Fixed-type constant velocity universal joint

A fixed type constant velocity universal joint of a track groove crossing type has track grooves of an inner joint member formed so as to be mirror-image symmetrical with the paired track grooves of an outer joint member with respect to a joint center plane at an operating angle of 0°. The track grooves of both the joint members each have a length corresponding to a maximum operating angle required for a rear-wheel drive shaft. Further, each axial clearance between the inner joint member and the cage is set larger than an axial clearance formed by a ball track clearance between each of balls and each track groove.

TECHNICAL FIELD

The present invention relates to a fixed type constant velocity universal joint to be used in a power transmission system of automobiles and various industrial machines, for allowing only angular displacement between two shafts on a driving side and a driven side. More particularly, the present invention relates to a fixed type constant velocity universal joint to be used in an automotive rear-wheel drive shaft or a propeller shaft.

BACKGROUND ART

As fixed type constant velocity universal joints, there have been publicly known joints of, for example, a so-called six-ball Rzeppa type (BJ) and a six-ball undercut-free type (UJ), and an eight-ball Rzeppa type (EBJ) and an eight-ball undercut-free type (EUJ). Those joints are used as appropriate in accordance with usage, required characteristics, and the like. Further, there have also been proposed various fixed type constant velocity universal joints of a so-called track groove crossing type (for example, Patent Literature 1).

Referring toFIG. 22AandFIG. 22B, description is given of a fixed type constant velocity universal joint of a track groove crossing type disclosed in Patent Literature 1.FIG. 22Ais a vertical sectional view of a state in which the fixed type constant velocity universal joint disclosed in Patent Literature 1 forms an operating angle of 0°, andFIG. 22Bis a vertical sectional view of a state in which the fixed type constant velocity universal joint forms an operating angle. The constant velocity universal joint121includes an outer joint member122, an inner joint member123, balls124, and a cage125. In the constant velocity universal joint121, a plurality of (for example, eight) arc-shaped track grooves127are formed in a spherical inner peripheral surface126of the outer joint member122. The track grooves127are formed so that planes including ball raceway center lines x of the track grooves127are inclined with respect to a joint axial line n-n and the track grooves127are adjacent to each other in a peripheral direction with their inclination directions opposite to each other (detailed illustration of states of the inclination is omitted). Further, although detailed illustration is omitted, a plurality of arc-shaped track grooves129are formed in a spherical outer peripheral surface128of the inner joint member123. The track grooves129are formed so as to be mirror-image symmetrical with the paired track grooves127of the outer joint member122with respect to a plane P including a joint center O at the operating angle of 0°. That is, the inner joint member123is assembled to an inner periphery of the outer joint member122so that the paired track grooves127and129cross each other.

As illustrated inFIG. 22A, curvature centers of the arc-shaped track grooves127of the outer joint member122and the arc-shaped track grooves129of the inner joint member123are each positioned at the joint center O. Each ball124is interposed in a crossing portion between the track groove127of the outer joint member122and the track groove129of the inner joint member123, which are paired with each other. The balls124are held by the cage125arranged between the outer joint member122and the inner joint member123. Curvature centers of a spherical outer peripheral surface132and a spherical inner peripheral surface133of the cage125are each positioned at the joint center O. In the constant velocity universal joint121, the paired track grooves127and129cross each other, and the balls124are interposed in those crossing portions. Therefore, when the joint forms an operating angle, the balls124are always guided in a plane bisecting an angle formed between axial lines of the outer joint member122and the inner joint member123. As a result, rotational torque is transmitted at a constant velocity between the two axes.

As described above, the track grooves127and129of the outer joint member122and the inner joint member123are adjacent to each other in the peripheral direction with their inclination directions opposite to each other. Therefore, when both the joint members122and123rotate relative to each other at the operating angle of 0° illustrated inFIG. 22A, forces in the opposite directions are applied from the balls124to pocket portions125aof the cage125that are adjacent to each other in the peripheral direction. Due to the forces in the opposite directions, the cage125is stabilized at the position of the joint center O. Thus, a contact force between the spherical outer peripheral surface132of the cage125and the spherical inner peripheral surface126of the outer joint member122, and a contact force between the spherical inner peripheral surface133of the cage125and the spherical outer peripheral surface128of the inner joint member123are suppressed. As a result, torque loss and heat generation are suppressed, and the durability is enhanced.

CITATION LIST

Patent Literature 1: JP 2009-250365 A

SUMMARY OF INVENTION

Technical Problem

Incidentally, the fixed type constant velocity universal joint121described above is designed for application to automotive drive shafts, specifically, front-wheel drive shafts (more specifically, on its outboard side) that form an especially high operating angle (practical maximum operating angle θ max of, for example, 40° or more). The track grooves of the fixed type constant velocity universal joint need to have lengths that prevent, even when the joint forms the maximum operating angle θ max, the balls from dropping off end portions on an opening side of the track grooves of the outer joint member, and end portions on an interior side of the track grooves of the inner joint member. Thus, in the fixed type constant velocity universal joint121described above, values of an axial dimension t1of a mouth portion122aof the outer joint member122, an axial dimension t2from the joint center O to the end portion of the outer joint member122on the opening side, an axial dimension t3of the inner joint member123, and an axial dimension t4of the cage125are set so that, even when the joint forms the maximum operating angle θ max, the balls124are not disengaged from the track grooves127and129.

On the other hand, operating angles to be formed by fixed type constant velocity universal joints for rear-wheel drive shafts are not as large as those to be formed by fixed type constant velocity universal joints for the front-wheel drive shafts. It is only necessary that an operating angle of approximately 20° be formed during travel of a vehicle. Further, in consideration of a folding angle at the time of mounting the drive shaft to the vehicle, and allowance for up-and-down bounce of the vehicle during travel on rough roads, it is only necessary that a maximum operating angle θ max of approximately 30° be formed. Operating angles to be formed by fixed type constant velocity universal joints for propeller shafts also are not as large as those to be formed by the fixed type constant velocity universal joints for the front-wheel drive shafts. It is only necessary that an operating angle of approximately 10° be formed during the travel of the vehicle. Further, in consideration of the folding angle at the time of mounting the propeller shaft to the vehicle, and the allowance for the up-and-down bounce of the vehicle during the travel on rough roads, it is only necessary that a maximum operating angle θ max of approximately 20° be formed. Thus, when the design concept of Patent Literature 1 is applied as it is to the fixed type constant velocity universal joint for the rear-wheel drive shaft or the fixed type constant velocity universal joint for the propeller shaft, there arise problems with compactification and weight reduction because the above-mentioned dimensions t1to t4are unnecessarily large.

