Patent Publication Number: US-10767518-B2

Title: Variable camshaft timing mechanism with a lock pin engaged by oil pressure

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of co-pending application Ser. No. 14/899,684, filed Dec. 18, 2015, entitled, “VARIABLE CAMSHAFT TIMING MECHANISM WITH A LOCK PIN ENGAGED BY OIL PRESSURE”, which was the National Stage of International Application No. PCT/US2014/041000, entitled “VARIABLE CAMSHAFT TIMING MECHANISM WITH A LOCK PIN ENGAGED BY OIL PRESSURE”, which was filed on Jun. 5, 2014, and which claims the benefit of Provisional Application No. 61/836,830, entitled, “VARIABLE CAMSHAFT TIMING MECHANISM WITH A LOCK PIN ENGAGED BY OIL PRESSURE”, filed Jun. 19, 2013; and Provisional Application No. 61/974,613 filed Apr. 3, 2014, entitled “VARIABLE CAMSHAFT TIMING MECHANISM WITH A LOCK PIN ENGAGED BY OIL PRESSURE”. The aforementioned applications are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention pertains to the field of variable cam timing. More particularly, the invention pertains to a variable camshaft timing mechanism with at least one lock pin engaged by oil pressure. 
     Description of Related Art 
     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). As shown in the figures, vane phasers have a rotor  105  with one or more vanes  104 , mounted to the end of the camshaft, 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&#39;s outer circumference  101  forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possibly from another camshaft in a multiple-cam engine. 
     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, an oil control valve (OCV) directs engine oil pressure to one working chamber in the VCT phaser while simultaneously venting the opposing working chamber defined by the housing assembly, the rotor assembly, and the vane. This creates a pressure differential across one or more of the vanes to hydraulically push the VCT phaser in one direction or the other. Neutralizing or moving the valve to a null position puts equal pressure on opposite sides of the vane and holds the phaser in any intermediate position. If the phaser is moving in a direction such that valves will open or close sooner, the phaser is said to be advancing and if the phaser is moving in a direction such that valves will open or close later, the 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 VCT phaser from moving in a direction opposite than being commanded, should it incur an opposing force such as a torque impulse caused by cam operation. 
     The auto industry has determined there are multiple strategies that can be used with an intake camshaft phasing mechanism. For example, a camshaft phaser locked at some intermediate start position is best for cold engine start emissions. An intake camshaft phaser commanded to full retard position is best for improved fuel economy during engine operation. 
     The problem with OPA or TA systems in executing the strategies discussed above is that the oil 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 phaser defaults to moving in one direction to an extreme stop where the lock pin engages. A bias spring may be used to preferentially guide the phaser to a desired position. The OPA or TA systems are unable to direct the VCT phaser to any other position during the engine start cycle when the engine is not developing any oil pressure. This limits the phaser to being able to move in one direction only in the engine shut down mode. In the past this was acceptable because at engine shut down and during engine start the VCT phaser would be commanded to lock at one of the extreme travel limits (either full advance or full retard). 
     Furthermore, by reducing the idling time of an internal combustion engine in a vehicle, the fuel efficiency is increased and emissions are reduced. Therefore, vehicles can use 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. During “stop-start”, it has been determined that the full retard phaser position reduces the energy required to start the engine and the full retard phase position reduces the engine Noise Vibration and Harshness (NVH) during a hot engine restart. Other strategies may be developed that require a different lock position than described. 
     The problem with an intake camshaft phaser design that has an extended range of authority and the ability to lock at the full retard stop is that if the engine is shut down with the intake camshaft phaser locked at or near the retard stop and the engine is allowed to cool down, then the engine may not be able to accomplish a successful cold start with the phaser locked near the retard stop. Therefore, it is desirable for the phaser to be unlocked and repositioned to the mid lock position during engine cranking. A typical hydraulic operated camshaft phaser uses a spring force to engage the lock pin and engine oil pressure to release the lock pin. However, during engine cranking there may not be sufficient engine oil pressure to release the lock pin. 
     SUMMARY OF THE INVENTION 
     In some embodiments, hydraulically operated camshaft phasing mechanisms have two lock pins. One of the lock pins engages at an intermediate position and an end lock pin engages near one of the stops at the advance or retard end of the phaser range of authority. At least one of the locking pins, preferably the end lock pin at the retard stop, is engaged by oil pressure and spring loaded to release when the oil pressure side of the end lock pin is vented. 
     In an alternate embodiment, an accumulator may be in fluid communication with the lock pin switching circuit to increase the time in which the end lock pin is engaged after engine shut down. 
     In an embodiment, the end lock pin releases before engine oil pressure is developed in the engine so the phaser can be repositioned during engine cranking to a more optimal position for a cold engine start, while maintaining a locked state when cranking during “stop-start”. 
     In another embodiment, a single lock pin is present which engages near one of the stops at the advance end or the retard end of the phaser&#39;s range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a schematic of a cam torque actuated (CTA) phaser of a first embodiment moving towards an advance position. 
         FIG. 2  shows a schematic of a cam torque actuated (CTA) phaser of a first embodiment in a full stop retard position with an end lock pin in a locked position, locking the phaser. 
         FIG. 3  shows a schematic of a cam torque actuated (CTA) phaser of a first embodiment in a holding position. 
         FIG. 4  shows a schematic of a cam torque actuated (CTA) phaser of a first embodiment with a hydraulic circuit in an open position and the intermediate lock pin in a locked position, locking the phaser. 
         FIG. 5  shows a schematic of a cam torque actuated (CTA) phaser of a first embodiment moving towards a retard position. 
         FIG. 6  shows a schematic of a cam torque actuated (CTA) phaser of a second embodiment with an accumulator in fluid communication with an retard end lock pin and the retard end lock pin in a locked position, locking the phaser. 
         FIG. 7  shows a schematic of a cam torque actuated (CTA) phaser of a third embodiment with the source oil and pressure to the intermediate lock pin downstream of the inlet check valve. 
         FIG. 8  shows a schematic of a cam torque actuated (CTA) phaser of an alternate embodiment in a full stop advance position with an end lock pin in a locked position, locking the phaser. 
         FIG. 9  shows a schematic of a torsion assist (TA) phaser of another alternate embodiment moving towards a full advance position. 
         FIG. 10  shows a schematic of a torsion assist (TA) phaser of another alternate embodiment moving towards a retard position. 
         FIG. 11  shows a schematic of a torsion assist (TA) phaser of another alternate embodiment in a full stop retard position with an end lock pin in a locked position, locking the phaser. 
         FIG. 12  shows a schematic of a torsion assist (TA) phaser of another alternate embodiment in a holding position. 
         FIG. 13  shows a schematic of a torsion assist (TA) phaser of another alternate embodiment with a hydraulic circuit in an open position and the intermediate lock pin in a locked position, locking the phaser. 
         FIG. 14  shows a schematic of a torsion assist (TA) phaser of another alternate embodiment moving from a position in which the advance detent line is exposed to the advance chamber and the intermediate lock pin is unlocked towards a mid-position in which the intermediate lock pin is locked via the hydraulic circuit. 
         FIG. 15  shows a schematic of a torsion assist (TA) phaser of another alternate embodiment moving from a position in which the retard detent line is exposed to the retard chamber and the intermediate lock pin is unlocked towards a mid-position in which the intermediate lock pin is locked via the hydraulic circuit. 
         FIG. 16  shows a schematic of a cam torque actuated (CTA) phaser of another embodiment moving towards an advance position. 
         FIG. 17  shows a schematic of a cam torque actuated (CTA) phaser of another embodiment in a retard locked position. 
         FIG. 18  shows a schematic of cam torque (CTA) phaser of another embodiment moving towards a retard position. 
         FIG. 19  shows a schematic of a cam torque actuated (CTA) phaser of another embodiment in a holding position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A hydraulically operated camshaft phasing mechanism of an embodiment has two lock pins, one of which is engaged by engine oil pressure before engine shut down and released by spring force which acts when the locking pin is vented to atmosphere, relieving the oil pressure. The other lock pin is engaged by spring force and released by oil pressure once the engine is running. 
     In an alternate embodiment, an accumulator may be in fluid communication with the lock pin switching circuit to increase the time in which the end lock pin is engaged after engine shut down. 
     In the embodiments described, the end lock pin is released before engine oil pressure is developed in the engine so the phaser can be repositioned during engine cranking to a more optimal position for a cold engine start. 
     In some embodiments, the control valve that controls the position and rate of actuation of the camshaft phasing mechanism or phaser also has a portion of the control valve that controls the lock pin switching function. In addition this same hydraulic circuit can be used to control a hydraulic detent valve that causes the camshaft phasing mechanism to find an intermediate locked position. 
     Although in some embodiments the end lock pin that was engaged by pressure was at the retard stop, the same concept could be used for locking at any other position within the range of authority of the phaser. 
