Abstract:
Two-part hubs for torsional vibration dampers are disclosed that have a main body made of a softer material than a seal nose and do not require a welded joint to join them together. The main body has a plate defining a front face and a back face, an annular core extending axially outward from the back face of the plate and defining an innermost, outer radial surface and a first bore through the main body, and an outermost, radial, elastomer-receiving surface spaced apart from the innermost outer radial surface by the plate. The seal nose is mated to the innermost, outer radial surface of the annular core and mechanically engaged with the main body for rotation together. Torsional vibration dampers that include the two-part hubs are also disclosed, as well as a front end accessory drive including the same, and methods of manufacturing the two-part hubs.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/032,319, filed Aug. 1, 2014, which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present invention relates to torsional vibration dampers for vehicle engines and, more particularly, to a two-part hub for such torsional vibration dampers. 
       BACKGROUND 
       [0003]    A crankshaft drives the front end assembly drive (FEAD) system of an engine. The crankshaft is turned by the firing of pistons, which exerts a rhythmic torque on the crankshaft, rather than being continuous. This constant application and release of torque causes vacillations, which can stress the crankshaft to the point of failure. Stated another way, the crankshaft is like a plain torsion-bar, which has a mass and a torsional spring rate, that causes the crankshaft to have its own torsional resonant frequency. The torque peaks and valleys, plus the inertia load from the acceleration of the reciprocating components, cause the crankshaft itself to deflect (rotationally) forward and backward while it is operating. When those pulses are near the crankshaft resonant frequency, they cause the crank to vibrate uncontrollably and eventually break. Accordingly, a torsional vibration damper (sometimes referred to as a crankshaft damper) is mounted on the crankshaft to solve this problem by counteracting torque to the crank, negating the torque twisting amplitude placed upon the crankshaft by periodic firing impulses, and to transfer rotational motion into the FEAD system, typically by driving an endless power transmission belt. 
         [0004]    Torsional vibration damper hubs are expected to be as light, strong, and cost effective as possible. The traditional means of producing a hub in the United States has been through casting the hub with either Nodular or Gray Cast Iron and then machining it to its final shape. However, this method of production has to keep a keen eye of the castability of the material (i.e. filling the mold, and not causing voids etc.) which then leads to a structure that is usually heavier than necessary. 
         [0005]    There are other means of production employed elsewhere in the world that yield much lighter and cheaper designs such as stamping and/or forming the hub. However, these methods do not allow for the incorporation of a seal nose because the material used in these processes is soft and does not provide sufficient abrasive/wear resistance needed because of the wear experienced by the seal nose. Some European designs have incorporated a two-piece construction (one of a formed soft steel for the main body of the hub and the other of a hardened or tough steel for the seal nose area) that are welded together to provide axial and angular integrity to the structure. Welding requires specialized capital investment in equipment and is esthetically unappealing, which makes welded two-part hub constructions more difficult to sell in the U.S. market. 
       SUMMARY 
       [0006]    The limitations disclosed in the background section are overcome in the disclosed two-part hub for torsional vibration dampers by eliminating the need for welding the two-part construction together. Nodular Iron (D4512 or equivalent) and Gray Cast Iron (G3500 or equivalent) have been used at the seal nose interface and have proven to have sufficient surface wear toughness to receive an engine seal without causing oil leaks. These tougher, wear resistant irons are used to make a seal nose that is mated, without welding, to a primary hub component that is made of soft(er) steel, in particular, by using a mechanical engagement that allows for both axial and angular integrity of the joint. 
         [0007]    In one aspect, two-part hubs are disclosed that include a main body and a seal nose mechanically engaged to one another. The main body has a plate having a front face and a back face, an annular core extending axially outward from the back face of the plate and defining an innermost, outer radial surface and a first bore through the main body, and an outermost, radial, elastomer-receiving surface spaced apart from the innermost outer radial surface by the plate. The seal nose is mated to the innermost, outer radial surface of the annular core and is mechanically engaged with the main body for rotation together without a welded joint. The main body comprises a first material and the seal nose comprises a second material that are different from one another, in particular the first material is softer than the second material, or. stated another way, the second material is more abrasion resistant than the first material. The seal nose has a front face seated in contact with the plate and a shoulder proximate, but spaced a distance apart from, a terminus of the annular core, and the seal nose defines a second bore that, collectively, with the first bore of the annular core defines a crankshaft-receiving bore. 
