GB2231914A

GB2231914A - Ball-and-socket joint

Info

Publication number: GB2231914A
Application number: GB8915886A
Authority: GB
Inventors: Tatsuyoshi Tsuji; Yasunori Hamaguchi; Tsuneharu Kobayashi
Original assignee: Musashi Seimitsu Industry Co Ltd
Current assignee: Musashi Seimitsu Industry Co Ltd
Priority date: 1989-05-17
Filing date: 1989-07-11
Publication date: 1990-11-28
Also published as: DE3924003A1; GB8915886D0; JPH02304210A

Description

1 - D 1 _el BALL-AND-SOCKET JOINT This invention relates generally to

ball-and-socket joints (hereinafter referred to as ball joints), particularly to those used in steering devices and suspension systems of automotive vehicles and other linkage mechanisms. More specifically the invention concerns ball joints each provided with a boot-shaped dust cover for preventing dust, water, and other foreign matter from infiltrating into the sliding parts of the ball joint, the skirt part of the dust cover being sealingly secured to the socket casing by a binding member called a snap ring, spring clip, or spiral circlip (herein referred to as a spiral. circlip or circlip) having a spirally wound shape as viewed in plan view.

An example of a ball joint of this kind is disclosed in Japanese Patent Laid-Open (Kokai) No. 60-188,616. In this known ball joint, an annular groove is formed around the outer periphery of the rim of opening of the socket casing nearest the ball stud, and in and around this groove is inserted the skirt part of a boot-shaped dust cover. Then, around the outer periphery of this skirt part, a spiral circlip is elastically fitted thereby to secure the skirt part of the dust cover to the socket casing.

In recent years, there is a trend to cause the spiral circlip to hold the dust cover more firmly than heretofore by increasing the clamping force of the circlip. This trend makes it necessary to provide a measure to prevent an edge of the extreme inner end of the spiral circlip from biting into the outer surface of the rim part of the skirt of the dust cover, fitted in the annular groove of the socket casing. It will be understood that the increased tightening force of the circlip tends to cause the inner edge of the spiral circlip to bite into the skirt of the dust cover. This must be avoided to prevent damages to the dust cover.

2 Accordingly, it is an object of this invention to provide a ball joint in which damaging of the dust cover due to the inner end of the circlip is avoided.

According to this invention, the above stated object is achieved by this invention which provides a ball-andsocket joint which comprises a socket and a ball head rotatably held within the socket and being integrally formed with a ball stud, and which is protected by a dust cover having one end sealingly fitted around the ball stud shank and the other end sealingly fitted around the socket and thus bound tightly by a spiral circlip fitted therearound, said spiral circlip being wound spirally and having windings of rectangular cross section, characterised in that the end edge on the radially inner side of the inner end of the spiral circlip is rounded as a smoothly curved surface over the entire height of said circlip.

The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a side view, partly in longitudinal section, showing one example of a ball joint according to this invention; FIG. 1A is an enlarged partial side view, in longitudinal section, showing the manner in which the dust cover is secured to the socket casing in the ball joint illustrated in FIG. 1; FIG. 2 is a plan view of one example of a spiral circlip according to the invention in its free state; FIG. 3 is a cross section taken along the plane indicated by line III-III in FIG. 1 as viewed in the arrow direction; FIG. 4 is a sectional view showing one example of a spiral circlip of the invention; 3 FIG. 5 is an enlarged, fragmentary plan view showing a spiral circlip with an inner end having a rounded end edge R; FIG. 6 is a plan view of a known circlip in its free 5 state; FIG. 7 is a section showing a state in which the circlip shown in FIG. 6 is applied around a socket; FIG. 8 is a side view of a known ball joint indicating a state wherein the outer end of the spiral circlip has become dislodged from its proper position in a groove; FIG. 9 is a plan view showing another example of a known circlip in its free state; FIG. 10 is a plan view, partly in cross section, showing the circlip of FIG. 9 fitted in place around the dust cover and socket; FIG. 11 is a plan view of another example of a spiral circlip according to the invention in its free state; 20 FIG. 12 is a plan view, partly in cross section, showing the circlip of FIG. 11 fitted in place around the dust cover and socket; FIG. 13 is a plan view showing still another example of a spiral circlip of the invention, in which the outer end part is formed in the shape of the letter S; FIG. 14 is a plan view, partly in cross section, showing the circlip of FIG. 13 fitted in place around the dust cover and socket; and FIG. 15 is an enlarged view showing a part of FIG.

