Abstract:
A dual stroke fuel injector including a shape memory alloy component for controlling the short and long strokes of the injector.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to fuel injectors and, more particularly, to a dual stroke fuel injector including a shape memory alloy (SMA).  
       BACKGROUND OF THE INVENTION  
       [0002]     Both single stroke and dual stroke fuel injectors are known. In a common fuel injector design, a needle valve controls fuel flow through the injector and into the combustion chamber. In a single stroke injector, the needle is only movable from the closed position to a single open position. In a dual stroke injector, the needle may be moved between two different opening positions each providing a different flow area through which fuel may flow out of the injector and into the combustion chamber or intake manifold. As such, a dual stroke injector allows for a variable injector stroke position that correlates to a respectively variable engine load condition. The movement of the valve needle in both the single stroke and dual stroke injectors may be controlled by an electromechanical, hydromechanical or piezoelectric actuator, for example, in response to prevailing engine load conditions.  
         [0003]     In a dual stroke fuel injector, the two stroke positions are typically referred to as the short stroke and long stroke corresponding to low fuel flow and high fuel flow conditions, respectively. Injectors are designed to open and close with a pulse width modulation that supplies the correct amount of fuel to the engine. During relatively low engine load conditions, a dual injector executes short strokes, opening and closing the valve very quickly with quick injections of fuel to the engine. At higher engine load conditions, the dual injector executes a long stroke to allow more fuel to flow to the engine.  
         [0004]     Dual stroke injectors require actuation for both the short stroke and long stroke stages of the injector. To accomplish this, many present day dual stroke injectors simply tend to add electromechanical actuator parts (e.g., a second solenoid) that make the injector more costly and bulky. A need therefore exists for an improved dual stroke injector that is cost efficient and not appreciably bigger than a single stroke injector.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention successfully addresses the above need by providing a dual stroke fuel injector that includes a shape memory alloy (SMA) actuator for executing the long stroke of the injector. More particularly, the SMA actuator is operable to retract one of a pair of armature stops within the injector. The armature controls movement of the valve needle in response to signals received by the engine. The first armature stop is fixed relative to the moving armature and needle. The second armature stop extends beyond the first armature stop to control the short stroke cycle of the injector. When the SMA actuator is energized, the second armature stop retracts relative to the first armature stop thereby allowing the valve needle to execute a long stroke. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0007]      FIG. 1  is a longitudinal cross-section of an embodiment of the inventive fuel injector shown in the closed position;  
         [0008]      FIG. 2  is the view of  FIG. 1  with the injector shown in the short stroke position; and  
         [0009]      FIG. 3  is the view of  FIG. 1  with the injector shown in the long stroke position. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0010]     Referring to the drawing figures, an embodiment of the inventive dual stroke fuel injector is shown generally by the reference numeral  10 . Fuel injector  10  includes a body  12  having a fuel inlet  14  and fuel outlet  16 . The fuel inlet  14  is adapted to be connected to a fuel line (not shown) for supply of fuel to the fuel injector  10 . Fuel outlet  16  is adapted to direct fuel from the injector into a combustion chamber or intake manifold of an engine (not shown). Fuel injector  10  may be made for gasoline, diesel, or any other engine which could receive the benefits of a dual stroke injector.  
         [0011]     A fuel injector valve needle  18  is disposed within body  12  and includes a tip  18   a  that is cooperatively formed with valve seat  20  such that when valve needle  18  is in the closed position, valve tip  18   a  abuts valve seat  20  to prevent fuel from exiting fuel outlet  16  (see  FIG. 1 ). When the engine is running, the fuel injectors open and close according to the designed pulse width modulation to deliver the correct amount of fuel to the engine.  
         [0012]     As described above, fuel injector  10  is designed as a dual stroke injector.  
         [0013]     As such, valve needle  18  may move from the fully closed position seen in  FIG. 1  to either a short stroke position as seen in  FIG. 2  or a long stroke position as seen in  FIG. 3  according to the received engine load signal. It is understood that injector  10 , through appropriate electrical connections, is operable to respond to engine load signals with the appropriate needle movement. Such connections are well known to those skilled in the art and will not be further elaborated upon herein.  