     In some embodiments, a phaser, which has an offset or remote piloted valve added to the hydraulic circuit aids in managing a hydraulic detent switching function, which provides a mid-position lock for cold starts of the engine, either during cranking or prior to complete engine shutdown is used. The mid-position locking of the phaser positions the cam at an optimum position for cold restarts of the engine once a current signal has been removed from the actuator, or variable force solenoid. The phaser may also be locked in a full retard position during an automatic “stop” of the engine in stop-start mode. 
     In some embodiments, the phasers have two lock pins. Both the lock pins may engage the outer end plate of the housing assembly when in a locked position, engage the inner end plate of the housing assembly when in a locked position or be split such that an intermediate lock pin, which in a locking position, engages an outer end plate of the housing assembly of the phaser and an end lock pin, which in a locking position, engages with the inner end plate of the housing assembly. In one embodiment, one of the lock pins is moved to a locked position when the phaser is in a full retard position and the other of the lock pins is moved to a locked position when the phaser is in a mid-position or intermediate phase angle. Alternatively, one of the lock pins is moved to a locked position when the phaser is in a full advance position and the other of the lock pins is moved to a locked position when the phaser is in a mid-position or intermediate phase angle. In another alternate embodiment, one of the lock pins may be moved to a locked position when the phaser is in a full advance position and the other of the lock pins may be moved to a locked position when the phaser is in a full retard position. 
     In other embodiments, the phasers have a lock pin that engages the outer end plate of the housing assembly when in a locked position or the inner end plate of the housing assembly when in a locked position, locking the rotation of the housing relative to the rotor. The lock pin preferably moves to a locked position when the phaser is in a full retard position. In order to move the lock pin to a locked position, pressure is required to move the body of the lock pin, against the force of a spring, into engagement of the outer end plate of the housing assembly or the inner end plate of the housing assembly depending on where the lock pin is located. 
     The piloted valve may be controlled on/off with the same hydraulic circuit that engages or releases one of the two lock pins. This shortens the variable cam timing (VCT) control valve to two hydraulic circuits, a VCT control circuit and a combined lock pin/hydraulic detent control circuit. Movement of the piloted valve to the first position is actively controlled by the remote on/off valve or the control valve of the phaser. 
     One of the advantages to using the remote piloted valve is that it can have a longer stroke than the control valve, since it is not limited by a solenoid. Therefore, the piloted valve can open up a larger flow passage for the hydraulic detent mode and improve actuation rate in the detent mode. In addition, the location of the remote piloted valve shortens and simplifies the hydraulic detent circuit and thereby increases performance of the VCT detent mode or intermediate phase angle position of the phaser. 
       FIGS. 1-5  show the operating modes of a CTA VCT phaser depending on the spool valve position. The positions shown in the figures define the direction the VCT phaser is moving to. It is understood that the phase 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 phase control valve can also operate in infinite intermediate positions and is not limited to the positions shown in the Figures. 
     Referring to  FIGS. 1-5 , 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 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. 
     The housing assembly  100  of the phaser has an outer circumference  101  for accepting drive force, an inner end plate (not shown) and an outer end plate (not shown). The rotor assembly  105  is connected to the camshaft and is coaxially located within the housing assembly  100 . The rotor assembly  105  has a 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 vane  104  is capable of rotation to shift the relative angular position of the housing assembly  100  and the rotor assembly  105 . Additionally, a hydraulic detent circuit  133  and a lock pin circuit  123  are also present. The hydraulic detent circuit  133  and the lock pin circuit  123  are essentially one circuit as discussed above, but will be discussed separately for simplicity. 
     The hydraulic detent circuit  133  includes a spring  131  loaded piloted valve  130  and an advance detent line  128  that connects the advance chamber  102  to the piloted valve  130  and the common line  114 , and a retard detent line  134  that connects the retard chamber  103  to the piloted valve  130 , line  129  connected to the piloted valve  130  and the common line  114 . The advance detent line  128  and the retard detent line  134  are a predetermined distance or length from the vane  104 . The piloted valve  130  is in the rotor assembly  105  and is fluidly connected to the lock pin circuit  123  and line  119   a  through line  132 . The lock pin circuit  123  includes an intermediate lock pin  143 , an intermediate lock pin spring  139 , line  132 , the piloted valve  130 , supply line  119   a , line  145 , exhaust line  121 , line  146 , the end lock pin  147 , and the end lock pin spring  144 . 
     The intermediate lock pin  143  and the end lock pin  147  are slidably housed in bores in the rotor assembly  105  and more preferably in the vane  104 . An end portion of the intermediate lock pin  143  is spring biased towards and fits into a recess  142  in an end plate of the housing assembly  100  by an intermediate lock pin spring  139 . An end portion of the end lock pin  147  is spring biased away from the recess  141  or hydraulically biased towards and fits into a recess  141  in an end plate of the housing assembly  100 . The opening and closing of the hydraulic detent circuit  133  and pressurization of the lock pin circuit  123  are both controlled by the switching/movement of the phase control valve  109 . 
     While the intermediate lock pin  143  and the end lock pin  147  are part of the overall lock pin circuit  123 , there are independent modes in which the end lock pin  147  is vented, while the intermediate lock pin is pressurized or filled. For example, when the spool is full in, or moving towards the advance position as shown in  FIG. 1 , the intermediate lock pin  143  is pressurized or filled and the end lock pin  147  is vented or not filled. During low duty cycle, the intermediate lock pin  143  is pressurized or filled and the end lock pin is also pressurized or filled as shown in  FIG. 2 . During 0% duty cycle, the intermediate lock pin  143  and the end lock pin are both vented or not filled as shown in  FIG. 4 . 
     A control valve  109 , preferably a spool valve, includes a spool  111  with cylindrical lands  111   a ,  111   b ,  111   c ,  111   d  slidably received in a sleeve  116 . The control valve 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. One end of the spool contacts spring  115  and the opposite end of the spool contacts a pulse width modulated variable force solenoid (VFS)  107 . The solenoid  107  may also be linearly controlled by varying current or voltage or other methods as applicable. Additionally, the opposite end of the spool  111  may contact and be influenced by a motor, or other actuators in place of the variable force solenoid  107 . 
     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. 
     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 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, the retard position or the retard lock position) of the phaser as well as whether the lock pin circuit  123  and the hydraulic detent circuit  133  are open (on) or closed (off) and whether the intermediate lock pin  143  or end lock pin  147  is in a locked or unlocked position. In other words, the position of the spool  111  actively controls the piloted valve  130 . The control valve  109  has an advance mode, a retard mode, a retard lock mode, a null mode (holding position), and a detent mode. 
     In the advance mode, 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 , fluid is blocked from exiting the advance chamber  102 , and the detent valve circuit  133  is off or closed. Both of the lock pins  147 ,  143  are in an unlocked position. 
     In the retard mode, 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 , and the detent valve circuit  133  is off and both of the lock pins  147 ,  143  are in an unlocked position. 
     In null mode, the spool  111  is moved to a position that blocks the exit of fluid from the advance and retard chambers  102 ,  103 , and the detent valve circuit  133  is off. 
     In the retard locking mode or end stop lock mode, the vane  104  has already been moved to a full retard position and flow from the advance chamber  102  through the spool  111  to the retard chamber continues with fluid blocked from exiting the retard chamber  103 . In this mode, the detent circuit is off, and the end lock pin  147  is pressurized, thus causing the end lock pin spring  144  to compress and allow the end lock pin  147  to engage the recess  141  of an end plate and move to a locked position. The “full retard position” is defined as when the vane  104  contacts the advance wall  102   a  of the chamber  117  or is substantially close to the advance wall  102   a  and may be referred to as a “retard end stop position” of the vane. 
     In the detent mode, three functions occur. 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 line  112  in between spool lands  111   a  and  111   b  from entering any of the other lines and line  113 , effectively removing control of the phaser from the control valve  109 . 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. The third function in the detent mode is to vent the lock pin circuit  123 , allowing the intermediate lock pin  143  to engage the recess  142  in an end plate of the housing assembly  100 . It should be noted that the end lock pin  147  is also vented and is spring biased by the end lock pin spring  144  to an unlocked position. 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 detent passages  128  and  134  are relative to the vane  104 . 
     Based on the duty cycle of the pulse width modulated variable force solenoid  107 , the spool  111  moves to a corresponding position along its stroke. When the duty cycle of the variable force solenoid  107  is approximately 40%, 60%, and greater than 60%, the spool  111  will be moved to positions that correspond with the retard mode/retard locking mode, the null mode (holding position), and the advance mode, respectively and the piloted valve  130  will be pressurized and moves to and remains in a first position, the hydraulic detent circuit  133  will be closed, and the intermediate lock pin  143  will be pressurized and released to an unlocked position. In the retard locking mode or end stop lock mode, the end lock pin  147  is pressurized and engages the recess  141  of an end plate of the housing assembly  100 . 
