Patent Application
20100077971
The present disclosure relates generally to fuel injected internal combustion engines, and relates more particularly to cooling an actuator for a fuel injector by way of passing cooling fuel through a body of the fuel injector and across a heat exchange interface of the actuator.
Many components of internal combustion engine systems are subjected to relatively high temperatures during operation. In some instances, without some dedicated means for cooling engine system components, operation of the engine system may be sub-optimal, or even compromised altogether. Certain fuel system components commonly used in internal combustion engines are one notable example where cooling may be desired. It is common for fuel injectors used in internal combustion engines to utilize relatively fast moving control valves, actuators and the like to control fuel injection into an associated engine cylinder. The relatively rapid actuation of electrical actuators commonly used in fuel injectors can generate heat, which in combination with heat generated by the engine itself, can raise the temperature of the actuator and associated components above desired levels.
In recent years, piezoelectric actuators have been increasingly used to actuate fuel injector components. Piezoelectric actuators typically consist of a piezoelectric element which changes conformation, typically by lengthening in response to application of an electrical potential. Conventional systems employ a piezoelectric actuator which relatively rapidly lengthens and shortens to control the position of a control valve, which is in turn responsible for controlling a timing of fuel injection. As a piezoelectric element cycles between an excited state and an unexcited state, it tends to generate a relatively large amount of heat. Where piezoelectric actuators are used, problems attendant to cooling may be particularly acute.
U.S. Pat. No. 4,553,059 to Abe et al. is directed to a cooling strategy for a piezoelectric actuator. In the design proposed by Abe et al., a piezoelectric actuator includes a housing wherein a piezoelectric element is disposed. The piezoelectric element is positioned within an enclosure, having a thermally conductive material in contact with the piezoelectric element. A cooling liquid is circulated through a space surrounding the enclosure, and is stated to absorb heat from the piezoelectric element which is transferred through the thermally conductive material. While the design in Abe et al. may have applicability in certain environments, the fluid connections necessary to supply and drain cooling fluid are relatively complex. Moreover, assembly and proper positioning of the piezoelectric actuator of Abe et al. may be cumbersome in an engine environment.
In one aspect, an internal combustion engine includes an engine housing having at least one cylinder therein, and a fuel injector having an injector body defining a first fuel inlet and a second fuel inlet, and having a control valve assembly positioned within the injector body. The internal combustion engine further includes an actuator subassembly associated with the control valve assembly, including an actuator and a heat exchange interface. The internal combustion engine further includes a fuel system having a plurality of fuel supply circuit segments, the fuel supply circuit connecting with the first fuel inlet of the fuel injector. The internal combustion engine still further includes a cooling system associated with the actuator subassembly, including a cooling circuit with a plurality of cooling circuit segments including a first cooling circuit segment in common with a first fuel supply circuit segment of the fuel system, a second cooling circuit segment connecting with the second fuel inlet and a third cooling circuit segment defined by the injector body which is configured to pass fuel across the heat exchange interface of the actuator subassembly to exchange heat herewith.
In another aspect, the fuel injector includes an injector body having a nozzle group and defining a first fuel inlet, a second fuel inlet, a nozzle supply passage connecting with the first fuel inlet, and at least one nozzle outlet. The fuel injector further includes an outlet check movable between a first position at which it blocks the at least one nozzle outlet from the nozzle supply passage and a second position at which the at least one nozzle outlet is open to the nozzle supply passage. The fuel injector further includes a control valve assembly coupled with the outlet check and an actuator subassembly configured to actuate the control valve assembly, the actuator subassembly including a fluidly sealed casing coupled with the injector body, a piezoelectric element and a preloading device for the piezoelectric element which are each fluidly sealed within the casing. The actuator subassembly further includes a heat exchange interface, and the injector body further includes a cooling circuit segment configured to pass fuel across the heat exchange interface to exchange heat therewith, the cooling circuit segment comprising an inlet passage connecting with the second fuel inlet of the injector body, and an outlet passage.
In still another aspect, a method of operating a fuel system for an internal combustion engine includes a step of establishing a fluid connection between a first fuel inlet of a fuel injector body and at least one nozzle outlet of the fuel injector body via activating an actuator for a control valve assembly. The method further includes the steps of transferring heat from the actuator to a heat exchange interface of an actuator subassembly which includes the actuator, and cooling the actuator subassembly at least in part via a step of passing fuel across the heat exchange interface by way of a cooling circuit segment connecting with a second fuel inlet of the fuel injector body and a fuel outlet of the fuel injector body.
