Abstract:
A two-stage proportional control valve assembly regulates flow of a first fluid such as an engine exhaust gas using a second fluid such as engine oil for power. A directional valve under control of an electrical actuator regulates flows of the second fluid to operate a fluid-powered actuator. A mechanical connection between the fluid powered actuator and a flow control valve for regulating flows of the first fluid enables the electrical actuator to indirectly control the flow control valve with a minimum draw.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/249,937, filed on Nov. 17, 2000, which provisional application is incorporated by reference herein. 
     
    
     
       TECHNICAL FIELD  
         [0002]    A valve assembly regulates flow of a fluid or movement of a device by controlling the flow of a separate working fluid responsive to an electrical control signal.  
         BACKGROUND  
         [0003]    Emission control systems for internal combustion engines recirculate a portion of the exhaust gases emitted from the engines back through the combustion process to lower harmful emissions. Exhaust gas recirculating valves (EGRV) connected to exhaust manifolds divert metered amounts of the exhaust gas to intake manifolds for re-burn by the engine. The exhaust gases are mixed with fresh air/fuel mixtures resulting in a lowering of combustion temperature and a reduction in the formation of harmful compounds such as nitrous oxide.  
         SUMMARY OF INVENTION  
         [0004]    The invention features a two-stage proportional flow control valve assembly that is particularly useful for regulating exhaust flow rates in exhaust gas re-circulating systems of internal combustion engines. Electrical control signals from an engine control module (ECM) regulate the exhaust flow rates through an exhaust valve utilizing engine oil pressure to produce a hydraulic actuating force. Since the electrical control signals are not required to provide the force for opening or closing the exhaust valve, my new two-stage proportional flow control valve assembly conserves electrical power for other functions.  
           [0005]    An exemplary two-stage proportional flow control valve assembly adapted for use as an exhaust gas recirculating valve incorporates an exhaust valve that regulates exhaust flow rates recirculated to an engine and a directional valve that utilizes engine oil pressure for regulating opening and closing of the exhaust valve proportional to control signals from an engine control module (ECM). Moveable components of the exhaust valve are preferably pressure balanced with respect to the flow of exhaust gas through the exhaust valve to optimize positional accuracy. A fluid-powered actuator movable under the influence of engine oil pressure provides the necessary force for opening and closing the exhaust valve. The directional valve controls flow of the pressurized engine oil to the fluid-powered actuator to adjust the position of the exhaust valve proportional to the control signal.  
           [0006]    The movable portion of the exhaust valve is preferably a pressure-balanced dual poppet head body with each of two poppet heads having an approximately equal opposing area exposed to exhaust gas pressures. The dual poppet heads translate along a central axis for opening and closing exhaust passages encircled by mating poppet seats. The fluid-powered actuator is preferably a double-acting cylinder having a piston mechanically coupled to the dual poppet head body for effecting common movement along the central axis. The directional valve is preferably a four-way servovalve in the form of a spool valve that regulates flows of pressurized engine oil to opposite faces of the piston. The spool valve includes a spool also movable along the central axis between (a) an initial position that charges a proximal face of the piston with the pressurized engine oil for moving the piston in a direction that closes the exhaust valve and (b) an actuated position that charges a distal face of the piston with the pressurized engine oil for moving the piston in a direction that opens the exhaust valve.  
           [0007]    An electrical actuator preferably in the form of a proportional solenoid under control of the electronic control module (ECM) converts the control signals of varying current into proportional forces imparted by an armature against the spool along the central axis. A feedback mechanism, preferably in the form of a compression spring, also located along the central axis, applies a separating force between the spool and the piston proportional to its displacement. An adjustable null compression spring or other biasing mechanism biases the solenoid armature against the spool. Thus, the spool and the armature are preferably biased together from opposite directions by two springs—the null spring acting on the spool in the same direction as the solenoid armature and the feedback spring acting on the spool in the opposite direction.  
           [0008]    In the absence of an actuating force from the solenoid, the feedback spring, which is the stronger of the two springs, biases the spool against an armature stop, which corresponds to the initial spool position at which the proximal face of the piston is pressurized for closing the exhaust valve. Compression of the null spring can be adjusted to establish a proper take-off current to the solenoid at which the sum of the forces imparted by the null spring and the solenoid are sufficient to move the spool against the feedback spring. Additional current moves the spool further against the feedback spring to the actuated position at which the distal face of the piston is pressurized for opening the exhaust valve.  
           [0009]    Upon reaching the actuated position, further movement of the spool is limited by contact between the solenoid armature and the armature stop. The initial and actuated positions can be adjusted to set maximum flow rates through the spool valve in either direction. Movement of the spool to the actuated position compresses the feedback spring up to the limit set by the armature stop. Movement of the piston in response to the charging of its distal face further compresses the compression spring until a counteracting force exerted by the piston through the compression spring momentarily exceeds the sum of the forces exerted on the spool by the null spring and solenoid and returns the spool to a so-called neutral position (i.e., a position between the actuated and the initial positions) at which further flow to the piston is stopped.  
