Patent Application
20100175670
The present disclosure relates generally to fuel injector systems, and in particular, to a squish film drag strategy to reduce variations in close coupled post injections.
Mechanically actuated electronically controlled unit injectors (MEUI) have seen great success in compression ignition engines for many years. In recent years, MEUI injectors have acquired additional control capabilities via a first electrical actuator associated with a spill valve and a second electrical actuator associated with a direct operated nozzle check valve. MEUI fuel injectors are actuated via rotation of a cam, which is typically driven via appropriate gear linkage to an engine's crankshaft. Fuel pressure in the fuel injector will generally remain low between injection events. As the cam lobe begins to move a plunger, fuel is initially displaced at low pressure to a drain via the spill valve for recirculation. When it is desired to increase pressure in the fuel injector to injection pressure levels, the first electrical actuator is energized to close the spill valve. When this is done, pressure quickly begins to rise in the fuel injector because the fuel pumping chamber becomes a closed volume when the spill valve closes. Fuel injection commences by energizing the second electrical actuator to relieve pressure on a closing hydraulic surface associated with the direct operated nozzle check valve. The closing hydraulic surface of the directly operated nozzle check valve is located in a needle control chamber which is alternately connected to the pumping chamber or a low pressure drain by moving a control valve assembly with the second electrical actuator. Such a control valve structure is shown, for example, in U.S. Pat. No. 6,889,918. The nozzle check valve can be opened and closed any number of times to create an injection sequence consisting of a plurality of injection events by relieving and then re-applying pressure onto the closing hydraulic surface of the nozzle check valve. These multiple injection sequences have been developed as one strategy for burning the fuel in a manner that reduces the production of undesirable emissions, such as NOx, unburnt hydrocarbons and particulate matter, in order to relax reliance on an exhaust aftertreatment system.
One multiple injection sequence that has shown the ability to reduce undesirable emissions includes a relatively large main injection followed closely by a small post injection. Because the nozzle check valve must inherently be briefly closed between the main injection event and the post-injection event, pressure in the fuel injector may surge due to the continued downward motion of the plunger in response to continued cam rotation. In addition, past experience suggests that conditions within the fuel injector immediately after a main injection event are highly dynamic, unsettled and somewhat unstable, making it difficult to controllably produce a small post injection quantity. If the dwell is too short, the post injection quantity is too variant. If the dwell between the main injection event and the post-injection event is too long, the increased pressure in the fuel injector may undermine the ability to produce small post injection quantities, but the more stable environment renders the post injection more controllable. In other words, the longer the dwell, the larger the post injection pressure coupled with greater controllability. Thus, the inherent structure and functioning of MEUI injectors makes it difficult to control fuel pressure during an injection sequence because the fuel pressure is primarily dictated by plunger speed (engine speed) and the flow area of the nozzle outlets, if they are open, but the potentially unstable time period immediately after main injection makes any post injection quantity more variable and less predictable. As expected, the pressure surging problem as well as the shrinking post injection timing window can become more pronounced at higher engine speeds and loads, which may be the operational state at which a closely coupled small post injection is most desirable. The inherent functional limitations of known MEUI systems may prevent small close coupled post injections both in desired quantity and timing relative to the end of the preceding main injection event in order to satisfy ever more stringent emissions regulations.
The problems set forth above are not limited solely to MEUI systems. Rather, most electronically controlled fuel injector systems including common rail systems, cam actuated systems and hydraulically actuated systems face these problems as well. U.S. Pat. No. 7,354,027 teaches the use of a damping chamber and a damping face, whose angle is altered to control the amount of damping in order to reduce armature bounce between the armature and the stator assembly. The prior art fails to appreciate that the armature bounce occurring when the armature is at its farthest point from the stator assembly may also play a significant role in close coupled post injections.
The present disclosure is directed to overcoming one or more of the problems set forth above.
