Abstract:
An engine structure is provided with a bedplate and an oil pan. The bedplate is configured to have an integrally formed balance shaft bearing support. A bearing cap is either a separate component or a component that is formed as an integral part of the oil pan. The bearing cap and the balance shaft bearing support structures are attachable to each other to capture the bearing portions of the balance shafts therebetween.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 11/949,425 filed on Dec. 3, 2007 now U.S. Pat. No. 7,617,810. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally related to a shaft of an engine having a counterweight and a housing structure disposed at least partially around the counterweight and, more particularly, to a balance shaft support structure of which portions are formed integrally with housing structures of the crankcase and/or oil pan. 
     2. Description of the Related Art 
     Many different products are known in which a shaft of some type is provided with an overmolded structure which encapsulates the shaft. 
     U.S. Pat. No. 4,508,069, which issued to Dobler et al. on Apr. 2, 1985, describes an internal combustion engine balance shaft bearing arrangement at a crankcase. The arrangement for the balance shafts for balancing second order inertia forces on an internal combustion engine is described. The shafts run parallel to the crankshaft on both longitudinal walls of a crankcase and have the ends carrying the balance weights supported by means of journal bearings within the crankcase and having driven ends supported by means of roller bearings outside the crankcase in the region of a crankcase end wall. 
     U.S. Pat. No. 5,401,199, which issued to Shibata on Mar. 28, 1995, describes an outboard motor engine. Two embodiments of balancer arrangements for internal combustion engines particularly adapted for use in outboard motors are described. In each embodiment, the balancer shaft is journaled within the crankcase chamber of the engine and is driven from the crankcase from a point between its ends. Single and twin balancer shaft arrangements are disclosed. 
     U.S. Pat. No. 5,850,764, which issued to Bostelmann et al. on Dec. 22, 1998, describes a crankshaft drive for an internal combustion engine. It comprises at least one cylinder having a cylinder head, and a crankcase housing a crankshaft rotating at a predetermined direction and at a predetermined speed and a balance shaft extending parallel to the crankshaft and rotating at the predetermined speed of the crankshaft in a direction opposite to the predetermined rotating direction of the crankshaft. The crankshaft and the balance shaft carry balance weight means for balancing a mass of first order. An auxiliary shaft extends parallel to the crankshaft and rotates at the predetermined speed of the crankshaft in the predetermined rotating direction of the crankshaft. The auxiliary shaft carries a counterweight for balancing a residual moment resulting from the rotating balance shaft with respect to the rotating crank shaft. 
     U.S. Pat. No. 5,893,346, which issued to Hosoya on Apr. 13, 1999, describes an engine balance shaft. A mounting arrangement for a balance shaft of a four cycle overhead cam shaft internal combustion engine is described wherein the balance shaft is driven from the crankshaft and is disposed within the crankcase chamber and is disposed below the axis of rotation of the crankshaft. The balance shaft is driven from an end of the crankshaft and is journalled at least in part by a detachable crankshaft journaling member. 
     U.S. Pat. No. 6,186,111, which issued to Hilbig et al. on Feb. 13, 2001, describes a support arrangement for the crankcase of a reciprocating piston internal combustion engine. The support arrangement for the open area of a crankcase facing an oil pan in an internal combustion engine has a plate-like component which is attached to the crankcase walls by lugs, thereby reinforcing the housing, and contains integral bearings rotatably supporting a balance shaft. 
     U.S. Pat. No. 6,189,499, which issued to Iwata et al. on Feb. 20, 2001, describes a balancing device for a reciprocating engine. There is provided a balancing device for a reciprocating engine comprising two balance shafts gear connected to each other, a chain/sprocket mechanism for coupling at least one of the balance shafts with a crankshaft in an interlocking fashion, a chain tensioner for automatically adjusting the tension of the chain and a pump receiving portion integrally provided in a balance shaft holder for supporting the balance shafts for receiving a rotor of a lubricating oil pump. 
