Plunging constant velocity universal joint for propeller shaft

Details Plunging constant velocity universal joint for propeller shaft Plunging constant velocity universal joint for propeller shaft

2000-04-20

2001-08-28

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

06280338

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plunging constant velocity universal joint for the propeller shaft of an automobile.
A propeller shaft is used to transmit torque from a transmission to a differential gear set in a four-wheel drive (4WD) vehicle or a front-engine, rear-drive (FR) vehicle. While the use of 2-joint type propeller shafts is common, 3-joint type and 4-joint type are also used depending on the vehicle structure and specification requirements.
The constant velocity universal joints are roughly divided into fixed type that allows for only angular displacement between two shafts, and plunging type that allows for both angular displacement and axial displacement (plunging), that are selected and used according to the operating conditions, application and other factors. The present invention concerns with a double offset type constant velocity universal joint, among the plunging types, that is specifically designed for the propeller shaft of an automobile, and is reduced in weight and size.
2. Description of the Prior Art
Cardan joint (universal joint employing a cross spider) is predominantly used for the propeller shafts of 4DW vehicles and FR vehicles, except for some luxury models. However, non-uniformity of torque transmission characteristic of the Cardan joint leads to poor NVH (commonly known as noise, vibration and harshness) characteristics. Also the Cardan joint does not have a plunging mechanism, a slide spline (or serration) is required in the propeller shaft to absorb the geometrical changes generated by bounding of the vehicle or the like. However, since this portion has significantly large play and high sliding resistance, unusual vibration such as stick slip may be generated when vibration or sliding occurs during rotation. Thus it has been known that ride comfort of the vehicle is compromised for the passenger who is subjected to uncomfortable noise and/or vibration. Accordingly, constant velocity universal joints have been employed for the propeller shaft as means for improving the NVH characteristics.
In the automobile power-trains, there have been many examples of using constant velocity universal joints in the drive shafts, and majority of the constant velocity universal joints used in the propeller shafts have been those designed for the use in the drive shaft. However, when the operating conditions are compared between the propeller shafts and the drive shafts, the torque applied to a propeller shaft is about a half that of a drive shaft, and the practical range of the operating angles of the propeller shaft is narrower than that of the drive shaft. Thus use of a constant velocity universal joint designed for a drive shaft on a propeller shaft may be regarded as over specification compared to the specification requirements for the propeller shaft, with further improvements remaining to be done in terms of weight reduction, size reduction and cost cut-down. In addition, since the propeller shaft rotates at a higher speed than the drive shaft, the joint is desired to be more compact to facilitate high-speed rotation.
SUMMARY OF THE INVENTION
An object of the present invention is, accordingly, to provide a plunging constant velocity universal joint for propeller shaft that is lighter in weight, more compact and is capable of contributing to the improvement of the NVH characteristic of the vehicle.
The present invention aims at improving a light weight and compact constant velocity universal joint designed for a drive shaft, thereby to further reduce the weight and size thereof by redesigning specifically for the use in a propeller shaft only.
According to an embodiment of the invention, a plunging constant velocity universal joint for propeller shaft comprises an outer joint member having eight straight guide grooves formed in the axial direction on the inner circumference thereof having a cylindrical shape, an inner joint member having eight straight guide grooves formed in the axial direction on the outer circumference thereof having a spherical shape and teeth formed on the inner circumference thereof for the purpose of coupling with a shaft, eight balls disposed in ball tracks formed by the guide grooves of the outer joint member and the guide grooves of the inner joint member, and a cage having hollows for encasing the balls, an outer circumference of convex spherical shape guided in contact by the inner circumference of the outer joint member, an inner circumference of concave spherical shape guided in contact by the outer circumference of the inner joint member, wherein center of curvature of the outer circumference of the cage and center of curvature of the inner circumference of the case are offset from the center of the hollow in the axial direction to the opposite sides (double offset), while the ratio of width W, between the center of curvature of the inner joint member and the end face, to the pitch circle diameter Ds of fitting portion of the inner joint member is set as W/D
s
>0.27.
The constant velocity universal joint can be made lighter in weight and more compact through redesigning specifically for the use in a propeller shaft. By making the width of the inner joint member smaller than that of the conventional one, in particular, reduction in the quantity of material used and reduction in weight can be achieved. Since the double offset type constant velocity universal joint for propeller shaft requires a narrower range of operating angles, less strength and less depth of tracks than those for a drive shaft, width of the inner joint member can be made smaller thus making it possible to set such a width that allows weight reduction. The reason for setting a value greater than 0.27, for the ratio (W/Ds) of width W between the center of curvature of the inner joint member and the end face to the pitch circle diameter Ds of the fitting portion of the inner joint member, is because it was found that the operating angle required for the constant velocity universal joint for propeller shaft can be allowed for when the ratio (W/Ds) is greater than 0.27. The value of W/Ds is desirable to be as small as possible for the purpose of reducing weight and size, and in this regard there is no substantial rationale for setting the lower limit for the value of W/Ds. However, it is necessary to set the lower limit in order to ensure the movement of the balls that is required to allow for the desired operating angle. Upper limit is set to the same level as in the conventional one.
The double offset type joints have particularly lower slide resistance than the slide-spline. Thus it is advantageous to mount the double offset type constant velocity universal joint on a propeller shaft with regard to the improvement of the NVH characteristic as well.
The allowable operating angle of the joint is preferably about 15°. Since the propeller shaft operates with a smaller normal operating angle, it can be designed with restricted operating angle for size reduction. Thus width of the inner joint member can be reduced since the ball contact area on the inner and outer track, namely the track axial length requirement of the ball movement, can be reduced by restricting the operating angle. More specifically, such a width of the inner joint member that allows for the operating angle of 15° can be obtained by setting a value greater than 0.27 for the ratio W/Ds of width W between the center of curvature of the inner joint member and the end face to the pitch circle diameter Ds of the fitting portion of the inner joint member.


REFERENCES:
patent: 4533339 (1985-08-01), Girguis
patent: 5106343 (1992-04-01), Sakaguchi et al.
patent: 5632683 (1997-05-01), Fukumura et al.
patent: 5853328 (1998-12-01), Kobayashi et al.
patent: 0 844 412 (1998-05-01), None
patent: 10-073129 (1998-03-01), None

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