Abstract:
A method for manufacturing a crankshaft for motor vehicles with passages being provided in the crankshaft for receiving lubricant. Prior to the casting process, place holders, which may include formed parts having cavities alone and/or together with a core, are inserted into the mold to form passages for receiving lubricant.

Description:
[0001]    Priority is claimed to German Patent Application No. DE 102 21 255.4-24, filed May 13, 2002, which is incorporated by reference herein.  
         BACKGROUND  
         [0002]    The present invention relates to a method for manufacturing a crankshaft for motor vehicles, with passages being provided in the crankshaft for receiving lubricant.  
           [0003]    Crankshafts, which have a partially hollow design to save weight or are provided with lubrication bores, are already generally known. To lubricate the pin and main bearings of the crankshaft, the oil passages are usually provided in the crankshaft using deep hole drilling methods. For manufacturing crankshafts, this operation is very complex and cost-intensive. Moreover, this manufacturing method allows only a compromise with respect to optimum inlet and outlet openings of the lubrication passages.  
         SUMMARY OF THE INVENTION  
         [0004]    An object of the present invention is to provide the cavities or lubrication passages in the crankshaft in such a manner that hydrodynamic conditions are taken into account and that the manufacturing method is simplified.  
           [0005]    The present invention provides a method for manufacturing a crankshaft ( 1 ) for motor vehicles, with passages being provided in the crankshaft ( 1 ) for receiving lubricant, wherein, prior to the casting process, place holders ( 12 ′) and/or formed parts ( 12 ) having cavities are inserted into a mold together with a lost core ( 3 ) to form cavities and/or passages for receiving lubricant. The place holders and/or formed parts being fixed in position by the core.  
           [0006]    In cast crankshafts, this makes it possible for the pressure passages to be integrated and/or kept available during the casting process. This results in a significant reduction in manufacturing costs, especially when using high-strength casting materials. Moreover, this method allows the outlet and inlet openings of the passages to be positioned at optimum locations in terms of technical function. The material from which the oil passages or lubricant passages are produced is easy to work and shape. When the oil passages are kept available, the place holders can be removed after the casting process. The formed part can be designed as an inlay or stiffening element.  
           [0007]    If the crankshaft has a hollow design, it is advantageous for the place holder (which may be a formed part having a cavity, such as a tube) to be designed as a straight part, a shaped part or as a part having equal or different cross-sections, and to be connected to the core. The tube and/or the place holder can be connected to the core for the later formation of the cavity in order for the place holder to be fixed in place within the mold and to be supported against the melt during the casting process. It is pointed out that the formed part can be round, oval or polygonal in cross-section and that it can have a nearly equal cross-section over its entire length. The material used for the place holders has a higher melting point than the surrounding casting material.  
           [0008]    When the passages are kept available, it is advantageous for the place holder to be composed of a material which can be mechanically destroyed and removed or washed out of the casting after the casting process.  
           [0009]    To this end, it is also advantageous for cavities formed by the tubes to be located in the region of the separation planes of the mold and to extend into different regions of the mold.  
           [0010]    Moreover, it is advantageous to provide at least one cavity that is formed by a lost core and located in the region of a separation plane of the mold, and to integrate the tubular parts with this core prior to the casting process in order to fix them in place; the tubes remaining in the mold and, at least partially, fusing with the casting that surrounds the tubular part. The tubes constituting the oil passages remain in the crankshaft and can, at least partially, fuse with the casting material that surrounds the tubular part. Fixation or support of the oil passages by the core offers the advantage that the oil passages do not necessarily have to penetrate the outer contour of the crankshaft and/or that it is possible to achieve better support against the melt during the casting process.  
           [0011]    The tube for forming an oil passage is fixed in place or supported by one or more jackets that are larger in diameter and/or by stiffening elements or inlays remaining in the component. The inlays remaining in the crankshaft have component-stiffening and/or weight-reducing properties.  
           [0012]    A further advantage is that the tubular parts can also be inserted into the mold in such a manner that they do not necessarily have to penetrate the outer contour of a crankshaft.  
           [0013]    It is also advantageous that the tubular parts are sealed prior to the casting process. However, this is provided only if they do not penetrate the outer contour of the crankshaft, because otherwise they would get filled up during the casting.  
           [0014]    Since the place holders or tubes are composed of steel and have also a melting point that is higher than the material to be melted, they can later remain in the mold and, possibly, also fuse with the surrounding casting material at least superficially so that they are firmly integrated into the finished crankshaft. With this manufacturing method, it is no longer required for the individual place holders or tubular parts to extend in a straight line. They can have any desired shape so that they can be adapted to the hydrodynamic conditions of the crankshaft without difficulty.  
