal to the axis of the sliding type constant velocity universal joint of FIG. 2. FIG. 6 is a front view schematically showing an induced thrust measuring device. FIG. 7 is a cross-sectional view showing a portion to which an axial load is applied when a double offset constant velocity universal joint rotates through an operating angle. FIG. 8 is a diagram showing the analysis results of induced thrust in a double offset constant velocity universal joint. FIG. 9 is a diagram showing the analysis results of induced thrust for each operating angle in a double offset constant velocity universal joint according to a conventional product. FIG. 10 is a diagram showing the analysis results of induced thrust for each operating angle in a double offset constant velocity universal joint according to an improved product. FIG. 11 is a diagram showing the analysis results of contact load between the outer joint member and the cage in the conventional product and the improved product.

[0021] 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.

[0022] 1 shows an electric vehicle (EV) that runs solely on the power of an electric motor. This electric vehicle has a front wheel drive unit 61 that drives the front wheels 51 and a rear wheel drive unit 62 that drives the rear wheels 52. Each wheel drive unit 61, 62 has a drive unit 63 including an electric motor and a drive shaft 64 as a power transmission system that transmits the driving force of the electric motor to the front wheels 51 or rear wheels 52. In the illustrated example, the drive unit 63 of the front wheel drive unit 61 is connected to the left and right front wheels 51 via left and right drive shafts 64, and the drive unit 63 of the rear wheel drive unit 62 is connected to the left and right rear wheels 52 via left and right drive shafts 64.

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

[0024] 2 and 3 , the sliding type constant velocity universal joint 1 of this embodiment includes a cup-shaped outer joint member 2 having one open axial end (the left end in FIG. 2 ), an inner joint member 3 disposed on the inner periphery of the outer joint member 2, a plurality of balls 4, and a cage 5 for holding the plurality of balls 4. An internal part 10 consisting of the inner joint member 3, the balls 4, and the cage 5 is housed on the inner periphery of the outer joint member 2 so as to be axially displaceable. An end of an intermediate shaft 66 (see FIG. 1 ) is coupled by spline fitting to an axial hole 11 of the inner joint member 3. In the following description, the axial direction of the outer joint member 2 and the inner joint member 3 in the state of an operating angle of 0° shown in FIG. 2 is referred to as the "axial direction," the bottom side of the outer joint member 2 (right side in FIG. 2 ) in the axial direction is referred to as the "joint deep side," and the opening side of the outer joint member 2 (left side in FIG. 2 ) is referred to as the "joint opening side."

[0025] Axial-direction extending linear track grooves 7 are formed at equal intervals in a plurality of positions in the circumferential direction on the cylindrical inner peripheral surface 6 of the outer joint member 2. Axial-direction extending linear track grooves 9 are formed at equal intervals in a plurality of positions in the circumferential direction on the spherical outer peripheral surface 8 of the inner joint member 3. One ball 4 is disposed between each of the track grooves 7 of the outer joint member 2 and the track groove 9 of the inner joint member 3, which are opposed in the radial direction, to transmit rotational torque between the two joint members 2, 3.

[0026] The cage 5 is substantially cylindrical, with pockets 12 formed at equal intervals in the circumferential direction. Each pocket 12 holds one ball 4. The outer peripheral surface of the cage 5 is formed with an outer peripheral spherical portion 13 that slides against the cylindrical inner peripheral surface 6 of the outer joint member 2, and tapered surfaces 14 that are provided on both axial sides of the outer peripheral spherical portion 13. The inner peripheral surface of the cage 5 is formed with an inner peripheral spherical portion 15 that comes into contact with the spherical outer peripheral surface 8 of the inner joint member 3. Note that while this embodiment shows a case in which the number of track grooves 7, 9, balls 4, and pockets 12 is eight, the number of these may be, for example, six.

[0027] At least one of the track grooves 7 of the outer joint member 2, the cylindrical inner peripheral surface 6 of the outer joint member 2, and the track grooves 9 of the inner joint member 3 is a forged surface. In this embodiment, the track grooves 7 of the outer joint member 2, the cylindrical inner peripheral surface 6, and the track grooves 9 of the inner joint member 3 are all forged surfaces. The spherical outer peripheral surface 8 of the inner joint member 3, the outer peripheral spherical portion 13 and inner peripheral spherical portion 15 of the cage 5, and the inner peripheral 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") on opposite axial sides from the joint center O (the intersection of a plane passing through the centers of all of the balls 4 and the axes of both joint members 2, 3), i.e., from 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 toward the back of the joint from the joint center O, and the center of curvature O2 of the inner spherical surface portion 15 of the cage 5 is offset toward the joint opening from the joint center O.

[0029] As a result, when an operating angle is applied between the outer joint part 2 and the inner joint part 3, the balls 4 held in the pockets 12 of the cage 5 are always maintained within the plane bisecting the operating angle regardless of the operating angle, thereby ensuring constant velocity between the outer joint part 2 and the inner joint part 3. Furthermore, the balls 4 held in the cage 5 roll on the track grooves 7 of the outer joint part 2, allowing the internal part 10 to move axially relative to the outer joint part 2. Note that, conversely to the above, the center of curvature O1 of the outer peripheral spherical part 13 of the cage 5 may be located on the joint opening side, and the center of curvature O2 of the inner peripheral spherical part 15 of the cage 5 may be located on the joint inner side.

