Patent Publication Number: US-8534252-B2

Title: Concentric camshaft with varying wall geometry and method of assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/100,770 filed on Apr. 10, 2008 (now U.S. Pat. No. 7,966,983, issued Jun. 28, 2011). The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to engine camshaft assemblies, and more specifically to concentric camshaft assemblies. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Engines typically include a camshaft to actuate intake and exhaust valves. Some camshafts are concentric camshafts that provide for relative rotation between 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 either arrangement, the lobes that are rotatably supported on the shaft may use an outer surface of the outer shaft as a bearing surface. The use of the outer surface of the shaft as a bearing surface may require tighter tolerances for the outer diameter of the outer shaft, and therefore more cumbersome assembly processes that result in additional cost. 
     SUMMARY 
     A camshaft may include a first shaft, a first lobe member, and a second lobe member. The first shaft may include an annular wall defining a first bore. The wall may include a first portion having a first radial outer surface and a second portion having a second radial outer surface that is radially offset relative to the first radial outer surface. The first lobe member may define a second bore having the first portion of the first shaft located therein and frictionally engaged with the first shaft for rotation with the first shaft. The second lobe member may define a third bore having the second portion of the first shaft located therein. The second lobe member may be rotatably disposed on the second portion of the first shaft. 
     A method may include locating first and second lobe members of a camshaft on a first shaft and deforming the first shaft to fix the first lobe member to the first shaft. The first shaft may include an annular wall that defines a first bore and may include a first portion having first radial inner and outer surfaces and a second portion having second radial inner and outer surfaces. The locating of the first lobe member may include the first portion of the first shaft being located within a second bore of the first lobe member. The locating of the second lobe member on the first shaft may include the second portion of the first shaft being located within a third bore of the second lobe member. An outward radial force may be applied from within the first bore to displace the first radial inner surface radially outwardly relative to the second radial inner surface and the first radial outer surface radially outwardly relative to the second radial outer surface. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples 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 illustration 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 of  FIG. 1 ; 
         FIG. 3  is a fragmentary section view of the camshaft of  FIG. 2  in a first state and a tool according to the present disclosure; 
         FIG. 4  is a fragmentary section view of the camshaft and tool of  FIG. 3  in a second state; 
         FIG. 5  is a perspective view of an alternate camshaft according to the present disclosure; 
         FIG. 6  is a fragmentary section view of the camshaft of  FIG. 5  in a first state; and 
         FIG. 7  is a fragmentary section view of the camshaft of  FIG. 5  in a second state. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     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 . The camshaft  26  may be supported by an engine structure such as an engine block. Pushrods  30  may be engaged with the camshaft  26  to actuate the rocker arms  32  and may 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 may be applicable to a variety of other engine configurations as well, such as overhead cam engines, where the camshaft  26  is supported by a cylinder head. 
     With reference to  FIG. 2 , the camshaft  26  may include first and second shafts  34 ,  36 , a first set of lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52  a second set of lobe members  54 ,  55 ,  56 ,  57 ,  58 ,  59 ,  60 ,  61 , bearing journals  62 ,  64 ,  66 ,  68 ,  70  and drive pins  72 . In the present example, the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52  may form an intake lobe set and the second set of lobe members  54 ,  55 ,  56 ,  57 ,  58 ,  59 ,  60 ,  61  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 ,  48 ,  50 ,  52  may form an exhaust lobe set and the second set of lobe members  54 ,  55 ,  56 ,  57 ,  58 ,  59 ,  60 ,  61  may form an intake lobe set. 
     The second shaft  36  may be rotatably disposed within the first shaft  34 . The first shaft  34  may include slots therethrough (not shown) and the second shaft  36  may include apertures  74  that receive the drive pins  72  therein and couple the second set of lobe members  54 ,  55 ,  56 ,  57 ,  58 ,  59 ,  60 ,  61  for rotation with the second shaft  36 . The slots in the first shaft  34  may generally allow for a rotational travel of the pins  72  therein. 
     The first set of lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52  and the bearing journals  62 ,  64 ,  66 ,  68 ,  70  may be fixed for rotation with the first shaft  34 . The engagement between the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52  and the first shaft  34  and the engagement between the bearing journals  62 ,  64 ,  66 ,  68 ,  70  and the first shaft  34  may include a friction fit engagement. The second set of lobe members  54 ,  55 ,  56 ,  57 ,  58 ,  59 ,  60 ,  61  may be disposed between adjacent ones of the first set of lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 . 