     U.S. Pat. No. 6,601,557, which issued to Hayman et al. on Aug. 5, 2003, describes an engine oil pump and balance shaft module. It includes a housing supporting a rotatable balance shaft carrying at opposite ends balance weights for offsetting unbalanced forces of the engine. The balance weights are enclosed in open top enclosures from which oil is pumped by veins on the weights and an associated gear, driven by the engine crankshaft. 
     U.S. Pat. No. 6,708,663, which issued to Stuckler on Mar. 23, 2004, describes a device for balancing out mass forces in internal combustion engines. The device compensates the inertia forces in reciprocating piston machines and consists of a balance shaft housing and balance weights mounted in the latter in friction bearings and having compensating weights. The balance shaft housing is fastened in one part and to the engine block. 
     U.S. Pat. No. 7,201,622, which issued to Hoi on Apr. 10, 2007, describes an internal combustion engine including improved balance shaft structure. An internal combustion engine is provided for a personal watercraft. A portion of the engine is enlarged to accommodate a balance shaft and is minimized in size, whereby the internal combustion engine is made compact. Balance shafts for preventing secondary vibration are arranged together with a crankshaft on a dividing plane between a crankcase and a cylinder block of an internal combustion engine. 
     U.S. Pat. No. 7,341,039, which issued to Jaszewski et al. on Mar. 11, 2008, discloses a lubrication system for a marine propulsion system with a tilted in-line engine. The lubrication system for an in-line engine which has a piston symmetry plane that is tilted relative to the vertical plane is provided with an oil pan and windage tray that facilitates the transfer of oil from a rotating crankshaft to the oil pan without excessive aeration. In addition, it facilitates the removal of entrained air from liquid oil as it passes from the crankshaft to a pool of oil collected in an oil pan. A windage tray is provided with a louver structure and a louver opening structure that assists this passage of oil droplets without undue aeration being caused. 
     The patents described above are hereby expressly incorporated by reference in the description of the present invention. 
     It would be significantly beneficial if balance shafts could be effectively supported with a minimal amount of hardware required. It would also be beneficial if the balance shafts could be efficiently enclosed within a housing structure below or adjacent to an engine. A significant improvement could be provided if the weight of the overall engine structure, with its balance shaft support components, could be reduced. Additionally, it would be beneficial if the overall number of components could be reduced so that assembly costs are minimized. 
     SUMMARY OF THE INVENTION 
     An internal combustion engine made in accordance with a preferred embodiment of the present invention comprises a bed plate attached to an engine to define a first cavity, a crankshaft of the engine disposed within the first cavity, an oil pan attached to the bedplate to define a second cavity, a balance shaft bearing support formed as integral part of the bedplate, and a first balance shaft disposed within the second cavity and supported by the balance shaft bearing support for rotation about a first axis, a second balance shaft disposed within the second cavity and supported by the balance shaft bearing support for rotation about a second axis, and a bearing cap which is attachable to the balance shaft bearing support to capture portions of the first and second balance shafts therebetween. The oil pan is suspended below the bedplate in a preferred embodiment of the present invention and the first and second axes are generally horizontal. 
