Abstract:
A fuel injector uses two or more individual piezoelectric devices. A first piezoelectric device is used to actuate a valve which allows pressurized fuel to pass from a pressure chamber through an outlet port. The fuel is pressurized by a second piezoelectric device. In certain applications, a return piezoelectric device is arranged in opposing configuration to the first piezoelectric device so that the valve can be positively moved both into its opened and closed positions rather than depending on the return force of a spring.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The preferred embodiment of the present invention is generally related to a fuel injector and, more particularly, to a fuel injector which uses piezoelectric devices to both pressurize the fuel and to control a valve by which the pressurized fuel is released through an outlet port of the fuel injector. 
     2. Description of the Prior Art 
     Many different types of fuel injectors are known to those skilled in the art. Piezoelectric devices, such as those devices using a lead zirconate titanate element are also known to those skilled in the art. In certain applications, piezoceramic elements made of a lead zirconate titanate (PZT) have been used to actuate a movable valve. 
     U.S. Pat. No. 6,291,929, which issued to Heinz et al. on Sep. 18, 2001, describes a piezoelectric actuator. The invention relates to a piezoelectric actuator, in particular for actuating control valves or injection valves in internal combustion engines of motor vehicles, having a piezoelectric actuator body in the form of a multi-layer laminate of stacked layers of piezoelectric material and metal or electrically conductive layers, acting as electrodes, located between them, in which one of the face ends of the actuator body is fixed to a stationary metal actuator base, and the other face end borders a metal retaining plate that is movable with the actuator stroke. 
     U.S. Pat. No. 5,094,429, which issued to Dostert on Mar. 10, 1992, describes a valve having a piezoelectric drive. A lever mechanism is provided with a prescribed lever ratio and includes a resilient steel fork for the amplitude transformation of the excursion of a piezoceramic element operating as a piezoelectric actuator, a valve lifter connected at one end to a deflectable end of the steel fork and at the other end to a valve needle of a fuel injector valve. 
     U.S. patent application Ser. No. 10/462,194, which was filed on Jun. 16, 2003, by Gatecliff et al., describes a piezoelectric valve actuation system. The system is intended for use in an internal combustion engine and includes a piezoelectric driver in the form of a prestressed wafer or strip including a layer of piezoceramic material such as lead zirconate titanate (PZT). The driver has a central portion which includes an aperture for direct engagement with a valve stem so that the valve is moved between open and closed positions directly by the piezoelectric driver. The piezoelectric driver can have end portions which attach to the engine cylinder head proximate the valve location. The piezoelectric actuator is driven by an electronic control module (ECM) providing electrical signals to control valve operation based various engine parameters along with user input. 
     U.S. Pat. No. 5,816,780, which issued to Bishop et al. on Oct. 6, 1998, describes a piezoelectrically actuated fluid pump. The pump includes a pump housing, a pump chamber, inlet and outlet ports for communicating the pump chamber with the exterior of the pump housing, valves for opening and closing the ports, two prestressed piezoelectric diaphragm members which are self-actuated, and a power source. The diaphragm members include a prestressed piezoelectric element which is durable, inexpensive and lightweight as compared with prior diaphragm pumps of comparable discharge capacity, and is actuated via electrical signals from an outside power source. 
     U.S. Pat. No. 6,042,345, which issued to Bishop et al. on Mar. 28, 2000, describes a piezoelectrically actuated fluid pump. The diaphragm members of the pump include a prestressed piezoelectric element which is durable and lightweight. 
     U.S. Pat. No. 4,927,084, which issued to Brandner et al. on May 22, 1990, describes a fuel injection valve. A reciprocable valving element is movable from closed to open positions by a piezoceramic moving unit having at least to flexural resonators in the form of laminated packages of metallic carriers, ceramic layers and foil shaped and/or ring shaped conductors connected to the poles of an energy source in such a way that energization entails deformation of packages in opposite directions, namely the deformed packages have confronting concave or convex sides. This increases the distance which is covered by the valving element in response to energization of the packages. 
     U.S. Pat. No. 4,437,644, which issued to Wilmers on Mar. 20, 1984, describes an electrically operable valve. The invention relates to valves for use in fuel injection systems for internal combustion engines. The valve has a housing having a valve seat, and receiving a valve body which can be raised from the valve seat in accordance with a variation in dimension of magnetostrictional device or a piezoceramic device caused by a current flow in the device. The valve body is spring loaded in a sense to close the valve and is connected via the device to a movable abutment unit which is so constituted that during the current induced variations in dimension it acts as a stationary abutment or anchorage for that end of the device which is remote from the valve body. 
