Abstract:
A system for detecting individual cylinder misfire in a multiple cylinder internal combustion (IC) engine having exhaust gas recirculation (EGR). The system includes: a device for predicting EGR flow rate on a cylinder to cylinder basis; a device for sensing actual EGR flow rate on a cylinder to cylinder basis with all cylinders firing; and a device for comparing the predicted EGR flow rate to the actual EGR flow to determine individual cylinder misfire.

Description:
FIELD OF THE INVENTION  
       [0001]    The invention relates to internal combustion engines and more particularly to systems and methods for sensing individual cylinder misfire. 
       BACKGROUND OF THE INVENTION  
       [0002]    In the decades long quest for increasing engine efficiency while at the same time meeting ever more stringent emissions standards, engines have been controlled electronically through the use of electronically controlled injectors to carefully meter and time the introduction of fuel for optimum efficiency and a reduction of exhaust components considered harmful for the environment. Such fuel systems may be a unit injector wherein the injection pressure is developed at the cylinder or in various common rail systems in which the pressure is generated elsewhere. 
         [0003]    In both instances, particularly for diesel engines, the fuel timing and quantity is especially important given the varied environmental and operational environment for the engine. The need for precise and flexible control is even more important in the case of diesel engines having exhaust gas recirculation (EGR). Such systems are important to reduce the oxides of nitrogen by reducing the combustion temperatures for the engine. While the oxides of nitrogen are properly reduced there is an increase in the quantity of particulates in the engine exhaust. Such increase requires various aftertreatment devices including particulate filters and in some cases catalysts. The problem with the use of devices of this type is that variations in the composition and flow of the exhaust, including the presence of un-burnt hydrocarbons, can be influenced by individual cylinder misfire. This is when the proper combustion does not occur for a variety of reasons, all of which can cause a variation in the composition of the exhaust flow and therefore the need for adjustment of the engine management strategy to remediate exhaust flow composition. 
         [0004]    It is difficult to detect cylinder misfire with the standard fuel system components for controlling the operation of the engine. As a result, additional components, usually in the form of pressure and/or temperature sensors in the exhaust flow are employed to determine the existence of a misfire by fluctuations in pressure and/or temperature. Such systems add additional complexity and cost to the system in addition to providing a further failure mode in that the additional sensors are exposed to the most harmful portion of the exhaust flow. 
         [0005]    What is needed therefore, in the art, is a system and method for simplifying and making effective the determination of cylinder misfire. 
       SUMMARY OF THE INVENTION  
       [0006]    In one form the invention is a system for detecting individual cylinder misfire in a multiple cylinder internal combustion (IC) engine having exhaust gas recirculation (EGR), said system including: a device for predicting EGR flow rate on a cylinder to cylinder basis; a device for sensing actual EGR flow rate on a cylinder to cylinder basis with all cylinders firing; and a device for comparing the predicted EGR flow rate to the actual EGR flow to determine individual cylinder misfire. 
         [0007]    In another form, the invention is a method of determining individual cylinder misfire in a multiple cylinder internal combustion engine (IC) engine having exhaust gas recirculation (EGR) including the steps of: predicting EGR flow rate on a cylinder to cylinder basis with all cylinders firing; sensing actual EGR flow rate on a cylinder to cylinder basis; and comparing the predicted EGR flow rate to the actual EGR flow rate to determine individual cylinder misfire. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a schematic diagram of an engine system for detecting individual cylinder misfire; and 
           [0009]      FIG. 2  shows the cyclic variation in exhaust gas recirculation (EGR) flow for the system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]    Referring to  FIG. 1 , there is shown an internal combustion engine system including an engine  10 . Engine  10  is a multi-cylinder reciprocating engine in which a plurality of pistons reciprocate within individual cylinders to produce a rotary output at flywheel  51 . Engine  10  may be one of a number of types of internal combustion engines but, for illustration purposes, the engine  10  may be a compression ignition or diesel engine in which the heat of compression of air produces a temperature high enough that fuel injected from a fuel system  52  via a delivery means illustrated by line  53  produces combustion to cause the cylinders to fire and drive the piston to produce rotation of flywheel  51  with a torque output. 
