Patent Publication Number: US-9885332-B2

Title: Filter assembly for a fuel injector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/EP2015/050475 filed Jan. 13, 2015, which designates the United States of America, and claims priority to EP Application No. 14151429.9 filed Jan. 16, 2014, the contents of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present disclosure concerns a filter assembly for a fuel injector. More specifically, the present invention concerns a filter assembly, a fuel injector, and a method for assembling the filter assembly. 
     BACKGROUND 
     A combustion engine, especially of the piston type, may use a fuel injector for injecting fuel into a combustion chamber. The fuel injector comprises a filter assembly that is commonly press-fitted into the injector in an axial direction during manufacturing the injector. 
     EP 1 229 239 A2 shows a fuel injector with such a filter. The filter assembly comprises a filter element and a tubular filter housing for receiving the filter element. The filter element has a side wall with a shoulder for supporting an axial end of the filter element on the filter housing. 
     As the filter assembly is press-fitted into the injector, considerable axial forces may act against the side wall in a region of the shoulder. The filter element may deform temporarily or permanently so that the position of an upper section of the filter assembly with respect to the injector may be poorly defined. In addition, considerable tension may occur between the shoulder and the axial end of the filter element. This may lead to a rupture of the filter element so that unfiltered fuel may pass towards the delicate valve system of the injector. 
     SUMMARY 
     It is an object of the present disclosure to describe a filter assembly, a fuel injector, and a method for assembling the filter assembly that resists deformation of the filter assembly during assembly or installation in the fuel injector. 
     Some embodiments may include a filter assembly ( 110 ) for an injector ( 100 ) for injecting fuel into a combustion engine. The filter assembly ( 110 ) may have a longitudinal axis ( 105 ) and comprise: a filter element ( 165 ) with a cylindrical section ( 180 ) having a first axial end ( 220 ) and a second axial end ( 225 ); a tubular filter housing ( 170 ) in which the filter element ( 165 ) is received; and a cap ( 175 ) for holding the filter element ( 165 ) at the second axial end ( 225 ). The filter housing ( 170 ) may have a radial protrusion ( 305 ) which supports the first axial end ( 220 ) of the cylindrical section ( 180 ). The cap ( 175 ) may encompass the filter housing ( 170 ) along an outer circumference. The second axial end ( 225 ) may rest directly against the cap ( 175 ). 
     In some embodiments, the cylindrical section ( 180 ) is provided with a chamfer ( 230 ) at its second axial end  255  and/or the cylindrical section ( 180 ) extends radially inwards further than the shoulder ( 305 ) of the filter housing ( 170 ). 
     In some embodiments, the filter element ( 165 ) comprises a filter screen ( 185 ) which is fixed to the cylindrical section ( 180 ) and wherein the cylindrical section ( 180 ) comprises or consists of a plastic material. 
     In some embodiments, the filter housing ( 170 ) and the cap ( 175 ) comprise a metal or an alloy or consist thereof. 
     In some embodiments, an axial length ( 320 ) of the filter housing between the protrusion ( 305 ) and the cap ( 175 ) is smaller than the axial length ( 315 ) of the cylindrical section ( 180 ) of the filter element ( 165 ). 
     In some embodiments, an inner diameter of the cap ( 175 ) is aligned with an outer diameter of the filter housing ( 170 ) such that the cap ( 175 ) is in force-fit engagement with the filter housing ( 170 ) with a predetermined frictional force. 
     In some embodiments, the filter cap ( 175 ) has an open end ( 325 ) which axially overlaps the filter housing ( 170 ) and a partially closed opposite end  330  which is positioned subsequent to the cylindrical section ( 180 ) in axial direction from the first axial end ( 220 ) towards the second axial end ( 225 ) and wherein the filter cap ( 175 ) comprises a first axial section ( 340 ) near the open end ( 325 ) and a second axial section ( 345 ) near the opposite end ( 330 ) and a taper ( 350 ) is located between said first and second axial sections ( 340 ,  345 ) such that an inner diameter of the second section ( 345 ) is smaller than an inner diameter of the first section ( 340 ). 
     In some embodiments, the inner diameter of the second section ( 345 ) is aligned with an outer diameter of the cylindrical section ( 180 ) of the filter element ( 165 ) such that the filter element ( 165 ) rests laterally against the second section ( 345 ). 
