Patent Publication Number: US-10316702-B2

Title: Rocker arm assembly and method of forming retention elements in a rocker arm

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. application Ser. No. 15/065,644, filed on Mar. 9, 2016, and claims priority to and all the benefits of U.S. Provisional Patent Application No. 62/131,023, filed on Mar. 10, 2015, both of which are hereby expressly incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates, generally, to engine valvetrain systems and, more specifically, to a rocker arm assembly for use in a valvetrain of a cylinder head of an internal combustion engine. 
     2. Description of the Related Art 
     Conventional engine valvetrain systems known in the art typically include one or more camshafts in rotational communication with a crankshaft supported in a block, one or more intake and exhaust valves supported in a cylinder head, and one or more intermediate members for translating radial movement from lobes of the camshaft into linear movement of the valves. The valves are used to regulate the flow of gasses in and out of cylinders of the block. To that end, the valves each have a head and a stem extending therefrom. The valve head is configured to periodically seal against the cylinder head. To that end, a compression spring is typically supported in the cylinder head, is disposed about the valve stem, and is operatively attached to the valve stem via a spring retainer. The valve stem is typically supported by a valve guide that is also operatively attached to the cylinder head, whereby the valve stem extends through the valve guide and travels therealong in response to engagement from the intermediate member. 
     As the camshaft rotates, the intermediate member translates force from the lobes into linear movement of the valve between two different positions, commonly referred to as “valve open” and “valve closed”. In the valve closed position, potential energy from the loaded spring holds the valve head sealed against the cylinder head. In the valve opened position, the intermediate member translates linear movement to compress the spring, thereby un-sealing the valve head from the cylinder head so as to allow gasses to flow into (or, out of) the cylinder of the block. 
     During engine operation, and particularly at high engine rotational speeds, close tolerance must me maintained between the camshaft lobe, the intermediate member, and the valve stem. Excessive tolerance results in detrimental engine performance as well as increased wear of the various valvetrain components, which leads to significantly decreased engine life. In order to maintain proper tolerances, in modern “overhead cam” valvetrain systems, the intermediate member is typically realized by a lash adjuster and a rocker arm. The lash adjuster is typically supported in the cylinder head spaced from the valve stem, with a lobe of the camshaft disposed above (“overhead of”) the lash adjuster and valve stem. Conventional lash adjusters utilize hydraulic oil pressure from the engine to maintain tolerances between the valve stem and the camshaft lobe under varying engine operating conditions, such as engine rotational speed or operating temperature. 
     Thus, in operation, force from the camshaft lobe is translated through the rocker arm to the lash adjuster and the valve stem. To that end, the rocker arm extends between and engages the lash adjuster and the valve stem, and also includes a bearing that engages the camshaft lobe. The bearing is typically supported by a shaft that is fixed to the rocker arm. The bearing rotates on the shaft, follows the profile of the lobe of the camshaft, and translates force to the rocker arm, via the shaft, so as to open the valve. 
     Each of the components of an engine valvetrain system of the type described above must cooperate to effectively translate movement from the camshaft so as to operate the valves properly at a variety of engine rotational speeds and operating temperatures and, at the same time, maintain correct valvetrain tolerances. In addition, each of the components must be designed not only to facilitate improved performance and efficiency, but also so as to reduce the cost and complexity of manufacturing and assembling the valvetrain system, as well as reduce wear in operation. While engine valvetrain systems known in the related art have generally performed well for their intended purpose, there remains a need in the art for an engine valvetrain system that has superior operational characteristics, and, at the same time, reduces the cost and complexity of manufacturing the components of the system. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages in the related art in a rocker arm assembly for use in an internal combustion engine valvetrain having a valve, a lash adjuster, and a camshaft having a lobe. The rocker arm assembly includes a shaft, a bearing rotatably supported by the shaft for engaging the lobe of the camshaft, and a rocker arm. The rocker arm has a pad for engaging the valve, and a socket spaced from the pad for engaging the lash adjuster. A pair of walls are disposed between the pad and the socket. Each of the walls has an inner wall surface and an outer wall surface. The walls define a valley between the inner wall surfaces for accommodating the shaft. A pair of upwardly-opening arc-shaped bearing surfaces are disposed longitudinally between the pad and the socket and are spaced laterally from each other. The arc-shaped bearing surfaces rotatably support the shaft when the bearing engages the lobe of the camshaft. A retention element is formed in each of the side walls with a depressed portion spaced laterally from the outer wall surface, and a lip portion arranged under the depressed portion and extending from the wall at least partially into the valley. The lip portions of the retention elements are disposed in spaced relation above the arc-shaped bearing surfaces such that the shaft is prevented from moving out of the valley in absence of engagement between the bearing and the lobe of the camshaft. 
