Abstract:
A camshaft ( 126 ) has a vane ( 160 ) secured to an end thereof for non-oscillating rotation therewith. The camshaft also carries a sprocket ( 132 ) that can rotate with the camshaft but is oscillatable with respect to the camshaft. The vane has opposed lobes ( 160   a   , 160   b ) that are received in opposed recesses ( 132   a   , 132   b ), respectively, of the sprocket. The recesses have greater circumferential extent than the lobes to permit the vane and sprocket to oscillate with respect to one another. The camshaft phase tends to change in reaction to pulses that it experiences during its normal operation, and it is permitted to change only in a given direction, either to advance or retard, by selectively blocking or permitting the flow of pressurized hydraulic fluid, preferably engine oil, from the recesses by controlling the position of a spool within a valve body ( 192 ) of a control valve. The sprocket has a passage ( 252 ) extending therethrough the passage extending parallel to and being spaced from a longitudinal axis of rotation of the camshaft. A pin ( 250 ) is slidable within the passage and is resiliently urged by a spring ( 254 ) to a position where a free end of the pin projects beyond the passage. The vane carries a plate ( 168 ) with a pocket ( 168   f ), which is aligned with the passage in a predetermined sprocket to camshaft orientation. The pocket receives hydraulic fluid, and when the fluid pressure is at its normal operating level, there will be sufficient pressure within the pocket to keep the free end of the pin from entering the pocket. At low levels of hydraulic pressure, however, the free end of the pin will enter the pocket and latch the camshaft and the sprocket together in a predetermined orientation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The subject matter of this application is related to the subject matter of commonly assigned, now abandoned provisional application Serial No. 60/173,330, and to the subject matter of commonly assigned application Ser. No. 60/173,330, which was filed on Dec. 28, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a variable camshaft timing (VCT) system for an automotive engine in which the circumferential position of an engine camshaft is varied relative to the crankshaft, or to another camshaft of the engine, by controllably transferring hydraulic fluid between opposed operators that cooperatively act to reposition the camshaft. More particularly, this invention relates to a VCT system of the foregoing character in which the opposed hydraulic operators are in the form of a diametrically opposed spaced apart pair of lobes of a vane that is secured to the camshaft whose position is to be varied. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 5,002,023 (Butterfield and Smith) and U.S. Pat. No. 5,046,460 (Butterfield, Smith and Dembosky) describe various forms of VCT systems that utilize opposed hydraulic actuators in the form of opposed cylinders to circumferentially reposition an automotive engine camshaft relative to a crankshaft, or relative to another camshaft of the same engine, by controllably transferring pressurized engine lubricating oil from one of the hydraulic cylinders to the other. Further, as is disclosed in U.S. Pat. No. 5,107,804 (Becker, Butterfield, Dembosky, and Smith), the disclosure of which is incorporated by reference herein, a VCT system using the principles of the aforesaid U.S. patents can be simplified in its mechanical and hydraulic aspects by using a vane with a diametrically spaced apart pair of lobes secured to the camshaft in combination with a surrounding housing that is oscillatable with respect to the camshaft, in place of the opposed hydraulic cylinders of the aforesaid patents. An arrangement in which the phase angle of an engine camshaft relative to that of the crankshaft is adjusted by hydraulic action against a series of vanes that are secured to the camshaft and are free to oscillate within chambers of a drive member that is driven in rotation by the crankshaft is also disclosed in U.S. Pat. No. 4,858,572 (Shirai et al.). 
