Abstract:
The present invention increases cold temperature oil flow through the variable cam timing (VCT) phaser to reduce the amount of time it takes to replace this oil with warmer low viscosity oil and thereby improve performance. Furthermore the oil flow through the VCT phaser is reduced once the oil temperature reaches the minimum operating temperature for the VCT phaser to operate and the VCT phaser is commanded to move from the park position. Therefore, the VCT phaser is charged with hot engine oil and is commanded to move from the parked position. The VCT phaser reduces oil flow through the phaser at high oil temperatures and low oil viscosity while adding the benefit of increased oil flow through the phaser at low oil temperatures and high oil viscosity to facilitate getting warmer oil into the VCT phaser sooner for increased VCT performance.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims one or more inventions which were disclosed in Provisional Application No. 61/167,407, filed Apr. 7, 2009, entitled “VENTING MECHANISM TO ENHANCE WARMING OF A VARIABLE CAM TIMING MECHANISM”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention pertains to the field of variable cam timing systems. More particularly, the invention pertains venting of the variable cam timing phaser or mechanism to enhance warming of a variable cam timing phaser. 
         [0004]    2. Description of Related Art 
         [0005]    During engine startup, when an engine is cold and the oil viscosity is high there is a delay in getting warm engine oil to flow through the variable cam timing (VCT) mechanism, and therefore delays occur in obtaining the increased performance of the VCT mechanism when hot oil is available. Since the VCT mechanism is a hydraulic mechanism that uses engine oil as its working fluid, the performance of the VCT mechanism is reduced at a higher oil viscosity. Therefore, it is desirable to introduce warm oil to the VCT mechanism as soon as possible to increase the VCT mechanism&#39;s performance. 
         [0006]    Most prior art VCT mechanisms are designed to limit oil consumption when the engine oil is hot and at low viscosities. This same design limitation also limits the exchange of oil in the phaser at low oil temperatures and higher viscosities. The low exchange rate of oil in a typical VCT therefore limits the rate at which warmer oil is introduced to the VCT during the engine warm up cycle. 
         [0007]    This design delays getting warm engine oil to flow through the VCT mechanism and therefore delays the increased performance the VCT mechanism experiences using hot oil. The VCT mechanism&#39;s performance can affect cold start emission and cold engine drivability so it is desirable to introduce warm oil into the VCT mechanism as soon as possible. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention increases cold temperature oil flow through the variable cam timing (VCT) phaser to reduce the amount of time it takes to replace this oil with warmer low viscosity oil and thereby improve performance. Furthermore the oil flow through the VCT phaser is reduced once the oil temperature reaches the minimum operating temperature for the VCT phaser to operate and the VCT phaser is commanded to move from the park position. Therefore, the VCT phaser is charged with hot engine oil and is commanded to move from the parked position. The VCT phaser reduces oil flow through the phaser at high oil temperatures and low oil viscosity while adding the benefit of increased oil flow through the phaser at low oil temperatures and high oil viscosity to facilitate getting warmer oil into the VCT phaser sooner for increased VCT performance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0009]      FIG. 1  shows a schematic of variable cam timing phaser of a first embodiment moving towards a retard position in which passage to a vent is closed and a lock pin is in a locked position. 
           [0010]      FIG. 2  shows a schematic of a variable cam timing phaser of a first embodiment moving towards a retard position in which passage to a vent is open and a lock pin is in a locked position. 
           [0011]      FIG. 3  shows a schematic of a variable cam timing phaser of a first embodiment moving towards an advance position in which passage to a vent is closed and a lock pin is unlocked. 
           [0012]      FIG. 4  shows a schematic of a variable cam timing phaser of a first embodiment in a null position in which passage to a vent is closed and a lock pin is unlocked. 
           [0013]      FIG. 5  shows a schematic of a cross-section of a variable cam timing phaser of a second embodiment in which vent holes on an outer plate are unblocked. 
           [0014]      FIG. 6  shows a schematic of a cross-section of a variable cam timing phaser of a second embodiment in which vent holes on an outer plate are blocked. 
           [0015]      FIG. 7  shows a cross-section along line  7 - 7  of  FIG. 5 . 
           [0016]      FIG. 8  shows a schematic of a cross-section of a variable cam timing phaser of a third embodiment in which slots on an inner plate are unblocked. 
           [0017]      FIG. 9  shows a schematic of a cross-section of a variable cam timing phaser of a third embodiment in which slots in an inner plate are blocked. 
           [0018]      FIG. 10  shows a cross-section along line  19 - 10  of  FIG. 8 . 