In one aspect, a fuel injector includes an injector body defining a nozzle outlet. A solenoid assembly includes a stator assembly that has a bottom stator surface, and an armature that has a top armature surface and a bottom armature surface. The stator assembly is closer to the top armature surface than the bottom armature surface. An electronically controlled control valve assembly includes a control valve member attached to the armature. The armature is movable between a first armature position and a second armature position inside an armature cavity that is defined by an inner surface of the injector body. A spring biases the armature away from the stator assembly towards the second armature position. A final air gap is a distance between the top armature surface and the bottom stator surface when the armature is in the first armature position. A final squish film drag gap is a distance between the bottom armature surface and an inner surface of the injector body when the armature is in the second armature position. The final squish film drag gap is about the same order of magnitude as the final air gap.
In another aspect, a method of operating a fuel injector includes initiating an injection event by energizing a solenoid assembly to move an armature inside an armature cavity from a second armature position to a first armature position, which is a final air gap away from a bottom stator surface of a stator assembly. The injection event ends by de-energizing the solenoid assembly to move the armature inside the armature cavity from the first armature position to the second armature position, which is a final squish film drag gap away from an inner surface of an injector body. Ending the injection event includes squish film dragging the motion of the armature when the armature moves from the first armature position to the second armature position. Squish film dragging the motion of the armature includes setting a final squish film drag gap to about the same order of magnitude as the final air gap.
In yet another aspect, a fuel system includes a rotatable cam and a mechanical electronic unit fuel injector actuated via rotation of the cam. The mechanical electronic unit fuel injector includes an injector body defining a nozzle outlet. The first electrical actuator is operably coupled to a spill valve and a second electrical actuator is operably coupled to control pressure in a needle control chamber. A solenoid assembly includes a stator assembly that has a bottom stator surface and an armature assembly that has a top armature surface and a bottom armature surface. The stator assembly is closer to the top armature surface than the bottom armature surface. An electronically controlled control valve assembly includes a control valve member attached to the armature. The armature is movable between a first armature position and a second armature position inside an armature cavity defined by an inner surface of the injector body. A spring biases the armature towards the second armature position. A final air gap is a distance between the top armature surface and the bottom stator surface when the armature is in the first armature position. A final squish film drag gap is a distance between the bottom armature surface and an inner surface of the injector body when the armature is in the second armature position. The final squish film drag gap is about the same order of magnitude as the final air gap.
a is a further enlarged side sectioned diagrammatic view of the armature assembly of the fuel injector shown in
b is an even further enlarged side sectioned diagrammatic view of the armature cavity shown in
a illustrates a graph representing the armature travel displacement from the second armature position of the fuel injector shown in
b illustrates three plots representing the armature travel displacement from the second armature position of three fuel injectors, one according to the prior art baseline, two having a having a squish film drag gap according to the present disclosure;
c illustrates two plots representing the armature travel displacement from the second armature position of two fuel injectors represented in
a illustrates the injection flow rate versus time for multiple injection events for a fuel injector having a squish film drag gap according to the present disclosure;
b illustrates varying injection flow rates versus time for multiple injection events for a fuel injector having a prior art baseline receiving a control signal suited for a fuel injector according to the present disclosure.
The present disclosure relates to a fuel injector having a squish film drag gap to slow armature movement compared to faster large gap predecessor fuel injectors, thereby allowing the fuel injector to counter-intuitively perform smaller close coupled post injection following a main injection event with more predictable and less variable injection quantities and timings. The present disclosure also provides the choice of performing injection sequences with smaller minimum controllable injection event durations than produced by predecessor fuel injectors.
Referring to
Fuel injector 10 includes an injector body 11 made up of a plurality of components that together define several fluid passageways and chambers. In particular, a pumping chamber 17 is defined by injector body 11 and a cam driven plunger 15. When plunger 15 is driven downward due to rotation of cam 9 acting on tappet 14, fuel is displaced into a spill passage 20, past spill valve 22, and out a drain passage (not shown) that is fluidly connected to fuel supply/return opening 13. As shown, tappet 14 extends outside of injector body 11. When first electrical actuator 21 is energized, a spill valve member 25 is moved with an armature 23 until a valve surface 26 comes in contact with an annular valve seat 29 to close spill passage 20. When this occurs, fuel pressure in pumping chamber 17 increases, as well as a fuel pressure in nozzle chamber 19 via the fluid connection provided by nozzle supply passage 18. Spill valve member 25 is normally biased to a fully open position via a compression biasing spring 36.
