DIFFERENTIAL BOX AND PRODUCTION METHOD DESCRIPTION OF THE INVENTION The present invention refers to a differential box comprising a bell of the box and a box cover, the hood of the box and the lid of the box being joined by a riveted joint produced by several rivets, and a method for its production and assembly. A differential box serves to house and guide the components of a differential gear that usually comprises the conical wheels and pinions that make up the differential mechanism as well as the drive wheel or front sprocket driven by the drive element. A differential box of this type also comprises on two opposite sides, preferably on the lid of the box and on the hood of the box openings for the drive shafts which exit the box coaxially towards different sides. According to the state of the art it is usual in the industry that the lid of the box and the bell of the box of a finished differential box to be assembled are joined to each other by means of several screws or rivets distributed on the circumference of the box. The mounting space that is available for a differential mechanism together with the differential box is extremely small proportions, particularly in
the case of frontal transmissions in a passenger car, so that assembly space savings are already desirable, even in the range of a few millimeters. Furthermore, for the assembly of the differential boxes of the type under consideration whose parts of the box are joined by conventional riveted joints, a multitude of operational steps are required. The parts of the box that must be connected must be provided in each case with the corresponding holes of perfect fit for the rivet, and before passing the rivet through the holes of both parts of the box, one must be precisely centered to another by centering pins. Furthermore, on both sides of the components to be joined to each other the rivets require construction space for the rivet closure head on one side and the rivet seating head on the other hand. Against this background it is the object of the present invention to eliminate the disadvantages described above and to provide a differential case of the type under consideration, space-saving, stable and simple to manufacture, as well as a corresponding method for its production and assembly. In accordance with the invention this problem is solved by a differential box according to claim 1 and a method for its production and assembly.
according to claim 7. The differential box according to the invention is characterized in that the rivets that establish the riveted connection between the lid of the box and the hood of the box are molded monolithically with the lid box or with the bell of the box. In the method according to the invention, for the assembly of the differential box the raw rivets formed in the lid of the box or in the hood of the box are passed through their free end through the holes associated with them in the another part of the box, and then its free ends are deformed to produce the riveted joint - by known deformation techniques. Accordingly, in a differential case according to the invention, separate rivets are not required to establish the riveted joint. By molding the raw rivets and the bores dedicated thereto, the relative position of both parts of the differential box is fixed, so that it is possible to dispense with separate centering pins during their assembly. Furthermore, it is not necessary to provide separate rivet holes in the part of the box in which the raw rivets are molded monolithically. In addition, in the differential box according to the invention - unlike the conventional riveted joint - no
a seat head or annoying closure of a conventional riveted connection protrudes on the side remote from the riveted connection of the part of the box provided with molded rivets, which constitutes a not insignificant saving of assembly space. The multi-part differential box according to the invention can be made of steel or other suitable metals and / or alloys such as, for example, aluminum or other lightweight construction metals. Although by the concept of "monolithically molded" selected to characterize the configuration of the rivet is preferably understood a monolithic molding of the same material, in the case of a differential box in accordance with the invention it is also optionally possible to provide full rivets or reinforcements of another material that extends into the molded rivet and / or a rivet coating that improves the riveted joint. For the production of the parts of the box together with the rivets molded monolithically to a part of the box, conventional casting and / or deformation techniques are available, such as, for example, forging. The differential box according to the invention allows a great flexibility in the exact configuration of the rough rivets that are molded monolithically in the lid of the box or in the hood of the
box . Although in principle it is also possible to provide cylindrical rough rivets, in a first preferred embodiment of the invention the rivets in the rough have a conical shape extending over their axial length. A cone angle is preferably provided in the range of 0 to 5o, or even more preferably 0.5 to 5o. The conical configuration of the rough rivet gives the rivet a better "base firmness" in the region of its molding to the box lid or box bell. In addition, the conical shape of the raw rivet facilitates its passage through the respective holes of the other part of the box and therefore facilitates its centering in correct position. During the process of deformation of the rivet head when actually establishing the riveted joint, the entire rivet rod - which still has conical configuration - is crushed and deformed so that in the preferably cylindrical holes of the other part of the box it is possible obtain a good contact in the surface area of the rod, which leads to a strong non-positive union of the riveted joint. According to a preferred refinement of the invention it is possible to provide that the rough rivets molded in the lid of the box or the hood of the box