     A vane-type hydraulically operated VCT system of the type described in the aforesaid U.S. Pat. No. 5,107,804 relies on the presence of pressurized engine lubricating oil or other hydraulic fluid within the VCT system to function properly and predictably. This condition is achieved during normal engine operation, when engine lubricating oil is used as the hydraulic fluid within the VCT system, since adequate pressurization of the engine lubricating oil inherently results from the operation of the engine. However, when an automotive engine is shut off, the pressure of the engine lubricating oil soon drops, and the oil within a VCT system of the aforesaid type will normally drain back to the engine crankcase. Thus, upon the restarting of such an engine, the supply of engine lubricating oil within the VCT system is likely to be inadequate in volume or pressure to ensure its proper operation. During these conditions it is desirable to be able to automatically lock or latch the position of the phase adjusted camshaft relative to that of the crankshaft in a predetermined position, preferably in a centered position between its fully advanced position and its fully retarded position, and to maintain the phase adjusted camshaft in such a locked or latched condition unless the pressure of the engine lubricating oil within the VCT system is adequately high to ensure normal, proper operation of the VCT system. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided an hydraulically-operated, vane-type variable camshaft timing (VCT) system for an automotive engine in which the vane that is secured to the camshaft is positively locked or latched in its position with respect to a crankshaft driven, rotatable housing during periods of low hydraulic system pressure, for example, during and shortly after engine starting in the case of a VCT system that uses pressurized engine lubricating oil as the hydraulic medium. The housing carries a pin therein that is slidable to and fro along an axis that is spaced from and extends parallel to the axis of rotation of the phase adjusted camshaft. Further, the camshaft has a plate that is secured thereto and that is rotatable therewith, and the plate has a recess therein that is adapted to receive a free, rounded end of the pin of the housing when the pin is circumferentially aligned with the recess and when the pin is at the outer limit of its range of travel. The pin is resiliently biased to the outer limit of its travel by a spring that acts on an opposed end of the pin, and is further biased away from the outer end of its range of travel, and thereby out of engagement with the recess, by pressurized hydraulic fluid within the recess that acts on the free end of the pin during the operation of the engine. The relationship between the hydraulic force that acts on the free end of the pin and the mechanical, spring force that acts on its opposed end is such that the hydraulic force is substantially greater during all normal operating conditions of the engine and the mechanical force is greater only temporarily upon restarting of the engine. Thus, in a VCT system according to the present invention the camshaft is mechanically locked or latched in a predetermined phase relative to the crankshaft, preferably in a centered phase between its fully advanced position and its fully retarded position, to ensure proper starting of the engine at a time when the VCT system could otherwise function unpredictably and unreliably because of inadequate hydraulic pressure within the system. Further, the VCT system according to the present invention prevents impacts between the VCT system components during and shortly after starting, when the system can be fully or partly filled with air and when such impacts could occur because of the compressibility of air and the sensitivity of a VCT system of the type described in the aforesaid U.S. Pat. No. 5,107,804 to torque fluctuations during each rotation of the camshaft. Thus, the latching or locking feature of the VCT system of the present invention prevents such impacts, and the damage and noise resulting therefrom, by ensuring that no phase adjustment can occur until the VCT system is filled with pressurized fluid and the associated check valves can function properly to prevent hydraulic fluid transfer within the system except when desired to effect a change in camshaft phase angle. 
     Accordingly, it is an object of the present invention to provide an improved vane-type hydraulic variable camshaft timing (VCT) system. More particularly, it is an object of the present invention to provide a VCT system of the foregoing character with a mechanical locking feature that will function to prevent changes in camshaft phase angle whenever the pressure of the hydraulic fluid within the VCT system is inadequate to ensure its proper operation. Specifically it is an object of the present invention to provide a VCT system of the foregoing character that utilizes pressurized engine lubricating oil as the hydraulic medium, and incorporates a locking or latching feature to prevent changes in camshaft phase angle during and shortly after the restarting of the engine, when the pressure of the engine lubricating oil within the variable camshaft timing system is inadequate to ensure its proper operation. 
    
    
     For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the preferred embodiment and to the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an end elevational view of a camshaft with elements of an embodiment of a variable camshaft timing system applied thereto; 
     FIG. 2 is a view similar to FIG. 1 with a portion of the structure thereof removed to more clearly illustrate other portions thereof: 
     FIG. 3 is a sectional view taken on line  3 — 3  of FIG. 2; 
     FIG. 4 is a sectional view taken on line  4 — 4  of FIG. 2; 
     FIG. 5 is a sectional view taken on line  5 — 5  of FIG. 2; 
     FIG. 6 is an end elevational view of an element of the variable camshaft timing system of FIGS. 1-5; 
     FIG. 7 is an elevational view of the element of FIG. 6 from the opposite end thereof; 
     FIG. 8 is a side elevational view of the element of FIGS. 6 and 7; 
     FIG. 9 is an elevational view of the element of FIG. 8 from the opposite side thereof; 
     FIG. 10 is a simplified schematic view of the variable camshaft timing arrangement of FIGS. 1-9; 
     FIG. 11 is a view generally similar to FIG. 2 illustrating a variable camshaft timing system with a locking or latching feature according to the preferred embodiment of the present invention incorporated therein; and 
     FIG. 12 is a sectional view taken on line  12 — 12  of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-10 illustrate a vane-type, hydraulic variable camshaft timing (VCT) system according to an embodiment of the aforesaid U.S. Pat. No. 5,107,804 in which a housing in the form of a sprocket  32  is oscillatingly journalled on a camshaft  26 . 
