Patent Publication Number: US-8113187-B2

Title: Delay compensation systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 12/570,280 filed on Sep. 30, 2009 and U.S. Provisional Application No. 61/247,049 filed on Sep. 30, 2009. The disclosures of the above applications are incorporated herein by reference in their entirety. 
     FIELD 
     The present disclosure relates to internal combustion engines and more particularly to oxygen sensors. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     A fuel control system controls provision of fuel to an engine. The fuel control system includes an inner control loop and an outer control loop. The inner control loop may use data from an exhaust gas oxygen (EGO) sensor located upstream of a catalyst in an exhaust system. The catalyst receives exhaust gas output by the engine. 
     The inner control loop may use the data from the upstream EGO sensor to control an amount of fuel provided to the engine. For example only, when the upstream EGO sensor indicates that the exhaust gas is rich, the inner control loop may decrease the amount of fuel provided to the engine. Conversely, the inner control loop may increase the amount of fuel provided to the engine when the exhaust gas is lean. Adjusting the amount of fuel provided to the engine based on the data from the upstream EGO sensor modulates the air/fuel mixture combusted within the engine at approximately a desired air/fuel mixture (e.g., a stoichiometry mixture). 
     The outer control loop may use data from an EGO sensor located downstream of the catalyst. For example only, the outer control loop may use the data from the upstream and downstream EGO sensors to determine an amount of oxygen stored by the catalyst and other suitable parameters. The outer control loop may also use the data from the downstream EGO sensor to correct the data provided by the upstream and/or downstream EGO sensors when the downstream EGO sensor provides unexpected data. 
     SUMMARY 
     A steady-state (SS) delay module determines a SS delay period for SS operating conditions based on an air per cylinder. A dynamic compensation module determines a predicted delay period based on first and second dynamic compensation variables for dynamic operating conditions, the SS delay period, a previous predicted delay period. The first dynamic compensation variable corresponds to a period between a first time when fuel is provided for a cylinder of an engine and a second time when exhaust gas resulting from combustion of the fuel and air is expelled from the cylinder. The SS and predicted delay periods correspond to a period between the first time and a third time when the exhaust gas reaches an exhaust gas oxygen sensor that is located upstream of a catalyst. A final equivalence ratio module adjusts fuel provided to the cylinder after the third time based on the predicted delay period. 
     A method comprises: determining a steady-state (SS) delay period for SS operating conditions based on an air per cylinder (APC); determining a predicted delay period based on first and second dynamic compensation variables for dynamic operating conditions, the SS delay period, a previous predicted delay period. The first dynamic compensation variable corresponds to a period between a first time when fuel is provided for a cylinder of an engine and a second time when exhaust gas resulting from combustion of a mixture of the fuel and air is expelled from the cylinder. The SS and predicted delay periods correspond to a period between the first time and a third time when the exhaust gas reaches an exhaust gas oxygen (EGO) sensor that is located upstream of a catalyst. The method further comprises adjusting an amount of fuel provided to the cylinder after the third time based on the predicted delay period. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of an exemplary implementation of an engine system according to the principles of the present disclosure; 
         FIG. 2  is a functional block diagram of an exemplary implementation of an engine control module according to the principles of the present disclosure; 
         FIG. 3  is a functional block diagram of an exemplary implementation of an inner loop module according to the principles of the present disclosure; 
         FIG. 4  is a functional block diagram of an expected upstream exhaust gas output module according to the principles of the present disclosure; and 
         FIG. 5  is a flowchart depicting exemplary steps performed by a method according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     An engine control module (ECM) may control an amount of fuel provided to an engine to create a desired air/fuel mixture. Exhaust gas resulting from combustion of an air/fuel mixture is expelled from the engine to an exhaust system. The exhaust gas travels through the exhaust system to a catalyst. An exhaust gas oxygen (EGO) sensor measures oxygen in the exhaust gas upstream of the catalyst and generates an output based on the measured oxygen. 
     The ECM determines an expected output of the EGO sensor based on an equivalence ratio (EQR) of the air/fuel mixture provided for combustion. The ECM selectively adjusts the amount of fuel provided during future combustion events based on a difference between the output of the EGO sensor and the expected output. The ECM of the present disclosure delays the use of the expected output to account for a period between when the fuel mixture is provided and when the output of the EGO sensor reflects the measurement of the exhaust gas resulting from combustion of the air/fuel mixture. 
     Referring now to  FIG. 1 , a functional block diagram of an exemplary implementation of an engine system  10  is presented. The engine system  10  includes an engine  12 , an intake system  14 , a fuel system  16 , an ignition system  18 , and an exhaust system  20 . The engine  12  may include, for example, a gasoline type engine, a diesel type engine, a hybrid type engine, or another suitable type of engine. 
