WO2007139737A2

WO2007139737A2 - Multi-source fuel system for variable pressure injection

Info

Publication number: WO2007139737A2
Application number: PCT/US2007/012029
Authority: WO
Inventors: Dennis H. Gibson
Original assignee: Caterpillar Inc.
Priority date: 2006-05-24
Filing date: 2007-05-18
Publication date: 2007-12-06
Also published as: JP2009538400A; JP2012177381A; WO2007139737A3; DE112007001288T5; JP5380281B2

Abstract

A fuel system for an engine is disclosed. The fuel system has a first source configured to pressurized fuel to a first pressure, and a second source configured to pressurized fuel to a second pressure. The fuel system also has a fuel injector (32) configured to receive and inject fuel into the engine, and a single valve (102) disposed between the fuel injector and the first and second sources. The single valve is in fluid communication with the first and second sources and the fuel injector, and able to deliver variable pressure fuel to the fuel injector.

Description

MULTI-SOURCE FUEL SYSTEM FOR VARIABLE PRESSURE INJECTION

Related Applications

This application claims the benefit of U.S. Patent Application No. 11/420,057 by Dennis H. GIBSON₅ filed 24 May 2006 entitled "Multi-Source Fuel System Having Grouped Injector Pressure Control", U.S. Patent Application No. 11/420,051 by Dennis H. GIBSON, filed 24 May 2006 entitled "Multi- Source Fuel System Having Closed Loop Pressure Control", and U.S. Patent Application No. 11/443,312 by Dennis H. GIBSON, filed 31 May 2006 entitled "Multi-Source Fuel System For Variable Pressure Injection", the disclosures of which are expressly incorporated herein by reference.

Technical Field

The present disclosure is directed to a fuel system and, more particularly, to a fuel system having multiple sources of pressurized fuel for providing variable pressure injection events.

Background

Common rail fuel systems provide a way to introduce fuel into the combustion chambers of an engine. Typical common rail fuel systems include an injector having an actuating solenoid that opens a fuel nozzle when the solenoid is energized. Fuel is then injected into the combustion chamber as a function of the time period during which the solenoid remains energized and the pressure of fuel supplied to the fuel injector nozzle during that time period.

To optimize engine performance and exhaust emissions, engine manufacturers may vary the pressure of the fuel supplied to the fuel injector nozzle. One such example is described in U.S. Patent Application Publication No. 2004/0168673 (the '673 publication) by Shinogle published 2 September 2004. The '673 publication describes a fuel system having a fuel injector fluidly connectable to a first common rail holding a supply of fuel, and a second common rail holding a supply of actuation fluid (e.g., oil). Each fuel injector of the '673 patent is equipped with an intensifier piston movable by the actuation fluid to increase the pressure of the fuel. By fluidly connecting the fuel injector to the first common rail, fuel can be injected at a first pressure. By fluidly connecting the fuel injector to the first and second common rails, fuel can be injected at a second pressure that is higher than the first pressure.

Although the fuel injection system of the '673 publication may adequately supply fuel to an engine at different pressures, it may be limited and problematic. Specifically, because the fuel injection system of the '673 publication can inject fuel at only two different pressures, it may be limited from some applications. In addition, because the system utilizes two different fluids, namely fuel and oil, care must be take not to contaminate one fluid with the other. If contamination does occur, the engine may not operate as desired and could possibly suffer damage. Further, because each fuel injector includes its own dedicated intensifier to vary the pressure of the fuel sprayed from that injector, the system may include a large number of components. This large number of components may increase the cost of the fuel injection system and the difficulty in precisely controlling the fuel system. Further, because the pressure of the injected fuel is regulated by controlling pump output a significant distance upstream of the injectors, the actual injected pressure may lag behind a desired injected pressure. This lag in pressure may result in injection profiles that deviate from intended injection profiles. The fuel system of the present disclosure solves one or more of the problems set forth above.

Summary of the Invention

One aspect of the present disclosure is directed to a fuel system for an engine. The fuel system includes a first source configured to pressurize fuel to a first pressure, and a second source configured to pressurize fuel to a second pressure. The fuel system also includes a fuel injector configured to receive and inject fuel into the engine. The fuel system also includes a single valve disposed between the fuel injector and the first and second sources, the single valve being in fluid communication with the first and second sources and the fuel injector, and able to deliver variable pressure fuel to the fuel injector.

Another aspect of the present disclosure is directed to a method of injecting fuel. The method includes pressurizing a first fuel stream to a first pressure, and pressurizing a second fuel stream to a second pressure. The method also includes receiving the first and second fuel streams at a single location, responsively generating a third fuel stream at a third pressure, directing the third fuel stream to an injector and selectively injecting the third fuel stream.

Brief Description of the Drawings

Fig. 1 is a schematic and diagrammatic illustration of an exemplary disclosed engine;

Fig. 2 is a schematic and cross-sectional illustration of an exemplary disclosed fuel system for use with the engine of Fig. 1 ;

Fig. 3 is a schematic and cross-sectional illustration of another exemplary disclosed fuel system for the engine of Fig. 1; Fig. 4 is a schematic and cross-sectional illustration of another exemplary disclosed fuel system for the engine of Fig. 1;

Fig. 5 is a schematic and diagrammatic illustration of another exemplary disclosed engine;

Fig. 6 is a schematic and cross-sectional illustration of an exemplary disclosed fuel system for the engine of Fig. 5; and

Fig. 7 is a schematic and cross-sectional illustration of another exemplary disclosed fuel system for the engine of Fig. 5. Detailed Description

Fig. 1 illustrates a machine 5 having an engine 10 and an exemplary embodiment of a fuel system 12. Machine 5 may be a fixed oτ mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, power generation, transportation, or any other industry known in the art. For example, machine 5 may embody an earth moving machine, a generator set, a pump, or any other suitable operation-performing machine.

For the purposes of this disclosure, engine 10 is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, that engine 10 may embody any other type of internal combustion engine such as, for example, a gasoline or a gaseous fuel-powered engine. Engine 10 may include an engine block 14 that defines a plurality of cylinders 16, a piston 18 slidably disposed within each cylinder 16, and a cylinder head 20 associated with each cylinder 16.