     In particular embodiments of the present invention, the bearing cap is formed as an integral part of the oil pan and is attached to the balance shaft bearing support. In alternative embodiments of the present invention, the bearing cap is a component which is separate from the oil pan and is attachable to the balance shaft bearing support. In some embodiments of the present invention, it further comprises a crankshaft bearing support formed as an integral part of the bedplate and disposed within the first cavity. The crankshaft is supported by the crankshaft bearing support. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more fully and completely understood from a reading of the description of the preferred embodiment in conjunction with the drawings, in which: 
         FIGS. 1 and 2  are section views of an engine structure showing the relative locations of balance shafts to other components of the engine; 
         FIG. 3  illustrates a balance shaft that can be used in accordance with a preferred embodiment of the present invention; 
         FIG. 4  illustrates a preferred embodiment of the present invention which overmolds the counterweights of the balance shaft with a polymer material; 
         FIGS. 5 and 6  show an embodiment of the present invention that uses cylindrical casings to cover the counterweights of a balance shaft; 
         FIGS. 7 and 8  show an alternative embodiment of the present invention which attaches a partial disc shaped casing to the counterweights of a balance shaft in order to provide a generally full and complete disc shaped structure with no discontinuities that would otherwise create turbulence and aeration of oil in which the balance shafts are submerged; 
         FIG. 9  is a section view showing an engine structure with balance shaft bearing supports formed as an integral part of a bedplate and a bearing cap formed as an integral part of an oil pan; 
         FIG. 10  is an isometric view of a bedplate in accordance with a preferred embodiment of the present invention; 
         FIG. 11  shows a bottom view of the bedplate in  FIG. 10  in combination with bearing caps that are formed as separated components from an oil pan; and 
         FIG. 12  shows an oil pan with integrally formed bearing caps according to one alternative embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Throughout the description of the preferred embodiment of the present invention, like components will be identified by like reference numerals. 
       FIG. 1  shows the lower part of an engine structure including a crankshaft counterweight  12  which is not shown in section view and a second crankshaft counterweight  14  which is shown in section view. An oil reservoir portion  16  is located at a lower portion of the engine and is separated from the crankshaft by a louvered member  18 . The lower surface  20  of the crankcase is disposed at an angle θ from a horizontal line  22 . Although the engine  10  shown in  FIG. 1  is tilted so that the movement of the reciprocating pistons is in a plane that is at an angle from the horizontal line  22 , this specific characteristic of the engine is not directly related to all applications of the basic concepts of the present invention. 
     With continued reference to  FIG. 1 , it can be seen that in the oil reservoir  16 , a support structure  26  is provided to support two balance shafts,  31  and  32 , for rotation about their respective axes,  35  and  36 . Although not shown in  FIG. 1 , the balance shafts,  31  and  32 , are connected in torque transmitting relation with the crankshaft in order to provide a balancing feature for the engine  10 . 
       FIG. 2  is an alternative section view of the engine  10  showing the counterweights  41  and  42 , of one particular embodiment of the present invention.  FIG. 2  will be described in greater detail below in conjunction with  FIG. 4 . 
       FIG. 3  illustrates a balance shaft used in conjunction with an internal combustion engine. It comprises a shaft  50  and a pair of counterweights,  52  and  54 . The counterweights are attached to the shaft  50  for rotation with the shaft about the axis of rotation  56 . Each of the counterweights has an individual center of gravity which is displaced radially from the axis of rotation. As can be seen in  FIG. 3 , the shapes of the counterweights,  52  and  54 , indicate that the center of gravity of the counterweights is above the axis  56  in  FIG. 3 . Also shown in  FIG. 3  is a gear  60  which allows the balance shaft to be connected in torque transmitting relation with a gear associated with the crankshaft of the engine. 
     With continued reference to  FIGS. 1-3 , it should be understood that the counterweights of the balance shaft, in certain engines of the type described above, are disposed within the oil reservoir  16 . When the balance shaft rotates about the axis of rotation  56 , the irregular shape of the outer surface of the counterweights will stir the oil in a highly disadvantageous manner. Since the balance shaft rotates at a relatively high speed, the repeated turbulent and violent contact between the external surfaces of the counterweights and the pool of oil in the oil reservoir  16  will deleteriously aerate the liquid oil as it is stored awaiting its travel to regions of the engine  10  requiring lubrication. This circumstance is highly disadvantageous. 
       FIG. 4  shows the balance shaft described above in conjunction with  FIG. 3 , but with the counterweights encased in a polymer material that is overmolded around the external surface of the counterweights. 