         [0014]     In the preferred embodiment, needle movement is effected via a solenoid comprising a coil  22  surrounding injector body  12  and an armature  24  within body  12  and to which needle  18  is attached. Upon fuel injector  10  receiving a signal to open the valve needle from the closed position seen in  FIG. 1 , coil  22  is energized causing movement of armature  24  in a direction away from the fuel outlet  16 , thereby lifting needle tip  18   a  from valve seat  20  to allow fuel to flow through outlet  16 .  
         [0015]     First and second armature stops  26  and  28 , respectively, are provided within injector body  12  and act to limit the linear travel of needle  18  in the direction away from the fuel outlet  16 . In the preferred embodiment, first armature stop  26  is fixed and second armature stop  28  is movable with respect to the first armature stop. Second armature stop is movable between the extended position seen in  FIG. 2  and the retracted position seen in  FIG. 3 . When in the extended position, the end wall  28   a  thereof extends beyond the end wall  26   a  of the first armature stop  26 .  
         [0016]     In the preferred embodiment shown, armature stops  26  and  28  are arranged in coaxial relationship with second armature stop  28  positioned for reciprocating movement within first armature stop  26 . It is understood, however, that the armature stops can be of any suitable shape and positional relationship depending on the particular injector design employed. Also, the movement of the movable armature stop may be along the longitudinal axis of the injector as shown, or may be adapted to move in a different direction such as radially, for example. It is furthermore noted that either or both armature stops may be made movable so long as they cooperatively operate to control movement of the armature between a short stroke and long stroke in accordance with the engine load signal received by the injector.  
         [0017]     When second armature stop  28  is in this extended position, it forms a stop against which armature  24  abuts when traveling in a direction away from the fuel outlet. This movement is considered the short stroke of the injector and the linear distance traveled by armature  24  is indicated by D 1  in  FIG. 2 .  
         [0018]     When armature stop  28  is in the retracted position seen in  FIG. 3 , end wall  28   a  lies in a plane that is at least flush or recessed with respect to end wall  26   a  of first armature stop  26 . As such, end wall  26   a  acts as the stop against which armature  24  abuts when traveling in a direction away from the fuel outlet. In this instance, end wall  28   a  does not influence the stroke of the injector. This movement is considered the long stroke of the injector and the linear distance traveled by armature  24  is indicated by D 2  in  FIG. 3  where D 1 &lt;D 2 .  
         [0019]     Movement of second armature stop  28 , and thus the long stroke of the injector, is controlled by a shape memory alloy (SMA) component  32  via circuitry  31 . In the preferred embodiment, the SMA component  32  is positioned between a fixed block  25  and a movable block  27 . A helical spring  30  is located between end wall  28   b  and a spring stop  21  adjacent fuel inlet  14  although other spring shapes and positions within the injector are of course possible.  
         [0020]     In the unactivated state, SMA component  32  has a first length L 1  that is not long enough to bear against and move movable block  27 . As such, spring  30  is extended to bias second armature stop  28  in the extended (short stroke) position of  FIG. 2 . When activated via circuitry  31 , SMA component  32  expands and lengthens to a length L 2  which bears against and moves movable block  27  upward to move end wall  28   b  and compress spring  30  ( FIG. 3 ). As such, the bias against second armature stop  28  by spring  30  is relieved.  
         [0021]     In this regard, it is seen that a core screw  40  and spring  40   a  extend from second armature stop  28  beyond end wall  28   a  to abut and bias armature  24  and needle  18  toward the closed position. Upon activation of coil  22 , armature  24  moves against the bias of spring  40   a  to execute either a short stroke (second armature stop  28  extended) or a long stroke (second armature stop  28  retracted) in accordance with the received engine load signal. Once SMA component  32  is deactivated, the bias of spring  30  assists in returning SMA component  32  to its smaller length L 1  state seen in  FIGS. 1 and 2 . This causes second armature stop  28  to extend for a short stroke of the injector or close altogether depending on the engine load signal.  
         [0022]     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.