Patent Application
20110315117
The present disclosure is directed to a fuel system and, more particularly, to a fuel system having accumulators and flow limiters.
Common rail fuel systems typically employ multiple fuel injectors to inject highly pressurized fuel into combustion chambers of an engine. The high-pressure fuel is supplied to the fuel injectors via a common rail or manifold that is secured along a length of the engine, and individual supply lines connected between the common rail and each of the injectors. In some configurations, flow limiters can be employed in the supply passages between the common rail and each of the fuel injectors to limit fuel leakage during catastrophic injector failure or to dampen pressure oscillations caused by normal operation of the fuel injectors.
Although functionally adequate, the common rail fuel system described above can be expensive and time consuming to fabricate. In particular, because of the high pressure of the fuel passing through the common rail, the common rail is generally made from heavy solid-stock material. The solid-stock material must be gun-drilled through its entire length to form a main bore having thick walls that can withstand the elevated pressures. In addition, each intersection of the common rail with the individual supply lines must be cross-drilled into the solid-stock material, and then treated, for example by way of autofrettage, ECM, abrasive flow, etc., to help ensure hermetic sealing of the intersections with little or no process contamination. These materials and processes used in the fabrication of the common rail increase a cost and a fabrication time of the fuel system.
One attempt to address the problems described above is disclosed in U.S. Pat. No. 6,851,412 (the '412 patent) of Jay issued on Feb. 8, 2005. Specifically, the '412 patent discloses a fuel injection system having an injector nozzle for each cylinder of an engine, and a dedicated pressure accumulator in direct connection with each nozzle. The dedicated pressure accumulators replace the common rail typical of such fuel systems. Each of the pressure accumulators is arranged at least partially within a cylinder head of the engine such that the cylinder head serves as a supporting casing for the accumulators, and extends from outside the cylinder head to the injector nozzles. Each pressure accumulator comprises a longitudinally elongated body part that defines at least two separate chambers in open fluid communication with each other and bounded by a common intermediate wall. A total volume of each pressure accumulator is at least 30 times greater than the volume of fuel injected by one injector nozzle during a single combustion stroke of the engine. The pressure accumulators fluidly communicate with each other by way of a tube system external to the cylinder head, the tube system being connected to a high pressure fuel pump driven by the engine.
Although the system of the '412 patent may reduce fuel system costs by replacing the common rail with dedicated pressure accumulators, the system may still be less than optimal. In particular, the multiple chambers within each accumulator of the '412 patent may increase a complexity of the accumulators, making the accumulators expensive and time consuming to fabricate. Further, the system of the '412 patent does not provide any way to limit fuel leakage during catastrophic injector failure or to dampen pressure oscillations caused by normal operation of an injector.
The system of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art.
One aspect of the present disclosure is directed to a fuel accumulator. The fuel accumulator may include a body having a first end, a second end, and a single chamber extending in a length direction of the body between the first end and the second end. The fuel accumulator may also include a cap configured to close off the first end and including a first inlet and a first outlet in fluid communication with the single chamber of the body, each of the first inlet and first outlet having a diameter. The single chamber may have a cross-sectional diameter greater than the diameters of the first inlet and the first outlet.
Another aspect of the present disclosure is directed to a flow limiter. The flow limiter may include a body having an inlet, an outlet, and a recess disposed between the inlet and the outlet. The fuel limiter may also include a first valve element disposed within the recess and configured to allow substantially unrestricted fuel flow from the inlet to the recess and to restrict fuel flow from the recess to the inlet. The fuel limiter may further include a second valve element disposed within the recess and configured to allow fuel flow from the recess to the outlet during a first condition, and to inhibit fuel flow from the recess to the outlet during a second condition.
In yet another aspect, the present disclosure is directed to fuel system for an engine. The fuel system may include a pump driven by the engine to pressurize fuel, and a plurality of fuel injectors configured to inject pressurized fuel into associated combustion chambers of the engine. Each of the plurality of fuel injectors may be located at least partially within a different cylinder head of the engine. The fuel system may also include a plurality of fuel accumulators associated with the plurality of fuel injectors. Each of the plurality of fuel accumulators may be disposed at least partially within a different cylinder head of the engine in fluid communication with an associated fuel injector of the plurality of fuel injectors and in fluid communication with adjacent fuel accumulators of the plurality of fuel accumulators. At least one of the plurality of fuel accumulators may also be in fluid communication with the pump. The fuel system may further include a plurality of flow limiters, each of the plurality of flow limiters disposed between an associated fuel accumulator of the plurality of fuel accumulators and an associated fuel injector of the plurality of fuel injectors.
