Patent Publication Number: US-11396831-B2

Title: Advance locked spool valve pump phaser with hydraulic detent valve

Description:
BACKGROUND 
     The present invention relates to variable cam timing phaser, and more specifically to an end position locked spool valve pump (SVP) phaser with a hydraulic detent valve. 
     Internal combustion engines have employed various mechanisms to vary the relative timing 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). Vane phasers have a rotor assembly with one or more vanes, mounted to the end of the camshaft, surrounded by a housing assembly with the vane chambers into which the vanes fit. It is possible to have the vanes mounted to the housing assembly, and the chambers in the rotor assembly, as well. The housing&#39;s outer circumference or other portion of the housing assembly 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. 
     In cam torque actuated (CTA) variable camshaft timing (VCT) systems, cam torques from the engine are used to move the one or more vanes and fluid is recirculated between the working chambers without exhausting the fluid to sump. A lock pin for locking and unlocking the movement between the housing assembly and the rotor assembly can be controlled by a control valve. During engine shutdown, the control valve is moved to a position such that fluid is maintained within the chambers via recirculation, and any fluid feeding to the lock pin is vented from the circuit through the control valve. 
     During engine cranking or shortly thereafter, there may not be sufficient oil pressure to release the lock pin because the engine&#39;s oil passages, including those leading to the phaser may have drained. Time is required for the oil pump, which is driven by the rotation of the engine, to re-fill and build pressure in the engine&#39;s oil circuit. 
     Apart from the camshaft torque actuated (CTA) variable camshaft timing (VCT) systems, the majority of hydraulic VCT systems operate under two principles, oil pressure actuation (OPA) or torsional assist (TA). In the oil pressure actuated VCT systems, a control valve directs engine oil pressure to one working chamber in the vane phaser while simultaneously venting the opposing working chamber defined by the housing assembly, the rotor assembly, and the one or more vanes. This creates a pressure differential across one or more of the vanes to hydraulically push the vane phaser in one direction or the other. Neutralizing or moving the control valve to a null position puts equal pressure on opposite sides of the one or more vanes and holds the vane phaser in any intermediate position. If the vane phaser is moving in a direction such that valves of the engine will open or close sooner, the vane phaser is said to be advancing and if the vane phaser is moving in a direction such that valves will open or close later, the vane phaser is said to be retarding. 
     The torsional assist (TA) systems operates under a similar principle with the exception that it has one or more check valves to prevent the vane phaser from moving in a direction opposite than being commanded, should it incur an opposing force such as torque. 
     The problem with OPA or TA systems is that the control valve defaults to a position that exhausts all the oil from either the advance or retard working chambers and fills the opposing chamber. In this mode, the vane phaser defaults to moving in one direction to an extreme stop where a lock pin engages, locking the movement of the rotor assembly relative to the housing assembly. The OPA or TA systems are unable to direct the vane phaser to any other position during the engine start cycle when the engine is not developing any oil pressure. This limits the vane phaser to being able to move in one direction only in the engine shut down. In the past this was acceptable because at engine shut down and during engine start the vane phaser would be commanded to lock at one of the extreme travel limits (either full advance or full retard). 
     Most engines with an intake phaser place the phaser in the retard position in engine shutdown using a lock pin or a series of lock pins, in preparation for the next start of a “stop-start mode” which automatically stops and automatically restarts the internal combustion engine to reduce the amount of time the engine spends idling when the vehicle is stopped, for example at a stop light or in traffic. This stopping of the engine is different than a “key-off” position or manual stop via deactivation of the ignition switch in which the user of the vehicle shuts the engine down or puts the car in park and shuts the vehicle off. In “stop-start mode”, the engine stops as the vehicle is stopped, then automatically restarts in a manner that is nearly undetectable to the user of the vehicle. In the past, vehicles have been designed primarily with cold starts in mind, since that is the most common situation. In a stop-start system, because the engine had been running until the automatic shutdown, the automatic restart occurs when the engine is in a hot state. It has long been known that “hot starts” are sometimes a problem because the engine settings necessary for the usual cold start—for example, a particular valve timing position—are inappropriate to a warm engine. 
     Unlocking the lock pin is dependent upon engine oil pressure available at start up. 
