FORM 2
THE PATENT ACT 1970 (39 of 1970)
The Patents Rules, 2003 COMPLETE SPECIFICATION (See Section 10, and rule 13)


TITLE OF INVENTION
RIGID AXLE FOR A COMMERCIAL MOTOR VEHICLE

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

ZF FRIEDRICHSHAFEN AG
GERMAN Company
8 8 038 FRIEDRICHSHAFEN
GERMANY

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


The invention relates to a rigid axle for a commercial motor vehicle, in accordance with the pre-characterising clause of patent claim 1.
Rigid axles of the generic type for commercial motor vehicles, which axles have two individual chassis struts which, in their neutral position, span a triangle in a common plane and at each end of which a joint is connected, on the one hand, to the structure of the vehicle and, on the other, to its axle, are known, for example from DE 43 38 651 Al, DE 101 18 623 Al or US 5,458,359. In addition, DE 103 48 645 Al indicates a chassis strut which has, at one end, an axial joint whose connecting pin is oriented coaxially with the longitudinal central axis of the chassis strut. At the opposite end from the axial joint, this chassis strut has a molecular joint or molecular bearing. The terms "molecular bearing" and "molecular joint" are to be understood as synonymous. Molecular joints or molecular bearings of this kind have a joint pin which is mounted inside a housing. The said joint pin is surrounded, within the housing, by an elastomeric member. It is a characteristic property of molecular joints or molecular bearings that they damp, by means of the elastomeric member, the movements introduced via the joint pin or chassis strut, so that the term "molecular bearing" is correct. Since, however, molecular bearings or molecular joints also permit relative movement of the components that are connected to one another via the elastomeric member, it is equally possible to speak of a "molecular joint". The elastomeric member may be connected to the housing and/or to the joint pin by vulcanisation. In addition, designs are known in which the elastomeric member has no fixedly adhering connection to the housing and/or to the joint pin. Because of their damping and vibration-insulating properties, molecular joints of this kind are used in a wide variety of variants in wheel-suspension systems in motor vehicles.
The chassis strut disclosed in the last-mentioned publication is inserted as a longitudinal guide rod between an axle of a commercial motor vehicle and the structure of said vehicle. In that instance, the axial joint is fastened to the structure of the vehicle. Axle designs, which have been known and in use for a long time, for guiding rigid axles have molecular joints on the axle in which the joint pins are