         [0008]    In one embodiment, the innermost, outer radial surface of the main body includes threads, and the seal nose has threads threadingly engaging the threads of the innermost, outer radial surface of the main body. A keyway is formed within at least the first bore of the annular core, which broaches the threads of the seal nose, thereby locking the threads of the annular core and the threads of the seal nose together. 
         [0009]    In another embodiment, the seal nose is press-fittingly engaged with the innermost, outer radial surface of the annular core, and one or more pins extend axially into a front face of the seal nose, and connect the seal nose to the main body for rotation together. 
         [0010]    In either embodiment, a geometric lock, comprising a hole defined by either or both of the seal nose or the annular core and a pin received in the hole, mechanically engages the main body to the seal nose. 
         [0011]    In another aspect, torsional vibration dampers are disclosed that include one of the two-part hubs described herein, an elastomeric damper member disposed in contact with an outermost, radial, elastomeric-receiving surface of the hub, and an inertia member seated against the elastomeric damper member thereby operably coupling the inertia member to the hub for rotation therewith. In one embodiment, the elastomeric member is an annular ring of elastomeric material seated against the outermost, radial elastomer-receiving surface of the main body of the hub, and the inertia member is an annular ring seated against the elastomeric member, both of which are concentric about an axis of rotation of the hub. 
         [0012]    In another aspect, any of the torsional vibration dampers disclosed herein may be mounted to the crankshaft as part of a front end accessory drive system. 
         [0013]    In another aspect, methods of manufacturing the two-part hub are disclosed. The methods include providing a main body portion comprised of a first material, having a front face and a back face, and having an annular core extending axially outward from the back face and defining a first bore therethrough, providing a seal nose defining a second bore and comprised of a second material that is more abrasive resistant than the first material, mating the seal nose to the annular core of the main body with the first bore and the second bore aligned to collectively define a crankshaft-receiving bore, mechanically engaging the seal nose with the main body for rotation together without a welded joint, and machining the crankshaft-receiving bore to meet selected axial and radial run-outs. 
         [0014]    In one embodiment, mating the seal nose to the annular core comprises threading the seal nose to the annular core of the main body, and the method further comprises, subsequently, forming a generally axially-oriented keyway recessed in the crankshaft-receiving bore to a depth that broaches the threads of the seal nose thereby locking threads of the annular core and threads of the seal nose together. In this embodiment, mating the seal nose to the annular core includes threading the seal nose to the annular core until a front face of the seal nose is seated against the plate, and if the seal nose includes a shoulder in the second bore, the shoulder is spaced apart from a back face of the annular core by a distance when the front face of the seal nose is seated against the plate. 
         [0015]    The methods may include forming the main body by stamping the first material to include the annular core defining an innermost, outer radial surface of the hub and an outermost, radial elastomer-receiving surface spaced apart from the innermost outer radial surface by a plate, and forming the seal nose by machining it from a piece of abrasion resistant material. In one embodiment, the seal nose comprises nodular iron or grey cast iron, and the main body comprises a low carbon steel. 
         [0016]    In another embodiment, in a front face of the seal nose, the seal nose comprises a plurality of axially extending receptacles or a plurality of protruding pins. In this embodiment, mating the seal nose to the annular core includes press-fitting the seal nose to the annular core while aligning the receptacles or protruding pins with openings defined in the plate of the main body. When the seal nose includes the plurality of axially extending receptacles aligned with openings defined in the plate, the method further comprises inserting a pin through each opening in the plate into a receptacle in the seal nose, thereby engaging the seal nose with the main body for rotation together without a welded joint. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]    Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0018]      FIG. 1  is a perspective view of components in a front end accessory drive. 
           [0019]      FIG. 2  is a side perspective, partial cut-away view of a two-part hub for a torsional vibration damper at a first stage of manufacture. 