Cylinder 16, piston 18, and cylinder head 20 may form a combustion chamber 22. In the illustrated embodiment, engine 10 includes six combustion chambers 22. However, it is contemplated that engine 10 may include a greater or lesser number of combustion chambers 22 and that combustion chambers 22 may be disposed in an "in-line" configuration, a "V" configuration, or any other suitable configuration.

As also shown in Fig. 1, engine 10 may include a crankshaft 24 that is rotationally disposed within engine block 14. A connecting rod 26 may connect each piston 18 to crankshaft 24 so that a sliding motion of piston 18 within each respective cylinder 16 results in a rotation of crankshaft 24.

Similarly, a rotation of crankshaft 24 may result in a sliding motion of piston 18. As crankshaft 24 rotates, combustion chambers 22 may fire in a specific order. The firing order, when numbering combustion chambers 22 from the left of Fig. 1, may be, for example, I₅ 5, 3, 6, 2, 4. That is, the first or left -most combustion chamber, may fire first (e.g., combust a mixture of fuel and air before the remaining cylinders within a single 360 degree revolution of crankshaft 24). Following the firing of the left-most combustion chamber 22, the fifth combustion chamber from the left may fire, and so on. In this manner, no adjacent combustion chambers 22 may fire consecutively.

Fuel system 12 may include components that cooperate to deliver injections of pressurized fuel into each combustion chamber 22. Specifically, fuel system 12 may include a tank 28 configured to hold a supply of fuel, and a fuel pumping arrangement 30 configured to pressurize the fuel and direct one or more streams of pressurized fuel to a plurality of fuel injectors 32. A fuel transfer pump 36 may be disposed within a fuel line 40 between the tank 28 and the fuel pumping arrangement 30 to provide low pressure feed to fuel pumping arrangement 30.

Fuel pumping arrangement 30 may embody a mechanically driven, electronically controlled pump having a first pumping mechanism 30a and a second pumping mechanism 30b. Each of first and second pumping mechanisms 30a, b may be operatively connected to a pump drive shaft 46 by way of rotatable cams (not shown). The cams may be adapted to drive piston elements (not shown) of first and second pumping mechanisms 30a, b through a compression stroke to pressurize fuel. Plungers (not shown) associated with first and second pumping mechanisms 30a, b may be closed at variable timings to change the length of the compression stroke and thereby vary the flow rate of first and second pumping mechanisms 30a, b. Alternatively, first and second pumping mechanisms 30a, b may include a rotatable swashplate, or any other means known in the art for varying the flow rate of pressurized fuel. It is contemplated that fuel pumping arrangement 30 may alternatively embody two separate pumping elements having fixed output capacities and being disposed in parallel or series relationship, if desired. First and second pumping mechanisms 30a, b may be adapted to generate separate flows of pressurized fuel. For example, first pumping mechanism 30a may generate a first flow of pressurized fuel directed to a first common manifold 34 by way of a first fuel supply line 42. Second pumping mechanism 30b may generate a second flow of pressurized fuel directed to a second common manifold 37 by way of a second fuel supply line 43. In one example, the first flow of pressurized fuel may have a pressure of about 100 MPa₅ while the second flow of pressurized fuel may have a pressure of about 200 MPa. A first check valve 44 may be disposed within first fuel supply line 42 to provide for unidirectional flow of fuel from first pumping mechanism 30a to first common manifold 34. A second check valve 45 may be disposed within second fuel supply line 43 to provide for unidirectional flow of fuel from second pumping mechanism 30b to second common manifold 37.

Fuel pumping arrangement 30 may be operatively connected to engine 10 and driven by crankshaft 24. For example, pump driveshaft 46 of fuel pumping arrangement 30 is shown in Fig. 1 as being connected to crankshaft 24 through a gear train 48. It is contemplated, however, that one or both of first and second pumping mechanisms 30a, b may alternatively be driven electrically, hydraulically, pneumatically, or in any other appropriate manner. Fuel injectors 32 may be disposed within cylinder heads 20 and connected to first and second common manifolds 34, 37 by way of a plurality of fuel lines 50. Each fuel injector 32 may be operable to inject an amount of pressurized fuel into an associated combustion chamber 22 at predetermined timings, fuel pressures, and fuel flow rates. The timing of fuel injection into combustion chamber 22 may be synchronized with the motion of piston 1 S. For example, fuel may be injected as piston 18 nears a top-dead-center (TDC) position in a compression stroke to allow for compression-ignited-combustion of the injected fuel. Alternatively, fuel may be injected as piston 18 begins the compression stroke heading towards a top-dead-center position for homogenous charge compression ignition operation. Fuel may also be injected as piston 18 is moving from a top-dead-center position towards a bottom-dead-center position during an expansion stroke for a late post injection to create a reducing atmosphere for aftertreatment regeneration. As illustrated in Fig. 2, each fuel injector 32 may embody a closed nozzle unit fuel injector. Specifically, each fuel injector 32 may include an injector body 52 housing a guide 54, a nozzle member 56, a needle valve element 58, a first solenoid actuator 60, and a second solenoid actuator 62.

Injector body 52 may be a generally cylindrical member configured for assembly within cylinder head 20. Injector body 52 may have a central bore 64 for receiving guide 54 and nozzle member 56, and an opening 66 through which a tip end 68 of nozzle member 56 may protrude. A sealing member such as, for example, an o-ring (not shown) may be disposed between guide 54 and nozzle member 56 to restrict fuel leakage from fuel injector 32. Guide 54 may also be a generally cylindrical member having a central bore 70 configured to receive needle valve element 58, and a control chamber 72. Central bore 70 may act as a pressure chamber, holding pressurized fuel continuously supplied by way of a fuel supply passageway 74. During injection, the pressurized fuel from fuel line 50 may flow through fuel supply passageway 74 and central bore 70 to the tip end 68 of nozzle member 56.

Control chamber 72 may be selectively drained of or supplied with pressurized fuel to control motion of needle valve element 58. Specifically, a control passageway 76 may fluidly connect a port 78 associated with control chamber 72 with first solenoid actuator 60. Port 78 may be disposed within a side wall of control chamber 72 that is radially oriented relative to axial movement of needle valve element 58 or, alternatively, within an axial end portion of control chamber 72. Control chamber 72 may be continuously supplied with pressurized fuel via a restricted supply passageway 80 that is in communication with fuel supply passageway 74. The restriction of supply passageway 80 may allow for a pressure drop within control chamber 72 when control passageway 76 is drained of pressurized fuel.

