Abstract:
An internal combustion engine exhaust emission control system has a module for conveying exhaust gas from an engine exhaust system to an engine intake system. Flow is measured by the difference between pressures at opposite sides of an orifice in the exhaust gas flow path. A valve selectively restricts the flow path. Passages communicate pressure reading ports of a pressure sensor to opposite sides of the orifice. One passage comprises a tube having an end portion passing through a through-hole in a side wall of the flow path in alignment with the orifice in the flow path and containing an orifice member that faces the flow path orifice to reduce turbulence in the pressure communicated through it to the sensor.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to automotive emission control valves and systems, such as exhaust gas recirculation (EGR) valves that are used in exhaust emission control systems of automotive vehicle internal combustion engines. More specifically, the invention relates to an improvement for measuring the gas flow in an emission control valve and/or system via pressure sensing ports on opposite sides of an orifice. 
     BACKGROUND OF THE INVENTION 
     Commonly owned U.S. Pat. No. 6,116,224 (Cook and Busato) discloses an EGR system comprising an EGR module. One element of that module is a pressure sensor that senses pressure differential across a circular orifice through which exhaust gas flow is constrained to pass when a valve of the module allows flow to the engine intake system. 
     A circular orifice of given diameter possesses a known relationship between flow through the orifice and pressure drop across the orifice. In other words, flow through the orifice, and hence flow through the module, can be calculated by measurement of pressure drop across the orifice and applying the known flow/pressure drop relationship to the pressure drop measurement. U.S. Pat. No. 6,116,224 shows various embodiments for communicating the pressure drop across the orifice to the pressure sensor. 
     U.S. Pat. No. 5,613,479 discloses an EGR system that uses a similar general principle for measurement of EGR flow. Sensing port taps sense pressure difference across an orifice through which exhaust gas flow is constrained to pass. The orifice is disposed in a straight section of pipe that is provided with openings in its side wall at opposite sides of the orifice. An end portion of a sensing port tube is fit to a respective opening such that a tip of the end portion protrudes slightly into the pipe. The tip end of each sensing port tube is necked down to create at the tube entrance a restrictor having a diameter less than the nominal diameter of the tube. The restrictor thereby forms an orifice as the tube entrance. Each sensing port tube is connected through a rubber hose to a differential pressure sensor. The restrictors are said to reduce audible noise emanating from the EGR system as a result of exhaust pulsations transmitted through the rubbers hoses. 
     SUMMARY OF THE INVENTION 
     One generic aspect of the invention relates to an internal combustion engine exhaust emission control system comprising a flow path for conveying exhaust gas from an exhaust system of the engine to an intake system of the engine and comprising an orifice through which exhaust gas flow is constrained to pass. A valve selectively restricts the flow path. A first port communicates pressure in the flow path at a location upstream of the orifice to a first pressure reading port. A second port communicates pressure in the flow path at a location downstream of the orifice to a second pressure reading port. The pressure communicated through the first port is communicated through a flow restrictor proximate the flow path that imposes a greater restriction on the communication of the flow path to the first pressure reading port than any restriction imposed on the communication of the flow path to the second pressure reading port. 
     A further generic aspect relates to an internal combustion engine exhaust emission control system comprising a flow path for conveying exhaust gas from an exhaust system of the engine to an intake system of the engine and comprising an orifice through which exhaust gas flow is constrained to pass. A valve selectively restricts the flow path. A first port communicates pressure in the flow path at a location upstream of the orifice to a first pressure reading port. A second port communicates pressure in the flow path at a location downstream of the orifice to a second pressure reading port. The pressure communicated through one of the ports to the corresponding pressure reading port is communicated through an orifice that faces the orifice in the flow path. 
     One more generic aspect relates to an exhaust gas recirculation valve comprising a valve body for conveying exhaust gas from an exhaust system of a combustion engine to an intake system of the engine and comprising an orifice through which exhaust gas flow is constrained to pass. A valve selectively restricts the flow path. A first port communicates pressure in the flow path at a location upstream of the orifice to a first pressure reading port. A second port communicates pressure in the flow path at a location downstream of the orifice to a second pressure reading port. The pressure communicated through one of the ports to the corresponding pressure reading port is communicated through an orifice that faces the orifice in the flow path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The accompanying drawing, which is incorporated herein and constitutes part of this specification, includes a preferred embodiment of the invention, and together with a general description given above and a detailed description given below, serves to disclose principles of the invention in accordance with a best mode contemplated for carrying out the invention. 
