Patent Application
20080047527
Referring to
Each fuel injector 14 is equipped with only a single electronic control valve 40 that includes an electrical actuator 41 coupled to move a valve member 42 against the action of a biasing spring 43. Those skilled in the art will appreciate that electronic control valve 40 may be a poppet type valve that avoids leakage by a fluid tight seal associated with a one or more conical valve seats. Thus, valve member 42 could be trapped to move between a high pressure conical valve seat and a low pressure conical valve seat by the action of biasing spring 43 and electrical actuator 41 in a manner well known in the art. Alternatively, valve member 42 could be moved via a pilot valve connected to electrical actuator 41 without departing from the present disclosure. Fuel injector 14 includes an injector body 15 having disposed therein several components and a variety of passageways and cavities in order to allow for the injection of fuel to the individual engine cylinder 19 at a pressure greater than that in common rail 13. In particular, an intensifier control cavity 52, a plunger cavity 53, an actuation cavity 51, a needle top cavity 54 and a nozzle cavity 55 are all disposed in the injector body 50. In addition, the injector body 50 defines high pressure inlet 25, a low pressure drain 26 and a nozzle outlet 29. The nozzle cavity 55 is fluidly connected via an unobstructed nozzle supply passage 56 to plunger cavity 53. In terms of the present disclosure, the term “unobstructed” means that no valve that can completely close the passageway is positioned in the passageway. Thus, an unobstructed passageway can include a flow restriction, but does not include either an electronically controlled or passive valve that may completely shut the passageway. For instance, plunger cavity 53 is also connected to high pressure line 57 via a plunger fill passage 59 that includes a check valve 47. Thus, in the context of the present disclosure, plunger fill passage 59 could not be considered as unobstructed. As shown in
Fuel injector 14 also includes an intensifier 48 that may be composed of one or more components to slide between a retracted position, as shown, and an advanced downward position. Intensifier 48 is normally biased toward its retracted position by a return spring 49, which is positioned in actuation cavity 51. Those skilled in the art will appreciate that return spring 49 could be positioned elsewhere to bias intensifier 48 toward its retracted position in a known manner. Intensifier 48 is guided in its movement between its retracted and advanced positions by annular guide surfaces 70 and 71 that define a relatively tight guide clearance fit between the intensifier and the internal walls of injector body 50. Thus, intensifier 48 and guide surfaces 70 and 71 can be thought of as fluidly separating the intensifier control cavity 52, actuation cavity 51 and plunger cavity 53 from each other. Intensifier 48 may include hollow portions adjacent guide portions 70 and 71 that may be exploited to reduce the guide clearance in those areas when high pressure slightly radially expands the intensifier during times when a pressure differential exists between one or more of the actuation cavity 51, intensifier control cavity 52 and plunger cavity 53. When the electronic control valve 40 is in its biased first position as shown, plunger cavity 53 is fluidly connected to intensifier control cavity 52 via fluid line 63 and control line 66. Fuel injector 14 is shown with intensifier 48 and electronic control valve 40 positioned as they would be between injection events. A fluid connection between plunger cavity 53 and intensifier control cavity 52 causes all of the internal cavities (actuation cavity 51, intensifier control cavity 52, plunger cavity 53, needle top cavity 54 and nozzle cavity 55) to be at the same pressure as common rail 13 between injection events. This prevents pressure differentials across guide portions 70 and 71 during the prolonged period between injection events, thus avoiding leakage along those guide surfaces sometimes observed in other fuel injection systems that maintain a pressure differential between injection events. When electrical actuator 41 moves control valve member 42 to its second position, intensifier control cavity 52 becomes fluidly connected to low pressure drain 26. When this occurs, the hydraulic force in actuation cavity 51 causes the intensifier 48 to move downward toward its advanced position against the action of return spring 49 to raise fuel pressure in plunger cavity 53 above that in common rail 13 according to the strength of spring 49 and the diameter ratios associated with the intensifier 48 in a manner well known in the art. When this occurs, check valve 47 closes. Fluid line 63 and control line 66 may include respective restricted orifices 64 and 67 to achieve some desired action out of fuel injector 14. For instance, restricted orifice 67 could be employed to reduce the movement rate of the intensifier 48 during an injection event. On the other hand, one or both of restricted orifices 64 and 67 could be utilized to slow the retraction rate of intensifier 48 after an injection event when the fuel injector is resetting itself for a subsequent injection event, such as to avoid cavitation. Thus, those skilled in the art will appreciate that restricted orifices 64 and 67 may have the same or different flow areas, and one or both may be excluded all together from fuel injector 14 if desired.
Fuel injector 14 also includes a needle 45 disposed therein. Needle 45 is guided in its movement via a guide surface 72, which along with needle 45 separates needle top cavity 54 from nozzle cavity 55. Needle 45 is normally biased downward in contact with a seat 28 via a needle biasing spring 46 in a conventional manner. When needle 45 is in contact with seat 28, nozzle cavity 55 is blocked from fluid communication with nozzle outlet 29 in a conventional manner. When needle 45 lifts towards its open position against the action of needle biasing spring 46, a fluid connection is created between nozzle cavity 55 and nozzle outlet 29 allowing fuel to be sprayed into the individual engine cylinders 19. Needle 45 includes opening hydraulic surfaces 44a and 44b that are exposed to fluid pressure in nozzle cavity 55. Thus, when both top cavity 54 is at rail pressure, as it always is, and nozzle cavity 55 is also at rail pressure, such as between injection events, the needle 45 is held in its downward position to close seat 28 by the needle biasing spring 46. However, when intensifier 48 is driven downward to greatly increase fuel pressure in plunger cavity 53, the fluid pressure is communicated to nozzle cavity 55 via nozzle supply passage 58, and this higher pressure acts upon the opening hydraulic surfaces 44a and 44b to lift needle 45 upward against the action of biasing spring 46 toward its open position. Although spring 46 is shown in nozzle cavity 55, it could equally be located elsewhere, such as in needle top cavity 54. Those skilled in the art will appreciate that the valve opening pressure as well as the opening and closing rates of needle 45 can be engineered by selecting the magnitude of pressure in common rail 13, the area ratios of intensifier 48, and hence expected injection pressure in plunger cavity 53, while also appropriately sizing opening hydraulic surfaces 44a, and 44b while selecting an appropriate pre-load on needle biasing spring 46, and finally by including or excluding the restricted orifice 61.
