FORM 2
THE PATENT ACT 1970 (39 of 1970)
&
The Patents Rules, 2003 COMPLETE SPECIFICATION
(See Section 10, and rule 13)
1. TITLE OF INVENTION : JOINT HOUSING
2. APPLICANT(S)

a) Name : ZF FRIEDRICHSHAFEN AG
b) Nationality : GERMAN Company
C) Address : 88038 FRIEDRICHSHAFEN
GERMANY
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed : -

Description
The invention relates to a joint housing, in particular for accommodating the bearing shell of a ball joint or for accommodating a molecular joint, of the type outlined in the introductory part of claim 1.
Joint housings of the generic type are used in the region of the chassis or wheel suspension of automotive vehicles, for example. In most cases, the purpose of the joint housing is to provide a connection for a bearing point, for example of a ball joint or a molecular joint, to the rod-type section or hollow section of a joint rod adjoining the joint housing. To this end, joint housings of the generic type have a housing region at one side which is used to accommodate the bearing shell of the ball joint or to accommodate the molecular joint, and a mounting shaft at the other side, which can be connected to the rod section or hollow section of the joint rod in an appropriate manner.
A known way of connecting the mounting shaft of joint housings to the hollow shaft of a joint rod is to insert the mounting shaft in the open end of the joint rod formed by the hollow section, for example a tube, after which the tube end and the inserted mounting shaft are cold pressed with one another.
In order to improve anchoring of the pressed connection between the mounting shaft and tube end, another known approach is to provide a grooved region, which usually comprises a plurality of grooves, in the essentially cylindrical surface of the mounting shaft This causes the contour of the tube end to adapt to the grooved surface of the mounting shaft due to the deformation which occurs when the tube end and mounting shaft are pressed, which results not just in a non-positive but also a positive pressed connection between the tube end and mounting shaft
In systems known from the prior art, however, the cross-sectional shape and/or the contour across the depth of the grooves disposed on the mounting shaft is usually
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decided on an empirical basis. However, this can lead to a situation in which the mounting shaft of the joint housing, the grooves of the mounting shaft and the pressed connection between the mounting shaft and tube end are not produced with optimum strength in terms of their shape, making optimum use of the material and with optimum strength values.
Criteria which are decisive in this connection, though by no means exclusively so, are the fibre grain of the material of the mounting shaft in the region of the grooved region, weakening of the cross-section of the mounting shaft in the region of the grooves, the notching effect of the cross-sectional changes caused by the grooves and the edges and radii imparted by the grooves, as well as strength and the degree of positive conformity of the pressed connection between the mounting shaft and tube end.
Against this background, the objective of the present invention is to propose a joint housing which overcomes the disadvantages known from the prior art. Accordingly, the pressed connection between the shaft of the joint housing and the tube end of the hollow section should specifically be optimised in terms of high strength and low component weight, and, by contrast with the prior art, this optimisation should not be achieved on an empirical basis but instead, should be achieved as far as possible on the basis of an analytical process.
This objective is achieved on the basis of a joint housing having the characterising features defined in claim 1. Preferred embodiments are defined by the subject matter of the dependent claims.
In a manner initially known per se, the joint housing proposed by the present invention has a housing region and a mounting shaft. This being the case, the bearing shell of a ball joint or a molecular joint may be mounted in the interior of the joint housing or in the interior of the housing region in particular. The mounting shaft may be inserted in the recess of the end region of a hollow section and can be
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pressed with the end region of the hollow section. In order to produce a positive pressed connection between the mounting shaft and hollow section, the mounting shaft of the joint housing has a grooved region with at least one groove, and the grooved region extends around the mounting shaft, running along at least parts of the shaft circumference. However, the joint housing proposed by the invention is distinctive due to the fact that the contour of the at least one groove in the shaft longitudinal section conforms to a portion of at least one mathematical curve function. In other words, this means that the groove contour is no longer of a shape resulting from an essentially empirical process such as used in the machine tool industry as is the case with the prior art, but instead is defined by and conforms to a mathematical curve function As a result, properties of the grooves such as the groove depth, transition radii or regions merging into the mounting shaft of the joint housing, volume of the grooves, angle of inclination and height of the groove sides, as well as the resulting properties and strength values of the positive connection between the mounting shaft and hollow section can be exactly defined, although this list is by no means exclusive. In this manner, all the properties, strength values and load bearing capacity of the pressed connection between the mounting shaft and hollow section can be subjected to analytical testing and optimisation.
