Abstract:
A variable camshaft timing device can operate using pressure generated by camshaft torque energy to transfer fluid from one working chamber to another work chamber or operate via an external fluid pressure source to fill one working chamber while simultaneously exhausting an opposing working chamber or operate using both modes simultaneously. The mode of the variable camshaft timing device is determined by the position of the control valve. The lock pin is controlled by fluid from one of the working chambers.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of copending application Ser. No. 14/840,683, filed Aug. 31, 2015, entitled “MULTI-MODE VARIABLE CAM TIMING PHASER”. The aforementioned application is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention pertains to the field of variable cam timing phasers. More particularly, the invention pertains to a multi-mode variable cam timing phaser. 
     Description of Related Art 
     It has been demonstrated that operating a variable camshaft timing device phaser utilizing the camshaft torque energy to phase the valve timing device is desirable because of the low amount of fluid required by a camshaft torque actuated variable camshaft timing device. However, not all engines provide enough camshaft torque energy throughout the entire engine operating range to effectively phase the variable camshaft timing device. 
     BorgWarner&#39;s U.S. Pat. No. 6,453,859 discloses a phaser that uses cam torque and oil pressure to move the phaser. The phaser has a single recirculating check valve that either recirculates fluid to the advance port or the retard port. The single recirculating check valve is located downstream of the control valve and not connected directly to the advance and retard chambers. 
     Hilite&#39;s U.S. Pat. No. 7,946,266 discloses another phaser that uses cam torque and pressure to move the phaser. The phaser has two recirculating check valves prior to exhaust fluid entering the control valve or upstream of the control valve. A recirculating check valve is required for each set of chambers—advance and retard. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a variable camshaft timing device can operate using pressure generated by camshaft torque energy to transfer fluid from one working chamber to another work chamber or operate via an external fluid pressure source to fill one working chamber while simultaneously exhausting an opposing working chamber or operate using both modes simultaneously. The mode of the variable camshaft timing device is determined by the position of the control valve. In this embodiment, the lock pin is controlled by fluid from one of the working chambers. 
     In another embodiment, a variable camshaft timing device uses camshaft torque energy to transfer fluid from one working chamber to another work chamber and selectively receive makeup fluid from a supply during recirculation. In this embodiment the lock pin is controlled by spool position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a schematic of a variable cam timing phaser operating in a first state or mode. 
         FIG. 2  shows a schematic of a variable cam timing phaser operating in a second state or mode. 
         FIG. 3  shows a schematic of a variable cam timing phaser operating in a third state or mode. 
         FIG. 4  shows a schematic of a variable cam timing phaser operating in a fourth state or mode. 
         FIG. 5  shows a schematic of a variable cam timing phaser operating in a fifth state or mode. 
         FIG. 6  shows a close-up of the control valve of the phaser operating in the first mode. 
         FIG. 7  shows close-up of the control valve of the phaser operating in the second mode. 
         FIG. 8  shows close-up of the control valve of the phaser operating in the third mode. 
         FIG. 9  shows a close-up of the control valve of the phaser operating in the fourth mode. 
         FIG. 10  shows a close-up of the control valve of the phaser operating in a fifth mode 
         FIG. 11  shows a schematic of a variable cam timing phaser of an alternate embodiment operating in a first mode. 
         FIG. 12  shows a schematic of a variable cam timing phaser of an alternate embodiment operating in a second mode. 
         FIG. 13  shows a schematic of a variable cam timing phaser of an alternate embodiment operating in a third mode. 
         FIG. 14  shows a close-up of the control valve of the phaser of  FIG. 11  operating in the first mode. 
         FIG. 15  shows a close-up of the control valve of the phaser of  FIG. 12  operating in the second mode. 
         FIG. 16  shows a close-up of the control valve of the phaser of  FIG. 13  operating in the third mode. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In an embodiment of the present invention, the control valve may direct fluid to exhaust from a working chamber to either a path through a recirculation check valve internal to the phaser leading to another chamber or to a path that exhausts fluid back to tank or sump or to do both simultaneously. 
     In the present invention, it is recognized that a single recirculation check valve and a single inlet check valve are used to accomplish multi-modes. Furthermore, the recirculation check valve and the inlet check valve are located internal to the control valve, which may reduce the radial package size. 
     The single inlet check valve and the single recirculation check valve may be the same type of check valve (plate type, ball type or disc type) or they may be different types of check valves. 
     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 assembly  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 possible from another camshaft in a multiple-cam engine. 
     The housing assembly  100  of the phaser has an outer circumference  101  for accepting drive force. The rotor assembly  105  is connected to the camshaft (not shown) and is coaxially located within the housing assembly  100 . The rotor assembly  105  has 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 . While only one advance chamber and one retard chamber are shown, multiple chambers may be present. Furthermore, in a phaser at least one set of advance and retard chambers are working or actively receiving or exhausting fluid and moving the vane  104 . 