     With reference to  FIGS. 2 and 4 , the section view in  FIG. 2  illustrates the relative positions of the counterweights (identified by reference numerals  41  and  42  in  FIG. 2 ) and their positions within the mass of polymer material. The overmolded polymer material in  FIG. 2  is identified by reference numerals  31  and  32  for the two balance shafts and by reference numeral  31  in  FIG. 4  for the illustrated balance shaft. With continued reference to  FIGS. 2 and 4 , it can be seen that the counterweights are completely surrounded by the polymer material (such as polyetheretherketone—PEEK). The resulting outer surface illustrated in  FIG. 4  causes significantly less turbulence in the oil reservoir than the uncoated counterweights,  52  and  54 , as illustrated in  FIG. 3 . The overmolded polymer material creates and defines a circumferential surface  68  which surrounds the counterweights and has a generally constant radius relative to the axis of rotation  56 . These characteristics cooperate to significantly reduce the resulting turbulence in the oil reservoir as the balance shaft rotates about its axis of rotation. 
       FIG. 5  shows an alternative embodiment of the present invention in which the counterweights  70  are provided with additional circumferential surfaces  74  that are sized to receive cylindrical casings,  76  and  78 . The inside diameters  80  of the casings are attached to the circumferential surfaces  74  in order to allow them to cover the various discontinuous surfaces that would otherwise create turbulence in the oil reservoir. It can also be seen that a surface  79  formed as part of the gear  60  is also shaped to receive the inside surface  80  of the cylindrical casing  78 . When the cylindrical casings are disposed at their intended positions of the balance shaft, the resulting configuration is that which is represented in  FIG. 6 . 
     In  FIG. 6 , it can be seen that the cylindrical casings,  76  and  78 , provide a cover that extends over the counterweight  70 , as shown in  FIG. 5 , and the extended circumferential surfaces  74  which are purposely used to provide a more stable base for the attachment of the casing,  76  and  78 . 
       FIG. 7  shows a balance shaft and two casings,  84  made in accordance with one of the alternative embodiments of the present invention. The casings  84  are made of a relatively light material, such as a polymer, so that they can fulfill the function of providing a relatively smooth outer surface without affecting the location of the center of gravity provided by the counterweights  80 . In the embodiment shown in  FIG. 7 , the counterweight comprises a segment of a disc, approximately two-thirds of a complete disc, which is shaped to cooperate with the counterweight  80  to define a generally disc-shaped structure when the casing is combined with the counterweight as will be described below. The casing comprises tabs  86  which are shaped to be received in slots  88 . 
       FIG. 8  shows the casings  84  assembled to the counterweights  80  with the tabs  86  disposed in the slots  88  to retain the casings in position as shown in  FIG. 8 . With the casings  84  in the position shown in  FIG. 8 , the outer surface of the combined structure of counterweight and casing is relatively smooth and provides a circumferential outer surface with a generally constant radius relative to the axis of rotation  56 . This type of structure, as described above, significantly reduces the likelihood that rotation of the balance shaft will cause turbulent splashing of the oil in which the balance shaft is at least partially submerged. 
     Throughout the description of the various embodiments of the present invention, the term “casing” has been used along with the term “housing structure” to describe the components identified by reference numerals  31 ,  76 ,  78 , and  84 . A well-accepted definition of the term “casing” is “a cover or shell that protects or encloses something.” Another definition of the word “casing” is “a container or cover that goes around something to hold it together or protect it.” As used in the description of the various embodiments of the present invention, this word is used to describe a component that covers at least a portion of the counterweight in order to give the counterweight a smooth outer surface while covering discontinuities in that surface that would otherwise create turbulence and cause aeration when the counterweight is rotated with the balance shaft while being submerged or partially submerged in oil within the crankcase of an engine, as described above in conjunction with  FIGS. 1 and 2 . Although other terms may be available to describe this type of component, it should be understood that the casing of the present invention is intended to perform the function of covering discontinuous surfaces and presenting a generally continuous surface in contact with the oil as the balance shaft rotates. In most embodiments of the present invention, this exposed surface of the casing is generally cylindrical and has a generally constant radial distance from the axis of rotation of the balance shaft. Although non-cylindrical surfaces may also be able to accomplish these goals and be within the scope of the present invention, the most preferred embodiments of the present invention are generally similar in character to the embodiments described above in conjunction with  FIGS. 3-8 . 