In a preferred embodiment of the invention, the groove contour is determined by portions of at least two mathematical curve functions adjoining one another, and the at least two curve functions preferably merge with one another at a tangent, or it may also be preferable to use different mathematical curve functions. This additionally extends the structural freedom when it comes to defining the design or shape of the groove contour on the mounting shaft, thereby enabling greater optimisation to be obtained and even greater bearing capacity of the pressed connection between the mounting shaft and hollow section.
In another preferred embodiment of the invention, the grooves of the grooved region have a variable contour or groove depth along the shaft circumference. In other words, this means that the grooves of the grooved region the mounting shaft are not
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of a constant depth along the circumference of the mounting shaft or do not extend around the entire circumference of the mounting shaft and instead, are of varying depths in different regions of the circumference of the mounting shaft
This likewise enables the pressed connection to be further optimised, especially from the point of view of the torsional strength of the pressed connection between the mounting shaft and hollow section of a joint housing. The increase in torsional strength achieved with this embodiment of the joint housing proposed by the invention is attributable to the fact that ramps are formed along the circumference of the mounting shaft due to the varying depth of the grooves, the inclination of which runs in the circumferential direction of the mounting shaft. Consequently, a positive connection is also obtained between the mounting shaft and hollow section acting in the circumferential direction, which reliably prevents twisting of the mounting shaft and joint housing relative to the hollow section.
In one embodiment of the invention, the profiled depth of the groove as measured along the shaft circumference conforms to at least one mathematical curve function. In another embodiment of the invention, the contour of the profiled base of the groove along a shaft transverse direction conforms to at least one mathematical curve function These two embodiments represent alternatives, which permit a definition of the contour of the groove depth or the contour of the profiled base of the groove, either along the shaft circumference or as viewed along shaft transverse direction, which is as universal as possible.
The at least one mathematical curve function describing the contour of the groove in the shaft longitudinal section or the contour of the profiled depth of the groove in the shaft cross section is preferably selected from the following list of curve functions:
circular arc segment (radius)
triangle trapezium
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jump function
totally rational function of the 1st degree to the n-th degree based on the
formula
f (x) = anxn + an-1x+ao
potential function based on the formula f(x) = axk
root function based on the formula f(x) = axp/q
exponential function based on the formula f (x) = ax
logarithmic function based on the formula f(x) = In x
trigonometric function based on the formula
• f (x) = sin x
• f (x) = cos x
• f (x) = tan x
• f(x) = cotx
arc function based on the formula
• f (x) = arcsin x
• f (x) = arccos x
• f (x) = arctan x
• f (x) = arccot x
hyperbolic function based on the formula
• f (x) = hsin x
• f (x) = hcos x
• f (x) = htan x
• f (x) = hcot x
• f (x) = sch x
• f (x) = csch x
area function based on the formula
• f (x) = arsinh x
• f (x) = arcosh x
• f (x) = artanh x
• f (x) = arcoth x algebraic curve of the n-th order
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involute
cycloid
helical
catenary
tractrix
Gaussian distribution or type related function
polygonal.
The specific advantage of these elementary curve functions is that they can be mathematically described or defined easily and can therefore be readily manipulated from an analytical point of view. This leads to an exact definition of the groove geometry and hence to a reliable calculation function that is less susceptible to errors, particularly in connection with the properties of the pressed connection between the mounting shaft and hollow section.
