Patent Publication Number: US-6659092-B2

Title: Bypass assembly with annular bypass venturi for an exhaust gas recirculation system

Description:
TECHNICAL FIELD 
     The present invention relates to exhaust gas recirculation systems in an internal combustion engine, and, more particularly, to an induction venturi in such exhaust gas recirculation systems. 
     BACKGROUND 
     An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine. 
     When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold. Likewise, the recirculated exhaust gas is preferably reintroduced to the intake air stream downstream of the compressor and air-to-air aftercooler (ATAAC). Reintroducing the exhaust gas downstream of the compressor and ATAAC is preferred due to the reliability and maintainability concerns that arise if the exhaust gas passes through the compressor and ATAAC. An example of such an EGR system is disclosed in U.S. Pat. No. 5,802,846 (Bailey), which is assigned to the assignee of the present invention. 
     With conventional EGR systems as described above, the charged and cooled combustion air which is transported from the ATAAC is at a relatively high pressure as a result of the charging from the turbocharger. Since the exhaust gas is also typically inducted into the combustion air flow downstream of the ATAAC, conventional EGR systems are configured to allow the lower pressure exhaust gas to mix with the higher pressure combustion air. Such EGR systems may include a venturi section which induces the flow of exhaust gas into the flow of combustion air passing therethrough. An efficient venturi section is designed to “pump” exhaust gas from a lower pressure exhaust manifold to a higher pressure intake manifold. However, because varying EGR rates are required throughout the engine speed and load range, a variable orifice venturi may be preferred. Such a variable orifice venturi is physically difficult and complex to design and manufacture. Accordingly, venturi systems including a fixed orifice venturi and a combustion air bypass circuit are favored. The bypass circuit consists of piping and a butterfly valve in a combustion air flow path. The butterfly valve is controllably actuated using an electronic controller which senses various parameters associated with operation of the engine. 
     With a venturi section as described above, the maximum flow velocity and minimum pressure of the combustion air flowing through the venturi section occurs within the venturi throat disposed upstream from the expansion section. The butterfly valve is used to control the flow of combustion air to the venturi throat, which in turn affects the flow velocity and vacuum pressure created therein. By varying the vacuum pressure, the amount of exhaust gas which is induced into the venturi throat of the venturi section can be varied. However, inducing the exhaust gas into the flow of combustion air in the venturi throat may affect the diffusion and pressure recovery of the mixture within the expansion section of the venturi. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a bypass venturi assembly for recirculating exhaust gas in an internal combustion engine is provided with a housing having an outlet, a combustion air inlet and an exhaust gas inlet. A center piece is positioned within the housing and in communication with the combustion air inlet. The center piece defines a combustion air bypass section therein. An annular venturi nozzle positioned between the housing and the center piece is in communication with the combustion air inlet and defines a combustion air venturi section. The venturi nozzle is in communication with the exhaust gas inlet and defines an exhaust gas venturi section. A combustion air bypass valve is positioned in association with the combustion air bypass section. An exhaust gas valve is positioned in association with the exhaust gas inlet. 
     In another aspect of the invention, a method of recirculating exhaust gas in an internal combustion engine is provided with the steps of: providing a housing having an outlet, a combustion air inlet and an exhaust gas inlet; positioning a center piece within the housing and in communication with the combustion air inlet, the center piece defining a combustion air bypass section therein; positioning an annular venturi nozzle between the housing and the center piece, the venturi nozzle in communication with each of the combustion air inlet and exhaust gas inlet; defining a combustion air venturi section between the venturi nozzle and the center piece; defining an exhaust gas venturi section between the center piece and the housing; positioning a combustion air bypass valve in association with the combustion air bypass section; positioning an exhaust gas valve in association with the exhaust gas inlet; controlling an operating position of each of the combustion air bypass valve and the exhaust gas valve; and inducting exhaust gas into a flow of combustion air using the venturi nozzle, dependent upon the controlling step. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of an embodiment of an internal combustion engine of the present invention; 
     FIG. 2 is a bottom view of an embodiment of a bypass venturi assembly of the present invention; 
     FIG. 3 is a plan view of the bypass venturi assembly shown in FIGS. 1 and 2; 
     FIG. 4 is a top view of the bypass venturi assembly shown in FIGS. 1-3; 
     FIG. 5 is a perspective, fragmentary view of a portion of the bypass venturi assembly shown in FIGS. 1-4; and 
     FIG. 6 is a partial, sectional view of the bypass venturi assembly shown in FIGS.  1 - 5 . 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, and more particularly to FIG. 1, there is shown an embodiment of an internal combustion engine  10 , including an embodiment of a bypass venturi assembly  12  of the present invention. Internal combustion engine  10  also includes a combustion air supply  14 , intake manifold  16  and exhaust manifold  18 . 
