Sliding constant velocity universal joint

Abstract

This reduces the torque loss rate of double offset constant velocity universal joints. [Solution] In a double offset type constant velocity universal joint 1 with a normal operating angle of 5° or less, a grease with a coefficient of friction greater than 0.08 is used as the grease sealed inside the outer joint member 2. This makes it possible to reduce the torque loss rate in the operating angle range near the normal operating angle, which is frequently used.

Description

Technical Field

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

Background Art

[0002] Constant velocity joints applied to automotive drive shafts and propeller shafts are roughly classified into a sliding type that allows both angular displacement and axial relative movement between two shafts, and a fixed type that allows angular displacement between two shafts but does not allow axial relative movement between the two shafts.

[0003] As sliding constant velocity joints, a double offset type constant velocity joint (DOJ) using balls as rolling elements for transmitting rotational torque and a tripod type constant velocity joint (TJ) using rollers as rolling elements are known. For example, Patent Document 1 below shows a double offset type constant velocity joint that is made lightweight and compact by increasing the number of balls from 6 to 8. Further, Patent Document 2 below shows a double offset type constant velocity joint that increases the maximum operating angle to 30° or more and further achieves weight reduction and compactness.

[0004] The double offset type constant velocity joint has the advantages of less circumferential play, excellent responsiveness, and low manufacturing cost compared to the tripod type constant velocity joint. On the other hand, it has the disadvantage of large sliding resistance (slide resistance) and is likely to transmit vehicle vibrations, particularly engine vibrations during idling. Therefore, various countermeasures against idling vibrations have been studied in the double offset type constant velocity joint. For example, Patent Document 3 below shows a technique for absorbing idling vibrations by providing a gap between the outer peripheral surface of the inner ring and the inner peripheral surface of the cage.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[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] However, even if idling vibration issues do not arise when applied to EVs and HEVs, as mentioned above, double-offset constant-velocity universal joints have a higher torque loss rate (i.e., poorer torque transmission efficiency) compared to tripod-type constant-velocity universal joints, where the parts primarily make contact by rolling, because the parts slide against each other. Therefore, if the torque loss rate of double-offset constant-velocity universal joints can be reduced, that is, if the torque transmission efficiency can be improved, they may be suitable for use in EVs and HEVs.

[0009] Therefore, the present invention aims to reduce the torque loss rate of a double-offset constant velocity universal joint. [Means for solving the problem]

[0010] The inventors investigated the relationship between the torque loss rate of a double-offset constant velocity universal joint and the friction coefficient of the grease sealed inside. Specifically, two types of grease, A and B, with different friction coefficients were prepared. The components contained in greases A and B are shown in Table 1 below.

[0011] [Table 1]

[0012] The coefficients of friction of greases A and B were measured by the SRV test, which is standardized in ASTM D5706 and D5707. An Optimol SRV5 vibration friction and wear tester was used as the test apparatus. The test conditions were as follows: the test specimens were a ball (diameter 3 / 8 inch, material SUSJ2, hardness HRC62) and a flat plate (material SCr450, hardness HRC59, surface roughness Ra0.7, polished finish). The coefficient of friction between the two test specimens was measured when they were slid at a pressure of 2 GPa, amplitude 3 mm, 25 Hz, and room temperature (25°C). As shown in Figure 4, the coefficient of friction after 5 minutes from the start of the test was 0.08 or higher (approximately 0.09) for grease A, while it was less than 0.08 (approximately 0.06) for grease B. Hereinafter, grease A, which has a relatively high coefficient of friction, will be referred to as "high μ grease A," and grease B, which has a relatively low coefficient of friction, will be referred to as "low μ grease B."

[0013] The torque loss rate was measured for double-offset constant velocity universal joints filled with high-μ grease A and double-offset constant velocity universal joints filled with low-μ grease B, each at different operating angles. As shown in Figure 5, at operating angles of 6° or more, the torque loss rate was lower when using low-μ grease B than when using high-μ grease A. On the other hand, at operating angles of 5° or less, the torque loss rate was lower when using high-μ grease A than when using low-μ grease B. In double-offset constant velocity universal joints, sliding contact occurs between internal parts as described above, so it is generally thought that a lower friction coefficient of grease results in a lower torque loss rate. However, the results in Figure 5 clearly show that in the low operating angle range of 5° or less, using grease with a high friction coefficient results in a lower torque loss rate.

