Patent Application
20080315009
The present disclosure relates generally to electronically controlled fuel injectors, and more particularly to pressure assisted needle control in fuel injectors that cycle through high and low pressure states during and between injection events, respectively.
Over the years, cam actuated fuel injectors have become increasingly complex in a search for ever expanding performance capabilities. The same is true for other types of fuel injectors including hydraulically actuated and common rail injectors with admission valves. In general, a fuel injection system with a broader range of capabilities is able to increase engine performance while at the same time reducing undesirable exhaust emissions, including particulate matter, unburned hydrocarbons, NOx, etc. One of the first innovations in improving the capabilities of cam actuated fuel injectors was to include an electronically controlled spill valve. This innovation is shown in many prior art references and allowed for some independence in injection timing from that dictated by a rotating cam lobe whose position was generally fixed with respect to the engine's crank shaft. Much later, a newer innovation was included that provided direct control over the injector's needle valve, to open and close the nozzle outlets at a selected timing that was somewhat independent of the pressurized state of the fuel injector.
For instance, co-owned U.S. Pat. No. 5,551,398 to Gibson et al. teaches a cam actuated fuel injector with electronic control over both pressurization via an electronically controlled spill valve and electronic control over injection timing via a separate needle control valve. Directly controlled fuel injectors generally have a needle valve that includes a closing hydraulic surface exposed to fluid pressure in a needle control chamber. A separate electronically controlled needle control valve can be actuated or deactuated to change the pressure conditions in the needle control chamber. When pressure is high in the needle control chamber, the needle stays in, or moves toward, its closed position. When pressure is low in the needle control chamber, the needle will lift to its open position, provided that fuel in the injector is above a needle valve opening pressure that can overcome a spring bias tending to hold the needle valve member in its closed position. This reference teaches a typical aspect of the conventional wisdom with regard to directly controlling needle valves in that steps are taken to minimize the volume of the needle control chamber in order to increase fluid tightness in the control circuit and hasten the needle's response to the control valve's movement. In other words, because fuel is not incompressible, there must inherently be some delay when raising the pressure in the needle control chamber to compress the fluid therein. As a consequence of this volume minimizing strategy, the needle's biasing spring must often be located at a different location outside of the needle control chamber. While the fuel injector taught in this reference shows considerable promise, it includes an increased complexity and part count in order to produce its superior performance.
Another cam actuated fuel injector is taught in U.S. Pat. No. 5,893,350 to Timms. This reference teaches the use of a single electrical actuator to control both pressurization through a spill valve and needle control via a needle control valve. While this fuel injector deletes one electrical actuator, it inherently couples injection timing to fuel pressurization and also suffers from an inability to do substantial end of injection rate shaping, which is more recently becoming recognized as a means by which emissions can be further reduced. In other words, this injector shows little ability to control the fuel pressure at the timing in which the needle valve closes at the end of an injection event.
The present disclosure is directed to an improved compromise between cost, complexity and part count on one hand and performance capabilities on the other hand.
In one aspect, a fuel injector includes an injector body with a needle valve seat and defines a nozzle chamber, a single nozzle outlet set and a needle control chamber. A one-piece needle valve member is positioned in the injector body and is moveable between a closed position in contact with the needle valve seat to close the single nozzle outlet set, and an open position out of contact with the needle valve seat to open the single nozzle outlet set. The one-piece needle valve member includes a closing hydraulic surface exposed to fluid pressure in the needle control chamber. The one piece needle valve member has an effective opening hydraulic surface area in its open position that is equal to an effective area of the closing hydraulic surface. A biasing spring is positioned in the needle control chamber and is operably coupled to bias the one-piece needle valve member toward its closed position. An electronically controlled pressure control valve is attached to the injector body and has a first position in which the nozzle chamber is fluidly connected to a spill passage, and a second position in which the nozzle chamber is closed to the spill passage. An electronically controlled needle control valve is attached to the injector body and has a first position in which the needle control chamber is fluidly connected to a low pressure passage, and a second position in which the needle control chamber is closed to the low pressure passage. First and second electrical actuators are attached to the injector body and are operably coupled to actuate the electronically controlled pressure control valve and the electronically controlled needle control valve, respectively.
