CN109505684B

CN109505684B - Injector for a reductant delivery unit having a fluid volume reduction assembly

Info

Publication number: CN109505684B
Application number: CN201811074587.5A
Authority: CN
Inventors: S.C.巴戈斯; J.L.哈特菲尔德; K.A.肖
Original assignee: Continental Automotive Systems Inc
Current assignee: Vitesco Technologies USA LLC
Priority date: 2017-09-14
Filing date: 2018-09-14
Publication date: 2021-06-01
Anticipated expiration: 2038-09-14
Also published as: US20190078488A1; JP2019056374A; KR20190030632A; FR3071011B1; CN109505684A; FR3071011A1; JP6661720B2; KR102127048B1; DE102018215678A1

Abstract

The fluid ejector includes: a fluid inlet, a fluid outlet, a fluid path from the fluid inlet to the fluid outlet; a tube; a filter disposed in the tube proximate the fluid inlet; and a calibrated filter tube disposed downstream of the filter. The calibrated filter tube includes a first end adjacent the filter and an axial through-hole defining at least a portion of a fluid path through the fluid ejector. An actuator unit is disposed within the fluid ejector and engages the second end of the calibrated filter tube. The valve assembly is operatively connected to the actuator unit. Calibrating the position of the filter tube within the tube sets the opening force of the valve assembly. The cap member has a sidewall defining an interior space that receives the filter, and the sidewall contacts and is attached to the first end of the calibrated filter tube.

Description

Injector for a reductant delivery unit having a fluid volume reduction assembly

Cross Reference to Related Applications

This application is related to U.S. patent application __ entitled "injection FOR REDUCTAT DELIVERY UNIT HAVING REDUCED FLUID VOLUME" (attorney docket number: 2017P03658 US), U.S. patent application __ entitled "SEAL MEMBER FOR REDUCTANT DELIVERY UNIT" (attorney docket number: 2017P03660 US), and U.S. patent application __ entitled "injection FOR REDUCTANT DELIVERY UNIT HAVING FLUID VOLUME REDUCTION ASSEMBLY" (attorney docket number: 2017P03659 US). The contents of the above application are hereby incorporated by reference in their entirety.

Technical Field

The present disclosure relates generally to Reductant Delivery Unit (RDU) fluid injectors, and in particular to robust RDU fluid injectors for non-scavenging applications.

Background

Emission legislation in europe and north america is driving the implementation of new exhaust aftertreatment systems, particularly lean-burn technologies such as compression-ignition (diesel) engines and stratified-charge spark-ignition engines (typically utilizing direct injection) operating under lean and ultra lean conditions. Lean-burn engines exhibit high nitrogen oxide (NOx) emission levels, which are difficult to address in the oxygen-rich exhaust environment characteristic of lean-burn combustion. Exhaust aftertreatment technologies are currently being developed to treat NOx under these conditions.

One of these techniques involves favoring ammonia (NH)₃) Reacts with nitrogen oxides (NOx) of the exhaust gas to produce nitrogen (N)₂) And water (H)₂O) is used as the catalyst. This technique is known as Selective Catalytic Reduction (SCR). Ammonia, in its pure form, is difficult to handle in the automotive environment, so these systems have traditionally used Diesel Exhaust Fluid (DEF) and/or urea (CO (NH) typically at 32%₂)₂) Aqueous urea solution in liquid form at concentration. This solution is known under the name AUS-32 and is also known under the name AdBlue. The reductant solution is typically delivered to the hot exhaust stream using an injector and converted to ammonia gas prior to entering the catalyst. More specifically, the solution is delivered to a hot exhaust stream and converted to ammonia gas in the exhaust after undergoing pyrolysis or thermal decomposition into ammonia gas and isocyanic acid (HNCO). The isocyanic acid then undergoes hydrolysis with the water present in the exhaust gas and is converted into ammonia and carbon dioxide (CO)₂) The ammonia gas produced by pyrolysis and hydrolysis then undergoes a catalytic reaction with the nitrogen oxides, as previously described.

AUS-32 or AdBlue have freezing points of-11 deg.C, and system freezing is expected to occur in cold climates. Since these fluids are aqueous, they expand in volume after being converted to a solid state after freezing. The expanding solid may exert a significant force on any enclosed volume, such as an injector. Such expansion may lead to damage of the injection unit, and therefore different SCR strategies exist for addressing the expansion of the reductant.

There are two known SCR system strategies on the market: purging systems and non-purging systems. In a scavenged SCR system, the reductant urea and/or DEF solution is scavenged from the RDU when the vehicle engine is shut off. In a non-scavenging SCR system, reductant remains in the RDU throughout the life of the vehicle. During normal operation of a non-scavenging SCR system, the RDU injector is operated at a temperature above the freezing point of the reductant such that the reductant in the RDU remains in a liquid state. However, when the vehicle engine is shut down in a non-scavenged SCR system, the RDU injector remains filled with reductant, making the RDU injector vulnerable to damage from expansion of the reductant under freezing conditions.

Disclosure of Invention

The exemplary embodiments overcome the disadvantages found in prior RDU fluid injectors and provide improved fluid injectors for non-scavenging SCR systems with reduced adverse effects of RDU being at temperatures below the freezing point of the reductant. According to an exemplary embodiment, the RDU includes a fluid ejector having: a fluid inlet disposed at the first end of the fluid injector and for receiving a reductant; and a fluid outlet disposed at the second end of the fluid injector and configured to discharge the reductant. The fluid injector defines a fluid path for reductant from a fluid inlet to a fluid outlet. The fluid ejector further includes: a tube member having an end disposed at or near a fluid inlet of the fluid injector, the tube member configured to convey a reductant along the fluid path; a filter disposed in the tube member proximate a fluid inlet of a fluid ejector; and a calibrated filter tube disposed in the tube member downstream of the filter with respect to a flow direction of the reducing agent along the fluid path from the fluid inlet to the fluid outlet of the fluid injector, the calibrated filter tube having: a first end adjacent the filter; and a second end, and further comprising an aperture defined in an axial direction through the calibration filter tube, the aperture defining at least a portion of a fluid path through the fluid ejector. An actuator unit is disposed within the fluid ejector downstream of the calibrated filter tube, the actuator unit engaging the second end of the calibrated filter tube. The valve assembly is operatively connected to the actuator unit, wherein the position of the calibrated filter tube within the tube member at least partially sets the opposing opening force of the valve assembly. The volume reducing member has an aperture through which the calibrated filter tube extends, the volume reducing member occupying the space between the outer surface of the calibrated filter tube and the inner surface of the tube member. In an exemplary embodiment, the filter, the calibrated filter tube, and the volume reducing member form an integral subassembly component of the fluid ejector.