[0014] To investigate the reasons for the above results, the inventors conducted a simulation to analyze how the contact load between the inner surface of the outer joint member and the outer surface of the cage changes with respect to the operating angle when the friction coefficients between the internal components of a double-offset constant velocity universal joint are different. As a result, as shown in Figure 6, it became clear that when the friction coefficient between the internal components is high (see solid line), i.e., when a grease with a high friction coefficient is used, the operating angle at which a contact load begins to occur between the outer joint member and the cage is shifted to the higher angle side (right side in the figure) compared to when the friction coefficient between the internal components is low (see dotted line), i.e., when a grease with a low friction coefficient is used. Thus, it is expected that the expansion of the operating angle range with small contact loads between internal components to the higher angle side by using a grease with a high friction coefficient is one of the reasons why the torque loss rate in the operating angle range of 5° or less was reduced.

[0015] Based on the above findings, the present invention provides an outer joint member having a plurality of linear track grooves formed on its cylindrical inner circumferential surface, An inner joint member having multiple straight track grooves formed on its spherical outer surface, A plurality of balls disposed between the track groove of the outer joint member and the track groove of the inner joint member, a cage having an outer spherical surface portion that slidably contacts the cylindrical inner peripheral surface of the outer joint member and an inner spherical surface portion that slidably contacts the spherical outer peripheral surface of the inner joint member, and holding the plurality of balls, and grease enclosed inside the outer joint member. In a sliding constant velocity universal joint in which the center of curvature of the outer spherical surface portion of the cage and the center of curvature of the inner spherical surface portion are offset by an equal distance in the axial direction opposite to the joint center, the normal angle is 5° or less, a sliding constant velocity universal joint is provided in which the friction coefficient of the grease is greater than 0.08.

[0016] As described above, in a double-offset constant velocity universal joint with a normal angle of 5° or less, by using grease with a relatively high friction coefficient (greater than 0.08), the torque loss rate in the operating angle range near the normal angle with high usage frequency can be suppressed. Note that the normal angle of the constant velocity universal joint refers to the operating angle that occurs in each constant velocity universal joint of the drive shaft when the steering is in a straight-ahead state in a vehicle with one passenger on a horizontal and flat road surface. Also, the friction coefficient of the grease is measured by the SRV test, and the specific test conditions are the same as the test conditions for the friction coefficients of the above greases A and B.

[0017] At least one of the track groove, the cylindrical inner peripheral surface of the outer joint member, and the track groove of the inner joint member of the above sliding constant velocity universal joint can be a forged surface.

[0018] The number of balls of the above sliding constant velocity universal joint can be, for example, eight.

[0019] The above sliding constant velocity universal joint can be suitably mounted on a vehicle having an electric motor as a drive source. Specifically, a wheel drive device can be obtained that includes 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 universal joint.

Advantages of the Invention

[0020] As described above, according to the present invention, it is possible to suppress the torque loss rate of a double offset constant velocity joint.

Brief Description of the Drawings

[0021] [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 of the sliding constant velocity joint of FIG. 2 in a direction perpendicular to the axis. [Figure 4] It is a graph showing the measurement results of the friction coefficient of grease. [Figure 5] It is a graph showing the change in the torque loss rate when the operating angle of the double offset constant velocity joint is changed. [Figure 6] It is a graph showing the analysis results of the contact load between the outer joint member and the cage when using greases with different friction coefficients.

Modes for Carrying Out the Invention

[0022] An embodiment of the sliding constant velocity joint according to the present invention will be described in detail below based on the drawings.

[0023] FIG. 1 shows an electric vehicle (EV) that runs only on the power of an electric motor. This electric vehicle has a front wheel drive device 61 that drives the front wheels 51 and a rear wheel drive device 62 that drives the rear wheels 52. Each wheel drive device 61, 62 has a drive unit 63 including an electric motor and a drive shaft 64 as a power transmission system that transmits the driving force of the electric motor to the front wheels 51 or the rear wheels 52. In the illustrated example, the drive unit 63 of the front wheel drive device 6 has a drive unit 63 of the front wheel drive device 61 connected to the left and right front wheels 51 via the left and right drive shafts 64, and the drive unit 63 of the rear wheel drive device 62 is connected to the left and right rear wheels 52 via the left and right drive shafts 64.

