PATENT ABSTRACT
A VCT phaser having a mechanical feedback in which no elaborate sensors and its concomitant electronic control loop is required. The phaser has center mounted spool valve controlling the flow of control fluid such that when a command positions the same at a predetermined position, passages within the phaser adjusts to a desired position through the mechanical feedback.

PATENT DESCRIPTION
REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of application Ser. No. 10/959,736, filed Oct. 6, 2004, entitled “CONTROL MECHANISM FOR CAM PHASER”, which claimed an invention disclosed in provisional application No. 60/510,373, filed Oct. 10, 2003, entitled, “CONTROL MECHANISM FOR CAM PHASER,” now abandoned. 
   This application also claims an invention which was disclosed in Provisional Application No. 60/701,265 filed Jul. 21, 2005, entitled “SERVO STYLE VARIABLE CAM TIMING PHASER”. The benefit under 35 USC §119(e) of the U.S. provisional application is hereby claimed, and the aforementioned applications are hereby incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The invention pertains to the field of variable cam timing systems. More particularly, the invention pertains to variable cam timing systems with a control mechanism including a valve with helical slots. 
   BACKGROUND OF THE INVENTION 
   The performance of an internal combustion engine may be improved by the use of dual camshafts, one to operate the intake valves of the various cylinders of the engine and the other to operate the exhaust valves. Typically, one of such camshafts is driven by the crankshaft of the engine, through a sprocket and chain drive or a belt drive, and the other of such camshafts is driven by the first, through a second sprocket and chain drive or a second belt drive. Alternatively, both of the camshafts may be driven by a single crankshaft powered chain drive or belt drive. Engine performance in an engine with dual camshafts may be further improved, in terms of idle quality, fuel economy, reduced emissions or increased torque, by changing the positional relationship of one of the camshafts, usually the camshaft which operates the intake valves of the engine, relative to the other camshaft and relative to the crankshaft, to thereby vary the timing of the engine in terms of the operation of intake valves relative to its exhaust valves or in terms of the operation of its valves relative to the position of the crankshaft. 
   U.S. Pat. No. 5,002,023 describes a VCT system within the field of the invention in which the system hydraulics includes a pair of oppositely acting hydraulic cylinders with appropriate hydraulic flow elements to selectively transfer hydraulic fluid from one of the cylinders to the other, or vice versa, to thereby advance or retard the circumferential position on of a camshaft relative to a crankshaft. The control system utilizes a control valve in which the exhaustion of hydraulic fluid from one or another of the oppositely acting cylinders is permitted by moving a spool within the valve one way or another from its centered or null position. The movement of the spool occurs in response to an increase or decrease in control hydraulic pressure, P C , on one end of the spool and the relationship between the hydraulic force on such end and an oppositely direct mechanical force on the other end, which results from a compression spring that acts thereon. 
   U.S. Pat. No. 5,107,804 describes an alternate type of VCT system within the field of the invention in which the system hydraulics include a vane having lobes within an enclosed housing which replace the oppositely acting cylinders disclosed by the aforementioned U.S. Pat. No. 5,002,023. The vane is oscillatable with respect to the housing, with appropriate hydraulic flow elements to transfer hydraulic fluid within the housing from one side of a lobe to the other, or vice versa, to thereby oscillate the vane with respect to the housing in one direction or the other, an action which is effective to advance or retard the position of the camshaft relative to the crankshaft. The control system of this VCT system is identical to that divulged in U.S. Pat. No. 5,002,023, using the same type of spool valve responding to the same type of forces acting thereon. 
   U.S. Pat. Nos. 5,172,659 and 5,184,578 both address the problems of the aforementioned types of VCT systems created by the attempt to balance the hydraulic force exerted against one end of the spool and the mechanical force exerted against the other end. The improved control system disclosed in both U.S. Pat. Nos. 5,172,659 and 5,184,578 utilizes hydraulic force on both ends of the spool. The hydraulic force on one end results from the directly applied hydraulic fluid from the engine oil gallery at full hydraulic pressure, P S . The hydraulic force on the other end of the spool results from a hydraulic cylinder or other force multiplier which acts thereon in response to system hydraulic fluid at reduced pressure, P C , from a PWM solenoid. Because the force at each of the opposed ends of the spool is hydraulic in origin, based on the same hydraulic fluid, changes in pressure or viscosity of the hydraulic fluid will be self-negating, and will not affect the centered or null position of the spool. 
   U.S. Pat. No. 5,289,805 provides an improved VCT method which utilizes a hydraulic PWM spool position control and an advanced control method suitable for computer implementation that yields a prescribed set point tracking behavior with a high degree of robustness. 
   In U.S. Pat. No. 5,361,735, a camshaft has a vane secured to an end for non-oscillating rotation. The camshaft also carries a timing belt driven pulley which can rotate with the camshaft and is oscillatable with respect to the camshaft. The vane has opposed lobes which are received in opposed recesses, respectively, of the pulley. The camshaft tends to change in reaction to torque pulses, which it experiences during its normal operation and it is permitted to advance or retard by selectively blocking or permitting the flow of engine oil from the recesses by controlling the position of a spool within a valve body of a control valve in response to a signal from an engine control unit. The spool is urged in a given direction by rotary linear motion translating means which, is rotated by an electric motor, preferably of the stepper motor type. 
   U.S. Pat. No. 5,497,738 shows a control system which eliminates the hydraulic force on one end of a spool resulting from directly applied hydraulic fluid from the engine oil gallery at full hydraulic pressure, P S , utilized by previous embodiments of the VCT system. The force on the other end of the vented spool results from an electromechanical actuator, preferably of the variable force solenoid type, which acts directly upon the vented spool in response to an electronic signal issued from an engine control unit (“ECU”) which monitors various engine parameters. The ECU receives signals from sensors corresponding to camshaft and crankshaft positions and utilizes this information to calculate a relative phase angle. A closed-loop feedback system which corrects for any phase angle error is preferably employed. The use of a variable force solenoid solves the problem of sluggish dynamic response. Such a device can be designed to be as fast as the mechanical response of the spool valve, and certainly much faster than the conventional (fully hydraulic) differential pressure control system. The faster response allows the use of increased closed-loop gain, making the system less sensitive to component tolerances and operating environment. 