In order to implement the invention, it is irrelevant how the housing region and mounting shaft of the joint housing are connected to one another, provided this connection between the mounting shaft and housing region is capable of withstanding at least the same loads as the joint itself and the connection between the mounting shaft and hollow section. In a preferred embodiment of the invention, however, the mounting shaft is integrally joined to the housing region or of an integral design with the housing region. A joint housing of this design offers specific advantages in terms of component weight, manufacturing costs and specific component strength.
In another preferred embodiment of the invention, at least one material cut-out or at least one orifice is disposed in the portion where the housing region merges into the mounting shaft This cut-out or this orifice is disposed in those regions of the transition area which account for only a low proportion of the axial or polar geometrical moment of inertia of the transition area.
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The background to this design is the fact that the transition between the housing region and the shaft region or mounting shaft is of crucial importance to the fatigue strength of the housing. Joint housings of the generic type known from the prior art have an arc at this point, for example, constituting the geometric shape of the transition between the housing region and shaft region Another known approach is to provide the connection on the housing region by means of a tangential straight line, which extends into the shaft region with a radius. However, the tangential contour is preferable from the point of view of optimising fatigue strength because the alternative incorporating an arc or radius causes significantly higher impact stress.
A disadvantage of a tangential connection on the housing region between the housing region and shaft region, on the other hand, is that it leads to a higher component weight compared with the connection based on an arc, which also leads to higher component costs. In the particular embodiment in question, the material cut-out or orifice extends at this point, in the transition area between the housing region and mounting shaft, because this enables the advantageous tangential contour of the transition area on the housing region to be selected without having to take on board the disadvantage of increased component weight.
In other words, providing the cut-out or orifice means that the material of the transition area which is disposed primarily in the vicinity of gravitational lines or in the vicinity of the centre of gravity of the shaft cross-section in the region of the transition area and hence contributes to the strength or rigidity of the transition area to only a small degree, is removed from the transition area due to the at least one material cut-out This results in a joint housing which has an optimised, particularly low component weight but virtually unchanged rigidity values.
In a preferred embodiment of the invention, the cut-out or orifice has an essentially triangular cross-sectional shape in the shaft longitudinal section. The triangular cross-sectional shape is particularly well adapted to the shape of the transition
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region between the housing region and mounting shaft and therefore leads to optimisation of the ratio between the weight reduction and rigidity of the transition region.
In another, likewise preferred embodiment, the edges and/or surface transitions of the cut-out or orifice are rounded. This design leads to a reduction in the notching effect, which can spread from the cut-out or orifice into the transition region
The invention will be explained in more detail below on the basis of an embodiment illustrated as an example in the appended drawings. Of these:
Fig. 1 is a schematic perspective diagram illustrating an embodiment of a
joint housing proposed by the present invention with a specifically adapted hollow section;
Fig. 2 is a schematic diagram of the shaft of the joint housing illustrated in
Fig. 1, shown in cross-section; and
Fig. 3 is a schematic perspective diagram of another embodiment of a joint
housing.
Firstly, Fig. 1 is a schematic diagram illustrating a joint housing 1. The joint housing 1 has a housing region 2, in the interior 2' of which the bearing shell of a ball joint -not illustrated here - or the elastomeric component of a molecular joint, likewise not illustrated, may be disposed, for example. The joint housing 1 also has a shaft region 3 or mounting shaft 3, which can be inserted in the hollow end of a hollow section 4, for example a joint rod 4, which is only partially illustrated.
For the sake of maintaining clarity, the mounting shaft 3 has not yet been inserted in the hollow section 4 in the diagram shown in Fig. 1. Once the mounting shaft 3 has been inserted in the hollow section 4, a pressed connection can be produced between
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the hollow section 4 and mounting shaft 3 by means of an appropriate pressing tool. Due to the grooved region 5 provided on the mounting shaft 3 of the joint housing 1, this creates a positive pressed connection between the mounting shaft 3 and hollow section 4.