     The intake system  14  includes a throttle  22  and an intake manifold  24 . The throttle  22  controls air flow into the intake manifold  24 . Air flows from the intake manifold  24  into one or more cylinders within the engine  12 , such as cylinder  25 . While only the cylinder  25  is shown, the engine  12  may include more cylinders. 
     The fuel system  16  controls the provision of fuel to the engine  12 . The ignition system  18  selectively ignites an air/fuel mixture within the cylinders of the engine  12 . The air of the air/fuel mixture is provided via the intake system  14 , and the fuel of the air/fuel mixture is provided by the fuel system  16 . In some engine systems, such as diesel type engine systems, the ignition system  18  may be omitted. 
     Exhaust gas resulting from combustion of the air/fuel mixture is expelled from the engine  12  to the exhaust system  20 . The exhaust system  20  includes an exhaust manifold  26  and a catalyst  28 . For example only, the catalyst  28  may include a catalytic converter, a three way catalyst (TVVC), and/or another suitable type of catalyst. The catalyst  28  receives the exhaust gas output by the engine  12  and reduces the amounts of various components of the exhaust gas. 
     The engine system  10  also includes an engine control module (ECM)  30  that regulates operation of the engine system  10 . The ECM  30  communicates with the intake system  14 , the fuel system  16 , and the ignition system  18 . The ECM  30  also communicates with various sensors. For example only, the ECM  30  may communicate with a mass air flow (MAF) sensor  32 , a manifold air pressure (MAP) sensor  34 , a crankshaft position sensor  36 , and other suitable sensors. 
     The MAF sensor  32  measures a mass flowrate of air flowing into the intake manifold  24  and generates a MAF signal based on the mass flowrate. The MAP sensor  34  measures pressure within the intake manifold  24  and generates a MAP signal based on the pressure. In some implementations, engine vacuum may be measured with respect to ambient pressure. The crankshaft position sensor  36  monitors rotation of a crankshaft (not shown) of the engine  12  and generates a crankshaft position signal based on the rotation of the crankshaft. The crankshaft position signal may be used to determine an engine speed (e.g., in revolutions per minute). The crankshaft position signal may also be used for cylinder identification. 
     The ECM  30  also communicates with exhaust gas oxygen (EGO) sensors associated with the exhaust system  20 . For example only, the ECM  30  communicates with an upstream EGO sensor (US EGO sensor)  38  and a downstream EGO sensor (DS EGO sensor)  40 . The US EGO sensor  38  is located upstream of the catalyst  28 , and the DS EGO sensor  40  is located downstream of the catalyst  28 . The US EGO sensor  38  may be located, for example, at a confluence point of exhaust runners (not shown) of the exhaust manifold  26  or at another suitable location. 
     The US and DS EGO sensors  38  and  40  measure oxygen concentration of the exhaust gas at their respective locations and generate an EGO signal based on the oxygen concentration. For example only, the US EGO sensor  38  generates an upstream EGO (US EGO) signal based on the oxygen concentration upstream of the catalyst  28 , and the DS EGO sensor  40  generates a downstream EGO (DS EGO) signal based on oxygen concentration downstream of the catalyst  28 . 
     The US and DS EGO sensors  38  and  40  may each include a switching EGO sensor, a universal EGO (UEGO) sensor (i.e., a wide range EGO sensor), or another suitable type of EGO sensor. A switching EGO sensor generates an EGO signal in units of voltage, and switches the EGO signal between a low voltage (e.g., approximately 0.2 V) and a high voltage (e.g., approximately 0.8 V) when the oxygen concentration is lean and rich, respectively. A UEGO sensor generates an EGO signal that corresponds to an equivalence ratio (EQR) of the exhaust gas and provides measurements between rich and lean. 
     Referring now to  FIG. 2 , a functional block diagram of an exemplary implementation of the ECM  30  is shown. The ECM  30  includes a command generator module  102 , an outer loop module  104 , an inner loop module  106 , and a reference generation module  108 . The command generator module  102  may determine engine operating conditions. For example only, the engine operating conditions may include, but are not limited to, the engine speed, air per cylinder (APC), engine load, and/or other suitable parameters. The APC may be predicted for one or more future combustion events in some engine systems. The engine load may be indicated by, for example, a ratio of the APC to a maximum APC of the engine  12 . 
     The command generator module  102  generates a base equivalence ratio (EQR) request. The base EQR request may correspond to a desired equivalence ratio (EQR) of the air/fuel mixture to be combusted within one or more cylinders of the engine  12 . For example only, the desired EQR may include a stoichiometric EQR (i.e., 1.0). The command generator module  102  also determines a desired downstream exhaust gas output (a desired DS EGO). The command generator module  102  may determine the desired DS EGO based on, for example, the engine operating conditions. 
     The command generator module  102  may also generate one or more open-loop fueling corrections for the base EQR request. The fueling corrections may include, for example, a sensor correction and an error correction. For example only, the sensor correction may correspond to a correction to the base EQR request to accommodate the measurements of the US EGO sensor  38 . The error correction may correspond to a correction in the base EQR request to account for errors that may occur, such as errors in the determination of the APC and errors attributable to provision of fuel vapor to the engine  12  (i.e., fuel vapor purging). 