     Intake manifold  16  and exhaust manifold  18  are each fluidly coupled with a plurality of combustion cylinders C 1  through C 6 , as indicated schematically by dashed lines  20  and  22 , respectively. In the embodiment shown, a single intake manifold  16  and a single exhaust manifold  18  are fluidly coupled with combustion cylinders C 1  through C 6 . However, it is also possible to configure intake manifold  16  and/or exhaust manifold  18  as a split or multiple-piece manifold, each associated with a different group of combustion cylinders. 
     Combustion air supply  14  provides a source of pressurized combustion air to bypass venturi assembly  12 , and ultimately to intake manifold  16 . Combustion air supply  14  includes a turbocharger and an ATAAC, each of which may be of common construction and thus not specifically shown in FIG. 1 for simplicity. The turbocharger includes a turbine and a compressor therein. The turbine, in known manner, is driven by exhaust gas received from exhaust manifold  18  via fluid line  24 . The turbine is mechanically coupled with the compressor, which receives ambient combustion air as indicated by arrow  26 . The compressor compresses the ambient combustion air and outputs compressed combustion air to the ATAAC. The compressed combustion air is at an elevated temperature as a result of the work which is performed thereon during the compression process within the turbocharger. The hot combustion air is then cooled within the ATAAC. 
     Bypass venturi assembly  12  receives cooled and compressed combustion air via line  28 , and also receives exhaust gas via line  30 . The exhaust gas line  30  may include an exhaust gas cooler (not shown). Bypass venturi assembly  12  controllably mixes a selected amount of exhaust gas with the cooled and compressed combustion air and outputs the air/exhaust gas mixture to intake manifold  16  via line  32 . 
     More particularly, and referring to FIGS. 2-4, bypass venturi assembly  12  includes a housing  34  having a combustion air inlet  36 , an outlet  38  and an exhaust gas inlet  40 . Housing  34 , in the embodiment shown, is constructed as a two-part housing for manufacturing purposes. Combustion air inlet  36  is connected and in communication with combustion air supply  14  via line  28 . Exhaust gas inlet  40  is connected and in communication with exhaust manifold  18  via line  30 . Outlet  38  is connected and in communication with intake manifold  16  via line  32 . 
     Bypass venturi assembly  12  includes a center piece  42  positioned within housing  34 . Center piece  42  is positioned adjacent to and in communication with combustion air inlet  36 . A sleeve  44  is also positioned within housing  34 . A plurality of holes  45  are positioned in the venturi assembly  12  between the housing  34  and the sleeve  44 . Center piece  42  is formed with an annular recess  46  which faces toward and receives an end of sleeve  44 . Center piece  42  and sleeve  44  conjunctively define a combustion air bypass section  48  therein which terminates at outlet  38 . In the embodiment shown, center piece  42  is annular shaped and has a through bore  50 . Through bore  50  within center piece  42  is substantially cylindrical shaped. However, the particular configuration of through bore  50  may vary, depending upon the particular application. 
     Combustion air bypass valve  52  is positioned within through bore  50  of center piece  42 . Combustion air bypass valve  52  is configured to selectively open and close combustion air bypass section  48 . In the embodiment shown, combustion air bypass valve  52  is in the form of a butterfly valve which is controllably actuated by an ECM (not shown) to thereby control an amount of combustion air which flows through combustion air bypass section  48 . 
     Exhaust gas valve  54  is positioned within exhaust gas inlet  40  and is controllably actuated to open and close exhaust gas inlet  40 . In the embodiment shown, exhaust gas valve  54  is in the form of a butterfly valve which is controllably actuated by an ECM. Exhaust gas inlet  40  is substantially cylindrical shaped with an inside diameter which is sized relative to exhaust gas valve  54  to be selectively opened and closed thereby. 
     Single shaft  56  is coupled with and carries each of combustion air bypass valve  52  and exhaust gas valve  54 . Single shaft  56  includes a pair of notches (not numbered) which respectively interface with combustion air bypass valve  52  and exhaust gas valve  54 . The notches are formed in single shaft  56  such that combustion air bypass valve  52  and exhaust gas valve  54  are positioned at a predetermined angular orientation a relative to each other, as shown in FIG.  2 . In the embodiment shown, combustion air bypass valve  52  and exhaust gas valve  54  are positioned relative to each other at the angle α such that when combustion air bypass valve  52  is completely closed exhaust gas valve  54  is completely opened, and vice versa. The manufactured angle α may be varied to obtain different mixer characteristics for various applications. 
