Abstract:
During normal operation of diesel engines the EGR valve poppet often becomes stuck to the valve seat in the closed position, due to excessive build up of exhaust gas debris, which renders the valve inoperable. This usually occurs after the engine is shut down and the valve is seated. Features, which locate the valve poppet in an unseated position when not in use, are implemented into the EGR valve design to prevent this sticking from occurring, thereby increasing product robustness and prolonging product life.

Description:
This application is a National Stage of International Application No. PCT/2006/008184 filed on 8 Mar. 2006. This application claims the benefit of PCT/2006/008184 filed on 8 Mar. 2006 and U.S. Provisional Application No. 60/659,478, filed 8 Mar. 2005. The disclosures of the above applications are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to an arrangement for maintaining an EGR valve in the open position for an amount of time after the engine has stopped. 
   BACKGROUND OF THE INVENTION 
   Federal and State legislation require control of vehicle exhaust emissions. Oxides of Nitrogen (NOx) are one of the exhaust gas emissions that must be controlled. The higher the combustion temperature, the greater amount of NOx is produced. A system, referred to as the exhaust gas recirculation (EGR) system, has been developed to reduce combustion temperatures which thus reduces the amount of NOx emissions from the vehicle. A schematic of this system is shown in  FIG. 1 . In the EGR system, a portion of the exhaust gas from the engine&#39;s exhaust manifold is recirculated back to the intake manifold where the exhaust gas is combined with incoming fresh air. The mixture of exhaust gas and fresh air are then compressed and ignited in the cylinder. This results in a lower combustion temperature and a reduction in NOx that is emitted from a vehicle&#39;s exhaust system. 
   Referring to  FIG. 1 , an EGR system  10  comprises of an EGR valve  12  that controls the flow of exhaust gas to the intake manifold. Space Conduits  14 ,  16 ,  18  provide the interconnection between an exhaust manifold  20 , the EGR valve  12 , and an intake manifold  22 . The system shown uses an electrically controlled EGR valve  12 . Thus, an engine control unit (ECU)  24  provides a signal that controls the open and closing of the EGR valve. As the EGR valve  12  opens and closes, the flow rate of exhaust gas to the intake manifold increases and decreases respectfully. It is also typical to have a throttle valve  26  to control airflow into the intake manifold and an exhaust gas cooler  28  to reduce temperature of recirculated exhaust gas prior to being mixed with the fresh air. 
   The required EGR valve  12  flow rate of recirculating exhaust gas is dependent upon several factors that include, but are not limited to, the displacement of the engine, and the pressure differential between the exhaust system and the intake system. Operating force of the EGR system is also a factor used in the selection criteria for the type of actuator used for the EGR valve. Higher flow rates require larger valves with greater area and higher operating forces. Lower pressure differential between the exhaust and intake manifold requires larger valves to achieve the desired flow rate. Furthermore, debris in the exhaust gas accumulates on the valve components and causes the valve components to stick to one another or restricts movement if sufficient operating force is not available to move the valve components once the debris has stuck to the valve components. 
   During normal operation of diesel engines the EGR valve poppet often becomes stuck to a valve seat when the EGR valve poppet is in the closed position. This condition renders the EGR valve inoperable. This is caused by excessive build up of exhaust gas debris in the EGR valve. This typically occurs after the engine is shut down and the EGR valve is in the closed position or the EGR valve poppet is seated on the valve seat. For example, EGR systems that run with cooled exhaust tend to produce a moist vapor like (lacquer) contamination, until the engine warms up, which builds up on the valve poppet and valve seat as exhaust gas flows past them as described in the previous paragraphs. Moreover, the lacquer contamination combines with a powdery (soot) type of contamination that is present in the exhaust gas at elevated (greater than 160° C.) exhaust gas temperatures. When the valve is commanded to the closed position the lacquer, soot, or a combination of the two, cures or hardens when the engine is shut off and causes a “bond” between the valve seat and poppet. This often happens after then engine is shut down for a duration of time such as 20 minutes or greater. When the engine is started again and the EGR valve is commanded to open, and the “bond” that has occurred prevents the valve from opening when there is insufficient force and or torque available from the EGR valve to overcome the bonded sticking force. 