[0030] In a double offset constant velocity universal joint, the cage 5 must be rotated in conjunction with changes in the working angle so that the balls 4 held in the cage 5 are always arranged within the plane bisecting the working angle. If the cage offset amount F is too small, the cage 5 will not rotate smoothly in conjunction with changes in the working angle, making the operation of the constant velocity universal joint unstable. Therefore, in conventional double offset constant velocity universal joints, in order to stabilize operation, the cage offset amount F is set to a certain degree, and specifically, the cage offset amount F and the pitch circle diameter PCD of the plurality of balls 4 are set to a certain degree. ＢＡＬＬ (See Figure 3) ＢＡＬＬ was set within the range of 0.07 to 0.11.

[0031] In contrast, the constant velocity universal joint 1 of this embodiment has a cage offset amount F that is smaller than that of the conventional product. Specifically, the cage offset amount F and the pitch circle diameter PCD of the plurality of balls 4 ＢＡＬＬ Ratio of F / PCD ＢＡＬＬ is less than 0.07. As a result, the operating angle at which induced thrust begins to be generated becomes larger than that of the conventional product, and the induced thrust in the operating angle range of 5° or less becomes 10 N or less (see FIG. 8). On the other hand, in order to ensure the operability of the constant velocity universal joint 1, F / PCD ＢＡＬＬ is set to 0.05 or greater.

[0032] When installed in a vehicle, the normal operating angle of the sliding type constant velocity universal joint 1 is often set to about 4 to 5 degrees. The normal 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 in a straight-ahead position in a vehicle with one occupant on a horizontal, flat road. In this case, when the vehicle starts, the sliding type constant velocity universal joint 1 is used at an operating angle of 5 degrees or less. Therefore, by keeping the induced thrust in the operating angle range of 5 degrees or less to 10 N or less as described above, vibration caused by resonance between the induced thrust of the sliding type constant velocity universal joint 1 and the vehicle body when the vehicle starts is reduced. Therefore, the above sliding type constant velocity universal joint 1 can be suitably used in electric vehicles (EVs) that are excellent in quietness.

[0033] The actual measurement of the induced thrust of the sliding-type constant velocity universal joint 1 is performed using the device shown in FIG. 4 . This figure shows a portion of a power circulation testing machine used to measure induced thrust force and sliding resistance force. In this figure, the double offset constant velocity universal joint of this embodiment is arranged on side A (hereinafter referred to as the "A-side joint"), and a fixed constant velocity universal joint (e.g., a Rzepper-type constant velocity universal joint) that forms a pair with it is arranged 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 working angle θ is applied to both joints. Furthermore, 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] When measuring induced thrust, a load torque of a predetermined rotational speed is input to the B-side joint. This load torque is transmitted from the B-side joint via the intermediate shaft to the A-side joint, causing the A-side joint to rotate at a rotational speed equal to the input rotational speed. At this time, induced thrust is generated inside the A-side joint, and this induced thrust is detected by the load cell via the outer joint member of the A-side joint.

[0035] For example, in the above device, the rotation speed is 150 min. －１The load torque is set to 900 N m, and the operating angle θ is swept from 0° to 12° at a constant swing speed. The measurement data is then subjected to frequency analysis to obtain the effective value (root mean square rms of the result of Fourier transforming the axial load data) of the nth order component (the 8th order component in this embodiment) as the induced thrust.

[0036] The present invention is not limited to the above-described embodiment. Other embodiments of the present invention will be described below, but redundant description of the same points as those in the above-described embodiment will be omitted.

[0037] The track grooves 7 and the cylindrical inner peripheral surface 6 of the outer joint member 2 and the track grooves 9 of the inner joint member 3 are generally forged to reduce manufacturing costs, but may be finished by cutting or grinding after heat treatment (quenching). Furthermore, the outer peripheral surface and the inner peripheral surface of the cage 5 are generally ground to reduce manufacturing costs, but may be finished by cutting or rolling after heat treatment (quenching).

[0038] In the above-described sliding type 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, thereby providing 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, thereby bringing the wall surface of the pocket 12 into contact with the ball 4 via a negative gap (interference).

[0039] Furthermore, the inner peripheral surface of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3 may be made movable in the axial direction relative to each other. The amount of this relative axial movement (axial gap) can be set, for example, within a range of 0.6 to 1.5 mm. Alternatively, the amount of 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 portion 15 of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3 may be aligned, and their radii of curvature may be made approximately the same. In this case, a slight radial gap is formed between the inner spherical surface portion 15 of the cage 5 and the spherical outer peripheral surface 8 of the inner joint member 3 to allow relative movement therebetween, but the amount of relative axial movement therebetween is substantially zero.

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

[0041] DESCRIPTION OF SYMBOLS 1 Sliding type constant velocity universal joint (double offset constant velocity universal joint) 2 Outer joint member 3 Inner joint member 4 Ball 5 Cage 7, 9 Track groove 10 Internal part 13 Outer peripheral spherical portion of cage 15 Inner peripheral spherical portion of cage F Cage offset amount O Joint center O1 Center of curvature of outer peripheral spherical portion of cage O2 Center of curvature of inner peripheral spherical portion of cage PCD ＢＡＬＬ Ball pitch diameter

Claims

1. A sliding type constant velocity universal joint comprising: an outer joint member having a plurality of linear track grooves formed on a cylindrical inner peripheral surface; an inner joint member having a plurality of linear track grooves formed on a spherical outer peripheral surface; a plurality of balls arranged between the track grooves of the outer joint member and the track grooves of the inner joint member; and a cage having an outer spherical portion in sliding contact with the cylindrical inner peripheral surface of the outer joint member and an inner spherical portion in sliding contact with the spherical outer peripheral surface of the inner joint member, and holding the plurality of balls, wherein 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 opposite sides of the joint center in the axial direction, ＢＡＬＬ ) and the ratio (F / PCD ＢＡＬＬ ) is 0.05 or more and less than 0.

07.

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

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

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

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

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