Patent Application
20070277784
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
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, a fuel pumping arrangement 30 configured to pressurize the fuel and direct the pressurized fuel to a plurality of fuel injectors 32 by way of a common rail 34.
Fuel pumping arrangement 30 may include one or more pumping devices that function to increase the pressure of the fuel and direct one or more pressurized streams of fuel to common rail 34. In one example, fuel pumping arrangement 30 includes a low pressure source 36 and a high pressure source 38 disposed in series and fluidly connected by way of a fuel line 40. Low pressure source 36 may be a transfer pump configured to provide low pressure feed to high pressure source 38. High pressure source 38 may be configured to receive the low pressure feed and to increase the pressure of the fuel to the range of about 30-300 MPa. High pressure source 38 may be connected to common rail 34 by way of a fuel line 42. A check valve 44 may be disposed within fuel line 42 to provide for one-directional flow of fuel from fuel pumping arrangement 30 to common rail 34.
One or both of low pressure and high pressure sources 36, 38 may be operably connected to engine 10 and driven by crankshaft 24. Low and/or high pressure sources 36, 38 may be connected with crankshaft 24 in any manner readily apparent to one skilled in the art where a rotation of crankshaft 24 will result in a corresponding rotation of a pump drive shaft. For example, a pump driveshaft 46 of high pressure source 38 is shown in
Fuel injectors 32 may be disposed within cylinder heads 20 and connected to common rail 34 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 18. For example, fuel may be injected as piston 18 nears a top-dead-center 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
Injector body 52 may embody a cylindrical member configured for assembly within cylinder head 20 and having one or more passageways. Specifically, injector body 52 may include a central bore 100 configured to receive actuator 59, a fuel inlet 102 and outlet 104 in communication with central bore 100, and a control chamber 106. Control chamber 106 may be in direct communication with a base end of needle valve element 58 and selectively drained of or supplied with pressurized fuel to affect motion of needle valve element 58. Injector body 52 may also include a supply passageway 110 that always fluidly communicates fuel inlet 102 with nozzle member 56 and control chamber 106 during operation of fuel injector 32.
Housing 54 may embody a cylindrical member having a central bore 60 for receiving guide 55 and nozzle member 56, and an opening 62 through which a tip end 64 of nozzle member 56 protrudes. A sealing member such as, for example, an o-ring (not shown) may be disposed between guide 55 and nozzle member 56 to restrict fuel leakage from fuel injector 32.
Guide 55 may also embody a cylindrical member having a central bore 68 configured to receive needle valve element 58 and a return spring 90. Return spring 90 may be disposed between a stop 92 and a seating surface 94 to axially bias needle valve element 58 toward tip end 64. A spacer 96 and a similar spacer 97 may be disposed between return spring 90 and seating surface 94 and between return spring 90 and stop 92, respectively, to reduce wear of the components within fuel injector 32. Central bore 68 may function as a pressure chamber and hold pressurized fuel supplied from supply passageway 110 in anticipation of an injection event.
Nozzle member 56 may likewise embody a cylindrical member having a central bore 72 in communication with central bore 68. Central bore 72 may receive needle valve element 58 and include one or more orifices 80 that pass the pressurized fuel from central bore 68 through central bore 72 into combustion chambers 22 of engine 10, as needle valve element 58 is moved away from orifices 80.
Needle valve element 58 may be an elongated cylindrical member that is slidingly disposed within guide 55 and nozzle member 56. Needle valve element 58 may be axially movable between a first position at which a tip end of needle valve element 58 blocks a flow of fuel through orifices 80, and a second position at which orifices 80 are open to spray fuel into combustion chamber 22. It is contemplated that needle valve member 58 may be a multi-member element having a needle member and a piston member or a single integral element.
Needle valve element 58 may have multiple driving hydraulic surfaces. For example, needle valve element 58 may include a hydraulic surface 112 tending to drive needle valve element 58, with the bias of return spring 90, toward a first or orifice-blocking position when acted upon by pressurized fuel. Needle valve element 58 may also include a hydraulic surface 114 that opposes the bias of return spring 90 to drive needle valve element 58 in the opposite direction toward a second or orifice-opening position when acted upon by pressurized fuel.