     SUMMARY 
     According to one embodiment of the present invention, a phaser of the present invention has three camshaft start positions which can be used at start-up during cranking before the engine can fire. The three camshaft start positions are full advance, full retard, and intermediate position. By having three possible start positions of the phaser, there is an increase in flexibility of the cam position at startup during cranking. The three start positions can also be achieved in open loop, reducing the complexity of the control system needed at cranking. 
     The determination of the which of the three camshaft start positions the phaser is moved to during cranking is determined based on a number of factors, which can include fuel type, grade of fuel, engine oil temperature, and altitude. 
     In general, the phasing speed of the camshaft in a retard direction is always greater than the advance direction because of cam friction. Cam friction is typically much higher at colder temperatures and at cranking rpm, making advancing under those conditions more difficult than retarding. Therefore, it is advantageous to park (with engine shutoff) the phaser in full advance position, so that if actuation is demanded during cranking, the phaser only has to move in retard direction and hence can reach target cam phase angle before engine starts quickly. If the engine control unit (ECU) wants the cam phaser to be in full advance before engine start the phaser is already in the full advance position (parked position). If the ECU wants cam position to be in full retard before engine start the phaser can move quickly to full retard stop. It is also noted that the phaser can alternatively be parked in the full retard position and the phaser moved to another position as demanded by the ECU. 
     Additionally, by adding the hydraulic detent circuit to the phaser, the phaser can be moved to a mid-position in a retard direction at cranking, giving an additional start position option between the two end stops. Furthermore, the addition of a spool valve pump provides a method of unlocking the lock pin if needed at cranking rpm when engine oil pressure is low or unavailable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic of a VCT phaser at cranking moving toward a retard position by cam torque with the lock pin being unlocked. 
         FIG. 2  shows a schematic of a VCT phaser at cranking moving toward an advance position by cam torque with the lock pin being unlocked. 
         FIG. 3  shows a schematic of a VCT phaser at cranking in a holding position with the lock pin being unlocked. 
         FIG. 4  shows a schematic of a VCT phaser at cranking retarding toward a mid position by cam torque with the lock pin being unlocked. 
         FIG. 5  shows a schematic of a VCT phaser at cranking retarding toward a mid position during a cam torque reversal. 
         FIG. 6  shows a schematic of a VCT phaser at cranking advancing toward a mid position with the lock pin being unlocked. 
         FIG. 7  shows a schematic of a VCT phaser at cranking advance towards mid position during a cam torque reversal. 
         FIG. 8  shows a schematic of a VCT phaser at cranking in a full advance position, with the lock pin being locked and ready to unlock using the spool valve pump. 
         FIG. 9  shows a schematic of a VCT phaser at idle moving toward the retard position. 
         FIG. 10  shows a schematic of a VCT phaser at idle moving toward an advance position. 
         FIG. 11  shows a schematic of a VCT phaser at idle in a holding position. 
         FIG. 12  shows a schematic of a VCT phaser at idle with the lock pin moving from unlocked to locked. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention includes a variable cam timing (VCT) phaser which has three different startup position options at the time of cranking before the engine fires. The different VCT phaser positions allow the camshaft to at an optimum position for engine restarts in various conditions. The determination by the ECU as to what position to command the VCT phaser to is based on sensor data which can include fuel type, grade of fuel, engine oil temperature, and altitude. 
     The VCT phaser includes a lock pin for locking the housing assembly relative to the rotor assembly of the VCT phaser. The lock pin is biased towards a locked position, in which the lock pin engages an inner end plate or an outer end plate of the housing assembly mainly by a spring. The lock pin is biased towards an unlocked position, in which the lock pin disengages the inner end plate or outer end plate of the housing assembly by oil pressure supplied from a spool valve pump. 
     The VCT phaser additionally includes a control valve that can be moved to a detent mode and a hydraulic detent circuit to direct the VCT phaser in either direction, advance or retard via detent valve to move the phaser to specific positions. 
     The figures show the operating modes the VCT phaser depending on the spool valve position of the control valve. The positions shown in the figures define the direction the VCT phaser is moving to. It is understood that the control valve has an infinite number of intermediate positions, so that the control valve not only controls the direction the VCT phaser moves but, depending on the discrete spool position, controls the rate at which the VCT phaser changes positions. Therefore, it is understood that the control valve can also operate in infinite intermediate positions and is not limited to the positions shown in the Figures. 