Nozzle member 56 may likewise embody a generally cylindrical member having a central bore 82 that is configured to receive needle valve element 58. Nozzle member 56 may further include one or more orifices 84 to allow injection of the pressurized fuel from central bore 82 into combustion chambers 22 of engine 10.

Needle valve element 58 may be a generally elongated cylindrical member that is slidingly disposed within housing guide 54 and nozzle member 56. Needle valve element 58 may be axially movable between a first position at which a tip end 86 of needle valve element 58 blocks a flow of fuel through orifices 84, and a second position at which orifices 84 are open to allow a flow of pressurized fuel into combustion chamber 22.

Needle valve element 58 may be normally biased toward the first position. In particular, each fuel injector 32 may include a spring 88 disposed between a stop 90 of guide 54 and a seating surface 92 of needle valve element 58 to axially bias tip end 86 toward the orifice-blocking position. A first spacer 94 may be disposed between spring 88 and stop 90, and a second spacer 96 may be disposed between spring 88 and seating surface 92 to reduce wear of the components within fuel injector 32.

Needle valve element 58 may have multiple driving hydraulic surfaces. In particular, needle valve element 58 may include a hydraulic surface 98 tending to drive needle valve element 58 toward the first or orifice-blocking position when acted upon by pressurized fuel, and a hydraulic surface 100 that tends to oppose the bias of spring 88 and drive needle valve element 58 in the opposite direction toward the second or orifice-opening position.

First solenoid actuator 60 may be disposed opposite tip end 86 of needle valve element 58 to control the opening motion of needle valve element 58. In particular, first solenoid actuator 60 may include a two-position valve element disposed between control chamber 72 and tank 28. The valve element may be spring-biased toward a closed position blocking fluid flow from control chamber 72 to tank 28, and solenoid-actuated toward an open position at which fuel is allowed to flow from control chamber 72 to tank 28. The valve element may be movable between the closed and open positions in response to an electric current applied to a coil associated with first solenoid actuator 60. It is contemplated that the valve element may alternatively be hydraulically operated, mechanically operated, pneumatically operated, or operated in any other suitable manner. It is further contemplated that the valve element may alternatively embody a proportional type of valve element that is movable to any position between the closed and open positions.

Second solenoid actuator 62 may include a two-position valve element disposed between first solenoid actuator 60 and tank 28 to control a closing motion of needle valve element 58. The valve element may be spring- biased toward an open position at which fuel is allowed to flow to tank 28, and solenoid-actuated toward a closed position blocking fluid flow to tank 28. The valve element may be movable between the open and closed positions in response to an electric current applied to a coil associated with second solenoid actuator 62. It is contemplated that the valve element may alternatively be hydraulically operated, mechanically operated, pneumatically operated, or operated in any other suitable manner. It is further contemplated that the valve element may alternatively embody a three-position type of valve element, wherein bidirectional flows of pressurized fuel are facilitated.

As also illustrated in Fig. 2, a pressure control valve 102 may be associated with each fuel injector 32. Specifically, pressure control valve 102 may include a first valve element 106, a second valve element 108, an actuator 104 connected to move valve element 108, a third valve element 110, and a bypass circuit 1 12. In response to the fuel pressures within first and second common manifolds 34, 37, and a current input to actuator 104, pressure control valve 102 may regulate the pressure of fuel directed through fuel supply passageway 74 to fuel injector 32. It is contemplated that pressure control valve 102 may be part of fuel injector 32 or a separate stand-alone component associated with one or more fuel injectors 32. Valve element 106 may embody a pilot-operated proportional valve element or other suitable device movable by fluid pressure acting at an end thereof to selectively pass a portion of the pressurized fuel from second common manifold 37 to central bore 82 of nozzle member 56. Specifically, valve element 106 may be movable from a first position at which a maximum amount of the first stream of pressurized fuel is directed to central bore 82, against the bias of a return spring 114 toward a second position at which no pressurized fuel from second common manifold 37 flows to central bore 82. Valve element 106 may also be movable to any position between the first and second positions to direct a portion of the maximum amount to tank 28 and the remaining portion of the maximum amount to central bore 82. The amount and ratio of the fuel directed by valve element 106 to central bore 82 and tank 28 may depend on the pressure of fluid acting on the end of valve element 106 and may affect the pressure of the fuel supplied to central bore 82. For example, as the fuel amount draining through valve element 106 to tank 28 increases (e.g., valve element 106 is moved toward, but not all the way to the second position), the pressure of the fuel directed to central bore 82 may decrease. Conversely, as the amount of the first fuel flow draining through valve element 106 to tank 28 decreases (e.g., valve element 106 is moved toward the first position), the pressure of the fuel directed to central bore 82 may increase. In this manner, variable injection pressures through orifices 84 and penetration depth into combustion chamber 22 may be attained.

Valve element 108 may also embody a proportional valve element or other suitable device and may be movable to affect the location of valve element 106 between the first and second positions. Specifically, valve element 108 may be movable between a first position at which pressurized pilot fuel from first common manifold 34 is communicated with the end of valve element 106, and a second position at which the pressurized pilot fuel at the end of valve element 106 is drained to tank 28. The speed at which the pilot fuel is drained or communicated with the end of valve element 106 may affect the rate at which the fuel pressure within fuel injector 32 changes. Fuel from upstream of valve element 108 may cooperate with the bias of an associated return spring to retain valve element 108 in contact with actuator 40.

Actuator 104 may embody a piezo electric mechanism having one or more columns of piezo electric crystals. Piezo electric crystals are structures with random domain orientations. These random orientations are asymmetric arrangements of positive and negative ions that exhibit permanent dipole behavior. When an electric field is applied to the crystals, such as, for example, by the application of a current, the piezo electric crystals expand along the axis of the electric field as the domains line up. Actuator 104 may be mechanically connected to move valve element 108 between the first and second positions in response to an applied current.

