Abstract:
An axle unit with a vehicle axle a rigid axle body as an axle tube, with one radial arm each on both ends thereof. The radial arms are rigidly connected with the axle body, and one region of the arms forms the lower support for a spring element. The axle body and the two radial arms jointly are formed of two integral cast part halves that have been welded with one another along a partition line extending substantially in a horizontal plane.

Description:
BACKGROUND OF THE INVENTION 
     This application corresponds to German Patent Application 101 13 674.9, the entire disclosure of which is herein incorporated by reference. 
     1. Field of the Invention 
     The invention relates to an axle unit with a vehicle axle comprising a rigid axle body, developed, for example, as an axle tube having one radial arm each on both sides of the vehicle&#39;s longitudinal mid-plane, which radial arm at a first front end is articulatable on a bearing point, stationary on the chassis, and, spaced apart therefrom, is rigidly connected with the axle body, and which forms in the region of its back end, opposing the first end, the lower support of a spring element, on whose upper side is stayed the vehicle chassis. 
     2. Description of Related Art 
     An exemplary axle unit as described above has been disclosed in EP-A-0 806 311 or EP-A-0 830 960. For example, a special axle tube can be used for the axle body, wherein the cross section or wall thickness in the region of the connection with the separate radial arms may be increased through a compression process. The radial arms are independent and essentially box-shaped, wherein the perpendicular sidewalls, bottom, and top walls are welded to one another. The rigid connection of the radial arms with the axle body is provided by at least regionally encircling circumferential welds, which require high precision in production, and which are subjected to high loads during use. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to further develop the axle unit cited in the introduction such that production, mounting expenses, as well as the weight can be further reduced at low manufacturing costs, without diminishing the reliability and strength of the axle unit. 
     An axle unit in accordance with the invention includes an axle body and two radial arms, wherein the axle unit comprises two cast part halves that are connected with one another. The two cast halves may be connected together substantially horizontally, along a partition line, such that the axle body rigidly connects both radial arms with one another. In an exemplary embodiment, the two cast halves are welded together. The upper axle body half and the lower axle body half are herein also each essentially integrally connected with two upper radial arm halves and two lower radial arm halves, respectively, which complement each other. 
     Such shell-like cast part halves can be cost-effectively manufactured from sheet metal with suitable pressing or forging devices at low cost and in large numbers. Bracing or welding of separate radial arms with the axle body, and the work-intensive joining of the radial arms from several wall elements, such as required in the prior art arrangements, can be omitted. In an exemplary embodiment of the axle unit of the present invention, welding is only required in order to connect the two cast part halves in the region of the substantially horizontally extending partition line, in which loading is low. Furthermore, casting of the cast part halves provides a weight and load-optimizing wall thickness distribution in the axle unit. Thus it is possible to increase the material thickness in the high-load region of the connection of the radial arms with the axle body, and correspondingly to decrease it in regions that are less subject to loading. The axle unit according to the invention thereby attains high rigidity while simultaneously retains low weight. 
     The rigidity of the axle unit can be further increased while maintaining a relatively low weight by connecting the two cast part halves having a hollow volume. With this hollow construction, bending and torque moments, which exert an effect on the axle unit, are especially well absorbed. 
     If a bearing sleeve is developed or disposed at the front ends of each radial arm to connect the radial arms with the vehicle chassis, it is possible, while retaining the geometry of the axle unit, to use bearing sleeves that are individually matched to the vehicle chassis. Additionally, in this manner different materials can be used for bearing sleeves and cast part halves. In an exemplary embodiment, the bearing sleeves may be made of copper alloys. The bearing sleeves can be simply, yet securely, fastened by welding them on the radial arms, wherein the strength of the axle body is simultaneously increased. 
     The axle unit according to the invention can be employed in different types of vehicle chassis. Specifically, several throughbores may be provided at the back ends of the radial arms, wherein the throughbores may extend substantially perpendicularly to the plane of the partition line, in order to fasten spring elements on the radial arms. The spring elements are fastened in different throughbores, as a function of the size of the spring elements, which are preferably formed by one pneumatic spring bellows each, and the geometry of the vehicle chassis. In an exemplary embodiment, the spring elements are fastened in the through bores with a threaded stem. Due to the broad applicability of the axle unit in a variety of vehicle chassis types, the production costs, and in particular the costs for the casting tools of the cast part halves, can be kept low. Furthermore, a shock absorber attachment can take place in a manner known per se. 
     In order to be able to dispose a brake, such as for example a fixed caliper disk brake, in a space-saving and protected manner and in accordance with a preferred implementation of the present invention, a through-opening each is provided in the radial arms between the region connected with the axle body and the front end. Functional elements of a brake system can be accommodated in this through-opening without unnecessarily enlarging the constructional space in the region of the wheel suspension. The strength of the axle unit can be further increased by positioning an annular lining in the through-opening and welding the annular lining to the cast part halves. 