     In the embodiment of the present invention described above in conjunction with  FIGS. 3 and 4 , the entire counterweight which extends from the shaft  50  is surrounded by a polymer overmolded material to create the smooth surfaces shown in  FIG. 4 . As illustrated in the section views of  FIG. 2 , the embodiment shown in  FIG. 4  completely surrounds the counterweight which is identified by reference numerals  41  and  42  in  FIG. 2  and by reference numerals  52  and  54  in  FIG. 3 . This causes both the circumferential surfaces  68  and axial surfaces  69  to comprise the polymer overmolded material. All of the other surfaces of the counterweights  54  extending away from the shaft  50  are covered by the casing  31 . 
     The embodiment of the present invention described above in conjunction with  FIGS. 5 and 6  differs slightly from the embodiment described in conjunction with  FIGS. 3 and 4  in that the casing,  76  and  78 , covers the radially outward surfaces of the counterweight  80 , but not the axial faces. In other words, the circumferential surfaces  71  are covered by the casings,  76  and  78 , but the axial faces  81  are not. However, the casings,  76  and  78 , serve the important function of providing a smooth and continuous surface that is unlikely to cause aeration when the balance shaft rotates within the liquid oil pool. The provision of the circumferential mounting surfaces  74  also assure that the exposed axial faces of the counterweights are also relatively smooth and without protrusions or discontinuities that would otherwise aerate the oil. 
     The embodiment of the present invention described above in conjunction with  FIGS. 7 and 8  provide a relatively smooth circumferential surface that, when the casing  84  is attached to the counterweight  80 , comprises the surface  85  of the counterweights with surface  87  of the casings  84  to provide a completely circumferential surface without any major discontinuities that could aerate the oil as the balance shaft  50  rotates. The axial faces of the combined casings  84  and counterweights  80 , as illustrated in  FIG. 8 , are also relatively flat without major discontinuities that could create turbulence in the oil pool. 
     With continued reference to  FIGS. 1-8 , it can be seen that a shaft of an engine made in accordance with a preferred embodiment of the present invention comprises a counterweight attached to the shaft for rotation with the shaft about an axis of rotation, wherein the counterweight has a center of gravity which is displaced radially from the axis of rotation. The present invention also comprises a casing disposed at least partially around the counterweight to define an outer surface surrounding the counterweight. The outer surface can comprise a generally circumferential surface which has a generally constant radius relative to the axis of rotation. The casing can comprise a polymer material which is overmolded on the counterweight. All surfaces of the counterweight in certain embodiments of the present invention, which are not directly in contact with the shaft, are completely encased within the polymer material. The casing, alternatively, can be a cylinder disposed in contact with a radially outward surface of the counterweight. The casing can also comprise a segment of a disc which is shaped to cooperate with the counterweight to define a generally disc shaped structure when the housing structure is combined with the counterweight. In that particular embodiment of the present invention, the casing can comprise a tab which is shaped to be received in a slot formed in the counterweight. In all embodiments of the present invention, the shaft can be a balance shaft which rotates in synchrony with a crankshaft of the engine. Alternatively, in some embodiments of the present invention, the shaft can be a crankshaft of the engine. 
       FIG. 9  is a schematic view of the present invention showing a boat hull  100  below an engine configuration  110 . A crankshaft counterweight  114  shows the relative position of the crankshaft to the louvered surface  118  of a first housing, or bedplate  116 . A second housing, or oil pan  120 , is attached to the bedplate  116  at a parting line  122 . In the embodiment shown in  FIG. 9 , a bearing cap  126  is formed as an integral part of the oil pan  120 . A first support member, or balance shaft bearing support  130 , is formed as an integral part of the bedplate  116 . 
