Rotary shafts – gudgeons – housings – and flexible couplings for ro – Coupling accommodates drive between members having... – Coupling transmits torque via radially spaced ball
Reexamination Certificate
1999-12-29
2001-12-25
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
C464S906000
Reexamination Certificate
active
06332844
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a propeller shaft for transmitting rotational power from the transmission to the differential in a four-wheel drive vehicle (4WD vehicle), front engine rear drive vehicle (FR vehicle), or the like. Although a propeller shaft of two-joint type is typical, a propeller shaft of three-joint type, four-joint type, or the like is also used according to the structure of the vehicle and the required characteristics.
At present, except for some luxury vehicles, it is the mainstream to use a Cardan joint (joint using a spider) for the propeller shaft of a four-wheel drive vehicle (4WD vehicle) or front engine rear drive vehicle (FR vehicle). Due to the non-constant velocity of the Cardan joint, however, the noise, vibration and harshness commonly known as NVH characteristics of the vehicle deteriorate. As means for improving the NVH characteristics, there is a tendency to use a constant velocity universal joint for the propeller shaft.
FIG. 6
shows a Rzeppa constant velocity universal joint (ball fixed constant velocity universal joint) used for a conventional propeller shaft. The constant velocity universal joint comprises: an outer joint member
11
in which six curved guide grooves
11
b
are formed in the axial direction on an spherical inner surface
11
a;
an inner joint member
12
in which six curved guide grooves
12
b
are formed in the axial direction on an spherical outer surface
12
a
and an engagement portion
12
c
having teeth (serration or spline) is formed on an inner surface; six torque transmitting balls
13
disposed in six ball tracks formed by the cooperation between the guide grooves
11
b
of the outer joint member
11
and the corresponding guide grooves
12
b
of the inner joint member
12
, respectively; and a cage
14
for holding the torque transmitting balls
13
.
The center O
1
′ of the guide groove
11
b
of the outer joint member
11
is offset from the spherical center of the inner surface
11
a,
and the center O
2
′ of the guide groove
12
b
of the inner joint member
12
is offset from the spherical center of the outer surface
12
a,
by an equal distance in the opposite axial directions (the center O
1
′ is offset to the left side in the diagram and the center O
2
′ is offset to the right side in the diagram). The ball tracks formed by the cooperation between the guide grooves
11
b
and the corresponding guide grooves
12
b
have therefore the shapes such that the ball tracks are widened toward one side in the axial direction (left side in the diagram) like wedge shapes. Both of the spherical center of the inner surface
11
a
of the outer joint member
11
and the spherical center of the outer surface
12
a
of the inner joint member
12
lie within the joint center plane O′ including the center O
3
′ of the torque transmitting ball
13
.
When the outer joint member
11
and the inner joint member
12
is displaced with each other by an angle &thgr;, the torque transmitting balls
13
guided by the cage
14
are maintained in the two-equally divided plane (&thgr;/2) of the angle &thgr; at any operating angle &thgr;, so that the constant velocity of the joint is assured.
A constant velocity universal joint has been often used for a drive shaft in the power transmitting mechanism of a vehicle. The conventional constant velocity universal joint for a propeller shaft is adopted the very design of the conventional constant velocity universal joint for a drive shaft. However, when the characteristics of the power transmission of the joint for the propeller shaft are compared with those of the joint for the drive shaft, the torque loaded on the propeller shaft is about the half of that loaded on the drive shaft and the practical range of the operating angle of the propeller shaft is narrower than that of the drive shaft. Consequently, the conventional specification adopting the design for the drive shaft as it is more than the required characteristics. It has room for improvement from the viewpoint of further reduction of the weight, size, and cost. Since the propeller shaft rotates higher than the drive shaft, it is preferable that the joint part is more compact also from the viewpoint of increase in the rotational speed.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a constant velocity universal joint for a propeller shaft, which is lighter, more compact, and cheaper.
In order to solve the problems, the invention provides a structure comprising: an outer joint member in which eight guide grooves extending in the axial direction are formed on an inner spherical surface thereof, an inner joint member in which eight guide grooves extending in the axial direction are formed on an outer spherical surface thereof and an engagement portion having teeth which come into tooth-engagement with a shaft portion of the propeller shaft is formed on an inner surface thereof; eight torque transmitting balls disposed in eight ball tracks, respectively, each formed by cooperation between the guide groove in the outer joint member and the corresponding guide groove in the inner joint member; and a cage for holding the torque transmitting balls, wherein the ball tracks are widened toward one side in the axial direction like wedge shapes, and the ratio Rw (=W/PCD
SERR
) between the width (W) in the axial direction of the inner joint member and the pitch circle diameter (PCD
SERR
) of the teeth of the engagement portion is 0.57<Rw≦0.95.
In this case, the “width (W) in the axial direction of the inner joint member” uses the dimension in the axial direction of the guide grooves in the inner joint member as a reference.
0.57<Rw≦0.95 is set for the following reason.
First, when each of the number of ball tracks and the number of the torque transmitting balls arranged is set to eight, the width in the circumferential direction of the outer surface of the inner joint member (L: dimension in the circumferential direction of the outer surface between the guide grooves) is relatively smaller than that in the conventional joint (ball fixed constant velocity universal joint using six balls) shown in FIG.
6
. This tendency becomes more conspicuous as the outer diameter of the inner joint member is reduced in order to make the joint more compact. On the other hand, in the case of forming the inner joint member by cold forging in order to improve quantity production, when the width (L) in the circumferential direction of the outer surface is too small, the material cannot sufficiently move in a forming die. Consequently, the guide grooves and the outer surface are not finished accurately and the life of the die is also shortened. As a result of experiments, it is confirmed that the minimum value of the width (L) in the circumferential direction of the outer surface at which preferable forming accuracy and life of the die can be obtained is 3.5 mm. In order to realize the cold forging to the inner joint member, it is necessary to assure 3.5 mm or larger as the width (L) in the circumferential direction (L≧3.5 mm).
The width (L) in the circumferential direction of the outer surface is not uniform in the axial direction. It drastically decreases from the center part in the axial direction to both ends and becomes the minimum value at the both ends. From the geometry shown in
FIG. 4
, the coordinates of the border part (shoulder part) between the outer surface
2
a
and the guide groove
2
b
of the inner joint member
2
can be obtained by solving the following two equations (the chamber in the shoulder part and the end face is not considered). Equation of the guide groove surface:
(
X+e
x
)
2
+{(
Y
2
+Z
2
)
½
−(
PCR+e
y
)}
2
=(&agr;
R
)
2
Equation of the outer surface:
X
2
+Y
2
+(
Z−f
)
2
=R
where,
X, Y, Z: coordinates
PCR: length of a line connecting the center O
2
of the guide groove
2
b
and the center O
3
of the torque transmitting ball
3
e
x
: offset amo
Hayama Yoshihiko
Nagatani Haruo
Arent Fox Kintner & Plotkin & Kahn, PLLC
Binda Greg
Browne Lynne H.
NTN Corporation
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