     In some embodiments, the filter assembly ( 110 ) is configured to be axially press-fitted with another component of the injector ( 100 ) by means of the filter housing ( 170 ). 
     In some embodiments, a fuel injector ( 100 ) includes a filter assembly ( 110 ) as taught above. The fuel injector may further comprise a body ( 125 ) which is a hollow valve body of the fuel injector ( 100 ) and a block ( 135 ) which is a pole piece of an electromagnetic actuator ( 145 ) of the fuel injector ( 100 ), wherein the filter assembly ( 110 ) is kept in its position in the fuel injector ( 100 ) by friction between the block ( 135 ) and the filter housing ( 170 ). 
     In some embodiments, the fuel injector may additionally comprise a valve needle and a calibration spring ( 160 ) for biasing the valve needle towards a closing position, wherein the filter housing ( 170 ) comprises a spring seat for the calibration spring ( 160 ) at its axial end remote from the cap ( 175 ). 
     Assembling a filter assembly ( 110 ) may include the following steps: inserting ( 405 ) the filter element ( 165 ) axially into the filter housing ( 170 ); and axially pressing ( 415 ) the cap ( 175 ) onto the filter housing ( 170 ) until the second axial end ( 225 ) of the cylindrical section ( 180 ) makes contact with the cap ( 175 ). 
     In some embodiments, the pressing is continued ( 420 ) until a predetermined pressing force is reached, the predetermined force exceeding a frictional force between the filter cap ( 175 ) and the filter housing ( 170 ). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the invention will now be described in more detail with reference to the enclosed figures in which: 
         FIG. 1  shows a fuel injector in a longitudinal section view, according to teachings of the present disclosure; 
         FIG. 2  shows a filter assembly being installed in the fuel injector of  FIG. 1  in a longitudinal section view; 
         FIG. 3  shows the filter assembly according to  FIG. 1 or 2  in a longitudinal section view, and 
         FIG. 4  shows different stages during a method for assembling a filter assembly according to  FIG. 1 or 3 . 
     
    
    
     DETAILED DESCRIPTION 
     In some embodiments, the filter assembly comprises a filter element with a cylindrical section having a first axial end and a second axial end. The cylindrical section may bed annularly shaped. That the section is a cylindrical section means in particular that it has a circumferential outer surface which has the basic shape of the lateral surface of a cylinder. The cylindrical section may have a central opening which extends axially through the cylindrical section. The cylindrical section may comprise a plastic material or consists of a plastic material. 
     Expediently, the filter element may comprise a filter screen. The filter screen may be fixed to the cylindrical section. The filter screen may axially overlap the cylindrical section and project beyond the first end of the cylindrical section. 
     In some embodiments, the filter assembly further comprises a tubular filter housing for receiving the filter element. The filter housing has a sidewall with a radial protrusion for supporting the first axial end of the cylindrical section. When the filter assembly is in its assembled state, the filter element is received in the tubular filter housing such that the first axial end of the cylindrical section is supported by—i.e. in particular in direct mechanical contact with—the shoulder. 
     In some embodiments, the filter assembly comprises a cap for holding the filter element at its second axial end. The cap encompasses the filter housing along an outer circumference. In particular for holding the filter element at its second axial end, the second axial end of the filter element rests directly against the cap. In this way, axial displacement of the cylindrical section may be blocked in one direction by the shoulder and in the opposite direction by the cap. 
     In some embodiments, the filter element of the present filter assembly is fixed in both axially directions without deforming the tubular filter housing—e.g. by bending an end of the filter housing radially inwards—after the filter elements has been inserted into the filter housing. In this way, undue axial strain on the filter assembly during manufacture is avoided. As axial forces during bending an end of the filter housing inwards can be as high as 1500 N and more, the filter assembly may thus be less prone to mechanical deformation or even failure during manufacture, installation or operation. 
     In some embodiments, the filter housing and/or the cap each comprise a metal or an alloy or, preferably, consist of a metal or of an alloy. In this way a high mechanical stability of the filter assembly is achievable. 
     For example, the fuel injector may comprise a valve needle and a calibration spring for biasing the valve needle towards a closing position. In this case, the filter housing may expediently comprise a spring seat for the calibration spring at its axial end remote from the cap. The filter housing may represent a calibration tube in this case and the filter assembly may be used to set a preload of the calibration spring during assembly of the fuel injection valve. The metallic housing and/or the metallic cap may provide sufficient mechanical resistance for such a calibration function of the filter assembly. 
