LU90704A1

LU90704A1 - High pressure filter cartridge for a high pressure fuel injection system

Info

Publication number: LU90704A1
Application number: LU90704A
Authority: LU
Inventors: Callisto Genco
Original assignee: Delphi Tech Inc
Priority date: 2000-12-18
Filing date: 2000-12-18
Publication date: 2000-12-18
Also published as: LU90704B1

Description

HIGH PRESSURE FILTER CARTRIDGE FOR A HIGH PRESSURE

FUEL INJECTION SYSTEM.

Field of the invention

The present invention relates to a high pressure filter cartridge for a high pressure fuel injection system.

Background of the invention

Today, fuel injection systems for Diesel engines have working pressures from 1000 to 2000 bar and it is not excluded that even higher working pressures will be used in the near future. Fuel injection systems with working pressures above 1000 bar will be referred to hereinafter as high pressure fuel injection systems.

As fuel injectors for high pressure fuel injection systems include a fuel injection control valve requiring high actuating forces and very short actuation times, they are equipped with an actuator having a very small actuation stroke, i.e. generally less than 50 pm. There is consequently a serious risk that these high pressure fuel injection valves stick in an open or closed position when solid particles with a size comparable to the stroke range are introduced with the fuel into an actuation chamber of the injector or between the injector needle and the injector nozzle. Electromagnetic fuel injectors, i.e. fuel injectors with a solenoid and a magnetic armature, are moreover exposed to the risk of accumulation of metallic particles on the magnetic armature, what may also result in a sticking of the injector in an open or closed position.

All fuel injection systems have a low pressure fuel filter in their low pressure circuit. This filter is capable of filtering particles down to 3 pm, but it does not protect the fuel injector against particles which have their origin in the high pressure circuit, such as e.g. small metallic chips introduced in the high pres sure circuit during assembling or maintenance of the high pressure circuit or small metallic chips due to abrasion problems downstream of the low pressure fuel filter.

In order to protect the high pressure fuel injector against particles having their origin in the high pressure circuit, it is known to fit the high pressure inlet of the fuel injector with a high pressure filter cartridge. Such a high pressure filter cartridge must satisfy at least following design criteria: (1) it must of course be resistant to Diesel fuel; (2) it should at least eliminate all particles bigger than 30 pm; (3) its maximum pressure drop should be between 20 and 30 bar for a flow rate of 0,04 ml/ms and a pulse frequency of 10-50 Hz; (4) it must be capable of withstanding a hydrostatic pressure of 2000 bar; (5) it must be capable of withstanding a pressure differential of at least 45 bar; (6) the outer dimensions of the cartridge should be small enough, so that the cartridge can be directly connected to the inlet port of a fuel injector; and (7) its useful life filtration capacity should be at least 3500 litres (corresponding to a kilometric performance of about 200.000 km for a passenger car Diesel engine).

The sole available filter cartridges that are presently capable of meeting the above design criteria are the so called edge filter cartridges, as described e.g. in US-A-5,584,999. Such an edge filter cartridge contains an elongate filter body incorporating a series of axial inlet channels, which are open at a first end of the filter body and closed at a second end of the filter body, and a series of axial outlet channels, which are closed at the first end of the filter body and open at the second end of the filter body. These axial inlet and outlet channels are alternately arranged about the surface shell of the elongate filter body, so as to be separated by axial ribs. The filter body is centred in a bore of a filter housing, so that its ribs have controlled radial clearances with the surface of the bore. The axially closed inlet channels are catching small solid particles, which are carried along with the high pressure fuel, wherein these particles tend to be broken down at the closed ends of the inlet channels. The debris of these particles may then pass through the controlled radial clearances into the adjacent axial outlet channels. A disadvantage of these edge filter cartridges is that they are not very efficient with regard to long, thin particles (e.g. particles having a length of 100 μΐη or more, with a diameter less than 50 pm), in particular if these particles are relatively flexible. However, such long and thin particles, which readily pass through standard edge filter cartridges, do constitute a potential danger for modern high pressure fuel injectors. Furthermore, as edge filter cartridges work according to the principle of breaking down bigger particles until they pass through a controlled radial clearance, they cannot avoid accumulation of small metallic particles on the armature of the solenoid in an electromagnetic fuel injector, which constitutes a serious risk for actuators with an actuating stroke smaller than 50 pm.

It is well known to use a fine metallic mesh screen as filter medium in low or medium pressure fuel injectors. But it is readily understood that such a fine mesh screen cannot be used in high pressure fuel injection systems. Indeed, a metallic mesh screen designed to warrant the required filter efficiency for the required flow rate in an high pressure Diesel fuel injector, would be exposed to a pressure differential resulting in unacceptable deformations of the screen.