Further, when the fixed type constant velocity universal joint is capable of absorbing vibration with a small amplitude, such as idling vibration that is transmitted into a cabin during stopping of an automobile, the fixed type constant velocity universal joint is capable of contributing to decrease of factors of noise, vibration, and harshness (NVH) of the automobile. However, in Patent Literature 1, the possibility of providing technical means for decreasing the NVH factors of automobiles to the fixed type constant velocity universal joint is not investigated at all. In terms of this, there is room for improvement.

In view of the circumstances, the present invention has an object to provide a compact and lightweight fixed type constant velocity universal joint that is suppressed in torque loss and heat generation, enhanced in efficiency, capable of contributing to decrease of NVH factors, and suited to rear-wheel drive shafts or propeller shafts.

Solution to Problem

According to a first invention, which is devised to attain the above-mentioned object, there is provided a fixed type constant velocity universal joint, comprising: an outer joint member having a spherical inner peripheral surface in which a plurality of track grooves are formed so as to extend in an axial direction of the outer joint member; an inner joint member having a spherical outer peripheral surface in which a plurality of track grooves are formed so as to be paired with the plurality of track grooves of the outer joint member; a plurality of balls for transmitting torque, the plurality of balls being interposed between the plurality of track grooves of the outer joint member and the plurality of track grooves of the inner joint member; and a cage comprising pockets for receiving the balls, the cage having: a spherical outer peripheral surface fitted to the spherical inner peripheral surface of the outer joint member; and a spherical inner peripheral surface fitted to the spherical outer peripheral surface of the inner joint member, wherein the plurality of track grooves of the outer joint member are each formed into an arc shape having a curvature center that is prevented from being offset in the axial direction with respect to a joint center, the plurality of track grooves of the outer joint member being inclined in a peripheral direction of the outer joint member with respect to a joint axial line and being adjacent to each other in the peripheral direction with their inclination directions opposite to each other, wherein the plurality of track grooves of the inner joint member are formed so as to be mirror-image symmetrical with the plurality of paired track grooves of the outer joint member with respect to a joint center plane at an operating angle of 0°, wherein the plurality of track grooves of the outer joint member and the plurality of track grooves of the inner joint member each have a length corresponding to a maximum operating angle required for a rear-wheel drive shaft, and wherein an axial clearance between the inner joint member and the cage is set larger than an axial clearance formed by a ball track clearance between each of the balls and each track groove.

Further, according to a second invention, which is devised to attain the above-mentioned object, there is provided a fixed type constant velocity universal joint, comprising: an outer joint member having a spherical inner peripheral surface in which a plurality of track grooves are formed so as to extend in an axial direction of the outer joint member; an inner joint member having a spherical outer peripheral surface in which a plurality of track grooves are formed so as to be paired with the plurality of track grooves of the outer joint member; a plurality of balls for transmitting torque, the plurality of balls being interposed between the plurality of track grooves of the outer joint member and the plurality of track grooves of the inner joint member; and a cage comprising pockets for receiving the balls, the cage having: a spherical outer peripheral surface fitted to the spherical inner peripheral surface of the outer joint member; and a spherical inner peripheral surface fitted to the spherical outer peripheral surface of the inner joint member, wherein the plurality of track grooves of the outer joint member are each formed into an arc shape having a curvature center that is prevented from being offset in the axial direction with respect to a joint center, the plurality of track grooves of the outer joint member being inclined in a peripheral direction of the outer joint member with respect to a joint axial line and being adjacent to each other in the peripheral direction with their inclination directions opposite to each other, wherein the plurality of track grooves of the inner joint member are formed so as to be mirror-image symmetrical with the plurality of paired track grooves of the outer joint member with respect to a joint center plane at an operating angle of 0°, wherein the plurality of track grooves of the outer joint member and the plurality of track grooves of the inner joint member each have a length corresponding to a maximum operating angle required for a propeller shaft, and wherein an axial clearance between the inner joint member and the cage is set larger than an axial clearance formed by a ball track clearance between each of the balls and each track groove.

Note that, the “joint axial line” in the first and second inventions refers to a longitudinal axial line that is a joint rotation center, and corresponds to a joint axial line N-N in the embodiments described later. Further, the “joint center plane at the operating angle of 0°” refers to a plane including the joint center at the operating angle of 0° and extending in a direction orthogonal to the joint axial line, and corresponds to a plane P in the embodiments described later. Further, the “ball track clearance” refers to a clearance formed between each of the balls and each of the track grooves in accordance with a PCD clearance that is obtained through subtraction of a PCD of the track grooves of the inner joint member from a PCD of the track grooves of the outer joint member (represented by ΔT inFIG. 9).

As described above, in the fixed type constant velocity universal joint according to the present invention, the track grooves of the outer joint member and the track grooves of the inner joint member each have the length corresponding to the maximum operating angle required for the rear-wheel drive shaft or the propeller shaft. That is, axial dimensions of the parts of the outer joint member, the inner joint member, and the cage, which directly influence the lengths of the track grooves, are decreased to be smaller than those in the fixed type constant velocity universal joint of Patent Literature 1. Thus, it is possible to attain a constant velocity universal joint that is lightweight, compact, and suited to the rear-wheel drive shaft or the propeller shaft. Further, the axial clearance between the inner joint member and the cage is set larger than the axial clearance formed by the ball track clearance between each of the balls and each track groove. With this, vibration with a small amplitude, such as idling vibration, can be effectively suppressed. Therefore, it is possible to attain a fixed type constant velocity universal joint capable of contributing to decrease of NVH factors of automobiles and the like.

Note that, the maximum operating angle required for the rear-wheel drive shaft may be set to 30°. Further, the maximum operating angle required for the propeller shaft may be set to 20°. In this case, the track grooves of the outer joint member and the track grooves of the inner joint member are each decreased to a length that is necessary and sufficient for the rear-wheel drive shaft or the propeller shaft. Thus, it is possible to attain a lightweight and compact fixed type constant velocity universal joint that is suited to application to the rear-wheel drive shaft or the propeller shaft.

It is preferred that the ball track clearance be set to take a positive value. With this, vibration with a small amplitude can efficiently be absorbed.

The curvature centers of the track grooves may be arranged on the joint axial line. With this, the depths of the track grooves can be set equal to each other, and processes thereon can be simplified. Further, the curvature centers of the track grooves may be arranged at positions offset in a radial direction with respect to the joint axial line. With this, track groove depths on an opening side and an interior side (opposite side to the opening) can be adjusted in accordance with the offset amount, and hence optimum track groove depth can be secured.

