Patent Application
20060016915
1. Field of the Invention
The invention generally relates to a fuel injector and to an optimized geometry of a clevis, and, more particularly, to a clevis having an optimized geometry for substantially eliminating side loading effects on a plunger during operation of the fuel injector, thereby maintaining fuel injector performance integrity.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports, and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or another type of suitable hydraulic fluid capable of providing pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current designs, a driver will deliver a current or voltage to the open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift a spool into the open position so as to align grooves or orifices (hereinafter referred to as “grooves”) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high-pressure working fluid then acts on an intensifier piston which pushes the plunger to compress fuel located within a high pressure fuel chamber. As the pressure in the high pressure fuel chamber increases, the fuel pressure will begin to rise above the needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will lift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine. The above process describes an injection event.
After an injection event, the driver will deliver a current or voltage to a closed side of the coil solenoid. The magnetic force generated in the closed coil solenoid will then shift the spool into a closed position, so as to align the grooves or orifices of the control valve body and the spool with a reservoir. At this time, the intensifier spring will force the plunger and piston upwards toward the working port to evacuate the working oil within the intensifier chamber to the reservoir via the working ports and aligned grooves. As the plunger moves upward, fuel is provided to the high pressure fuel chamber. This cycle is referred to as the return or fill stroke. After the high pressure fuel chamber is completely filled and the piston and plunger are stopped, the parts remain in this state until the next injection event. This cycle is referred to as a dwell time between injection events.
In the related art, as represented in
In the related art, the plunger head 112A is held tightly between the lip portion 120 of the clevis 110 and the piston 102, with no clearance. In this manner, during operation the spring force will act on the shoulder 118 of the clevis 110 where such force will be transferred to the lip 120 of the clevis 110. This spring force will then act on the plunger and create a side loading effect on the plunger 112 that results, over time, in removal or scuffing of a film on the plunger (e.g., 0 to 2 μm of film deterioration) and/or wear on the metal surfaces of both the plunger and wall of the intensifier chamber (e.g., up to 50 μm or more of wear). This is due to uneven spring forces generated on the shoulder 118 of the clevis 110. In the related art scuffing and/or wearing is caused by interaction between the spring 116 and the clevis 110 and results in an increased clearance or gap between the plunger 112 and the intensifier chamber wall. This results in pressure loss within the intensifier chamber; mixing of the fuel with oil, since fuel will be able to leak into a spring cavity and eventually into the cylinder head; loss of sealing capabilities; and an overall loss of injector performance. This ultimately leads to degradation of injector performance.
In this equation, D is diameter of the plunger, C is the radial clearance, L is the length of the plunger (flow path) in sealing region, ρ is the density of the fluid, ν is the kinematic viscosity of the fluid, and P is the pressure. Comparing the experimental results to the theoretical results, it can be determined that the experimental results are far worse than predicted. For example, at a plunger clearance of 30 μm the equation indicates a fuel leak rate of approximately a 0.5 cc/s, whereas experiments demonstrate an actual fuel leak rate of approximately 2.8 cc/s. Accordingly, there is a need for an improved injector that minimizes or eliminates the disadvantages of the related art.
The invention is directed towards overcoming one or more of the problems and disadvantages of the related art.
In an aspect of the invention an apparatus is provided that substantially eliminates side loading effects on a plunger. For example, a clevis is provided having a geometry which substantially eliminates side loading effects on a plunger during operation. In another aspect of the invention a device comprises a clevis having a geometry that substantially eliminates frictionally induced deterioration on a body portion of a plunger.
In a further aspect of the invention, an injector structure comprises a piston, a plunger including a first portion and a second portion, and a clevis. The clevis comprises a structure in communication with a first portion of the plunger, wherein the clevis structure substantially eliminates side loading effects generated from a spring force being transferred to the plunger during operation.