     In addition, the present invention is also directed towards a method of forming a retention element in a rocker arm of a rocker arm assembly having a shaft and a bearing rotatably supported by the shaft for engaging the lobe of a camshaft of an internal combustion engine valvetrain. The valvetrain further includes a valve and a lash adjuster. The method includes the steps of: providing a rocker arm having: a pad for engaging the valve; a socket spaced from the pad for engaging the lash adjuster; a pair of walls disposed between the paid and the socket with each of the walls having an inner wall surface and an outer wall surface, the walls defining a valley between the inner wall surfaces for accommodating the shaft; and a pair of upwardly-opening arc-shaped bearing surfaces spaced laterally from each other and disposed longitudinally between the pad and the socket for rotatably supporting the shaft when the bearing engages the lobe of the camshaft; providing a tool having: a shank extending to a shank end; an insertion portion extending longitudinally from the shank end; and a pair of braces extending from the shank laterally away from each other and arranged longitudinally adjacent to the shank end, the braces each having a tip surface with a protrusion extending laterally therefrom towards the insertion portion; positioning the insertion portion of the tool above the arc-shaped bearing surfaces of the rocker arm; and urging the insertion portion of the tool towards the arc-shaped bearing surfaces of the rocker arm so as to bring at least a portion of the braces of the tool into engagement with the walls of the rocker arm to form a retention element in each of the walls. 
     In this way, the present invention significantly reduces the complexity and packaging size of the valvetrain system and its associated components. Moreover, the present invention reduces the cost of manufacturing valvetrain systems that have superior operational characteristics, such as improved engine performance, control, lubrication, efficiency, as well as reduced vibration, noise generation, engine wear, and packaging size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features, and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description taken in connection with the accompanying drawing wherein: 
         FIG. 1  is a partial front sectional view of an automotive engine with an overhead-cam configuration including a valvetrain mounted in a cylinder head. 
         FIG. 2  is a front view of a portion of the valvetrain of  FIG. 1  showing a valve, a camshaft, a lash adjuster, and a rocker arm assembly according to one embodiment of the present invention. 
         FIG. 3  is a perspective view of a first embodiment of the rocker arm assembly according to the present invention including a shaft, a bearing, and a rocker arm. 
         FIG. 4  is an exploded perspective view of the rocker arm assembly of  FIG. 3 . 
         FIG. 5  is a front plan view of the rocker arm assembly of  FIG. 3  with the shaft, a portion of the bearing, and internal features and structure of the rocker arm shown in phantom. 
         FIG. 6  is a sectional view taken along a longitudinal centerline of the rocker arm assembly of  FIG. 3 . 
         FIG. 7  is a sectional view taken along a lateral centerline of the shaft of the rocker arm assembly of  FIG. 3 . 
         FIG. 8  is a perspective view of the rocker arm of  FIG. 3  shown having retention elements formed according to one embodiment of the present invention. 
         FIG. 9  is a perspective view of the rocker arm of  FIG. 8  shown prior to formation of the retention elements. 
         FIG. 10  is a perspective view of the rocker arm of  FIG. 9  shown adjacent to a tool for forming the retention elements depicted in  FIG. 8  according to one embodiment of the present invention. 
         FIG. 11  is a perspective view of the rocker arm and tool of  FIG. 10  shown with the tool engaging the rocker arm to form the retention elements depicted in  FIG. 8 . 
         FIG. 12  is a broken sectional view taken along a lateral centerline of the rocker arm assembly and the tool of  FIG. 11  depicting formation of the retention elements by the tool. 
         FIG. 13  is a broken perspective view of the tool of  FIGS. 10-12 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, where like numerals are used to designate like structure, a portion of an internal combustion engine is illustrated at  20  in  FIG. 1 . The engine  20  includes a block  22  and a cylinder head  24  mounted to the block  22 . A crankshaft  26  is rotatably supported in the block  22 , and a camshaft  28  is rotatably supported in the block  22  spaced from the crankshaft  26 . The crankshaft  26  drives the camshaft  28  via a timing chain or belt (not shown, but generally known in the art). The block  22  typically includes one or more cylinders  30  in which a piston  32  is supported for reciprocal motion therealong. The piston  32  is pivotally connected to a connecting rod  34 , which is also connected to the crankshaft  26 . In operation, combustion in the cylinders  30  of the engine  20  moves the pistons  22  in reciprocal fashion within the cylinders  30 . 
