Title:
Hybrid multi-position cam indexer having controls located in rotor
Kind Code:
A1


Abstract:
An infinitely variable cam indexer utilizes engine oil pressure to actuate a cam and preferably uses an inlet check valve in the oil source to minimize back flow during a torque reversal. The control system is in the center of the rotor and uses an electromechanical actuator, preferably a variable force solenoid, acting directly on the spool to control oil flow. This design reduces leakage and improves the response of the phaser. There are shorter oil passages as compared to a control system mounted at the cam bearing.



Inventors:
Gardner, Marty (Ithaca, NY, US)
Duffield, Michael (Medina, NY, US)
Application Number:
10/198318
Publication Date:
02/20/2003
Filing Date:
07/18/2002
Assignee:
GARDNER MARTY
DUFFIELD MICHAEL
Primary Class:
International Classes:
F01L1/34; F01L1/344; (IPC1-7): F01L1/34
View Patent Images:
Related US Applications:



Primary Examiner:
CHANG, CHING
Attorney, Agent or Firm:
BORGWARNER INC. (Ithaca, NY, US)
Claims:

What is claimed is:



1. A phaser for adjusting timing between a camshaft and a timing gear coupled to a crankshaft of an engine, comprising: a rotor having first and second circumferentially spaced apart vanes and a central cylindrical recess located along an axis of rotation, the rotor being connectable to the camshaft for rotation therewith; a housing connectable to the timing gear for rotation therewith, having a body coaxially surrounding the rotor, the body having a first recess and a second recess circumferentially spaced apart for receiving the first vane and the second vane of the rotor, and permitting rotational movement of the first vane and the second vane therein, wherein each of the first vane and second vane respectively divides each of the first recess and second recess into a first portion and a second portion, the first portion and the second portion of the first recess and the second recess being capable of sustaining fluid pressure, such that introduction of a fluid under pressure into the first portion causes the rotor to move in a first rotational direction relative to the housing and introduction of a fluid under pressure into the second portion causes the rotor to move in an opposite rotational direction relative to the housing; and a spool located within the cylindrical recess of the rotor and being slidably movable along the axis of rotation of the rotor, the spool comprising a plurality of lands which block and connect a plurality of passageways in the rotor, such that by slidably moving the spool in the cylindrical recess of the rotor, the flow of fluid from a fluid input to the first portion and the second portion is controlled, varying the rotational movement of the housing relative to the rotor.

2. The phaser of claim 1, in which: the spool comprises length and a first land and a second land, spaced apart a distance along the length, such that the first land and the second land have a circumference which provides a fluid blocking fit in the cylindrical recess, and the length has a lesser circumference than the first land and second land to permit fluid to flow; and the cylindrical recess of the rotor comprising, in spaced-apart relationship along a length of the cylindrical recess from a first end of the cylindrical recess most distant from the camshaft to a second end of the cylindrical recess closest to the camshaft: a first exhaust vent connecting the cylindrical recess to atmosphere; a first return line connecting the first portion to the cylindrical recess; a first movement line connecting the cylindrical recess to the first portion; a central inlet line connecting a central location in the cylindrical recess to a source of fluid; a second movement line connecting the cylindrical recess to the second portion; a second return line connecting the second portion to the cylindrical recess; a second exhaust vent connecting the cylindrical recess to atmosphere; the first exhaust vent, second exhaust vent, first return line, second return line, first movement line, second movement line and central inlet line being spaced apart along the length of the cylindrical recess, and the first land and the second land being of sufficient length and distance apart such that: when the spool is in a central position between the first end of the central recess and the second end of the central recess, the first land blocks the first return line and the first movement line, and the second land blocks the second movement line and the second return line; when the spool is in a position nearer the first end of the central recess, the first movement line and second return line are unblocked, fluid from the central inlet line flows into the first movement line and the first portion, and fluid from the second portion flows into the second return line and the second exhaust vent; and when the spool is in a position nearer the second end of the central recess, the second movement line and first return line are unblocked, fluid from the central inlet line flows into the second movement line and the second portion, and fluid from the first portion flows into the first return line and the first exhaust vent.

