FORM 2
THE PATENT ACT 197 0 (39 of 1970)
The Patents Rules, 2003 COMPLETE SPECIFICATION (See Section 10, and rule 13)
1. TITLE OF INVENTION BALL JOINT

APPLICANT(S)
a) Name
b) Nationality
c) Address

ZF FRIEDRICHSHAFEN AG GERMAN Company 88038 FRIEDRICHSHAFEN GERMANY


PREAMBLE TO THE DESCRIPTION

The following specification particularly describes the invention and the manner in which it is to be performed : -


ENGLISH TRANSLATION VERIFICATION
CERTIFICATE u/r. 20(3)(b)
I, Mr. HIRAL CHANDRAKANT JOSHI, an authorized agent for the applicant, ZF FRIEDRICHSHAFEN AG do hereby verify that the content of English translated complete specification filed in pursuance of PCT International application No. PCT/DE2007/000718 thereof is correct and complete.

HIRAL CHANDRAKANT IOSHI AGENT FOR
ZF FRIEDRICHSHAFEN AG

The invention relates to a ball joint, in particular for the wheel suspension of a motor vehicle, having a ball stud, which is provided with a first spheroidal bearing surface pivotably and rotatably mounted in a housing, a rolling bearing being present between the first spheroidal bearing surface and a further spheroidal bearing surface mounted in the housing and connected to the ball stud.
Ball joints, such as those used in particular for wheel suspensions in motor vehicles, are subjected in some cases to extreme loads which may consist of mechanical stresses or be caused by thermal or chemical influences. Today, they are designed in such a way that under normal circumstances they do not have to be replaced and maintained during the service life of a motor vehicle.
Ball joints in motor vehicles are subjected to radial and axial forces which in some cases may assume considerable proportions. Moreover, the ball stud must also enable a rotational movement about its centre axis. With increasing size of a ball joint, the torques or moments of friction to be found in the ball joint also increase. This has an adverse effect particularly in the steering system, since increased forces have to be applied here in order to ensure the steerability of the motor vehicle. Furthermore, high torques and moments of friction inside the ball joint lead to wear and also to the danger that legal requirements regarding the steering return may not be complied with.
To reduce the torques or moments of friction inside a ball joint, the ball joints known for example from US 2,954,993 and US 2,645,510 have a ball stud, which is provided with a first spheroidal bearing surface pivotably and rotatably mounted in a housing, a rolling bearing being present between the first spheroidal bearing surface and a further spheroidal bearing surface mounted in the housing and connected to the ball stud. The rolling bearings used according to the disclosure content of the said documents are single-row deep groove ball bearings. The joint ball in these solutions consists of two separate component parts in each case, the described rolling bearing being received between the joint ball parts. With such a ball joint,
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owing to the low rolling friction of the rolling bearings, a rotational movement of the ball stud can be implemented with very low moments of friction.
However, the ball joints known from the said publications also have disadvantages. For instance, the bearing surfaces thereof are in each case metallic, spheroidal bearing surfaces which are mounted directly in a housing likewise composed of metal. As a result of the metal/metal contact pairing, vibrations introduced from the road via the wheel suspension and the ball joint situated therein are transmitted directly, i.e. without damping, to the motor vehicle components receiving the ball joint and can thus be felt by the vehicle driver. With this, however, comes a loss of comfort, which is not acceptable. Furthermore, owing to the bearing pairing used, it is necessary to maintain the ball joints regularly. The maintenance in the present case involves having to refill grease via lubricant filling openings present on the ball joint.
The most significant disadvantage of the ball joint designs known from US 2,954,993 and US 2,645,510 is, however, to be seen in the fact that the rolling bearings used are designed solely for loading in the axial direction, with respect to the non-deflected ball stud. The rolling bearings used here are not suitable for taking or transmitting radial forces.
A further problem with such rolling bearings is that, on the occurrence of joint wear and an accompanying loosening of the internal joint components, the play inside the rolling bearing also increases. As a result, however, it may happen that the rolling bodies are displaced and jam and thus their trouble-free functioning is not longer reliably ensured. The inevitably resulting consequence for the ball joint concerned would involve replacing it altogether.
Another solution is disclosed in US 2,544,583. The ball joint described therein is designed for wheel suspensions in motor vehicles. It has a ball stud, which is provided with a first spheroidal bearing surface pivotably and rotatably mounted in a housing, a rolling bearing being present between the first spheroidal bearing
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surface and a further spheroidal bearing surface mounted in the housing and connected to the ball stud. The rolling bearing used in this document is a cylindrical roller bearing. Such cylindrical roller bearings are suitable for taking high radial forces with respect to the axis of rotation of the rolling bodies. However, cylindrical roller bearings can transmit only extremely low, if any, axial forces. Given the complex loading of a ball joint in a motor vehicle, which also entails superimposed force and moment effects in the axial and radial direction, such a ball joint is only of very limited use. The embodiment described in this document also constitutes a metal/metal bearing, since not only the parts of the joint ball but also the housing are produced from a metallic material and form a direct contact pairing. The joint according to US 2,544,583 therefore also requires permanent maintenance at specified intervals, involving grease lubrication as in the above-described ball joints known from the prior art. For this purpose, the ball joint described in US 2,544,583 also has a lubricant filling opening.
The object on which the invention is based is to provide a ball joint which is capable of taking and accordingly compensating for both axial and radial loads via the ball stud. The ball joint should be of simple construction and thus be capable of production at low cost.
