WO2008076239A2

WO2008076239A2 - Fuel injector having a balanced valve member

Info

Publication number: WO2008076239A2
Application number: PCT/US2007/025201
Authority: WO
Inventors: John Enrietto
Original assignee: Wabash Technologies, Inc.
Priority date: 2006-12-15
Filing date: 2007-12-10
Publication date: 2008-06-26
Also published as: WO2008076239A3

Abstract

A fuel injector (10) including a valve body (12) defining a fuel chamber (30) for containing a pressurized fuel (F) and having at least one fuel inlet (34) and at least one fuel outlet (36), each in communication with the fuel chamber (30) The fuel injector (10) also includes a valve member (14) at least partially positioned within the fuel chamber (30) and configured for reciprocating movement along an actuation axis (L) The valve member (14) includes a first valve surface (96) facing a first axial direction and a second valve surface (98) facing a second axial direction generally opposite the first axial direction, with each of the first and second valve surfaces (96, 98) exposed to the pressurized fuel (F) within the fuel chamber (30)

Description

FUEL INJECTOR HAVING A BALANCED VALVE MEMBER

CROSS-REFERENCE TO RELATED APPLICATIONS In accordance with applicable treaties, the present application claims foreign priority to U.S. Patent Application Number 60/875,155 filed on 15 December 2006, and is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of fuel injectors, and more specifically relates to a fuel injector having a balanced valve member.

BACKGROUND

Electronically-controlled fuel injectors are designed to inject regulated amounts of fuel into a combustion chamber of an internal combustion engine. The fuel injectors include internal fuel chambers, fuel passages, and one or more control valves that control the flow of fuel through the injector between injection sequences. During the injection process, one or more control valves move in a timed sequence to open and close the various fuel passages and fuel chambers such that pressurized fuel is injected from an injector tip and into the combustion chamber at the appropriate times in the injection process.

Several types of fuel injectors are used to deliver fuel into the combustion chamber. One type of commonly used fuel injector is a port-type fuel injector. A port- type fuel injector is generally classified as one of two types, including spray nozzles where fuel flow is controlled at the fuel pump by tight regulation of 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 combustion chamber.

Although fuel injectors have become an increasingly common component of internal combustion engines, particularly with regard to use in automobiles, the actuation of fuel injectors can be problematic. For example, control valves within the injector are sometimes actuated by one or more solenoids that receive electrical control signals from an electronic controller. In response to the control signals, actuation of the solenoids causes the control valves to move from one position to another to communicate fuel through the injector to the injector tip for injection into the combustion chamber. However, it is often difficult to accurately control movement and positioning of the control valves via the electronic control signals applied to the solenoids. Solenoid- controlled valves, by their very nature, are susceptible to variability in their operation due to inductive delays, eddy currents, spring pre-loads, solenoid force characteristics, and varying fluid flow forces. Moreover, the response time of solenoids limits the minimum possible dwell times between multiple injection events, and also makes the fuel injector generally more susceptible to various sources of variability.

Control valves within a fuel injector may also be actuated by one or more piezoelectric actuators that receive control signals from an electronic controller which activates and deactivates the actuator. However, the actuation force generated by a piezoelectric actuator is limited. Therefore, the amount of force that may be exerted onto the injector valve via a piezoelectric actuator is likewise limited. Accordingly, most piezoelectric actuators are not suitable for use in association with high pressure fuel applications that are becoming more prevalent in uses involving diesel engines to achieve requisite emission levels. Such high pressure fuel applications can reach fuel pressure levels of approaching 30,000 psi. In some high pressure fuel applications, multiple piezoelectric actuators are stacked to increase the amount of force generated by the piezoelectric actuator assembly. A hydraulic valve system is also provided between the piezoelectric actuator assembly and the injector valve to amplify the force exerted onto the injector valve to provide the amount of force required in high pressure fuel applications. The hydraulic valve assembly typically includes a hydraulic oil pump, hydraulic tubing and connectors, and intricate components to control the flow of oil. As should be appreciated, the use of multiple piezoelectric actuators and/or the inclusion of a hydraulic valve assembly is expensive, increases the complexity of the fuel injector assembly, adds to the overall weight of the fuel injector assembly, and may result in operational delay times which may negatively impact fuel injector performance.

Additionally, proper material selection for the components associated with the fuel injector is important to ensure proper operation and performance. For example, fuel contamination, high contact surface pressures, greater timing control allowing up to 5-7 fuel injections per engine cycle, and long life requirements all contribute to the importance of proper material selection. Additionally, contamination of fuels with low levels of water and a tendency to reduce the sulfur content in the fuel (resulting in a reduction in lubricating agents) may cause problems with regard to seizing of metal-on- metal components within the fuel injector. Moreover, as indicated above, high pressure fuel applications can reach fuel pressure levels approaching 30,000 psi. These factors underscore the importance of proper material selection of the fuel injector components, particularly with regard to elements of the fuel injector that move and which are exposed to fuel, such as, for example, the valve element and/or portions of the actuator. Furthermore, proper control and performance of the fuel injector requires precise dispensing of fuel at relatively high pressures via opening and closing of passages and shutoff points with precise timing that may approach the mili- to micro-second range. The injector valve and actuator components typically must act and move precisely for several billion cycles over temperature extremes ranging up to 250 degrees C. Thus, there is a general need in the industry to provide an improved fuel injector.

The present invention meets this need and provides other benefits and advantages in a novel and unobvious manner.

SUMMARY The present invention relates generally to a fuel injector having a balanced valve member. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the preferred embodiments disclosed herein are described briefly as follows. In one form of the present invention, a fuel injector is provided including a valve body defining a fuel chamber for containing a pressurized fuel and having at least one fuel inlet and at least one fuel outlet, each in fluid communication with the fuel chamber. The fuel injector also includes a valve member at least partially positioned within the fuel chamber and configured for reciprocating movement along an actuation axis. The valve member includes a first valve surface facing a first axial direction and a second valve surface facing a second axial direction generally opposite the first axial direction, with each of the first and second valve surfaces exposed to the pressurized fuel within the fuel chamber. The fuel injector further includes at least one actuator coupled to the valve member such that activation of the actuator results in axial displacement of the valve member to control a flow of the pressurized fuel through the at least one fuel outlet.