       FIGS. 1-8  show the VCT phaser at cranking moving towards various position. 
     The housing assembly  100  of the phaser has an outer circumference  101  for accepting a drive force. Alternatively, acceptance of the drive force is through an end plate of the housing assembly  100 . The housing assembly  100  of the phaser includes an inner face plate  100   a  and an outer face plate  100   b . The rotor assembly  105  is connected to the camshaft (not shown) and is coaxially located within the housing assembly  100 . The rotor assembly  105  has at least one vane  104  separating a chamber  117  with an advance wall  102   a  and a retard wall  103   a  formed between the housing assembly  100  and the rotor assembly  105  into working chambers such as an advance chamber  102  and a retard chamber  103 . The vane  104  is capable of rotation to shift the relative angular position of the housing assembly  100  and the rotor assembly  105 . 
     A lock pin  142  is slidably housed in a bore  141  in the rotor assembly  105  and has a plurality of cylindrical lands,  142   a ,  142   b ,  142   c ,  142   d . The lock pin  142  has a first, unlocked position in which the first end portion  125   a  of the lock pin  142  does not engage the recess  155  and a second, locked position in which the first end portion  125   a  of the lock pin  142  engages the recess  155 , locking the relative movement of the rotor assembly  105  relative to the housing assembly  100 . The second end  125   b  of the lock pin  142  is in fluid communication with tank. Depending on the position of the lock pin  142 , the recess  155  is in fluid communication with the control valve  109  and more specifically the spool valve pump  150 , as well as with inlet supply  118  via line  149 . The lock pin  142  additionally has a t-shaped internal passage  170 . The t-shaped internal passage  170  has a horizontal portion  143  and a vertical portion  144  within the lock pin  142 . Depending on the position of the lock pin  142 , the t-shaped internal passage  170  connects line  146  to passage  147  between the first land  142   a  and the second land  142   b  of the lock pin  142 , such that fluid can reach passage  147  to bias the lock pin against spring  145  and move to an unlock position. Therefore, pressurization of the lock pin  142  is controlled by the switching/movement of the control valve  109  as well as inlet supply  118  from the oil gallery. The first end  125   a  of the lock pin  142  is biased towards and fits into a recess  155  in the inner plate  100   a  of the housing assembly  100  by a spring  145 , for example as shown in  FIG. 8 . 
     While note shown, the lock pin  142  may be alternatively housed in the housing assembly  100  and be spring  145  biased towards a recess  155  in the rotor assembly  105 . 
     Typically, during engine cranking, after an engine shutdown, there is no oil pressure present to unlock the lock pin  142  and no phasing can begin until after the lock pin  142  has been pressure biased to an unlocked position. 
     A control valve  109 , preferably a spool valve, includes a spool  111  with a plurality of cylindrical lands  111   a ,  111   b ,  111   c  is slidably received in a sleeve  116  within a bore in the rotor assembly  105  and pilots in the camshaft (not shown). The control valve  109  may be located remotely from the phaser, within a bore in the rotor assembly  105  which pilots in the camshaft, or in a center bolt of the phaser, with or without a sleeve, such that the center belt acts as the sleeve. 
     The sleeve  116  of the control valve  109  has a series of ports  160 - 166 . Port  160  is in fluid communication the detent valve  130  of the hydraulic detent circuit. Port  161  is in fluid communication with inlet supply  118  via line  153 . Fill port  162  is in fluid communication with line  148 . In addition, fill port  162  is in communication with spool valve pump chamber  150  during engine shutdown, engine cranking and engine stop. Port  163  is in fluid communication with the advance line  112 . Port  164  is in fluid communication with common line  114 . Port  165  is in fluid communication with retard line  113 . Port  166  is in fluid communication with line  152  which connects to common line  114 . 
     One end of the spool  111  contacts spring  115  and the opposite end of the spool  111  contacts a variable force solenoid (VFS)  107 . The solenoid  107  may also be linearly controlled by varying current or voltage or other methods as applicable. Between the end of the spool  111  which contacts the spring  115  and the inner diameter  116   a  of the sleeve  116  is formed a spool valve pump chamber  150 . The spool valve pump chamber  150  stores supply oil during engine shutdown and engine stop where the pump chamber  150  is filled and the pressure of the oil in this spool valve pump chamber  150  is pumped up or increased in pressure by the movement of the spool  111 . The spool valve pump chamber  150  is also in fluid communication with lock pin  142 , for example via line  146  and line  148 . 