         [0011]    The products of combustion are delivered to an exhaust manifold  14  which leads to a conduit  16  extending to a turbine  18  of a turbocharger  20 . From there, the gases that have passed over the turbine  18  are delivered to an outlet conduit  24 . A conduit  26  branches off the exhaust conduit  16  and extends to a mass flow sensor  28 . Mass flow sensor  28  connects to a conduit  30  leading to a mixer  32  that mixes exhaust gas into air flowing into a conduit  40  leading to the intake manifold  12 . Exhaust gas recirculation (EGR) has been used extensively to reduce oxides of nitrogen in engine exhaust. The mixer  32  receives a supply of fresh air from conduit  34  leading to a compressor  36  incorporated in the turbocharger  20  and driven by turbine  18 . Compressor  36  receives filtered inlet air from a conduit  38 . The mixer  32  may also have a control mechanism to determine when EGR should take place. 
         [0012]    Mass flow sensor  28  is a differential pressure device for measuring flow through the EGR line and may take one of a number of forms. In general terms, the flow sensor presents an obstruction to flow through the EGR line and the pressure drop across the obstruction reflects the mass flow rate. In one form, the mass flow sensor  28  may be a venturi. This form of a mass flow sensor has been used since Roman times to measure flow using variations in pressure between an upstream location and a throat of the venturi unit. It uses the Bernoulli principle which incorporates pressure differential and other variables to compute mass flow. In another form the mass flow sensor may be a simple orifice in which the pressure differential is measured between a point upstream of the orifice and at the “vena contracts”, just downstream of the orifice to determine mass flow. This device also uses the Bernoulli principle. Still other forms of pressure differential flow sensors using the Bernoulli principle may be a nozzle, segmental wedge, V-cone, Dall tube, and others. 
         [0013]    The engine  10  is controlled by an ECU  42  that receives crankshaft position signals via line  46  from a crankshaft position sensor  48  positioned adjacent flywheel  51 . The ECU  42  has a signal line  44  extending to mass flow sensor  28  that measures pressure differential across the mass flow sensor  28  through the use of appropriate pressure sensors (not shown in detail) and therefore the mass flow rate of the EGR. 
         [0014]    The capability of the pressure sensors to determine pressure differential is advanced to the point where the pressure differential across mass flow sensor  28  is sub-cyclic in response time. That is, the pressure sensors respond to changes in less than a full engine cycle. The crankshaft position sensor  48  provides a signal to ECU  42  that correlates the pressure signals at the mass flow sensor  28  to individual engine cylinder activity. 
         [0015]    This rapid response is employed to provide an indication of cylinder misfire. The flow through the EGR line  26  is pulsating in nature due to the cylinder firing intervals of engine  10 . When the cylinders are all firing, the differential pressure in the mass flow sensor  28  has peaks and valleys as indicated in  FIG. 2  showing differential pressure versus time in seconds. When all cylinders are firing, the differential pressure produces a regular periodic wave having peaks  54 ,  56 ,  60 ,  62  and  64 . These pulses are not as great as the pressure pulses experienced directly in the exhaust pipe  16  but they are discrete enough to detect variations in pressure, and therefore variations in EGR mass flow caused by a cylinder misfire. Such a misfire is shown in  FIG. 2  as the absence of a peak  58 , in this case for cylinder  3  of a six cylinder engine. The absence of a normal peak as exhibited by  58  is fed to the ECU  42 . 
         [0016]    ECU  42  stores recent history of EGR flow to produce a predicted EGR flow on a cylinder to cylinder basis. The real-time pressure sensor signals from the mass flow sensor  28  are compared to the predicted signals to determine whether a misfire has occurred. Once the ECU determines that a misfire has occurred, it provides a control function via line  50  to a fuel control system  52  to adjust the engine management strategy as needed to correct the misfire. Such a corrective action is important to insure that any exhaust aftertreatment does not suffer by undetected hydrocarbons entering the exhaust conduit of the engine  10 . 
         [0017]    The above feature is provided without adding any new and expensive hardware in the engine exhaust line  16  or exhaust manifold which would add additional cost, complexity and the potential for reduced reliability. 
         [0018]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.