3. The phaser of claim 1, further comprising a variable force actuator, such that the variable force actuator controls the position of the spool in response to a signal issued from an engine control unit.

4. The phaser of claim 3, wherein the variable force actuator is an electromechanical variable force solenoid.

5. The phaser of claim 4, further comprising a spring for biasing the spool valve to a full advance position during periods when the electromechanical variable force solenoid is deenergized.

6. The phaser of claim 3, wherein the variable force actuator is a pulse-width modulated solenoid.

7. The phaser of claim 1, further comprising an inlet check valve which controls a backflow of fluid entering the fluid input.

8. The phaser of claim 1, wherein the fluid comprises engine lubricating oil.

9. An internal combustion engine, comprising: a crankshaft, the crankshaft being rotatable about a first axis; a camshaft, the camshaft being rotatable about a second axis, the camshaft being subject to torque reversals during rotation thereof; a phaser for adjusting timing between a camshaft and a timing gear coupled to a crankshaft of an engine, comprising: a rotor having first and second circumferentially spaced apart vanes and a central cylindrical recess located along an axis of rotation, the rotor being connectable to the camshaft for rotation therewith; a housing connectable to the timing gear for rotation therewith, having a body coaxially surrounding the rotor, the body having a first recess and a second recess circumferentially spaced apart for receiving the first vane and the second vane of the rotor, and permitting rotational movement of the first vane and the second vane therein, wherein each of the first vane and second vane respectively divides each of the first recess and second recess into a first portion and a second portion, the first portion and the second portion of the first recess and the second recess being capable of sustaining fluid pressure, such that introduction of a fluid under pressure into the first portion causes the rotor to move in a first rotational direction relative to the housing and introduction of a fluid under pressure into the second portion causes the rotor to move in an opposite rotational direction relative to the housing; a spool located within the cylindrical recess of the rotor and being slidably movable along the axis of rotation of the rotor, the spool comprising a plurality of lands which block and connect a plurality of passageways in the rotor, such that by slidably moving the spool in the cylindrical recess of the rotor, the flow of fluid from a fluid input to the first portion and the second portion is controlled, varying the rotational movement of the housing relative to the rotor; an electromechanical actuator mechanically coupled to the spool; and an engine control unit coupled to the electromechanical actuator, such that, the electromechanical actuator controls the position of the spool in response to a signal issued from the engine control unit.

10. The internal combustion engine of claim 9, in which: the spool comprises length and a first land and a second land, spaced apart a distance along the length, such that the first land and the second land have a circumference which provides a fluid blocking fit in the cylindrical recess, and the length has a lesser circumference than the first land and second land to permit fluid to flow; and the cylindrical recess of the rotor comprising, in spaced-apart relationship along a length of the cylindrical recess from a first end of the cylindrical recess most distant from the camshaft to a second end of the cylindrical recess closest to the camshaft: a first exhaust vent connecting the cylindrical recess to atmosphere; a first return line connecting the first portion to the cylindrical recess; a first movement line connecting the cylindrical recess to the first portion; a central inlet line connecting a central location in the cylindrical recess to a source of fluid; a second movement line connecting the cylindrical recess to the second portion; a second return line connecting the second portion to the cylindrical recess; a second exhaust vent connecting the cylindrical recess to atmosphere; the first exhaust vent, second exhaust vent, first return line, second return line, first movement line, second movement line and central inlet line being spaced apart along the length of the cylindrical recess, and the first land and the second land being of sufficient length and distance apart such that: when the spool is in a central position between the first end of the central recess and the second end of the central recess, the first land blocks the first return line and the first movement line, and the second land blocks the second movement line and the second return line; when the spool is in a position nearer the first end of the central recess, the first movement line and second return line are unblocked, fluid from the central inlet line flows into the first movement line and the first portion, and fluid from the second portion flows into the second return line and the second exhaust vent; and when the spool is in a position nearer the second end of the central recess, the second movement line and first return line are unblocked, fluid from the central inlet line flows into the second movement line and the second portion, and fluid from the first portion flows into the first return line and the first exhaust vent.