This object is achieved by the features of the first claim. Advantageous developments of the invention are the subject-matter of subordinate claims.
Accordingly, the inventor proposes developing a ball joint having a ball stud, which is provided with a first spheroidal bearing surface pivotably and rotatably mounted in a housing, a rolling bearing being present between the first spheroidal bearing surface and a further spheroidal bearing surface mounted in the housing and connected to the ball stud, in such a way that the rolling bearing is a rolling bearing which transmits radial and axial forces.
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A ball joint equipped in this way is distinguished in particular by extremely low torques or moments of friction about the longitudinal axis of the ball stud. At the same time, high axial and radial forces can be transmitted. Plays between the joint components which may arise in the course of the service life of such a ball joint can be compensated for by the rolling bearing according to the invention, so that in this case no repercussions on the further usability of the ball joint are to be feared. The configuration of a ball joint in accordance with the invention has provided the possibility of completely separating the rotational movement of the ball stud about its axial centre axis from the pivoting movement of the ball stud. Altogether, this gives rise to completely new constructional ways of designing such ball joints. A low-cost variant of a ball joint is provided which, owing to its simple construction, considerably reduces the manufacturing complexity and hence the production costs.
According to a first advantageous configuration of the invention, the inventors propose that the rolling bearing forms a double-row angular ball bearing, a taper roller bearing or a spherical roller bearing. These aforementioned types of rolling bearings are each suitable, in a manner according to the invention, for taking both axial and radial loads and transmitting forces so directed.
The construction of a double-row angular ball bearing corresponds to a pair of single-row angular ball bearings in an O-arrangement. Such bearings have very low plays owing to their design.
The aforementioned taper roller bearings are distinguished by a very high bearing capacity and can take combined and complex loads. In this case, to take axial forces, it may be necessary to provide a second, mirror-invertedly arranged taper roller bearing in order thereby to enable counter-guidance.
The spherical roller bearings proposed are suitable for extremely heavy loading. In the case of such a spherical roller bearing, two rows of barrel-shaped rollers run on a hollow-spherical path. The rollers are guided on fixed rims, so that besides the radial
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loads it is thereby also possible to take axial forces. One of these rolling bearings can be selected, depending on the intended application of the ball joint according to the invention.
A further essential advantage of the invention is also to be seen by the inventors in the fact that the axis of rotation of the rolling bodies of the rolling bearings encloses an angle a with the longitudinal axis of the ball stud. Practically speaking, this means that the rolling bodies are in an oblique position. This arrangement of the rolling bodies makes it possible to take both radial and axial loads in an improved manner, without reducing the positive properties of the ball joint, which are to be seen in particular in the extremely low friction upon rotational movement of the ball stud.
According to a further configuration of this concept, the angle a may be between 0° and 90°. However, arrangements of the rolling bodies in relation to the longitudinal axis of the ball stud at an angle a of 45° are preferred. It has turned out that in particular the arrangement less than 45° enables a very advantageous force transmission and thus is best able to cope with the demands on the ball joint.
By way of simplified manufacture and an accompanying cost reduction during the production of ball joints according to the invention, it is further proposed to provide a kind of modular system. Accordingly, one solution of the invention is that the ball stud has an at least two-part joint ball and the rolling bearing is received inside the assembled joint ball. The at least two-part design of the joint ball results in latitude of construction, enabling a high degree of variability of the individual components depending on the demands placed on the joint. The great flexibility includes the possibility of using standardised components.
The inventors have extended this above-described inventive concept to the effect that the rolling bodies can be arranged loosely in running path surfaces, suitable therefor, between the corresponding joint ball parts. This means that it is not
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necessary to use any previously finished rolling bearings to implement the solution according to the invention, but rather it is thereby possible to implement a very simple assembly of the ball joint according to the invention using a running path inside the mutually corresponding joint ball parts and rolling bodies inserted therein and furthermore to be able to provide for the arrangement of the rolling bodies between the joint ball parts in any desired manner. The initially mentioned oblique positions of the rolling bodies relative to the longitudinal axis of the ball stud can thus also be implemented without difficulties. The running path surfaces provided inside the joint ball parts have merely to be suitable for receiving the rolling bodies and appropriately guiding them.
One configuration of the invention may be seen in the fact that the rolling bearing inside the ball joint forms a rotary ring.
For improved comfort and reduction of the transmission of structure-borne noise of a ball joint according to the invention, the inventors furthermore propose pivotably mounting the joint ball, as a whole, in a bearing shell received in the housing. Such a bearing shell has the advantage that, on the one hand, it reduces, i.e. damps, vibrations introduced via the ball joint and, on the other hand, results in freedom of the ball joint from maintenance. By using an elastic bearing shell, subsequent lubrication of the ball joint with grease at prescribed maintenance intervals is accordingly not required. Suitable bearing shell materials are known from the prior art. Materials that can be used particularly advantageously are, for example, POM, PEEK or similar materials with good tribological properties, which reduce the tilting moments to a minimum in the present case. These maintenance-free materials in some cases have self-lubricating properties, while additionally affording the aforementioned damping properties.