The fuel system of the present disclosure finds potential application in any internal combustion engine, but is particularly adapted to compression ignition engines wherein fuel is directly injected into individual engine cylinders 19 and compression ignited in a manner well known in the art. between injection events, electrical actuator 41 is de-energized and control valve member 41 is positioned in its first or biased position, as shown, via biasing spring 43. When this occurs, the intensifier control cavity 52 is fluidly connected to common rail 13 via control line 66, fluid line 63, check valve 47 positioned in plunger cavity 59 and high pressure line 57 and rail branch passage 32. Thus, the only pressure differential existing in fuel injector 14 between injection events occurs in electronic control valve 41. However, because this valve may include a poppet type valve member that seals a conical valve seat, no leakage occurs from fuel injector 14 between injection events. Likewise, no leakage occurs across needle 45 since it is securely seated at seat 28, and no pressure differential exists between needle top cavity 54 and nozzle cavity 55.
An injection event is initiated by electronic control module commanding the energization of electrical actuator 41 to move control valve member 42 from its first position, as shown, to its second position that fluidly connects intensifier control cavity 52 to low pressure drain 26 via control line 66. When this occurs, the rail pressure acting in actuation cavity 51 pushes intensifier 48 downward against the action of return spring 49 to raise fuel pressure in plunger cavity 53. When that pressure rises above a valve opening pressure for needle 45, it lifts to an open position against the action of needle biasing spring 46 to fluidly connect nozzle cavity 55 to nozzle outlets 29 to commence the spraying of fuel into engine cylinder 19. Shortly before the desired amount of fuel is injected, the control signal de-energizes electrical actuator 41 causing it to return to its first position under the action of biasing spring 43. This reconnects intensifier control cavity 52 to common rail 13 via control line 66, the fluid line 63, plunger cavity 53 and plunger fill passage 59. When this occurs, the fuel pressure in nozzle cavity 55 drops below a valve closing pressure and needle 55 is driven downward to re-seat on seat 28 via needle biasing spring 46. After the injection event, flow from rail 13 and fuel displaced from actuation cavity 51 allows intensifier 48 to retract under the action of return spring 49 to refill both plunger cavity 53 and intensifier control cavity 52 in preparation for a subsequent injection event.
As in a typical diesel engine, when fuel is combusted by compressing air in the engine cylinder 19 beyond an auto ignition point of the liquid fuel injected from fuel injector 14. Those skilled in the art will appreciate that the fuel may be injected into the cylinder before or after the air has been compressed above the auto ignition point. In a typical case, the air is compressed beyond an auto ignition point and the fuel is injected at or near top dead center for the piston associated with that individual cylinder. Nevertheless, the fuel system 12 of the present disclosure can accommodate so called homogeneous charge compression ignition mode of operation where fuel is injected into the engine cylinder and allowed to mix with air before being compressed beyond on the auto ignition point of the fuel.
Those skilled in the art will appreciate that the fuel system of the present disclosure leverages known technology associated with relatively high pressure common fuel rail systems. This leveraging is accomplished via the use of an intensifier to substantially increase injection pressures above that of the common rail, and only do so within the fuel injector for the brief duration of the injection event. While many current production common rail systems can achieve injection pressures on the order of 160-180 Mpa, it is generally recognized that there are significant structural challenges for the fuel system (pump, line rail, injector, pressure sensor, pressure regulator, etc.) to endure beyond 200 Mpa injection pressures for an entire engine life. However, the fuel system of the present disclosure has the ability to briefly raise fuel pressures only in the fuel injector well above 200 Mpa for relatively high pressure injections not currently possible with most common rail systems. And this is accomplished with a single electrical actuator. Those skilled in the art will appreciate that these extremely high pressures can be useful in further reducing undesirable engine emissions while without sacrificing engine performance. In addition, very high injection pressures can be achieved without sacrificing efficiency via substantial fuel leakage within the fuel injector between injection events. The only substantial losses are those associated with once pressurized fuel displaced from the intensifier control cavity 52 during an injection. In addition, while some leakage may occur along the guide surfaces 70, 71 and 72 during an injection event, that relatively small leakage can be further reduced, for instance, by utilizing a hollow plunger portion for intensifier 48 that reduces the guide clearance during the downward intensifier stroke to further reduce fuel migration and leakage along guide surface 70. Those skilled in the art will appreciate that by appropriate sizing of the area ratios and spring strike associated with needle 45 as well as restricted orifice 61, the fuel injection rate could be made more square or more ramp in a manner well known in the art. In addition, the structure of the present disclosure always facilitates a valve opening pressure higher than that in the common rail 13, and the orifice 61 adjacent needle top cavity 54 will regulate flow into and out of check top cavity 54, thus controlling the check opening and closings velocities.
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 invention in any way. Thus, those skilled in the art will appreciate that other aspects of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.
