Abstract:
A variable camshaft timing phaser ( 10; 110; 210 ) in which a rotor ( 12; 112;212 ) that is secured to a rotatable camshaft is selectively advanced or retarded in position relative to a surrounding rotatable housing ( 14; 114, 214 ), the rotor having at least one outwardly extending vane ( 20; 120; 220 ) that is received in an inwardly facing recess ( 18; 118; 218 ). Pressurized oil is selectively delivered to one of an advance portion or a retard portion of the recess, and simultaneously withdrawn from the other of the advance portion and the retard portion, by adjusting the axial position of an axially shiftable spool valve ( 22; 122; 222 ). The spool valve has a null position, and the relative positions of the rotor and the housing are positively locked in position when the spool valve is in its null position by a locking pin ( 48; 148; 248 ). The locking pin is resiliently biased towards a locking position by a spring ( 52; 152; 252 ), and is urged away from its locking position by pressurized oil from a source.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     REFERENCE TO MICROFICHE APPENDIX 
     Not Applicable. 
     FIELD OF THE INVENTION 
     This invention relates to an hydraulic variable camshaft timing (“VCT”) system for an internal combustion engine. More particularly, this invention relates to a system of the foregoing character with a moveable locking pin to lock the relative positions of a rotor attached to a rotating camshaft and a surrounding rotatable housing, which is otherwise relatively oscillatable with respect to the camshaft, during periods of low engine oil pressure and when an engine control system is operating to prevent relative oscillation between the camshaft and the surrounding housing. 
     BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE RELATED ART INCLUDING INFORMATION DISCLOSED UNDER 37 CFR §1.97, 1.98 
     Commonly assigned U.S. Pat. No. 6,250,625 describes an hydraulic VCT system of the self-powered type, that is, a type in which relative oscillating movement between a rotor secured to a rotating camshaft and a rotatable housing that surrounds the camshaft rotor is actuated by torque pulsations in the camshaft as the camshaft alternatingly opens and closes engine intake or outtake valves. The disclosure of the aforesaid U.S. Pat. No. 6,250,625 is incorporated by reference herein. 
     As is disclosed in the foregoing reference, it is desirable to prevent relative oscillation between the camshaft rotor and surrounding housing during periods of low engine oil pressure. To that end, the aforesaid reference teaches the use of an annular locking plate that rotates with the camshaft and is axially moveable relative to the camshaft and the surrounding housing to move into or out of engagement with the housing. Such movement serves to prevent relative oscillating movement between the housing and the camshaft when the locking plate is in engagement with the housing. The locking plate is biased away from locking engagement by engine oil pressure that acts on a surface thereof, and is spring biased into engagement during periods of normal operations by the biasing force of a spring acting on an opposed surface of the locking plate, the oil pressure being sufficient to overcome the biasing force of the spring to keep the locking plate out of its locking position during such periods of normal operation; however, during engine start-up or other periods of low engine oil pressure, the force of the biasing spring will overcome the opposed force of the engine oil, and will move the locking plate into its locking position. 
     Commonly assigned, co-pending U.S. patent application Ser. No. 09/488,903, now U.S. Pat. No. 6,311,655 B1, the disclosure of which is also incorporated by reference herein, also discloses an hydraulic VCT system with an arrangement to prevent relative oscillation between a rotating camshaft, specifically, a vane-carrying rotor that is secured to the camshaft, and a rotating housing that surrounds the camshaft rotor during periods of low engine oil pressure. The VCT system of the &#39;903 application is a system that relies on engine oil pressure for its actuation, rather than camshaft torque pulsations, to cause relative oscillation between the camshaft and the housing, and it relies on a slidable locking piston carried by a lobed rotor attached to the camshaft to slide a locking pin into a position in engagement with the housing during periods of low engine oil pressure. 
     Other patents that disclose various other hydraulic VCT arrangements for preventing relative oscillation between a camshaft and a surrounding housing during periods of low engine oil pressure include U.S. Pat. Nos. 6,053,138 (Trzmiel et al.), 4,858,572 (Shirai et al.) and U.S. Pat. No. 5,797,361 (MiKame et al.). 