In the structure described above, the number of the balls to be used is not particularly limited, and may be set to, for example, any one of six, eight, ten, and twelve. The number of the balls may be set in accordance with the required characteristics. Specifically, when the number of the balls is set to six, there are such advantages in that the total number of components is smaller than that in the case where the number of the balls is set to eight, that satisfactory processability and assembly efficiency of the members can be achieved, and that a load capacity can be increased in accordance with increase in size of the balls. On the other hand, when the number of the balls is set to eight, there are such advantages in that further weight reduction and compactification, and less torque loss can be achieved as compared to the case where the number of the balls is set to six.

Advantageous Effects of Invention

As described above, according to the present invention, it is possible to attain the compact and lightweight fixed type constant velocity universal joint that is suppressed in torque loss and heat generation, enhanced in efficiency, capable of contributing to the decrease of NVH factors of automobiles, and suited to the rear-wheel drive shafts or the propeller shafts.

DESCRIPTION OF EMBODIMENTS

FIG. 1Ais a partial vertical sectional view of a fixed type constant velocity universal joint1according to a first embodiment of the present invention, andFIG. 1Bis a front view of the constant velocity universal joint1(right-hand side view ofFIG. 1A). The constant velocity universal joint1is used in a state of being assembled to a rear-wheel drive shaft, and comprises an outer joint member2, an inner joint member3, balls4, and a cage5.

As illustrated also inFIG. 2AandFIG. 2B, eight track grooves7are formed in a spherical inner peripheral surface6of a mouth portion2aof the outer joint member2so as to extend along an axial direction. The track grooves7comprise track grooves7A and7B that are inclined at an angle γ in a peripheral direction with respect to a joint axial line N-N and adjacent to each other in the peripheral direction with their inclination directions opposite to each other. As illustrated also inFIG. 3AandFIG. 3B, eight track grooves9are formed in a spherical outer peripheral surface8of the inner joint member3so as to extend along the axial direction. The track grooves9comprise track grooves9A and9B that are inclined at the angle γ in the peripheral direction with respect to the joint axial line N-N and adjacent to each other in the peripheral direction with their inclination directions opposite to each other. In addition, each ball4is arranged in a crossing portion between the paired track grooves7and9of the outer joint member2and the inner joint member3. Note that, the track grooves7and9are illustrated inFIG. 1Aunder a state in which cross sections taken along a plane M illustrated inFIG. 2Aand a plane Q illustrated inFIG. 3Aare rotated to an inclination angle of γ=0°.

The term “ball raceway center line” is hereinafter used to accurately describe forms (such as inclined state and curved state) of the track grooves. The ball raceway center line refers to a trajectory of the center of the ball when the ball moves along the track groove. Thus, the form of the track grooves corresponds to a form of the ball raceway center lines.

As illustrated inFIG. 1A, a ball raceway center line X of each track groove7of the outer joint member2and a ball raceway center line Y of each track groove9of the inner joint member3are each formed into an arc shape having a curvature center at a joint center O. In this way, the curvature centers of the ball raceway center line X of each track groove7of the outer joint member2and the ball raceway center line Y of each track groove9of the inner joint member3are each arranged on the joint center O, that is, on the joint axial line N-N. With this, depths of the track grooves can be set equal to each other, and processes therefor can be simplified.

Although detailed illustration is omitted, the track grooves7and9are formed into an elliptical shape or a Gothic arch shape in horizontal cross section, and the track grooves7and9are held in so-called angular contact with each ball4at a contact angle of approximately from 30° to 45°. Thus, the ball4is held in contact with side surface portions of the track grooves7and9, which are slightly spaced apart from groove bottoms of the track grooves7and9.

Now, supplementary description is given of the reference symbols of the track grooves. Reference symbol7represents the track grooves of the outer joint member2as a whole. When the track grooves having different inclination directions are to be distinguished from each other, reference symbol7A represents a track groove inclined on one side in the peripheral direction with respect to the joint axial line N-N, and reference symbol7B represents a track groove inclined on the other side in the peripheral direction with respect to the joint axial line N-N. The track grooves9of the inner joint member3are represented by the reference symbols in a similar manner.

Referring toFIG. 2AandFIG. 2B, description is given of a state in which the track grooves7of the outer joint member2are inclined in the peripheral direction with respect to the joint axial line N-N. As illustrated inFIG. 2(a), a plane M including the ball raceway center line X of each track groove7A and the joint center O is inclined at an angle γ on one side in the peripheral direction with respect to the joint axial line N-N. Further, a plane M (not shown) including the ball raceway center line X of each track groove7B adjacent to the track groove7A in the peripheral direction and the joint center O is inclined at an angle γ on the other side in the peripheral direction with respect to the joint axial line N-N (opposite direction to the inclination direction of the track groove7A).

Referring toFIG. 3AandFIG. 3B, description is given of a state in which the track grooves9of the inner joint member3are inclined in the peripheral direction with respect to the joint axial line N-N. As illustrated inFIG. 3A, a plane Q including the ball raceway center line Y of each track groove9A and the joint center O is inclined at an angle γ on one side in the peripheral direction with respect to the joint axial line N-N. Further, a plane Q (not shown) including the ball raceway center line Y of each track groove9B adjacent to the track groove9A in the peripheral direction and the joint center O is inclined at an angle γ on the other side in the peripheral direction with respect to the joint axial line N-N (opposite direction to the inclination direction of the track groove9A). It is preferred that the above-mentioned angle (inclination angle) γ be set within a range of from 4° to 12° in consideration of operability of the constant velocity universal joint1and a spherical width F between the closest sides of the track grooves of the inner joint member3. The track grooves9of the inner joint member3are formed so as to be mirror-image symmetrical with the paired track grooves7of the outer joint member2with respect to a joint center plane P at an operating angle of 0°.

Next, referring toFIG. 4, detailed description is given of the track grooves of the outer joint member2when viewed in a vertical cross section. Note that,FIG. 4is a sectional view taken along the plane M including the ball raceway center line X of the track groove7A and the joint center O illustrated inFIG. 2A. That is,FIG. 4is a sectional view in the plane including an inclined axis N′-N′, which is inclined at the angle γ in the peripheral direction with respect to the joint axial line N-N. InFIG. 4, in the track grooves7A and7B having different inclination directions from each other, only the track groove7A is illustrated. In the spherical inner peripheral surface6of the outer joint member2, the track grooves7A are formed along the axial direction. The track groove7A has the arc-shaped ball raceway center line X having a curvature center at the joint center O (not offset in the axial direction). When assuming that K represents a perpendicular line at the joint center O, which is perpendicular to the inclined axis N′-N′ projected onto the plane M (seeFIG. 2A) including the ball raceway center line X of the track groove7A and the joint center O, the perpendicular line K is located on the joint center plane P at the operating angle of 0°.