In an exemplary embodiment, the volume reducing member is formed of a compressible material, the compressible material being one of a rubber composition and a closed cell foam.

In an exemplary embodiment, the volume reducing member includes a sidewall that is contoured in a direction along a longitudinal axis of the fluid injector.

The fluid injector may also include a cap member including a sidewall defining an interior space in which the filter is disposed, the sidewall contacting the first end of the calibrated filter tube. The first end of the calibrated filter tube is disposed in the interior space of the cap member. The first end of the calibrated filter tube may be attached to the sidewall of the cap member such that the calibrated filter tube, the cap member, the volume reduction member, and the filter form an integral subassembly component of the fluid injector.

The actuator unit may include: a pole piece disposed in a fixed position within the fluid injector and having a bore defined axially therethrough; and an armature movably positioned within the fluid injector and having a pocket. The actuator unit may further comprise a coil disposed adjacent the pole piece and the armature; and a spring disposed at least partially in the pocket of the armature. In an exemplary embodiment, the calibrated filter tube is disposed in the bore of the pole piece such that the second end of the calibrated filter tube contacts the spring, and the spring biases the armature away from the pole piece in the absence of current through the coil, such that the valve assembly is placed in a closed position to prevent passage of reductant through the fluid outlet.

The calibrated filter tube includes a second portion extending axially from the first end of the calibrated filter tube and a third portion disposed between the second portion and the second end of the calibrated filter tube. The volume reducing member is disposed about the second portion, the third portion is disposed in the bore of the pole piece, and a downstream end of the volume reducing member is proximate an upstream end of the pole piece relative to a flow direction of the reductant along the fluid path.

The outer diameter of the second portion of the calibrated filter tube may be greater than the outer diameter of the third portion thereof.

In another exemplary embodiment, an RDU fluid ejector has a fluid inlet disposed at a first end and configured to receive a fluid, and a fluid outlet disposed at a second end of the fluid ejector for discharging the fluid, the fluid ejector defining a fluid path for the fluid from the fluid inlet to the fluid outlet. The tube member has an end disposed at or near a fluid inlet of the fluid ejector, the tube member configured to convey a fluid along a fluid path. A filter is disposed in the tube member proximate the fluid inlet of the fluid ejector. A calibrated filter tube is disposed in the tube member downstream of the filter with respect to a fluid flow direction along the fluid path from the fluid inlet to the fluid outlet of the fluid ejector. The calibrated filter tube has a first end adjacent the filter, a second end, and an aperture defined in an axial direction through the calibrated filter tube, the aperture defining at least a portion of a fluid path through the fluid ejector. An actuator unit is disposed within the fluid ejector downstream of the calibrated filter tube, the actuator unit engaging the second end of the calibrated filter tube. The valve assembly is operatively connected to the actuator unit, wherein calibrating the position of the filter tube within the tube member sets the opposing opening force of the valve assembly. The fluid injector also includes a cap member having a sidewall defining an interior space in which the filter is disposed. In an exemplary embodiment, the sidewall contacts and is attached to the first end of the calibrated filter tube such that the cap member, the filter, and the calibrated filter tube form a single subassembly component of the fluid ejector.

Drawings

Aspects of the invention will be described in detail below with reference to exemplary embodiments in conjunction with the following drawings, wherein:

FIG. 1 is a cross-sectional side view of an RDU for a non-scavenging SCR system in accordance with an exemplary embodiment;

FIG. 2 is a cross-sectional side view of a fluid ejector of the RDU of FIG. 1;

FIG. 3 is an enlarged cross-sectional view of an inlet portion of the fluid ejector of the RDU of FIG. 1 in accordance with an exemplary embodiment;

FIG. 4 is an exploded perspective view of components of the fluid ejector of the RDU of FIG. 1 in accordance with an exemplary embodiment;

FIG. 5 is an enlarged cross-sectional view of an outlet portion of the fluid ejector of the RDU of FIG. 1 in accordance with an exemplary embodiment;

FIG. 6 is an enlarged cross-sectional view of an inlet portion of the fluid ejector of the RDU of FIG. 1 in accordance with another exemplary embodiment;

FIG. 7 is an exploded perspective view of components of the fluid ejector of FIG. 6;

FIG. 8 is a cross-sectional view of the component of FIG. 6;

FIG. 9 is an enlarged cross-sectional view of an inlet portion of the fluid ejector of the RDU of FIG. 1 in accordance with yet another exemplary embodiment;

FIG. 10 is a cross-sectional view of components of the fluid ejector of FIG. 9;

FIG. 11 is a perspective view of components of the fluid ejector of FIG. 9;

FIG. 12 is a cross-sectional view of an inlet portion of the fluid ejector of the RDU of FIG. 1 in accordance with another exemplary embodiment;

FIG. 13 is a cross-sectional view of integral components of the fluid ejector of FIG. 12;

FIG. 14 is an exploded perspective view of components of the fluid ejector of FIG. 13;

FIG. 15 is a cross-sectional view of an inlet portion of the fluid ejector of the RDU of FIG. 1 in accordance with another exemplary embodiment;

FIG. 16 is a cross-sectional view of integral components of the fluid ejector of FIG. 15;

fig. 17 is an exploded perspective view of components of the fluid ejector of fig. 15.

Detailed Description

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

Exemplary embodiments are generally directed to RDUs for non-scavenged SCR systems in which the damaging effects of reductant, DEF, and/or urea solution freezing in the RDU injector are reduced.

FIG. 1 illustrates an RDU10 of a non-scavenging SCR system in accordance with an exemplary embodiment. The RDU10 includes a solenoid fluid injector, generally indicated at 12, that provides a metering function for the fluid and, in a metered application, provides a spray preparation of the fluid into the exhaust path of the vehicle. Thus, fluid injector 12 is constructed and arranged to be associated with an exhaust flow path upstream of a Selective Catalytic Reduction (SCR) catalytic converter (not shown). The fluid injector 12 may be an electric solenoid fuel injector. As shown in fig. 1 and 2, the fluid injector 12 includes an actuator unit having a coil 14 and a movable armature 16. The components of the injector 12 define a fluid path for the reductant, DEF, and/or urea solution through the injector 12. For simplicity, the reductant, DEF, and/or urea solution that the RDU10 is configured to inject into the exhaust path of a vehicle engine is hereinafter referred to as the "reductant".