   Therefore it is desirable to develop an EGR valve, wherein the EGR valve poppet is not seated on the EGR valve seat when the engine is shut down. Thus, the EGR valve design prevents the EGR poppet valve from sticking to the valve seat, thereby increasing product robustness and prolonging product life. The following paragraphs and figures describe the application and use of an EGR valve with features that locate the poppet in a resting position when the valve is not in use so that at least a portion of the poppet valve is not contacting the valve seat. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a mechanism for preventing a poppet valve in an exhaust gas recirculation (EGR) valve assembly in a motor vehicle from sticking to a valve seat resulting in the EGR valve being inoperable. The EGR valve assembly includes an EGR valve body having an inlet port and an outlet port with the valve body defining a pass through for fluid flow between the inlet port and the outlet port. A valve seat is disposed between the inlet port and outlet port and has an aperture positioned in the path of fluid flow. A valve stem is positioned in the valve body and has a poppet valve member disposed on the end of the valve stem. The valve stem is configured to slide axially along its longitudinal axis to bring the poppet valve in contact with the valve seat and to move the poppet valve member away from the valve seat to place the valve mechanism in a position where at least a portion of the poppet valve does not contact the valve seat. In a preferred embodiment, the poppet valve is fully disconnected from the valve seat when in the resting position. An actuator is connected to the valve stem and causes the valve stem to slide axially along its longitudinal axis. A pinion gear is connected to the actuator and is in meshed engagement with a second gear that is mounted to the valve shaft. A default position arrangement is operably configured with the valve stem for placing the poppet valve in a resting position where at least a portion of the poppet valve does not contact the seat when the actuator is idle from its normal operation. 
   The default position arrangement takes several different forms. For example, the default position arrangement is a light load return spring that acts on the valve stem to hold the poppet valve at the resting position away from the valve seat when the actuator is energized and then suddenly becomes de-energized. The default position arrangement is also a reverse full open spring that acts on the valve stem by applying torque to the spur gear in order to place the poppet valve in the resting position when the actuator is de-energized. In an alternate embodiment, the default position arrangement is also configured so that a small amount of electrical current is applied to the actuator in order to hold the poppet valve in the resting position when the actuator is shut down from its normal operation. Lastly, the default position arrangement includes a drive pin and ramp assembly having a holding feature so that when the actuator opens the poppet valve to a maximum position and becomes de-energized the holding feature holds the poppet valve open until the actuator applies torque to drive the poppet valve which moves the poppet valve to the closed position. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a schematic diagram of a combustion engine system having an EGR valve incorporated thereon; 
       FIG. 2  is a partial cross-section perspective side view of an EGR valve body having an actuator connected thereon; 
       FIG. 3   a  is a cross-sectional side view of a sub-assembly with the stem, shield, and poppet valve members in a closed position; 
       FIG. 3   b  is a cross-sectional side view of the sub-assembly with the stem, shield, and poppet valve members in an open position; 
       FIG. 4  is a cross-sectional perspective view of an EGR valve body with an actuator having a torsion spring acting thereon; 
       FIG. 5  is a cross-sectional perspective view of an EGR valve having a reverse torsion spring; 
       FIG. 6  is a partial cross-section view of the valve seat with the sub-assembly; 
       FIG. 7  is an overhead perspective view of the valve body and spur gear having a default position spring; and 
       FIG. 8  is a perspective view of the EGR valve seat having a wedge ramp feature. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   Referring to  FIG. 2 , an exhaust gas recirculation (EGR) valve assembly is generally shown at  30 . The actuator  100  is connected to a valve body assembly  36  through the use of fasteners  32 ; a gasket  38  is used to prevent leakage from occurring between the actuator  100  and the valve body assembly  36 . Fasteners  32  are used to locate the actuator  100  and the valve body assembly  36 . The EGR valve  30  is typically mounted to the engine&#39;s intake manifold by mounting bolts. The exhaust gas flows from inlet  92 , into chamber  94 , through valve seat  90 , by poppet valve  76 , into cavity  98 , and to outlet  96  when poppet valve  76  is unseated from valve seat  90  and there is a sufficient pressure differential between the inlet  92  and outlet  96 . In a preferred embodiment, the pressure in chamber  94  is positive. However, in an alternate embodiment, the pressure in chamber  94  is negative or fluctuates between a positive and negative pressure. 