     The axial length of the filter housing between the protrusion and the cap may be smaller than the axial length of the cylindrical section of the filter element. In this way, an axial force pressing the cap down onto the filter housing is not transferred to the section of the radial protrusion through sidewalls of the filter housing but rather through the cylindrical section of the filter element. In other words, a form fit connection between the cap and the tubular filter housing can be avoided in this way, which form-fit connection could otherwise unintentionally transfer unduly large axial forces from the cap to the filter housing during assembling the filter assembly or during manufacture of the fuel injection valve when the filter assembly is press fitted into another component of the fuel injection valve by pressing on the cap. 
     The radial protrusion may be part of a shoulder in the filter housing. The cylindrical section may extend radially inwards further than the shoulder. In this manner, a predetermined distance between the filter screen which axially protrudes beyond the cylindrical section and the filter housing can be guaranteed. Additionally or alternatively, due to the small radial extension of the shoulder, the axial force can be efficiently transferred to a tubular section of the filter housing beyond the shoulder section with a reduced risk of deformation of the filter housing. 
     For establishing a force-fit connection between the cap and the filter housing with a predetermined friction force during assembling the filter assembly, an inner diameter of the cap may be aligned with an outer diameter of the filter housing. Namely, the cap may be press-fitted to the filter housing. This may provide an easy installation of the cap and a secure hold of the cap on the filter housing. Consequently, the inner diameter of the cap may be aligned with the outer diameter of the filter housing such that the cap is in a force-fit engagement with the filter housing with the predetermined friction when the filter assembly is in its assembled state. 
     In some embodiments, the filter cap has an open end which axially overlaps the filter housing. It further has an opposite end which is positioned subsequent to the cylindrical section in axial direction from the first axial end towards the second axial end of the cylindrical section. Said opposite end is in particular partially closed. For example, it is comprised by a radially extending lid portion of the cap which is perforated in axial direction by one or more through holes. In this way, fluid can flow through the cap into the central opening of the cylindrical section and further through the filter screen into the filter housing before leaving the filter assembly at an axial end of the filter housing remote from the cap. 
     In some embodiments, the filter cap comprises a first axial section near its open end and a second axial section near its opposite end wherein a taper is located between said sections in such a way that an inner diameter of the second section is smaller than an inner diameter of the first section. The first section may thus be more easily pushed over the cylindrical section of the filter element during installation of the cap. 
     In some embodiments, the inner diameter of the second section is aligned with an outer diameter of the cylindrical section of the filter element for resting the filter element laterally against the second section. The alignment can be varied. For instance, a loose fit may be chosen if lateral stabilization is less important while a tight fit may be implemented for holding the filter element, the cap and the filter housing together in an improved manner. In particular, the cap may be configured to fix the position of the second axial end of the cylindrical section in radial direction by means of mechanical interaction with the second section of the cap. 
     In some embodiments, the filter assembly is adapted to be axially press-fitted with another component of the injector by means of the filter housing. For this purpose, the filter assembly may be configured such that an axial force on the cap is smoothly transferred to a part of the filter housing beyond the cylindrical section of the filter element, e.g. to a part of the filter housing which is positioned in axial direction on the side of the shoulder remote from the cap. This may imply straight walls of the filter housing to as high an extent as possible. Tapers of chamfers, however, may be added as required. 
     In some embodiments, the cylindrical section is provided with a chamfer at its second axial end. In this way, the risk that an unintended deformation of the cylindrical section occurs at the outer circumference of its upper edge is particularly small. 
     In some embodiments, the fuel injector comprises a body which is in particular a hollow valve body of the fuel injector and a block which is in particular a pole piece of an electromagnetic actuator of the fuel injector. The block may be positioned inside the body, in particular in the recess of the hollow valve body. It may expediently be positionially fixed relative to the body. The filter assembly may be kept in its position in the fuel injector by friction between the block and the filter housing. In particular, the pole piece has a central opening and the filter assembly is kept in its position by friction with a circumferential surface of the central opening of the pole piece. This may allow easily setting the preload of the calibration spring when the filter assembly has as a spring seat for the calibration spring. 
     According to a further aspect, a method for assembling the filter assembly is disclosed. The method for assembling the filter assembly according to at least one of the above mentioned embodiments comprises steps of inserting the filter element axially into the filter housing and axially pressing the cap onto the filter housing until the second axial end of the cylindrical section makes contact with the cap. 