Many other types of filters have been developed for various filtration applications in food and beverage industry, general process engineering, laboratory technology, medicine technology, environmental technology, filtration of lubricating liquids etc. To date, however, none of these filters has qualified as a technical alternative to edge filter cartridges for protecting the high pressure inlet of a high pressure fuel injector against penetration of solid particles in the micrometer range.

Object of the invention A technical problem underlying the present invention is to provide a very compact high pressure filter cartridge for a high pressure fuel injection system that is capable protecting the fuel injector against penetration of solid particles in the micrometer range. This problem is solved by a filter cartridge as claimed in claim 1.

Summary of the invention

In accordance with the invention, a high pressure filter cartridge for a high pressure fuel injection system, i.e. a fuel injection system with working pressures above 1000 bar, comprises a filter housing enclosing a filter chamber with a high pressure fuel inlet and a high pressure fuel outlet. A tubular filter element of porous sintered metal is axially clamped in the filter chamber, so as to separate the high pressure fuel inlet from the high pressure fuel outlet. It will be appreciated that such a filter cartridge is capable of retaining particles in the micrometer range and can be designed compact enough to replace a standard edge filter cartridge in the high pressure fuel inlet of a fuel injector. Furthermore, it has been found out that such a compact high pressure filter cartridge causes a pressure drop that is surprisingly not higher than the pressure drop caused, at identical flow rates, by a standard edge filter cartridge for high pressure fuel injectors, which lets through much bigger particles. It remains to be noted that the axial clamping of the tubular filter element and the excellent mechanical characteristics of a sintered metal body warrant that the tubular filter element is perfectly capable of withstanding the high differential pressures to which it is subjected. In conclusion, the above-defined design and material specifications co-operate to qualify the filter cartridge of the present invention as a real improvement over edge filter cartridges, which are presently the state of the art for protecting the high pressure inlet of a high pressure fuel injector against penetration of solid particles.

In an improved embodiment, the tubular filter element includes a thick- walled support tube of sintered metal with a rather coarse porosity. This support tube provides the required mechanical stability to the tubular filter element without significantly contributing to the pressure drop of the filter element. A surface filter membrane, which coats the support tube on the side of the high pressure fuel inlet, provides the desired filter grade to the tubular filter element. In other words, the tubular filter element achieves a surface filtration on the thick-walled support tube, thereby warranting a higher useful life filtration capacity. Furthermore, it will be appreciated that such a thin surface filter membrane can be easily designed to be highly porous to fuel and to simultaneously retain all solid particles in the lower micron range. It may e.g. be designed to retain particles down to 5 μηη, whereas a standard edge filter cartridge is only capable of retaining particles down to 50 pm. Such a surface filter membrane can be obtained for example as a metallic coating that is applied by diffusion on the thick-walled support tube and is bonded to the tube material by sintering. To increase the filter surface of the surface filter membrane, it is of advantage that the support tube has an outer surface with a folded or corrugated configuration to which the surface filter membrane is bonded.

In a preferred embodiment, the tubular filter element partitions the filter chamber into an annular outer filter chamber, which surrounds the tubular filter element, and a central inner filter chamber, which is enclosed by the tubular filter element. The high pressure fuel inlet of the housing leads the high pressure fuel into the annular outer filter chamber, from where it passes through the tubular filter element into the central inner filter chamber, whereby it is filtered. The high pressure fuel outlet of the housing leads the filtered high pressure fuel out of the central inner filter chamber. In this embodiment, the tubular filter element has its largest surface exposed to fuel from the high pressure inlet, which results in a reduced pressure drop and an improved resistance to differential pressures, which are due to the pressure drop in the tubular filter element.

The axial clamping and sealing of the tubular filter element can be achieved in a very simple and compact way. The filter chamber is e.g. axially delimited by a bottom wall and includes an internal thread that is axially spaced from the bottom wall. A threaded plug is screwed into this internal thread of the filter chamber and bears on a first end of the tubular filter element, so as to axially press a second end of the tubular filter element against the bottom wall. The threaded plug advantageously has an annular shoulder with a first sealing ring. The bottom wall advantageously has an annular groove with a second sealing ring. The threaded plug bears with its first sealing ring on a first end surface of the tubular filter element for axially pressing a second end surface of the tubular filter element against the second sealing ring in the annular groove. Thus, it is warranted that contaminated high pressure fuel cannot by-pass the tubular filter element. In a preferred embodiment, the threaded plug axially separates a fuel inlet chamber from the filter chamber. The high pressure fuel inlet discharges the high pressure fuel into this fuel inlet chamber. This threaded plug axially seals off the central inner filter chamber at the first end of the tubular filter element and includes fuel passages along the outer border of its annular shoulder for hydraulically connecting the fuel inlet chamber to the annular outer filter chamber.