have on their axial length two regions with different cone angle. These conical regions may be either directly adjacent and squared or preferably also transformed into one another in continuous transition. In addition, it can be envisaged that the rough rivets have their free end chamfered. The conicity of a rough rivet can also continuously increase in total over its entire axial length towards its free end. With several conical regions or respectively a taper of continuous extension of the rivet it is possible, with suitable conical angles, to further improve the mutual centering of both parts of the box during its assembly. In addition, with a taper that increases continuously or stepwise - in the direction towards the head of the rivet it is possible to reduce the dimension of the closing head that occurs after deforming the free end of the rivet, which turns out to be favorable in particular with a space of reduced assembly. And it is that in the case of a riveted joint it is not the thickness or the diameter of the closing head that has a definite importance; rather, the kinematic force bond is produced largely by the surface pressure of the rivet rod within the bore. In accordance with another preferred configuration of the present invention, the lid of the box, the bell of
The case and rivets that are molded monolithically to the lid or bell are produced from aluminum or from an aluminum alloy. For this purpose, known techniques of casting or deformation are available, such as, for example, forging. It was found that the aluminum rivets molded monolithically to the box lid or to the bell of the box produce a suitable prestress for the present purpose between the parts of the box when establishing the riveted joint. The deformation process for producing the closing head in a rivet causes a certain heating of the rivet during the establishment of the riveted joint, so that an adequate pre-tension is adjusted as a result of the subsequent cooling process and the contraction attached thereto. By forging the parts of the box together with the molded raw rivet it is possible to ensure excellent material properties for a differential case according to the invention. However, due to costs, it is particularly favorable that the lid of the box, the hood of the box and the raw rivets molded with one are manufactured by the so-called method of casting in shell to counter pressure (counter pressure casting as know in English). This method of production, which as such is known to the expert, guarantees a micro-porosity
particularly low material, which simultaneously ensures a high extension limit and a good ductility in addition to high strength. These properties of material are good in particular for the present riveted joint in that it is possible to obtain a still stronger non-positive union of the riveted joint. Another favorable configuration of the invention proposes that the raw rivets be heated before establishing the riveted connection itself by deformation of the free ends of the rivets. As a result of the configuration according to the invention of the differential case, this can be achieved in a very simple manner by correspondingly heating that part of the case in which the rivets are molded monolithically. With this, it is possible to further increase the prestressing of the riveted joint -adapted to the respective material properties. And is that as a result of the higher temperature of the material to produce the riveted joint greater stress occurs in the subsequent cooling process than is the case with a lower initial temperature. Finally, in the differential case according to the invention, the drive gear is preferably fixed immobilized by rotation between the cover
of the ca a and bell of the box by means of the rough rivets molded in a part of the box. For this purpose, the corresponding holes for the passage of the rivets must also be provided on the drive sprocket. The prestressing of the riveted joint also in this case obtains a particularly good hold of the driving sprocket between the parts of the differential box housing. In addition, the assembly is further facilitated in that the monolithically molded rivets with a part of the housing and the holes of the sprocket and the other part of the housing predetermine the relative position of the drive sprocket relative to the sprockets. two parts of the ca As an additional advantage of the differential box according to the invention, it results that in a favorable configuration of the invention the molded rivets can also be configured with a shape that differs from a rotational symmetry in its axial extension. In this respect, the bore cross-sections of the bores must be adapted to the other part of the box and optionally to the drive cog according to the asymmetric rivet form. Otherwise the free end of the raw rivets can be configured either flat, convex or concave, as
require In the following the invention is explained in more detail by means of the drawing. They show: Figure 1 in sectional view, an exemplary embodiment of an assembled differential box in accordance with the invention, Figures 2 to 7 schematic views of five different embodiments of a rough shaped molded rivet, and Figures 8 to 14 representations in FIG. Detailed cut of different riveted joints molded so. Figure 1 shows in sectional view an embodiment of a differential box 1 according to the invention, the cutting plane extending through the axis A of both coaxial drive shafts 2, 3 and therefore centrally through the differential mechanism. The differential box 1 comprises a cover 4 of the box and a hood 5 of the box, between which the driving toothed wheel 6 is fastened by means of a riveted joint 7. The riveted joint 7 is established by several rivets distributed on the circumference of the box and in each case monolithically molded on the cover 4 of the box, of which in the cut of figure 1 only
represents a rivet 8. Prior to the deformation of the free end of the raw rivet to produce the riveted joint 7, the free end of the rivet 8 monolithically molded into the lid 4 of the case is first passed through a hole 9 in the 6 toothed wheel 6 and a hole 10 in the bell 5 of the box, whereby simultaneously the components to be joined are centered in the correct position one in relation to another. The free end was then deformed in the usual manner in the branch to establish the riveted joint 7, whereby the closing head 11 is formed in the rivet 8. The cover 4 of the box and the bell 5 of the box form the corresponding lubricating oil channels 12, 13 for the supply of lubricating oil to the differential mechanism. The conical wheels 16, 17 connected in an immobilized manner of rotation with respectively a drive shaft 2 and 3 by means of an engaged connection 14 and 15 engage on different sides with two pinions 18 mounted in bearing in the hood of the box, of which a As a result of the cutting plane selected in FIG. 1, only one can be identified in front plan view. At its end remote from the toothing the conical wheels 16, 17 are seated by suitable disks 19, 20 against the box part 4, 5 in each adjacent case. The driving trees 2, 3 that are
extend coaxial they leave the box 1 of the differential on different sides. For this purpose, an opening 21 is provided centrally in the cover 4 of the box and in the hood 5 of the box there is a corresponding opening 22 in which the drive shafts 2, 3 are mounted rotatably in bearing. Figures 2 to 7 show schematic views of five different embodiments of a raw rivet of differential boxes according to the invention that can be molded monolithically with the box lid or the bell of the box. The rivet 23 of Figure 2 is conical in shape and has a constant taper angle α over its entire axial length. In contrast, the rivet 24 of FIG. 3 has two regions 25, 26 with different angles α and α 2 of conicity along the conical extension of their axial length, which abut one another directly. Finally figure 4 shows another configuration of a rivet 27 whose conicity increases constantly and continuously towards its free end. While in the rivets of figures 2 to 4 the free end extends flat in relation to the surface to which they are molded monolithically, in the rivets 28, 30 and 32 of figures 5 to 7 their free end shows a different configuration. The free end 29 of the rivet 28 of FIG. 4 is configured concave, as is the free end 31
of rivet 30 of figure 6. The rivets of figures 5 and 6 differ only by the concrete configuration of the concave end of the respective rivet. In contrast the rivet 32 of Figure 7 is configured with a convex free end 33, being that the transition between the rod of the rivet and the free end is of continuous extension. With the flexibility in the particular embodiment of the raw rivets represented by figures 2 to 7 it is possible to adapt to the respective requirements the riveted joint produced by deformation of the free end of the raw rivets. In particular, by increasing the taper in the region of the free end of the rough rivets 24 and 27 shown in FIGS. 3 and 4, it is possible to reduce the size of the closing head that is produced after the riveted connection is made . With the concave configuration of the free end of the raw rivets 28, 30 of FIGS. 5 and 6 it is possible that with the use of a correspondingly shaped deformation tool the material flow is optimized by deforming the free end of the rough rivet - to increase the surface pressure of the rivet rod within the bore and thereby the non-positive union of the finished riveted joint. Finally figures 8 to 14 show still
more detailed representations of different riveted joints of other embodiments of a differential box according to the invention. In all the detailed representations of FIGS. 8 to 14, the lid 4 of the housing, the driving toothed wheel 6 and the bell 5 of the housing are joined to each other by means of a connection riveted with rivets that are molded monolithically with the cover 4 of the box, as already explained by figure 1. The riveted joints shown differ only in that in figures 8, 10, 12 and 14 the bore of the hood of the box has a chamfer 34 on the side in which the closing head of the rivet is found, by means of which the non-positive union of the riveted joint is improved. In addition, the closing head of the rivet of figure 8 - like that of figure 1 - is convex, while instead the closing heads of the riveted joints according to figures 9 and 10 are flat and those of the concave figures 11 to 14.