The control valve assembly 30 includes the control valve member 40, which is attached to the armature 60 and moves between a high pressure conical valve seat 41 and a low-pressure flat valve seat 42 when the armature 60 moves between a second armature position and a first armature position, respectively. For the sake of brevity, the armature 60 and the control valve member 40 may collectively be referred to as the armature assembly 59. In one embodiment, the armature assembly 59 may further include a guide piece 61 that connects the armature 60 to the control valve member 40. Biasing spring 36 also serves to bias the armature 60 away from the stator assembly 80 towards the second armature position and bias the control valve assembly 30 to a closed configuration.
The fuel injector 10 also includes a direct controlled nozzle check valve 32 that has an opening hydraulic surface 39 exposed to fluid pressure inside a nozzle chamber 19 and a closing hydraulic surface 34 exposed to fluid pressure inside a needle control chamber 33. The electrically actuated solenoid assembly 75 controls the movement of the armature 60 between the first armature position, which is a final air gap (See 69 in
When the electrically actuated solenoid assembly 75 is de-energized, the armature 60 is in the second armature position, the control valve member 40 is seated at the low-pressure flat valve seat 42 and the control valve assembly 30 is in the closed configuration. The control valve assembly 30 fluidly blocks the needle control chamber 33 from a low-pressure drain passage 49, and fluidly connects to pressure connection passage 35, which is fluidly connected to nozzle supply passage 18. Pressure in the needle control chamber 33 acts upon the closing hydraulic surface 34 associated with nozzle check valve 32. As long as pressure in needle control chamber 33 is high, nozzle check valve 32 will remain in, or move toward, a closed configuration, blocking nozzle outlets 12.
When the electrically actuated solenoid assembly 75 is energized, the armature 60 is in the first armature position, the control valve member 40 is seated at the high-pressure conical valve seat 41 and the control valve assembly 30 is in the open configuration and fluidly connects needle control chamber 33 to the low-pressure drain 49. Pressure in needle control chamber 33 is reduced and the nozzle check valve 32 will remain in, or move towards, an open configuration, allowing fuel inside the nozzle chamber 19 to flow through the nozzle outlets 12, if fuel pressure is above a valve opening pressure sufficient to overcome spring 38. The armature 60 has an armature travel distance defined by the distance between the first armature position and the second armature position. The nozzle check valve 32 has a nozzle check valve travel distance defined by the distance the nozzle check valve 32 travels between the open configuration and the closed configuration. The nozzle check valve travel distance may be larger than the armature travel distance, and in one embodiment, the nozzle check valve travel distance is about an order of magnitude larger than the armature travel distance.
Referring more specifically to
The fuel injector further includes a squish film drag gap 68 and an air gap 69, which are fluidly connected via a clearance gap 66 and holes 67. A clearance gap 66 is defined between outer side 63 of armature 60 and the inner side wall 73 of the injector body 11. Those skilled in the art may recognize that the clearance gap 66 should be sized such that the clearance gap 66 does not affect the flow of fuel that moves through the clearance gap 66, adversely affecting the motion of the armature 60. A clearance gap 66 that is too small may restrict the flow of fuel from the squish film drag gap 68 to the air gap 69, thereby adversely affecting the motion of the armature 60 in an unpredictable manner.
The squish film drag gap 68 is the distance between the bottom armature surface 62 and the inner surface 72 of the injector body 11 and the air gap 69 is the distance between the top armature surface 64 and the bottom stator surface 76 of the stator assembly 80. Both the squish film drag gap 68 and the air gap 69 vary in size as the armature moves between the first and second armature positions. Moreover, the sum of the size of the air gap and the squish film drag gap is fixed, such that when the squish film drag gap 68 is reduced by a certain amount, the air gap 69 increases by the same certain amount. Therefore, as the armature 60 reduces the squish film drag gap 68, the volume of the air gap 69 increases and pressure in the air gap 69 decreases.
