Abstract:
A vane-type camshaft phaser for varying the timing of combustion valves in an internal combustion engine includes a seat formed in the sprocket at the appropriate position of intermediate rotation and a locking pin slidably disposed in a vane of the rotor for engaging the seat to lock the rotor at the intermediate position. A bias spring system disposed on a cover plate urges the rotor toward the locking position from any position retarded of the locking position. A first spring system embodiment comprises a pair of compression spring assemblies. A second spring system embodiment comprises an internal torsion spring. In each embodiment, the phaser may be assembled without having the spring system coupled to the rotor, thereby overcoming a rotor cocking problem inherent in prior art phasers, assuring reliable mounting of an assembled phaser onto an engine camshaft.

Description:
TECHNICAL FIELD 
   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 locking pin assembly is utilized to lock the phaser rotor with respect to the stator at certain times in the operating cycle; and most particularly, to a phaser having a bias spring system to assist in locking a phaser rotor at a rotational position intermediate between full phaser advance and full phaser retard positions. 
   BACKGROUND OF THE INVENTION 
   Camshaft phasers 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 retard chambers as required to meet current or anticipated engine operating conditions. 
   In a typical prior art vane-type cam phaser, a locking pin, disengage-able by oil pressure, is slidingly disposed in a bore in a rotor vane to permit rotational locking of the rotor to the stator (or sprocket wheel or pulley) under certain conditions of operation of the phaser and engine. In older prior art phasers, it is desired that the rotor be locked at its parked position at an extreme of the rotor authority, either at the full retard position as in the case of an intake camshaft phaser or at the full advance position as in the case of an exhaust camshaft phaser. To assist in positioning the rotor for lock pin engagement, it is known to incorporate a mechanical stop for the rotor and a torsional bias spring acting between the rotor and the stator to urge the rotor against the stop for locking. 
   In newer prior art phasers as disclosed in co-pending application having Ser. No. 11/225,772, it is desirable that the rotor be lockable to the stator at an intermediate position, preferably within an increased rotor range of rotational authority. A known problem in such phasers is that there is no mechanical means such as a stop to assist in positioning the rotor for locking in an intermediate position; thus, locking is not reliable, and an unacceptably high rate of locking failures may occur. 
   Further, in prior art phasers, the torsion spring may generate an unwanted torque on the rotor about an axis orthogonal to the rotor axis, causing the rotor to become slightly cocked within the stator chamber before the phaser is installed onto the end of a camshaft during engine assembly. This cocking is permitted by necessary clearances between the rotor and the stator. Although relatively slight, such cocking can be large enough to prohibit entry of the camshaft into the rotor during engine assembly. 
   What is needed in the art is an improved vane-type camshaft phaser having additional range of rotational authority wherein the rotor may be reliably locked to the stator at an intermediate position within the range of authority. 
   What is further needed in the art is an improved vane-type camshaft phaser wherein the rotor of an assembled phaser may be reliably entered onto the end of a camshaft during engine assembly. 
   It is a principal object of the present invention to cause a rotor lock pin to be properly positioned for engagement with a stator. 
   It is a further object of the present invention to increase the reliability of entry of the rotor of an assembled phaser onto an engine camshaft during engine assembly. 
   SUMMARY OF THE INVENTION 
   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, the interspersion of vanes and lobes defining a plurality of alternating valve timing advance and valve timing retard chambers with respect to the engine crankshaft. The rotational authority of the rotor within the stator with respect to top-dead-center of the crankshaft is preferably between about 40 crank degrees before TDC (valve timing advanced) and about 20 crank degrees after TDC (valve timing retarded). It is generally desirable that an engine be started at a camshaft position of about 10 crank degrees valve retard. Thus, an improved phaser in accordance with the present invention includes a lock pin seat formed in the stator at the appropriate position of intermediate rotation and a locking pin slidably disposed in a vane of the rotor for engaging the seat to lock the rotor at the intermediate position for engine starting. 
   A pre-loaded bias spring system disposed on the phaser cover plate urges the rotor toward the locking position from any rotational position retarded of the locking position. When the rotor is moving in a phase-advance direction, at or near the rotor locking position the bias spring system becomes disengaged from the rotor. When the rotor is moving in a phase-retard direction, at or near the rotor locking position the bias spring system is engaged, causing the rotor to decelerate and thereby increasing the reliability of locking. 
   Two embodiments of such a bias spring system are presented, one comprising a torsion spring and the other comprising a pair of compression springs. In each embodiment, the phaser may be assembled without having the spring system coupled to the rotor, thereby overcoming the rotor cocking problem inherent in prior art phasers and assuring reliable mounting of an assembled phaser onto a camshaft during engine assembly. 