     A lock pin assembly  145  is present within the phaser. A lock pin  147  is slideably housed in a bore in the rotor assembly  105  and has an end portion that is biased towards and fits into a recess  146  in the housing assembly  100  by a spring  148 . Alternatively, the lock pin  147  may be housed in the housing assembly  100  and be spring  148  biased towards a recess  146  in the rotor assembly  105 . The engagement and disengagement of the lock pin  147  with the recess  146  is controlled by fluid in the retard chamber  103  and the position of the spool  111 . Alternatively, the engagement and disengagement of the lock pin  147  with the recess  146  is controlled by fluid in the advance chamber  102  and the position of the spool  111 . 
     A control valve  109 , preferably a spool valve, includes a spool  111  with cylindrical lands  111   a ,  111   b ,  111   c ,  111   d ,  111   e  slideably received in a sleeve  114  within a bore  108  of a center bolt  110 . The sleeve  114  has a plurality of ports  125 ,  126 ,  127 ,  129  and a recess  128  which connects ports  126  and  129 . The recess  128  forms a passage  139  for fluid to flow with the bore  108  of the center bolt  110 . 
     The center bolt  110  is preferably received by the camshaft (not shown). The center bolt  110  has a port  120  connected to the advance chamber  102  and in fluid communication with port  125  of the sleeve  114 , a port  121  connected to the retard chamber  103  and in fluid communication with port  126  of the sleeve  114  and a port  122  connected to the supply  142  and in fluid communication with port  127  of the sleeve  114 . 
     The spool  111  has a central passage which is divided into a working central passage  136  and an inlet central passage  135  by a recirculation check valve  124  and an inlet check valve  123 . The recirculation check valve  124  includes a plug  140 , a plate  117 , and a spring  116 , with the first end of the spring  116  contacting the plug  140  and the second end contacting the plate  117 . The inlet check valve  123  includes a plug  140 , a plate  119 , and a spring  118 , with the first end of the spring  118  contacting the plug  140  and the second end contacting the plate  119 . Between the first land  111   a  and the second land  111   b  is an opening  130  leading to the working central passage  136 . Between the second land  111   b  and the third land  111   c  are two openings, with one of the openings  131  leading to the recirculation check valve  124  and the other opening  132  leading to the inlet check valve  123 . Between the third land  111   c  and the fourth land  111   d  is an annular groove  133 . Between the fourth land  111   d  and the fifth land  111   e  is an opening  134  leading to inlet central passage  135 . 
     One end of the spool  111  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. 
     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 mode or state of the phaser as well as whether the lock pin  147  is engaged or disengaged. The control valve  109  has five modes. A first mode in which the spool  111  is positioned such that the vane  104  is moved by both cam torque actuation and torsion assist in the advance direction. A second mode in which the spool  111  is positioned such that the vane  104  is cam torque actuated in the advance direction. A third mode in which the spool  111  is positioned such that the vane  104  is held in position. A fourth mode in which the spool  111  is positioned such that the vane  104  is cam torque actuated in the retard direction and a fifth mode in which the spool  111  is positioned such that the vane  104  is moved by both cam torque actuation and torsion assist in the retard direction. 
     Cam torque actuation of a variable camshaft timing (VCT) of a phaser uses torque reversals in the camshaft caused by the forces of opening and closing engine valves to move the vane  104 . The advance and retard chambers  102 ,  103  are arranged to resist positive and negative torque pulses in the camshaft (not shown) 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. 
     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 to the OPA system 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. 
       FIGS. 1-10  show operating modes of a multi-mode VCT phaser depending on the spool valve position. The positions shown in the figures define the direction the VCT phaser is moving. 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. 
     In the first mode, the spool  111  of the control valve  109  is moved to a position so that fluid may flow from the retard chamber  103 , through the spool  111  and the recirculation check valve  124  within the spool  111 , to the advance chamber  102 . Fluid from the retard chamber  103  may also flow out of the spool  111  to tank T. Fluid from a supply S provides fluid to the advance chamber  102  through the spool  111  and the inlet check valve  123  within the spool  111 . Fluid from supply S is prevented from flowing to tank T by the spool  111 . The lock pin  147  is engaged with the recess  146  or is locked. 
     In the second mode, the spool  111  of the control valve  109  is moved to a position so that fluid may flow from the retard chamber  103  through the spool  111  and the recirculation check valve  124  within the spool, to the advance chamber  102 . Fluid is blocked from exiting the advance chamber  102 . Fluid from a supply S provides makeup fluid only to the advance chamber  102  through the spool  111  and the inlet check valve  123  within the spool  111 . Fluid from supply S and the advance chamber  102  is prevented from flowing to tank T by the spool  111 . The lock pin  147  does not engage the recess  146  or is unlocked. 
     In a third mode, the spool  111  is moved to a position that blocks the exit of fluid from the advance and retard chambers  102 ,  103 , but a small amount of fluid from supply S is able to enter the advance and retard chambers  102 ,  103  through the spool  111 . The lock pin  147  is disengaged from the recess  146  or is unlocked. 