     The outer loop module  104  may also generate one or more open-loop fueling corrections for the base EQR request. The outer loop module  104  may generate, for example, an oxygen storage correction and an oxygen storage maintenance correction. For example only, the oxygen storage correction may correspond to a correction in the base EQR request to adjust the oxygen storage of the catalyst  28  to a desired oxygen storage within a predetermined period. The oxygen storage maintenance correction may correspond to a correction in the base EQR request to modulate the oxygen storage of the catalyst  28  at approximately the desired oxygen storage. 
     The outer loop module  104  estimates the oxygen storage of the catalyst  28  based on the US EGO signal and the DS EGO signal. The outer loop module  104  may generate the fueling corrections to adjust the oxygen storage of the catalyst  28  to the desired oxygen storage and/or to maintain the oxygen storage at approximately the desired oxygen storage. The outer loop module  104  may also generate the fueling corrections to minimize a difference between the DS EGO signal and the desired DS EGO. 
     The inner loop module  106  determines an upstream EGO correction (US EGO correction) based on a difference between the US EGO signal and an expected US EGO (see  FIG. 3 ). The US EGO correction may correspond to, for example, a correction in the base EQR request to minimize the difference between the US EGO signal and the expected US EGO. 
     The reference generation module  108  generates a reference signal. For example only, the reference signal may include a sinusoidal wave, triangular wave, or another suitable type of periodic signal. The reference generation module  108  may selectively vary the amplitude and frequency of the reference signal. For example only, the reference generation module  108  may increase the frequency and amplitude as the engine load increases and may decrease the frequency and amplitude as the engine load decreases. The reference signal may be provided to the inner loop module  106  and one or more other modules. 
     The inner loop module  106  determines a final EQR request based on the base EQR request and the US EGO correction. The inner loop module  106  determines the final EQR request further based on the sensor correction, the error correction, the oxygen storage correction, and the oxygen storage maintenance correction, and the reference signal. For example only, the inner loop module  106  determines the final EQR request based on a sum of the base fuel command, the US EGO correction, the sensor correction, the error correction, the oxygen storage correction, and the oxygen storage maintenance correction, and the reference signal. The ECM  30  controls the fuel system  16  based on the final EQR request. 
     Referring now to  FIG. 3 , a functional block diagram of an exemplary implementation of the inner loop module  106  is presented. The inner loop module  106  may include an expected US EGO module  202 , an error module  204 , a scaling module  206 , a compensator module  208 , and a final EQR module  210 . 
     The expected US EGO module  202  determines the expected US EGO. The expected US EGO module  202  determines the expected US EGO based on the final EQR request. However, delays of the engine system  10  prevent the exhaust gas resulting from combustion from being immediately reflected in the US EGO signal. The delays of the engine system  10  may include, for example, an engine delay, a transport delay, and a sensor delay. 
     The engine delay may correspond to a period between, for example, when fuel is provided for a cylinder of the engine  12  and when the resulting burned air/fuel (exhaust gas) mixture is expelled from the cylinder. The transport delay may correspond to a period between when the resulting exhaust gas is expelled from the cylinder and when the resulting exhaust gas reaches the location of the US EGO sensor  38 . The sensor delay may correspond to the delay between when the resulting exhaust gas reaches the location of the US EGO sensor  38  and when the resulting exhaust gas is reflected in the US EGO signal. 
     The expected US EGO module  202  stores the EQR of the final EQR request. The expected US EGO module  202  determines a delay based on the engine, transport, and sensor delays. The expected US EGO module  202  delays use of the stored EQR until the delay has passed. Once the delay has passed, the stored EQR should correspond to the EQR measured by the US EGO sensor  38 . 
     The error module  204  determines an upstream EGO error (US EGO error) based on the US EGO signal provided by the US EGO sensor  38  and the expected US EGO provided by the expected US EGO module  202 . More specifically, the error module  204  determines the US EGO error based on a difference between the US EGO signal and the expected US EGO. 
     The scaling module  206  determines a fuel error based on the US EGO error. The scaling module  206  may apply one or more gains or other suitable control factors in determining the fuel error based on the US EGO error. For example only, the scaling module  206  may determine the fuel error using the equation: 
                     Fuel   ⁢           ⁢   Error     =       MAF   14.7     ⁢           ⁢           *     ⁢   US     ⁢           ⁢   EGO   ⁢           ⁢     Error   .               (   1   )               
In another implementation, the scaling module  206  may determine the fuel error using the equation:
 
