Abstract:
A pendulum crankshaft for an internal combustion engine includes a pendulum crankshaft having pendulum crank rolling path inserts that are cast into the component during the casting process. The rolling path inserts are positioned in a mold prior to casting. By including the rolling path inserts in the component during the molding process, the need to press the rolling path insert into the component after the component is cast eliminates the resulting stresses that would otherwise result. Machining and subsequent heat treatment are unnecessary. The component can be one or both of the crankshaft pendulum and the pendulum carrier. The rolling path may be formed from a metal such as sintered powdered metal. The flowable material may be a metal such as iron. The resulting component is free of stress regions, such as on the carrier strap, that normally result from methods that involve press-fitting the rolling path insert into the component.

Description:
TECHNICAL FIELD 
       [0001]    The disclosed inventive concept relates generally to crankshaft pendulums for internal combustion engines. More particularly, the disclosed inventive concept relates to crankshaft pendulum assembly for a crankshaft pendulum having cast-in near net shape hardened cycloid sleeve inserts that provide rolling pathways. 
       BACKGROUND OF THE INVENTION 
       [0002]    Internal combustion engines having a relatively small number of cylinders provide automobile makers with an attractive solution to the need for improved fuel economy. In order to compensate for reduction of cubic capacity vehicle manufacturers developed technologies to improve engine power, such as direct fuel injection, turbocharging, and variable timing for inlet and exhaust camshafts. In this way six- and eight-cylinder engines can be scaled down without losing available horsepower. 
         [0003]    An undesirable consequence of engines having higher cylinder pressures or a smaller number of cylinders is that the engine order torsionals increase. This can cause gear rattle in the transmission and increase interior NVH such as steering wheel vibration. 
         [0004]    Engineers managed these vibrations to one extent or another through a variety of approaches, many of which increase the cost of construction and reduce fuel economy. One accepted solution to overcome excessive vibration is the provision of one or more pendulums on the crankshaft to lower the torsional vibration of the crankshaft and the consequent driveline and interior NVH. Such crankshaft-mounted pendulums function as vibration absorbers as they are tuned to address and thus cancel out vibrations generated by crankshaft rotation, thus smoothing torque output of the crankshafts. This approach is taken as well by designers of some airplane piston engines where the pendulums smooth output torque. 
         [0005]    An example of a pendulum vibration absorber associated with an engine crankshaft is set forth in U.S. Pat. No. 4,739,679, assigned to the assignee of the instant application. According to the arrangement set forth in this patent, a pendulum includes an inner curved cam follower surface that is alternately engaged and disengaged from a pin type cam fixed on the pendulum carrier. 
         [0006]    The crankshaft pendulum is interconnected with the pendulum carrier by pendulum rolling pins. Each pendulum rolling pin rides on a rolling path formed in the pendulum and in the carrier. The cycloid shape is itself difficult and expensive to machine. Instead of machining the shape, one solution is to use a near net shape powder metal insert which is less expensive to produce. The insert is press-fitted into the ear of the pendulum carrier. However, the required press to fit the inserts into position results in unacceptably high stresses in the area adjacent to the insert. Therefore this concept is not a practical solution in an actual manufacturing environment. An alternative approach is to provide a fully machined pendulum made of forged steel yields at the rolling pin contact. However, this approach is also impractical as expensive heat treatment and subsequent hard machining is required. 
         [0007]    Accordingly, a new approach to forming rolling path inserts for use in pendulum crankshaft assemblies is needed to address the problems associated with known arrangements. 
       SUMMARY OF THE INVENTION 
       [0008]    The disclosed inventive concept overcomes the problems associated with known crankshaft pendulums for internal combustion engines by providing a crankshaft pendulum having cast-in near net shape hardened cycloid sleeves or inserts formed from a metal such as sintered powdered metal. The rolling path inserts are positioned in a mold prior to casting. By including the rolling path inserts in the component during the molding process, the need to press the rolling path insert into the component after the component is cast eliminates the resulting stresses that would otherwise result. The cast-in production approach of the disclosed inventive concept also avoids the need for machining and subsequent heat treatment required if the component is made from a material such as cast iron. 