     When the duty cycle of the variable force solenoid  107  is 0%, the spool  111  is moved to the detent mode such that the piloted valve  130  vents and moves to a second position, the hydraulic detent circuit  133  will be open, and the intermediate lock pin  143  vented and engaged with the recess  142 . The end lock pin  147  is also vented through line  146  to exhaust line  121 , such that the end lock pin spring  144  biases the end lock pin  147  out of engagement with the recess  141  and is therefore in an unlocked position. A duty cycle of 0% was chosen as the extreme position along the spool stroke to open the hydraulic detent circuit  133 , vent the piloted valve  130 , and vent and engage the intermediate lock pin  143  with the recess  142 , since if power or control is lost, the phaser will default to a locked position. It should be noted that the duty cycle percentages listed above are an example and they may be altered. Furthermore, the hydraulic detent circuit  133  may be open, the piloted valve  130  vented, and the intermediate lock pin  143  vented and engaged with the recess  142  at 100% duty cycle, if desired. 
     When the duty cycle is set to be greater than 60%, the vane of the phaser is moving toward and/or in an advance position. The stroke of the spool or position of the spool relative to the sleeve is between 3.5 and 5 mm for the advance position. 
       FIG. 1  shows the phaser moving towards the advance position. To move towards the advance position, the duty cycle is increased to greater than 60%, the force of the VFS  107  on the spool  111  is increased and the spool  111  is moved to the right by the VFS  107  in an advance mode, until the force of the spring  115  balances the force of the VFS  107 . In the advance mode shown, spool land  111   a  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  to move towards the retard wall  103   a . Fluid exits from the retard chamber  103  through line  113  to the control valve  109  between spool lands  111   a  and  111   b  and recirculates back to central line  114  and line  112  leading to the advance chamber  102 . 
     Makeup oil is supplied to the phaser from supply S by pump  140  to make up for leakage and enters line  119 . If the control valve  109  is in the camshaft, line  119  may be drilled through a bearing. 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 the advance check valves  108  and flows to the advance chamber  102 . 
     Line  119   a  leads to two different lines, line  146  to the end lock pin  147  and to line  145  to the intermediate lock pin  143 . Line  145  further branches into line  132  which leads to the piloted valve  130 . The pressure of the fluid in line  119   a  moves through the spool  111  between lands  111   c  and  111   d  into line  145  to bias the intermediate lock pin  143  against the intermediate lock pin spring  139  to a released position. The fluid in line  145  also flows through line  132  and pressurizes the piloted valve  130  against the spring  131 , moving the piloted valve  130  to a position where retard detent line  134 , advance detent line  128  and line  129  are blocked as shown in  FIG. 1  and the detent circuit is off. At the same time, fluid from line  146  in fluid communication with the end lock pin  147 , is vented to exhaust line  121 , such that the end lock pin spring  144  biases the end lock pin  147  out of engagement with the recess  141  and is therefore in an unlocked position. Exhaust line  121  is blocked by spool land  111   c  preventing line  145  from venting. Spool land  111   b  prevents fluid from line  113  from venting through exhaust line  121 . 
     When the duty cycle is set between 40-60%, the vane of the phaser is moving toward and/or in a retard position. The stroke of the spool or position of the spool relative to the sleeve is between 2 and 3.5 mm for the retard position. 
       FIG. 5  shows the phaser moving towards the retard position. To move towards the retard position, the duty cycle is changed to greater than 40% but less than 60%, the force of the VFS  107  on the spool  111  is reduced and the spool  111  is moved by spring  115 , until the force of spring  115  balances the force of the VFS  107 . In the retard mode, spool land  111   b  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 towards the advance chamber wall  102   a . Fluid exits from the advance chamber  102  through line  112  to the control valve  109  between spool lands  111   a  and  111   b  and recirculates back to central line  114  and line  113  leading to the retard chamber  103 . 
     Makeup oil is supplied to the phaser from supply S by pump  140  to make up for leakage and enters line  119 . 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 the retard check valve  110  and flows to the retard chamber  103 . 
     Line  119   a  leads to two different lines, line  146  to the end lock pin  147  and to line  145  to the intermediate lock pin  143 . Line  145  further branches into line  132  which leads to the piloted valve  130 . The pressure of the fluid in line  119   a  moves through the spool  111  between lands  111   c  and  111   d  into line  145  to bias the intermediate lock pin  143  against the intermediate lock pin spring  139  to a released position, filling the lock pin circuit  123  with fluid. The fluid in line  145  also flows through line  132  and pressurizes the piloted valve  130  against the spring  131 , moving the piloted valve  130  to a position where retard detent line  134 , advance detent line  128  and line  129  are blocked and the detent circuit is off. Line  146 , is partially open to exhaust line  121  between spool lands  111   c  and  111   d . The end lock pin  147  will remain partially biased against the spring  144  in a released position until the recess  141  of the end plate aligns with the end lock pin  147  as shown in  FIG. 2 . Exhaust line  121  is blocked by spool land  111   c , preventing lines  145  and  146  from venting. 
     When the duty cycle is set between 40-60%, the vane of the phaser is moving toward and/or in a retard locking position. The stroke of the spool or position of the spool relative to the sleeve is approximately 2 mm for the retard locking position. 
       FIG. 2  shows the phaser in the retard locking position at the full retard position or retard end stop position. To move towards the full retard position, the duty cycle is changed to greater than 40% but less than 60%, the force of the VFS  107  on the spool  111  is reduced and the spool  111  is moved to the left in an end stop lock mode in the figure by spring  115 , until the force of spring  115  balances the force of the VFS  107 . In the end stop lock mode shown, spool land  111   b  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 towards the advance chamber wall  102   a . Fluid exits from the advance chamber  102  through line  112  to the control valve  109  between spool lands  111   a  and  111   b  and recirculates back to central line  114  and line  113  leading to the retard chamber  103 . The phaser is in a full retard position or retard end stop position when the vane  104  contacts the advance wall  102   a  or is substantially close the advance wall  102   a.    
     Makeup oil is supplied to the phaser from supply S by pump  140  to make up for leakage and enters line  119 . 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 the retard check valve  110  and flows to the retard chamber  103 . 
     Line  119   a  leads to two different lines, line  146  to the end lock pin  147  and to line  145  to the intermediate lock pin  143 . Line  145  further branches into line  132  which leads to the piloted valve  130 . The pressure of the fluid in line  119   a  moves through the spool  111  between lands  111   c  and  111   d  into line  145  to bias the intermediate lock pin  143  against the spring  144  to a released position, filling the lock pin circuit  123  with fluid. The fluid in line  145  also flows through line  132  and pressurizes the piloted valve  130  against the spring  131 , moving the piloted valve  130  to a position where retard detent line  134 , advance detent line  128  and line  129  are blocked and the detent circuit is off. Line  146  also receives fluid from line  119   a . The fluid in line  146  biases the end lock pin  147  into the recess  141  of an end plate  171  and is in a locked position, locking the housing assembly  100  relative to the rotor assembly  105 . Exhaust line  121  is blocked by spool land  111   c  preventing lines  145  and  146  from venting. 
     The end lock pin  147  engages or is locked using pressure just before shutting down a hot engine. The spool valve  111  would stay in the 2 mm (end stop lock mode) position, trapping the oil behind the end lock pin  147  and holding the end lock pin  147  engaged for as long as the oil will remain in the lock pin chamber. If the engine goes to a customer initiated “key off” mode as opposed to an engine controlled shut down such as is used in “stop-start” engine technology then at “key off” the control valve  109  would move to the zero position, thereby venting and releasing the full stop lock. This would allow the phaser to return to the optimum cold start position during the next engine cranking cycle. 
     The holding position of the phaser preferably takes place between the retard and advance position of the vane relative to the housing. The stroke of the spool or position of the spool relative to the sleeve is 3.5 mm. 
       FIG. 3  shows the phaser in the null position. In this position, the duty cycle of the variable force solenoid  107  is approximately 60% and the force of the VFS  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   a  and  111   b  block the flow of fluid from lines  112  and  113  respectively. Makeup oil is supplied to the phaser from supply S by pump  140  to make up for leakage and enters line  119 . 
     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  and flows to the advance or retard chambers  102 ,  103 . Line  119   a  leads to line  145  and to the intermediate lock pin  143 . Line  145  further branches into line  132  which leads to the piloted valve  130 . The pressure of the fluid in line  119   a  moves through the spool  111  between lands  111   c  and  111   d  into lines  145  to bias the intermediate lock pin  143  against the intermediate lock pin spring  139  to a released position. The fluid in line  145  also flows through line  132  and pressurizes the piloted valve  130  against the spring  131 , moving the piloted valve  130  to a position where retard detent line  134 , advance detent line  128  and line  129  are blocked and the detent circuit is off. Exhaust line  121  is blocked by spool land  111   c  preventing line  145  from venting. Fluid in line  146  vents between spool lands  111   b  and  111   c  through exhaust line  121 . The venting of line  146  allows the end lock pin spring  144  to bias the end lock pin  147  away from the recess to an unlocked position. 
     When the duty cycle is 0%, the vane of the phaser is in the mid-position or intermediate phase angle position. The stroke of the spool (position of the spool relative to the sleeve) is 0 mm. 