Similarly, referring toFIG. 5, detailed description is given of the track grooves of the inner joint member3.FIG. 5is a sectional view taken along the plane Q including the ball raceway center line Y of the track groove9A and the joint center O illustrated inFIG. 3A. That is,FIG. 5is an illustration of a cross section in the plane including the inclined axis N′-N′, which is inclined at the angle γ in the peripheral direction with respect to the joint axial line N-N. InFIG. 5, in the track grooves9A and9B having different inclination directions from each other, only the track groove9A is illustrated. In the spherical outer peripheral surface8of the inner joint member3, the track grooves9A are formed along the axial direction. The track groove9A has the arc-shaped ball raceway center line Y having a curvature center at the joint center O (not offset in the axial direction). When assuming that K represents a perpendicular line at the joint center O, which is perpendicular to the inclined axis N′-N′ projected onto the plane Q (seeFIG. 3A) including the ball raceway center line Y of the track groove9A and the joint center O, the perpendicular line K is located on the joint center plane P at the operating angle of 0°.

FIG. 6AandFIG. 6Bare illustrations of a dimensional feature of the rear-wheel drive shaft-specific constant velocity universal joint1according to this embodiment. Note that, both ofFIG. 6AandFIG. 6Bare illustrations of a cross section taken along the joint axial line N-N. The track grooves7and9are illustrated inFIG. 6AandFIG. 6Bunder a state in which the cross sections taken along the plane M illustrated inFIG. 2Aand the plane Q illustrated inFIG. 3Aare rotated to the inclination angle of γ=0°.

As illustrated inFIG. 6B, when the constant velocity universal joint1forms a maximum operating angle θ max, a center Ob of the ball4moves to the position of θ max/2 with respect to the joint center plane P at the operating angle of 0°. Therefore, when the maximum operating angle θ max is set to 30°, the center Ob of the ball4moves by 15° with respect to the joint center plane P at the operating angle of 0°. Lengths of the track grooves7and9are set so that, in this state, the balls4are reliably held in contact with the track grooves7of the outer joint member2and the track grooves9of the inner joint member3. Specifically, as in the illustration, the lengths of the track grooves are set so that allowance amounts are secured between contact points So and Si between the track grooves7and9and the ball4, and end portions of the track grooves7and9. In this case, the description specified in the scope of claims “the plurality of track grooves of the outer joint member and the plurality of track grooves of the inner joint member each have a length corresponding to a maximum operating angle required for a rear-wheel drive shaft” means that, as described above, “the track grooves have the lengths that are necessary and sufficient for reliably holding the balls in contact with the track grooves when the joint forms the maximum operating angle θ max.”

Based on the lengths of the track grooves, for example, axial dimensions of the outer joint member2and the inner joint member3are determined. The maximum operating angle θ max of the fixed type constant velocity universal joint1is set to 30°. Thus, as illustrated inFIG. 6A, an axial dimension T1of the mouth portion2aof the outer joint member2, an axial dimension T2from the joint center O to an end portion of the outer joint member2on an opening side, an axial dimension T3of the inner joint member3, and an axial dimension T4of the cage5are decreased to be sufficiently smaller than those in the fixed type constant velocity universal joint121illustrated inFIG. 22, in which the maximum operating angle θ max is set to 40°.

As described above, the axial dimensions T1and T2of the outer joint member2can be decreased, and hence a weight of the outer joint member1and a weight of a material thereof to be loaded can be decreased. Further, lengths of a finishing process on the track grooves7and the spherical inner peripheral surface6can be decreased. Similarly, the axial dimension T3of the inner joint member3can be decreased, and hence a weight of the inner joint member3and a weight of a material thereof to be loaded can be decreased. Further, lengths of a finishing process on the track grooves9and the spherical outer peripheral surface8can be decreased. In addition, in accordance with downsizing of an interior space of the joint, a use amount of a lubricant (such as grease) can be decreased. With this, the constant velocity universal joint1according to this embodiment is even more lightweight and compact than the fixed type constant velocity universal joint121illustrated inFIG. 22, which is designed for application to front-wheel drive shafts.

In the constant velocity universal joint1according to this embodiment, a configuration capable of absorbing vibration with a small amplitude is employed in addition to the configuration described above. Detailed description is given of the configuration with reference toFIG. 7toFIG. 11.

FIG. 7AandFIG. 7Brespectively are schematic views of held states of the ball4arranged between the track grooves7and9when viewed in a direction of the arrow A and a direction of the arrow B inFIG. 1B. InFIG. 7A, an actual wedge angle2γ′ between contact points SoA and SiA formed between the ball4and the track grooves7A and9A is illustrated. InFIG. 7B, an actual wedge angle2γ′ between contact points SoB and SiB formed between the ball4and the track grooves7B and9B is illustrated. InFIG. 7AandFIG. 7B, for the sake of convenience of description, the contact points SoA, SiA, SoB, and SiB are positioned in a plane of the drawing sheet.

Supplementary description is given ofFIG. 7A. Reference symbols CoA and CoA′ inFIG. 7Arepresent contact point trajectories between the track groove7A of the outer joint member2and the ball4, and reference symbols CiA and CiA′ represent contact point trajectories between the track groove9A of the inner joint member3and the ball4. Under a state in which rotational torque in a direction indicated by the hollow arrow inFIG. 1Bis applied to the inner joint member3, the contact point trajectories CoA and CiA correspond to a load side, and the contact point trajectories CoA′ and CiA′ correspond to a non-load side. The contact point trajectories CoA and CiA on the load side form the wedge angle2γ′ in a manner of sandwiching the ball4, and the contact point trajectories CoA′ and CiA′ on the non-load side form a wedge angle (not shown) that increases in an opposite direction to the direction in which the wedge angle2γ′ formed between the contact point trajectories CoA and CiA on the load side increases.

Further, supplementary description is given ofFIG. 7B. Reference symbols CoB and CoB′ inFIG. 7Brepresent contact point trajectories between the track groove7B of the outer joint member2and the ball4, and reference symbols CiB and CiB′ represent contact point trajectories between the track groove9B of the inner joint member3and the ball4. Under a state in which rotational torque in a direction indicated by the hollow arrow inFIG. 1Bis applied to the inner joint member3, the contact point trajectories CoB and CiB correspond to the load side, and the contact point trajectories CoB′ and CiB′ correspond to the non-load side. The contact point trajectories CoB and CiB on the load side form the wedge angle2γ′ in a manner of sandwiching the ball4, and the contact point trajectories CoB′ and CiB′ on the non-load side form a wedge angle (not shown) that increases in an opposite direction to the direction in which the wedge angle2γ′ formed between the contact point trajectories CoB and CiB on the load side increases.