           [0015]    Instead of using steel tubes, it is also possible to choose a material for the tubes which is able to be mechanically or chemically destroyed by a suitable substance after the casting process which will allow the cavity-forming parts to be washed out of the remaining cavity of the mold. Using this method, it is possible for the oil passages to be molded into the crankshaft as it is cast such that the position of the oil passages and the openings of the inlet and outlet points do not constitute an impairment with respect to strength, stiffness and oil supply.  
           [0016]    The surface between an oil passage and the surrounding cast iron material can be influenced by suitable coating systems. For example, it is possible to roughen the surface in order to achieve sufficient mechanical interlocking (positive fit) with the coating. This coating can contribute to prevent the inserted oil passages from getting partially or completely fused or melted through. The coating or the roughening can advantageously be carried out locally to thereby achieve selective protection or selective improved connection to the surrounding material. The coating can be applied, for example, using thermal spraying methods, core dressing, electroplating or dipping methods.  
           [0017]    The oil passages inserted into the mold can be inserted such that, sometimes, they penetrate the outer contour of the crankshaft and sometimes not. If the intention is for the oil passages not to penetrate the outer contour, it is necessary for them to be fixed in place or positioned by a lost core or by inlays that remain in the component. If, for example, the oil passages are intended to penetrate the outer contour of the crankshaft, then they are inserted into the mold in a manner ensuring easy castability, in which case the oil passage should then be located in the separation plane of the mold, to prevent undercuts. It is also advantageous for the tubular parts for forming the oil passages to be inserted into the mold such that the inlet/outlet points are situated at optimum locations in terms of technical function, thereby increasing the performance of the crankshaft.  
           [0018]    Penetration of the outer contour of the crankshaft by the pressure-medium or lubricant passages has the advantage that no further processing of the inner contour of the passages is required after the casting process. This method offers itself for all crankshaft designs. For cavity design or stiffening, the lubricant passage can be integrated into the core in different ways. For example, it is possible for the tubular element for forming the lubricant passage to be fixed in place by a stiffening element/inlay which serves as a supporting element in the mold to ensure a very accurate fixation of the tubular element during the casting process, thus also satisfying tolerance requirements.  
           [0019]    The tubular parts or cavity-forming parts can also be placed such that they do not penetrate the outer contour of the crankshaft, with the advantage that the positioning of the oil passage can be accomplished in an easy and inexpensive way, independently of separation plane of the mold. In this case, the oil passage is fixed in place only by a core or by an inlay that remains in the component. In this case, attention must be paid that the individual tubular parts are sealed prior to the casting process. During later processing, the oil passages have to be opened by boring or bored into from the surface of the crankshaft. Here too, very little work is required to complete the lubricant passages. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    Further advantages and details of the present invention are explained in the patent claims and in the specification, and shown in the drawings, in which:  
         [0021]    [0021]FIG. 1 shows a schematic arrangement of a crankshaft, including pin and main bearings as well as separation plane Y;  
         [0022]    [0022]FIG. 2 shows a core which has connected thereto the tubular parts or place holders that are inserted into the mold for producing the crankshaft;  
         [0023]    [0023]FIG. 3 is a sectional view of the mechanical clamping of the tube or place holder in the casting material surrounding the place holder;  
         [0024]    FIGS.  4 - 9  show different embodiments of the crankshaft, including differently inserted inlays for forming the cavities or lubricant passages. 
     
    
     DETAILED DESCRIPTION  
       [0025]    In the drawings, reference numeral  1  denotes a crankshaft, which is shown in FIG. 1 only by contour lines with a main bearing  6  and a pin bearing  7 . A Y-line  15  shown in FIG. 1 corresponds to the separation plane of the mold.  
         [0026]    [0026]FIG. 2 represents a core  3  which is inserted into a mold and which is used to form a cavity upon completion of the casting process and removal of the core material.  
         [0027]    For adequate lubrication of pin and main bearings  7  and  6 , cavities  14 , which are shown in FIGS. 4 through 8, are provided in crankshaft  1 . Cavities  14  constitute the lubricant passages for lubricant supply to pin bearing  7  or main bearing  6 . The individual lubricant passages  14  are in communication with a cavity  13 , which is provided in crankshaft  1  in a concentric manner, as shown in FIGS. 4 and 9.  
         [0028]    In the casting process, the previous manufacturing method involved a considerable portion of costs for producing the crankshaft, especially when using high-strength casting materials. Moreover, the method known heretofore allowed only a compromise with respect to the optimum inlet and outlet points of the lubricant passages. These were made by normal boring processes only after the casting of the crankshaft had been completed.  
