Patent Publication Number: US-7900604-B2

Title: Dampening stop pin

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/690,899, filed on Jun. 16, 2005, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention generally relates to a fuel injector and, more particularly, to a dampened stop pin that reduces the closing speed of the needle prior to seating at a needle seat to block the passage of fuel out of the nozzle spray holes. 
     2. Background Description 
     There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber. 
     In current designs, a driver delivers a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid shifts a spool into the open position so as to align grooves or orifices (hereinafter referred to as “grooves”) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high-pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high-pressure plunger chamber. As the pressure in the high-pressure plunger chamber increases, the fuel pressure will begin to rise above a valve opening pressure. At the prescribed fuel pressure level, the needle will shift against the stop pin and the biasing force of the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine. 
     It is desirable to provide rapid closing of the needle after a fuel injection event in order to limit undesirable noise and improve engine emissions. The needle spring, however, contains a high mechanical load force when fully opened. As a result, closing the needle at a relatively high speed causes the needle to strike the needle seat proximate the nozzle tip with great force. Such an impact can severely damage the needle or may even cause the nozzle body to crack. 
     SUMMARY OF THE INVENTION 
     The invention solves the foregoing problems and avoids the disadvantage and drawbacks of the prior art by dampening the closing force of the needle by creating a fuel cushion and venting a quantity fuel from the cushion. 
     The invention may be implemented in a number of ways. In accordance with an embodiment of the invention, a nozzle body for a fuel injector includes a nozzle having at least one injection hole at a first section of said; a nozzle sealing surface at a second section that is spaced from the first section; and nozzle bore disposed between the first and second sections. The nozzle body may further include a movable needle having a portion disposed within the nozzle bore, a cage having an inner surface defining a cage bore, and a biasing mechanism disposed within the cage bore that biases the needle towards the injection hole in a closed position. Moreover the nozzle body has a dampening stop pin having a first portion upon which said biasing mechanism applies its biasing force, a second portion disposed adjacent said nozzle sealing surface, and a third portion disposed adjacent the inner surface of said cage. The second portion is spaced apart from the nozzle sealing surface at a first distance between approximately 180μ-320μ when the needle is in the closed position, and the third portion is spaced apart from the inner surface of the cage at a second distance between approximately 40μ-100μ. 
     In accordance with another embodiment of the invention, a method for dampening a closing force of a needle having open and closed positions in a fuel injector includes compressing fuel in a gap between a bottom surface of a stop pin flange and a nozzle sealing surface to provide a fuel cushion dampening the closing force of the needle, and venting a quantity of fuel from the gap through a diametrical clearance between an outer circumferential edge of the stop pin flange and an inner surface of a spring cage. The gap is about 180μ-320μ when the needle is in the closed position. 
     In accordance with yet another embodiment of the invention, a nozzle body for a fuel injector includes a nozzle having at least one injection hole at a first section, a nozzle sealing surface at a second section of the nozzle spaced from the first section; and a nozzle bore disposed between the first and second sections. The nozzle body also has a movable needle having a portion disposed within the nozzle bore, a cage having an inner surface defining a cage bore, and a biasing mechanism disposed within the cage bore that biases the needle towards the injection hole in a closed position. The nozzle body further includes a dampening stop pin having a portion upon which said biasing mechanism applies its biasing force and means for dampening the closing force of the needle by compressing fuel in a gap formed at least in part by the dampening stop pin and permitting a quantity of fuel to vent from the gap. 
     Additional features, advantages, and embodiments of the invention may be set forth or apparent from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the invention and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the detailed description serve to explain principles of the invention. No attempt is made to show structural details of the invention in more detail than may be necessary for a fundamental understanding of the invention and the various ways in which it may be practiced. In the drawings: 
         FIG. 1  illustrates an elevational cross-sectional view of a hydraulic actuated fuel injector using a dampening stop pin according to the principles of the invention; 
         FIG. 2  illustrates an elevational cross-sectional view of a typical prior art stop pin; 
         FIG. 3  illustrates a side elevational view of one embodiment of a dampening stop pin according to the principles of the invention; 
         FIG. 3A  is an enlarged view of the dampening stop pin of  FIG. 3 ; and 
         FIG. 4  is a graph comparing the needle impact vs. lug curve point of fuel injector having a dampening stop pin according to the principles of the invention with a fuel injector having a typical prior art stop pin. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiments of the invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of one embodiment may be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the embodiments of the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the invention may be practiced and to further enable those of skill in the art to practice the embodiments of the invention. Accordingly, the examples and embodiments herein should not be construed as limiting the scope of the invention, which is defined solely by the appended claims and applicable law. Moreover, it is noted that like reference numerals represent similar parts throughout the several views of the drawings. 