Fluid ejectors 12 are disposed in an internal tray 18 of RDU10, as shown in fig. 1. A sprayer shroud, generally indicated at 20, is formed of an upper shroud 20A and a lower shroud 20B, the upper shroud 20A and the lower shroud 20B surrounding the sprayer 12 and being connected to the bracket 18 by folding the tangs of the flanges 22 of the lower shroud 20B over the shelf features of the bracket 18 and the upper shroud 20A. As a result, shroud 20 and carrier 18 are fixed relative to injector 12.

The inlet cup structure (generally indicated at 24 in fig. 1) of the RDU10 includes a cup 26 and a fluid supply tube 28 integrally formed with the cup 26. Fluid supply line 28 communicates with a reductant source (not shown) that is delivered to a fluid inlet 30 of injector 12 for injection from a fluid outlet 32 thereof and into the exhaust stream of a vehicle engine (not shown). The fluid inlet 30 of the ejector 12 is in fluid communication with the fluid supply conduit 28. The fluid outlet 32 is fluidly connected to the flange outlet 34 of the exhaust flange 36, and the exhaust flange 36 is directly connected to the end of the lower shroud 20B of the RDU 10.

Injector 12 includes an injector body structure in which components of injector 12 are disposed. The injector body structure includes: the first injector body portion 38, the coil 14 and the armature 16 are disposed in the first injector body portion 38; and a valve body portion 40, the valve assembly of injector 12 being at least partially disposed in valve body portion 40. The first injector body portion 38 and the valve body portion 40 are fixedly connected to one another, either directly or indirectly.

Referring to fig. 1-3, fluid injector 12 includes a tube member 42, with tube member 42 at least partially disposed within first injector body portion 38. The outer surface of the tube member 42 contacts the inner surface of the first injector body portion 38. An open end of the tube member 42 is disposed within the cup 26 and is in fluid communication with the fluid supply tube 28. An O-ring 44 is disposed within the cup 26 between its inner surface and the outer surface of the tube member 42, near the open end of the tube member 42. O-ring 44 is used to ensure that reductant exiting fluid supply tube 28 enters the open end of tube member 42 of injector 12.

The actuator unit of fluid injector 12 also includes a pole piece 46, pole piece 46 being fixedly disposed within first injector body portion 38. The coil 14 at least partially surrounds the pole piece 46 and the armature 16. A pole piece 46 is disposed within the injector 12 upstream of the armature 16. The pole piece 46 includes a central bore defined axially therethrough.

The armature 16 includes a U-shaped section that defines a pocket in which at least a portion of the spring 50 is disposed. The spring 50 is part of the actuator unit and biases the movable armature 16 such that the armature 16 is spaced from the pole piece 46 when no current is passed through the coil 14. The spring 50 extends partially within the central bore of the pole piece 46. The end of the spring 50 extending within the pole piece 46 is in contact with a spring adjustment tube 52. A spring adjustment tube 52 is at least partially disposed within the central bore of pole piece 46 upstream (relative to the direction of flow of reductant through injector 12) of spring 50. The spring adjustment tube 52 includes a bore defined axially therethrough. The through-hole of spring-regulated tube 52 partially defines a fluid path for the reductant in fluid injector 12 and defines the only fluid path for the reductant through pole piece 46. Spring regulator tube 52 is used to calibrate the dynamic flow of reductant through fluid injector 12 due to its engagement with spring 50.

The armature 16 also includes one or more passages 60 (fig. 1 and 2) defined through the armature 16 from the interior of the pocket to the upstream end of the pin member 58. The channels 60 may be equally spaced around the armature 16. In the exemplary embodiment, armature 16 includes a single channel that is defined completely around the base of the pocket formed by pocket wall 16A. The passage 60 allows reductant to flow from the pocket of the armature 16 to the space around the upstream end of the pin member 58. Together, the pockets of armature 16 and passage 60 partially define the reductant fluid path of fluid injector 12 and define the only portion of the fluid path that passes through or around armature 16.

Referring to fig. 1, 2, and 5, the valve assembly of injector 12 includes a sealing member 54 and a seat 56. The sealing member 54 is connected to the armature 16 by a pin member 58, the pin member 58 being disposed between the sealing member 54 and the downstream end of the armature 16. The sealing member 54, the pin member 58, and the armature 16 may combine to form an armature assembly. When the coil 14 is energized, the coil 14 generates an electromagnetic force acting on the armature 16 that overcomes the biasing force from the spring 50 and moves the armature 16 toward the pole piece 46, which in turn moves the pin member 58 such that the seal member 54 is lifted and disengages from the seat 56, thereby moving the armature assembly to the open position and thus allowing reductant to pass through the fluid outlet 32 to the flange outlet 34 and into the exhaust path of the vehicle engine. When the coil 14 is de-energized, the electromagnetic force dissipates and the spring 50 biases the armature 16 to move the armature 16 away from the pole piece 46, causing the sealing member 54 to sealingly engage the seat 56, changing the armature assembly back to the closed position. With the armature assembly in the closed position, reductant is prevented from flowing through the seat 56 and the flange outlet 34 and into the exhaust path of the vehicle engine.

As noted above, RDU10 forms part of a non-scavenging SCR exhaust aftertreatment system. As a result, reductant remains in fluid injector 12 after the vehicle engine is shut off. In the exemplary embodiment, fluid injector 12 is configured such that an amount of reductant in fluid injector 12 is reduced. In other words, the total volume of the fluid path of the reductant through fluid injector 12 is reduced. By having less reductant space in injector 12, the amount of reductant in RDU10 that may potentially freeze is reduced, thereby reducing the susceptibility of injector 12 to damage by the expansive forces of the frozen reductant.

To reduce the volume of the reductant fluid path in fluid injector 12, the thickness of valve body portion 40 is increased. In addition, the pin member 58 is configured as a solid element such that the reductant flows around the outer surface of the pin member 58 rather than through it. The spacing between the outer surface of pin 58 and the inner surface of valve body portion 40 is narrowed, which partially defines the fluid path for the reductant through injector 12. This narrowed portion of the fluid path is the only fluid path for the reductant between the armature 16 and the seat 56 in the fluid injector 12. The narrowed fluid path between pin 58 and valve body portion 40 provides a sufficient flow rate of reductant through fluid injector 12 to perform reductant injection during normal operation of RDU10 while maintaining a relatively small volume of reductant within injector 12 to reduce the risk of injector 12 being damaged by freezing of reductant therein.

