Patent Application
20100096473
The present disclosure relates generally to mechanically actuated electronically controlled fuel injection systems, and more particularly to a variable flow rate valve for a direct operated needle valve, such as to achieve small close coupled post injections.
Mechanically actuated electronically controlled unit injectors (MEUI) have seen great success in compression ignition engines for many years. In recent years, MEUI injectors have acquired additional control capabilities via a first electrical actuator associated with a spill valve and a second electrical actuator associated with a direct operated needle valve. MEUI fuel injectors are actuated via rotation of a cam, which is typically driven via appropriate gear linkage to an engine's crankshaft. Fuel pressure in the fuel injector will generally remain low between injection events. As the cam lobe begins to move a plunger, fuel is initially displaced at low pressure to a drain via the spill valve for recirculation. When it is desired to increase pressure in the fuel injector to injection pressure levels, the first electrical actuator is energized to close the spill valve. When this is done, pressure quickly begins to rise in the fuel injector because the fuel pumping chamber becomes a closed volume when the spill valve closes. Fuel injection commences by energizing the second electrical actuator to relieve pressure on a closing hydraulic surface associated with the direct operated needle valve. The closing hydraulic surface of the directly operated needle valve is located in a needle control chamber which is alternately connected to the pumping chamber or a low pressure drain by moving a needle control valve with the second electrical actuator. Such a control valve structure is shown, for example, in U.S. Pat. No. 6,889,918. The needle valve can be opened and closed any number of times to create an injection sequence consisting of a plurality of injection events by relieving and then re-applying pressure onto the closing hydraulic surface of the needle valve. These multiple injection sequences have been developed as one strategy for burning the fuel in a manner that reduces the production of undesirable emissions, such as NOx, unburnt hydrocarbons and particulate matter, in order to relax reliance on an exhaust aftertreatment system.
One multiple injection sequence that has shown the ability to reduce undesirable emissions includes a relatively large main injection followed closely by a small post injection. Because the needle valve must inherently be briefly closed between the main injection event and the post-injection event, pressure in the fuel injector may surge due to the continued downward motion of the plunger in response to continued cam rotation. In addition, past experience suggests that conditions within the fuel injector immediately after a main injection event are highly dynamic, unsettled and somewhat unstable, making it difficult to controllably produce a small post injection quantity. If the dwell is too short, the post injection quantity is too variant. If the dwell between the main injection event and the post-injection event is too long, the increased pressure in the fuel injector may undermine the ability to produce small post injection quantities but the more stable environment renders the post injection more controllable. In other words, the longer the dwell, the larger the post injection pressure coupled with greater controllability. Thus, the inherent structure and functioning of MEUI injectors makes it difficult to control fuel pressure during an injection sequence because the fuel pressure is primarily dictated by plunger speed (engine speed) and the flow area of the nozzle outlets, if they are open, but the potentially unstable time period immediately after main injection makes any post injection quantity more variable and less predictable. As expected, the pressure surging problem as well as the shrinking post injection timing window can become more pronounced at higher engine speeds and loads, which may be the operational state at which a closely coupled small post injection is most desirable. The inherent functional limitations of known MEUI systems may prevent small close coupled post injections both in desired quantity and timing relative to the end of the preceding main injection event in order to satisfy ever more stringent emissions regulations.
The present disclosure is directed to overcoming one or more of the problems set forth above.
In one aspect, a fuel injector includes an injector body that defines a nozzle outlet. A cam actuated plunger is slidably positioned in the injector body and is coupled to a tappet extending outside the injector body. A direct control needle valve includes a closing hydraulic surface exposed to fluid pressure in a needle control chamber, and an opening hydraulic surface exposed to fluid pressure in a nozzle chamber. The plunger and the injector to body define a pumping chamber fluidly connected to the nozzle chamber via a nozzle supply passage. A needle control valve is positioned in the injector body and movable between a first position at which the needle control chamber is fluidly connected to a low-pressure passage, and a second position at which the needle control chamber is fluidly connected to the nozzle supply passage. A variable flow rate valve is positioned in a pressure communication passage that extends between the needle control chamber and the needle control valve.