     The camshaft  26  may be considered to be the only camshaft of a single camshaft engine, either of the overhead camshaft type or the in block camshaft type. Alternatively, the camshaft  26  may be considered to be either the intake valve operating camshaft or the exhaust valve operating camshaft of a dual camshaft engine. In any case, the sprocket  32  and the camshaft  26  are rotatable together, and are caused to rotate by the application of torque to the sprocket  32  by an endless roller chain  38 , shown fragmentarily, which is trained around the sprocket  32  and also around a crankshaft, not shown. As will be hereinafter described in greater detail, the sprocket  32  is oscillatingly journalled on the camshaft  26  so that it is oscillatable at least through a limited arc with respect to the camshaft  26  during the rotation of the camshaft, an action that will adjust the phase of the camshaft  26  relative to the crankshaft. 
     An annular pumping vane  60  is fixedly positioned on the camshaft  26 , the vane  60  having a diametrically opposed pair of radially outwardly projecting lobes  60   a ,  60   b  and being attached to an enlarged end portion  26   a  of the camshaft  26  by bolts  62  that pass through the vane  60  into the end portion  26   a . In that regard, the camshaft  26  is also provided with a thrust shoulder  26   b  (FIG. 3 ) to permit the camshaft to be accurately positioned relative to an associated engine block, not shown. The pumping vane  60  is also precisely positioned relative to the end portion  26   a  by a dowel pin  64  that extends therebetween. The lobes  60   a ,  60   b  are received in radially outwardly projecting recesses  32   a ,  32   b , respectively, of the sprocket  32 , the circumferential extent of each of the recesses  32   a ,  32   b  being somewhat greater than the circumferential extent of the vane lobe  60   a ,  60   b  that is received in such recess to permit limited oscillating movement of the sprocket  32  relative to the vane  60 . The recesses  32   a ,  32   b  are closed around the lobes  60   a ,  60   b , respectively, by spaced apart, transversely extending annular plates  66 ,  68  (FIG. 21) that are fixed relative to the vane  60 , and, thus, relative to the camshaft  26 , by bolts  70 , which extend from one to the other through the same lobe,  60   a  or  60   b . Further, the inside diameter  32   c  of the sprocket  32  is sealed with respect to the outside diameter of the portion  60   d  of the vane  60 , that is between the lobes  60   a ,  60   b , and the tips of the lobes  60   a ,  60   b  of the vane  60  are provided with seal receiving slots  60   e ,  60   f , respectively. Thus each of the recesses  32   a ,  32   b  of the sprocket  32  is capable of sustaining hydraulic pressure, and within each recess  32   a ,  32   b  the portion on each side of the lobe  60   a ,  60   b , respectively, is capable of sustaining hydraulic pressure. 
     The functioning of the structure of the embodiment of FIGS. 1-9, as thus far described, may be understood by reference to FIG.  10 . Hydraulic fluid, illustratively in the form of engine lubricating oil, flows into the recesses  32   a ,  32   b  by way of a common inlet line  82 . The inlet line  82  terminates at a juncture between opposed check valves  84  and  86  that are connected to the recesses  32   a ,  32   b , respectively, by branch lines  88 ,  90 , respectively. The check valves  84 ,  86  have annular seats  84   a ,  86   a , respectively, to permit the flow of hydraulic fluid through the check valves  84 ,  86  into the recesses  32   a ,  32   b , respectively. The reverse flow of hydraulic fluid through the check valves  84 ,  86 , is blocked by floating balls  84   b ,  86   b , respectively, which are urged against the seats  84   a ,  86   a  by springs  84   c ,  86   c , respectively. The check valves  84 ,  86 , thus, permit the initial filling of the recesses  32   a ,  32   b  and provide for a continuous supply of make-up hydraulic fluid to compensate for leakage therefrom. Hydraulic fluid enters the line  82  by way of a spool valve  92 , which is incorporated within the camshaft  26 , and hydraulic fluid is returned to the spool valve  92  from the recesses  32   a ,  32   b  by return lines  94 ,  96 , respectively. 
