Patent Application
20050173563
The present invention relates generally to common rail fuel injection systems, and more particularly to a method of injecting fuel with a fuel injector equipped with a multi-position admission valve.
In one class of common rail fuel injection system, a plurality of fuel injectors are fluidly connected via separate branch passages to a common rail that contains fuel pressurized to injection levels. An electrical actuator attached to each of the fuel injectors controls the timing and duration of each injection event. In one alternative, these electrical actuators are operably coupled to a needle control valve that acts to apply or relieve fuel pressure on a closing hydraulic surface of a needle valve member. The needle valve member moves to open and close the nozzle outlets to permit fuel injection and end injection events, respectively. In this type of system, fuel at injection pressure levels is always present within the fuel injectors, and around their respective needle valve members. However, injection does not take place until pressure on the closing hydraulic surface of the needle is relieved. Depending upon the particular fuel injector, the needle control valve can be positioned on the high pressure side upstream from a needle control chamber or on the low pressure drain side leading away from the needle control chamber. The closing hydraulic surface of the needle valve member is exposed to fluid pressure in a needle control chamber. While many of these types of fuel injectors have performed well and provided additional control over injection timing and quantity, they sometimes actually tend to end injection events too abruptly, causing an increase in undesirable emissions, particularly smoke emissions. In other words, engineers have observed that these supposedly more sophisticated fuel injectors can sometimes, and at some conditions, produce more smoke emissions than their simpler counterparts that rely upon a fuel pressure drop and the action of a biasing spring to close the nozzle outlets to end an injection event. In addition, depending upon the location of the needle control valve, these fuel injectors can sometimes suffer from chronic leakage problems due at least in part to the fact that they are always pressurized, even between injection events.
In another common rail fuel injector strategy, an admission valve either opens a nozzle passage to a high pressure supply passage connected to the common fuel rail, during an injection event, or connects the nozzle passage to a low pressure drain passage between injection events. For instance, a Dutch Publication entitled, Common Rail Fuel Injection System For High Speed Large Diesel Engines, by Robert Bosch AG, © CIMAC Congress 1998 Copenhagen shows such a common rail fuel injector. It has a pilot operated three-way admission valve that fluidly connects the nozzle passage to either the high pressure supply passage or a low pressure drain passage. The nozzle passage is fluidly connected to the nozzle outlets when the needle valve member is lifted to its open position. The needle valve member in this injector appears to be a simple check valve, in that the needle valve member is biased towards a closed position with a pre-load on a biasing spring positioned in a vented chamber. Thus, the opening and closing of the nozzle outlets is controlled by fuel pressure in the nozzle passage that is acting against a simple biasing spring. Although the strategy presented by this fuel injector may have promise, it appears to suffer from several drawbacks, the least of which being the reliance upon a pilot operated admission valve. In other words, an electrical actuator is operably coupled to move with a pilot valve member. Depending upon the position of the pilot valve member, a control surface on a slave valve member is either exposed to low pressure or high pressure to move the same to a desired position. Because of the additional moving parts and close dynamic coupling between the pilot valve and the slave valve, there appears to be substantial likelihood of difficulty in mass producing fuel injectors of this type to reliably behave similar to one another, as would be necessary in order to gain the full potential benefits of a fuel injector design.
In addition, those skilled in the art will appreciate that rate shaping in common rail fuel injection systems is problematic.
The present invention is directed to one or more of the problems set forth above.
In one aspect, a fuel injector includes an injector body that includes a supply passage, a drain passage and a nozzle passage disposed therein.
An admission valve includes a valve member that is trapped to move between a drain valve seat and supply valve seat. The valve member is stoppable at a middle position out of contact with both the drain and supply valve seats. The supply passage is fluidly connected to both the nozzle passage and the drain passage when the valve member is in its middle position. The nozzle passage is open to the drain passage but closed to the supply passage when the valve member is in a closed position in contact with the supply valve seat. The nozzle passage is open to the supply passage, but closed to the drain passage, when the valve member is in a fully open position in contact with the drain valve seat.
In another aspect, a method of injecting fuel includes a step of injecting fuel at a low rate at least in part by stopping an admission valve member at a middle position out of contact with a drain valve seat and a supply valve seat.
Fuel is injected at a high rate at least in part by stopping the admission valve member in a fully open position in contact with the drain valve seat. Fuel injection is ended at least in part by stopping the admission valve member in a closed position in contact with supply valve seat.
In still another aspect, a fuel injection system includes a means for stopping an admission valve member in an injector body at a middle position out of contact with a drain seat and a supply seat to inject fuel at a low rate. The system also includes a means for stopping the admission valve member at a fully open position in contact with a drain seat to inject fuel at a high rate. Finally, the system includes means for stopping the admission valve member at a closed position in contact with the supply seat to end fuel injection.
a-5c are graphs of control signal, valve position and injection rate verses time, respectively, according to an aspect of the present invention; and
a-b are graphs of valve position and injection rate according to another aspect of the present invention.