   U.S. Pat. No. 5,657,725 shows a control system which utilizes engine oil pressure for actuation. The system includes a camshaft that has a vane secured to an end thereof for non-oscillating rotation therewith. The camshaft also carries a housing which can rotate with the camshaft but which is oscillatable with the camshaft. The vane has opposed lobes which are received in opposed recesses, respectively, of the housing. The recesses have greater circumferential extent than the lobes to permit the vane and housing to oscillate with respect to one another, and thereby permit the camshaft to change in phase relative to a crankshaft. The camshaft tends to change direction in reaction to engine oil pressure and/or camshaft torque pulses which it experiences during its normal operation, and it is permitted to either advance or retard by selectively blocking or permitting the flow of engine oil through the return lines from the recesses by controlling the position of a spool within a spool valve body in response to a signal indicative of an engine operating condition from an engine control unit. The spool is selectively positioned by controlling hydraulic loads on its opposed end in response to a signal from an engine control unit. The vane can be biased to an extreme position to provide a counteractive force to a unidirectionally acting frictional torque experienced by the camshaft during rotation. 
   U.S. Pat. No. 6,477,999 shows a camshaft that has a vane secured to an end thereof for non-oscillating rotation therewith. The camshaft also carries a sprocket that can rotate with the camshaft but is oscillatable with respect to the camshaft. The vane has opposed lobes that are received in opposed recesses, 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 of a control valve. The sprocket has a passage extending there through. The passage extends parallel to and is spaced from a longitudinal axis of rotation of the camshaft. A pin is slidable within the passage and is resiliently urged by a spring to a position where a free end of the pin projects beyond the passage. The vane carries a plate with a pocket, 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 is 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 enters the pocket and latches the camshaft and the sprocket together in a predetermined orientation. 
   In addition, it is known to have an electronic feedback loop involving sensors sensing the positions of shafts such as camshaft or crankshaft in a VCT system. For example, pulse wheels are rigidly affixed onto the shafts for the sensors sensing purposes. The sensed pulses are in turn processed into information wherein derived positional information of a rotor or vane in relation to a housing is used to control a control valve (spool) which in turn is used to control a phase relationship. Typically, the spool valve comprises two lands thereon for stopping fluid communications as desired. 
   In Melchior&#39;s U.S. Pat. No. 5,645,017, U.S. Pat. No. 5,649,506, and U.S. Pat. No. 5,507,254, a rotary cylinder is connected to and rotates with a drive shaft by means of a gear pinion. A piston having a vane is connected to the driven shaft. One-way communication circuits are provided in the rotary piston, with check valves carried in the vane. The shaft of the piston is hollow and carries a slidable slide that rotates in synchronism with the driving shaft. The slide includes two external recesses that are separated by an axially extending rib that is helical in shape. The unidirectional circuits include a common section with an end leading to an orifice, which depending on the position of the slide is open to the recesses or closed by the axially extending valve rib. When the slide is in the null position, the fluid cannot move between the chambers, in the chambers or out of the chambers. When some leakage has occurred, causing an undesirably or uncontrolled phase shift, the orifice is uncovered or no longer blocked by the axially extending valve rib, allowing a direct one-way fluid flow passage from a first chamber to a second chamber through a check valve to a common passage, through a recess and back to the other passage leading to the second chamber. The shift in fluid from the first chamber to the second chamber causes the piston and axially extending valve rib to rotate relative to the cylinder until the orifice of the common passage is completely obstructed by the axially extending valve rib. 
   While advancing and retarding of the phase coupling are described as leakage between the chambers, eventually the remaining fluid in the phase coupling will be inadequate to alter the timing between the drive shaft and the driven shaft, due to leakage of the phase coupling as a whole, since a makeup line is not disclosed. The leakage cannot be fixed by moving fluid from one chamber to the other and vice versa, causing the chambers to have an inadequate amount of fluid to properly alter the phase between the drive shaft and the driven shaft. 
   Melchior cannot provide a makeup source to the chambers. Due to the position of the common passage/orifice and the positioning of the axially extending valve rib, makeup fluid cannot enter the chambers when the phase coupling is in the null position or in other positions based on the unidirectional circuits. 
   Since the phase coupling in Melchior&#39;s U.S. Pat. No. 5,645,017, U.S. Pat. No. 5,649,506, and U.S. Pat. No. 5,507,254 cannot be supplied with makeup oil from a supply due to the axially extending valve rib, the axially extending valve rib cannot be used with phasers that require a constant or semi-constant source of oil pressure to operate, such as a torsion assist phaser, an oil pressure actuated phaser, or a hybrid phaser disclosed infra. In an oil pressure actuated or a torsion assist phaser, the main force in moving the vanes is engine oil pressure, with fluid being supplied to a first chamber and simultaneously exhausted from the other chamber to sump. A constant source of pressurized fluid is required in order to actuate the phaser, and thus alternate the phase. In a hybrid phaser, cam torque is used in conjunction with an oil pressure to actuate the phaser and alter the phase. The oil pressure portion of the phaser is used when the cam torque is not large enough or will not be sufficient to alter the phase. Melchior also discloses a stepped shaped rib with similar problems as described above. 
   SUMMARY OF THE INVENTION 
   A VCT phaser having a mechanical feedback in which no elaborate sensors and concomitant electronic control loop is required. The phaser has a center mounted spool valve controlling the flow of control fluid such that when a command positions the same at a predetermined position, passages within the phaser adjust to a desired position through the mechanical feedback. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an exploded view of a phaser assembly of the present invention. 
       FIG. 2  shows a side view of the phaser of the present invention. 
       FIG. 3  shows a perspective view of the phaser of the present invention. 
       FIG. 4  shows a front view of the phaser of the present invention. 
       FIG. 5   a  shows an exemplified phaser of the present invention moving towards a retard position. 
       FIG. 5   b  shows the shape or formation of helical slot in the spool valve in the retard position. 
       FIG. 5   c  shows a cross-sectional view of the relationship of the spool valve to the passages leading to the chambers. 
       FIG. 6   a  shows an exemplified phaser of the present invention moving towards the advance position. 
       FIG. 6   b  shows the shape or formation of helical slot in the advance position. 
       FIG. 6   c  shows a cross-sectional view of the relationship of the spool valve to the passages leading to the chambers. 
       FIG. 7   a  shows a schematic of an oil pressure actuated phaser of a second embodiment in an equilibrium position. 