The housing of the filter cartridge advantageously includes a housing body and a housing cap. The filter chamber extends axially from an access opening in a front face at a first end of the housing body towards a bottom wall at an opposite second end of the housing body. The housing cap is screwed on the housing body for closing the access opening. The high pressure fuel inlet is advantageously formed in the housing cap. The high pressure fuel outlet is advantageously formed in the bottom wall.

Brief description of the drawings A preferred embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1: is a schematic view of a high pressure fuel injector equipped with a filter cartridge; and

Figure 2: is a schematic longitudinal section through a filter cartridge in accordance with the present invention.

Detailed description of a preferred embodiment FIG. 1 shows a high pressure fuel injector 10 for a Diesel engine. This fuel injector 10 has an injector housing 12 with a high pressure fuel inlet connection 14, a return fuel connection 16 and an injection nozzle end 18. Reference number 20 identifies an electromagnetic actuator for hydraulically opening and closing, by means of an internal pilot valve that is operated with the high pressure fuel, a needle valve that is housed in the injection nozzle end 18. A high pressure filter cartridge 22 is screwed with one end into the fuel inlet connection 14. A pipe coupling 24 is screwed on the other end of the filter cartridge 22 for connecting a high pressure fuel feed pipe 25 thereto. Such a high pressure fuel injector 10 is for example designed for an injection pressure of 2000 bar, a maximum injection rate of 0,04 ml/ms and a pulse frequency of 10-50 Hz.

The basic design of a high pressure filter cartridge 22 in accordance with the invention will now be described with reference to FIG. 2. Reference number 26 globally identifies a filter housing including a substantially cup-shaped housing body 28 and a housing cap 30. This filter housing 26 encloses a cylindrical filter chamber 32, which extends axially from an access opening 34 in a front face 36 at a first end of the housing body 28 towards a bottom wall 38 at an opposite second end of the housing body 28. This access opening 34, which has a slightly bigger cross-section than the rest of the filter chamber 32, is closed by the housing cap 30 (shown with doted lines in FIG. 2), which is screwed onto the second end of the housing body 28, which is fitted for this purpose with an external thread 40. The threaded joint between the housing body 28 and the housing cap 30 is sealed by means of an axially working sealing ring 42. The pipe coupling 24 (shown in FIG. 1, but not in FIG. 2) is connected to a high pressure fuel inlet 44 in the housing cap 30. A threaded connecting nipple 46 forms a high pressure fuel outlet 48 in the bottom wall 38 of the housing body 28. This connecting nipple 46 is used for screwing the filter cartridge 22 into the fuel inlet connection 14 of the fuel injector 10.

In the cylindrical filter chamber 32 is mounted a tubular filter element 50, so as to be co-axial with a central axis 51 of the cylindrical filter chamber 32. This tubular filter element 50 has a cross-section that is slightly smaller than the cross-section of the cylindrical filter chamber 32. It follows that the tubular filter element 50 partitions the filter chamber 32 into an annular outer filter chamber 54, which radially surrounds the tubular filter element 50 in the filter chamber 32, and a central inner filter chamber 56, which is enclosed by the tubular filter element 50.

The tubular filter element 50 is axially clamped into the filter chamber 32 by means of a threaded plug 58, which is screwed into an internal thread 60 located close to the access opening 34. The threaded plug 58 has a central cylindrical portion 62, which is engaged in the central inner filter chamber 56 of the tubular filter element 50, and an annular peripheral shoulder 64, which is fitted with a first axially working sealing ring 66. With this first sealing ring 66 the threaded plug 58 bears on a first end surface 68 of the tubular filter element 50. the axially opposite end of the tubular filter element 50 is introduced into an annular groove 70 in the bottom wall 38. It has a second end surface 72 that bears on a second axially working sealing ring 74, which is housed in the annular groove 70. In other words, the threaded plug 58 bears with its first sealing ring 66 on the first end surface 68 of the tubular filter element 50 for axially pressing the second end surface 72 of the tubular filter element 50 against the second sealing ring 74 in the annular groove 70. A hexagonal head 75 (or an equivalent means) allows to tighten the threaded plug 58 in its internal thread 60, so as to produce the required sealing pressure on the sealing rings 66, 74 and exert an initial compression on the tubular filter element 50. This “pre-compression” of the tubular filter element 50 helps the latter to better withstand the stresses due to the important pressure difference between the annular outer filter chamber 54 and the centra! inner filter chamber 56. It will be noted that the threaded plug 58 axially separates a fuel inlet chamber 76 from the rest of the filter chamber 32, wherein the high pressure fuel inlet 44 discharges the high pressure fuel into this fuel inlet chamber 76. The central part of the threaded plug 58 axially seals off the central inner filter chamber 56. The shoulder 64 of the threaded plug 58 includes small fuel passages 78 at its outer border, which hydraulically connect the fuel inlet chamber 76 to the annular outer filter chamber 54.