           [0020]      FIG. 3  is a side perspective, partial cut-away view of the two-part hub in  FIG. 2  after a second stage of manufacture. 
           [0021]      FIG. 4  is a side perspective, partial cut-away view of a completed two-part hub after a third stage of manufacture. 
           [0022]      FIG. 5  is a longitudinal cross-sectional, perspective view of a second embodiment of a two-part hub for a torsional vibration damper. 
           [0023]      FIG. 6  is a side, perspective view of a torsional vibration damper having the two-part hub of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Reference is now made in detail to the description of the embodiments as illustrated in the drawings. While several embodiments are described in connection with these drawings, there is no intent to limit the disclosure to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents. 
         [0025]    Referring now to  FIG. 1 , an example of one embodiment of a FEAD system  18  is shown, merely for illustration purposes, that includes an integrated housing  15 , having a front surface  30  and a rear surface  27 . The rear surface  27  of the integrated housing  15  is preferably mounted to an engine. The FEAD system  18  may be utilized with any engine, including vehicle, marine and stationary engines. The shape and configuration of the integrated housing  15  depends upon the vehicle engine to which it is to be mounted. Accordingly, the integrated housing  15  and more specifically the FEAD system  18  may vary along with the location of engine drive accessories  9  and still achieve the objects of the present invention. It should be understood that the location and number of engine drive accessories  9  may be varied. For example, a vacuum pump, a fuel injection pump, an oil pump, a water pump, a power steering pump, an air conditioning pump, and a cam drive are examples of other engine drive accessories  9  that may be mounted on the integrated housing  15 , for incorporation into the FEAD system  18 . The engine drive accessories  9  are preferably mounted to the integrated housing  15  by bolts or the like at locations along the surface that are tool accessible for easy mounting and also service accessible. In  FIG. 1 , the integrated housing  15  has a plurality of engine drive accessories  9  including an alternator  12  and a belt tensioner  21 . 
         [0026]    The engine drive accessories  9  are driven by at least one endless drive belt  6 , which may be a flat belt, a rounded belt, a V-belt, a multi-groove belt, a ribbed belt, etc., or a combination of the aforementioned belts, being single or double sided. The endless drive belt  6  may be a serpentine belt, and is wound around the engine drive accessories  9 , the alternator  12  and the torsional vibration damper  3 , which is connected to the nose  10  of the crankshaft  8 . The crankshaft drives the torsional vibration damper  3  and thereby drives the endless drive belt  6 , which in turn drives the remaining engine drive accessories  9  and the alternator  12 . The belt tensioner  21  automatically adjusts the tension of the endless drive belt  9  to keep it tight during operation and also prevent wear. 
         [0027]    The improvement to the FEAD system  18  herein is a torsional vibration damper having a two-part hub as shown in  FIGS. 2-4  or in  FIG. 5 , which is made without welding and provides an abrasion/wear resistant seal nose  104  as a portion thereof. In the assembled view of  FIG. 4 , the hub  100  includes a main body  102  and a seal nose  104  threadingly mated thereto. The seal nose  104  has a front face  122 , a back face  128 , and threads  120  that terminate at a terminus  126  proximate a shoulder  128 . The main body  102  includes a plate  109 , an annular core  101  extending axially, outward from the plate  109 , in particular, from a back face of the plate  109 , and defining an innermost, outer radial surface  106  ( FIG. 2 ), and an outermost radial surface  108  spaced apart from the innermost, outer radial surface  106  by the plate  109 . The annular core  101  includes threads  110  as part of the innermost, outer radial surface  106  and defines a bore  112  through the hub  100  for receiving a shaft. The seal nose  104  has threads  120  threadingly mated to the threads  110  of the annular core  101 . 
