Patent Publication Number: US-8523089-B2

Title: Pressure swirl atomizer with closure assist

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional application Ser. No. 61/324,793 filed Apr. 16, 2010 entitled FUEL INJECTOR CLOSURE ASSIST, the entire disclosure of which is hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to pressure swirl atomizers, and more particularly to a pressure swirl atomizer system that has a mechanism to assist in closing an exit flow path. 
     BACKGROUND OF THE INVENTION 
     Pressure swirl atomizers are used in various applications, including fuel injection systems and exhaust aftertreatment systems. Atomizers disperse fluid into a fine spray by directing fluid from tangential swirl channels into a swirl chamber and then opening a central exit orifice to allow the fluid to exit in a spray pattern. More particularly, the tangential swirl channels causes fluid entering the swirl chamber to swirl in a circular motion and increase its angular velocity as it moves toward the exit orifice. The centrifugal force generated by the swirling motion generates a low pressure zone along the central axis of the swirl chamber. 
     When the exit orifice is opened, exhaust gas enters the atomizer through the exit orifice and forms an air core through the exit orifice. The fluid forms a “wall” around the air core. Aerodynamic forces break the fluid wall into droplets after it exits the injector. The thickness of this fluid wall and the dimensions of the air core depend on the fluid supply pressure and on the ratio of the diameter of the swirl chamber and the diameter of the exit orifice, and these dimensions in turn control the characteristics of the spray pattern as fluid leaves the exit orifice. 
     A solenoid-controlled pintle opens and closes the exit orifice to allow or block fluid flow out of the atomizer. In applications where a variable flow rate is desired, the exit orifice may be opened and closed via pulse width modulation (PWM) of the pintle between the open and closed positions. When the solenoid is energized, it generates a magnetic force that pulls the pintle away from the exit orifice and toward a pole piece until the pintle seats against the pole piece. When the solenoid is de-energized, the pintle should return to the closed position and block the exit orifice. However, the pintle may stick in the open position, creating an unpredictable response delay before the exit orifice is closed again. This delay makes it difficult to obtain consistent fuel flow, especially at high duty cycles. 
     There is a desire for a pressure swirl atomizer having a more predictable, consistent pintle response. 
     SUMMARY OF THE INVENTION 
     A pressure swirl atomizer according to one embodiment of the invention includes a nozzle having an exit orifice and a plurality of tangential swirl channels and a pintle that is movable within a pintle bearing between a closed position that closes the exit orifice and an open position that opens the exit orifice. The atomizer also has a pole piece having a channel, and the pole piece and the pintle are separated by an air gap when the pintle is in the closed position. A space between the pintle and the pintle bearing, the air gap, and the channel together form at least a part of a return path. Fluid from the tangential swirl channels drains through the return path when the pintle is in the closed position. To open the atomizer, a solenoid generates a magnetic force when energized, attracting the pintle toward the pole piece into the open position. A check valve disposed in the return path generates a fluid back pressure when the solenoid is de-energized to push the pintle toward the closed position. The back pressure helps prevent the pintle from getting stuck in the open position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a pressure swirl atomizer according to one embodiment of the invention shown in the closed position; 
         FIG. 2  is a cross-sectional view of the pressure swirl atomizer of  FIG. 1  in the open position; 
         FIG. 3  is a plan view of the underside of one embodiment of a nozzle used in the pressure swirl atomizer of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a pressure swirl atomizer  10  according to one embodiment of the invention. The atomizer  10  has a pintle  12  disposed in a pintle bearing  14 . In one embodiment, the pintle bearing  14  acts as a flux collector. The pintle  12  is movable to open and close an exit orifice  15  disposed at the center of a nozzle  16 . As shown in  FIG. 2 , the nozzle  16  has a swirl chamber  18  to accelerate fluid in a swirl pattern before it sprays out of the exit orifice  15 . 
     As shown in  FIG. 3 , a plurality of tangential swirl channels  19  are arranged tangentially to the perimeter of the swirl chamber  18  and direct fluid to the swirl chamber  18 . A perimeter of the central swirl chamber  18 , as defined by the contact points between the swirl channels  19  and the swirl chamber  18 , forms a circle having a first diameter. The exit orifice  15  has a second diameter. The ratio between the first and second diameters controls the spray pattern of the atomizer  10  by controlling the size of an air core formed by the swirling fluid, the wall thickness of the swirling fluid itself, and the angular momentum of the fluid. As the fluid moves closer to the center of the swirl chamber  18 , and therefore closer to the exit orifice  15 , the angular velocity of the fluid increases. 
     A solenoid  22  controls operation of the atomizer  10  by moving the pintle  12  between an open position ( FIG. 1 ) and a closed position ( FIG. 2 ). In one embodiment, when the solenoid  22  is energized, it generates a magnetic force that pulls the pintle  12  toward a core  26  and away from the exit orifice  15  as shown in  FIG. 1 , allowing fluid to spray through the exit orifice  15  out of the atomizer  10 . In one embodiment, the core  26  acts as a pole piece. 
