Abstract:
A method of controlling a diesel engine connected to a load, the method including the steps of detecting an increased torque requirement and matching a fuel flow with an airflow. The detecting an increased torque requirement step detects an increased torque requirement for the engine, the increased torque requirement taking place during a period of time. The matching a fuel flow step matches a fuel flow with an airflow going to the engine during the increased torque requirement, the matching step keeps the airflow and the fuel flow during the period of time at a substantially stoichiometric level enabling the use of a three-way catalyst to reduce NOx emissions during transients.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus to control the fuel/air mixture of a diesel engine and, more particularly, to a method and apparatus to control the fuel and air ratio of a diesel engine during a load increase. 
     2. Description of the Related Art 
     In modern low-emission diesel engines, the fuel/air mixture is typically set lean of the stoichiometric level with exhaust gas recirculation (EGR) used to reduce NOx during steady state operation. During rapid load increases on turbocharged diesel engines, the air flow increase lags behind the fuel flow increase and results in relatively rich operating conditions. This results in increased smoke and particulate emissions. Typically, the EGR flow is reduced or eliminated during rapid load increases to reduce smoke and particulates. However, this causes high NOx emissions from the engine. 
     In internal combustion engines, EGR is a NOx emission reduction technique used in most gasoline and diesel engines. EGR works by recycling a portion of an engine&#39;s exhaust gas back to the engine cylinders. Often, the EGR gas is cooled through a heat exchanger to allow introduction of a greater mass of the recirculated gas into a diesel engine. Since diesel engines are typically unthrottled, EGR does not lower throttling losses in the way that it does for gasoline engines. However, the exhaust gas, which is largely carbon dioxide and water vapor, has a much lower oxygen mass fraction than air, and so it serves to lower peak combustion temperatures. There are tradeoffs, however, adding EGR to a diesel reduces the specific heat ratio of the combustion gases in the power stroke. This reduces the amount of power that can be extracted by the piston. EGR also tends to reduce the amount of fuel burned in the power stroke. This is evident by the increase in particulate emissions that correspond to an increase in EGR. Particulate matter, which may mainly be composed of carbon, but is not burned in the power stroke is wasted energy. 
     Usually, an engine recirculates exhaust gas by piping it from the exhaust manifold to the inlet manifold. A control valve (EGR valve) within the EGR circuit regulates the time and the amount of return flow. 
     The air/fuel ratio is the mass ratio of air to fuel present during combustion. When all of the fuel is combined with all of the free oxygen, typically within a vehicle&#39;s combustion chamber, the mixture is chemically balanced and this air/fuel ratio is called a stoichiometric mixture. In theory, a stoichiometric mixture has just enough air to completely burn the available fuel. In practice, this is never quite achieved, due primarily to the very short time available for the combustion in an internal combustion engine for each combustion cycle. 
     What is needed in the art is a method and an apparatus to reduce pollutants during an increased torque requirement transition for diesel engines. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method and apparatus for controlling fuel/air mixture ratio during a load increase transition in a diesel engine. 
     The invention in one form is directed to a method of controlling a diesel engine connected to a load including the step of detecting the need for a higher torque output by the engine and matching a fuel flow with the airflow going to the engine during the load increase. The matching of the fuel flow with the air flow keeps the fuel flow and airflow during the load increase at a substantially stoichiometric level. 
    
    
     
       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 vehicle having a diesel engine utilizing an embodiment of the fuel control system of the present invention; 
         FIG. 2  is a block diagram illustrating an apparatus that utilizes the method used in  FIG. 1 ; 
         FIG. 3  illustrates the steps of an embodiment of the method utilized in the apparatus of  FIG. 2 ; and 
         FIG. 4  illustrates an embodiment of another method utilized in conjunction with the method of  FIG. 3  of the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate 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 now to the drawings, and more particularly to  FIG. 1 , there is illustrated a vehicle  10  in the form of an agricultural vehicle  10  also known as a tractor  10  having a loader attached thereto. Vehicle  10  includes a power generating system  12  that provides power to various aspects of vehicle  10  including motive power for wheels  14 . Although vehicle  10  is illustrated as a tractor  10 , it is to be understood that the present invention relates to any vehicle  10  and, more generally, to any power generating system  12  whether utilized by vehicle  10  or not. 
     Now, additionally referring to  FIG. 2 , there is illustrated details of power generating system  12  including engine  16  having an air cleaner  18 , a turbocharger compressor  20 , an air cooler  22 , an EGR cooler  24 , an EGR valve  26 , an EGR mixer  28 , a turbocharger turbine  30 , a diesel oxidization catalyst  32 , a diesel particulate filter  34 , a controller  36 , a torque or speed sensor  38 , a gas sensor  40 , and a fuel metering system  42 . Ambient air flows through air cleaner  18 , is compressed in turbocharger compressor  20 , is then cooled by cooler  22 , has exhaust gas mixed with the airflow in EGR mixer  28 , the mixture then flows to combustion chambers in engine  16 . Assuming, for the sake of clarity, that engine  16  is a diesel engine, fuel is then injected into each of the cylinders when the compression and cycle of the engine is appropriate for the injection thereof. Fuel is injected by way of fuel metering system  42  causing combustion to take place in the cylinders and the exhaust flows out from engine  16  passing either to an EGR cooler  24  or past turbocharger turbine  30 . The exhaust gas flow past turbocharger turbine  30  causes it to rotate and drives turbocharger compressor  20 . The exhaust gas flows by gas sensor  40  and then continues through diesel oxidization catalyst  32  and particulate filter  34  and the remaining gas is exhausted to the ambient atmosphere. 