     Single shaft  56  is controllably actuated using a single actuator  58 , which in turn is controllably actuated using an ECM. Control by the ECM may be dependent upon selected input parameters received from sensor signals, such as engine load, intake manifold pressure, engine temperature, etc. The ECM may be configured to carry out the control logic using software, hardware, and/or firmware, depending upon the particular configuration. 
     Single shaft  56  is biased using a leaf-type coil spring  60 . Shaft  56  is biased in a rotational direction such that combustion air bypass valve  52  is biased to an open position. Thus, if control of actuator  58  fails, combustion air bypass valve is biased in a fail safe manner to the open position to allow combustion air to flow therethrough. 
     Venturi nozzle  62  is attached to and carried by housing  34 . Venturi nozzle  62  is positioned within housing  34  in association with each of combustion air inlet  36  and exhaust gas inlet  40 . Venturi nozzle  62  defines a combustion air venturi section  64  with sleeve  44 . Likewise, venturi nozzle  62  defines an exhaust gas venturi section  66  with housing  34  through which exhaust gas flows. Venturi nozzle  62  includes a distal end which defines an induction area  68  at which exhaust gas is inducted into the flow of passing combustion air. 
     Center piece  42  supports shaft  56 , and in turn supports combustion air bypass valve  52  and exhaust gas valve  54 . More particularly, center piece  42  supports shaft  56  on opposite sides of combustion air bypass valve  52 . Additionally, center piece  42  supports the end of shaft  56  and exhaust gas valve  54  in a cantilever manner as best seen in FIG.  3 . By supporting shaft  56  in this manner using center piece  42 , only two areas of contact occur with shaft  56 , thereby eliminating alignment errors which might otherwise occur if an additional opening and support area were defined in the far distal end of housing  34  adjacent exhaust gas inlet  40 . This improves reliability and reduces manufacturing costs. Additionally, openings are eliminated from housing  34  which might tend to allow leakage of exhaust gas to the ambient environment. 
     Industrial Applicability 
     During use, combustion occurs within combustion cylinders C 1  through C 6  which produces exhaust gas received within exhaust manifold  18 . Exhaust gas is transported to the turbocharger within combustion air supply  14  via fluid line  24  for rotatably driving the turbine within the turbocharger. The turbine rotatably drives the compressor, which in turn compresses the combustion air and outputs hot, compressed combustion air to the ATAAC, where it is cooled and transported via line  28  to combustion air inlet  36  of bypass venturi assembly  12 . 
     The ECM controllably actuates actuator  58 , which in turn rotates shaft  56 , combustion air bypass valve  52  and exhaust gas valve  54  to a desired position. The position of combustion air bypass valve  52  controls the amount of compressed combustion air which bypasses through combustion air bypass section  48  within center piece  42  and sleeve  44 . The amount of combustion air flowing through combustion air bypass section  48  in turn controls the amount of combustion air which flows through combustion air venturi section  64  adjacent venturi nozzle  62 . As the combustion air flows through combustion air venturi section  64 , the velocity thereof increases and the pressure decreases. Exhaust gas flows through exhaust gas venturi section  66  and is inducted into the flow of reduced pressure combustion air within induction area  68 . Depending upon the pressure and velocity of combustion air which flows through combustion air venturi section  64 , the amount of exhaust gas which is inducted into the passing flow of combustion air at induction area  68  is varied. The combustion air and exhaust gas mixture flow downstream from induction area  68  and mix with the combustion air flowing through combustion air bypass section  48  through the plurality of holes  45  at the downstream end of the venture assembly  12 . The combustion air/exhaust gas mixture is then transported from outlet  38  to intake manifold  16  via line  32 . By varying the position of each of combustion air bypass valve  52  and exhaust gas valve  54  using the ECM based upon varying operating parameters as described above, the amount of exhaust gas which is inducted into the combustion air may likewise be varied. 
     Bypass venturi assembly  12  of the present invention allows exhaust gas to be effectively and controllably inducted into a pressurized flow of combustion air using a venturi assembly having a minimized overall length. The reduced overall size of bypass venturi assembly  12  allows it to be positioned within the tight geometric constraints of an engine compartment in a motor vehicle. The bypass venturi assembly may either be carried by the frame of the vehicle, engine block, cylinder head or other suitable mounting location within the engine compartment. Venturi nozzle  62  is separate from housing  34  so that a nozzle with a particular configuration may be utilized, depending upon the particular application. Housing  34  splits adjacent venturi nozzle  62  so that a particularly configured venturi nozzle may be easily installed within bypass venturi assembly  12 . Thus, the bypass venturi assembly provides a compact design with simple and efficient operation. 
     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.