     Reciprocal motion of the piston  32  generates rotational torque that is subsequently translated by the crankshaft  26  to the camshaft  28  which, in turn, cooperates with a valvetrain, generally indicated at  36 , to control the flow and timing of intake and exhaust gasses between the cylinder head  24 , the cylinders  30 , and the outside environment. Specifically, the camshaft  28  controls what is commonly referred to in the art as “valve events,” whereby the camshaft  28  effectively actuates valves  38  supported in the cylinder head  24  at specific time intervals with respect to the rotational position of the crankshaft  26 , so as to effect a complete thermodynamic cycle of the engine  20 . To that end, the valves  38  each have a head  40  and a stem  42  extending therefrom (see  FIG. 2 ). The valve head  40  is configured to periodically seal against the cylinder head  24  adjacent the cylinder  30 , such as with a compression spring  44  supported in the cylinder head  24 , disposed about the valve stem  42 , and operatively attached to the valve  38  via a retainer  46 . The valve stem  42  is typically supported by a valve guide  48  that is also operatively attached to the cylinder head  24 , whereby the valve stem  42  extends through the valve guide  48  and travels therealong in response to force translated via rotation of the camshaft  28  (see  FIG. 2 ). To this end, the camshaft  28  has lobes  50  with a predetermined profile configured to cooperate with the valvetrain  36  such that radial movement from the camshaft  28  is translated into linear movement of the valves  38  so as to control the valve events, as discussed above. More specifically, the valvetrain  36  also includes a lash adjuster  52  and a rocker arm assembly, generally indicated at  54  and according to the present invention. Conventional lash adjusters  52  utilize hydraulic oil pressure from the engine  20  to maintain tolerances between the valve stem  42  and the camshaft lobe  50  under varying engine operating conditions, such as engine rotational speed or operating temperature. To that end, the lash adjuster  52  is supported in the cylinder head  24  and is spaced from the valve stem  42  and cooperates with the rocker arm assembly  54  to effect translation of force to the valve  38 , as will be described in greater detail below. While the lash adjuster  52  shown in  FIGS. 1 and 2  is a hydraulic lash adjuster, it will be appreciated that the lash adjuster  52  could be of any suitable type or configuration without departing from the scope of the present invention. 
     Those having ordinary skill in the art will recognize the valvetrain  36  described herein as forming what is commonly referred as an “overhead cam” configuration, whereby rotation of the camshaft  28  is translated to the rocker arm assembly  54  which, in turn, engages and directs force to the valve  38  and the lash adjuster  52 . While the engine  20  illustrated in  FIG. 1  is an inline-configured, single overhead cam, spark-ignition, Otto-cycle engine, those having ordinary skill in the art will appreciate that the engine  20  could be of any suitable configuration, with any suitable number of cylinder heads  24  and/or camshafts  28  disposed in any suitable way, controlled using any suitable thermodynamic cycle, and with any suitable type of valvetrain  36 , without departing from the scope of the present invention. By way of non-limiting example, the engine  20  could be a so-called “dual overhead-cam V8” with an eight-cylinder V-configured block  22  and a pair of cylinder heads  24  each supporting a respective pair of camshafts  28  (not shown, but generally known in the art). Further, while the engine  20  is configured for use with automotive vehicles, those having ordinary skill in the art will appreciate that the present invention could be used in any suitable type of engine  20 . By way of non-limiting example, the present invention could be used in connection with passenger or commercial vehicles, motorcycles, all-terrain vehicles, lawn care equipment, heavy-duty trucks, trains, airplanes, ships, construction vehicles and equipment, military vehicles, or any other suitable application without departing from the scope of the present invention. 
     As noted above, the present invention is directed toward a rocker arm assembly  54  for use in the engine  20  valvetrain  36 . More specifically, the rocker arm assembly  54  cooperates with the valve  38 , the lobe  50  of the camshaft  28 , and the lash adjuster  52 . As will be appreciated from the subsequent description below, the rocker arm assembly  54  can be configured in a number of different ways without departing from the scope of the present invention. 
