Abstract:
Fuel injectors with intensified fuel storage and methods of operating an engine therewith. At least one storage cavity is provided in the intensifier type fuel injector, with a check valve between the intensifier and the needle chamber and storage cavity preventing loss of injection pressure while the intensifier plunger cylinder is refilling with fuel. This provides very efficient injector operation, particularly at low engine loads, by eliminating the wasted energy of compressing, venting and recompressing fuel for injection. Various injector designs and methods of operating the same in an engine are disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/502,827 filed Jul. 14, 2009 which claims the benefit of U.S. Provisional Patent Application No. 61/080,955 filed Jul. 15, 2008, U.S. Provisional Patent Application No. 61/101,925 filed Oct. 1, 2008 and U.S. Provisional Patent Application No. 61/145,874 filed Jan. 20, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of fuel injectors and fuel injection systems. 
     2. Prior Art 
     Fuel injector performance, particularly in diesel engines, has a substantial influence in overall engine performance, especially with respect to emissions. Of particular importance is the speed at which fuel injection can be terminated. In particular, if fuel injection is terminated merely by the reduction in injection pressure it is difficult to rapidly terminate injection because of the compressability of the fuel and actuation fluid in an intensifier type fuel injector, resulting in a trail off in atomization resulting in unacceptable levels of unburned fuel in the exhaust. Accordingly various types of direct needle control have been proposed to provide injection control other than by controlling injection pressure. 
     Also fuel injectors, particularly diesel fuel injectors, are using ever increasing injection pressures, now going as high as 3000 bar (45,000 psi). Diesel fuel has a compressibility of approximately 1% per 67 bar (1000 psi), so that at the injection pressure, the fuel has been substantially compressed. In intensifier type fuel injectors, injection occurs directly as a result of intensification, so that injection begins on intensification and terminates on termination of intensification. Consequently the volume of fuel intensified is set equal to the maximum injection volume needed, plus of course some overhead volume for the needle chamber, passageways to the needle chamber, etc. At a partial power setting for the engine, much less than the maximum injection volume is needed, yet the full amount is compressed and then depressurized, losing the energy required for the compression of the fuel not injected, which at low power settings and at idle, can be most of the substantial amount of energy used for intensification. In fuel injectors having direct needle control, the operation is a bit different, in that intensification occurs, then injection by the direct needle control, then termination of injection, again by direct needle control, and then depressurization to refill the intensification chamber for the next cycle. While this cycle is a bit different, the losses of intensification energy are not different. 
     Injectors using direct needle control to control injection of fuel supplied to the injector at injection pressure are also known. These injection systems are more efficient because fuel, once compressed, is sooner or later all injected regardless of the engine power setting. They also have the advantage of not cycling the fuel pressure in the needle chamber on each injection event, helping reduce, but not eliminate, the possibility of eventual injector tip breakage. However such systems have serious drawbacks. Aside from the safety issues of having a rail at injection pressures and the associated plumbing problems, there is a serious risk to the engine, in that if an injection tip breaks off, a direct and continuous flow path from the high pressure rail to the combustion chamber is provided, which could result in a hydraulic lock of the engine with catastrophic results. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross section of a fuel injector in accordance with the present invention. 
         FIG. 2  is an illustration of the high pressure fuel storage in the lower section of the fuel injector. 
         FIG. 3  is a cross section of an alternate embodiment. 
         FIG. 3A  is a cross section taken along line  3   a _ 3   a  of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the description to follow, the phrase injection event refers to a complete injection event, which may comprise sub-events, such as, by way of one example, a pre-injection, followed by a main injection, either as a single main injection, or a series of smaller injections. An injection event may begin at any time after the end of a combustion cycle (power stroke) and will end before the end of the next combustion cycle (power stroke). Thus successive injection events in an engine operating in a two stroke or two cycle mode will occur each engine crankshaft rotation (each 360 degrees of crankshaft rotation), while successive injection events in an engine operating in a four stroke or four cycle mode will occur each pair of engine crankshaft rotations (each 720 degrees of crankshaft rotation). 