     FIGS. 3   a  and  3   b  show the open and closed positions of the poppet valve  76 . More specifically,  FIG. 3   a  shows the closed position of the poppet valve  76 , and  FIG. 3   b  shows the open position of the poppet valve  76 .  FIGS. 3   a  and  3   b  also show a deflector  102  connected to poppet valve  76 , which is used for deflecting away debris from the valve stem  74 . 
   Referring to  FIGS. 4 ,  5 , and  6 , EGR valve assembly  30  has a housing  40  designed to accept an electrical connector  42 . In a preferred embodiment, a motor  44 , and an integral bracket  64  are secured by screws  46  to the housing  40 . The motor  44  is electrically connected to the electrical connector  42 , such that the motor  44  draws electrical current when in use. 
   A bushing  48  and roller bearing  50  are fit into housing  40 . A gear  52  is fastened to shaft  54 . A torsion spring  56  and spring bushing  58  are placed over the shaft  54 . The shaft  54  extends through the bearing  50  and bushing  58  and is retained by a clip  60 . A gear  62 , fastened to a motor shaft  88 , engages gear  52 . Thus, gear  52  rotates with respect to gear  62 . The torsion spring  56  engages features on the housing  40  and gear  52  to provide torsional force that acts upon shaft  54 . 
   A valve subassembly  68  consists of retainer housing  78 , bearing guide  66 , valve stem  74 , pin  70 , bearings  72 , and poppet valve  76 . Bearing  72  is fastened at one end of pin  70 . The pin  70  is placed through an engagement hole at one end of valve stem  74 . A second bearing is fastened to the opposite end of the pin (not shown). The valve stem  74  is installed by inserting it through the integral bearing section of bearing guide  66 . The valve stem  74  is inserted until the bearing  72  contacts integral slotted guide ramp portion  84  of the bearing guide  66 . The slotted guide ramp portion  84  has ramp surfaces  86  that contain and guide the bearing  72  when torque is applied to the pin  70  which forces the valve stem  74  to rotate about its longitudinal axis. The valve stem  74  moves in an axial direction as the bearing  72  moves along the slotted guide ramp portion  84 . The slotted guide ramp portion surfaces  86  has a defined slope that causes the desired axial movement of the valve stem  74 . The slotted guide ramp portion  84  is shown in more detail in  FIGS. 4 ,  6 , and  8 . In a preferred embodiment, the slotted guide ramp portion  84  is machined into a one-piece bearing guide  66 , as shown in  FIG. 4 . In an alternate embodiment, the slotted guide ramp portion  84  is made in more than one-piece to accommodate various assembly methods. For example, the slotted guide ramp portion  84  has an upper and lower section, each having a portion of either slotted guide ramp. 
   In a preferred embodiment, a poppet valve  76  is installed and retained on valve stem  74  by suitable means, such as, but not limited to, swaging. In an alternative embodiment, the poppet valve  76  is keyed to the shaft in a manner that will cause the poppet valve  76  to rotate with the shaft. 
   Also in a preferred embodiment, the bearing guide  66  of valve sub-assembly  68  is secured in the retainer body  78  by suitable means, such as, but not limited to, swaging as shown in  FIG. 4 . The actuator  100  and valve sub-assembly  68  are aligned by suitable locating features and are held together by fasteners (not shown). Gear  52  also has an integral fork feature  85  that engages pin  70 . When the engine control unit provides a suitable control signal to the motor  44 , it causes gears  62  and  52  to rotate. The integral fork feature  85  causes pin  70  to move bearing  72  along ramp  86  resulting in rotary-axial movement of the valve stem  74  and poppet valve  76 . The control signal causes the motor  44  and gears  62  and  52  to rotate in either a clockwise or counter-clockwise direction, therefore, the valve stem  74  and poppet valve  76  are capable of moving in either direction. 
   Also, the EGR valve assembly  30  has a default position arrangement, which has several embodiments described below. The default position arrangement places the poppet valve  76  in any predetermined position besides the closed position. Preferably, when the poppet valve  76  is in the resting position the poppet valve  76  does not contact the valve seat  90 . However, the resting position can be a position where the poppet valve  76  is only partially contacting the valve seat  90  when compared to the contact between the poppet valve  76  and valve seat  90  when the poppet valve  76  is in the closed position. 