     The spool valve  92  is made up of a cylindrical member  98  and a spool  100  is slidable to and fro within the member  98 . The spool  100  has cylindrical lands  100   a  and  100   b  on opposed ends thereof, and the lands  100   a  and  100   b , which fit snugly within the member  98 , are positioned so that the land  100   b  will block the exit of hydraulic fluid from the return line  96 , or the land  100   a  will block the exit of hydraulic fluid from the return line  94 , or the lands  100   a  and  100   b  will block the exit of hydraulic fluid from both the return lines  94  and  96 , as is shown in FIG. 10, where the camshaft  26  is being maintained in a selected position relative to the crankshaft of the associated engine. 
     The position of the spool  100  within the member  98  is influenced by an opposed pair of springs  102 ,  104 , which act on the ends of the lands  100   a ,  100   b , respectively. Thus, the spring  102  resiliently urges the spool  100  to the left, in the orientation illustrated in FIG. 10, and the spring  104  resiliently urges the spool  100  to the right in such orientation. The position of the spool  100  within the member  98  is further influenced by a supply of pressurized hydraulic fluid within a portion  98 a of the member  98 , on the outside of the land  100   a , which urges the spool  100  to the left. The portion  98   a  of the member  98  receives its pressurized fluid (engine oil) directly from the main oil gallery (“MOG”)  130  of the engine, and this oil is also used to lubricate a bearing  132  in which the camshaft  26  of the engine rotates. 
     The control of the position of the spool  100  within the member  98  is in response to hydraulic pressure within a control pressure cylinder  134  whose piston  134   a  bears against an extension  100   c  of the spool  100 . The surface area of the piston  134   a  is greater than the surface area of the end of the spool  100  that is exposed to hydraulic pressure within the portion  98 , and is preferably twice as great. Thus, the hydraulic pressures that act in opposite directions on the spool  100  will be in balance when the pressure within the cylinder  134  is one-half that of the pressure within the portion  98   a . This facilitates the control of the position of the spool  100  in that, if the springs  102  and  104  are balanced, the spool  100  will remain in its null or centered position, as illustrated in FIG. 10, with less than full engine oil pressure in the cylinder  134 , thus allowing the spool  100  to be moved in either direction by increasing or decreasing the pressure in the cylinder  134 , as the case may be. 
     The pressure within the cylinder  134  is controlled by a solenoid  106 , preferably of the pulse width modulated type, (PWM), in response to a control signal from an electronic engine control unit (ECU)  108 , shown schematically, which may be of conventional construction. With the spool  108  in its null position when the pressure in the cylinder  134  is equal to one-half the pressure in the portion  198   a , as heretofore described, the on-off pulses of the solenoid  106  will be of equal duration; by increasing or decreasing the on duration relative to the off duration, the pressure in the cylinder  134  will be increased or decreased relative to such one-half level, thereby moving the spool  100  to the right or to the left, respectively. The solenoid  106  receives engine oil from the engine oil gallery  130  through an inlet line  140  and selectively delivers engine oil from such source to the cylinder  134  through a supply line  138 . As is shown in FIGS. 3 and 4, the cylinder  134  may be mounted at an exposed end of the camshaft  26  so that the piston  134   a  bears against an exposed free end  100   c  of the spool  100 . In this case, the solenoid  106  is preferably mounted in a housing  134   b  that also houses the cylinder  134   a.    
     Make-up oil for the recesses  32   a ,  32   b  of the sprocket  32  to compensate for leakage therefrom is provided by way of a small, internal passage  120  within the spool  100 , from the passage  98   a  to an annular space  98   b  of the cylindrical member  98 , from which it can flow into the inlet line  82 . A check valve  122  is positioned within the passage  120  to block the flow of oil from the annular space  98   b  to the portion  98   a  of the cylindrical member  98 . 