     In the fourth mode, the spool  111  is moved to a position so that fluid may flow from the advance chamber  102  through the spool  111  and the recirculation check valve  124  within the spool, to the retard chamber  103 . Fluid is blocked from exiting the retard chamber  103 . Fluid from a supply S provides fluid to the retard chamber  103  through the spool  111  and the inlet check valve  123  within the spool  111 . Fluid from supply S is prevented from flowing to tank T by the spool  111 . The lock pin  147  is disengaged from the recess  146  or is unlocked. 
     In a fifth mode, the spool  111  is moved to a position so that fluid may flow from the advance chamber  102 , through the spool  111  and the recirculation check valve  124  within the spool  111 , to the retard chamber  103 . Fluid from the advance chamber  102  may also flow out of the spool  111  to tank T. Fluid from a supply S provides fluid to the retard chamber  103  through the spool  111  and the inlet check valve  123  within the spool  111 . Fluid from the supply S and the retard chamber  103  is prevented from flowing to tank T by the spool  111 . The lock pin  147  is disengaged from the recess  146  or is unlocked. 
     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, for example 0 mm stroke, 1 mm stroke, 2.5 mm stroke, 4 mm stroke, and 5 mm stroke. The duty cycle of the variable force solenoid  107  is varied to correspond to the specific position along its stroke. 
     Referring to  FIGS. 1 and 6 , the phaser moving towards the advance position. To move towards the advance position, the duty cycle of the VFS  107  is such that the stroke of the spool  111  is 0 mm and the spool  111  is moved by the force of the spring  115  until the force of the spring  115  balances the force of the VFS  107 . 
     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.    
     With the position of the spool  111  in the first mode, fluid from the retard chamber  103  or opposing chamber (indicated by a dashed line in  FIG. 6 ) flows through line  113  to the control valve  109 . From line  113 , fluid flows into the control valve  109  through port  121  of the center bolt  110  and port  126  of the sleeve  114 . From port  126 , fluid flows around the annular groove  133  between spool lands  111   c  and  111   d  to the recess  128  and the passage  139  formed between the sleeve  114  and the center bolt  110 . 
     From the passage  139 , fluid can flow to both tank T and the advance chamber  102 . The fluid flowing to tank T, flows from the passage  139 , through port  129  of the sleeve  114  and out through a passage  137  formed between the spool  111 , the sleeve  114 , and the center bolt  110 . 
     The fluid flowing to the advance chamber or working chamber  102  in this mode, flows from the passage  139 , through port  129  of the sleeve  114  through an opening  130  between spool land  111   a  and  111   b  to a working central passage  136 . The pressure of the fluid from the retard chamber  103  on the plate  117  is great enough to overcome the force of the spring  116  of the recirculation check valve  124  and flow out to the advance chamber  102  through opening  131  between spool lands  111   b  and  111   c  and through ports  125  and  120  in fluid communication with the advance chamber  102 . 
     Fluid is also supplied to the advance chamber  102  from a supply S. The supply S is in fluid communication with the ports  122  and  127  through supply line  142  (indicated by the solid line in  FIG. 6 ). Fluid flows from the ports  122  and  127  to an opening  134  in the spool between spool lands  111   d  and  111   e . From the opening  134 , fluid flows to the inlet central passage  135  of the spool  111 . The pressure of the fluid from supply S on the plate  119  is great enough to overcome the force of the spring  118  of the inlet check valve  123  and flow out to the advance chamber  102  through opening  132  between spool lands  111   b  and  111   c  and through ports  125  and  120  in fluid communication with the advance chamber  102 . 
     Therefore, when the control valve  109  and the phaser are in this first mode, both cam torque actuation (fluid is recirculated from the retard chamber  103  to the advance chamber  102  through recirculation check valve  124 ) and torsion assist (fluid from supply S flows to the advance chamber  102  through an inlet check valve  123  and draining of fluid from the retard chamber to tank T) are simultaneously used to move the vane  104 . 
     Since fluid from the retard chamber  103  is draining and recirculated to the advance chamber  102 , the pressure of the fluid on the lock pin  147  is not great enough to overcome the force of the lock pin spring  148 , and the lock pin  147  engages the recess  146 , locking the housing assembly  101  relative to the rotor assembly  105 . 
       FIG. 2  shows the phaser moving towards the advance position and  FIG. 7  shows a close up of the fluid flow through the control valve. To move towards the advance position, the duty cycle of the VFS  107  is such that the stroke of the spool  111  is 1 mm and the spool  111  is moved by the force of the VFS  107  until the force of the spring  115  balances the force of the VFS  107 . 
     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.    
     With the position of the spool  111  of the control valve  109  in the second mode, fluid from the retard chamber  103  (indicated by a dashed line in  FIG. 6 ) flows through line  113  to the control valve  109 . From line  113 , fluid flows into the control valve through port  121  of the center bolt  110  and port  126  of the sleeve  114 . From port  126 , fluid flows around the annular groove  133  between spool lands  111   c  and  111   d  to the recess  128  and the passage  139  formed between the sleeve  114  and the center bolt  110 . From the passage  139 , fluid can only recirculate to the advance chamber  102 . Unlike in the first mode, fluid is prevented from venting to tank T by the interface  141  of spool land  111   a  and the sleeve  114 . 