11. The internal combustion engine of claim 9, further comprising a variable force actuator, such that the variable force actuator controls the position of the spool in response to a signal issued from an engine control unit.

12. The internal combustion engine of claim 11, wherein the variable force actuator is an electromechanical variable force solenoid.

13. The internal combustion engine of claim 12, further comprising a spring for biasing the spool valve to a full advance position during periods when the electromechanical variable force solenoid is deenergized.

14. The internal combustion engine of claim 11, wherein the variable force actuator is a pulse-width modulated solenoid.

15. The internal combustion engine of claim 9, further comprising an inlet check valve which controls a backflow of fluid entering the fluid input.

16. The internal combustion engine of claim 9, wherein the fluid comprises engine lubricating oil.

Description:

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims an invention which was disclosed in Provisional Application Number 60/312,285, filed Aug. 14, 2001, entitled “HYBRID MULTI-POSITION CAM INDEXER HAVING CONTROLS LOCATED IN ROTOR ”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention pertains to the field of variable camshaft timing (VCT) systems. More particularly, the invention pertains to an infinitely variable camshaft indexer with controls in the center of the rotor.

[0004] 2. Description of Related Art

[0005] There are many vane type VCTs on the market today that use a conventional 4-way valve mounted in a valve body to control the phaser. The “phaser” is all of the parts of the engine which allow the camshaft to run independently of the crankshaft. Typically, the valve body is integrated into the front cam bearing which introduces a leak path between the phaser and the control system. This leakage is significant in terms of performance and oil consumption. Therefore, there is a need in the art to decrease oil leakage to maximize performance and minimize oil consumption.

[0006] There have been a number of VCT systems patented in the past.

[0007] U.S. Pat. No. 5,386,807 uses torque effects at high speed, and engine pressure at low speed. The control valve is in the phaser core. The phaser has a built-in oil pump to provide oil pressure at low speeds. The oil pump is preferably electromagnetically controlled.

[0008] U.S. Pat. No. 6,053,138 discloses a device for hydraulic rotational angle adjustment of a shaft to a drive wheel, especially the camshaft of an internal combustion engine. This device has ribs or vanes that are nonrotatably connected with the shaft. These ribs or vanes are located in the compartments of a compartmented wheel. The compartments of the compartmented wheel and the ribs and/or vanes produce pressure chambers by whose hydraulic pressurization the two structural elements can be rotated relative to one another. In order to reduce undesired rotation when an insufficient adjusting or retaining pressure is present, a common end face of the compartmented wheel and of the ribs and/or vanes works with an annular piston that exerts a releasable clamping action on the parts that are rotatable relative to one another.

[0009] A related patent, U.S. Pat. No. 6,085,708, shows a device for changing the relative rotational angle of the camshaft of an internal combustion engine relative to its drive wheel. This device has an inner part connected with ribs or vanes that is located rotationally movably in a compartmented wheel. This driven compartmented wheel has a plurality of compartments distributed around the circumference divided by ribs or vanes into two pressure chambers each. The change in rotational angle is produced by their pressurization. To minimize the influence of overlapping alternating torque influences from the valve drive of the internal combustion engine, a damping structure is integrated into this device to hydraulically damp the change in rotational position.

[0010] Consideration of information disclosed by the following U.S. Patents, which are all hereby incorporated by reference, is useful when exploring the background of the present invention.

[0011] U.S. Pat. No. 5,002,023 describes a VCT system within the field of the invention in which the system hydraulics includes a pair of oppositely acting hydraulic cylinders with appropriate hydraulic flow elements to selectively transfer hydraulic fluid from one of the cylinders to the other, or vice versa, to thereby advance or retard the circumferential position on of a camshaft relative to a crankshaft. The control system utilizes a control valve in which the exhaustion of hydraulic fluid from one or another of the oppositely acting cylinders is permitted by moving a spool within the valve one way or another from its centered or null position. The movement of the spool occurs in response to an increase or decrease in control hydraulic pressure, Pc, on one end of the spool and the relationship between the hydraulic force on such end and an oppositely direct mechanical force on the other end which results from a compression spring that acts thereon.