     Referring now to  FIGS. 3-7 , the rocker arm assembly  54  of the present invention is shown. The rocker arm assembly  54  includes a shaft  56 , a bearing  58 , and a rocker arm, generally indicated at  60 . The bearing  58  is rotatably supported by the shaft  56  and is adapted to engage the lobe  50  of the camshaft  28 . More specifically, the bearing  58  follows the profile of the lobe  50  such that when the camshaft  28  rotates, force is translated to the bearing  58  which simultaneously rotates the bearing  58  about the shaft  56  and urges the bearing  58  away from the camshaft  28  toward the valve  38  and the lash adjuster  52 . While the representative embodiment of the rocker arm assembly  54  depicted throughout the drawings employs a conventional journal bearing arrangement with the bearing  58  supported directly on the shaft  56 , those having ordinary skill in the art will appreciate that the bearing  58  could be indirectly supported on the shaft  56 , such as with a plurality of needle bearing elements (not shown) interposed between the shaft and the bearing in a conventional needle bearing arrangement. However, those having ordinary skill in the art will appreciate that any suitable bearing arrangement could be utilized, with or without the use of needle bearing elements, without departing from the scope of the present invention. 
     It will be appreciated that force which urges the bearing  58  away from the camshaft  28  is translated to the rocker arm  60  via the shaft  56 , whereby the rocker arm  60  subsequently translates force to the lash adjuster  52  and the valve stem  42  to open the valve  38  so as to control the flow of gasses into (or, out of) the cylinder  30 , as discussed above. To that end, the rocker arm  60  includes a pad  62  for engaging the valve  38 , and a socket  64  spaced from the pad  62  for engaging the lash adjuster  52 . The pad  62  and the socket  64  are adapted to press against and remain substantially engaged to the valve  38  and the lash adjuster  52 , respectively, as the camshaft  28  rotates in operation (see also  FIG. 2 ). In one embodiment, the rocker arm  60  also includes a pair of pad braces  66  depending from the pad  62  that help align the rocker arm assembly  54  to the valve  38 , such as during installation of the rocker arm assembly  54  into the cylinder head  24 . Similarly, the socket  64  has a curved pocket  68  for accommodating and aligning with a portion of the lash adjuster  52  (not shown in detail, but generally known in the art). In the representative embodiment illustrated herein, the rocker arm  60  also includes a lubrication port, generally indicated at  70 , formed through the socket  64  and in communication with the curved pocket  68  for directing lubricating oil from to lash adjuster  52  towards the bearing  58  and the shaft  56  in operation. However, those having ordinary skill in the art will appreciate that the pad  62  and/or socket  64  could be configured in any suitable way without departing from the scope of the present invention. 
     As is shown best in  FIG. 4 , the rocker arm  60  includes a pair of walls  72  disposed between the pad  62  and the socket  64 . The walls  72  each have an inner wall surface  74  and an outer wall surface  76 . The walls  72  define a valley, generally indicated at  78 , between the inner wall surfaces  74  for accommodating the shaft  56 . The rocker arm  60  also includes a pair of upwardly-opening arc-shaped bearing surfaces, generally indicated at  80 . The arc-shaped bearing surfaces  80  are spaced laterally from each other and are disposed longitudinally between the pad  62  and the socket  64 . The arc-shaped bearing surfaces  80  rotatably support the shaft  56  when the bearing  58  engages the lobe  50  of the camshaft  28 , as is described in greater detail below. The rocker arm  60  also includes a pair of retention elements  82  formed in each of the walls  72  with a depressed portion  84  spaced laterally from the outer wall surface  76  and a lip portion  86  arranged under the depressed portion  84  and extending from the wall  72  at least partially into the valley  78 . The lip portions  86  of the retention elements  82  are disposed in spaced relation above the arc-shaped bearing surfaces  80  such that the shaft  56  is prevented from moving out of the valley  78  in absence of engagement between the bearing  58  and the lobe  50  of the camshaft  28 . 
     When the rocker arm assembly  54  is installed into the cylinder head  24  and engages the lobe  50  of the camshaft  28 , a certain amount of pre-load force is exerted against the bearing  58  which, in turn, pushes the shaft  56  against the arc-shaped bearing surfaces  80 , thereby pushing the rocker arm  60  against the valve  38  and the lash adjuster  52 . This pre-load force keeps the shaft  56  against the arc-shaped bearing surfaces  80  in operation. As such, the shaft  56  need only be radially supported by the rocker arm  60  and not radially constrained. To this end, the retention elements  82  keep the shaft  56  in the valley  78  until the rocker arm assembly  54  is installed; specifically, until the bearing  58  engages the lobe  50  of the camshaft  28 . In one embodiment, the retention elements  82  are spaced above the shaft  56  when the shaft engages the arc-shaped bearing surfaces  80  (see  FIG. 7 ). 
