Patent Publication Number: US-8113163-B2

Title: Concentric camshaft and method of assembly

Description:
FIELD 
     The present disclosure relates to engine camshaft assemblies. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Engines typically include a camshaft to actuate intake and exhaust valves. Some camshafts are concentric camshafts that provide for relative rotation between, for example, the intake and exhaust lobes. The intake lobes may be fixed to an outer shaft for rotation with the shaft and the exhaust lobes may be rotatably supported on the shaft. Alternatively, the exhaust lobes may be fixed to the outer shaft for rotation with the shaft and the intake lobes may be rotatably supported on the shaft. In any arrangement, the lobes that are rotationally fixed on the outer shaft may be axially and rotationally located on the outer shaft in a predetermined orientation before being fixed thereto. The locating may include engaging an outer radial surface of the lobe, necessitating further machining of the lobe. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not comprehensive of its full scope or all of its features. 
     A camshaft may include a first shaft, a stop member, and a first lobe member. The first shaft may include an outer radial surface having a first recess extending radially therein. The stop member may be axially fixed within the first recess. The first lobe member may define an inner bore located on the outer radial surface of the first shaft. The first lobe member may include a second recess extending radially into the inner bore. The stop member may extend into the second recess to axially locate the first lobe member on the first shaft. 
     The camshaft may be included in an engine assembly and may be rotatably supported on an engine structure. 
     A method of locating a cam lobe member on a camshaft may include forming a first recess in an outer radial surface of a first shaft of the camshaft. A stop member may be secured axially within the first recess. The lobe member may be located axially on the outer radial surface of the first shaft. The stop member may be received within a second recess located in an inner bore of the lobe member. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic illustration of an engine assembly according to the present disclosure; 
         FIG. 2  is a perspective view of the camshaft and cam phaser of  FIG. 1 ; 
         FIG. 3  is a perspective exploded view of the camshaft of  FIG. 1 ; 
         FIG. 4  is an additional perspective exploded view of the camshaft of  FIG. 1 ; 
         FIG. 5  is a perspective view of a lobe member of the camshaft of  FIG. 1 ; and 
         FIG. 6  is a fragmentary section view of the camshaft of  FIG. 1 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Examples of the present disclosure will now be described more fully with reference to the accompanying drawings. The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring now to  FIG. 1 , an exemplary engine assembly  10  is schematically illustrated. The engine assembly  10  may include an engine  12  including a plurality of cylinders  14  having pistons  16  disposed therein. The engine  12  may further include an intake valve  18 , an exhaust valve  20 , and intake and exhaust valve lift mechanisms  22 ,  24  for each cylinder  14 , as well as a camshaft  26  and a cam phaser  28 . 
     The intake valve lift mechanism  22  may include a pushrod  30  and a rocker arm  32 . The exhaust valve lift mechanism  24  may additionally include a pushrod  30  and a rocker arm  32 . Pushrods  30  may be engaged with the camshaft  26  to actuate the rocker arms  32  and selectively open the intake and exhaust valves  18 ,  20 . While the engine assembly  10  is illustrated as a pushrod engine, it is understood that the present disclosure is not limited to pushrod engines and may be applicable to a variety of other engine configurations as well, such as overhead cam engines. 
     With reference to  FIGS. 2-6 , the camshaft  26  may include first and second shafts  34 ,  36 , a first set of lobe members  38 ,  40 ,  42 ,  44 ,  46 , a second set of lobe members  48 ,  50 ,  52 ,  54 , and fasteners  56 . In the present example, the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46  may form an intake lobe set and the second set of lobe members  48 ,  50 ,  52 ,  54  may form an exhaust lobe set. However, it is understood that alternate arrangements may be provided where the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46  may form an exhaust lobe set and the second set of lobe members  48 ,  50 ,  52 ,  54  may form an intake lobe set. Further, each of the first and second sets of lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54  are not limited to only intake or exhaust valves. For example, the first and second sets of lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54  may each include an intake lobe and/or an exhaust lobe. The first shaft  34  may be fixed for rotation with a first phaser member  58  and the second shaft  36  may be fixed for rotation with a second phaser member  60 . The first and second phaser members  58 ,  60  may be rotatable relative to one another and relative to a rotationally driven member  62  of the phaser  28 . 
     The first shaft  34  may include an annular wall  64  defining an inner bore  66 . The second shaft  36  may be rotatably disposed within the inner bore  66  of the first shaft  34 . The first shaft  34  may include slots  68  and recesses  70  (seen in  FIGS. 4 and 6 ) therethrough and the second shaft  36  may include apertures  72  (seen in  FIG. 3 ) that receive the fasteners  56  therein and couple the second set of lobe members  48 ,  50 ,  52 ,  54  for rotation with the second shaft  36 . The slots  68  may form radial bores through the first shaft  34  and the apertures  72  may form radial bores through the second shaft  36 . The slots  68  in the first shaft  34  may generally allow for a rotational travel of the fasteners  56  therein. 