     FIG. 1 is a front elevation view, partly in cross section, of an exemplary module embodying principles of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 discloses a module  20  embodying principles of the invention and comprising an emission control valve body  22 , a fluid-pressure-operated actuator  24 , an electric-operated pressure regulator valve  26 , and a sensor  28 . Valve  26  is an electric-operated vacuum regulator valve, sometimes referred to as an EVR valve, and sensor  28  is a pressure sensor that provides an electric signal related to the magnitude of sensed vacuum. 
     Valve body  22  comprises an internal main flow passage  30  extending between a first port  32  and a second port  34 . An annular valve seat element  36  is disposed in valve body  22  to provide an annular seat surface  38  circumscribing a transverse cross-sectional area of passage  30 . A valve member  40  comprising a non-flow-through valve head  42  is disposed within body  22  coaxial with an imaginary axis  44 . Valve head  42  is shown seated on seat surface  38  closing passage  30  to flow between ports  32  and  34 . 
     A stem  48  extends from valve head  42  to operatively connect head  42  with actuator  24  for operating valve member  40  via the actuator. Stem  48  passes with a close sliding fit through a bushing  50  that is fit to body  22  and guides valve member  40  for straight line motion along axis  44 . Bushing  50  also captures the outer margin of a circular flange of a generally cylindrical walled metal shield  52  on an internal shoulder of valve body  22 . Shield  52  surrounds a portion of stem  48  to direct exhaust gas heat away from the stem when exhaust gas flows through valve body  22 . A thin orifice member  54  comprising a circular orifice  56  is disposed at port  34  such that flow through main flow passage  30  is constrained to pass through orifice  56 . 
     Fluid-pressure-operated actuator  24  comprises a body  58  that is in assembly with valve body  22  coaxial with axis  44 . Actuator body  58  comprises a first body part  60  and a second body part  62 . Body part  62  comprises sheet metal formed to a generally circular shape having a central through-hole  64  that allows the part to fit over a protruding end of bushing  50 . An annular gasket  66  is sandwiched between actuator body part  62  and valve body  22 . Actuator body part  62 , gasket  66 , and valve body  22  each contains a like hole pattern that provides for the secure attachment of part  62  to valve body  22  by headed screws  70  whose threaded shanks are passed through aligned holes in part  62  and gasket  66  and tightened into threaded holes in body  22 . 
     Actuator body  58  comprises an interior that is divided into two chamber spaces  72 ,  74  by a movable actuator wall  76 . Movable actuator wall  76  comprises an inner formed metal part  78  and an outer flexible part  80 . Part  80  has a circular annular shape including a convolution that rolls as wall  76  moves. Part  80  also has a bead  82  which extends continuously around its outer margin and is held compressed between parts  60  and  62  by an outer margin of body part  62  being folded around and crimped against the outer margin of part  60 , thereby securing parts  60 ,  62 , and  76  in assembly and sealing the outer perimeters of chamber spaces  72  and  74 . The inner margin of part  80  is insert-molded onto the outer margin of part  78  to create a fluid-tight joint uniting the two parts. Several through-holes in part  62  communicate chamber space  74  to atmosphere. A helical coil compression spring  84  is disposed within chamber space  72  to resiliently bias movable wall  76  axially toward valve seat surface  38 , thereby urging valve head  42  toward seating on seat surface  38 , and thereby closing passage  30  to flow between ports  32  and  34 . 
     EVR valve  26  comprises a body having an atmospheric inlet port for communication to atmosphere, a source vacuum inlet port for communication to engine intake system vacuum, and a regulated vacuum outlet port. It contains an internal regulating mechanism like that of the EVR valves described in U.S. Pat. Nos. 5,448,981, and 6,116,224. 