     The structure of the first shaft  34  at each of the lobe members  38 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52  and at each of the bearing journals  62 ,  64 ,  66 ,  68 ,  70  may be generally similar. Therefore, the structure of the first shaft  34  at the lobe member  38  and at the bearing journal  62 , the structure of the lobe member  38  and the bearing journal  62 , the engagement between the lobe member  38  and the first shaft  34 , and the engagement between the bearing journal  62  and the first shaft  34  will be described with the understanding that the description applies equally to the lobe members  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52  and the bearing journals  64 ,  66 ,  68 ,  70 . The structure of the first shaft  34  at each of the lobe members  54 ,  55 ,  56 ,  57 ,  58 ,  59 ,  60 ,  61  may be also be generally similar. Therefore, the structure of the first shaft  34  at the lobe member  54 , the structure of the lobe member  54 , and the engagement between the lobe member  54  and the first shaft  34  will be described with the understanding that the description applies equally to the lobe members  55 ,  56 ,  57 ,  58 ,  59 ,  60 ,  61 . 
     With additional reference to  FIG. 3 , the camshaft  26  is schematically illustrated in an initial state before the lobe member  38  and the bearing journal  62  are fixed for rotation with the first shaft  34 . The first shaft  34  may include an annular wall  76  that defines a bore  78 . The annular wall  76  may include first, second, and third portions  80 ,  82 ,  84 . The first portion  80  may be axially aligned with the lobe member  38 , the second portion  82  may be axially aligned with the lobe member  54 , and the third portion  84  may be axially aligned with the bearing journal  62 . 
     The first portion  80  may have a first radial inner surface  86  and a first radial outer surface  88 . The second portion  82  may have a second radial inner surface  90  and a second radial outer surface  92 . The third portion  84  may have a third radial inner surface  94  and a third radial outer surface  96 . In the initial state, the first and third radial inner surfaces  86 ,  94  may be radially offset relative to the second radial inner surface  90 . 
     In the present example, the second radial inner surface  90  may be offset radially outwardly relative to the first and third radial inner surfaces  86 ,  94 . The outward radial extent of the first, second, and third radial outer surfaces  88 ,  92 ,  96  may be generally equal to one another. The lobe member  38  may have a bore  98  that has an outward radial extent that is greater than the initial outward radial extent of the first radial outer surface  88 . The lobe member  54  may have a bore  100  that has an outward radial extent that is greater than the initial outward radial extent of the second radial outer surface  92 . The journal bearing  62  may have a bore  102  that has an outward radial extent that is greater than the initial outward radial extent of the third radial outer surface  96 . 
     For example, the first portion  80  may have an initial inner diameter (D 1   i   i ) and an initial outer diameter (D 1   o   i ) defining a first wall thickness (T 1 ) for the first portion  80 . The second portion  82  may have an initial inner diameter (D 2   i   i ) and an initial outer diameter (D 2   o   i ) defining a second wall thickness (T 2 ) for the second portion  82 . The third portion  84  may have an initial inner diameter (D 3   i   i ) and an initial outer diameter (D 3   o   i ) defining a third wall thickness (T 3 ) for the third portion  84 . The first wall thickness (T 1 ) and the third wall thickness (T 3 ) may be greater than the second wall thickness (T 2 ). The bore  98  of the lobe member  38  may have a first diameter (D 1 ) that is greater than the initial outer diameter (D 1   o   i ) of the first portion  80  forming a first clearance (C 1 ) between the first shaft  34  and the lobe member  38 . The bore  100  of the lobe member  54  may have a second diameter (D 2 ) that is greater than the initial outer diameter (D 2   o   i ) of the second portion  82  forming a second clearance (C 2 ) between the first shaft  34  and the lobe member  54 . The bore  102  of the journal bearing  62  may have a third diameter (D 3 ) that is greater than the initial outer diameter (D 3   o   i ) of the third portion  84  forming a third clearance (C 3 ) between the first shaft  34  and the bearing journal  62 . 
