Abstract:
A fuel or liquid injector includes a needle valve and a piezoelectric actuator that bears a hydraulic acceleration piston on its distal end. The actuator expands moving the piston toward the needle valve. The needle valve has a ball end, restrained against the valve seat by a spring, sealing the valve until the spring force is overcome by mechanical and hydraulic forces on the piston. When closed, the piston rests against the needle valve. Expansion of the piezoelectric actuator mechanically actuates the piston, and then increases the hydraulic pressure, which closes the fuel check valve, and accelerates the forward movement of the piston attached to the needle valve. When the restraining force on the needle valve is overcome, the ball end of the needle valve is unseated, and compressed fluid in the lower hydraulic chamber is released in a high velocity spray.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of the earlier filing of U.S. Provisional Application No. 60/709,082 filed on Aug. 17, 2005 incorporated herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to liquid injectors for use in supplying pressurized liquids. More particularly, the present invention relates to a liquid injector for use in supplying pressurized liquid, which injector is piezoelectrically actuated.  
       BACKGROUND  
       [0003]     Standard fuel injectors, including piezoelectric actuated fuel injectors, are designed to inject a given amount of fuel at very high pressures for good atomization of the fuel. Existing fuel injectors inject fuel at various points in the Otto cycle. Various approaches have been used to achieve a homogenous air and fuel mixture. Fuel injected during the intake stroke is typically injected into the intake air stream, not directly into the combustion chamber. The fuel is injected either in sequential sprays or in a single injection close to top dead center. Late injection of fuel does not induce a lot of mixing, resulting in uneven combustion. To compress fuel to very high pressures (up to 200 bar or 20 MPa) requires very high energy, and time. A standard in-tank fuel pump has an exit pressure of 1 to 2 bar (0.1 to 0.2 MPa). To achieve a 100 bar (10 MPa) standard fuel rail pressure requires a big fuel pump and a lot of power. The fuel has to be compressed further in the fuel injector to reach the final injection pressure of about 200 bar (20 MPa), achieved in existing fuel injectors.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an object of the present invention to provide a high velocity, high frequency fuel injector, which is electrically actuated and has various electronically controlled flow rates.  
         [0005]     It is a further object of the present invention to provide a high frequency fuel injector, which has various electronically controlled flow rates, and can handle multiple fuels (e.g., Diesel, JP8 and JP5).  
         [0006]     It is a further object of the present invention to provide such a high frequency fuel injector, which is scalable, and small and lightweight.  
         [0007]     It is yet another object of the present invention to provide such a high frequency fuel injector, which is piezoelectric actuated, and has the ability to inject very small amounts of fuel as well as greater amounts of fuel required at full power.  
         [0008]     The fuel injector of the present invention is simple to build, easy to assemble, and simple to calibrate; yet is able to handle high compression rates for late injection, and to disperse the fuel into particles 12 Microns or smaller.  
         [0009]     These objects, as well as other objects which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, which comprises a piezoelectric liquid injector, which comprises a needle valve disposed within a housing so as to define at least two hydraulic chambers, each with a fluid inlet. The needle valve is contained in the housing by a proximal retaining cap, attached to an outer sleeve, attached to the main fuel injector body, comprising means of attachment to e.g., a fuel rail, with the distal end extending into a combustion chamber. The injector further comprises a piezoelectric actuator the proximal end of which is contained by a piezo end cap, secured within the retaining cap. The piezoelectric actuator bears a hydraulic acceleration piston on its distal end. Upon the application of a controlled voltage, the actuator expands, moving the piston through the upper hydraulic chamber toward the proximal end of the needle valve and the lower hydraulic chamber. The lower end of the needle valve comprises a ball end, restrained against the valve seat by a spring, sealing the valve until the restraining force of the spring is overcome by the mechanical and hydraulic forces on the piston at the proximal end of the needle valve. In its closed position, the piston rests against the proximal end of the needle valve. Expansion of the piezoelectric actuator mechanically actuates the hydraulic acceleration piston, and then increases the hydraulic pressure in the upper hydraulic chamber, which closes the fuel check valve, and accelerates the forward movement of the fuel accelerator piston, attached to the near the proximal end of the needle valve. When the restraining force on the needle valve is overcome, the ball end of the needle valve is unseated, and compressed fluid in the lower hydraulic chamber is released in a high velocity spray in an, e.g., cone pattern. The piezoelectric actuator is pre-stressed in the calibration of the injector, prior to actuation. If desired, the spray pattern may be a pulsed pattern, rather than a continuous pattern. Matching the frequency of the restraining force with the frequency of the piezoelectric actuator increases the degree of control of the valve and of the spray pattern.  