An exemplary embodiment of an engine 10 having a fuel system 12 is illustrated in
Cylinder 16, piston 18, and cylinder head 20 may together form a combustion chamber 22. In the illustrated embodiment, engine 10 includes four 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 in any other suitable configuration.
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 24 configured to hold a supply of fuel, a fuel pumping arrangement 26 configured to pressurize the fuel, and a plurality of fuel injectors 28 configured to receive the pressurized fuel by way of a plurality of distributed accumulators 30. Each fuel injector 28 may be associated with a different cylinder head 20 and be operable to inject an amount of pressurized fuel into an associated combustion chamber 22 at specific timings, fuel pressures, and fuel flow rates.
Fuel pumping arrangement 26 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 accumulators 30 and fuel injectors 28. In one example, fuel pumping arrangement 26 may include a low-pressure source 32 and a high-pressure source 34 disposed in series and fluidly connected by way of a fuel line 36. Low-pressure source 32 may be a transfer pump configured to draw fuel from tank 24 and provide low-pressure feed to high-pressure source 34. High-pressure source 34 may be configured to receive the low pressure feed and increase the pressure of the fuel to, in some embodiments, about 200-400 MPa. High-pressure source 34 may be connected to accumulators 30 by way of a fuel line 38. A check valve 40 may be disposed within fuel line 38 to provide for a unidirectional flow of fuel from fuel pumping arrangement 26 to accumulators 30.
As shown in
Each accumulator 30 may include an inlet 50 and an outlet 52 oriented in general oppositional alignment with each other and orthogonally to the axial flow direction of accumulator 30. The accumulator 30 located furthest upstream may have its inlet 50 fluidly connected to fuel line 38, while the accumulator 30 located furthest downstream may have its outlet 52 plugged or otherwise capped off. The remaining accumulators 30 may have their inlets 50 fluidly connected to the outlets 52 of upstream accumulators 30 by way of supply passages 48. It is contemplated that outlet 52 of the furthest downstream accumulator may alternatively be fluidly connected back to tank 24, if desired, for example by way of a pressure relief valve (not shown).
As shown in
Cap 59 may at least partially define inlet 50 and outlet 52, and include a generally hollow protrusion 68 orthogonal to inlet 50 and outlet 52 that is received by a recess 70 of body 54 to close off chamber 60 at first end 56. Cap 59 may also include shoulders 72 that engage first end 56, and one or more fasteners 74 that pass through cap 59 and into first end 56 of body 54 to secure cap 59 in place. A sealing member 76 may be received within an external groove 78 of protrusion 68 to create a fluid seal between cap 59 and body 54. In this manner, cap 59 may fluidly communicate inlet 50 and outlet 52 with chamber 60 via hollow protrusion 68. Chamber 60 may have a cross-sectional diameter greater than diameters of inlet 50 and outlet 52.
In one embodiment, an insert 79 may be positioned within hollow protrusion 68 and include internal passages 81 that fluidly interconnect inlet 50, outlet 52, and chamber 60. Internal passages 81 may be arranged in a general T-shape, and have smaller diameters than that of chamber 60. Insert 79 may be fabricated from a material or through a process different from those associated with cap 59, if desired. For example, insert 79 may be fabricated from a material having a higher strength and/or through a process having a higher precision. By utilizing insert 79, the cost and time associated with fabricating cap 59 may be relatively low.
Each fuel injector 28 may be a closed nozzle-type unit injector having a nozzle member 80. Nozzle member 80 may be a generally cylindrical body configured to receive a needle valve 82. One or more orifices 84 may be located at a tip end of nozzle member 80 and selectively blocked and unblocked by needle valve 82 to allow injections of pressurized fuel into an associated combustion chamber 22.
