Patent Publication Number: US-6209798-B1

Title: Tappet retention for a fuel injector

Description:
RELATION TO OTHER PATENT APPLICATION 
     This application is a continuation-in-part of application Ser. No. 08/955,588, filed Oct. 22, 1997, and entitled TAPPET RETENTION FOR A FUEL INJECTOR and now abandoned. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to tappet assemblies for fuel injectors, and more particularly to a mechanism that maintains a tappet connected to the body of a fuel injector during shipping, handling and installation. 
     BACKGROUND ART 
     One class of fuel injectors are mechanically actuated via a rocker arm assembly that moves with each rotation of an engine&#39;s cam shaft. The rocker arm moves a tappet downward, and a plunger underneath the tappet pressurizes fuel during the downward stroke. A spring retracts the plunger and tappet between injection events. The spring, which is always compressed, also maintains the tappet in contact with the rocker arm throughout the operation of the system. In most of these types of injectors, the compression spring pushes the tappet away from the injector body, but the rocker arm limits how far the tappet can be moved away from the injector body, and thus prevents the tappet from disconnecting from the injector body after installation. 
     During assembly, shipping and handling before the injector is installed in an engine, there is often the possibility that the tappet will accidentally disconnect from the injector body. This occurs because the tappet return spring pushes the tappet away from the injector body, and there is often no means provided for holding the tappet connected to the injector body prior to installation. In some instances, it is possible to use an external clamping mechanism to hold the tappet to the injector body prior to, and during, installation in an engine. However, in many cases space constraints during installation are so severe that no room on the outside of the assembled injector is available for retaining the tappet in the injector body. In these cases, one must either include an internal retention means or accept the risk that some tappets will become disconnected from their respective injector bodies during pre-installation shipping and handling. Oftentimes internal retention means are limited or unavailable due to internal structural and space constraints. In addition, any retention means should be either removable upon installation or arranged such that the same will not interfere with normal operation of the injector after being installed in an engine. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     DISCLOSURE OF THE INVENTION 
     A fuel injector includes a tappet assembly mounted on an injector body. At least one of the tappet assembly and the injector body define a retention opening therethrough. A retention member is positioned in the retention opening and concealed by at least one of the tappet assembly and the injector body. The tappet assembly is moveable with respect to the injector body an unadjustable displacement distance between an advanced position and an extended position. The height of the retention opening is less than the unadjustable displacement distance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectioned side diagramatic view of an engine with a fuel injector according to the present invention installed therein. 
     FIG. 2 is a sectioned side diagramatic view of an upper portion of a fuel injector according to one embodiment of the present invention. 
     FIG. 3 is a sectioned side diagramatic view of an upper portion of a fuel injector according to another embodiment of the present invention. 
     FIG. 4 is a sectioned side side diagramatic view of an upper portion of a fuel injector according to still another embodiment of the present invention. 
     FIG. 5 is a sectioned side diagramatic view of an upper portion of a fuel injector according to still another embodiment of the present invention. 
     FIG. 6 is a sectioned side diagramatic view of an upper portion of a fuel injector according to yet another embodiment of the present invention. 
     FIG. 7 is a sectioned side diagramatic view of an upper portion of a fuel injector according to still another embodiment of the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring now to FIG. 1, an engine  10  has a fuel injector  11  installed such that nozzle outlet  13  opens to a cylinder bore, as in a conventional diesel type engine. With each cycle of the engine, a lifter assembly  19  is moved upward about lifter group shaft  18 . Lifter assembly  19  acts upon rocker arm assembly  16 , which is mounted to pivot about rocker arm shaft  17 . A portion of rocker arm assembly  16  is in contact with a tappet  14  that is mated to injector body  12  of fuel injector  11 . A compression spring  15  has one end in contact with injector body  12  and its other end in contact with tappet  14 . Compression spring  14  normally pushes tappet  14  away from injector body  12 , such that rocker arm assembly  16  maintains contact with tappet  14  in a conventional manner. With each cycle of engine  10 , tappet  14  is driven downward to move a plunger within injector body  12 . The downward stroke of the plunger within fuel injector  11  pressurizes fuel so that fuel commences to spray out of nozzle outlet  13  in a manner well known in the art. 
