Patent Application
20080203347
Exemplary embodiments of the present invention generally relate to fuel injection systems for internal combustion engines. More particularly, exemplary embodiments of the present invention relate to control valves for controlling the pressure and/or flow of a fluid delivered to injector valves in an engine.
For many decades, gasoline internal combustion engines employed a carburetor to mix fuel with incoming air. The resulting air/fuel mixture was distributed through an intake manifold and mechanical intake valves to each of the engine cylinders. For most engines, the carburetion systems have been replaced by multi-port fuel injection systems. In a multi-port fuel injection system, there is a separate fuel injector valve that injects gasoline under pressure into the intake port at each cylinder where the gasoline mixes with air flowing into the cylinder. Even with multi-port fuel injection, however, there are limits to the fuel supply response and combustion control that can be achieved.
More recently, a third approach to supplying fuel into the engine cylinders has been devised. This technique, known as “gasoline direct injection” or “GDI”, injects the fuel directly into the combustion cylinder through a port that is separate from the air inlet passage. Thus, the fuel does not premix with the incoming air, thereby allowing more precise control of the amount of fuel supplied to the cylinder and the point during the piston stroke at which the fuel is injected. GDI systems provide higher power output and efficiency with lower fuel consumption.
Specifically, when the engine operates at higher speeds or higher loads, fuel injection occurs during the intake stroke to optimize combustion under those conditions. During normal driving conditions, fuel injection happens at a latter stage of the compression stroke and provides an ultra-lean air to fuel ratio for relatively low fuel consumption. Because the fuel may be injected while high compression pressure exists in the cylinder, gasoline direct injection requires that the fuel be supplied to the injector valve at a very high pressure. It has also been determined that increasing the injection pressure has a great impact on fuel economy and emissions through its effects on fuel “atomization,” that is, delivery of the fuel in such a way that it easily mixes with the air in the chamber and penetrates the compressed air in the combustion chamber.
The most important characteristics of a direct injection system are high-pressure generation and supply, exact control of injection timing and injected fuel quantity, and thorough fuel dispersion and mixture preparation together with the in-cylinder charge motion. In particular, the desire to increase pressure injection pressures and thereby transfer the quantity of fuel into the cylinder within more limited time periods has had a major influence on system design. Modern fuel injection pressures range from 135-200 Bars (2000 to 2900 Psi) and are expected to continue to increase. Thus, the fuel system must be capable of handling these high pressures while still providing accurate precise injection timing and metering.
Electromechanical actuators are used in vehicle applications to activate valves that control the flow and/or pressure of supplied fluid through one or more fluid passages. In many systems, such a valve will provide pressure or flow output control that is proportional to an input electrical signal that is provided to the electromechanical actuator. The signal is provided by an engine computer that determines the optimum valve timing based on the operating conditions occurring at any given point and time. These conditions can include, for example, engine speed, engine load, the amount of fuel required, and other factors, particularly the angle of the cam when the fuel is supplied by a piston pump that is directly operated by a camshaft.
In more specialized systems, the actuator and valve design must be customized to meet the needs of the application such as, for instance, the very fast switching requirements and tight variation tolerances in response time of the high pressure injection cycle in a gas direct injection system. Thus, the control valve is a critical element in the proper operation of the engine. The control valve must adequately manage the magnetic, mechanical, and hydraulic forces to produce the desired fuel pressure and/or flow rate. Factors such as friction, hydraulic stiction, component misalignment, under-over damping, inertia, and mass, among others, should be minimized to reduce actuator performance variation and enhance part reliability.
Accordingly, it is desirable to provide a flow control valve for a fuel system that is capable of handling these high pressures while still providing extremely fast, accurate, and precise regulation of injection timing and metering.
In accordance with exemplary embodiments of the present invention, a control valve for a gas direct injection fuel delivery system is provided. The control valve comprises a valve body, a poppet movably received within the valve body, and an actuator disposed within the valve body. The valve body has a first fluid path, a second fluid path, and a valve seat providing fluid communication therebetween. The poppet is capable of movement between a first position and a second position. When disposed in the first position, the poppet seals the valve seat to block fluid communication between the first fluid path and the second fluid path. The poppet permits fluid communication between the first fluid path and the second fluid path as the poppet moves from the first position to the second position. The poppet is configured so that a pressure in the first fluid path produces a force that tends to move the poppet toward the second position and a pressure in the second fluid path produces a force that tends to move the poppet toward the first position. The actuator is configured to transition between an activated and a de-activated state. The actuator prevents the poppet from being disposed in the first position when in the de-activated state and the pressure in the second fluid path does not exceed the pressure in the first fluid path by at least a first pressure differential. The actuator permits the poppet to be disposed in the first position when in the activated state.