           [0010]    Actuating forces exerted by the solenoid above the take-off current temporarily move the spool beyond the neutral position until the counteracting force of the piston returns the spool to the neutral position. Although the spool returns to the same neutral position throughout the intended range of solenoid actuating forces above the take-off current, the piston&#39;s position (and with it the position of the dual poppet head body of the exhaust-valve) varies directly with the compression of the feedback spring. Any change in the actuating force produces a corresponding change in the compression of the feedback spring, which exerts a force equal and opposite to the sum of the forces exerted on the spool by the null spring and the solenoid. The force exerted by the null spring remains the same at the neutral position, so the change in the force exerted by the feedback spring matches the change in the force exerted by the solenoid.  
           [0011]    The feedback spring is the sole mechanical connection between the piston and the spool. The amount that the feedback spring is compressed is controlled by the amount of current that is applied to the solenoid. Movement of the spool to the actuated position starts the compression of the feedback spring, and the engine-oil powered displacement of the piston completes the required compression of the feedback spring while restoring the spool to the neutral position. The amount of compression of the feedback spring determines the spacing of the piston from the spool in the neutral position. Changes in the position of the piston are accompanied by corresponding changes in the position of the dual poppet head body of the exhaust valve.  
           [0012]    The control signal (i.e., current) to the solenoid provides a proportional control that modulates both opening and closing of the exhaust valve, while the force for actually operating the exhaust valve is derived from engine oil pressure. Neither changes in the engine oil pressure nor changes in the external pressure applied to the dual poppet head body unduly affect the exhaust valve position. The spool valve maintains the position of the piston independently of overall oil pressure, which can affect flow rates but not ultimate positions of the valve components. The neutral position blocks flows to or from either side of the piston to maintain the exhaust valve in a desired position. Balancing the dual poppet head body to exhaust gas pressures also limits the influence of the exhaust gas pressures or flow rates on the valve position. This independence of the new two-stage proportional control valve from changes in the exhaust and engine oil pressures, together with the linear and proportional modulation of flow rates through the exhaust valve with respect to the electrical control signal, makes this new valve particularly accurate, reliable, and robust.  
           [0013]    The new valve is expected to contribute to reducing harmful engine emissions while operating more efficiently by utilizing engine oil pressure to move the exhaust valve. The valve is also expected to have a variety of other uses in situations where proportional movement of a valve or other device is modulated by low-power control signals regulating the flow of working fluid in an intermediate actuator. 
       
    
    
     DRAWINGS  
       [0014]    [0014]FIG. 1 is a plan view of an exemplary exhaust gas re-circulation (EGR) valve in accordance with my invention.  
         [0015]    [0015]FIG. 2 is a side cross-sectional view through the valve.  
         [0016]    [0016]FIG. 3 is an enlarged cut away of the view in FIG. 2 showing a spool valve portion in clearer detail. 
     
    
     DETAILED DESCRIPTION  
       [0017]    The exhaust gas re-circulating valve of the three drawing figures is a two-stage proportional control valve assembly  10  having a housing  12  that can be bolted or otherwise attached (e.g., through bolt holes  14 ) to an internal combustion engine exhaust manifold  16  shown by phantom line in FIG. 2. Within the housing  12  are assembled an exhaust valve  20  and a four-way servovalve  22  interconnected in succession by a double-acting cylinder  24  and a feedback compression spring  26 . A heat shield  18  protects the servovalve  22  and the double-acting cylinder  24  from exposure to heat from the exhaust manifold  16 .  
         [0018]    The exhaust valve  20  regulates flows between two exhaust gas inlet passages  30  and  32  and a combined exhaust gas outlet passage  34  formed within the housing  12 . The two exhaust gas inlet passages  30  and  32  admit exhaust gases from the engine exhaust manifold  16 . The exhaust gas outlet passage  34  directs a metered flow of the exhaust gases toward an engine inlet manifold (not shown).  
         [0019]    Flows between the exhaust gas inlet passages  30  and  32  and the combined exhaust gas outlet passage  34  are interrupted by a dual poppet head body  36  that is movable along a central axis  38 . The dual-poppet head body  36 , includes (a) a first poppet head  40  that mates with a seat  42  encircling an end of the inlet passage  30  for restricting flows between the inlet passage  30  and the combined outlet passage  34  and (b) a second poppet head  44  that mates with a seat  46  encircling an end of the inlet passage  32  for restricting flows between the inlet passage  32  and the combined outlet passage  34 . The two poppet head seats  42  and  46  have equally sized pressure areas, and the inlet passages  30  and  32  apply exhaust gas pressure to the two poppet heads  40  and  44  from opposite directions to balance the dual poppet head body  36  with respect to the exhaust gas pressure. The dual poppet head body  36  also includes a shank  48  mounted within a guide bore  50  of a housing flange  52 . The shank  48  communicates motion along the central axis  38  for opening and closing the exhaust valve  20 .  
