Abstract:
A die cast aluminum front cover plate for application in a vane-type camshaft phaser includes a plurality of bores and a plurality of steel threaded inserts press fitted into the bores. Steel threaded inserts add the required strength to the stator bolt threads to enable a shorter thread engagement, which in turn enables a thinner aluminum front cover plate that may be packaged in tight applications where prior art aluminum front covers cannot be used due to their larger thickness. The steel threaded inserts not only provide a higher stiffness but also have a flanged shape that effectively spreads the clamp load generated during the tightening of the stator bolts further out preventing local clamp load points and, consequently, reducing cover deflection over the span of the front cover plate.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to vane-type camshaft phasers for varying the phase relationship between crankshafts and camshafts in internal combustion engines; more particularly, to such phasers wherein a front cover plate clamps and seals against a stator; and most particularly, to a phaser having an improved front cover plate. 
       BACKGROUND OF THE INVENTION 
       [0002]    Camshaft phasers, also referred to herein simply as a cam phaser, for varying the phase relationship between the crankshaft and a camshaft of an internal combustion engine are well known. A prior art vane-type phaser generally comprises a plurality of outwardly extending vanes on a rotor interspersed with a plurality of inwardly extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is supplied via a multiport oil control valve (OCV), in accordance with an engine control module, to either the advance or the retard chambers as required to meet current or anticipated engine operating conditions. In a typical prior art vane-type camshaft phaser a front cover clamps and seals against a stator to prevent internal oil leakage across the rotor arms. 
         [0003]    A first known front cover is made from powdered metal steel and typically requires significant secondary high-level precision machining, deburring, grinding, and cleaning. Packaging requirements necessitate the front cover geometry to have thin sections that are typically difficult to execute in powdered metal tooling. Especially a section of the cover that interfaces with a bias spring in the assembled cam phaser is prone to cracking because of its thin cross-section. Typically, powdered metal front covers are manufactured to have a thickness of about 7 mm. 
         [0004]    A second known front cover is die cast from aluminum, requires secondary high-level precision machining, and includes a steel insert at a lock pin seat wear interface. Compared to the first known front cover, the aluminum front cover provides mass savings and is not prone to cracking at the interface with the bias spring. However, the aluminum die cast front cover must be thicker than the powdered metal steel front cover, since additional length for adequate stator bolt thread engagement into aluminum threads is needed. This additional length is not acceptable for some applications where packaging is tight. A typical minimum thickness for a die cast aluminum front cover where the threads are cut directly into the aluminum is about 9 mm. Furthermore, the aluminum front cover typically clamps against the stator by tightening the bolts in several locations thereby generating local clamp load points. These local clamp loads may cause deflection to occur in the span of the cover between the bolts. Such deflection of the front cover may reduce the effective clamp load between cover and stator and may increase localized end clearances on top of the rotor arm, which in turn may increase internal oil leakage across the rotor arms. 
         [0005]    What is needed in the art is an improved front cover that fulfills the packaging requirements. 
         [0006]    What is further needed in the art is an improved front cover that effectively spreads the clamp load further out, reducing cover deflection and improving the effective clamp load between cover and stator. 
         [0007]    It is a principal object of the present invention to provide mass reduction while providing a rigid sealing surface. 
         [0008]    It is a further object of the present invention to enable the use of aluminum for manufacturing the front cover of a cam phaser to be packaged in the tightest application by increasing the thread strength of the bolt bores. 
       SUMMARY OF THE INVENTION 
       [0009]    Briefly described, a vane-type camshaft phaser in accordance with the invention for varying the timing of combustion valves in an internal combustion engine includes a rotor having a plurality of vanes disposed in a stator having a plurality of lobes and a front cover plate that clamps and seals against the stator lobes. The front cover plate in accordance with the invention is die cast from aluminum followed by precision machining. The front cover plate includes four bolt bores for receiving stator bolts and a well that receives a hardened, ground bushing functioning as a lock pin seat. Formed steel threaded inserts are press fitted into the bolt bores of the aluminum front cover plate. This adds the required strength to the stator bolt threads to enable a shorter thread engagement, which in turn enables a thinner aluminum front cover plate that may be packaged in tight applications where prior art aluminum front covers cannot be used due to their greater thickness. 
         [0010]    The steel threaded inserts not only provide a higher stiffness but also have a flanged shape that effectively spreads the clamp load generated during the tightening of the stator bolts further out preventing local clamp load points and, consequently, reducing cover deflection over the span of the front cover plate. Reduced cover deflection results in an improved effective clamp load between cover and stator and reduced oil leakage from valve timing advance and valve timing retard chambers formed by the rotor and the stator. 