       FIG. 7   b  shows a schematic of the relationship of the spool valve to the passages leading to the chambers when the oil pressure actuated phaser is moving towards a retard position. 
       FIG. 7   c  shows a schematic of the relationship of the spool valve to the passages leading to the chambers when the oil pressure actuated phaser is moving towards an advance position. 
       FIG. 8   a  shows the position of the spool valve and the helical slot relative to the passages leading to the chambers in an equilibrium position shown of the phaser shown in  FIG. 7   a.    
       FIG. 8   b  shows the position of the spool valve and the helical slot relative to the passages leading to the chambers in the retard position shown of the phaser shown in  FIG. 7   b.    
       FIG. 8   c  shows the position of the spool valve and the helical slot relative to the passages leading to the chambers in the advance position shown of the phaser shown in  FIG. 7   c.    
       FIG. 9  shows a schematic of a torsion assist phaser of a third embodiment in an equilibrium position. 
       FIG. 10  shows a graph of phase angle versus axial spool position. 
       FIG. 11  shows a top down view of a spool valve of a fourth embodiment. 
       FIG. 12  shows an isometric view of the spool valve shown in  FIG. 11 . 
       FIG. 13   a  shows a preferred way to implement an angular constraint. 
       FIG. 13   b  shows a cross-sectional view of  FIG. 13   a.    
       FIG. 14  shows a schematic of a cam torque actuated variable cam timing phaser of a fourth embodiment in an equilibrium position. 
       FIG. 15  shows a schematic of a cam torque actuated variable cam timing phaser of the fourth embodiment moving to the advance position. 
       FIG. 16  shows a schematic of a cam torque actuated variable cam timing phaser of the fourth embodiment in the advance position at equilibrium. 
       FIG. 17  shows a schematic of a cam torque actuated variable cam timing phaser of the fourth embodiment moving to the retard position. 
       FIG. 18  shows a schematic of a cam torque actuated variable cam timing phaser of the fourth embodiment in the retard position at equilibrium. 
       FIG. 19  shows a top down view of the spool valve of an oil pressure actuated variable cam timing phaser of a fifth embodiment. 
       FIG. 20  shows an isometric view of an oil pressure actuated variable cam timing phaser of a fifth embodiment. 
       FIG. 21  shows a schematic of an oil pressure actuated variable cam timing phaser of a fifth embodiment in an equilibrium position. 
       FIG. 22  shows an oil pressure actuated variable cam timing phaser of a fifth embodiment moving to the retard position. 
       FIG. 23  shows a schematic of an oil pressure actuated variable cam timing phaser of a fifth embodiment in the retard position at equilibrium. 
       FIG. 24  shows a schematic of an oil pressure actuated variable cam timing phaser of a fifth embodiment moving to the advance position. 
       FIG. 25  shows a schematic of an oil pressure actuated variable cam timing phaser of a fifth embodiment in the advance position at equilibrium. 
       FIG. 26  shows a schematic of a torsional assist variable cam timing phaser of a sixth embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1 through 4 , a phaser  10 , preferably a cam torque actuated phaser, of a first embodiment is mounted on one end of a camshaft (not shown) with a rotor  14  rigidly affixed onto one end. A control valve  19 , preferably a spool valve is coupled to a sprocket  12 , which is coupled to a crankshaft by means of a timing chain (not shown). Angular adjustment may be achieved by relative movement of the sprocket  12  in relation to rotor  14 . According to the present invention, the angular adjustment is accomplished by moving control valve  19  translationally along axis  34  relatively to the other members of phaser  10 . By positioning spool valve  19  at a plurality of predetermined positions along axis  34 , mechanical feedback or self-adjustment mechanism (details shown infra) adjusts the angular relationship between the sprocket  12  and the rotor  14  and thus the camshaft and the crankshaft. 
     FIG. 2  shows a side view of the assembled phaser  10  of a first embodiment of the present invention. A housing  16  is fixedly attached to a sprocket  12  having an outer circumference of teeth  24  for accepting drive force. A back plate  18  is mounted to the opposite side of the housing  16 . A central bore, shown in  FIG. 1 , is present along axis  34  and slidably receives a spool valve  19 . The spool  20  of the spool valve  19  translationally moves along axis  34 . 
   Referring to  FIGS. 1 and 3 , phaser  10  includes a housing  16  for receiving a rotor  14 . The housing  16  is attached to a back plate  18  and sprocket  12 . Sprocket  12  has teeth  24  on its outer circumference for accepting drive force and a central inner portion  26  that is substantially cylindrical shaped. The central inner portion  26  has a center opening  28  for accommodating control valve  19 , preferably a spool valve. Sprocket  12  also has a key  27  of an elongated shape that protrudes from the central inner portion  26  into center opening  28  for slidably engaging and being received by a notch  30  formed axially on the outer circumference of spool  20 . Sprocket  12  further includes a set of inner openings  29 , of which only three are shown, on the central inner portion  26  of the sprocket  12  for accommodating the maintenance of coupling elements to affix the rotor  14  onto a third member such as a camshaft (not shown). Sprocket  12  also has a set of outer openings  51 , of which only six are shown for affixing the same onto the housing  16  and the back plate  18 . A check valve  22  is also provided. 
   Rotor  14  has a bore  47  centrally located and aligned with the center opening  28  of the sprocket  12 , to allow for the axial movement of spool  20  along an axis  34 . Furthermore, rotor  14  can rotate in relation to spool  20 . Rotor  14  further comprises a first vane  36  and a second vane  38  with the first vane  36  being diametrically opposite from the second vane  38 . The second vane  38  has an opening therein disposed for receiving at least one check valve  22 . 
   The housing  16  encloses the rotor  14 , forming a pair of cavities  40 . The cavities  40  are further divided into advance and retard chambers by the first vane  36  and the second vane  38 , which oscillate therein. The housing  16  has a set of openings  42  identical in numbers as that of outer openings  51  on the back plate  18 . Housing  16  further has an inner bearing surface  46  for rotatably coupling with an outer surface  48  of rotor  14 . 
   Back plate  18  has a center opening  50  having a diameter that is less than the diameter  48  of rotor  14  for contributing to the closure of a set of passages  86 ,  88  for fluid communication between advance and retard chambers defined within cavities  40  and delimited by first vane  36  or the second vane  38 . In other words, part of the back plate  18 , along with portions of the rotor  14  form passages  86 ,  88 , seen in  FIGS. 5   a  and  6   a . Back plate  18  further has a set of openings  51  having identical numbers as that of opening  42  or outer openings  51 . 
