Patent Application
20050120872
The present invention relates generally to high speed liquid valves with a small flow volume, and more particularly to a three way control valve for use in an electro-hydraulic actuator, such as a portion of a fuel injector.
Electro-hydraulic actuators, such as those used in conjunction with fuel injectors having a direct control needle valve, rely upon relatively small and fast valves in order to control fuel injection characteristics. In one class of fuel injection systems, a direct control needle valve opens and closes the nozzle outlet of the fuel injector. The direct control needle valve is controlled hydraulically via a relatively high speed needle control valve that has the ability to apply either low pressure or high pressure to a closing hydraulic surface associated with the direct control needle valve. One such direct control needle valve and accompanying needle control valve is disclosed in co-owned U.S. Pat. No. 5,669,355 to Gibson et al. That reference teaches a fuel injector that includes a needle control valve with the ability to apply high pressure or low pressure oil to a closing hydraulic surface of a direct control needle valve. When high pressure is applied to the closing hydraulic surface, the needle valve stays in, or moves toward, its closed position to end the spray of fuel. When low pressure is applied to the closing hydraulic surface, and the fuel is at injection pressure levels, the needle valve will stay in, or move toward, its open position to allow fuel to spray out of the nozzle outlets of the fuel injector. In order to accomplish various goals, such as reducing undesirable emissions from an engine, engineers are constantly seeking ways of improving performance of direct control needle valves, especially by addressing problems associated with needle control valves.
One of the problems that could be addressed in improving a needle control valve is to reduce response time. This problem can then be broken down into seeking ways to reduce the valve member's travel distance, increasing the travel speed and/or acceleration of the valve member, decreasing the influence of fluid flow forces on valve member movement, and other issues known in the art. In addition, it is desirable to employ strategies that hasten the rate at which pressure changes can occur within the needle control chamber that applies the hydraulic force to the closing hydraulic surface of the needle valve member. These problems are further compounded by issues relating to an available space envelope for the valve, and maybe more importantly the ability to address all of these problems with a structure that allows for the valve to be mass produced with consistent behavior from one valve to another. Still another problem that could be addressed relates to efficiency. For instance, reducing leakage through the valve can make a difference in the overall viability of a given valve.
The present invention is directed to one or more of the problems set forth above.
In one aspect, a three way control valve includes a valve body with a first passage, a second passage, a third passage, a first seat and a second seat. A valve member is at least partially positioned in the valve body and movable between the first seat and the second seat. The first passage is open to the third passage across the first seat when the valve member is in contact with the second seat. One of the first passage and the third passage has a flow restriction relative to the flow area across the first seat. The second passage is open to the third passage across the second seat when the valve member is in contact with the first seat. One of the second passage and the third passage has a second flow restriction relative to a flow area across the second seat.
In another aspect, an electro-hydraulic actuator includes a three way control valve with a closed control pressure volume, with a control passage a high pressure passage fluidly connected to a source of high pressure liquid, and a low pressure passage fluidly connected to a low pressure liquid reservoir. The three way control valve includes a valve member trapped to move between a high pressure seat and a low pressure seat. A movable piston with a control hydraulic surface is exposed to fluid pressure in the control pressure volume. An electrical actuator is operably coupled to the valve member. The low pressure passage is open to the control passage across the low pressure seat when the valve member is in contact with the high pressure seat. One of the low pressure passage and the control passage has a first flow restriction relative to a flow area across the low pressure seat. The high pressure passage is open to the control passage across the high pressure seat when the valve member is in contact with the low pressure seat. One of the high pressure passage and the control passage has a second flow restriction relative to a flow area across the high pressure seat.
In still another aspect, a method of operating a three way control valve includes a step of fluidly connecting a first passage to a third passage across a first valve seat at least in part by positioning a valve member in contact with a second seat. Liquid flow from the third passage to the first passage is restricted at least in part by locating a first flow restriction in one of the first passage and the control passage, wherein the first flow restriction is restrictive relative to a flow area across the first seat. The second passage is fluidly connected to the third passage across an second seat at least in part by moving the valve member into contact with the first seat. Liquid flow from the second passage to the third passage is restricted at least in part by locating a second flow restriction in one of the second passage and the control passage, wherein the second flow restriction is restrictive relative to a flow area across the second seat.
Referring to
Within fuel injector 10, fuel arriving from high pressure fuel source 18 travels through an unobstructed nozzle supply passage 24 to arrive at a nozzle chamber 25, which is shown blocked from fluid communication with nozzle outlet 23 by a needle portion 30 of direct control needle valve 11. Needle portion 30 includes an opening hydraulic surface 34 exposed to fluid pressure in nozzle chamber 25. Direct control needle valve 11 is normally biased downward to its closed position, as shown, by the action of a biasing spring 35 acting on a lift spacer 31, which is in contact with a top surface of needle portion 30. Direct control needle valve 11 also includes a piston portion 32 with a closing hydraulic surface 33 exposed to fluid pressure in a needle control chamber 37. Opening hydraulic surface 34 is in opposition to closing hydraulic surface 33. When three way valve 14 is in a first position, needle control chamber 37 is fluidly connected to source of high pressure fuel 18 via a high pressure passage 40 that connects at one end into nozzle supply passage 24. When valve 14 is at its second position, needle control chamber 37 is fluidly connected to low pressure reservoir 20 via a low pressure passage 41. Three way valve 14 is moved between its first position and its second position by energizing and deenergizing electrical actuator 16. When high pressure exists in needle control chamber 37, direct control needle valve 11 will stay in, or move toward, its downward closed position, as shown. When needle control chamber 37 is connected to low pressure, direct control needle valve 11 will lift to its upward open position if fuel pressure acting on opening hydraulic surface 34 is above a valve opening pressure, which is preferably determined by a biaser, such as the preload of biasing spring 35. In practice, the valve opening pressure of direct control needle valve 11 is adjusted by choosing a VOP spacer 36 of an appropriate thickness. In addition, the lift distance of direct control needle valve 11 is controlled by choosing an appropriate thickness for lift spacer 31. Those skilled in the art will appreciate that in the disclosed embodiment, needle control chamber is a closed volume.
Referring to
Valve member 42 is preferably operably coupled in a known manner to the moveable portion of an electrical actuator. In the illustrated embodiment, valve member 42 is attached to an armature 62 via a nut 63 that is threaded onto one end of valve member 42. In particular, an armature washer 63 rests upon an annular shoulder 58 (
In order to aid in concentrically aligning upper seat 50 with lower seat 51 along common centerline 38, valve member 42 includes an upper guide portion 54 with a close diametrical clearance (i.e. a guide clearance) with an upper guide bore 55 located in upper seat component 43. In addition, valve member 42 also preferably includes a lower guide portion 56 having a relatively close diametrical clearance with a lower guide bore 57 located in lower seat component 45. Thus, these guide regions tend to aid in concentrically aligning upper and lower seats 50 and 51 during the assembly of three way valve 15 (
In order to reduce the influence of fluid flow forces on the movement of valve member 42, high pressure passage 40 and low pressure passage 41 preferably include flow restrictions that are restrictive relative to a flow area across respective seats 50 and 51. While these flow restrictions could be located in upper seat component 43 and/or lower seat component 45, they are preferably located in valve lift spacer 44 as shown in
In order to accommodate for the possibility of a slight angular misalignment between the centerline of valve member 42 and the respective centerlines of upper and lower seats 50 and 51, valve member 42 preferably includes spherical valve surfaces 52 and 53, which have a common center as shown in
Although piston 32 could be located in a common body as lower seat component 45, it is preferably separated from the same by a relatively thin separator 75 and housed in its own piston guide body 76, as shown in
Referring now to
When needle valve member 42 is in its upward position closing high pressure seat 150, fluid can flow from needle control chamber 37 (
Referring now to
Industrial Applicability
The present invention finds potential application in any valve whose performance characteristics must be relatively tightly controlled while at the same time providing a structure that permits mass production and consistent performance from one valve to another. In addition, the present invention preferably finds particular application in the case of high speed valves that are required to accommodate relatively low flow volumes, such as pressure control valves employed in fuel injection systems.
When fuel injector 10 is in operation, electro-hydraulic actuator 12 works in conjunction with direct control needle valve 11 to control both timing and quantity of each injection event. Each injection event is initialized by raising fuel pressure in high pressure source 18 to injection levels. In some systems, this is accomplished by maintaining a common rail at some desired pressure. Alternatively, source 18 can be a fuel pressurization chamber within a unit injector which is pressurized when a plunger is driven downward, which is usually accomplished with a cam or a hydraulic force. Because valve member 42 is biased downward to close low pressure seat 51, direct control needle valve 11 will stay in its downward closed position due to the high pressure force acting on closing hydraulic surface 33 of piston portion 32. Shortly before the timing at which the injection event is desired to start, electrical actuator 16 is preferably energized by supplying an excessive current to coil 60. Because the speed at which electrical actuator 16 operates is related to the current level supplied to coil 60, one preferably supplies the maximum available current, which can be substantially higher than an amount of current necessary to cause the armature to move against the action of the spring bias. When sufficient magnetic flux builds, armature 62 and valve member 42 are pulled upwards until spherical valve surface 52 contacts upper or high pressure seat 50, 150, 250. When this occurs, needle control chamber 37 is fluidly connected to low pressure fuel reservoir 20 via low pressure passage 41, 141, 241. In order for direct control needle valve 11 to lift to its upward open position, fluid must be displaced from needle control chamber 37 toward low pressure reservoir 20. The rate at which direct control needle valve 11 opens is slowed by restricting this flow through cylindrical segment 48, 148, 248. This aids in allowing fuel injector 10 to produce some rate shaping. Shortly before the desired end of an injection event, current to electrical actuator 16 is reduced or terminated to a level that allows spring 67 to push armature 62 and valve member 42 downward until spherical seat 53 comes in contact with low pressure seat 51, 151, 251. When this occurs, high pressure fluid originating in nozzle supply passage 24 flows through high pressure passage 40, 140, 240 past high pressure seat 50, 150, 250 and into needle control chamber 37. The rate at which pressure builds in needle control chamber 37 and hence the response time from when current is terminated until direct control needle valve 11 moves toward its closed position can be influenced by appropriately sizing cylindrical segment 47, 147, or the combined flow area of cylindrical segments 247 and 248.
In order to produce fuel injectors 10 that behave consistently, the present invention preferably includes a structure for three way valve 15 that alleviates some of the problems that have plagued past valves. By including flow restrictions (cylindrical segments 47, 147, 247 and 48, 148, 248) away from valve seats 50, 150, 250 and 51, 151, 251, respectively fluid flow forces that can interfere with movement of the valve member 42 are reduced since the pressure differentials often associated with valves are moved away from the valve seats. Furthermore, by locating these flow restrictions in the valve lift spacer 44 (
Another feature of the three way valve 15 of the present invention that can provide for more consistent performance includes the use of a valve lift spacer as a category part. In other words, in order for consistency to be maintained, the valve travel distance from one valve to another should be made as consistent as possible. In the case of the present valve, this is accomplished by choosing a valve lift spacer for each individual valve with a thickness that results in a relatively uniform travel distance from one valve to another. In other words, each valve should have relatively uniform travel distances, but this is accomplished by employing valve lift spacers of a variety of thicknesses in each of the different valves. In the case of the present invention, the valve travel distance is preferably on the order of about 30 microns, or between 25 and 35 microns. In any event, the strategy of the present invention can be employed to reliably produce valves with consistent lifts less than about 50 microns. This is accomplished by grouping valve lift spacers in a plurality of different thickness groups. Preferably, each of these groups contain valve lift spacers of a specific predetermined thickness plus or minus about three microns.
Another strategy employed by the present invention in order to improve response time includes defining the needle control chamber, which is referred to in the claims as the “third passage”, at least in part with volume reducing features. Ordinarily, this will be accomplished by paying attention to machining the various components that make up needle control chamber 37 in order to reduce its volume. By reducing its volume, it can respond to pressure changes more quickly. For instance, in the present invention, this strategy is employed, for example, by making the vertical portion of needle control chamber 37 only extend a portion of the way into valve lift spacer 44. Thus, the top surface of this segment could be considered a volume reducing surface feature.
Those skilled in the art will appreciate that leakage through the valve, especially during fuel injection events, is generally undesirable. Fluid leakage is generally reduced by relying upon a three way valve as in the present invention instead of a two way valve that relies upon leakage to produce its pressure changes as in some other known needle control strategies. In addition, the embodiments of
Those skilled in the art will appreciate that that various modifications could be made to the illustrated embodiment without departing from the intended scope of the present invention. For instance, the third passage (needle control chamber 37) need not necessarily be a closed volume in another application of the present invention. Thus, those skilled in the art will appreciate the other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.