         [0028]    As labeled in  FIGS. 2 and 3 , the plate  109  has a front face FF designated by an arrow in the figures, and an opposing face, the back face BF, as shown by the second arrow in the figures. The plate  109  may define one or more apertures  130  and/or a recesses  132 . The apertures  130  may each be arcuate since these may receive a portion of an elastomeric member (not shown), which is typically an annular member. While the plate  109  is illustrated as having a recess  132 , the plate  109  could instead have one or more protrusions for mating with an elastomeric member. Any one or more of the apertures  130  may be positioned to receive a fastener to hold components of the torsional vibration damper together or to reduce the amount of material needed in the hub  100  to reduce weight and/or cost. Plate  109  should not be construed as requiring a flat, one-planar construction. It may have such a construction, but it may be irregular shaped as seen in the figures. In  FIGS. 2 and 3 , the plate  109  portion of the main body  102  has a stair-step configuration when viewed from either the front face FF or the back face BF. 
         [0029]    As seen in  FIGS. 2-4 , the nose seal  104  is a femalely-threaded component and the annular core  101  is a malely-threaded component. The threads  110 ,  120  thereof are threadingly mated into a fully assembled position ( FIG. 4 ) where the seal nose  104  has its front face  122  seated in contact with the plate  109 . Further, the fully assembled position has a shoulder  124  of the seal nose  104 , which is proximate the terminus  126  of its threads, spaced apart from a back face  113  of the annular core  101  by a distance, thereby defining a gap  130  as shown in  FIG. 4 . Accordingly, the shoulder  124  is not seated against the annular core  101 . This configuration provides for contact between only one face of each of the nose seal  104  and the main body  102  to provide proper axial alignment of these two components with respect to one another. The advantage of this construction is axial integrity of the joint formed by threadingly mating the components together. Moreover, once a crank-bolt secures the hub to a crankshaft, the seal nose  104  and the main body  102  cannot be axially separated from one another. 
         [0030]    Still referring to  FIG. 4 , a keyway  114  is formed through the bore  112  of the annular core  101  into the threads  120  of the seal nose  104  thereby locking the threads  110  of the annular core  101  and the threads  1120  of the seal nose  104  together, which also provides axial integrity to the joint. The formation of the keyway  114  causes some of the first material, since it is a softer material than the second material, to fill any spaces between the threads  110 ,  120  at the site of the keyway  114  thereby locking the threads together and providing angular integrity to the joint. The keyway  114  is also beneficial to prevent angular deflection of the joint by receiving a shaft in the bore  112  that has a matching key that is received in the keyway  114 . 
         [0031]    In one embodiment, the threads  110  and/or  120  may include a coating that enhances the rigidity and/or seal of the joint. In one embodiment, Loctite® threadlocker may be used to coat the threads. 
         [0032]    The main body  102  includes a first material that is abrasion/wear resistant. The seal nose  104  includes a second material that is different from the first material and is more abrasive resistant than the first material. Accordingly, the first material is softer than the second material. In one embodiment, the seal nose  104  includes nodular iron (grade D4512 or equivalent, also known as ductile iron). In another embodiment, the seal nose  104  includes gray cast iron (grade G3500 or equivalent). The main body  102  may include a low carbon steel. In one embodiment, the main body includes a DD13 grade low carbon steel or its equivalent. Other suitable materials for the main body include iron, steel, aluminum, other suitable metals, plastics, or a combination thereof as long as it is different, softer, and/or cheaper from the material included in the seal nose  104 . 
         [0033]    The hub  100  may be manufactured as illustrated by the sequence of  FIGS. 2-4 . In  FIG. 3 , a main body  102  comprised of a first material and having an annular core  101  defining a bore  112  therethrough for mounting the hub  100  to a shaft (not shown) and having threads  110  on a surface of the annular core  101  is provided along with a seal nose  104  having threads  120  and including a second material that is more abrasive resistant than the first material. Then, as illustrated in  FIG. 4 , the seal nose  104  was threadingly mated to the annular core  101  by mating the threads  110 ,  120 . And thereafter, a keyway  114  is formed through the bore  112  into the threads  120  of the seal nose  104  thereby locking the threads  110  of the annular core  101  and the threads  120  of the seal nose  104  together. The formation of the keyway  114  causes some of the first material, since it is a softer material than the second material, to fill any spaces between the threads  110 ,  120  at the site of the keyway  114  thereby locking the threads together and providing angular integrity to the joint. The keyway  114  typically extends the full axial length of the bore  112 . 
         [0034]    The method for manufacturing the hub  100  may also include providing the main body  102  as described above, but without the threads as shown in  FIG. 2 . In this manner the main body  102  may be a stamped piece and the method may include stamping a first material into the shape of the main body  102  and thereafter forming threads  110  as shown in  FIG. 3 . Threads  110  may be formed on the innermost, outer radial surface  106  of the annular core  101  by tapping, machining, or other known or hereinafter developed techniques. 
         [0035]    In other embodiments, the main body  102  may be cast, spun, forged, or molded using known or hereinafter developed techniques with or without the threads  110 . Threads  110  may be formed by tapping, machining, or other known or hereinafter developed techniques. 
         [0036]    The method of manufacturing the hub  100  may include forming the seal nose  104  by machining it from a piece of abrasion resistant material such as nodular iron or grey cast iron, including tapping or machining the threads  120  thereof. 
         [0037]    In the method, threading the seal nose  104  to the annular core  101  includes threadingly mating the seal nose  104  to the main body  102  until the front face  122  of the seal nose  104  contacts the plate  109 . The front face  122  of the seal nose  104  once in contact with the plate  109  places its shoulder  124  ( FIGS. 2 and 3 ), which is proximate the terminus  126  of its threads  120 , spaced apart from a back face  113  of the annular core  101  by a distance thereby defining gap  130  ( FIG. 4 ). 
         [0038]    After the seal nose  104  is threadingly mated to the annular core  101 , the method may include honing the bore  112  of the annular core  101  for a press-fit to a selected shaft. 
         [0039]    In another embodiment, the threads  110  of the annular core  101  and the threads  120  of the seal nose  104  are self-locking, thereby providing axial rigidity to the threadingly mated connection therebetween. In this embodiment, the formation of keyway  114  is not necessary and may be omitted. Without the keyway, another mechanism should be introduced to provide angular rigidity to the joint (i.e., prevent angular motion between the seal nose  104  and the main body  102 ). One such mechanism is a geometric lock. In one embodiment, a geometric lock includes a generally D-shaped hole defined by either the nose seal  104  or the annular core  101  of the main body  102 , or both and a generally D-shaped shaft received in the generally D-shaped hole(s), which may be an independent shaft or may extend from either component. In another embodiment, the geometric lock may be a plurality of pins extending axially through the plate of the hub into the nose as illustrated and explained in more detail with respect to  FIG. 5 . 
         [0040]    With reference to  FIG. 6 , the method of manufacturing includes disposing an elastomer ring  302  circumferentially about the damper assembly-receiving surface  108  of the main body  102  to be concentric with the axis of rotation A of the hub  100  and disposing an inertia ring  304  circumferentially about the elastomer ring  302  to be concentric with the axis of rotation A to form a torsional vibration damper  300 . In one embodiment, the inertia ring  304  is positioned first relative to the hub  100  and the elastomer ring  302  is press fit into a gap between the inertia ring  304  and the damper assembly-receiving surface  108  of the main body  100 . The inertia ring  304  may include an outer radial belt-engaging surface  306 . 
         [0041]    Referring now to  FIG. 5 , a second embodiment of a two-part hub  200  is shown. The two-part hub  200  includes a main body  202  and a seal nose  204  press-fittingly mated thereto. The main body  202  include a plate  209 , an annular core  203  extending from the plate  209  and defining an innermost, outer radial surface  206 , and a damper assembly-receiving surface  208  spaced apart from the innermost, outer radial surface  206  by the plate  209 . The annular core  203  defines a bore  212  through the hub  200 . The plate  209  may define one or more apertures  230  positioned to receive a fastener to hold components of the torsional vibration damper together or to reduce the amount of material needed in the hub  100  to reduce weight and/or cost. Plate  209  should not be construed as requiring a flat, one-planar construction. It may have such a construction, but it may be irregular shaped as seen in the figures. In  FIGS. 2-4  and  FIG. 5 , the plate  209  portion of the main body  202  has a stair-step configuration when viewed from either the front face FF or the back face BF. The front face of the plate  209  at the annular core  203  has an annular recess  244  formed therein to receive the head of a crank-bolt or a washer positioned on the crank-bolt adjacent to the head thereof. Positioned within the annular recess  244  at positions that align with the front face  222  of the seal nose  204 , in particular, each aligned with a receptacle  242  in the seal nose  204 , are a plurality of holes  246  extending through the plate  209 . 