oriented transversely to the longitudinal central axis of the chassis strut. However, axle designs of this kind require considerable installation space in the region of the vehicle axle. Moreover, because the molecular joints of the chassis struts are mounted at a distance from the geometrical centre point of the rigid axle, moments which have to be compensated for during travel are set up at said chassis struts. Moreover, the chassis struts most frequently used have a molecular joint at both ends, a fact which makes their manufacture complicated and cost-intensive as a whole.
The underlying object of the invention is to develop a rigid axle for a commercial motor vehicle, the chassis struts of which permit a low installation height and which is also simple and cost-effective to manufacture.
The invention achieves this objective by means of the features in patent claim 1. Further refinements of the invention are described in the subclaims that follow said claim.
A rigid axle for a commercial motor vehicle, which axle has two individual chassis struts which span a triangle in a common plane and at each end of which a joint is connected, on the one hand, to the structure of the vehicle and, on the other, to its axle, was further developed, according to the invention, to the effect that an axial pin for connecting the chassis struts to the vehicle axle is inserted in said chassis struts in each case, at least at the axle end.
The particular advantage of the solution according to the invention can be seen in the fact that a smaller installation space is required than was the case in solutions having molecular joints for connecting the vehicle axle to the chassis struts. It is also possible to reduce the structural height of the flanges required for attaching the chassis struts to the vehicle axle. There is even the possibility of integrating the fastening points for the chassis struts directly into the vehicle axle. A design of this kind cannot be realised with molecular joints. Because of the reduction in the
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installation height in the region of the vehicle axle, it is possible, for example, by means of the solution according to the invention, to set the vehicle as a whole lower. As a result of the simplification of chassis struts according to the invention for a rigid axle, it is also possible to use standard components and subassemblies for different applications. A module system can thereby be provided which makes it possible to focus on a small number of standard components. Consequently, the result is also a decisive cost advantage in addition to the considerable simplification.
A first refinement of the invention makes provision for the point of intersection of the geometrical longitudinal central axes of the chassis struts in their neutral position to lie in the immediate vicinity of the geometrical centre point of the axle, or of the centre line of the vehicle axle. By designing the attachment of the chassis struts according to the invention to a rigid axle in this way, it is possible to avoid, or at least reduce to a decisive extent, troublesome moments at the components of the vehicle's suspension when said motor vehicle is in use, a fact which means that the mechanical loading on the chassis struts as a whole is reduced. The approach adopted in this connection is to provide for the attachment of the chassis struts as close as possible to the centre of the axle or to the centre line of the vehicle axle, this being also understood to mean an arrangement located, in the longitudinal direction of the vehicle, slightly in front of, or behind, this crossing point.
The same advantage as has already been mentioned previously in connection with the point of intersection of the geometrical longitudinal central axes can be achieved if the point of intersection of the geometrical longitudinal central axes of the chassis struts in their neutral position lies perpendicularly above the geometrical centre point of the axle or the centre line of the vehicle axle. With these designs which have been mentioned previously, the constructional position of the chassis struts in each case, and in particular the attachment of their joints at the axle end, is brought as close as possible to the centre point of the axle or the centre line of the vehicle axle.
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Another variant of embodiment of the invention makes provision for the centre point of the joint ball of the axial pin of the axial joint of the chassis struts, which joint is formed by means of said pin, to lie in a plane that runs perpendicularly through the geometrical centre line of the vehicle axle. In an embodiment of this kind, although the geometrical point of intersection of the longitudinal central axes of the chassis struts is arranged behind the rigid axle of the motor vehicle, this nevertheless results in the advantage that a pitching movement, that is to say a pivoting of the structure of the vehicle about the transverse axis of the latter, can be largely prevented or at least considerably reduced. A variant of embodiment that additionally lies within the scope of this proposed solution may have a slight distance between the centre point of the joint ball of the axial pin and the plane that runs perpendicularly through the geometrical centre line of the vehicle axle.
The chassis struts which together span a geometrical triangle advantageously have an angle of between 45° and 60° which they form with one another. In this region in which the chassis struts are arranged in relation to one another, they form a triangular guide which permits optimum support for the rigid axle of the commercial motor vehicle in respect of both longitudinal and transverse loads. With axle guidance of this kind, it is possible to dispense with additional expensive components such as, for example, Panhard rods.
With a view to simplifying the guidance of the entire rigid axle according to the invention for a commercial motor vehicle, it is further proposed, in a manner corresponding to a very advantageous further development of the invention, that the chassis struts have a rod-shaped or tubular member which is manufactured, as a whole, from cast iron and has a joint housing which is constructed at at least one of its ends. The production of chassis struts of this kind has been simplified to a decisive extent, compared to the known forged designs. Moreover, the number of individual parts can be decisively reduced by an arrangement of this kind according to the invention. A spheroidal graphite cast iron is suitable, in particularly advantageous manner, for the cast member. That is to say, in addition to optimum

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strength, this material also has lubricating properties so that it is possible, by means of said material, to form the joint housing or housings directly onto the tubular or rod-shaped member of the chassis strut.
Pursuing this concept, it is additionally proposed that the axial pins are inserted directly in those parts of the chassis struts that are constructed as joint housings. Said axial pins are thereby also mounted directly in the joint housing. In this case, the properties of the spheroidal graphite which have already been mentioned and which permit lubrication of the mounting point to a limited extent, play an essential role. By this means it was possible to provide a mounting arrangement for the axial pin which is very robust and of simple construction and which, in addition, is of extremely low-friction design.
Depending upon requirements that are imposed upon the chassis struts of a rigid axle according to the invention, however, it may also be desirable or necessary to insert in the joint housing at least one bearing shell made of plastic or metal for receiving a joint ball belonging to the axial pin.
Furthermore it is possible, both in the case of direct mounting of the axial pin in the joint housing of the chassis strut and also when said axial pin is mounted within a bearing shell, to additionally incorporate at least one damping element in the joint housing. This damping element, which preferably consists of an elastomeric material such as rubber for example, is suitable for absorbing vibrations of the individual parts of such a chassis strut which are capable of moving relative to one another.
Each of the designs previously mentioned for the mounting of the axial pin may be further improved, in terms of its frictional properties, by a sliding layer provided in the joint housing or in the bearing shell.