         [0020]    The double-acting cylinder  24 , which functions as a hydraulic actuator, includes a piston  60  having a head  62  that divides a housing bore  64  into two separately pressurizable chambers  66  and  68  (shown in FIG. 3). A shank  70  connected to the piston head  62  is coupled directly to the shank  48  of the dual poppet head body  36 . A guide bore  72  formed within a housing flange  74  supports movement of the entire piston  60  along the central axis  38 .  
         [0021]    The four-way servovalve  22  is a spool valve having a supply port  76  connected to source of engine oil pressure (not shown) and a tank port  78  connected to an engine oil sump (also not shown). Within the housing  12 , a spool guide tube  80  supports a spool  82  for movement along the central axis  38 . The supply port  76  feeds pressurized oil through the housing  12  to a supply passage  84  in the guide tube  80 . Oil collected in a return passage  86  in the guide tube  80  returns through the housing  12  to the tank port  78 . A working passage  88  also formed in the guide tube  80  and the housing  12  directs flows of the engine oil to or from the cylinder chamber  66 . An axial bore  90  within the spool  82  communicates openly with the cylinder chamber  68 .  
         [0022]    On its peripheral surface, the spool  82  has a pair of annular lands  92  and  94  that open and close alternative flow paths between the supply passage  84  and the return passage  86 . Both the supply passage  84  and the return passage  86  are alternately connectable to the working passage  88  and the axial bore  90  for charging and discharging the cylinder chambers  66  and  68  on opposite sides of the piston head  62 . An annular recess  96  formed in the circumference of the spool  82  between the spool lands  92  and  94  alternately connects the working passage  88  to either the supply passage  84  or the return passage  86 . Radial bores  100  and  102  formed through the spool  82  straddling the two annular lands  92  and  94  alternately connect the axial bore  90  to either the supply passage  84  or the return passage  86 . The spool  82  is balanced with respect to the engine oil pressure.  
         [0023]    The feedback compression spring  26  extends between the piston head  62  and the spool  82 . One end of the compression spring  26  is mounted within a recess  108  in a proximal face  110  of the piston head  62 , and the other end of the spring  26  is mounted in an open end face  112  of the spool  82 . The feedback spring  26  exerts a reactionary force inversely proportional to the amount of separation between the piston head  62  and the spool  82 .  
         [0024]    A solenoid  116 , which functions as an electrical force motor actuator, pushes the spool  82  against the feedback compression spring  26  through a limited range of travel. A coil  118  powered by a range of electrical currents regulated by an electronic control module (ECM)  120  generates a magnetic force on an armature  122 , which is moveable along the central axis  38  within a solenoid guide bore  124 . An actuator rod  126  passing through an armature stop  128  connects the armature  122  to the spool  82 . A null compression spring  130  biases the armature  122  and the actuator rod  126  against one end of the spool  82  with an initial force that is slightly less than the initial force exerted on the other end of spool  82  by the feedback spring  26 .  
         [0025]    When no current is applied to the solenoid  116 , the stronger feedback spring  26  biases the spool  82  to an initial position shown in FIGS. 2 and 3. The spool  82  is forced back against the armature stop  128  to the initial position that partially opens a passageway through the radial bore  100  between the supply passage  84  and the axial bore  90  for charging the cylinder chamber  68 . At the same initial position, a passageway through the annular recess  96  provides an opening between the working passage  88  and the return passage  86  for discharging the cylinder chamber  66 . The pressure in cylinder chamber  68  produces a hydraulic force against the proximal face  110  of the piston head  62  and pushes the piston  60  in a direction that maintains the exhaust valve  20  in a closed position.  
         [0026]    Applying current to the solenoid  116  above a given take-off current moves the spool  82  away from the armature stop  128  and further compresses the feedback spring  26 . The further movement of the spool is limited by contact between the solenoid armature  122  and the armature stop  128  at an actuated position that discharges the cylinder chamber  68  and charges the cylinder chamber  66 . At the actuated position, the annular recess  96  connects the supply passage  84  to the working passage  88  for charging the cylinder chamber  66 , and the radial bore  102  connects the axial bore  90  to the return passage  86  for discharging the cylinder chamber  68 .  
         [0027]    The accumulating pressure in the cylinder chamber  66  produces a hydraulic force against a distal face  134  of the piston head  62  that moves the piston head  62  together with the dual poppet head body  36  in a direction that compresses the feedback spring  26  and opens the exhaust valve  20 . The movement of the piston head  62  further compresses the feedback spring by an amount required to momentarily overcome the combined forces of the solenoid  116  and the null spring  130  and return the spool  82  to a neutral position at which further flows to and from the double-acting cylinder  24  are blocked.  