     The detent circuit is kept on when there is no oil pressure, such as during engine cranking and engine stop. 
     A pump chamber circuit is comprised of a supply lines  143 ,  149 ,  148 ,  146 ,  147 ,  122  in fluid communication with the lock pin  142 , the lock pin  142 , and the pump chamber  150 , line  146  in fluid communication with pump chamber  150  and the lock pin  142 . The pump chamber  150  fills by decaying oil pressure as engine oil pressure drops in line  148 . The filling occurs as soon as the spool valve  111  moves to a full out position, such that fill port  162  is open. 
     The pump chamber circuit is filled during engine shutdown (idle to stop). All fluid associated with the lock pin  142 , such that any fluid present in lines  147  and  155  gets pushed back into the spool valve pump chamber  150  and any fluid present in the phaser itself drains back into the pump chamber  150 . Residual pressure from the oil system fills the pump chamber circuit until either the pressure is no longer sufficient to force fluid into the pump chamber  150  or the pump chamber  150  is full or the pressure in passage  148  and spool valve pump chamber  150  is the same. 
     The position of the control valve  109  is controlled by an engine control unit (ECU)  106  which controls the duty cycle of the variable force solenoid  107 . The ECU  106  preferably includes a central processing unit (CPU) which runs various computational processes for controlling the engine, memory, and input and output ports used to exchange data with external devices and sensors. For example, sensors can at least provide one or more of altitude, fuel type, engine oil pressure temperature, engine oil pressure, position of the phaser, position of the camshaft and position of the crankshaft. 
     The position of the spool  111  is influenced by spring  115  and the solenoid  107  controlled by the ECU  106 . Further detail regarding control of the VCT 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) during idle and other position during cranking of the VCT phaser as well as what fluid is used to lock or unlock the lock pin  142 . 
     A hydraulic detent circuit  133  is also present and includes a spring  131  loaded detent valve  130 , an advance detent line  128  that connects the advance chamber  102  to the detent valve  130  and the common line  114  when the detent valve  130  is in a first position (on), and a retard detent line  134  that connects the retard chamber  103  to the detent valve  130  and the common line  114  when the detent valve is in a first position (on). The advance detent line  128  and the retard detent line  134  are present within the vane  104 . In a second position (oft), the retard detent line  134  or the advance detent line  128  are not connected to the common line  114 . 
     The phaser has a CTA retard cranking mode, a detent cranking mode, a full advance cranking mode, an advance mode, a retard mode, and a null mode. The advance mode, retard mode, and null mode take place during idling or greater, which occurs after cranking. 
     In the advance mode during engine idling, the spool  111  is moved to a position so that fluid may flow from the retard chamber  103  into the spool  111  and through the advance recirculating check valve  110  into advance line  112  and into advance chamber  102 . Fluid is blocked from exiting the advance chamber  102  through detent line  128  via detent valve  130 . Fluid from inlet supply  118  is additionally supplied to bias the detent valve  130  to a position such that line  128  is blocked and the detent circuit is off. The lock pin  142  is unlocked. 
     In the retard mode during engine idling, the spool  111  is moved to a position so that fluid may flow from the advance chamber  102  through the spool  111  and through the retard recirculating check valve  108  into retard line  113  and into the retard chamber  103 . Fluid is blocked from exiting the retard chamber  103  and via the detent line  134  of the detent valve  130 . Fluid from the inlet supply  118  is additionally supplied to bias the detent valve  130  to a position such that line  134  is blocked and the hydraulic detent circuit is off. The lock pin  142  is in an unlocked position. 
     In null or holding mode during engine idling, the spool  111  is moved to a position that blocks the exit of fluid from the advance and retard chambers  102 ,  103 . Fluid is supplied to the detent valve  130  from inlet supply  118  and the detent valve circuit is off. The lock pin  4142  is unlocked. 
     In the detent cranking mode, two functions occur simultaneously. The first function in the detent mode is that the spool  111  moves to a position in which spool land  111   b  blocks the flow of fluid from supply line  153 , port  164  (spool is full in). 