[0012] U.S. Pat. No. 5,107,804 describes an alternate type of VCT system within the field of the invention in which the system hydraulics include a vane having lobes within an enclosed housing which replace the oppositely acting cylinders disclosed by the aforementioned U.S. Pat. No. 5,002,023. The vane is oscillatable with respect to the housing, with appropriate hydraulic flow elements to transfer hydraulic fluid within the housing from one side of a lobe to the other, or vice versa, to thereby oscillate the vane with respect to the housing in one direction or the other, an action which is effective to advance or retard the position of the camshaft relative to the crankshaft. The control system of this VCT system is identical to that divulged in U.S. Pat. No. 5,002,023, using the same type of spool valve responding to the same type of forces acting thereon.

[0013] U.S. Pat. Nos. 5,172,659 and 5,184,578 both address the problems of the aforementioned types of VCT systems created by the attempt to balance the hydraulic force exerted against one end of the spool and the mechanical force exerted against the other end. The improved control system disclosed in both U.S. Pat. Nos. 5,172,659 and 5,184,578 utilizes hydraulic force on both ends of the spool. The hydraulic force on one end results from the directly applied hydraulic fluid from the engine oil gallery at full hydraulic pressure, Ps. The hydraulic force on the other end of the spool results from a hydraulic cylinder or other force multiplier which acts thereon in response to system hydraulic fluid at reduced pressure, Pc, from a PWM solenoid. Because the force at each of the opposed ends of the spool is hydraulic in origin, based on the same hydraulic fluid, changes in pressure or viscosity of the hydraulic fluid will be self-negating, and will not affect the centered or null position of the spool.

[0014] In U.S Pat. No. 5,361,735, a camshaft has a vane secured to an end for non-oscillating rotation. The camshaft also carries a timing belt driven pulley which can rotate with the camshaft but which is oscillatable with respect to the camshaft. The vane has opposed lobes which are received in opposed recesses, respectively, of the pulley. The camshaft tends to change in reaction to torque pulses which it experiences during its normal operation and it is permitted to advance or retard by selectively blocking or permitting the flow of engine oil from the recesses by controlling the position of a spool within a valve body of a control valve in response to a signal from an engine control unit. The spool is urged in a given direction by rotary linear motion translating means which is rotated by an electric motor, preferably of the stepper motor type.

[0015] U.S. Pat. No. 5,497,738 shows a control system which eliminates the hydraulic force on one end of a spool resulting from directly applied hydraulic fluid from the engine oil gallery at full hydraulic pressure, Ps, utilized by previous embodiments of the VCT system. The force on the other end of the vented spool results from an electromechanical actuator, preferably of the variable force solenoid type, which acts directly upon the vented spool in response to an electronic signal issued from an engine control unit (“ECU”) which monitors various engine parameters. The ECU receives signals from sensors corresponding to camshaft and crankshaft positions and utilizes this information to calculate a relative phase angle. A closed-loop feedback system which corrects for any phase angle error is preferably employed. The use of a variable force solenoid solves the problem of sluggish dynamic response. Such a device can be designed to be as fast as the mechanical response of the spool valve, and certainly much faster than the conventional (fully hydraulic) differential pressure control system. The faster response allows the use of increased closed-loop gain, making the system less sensitive to component tolerances and operating environment.

[0016] In all the systems described above, the controls for camshaft timing are located in the camshaft itself, or downstream of the camshaft, increasing the likelihood for leakage as the hydraulic fluid moves from the spool valve into the vanes of the rotor. Therefore, there is a need in the art for an infinitely variable VCT multi-position cam indexer which decreases leakage during operation.

SUMMARY OF THE INVENTION

[0017] The present invention is an infinitely variable camshaft timing device (phaser) with a control valve located in the rotor. Since the control valve is in the rotor, the camshaft need only provide a single passage for supplying engine oil or hydraulic fluid, and does not need multiple passageways for controlling the phaser, as was the prior art. The main advantage to putting the spool in the rotor is to reduce leakage and to improve response of the phaser. This design allows for shorter fluid passages when compared to a control system mounted at the cam bearing.