Actuator 59 may be disposed opposite nozzle member 56 to control the forces on needle valve element 58. In particular actuator 59 may include an electro-expansive module such as a piezo electric motor. A piezo electric motor may include one or more stacks of disk-type piezo electric crystals. The crystals may be 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 stacks of crystals, such as, for example, by the application of a current, the stacks expand along the axis of the electric field as the domains line up. In one embodiment, the expansion of actuator 59 may be about 40 μm.
Actuator 59 may be connected to needle valve element 58 by way of actuator valve assembly 61. In particular, actuator valve assembly 61 may include a first piston 116, a second piston 118, and a control valve element 120. A check valve 119 may be disposed between first piston 116 and second piston 118 to provide unidirectional flow of fuel from control chamber 106 to a hydraulic coupling 123.
First piston 116 may be connected to move with the expansion and retraction of actuator 59. Specifically, first piston 116 may be retained in mechanical engagement with the crystal stack of actuator 59 by way of a return spring 125. Return spring 125 may be disposed between a flange 116a of first piston 116 and a cage element 128. As actuator 59 is charged and expands or de-energized and contracts, first piston 116 may move within central bore 100 to reduce or increase the volume of hydraulic coupling 123. It is contemplated that first piston 116 may be fixedly connected to actuator 59, is desired.
Second piston 118 may be separated from first piston 116 by a distance, thereby forming hydraulic coupling 123. As first piston 116 is moved to decrease the volume of hydraulic coupling 123, the pressure of the fuel within hydraulic coupling 123 may correspondingly increase. The increasing pressure of the fuel within hydraulic coupling 123 may act against an end of second piston 118, thereby urging second piston 118 to move downward against control valve element 120. As first piston 116 is moved to increase the volume of hydraulic coupling 123, the pressure of the fuel within hydraulic coupling 123 may correspondingly decrease, thereby allowing control valve element 120 to return second piston 118 to its original position. It is contemplated that a return spring (not shown) may be associated with second piston 118 to retain second piston 118 in contact with control valve element 120, if desired.
Control valve element 120 may be moved into and out of contact with a seat 122 to selectively drain control chamber 106, thereby initiating the injection of fuel. When control valve element 120 is engaged with seat 122 or in the non-injecting position, fuel may flow from fuel inlet 102 through supply passageway 110 into control chamber 106 via a branch passageway 124. As pressurized fuel builds within control chamber 106, the downward force generated at hydraulic surface 112 combined with the force of return spring 90 may overcome the upward force at hydraulic surface 114, thereby closing orifices 80 and terminating fuel injection. When control valve element 120 is moved against the bias of a return spring 127, out of engagement with seat 122, and into the injecting position, fuel may flow from control chamber 106 to tank 28 via a restricted orifice 121, central bore 100, and fuel outlet 104. As fuel from control chamber 106 drains to tank 28, the upward force at hydraulic surface 114 may urge needle valve element 58 against the bias of return spring 90, thereby opening orifices 80 and initiating fuel injection into combustion chambers 22. When actuator 59 is de-energized, return spring 127 may return control valve element 120 to the non-injecting position.
Check valve 119 may replenish fuel leaked from hydraulic coupling 123. In particular, during operation of fuel injector 32, it may be possible for fuel from within the space between first and second pistons 116, 118 to leak through central bore 100 to fuel outlet 104. If the amount of fuel, and subsequently the pressure, within this space fluctuates, the motion of first piston 116 may result in an undesired motion of second piston 118 and control valve element 120. For example, if hydraulic coupling 123 has leaked fuel, first piston 116 may have to move further to produce the pressure required to initiate movement of second piston 118. In some situations, this additional distance may result in less or even no movement of second piston 118. Check valve 119 may selectively allow fuel from control chamber 106 to replenish the fuel lost from hydraulic coupling 123.