       FIG. 1  illustrates a hydraulic actuated fuel injector  100 , which may include a control valve body  110 , an intensifier body  130 , and a nozzle body assembly unit  150 . Here, the control valve body  110  may have an inlet  111  and outlets  113 ,  115  that permit the flow of an actuating hydraulic fluid, such as oil, to enter and exit the intensifier body  130  at working ports  128 . There may also be a longitudinally-slidable spool  116  having at least one orifice  117 , or groove, that selectively allows fluid communication between the inlet  111  and outlets  113 ,  115  and the working ports  128 . The control valve body  110  may further include a pair of opposing solenoid coils, an open coil  120   a  and a closed coil  120   b , to actuate movement of the spool  116 . A single bolt  118 , which extends into a hollow interior space of the spool  116 , may be used to fasten the solenoid end caps  120   a ,  120   b  to control valve body  110 . Other types of fuel injector control bodies, such as a piezoelectric control body (not shown), may be used in lieu of the solenoid-type control body shown here. 
       FIG. 1  also shows an intensifier body  130  that may include a piston  132  and a plunger  134  biased toward the control valve body  110  by an intensifier spring  138 . At an end of the plunger  134  opposite the piston  132 , there may be an intensifier chamber  140  for pressurizing fuel that is in fluid communication with a fuel source (not shown) via a fuel inlet  142 . A pressurized fuel path  148  may provide fluid communication between the intensifier chamber  140  and the nozzle body assembly unit  150 . While one arrangement for pressurizing fuel is shown in  FIG. 1 , any suitable apparatus can be used for pressurizing fuel in accordance with the principles of the invention. 
     The intensifier body  130  may be coupled to the nozzle body assembly unit  150  using a nut  152 , or any other suitable means, such as, for example, a press-fit or threading. The nozzle body assembly unit  150  includes a spring cage  154  and a nozzle  160 . The spring cage  154  may have a needle spring  156  biasing a stop pin  158  towards the nozzle. The nozzle  160  can include a needle  166  that is biased by the stop pin  158  in a closed position against a needle seat  168  to occlude at least one injection or spray hole  163  located at the nozzle tip  161 . The stop pin  158  and needle  166  can be separate components or one unitary piece. The nozzle  160  may also have a nozzle fuel chamber  167  that receives pressurized fuel from the intensifier chamber  140  via the pressurized fuel path  148 . 
       FIG. 2  shows a prior-art stop pin  200 . The stop pin  200  has a substantially frustconical-shaped flange  205  and is biased towards needle  266  by a needle spring  256  disposed within spring cage  254 . When the needle is seated in a closed position, there can be a gap (G′) of approximately 0.7 mm between a bottom surface  205   a  of flange  205  and a sealing surface  265  of the nozzle  260 . Further, a typical stop-pin, such as the one illustrated in  FIG. 2 , may have a diametrical clearance (C′) of approximately 0.25 mm between the outermost portion of flange  205  and an inner, cylindrical surface  254   a  defining a bore within the spring cage  254 . 
       FIG. 3  illustrates an embodiment of a stop pin constructed in accordance with the principles of the invention. Stop pin  158  may comprise a substantially cylindrical-shaped flange  305 . When the needle  166  is seated against the needle seat  168  in a closed position, a gap (G) between a bottom surface  305   a  of flange  305  and a sealing surface  165  of nozzle  160  is approximately 180μ-320μ, as best shown in the enlarged view of  FIG. 3A . Further, the diametrical clearance (C) between the outermost circumferential edge  305   b  of flange  305  and an inner cylindrical surface  154   a , which defines a bore within the needle spring cage  154 , is sized approximately 40μ-100μ. Moreover, the height (H) of the flange  305  at its circumferential edge  305   b  preferably should not exceed about 1.2 mm-2.0 mm. 
     The stop pin may  158  further include a shim  310  at an end opposite the flange  305 , as shown in  FIG. 3 . The shim  310  and flange  305  can be formed by stamping or turning, as well as any other suitable method, and may be joined by a cylindrical pin  315 . The needle spring  156  may have dead end coils  320  that have a smaller outer diameter than the working coils  325 . These dead end coils  320  may be disposed at either end, or both ends, of spring  156  to guide the axial motion of cylindrical pin  315  during the opening and closing of needle  166 . 