[0018] The rotor is connected to the camshaft, and the outer housing and gear move relative to the rotor and camshaft. Source oil is supplied through the center of the camshaft. In a preferred embodiment, the oil passes through an inlet check valve and is ported to the center of the spool valve. The inlet check valve eliminates oil from back flowing through the source during a torque reversal. The position of the spool valve determines if the phaser will advance or retard.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows a blown-up side view of the camshaft in an embodiment of the present invention.

[0020] FIG. 2 shows a top-down view of the camshaft of FIG. 1.

[0021] FIG. 3 shows a less-detailed top-down view of the camshaft of FIG. 1.

[0022] FIG. 4 shows a fragmentary view of the camshaft taken along line A-A of FIG. 3.

[0023] FIG. 5 shows a fragmentary view of the camshaft taken along line B-B of FIG. 3.

[0024] FIG. 6 shows a cam indexer with a center spool and inlet check valve in the null position in a preferred embodiment of the invention.

[0025] FIG. 7 shows a cam indexer with a center spool and inlet check valve in the advance position in a preferred embodiment of the invention.

[0026] FIG. 8 shows a cam indexer with a center spool and inlet check valve in the retard position in a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Referring to FIGS. 1 through 5, an internal combustion engine has a crankshaft, to which is driven by the connecting rods of the pistons, and one or more camshafts, which actuate the intake and exhaust valves on the cylinders. The timing gear on the camshaft is connected to the crankshaft with a timing drive, such as a belt, chain or gears. Although only one camshaft (9) is shown in the figures, it will be understood that the camshaft (9) may be the only camshaft of a single camshaft engine, either of the overhead camshaft type or the in-block camshaft type, or one of two (the intake valve operating camshaft or the exhaust valve operating camshaft) of a dual camshaft engine, or one of four camshafts in a “V” type overhead cam engine, two for each bank of cylinders.

[0028] In a variable cam timing (VCT) system, the timing gear on the camshaft is replaced by a variable angle coupling known as a “phaser”, having a rotor connected to the camshaft and a housing connected to (or forming) the timing gear, which allows the camshaft to rotate independently of the timing gear, within angular limits, to change the relative timing of the camshaft and crankshaft. The term “phaser”, as used here, includes the housing and the rotor, and all of the parts to control the relative angular position of the housing and rotor, to allow the timing of the camshaft to be offset from the crankshaft. In any of the multiple-camshaft engines, it will be understood that there would be one phaser on each camshaft, as is known to the art.

[0029] A rotor (1) is fixedly positioned on the camshaft (9), by means of mounting flange (8), to which it (and rotor front plate (4)) is fastened by screws (14). The rotor (1) has a diametrically opposed pair of radially outwardly projecting vanes (16), which fit into recesses (17) in the housing body (2). The inner plate (5), housing body (2), and outer plate (3) are fastened together around the mounting flange (8), rotor (1) and rotor front plate (4) by screws (13), so that the recesses (17) holding the vanes (16), enclosed by outer plate (3) and inner plate (5), form fluid-tight chambers. The timing gear (11) is connected to the inner plate (5) by screws (12). Collectively, the inner plate (5), housing body (2), outer plate (3) and timing gear (11) will be referred to herein as the “housing”.

[0030] The vanes (16) of the rotor (1) fit in the radially outwardly projecting recesses (17), of the housing body (2), the circumferential extent of each of the recesses (17) being somewhat greater than the circumferential extent of the vane (16) which is received in such recess to permit limited oscillating movement of the housing relative to the rotor (1). The vanes (16) are provided with vane tips (6) in receiving slots (19), which are biased outward by linear expanders (7). The vane tips (6) keep engine oil from leaking between the inside of the recesses (17) and the vanes (16), so that each recess is divided into opposed chambers (17a) and (17b). Thus, each of the chambers (17a) and (17b) of the housing (2) is capable of sustaining hydraulic pressure. Thus, application of pressure to chambers (17a) will move the rotor clockwise relative to the rotor (1), and application of pressure to chambers (17b) will move the rotor counterclockwise relative to the rotor (1).