Referring to
Actuator subassembly 24 may include an electrical actuator (not shown in
Engine 8 may further include a cooling system 36 for actuator subassembly 24 which includes a cooling circuit 38 also having a plurality of segments, including a segment in common with a segment of fuel system 30. In one embodiment, cooling circuit 38 includes a first segment 40a which is coextensive with first segment 34a of fuel supply circuit 32. Cooling circuit 38 may include a second segment 40b which connects with second fluid inlet 20, and a third segment 40c defined at least in part by injector body 16 which is configured to pass fuel across heat exchange interface 28 to exchange heat therewith. Second segment 40b may also extend in engine head 80, and in a multi-cylinder embodiment of engine 8, may include a plurality of low pressure fuel supply conduits 86 which each supply fuel to one of fuel injectors 14 for cooling thereof, as further described herein. Cooling circuit 38 may further include a fourth segment 40d which extends from engine head 80 back to an inlet 58 of fuel tank 56. In a multi-cylinder embodiment, fourth segment 40d may include a plurality of drain conduits 84 connecting each of fuel injectors 14 with fuel tank 56. Fuel supply circuit 32 and cooling circuit 38 may be fluidly isolated from one another apart from the common segments identified herein. It may be recalled that segment 34a of fuel supply circuit 32 and segment 40a of cooling circuit 38 may comprise a common segment. Since second segment 40b of cooling circuit 38 connects with second segment 34b of fuel supply circuit 32, fuel transfer pump 62 might also be considered a common segment. In addition, as further described herein, fuel supplied via fourth segment 34d of fuel supply circuit 32 which is not injected, but rather passed to a drain, may be drained into drain conduits 84 and thus supplied to fourth segment 40d of cooling circuit 38. Accordingly, fourth segment 40d may also be considered a common segment between cooling circuit 38 and fuel supply circuit 32, however, in other embodiments, the common drain strategy might not be used. In any event, each injector body 16 may further include a low pressure fuel outlet 72 which transfers fuel to a drain conduit 70 including fourth segment 40d.
Referring now to
Actuator subassembly 46 may be controllably coupled with control valve assembly 22 via a rod 47 in one embodiment. Thus, actuation of actuator subassembly 46 can move rod 47 such that a position of control valve member 45 is varied to vary a fluid pressure acting on control surface 49. When a relatively higher pressure is applied to control surface 49, outlet check 21 blocks outlet 19 from nozzle supply passage 17. When a relatively low pressure is applied to control surface 49, such as when control passage 96 is connected to low pressure outlet 72, a pressure of fuel in nozzle supply passage 17 may be sufficient to lift outlet check 21 to open nozzle outlet 19, establishing a fluid connection with inlet 18 for injecting fuel.
Also shown in
It will be recalled that actuator subassembly 46 may include a heat exchange interface 28. In one embodiment, fuel supplied via inlet passage 23 may be passed across heat exchange interface 28 to exchange heat therewith, and may thenceforth flow to an outlet passage 25 of third segment 40c. Outlet passage 25, also defined by injector body 16, may fluidly connect with low pressure outlet 72 such that fuel may be circulated through injector body 16 to cool actuator subassembly 46, and then drain into drain conduit 84 from outlet 72. In the
Referring also to
In one embodiment, spring 50 may be part of a multi-function spring assembly having a first segment 51 which comprises a piston 53 having contact element 44 thereon, a second segment 55 which comprises an elastically deformed segment exerting the preloading force on piezoelectric element 29 and including spring 50, and a third segment 57. In one embodiment, third segment 57 may be configured for setting and/or adjusting a preload on piezoelectric element 29. To this end, third segment 57 may include a set of threads 59 which are configured to receive a threaded locking element 61 such as an externally threaded nut. Threadedly engaging locking element 61 with third segment 57 can expand or contract second segment 55 to vary an effective preloading force applied to piezoelectric element 29 via spring 50. The configuration and use of locking element 61, as well as the multi-function spring or spring assembly of which spring 50 is a part is more fully explained in commonly owned U.S. patent application Ser. No. 11/998,642. A preload control element 63, for example a thermally expansive material such as aluminum, may be disposed between piezoelectric element 29 and locking element 61 or other components such as spacers, etc. Preload control element 63 may expand or contract in response to temperature changes to maintain or control a preload applied to piezoelectric element 29 via preloading spring 50. Preloading spring 50 may be coupled with casing 46 via a flexible diaphragm 48 which moves when piezoelectric actuator 26 is activated and deactivated to control a position of rod 47 and in turn control fuel injection with fuel injector 14, as described herein. In certain embodiments, a sealing element other than a flexible diaphragm, such as an O-ring, might be used. In one embodiment, actuator subassembly 24 and injector body 16 may together define an annular cavity 52 which surrounds contact element 44 and adjoins diaphragm 48. Diaphragm 48 may include an outer surface 54 which is exposed to cavity 52. Heat exchange interface 28 may include outer surface 54. It will be noted in the