Valve element 110 may embody a pressure regulating valve element configured to affect the pressure of fuel flowing through valve element 106 to fuel injector 32. In particular, valve element 110 may be disposed between valve element 106 and tank 28, such that as valve element 106 is moved away from the first position, some fuel is passed through valve element 106 to valve element 110. A first end of valve element 110 may be in communication with fuel from first common manifold 34 and, together with the bias of a return spring, urge valve element 110 toward a flow blocking position. When in the flow blocking position, substantially no fuel may passed through valve element 110 to tank 28. A second end of valve element 110 may be in communication with the fuel passed through valve element 106 and may urge valve element 110 toward a flow passing position. When in the flow passing position, the amount of fuel allowed to drain to tank 28 may be dependent on the amount of fuel passed through valve element 106, the resulting pressure of the passed fuel, and the pressure of the fuel from first common manifold 34 supplied to the opposing end of valve element 110. In this manner, the pressure of the fuel within first common manifold 34 may affect the pressure of the fuel from second common manifold 37 passed to fuel injector 32.

Bypass circuit 112 may ensure a minimum pressure of fuel is always available to fuel injector 32. In particular, when valve element 106 is in the second position the only source of fuel for injector 32 may be first common manifold 34 by way of bypass circuit 112. Bypass circuit 112 may include a check valve 116 that ensures unidirectional flow of fuel through bypass circuit 112 such that fuel flows through bypass circuit 112 only when a fuel pressure within injector 32 drops below fuel pressure within first common manifold 34. Fig. 3 illustrates an alternative embodiment to fuel system 12 of Fig. 2. Similar to fuel system 12 of Fig. 2, fuel system 12 of Fig. 3 may include fuel injector 32 receiving flows of pressurized fuel from first and second common rails 34 and 37 via fuel line 50. However, in contrast to the pressure control device 102 depicted in Fig. 2, the embodiment of Fig. 3 may include a different pressure control device 302. Pressure control devices 302 may include an actuator 304 operatively connected to a valve element 306 and in communication with a control system 316. Valve element 306 may be associated with fuel injector 32, and movable by actuator 304 to selectively combine and/or direct the first and second flows of pressurized fuel to fuel injector 32. It is contemplated that actuator 304 and valve element 306 may be integral with fuel injector 32 or separate as stand alone components.

Actuator 304 may be substantially identical to 104 and embody a piezo electric device having one or more columns of piezo electric crystals. When an electric field is applied to the crystals of 304, such as, for example, by the application of a current, the piezo electric crystals expand along its axis to affect movement of 306.

Actuator 304 may be connected to move valve element 306 by way of pilot fluid. In particular, a pilot element 320 connected to actuator 304 may be movable between a first position at which pilot fluid from common rail 34 is communicated with an end of valve element 306, and a second position at which the pilot fluid from the end of valve element 306 is allowed to drain to tank 28. As current is applied to the piezo electric crystals of actuator 304, actuator 304 may expand to move pilot element 320 from the first position toward the second position. In contrast, as the current is removed from the piezo electric crystals of actuator 304, actuator 304 may contract to return pilot element 320 toward the first position. It is contemplated that the piezo electric crystals of actuator 304 may be omitted, if desired, and the movement of pilot element 320 be controlled in another suitable manner. It is further contemplated that actuator 304 may alternatively be directly and mechanically connected to move valve element 306 without the use of pilot element 320, if desired.

Valve element 306 may embody a proportional valve element or other suitable device movable in response to the pilot fluid described above. Specifically, when sufficient pilot fluid from common rail 34 is in contact with the end of valve element 306, valve element 306 may be in or urged toward a first position, at which only the second flow of pressurized fuel is directed to central bore 82. As the pilot fluid is drained away from the end of valve element 306, a spring 322 may bias valve element 306 toward a second position, at which only the first flow of pressurized fuel is directed to central bore 82. Valve element 306 may be movable by way of the pilot fluid to any position between the first and second positions to direct a portion of the first and second pressurized flows of fuel to central bore 82. The amount and ratio of the first or second flows directed by valve element 306 to central bore 82 may depend on the current applied to the piezo electric crystals of actuator 304 and may affect the resultant pressure of the fuel supplied to central bore 82. In addition, the speed of the fluid flowing through pilot element 320 may affect the actuation speed of valve element 320 and the resulting rate at which the injection pressure within central bore 82 changes. This modulating/combining of pressurized fuel may allow for a variable pressure of fuel with central bore 82, resulting in a variable injection rate of fuel through orifices 84 and penetration depth into combustion chamber 22. Control system 316 may include components that cooperate to regulate the operation of pressure control device 302 and/or fuel injector 32 in response to one or more inputs. In particular, control system 316 may include a sensor 317 operatively associated with the combined flow of fuel from pressure control device 302, and a controller 318. Controller 318 may regulate the current applied to actuator 304 in response to signals from sensor 317.

Sensor 317 may embody a pressure sensor configured to sense a pressure of the combined fuel flow exiting pressure control device 302 and to generate a signal indicative of the pressure. It is contemplated that sensor 317 may alternatively sense a different or additional parameter of the fuel associated with the combined fuel flow such as, for example, a temperature, a viscosity, a flow rate, or any other parameter known in the art.

Controller 318 may embody a single microprocessor or multiple microprocessors that include a means for controlling an operation of fuel system 12. Numerous commercially available microprocessors can be configured to perform the functions of controller 318. It should be appreciated that controller 318 could readily embody a general engine microprocessor capable of controlling numerous engine functions. Controller 318 may include a memory, a secondary storage device, a processor, and other components for running an application. Various other circuits may be associated with controller 318 such as power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other types of circuitry. One or more maps relating injection timing and desired injection pressure may be stored in the memory of controller 318. Each of these maps may be in the form of tables, graphs, and/or equations. In one example, injection timing and desired injection pressure may form the coordinate axis of a 2-D table for control of actuator 304. Desired pressure, pilot element position, and/or command current associated with the expansion and contraction of the piezo crystals of actuator 304 may be related in a separate 2-D map. It is also contemplated that the injection timing may be directly related to pilot element position and/or command current in a single 2-D map, if desired. Controller 318 may be configured to receive the signal generated by sensor 317 and operate actuator 304 in response thereto. In particular, controller 318 may be in communication with sensor 317 to receive the signal from sensor 317. Controller 318 may reference the map(s) stored in the memory thereof, compare the signal from sensor 317 to the desired pressure value found in the map(s), and modulate the current directed to the piezo crystals of actuator 304 in response to the comparison. For example, after referencing the relationship map(s) and determining a desired injection pressure, comparing the measured pressure to the desired injection pressure, and determining that the measured pressure is significantly less than the desired pressure (e.g., less than the desired pressure by a predetermined amount), controller 318 may decrease the current supplied to actuator 304, thereby communicating low pressure fuel from common rail 34 with valve element 306 and causing valve element 306 to move toward the second position. This movement toward the second position may result in an increase in the pressure of the fuel directed through valve element 306. In contrast, if the comparison indicates that the measured pressure is significantly more than the desired pressure (e.g., more than the desired pressure by a predetermined amount), controller 318 may increase the current supplied to actuator 304, thereby communicating valve element 306 with tank 28 and causing valve element 306 to move toward the first position. This movement toward the first position may result in a decrease in the pressure of the fuel directed through valve element 306.