     BRIEF DESCRIPTION OF INVENTION 
     The present invention relates to a VCT system, either of the cam torque actuated (“CTA”) type or the engine oil pressure actuated (“OPA”) type, in which the positions of the relatively oscillating camshaft rotor and a surrounding housing can be locked when desired, even during normal operating conditions when engine oil pressure is relatively high. The camshaft rotor carries a slidable pin, which is slidable into and out of locking position with respect to the housing, and the sliding action of the slidable pin is controlled, not strictly as a function of engine oil pressure, but by the position of a control spool valve that is slidable along its axis to selectively control flow into and out of advance and retard chambers of the housing. 
     The control spool valve of the present invention has a centered or null position in which flow into and out of the advance and retard chambers is blocked. At the null position of the spool valve, however, a separate passage that contains the locking pin, which is spring biased towards its locking position and is subject to an opposing hydraulic force to urge it to its unlock position, is depressurized, which results in the locking of the rotor and the housing elements relative to one another. When the spool valve is on one side or another of its null position, the locking pin passage is pressurized to move the pin to its unlock position, at least during periods of adequate engine oil pressure, and oil will flow into one of the advance and retard chambers, and out of the other, to thereby lead to a phase change between the camshaft rotor and the surrounding housing. Thus, the rotor and housing are always positively locked in position relative to one another when there is no need to change the phase therebetween, which is the condition in which the engine control system controls the spool valve to maintain it at its null position. The locking of the positions of the rotor and housing relative to one another can occur at any of many potentially relative positions therebetween, depending on when the control system operates to reposition the spool valve to its null position. 
     Accordingly, it is an object of the present invention to provide an improved hydraulic VCT system. More particularly, it is an object of the present invention to provide a VCT system in which the relative positions of a camshaft rotor and a surrounding housing are positively locked when the control system is operating to control such elements without relative oscillating motion therebetween. 
     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 DESCRIPTIONS OF THE DRAWINGS 
     FIG. 1 is a fragmentary schematic of an hydraulic VCT system according to the present invention in a certain operating condition of the elements thereof; 
     FIG. 2 is a partial fragmentary schematic of the VCT system according to FIG. 1 in a different operating condition of the elements thereof; 
     FIG. 3 is a view like FIG. 1 of a different hydraulic VCT system according to the present invention in a certain operating condition of the elements thereof; 
     FIG. 4 is a partial fragmentary schematic view of the VCT system of FIG. 3 in a different operating condition of the elements thereof; 
     FIG. 5 is a partial, fragmentary schematic view like FIG.  1  and FIG. 3 of yet another hydraulic VCT system according to the present invention in a certain operating condition of the elements thereof; and 
     FIG. 6 is a partial fragmentary schematic view of the VCT system of FIG. 5 in a different operating condition in the elements thereof. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A camshaft phaser according to the present invention is generally identified by reference number  10  in FIG.  1 . The camshaft phaser has a rotor  12  that is secured to a rotatable camshaft, otherwise not shown, and a housing  14  that surrounds the rotor  12 , the housing  14  being rotatable with the rotor  12  and having teeth  16  on its outer periphery to permit it to be driven by a belt or chain from a crankshaft or another camshaft, as is known in the art. The housing  14  has a multitude of inwardly facing recesses  18 , and the rotor  12  carries a multitude of outwardly extending vanes  20 , each of which extends into a recess  18 . The circumferential extent of each recess  18  is greater than that of the vane that extends thereinto, to permit limited oscillating motion of the rotor  12  and the housing  14  with respect to one another. In that regard, each recess has an advance portion  18 A and a retard portion  18 R, which are sealingly separated from one another by the vane  20  that extends into such recess  18 , and the addition of pressurized oil into the advance portion  18 A of the recess  18 , with the simultaneous withdrawal of pressurized oil from the retard portion  18 R of the recess  18 , in a manner that will be hereinafter described in greater detail, will cause the rotor  12  to advance in position relative to the housing  14 . Likewise, the addition of pressurized oil into the retard portion  18 R of the recess  18 , with the simultaneous withdrawal of pressurized oil from the advance portion  18 A of the recess  18 , will cause the rotor  12  to retard in its position relative to the housing  14 . 