In another form of the present invention, a fuel injector is provided including a valve body defining a fuel chamber for containing a pressurized fuel and including at least one fuel inlet and at least one fuel outlet, each in fluid communication with the fuel chamber, and with the fuel outlet transversely intersecting the fuel chamber to form a fuel outlet opening extending through a wall of the fuel chamber. The fuel injector also includes a spool valve at least partially positioned within the fuel chamber and configured for reciprocating movement along an actuation axis, with the spool valve including a first spool and a second spool axially offset from the first spool to define a space therebetween for receiving the pressurized fuel. The fuel injector further includes at least one actuator coupled to the spool valve such that activation of the actuator results in axial displacement of the spool valve to selectively position one of the first and second spools over the fuel outlet opening to restrict a flow of the pressurized fuel through the at least one fuel outlet.

In another form of the present invention, a fuel injector is provided including a valve body defining a fuel chamber for containing a pressurized fuel and including at least one fuel inlet and at least one fuel outlet, each in fluid communication with the fuel chamber, and with the at least one fuel inlet transversely intersecting the fuel chamber to form a fuel inlet opening extending through a wall of the fuel chamber. The fuel injector also includes a spool valve at least partially positioned within the fuel chamber and configured for reciprocating movement along an actuation axis, with the spool valve including a first spool and a second spool axially offset from the first spool to define a space therebetween for receiving the pressurized fuel. The fuel injector further includes at least one actuator coupled to the spool valve such that activation of the actuator results in axial displacement of the spool valve, and with the fuel inlet opening positioned between the first and second spools at some point during axial displacement of the spool valve to allow a flow of the pressurized fuel through the at least one fuel inlet and into the fuel chamber. In another form of the present invention, a fuel injector is provided including a valve body defining a fuel chamber for containing a pressurized fuel and including at least one fuel inlet, at least one fuel outlet, and at least one low pressure fuel return outlet, each in fluid communication with the fuel chamber. The fuel injector also includes a spool valve at least partially positioned within the fuel chamber and configured for reciprocating movement along an actuation axis, with the spool valve including an actuation shaft and first and second spools engaged with the actuation shaft, and with the first spool axially offset from the second spool to define a space therebetween for receiving the pressurized fuel. The actuation shaft defines a fuel return passage extending axially along at least a portion of the actuation shaft and communicating between the low pressure fuel return outlet and a portion of the fuel chamber disposed outside of the space between the first and second spools. The fuel injector further includes at least one actuator coupled to the spool valve such that activation of the actuator results in axial displacement of the spool valve. In another form of the present invention, a fuel injector is provided including a valve body defining a fuel chamber for containing a pressurized fuel and having at least one fuel inlet and at least one fuel outlet, each in fluid communication with the fuel chamber. The fuel injector also includes a spool valve at least partially positioned within the fuel chamber and configured for reciprocating movement along an actuation axis. The spool valve includes an actuation shaft and at least one spool engaged with the actuation shaft, with the at least one spool formed of a ceramic material. The fuel injector further includes at least one actuator coupled to the spool valve such that activation of the actuator results in axial displacement of the spool valve. In one specific embodiment, the at least one spool is formed of a ceramic material selected from a group consisting of zirconia and silicon nitride.

It is one object of the present invention to provide an improved fuel injector. Further objects, features, advantages, benefits, and further aspects of the present invention will become apparent from the drawings and description contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partially cross-sectioned side view of a fuel injector according to one form of the present invention, as shown in a closed position.

FIG. 2 is a schematic partially cross-sectioned side view of the fuel injector illustrated in FIG. 1, as shown in an open position. FIG. 3 is a schematic exploded side view of the fuel injector illustrated in FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation on the scope of the invention is hereby intended, and that alterations and further modifications in the illustrated devices and further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates. Referring to FIGS. 1-3, shown therein is a fuel injector 10 according to one form of the present invention. The fuel injector 10 is generally comprised of a valve body 12, a valve member 14 positioned within the valve body 12, and a valve actuator 16 positioned within an actuator housing 18. In the illustrated embodiment of the invention, the valve body 12 and the actuator housing 18 are formed separately and subsequently assembled and attached together such as, for example, by welding, to form an integrated structure. However, it should be understood that in other embodiments, the valve body 12 and the actuator housing 18 may be formed integral with one another as a single- piece, unitary structure. In one embodiment of the invention, the valve member 14 cooperates with the valve body 12 to control the flow of fuel between a pressurized fuel inlet port and a number of fuel outlet ports, the details of which will be discussed below. The valve actuator 16 cooperates with the valve member 14 to displace the valve member 14 generally along a longitudinal actuation axis L between a closed position (FIG. 1) and an open position (FIG. 2) so that fuel may be selectively injected into a combustion chamber or cylinder of an internal combustion engine (not shown). Further details regarding the various components and operation of the fuel injector 10 will be discussed below. In one embodiment of the invention, the fuel injector 10 is used association with a diesel engine to control the flow of diesel fuel into a combustion chamber. However, it should be understood that the fuel injector 10 may be used in association with other types of engines and other types of fuels such as, for example, gasoline.