FIG. 8is a view for illustrating the held state of the ball4illustrated inFIG. 7A(state before displacement), and the held state of the ball4when the inner joint member3is moved relative to the outer joint member2in the axial direction (state after the displacement) in a superimposed manner. Similarly toFIG. 7, the contact points between the ball4and the track grooves are positioned in the plane of the drawing sheet. Reference symbols H1and H2inFIG. 8respectively represent an axial position of a center Ob1of the ball4before the displacement, and an axial position of a center Ob2of the ball4after the displacement. Further, reference symbols CiA1and CiA1′ inFIG. 8represent contact point trajectories between the track groove9A of the inner joint member3and the ball4under the state before the displacement, and reference symbols CiA2and CiA2′ represent contact point trajectories between the track groove9A of the inner joint member3and the ball4under the state after the displacement.

In the constant velocity universal joint1according to this embodiment, curvature centers of the arc-shaped track grooves7(7A and7B) and9(9A and9B) are arranged at the joint center O (track grooves7and9are not offset in the axial direction). Accordingly, the wedge angle2γ′ is determined based on the inclination angles γ of the track grooves7and9, that is, the inclination angles γ of the ball raceway center lines X and Y. Thus, as illustrated inFIG. 8, even when the axial position of the ball4varies along with the relative movement between the outer joint member2and the inner joint member3in the axial direction, crossing angles between the track grooves7A and9A remain unchanged. That is, the wedge angle2γ′ formed between the contact point trajectory CoA between the track groove7A of the outer joint member2and the ball4, and the contact point trajectories CiA (CiA1and CiA2) between the track groove9of the inner joint member3and the ball4remain unchanged as well. The same applies to the contact point trajectories CoB and CiB of the track grooves7B and9B. Thus, the forces of the ball4to the cage5, which are generated at the wedge angle2γ′ between the contact point trajectories CoA and CiA and the wedge angle2γ′ between the contact point trajectories CoB and CiB, are balanced with each other.

Next, description is given of spherical clearances between the cage5and both the joint members2and3, and ball track clearances between the ball4and the track grooves7and9. In general, an amount of the axial displacement between both the joint members2and3in the fixed type constant velocity universal joint is relevant to the clearances of the above-mentioned types (clearance widths thereof). In the constant velocity universal joint1according to this embodiment, based on the above-mentioned feature that the wedge angle2γ′ remains unchanged even when the axial position of the ball4varies, the clearances of the above-mentioned types are set so as to achieve smooth operation by absorbing a larger amount of vibration with a small amplitude. Now, referring toFIG. 9toFIG. 11, description is given of a relationship between ball track clearances ΔT between the ball4and the track grooves7and9, and the spherical clearances between the cage5and both the joint members2and3.

First, description is given of the ball track clearances ΔT between the ball4and the track grooves7and9with reference toFIG. 9andFIG. 10.FIG. 9is a partial horizontal sectional view taken along the joint center plane P of the constant velocity universal joint1illustrated inFIG. 1A. The track grooves7(7A) and9(9A) illustrated in the cross section inFIG. 9are perpendicular to the ball raceway center lines X and Y of the track grooves7(7A) and9(9A).

At the time of torque transmission, the ball4and each of the track grooves7(7A) and9(9A) of both the joint members2and3are held in angular contact at contact angles δ illustrated inFIG. 9, and the ball track clearances ΔT each taking a positive value are formed in the directions of the contact angles δ under a state in which both the joint members2and3are located at neutral positions in the peripheral direction (non-load state). Note that, inFIG. 9, for the sake of better understanding, the ball track clearances ΔT are illustrated on an exaggerated scale.

FIG. 10is a partial enlarged view ofFIG. 8, specifically,FIG. 10is an illustration of a state in which the axial position H1before the displacement, which is illustrated inFIG. 8, is matched with the joint center OP under the state in which both the joint members2and3are located at the neutral positions in the peripheral direction (non-load state). As described with reference toFIG. 9, the ball track clearances ΔT are formed between the ball4and the track grooves7(7A) and9(9A). Thus, an axial clearance ΔTao is formed between the ball4and the contact point trajectory CoA′ of the track groove7(7A) of the outer joint member2, and an axial clearance ΔTai is formed between the ball4and the contact point trajectory CiA1of the track groove9(9A) of the inner joint member3. Although illustration is omitted, similarly, the axial clearance ΔTao is formed between the ball4and the contact point trajectory CoA of the track groove7(7A) of the outer joint member2, and the axial clearance ΔTai is formed between the ball4and the contact point trajectory CiA1′ of the track groove9(9A) of the inner joint member3.

Next, referring toFIG. 11, description is given of the spherical clearances formed between the cage5and both the joint members2and3.FIG. 11is a partial sectional view of the constant velocity universal joint1under the non-load state (sectional view taken along the line O-C′ inFIG. 1B). As illustrated inFIG. 11, a spherical clearance ΔSo is formed between the spherical inner peripheral surface6of the outer joint member2and a spherical outer peripheral surface12of the cage5, and a spherical clearance ΔSi is formed between the spherical outer peripheral surface8of the inner joint member3and a spherical inner peripheral surface13of the cage5. The spherical clearance ΔSi comprises axial clearances ΔSia1and ΔSia2that are formed between the inner joint member3and the cage5and cause the inner joint member3and the cage5to be spaced apart from each other in the axial direction respectively on the opening side and an interior side (opposite side to the opening) of the outer joint member2.

The constant velocity universal joint1according to this embodiment is configured so that the following relational expressions are established between the axial clearances ΔSia1and ΔSia2between the inner joint member3and the cage5, and the axial clearances ΔTao and ΔTai formed by the above-mentioned ball track clearances ΔT.
ΔSia1>(ΔTao+ΔTai)
ΔSia2>(ΔTao+ΔTai)

In this case, the description specified in the scope of claims of the present application “an axial clearance between the inner joint member and the cage is set larger than an axial clearance formed by a ball track clearance between each of the balls and each track groove” means that the above-mentioned relational expressions are established.