       FIG. 3  additionally illustrates a tool  104  that deforms the first shaft  34 . The tool  104  may include a shaft  106  and a deforming member  108 . The deforming member  108  may have an outward radial extent that is greater than an initial outward radial extent of the first and third radial inner surfaces  86 ,  94  and that is less than the outward radial extent of the third radial inner surface  90 . In the present example, the deforming member  108  may be a spherical member that has a diameter (D 4 ) that is greater than the first and third initial inner diameters (D 1   i   i , D 3   i   i ) and that is less than the second initial inner diameter (D 2   i   i ). 
     During assembly of the camshaft  26 , the lobe member  54  may be located on the second portion  82  of the first shaft  34 , the lobe member  38  may be located on the first portion  80  of the first shaft  34 , and the bearing journal  64  may be located on the third portion  84  of the first shaft  34 . The deforming member  108  of the tool  104  may be forced through the bore  78  of the first shaft  34  to create a frictional engagement (or interference fit) between the lobe member  38  and the first shaft  34  and between the bearing journal  62  and the first shaft  34 . More specifically, the displacement of the deforming member  108  through the bore  78  may generally eliminate the first clearance (C 1 ) and the third clearance (C 3 ), while maintaining the second clearance (C 2 ) due to the relationship between the diameter (D 4 ) of the tool  104  and the first, second, and third initial inner diameters (D 1   i   i , D 2   i   i , D 3   i   i ). 
     With additional reference to  FIG. 4 , the camshaft  26  is schematically illustrated in a final state where the lobe member  38  and the bearing journal  64  are fixed for rotation with the first shaft  34 . In the final state, the first radial outer surface  88  of the first shaft  34  and the third radial outer surface  96  of the first shaft  34  may each have an outward radial extent that is greater than an outward radial extent of the second radial outer surface  92  of the first shaft  34 . The outward radial extent of the first radial outer surface  88  may be generally similar to the outward radial extent of the bore  98  of the lobe member  38  and the outward radial extent of the third radial outer surface  96  may be generally similar to the outer radial extent of the bore  102  of the bearing journal  62 . Therefore, the lobe member  38  may be frictionally engaged with the first portion  80  of the first shaft  34  and the bearing journal  62  may be frictionally engaged with the third portion  84  of the first shaft  34 . 
     For example, the first portion  80  may have a final inner diameter (D 1   i   f ) and a final outer diameter (D 1   o   f ), the second portion  82  may have a final inner diameter (D 2   i   f ) and a final outer diameter (D 2   o   f ), and the third portion  84  may have a final inner diameter (D 3   i   f ) and a final outer diameter (D 3   o   f ). The bore  98  of the lobe member  38  may have a first diameter (D 1 ) that is approximately equal to the final outer diameter (D 1   o   f ) of the first portion  80  frictionally locking the lobe member  38  for rotation with the first shaft  34 . The bore  100  of the lobe member  54  may have a second diameter (D 2 ) that is greater than the final outer diameter (D 2   o   f ) of the second portion  82 . The final outer diameter (D 2   o   f ) of the second portion  82  may be approximately equal to the initial outer diameter (D 2   o   i ) of the second portion  82 , maintaining the second clearance (C 2 ) between the first shaft  34  and the lobe member  54 . The bore  102  of the journal bearing  62  may have a third diameter (D 3 ) that is approximately equal to the final outer diameter (D 3   o   f ) of the third portion  84 , frictionally locking the bearing journal  62  for rotation with the first shaft  34 . The final inner diameter (D 1   i   f ) of the first portion and the final inner diameter (D 3   i   f ) of the third portion may be generally equal to the diameter of the deforming member  108 . 
     Referring now to  FIGS. 5-7 , an alternate camshaft  226  is shown. The camshaft  226  may be incorporated into an engine assembly similar to the engine assembly  10  and may function similar to the camshaft  26 . The camshaft  226  may include first and second shafts  234 ,  236 , a first set of lobe members  238 ,  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252  a second set of lobe members  254 ,  255 ,  256 ,  257 ,  258 ,  259 ,  260 ,  261 , bearing journals  262 ,  264 ,  266 ,  268 ,  270  and drive pins  272 . In the present example, the first set of lobe members  238 ,  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252  may form an intake lobe set and the second set of lobe members  254 ,  255 ,  256 ,  257 ,  258 ,  259 ,  260 ,  261  may form an exhaust lobe set. However, it is understood that alternate arrangements may be provided where the first set of lobe members  238 ,  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252  may form an exhaust lobe set and the second set of lobe members  254 ,  255 ,  256 ,  257 ,  258 ,  259 ,  260 ,  261  may form an intake lobe set. 
