Abstract:
A hybrid fuel injection system which allows electronic control over the injection processes, wherein selective rate shaping and multiplicity of injections is possible. The hybrid fuel injection system consists of an add-on common rail system (CRS) which provides supplemental fuel injections with respect to the main fuel injections provided by a unit pump system (UPS). Additionally, the CRS can serve to provide fuel injections as necessary to effect a “limp-home” mode of engine operation in the event of a failure of the UPS. Both the CRS and the UPS use common fuel supply, return, injector, and electronic controller.

Description:
TECHNICAL FIELD 
   The present invention relates to fuel injection systems for internal combustion engines, particularly diesel engines. More particularly, the present invention relates to an electronically-controlled hybrid fuel injection system for providing selective fuel injection rate shaping and multiplicity of injections. 
   BACKGROUND OF THE INVENTION 
   To meet future EPA emissions standards, large bore medium speed diesel engines need greater flexibility and reliability on the fuel injection equipment with regard to fuel metering, injection timing, injection pressure, rate of injection (rate shaping) and multiple (pre-, post-, or split) injections independent of engine speed. A production unit pump system (UPS) offers the advantage of design simplicity with flexibility on electronically-controlled injection timing. 
   However, the rate of injection and injection pressure are solely dependent upon cam profile and engine speed, and are optimized for full load operating conditions. It is impossible to provide split injections and/or injection pressure control and pressure level. At engine idle and lower speeds, the UPS cannot generate adequate high injection pressures that are necessary to achieve complete combustion. 
   In order to overcome these shortcomings, advancements to the UPS such as current controlled rate shaping (CCRS) and advanced unit pump system (AUPS) are being developed by the fuel injection equipment manufacturers. For example, see International Council on Combustion Engines, 2001 Congress, Hamburg, Germany, pages 511 through 517. Also, several new injection systems, such as common rail system (CRS) and amplifier piston common rail system (APCRS), are currently being developed. The CCRS concept offers the advantage of excellent retrofit capability with incremental cost, and it can provide initial injection rate shaping (boot injection) but limited by the cam profile, engine speed, and needle valve opening pressure. The AUPS can provide controlled injection pressure that is independent of engine speed. However, it cannot provide split injections that are essential to reduce certain exhaust emissions, engine noise, and improve fuel efficiency. 
   The CRS and APCRS systems (both being non-UPS) offer flexibility to control the injection timing and injection pressure independent of cam profile and/or engine speed. However, the high pressure CRS allows only controlling simple and multiple injections. Higher pressure peaks at the end of injection event and pressure pulsations at higher injection quantities limit its application to medium speed, large bore diesel engines. The APCRS, using either hydraulically- or mechanically-controlled pressure amplifier concepts, has the potential to permit pre- and post-injections, and variations in injection rate shaping. However, the boot pressure ratio is not variable because of a geometrically-fixed amplification ratio. 
   A more critical hardware constraint is the layout of the low-pressure system avoiding pressure pulsations. In comparison, the production UPS and the delineated alternative fuel systems cannot offer the desired flexible injection (cam and speed independent injection pressure, rate shaping, and multiple injections) while maintaining the reliability and cost effective retrofit capability. 
   Accordingly, what remains needed in the art is a fuel injection system which is a hybrid, the system allowing electronic control over the injection processes, wherein selective rate shaping and multiplicity of injections is made possible. 
   SUMMARY OF THE INVENTION 
   The present invention is a hybrid fuel injection system which allows electronic control over the injection processes, wherein selective rate shaping and multiplicity of injections is made possible. 
   The hybrid fuel injection system according to the present invention combines the benefits of both the high pressure common rail system (CRS) and the unit pump system (UPS) to achieve greater flexibility on fuel metering, injection timing, injection pressure, rate of injection, pre-injection, split injections, and post-injection. Further, it has excellent retrofit capability because the CRS will be added to the existing UPS. The hybrid fuel injection system combines the benefits of UPS and CRS with a potential to provide a CRS retrofit kit to an existing UPS. The hybrid fuel injection system offers the potential of providing pre-, post-, or multiple (split) fuel injections independent of cam profile and engine speed while combing the benefits of advanced unit pump systems (which can provide controllable injection pressure and rate shaping). 