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A more extensive concept of the invention involves the fact that both the chassis struts that form a triangular guide, and also additional longitudinal guide rods which are fastened at one end to the vehicle axle and at the other end to the structure of the vehicle in a manner differing from the chassis struts in vertical position, are each fastened to the vehicle axle via a joint designed as an axial joint. It is thereby not only possible to apply the principle according to the invention to the initially mentioned design of the chassis struts along the lines of a triangular-guide arrangement, but said principle can also be transferred to other guide rods for guiding the rigid axle of a commercial motor vehicle.
In addition to the embodiment mentioned, which has one axial joint on each of the chassis struts, solutions in which an axial joint is present at each of the two ends of said chassis strut are also included within the purposes of the invention.
The invention will be explained in greater detail below with the aid of the appended drawings. The exemplified embodiments shown do not constitute a restriction to the variants represented, but merely serve to explain the principle of the invention. In the said embodiments, components which are identical or similar are designated by the same reference numerals. In order to be able to illustrate the mode of functioning according to the invention, the figures show only greatly simplified basic representations in which the components which are not essential to the invention have been dispensed with. However, this does not mean that such components are not present in a solution according to the invention.
Figure 1 shows a view from above of a rigid axle for a commercial motor
vehicle;
Figure 2 shows a view of the rigid axle shown in figure 1 in the direction of the arrow II from figure 1;

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Figure 3 shows a view of the rigid axle in a manner corresponding to the arrow III in figure 2, that is to say from the underside of the vehicle;
Figure 4 shows, in a diagrammatically simplified manner, a first possible
arrangement of a chassis strut on a rigid axle according to the invention;
Figure 5 shows another possibility for the arrangement of a chassis strut on a
rigid axle according to the invention; and
Figure 6 shows, in the form of a detail and in section, a chassis strut for use in a rigid axle according to the invention, as a representation of the individual component.
The view, which is shown in figure 1, of a rigid axle from the upper side of the vehicle, that is to say from above, shows two chassis struts 1 and 2 which together span a triangle in a common plane. Said chassis struts 1 and 2 have a joint at each of their ends. Figure 1 shows those joints 3 and 4 of the chassis struts 1 and 2 which are at the axle end. In this representation, it is not possible to make out the oppositely-located joints 5 and 6 of the chassis struts 1 and 2, which joints are mounted on the structure 7 of the vehicle. In this instance, the structure 7 of the vehicle is designed as a self-contained frame (chassis). The axial pins of the joints 3 and 4 of the chassis struts 1 and 2 are screwed into a flange which is mounted on the vehicle axle 8. Two longitudinal guide rods 17 and 18, which are connected to the vehicle axle at one end and to the structure 7 of the vehicle at the other, are also mounted underneath the vehicle axle 8, in a manner differing in vertical position from the fastening of the chassis struts 1 and 2. A stabiliser 21 also serves to offset rolling movements.
The fastening of the chassis struts 1 and 2 and also of the longitudinal guide rods 17 and 18 to the vehicle axle 8, which struts and rods are fastened differently from one another in terms of their vertical position, is indicated more distinctly from the