   The control valve  19 , preferably the spool valve comprises a pair of helical slots  52  (only one shown) on an outer circumference  20   a  of a spool  20 , which function as a conduit and serve to regulate the flow to the advance and retard chambers. “Slot” being defined as a passage or opening recessed into the outside circumference of the spool. The control valve may be positioned by an actuator (not shown). Key  27  of inner portion  26  is received by or mates with notch  30  of spool  20 , with spool  20  located within center bore  28  of inner portion  26 . Through the mating of key  27  and the notch  30 , sprocket  12  and spool  20  engage each other and rotate in unison together forming a predetermined angular relationship between the sprocket  12  and the spool  20 . Therefore, spool  20  rotates in unison with sprocket  12 , yet spool  20  can still translationally slide along axis  34 . As shown earlier, rotor  14  has an inner bearing surface  46  in which the spool  20  rotates. 
   Referring specifically to  FIG. 4 , an elevated perspective view of phaser  10  is shown. Note the inner openings  29  facilitate the three bolts  54  going through rotor  14 . It is noted that  FIG. 4  merely shows a special case of the angular relationship between sprocket  12  and rotor  14 , in which inner openings  29  of sprocket  12  happens to permit a top view of bolts  54 . Bolts  54  are not affixed onto sprocket  12 , but instead bolts  54  are affixed onto rotor  14  which rotates relative to sprocket  12 . Therefore, at other angular relationships, bolts  54  may only be partially shown or not shown at all. Further, the present figure shows another view of key  27  of sprocket  12  disposed to engage and rotate with spool  20  by way of key  27  engaging notch  30  of spool  20 . In addition, opening  60  may be used to rigidly affix sprocket  12  onto housing  16 . 
     FIGS. 5   a  through  6   c  show schematics of a cam torque actuated (CTA) phaser of a first embodiment of the present invention.  FIGS. 5   a  and  6   a  show a schematic of the CTA phaser of the first embodiment moving towards a retard position and an advance position respectively.  FIGS. 5   b  and  6   b  show the positioning of the helical slot  52  of the spool in relation to the passages  72 ,  74 , and  68 .  FIGS. 5   c  and  6   c , showing an enlarged view of the rotor  14  in relation to the chambers  41   a ,  41   b ,  41   c ,  41   d  and the paths fluid takes to and from the chambers. 
   Torque reversals in the camshaft caused by the forces of opening and closing engine valves move the vanes  36 ,  38 . The advance and retard chambers  41   a ,  41   b ,  41   c ,  41   d  are arranged to resist positive and negative torque pulses in the camshaft (not shown) and are alternatively pressurized by the cam torque. The spool valve  19  in the cam torque actuated system allows the vanes  36 ,  38  in the phaser to move, by permitting fluid flow from the advance chamber  41   a , 41   c  to the retard chamber  41   b ,  41   d  or vice versa, depending on the desired direction of movement. 
   Cavities  40  formed between the housing  16  and the rotor  14  are each subdivided into first and second advance chambers  41   a ,  41   c  and first and second retard chambers  41   b ,  41   d  by a first vane  36  and a second vane  38 . The first advance chamber  41   a  is in fluid communication with the second advance chamber  41   c  through passage  86  and the first retard chamber  41   b  is in fluid communication with the second retard chamber  41   d  through passage  88 . A common passage  62  formed within rotor  14  extends to the second vane  38  with a first end always in fluid communication with a passage  68  in spool  20  via helical slot  52  and a second end ending in a passage  66  in the second vane  38 . “Slot” being defined as a passage or opening recessed into the outside circumference of the spool. A pair of check valves  70 ,  71  in passage  66  is provided to selectively permit control fluid to flow either to the second advance chamber  41   c , or the second retard chamber  41   d.    
   The first retard chamber  41   b  is also selectively coupled to the second advance chamber  41   c  through passages  72 ,  68 ,  62 ,  66  in which at least one of the passages is controlled by helical slot  52  of the spool  20 . Passage  72  connects the first retard chamber  41   b  to the spool  20  and the helical slot  52 . Similarly, the first advance chamber  41   a  is selectively coupled to the second retard chamber  41   d  through passages  74 ,  68 ,  62 ,  66  in which at least one of the passages is controlled by helical slot  52  of the spool  20 . Passage  74  connects the first advance chamber  41   a  to the spool  20  and helical slot  52 . 
   The helical slot  52  of the spool  20  is formed such that as the spool  20  moves translationally along axis  34 , the edges of the helical slot  20  may block the passage  74  or passage  72 , as shown in  FIGS. 5   a  and  6   a . Helical slot  52  is a hollowed out portion or region of spool  20  thereon its outer surface circumference  20   a . Helical slot  52  has six edges. Two of the six edges, specifically longer edges  90  and  92  have a pair of non-zero angles in relation to the generally symmetrical shape of spool  20 . In other words, angle θ 1  and angle θ 2  are of a non-zero value. Further, edges  90  and  92  are of a sufficient length to be at least longer than the diameter of passage  72  or passage  74  respectively. When spool  20  moves translationally back and forth along axis  34 , either passages  68  and  74 , or passages  68  and  72  are permitted to communicate. Therefore, fluid from either retard chamber  41   b ,  41   d  flows toward advance chamber  41   a ,  41   c  or vice versa. The result is that rotor  14  rotates in relation to housing  16 . As shown in  FIG. 10 , the axial position of the spool  20  directly determines the angle or phase of the rotation between rotor  14  and housing  16 . 
   Unlike passage  68  which is part of or formed within spool  20 , passage  72  and passage  74  are not part of spool  20  but a part of rotor. A supply line  89  is in fluid communication with line  68 , providing the necessary makeup oil to the chambers  41   a ,  41   b ,  41   c ,  41   d.    
