Abstract:
A fuel injector intended for use on an internal combustion engine contains an injector needle that is longitudinally driven by an ultrasonic actuator during the time the injector valve is open to provide an atomized fuel spray output of sub-micron droplet sizes. A piezoelectric disk stack is mounted within the injector housing to surround a portion of the injector needle component and is used to provide the mechanical ultrasonic stimulation to the injector valve at the end of the injector needle and set up a corresponding wave-front at the injector valve to atomize the fuel as it leaves the injector nozzle.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 60/966,862 filed on Aug. 28, 2007, under 35 U.S.C. 119(e). 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The invention is directed to the field of fuel injectors of the type employed in internal combustion engines and more specifically to the area of spray control. 
         [0004]    2. Description of the Prior Art 
         [0005]    Fuel injectors typically use needle valves and various devices to control the movement of a needle from its normally closed valve seat to an open position in order to allow pressurized fuel to be sprayed into a combustion chamber of an internal combustion engine. 
         [0006]    A major goal in the development of fuel injectors is to obtain a fine or atomized spray of fuel vapor into the combustion chamber. The smaller the droplets the more surface area is provided for mixing with air in the combustion chamber. The greater the mixture, the more even and thorough is the subsequent combustion. This results in a more efficient power usage and less waste by-products. 
         [0007]    Traditionally, this has involved more and smaller spray nozzle orifices and fuel pumped at very high pressures through the orifices. In each case, the challenges to producing the desired fine spray are significant. For example, multiple but smaller orifices present more surface area and resistance to the fuel passing through and are more susceptible to blockage by particles or coking. Higher pump pressures also present the need for stronger connections, piping and injector springs, as well as more expensive pumping sources. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention achieves the goal of atomizing the spray of fuel vapor from a fuel injector by applying an ultrasonic vibration to the needle when the needle valve is in an open condition. 
         [0009]    The longitudinal vibrations of the needle, preferably at its natural frequency, cause the end tip of the needle to ultrasonically drive or pump the fuel through the nozzle orifices and to generate an atomized spray into the combustion chamber. 
         [0010]    Because the fuel is driven at the nozzle orifices by the tip of the needle, the fuel pressure need not be increased beyond that which is necessary to drive the needle to its open position, nor is it necessary to provide exceptionally small orifices in the nozzle to achieve the desired atomized spray. The vibration of the tip at an ultrasonic frequency enhances the spray and reduces the size of the droplets to sub-micron sizes. 
         [0011]    An embodiment of the invention is shown to be a modification of a conventionally driven and activated fuel injector. The modification includes a piezoelectric stack that forms an ultrasonic actuator mounted to surround a portion of the needle. The actuator is activated by an electrical signal to vibrate the needle longitudinally at the desired ultrasonic frequency during its open condition, i.e., during the time the needle is raised from its seated closed position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  represents a prior art fuel injector. 
           [0013]      FIG. 2  is a cross-sectional plan view of the lower end of a fuel injector containing elements of the present invention. 
           [0014]      FIG. 3  is an enlarged view of the nozzle end of the fuel injector shown in  FIG. 2 . 
           [0015]      FIG. 4  is a cross-sectional plan view of the lower end of a fuel injector containing additional elements of the present invention. 
           [0016]      FIG. 4A  is an end view representation of the piezo stack and wiring within the actuation chamber shown in  FIG. 4 . 
           [0017]      FIG. 5  is an enlarged view of the ultrasonic actuation portion of the fuel injector shown in  FIG. 3  with the needle in its closed position. 
           [0018]      FIG. 6  is an enlarged view of the ultrasonic actuation portion of the fuel injector shown in  FIG. 3  with the needle in its fully open position. 
           [0019]      FIG. 7  is a plot representation of the movement of the needle tip during the open portion of the injector valve cycle. 