representation in figure 2. This figure also contains an arrow I which shows the view of the rigid axle according to the representation in figure 1. The axial joint 3 of the chassis strut 1 which is visible here is screwed directly into a flange which is fastened on the vehicle axle 8. On the opposite end of the chassis strut 1, said strut has a molecular joint 5 which is connected to the structure 7 of the vehicle. In order to improve the driving qualities of the rigid axle shown in figure 2, said axle also has a shock absorber 26. In addition, there also runs along, underneath the vehicle axle 8, a stabiliser 21 which is connected to the structure 7 of the vehicle by a connecting guide rod 22 and also a holder 24. In the exemplified embodiment shown, the longitudinal guide rod likewise has, at the axle end, an axial joint 19 underneath the vehicle axle 8. This axial joint 19 is screwed into a suitable flange on said vehicle axle 8. On the opposite end from the axial joint 19, the guide rod 17 has a molecular joint, of which no further details are indicated.
The view of the rigid axle in figure 3 corresponds to the direction of the arrow III in figure 2. The arrangement of the stabiliser 21 becomes clear, once again, from the said view. Said stabiliser connects the part which is the left-hand part in the direction of travel to the right-hand part of the structure 7 of the vehicle, which structure is designed as a chassis. The stabiliser offsets twisting of the axle such as occurs, for example, when travelling round a bend. The attachment of the longitudinal guide rods 17 and 18 to a flange on the vehicle axle 8 in each case via axial joints 19 and 20 respectively also becomes apparent from figure 3. Since the longitudinal guide rods 17 and 18 are mounted underneath the vehicle axle 8, and the chassis struts 1 and 2 are mounted above said axle, the possibility of identifying the chassis struts 1 and 2 is limited in the view in figure 3.
Finally, figure 4 shows a first possible arrangement of the chassis strut 1 on the vehicle axle 8. In this instance, the chassis strut 1 has a joint 3 which is designed as an axial joint. On the opposite end from the axial joint 3, the chassis strut 1 has a molecular joint 5. In this case, the axial pin 9 of the axial joint 3 on the chassis strut 1 has, when in its non-deflected position, a longitudinal central axis which runs
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coaxially with the longitudinal central axis 10 of the chassis strut 1. However, the axial pin 9 may equally well be arranged, when in its neutral installed position, at an angle with respect to the longitudinal central axis 10.
Now the particular feature of the attachment of the chassis strut 1 in figure 4 consists in the fact that the axial pin 9 is fastened to a flange 28 on the vehicle axle 8 in such a way that the prolongation of the longitudinal central axis 10 of the chassis strut above the centre point MA of the axle has a point of intersection SL with the centre line 11 of the vehicle axle 8.
What is achieved by fastening the chassis strut 1 to the vehicle axle 8 in this way is equally optimum guidance of the vehicle axle via the chassis struts, such as is also possible by means of another variant for the attachment of the chassis strut 1 to the vehicle axle 8 in accordance with figure 5. In this variant, the chassis strut 1 is fastened to the vehicle axle 8 in such a way that the centre point MG of the joint ball of the axial pin 9, which is designed as a ball pin, directly coincides with the centre line 11 of the vehicle axle 8 and lies, when projected onto a common plane, in the immediate vicinity of the geometrical centre point MA of the axle. The axial pin 9 is, once again, attached to the flange 28 on the vehicle axle 8. In figures 4 and 5, an angle a, which is preferably between 45° and 60°, is indicated in order to represent the splayed arrangement of the chassis struts 1 and 2. In the exemplified embodiment, a = 50°. For reasons of simplification, only one of the two symmetrically arranged chassis struts 1 and 2 is shown in each of the representations in figures 4 and 5.
The possible structure of a particularly preferred variant of embodiment of a chassis strut 1 for use in a rigid axle according to the invention is apparent from figure 6. In this connection, it should be noted that the chassis strut 1 consists, as a whole, of a one-piece cast component, the material used for this purpose being a spheroidal graphite material. Joint housings, 13 and 14 respectively, are formed on, adjacent to the rod-shaped member 12, at each end of the chassis strut 1. Said chassis strut 1,
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consisting of the rod-shaped member 12 and the joint housings 13 and 14, can therefore be manufactured as a one-piece component in a casting operation. The structure of the joints 3 and 5 can be explained in greater detail using the example of the chassis strut 1 which is represented in section in simplified form in figure 6. The joint 3 is designed as an axial joint. It has an axial pin 9. The said axial pin 9, which has a joint ball 15, is inserted, by means of said joint ball 15, directly in a suitable clearance in the joint housing 13 of the chassis strut 1, so that a bearing shell is unnecessary in this instance. A clearance, in which a damping element 16 is inserted, is present in the joint housing 13 in order to damp vibrations and improve the elastic properties. A closing ring 29 which abuts, with its inner superficies, directly against the joint ball 15 and thus also forms a metal abutment for said joint ball 15, serves to close the aperture of the joint housing 13. On the opposite side from the joint ball 15, the closing ring 29 has a shoulder against which a reshaped section 30 of the joint housing 13 is applied. The deforming of this reshaped section 30 takes place after the components of the ball joint have been assembled. However, the closing ring 29 may also be fixed in the housing 13 in some other way. A screwed connection may be mentioned at this point, merely by way of an example. The closing ring 29 also serves, by means of a groove which is present on its outer superficies outside the joint housing 13, for the rim of a sealing bellows 31, which seals off the inner components of the joint, to abut against. The second rim of the sealing bellows 31 abuts directly against the axial pin 9. For fixing purposes and for improving the sealing action, the two rim sections of the sealing bellows 31 are secured against the aforesaid component by means of clamping rings, of which no further details are indicated. In order to connect the axial pin 9 to a connecting flange 28 on the vehicle axle 8, said axial pin 9 has a connecting thread 32 at its end. A molecular joint 5 is present on the opposite end of the chassis strut 1 from the axial joint 3. This molecular joint is distinguished by an almost circular-cylindrical housing 14. An elastomeric member 33 is inserted in a through-bore incorporated in said joint housing 14. This elastomeric member 33, which is provided, in the present example, with multiple layers and with intermediate plies for improving the supporting properties, receives a connecting pin 34 which, in this instance, is

designed as a cylindrical pin. It is important, in the case of the molecular joint shown, that the connecting pin 34 has a longitudinal central axis which runs transversely to the longitudinal central axis 10 of the chassis strut 1, a fact which is characteristic of molecular joints and the fastening thereof to vehicle axles or to the structure of the vehicle, as the case may be.