In addition, as described above, the ball track clearances ΔT between the ball4and the track grooves7and9are each set to take a positive value. Thus, even when idling vibration (axial small vibration) is transmitted to the inner joint member3of the fixed type constant velocity universal joint1via a differential gear, a plunging type constant velocity universal joint, and an intermediate shaft (not shown), the balls4can be caused to smoothly roll along the track grooves7and9, that is, the outer joint member2and the inner joint member3can smoothly be displaced relative to each other in the axial direction. Also at the time of the relative displacement described above, the axial clearances between the spherical surfaces can be secured because, as described above, the axial clearances ΔSia1and ΔSia2between the inner joint member3and the cage5are each set larger than the axial clearances (ΔTao+ΔTai) formed by the ball track clearances ΔT. In addition, the forces of the ball4to the cage5, which are generated at the wedge angle2γ′ formed between the contact point trajectories CoA and CiA and the wedge angle2γ′ formed between the contact point trajectories CoB and CiB, are balanced with each other. With this, the axial clearances between the spherical surfaces can be maintained without causing the cage5to be biased in the axial direction. Those mutual effects enable both the joint members2and3to be displaced relative to each other in the axial direction without causing contact (spherical contact) between the spherical outer peripheral surface8of the inner joint member3and the spherical inner peripheral surface13of the cage5. With this, axial vibration with a small amplitude, such as idling vibration, can smoothly be absorbed.

The above-mentioned configuration capable of absorbing vibration with a small amplitude is employed also in fixed type constant velocity universal joints according to other embodiments described later. However, in the other embodiments described later, detailed description thereof is omitted for the sake of simplicity of description.

Note that, the axial clearances ΔSia1and ΔSia2between the inner joint member3and the cage5, and the axial clearances ΔTao and ΔTai formed by the ball track clearances ΔT between the ball4and the track grooves7and9are set so as to satisfy the above-mentioned relational expressions. Thus, it is only necessary that the spherical clearance ΔSo between the spherical inner peripheral surface6of the outer joint member2and the spherical outer peripheral surface12of the cage5have such a minimum value that flexing movement (angular displacement) of both the joint members2and3is not disturbed.

Further, as described above, in the fixed type constant velocity universal joint of a track groove crossing type, the wedge angle2γ′ formed between the contact point trajectories CoA and CiA between the ball4and the track grooves7A and9A, and the wedge angle2γ′ formed between the contact point trajectories CoB and CiB between the ball4and the track grooves7B and9B each remain unchanged. Thus, the forces applied from the ball4to the cage5are balanced with each other. Accordingly, there occurs no contact (spherical contact) between the spherical inner peripheral surface6of the outer joint member2and the spherical outer peripheral surface12of the cage5, or no contact (spherical contact) between the spherical outer peripheral surface8of the inner joint member3and the spherical inner peripheral surface13of the cage5. Heat generation to be caused by the spherical contact is effectively suppressed or prevented, and hence torque transmission efficiency and durability can be enhanced.

FIG. 12is an illustration of an automotive rear-wheel drive shaft20, to which the fixed type constant velocity universal joint1described above is assembled. The fixed type constant velocity universal joint1is coupled to one end of an intermediate shaft11, and a plunging type constant velocity universal joint15is coupled to the other end of the intermediate shaft11. At a portion between an outer peripheral surface of the fixed type constant velocity universal joint1and an outer peripheral surface of the intermediate shaft11, and at a portion between an outer peripheral surface of the plunging type constant velocity universal joint15and the outer peripheral surface of the intermediate shaft11, bellows boots16aand16bare respectively fixed by being fastened with boot bands18(18a,18b,18c, and18d). Grease is sealed inside the joint as a lubricant. Through use of the fixed type constant velocity universal joint1according to this embodiment, it is possible to attain a rear-wheel drive shaft20that is suppressed in torque loss and heat generation, enhanced in efficiency, capable of effectively absorbing vibration with a small amplitude, and is lightweight and compact. An automobile having the drive shaft20mounted therein is improved in torque transmission efficiency, and hence can be suppressed in fuel consumption. In addition, factors of noise, vibration, and harshness (NVH) are decreased.

FIG. 13Ais a partial vertical sectional view of a fixed type constant velocity universal joint21according to a second embodiment of the present invention, andFIG. 13Bis a front view of the fixed type constant velocity universal joint21(right-hand side view ofFIG. 13A). The constant velocity universal joint21according to this embodiment is used in a state of being assembled into a propeller shaft (detailed description is given later), and is common to the fixed type constant velocity universal joint1illustrated inFIG. 1and the like in that the constant velocity universal joint21comprises an outer joint member22, an inner joint member23, balls24, and a cage25, but is different from the fixed type constant velocity universal joint1illustrated inFIG. 1and the like in that the outer joint member22formed into a disc shape (ring shape) is used.

As illustrated inFIG. 13A, the ball raceway center line X of each track groove27of the outer joint member22and the ball raceway center line Y of each track groove29of the inner joint member23are each formed into an arc shape having a curvature center at the joint center O. In this way, the curvature centers of the ball raceway center line X of each track groove27of the outer joint member22and the ball raceway center line Y of each track groove29of the inner joint member23are each arranged on the joint center O, that is, on the joint axial line N-N. With this, depths of the track grooves can be set equal to each other, and processes thereon can be simplified.

Although detailed illustration is omitted, the track grooves27and29are formed, for example, into an elliptical shape or a Gothic arch shape in horizontal cross section (cross section orthogonal to the axis), and the track grooves27and29are held in so-called angular contact with each ball24at the contact angle of approximately from 30° to 45°. Thus, the ball24is held in contact with side surface portions of the track grooves27and29, which are slightly spaced apart from groove bottoms of the track grooves27and29.

Referring to the partial vertical cross section of the outer joint member22illustrated inFIG. 14A, and the front view of the outer joint member22illustrated inFIG. 14B(right-hand side surface ofFIG. 14A), description is given of a state in which the track grooves27of the outer joint member22are inclined in the peripheral direction with respect to the joint axial line N-N. As illustrated inFIG. 14A, the plane M including the ball raceway center line X of each track groove27A and the joint center O is inclined at the angle γ on one side in the peripheral direction with respect to the joint axial line N-N. Further, the plane M (not shown) including the ball raceway center line X of each track groove27B adjacent to the track groove27A in the peripheral direction and the joint center O is inclined at the angle γ on the other side in the peripheral direction with respect to the joint axial line N-N (opposite direction to the inclination direction of the track groove27A).