           [0020]      FIG. 8  is an enlarged view of the nozzle end of the fuel injector during the open portion of the injector valve cycle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    A prior art fuel injector  10  is shown in  FIG. 1 . The injector  10  includes an upper housing  1  which is mountable to a cylinder of an internal combustion engine. (not shown). The upper housing  1  is a cylindrically formed element that supports all the other parts of the injector. The upper housing includes a central needle bore  2  and other cavities to support a metering valve  12  at its exposed upper end and an upper needle spring  14 . A fuel passage  9  is also contained in the upper housing  1  to deliver fuel under high pressure from an injector pump (not shown) to the lower end of the injector. A lower housing  4  is shown attached to the lower end of the upper housing  1 . Lower housing  4  is an extension of the upper housing  1  and is used in the manufacturing assembly of the injector. Lower housing  4  supports and captures a valve housing  8  while attaching the same to the upper housing  1 . Valve housing  8  defines an internal nozzle chamber  11  that is in communication with fuel passage  9  and a nozzle  3  at the end of housing  8 . Nozzle  3  contains one or more orifices and housing  8  provides an internal valve seat for injector needle tip  7  upstream of nozzle  3 . An injector needle  5  is slideably mounted within needle bore  2  and is held in a normally closed position by an upper spring  14  and the pressure of fuel present in the upper chamber  15  that is located in upper housing  1 . Injector Needle  5  can be made of one or more elements of lightweight (low mass) metal designed to allow its instantaneous movement within the bore and provide low inertia mass resistance to the movement. In response to actuation of metering valve  12 , the pressure in upper chamber  15  is released and high pressure fuel in nozzle chamber  11  acts on the shoulder of needle  5  within nozzle chamber  11  to move the needle up, overcoming the biasing force of spring  14 . Simultaneously, as needle  5  is moved to cause its tip  7  to become unseated and open the valve, the fuel entering that space, from bore  2  surrounding the lower end of needle  5 , provides pressure against tip  7  and adds to the pressure present at the shoulder. This additional pressure forces the needle further up to fully open the valve, thereby allowing the high pressure fuel to escape the injector at full volume through nozzle  3  and to be sprayed into the combustion chamber. 
         [0022]    The present invention is embodied in a fuel injector and is suitable to be implemented in prior art injectors, such as that shown in  FIG. 1  or other injectors designed to take advantage of the superior results offered by the invention. 
         [0023]    In  FIG. 2 , the lower end of a fuel injector  100  containing the present invention is shown in cross-section. An upper housing  101 , a lower housing  104  and a valve housing  108  together form the support structure of injector  100 . Upper housing  101  and valve housing  108  contain aligned needle bores  117  and  102 , respectively, into which an injector valve needle  105  is located for axial movement therein. A nozzle  103  containing a plurality of orifices is formed in the end of valve housing  108  and communicates with needle bore  102 . An actuation chamber  121  is formed in upper housing  101  as an extension of a spring chamber  116 . High pressure fuel passage  109  extends through upper housing  101  to a nozzle chamber  111  location between actuation chamber  121  and nozzle  103 . 
         [0024]    Valve needle  105  is made up of several elements which include a plunger  150 , a plunger flange  120 , an actuator rod  110 , a casing  106 , a needle body  125  with a tapered surface valve tip  107 . Plunger  150  is controlled in a conventional way from the upper portion of the housing by a metering valve or other suitable control mechanism. Such control provides a biasing pressure on plunger  150  over and above the bias pressure from biasing spring  114  to hold the valve closed when no fuel injection is desired and to relieve the pressure when fuel injection is desired. Plunger  150  extends into spring chamber  116  and actuation chamber  121  where its flange  120  abuts against biasing spring  114 . Spring  114  is compressed between the closed wall  118  of the spring chamber and the plunger flange  120  to provide the desired amount of biasing force to the valve needle  105 . 
         [0025]    Actuator rod  110  is preferably a solid metal structure that has a desired degree of axial elasticity. Actuator rod  110  is fixedly attached to plunger  150  and casing  106 . Plunger  150  contains a central bore  123 . Needle body  125  and casing  106  together contain an axial void  112  to provide reduced mass in valve needle  105 . Actuator rod  110  has one end fixedly secured in the upper end of void  112  in casing  106 , and its other end fixedly secured in bore  123  of plunger  150 . The opposite end of needle body  125  contains a tapered valve tip  107  that conforms to the inner valve seat  113  in valve housing  108 . An ultrasonic actuator  130  is located between the outer face  122  of plunger flange  120  and the face  119  of casing  106 . 