A preferred embodiment of the tubular filter element 50 comprises a support tube 80 that is provided with a surface filter membrane 82 on its outer surface, i.e. on the inlet side of the high pressure fuel. The support tube 80 is a thick-walled tube of sintered metal with a rather coarse porosity. This support tube 80 has no significant filtering function, but good mechanical characteristics. It provides the required mechanical stability to the tubular filter element 50, without significantly contributing to the pressure drop of the filter element 50. The surface filter membrane 82 provides the desired filter grade to the tubular filter element 50. Such a surface filter membrane 82 is e.g. obtained by coating the outer wall of the support tube 80 by diffusion with a metal, which is then bonded by sintering to the tube material. It will be appreciated that such a sintered metal membrane 82 can be designed to be highly porous to fuel, while retaining all solid particles in the lower micron range. Filter elements of this type are e.g. produced by GKN Sintermetals® under the model designation SIKA-R...AS®. It is a merit of the present inventor to have recognised that these filter elements, which have been conceived for other purposes, are particularly suitable as filter medium in the new high pressure filter cartridges 22 designed to replace standard edge filter cartridges of high pressure fuel injectors.

Arrows 90 represent high pressure fuel entering through the high pressure fuel inlet 44 in the housing cap 30 into the fuel inlet chamber 76. From this fuel inlet chamber 76 the fuel flows through the small fuel passages 78 into the annular outer filter chamber 54. In the latter, the sintered metal membrane 82 works as a surface filter. The sintered metal support tube 80 has an object to provide mechanical stability with a minimum of pressure drop. The surface filter membrane 82 is preferably designed to retain particles greater than 5 pm in the annular outer filter chamber 54 of the filter cartridge 22. This means that the filter cartridge 22 is designed to have substantially the same filter characteristic as a main fuel filter in a low pressure feeding line of a high pressure injection pump. The surface filter membrane 82 may of course be designed to retain particles even smaller than 5 pm, should the filtering efficiency of the main fuel filter be improved. Particles that are big enough to be retained by the surface filter membrane 82 accumulate in the outer annular filter chamber 54. Particles that are too small to be retained by the surface filter membrane 82 readily pass through the much coarser porosity of the support tube 80 into the central inner filter chamber 54. Arrows 92 represent the high pressure fuel flowing through the tubular filter element 50 into the central inner filter chamber 54. The filtered fuel leaves the central inner filter chamber 54 via the high pressure fuel outlet 48 in the bottom wall 38 of the housing body 28, as indicated by arrows 94.

The tubular filter element 50 described above has been tested on an injector system test rig with European Diesel fuel and ISO 4113 fuel. It was surprising to notice that for the same flow rate the filter cartridge 22 causes a slightly . lower pressure drop than a standard edge filter cartridge for a high pressure fuel injectors. The following table resumes these surprising test results for the new filter cartridge 22:

In this context it will also be pointed out that the tubular filter element 50, which is mounted in the filter chamber 32 as described above, is capable of withstanding, without any stability problems, differential pressures of at least 45 bar.

Whereas a standard edge filter cartridge eliminates particles down to 50 pm, the new filter cartridge 22 allows to retain particles down to at least 5 pm, thus avoiding that the injector sticks in an open or closed position. Furthermore, whereas a standard edge filter cartridge “grinds” metallic particles and thereby causes an accumulation of metallic particle debris on the magnetic armature of an electromagnetic actuator of the high pressure fuel injector, the new filter cartridge 22 retains all metallic particles down to at least 5 pm in the outer filter chamber 54.

The tests have also shown that it is reasonable to expect that the new filter cartridge 22 will have a useful life filtration capacity of at least 3500 litres in a Diesel engine (this corresponds to a kilometric performance of about 200.000 km for a passenger car Diesel engine). It will be noted in this context that the fuel flowing axially along the surface filter membrane 82 in the new filter cartridge 22 will to a large extend prevent the formation of a compacted pressure drop increasing filter cake on the surface filter membrane 82.