Referring to the side view of the inner joint member23illustrated inFIG. 15A, and the front view of the inner joint member23illustrated inFIG. 15B, description is given of a state in which the track grooves29of the inner joint member23are inclined in the peripheral direction with respect to the joint axial line N-N. As illustrated inFIG. 15A, the plane Q including the ball raceway center line Y of each track groove29A and the joint center O is inclined at the angle γ on one side in the peripheral direction with respect to the joint axial line N-N. Further, the plane Q (not shown) including the ball raceway center line Y of each track groove29B adjacent to the track groove29A in the peripheral direction and the joint center O is inclined at the angle γ on the other side in the peripheral direction with respect to the joint axial line N-N (opposite direction to the inclination direction of the track groove29A). It is preferred that the above-mentioned angle (inclination angle) γ be set within the range of from 4° to 12° in consideration of operability of the constant velocity universal joint21and the spherical width F between the closest sides of the track grooves of the inner joint member23. The track grooves29of the inner joint member23are formed so as to be mirror-image symmetrical with the paired track grooves27of the outer joint member22with respect to the joint center plane P at the operating angle of 0°.

Next, referring toFIG. 16, detailed description is given of the track grooves in a vertical cross section of the outer joint member22. Note that,FIG. 16is a sectional view taken along the plane M illustrated inFIG. 14Aincluding the ball raceway center line X of the track groove27A and the joint center O. That is,FIG. 16is a sectional view in the plane including the inclined axis N′-N′, which is inclined at the angle γ in the peripheral direction with respect to the joint axial line N-N. InFIG. 16, in the track grooves27A and27B having inclination directions different from each other, only the track groove27A is illustrated. In a spherical inner peripheral surface26of the outer joint member22, the track grooves27A are formed along the axial direction. The track groove27A has the arc-shaped ball raceway center line X having a curvature center at the joint center O. When assuming that K represents a perpendicular line at the joint center O, which is perpendicular to the inclined axis N′-N′ projected onto the plane M (seeFIG. 14A) including the ball raceway center line X of the track groove27A and the joint center O, the perpendicular line K is formed in the joint center plane P at the operating angle of 0°.

Similarly, referring toFIG. 17, detailed description is given of the track grooves of the inner joint member3.FIG. 17is a sectional view taken along the plane Q illustrated in FIG.15A including the ball raceway center line Y of the track groove29A and the joint center O. That is,FIG. 17is an illustration of a cross section in the plane including the inclined axis N′-N′, which is inclined at the angle γ in the peripheral direction with respect to the joint axial line N-N. InFIG. 17, in the track grooves29A and29B having inclination directions different from each other, only the track groove29A is illustrated. In a spherical outer peripheral surface28of the inner joint member23, the track grooves29A are formed along the axial direction. The track groove29A has the arc-shaped ball raceway center line Y having a curvature center at the joint center O. When assuming that K represents a perpendicular line at the joint center O, which is perpendicular to the inclined axis N′-N′ projected onto the plane Q (seeFIG. 15A) including the ball raceway center line Y of the track groove29A and the joint center O, the perpendicular line K is formed in the joint center plane P at the operating angle of 0°.

InFIG. 18, a dimensional feature of the propeller shaft-specific constant velocity universal joint21according to this embodiment is illustrated. Note that,FIG. 18is an illustration of a cross section taken along the joint axial line N-N. The track grooves are illustrated inFIG. 18under a state in which the cross sections taken along the plane M illustrated inFIG. 14Aand the plane Q illustrated inFIG. 15Aare rotated to the inclination angle of γ=0°. Although illustration is omitted, when the constant velocity universal joint21forms the maximum operating angle θ max (20° in this case), the center Ob of the ball24moves to the position of θ max/2 with respect to the joint center plane P at the operating angle of 0°. Thus, when the maximum operating angle θ max is set to 20° as in this embodiment, the center Ob of the ball24moves by 10° with respect to the joint center plane P at the operating angle of 0°. Lengths of the track grooves27and29are set so that, in this state, the balls24are reliably held in contact with the track grooves27of the outer joint member22and the track grooves29of the inner joint member23. Specifically, the lengths of the track grooves are set so that allowance amounts are secured between contact points between the track grooves27and29and the ball24, and end portions of the track grooves27and29. The description in the scope of claims “the plurality of track grooves of the outer joint member and the plurality of track grooves of the inner joint member each have a length corresponding to a maximum operating angle required for a propeller shaft” means that, as described above, “the track grooves have the lengths that are necessary and sufficient for reliably holding the balls in contact with the track grooves when the joint forms the maximum operating angle θ max.”

Based on the lengths of the track grooves, for example, axial dimensions of the outer joint member22and the inner joint member23are determined. The maximum operating angle θ max of the fixed type constant velocity universal joint21is set to 20°. Thus, as illustrated inFIG. 18, an axial dimension T11of the outer joint member22, an axial dimension T12from the joint center O to the end portion of the outer joint member22on the opening side, an axial dimension T13of the inner joint member23, and an axial dimension T14of the cage25are decreased to be sufficiently smaller than those in the related-art fixed type constant velocity universal joint121illustrated inFIG. 22, in which the maximum operating angle θ max is set to 40°.

As described above, the axial dimensions T11and T12of the outer joint member22can be decreased, and hence a weight of the outer joint member22as a finished product and a weight of a material thereof to be loaded can be decreased. Further, lengths of a finishing process on the track grooves27and the spherical inner peripheral surface26can be decreased. Similarly, the axial dimension T13of the inner joint member23can be decreased, and hence a weight of the inner joint member23as a finished product and a weight of a material thereof to be loaded can be decreased. Further, lengths of a finishing process on the track grooves29and the spherical outer peripheral surface28can be decreased. In addition, in accordance with downsizing of an interior space of the joint, a use amount of the lubricant (such as grease) can be decreased. With this, the constant velocity universal joint21according to this embodiment is even more lightweight and compact than the related-art fixed type constant velocity universal joint121illustrated inFIG. 22, which is designed for application to front-wheel drive shafts.

FIG. 19is a schematic sectional view of a propeller shaft comprising the fixed type constant velocity universal joint21according to the second embodiment described above. The propeller shaft40comprises the fixed type constant velocity universal joint21, a shaft42comprising one axial end that is spline-coupled to a hole portion of the inner joint member23, and a boot41mounted to an outer peripheral surface of the outer joint member22and an outer peripheral surface of the shaft42so as to prevent the lubricant (such as grease) sealed inside the joint from leaking to an outside. The shaft42comprises a large-diameter pipe portion42a, and another fixed type or plunging type constant velocity universal joint (not shown) is coupled to the other axial end of the shaft42. The boot41comprises a sealing ring41afixed to the outer peripheral surface of the outer joint member22, and an elastic boot portion41bcomprising one end fixed to the sealing ring41aand the other end mounted to the shaft42with a boot band43. Note that, although detailed illustration is omitted, the sealing ring41aof the boot41is fixed to the outer peripheral surface of the outer joint member22, for example, by crimping.