           [0019]      FIG. 11  shows a schematic of a variable cam timing phaser of a fourth embodiment moving towards a retard position in which fluid vents through the spool and a lock pin is locked. 
           [0020]      FIG. 12  shows a schematic of a variable cam timing phaser of a fourth embodiment in a null position in which fluid is prevented from venting through the spool and a lock pin is unlocked. 
           [0021]      FIG. 13  shows a schematic of a variable cam timing phaser of a fourth embodiment moving towards an advance position in which fluid is prevented from venting through the spool and the lock pin is unlocked. 
           [0022]      FIG. 14  shows a cross-section of a variable cam timing phaser of a first embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIGS. 1 through 14  show the operating modes of a variable cam timing (VCT) mechanism or phaser depending on spool valve position. The positions shown in the figures define a direction the VCT phaser is moving to. It is understood that the phase control valve  109 ,  159  has an infinite number of intermediate positions and is not limited to the positions shown in the Figures. 
         [0024]    Internal combustion engines have employed various mechanisms to vary the angle between the camshaft and the crankshaft for improved engine performance or reduced emissions. The majority of these variable camshaft timing (VCT) mechanisms use one or more “vane phasers” on the engine camshaft (or camshafts, in a multiple-camshaft engine). In most cases, the phasers have a rotor assembly  105  with one or more vanes  104 , mounted to the end of the camshaft  126 , surrounded by a housing assembly  100  with the vane chambers into which the vanes fit. It is possible to have the vanes  104  mounted to the housing assembly  100 , and the chambers in the rotor assembly  105 , as well. The housing assembly  100  of the VCT phaser is attached to a first outer end plate  175  on a first side and a second inner end plate  176  on an opposite side. The first outer end plate  175  and the second inner end plate  176  close off the chambers formed between the housing assembly  100  and the rotor assembly  105  that receive the vanes of the rotor assembly  105  and define the advance chambers  102  and the retard chambers  103 . The second inner end plate  176  has a circumference  101  that forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possible from another camshaft in a multiple-cam engine. 
         [0025]    Alternatively, the housing assembly  100  may have a circumference  101  that forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possible from another camshaft in a multiple-cam engine. 
         [0026]    Referring to  FIGS. 1-3  of the first embodiment, torque reversals in the camshaft  126  caused by the forces of opening and closing engine valves move the vane  104 . The advance and retard chambers  102 ,  103  are arranged to resist positive and negative torque pulses in the camshaft  126  and are alternatively pressurized by the cam torque. The control valve  109  allows the vane  104  in the phaser to move by permitting fluid flow from the advance chamber  102  to the retard chamber  103  or vice versa, depending on the desired direction of movement. 
         [0027]    The rotor assembly  105  is connected to the camshaft  126  and is coaxially located within the housing assembly  100 . The rotor assembly  105  has at least one vane  104  separating a chamber formed between the housing assembly  100  and the rotor assembly  105  into an advance chamber  102  and a retard chamber  103 . The vanes  104  are capable of rotation to shift the relative angular position of the housing assembly  100  and the rotor assembly  105 . 
         [0028]    A lock pin  125  is slidably housed in a bore in the rotor assembly  105  and has an end portion that is biased towards and fits into a recess  127  in the housing assembly  100  by a spring  124 . Alternatively, the lock pin  125  may be housed in the housing assembly  100  and be spring  124  biased towards a recess  127  in the rotor assembly  105 . The pressurization of line  132  leading to the lock pin  125  is controlled by the switching/movement of the phase control valve  109 . 
         [0029]    A control valve  109 , preferably a spool valve, includes a spool  111  with cylindrical lands  111   a ,  111   b , and  111   c  slidably received in a sleeve  116  within a bore in the rotor assembly  105  and pilots in the camshaft  126 . One end of the spool contacts spring  115  and the opposite end of the spool contacts a control means  107 . The control means may be a pulse width modulated variable force solenoid (VFS)  107 , a motor, other actuators, or a solenoid that is linearly controlled by varying current or voltage or other methods as applicable. 
         [0030]    The position of the spool  111  is influenced by spring  115  and the control means  107  controlled by an ECU (not shown). Further detail regarding control of the phaser is discussed in detail below. The position of the spool  111  controls the motion (e.g. to move towards the advance position, holding position, or the retard position) of the phaser, whether the lock pin  125  is locked or unlocked, and whether fluid source oil may flow continuously through the variable cam timing phaser to vent or sump  122  to bring warm oil from the engine sump to the VCT phaser sooner during the engine warm-up cycle. 