     The vane  60  is alternatingly urged in clockwise and counterclockwise directions by the torque pulsations in the camshaft  26  and these torque pulsations tend to oscillate the vane  60 , and, thus, the camshaft  26 , relative to the sprocket  32 . However, in the FIG. 10 position of the spool  100  within the cylindrical member  98 , such oscillation is prevented by the hydraulic fluid within the recesses  32   a ,  32   b  of the sprocket  32  on opposite sides of the lobes  60   a ,  60   b , respectively, of the vane  60 , because no hydraulic fluid can leave either of the recesses  32   a ,  32   b , since both return lines  94 ,  96  are blocked by the position of the spool  100 , in the FIG. 10 condition of the system. If, for example, it is desired to permit the camshaft  26  and the vane  60  to move in a counterclockwise direction with respect to the sprocket  32 , it is only necessary to increase the pressure within the cylinder  34  to a level greater than one-half that in the portion  98   a  of the cylindrical member. This will urge the spool  100  to the right and thereby unblock the return line  94 . In this condition of the apparatus, counterclockwise torque pulsations in the camshaft  26  will pump fluid out of a portion of the recess  32   a  and allow the lobe  62   a  of vane  60  to move into the portion of the recess which has been emptied of hydraulic fluid. However, reverse movement of the vane will not occur as the torque pulsations in the camshaft become oppositely directed unless and until the spool  100  moves to the left, because of the blockage of fluid flow through the return line  96  by the land  100   b  of the spool  100 . While illustrated as a separate closed passage in FIG. 10, the periphery of the vane  60  has an open oil passage slot, element  60   c  in FIGS. 1,  2 ,  6 ,  7  and  8 , which permits the transfer of oil between the portion of the recess  32   a  on the right side of the lobe  60   a  and the portion of the recess  32   b  on the right side of the lobe  60   b , which are the non-active sides of the lobes  60   a ,  60   b ; thus, counterclockwise movement of the vane  60  relative to the sprocket  32  will occur when flow is permitted through return line  94  and clockwise movement will occur when flow is permitted through return line  96 . Further, the passage  82  is provided with an extension  82   a  to the non-active side of one of the lobes  60   a ,  60   b , shown as the lobe  60   b , to permit a continuous supply of make-up oil to the non-active sides of the lobes  60   a ,  60   b  for better rotational balance, improved damping of vane motion, and improved lubrication of the bearing surfaces of the vane  60 . 
     The elements of the structure of FIGS. 1-9 that correspond to the elements of FIG. 10, as described above, are identified in FIGS. 1-9 by the reference numerals that were used in FIG. 10, it is being noted that the check valves  84  and  86  are disc-type check valves in FIGS. 1-9 as opposed to the ball type check valves of FIG.  10 . While disc-type check valves are preferred for the embodiment of FIGS. 1-9, it is to be understood that other types of check valves can also be used. 
     In the embodiment of FIGS. 11 and 12, the various elements are identified by 3 digit reference numerals when an element of the embodiment of FIGS. 11 and 12 corresponds to an element of the embodiment of FIGS. 1-10; the last 2 digits of the element of the embodiment of FIGS. 11 and 12 are the reference numerals for the corresponding element of the embodiment of FIGS. 1-10 and the first digit is 1 digit higher than that of the corresponding element of the embodiment of FIGS. 1-10. Thus in the embodiment of FIGS. 11 and 12, there is provided a variable camshaft timing (VCT) system in which a housing in the form of a sprocket  132  is oscillatingly journalled on a camshaft  126 . The camshaft  126  may be considered to be the only camshaft of a single camshaft engine, either of the overhead camshaft type or the in block camshaft type. Alternatively, the camshaft  126  may be considered to be either the intake valve operating camshaft or the exhaust valve operating camshaft of a dual camshaft engine. In any case, the sprocket  132  and the camshaft  126  are rotatable together, and are caused to rotate by the application of torque to the sprocket  132  by an endless roller chain  138 , shown fragmentarily, which is trained around the sprocket  132  and also around a crankshaft, not shown. As will be hereinafter described in greater detail, the sprocket  132  is oscillatingly journalled on the camshaft  126  so that it is oscillatable at least through a limited arc with respect to the camshaft  126  during the rotation of the camshaft, an action that will adjust the phase of the camshaft  126  relative to the crankshaft. 
