The present invention relates to improving volumetric efficiency of an engine, particularly, but not exclusively, to improving volumetric efficiency using a variable geometry camshaft.
All variable valve lift and timing mechanisms are designed with the objective of improving volumetric efficiency. A review of the tenets of cam design is presented to identify ideal valve operation and function across a range of engine rotation speeds. This summary also identifies the inherent compromises of fixed cam lobe design that must balance engine economy with output power. Using a “gold standard”, for purposes of objective comparison, all devices that claim variable valve operation should be assessed in their ability to emulate ideal characteristics of operation and function over a range of engine speeds. The competing devices should then be judged by cost verses improvement to volumetric efficiency. The expense of integrating a variable valve operation device into production will include: the total number of device components, the sophistication level of material processing, the number of labor hours for assembly, and the dimension tolerances required for the components to meet design specifications.
A set of “pie” diagrams are shown in
The “M.P.” represents “Mid-Point” in the “Pie” Diagrams of
In sequence, from
In
a through 2e show the incremental expansion of a set of envelopes for the period of exhaust valve opening duration. As the exhaust envelope expands, its Mid-Point will shift direction opposite to the Mid-Point shift of the intake envelopes. In
Up to a point of diminishing returns, a greater level of valve lift from the valve seat poses less restriction to the flow of air or exhaust gases.
Compare the lift profiles as an intake and exhaust set over
a through 3e and 4a through 4e show a symmetrical set of lift profiles across each of the duration envelopes. Maximum valve lift and the Mid-Point of each envelope is at the half way mark through the valve opening duration.
During the intake stroke, the maximum piston velocity occurs when the crankshaft is at ninety degrees (90°) and the piston is half-way to B.D.C. At this crank position, the velocity of the air entering the cylinder lags behind the velocity of the piston. After the piston passes ninety degrees (90°), piston speed will decrease during its descent toward bottom dead center. During the second phase of the intake stroke, the increasing velocity of the air column entering the cylinder will exceeds the decreasing piston velocity. Efficient cylinder filling is optimized when the intake valve reaches its maximum lift at, or near, bottom dead center.
A variable valve device that emulates the duration envelopes and the intake lift profiles of
With an increase in the engine rotation speed, the level of intake valve lift can be chosen to slightly restrict airflow into the cylinder. This restriction will increase the air velocity around the intake valve. The longer rotation period of the cam and the gradual rise of intake valves to maximum lift, provides an opportunity to use the high velocity airflow to create a more uniform dispersion of smaller fuel droplets within the cylinder.
At high levels of engine speed, the use of an asymmetrical lift profile also addresses the problem of time lost at the start of the valve opening envelope. As the intake valve opens there is a period of lost intake duration time due to the inertia of the stationary air column entering the cylinder. As engine speed increases to the high end of the r.p.m bandwidth, this time loss due to air column inertia poses a increasing detriment to volumetric efficiency. The problem is partially rectified by expanding the duration period of valve opening further into the exhaust and compression strokes to gain additional time to fill the cylinder.
Refer to the high speed “pie” diagrams of
The Variable Geometry Camshaft expands the intake duration envelope into the compression stroke only as increasing engine speed would warrant the intrusion. The maximum available compression ratio can be used at idle, and the lower speeds of engine operation. During the operation of a V.G.C. engine at cruise levels and above, it is expected that the asymmetrical intake-valve lift profile of the invention will mitigate the amount of valve opening encroachment into the compression stroke. Over the bandwidth of engine operation speeds there is a less sacrifice of the compression ratio. The Variable Geometry Camshaft will continuously adjust the close of intake valves to improve volumetric efficiency and minimize the loss of actual compression at the higher levels of engine speed.
An optimum set of duration envelopes and valve lift profiles for the exhaust valves are presented in
With increasing engine speed, greater exhaust valve lift over an expanded opening duration is also used to offset the reduction in available time to evacuate the cylinder. For operation at idle speed, it is aimless to open the exhaust valve to a maximum level of lift. If the cam lobe is not required to overcome the greater resistance from full travel of the exhaust valve spring, there is a gain in economy due to the reduction of internal resistance.
