Patent Publication Number: US-9885300-B2

Title: Method and system for controlling engine using combustion pressure sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to Korean Patent Application No. 10-2014-0142065 filed in the Korean Intellectual Property Office on Oct. 20, 2014, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a method and system for controlling an engine using a combustion pressure sensor, and more particularly, to a method and system for controlling an engine using a combustion pressure sensor capable of improving idle stability by reducing an indicated mean effective pressure (IMEP) deviation for each cylinder and an IMEP deviation for each driving cycle for the engine. 
     BACKGROUND 
     When an ignition switch of a vehicle is on, a starting motor rotates and starts an engine in which a mixed gas of air and fuel may be combusted and explode in a combustion chamber of the engine. When an engine speed is equal to or more than a predetermined speed (for example, 800 RPM) after the engine starts, an engine control unit (ECU) controls the engine in an idle condition or an idle region. The ECU controls a fuel injection amount so that the engine speed may be a target speed in the idle region. 
     In the conventional engine control system and method, optimal values of engine control parameters (for example, an exhaust-gas recirculation (EGR) parameter, a boost parameter, an injection parameter, and so on) are logically inputted to control the engine in a room temperature condition, while engine developers analyze data with respect to an engine start test to search and apply optimal values in a low temperature condition of the engine. 
     Therefore, according to the conventional engine control system and method, since many tests are performed for each temperature and atmospheric pressure condition, development time and cost increase. 
     In addition, according to the conventional engine control system and method, when startability and idle stability deteriorate due to deterioration of hardware of the engine, a combustion state related to deterioration of the startability and idle stability may not be monitored. 
     Furthermore, according to the conventional engine control system and method, since a fuel injection amount is controlled to maintain engine idle speed in an idle region, indicated mean effective pressure (IMEP) control is difficult. 
     In the conventional engine control system and method, although a target control value for mass fraction burned 50% (MFB50), which is a point of time of 50% of the total amount of combustion heat is corrected considering influence by atmospheric temperature, atmospheric pressure, and coolant temperature, it is difficult to improve the idle stability due to the deterioration of the engine and an environmental condition in spite of performing MFB50 control with the corrected target control value. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY 
     The present disclosure has been made in an effort to provide a method and system for controlling an engine using a combustion pressure sensor installed in a cylinder of the engine capable of improving idle stability by reducing an indicated mean effective pressure (IMEP) deviation for each cylinder and an IMEP deviation for each driving cycle for the engine using a combustion signal detected by the combustion pressure sensor. 
     As is well-known to a person of ordinary skill in the art, the IMEP indicates a torque generated during combustion and is a standard for determining combustion efficiency of an engine. 
     According to an exemplary embodiment of the present inventive concept, a method for controlling an engine having a combustion pressure sensor includes receiving a combustion pressure signal from the combustion pressure sensor. An IMEP deviation for each cylinder and an IMEP deviation for each driving cycle for the engine are calculated based on a combustion pressure according to the received combustion pressure signal. A main injection timing is set based on a difference between the calculated IMEP deviations for the each cylinder and a difference between the calculated IMEP deviations for the each driving cycle. The engine runs by injecting a fuel according to the set main injection timing. 
     The method may further include comparing the difference between the calculated IMEP deviations for the each cylinder and the difference between the calculated IMEP deviations for the each driving cycle with a IMEP deviation reference. A target ignition timing is advanced by a predetermined angle when the difference between the calculated IMEP deviations for the each cylinder or the difference between the calculated IMEP deviations for the each driving cycle is greater than the IMEP deviation reference. 
     The step of advancing the target ignition timing may include advancing a 50% mass fraction burned (MFB50) target control value. 
     The main injection timing may be updated according to the MFB50 target control value. 
     The calculated IMEP deviations for the each cylinder and the calculated IMEP deviations for the each driving cycle may be calculated by the following equation,
 
IMEP deviation=(standard deviation IMEP)/(average IMEP).
 
