Title of Invention

FOUR-POINT STEERING SYSTEM FOR THE AXLE SUSPENSION OF A RIGID AXLE

Abstract

The invention relates to a four-point steering system 1 for the axle suspension of a rigid axle, in particular of a utility vehicle. The four-point steering system 1 has four bearing eyes 7, 8, 9, 10, and two of the bearing eyes 9, 10 can be articulatingly connected to the rigid axle respectively and two bearing eyes 7, 8 to the vehicle frame respectively. The four-point steering system 1 is effectively designed as an integral hollow housing 2, 3, 4, 5, 6 inscribed in the rectangle or trapezium formed by the bearing eyes, which is capable of twisting. The four-point steering system 1 proposed by the invention is distinctive due to the fact that the hollow housing 2, 3, 4, 5, 6 is essentially formed by a tube open at both ends with an essentially rounded rectangular cross-section to O-shaped cross-section, disposed in a lying position by reference to the vehicle.

Full Text

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 FOUR-POINT SUSPENSION ARM 2. 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 VARIFICATION CERTIFICATE u/r. 20(3) (b) I, Mr. HIRAL CHANDRAKANT IOSHI, 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/DE2005/000351 thereof is correct and complete. HIRAL CHANCHDRAKANT IZF FRIEDRICHSHAFEN AG Description The invention relates to a four-point steering system for the suspension of a rigid axle, in particular for a utility vehicle, of the type outlined in the introductory part of claim 1. Four-point steering systems of the above type have been in use for some years, especially on heavy goods vehicles and other utility vehicles. Such four-point steering systems combine a number of functions and tasks in a single component, for which a plurality of steering systems and components were previously needed in the region of the cylindrical axle guide. Amongst other things, using a four-point steering system obviates the need for additional transverse stabilizers to stabilize the vehicle body and prevent rocking because the four-point steering system, together with the longitudinal control arms which are provided for example, assumes the task of both guiding the axle in the transverse and longitudinal direction and the task of supporting torques and transverse stabilisation. The three-point steering systems which were previously necessary can also be dispensed with. This makes for a considerable saving in terms of structural complexity and also vehicle weight, which reduces the cost of producing, running and maintaining the utility vehicle. The fact that the four-point steering systems provide transverse stabilisation not at the torsion bar which is usually to the rear of the vehicle axle but by transmitting force into the vehicle frame, usually in the region in front of the vehicle axle, also obviates the need to provide a reinforced tail cross-member on the vehicle in addition, under certain circumstances, to absorb rocking moments. This results in extra savings in costs and reductions in weight. Due to the sum of these advantageous properties, the four-point steering system, which is usually based on a cross-shaped or X-shaped structure for reasons due to -2- production technology, as well as cost and strength reasons, and due to the low component weight, has gained ground and become commonplace extremely quickly, especially in the heavy goods-utility vehicle sector. Accordingly, four-point steering systems of a forged and also sheet metal construction have become known from the prior art, as well as four-point steering systems made from a cast component, for example from patent specifications DE 195 21 874 or DE 102 06 809. In the case of the forging process, however, it is usually necessary to use an essentially solid rectangular cross-section for the arms of the four-point steering system for production reasons, which results in a high component weight and hence high associated production costs, as well as increased fuel consumption and reduced payload of the utility vehicle. Constructed or welded four-point steering systems are also complex and hence expensive to produce. Known four-point steering systems produced as a cast component, on the other hand, such as that illustrated in Figures 7, 8 or 11 of publication DE 195 21 874, are also complex from various points of view and less reliable to produce in terms of processing. With four-point steering systems with a closed hollow geometry, for example, it is possible to support the casting cores forming the cavity so that, during casting, the casting cores do not float and thus cause unevenly thick wall thicknesses on the casting, but only under severe constraints, and this has a detrimental effect on strength properties as a result. As a result of these same problems, such cast four-point steering systems can not be produced with the desired large cross-sections and slim wall thicknesses at the same time in order to obtain a lightweight structure, which in turn leads to cast components and four-point steering systems with an unnecessarily high weight. Other four-point steering systems, such as that illustrated in Fig. 11 of publication DE 195 21 874, especially four-point steering systems which can be made by casting, need a plurality of casting cores for the production process, which again complicates -3- production and makes it expensive. In addition, the illustrated four-point steering system can not be optimally adapted to the prevailing load situation, which is usually characterised by a combination of pushing and bending but in particular high torsional loads, due to the lack of cavities. Against this background, the objective of the present invention is to propose a four-point steering system by means of which the disadvantages of the generic prior art outlined above can be overcome. In particular, the four-point steering system should also be simple, have excellent reproducibility and at the same