     U.S. Pat. No. 4,593,658, which issued to Moloney on Jun. 10, 1986, describes a valve operating mechanism for internal combustion engines and like valved engines. The valve operating mechanism for an internal combustion engine comprises a piezoelectric control device arranged to control the operating movement of an engine valve in accordance with the extension of the control device and control means for controlling the electrical feed to the piezoelectric device in accordance with parameters of the engine operation fed to it. 
     U.S. Pat. No. 4,739,929, which issued to Brandner et al. on Apr. 26, 1988, describes a fuel injection valve. The valve has a piezoceramic valve body comprising a plurality of superposed ceramic plates each having one conductor layer on each side and voltage leads to the conductor layers. Each ceramic plate is arranged on a carrier plate. Between each unit, consisting of a ceramic plate and a carrier plate, an insulating foil is provided with conductor foils arranged on each side as conductor layers. Each insulating foil comprises two terminal lugs. Each insulating foil, in the region of a terminal lug, is laminated on one side with one conductor foil. The correlated terminal lugs are connected in each case to an electrical contact with the correlated conductor foils. 
     U.S. Pat. No. 4,813,601, which issued to Schwerdt et al. on Mar. 21, 1989, describes a piezoelectric control valve for controlling fuel injection valves in internal combustion engines. A piezoelectric control valve includes a hydraulic plate compensation element inside the control valve on the one side which automatically compensates for possible changes in length of the reference system as a result of piezoceramic setting actions in the piezoelectric actuator so that, at the same working stroke of the piezoelectric actuator, an identical stroke at the valve is also always ensured. A hydraulic stroke transmission inside the control valve on the other side, provides a valve stroke corresponding to a multiple of the working stroke. 
     U.S. Pat. No. 5,203,537, which issued to Jacobs et al. on Apr. 20, 1993, describes a piezoceramic valve actuator sandwich assembly and valve incorporating such an assembly. The valve includes a valve actuator sandwich assembly including a piezoceramic bending element flexibly bonded between two metal sheets. Flexible elastomeric sheets are bonded to outer surfaces of the metal sheets, respectively, to form the sandwich assembly. The valve includes a first supporting member which sealingly engages an outer surface of the first elastomeric sheet and a second supporting member which sealingly engages an outer surface of the second elastomeric sheet to flexibly support the valve actuator sandwich assembly between the two supporting members. The valve actuator is engageable with a valve seat to prevent flow through the valve and is deflectable away from the valve seat to allow flow through the valve. The piezoceramic bending element is isolated in the valve actuator sandwich assembly from the flow stream to prevent diffusion of low molecular weight gases through the porous ceramic and to isolate electrically active elements of the bending element from the flow stream. 
     The patents described above are hereby expressly incorporated by reference in the description of the present invention. 
     A thesis entitled “A Comprehensive Piezoceramic Actuator Review and Its Application to the Design of a Direct-Injection Fuel Injector”, which was presented by Christopher John Taylor in partial fulfillment of the requirements for the Degree Master of Science in the Graduate School of The Ohio State University, describes the technology relating to piezoceramic actuators along with a description and analysis of various characteristics of specific types of piezoceramic actuators. 
     A document titled “Thunder White Paper” was published in 2001 by the Face International Corporation. That White Paper, which is available on the Internet, describes the technology relating to lead zirconate titanate (PZT) piezoceramic and piezoelectricity along with illustrations showing the construction and advantages of certain devices manufactured and sold by Face International Corporation. Various application notes are also described in detail therein. 
     An article titled “Application Notes” was published in 2002 by Face International Corporation. This article is available on the Internet and specifically discusses an element, or component, relating to a thin layer Unimorph Ferroelectric Driver and Sensor which is commercially available from Face International Corporation under the name “THUNDER”. This paper describes the underlying technology relating to the PZT element and illustrates certain advantageous application techniques relating to using the PZT component in various applications. 
     It would be advantageous if a fuel injector could be made with a pressurizing portion and an actuation portion both utilizing piezoelectric elements. This type of device could advantageously control the pressurization and injection of fuel in an internal combustion engine. It could provide a reliable and durable structure for such a fuel injector. 