     Referring now to FIG. 2, the upper portion  20  of fuel injector  11  is shown as it would appear during pre-installation shipping and handling. In this embodiment, injector body  12  defines a tappet bore  31  through a tappet barrel  30 , which defines an annular indentation  32 . Indentation  32  and bore  31  are centered about centerline axis  26 . A portion of annular indentation  32  is defined by an annular ledge  33  that preferably lies in a plane perpendicular to axis  26 . Annular ledge  33  can be thought of as an upper retention surface. Although annular ledge  33  is shown horizontal, it can also have a rounded, frusto conical, or other shape depending on machining and other considerations. A plunger  22  includes an annulus  23  near its upper end that receives a retainer ring  24  to connect plunger  22  to holder member  40 . 
     Tappet assembly  14  includes plunger  22 , plug member  45  and holder member  40 , which has a male extension portion that is guided in tappet bore  31 , which can be considered a female portion. Together, holder member  40  and plug member  45  can be thought of as the tappet for tappet assembly  14 . Holder member  40  also includes a plug bore  41  and a retention opening  42  within which is positioned a retention member  50 . In this embodiment, retention opening  42  is preferably circular, and retention member  50  is preferably a cylindrical pin. Opening  42  preferably has a diameter just larger than that of cylindrical pin  50 . The bottom portion of side opening  42  acts as a lower retention surface  43 . A plug member  45  rests on a ledge in plug bore  41  and has one end adjacent plunger  22  and an other end that includes a rocker arm contact surface  46 . Plug member  41  includes an annulus  48  that receives an o-ring  49  that creates a friction fit to prevent the plug member  41  from falling out of holder member  40  during pre-installation shipping and handling. 
     A compression spring  15  normally pushes tappet assembly  14  away from injector body  12  to an extended position  60 , as shown, in which cylindrical pin  50  is pinched between upper retention surface  33  and lower retention surface  43 . This occurs because cylindrical pin  50  has a length that is greater than the wall thickness of holder member  40 . Annular surface  34  of plug member  45  maintains cylindrical pin  50  a minimum distance away from centerline axis  26 . This insures that a portion of cylindrical pin  50  always protrudes into annular indentation  32  so that pin  50  comes in contact with upper retention surface  33  when compression spring  15  pushes tappet assembly  14  upward. After installation, tappet assembly  14  moves between an installed retracted position  61  and an advanced position  62  during normal operation of fuel injector  11 . Thus, after installation, cylindrical pin  50  no longer has the possibility of coming in contact with upper retention surface  33 . This prevents cylindrical pin  50  from having any significant effect on the operation of fuel injector  11  after the same is properly installed in an engine. 
     During assembly, retainer ring  24  is attached to plunger  22  and the same is inserted into holder member  40  away from injector body  12 . This subassembly is then mated to injector body  12  by inserting the male portion of tappet assembly  14  into the female portion of injector body  12  such that plunger  22  is located in its guide bore  35 . After this occurs, cylindrical pin  50  is positioned in opening  42  and plug member  45  is advanced into plug bore  41 . This traps pin  50  in side opening  42  between annular surface  34  of plug member  41  and injector body  12 . 
     Referring now to FIG. 3, an alternative embodiment of the present invention is illustrated in which a tappet assembly  114  guided on the outer surface of injector body  112 , instead of vice versa as in the previous embodiment. In other words, in this embodiment injector body  112  includes a male portion that is mated to a female portion of tappet assembly  114 , whereas the opposite was true for the previous embodiment. This embodiment also differs in that the side opening  143  is made through injector body  112 , and the cylindrical pin  50  is trapped between annular surface  148  of plunger  147  and holder member  140 . Plunger  147  is guided in plunger bore  135 , which is an inner surface of injector body  112 . In this embodiment, the outer surface  148   a  of plunger  147  maintains cylindrical pin  50  a minimum distance away from injector centerline axis  126 . Tappet assembly  114  is locked onto injector body  112  since pin  50  has a length greater than the wall thickness of tappet barrel  130 , which is received in guide bore  142 . This ensures that a portion of pin  50  always protrudes into an indentation  132  made in holder member  140 . 
     FIG. 3 shows fuel injector  110  in its installed retracted position, in which cylindrical pin  50  is away from lower retention surface  146 . Before installation in an engine, compression spring  149  naturally pushes tappet assembly  114  to an extended position in which cylindrical pin  50  is pinched between lower retention surface  146  and upper retention surface  133 . Upper retention surface  133  is the upper portion of opening  143  through the tappet barrel portion  130  of injector body  112 . A subtle advantage of this embodiment relates to the vertical conservation of design space by simultaneously guiding holder portion  140  and plunger  147  on respective inner and outer surfaces of injector body  112  over an identical segment of centerline  126 . 