   The first embodiment of the present invention is comprised of a low-torque torsion spring  56 , which is placed over a shaft along with the spring bushing  58 . In this embodiment, the torsion spring  56  engages the housing and the gear  52  in order to provide torsion force against the shaft  54 . Thus, the torsion spring  56  is configured so that after the poppet valve  76  is opened to its fully open position, and power to the motor  44  is cut off, the torsion exerted by the torsion spring  56  is not forceful enough to overcome the system friction required to bring the poppet valve  76  back into contact with the valve seat  90  or prevents the poppet valve  76  from fully contacting the valve seat  90 . The poppet valve  76  being prevented from being placed in the closed position while the EGR valve assembly  30  is not in operation prevents the poppet valve  76  from sticking to valve seat  90  as the system cools, and any debris build-up in the system cools as well. 
   A second embodiment of the present invention comprises having the torsion spring  56  configured to bias the poppet valve  76  toward the open position. This is achieved by using a torsion spring  56  that has a winding direction opposite that of a spring that biases poppet valve  76  in the closed position. When power to the motor  44  is cut off, and no load besides the load from the torsion spring  56  is being applied to poppet valve  76 , poppet valve  76  is held in an open position, until power is supplied to the motor  44 . When the motor  44  is actuated, the bias force of the torsion spring  56  is overcome and the poppet valve  76  closes. This embodiment can be achieved by using a slotted guide ramp portion  86  geometry that is reversed rather than a torsion spring  56  that has a winding direction that is reversed. 
   In a third embodiment of the present invention, the torsion spring  56  is configured to provide a default position for the poppet valve  76 . This default, or intermediate, position of gear  52  is shown in  FIG. 7 . The torsion spring  56  geometry and the actuator housing  40  geometry are designed such that when the motor  44  is un-powered, the poppet valve  76  is located in a default or intermediate position that is a specified distance off of the valve seat  90 . This is accomplished by using a torsion spring  56  that has a sufficient amount of force to move the poppet valve  76  to the default position. 
   In a fourth embodiment of the present invention, the poppet valve  76  is electronically placed in the open position or in a position where at least part of the poppet valve  76  is not contacting the valve seat  90 . In this embodiment, a small amount of electrical current is used to power the poppet valve  76  to an unseated position when the engine is shut down. The small amount of electrical current flows through the actuator  100  keeping the poppet valve  76  in the open position or prevents it from fully contacting the valve seat  90  for a predetermined period of time. Typically, the predetermined amount of time is a time period that is long enough for the contamination to cure or harden; thereby, preventing the “bonding” of the poppet valve  76  to the valve seat  90 . No geometry or hardware changes are required for this method, but the Engine Control Module (ECM) has to be altered to provide electrical power in a shutdown mode without draining the vehicle battery. 
   The fifth embodiment of the present invention is shown in  FIG. 8 . In this embodiment, a holding feature  82  is added to the bearing slotted guide ramp portion  84  or cam mechanism such that the poppet valve  76  is electrically powered past the maximum allowable flow position before engine shutdown. Therefore, the poppet valve  76  remains above the holding feature  82  in a full stroke unseated position until the motor  44  direction is reversed and electrical current is applied to power the drive bearing  72  back over the holding feature  82  onto the active part of the ramps  86 . Examples of the holding feature  86  are, but not limited to, a wedge, an even surface, a bump, or a detent area, where the bearing  72  contacts the holding feature  86  when moving along the slotted guide ramp member  86 . Thus, a force is applied to the bearing  72  in order for bearing  72  to pass back over the holding feature  86 , where the poppet valve  76  moves towards the closed position. 
   All five of the aforementioned embodiments keep the poppet valve  76  and valve seat  90  out of contact with each other or partially out of contact with each other while the debris is curing or hardening which would ultimately cause the poppet valve  76  to bond to the valve seat  90  making the EGR valve assembly  30  inoperable. In a preferred embodiment, the embodiments do not allow the poppet valve  76  from contacting the valve seat  90  during the curing process to ensure there is no bonding between the two parts. Alternatively, the above embodiments, allow the poppet valve  76  to partially contact the valve seat  90 , which reduces the amount of surface area of the poppet valve  76  and the valve seat  90  that bond together. Thus, the bonding that does occur is overcome by the torque applied to the poppet valve  76 , which is a lesser torque than needed to separate the poppet valve  76  from the valve seat  90  when the poppet valve  76  is in the closed position during the curing process. 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.