     The camshaft phaser  10  further has a spool valve with a spool  22  that is axially shiftable within a passage  24  within the rotating camshaft. The spool  22  has a spaced apart pair of lands  22 A,  22 B that slide snuggly within the passage  24 , and a reduced diameter central portion  22 C between the lands  22 A and  22 B. Pressurized engine oil is delivered from the engine (not shown) to the passage  24  from an inlet line  26 , which discharges the oil into the passage in alignment with the central portion  22 C of the spool  22  in the position of the spool  22  that is shown in FIG. 1, the inlet line  26  being provided with a one-way flow check valve  28  to prevent reverse flow from the passage  24  through the inlet line  26 . Depending on the axial position of the spool  22 , oil from the inlet line can flow from the central portion  22 C into the advance portion  18 A of the recess  18  through an inlet line  30 , or into the retard portion  18 R of the recess  18  through an inlet line  32 , inlet lines  30 ,  32  being provided with one-way flow, check valves  34 ,  36 , respectively, to prevent reverse flow from the advance portion  18 A and the retard portion  18 R to the inlet line  26  through the inlet lines  30  or  32 . 
     The spool  22  is resiliently urged to the right, as shown in FIG. 2 by a spring  38  that acts on an end of the spool  22 , and is urged to the left by a variable force solenoid, shown schematically as element  40 , that acts on the opposed end of spool  22 . In the FIG. 1, null position of the spool  22 , there will be no flow into or out of either the advance portion  18 A or the retard portion  18 R because return lines  42 ,  44  from the advance portion  18 A, and the retard portion  18 R, respectively, are blocked by the lands  22 B,  22 A of the spool  22 , respectively. During this time, oil pressure from the central portion  22   c  of the spool  22  is imposed through an inlet line  46  on a locking pin  48  in a radially extending passage  50  within the rotor  32  to maintain the locking pin  48  out of locking engagement with the housing  14 , notwithstanding that the pin is resiliently biased into such locking engagement by a spring  52  (FIG.  2 ). When the spool  22  is moved either to the right (FIG. 2) of its null position (FIG. 1) or to the left thereof (not shown) by a variation in force imposed on the spool  22  by the solenoid  40 , the inlet line  46  will be blocked either by land  22 B or land  22 A, as the case may be, and the rotor will then be locked in an advance position (not shown) relative to the housing  14  (not shown) or a retard position (FIG. 1) until a control system (not shown) that controls the position of the solenoid  40  acts to return the spool  22  to its null position. Of course, the spring  52  will also act to lock the position of the rotor  12  relative to the housing  14  during periods of low engine oil pressure, even when the spool  22  is in its null position, because the force of the oil pressure on the locking pin  48  will be insufficient to overcome the opposed force imposed on the spool  22  by the spring  52 . It is also contemplated that controlled leakage from the passage  50  may be desirable to prevent the locking pin  48  from moving too rapidly from its unlocked position to its locking position, and to that end an oil outlet line (not shown) with a suitably sized orifice may be provided to permit some slow escape of oil from the passage  50  to the engine sump (not shown). 
     A camshaft torque pulse phaser according to an alternative embodiment of the present invention is generally identified by reference number  110  in FIGS. 3,  4 ; in that regard, each element of FIGS. 3,  4  that corresponds to an element of the embodiment of FIGS. 1,  2  is indicated by a  100  series reference numeral, the last two digits of which are the two digits of the corresponding embodiment of FIGS. 1,  2 . In any case, the phaser  110  has a rotor  112  that is secured to a rotatable camshaft, otherwise not shown, and a housing  114  that surrounds the rotor  112  and it rotatable therewith, the housing  114  having teeth  116  on its outer periphery to permit it to be driven by a belt or chain from a crankshaft or another camshaft, as is known in the art. The housing  114  has a multitude of inwardly facing recesses  118 , and the rotor  112  carries a multitude of outwardly extending vanes  120  each of which extends into a recess  118 . The circumferential extent of each recess  118  is greater than that of the vane  120  that extends thereinto, to permit limited oscillation of the rotor  112  and the housing  114  with respect to one another. In that regard, each recess  118  has an advance portion  118 A and a retard portion  118 R on opposite sides of the vane  120 , and the addition of pressurized oil into the advance portion 1   18 A of the recess  118 , with the simultaneous withdrawal of pressurized oil from the retard portion of  118 R of the recess  118 , in a manner that will be described in greater detail, will cause the rotor  112  to advance in position relative to the housing  114 . Likewise, the addition of pressurized oil into the retard portion 1   18 R of the recess  118 , and the simultaneous withdrawal of pressurized oil from the advance portion  118 A of the recess  118 , will cause the rotor  112  to retard in its position relative to the housing  114 . 