     Referring now to FIG. 4, still another embodiment of a fuel injector  210  according to the present invention is illustrated. This embodiment shares the vertical design space conservation feature of the previous embodiment by at lease partly guiding its tappet and plunger at an overlapping segment of centerline  226 . This embodiment differs from the embodiment of FIG. 3 in that the indentation has been moved from the inner surface of the holder member to the outer surface of the plunger. However, the retention member is still a cylindrical pin, and the retention surfaces are oriented perpendicular to centerline  226  as in the previous embodiments. This embodiment is also necessarily assembled in a different order from the preceding embodiments. 
     First, plunger  247  is advanced into plunger bore  235 . Next, the retention member  250  is positioned in side opening  243 , which is preferably circular and made through the wall of tappet barrel  230 . Retention member  250  preferably has a uniform diameter just smaller than the diameter (height) of side opening  243 . Next, the biasing compression spring  249  is positioned on top of injector body  212 . Holder member  240  is then advanced so that tappet barrel  230  is received in a guide bore  242  in holder member  240 . Holder member  240  is advanced far enough that a retaining clip  224  can be attached to plunger  247 . Finally, a plug member  245  is attached to holder member  240  in the position shown. 
     By assembling the tappet assembly for the fuel injector  210  in this order, the assembly will not come apart, even under the action of compression spring  249 . Retention member  250  is longer than the thickness of the wall of tappet barrel  230  such that a portion of it always protrudes into an annular indentation  232  that is machined around the side of plunger  247 . A portion of annular indentation  232  is defined by a lower retention surface  246  that contacts retention member  250  when tappet assembly  214  is at its extended position, as shown. When in this position, retention member  250  is pinched between upper retention surface  233 , which is a portion of side opening  243 , and lower retention surface  246 . At the same time, retention member  250  is trapped between the inner surface of holder member  240  and annular surface  248 , to maintain the same a minimum distance from centerline  226 . 
     Referring now to FIG. 5, yet another embodiment of the present invention is illustrated. Note that the FIG. 5 embodiment is substantially similar to the embodiment illustrated in FIG. 2, with the exception that cylindrical pin  50  has been replaced by a retention ball  350 . While the embodiment illustrated in FIG. 2 including a cylindrical pin is preferable, retention ball  350  could instead be utilized as shown in FIG. 5 with adequate results. 
     The use of a ball is less desirable than a cylindrical pin at least in part because of the tendancy of the ball to exert side forces on the tappet assembly when in the extended position, as shown. In addition, the invention can usually be accomplished with a pin having a substantially diameter than a ball, because of the need for an adequate amount of the retention member to protrude into the indentation. Thus, by utilizing a cylindrical pin over that of a ball, one can gain additional precious vertical design space for other portions of the fuel injector. 
     As with the FIG. 2 embodiment, a holder member  340  includes a plug bore  341  and a retention opening  342  within which retention ball  350  is placed. Opening  342  has a diameter that is just larger than that of retention ball  350 . The bottom of side opening  342  acts as a lower retention surface  343 . As with the FIG. 2 embodiment, a compression spring  315  normally pushes tappet assembly  314  away from injector body  312  to an extended position  360 , as shown, in which retention ball  350  is pinched between an upper retention surface  333  and lower retention surface  343 . This occurs because retention ball  350  has a diameter that is greater than the wall thickness of holder member  340 . Annular surface  334  of plug member  345  maintains retention ball  350  a minimum distance away from centerline axis  326  to insure that a portion of retention ball  350  always protrudes into annular indentation  332  so that ball  350  comes in contact with upper retention surface  333  when compression spring  315  pushes tappet assembly  314  upward. After installation, tappet assembly  314  moves between an installed retracted position  361  and an advanced position  362  during normal operation of fuel injector  311 . Thus, after installation, retention ball  350  no longer has the possibility of coming in contact with upper retention surface  333 . As with cylindrical pin  50  in the FIG. 2 embodiment, this prevents retention ball  350  from having any significant effect on the operation of fuel injector  11  after the same is properly installed in an engine. 