As illustrated in
As also illustrated in
Guide element 138 may minimize the likelihood of check valve 119 becoming stuck within central bore 130 or the space between first and second pistons 116, 118 during movement of check valve 119. Although check valve 119 is described as being biased by only fuel pressures and gravity, it is contemplated that a return spring (not shown) may alternatively be disposed within central bore 130 or hydraulic coupling 123 to bias check valve 119 and thereby affect the opening or closing pressure differential of check valve 119, if desired. However, the use of a return spring may increase the complexity of check valve 119 and the associated cost and unreliability.
The fuel injector control system of the present disclosure has wide applications in a variety of engine types including, for example, diesel engines, gasoline engines, and gaseous fuel-powered engines. The disclosed fuel injector control system may be implemented into any engine where consistent and predictable fuel injector performance is important. The injection control of fuel injectors 32 will now be described.
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 100 may flow into control chamber 106 to act on hydraulic surface 112. Simultaneously, pressurized fuel from fuel supply passageway 100 may flow into central bores 68 and 72 in anticipation of injection. The force of spring 90 combined with the force generated at hydraulic surface 114 may be greater than an opposing force generated at hydraulic surface 112 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 72 into combustion chamber 22, current may be sent to actuator 59 causing an expansion that moves first piston 116 to pressurized hydraulic coupling 123. The increasing pressure of hydraulic coupling 123 may act to move second piston 118 and engaged control valve element 120 such that fuel drains away from control chamber 106 and hydraulic surface 112. This decrease in pressure acting on hydraulic surface 112 may allow the opposing force acting across hydraulic surface 114 to overcome the biasing force of spring 90, 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, actuator 59 may be de-energized. In particular, as the stack of piezo crystals within actuator 59 contract, first piston 116 may retract from hydraulic coupling 123, resulting in a drop in pressure therein. This reduction in pressure may allow spring 127 to return control valve element 120 and engaged second piston 118 to their flow blocking positions. When control valve element 120 is in the flow blocking position, fuel from control chamber 106 may be prevented from draining to tank 28. Because pressurized fuel is continuously supplied to control chamber 106 via restricted branch passageway 124, pressure may rapidly build within control chamber 106 when drainage therefrom is prevented. The increasing pressure within control chamber 106, combined with the biasing force of spring 90, may overcome the opposing force acting on hydraulic surface 114 to urge needle valve element 58 toward the closed position.
As the pressure of hydraulic coupling 123 decreases due to leakage, check valve 119 may replenish hydraulic coupling 123 with pressurized fuel. In particular, in response to a pressure differential between hydraulic coupling 123 and central bore 130 crossing a predetermined threshold, check valve 119 may move against gravity to allow fuel to flow from central bore 100, through transverse passageways 132, 133 and central bore 130, and into hydraulic coupling 123. In this manner, the non-actuated volume and thus pressure within hydraulic coupling 123 may be kept substantially constant, resulting in substantially constant and predictable injection events.
Check valve 119 may provide high hydraulic coupling pressures and be robust enough to handle the high pressures. In particular, because check valve 119 allows only unidirectional flow of fuel from central bore 130 into hydraulic coupling 123, minimal fuel may leak from hydraulic coupling 123 during the downward displacing movement of first piston 116. By minimizing leakage during this movement to first piston 116, the pressure within hydraulic coupling 123 may increase to a significantly high value at a rate directly proportional to the movement of first piston 116, with minimal efficiency loss. In addition, because of the partial-ball nature of check valve 119, minimal volume within hydraulic coupling 123 is required to accommodate check valve 119. This minimized volume within hydraulic coupling 123 may reduce the travel that first piston 116 must complete in order to pressure hydraulic coupling 123 to the desired pressure. Less travel required of first piston 116 may either reduce the cost of actuator 59 or allow for even higher pressures generated within hydraulic coupling 123. Further, because of the partial-ball nature of check valve 119, check valve 119 may be sturdy enough to withstand these high pressures without deformation or damage.
It will be apparent to those skilled in the art that various modifications and variations can be made to the control 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 control system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.
