Abstract:
An EGR control method to prevent condensation within the EGR system uses a temperature sensor signal from an EGR cooler exhaust gas outlet to model or estimate exhaust manifold gas temperature upstream of the cooler. If the estimated exhaust manifold gas temperature falls below a predetermined level, the engine control system closes or partially closes the EGR control valve to stop EGR flow through the cooler and the EGR valve.

Description:
FIELD OF THE INVENTION 
     This invention relates to internal combustion engines, including but not limited to engines having cooled exhaust gas recirculation (EGR). 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines, especially compression ignition engines such as diesel engines, utilize EGR to reduce emissions. An EGR system typically includes a flow circuit between the engine exhaust system and the engine intake system with an EGR cooler and an EGR valve within the flow circuit. EGR coolers are heat exchangers that typically use engine coolant to cool exhaust gas being recirculated into the intake system of the engine. Engine exhaust gas typically includes combustion by-products, such as unburned fuel, many types of hydrocarbon compounds, sulfur compounds, water, and so forth. 
     Various compounds may condense and deposit on interior surfaces of engine components when exhaust gas is cooled. The EGR cooler and the EGR valve are prone to condensation of compounds in the exhaust gas passing through it. The condensation is especially evident during cold ambient conditions, low exhaust gas temperatures, and/or low exhaust gas flow rates through the EGR cooler such as during idling. In some systems, in order to mitigate fouling of the EGR system components, the EGR valve is commanded to close by the Engine Control Unit (ECU) after sensing extended engine idling. 
     Condensation inside the EGR cooler, or fouling, decreases the percent-effectiveness of the EGR cooler. EGR coolers are designed to cope with condensation of hydrocarbons by incorporating anti-fouling features, such as appropriate geometries that inhibit excessive accumulation of condensates and a designed-in extra capacity that is intended to be lost to fouling during service of the cooler. 
     The incorporation of anti-fouling features, and the increased size of EGR coolers make cooler design complicated and costly. Accordingly, the present inventors have recognized that there is a need for an EGR system having an EGR cooler that is able to maintain higher efficiency without requiring complicated anti-fouling mechanisms or an increased cooler size. 
     The present inventors have recognized that there is a need to provide an EGR system with reduced fouling due to hydrocarbon condensation at low exhaust manifold gas temperatures. 
     SUMMARY 
     An exemplary method of the invention uses a temperature sensor signal from an EGR cooler exhaust gas outlet to model or estimate exhaust manifold gas temperature to more effectively reduce EGR system component fouling by protecting the EGR system from the condensation of hydrocarbons under certain engine operating conditions. The exemplary method allows for the use of a pre-existing temperature sensor downstream of the EGR cooler operating at a lower temperature to calculate the exhaust gas manifold temperature upstream of the cooler. 
     An exemplary embodiment of the invention utilizes the engine electronic control unit (ECU) to process a temperature sensor signal from the EGR cooler exhaust gas outlet, then the engine control unit computes a model-based exhaust manifold gas temperature value, and then commands the EGR valve to go to the closed position. 
     Alternatively, an inferred or estimated exhaust manifold gas temperature can be calculated utilizing the temperature sensor signal from the EGR cooler exhaust gas outlet along with various engine control system parameters to develop a correlation relationship. 
     Preferably, the engine electronic control unit processes the temperature sensor signal from the EGR cooler exhaust gas outlet, then the ECU computes a model-based exhaust manifold gas temperature value, then the ECU uses a lookup table to determine when exhaust manifold gas temperature is low enough to cause hydrocarbon condensation, and then the algorithm commands the EGR valve to go to a closed or partially closed position, which should prevent EGR valve fouling. 
     In addition, engine application-specific entry conditions can be monitored to allow the EGR valve to be commanded off. These application-specific entry conditions indicate when engine is running at low speed and light loads, during which exhaust gas temperature is expected to be low enough for hydrocarbon condensation. 
     Numerous other advantages and features of the present invention will be become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an internal combustion engine having an EGR system; and 
         FIG. 2  is signal diagram of a control scheme for operating the EGR system described in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
     The following describes an apparatus for and method of operating an EGR valve for an internal combustion engine. The engine includes an EGR system having an EGR cooler fluidly communicating with the engine. A block diagram of an engine having a high-pressure EGR system is shown in  FIG. 1 . Other EGR circuits are shown in U.S. Pat. No. 7,281,529, herein incorporated by reference. 
     A base engine  100  contains a plurality of cylinders housed in an engine block  101 . A compressor  102  is connected to an air cleaner (not shown) and a turbine  103 . An outlet of the compressor  101  is connected to a charge cooler  105 , which in turn is connected to an intake system  117 . The turbine  103  is connected to an exhaust system  109 . The exhaust system  109  is connected to the engine block  101 , and also connected to an EGR cooler  111 . The EGR cooler  111  is connected to an EGR valve  113 . 
     The EGR cooler  111  includes a housing and a heat transfer structure within the housing, such as a tube bundle or passages, that separate engine coolant from exhaust gas but allow heat transfer between the engine coolant and exhaust gas within the housing. A coolant inlet  111   a  and an outlet  111   b  direct coolant through the heat transfer structure. 
     During engine operation, air from the air cleaner (not shown) enters the compressor  102 . Exhaust gas from the engine block  101  enters the exhaust system  109 . A portion of the exhaust gas in the exhaust system  109  operates the turbine  103 , and a portion enters the EGR cooler  111 . The exhaust gas entering the turbine  103  forces a turbine wheel (not shown) to rotate and provide power to a compressor wheel (not shown) that compresses air. The compressed air travels from the output of the compressor  102  to the charge air cooler  105  where it is cooled. The cooled compressed air is then ingested by the engine through the intake system  117 . 
     Exhaust gas entering the EGR cooler  111  is cooled before entering the EGR valve  113 . The EGR valve  113  is shown downstream of the EGR cooler  111 , but may alternatively be positioned upstream of the EGR cooler  111 . The EGR valve  113  controls the quantity of exhaust gas the engine  100  will ingest. The exhaust gas exiting the EGR valve  113  mixes with the compressed and cooled air coming from the charge cooler  105  upstream of the intake system  117 . 
     A temperature sensor  120  generates a signal  121  representative of the temperature of the exhaust gas exiting the cooler  111 . This signal  121  is sent to the engine electronic control unit (ECU)  126 . The ECU  126  typically monitors and controls the operation of the engine, such as the timing and operation of the fuel injectors, the operation of the EGR valve and other engine controls. The ECU  126  normally controls the percentage open or closed of the EGR valve  113  depending on the engine parameters, to control exhaust emissions. 
     In heretofore known EGR control schemes, the position of the EGR valve which determines the amount of EGR during steady state engine operation is controlled by a variety of factors but predominantly engine speed and indicated torque. When the accelerator is depressed or released, a changed amount of fuel is delivered into the engine. For reducing emissions and for maintaining engine efficiency, the engine control sets a mass air flow rate and the EGR valve is adjusted according to the pre-set relationship programmed into the control, such as described in U.S. published application 2008/0078176. 
     In this regard, many engine parameters are input into the ECU  126  such as described in U.S. published patent application 2008/0078176 or U.S. Pat. Nos. 7,353,648; 6,973,382 or 6,401,700 all herein incorporated by reference. 
     Three parameters that are useful in the exemplary method of the present invention are the sensed temperature signal  121 , an engine coolant temperature signal  132  and an EGR flow rate signal  136 . The engine coolant temperature signal can be taken at the inlet  111   a  or upstream of the cooler. The EGR flow rate can be measured or calculated by the ECU  126  based on the percentage open of the EGR control valve  113  and/or other engine parameters. The mass flow rate of EGR gas can be measured by the EGR valve position and pressure drop across the valve. Alternately, the mass flow rate of EGR can be determined by the calculated difference between the total mass air flow through the engine calculated by the ECU  126  using the engine displacement and the RPM, and the mass flow of fresh air from the engine MAF sensor. 
     According to the exemplary method, sensed temperature signal  121  from the sensor  120 , an engine coolant temperature signal  132 , and an EGR mass flow rate  136  are used to cause the ECU  126  to close the EGR valve to stop EGR flow and prevent fouling of the EGR system under certain engine operating conditions. 
     As demonstrated in  FIG. 2 , the EGR mass flow rate  136  is input into an EGR cooler efficiency calculation module or look up table module  142  within the ECU  126 . Based on the EGR mass flow rate, and known heat transfer characteristics of the particular cooler, i.e., the heat transfer structure, an EGR cooler efficiency parameter  146  is generated. 
     The temperature signal  121  from the sensor  120 , the engine coolant temperature signal  132  and the efficiency parameter  146  are input into a calculation module  152  within the ECU  126 , wherein the module does the calculation: 
     
