Abstract:
Vapors in the fuel tank of a vehicle are collected in a carbon canister. An ejector or aspirator is used to purge the carbon canister in a pressure-charged engine in which a positive pressure exists in the intake. A compact ejector includes a substantially planar flange and a venturi tube coupled to the flange with a central axis of the venturi tube substantially parallel to the flange. By mounting the ejector on an intake component, having the venturi tube on the inside of the intake component, and having the venturi tube parallel to the flange yields a very compact package and protects the ejector from damage from other engine components.

Description:
FIELD OF INVENTION 
     The present disclosure relates to a vapor purge system for an internal combustion engine, particularly related to an ejector for aiding purge during boosted operation. 
     BACKGROUND 
     Vehicles are equipped with an evaporative emission control system that traps fuel vapors from the fuel tank of the vehicle and stores them in a canister in which charcoal particles or other suitable media are disposed. The fuel vapors are absorbed onto the charcoal particles. To avoid overloading the canister such that the charcoal particles have no further capacity to absorb fuel vapors, the canister is purged regularly. 
     In a naturally-aspirated internal combustion engine, the pressure in the intake manifold is depressed. This vacuum is used to draw fresh air through the canister. The vapor-laden air is then inducted into the engine and combusted. A purge valve or port is provided that fluidly couples the canister with the intake of the engine when purging is desired. 
     In boosted engines, i.e., turbocharged, supercharged, or boosted by any suitable device, pressure in the engine&#39;s intake is often above atmospheric thereby reducing the available times for purging. To obtain a vacuum to drive purge flow, a tube with a throat (reduced diameter section) causes a higher flowrate which causes the vacuum. The component in which the throat is included is called an ejector or an aspirator. 
     An example of a prior art configuration in  FIG. 1 . An engine  10  has an air intake system including a manifold  12  and a throttle body  14 . Throttle body  14  has an air passage  16  and a throttle valve  18  to control the quantity of air flowing into manifold  12 . Throttle body  14  has an inlet  20  fluidly connected to an outlet  22  of a turbocharger assembly  24 . 
     Turbocharger assembly  24  includes a compressor  26  and a turbine  28 . Compressor  26  and turbine  28  are both mounted upon a common shaft  30 . Exhaust gases are directed through a duct  32  to turbine  28  and discharged through an outlet tube  34 . 
     Compressor  26  receives air from an inlet duct  36 . Air is pressurized by compressor  26  and discharged into outlet  22  and then into throttle body  14  or charge air cooler into manifold  12  and then into engine  10 . 
     Modern engines are equipped with vapor emission control systems which include a fuel vapor storage canister  38 . Vapor storage canister  38  has a quantity of activated charcoal particles  40  or other suitable adsorbent material. Activated charcoal absorbs fuel vapor and stores them. Charcoal particles  40  are secured between a lower screen  42  and an upper screen  44 . Fuel vapors and air are routed to the interior of canister  38 . 
     Charcoal  40  has a finite storage capacity of fuel vapor. Therefore, the canister is purged periodically to remove fuel vapor from the charcoal by drawing air from the atmosphere into the canister and through the activated charcoal bed. Atmospheric air flows through picks up molecules of fuel vapor in an adsorption process. The fuel laden air is drawing into combustion chambers of engine  10  and burned. An air inlet  46  is provided to allow purge air to engine canister  38 . Air from inlet  46  passes downward through a duct  48  to a space  50  beneath the screen  42  and above the bottom of canister  38 . 
     Canister  38  has an outlet opening  52  to allow purge air and fuel vapors to be discharged from canister  38 . Normally, purge air and fuel vapor is desorbed from the charcoal through a conduit  54  to either of conduits  56  or  58 ; alternatively, the conduit can be coupled to the intake manifold. When engine  10  is idling, throttle valve  18  assumes a position  18 ′ and the interior of throttle body  14  downstream of throttle valve  18  is at a vacuum. During this period, purge air is drawn from conduit  56  through an orifice  60 . Excessive purge can interfere with engine performance. A fuel vapor management valve  62  controls air-fuel vapor purge based on engine operating conditions into intake manifold  12 . 
     When engine  10  is operating at part throttle, i.e. with throttle valve  18  between the idle position and wide open throttle (position shown as element  18  in  FIG. 1 ). The portion of throttle body  14  upstream of throttle valve  18  is exposed to manifold vacuum pressure. This vacuum includes air flow through conduit  58 , check valve  64 , an orifice  66 , and port  68  into throttle body  14 . Purge flow is influenced by the relative position of throttle valve  18  to port  68  and by the size of the orifice. Orifice  66  limits the purge air flow into engine  10  as appropriate for good operation. 