Furthermore, the diameter of the pocket of the armature 16 (in which the spring 50 is at least partially disposed) is reduced, which allows the thickness of the pocket wall 16A of the armature 16 to be increased. In an exemplary embodiment, the thickness of pocket wall 16A is between 45% and 75% of the pocket diameter, e.g., about 60%. The increased thickness of the pocket wall 16A, as well as the increased thickness of the valve body portion 40 and the pin member 50 being a solid pin, results in the components of the injector 12 being reinforced and thus more resistant to reductant freezing forces.

Further, the bore of spring regulated tube 52 is sized for reducing the volume of the reductant fluid path in injector 12. In an exemplary embodiment, the diameter of the bore of the spring adjustment tube 52 is between 12% and 22%, particularly between 16% and 19%, of the outer diameter of the pole piece 46.

Fig. 3 shows an upstream portion of the ejector 12. The tube member 42 extends at least partially through the injector 12. The reductant fluid path through injector 12 passes through a tube member 42. The eductor 12 includes a filter 204 disposed in the tube member 42 near the open end thereof. The filter 204 is a sintered metal filter that is structurally rigid, such as a stainless steel material, to better withstand the expansion forces from the freezing of the reducing agent. The filter 204 may have a supporting outer structure for added strength. As best shown in fig. 3, the filter 204 is disposed within the cap member 206. The cap member 206 is generally cylindrical with a circumferentially extending sidewall 206A that defines an interior volume sized to receive the filter 204 therein. The cap member 206 is sized to fit within the tube member 42, and in particular such that the outer surface of the sidewall 206A of the cap member 206 contacts the inner surface of the tube member 42. The cap member 206 also includes an annular member 206B disposed along an axial end of the cap member 206 and extending radially inward from the sidewall 206A. The annular member 206B is used to hold the filter 204 in a fixed position within the cap member 206. The cap member 206 is constructed of metal or similar composition.

The injector 12 also includes a retaining ring 207 disposed in the tube member 42 upstream of the cap member 206 and in contact with the cap member 206, as shown in fig. 1-3. The retaining ring 207 is secured along its inner surface to the tube member 42. A retaining ring 207 secured in place along tube member 42 is used to retain downstream components of injector 12 in a fixed position within first injector body portion 38. In the exemplary embodiment, retaining ring 207 is welded along an inner surface of tube member 42. This welded connection is formed along the entire periphery of the upper edge of the retaining ring 207. It should be understood, however, that other attachment mechanisms may be used to secure the retaining ring 207 to the tube member 42.

1-4, injector 12 also includes a volume reducing member 208 for further reducing the volume of the reductant fluid path within injector 12. The reducing member 208 is generally cylindrical in shape, as shown in FIG. 4, having a top (upstream) end and a bottom (downstream) end. In one embodiment, the volume-reducing member 208 is constructed of a metal, such as stainless steel. It should be understood that the volume-reducing member 208 may be formed from other metals or metal compositions. The outer surface of the volume reducing member 208 is sized to contact the inner surface of the tubular member 42.

The volume reducing member 208 also includes a bore 208A (fig. 2 and 3) defined through the volume restraining member 208 in an axial direction from one axial (top) end to the other axial (bottom) end. Bore 208A is located along a longitudinal axis of reduced-volume member 208 and itself forms a portion of a fluid path for the reductant to pass through injector 12. The aperture 208A forms the only fluid path for the reductant to pass through or around the volume reducing member 208. In an exemplary embodiment. The diameter of the aperture 208A is between 12% and 20%, for example about 16%, of the outer diameter of the volume reducing member 208. Because volume reducing member 208 extends radially to the inner surface of tube member 42, and because the diameter of bore 208A is small relative to the outer diameter of volume reducing member 208, volume reducing member 208 reduces the space or volume in which reductant may reside within injector 12, thereby reducing the volume of the fluid path of the reductant therein. Volume reducing member 208 also helps to hold spring adjustment tube 52 in place within injector 12 so that pin adjustment tube 52 maintains the required force on spring 50, thereby preventing loss of calibration. Specifically, the retaining ring 207 maintains the position of the filter 204 and the corresponding cap member 206, which maintains the position of the volume reducing member 208, which maintains the position of the spring adjustment member 52.

Referring to fig. 1-4, fluid injector 12 further includes a volume compensation member 210 disposed between a bottom (downstream) end of volume reduction member 208 and a top of pole piece 46. Volume compensating member 210 is constructed of an elastomeric material and is configured to occupy the space between volume reducing member 208 and pole piece 46 to further reduce the volume of the reductant fluid path in injector 12. When assembled, volume compensation member 210 may be in a compressed state in injector 12 and contact volume reduction member 208, pole piece 46, the inner surface of tube member 42, and the outer surface of spring adjustment member 52.

Fig. 5 shows the downstream end of the fluid ejector 12. It can be seen that the seat 56 includes a bore defined axially through the seat 56. In the exemplary embodiment, the length of the through-hole of seat 56 is reduced to further reduce the volume of the reductant fluid path through seat 56, and in particular, the pressure chamber (sac) volume below the sealing band of seat 56 that engages sealing member 54.

According to an exemplary embodiment, fluid ejector 12 includes a plurality of orifice discs 212 disposed in a stacked arrangement. The orifice disc stack is disposed against the downstream end of the seat 56. In the exemplary embodiment shown in fig. 5, the disc stack includes a first disc 212A having one or more apertures configured to provide a desired spray pattern of reductant exiting injector 12. It should be appreciated that the size and location of the apertures of the first disk 212A may vary and depend on the reductant dosing requirements of a particular vehicle engine. The disc stack further includes a second disc 212B, the second disc 212B being disposed downstream of the first disc 212A and including holes through which the reducing agent is sprayed. The second disk 212B has a thickness greater than that of the first disk 212A and is disposed against the first disk 212A and supports the first disk 212A to prevent the thinner first disk 212A from being deformed by an expansion force from the frozen reducing agent upstream of the first disk 212A.