time be inexpensive to make. In view of the fact that it is also desirable to provide a lightweight structure on the utility vehicle, it should also be possible to produce four-point steering systems to which outstanding mechanical properties can be specifically imparted whilst simultaneously reducing weight, based on a reliable and inexpensive process. This objective is achieved on the basis of a four-point steering system having the characterizing features defined in claim 1. Preferred embodiments are defined in the dependent claims. Firstly, the four-point steering system proposed by the present invention as a means of guiding a rigid axle, in particular of a utility vehicle, is provided in the form of an essentially integral hollow housing in a manner known per se, with four bearings for connecting it to the axle and to the vehicle frame. This being the case, the hollow housing inscribed in the rectangle or trapezium formed by the bearing eyes constituting its external contour, is able to twist, at least slightly, in order to absorb axle twisting. However, the four-point steering system proposed by the invention is characterised by the fact that the hollow housing is essentially provided in the form of a multi-sided tube which is open at two ends for example, disposed in a lying position on -4- the vehicle by reference to the fitted situation. Accordingly, the hollow housing or tube has a cross-section which is of a rounded rectangular shape (or what might be described a the shape of a stadium) to O-shaped or parabola-shaped. A hollow housing of this design for a four-point steering system can firstly be produced extremely easily on the basis of a reliable process and can be so largely irrespective of what manufacturing process is used. This is already attributable to the fact that the open tubular shape of the hollow housing is of a relatively simple basic shape which requires only relatively simple tools regardless of a specific manufacturing process, and which also has only a slight or simple undercut which is not split and does not have any closed cavities. In terms of the production process, the four-point steering system proposed by the invention, open at both ends and having an essentially tubular housing, lends itself particularly well to a casting process, although it is in no way restricted to such a process. The reason for this is that the core needed to produce the cavity during casting can be perfectly well supported because the two ends of the tubular hollow housing are open, as a result of which any hydrostatic floating of the core can be prevented with a high degree of reliability. Furthermore, this being the case, it is even possible to use a single casting core, which forms the shape of both the entire interior of the hollow housing of the four-point steering system and the four bearing eyes of the four-point steering system. This means that the four-point steering system can be produced with a high degree of process reliability and also extremely inexpensively, but at the same time, it is nevertheless possible to obtain thin-walled geometries of a large volume that are therefore stiff and lightweight without any problem and with a high degree of precision. -5- Due to its simple geometry, however, the inventive shape of the four-point steering system is extremely advantageous in the case of four-point steering systems produced by other methods, for example in the case of forged or deep-drawn parts. Above all, the invention can be implemented irrespective of whether the longitudinal axis of the tube forming the hollow housing runs along the vehicle longitudinal axis or along the vehicle transverse axis when the four-point steering system is fitted in a motor vehicle. For example, it would be conceivable for the longitudinal axis of the tube forming the hollow housing to be disposed in the direction of the vehicle longitudinal axis, in which case, depending on the cross-sectional shape and cross-sectional size, particularly high axial and/or polar surface moments of inertia and particularly high section moduli can be achieved with respect to twisting about the vehicle longitudinal axis due to swaying. In a preferred embodiment of the invention, however, the longitudinal axis of the tube forming the hollow housing extends transversely to the vehicle longitudinal axis or in the vehicle transverse direction. This embodiment is of particular advantage if specific defined stiffness levels or flexing capacity is required with regard to torsion or if a specific defined deformation behaviour of the four-point steering system is necessary with respect to the swaying movements of the vehicle body. As regards implementing the invention, the exact design of the hollow housing is also not of decisive importance as long as the hollow housing is of the described essentially tubular shape which is, easy to produce. This being the case, the invention is naturally not restricted to four-point steering systems with a prismatic tubular hollow housing but also includes tubular shapes other than the prismatic shape, in particular tubes with a variable diameter, a variable cross-sectional shape and variable wall thickness across the tube length. -6- In this connection, a preferred embodiment is one where the hollow housing of the four-point steering system has a narrowed region by reference to the vehicle longitudinal axis or/and by reference to the vehicle transverse axis if the vehicle is viewed from above. In other words, this means that the hollow housing as seen in a plan view onto the vehicle may essentially have any shape (with no narrowed region) of rectangle or trapezium, including a trumpet-shaped contour on one side or both sides (with a narrowed region only by reference to the vehicle longitudinal axis OR by reference to the vehicle transverse axis) through to a cross shape or X-shape (with a narrowed region by reference to the vehicle longitudinal axis AND by