     An annular pumping vane  160  is fixedly positioned on the camshaft  126 , the vane  160  having a diametrically opposed pair of radially outwardly projecting lobes  160   a ,  160   b  and being attached to an enlarged end portion  126   a  of the camshaft  126  by bolts  162  that pass through the vane  160  into the end portion  126   a . The lobes  160   a ,  160   b  are received in radially outwardly projecting recesses  132   a ,  132   b , respectively, of the sprocket  132 , the circumferential extent of each of the recesses  132   a ,  132   b  being somewhat greater than the circumferential extent of the vane lobe  160   a ,  160   b  that is received in such recess to permit limited oscillating movement of the sprocket  132  relative to the vane  160 . The recesses  132   a ,  132   b  are closed around the lobes  160   a ,  160   b , respectively, by spaced apart, transversely extending annular plates  166 ,  168  that are fixed relative to the vane  160 , and, thus, relative to the camshaft  126 , by bolts  170  which extend from one to the other through the same lobe,  160   a  or  160   b . Further, the inside diameter  132   c  of the sprocket  132  is sealed with respect to the outside diameter of the portion  160   d  of the vane  160  that is between the lobe  160   a ,  160   b , and the tips of the lobes  160   a ,  160   b  of the vane  160  are provided with seal receiving slots  160   e ,  160   f , respectively, which are adapted to sealingly engage the diametrical surface  132   d  within each of the recesses  132   a ,  132   b . Thus, each of the recesses  132   a ,  132   b  of the sprocket  132  is capable of sustaining hydraulic pressure, and within each recess  132   a ,  132   b  the portion on each side of the lobe  160   a ,  160   b , respectively, is capable of sustaining hydraulic pressure. The annular plate  168  is provided with a plurality of radial projections  168   a-   168   e  non evenly spaced around its exterior to permit a position sensor, not shown, to determine the circumferential position of the plate  168  and the vane  160  based on the spacing detected between an adjacent pair of such projections during a sensing step. 
     The VCT system of the embodiment of FIGS. 11 and 12 is provided with a spool valve  192  and check valves  184 ,  186 , which correspond in structure and function to the spool valve  92  and the check valves  84 ,  86 , respectively, of the embodiment of FIGS. 1-10. 
     During times of low hydraulic fluid pressure within the sprocket  132 , for example, during and shortly after the restarting of the engine incorporating such VCT system in the case of a VCT system that is operated by pressurized engine lubricating oil, the vane  160  is positively latched to the sprocket  132  by a pin  250  that is slidable to and fro within a passage  252  in the sprocket  132 , the passage  252  being spaced from and extending parallel to the longitudinal axis of rotation of the camshaft  126 . The pin  250  has an outer or leading end  250   a  that is hemispherical in shape, and the opposed end of the pin  250  is acted on by a compression spring  254  that is trapped within the passage by a retainer  256  to bias the end  250   a  of the pin  250  outwardly from the passage  252 . The advance of the pin  250  outwardly from the passage  252  is limited by the plate  168 , which rotates with the vane  160 , as heretofore described. 
     The plate  168  has an externally projecting bulge  168   f , which defines an inwardly facing pocket  168   g  of hemispherical configuration, whose radius of curvature is somewhat greater than that of the end  250   a  of the pin  250 . The pocket  168   g  is axially aligned with the passage  252  in a predetermined position of the vane  160  relative to the sprocket  132 , preferably when each of the lobes  160   a ,  160   b  is positioned at the midpoint of its range of travel within its recess  132   a ,  132   b , respectively. Thus, the spring  254  is free to drive the end  250   a  of the pin  250  into the pocket  168   g of the plate  168  when the passage  252  and the pocket  168   g  are in alignment. However, the pocket  168   g  is in communication with the engine oil or other hydraulic fluid that is being used in the VCT system of this embodiment through a passage  132   e  in the sprocket  132 , and when this hydraulic fluid is under pressure, as it will be during normal operation of the engine, hydraulic pressure within the pocket  168   g  will keep all portions of the pin  250  within the passage  252 , to thereby permit oscillation of the vane  160  relative to the sprocket  132  as directed by an engine controller corresponding to the engine control unit  108  of the embodiment of FIGS. 1-10, or otherwise. In this way, the pin  250  will automatically function to latch or lock the position of the vane  160  relative to the sprocket  132  only during periods of low system hydraulic pressure when the vane  160  could otherwise behave erratically because of inadequate hydraulic pressure to ensure its proper operation. Such a condition could otherwise lead to undesired impacts between the lobes  160   a ,  160   b  of the vane  160  and the surfaces of the recesses  132   a ,  132   b , respectively, of the sprocket  132  in which they are received, with excessive noise and impact damage possibly resulting therefrom. 
     Although the best mode contemplated by the inventor for carrying out the present invention as of the filing date hereof has been shown and described herein, it will be apparent to those skilled in the art that suitable modifications, variations, and equivalents may be made without departing from the scope of the invention, such scope being limited solely by the terms of the following claims and the legal equivalents thereof.