As described above, fluid injector 12, and in particular components thereof, are configured to reduce the volume of the reductant fluid path in injector 12. In the exemplary embodiment, a ratio of a volume of a fluid path in fluid injector 12 to a volume of components of injector 12 (including, but not necessarily limited to, coil 14, armature 16, pole piece 46, spring adjustment tube 52, volume reduction member 208, volume compensation member 210, filter 204, retaining ring 207, spring 50, pin member 58, seal member 54, seat 56, first injector body portion 20A, and valve body portion 40) is between 0.08 and 0.30, specifically between 0.12 and 0.20, such as approximately 0.15. These volumetric quantities are calculated between perpendicular planes relative to the longitudinal axis of fluid injector 12-from a first plane along the open end of tube member 42 (i.e., fluid inlet 30) and a second plane along the lowermost (downstream) surface of second disk 212B (i.e., fluid outlet 32). It should be appreciated that the particular ratio of the volume of the reductant path to the volume of the injector components within fluid injector 12 may vary depending on a number of cost and performance related factors, and may be any value between approximately 0.08 and approximately 0.30. Providing a fluid injector having a reduced ratio of reductant fluid path volume to injector component volume to fall within the above-described ranges advantageously results in less reductant in injector 12, which reduces the susceptibility of RDU10 to damage if the reductant in injector 12 freezes.

In another exemplary embodiment, as shown in fig. 6-8, fluid injector 12 includes a volume reducing member 308 having many of the features of volume reducing member 208 discussed above with respect to fig. 1-5. Similar to volume reducing member 208, volume reducing member 308 is constructed of stainless steel or a similar composition and is disposed in tube member 42 of fluid injector 12 between volume compensating member 210 and filter 204. However, the volume-reducing member 308 includes a first portion 308A and a second portion 308B. As shown in fig. 7, each of the first portion 308A and the second portion 308B has a cylindrical shape, and the outer diameter of the first portion 308A is smaller than the outer diameter of the second portion 308B. The outer diameter of the first portion 308A is less than the diameter of the second portion 308B by the thickness of the sidewall 306A of the cap member 306, as will be explained in more detail below. The volume-reducing member 308 includes top (upstream) and bottom (downstream) ends that form axial ends of the first portion 308A and the second portion 308B, respectively. The outer surface of the second portion 308B is sized to contact the inner surface of the tubular member 42.

As mentioned, the first portion 308A of the volume reducing member 308 has an outer diameter that is less than an outer diameter of the second portion 308B thereof. As shown in fig. 6-8, the volume-reducing member 308 includes an angled annular surface or skirt 308D that extends in an axial direction between an outer surface of the first portion 308A and an outer surface of the second portion 308B and serves as a physical interface therebetween. The angle of the angled surface 308D relative to the longitudinal axis of the volume reducing member 308 and/or the injector 12 is acute. Optionally, the angle of angled surface 308D is perpendicular to the longitudinal axis of volume reducing member 308 and/or injector 12.

The volume reducing member 308 also includes a bore 308C, the bore 308C defined through the volume restraining member 308 in an axial direction from one axial (top) end to the other axial (bottom) end. The aperture 308C is located along the longitudinal axis of the volume reducing member 308 and itself forms part of the reductant fluid path for the reductant to pass through the injector 12 and is the only reductant fluid path through or around the volume reducing member 308. In the exemplary embodiment, a diameter of bore 308C is between 12% and 20%, such as about 16%, of an outer diameter of volume-reducing member 308. Because volume reducing member 308 extends to the inner surface of tube member 42 and because the diameter of bore 308C is relatively small relative to the outer diameter of volume reducing member 308, volume reducing member 308 occupies a volume within injector 12 that reduces the space or volume of the reductant fluid path through injector 12, thereby reducing the amount of reductant in injector 12 that may freeze and possibly damage injector 12.

The cap member 306 includes many of the same features of the cap member 206 described above with reference to fig. 1-5. As shown in FIG. 7, the cap member 306 is generally cylindrical in shape, having a sidewall 306A extending circumferentially and defining an interior volume sized to receive the filter 204 therein. The cap member 306 is sized to fit within the tube member 42, and in particular such that the outer surface of the sidewall 306A of the cap member 306 contacts the inner surface of the tube member 42. Cap member 306 also includes an annular member 306B disposed along an axial (upstream) end of cap member 306 and extending radially inward from sidewall 306A. The ring member 306B is used to hold the filter 204 in a fixed position within the cap member 306. Similar to the cap member 206, the cap member 306 is constructed of metal or similar composition and provides structural support for the filter 204.

In the exemplary embodiment, cap member 306 is engaged with volume reducing member 308 and is secured to volume reducing member 308. In this manner, the filter 204, the cap member 306, and the volume-reducing member 308 form a single, unitary component, as shown in FIG. 8. Having a single unitary component formed by filter 204, cap member 306, and volume reduction member 308 advantageously allows for a simpler and less complex process for assembling injector 12 during its manufacture.

In the exemplary embodiment, cap member 306 fits over and engages or is otherwise attached to at least a portion of first portion 308A of volume reducing member 308, as shown in fig. 6 and 8. In an exemplary embodiment, cap member 306 forms a press fit engagement with first portion 308A. In another exemplary embodiment, cap member 306 is welded to first portion 308A, such as a fillet weld between bottom surface 306C of cap member 306 and a radially outer surface of first portion 308A. In each such embodiment, angled surface 308D provides sufficient spacing to secure cap member 306 to first portion 308A. It should be appreciated that the cap member 306 may be secured to the first portion 308A of the volume reducing member 308 by other mechanisms.

With the cap member 306 fitted over the first portion 308A of the volume reducing member 308, the outer diameter of the sidewall 306A is the same or nearly the same as the outer diameter of the second portion 308A. See fig. 6 and 8.

As described above, according to an exemplary embodiment, the volume-reducing member 308 is composed of a metal (e.g., stainless steel). In another exemplary embodiment, a portion of the second portion 308B is constructed of plastic or similar composition. Specifically, as shown in fig. 9-11, the first portion 308A and the first section 308B-1 of the second portion 308B are formed as a single metal member, and the second section 308B-2 of the second portion 308B is plastic overmolded around its first section. FIG. 11 shows a first section 308B-1 of a metallic first portion 308A and a second portion 308B. The first section 308B-1 of the second portion 308B includes an intermediate section 308B-3 that extends away from the first portion 308A in the axial (downstream) direction, and a distal section 308B-4 that is attached to and extends in the axial (downstream) direction from the intermediate section 308B-3, as shown in FIG. 10. Distal segment 308B-4 extends further in a radial direction from the longitudinal axis of volume-reducing member 308 (and/or injector 12) than the radial extension of intermediate segment 308B-3, forming a ledge. The second section 308B-2 of the second portion 308B, which is made of overmolded plastic or other similar composition, is formed around the ledge formed by the intermediate section 308B-3 and the distal section 308B-4 to form the volume-reducing member 308 as a single, integral, unitary component. As described above, volume reducing member 308 is coupled to cap member 306 so as to result in volume reducing member 308, filter 204, and cap member 306 forming a single assembly component for assembling injector 12.