A final air gap 69 is the distance between the top armature surface 64 and the bottom stator surface 76 of the stator assembly 80 when the armature 60 is in the first armature position. A final squish film drag gap 68 is the distance between the bottom armature surface 62 and the inner surface 72 of the injector body 11 when the armature 60 is in the second armature position and the final squish film drag gap 68 is about the same order of magnitude as the final air gap 69. In the present embodiment, the final squish film drag gap is set to about the same order of magnitude as the final air gap, such that the armature 60 experiences squish film dragging when the armature moves from the first armature position to the second armature position.
The term “about” means that when a number is rounded to a like number of significant digits, the numbers are equal. Thus both 0.5 and 1.4 are about equal. The term “same order of magnitude ” means that one is less than ten times the other. 10 and 90 are the same order of magnitude but 10 and 110 are not. Therefore, for instance, if the final air gap is 50 microns and the final squish film drag gap is the same order of magnitude as the final air gap, the final squish film drag gap could lie anywhere from 5.1 to 499 microns. In one embodiment, the final squish film drag gap 68 is about twice the size of the armature travel distance. Furthermore, in one embodiment, both the final squish film drag gap 68 and the final air gap 69 are about 50 microns. In another embodiment, the final squish film drag gap 68 is about 25 microns and the final air gap 69 is about 50 microns.
For years, manufacturers have designed fuel injectors with ever smaller final air gaps to improve armature control. Therefore, in the present disclosure, the armature may be expected to experience squish film dragging when the armature approaches both the first armature position as well as the second armature position because the fuel injector has a final air gap and a final squish film drag gap of about the same order of magnitude. In predecessor fuel injectors that had final air gaps that were about 50 microns, the armature may have experienced squish film dragging as the armature neared the first armature position. However, because of the increased magnetic force acting on the armature from the solenoid assembly, the effect of squish film dragging may have had only a secondary effect, if any, on the motion of the armature. The squish film dragging may have been likely to be coincidental as some armatures in predecessor fuel injectors included grooves on the top surface of the armature that would inhibit any effect the squish film dragging had during the motion of the armature. However, in one embodiment of the present disclosure, a fuel injector may experience squish film dragging as the armature moves from the second armature position to the first armature position, as well as from the first armature position to the second armature position. In the illustrated embodiment, the squish film drag effect is reduced due to presence of holes through the armature that makes displacement of fuel during armature movement easier. Thus, the squish film drag effect might be tuned via the size of the final air gap 69, no planar surface feature on the armature, and even via holes (size, number and location) through the armature.
In the present disclosure, fuel inside the squish film drag gap 68 resists the motion of the armature 60 as the armature 60 moves from the first armature position to the second armature position. As the bottom armature surface 62 exerts a downward force on the fuel inside the squish film drag gap 68, the fuel inside the squish film drag gap 68 is being exposed to pressure exerted by the armature 60 causing the fuel to move towards a region having lower pressure. Because the volume in the air gap 69 is increasing as the volume of the squish film drag gap 68 is decreasing, the pressure in the air gap 69 decreases while the pressure in the squish film drag gap 68 increases causing fuel from the squish film drag gap 69 to escape to the air gap via the clearance gap 66 and holes 67. As the squish film drag gap 68 becomes smaller, the fuel inside the squish film drag gap 68 offers a greater resistive force to the motion of the armature 60 further increasing the deceleration on the armature 60, thereby reducing the speed of the armature quicker. Thus the valve's speed is reduced as it approaches its seat, reducing a tendency to bounce.
Squish film dragging may be understood by imagining moving two parallel planes towards each other in a fluid. As the planes are moved closer, the fluid between the planes offers some resistance to the motion. As the planes come closer, more force is required to move the planes the same distance because the fluid offers a greater resistance. When the planes are very close together, a much larger force is needed to bring the planes together. Now imagine that the force being applied to the planes is constant and the planes were moving towards each other inside the volume of fluid. As they got closer, the resistive force of the fluid got larger causing the planes to slow down. A graphical representation of the phenomenon is discussed later in relation to
Applying the plane concept to the motion of the armature 60 inside the squish film drag gap 68, the armature 60 is one of the planes and the inner surface 72 of the injector body 11 is the other plane. The armature 60 is being pushed by the force exerted by the biasing spring 36, while the inner surface 72 of the injector body 11 experiences no external pushing force. As the armature 60 gets closer to the inner surface 72 and the squish film drag gap 68 is becoming smaller, the armature gradually slows down. Furthermore, the amount of deceleration in the armature 60 increases as the thickness of the squish film drag gap 68 decreases causing the armature 60 to decelerate quicker as the armature 60 moves closer to the second armature position.