     The second function in detent mode is to open or turn on the detent valve circuit  133 . The detent valve circuit  133  has complete control over the phaser moving to advance or retard, until the vane  104  reaches the intermediate phase angle position, such that the advance detent line  128  is connected to line  151 . 
     The intermediate phase angle position or mid-position is when the vane  104  is somewhere between the advance wall  102   a  and the retard wall  103   a  defining the chamber between the housing assembly  100  and the rotor assembly  105 . The intermediate phase angle position can be anywhere between the advance wall  102   a  and retard wall  103   a  and is determined by where the advance detent line  128  and the retard detent line  134  are placed relative to the vane  104 . 
     Prior to the advance mode, retard mode and null mode at idling, the phaser is moved to a position during cranking before engine starts or fires to allow the VCT phaser to reach the appropriate mode for idling as quickly as possible. In a first option, during cranking, the VCT phaser is maintained at either a retard, advance or null mode via cam torque and the lock pin is moved to an unlocked position in a CTA retard cranking mode. In a second option, the VCT phaser is moved to a mid-position and the lock pin is moved to an unlocked position in a detent cranking mode. In a third option, the VCT phaser is moved to a full advance position, with the lock pin in a locked position, ready to be unlocked by the spool valve pump in a full advance cranking mode. 
       FIGS. 1-3  show the VCT phaser at cranking RPM in which the VCT phaser is moved using cam torque actuation in a CTA cranking mode. 
       FIG. 1  shows a schematic of a VCT phaser at cranking moving toward a retard position by cam torque with the lock pin being unlocked. During engine cranking, the spool  111  of the control valve  109  is moved to a position by the VFS  107 , against the force of the spring  115 , between the null position and the spool full in position. 
     During engine cranking, in order to unlock the lock pin, the lock pin  142  starts in the lock position as shown in  FIG. 8 . The phaser is at the full advance position. In the full advance position, the vane  104  contacts the retard wall  103   a  of the chamber  117 . The duty cycle of VFS  107  starts at 0% and moves to greater than 60%, to force the control valve  109  to expel the fluid present in the pump chamber  150 . Fluid present in the spool valve pump chamber  150  is pushed out of the chamber  150  and into line  146 . From line  146 , the fluid flows between lock pin lands  142   b  and  142   c  into line  147  and recess  155 , which moves the lock pin  142  out of the recess  155  and against the force of the lock pin spring  145 . Fluid is additionally provided from the inlet supply  118 , through inlet check valve  119  and into line  149 . From line  149 , fluid flows between lock pin lands  142   c  and  142   d  to line  148 , which supplies additional fluid to the spool valve pump chamber  150  until enough fluid has passed into recess  155  from the spool valve pump chamber  150  via lines  146 ,  147 . 
     Once the lock pin  142  has been moved to an unlocked position as shown in  FIG. 1 , fill port  162  is blocked by spool land  111   d , removing additional fluid being supplied by line  148  from inlet supply  118 . It is noted that with the spool valve chamber  150  vented, the spool  111  can move to other positions in which the spool valve chamber  150  is compressed. In addition, any fluid present in line  146  is now in fluid communication with the internal t-passage  170  between lock pin lands  142   a ,  142   b  and vents through passage  144  through the end of the spool  125   b  to tank via line  122 . 
     After the lock pin  142  has been unlocked, the ECU  106  controls the VFS  107  to a position against the force of spring  115  in which the spool land  111   b  blocks ports  160 ,  165  and  166 , spool land  111   c  blocks fill port  162 , and ports  163 ,  164  and  161  are open. Fluid from the advance chamber  102  exits the advance chamber  102  through advance line  112  to port  163  of the sleeve  116 . From port  163 , fluid flows though the spool  111  between spool lands  111   b  and  111   c , through port  164  into common line  114 . From the common line  114 , fluid flows through the retard recirculation check valve  108 , into retard line  113  to the retard chamber  103 , moving the vane  104  towards the advance wall  102   a  of the chamber  117  with the aid of cam torque in the same direction. It is noted that in this position, fluid is prevented from flowing into the common line  114  directly from the advance line  112  by advance recirculation check valve  110 . 