During assembly of injector 12, the individual assembly components (filter 204, cap member 306, and volume reduction member 308) are inserted under pressure within tube member 42 while contacting volume compensator 212. After insertion and while still under pressure, the cap member 306 is welded to the tube member 42 along the top of the tube member 42 all along its intersection. In one embodiment, the welded connection is a fillet weld.

FIG. 12 illustrates a fluid ejector 12 according to another exemplary embodiment. In this embodiment, fluid injector 12 includes a filter 204 and a cap member 306, with filter 204 disposed in cap member 306, as described above. In addition, the fluid ejector 12 includes a calibrated filter tube 402 and a volume reduction member 408. The calibration filter tube 402 includes an aperture 402A defined axially through the calibration filter tube 402. At one (upstream) end of the calibrated filter tube 402, the aperture 402A is in fluid communication with the filter 204 for receiving reductant therefrom. At the other (downstream) end of the calibrated filter tube 402, the orifice 402A provides the reducing agent to the armature 16. In this manner, the calibrated filter tube 402 forms a portion of the fluid path of the reductant through the fluid injector 12 and forms the only such fluid path from the filter 204 to the armature 16. With the diameter of the bore 402A of the calibration filter tube 402 being small relative to the inner diameter of the tubular member 42, the volume of the fluid path of the reductant through the injector 12 is reduced, thereby reducing the adverse effects of freezing of the reductant therein.

As shown in fig. 12-14, the calibration filter tube 402 also includes a first end 402B that is at least partially disposed within the cap member 306 and contacts the filter 204. First end 402B is generally disc-shaped having a sidewall 402C in contact with an inner surface of sidewall 306A of cap member 306. In the exemplary embodiment, first end 402B of calibration fluid member 402 is attached to cap member 306 such that cap member 306, filter 204, and calibration filter tube 402 form a single, integral, unitary subassembly component to facilitate simplified assembly of fluid injector 12. In one exemplary embodiment, cap member 306 engages, and particularly forms a press fit engagement with, first end 402B. In another exemplary embodiment, cap member 306 is welded to first end 402B, e.g., a fillet weld connection between an axial end of sidewall 306A of cap member 306 and an outer surface of sidewall 402C of first portion 402A. It should be appreciated that alternatively or additionally, the cap member 306 may be secured to the first end 402B of the calibration filter tube 402 using other techniques.

The calibration filter tube 402 also includes an elongated second portion 402D that extends in an axial direction from the first portion 402A, as shown in fig. 12-14. The second portion 402D is sized to extend into the pole piece 46 such that a second end 402E opposite the first end 402B engages the spring 50 (fig. 12). The second portion 402D is generally cylindrical with a bore 402A disposed therein. The calibration filter tube 402 also includes an annular tab 402F that extends radially outward from the outer surface of the second portion 402D. The tabs 402F extend slightly outwardly from the outer surface of the second portion 402D of the calibration filter tube 402 and are positioned along the second portion 402D so as to contact the inner surface of the pole piece 46 defining its central bore. This contact between the tabs 402F and the central bore of the pole piece 46 results in a press-fit attachment of the calibrated filter tube 402 to the pole piece 46.

As described above, the second end 402E of the calibration filter tube 402 is in contact with and engages the spring 50. Due to the engagement between the calibration filter tube 402 and the spring 50 and the engagement between the armature 16 and the spring 50, the calibration filter tube 402 is used to calibrate the dynamic flow of reductant through the fluid injector 12. In particular, where cap member 306, filter 204, and calibration filter tube 402 are formed as a single, unitary, integral subassembly component, positioning of calibration filter tube 402 at a desired location within tube member 42 prior to welding cap member 306 thereto is simplified for providing the required calibration force for spring 50.

The calibration filter tube 402 is formed from a metallic composition, such as stainless steel.

With continued reference to fig. 12-14, the ejector 12 further includes a volume reduction member 408 disposed about the second portion 402D of the calibration filter tube 402. The volume reducing member 408 has a cylindrical shape with a central bore defined axially through the volume reducing member 408. The central bore of the volume reducing member 408 is sized to receive the calibrated filter tube 402 therein. As shown in fig. 12, the outer radial surface of the volume reducing member 408 contacts the inner surface of the tubular member 42. One axial (upstream) end of the volume reducing member 408 is disposed adjacent to and in contact with the first end 402B of the calibration filter tube 42, and the other axial (downstream) end of the volume reducing member 408 is disposed against and in contact with the upstream end of the pole piece 46. In this manner, the volume reducing member 408 occupies the space between the second portion 402D of the calibrated filter tube 402 and the tube member 42, which is upstream of the pole piece 46 and downstream of the first end 402B of the calibrated filter tube 402. In the exemplary embodiment, volume reduction member 408 is attached to calibration filter tube 402 such that volume reduction member 408 forms a single, integral, unitary subassembly component with cap member 306, filter 204, and calibration filter tube 402.

In the exemplary embodiment, volume reducing member 408 is composed of a resilient and compressible material and is compressible at least along an axial direction of fluid injector 12. Volume reducing member 408 is compressible in an axial direction allowing the individual assembly components (cap member 306, filter 204, and calibration filter tube 402) to be adjustably positioned within tube member 42 relative to pole piece 46 such that the opening and closing forces of the valve assembly of fluid injector 12 may be easily calibrated as desired. In one embodiment, the volume reducing member 408 is constructed of closed cell foam. It should be understood that the volume reducing member 408 may be constructed of other compressible materials. If constructed of closed cell foam, the volume reducing member 408 is compressible in both the axial (longitudinal) and radial (transverse) directions. In the exemplary embodiment, volume reducing member 408 is in a compressed state within fluid injector 12.

15-17 illustrate a fluid ejector 12 according to another exemplary embodiment. In this embodiment, fluid injector 12 includes a filter 204 and a cap member 306, with filter 204 disposed in cap member 306, as described above. In addition, fluid ejector 12 includes a calibrated filter tube 502. The calibrated filter tube 502 shares many of the features of the calibrated filter tube 402 described above with reference to FIGS. 12-14.

