Exhaust gas flow measurement device

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. A valve selectively restricts the flow path. A pressure sensing passage communicates a pressure sensing port of a pressure sensor to the flow path. The pressure sensing passage comprises a tube having an end portion passing through a through-hole in a side wall of the flow path. In one embodiment, an open free end of the tube is disposed within the flow path in spaced relation to the side wall opposite an orifice that creates a pressure drop for obtaining a flow measurement using pressure sensed via the tube as one input. In another embodiment, the open free end of the tube is disposed flush with the side wall opposite a nozzle.

Description: 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. Commonly owned U.S. Patent 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. Patent No. 6,116,224 shows various embodiments for communicating the pressure drop across the orifice to the pressure sensor. Actual measurements of flow through such modules at different pressure drops across their orifices have shown a certain amount of scatter relative to a relationship that should theoretically exist for an ideal orifice. It is believed that greater precision in flow control can be obtained if the amount of scatter can be reduced, and it is toward that objective that the present invention is directed. US 4,022,237 Wertheimer discloses an internal combustion engine exhaust emission control system as recited in the precharacterising portion of the independent claim. The invention arises out of several discoveries. A first discovery is that scatter can be reduced by how the sensing port of a pressure sensor is communicated to the gas flow passage that extends through a module. A second discovery is that scatter can be reduced by using a nozzle instead of an orifice. A third discovery results from combining the first two discoveries. According to the invention there is provided an internal combustion exhaust emission control system as set forth in independent claim 1. The accompanying drawings, which are incorporated herein and constitute part of this specification, include one or more presently preferred embodiments of the invention, and together with a general description given above and a detailed description given below, serve to disclose principles of the invention in accordance with a best mode contemplated for carrying out the invention. Figure 1 is a front elevation view, partly in cross section, of a first embodiment which does not fall within the scope of claim 1. Figure 2 is a partial front elevation view in cross section of a second embodiment which falls within the scope of claim 1. Figure 3 is an enlarged view of one element of the second embodiment shown by itself. Figure 4 is full end view in the direction of arrow 4 in Figure 3. Figure 5 is a graph plot related to the first embodiment. Figure 6 is a graph plot related to the second embodiment. Figure 7 is a graph plot related to yet another embodiment. Figure 1 discloses a module 20 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. However, in an embodiment within the scope of the claims the orifice member 54 is replaced by a nozzle as shown in Figure 2. 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. Patent No. 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 sensing port of sensor 28. Sensor 28 comprises a second pressure sensing 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 dispose open free end 94 within main flow path 30 in spaced relation to the valve body wall containing through-hole 96. 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 open free end is accurately positioned at a desired distance from 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. Figure 5 is a desired graph plot 110 of flow rate through orifice 56 versus pressure drop across orifice 56 based on data from testing various modules 20. While some scatter in the data points is present, the scatter is less than in modules where tube 88 does not protrude into main flow passage 30. Hence, it is believed that extending the tube into the passage so that the open free end is spaced from the passage wall represents a meaningful improvement. Figures 2, 3, and 4 disclose a second embodiment of module that is like the first except in two respects. Like reference numerals designate like parts in both Figures 1 and 2, and so Figure 2 will be described only to the extent that it differs from Figure 1. A nozzle member 120 replaces orifice member 54, and the open free end 94 of tube 88 is substantially flush with the interior wall surface containing through-hole 96. Nozzle member 120 comprises a flow nozzle 122 that is profiled to contract the flow as the flow passes through it. Nozzle member 120 is fitted concentric with port 34 via a rim 123 to constrain the flow to pass through flow nozzle 122, and flow nozzle 122 is coaxial with open free end 94 of tube 88. The entrance 124 of flow nozzle 122 is profiled to follow the shape of segment of an ellipse, a profile that is preferred, although a non-elliptically contoured profile may be suitable in some modules. The nozzle exit 126 is cylindrical. Figure 6 shows a desired graph plot 130 of flow rate through flow nozzle 122 versus pressure drop across flow nozzle 122 based on data from testing various Figure 2 modules. Very little scatter in the data points is present. Hence, it is believed that the use of a nozzle may provide even more precision in production modules. Figure 7 shows a desired graph plot 140 of flow rate through a valve like the one of Figure 1, except having a different sized orifice, versus pressure drop across the orifice. The plots 142, 144 represent 1% tolerance limits based on testing a number of valves at several different magnitudes of vacuum. It is believed that this shows that substantial accuracy in the flow characteristic can be obtained in production valves. In all three Figures 5, 6, and 7, the horizontal axis is presented as the product of MAP (manifold absolute pressure of the engine) and DP (pressure difference across the orifice or nozzle). Although not specifically shown in the drawings, another embodiment of module may be like Figure 2, but with the open free end 94 of tube 88 disposed in the manner of Figure 1. 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.

Claims: An internal combustion engine exhaust emission control system (20) comprising: a flow path (30) for conveying exhaust gas from an exhaust system of the engine to an intake system of the engine and comprising a side wall (20) bounding a portion of the flow path and comprising a valve body (22) having a through-passage extending between an inlet port and a valve seat disposed between the inlet port and the outlet port circumscribing the through-passage, a pressure sensor (28) having a pressure sensing port, and a pressure sensing passage (88, 94) comprising a tube (88) with an open free end (94) communicating the pressure sensing port to the flow path, a device which is disposed downstream of where the pressure sensing passage communicates to the flow path, through which flow through the flow path is constrained to pass, and which creates a pressure drop in the flow path that bears a known relationship to flow rate through the device for correlating rate of flow through the device to pressure drop across the device, a through-passage comprising a bend between the valve seat and the outlet port and characterised in that the device is a nozzle (122) disposed downstream of the bend with the open free end of the tube facing the nozzle. An internal combustion engine exhaust emission control as set further in claim 1 wherein the pressure sensing passage comprises a tube having an end portion (94) passing through a through-hole in the side wall of the flow path to dispose an open free end of the tube substantially flush with the side wall. An internal combustion engine exhaust emission control system as set forth in claim 1 wherein the pressure sensing passage comprises a fuse having an end portion (94) passing through a through-hole in the side wall of the flow path to dispose an open free end of the tube within the flow path in spaced relation to the side wall. An internal combustion engine exhaust emission control system as set forth in claim 1 in which the open end of the tube is coaxial with the device. An internal combustion engine exhaust emission control system as set forth in claim 4 in which the valve comprises a head (42) that coacts with the valve seat (38) to selectively restrict flow through the flow path, and a steam (48) that extends from the valve head to an actuator (24) for positioning the valve head relative to the valve seat and that is disposed between the open free end of the tube and the device. An internal combustion engine exhaust emission control system as set forth in claim 5 wherein a shield (52) is positioned coaxially over part of the valve stem to shield that part of the valve stem from exhaust gases.

Inventors: GAGNON FREDERIC, HUENIKEN PETER, NYDAM KENNETH PETER, GAGNON, FREDERIC, HUENIKEN, PETER, NYDAM, KENNETH PETER
Applicants: SIEMENS VDO AUTOMOTIVE INC, SIEMENS VDO AUTOMOTIVE INC.
Application year: 2000
Main classification: F02M25
IPC codes: F02M25