     Referring now to FIG. 6, still another alternative embodiment of the present invention is illustrated that is substantially similar to the FIG. 3 embodiment, except retention ball  350  has been substituted for cylindrical pin  50 . In this embodiment, a tappet assembly  414  moves along the outer surface of injector body  412 , as in FIG.  3 . In other words, injector body  412  includes a male portion that is mated to a female portion of tappet assembly  414 . Additionally, the side opening  443  is made through injector body  412 , and the retention ball  350  is trapped between annular surface  448  of plunger  447  and holder member  440 . Plunger  447  moves in plunger bore  435 . In this embodiment, as with the FIG. 3 embodiment, the outer surface of plunger  447  maintains retention ball  350  a minimum distance away from injector centerline axis  426 . Tappet assembly  414  is locked onto injector body  412  since ball  350  has a diameter greater than the wall thickness of tappet barrel  430 , which is received in guide bore  442 . This ensures that a portion of ball  350  always protrudes into an indentation  432  made in holder member  440 . 
     FIG. 6 shows fuel injector  410  in its installed retracted position, in which retention ball  350  is away from lower retention surface  446 . Before installation in an engine, compression spring  449  naturally pushes tappet assembly  414  to an extended position in which retention ball  350  is pinched between lower retention surface  446  and upper retention surface  433 . Upper retention surface  433  is the upper portion of opening  443  through the tappet barrel portion  430  of injector body  412 . 
     Referring now to FIG. 7, yet another embodiment of a fuel injector  510  according to the present invention is illustrated. Note that the FIG. 7 embodiment is substantially similar to the embodiment illustrated in FIG.  4 . However, this embodiment differs from the embodiment of FIG. 4 in that the retention member has an oblong non-spherical shape, rather than a cylindrical pin. Assembly of this embodiment, however, is similar to that of the FIG. 4 embodiment. First, plunger  547  is advanced into plunger bore  535 . Next, the oblong shaped retention member  550  is positioned in side opening  543 , which is made through the wall of tappet barrel  530 . Retention member  550  preferably has a small diameter just smaller than the diameter of side opening  543 . Next, the biasing compression spring  549  is positioned on top of injector body  512 . Holder member  540  is then advanced so that tappet barrel  530  is received in a guide bore  542  in holder member  540 . Holder member  540  is advanced far enough that a retaining clip  524  can be attached to plunger  547 . Finally, a plug member  545  is attached to holder member  540  in the position shown. 
     INDUSTRIAL APPLICABILITY 
     The present invention finds potential applicability in any tappet driven fuel injector, especially those that face the possibility of becoming disconnected during shipping and handling prior to installation. The present invention finds particular applicability in tappet assemblies for mechanically actuated fuel injectors, but could also be used with other mechanical devices. The retention means of the present invention is especially applicable for use in those cases where space and structural constraints limit available space for external clamps and the like. When the invention is assembled it cannot come apart, and the means by which this is accomplished does not affect the operation of the fuel injector after installation. Because the retention means of the present invention preferably does not come into play after the fuel injector is installed in an engine, the displacement distance between the advanced position and the extended position need not be adjustable, which simplifies the structure versus some other devices. 
     The most preferred embodiment of the present invention, FIG. 4, includes several subtle but important advantages. First, the retention opening is circular, which is far easier to machine than the elongated slots that appear in many devices. Second, The retention member is concealed so that one potential opening for debris to enter the fuel injector is eliminated. Third, vertical design space is conserved since the plunger and tappet are partially guided on inner and outer surfaces of the injector body that overlap along a segment of the injectors length. Fourth, by using a cylindrical pin and retention surfaces that are perpendicular to the centerline, undesireable side forces on the tappet assembly are reduced or eliminated. Fifth, the use of a cylindrical pin also conserves a small but significant amount of vertical design space over rounded, especially spherical, retention members. Sixth, unlike some devices, the tappet assembly can rotate with respect to the injector body without interference from the retention means. This can further reduce the possibility of seizure after installation and simplifies the machining and assembly of the relevant injector components. 
     Those skilled in the art will appreciate that numerous modifications and alternative embodiments of the present invention will be apparent in view of the foregoing description. For instance, although the retention member in the FIGS. 2 and 3 embodiments has been illustrated as being a cylindrical pin, those skilled in the art will appreciate that retention members having other shapes, such as the oblong shape of FIG. 7, could work equally well. In addition, the indentation in which the retention member is trapped is preferably annular such that the tappet assembly can rotate with respect to the injector body both before and after installation; however, in some instances it may be desirable to make the indentation simply a vertical groove within which the cylindrical pin travels up and down during movement of the tappet assembly, but otherwise prevents the tappet assembly from rotating with respect to the injector body. This alternative is shown for example in FIG.  3 . Accordingly, this description is to be construed as illustrative only, and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure may be varied substantially without departing from the spirit of the invention, the scope of which is defined in terms of the claims as set forth below.