In the illustrated embodiment of the invention, the valve body 12 includes an injector body portion 20 and an injector tip portion 22. The valve body 12 is at least partially disposed within an opening formed in the engine head and positioned in communication with the combustion chamber. The valve body 12 may be provided with external threads for threading engagement within an opening formed in the engine head and/or within a portion of the combustion chamber for securing the fuel injector to the engine block. However, other methods and techniques for engaging the fuel injector to the engine block are also contemplated as would occur to one or ordinary skill in the art. The valve body 20 defines a fuel chamber 30 extending generally along the actuation axis L which is bound by an axially-extending fuel chamber wall 32. The fuel chamber 30 extends through the injector body portion 20 and partially through the injector tip portion 22. Notably, the fuel chamber 30 does not extend entirely through the valve body 12, but instead terminates at a closed distal end 31 adjacent the injector tip portion 22. The valve body 12 further defines a fuel inlet passage 34, a number of fuel outlet passages 36 positioned along the injector tip portion 24, and a low pressure fuel return passage 38, with each of the fuel passages 34, 36 and 38 positioned in fluid communication with the fuel chamber 30. In one embodiment, the fuel outlet passages 36 extend from the fuel chamber 30 and open onto an outer surface of the injector tip portion 22 of the valve body 12 at an exit angle of approximately 45 degrees (relative to the axis L). However, it should be understood that other embodiments of the invention are also contemplated wherein the exit angle of the fuel outlet passages 36 is less than or greater than 45 degrees. In the illustrated embodiment of the invention, each of the fuel passages 34, 36 and 38 transversely intersects the axially-extending fuel chamber wall 32 so as to define a transverse fuel inlet opening 34,, a number of transverse fuel outlet openings 36_O, and a transverse fuel return opening 38_r. Although a specific embodiment of a valve body 20 has been illustrated and described herein, it should be understood that other types and configurations of valve bodies are also contemplated for use in association with the present invention.

The fuel inlet passage 34 is positioned in communication with a pressurized fuel source to deliver pressurized fuel F to the fuel chamber 30. In one embodiment, pressurized fuel F is provided to the fuel inlet passage 34 via a fuel pump P. However, other means for delivering pressurized fuel to the fuel injector are also contemplated as would occur to one of ordinary skill in the art. As shown in FIG. 2, when the valve member 14 is moved to the open position, pressurized fuel F is delivered to the fuel outlet passages 36 for injection into the combustion chamber C of an internal combustion engine. As will be discussed below, any fuel leakage associated with the valve member 14 is conveyed to the low pressure fuel return passage 38 for transmission back to the fuel pump P. In one embodiment of the invention, the fuel pump P is a high pressure fuel pump capable of pressurizing the fuel up to 30,000 psi. Although one embodiment of the present invention contemplates use of the fuel injector 10 in association with high pressure fuel applications, it should be understood that use of the present invention in association with low pressure fuel applications is also contemplated.

In one embodiment of the invention, the valve member 14 is a spool-type valve including an actuator shaft or pin 50 and first and second spools or flange portions 52, 54 positioned along the actuator shaft 50. The valve member 14 is mounted for reciprocal movement within the valve body 12 along the actuation axis L to open and close the fuel injector 10 to selectively inject pressurized fuel into the combustion chamber C. In the illustrated embodiment, the first and second spools 52, 54 are formed separate from the actuator shaft 50 and subsequently assembled to the actuator shaft 50 to form an integrated valve member 14. In one embodiment, the spools 52, 54 are attached to the actuator shaft 50 by pins that are press fit into transverse openings extending through respective ones of the spools 52, 54 and the actuator shaft 50. However, other methods and techniques for attaching the spools 52, 54 to the actuator shaft 50 are also contemplated including, for example, via welding, bonding or fastening. Additionally, in another embodiment of the invention, the spools 52, 54 may be formed integral with the actuator shaft 50 to form a single-piece, unitary valve member 14.

In the illustrated embodiment, a fuel return channel 56 extends through a portion of the actuator shaft 50 and includes an axial portion 58a and a transverse portion 58b. The axial portion 58a extends from the distal end 50_d of the actuator shaft 50 and is positioned in communication with the fuel chamber 30. The transverse portion 58b is in communication with the axial portion 58a and transversely opens onto an outer surface of the actuator shaft 50 at a location just beyond the upper spool 52 such that the fuel return channel 56 is positioned in communication with the fuel chamber 30, and more specifically the fuel return passage 38.

As indicated above, the valve member 14 is displaced generally along the actuation axis L between a closed position (FIG. 1) and an open position (FIG. 2) so that fuel may be selectively injected into a combustion chamber C of an internal combustion engine. To facilitate guiding movement of the valve member 14 generally along the actuation axis L, each of the upper and lower spools 52, 54 has an outer surface 60 defining an outer profile that corresponds to the inner profile defined by the inner surface of the fuel chamber wall 32 surrounding the fuel chamber 30. In one embodiment, the outer profile of the spools 52, 54 are sized in relatively close tolerance with the inner profile of the fuel chamber wall 32 to minimize the leakage of fuel around the outer surfaces 60 of the spools 52, 54. However, as will be set forth below, since the fuel injector 10 includes features that accommodate for the return of fuel leakage around the upper and lower spools 52, 54, the tolerance levels between the spools 52, 54 and the fuel chamber 30 are not critical.

In the illustrated embodiment of the invention, the valve actuator 16 is generally comprised of a piezoelectric actuator 70 and a biasing element 72. However, it should be understood that in other embodiments of the invention, the valve actuator 16 may include other types of actuators such as, for example, electronic solenoids or any other suitable actuator device that would occur to one of ordinary skill in the art for use in association with a fuel injector system. In one embodiment of the invention, the valve member 14 is biased toward the closed position illustrated in FIG. 1 via the biasing element 72, and is displaced toward the open position illustrated in FIG. 2 via activation of the piezoelectric actuator 70. However, it should be understood that these functions may be reversed such that the piezoelectric actuator 70 is used to displace the valve member 14 to the closed position and the biasing element 72 is used to displace the valve member 14 to the open position. As should be appreciated, the axial force generated by the piezoelectric actuator

70 to open the valve must be large enough to counter the axial force produced by the biasing element 72 and to displace the valve member 14 to the open position illustrated in FIG. 2. As will be discussed below, the requisite amount of axial force generated by the piezoelectric actuator 70 to displace the valve member 14 to the open position illustrated in FIG. 2 is significantly reduced due to the balanced nature of the valve member 14. Additionally, the requisite amount of axial force produced by the biasing element 72 to displace the valve member 14 to the closed position illustrated in FIG. 1 is likewise significantly reduced due to the balanced nature of the valve member 14. Furthermore, reducing the amount of biasing force required to close the valve member 14 further reduces the amount of axial force that must be generated by the piezoelectric actuator 70 to counter the axial force produced by the biasing element 72 during displacement of the valve member 14 to the open position.

In one embodiment of the invention, the piezoelectric actuator 70 comprises a pre-stressed, electro-active actuator plate 74 which may be thermally, mechanically or otherwise pre-stressed, and which changes its shape via deformation or bending in an axial direction in response to a control signal applied by an electronic control module (ECM) or any other suitable electronic control device that would occur to one of skill in the art. As would be apparent to those of skill in the art, the control signal may comprise a voltage control signal or a current control signal. In the illustrated embodiment, the actuator plate 74 has a circular, disc-like configuration and includes at least one electro- active plate element positioned between a pair of electrode elements (not shown). However, other configurations of piezoelectric actuators are also contemplated as falling within the scope of the present invention including, for example, piezoelectric actuators having rectangular or other non-circular shapes and/or piezoelectric actuators including two or more electro-active plate elements.

In one embodiment of the invention, the piezoelectric actuator 70 is manufactured by Face International Corporation of Norfolk, Virginia under Model No. TH-5C. However, it should be understood that other suitable piezoelectric actuators are also contemplated for use in association with the present invention. Additionally, in other embodiments of the invention, the piezoelectric actuator 70 may comprise a plurality of electro-active actuator plates (arranged in parallel or series) that are stacked or bonded together to form an integrated, multi-layered actuator element to increase the axial force generated by the piezoelectric actuator and/or to increase the axial stroke of the valve member 14 upon activation of the piezoelectric actuator.

The piezoelectric actuator 70 is mounted within a cavity 76 formed in the actuator housing 18 and is secured within the cavity 76 by an annular clamp ring or spacer 78 that serves to compress the outer peripheral portion of the actuator plate 74 against an annular shoulder 80 defined by the actuator housing 18. In one embodiment, at least the portion of the clamp ring 78 positioned in direct contact with the actuator plate 74 is formed of an electrically non-conducting material. Since only the outer peripheral portion of the actuator plate 74 is constrained, the inner portion of the actuator plate 74 is permitted to deform or bend in an axial direction (i.e., generally along the actuation axis L).

The actuator housing 18 includes a cover or lid 82 positioned over the open end of the cavity 76. In addition to protecting the components positioned within actuator housing 18 from the outer environment, the cover 82 may also serve to compress the annular clamp ring 78 against the outer peripheral portion of the actuator plate 74. As should be appreciated, the clamp ring 78 may also be used to preload or prestress the actuator plate 74 by adjusting the clamping force applied to the actuator plate 74 by the clamp ring 78. Additionally, the cover 82 may be attached to the actuator housing 18 by any number of methods including, for example, by providing threads along the outer periphery of the cover 82 for threading engagement with internal threads formed along the inner walls of the actuator housing 18. In other embodiments, the cover 82 may be attached to the actuator housing 18 by a number of fasteners, by welding or by any other suitable attachment technique that would occur to one of skill in the art.

As shown in FIG. 1 , when the piezoelectric actuator 70 is in a de-activated or de- energized state, the actuator plate 74 has a slightly domed or outwardly bent configuration, with a central portion 74_C of the actuator plate 74 positioned adjacent to and preferably contacting the proximal end portion 84 of the actuator shaft 50. However, when the piezoelectric actuator 70 is energized or activated in response to a voltage or current control signal supplied by the ECM, the actuator plate 74 will deform or deflect in an axial direction toward the actuator shaft 50. Specifically, activation of the piezoelectric actuator 70 results in axial deformation or bending of the actuator plate 74, which in turn causes the actuator plate 74 to transition from the de-activated domed configuration shown in FIG. 1 toward the substantially flattened configuration shown in FIG. 2. In one embodiment, the actuator shaft 50, or at least the proximal end portion of the actuator shaft 50, is formed of an electrically non-conducting material such as, for example, a ceramic material such as zirconia to electrically isolate the actuator shaft 50 from the actuator plate 74. However, other electrically insulating materials are also contemplated as would occur to one of skill in the art.

As should be appreciated, axial deflection of the actuator plate 74 toward the valve member 14 compresses the central portion 74_C of the actuator plate 74 against the proximal end portion 84 of the actuator shaft 50, which in turn displaces the valve member 14 generally along the actuation axis L in the direction of arrow A to reposition the valve member 14 from the closed position shown in FIG. 1 toward the open position shown in FIG. 2. The proximal end portion 84 of the actuator shaft 50 may be rounded to prevent the actuator shaft 50 from gouging, cutting into, or otherwise damaging the actuator plate 74. In the illustrated embodiment of the invention, engagement between the central portion 74_cof the actuator plate 74 and the proximal end portion 84 of the actuator shaft 50 is abutting engagement. In other words, the actuator plate 74 is not positively engaged or attached to the actuator shaft 50. However, other embodiments are also contemplated wherein the actuator plate 74 may be positively engaged or attached to the actuator shaft 50 by a fastener, by an adhesive, by welding or bonding, or by any other suitable attachment technique that would occur to one of skill in the art.

In the illustrated embodiment of the invention, electronic operation of the piezoelectric actuator 70 is uni-directional. In other words, activation of the piezoelectric actuator 70 in response to a control signal supplied by the ECM results in axial deformation or deflection of the actuator plate 74 direction toward the actuator shaft 50 to correspondingly displace the valve member 14 in the direction of arrow A. However, deactivation of the piezoelectric actuator 70 in response to removal of or a change in the control signal supplied by the ECM causes the actuator plate 74 to resiliently return to the initial, bent configuration shown in FIG. 1. Since the resilient nature of the actuator plate 74 may not be sufficient to timely displace the valve member 14 back toward the closed position shown in FIG. 1, the biasing element 72 exerts an axial force onto the actuator shaft 50 (toward the actuator plate 74) to correspondingly displace the valve member 14 in the direction of arrow B.

However, it should be understood that in other embodiments of the invention, electronic operation of the piezoelectric actuator 70 may be bi-directional such that activation of the piezoelectric actuator 70 in response to a control signal of a first polarity results in axial deformation or deflection of the actuator plate 74 in the direction of arrow A, whereas activation of the piezoelectric actuator 70 in response to a control signal of an opposite polarity results in axial deformation or deflection of the actuator plate 74 in the direction of arrow B. As should be appreciated, in the case of bi-directional electronic operation of the piezoelectric actuator 70, the actuator plate 74 must be positively engaged or attached to the actuator shaft 50. As should also be appreciated, bi- directional electronic operation of the piezoelectric actuator 70 may eliminate the need for a separate biasing element 72 to return the valve member 14 to the closed position shown in FIG. 1.