14.

In one embodiment of this invention as illustrated in FIG. 1, the ball joint 1 has a cylindrical socket casing 11 encompassing and supporting a bearing member 12 made of a material such as a synthetic resin. This bearing member 12 is formed to snugly hold a spherical ball head 4, which is thereby slidably supported in a manner permitting its free rotation within limits about 4 three coordinate axes. This ball head 4 is formed integrally with a ball stud 2 and a shank 3.

The socket casing 11 is open at its top and bottom as viewed in FIG. 1. The larger bottom opening is closed and sealed by a sealing disc 13 comprising a disc spring and covered by rubber layers 14. The rim of the other upper opening 16 of the socket casing 11 encircles the necked lower part of the shank 3 of the ball stud 2. The shank 3 is provided at its part spaced apart from the ball head 4 with an integrally and coaxially formed flange 3a.

A boot or dust cover 5 of bulbous shape is provided envelopingly between this flange 3a of the shank 3 and the upper part of the socket casing 11, thereby sealing the upper opening 16 of the socket casing 11 and the space immediately thereabove from the outside air and thereby preventing dust and other foreign matter from infiltrating into the ball joint. The upper small opening rim 7 of this dust cover 5 is fitted tightly in a peripheral groove formed around the flange 3a, while the lower larger opening rim 8 is fitted in a peripheral groove formed around the upper outer periphery of the socket casing 11.

As shown as an enlarged view in FIG. 1A, the lower larger opening rim 8 of the dust cover 5 is provided around its outer periphery with a radially outwardly facing peripheral groove 9. In this dust cover groove 9 is fitted a coiled circlip 10 wound spirally as viewed in plan view and applying a constrictive clamping force on the lower skirt part of the dust cover 5 against the socket casing 11.

The dust cover 5 is fabricated from a suitable synthetic rubber and has a bulbous shape with an outwardly bulging middle section 6 intermediate between its upper and lower opening rims 7 and 8.

In this connection, it is instructive to review a known spirally wound circlip 10a shown in FIG. 6. As shown in FIG. 7, when this spiral circlip 10a is fitted in a specified position on the ball joint 1, the circlip 10a assumes a wound state of approximately two winding turns. In this case, because of this fitting, there are formed a portion 25 of relatively small radius of curvature of the circlip 10a near the outer peripheral end thereof and a gap 24 between the portion 25 and adjacent winding. This portion, 25 of small radius of curvature, as shown in FIG. 7, protrudes outwardly in the radial direction. The portion 25 and the gap 24 should be eliminated because they tend to reduce the clamping force of the circlip 10a. Furthermore, as shown in FIG.

8, disengagement of the outer peripheral end 21 of the circlip from the annular groove is apt to occur.

Another problem accompanying this known circlip 10a is caused by the sharp end edge 20a of the inner end thereof as shown in FIG. 6. This sharp end edge 20a, which is formed by cutting the hoop steel stock from which the circlip 10a is fabricated, is continually in contact with the outer surface of the dust cover 5 as shown in FIG. 7. As a consequence, the dust cover 5 undergoes an abrasive contact with this end edge 20a whenever it is fluctuatively moved.

Another example of a known circlip is shown in FIGS.