       FIG. 4  shows the phaser in the mid-position or intermediate phase angle position, where the duty cycle of the variable force solenoid is 0%, the spool  109  is in detent mode, the piloted valve  130  is vented through the spool to exhaust line  121  leading to sump or exhaust, and the hydraulic detent circuit  133  is open or on. 
     Depending on where the vane  104  was prior to the duty cycle of the variable force solenoid  107  being changed to 0%, either the advance detent line  128  or the retard detent line  134  will be exposed to the advance or retard chamber  102 ,  103  respectively. In addition, if the engine had an abnormal shut down (e.g. the engine stalled), when the engine is cranking, the duty cycle of the variable force solenoid  107  would be 0% the rotor assembly  105  would move via the detent circuit to the mid-position or intermediate phase angle position and the intermediate lock pin  143  would be engaged in mid-position or intermediate phase angle position regardless of what position the vane  104  was in relative to the housing assembly  100  prior to the abnormal shut down of the engine. 
     The ability of the phaser of the present invention to default to a mid-position or intermediate phase angle position without using electronic controls allows the phaser to move to the mid-position or intermediate phase angle position even during engine cranking when electronic controls are not typically used for controlling the cam phaser position. In addition, since the phaser defaults to the mid-position or intermediate phase angle position, it provides a fail-safe position, especially if control signals or power or lost, that guarantees that the engine will be able to start and run even without active control over the VCT phaser. Since the phaser has the mid-position or intermediate phase angle position upon cranking of the engine, longer travel of the phase of the phaser is possible, providing calibration opportunities. In the prior art, longer travel phasers or a longer phase angle is not possible, since the mid-position or intermediate phase angle position is not present upon engine cranking and startup and the engine has difficulty starting at either the extreme advance or retard stops. 
     When the duty cycle of the variable force solenoid  107  is just set to 0%, the force on the VFS on the spool  111  is decreased, and the spring  115  moves the spool  111  to the far left end of the spool&#39;s travel to a detent mode. In the detent mode, spool land  111   b  blocks the flow of fluid from line  112  in between spool lands  111   a  and  111   b  from entering any of the other lines and line  113 , effectively removing control of the phaser from the control valve  109 . At the same time, fluid from supply may flow through line  119  to line  119   b  and inlet check valve  118  to the common line  114  around the bore within the sleeve  116 . 
     Fluid is prevented from flowing from line  119   a  to line  145  and line  132  to the piloted valve  130  by spool land  111   d . Since fluid cannot flow to lines  145  and  132 , the piloted valve  130  vents to exhaust line  121 , opening passage between the advance detent line  128  and the retard detent line  134  through the piloted valve  130  to line  129  and the common line  114 , in other words, opening or turning on the hydraulic detent circuit  133 . With exhaustion of fluid from lines  132  and  145 , the intermediate lock pin spring  139  biases the intermediate lock pin  143  to engage the recess  142  in an end plate of the housing assembly  100  and lock the housing assembly  100  relative to the rotor assembly  105 . At the same time, fluid is also exhausted from line  146  through exhaust line  121 . With fluid exhausting from line  146 , the end lock pin spring  147  biases the end lock pin  147  to a released, unlocked position. 
     If the vane  104  was positioned within the housing assembly  100  near or in the advance position and the advance detent line  128  is exposed to the advance chamber  102 , then fluid from the advance chamber  102  will flow into the advance detent line  128  and through the open piloted valve  130  and to line  129  leading to common line  114 . From the common line  114 , fluid flows through check valve  110  and into the retard chamber  103 , moving the vane  104  relative to the housing assembly  100  to close off or block advance detent line  128  to the advance chamber  102 . As the rotor assembly  105  closes off the advance detent line  128  from the advance chamber  102 , the vane  104  is moved to a mid-position or intermediate phase angle position within the chamber formed between the housing assembly  100  and the rotor assembly  105 . 
     If the vane  104  was positioned within the housing assembly  100  near or in the retard position and the retard detent line  134  is exposed to the retard chamber  103 , then fluid from the retard chamber  103  will flow into the retard detent line  134  and through the open piloted valve  130  and to line  129  leading to common line  114 . From the common line  114 , fluid flows through check valve  108  and into the advance chamber  102 , moving the vane  104  relative to the housing assembly  100  to close off the retard detent line  134  to the retard chamber  103 . As the rotor assembly  105  closes off line the retard detent  134  from the retard chamber  103 , the vane  104  is moved to a mid-position or intermediate phase angle position within the chamber formed between the housing assembly  100  and the rotor assembly  105 . 
     It should be noted that while the end stop lock mode was described as locking the phaser in a full retard position, the full retard position may be replaced with a locking of the phaser in a full advance position. In this position, full advance position is when the vane  104  contacts the retard wall  103   a  or is substantially close to the retard wall  103   a  as shown in  FIG. 8  and may be referred to as an “advance end stop position” of the vane. 
     For a phaser with the end stop lock mode in a full advance position, in the advance mode, 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 , fluid is blocked from exiting the advance chamber  102 , and the detent valve circuit  133  is off or closed. Both of the lock pins  147 ,  143  are in an unlocked position. 
     In the retard mode, 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 , and the detent valve circuit  133  is off and both of the lock pins  147 ,  143  are in an unlocked position. 
     In null mode, the spool  111  is moved to a position that blocks the exit of fluid from the advance and retard chambers  102 ,  103 , and the detent valve circuit  133  is off. 
     In the advance locking mode, the vane  104  has already been moved to a full advance position and flow from the retard chamber  103  through the spool  111  to the advance chamber  102  continues with fluid blocked from exiting the advance chamber  102 . In this mode, the detent circuit is off, and the end lock pin  147  is pressurized, thus causing the spring  144  to compress and allow the end lock pin  147  to engage the recess  141  of an end plate and move to a locked position. The “full advance position” is defined as when the vane  104  contacts the retard wall  103   a  of the chamber  117  or is substantially close to the retard wall  103   a  and may be referred to as an “advance end stop position” of the vane. 
     In the detent mode, three functions occur. 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 line  112  in between spool lands  111   a  and  111   b  from entering any of the other lines and line  113 , effectively removing control of the phaser from the control valve  109 . 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. The third function in the detent mode is to vent the lock pin circuit  123 , allowing the intermediate lock pin  143  to engage the recess  142  in an end plate of the housing assembly  100 . It should be noted that the end lock pin  147  is also vented and is spring biased by the end lock pin spring  144  to an unlocked position. 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 detent passages  128  and  134  are relative to the vane  104 . 
     Based on the duty cycle of the pulse width modulated variable force solenoid  107 , the spool  111  moves to a corresponding position along its stroke. When the duty cycle of the variable force solenoid  107  is approximately 40%, 60%, and greater than 60%, the spool  111  will be moved to positions that correspond with the advance mode/advance locking mode, the null mode, and the retard mode, respectively and the piloted valve  130  will be pressurized and moves to and remains in a first position, the hydraulic detent circuit  133  will be closed, and the intermediate lock pin  143  will be pressurized and released to an unlocked position. In the retard locking mode or end stop lock mode, the end lock pin  147  is pressurized and engages the recess  141  of an end plate of the housing assembly  100 . 
     When the duty cycle of the variable force solenoid  107  is 0%, the spool  111  is moved to the detent mode such that the piloted valve  130  vents and moves to a second position, the hydraulic detent circuit  133  will be open, and the intermediate lock pin  143  vented and engaged with the recess  142 . The end lock pin  147  is also vented through line  146  to exhaust line  121 , such that the end lock pin spring  144  biases the end lock pin  147  out of engagement with the recess  141  and is therefore in an unlocked position. A duty cycle of 0% was chosen as the extreme position along the spool stroke to open the hydraulic detent circuit  133 , vent the piloted valve  130 , and vent and engage the intermediate lock pin  143  with the recess  142 , since if power or control is lost, the phaser will default to a locked position. It should be noted that the duty cycle percentages listed above are an example and they may be altered. Furthermore, the hydraulic detent circuit  133  may be open, the piloted valve  130  vented, and the intermediate lock pin  143  vented and engaged with the recess  142  at 100% duty cycle, if desired. 
     When the duty cycle is set to be greater than 60%, the vane of the phaser is moving toward and/or in a retard position. The stroke of the spool or position of the spool relative to the sleeve is between 3.5 and 5 mm for the retard position. 
     When the duty cycle is set between 40-60%, the vane of the phaser is moving toward and/or in an advance position. The stroke of the spool or position of the spool relative to the sleeve is between 2 and 3.5 mm for the advance position. 
     The holding position of the phaser preferably takes place between the retard and advance position of the vane relative to the housing. The stroke of the spool or position of the spool relative to the sleeve is 3.5 mm. 
     When the duty cycle is 0%, the vane of the phaser is in the mid-position or intermediate phase angle position. The stroke of the spool (position of the spool relative to the sleeve) is 0 mm. 
