Combustion state diagnosing system and combustion state diagnosing method for diagnosing engine and recording medium

Abstract

It is an object of the present invention to provide a low-cost combustion state diagnosing system and a combustion state diagnosing method capable of accurately detecting misfires which occur at a low frequency while a multiple-cylinder engine is operating at a high engine speed under a low load. The object can be achieved, when diagnosing combustion state, by extracting specific rotation period component of a period synchronous with rotation from a combustion state parameter for at least two rotations, and judging combustion state on the basis of the extracted specific rotation period component. The combustion state parameter may be the engine speed or the output torque of a multiple-cylinder engine which varies according to the combustion state of the engine.

What is claimed is:  
     
         1 . A combustion state diagnosing system for diagnosing a combustion state of a multiple-cylinder engine by measuring a parameter of the combustion state varying according to the combustion state of the engine, such as engine speed or output torque, diagnosing the combustion state on the basis of the parameter of the combustion state, said diagnostic system comprising: 
 a combustion state parameter measuring means which measures values of parameter of the combustion state N times (at least once) in one ignition cycle of the multiple-cylinder engine at times corresponding to a predetermined crank angle;    a specific rotation period component extracting means for extracting a specific rotation period component of a period synchronous with rotation of a crankshaft from values of the parameter of the combustion state measured by the combustion state parameter measuring means at least in two rotations of a crankshaft; and    a combustion state judging means for judging the combustion state on the basis of the specific rotation period component extracted by the specific rotation period component extracting means.    
     
     
         2 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to  claim 1 , wherein the combustion state parameter measuring means measures necessary times T(i) each necessary for the crankshaft to turn through an angle between predetermined crank angles N times in each ignition cycle of the engine, and 
 the specific rotation period component extracting means is provided with a high-pass filter means which filters out low-frequency components of the necessary times T(i) to calculate filtered necessary times Tf(i) to extract specific rotation period components of a period synchronous with the rotation of the crankshaft from the filtered necessary times Tf(i).    
     
     
         3 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to  claim 2 , wherein the high-pass filer means filters out the components of periods longer than a time necessary for two rotations of the crankshaft of the engine.  
     
     
         4 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to  claim 2 , wherein the high-pass filter means calculates the difference [T(i)−T(i−N)] from the necessary times T(i) corresponding to the cylinders successive in ignition order to use the same as the filtered necessary time Tf(i).  
     
     
         5 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to  claim 1 , wherein the measured varying values of torque are used directly as those of the combustion state parameter.  
     
     
         6 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to claims  1 , wherein the specific rotation period component extracting means is provided with an arithmetic means which extracts a specific rotation period component which is a variable component of X (=Tf) of a period synchronous with the rotation of the crankshaft from the sum of the products of values of the combustion state parameter for at least two rotations of the crankshaft or Tf (=X), i.e., X(i), X(i−1), . . . , X(i−c+1), where c is greater than or equal to the product of N and the number of cylinders of the engine, and at least two sets each of c pieces of weighting coefficients.  
     
     
         7 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to  claim 6 , wherein the weighting coefficients are set so as to extract a two-rotation period component of a period synchronous with two rotations of the crankshaft of the engine.  
     
     
         8 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to claims  1 , wherein the specific rotation period component extracting means extracts components synchronous with two rotations of the crankshaft of the engine.  
     
     
         9 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to  claim 1 , wherein the specific rotation period component extracting means extracts components synchronous with one rotation of the crankshaft of the engine.  
     
     
         10 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to  claim 1 , wherein the combustion state judging means counts the frequency of successive values of the specific rotation period component exceeding a predetermined value, judges that a misfire occurred every ignition cycle if the count of the frequency is greater than a predetermined number, and judges that a misfire occurred at intervals if the count of the frequency is not greater than the predetermined value.  
     
     
         11 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to claims  1 , wherein the specific rotation period component extracting means includes a phase calculating means for calculating the phase of the specific rotation period component, and the combustion state judging means includes a misfiring cylinder identifying means for finding the number of misfiring cylinders and/or misfiring cylinders on the basis of at least the phase of the specific rotation period component.  
     
     
         12 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to  claim 1 , wherein the combustion state judging means specifies a pattern indicating a maximum from the sum of the products of a plurality of values of the combustion state parameters or Tf (=X), i.e., X(i), X(i−1), . . . , X(i−d+1), where d is a constant, and d pieces of weighting coefficients for a plurality of predetermined patterns when it is judged that a misfire occurred, and identifies a misfiring cylinder on the basis of the maximum and the specified pattern.  
     
     
         13 . The combustion state diagnosing system for diagnosing combustion state of a multiple-cylinder engine according to  claim 1  further comprising a misfire counting means for counting the frequency of judgement that a misfire occurred made by the combustion state judging means in a predetermined period, and an alarm means for giving an alarm to the driver when the frequency exceeds a predetermined number and/or a misfire information storage means for storing misfire information.  
     
     
         14 . An engine combustion state diagnosing program storage medium storing a program for measuring a combustion state parameter varying according to the combustion state of a multiple-cylinder engine, such as engine speed at which the multiple-cylinder engine is operating or output torque of the multiple-cylinder engine and judging combustion state on the basis of the combustion state parameter; wherein the program specifies steps of: 
 measuring the combustion state parameter N times (at least once) in one ignition cycle of each cylinder at a predetermined crank angle,    extracting a specific rotation period component of a period synchronous with rotation from at least the two values of the combustion state parameter, and    judging combustion state on the basis of the extracted specific rotation period component.