Patent Application
20120012681
This invention relates to plungers for high pressure fuel injectors, and high pressure fuel injectors, for injecting fuel into an internal combustion engine.
In most fuel supply systems applicable to internal combustion engines, fuel injectors are used to direct fuel pulses into the engine combustion chamber. A commonly used injector is a closed-nozzle injector which includes a nozzle assembly having a spring-biased nozzle valve element positioned adjacent the nozzle orifice for resisting blow back of exhaust gas into the pumping or metering chamber of the injector while allowing fuel to be injected into the cylinder. The nozzle valve element also functions to provide a deliberate, abrupt end to fuel injection thereby preventing a secondary injection which causes unburned hydrocarbons in the exhaust. The nozzle valve is positioned in a nozzle cavity and biased by a nozzle spring to block fuel flow through the nozzle orifices. In many fuel systems, when the pressure of the fuel within the nozzle cavity exceeds the biasing force of the nozzle spring, the nozzle valve element moves outwardly to allow fuel to pass through the nozzle orifices, thus marking the beginning of injection. In another type of system, such as disclosed in U.S. Pat. No. 5,676,114 to Tarr et al., the beginning of injection is controlled by a servo-controlled needle valve element. The assembly includes a control volume positioned adjacent an outer end of the needle valve element, a drain circuit for draining fuel from the control volume to a low pressure drain, and an injection control valve positioned along the drain circuit for controlling the flow of fuel through the drain circuit so as to cause the movement of the needle valve element between open and closed positions. Opening of the injection control valve causes a reduction in the fuel pressure in the control volume resulting in a pressure differential which forces the needle valve open, and closing of the injection control valve causes an increase in the control volume pressure and closing of the needle valve.
U.S. Pat. No. 6,499,467 issued to Morris et al. discloses a servo-controlled needle valve injector which also includes an inner restriction orifice to restrict the flow of fuel from a spring chamber to an inner control volume to create a desired force profile on the needle valve element. Likewise,
This disclosure provides a closed nozzle injector for injecting fuel at high pressure into the combustion chamber of an engine, comprising an injector body including an upper supply chamber and a nozzle housing, wherein the nozzle housing includes a lower supply chamber, a plunger seat, and injector orifices. An injector plunger is positioned in the nozzle housing for movement between a closed position in abutment against the plunger seat to block fuel flow through the injector orifices and an open position positioned a spaced distance from the plunger seat to permit fuel flow through the injector orifices. The injector plunger includes a lower guide sized to form a close sliding fit with the nozzle housing to guide the injector plunger during reciprocal movement. The lower guide is positioned axially between the lower supply chamber and the injection orifices. The injector plunger further includes a plurality of restriction orifices formed in the injector plunger and positioned symmetrically about the injector plunger to restrict fuel flow from the upper supply chamber to the lower supply chamber.
The plurality of restriction orifices may be limited to two orifices having central axes positioned in a common plane extending through a longitudinal axis of the injector plunger. The injector plunger may include an upper guide sized to form a close sliding fit with the nozzle housing to create a substantial fluid seal between the upper guide and the nozzle housing, and the plurality of restriction orifices may be formed in the upper guide. The nozzle housing may include a lower bore positioned between the lower supply chamber and the injector orifices to receive the injector plunger. The lower bore may have an outer diameter less than the outer diameter of the lower supply chamber. The lower guide may be positioned in the lower bore. The lower supply chamber may be defined at one end by the upper guide and at an opposite end by one end of the lower bore. The lower supply chamber may include an axial extent greater than an axial extent of the upper guide. Each of the plurality of restriction orifices may be positioned entirely on an opposite diametric side of the injector plunger from another one of the plurality of restriction orifices and in a common transverse plane extending perpendicular to a longitudinal axis of the injector plunger. The nozzle housing may be formed as one-piece and each of the plurality of restriction orifices, the upper guide, and the lower guide may be positioned in the one-piece nozzle housing. The lower guide may include fuel passages sized to permit unrestricted fuel flow through the fuel passages. The plurality of restriction orifices may each be linear passages having a longitudinal axis extending in a plane parallel to a longitudinal axis of the plunger. The injector plunger may further include a plurality of flow passages formed in the upper guide, and each of the plurality of flow passages may connect to, and have a larger cross-sectional flow area than, a respective one of the plurality of restriction orifices. A greater longitudinal portion of the lower bore is preferably positioned between the lower guide and the lower supply chamber than is positioned between the lower guide and the injector orifices.
This disclosure also provides a closed nozzle injector for injecting fuel at high pressure into the combustion chamber of an engine, comprising an injector body including an upper supply chamber and a nozzle housing, wherein the nozzle housing includes a lower supply chamber, a plunger seat, and injector orifices. An injector plunger is positioned in the nozzle housing for movement between a closed position in abutment against the plunger seat to block fuel flow through the injector orifices and an open position positioned a spaced distance from the plunger seat to permit fuel flow through the injector orifices. The injector plunger includes a lower guide sized to form a close sliding fit with the nozzle housing to guide the injector plunger during reciprocal movement and an upper guide sized to form a close sliding fit with the nozzle housing to create a substantial fluid seal between the upper guide and the nozzle housing. The injector plunger further includes a plurality of restriction orifices formed in the upper guide and positioned about the injector plunger. The plurality of restriction orifices are sized to restrict fuel flow from the upper supply chamber to the lower supply chamber.