       FIG. 6  shows a phaser of a second embodiment in the retard locking position at the full retard position or retard end stop position. This phaser is similar to the phaser of  FIG. 2 , with an accumulator  200  added to line  146 . Since it is anticipated that the oil behind the end lock pin  147  may leak out sooner than desired allowing the end lock pin  147  to disengage before the hot engine is restarted, an accumulator  200  may be in fluid communication with line  146  of the lock pin switching circuit  123 . The accumulator  200  increases the time in which the end lock pin  147  is engaged with the recess  141  after engine shut down. The accumulator  200  is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source  201 ,  202 . In this embodiment, the external source is a spring  201  biased piston  202 . The external source can also be a spring, a raised weight, or a compressed gas. The other positions, for example the null mode (holding position), the advance mode, the retard mode and the detent mode are as discussed above relative to  FIGS. 1, 3, 4 and 5  and are incorporated here by reference. 
     It should be noted that in  FIG. 6 , the accumulator  200  could also communicate with lines  119  and  119   a  and produce similar results as when the accumulator is placed in line  146 . 
       FIG. 7  shows a phaser of a third embodiment in the retard locking position at the full retard position or retard end stop position. This phaser is similar to the phaser of  FIG. 6 , with an accumulator  200  added to line  146 . The difference between this phaser and the phaser of  FIG. 6  is the placement of the inlet check valve  118 . In the phaser of  FIG. 7 , fluid is supplied to the intermediate lock pin  143  and the end lock pin  147  from a source S and flows through the inlet check valve  118  as opposed to prior to the inlet check valve  118  as shown in  FIGS. 1-5 . 
     It should be noted that in  FIG. 6 , the accumulator  200  could also communicate with lines  119 ,  119   a  or  119   b  and produce similar results as when the accumulator is placed in line  146 . 
     It should be noted that while the end stop lock mode in  FIGS. 6-7  were described as locking the phaser in a full retard position, the full retard position may be replaced with a locking of the phaser in a full advance position. In this position, full advance position is when the vane  104  contacts the retard wall  103   a  or is substantially close to the retard wall  103   a  as shown in  FIG. 8  and may be referred to as an “advance end stop position” of the vane. 
       FIGS. 9-15  show the operating modes of TA VCT phaser depending on the spool valve position. The positions shown in the figures define the direction the VCT phaser is moving to. It is understood that the phaser 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 phaser control valve can also operate in infinite intermediate positions and is not limited to the positions shown in Figures. 
     Oil pressure from an oil supply  140  moves the vane  104 . The control valve  209  allows the vane  104  in the phaser to move by permitting fluid flow from the supply  140  to the advance chamber  102  and from the retard chamber  103  to an exhaust line  122  or from supply  140  to the retard chamber  103  and from the advance chamber  102  to an exhaust line  121 , depending on the desired direction of movement. 
     The housing assembly  100  of the phaser has an outer circumference  101  for accepting drive force, an inner end plate (not shown) and an outer end plate (not shown). The rotor assembly  105  is connected to the camshaft and is coaxially located within the housing assembly  100 . The rotor assembly  105  has a 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 vane  104  is capable of rotation to shift the relative angular position of the housing assembly  100  and the rotor assembly  105 . 
     Additionally, a hydraulic detent circuit  233  (not shown) and a lock pin circuit  123  (not shown) are also present. The hydraulic detent circuit  233  and the lock pin circuit  123  are essentially one circuit as discussed above, but will be discussed separately for simplicity. 
     The hydraulic detent circuit  233  includes a spring  131  loaded piloted valve  130  and an advance detent line  128  that connects the advance chamber  102  to the piloted valve  130  and the common line  214 , a retard detent line  134  that connects the retard chamber  103  to the piloted valve  130 , and a line  129  connected to the piloted valve  130  and the common line  214 . It should be noted that in this phaser, the common line  214  is only connected to the piloted valve  130  and does not connect directly to control valve  209 . The common line  214  is further in fluid communication with an advance check valve  108  and a retard check valve  110 . The advance and retard check valves  108 ,  110  prevent fluid from the advance and retard chambers  102 ,  103  from entering line  129  and the hydraulic detent circuit  233 . 
     The advance and retard check valves  108 ,  110  always prevent oil from entering line  129  whether the piloted valve  130  is open or closed. The piloted valve  130  prevents forward flow from advance detent line  128  and retard detent line  134  when closed. The check valves  108 ,  110  prevent back flow at all times. 
     The advance detent line  128  and the retard detent line  134  are a predetermined distance or length from the vane  104 . The piloted valve  130  is in the rotor assembly  105  and is fluidly connected to the lock pin circuit  123  and line  119   a  through line  132 . The lock pin circuit  123  includes an intermediate lock pin  143 , an intermediate lock pin spring  139 , line  132 , the piloted valve  130 , supply line  119   a , line  145 , exhaust line  121 , line  146 , the end lock pin  147 , and the end lock pin spring  144 . 
     The intermediate lock pin  143  and the end lock pin  147  are slidably housed in bores in the rotor assembly  105  and more preferably in the vane  104 . An end portion of the intermediate lock pin  143  is spring biased towards and fits into a recess  142  in an end plate of the housing assembly  100  by an intermediate lock pin spring  139 . An end portion of the end lock pin  147  is biased away from the recess  141  and hydraulically biased towards and fits into a recess  141  in an end plate of the housing assembly  100 . The opening and closing of the hydraulic detent circuit  233  and pressurization of the lock pin circuit  123  are both controlled by the switching/movement of the phase control valve  209 . 
     While the intermediate lock pin  143  and the end lock pin  147  are part of the overall lock pin circuit  123 , there are independent modes in which the end lock pin  147  is vented, while the intermediate lock pin is pressurized or filled. For example, when the spool is full in, or moving towards the advance position as shown in  FIG. 9 , the intermediate lock pin  143  is pressurized or filled, moving the intermediate lock pin  143  to an unlocked position and the end lock pin  147  is vented or not filled, moving the end lock pin to an unlocked position. During low duty cycle, the intermediate lock pin  143  is pressurized or filled, moving the intermediate lock pin  143  to an unlocked position and the end lock pin  147  is also pressurized or filled, moving the end lock pin  147  to a locked position as shown in  FIG. 11 . During 0% duty cycle, the intermediate lock pin  143  and the end lock pin  147  are both vented or not filled, such that the intermediate lock pin  143  is moved to a locked position and the end lock pin  147  is moved to an unlocked position as shown in  FIG. 13 . 
     A control valve  209 , preferably a spool valve, includes a spool  211  with cylindrical lands  211   a ,  211   b ,  211   c ,  211   d ,  211   e  slidably received in a sleeve  116 . The control valve 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. One end of the spool contacts spring  115  and the opposite end of the spool contacts a pulse width modulated variable force solenoid (VFS)  107 . The solenoid  107  may also be linearly controlled by varying current or voltage or other methods as applicable. Additionally, the opposite end of the spool  211  may contact and be influenced by a motor, or other actuators in place of the variable force solenoid  107 . 
     The position of the control valve  209  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. 
     The position of the spool  211  is influenced by spring  115  and the solenoid  107  controlled by the ECU  106 . Further detail regarding control of the phaser is discussed in detail below. The position of the spool  211  controls the motion (e.g. to move towards the advance position, holding position, the retard position or the retard lock position) of the phaser as well as whether the lock pin circuit  123  and the hydraulic detent circuit  233  are open (on) or closed (off) and whether the intermediate lock pin  143  or end lock pin  147  is in a locked or unlocked position. In other words, the position of the spool  211  actively controls the piloted valve  130 . The control valve  209  has an advance mode, a retard mode, a retard lock mode, a null mode (holding position), and a detent mode. 
     In the advance mode, the spool  211  is moved to a position so that fluid may flow from the supply  140 , through the spool  211  and into the advance chamber  102 . Fluid is blocked from exiting the advance chamber  102  by the spool  211 . Fluid in the retard chamber  103  vents through the spool  211  to an exhaust line  122 . The detent valve circuit  133  is off or closed. Both of the lock pins  147 ,  143  are in an unlocked position. 
     In the retard mode, the spool  211  is moved to a position so that fluid may flow from the supply  140 , through the spool  211  to the retard chamber  103 . Fluid is blocked from exiting the retard chamber  103  by the spool  211 . Fluid in the advance chamber  102  vents through the spool  211  to an exhaust line  121 . The detent valve circuit  233  is off and both of the lock pins  147 ,  143  are in an unlocked position. 
     In null mode, the spool  211  is moved to a position that blocks the exit of fluid from the advance and retard chambers  102 ,  103 , and the detent valve circuit  233  is off. 
     In the retard locking mode or end stop lock mode, the vane  104  has already been moved to a full retard position or retard end stop position and fluid from the advance chamber  102  flows through the spool  211  to exhaust line  121 . Fluid is still provided to the retard chamber from the supply  140 . In this mode, the detent circuit is off, and the end lock pin  147  is pressurized, thus causing the spring  144  to compress and allow the end lock pin  147  to engage the recess  141  of an end plate and move to a locked position. The “full retard position” is defined as when the vane  104  contacts the advance wall  102   a  of the chamber  117  or is substantially close to the advance wall  102   a  and may be referred to as a “retard end stop position” of the vane. 