An injection sequence that includes a main injection event followed by a small, closely coupled post injection event helps improve combustion efficiency. The settling time and the armature travel speed of the armature may affect a fuel injector's ability to perform a small, closely coupled post injection event. Varying the size of the final squish film drag gap 68 alters the armature travel speed, and consequently the settling time of the armature 60. A dwell time between two injection events includes a travel time and a settling time. The travel time is the time the armature takes to move from one armature position to an other armature position. The settling time is the time the armature takes to come to rest at the second armature position after the travel time. The present disclosure reduces the sum of the travel time and settling time via a slight increase in travel time summed with a substantially smaller settling time. This permits shorter dwell times between injection events.
The present disclosure finds potential application to any fuel system including a fuel injector having an armature controlled nozzle check valve and a particular application to any fuel system including a mechanically actuated electronically controlled fuel injector with at least one electrical actuator operably coupled to a spill valve and a nozzle check valve. Although both the spill valve and the nozzle check valve may be controlled with a single electrical actuator within the intended scope of the present disclosure, a typical fuel injector according to the present disclosure includes a first electrical actuator associated with the spill valve and a second electrical actuator associated with the nozzle check valve. Any electrical actuator may be compatible with the fuel injectors of the present disclosure, including solenoid actuators as illustrated, but also other electrical actuators including piezo actuators. The present disclosure finds particular suitability in compression ignition engines that benefit from an ability to produce injection sequences that include a relatively large main injection followed by a closely coupled small post-injection, especially at higher speeds and loads in order to reduce undesirable emissions at the time of combustion rather than relying upon after-treatment systems. The present disclosure also recognizes that every fuel injector exhibits a minimum controllable injection event duration, below which behavior of the injector becomes less predictable and more varied.
The minimum controllable injection event duration for a given fuel injector relates to that minimum quantity of fuel that can be repeatedly injected with the same control signal without substantial variance. This phenomenon recognizes that in order to perform an injection event, certain components must move from one position and then back to an original position with some predictable repeated behavior in order to produce a controllable event. When the durations get too small, pressure fluctuations are too large and components are less than settled, components tend to exhibit erratic behavior due to flow forces, pressure dynamics and possibly mechanical bouncing before coming to a stop, which may give rise to nonlinear and erratic behavior at various short and small quantity injection events.
The present disclosure is primarily associated with the minimal controllable injection event, especially when such an event occurs after a large main injection event. Thus, the present disclosure recognizes that simply decreasing the duration of the post-injection event may theoretically produce a smaller injection quantity, but the uncontrollable variations on that quantity may become unacceptable, thus defeating that potential strategy for producing ever- smaller injection event quantities.
Those skilled in the art may appreciate that one way of improving combustion efficiency is to perform an injection sequence that includes a large main injection 94 and a closely coupled small post injection 95. Any injection sequence generally begins when the lobe of cam 9 starts to move plunger 15. As plunger 15 begins moving, first electrical actuator 21 is energized to close spill valve 22. As cam 9 continues to rotate, pressure in nozzle chamber 19 begins to ramp up. The spill valve 22 is closed by the movement of spill valve member 25 from a fully open position 60 to a closed position 61. At this time, second electrical actuator 31 remains de-energized to facilitate a fluid connection via pressure connection passage 35 and pressure communication passage 44 to needle control chamber 33 so that the pressure therein tracks closely with the pressure increase in the nozzle chamber 19. After spill valve member 25 comes to rest at the closed position, the current or control signal to electrical actuator 21 may be dropped to a hold-in level that is sufficient to hold spill valve member 25 in the fully closed position 61.