     SUMMARY OF THE INVENTION 
     A fuel injection system made in accordance with a preferred embodiment of the present invention comprises an outlet port and a valve which is movable along a path between a first position and a second position, wherein the outlet port is blocked by the valve when the valve is in the first position and wherein the outlet port is unblocked by the valve when the valve is in the second position. A first piezoelectric device is disposed in force transmitting association with the valve to selectively move the valve along the path. The preferred embodiment of the present invention further comprises a pressure chamber and a second piezoelectric device disposed in pressure increasing association with the pressure chamber. Movement of the second piezoelectric device increases the pressure of a fuel within the pressure chamber and movement of the valve under the influence of the first piezoelectric device causes the fuel, which is pressurized within the pressure chamber, to flow from the pressure chamber and through the outlet port. 
     In a particularly preferred embodiment of the present invention, it further comprises a first resilient member configured to urge the valve toward the first position. The first resilient member can be a spring which provides a force in opposition to the force provided by the first piezoelectric device. In other words, the first piezoelectric device is used to move the valve from the first position toward the second position and the spring, or first resilient member, is used to provide a force in the direction which moves the valve from the second position toward the first position. The first piezoelectric device can be configured to cause the valve to move toward the second position when the first piezoelectric device is activated. The second piezoelectric device can be configured to increase a pressure of the fuel within the pressure chamber during each actuation of the second piezoelectric device. The fuel injection system can be a fuel injector which contains both the first and second piezoelectric devices within a common structure. 
     In a preferred embodiment of the present invention, both the first and second piezoelectric devices comprise piezoceramic elements which, in turn, comprise lead zirconate titanate components. 
     In one embodiment of the present invention, a return piezoelectric device is disposed in force transmitting association with a valve to selectively move the valve along the path, wherein the return piezoelectric device is configured to provide a force in a direction which is opposite to the direction of force provided by the first piezoelectric device. As a result, actuation of the first piezoelectric device moves the valve toward the second position and actuation of the return piezoelectric device moves the valve toward the first position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The preferred embodiment of the present invention will be more fully and completely understood from a reading of the description of the preferred embodiment in conjunction with the drawings, in which: 
         FIG. 1  shows a piezoelectric device used to pressurize and inject fuel from a pressurizing cavity through an outlet port; 
         FIG. 2  is generally similar to  FIG. 1  but with a force multiplier lever used to increase the resulting force obtained from the piezoelectric device; 
         FIG. 3  is a schematic representation of the valve actuation and fuel pressurization portions of a fuel injector made in accordance with the preferred embodiment of the present invention; 
         FIG. 4  shows the valve actuation portion in actuated position; 
         FIG. 5  shows the actuation and pressurization portions of the present invention configured in a common structure; and 
         FIG. 6  shows an alternative embodiment of the preferred embodiment of the present invention using a return piezoelectric device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Throughout the description of the preferred embodiment of the present invention, like components will be identified by like reference numerals. 
       FIG. 1  shows a fuel injector  10  that comprises a piston  12  disposed within a cylinder  14 . Actuation of a stack  18  of piezoceramic elements causes the piston  12  to move downward in  FIG. 1 . This pressurizes the fuel in the cylinder  14  below the piston  12  and causes the fuel to flow out of the outlet port  20  of the fuel injector  10 . 
       FIG. 2  is a slight modification of the component shown in  FIG. 1 . A lever mechanism  24  is provided to magnify the force exerted on the piston  12  in a downward direction. The stack  18  of piezoceramic elements exerts an upward force on a first end  30  of the lever  24 . This results in a downward force by the second end  32  of the lever  24  on the shaft  36  which drives the piston  12  downward. This structure shown in  FIG. 2  magnifies the force that is exerted on the piston  12  in a downward direction. 