   The hybrid fuel injection system consists of an add-on CRS which provides supplemental fuel injections with respect to the main fuel injections provided by a UPS (inclusive of an advanced UPS and CCRS). The CRS consists of a small size high pressure pump that can generate high injection pressures independent of engine speed/cam profile and a high pressure rail accommodating fuel quantity that is sufficient for pre-, post- (at all engine speed/load conditions), or main fuel injection quantity at engine idle condition. Additionally, the CRS can serve to provide fuel injections as necessary to effect a “limp-home” mode of engine operation in the event of a failure of the UPS. Both the CRS and the UPS use common fuel supply, return, injector, and electronic controller. 
   In a first embodiment, the CRS has an electronically-controlled solenoid for each cylinder which effects the beginning and end of supplemental fuel supply directly to the fuel passage communicating with the nozzle passage of the nozzle assembly of the fuel injector. In this first embodiment, the UPS and the CRS both utilize the nozzle assembly of the fuel injector to control fuel exiting the fuel injector. In a second embodiment, the electronically-controlled solenoid directs fuel into an auxiliary passage in the fuel injector which communicates with a sac. In this second embodiment, injection of fuel by the CRS is entirely independent of the UPS and of the nozzle assembly and its needle motion. 
   In operation during engine idle and part load conditions, only CRS may be functional, wherein opening of the electronically-controlled solenoid turns off the UPS. The high pressure solenoid in the CRS will deliver high pressure fuel either in the form of a single injection or in the form of multiple injections. The high pressure pump in the CRS, driven by, for example, an electrical motor or the crankshaft, pressurizes the fuel and maintains the accumulator at a preset pressure. The entire CRS unit acts independent of UPS, but the operation logic is preferably built into a single electronic control unit (ECU). 
   During medium through full load/speed engine operating conditions, the CRS will begin the pre-injection and/or multiple injections of a small fuel quantity followed by the main fuel injection event actuated by the UPS. Subsequent to the UPS main fuel injection event, the CRS can perform one or more additional fuel injections post the main fuel injection event, if necessary. In this mode of operation, the majority of the fuel is still delivered by the UPS whose injection pressures and rate of injection are dictated by the cam profile, engine speed, and actuation of its solenoid. In the event of actuation of the aforementioned “limp-home” mode, the CRS will completely control the delivery of fuel to the cylinders. 
   Accordingly, it is an object of the present invention to provide a hybrid fuel injection system for providing a main fuel injection event and further providing selection of fuel injection rate shaping and multiple fuel injections. 
   This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a first schematic depiction of a hybrid fuel injection system according to a first embodiment of the present invention. 
       FIG. 2  is a second schematic depiction of the hybrid fuel injection system according to the first embodiment of the present invention. 
       FIG. 3  is a schematic depiction of a hybrid fuel injection system according to a second embodiment of the present invention. 
       FIG. 4  is a detailed, partly-sectional view of the tip of a fuel injector according to the second embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawing,  FIG. 1  depicts a first embodiment of the hybrid fuel injection system  100  according to the present invention. A fuel tank  102  supplies fuel via various fuel lines to both a unit pump system (UPS)  104  and a common rail system (CRS)  106 . The outputs of the UPS  104  and the CRS  106  are input to a fuel injector  108 . In this regard, there is one UPS respectively for each fuel injector, and the CRS is common to all fuel injectors. 
   Each UPS  104  provides the main fuel injection to its respective fuel injector  108 . The UPS is of common construction, including, for example a cam roller follower  110  for following a cam  115 , a plunger  112 , a pumping space  114 , a pump solenoid valve  116  operatively connected to an electronic control unit (ECU)  118 , a fuel inlet  120 , a leakage fuel drain  122  and a pressurized fuel outlet  124  which is connected via tubing to a UPS check valve  126 , which, in turn, communicates with the fuel input  128  of the fuel injector  108 . 
   The CRS  106  includes an electrically-operated high pressure fuel pump  130  which receives fuel at a low pressure fuel inlet  132  and is operated on command of the ECU  118  via a throttle valve  135 . The high pressure fuel pump  130  supplies highly pressurized fuel to a high pressure accumulator  134 . A CRS solenoid valve  136  is provided respectively for each fuel injector. The solenoid valve  136  provides high pressure fuel, selectively at the command of the ECU  118  in association with a pressure sensor  145 , from the high pressure accumulator  134  to a CRS check valve  138 , which, in turn, communicates with the fuel input  128  of the fuel injector  108 . A maximum pressure valve  158  prevents over pressurization of the accumulator  134 . 
   Fuel is delivered from the fuel tank  102  via a fuel pump  140  to a low pressure delivery rail  142  which supplies fuel to the UPS fuel inlet  120  and the CRS fuel inlet  132 . A low pressure return rail  144  accepts return of fuel. 