In another aspect of the invention, a fuel injector comprises a body control valve having an inlet port and working ports. At least one solenoid coil is positioned at an end or ends of the body control valve and an intensifier chamber. Alternatively, a solenoid and/or spring can provide the desired opposing forces. The intensifier chamber comprises a piston, a plunger having a first portion and a second portion, a spring positionable substantially about the second portion of the plunger, and a clevis having a receiving portion. Further, the receiving portion has a profile which allows the plunger to free float therein. A contacting portion moves the piston from a first position to a second position during a return time between injection events via a spring loading force exerted on the loading portion of the clevis. A high pressure fuel chamber is arranged below the second portion of the plunger and a needle chamber having a needle responsive to an increased fuel pressure created in the high pressure fuel chamber.
In yet another aspect of the invention, a device comprises a means for substantially eliminating side loading effects on a plunger during operation and a biasing means contacting the eliminating means. The biasing means moves a piston from a first position to a second position.
The invention is directed to an oil-activated electronically, mechanically or hydraulically controlled fuel injector, including a clevis having an optimized geometry for maintaining the performance integrity of the fuel injector. This geometry substantially prevents or eliminates scuffing of a film on a plunger, as well as metal-to-metal (or alloy) wear on the plunger and intensifier chamber. The substantial prevention or elimination of scuffing and/or wearing reduces or prevents fuel leaking and maintains performance integrity of the fuel injector. This is accomplished by allowing the plunger to “free float” within the clevis; that is, an optimized geometry of the clevis of the invention substantially eliminates side loading effects on the plunger, thereby maintaining performance integrity of the fuel injector.
Additionally, as shown in
The plunger head 316 is arranged between the sidewalls of the clevis 300. For example, the plunger head 316 is arranged inside the inner circumference portion of the clevis 300. A portion of the spring (not shown) is arranged along an outer circumference of the clevis and in contact with the loading portion 306 of the shoulder 302. It should be understood that the clevis may take on any geometry in order to substantially eliminate side loading effects of a plunger assembly during operation and, in one aspect, a non-injection event.
In this configuration there is no slit or opening as in the previous embodiments. As a result, the plunger 408 may have a substantially uniform diameter throughout. The plunger head 410 is arranged in the receiving portion 408 of the clevis 400 by inserting the plunger through the receiving portion 408. Accordingly, the plunger is configured to have a smaller diameter than the inner circumference F of the clevis 400 to allow for movement of the plunger. Optionally, the diameter of the plunger does not have to be substantially uniform. For example, the plunger 408 may have a neck portion as previously described in foregoing embodiments.
Still referring to
The clevis 603 may include a shoulder portion 602 with loading portion 606 for receiving spring forces and a contact portion 605 for contacting a piston 602. A receiving portion 614 is capable of receiving a portion of the plunger head 612A. The clevis 603 further includes an optional lip portion 610 including an upper surface 612 for contacting a portion of a plunger during a low or no fuel condition. The clevis 603 includes an optimized geometry having a profile or height measured by the distance between the upper surface 612 and the upper surface of the contact portion 605.
In implementation, the profile of the clevis (e.g., the substantially vertical wall between the shoulder and lip portion) is greater than a head portion 612A of the plunger 612. In this manner, the plunger 612 is free floating within the intensifier chamber 600, and more particularly, within the receiving portion 614 of the clevis. As discussed in detail, the profile of the clevis in relation to the head portion 612A of the plunger 612 substantially eliminates or prevents wear and/or scuffing of the plunger body 612B, as well as wear and/or scuffing on the wall of the intensifier chamber during a dwell time between injection events and during an injection event.
Optionally, as discussed, the clevis 603 may have an opening or slit portion 609 for receiving a head portion 612A of the plunger, and a neck portion 612C of the plunger 612. In this configuration, the neck portion 612C has a smaller diameter than the rest the plunger 612 and the opening 609. The neck portion 612C is inserted into the opening or slit portion 609 allowing the plunger head 612A to be arranged within the receiving portion 614 of the clevis 603.