In order to initiate the main injection event, the electrically actuated solenoid assembly 75 is energized, the armature 60 is moved from the second armature position to the first armature position due to the magnetic force exerted by the energized solenoid assembly 75. Although biasing spring 36 exerts a force opposing the magnetic force exerted by the solenoid assembly 75, the armature 60 still moves from the second armature position to the first armature position. As the armature 60 moves towards the first armature position, the control valve member 40 moves towards the high pressure conical valve seat 41, allowing fuel to move from the needle control chamber 33 to the low pressure drain passage 49, thereby relieving pressure acting on the closing hydraulic surface 34 of the nozzle check valve 32 inside the needle control chamber 33. As the pressure is relieved, the nozzle check valve 32 moves towards the open configuration, allowing fuel to flow through the unblocked nozzle outlets 12. Furthermore, when the armature 60 is at the first armature position, at least one component of the armature assembly 59 is in contact with a stop surface. In one embodiment, the control valve member 40 may be in contact with the high-pressure conical valve seat 41, which acts as a stop surface or a stop surface located on the stator assembly. In another embodiment, the guide piece 61 may be in contact with a stop surface on the bottom stator surface 76 of the stator assembly 80.
In order to end the main injection event, the electrically actuated solenoid assembly 75 is de-energized. The solenoid assembly 75 no longer exerts a magnetic force on the armature 60 allowing the biasing spring to move the armature 60 from the first armature position to the second armature position. As the armature 60 moves towards the second armature position, the control valve member 40 moves towards the low pressure flat valve seat 42, allowing fuel to move from the nozzle chamber 19 to the needle control chamber 33 via the nozzle supply passage 18, thereby increasing pressure acting on the closing hydraulic surface 34 of the nozzle check valve 32 inside the needle control chamber 33. As the pressure is increased, the nozzle check valve 32 moves towards the closed configuration, blocking fuel to flow through the unblocked nozzle outlets 12. As the armature 60 moves from the first armature position to the second armature position inside the squish film drag gap 68, the fluid inside the squish film drag gap 68 exerts a braking force on the armature 60, causing the armature travel speed to rapidly reduce, as shown at Curve 135 in
In order to initiate a post injection event, the electrical actuated solenoid assembly 75 is energized after the armature 60 returns to the second armature position during the main injection event. The post injection event is ended when the solenoid assembly 75 is de-energized, returning the armature 60 back to the second armature position. In order to perform a small post injection, the solenoid assembly 75 should be energized for a small period of time.
a illustrates a graph representing the armature travel displacement from the second armature position of the fuel injector shown in
At some point along the curves 134 and 135, the nozzle check valve 32 returns to a closed configuration. Position 136 signifies the armature 60 has reached the second armature position. The time taken from Position 133 to Position 136 is the time the armature 60 takes to move from the first armature position to the second armature position.
The speed at which the armature assembly 59 contacts the flat valve seat 42 is the armature's 60 final armature travel speed. The final armature travel speed of the armature 60 in the present embodiment is much smaller than the final armature travel speed of predecessor fuel injectors. Hence, the magnitude of any resultant armature and valve bounce is much lower in the present embodiment compared to predecessor fuel injectors. Depending upon the final armature travel speed, the armature 60 may experience some, none or a lot of bouncing. The magnitude of the armature bounce may be proportional to the final armature travel speed. The bouncing occurs due to the force generated by the impact of the armature assembly 59 with the flat valve seat 42. In one embodiment, by moving the armature inside the squish film drag gap, fuel inside the squish film drag gap is squish film dragging the motion of the armature, thereby slowing the speed of the armature. As a result, the control valve member impacts the flat seat 42 at a slower speed, reducing the magnitude of bounce and thereby reducing settling time.
Position 136 represents the beginning of the settling time for the armature 60. Position 137 represents the armature bounce and Position 138 signifies the end of the armature bounce as well as the end of the settling time. The time taken from Position 136 to Position 138 is the settling time of the armature 60. If the final armature travel speed is high, the armature 60 may exhibit multiple armature bounces until it eventually reduces in speed such that it stops bouncing.
A post injection event may begin at any point after Position 136. If the post injection event begins before the armature 60 has settled, the post injection quantity and timing will be varied and less predictable. However, if the post injection event begins after the armature 60 has settled, repeated post injections will produce consistent injection quantities and injection timings. In
b illustrates three plots representing the armature travel displacement from the second armature position of three fuel injectors, each having a squish film drag gap of a different size. Graph 91 represents a predecessor fuel injector having a squish film drag gap 68 that is at least two orders of magnitude bigger than the squish film drag gap 68 of the present embodiment. Graph 92 represents fuel injector shown in
Comparing the three graphs 91, 92 and 93, graph 91 has the smallest travel time, which illustrates that the fluid in the enlarged squish film drag gap 68 may not have affected the speed of the armature 60 as it moved between the first armature position and the second armature position. Graph 93 shows a very large travel time, which suggests that the final squish film drag gap may be so small that it reduced the armature travel speed significantly. Graph 92 had a travel time slightly larger than that of graph 91 but significantly smaller than that of graph 93.
Referring to the armature bounces shown in
In the embodiment shown in
Referring to
a-b illustrate the injection quantities produced during a main injection event followed by a close-coupled post injection event by representative fuel injectors embodied in graphs 91 and 92, respectively when the same control signal is repeatedly sent to each of the fuel injectors represented by graphs 91 and 92. In
In
Close-coupled post injections that are performed before the armature is settled may produce erratic injection quantities because the close-coupled post injection event may begin when the armature is already at a distance away from the second armature position. In order to perform a controlled close-coupled post injection with a high degree of accuracy and control, the controlled close-coupled post injection should begin after the armature has settled to the second armature position. The size of the injection quantity may be kept small if the armature is traveling at a fast enough armature travel speed that may move the nozzle check valve between the open and closed configuration quickly enough to only allow a small quantity of fuel to flow out through the nozzle outlets.
Therefore by reducing the size of the squish film drag gap over predecessor fuel injectors, the present disclosure allows manufacturers to design fuel injectors that produce minimum controllable injection event quantities smaller than predecessor fuel injectors with shorter dwells between injection events than ever before. On the other hand, if the gap is too small (Curve 93), then the result may be worse than the predecessor fuel injector.
People skilled in the art may choose a squish film drag gap according to specific requirements and preferences. By decreasing the squish film drag gap to a very small size, the armature travel speed throughout the armature travel distance is significantly reduced, inhibiting the ability to produce small injection quantities. Having a very large squish film drag gap may not have a strong enough squish film drag effect on the armature, thereby not reducing the armature's speed as it comes closer to the stop surface, resulting in a higher final armature travel speed and more armature bounce. The resulting settling time is larger, and therefore prevents the fuel injector's from performing consistent post injections at dwell times shorter than the settling time of the fuel injector.
People skilled in the art may recognize that adjusting the control signal of the electrical actuator will allow operators to produce consistent injection quantities as long as the dwell time is larger than the settling time of the fuel injector. Post injection events that do not require consistent post injection quantities may be performed with dwell times smaller than the settling time.
The present disclosure has the advantage of consistently achieving smaller post injection quantities 95 (
Although the present disclosure has been illustrated in the context of an injection sequence that includes a large main injection followed by a small post injection, it is foreseeable that the same techniques could be utilized to reduce the minimum controllable injection quantity of fuel injector for any injection event alone or as part of a sequence. For example, the added capabilities provided by the reduced squish film drag gap could be exploited at other operating conditions, such as to produce small split injections at idle. And in addition, smaller pilot injections may also be available via the improvement introduced in the present disclosure. Thus, the ability to incrementally decrease the minimum controllable fuel injection quantity at all operating conditions and pressures could conceivably be exploited in different ways across an engine's operating range apart from the illustrative example that included an injection sequence with a large main injection followed by a closely coupled post injection.
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. Those skilled in the art will appreciate that the drag phenomenon of the present disclosure can be adjusted by a number of features, including but not limited to: The relative diameter of the armature 160 to the diameter of the drag gap spacer 180, the number and size of holes 67, the OD clearance of the armature, and of course the viscosity of the fluid. 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