In some situations, it may be possible for a portion of nozzle member 80 to erode, crack, or completely break away. In order to inhibit unchecked fuel leakage from the damaged nozzle member 80 into combustion chamber 22 (referring to
A coupling 90 may connect a filter housing 88 to second end 58 of accumulator 30 to close off recess 87 and thereby retain flow limiter 86 in place. Filter housing 88 may include a central passage 89 that accommodates a filter 91, for example an edge filter, that may be used to remove debris from the flow of fuel passing from accumulator 30 to injector 28. Coupling 90 may include an internal flange 92 that engages shoulders 94 of filter housing 88, and threads 96 that engage second end 58 of accumulator 30. With this configuration, a rotation of coupling 90 may serve to draw an end face 100 of filter housing 88 against a biting edge 102 of accumulator 30 to create a fluid seal. A tip end 98 of filter housing 88 may directly engage fuel injector 28 at an inlet 104 such that fuel passing from accumulator 30 through flow limiter 86 may be directed to injector 28 via central passage 89. As fasteners 69 are tightened into cylinder head 20 (referring to
Flow limiter 86 may be configured to inhibit unchecked fuel flow to a leaking fuel injector 28 in response to a pressure differential between accumulator 30 and the leaking fuel injector 28. That is, when the integrity of nozzle member 80 is compromised (e.g., when nozzle member 80 is cracked, eroded, broken, etc.), the fuel within the compromised fuel injector 28 may flow substantially unimpeded into the associated combustion chamber 22 (referring to
As illustrated in
Second valve element 108 may include a ball 126 received within a sleeve 128 of first valve element 106 and biased away from fuel injector 28 and toward accumulator 30 by a spring 130. Ball 126, sleeve 128, and spring 130 may be received within spring 122 of first valve element 106. Ball 126 may be configured to compress spring 122 during catastrophic failure of injector 28 (i.e., during a failure of injector 28 that results in a pressure gradient across flow limiter 86 greater than a threshold amount) and engage an inner conical seat 131 of filter housing 88. When ball 126 engages seat 131, little or no fuel may flow to injector 28. Under normal conditions (i.e., when a tip end of nozzle member 80 has not been compromised), ball 126 may be held away from seat 131 by the force of spring 130.
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 high pressure fuel supply and closed orifice-type fuel injectors where fabrication time and cost are concerns, and flow limiting is desired. Operation of fuel system 12 will now be described in detail.
Referring to
Referring to
The return of needle valve 82 against the tip end of nozzle member 80 may generate pressure oscillations within injector 28 and accumulator 30. In particular, the flow of fuel from accumulator 30 to injector 28 during an injection event may have a corresponding momentum related to the flow rate and the flow volume. The sudden closing of the needle valve 82 at the end of the injection event may instantaneously block the fuel flow and cause the corresponding momentum to rebound in the opposite direction, resulting in a reverse pressure wave traveling from injector 28 back through accumulator 30. If unaccounted for, this pressure wave could travel to adjacent accumulators 30 and interfere with subsequent injection events (i.e., the reverse traveling pressure wave could cause needle valve 82 of the same or other injectors 28 to dither and open early, close early, or open additional times).
Flow limiter 86 may help to dampen pressure oscillations within fuel system 12. Referring to
Flow limiter 86 may also inhibit fuel supply to injector 28 during catastrophic failure of injector 28. In particular, as the pressure differential between accumulator 30 and injector 28 reaches a threshold limit indicative of an injector failure condition, the pressure differential may move ball 126 against the bias of spring 130 to engage seat 131. In this position, little or no fuel may pass through flow limiter 86 to injector 28. Once the injector failure condition has been remedied, or the pressure differential across flow limiter 86 has otherwise been reduced (such as at engine shutdown), spring 130 may move ball 126 away from seat 131 to restore the flow of fuel to injector 28.
Numerous advantages of the disclosed fuel system may be realized. For example, because the disclosed fuel system utilizes simple distributed accumulators that are relatively easy to fabricate compared to traditional common rail construction, the overall cost of the fuel system may be low. In addition, the use and location of flow limiters may help to dampen pressure oscillations within the fuel system that could disrupt normal injection events, as well as inhibit fuel leakage during a failure condition of a downstream component.
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 disclosure being indicated by the following claims and their equivalents.