It finally remains to be noted that the tubular filter element 50 described above has a cylindrical outer surface, i.e. the surface filter membrane 82 is cylindrical too. In order to increase the filtration surface of the surface filter membrane 82, i.e. to further decrease the pressure drop, it is interesting to provide a folded or corrugated configuration to the outer surface of the tubular filter element 50.

Claims

1. A high pressure filter cartridge (22) for a high pressure fuel injection system comprising: a filter housing (26) enclosing a filter chamber (32) with a high pressure fuel inlet (44) and a high pressure fuel outlet (48); characterised by a tubular filter element (50) of porous sintered metal, said tubular filter element (50) being axially clamped in said filter chamber (32), so as to separate said high pressure fuel inlet (44) from said high pressure fuel outlet (48).

2. The high pressure filter cartridge (22) as claimed in claim 1, characterised in that said tubular filter element (50) includes: a thick-walled support tube (80) of porous sintered metal, said support tube (80) providing the required mechanical stability to the tubular filter element (50) without significantly contributing to the pressure drop of the filter element (50); and a surface filter membrane (82) coating said support tube (80) on the side of said high pressure fuel inlet (44), said surface filter membrane (82) providing the desired filter grade to the tubular filter element (50).

3. The high pressure filter cartridge (22) as claimed in claim 2, characterised in that said surface filter membrane (82) is a metallic coating that is bonded to the tube material by sintering.

4. The high pressure filter cartridge (22) as claimed in claim 2 or 3, characterised in that said surface filter membrane (82) is capable of retaining particles down to 5 μηη.

5. The high pressure filter cartridge (22) as claimed in any one of claims 2 to 4, characterised in that said support tube (80) has an outer surface with a folded or corrugated configuration to which said surface filter membrane (82) is bonded.

6. The high pressure filter cartridge (22) as claimed in any one of claims 1 to 5, characterised in that: said tubular filter element (50) partitions said filter chamber (32) into an annular outer filter chamber (54), which surrounds said tubular filter element (50), and a central inner filter chamber (56), which is enclosed by said tubular filter element (50); said high pressure fuel inlet (44) of said housing (26) leads said high pressure fuel into said annular outer filter chamber (54), from where it passes through said tubular filter element (50) into said central inner filter chamber (56); and said high pressure fuel outlet (48) of said housing (26) leads said high pressure fuel out of said central inner filter chamber (56).

7. The high pressure filter cartridge (22) as claimed in any one of claims 1 to 6, characterised in that: said filter chamber (32) is axially delimited by a bottom wall (38) and includes an internal thread that is axially spaced from said bottom wall (38); and said high pressure filter cartridge (22) further includes a threaded plug (58) screwed into said internal thread (60) of said filter chamber (32) and bearing on a first end of said tubular filter element (50) so as to axially press a second end of said tubular filter element (50) against said bottom wall (38).

8. The high pressure filter cartridge (22) as claimed in claim 7, characterised in that: said tubular filter element (50) has a first end face (68) and an axially opposite second end face (72); said threaded plug (58) has an annular shoulder (64) with a first sealing ring (66); said bottom wall (38) has an annular groove (70) with a second sealing ring (74); and said threaded plug (58) bears with its first sealing ring (66) on said first end surface (68) of said tubular filter element (50) for axially pressing said second end surface (72) of said tubular filter element (50) against said second sealing ring (74) in said annular groove (70).

9. The high pressure filter cartridge (22) as claimed in claim 6 and any one of claims 7 or 8, characterised in that: said threaded plug (58) axially seals off said central inner filter chamber (56) at said first end of said tubular filter element (50); said threaded plug (58) axially separates a fuel inlet chamber (76) from said filter chamber (32), wherein said high pressure fuel inlet (44) leads said high pressure fuel into said fuel inlet chamber (76); and said threaded plug (58) includes fuel passages (78) along the outer border of its annular shoulder (64) for hydraulically connecting said fuel inlet chamber (76) to said annular outer filter chamber (54).

10. The high pressure filter cartridge (22) as claimed in any one of claims 1 to 9, characterised in that said housing (26) includes: a housing body (28) in which said filter chamber (32) extends axially from an access opening (34) in a front face (36) at a first end of the housing body (28) towards a bottom wall (38) at an opposite second end of the housing body (28); and a housing cap (30) screwed on said housing body (28) for closing said access opening (34).

11. The high pressure filter cartridge (22) as claimed claim 10, characterised in that: said a high pressure fuel inlet (44) is formed in said housing cap (30); and said a high pressure fuel outlet (48) is formed in said bottom wall (38).

12. A high pressure fuel injector (10) comprising a high pressure filter cartridge (22) as claimed in any one of the preceding claims.