To achieve nearly complete cylinder evacuation at higher levels of engine speed, the invention increases the point of exhaust valve opening before the piston reaches bottom dead center on the power stroke. The escaping exhaust gases produce a reactive force on the downward moving piston that is often referred to as the “kick.” A rapid opening of the exhaust valve will maximize the amount of additional reactive force or “kick” on the piston before B.D.C.
A fixed camshaft requires compromises in the selection of lobe dimensions that limit volumetric efficiency to a narrow range of engine speeds. A design for a fixed cam lobe must balance the competing interests of economy and the ability to obtain high output power on demand. The Variable Geometry Camshaft provides an alternative to the inherent compromises of fixed cam valve timing, the level of valve lift and the extent of valve opening duration.
a through 7f, show a cam lobe with a Thirty degree (30°) slope with respect to a centerline that extends through the camshaft axis to lobe apex. In
In
In
The patent of Griffiths (U.S. Pat. No. 6,189,497) presented this method of changing valve lift and valve opening duration through the limited movement of the cam axis around a d-rive gear as shown in
The patent of Griffiths is an improvement over the limitations of a fixed dimension camshaft. This patent is, however, restricted in delivering an optimum level of volumetric efficiency. Notice that maximum valve lift occurs at the Mid-Point of the duration envelope. This method of cam to lifter engagement will produce lift profiles similar to
The U.S. Pat. No. 6,189,497 provided the basic concept of permitting the cam axis to rotate in a limited arc to change the geometry of its interation with the valve train. The present invention offers a method of increasing the length of the arc of cam axis rotation. The present invention also coordinates an asymmtrical valve lift to suit the requirements of intake or exhaust operation. Moreover, the present invention offers a unique method of continuous mechanical control of all of the functions of variable valve operation.
The Variable Geometry Camshaft is capable of emulating a nearly ideal set of valve operation functions over a wide range of engine rotation speed. The invention delivers a continuous change to maximum valve lift, the timing of cam to valve contact and the duration of valve opening. The invention anticipates using a engine management system with feedback loops that sense environmental and operational conditions. E.M.S. output control signals can drive actuators to “fine tune” the position of the cam axis and cam follower fulcrum without compromising mechanical reliability.
To achieve maximum benefit, the invention should be integrated with a new head casting design. The V.G.C. head can then be mated to a conventional engine block casting and its rotating assembly. The components of the invention can be fabricated to be rugged and durable. The invention does not require the use of exotic materials or unusual methods of assembly. The invention may prove to be less complex and require fewer components than other mechanically based systems for variable valve operation. The invention is compatible with mass production technology, and, potentially, other innovations to improve the economy and power of the internal combustion engine.
The constituents of comprehensive valve operation include; the amount of maximum lift, the amount of minimum lift, the rate of the valve lift and the rate of its descent. Attaining optimum valve operation also requires adjusting the timing of the valve opening in relation to the crankshaft position (in degrees). The duration period of valve opening and the point of valve closing comprise a complete inventory of functions for comprehensive valve operation.
The Variable Geometry Camshaft (V.G.C.) permits a fluent adjustment to the valve operation of a four (4) cycle engine over a range of rotation speed. Volumetric efficiency is improved by adjusting the axial position of the cam and the rotational position of the cam lobe as it engages a cam follower. A coordinated change of position by the device components contributes to the continuous adjustment of each function of variable valve operation.
The invention teaches how to control the position change of three (3) sub-assemblies that vary the geometry of mechanical interaction between the cam lobe, the cam follower and the valve. The Variable Geometry Camshaft provides a continuous sixty degree (60°) asymmetrical expansion or contraction of the valve opening duration. This asymmetry is caused by a coordinated timing shift of cam contact with the cam follower. The invention can continuously control the valve's rate of ascent and descent. Asymmetrical lift profiles result in maximum lift of the intake and exhaust valves at, or near, bottom dead center. The V.G.C. also allows design diversity in choosing the operational range of maximum valve lift.
The valve lift is limited to an amount necessary for a given engine speed. This reduces the power consumed internally to overcome the spring resistance to cam rotation. A continuous and coordinated adjustment of all valve functions will improve the engine's volumetric efficiency. By eliminating the compromises of conventional fixed cam operation, a V.G.C engine gains fuel economy, reduces the exhaust emissions and increases its torque output.