         [0026]    Ultrasonic actuator  130  is a made up of a stack of piezoelectric discs or plates, which are individually coated with an electrically conductive surface layer. Each disk is individually contacted electrically and energized by the electrical source. Due to the nature of piezoelectric crystals, they expand and contract when electrically energized. In this case, the stack axis is the axis of linear motion. Each disk is annular in shape and surrounds the actuator rod  110 . By applying a voltage across each disk the total stack lengthens. The elongation of a stack is roughly proportional to the stack&#39;s length (the longer the stack, the larger the expansion) and generally, the maximum achievable strain is on the order of 1-2%. When an alternating voltage is applied, the stack expands and contracts at that frequency. A natural or resonant frequency of the valve needle can be selected to gain efficiencies. 
         [0027]      FIG. 3  is an enlarged illustration of the injector valve tip  107  extending from needle  105 . Tip  107  is shown resting against seat  113  which is adjacent nozzle  103  and stack  115 . Tip  107  is shown in its normally biased closed condition to seal and prevent fuel present in needle bore  102  from escaping through nozzle  103  and into the combustion chamber. 
         [0028]    When injector needle  105  is moved in a conventional manner (to the right in the drawings) to disengage valve tip  107  from its contact with seat  113 , fuel present in needle bore  102  will escape under pressure through nozzle  103  and into the combustion chamber. The location of needle  105  to its open position is represented in  FIG. 8 . 
         [0029]      FIGS. 4 and 4A  additionally show wires  160  that are individually connected between an ultrasonic energy source (not shown) and each electrode of the piezoelectric disks that make up the ultrasonic actuator  130 . The figures further show a preferred routing of wires  160  through a passage  140  and into actuation chamber  121 . In this case, (see  FIG. 4A ) actuator chamber  121  is structured as a cylinder that is considerable larger than the piezoelectric stack in order to accommodate all of the actuator components. Actuator  130 , which is centered on actuator rod  110  within lower housing  104  and valve housing  108 , is located to one side of actuator chamber  121 . This location provides sufficient clearance for wires  160 , and accommodates the lower opening of passage  140 . The size is further determined by how much movement the wires require when the injector needle  105  is moved in a conventional manner during operation without incurring excessive wear on the wires. 
         [0030]      FIGS. 5 and 6  show the location of plunger  150 , plunger flange  120 , wires  160  and other actuation components when injector needle tip  107  is in both closed ( FIG. 5 ) and open ( FIG. 6 ) conditions. As can be seen from these figures, when the plunger  150  is biased to hold the injector closed, casing face  119  is located at a distance (d) as measured from a reference point in actuation chamber  121 , such as from forward wall  117 . When the pressure on plunger  150  is released, and fuel pressure forces needle  105  to be moved to an open condition. Therefore, plunger  150 , plunger flange  120  and the ultrasonic actuator components, including casing face  119  all move to a second position. That position is shown in  FIG. 6  as the distance (d′) measured from the reference point mentioned above to casing face  119 . 
         [0031]    When energized while the injector valve is open ( FIG. 6 ), piezoelectric disks that make up the ultrasonic actuator  130  expand and contract at a predetermined frequency and cause corresponding axial movement of the casing  106  and the needle tip  103  by expanding and contracting the length of actuator rod  110 . When energized to vibrate at a predetermined ultrasonic frequency that is selected to be the fundamental resonant frequency of the needle  105 , valve tip  107  is moved from its fully open position at (d′) a slight amount (d″) towards its closed position that is represented in  FIGS. 7 and 8 . 
         [0032]    This application of ultrasonic vibration to the injector needle occurs only during the time the injector needle valve is open. When the valve is closed (between injection portions of the engine cycle), the actuator  130  is not energized. During the time the actuator  130  is energized, a wave-front is established at valve tip  107  to cause to cause ultrasonic pulsation and cavitation of the fuel being injected through nozzle  103 . The resulting fuel cloud  300  is atomized and provides sub-micron sized droplets that, in total, present greater surface area than conventional droplets. Because of the greater surface area, the atomized spray serves to enhance the mixing of the fuel with air. This results in more complete and even burning during the combustion portion of the associated engine cycle. Complete and even burning increases the power efficiency of the engine by reducing wasted combustion gases and heat, since more complete burning means more of the energy is converted to mechanical expansion power. 
         [0033]    As can be seen by the drawings and accompanying explanation, the present invention is a unique improvement over conventional fuel injectors. And while the embodiment shown here is the preferred embodiment, it shall not be considered to be a restriction on the scope of the claims set forth below.