     According to another embodiment of the present inventive concept, a system for controlling an engine having a combustion pressure sensor includes a coolant sensor configured to detect a coolant temperature. An atmospheric pressure sensor is configured to detect atmospheric pressure. An atmospheric temperature sensor is configured to detect atmospheric temperature. An engine controller is configured to receive signals from the combustion pressure sensor, the coolant sensor, the atmospheric pressure sensor, and the atmospheric temperature sensor, and to control the engine based on the received signals. 
     As described above, according to an embodiment of the present invention, the method and system for controlling an engine using a combustion pressure sensor installed in a cylinder of an engine can be provided to improve an idle stability by reducing an indicated mean effective pressure (IMEP) deviation for each cylinder and an IMEP deviation for each driving cycle for an engine using a combustion signal detected by the combustion pressure sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a system for controlling an engine using a combustion pressure sensor according to an exemplary embodiment of the present inventive concept. 
         FIG. 2  is a flowchart of a method for controlling an engine using a combustion pressure sensor according to an exemplary embodiment of the present inventive concept. 
         FIGS. 3 to 5  are graphs for illustrating operation of a system and method for controlling an engine using a combustion pressure sensor according to an exemplary embodiment of the present inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the inventive concept are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure. 
     In addition, in the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
       FIG. 1  is a block diagram of a system for controlling an engine using a combustion pressure sensor according to an exemplary embodiment of the present inventive concept. 
     The system according to an exemplary embodiment of the present inventive concept improves idle stability of an engine in which a combustion pressure sensor is installed. 
     The system according to an exemplary embodiment of the present inventive concept includes a coolant sensor  110  configured to detect coolant temperature, an atmospheric pressure sensor  120  configured to detect atmospheric pressure, and an atmospheric temperature sensor  130  configured to detect atmospheric temperature. An engine controller  100  is configured to receive signals from a combustion pressure sensor  20 , the coolant sensor  110 , the atmospheric pressure sensor  120 , and the atmospheric temperature sensor  130 , and to control an engine  10  based on the received signals. 
     The coolant sensor  110 , the atmospheric pressure sensor  120 , and the atmospheric temperature sensor  130  output the signals for correction associated with environmental change while the engine  10  is controlled, but it should be understood that the scope of the present disclosure is not limited thereto. The technical spirit of the present disclosure may be applicable to other sensors that can substantially output signals for correction associated with environmental change while the engine  10  is controlled. 
     The combustion pressure sensor  20  is installed in a cylinder of the engine  10  to detect a combustion pressure in the cylinder. The combustion pressure sensor  20  may be installed in each cylinder of the engine  10  or a selective cylinder(s) considering design and cost of the engine  10 . 
     Since the combustion pressure sensor  20  applied to the present disclosure is well-known to a person of an ordinary skill in the art, a detailed description for configuration and operation thereof will be omitted. 
     The engine controller  100  is one or more microprocessors and/or hardware including a microprocessor that can be operated by a predetermined program, and the predetermined program may include a series of commands for executing the method for controlling the engine using the combustion pressure sensor to be described later according to the exemplary embodiment of the present inventive concept. 
     In the present disclosure, the engine controller  100  may be included in a conventional ECU, or may include the conventional ECU. 
     A method for controlling an engine using a combustion pressure sensor will now be described in detail with reference to the accompanying drawings. 
       FIG. 2  is a flowchart of a method for controlling an engine using a combustion pressure sensor according to an exemplary embodiment of the present inventive concept. 
     As shown in  FIG. 2 , the engine controller  100  determines whether the engine  10  has started and then is in an idle state (S 110 ). 
     The process until the engine  10  starts and is in the idle state is shown in  FIG. 3  as is well-known to a person of an ordinary skill in the art. 
     When the engine  10  runs in the idle state, the engine controller  100  receives a combustion pressure signal from the combustion pressure sensor  20  (S 120 ). 
     When the engine controller  100  receives the combustion pressure signal, the engine controller  100  may also receive signals from the coolant sensor  110 , the atmospheric pressure sensor  120 , the atmospheric temperature sensor  130  and so on, as is well-known to a person of an ordinary skill in the art. 
     When the combustion pressure signal is received, the engine controller  100  calculates an IMEP for each cylinder and an IMEP for each driving cycle for the engine  10  based on a combustion pressure corresponding to the received combustion pressure signal. The engine controller  100  then calculates IMEP deviations (IMEP_COV_act1) for each cylinder and IMEP deviations (IMEP_COV_act2) for each driving cycle based on the calculated IMEP for each cylinder and the calculated IMEP for each driving cycle. Further, the engine controller  100  calculates a predetermined IMEP deviation (IMEP_COV_ref1) for each cylinder and a predetermined IMEP deviation (IMEP_COV_ref2) for each driving cycle (S 130 ). The COV refers to coefficient of variation. 
     The IMEP deviation for each cylinder and the IMEP deviation for each driving cycle may be calculated by the following equation.
 