         [0010]     The liquid injector of the present invention provides an accurate, finely controlled spray pattern. In an engine, the liquid injectors make good fuel injectors, providing accurate ratios of mixing of fuel and compressed air, and a high velocity spray which improved atomization of the fuel, and mixing with the air.  
         [0011]     For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention will be further described with reference to the accompanying drawings, wherein like reference numerals refer to like parts in the several views, and wherein:  
         [0013]      FIG. 1  depicts a cross-section of an exemplary embodiment of a fuel injector in an open/spray position according to one aspect of the present invention.  
         [0014]      FIG. 2  depicts a cross-section of an exemplary embodiment of a fuel injector in a closed position according to another aspect of the present invention.  
         [0015]      FIG. 3  depicts a cross section of an upper body detail of the exemplary embodiments shown in  FIGS. 1 and 2  according to yet another aspect of the present invention.  
         [0016]      FIG. 4  depicts a block diagram for an exemplary embodiment of a liquid injector control system according to still another aspect of the present invention.  
         [0017]      FIG. 5  depicts a block diagram of an exemplary embodiment of a fuel delivery system according to yet another aspect of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0018]     It is worthy to note that any reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.  
         [0019]     An exemplary embodiment of the present invention will now be described with reference to FIGS.  1  to  5  of the drawings. Identical elements in the various figures are designated with the same reference numerals.  
         [0020]     A Piezo stack actuator works much like a spring. It is built of many layers like the coils on a spring. Each layer expands a given rate if voltage is applied to the crystal. Each layer on a Piezo actuator expands anywhere from 50 nanometers to 200 nanometers, depending on the material. In order to create a Piezo stack actuator with a travel of 40 micrometers; if the base crystal has an expansion of 200 nanometers, 200 layers are needed. Like a spring, if its compressed it has a lot of force; but the more it extends itself it looses force exponentially. If each Piezo layer has a expansion force of 10N the total starting force of the Piezo actuator is 2000N. But as it expands it loses 10N in force for every 200 nanometer of expansion. Therefore, if the actuator with a total travel of 40 microns and a total force of 2000N has expanded to 20 micron, the total available force at that point is only 1000N.  
         [0021]     A Piezo actuator expands proportionally to the voltage applied; e.g., if it&#39;s a 150V Piezo actuator with a total travel of 30 microns it will expand 10 microns if we apply 50 volts, and 20 microns if we apply 100 volt.  
         [0022]     Each Piezo stack actuator is rated (based on materials and construction) at a given resonant frequency. This is the highest frequency it can sustain. It is recommended to run Piezo stack actuators when fully loaded at no more than ⅓ of their resonant frequency.  
         [0023]     For example, if a Piezo stack actuator has a resonant frequency of 30 Kilohertz (which means it can cycle 30,000 times per second) it should be operated at no more than 10 Kilohertz (10,000 cycles per second).  
         [0024]     A Piezo stack actuator can expand under no load equal to the voltage applied; e.g., if we have a voltage rise of 50 nanoseconds from 0 to 150 volt a 150-volt actuator will fully expand at that rate. The minimizing factor on a stack is the internal harmonic between the individual layers and the way it is glued together.  
         [0025]     If a load is applied, the expansion time will decrease based on the load applied much like a spring. In order to reach a given frequency, the actuator has to have a given force based on the load.  