     The phaser  110  has a spool valve with a spool  122  that is axially shiftable within a passage  124  within the rotating camshaft. The spool  122  has a spaced apart pair of lands  122 A,  122 B that slide snugly within the passage  124 , and a reduced diameter central portion  122 C between the lands  122 A,  122 B. Pressurized engine oil is delivered to the passage  124  from an inlet line  126 , which discharges the oil into the passage  124  in alignment with the central portion  122 C of the spool  122  in the position of the spool  122  that is shown in FIG. 3, the inlet line  126  being provided with a one-way flow, check valve  128  to prevent reverse flow from the passage  124  through the inlet line  126 . Depending on the axial position of the spool  122 , oil from the inlet line  126  can flow from the reduced diameter portion  122 C of the spool  122  into the advance portion  118 A of the recess  118  through an inlet line  130 , or into the retard position  118 R of the recess  118  through an inlet line  132 , the lines  130 ,  132  being provided with one-way flow, check valves  134 , 136 , respectively, to prevent reverse flow from the advance portion  118 A and the retard portion A  118 R of the recess  118  to the inlet line  126  through the inlet lines  130 ,  132 . 
     The spool  122  is resiliently urged to the right, as shown in FIG. 3, by a spring  138  that acts on an end of the spool  122 , and is urged to the left by a variable force solenoid, shown schematically as element  140 , that acts on the opposed end of the spool  122 . In the FIG. 3, null position of the spool  122 , there will be no flow into or out of either the advanced portion  118 A or the retard portion  118 R of the recess  118  because return lines  142 ,  144  from the advance portion  118 A and the retard portion  118 R, respectively, are blocked by the lands  122 B,  122 A of the spool  122 , respectively. During this time, oil pressure from the portion  122 C of the spool  122  is imposed through an inlet line  146  on a locking pin  148  in a radially extending passage  150  within the rotor  112 , to maintain the locking pin  148  out of locking engagement with the housing  114 , notwithstanding that it is resiliently biased into such locking engagement by a spring  152  (FIG.  3 ). 
     When the spool  122  is moved either to the right (FIG. 4) of its null position (FIG. 3) or to the left thereof (not shown) by a variation in force imposed on the spool  122  by the solenoid  140 , pressurized oil in the inlet line  146 , which is selectively opened or closed to flow by a valve  160 , will put pressure on the locking pin  148  to drive it out of locking engagement with the housing  114 , against the biasing force of the spring  152 . The valve  160  is selectively opened or dosed under a command from an electronic control  162 , which also controls the force level on the solenoid  140 . Of course, during periods of low engine oil pressure, even when the valve  160  is opened to permit oil to flow through the line  146  to impose a force on the locking pin  148 , such force will be insufficient to overcome the opposed force on the locking pin  148  that is imposed by the spring  152 . Thus, the relative positions of the rotor  112  and the housing  114  are locked on command by the signal imposed on the valve  160  by the electronic control unit  162 , so that no advance or retard movement of the rotor  112  will occur at times when such advance or retard movement is not desired. 
     In the embodiment of FIGS. 5,  6 , elements are identified by the  200  series reference numerals, the last two digits of which are the two digits of the corresponding element of the embodiment of FIGS. 1,  2 , or the last two digits of the corresponding element of the embodiment of FIGS. 3,  4 , as the case may be. 
     The camshaft phaser illustrated in FIGS.  5 , 6  is generally identified by reference numeral  210 , and the phaser  210  has a rotor  212  that is secured to a rotatable camshaft, otherwise not shown, and a housing  214  that surrounds the rotor  212  and is rotatable therewith, the housing  214  having teeth  216  on its outer periphery to permit it to be driven by a belt or chain from a crankshaft or another camshaft, as is known on the art The housing  214  has a multitude of inwardly facing recesses  218 , and the rotor  212  carries a multitude of outwardly extending vanes  220  each of which extends into a recess  218 . The circumferential extent of each recess  218  is greater than that of the vane  220  that extends thereinto to permit limited oscillation of the rotor  212  and the housing  214  with respect to one another. In that regard, each recess  218  has an advance portion  218 A and a retard portion  218 R, and the addition of pressurized oil into the advance portion  218 A, with the simultaneous withdrawal of pressurized oil from the retard portion  218 R, in a manner that will be hereinafter described in greater detail, will cause the rotor  212  to advance in position relative to the housing  214 . Likewise, the addition of pressurized oil into the retard portion  218 R, with the simultaneous withdrawal of pressurized oil from the advance portion  218 A will cause the rotor  212  to retard in its position relative to the housing  214 . 