     When engine  10  is operating under boost conditions, compressor  26  generates a greater pressure at outlet  22  of turbocharger  24  than at inlet  36 . Under these conditions, compressor  26  generates a positive pressure in throttle body  14  and in manifold  12 . Check valves  62 ,  64  prevent air flow from throttle body  14 . The positive pressure at outlet  22  causes air to flow through a conduit  70  to an inlet end portion  72  of an ejector  74 . Ejector  74  includes a housing defining inlet end portion  72 , outlet end portion  66  and a reduced dimension passage  78  (throat) there between. Air passes from inlet  72  through throat  78  to an outlet  76  and then through conduit  80  to inlet  36  of compressor  26 . Flow of air through throat  78  reduces pressure as is well known by one skilled in the art. 
     Ejector  74  also includes a purge air passage  82  which opens into passage  78 . Conduit  54  is connected to the purge air passage of ejector  74 . A check valve  84  allows the flow of air and vapors from conduit  54  into passage  82  and then into passage  78 . Finally, purge air and vapor pass through conduit  70  into throttle body  14  and then into engine  10 . During non-boost operation of engine  10 , check valve  84  prevents air flow from ejector  74  back to canister  38 . 
     The above-described emissions control operates effectively to route purged vapors to engine  10  and treatment by a catalytic converter (not shown). However, under some conditions, it is undesirable to purge canister  38 . For example, when the catalytic converter is too cool to effectively process exhaust gases, provision is made to prevent canister purging. A control valve  86  is provided downstream of outlet opening  52  from canister  38 . Valve  86  has an outlet port  88  formed by a valve seat  90 . A movable valving member such as a diaphragm  92  is normally positioned by a spring  94  against seat  90  so that air cannot flow through valve  86 . This is the condition of the valve when no purge is desired as mentioned above. 
     When air flow through valve  86  is desired, a vacuum pressure is introduced into valve  86  above the diaphragm  92  which unblocks port  88 . Vacuum is directed to valve  86  through a conduit  96  which is connected to a port of a solenoid controlled on-off valve  98 . Another port of valve  108  is connected to a conduit  100 . In turn, the conduit is connected to a conduit  104 . An electric solenoid valve  108  is connected to a conduit  100 . In turn, conduit  100  is connected to check valve  102  which is connected to a conduit  104 . When open, vacuum is communicated to the space above diaphragm  92  thus allowing purging. When closed, no vacuum is routed to the space above diaphragm  92  thus allowing purging. When closed, no vacuum is routed to the space above the diaphragm and port  88  is blocked thus preventing purging of canister  38 . Solenoid valve  108  is commanded to energize by an engine electronic control unit  110  (ECU). 
     The componentry shown in  FIG. 1  is provided merely as background to the present disclosure and is not intended to be limiting in any way. The components are known to be coupled in alternative ways to that shown in  FIG. 1 . 
     Ejector  74  of  FIG. 1  suffers from multiple deficiencies. It is a stand-alone part that must be separately packaged, protected from damage, and supported. It is known to mount an ejector on an engine intake component, such as shown in  FIG. 4 . Referring first to  FIG. 2 , an ejector  120  is shown that has a flange  122  through which tubes  124  and  126  extend. Ejector  120  is shown in cross section in  FIG. 3 . Disposed in tube  124  is an insert  130  with a reduced cross section. Insert  130  has a throat  132  with a small cross section. The speed at which gases move through throat  132  is much greater than the speed of the flow at an inlet of tube  124 . Downstream of insert  130  is a straight section  136 . It would be preferable to have this be a diverging tube. Prior art manufacturing methods led to tube  136  being straight. Tube  134  couples to tube  124  at the location of throat  132  via a tee tube  134  to thereby induce flow through  126 . In the fabrication of ejector  120 , the inside diameter of tube  134  is formed through an orifice proximate a plug  128 . After fabrication, tee tube  134  is sealed via plug  128 . Ejector  120  is shown mounted to an air box  150  in  FIG. 4 . 