9 and 10. This circlip 10a is so formed that, when it is in its free state, it is wound in the form of a circle with substantially the same radius of curvature over its entire length. However, when this circlip 10a is fitted around the skirt of a dust cover 5 to secure it to a socket casing 11 as shown in FIG. 10, a portion 25 of relatively small radius of curvature is formed in the spiral circlip 10a in its part near its inner end 20a.

Moreover, gaps 24, 26, and 27 are formed on the inner side of the portion 25 of small radius of curvature and both sides thereof in the circumferential direction, whereby the effect of sealing of the skirt of the dust 6 cover 5 is reduced compared with the sealing effect as originally intended.

Still another problem is that the sharp end edge of the inner end 20a of the circlip loa is caused by the formation of this portion 25 to contact the groove in the skirt of the dust cover with even greater force. This must be avoided to prevent rupture of the dust cover.

The above described problems encountered in the prior art have been solved by this invention which will now be described in greater detail with respect to preferred embodiments thereof.

In a first embodiment of the invention as shown in FIG. 3, the spiral circlip 10 is so designed and fabricated beforehand that it will have approximately 11.

winding turns in fitted state around the skirt of the dust cover 5 and that it will have approximately 2 winding turns in its free state as shown in FIG. 2. This spiral circlip 10 is made of a metal or some other suitable material and has a rectangular cross-sectional shape as shown in FIG. 4. Moreover, a portion 22 of relatively large radius of curvature is formed in this circlip 10 near its inner end 20 in its free state. This portion 22 is formed beforehand with a large radius of curvature such that it will be substantially equal to the radius of curvature this portion 22 assumes when the circlip 10 is normally fitted around the skirt of the dust cover 5 in intimate constrictive contact therewith.

Another feature of this circlip 10 is that the inner end 20 thereof has an inner end edge which is smoothly rounded as indicated by the letter R in FIG. 5. This curved surface R is formed to extend over the axial thickness H (as shown in FIG. 4) of the circlip.

When the spiral circlip 10 in free state is to be fitted in place, it is first expanded to increase its inner diameter to the necessary value, and then it is fitted in the annular groove 9 of the dust cover 5. As a result, the spiral circlip 10 constrictively clamps the 7 large opening rim 8 of the dust cover 5 into and against the peripheral groove 15 of the socket casing 11. Then, at the outer end part of the circlip 10, a portion of relatively small radius of curvature is formed without its protruding outward and without the forming of portion of small radius of curvature in the portion a of the circlip 10 near its inner end 20 as shown in FIG. 3, which is a sectional view taken in the plane indicated by line III-III in FIG. 1. Thus, the circlip 10 presses in intimate contact in the annular groove 9 of the dust cover 5. The above described curved surface R of the inner end 20 of the circlip 10 then comes in contact with the outer surface of the dust cover 5. Therefore, when the dust cover 5 is deformed, damaging of the dust cover 5 is prevented even when the curved surface R of the inner end 20 of the circlip contacts the dust cover 5.

Thus, according to this invention as illustrated by two examples thereof described above, portions of small radii of curvature and gaps are not formed near the outer end and the inner end of the spiral circlip when it is fitted in place. Therefore rupturing of the dust cover and detachment of the spiral circlip is prevented. moreover, damaging of the dust cover by the inner end edge of the circlip is prevented, and stabilization of the dust cover function is facilitated.

In another embodiment of the invention as shown in FIGS. 11 and 12, the spiral circlip 10 is so designed and fabricated beforehand that, when it is fitted in place, the number of its winding turns will be approximately 2.

This spiral circlip 10 is formed with a length such that it will have 241 winding turns in its free state as shown in FIG. 11. At the same time, a portion 22 of relatively large radius of curvature is formed near its inner end 20. In the vicinity of the outer end 21 of this spiral circlip in its free state, there is formed a portion 23 of a large radius of curvature such that the quantity of 8 increase of its radius of curvature is greater than the quantity of increase of an intermediate part.