         [0031]    Normally, to minimize oil consumption, the locking pin passage  132  would only communicate to the source oil pressure  121  to release the locking pin  125  from recess  127  or it would only communicate to the venting passage  122  to engage the locking pin  125  but not both source oil  121  and venting to vent passage  122  at the same time. 
         [0032]    In the first embodiment the spool valve  109  is such that the fluid from lock pin passage  132  is open to vent to vent passage  122  and source oil  121  is also connected to the venting passage  122 , such that there is simultaneously continuous oil flowing out of the vent passage  122  from the lock pin  125  and source oil  121 . This increased oil flow would bring warm oil from the engine sump to the VCT phaser sooner during the engine warm up cycle. Once the VCT phaser is warm and commanded to move the vent passage  122  would be blocked or substantially reduced. By including a venting position within a VCT phaser, increased flow of cold oil for reduced time to introduce warm oil to the VCT phaser and reducing oil flow once the VCT phaser is operational with hot oil may be achieved. 
         [0033]    It should be noted that the phase control valve  109  is an active control system for allowing for continuous venting from source oil  121  to sump  122  when the spool  111  is in a base timing position or default position in which the spool  111  is biased out from the sleeve  116  completely by the spring  115  only without any influence from the actuator  107 . The base timing position or parking position is also the position of the spool  111  in which engine warm-up occurs. 
         [0034]    In the advance mode, as shown in  FIG. 3 , the spool  111  is moved to a position so that fluid may flow from the retard chamber  103  through the spool  111  to the advance chamber  102 , and fluid is blocked from exiting the advance chamber  102 . Fluid from source  121  unlocks the lock pin  125  by pressurizing line  132 , and venting of fluid from source  121  through spool  111  is prevented. 
         [0035]    In a retard mode as shown in  FIG. 1 , the spool  111  is moved to a position so that fluid may flow from the advance chamber  102  through the spool  111  to the retard chamber  103 , fluid is blocked from exiting the retard chamber  103 . The lock pin  125  is locked and venting of fluid from source  121  through the spool  111  is prevented. 
         [0036]    In venting mode as shown in  FIG. 2 , the spool  111  is moved to a position so that fluid may flow from the advance chamber  102  through the spool  111  to the retard chamber  103 , fluid is blocked from exiting the retard chamber  103 , a lock pin  125  is locked, and a small amount of fluid from source  121  may flow through a line  119   a  and the spool  111  to sump or vent  122 . 
         [0037]    In null mode as shown in  FIG. 4 , the spool  111  is moved to a position that blocks the exit of fluid from the advance and retard chambers  102 ,  103 , and venting of fluid from source  121  to vent  122  is not permitted. Makeup oil may be supplied to the advance and retard chambers  102 ,  103  as needed. Fluid from source  121  unlocks the lock pin  125  by pressurizing line  132 . 
         [0038]      FIG. 1  shows the phaser moving towards the retard position. To move towards the retard position, the force of the control means  107  on the spool  111  is changed, such that the spool  111  is moved to the left in a retard mode in the figure by spring  115 , until the force of spring  115  balances the force of the control means  107 . In the retard mode shown, spool land  111   c  blocks line  113  and lines  112  and  114  are open. Camshaft torque pressurizes the advance chamber  102 , causing fluid in the advance chamber  102  to move into the retard chamber  103 , and the vane  104  to move accordingly. Fluid exits from the advance chamber  102  through line  112  to the control valve  109  between spool lands  111   b  and  111   c  and recirculates back to central or common line  114  and line  113  leading to the retard chamber  103 . 
         [0039]    Makeup oil is supplied to the phaser from supply S  121  to make up for leakage and enters line  119  through a bearing  120 . Line  119  splits into two lines  119   a  and  119   b . Line  119   b  leads to an inlet check valve  118  and the control valve  109 . From the control valve  109 , fluid enters line  114  through either of the check valves  108 ,  110 , depending on which is open to the chambers  102 ,  103 . Line  119   a  leads to control valve  109  and is blocked by land  111   b  from pressurizing line  132  and from biasing the lock pin  125  to an unlocked position, and therefore, the lock pin  125  remains in a locked position, engaged with recess  127 . Exhaust line  122  is open to line  132 , so while any fluid that may have been present in this line vents, there is no constant amount of fluid that vents when the spool is in this position and would not contribute to warming up of the phaser. 