For the purpose of the invention, the contour of the grooved surface of the grooved profile along the shaft longitudinal axis conforms to a portion of at least one defined mathematical curve function. This enables the dimensions and properties of the grooves 5 to be exactly defined or determined on an analytical basis, in particular the depth of the grooves 5, the transition radii to the surface of the mounting shaft 3, the
groove volume, angle and shape of the groove sides as well as the resultant groove properties and strength and rigidity values of the positive pressed connection
between the mounting shaft 3 and hollow section 4. As a result of the invention, this means that the properties, strength values and in particular load-bearing capacity of the connection between the mounting shaft 3 and hollow section 4 can be optimised particularly efficiently on the basis of an analytical approach.
Fig. 2 is a schematic diagram on a larger scale than Fig. 1 illustrating a cross-section through the shaft 3 of the joint housing 1 illustrated in Fig. 1 in the region of one of the grooves 5 of the grooved region. As illustrated, the profiled depth of the groove 5 along the shaft circumference varies from a maximum located respectively at 12 o'clock or 6 o'clock to a minimum located respectively at 3 o'clock or 9 o'clock.
Accordingly, the contour of the depth of the groove 5 along the shaft circumference or the contour of the profiled base 6 of the groove 5 across the shaft transverse direction in turn conforms to a portion of a defined mathematical curve function.
This results in additional optimisation of the pressed connection between the mounting shaft 3 and hollow section 4, particularly as regards the torsional strength of the pressed connection. The increase in torsional strength is achieved due to ramps 6 formed as a result of the variable depth of the groove 5 along the shaft
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circumference, the inclination of which runs in the circumferential direction of the mounting shaft 3, as result of which a positive-type connection is also obtained between the shaft 3 and hollow section 4 in the shaft circumferential direction. This reliably prevents the mounting shaft 3 and joint housing 1 from twisting relative to the hollow section 4.
Finally, Fig. 3 illustrates another embodiment of a joint housing 1. The joint housing 1 schematically illustrated in Fig. 3 has an approximately triangular cut-out 8 in the transition area 7 between the housing region 2 and mounting shaft 3 on both sides, although only the cut-out 8 directed upwards by reference to the drawing is visible in the diagram show in Fig. 3.
These cut-outs 8 are disposed in those regions of the transition area 7 which are responsible for only a small proportion of the geometrical moment of inertia of the cross-section of the transition area 7. In other words, this means that material is saved as a result of the cut-outs 8, especially in the vicinity of the torsional centre of gravity and in the vicinity of the bending gravitational line of the cross-section of the transition area 7, thereby enabling the weight of the joint housing 1 to be reduced.
In practical terms, since the regions where weight is saved are disposed in parts of the transition area 1 close to the centre of gravity, the polar or axial moment of inertia and hence the torsional and bending strength of the transition area 7 is not reduced as result. This means that the joint housing 1 obtained in this manner will be significantly lighter but will have practically unchanged rigidity and strength values.
As a result, it is therefore clear that the invention enables the geometry of the grooved region, which determine the properties of the pressed connection between the housing shaft and hollow section in particular, to be optimised in order to achieve the highest possible component strength for a low component weight. This
optimisation can be achieved as far as possible on the basis of an analytical approach. This makes it possible to design, dimension and construct joint housings
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more quickly and more economically.
The invention therefore makes a significant contribution to ensuring particularly economical production of high-quality but lightweight joint housings for ball joints, wheel suspensions, stabilisers and such like.
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List of reference numbers
1 Joint housing
2 Housing region
2' Interior
3 Mounting shaft
4 Hollow section
5 Groove
6 Profiled base
7 Transition area
8 Cut-out, orifice

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WE CLAIM:
1. Joint housing (1), in the interior (21) of which in particular a bearing shell or a
molecular joint can be mounted, the joint housing (1) comprises a housing
region (2) and a mounting shaft (3), which mounting shaft (3) can be inserted
in a recess of the end region of a hollow section (4) and pressed with the end
region of the hollow section (4), and the mounting shaft (3) has a grooved
region comprising at least one groove (5) extending around at least parts of
the shaft circumference, characterised in that
the contour of the at least one groove (5) in the shaft longitudinal section conforms to a portion of at least one mathematical curve function.
