Patent Application
20120024973
The present disclosure relates generally to common rail fuel systems for large bore engines, and more particularly to reducing leakage in a large bore fuel system.
Common rail fuel injectors spend only a small fraction of their operational time actually injecting fuel, and a vast majority of the remaining time standing by in a pressurized state ready for a subsequent injection event. In many cases, a pressurized area within the fuel injector can be separated from a low pressure area by a guide surface of a movable valve member. Because pressure differentials between the pressurized area and the low pressure area can be relatively high, the pressure gradient tends to cause fuel to migrate up through the guide area to the low pressure region, and this migration of fuel can account for a majority of fuel leakage from a fuel injector. As fuel injection pressures continue to rise, this type of fuel leakage problem can correspondingly become more acute. In addition, as common rail fuel injection systems are scaled for larger and larger engines, the associated fuel injectors can be expected to have larger clearance areas for their larger internal components. Thus, in high pressure common rail systems associated with large bore fuel systems, the fuel leakage along guide surfaces can become unacceptable. Simply scaling up proven solutions from smaller bore fuel injection systems to larger bore fuel injection systems can also be problematic. First, the physics with regard to fluid dynamics, mass properties and pressures, etc. do not scale well. And even if they did scale, the larger bore fuel systems must then necessarily have different components thereby increasing the parts catalog count for an engine manufacturer that manufactures both small and large bore fuel systems and associated engines.
The present disclosure is directed toward one or more of the problems set forth above.
In one aspect, a large bore fuel system includes a common rail fluidly connected to at least one of a source of heavy fuel oil and a source of distillate diesel fuel. A plurality of fuel injectors each include a cooling inlet, a cooling outlet, and an electrical actuator coupled to a direct operated nozzle check valve by a pilot valve member and a control valve member.
In another aspect, a large bore fuel injector includes an injector body that defines at least one common rail inlet, a drain outlet, a nozzle outlet, a cooling inlet and a cooling outlet. A pilot control chamber, an intermediate control chamber, a needle control chamber and a nozzle chamber are all disposed in the injector body. A pilot valve member is movable between a first position at which the pilot control chamber is fluidly connected to the drain outlet, and a second position at which the pilot control chamber is blocked from the drain outlet. A control valve member has a guide surface separating a first hydraulic surface exposed to fluid pressure in the pilot control chamber, and a second hydraulic surface exposed to fluid pressure in the intermediate control chamber. A needle valve member includes a guide surface separating an opening hydraulic surface exposed to fluid pressure in the nozzle chamber, and a closing hydraulic surface exposed to fluid pressure in the needle control chamber.
In still another aspect, a method of operating a large bore fuel injector includes fluidly connecting a drain outlet to a common rail inlet during an injection event. The drain outlet is blocked from the common rail inlet between injection events. Fuel leakage from the fuel injector is reduced between injection events by equalizing pressures in a pilot control chamber and an intermediate control chamber that are separated by a guide surface of a control valve member, and equalizing pressures in a nozzle chamber and a needle control chamber that are separated by a guide surface of the needle valve member.
Referring to
Each of the fuel injectors 30 is electronically controlled. As such, during injection events, the control function within the individual fuel injectors 30 may require that the respective common rail 16a or 16b be fluidly connected to a return line 19 in order to electronically control each injection event. In the illustrated embodiment, only one return line 19 is shown and it is for returning fuel that arrives at the fuel injectors 30 but is not injected, and instead expelled during control of an injection event to be routed to the source of heavy fuel oil 12 for potential recirculation and injection in a subsequent event. Return line 19 is shown fluidly connected to source of heavy fuel oil 12 instead of source of distillate diesel fuel 14 because it is often more desirable to dilute the heavy fuel oil with distillate diesel fuel, rather than vice versa.
Referring now to
The direct operated nozzle check valve 25 includes needle valve member 50, which is biased to a position to close nozzle outlets 32 by a spring 54. Needle valve member 50 includes an opening hydraulic surface 52 exposed to fluid pressure in a nozzle chamber 60, and a closing hydraulic surface 53 exposed to fluid pressure in needle control chamber 61. Needle valve member 50 is guided in its movement by interaction between guide surface 51 and a guide bore 64. The guide clearance 55 between guide surface 51 and guide bore 64 is relatively small, but inherently allows for some fluid communication between nozzle chamber 60 and needle control chamber 61. However, between injection events, both nozzle chamber 60 and needle control chamber 61 are maintained at rail pressure via nozzle supply passage 68 and main balance orifice 80. Nozzle supply passage 68 extends between nozzle chamber 60 and common rail inlet 33, while main balance orifice 80 fluidly connects needle control chamber 61 to nozzle supply passage 68 via a constricted but always open flow area. During an injection event, when pressure is reduced in needle control chamber 61, some fuel can migrate along guide clearance 55 from nozzle chamber 60 to needle control chamber 61.