       FIG. 3  is a simplified schematic representation of a fuel injection system made in accordance with a preferred embodiment of the present invention. It should be understood that the valve actuation portion  40  and the fuel pressurization portion  50  are intended to be disposed within a common structure of a fuel injector. However, for purposes of clarity and to simplify the illustration, the valve actuation portion  40  and the fuel pressurization portion  50  are shown as separate components in  FIG. 3 . A valve  42  is shaped to be received in a valve seat  43  of the valve actuation portion  40 . The valve  42  has a valve stem  44  attached to it. The valve  42  is movable along a path represented by arrow A in  FIG. 3 . The valve  42  is movable between a first position, shown in  FIG. 3 , and a second position which is achieved when the valve  42  is moved downwardly from the position shown in  FIG. 3 . When the valve  42  is in the first position, the outlet port is blocked by the valve  42  as shown. When the valve  42  is in the second position, the outlet port is unblocked. A first piezoelectric device  60  is disposed in force transmitting association with the valve  42  to selectively move the valve  42  along the path A in a downward direction toward its second position. The first piezoelectric device  60  is provided with a platform  62  against which it can exert a downward force. A seal member  64  is also provided. When the first piezoelectric device  60  is actuated, it exerts a downward force on the platform  62  which moves the valve stem  44  downward to move the valve  42  away from the valve seat  43  and unblock the outlet port of the fuel injector. 
     With reference to the pressurizing portion  50  in  FIG. 3 , the preferred embodiment of the present invention provides a pressure chamber  52  and a second piezoelectric device  54  which is disposed in pressure increasing association with the pressure chamber  52 . When the second piezoelectric device  54  is actuated, it exerts a downward force on the platform  56  to cause the piston  57  to move downward. The piston  57  travels along the path represented by arrow B. A seal  58  is provided. 
     When the piston  57  moves downward, the pressure within the cavity identified by reference numeral  70  increases. With this increasing pressure, a downward force on ball  72  is provided which moves the ball downwardly against the upward force of spring  74 . As a result, fuel can flow from chamber  70  as represented by arrows D. When the second piezoelectric device  54  is deactivated, piston  57  and platform  56  move upwardly and liquid fuel is drawn through a check valve, which comprises ball  76  and an associated spring, as represented by arrows E. Therefore, it can be seen that sequential activation and deactivation of the second piezoelectric device  54  will cause liquid fuel to be pumped in the directions represented by arrows D and E. 
     With continued reference to  FIG. 3 , it should be understood that conduits  80  and  82  are intended to be a continuous conduit through which liquid fuel flows as represented by arrows D. This liquid fuel flows into the cavity  84  above the valve  42 . Therefore, it should be understood that the pressure chamber of the device shown in  FIG. 3 , comprises the cavities identified by reference numerals  52 ,  70 , and  84 . Within these cavities, fuel is pressurized so that movement of the valve  42  in a downward direction will release the pressurized fuel through the outlet port of the fuel injector. 
       FIG. 3  also shows an engine control module  90  associated with an actuator  92 , or driver, for the first piezoelectric device  60  and another actuator  94 , or driver, for the second piezoelectric device  54 . These connections allow the engine control module  90  to control the activation and deactivation of the first and second piezoelectric devices,  60  and  54 . 
       FIG. 4  illustrates the actuation portion  40  of the fuel injector with the valve  42  and its valve stem  44  being pushed downwardly to open the outlet port  20  and allow liquid fuel to pass out of chamber  84 . Although not illustrated in  FIG. 4 , it should be understood that the fuel in chamber  84  was conducted through conduit  82  from conduit  80  and chamber  52  described above in conjunction with  FIG. 3 . In  FIG. 4 , the valve  42  is shown in its second position, whereas the valve  42  was shown in its first position in  FIG. 3 . 
     With continued reference to  FIG. 4 , it can been seen that actuation of the first piezoelectric device  60  causes a downward force against pedestal  62  which pushes the valve stem  44  and the valve  42  downwardly against the force of spring  100 . When this occurs, and the outlet port  20  is opened as shown in  FIG. 4 , liquid fuel passes out of chamber  84  as represented by arrows F. 
     With reference to  FIGS. 3 and 4 , it should be understood that the actuation of the second piezoelectric device  54  can occur both before and after the actuation of the first piezoelectric device  60 , with its subsequent downward movement of valve  42 . In other words, with the valve  42  in its first position as shown in  FIG. 3 , actuation of the second piezoelectric device  54  will raise the pressure of the fuel within the chambers identified by reference numerals  70 ,  52 , and  84 . When the first piezoelectric device  60  is actuated and the valve  42  moves downwardly, to its second position shown in  FIG. 4 , the pressure within chamber  84  immediately drops as the fuel F exits through the outlet port  20 . It should be understood that the second piezoelectric device  54  can be repeatedly actuated after the first piezoelectric device  60  is actuated. In other words, with the valve  42  in its second position, as illustrated in  FIG. 4 , the second piezoelectric device can be actuated to cause subsequent injections of fuel to pass in the directions identified by reference numerals D and F. With the valve  42  in the second position and the outlet port  20  opened, these subsequent actuations of the second piezoelectric device  54  will cause pulsed flows of fuel through the opened outlet port  20 . In certain applications, this subsequent pulsing of injected fuel after the initial opening of the outlet port  20  is highly beneficial. 