   In moving towards the retard position of the phaser, as shown in  FIG. 5   a , the spool  20  having an outer circumference  20   a  with at least one helical slot  52  is received in a bore in the rotor  14  with a biasing spring (not shown). An actuator (not shown), which may be controlled by an ECU, moves the spool  20  within the rotor  14 . In moving towards the retard position, the force of the actuator was reduced and the spool  20  was moved by the spring, until the force of the spring balanced the force of the actuator. In the position shown, the outer circumference  20   a  without slot  52  blocks line  72 , and lines  68  and  74  are open. Camshaft torque pressurizes the first and second advance chambers  41   a ,  41   c , causing fluid in the advance chambers  41   a ,  41   c  to move into the retard chambers  41   b ,  41   d . When the first advance chamber  41   a  is pressurized and selected to be in fluid communication with second retard chamber  41   d  through passages  74 ,  68 ,  62 , controlled by helical slot  52  of spool  20 , a first control fluid path  82  is formed (shown in  FIG. 5   c ), and the first vane  36  and the second vane  38  are retarded, forcing fluid out of the first advance chamber  41   a  and into passage  74  leading to the spool  20 . From passage  74 , fluid flows through helical passage  52  and passage  68  to common passage  62 , leading to passage  66  and through check valve  70  and into the second retard chamber  41   d . Fluid from the second retard chamber  41   d  may flow through passage  86  to the first retard chamber  41   b  and vice versa. Fluid from the second advance chamber  41   c  exits the chamber through line  86  connected to the first advance chamber  41   a . The first retard chamber  41   b  is not in fluid communication with the second advance chamber  41   c . Fluid is prevented from flowing out of the first retard chamber  41   b  and through passage  72  to the spool  20  by the outer circumference  20   a  without slot  52 . 
   Makeup oil is supplied to the phaser from supply S to make up for leakage and enters line  89  to the spool valve  19 . An inlet check valve (not shown) may be present in the line  89 . From the helical slot  52  in the spool valve  19  fluid enters line  68  and  62  and then passage  66  and through either of the check valves  70 ,  71 , to the advance chambers and/or the retard chambers  41   a ,  41   b ,  41   c ,  41   d.    
   In moving towards the advance position of the phaser, as shown in  FIG. 6   a , the spool  20  having an outer circumference  20   a  with at least one helical slot  52  is received in a bore in the rotor with a biasing spring (not shown). An actuator (not shown), which may be controlled by an ECU, moves the spool  20  within the rotor  14 . In moving towards the advance position, the force of the actuator was greater than the force of a spring on the opposite side of the spool valve  19 , and the spool  20  was moved by the actuator, until the force of the spring balanced the force of the actuator. In the position shown, the outer circumference  20   a  without slot  52  of the spool blocks line  74 , and lines  68  and  72  are open. Camshaft torque pressurizes the first and second retard chambers  41   b ,  41   d , causing fluid in the retard chambers  41   b ,  41   d  to move into the advance chambers  41   a ,  41   c . When the first retard chamber  41   b  is selected to be in fluid communication with second advance chamber  41   c  through passages  72 ,  68 ,  62 , controlled by helical slot  52  of spool  20 , a second control fluid path  80  is formed (shown in  FIG. 6   c ), and the first vane  36  and the second vane  38  are advanced, forcing fluid out of the first retard chamber  41   b  and into passage  72  leading to the spool  20 . From passage  72 , fluid flows through helical passage  52  through passage  68  to common passage  62 , leading to passage  66  and through check valve  71  and into the second advance chamber  41   c . Fluid from the second advance chamber  41   c  may flow through passage  86  to the first advance chamber  41   a  and vice versa. Fluid from the second retard chamber  41   d  exits the chamber through line  88  connected to the first retard chamber  41   b . The first advance chamber  41   a  is not in fluid communication with the second retard chamber  41   d . Fluid is prevented from flowing out of the first advance chamber  41   a  and through passage  74  to the spool by the outer circumference  20   a  without slot  52 . 
   Makeup oil is supplied to the phaser from supply S to make up for leakage and enters line  89  to the spool valve  19 . An inlet check valve (not shown) may be present in the line  89 . From the helical slot  52  in the spool valve  19  fluid enters lines  68  and  62  and then passage  66  and through either of the check valves  70 ,  71 , to the advance chambers and/or the retard chambers  41   a ,  41   b ,  41   c ,  41   d.    
   The cam torque actuated phaser of the first embodiment provides makeup oil to the chambers through a helical slot  52  in the spool valve  19  that is always open to at least one advance chamber  41   a ,  41   c  and one retard chamber  41   b ,  41   d , through common passage  66  with check valves  70 ,  71  connected to passages  68  and  62  in fluid communication with supply line  89 , allowing fluid to be replenished to the system as necessary due to leakage. Without makeup oil, the phaser would eventually have little or no fluid, preventing adequate control of the phase between the camshaft and the crankshaft or driving and driven members. An inadequate amount of fluid in the phaser may also cause the vanes  36 ,  38  to slam into the walls of the chambers, creating excessive noise. 
     FIGS. 7   a  through  8   c  show an oil pressure actuated (OPA) phaser of a second embodiment. In an oil pressure actuated phaser, engine oil pressure is applied to one side of the vane  36 ,  38  or the other by a control valve  19 . Oil from the opposing chamber is exhausted back to oil sump. The applied engine oil pressure alone is used to move the vanes  36 ,  38 .  FIG. 7   a  shows a schematic of the oil pressure actuated phaser of the second embodiment including a center mounted spool  20  with a helical slot  52  in an equilibrium position.  FIG. 8   a  shows another view of the spool  20  with the helical slot  52  when the phaser is in an equilibrium position.  FIG. 7   b  shows schematic of center mounted spool  20  relative to the passages  23 ,  25   17 ,  13  leading to the chambers when the phaser is moving towards the retard position.  FIG. 8   b  shows another view of the spool  20  with the helical slot  52 , when the phaser is moving towards the retard position.  FIG. 7   c  shows a schematic of a center mounted spool  20  relative to the passages  23 ,  25   17 ,  13  leading to the chambers  41   a ,  41   b ,  41   c ,  41   d , when the phaser is moving towards an advance position.  FIG. 8   c  shows another view of the spool  20  with the helical slot  52  when the phaser is moving towards the advance position. 
   In  FIGS. 7   a  and  8   a , the oil pressure actuated phaser is in an equilibrium position. Lines  23  and  17  leading to sump are blocked by the outer circumference  20   a  of the spool  20  without slot  52 . Advance and retard lines  25 ,  13  are partially open to slot  52  and thus line  68  connected to supply line  89 . The supply line  89  connected to supply and to line  68  supplies the phaser with fluid for actuation and provides any fluid to compensate for leakage. The first advance chamber  41   a  is in fluid communication with the second advance chamber  41   c  via line  86 . The first retard chamber  41   b  is in fluid communication with the second retard chamber  41   d  via line  88 . 