Needle control chamber 61 is fluidly connected to an intermediate control chamber 62 via a pressure control passage 73 that includes a main control orifice 81. Control valve member 45, which was mentioned earlier, moves in intermediate control chamber 62 into and out of contact with a conical seat 29. A spring 28 biases control valve member 45 into contact with seat 29 to close the fluid connection between intermediate control chamber 62 and a low pressure drain passage 77 that fluidly connects to drain outlet 37a. Thus, when control valve member 45 lifts out of contact with seat 29, a direct fluid connection is made between the common rail 16 and drain outlet 37a via nozzle supply passage 68, through main balance orifice 80, through needle control chamber 61, up through pressure control passage 73, past seat 29 and through low pressure drain passage 77. When in this condition, pressure will drop in needle control chamber 61 by sizing main balance orifice 80 to be smaller than main control orifice 81. When this occurs, needle valve member 50 can lift to an open position to allow fuel to spray through nozzle outlets 32.
Control valve member 45 includes an opening hydraulic surface 48 exposed to fluid pressure in intermediate control chamber 62, and a closing hydraulic surface 47 exposed to fluid pressure in a pilot control chamber 63. The movement of control valve member 45 is guided by an interaction between a guide surface 46 and a guide bore 65. Although intermediate control chamber 62 is substantially fluidly isolated from pilot control chamber 63, some fluid communication exists along the small guide clearance 49 defined between guide surface 46 and guide bore 65. Pilot control chamber 63 is always fluidly connected to common rail pressure via pilot balance orifice 82 that opens at one end into nozzle supply passage 68 and at its other end into pilot control chamber 63. When electrical actuator 40 is energized, a pilot valve member 41 can lift off of a flat seat 42 to fluidly connect pilot control chamber 63 to low pressure drain 37b via pilot control orifice 83 and low pressure drain passage 75. By carefully selecting the flow areas of main balance orifice 80, main control orifice 81, pilot balance orifice 82 and pilot control orifice 83 as well as the pre-load on spring 28 and the relative sizes of opening hydraulic surface 38 and closing hydraulic surface 47, control valve member 45 will move off of seat 29 when pilot valve member lifts off of flat seat 42 to fluidly connect pilot control chamber 63 to drain. In general, main balance orifice 80 will be smaller than main control orifice 81, and pilot balance orifice 82 will have a smaller flow area than pilot control orifice 83. But the sizing must be such that when control valve member 45 is off of seat 29 to fluidly connect intermediate control chamber 62 to drain passage 77, there should be sufficient pressure acting on opening hydraulic surface 48 to overcome both spring 28 and the residual lower pressure on closing hydraulic force on closing hydraulic surface 47. Between injection events, pilot valve member 41 is in a downward position to close flat seat 42 resulting in pressure in pilot control chamber 63 and intermediate control chamber 62 being at rail pressure. Thus, between injection events there should be little to no leakage in fuel injector 30 since nozzle outlets 32 are closed, control valve member 45 is seated to close low pressure drain passage 77, and pilot valve member 41 is seated to close pilot control orifice 83. Although readily apparent, nozzle chamber 62, needle control chamber 61, intermediate control chamber 62 and pilot control chamber 63 are all disposed in injector body 31.
