Abstract:
A fuel injector including a piezoelectric actuator directly attached to a metering rod wherein when the actuator is distorted in proportion to an input voltage, the metering rod moves to vary the size of a discharge spray orifice. The input voltage, and therefore the distortion of the actuator, may be varied in accordance with the readings from a throttle position sensor or an oxygen sensor, for example. A dual actuator type of fuel injector is also provided which has an injector body in engagement with the combustion chamber and a fuel chamber therein to receive low pressure fuel. A piezoelectric actuator moves a piston to close the fuel chamber inlet and pressurize the fuel therein. A second piezoelectric actuator moves the metering rod to open the discharge orifice. The amount of distortion of the respective actuators effects proportional movement of the piston or the metering rod.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to internal combustion engines, and specifically to fuel injectors for small internal combustion engines.  
           [0003]    2. Description of the Related Art  
           [0004]    Internal combustion engines have at least one combustion chamber defined therein, each chamber having a spark plug associated therewith. Fuel enters the combustion chamber and is ignited by the spark plug to operate the engine. One method of moving fuel into the combustion chamber is to use fuel injectors which inject a regulated amount of fuel into the chamber to be ignited.  
           [0005]    There are several types of fuel injectors used to deliver fuel to the engine&#39;s combustion chambers. One type of commonly used fuel injector is a port type fuel injector. Port type fuel injectors are generally classified as one of two types including spray nozzles where the fuel flow is controlled at the fuel pump by fuel pressure, and spray nozzles including a control device such as a solenoid to control the duration of the spray action. Another type of fuel injector is a direct type fuel injector which provides injection of fuel directly into the compression chamber. This type of fuel injector has two actuators, one for controlling a metering rod or needle, and one for controlling the volume and pressure of a fuel chamber defined in the injector adjacent the discharge orifice.  
           [0006]    Although fuel injectors have become an increasingly common component of internal combustion engines, particularly those used in automobiles, the actuation of fuel injectors used in small engines can be problematic. Previous actuation methods for fuel injectors have included the use of solenoids to control the injection of the fuel into the combustion chamber. However, such solenoids generally allow for only a single injection rate of fuel, and thus would be unable to adjust the amount of fuel being injected to correspond to different applications or environments of the engine.  
           [0007]    Other actuation methods have included the use of certain piezoelectric devices. In U.S. Pat. No. 6,435,430 (Ruehle et al.), the piezoelectric actuator is used to actuate a fuel injector. The actuator is mounted to a base plate to which a needle is attached. As the actuator expands, the base plate is forced upwardly thus causing the needle to unseat from the discharge port. A compression spring is located between the base plate and fuel inlet connection piece of the fuel injector housing to return the needle to its seated position. Although Ruehle et al. uses a piezoelectric actuator to operate the fuel injector, the assembly of the fuel injector is complicated requiring several components. Further, a spring is required to return the needle to its closed position.  
           [0008]    A fuel injector which would be simple, inexpensive, and accurate for the operating conditions of the engine is desirable.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention relates to fuel injectors for use with small internal combustion engines. A first embodiment provides a port type fuel injector having a metering rod for controlling the flow of fuel through a spray orifice in the body of the fuel injector. A piezoelectric actuator is attached directly to the metering rod and the piezoelectric actuator and metering rod assembly is mounted to the fuel injector body by a vented retaining or end cap. When the piezoelectric actuator is distorted in proportion to an input voltage, the actuator moves the metering needle to open the spray orifice. The input voltage, and subsequently the distortion of the actuator, may be varied in accordance with the readings from a throttle position sensor, or an oxygen sensor, for example.  
           [0010]    A second embodiment of the present invention uses piezoelectric actuators in a dual actuator, or direct, type fuel injector. The direct type fuel injector has a injector body in communication with the combustion chamber and which receives low pressure fuel into a fuel chamber thereof. A piezoelectric actuator is used to move a piston that defines with the fuel injector body a fuel chamber. The piston is moved by the actuator to close the fuel chamber inlet and pressurize the fuel located in the chamber. A second piezoelectric actuator is directly connected to the metering needle to facilitate movement thereof. The fuel injection is then controlled by both the duration that the inlet port is open and distance the metering needle is lifted from its seat.  
           [0011]    One advantage of the fuel injectors of the present invention is that the piezoelectric actuators are mounted directly to the metering needle or piston which allows for accuracy when delivering fuel to the combustion chamber. Further, the piezoelectric actuators are mounted in the fuel injectors by the end caps thereof, simplifying assembly and reducing the cost of the fuel injector.  