     The ejector system shown in  FIG. 4  presents some deficiencies. Referring to  FIG. 4 , the depth that the ejector extends into air box  150  is shown by numeral  140  and the width of ejector  120  within air box  150  is shown by numeral  142  in  FIG. 3 . This presents considerable encroachment on the interior of air box  150 . Air boxes have unique designs depending on the engine, the vehicle, and other package considerations such as other accessories. Although it would be desirable for a vehicle manufacturer to have three or four standard air boxes, in reality, there is little crossover among different vehicles. It is likely that many unique ejectors would be required to mate to a variety of air boxes. The considerable encroachment can also cause higher flow restriction for the air passing through the duct. The ejector of  FIGS. 2-4  has three elements: the main body of ejector  120 , a cap  144 , and insert  130 . Insert  130  is sometimes molded separately to avoid a molding process in which a thin pin is used to form the opening. A tube  136  downstream of insert  130  is straight because a pin is pulled to form tube  136 . This is not the preferred shape, simply what is available based on the manufacturing process. Disadvantages in the prior art include: the requirement of molding a separate piece for the insert and a plug; obtaining an ejector with less than desired flow characteristics (due to having straight section downstream of the throat); and the resulting ejector is bulkier than desired. 
     An ejector that is compact and easy to manufacture while maintaining tight tolerances, particularly in the throat area, is desired. 
     SUMMARY 
     To overcome at least one problem in the prior art, an ejector for a canister purge system of a boosted engine is disclosed that has a flange, a venturi tube coupled to the flange, and first and second tubes extending through the flange. The first tube fluidly couples to one end of the venturi tube. The second tube fluidly couples to a downstream end of a throat of the venturi tube. The ejector comprises first and second pieces coupled together. The first piece comprises the first and second tubes, the flange, and an upper half of the venturi tube. The second piece comprises a lower half of the venturi tube. 
     The flange is substantially planar and a centerline of the venturi tube is substantially parallel to the flange. 
     The second tube is substantially perpendicular to the flange and a centerline of the first tube and a centerline of the second tube form an acute angle. Or in other embodiments, a centerline of the first tube and a centerline of the second tube are substantially parallel; and the centerline of the first tube is substantially perpendicular to the flange. 
     The first piece and the second piece are coupled sonic welding, vibration welding, induction welding, laser welding, ultrasonic welding, hot plate, and infrared welding, or thermal welding. In other embodiments, the first and second pieces are coupled by a plurality of snap fit connectors arranged around the periphery of the first and second pieces. A seal between the first and second pieces is provided by one of: an adhesive material provided on the interface surfaces of the first and second pieces and a groove in at least one of the interface surfaces with an O-ring disposed in the groove. In some embodiments, the seal is unnecessary. 
     The venturi tube comprises a converging section to which the first tube is fluidly coupled, the throat, and a diverging section. In some embodiments, the throat diverges. 
     In some embodiments, a centerline of the diverging section angles downward slightly with respect to the flange. In some embodiments, the diverging section has a circular cross section at the throat and a cross section of a flattened circle at the exit with the portion of the circle that is flattened is proximate the flange. 
     Also disclosed is an ejector system with an ejector that includes a venturi tube having a converging section, a throat, and a diverging section; a first tube fluidly coupled to the converging section; and a second tube fluidly coupled to the throat. The venturi tube has first and second pieces welded together. 
     An interface between the first and second pieces of the ejector is substantially coincident with a diameter of the venturi tube. 
     The first piece of the ejector includes the first and second tubes and a flange through which the first and second tubes pass. 
     The ejector system further has an intake system component defining an opening and having a flat surface at the periphery of the opening. A periphery of the flange also has a flat surface. The flat surface of the flange is welded or otherwise attached or integrated to the flat surface of the opening associated with the intake system component. 
     The intake system component is an air cleaner box or an air duct. 
     Flash traps are provided adjacent to the surface of the opening associated with the intake system component. Such flash traps largely prevent flowing material from getting into places that would interfere with the performance of the ejector. 
     At least one flash trap is provided in the flange of the ejector immediately adjacent to the surface of the flange that is welded to the intake system component. 
     The first tube is also fluidly coupled to an air intake and the second tube is also fluidly coupled to a volume associated with a fuel tank. 
     An ejector system for a boosted engine includes: an air duct and an ejector coupled to the air duct. The ejector has: a first piece having a first tube, a second tube, a flange with a flat surface around the periphery, and a first portion of a venturi tube; and a second piece that is coupled to the first piece and comprises a second portion of the venturi tube. The first and second pieces are affixed by welding, snap fitting, and mechanical fasteners. 