reference to the vehicle transverse axis), without departing from the principle of the tubular hollow housing open at both ends as proposed by the invention. Against this background, another particularly preferred embodiment of the invention is one where the hollow housing has an essentially integral cross-shaped or X-shaped design as seen in a plan view onto the vehicle. This being the case, the hollow housing seen in plan view can be broken down into a perceptible central housing region and four peripheral steering arms supporting the bearing eyes, but without, as a result, departing from the basic principle of the invention whereby the hollow housing is made from nothing more than a tube. This shape of the steering system housing is already of advantage due to the fact that it essentially corresponds to the long proven X-shape used for solid or forged four-point steering systems. However, the pronounced narrowed region on four sides of the open tube forming the hollow housing as seen in plan view combined with this design further improves the ability to produce the four-point steering system by a simple and reliable process, although it is not restricted in any way to four-point steering systems made by a casting process. -7- This is attributable to the fact that the pronounced narrowed region significantly reduces the undercuts formed due to the interior of the hollow housing, on the one hand, and the remaining undercuts are also of a pronounced conical or converging design on the other hand. This is of particular advantage when producing the four-point steering system by a casting process, although not exclusively so, because as a result, the free supporting length of the casting core can be kept particularly small, thereby enabling the casting core to be better supported to prevent it from floating. In another preferred embodiment of the invention, the steering arms are designed as profiled flexural supports in the cross-section and have an essentially C-shaped or U-shaped cross-section. Providing the steering arms as profiled flexural supports, in particular as flexural supports with a C-shaped or U-shaped cross-section, is of advantage because some of the not inconsiderable deformations which occur during operation of the four-point steering system can already be compensated by the steering arms as a result. Also as a result of this, the steering arms can be made in a more lightweight design, especially compared with the known four-point steering arms made as solid forged parts. However, the C-shaped cross-section is also more practical than the known double T-shaped cross section of the steering arms of four-point steering systems made by casting because a C-shaped cross-section simplifies the ability to produce the four-point steering system and thus saves on costs due to the fact that it has a recess on one side only. The latter applies in particular if, as is the case in another particularly preferred embodiment of the invention, the hollow housing is a cast part. Another design based on a shaped sheet metal part would also be conceivable. In addition to the general advantages already described above with respect to producing the four-point steering system proposed by the invention, there is an -8- added advantage in the case of casting with respect to designing the four-point steering system in the X-shape for example, because all the cavities or recesses of the four-point steering system, including in particular the recess of the C-shaped steering arms, and including the recesses for the bearing eyes under certain circumstances, can be produced with only a single casting core. It will be immediately obvious to a person skilled in the art of casting that a four-point steering system can be produced with an extremely high degree of precision and process reliability and requires only a single casting core, which, moreover, can be perfectly well supported, in spite of the structurally demanding task of producing a central, hollow housing region and four steering arms with a profiled cross-section. This in turn offers the advantage of freedom in terms of construction, which means that the four-point steering system can be produced with a voluminous cross-section yet with relatively slim wall thicknesses at the same time, without leading to inadmissible tolerances or difficulties with regard to the reproducibility of the wall thicknesses. All of this offers advantages with regard to the component quality, resistance to failure and in particular the resultant reduction in weight which can be achieved with a four-point steering system proposed by the invention. In another preferred embodiment of the invention, the hollow housing of the four-point steering system is made from bainitic cast iron. A four-point steering system of the design proposed by the invention and which is also made from bainitic cast iron can also be optimised with regard to a particularly low weight, with a view to achieving the stiffness and flexibility properties needed for structural reasons as well as a high resistance to failure. This is attributable to the fact that bainitic cast iron, which, amongst other things, is also used as a lightweight construction material in mechanical engineering and -9- automotive construction due to its superior strength and plasticity properties, has material values comparable with the corresponding material characteristics of high-quality heat-treatable steel. This applies in particular to material characteristic values such as tensile strength, yield strength and elongation at break, which are important from a construction point of view. However, bainitic cast iron has another important property. As already stated, in terms of the material characteristic values mentioned above, it largely corresponds to high quality construction steels but has a modulus of elasticity which is approximately one quarter of that of these steels, which, in the context of the four-point