     FIGS. 7   b  and  8   b  show the oil pressure actuated phaser moving towards retard. Only one set of chambers are shown for simplicity. The spool valve  19  is internally mounted in the rotor  14  with a bore receiving a spool  20  with an outer circumference  20   a  having at least one helical slot  52  and a biasing spring  11 . An actuator  9 , which may be controlled by an ECU, moves the spool  20  within the sleeve  15 . In moving towards the retard position, the force of the actuator  9  was less than the force of a spring  11  on the opposite side of the spool  20 , and the spool  20  was moved by the spring  11 , until the force of the spring  11  balanced the force of the actuator  11 . With the spool  20  in this position, fluid from supply  68  is supplied to the retard line  13 , moving the first vane  36  and the second vane  38  in the direction shown, forcing fluid to exit the advance chambers  41   a ,  41   c  through sump line  23  to sump or atmosphere. Advance line  25  and sump line  17  are blocked by the outer circumference  20   a  of the spool without helical slot  52 . 
     FIGS. 7   c  and  8   c  show the oil pressure actuated phaser moving towards an advance position. The spool valve  19  is internally mounted in the rotor  14  having a bore receiving a spool with at least one helical slot  52  and a biasing spring  11 . An actuator  9 , which may be controlled by an ECU, moves the spool  20  within the rotor  14 . In moving towards the retard position, the force of the actuator  9  was greater than the force of the spring  11  on the opposite side of the spool  20 , and the spool  20  was moved by the spring  11 , until the force of the spring  11  balanced the force of the actuator  9 . With the spool  20  in this position, fluid from supply  68  is supplied to the advance line  25 , moving the first vane  36  in the direction shown, forcing fluid to exit the first and second retard chambers  41   b ,  41   d  through sump line  17  to sump or atmosphere. Retard line  13  and sump line  23  are blocked by the outer circumference  20   a  of the spool  20  without the helical slot  52 . 
   In a third embodiment, shown in  FIG. 9 , a torsion assist phaser may also be used with the center mounted spool  20  including a helical slot  52 . In torsion assist phasers, the engine oil pressure is the main force in which moves the vanes  36 ,  38  in the desired direction. A check valve  101  is added in the oil supply line  89  to block oil pressure. Alternatively, two check valves may be added in the supply line to each of the chambers. U.S. Pat. No. 6,883,481 and U.S. Pat. No. 6,763,791 also disclose torsion assist phasers and are hereby incorporated by reference. 
   Referring to  FIGS. 11 ,  12 , and  14  through  17 , a single chamber cam torque actuated (CTA) variable cam timing (VCT) phaser  210  of a fourth embodiment is shown. The phaser is mounted on an end of a camshaft (not shown) with a rotor  214  rigidly affixed onto one end. The housing  216  of the phaser has an outer circumference for accepting drive force (not shown). The rotor  214  is connected to the camshaft (not shown) and is coaxially located within the housing  216 . The rotor  214  has at least one outwardly extending vane  236 , dividing the cavity formed between the housing  216  and the rotor  214  into an advance chamber  241   a  and a retard chamber  241   b . The vane  236  is capable of rotation to shift the relative angular position of the housing  216  and the rotor  214 . A spool valve  219  with a spool  220  is received in a bore of the rotor  214 . The spool  220  has a plurality of lands  220   b ,  220   c  each with an uncut or square edge outer circumference  220   a  and two edges  251   a ,  251   b ,  21   d ,  251   d  forming slots  252   a ,  252   b . The two edges  251   a ,  251   b  forming the first slot  252   a  are at an angle α 1  relative to each other. The two edges  251   c ,  251   d  forming the second slot  252   b  are at an angle α 2  relative to each other. The α angles are preferably the same. The edge  251   a  is at an angle β 1  with respect to axis  234  and the edge  251   c  is at an angle β 2  with respect to axis  234 . The β angles are preferably the same. 
   Two passages  272 ,  274  are present in the rotor  214  and lead from the spool valve  219  to the advance chamber  241   a  and the retard chamber  241   b . The passages  272 ,  274  are connected to each other through passage  268  leading to passage  266  containing check valves  270 ,  271 . The circumferences of the inner openings or flow ports  272   a ,  274   a  of passages  272 ,  274  are tangent to edges  251   a ,  251   c  on the spool  220 , as shown in  FIG. 11  and  FIG. 12 . 
     FIGS. 13   a  and  13   b  shows a preferred way in which the spool  220  is engaged with the housing  216  forming an angular constraint. A pin  230  fixed to the housing  216 , slides in a groove  227  on the spool  220 . While the pin  230  is shown at the back of the phaser, it may also be present at the front end of the phaser. The spool valve  219  is fixed with the housing  216  through the angular constraint of the pin  230  and groove  227 , such that the spool valve  219  has a fixed relative angular position with respect to the housing  216 , but can move freely along the axial direction on axis  234 , as shown in the figures. The angular restraint shown in  FIGS. 13   a  and  13   b  may be present on the oil pressure actuated phaser and the torsion assist phaser described below. 
   Referring to  FIGS. 14 through 18 , torque reversals in the camshaft (not shown) caused by the forces of opening and closing engine valves move the vane  236 . The advance and retard chambers  241   a ,  241   b  are arranged to resist positive and negative torque pulses in the camshaft and are alternatively pressurized by the cam torque. The spool valve  219  in cam torque actuated system allows the vane  236  in the phaser to move, by permitting fluid flow from the advance chamber  241   a  to the retard chamber  241   b  or vice versa, depending on the desired direction of movement. 
   The position of the spool  220  is influenced by spring  209  and an actuator  211  controlled by an ECU. The position of the spool  220  controls the motion, (e.g. to move towards the advance position or the retard position) of the phaser. 
     FIG. 14  shows CTA phaser of the fourth embodiment in an equilibrium position. In the equilibrium position, fluid is prevented from leaving lines  272  and  274  by the outer circumference  220   a  of the spool without edges  251   a ,  251   b ,  251   c ,  251   d  and from the passage  266  by check valves  270  and  271 . Makeup oil is supplied to the phaser from supply S to make up for leakage and enters line  289  and through inlet check valve (not shown) to the spool valve  219 . From the spool valve  219  fluid enters line  268  through either of the check valves  270 ,  271 , to the advance chamber  241   a  or the retard chamber  241   b.    