Fuel Error= k (MAP,RPM)*US EGO Error,  (2)
 
where RPM is the engine speed and k is based on a function of the MAP and the engine speed. In some implementations, k may be based on a function of the engine load.
 
     The compensator module  208  determines the US EGO correction based on the fuel error. For example only, the compensator module  208  may apply a proportional-integral (PI) control scheme, a proportional (P) control scheme, a proportional-integral-derivative (PID) control scheme, or another suitable control scheme in determining the US EGO correction based on the fuel error. 
     The final EQR module  210  determines the final EQR request based on the base EQR request, the reference signal, the US EGO correction, and the one or more open-loop fueling corrections. For example only, the final EQR module  210  may determine the final EQR request based on the sum of the base EQR request, the reference signal, the US EGO correction, and the open-loop fueling corrections. The fuel system  16  controls the provision of fuel to the engine  12  based on the final EQR request. The use of the reference signal in determining the final EQR request may be implemented to, for example, improve the efficiency of the catalyst  28 . Additionally, the use of the reference signal may be useful in diagnosing faults in the US EGO sensor  38 . 
     Referring now to  FIG. 4 , a functional block diagram of an exemplary implementation of the expected US EGO module  202  is presented. The expected US EGO module  202  may include a storage module  314 , a retrieval module  316 , a steady-state delay (SS delay) module  320 , and a dynamic compensation module  322 . The expected US EGO module  202  may also include a floor module  324 , a sensor delay module  326 , and a sensor output module  328 . 
     The storage module  314  stores the EQR of the final EQR request in a buffer. For example only, the storage module  314  may include a ring or circular buffer. When the final EQR request is received, the storage module  314  stores the current EQR of the final EQR request in a next location in the buffer. The next location may correspond to, for example, a location in the buffer where an oldest EQR is stored. 
     The buffer may include a predetermined number of locations. In this manner, the buffer may include the current EQR and N number of stored EQRs, where N is an integer greater than zero and less than the predetermined number. The predetermined number may be calibratable and may be set to, for example, greater than a maximum number of events between when the fuel of the final EQR request is provided and when the resulting burned air/fuel mixture is reflected in the US EGO signal. An event may occur, for example, each time that an air/fuel mixture is ignited within a cylinder of the engine  12  (e.g., a combustion event). For example only, the maximum number may vary between approximately 3 and approximately 4 times the number of cylinders of the engine  12 , and the predetermined number may be approximately 5 times the number of cylinders of the engine  12 . 
     The retrieval module  316  selectively retrieves one or more of the N stored EQRs from the storage module  314  and determines a retrieved EQR based on the one or more of the N stored EQRs. For example only, the retrieval module  316  may determine the retrieved EQR based on two of the N stored EQRs. The retrieval module  316  determines the retrieved EQR further based on a predicted delay and an integer delay. The integer delay may correspond to the number of locations in the buffer between the current EQR of the final EQR request and one of the N stored EQRs. The exhaust gas that is likely present at the location of the US EGO sensor  38  is the result of combustion of the air/fuel mixture provided based on the retrieved EQR. 
     For example only, the retrieval module  316  may determine the retrieved EQR at a given event (k) using the equation:
 
Retrieved EQR( k )=(1+ID( k )−PD( k ))*StoredEQR( k −ID( k ))+(PD( k )−ID( k ))*StoredEQR( k −ID( k )−1),  (3)
 
where ID(k) is the integer delay at the event k, PD(k) is the predicted delay at the event k, stored EQR(k−ID(k)) is the stored EQR in the buffer k−ID(k) number of events ago, and stored EQR(k−ID(k)−1) is the stored EQR in the buffer k−ID(k)−1 number of events ago. The determination of the integer delay and the predicted delay are discussed further below.
 