Fig. 4 illustrates an alternative embodiment to fuel system 12 of Fig. 3. Similar to fuel system 12 of Fig. 3, fuel system 12 of Fig. 4 may include fuel injector 32 receiving flows of pressurized fuel from first and second common rails 34 and 37 via fuel line 50 and actuator 304. However, in contrast to the single valve element 306 associated with actuator 304 depicted in Fig. 3, actuator 304 of Fig. 4 may include two separate valve elements 408 and 410.

During an injection event when the first and second flows of pressurized fuel are directed through valve element 306 (referring to Fig. 3), it is possible for the higher pressure fuel from first common rail 37 to flow in reverse direction into second common rail 34. This reverse flow can reduce the efficiency of fuel system 12. To improve the efficiency of fuel system 12, actuator 304 of Fig. 4 may implement separate valve elements 408 and 410. Similar to valve element 306, valve element 408 may embody a proportional valve element or other suitable device movable by actuator 304. Although actuator 304 is illustrated in this embodiment as being directly and mechanically coupled to valve element 408, it is contemplated that actuator 304 may alternatively be indirectly connected to valve element 408 by way of a pilot element (not shown) similar to pilot element 320 of Fig. 3. Valve element 408 may be movable between a first position at which pressurized fuel from first common rail 34 is blocked from fuel injector 32, and a second position at which a maximum amount of fuel from first common rail 34 is directed to fuel injector 32. Valve element 408 may also be movable to any position between the first and second positions to direct a portion of the first pressurized flow of fuel to fuel injector 32. The amount of the first flow of pressurized fuel from first common rail 34 directed by valve element 408 to fuel injector 32 may correspond to the current applied to the piezo electric crystals of actuator 304. In contrast to valve element 408, valve element 410 may embody a two-position, solenoid-actuated valve element. Valve element 410 may be movable from a first position at which substantially no pressurized fuel from second common rail 37 is directed to central bore 82, to a second position at which a maximum amount of fuel from the second common rail 37 is directed to fuel injector 32. Valve elements 408 and 410 may be separately or simultaneously operated to independently direct pressurized fuel from either the first common rail 34, the second common rail 37, or both of the first and second common rails 34, 37. This combining of pressurized fuel from first and second common rails 34, 37 may allow for a variable pressure of fuel with central bore 82, resulting in a variable injection rate of fuel through orifices 84 and penetration depth into combustion chamber 22.

Fig. 5 illustrates an alternative embodiment of fuel system 12. Similar to fuel system 12 of Fig. 3, fuel system 12 of Fig. 5 may include fuel injector 32 receiving flows of pressurized fuel from first and second common rails 34 and 37 via fuel line 50. However, in contrast to the pressure control devices 302 associated with each individual injector depicted in Fig. 3, one pressure control devices 502 may be associated with multiple fuel injectors 32. Specifically, a first pressure control device 502 may be associated with a first group of fuel injectors 32, while a second pressure control device 502 may be associated with a second group of fuel injectors 32. Each of the first and second groups of fuel injectors 32 may be associated with only non-consecutively firing combustion chambers 22. For example, those fuel injectors 32 associated with combustion chambers 22 numbered 1 , 2, and 3 may be in the first group of fuel injectors 32, while those fuel injectors 32 associated with combustion chambers 22 numbered 4, 5, and 6 may be in the second group. In this manner, the fuel injectors 32 within a single group may never inject fuel consecutively.

By limiting consecutive injections of fuel from a group of commonly pressure regulated fuel injectors 32, adequate time may be provided for pressure control device 502 to respond to varying pressure requirements between injection events. That is, by alternating injection events between the groups of fuel injectors 32, twice as much time is afforded pressure control device 502 for responding to a required injection pressure, as compared to consecutive injections from within the same group of fuel injectors 32. In this manner, each pressure control device 502 must only respond fast enough to regulate the pressure of every other injection event.

As illustrated in Fig. 6, each pressure control device 502 may include an actuator 604 operatively connected to a valve element 606. Valve element 606 may be movable by actuator 604 to selectively combine the first and second flows of pressurized fuel and direct the combined flow to the corresponding first or second groups of fuel injectors 32.

Actuator 604 may be substantially identical to actuator 304 and embody a piezo electric device having one or more columns of piezo electric crystals. When an electric field is applied to the crystals of 604, such as, for example, by the application of a current, the piezo electric crystals expand along the axis to affect movement of valve element 606.

Actuator 604 may be connected to move valve element 606 by way of pilot fluid. In particular, a pilot element 620 connected to actuator 604 may be movable between a first position at which pilot fluid from second common rail 37 is communicated with an end of valve element 606, and a second position at which the pilot fluid from the end of valve element 606 is allowed to drain to tank 28. As current is applied to the piezo electric crystals of actuator 604, actuator 604 may expand to move pilot element 620 from the first position toward the second position. In contrast, as the current is removed from the piezo electric crystals of actuator 604, actuator 604 may contract to return pilot element 620 toward the first position. It is contemplated that the piezo electric crystals of actuator 604 may be omitted, if desired, and the movement of pilot element 620 be controlled in another suitable manner. It is further contemplated that actuator 604 may alternatively be directly and mechanically connected to move valve element 606 without the use of pilot element 620, if desired.