         [0040]      FIG. 2  shows the phaser moving towards a venting position. To move towards a venting position, the force of the control means  107  on the spool  111  is changed and the spool  111  is moved to a venting mode in the figure, until the force of spring  115  balances the force of the control means  107 . In a venting mode shown, spool land  111   c  blocks line  113  and lines  112  and  114  are open. Camshaft torque pressurizes the advance chamber  102 , causing fluid in the advance chamber  102  to move into the retard chamber  103 , and the vane  104  to move accordingly. Fluid exits from the advance chamber  102  through line  112  to the control valve  109  between spool lands  111   b  and  111   c  and recirculates back to central line  114  and line  113  leading to the retard chamber  103 . 
         [0041]    Makeup oil is supplied to the phaser from supply S  121  to make up for leakage and enters line  119  through a bearing  120 . Line  119  splits into two lines  119   a  and  119   b . Line  119   b  leads to an inlet check valve  118  and the control valve  109 . From the control valve  109 , fluid enters line  114  through either of the check valves  108 ,  110 , depending on which is open to the chambers  102 ,  103 . Line  119   a  leads to control valve  109  and is open such that fluid may continuously flow from supply or source oil  121  to vent passage  122  through the spool  111  between lands  111   a  and  111   b . The pressure of the fluid that flows between line  119   a  and vent passage  122  is not great enough to pressurize line  132  and bias the lock pin  125  away from recess  127 , and therefore, the lock pin  125  remains in a locked position, engaged with recess  127 . Exhaust line  122  is open to line  132 , so while any fluid that may have been present in this line vents, there is no constant amount of fluid from line  132  and would not contribute to warming up of the phaser. 
         [0042]      FIG. 3  shows the phaser moving towards the advance position. To move towards the advance position, the force of the control means  107  on the spool  111  is increased and the spool  111  is moved to the right by the control means  107  in an advance mode, until the force of the spring  115  balances the force of the control means  107 . In the advance mode shown, spool land  111   b  blocks line  112  and lines  113  and  114  are open. Camshaft torque pressurizes the retard chamber  103 , causing fluid to move from the retard chamber  103  and into the advance chamber  102 , and the vane  104  moves accordingly. Fluid exits from the retard chamber  103  through line  113  to the control valve  109  between spool lands  111   b  and  111   c  and recirculates back to central line  114  and line  112  leading to the advance chamber  102 . 
         [0043]    Makeup oil is supplied to the phaser from supply S  121  to make up for leakage and enters line  119  through a bearing  120 . Line  119  splits into two lines  119   a  and  119   b . Line  119   b  leads to an inlet check valve  118  and the control valve  109 . From the control valve  109 , fluid enters line  114  through either of the check valves  108 ,  110 , depending on which is open to the chambers  102 ,  103 . Line  119   a  leads to control valve  109  and is open to line  132  leading to the lock pin  125  The pressure of the fluid in line  119   a  moves through the spool  111  between lands  111   a  and  111   b  to pressurize line  132  and bias the lock pin  125  against the spring  124  to a released position. Exhaust line  122  is blocked by spool land  111   a , preventing the lock pin  125  from venting. 
         [0044]    When the phaser in the holding position as shown in  FIG. 4 , the force of the control means  107  on one end of the spool  111  equals the force of the spring  115  on the opposite end of the spool  111  in holding mode. The lands  111   b  and  111   c  block the flow of fluid to lines  112  and  113  respectively. Makeup oil is supplied to the phaser from supply S  121  by to make up for leakage and enters line  119  through a bearing  120 . Line  119  splits into two lines  119   a  and  119   b . Line  119   b  leads to inlet check valve  118  and the control valve  109 . From the control valve  109 , fluid enters line  114  through either of the check valves  108 ,  110 , depending on which is open to the chambers  102 ,  103 . Fluid from source  121  unlocks the lock pin  125  by pressurizing line  132 . 
         [0045]    The lock pin  125  may be used without using a control means  107  (i.e. use it as a passive system) by increasing venting that occurs at the default spool valve position or at a base timing of the phaser that occurs in the VCT phaser when the control system is turned off. Base timing or default position of the spool is when the spool  111  is biased out from the sleeve  116  completely by the spring  115  only without any influence from the actuator  107 . The base timing position or parking position is also the position of the spool  111  in which engine warm-up occurs. 
         [0046]    Preferably, and as shown in  FIG. 2  the lock pin  125  may be used with a control means  107  to manage the venting process and the spool valve porting is designed such that a low amount of duty cycle or no duty cycle applied to the control valve  109  of the VCT phaser would move the spool  111  to a position of continuous venting of the source oil  121  out the vent passage  122  until the VCT phaser is commanded to move and the venting is substantially reduced. 