     In the detent mode, three functions occur. The first function in the detent mode is that the spool  211  moves to a position in which spool land  211   b  blocks the flow of fluid from line  113  and the retard chamber  103  from exiting to the exhaust line  122 , and spool land  211   d  blocks the flow of fluid from line  112  and the advance chamber  102  from exiting to the exhaust line  121 , effectively removing control of the phaser from the control valve  209 . The second function in detent mode is to open or turn on the detent valve circuit  233 . The detent valve circuit  233  has complete control over the phaser moving to advance or retard, until the vane  104  reaches the intermediate phase angle position. The third function in the detent mode is to vent the lock pin circuit  123 , allowing the intermediate lock pin  143  to engage the recess  142  in an end plate of the housing assembly  100 . It should be noted that the end lock pin  147  is also vented and is spring biased by the end lock pin spring  144  to an unlocked position. 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 detent passages  128  and  134  are relative to the vane  104 . 
     Based on the duty cycle of the pulse width modulated variable force solenoid  107 , the spool  211  moves to a corresponding position along its stroke. When the duty cycle of the variable force solenoid  107  is approximately 40%, 60%, and greater than 60%, the spool  211  will be moved to positions that correspond with the retard mode/retard locking mode, the null mode, and the advance mode, respectively and the piloted valve  130  will be pressurized and moves to and remains in a first position, the hydraulic detent circuit  233  will be closed, and the intermediate lock pin  143  will be pressurized and released to an unlocked position. In the retard locking mode or end stop lock mode, the end lock pin  147  is pressurized and engages the recess  141  of an end plate of the housing assembly  100 . 
     When the duty cycle of the variable force solenoid  107  is 0%, the spool  211  is moved to the detent mode such that the piloted valve  130  vents and moves to a second position, the hydraulic detent circuit  233  will be open, and the intermediate lock pin  143  vented and engaged with the recess  142 . The end lock pin  147  is also vented through line  146  to exhaust line  121 , such that the end lock pin spring  144  biases the end lock pin  147  out of engagement with the recess  141  and is therefore in an unlocked position. A duty cycle of 0% was chosen as the extreme position along the spool stroke to open the hydraulic detent circuit  133 , vent the piloted valve  130 , and vent and engage the intermediate lock pin  143  with the recess  142 , since if power or control is lost, the phaser will default to a locked position. It should be noted that the duty cycle percentages listed above are an example and they may be altered. Furthermore, the hydraulic detent circuit  233  may be open, the piloted valve  130  vented, and the intermediate lock pin  143  vented and engaged with the recess  142  at 100% duty cycle, if desired. 
     When the duty cycle is set to be greater than 60%, the vane of the phaser is moving toward and/or in an advance position. The stroke of the spool or position of the spool relative to the sleeve is between 3.5 and 5 mm for the advance position. 
       FIG. 9  shows the phaser moving towards the advance position. To move towards the advance position, the duty cycle is increased to greater than 60%, the force of the VFS  107  on the spool  211  is increased and the spool  211  is moved to the left by the VFS  107  in an advance mode, until the force of the spring  115  balances the force of the VFS  107 . 
     In the advance mode, spool land  211   c  prevents fluid from the advance chamber  102  and from supply from exhausting into exhaust line  121 . Fluid is supplied to the phaser from supply S by pump  140  and enters line  119 . If the control valve  209  is in the camshaft, line  119  may be drilled through a bearing. 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  209 . From line  119   b  fluid is supplied through the spool  211  between spool lands  211   b  and  211   c  to the advance chamber  102  through line  112 . At the same time, fluid in the retard chamber  103  is exhausted through line  113 , through the spool  211  between spool lands  211   a  and  211   b  to the exhaust line  122 . Fluid is prevented from being supplied from supply  140  to the retard chamber  103  by spool land  211   b . The fluid in the advance chamber  102  moves the vane  104  towards the retard wall  103   a.    
     Line  119   a  leads to two different lines, line  146  to the end lock pin  147  and line  145  to the intermediate lock pin  143 . Line  145  further branches into line  132  which leads to the piloted valve  130 . The pressure of the fluid in line  119   a  moves through the spool  211  between lands  211   d  and  211   e  into line  145  to bias the intermediate lock pin  143  against the intermediate lock pin spring  139  to a released position. The fluid in line  145  also flows through line  132  and pressurizes the piloted valve  130  against the spring  131 , moving the piloted valve  130  to a position where retard detent line  134 , advance detent line  128  and line  129  are blocked as shown in  FIG. 9  and the detent circuit is off. At the same time, fluid from line  146  is in fluid communication with the end lock pin  147  and is vented to exhaust line  121  between spool lands  211   d  and  211   c , such that the end lock pin spring  144  biases the end lock pin  147  out of engagement with the recess  141  and is therefore in an unlocked position. Exhaust line  121  is blocked by spool land  211   d  preventing line  145  from venting. 
     When the duty cycle is set between 40-60%, the vane of the phaser is moving toward and/or in a retard position. The stroke of the spool or position of the spool relative to the sleeve is between 2 and 3.5 mm for the retard position. 
       FIG. 10  shows the phaser moving towards the retard position. To move towards the retard position, the duty cycle is changed to greater than 40% but less than 60%, the force of the VFS  107  on the spool  211  is reduced and the spool  211  is moved by spring  115 , until the force of spring  115  balances the force of the VFS  107 . 
     In the retard mode, spool land  211   b  prevents fluid from the retard chamber  103  and from supply S from exhausting into exhaust line  122 . Fluid is supplied to the phaser from supply S by pump  140  and enters line  119 . If the control valve  209  is in the camshaft, line  119  may be drilled through a bearing. 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  209 . From line  119   b  fluid is supplied through the spool  211  between spool lands  211   b  and  211   c  to the retard chamber  103  through line  113 . At the same time, fluid in the advance chamber  102  is exhausted through line  112 , through the spool  211  between spool lands  211   c  and  211   d  to the exhaust line  121 . Fluid is prevented from being supplied from supply  140  to the advance chamber  102  by spool land  211   c . The fluid in the retard chamber  103  moves the vane  104  towards the advance wall  102   a.    
     Line  119   a  leads to two different lines, line  146  to the end lock pin  147  and line  145  to the intermediate lock pin  143 . Line  145  further branches into line  132  which leads to the piloted valve  130 . The pressure of the fluid in line  119   a  moves through the spool  211  between lands  211   d  and  211   e  into line  145  to bias the intermediate lock pin  143  against the intermediate lock pin spring  139  to a released position, filling the lock pin circuit  123  with fluid. The fluid in line  145  also flows through line  132  and pressurizes the piloted valve  130  against the spring  131 , moving the piloted valve  130  to a position where retard detent line  134 , advance detent line  128  and line  129  are blocked and the detent circuit is off. Line  146  is pressurized with fluid from line  119   a  and the end lock pin  147  will remain partially biased against the spring  144  in a released position until the recess  141  of the end plate aligns with the end lock pin  147  as shown in  FIG. 10 . Exhaust line  121  is blocked by spool land  211   d  preventing lines  145  and  146  from venting. 
     When the duty cycle is set between 40-60%, the vane of the phaser is moving toward and/or in a retard locking position. The stroke of the spool or position of the spool relative to the sleeve is approximately 2 mm for the retard locking position. 
       FIG. 11  shows the phaser in the retard locking position at the full retard position or retard end stop position. To move towards the full retard position, the duty cycle is changed to greater than 40% but less than 60%, the force of the VFS  107  on the spool  211  is reduced and the spool  211  is moved to the right in an end stop lock mode in the figure by spring  115 , until the force of spring  115  balances the force of the VFS  107 . 
     In the end stop lock mode shown, spool land  211   b  prevents fluid from the retard chamber  103  and from supply S from exhausting into exhaust line  122 . Fluid is supplied to the phaser from supply S by pump  140  and enters line  119 . If the control valve  209  is in the camshaft, line  119  may be drilled through a bearing. 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  209 . From line  119   b  fluid is supplied through the spool  211  between spool lands  211   b  and  211   c  to the retard chamber  103  through line  113 . At the same time, fluid in the advance chamber  102  is exhausted through line  112 , through the spool  211  between spool lands  211   c  and  211   d  to the exhaust line  121 . Fluid is prevented from being supplied from supply  140  to the advance chamber  102  by spool land  211   c . The fluid in the retard chamber  103  moves the vane  104  towards the advance wall  102   a . It should be noted that the end stop lock mode is similar to the retard mode shown in  FIG. 10 , except that the vane  104  has been moved into approximate contact with the advance wall  103   a , allowing the end lock pin  147  to align and engage in recess  141  of the end plate of the housing assembly  100 . The engagement of the end lock pin  147  with the recess  141  of the end plate of the housing assembly  100 , locks the vane  104  relative to the rotor assembly  105  in a position with the vane  104  at an extreme end of travel. The intermediate lock pin  143  remains in a released position. Exhaust line  121  is blocked by spool land  211   d  preventing lines  145  and  146  from venting. 