In another aspect, a method of operating a fuel injector includes closing a spill valve while a plunger of the fuel injector is moving in response to rotation of a cam. A needle valve is opened by fluidly connecting the needle control chamber to a low pressure passage via a pressure communication passage. The needle valve is closed by fluidly connecting the needle control chamber to a nozzle supply passage. The opening step includes configuring a variable flow rate valve in a restricted flow configuration, and the closing step includes configuring the variable flow rate valve in an unrestricted flow configuration.
a-f represent graphs of a first electrical actuator control signal, spill valve position, a second electrical actuator control signal, needle control chamber pressure, injection pressure, and injection rate, respectively, versus time for an example main plus post injection sequence according to the present disclosure, and with a comparison to a predecessor fuel injector.
Referring to
Pressure in needle control chamber 33 acts upon a closing hydraulic surface 34 associated with needle valve 32. As long as pressure in needle control chamber 33 is high, needle valve 32 will remain in, or move toward, a closed position blocking nozzle outlets 12. When second electrical actuator 31 is energized, needle control valve 30 moves to a position that blocks pressure connection passage 35, and instead fluidly connects needle control chamber 33 to low pressure fuel supply/return opening 13 via a low pressure passage 49 partially shown in
The features associated with nozzle control are shown in greater detail in
When electrical actuator 31 is de-energized and control valve member 40 is in the downward position to close flat low-pressure seat 42, needle control chamber 33 is fluidly connected to nozzle supply passage 18 via connection passage 35 and pressure communication passage 44. As such, high pressure in nozzle supply passage 18 enters needle control chamber 33 to act upon closing hydraulic surface 34 to hold needle valve 32 in a closed position, or move the same toward a closed position where a check lift spacer 92 may be out of contact with stop surface 93. Pressure in needle control chamber 33 drops when control valve member 40 is lifted to close conical high-pressure seat 41 and open the fluid connection to drain passage 49. The various areas of closing hydraulic surface 34 and opening hydraulic surface 39 are sized such that needle valve 32 will lift and move upward toward its open position in contact with stop surface 93 when pressure in nozzle chamber 19 is above a valve opening pressure associated with the pre-load on biasing spring 48, which normally biases needle valve 32 downward toward a closed position. As shown, the needle control chamber 33, variable flow rate valve 37 and the needle biasing spring 48 may be disposed in a spring cage component 43 of injector body 1. Although needle valve 32 may be of unitary construction, in the illustrated embodiment the needle valve 32 includes a needle 90, a check lift spacer 92 and a piston 91. Together, piston 91 and spring cage component 43 define needle control chamber 33. Also, the needle biasing spring 48 is received in an annular cavity 95 defined by spring cage component 43. Nevertheless, numerous alternative structural details would fall within the intended scoped of the disclosure.
The structure illustrated in
Variable flow rate valve 37 may be configured to include a round plate 38 that is positioned for guided movement in any guide bore 45 defined by spring cage component 43 between the a downward position, as shown in
When plate 38 is in contact with first-stop 27, fluid may flow into pressure communication passage 44 toward needle control chamber 33 via an orifice 66 defined by plate 38 and also along one portion of its outer edge and adjacent bottom bevel surface 78. Plate 38 may include indentations 69 to make orifice 66 easier to manufacture at a length that is less than a thickness of plate 38. When plate 38 is in the upward position in contact with second stop 28, the first communication passage 44 is configured to limit flow only through orifice 66. Thus, when plate 38 is in the lower position in contact with first stop 27, the plate 38 may be said to be in an unrestricted flow configuration because fluid flow in pressure communication passage 44 has a relatively large flow area due to the combined flow area through orifice 66 and around the edge of lower bevel surface 78. On the other hand, when plate 38 is in the upper position in contact with second stop 28, the plate 38 may be said to be in a restricted flow configuration because the flow is limited or restricted to orifice 66. Although variable flow rate valve 37 is illustrated as including a round plate, those skilled in the art will appreciate that other valve configurations would fall within the intended scope of the present disclosure, provided they could be configured in a relatively restricted configuration and a relatively unrestricted configuration.
In the illustrated structure, several design considerations are available for adjusting the operation of the nozzle control features and the operation of fuel injector 10. These design considerations allow some influence over the rate at which pressure may drop in needle control chamber 33 relative to the rate at which pressure may be increased in the same. Among the design considerations are the flow area of orifice 66. As expected, as the flow area decreases, the rate at which pressure may drop in needle control chamber 33, and hence the rate at which the needle valve 32 may open, is slowed. On the other hand, if the area for orifice 66 is made too large, there may not even be a flow restriction, and the fuel injector might exhibit very little difference in behavior relative to the predecessor fuel injector. A couple of related design considerations relate to the volume of the needle control chamber 33 (fuel compressibility) along with the travel distance D, which corresponds to a volume swept out by movement of plate 38. For instance, if the travel distance is made too large or the chamber volume too large, the variable flow rate valve 37 may again have little to no effect on the action of the fuel injector relative to the predecessor, at least in regard to close coupled post injections. On the other hand, if the travel distance is made too small, there may be difficulty in mass production of fuel injectors that include a variable flow rate valve with consistent behavior. Between these two extremes may lie a range of travel distances that show a dramatic change between the behavior of the predecessor fuel injector and a slowed pressure drop action in needle control chamber 33.