     The air duct defines an opening with a flat surface surrounding the opening. The flange of the ejector has a flat surface that interfaces with the flat surface of the air duct. The flat surface of the ejector is welded to the flat surface of the air duct with the venturi tube of the ejector located inside the air duct. 
     The venturi tube of the ejector includes a converging section, a throat, and a diverging section. A centerline of the converging section and a centerlines of the throat are substantially parallel to the flange. A centerline of the diverging section dips downward from plane of the flange as considered in the direction of flow. 
     In one embodiment, an ejector for a canister purge system of a boosted engine, includes: a flange; a venturi tube coupled to the flange, the venturi tube comprising a converging section, a throat, and a diverging section (alternatively called a diffuser); a first tube fluidly coupled to the venturi tube upstream of the converging section; a second tube fluidly coupled immediately downstream of the throat; and an intake system component defining an opening and having a surface at the periphery of the opening. A periphery of the flange has a surface that is affixed to the surface of the opening associated with the intake system component. 
     In some embodiments in which the first and second pieces of the ejector are welded, one of the two pieces of the ejector has a skirt extending from a periphery of the ejector. The skirt forms a butt weld and the mating surfaces form a butt weld. The skirt serves as a pilot to locate the two pieces before welding. 
     The ejector is formed by one of: injection molding, 3-D printing, casting, vacuum forming, blow molding, rotomolding, resin transfer molding, and machining from a blank. 
     In some embodiments, a centerline of the diverging section is offset from a centerline of the converging section of the venturi tube. The offset can be in vertically upward or downward direction. 
     The ejector is affixed to the intake air component by one of: a weld, screws, mechanical fasteners, rivets, and an adhesive. 
     In some embodiments, the ejector is a single piece, such as with 3-D printing. In other embodiments, the majority of the ejector is made in a single piece with a plug in one end. The plug could be threaded or affixed in any suitable manner. Such embodiments are suitable for traditional casting processes or machining from a blank, as non-limiting examples. 
     In some ejectors one of the tube is canted with respect to the flange in in some embodiments both tubes are canted with respect to the flange, i.e., a centerline of the tube forms an acute angle with the flange. 
     To prevent recirculation at some operating conditions, it has been found helpful to provide a divot that extends into the flow path of the diverging section of the ejector. In some embodiments, the divot is like an extended tear drop and in other embodiments, it is squared off. Other shapes are also within the scope of the disclosure. 
     By placing the venturi tube within the air system component, the ejector system is more protected from potential breakage by carelessness or in a crash than when the ejector is primarily external. 
     Having the venturi tube substantially parallel to the flange of the ejector means the ejector extends into the air system component to which it is affixed to a much lesser extent than if the venturi tube is perpendicular to the flange, such as in the prior art shown in  FIGS. 2 and 3 . 
     Advantages of the disclosed embodiments include: simplified construction, improved quality, fewer parts, lower piece cost, lower tooling investment, fewer assembly steps, lower weight, and more reliable and repeatable manufacturing and assembly. 
     In applications where packaging is tight, the embodiment in which one of the tubes is canted with respected to the other tube shortens the ejector length. If further shortening is desired, the flange is shortened in the vicinity of the exit of the diverging section. Both shortening embodiments can be combined to provide a very compact injector. 
     In the prior art method of making an ejector, as will be discussed in more detail below, a pin is used to form the throat. In some applications, the pin to form the throat of the venturi is so thin and long that it is very likely to break causing manufacturing downtime. The ejector disclosed herein eliminates such need for a pin at all. 
     Another issue that occurs due to the pin is molding flash, i.e., excess material that moves into a spot wherein it is not intended to be. For the converging and diverging sections of the venturi, the diameter is fairly large and a bit of flashing doesn&#39;t cause substantial blockage. It may disrupt the flow a bit and cause some flow losses. However, flashing in the throat area is particularly troublesome and will cause variation in performance, at least, and will likely fail. Furthermore, it could become a source of contamination. It is a quality problem and a scrap problem. 