a and 7b are side views of an exemplary poppet;
Exemplary embodiments of the present invention illustrated in the attached drawings relate to control valves for controlling the flow and/or pressure of fluid through a fluid path during a high-pressure fluid supply pump's fuel metering cycle. The description in the following specification relates to the exemplary embodiments illustrated in the attached drawings, but it is to be understood that the present invention is not limited to the specific embodiments disclosed herein and may assume various alternative orientations and applications. The specific devices and processes illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts disclosed herein. Therefore, it should be understood that specific dimensions, orientations, applications, and other physical characteristics relating to the embodiments disclosed herein are not considered to be limiting.
With initial reference to
This latter supply pump 6 can then generate a force to furnish the gasoline under high pressure (for example, 120-250 bar) through a pump outlet line 7 that is joined to the pump chamber to a high-pressure common fuel rail 8, which feeds a plurality of individual fuel injectors 11 for the engine cylinders. Common rail 8 is open only when the supply pressure is above the high operating pressure of the rail, as determined by a high-pressure sensor 9. A standard mechanical pressure relief valve 13 is provided in parallel with supply pump 6 to relieve any dangerously high pressure from occurring in pump outlet line 7 (for instance, if common rail 8 is inadvertently closed while the pump is running). Relief valve 13 can be set below the maximum pressure rating that the piping, tubing, or any other components can withstand.
In accordance with an exemplary embodiment of the present invention, a control valve 10 controls fluid communication between low-pressure fuel tank 3 and the chamber of the supply pump 6, and manages the instantaneous outlet pressure of the supply pump by diverting and modulating the pressure of the discharge gasoline flow in pump inlet and outlet lines 5, 7. Specifically, control valve 10 remains open so that fuel can be fed to the chamber of supply pump 6 and to relieve the high pressure at pump outlet line 7 by returning the gasoline to lower pressure inlet line 5 for the pump. Control valve 10 closes so that supply pump 6 can pressurize fuel within the pump chamber and delivery fuel to injectors 11 at precise, adjustable flow rates. In the example in which supply pump 6 is driven by a piston, when the piston moves upward (the discharge stroke), the mechanical energy of the piston transfers pressure energy to the fuel in the supply chamber so that the fuel is pressurized. This pressurized fuel, in addition to forcing common rail 8 to open, can force control valve 10 to remain closed while being delivered to the common rail.
Therefore, control valve 10 is normally open and closes when an electrical actuator is energized or when needed to create the desired loading, spilling, and pumping flow conditions of the GDI system, as will be described in greater detail in the exemplary embodiments presented below. As with supply pump 6, the operation of control valve 10 can be synchronized with the camshaft so that the valve can be activated according to the angle of the cam and the desired flow and/or pressure of fuel being delivered to the injectors.
The timing and duration of electrical activation and the operation of the supply pump are controlled by the engine management system that includes an electronic control unit (ECU) (not shown) for controlling the flow of gasoline through control valve 10. The ECU, which can comprise a microprocessor to provide real-time processing, monitors engine-operating parameters via various sensors and interprets these parameters to calculate the appropriate amount of fuel to be injected for each individual injection event. The optimum amount of injected fuel can depend on conditions such as engine and ambient temperatures, engine speed and workload, and exhaust gas circulation. The timing of fuel injection can then depend on the amount of fuel desired for delivery and, in the example of a piston-driven supply pump, the current angle of the cam operating on the piston, which determines the volume of fuel that the supply chamber can hold at a given moment. The ECU also electrically operates the fuel injectors 11, which act as fuel-dispensing nozzles to inject fuel directly into the engine's air stream.
During steady state operation above the idle speed of the engine, the fuel injections from exemplary GDI system 1 into the cylinders are discrete events, beginning at regular time intervals and having substantially identical duration. During each injection event, control valve 10 will close so that pressure in pump outlet line 7 rises so that fuel can be supplied at the desired high-pressure level (for example, 200 bar) to fuel injectors 11. Between fuel injection events, control valve 9 will open so that fuel can be fed from fuel tank 3 to load supply pump 6 for the next injection event. Control valve 10 will also remain open between loading pumping so that fuel can be expelled from the supply chamber through the valve back to fuel line 4 and return through the valve to the supply chamber during rotation of the camshaft. While the injection event, control valve activation, and high-pressure delivery of fuel by the supply pump are all substantially controlled by the ECU, they are not synchronized with one another and do not occur exactly simultaneously, as will be described with reference to the exemplary embodiments below. U.S. Pat. No. 6,494,182, the contents of which are incorporated herein by reference thereto, describes the operation of a type of gasoline direct injection system that can utilize the exemplary control valves described below.
With reference now to
A longitudinal bore 16 extends through the respective bodies of valve stem 20 and end flange 12 jointly to provide fluid communication between an outlet fluid passage 18 and an inlet fluid passage 22. Bore 16 includes a region 16a of enlarged diameter, a region 16b of reduced diameter, and a region 16c of further reduced diameter. An outlet port 24 is formed as an open end of bore region 16c at end flange 12. Outlet port 24 that communicates with outlet passage 18, and a transverse inlet port 26 opens into bore 26 to communicate with inlet passage 22, which extends transversely into the bore. Thus, outlet passage 18 is configured to extend between the inlet and outlet lines of a fuel supply pump and a control chamber 32 within bore region 16c, while inlet passage 22 is configured to extend transversely from bore region 16b to connect to a fuel inlet line carrying from the fuel tank of an engine.
A valve seat 28 that is integral formed with valve stem 20 proximate to inlet passage 22 extends transversely from the valve stem into the bore between regions 16b and 16c. Valve seat 28 has an orifice 30 that opens into control chamber 32, which is located between outlet passage 18 and inlet passage 22 within bore region 16c. A valve poppet 34 is slidably received within control chamber 32 and moves with respect to valve seat 28 and a valve stop 46 between outlet passage 18 and inlet passage 22.
In the present exemplary embodiment, poppet 34 is cup-shaped with a generally round disk 36 and a generally annular sidewall 38 extending longitudinally therefrom, as illustrated in
A return spring 42 is also received within control chamber 32. An upper end 41 of return spring 42 engages bottom surface 35 of poppet disk 36, and an opposing lower end 43 of the return spring engages valve stem 20 at end flange 12. Return spring 42 is configured to bias poppet 34 toward a closed position in which the poppet abuts valve seat 28, as illustrated in
When poppet 34 is moved away from valve seat 28, fluid communication is provided between inlet passage 22 and control chamber 32, which is on a remote side of poppet 34 from valve seat 28 and in fluid communication with outlet passage 18. Thus, outlet passage 18 moves into and out of fluid communication with inlet passage 22 as poppet 34 slides within bore region 16c. As illustrated in
On the opposite side of poppet 34 from control chamber 32, a rod-shaped valve element 48 is slidably received within bore 16 of the valve stem 20. The diameter of the portion valve element 48 within bore region 16b is substantially the same as region 16b so that movement of the valve element can be guided within bore 16. The diameter of valve element 48 tapers from an exterior end 47 within bore region 16a to a substantially cylindrical interior end 49 within bore region 16b having a tip or nib 50 that extends toward poppet 34 through valve orifice 30. In exemplary embodiments, the distances that nib 50 extends past valve orifice 30, or the stroke of poppet 34, can be designed according to the dimensions of the control valve and the length of valve element 48.
Exterior end 49 of valve element 48 is mechanically joined, such as by brazing or welding for example, within a central aperture of an armature 52 that is slidably received within bore region 16a. Bore region 16a and armature 52 together define a clearance gap for wider end 49 of valve element 48 that serves to limit the extent of movement of the valve element within the bore, as will be described below. In exemplary embodiments, the components of control valve 10 can be configured to minimize the longitudinal length of this clearance gap to provide the valve with a very fast response time.
As illustrated in
Armature 52 is located proximate to an electrical actuator 54, which operates control valve 10. Actuator 54 comprises a solenoid coil 56 wound on a non-magnetic bobbin 58, which can be formed of a plastic in exemplary embodiments. In exemplary embodiments, solenoid coil 56 can be sealed off from fluid communication within the control valve to improve the body leakage performance and reduce hydro-carbon emissions carried by fuel vapors. A metal pilot plate 62 extends around valve stem 20 and closes the open end of actuator 54 to complete the magnetic circuit. Armature 52, which projects from bobbin 58 into bore region 16a, slidably moves within the bobbin, and valve element 48 moves jointly with the armature within bore region 16a.
