Fuel injector with needle control system that includes F, A, Z and E orifices

A common rail fuel injector includes a needle valve member that moves to open and close nozzle outlets for a fuel injection event responsive to pressure in a needle control chamber. Between injection events, the needle control chamber is fluidly connected to the fuel inlet by a first pathway that includes a Z orifice, and fluidly connected to the fuel inlet by a second pathway that includes an F orifice, an intermediate chamber and an A orifice. During an injection event, the needle control chamber is fluidly connected to a drain outlet by a third pathway that includes the A orifice, the intermediate chamber and an E orifice. Different performance characteristics are achieved by adjusting the sizes of the respective of F, A, Z and E orifices.

TECHNICAL FIELD

The present disclosure relates generally to direct control needle valves for fuel injectors, and more particularly to a needle control system that includes variously sized F, A, Z and E orifices.

BACKGROUND

Today's electronically controlled compression ignition engines typically include an electronically controlled fuel injector with a direct operated check valve. The direct operated check valve includes a closing hydraulic surface exposed to pressure in a needle control chamber. Pressure is relieved in the needle control chamber to initiate an injection event by actuating a two way or three way valve to fluidly connect the needle control chamber to a low pressure drain outlet. The injection event is ended by de-energizing the electronically controlled two way or three way valve to repressurize the needle control chamber. Co-owned U.S. Pat. No. 7,331,329 shows an example of such a fuel injector with a three way valve, whereas U.S. Pat. No. 6,986,474 shows an example fuel injector with a two way valve. In general, a three way valve version can provide greater performance capabilities relative to a two way valve counterpart, but does so at the expense of increased complexity and difficultly to manufacture, especially mass producing fuel injectors with consistent performance behaviors.

Early versions of the two way valve typically included the needle control chamber fluidly connected to a nozzle supply passage via an unobstructed Z orifice, and the two way valve permitted fluid communication between the needle control chamber and a low pressure drain outlet through a so called A orifice. During an injection event, the nozzle supply passage is fluidly connected directly to the low pressure drain via the Z orifice, the needle control chamber and the A orifice. Thus there was an initial motivation to make the A and Z orifices relatively small in order to reduce losses during an injection event. This motivation quickly lead to a problem associated with a general desirability to end injection events abruptly, which is accomplished by quickly raising pressure in the needle control chamber. A small Z orifice slows the rate at which pressure may grow in the needle control chamber at the end of an injection event. This problem was addressed by adding an additional orifice to facilitate the quick repressurization in the needle control chamber toward the end of injection event. For instance, previously identified U.S. Pat. No. 6,986,474 includes an additional orifice14that facilitates repressurization of its needle control chamber4via both the Z orifice5as well as through the A orifice6by way of the additional fill or F orifice14. The three way valve fuel injector counterpart identified above in co-owned U.S. Pat. No. 7,331,329 likewise includes three orifices, which include a Z orifice112, and two other orifices110and111, that most closely resemble in performance the F orifice and A orifice, respectively for the counterpart two way valve fuel injector.

Because of the complexity and difficulty in manufacturing a three way valve that performs consistently with mass produced fuel injectors, there is a growing desire toward utilizing a two way control valve to perform the pressure control function in a direct control check valve for a fuel injector. Unfortunately, current strategies with regard to utilization of two way valves, even with the inclusion of F, A and Z orifices, result in less than satisfactory performance relative to the counterpart three way valve control strategy. For instance, while the inclusion of an F orifice can aid in hastening the end of an injection event, the F orifice may not assist in retarding the rate at which the needle valve member opens to commence an injection event, which is also sometimes a desirable fuel injector attribute. In addition, variations in flow areas among control valves for mass produced fuel injectors can result in an unacceptable variance in performance among the fuel injectors.

The present disclosure is directed to one or more of the problems set forth above.