     When the solenoid  22  is de-energized, the pintle  12  moves away from the core  26  and closes the exit orifice  15  as shown in  FIG. 2 . In one embodiment, a resilient member, such as a spring  27 , applies a biasing force to bias the pintle  12  toward the closed position. The spring  27  may be disposed in a recess  28  in the core  26 . 
     The solenoid  22  may operate via pulse width modulation (PWM) control to move the pintle  12  over a selected duty cycle to vary the flow rate of the atomizer  10 . The solenoid  22  may be designed to provide a quick response at low duty cycles so that the pintle  12  can be moved quickly between the open and closed positions. 
     A housing  30  may house at least a portion of the nozzle  16 , pintle  12 , pintle bearing  14 , solenoid  22 , and core  26  into a single unit. 
     The operation of the components in the atomizer  10  will now be explained in greater detail with respect to  FIGS. 1 and 2 . When the solenoid  22  is de-energized, the pintle  12  is in the closed position as shown in  FIG. 1  to block fluid from exiting the exit orifice  15 . Fluid may continue to flow from the swirl channels  20  to the swirl chamber  18 , but since the fluid cannot exit the atomizer  10 , it drains through one or more return paths. In one embodiment, a portion of the return path is disposed in a space  32  between the pintle  12  and the pintle bearing  14 . 
     When the pintle  12  is in the closed position, a magnetic air gap  34  forms between the pintle  12  and the core  26 . This air gap  34  also forms part of the return path. In one embodiment, fluid flows through the air gap  34  into the core  26  through the recess  28  and a return channel  36 . The recess  28  and return channel  36  also form part of the return path. The return path  32 ,  34 ,  36  may direct fluid to the solenoid  22  to cool it. 
     When the solenoid  22  is energized, the generated magnetic force pulls the pintle  12  toward the core  26  and away from the exit orifice  15 . This attractive magnetic force causes the pintle  12  to contact the core  26  and close the magnetic air gap  34  between them, blocking fluid flow through the recess  28  and the channel  36  and forcing fluid to exit through the exit orifice  15  in a spray pattern. In one embodiment, the pintle  12  has a large magnetically attractive surface area to ensure that the pintle  12  responds quickly to the magnetic force. 
     When the solenoid  22  is de-energized again, the biasing force from the spring  27  urges the pintle  12  to the closed position. However, the large magnetically attractive surface area on the pintle  12  may cause the pintle  12  to stick in the open position or move too slowly toward the closed position if there is not enough hydraulic and/or spring force applied to the pintle  12  to force it away from the core  26 . 
     To provide additional hydraulic pressure onto the pintle  12 , a check valve  38  may be disposed in the return path to provide additional hydraulic force onto the pintle  12  to move it toward the closed position. The check valve  38  may be disposed anywhere along the return path, in any of the paths formed by the space  32  between the pintle  12  and pintle bearing  14 , the air gap  34 , and/or the channel  36 , and either within the atomizer  10  or, as shown in  FIGS. 1 and 2 , mounted outside the atomizer  10 . 
     In one embodiment, the check valve  38  is a low-leak check valve that is normally closed. When the pintle  12  is in the closed position, the pressure of fluid draining from the swirl chamber  18  is higher than a threshold pressure of the check valve  38 , pushing the check valve  38  open. This allows the fluid to flow past the check valve  34  along the return path  32 . This fluid circulation may cool portions of the atomizer, such as the solenoid  22 . 
     When the pintle  12  is in the open position, the check valve  34  closes because the fluid pressure in the return path  28  drops below the threshold pressure of the check valve  34  due to the blockage of the return path  28  via closure of the air gap  30  by the pintle  12 . The pintle  12  starts to move toward the closed position when the solenoid  22  is de-energized, allowing some fluid to flow through the air gap  30  and into the recess  28  and channel  32 . However, since the check valve  34  is still closed, fluid quickly accumulates in the return path  28  between the check valve  34  and the pintle  12 , increasing the back pressure against the pintle  12 . This back pressure, combined with the biasing force of the spring  27 , pushes the pintle  12  toward the closed position. The additional force provided by the fluid back pressure ensures that the pintle  12  quickly and reliably moves to the closed position when the solenoid  22  is de-energized. 
     Thus, by incorporating a check valve  34  in the return path  32 , the fluid back pressure in the return path  32  pushes against the pintle  12  and prevents the pintle  12  from sticking in the open position when the atomizer  10  is commanded to close (e.g., via de-energization of the solenoid  22 ). 
     Although the embodiment described above has a flux collector as the pintle bearing  14  and a pole piece as the core  26 , those of ordinary skill in the art will understand that these elements can be switched (i.e., the pintle bearing  14  can be the flux collector and the core  28  can be the pole piece). Other modifications may also be made without departing from the scope of the invention. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.