FUEL INJECTOR

Abstract: A fuel injector (10) having pressure equalization passages (20) is provided to equalize the pressure differential across an armature (80) in high vapor pressure fuels. At least one through passage (20) is included that extends from a chamber (60) beneath the armature to a chamber (50) atop the armature to prevent different pressure buildup when the injector is closed. The passages enable communication between the areas above and below the armature to rapidly equalize the pressure acting on the armature as the boiling bubbles burst and the fuel "explodes".

Description: FUEL INJECTOR BACKGROUND OF THE INVENTION This invention relates to fuel injectors and more particularly to a fuel injector in which the pressures across the armature must be equalized. During hot soak of liquid petroleum gas (LPG) and other high vapor pressure fuel vehicles having spark ignition, port injected engines, vapor leakage from the tips of the fuel injectors can fill the intake manifolds. This condition results in long starting times and can be attributed to a number of factors. For example, the manifold may fill with LPG vapors, little or no air may be present to support combustion, and the injectors may not be metering properly since they are calibrated to meter liquid; but may be filled with vapor. Observations of injector rails and pods which were lifted out of intake manifolds during hot soak have shown that the injectors were being caused to open momentarily on a random basis during the hot soak period. This random nature of injector opening suggests that the filling of the intake manifold by vapor is not only due to simple leakage from the fuel injectors, but is largely caused by the fuel injectors opening when the engine is not running, and the injectors are under pressure. It seems likely that the displacement of this vapor is caused as a result of violent boiling of the high vapor pressure fuel in the fuel injector which creates a pressure differential across the armature, causing the armature to move, and thus open the valve. This phenomenon can occur because these high vapor pressure fuels can boil violently at relatively low temperatures. Although vehicles which do not use these high vapor pressure fuels have been observed to have undesirable vapor formation in injectors as a result of engine heat, these vapors do not boil and "explode" as do the high vapor pressure fuels. Thus, the formed vapors are generally transported away from the injector by flushing them away in the return fuel through a fuel return path, as disclosed in U.S. Patent No. 4,71 1 ,397 issued to Lahiff and U.S. Patent No. 4,982,902 issued to Knapp et al. Although these vapor removal techniques are satisfactory for typical low vapor pressure fuels, such techniques do not address the problem of equalizing the pressure differentials created across an armature as a result of the violent boiling of high vapor pressure fuels. It is therefore an object of the present invention to provide a fuel injector in which the differential pressure which typically occurs across the armature in vehicles using high pressure fuels can be avoided in order to reduce or eliminate the resulting liquid or vapor leakage from the fuel injector tip into the intake manifold. SUMMARY OF THE INVENTION The above-recited objects are achieved by providing a fuel injector, typically a bottom fed injector calibrated for LPG applications, having at least one through passage that extends from a chamber beneath the armature to a chamber atop at least a portion of the armature to prevent differential pressure buildup when the injector is closed. The passages enable communication between the areas above and below the armature to rapidly equalize the pressures acting on the armature as the boiling bubbles burst and the fuel "explodes" . Without the presence of the pressure equalizing passages the armature momentarily lifts the needle when the bubble bursts under the armature, and relatively large amounts of fuel are admitted into the intake manifold during hot soak. When this happens, the manifold can fill with vaporized fuel, making hot start difficult or impossible, depending on the exact conditions in the manifold. The number, size and placement of the passages are determined as a function of the anticipated pressure differential across the armature, depending on the specific application. DESCRIPTION OF THE DRAWINGS Figure 1 is a top schematic view of the top area of the valve body of a fuel injector according to the present invention. Figure 2 is a cross sectional view of the valve body of Figure 1 . Figure 3 is a more detailed cross sectional view of a fuel injector having pressure equalization passages according to the present invention. DETAILED DESCRIPTION As shown in Figures 1 and 3, the fuel injector 1 0 has a plurality of pressure equalization passages 20 spaced around the top surface 30 of the valve body 40 and communicating with an upper chamber 50 and a lower chamber 60. As can be seen more clearly in Figures 2 and 3, the lower chamber 60 is partially defined by the bottom surface 70 ' of the armature 80 and the upper chamber 50 is partially defined by the upper flange surface 90 of the armature 80. Thus, the passages 20 permit vapor to move rapidly between the upper chamber 50 and the lower chamber 60 so that pressures acting on the bottom surface 70 and the upper flange surface 90 of the armature 80 in the chambers 50,60 are quickly equalized. As can be seen from Figure 3, without the presence of the passages 20, a sudden increase in pressure in the lower chamber 60 would cause the armature 80 to travel upward, and permit the escape of vapor from the tip 1 00 of the fuel injector 1 0 as the injector needle 1 1 0 was lifted by the armature 80. As shown in Figure 1 , the fuel injector 1 0 has four substantially equally and angularly spaced pressure equalization passages 20 connecting the chambers 50, 60. However, the number of passage 20 may vary as desired to achieve the desired rate of pressure equalization between the chambers 50, 60. Although a passage diameter of about one mm is suitable for most fuel injectors having four passages 20, there can be one or a plurality of passages, as long as the number and size of passages 20 permit sufficiently rapid pressure equalization between the chambers 50,60 to prevent the armature from being lifted by the violent boiling action of the fuel in the bottom chamber 60 of the fuel injector 10. It is understood that, while the detailed description and drawings show specific examples of the present invention, they are for purpose of illustration only. The present invention is not limited to the precise details and conditions disclosed. For example, linear passages operate most efficiently, but the passages may be non-linear if desired or required by design constraints of the injector. In addition, when the valve body has a plurality of passages, the passages can be unequally spaced. The passages can also be unequally sized and spaced, such that the diameters of the plurality of passageways varies from one to another.

Claims: What is claimed is: 1 . An electromagnetic fuel injector for high vapor pressure fuels, said fuel injector comprising: an armature slidably disposed in a valve body, said valve body having a lower chamber below the armature and an upper chamber above at least a portion of said armature; and means for rapid equalization of pressure between said lower chamber and said upper chamber. 2. The fuel injector of claim 1 , wherein the means for rapid equalization of pressure is at least one passageway extending through said valve body from said lower chamber to said upper chamber, said at least one passageway being sized to permit rapid pressure equalization between said lower chamber and said upper chamber. 3. The fuel injector of claim 2, wherein the fuel injector is a bottom-feed injector. 4. The fuel injector of claim 2, including a plurality of passageways. 5. The fuel injector of claim 4, wherein the passageways are substantially equally and angularly spaced about the armature. 6. The fuel injector of claim 5, having four passageways, each of said passageways being about one mm in diameter. 7. A method of equalizing differential pressure in an electromagnetic fuel injector for high vapor pressure fuels, said injector having an armature slidably disposed in a valve body, and having a lower chamber below the armature and an upper chamber above at least a portion of the armature, comprising the step of: providing at least one passageway extending through the valve body from the lower chamber to the upper chamber, said at least one passageway being sized to permit rapid pressure equalization between the lower chamber and the upper chamber. 8. The method of claim 7, wherein the fuel injector is a bottom-feed injector. 9. The method of claim 7, including providing a plurality of passageways. 1 0. The method of claim 9, wherein the passageways are substantially equally and angularly spaced about the armature. 1 1 . The method of claim 1 0, having four passageways, each of said passageways being about one mm in diameter.

Inventors: DEGRACE LOUIS G, DEGRACE, LOUIS, G.
Applicants: SIEMENS AUTOMOTIVE CORP LP, SIEMENS AUTOMOTIVE CORPORATION
Application year: 1998
Main classification: F02M51
IPC codes: F02M21, F02M51, F02M63