     The phaser  210  has a spool valve with a spool  222  with four spaced apart lands, namely  222 A, at one end thereof,  222 B, at an opposed and thereof, and spaced apart intermediate lands  222 D,  222 E, which are positioned between the lands  222 A  222 B. This spool further has a first reduced diameter portion  222 F, which is positioned between the lands  222 A,  222 D, a second reduced diameter portion  222 G, which is positioned between the lands  222 B,  222 E, and a third reduced diameter portion  222 C, which is positioned between the lands  222 E,  222 D. The spool  222  is axially slidable within a passage  224  within the rotating camshaft, with the lands  222 A,  222 D,  222 E,  222 B fitting snugly within the passage  224 . 
     Pressurized engine oil is delivered to the passage  224  from an inlet line  226 , which discharges it in alignment with the reduced diameter portion  222 C of the spool  222  in the FIG. 5 position of the spool  222 , which it is its null position. Such pressurized engine oil will then flow either into the advanced portion  218 A of the recess  218 , or the retard portion  218 R, when the spool  222  moves one way or the other from its null position, through a line  230  or a line  232 , as the case may be. When the spool  222  moves from its null position, to permit the rotor  212  to advance or retard which respect to the housing  214 , oil will flow from one or the her of the advance portion  218 A or the retard position  218 R through the line  230  or the line  232 , depending on whether the phaser  210  is operating in an advance mode or retard mode. When t phaser  210  is operating a retard mode, the oil from the advance portion  218 A that flows through the line  230  will then enter the reduced diameter portion  222 G of the spool  222 , from which it will return to a sump (not shown) through a first return line  246 - 1 . Likewise, when the phaser  210  is operating in an advance mode, the oil tom the retard portion  218 R that flows through the line  232  will then enter the reduced diameter portion  222 F of the spool  222 , from which it will return to a sump pump through a second return line  246 - 2 . 
     The spool  222  is resiliently biased to the left, in the orientation shown in FIG. 5, by a spring  238  that acts against an end thereof. A variable force solenoid  240  acts against an opposed end of the spool  222 . At the null or FIG. 1 position of the spool  222 , the solenoid will be operating at 50% of its maximum duty cycle. Thus, if the solenoid  240  operates at more than 50% of its duty cycle, the spool will move to the right, oil will flow into the retard portion  218 R of the recess  218  and out of the advance portion  218 A, and the rotor will retard in its position relative to the housing  214 . Conversely, if the solenoid  240  operates at less than 50% of its duty cycle, the spool  222  will move to the left, and oil will flow into the advance portion  218 A of the recess  218  and out of the retard portion  218 R, and the rotor  212  will advance in its position relative to the housing  214 . 
     A locking pin  248  is slidably positioned in a passage  250  in the rotor  212 , and the locking pin  248  is normally pressurized by engine oil pressure from an inlet line  246 , against an opposing force imposed by a spring  252 , to its unlock position. The oil pressure on the locking pin  248  is controlled by a shut off valve  260  that is controlled by an electronic control unit (not shown), which may be the electronic control unit that controls the operation of the solenoid  240 , to positively lock the positions of the rotor  212  and the housing  214  relative to one another in the null or FIG. 5 position of the-spool  222 , when it is not desired to either advance or retard the positions of the rotor  212  and the housing  214  relative to one another. Movement of the locking pin  248  between its locked and unlocking conditions is slowed by bleeding oil from the advance portion  218 A of the recess  218  into the passage  250  through a branch line  230 - 1 , or by bleeding oil from the retard portion  218 R through a branch line  230 - 2 . The branch lines  230 - 1 ,  230 - 2  are provided with one ay flow control valves  2701 ,  2702  to prevent backflow of oil from the passage  250  into the lines  230 ,  232 , respectively. 
     Although the best mode contemplated by the inventors 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 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.