[0024] 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.

[0025] 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."

[0026] 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 (see Figure 3). 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.

[0027] 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 (see Figure 2). The inner circumferential surface of the cage 5 has an inner spherical portion 15 that slides against 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.

[0028] 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.

[0029] The curvature centers O1 of the outer spherical portion 13 and O2 of the inner spherical portion 15 of the cage 5 (i.e., the curvature centers of the spherical outer surface 8 of the inner joint member 3) are offset by an equidistant distance F on the opposite side of the axial direction from the joint center O (the intersection of the plane passing through the centers of all the balls 4 and the axes of both joint members 2 and 3), that is, from the axial center of the pocket 12 (see Figure 2). In the illustrated example, the curvature center O1 of the outer spherical portion 13 of the cage 5 is offset towards the joint back side relative to the joint center O, and the curvature center O2 of the inner spherical portion 15 of the cage 5 is offset towards the joint opening side relative to the joint center O. Alternatively, the curvature center O1 of the outer spherical portion 13 of the cage 5 may be positioned towards the joint opening side, and the curvature center O2 of the inner spherical portion 15 of the cage 5 may be positioned towards the joint back side.

[0030] As a result, when an operating angle is applied 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 within the plane that bisects the operating angle, thereby ensuring constant velocity between the outer joint member 2 and the inner joint member 3. Furthermore, as 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 able to move axially relative to the outer joint member 2.

[0031] When installed in a vehicle, the operating angle of the sliding constant velocity universal joint 1 is set to 5° or less. In other words, this sliding constant velocity universal joint 1 is mainly used when the operating angle is 5° or less.

[0032] A boot (not shown) is fitted between the intermediate shaft 66 inserted into the axial hole 11 of the inner joint member 3 and the opening of the outer joint member 2. Grease is sealed into the internal space of the outer joint member 2, which is sealed by this boot. In this embodiment, a grease with a coefficient of friction greater than 0.08 is used. The coefficient of friction of the grease is, for example, 0.15 or less. The coefficient of friction of the grease is measured by an SRV test and is the coefficient of friction after 5 minutes from the start of the test. The detailed test conditions are the same as the test conditions for the coefficient of friction of greases A and B described above.

[0033] Thus, by using grease with a friction coefficient greater than 0.08, the torque loss rate when rotating at an operating angle of 5° or less can be suppressed. For example, the torque loss rate at an operating angle of 5° can be suppressed to 0.2% or less, preferably 0.1% or less. As a result, the torque loss rate of the sliding constant velocity universal joint 1 is suppressed when operating at an operating angle near the frequently used common angle, thereby improving the torque transmission efficiency. Note that the torque loss rate is calculated by inputting a torque of 200 N·m to the outer joint member 2 of the sliding constant velocity universal joint 1 and running it for 700 min⁻¹. -1 When rotated, the torque output to the inner joint member 3 is measured, and the value is calculated as 100 * (input torque - output torque) / (input torque).

[0034] 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.

[0035] 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 machining or grinding after heat treatment (quenching). Similarly, the outer and inner surfaces of the cage 5 are generally ground to finish them, but they may also be finished by machining or rolling after heat treatment (quenching).

[0036] 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).

[0037] 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.

[0038] Furthermore, if the operating angle of the sliding constant velocity universal joint 1 is greater than 5°, it is preferable to use a grease with a low coefficient of friction, for example, a grease with a coefficient of friction of 0.08 or less.

[0039] 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]

[0040] 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 O joint center

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, A cage having 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 holding the plurality of balls, The outer joint member comprises grease sealed inside, In a sliding constant velocity universal joint in which the center of curvature of the outer spherical portion of the cage and the center of curvature of the inner spherical portion are offset by an equal distance on the opposite side of the joint center in the axial direction, The commonly used angle is 5° or less. A sliding constant velocity universal joint in which the friction coefficient of the grease is greater than 0.

08.

2. 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.

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

4. 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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