The previous invention of Griffiths presented a method for improving the “breathing” capability of an engine. In U.S. Pat. No. 6,189,497, a camshaft is suspended about a drive gear. The cam axis position is controlled across a limited arc which is aligned with a telescoping lifter. Moving the cam axis position across this arc alters the timing of cam contact and release from a partially or fully compressed lifter. This position change of the cam axis changes the duration of valve opening and the valve lift.
Although U.S. Pat. No. 6,189,487, demonstrates a unique method of adjusting valve functions, the overall operation is not optimum. The length of the cam axis rotation about the drive gear is short in relation to the present invention. A sixty degree (60°) range of expansion or contraction of valve opening duration is controlled by only a four to eight degree (4–8°) rotation of the cam axis about the drive gear. In a multi-cylinder engine, this limited movement of the cam axis may yield an undesirable variance range with respect to the amount of lift for each valve and its opening duration. Moreover, the valve's lift and descent is symmetrical. Maximum lift for the intake valve occurs at a non-ideal crankshaft rotation point with respect to the descending piston during the intake stroke.
The novelty of the present invention is supported by an “x” and “y” cam axis movement over an arc that is three (3) times the length of the previous invention. The movement along the cam's “x” axis alters the location of cam lobe contact on the camfollower. The “y” axis motion of the cam adjusts the space between the cam heel and the contact surface of the cam follower. The “y” axis spacing, between cam heel and contact lever, sets the rotational position where the cam lobe begins to exert a force upon the cam follower to begin the period of valve opening.
The V.G.C. uses Four-to-One (4:1) gear reduction assemblies to drive suspended dedicated cams that sweep across twenty-four degrees (24°) of arc. The drive gear turns at twice the crank speed and the reduction ratio rotates the cam at one-half (½) the crank speed. Four degrees (4°) of cam movement along the arc causes the timing of cam to cam follower contact to be retarded or advanced by one degree (1°). An asymmetrical expansion or contraction of valve opening is produced by this timing shift in cam to cam follower contact. The cam follower is mounted on a sliding tower and its motion is aligned with the cam's movement on the “x” axis. Moving the cam along the “x” axis of the cam follower changes the mechanical advantage of the rocker arm lever on the valve. The position of the cam follower fulcrum is adjusted to augment or diminish the amount of valve lift with an increasing or decreasing duration of valve opening. The V.G.C. concept provides unique options in the design of valve operation characteristics. The intake valve can exhibit a wide range of maximum lift. The device can cause gradual opening of the intake valve with the achievement of maximum lift as the piston nears bottom dead center. The exhaust valve can be designed for quick opening to maximum lift and then taper to closure. The duration envelopes for intake and exhaust, in their contracted state, can be set up to exhibit negative valve overlap at idle speed. With an increase in engine speed, the expanding intake and exhaust envelopes will then exhibit an increased overlap condition. “Pie” diagrams are used to represent the functions of intake and exhaust valves over a range of engine speed and compare valve lift profiles with the rotation position of the crankshaft (in degrees).
The utility of the Variable Geometry Camshaft is based upon achieving functional goals of a system capable of:
The utility of the Variable Geometry Camshaft is furthered by its ability to be adapted:
The novelty of the present invention for a Variable Geometry Camshaft is based on the design features that:
a through 1e—Pie Diagrams for the Intake valve.
a through 2e—Pie Diagrams for the Exhaust valve.
a through 3e—Pie Diagrams for the Intake valve with superimposed lift profiles.
a through 4e—Pie Diagrams for the Exhaust valve with superimposed lift profiles.
a through 5e—Pie Diagrams for the Intake valve with asymmetrical superimposed lift profiles.
a through 6e—Pie-Diagrams for the Exhaust valve with asymmetrical superimposed lift profiles.
a through 7f—Cam interaction with solid lifter.
a through 8f—Cam interaction with solid lifter.
a through 9f—Cam interaction with solid lifter.
FIG. 10—Suspension assembly supported cam with valve train, reprint of U.S. Pat. No. 6,189,497, Griffiths
FIG. 11—Side view of gear reduction, cam cam follower on sliding base, and hydraulic actuator.
FIG. 12—Conventional aviation methods of driving over head camshafts.
a through 13e—Rotation of the cam, reduction gear and suspension-assembly; resulting change to cam heel position.
FIG. 14—Movement of the cam heel across Arc # 2 with rotation around the axis point of the drive gear.