         [0026]     The piezoelectric liquid injector of the present invention was designed using these principles; giving it the ability to dispense fuel in very small high frequency bursts.  
         [0027]     The injector shown in  FIGS. 1-3 , containing the numbered parts listed below, functions as follows: 
         1  CALIBRATION SCREW      2  COUNTER NUT      3  RETAINING CAP      4  ELECTRICAL PIN CONNECTOR      5  ELECTRICAL PIN RETAINER      6  PIEZO STACK ACTUATOR      7  PIEZO SEALS      7 A PIEZO SEALS      8  UPPER ACTUATOR PISTON      9  OUTER FUEL INJECTOR SLEEVE      10  UPPER NEEDLE (FUEL COMPRESSION) PISTON      11  VALVE CLOSING SPRING      12  INNER VALVE PISTON SLEEVE      13  FUEL CHECK VALVE      14  MAIN FUEL INJECTOR BODY      15  FUEL RAIL      16  ENGINE HEAD      17  LOWER FUEL INJECTOR      18  VALVE SEAT WITH NEEDLE GUIDE AND FUEL PORTS      19  FUEL SPRAY      20  UPPER FUEL INLETS      21  PIEZO END CAP      22  SEALS      23  FUEL PORT      24  VALVE NEEDLE WITH BALL END      31  VISCOSITY SENSOR        
 
         [0054]     A Piezo stack actuator  6  pushes against the upper actuator piston  8 . This piston  8  touches the upper surface of the injector needle valve  24 , which is held in the closed position by the closing spring  11 .  
         [0055]     There is fuel between the upper actuator piston  8  and the upper valve needle piston  10 .  
         [0056]     As the Piezo stack actuator  6  expands it pushes immediately against the needle valve  24 , and the valve starts to open. At the same time the fuel in between the upper actuator piston  8  and the upper needle piston  10  is sealed by the fuel check valve  13 , and compressed, and acts like a hydraulic transmission increasing the opening distance and speed by the factor of piston size; e.g., if the actuator piston  8  has a diameter of twelve (12) mm and the needle piston  10  has a diameter of four (4) mm. it creates a three-to-one (3:1) transmission in travel and speed. For example, as the Piezo stack actuator  6  moves the upper actuator piston  8  thirty (30) microns the needle valve should travel ninety (90) microns via the hydraulic transmission. Fluid compressibility (approximately 1% per 1000 PSI) will reduce the actual travel to about eighty-one (81) microns.  
         [0057]     The fuel enters from the fuel rail  15  at a pressure of eighty-five (85) PSI and equalizes pressure throughout the fuel injector. The fuel enters the injector thru two small holes in the sleeve  9 , between the upper actuator piston  8  and the upper needle piston  10 , where the fuel is used as a transmission fluid. The fuel also enters thru the fuel check valve  13 .  
         [0058]     The valve needle  24  has a ball end (actual valve body) a needle stem and an upper piston  10 . The ball end seats into the valve seat  18  and the closing spring  11  pushes against the upper needle piston  10  holding the valve closed. The fuel pressure against the valve seat  18  is a constant eighty-five (85) PSI.  
         [0059]     As the injector is actuated the upper actuator piston  8  pushes (first mechanically and then hydraulically) against the upper needle piston  10 . The needle valve  24  moves down against the spring force of the closing spring  11  and opens the valve by unseating the ball end from the valve seat  18 . At the same time the lower surface of the upper needle piston  10  compresses the fuel and forces it out of the opening created by the unseating of the valve  24 . There is an increase in pressure across the valve opening by a ratio of valve opening surface to upper needle piston surface. So, for example, if the upper needle piston surface is 10 square-millimeters and the opening is 0.1 square-millimeters we have a pressure increase of 1:100, which means the fuel exit pressure rises momentarily from 85 PSI to 8500 PSI. The pressure on the initial opening has a compression factor of 285:1. Thus, the initial opening starts at 0.035 square-millimeters at a pressure burst of 24,000 PSI, decreasing exponentially as the valve opens further and settling at 85 PSI at full open and return stroke.  
