Patent Publication Number: US-7721692-B2

Title: Cam phaser having pre-loaded spring for biasing the rotor through only a portion of its range of authority

Description:
TECHNICAL FIELD 
   The present invention relates to phasers for varying the phase of valving with respect to a crankshaft in an internal combustion engine; more particularly, to such a phaser employing a spring for biasing the rotational position of a phaser rotor with respect to an associated phaser stator through at least a portion of the rotor range of authority; and most particularly, to such a phaser wherein a pre-loaded bias spring is active through only a portion of the range of authority of rotor rotation. 
   BACKGROUND OF THE INVENTION 
   Camshaft phasers for varying the timing of combustion valves in an internal combustion engine transmit crankshaft torque to the engine camshaft, allowing varied timing of the camshaft relative to the crankshaft position. Traditionally, intake phasers have authority to only advance this timing from their locked position. When insufficient oil pressure is available for controlled phasing, cam torque and the available oil pressure are used to drive the rotor to the fully retarded position where a lock pin in the rotor aligns with a seat in the stator. As engine speed decreases, oil pressure drops below the retraction pressure for the lock pin and the pin&#39;s bias spring urges the pin to move into engagement with its seat, preventing undesired phase angle changes until sufficient oil pressure is again available. 
   Phasers requiring an intermediate lock pin position between full rotor advance and full rotor retard cannot rely on the contract between the rotor and stator to realign the lock pin to its seat. Therefore, when oil pressure is low, some form of assistance is needed to advance the rotor away from full retard to align the lock pin to the seat at the intermediate rotor position. If the assistance were torque from a simple spring-arm system, the bias spring would cause the phaser to advance the rotor through the entire range of rotor authority and past the point where the lock pin aligns with its seat when resistive torque through the phaser system from the camshaft was less than the applied spring torque. 
   What is needed in the art is an improved bias system for a modern phaser having a rotor lock position intermediate in the rotor range of authority wherein the rotor is biased toward the lock position from all retard positions but is not biased toward the lock position from any advance position. 
   It is a principal object of the present invention to provide an improved phaser bias system. 
   SUMMARY OF THE INVENTION 
   Briefly described, the invention uses an applied torque between a phaser cover plate, mounted to the stator/sprocket, and phaser rotor to assist in aligning a lock pin to a seat in the stator at an intermediate position in the rotor range of authority. During assembly of the phaser, the bias spring is captured and guided by a spring retainer that is fitted or formed into the cover. The spring retainer allows the bias spring to be installed into the cover in its pre-load position and to be conveniently retained therein as both the grounded and active legs are captured in separate slot features in the spring retainer. This sub-assembly (cover, retainer, bias spring) is then readily attached to the remaining phaser components to complete the full assembly. 
   A pocket within the rotor receives the active leg of the bias spring extending from the spring retainer. The rotor pocket preferably has a tapered bottom face (ramp) that lifts the active leg of the bias spring off the axial slot wall in the spring retainer and locates the active leg against the wall of the rotor pocket when the rotor moves from the locked position in a retarding direction. Lifting the active tang of the bias spring removes any friction between the bias spring and the retainer slot wall that would occur as the rotor moves in a retarded direction from its intermediate locked position. 
   As the rotor moves in an advancing direction and the phase angle approaches the angle where locking would occur, the bias spring&#39;s rotation stops when the active tang contacts the end of the spring retainer slot. Contact between the active tang of the bias spring and the end of the slot in the spring retainer removes spring torque that otherwise would bias further advancement of the rotor. This permits the rotor to self-align to its locking position when oil pressure is removed during engine shut down or stall. 
   Further rotor motion in an advancing direction causes the tapered face in the bottom of the pocket in the rotor to lose contact with the bias spring tang, removing any axial contact between the bias spring active leg and the bottom face of the pocket in the rotor, and therefore prevents friction that otherwise would occur between the bias spring active tang and the rotor during rotor advance. 
   Without the spring retainer slot wall capturing the active tang of the bias spring, the spring would tip from axial alignment within the phaser and would continue to make contact with the bottom of the pocket in the rotor, creating frictional drag on the rotor as the rotor advances from the locking position. 
   The features of the invention therefore serve two purposes: easing phaser assembly, thus reducing cost and improving safety; and eliminating unwanted friction between the bias spring and rotor, thus improving performance and durability. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is an exploded isometric view of a vane-type camshaft phaser in accordance with the invention; 
       FIG. 2  is an exploded isometric view of a cover plate subassembly in accordance with the invention; 
       FIG. 3  is an exploded view derived from  FIG. 2  showing the spring retainer fitted into the cover plate with the first slot and the cover plate notch aligned; 
       FIG. 4  is an isometric view of the cover plate subassembly; 
       FIG. 5  is an isometric view of an assembled camshaft phaser including a cross-sectional view taken off-axis through a pocket in the rotor, showing the rotor fully retarded from locked position; 
       FIG. 6  is an isometric view of an assembled camshaft phaser including a cross-sectional view taken off-axis through a pocket in the rotor, showing the rotor in locked position; 
       FIG. 7  is an isometric view of an assembled camshaft phaser including an axial cross-sectional view, also showing the rotor in locked position; and 
       FIG. 8  is an isometric view of an assembled camshaft phaser including a cross-sectional view taken off-axis through a pocket in the rotor, showing the rotor in an advanced position. 
   