     FIG. 15  shows the CTA phaser of the fourth embodiment moving towards the advance position and  FIG. 16  shows the CTA phaser of the fourth embodiment in the advance position at equilibrium. 
   Referring to  FIG. 15 , the force of the actuator  209  was increased and the spool  220  was moved to the right by the actuator  209 , against the force of spring  211  in the bore  247 , until the force of the spring  211  balances the force of the actuator  209 . In the position shown, the outer circumference  220   a  of spool land  220   b  without edges  251   a ,  251   b ,  251   c ,  251   d  blocks the exit of fluid from line  274 . Flow port  272   a  is open to slot  252   b  made by edges  251   c . Line  268  is also open. 
   Camshaft torque pressurizes the retard chamber  241   b , causing fluid in the retard chamber  241   b  to move into the advance chamber  241   a . Fluid exiting the retard chamber  241   b  moves through line  272  and flow port  272   a , open to slot  252   b  of the spool  220 . From slot  252   b  of the spool, fluid enters line  268  and travels through open check valve  270  into line  272  and the advance chamber  241 , moving the vane as shown in  FIG. 16 . Check valve  271  is closed. Fluid is prevented from exiting the advance chamber  41   a  by blocked port  274   a.    
   As soon as the rotor  214  and vane  236  move in the advancing direction, the rotor  214  starts to cover the open flow port  272   a . The area of the flow port  272   a  gets smaller and smaller and the vane  236  moves slower and slower as the rotor  214  continues to move in the advancing direction, reducing flow port  272   a  opening until it is blocked or closed by the outer circumference  220   a  of land  220   c  without edges  251   a ,  251   b ,  251   c ,  251   d . Finally, the phaser stops at a new position and reaches equilibrium, where both flow ports  272   a , and  274   a  are blocked as shown in  FIG. 16 . 
   Makeup oil is supplied to the phaser from supply to make up for leakage and enters line  268  and moves through inlet check valve (not shown) to the spool valve  219 . From the spool valve  219  fluid enters line  268  through either of the check valves  270 ,  271 , to either the advance chamber  241   a  or the retard chamber  241   b.    
     FIG. 17  shows the CTA phaser of the fourth embodiment moving towards the retard position and  FIG. 18  shows the CTA phaser of the fourth embodiment in the retard position. 
   Referring to  FIG. 17 , the force of the actuator  209  was decreased and the spool  220  was moved to the left by the spring  211 , against the force of spring  211  in the bore  247 , until the force of the spring  211  balances the force of the actuator  209 . In the position shown, the outer circumference  220   a  of spool land  220   c  blocks the exit of fluid from line  272 . Flow port  274   a  is open to slot  252   a  made by edge  251   a . Line  268  is also open. 
   Camshaft torque pressurizes the advance chamber  241   a , causing fluid in the advance chamber  241   a  to move into the retard chamber  241   b . Fluid exiting the advance chamber  241   a  moves through line  274  and flow port  274   a , open to slot  252   a  of the spool  220 . From slot  252   a  of the spool, fluid enters line  268  and travels through open check valve  271  into line  274  and the retard chamber  241   b , moving the vane  236  as shown in  FIG. 18 . Check valve  270  is closed. Fluid is prevented from exiting the retard chamber  41   b  by blocked port  272   a.    
   As soon as the rotor  214  and vane  236  move in the retard direction, the rotor  214  starts to cover the open flow port  274   a . The area of the flow port  274   a  gets smaller and smaller and the vane  236  moves slower and slower as the rotor  214  continues to move in the retard direction, reducing flow port  274   a  opening until it is blocked or closed by the outer circumference  220   a  of land  220   b  without edges  251   a ,  251   b ,  251   c ,  251   d . Finally, the phaser stops at a new position and reaches equilibrium, where both flow ports  272   a , and  274   a  are completely blocked, by spool lands  220   b ,  220   c  as shown in  FIG. 18 . 
   Makeup oil is supplied to the phaser from supply to make up for leakage and enters line  268  and moves through inlet check valve (not shown) to the spool valve  219 . From the spool valve  219  fluid enters line  268  through either of the check valves  270 ,  271 , to either the advance chamber  241   a  or the retard chamber  241   b.    
     FIGS. 19 and 20  show an oil pressure actuated (OPA) variable cam timing (VCT) phaser  310 . The phaser is mounted on an end of a camshaft (not shown) with a rotor  314  rigidly affixed onto one end. The housing  316  of the phaser has an outer circumference for accepting drive force. The rotor  314  is connected to the camshaft (not shown) and is coaxially located within the housing  316 . The rotor  314  has at least one outwardly extending vane  336 , dividing the cavity  340  formed between the housing  316  and the rotor  314  into an advance chamber  341   a  and a retard chamber  341   b . The vane  336  is capable of rotation to shift the relative angular position of the housing  316  and the rotor  314 . The rotor  314  also has a bore  347  with a sleeve  315  that slidably receives a spool valve  319  with a spool  320 . The spool  320  has a plurality of lands  320   b ,  320   c  each with an uncut or square edge outer circumference  320   a  and slots  352   a ,  352   b ,  352   c ,  352   d . With land  320   b  having slots  352   a  and  352   b  and land  320   c  having slots  352   c  and  352   d . Each slot is made by two edges at an angle α to each other. Slot  352   a  is formed by edges  351   a  and  351   b  at an angle α 1  relative to each other. Slot  352   b  is formed by edges  351   c  and  351   d  at an angle α 2  relative to each other. Slot  352   c  is formed by edges  351   e  and  351   f  at an angle α 3  relative to each other. Slot  352   d  is formed by edges  351   g  and  351   h  at an angle α 4  relative to each other. The α angles are preferably the equal. The edge  351   a  is at an angle β 1  with respect to axis  334 , the edge  351   c  is at an angle β 2  with respect to axis  334 , the edge  351   e  is at an angle β 3  with respect to axis  334 , and the edge  351   g  is at an angle β 4  with respect to axis  334 . The β angles are preferably equal. Edges  351   a ,  351   c ,  351   e ,  351   g  are preferably are parallel to each other. A supply line  389  provides oil from a supply to the spool valve  319 . 