         [0047]      FIGS. 5 through 10  show schematics of cross-sections of a variable cam timing phaser of second and third embodiments. The variable cam timing phaser in  FIGS. 5-10  each have a rotor assembly  105  is connected to the camshaft and is coaxially located within the housing assembly  100 . The rotor assembly  105  has at least one vane  104  separating a chamber formed between the housing assembly  100  and the rotor assembly  105  into an advance chamber  102  and a retard chamber  103 . The vanes  104  are capable of rotation to shift the relative angular position of the housing assembly  100  and the rotor assembly  105 . It is possible to have the vanes  104  mounted to the housing assembly  100 , and the chambers in the rotor assembly  105 , as well. The housing assembly  100  of the VCT phaser of the second and third embodiments is attached to a first outer end plate  175  on a first side and a second inner end plate  176  on an opposite side. The first outer end plate  175  and the second inner end plate  176  close off the chambers formed between the housing assembly  100  and the rotor assembly  105  that receive the vanes of the rotor assembly  105  and define the advance chambers  102  and the retard chambers  103 . The second inner end plate  176  has a circumference  101  that forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possible from another camshaft in a multiple-cam engine. 
         [0048]    Torque reversals in the camshaft caused by the forces of opening and closing engine valves move the vane  104 . The advance and retard chambers  102 ,  103  are arranged to resist positive and negative torque pulses in the camshaft  126  and are alternatively pressurized by the cam torque. A control valve, not shown in  FIGS. 5-10 , but similar to control valve  109  discussed above, allows the vane  104  in the phaser to move by permitting fluid flow from the advance chamber  102  to the retard chamber  103  or vice versa, depending on the desired direction of movement. 
         [0049]    In the second and third embodiments, a controlled leak path or venting mechanism is created in the chambers  103  by including vent holes  145  or vent grooves  146  on the first outer end plate  175 , in the second inner end plate  176 , or both the first outer end plate  175  and the second inner end plate  176  to allow source oil  121  to flow into a common passage, such as passage  114  shown in  FIGS. 1-3  to the chambers  103 , such that a controlled leak path out of one or more of the VCT chambers  103  is present. The vent grooves  146  are preferably net-formed or worm trails, eliminating the need to drill holes in the second inner end plate  176 . Additionally, the vent grooves  146  are preferably placed so that they are open or unblocked by the vane  104  when the VCT phaser is at a base timing and are closed off or blocked by the vane  104  of the rotor assembly  105  as it rotates away from base timing. 
         [0050]    Preferably, more than one of the chambers  102 ,  103  has a leak path present. Furthermore, the leak path is shown to be in the retard chambers  103 , however, the leak path may also be present in the advance chambers  102  of the variable cam timing phaser. 
         [0051]    The vent groove  146  or vent holes  145  may also be equipped with a pressure relief valve, a one way check valve, or a temperature compensating valve. Source oil is typically higher at cold temperatures. A pressure relief valve may be used that would allow the higher oil pressure to leak at cold temperatures and would stay shut (supply oil pressure below valve pop off pressure) once the supply oil pressure reduced at warmer temperatures. If there is sufficient variation in source oil pressure, the amount of oil leaking from the phaser is limited once the oil is warm. If there is not enough variation in the oil pressure between hot and cold a spring loaded check valve would prevent oil from leaking out of the chambers  102 ,  103  when the engine is off. It will also prevent air from entering the chambers. 
         [0052]    A temperature compensating valve may also be used to allow oil to vent at cold temperature and prohibit the flow of oil through the vent(s) after the oil warms up. This would allow for the exchange of cold oil after soaking the VCT phaser at cold temperature, but would eliminate oil loss at warm temperature. 
         [0053]    Any of the above described embodiments may also include a flow path for the warmer source oil that increases the surface area exposed as the oil is flowing through the phaser. An example of this would be to require the oil to flow through a groove on the face of the rotor or cam end while it is being vented. This would increase the surface area and increase the volume of warm oil in the VCT phaser, increasing the warming rate of the oil in the phaser. 
         [0054]    Referring to  FIGS. 5-7 , vent holes  145  are present on a first outer end plate  175  and the second inner end plate  176  of the phaser. When the phaser is in a retard position as shown in  FIG. 5 , and the vane  104  is adjacent an advance wall  147  in the chamber defined between the rotor assembly  105  and the housing assembly  100 , the vent hole  145  is exposed to fluid in the retard chamber  103 . When the phaser is in an advanced position as shown in  FIG. 6 , and the vane  104  is adjacent the retard wall  148 , the vent hole  145  is blocked by the vane  104 , preventing any controlled leakage of fluid from the retard chamber  103 . 
         [0055]    Referring to  FIGS. 8-10 , vent grooves  146  are present on a second inner end plate  176  and the first outer end plate  175  of the phaser. When phaser is in a retard position as shown in  FIG. 8 , and the vane  104  is adjacent an advance wall  147  in the chamber defined between the rotor assembly  105  and the housing assembly  100 , the vent groove  146  is exposed to fluid in the retard chamber  103 . When the phaser is in an advanced position as shown in  FIG. 9 , and the vane  104  is adjacent the retard wall  148 , the vent groove  146  is blocked by the vane  104 , preventing any controlled leakage of fluid from the retard chamber  103 . 
         [0056]    By using the mating components of the rotor assembly  105  and the first outer end plate  175  and the rotor assembly  105  and the second inner end plate  176  as a sort of “on/off” valve, the oscillation of the phaser will not increase due to the leakage from the controlled venting of the controlled leak path through the vent grooves  146  or vent holes  145  when the phaser is off the base stop or not in a base timing position. Furthermore, the system is passive and does require active control from the control valve as described above relative to  FIGS. 1-4 . The “on/off” valve may also be accomplished, in addition to the examples described above by placing a vent groove or vent hole on a sealing face of one of the end plates near an edge of the rotor assembly, such as the lock pin vane, when the rotor assembly is at base position or base timing. The “on/off” valve could be accomplished in the radial direction between mating components if the fit is tight enough to act as a seal. Using the mating sealing faces of the components as an “on/off” valve eliminates the need for additional components and keeps cost low. 
         [0057]    Any of the above described embodiments may also include a flow path for the warmer source oil that increases the surface area exposed as the oil is flowing through the phaser. An example of this would be to require the oil to flow through a vent groove on the face of the rotor assembly  105  or cam end while it is being vented. This would increase the surface area and increase the volume of warm oil in the VCT phaser, increasing the warming rate of the oil in the phaser. 
         [0058]    If only one chamber  102 ,  103  of the VCT phaser contains a vent groove  146  or vent hole  145 , the vented chamber  102 ,  103  is selected so the oil is required to flow around the annulus groove in the sleeve of the control valve to reach the vented chamber. This would increase the contact area exposed to the warmer oil improving the warming rate of the VCT phaser. 
         [0059]      FIG. 11 through 13  show schematics of a variable cam timing phaser of a fourth embodiment. In this embodiment, the control valve  159  of the VCT phaser or mechanism has been shortened such that at a spool out position or at base timing of the phaser, the porting  112  or  113  leading to the chambers  102 ,  103  is exposed to the back of the control valve  159  which is vented to atmosphere or sump. 
         [0060]    Internal combustion engines have employed various mechanisms to vary the angle between the camshaft and the crankshaft for improved engine performance or reduced emissions. The majority of these variable camshaft timing (VCT) mechanisms use one or more “vane phasers” on the engine camshaft (or camshafts, in a multiple-camshaft engine). In most cases, the phasers have a rotor assembly  105  with one or more vanes  104 , mounted to the end of the camshaft  126 , surrounded by a housing assembly  100  with the vane chambers into which the vanes fit. It is possible to have the vanes  104  mounted to the housing assembly  100 , and the chambers in the rotor assembly  105 , as well. The housing assembly  100  may have a circumference  101  that forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possible from another camshaft in a multiple-cam engine. Alternatively, a circumference that forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possible from another camshaft in a multiple-cam engine may be present on an end plate of the phaser as shown in  FIG. 14 . 
         [0061]    Torque reversals in the camshaft caused by the forces of opening and closing engine valves move the vane  104 . The advance and retard chambers  102 ,  103  are arranged to resist positive and negative torque pulses in the camshaft  126  and are alternatively pressurized by the cam torque. The control valve  159  allows the vane  104  in the phaser to move by permitting fluid flow from the advance chamber  102  to the retard chamber  103  or vice versa, depending on the desired direction of movement. 
         [0062]    The rotor assembly  105  is connected to the camshaft  126  and is coaxially located within the housing assembly  100 . The rotor assembly  105  has at least one vane  104  separating a chamber formed between the housing assembly  100  and the rotor assembly  105  into an advance chamber  102  and a retard chamber  103 . The vanes  104  are capable of rotation to shift the relative angular position of the housing assembly  100  and the rotor assembly  105 . 
         [0063]    A lock pin  125  is slidably housed in a bore in the rotor assembly  105  and has an end portion that is biased towards and fits into a recess  127  in the housing assembly  100  by a spring  124 . Alternatively, the lock pin  125  may be housed in the housing assembly  100  and be spring  124  biased towards a recess  127  in the rotor assembly  105 . The pressurization of line  132  leading to the lock pin  125  is controlled by the switching/movement of the phase control valve  159 . 