a is a side view of a portion of the plunger showing the upper guide;
b is a cross-sectional view of the plunger taken along plane 4b-4b in
a and 5b are views within of cylinder of an engine facing upwardly showing the spray pattern of fuel from injector orifices of a conventional injector (
a and 6b are injection rig measurement data comparing the shot-to-shot end of injection variation of a conventional injector and the injector of
Referring to
The annular radially protruding upper guide 22 is positioned at one end of an annular lower supply chamber 24 formed in the nozzle valve assembly 16 upstream of a lower guide 14 positioned in nozzle valve assembly 16 closely adjacent plunger seat 18. The lower supply chamber 24 is positioned longitudinally between the upper guide 22 and the lower guide 14 and includes an axial extent or length greater than an axial extent of the upper guide 22, and a radial width at least as wide as the radial width of the upper guide 22 resulting in a lower supply chamber 24 having a larger volume than other fuel passages located between upper guide 22 and lower guide 14. Both the upper guide 22 and the lower guide 14 are formed in, preferably, a one-piece nozzle housing 28 when the plunger 12 is assembled in the injector 10. The upper guide 22 is positioned adjacent an outer end of the nozzle housing 28 and includes an outer annular surface or extent 29 sized and positioned to form a close sliding fit with the inner wall or surface of the nozzle housing 28 to create a substantial fluid seal while permitting unhindered reciprocal movement. The lower guide 14 is positioned in a lower bore 26 having an outer diameter less than the outer diameter of the lower supply chamber 24. As shown in
The plunger 12 further includes two flow passages 34, 36 formed in the upper guide 22 to connect an upper supply chamber 38 to the lower supply chamber 24. A respective gain orifice 40, 42, having a smaller cross-sectional flow area than the respective flow passage, is formed in each flow passage 34, 36 to restrict the flow of fuel from the upper supply chamber 38 to the lower supply chamber 24 to create a desired force profile on the plunger 12. The general operation of an inner restriction passage is discussed in U.S. Pat. No. 6,499,467, the entire contents of which is hereby incorporated by reference. The injector of U.S. Pat. No. 6,499,467 is also shown in
As shown in
An unexpected benefit of the plunger 12 and injector 10 is improved shot-to-shot EOI (end of injection) variation, resulting from the improved guiding and alignment. Another unexpected benefit of this design is a faster injection rate at the start of injection due to more volume downstream of the gain orifices 40, 42 (larger lower supply chamber 24), in addition to the improved guiding and alignment of the plunger 12. This benefit may also be due to less pressure reduction downstream of the gain orifices 40, 42 when the plunger lifts.
The balanced and guided plunger 12 has the following improvements:
1. Structural symmetry: The dual gain orifices 40, 42 are symmetrically positioned to advantageously eliminate bending in the injector plunger. Conventional designs using a single, or asymmetrical, inner restriction orifice, result in bending of the plunger around the notch when the injector is pressurized with fuel and the lower plunger is loaded, thereby undesirably creating eccentricity between the plunger tip and nozzle seat.
2. Hydraulic symmetry: The dual gain orifices 40, 42 balance the flow so there is not a hydraulic side force generated that pushes the plunger eccentrically when the plunger is lifted. The symmetrical positioning of the gain orifices allows fluid pressure and flow forces in one orifice/passage on one side of the plunger to be counteracted by fluid pressure and flow forces in the other orifice/passage on the other side of the plunger. As a result, the plunger reciprocates in a more linear manner along the desired longitudinal axis.
3. Improved guiding: At least the following features maintain the plunger tip centered on the nozzle seat 18 when the plunger lifts.
a. The upper 22 and lower 14 guides are spaced far apart in the nozzle housing 28.
b. The lower guide 14 is close to the nozzle seat 18.
c. The lower diameter guide is less subject to increased clearance when the nozzle housing 28 is pressurized and therefore provides improved guiding under pressure.
Calculations at 2600 bar indicate a 8 mm ID of the upper nozzle bore dilates 0.024 mm diametrically, whereas a 4 mm ID of the lower nozzle bore only dilates 0.010 mm diametrically. Optional machining of the gain orifices 40, 42 may also be used to provide through hole drilling for improved machining and less chance of burrs in drilling intersections. The improved guiding is evident by comparing the spray visualization photos of
The balanced and guided plunger 12 also results in improved shot to shot EOI variation.
Another unexpected improvement has been a faster injection rate at the start of injection. The faster injection rate may be due to more volume downstream of the gain orifice as provided by the enlarged lower supply chamber, and also the improved guiding and alignment of the plunger. This benefit may also be due to less pressure reduction downstream of the gain orifices when the plunger lifts. CFD modeling with a centered plunger showed no spray hole cavitation. The CFD results have been confirmed with improvement in spray hole cavitation in several cavitation rig tests when comparing the conventional plungers with the present balanced and guided plunger 12.
While various embodiments in accordance with the present disclosure have been shown and described, it is understood that the disclosure is not limited thereto. The present disclosure may be changed, modified and further applied by those skilled in the art. Therefore, this disclosure is not limited to the detail shown and described previously, but also includes all such changes and modifications.
| Number | Date | Country | |
|---|---|---|---|
| 61364520 | Jul 2010 | US |