   
     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 elevational cross-sectional view of a prior art vane-type camshaft phaser, showing direct entry of an engine camshaft into a rotor, and also showing an internal torsion bias spring for biasing the rotor to a fully retarded position within the stator; 
       FIG. 1   a  is an exploded isometric view of a partial cam phaser including the pulley/sprocket, the stator, the rotor and the locking pin mechanism. 
       FIG. 2  is a plan view of an improved camshaft phaser showing a first embodiment of a bias spring system in accordance with the invention; 
       FIG. 3  is an isometric view of the phaser and bias spring system shown in  FIG. 2 ; 
       FIG. 4  is an exploded isometric view of an improved camshaft phaser showing a second embodiment of a bias spring system in accordance with the invention; 
       FIG. 5  is an assembled view of the phaser shown in  FIG. 4 ; and 
       FIG. 6  is a cutaway isometric view from below of a portion of the second embodiment shown in  FIGS. 4 and 5 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a typical prior art vane-type camshaft phaser  10  includes a pulley or sprocket  12  for engaging a timing chain or belt (not shown) operated by an engine crankshaft (not shown). A stator  14  is disposed against pulley/sprocket  12  and is rotationally immobilized with respect to pulley/sprocket  12 . Stator  14  is provided with a central chamber  16  for receiving a rotor  18  having a hub  20 . Hub  20  is provided with a recess  22  that is coaxial with a central bore  24  in pulley/sprocket  12 , allowing access of an end of engine camshaft  26  into rotor hub  20  during mounting of phaser  10  onto an internal combustion engine  27  during assembly thereof. Central chamber  16  is closed by a cover plate  28 , forming advance and retard chambers between the rotor and the stator in chamber  16 . A rotor hub extension  30  is pressed into a recess in rotor hub  20  and extends rotatably through a central opening in cover plate  28 . A target wheel  32  is mounted onto rotor hub extension  30  by an axial mounting bolt (not shown) that attaches phaser  10  to camshaft  26  during assembly of engine  27 . Thus target wheel  32  turns with and is indicative of the rotational position of rotor  18  and camshaft  26 . Cover plate  28  and stator  14  are secured to pulley/sprocket  12  via a plurality of binder screws  34  extending through stator  14  outside of chamber  16 . A torsional bias spring  36  is disposed coaxially of rotor hub extension  30 , having a first tang  38  anchored to sprocket/pulley  12 , as for example, by engagement with the protruding head of a binder screw  34 , and having a second tang  40  anchored to rotor  18 , as for example, by engagement with a stop  42  on target wheel  32 . Bias spring  36  is pre-loaded between the rotor and stator during assembly of phaser  10  to urge rotor  18  toward the full operational retard position within chamber  16 , thereby causing the rotor cocking problem described above. 
   Referring now to  FIG. 1   a , locking pin mechanism  44  comprises locking pin  46  having annular shoulder  47 , return spring  48 , and bushing  49 . Spring  48  is disposed inside pin  46 , and bushing, pin, and spring are received in a longitudinal bore  50  formed in oversized vane  52  of rotor  18 , an end of pin  46  being extendable by spring  48  from the underside of the vane. A pin seat  54  is formed in the inside surface of pulley/sprocket  12  for receiving an end portion of pin  46  when extended from bore  50  to rotationally lock rotor  18  to pulley/sprocket  12  and, hence, stator  14 . The operation of locking mechanism  44  is described in co-pending application Ser. No. 11/225,772. Note that, by angularly positioning bore  54  on the inside surface of pulley/sprocket  12 , within the range of rotational authority  56  of rotor  18 , engagement of the locking mechanism can cause the rotor to be locked in its full retard position ( 54   a ), its full advance position ( 54   c ), or any intermediate position ( 54   b ) therebetween. 