       FIG. 10  is an isometric representation of the bedplate  116 . It has a plurality of crankshaft bearing supports which are shaped to define crankshaft journals  142 . The crankshaft bearing supports  140  are formed as an integral part of the bedplate  116  and disposed within a first cavity  150  which is defined by the bedplate  116  and its attachment to the engine. The crankshaft journals  142  are shaped to support the crankshaft or bearings which, in turn, support the crankshaft. 
       FIG. 11  is an isometric view showing the bottom of the bedplate  116  which is described above in conjunction with  FIG. 10 . Balance shaft bearing supports  160  are shaped to define balance shaft journals  162 . The balance shaft journals  162  are shaped to receive the balance shafts or bearings which support the balance shafts. In a preferred embodiment of the present invention, the balance shaft bearing supports  160  are formed as an integral part of the bedplate  116 . 
     With continued reference to  FIGS. 9-11 , the function of the bearing cap  126  described above in conjunction with  FIG. 9 , can be provided by bearing caps  166  shown in  FIG. 11 . Depending on the embodiment of the present invention, the bearing cap  126  can be an integral part of the oil pan  120  or a separate component  166  that is attachable to the balance shaft bearing supports  160 . Depending on the application, alternative embodiments of the present invention can use either separate bearing caps  166  or integral bearing caps  126 . 
       FIG. 12  is an isometric view of the oil pan  120  showing the integral bearing caps  126  which are shaped to provide balance shaft journals  127 . With reference to  FIGS. 9 and 12 , it can be seen that this embodiment of the present invention provides integral bearing caps  126  that are formed as an integral portion of the oil pan  120  and it can also be seen that the integral bearing caps  126  are hollow with a cavity  129  formed within its structure. This cavity  129  significantly reduces the weight of the overall oil pan  120 . 
     With reference to  FIGS. 9-12 , it can be seen that the separate oil caps  166  are provided with balance shaft journals  167  that cooperate with bearing shaft journals  166  of the balance shaft bearing supports  160  to confine the balance shafts, or associated bearings, and support the balance shafts for rotation about their respective axes,  35  and  36 , as described above in conjunction with  FIG. 1 . 
     With continued reference to  FIGS. 9-12 , it can be seen that the provision of integral balance shaft bearing supports  160  can significantly reduce the overall weight and complexity of the structure. Since they are integral to the bedplate  116 , no additional hardware is required to attach them to the bedplate. This, in itself, significantly reduces the complexity and assembly time of the structure. In addition, integral balance shaft bearing supports  160  can be made hollow and do not need the additional protrusions or extensions that would typically be necessary to permit them to be attached to the bedplate  116  through the use of additional hardware, such as bolts or screws. Although certain embodiments of the present invention can utilize separate bearing caps  166 , the use of integral bearing caps  126  provide these additional advantages of not requiring fastening hardware and allowing cavities  126  to be formed to reduce the overall weight of the structure. The integral bearing caps  126  also allow spaces, such as those identified by reference numeral  170 , which further reduce the overall weight of the structure. 
     With continued reference to  FIGS. 9-12 , it can be seen that preferred embodiments of the present invention comprise a bedplate  116  which is attached to an engine  110  to define a first cavity  150 , a crankshaft  114  of the engine  110  disposed within the first cavity  150 , an oil pan  120  attached to the bedplate  116  to define a second cavity  161 , a balance shaft bearing support  160  formed as an integral part of the bedplate  116  and first and second balance shafts,  31  and  32 , disposed within the second cavity  161  and supported by the balance shaft bearing supports  160  for rotation about their first and second axes,  35  and  36 . The bearing caps can be integral to the oil pan  120 , such as bearing cap  126 , or separate from the oil pan  120  such as bearing cap  166 . 
     Although the present invention has been described in particular detail and illustrated to show a preferred embodiment, it should be understood that alternative embodiments are also within its scope.