Abstract:
An air breathing fuel consuming internal combustion engine with EGR and a control for the quantity of EGR. The total gas flow of the engine is calculated by measuring temperature and pressure at the intake to the engine. The fresh air flow is measured by an orifice or venturi at any point in the flow path for fresh air for combustion by the engine prior to the introduction of the EGR flow. The difference between the calculated total flow and fresh air flow is the actual EGR flow which is used to set the EGR relative to total flow according to one of a number of selected control algorithms.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to internal combustion engines with exhaust gas recirculation (EGR) systems and the measurement of EGR flow. 
     2. Description of the Related Art 
     One of the essential elements in the over 30-year quest for reducing emissions in the United States has been the use of exhaust gas recirculation or EGR. This is a way in which a selected percentage of products of combustion are recirculated to the intake of an air-breathing, fuel-consuming internal combustion engine to lower combustion temperatures and thus reduce the quantity of oxides of oxygen produced during the combustion process. EGR was initially used on spark ignition gasoline fuel automotive engines. The early EGR approaches, while suppressing oxides of nitrogen, added complexity to the system and otherwise compromised performance and flexibility of the engine with which it is associated. 
     In succeeding years, the use of EGR has been made significantly more sophisticated with the use of electronic control, oxygen sensors, and other means for closed-loop control of the EGR. In recent years, the application of EGR has been required for compression ignition, or diesel, engines owing to mandatory Environmental Protection Agency (EPA) required reductions in emissions. The application of EGR to diesel engines posed a new challenge for the design of systems, especially in view of the nature of the duty cycle for the diesel engine. Diesel engines, particularly in the off highway field, operate under extremely difficult ambient environments and require control systems for the EGR to be rugged enough to withstand the required engine duty cycle but sufficiently accurate to maintain the required levels of emissions. 
     In order to control the percentage of EGR relative to the fresh air introduced to the engine, a measurement of EGR flow is required. Currently, such measurement involves either a venturi or orifice positioned within the passage that carries EGR from the exhaust of the engine to the engine intake. While providing some measure of EGR flow, the nature of the gas constituent in the EGR passage is such that it can affect the accuracy of the measurement. Furthermore, the EGR flow passage is subject to significant pressure pulse variations owing to the fact that multicylinder reciprocating internal combustion engines generate discrete exhaust pulses which are reflected in the flow through the EGR passage. This, in turn, can have a significant and adverse effect on the measurement of EGR flow within the EGR passage. In addition to this problem, the use of a venturi or orifice-like restriction in the EGR passage is a direct fuel efficiency penalty since additional pumping work must be done by the engine because of the orifice or venturi restriction. 
     Accordingly, what is needed in the art is a more effective and accurate measurement of EGR in an internal combustion engine. 
     SUMMARY OF THE INVENTION 
     In one form, the invention is a control system for an exhaust gas recirculation (EGR) system of an internal combustion (IC) engine which includes a device for controlling the flow of EGR in response to the differential of at least two input signals. A first device calculates the flow of gasses consumed by the IC engine and provides a signal proportional to the total gas flow to the flow control device. A second device measures the fresh air flow to the IC engine and provides a signal proportional to the fresh air flow to the flow control device so that the difference between the total flow and the fresh air flow is the actual EGR flow. 
     In another form, the invention is an internal combustion (IC) engine system including an air breathing, IC engine having an intake for receiving gas for combustion and an exhaust for discharging products of combustion. A flow control device selectively fluidly connects a controlled percentage of the products of combustion to the intake of the IC engine. A device actuates the flow control device in response to the differential of at least two input signals. A first device calculates the total flow of gasses consumed by the IC engine and provides a signal proportional to the IC engine total gas flow to the flow control device. A second device measures the fresh air flow to the IC engine and provides a signal proportional to the fresh air flow to the flow control device so that the difference between the total flow and the fresh air flow is the actual EGR flow. 
     In still another form, the invention is a method of operating an air-breathing, internal combustion (IC) engine having exhaust gas recirculation (EGR) and a device for controlling EGR. The method includes the steps of calculating the total flow of gasses consumed by the IC engine. The actual fresh air flow is subtracted from the total flow to provide a measure of EGR flow which is used as an input to the device for controlling EGR. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic drawing of an internal combustion engine having EGR and which embodies the present invention 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , there is shown an internal combustion engine system  10  having at its heart an air-breathing, fuel-consuming, multicylinder internal combustion engine  12  that receives combustion air from an intake manifold  14  and has a fuel system  16  supplying fuel for combustion which is discharged through exhaust manifold  18 . Internal combustion engine  12  can be a reciprocating type in which pistons reciprocate within cylinders in an appropriate in-line or V configuration and are connected to a crank shaft so that their up and down motion is converted into a rotary torque output. 