         [0064]    A control valve  159 , preferably a spool valve, includes a spool  161  with cylindrical lands  161   a ,  161   b , and  161   c  slidably received in a sleeve  116  within a bore in the rotor assembly  105  and pilots in the camshaft  126 . The spool  161  has an axial spool vent passage  162  that runs from the first land  161   a  through to the third land  161   c  and is in fluid communication radial spool vent passage  164  in the first land  161   a  of the spool  161  to vent any fluid to atmosphere or sump. One end of the spool contacts spring  115  and the opposite end of the spool contacts a control means  107 . The control means may be a pulse width modulated variable force solenoid (VFS)  107 , a motor, other actuators, or a solenoid that is linearly controlled by varying current or voltage or other methods as applicable. 
         [0065]    The position of the spool  161  is influenced by spring  115  and the control means  107  controlled by an ECU (not shown). Further detail regarding control of the phaser is discussed in detail below. The position of the spool  161  controls the motion (e.g. to move towards the advance position, holding position, or the retard position) of the phaser, whether the lock pin  125  is locked or unlocked, and whether fluid source oil may flow continuously through the variable cam timing phaser to vent or sump  122  to bring warm oil from the engine sump to the VCT phaser sooner during the engine warm-up cycle. 
         [0066]    In this embodiment, the control valve  159  of the VCT phaser or mechanism has been shortened such that at the spool out position or at base timing of the phaser, the porting leading to the advance or retard chambers  102 ,  103  is exposed to the back of the spool  161  which is vented to atmosphere or sump through spool vent passages  162 ,  164 . In this position, as shown in  FIG. 11 , fluid from source  121  enters the common passage  114  and flows through the retard passage  113  within the VCT phaser to the back of the control valve  159  and out the spool vent passages  162 ,  164 . It should be noted that a small amount of fluid that is present between the sleeve  116  and the spool  161  when the phase is moving towards the advance position as shown in  FIG. 13  would also vent. This venting of fluid would not be continuous since there is not a direct feed between the retard chamber  103  and the back of the spool  161 . 
         [0067]    When the spool  161  moves in, the retard passage  113  is blocked and the venting flow of fluid from the spool venting passages  162 ,  164  is substantially reduced. By having increased flow at the spool out position or at base timing, allows hot oil to fill the VCT phaser sooner. The closed vent during operation of the VCT phaser or phaser minimizes oil usage when the VCT phaser is in operation and oil is hot. 
         [0068]    It should be noted that the phase control valve  159  is an active control system for allowing for continuous venting from the retard chamber  103  to sump  122  when the spool  161  is in a base timing position or default position in which the spool  161  is biased out from the sleeve  116  completely by the spring  115  only without any influence from the actuator  107 . The base timing position is also the position of the spool  161  in which engine warm-up occurs. While the continuous venting is shown from the retard chamber  103 , continuous venting may also occur through the advance chamber  102  as well. 
         [0069]    In the advance mode, as shown in  FIG. 13 , the spool  161  is moved to a position so that fluid may flow from the retard chamber  103  through the spool  161  to the advance chamber  102 , and fluid is blocked from exiting the advance chamber  102 . Fluid from source  121  may unlock the lock pin  125  by pressurizing line  132 , and venting of fluid from source  121  and the retard chamber  103  through the retard passage  113  through the back of the spool  161  is prevented. It should be noted that a small amount of fluid that is present between the sleeve  116  and the spool  161  when the phase is moving towards the advance position would also vent. This venting of fluid would not be continuous since there is not a direct feed between the retard chamber  103  and the back of the spool  161 . 
         [0070]    In a retard mode as shown in  FIG. 11 , the spool  161  is moved to a position so that fluid may flow from the advance chamber  102  through the spool  161  to the retard chamber  103 , fluid may vent from the retard chamber  103  to the retard passage  113  and through the back of the spool  161  to atmosphere or sump. Fluid from source supplies a constant fluid pressure to maintain fluid to the retard chamber  103  and to spool vent passages  162 ,  164 . The lock pin  125  is locked. 
         [0071]    In null mode as shown in  FIG. 12 , the spool  161  is moved to a position that blocks the exit of fluid from the advance and retard chambers  102 ,  103 , and venting of the retard chamber  103  through the back of the spool  161  through spool vent passages  162 ,  164  is not permitted. Makeup oil may be supplied to the advance and retard chambers  102 ,  103  as needed. Fluid from source  121  unlocks the lock pin  125  by pressurizing line  132 . 