     By using said method, a faster and more cost efficient assembly of the filter assembly may be achieved. By doing away with the risk of physical deformation of the filter housing during the manufacturing process, mechanical stability and integrity of the filter assembly may be maintained. 
       FIG. 1  shows an example fuel injector  100  for injecting fuel into a combustion engine, in particular in a power train of a motor vehicle. The fuel injector  100  extends along a longitudinal axis  105  and comprises a filter assembly  110  for filtering fuel on its way through the injector  100  between an inlet  115  and a tip  120 . The filter assembly  110  and the fuel injector  100  may share the longitudinal axis  105  as a common longitudinal axis. 
     In the exemplary embodiment, the fuel injector  100  furthermore comprises a body  125 , a cover  130 , and a block  135 . The block  135  is adapted to receive the filter assembly  110  from an axial direction and the filter assembly  110  may be adapted for press-fitting into the block  135 . 
     The body  125  may comprise a hollow valve body of the fuel injector. The cover  130  is in particular a fuel inlet tube of the fuel injector which is hydraulically connected to the valve body to enable fluid flow from the inlet  115 , which is in particular comprised by the fuel inlet tube, to the tip  120  which is in particular comprised by the valve body. The block  135  may be a pole piece of an electromagnetic actuator  145  of the fuel injector  100 . The block  135  is positionally fixed with respect to the body  125 . 
     Some embodiments may include a valve  140  for controlling a flow of fuel through the tip  120  and an actuator  145  for operating the valve  140 . The actuator  145  may comprise a solenoid  150  and an armature  155 . When the solenoid  150  is energized it attracts the armature  155  which is coupled to the valve  140  to displace a valve needle of the valve  140  away from its closing position so that a flow of fuel through the injector  100  is permitted. 
     The valve needle may be loaded with a calibration spring  160  which pushes the valve needle in a direction opposite to the attraction force of the solenoid  150  and towards the closing position. In the present embodiment, the filter assembly  110  is in contact with the calibration spring  160  on an axial side of the calibration spring  160  remote from the valve needle. The preloading force on calibration spring  160  may be adjusted by changing the axial position of filter assembly  110  with respect to block  135 . Through this, dynamic flow characteristics of the injector  100  may be calibrated. Such calibration may be performed during manufacturing the injector  100 . 
     The filter assembly  110  may comprise a filter element  165 , a filter housing  170 , and a filter cap  175 . The filter element  165  has a cylindrical section  180 , to which a screen  185  for filtering is attached. The screen  185  may comprise a fine sieve, a fleece, a woven, or non-woven fabric or the like. The cylindrical section  180  may be manufactured from a plastic by means of molding. The screen  185  may be molded to the frame  180  in the same or a successive process. The cylindrical section  180  has an annular shape with a central opening extending through the cylindrical section  180  in axial direction. Thus, the cylindrical section  180  may also be denoted as a cylindrical frame. 
     The filter housing  170  may be a metal part, for instance manufactured from a metal sheet by deep-drawing. The cap  175  may also comprise a formed sheet metal and it may also be manufactured by deep-drawing. The cap  175  may be press-fitted onto the filter housing  170 . It is preferred that the cap  175  comprises an aperture for permitting a flow of fuel towards the filter element  165 . After passing through the filter element  165 , the fuel may exit through another aperture in the filter housing  170 , near the bottom of filter assembly  110  in  FIG. 1 , to flow towards the valve  140 . 
       FIG. 2  shows the filter assembly  110  during installation in the fuel injector  100  of  FIG. 1 . A pressing force  205  is exerted to the filter cap  175  from where it is transferred to the filter housing  170  via the force-fit coupling between the cap  185  and the filter housing  180 . Additionally, the pressing force  205  may be transferred to the filter housing  180  via the cylindrical section  180  of the filter element  165 . The pressing force may lie in the range of 200-1000 N or even more. 
     Lateral friction between the filter housing  170  and the block  135  creates a resisting force  210  acting in a direction opposite to pressing force  205 . Furthermore, a preloading force  215  of calibration spring  160  acts on the filter housing  170  against pressing force  205 . If the pressing force  205  exceeds the sum of the resisting force  210  and the preloading force  215 , the filter assembly  110  is press-fitted further into block  135  of injector  100 . The press-fitting of filter assembly  110  may be carried out until a flow rate of a fluid through injector  100  has reached a desired value. Then the pressing force  205  may be removed and the filter assembly  110  is kept in its position with respect to block  135  by friction between the block  135  and the filter housing  170 . Thus, the filter housing  170  may also be denoted as a calibration tube. 