     As seen in  FIG. 6 , the recesses  70  may have a depth (D) less than a wall thickness (T) of the annular wall  64  of the first shaft  34 . The recesses  70  may each include first and second portions  74 ,  76 . The first portion  74  may extend generally parallel to a rotational axis (A 1 ) of the camshaft  26 , as seen in  FIG. 2 . The second portion  76  may extend generally perpendicular to the first portion  74  and may intersect a first end of the first portion  74 . Stop members  78  may be located within the recesses  70  to axially locate the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46 . Each of the stop members  78  may include a generally longitudinal body extending within the first portion  74  of the recesses  70  and abutting a wall  80  defined by the second portions  76 . The engagement between the stop members  78  and the walls  80  may axially fix the stop members  78  within the recesses  70 . 
     The first set of lobe members  38 ,  40 ,  42 ,  44 ,  46  may engage the stop members  78  to axially locate and rotationally fix the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46  on an outer radial surface of the first shaft  34 . The engagement between each of the lobe members  38 ,  40 ,  42 ,  44 ,  46  and the stop members  78  may be generally similar, therefore lobe member  40  will be discussed in detail with the understanding that the description applies equally to lobe members  38 ,  42 ,  44 ,  46 . 
     The lobe member  40  may include a journal portion  82  and first and second lobes  84 ,  86 . The journal portion  82  and the first and second lobes  84 ,  86  may be rotationally fixed relative to one another. The lobe member  40  may define an inner bore  88  supported on the outer radial surface of the first shaft  34 . The inner bore  88  may include a recess  90  extending into a first end thereof. The recess  90  may include an axial end stop  92  and first and second side walls  94 ,  96 . 
     During assembly, the lobe member  40  may be displaced axially along the outer radial surface of the first shaft  34  in a direction (A 2 ) seen in  FIG. 6 . The recess  90  in the bore  88  of the lobe member  40  may be rotationally aligned with the stop member  78 . The lobe member  40  may be advanced axially along the first shaft  34  until the stop member  78  is received within the recess  90  and abuts the axial end stop  92  therein, axially locating the lobe member  40  relative to the stop member  78 . Since the stop member  78  is axially fixed relative to the wall  80  defined by the recess  70 , the lobe member  40  may be axially fixed relative to the wall  80  of the recess  70  as well. In addition to axially locating the lobe member  40 , the stop member  78  may additionally rotationally fix the lobe member  40  relative to the first shaft  34 . More specifically, the stop member  78  may be rotationally fixed within the first portion  74  of the recess  70 . The stop member  78  may be secured between walls  94 ,  96  of the recess  90  in the lobe member  40 , limiting rotation between the lobe member  40  and the first shaft  34 . 
     By way of non-limiting example, the stop members  78  may be secured within the recesses  70  in a variety of ways including an interference fit engagement. The stop member  78  may be located within the recesses  70  as the first and second sets of lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54  are located on the outer radial surface of the first shaft  34 . More specifically, a first stop member  78  may be located within a first of the recesses  70  at a first end  98  of the first shaft  34 . After the stop member  78  is secured within the recess  70 , the lobe member  38  may be advanced axially along the first shaft  34  in the direction (A 2 ) until engaged with the stop member  78  as discussed above. 
     Next, the lobe member  48  may be advanced axially along the first shaft  34  and axially fixed relative thereto by the fastener  56 . Once the lobe member  48  has been advanced past the adjacent recess  70 , another stop member  78  may be located in the recess  70  and the lobe member  40  may be placed on the first shaft  34  and advanced axially until engaged with the stop member  78 . The process may be continued, alternating between the first and second sets of lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54  until each of the lobe members are located on the first shaft  34 . 
     The use of the stop member  78  in the recesses  70 ,  90  may eliminate the need for machining the outer surfaces of the lobe members after assembly. Specifically, during the location of the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46  on the first shaft  34 , outer radial surfaces of the lobe members may be free from engagement with a tool. Rather, an axial end surface may be engaged by a tool to advance the lobe members along the first shaft  34 . 
     Additionally, as discussed above, the stop members  78  may rotationally fix the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46  relative to the first shaft  34 , reducing the requirements for an additional assembly method used to axially and rotationally fix the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46  to the first shaft  34 . For example, if a ballizing process is used to fix the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46  to the first shaft  34 , a lower deformation requirement of the first shaft  34  may be acceptable. Alternatively, if a shrink fit process is used to fix the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46  to the first shaft  34 , interference fit requirements may be relaxed as well. The stop members  78  may generally reduce the torque-to-turn requirement for a ballizing or shrink fit processes, as the stop members  78  may generally provide the desired torque-to-turn specification. 
     While discussed as a concentric camshaft, it is understood that the present disclosure is not limited to concentric camshafts and applies equally to fixed-lobe camshafts.