IMEP deviation=(standard deviation IMEP)/(average IMEP)
 
     The engine controller  100  may calculate a standard deviation IMEP and an average IMEP based on the combustion pressure, as is well-known to a person of an ordinary skill in the art. 
     The predetermined IMEP deviation (IMEP_COV_ref1) and the predetermined IMEP deviation (IMEP_COV_ref2) may be calculated by the following equations, or may be obtained through simulation and experiment. 
     
       
         
           
             
               
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     where Q: combustion heat, θ: crank angle, k: coefficient, V: cylinder volume, and P: combustion pressure 
       FIG. 4  is a graph associated with the equations for calculating the IMEP. 
     When the IMEP deviation (IMEP_COV_act1), IMEP deviation (IMEP_COV_act2), the predetermined IMEP deviation (IMEP_COV_ref1), and the predetermined IMEP deviation (IMEP_COV_ref2) are calculated, the engine controller  100  determines a main injection timing based on difference (IMEP_COV_Dvt1) between the calculated IMEP deviations (IMEP_COV_act1) (IMEP_COV_act2) and difference (IMEP_COV_Dvt2) between the calculated IMEP deviations (IMEP_COV_ref1)(IMEP_COV_ref2) (S 140 ). 
     The difference (IMEP_COV_Dvt1) and the difference (IMEP_COV_Dvt2) may be calculated by the following equations.
 
IMEP_COV_Dvt1=IMEP_COV_act1−IMEP_COV_ref1
 
IMEP_COV_Dvt2=IMEP_COV_act2−IMEP_COV_ref2
 
     When the difference (IMEP_COV_Dvt1) and the difference (IMEP_COV_Dvt2) are calculated, the engine controller  100  determines whether the difference (IMEP_COV_Dvt1) and the difference (IMEP_COV_Dvt2) are greater than a predetermined value, e.g., 0 (S 150 ). 
     When at least one of the difference (IMEP_COV_Dvt1) and the difference (IMEP_COV_Dvt2) is greater than the predetermined value, the engine controller  100  determines that the engine  10  is unstable and then advances a target ignition timing (that is, an MFB50 target control value) by a predetermined angle to improve combustion stability (S 160 ). 
     When both the difference (IMEP_COV_Dvt1) and the difference (IMEP_COV_Dvt2) are greater than the predetermined value, the engine controller  100  may advance the target ignition timing by a predetermined angle to improve the combustion stability considering design and characteristics of the engine  10 . 
     When the MFB50 target control value is advanced by the predetermined angle, the engine controller  100  operates the engine  10  with updating the main injection timing to follow the predetermined MFB50 target control value (S 170  and S 180 ). 
       FIG. 5  is a graph for illustrating an operation of a method for controlling an engine using a combustion pressure sensor according to an exemplary embodiment of the present inventive concept. 
     Here, when both the difference (IMEP_COV_Dvt1) and the difference (IMEP_COV_Dvt2) are less than the predetermined value, the engine controller  100  may control the engine according to a conventional engine control method. 
     Accordingly, idle stability may be improved by reducing indicated mean effective pressure (IMEP) deviations for each cylinder and IMEP deviations for each driving cycle for an engine using a combustion signal red by a combustion pressure sensor according to the present disclosure. 
     While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.