         [0060]     The rapid rise in pressure may be used to create many high pressure bursts to break up the fuel particles and create even dispersion into the air.  
         [0061]     The Piezo actuator disburses an exact amount of fuel in a high pressure burst at every stroke.  
         [0062]     The fuel injector Piezo stack is designed to have a resonant frequency of 36 kilohertz and a force of 6500N and may be operated at a frequency of 12 kilohertz.  
         [0063]     The forces of the closing spring  11  and the Piezo actuator  6  oppose each other. The highest resonance frequency of a spring is based on the load applied, the travel required and the force of the spring. In order to have a closing spring with a high enough force and frequency, a Belleville spring stack was selected as the closing spring  11 . The preferred fuel injector uses eight Belleville spring discs with a force of 80 N each and a total travel of 30 microns each yielding a total travel of 240 microns and a total closing force of 640 N. Based on the load (weight of the needle, seal friction, upper fluid weight and actuator piston) a resonant spring frequency of 10 kilohertz may be achieved.  
         [0064]     When the engine runs at 2000 RPM on a two-stroke cycle (7.5 milliseconds/stroke) all the fuel must be injected in about 5 milliseconds. At 10 kilohertz the injector of the present invention can inject 50 spurts of fuel per single stroke of the piston.  
         [0065]     At lower speeds even more spurts per cycle may be achieved. To inject a smaller amount of fuel the voltage to the Piezo actuator may be changed, so that the needle valve  24  travels a smaller distance dispersing less fuel. This injector is a positive displacement injector because it is based on the travel of the valve  24 . The injector can mechanically break up all the fuel into micro particles to be easily absorbed into the air to create an air/fuel mixture, which is easily lit.  
         [0066]     For the injector to work for multi-fuels a sensor  31  detects the viscosity of the given fuel and adjusts the injector timing based on the reading.  
         [0067]     The injector is designed to screw into a fuel rail  15  on top of the engine. The incoming fuel is sealed off with two O-rings next to the fuel inlet port  23 .  
         [0068]     The fuel injector is easily calibrated with a screw  1  pressing via cap  3  against the Piezo actuator  6  and the needle valve  24 . The screw  1  can be secured in its final setting by a counter nut  2 .  
         [0069]     The injector can be plugged into an electronic control board with its upper pin connector.  
         [0070]     Controlling the injector requires a power source of 150 VDC. The applied voltage is regulated by a digital-to-analog 0-150 volt regulator that is adjusted by the digital signal processor (DSP). A solid-state relay switches the power to the Piezo on and off. The circuit has to switch to a fast ground every time the Piezo is turned off because the Piezo reacts like a capacitor and only retracts after bleeding the voltage to ground. The DSP has to toggle the ground. To control the injector the following is required: 
        Digital signal processor     Power source (e.g., battery)     Power converter 12-150 Volt     Digital-to-analog voltage regulator 0-150 Volt     Three (3) solid-state relays        
 
         [0076]     The DSP generates the high frequency outputs, requiring fast switching speeds for the solid-state relays. The fuel injector produces a pulsing cone pattern. This pattern gives the best mixing effect for fuel atomization and absorption of the fuel into the air stream. The spray pattern can be changed in the fuel injector. It is based on the valve shape so the fuel injector valve has to match the combustion chamber design. For example the valve can be designed to create a spray to one side only up to a given opening valve travel and then change to a full cone once the valve opens further. So basically many spray patterns are possible and the pattern may be adjusted based on the combustion chamber design. The drawing below is a rendering of a version of this injector.  
         [0077]     Referring to  FIG. 4 , the operation of the present invention is controlled by a Digital Signal Processor (DSP)  300  although it is envisioned that other means of mechanical or electrical control known in the art could be used for control.  