     Since fluid is not supplied by the inlet supply  118 , the detent valve  130  is biased by the spring  131  toward an on position in which fluid can flow through the detent valve  130  from line  151 , the advance detent line  128  and the retard detent line  134 . It is noted that fluid from the retard chamber  103  can flow through the retard detent line  134 , and through the detent valve  130 , however the advance detent line  128  is blocked by the rotor assembly  105  and line  151  connected to the retard detent line  134  and the advance detent line  128  through the detent valve  130  is blocked by spool land  111   b.    
       FIG. 2  shows a schematic of a VCT phaser at cranking moving toward an advance position by cam torque with the lock pin being unlocked. 
     After the lock pin  142  has been unlocked, the ECU  106  controls the VFS  107  to a position against the force of spring  115  in which the spool land  111   b  blocks ports  160  and  166 , spool land  111   c  blocks port  163  and partially blocks fill port  162  and ports  164 ,  165  and  161  are open. 
     Fluid from the retard chamber  103  exits the chamber  103  through retard line  113  to port  165  of the sleeve  116 . From port  165 , fluid flows though the spool  111  between spool lands  111   b  and  111   c , through port  164  into common line  114 . From the common line  114 , fluid flows through the advance recirculation check valve  110 , into advance line  112  to the advance chamber  102 , moving the vane  104  towards the retard wall  103   a  of the chamber  117  with the aid of cam torque in the same direction. It is noted that in this position, fluid is prevented from flowing into the common line  114  directly from the retard line  113  by retard recirculation check valve  108 . 
     Since fluid is not supplied by the inlet supply  118 , the detent valve  130  is biased by the spring  131  toward an “on” position in which fluid can flow through the detent valve  130  from line  151 , the advance detent line  128  and the retard detent line  134 . It is noted that fluid from the advance chamber  102  can flow through the advance detent line  128 , and through the detent valve  130 , however the retard detent line  134  is blocked by the rotor assembly  105  and line  151  connected to the retard detent line  134  and advance detent line  128  through the detent valve  130  is blocked by spool land  111   b.    
       FIG. 3  shows a schematic of a VCT phaser at cranking in a holding position with the lock pin being unlocked. 
     After the lock pin  142  has been unlocked, the ECU  106  control the VFS  107  to a position against the force of spring  115  in which the spool land  111   b  blocks ports  166 ,  165   160 , and spool land  111   c  blocks fill port  162  and  163 . Ports  161  and  164  are open. Fluid from the advance chamber  102  is blocked from flowing through the control valve  109  by spool land  111   c  and fluid from the retard chamber  103  is blocked from flowing through the control valve  109  by spool land  111   b . Advance and retard recirculation check valve  108 ,  110  also prevent fluid from the advance and retard chambers  102 ,  103  from entering the common line  114 . 
     Since fluid is not supplied by the inlet supply  118 , the detent valve  130  is biased by the spring  131  toward an “on” position in which fluid can flow through the pilot valve  130  from the blocked advance detent line  128  and the blocked retard detent line  134 . 
       FIGS. 4-7  show the VCT phaser at cranking RPM in which the VCT phaser is moving toward a mid-position using cam torque actuation in a mid-position cranking mode. 
       FIG. 4  shows the VCT phaser at cranking RPM moving toward the mid position from an advance position (retarding).  FIG. 5  shows the VCT phaser at cranking moving toward the mid position from an advance position during a cam toque reversal. 
     During cranking, the VCT phaser is moved from an initial full advance position in which the vane  104  contacts the retard wall  103   a  to a mid-position between the advance wall  102   a  and the retard wall  103   a  in the same direction as the cam torque which in this case is toward the advance wall  102   a.    
     First, the ECU  106  controls the VFS  107  such that the spool  111  of the control valve  109  is moved to a position which pumps the spool valve chamber  150  and forces fluid present in the spool valve chamber  150  to flow through line  146 , through the horizontal portion  143  of the t-passage  170  of the lock pin  142 , through line  147  into recess  155  to bias the lock pin  142  against spring  145 , such that the lock pin  142  is moved to an unlocked position in which the lock pin  142  no longer engages recess  155 . Once the lock pin  142  has been moved to an unlocked position, the fill line  149  in communication with the inlet supply  118  is blocked along with the fill line  148  in communication with fill port  162  for filling the spool valve pump chamber  150 . 
