Abstract:
A core structure for a cast crankshaft is provided which eliminates the need to machine and install plugs in one or more of the main bearing lightening holes. This is achieved by configuring the core structure to take out all but a thin wall of material in the center of the main bearing journals.

Description:
FIELD 
     The present disclosure relates to a core structure for a cast crankshaft. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Typical practice for engine dry sump lubrication systems with high RPM (8000 RPM+) and high-performance is to have individual crankcase bays in order to prevent bay-to-bay pumping losses. To do this with main journals that have been hollowed for weight reduction, a machining hole in the main journal needs to be plugged to prevent bay-to-bay pumping. 
     It is desirable in the art to provide a crankshaft that does not require the additional machining and plug pressing operations. In addition, it is desirable to provide a lower mass crankshaft with greater mass reduction as compared to the machined method which only has limited hollowing capability to take out material from a crankshaft. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A core structure for a cast crankshaft is provided which eliminates the need to machine and install plugs in one or more of the main bearing lightening holes. This is achieved by configuring the core structure to take out all but a thin wall of material in the center of the main bearing journals. The core structure includes a pair of end main bearing core segments with a first pair of counterweight core segments connected to the pair of end main bearing core segments by a first pair of pass-through core segments. A pair of intermediate crank pin core segments are connected to the first pair of counterweight core segments by a second pair of pass-through core segments. A pair of intermediate main bearing journal core segments are adjacent to the first pair of counterweight core segments which straddle the pair of intermediate main bearing journal core segments with a void region between the pair of intermediate main bearing journal core segments and the first pair of counterweight core segments. A second pair of counterweight core segments are connected to the pair of intermediate main bearing journal core segments by a third pair of pass-through core segments. A pair of end crank pin core segments are connected to the second pair of counterweight core segments by a fourth pair of pass-through core segments. The void region between the pair of intermediate main bearing journal core segments and the first pair of counterweight core segments allows the core structure to take out all but a thin wall of material in the center of the main bearing journals that eliminate the need to install plugs. The thin wall of material blocks the flow of oil from going through the main bearing journal but still enables mass-reduction within the main bearing journal. 
     The core structure of the present disclosure provides an improvement over a crankshaft with plugs because it has the potential to eliminate machining and plug-pressing operations and to result in a lower mass crankshaft because the cast structure allows the removal of more material than the machining techniques. The core structure can be made as a single or multi-piece core 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a plan view of an exemplary cast crankshaft according to the principles of the present disclosure; 
         FIG. 2  is a plan view of a multi-piece core design with the crankshaft shown in phantom for illustrative purposes; 
         FIG. 3  is a plan view of a single-piece core design with the crankshaft shown in phantom for illustrative purposes; 
         FIG. 4  is a longitudinal cross-sectional view of an exemplary cast crankshaft showing the hollow sections formed using the core structure according to the principles of the present disclosure; and 
         FIG. 5  is a schematic diagram of a casting die with the core structure according to the principles of the present disclosure. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     With reference to  FIG. 1 , an exemplary cast crankshaft  10  having hollow sections formed by the core structure according to the principles of the present disclosure will now be described. The cast crankshaft  10  can include a front main bearing journal  12 , a rear main bearing journal  14 , a center main bearing journal  16  and a pair of intermediate main bearing journals  18  that are all linearly aligned along a center axis X. The cast crankshaft  10  includes a pair of end crank pins  20 A,  20 B connected to the respective front and rear main bearing journals  12 ,  14  and a pair of intermediate crank pins  20 C,  20 D connected between the center main bearing journal  16  and the respective intermediate main bearing journals  18 . The crank pins  20 A- 20 D are offset from the center axis X. Counterweights  22 A- 22 D are connected to the respective crank pins  20 A- 20 D on an opposite side of the center axis X from the crank pins  20 A- 20 D. Each of the crank pins  20 A- 20 D is flanked by a respective pair of crank webs  24 A- 24 D which connect the crank pins  20 A- 20 D to the adjacent main bearing journals  12 - 18  with the counterweights  22 A- 22 D being generally within a same orthogonal plane as the crank webs  24 A- 24 D. The counterweights  22 A- 22 D counterbalance the mass of the crank pins  20 A- 20 D and a lower portion of the connecting rods. 