steering systems in question, does not represent a disadvantage and instead constitutes a decisive advantage. The reason for this is that the lower modulus of elasticity means that, with the same stiffness as steel, a four-point steering system made from bainitic cast iron may have a cross-section of a bigger volume but the mechanical stress occurring in the four-point steering system - under the same amount of deformation - would be no higher. This aspect is important for a four-point steering system, not least because, in addition to what are usually dynamic bending ad torsion stresses prevailing during operation, extreme loads can also occur which can take the form of extremely high torsional moments and - for example in the case of severe swaying in the axle on uneven terrain - can even take the form of specific, forced angles of torsion. Another important aspect in this same connection is the fact that, in the case of a four-point steering system made from (bainitic) cast iron but with the same geometry as a four-point steering system made from steel, lower mechanical stresses will occur in the component when subjected to the same amount of deformation due to the lower modulus of elasticity. This means that a four-point steering system made from bainitic cast iron will permit a higher reserve of nominal operating -10- stresses in terms of the maximum stresses which occur and in particular as regards the maximum deformations that will occur. As far as construction is concerned, this advantageously offers the possibility of using reduced wall thicknesses and/or bigger cross-sectional volumes and hence increased stiffness and/ or reduced weight. In another, particularly preferred embodiment of the invention, the bearing eyes are integrally formed on the hollow housing. This is of particular practical advantage in the case of four-point steering systems made from cast iron as proposed by the invention, although not exclusively so, because it enables a particularly homogeneous and load-optimised fibre or wall thickness pattern to be created in the component. It also results in other weight advantages and hence cost savings both in respect of the untreated part and the finished part. As already explained above, not least is the fact that in such an embodiment, only a single casting core is needed in principle, which forms both the cavity in the central housing region and the recesses of the C-shaped profiled steering arms as well as the recesses of the bearing eyes that will subsequently accommodate the joints. In another preferred embodiment of the invention, the bearing eyes of the four-point steering system have elastomer joints or molecular joints. Where molecular joints differ in particular from plain bearings such as ball bearings, is the fact that the ball piece is vulcanised inside the bearing eye in rubber. This is of advantage on the one hand because it completely obviates the need to seal the joint against water and dirt as would otherwise be necessary. On the other hand, in addition to improved noise damping, molecular joints also have a potentially longer service life than conventional ball joints. In addition, the radial or all-round elasticity of molecular joints prevents the kinematic over-control, which is known to occur precisely on axle suspensions, and the associated damaging overload on joints, steering arms and other vehicle components. -11- However, molecular joints are also of particular advantage from another point of view. In another, likewise preferred embodiment of the invention, the radial stiffness of two or four of the elastomer joints of the four-point steering system by reference to the vehicle swaying direction is different from the radial stiffness by reference to the direction perpendicular to the swaying direction, in particular is lower in the swaying direction than it is perpendicular to the swaying direction. In other words, this means that the four-point steering system and molecular joints exhibit a higher elasticity with respect to swaying movements of the vehicle than with respect to movements of the axle relative to the vehicle body in the horizontal plane. This results in a particularly stable and reliable axle and wheel guiding action but at the same time permits the requisite flexibility of the four-point steering system intrinsic in the construction with respect to swaying movements or twisting in the axle during operation of the vehicle. If the elastomer joints are designed so that they are more flexible or have a lower stiffness with respect to movements in the vehicle swaying direction, the four-point steering system therefore forces a higher proportion of the deformation incurred by the swaying movements or twisting in the axle into the elastomer joints, which in turn reduces the maximum stresses and maximum deformations which occur in the four-point steering system housing. This being the case, increased stiffness can be imparted to the four-point steering system by structural means, for example by making the cross-sectional volume bigger whilst reducing the wall thicknesses, without causing the inadmissibly high stresses in the four-point steering system that would occur in the event of a given overall deformation. This makes for an additional saving on weight, thereby enabling costs to be reduced, both during production and during operation of the four-point steering system. -12- The invention will be explained in more detail below on the basis of only one example of an embodiment, with reference to the appended drawings. Of these: Fig. 1 is a perspective diagram of an embodiment of a four-point steering system as proposed by the present invention; Fig. 2 is a diagram in partial section showing the four-point steering system illustrated in Fig. 1 in a plan view; and Fig. 3 is a side view of the four-point steering system illustrated in Figs. 1 and 2. Fig. 1 is an isometric or perspective view of an embodiment of a