     The operation of the fuel injector illustrated in  FIG. 1  will now be discussed in detail. 
     A hydraulic fluid, such as oil, will enter the control valve body  110  at inlet  111 . A driver will apply current to the open solenoid coil  120   a  to move the spool  116  into the open position to selectively permit fluid communication between the inlet  111  and the working ports  128  via grooves  117 . The fluid at the working ports  128  passes into the intensifier body  130  and acts on the piston  132  and plunger  134  against the biasing force provided by the intensifier spring  138 . The downward movement of the plunger  134 , in response to hydraulic fluid, pressurizes the fuel in the intensifier chamber  140  supplied at the fuel inlet. The pressurized fuel proceeds to the nozzle body  160  via the pressurized fuel path  148 . 
     The pressurized fuel enters the fuel chamber of nozzle body  160  and applies force to the needle  166 , which moves the stop pin upwardly against the biasing provided by the needle spring  156  to unseat the needle  166  from its seat  168  and expose the injection holes  163  in the nozzle tip  161 . A quantity of pressurized fuel can then be injected into a combustion chamber of an internal combustion engine or the like. 
     After a desired fuel injection period, the driver will supply current to a closed solenoid coil  120   b  that actuates movement of the spool  116  to a closed position that will block fluid communication between the inlet  111  and the working ports  128 , and instead allow the hydraulic fluid to exit the intensifier body  130  by permitting fluid communication between the working ports  128  and the outlets  113 ,  115 . The plunger  132  will then move upwardly in response to the biasing force provided by the intensifier spring  138  that no longer has the pressurized hydraulic fluid acting upon it. The upward movement of the plunger  132  may also suction a quantity of fuel into the intensifier chamber  140  for the next injection event. 
     Now the needle spring  156 , which no longer has the pressurized fuel acting against its biasing force, will bias the stop pin  158  downwardly to rapidly reseat the needle  166  and occlude the injection holes  163 . As the stop pin  158  returns to needle  166  the closed position, it will compress the fuel trapped in the gap (G) between the bottom surface  305   a  of stop pin flange  305  and the nozzle sealing seat  165 . This compressed fuel can vent though the diametrical clearance (C) between the outer edge of flange  305   a  and the spring cage inner surface  154   a  and provides a fuel cushion that dampens the closing force of the stop pin  158 . 
     If the gap (G) between the flange  305  and nozzle sealing surface  165  is too large, the fuel trapped in that gap will not be compressed enough to provide cushioning required for dampening. If this gap (G) is too small, however, the compressed fuel may interfere with needle closing and could even separate the stop pin  158  from the needle  166 . Accordingly, a gap (G) between approximately 180μ-320μ is suitable for providing dampening while not adversely affecting needle closing. 
     Moreover, a portion of the compressed fuel needs to vent through the diametrical clearance (C) from the gap (G) to provide dampening without interfering with needle closing. If the diametrical clearance (C) is too small, then undesired high pressure may build up in the gap to interfere with needle closing. This undesired high pressure can also result if the fuel escape path along the clearance (C) is too long due to the thickness of the flange  305 . On the other hand, if the diametrical clearance (C) is too large, the compressed fuel can escape too easily from the gap (G) and will not provide the desired dampening effect. Likewise, a diametrical clearance (C) between approximately 40μ-100μ is suitable for providing dampening while not adversely affecting needle closing. 
       FIG. 4  illustrates the performance of a dampening stop pin of the invention, as shown in  FIG. 3 , as compared to a prior art stop pin, shown in  FIG. 2 , over 300 fuel injection events. The graph shows that at all points of the lug-curve, the measured needle impact (in terms of percentage) is substantially lower using the dampening stop pin of the invention than the prior art stop-pin. 
     In summary, it is desirable to provide a gap between a flange of a dampening stop pin and a nozzle sealing surface large enough to prevent pressure from building up too high at an early stage of needle closing. At the same time, it is critical that this gap is small enough to maintain a fuel cushion as the needle becomes seated at the needle seat. By configuring the stop pin to provide dampening in such a manner, the invention can maintain a fast needle closing motion without substantially affecting the needle&#39;s opening properties. 
     While the invention has been described in terms of particular embodiments, those skilled in the art will recognize that the invention can be practiced with modifications in the spirit and scope of the appended claims. These examples given above are merely illustrative and are not meant to be an exhaustive list of all possible designs, embodiments, applications, or modifications of the invention.