Abstract:
Multiple intensifier injectors with positive needle control and methods of injection that reduce injector energy consumption. The intensifiers are disposed about the axis of the injectors, leaving the center free for direct needle control down the center of the injector. Also disclosed is a boost system, increasing the needle closing velocity but without adding mass to the needle when finally closing. Direct needle control allows maintaining injection pressure on the fuel between injection events if the control system determines that enough fuel has been pressurized for the next injection, thus saving substantial energy when operating an engine at less than maximum power, by not venting and re-pressurizing on every injection event.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/928,578 filed May 9, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to the field of fuel injectors. 
         [0004]    2. Prior Art 
         [0005]    Intensifier type fuel injectors are well known in the prior art. Such injectors use a larger first piston driven by a working fluid under pressure to drive a smaller piston to pressurize fuel for injection. Piston area ratios and thus intensification ratios typically on the order of 10 to 1 allow high injection pressures with only moderate pressure working fluid. Diesel fuel is fairly compressible at the applicable pressures. By way of example, diesel fuel compresses approximately 1% per 1000 psi. With injection pressures of 30,000 psi and higher, the compression of the fuel is substantial. The energy required for compression of the fuel not used for an injection event is generally wasted by the venting of the working fluid over the larger piston of the intensifier to a low pressure reservoir. Consequently, when an engine is running at substantially less than full power, a substantial part of the energy used for compression of a full injection charge is wasted. 
         [0006]    Also in diesel fuel injectors, it is important to obtain a sharp start and stop of injection. A slow termination of injection, such as by a slowly decreasing injection pressure, results in poor atomization, or even no real atomization at the end of injection, resulting in incomplete combustion of the fuel, and unacceptable unburned hydrocarbon emissions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a cross section of one embodiment of the present invention. 
           [0008]      FIG. 2  is a cross section of the embodiment of  FIG. 1  showing half sections taken 90 degrees apart. 
           [0009]      FIG. 3  is a cross section of another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0010]      FIGS. 1 and 2  illustrate an injector in accordance with the present invention. These Figures illustrate the injector in the needle open position, as during injection.  FIG. 1  is a cross-section of an injector having two intensifiers, while  FIG. 2  is a cross-section of the same injector illustrating the same cross-section on the right half of the Figure, though illustrating a cross-section ninety degrees therefrom on the left half of the Figure. In this injector, a needle  20  is provided which is almost pressure balanced so that when fuel at injection pressures is present in the needle chamber around the needle, there will be a relatively modest upward force on the needle. 
         [0011]    Fuel is delivered to the needle chamber  21  in the injector tip  22  through port  24  and slots in member  26  from either or both intensifier chambers  28  and  29 . The intensifier pistons  30  and  32  have spring returns  34  and  36  and are supplied with fuel on their return to the upper position through check valves  38  and  40 . The intensifiers are powered by pistons  42  and  44 , as controlled by control valves  46  and  48 , respectively, preferably solenoid actuated spool valves. If fuel is being delivered to the needle chamber  21  by one intensifier only through the channel under the check valves and channels  24 , then the other of check valves  50  and  52  will close, preventing the intensified pressure from being coupled to the non-operative intensifier. 
         [0012]    The use of two intensifiers spaced radially outward from the center of the injector has the advantage of allowing direct needle control through the axis of the injector. In particular, member  54 , which might be in one or more sections (more than one section being illustrated), extends all the way from the top of the needle  20  to a pressure chamber  56  at the top of the injector. Thus when actuation fluid control valve  58  applies pressure to the chamber  56 , member  54  is hydraulically urged downward to close the needle by the actuation fluid pressure acting on the top piston area of member  54 , the various parts in the preferred embodiment being proportioned to assure that the needle will positively close against intensified pressure in the needle chamber. 
         [0013]    For initial needle closure, a boost system is used which assures rapid needle closure. In particular, the hydraulic pressure in chamber  56  also acts on the top of member  60 , a boost piston which, as may be seen at the left side of  FIG. 2 , pushes down on pins  62 , only one of the pins being shown in  FIG. 2  as the other half of the cross-section is taken only ninety degrees therefrom. Pins  62  in turn push on pin  64  which pushes against member  66 , which in turn pushes the needle  20  toward the closed position. However the bottom of member  66  will hit the top of member  26  before the needle finally closes, which substantially reduces the impact of needle closure, thereby allowing a very fast needle closure without risk of breaking the tip off of the needle chamber. Note that the stop for the boost assembly is relatively near the needle, minimizing the effects of differential expansion so that the boost may be repeatedly operative until just before needle closure. However the control valve  58  is located at the top of the injector, simplifying the electrical connections to the control valve. Also because all control valves, preferably solenoid actuated spool valves, are similarly located, actuation coils for all three valves may be printed on a multiplayer printed circuit board, further simplifying the electrical interconnection of components. Also the use to two intensifier assemblies allows use of smaller (faster) control valves. 