     The spool  111  is then moved to a position by the VFS  107  via the ECU  106  in which all supply lines, supply line  153  from the inlet supply  118 , and supply line  148  to the spool valve pump chamber  150  are blocked. Additionally, the spool  111  blocks the flow of fluid through the common line  114  from port  164 . 
     Fluid present in the advance chamber  102  exits the advance chamber  102  through the advance detent line  128  and flows through the pilot valve  130  between the first land  130   a  and the second land  130   b . From the pilot valve  130 , fluid flows to recirculation line  151  to port  160  of the spool valve, between spool lands  111   a  and  111   b  to port  166  and line  152  which is connected to common line  114 . From common line  114 , fluid flows through the advance recirculation check valve  108  and into retard line  113  and the retard chamber  103  to move vane  104  toward the advance wall  102   a . The vane  104  continues to move toward the advance wall  102   a  until the advance detent line  128  is no longer exposed to the advance chamber  102  and is blocked by the housing assembly  100 . 
       FIG. 5  shows the VCT phaser of  FIG. 4  during a cam torque reversal. During a cam torque reversal, which in this case has the cam torque attempting to move the vane  104  towards the retard wall  103   a , the position of the VCT phaser is essentially held in place, with any fluid that that is moved to exit the retard chamber  103  by the cam torque reversal is prevented by the spool land  111   b  blocking line  113 . 
       FIG. 6  shows the VCT phaser at cranking RPM moving toward mid position from a retard position (advancing).  FIG. 7  shows the VCT phaser at cranking moving toward the mid position from a retard position during a cam torque reversal. 
     During cranking, the VCT phaser is moved from an initial full retard position in which the vane  104  contacts the advance wall  102   a  to a mid-position between the advance wall  102   a  and the retard wall  103   a  in the same direction as the cam torque, which in this case is toward the retard wall  103   a.    
     First, the ECU  106  controls the VFS  107  such that the spool  111  of the control valve  109  is moved to a position which pumps the spool valve chamber  150  and forces fluid present in the spool valve chamber  150  to flow through line  146 , through the horizontal portion  143  of the t-passage  170  of the lock pin  142 , through line  147 , into recess  155  to bias the lock pin  142  against spring  145 , such that the lock pin  142  is moved to an unlocked position in which the lock pin  142  no longer engages recess  155 . Once the lock pin has been moved to an unlocked position, the fill line  149  in communication with the inlet supply  118  is blocked along with the fill line  148  in communication with fill port  162  for filling the spool valve chamber  150 . 
     The spool  111  is then moved to a position by the VFS  107  via the ECU  106  in which all supply lines, supply line  153  from the inlet supply  118 , and supply line  148  to the spool valve chamber  150  are blocked. Additionally, the spool  111  blocks the flow of fluid through the common line  114  from port  164 . 
     Fluid present in the retard chamber  103  exits the retard chamber  103  through the retard detent line  134  and flows through the pilot valve  130  between the first land  130   a  and the second land  130   b . From the pilot valve  130 , fluid flows to recirculation line  151  to port  160  of the spool valve, between spool lands  111   a  and  111   b  to port  166  and line  152  which is connected to common line  114 . From common line  114 , fluid flows through the retard recirculation check valve  110  and into advance line  112  and the advance chamber  102  to move vane  104  toward the retard wall  103   a . The vane  104  continues to move toward the retard wall  103   a  until the retard detent line  134  is no longer exposed to the retard chamber  103  and is blocked by the housing assembly  100 . 
       FIG. 7  shows the VCT phaser of  FIG. 6  during a cam torque reversal. During a cam torque reversal, which in this case has the torque attempting to move the vane  104  towards the advance wall  102   a , the position of the phaser is essentially held in place, with any fluid that that is moved to exit the advance chamber  102  by the cam torque reversal is prevented by the spool land  111   b  blocking line  112 . 
       FIGS. 9-12  show the VCT phaser modes at idling.  FIG. 9  shows the VCT phaser moving toward a retard position in the retard mode.  FIG. 10  shows a schematic of a VCT phaser at idle moving toward an advance position.  FIG. 11  shows a schematic of a VCT phaser at idle in a holding position.  FIG. 12  shows a schematic of a VCT phaser at idle with the lock pin moving from unlocked to locked. 