     The fluid in line  145  also flows through line  132  and pressurizes the piloted valve  130  against the spring  131 , moving the piloted valve  130  to a position where retard detent line  134 , advance detent line  128  and line  129  are blocked and the detent circuit is off. 
     The end lock pin  147  engages or is locked using pressure just before shutting down a hot engine. The spool valve  211  would stay in the 2 mm (end stop lock mode) position, trapping the oil behind the end lock pin  147  and holding the end lock pin  147  engaged for as long as the oil will remain in the lock pin chamber. If the engine goes to customer initiated “key off” mode as opposed to an engine controlled shut down such as is used in “stop-start” engine technology then at “key off” the control valve  209  would move to the zero position thereby venting and releasing the full stop lock. This would allow the phaser to return to the optimum cold start position during the next engine cranking cycle. 
     The holding position of the phaser preferably takes place between the retard and advance position of the vane relative to the housing. The stroke of the spool or position of the spool relative to the sleeve is 3.5 mm. 
       FIG. 12  shows the phaser in the null position. In this position, the duty cycle of the variable force solenoid  107  is approximately 60% and the force of the VFS  107  on one end of the spool  211  equals the force of the spring  115  on the opposite end of the spool  211  in holding mode. The lands  211   b  and  211   c  allow a small amount of fluid to flow from supply S, through line  119  and the inlet check valve  118 , to line  119   b , through the spool  211  and into lines  112  and  113  to the advance chamber  102  and the retard chamber  103 , respectively. 
     Line  119   a  leads to line  145  and to the intermediate lock pin  143 . Line  145  further branches into line  132  which leads to the piloted valve  130 . The pressure of the fluid in line  119   a  moves through the spool  211  between lands  211   d  and  211   e  into lines  145  to bias the intermediate lock pin  143  against the intermediate lock pin spring  139  to a released position. The fluid in line  145  also flows through line  132  and pressurizes the piloted valve  130  against the spring  131 , moving the piloted valve  130  to a position where retard detent line  134 , advance detent line  128  and line  129  are blocked and the detent circuit is off. Exhaust line  121  is blocked by spool land  211   d  preventing line  145  from venting. Fluid is also provided from line  119   a  to line  146 . Even though the end lock pin  147  is pressurized to lock, the end lock pin  147  cannot lock the housing assembly  100  relative to the rotor assembly  105  since the recess  141  for receiving the end lock pin  147  is only present at an extreme end of travel of the vane  104 . Therefore, the end lock pin  147  remains in an unlocked position. 
     When the duty cycle is 0%, the vane of the phaser is in the mid-position or intermediate phase angle position. The stroke of the spool (position of the spool relative to the sleeve) is 0 mm. 
       FIG. 13  shows the phaser in the mid-position or intermediate phase angle position, where the duty cycle of the variable force solenoid is 0%, the spool  209  is in detent mode, the piloted valve  130  is vented through the spool to exhaust line  121  leading to sump or exhaust, and the hydraulic detent circuit  233  is open or on. 
     Depending on where the vane  104  was prior to the duty cycle of the variable force solenoid  107  being changed to 0%, either the advance detent line  128  or the retard detent line  134  will be exposed to the advance or retard chamber  102 ,  103  respectively. In addition, if the engine had an abnormal shut down (e.g. the engine stalled), when the engine is cranking, the duty cycle of the variable force solenoid  107  would be 0%, the rotor assembly  105  would move via the detent circuit  233  to the mid-position or intermediate phase angle position, and the intermediate lock pin  143  would be engaged in mid-position or intermediate phase angle position regardless of what position the vane  104  was in relative to the housing assembly  100  prior to the abnormal shut down of the engine. 
     The ability of the phaser to default to a mid-position or intermediate phase angle position without using electronic controls allows the phaser to move to the mid-position or intermediate phase angle position even during engine cranking when electronic controls are not typically used for controlling the cam phaser position. In addition, since the phaser defaults to the mid-position or intermediate phase angle position, it provides a fail-safe position, especially if control signals or power is lost, that guarantees that the engine will be able to start and run even without active control over the VCT phaser. Since the phaser has the mid-position or intermediate phase angle position upon cranking of the engine, longer travel of the phase of the phaser is possible, providing calibration opportunities. In the prior art, longer travel phasers or a longer phase angle is not possible, since the mid-position or intermediate phase angle position is not present upon engine cranking and startup and the engine has difficulty starting at either the extreme advance or retard stops. 
     When the duty cycle of the variable force solenoid  107  is just set to 0%, the force on the VFS on the spool  211  is decreased, and the spring  115  moves the spool  211  to the far right end of the spool&#39;s travel to a detent mode. Fluid is prevented from flowing from line  119   a  to line  145 , line  132  and to the piloted valve  130  by spool land  211   e . Since fluid cannot flow to lines  145  and  132 , the piloted valve  130  vents to exhaust line  121 , opening passage between the advance detent line  128  and the retard detent line  134  through the piloted valve  130  to line  129  and the common line  214 , in other words, opening or turning on the hydraulic detent circuit  233 . With exhaustion of fluid from lines  132  and  145 , the intermediate lock pin spring  139  biases the intermediate lock pin  143  to engage the recess  142  in an end plate of the housing assembly  100  and lock the housing assembly  100  relative to the rotor assembly  105 . At the same time, fluid is also exhausted from line  146  through exhaust line  121 . With fluid exhausting, the end lock pin spring  147  biases the end lock pin  147  to a released, unlocked position. 
     Fluid also flows from line  119   b  through spool land  211   c , which restricts oil from supply S to both the advance line  112  and the retard line  113 , but allows a continuous small amount of fluid to enter the advance and retard chambers  102 ,  103 . Fluid is prevented from exhausting from the advance chamber  102  and advance line  112  by spool land  211   d . Fluid is also prevented from exhausting from the retard chamber  103  and retard line  113  by spool land  211   b , effectively removing control of the phaser from the control valve  209 . 
     If the vane  104  was positioned within the housing assembly  100  near or in the advance position as shown in  FIG. 14 , and the advance detent line  128  is exposed to the advance chamber  102 , then fluid from the advance chamber  102  will flow into the advance detent line  128  and through the open piloted valve  130  and to line  129  leading to common line  214 . From the common line  214 , fluid flows through retard check valve  110  and into the retard chamber  103 , moving the vane  104  relative to the housing assembly  100  to close off or block advance detent line  128  to the advance chamber  102 . As the rotor assembly  105  closes off the advance detent line  128  from the advance chamber  102 , the vane  104  is moved to a mid-position or intermediate phase angle position within the chamber formed between the housing assembly  100  and the rotor assembly  105 . 
     If the vane  104  was positioned within the housing assembly  100  near or in the retard position as shown in  FIG. 15 , and the retard detent line  134  is exposed to the retard chamber  103 , then fluid from the retard chamber  103  will flow into the retard detent line  134  and through the open piloted valve  130  and to line  129  leading to common line  214 . From the common line  214 , fluid flows through advance check valve  108  and into the advance chamber  102 , moving the vane  104  relative to the housing assembly  100  to close off the retard detent line  134  to the retard chamber  103 . As the rotor assembly  105  closes off the retard detent line  134  from the retard chamber  103 , the vane  104  is moved to a mid-position or intermediate phase angle position within the chamber formed between the housing assembly  100  and the rotor assembly  105 . 
     It should be noted that while the end stop lock mode was described as locking the phaser in a full retard position or retard end stop position, the full retard position may be replaced with a locking of the phaser in a full advance position or advance end stop position. In this position, full advance position is when the vane  104  contacts the retard wall  103   a  or is substantially close to the retard wall  103   a  and may be referred to as an “advance end stop position” of the vane. 
       FIGS. 16-19  show positions of a cam torque actuated phaser in another embodiment. 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 and are alternatively pressurized by the cam torque. The control valve  309  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. 
     The housing assembly  100  of the phaser has an outer circumference  101  for accepting drive force, an inner end plate (not shown) and an outer end plate (not shown). The rotor assembly  105  is connected to the camshaft and is coaxially located within the housing assembly  100 . The rotor assembly  105  has a 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 vane  104  is capable of rotation to shift the relative angular position of the housing assembly  100  and the rotor assembly  105 . 
     An end lock pin  347  is slidably housed in a bore in the rotor assembly  105  and more preferably in the vane  104 . An end portion of the end lock pin  347  is spring biased away from the recess  141  and hydraulically biased towards and fits into a recess  141  in an end plate of the housing assembly  100 . The pressurization of the end lock pin  347  is controlled by the movement of the control valve  309 . 
     A control valve  309 , preferably a spool valve, includes a spool  311  with cylindrical lands  311   a ,  311   b ,  311   c  slidably received in a sleeve  116 . The control valve  309  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. One end of the spool contacts spring  115  and the opposite end of the spool contacts a pulse width modulated variable force solenoid (VFS)  107 . The solenoid  107  may also be linearly controlled by varying current or voltage or other methods as applicable. Additionally, the opposite end of the spool  311  may contact and be influenced by a motor, or other actuators in place of the variable force solenoid  107 . 