     The second shaft  236  may be rotatably disposed within the first shaft  234 . The first shaft  234  may include slots therethrough (not shown) and the second shaft  236  may include apertures  274  that receive the drive pins  272  therein and couple the second set of lobe members  254 ,  255 ,  256 ,  257 ,  258 ,  259 ,  260 ,  261  for rotation with the second shaft  236 . The slots in the first shaft  234  may generally allow for a rotational travel of the pins  272  therein. 
     The first set of lobe members  238 ,  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252  and the bearing journals  262 ,  264 ,  266 ,  268 ,  270  may be fixed for rotation with the first shaft  234 . The engagement between the first set of lobe members  238 ,  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252  and the first shaft  234  and the engagement between the bearing journals  262 ,  264 ,  266 ,  268 ,  270  and the first shaft  234  may include a friction fit engagement. The second set of lobe members  254 ,  255 ,  256 ,  257 ,  258 ,  259 ,  260 ,  261  may be disposed between adjacent ones of the first set of lobe members  238 ,  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252 . 
     The structure of the first shaft  234  at each of the lobe members  238 ,  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252  and at each of the bearing journals  262 ,  264 ,  266 ,  268 ,  270  may be generally similar. Therefore, the structure of the first shaft  234  at the lobe member  238  and at the bearing journal  262 , the structure of the lobe member  238  and the bearing journal  262 , the engagement between the lobe member  238  and the first shaft  234 , and the engagement between the bearing journal  262  and the first shaft  234  will be described with the understanding that the description applies equally to the lobe members  240 ,  242 ,  244 ,  246 ,  248 ,  250 ,  252  and the bearing journals  264 ,  266 ,  268 ,  270 . The structure of the first shaft  234  at each of the lobe members  254 ,  255 ,  256 ,  257 ,  258 ,  259 ,  260 ,  261  may be also be generally similar. Therefore, the structure of the first shaft  234  at the lobe member  254 , the structure of the lobe member  254 , and the engagement between the lobe member  254  and the first shaft  234  will be described with the understanding that the description applies equally to the lobe members  255 ,  256 ,  257 ,  258 ,  259 ,  260 ,  261 . 
     With reference to  FIG. 6 , the camshaft  226  is shown in an initial state before the first set of lobe members  238  and the bearing journals  262  are fixed for rotation with the first shaft  234 . The first shaft  234  may include an annular wall  276  that defines a bore  278 . The annular wall  276  may include first, second, and third portions  280 ,  282 ,  284 . The first portion  280  may be axially aligned with the lobe member  238 , the second portion  282  may be axially aligned with the lobe member  254 , and the third portion  284  may be axially aligned with the bearing journal  262 . 
     The first portion  280  may have a first radial inner surface  286  and a first radial outer surface  288 . The second portion  282  may have a second radial inner surface  290  and a second radial outer surface  292 . The third portion  284  may have a third radial inner surface  294  and a third radial outer surface  296 . In the initial state, the first and third radial inner surfaces  286 ,  294  may be radially offset relative to the second radial inner surface  290 . 
     In the present example, the second radial inner surface  290  may be offset radially inwardly relative to the first and third radial inner surfaces  286 ,  294 . The outward radial extent of the first, second, and third radial outer surfaces  288 ,  292 ,  296  may be generally equal to one another. The lobe member  238  may have a bore  298  that has an outward radial extent that is greater than the initial outward radial extent of the first radial outer surface  288 . The lobe member  254  may have a bore  300  that has an outward radial extent that is greater than the initial outward radial extent of the second radial outer surface  292 . The journal bearing  262  may have a bore  302  that has an outward radial extent that is greater than the initial outward radial extent of the third radial outer surface  296 . 