     In the embodiments illustrated throughout the figures, the rocker arm  60  is formed as a unitary, one-piece component. More specifically, the rocker arm  60  is manufactured from a single piece of sheet steel that is stamped and bent to shape and the retention elements  82  subsequently formed therein, as described in greater detail below. Thus, as shown best in  FIG. 7 , the arc-shaped bearing surfaces  80  each have a bearing width  88  that is substantially equal to a wall width  90  of the walls  72 . However, those having ordinary skill in the art will appreciate that the rocker arm  60  could be formed or otherwise manufactured in any suitable way from any suitable material without departing from the scope of the present invention. 
     As noted above, the retention elements  82  extend from the walls  72  into the valley  78 . As shown best in  FIGS. 4 and 7 , in one embodiment, the retention elements  82  each extend from one of the inner wall surfaces  74  of the walls  72  to a respective retention element edge  92 , with the lip portions  86  merging the each of the retention element edges  92  with the respective walls  72 . As shown best in  FIG. 7 , the lip portions  86  have a substantially curved profile. Similarly, as best shown in  FIGS. 4 and 8 , in one embodiment, the depressed portions  84  of the retention elements  82  of the rocker arm  60  have a substantially cylindrical profile. In one embodiment, the arc-shaped bearing surfaces  80  each have an inner lateral edge  94  and an outer lateral edge  96 , and the retention element edges  92  are each positioned: laterally between the inner lateral edge  94  and the outer lateral edge  96  of the respective arc-shaped bearing surface  80 ; and vertically above the respective arc-shaped bearing surfaces  80  (see  FIG. 7 ). However, it will be appreciated that the edges  92 ,  94 ,  96  and/or the lip portion  86  be configured in a number of different ways, without departing from the scope of the present invention. By way of non-limiting example, while the upwardly-opening arc-shaped bearing surfaces  80  are each formed with a generally U-shaped surfaces having a single radius of curvature, it will be appreciated that the bearing surfaces  80  could be defined by any suitable arrangement of continuous or discrete surfaces which cooperate to rotatably support the shaft  56  in response to engagement between the bearing  58  and the lobe  50  of the camshaft  28 , without departing from the scope of the present invention. Moreover, it will be appreciated the retention elements  82  could be configured in any suitable way sufficient to keep the shaft  56  in the valley  78  until the bearing  58  engages the lobe  50  of the camshaft  28  without departing from the scope of the present invention. 
     As noted above, the shaft  56  rotates with respect to the arc-shaped bearing surfaces  80 . By allowing the shaft  56  to rotate independent from the bearing  58 , spalling is substantially eliminated that may otherwise occur between the shaft  56  and the bearing  58  and/or arc-shaped bearing surfaces  80 . Thus, the rocker arm assembly  54  can be designed to optimize material and/or application specifications so as to decrease cost and maximize component life. In addition to rotating with respect to the rocker arm  60 , the shaft  56  may also be configured to move axially with respect to the rocker arm  60  so as to further reduce wear and increase component life. To that end, in one embodiment, the shaft  56  has a shaft length  98 , the rocker arm  60  has an arc outer lateral edge distance  100  measured between the outer lateral edges  96  of the arc-shaped bearing surfaces  80 , and the shaft length  98  is less than the arc outer lateral edge distance  100  (see  FIG. 7 ). Similarly, in one embodiment, the rocker arm  60  has a retention element distance  102  measured between the retention element edges  92  of the retention elements  82 , and the shaft length  98  is less than the retention element distance  102 . Further, in one embodiment, the shaft  56  has a shaft diameter  104  and the retention elements of the rocker arm  60  each have a longitudinal element width  106  that is less than the shaft diameter  56  (see  FIG. 5 ). These relationships help ensure that the shaft  56  remains within the valley  78  while, at the same time, allowing for rotation and slight axial movement so as to optimize performance and component life, as discussed above. In the representative embodiment illustrated herein, the retention elements  82  are similarly shaped and, thus, have substantially equivalent longitudinal element widths  106 . However, as noted above, the retention elements  82  could be configured in any suitable way, with the same or different configurations from one another, without departing from the scope of the present invention. 