     The SS delay module  320  may determine a steady-state delay (SS delay) based on the APC. For example only, the SS delay module  320  may determine the SS delay based on a steady-state delay model (SS delay module) that includes a mapping of SS delays indexed by APC. In other implementations, the SS delay module  320  may determine the SS delay based on the MAF, the engine load, or another suitable parameter. The length of the SS delay may correspond to a sum of the engine and transport delays during steady-state operating conditions. 
     The dynamic compensation module  322  determines the predicted delay based on the SS delay. More specifically, the dynamic compensation module  322  determines the predicted delay to account for transients in the APC (i.e., system dynamics) that may cause the SS delay to deviate from an actual delay between when the air/fuel mixture is provided for a cylinder and when the resulting burned air/fuel mixture reaches the location of the US EGO sensor  38 . For example only, an increasing APC transient may cause the actual delay to be less than the SS delay. The opposite may be true (i.e., the actual delay may be greater than the SS delay) when a decreasing APC transient occurs. 
     The dynamic compensation module  322  accounts for APC transients and outputs the predicted delay accordingly. For example only, the dynamic compensation module  322  may determine the predicted delay at a given combustion event (k) using the equation:
 
Predicted Delay( k )=( K )*SSDelay( k−n )+(1 −K )*PD( k− 1),  (4)
 
where SSDelay(k−n) is the SS Delay n number of combustion events ago and PD(k−1) is a last predicted delay output by the dynamic compensation module  322 . n and K may be referred to as dynamic compensation variables. The dynamic compensation variables account for APC transients. For example only, the value of K may be set based on whether the APC is increasing or decreasing. The value of n may correspond to a number of events between the fuel injection event and the exhaust event of a cylinder. For example only, the value of n may be equal to 4 in four-cylinder engines and may vary between 6 and 8 in eight-cylinder engines.
 
     The floor module  324  receives the predicted delay and determines the integer delay based on the predicted delay. More specifically, the floor module  324  may apply a floor function to the predicted delay to determine the integer delay. In other words, the floor module  324  may round the predicted delay down to a nearest integer. The floor module  324  provides the integer delay to the retrieval module  316 . The retrieval module  316  determines the retrieved EQR based on the predicted delay, the integer delay, and one or more of the stored EQRs as discussed above. 
     The sensor delay module  326  receives the retrieved EQR from the retrieval module  316 , accounts for the sensor delay, and determines an expected EQR based on one or more characteristics of the US EGO sensor  38 . The characteristics of the US EGO sensor  38  may include, for example, time constant, porosity, and other suitable characteristics. For example only, the sensor delay module  326  may determine the expected EQR at a given combustion event (k) using the equation: 
     
       
         
           
             
               
                 
                   
                     
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     where τ is a time constant of the US EGO sensor  38  (e.g., seconds), N is the engine speed, Expected EQR(k−1) is a last expected EQR output by the sensor delay module  326 , and Retrieved EQR(k) is the retrieved EQR received from the retrieval module  316  for the event k. 
     The sensor output module  328  receives the expected EQR from the sensor delay module  326  and determines the expected US EGO based on the expected EQR. For example only, the sensor output module  328  may translate the expected EQR into the units of the US EGO signal (e.g., a voltage when the US EGO sensor  38  includes a switching EGO sensor). In some implementations, such as where the US EGO sensor  38  includes a wide-range EGO sensor, the sensor output module  328  may be omitted and the expected EQR may be compared with the US EGO signal. The sensor output module  328  provides the expected US EGO to the error module  204  for comparison with the US EGO signal provided by the US EGO sensor  38 . 
     Referring now to  FIG. 5 , a flowchart depicting an exemplary method  500  is presented. Control may begin in step  501  where control stores the EQR of the final EQR request. In other words, control stores the current final EQR in step  501 . In step  502 , control determines the SS delay. Control may determine the SS delay based on, for example, the APC. Control determines the predicted delay in step  506 . For example only, control may determine the predicted delay using equation (4) as discussed above. 
     In step  510 , control determines the integer delay. Control may determine the integer delay based on the application of a floor function to the predicted delay. In other words, control may round the predicted delay down to the nearest integer to determine the integer delay in step  510 . Control determines the retrieved EQR in step  514 . Control may determine the retrieved EQR based on the predicted delay, the integer delay, and one or more of the N stored EQRs. For example only, control may determine the retrieved EQR using equation (3) as discussed above. 
     Control determines the expected EQR in step  518 . Control may determine the expected EQR based on the stored EQR and the characteristics of the US EGO sensor  38 . For example only, control may determine the expected EQR using equation (5) as discussed above. Control determines the expected US EGO in step  522 . For example only, control may determine the expected US EGO by translating the expected EQR into the units of the US EGO signal. Control then returns to step  501 . 
     The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.