This spiral circlip 10 is so formed that the radius of curvature of the portion 23 of large radius of curvature on the side of the outer peripheral end 21 will be equal to or somewhat smaller than the radius of curvature of the portion in the vicinity of the outer peripheral end 21 when the circlip has been fitted properly in place in intimate contact with the skirt of the dust cover 5.

When this circlip 10 is fitted in place around the skirt of the dust cover 5 over the peripheral groove 15 of the socket casing 11, its portion in the vicinity of its outer peripheral end 21 does not exhibit a relatively small radius of curvature but assumes a curvature such as to intimately hug the adjacent winding turn without a gap therebetween.

This spiral circlip 10 is ordinarily fabricated from a hard steel possessing a high elasticity but it can also be made of a stainless steel.

When a stainless steel is used, the holding force of the circlip is increased. The holding force of the circlip expressed as the dust cover pull-off load as determined by tests are set forth below.

1 9 Spiral circlip material: Hard steel Stainless wire (SWC) steel wire (JIS) for springs Dimensions and (SUS 304) other values (JIS) Diam. of wire stock 1.2 mm 1.2 mm material Tensile strength of 195 to 220 180 to 205 material kg/MM2 kg/mm2 outer diam., free state 28.73 mm 28.72 mm Number winding turns, free state 2 turns 2 turns Outer diam., fitted part 26.6 mm 26.6 mm Dust cover pull-off load 237 N 247 N Permanent set from 6.08% 3.75% expansion of inner diam. to 40 mm then release to contract freely As is clearly apparent f rom the above test results, the dust cover pull- off load of the stainless steel circlip is greater than that of the circlip made from hard steel wire in spite of the lower tensile strength of the stainless steel as a material.

As described and demonstrated above, by fabricating the spiral circlip of a plurality of winding turns of a ball joint from a stainless steel, the dust cover pull- off load can be made greater for the same dimensions. Therefore, by reducing the difference between the freestate diameter of the circlip and its expanded diameter, the formation of the portion of small radius of curvature and the accompanying gap near the outer peripheral end of the circlip can be suppressed while still retaining the desired dust cover pull-off load.

The spiral circliP 10 can be made of a shape memory alloy. In this case, the circlip is cgused to memorize its spiral shape of a diameter suitable for constrictively clamping the skirt of the dust cover in the peripheral groove 15 of the socket casing 11.

When this spiral circlip 10 is to be fitted in place within the annular groove 9 of the dust cover 5, the circlip 10 is first expanded in diameter until its inner diameter will easily pass over the maximum outer diameter of the dust cover 5. Then the circlip 10 is set around the outer periphery of the annular groove 9 of the dust cover 5. Thereafter the circlip is heated to cause it to be restored to its memorized shape. As a result, the spiral circlip 10 constrictively clamps the skirt of the dust cover 5 against the upper periphery of the socket casing 11 with the desired tight binding force.

By this mode of practice of this invention, the circlip is deformed into a free shape, exceeding its elastic limit, placed in its binding position, and thereafter heated thereby to restore it to its desired shape and cause it to generate its tight binding force. For this reason, even when the circlip is excessively expanded in diameter in order to f it it in the annular groove 9 and thus looses its binding force, this circlip can still carry out amply its binding function.

In a further example of the spiral circlip as shown in FIG. 13 to FIG. 15, the part of the outer peripheral end 21 of the spiral circlip illustrated in FIG. 2 is formed as a part 29 of the shape of the letter S with its extreme end directed outwardly. The part 29 comprises an outwardly directed part 29a, an inwardly convex part 29b and an outwardly convex part 29c. When the circlip 10 shown in FIG. 13 is fitted around the socket 11 as shown in FIG. 14, the inwardly convex part 29b presses inwardly against the adjoining turn of the clip to impart a radially inwardly directed clamping force 30 to the dust cover 5. As indicated in FIG. 15, the inner end 20 of i 11 the circlip has an edge R which is smoothly rounded to prevent it from biting into the dust cover 5.