   Referring now to  FIGS. 2 and 3 , a first embodiment  110  of an improved camshaft phaser in accordance with the invention includes an improved bias spring system  136  that replaces prior art torsional bias spring  36 . System  136  comprises at least one compression spring assembly  160  disposed on cover plate  128  and a torque arm  162  mounted for rotation with a phaser rotor (not visible in  FIGS. 2 and 3 ) as by being secured thereto by a nut  164  screwed onto a threaded stud  165  extending from a phaser mounting bolt. (A conventional target wheel, not shown, also may be mounted by obvious means onto stud  165 .) Compression spring assembly  160  comprises a coil spring  166  mounted in a bore formed in a housing  168  on cover plate  128  and having a plunger  170  extending therefrom for engagement with torque arm  162 . Housing  168  is rotationally formed on cover plate  128 , and torque arm  162  is rotationally positioned on the rotor after the phaser is installed onto a camshaft, such that in all positions of rotor advance phase angle (advance direction  172 ) from the position shown in  FIGS. 2 and 3 , rotor motion is not influenced by bias spring system  136  because torque arm  162  is moving away from plunger  170 . However, in all positions of rotor retard phase angle (retard direction  174 ) from the position shown in  FIGS. 2 and 3 , rotor motion is influenced by bias spring system  136  because torque arm  162  is engaged by spring-loaded plunger  170 . In a currently preferred embodiment, the position of the rotor and torque arm shown in  FIGS. 2 and 3 , wherein retard motion of the torque arm is braked by bias spring system  136 , corresponds to the intermediate locking position ( 54   b  in  FIG. 1   a ) of an internal lock pin system (not visible in  FIGS. 2  or  3 ). Further in a currently preferred embodiment, the intermediate locking position separates the rotor range of authority into a phase-advance range ( 58   b  in  FIG. 1   a ) and a phase-retard range ( 58   a  in  FIG. 1   a ), and a bias spring system in accordance with the invention is engageable with the rotor only within the phase-retard range. 
   Thus, in operation bias spring system  136  creates a time window wherein the lock pin and seat are roughly aligned for locking. Bias spring system  136  is active only in retard modes of phaser operation, wherein system  136  will always tend to return the rotor to its locking position when the retard mode is deactivated. Further, bias spring system  136  cannot cause the undesirable rotor cocking described above in prior art phasers. Preferably, improved phaser  110  is assembled and installed with the rotor in a locked position within the stator, and then torque arm  162  is secured in position against plungers  170  by nut  164 . 
   In a presently preferred embodiment, improved bias spring system  136  comprises two torque arms  162  disposed 180° apart and two compression spring assemblies  160  disposed 180° apart, as shown in  FIGS. 2 and 3 , which arrangement imposes a balanced torque on the rotor in operation. 
   Referring now to  FIGS. 4 through 6 , a second embodiment  210  of an improved camshaft phaser in accordance with the invention includes an improved bias spring system  236  that replaces prior art torsional bias spring  36 . In spring system  236 , the torsion bias spring is mounted substantially as shown for prior art spring  36  in  FIG. 1 . Spring  236  is mounted on rotor hub extension  230 , and first tang  238  engages a bolt head  34  to ground the spring to sprocket  12 . However, in an improvement over prior art spring system  36 , a spring stop  280  extends from cover plate  228  toward modified target wheel  232  for engaging second spring tang  240 . Stop  280  is located radially inboard of target wheel modified stop  242 . Further, stop  280  is located substantially coaxially with the locking position of an internal lock pin system (not visible). Thus the torsion spring as installed, and shown in  FIG. 4 , is grounded at both tangs  238 ,  240  to the cover plate and exerts no torque or cocking moment on the rotor hub extension  230  or the rotor, permitting reliable installation of the improved phaser  210  onto a camshaft end  26  during assembly of engine  27  ( FIG. 1 ). During such installation, after the phaser is positioned on the camshaft end, target wheel  232  is installed over spring  236  and rotated counterclockwise (retard direction  274 ) until stop  242  engages second spring tang  240  outboard of spring stop  280 . The camshaft mounting bolt (not shown) is then tightened, fixing the rotational relationship between stop  280 , second tang  240 , and target wheel stop  242 . 
   The operational characteristics of improved phaser  210  are identical with those of improved phaser  110  as previously described. In operation, during all phase-advance modes ( 58   a  in  FIG. 1   a ), target wheel stop  242  is not engaged with second tang  240 , and thus spring  236  has no influence on motion of the rotor. As in first embodiment  110 , in all positions of rotor retard phase angle (retard direction  274 ) from the position shown in  FIGS. 4 and 6  rotor motion is influenced by bias spring system  236  because second tang  240  is engaged by target wheel stop  242 . As noted above, the position of the target wheel and second tang shown in  FIGS. 4 and 6 , wherein retard motion of the rotor is braked by bias spring system  236 , corresponds to the locking position of an internal lock pin system (not visible) into the stator. Thus, bias spring system  236  creates a time window where the lock pin and seat are roughly aligned for locking. Bias spring system  236  is active only in retard modes of phaser operation, wherein the spring system will always tend to return the rotor to its locking position when the retard mode is deactivated. 
   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.