         [0029]    Using the method according to the present invention, place holders  12 ′, which may be in the form of so-called tubular elements  12 , are inserted into a mold  18  prior to the casting process in addition to the actual core  3 . As can be inferred from FIG. 2, bent tubular element  12  is connected to core  3 . Tubular element  12  can also be provided with enlarging elements  17  which, according to FIG. 2, are provided, for example, in the region of the tube end. These enlarging elements are used for mechanical clamping or interlocking in casting material  18 , as shown in FIG. 3, so that a positive fit can be achieved between the casting material and the tubular element after the casting process, since core  3  is destroyed after the casting process and washed out of the cavity. Instead of enlarging elements  17 , it is also possible to connect other profiled elements and grooved parts to tube  12  or to place holder  12 ′, the profiled elements and grooved parts being used for proper positioning of the tubular element in the mold and also helping the tubular element or the place holder to maintain their position in the mold during the casting process. Using this casting method, the inlet and outlet points of lubricant passages  14  can be placed at optimum locations so as not to weaken the crankshaft while taking into account hydrodynamic conditions. Subsequent creation of lubricant passages by mechanical boring is eliminated in the casting method according to the present invention.  
         [0030]    According to FIG. 2, tubular element  12  has a bent shape and is connected to core  3  with its outlet ends. After the casting process, the tubular element formed of steel remains in the mold so that cavity  13  formed by core  3  (compare FIG. 9) is in flow-through connection with the cavities of tubular part  12 , that is, with lubricant passage  14 .  
         [0031]    For example, if the crankshaft has a solid construction and does not feature such a cavity  13  according to FIG. 9, then the crankshaft can still be provided with pressure-agent passages by means of tubular elements  12  according to the different embodiments shown in FIGS. 5, 6, and  9 . The individual tubular elements  12  or place holders  12 ′ are inserted into the mold in such a manner that the oil passages or inlet and outlet points  19  and  20  are positioned at optimum locations so as not to impair the strength, stiffness and the oil supply to the crankshaft.  
         [0032]    The contact surface of the oil passage with the surrounding casting material can be optimally influenced by suitable coating systems. This coating can also have the task to prevent the steel oil passages from getting completely fused or melted through. The coating or roughening of the surface of the tubular element or inlay can also be done locally so that the surface of the tubular element or of the inlay is selectively connected to the surrounding casting material.  
         [0033]    As already mentioned, the oil passages can be arranged such that they penetrate the outer contour of the crankshaft (compare FIG. 9). If provision is made for the outer contour of the crankshaft to be penetrated by the lubricant passages, then the corresponding inlays or tubular parts have to be inserted into the mold at the corresponding locations prior to the casting process, in which case attention must be paid that the inlet point of lubricant passage  14  is situated on the X-axis according to FIG. 1, and that the outlet point is situated on the Y-axis (compare FIG. 7).  
         [0034]    According to FIG. 6, oil passages  14  or the associated tubes  12  or place holders  12 ′ can have a straight shape (FIG. 5) or a bent or angled shape (FIG. 6). There is no need for subsequent machining of the crankshaft. The inserted tubular parts  12  or  12 ′ must have a higher melting point than the cast iron surrounding the tubular parts.  
         [0035]    Also in the case of solid crankshafts according to FIG. 6 or  8 , one simply inserts tubular parts  12  into the mold prior to the casting process so that upon casting, the remaining tubular parts form cavities in the crankshaft, which are capable of being used for pressure-agent or lubricant supply. The fixation of the tubular parts prior to the casting process is accomplished by means of mold or, according to FIG. 4, by the cores or inlays  3  used.  
         [0036]    In the case of a hollow crankshaft design or a stiffened crankshaft, lubricant passages  14  can be integrated into core  3  by suitably installing the tubes (FIG. 4).  
         [0037]    Due to the advantageous arrangement of the cores or inlays  3  in conjunction with tubular parts  12  or place holders  12 ′, it is possible to reduce the processing costs in connection with high-strength casting material such as ADI (Austempered Ductile Iron) material. Moreover, the stiffness of the crankshaft is improved because lubricant passages  14  can be arranged at optimum locations within the crankshaft. By advantageously selecting the tube and rod diameters, the original stiffness of a crankshaft can be further improved. Due to the possibilities of varying the locations of lubricant passages  14 , for example, movement to regions that are subjected to less mechanical stress, the component strength of the crankshaft can be considerably increased. Due to the advantageous core geometry, the cavity design can be simplified as well. Using the advantageous casting method, inlet and outlet openings  19 ,  20  of lubricant passages  14  can be moved to regions that are convenient in terms of technical function. In this method, it is also possible to combine the core and pressure oil passages. Optimum fixation of the tubular parts for forming the lubricant passages ensures that these parts accurately maintain their position also after the casting process.  
         [0038]    Place holders can be used in hollow and stiffened crankshafts. In the case of the solid crankshaft, fixation is accomplished by means of the mold. When using inlays, additional fixation or support can be accomplished by means of the inlay. Here, it is also possible to position the place holders at optimum locations (in terms of function). The particular geometry of the formed parts/place holders also deserves special mention. FIG. 8 and also FIG. 9 show how easily tubular parts  12  can be positioned in the mold, especially also in connection with a hollow design.