     First referring to  FIG. 1 , a cross section of one embodiment injector in accordance with the present invention may be seen. The injector includes a needle  20 , normally held in the closed position by a spring  22  acting on a member  24  pushing against the top of the needle  20 . The injector is an intensifier type injector with intensifier piston  26  actuated by lower pressure actuation fluid acting against the top of plunger  28 , with coil spring  30  and fuel inlet pressure through a check valve (not shown) returning the intensifier piston  26  and plunger  28  to their unactuated position between injections. At the top of the injector is a single solenoid actuated three-way spool valve generally indicated by the numeral  32 , with spring return  34 , which valve when in a first position will couple actuation fluid through port  36  to the region above the intensifier piston  26  or, alternatively, when in the second position, will couple the region above intensifier piston  26  to vents  38 . 
     A second smaller spool valve generally indicated by the numeral  40  is coupled to the side of the injector for direct needle control. In a preferred embodiment, spool valve  40  is a three-way magnetically latching spool valve, magnetically latching on actuation, and releasing for spring return on receipt of a small reverse current, though other types of valves, including other spool valves may be used if desired. In the embodiment disclosed, the valve either couples actuation fluid pressure in line  42  to line  44  when actuated, or alternatively, blocks the flow of actuation fluid in line  42  and couples line  44  to a low pressure vent  46  when the spool is released. Through the three-way valve  40 , pressure in line  44  controllably pressurizes the region under piston  48 , which in turn controls actuator pin  24 . The area above piston  48  is permanently coupled to the source of actuation fluid under pressure, and accordingly is always pressurized when the engine is running. For piston  48  and the intensifier, the actuation fluid is preferably engine oil, though some other actuation fluid may be used, such as fuel. 
     In operation, with the area under piston  48  vented, spring  22  and actuation fluid pressure above piston  48  will hold the needle closed, even against intensified fuel pressure in the needle chamber. When injection is to occur, needle control valve  40  is actuated to couple actuation fluid pressure to the region below piston  48 , which pressure balances the piston, allowing intensified fuel pressure in the needle chamber to force the needle open against spring  22 . Of course at the end of injection, the needle control valve  40  is released, to again vent the area under piston  48  to allow actuation fluid pressure over piston  48  to force the needle closed. Of course the needle control valve  40  may be operated more than once, first to provide a pre-injection, followed by a second injection, or even to provide pulsed injections. 
     Of particular importance to the present invention are the large storage volumes  50 , also shown in the cross section of  FIG. 2 , the generous porting  52  and the (ball) check valve  54 . This is contrary to the prior art, where this would be considered energy wasting volume because of its constant pressurization and depressurization. In the present invention, the storage of fuel at the intensified pressure is facilitated by check valve  54 , which prevents depressurization of the intensified fuel pressure when the intensifier is recycled. Instead, injection is controlled by the needle control valve  40 . Thus the pressurized actuation fluid may be left acting on intensifier piston  26  until recycling the intensifier after it begins to reach the limit of its stroke. This allows essentially all fuel having a pressure intensified by the intensifier, including that stored in the storage volumes  50  and generous porting and that still in the intensifier below plunger  28 , be used for injection, typically during multiple successive injection events. The intensifier need only be recycled on an as required basis, rather on each injection event. The electronic control system that controls injection may also keep track of the amount of fuel injected on each injection event, and recycle the intensifier when required. At idle and during low power settings, the intensifier need only be recycled after numerous injection events. Even at a maximum power setting, preferably the storage provided is adequate for multiple injection events. This can allow injection to actually occur during recycling of the intensifier, albeit with a temporarily decreasing injection pressure. This can be useful when an engine goes from a low power setting wherein the fuel at the intensified pressure is adequate for multiple further injections, to a high power setting requiring the injection of more fuel than is left under the plunger  28 . Even at a fixed power setting, this can allow letting the intensifier approach the limit of its travel before recycling during an injection event. Depending on the relative volumes, initially the intensifier may need to be cycled more than once to adequately pressurize the fuel in the storage volume  50 . 
     Alternatively, a sensor such as a Hall effect sensor may be used to sense when the intensifier reaches or approaches the limit of its travel to trigger intensifier recycling, regardless of whether injection is occurring or not, or between injection events. As a further alternative, the intensifier may have a displacement less than the volume of fuel injected during an injection event at maximum engine power, and be operated multiple times between and during an injection event at maximum power. 