     The fluid flowing to the advance chamber  102 , flows from the passage  139 , through port  129  of the sleeve  114  through an opening  130  between spool land  111   a  and  111   b  to a working central passage  136 . The pressure of the fluid from the retard chamber  103  on the plate  117  is great enough to overcome the force of the spring  116  of the recirculation check valve  124  and flow out to the advance chamber  102  through opening  116  between spool lands  111   b  and  111   c  and through ports  125  and  120  in fluid communication with the advance chamber  102 . 
     Fluid is also supplied to the advance chamber  102  from a supply S to make up for leakage and is not used to move the vane  104 . The supply S is in fluid communication with the ports  122  and  127  through supply line  142  (indicated by the solid line in  FIG. 6 ). Fluid flows from the ports  122  and  127  to an opening  134  in the spool between spool lands  111   d  and  111   e . From the opening  134 , fluid flows to the inlet central passage  135  of the spool  111 . The pressure of the fluid from supply S on the plate  119  is great enough to overcome the force of the spring  118  of the inlet check valve  123  and flow out to the advance chamber  102  through opening  118  between spool lands  111   b  and  111   c  and through ports  125  and  120  in fluid communication with the advance chamber  102 . 
     Therefore, when the control valve  109  and the phaser are in this second mode, only cam torque actuation (fluid is recirculated from the retard chamber  103  to the advance chamber  102  through recirculation check valve  124 ) is used to move the vane  104 . Fluid is not vented from the system. Fluid provided from supply is used to make up for leakage. When cam torque energy reverses, both the inlet check valve  123  and the recirculation check valve  124  prevent fluid from leaving the advance chamber  102  or working chamber. 
     Since fluid from the retard chamber  103  is draining and recirculated to the advance chamber, but not venting to sump or atmosphere, the pressure of the fluid on the lock pin  147  is great enough to overcome the force of the lock pin spring  148  while actuating, and the lock pin  147  remains disengaged from the recess  146 , and is therefore unlocked. 
       FIG. 3  shows the phaser in the null position and  FIG. 8  shows a close up of the fluid flow through the control valve. In this position, the duty cycle of the variable force solenoid  107  is such that stroke of the spool is 3 mm. 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 null position. 
     With the position of the spool in the third mode, fluid from the supply S is provided to the inlet central passage  135  of the spool  111  through a port  122  of the central bolt  110  and a port  127  of the sleeve  110 . From the central passage  135 , make up fluid is provided to the advance and retard chambers  102 ,  103  through the inlet check valve  123 . While the spool valve lands  111   b  and  111   c  appear to completely block off passage from the openings  116  and  118  to the ports  120 ,  125 ,  126 ,  121  leading to the advance and retard chambers  102 ,  103 , there is a small undercut or gap to allow fluid to flow to the advance and retard chambers  102 ,  103 . 
     Since fluid is present in the retard chamber  103  and being provided to the retard chamber  103 , the pressure of the fluid on the lock pin  147  is greater than the force of the lock pin spring  148 , the lock pin  147  disengages the recess  146  and allowing the rotor assembly  105  to move relative to the housing assembly  101 . 
       FIG. 4  shows the phaser moving towards the retard position and  FIG. 9  shows a close up of the fluid flow through the control valve. To move towards the retard position, the duty cycle of the VFS  107  is such that the stroke of the spool  111  is 4 mm and the spool  111  is moved by the force of the VFS  107  until the force of the spring  115  balances the force of the VFS  111 . 
     Camshaft torque pressurizes the retard chamber  103 , causing fluid to move from the advance chamber  102  and into the retard chamber  103 , and the vane  104  to move towards the advance wall  102   a.    
     With the position of the spool in the fourth mode, fluid from the advance chamber  102  (indicated by a dashed line in  FIG. 9 ) flows through line  112  to the control valve  109 . From line  112 , fluid flows into the control valve  109  through port  120  of the center bolt  110  and port  125  of the sleeve  114 . From port  125 , fluid flows through port  130  to working central passage  136 . The pressure of the fluid from the advance chamber  102  on the plate  117  is great enough to overcome the force of the spring  116  of the recirculation check valve  124  and flow out to the retard chamber  103  through opening  116  between spool lands  111   b  and  111   c  and through ports  126  and  121  in fluid communication with the retard chamber  103 . Fluid can only recirculate from the advance chamber  102  to the retard chamber  103 . Fluid is prevented from venting to tank T by the interface  141  of spool land  111   a  and the sleeve  114 . Any fluid that flows into passage  139  is blocked from reaching retard chamber  103  by spool lands  111   c  and  111   d.    