In the illustrated embodiment of the invention, the biasing element 72 comprises a number of spring elements 86 configured to bias the valve member 14 in the direction of arrow B toward the closed position shown in FIG. 1. In a specific embodiment, the spring elements 86 comprise a number of washer springs such as, for example, Bellville- type washer springs. Each of the washer springs 86 defines a central aperture 88 sized to receive the proximal end portion 86 of the actuator shaft 50 therethrough. The washer springs 86 are maintained in position within the cavity 76 of the actuator housing 18 via a retainer element 90. In the illustrated embodiment, the retainer element 90 comprises an annular ring positioned adjacent the outer peripheral portion of the upper washer spring 86 to capture and retain the washer springs 86 between the annular ring 90 and an annular shoulder 92 defined by the actuator housing 18. In one embodiment, the washer springs 86 and the retainer element 90 are formed of a metallic material such as, for example, hardened steel, stainless steel or aluminum. However, other suitable materials are also contemplated as falling within the scope of the present invention. The axial force produced by the washer springs 86 is transmitted to the actuator shaft 50 via engagement of the upper washer spring against a flange element 94 extending transversely from the actuator shaft 50. However, it should be understood that other elements and techniques may be used to capture and retain the washer springs 86 within the actuator housing 18 and to engage the washer springs 86 with the actuator shaft 50. In the illustrated embodiment, three washer springs 86 are provided to bias the valve member 14 in the direction of arrow B (e.g. toward the closed position shown in FIG. 1). However, it should be understood that any number of washer springs 86 may be used, including a single washer spring, two washer springs, or four or more washer springs. It should also be understood that other types of spring elements are also contemplated for use in association with the present invention, including a wire wound die spring, a coil spring, a leaf spring, or any other type of spring element that would occur to one of skill in the art. Additionally, other types and configurations of biasing elements 72 are also contemplated as falling within the scope of the present invention including, for example, any type of device capable of urging the valve member 14 in the direction of arrow B toward the closed position shown in FIG. 1. It should further be understood that the functions associated with the piezoelectric actuator 70 and the biasing element 72 may be reversed such that the biasing element 72 urges the valve member 14 in the direction of arrow A toward the open position shown in FIG. 2, and activation of the piezoelectric actuator 70 causes the actuator plate 74 to displace the valve member 14 in the direction of arrow B toward the closed position shown in FIG. 1. However, since the illustrated embodiment of the invention results in a fail closed position of the valve member 14, the illustrated embodiment of the invention is preferred.

In the illustrated embodiment of the invention, a mechanical seal 95 is positioned between the piezoelectric actuator 70 and the valve body 12 to prevent fuel from entering the portion of the actuator housing cavity 76 containing the piezoelectric actuator 70. In one embodiment, the seal 95 comprises a metal diaphragm that is operably attached to the actuator housing 18 and to the proximal end portion 84 of the actuator shaft 50. However, other types and configurations of seals are also contemplated as falling within the scope of the present invention. In one embodiment, the metal diaphragm 95 is engaged to the actuator housing 18 and to the proximal end portion 84 of the actuator shaft 50 by welding. However, other attachment techniques are also contemplated such as, for example, by bonding, fastening, or any other suitable attachment technique that would occur to one of skill in the art. As should be appreciated, since the metal diaphragm 95 is engaged to the actuator shaft 50, the diaphragm must be sufficiently flexible to accommodate for axial displacement of the actuator shaft 50 during displacement of the valve member 14 between the open and closed positions.

Having described the various elements and features associated with the fuel injector 10, reference will now be made to the operation of the fuel injection 10 according to one form of the present invention.

As indicated above, the valve member 14 is biased toward the closed position shown in FIG. 1 via the axial force exerted onto the actuator shaft 50 by the spring elements 86. As should be appreciated, the valve member 14 will remain in the closed position shown in FIG. 1 until the piezoelectric actuator 70 is activated. Additionally, when the valve member 14 is in the closed position, the fuel outlet opening 36_O are covered or closed off via the outer surface 60 of the lower spool 54 to substantially prevent the passage of fuel through the fuel outlet passages 36 and into the combustion chamber C. Additionally, as also shown in FIG. 1, when the valve member 14 is in the closed position, the fuel inlet opening 34, is positioned between the upper and lower spools 52, 54 so as to permit the flow of pressurized fuel F through the fuel inlet passage 34 and into the fuel chamber 30 in the area between the upper and lower spools 52, 54. However, it should be understood that in another embodiment of the invention, the valve member 14 may be configured such that when positioned in the closed position, the fuel inlet opening 34, is covered or closed off by the outer surface 60 of the upper spool 52 to substantially prevent introduction of pressurized fuel into the fuel chamber 30 prior to initiation of an injection sequence.

Notable, any leakage of pressurized fuel F around the upper spool 52 is conveyed to the low pressure fuel return passage 38 for transmission back to the fuel pump P. Similarly, any leakage of pressurized fuel around the lower spool 54 will enter the portion of the fuel chamber 30 between the lower spool 54 and the closed distal end 31 of the fuel chamber, and will be conveyed through the fuel return channel 56 extending along the actuator shaft 50 and fed into the low pressure fuel return passage 38 for transmission back to the fuel pump P. Accordingly, fuel leakage around the upper and lower spools 52, 54 will not appreciably affect the operation or performance of the fuel injector 10, which might otherwise be the case if pressurized fuel were maintained between the upper spool 52 and the fluid seal 94 and/or the lower spool 54 and the closed distal end 31 of the fuel chamber 30.