-12-.

Claims

CLAIMS:

1. A ball-and-socket joint which comprises a socket and a ball head rotatably held within the socket and being integrally formed with a ball stud, and which is protected by a dust cover having one end sealingly fitted around the ball stud shank and the other open end sealingly fitted around the socket and thus bound tightly by a spiral circlip fitted therearound, said spiral circlip being wound spirally and having windings of rectangular cross section, the end edge on the radially inner side of the inner end of the spiral circlip being rounded as a smoothly curved surface over the axial thickness of said circlip.

2. A ball-and-socket joint according to Clain. 1 wherein the nun.ber of winding turns of the spiral circlip at the time of fittina thereof around said other end of the dust cover is approximately one and threequarter turns.

3. A ball-andsocket joint according to Claim. 1 or 21 wherein the radius of curvature of said inner end of the spiral circlip in the free state thereof is made greater than the radius of curvature of the neighbouring intermediate portion of the spiral circlip.

4. A ball-and-socket joint according to Clair 1 wherein the increase of the radius of curvature of a portion in the vicinity of outer peripheral end of the spiral circlip in the free state thereof is made greater than the increase of that of the intermediate part of the spiral 1 1 circlip.

5. A ball-and-socket joint according to Clair, the spiral circlip is made of a stainless steel.

6. A ball-and-socket joint according to Clairr, 1 wherein the spiral circlip is made of a shape memory alloy.

according to Clain, 1 wherein circlip in the vicinity of the outer peripheral end is formed in the shape of the letter S with the end thereof directed outward. 8. A ball- and-socket joint substantially as described with reference to Figures 1 to 5 and to 15 of the accompanying drawings.

7. A ball-and-socket joint the extreme end of the spiral 1 wherein herein Ficures 11 - I/t_ Amendments to the claims have been filed as follows 1. A ball-and-socket joint which comprises a socket and a ball head rotatably held within the socket and being integrally formed with a ball stud, and which is protected by a dust cover having one end sealingly fitted around the ball stud shank and the other open end sealingly fitted around the socket and thus bound tightly by a spiral circlip fitted therearound, said spiral circlip being wound spirally in a plane and having windings of rectanaular cross-section, the end edge on the radially inner side of the inner end of the spiral circlip being rounded as a smoothly curved surface over the axial thickness of said circlip. 2. A ball-and-socket joint according to Claim 1 wherein the number of winding turns of the spiral circlip at the time of fittina thereof around said other end of the dust cover is approximately one and threequarter turns. 3. A ball-and-socket joint according to Claim 1 or 2 wherein the radius of curvature of said inner end of the spiral circlip in the free state thereof is made greater than the radius of curvature of the neighbouring intermediate portion of the spiral circlip. 4. A ball-and- socket joint according to Claim 1 wherein the increase of the radius of curvature of a portion in the vicinity of outer peripheral end of the spiral circlip in the free state thereof is made greater than the increase of that of the intermediate part of the spiral circlip. 5. A ball-and-socket joint according to Claim 1 wherein the spiral circlip is made of a stainless steel. 6. A ball-and-socket joint according to Claim the spiral circlip is made of a shape 7.

1 wherein memory alloy.

A ball-and-socket joint according to Clair, 1 wherein the extreme end of the spiral circlip in the vicinity of the outer peripheral end is formed in the shape of the letter S with the end thereof directed outward.

8. A ball-and-socket joint substantially as herein described with reference to Figures 1 to 5 and Figures 11 to 15 of the accompanying drawings.

P"I.IshedIggaT--er-ac:Off--.S ---n:. - a. -5e.66, 1 High Ho' lborn. London WC1R 4TP. Further copies may be obtained froin The Patent Office.

Sales Brancli. St Mary Cray. Orpington. Kent BR5 3RD Printed by Multiplex techniques ltd. St Ma._% Cray. Kent. Con. 1 1 '87