         [0009]    The advantages of the disclosed inventive concept over the prior art are achieved by producing a component for a crankshaft pendulum assembly by forming a mold for the component, forming a rolling path insert, positioning the rolling path insert into the mold, and injecting a flowable material into the mold to form the finished component. 
         [0010]    The component can be one or both of the crankshaft pendulum and the pendulum carrier. The rolling path insert may be formed from a metal such as sintered powdered metal. The flowable material may be a metal such as iron. The resulting component is finished or substantially finished out of the mold and requires either no machining or minimal machining. The resulting component is free of stress regions, such as on the carrier strap, that normally result from methods that involve press-fitting the rolling path insert into the component. In addition, no heat treatment is required after the component is formed. 
         [0011]    The above advantages and other advantages and features will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For a more complete understanding of this invention, reference should now be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention wherein: 
           [0013]      FIG. 1  is a front view of a pendulum carrier and one half of a crankshaft pendulum attached to the pendulum carrier in which the pendulum carrier includes rolling path inserts according to known technology; 
           [0014]      FIG. 2  is a perspective view of a portion of the pendulum carrier of known technology from which the insert has been removed to illustrate the stress in the area adjacent the insert hole that results from placement of the insert into the pendulum carrier ear; 
           [0015]      FIG. 3  is a front view of a cast iron pendulum carrier having machined rolling pathways according to known technology; 
           [0016]      FIG. 4  is a front view of half of a crankshaft pendulum having cast-in near net shape hardened cycloid sleeve inserts according to the disclosed inventive concept; 
           [0017]      FIG. 5  shows a perspective view of the crankshaft pendulum half of  FIG. 4 ; 
           [0018]      FIG. 6  is a perspective view of a portion of the pendulum carrier of the disclosed inventive concept illustrating the cast-in cycloid sleeve insert; and 
           [0019]      FIG. 7  is a plan view of a mold having a mold cavity in which a pair of hardened cycloid sleeve inserts have been placed prior to injection of the molten material. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    In the following figures, the same reference numerals will be used to refer to the same components. In the following description, various operating parameters and components are described for different constructed embodiments. These specific parameters and components are included as examples and are not meant to be limiting. 
         [0021]    As illustrated in  FIGS. 1 through 3 , two different approaches to forming a rolling pathway in the parts of a crankshaft pendulum assembly according to known technology are illustrated.  FIGS. 4 through 6  illustrate components of the crankshaft pendulum assembly according to the disclosed inventive concept in which cast-in cycloid sleeve inserts are provided. 
         [0022]    Referring to  FIG. 1 , a front view of a crankshaft pendulum and pendulum carrier assembly according to known technology, generally illustrated as  10 , is shown. The assembly  10  includes a crankshaft pendulum half  12  movably attached to a pendulum carrier  14 . The pendulum carrier  14  is attached to an engine crankshaft (not shown). The crankshaft pendulum half  12  represents one-half of a whole crankshaft pendulum (not shown), the one-half being removed so that the pendulum carrier  14  can be illustrated in relation to the crankshaft pendulum half  12 . 
         [0023]    The crankshaft pendulum half  12  includes a centrally-formed raised area  16  and a pair of recessed areas  18  and  18 ′ formed laterally of the centrally-formed raised area  16 . A pair of fastener holes  20  and  20 ′ are formed in the centrally-formed raised area  16  for fasteners (not shown) that are used to fix the two halves of the crankshaft pendulum together. 