   Two passages  372  and  374  are present in the rotor  314  and lead from the spool valve  319  to the advance chamber  341   a  and the retard chamber  341   b . The circumferences of the inner openings or flow ports  372   a ,  374   a  of passages  372 ,  374  are tangent to both edges  351   a ,  351   c ,  351   e ,  351   g  on the spool  320 , as shown in  FIGS. 19 and 20 . 
     FIGS. 21 through 26  show an oil pressure actuated (OPA) phaser of a fifth embodiment. In an oil pressure actuated phaser, engine oil pressure is applied to one side of the vane  336  or the other by a spool valve  319 . Oil from the opposing chamber is exhausted back to oil sump. The applied engine oil pressure alone is used to move the vane  336 . 
     FIG. 21  shows the oil pressure actuated phaser in equilibrium steady state position. Fluid is prevented from moving from the advance chamber  341   a  to the retard chamber  341   b  or vice versa. Ports  374   a  and  372   a  of passages  372 ,  374  are partially open a small amount to receiving makeup fluid to from supply line  389  as necessary. 
     FIGS. 22  shows the OPA phaser of the fifth embodiment moving towards the retard position and  FIG. 23  shows the OPA phaser of the fifth embodiment in the retard position. 
   Referring to  FIG. 22 , the force of the actuator  309  was increased and the spool  320  was moved to the right by the spring  311 , until the force of the spring  311  balances the force of the actuator  309 . In the position shown, flow ports  374   a  and  372   a  are open to slots  352   a  and  352   c . More specifically, flow port  374   a  is open to slot  352   a  on edge  351   a  and flow port  372   a  is open to slot  352   c  on edge  351   e . Through the slot  352   a  made by angular edges  351   a  and  351   b , flow port  374   a  is open to the atmosphere and slot  352   c  made by angular edges  351   e  and  351   f , flow port  372   a  is open to the source oil supply from line  389 . Assuming the source oil pressure is adequate, fluid from supply line  389  enters port  372   a  and moves through line  372  to the retard chamber  341   b , moving the vane  336  in the direction shown in  FIG. 23 , forcing fluid in the advance chamber  341   a  to exit. Fluid from the advance chamber  341   a  exits through line  374  and through port  374   a  leading to sump or atmosphere. 
   As soon as the OPA phaser rotates in retard direction, the rotor starts to cover both of the open flow ports  372   a ,  374   a . The exposed flow port areas  372   a ,  374   a  become smaller and smaller. Consequently, the SOPA phaser moves slower and slower. Finally, the SOPA phaser stops at a new equilibrium position when the flow ports  372   a ,  374   a  are partially open to receive makeup fluid from supply line  389 , as shown in  FIG. 23 . 
     FIGS. 24  shows the OPA phaser of the fifth embodiment moving towards the advance position and  FIG. 25  shows the OPA phaser of the fifth embodiment in the advance position. 
   Referring to  FIG. 24 , the force of the actuator  309  was decreased and the spool  320  was moved to the left by the spring  311 , against the force of spring  311  in the bore  347 , until the force of the spring  311  balances the force of the actuator  309 . In the position shown, flow ports  374   a  and  372   a  are open to slots  352   b  and  352   d . More specifically, flow port  374   a  is open to slot  352   b  on edge  351   c  and flow port  372   a  is open to slot  352   d  on edge  351   g . Through the slot  352   b  made by angular edge  351   c  and  351   d , flow port  374   a  is open to the source oil supply from line  389  and slot  352   d  made by angular edge  351   g  and  351   h , flow port  372   a  is open to the atmosphere or sump. Assuming the source oil pressure is adequate, fluid from supply line  389  enters port  374   a  and moves through line  374  to the advance chamber  341   a , moving the vane  336  in the direction shown in  FIG. 25 , forcing fluid in the retard chamber  341   b  to exit. Fluid from the retard chamber  341   b  exits through line  372  and through port  372   a  leading to sump or atmosphere. 
   As soon as the OPA phaser rotates in advance direction, the rotor starts to cover both of the open flow ports  372   a ,  374   a . The exposed flow port areas  372   a ,  374   a  become smaller and smaller. Consequently, the OPA phaser moves slower and slower. Finally, the OPA phaser stops at a new equilibrium position when the flow ports  372   a ,  374   a  are partially open to receive makeup fluid from supply line  389 , as shown in  FIG. 25 . 
     FIG. 26  shows a torsion assist (TA) phaser of a sixth embodiment. The torsion assist phaser operates in the same way as OPA phaser with added benefit of using alternating cam torque to help moving VCT by including an inlet check valve  402  in line  389 . U.S. Pat. No. 6,883,481 and U.S. Pat. No. 6,763,791 also disclose torsion assist phasers and are hereby incorporated by reference. 
   By utilizing a center-mounted spool which is located rotationally to the housing as the control valve in the fourth, fifth, and sixth embodiments, the spool has two helical slots which serve to regulate the flow to the advance and retard chambers. Axial displacement or translational movement of the spool allows either the advance or retard chambers to communicate with the common chamber such as common passage of rotor or a supply line. This results in the rotor displacing rotationally until the common chamber or supply line no longer communicates with either the advance or retard chambers. At this point a new equilibrium rotational position for the rotor relative to the housing/spool is reached. Displacements of the rotor from the null position are counteracted by the common chamber or supply line communicating to either the advance and retard chambers. Therefore the rotational position is directly related to the axial position of the center spool. 
   The center spool can be positioned with or actuated upon by such actuators as a variable force solenoid, step motor of by a pressure/force balance (a pressure on one side of the spool reacting against a spring), etc. 
   Slot as used in the present application is defined as a passage or opening recessed into the outside circumference of the spool. 
   The spool valves described above may also be used with a hybrid phaser, which is a CTA phaser with proportional oil pressure as discussed in U.S. Pat. No. 6,997,150 which is hereby incorporated by reference. 
   The actuator in the above embodiments may a variable force solenoid, an differential pressure control system, a regulated pressure control system, or other similar actuators. 
   In phasers of the above embodiments, the axial position of the spool directly determines the angle or phase between the rotor and housing as shown in  FIG. 10 . By having a direct relationship between the axial spool position and the phase angle, a less complicated control system is therefore needed. In conventional phasers, there is a direct relationship between axial spool position and the rate of change of the phaser, therefore needing a higher performance feedback system to control the phaser. 
   Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments are not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.