         [0028]    At the neutral position of the spool  82 , which is located between the initial and actuated positions, the spool  82  locks fluid in the cylinder chambers  66  and  68 , thus locking the position of the double-acting cylinder  24  and the exhaust valve  20 . The feedback spring  26  is compressed by an amount that exerts a force against one end of the spool  82  equal and opposite to the combined forces exerted by the solenoid  116  and the null spring  130  against the opposite end of the spool  82 . Any movement of the piston head  68  that would change the compression the feedback spring  26  reverses flow through the double-acting cylinder  24  and restores the piston head  26  to the position required to maintain the spool  82  in the neutral position.  
         [0029]    The minimum actuating force of the solenoid  116  (i.e., the takeoff current) required for opening the exhaust valve  20  compresses the feedback spring  26  by an amount that moves the spool  82  just beyond the neutral position. The counteracting hydraulic force generated by the double-acting cylinder  24  moves the piston head  62  and with it the dual poppet head body  36  by an amount required to return the spool  82  to the neutral position. The exhaust valve  20  opens by the amount the feedback spring  26  is compressed by the movement of the spool  82  beyond the neutral position.  
         [0030]    Applying more current to the solenoid  116  momentarily moves the spool  82  to the full activated position at which further movement of the spool is stopped by contact between the solenoid armature  122  and the armature stop  128 . Differential pressure across the piston head  62  builds until a hydraulic force against the distal face  134  of the piston acting through the feedback spring  26  forces the spool  82  to return to the neutral position. Initially, the feedback spring  26  is compressed by movement of the spool  82  toward the piston head  62  until the spool  82  reaches the actuated position. In response, the piston head  62  moves toward the travel-limited spool  82 , additionally compressing the feedback spring by an amount required to overcome the remaining combined forces of the solenoid  116  and the null spring  130  and thereby return the spool  82  to the neutral position.  
         [0031]    The change in position of the piston head  62  along with the dual poppet head body  36  can be far beyond the limited range of spool travel and is substantially proportional to the change in the solenoid actuating force. The travel range of the spool  82  is limited to control maximum flow rates to and from the double-acting cylinder  24  as a compromise between response time and valve stability. The travel range of the piston head  62  of the double-acting cylinder  24  corresponds to the desired range of travel of the dual poppet head body  36  of the exhaust valve  20 . The spring rate of the feedback spring  26  is set so that the change in compression of the feedback spring  26  in response to the range of actuating forces imparted by the solenoid  116  matches the desired range of travel of the dual poppet head body  36 .  
         [0032]    Applying less current to the solenoid  116  momentarily moves the spool  82  toward the initial position, where the spool remains until movement of the piston head  62  in the opposite direction decompresses the compression spring  26  equal to the reduced solenoid actuating force. Differential pressure across the piston head  62  is reduced or, if necessary, momentarily reversed to restore the spool  82  to the neutral position. A new equilibrium is restored at the neutral position of the spool  82  with the feedback spring  26  less compressed and with the dual poppet head body  36  in a less open position of the exhaust valve  20 .  
         [0033]    The maximum actuating force of the solenoid  116  is only required to withstand the maximum compression of the feedback spring  26 , whose spring rate can be specifically tailored to the force range of the solenoid  116 . The hydraulic force produced by the double-acting cylinder  24  provides whatever force is actually necessary to move the dual poppet head body  36  and to counteract the forces imparted by the solenoid  116 . Thus, engine oil pressure provides the primary force for opening and closing the exhaust valve  20 , while electrical current is required mainly for purposes of control (i.e., choosing the desired position of the exhaust valve). In fact, the actuating force imparted by the solenoid  116  for opening the exhaust valve  20  points in a direction opposite to the direction the double-acting cylinder  24  moves the dual poppet head body  36  for opening the exhaust valve  20 .  
         [0034]    Although specific examples have been given of flow control valves or devices, directional valves, biasing mechanisms, and fluid-powered and electrical actuators for use in my new two-stage proportional flow control valve assembly, other such valves, devices, mechanisms, and actuators can be substituted in accordance with the overall teaching of this invention for regulating not only flows of exhaust but other fluid flows or mechanical movements that are independent of the source of fluid pressure for operating the valve assembly. For example, the exhaust valve can be a flow control valve having the same or different seating action for regulating flow rates. The source of fluid pressure for operating my new valve is preferably different from both the fluid flows regulated by the valve and the control signals imparted to the valve. Instead of opening and closing a flow control valve, the proportional control can be arranged to adjust the operating positions of other hydraulic or mechanical devices as a function of a low-power control signal.