         [0042]    The seal nose  204  has a front face  222 , a back face  228 , and an inner bore  225  shaped with at least a portion  227  thereof dimensioned to be press-fit to the innermost, outer radial surface  206  defined by the annular core  203  of the main body  202 . The front face  222  of the seal nose  204  includes a plurality of receptacles  242  extending axially into the seal nose  204  that are each shaped to receive a pin  240 . In one embodiment, each pin  240  is press-fit into a receptacle  242  through a hole  246  through the plate  209  of the main body  202  at a position that align with the receptacle  242  in the seal nose. The press-fit does not have to overly tight because once a crank-bolt (not shown) secures the hub  200  to a crankshaft (not shown), the head of the bolt or a washer and head of the bolt holds the pins  240  in position during operation of the FEAD system. In another embodiment, the front face  222  of the seal nose  204  includes a plurality of pins protruding axially therefrom, which are received in the holes  246  in the plate  209  when the seal nose  204  is press-fit to the annular core  204 . In both embodiments, the pins  240  lock the main body  202  and seal nose  204  together without welding, but also provide axial rigidity to the hub  200  at reduced expense because the main body  202  can be made of a cheaper, even softer material by a cheaper method of manufacture than the nose seal  204 , as explained above with respect to the embodiment in  FIGS. 2-4 . The same materials and methods of manufacture for the main body  202  and the seal nose  204  discussed above apply here. The seal nose  204  includes a second material that is different from the first material that the main body  202  is made of and is more abrasive resistant than the first material. 
         [0043]    In one embodiment, the hub  200  may be manufactured by stamping a first material into the shape of the main body  202  with or without the holes  240 . If the holes  240  are not formed in the stamping process, they are formed thereafter by any suitable method, such as drilling, etching, punching, etc. The manufacturing process further includes forming the seal nose  204  by casting it from a second material, such as a nodular iron or grey cast iron, that is more abrasion resistant than the first material. The casting may include the formation of the receptacles  242  in the front face  222  of the seal nose or a step of machining the receptacles  242  therein may be completed after the casting is complete. Once both the main body  202  and the seal nose  204  are provided, manufacturing includes press-fitting the seal nose  204  to the annular core  203  of the main body  202 , inserting pins  240 , one each, into a receptacle  242  in the front face  222  of the seal nose through the holes  246  in the plate  209  of the main body  202 , machining the annular recess  244  into the plate  209 , machining the back face of the seal nose  204  and the bore B of the hub  200  defined collectively by the bores  212 ,  225  of the main body  202  and seal nose  204  to meet axial and radial run-out specifications. 
         [0044]    Also, the method of manufacturing includes disposing an elastomer ring (not shown) circumferentially about the damper assembly-receiving surface  208  of the main body  202  to be concentric with the axis of rotation of the hub  200  and disposing an inertia ring (not shown) circumferentially about the elastomer ring to be concentric with the axis of rotation to form a torsional vibration damper. In one embodiment, the inertia ring is positioned first relative to the hub and the elastomer ring is press fit into a gap between the inertia ring and a damper assembly-receiving surface  208 . 
         [0045]    Once the hub  200  is assembled per the manufacturing method discussed above, it can be mounted onto the crankshaft. In this embodiment, the hub is slip fit onto the crankshaft and no keyway and key mechanism is needed between the crankshaft and the hub to provide axial rigidity to the hub. Instead the pins  240  provide the axial rigidity, and as explained above, the crank bolt or crank bolt and washer hold the pins in place axially once the hub  200  is bolted to the crankshaft. 
         [0046]    Although the invention is shown and described with respect to certain embodiments, it is obvious that modifications will occur to those skilled in the art upon reading and understanding the specification, and the present invention includes all such modifications.