four-point steering system 1 proposed by the invention. Illustrated, firstly, is the essentially cross-shaped or X-shaped design of the four-point steering system housing with a central hollow housing region 2 and four steering arms 3, 4, 5, 6 integrally formed on the housing region 2. Also illustrated are the bearing eyes 7, 8, 9,10 formed respectively on the outer ends of the steering arms 3, 4, 5, 6, each of the bearing eyes 7, 8, 9,10 being already fitted with the respective ball joint or elastomer joint 11,12,13,14 in the diagram shown in Fig. 1. As may also be seen from the diagram shown in Fig. 1, the hollow housing 2, 3, 4, 5, 6 of the illustrated four-point steering system 1 is of the tubular design open at both ends proposed by the invention. The hollow housing 2, 3, 4, 5, 6 has widened trumpet-shaped regions at 15 and 16, although it is still tubular in principle as before, and has a pronounced narrowed region on all four sides, thereby imparting the illustrated cross-shaped or X-shaped design to the four-point steering system 1 with the clearly illustrated steering arms 3,4, 5, 6. -13- In the illustrated four-point steering system 1, this also forms the extremely homogeneous, flowing transition of the steering arms 3, 4, 5, 6 with a C-shaped cross-section into the tubular central housing region 2, the advantage of which is that forces can be transmitted particularly uniformly, thereby avoiding any load peaks in the material. Also particularly evident from the diagram of Fig. 1 is the fact that the illustrated four-point steering system 1 lends itself extremely well to a casting process. The reason for this is that only a single, common casting core (not illustrated) is needed in order to produce the illustrated four-point steering system 1 by casting as a means of forming the inner cavity 15, 16 as well as for forming the recesses 17, 18 of the steering arms 3, 4, 5, 6 with a C-shaped cross-section. Furthermore, as the person skilled in the field of casting technology will immediately see without an explicit explanation of the casting core, this casting core can be perfectly supported in the casting mould because of the pronounced narrowed region on all sides of the four-point steering system 1, thereby ruling out any possibility of the casting core floating and hence any unforeseen change in the wall thicknesses of the casting. This makes for process reliability during the casting process, renders production inexpensive and results in a high-precision component and hence the desired lightweight structure of the four-point steering system 1. Furthermore, if necessary, the four bearings 7, 8, 9, 10 of the four-point steering system, which are illustrated in the diagram of Fig. 1 already fitted with the cooperating elastomer joints 11, 12, 13,14, can also be created with one and the same casting core as that also used to create the cavity 15,16 of the central housing region 2 as well as the recesses 17, 18 of the steering arms 3, 4, 5, 6. As a result, the four-point steering system 1 illustrated in Fig. 1 can be produced on the basis of an almost ideal combination of low production costs, high process reliability and high component precision. -14- Fig. 2 shows the four-point steering system 1 illustrated in Fig. 1 in a plan view - by reference to the mounted situation on the utility vehicle. Here, regions a, b of the central housing region 2 are shown partially open or cut out in order to make the design and structure of the illustrated the four-point steering system 1 visible. Furthermore, the cross-section of the steering arms 3, 4, 5, 6 is incorporated as an example at c. As illustrated, a four-point steering system 1 of the type illustrated in Fig. 2 is distinctive due to its extremely harmoniously flowing overall shape, which is conducive to a uniform distribution of forces. As a result of the shape proposed by the invention, the four-point steering system 1 also can be constructed to obtain the best conceivable load-optimised design in spite of having uniform wall thickness contours a, b, c. Particular attention is drawn to the completely flowing transition where the steering arms 3, 4, 5, 6 with a C-shaped cross-section merge into the central, tubular housing region 2. All this results both in a high component quality and a high ability to withstand load, even though the four-point steering system 1 is low in weight. As a person skilled in the art of casting technology will readily see from the plan view illustrated in the diagram of Fig. 2, the four-point steering system 1 illustrated -apart from being of a load-optimised design - is also optimally adapted to casting, which is the preferred production method. Worth noting in this respect is the pronounced narrowed region on all sides, which specifically enables the integral casting core to be optimally supported due to the short free-supporting length of the casting core made possible as a result, which is in turn conducive to achieving the component quality and exact reproduction of the resultant wall thicknesses a, b, c. Fig. 3 illustrates the four-point steering system 1 from Figs. 1 and 2, again from a side view. Readily visible again is the flowing design of the four-point steering -15- system 1, which continues through to the bearing eyes 8, 9, with the uniform wall thicknesses made possible as a result and the simultaneous load optimisation due to the hollow cross-sections of different sizes. This design is again of advantage both as regards problem-free production of the four-point steering system 1 by casting and due to the fact that the four-point steering system 1 can be made with the lowest possible weight particularly if bainitic cast iron is used as the material for making the four-point steering system 1 as described above. As a result, it is clear that, due to the invention, four-point steering systems for guiding the axle of utility vehicles in particular can be made to a conceivably ideal