     The filter housing  170  has a shoulder where an inner diameter of the filter housing  170  is reduced downstream the filter cap  175 . The cylindrical section  180  has a first axial end  220  near the shoulder and a second axial end  225  near the cap  175  in  FIG. 2 . Generally, the pressing force  205  is transferred from the filter element  165  to the filter housing  170  via the cylindrical section  180  being in axial contact with the shoulder. 
     In some embodiments, the cylindrical section  180  includes a chamfer  230  at its second axial end  225  to ensure that a bending radius of the cap  170  between radial and axial surfaces does not get in the way of the cylindrical section  180 . 
       FIG. 3  shows the filter assembly  110  according to  FIGS. 1 and 2 . Details that are not significant for the present invention may differ from the embodiments depicted in  FIGS. 1 and 2 . 
     The filter element  165  is received inside of the filter housing  170 . The first axial end  220  abuts on a protrusion  305  which is, in the present example, implemented as a shoulder in the filter housing  170 . The protrusion  305  may be accomplished in another way like with a diaphragm. A section of the filter housing  170  which lies on an end of the cylindrical section  180  remote from the filter element  165  may be configured for press-fitting into an element—like block  135 —of the injector  100 . In some embodiments, the filter housing  170  has straight walls in this section to as far an extent as possible. However, one or more tapers  310  may be introduced. 
     In some embodiments, the axial length  315  of cylindrical section  180  of filter element  165  exceeds the axial length  320  of a section of the filter housing  170  that extends from the protrusion  305  towards the second axial end  225  of the cylindrical section  180 . This makes sure that a physical contact between the second axial end  225  of the cylindrical section  180  and an inner side of the cap  175  may be made and a radially extending lid portion of cap  175  remains axially spaced apart from the filter housing  170 . 
     The cap  175  has an open end  325  for receiving the filter housing  170  and a lid end  330  at the opposite axial side for resting against the cylindrical section  180  on an inner side. In some embodiments, the cap  175  has an aperture  335  at the lid end  330  for permitting flow of fuel into the filter assembly  110 . An inner diameter of cap  175  may be aligned with an outer diameter of the filter housing  170  in the region where it axially overlaps the filter housing  170 . The alignments may be chosen in such a way that frictional forces between the cap  175  and the filter housing  170  prevent the filter housing  170  from sliding out of the cap  175 . 
     In the present embodiment, the cap  175  comprises a first axial section  340  adjacent to the open end  325  and a second axial section  345  adjacent to the lid end  330 . Between sections  340  and  345  lies a taper  350  and the inner diameter of the first section  340  is wide enough to receive the filter housing  170  while the second section  345  preferably has a smaller diameter. A bending radius of the cap  175  between the radial and axial segments—between the radially extending lid portion and the circumferential sidewall extending from the lid end  330  to the open end  325 —may be sized so the chamfer  230  of the cylindrical section  180  makes no contact with the cap  175  in the bent area. 
       FIG. 4  shows different stages of a method  400  for assembling the filter assembly  110  according to  FIGS. 1 to 3 . In a first step  405 , the filter element  165  is axially inserted into the filter housing  170 . A second step  410  shows the filter element  165  installed at a filter housing  170  in such a way that the first end  220  of cylindrical section  180  abuts on the protrusion  305  of the filter housing  170 . 
     In a subsequent step  415 , the cap  175  is axially pressed onto the filter housing  170  until an axial surface of cap  175  at lid end  330  makes contact with the second axial end  225  of cylindrical section  180  of filter element  165  as shown in a step  420 . This may require a pressing force which overcomes a frictional force between the first axial section  340  and the filter housing  170  and/or between the second axial section  345  and the cylindrical section  180 . The frictional forces may be determined by an alignment of inner diameters of the cap  175  and outer diameters of the cylindrical section  180  or the housing  170 . 
     In some embodiments, the pressing continues until the pressing force exceeds a predetermined force which is larger than the sum of the predetermined frictional forces. This serves to ensure that the cylindrical section  180  lies between the lid end  330  of the cap  175  and the protrusion  305  of the filter housing  170  in an axial manner.