       FIG. 5  shows a fuel injector that incorporates both the valve actuation portion  40  and the fuel pressurization portion  50  in a common integral package. The components identified in  FIGS. 3 and 4  and described above are identified in  FIG. 5  with the same reference numerals. Fluid conduits  80  and  82  are integral to each other and conduct pressurized fluid from cavity  52  to cavity  84 . Actuation of the second piezoelectric device  54  raises the pressure in cavity  52  by sequentially causing fuel to be drawn past ball  76  of a first check valve and then past ball  72  of the second check valve. This raises the pressure in cavity  84  so that actuation of the first piezoelectric device  60  can effectively inject fuel through the outlet port  20  when the valve  42  is moved downwardly as described above. 
     In certain embodiments of the present invention, it is beneficial to use an additional piezoelectric device  116  as a return piezoelectric device to move the valve  42  back to its first position from its second position rather than depend on the spring  100  described above in conjunction with  FIGS. 3–5 . This type of embodiment is shown in  FIG. 6 . This provides piezoelectric devices to force the valve  42  in both directions. The embodiments described above in conjunction with  FIGS. 3–5  use a first a piezoelectric device  60  to move the valve  42  from its first position to its second position, but relies on the spring  100  to return the valve  42  from its second position back to its first position. In the embodiment shown in  FIG. 6 , a return piezoelectric device  116  is used for this purpose instead of the spring. In certain applications, a more positive return to the first position is desirable. By using a return piezoelectric device  116 , the return from the second position to the first position of the valve  42  can be much faster than if a spring was relied on for this purpose. Although  FIG. 6  is shown in a highly simplified schematic representation, it can be seen that actuation of the return piezoelectric device  116  causes the pedestal  62 , the valve stem  44 , and the valve  42  to all move upwardly to place the valve  42  in its first position which closes or blocks the outlet port  20 . 
     With continued reference to  FIGS. 1–6 , it can been seen that the preferred embodiment of the present invention provides a method for injecting fuel for an internal combustion engine which comprises the steps of providing a first piezoelectric device  60  associated in force transmitting relation with a valve  42 , providing a second piezoelectric device  54  associated in pressure increasing relation with a pressure chamber  52 . The pressure chamber  52  and cavity  84  are provided with an outlet port  20 . The method of the preferred embodiment of the present invention further comprises the step of increasing the pressure of a fluid, such as liquid fuel, within the pressure chamber  52  by actuating the second piezoelectric device  54  and moving the valve  42  from a first position, which blocks the outlet port  20 , toward a second position which does not block the outlet port  20 . This is done by actuating the first piezoelectric device  60 . As a result, pressurized fluid flows through the outlet port  20  from the pressure chamber,  52  and  84 , when the valve  42  moves away from its first position. The preferred embodiment of the present invention further comprises the step of actuating the second piezoelectric device  54  when the valve is in the second position. This subsequent actuation of the second piezoelectric device  54  when the valve  42  is in the second position is not a requirement in all embodiments but, as described above, can be significantly advantageous by creating subsequent injections of fuel during the period of time when the valve  42  is in its second position and the outlet port  20  is opened. The pressure increasing step performed by the second piezoelectric device  54  can typically be performed when the valve  42  is in its first position so that pressure within the pressure chamber,  52  and  84 , is increased. This pressure increasing step can be performed a plurality of times either when the valve  42  is in its first position or after it is moved into its second position. As described above, fluid is drawn into the pressure chamber  52  in response to actuation and subsequent deactivation of the second piezoelectric device  54  as a result of the action of the two check valves which incorporate balls  72  and  76 . 
     The first, second, and return piezoelectric devices described above can be piezoceramic devices such as those which use lead zirconate titanate (PZT) elements. 
     Although the preferred embodiment of the present invention has been described in particular detail and illustrated to show a preferred embodiment, it should be understood that alternative embodiments are also within its scope.