         [0014]    By control of control valve  58 , the needle  20  may be pushed downward to the closed position independent of the pressure in the needle chamber around the needle. Coil spring  68 , a relatively light coil spring, merely assures that needle closure pin  54  remains at rest against the needle whether the needle is open or closed. 
         [0015]    Thus to close the needle in the presence of intensified fuel, control valve  58  is open to provide fluid pressure in chamber  56 , with pin  54  as well as the boost assembly just described, accelerating the needle toward the closed position, the boost being stopped just before the needle reaches the closed position to greatly reduce the inertia, and thus the impact on needle closure. In a preferred embodiment, the actuation fluid for the intensifier pistons  42  and  44  and for pin  54  and member  60  is engine oil, though other fluids such as fuel may be used if desired. 
         [0016]    The advantages of using two intensifier assemblies as hereinbefore described are numerous. If the intensification ratios are different, then with a single actuation fluid pressure, two different injection pressures may be selectably obtained by operating one or the other intensifier. Two intensifier assemblies are still advantageous, even if they have the same intensification ratios. In particular, fuel injectors in general require a substantial amount of power. In the prior art, intensifiers are typically operated once for each injection and then depressurized to refill the intensifier chamber with fuel. Obviously the intensifier chamber must be large enough to intensify enough fuel for a single injection under the maximum requirements for the engine. Since injection pressures being used or desired to be used are 30,000 psi and higher, and fuel typically has a compressability of approximately one percent per 1,000 psi, the fuel to be injected is compressed approximately twenty to thirty percent. In addition to compressing the fuel to be injected, there is also some overhead volume associated with the intensified fuel, including passages to get the intensified fuel to the needle chamber, and of course, the needle chamber itself. In the prior art, this full amount of energy required to pressurize fuel for maximum injection is used, independent of the engine operating conditions, even at engine idle. 
         [0017]    In the present invention, however, at lighter engine loads where less fuel must be delivered to the combustion chamber, only a single intensifier assembly may be operated, thus essentially reducing the power required by the injector by fifty percent, assuming that not only are the intensification ratios the same, but also the intensifier pistons themselves are of the same diameter. 
         [0018]    As an alternative, intensification ratios could be the same though one intensifier assembly could have twice the area, or twice the stroke ( FIG. 3 ), or some combination of area and stroke differences to have twice the intensified fuel capacity of the other. Now when full injection is required, both intensifier assemblies could be used. When the engine is running at a lighter load only the larger intensification assembly might be used, and when running at a still lighter load, only the smaller intensification injection assembly may be used, thereby saving a very substantial amount of the energy otherwise required by injectors of the prior art. 
         [0019]    Another way of operating injectors in accordance with the present invention, or even single intensifier assembly injectors having direct needle control, is as follows. First intensify at least as much fuel as required to at least meet the maximum injection requirements for a single injection event for that engine. (A single injection event may include, for example, a pre-injection, followed by a main injection.) However when the engine is operating under a lighter load, rather than depressurize and repressurize the intensifier assembly to depressurize and repressurize fuel for injection as is now done, simply maintain actuation fluid pressure over the intensifier, but control injection itself by control of the needle, such as, by way of example, is shown in  FIGS. 1 ,  2  and  3 . 
         [0020]    Such operation can save a large fraction of the power required to operate the injector by simply intensifying once for multiple injections, the number of injections depending on the engine load and easily determined by the controller controlling the amount of fuel injected on each injection. For instance, using the present invention at idle, perhaps only one intensifier assembly need be operated with a single intensification providing six or more injections before needing to depressurize the intensifier to refill with fuel for intensification for subsequent injections. Thus the energy used in intensification may readily be made dependent on engine load conditions, and very substantially reduced as engine load is very substantially reduced. Thus while the prior art intensifies the maximum charge required for the engine, whether or not the maximum charge injection is required, the present invention may either intensify only the approximate amount of fuel needed for injection, or intensify a larger amount of fuel than needed for one injection, but maintain intensification for two or more injections, or both. The electronic control system for the injector valves may readily keep track of the amount of fuel injected on each injection to predict when re-intensification would be needed without requiring a feedback measurement. The electronic control may, by way of example, determine whether after an injection event, there remains enough intensified fuel for an equal injection event. If so, intensification is continued after the needle control closes the needle and the next injection event is executed through needle control, that injection event being limited to the amount of fuel at the intensified pressure that can be injected if the engine power setting has increased. 
         [0021]    Thus while certain preferred embodiments of the present invention have been disclosed and described herein for purposes of illustration and not for purposes of limitation, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.