         [0078]     Power to the injector is provided from a power source, such as a battery  310 . A power converter  320  converts the source voltage to an acceptable voltage range for the piezo actuator  60 , preferably 0-150 VDC. The applied voltage is regulated by a digital-to-analog regulator  330 , also controlled by the DSP  300 . The magnitude of the actual voltage is determined by the DSP  300  based on the fuel requirements.  
         [0079]     To actuate the piezo actuator  60  the DSP  300  provides a gate signal to the power switching relay  340  and to the ground switching relay  350  supplying both power and ground  360  to the piezo actuator  60 . The DSP  300  turns off the piezo actuator  60  by removing the gate signal from the power-switching relay  340  and the ground-switching relay  350 . The DSP  300  then applies a gate signal to the grounding relay  370  shorting the piezo actuator  60  to ground  360  in order to drain any stored energy in the piezo actuator  60 . The gate to the grounding relay  370  is then removed.  
         [0080]     The expansion and retraction happens in a very short time; i.e., it happens simultaneously with the voltage wave. If the Piezo is grounded to make it retract it will do so in about 20-50 microseconds. This fast retraction or expansion puts a lot of stress on the glue joints of the actuator. So pre-stressing the actuator prevents delaminating of the actuator and extends its lifetime.  
         [0081]     Referring to  FIG. 5 , fuel is stored at or near ambient pressure within the fuel tank  200 . The fuel pump  201  delivers pressurized fuel to the fuel rail  210 . Fuel is heated in the fuel heater  211  to the desired fuel delivery temperature. Fuel is pressurized by both the fuel pump  201  and by the heating of the fuel by the fuel heater  211 . Rail pressure is regulated by the fuel pressure control valve  220 .  
         [0082]     In the present invention, fuel is delivered from the fuel rail  210  to the injector  10  at relatively low pressure, e.g. 5.8 bar, or 85 psi. This initial pressurization of the liquid both pre-compresses the liquid and pre-stresses the piezo actuator  60 . The piezo actuator  60  is pre-stressed by both the upper compression seal  7  and the pressurized fluid in the upper hydraulic chamber. Pre-stressing of the piezo actuator and pre-compressing the fuel allows the piezo actuator to rapidly compress the fuel.  
         [0083]     There are two seals,  7  and  7 A, around the upper actuator piston and these seals  7 ,  7 A protect the Piezo from the fuel. The lower seal  7 A is a moving O-ring and the upper seal  7  is a compression O-ring. Every time the Piezo expands the O-ring is compressed. This O-ring is also used to pre-stress the Piezo element. A softer Viton rubber is used for this seal. This rubber has a very high resonance rate. The Piezo actuator expands only 60 microns so the compression during Piezo actuation is very small.  
         [0084]     Unlike the prior art, the current invention atomizes liquid without high pressurization. Instead, atomization of the liquid and mixing of the fuel and air within the combustion chamber is achieved by rapid compression of the fuel within the injector and simultaneously injecting the liquid at high velocity into the combustion chamber.  
         [0085]     Fuel is stored at ambient pressure within the fuel tank. The fuel pump delivers pressurized fuel to the fuel rail. Within the fuel rail, the fuel is heated by the fuel heater to the desired fuel delivery temperature. Fuel is pressurized by both the fuel pump and the fuel heater. Rail pressure is regulated by the fuel pressure control valve and excessive pressure is relieved by returning fuel to the fuel tank.  
         [0086]     Fuel is delivered from the fuel rail to the injector at 5.8 bar, or 85 psi. This initial pressurization of the liquid both pre-compresses the liquid and pre-stresses the piezo actuator, which allows the piezo actuator to rapidly compress the fuel. In addition to hydraulically compressing the fuel, the piezo actuator, which is in mechanical communication with the injector needle, unseats the needle valve. The simultaneous compression and injection of the fluid raises the fuel pressure within the injector above the internal pressure in the combustion chamber and injects the fuel at high velocity into the combustion chamber. Because the fuel is injected at a slightly higher pressure than the pressure within the combustion chamber, preferably 30 bar, or 425 psi, the injected fuel can move freely within the compressed gas in the combustion chamber. The high velocity atomizes the fuel and induces mixing of the fuel with the compressed air.  