         [0024]    Each of the crankshaft pendulum half  12  and the pendulum carrier  14  have rolling pathways formed therein. Specifically, the crankshaft pendulum half  12  includes a first pendulum rolling pathway  22  and a second pendulum rolling pathway  22 ′. The pendulum carrier  14  includes a first pendulum carrier rolling pathway  24  and a second pendulum carrier rolling pathway  24 ′. A pendulum roller  26  is positioned within both the first pendulum rolling pathway  22  and the first pendulum carrier rolling pathway  24 . A pendulum roller  26 ′ is positioned within both the first pendulum rolling pathway  22 ′ and the first pendulum carrier rolling pathway  24 ′. As illustrated in  FIG. 1 , the crankshaft pendulum half  12  is in its full out position relative to the pendulum carrier  14 . 
         [0025]    The pendulum carrier  14  includes a body  27  having carrier ears  28  and  28 ′. The carrier ear  28  includes a carrier strap  29  and the carrier ear  28 ′ includes a carrier strap  29 ′. The body  27  is attached to the crankshaft (not shown). 
         [0026]    The carrier ear  28  includes an insert hole  30  formed by the carrier strap  29  and the carrier ear  28 ′ includes an insert hole  30 ′ formed by the carrier strap  29 ′. A carrier insert  32  is press-fitted into the insert hole  30  of the carrier ear  28 . A carrier insert  32 ′ is press-fitted into the insert hole  30 ′ of the carrier ear  28 ′. The press-fitted carrier inserts  32  and  32 ′ may be made from a hardened metal, such as hardened powder metal or hardened steel. A pin  34  is provided to aid in the orientation of the pressed-in carrier insert  32  relative to the carrier ear  28  during assembly. In the same manner, a pin  34 ′ is provided to aid in the orientation of the pressed-in carrier insert  32 ′ relative to the carrier ear  28 ′ during assembly. 
         [0027]    According to known crankshaft pendulum construction, the pressed-in carrier insert is press-fitted into the pendulum carrier by a press suitable for such a purpose. Because the fit between the pressed-in carrier insert and the carrier ear is typically an interference fit, insertion of the carrier insert into the insert hole results in undesirable stress on the area of the carrier ear adjacent to the insert hole. This situation is illustrated in  FIG. 2 , in which a perspective view of a portion of the pendulum carrier  14  of  FIG. 1  is shown. Particularly, the carrier ear  28  is shown without the pressed-in carrier insert in place to illustrate the stress created in the area adjacent the insert hole  30  after the carrier insert is installed. 
         [0028]    Referring to  FIG. 2 , the installation of the carrier insert by press-fitting can generate a Von Mises stress in the carrier strap  29  of more than 3000 MPa. The distribution of Von Mises stress is illustrated in  FIG. 2  in which the areas designated as  34  undergo the greatest level of stress of over 450 MPa, while the area designated as  36  undergo the second greatest level of stress of over 400 MPa. As illustrated, the greatest concentration of stress is in the thinnest area of the carrier strap  29 , whereas the lowest level of stress is an area  38  that defines the neck connecting the carrier strap  29  to the body  27  of the pendulum carrier  14 . The illustrated Von Mises stress on the carrier strap  29  that results upon insertion of the pressed-in carrier insert is an undesirable result of known assembly techniques. 
         [0029]    In an effort to eliminate the stresses created in the carrier strap by known approaches, cycloids have been machined directly in cast iron pendulums and pendulum carriers. According to this approach, no insert is required, and thus stresses to the local environment are avoided. An example of a component of the crankshaft pendulum carrier assembly that is cast and machined is illustrated in  FIG. 3  in which a front view of a cast pendulum carrier  40  is illustrated. The cast pendulum  40 , typically made from cast iron, includes carrier ears  42  and  42 ′ attached to a carrier body  44 . A rolling path  46  is machined directly into the carrier ear  42  and a rolling path  46 ′ is machined directly into the carrier ear  42 ′. Rolling pins (not shown) are movably fitted within the rolling paths  46  and  46 ′. 