Valve element 606 may embody a proportional valve element or other suitable device movable in response to the pilot fluid described above. Specifically, when sufficient pilot fluid from common rail 34 is in contact with the end of valve element 606, valve element 606 may be in or urged toward a first position, at which only the second flow of pressurized fuel is directed to the corresponding group of fuel injectors 32. As the pilot fluid is drained away from the end of valve element 606, a spring 622 may bias valve element 606 toward a second position, at which only the first flow of pressurized fuel is directed to the corresponding fuel injector group. Valve element 606 may be movable by way of the pilot fluid to any position between the first and second positions to direct a portion of the first and second pressurized flows of fuel to the fuel injector group. The amount and ratio of the first or second flows directed by valve element 606 may depend on the current applied to the piezo electric crystals of actuator 604 and may affect the resultant pressure of the supplied fuel. In addition, the speed of the fluid flowing through pilot element 620 may affect the actuation speed of valve element 620 and the resulting rate at which the injection pressure changes. This modulating/combining of pressurized fuel may allow for a variable pressure of fuel with central bores 82, resulting in a variable injection rate of fuel through orifices 84 and penetration depth into combustion chambers 22.

Fig. 7 illustrates an alternative embodiment to fuel system 12 of Fig. 6. Similar to fuel system 12 of Fig. 6, fuel system 12 of Fig. 7 may include two groups of fuel injectors 32 receiving flows of pressurized fuel from first and second common rails 34 and 37 via fuel line 50 and two pressure control devices 502. However, in contrast to the single valve element 606 associated with each actuator 604 depicted in Fig. 6, each actuator 604 of Fig. 7 may include two separate valve elements 708 and 710. During an injection event when the first and second flows of pressurized fuel are directed through valve element 606 (referring to Fig. 6), it is possible for the higher pressure fuel from first common rail 37 to flow in reverse direction into second common rail 34. This reverse flow can reduce the efficiency of fuel system 12. To improve the efficiency of fuel system 12, actuator 604 of Fig. 7 may implement separate valve elements 708 and 710.

Similar to valve element 606, valve element 708 may embody a proportional valve element or other suitable device movable by actuator 604. Although actuator 604 is illustrated in this embodiment as being directly and mechanically coupled to valve element 708, it is contemplated that actuator 604 may alternatively be indirectly connected to valve element 708 by way of a pilot element (not shown) similar to pilot element 620 of Fig. 6. Valve element 708 may be movable between a first position at which pressurized fuel from first common rail 34 is blocked from the corresponding group of fuel injectors 32, and a second position at which a maximum amount of fuel from first common rail 34 is directed to the group of fuel injectors 32. Valve element 708 may also be movable to any position between the first and second positions to direct a portion of the first pressurized flow of fuel to the fuel injector group. The amount of the first flow of pressurized fuel from first common rail 34 directed by valve element 708 to the group of fuel injectors 32 may correspond to the current applied to the piezo electric crystals of actuator 604.

In contrast to valve element 708, valve element 710 may embody a two-position, solenoid-actuated valve element. Valve element 710 may be movable from a first position at which substantially no pressurized fuel from second common rail 37 is directed to the corresponding fuel injector group, to a second position at which a maximum amount of fuel from the second common rail 37 is directed to the group of fuel injectors 32. Valve elements 708 and 710 may be separately or simultaneously operated to independently direct pressurized fuel from either the first common rail 34, the second common rail 37, or both of the first and second common rails 34, 37. This combining of pressurized fuel from first and second common rails 34, 37 may allow for a variable pressure of fuel with the central bores 82 of the corresponding fuel injector group, resulting in a variable injection rate of fuel through orifices 84 and penetration depth into combustion chamber 22.

Industrial Applicability

The fuel system of the present disclosure has wide application in a variety of engine types including, for example, diesel engines, gasoline engines, and gaseous fuel-powered engines. The disclosed fuel system may be implemented into any engine that utilizes a pressurizing fuel system wherein it may be advantageous to provide a variable pressure supply of fuel. The operation of fuel system 12 will now be explained.

Needle valve element 58 may be moved by an imbalance of force generated by fuel pressure. For example, when needle valve element 58 is in the first or orifice-blocking position, pressurized fuel from fuel supply passageway 74 may flow into control chamber 72 to act on hydraulic surface 98. Simultaneously, pressurized fuel from fuel supply passageway 74 may flow into central bores 70 and 82 in anticipation of injection. The force of spring 88 combined with the hydraulic force generated at hydraulic surface 98 may be greater than an opposing force generated at hydraulic surface 100 thereby causing needle valve element 58 to remain in the first position to restrict fuel flow through orifices 84. To open orifices 84 and inject the pressurized fuel from central bore 82 into combustion chamber 22, first solenoid actuator 60 may move its associated valve element to selectively drain the pressurized fuel away from control chamber 72 and hydraulic surface 98. This decrease in pressure acting on hydraulic surface 98 may allow the opposing force acting across hydraulic surface 100 to overcome the biasing force of spring 88, thereby moving needle valve element 58 toward the orifice-opening position. To close orifices 84 and end the injection of fuel into combustion chamber 22, second solenoid actuator 62 may be energized. In particular, as the valve element associated with second solenoid actuator 62 is urged toward the flow blocking position, fluid from control chamber 72 may be prevented from draining to tank 28. Because pressurized fluid is continuously supplied to control chamber 72 via restricted supply passageway 80, pressure may rapidly build within control chamber 72 when drainage through control passageway 76 is prevented. The increasing pressure within control chamber 72, combined with the biasing force of spring 88, may overcome the opposing force acting on hydraulic surface 100 to force needle valve element 58 toward the closed position. It is contemplated that second solenoid actuator 62 may be omitted, if desired, and first solenoid actuator 60 used to initiate both the opening and closing motions of needle valve element 58.