     Fluid is also supplied to the retard chamber  103  from a supply S to make up for leakage and is not used to move the vane  104 . The supply S is in fluid communication with the ports  122  and  127  through supply line  142  (indicated by the solid line in  FIG. 9 ). Fluid flows from the ports  122  and  127  to an opening  134  in the spool between spool lands  111   d  and  111   e . From the opening  134 , fluid flows to the inlet central passage  135  of the spool  111 . The pressure of the fluid from supply S on the plate  119  is great enough to overcome the force of the spring  118  of the inlet check valve  123  and flow out to the retard chamber  103  through opening  118  between spool lands  111   b  and  111   c  and through ports  126  and  121  in fluid communication with the retard chamber  103 . 
     Therefore, when the control valve  109  and the phaser are in this fourth mode, only cam torque actuation (fluid is recirculated from the advance chamber  102  to the retard chamber  103  through recirculation check valve  124 ) is used to move the vane  104 . Fluid is not vented from the system. Fluid provided from supply S is used to make up for leakage. When cam torque energy reverses, both the inlet check valve  123  and the recirculation check valve  124  prevent fluid from leaving the retard chamber  103  or working chamber. 
     Since fluid is being supplied to the retard chamber  103  by the advance chamber through recirculation, the pressure of the fluid on the lock pin  147  is great enough to overcome the force of the lock pin spring  148 , and the lock pin  147  disengages the recess  146 , allowing the housing assembly  101  to move relative to the rotor assembly  105 . 
       FIG. 5  shows the phaser moving towards the retard position and  FIG. 10  shows a close up of the fluid flow through the control valve. To move towards the retard position, the duty cycle of the VFS  107  is such that the stroke of the spool  111  is 5 mm and the spool  111  is moved by the force of the spring  115  until the force of the spring  115  balances the force of the VFS  111 . 
     Camshaft torque pressurizes the advance chamber  102 , causing fluid to move from the advance chamber  102  to the retard chamber  103 , and the vane  104  to move towards the advance wall  102   a.    
     With the position of the spool  111  in the fifth mode, fluid from the advance chamber  102  or opposing chamber (indicated by a dashed line in  FIG. 10 ) flows through line  112  to the control valve  109 . From line  112 , fluid flows into the control valve  109  through port  120  of the center bolt  110  and port  125  of the sleeve  114 . From port  125 , fluid flows through port  130  to working central passage  136 . The pressure of the fluid from the advance chamber  102  on the plate  117  is great enough to overcome the force of the spring  116  of the recirculation check valve  124  and flow out to the retard chamber  103  through opening  116  between spool lands  111   b  and  111   c  and through ports  126  and  121  in fluid communication with the retard chamber  103 . 
     From the working central passage  136 , fluid can also flow to passage  137  through opening  130  into port  129  of the sleeve  114 . From port  129 , fluid flows to tank T through passage  137 , with passage  137  being defined between spool land  111   a  and sleeve land  111   a . Any fluid that flows into passage  139  is blocked from reaching retard chamber  103  by spool lands  111   c  and  111   d.    
     Fluid is also supplied to the retard chamber  103  from a supply S to make up for leakage and is not used to move the vane  104 . The supply S is in fluid communication with the ports  122  and  127  through supply line  142  (indicated by the solid line in  FIG. 9 ). Fluid flows from the ports  122  and  127  to an opening  134  in the spool between spool lands  111   d  and  111   e . From the opening  134 , fluid flows to the inlet central passage  135  of the spool  111 . The pressure of the fluid from supply S on the plate  119  is great enough to overcome the force of the spring  118  of the inlet check valve  123  and flow out to the retard chamber  103  through opening  118  between spool lands  111   b  and  111   c  and through ports  126  and  121  in fluid communication with the retard chamber  103 . 
     Therefore, when the control valve  109  and the phaser are in this fifth mode, both cam torque actuation (fluid is recirculated from the advance chamber  102  to the retard chamber  103  through recirculation check valve  124 ) and torsion assist (fluid from supply S flows to the retard chamber  103  through an inlet check valve  123  and draining of fluid from the advance chamber to tank T) are simultaneously used to move the vane  104 . 
     Since fluid is being supplied to the retard chamber  103  by the advance chamber  102  through recirculation, the pressure of the fluid on the lock pin  147  is great enough to overcome the force of the lock pin spring  148 , and the lock pin  147  disengages the recess  146 , allowing the housing assembly  101  to move relative to the rotor assembly  105 . 
     By having a phaser which can operate in modes that use both TA and CTA to move the vane  104 , the phaser can take advantage of the advantages that both TA and CTA offer. For example, CTA is most effective at low speeds, but has limited affect at high speeds and TA is most effective at high speeds. For a four cylinder engine, for example, the phaser may be placed in the second and fourth modes which use cam torque actuation only and fluid consumption is low since fluid is recirculated. The phaser may be placed in the first and fifth modes at high speed, which use cam torque and torsion assist, such that at high speeds oil pressure will compensate for any losses in cam torque energy. 