         [0030]    In operation, the rolling paths  46  and  46 ′ of the cast pendulum carrier  40  yield at the rolling pin contact. To prevent this undesirable result, heat treatment of the cast iron component is required following machining. The step of heat treatment, added to the expense of machining, renders this approach to providing a solution to the problem of costly crankshaft pendulum assembly components impractical. But the added step of heat treatment may not provide satisfactory results, in that the cast iron (even austempered ductile iron [ADI], a heat treated cast iron) often experience unacceptable wear. Thus a forged or stamped steel design that is hardened is required. However, the hardening process itself causes distortion in the steel and subsequent “hard” machining. 
         [0031]    The disclosed inventive concept avoids known inadequacies in methods and material by providing an alternative to known approaches to constructing a crankshaft pendulum assembly. Particularly, and referring to  FIGS. 4 through 6 , components of a crankshaft pendulum assembly incorporating cast-in cycloid sleeve inserts are illustrated. 
         [0032]      FIG. 4  illustrates a front view of a portion of a crankshaft pendulum half  50  constructed according to the disclosed inventive concept is illustrated.  FIG. 5  illustrates a perspective view of the crankshaft pendulum half  50 . Referring to both  FIG. 4  and  FIG. 5 , the crankshaft pendulum half  50  is attached to a pendulum carrier (not shown) which is itself attached to the crankshaft. The crankshaft pendulum half  50  represents one-half of a whole crankshaft pendulum (not shown). The covering half is removed for purposes of illustration. 
         [0033]    The crankshaft pendulum half  50  includes a centrally-formed raised area  52  and a pair of recessed areas  54  and  54 ′ formed laterally of the centrally-formed raised area  52 . A pair of fastener holes  56  and  56 ′ are formed in the centrally-formed raised area  52  for fasteners (not shown) that are used to fix the two halves of the crankshaft pendulum together. 
         [0034]    The crankshaft pendulum half  50  includes cast-in, near net shape hardened rolling path insert sleeves  60  and  60 ′. The rolling path insert sleeves  60  and  60 ′ are preferably formed from a powdered or sintered metal, although other materials such as hardened steel may be suitable. 
         [0035]    The crankshaft pendulum halves are not the only components of the crankshaft pendulum assembly that can be formed with rolling path insert sleeves. In addition or in the alternative, the pendulum carrier may also be formed with rolling path insert sleeves, as illustrated in  FIG. 6 . With reference to that figure, a perspective view of a portion of a pendulum carrier  62  is illustrated. The pendulum carrier  62  includes a pendulum carrier ear  64  that is attached to a pendulum carrier body  66 . A cast-in, near net shape hardened rolling path insert sleeve  68  is provided. Like the rolling path insert sleeves  60  and  60 ′, the rolling path insert sleeve  68  is preferably formed from sintered powdered metal, although other materials may be suitable. 
         [0036]    To manufacture either the crankshaft pendulum or the pendulum carrier, the cycloid sleeves are first positioned within the appropriate mold. An example of the positions of the cycloid sleeves within a mold is shown in  FIG. 7  in which a mold  70  for a crankshaft pendulum half is shown. The mold  70  includes a mold body  72  having a mold cavity  74  defined therein. Once formed, the rolling path insert sleeves  60  and  60 ′ (or the rolling path insert sleeve  68  in the case of a pendulum carrier) are positioned within the mold  70  prior to injection. Once correctly positioned, the mold is closed and the flowable material, such as cast iron, is injected into the mold  70 . 
         [0037]    Use of the cast-in, near net shape hardened rolling path insert sleeve in either or both of the crankshaft pendulum and the pendulum carrier according to the disclosed inventive concept avoids the stresses caused by press fitting as is known to result from assembly based on known technology. In addition, use of the cast-in, near net shape hardened rolling path insert sleeve in either or both of the crankshaft pendulum and the pendulum carrier according to the disclosed inventive concept avoids the added cost associated with the need to machine and heat treat a cast metal part. The disclosed inventive concept provides the benefit of a hardened near net shape rolling path insert while eliminating the disadvantages attendant the known technologies. 
         [0038]    In addition to providing the specified advantages over known approaches to forming a rolling path insert in crankshaft pendulum assemblies, one skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.