In the exemplary embodiment of Fig. 2, pressure control valve 102 may affect the pressure of fuel supplied to central bores 70 and 82, and subsequently injected into combustion chamber 22. Specifically, in response to a current applied to the piezo electric crystals of actuator 104, actuator 104 may move valve element 108 to drain pressurized fuel from the end of valve element 106, allowing valve element 106 to move toward its first position and decrease the amount of pressurized fuel draining from second common manifold 37 to tank 28. The decreased amount of fuel draining to tank 28 may result in an increase in pressure within fuel injector 32. In contrast, as current is removed from actuator 104, valve element 108 may move to communicate pressurized fuel from first common manifold 34 with the end of valve element 106, thereby urging valve element 106 toward its second position to increase the amount of pressurized fuel draining from second common manifold 37 to tank 28. The increased amount of fuel draining to tank 28 may act to lower the pressure of the fuel supplied to fuel injector 32. As the draining fuel reaches valve element 110, it may continue toward drain 28 or may be blocked in response to a pressure differential across valve element 110. Specifically, if the force on valve element 1 10 resulting from the pressure of the fuel draining through valve element 106 is greater than the force resulting from the pressure of fuel within first common manifold 34 and the bias of the associated return spring, valve element 110 may open to pass the draining fuel to tank 28. However, if the force resulting from the fuel draining through valve element 106 is less than the force resulting from the pressure of the fuel within first common manifold 34 and the bias of the return spring, the draining fuel may be blocked from tank 28. In this manner, the pressure of the fuel within first common manifold 34 may affect the pressure of the fuel directed to fuel injector 32.

Fuel may always be available to injector 32, regardless of the operation of pressure control valve 102. In particular, bypass circuit 112 may ensure that any time the fuel pressure within fuel injector 32 falls below the pressure of the fuel within first common manifold 34, the fuel within first common manifold 34 is allowed to flow to injector 32.

Fuel system 12 may provide an infinite range of injection pressures. In particular, because the pressure of the injected fuel may vary in response to a position of valve element 106, and because valve element 106 may be moved to any position between its first and second position, many different pressures may available for injection. In addition, because fuel system 12 may utilize only fuel to affect these pressure changes, contamination between dissimilar fluids is not an issue. As depicted in alternative embodiments of fuel system 12 illustrated in Figs. 3 and 4, pressure control device 302 may affect pressure of the fuel supplied to central bores 70 and 82, and subsequently injected into combustion chamber 22. Specifically, in response to a current applied to the piezo electric crystals of actuator 304, actuator 304 may affect movement of valve elements 306 (referring to Fig. 3) and 408 (referring to Fig. 4) to increase or decrease the amount of pressurized fuel flowing from first common rail 34 into fuel injector 32. With regard to the embodiment of Fig. 3, the movement of actuator 304 may also simultaneously control the amount of pressurized fuel flowing from second common rail 37 into fuel injector 32. In contrast, with regard to the embodiment of Fig. 4, valve element 410 may be independently controlled to allow or block the flow of fuel from second common rail 37 into fuel injector 32.

Controller 318 may enable precise control over the pressure of a fuel injection event. In particular, during different stages of injection (pilot, main, post, etc.), it may be desirable to change the pressure of the injected fuel. To accomplish this pressure change, controller 318 may reference the relationship map(s) stored in the memory thereof and determine a desired pressure corresponding to the current timing stage of fuel injector 32. This desired pressure may then be compared by controller 318 to the signal from sensor 317 to determine an error value. If the error value exceeds a predetermined value, controller 318 may modulate the current supplied to actuator 304, thereby varying the ratio of low pressure fuel to high pressure fuel directed through valve element 306 (referring to the embodiment of Fig. 3) or through valve elements 408 and 410 (referring to the embodiment of Fig. 4).

This change in the flow rates of fuel from first and second common rails 34, 37 may directly and immediately affect the pressure of fuel within central bores 70 and 82. For example, an increased current applied to actuator 304 may cause a decrease in the flow rate of pressurized fuel from first common rail 34 and a resulting higher pressure of fuel within central bores 70 and 82. In contrast, a decreased current applied to actuator 304 may cause an increase in the flow rate of pressurized fuel from first common rail 34 and a resulting higher pressure of fuel within central bores 70 and 82. With regard to Fig. 3, the changes in flow rate of pressurized fuel from second common rail 37 may simultaneously correspond to an inverse change in flow rate of pressurized fuel from first common rail 34. With regard to Fig. 4, the flow rate of pressurized fuel from second common rail 37 may be independently controlled via solenoid- actuated valve element 410. Because fuel system 12 may vary the pressure of injected fuel by combining and/or directing two different flows of pressurized fuel to a single injector, the number of different levels of fuel pressure available for injection may be infinite. In particular, fuel system 12 may not be limited to specific predetermined pressure levels. This flexibility in the pressure of injected fuel may extend the use of fuel system 12 to different applications, as well as the operational range and efficiency of engine 10. In addition, this flexibility may allow compliance with emission standards under a wider range of operating conditions.

Further, because fuel system 12 may vary the pressure of injected fuel with a minimal number of additional components, the complexity and cost of fuel system 12 may be low. Specifically, the addition of pressure control device 302 may add very little complexity or cost to fuel system 12.

In addition, because of the configuration of fuel system 12, the responsiveness of fuel system 12 may be high. In particular, because the pressure of the fuel directed through valve elements 306 or through valve elements 408 and 410 may be regulated based on a measured pressure immediately downstream of the valve elements, very little lag between desired fuel pressure and actual injected fuel pressure may exist. This increased responsiveness may result in higher fuel efficiency, lower exhaust emissions of engine 10, and improved responsiveness of machine 5.

In the alternative embodiments of fuel system 12 illustrated in Figs. 6 and 7, each pressure control device 502 may affect pressure of the fuel supplied to a corresponding group of fuel injectors 32 in response to the pressure required by only the actuated one of the fuel injectors 32 within the group. Specifϊcally, in response to a current applied to the piezo electric crystals of actuator 604, actuator 604 may affect movement of valve elements 606 (referring to Fig. 6) and 708 (referring to Fig. 7) to increase or decrease the amount of pressurized fuel flowing from first common rail 34 to the group of fuel injectors 32 for use by the fuel injector 32 being actuated. With regard to the embodiment of Fig. 6, the movement of actuator 604 may also simultaneously control the amount of pressurized fuel flowing from second common rail 37 into the corresponding group of fuel injectors 32. In contrast, with regard to the embodiment of Fig. 7, valve element 710 may be independently controlled to allow or block the flow of fuel from second common rail 37 to the group of fuel injectors 32.