       FIGS. 11-16  show an alternate embodiment of the present invention. This embodiment differs from the phaser of  FIGS. 1-10  since it only uses the second, third and fourth modes of  FIGS. 1-10  and the lock pin is unlocked or locked based on spool position, since the lock pin is not in direct fluid communication with the either of the working chambers. The second, third, and fourth modes of the first embodiment have been renumbered to the first, second and third in the second embodiment. 
     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 assembly  205  with one or more vanes  204 , mounted to the end of the camshaft, surrounded by a housing assembly  200  with the vane chambers into which the vanes fit. It is possible to have the vanes  204  mounted to the housing assembly  200 , and the chambers in the rotor assembly  205 , as well. The housing&#39;s outer circumference  201  forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possible from another camshaft in a multiple-cam engine. 
     The housing assembly  200  of the phaser has an outer circumference  201  for accepting drive force. The rotor assembly  205  is connected to the camshaft (not shown) and is coaxially located within the housing assembly  200 . The rotor assembly  205  has a vane  204  separating a chamber formed between the housing assembly  200  and the rotor assembly  205  into an advance chamber  202  and a retard chamber  203 . The vane  204  is capable of rotation to shift the relative angular position of the housing assembly  200  and the rotor assembly  205 . While only one advance chamber and one retard chamber are shown, multiple chambers may be present. Furthermore, in a phaser at least one set of advance and retard chambers are working or actively receiving or exhausting fluid and moving the vane. 
     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  slideably received in a sleeve  214  within a bore  208  of a center bolt  210 . The sleeve  214  has a plurality of ports  225 ,  226 ,  227 ,  229 ,  250 ,  252 ,  254 , a first recess  256  which connects ports  252  and  254 , and a second recess  228  which connects ports  226  and  229 . The first recess  256  forms a passage  257  with the bore  208  of the center bolt  210 , for fluid flow to and from the lock pin assembly  245 . The second recess  228  forms a passage  239  with the bore  208  of the center bolt  210  for fluid to flow. 
     The center bolt  210  is preferably received by the camshaft (not shown). The center bolt  210  has a port  220  connected to the advance chamber  202  and in fluid communication with port  225  of the sleeve  214 , a port  221  connected to the retard chamber  203  and in fluid communication with port  250  of the sleeve  214 , a port  222  connected to the supply  242  and in fluid communication with port  227  of the sleeve  214  and port  260  connected to the lock pin assembly  245  via passage  244  and in fluid communication with port  252  of the sleeve  214 . 
     The spool  211  has a working central passage  236  with a recirculation check valve  224  and an axial inlet passage  234  which is in fluid communication with an inlet check valve  223  through passage  235 . The recirculation check valve  224  includes a plug  240 , a plate  217 , and a spring  216 , with the first end of the spring  216  contacting the plug  240  and the second end contacting the plate  217 . The inlet check valve  223  includes a plug  240 , a ball  219 , and a spring  218 , with the first end of the spring  218  contacting the plug  240  and the second end contacting the ball  219 . Between the first land  211   a  and the second land  211   b  is an opening  230  leading to the working central passage  236 . Between the second land  211   b  and the third land  211   c  is an opening  231  leading to the recirculation check valve  224  and the inlet check valve  223 . Between the third land  211   c  and the fourth land  211   d  is an annular groove  233 . Between the fourth land  211   d  and the fifth land  211   e  is an opening  258  leading to the axial inlet passage  234 . 
     One end of the spool  211  contacts spring  215  and the opposite end of the spool  211  contacts a pulse width modulated variable force solenoid (VFS)  207 . The solenoid  207  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. 
     The position of the control valve  209  is controlled by an engine control unit (ECU)  206  which controls the duty cycle of the variable force solenoid  207 . The ECU  206  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  215  and the solenoid  207  controlled by the ECU  206 . Further detail regarding control of the phaser is discussed in detail below. The position of the spool  211  controls the mode of the phaser as well as whether the lock pin  247  is engaged or disengaged. 
     The control valve  209  has three modes. In the first mode, the spool  211  of the control valve  209  is positioned such that the vane  204  is moved by cam torque actuation in an advance direction. In the second mode, the spool  211  is positioned such that the vane  204  is moved by cam torque actuation in the retard direction. In the third mode, the spool  211  is positioned such that the vane  204  is held in position. 
     A lock pin assembly  245  is present within the phaser. A lock pin  247  is slideably housed in a bore in the rotor assembly  205  and has an end portion that is biased towards and fits into a recess  246  in the housing assembly  200  by a spring  248 . Alternatively, the lock pin  247  may be housed in the housing assembly  200  and be spring  248  biased towards a recess  246  in the rotor assembly  205 . The engagement and disengagement of the lock pin  247  with the recess  246  is controlled by a land  211   e  of the spool  211 . 
     Cam torque actuation of a variable camshaft timing (VCT) of a phaser uses torque reversals in the camshaft caused by the forces of opening and closing engine valves to move the vane  204 . The advance and retard chambers  202 ,  203  are arranged to resist positive and negative torque pulses in the camshaft (not shown) and are alternatively pressurized by the cam torque. The control valve  209  allows the vane  204  in the phaser to move by permitting fluid flow from the advance chamber  202  to the retard chamber  203  or vice versa, depending on the desired direction of movement. 