Alternatively, the head portion 612A, neck portion 612C, and body portion 612B of the plunger 612 may have substantially the same diameter, as described with reference to
Additionally, the invention may be a replacement kit for a fuel injector assembly. For example, a replacement kit includes the clevis having an optimized geometry for substantially eliminating side loading effects on a plunger. The kit may include a replacement plunger configured to operate with the replacement clevis and original injector. That is, by using the replacement kit on a used injector, it can be modified to ensure that there is substantially no deterioration in performance after a period of use of operation (e.g., injection events). Optionally, boring and/or resurfacing the intensifier chamber may be utilized to ensure proper tolerances between the plunger and the intensifier chamber. Additionally, the boring will substantially eliminate any damage which may have occurred to the intensifier chamber.
The nozzle generally depicted as reference numeral 840 is in fluid communication with the high-pressure chamber 830 via a fuel bore 834. It should be recognized that the fuel bore 834 may be straight or angled or at other known configurations. Upon fuel compression into the high-pressure chamber 830, fuel flows from the high-pressure chamber 830 to the nozzle 840. A spring cage 842 (which may be a separate component from the nozzle 840), which typically includes a centrally located bore, is bored into the nozzle 840. A spring 844 and a spring seat 840 are positioned within the centrally located bore of the spring cage 842. The nozzle 840 further includes a discharge path 848 in alignment with the fuel bore 834. A needle 850 is preferably centrally located with the nozzle 840 and is urged downwards by the spring 844. A fuel chamber 852 surrounds the needle 850 and is in fluid communication with the discharge path 848.
In operation, a driver (not shown) will first energize the coil and in this position the working fluid pressure within the pressure chamber 830 should be much lower than the rail inlet pressure. The energized coil will then shift the spool 810 to an open position. In one embodiment, a coil and opposing spring can provide forces to move the spool. In the open position, the groove 812 will overlap with the bore and the cross bore (not shown in detail.) This will allow the working fluid to flow between the inlet port 802 and the intensifier chamber via the working port 806, and simultaneously seal the vent port.
During an injection event the pressurized working fluid is allowed to flow into the working port 806 where it begins to act on the piston and the plunger. That is, the pressurized working fluid will begin to push the piston and the plunger downwards, compressing the intensifier spring. As the piston is pushed downward, fuel in the high pressure fuel chamber will begin to be compressed via the end portion of the plunger. A quantity of compressed fuel will be forced through the bores into the heart chamber which surrounds the needle. As the pressure increases, the fuel pressure will rise above the needle check valve opening pressure until the needle and needle spring are urged upwards. At this stage, the injection holes in the nozzle are open allowing a main fuel quantity to be injected into the combustion chamber of the engine. During this event, the spring forces will act on the clevis, and not exert any a side loading force on the plunger.
To end the injection event and start a non-injection event, the driver will energize the closed coil. The magnetic force generated in the coil will then shift the spool 810 into the closed position, which will offset the groove from the cross bore. This will open the vent port and allow fluid to flow from the intensifier chamber through the vent port. Also, the inlet port 802 will no longer be in fluid communication with the bore (and intensifier chamber). The working fluid within the intensifier chamber will then be vented to ambient pressure and the needle spring will urge the needle downward towards the injection holes of the nozzle thereby closing the injection holes. Similarly, the intensifier spring will exert a force on the clevis for urging the plunger and the piston into the closed or first position adjacent to the valve.
During this time, the plunger will move upward by forces in the high pressure chamber and fuel will again begin to flow into the high-pressure chamber of the intensifier body. Also, the spring forces will act on the clevis in order to move the piston from a first position to a second position. However, as discussed above, due to the geometry of the clevis and the clevis allowing the plunger to free float, no spring forces or loads will be transferred to the plunger, substantially eliminating side loading effects on the plunger during the non-injection event. This prevents or eliminates scuffing and wear of the plunger thus maintaining the performance integrity of the fuel injector.
While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.