load-optimised design. In this respect however, because of the specific geometry of the four-point steering system proposed by the invention, production of the four-point steering system can be significantly simplified at the same time by casting and the process reliability significantly improved. This makes for particularly cost-effective production of the four-point steering system, whilst at the same time improving the component quality of the four-point steering system significantly. Due to the load-optimised design of the four-point steering system made possible by the invention, the weight of the four-point steering system can be reduced significantly, even though the stiffness values and resistance to failure are unchanged, the particular advantage of which is that it makes the utility vehicle inexpensive to run. The invention therefore makes a significant contribution to improving the axle guidance and axle suspension of utility vehicles, whilst simultaneously reducing production costs for the resultant four-point steering system. The advantages of this, not least, are the reduction in fuel consumption, improved driving safety, cost-effective production and the improved system technology on the utility vehicle. -16- List of reference numbers 1 Four-point steering system 2 Hollow housing region 3 Steering arm 4 Steering arm 5 Steering arm 6 Steering arm 7 Bearing eye 8 Bearing eye 9 Bearing eye 10 Bearing eye 11 Elastomer joint 12 Elastomer joint 13 Elastomer joint 14 Elastomer joint 15 Cavity 16 Cavity 17 Recess 18 Recess a Wall thickness b Wall thickness c Wall thickness -17- WE CLAIM: 1. Four-point steering system (1) for the axle suspension of a rigid axle, in particular of a utility vehicle, which four-point steering system (1) has four bearing eyes (7, 8, 9, 10), two of which bearing eyes (9, 10) can be articulatingly connected to the axle and two bearing eyes (7, 8,) can be articulatingly connected to the vehicle frame, and the four-point steering system (1) is designed as an integral, rectangular or trapezium-shaped hollow housing (2, 3, 4, 5, 6) defined by the bearing eyes (7, 8, 9,10) which is capable of twisting, characterised in that the hollow housing (2, 3, 4, 5, 6) is essentially formed by a multi-sided open tube with an essentially rounded rectangular to O-shaped cross-section disposed in a lying position on the vehicle. 2. Four-point steering system as claimed in claim 1, characterised in that the hollow housing (2, 3, 4, 5, 6) is provided in the form of a tube open at two ends. 3. Four-point steering system as claimed in claim 1 or 2, characterised in that the longitudinal axis of the tube forming the hollow housing (2,3,4,5, 6) extends transversely to the vehicle longitudinal axis. 4. Four-point steering system as claimed in one of the preceding claims, characterised in that the hollow housing (2, 3, 4, 5, 6) has a narrowed region by reference to the vehicle longitudinal axis as seen in a plan view of the vehicle. -18- Four-point steering system as claimed in one of the preceding claims, characterised in that the hollow housing (2, 3, 4, 5, 6) has a narrowed region by reference to the vehicle transverse axis as seen in a plan view of the vehicle. Four-point steering system as claimed in one of the preceding claims, characterised in that the hollow housing (2, 3, 4, 5, 6) has an essentially integral cross-shaped or X-shaped design with a central housing region (2) and four peripheral steering arms (3, 4, 5, 6) supporting the bearing eyes (7, 8, 9,10) as seen in a plan view of the vehicle. Four-point steering system as claimed in claim 6, characterised in that the steering arms (3, 4, 5, 6) are designed as profiled flexural supports in the cross-section (c). Four-point steering system as claimed in claim 6 or 7, characterised in that the cross-sectional shape (c) of the steering arms (3, 4, 5, 6) is essentially that of a C-shape or U-shape lying on its side. Four-point steering system as claimed in one of the preceding claims, characterised in that the hollow housing (2, 3, 4, 5, 6) is a casting or a sheet metal part. Four-point steering system as claimed in claim 9, characterised in that the hollow housing (2, 3, 4, 5, 6) is made from bainitic cast iron. Four-point steering system as claimed in one of the preceding claims, characterised in that the bearing eyes (7, 8, 9,10) are integrally formed on the hollow housing (2, 3,4, 5, 6). -19- 12. Four-point steering system as claimed in one of the preceding claims, characterised in that the bearing eyes (7, 8, 9, 10) of the four-point steering system (1) have elastomer joints or molecular joints (11,12,13,14). 13. Four-point steering system as claimed in one of the preceding claims, characterised in that the radial stiffness of two or four of the elastomer joints (11, 12, 13, 14) is lower in the vehicle swaying direction than it is perpendicular to the swaying direction. Dated this 6th day of October, 2006. HIRAL CHA^DRAKANT JOSHI ^GENT FOR ZF FRIEDRICHSHAFEN AG -20- Abstract The invention relates to a four-point steering system 1 for the axle suspension of a rigid axle, in particular of a utility vehicle. The four-point steering system 1 has four bearing eyes 7, 8, 9, 10, and two of the bearing eyes 9, 10 can be articulatingly connected to the rigid axle respectively and two bearing eyes 7, 8 to the vehicle frame respectively. The four-point steering system 1 is effectively designed as an integral hollow housing 2, 3, 4, 5, 6 inscribed in the rectangle or trapezium formed by the bearing eyes, which is capable of twisting. The four-point steering system 1 proposed by the invention is distinctive due to the fact that the hollow housing 2, 3, 4, 5, 6 is essentially formed by a tube open at both ends with an essentially rounded rectangular cross-section to O-shaped cross-section, disposed in a lying position by reference to the vehicle. To The Controller of Patents The Patent Office Mumbai 1/2 Figure 1 -21-