     Referring now to  FIGS. 8-13 , as noted above, the present invention is also directed towards a method of forming the retention elements  82  in the rocker arm  60  of the rocker arm assembly  54 . To that end, the method concerns forming retention elements  82  in an unfinished rocker arm  60 A (see  FIG. 9  and compare to  FIG. 8 ) using a tool, generally indicated at  108  (see  FIGS. 10-13 ), as is described in greater detail below. As is best shown in  FIG. 13 , the tool  108  has a shank  110  which extends to a shank end  112 , an insertion portion  114  extending longitudinally from the shank end  112 , and a pair of braces  116  extending from the shank  110  laterally away from each other. Here, the braces  116  are arranged longitudinally adjacent to the shank end  112 , and each has a tip surface  118  with a protrusion  120  extending laterally therefrom towards the insertion portion  114 . Once the unfinished rocker arm  60 A and the tool  108  are provided, the method includes the steps of positioning the insertion portion  114  of the tool  108  above the arc-shaped bearing surfaces  80  of the unfinished rocker arm  60 A (see  FIG. 10 ), and then urging the insertion portion  114  of the tool  108  towards the arc-shaped bearing surfaces  80  of the unfinished rocker arm  60 A (see  FIG. 11 ) so as to bring at least a portion of the braces  116  of the tool  108  into engagement with the walls  72  of the unfinished rocker arm  60 A to form a retention element  82  in each of the walls  72  of the rocker arm  60  (see  FIGS. 12 and 8 ). In one embodiment, the protrusions  120  of the braces  116  are brought into engagement with the walls  72  of the unfinished rocker arm  60 A to form the depressed portion  84  and the lip portion  86 , as described above. 
     With reference again to  FIG. 13 , the shank end  112  of the shank  110  has a generally rectangular profile, and the insertion portion  114  has a generally inverted U-shaped profile extending longitudinally from the shank end  112 . In the representative embodiment illustrated herein, the shank  110  has first and second pairs of shank sides  122 ,  124 , and the insertion portion  114  has first and second pairs of insertion sides  126 ,  128 . The first pair of shank sides  122  are formed integrally with the first pair of insertion sides  126 , and the second pair of insertion sides  128  are spaced inwardly from the second pair of shank sides  124  so as to define a pair of steps  130 . Here, the insertion portion  114  is shaped to be accommodated in the valley  78 , and may advantageously be spaced from the arc-shaped bearing surfaces  80 , while the retention elements  82  are being formed (see also  FIG. 12 ). The braces  116  have a generally inverted V-shaped profile extending laterally outwardly from the first pair of shank sides  122  to respective brace sides  132 . The protrusions  120  similarly extend laterally outwardly from the first pair of shank sides  122  and terminate at respective protrusion sides  134  spaced laterally between the respective first shank side  122  and brace side  132 . 
     In the representative embodiment illustrated herein, the tip surfaces  118  are aligned with the shank end  112 , and the protrusions  120  extend from the respective tip surfaces  118 , longitudinally away from the shank  110 . Here, the protrusions  120  and the tip surfaces  118  are shaped to form the depressed portion  84  and, thus, the lip portion  86  in response to engagement with the walls  72  of the unfinished rocker arm  60 A, whereby the protrusions  120  form the complimentarily-shaped cylindrical depressed portions  84  with the top surface  118  abutting the wall  72  adjacent thereto (see  FIG. 12 ). 
     In this way, the rocker arm assembly  54  and method of the present invention significantly reduces the cost and complexity of manufacturing and assembling the valvetrain  36  and associated components. Specifically, it will be appreciated that the configuration of the retention elements  82  enables consistent and simple installation of the shaft  56  to the rocker arm  60  while, at the same time, ensuring that the shaft  56  is kept within the valley  78  until the bearing  58  engages the lobe  50  of the camshaft  28 . Specifically, it will be appreciated that the configuration of the rocker arm assembly  54  allows the shaft  56  to be retained with respect to the rocker arm  60  until the rocker arm assembly  54  is installed in the cylinder head  24 , thereby significantly reducing the cost and complexity of manufacturing and assembling the valvetrain  36 . Further, it will be appreciated that the present invention affords opportunities for superior engine  20  operational characteristics, such as improved performance, component life and longevity, efficiency, weight, load and stress capability, and packaging orientation. 
     The invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.