     For example, the first portion  280  may have an initial inner diameter (D 11   i   i ) and an initial outer diameter (D 11   o   i ) defining a first wall thickness (T 11 ) for the first portion  280 . The second portion  282  may have an initial inner diameter (D 22   i   i ) and an initial outer diameter (D 22   o   i ) defining a second wall thickness (T 22 ) for the second portion  282 . The third portion  284  may have an initial inner diameter (D 33   i   i ) and an initial outer diameter (D 33   o   i ) defining a third wall thickness (T 33 ) for the third portion  284 . The first wall thickness (T 11 ) and the third wall thickness (T 33 ) may be less than the second wall thickness (T 22 ). The bore  298  of the lobe member  238  may have a first diameter (D 11 ) that is greater than the initial outer diameter (D 11   o   i ) of the first portion  280  forming a first clearance (C 11 ) between the first shaft  234  and the lobe member  238 . The bore  300  of the lobe member  254  may have a second diameter (D 22 ) that is greater than the initial outer diameter (D 22   o   i ) of the second portion  282  forming a second clearance (C 22 ) between the first shaft  234  and the lobe member  254 . The bore  302  of the journal bearing  262  may have a third diameter (D 33 ) that is greater than the initial outer diameter (D 33   o   i ) of the third portion  284  forming a third clearance (C 33 ) between the first shaft  234  and the bearing journal  262 . 
     During assembly of the camshaft  226 , the lobe member  254  may be located on the second portion  282  of the first shaft  234 , the lobe member  238  may be located on the first portion  280  of the first shaft  234 , and the bearing journal  264  may be located on the third portion  284  of the first shaft  234 . A pressurized fluid may be supplied within the bore  278  of the first shaft  234  to create a frictional engagement (or interference fit) between the lobe member  238  and the first shaft  234  and between the bearing journal  262  and the first shaft  234 . More specifically, the pressurized fluid within the bore  278  may generally eliminate the first clearance (C 1 ) and the third clearance (C 3 ), while maintaining the second clearance (C 2 ) due to the greater wall thickness (T 22 ) of the second portion  282  of the first shaft  234 . 
     With reference to  FIG. 7 , the camshaft  226  is shown in a final state where the first set of lobe members  238  and the bearing journals  262  are fixed for rotation with the first shaft  234 . In the final state, the first radial outer surface  288  of the first shaft  234  and the third radial outer surface  296  of the first shaft  234  may each have an outward radial extent that is greater than an outward radial extent of the second radial outer surface  292  of the first shaft  234 . The outward radial extent of the first radial outer surface  288  may be generally similar to the outer radial extent of the bore  298  of the lobe member  238  and the outward radial extent of the third radial outer surface  296  may be generally similar to the outer radial extent of the bore  302  of the bearing journal  262 . Therefore, the lobe member  238  may be frictionally engaged with the first portion  280  of the first shaft  234  and the bearing journal  262  may be frictionally engaged with the third portion  284  of the first shaft  234 . 
     For example, the first portion  280  may have a final inner diameter (D 11   i   f ) and a final outer diameter (D 11   o   f ), the second portion  282  may have a final inner diameter (D 22   i   f ) and a final outer diameter (D 22   o   f ), and the third portion  284  may have a final inner diameter (D 334 ) and a final outer diameter (D 33   o   f ). The bore  298  of the lobe member  238  may have a first diameter (D 11 ) that is approximately equal to the final outer diameter (D 11   o   f ) of the first portion  280 , frictionally locking the lobe member  238  for rotation with the first shaft  234 . The bore  300  of the lobe member  254  may have a second diameter (D 22 ) that is greater than the final outer diameter (D 22   o   f ) of the second portion  282 . The final outer diameter (D 22   o   f ) of the second portion  282  may be approximately equal to the initial outer diameter (D 22   o   i ) of the second portion  282 , maintaining the second clearance (C 22 ) between the first shaft  234  and the lobe member  254 . The bore  302  of the journal bearing  262  may have a third diameter (D 33 ) that is approximately equal to the final outer diameter (D 33   o   f ) of the third portion  284  frictionally locking the bearing journal  262  for rotation with the first shaft  234 . The final inner diameter (D 11   i   f ) of the first portion  280  and the final inner diameter (D 334 ) of the third portion  284  may be greater than the initial inner diameter (D 11   i   i ) of the first portion  280  and initial inner diameter (D 33   i   i ) of the third portion  284  due to the deformation caused by the pressurized fluid.