Referring to
Fuel pressurization chamber 16 is fluidly connected to a nozzle chamber 28 via a nozzle supply passage 27. A one piece needle valve member 40 is partially positioned in nozzle chamber 28, and is biased downward into contact with needle valve seat 30 to close to single nozzle outlet set 29 via a biasing spring 70. One piece needle valve member 40 is formed or machined from a single solid metallic blank to include a uniform diameter guide portion 43 that separates a closing hydraulic surface 59 from a first opening hydraulic surface 41. Those skilled in the art will appreciate that single nozzle outlet set 29 could include one or more nozzle outlets, but all of the nozzle outlets belong to a single set. In other words, the present disclosure is not believed applicable to fuel injectors having two or more separate sets of nozzle outlets that are opened and closed via two or more needle valve members. Those skilled in the art will appreciate that first opening hydraulic surface 41 includes an annular ledge portion where the diameter of the needle valve member changes as well as including a portion of a slanted or rounded valve surface that is located above needle valve seat 30 when the needle valve member is in its closed position. Guide portion 43 has a relatively close clearance and a sufficient length to fluidly isolate needle control chamber 56 from nozzle chamber 28. Needle valve member 40 is normally biased downward such that it comes in contact with needle valve seat 30 to close nozzle outlet set 29. However, when in its upward open position, the needle valve member includes a second opening hydraulic surface 42 that is then exposed to fluid pressure in nozzle chamber 28. In other words, second opening hydraulic surface 42 consists substantially of that portion of needle valve member 43 that is at and below seat 30 when the needle valve member is in its downward closed position, as shown.
When needle valve member 40 is in its upward open position, it is hydraulically balanced, in that the effective hydraulic surface area of closing hydraulic surface 59 is equal to the combined affective surface areas of first and second opening hydraulic surfaces 41 and 42. In other words, guide portion 43 has a uniform diameter along its length. In order to establish the valve opening pressure for needle valve member 40, biasing spring 70 is chosen with a predetermined pre-load that is trimmed using a category part VOP spacer 65, which has a relatively large clearance to permit fluid displacement around its perimeter. It might alternatively include through holes to facilitate this fluid displacement. The maximum lift of needle valve member 40 is determined by needle stop component 66 that sits atop VOP spacer 65. When the needle valve member 40 lifts to its open position, needle stop component 66 comes in contact with the injector body component positioned above it.
The opening and closing of needle valve member 40 is controlled by a needle control valve 50, which is operably coupled to be actuated by a second electrical actuator 51 via movement of an armature 52. A needle control valve member 53 is trapped to move between a high pressure seat 54 and a low pressure seat 55, but is biased downward into contact with low pressure seat 55 via a biasing spring 60. Needle control valve member 53 is attached to move with, or is otherwise operably coupled to, armature 52 in a conventional manner. When needle control valve member 53 is in the downward position, as shown, needle control chamber 56 is fluidly connected to nozzle chamber 27 via pressure communication passage 58 and high pressure passage 57. Thus, when needle valve member 53, its diameter φ1 above high pressure seat 54 is preferably of a larger diameter than its lower portion below seat 54 indicated by diameter φ2.
Referring now to
For example, in case of solenoid 51 failure, the valve member 53 will lift and open at some pressure that prevents over pressurization within the injector 10. Spring 60 preload can be adjusted to set the pop-off pressure. Therefore, valve member 53 has a net opening hydraulic surface when in its downward position, as in
Referring now to
Referring now to
Referring now to
All of the injectors according to the present disclosure can find potential application in reducing undesirable emissions from compression ignition engines. In addition, this can be accomplished with a reduced part count and complexity over other directly controlled fuel injectors of the prior art. In particular, the present disclosure reduces complexity in the area of the needle valve member by eliminating a needle piston (or a needle with a stepped guide region), which is common in prior art fuel injectors, and serves as a means of magnifying the pressure closing force on the needle valve member. In addition, the machining structure of the components in the vicinity of the needle valve member can be simplified over other similar fuel injectors that seek to minimize the fluid volume of the needle control chamber by positioning the needle's biasing spring elsewhere in the injector body. In other words, all versions of the present disclosure include a one piece needle valve member that is hydraulically balanced when in its upward open position, and include a needle biasing spring that is positioned in the needle control chamber, rather than elsewhere as per the conventional wisdom. While this structure can result in some lessening of fluid tightness with regard to the pressurizing and de-pressurizing the needle control chamber, the decrease in part count and complexity coupled with the still available superior performance and controllability options render the present disclosure more attractive over more expensive and more complex fuel injectors known in the art.
All of the illustrated fuel injectors can perform substantially similarly, but differ from one another in the use of either a two way or a three way needle control valve, and also differ from one another as to whether the needle control valve actuator needs to be energized or de-energized to control injection timing. In other words, an injection event in one of the injectors might require energizing the second electrical actuator, whereas the same control movement might require de-energizing the second electrical actuator in a different embodiment. Although the present disclosure has been illustrated in the context of a cam actuated electronically controlled fuel injector, those skilled in the art will appreciate that the present disclosure finds potential application in any fuel injector that undergoes cyclic high pressure and low pressure states during and between injection events, respectively. Such injectors include, but are not limited to hydraulically actuated fuel injectors that use fluid pressure to move a plunger, and common rail fuel injectors equipped with an admission valve that fluidly connects and disconnects the internal plumbing of the fuel injector to the high pressure common rail to perform an injection event. Thus, in the case of an admission valve alternative to the illustrated embodiments, the equivalent of closing the spill passage would be to open the admission valve to raise fuel pressure in the fuel injector.
By utilizing a one piece needle valve member that is hydraulically balanced when in its upward open position, the present disclosure allows for some control over the closure rate of the nozzle outlet set toward the end of an injection event. In other words, the closure rate of the needle valve member in most conditions will be based upon the preload of the needle valve member's biasing spring whereas the prior art closure rate is often coupled to the fuel pressure in the fuel injector, which can be a function of engine speed.
Because the pressurization and timing aspects of the injector control are somewhat independent of one another via separate first and second electrical actuators, the present disclosure can achieve some front and back end rate shaping control to advantageously allow for a reduction in undesirable emissions at certain engine operating conditions. While the base valve opening pressure of the needle valve member is set via the preload on the needle biasing spring, the present disclosure allows for control over the valve opening pressure to be anywhere between the base valve opening pressure and the maximum injection pressure. If it is desired for the needle valve member to open at the base valve opening pressure, the needle control chamber 56 is fluidly connected to the low pressure passage by a suitable positioning of the needle control valve prior to energizing the first electrical actuator to close the spill passage 18 to pressurize fuel in the fuel injector. If it is desired to raise the valve opening pressure above the base valve opening pressure, the needle control chamber can be closed to the low pressure passage while pressure is building in the fuel injector due to closure of the spill passage via energization of the first electrical actuator. When the pressure in the fuel injector reaches a desired level, the needle control chamber can be opened to the low pressure passage to relieve pressure on the closing hydraulic surface of the needle valve member and allow the same to lift upward to its open position to commence the spraying of fuel into the combustion space. Thus, the relative timing in actuating the first and second electrical actuators can not only affect the valve opening pressure at the beginning of an injection event but also be exploited to affect the initial injection rate depending upon the engine operating condition to further lower undesirable exhaust emissions. Those skilled in the art will appreciate that the ability to control fuel pressure at the beginning and end of the injection event is equally applicable to other types of fuel injectors that raise and lower fuel pressure at the beginning and end of injection events, respectively. For instance, hydraulically actuated fuel injectors raise fuel pressure by opening the fuel injector to a high pressure actuation fluid supply, and reduce fuel pressure at the end of an injection event by closing that fluid connection to the high pressure actuation fluid supply. Likewise, a common rail fuel injector equipped with an admission valve raises fuel pressure in the injector by opening the admission valve and reduces fuel pressure by closing the same, and opening a spill passage, at the end of an injection event.
The present disclosure has the ability to allow the injection event to be initiated at a selected fuel pressure between a base valve opening pressure and a maximum injection pressure, and also allows the injection event to be ended at a selected fuel pressure between the maximum injection pressure and the base valve closing pressure. Recalling that the base valve opening pressure and the base valve closing pressure are based upon the preload of the needle biasing spring 70. Because the needle valve member is hydraulically neutral or balanced when in its upward open position, the closure rate of the needle valve member can also be adjusted by selecting a particular spring preload since the hydraulic forces are balanced on the needle when the spring alone pushes the needle toward its closed position to end an injection event. In addition, by selecting a particular spring preload, the base valve opening pressure can be selected along with affecting the opening rate of the needle valve member to allow the fuel injector to perform front end rate shaping by affecting the opening rate of the needle valve member toward the beginning of an injection event. Apart from the ability of the fuel injectors according to the present disclosure to selectively control front end and back end rate shaping via selecting a particular spring preload along with relative timing in the actuation and de-actuation of the first and second electrical actuators, the fuel injectors of the present disclosure can also produce split injections. This is accomplished by moving the needle control valve from a position in which the needle control chamber is fluidly connected to a low pressure passage, closing that fluid connection, and then reopening the fluid connection between the needle control chamber and the low pressure passage while fuel pressure in the injector is above the base valve opening pressure. This is accomplished by maintaining the first electrical actuator energized to maintain the spill passage closed while the needle control valve is moved back and forth between positions. In other words, split injections are normally accomplished by maintaining fuel pressure in the injector high while moving the needle valve member via back and forth movement of the needle control valve to relieve, apply and then again relieve pressure on the closing hydraulic surface of the needle valve member. When the dwell between injection events is longer, the present disclosure also allows for some rate shaping affects at least in part by moving the pressure control valve alone or at some relative timing respected to moving the needle control valve to produce the pressure changing effects described above.
Fuel injectors according to the present disclosure can be thought of as having at least three different nozzle closure modes. In a first mode, the needle control chamber is maintained opened to the low pressure passage and the needle moves toward its closed position when fuel pressure drops below a valve closing pressure after the first electrical actuator has been de-energized to open the spill passage and lower fuel pressure in the injector. Thus, in this first closure mode, the needle behaves much like a simple spring biased check valve associated with many fuel injectors known in the art. In a second closure mode, the pressure forces on the needle valve member are hydraulically balanced by closing the needle control chamber to the low pressure passage. When this is done before the first electrical actuator has been de-energized to open the spill passage and lower fuel pressure, the fuel injection event can be relatively abruptly ended while fuel pressure remains high. Although the needle valve member is hydraulically balanced, it will move toward its closed position under the action of the biasing spring 70 substantially alone. In a third closure mode, the needle valve member is hydraulically balanced after the first electrical actuator has been energized to open the spill passage to lower fuel pressure. Thus, in the third closure mode, fuel pressure in the injector is dropping, but is still above the base valve closing pressure determined by the hydraulic surface areas and preload of biasing spring 70. Thus, in the third closure mode, the needle can be made to move toward its closed position at a desired timing as fuel pressure is dropping due to the opening of the spill passage. In other fuel injectors, the fuel pressure drop is accomplished by moving an admission valve toward a closed position in the case of the common rail fuel injector while simultaneously connecting the injector to a low pressure return passage, or closing an actuation fluid valve in the case of a hydraulically actuated fuel injection. Depending upon the particular engine operating condition, one of these closure modes can be selected to reduce undesirable emission at that particular operating condition.
Thus, the fuel injectors of the present disclosure have performance capabilities approaching and sometimes exceeding more complicated fuel injectors with direct pressure control over the needle valve member. In those fuel injectors, the opening and closure rates of the needle valve member are more coupled to the fuel pressure existing in the injector at that time than they are to the selection of spring preloads as in the present disclosure. Thus, the present disclosure not only allows for the elimination of some costly machining and a reduction in part count, but also allows for a more expanded range of capabilities with only a slight potential compromise in needle control fluid tightness over some fuel injectors with extremely small volume needle control chambers. However, this aspect of the disclosure can also be affected by choosing a VOP spacer and needle stop component that occupy much of the volume in the needle control chamber so that the fuel injectors of the present disclosure can approach the fluid tightness and minute timing control capabilities of some prior art fuel injectors with direct pressure control over the needle valve member movement. The present disclosure also subtly disassociates an aspect of the control circuit from engine speed. In many cases, the fuel pressure (i.e. control pressure) within the injector will be at least indirectly related to engine speed. In other words, at high engine speeds, a tappet is driven faster and so higher fuel pressures are achieved. When the engine is operating slower, the tappet is driven at a slower rate and results in lower fuel pressures. In many prior art fuel injectors, the needle control aspect of the injector is controlled via the fuel pressure, and hence the rates at which the needle moves toward its open and closed position is indirectly related to engine speed. The present disclosure, on the other hand, relies primarily. on a spring pre-load in order to set opening and closure rates of the needle valve member, even though the fuel injector experiences fuel pressures that are a function of engine speed as in many prior art fuel injectors.
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. For instance, although the disclosure has been illustrated with solenoid actuators, other electrical actuators such as piezo actuators, could be substituted. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
This is a divisional of U.S. patent application Ser. No. 10/792,169, filed Mar. 3, 2004 with the same title.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10792169 | Mar 2004 | US |
| Child | 12229082 | US |
