Patent Application
20070235554
The present invention relates to fuel injectors and, more particularly, to a dual stroke fuel injector including a shape memory alloy (SMA).
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.
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.
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.
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.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
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.
A fuel injector valve needle 18 is disposed within body 12 and includes a tip 18a that is cooperatively formed with valve seat 20 such that when valve needle 18 is in the closed position, valve tip 18a abuts valve seat 20 to prevent fuel from exiting fuel outlet 16 (see
As described above, fuel injector 10 is designed as a dual stroke injector.
As such, valve needle 18 may move from the fully closed position seen in
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
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
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.
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 D1 in
When armature stop 28 is in the retracted position seen in
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 28b and a spring stop 21 adjacent fuel inlet 14 although other spring shapes and positions within the injector are of course possible.
In the unactivated state, SMA component 32 has a first length L1 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
In this regard, it is seen that a core screw 40 and spring 40a extend from second armature stop 28 beyond end wall 28a 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 40a 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 L1 state seen in
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.