   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 
   Referring to  FIGS. 1 through 8 , a vane-type camshaft phaser  10  in accordance with the invention comprises a driving element  12  in the form of a sprocket wheel integral with a stator  14  having a plurality of inward-extending lobes  16 . Of course, driving element  12  may take the form, as is known in the art, of a notched wheel for receiving a toothed timing belt or a gear for meshing with a timing gear. A bottom plate  18  forms a first wall of chambers formed within stator  14  between lobes  16 . A rotor  20  having four vanes  22   a - d  is disposed for rotation within stator  14  in known fashion. Rotor  20  has at least one, and preferably two, lock pins assemblies  24  hydraulically extendable to engage seats  26  in a cover plate  28  for rotationally locking the rotor to the stator as may be desired. Cover plate  28  defines a second wall of the chambers in stator  14 . Binder screws  30  extend through bottom plate  18  and stator  14 , and are threadedly received in cover plate  28 . A thrust washer  31  is disposed against the hub of rotor  20  for receiving a camshaft-mounting bolt (not shown) during assembly of engine  33 . A spring retainer  32  receives a helical bias spring  34  having first and second radially-extending tangs  36 , 38 . First tang  36  is grounded in a first axial slot  40  formed in the wall of spring retainer  32  and is defined herein as the “inactive” tang. Second tang  38  is grounded in a second slot  42  formed in the wall of spring retainer  32  and is defined herein as the “active” tang. Second slot  42  preferably includes an axial entry portion and a circumferential portion permitting rotation of second tang  38  during operation of the phaser. Spring retainer  32  extends through an opening  44  in cover plate  28  and includes a collar  46  that grounds against the outer surface  48  of cover plate  28  during assembly. Preferably a notch  50  is provided in the rim of opening  44  for receiving first tang  36  extending beyond the wall of spring retainer  32 . Alternatively, retainer  32  may be formed into the cover such as, for example, by casting. 
   During assembly of phaser  10 , bias spring  34  is captured and guided by spring retainer  32  that is press fit or formed into cover plate  28  with first slot  40  aligned with notch  50 . Referring to  FIGS. 2 through 4 , in forming a cover plate subassembly  52 , first tang  36  is inserted into slot  40  to a depth until second tang  38  engages the end of spring retainer  32 . Bias spring  34  is then wound until second tang  38  aligns with second slot  42 ; the spring is then pushed further into spring retainer  32  and then released, thus the spring is captured at a pre-load position, creating subassembly  52 . The spring retainer allows the bias spring to be installed into the cover in its pre-load position and to be conveniently retained therein as both the inactive and active tangs are captured in separate slot features in the spring retainer. 
   Subassembly  52  is then attached by binder screws  30  to the remaining phaser components to complete the full phaser assembly  10 . An annular well  54  in rotor  20  receives the portion of subassembly  52  extending beyond cover plate  28 . A pocket  56  within the rotor and outboard of well  54  receives active tang  38  and preferably has a tapered bottom face defining a ramp  58 . Ramp  58  extends angularly across the lower wall  60  of second slot  42  and receives active tang  38  as spring  34  is torsionally actuated by rotation of rotor  20 . 
   In operation, when the rotor moves in a retarding direction ( FIG. 5 ), from an intermediate position in which the rotor may be locked, rotor ramp  58  lifts active tang  38  off the lower slot wall  60  (hidden in  FIG. 5 ) and positions tang  38  against a first end wall  62  of rotor pocket  56 . Lifting the active tang of the bias spring removes any friction between the spring tang and the slot wall that would otherwise occur as the rotor moves in a retarded direction toward a full retarded authority position from its intermediate position. 
   As rotor  20  moves in an advancing direction from a retard position and approaches the phase angle at which locking can occur ( FIGS. 6 and 7 ), the torsional rotation of bias spring  34  stops when active tang  38  makes contact with end wall  64  ( FIGS. 2 and 3 ) of spring retainer slot  42 . Contact between the active leg of the bias spring and the end of the slot in the spring retainer arrests the spring from further uncoiling and thus prevents spring torque from biasing the advance of the rotor in the advance direction past the locking point. This permits the rotor to self-align to its locking position when oil pressure is removed during engine shut down or stall. 
   Further motion of rotor  20  past the locking position in an advancing direction toward a full advanced authority position ( FIG. 8 ) causes ramp  58  to be disengaged from active tang  38 , removing any axial contact between the bias spring active tang and the non-ramp bottom face  66  of pocket  56 , and therefore prevents frictional drag that otherwise would occur between the bias spring active tang and the rotor during rotor advance. 
   Without slot wall  64  capturing active tang  38 , the spring would tip from axial alignment within the phaser and would continue to make contact with bottom face  66  as the rotor advances from the intermediate position. 
   The present invention has been described above in terms of a novel camshaft phaser being applied to an intake valve camshaft and biasing the rotor in the advance direction from retard positions. However, those of ordinary skill in the phaser art will realize that the disclosed invention is not so limited and may be applied to exhaust valve camshafts as well as to biasing the rotor in the retard direction from advanced positions as may be desired. 
   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.