FIG. 15—Cam profiles based on five-to-one relationship of R1, base and R3, apex. Equations for determining the cam heel separation distance.
FIG. 16—Identification of incremental cam heel positions across Arc #2.
FIG. 17—Side view of complete device for intake valve operation.
a, 18b & 18c—Three levels of extension by the hydraulic actuator, a fixed cam position and the resulting change in valve lift.
FIG. 19—Determining maximum deflection of the intake valve cam follower through full rotation of the cam.
FIG. 21—Determining maximum deflection of the exhaust valve cam follower through full rotation of the cam.
a, 22b & 22c—Cam heel at idle position with valve rising to maximum level.
a, 23b & 23c—Cam heel at cruise position with valve rising to maximum level.
a, 24b & 24c—Cam heel at high r.p.m. position with valve rising to maximum level.
FIG. 25—Partial Assembly of Alternative Design; VGC-ICR, Intermeshed Cam follower and Rocker arm.
a & 26b—Side & Top view; Rocker Arm Frame
a,b,c & d.—Cam axis, sixty-two degrees (62°) from horizontal, Fig. a,b,c & d show a sequential rotation of the cam to maximum lift.
a,b,c & d.—Cam axis, seventy degrees (70°) from horizontal, Fig. a,b,c & d show a sequential rotation of the cam to maximum lift.
a,b,c & d.—Cam axis, seventy eight degrees (78°) from horizontal, Fig.a,b,c&d show a sequential rotation of the cam to maximum lift.
a,b,c & d. Cam axis, eighty six degrees (86°) from horizontal, Fig. a,b,c & d show a sequential rotation of the cam to maximum lift.
The present invention is based on the ability to control the mechanical interaction among Three (3) component sub-assemblies; 1.) a suspension bracket, camshaft, and gear reduction assembly, 2.) a camfollower contact lever, fulcrum, rocker arm, and sliding base assembly, and 3.) a valve, valve guide, valve spring, and valve piston assembly. The functions and contributions of these component sub-assemblies to the utility of the invention concept will be presented and described in the foregoing order.
Suspension Bracket, Camshaft, and Gear Reduction Assembly
The V.G.C., or Variable Geometry Camshaft concept is based on the position of the cam axis, its contact location and its direction of engagement with a camfollower in Two (2) distinct orientations that assist either the intake or exhaust functions.
With the drive gear, 3, turning at twice the speed of the crankshaft, the Four-to-One (4:1) speed reduction will turn the camshaft at the usual one-half (½) of the crankshaft rotation speed. A drive shaft mechanism, similar to the examples shown in
In a progression,
In
With an extension of the hydraulic control piston, 8, the bracket, 2, and cam, 1, rotate in the same clockwise direction as the drive gear. A full extension of the hydraulic piston moves the cam axis across the limited arc of Twenty-Four degrees (24°). The timing of cam lobe engagement with the camfollower contact lever, 9, in
2(R2)+2(R3)=Lobe Rise
To calculate the appropriate amount of separation distance between the cam heel and cam follower, the graphical relationship is shown in
By substituting for R1, the value of DS can be calculated in terms of R2.
Because: R1=5(R2)
In cam 100 the centerline from the cam axis through the apex of the lobe is thirty degrees (30°) from horizontal and one side of the lobe runs parallel to the ceiling line. Graphically it appears that there is no separation distance between the cam heel and the ceiling line. This is proven by:
Separation Distance=DS=(sine 86°(D1)+R1)−(sine 62°(D1)+R1)
DS=sine 86° (D1)−sine 62°(D1)
DS=D1 [sine 86°−sine 62°]
DS=D1 [0.9976−0.8829]=D1 [0.1146]
Substituting for DS using the result from the previous set of equations:
D
1=27.234 R2−2.556 R1
Substituting for R1; R1=5(R2)
D1=27.234 R2−5(R2)×2.556
D1=27.234 R2−12.78 R2=14.454 R2
Arc # 2 is the path that is traced by the highest point on the cam heel as the cam axis rotates around the drive gear. The lower and upper limit lines of Arc #2, along with the “Floor” and the “Ceiling” lines, enclose the rotational position of the cam heel.
Lobe height=4R2
Lobe lift @ (45°)=4R2−Separation Distance Forty-Five degrees
Substituting for the Separation Distance in terms of R2; DS 1.657 R2
Lobe lift @ (45°)=4R2−1.657 R2=2.343 R2 Forty-Five degrees
Using sine functions for the upper and lower limits of the Arc #1, an interpolation is made to determine separation distance at the beta position of sixty-six degrees (66°) from horizontal.
sine (86°) (0.997564)−sine (62°) (0.882948)=0.1146
sine (66°) (0.9135)−sine (62°) (0.8829)=0.0306
% of sine increase=26.7%
This percentage of sine function increase also represents the percentage decrease in the separation distance at the beta position of the cam heel. Because the available separation distance at the alpha position is:
DS=1.657 R2,
then; DS beta=(73.3%) 1.657 R2=1.214 R2,
Using a previous equation the known amount of the sine function is replaced by the unknown sine (theta)°:
DS beta=[sine (theta)° (3R2+R1)+R2]−R1,
And because: R1=5R2
1.214 R2=[sine (theta)° (3R2+5R2)+R2]−5R2
5.214 R2=sine (theta)° (8R2)
Therefore: arc sine (0.6517)=(theta)°=40.67°
Lobe lift @ (40.67°)=4R2−1.214 R2=2.786 R2, Forty and 67/100
Using the above method for each of the intermediate cam positions, the variables of duration period and lobe lift can be tabulated as a step towards producing a set of “pie” diagrams. Table 1 and 2, at the end of the text, lists the calculated values of cam operation for each of the cam heel positions identified in
The sine function of the last four or five degrees (4–5°) before vertical, limits the cam heel to a minimal rise in closing the separation distance between the cam heel and the cam follower. If the upper limit position of cam heel travel along Arc #2 was the vertical reference line, the period of valve opening duration would have nearly reached full expansion at a position of five or six degrees (5–6°) before the vertical limit. The desired amount of cam contact timing shift would lag too much behind the expansion of the duration envelope. Choosing the upper limit position of Arc #1 to be four degrees (4°) before vertical helps to synchronize the desired amount of cam contact timing shift with the expanding or contracting valve duration envelope. The relationship between the cam lobe profile shown in 14a, the separation distance, DS, and the distance between the drive gear axis and cam axis, D1, provides the foundation for the selection or derivation of all other component dimensions of the invention.
Cam Follower, Fulcrum, Rocker Arm and Sliding Tower Assembly
The cam follower is a first class lever. The cam follower fulcrum separates the cam follower contact lever, 9, and the rocker arm lever, 13, that operates upon the valve assembly.
The coordinated movement of the cam follower tower prevents an unacceptable change in the rocker arm ratio due to the significant movement of the cam axis along the “x” axis as shown in
Further gains in volumetric efficiency will be realized with maximum deflection of the contact lever, and maximum valve lift, occurring after the half-way mark of cam to cam follower contact.
Position F of
The ability of the device to deliver maximum lift to the intake valve during the second phase of cam lobe contact is due to the employment of the sliding fulcrum working in concert with the rotation of the cam and gear reduction assembly. The cam lobe is released from the contact lever in close proximity to the fulcrum throughout the range of cam axis and gear assembly rotation around the drive gear. The invention produces a lift profile of intake valve operation that corresponds to the ideal lift profiles that are shown in the “pie” diagrams of
Valve, Valve Spring, and Valve Piston Assembly
The Arc of Travel by the rocker arm is essentially linear and nearly parallel to the center line of valve travel.
c shows the device component interactions for engine operation at the higher levels of rotation speed. The deflection of the rocker arm will be larger due to a closing of the separation distance and the nearly full rise of the cam lobe upon the cam follower contact lever. Moreover, the release position of the cam lobe is closer to the fulcrum. The travel of the fulcrum and sliding tower has moved the resting position of the rocker arm roller out of the center of the valve piston. The curvature and length the Arc of Travel by the rocker arm roller to maximum lift, will draw the roller contact point back into the center of the valve piston. The lateral forces from the operation of the rocker arm are dispersed across the contact surfaces of the valve piston, 17, and the valve piston cylinder, 18. This employment of a valve piston and cylinder will reduce wear on the valve guide, 22, and maintain proper alignment and contact between the valve, 20, and the valve seat, 23. The rocker arm roller can be slightly offset on the valve piston to cause a gradual rotation of the valve piston around the valve cylinder and avoid a stationary wear pattern.
Exhaust Valve Operation
In
Because it is desirable to open the exhaust valve rapidly to its maximum valve level of lift, the cam lobe engages the contact lever of the camfollower at a point closest to the fulcrum. The cam lobe will then push the contact lever to its maximum rotation before the half-way mark of cam to cam follower contact duration.
a through 22c show a retracted hydraulic piston with the cam and suspension bracket assembly pulled back to the lower limit of rotation. As previously shown with the operation of the intake valve, this “idle speed” position has the greatest amount of separation distance between the cam heel and the cam follower contact lever. In
In
With the tie rod, 14, that links the cam follower tower to the rotating bracket assembly, the amount of fulcrum movement can be set to correspond to the same amount of “x” axis travel by the cam axis. The rocker arm ratio will then remain constant and the level of maximum valve lift can be held within a narrow range.
Enhancements to the Preferred Embodiments
The invention anticipates that alternative designs can be based on the innovation of cam axis movement affecting the valve timing, valve opening duration and valve lift. The design shown in
An alternative design is presented in the following paragraphs that provides greater economy in mass production by eliminating the complexity of a sliding fulcrum. Instead, the design relies on an intermeshed cam follower and rocker arm that pivot on their own dedicated mounting stands. Moreover, less space or “real estate” on top of the cylinder head is required. This design will be identified as the VGC-ICR; “Intermeshed Cam follower and Rocker arm”. The design compromise of the VGC-ICR is the loss of cam operation in close proximity to the cam follower fulcrum. The lift profiles of the VGC-ICR are not as asymmetrically pronounced as those developed by the VGC-SF. For low r.p.m. engines, the VGC-ICR design economy may be worth the sacrifice of optimum lift profiles.
The VGC-ICR Design
Limited Rotation of the Cam Axis with the Gear Reduction Assembly
FIGS. 10 and 11 of U.S. Pat. No. 6,189,497, Griffiths, show a method of transferring the force created by centrifugal weights on the flywheel to rotate the cam and suspension bracket assembly. FIG. 11 of the patent shows the motion of a rotor, 45, along the drive shaft axis. This design can be used to drive a hydraulic master cylinder to activate the slave cylinder, 8, as shown in
The invention also anticipates that solenoids, stepper motors or other electrical actuators can be used to rotate the cam and gear reduction assembly. The use of electrical components, as the primary force to move the cam and gear reduction assembly will, however, compromise the inherent reliability of the system.
Electrical actuators are better employed as non-critical components that respond to feedback directives from an engine management system to further improve operational economy. The sensed changes to engine load, engine speed, and air density can trigger adjustments to a lever ratio or cause a timing shift in cam lobe contact. The failure of a sensor, actuator or circuit will not significantly impair the variable operation of the valve system or compromise the continued operation of the engine.
Variable Geometry Camshaft Sliding Fulcrum, VGC-SF
The present invention claims the benefit of U.S. Provisional Patent Application No. 60/479,621, filed 18 Jun. 2003, which is hereby incorporated by reference.
Number | Name | Date | Kind |
---|---|---|---|
6189497 | Griffiths | Feb 2001 | B1 |
6220211 | Line | Apr 2001 | B1 |
6230675 | Kobayashi et al. | May 2001 | B1 |
6234125 | Neubauer et al. | May 2001 | B1 |
6289860 | Speckhart et al. | Sep 2001 | B1 |
6357406 | Simpson | Mar 2002 | B1 |
6484675 | Pierik | Nov 2002 | B2 |
6523512 | Axmacher et al. | Feb 2003 | B2 |
6578534 | Nohara et al. | Jun 2003 | B2 |
6591802 | Pierik | Jul 2003 | B1 |
6655330 | Pierik | Dec 2003 | B2 |
6659053 | Cecur | Dec 2003 | B1 |
6659054 | Sugiyama et al. | Dec 2003 | B2 |
6675752 | Kunne et al. | Jan 2004 | B1 |
6679209 | Hibi et al. | Jan 2004 | B2 |
6681733 | Ichimoto et al. | Jan 2004 | B2 |
6684833 | Moteki et al. | Feb 2004 | B2 |
6814044 | Elliott et al. | Nov 2004 | B2 |
Number | Date | Country | |
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60479621 | Jun 2003 | US |