The propeller shaft40uses the fixed type constant velocity universal joint21according to the second embodiment, and hence it is possible to attain a propeller shaft that is further suppressed in torque loss and heat generation, enhanced in efficiency, capable of effectively absorbing vibration with a small amplitude, and is lightweight and compact. An automobile having the propeller shaft40mounted therein is excellent in torque transmission efficiency, and hence can be suppressed in fuel consumption. In addition, factors of noise, vibration, and harshness (NVH) are decreased.

FIG. 20Ais a partial sectional view of an outer joint member to be used in a fixed type constant velocity universal joint according to a third embodiment of the present invention, which is a modification example of the fixed type constant velocity universal joint21according to the second embodiment.FIG. 20Bis a partial sectional view of an inner joint member to be used in a fixed type constant velocity universal joint according to a fourth embodiment of the present invention. Note that, similarly toFIG. 16,FIG. 20Ais a partial sectional view of the outer joint member taken along the plane M (seeFIG. 14A) including the ball raceway center line X of the track groove27A and the joint center O. Similarly toFIG. 17,FIG. 20Bis a partial sectional view of the inner joint member taken along the plane Q (seeFIG. 15A) including the ball raceway center line Y of the track groove29A and the joint center O. The constant velocity universal joints according to the third and fourth embodiments are different from the fixed type constant velocity universal joint21according to the second embodiment illustrated inFIG. 13and the like mainly in that the curvature center of each of the track grooves (ball raceway center lines) is arranged at a position offset by “f” in a radial direction with respect to the joint axial line N-N (not offset in the axial direction with respect to the joint center O). That is, in the third and fourth embodiments, the curvature center of the ball raceway center line of each of the track grooves is offset by “f” in the radial direction in the joint center plane P including the perpendicular line K at the operating angle of 0°.

Under the state illustrated inFIG. 20A, when the curvature center of the ball raceway center line X of the track groove27(27A or27B) of the outer joint member22is offset by “f” in the radial direction with respect to the joint axial line N-N, the groove depth of the track groove27(27A or27B) of the outer joint member22can be increased (see reference symbols R and R′ inFIG. 20A; note that, in this case, the groove depths of the track grooves29of the inner joint member23assembled to the inner periphery of the outer joint member22are decreased). On the other hand, under the state illustrated inFIG. 20B, when the curvature center of the ball raceway center line Y of the track groove29(29A or29B) of the inner joint member23is offset by “f” in the radial direction with respect to the joint axial line N-N, the groove depth of the track groove29(29A or29B) of the inner joint member23can be increased (see reference symbols R and R′ inFIG. 20B; note that, in this case, the groove depths of the track grooves27of the outer joint member22having the inner periphery to which the inner joint member23is assembled are decreased). In short, as illustrated inFIG. 20AandFIG. 20B, when the curvature center of the ball raceway center line of each of the track grooves is offset in the radial direction with respect to the joint axial line N-N, the depths of the track grooves can be adjusted in accordance with the direction and the amount of the offset. Note that, other structural features are common to those of the fixed type constant velocity universal joint21according to the second embodiment, and hence detailed description thereof is omitted.

Although illustration is omitted, the same configuration (configuration in which the curvature centers of the track grooves are offset in the radial direction with respect to the joint axial line N-N) can be employed also in the fixed type constant velocity universal joint1according to the first embodiment, which is illustrated inFIG. 1and the like.

FIG. 21AandFIG. 21Bare illustrations of a fixed type constant velocity universal joint21according to a fifth embodiment of the present invention. The constant velocity universal joint21illustrated inFIG. 21AandFIG. 21Bis an modification example of the fixed type constant velocity universal joint21according to the second embodiment illustrated inFIG. 13and the like, and is structurally different from the fixed type constant velocity universal joint21according to the second embodiment in that the number of the balls is set to six. When the number of the balls is set to six as in this case, there are advantages in that the total number of components is smaller than that in the case where the number of the balls is set to eight, that satisfactory processability and assembly efficiency of the members can be achieved, and that a load capacity can be increased in accordance with increase in size of the balls.

Although illustration is omitted, the same configuration (configuration in which the number of the balls is set to six) can be employed also in the fixed type constant velocity universal joint1according to the first embodiment, which is illustrated inFIG. 1and the like.

In the above description, the present invention is applied to the fixed type constant velocity universal joint comprising the eight or six balls. However, the present invention is also suitably applicable to a fixed type constant velocity universal joint comprising ten or twelve balls.

Further, the above description is directed to the case where the present invention is applied to the fixed type constant velocity universal joint having the track grooves arranged at a regular pitch in the peripheral direction. However, the present invention is also suitably applicable to a fixed type constant velocity universal joint having the track grooves arranged at an irregular pitch. Still further, in the above-mentioned fixed type constant velocity universal joint, the inclination angles γ of the track grooves with respect to the joint axial line N-N are set equal to each other in all the track grooves, but the present invention is not limited thereto. As long as the inclination angles γ of the paired track grooves of the outer joint member and the inner joint member are set equal to each other, the inclination angles γ of the track grooves may be set unequal to each other. In short, it is only necessary that the inclination angles be set so that the axial forces of the balls are applied in a balanced manner as a whole to all the pockets of the cage. Further, in the above description, the present invention is applied to the fixed type constant velocity universal joint configured so that the track grooves and the balls are held in contact (angular contact) at a contact angle. However, the present invention is not limited thereto. The present invention is also suitably applicable to a fixed type constant velocity universal joint configured so that the track grooves and the balls are held in circular contact by forming the track grooves into an arc shape in horizontal cross section.

The present invention is not limited to the embodiments described above, and as a matter of course, may be carried out in various other embodiments without departing from the spirit of the present invention. The scope of the present invention is defined in the claims, and encompasses meaning of equivalents described in the claims and all modifications within the scope of claims.

REFERENCE SIGNS LIST

1,21fixed type constant velocity universal joint2,22outer joint member3,23inner joint member4,24ball5,25cage6,26spherical inner peripheral surface7,27track groove8,28spherical outer peripheral surface9,29track groove12,32spherical outer peripheral surface13,33spherical inner peripheral surface20rear-wheel drive shaft40propeller shaftK perpendicular lineM plane (plane including ball raceway center line)N joint axial lineO joint centerP joint center plane (joint center plane at operating angle of) 0°)Q plane (plane including ball raceway center line)X ball raceway center lineY ball raceway center lineγ inclination angleθ operating angleΔT ball track clearanceΔTai axial clearance (formed by ball track clearance)ΔTao axial clearance (formed by ball track clearance)ΔSi spherical clearanceΔSo spherical clearanceΔSia1axial clearance (formed between inner joint member and cage)ΔSia2axial clearance (formed between inner joint member and cage)