2. Joint housing as claimed in claim 1, characterised in that
the groove contour (5) is defined by at least two adjoining portions of mathematical curve functions.
3. Joint housing as claimed in claim 2, characterised in that
the at least two mathematical curve functions merge with one another at a tangent.
4. Joint housing as claimed in claim 2 or 3, characterised in that
the at least two portions merging into one another at a tangent are derived from different mathematical curve functions.
5. Joint housing as claimed in one of claims 1 to 4, characterised in that
the profiled depth of the at least one groove (5) varies along the shaft circumference in the shaft cross section.
6. Joint housing as claimed in claim 5, characterised in that
the profiled depth of the at least one groove (5) of the shaft circumference conforms to a portion of at least one mathematical curve function.
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7. Joint housing as claimed in claim 5, characterised in that
the contour of the profiled base (6) of the at least one groove (5) along a shaft transverse direction conforms to a portion of at least one mathematical curve function.
8. Joint housing as claimed in one of claims 1 to 7, characterised in that
the at least one mathematical curve function is contained in the following list
of curve functions:
-circular arc segment (radius)
-triangle
-trapezoid
-jump function
-totally rational function of the 1st degree to the n-th degree of the form
f (x) = anxn + an-1x+ao
-potential function of the form f(x) = axk -root function of the form f (x) = axp/q
-exponential function of the form f (x) = ax
-logarithmic function of the form f(x) = In x -trigonometric function of the form
f (x) = sin x
f (x) = cos x
f(x) = tan x
f (x) = cot x
-arcuate function of the form
f (x) = arcsin x
f (x) = arccos x
f (x) = arctan x
f (x) = arccot x
-hyperbolic function of the form
f(x) = hsin x f(x) = hcosx
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algebraic curve of the n-th order
involute
cycloid
helical
catenary
tractrix
Gaussian distribution or type related function
polygonal.
9. Joint housing as claimed in one of claims 1 to 8, characterised in that
the mounting shaft (3) is integrally joined to the housing region (2) of the joint housing (1).
10. Joint housing as claimed in one of claims 1 to 9, characterised in that
at least one cut-out (8) is provided in a transition area (7) between the housing region (3) and mounting shaft (2) in regions accounting for a low proportion of the geometrical moment of inertia.
11. Joint housing as claimed in one of claims 1 to 10, characterised in that
at least one orifice (8) is provided in a transition area (7) between the housing region (3) and mounting shaft (2) in regions accounting for a low proportion of the geometrical moment of inertia.
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12. Joint housing as claimed in claim 10 or 11, characterised in that
the cut-out (8) or orifice (8) in the shaft longitudinal section have an essentially triangular cross-sectional shape.
13. Joint housing as claimed in one of claims 10 to 12, characterised in that
the edges or surface transitions of the cut-out (8) or orifice (8) are rounded.
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Dated this 7th day of February, 2007


Abstract
The invention relates to a joint housing (1), in the interior (2’) of which a bearing shell or a molecular joint can be mounted, for example. The joint housing (1) has a housing region (2) and a mounting shaft (3), which mounting shaft (3) can be inserted in a recess of the end region of a hollow section (4) and pressed with the end region of the hollow section (4). In this connection, the mounting shaft (3) is provided with a grooved region (5) extending around at least parts of the circumference for producing a positive pressed connection between the mounting shaft (3) and hollow section (4).
The joint housing (1) proposed by the invention is distinctive due to the fact that the contour of the grooves (5) of the grooved region in the shaft longitudinal section conforms to a portion of at least one mathematical curve function.
The invention leads to economic production of high-strength, lightweight joint housings for ball joints, wheel suspensions, stabilisers and such like. This is made possible in particular because the geometry of the grooved region determining the properties of the pressed connection between the housing shaft and hollow section can be optimised on the basis of an analytical process, due to the invention.
To
The Controller of Patents
The Patent Office
Mumbai
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