Constant velocity joint having eight torque transmitting balls

Details Constant velocity joint having eight torque transmitting balls Constant velocity joint having eight torque transmitting balls

2000-02-09

2002-05-14

Browne, Lynne H. (Department: 3629)

Rotary shafts, gudgeons, housings, and flexible couplings for ro

Coupling accommodates drive between members having...

Coupling transmits torque via radially spaced ball

Reexamination Certificate

active

06386983

ABSTRACT:

The present invention relates to a constant velocity joint having 8 torque transmitting balls.
Constant velocity joints are classified roughly into the fixed type allowing only angular displacement between two axes and the plunging type allowing angular displacement and axial displacement between two axes. One of the features of the fixed type constant velocity joint, as compared with the plunging type, is that it is capable of taking a high operating angle. For example, the fixed type constant velocity joint used in the drive shaft of an automobile is required to have a maximum operating angle of, e.g., 45° or more; however, such high operating angle can be provided only by the fixed type. On the other hand, the fixed type constant velocity joint, as compared with the plunging type, inevitably has its internal construction somewhat complicated.
FIGS. 23A and 23B
show a Rzeppa type constant velocity joint typical of the fixed type constant velocity joint. This constant velocity joint comprises an outer joint member
11
having a spherical inner surface
11
a
axially formed with 6 curved guide grooves
11
b
, an inner joint member
12
having a spherical outer surface
12
a
axially formed with 6 curved guide grooves
12
b
and an inner surface formed with serrations (or splines)
12
c
for connection to a shaft, 6 torque transmitting balls
13
disposed in ball tracks defined between the guide grooves
11
b
and
12
b
of the outer and inner joint members
11
and
12
, respectively, and a cage
14
for retaining the torque transmitting balls
13
.
The centers A and B of the guide grooves
11
b
and
12
b
of the outer and inner joint members
11
and
12
, respectively, are offset with respect to the spherical centers of the inner and outer surfaces
11
a
and
12
a
, respectively, by an equal distance in opposite directions (the guide groove center A is offset toward the open side of the joint, and the guide groove center B toward the innermost side of the joint). As a result, the ball track defined between the guide groove
11
b
and the guide groove
12
b
corresponding thereto is wedge-wise enlarged toward the open side of the joint. The spherical centers of the inner and outer surfaces
11
a
and
12
a
of the outer and inner joint members
11
and
12
are located in the joint center plane O including the centers of the torque transmitting balls
13
.
When the outer and inner joint members
11
and
12
make an angular displacement of angle &thgr;, the torque transmitting balls
13
guided by the cage
14
are maintained in the bisector plane (&thgr;/2) bisecting the angle &thgr; irrespective of the value of the operating angle &thgr;, and hence uniform velocity is secured.
SUMMARY OF THE INVENTION
An object of the present invention is to make this type of constant velocity joint more compact and secure the strength, load capacity and durability which are at least equal to those in a comparative article (such as a 6-ball constant velocity joint as shown in FIG.
23
).
To achieve the above object, the invention provides a constant velocity ball joint comprising an outer joint member having a plurality of axially extending curved guide grooves formed in the spherical inner surface thereof, an inner joint member having a plurality of axially extending curved guide grooves formed in the spherical outer surface thereof, a plurality of ball tracks defined between the guide grooves of the outer joint member and the guide grooves of the inner joint member corresponding thereto, said ball tracks being enlarged in one sense of the axial direction, a torque transmitting ball disposed in each of the plurality of ball tracks, a cage having a plurality of pockets for storing the torque transmitting balls, said constant velocity joint being characterized in that the number of said ball tracks and the number of said torque transmitting balls disposed are eight.
The ratio r
1
(=PCD
BALL
/D
BALL
) of the pitch circle diameter (PCD
BALL
) of the torque transmitting balls to the diameter (D
BALL
) of said torque transmitting balls may be within the range 3.3≦r
1
≦5.0. The pitch circle diameter (PCD
BALL
) of the torque transmitting balls is twice the length of a line segment connecting the centers of the guide grooves of the outer or inner joint member and the centers of the torque transmitting balls (the length of a line segment connecting the centers of the guide grooves of the outer joint member and the centers of the torque transmitting balls and the length of a line segment connecting the centers of the guide grooves of the inner joint member and the centers of the torque transmitting balls are equal), whereby the nature of constant velocity of the joint is secured, said length being hereinafter referred to as (PCR)); thus, PCD
BALL
=2×PCR.
The reason for selection of 3.3≦r
1
≦5.0 is that the strength of the outer joint member, the joint load capacity and durability should be made at least as high as in a comparative article (6-ball constant velocity joint). That is, in constant velocity joint, it is very hard to drastically change the diameter (PCD
BALL
) of said torque transmitting balls in the limited space. Thus, the value of r
1
depends mainly on the diameter D
BALL
of said torque transmitting balls.
If r
1
<3.3 (mainly when the diameter D
BALL
is large), the thickness of the other parts (the outer joint member, inner joint member, etc.) would be too small, causing anxiety about the strength. On the contrary, if r
1
>5.0 (mainly when the diameter D
BALL
is small), the load capacity would be too small, causing anxiety about the durability. Also caused is the anxiety that the surface pressure on the surface of contact between the torque transmitting balls and the guide grooves would increase (because the contact oval area decreases with decreasing diameter D
BALL
), forming a main cause of the chipping of the edges of the guide grooves.
The range 3.3≦r
1
≦5.0 provides greater degrees of strength of the outer joint member, of load capacity and durability of the joint than in the comparative article (6-ball constant velocity joint. This is proved to some extent by tests.
As shown in Table 1 (
FIG. 24A
) (which shows the estimation of the results of comparative tests), when r
1
=3.2, sufficient strength for the outer and inner joint members and cage was not obtained, an undesirable result. When r
1
=3.3, or 3.4, a rather good result was obtained in respect of strength. Particularly, when r
1
≧3.5, sufficient strength for the outer and inner joint members and cage was obtained, a desirable result. In addition, for the range r
1
>3.9, though no test has been conducted, it is expected that as good a result as the above will be obtained. If r
1
>5.0, however, it is considered that problems will arise in respect of durability and the outer and inner joints, as described above; thus, it is desirable that r
1
≦5.0.
From the above, it is desirable that r
1
be in the range 3.3≦r
1
≦5.0, preferably 3.5≦r
1
≦5.0.
Further, in addition to the above arrangement, it is desirable that the ratio r
2
(=D
OUTER
/PCD
SERR
) of the outer diameter (D
OUTER
) of the outer joint member to the pitch circle diameter (PCD
SERR
) of the tooth profile formed in the inner surface of said inner joint member
2
be within the range 2.5≦r
2
≦3.5.
The reason for selection of 2.5≦r
2
≦3.5 is as follows: The pitch circle diameter (PCD
SERR
) cannot be widely changed because of the relation to the strength of the mating shaft. Therefore, the value of r
2
depends of the outer diameter (D
OUTER
) of the outer joint member. If r
2
<2.5 (occurring mainly when the outer diameter D
OUTER
is small), the wall thickness of the each part (outer and inner joint members, etc.,) would be too thin, causing anxiety in respect of strength. On the other hand, if r
2
>3.5 (occurring mainly when the outer diameter D
OUTER
is large), a problem would sometimes arise from a dimensional aspect and the object of making the joi

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