     An axle journal is preferably rigidly fastened in both side openings of the axle body in order to connect wheels with the axle unit. This axle journal can be pressed into the axle body, developed as an axle tube, and, if appropriate, welded to, or connected with, the axle unit in other ways. In this way, it is possible to employ differently dimensioned axle journals with a single axle unit geometry. 
     According to another implementation of the invention, roller bearings are provided in both side openings of the axle body. In this implementation, the wheels can be received in the bearing unit in the axle body via an extension of the wheel hub. In this development of the axle unit, the structuring of the wheels, or the brake, is also largely independent of the geometry of the axle unit, such that it can be variably employed for different vehicle types. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the following, an embodiment of the invention will be described by example and with reference to the drawing. 
     The sole FIGURE shows an exemplary axle unit according to the invention, in a schematic perspective view. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The axle unit  1  is combined of a lower cast part half  2 , and an upper cast part half  3 . Along a substantially horizontally extending partition line  4 , the two cast part halves  2  and  3  are connected with one another via a welding seam  5  and define a hollow volume between them. The two cast part halves  2  and  3  are each profiles that are pressed or forged from sheet metal, which have a wall thickness of a few centimeters, e.g., approximately 5 mm. 
     Each of the cast part halves  2  and  3  is developed in the form of an H with two radial arm halves  6   a ,  7   a , and  6   b ,  7   b , respectively, parallel to one another. The radial arm halves  6   a ,  6   b  and  7   a ,  7   b  are each integrally connected via axle body halves  8   a  and  8   b  respectively, such that the axle body halves  8   a ,  8   b  extend approximately perpendicularly to the radial arm halves  6   a ,  6   b  and  7   a ,  7   b . The radial arm halves  6   a ,  6   b  and  7   a ,  7   b  when combined, form radial arms  6  and  7 , respectively, in whose center region, the axle body  8 , combined of axle body halves  8   a ,  8   b , branches off in the form of an axle tube. In the exemplary embodiment shown, the axle tube  8  has a diameter of approximately 200 mm. 
     The ends  9  and  10 , which are the front of the radial arms  6  and  7  in the direction of travel indicated by arrow F, respectively, are articulatable on a bearing point on the vehicle chassis (not shown in the FIGURE). To this end, bearing sleeves  11  and  12 , respectively, are developed or disposed in the front ends  9  and  10  of radial arms  6  and  7 . In the embodiment depicted in the FIGURE, each front end  9  and  10 , of radial arms  6  and  7 , comprise a half-cylindrical recess, into which the annular bearing sleeve  11  and  12 , respectively, are welded around the circumference. Bearing sleeves  11  and  12  themselves can be coated on the inside, for example, with a copper alloy, or they can be formed entirely of an alloy, with good bearing properties. 
     Between bearing sleeves  11  and  12  and the branches of the axle body  8 , through-openings  13  and  14  are provided in each radial arm  6  and  7 , respectively, into which annular linings  15  and  16 , respectively, are welded to increase the strength of the axle unit  1 . In each instance, in these through-openings  13  and  14 , functional elements of a brake system (not shown) can be received in proximity to the axle after axle unit  1  is mounted. The contour of through-openings  13  and  14  as well as linings  15  and  16  inserted therein, are not limited to a circular shape. On the contrary, an elliptical geometry or any other geometry can be used depending on the dimension and structure of the brake system. 
     Two sets of three through holes  19  and  20  are provided in flattened ends  17  and  18 , respectively, which are the rearward ends of radial arms  6  and  7  with respect to the direction of travel F, respectively. Through holes  19  and  20  are offset with respect to one another, perpendicularly to the vertical longitudinal vehicle mid-plane. By means of threaded stems, spring elements (not depicted) can be fastened in one or several of through holes  19  and  20  on radial arms  6  and  7 , respectively, such that the back ends  17  and  18  of radial arms  6  and  7 , respectively, form supports for these spring elements. Non-limiting examples of spring elements include pneumatic spring bellows. The vehicle chassis may be placed in this case, on the upper side of the spring elements. By providing several through holes  19  and  20  in radial arms  6  and  7 , respectively, it is possible to fasten the spring elements, depending on the dimensions of the vehicle chassis, at differing spacings from the perpendicular longitudinal vehicle mid-plane. 
     In the embodiment depicted in the FIGURE, axle journals  21  and  22  are received in the two opposing side openings of axle body  8  and joined with it by being pressed and/or welded into the axle tube opening. On axle journals  21  and  22 , in known manner, one or more wheels (not shown) can be received. To this end, each axle journal  21 ,  22  has threaded sections on its end facing outwardly. 
     According to an alternative implementation, it is also possible to dispose in axle body  8 , instead of the axle journals  21  and  22  depicted in the FIGURE, roller bearings with which wheel hubs can be rotatably supported, with the outer bearing ring being securely connected with axle body  8 . 
     The foregoing description of various preferred embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments, as described above, were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.