   In general operation, the UPS  104  supplies the major fuel injection event, and the CRS  106  supplies one or more auxiliary fuel injections which may precede, coincide with, or follow the main injection event of the UPS. Accordingly, the rate shape of the main fuel injection event may be electronically configured by commands of the ECU and/or the UPS (inclusive of an advanced UPS and CCRS), and/or one or more fuel injections may additionally be effected. 
   In the hybrid fuel injection system  100 ′ depicted at  FIG. 2 , the foregoing description applies, wherein now the fuel injector  108 ′ is modified to integrally include the check valves  126  and  138 . 
   In the present embodiments as depicted at  FIGS. 1 and 2 , the injections of both the UPS and the CRS are effected through a common injector passage  148  to the nozzle assembly  150 , wherein there must be physical movement of the injector needle  152  with respect to its seat  154  in order for fuel from either the UPS or the CRS to pass out the nozzle  156  and thereby be injected into the cylinder by either of the UPS and CRS, operating singly or in combination. 
   Referring now additionally to  FIGS. 3 and 4 , a second embodiment of the hybrid fuel injection system  100 ″ according to the present invention will be detailed. In this regard, the unit pump system  104 , the common rail system  106  and the ECU  118  as discussed hereinabove with respect to  FIGS. 1 and 2  are utilized. 
   Now, the fuel injector  108 ″ has an injector passage  148 ′ which only communicates with the UPS  104 . The CRS  106  is connected via tubing to a CRS solenoid valve  136 ′ and then via tubing  160  to a port  162  in the fuel injector  108 ″. The port  162  communicates with a sac  164  via a passageway  166  internal to the fuel injector  108 ″. The CRS solenoid valve  136 ′ is operated under command from the ECU  118 . 
   Operationally, the UPS  104  supplies the major fuel injection event, and the CRS  106  supplies one or more auxiliary fuel injections which may precede, coincide with, or follow the main injection event of the UPS. Accordingly, the rate shape of the main fuel injection event may be electronically configured by commands of the ECU and or UPS (inclusive of advanced UPS and CCRS), and/or one or more fuel injections may additionally be accomplished. In this regard, it will be appreciated that the fuel injections by the CRS  106  are entirely independent of the nozzle assembly  150 ′ wherein there is no need for movement of the injector needle  152 ′ with respect to its seat  154 ′ to effect a CRS fuel injection. CRS fuel injection occurs when the CRS solenoid valve  136 ′ opens, whereupon fuel under pressure flows into the sac  164  and then injects into the cylinder through the apertures of the nozzle  156 ′. 
   In operation with respect to the recounted embodiments  100 ,  100 ′,  100 ″ during engine idle and part load conditions, only the CRS  106  may be functional, wherein opening of the electronically controlled solenoid valve  136 ,  136 ′ turns off the UPS  104 . The high pressure solenoid valve  136 ,  136 ′ in the CRS  106  will deliver high pressure fuel either in the form of a single injection or in the form of multiple injections. The high pressure pump  130  in the CRS, which is driven by, for example, an electrical motor or the crankshaft, will pressurize the fuel and maintain the accumulator  134  at a preset pressure. The entire CRS unit acts independent of the UPS but the operation logic is built into the ECU  118 . 
   During medium through full load/speed engine operating conditions, the CRS  106  will begin the pre-injection and/or multiple injections of a small fuel quantity, for example less than 20% of the total fuel injection quantity, followed by the main fuel injection event actuated by the UPS  104 . Subsequent to the UPS main fuel injection event, the CRS can perform one or more additional fuel injections post the main fuel injection event, if necessary. In this mode of operation, the majority of the fuel is still delivered by the UPS whose injection pressures and rate of injection are dictated by the profile of its cam  115 , engine speed, and actuation of its pump solenoid valve  116 . In the event of actuation of an ECU instituted and controlled “limp-home” mode due to a failure of the UPS, the CRS will completely control the delivery of fuel to the cylinders. 
   For engines having a production UPS, the hybrid fuel injection system  100 ,  100 ′,  100 ″ may be provided by installation of a retrofit kit. The retro-fit kit consists of a CRS  106  and appropriate tubing, a new ECU  118  or a reprogrammed existing ECU. In the case of the hybrid fuel injection system  100 ′,  100 ″ depicted at  FIGS. 2 through 4 , a modified fuel injector  108 ′,  108 ″ is respectively provided for each cylinder. 
   To those skilled in the art to which this invention appertains, the above-described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.