Referring to
Referring now in addition to
A multi-position admission valve (34) is attached to each injector body (31) and acts as the means by which nozzle passage (38) is fluidly connected to supply passage (36) and/or drain passage (40), which is fluidly connected to drain passage (26) via a flow restriction orifice (42). The flow orifice (42) is preferably restrictive to fluid flow relative to flow through admission valve (34).
Referring specifically to
When a solenoid is energized, and both armature (52) and valve member (50) begin moving upwards, before valve member (50) comes in contact with drain seat (45), stop spacer (58) will come in contact with middle stop surface (60). Thus, over the first portion of the valve member's travel between supply seat (41) and stop surface (60), only biasing spring (61) acts in opposition to the solenoid force. This is also accomplished by setting the pre-load on biasing spring (56) substantially higher than that of spring (61). Thus, when the solenoid is appropriately energized, an equilibrium position will exist where stop spacer (58) is in contact with stop surface (60), and valve member (50) will be out of contact with both supply seat (41) and drain seat (45). In this middle position, supply passage (36) is fluidly connected both to nozzle passage (38) and drain passage (40). When the solenoid is further energized, the higher attractive force pulls armature (52) and valve member (50) further upwards compressing biasing spring (56) and (61) until valve member (50) comes in contact with drain seat (45) at its fully open position. Thus, in this illustrated embodiment, the various structures described constitute a means (73) for stopping the valve member at a closed position in contact with supply seat (41). In addition, the various components, especially the dual spring design, constitutes portions of a means (70) for stopping the valve member (50) at a middle position. Finally, the various components described including the electrical actuator (51) comprise a means (71) for stopping the valve member (50) at a fully open position in contact with drain seat (45).
The orifice (42) that presents a flow restriction in drain passage (40) is present for a number of reasons. Among these reasons is to preferably create a flow restriction relative to a flow area past drain seat (45) when valve member (50) is in its middle position. This aspect of the invention helps to desensitize injector performance to inevitable variations in flow areas past drain seat (45) among a plurality of fuel injectors. Nevertheless, the present invention could be constructed in a way such that the flow area past drain seat (45) could be tightly controlled through known geometrical tolerance techniques and allow for the elimination of orifice (42). However, by including orifice (42), one can control the flow area that directly connects the high pressure supply passage (36) to the drain passage (40) such that pressure in nozzle passage (38) can be indirectly selected as a function of rail pressure and orifice diameter when valve member (50) is at its middle position to inject fuel at a low pressure. When the valve member (50) is in its fully open position in contact with drain seat (45), orifice (42) is substantially out of play and high pressure supply passage (36) is fluidly connected only to nozzle passage (38) to inject fuel at a high pressure.
Referring now to
Referring now to
The present invention allows for the injection of fuel at a relatively low rate by stopping the valve member at a middle position, and allows for injection of fuel at a high rate by stopping the valve member at a fully open position. Those skilled in the art will appreciate that the two injection rates can be accomplished in a single injection event or in separate injection events. For instance, the fuel injector of the present invention could inject a small pilot injection at a low injection rate and follow that with a main injection at a high rate and then follow that main injection event with a post injection event at a low or high rate. Those skilled in the art will appreciate that the
Referring now to
Depending upon the alternative chosen, the present invention can provide substantial advantages over prior art fuel injection systems. Firstly, because the control is gained through an admission valve, chronic leakage problems associated with prior art fuel injectors can be reduced and possibly eliminated. In addition, by having the admission valve member directly moved by an electrical actuator, the complications and uncertainties associated with pilot operation can also be avoided. Finally, by utilizing a drain orifice with a flow restriction relative to flow through the valve, the performance of the fuel injector can be desensitized to inevitable small variations in the flow areas through the valve due to such things as ordinary geometrical tolerances employed to manufacture the valve. By carefully controlling the signal to the electrical actuator, those skilled in the are will appreciate that the fuel injector of the present invention can exhibit the ability to produce front end rate shapes that include square front end, a ramp front end, a boot shaped front end and others. In addition, because the fuel injector employs a conventional spring bias needle and relies upon pressure decay to close the nozzle outlets at the end of an injection event, smoke emissions levels can predictably be reduced over counterpart common rail injectors that rely upon direct control needles to end injection events arguably too abruptly when pressure is still high. This fuel injector also has the advantage over drain mounted direct control common rail injectors in that leakage to tank occurs intentionally only when injecting at a low rate, which is likely to be for very short durations in the overall scheme of things. The piezo bender version of the present invention can potentially provide even more performance advantages in that with a suitable feedback strategy of a type known in the art, the injector could be tuned to inject fuel at a plurality, and possibly a continuum of different rates, depending upon the magnitude of electrical energy being supplied to the actuator at any given time.
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 invention in any way. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.