     With reference to  FIG. 2 , a multi-piece core structure  30  for the cast crankshaft  10  shown in  FIG. 1  will now be described. The core structure  30  includes a first core member  30 A and a second core member  30 B. The first core member  30 A includes a pair of end main bearing core segments  32 ,  34  that are provided to form the hollow segments within the forward and rear main bearing journals  12 ,  14 , respectively. A first pair of counterweight core segments  36 A,  36 B are connected to the pair of end main bearing core segments  32 ,  34  by a first pair of pass-through core segments  38 A,  38 B. The counterweight core segments  36 A,  36 B are so named because they define a region between respective pairs of counterweights  22 A,  22 B of the cast crankshaft  10 . The pass-through core segments  38 A- 38 B are so named because they pass-through the crank webs  24 A,  24 B and define a hollow region therein along the center axis X. A pair of intermediate crank pin core segments  40 A,  40 B are connected to one another by connecting core piece  41  and to the first pair of counterweight core segments  36 A,  36 B by extensions  42 A,  42 B of the counterweight core segments that pass through portions of the counterweights  22 A,  22 B as well as portions of the intermediate crank webs  24 C,  24 D, respectively. 
     The second core member  30 B includes a center main bearing journal core segment  44  and a pair of intermediate main bearing journal core segments  46 A,  46 B. The pair of intermediate main bearing journal core segments  46 A,  46 B are provided to define the hollow region within the intermediate main bearing journals  18  and the center main bearing journal core segment  44  is provided to define the hollow region within the center main bearing journal  16 . The intermediate main bearing journal core segments  46 A,  46 B are adjacent to and straddled by the first pair of counterweight core segments  36 A,  36 B of the first core member  30 A. A pair of void regions  48  are provided between the pair of intermediate main bearing journal core segments  46 A,  46 B and the first pair of counterweight core segments  36 A,  36 B. A second pair of intermediate counterweight core segments  50 A,  50 B are connected between respective ones of the pair of intermediate main bearing journal core segments  46 A,  46 B and the center main bearing journal core segment  44  by pass-through core segments  52 A- 52 D which pass through the crank webs  24 C,  24 D of the crankshaft  10 . A pair of end crank pin core segments  54 A,  54 B are connected to the second pair of intermediate counterweight core segments  50 A,  50 B by extensions  56 A,  56 B of the counterweight core segments  50 A,  50 B. The pair of intermediate counterweight core segments  50 A,  50 B can be connected one another by an extension  56 C. 
     In the embodiment shown in  FIG. 2 , the core structure  30  is made up of two separate core members  30 A,  30 B. As an alternative, as illustrated in  FIG. 3 , the core structure  30 ′ can be made as a single core design wherein a pair of bridge core segments  60 A,  60 B connect the ends of the core members  30 A and  30 B. 
     With reference to  FIG. 4 , a longitudinal cross-section of the cast crankshaft  10  using the core according to the principles of the present disclosure is shown. The crankshaft  10  includes a hollow section  72  within the front main bearing journal  12 , a hollow section  74  within the rear main bearing journal  14 , a hollow section  76  within the center main bearing journal  16  and a pair of hollow sections  78  within the pair of intermediate main bearing journals  18  that are all linearly aligned along the center axis X. The hollow sections  72 - 78  are each formed by the main bearing core segments  32 ,  34 ,  44 ,  46 A and  46 B, respectively. Each of the hollow sections  72 - 78  are connected to at least one opening  79  that has an opening dimension in a direction orthogonal to the longitudinal axis X that is smaller than the cross-sectional dimension of the hollow sections  72 - 78  in a direction orthogonal to the longitudinal axis X. The openings  79  are formed by the pass-through core segments  38 A,  38 B,  52 A- 52 D. The cast crankshaft  10  includes a pair of hollow sections  80 A,  80 B within the end crank pins  20 A,  20 B and a pair of hollow sections  80 C,  80 D within the intermediate crank pins  20 C,  20 D. The hollow sections  80 A- 80 D are formed by the crank pin core segments  40 A,  40 B,  54 A,  54 B of the core structure  30 . Each of the hollow sections  80 A- 80 D are connected to an opening  82  that has an opening dimension which is smaller than the cross-sectional dimension in a direction orthogonal to the longitudinal axis X of the hollow sections  80 A- 80 D. The openings  82  are formed by pass-through core segments  42 A,  42 B,  41 ,  56 A,  56 B. As mentioned above, each of the counterweights  22 A- 22 D can be provided with hollow sections or openings therethrough  84  that are formed by extensions of the counterweight core segments of the core structure  30 . 
     The pair of void regions  48  that are provided between the pair of intermediate main bearing journal core segments  46 A,  46 B and the counterweight core segments  36 A,  36 B define a closed end  88  of the hollow sections  78 . This as-cast closed end feature  88  blocks flow of air and oil from going through the main bearing journal from the end bays to the center bays of the engine crankcase and vice versa. The addition of the cast closed end feature  88  eliminates the need for additional machining and for holes to be plugged by separate operations. 
     As illustrated in  FIG. 5 , the core structure  30  is placed in a molding die cavity  100  and molten metal is poured into the cavity around the core structure  30 . The molten metal is allowed to cool and the molded crankshaft  10  is removed from the die cavity  100 . The molded crankshaft  10  is then shaken and otherwise treated to remove the core material from the hollow sections of the crankshaft  10 . 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.