         [0087]     Fuel is only injected at high velocity during the period of expansion of the piezo electric. During the expansion of the piezo actuator only a portion of the required fuel volume is injected into the combustion chamber, therefore the piezo electric must be rapidly fired with high frequency pulses. The pulsing of the fluid helps the turbulence inside the chamber and increases molecular absorption (mixing) of the fuel into (with) the gas creating a more even fuel air mixture.  
         [0088]     The rise time of the voltage driving the piezo actuator is critical to the proper operation of the present invention. This is because the rate of expansion of the piezo actuator determines the velocity of the fuel. Each voltage pulse delivers a pulse of high velocity fuel into the combustion chamber. The volume of each pulse is equal to a fraction of the required injection.  
         [0089]     Turning to  FIG. 6 , shown therein is an exemplary embodiment of a method  60  for injecting a liquid, such as fuel using one or more of the exemplary embodiments described above, according to another aspect of the present invention.  
         [0090]     In element  61 , initially, an electronically controlled actuator (e.g., a piezoelectric stack actuator) in a liquid injector may be calibrated to place some predetermined stress on the actuator. In addition, the actuator may be further pre-stressed using compression of the liquid and/or an outer compression ring, such as an O-ring. This calibration and pre-stressing would typically occur prior to receiving a voltage to control or initiate actuation of the piezoelectric stack actuator.  
         [0091]     In element  62 , a voltage signal is applied to the actuator. For example, the voltage signal could comprise a plurality of pulses with steep pulse edges, which is applied to the piezoelectric actuator to rapidly expand and contract the actuator and therefore to rapidly inject the liquid in one or more short spurts. As the pressure of the spurts is highest at the initial injection, using several short spurts as opposed to one long burst will increase the atomization of the fuel, as described above.  
         [0092]     In element  63 , movement of a first piston is controlled with an expansion of the piezoelectric actuator. The first piston could comprise the upper actuator piston  8  in  FIGS. 1-3 .  
         [0093]     In element  64 , movement of a second piston coupled to a needle valve injector is controlled with movement of the first piston. The second piston could comprise the upper needle piston  10  shown in  FIGS. 1-3 .  
         [0094]     In element  65 , an hydraulic pressure between the first piston and the second piston is increased due to expansion of the piezoelectric actuator. Expanding the actuator increases the pressure on the liquid inside the injector.  
         [0095]     In element  66 , a check valve controlling an input of the liquid is closed due to increased hydraulic pressure resulting from expansion of the actuator.  
         [0096]     In element  67 , movement of the second piston is accelerated using a hydraulic transmission based on a larger active surface area of the first piston relative to a smaller active surface of the second piston, as was described above.  
         [0097]     In element  68 , the needle valve injector is maintained closed by seating a ball end of the needle valve injector against a valve seat with a predetermined restraining force.  
         [0098]     In element  69 , the needle valve injector is opened when the restraining force maintaining the needle valve injector closed is overcome by a sum of mechanical force and hydraulic forces generated by expansion of the actuator and movement of the first piston to inject the liquid at a higher pressure relative to a received pressure of the liquid, as has been described above.  
         [0099]     In element  70 , a frequency of the predetermined restraining force is matched with a frequency of the piezoelectric actuator. For example, the frequency of the spring is matched with the frequency of the expansion of the actuator to achieve optimal results.  
         [0100]     In element  71 , the compressed fluid is released from the injector at an initial pressure in excess of one hundred times a liquid pressure in a high velocity spray when the needle valve injector is opened.  
         [0101]     While the above exemplary embodiment of a method for injecting the liquid includes multiple steps, not all steps are necessary to practice the present invention. In other words, some steps are optional without departing from the scope of the present invention. Moreover, the order of the steps in the method is not important, other than those steps that specifically require a prior step to be performed.  
         [0102]     There has thus been shown and described a novel liquid injector device which fulfills all the objects and advantages sought therefore. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention.