Abstract:
A welded crankshaft having a number of individual elements and cavities formed in the region of the main bearing journals and crank journals. The individual elements are configured so that oil passages in the overlap region between the main bearing journals and crank journals run substantially in the axial direction, and transition via radial orifices directly into the journal surface. The cavities of the main bearing journals and crank journals can be made very large, so that the weight of the crankshaft is kept light. In addition, because of the simple geometry of the oil passages, the crankshaft can be manufactured in modular fashion from the individual elements.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a welded crankshaft having a number of individual elements and having cavities in the region of the main bearing journals and crank journals. 
     RELATED TECHNOLOGY 
     European Patent Document No. EP 0 090 013 B1 describes an assembled crankshaft whose individual elements each comprise a crank web having tubular segments shaped onto both sides. The individual elements are welded to one another in the region of the main bearing journals and crank journals, yielding a crankshaft whose crank journals and main bearing journals contain cavities in their interiors. This results in a considerable weight reduction compared to conventional crankshafts. In order to lubricate the bearings, oil lines that are constituted by inserted tubular lines which terminate via orifices on the outer peripheries of the journals, and are connected to one another via passages in the interior of the crankshaft, are provided in the cavities of the crank journals and main bearing journals. These oil lines make possible a directed oil flow with minimum oil volume, which provides sufficient lubrication of the bearing regions. This carries the risk, however, that the inserted tubular lines may detach during operation and damage the bearings. In addition, this type of oil guidance system via inserted small tubes is very complex to manufacture and assemble. 
     European Patent Document No. EP 0 090 013 B1 also describes a crankshaft in which the crank journals and main bearing journals are joined to one another by an oblique orifice. The result of this, however, is to make the cavities smaller, since additional material through which these orifices are guided must be provided in the interior of the individual elements. This diminishes the weight saving achieved by way of the cavities. 
     German Patent Document No. DE 195 36 349 C1 describes a friction-welded crankshaft that also has cavities in the interiors of the main bearing journals and crank journals. In this case delivery of lubricating oil along the shaft is accomplished via additional cavities that are configured in the journal region partially as annular spaces, and that are connected to one another via oil passages. A directed and effective oil flow in the regions of the bearings can thereby be ensured. However, the oil flows around the friction-welded seams in the region of the annular spaces, so that residual particles can be entrained into the oil circulation system. In addition, the wall thicknesses are kept relatively thin in configuring the double cavities, which results in a low geometrical moment of inertia for the weld surface, and accordingly in a weaker join between the individual elements. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an assembled crankshaft that is hollow in the journal region, while maintaining simplicity of manufacture, in such a way that on the one hand weld surfaces with a large geometrical moment of inertia are created between the individual elements, and on the other hand a directed oil flow for lubricating the bearings is ensured, without bringing the oil into contact with welding burr. At the same time, the lowest possible weight is to be achieved. 
     The present invention provides a welded crankshaft including a number of individual elements which each include a crank web having tubular segments shaped onto both sides, and are welded to one another in such a way that the tubular segments of adjacent individual elements together form main bearing journals and crank journals which respectively contain weight-reducing cavities in their interiors, the main bearing journals and crank journals each partially overlapping one another radially. The crankshaft is furthermore equipped with oil passages which include axial orifices that run substantially in the axial direction of the crankshaft, and which furthermore include radial orifices that connect the axial orifices to the journal surfaces. The oil passages ( 10 ), with the exception of the outlet openings of the radial orifices ( 12 , 13 ), lie completely in the overlap region ( 15 ) of the main bearing journals and crank journals ( 6 , 7 ), and the walls of the tubular journals ( 6 , 7 ) are of cavity-free configuration aside from the oil passages ( 10 ). 
     According to the present invention, the oil passages are implemented by orifices that run substantially in the axial direction in the overlap region between the main bearing journals and crank journals, and that transition via a radial orifice directly into the journal surface. Very little manufacturing and assembly effort is required for this, and the oil passages are free of contaminating welding burrs. The tubular journals are moreover of solid configuration, i.e., have no cavities aside from the oil orifice, so that the weld surfaces between the individual elements are particularly large and the strength and weight of the crankshaft are optimized. The weight-reducing cavities, however, can be configured at optimum size. 
     According to the present invention, the radial oil supply lines are located on the centrifugally inner side, overcoming the prejudice that oil delivery along the centrifugal force vector is necessary for proper lubrication. This aspect of the present invention stands in contrast to the crankshafts described in German Patent Document No. DE 195 36 349 C1 and European Patent Document No. EP 0 090 013 B1, whose oil supply lines each terminate on the centrifugally outer side of the crank journals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is explained in further detail below with reference to the drawings, in which: 
     FIG. 1 shows a lateral section through the crankshaft of an in-line engine; 
     FIG. 2 shows a detail view of the oil passage of FIG. 1; 
     FIG. 3 shows an axial view or plan view of the radial overlap region between the main bearing journal and crank journal along line III—III in FIG. 1, 
     in FIG. 3 a  for stroke H=H max , 
     in FIG. 3 b  for a shorter stroke H&lt;H max , and 
     in FIG. 3 c  for an even shorter stroke H&lt;&lt;H max ; 
     FIG. 4 shows a lateral section through the crankshaft of a V-engine with single-side oil passages; 
     FIG. 5 shows a lateral section through the crankshaft of a V-engine with double-side oil passages; 
     FIG. 6 shows a detail view of the oil passages in the region circled in FIG. 5, 
     in FIG. 6 a  with a spherical insert, 
     in FIG. 6 b  with a cylindrical insert, 
     in FIG. 6 c  with a weld bead; and 
     FIG. 7 shows a lateral section through a portion of the crankshaft having centeredly positioned radial orifices in the main bearing journal. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a portion of a crankshaft  1  for an in-line engine, which is assembled from multiple individual elements  2 . The number of individual elements is defined by the number of cylinders of the engine in question. Each individual element  2  comprises a crank web  3  with tubular segments  4  and  5  shaped onto both sides, and is joined to the adjacent individual elements  2 ′ and  2 ″ in such a way that the assembled tubular segments  4  and  4 ′ and  5  and  5 ″ together form main bearing journals  6  and crank journals  7 , which contain cavities  8  and  9  in their respective interiors. 
     In order to deliver lubricating oil from main bearing journals  6  to crank journals  7 , every second individual element  2  contains an oil passage  10  that comprises an axial orifice  11  into which open two radial orifices  12 ,  13  that proceed centeredly from the outer sides of the crank journals and main bearing journals. Tubular segments  4 ,  4 ′ and  5 ,  5 ″ of adjacent individual elements  2 ,  2 ′,  2 ″ are alternatingly of different lengths, so that weld beads  14  between individual elements  2 ,  2 ′, and  2 ″ are offset with respect to the journal centers, and thus each oil line  10  runs completely inside a single individual element  2 . 
     The feasibility of an axial orifice  11  which passes through the entire length of individual element  2  results in certain limitations in the dimensioning of the crankshaft. In approximate terms, the axial arrangement  11  of oil passages  10  requires that crank journal  7  and main bearing journal  6  have a radial overlap region  15  (shown cross-hatched in FIG. 3) which is large enough to accommodate the oil passage. This results in the following: 
     1) wall thicknesses W 1  and W 2  of the tubes of which main bearing journals  6  and crank journals  7  are constructed must be larger than diameter d of axial orifice  11 , i.e., W 1 , W 2 &gt;d+2Δ,Δ being the minimum required wall thickness of the oil passage (see FIG.  2 ); and 
     2) stroke H of the crankshaft must not exceed a maximum value H max =R 1 +R 2 −d−2Δ, R 1  and R 2  being the radii of main bearing journal  6  and crank journal  7 , d the diameter of axial orifice  11 , and Δ the minimum required wall thickness for the oil supply line (see FIG.  1 ). 
     At the maximum possible stroke H=H max , axial orifice  11  of oil passage  10  runs, as shown in FIG. 3 a,  along overlap region  15  (which in this case is minimal) of main bearing journal  6  and crank journal  7 . At shorter strokes H&lt;H max  of the shaft, overlap region  15  becomes larger (FIG. 3 b ). At even shorter strokes H&lt;&lt;H max , as shown in FIG. 3 c,  two discontinuous overlap regions  15 ′ and  15 ″ are created between main bearing journal  6  and crank journal  7 ; in this case axial orifice  11 ,  11 ′ can selectably be housed in one of the two regions. 
     The manufacturing procedure is preferably configured so that axial passage  11  and the two radial passages  12 ,  13  are drilled or electrodischarge machined into the individual elements, which are largely premachined to final dimensions, before the latter are welded to one another. As is apparent from FIG. 1, the result of the welding operation is that axial orifice  11  is closed off at both of its ends  20  by the adjacent individual elements  2 ′,  2 ″, creating a separate and sealed oil line  10  which joins main bearing journal  6  and crank journal  7 . The shaft can thus be assembled in modular fashion from easy-to-manufacture individual elements  2 ,  2 ′; metal-cutting machining of the completely assembled shaft is superfluous, except for the final precision machining of the bearing surfaces. This results in a reduction in the number of manufacturing steps as compared to previously used methods, and moreover results in a simple and robust structure for the crankshaft. Fitting together the individual elements by friction welding offers the additional advantage that a broad spectrum of materials, including, in particular, different materials, can be welded to one another with this method, and the crankshaft can thus be constructed specifically from the most suitable materials. 
     FIG. 4 shows an exemplary embodiment of a crankshaft  1 ′ for V-engines. The difference as compared to the crankshaft shown in FIG. 1 is the fact that here, two connecting rods engage on each crank journal  7 . Correspondingly, two oil outlets  13  also terminate on each crank bearing journal. For oil delivery, by analogy with crankshaft  1  for in-line engines (FIG.  1 ), in this case each second individual element  2  contains an oil passage  10  that comprises an axial orifice into which three radial orifices  12 ,  13  open. Orifice  12  proceeds centeredly from the main bearing journal, while orifices  13  proceed from the connecting-rod bearings. Tubular segments  4 ,  4 ″ and  5 ,  5 ′ of adjacent individual elements  2 ,  2 ′,  2 ″ are alternatingly of different lengths; as a result, weld beads  14  between individual elements  2 ,  2 ′,  2 ″ are offset with respect to the journal center, and each oil line  10  runs completely inside a single individual element  2 . The process steps for manufacturing this crankshaft are analogous to those of the crankshaft for in-line engines described above. 
     In the embodiment depicted in FIG. 4, lubrication of the two connecting-rod bearings takes place via the same oil line  10  and a common inlet  12 . This entails the risk, especially with narrow oil lines  10 , that too little lubricating oil might be delivered to outlet  13  located farther away from inlet  12 , and that inhomogeneous lubrication of the two connecting rods might occur if the two orifices  13  have the same radius. An embodiment which overcomes these potential disadvantages is depicted in FIG.  5 . Here two oil passages  10 ,  10 ′ are provided in each crank journal, supplying the two bearings with lubricant via outlets  13 ,  13 ′ independently of one another. Two oil passages, whose discharge openings are offset radially by an angle that is determined by the arrangement of the cylinders, accordingly also terminate on each main bearing journal. In this instance tubular segments  4 ,  4 ″ and  5 ,  5 ′ of adjacent individual elements  2 ,  2 ′,  2 ″ are of equal length, so that weld beads  14  are arranged centeredly on main bearing journal  6  and crank journal  7 . 
     A further advantage of this embodiment for V-engines is the fact that the crankshaft can be built up from identical individual elements, so that manufacturing costs can be reduced. Production proceeds in a manner similar to that described above for the in-line engine: first, axial passage  11  and the two radial passages  12 ,  13  are drilled into each individual element  2 . Then the individual elements are welded to one another. Welding causes the axial orifice to be closed off at the ends by the adjacent individual elements. In order to achieve uniform lubricating oil delivery to the crank bearings, it may be advantageous, in particular, for the two oil passages  10 ,  10 ′ that end on one crank journal  7  also to be separated from one another. This can be achieved in various ways, depending on the geometry of the crankshaft. If stroke H of the crankshaft is short (H&lt;&lt;H max ), then main bearing journal  6  and crank journal  7  possess, as shown in FIG. 3 c,  two discontinuous overlap regions  15  and  15 ′ in which axial orifices  11 ,  11 ′ of the two oil passages  10 ,  10 ′ can be housed. In the course of welding of the double elements in the region of the crank journals, each axial orifice  11 ,  11 ′ is then respectively closed off at its end by the adjacent double element, thereby creating automatically closed oil supply lines  10 ,  10 ′ that connect main bearing journal  6  and crank journal  7 . 
     Similarly, with shorter strokes H&lt;H max  for the shaft, the two axial orifices  11 ,  11 ′ can be guided next to one another in overlap region  15  (FIG. 3 b ). With the maximum possible stroke, however (H=H max ; FIG. 3 a ), the overlap region is so small that axial orifices  11 ,  11 ′ transition directly into one another. In order to seal off the oil passages from one another in this case as well, a spherical (FIG. 6 a ) or cylindrical (FIG. 6 b ) insert  17  is pressed into axial orifice  11  before the double elements are welded. Alternatively (FIG.  6   c ), the closure can be produced by the weld itself, if the method used (e.g., friction welding) creates a ridge  18  that interrupts axial orifices  11 ,  11 ′ in the weld region. 
     In the exemplary embodiment depicted in FIG. 5, inlet openings  12 ,  12 ″ of the oil passages are located not centeredly on main bearing journal  6 , but rather slightly offset to the side. This has the advantage in terms of production engineering that, as described above, individual elements  2  can be completely equipped with the oil supply lines before they are welded to one another. Oil delivery from the crankcase, however, usually is accomplished centeredly to the main bearing journals. It may therefore be advantageous also to position inlet openings  12 ,  12 ′, as shown in FIG. 7, centeredly on the main bearing journals. In this case the manufacturing procedure is advantageously configured so that first of all each two adjacent individual elements  2 ,  2 ″ are welded to one another in the region of main bearing journal  6 . The two axial passages  11 ,  11 ′ and the total of four radial passages  12 ,  12 ′,  13 ,  13 ′ are then drilled into the resulting double element  19 , the orifices being applied centeredly, i.e., in the region of the weld bead, onto the main bearing journals. Lastly, double elements  19  are welded together to form crankshaft  1 . 
     The weight of the crankshaft can be further reduced if, as shown in FIGS. 4 and 5, crank webs  3  are equipped in the region of principal axis  16  with through holes  21 , so that cavities  8  of main bearing journals  6  are open on both sides. For stability reasons, this through hole  21  should preferably not exceed the inside diameter of main bearing journal  6 .