       FIGS. 11-16  show operating modes of a multi-mode VCT phaser depending on the spool valve position. The positions shown in the figures define the direction the VCT phaser is moving. 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. 
     In the first mode, the spool  211  is moved to a position so that fluid may flow from the retard chamber  203 , through the spool  211  and the recirculation check valve  224  within the spool  211 , to the advance chamber  202 . Fluid from a supply S provides fluid from the supply line  242  to the advance chamber  202  only through the spool  211  and the inlet check valve  223  within the spool  211  for makeup fluid only. The lock pin  247  is engaged with the recess  246  or is locked since fluid is prevented from entering the line  244  to the lock pin  245  from supply by spool land  211   e.    
     In a second mode, the spool  211  is moved to a position so that fluid may flow from the advance chamber  202 , through the spool  211  and the recirculation check valve  224  within the spool  211 , to the retard chamber  203 . Fluid from a supply S provides fluid to only the retard chamber  203  through the spool  211  and the inlet check valve  223  within the spool  211  for makeup fluid only. The lock pin  247  is disengaged from the recess  246  or is unlocked. 
     In a third mode, the spool  211  is moved to a position that blocks the exit of fluid from the advance and retard chambers  202 ,  203 , but a small amount of fluid from supply S is able to enter the advance and retard chambers  202 ,  203  through the spool  111 . The lock pin  247  is disengaged from the recess  246  or is unlocked. 
     Based on the duty cycle of the pulse width modulated variable force solenoid  207 , the spool  211  moves to a corresponding position along its stroke, for example 0 mm stroke, 2.5 mm stroke, and 5 mm stroke. The duty cycle of the variable force solenoid  207  is varied to correspond to the specific position along its stroke. 
     Referring to  FIGS. 11 and 14 , the phaser moving towards the advance position. To move towards the advance position, the duty cycle of the VFS  207  is such that the stroke of the spool  211  is 0 mm and the spool  211  is moved by the force of the spring  215  until the force of the spring  215  balances the force of the VFS  211 . 
     Camshaft torque pressurizes the retard chamber  203 , causing fluid to move from the retard chamber  203  and into the advance chamber  202 , and the vane  204  to move towards the retard wall  203   a.    
     With the position of the spool in the first mode, fluid from the retard chamber  203  (indicated by a dashed line in  FIG. 14 ) flows through line  213  to the control valve  209 . From line  213 , fluid flows into the control valve through port  221  of the center bolt  210  and port  250  of the sleeve  214 . From port  250 , fluid flows around the annular groove  233  between spool lands  211   c  and  211   d  to the recess  228  and the passage  239  formed between the recess  228  of the sleeve  214  and the center bolt  210 . From the passage  239 , fluid can only recirculate to the advance chamber  202 . 
     The fluid flowing to the advance chamber  202 , flows from the passage  239 , through port  229  of the sleeve  214  through an opening  230  between spool land  211   a  and  211   b  to a working central passage  236 . The pressure of the fluid from the retard chamber  203  on the plate  217  is great enough to overcome the force of the spring  216  of the recirculation check valve  224  and flow out to the advance chamber  202  through opening  231  between spool lands  211   b  and  211   c  and through ports  225  and  220  in fluid communication with the advance chamber  202 . 
     Fluid is also supplied to only the advance chamber  202  from a supply S to make up for leakage and is not used to move the vane  204 . The supply S is in fluid communication with the ports  222  and  227  through supply line  242  (indicated by the solid line in  FIG. 14 ). Fluid flows from the ports  222  and  227  to an axial passage  234  and passage  235  in the spool between spool lands  211   d  and  211   e . The pressure of the fluid from supply S on the ball  219  is great enough to overcome the force of the spring  218  of the inlet check valve  223  and flow out to the advance chamber  202  through opening  231  between spool lands  211   b  and  211   c  and through ports  225  and  220  in fluid communication with the advance chamber  202 . 
     Therefore, when the control valve  209  and the phaser are in this mode, only cam torque actuation (fluid is recirculated from the retard chamber  203  to the advance chamber  202  through check valve  224 ) is used to move the vane  204 . Fluid is not vented from the system. Hydraulic fluid is provided to the working chamber, which in this case is the advance chamber  202 , from supply S to make up for leakage. When cam torque energy reverses, both the inlet check valve  223  and the recirculation check valve  224  prevent fluid from leaving the advance chamber  202  or working chamber. 
     Based on the position of the spool  211 , fluid from supply S is prevented from providing fluid to line  244  by spool land  211   e  and the sleeve  214 . Fluid from line  244  drains through passage  257  and passage  238  of the central bolt  210  to sump (not shown). The force of the lock pin spring  248  moves the lock pin  247 , such that it engages the recess  246 , locking the housing assembly  201  relative to the rotor assembly  205 . 