Documents:

1204-mumnp-2006-abstract(29-9-2007).doc

1204-mumnp-2006-abstract(29-9-2007).pdf

1204-mumnp-2006-abstract.doc

1204-mumnp-2006-cancelled pages(29-9-2007).pdf

1204-mumnp-2006-claims(granted)-(29-9-2007).doc

1204-mumnp-2006-claims(granted)-(29-9-2007).pdf

1204-mumnp-2006-claims.doc

1204-mumnp-2006-claims.pdf

1204-mumnp-2006-correspondence(9-8-2007).pdf

1204-mumnp-2006-correspondence(ipo)-(25-8-2008).pdf

1204-mumnp-2006-correspondence-others.pdf

1204-mumnp-2006-correspondence-received.pdf

1204-mumnp-2006-description (complete).pdf

1204-mumnp-2006-drawing(29-9-2007).pdf

1204-mumnp-2006-drawings.pdf

1204-mumnp-2006-form 1(29-9-2007).pdf

1204-mumnp-2006-form 18(9-10-2006).pdf

1204-mumnp-2006-form 2(granted)-(29-9-2007).doc

1204-mumnp-2006-form 2(granted)-(29-9-2007).pdf

1204-mumnp-2006-form 26(9-10-2006).pdf

1204-mumnp-2006-form 3(29-9-2007).pdf

1204-mumnp-2006-form 3(9-10-2006).pdf

1204-mumnp-2006-form 5(9-10-2006).pdf

1204-mumnp-2006-form-1.pdf

1204-mumnp-2006-form-2.doc

1204-mumnp-2006-form-2.pdf

1204-mumnp-2006-form-3.pdf

1204-mumnp-2006-form-5.pdf

1204-mumnp-2006-form-pct-ib-301.pdf

1204-mumnp-2006-form-pct-ib-304.pdf

1204-mumnp-2006-form-pct-isa-210(9-10-2006).pdf

1204-mumnp-2006-form-pct-isa-210.pdf

1204-mumnp-2006-form-pct-ro-101.pdf

1204-mumnp-2006-other document(9-10-2006).pdf

1204-mumnp-2006-pct-search report.pdf

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