Fuel injector 30 can be thought of as having a non-injection configuration in which electrical actuator 40 is deenergized, pilot valve member 41 is in its downward position in contact to close flat seat 42, control valve member 45 is biased downward via spring 28 to close seat 29, and needle valve member 50 is in its downward position to close nozzle outlets 32. Fuel injector 30 can also be thought of as having an injection configuration in which needle valve member 50 is moved upward to open nozzle outlets 32, control valve member 45 is moved upward to open intermediate control chamber 62 to low pressure drain passage 77, and pilot valve member 41 is moved upward by electrical actuator 40 to fluidly connect pilot control chamber 63 to low pressure drain passage 75. Thus, when fuel injector 30 is in its injection configuration, drain outlet 37a and 37b are fluidly connected to common rail inlet 33 through two different passageways. One of these passageways includes low pressure drain passage 75, pilot control orifice 83, pilot control chamber 63, pilot balance passage 69 and a short segment of nozzle supply passage 68. The second of these passageways includes to flow pressure drain passage 77, intermediate control chamber 62, pressure control passage 73, needle control chamber 61, main balance orifice 80, and a segment of nozzle supply passage 68. Thus, during injection events, one could expect some fuel low to drain outlets 37a and 37b to be returned to source of heavy fuel oil 12 via return line 19 (
Referring now to
Referring now to
The present disclosure finds general applicability to large bore fuel systems capable of injecting either heavy fuel oil or distillate diesel fuel into the combustion spaces of relatively large compression ignition engines. The present disclosure also finds applicability in reducing leakage in large bore fuel systems. Finally the present disclosure finds particular applicability in leveraging components associated with low leakage small bore fuel systems, and using those proven components and strategies in an almost identical manner in a large bore fuel system.
This aspect of the disclosure is demonstrated by control valve member 45 being substantially identical to a needle valve member of a counterpart small bore fuel injector, with seat 29 corresponding to the seat adjacent the sac region of the fuel injector, and drain passage 77 corresponding to the nozzle outlets of the counterpart small bore fuel injector. In addition, one might expect to see a virtually identical electrical actuator 40 and pilot valve member 41 in use with a counterpart small bore fuel injector.
With regard to
Fuel leakage from the fuel injector between injection events may be reduced by equalizing pressures in the pilot control chamber 63, 163 with that intermediate control chamber 62, 162. In the context of the present disclosure, equalizing pressure between the pilot control chamber 163 and the intermediate control chamber 162 means that the pressure differential between these two chambers is at or less than the pressure difference between common rails 117 and 116. Those skilled in the art will appreciate that if the duration between injection events is sufficiently long, pressure will equalize in these two chambers by the fluid communication along guide surface 149. Fuel leakage is also reduced by equalizing the pressures in the nozzle chamber 60 with the needle control chamber 61 by closing seat 29 and maintaining both of the chambers fluidly connected to nozzle supply passage 68 between injection events. Thus in the case of nozzle chamber 60, equalizing pressure with needle control chamber 61, in the context of the present disclosure that literally means that they are equal since they are fluidly connected to the same common rail via the shared nozzle supply passage 68. Thus, in the context of the present disclosure, the term “equalizing” means that given an adequate time for pressure fluctuations to damp out to the grade toward the pressure in the respective spaces to become equal. However, the durations between injection events may be so short that inadequate time is available for the pressures to actually become equal. On the other hand, in the case of the embodiment shown in
Injection events are initiated and maintained by de-equalizing pressures in the pilot control chamber 63, 163 relative to that of intermediate control chamber 62, 162, and de-equalizing pressures between nozzle chamber 60 and needle control chamber 61. This is accomplished by energizing electrical actuator 40 to lift pilot valve member 41 to fluidly connect pilot control chamber 63, 163 to low pressure drain outlet 37b, 137b. Because the flow area through pilot balance orifice 82 is smaller than the flow area through pilot control orifice 83, pressure will drop in pilot control chamber 63, 163. When this occurs, the pressure acting on opening hydraulic surface 48 will overcome spring 28 and cause intermediate valve member 45 to lift to open seat 29. When this occurs, intermediate control chamber 62 is fluidly connected to low pressure drain outlet 37a. By making main balance orifice 80 with a smaller flow area than main control orifice 81, fluid pressure will drop in needle control chamber 61 allowing the hydraulic force on opening hydraulic surface 52 to overcome spring 54 and lift needle valve member 50 to its opening position. However, the sizes of the orifices 80, 81, 82 and 83 should be sized such that the pressure in intermediate control chamber 62 remains sufficiently high during an injection event that control valve member 45 remains off of seat 29 during the injection event. Otherwise, one could expect cyclic pressure changes in intermediate control chamber 62 causing the needle valve member 50 to chatter and repeatedly close the nozzle outlets, which may in some circumstances be desirable. By appropriately positioning valves 11 and 13 (
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