Referring to FIG. 2, during an injection sequence, the ECM applies a control signal to the piezoelectric actuator 70, which in turn causes the actuator plate 74 to axially deform or bend toward a flattened configuration. Axial deformation of the actuator plate 74 toward a flattened configuration generates an axial force that is transmitted to the actuator shaft 50, which in turn results in axial displacement of the valve member 14 in the direction of arrow A (toward the open position illustrated in FIG. 2). In essence, the piezoelectric actuator 70 is configured such that the actuator plate 74 "pushes" the valve member 14 toward the open position. This feature differs from other fuel injector applications wherein the piezoelectric actuator is configured such that the actuator plate "pulls" the valve member 14 toward the open position. As indicated above, the axial force generated by the piezoelectric actuator 70 and transferred to the actuator shaft 50 must be sufficient to overcome the opposing biasing force exerted onto the actuator shaft 50 by the spring elements 86 and to axially displace the valve member 14 toward the open position.

When the valve member 14 is repositioned to the open position shown in FIG. 2, the lower spool 54 is axially displaced such that the outer surface 60 of the lower spool 54 no longer covers or closes off the fuel outlet opening 36_O. Accordingly, pressurized fuel F is permitted to flow from the fuel chamber 30, into the fuel outlet opening 36_O, and through the fuel outlet passages 36 for injection into the combustion chamber C. In the illustrated embodiment, when the valve member 14 is in the open position, the upper spool 52 does not cover the fuel inlet opening 34,. Instead, the fuel inlet opening 34, remains open to permit continued flow of pressurized fuel through the fuel inlet passage 34 and into the fuel chamber 30 in the region between the upper and lower spools 52, 54. However, it should be understood that in another embodiment of the invention, the valve member 14 may be configured such that when positioned in the open position, the fuel inlet opening 34, is covered or closed off by the outer surface 60 of the upper spool 52 to substantially prevent further introduction of pressurized fuel into the fuel chamber 30 during the injection sequence.

After the injection sequence is complete, the control signal is changed or removed from the piezoelectric actuator 70, thereby causing the actuator plate 74 to relax and return to the initial domed configuration shown in FIG. 1. As should be appreciated, removal of the axial force generated by the piezoelectric actuator 70 from the actuator shaft 50 allows the axial force produced by the spring elements 86 to drive the actuator shaft 50 in the direction of arrow B to return the valve member 14 back to the closed position shown in FIG. 1. Once the valve member 14 is repositioned back to the closed position, the fuel outlet opening 36_O are once again covered or closed off by the outer surface 60 of the lower spool 54 to substantially prevent the passage of pressurized fuel through the fuel outlet passages 36 and into the combustion chamber.

As indicated above, the requisite amount of axial force generated by the piezoelectric actuator 70 to displace the valve member 14 to the open position illustrated in FIG. 2 is significantly reduced due to the balanced nature of the valve member 14. Additionally, the requisite amount of axial force produced by the spring elements 84 to displace the valve member 14 to the closed position illustrated in FIG. 1 is likewise significantly reduced due to the balanced nature of the valve member 14. Moreover, reducing the amount of biasing force required to close the valve member 14 further reduces the amount of axial force that must be generated by the piezoelectric actuator 70 to counter the axial force produced by the biasing element 72 during displacement of the valve member 14 to the open position.

As should be appreciated, the balanced nature of the valve member 14 is primarily provided by the upper and lower spools 52, 54. Specifically, the upper spool 52 includes a first axially-facing surface 96 and the lower spool 54 includes a second axial Iy- facing surface 98 arranged generally opposite the first axially-facing surface 96. Notably, the pressurized fuel F within the fuel chamber 30 is positioned between the first and second axially-facing surfaces 96, 98, regardless of whether the valve member 14 is in the open position or the closed position. In the illustrated embodiment of the invention, the first and second axially-facing surfaces 96, 98 have virtually the same surface area exposed to the pressurized fuel F.

As would be apparent to one of ordinary skill in the art, the amount of force/ exerted onto a surface by a fluid is equal to the pressure of the fluid/? multiplied by the surface area a against which the fluid acts (f=p* a). Since the pressurized fuel F exerts the same pressure onto each of the upper and lower surfaces 96, 98 of the spools 52, 54, and since the surface area of the upper and lower surfaces 96, 98 is virtually equal, the upward force/_/ exerted onto the upper spool 52 is approximately equal to the downward force/ exerted onto the lower spool 54. The upward and downward forces/,/ in effect cancel one another out, thereby "balancing" the valve member 14. As indicated above, in the illustrated embodiment, the first and second axially-facing surfaces 96, 98 have virtually the same surface area exposed to the pressurized fuel F. However, in other embodiments of the invention, the first and second axially-facing surfaces 96, 98 may define surface areas that are different from one another to thereby provide a net upward or net downward force onto the valve member 14. Additionally, since any leakage of pressurized fuel around the upper and lower spools 52 is conveyed to the low pressure fuel return passage 38 for transmission back to the fuel pump P, fuel leakage around the upper and lower spools 52, 54 will not appreciably affect the operation or performance of the fuel injector 10. As should be appreciated, unlike prior fuel injector designs, due to the balanced nature of the valve member 14, the pressurized fuel F has very little, if any, effect on the amount of axial force that must be exerted onto the valve member 14 to reposition the valve member 14 between the open and closed positions. Accordingly, a piezoelectric actuator 70 may be used to directly control high and low pressure fuels without the need for a hydraulic system to amplify the force generated by the piezoelectric actuator 70 for exertion onto the valve member. Additionally, the balanced nature of the valve member 14 allows for the use of a relatively low force, high speed piezoelectric actuator to directly control high and low pressure fuels. As indicated above, the balanced valve member 14 makes the fuel injector 10 particularly suitable for use in association with high pressure fuel application including, for example, uses in association with diesel engines. However, it should be understood that the fuel injector 10 may also be used in association with lower pressure fuel applications as well including, for example, uses in association with gasoline engines.

In one embodiment of the invention, the valve body 12, the actuator housing 16 and the cover 82 are formed of a metallic material such as, for example, hardened steel, stainless steel or aluminum. However, other suitable materials are also contemplated as falling within the scope of the present invention. In a further embodiment of the invention, the upper and lowers spools 52, 54 of the valve member 14 are formed of a ceramic material such as, for example, silicon nitride or zirconia. However, other types of ceramic materials are also contemplated as falling within the scope of the present invention. Additionally, it should be understood that in other embodiments of the invention, the upper and lowers spools 52, 54 of the valve member 14 may be formed of other materials such as, for example, metallic materials including hardened steel.