           [0012]    One form of the present invention provides a fuel injector having a fuel injector body defining a fuel chamber therein. The fuel injector body includes at least one inlet in communication with the fuel chamber and has a retaining cap secured thereto. At least one outlet is defined in the fuel injector body. At least one control member is in the fuel chamber selectively variably engaging the outlet to cause the outlet to be in one of a range of conditions from fully open to fully closed. At least one piezoelectric actuator is directly connected to the control member. The actuator is secured to the injector body by the retaining cap and is distorted when an external voltage is applied thereto. When the actuator is distorted, the control member is moved, selectively changing the condition of the outlet.  
           [0013]    In another form of the present invention the fuel injector body includes at least one inlet in communication with the fuel chamber. At least one outlet is defined in the fuel injector body. At least one control member is in the fuel chamber selectively variably engaging the outlet to cause the outlet to be in one of a range of conditions from fully open to fully closed. A piston is mounted in the injector body in surrounding relationship of the control member. A first piezoelectric actuator is directly connected to the control member and a second piezoelectric actuator is directly connected to the piston. The actuator is distorted when an external voltage is applied thereto which moves the control member and selectively changes the condition of the outlet. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The above-mentioned and other features and objects of this invention will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0015]    [0015]FIG. 1 is a sectional view of a port type fuel injector in accordance with one embodiment of the present invention; and  
         [0016]    [0016]FIG. 2 is a sectional view of dual actuator type fuel injector in accordance with a second embodiment of the present invention. 
     
    
       [0017]    Corresponding reference characters indicate corresponding parts throughout the two views. Although the drawings represent two embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present invention. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION  
       [0018]    With reference to FIGS. 1 and 2, fuel injectors  20 A and  20 B are shown with each injector having injector body  22 A and  22 B, and retaining caps  24 A and  24 B respectively mounted to bodies  22 A and  22 B. Cap  24 B is shown as being threadedly secured to injector body  22 B. However, any suitable method providing a sealed engagement between the end cap and injector body may be used to assemble the fuel injector housing.  
         [0019]    Referring now to FIG. 1, fuel injector  20 A of the first embodiment includes fuel line connection or inlet  26  integrally formed with and extending from body  22 A. Fuel inlet  26  has threads  28  formed near the end thereof to provide a sealing connection with a fuel line (not shown) through which pressurized fuel from the fuel pump (not shown) of the engine (not shown) enters injector  20 A. The pressurized fuel entering injector body  22 A is received in chamber  30  defined therein in which a control member in the form of metering rod or needle  32  is located. Metering needle  32  is directly attached to piezoelectric actuator  34  at a top end thereof with needle  32  extending substantially perpendicularly from actuator  34 . The lower end of needle  32  is partially seated within discharge opening or orifice  36  formed in the lower end of injector body  22 A. Metering needle  32  includes tapered end  38  which, in conjunction with discharge orifice  36 , restricts the clearance between needle  32  and orifice  36  to control the flow of pressurized fuel from chamber  30 .  
         [0020]    Piezoelectric actuator  34  may be disk-shaped with circumferential edge  39  being sandwiched between retaining cap  24 A and injector body  22 A to mount the actuator and needle assembly within the injector. Retaining cap  24 A also includes vent hole  48  defined in the center thereof to vent fluid such as air or fuel vapors from the space above piezoelectric actuator  34  as it is actuated. Alternatively, vent hole  48  may be eliminated and the piezoelectric disk  34  provided with a vent hole (not shown) therein. Furthermore, the piezoelectric actuator  34  could be disk-shaped, thereby providing greater displacement when actuated and eliminating the need for vent hole.  
         [0021]    Piezoelectric actuator  34  may be of the type produced by Face International, under the “Thunder” trademark, such as disclosed in U.S. Pat. No. 5,632,841 (Hellbaum et al.), the complete disclosure of which is expressly incorporated herein by reference.  
         [0022]    Piezoelectric actuator  34  is a composite in which individual materials are layered, wherein the bottom layer is stainless steel, the middle layer PZT ceramic, and the top layer aluminum. The layers are bonded to each other by means of an adhesive applied therebetween. As the laminate is autoclaved during processing, the laminate is heated and compressed, allowed to cook and then cooled to room temperature. During cooling, the mismatch in coefficients of thermal expansion cause the material and ceramic layers to contract at different rates thereby putting the ceramic in compression at room temperature. This results in a pre-stress internal to the individual layers which provides the characteristic curvature of the device.  
         [0023]    The pre-stress keeps the ceramic in compression and allows the device  34  to be deflected far more than standard piezoceramics without cracking. When a voltage is applied, the radius of curvature will either increase or decrease, depending on the polarity, thereby creating a pumping motion with relatively large displacements. The design of piezoelectric actuator  34  provides a rapid response time and large displacement of needle  32 .  
         [0024]    Lower end  40  of injector body  22 A includes threads  42  formed thereon for sealed connection to the head or combustion chamber of the engine. Flange  44  is integrally formed on injector body  22 A and is located immediately above threads  42 . Annular gasket  46  is seated against flange  44  to provide a seal between the injector  20 A and the engine.  