The present disclosure finds potential application to any fuel system that utilizes mechanically actuated electronically controlled fuel injectors with at least one electrical actuator operably coupled to a spill valve and a needle valve. Although both the spill valve and the needle valve may be controlled with a single electrical actuator within the intended scope of the present disclosure, a typical fuel injector according to the present disclosure includes a first electrical actuator associated with the spill valve and a second electrical actuator associated with the needle valve. Any electrical actuator may be compatible with the fuel injectors of the present disclosure, including solenoid actuators as illustrated, but also other electrical actuators including piezo actuators. The present disclosure finds particular suitability in compression ignition engines that benefit from an ability to produce injection sequences that include a relatively large main injection followed by a closely coupled small post-injection, especially at higher speeds and loads in order to reduce undesirable emissions at the time of combustion rather than relying upon after-treatment systems. The present disclosure also recognizes that every fuel injector exhibits a minimum controllable injection event duration, below which behavior of the injector becomes less predictable and more varied.
The minimum controllable injection event duration for a given fuel injector relates to that minimum quantity of fuel that can be repeatedly injected with the same control signal without substantial variance. This phenomenon recognizes that in order to perform an injection event, certain components must move from one position and then back to an original position with some predictable repeated behavior in order to produce a controllable event. When the durations get too small, pressure fluctuations are too large and components are less than settled, components tend to exhibit erratic behavior due to flow forces, pressure dynamics and possibly mechanical bouncing before coming to a stop and other phenomena that give rise to nonlinear and erratic behavior at various short and small quantity injection events. The present disclosure is primarily associated with the minimal controllable injection event, especially when such an event occurs after a large main injection event. Thus, the present disclosure recognizes that simply decreasing the duration of the post-injection event may theoretically produce a smaller injection quantity, but the uncontrollable variations on that quantity may become unacceptable, thus defeating that potential strategy for producing ever- smaller injection event quantities.
Referring now to
When it comes time to initiate the main injection event 51, second electrical actuator 31 is energized to a pull-in current level 70 (
Between the injection events, pressure begins to increase as per pressure surge 57 (
The present disclosure has the advantage of achieving smaller post injections 52 following relatively large main injections 50 with an increased, decreased or same dwell D between injection events. A smaller quantity post injection 52 may achieve better emissions with only a small change to existing hardware, namely, the inclusion of variable flow rate valve 37. Those skilled in the art will recognize that the addition of variable flow rate valve 37 could be utilized to reduce the post injection quantity even if the dwell were matched or reduced relative to that of the predecessor fuel injector via a suitable adjustment to the control signal for the second electrical actuator 31. The presence of variable control rate valve 37 also reduces the magnitude of the pressure swings that occur in needle control chamber 33 during the post-injection event 52, and this aspect may enhance the controllability of the post-injection event relative to the predecessor fuel injector. This enhanced controllability may also permit designers to select a dwell D that may be shorter, the same or longer than what is consistently possible with the predecessor fuel injector. In summary, the variable flow rate valve 37 may allow for a decrease in the post injection quantity 52 over the predecessor post-injection quantity 53 (
Although the present disclosure has been illustrated in the context of an injection sequence that includes a large main injection followed by a small post injection, it is foreseeable that the same techniques could be utilized to reduce the minimum controllable injection quantity of fuel injector 10 for any injection event alone or as part of a sequence. For example, the added capabilities provided by variable flow rate valve 37 could be exploited at other operating conditions, such as to produce small split injections at idle. And in addition, smaller pilot injections may also be available via the inclusion of the variable flow rate valve 37. Thus, the ability to incrementally decrease the minimum controllable fuel injection quantity at all operating conditions and pressures could conceivably be exploited in different ways across an engine's operating range apart from the illustrative example that included an injection sequence with a large main injection followed by a closely coupled post injection.
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. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