     The position of the control valve  309  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. 
     The position of the spool  311  is influenced by spring  115  and the solenoid  107  controlled by the ECU  106 . Further detail regarding control of the phaser is discussed in detail below. The position of the spool  311  controls the motion (e.g. to move towards the advance position, holding position, the retard position or the retard lock position) of the phaser as well as whether the end lock pin  347  is in a locked or unlocked position. The control valve  309  has an advance mode, a retard mode, a retard lock mode, and a null mode (holding position). 
     In the advance mode, the spool  311  is moved to a position so that fluid may flow from the retard chamber  103  through the spool  311  to the advance chamber  102 , fluid is blocked from exiting the advance chamber  102 . The end lock pin  347  is in an unlocked position. 
     In the retard mode, the spool  311  is moved to a position so that fluid may flow from the advance chamber  102  through the spool  311  to the retard chamber  103 , fluid is blocked from exiting the retard chamber  103 . The end lock pin  147  is in an unlocked position. 
     In null mode, the spool  311  is moved to a position that blocks the exit of fluid from the advance and retard chambers  102 ,  103 . 
     In the retard locking mode or end stop lock mode, the vane  104  has already been moved to a full retard position and flow from the advance chamber  102  through the spool  311  to the retard chamber  103  continues with fluid blocked from exiting the retard chamber  103 . In this mode, the end lock pin  347  is pressurized, thus causing the spring  344  to compress and allow the end lock pin  347  to engage the recess  341  of an end plate and move to a locked position. The “full retard position” is defined as when the vane  104  contacts the advance wall  102   a  of the chamber  117  or is substantially close to the advance wall  102   a  and may be referred to as a “retard end stop position” of the vane. 
     Based on the duty cycle of the pulse width modulated variable force solenoid  107 , the spool  311  moves to a corresponding position along its stroke. When the duty cycle of the variable force solenoid  107  is approximately 40%, 60%, and greater than 60%, the spool  311  will be moved to positions that correspond with the retard mode/retard locking mode, the null mode, and the advance mode, respectively. In the retard locking mode or end stop lock mode, the end lock pin  347  is pressurized and engages the recess  341  of an end plate of the housing assembly  100 . It should be noted that the duty cycle percentages listed above are an example and they may be altered. 
     When the duty cycle is set to be greater than 60%, the vane of the phaser is moving toward and/or in an advance position. The stroke of the spool or position of the spool relative to the sleeve is between 3.5 and 5 mm for the advance position. 
       FIG. 16  shows the phaser moving towards the advance position. To move towards the advance position, the duty cycle is increased to greater than 60%, the force of the VFS  107  on the spool  311  is increased and the spool  311  is moved to the right by the VFS  107  in an advance mode, until the force of the spring  115  balances the force of the VFS  107 . In the advance mode shown, spool land  311   a  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  to move towards the retard wall  103   a . Fluid exits from the retard chamber  103  through line  113  to the control valve  309  between spool lands  311   a  and  311   b  and recirculates back to common line  114  and line  112  leading to the advance chamber  102 . 
     Makeup oil is supplied to the phaser from supply S by pump  140  to make up for leakage and enters line  119 . If the control valve  309  is in the camshaft, line  119  may be drilled through a bearing. Line  119  splits into two lines  119   a  and  119   b.    
     Line  119   a  leads to line  346  and to the end lock pin  347 . Line  119   b  leads to an inlet check valve  118  and the control valve  309 . From the control valve  309 , fluid enters line  114  through the advance check valve  108  and flows to the advance chamber  102 . 
     The pressure of the fluid in line  119   a  is blocked by spool land  311   b  and prevents fluid from line  113  from venting to exhaust line  121 . Fluid from line  346  which is in fluid communication with the end lock pin  347  is vented to exhaust line  121  between spool lands  311   b  and  311   c , such that the end lock pin spring  344  biases the end lock pin  347  out of engagement with the recess  341  and is therefore in an unlocked position. Spool land  311   a  prevents any fluid from exhausting from the advance chamber  103  and from line  112 . 
     When the duty cycle is set between 40-60%, the vane of the phaser is moving toward and/or in a retard position. The stroke of the spool or position of the spool relative to the sleeve is between 2 and 3.5 mm for the retard position. 
       FIG. 18  shows the phaser moving towards the retard position. To move towards the retard position, the duty cycle is changed to greater than 40% but less than 60%, the force of the VFS  107  on the spool  311  is reduced and the spool  311  is moved by spring  115 , until the force of spring  115  balances the force of the VFS  107 . In the retard mode, spool land  311   b  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 towards the advance chamber wall  102   a . Fluid exits from the advance chamber  102  through line  112  to the control valve  309  between spool lands  311   a  and  311   b  and recirculates back to common line  114  and line  113  leading to the retard chamber  103 . 
     Makeup oil is supplied to the phaser from supply S by pump  140  to make up for leakage and enters line  119 . Line  119  splits into two lines  119   a  and  119   b . Line  119   a  leads to line  346  to the end lock pin  347 . Line  119   b  leads to an inlet check valve  118  and the control valve  309 . 
     From the control valve  309 , fluid enters line  114  through the retard check valve  110  and flows to the retard chamber  103 . The pressure of the fluid in line  119   a  is blocked by spool land  311   b  and prevents fluid from line  112  from venting to exhaust line  121 . Fluid from line  346  is in fluid communication with the end lock pin  347  and is pressurized with fluid from supply  140 . It should be noted that the end lock pin  347  is not in a locked position as the recess  341  is not aligned to receive the end of the end lock pin  347 . Spool land  311   b  prevents any fluid from exhausting from the retard chamber  103  and from line  113 . 
     When the duty cycle is set between 40-60%, the vane of the phaser is moving toward and/or in a retard locking position. The stroke of the spool or position of the spool relative to the sleeve is approximately 2 mm for the retard locking position. 
       FIG. 17  shows the phaser in the retard locking position at the full retard position or retard end stop position. To move towards the full retard position, the duty cycle is changed to greater than 40% but less than 60%, the force of the VFS  107  on the spool  311  is reduced and the spool  311  is moved to the left in an end stop lock mode in the figure by spring  115 , until the force of spring  115  balances the force of the VFS  107 . In the end stop lock mode shown, spool land  311   b  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 towards the advance chamber wall  102   a . Fluid exits from the advance chamber  102  through line  112  to the control valve  309  between spool lands  311   a  and  311   b  and recirculates back to common line  114  and line  113  leading to the retard chamber  103 . The phaser is in a full retard position when the vane  104  contacts the advance wall  102   a  or is substantially close the advance wall  102   a  and may be referred to as a “retard end stop position” of the vane. 
     Makeup oil is supplied to the phaser from supply S by pump  140  to make up for leakage and enters line  119 . 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  309 . From the control valve  309 , fluid enters line  114  through the retard check valves  110  and flows to the retard chamber  103 . 
     Line  119   a  leads to line  346  and to the end lock pin  347 . The fluid in line  346  biases the end lock pin  347  into the recess  341  of an end plate  171  and is in a locked position, locking the housing assembly  100  relative to the rotor assembly  105 . Exhaust line  121  is blocked by spool land  311   c  preventing line  346  from venting. 
     The end lock pin  347  engages or is locked using pressure just prior to engine shutdown, including engine shutdown and customer initiated “key off”. During engine cranking, the phaser may be moved to a different starting position than the phaser was locked into just prior to engine shutdown or customer initiated “key off”. This can prove to be advantageous for “flex fuel” vehicles in which varying levels of ethanol are present to fuel the vehicle and based on those levels of ethanol, different starting positions of the phaser are advantageous. 
     The holding position of the phaser preferably takes place between the retard and advance position of the vane relative to the housing. The stroke of the spool or position of the spool relative to the sleeve is 3.5 mm. 
       FIG. 19  shows the phaser in the null position. In this position, the duty cycle of the variable force solenoid  107  is approximately 60% and the force of the VFS  107  on one end of the spool  311  equals the force of the spring  115  on the opposite end of the spool  311  in holding mode. The lands  311   a  and  311   b  block the flow of fluid from lines  112  and  113  respectively. Makeup oil is supplied to the phaser from supply S by pump  140  to make up for leakage and enters line  119 . 
     Line  119  splits into two lines  119   a  and  119   b . Line  119   b  leads to inlet check valve  118  and the control valve  309 . From the control valve  309 , fluid enters common line  114  through either of the check valves  108 ,  110  and flows to the advance or retard chambers  102 ,  103 . Fluid in line  346  vents between spool lands  311   b  and  311   c  through exhaust line  121 . The venting of line  346  allows the end lock pin spring  344  to bias the end lock pin  347  away from the recess  341  to an unlocked position. 
     While  FIGS. 14-17  show and describe the end stop lock mode as being in the retard position, the end stop lock mode may also be in the full advance mode when the vane  104  is in contact or substantially in contact with the retard wall  103   a.    
     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.