SUMMARY OF THE DISCLOSURE

In one aspect, a fuel injector includes an injector body that defines a fuel inlet, at least one nozzle outlet and a drain outlet, and has disposed therein a nozzle chamber, a needle control chamber and an intermediate chamber. The needle control chamber is fluidly connected to the fuel inlet by a first pathway that includes a Z orifice, and the needle control chamber is fluidly connected to the fuel inlet by a second pathway that includes an F orifice, the intermediate chamber and an A orifice. An electronically controlled valve is attached to the injector body and includes a control valve member movable between a first position in contact with a seat and a second position out of contact with the seat. The needle control chamber is fluidly connected to a drain outlet by a third pathway that includes the A orifice, the intermediate chamber and an E orifice when the control valve member is at the second position, but the needle control chamber is blocked from the drain outlet when the control valve member is at the first position. A needle valve member includes an opening hydraulic surface exposed to fluid pressure in the nozzle chamber, and a closing hydraulic surface exposed to fluid pressure in the needle control chamber.

In another aspect, a method of operating the fuel injector includes starting an injection event by moving fuel from the needle control chamber through the A orifice, and from the nozzle chamber through the F orifice, toward the intermediate chamber. In addition, the injection event is started by moving fuel from the intermediate chamber toward the drain outlet through the E orifice. Afterwards, the injection event is ended.

DETAILED DESCRIPTION

Referring toFIGS. 1 and 2, a fuel injector10includes an injector body that defines a fuel inlet44, at least one nozzle outlet45and a low pressure drain outlet46. Fuel inlet44includes a conical seat40to facilitate connection between fuel injector10and a common rail via a quill of a type well known in the art. Low pressure drain outlet46would be fluidly connected to tank to return for recirculation any fuel expended for the control function and/or from leakage. The nozzle outlets45would be positioned in the combustion space of a compression ignition engine to facilitate direct fuel injection into the engine cylinder. Fuel injector10includes a direct operated check13of a type briefly described in the background section. Disposed within injector body11, which includes all hardware except electrical and moving components, are a number of fluid passageways and chambers. Among these are a nozzle chamber50, a needle control chamber52and an intermediate chamber54. As used in this disclosure, the term “injector body” means various stationary components of fuel injector10that define fluid passageways, chambers and the like. In the illustrated embodiment, nozzle chamber50is fluidly connected to fuel inlet44via an unobstructed nozzle supply passage49as is conventional in a common rail fuel injector. The term “unobstructed” means a fluid passage without valves or the like that change a flow area through the passage or possibly even block fluid flow through the same. Although the present disclosure is illustrated in the context of a common rail fuel injector10, the principles surrounding the direct operated check13to be discussed infra could be equally applicable to other types of fuel injectors, including but not limited to, cam actuated fuel injectors, and may be hybrid common rail cam actuated fuel injectors.

Referring especially toFIG. 2, the needle control chamber52is fluidly connected to the fuel inlet44by a first pathway61that includes a Z orifice66and a segment of nozzle supply passage49. As used in this disclosure, the term “orifice” means a flow restriction defined by a cylindrical passage with a uniform diameter and hence flow area. Thus, those skilled in the art will appreciate that flow restrictions may appear elsewhere in a fuel injector, such as at a clearance between a valve member and a valve seat, but such flow restrictions would not be considered orifices in the context of the present disclosure. The needle control chamber52is also fluidly connected to the fuel inlet44by a second pathway62that includes an F orifice68, the intermediate chamber54, A orifice67as well as nozzle chamber50and nozzle supply passage49.

An electronically controlled valve20is attached to the injector body11and includes a control valve member22movable between a first position in contact with a seat23, and a second position out of contact with the seat23. In the illustrated embodiment, the electronically control valve20includes a solenoid with an armature24that is attached to a pusher27in contact with control valve member22. Thus, in the illustrated embodiment electrical actuator25is a solenoid, but could be another electrical actuator, such as a piezo, without departing from the present disclosure. In addition, control valve member22is shown movable into and out of contact with a seat23, which is a flat seat, but could be a counterpart conical seat without departing from the present disclosure. Finally, although fuel injector10includes only one electrical actuator25, the present disclosure could find potential application in fuel injectors with two or more electrical actuators, such as, for instance, a first electrical actuator associated with a spill valve and a second electrical actuator associated with a direct operated check as might be typical in the case of a cam actuated fuel injector. A spring29normally biases pusher27and control valve member22downward into contact with flat seat23. The term “flat seat” means a valve seat that is part of a planar surface, and thus a flat seat is something different from a conical seat associated with a poppet valve or an edge seat associated with a spool valve.