The calibration filter tube 502 includes an aperture 502A defined axially through the calibration filter tube 502. At one (upstream) end of the calibrated filter tube 502, an aperture 502A is in fluid communication with the filter 204 for receiving reductant therefrom. At the other (downstream) end of the calibration filter tube 502, an orifice 502A provides reducing agent to the armature 16. In this manner, calibrated filter tube 502 forms a portion of the fluid path for the reductant through fluid injector 12 and forms the only such fluid path from filter 204 to armature 16. With the diameter of the bore 502A of the calibration filter tube 502 being small relative to the inner diameter of the tube member 42, the volume of the fluid path of the reductant through the injector 12 is reduced, thereby reducing the adverse effects of freezing of the reductant therein.

As shown in fig. 15-17, the calibration filter tube 502 also includes a first end 502B that is at least partially disposed within the cap member 306 and contacts the filter 204. First end 502B is generally disc-shaped having a sidewall 502C in contact with an inner surface of sidewall 306A of cap member 306. In the exemplary embodiment, first end 502B of calibration fluid member 502 is attached to cap member 306 such that cap member 306, filter 204, and calibration filter tube 502 form a single, integral, unitary subassembly component to facilitate simplified assembly of fluid injector 12. In one exemplary embodiment, cap member 306 engages, and particularly forms a press fit engagement with, first end 502B. In another exemplary embodiment, cap member 306 is welded to first end 502B, e.g., a fillet weld connection between an axial end of sidewall 306A of cap member 306 and an outer surface of sidewall 502C of first portion 502B. It should be understood that cap member 306 may additionally or alternatively be secured to first end 502B of calibration filter tube 502 using other techniques.

The calibration filter tube 502 also includes an elongated second portion 502D extending in an axial direction from the first portion 502A, and an elongated third portion 502E extending in an axial direction from the second portion 502D, as shown in fig. 15-17. The third portion 502E is sized to extend into the pole piece 46 such that a second end 502F of the calibration filter tube 502 opposite the first end 502B engages the spring 50 (fig. 12). The second portion 502D and the third portion 502E are generally cylindrical with a bore 502A disposed therein.

In the exemplary embodiment, an outer diameter of second portion 502D is greater than an outer diameter of third portion 502E. The outer diameter of the third portion 502E is sized to be received in the central bore of the pole piece 46.

The calibration filter tube 502 also includes an annular tab 502G (fig. 17) that extends radially outward from the outer surface of the third portion 502E. The tabs 502G extend slightly outwardly from the outer surface of the third portion 502E of the calibration filter tube 502 and are positioned axially therealong so as to contact the inner surface of the pole piece 46 defining its central bore. This contact between the tabs 502G and the central bore of the pole piece 46 results in the calibrated filter tube 502 forming a press-fit engagement with the pole piece 46.

The calibrated filter tube 502 is formed from a metallic composition, such as stainless steel.

As described above, the second end 502F of the calibrated filter tube 502 is in contact with and engaged by the spring 50. Due to the engagement between the calibration filter tube 502 and the spring 50 and the engagement between the spring 50 and the armature 16, the calibration filter tube 502 is used to calibrate the dynamic flow of reductant through the fluid injector 12. In particular, where cap member 306, filter 204, and calibration filter tube 502 are formed as a single, unitary, integral subassembly component, positioning calibration filter tube 502 in a desired position within tube member 42 prior to welding cap member 306 thereto is simplified for providing the required calibration force for spring 50 to set the opposing opening and closing forces of the valve assembly of fluid injector 12.

With continued reference to fig. 15-17, the ejector 12 further includes a volume reducing member 508 disposed about the second portion 502D of the calibration filter tube 502. The volume reducing member 508 has a generally cylindrical shape with a central bore defined axially through the volume reducing member 508. The central bore of the volume reducing member 508 is sized for receiving the second portion 502D of the calibration filter tube 502 therein. As shown in fig. 12, the outer radial surface of the volume reducing member 508 contacts the inner surface of the tubular member 42. One axial (upstream) end of the volume reducing member 508 is disposed adjacent to and in contact with the first end 502B of the calibration filter tube 42, and the other axial (downstream) end of the volume reducing member 508 is disposed against and in contact with the upstream end of the pole piece 46. In this manner, the volume reducing member 508 occupies the space between the second portion 502D of the calibration filter tube 502 and the tube member 42, which is upstream of the pole piece 46 and downstream of the first end 502B of the calibration filter tube 502.

In the exemplary embodiment, volume reducing member 508 is composed of a compressible material, such as compressible along fluid ejector 12 at least in an axial direction. Volume reducing member 508 is compressible in at least an axial direction allowing the individual component parts (cap member 306, filter 204, and calibration filter tube 502) to be adjustably positioned within tube member 42 relative to pole piece 46 such that the valve assembly of fluid injector 12 may be calibrated as desired. In the exemplary embodiment, volume reducing member 508 is in a compressed state within fluid injector 12.

As shown in fig. 15-17, the volume-reducing member 508 includes a sidewall 508A extending between two axial ends. A downstream axial end wall 508B of the volume reducing member 508 extends radially inward from the side wall 508A and contacts the outer surface of the third portion 502E of the calibrated filter tube 502. The upstream axial end of the volume reducing member 508 may be open and contact the downstream surface of the first portion 502B of the calibration filter tube 502.

The sidewalls 508A of the volume reducing member 508 are undulating in an axial direction, as shown in fig. 15-17, alternating between sidewall peaks and valleys in an undulating pattern relative to the longitudinal axis of the volume reducing member 508 and/or the injector 12. Having the undulating sidewalls 508A facilitates the sidewalls 508A to be compressible or otherwise partially collapsible in both the axial (longitudinal) and radial (transverse) directions. In an exemplary embodiment, the volume reducing member 508 is constructed of a compressible, resilient material, such as a rubber composition or other similar material. Volume reducing member 508 may be in a compressed state within fluid injector 12.

Example embodiments have been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The description above is merely exemplary in nature and, thus, variations may be made without departing from the spirit or scope of the invention as defined in the appended claims.