         [0011]    Furthermore, by utilizing steel inserts having a higher strength than aluminum materials, mass savings, and consequently manufacturing costs savings, compared to prior art powdered metal front covers are achieved by enabling the use of aluminum as material for the front cover plate while fulfilling packaging requirements for tight applications. Still further, the use of steel threaded inserts in accordance with the present invention enables the design of an aluminum die cast front cover plate that has the potential to work with the currently existing envelope at current or lower costs and that enables the use of the existing bias spring. 
         [0012]    Therefore, the addition of steel threaded inserts pressed into the aluminum die cast front cover plate in accordance with the invention solves the problem of aluminum threat strength and localized clamp loads and, therefore, overcomes the shortcomings of prior art aluminum die cast front covers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0014]      FIG. 1  is an exploded isometric view of a vane-type camshaft phaser in accordance with the invention; 
           [0015]      FIG. 2  is an exploded isometric top view of a front cover plate in accordance with the invention; 
           [0016]      FIG. 3  is an isometric top view of the front cover plate with steel threaded inserts installed in accordance with the invention; 
           [0017]      FIG. 4  is an exploded isometric bottom view of the front cover plate in accordance with the invention; 
           [0018]      FIG. 5  is an isometric bottom view of the front cover plate with steel threaded inserts installed in accordance with the invention; and 
           [0019]      FIG. 6  is a cross-sectional view of the front cover plate taken through a bore and a lock pin seat in accordance with the invention. 
       
    
    
       [0020]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Referring to  FIG. 1 , a vane-type cam phaser  10  in accordance with the invention includes a rear cover  12  having bores  14  for receiving bolts  16 . The heads of bolts  16  are received in countersinks in rear cover  12  and the threaded ends of bolts  16  are received in front cover plate  20 . A pulley or sprocket  18  is formed integrally with a stator  22 , also referred to as a stator/sprocket. Pulley or sprocket  18  is typically used for engaging a timing chain or belt (not shown) operated by an engine crankshaft (not shown). Stator  22  is provided with a plurality of inwardly extending lobes  24  circumferentially spaced apart for receiving a rotor  26  including outwardly extending vanes  28  which extend into the spaces between lobes  24 . Hydraulic advance and retard chambers are thus formed between lobes  24  and vanes  28  as known in the art. Each rotor vane  28  is provided with an axial groove along the vane tip for receiving a resilient seal element  32  for sealingly wiping a cylindrically concave inner wall of stator  22 . Likewise, each stator lobe  24  may be provided with an axial groove along the lobe tip for receiving a resilient seal element  32  for sealingly wiping a cylindrically convex outer wall  33  of the hub of rotor  26 . 
         [0022]    Rear cover  12  and front cover plate  20  clamp against stator lobes  24  at opposite sides. Bolts  16  extend through bores  14  included in rear cover  12  and through bores  34  positioned in stator lobes  24  and the threaded ends of bolts  16  are received in threaded inserts  202  press fitted into bores  204  of cover plate  20 . A hub of a target wheel  52  passes through front cover plate  20  and is fixed to rotor  21  for rotation therewith. Target wheel  52  spins in front of a sensor creating timed pattern of high/low signals for the purpose of sensing and/or controlling the position of phaser  10 . A coiled bias spring  36  is disposed in a central well  38  formed in rotor  26  and is anchored to front cover plate  20  by tang  42  for urging rotor  26  to a predetermined rest position relative to the position of the stator, for example, fully retarded at engine shutdown. A locking pin mechanism  44  is received in a longitudinal bore  46  formed in an oversize vane  28  of rotor  26 . A well  206  formed in front cover plate  20  (shown in  FIGS. 4 through 6 ) receives bushing  48  of locking pin mechanism  44  and is utilized as lock pin seat. Locking pin mechanism  44  may rotationally lock and unlock rotor  26  to and from stator  22 . In installation to an engine camshaft, cam phaser  10  is secured via a central bolt (not shown). 
