Plunging type constant velocity joint

Details Plunging type constant velocity joint Plunging type constant velocity joint

1998-05-15

2001-10-09

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

C464S144000

Reexamination Certificate

active

06299543

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a plunging type constant velocity joint equipped with eight torque transmitting balls, and especially preferably used for a power transmission mechanism for automobile.
There are two types in a constant velocity joint, one of which is a ball fixed type which is able to permit only angular displacement between two axes and the other of which is a plunging type which is able to permit both angular displacement and axial displacement between two axes. They are selectively used, depending on the use conditions, applications, etc. A Zepper type constant velocity joint is representative as the fixed type, and a double offset type constant velocity joint and a tripod type constant velocity joint are representative as the plunging type. As for the plunging type, the tripod type constant velocity joint uses rollers as torque transmitting members, and the others use balls as torque transmitting members.
For example, a double offset type constant velocity joint comprises an outer joint member in which six linear guide grooves are axially formed on an inner cylindrical surface thereof, an inner joint member in which six linear guide grooves are axially formed on an outer spherical surface thereof, six torque transmitting balls disposed in ball tracks formed by cooperation of the guide grooves of the outer joint member and the guide grooves of the inner joint member, and a cage for retaining the torque transmitting balls. Since the spherical center of the outer spherical surface of the cage and the spherical center of the inner spherical surface thereof are offset to the opposite side in the axial direction from the center of pockets, they are called “double offset type”. When this kind of joint transmits a torque while taking an operating angle, the cage rotates to the position of the torque transmitting balls moving in the ball tracks in response to the inclination of the inner joint member to retains the torque transmitting balls on the bisector plane bisecting the operating angle. Furthermore, as the outer joint member and the inner joint member relatively displace in the axial direction, a slipping occurs between the outer spherical surface of the cage and the inner cylindrical surface of the outer joint member to ensure a smooth axial displacement (plunging).
SUMMARY OF THE INVENTION
It is therefore an object of the invention, in a plunging type constant velocity joint described above, to make further compact in size and to secure a strength, load capacity and durability equivalent to or exceeding those of a comparative article (a plunging type constant velocity joint having six torque transmitting balls as described above), thereby to provide a plunging type constant velocity joint especially preferably used for a power transmission mechanism in automobile.
In order to achieve the above mentioned object, the invention provides a plunging type constant velocity joint equipped with an outer joint member having a plurality of linear guide grooves axially formed on an inner cylindrical surface thereof, an inner joint member having a plurality of linear guide grooves axially formed on an outer spherical surface thereof, torque transmitting balls disposed in ball tracks formed by cooperation of the guide grooves of the outer joint member and those of the inner joint member, a cage having pockets for retaining torque transmitting balls. An outer spherical surface of the cage brought into contact with the inner cylindrical surface of the outer joint member to be guided by the same, and an inner spherical surface of the cage brought into contact with the outer spherical surface of the inner joint member to guided by the same. The spherical center of the outer spherical surface and the spherical center of the inner spherical surface of the cage are axially offset to the opposite side with respect to the center of the pockets. The number of the ball tracks and that of the torque transmitting balls are respectively eight.
The ratio r
1
(=PCD
BALL
/D
BALL
) of the pitch circle diameter (PCD
BALL
) to the diameter (D
BALL
) of the torque transmitting balls can be in the range of 2.9≦r
1
≦4.5, wherein the pitch circle diameter (PCD
BALL
) of the torque transmitting balls is equal to the distance between the centers of two torque transmitting balls positioned in ball tracks 180° opposed to each other at operating angle 0 deg.
The reason why the range of 2.9≦r
1
≦4.5 is employed resides in that the strength of the outer joint members, etc., load capacity and durability of the joints are made equivalent to or exceed those of the comparative article (a plunging type constant velocity joint having six balls). That is, since it is difficult to greatly change the pitch circle diameter (PCD
BALL
) of the torque transmitting balls in a limited space in a constant velocity joint, the figure of r
1
mainly depends on the diameter (D
BALL
) of the torque transmitting balls. If r
1
<2.9 (mainly in a case where the diameter D
BALL
is greater), the thickness of other components (outer joint member, inner joint member, etc.) is made too thin, there arises a worry in view of the strength. Contrarily, if r
1
>4.5 (mainly in a case where the diameter D
BALL
is smaller), the load capacity is decreased and there arises a worry in view of the durability. Furthermore, if the constant pressure at the contacting area between the torque transmitting balls and the guide grooves is increased (since the contacting ellipse at the contacting are is decreased if the diameter D
BALL
is decreased), there is a possibility that this results in a damage of the groove shoulder edge portion of the guide groove.
By establishing 2.9≦r
1
≦4.5, it is possible to secure the strength of the outer joint member, etc., load capacity and durability of the joint equivalent to or exceeding those of the comparative article (a plunging type constant velocity joint having six balls). This has been proven to some degree by tests.
As shown in Table 1 (which shows the evaluation on the basis of comparison tests), when r
1
is established to be 2.8, a sufficient strength of the outer joint member, the inner joint member and a cage can not be secured, and unfavorable results are produced. When r
1
is established to 2.9 or 3.0, a roughly satisfactory result could be obtained in view of the strength thereof. Especially, in a case where r
1
≧3.1 is established, the strength of the outer joint member, the inner joint member and the cage, and the durability of the joint can be sufficiently secured, and a favorable result can be obtained. Furthermore, in a case where r
1
>3.7, the test has not been carried out yet. But it can be presumed that a favorable result can be obtained as in the above. However, if r
1
>4.5, it is considered that a problem arises in view of the durability and strength of the outer joint member and the inner joint member. It is better that r
1
≦4.5 is established.
Based on the above description, it is better that r
1
is established to be 2.9≦r
1
≦4.5, more favorably 3.1≦r
1
≦4.5.
Furthermore, in addition to the above construction, it is better 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 serrations formed on an inner surface of the inner joint member is established to be 2.5≦r
2
≦3.5.
The reason why 2.5≦r
2
≦3.5 is established resides in that the pitch circle diameter (PCD
SERR
) of the serrations of the inner joint member can not be greatly changed in view of the strength of a shaft connecting thereto. Therefore, the figure of r
2
depends mainly on the outer diameter (D
OUTER
) of the outer joint member. If r
2
<2.5 is established (mainly in a case where the outer diameter D
OUTER
is smaller), the thickness of the respective components (outer joint member, inner joint member, etc.) is made too thin, a worry arises in view of the strength. On the other hand, r
2
>3.5 is established (mainly in

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