     The present invention provides all the advantages and eliminates the disadvantages of a fuel rail at high injection pressures. In that regard, preferably the total storage volume, intensifier plus storage in porting and storage  50 , is less than that that would cause a hydraulic lock in the engine cylinder is dumped into the cylinder on breakage of the injector tip. Also, the storage volume should not be so large as to jeopardize the structural integrity of the injector. Of course, while one exemplary form of direct needle control has been disclosed for purposes of setting the environment for the present invention, substantially any form of direct needle control may be used. Also while the check valve  54  is shown as a ball valve, other forms of check valves may also be used. 
     The exemplary embodiment of injector disclosed herein also uses intensifier actuation fluid for direct needle control. Alternatively, intensified fuel pressure may be used for direct needle control. This is not preferred however, because of the valving difficulties at the intensified pressure. Of course, substantially any method of direct needle control may be used with the present invention, as it is the combination of direct needle control, however done, together with the ability to store fuel at the intensified pressure, that provides the performance and efficiency characteristics of the present invention. 
     Now referring to  FIG. 3 , and alternate embodiment of the present invention may be seen. This embodiment is functionally the same as the previously embodiment, though has a more convenient mechanical arrangement. The embodiment of  FIG. 3  includes a needle  20  with large storage regions  50  and generous porting  52  between the needle  20  and the storage regions  50 . The major difference between the embodiment of  FIG. 3  and  FIG. 1 , however, is the general arrangement of the intensifier and direct needle control. In particular, needle control pins  56  and  58  extend upward along the axis of the injector to a direct needle control piston  62  adjacent the top of the injector. 
     In the embodiment of  FIG. 3 , the intensifier piston  26 ′ is concentric with the needle control pin  58  and operates against multiple plunger pins  60 . In one embodiment, this comprises three plunger pins (see  FIG. 3A ), plumbed together and ported to storage regions  50  through porting not shown in the Figure. Between the plunger pins  60  are additional storage volumes  64 , which are also plumbed to the storage volumes  50 . The upper needle control pin  58  in this embodiment is encouraged to its downward most position by a relatively light spring  66 , with an additional return spring  68  for the intensifier piston  26 . The return of the plunger pins  60  is by way of fuel pressure provided underneath the plunger pins  60  from a relatively low pressurized fuel source through a ball valve which subsequently seals against intensified fuel pressures, as is well known in the art. 
     The operation of the embodiment of  FIG. 3  is as follows. Engine oil under pressure is provided through port  70  to a small spool valve  72 , shown schematically, and a larger spool valve  74 , also shown schematically. The two spool valves  72  and  74  are preferably three-way valves. The spool valve  72  provides direct needle control, and when porting the engine oil through port  70  to the top of piston  62 , holds the needle  20  down against the needle seat to seal the same against fuel at intensified pressure. Thus as before, spool valve  74  may be used to port engine oil through port  70  to the top of intensifier piston  26 ′ to intensify the fuel pressure, with the intensification remaining typically through a plurality of injections as controlled by the needle control spool valve  72 . When the intensifier piston  26 ′ approaches the bottom of its range of travel, spool valve  74  is actuated to cut off engine oil communication between port  70  and the top of the intensifier piston  26 ′, and instead will couple the region above intensifier  26 ′ to a vent or low pressure oil sump, typically directly or indirectly back to the engine crankcase. During this time a ball valve  76  similar to ball valve  54  of  FIG. 1  is used to retain the intensification pressure on the remaining intensified fuel while the intensifier is cycled to intensify another charge, preferably between injection events. 
     The preferred method of operating the present invention is to operate the intensifier throughout the full duration of the injection event, recycling the intensifier only between injection events. This has the advantages of maintaining the highest pressure, and a uniform pressure, throughout the injection event, providing maximum atomization and repeatability in the injector operation. 
     Thus one aspect of the present invention is that it can very substantially reduce the energy loss of prior art intensifier type fuel injectors and methods of operation thereof by using (injecting) all or substantially all the fuel at the intensified pressure before intensifying another fuel charge. This may allow a single intensification for use over multiple injection events (injection over multiple combustion cycles), particularly at low engine power settings, where depressurizing (de-intensifying) and re-intensification a large part of the intensified fuel not used in an injection event is particularly wasteful of the quite substantial energy used for intensification. 
     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.