A plastic enclosure 60 is molded around the coil and bobbin assembly and projects outwardly from there. An electrical connector 66 is formed at the remote end of the projecting section of enclosure 60. Electrical connector 66 has a pair of terminals that are connected to solenoid coil 56 by wires (not visible). A controller (not shown) that governs engine operation is coupled to electrical connector 66. To drive control valve 10, the controller produces a pulse width modulated (PWM) signal having a duty cycle that is varied to force poppet 34 toward a desired position in valve stem 20 as will be described. Moveable armature 52 is thus able to slide longitudinally within bobbin 58 in response to a magnetic field produced by application of electric current to the solenoid coil 56.
A magnetically conductive outer stop housing 64 is disposed within bobbin 58. Stop housing 64, preferably formed of plastic, has a central aperture 68. A stop spring 70 and a nose 72 are received within central aperture 68, with nose 72 extending therefrom into bore 16 and within an opening in exterior end 47 of valve element 48. When solenoid coil 56 is in its normal de-energized state, stop spring 70 acts to bias nose 72 to force valve element 48 toward control chamber 32 such that nib 50 extends through orifice 30 to engage top surface 37 of disk 36 and push poppet 34 away from valve seat 28 to open control valve 10.
As illustrated in the exemplary embodiment of
As illustrated in
With valve element 48 then no longer biasing poppet 34 away from valve seat 28, the force from return spring 42 can bias the poppet in the opposite direction toward the valve seat and to the closed position. Movement of armature 52 and valve element 48 away from valve seat 20 in this fashion thus permits poppet 34 to abut valve seat 28 and close control passage 44, thereby terminating fluid communication between the outlet passage 18 and inlet passage 22, as illustrated in
Operation of control valve 10 of the present exemplary embodiment during the load, spill, and delivery stages of fuel metering cycle are illustrated in
As described above, when control valve 10 is not being activated by electric current applied to the solenoid actuator 54, stop spring 70 overcomes the weaker force of return spring 42 to actuate valve element 48 to bias poppet 34 away from valve seat 28 and maintain the valve in an open condition. This provides for fluid communication between inlet passage 22 and outlet passage 18 so that fuel can be loaded into the supply pump. With the valve open, fluid from the fuel tank can flow to inlet passage 22 and through control passage 44 and control chamber 32 to outlet passage 22 and into the pump. Additionally, while the extension of valve element 48 pushing poppet 34 away from valve seat 28 is limited by element stop 76, the heightened fluid pressure in inlet passage 22 caused by fuel flow from the fuel tank can act on top surface 37 of disk 36 to disengage the poppet from the valve element and move the poppet further from valve seat 28. In other words, when the pump is loading fuel from the fuel tank, fluid pressure in inlet passage 22 can further compress return spring 42 to move poppet 34 away from valve seat 28 until the force of the return spring counter balances the force produced by the fuel that is loading or until the poppet is stopped by valve stop 46 in a fully opened position. Thus, exemplary control valve 10 provides a poppet over-stroke to permit higher fuel flow rates during fuel loading, as shown in
In exemplary embodiments, poppet 34 can be configured to move further from valve seat 28 and/or more quickly in response to a given amount of fluid pressure in inlet passage 22 by inserting a weaker return spring. Similarly, using a stronger return spring will decrease the distance and/or the rate at which that poppet 34 moves for a given amount of inlet fluid pressure. Thus, in exemplary embodiments, control valve 10 can be configured so that control passage 44 can be maintained at a size that permits the desired fuel flow rate to occur through the valve during fuel loading.
Once the pump has completed a suction stroke and loaded fuel from the fuel tank, it awaits a signal from the ECU instructing it to begin the delivery stage and inject fuel into the cylinders. As discussed, the ECU measures factors such as engine load, calculates the amount of fuel needed, and sends a signal instructing the supply pump to begin pumping fuel at the precise moment the angle of the cam operating on the supply pump causes the supply chamber to have the desired volume of fuel for the next delivery. Nevertheless, unless the full piston stroke of the supply pump will be needed for the next delivery, some fuel from the chamber must be spilled back through the valve to the fuel inlet line during the discharge stroke of the supply pump. Therefore, control valve 10 must remain open during this spill stage until the supply pump is instructed to begin pumping. This is accomplished by keeping solenoid coil 56 de-energized during the spill stage. As discussed above, when control valve 10 is not being activated by electric current applied to the solenoid actuator 54, stop spring 70 overcomes the weaker force of return spring 42 to actuate valve element 48 to bias poppet 34 away from valve seat 28 and maintain the valve in an open condition. Thus, so long as the pressure caused by return flow from the supply chamber is not high enough to overcome the resistance of stop spring 70, control valve 10 remains open and the supply pump can discharge fuel through control passage 44 to the fuel inlet line until the supply chamber contains the desired amount of fuel for delivery in the delivery stage, as illustrated in
When signaled by the ECU, the supply pump must rapidly transition into the delivery of high-pressure fuel into the cylinders. Thus, because control passage 44 creates a fluid path that reduces the pressure within control chamber 32, the valve must rapidly close the control passage so that the pump can supply high-pressure fuel flow to the engine. To close the valve, the ECU sends a signal to controller 66 to energize solenoid coil 56, which attracts armature 52 toward stop housing 64 and retracts valve element 48 from poppet 34. The duration of the pulse width sent from controller 66 to retract valve element 48 need not extend beyond the moment the supply pump begins delivery fuel to the common rail at the desired high-pressure level. When nib 50 of valve element 48 no longer projects through orifice 30 and past valve seat 28, the force of return spring 42 acts to bias poppet 34 against the valve seat to terminate fluid flow between inlet passage 22 and the control chamber 32, as illustrated in
In exemplary embodiments, valve control 10 need not be required to wait for solenoid coil 56 to be energized before the switch from the spill stage to the delivery stage is complete. Rather, as the pump beings to push fuel flow before solenoid coil 56 is fully energized, once the pump begins pushing fuel flow at a sufficiently high pressure, the fluid pressure in control chamber 32, in combination with force provided by return spring 42, can act on bottom surface 35 of disk 36 to overcome the strength of stop spring 70 and force the poppet to engage valve seat 28. In this exemplary embodiment, the high-pressure pumping acts to close the valve and terminate communication between inlet passage 18 and control chamber 32 before solenoid actuator 54 has been fully energized.
The present exemplary embodiment allows the transition period to the delivery stage to be achieved with much tighter tolerances. Moreover, control valve 10 will remain closed to maintain fuel pressurization until the delivery stage in completed even if solenoid coil 56 is de-energized during the injection event, as the fuel pressure within control chamber 32 during will combine with the force of return spring 42 to overcome the force of stop spring 70 and prevent poppet 34 from being moved away from valve seat 28. Thus, the valve will be maintained in the closed state until fuel is no longer being supplied by the pump at a sufficiently high-pressure level.
When the pump has completed the delivery stage and is no longer pushing fuel into the cylinders, the metering cycle is ready to transition back to the load stage. The unique design of valve control 10 also allows for a rapid switch from the delivery stage to the load stage, even where solenoid coil 56 is not fully de-energized at the outset of the load stage. Specifically, even if solenoid actuator 54 is activated and control passage 44 is closed due to the force of return spring 42, the fuel tank can begin feeding fuel through the fuel inlet line into inlet passage 22, and when the fluid pressure in the inlet passage creates a force acting on top surface 37 of disk 36 that is sufficient to overcome the force exerted by return spring 42 on bottom surface 35, the resultant net force on poppet 34 will urge it to move away from valve seat 28. Thus, the valve will open to permit fuel from the fuel tank to flow to inlet passage 22 and through control passage 44 and control chamber 32 to outlet passage 18 and into the pump, even if solenoid coil 56 has not yet been de-energized.
Therefore, the present exemplary control valve 10 has particular use in regulating fuel pressure and flow rate in a GDI fuel system for an internal combustion engine in which the timing and amount of fuel delivery requires precise control and can vary according to operating conditions (for example, the exemplary fuel injection system 1 of
The metering cycle of the control valve of the present exemplary embodiment is illustrated graphically in
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. For example, in accordance with an exemplary embodiment of the present invention, the interface can be accomplished by engaging a spherical flare on the outer end of an end cone assembly with a spherical end of a conduit tube. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. For example, in accordance with another exemplary embodiment of the present invention, the interface at the junction between a conduit and a spherical component can further comprise a flex-joint. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the present application.