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List of reference numerals

1 chassis strut
2 chassis strut
3 joint
4 joint
5 joint
6 joint
7 structure of the vehicle (chassis)
8 vehicle axle
9 axial pin
10 longitudinal central axis of the chassis strut
11 centre line of the vehicle axle
12 rod-shaped or tubular member
13 joint housing
14 joint housing
15 joint ball
16 damping element
17 longitudinal guide rod
18 longitudinal guide rod
19 axial joint
20 axial joint
21 stabiliser
22 connecting guide rod
23 connecting guide rod
24 holder
25 holder
26 shock absorber
27 shock absorber
28 flange
29 closing ring

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30 reshaped section
31 sealing bellows
32 connecting thread
33 elastomeric member
34 connecting pin

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CLAIM:
1. Rigid axle for a commercial motor vehicle, which axle has two individual
chassis struts (1, 2) which span a triangle in a common plane and at each end
of which a joint (3, 4, 5, 6) is connected, on the one hand, to the structure (7) of
the vehicle and, on the other, to the axle (8) of said vehicle,
characterised in that
an axial pin (9) for connecting the chassis struts (1, 2) to the vehicle axle (8) is inserted in said chassis struts (1, 2) in each case, at least at the axle end.
2. Rigid axle according to claim 1,
characterised in that
the point of intersection (SL) of the geometrical longitudinal central axes (10) of the chassis struts (1, 2) in their neutral position lies in the immediate vicinity of the geometrical centre point (MA) of the axle, or of the centre line (11) of the vehicle axle (8).
3. Rigid axle according to claim 1,
characterised in that
the point of intersection (SL) of the geometrical longitudinal central axes (10) of the chassis struts (1, 2) in their neutral position lies perpendicularly above the geometrical centre point (MA) of the axle or the centre line (11) of the vehicle axle (8).
4. Rigid axle according to claim 1,
characterised in that
the centre point of the joint ball (MG) of the axial pin (9) of the axial joint (3, 4) of the chassis struts (1, 2), which joint is formed by means of said pin, lies in a plane that runs perpendicularly along the geometrical centre line (11) of the vehicle axle (8).

5. Rigid axle according to one of the abovementioned claims,
characterised in that
the chassis struts (1, 2), which together span a geometrical triangle, form an angle (a) of between 45° and 60° with one another.
6. Rigid axle according to one of the abovementioned claims,
characterised in that
the chassis struts (1, 2) have a rod-shaped or tubular member (12) which is manufactured, as a whole, from cast iron and has a joint housing (13, 14) which is constructed at at least one of its ends.
7. Rigid axle according to claim 6,
characterised in that
the axial pins (9) are inserted directly in those parts of the chassis struts (1, 2) which are constructed as joint housings (13).
8. Rigid axle according to claim 6,
characterised in that
at least one bearing shell made of plastic or metal for receiving the joint ball (15) belonging to the axial pin (9) is inserted in the joint housing (13).
9. Rigid axle according to either of claims 6 or 7,
characterised in that
at least one damping element (16) consisting of an elastomeric material is inserted in the joint housing (13).
10. Rigid axle according to one of claims 6 to 8,
characterised in that
at least one sliding layer is present in the joint housing (13) or in the bearing shell.

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11. Rigid axle according to one of the abovementioned claims, characterised in that
both the chassis struts (1, 2) that form a triangular guide, and also longitudinal guide rods (17, 18) which are fastened at one end to the vehicle axle (8) and at the other end to the structure (7) of the vehicle in a manner differing in vertical position from the chassis struts (1, 2), are fastened to the vehicle axle (8) via a joint designed as an axial joint (19, 20).
Dated this 6th day of August, 2009
HIRAL CHANDRAKANT JOSHI AGENT FOR ZF FRIEDRICHSHAFEN AG

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