Actuator subassembly 24 may further define a thermal transfer pathway from piezoelectric element 29 to heat exchange interface 28. It may be recalled that thermal compensation material 31 may surround piezoelectric element 29 and be in thermal contact therewith. Thermal compensation material 31 may be formed as a thermal transfer material such as thermally conductive silicon oil, including any of a variety of proprietary and/or commercially available materials. Second segment 55 of spring 50, may have a helical configuration. A cavity 33 may be defined in part by spring 50 and also in part by casing 46. In one embodiment, thermal compensation material 31 may be positioned within cavity 33. In one further embodiment, thermal compensation material 31 may also be positioned in a cavity 33a which surrounds piezoelectric element 29 and is defined in part by piezoelectric element 29. Cavity 33 may be fluidly separated from cavity 33a via a barrier 29a. Barrier 29a may be a housing for piezoelectric element 29a. Each cavity 33 and 33a may be filled or substantially filled with thermal compensation material 31, for example by injecting thermal compensation material 31 therein. In embodiments where each cavity 33 and 33a is filled with thermal compensation material 31, actuator subassembly 24 may be at least substantially free of air, improving thermal transfer between components thereof. Thermal transfer pathway 27 may extend from piezoelectric element 29 to heat exchange interface 28, and may include thermal compensation material 31, and may also include portions of spring 50. In other words, spring 50 or other components of the multi-function spring of which spring 50 is a part, such as piston 53, may be disposed in thermal transfer pathway 27, and may thus serve to conduct heat from piezoelectric element 29 to heat exchange interface 28, and thenceforth to cooling fuel in cavity 52. Thermal compensation material 31 will typically be in thermal contact with both spring 50 and piezoelectric element 29, and at least a portion of thermal compensation material 31 will typically be between spring 50 and piezoelectric element 29.
It may further be noted that a portion of casing 46 extends from engine head 80. In other words, in one embodiment, actuator subassembly 24 may be positioned such that it extends upwardly from engine head 80 when mounted therein. This allows at least a portion of casing 46, for example 40% or more of an exterior of casing 46, to be exposed to a space defined by engine head 80 and a valve cover 81. This can enhance the cooling efficacy, as casing 46 may radiate heat into the space defined by valve cover 81 and engine head 80, and oil splash on casing 46 may also conduct heat therefrom.
Turning now to
Referring to
As alluded to above, common strategies for cooling piezoelectric actuators in particular tend to be relatively ineffective, or unwieldy. By implementing the teachings of the present disclosure, actuator subassemblies 24, 124 may be installed in an engine such as engine 8 relatively easily. Since fuel injectors 14 may be purpose built with internal cooling circuit segment 40c, once actuator subassembly 24, 124 is coupled therewith, no additional fluid connections need be made between components of actuator subassembly 24, 124 and/or fuel injector 14. Whereas earlier strategies such as Abe et al., described above, relied upon establishing fluid connections under a valve cover once an actuator or fuel injector was mounted in an engine, assembled fuel injectors according to the present disclosure can be installed in engine head 80 and successfully operate as well as be cooled without further assembly or connecting steps.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope of the present disclosure. For example, while the present description focuses primarily on cooling piezoelectric actuators, it is not limited thereto. In other embodiments, solenoid actuators, or other electrical or even mechanical actuators could be successfully cooled according to the teachings of the present disclosure. Moreover, while common rail systems will often be used in engines contemplated herein, the present disclosure is also not limited in this regard. Unit pumps associated with each of a plurality of fuel injectors, such as cam actuated pumps, might also be used, and the presently described cooling strategy used to cool electrical actuators associated with the cam actuated fuel injectors. Other aspects and features will be apparent upon an examination of the attached drawings and appended claims.