[0031] Referring to FIGS. 4 and 5, the spool (27) of the spool valve (20) is located within the rotor (1), in a cylindrical recess (25) along its central axis (26). Passageways lead oil from the spool valve to the chambers (17a)(17b), as will be seen in schematic form below. The engine oil or other operating fluid enters the side of the mounting flange (8) and into the rotor (1) through passage (21). Since the spool valve (20) is in the rotor (1) and not the camshaft (9), the camshaft (9) is much easier to manufacture, since fluid only needs to travel through the phaser into the spool valve (20) in the rotor (1)—no elaborate passages need be machined into the camshaft (9), and no externally mounted valves are needed. Having the spool valve (20) in the rotor (1) reduces leakage and improves the response of the phaser. This design allows for shorter fluid passages when compared to a control system mounted at the cam bearing.

[0032] Referring also to FIGS. 6 through 8, the phaser operating fluid (122), illustratively in the form of engine lubricating oil, flows into the recesses (17a) (labeled “A” for “advance”) and (17b) (labeled “R” for “retard”) by way of a common inlet line (110). In a preferred embodiment shown in FIGS. 6-8, an inlet check valve (105) prevents the hydraulic fluid from backflow into the engine oil supply. However, the invention also operates without the inlet check valve (105), without deviating from the spirit of the invention. Inlet line (110) terminates as it enters the spool valve (109). The spool valve (109) is made up of a spool (104) and a cylindrical member (115). The spool (104), which is preferably a vented spool, is slidable back and forth. The spool (104) includes spool lands (104a) and (104b) on opposed ends thereof, which fit snugly within cylindrical member (115). The spool lands (104a) and (104b) are preferably cylindrical lands and preferably have three positions, described in more detail below.

[0033] Control of the position of spool (104) within member (115) is in direct response to a variable force solenoid (103). The variable force solenoid (103) is preferably an electromechanical actuator (103). U.S. Pat. No. 5,497,738, entitled “VCT Control with a Direct Electromechanical Actuator”, which discloses the use of a variable force solenoid, issued Mar. 12, 1996, is herein incorporated by reference. Briefly, in the preferred embodiment an electrical current is introduced via a cable through the solenoid housing into a solenoid coil which repels, or “pushes” an armature (117) in the electromechanical actuator (103). The armature (117) bears against extension (104c) of spool (104), thus moving spool (104) to the right. If the force of spring (116) is in balance with the force exerted by armature (117) in the opposite direction, spool (104) will remain in its null or centered position. Thus, the spool (104) is moved in either direction by increasing or decreasing the current to the solenoid coil, as the case may be. In an alternative embodiment, the configuration of electromechanical actuator (103) may be reversed, converting the force on spool extension (104c) from a “push” to a “pull.” This alternative requires the function of spring (116) to be redesigned to counteract the force in the new direction of armature (117) movement.

[0034] The variable force electromechanical actuator (103) allows the spool valve to be moved incrementally instead of only being capable of full movement to one end of travel or the other, as is common in conventional camshaft timing devices. The use of a variable force solenoid eliminates slow dynamic response. The faster response allows the use of increased closed-loop gain, making the system less sensitive to component tolerances and operating environment. Also, a variable force solenoid armature only travels a short distance, as controlled by the current from the Engine Control Unit (ECU) (102). In a preferred embodiment, an electronic interface module (EIM) provides electronics for the VCT. The EIM interfaces between the actuator (103) and the ECU (102).

[0035] Because the travel required rarely results in extremes, chattering is eliminated, rendering the system virtually noise-free. Perhaps the most important advantage over the conventional differential pressure control system is the improved control of the basic system. A variable force solenoid provides a greatly enhanced ability to quickly and accurately follow a command input of VCT phase.