     The exhaust gas that flows by gas sensor  40  has a particular NOx and/or oxygen content, which is sensed by gas sensor  40 . The exhaust gas that is diverted through the exhaust gas recirculation system first goes through a cooling process by EGR cooler  24  and EGR valve  26  is under the control of controller  36  which can moderate the flow or completely shut-off the flow of the EGR. Exhaust gas that is recirculated may enter directly into EGR mixer  28  rather than into the flow as shown in  FIG. 2 . Controller  36  is communicatively connected to speed sensor  38 , gas sensor  40 , fuel metering device  42 , and EGR valve  26 . 
     Now, additionally referring to  FIGS. 3 and 4 , there is illustrated methods  100  and  150  that carry out the control steps of the present invention. The steps may be carried out by way of hardware, an algorithm stored in controller  36 , or a combination of hardware and software. At step  102 , there is a detection of an increase in torque requirement for engine  16  that is sensed by speed sensor  38  and conveyed to controller  36 . Although schematically shown as a speed sensor connected to engine  16 , the sensing of torque requirement can be a combination of an anticipated load sensing system as well as increased load detection. Once the increase in needed torque is detected, the amount of the torque that is anticipated is utilized in step  104  to select the amount of fuel to match with the available airflow to engine  16 . The selection of the amount of fuel can be a selection based upon an entry in a look-up table having an amount that matches the detected torque requirement to a selected fuel amount or the amount of fuel may be determined as a result of an algorithm that may include fixed and changeable coefficients. 
     At step  106 , the fuel and air is matched and sent to engine  16  based upon the selection that occurred in step  104 . The selection at step  104  and the matching of the fuel to the air at step  106  is part of the adaptive control system of the present invention and is carried out to cause the fuel and air mixture to be substantially stoichiometric during the load increase. 
     While the fuel is being sent to engine  16 , the EGR may be shut off at step  108  or be moderated at step  108  for a certain period of time and then subsequently turned on at step  110  which may correspond to the meeting of the torque increase and engine  16  is then operating at a new static load level. At step  112 , the engine control is returned to its normal operating mode. The normal operating mode may include active controls that adjust the EGR flow as well as the fuel metering based upon information from gas sensor  40 . However, it should be noted that during the carrying out of the steps of the present invention that the current input from the gas sensor  40  is not utilized to select the fuel and air flow to engine  16 , rather, fuel is selected based upon the detected torque requirement and the amount of fuel is determined from a data look-up table or an algorithm based on the available air as previously discussed. Controller  36  evaluates the performance of engine  16  during the torque increase response with data from, among other things, gas sensor  40  and, in the event the information indicates a need to adjust the look up table and/or algorithm utilized by step  104 , controller  36  updates the values and/or variables so that the next time an increase in torque in the amount encountered occurs a more appropriate fuel selection can be utilized by controller  36 . This adaptive control system is needed since the open loop response inherent in such a system is evaluated and updated for an improved response the next time a torque requirement in a similar amount is encountered. 
     This updating process is illustrated in method  150  where the detection of NOx or O 2  carried out at step  152  by utilizing gas sensor  40  and the data is updated at step  154 . Method  150  may run in parallel to method  100  as part of the adaptive control system. 
     In the present invention, it can be considered that engine  16  is calibrated so that rapid load increases occur with a substantially stoichiometric fuel/air ratio, preferably with little or no EGR. Because the load increases will occur at or near stoichiometric conditions, the three-way catalyst which may be diesel oxidization catalyst  32 , which consists of one or more precious metal such as palladium, platinum, rhodium, etc., can be used to remove NOx emissions from the exhaust gas. Catalyst  32  and filter  32  could be modified to enhance the NOx removing function by changing the catalyst wash coat or precious metal. 
     As methods  100  and  150  are carried out, engine  16  operates at or substantially at stoichiometric conditions, with or without EGR, during rapid load increases. Catalyst  32  serves to react with and remove NOx emissions from the exhaust gas. The operating range of the catalyst is approximately 200° C. to above 1000° C. so it will effectively remove NOx throughout the operating range of engine  16 . 
     Gas sensor  40  may be a switching oxygen sensor that is used to confirm that the fuel/air mixture was substantially stoichiometric during the rapid load increase as described regarding method  150 , and the calibration elements contained in a data table are adjusted if the mixture has strayed from stoichiometric conditions due to changes in power generating system  12 , such as fuel injector wear, air flow measurement drift, or other changes to the engine. 
     Advantageously, the present invention controls the engine operating conditions during torque load increases so that a near stoichiometric combustion occurs during these rapid load increases, thereby reducing NOx due to the high efficiency of the catalyst and high torque is output because fueling is appropriate to the air flowing into engine  16 . If the torque demand and trapped air is such that the fueling would not be sufficient to reach stoichiometric, EGR would be added to reduce the trapped air to reach near stoichiometric exhaust conditions. Advantageously, this concept provides a more responsive engine with lower NOx than conventional fueling controls. It does not require additional hardware on an engine that already has a catalyst for hydrocarbon control or a diesel particulate regeneration or a diesel particulate filter for diesel particulate removal. Advantageously, the switching oxygen sensor  40  is used to adjust the calibration to compensate for engine wear and other changes to power generating system  12 . The present invention can be used with or without EGR, although low emission diesel engines typically have EGR. 
     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.