To fix the bearing shell inside the housing, a retaining ring may be used. This retaining ring is also suitable for elastically prestressing the bearing shell to a limited extent. This results in the essential advantage that the bearing shell, even in the case
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of deterioration due to wear in the course of the service life of the ball joint, undergoes automatic tightening, so that the joint components inside the ball joint do not become loose. The ball joint according to the invention is thus designed for a very long service life under extremely high loads both radial and axial. The retaining ring may be secured in the housing by a form fit or frictional connection, for example by the deformation of a partial region of the housing edge, and at the same time fixes the bearing shell in the above-described manner.
Further features and advantages of the invention will become apparent from the subclaims and the following description of preferred exemplary embodiments with reference to the drawings, in which specifically:
Figure 1 shows a partial cross-section through an example of a ball joint
according to the invention,
Figure 2 shows the section II from Figure 1.
Illustrated in Figure 1, by way of example and in partial section, is one embodiment variant of a ball joint according to the invention. This ball joint has a ball stud 1, which is pivotably and rotatably mounted in a housing 2. In the example illustrated, the housing-side end region of the ball stud 1 has a first spheroidal bearing surface 3, which, together with a second spheroidal bearing surface 4 connected to the ball stud 1, forms a joint ball, denoted as a whole by 9.
Between the joint ball parts 9.1 and 9.2 is placed a rolling bearing 5. This rolling bearing 5 comprises running paths 10, present in the joint ball parts 9.1 and 9.2, into which paths numerous loose rolling bodies 7 are inserted. The special feature according to the invention consists then in the fact that the rolling bodies 7 are in an oblique position with respect to the longitudinal centre axis 8 of the ball stud 1. Oblique position is understood here to mean an inclined installation position, so that the axis of rotation 6 of the rolling bodies 7 encloses an angle a with the longitudinal
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centre axis 8 of the ball stud 1. In the exemplary embodiment of a ball joint according to the invention shown in Figure 1, the angle a = 45°. This positioning of the rolling bodies 7 between the joint ball parts 9.1 and 9.2 enables an optimum transmission of the axial forces applied to the ball stud 1 and the radial loads of the ball joint. The joint ball 9 is, as a whole, pivotably mounted inside a bearing shell 11. The rolling bearings 5 ensure the reduction of the moments of friction of the rotational movement of the ball stud 1, while the pivoting movement of the ball stud 1 inside the housing 2 is provided with predefined coefficients of friction by the bearing shell 11.
The ball joint shown in the exemplary embodiment of Figure 1 has a housing 2 open on one side. In the opening-side region of the housing 2 there is a retaining ring 12, which is fixed by an at least partial deformation of a housing region. The retaining ring 12 serves to fix in position inside the housing 2 the bearing shell and with it the joint ball 9, received therein, of the ball stud 1. For this purpose, it is advantageous for the bearing shell 11 to be produced from a plastic and to have elastic properties. The inherent elasticity of the bearing shell 11 also enables an automatic adjustment of the joint components, should a play arise between the bearing components in the course of the service life of the ball joint. The ball joint as a whole is thus free from maintenance for the entire designed service life. To protect the internal joint components from the ingress of moisture and impurities, a sealing bellows 13 is used. The latter is, on the one hand, sealingly placed against the ball stud 1. On the other hand, the sealing bellows 13 lies with its second edge region against the housing 2. To improve the sealing action, clamping rings 14 and 15 are additionally arranged in the respective edge regions of the sealing bellows 13. These clamping rings fix the sealing bellows on the said components. To avoid an axial movement of the sealing bellows edge lying against the ball stud 1 in the direction of the internal joint components, a sealing bellows retaining ring 16 is additionally provided in the region of the neck 17 present on the ball stud 1. This ring supports the sealing bellows edge and fixes it on the ball stud 1.
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In Figure 2 a sectional illustration according to the cutting plane line II-II from Figure 1 is shown. This reveals the design of the rolling bearings 5. The illustration in Figure 2 shows a view of the first joint ball part 9.1 in the region of the rolling bearings 5 placed therein. For this purpose, running paths 10 are provided in the joint ball part 9.1, into which paths, in the present exemplary embodiment, loose rolling bodies 7 are inserted. A corresponding opposite running path is situated in the second joint ball part 9.2, not visible in Figure 2. The joint ball is mounted, as a whole, inside the bearing shell 11, which for its part is inserted into the housing 2. The individual components are shown schematically in a simplified manner in the illustration of Figure 2, in order merely to explain the principle of the invention. The rolling bodies 7 guided inside the running paths 10 form, as a whole, a rotary ring inside the joint ball 9 of the ball stud 1.
It will also be understood that the above-mentioned features of the invention are usable not only in the particular combination given, but also in other combinations or on their own, without going beyond the scope of the invention. Similarly, it is within the scope of the invention to effect a mechanical reversal of the functions of the individual mechanical elements of the invention.
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List of reference symbols