     The engine  12  may utilize any one of a number of operating cycles including a spark ignition engine in which fuel is mixed with combustion air prior to entry in the engine cylinders and ignited by an ignition source. Alternatively, the engine may be a compression ignition or diesel cycle in which the heat of compression is used to ignite fuel that is directly injected into the individual cylinders for combustion. Still another form may be what is referred to as homogenous charge compression ignition engines in which fuel is mixed with the combustion air prior to entry to the cylinder and various parameter controls or devices are used to initiate combustion. With any one of these systems, the products of combustion contain oxides of nitrogen, CO 2 , and other exhaust components. 
     The products of combustion are passed through an exhaust conduit  24  leading to a turbine  30  of a high pressure turbocharger  32 . The gasses discharged from turbine  30  pass through line  34  to turbine  36  of a low pressure turbocharger  38 . The gasses then pass from turbine  36  via line  40  to ambient A. An exhaust after treatment device  22  which typically includes an oxidization catalyst and a particulate filter may be positioned in line  40  as shown or may be located at any point in the exhaust flow path from the engine to ambient A. It should be apparent to those skilled in the art that some form of sound suppression may also be provided in line  40 . It should also be apparent that the internal combustion engine system  10  may be employed with or without one or both of the turbochargers  32  and  38  in accordance with the present invention. Furthermore, one or both of the turbocharger turbines  30  and  36  may employ variable geometry, as illustrated by the diagonal arrows, which controls air flow and the EGR fraction. 
     The low pressure turbocharger  38  has a central shaft  42  connected to drive a compressor  44  which receives fresh air from ambient A via intake line  46 . The air thus pressurized by compressor  44  passes through line  48  through an intercooler  50  to line  52 . Line  52  provides an inlet for air to compressor  54  of high pressure turbocharger  32  which is driven by turbine  30  through shaft  56 . 
     The output from compressor  54  passes through line  56 , an aftercooler  58  and finally through line  60  to intake manifold  14 . It should be noted by those skilled in the art that the intercooler  50  and aftercooler  58  may be incorporated or not incorporated depending upon the particular application for the engine system  10 . 
     The engine system  10  of  FIG. 1  incorporates EGR and to that end a line  62  has a T connection with line  24 . An EGR valve  26  is positioned within line  62  which extends through a cooler  64  and line  66  to connect with line  60  extending to intake manifold  14 . EGR valve  26  may take a number of forms but has the functional capability of allowing more or less products of combustion from line  24  to be passed through line  62 , cooler  64 , and line  66  to the intake  14  of IC engine  12 . The EGR valve  26  is actuated by control signals from a line  68  leading to an ECM  70  which may also provide control of the fuel system  16  via signal line  72 . 
     The ECM  70  is programmed to control the valve  26  and variable geometry turbines to produce one of several control algorithms. The first group includes an O 2  (mole/mass) fraction, EGR fraction and diluent to air ratio which are measures of EGR The second group includes Lambda, Phi and exhaust O 2  (mole/mass fraction) which are measures of fresh air to fuel ratio. A typical control scheme would control to one of the EGR measures and one of the fresh air to fuel ratio measures. This can be done by controlling the EGR valve  26  and the variable geometry turbines  30  and/or  36 . For all of these control logics, it is necessary to provide a measurement of the EGR flow through line  66 . Heretofore, this measurement has been taken directly in line  66  or  62  with the attendant deficiencies described above. 
     In accordance with the present invention, the internal combustion engine system  10  incorporates the following novel EGR measurement. The total flow of gasses to engine  12  is calculated using the temperature and pressure at the intake manifold  14 , measured by a sensor  74  and providing a signal to ECM  70  via line  76 . This measurement provides an accurate and responsive measurement of the total flow of gasses consumed by engine  12 . The fresh air flow is measured by any one of a number of flow sensors  78 ,  82 ,  84 , and  86 . The signal from any one of these locations is fed by lines indicated by dashed lines  88  to a signal line  90  extending to ECM  70 . The flow sensors  78 - 86  may either be a venturi or orifice in which pressure, temperature, and differential pressure are used to calculate the air flow past a sensor. Although a venturi and orifice are described, it should be noted to those skilled in the art that other forms of flow sensors may also be employed. The signal from any one of the sensors  78 - 86  is fed to the ECM  70  which is configured to subtract the fresh air flow, as sensed by these flow sensors, from the total air flow as calculated by the ECM  70  to provide a signal representing the actual flow of gasses through the EGR lines  62  and  66 . 
     Because the sensors are in the fresh air line, they are not subject to the adverse impact of pulsating flow when measuring in the EGR passages. This results in a signal that is significantly more stable and accurate than the prior methods of measuring flow actually in the EGR passages. It should be noted that any one of the locations for the sensors  78 - 86  may be selected depending upon the delta P ranges at that point and local velocity variations. The resultant system offers a significant increase in reliability and effectiveness. In addition, using the restriction in the fresh air line does not have the adverse impact on pumping losses that are found when measuring directly in the EGR loop. 
     While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.