The needle control chamber52is fluidly connected to the low pressure drain outlet46by a third pathway63that includes the A orifice67, the intermediate chamber54, an E orifice69and a low pressure clearance space between valve body21and a first orifice disk16when the control valve member is at the second position. In other words, the fluid connection between needle control chamber52and low pressure drain outlet46only occurs when control valve member22is out of contact with flat seat23. Needle control chamber52is therefore blocked from low pressure drain outlet46when the control valve member22is at its first position with control valve member in contact with flat seat23.

A needle valve member30is positioned in injector body11and movable between a first position in which nozzle outlets45are blocked from nozzle chamber50, and a second raised position in which nozzle chamber50is fluidly connected to nozzle outlets45for an injection event. The needle valve member30includes an opening hydraulic surface31exposed to fluid pressure in nozzle chamber50, and a closing hydraulic surface32exposed to fluid pressure in needle control chamber52. A centerline35of needle valve member30intersects an opening of the third pathway63into needle control chamber52. This structure creates a so called hydraulic stop when the needle valve member30is in its upward open position, which is to be contrasted with a mechanical stop in which a valve member actually comes in contact with a stop surface when in its open position. In the case of a hydraulic stop, the needle valve member30with hover just out of contact with the lower surface of second orifice disk17during an injection event. The hydraulic stop strategy has the advantage of rendering the needle valve member more responsive than an equivalent counterpart with identical features except a mechanical stop. Nevertheless, the teachings of the present disclosure also find potential applicability to needle valve members that contact a mechanical stop in its open position. Needle controlled chamber52is separated from nozzle chamber50by a guide segment34of needle valve member30that is guided in its movement via a guide bore39defined by needle guide component18.

Referring in addition toFIGS. 3-5, the E orifice69may be defined by the first disk16that is stacked between valve body21and the second orifice disk17. In particular, first orifice disk16contacts valve body21over a plurality of non contiguous sealing lands41a-d(FIG. 3) that are defined by raised surfaces. Thus, the third pathway63discussed earlier includes the flow area between the control valve member22and flat seat23, as well as the open space between the raised surface sealing lands41a-d. Those skilled in the art will recognize that each high pressure passageway, such as nozzle supply passage49is completely surrounded by a sealing land41din a manner similar to the sealing land41bthat completely surrounds and defines a portion of flat seat23. By utilizing raised sealing lands, less clamping pressure may be necessary in the fuel injector in order to inhibit leakage between components of the injector stack, which is a portion of the injector body11. Thus, the injector body includes valve body21, first orifice disk16, second orifice disk17and needle guide component18. First orifice disk16also includes on its underside a plurality of non contiguous sealing lands41e-gthat contact with an upper planar surface70of second orifice disk17. Second orifice disk17defines the F orifice, the A orifice and the Z orifice as best shown inFIG. 2. The intermediate chamber54is defined partly by first orifice disk16and partly by second orifice disk17, also as best shown inFIG. 2. The orifice second disk17is stacked between first orifice disk16and needle guide component18. As used in the present disclosure, the term “disk” means a relatively thin object that likely will have a circular cross section (as shown) but need not necessarily have a circular shaped cross section. The thinness of the object, in the case of first orifice disk16is defined by the non-contiguous sealing lands41a-don the top side and41e-gon the bottom side, which lay in parallel planes. In the case of second orifice disk17, both the upper and lower surfaces are planar. Those skilled in the art will appreciate that the non-contiguous sealing land strategy can be located elsewhere, such as the underside of valve body21, or on one or both of the upper and lower surfaces of second orifice disk17without departing from the present disclosure. In addition, although the F, A, Z and E orifices are defined by disks in the fuel injector10of the present disclosure, those skilled in the art will appreciate that this need not necessarily be the case and a fuel injector according to the present disclosure could be made without inclusion of any disks. Disk16includes dowel holes72and73that should align with dowel holes74and75in disk17when fuel injector10is assembled so that the various passageways align with one another as best shown inFIG. 2.

When the electrical actuator25is energized to move valve member22out of contact with flat seat23, the fluid connection between needle control chamber52and low pressure drain outlet46is facilitated for an injection event. In order to desensitize fuel injector performance to variations in control valve lift, the flow area through orifice E may be smaller than a flow area defined by flat seat23and control valve member22at the second or open position. Thus, one could expect some variance on control valve lift and hence the flow area between control valve member22and flat seat23in the mass production of fuel injectors, and also expect control valve lift to possibly grow with time as the fuel injector breaks in over time with many injection events. By sizing E orifice to be smaller than the flow area between flat seat23and control valve member22, the performance of the fuel injector can be desensitized to variations in control valve lift as well as growth in control valve lift over time. Nevertheless, the flow area through orifice E could be larger than other flow restrictions in the third pathway63without departing from the present disclosure.

Although not necessary, the F, A, Z and E orifices may all have flow areas of a same order of magnitude. The phrase “same order of magnitude” means that the flow area through any orifice is not more than ten times the flow area through any of the other orifices. Depending upon the particular application, some experimentation may be necessary in order to arrive at a set of orifice flow areas that produce desired performance results across a fuel injector's operating range. For instance, a set of orifice flow areas that work well at one injection pressure may be undesirable or maybe even unacceptable at a different injection pressure. For instance, the best set of flow areas at high injection pressures may be incompatible with the operation of the same fuel injector at low injection pressures, such as at idle, and vice versa. Thus, the respective flow areas of the different orifices may be some compromise to produce acceptable performance from the fuel injector at all operating conditions, and thus one could expect some experimentation necessary to find a combination of orifice flow areas for a specific fuel injector application.

Industrial Applicability

The present disclosure finds generally applicability to any fuel injector with a direct operated check, including but not limited to common rail fuel injectors, cam actuated fuel injectors and hybrids. The present disclosure finds particular applicability to fuel injectors with direct operated checks that utilize a two way valve, but could find potential application in fuel injectors that utilize a three way valve. The present disclosure finds specific applicability to common rail fuel injectors that include a two way control valve. By appropriately choosing the flow areas for each of the different orifices, certain desirable performance characteristics can be achieved, including slowing the initial start of injection front end rate shape, as well as facilitating an abrupt end to any injection event.

Between injection events, electrical actuator25is de-energized and control valve member22is in its downward closed position in contact with flat seat23to block fluid communication between needle control chamber52and the low pressure drain outlet46. High pressure, which should be about the same as the rail pressure, should prevail in nozzle supply passage49, nozzle chamber50, needle control chamber52and intermediate chamber54as well as the F, A, Z and E orifices. Those skilled in the art will appreciate that fuel injector10is free of locations where a low pressure space is separated from a high pressure space between injection events by a movable guide member surface. As such, fuel injector10can be expected to exhibit low static leakage.

Each injection event is initiated by energizing electrical actuator25to move control valve member22out of contact with seat23. In particular, and referring to the first two strip graphs ofFIG. 6, electrical actuator25is initially energized to a pull in current, and then stepped down to a hold in current as control valve member22moves and becomes relatively stationary at its upward open position. When this occurs, fuel begins moving from needle control chamber52through A orifice67, and at the same time from nozzle chamber50through F orifice68toward intermediate chamber54. At the same time, fuel begins moving from intermediate chamber54toward low pressure drain outlet46through E orifice69and past valve member22. This movement of fuel causes pressure to drop in needle control chamber52as shown in the fourth graph ofFIG. 6and to a lesser extent in intermediate chamber54as shown in the third graph of56. When pressure drops sufficiently in needle control chamber52, the upward opening hydraulic force on lifting hydraulic surface31overcomes the downward closing force from spring29and the closing hydraulic force on closing hydraulic surface32allowing needle valve member30to lift to its upward open position as shown in the fifth graph ofFIG. 6to commence the start of injection (SOI) as shown in the sixth graph ofFIG. 6. The injection event is ended by de-energizing electrical actuator25and allowing valve member22to move downward into contact with seat23under the action of spring29. This blocks further movement of fuel toward low pressure drain outlet46causing pressure to again rise in both needle control chamber52and intermediate chamber54. When pressure and needle control chamber52exceeds the valve closing pressure sufficient to overcome the opening hydraulic force, needle valve member30moves downward to close the nozzle outlets45as shown in the fifth graph ofFIG. 6to facilitate the end of injection (EOI) as shown in the sixth graph ofFIG. 6. The two different curves inFIG. 6are included to illustrate how two different sized flow areas of the F orifice affect the abruptness of the end of injection. The dotted lines show when the F orifice has a zero flow area or is eliminated all together showing that a substantial delay occurs between the control valve member closing at its seat as shown in the second graph until the needle valve member30finally reaches its downward closed position for an end of injection as shown in the fifth and sixth graphs ofFIG. 6. On the other hand, when the F orifice is made small like that shown in the solid line, the delay between the de-energization of electrical actuator25and the end of injection as shown by the first and sixth graphs as relatively short. Thus, the F orifice can facilitate close in time sequences of injection events, such as a main injection event followed by a close coupled post injection event with an intervening dwell time that would not be possible if the F orifice were eliminated.

The graphs ofFIG. 7are included to illustrate a sensitivity to the size of the A orifice with the solid lines showing a small sized A orifice and a dotted line showing the injector performance for a relatively large flow area through A orifice67. As can be seen, the size of the A orifice primarily effects injection performance at the beginning of the injection event and has little effect at the end of injection. Over many years, engineers have come to recognize that some performance improvements, may be especially relating to reducing undesirable emissions, can be achieved by a slower build up of injection rate rather than an injection rate that goes from zero almost instantaneously to maximum injection rate, as shown by the dotted line when the A orifice is large. In other words, as the flow area through the A orifice is reduced, the ability of pressure to drop in needle control chamber52at the beginning of an injection event is hindered, thus slowing the lifting rate of the needle valve member30and producing a more gradual rise in front end injection rate as shown in the fifth and sixth graphs ofFIG. 7. As the flow area through orifice A becomes larger and larger, the start of injection rate shape becomes nearly vertical.

Referring toFIG. 8, the E orifice can work together with the F orifice to slow the start of injection rate shape as shown by the fifth and sixth graphs ofFIG. 8. It is believed that this occurs by fuel entering the intermediate chamber54through the F orifice hindering the flow of fuel into the intermediate chamber54from the needle control chamber52through the A orifice, thus slowing the lifting rate of needle valve member30(graph 5) and slowing the initial build up of injection rate at the start of injection as shown in the sixth graph. If the E orifice is too big, the start of injection effect facilitated by the F orifice may be defeated. If the E orifice is too small, there may not be sufficient pressure drop in needle control chamber52to allow the needle valve member to even lift to perform an injection event at law injection pressures. The solid line and dash line graphs ofFIG. 8are intended to show the different performance effects when the E orifice is relatively big as in the solid line or relatively small as in the dashed line. As expected, the size of the E orifice as little effect on the end of injection performance characteristics as revealed by the graphs ofFIG. 8.

Another subtle by important concern is the fact that, especially in the case of a common rail fuel injector, injection pressures may be substantially different engine at different operating conditions, and it may be difficult to find an E orifice flow area that produces acceptable fuel injector performance at both high and low rail pressures. Those skilled in the art will appreciate that the flow characteristics through the orifices, and hence the emergent fuel injector performance resulting therefrom, is related to the pressure gradient across the orifice, which will be different at different rail pressures. One possible starting point for selecting F, A, Z and E orifice sizes would be to set the initial flow areas as some percentage of the total flow area through nozzle outlets45. For instance, an initial sizing on the order of 10-20% of the total flow area through the nozzle outlets45could be a good starting point. Next, the flow areas, the various spring pre-loads, seat diameters, etc. need to be chosen such that the fuel injector will work at the extreme high and low expected rail pressures. Next, the various orifices can be tweaked in size to achieve desired performance characteristics using, for instance, the graphs ofFIGS. 6,7and8for guidance. By utilizing a two way control valve strategy in conjunction with appropriately sized F, A, Z and E orifices, injector performance characteristics can mimic and approach that of a three way valve counterpart with the added complexity and expense associated with three way valves.