       
         
           
             
               
                 
                   ( 
                   
                     EGRC_OUT 
                     ⁢ 
                     _Temp 
                   
                   ) 
                 
                 - 
                 
                   
                     ( 
                     EFF 
                     ) 
                   
                   * 
                   
                     ( 
                     TCO 
                     ) 
                   
                 
               
               
                 ( 
                 
                   1 
                   - 
                   EFF 
                 
                 ) 
               
             
             , 
           
         
       
     
     or stated another way, 
                 (     signal   ⁢           ⁢   121     )     -     (       (     signal   ⁢           ⁢   146     )     *     (     signal   ⁢           ⁢   132     )       )         (     1   -     signal   ⁢           ⁢   146       )           
generates an estimated exhaust manifold exhaust gas temperature  156 .
 
     The estimated exhaust manifold exhaust gas temperature  156  is communicated to EGR valve signal generator module  162  within the ECU  126  that, depending on the estimated exhaust manifold gas temperature  156 , generates a shutoff signal  170  sufficient to close or partially close the EGR valve. The shutoff signal  170  is communicated through a logic switch  174  within the ECU  126  that passes the signal as an EGR shutoff signal  178  to the EGR valve  113 . 
     In addition to the signal  170 , the logic switch can receive a shutoff signal  182  from application specific entry conditions from a control module  184  within the ECU  126 . Different applications may have different conditions which would dictate that the valve be closed once the conditions are met. If the conditions would require the EGR to be shut off immediately, then the input selection signal  182  would go to zero. An example would be if load demand suddenly goes from low to high, EGR would be shut off. Another example would be if one of the engine sensors reports a fault that would cause the model to be inaccurate or non-operational, then the EGR would be shut off. 
     The modules  142 ,  152 ,  162 ,  174 ,  184  within the ECU  126  can be pre-programmed into an existing ECU  126  or can be one or more electronic processor chips, programmable logic controllers, logic processors, memory circuits, RAMs, ROMs, electronic chips, and or microprocessors. 
     Once the EGR valve is closed the ECU  126  continues to monitor the various engine parameters, and once the conditions are met to allow EGR flow, the EGR valve is commanded to open and resume responding to normal operational commands from the ECU  126 . For example responding to engine speed and indicated torque. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred.