Patent ID: 12222027

DETAILED DESCRIPTION OF THE INVENTION

A differential housing1which has a bell body2, a wheel body3and two bearing bodies4,5is shown in different views inFIG.1andFIG.2. The differential housing1is designed as a cast part from a nodular cast iron material. Preferably, the casting material used is a nodular cast iron material which has the abbreviation GJS 700 or GJS 800.

A gearing6, which is designed as a spur gearing and is machined, is configured to extend radially outwardly on the wheel body3. The bell body comprises a recesses7for passing through shafts, not shown. The bell body2also comprises a plurality of balancing bores8.

The production costs can be reduced by designing the differential housing1as a cast part. By combining a green machining of the gearing, a dual frequency hardening and a blasting treatment, which can be carried out optionally before or after a gear grinding, the casting material which is more cost-effective but inferior regarding the operational stability can be used as a material for running gears subjected to high stress. Moreover, the noise damping can be effectively improved by the nodular cast iron material, during the operation of the differential housing1.

By the variants described hereinafter, relative to service life or fatigue, the differential housing1which is made of the nodular cast iron material can replace a conventional differential housing which has a gearwheel made of a case-hardened steel or heat-treated steel. In addition to cost savings and NVH optimization, the weight of the differential housing1can be reduced. In this case, a high requirement for the casting quality, a more elaborate green machining before the hardening, in particular before a surface hardening, are taken into account. Moreover, additional measures for increasing strength, such as for example shot peening, are carried out for increasing the flank load-bearing capacity or the tooth root load-bearing capacity.

A tooth10of the gearing6of the differential housing ofFIG.1andFIG.2is shown schematically in section inFIG.3andFIG.4. The tooth10has a tip region11, a flank region12and a root region13. An oversize, which is removed during the machining of the tooth10, is indicated by dotted lines inFIG.3andFIG.4. In the tooth10shown inFIG.3, the oversize is only provided in the flank region12. In the tooth10shown inFIG.4, the oversize is provided both in the flank region12and in the root region13.

The tooth10inFIG.3relates to a first, a second and a third variant of the claimed method. The tooth10inFIG.4relates to a fourth variant of the claimed method.

InFIG.5andFIG.6, two flow charts of a total of the four variants of the claimed method are shown.FIG.5comprises a total of nine method steps21to29.FIG.6comprises a total of ten method steps31to40.

The method steps21;31represent casting an unmachined part of the differential housing from the nodular cast iron material. The method steps22;32represent soft turning the cast unmachined part. The method steps23;33represent washing the soft-turned cast part. The method steps24;34represent gear milling the gearing. The method steps25;35represent dual frequency hardening.

The method steps27;38represent balancing the differential housing. The method steps28;39represent washing the differential housing. The method steps29;40represent mounting the differential housing.

FIG.5relates to the first variant of the claimed method. The gearing is already completed in the tooth root region in a pre-machining process during the gear milling34. After the inductive hardening26, in the method step27in a post-machining process the oversize in the flank region of the gearing is removed by gear grinding or honing.

By producing the tooth root region to the finished size in the soft machining process, the inductively hardened layer in the tooth root region is advantageously not reduced by the hard finishing, in particular, by gear grinding and/or honing, in the method step26.

In variants two and three of the claimed method, a root region which has a tooth root radius is also already completed in the pre-machining process in step34by gear milling. In variants two and three, the gearing is subsequently hardened, and namely inductively, primarily by dual frequency hardening in the method step35.

In the second variant of the method, a blasting operation is carried out by shot peening in the method step36. During the blasting of the gearing, the focus is directed toward the tooth root region. Subsequently in the method step37only the tooth flank region is post-machined. The post-machining is also denoted as hard finishing. In this case, the tooth flank region of the gearing is machined by gear grinding or honing. The tooth root region is not machined during the post-machining process.

By producing the tooth root region to the finished size in the soft machining process, the inductively hardened edge layer in the tooth root is not reduced by the hard finishing. Due to the shot peening after hardening and before the hard finishing, such as grinding or honing, in combination with a tooth root which has already been machined to the finished size in the soft machining process, the end result is a fine-machined flank and a tooth root which has been blasted in order to increase the operational stability.

In the third variant of the method, the hard finishing or post-machining of the tooth flank region is carried out in the method step36without the tooth root after the hardening in step35. The tooth root region in this case is not post-machined. After the post-machining in step36the gearing is subjected to a blasting operation in step37, in particular by shot peening of the gearing, wherein the focus is directed both toward the flank region and toward the tooth root region.

By producing the tooth root in the soft machining process to the finished size, the inductively hardened layer in the tooth root is not reduced by the hard finishing. The load-bearing capacity of the tooth flank and tooth root is correspondingly increased by the shot peening after the hardening and the hard finishing, by grinding or honing.

In the fourth variant of the claimed method, the tooth root region of the gearing is produced with an oversize for a subsequent gear grinding/gear honing, as indicated inFIG.4. In the method step35the gearing is inductively hardened, in particular by dual frequency hardening. In the method step36, the hard finishing of the gearing is carried out by gear grinding or honing, wherein both the tooth flank region and the tooth root region are hard-finished. In the method step37the gearing is blasted in the finished state.

The flank load-bearing capacity and the tooth root strength are increased by the shot peening after the hardening and the hard finishing by grinding or honing. The tooth root, which has been ground, exhibits advantages by the reduced roughness and surface oxidation.