     Referring to  FIG. 9 , to move towards the retard position, the duty cycle is adjusted to a range greater than 60% of the force of the VFS  107  on the spool  111  is changed and the spool  111  is moved to the right in a retard mode in the figure by VFS  107 , until the force of the VFS  107  balances the force of the spring  115 . Fluid exits from the advance chamber  102  through advance line  112  to port  163 . From port  163 , fluid flows through port  164  to common line  114 . From common line  114 , fluid flows through the retard recirculation check valve  108 , into retard line  113  and the retard chamber  103 . 
     Makeup oil or source is supplied to the phaser from source inlet supply  118  into inlet line  153 , and detent supply line  120 . Detent supply line  120  moves the pilot valve to a closed position, against the force of spring  131 , such that detent land  130   b  blocks the flow of fluid between the advance detent line  128  and the retard detent line  134 . 
     Makeup oil or source  118  provided to inlet line  153  moves through inlet check valve  119  and through port  161  of the control sleeve  116 . From port  161 , fluid flows between spool lands  111   b  and  111   c  to the common line  114 . From the common line  114 , fluid flows through the retard recirculation check valve  108  and through line  113  to the retard chamber  103 . 
     The lock pin  142  maintains the unlocked position from during cranking. 
       FIG. 10  shows the VCT phaser moving toward the advance position. To move to the advance position, the duty cycle is less than 60% of the force of the VFS  107  on the spool  111  is changed and the spool  111  is moved to the left in an advance mode in the figure by the VFS  107 , until the force of the VFS  107  balances the force of the spring  115 . Fluid exits from the retard chamber  103  through retard line  113  to port  165 . From port  165 , fluid flows through port  164  to common line  114 . From common line  114 , fluid flows through the advance recirculation check valve  110 , into advance line  112  and into the advance chamber  102 . 
     Makeup oil or source is supplied to the phaser from source inlet supply  118  into inlet line  153  and detent supply line  120 . Detent supply line  120  moves the pilot valve  130  to a closed position, against the force of spring  131 , such that detent land  130   b  blocks the flow of fluid between the advance detent line  128  and the retard detent line  134 . 
     Makeup oil or source  118  provided to inlet line  153  moves through inlet check valve  119  and through port  161  of the control sleeve  116 . From port  161 , fluid flows between spool lands  111   b  and  111   c  to the common line  114 . From the common line  114 , fluid flows through the advance recirculation check valve  110  and through advance line  112  to the advance chamber  102 . 
     The lock pin  142  maintains the unlocked position from during cranking. 
       FIG. 11  shows the VCT phaser in a holding position. Makeup oil or source  118  provided to inlet line  153  moves through inlet check valve  119  and through port  161  of the control sleeve  116 . From port  161 , fluid flows between spool lands  111   b  and  111   c  to the common line  114 . From the common line  114 , fluid flows through the retard check valve  110  and through advance line  112  to the advance chamber  102  or to the advance check valve  108  and through the retard line  113  to the retard chamber  103 . 
     In the holding position, fluid is additionally supplied from source inlet supply  118  into inlet line  153  and detent supply line  120 . Detent supply line  120  moves the pilot valve to a closed position, against the force of spring  131 , such that detent land  130   b  blocks the flow of fluid between the advance detent line  128  and the retard detent line  134 . 
     The lock pin  142  maintains the unlocked position from during cranking. 
       FIG. 12  shows the VCT phaser at idle with the lock pin moving from an unlocked position to a locked position. 
     Fluid communication through fill port  162  between line  148  and the spool valve pump chamber  150  is blocked by spool land  111   d . With fill port  162  blocked, fluid cannot enter the spool valve pump chamber  150  and also cannot flow to recess  155 . Therefore, no pressurization of the spool  111  or lock pin  142  to bias the lock pin  142  to an open position can occur. Any fluid that is present in recess, line  147  or line  146  are vented to through the internal t-passage  170  of the lock pin through the second end  125   b  of the lock pin  142  and through line  122  to tank. Once the first end  125   a  of the lock pin  142  is aligned with the recess  155 , the lock pin spring  145  biases the lock pin  142  into the recess  155 . 
     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.