1 ball stud
2 housing
3 first spheroidal bearing surface
4 second spheroidal bearing surface
5 rolling bearing
6 axis of rotation of the rolling bodies
7 rolling bodies
8 centre axis
9 joint ball
9.1 first joint ball part
9.2 second joint ball part
10 running path
11 bearing shell
12 retaining ring
13 sealing bellows
14 first clamping ring
15 second clamping ring
16 sealing bellows retaining ring
17 neck
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WE CLAIM:
1. Ball joint, in particular for the wheel suspension of a motor vehicle, having a
ball stud (1), which is provided with a first spheroidal bearing surface (3)
pivotably and rotatably mounted in a housing (2), a rolling bearing (5) being
present between the first spheroidal bearing surface (3) and a further
spheroidal bearing surface (4) mounted in the housing (2) and connected to
the ball stud (1),
characterised in that the rolling bearing (5) is a rolling bearing which transmits radial and axial forces.
2. Ball joint according to Claim 1,
characterised in that the rolling bearing (5) forms a double-row angular ball bearing, a taper roller bearing or a spherical roller bearing.
3. Ball joint according to Claim 1 or 2,
characterised in that the axis of rotation (6) of the rolling bodies (7) encloses an angle (a) with the longitudinal axis (8) of the ball stud (1).
4. Ball joint according to Claim 3,
characterised in that the angle (a) is between 0° and 90°, preferably 45°.
5. Ball joint according to one of Claims 1 to 4,
characterised in that the ball stud (1) has an at least two-part joint ball (9) and the rolling bearing (5) is received inside the assembled joint ball (9).
6. Ball joint according to Claim 5,
characterised in that the rolling bodies (7) are arranged loosely in running path surfaces (10), suitable therefor, between the corresponding joint ball parts (9.1, 9.2).
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7. Ball joint according to one of Claims 1 to 6,
characterised in that the rolling bearing (5) forms a rotary ring.
8. Ball joint according to one of Claims 1 to 7,
characterised in that the joint ball (9) is pivotably mounted, as a whole, in a
bearing shell (11) received in the housing (2).
9. Ball joint according to Claim 8,
characterised in that the bearing shell (11) is produced from a material having elastic properties.
10. Ball joint according to Claim 8 or 9,
characterised in that the bearing shell (11) is positioned in the housing (2) by a retaining ring (12).
Dated this 5th day of August, 2008

HIRAL CHANDRAKANT JOSHI AGENT FOR ZF FRIEDRICHSHFEN AG
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