     The ejector according to embodiments disclosed herein provide a substantial performance advantage of about 25% greater flow over the boost range compared to prior art ejectors. The reason for the advantage in flow is due to the two-piece sectioning of the ejector through the venturi affording the ability to optimize the geometry in the venturi. The advantage also applies to one-piece ejectors in which the geometry is similarly controlled in a manner superior to prior art ejectors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a canister purge system which includes an ejector according to the prior art; 
         FIG. 2  is a prior art ejector; 
         FIG. 3  is the ejector of  FIG. 2  in cross section; 
         FIG. 4  is the ejector of  FIG. 2  shown installed in an air box; 
         FIG. 5  is an ejector according to an embodiment of the disclosure; 
         FIG. 6  is the ejector of  FIG. 5  shown in cross section; 
         FIG. 7  is an ejector according to an embodiment of the disclosure shown in cross section; 
         FIG. 8  is a cross section of an exit section of a venturi tube according to an embodiment of the disclosure; 
         FIG. 9  is a graph of flowrate as a function of boost pressure comparing a prior art ejector and a presently disclosed ejector; 
         FIGS. 10 and 11  are cross sections of a portion of ejectors having snap fit connections; 
         FIG. 12  is a flowchart illustrating a prior art process by which an ejector can be fabricated; 
         FIG. 13  is a flowchart illustrating a process, according to the present disclosure, by which an ejector can be fabricated; 
         FIGS. 14 and 15  are flowcharts showing alternative processes to those shown in  FIG. 13 ; 
         FIG. 16  is a flowchart showing processes involved in installing the ejector into an engine air component; 
         FIG. 17  is an illustration showing an air duct and an ejector prior to assembly; 
         FIG. 18  is a cross section of the air duct and the ejector after assembly; 
         FIG. 19  is a cross-sectional view of a shortened ejector; 
         FIG. 20  is an illustration showing an air duct with the shortened ejector of  FIG. 19  prior to assembly; 
         FIG. 21  is a one-piece embodiment of the ejector that provides tight tolerance for the diverging section, the converging section, and the throat; 
         FIG. 22  is a two-piece embodiment of the ejector in which the centerline of the converging section is offset from the centerline of the diverging section; 
         FIG. 23  is an expanded, cross-sectional view of a portion of the two pieces of ejector, showing an energy director and a skirt; 
         FIG. 24  is an isometric view of an ejector having a divot proximate the exit of the diverging section; 
         FIGS. 25 and 26  are two views of the diverging section of the ejector of  FIG. 24 ; and 
         FIG. 27  is an isometric view of an ejector having a squared off divot proximate the exit of the diverging section. 
     
    
    
     DETAILED DESCRIPTION 
     As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
     One embodiment of an ejector  150  according to the disclosure is shown in  FIGS. 5 and 6 . Ejector  150  has a flange  152  with a surface  154 . Surface  154  allows coupling with the periphery of an opening in an intake component. Flange  152  has a first tube  160  having a centerline  164  and a second tube  162  having a centerline  166  extending there through. First tube  160  is coupled to an air inlet (not shown) to bring in fresh air. Second tube  162  is coupled to a carbon canister (also not shown) to purge the carbon canister. A venturi tube  170  is at the bottom of ejector  150 . A first end  172  of venturi tube  170  is closed and a second end  174  is open. The fresh air through first tube  160  and the fuel vapor laden gases of second tube  162  that are mixed in venturi tube  170  exits through second end  174 . Ejector  150  is made up of two pieces that are welded together at an interfaces of the two parts to form weld joint  176 . Weld joint  176  is slightly angled in ejector  150 . In other embodiments, weld joint is planar. The first piece includes the elements above weld joint  176 , i.e., first tube  160 , second tube  162 , flange  152  and an upper portion of venturi tube  170 . The second piece includes a lower portion of venturi tube  170 . 
     Weld joint  176  is substantially parallel to flange  152  and is coincident with a diameter of an opening through venturi tube  170 . Referring now to  FIG. 6 , which is a cross-sectional view of  FIG. 5 , an internal shape of venturi tube is shown. An entrance section  180  receives fresh air from tube  160 . The purpose of entrance section  180  is to straighten the flow after traveling through the 90-degree bend between tube  160  and entrance section  180 . A converging section  182  is downstream of entrance section  180 . Flow is accelerated in converging section  182 . Flow from converging  182  is introduced into a throat  184 . Throat  184  includes the smallest cross-sectional portion of venturi tube  170 . The embodiment of throat  184  shown in  FIG. 6  slightly diverges. The downstream end of second tube  162  couples to venturi tube  170  immediately downstream throat  184 . As is well known by one skilled in the art, the acceleration of flow in the throat area leads to a drop in pressure, which draws the flow through tube  162 . Downstream of throat  184  is diverging section  186 . In the embodiment in  FIG. 6 , a centerline of diverging section  184  dips downward as considered from left to right. This improves flow characteristics. In other embodiments, the centerline of the venturi tube is straight. In some embodiments, such as shown in  FIG. 6 , tube  162  expands near a downstream end, such as the portion  165  of tube  162  shows. In some embodiments, the weld between the two pieces of ejector  150  in  FIG. 6  is a combination of a butt weld at the interface between the two surfaces and a shear weld. The shear weld comes about by providing a skirt  168  on the lower piece of ejector  150  that extends toward the upper piece. In an alternative embodiment, the skirt can be provided on the upper piece of ejector  150 . 