Claims

1. A reductant delivery unit, comprising:

a fluid ejector having: a fluid inlet disposed at the first end of the fluid injector and for receiving a reductant; and a fluid outlet disposed at a second end of the fluid injector and configured to discharge the reductant, the fluid injector defining a fluid path for the reductant from the fluid inlet to the fluid outlet, the fluid injector comprising:

a tube member having an end disposed at or near a fluid inlet of the fluid injector, the tube member configured to convey a reductant along the fluid path;

a filter disposed in the tube member proximate a fluid inlet of a fluid ejector;

a calibrated filter tube disposed in the tube member downstream of the filter with respect to a flow direction of the reductant along the fluid path from the fluid inlet to the fluid outlet of the fluid injector, the calibrated filter tube having: a first end adjacent the filter; and a second end, and further comprising an aperture defined in an axial direction through the calibration filter tube, the aperture defining at least a portion of a fluid path through the fluid ejector;

an actuator unit disposed within the fluid ejector downstream of the calibrated filter tube, the actuator unit engaging the second end of the calibrated filter tube;

a valve assembly operably connected to the actuator unit, wherein calibrating the position of the filter tube within the tube member at least partially sets the opposing opening force of the valve assembly; and

a volume reducing member having an aperture through which the calibrated filter tube extends, the volume reducing member occupying the space between the outer surface of the calibrated filter tube and the inner surface of the tube member,

wherein the filter, the calibrated filter tube and the volume reducing member form an integral subassembly component of the fluid ejector.

2. The reductant delivery unit of claim 1, wherein the volume-reducing member is formed of a compressible material.

3. The reductant delivery unit of claim 2, wherein the compressible material includes one of a rubber composition and a closed-cell foam.

4. The reductant delivery unit of claim 2, wherein the volume-reducing member includes a sidewall that is contoured in a direction along a longitudinal axis of the fluid injector.

5. The reductant delivery unit of claim 1, wherein the fluid injector further includes a cap member including a sidewall defining an interior space in which the filter is disposed, the sidewall contacting the first end of the calibrated filter tube.

6. The reductant delivery unit of claim 5, wherein the first end of the calibrated filter tube is disposed in the interior space of the cap member.

7. The reductant delivery unit of claim 5, wherein the first end of the calibrated filter tube is attached to a sidewall of the cap member such that the calibrated filter tube, the cap member, the volume reduction member, and the filter form an integral subassembly component of the fluid injector.

8. The reductant delivery unit of claim 1, wherein the actuator unit includes: a pole piece disposed in a fixed position within the fluid injector and having a bore defined axially therethrough; an armature movably positioned within the fluid injector and including a pocket; a coil disposed adjacent the pole piece and the armature; and a spring disposed at least partially in the pocket of the armature, the calibrated filter tube being disposed in the bore of the pole piece such that the second end of the calibrated filter tube contacts the spring, and the spring biasing the armature away from the pole piece in the absence of current through the coil, whereby the valve assembly is placed in a closed position to prevent reductant from passing through the fluid outlet.

9. The reductant delivery unit of claim 8, wherein the calibrated filter tube includes a second portion extending axially from the first end of the calibrated filter tube and a third portion disposed between the second portion and the second end of the calibrated filter tube, the volume-reducing member being disposed about the second portion, the third portion being disposed in the bore of the pole piece and a downstream end of the volume-reducing member being proximate an upstream end of the pole piece relative to a direction of flow of reductant along the fluid path.

10. The reductant delivery unit of claim 9, wherein the second portion of the calibrated filter tube has an outer diameter greater than an outer diameter of the third portion thereof.

11. A fluid ejector comprising:

a fluid inlet disposed at the first end and configured to receive a fluid, and a fluid outlet disposed at the second end of the fluid ejector and configured to discharge the fluid, the fluid ejector defining a fluid path for the fluid from the fluid inlet to the fluid outlet;

a tube member having an end disposed at or near a fluid inlet of the fluid ejector, the tube member configured to convey fluid along a fluid path;

a filter disposed in the tube member proximate the fluid inlet of the fluid ejector;

a calibrated filter tube disposed in the tube member downstream of the filter with respect to a fluid flow direction along the fluid path from the fluid inlet to the fluid outlet of the fluid ejector, the calibrated filter tube having a first end adjacent the filter and a second end, and further comprising an aperture defined in an axial direction through the calibrated filter tube, the aperture defining at least a portion of the fluid path through the fluid ejector;

a valve assembly operatively connected to the actuator unit, wherein calibrating the position of the filter tube within the tube member sets the opposing opening force of the valve assembly;

a cap member having a sidewall defining an interior space in which the filter is disposed, the sidewall contacting and being attached to the first end of the calibrated filter tube such that the cap member, the filter, and the calibrated filter tube form a single subassembly component of the fluid ejector; and

a volume reducing member having an aperture through which the calibrated filter tube extends, the volume reducing member occupying a space between an outer surface of the calibrated filter tube and an inner surface of the tube member, the volume reducing member, the cap member, the filter, and the calibrated filter tube forming a single subassembly component of the fluid ejector.

12. The fluid ejector of claim 11, wherein the volume reducing member is compressible.

13. The fluid ejector of claim 12, wherein the volume reducing member is formed from one of a rubber composition and a closed cell foam.

14. The fluid ejector of claim 11, wherein the volume reducing member includes a sidewall that undulates along a longitudinal axis of the fluid ejector.

15. The fluid ejector of claim 11, wherein the actuator unit includes: a pole piece disposed in a fixed position within the fluid injector and having a bore defined axially therethrough; an armature movably positioned within the fluid injector and including a pocket; a coil disposed adjacent the pole piece and the armature; and a spring at least partially disposed in the pocket of the armature, wherein the calibrated filter tube is disposed in the bore of the pole piece such that the second end of the calibrated filter tube contacts the spring, the spring biasing the armature away from the pole piece in the absence of current through the coil, whereby the valve assembly is placed in a closed position to prevent fluid from passing through the fluid outlet.

16. The fluid injector of claim 14, wherein the calibrated filter tube includes a second portion extending axially from the first end of the calibrated filter tube and a third portion disposed between the second portion and the second end of the calibrated filter tube, the volume-reducing member disposed about the second portion, the third portion disposed in the bore of the pole piece and a downstream end of the volume-reducing member proximate an upstream end of the pole piece relative to a direction of flow of the fluid along the fluid path.

17. The fluid ejector of claim 16, wherein the outer diameter of the second portion of the calibrated filter tube is greater than the outer diameter of the third portion thereof.

18. The fluid injector of claim 16, wherein the calibration filter tube further comprises an annular tab extending from the third portion of the calibration filter tube, disposed within the bore of the pole piece and in press-fit engagement therewith.

19. The fluid ejector of claim 11, wherein the first end of the calibrated filter tube is disposed in the interior space of the cap member.