In a further embodiment of the invention, the actuator shaft 50 is formed of a hardened steel. However, in other embodiments, the actuator shaft 50 may be formed of other types of metallic materials and/or a ceramic material including, for example, ceramic materials such as silicon nitride or zirconia. As indicated above, in the illustrated embodiment, the upper and lower spools 52, 54 are formed separate from the actuator shaft 50 and are subsequently assembled with the actuator shaft 50 to form an integral valve member 14. However, other methods and techniques for attaching the spools 52, 54 to the actuator shaft 50 are also contemplated including, for example, by welding or bonding. Additionally, in another embodiment of the invention, the spools 52, 54 may be integrally formed with the actuator shaft 50 to form a single-piece, unitary valve member 14.

It should be appreciated that with regard to forming the upper and lowers spools 52, 54 from a ceramic material, the porosity and grain size of the ceramic material are important design aspects. However, the selection of an appropriate ceramic material, such as silicon nitride or zirconia, has been shown to survive the stresses encountered in high pressure fuel injector applications. Additionally, silicon nitride or zirconia ceramics exhibit good machining characteristics including, for example, the ability to finish the outer surfaces 60 of the spools 52, 54 to sub single digit micron tolerances, and to create sharp edges or corners on the spools 52, 54, which in turn allows for precise timing control of the fuel injection process. The use of silicon nitride or zirconia ceramics also provides the ability to finish the sharp edges or corners on the spools 52, 54 to sub single digit micron tolerances. By precisely controlling the tolerances of the sharp edges or corners of the spools 52, 54, control over fuel delivery in the micro-second timing range is made possible, which in turn tends to provide proper combustion, increased fuel economy, and reduced emissions. While the present invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims

What is claimed is:

1. A fuel injector, comprising: a valve body defining a fuel chamber for containing a pressurized fuel and including at least one fuel inlet and at least one fuel outlet, each of said fuel inlet and said fuel outlet in fluid communication with said fuel chamber; a valve member at least partially positioned within said fuel chamber and configured for reciprocating movement along an actuation axis, said valve member including a first valve surface facing a first axial direction and a second valve surface facing a second axial direction generally opposite said first axial direction, each of said first and second valve surfaces exposed to said pressurized fuel within said fuel chamber; and at least one actuator coupled to said valve member such that activation of said at least one actuator results in axial displacement of said valve member to control a flow of said pressurized fuel through said at least one fuel outlet.

2. The fuel injector of claim 1, wherein said first and second valve surfaces are substantially planar and are arranged substantially parallel to one another.

3. The fuel injector of claim 1, wherein said valve member comprises a spool valve including a first spool defining said first valve surface and a second spool defining said second valve surface.

4. The fuel injector of claim 1, wherein said fuel outlet transversely intersects said fuel chamber to form a fuel outlet opening extending transversely through a wall of said fuel chamber; and wherein said axial displacement of said valve member selectively positions a portion of said valve member over said fuel outlet opening to restrict a flow of said pressurized fuel through said fuel outlet; and wherein said axial displacement of said valve member selectively uncovers said portion of said valve member from said fuel outlet opening to allow a flow of said pressurized fuel through said fuel outlet.

5. The fuel injector of claim 1, wherein said fuel inlet transversely intersects said fuel chamber to form a fuel inlet opening extending transversely through a wall of said fuel chamber, said fuel inlet opening positioned between said first and second valve surfaces at some point during said axial displacement of said valve member to allow a flow of said pressurized fuel through said fuel inlet and into said fuel chamber.

6. The fuel injector of claim 5, wherein said fuel inlet opening is positioned between said first and second valve surfaces at all points during said axial displacement of said valve member.

7. The fuel injector of claim 1, wherein said valve body further includes at least one low pressure fuel return outlet in fluid communication with said fuel chamber, said valve member defining a fuel return passage extending axially along at least a portion of said valve member to convey low pressure fuel from a portion of said fuel chamber to said low pressure fuel return port.

8. The fuel injector of claim 1, wherein said actuator comprises a piezoelectric actuator.

9. The fuel injector of claim 8, wherein said piezoelectric actuator bends in response to application of an electrical control signal thereto, bending of said piezoelectric actuator resulting in said axial displacement of said valve member.

10. The fuel injector of claim 8, wherein said piezoelectric actuator has a curved configuration when in a non-actuated state.

1 1. The fuel injector of claim 10, wherein said piezoelectric actuator has a domed configuration when in said non-actuated state.

12. The fuel injector of claim 1, further comprising a biasing device coupled to said valve member to bias said valve member in an axial direction opposite said axial displacement of said valve member occurring in response to said activation of said actuator.

13. The fuel injector of claim 12, wherein said biasing device comprises at least one washer spring.

14. The fuel injector of claim 1, wherein said first valve surface and said second valve surface have approximately the same surface area such that a first fluid force exerted onto said first valve surface is approximately equal to a second fluid force exerted onto said second valve surface so as to substantially balance said valve member.

15. A fuel injector, comprising: a valve body defining a fuel chamber for containing a pressurized fuel and including at least one fuel inlet and at least one fuel outlet, each of said fuel inlet and said fuel outlet in fluid communication with said fuel chamber, said fuel outlet transversely intersecting said fuel chamber to form a fuel outlet opening extending transversely through a wall of said fuel chamber; a spool valve at least partially positioned within said fuel chamber and configured for reciprocating movement along an actuation axis, said spool valve including a first spool and a second spool axially offset from said first spool to define a space therebetween for receiving said pressurized fuel; and at least one actuator coupled to said spool valve such that activation of said actuator results in axial displacement of said spool valve to selectively position one of said first and second spools over said fuel outlet opening to restrict a flow of said pressurized fuel through said fuel outlet.

16. The fuel injector of claim 15, wherein said first spool defines a first valve surface facing a first axial direction, said second spool defining a second valve surface facing a second axial direction generally opposite said first axial direction, each of said first and second valve surfaces exposed to said pressurized fuel within said fuel chamber, said first valve surface and said second valve surface having approximately the same surface area such that a first fluid force exerted onto said first valve surface is approximately equal to a second fluid force exerted onto said second valve surface so as to substantially balance said spool valve.

17. The fuel injector of claim 15, wherein said axial displacement of said spool valve selectively uncovers said one of said first and second spools from said fuel outlet opening to allow a flow of said pressurized fuel through said fuel outlet.

18. The fuel injector of claim 15, wherein said fuel inlet transversely intersects said fuel chamber to form a fuel inlet opening extending transversely through a wall of said fuel chamber; and wherein said fuel inlet opening is positioned between said first and second spools at some point during said axial displacement of said spool valve to allow a flow of said pressurized fuel through said fuel inlet and into said fuel chamber.

19. The fuel injector of claim 15, wherein said valve body further includes at least one low pressure fuel return outlet in fluid communication with said fuel chamber, said spool valve defining a fuel return passage extending axially along at least a portion of said spool valve to convey low pressure fuel from a portion of said fuel chamber to said low pressure fuel return port.

20. The fuel injector of claim 15, wherein said actuator comprises a piezoelectric actuator, said piezoelectric actuator bending in response to application of an electrical control signal thereto, said bending resulting in said axial displacement of said spool valve.

21. The fuel injector of claim 15, wherein said first and second spools are formed of a ceramic material selected from the group consisting of zirconia and silicon nitride.

22. A fuel injector, comprising: a valve body defining a fuel chamber for containing a pressurized fuel and including at least one fuel inlet and at least one fuel outlet, each of said fuel inlet and said fuel outlet in fluid communication with said fuel chamber, said at least one fuel inlet transversely intersecting said fuel chamber to form a fuel inlet opening extending transversely through a wall of said fuel chamber; a spool valve at least partially positioned within said fuel chamber and configured for reciprocating movement along an actuation axis, said spool valve including a first spool and a second spool axial Iy offset from said first spool to define a space therebetween for receiving said pressurized fuel; and at least one actuator coupled to said spool valve such that activation of said actuator results in axial displacement of said spool valve, said fuel inlet opening positioned between said first and second spools at some point during said axial displacement of said spool valve to allow a flow of said pressurized fuel through said fuel inlet and into said fuel chamber.

23. The fuel injector of claim 22, wherein said first spool defines a first valve surface facing a first axial direction, said second spool defining a second valve surface facing a second axial direction generally opposite said first axial direction, each of said first and second valve surfaces exposed to said pressurized fuel within said fuel chamber, said first valve surface and said second valve surface having approximately the same surface area such that a first fluid force exerted onto said first valve surface is approximately equal to a second fluid force exerted onto said second valve surface so as to substantially balance said spool valve.

24. The fuel injector of claim 22, wherein said fuel inlet opening is positioned between said first and second valve surfaces at all points during said axial displacement of said spool valve.

25. The fuel injector of claim 22, wherein said fuel outlet transversely intersecting said fuel chamber to form a fuel outlet opening extending transversely through a wall of said fuel chamber; and wherein said axial displacement of said spool valve selectively positions one of said first and second spools over said fuel outlet opening to restrict a flow of said pressurized fuel through said fuel outlet; and wherein said axial displacement of said spool valve selectively uncovers said one of said first and second spools from said fuel outlet opening to allow a flow of said pressurized fuel through said fuel outlet.

26. The fuel injector of claim 22, wherein said valve body further includes at least one low pressure fuel return outlet in fluid communication with said fuel chamber, said spool valve defining a fuel return passage extending axially along at least a portion of said spool valve to convey low pressure fuel from a portion of said fuel chamber to said low pressure fuel return port.

27. The fuel injector of claim 22, wherein said actuator comprises a piezoelectric actuator, said piezoelectric actuator bending in response to application of an electrical control signal thereto, said bending resulting in said axial displacement of said spool valve.

28. The fuel injector of claim 22, wherein said first and second spools are formed of a ceramic material selected from the group consisting of zirconia and silicon nitride.

29. A fuel injector, comprising: a valve body defining a fuel chamber for containing a pressurized fuel and including at least one fuel inlet, at least one fuel outlet, and at least one low pressure fuel return outlet, each of said fuel inlet, said fuel outlet, and said low pressure fuel return outlet in fluid communication with said fuel chamber; a spool valve at least partially positioned within said fuel chamber and configured for reciprocating movement along an actuation axis, said spool valve including an actuation shaft and first and second spools engaged with said actuation shaft, said first spool axially offset from said second spool to define a space therebetween for receiving said pressurized fuel, said actuation shaft defining a fuel return passage extending axially along at least a portion of said actuation shaft and communicating between said low pressure fuel return outlet and a portion of said fuel chamber disposed outside of said space between said first and second spools; and at least one actuator coupled to said spool valve such that activation of said actuator results in axial displacement of said spool valve.

30. The fuel injector of claim 29, wherein said first spool defines a first valve surface facing a first axial direction, said second spool defining a second valve surface facing a second axial direction generally opposite said first axial direction, each of said first and second valve surfaces exposed to said pressurized fuel within said fuel chamber, said first valve surface and said second valve surface having approximately the same surface area such that a first fluid force exerted onto said first valve surface is approximately equal to a second fluid force exerted onto said second valve surface so as to substantially balance said spool valve.

31. The fuel injector of claim 29, wherein said fuel outlet transversely intersecting said fuel chamber to form a fuel outlet opening extending transversely through a wall of said fuel chamber; and wherein said axial displacement of said spool valve selectively positions one of said first and second spools over said fuel outlet opening to restrict a flow of said pressurized fuel through said fuel outlet.

32. The fuel injector of claim 29, wherein said fuel inlet transversely intersects said fuel chamber to form a fuel inlet opening extending transversely through a wall of said fuel chamber; and wherein said fuel inlet opening is positioned between said first and second spools at some point during said axial displacement of said spool valve to allow a flow of said pressurized fuel through said fuel inlet and into said fuel chamber.