     Referring to  FIG. 7 , an alternative embodiment of an ejector  200  is shown that includes a flange  202  and first and second tubes  210  and  212 , respectively, which extend through flange  202 . First tube  210  is canted with respect to second tube  212 . A centerline  220  of first tube  210  forms an acute angle  230  with respect to flange  202 . An advantage of such a configuration is that tube  210  doubles as an entrance section of the venturi tube. A converging section  232  couples directly with first tube  210 . A throat  234  is downstream of converging section  232 . A diverging section  226  is downstream of throat  234 . Ejector  200  is made up of two separately formed pieces that are affixed at a weld joint  226 . Alternatively, these can be snap fit, twist locked, mechanically fastened, or coupled with an adhesive. 
     One of the advantage of ejector  200  of  FIG. 7  is that the length of ejector  200  is shown as  240  compared to length  190  of ejector  150  of  FIG. 6  is shorter. Such a configuration requires a smaller opening in an air intake component to accommodate it. In an application where the intake duct has many curves and bends, there may be only a short section that is straight enough to accommodate the ejector. Thus, a short ejector is particularly useful in certain applications. 
     As will be discussed below, ejector  200  is coupled to an air intake component. In some embodiments, a surface  240  on the underside of flange  202  interfaces or mates with a surface on the intake air component. As discussed, some of the material is displaced into a place where it is not wanted during the molding process, molding flash. When ejector  200  is welded to the air intake component, welding flash develops. To present welding flash from going into places that would interfere with the function of the ejector, flash traps  242  and  244  are provided on either side of ejector  200 . 
     Analysis of the design has indicated that it is preferable for exit cross section of the ejector ( 150 ,  200 , as examples) to be a flattened circle. An exit  190  of an ejector is shown in  FIG. 8 . The upper portion  192  of exit  190  is flattened. Exit  190  is made up of two pieces that are welded together at interfaces  194 . 
     Flowrate  850  of a prior art ejector and flowrate  860  of the ejector of  FIGS. 7 and 8  have been compared and are shown in  FIG. 9 . The ejector, according to the present disclosure, has significantly improved flowrate at all boost pressures. The improved flowrate is due to the venturi tube having a distinct converging and diverging sections rather than straight tubes found in the prior art. 
     In an alternative embodiment in  FIG. 10 , an alternative method of affixing the upper piece  502  and lower piece  504  of a cross section of a portion of an ejector  500  is shown. Lower piece  504  is provided with a groove  506  in a face of lower piece  504  that interfaces with lower piece  502 . An O-ring  508  is placed into groove  506 . Upper piece  502  is provided with a recess  510  along an outer surface. Recess  510  does not extend all the way to the interface with lower piece  502 . A lip  514  extends outwardly. Lower piece  512  is molded with a flexible finger  510  that engages with lip  514 . 
     In another embodiment in  FIG. 11 , a cross section of a portion of an ejector  520  has an upper piece  522  and a lower piece  524 . Upper piece  520  has a wedge  530  that extends outwardly from the surface. Lower piece  524  has a flexible finger  532  that engages with wedge  530 . In the embodiment in  FIG. 11 , an adhesive  526  has been applied to the interface surface of upper part  522  and/or the interface surface of lower part  524 . In the discussion of  FIGS. 10 and 11 , the flexible finger is on the lower part. However, this is simply a non-limiting example. Variations of these examples are also within the scope of the disclosure 
     The improved design of the ejector disclosed herein is at least partially due to a new method of manufacturing such ejectors. A prior art process is shown in  FIG. 12 . In blocks  300  and  302 , the resin to provide to the injector molder is of the appropriate specification and that is properly dried, respectively. In block  304 , the resin is injected into the three molds to produce: an ejector body, a plug, and an orifice piece that includes at least the throat of the venturi. The orifice part is molded separately because the orifice size at the throat is small. It is possible to integrate the orifice piece into the ejector body. However, a thin pin is required to form the throat. A rule of thumb is that the length of the pin should be no more than 3.5 times the diameter of the pin. Such a pin for an integrated throat would exceed this safe number by at least an order of magnitude. Such a thin pin that much extend into the ejector body at such a distance is likely to lead to failures of the pin. This causes breakage, downtime, increases scrap, and generally increases the cost of the manufacturing process. The more robust method to manufacture, according to the prior art, is to make the orifice piece separately. In block  306 , the orifice part is inserted into the ejector body. Each of the ejector bodies is inspected in block  308 . If improperly installed, the part is rejected in block  310 . If proper installation, the plug is affixed to the ejector body in block  312 . In the prior art ejector such as shown in  FIGS. 2 and 3 , almost the entire ejector is formed in one piece. To form tube  134  of  FIG. 3 , an opening at one end is provided that is closed off by plug  144 . 
     Quality assurance measures begin in block  350  in which all of leak, flow and vacuum draw are measured and it is determined whether they are in acceptable ranges. If so, the ejector is ready for assembly into an engine intake component, in block  352 . If out of specification in block  350 , it is determined whether the flaw was caused by the molding process or molding flash (excess material on the part) in block  360 . If that is determined to be the issue, in block  362 , the molding process is adjusted or machine maintenance is performed and it is verified that the correction is effective before resuming. If a negative result from block  360 , in block  370 , it is determined whether the flaw was caused by the welding process. If so, the weld tooling or process is adjusted in block  372 . Also, in block  372 , it is determined whether the correction is effective. If a negative result in block  370 , in block  380 , it is determined whether the flaw is caused by excess moisture and/or whether the resin material is out of specification. If the dryness is causing the flaw, the material drying process is adjusted and verified. If the material is out of specification, the proper material is obtained and loaded into the molding machine, in block  382 . In any case with an out of specification part, the part is scrapped in block  392 . If a negative result in block  390 , additional review of the processes is continued until cause of the flaw is determined and rectified. 
     A flow chart showing processes undertaken to produce the disclosed ejector is shown in  FIG. 13 . Blocks  300 ,  302 ,  350 ,  352 , etc. are mostly the same for the disclosed process and the prior art process. Thus, they are not separately described here. Starting in block  320 , the upper and lower pieces of the ejector are injection molded. In block  322 , the two pieces are affixed. In one embodiment, the pieces are affixed by welding: sonic, ultrasonic, thermal, or any suitable type of welding. An alternative embodiment is shown in  FIG. 14  in which an O-ring is placed in a groove in an interface of the first or second pieces in block  324 . One of the first and second pieces has a flexible finger that engages with a feature on the other piece in block  326 . When the pieces are snapped together, the O-ring is pressed into the groove and seals the first piece with the second piece. In another alternative in  FIG. 15 , the interfaces between the first and second piece is flat. At least one of the interfaces has adhesive applied, block  328 , so that when the first and second pieces are snapped together in block  330 , the adhesive seals the interface between the first and second pieces. 
     In  FIG. 16 , an ejector is manufactured in block  400 , such as by the process in  FIGS. 13-16 . In block  402 , the air intake component is manufactured with an opening to accommodate the ejector. In some embodiments, the flange of the ejector is as short as possible so that the opening in the intake air component is as small as possible. This is particularly useful when the desired location is in an engine duct with lots of turns, i.e., a limited straight run to accommodate the ejector. In such cases with short flanges, the exit portion of the ejector is tilted downward to access the opening in block  410 . In some other embodiments, the ejector can be put into the orifice directly without tilting. In block  412 , the interface of the flange of the ejector is aligned with the interface of the air intake component, i.e., a raised portion around the opening in the air intake component that is provided for this purpose. The ejector is welded onto the intake air component, in block  414 . 
     In  FIG. 17 , an ejector  600  is shown above an air duct  610  prior to assembly. Ejector  600  has a flange  602 , first and second tubes  604  and  606 , and a venturi tube  608 . Air duct  610  has a protuberance  618  that accommodates forming a flat surface  616  onto which a flange  602  mounts. Surface  616  surrounds an opening  614  into which venturi tube  608  be placed. Opening  614  is large enough to allow venturi tube  608  to go into opening  614  straight on, as shown by arrows  630 . Ejector  600  is affixed to air duct  610  by friction welding or any other suitable process. A cross section of an ejector-air duct assembly is shown in  FIG. 18 . The underside of flange  602  is affixed to the periphery of the opening, surface  616  of  FIG. 17 . 