       FIG. 12  shows the phaser moving towards the retard position and  FIG. 15  shows a close up of the fluid flow through the control valve. To move towards the retard position, the duty cycle of the VFS  207  is such that the stroke of the spool  211  is 5 mm and the spool  211  is moved by the force of the VFS  207  until the force of the spring  215  balances the force of the VFS  211 . 
     Camshaft torque pressurizes the advance chamber  202 , causing fluid to move from the advance chamber  202  and into the retard chamber  203 , and the vane  204  to move towards the advance wall  202   a.    
     With the position of the spool in the second mode, fluid from the advance chamber  202  (indicated by a dashed line in  FIG. 15 ) flows through line  212  to the control valve  209 . From line  212 , fluid flows into the control valve  209  through port  220  of the center bolt  210  and port  225  of the sleeve  214 . From port  225 , fluid flows into the working central passage  236  through an opening  230  between spool land  211   a  and  211   b . The pressure of the fluid from the advance chamber  202  on the plate  217  is great enough to overcome the force of the spring  216  of the recirculation check valve  224  and flow out to the retard chamber  203  through opening  231  between spool lands  211   b  and  211   c  and through ports  250  and  221  in fluid communication with the retard chamber  203 . 
     Fluid is also supplied to only the retard chamber  203  from a supply S to make up for leakage and is not used to move the vane  204 . The supply S is in fluid communication with the ports  222  and  227  through supply line  242  (indicated by the solid line in  FIG. 15 ). Fluid flows from the ports  222  and  227  to an axial passage  234  and passage  235  in the spool between spool lands  211   d  and  211   e . The pressure of the fluid from supply S on the ball  219  is great enough to overcome the force of the spring  218  of the inlet check valve  223  and flow out to the retard chamber  203  through opening  231  between spool lands  211   b  and  211   c  and through ports  250  and  221  in fluid communication with the retard chamber  203 . 
     Therefore, when the control valve  209  and the phaser are in this mode, only cam torque actuation (fluid is recirculated from the advance chamber  202  to the retard chamber  203  through check valve  224 ) is used to move the vane  204 . Fluid is not vented from the system. Hydraulic fluid is provided to the working chamber, which in this case is the retard chamber  203 , from supply S to make up for leakage. When cam torque energy reverses, both the inlet check valve  223  and the recirculation check valve  224  prevent fluid from leaving the retard chamber  203  or working chamber. 
     Based on the position of the spool  211 , fluid from supply S provides fluid to line  244  through axial passage  234 . From the axial passage  234 , fluid flows through opening  258  between spool lands  211   d  and  211   e  to the first recess  256 . Fluid flows in the passage  258  formed by the first recess  256  of the sleeve  214  and the bore  208  of the center bolt  210  to port  252  and port  260  leading to line  244 . The force of the pressure of the fluid from supply S is greater than the force of the lock pin spring  248 , and moves the lock pin  247 , such that it disengages the recess  246 , and the housing assembly  201  can move relative to the rotor assembly  205 . 
       FIG. 13  shows the phaser in the null position and  FIG. 16  shows a close up of the fluid flow through the control valve. In this position, the duty cycle of the variable force solenoid  207  is such that stroke of the spool is 2.5 mm. The force of the VFS  207  on one end of the spool  211  equals the force of the spring  215  on the opposite end of the spool  211  in null position. 
     With the position of the spool in the third mode, fluid from the supply S is provided to the advance chamber  202  and retard chamber  203  by ports  222  and  227  through supply line  242  (indicated by the solid line in  FIG. 16 ). Fluid flows from the ports  222  and  227  to an axial passage  234  and passage  235  in the spool between spool lands  211   d  and  211   e . The pressure of the fluid from supply S on the ball  219  is great enough to overcome the force of the spring  218  of the inlet check valve  223  and flow out to the retard chamber  203  through opening  231  between spool lands  211   b  and  211   c  and through ports  250  and  221  in fluid communication with the retard chamber  203  and to the advance chamber  202  through opening  231  through ports  225  and  220 . 
     While the spool valve lands  211   b  and  211   c  appear to completely block off passage from the opening  231  to the ports  225 ,  220 ,  221 ,  250  leading to the advance and retard chambers  202 ,  203 , there is a small undercut or gap to allow fluid to flow to the advance and retard chambers  202 ,  203 . 
     Based on the position of the spool  211 , fluid from supply S provides fluid to line  244  from axial passage  234 . From the axial passage  234 , fluid flows through opening  258  between spool lands  211   d  and  211   e  to the first recess  256 . Fluid flows in the passage  257  formed by the first recess  256  of the sleeve  214  and the bore  208  of the center bolt  210  to port  252  and  260  leading to line  244 . The force of the pressure of the fluid from supply S is greater than the force of the lock pin spring  248 , and moves the lock pin  247 , such that it disengages the recess  246 , and the housing assembly  201  can move relative to the rotor assembly  205 . 
     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.