         [0072]      FIG. 11  shows the phaser moving towards the retard position. To move towards the retard position, the force of the control means  107  on the spool  161  is changed, such that the spool  161  is moved to the left in a retard mode in the figure by spring  115 , until the force of spring  115  balances the force of the control means  107 . In the retard mode shown, spool land  161   c  slightly blocks line  113  and lines  112  and  114  are open. Spool land  161   c  is in a position such that fluid from the retard passage  113  may flow to the back of the spool  161  to the spool vent passages  162 ,  164  to atmosphere or sump. Source oil from supply  121  provides a continuous supply of fluid to the retard chamber  103  and therefore to vent to atmosphere or sump through the retard passage  113  and the spool vent passages  162 ,  164 . Camshaft torque pressurizes the advance chamber  102 , causing fluid in the advance chamber  102  to move into the retard chamber  103 , and the vane  104  to move accordingly. Fluid exits from the advance chamber  102  through line  112  to the control valve  159  between spool lands  161   b  and  161   c  and recirculates back to central or common line  114  and line  113  leading to the retard chamber  103 . 
         [0073]    Makeup oil to make up for any leakage and oil to supply continuous venting of fluid to warm up the phaser is supplied to the phaser from supply S  121  and enters line  119  through a bearing  120 . Line  119  splits into two lines  119   a  and  119   b . Line  119   b  leads to an inlet check valve  118  and the control valve  159 . From the control valve  159 , fluid enters line  114  through either of the check valves  108 ,  110 , depending on which is open to the chambers  102 ,  103 . Line  119   a  leads to control valve  159  and is blocked by land  161   b  from pressurizing line  132  and from biasing the lock pin  125  to an unlocked position, and therefore, the lock pin  125  remains in a locked position, engaged with recess  127 . Exhaust line  122  is blocked from receiving fluid from line  119   a  by spool land  161   b.    
         [0074]      FIG. 13  shows the phaser moving towards the advance position. To move towards the advance position, the force of the control means  107  on the spool  161  is increased and the spool  161  is moved to the right by the control means  107  in an advance mode, until the force of the spring  115  balances the force of the control means  107 . In the advance mode shown, spool land  161   b  blocks line  112  and lines  113  and  114  are open. Camshaft torque pressurizes the retard chamber  103 , causing fluid to move from the retard chamber  103  and into the advance chamber  102 , and the vane  104  moves accordingly. Fluid exits from the retard chamber  103  through line  113  to the control valve  159  between spool lands  161   b  and  161   c  and recirculates back to central line  114  and line  112  leading to the advance chamber  102 . 
         [0075]    Makeup oil is supplied to the phaser from supply S  121  to make up for leakage and enters line  119  through a bearing  120 . Line  119  splits into two lines  119   a  and  119   b . Line  119   b  leads to an inlet check valve  118  and the control valve  159 . From the control valve  159 , fluid enters line  114  through either of the check valves  108 ,  110 , depending on which is open to the chambers  102 ,  103 . Line  119   a  leads to control valve  159  and is open to line  132  leading to the lock pin  125  The pressure of the fluid in line  119   a  moves through the spool  161  between lands  161   a  and  161   b  to pressurize line  132  and bias the lock pin  125  against the spring  124  to a released position. Exhaust line  122  is blocked by spool land  161   a , preventing the lock pin  125  from venting. 
         [0076]    When the phaser in the holding position as shown in  FIG. 12 , the force of the control means  107  on one end of the spool  161  equals the force of the spring  115  on the opposite end of the spool  161  in holding mode. The lands  161   b  and  161   c  block the flow of fluid to lines  112  and  113  respectively. Makeup oil is supplied to the phaser from supply S by to make up for leakage and enters line  119  through a bearing  120 . Line  119  splits into two lines  119   a  and  119   b . Line  119   b  leads to inlet check valve  118  and the control valve  159 . From the control valve  159 , fluid enters line  114  through either of the check valves  108 ,  110 , depending on which is open to the chambers  102 ,  103 . Fluid from source  121  unlocks the lock pin  125  by pressurizing line  132 . 
         [0077]    The lock pin  125  may be used without using a control means  107  (i.e. use it as a passive system) by increasing venting that occurs at the default spool valve position or at a base timing of the phaser that occurs in the VCT phaser when the control system is turned off. Base timing or default position of the spool is when the spool  161  is biased out from the sleeve  116  completely by the spring  115  only without any influence from the actuator  107 . The base timing position is also the position of the spool  161  in which engine warm-up occurs. 
         [0078]    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 is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.