     The duct shown in  FIGS. 17 and 18  has a straight section that is long enough to accommodate an opening  614  (shown in  FIG. 17 ) for ejector  610 . However, in some applications, air ducts have limited ability to accommodate ejector  610 , or even the shorter ejector shown in  FIG. 7 . A shorter version of ejector  150  of  FIG. 6  is shown in  FIG. 19 . Ejector  188  is nearly identical to ejector  150 , of  FIG. 6 , except that flange  192  couples to diverging section  174  at location  196 , which is closer to tube  162  than in  FIG. 6 . The length of ejector  188  is shown having a length  198  in  FIG. 19 , which is shorter than ejector  150  of  FIG. 6  that has a length  190 . 
     In  FIG. 20 , a shortened ejector  640  is shown that has a shortened flange  642  (similar to the shortened flange in  FIG. 19 ) with tubes  604  and  606  extending from flange  642 . Air duct  650  has a protuberance  658  that has an opening  654  (also shortened) that has a surrounding surface  656  to which flange  642  is affixed. Because venturi tube  608  sticks out beyond flange  642  compared to venturi tube  608  in relation to flange  602  of  FIG. 17 , venturi tube  608  cannot be installed into opening  654  directly but must be tipped, as shown in  FIG. 20 . After venturi tube  608  enters opening  654 , ejector  640  can be straightened out so that flange  642  meets with surface  656 . This tilting and then straightening is illustrated by arrow  660 . 
     It is known to manufacture the ejectors by injection molding. In the prior art, such manufacturing technique leads to the difficulty in making diverging and converging sections in the ejector because such sections are formed by cylindrical pins. According to embodiments disclosed above, the two-piece version that is split along venturi tube allows a complicated shape can be formed with a converging section, a diverging section, and a throat, that in some embodiments, slightly diverges. In the prior art, throats are typical straight. However, in some applications, it has been found that the diverging throat yields improved flow efficiency approaching supersonic flow. In some embodiments, the diverging section has a non-uniform shape and in some embodiments, tilts downwardly; such features are easily accomplished with the two-piece ejector disclosed herein. Although it might be less expensive to injection mold the ejector out of two pieces, there are alternative manufacturing techniques that allow the desired shape in one piece. A 3-D printing process is one alternative. The resulting could be like any of  FIGS. 5-7 , except that the ejector would be of one piece. The difference between a 3-D printed ejector according to an embodiment of the present disclosure compared to the prior art in  FIGS. 2-4  is that the ejector in  FIGS. 2-4  have straight tube, whereas a 3-D printed ejector can have a converging section, a throat of controlled diameter, and a diverging section. In yet another embodiment shown in  FIG. 21 , an ejector, according an embodiment of the disclosure, is formed in one piece via a traditional casting method. To remove the core pieces, i.e., that provide the openings within the venturi tube, a plug is provided proximate the upstream end of the venturi tube. Finally, although very costly, the ejector can be machined from a blank. 
     In  FIG. 22 , an ejector  710  has a throat  715  with a converging section to the left (upstream) and a diverging section to the right (downstream). A centerline  712  of the converging section is offset from a centerline  714  of the diverging section. A left tube  716  of ejector  710  is canted. A right tube  718  is also canted in ejector  710 . It has been found through modeling that such an offset provides greater flow, particularly when both tube  716  and  718  are canted as shown in  FIG. 22 . 
     As described above, some embodiments show a snap fit to affix the two pieces of the ejector. In such embodiments, an O-ring, adhesive, or other sealant can be used. Alternatively, a bump near the periphery of one of the pieces causes an interference with the other piece of the ejector. 
     In  FIG. 23 , a detail of a lower portion  900  of the ejector is shown. A surface  902  has an energy director  904  that is useful in the welding process. Energy director  904  is typically sits proud of the surface by about 0.6 mm. Surface  902  forms a butt weld with respect to a mating surface (not shown). A skirt  908  has two functions: serves as a pilot to locate the mating surface during assembly. Furthermore, the surface  908  forms a shear weld with a portion of the mating part. 
     An isometric view of an ejector has a diverging section  1000  in which a divot  1002  is formed is shown in  FIG. 24 .  FIG. 25  is a top view of diverging section  1000  with divot  1002  and  FIG. 26  is a side view.  FIG. 27  shows an isometric view of an ejector  1100  in which a diverging section  1002  is provided with a squared-off divot  1106  that has a short wall  1104 . Divots  1002  and  1106  are provided to prevent recirculation, which would diminish flow through the ejector, that occurs at some operating conditions. 
     While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, efficiency, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.