This change in the flow rates of fuel from first and second common rails 34, 37 may directly and immediately affect the pressure of fuel within central bores 70 and 82. For example, an increased current applied to actuator 604 may cause a decrease in the flow rate of pressurized fuel from second common rail 37 and a resulting lower pressure of fuel directed to a common group of fuel injectors 32. In contrast, a decreased current applied to actuator 604 may cause an increase in the flow rate of pressurized fuel from second common rail 37 and a resulting higher pressure of fuel directed to the common group of fuel injectors 32. With regard to Fig. 6, the changes in flow rate of pressurized fuel from second common rail 37 may simultaneously correspond to an inverse change in flow rate of pressurized fuel from first common rail 34. With regard to Fig. 7, the flow rate of pressurized fuel from second common rail 37 may be independently controlled via solenoid-actuated valve element 710.

Because fuel system 12 may utilize common pressure control devices 502, the complexity and cost of fuel system 12 may be low. Specifically, because one pressure control device 502 may be utilized to control the injection pressure of multiple fuel injectors 32, the number of components of fuel system 12 may low, resulting a simple, inexpensive system. Further, because each pressure control device is associated with only non-consecutively firing combustion chambers, the responsiveness of pressure control devices 502 may be sufficient for a wide variety of applications. It will be apparent to those skilled in the art that various modifications and variations can be made to the fuel system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the fuel system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.

Claims

1. A fuel system for an engine, comprising: a first source configured to pressurize fuel to a first pressure; a second source configured to pressurize fuel to a second pressure; a fuel injector configured to receive and inject fuel into the engine; and a single valve disposed between the fuel injector and the first and second sources, the single valve being in fluid communication with the first and second sources and the fuel injector, and able to deliver variable pressure fuel to the fuel injector.

2. The fuel system of claim 1, wherein: the fuel injector is configured to receive fuel at the first pressure and the second pressure; and the single valve is configured to modify the pressure of fuel from the first source based on a pressure of fuel from the second source.

3. The fuel system of claim 2, wherein the single valve is further configured to selectively pass fuel from only the first source to the fuel injector.

4. The fuel system of claim 2, wherein the single valve modifies the pressure of the fuel from the first source by selectively passing a portion of the fuel from the first source to a drain.

5. The fuel system of claim 2, wherein the portion of the fuel from the first source selectively passed to the drain is dependent on a pressure of the fuel from the second source.

6. The fuel system of 5, wherein: the fuel from the first source is at a higher pressure than the fuel from the second source; and modifying includes only lowering the pressure of the fuel from the first source.

7. The fuel system of claim 1, wherein: the fuel injector is one of a first plurality of fuel injectors; and the single valve is a first valve associated with the first plurality of fuel injectors and configured to selectively direct fuel from the first source and fuel from the second source to only the first plurality of fuel injectors; and the fuel system further includes: a second plurality of fuel injectors; and a second valve associated with the second plurality of fuel injectors and configured to selectively direct fuel from the first source and fuel from the second source to only the second plurality of fuel injectors.

8. The fuel system of claim 7, wherein the first and second valves are configured to selectively combine fuel from the first source and fuel from the second source to create a flow of fuel at a third pressure.

9. The fuel system of claim 7, wherein: the first plurality of fuel injectors is associated with only non- consecutively firing combustion chambers of the engine; and the second plurality of fuel injectors is associated with only non- consecutively firing combustion chambers of the engine.

10. The fuel system of claim 1 , wherein the fuel injector is configured to receive fuel from the first and second sources, and further including a controller in communication with the single valve and being configured to affect operation of the single valve and a resulting fuel pressure based on a desired injection pressure.

11. The fuel system of claim 10, further including a pressure sensor disposed between the single valve and a tip of the fuel injector and being configured to provide a signal indicative of the pressure of fuel being injected, wherein the controller is further configured to affect operation of the single valve and the resulting fuel pressure in further response to the signal.

12. The fuel system of claim 10, wherein the single valve includes a main valve element movable between a first position at which fuel from only the first source is communicated with the fuel injector, and a second position at which fuel from only the second source is communicated with the fuel injector.

13. The fuel system of claim 10, wherein the single valve is further configured to selectively combine the fuel at the first pressure with the fuel at the second pressure to supply to the fuel injector fuel at the desired injection pressure.

14. An engine, comprising: a plurality of combustion chambers; a first source of fuel at a first pressure; a second source of fuel at a second pressure; a fuel injector configured to receive and inject fuel into the engine; and a single valve disposed between the fuel injector and the first and second sources, the single valve being in fluid communication with the first and second source and the fuel injector, and able to deliver variable pressure fuel to the fuel injector.

15. The engine of claim 14, wherein: the fuel injector is configured to receive fuel at the first pressure and the second pressure; and the single valve is configured to modify the pressure of fuel from the first source based on a pressure of fuel from the second source.

16. The engine of claim 14, wherein: the fuel injector is one of a first plurality of fuel injectors; and the single valve is a first valve associated with the first plurality of fuel injectors and configured to selectively direct fuel from the first source and fuel from the second source to only the first plurality of fuel injectors; and the engine further includes: a second plurality of fuel injectors; and a second valve associated with the second plurality of fuel injectors and configured to selectively direct fuel from the first source and fuel from the second source to only the second plurality of fuel injectors.

17. The engine of claim 14, wherein the fuel injector is configured to receive fuel from the first and second sources, and further including a controller in communication with the single valve and being configured to affect operation of the single valve and a resulting fuel pressure based on a desired injection pressure.

18. A method of injecting fuel, the method comprising: pressurizing a first fuel stream to a first pressure; pressurizing a second fuel stream to a second pressure; receiving the first and second fuel streams at a single location and responsively generating a third fuel stream at a third pressure; directing the third fuel stream to an injector; and selectively injecting the third fuel stream.

19. The method of claim 18, wherein responsively generating includes combining fuel at the first pressure and fuel at the second pressure to produce a flow of fuel at a third pressure.

20. The method of claim 18, wherein: the third fuel stream only includes fuel from the first fuel stream; and the pressure of third fuel stream is modified from the first fuel stream based on the pressure of the second fuel stream.