         [0025]    The operation of injector  20 A is based upon the distortion in piezoelectric actuator  34  induced by application of an input voltage to actuator  34 . Piezoelectric actuator  34  acts as a positioning device for metering needle  32  in that the greater the distortion of actuator  34 , the greater distance metering needle  32  is moved upwardly within fuel chamber  30 . As needle  32  moves, tapered end  38  moves away from its seated position to increase the clearance between orifice  36  and needle  32 , and thereby control the flow of fuel through discharge orifice  36 . The distortion of actuator  34  is directly proportional to the input voltage applied thereto, with the input voltage being determined by feedback received from sensors in other portions of the engine, such as a throttle position sensor (not shown) or an oxygen sensor (not shown). Such sensors provide a signal relaying the amount of oxygen in the fuel-air mixture, or the position of the throttle to allow the engine to demand a certain amount of fuel be injected. Actuator  34  may be controlled by an external microprocessor which meters the amount of fuel needed in the combustion chamber.  
         [0026]    Referring now to FIG. 2, injector  20 B of the second embodiment includes two piezoelectric actuators  50  and  52 . Injectors  50  and  52  are structurally similar to actuator  34  of embodiment  20 A, specifically being either disk-shaped or strip-shaped and capable of distorting responsive to an input voltage. To show such distortion, actuator  50  is also shown in phantom in its uppermost position within valve body  22 B. Piezoelectric actuators  50  and  52  may be of the type produced by Face International, under the “Thunder” trademark or of the type disclosed in U.S. Pat. No. 5,632,841, the complete disclosure of which is expressly incorporated herein by reference.  
         [0027]    As described above, cap  24 B is threadedly secured to valve body  22 B. Valve body  22 B includes low pressure fuel inlet  54  extending therefrom, and which has no threads, unlike the fuel line connection  26  of first embodiment injector  20 A. Inlet  54  may be secured to the fuel line by any suitable means including an interference fit, adhesive, or the like. Lower extending portion  56  having thread  58  thereon extends from the lower end surface of injector body  22 B for threaded engagement with the head or combustion chamber of the internal combustion engine. Retaining cap  24 B has rounded portion  60  thereon to accommodate the upward distortion of piezoelectric actuator  50 .  
         [0028]    Body  22 B defines chamber  62  between actuators  50  and  52  with spacer  64  being placed between actuators  50  and  52  to maintain a desired distance therebetween. Pairs of annular o-rings  66  are located along the circumferential edge of each actuator  50  and  52 . With retaining cap  24 B threadedly secured to injector body  22 B, the circumferential edges of each actuator  50  and  52 , spacer  64 , and o-rings  66  are sandwiched between the retaining cap and injector body to mount the actuators in the fuel injector. Defined within lower portion  56  of injector body  22 B is fuel chamber  68  having a control member in the form of metering rod or needle  70  directly connected to actuator  50 , extending through actuator  52  and into chamber  68 . Nozzle or orifice  72  is located at the lower end of extending portion  56  and is in fluid communication with chamber  68 . Fuel flows through nozzle  72  into the head or combustion chamber of the engine. Piston  74  is located in injector body  22 B in surrounding relation of a portion of metering rod  70  and is directly attached to actuator  52 . Piston  74  has slot  76  formed therein which may be in fluid communication with inlet  54  depending upon the position of piston  74  within fuel chamber  68 .  
         [0029]    To operate injector  20 B, fuel flows into low pressure inlet  54 , past piston  74  via slot  76 , and into fuel chamber  68 . The amount of fuel within chamber  68  is varied by the movement of piston  74 , or by the amount of time that the inlet port is opened, i.e., the time that slot  76  is in communication with inlet  54 . To vary the length of time, or to move piston  74 , a voltage is applied to actuator  52  to cause downward distortion thereof, thereby moving piston  74  further into chamber  68  and moving slot  76  out of fluid communication with inlet  54 . Further downward movement of piston  74  pressurizes the fuel in chamber  68 .  
         [0030]    The fuel within chamber  68  is injected into the combustion chamber of the cylinder head by upward movement of rod  70 , and thus movement of tapered needle end  78  relative to orifice  72 . To open nozzle  72 , a voltage is applied to actuator  50  to cause upward distortion thereof, thereby lifting rod  70  from its seated position in nozzle  72  and allowing the pressurized fuel in chamber  68  to flow into the combustion chamber.  
         [0031]    The injection rate can be controlled by the movement of metering rod  70  including the amount of displacement of metering rod  70  from its seated position, and the rate of travel of piston  74  as controlled by actuator  52 . Both actuators  50  and  52  may be controlled by an external microprocessor which meters the amount of fuel needed in the combustion chamber.  
         [0032]    While this invention has been described as having exemplary structures, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.