[0036] Preferred types of variable force solenoids include, but are not limited to, a cylindrical armature, or variable area, solenoid, and a flat faced armature, or variable gap, solenoid. The electromechanical actuator employed could also be operated by a pulse-width modulated supply. Alternatively, other actuators such as hydraulic solenoids, stepper motors, worm- or helical-gear motors or purely mechanical actuators could be used to actuate the spool valve within the teachings of the invention.

[0037] To maintain a phase angle, the spool (104) is positioned at null, as shown in FIG. 6. The camshaft (9) is maintained in a selected intermediate position relative to the crankshaft of the associated engine, referred to as the “null” position of the spool (104). Make up oil from the supply fills both chambers (17a) and (17b). When the spool (104) is in the null position, spool lands (104a) and (104b) block both of the return lines (112) and (114), as well as inlet lines (111) and (113).

[0038] Since the hydraulic fluid (122) is essentially trapped in the center cavity (119) of the spool valve (109), the pressure is maintained, and hydraulic fluid (122) does not enter or leave either of the chambers (17a) and (17b). However, there is inevitably leakage from the chambers (17a) and (17b). So, the spool valve is “dithered” to allow a small bit of movement. That is, the spool (104) wiggles back and forth enough so that if the advance (17a) and retard (17b) chambers begin losing pressure, make-up fluid (122) restores the pressure. However, the movement is not sufficient to let fluid out exhaust ports (106)(107). Center cavity (119) is preferably tapered at the edges to allow easier transport of make-up fluid during dithering.

[0039] Since the force of armature (117) corresponds to the electrical current applied to the solenoid coil, and the force of spring (116) is also predictable (with respect to spring position), the position of spool (104) is readily ascertainable based on solenoid current alone. By using only imbalances between an electrically-generated force on one end (104b) of spool (104) and a spring force on the other end (104a) for movement in one direction or another (as opposed to using imbalances between hydraulic loads from a common source on both ends), the control system is completely independent of hydraulic system pressure. Thus, it is not necessary to design a compromised system to operate within a potentially wide spectrum of oil pressures, such that may be attributed to individual characteristics of particular engines. In that regard, by designing a system which operates within a narrower range of parameters, it is possible to rapidly and accurately position the spool (104) in its null position for enhanced operation of a VCT system.

[0040] Referring to FIG. 7, to advance the phaser, source hydraulic fluid (122) is ported to the advance chamber (17a) by shifting the spool valve (104) to the left. At the same time, the retard chamber (17b) is exhausted to atmosphere—that is, to a location of lower pressure, where the fluid may be recycled back to the fluid source. In most cases, “atmosphere” means into a location where the engine oil can drain back into the oil pan at the bottom of the engine, for example into the timing chain cover or a return line connected to the oil pan. In this configuration, land (104b) blocks the entrance of hydraulic fluid into the retard chamber inlet line (113). Cavity (119) is now lined up with advance chamber inlet line (111), allowing additional hydraulic fluid (122) to enter the retard chamber (17a). Land (104a) blocks the exit of hydraulic fluid (122) from the advance chamber return line (112). Cavity (121) allows the exhaust of hydraulic fluid (122) through the retard chamber return line (114) and out the retard chamber exhaust (107) to atmosphere.

[0041] Referring to FIG. 8, to retard the phaser, the spool valve (104) is moved to the right, and source hydraulic fluid (122) is ported to the retard chamber (17b) and the hydraulic fluid (122) in the advance chamber (17a) is exhausted to the atmosphere. In this configuration, land (104b) blocks the exit of hydraulic fluid from retard chamber return line (114). Cavity (119) is now lined up with retard chamber inlet line (113), allowing hydraulic fluid (122) into the retard chamber (17b). Land (104a) blocks the entry of hydraulic fluid (122) into advance chamber inlet line (111). Cavity (120) allows the exhaust of hydraulic fluid (122) through the advance chamber return line (112) and out the advance chamber exhaust (106) to atmosphere.

[0042] In a preferred embodiment, a lock mechanism is included for start up, when there is insufficient oil pressure to hold the phaser in position. For example, a single position pin can be inserted into a hole, locking the rotor and housing together, or another shift and lock strategy as known to the art used.

[0043] 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.