         [0023]    Referring now to  FIGS. 2 and 3 , an improved die cast aluminum front cover plate  20  of a camshaft phaser  10  in accordance with the invention has a generally circular shape with a generally circular central opening  208  and extends longitudinally from an outer surface  216  to an inner surface  218  for a thickness  220 . A groove  210  for receiving tang  42  of bias spring  36  ( FIG. 1 ) extends for a distance from central opening  208  towards the outer perimeter  214  of front cover plate  20  and is formed in outer surface  216  during the die casting process and later machined. A window  236  leading to groove  210  is machined into front cover plate  20 . A lip  212  for guiding bias spring  36  extends into central opening  208  proximate to groove  210 . Front cover plate  20  includes bores  204  positioned in indentations  222  and proximate to outer perimeter  214 . Bores  204  are also positioned to be in line with stator bores  34  included in stator lobes  24 , as shown in  FIG. 1 . If stator  22  includes four lobes  24  and thus four bores  34  as shown in  FIG. 1 , front cover plate  20  includes four bores  204  for receiving four bolts  16 . In a currently preferred embodiment, bores  204  are machined into front cover plate  20 . Bores  204  and indentations  222  are designed to receive steel threaded inserts  202 . Bore  204  receives knurled shaft  226  and flange  228  rests in indentation  222 . Additional indentations  224  in outer surface  216  may be included in front cover plate  20  to enable mass reduction while still providing a rigid sealing surface. 
         [0024]    Threaded inserts  202  include shaft  226 , flange  228 , and threaded axial bore  232 . Threaded inserts  202  are in a currently preferred embodiment manufactured from steel. The shaft  226  is provided with knurls  230 , a series of small ridges or grooves on the surface of shaft  226 , that enable to press fit steel threaded inserts  202  into bores  204 . Knurls  230  support press fitting steel threaded inserts  202  into bores  204  and, thus, the convenient subassembly of front cover plate  20 , and eliminate the need to grind or otherwise extensively machine the inner surface of bores  204  to receive the inserts  202 . Flange  228  horizontally extends from shaft  226  orthogonally in all directions. 
         [0025]    While flange  228  is shown to have a “D” shape, flange  228  may have any desired shape, such as circular, rectangular, square, hexagonal etc. Threaded bore  232  extends through shaft  226  and flange  228  and receives the threaded end of bolt  16  shown in  FIG. 1 . The length  234  of threaded bore  232  and, therefore, the length of steel threaded insert  20 , is determined by the size of bolts  16 , since the thread length needs to have at least the same value as the diameter of the received bolt. Thus, for example, if bolt  16  is a size M6 with a diameter of 6 mm (millimeters), length  234  of threaded bore  232  preferably should be at least 6 mm. Since indentations  222  are designed such that flange  228  of steel threaded insert  202  is level with outer surface  216  of front cover plate  20  when installed, thickness  220  of cover plate  20  has nominally the same value as length  234  of threaded bore  232  and, thus, of steel threaded insert  202 . Consequently, thickness  220  of front cover plate  202  needs to be at least 6 mm if, for example, M6 bolts  16  are used. With a minimal possible thickness  220  of 6 mm, front cover plate  20  is suitable for applications where packaging requirements necessitate a maximum thickness  220  of, for examples 7 mm. 
         [0026]    Referring now to  FIGS. 4 through 6 , front cover plate  20  includes a well  206  formed in inner surface  218  for receiving bushing  48  of locking pin mechanism  44  (shown in  FIG. 1 ). Well  206  is utilized as a lock pin seat for locking pin mechanism  44 . Since camshaft phaser  10  is exemplary shown in  FIG. 1  to include only one locking pin mechanism  44 , front cover plate  20  is shown in  FIGS. 5 and 6  to include only one well  206 . As can be seen, well  206  is positioned in relative close proximity to one of bores  204 . As can be seen in  FIG. 6 , cover plate  20  is designed such that steel threaded insert  202  can be positioned in indentation  222  formed in outer surface  216  without interfering with well  206  formed in inner surface  218 . This enables the use of front cover plate  20  with currently existing manufacturing envelopes. 
         [0027]    By utilizing steel threaded inserts  202  as in a currently preferred embodiment the problem of aluminum thread strength found in prior art die cast aluminum front covers is solved and, consequently, a more compact (smaller thickness  220 ) die cast aluminum front cover plate  20  is enabled, allowing for packaging of cam phaser  10  in tighter applications where prior art aluminum front covers will not fit. By allowing for a smaller thickness  220  steel threaded inserts  202  enable a mass savings compared to prior art front covers. 
         [0028]    Furthermore, by horizontally extending shaft  226  and, thus, diameter of bore  204 , flange  228  effectively spreads a clamp load created during tightening of bolts  16  beyond the diameter of bolt  16 . Consequently, utilizing steel threaded inserts  202  enables the clamp load to be evenly distributed throughout an area surrounding bore  204  preventing local load points. Thus, deflection of front cover plate  20  is reduced and the overall effective clamping load of the front cover against the stator, compared to prior art die cast aluminum front covers, is improved. 
         [0029]    While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.