     The internal mechanism of EVR valve  26  further comprises a solenoid that is operated by pulse width modulation. The pulse width modulation of the solenoid modulates the bleeding of vacuum to atmosphere to cause the vacuum in an internal chamber space to be regulated in accordance with the degree of signal modulation within a range that extends essentially from full intake system vacuum applied at the vacuum inlet port to essentially atmospheric pressure applied at the atmospheric inlet port. The regulated vacuum outlet port is directly in communication with that internal chamber space. An internal passage extends from that the regulated vacuum outlet port to actuator chamber space  72  to place the latter in fluid communication with the regulated vacuum in EVR valve  26 . Because the regulated vacuum is established by modulation of the solenoid and is communicated to chamber space  72 , the extent to which wall  76 , and hence valve member  40 , is moved along axis  44  against the resistance of spring  84  is controlled by the electric signal applied to the EVR solenoid. In this way, EGR flow to the engine intake system is closely controlled. 
     Intake system vacuum is communicated to a first pressure sensing port of sensor  28  in any suitable way, for example such as through a tube schematically shown at  86 . The tube communicates the intake system side of orifice  56  to the first pressure reading port of sensor  28 . 
     Sensor  28  comprises a second pressure reading port that is communicated to pressure at the opposite side of orifice  56 . The communication is established by a conduit comprising two tubes  88 ,  90  fitted together end-to-end. The side wall of valve body  22  bounding main flow path  30  comprises a right angle bend marked generally by the arrow  92 . That bend is disposed between valve seat surface  38  and orifice member  54 . Hence, orifice  56  is disposed downstream of the bend. 
     Tube  88  is a formed metal tube having an open free end  94  that is opposite the end that is fitted to tube  90 . An end portion of tube  88  passes through a through-hole  96  in the wall of valve body  22  to communicate open free end  94  to main flow path  30 . Through-hole  96  is coaxial with orifice  56 , and open free end  94  faces and is also coaxial with orifice  56 . Although stem  48  is disposed between open free end  94  and orifice  56 , pressure in the flow path upstream of the orifice can be accurately transmitted to pressure sensor  28 . Tube  88  includes an external shoulder  98  that abuts the exterior of valve body  22  surrounding through-hole  96  so that the open free end is accurately positioned at a desired distance in relation to the interior wall surface of main flow path  30  that contains the through-hole. 
     An electric connector  100  provides for sensor  28  and EVR valve  26  to be connected with an electric control circuit (not shown). Connector  100  contains five electric terminals, three of which are associated with sensor  28  and two of which, with EVR valve  26 . When connector  100  is connected with a mating connector (not shown) leading to the electric circuit that operates module  20 , two electric terminals carry pulse width modulated current to the EVR solenoid, and three terminals carry electric current signals related to pressures sensed at the two sensing ports of sensor  28 . 
     The improvement provided by the present invention comprises an orifice member  100 ′ disposed inside tube  88 , just interior of free end  94 . Orifice member  100 ′ comprises an outer margin that is fit to the tube wall and sealed thereto in a secure manner, and at its center, it comprises a circular orifice  102 ′. Hence pressure read by sensor  28  through tubes  88 ,  90  is communicated through orifice  102 ′. Orifice  102 ′ and orifice  56  are disposed in spaced apart, parallel planes, and the two are centered on a common linear axis. 
     No corresponding orifice in pressure sensing tube  86  is necessarily required. Prior to inclusion of orifice member  100 ′, a certain turbulence was affecting the static pressure measurement reading at the upstream sensing port, i.e. at the second pressure reading port of sensor  28  communicated through tubes  90 ,  88 , to main flow path  30  proximate bend  92 . The inclusion of orifice member  100 ′ was found to reduce errors in the readings due to turbulence. It was also discovered that the inclusion of orifice member  100 ′ provided better resolution, and hence greater accuracy, in readings taken at low EGR flow rates. 
     It is to be understood that because the invention may be practiced in various forms within the scope of the appended claims, certain specific words and phrases that may be used to describe a particular exemplary embodiment of the invention are not intended to necessarily limit the scope of the invention solely on account of such use.