Patent Publication Number: US-2017370318-A1

Title: Control device for diesel engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2016-125721, filed on Jun. 24, 2016. The contents of this application are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present application relates to a control device for a diesel engine, and particularly relates to a control device which is configured to control a diesel engine mounted on a vehicle. 
     BACKGROUND ART 
     A diesel engine comprising a glow plug integrated type in-cylinder pressure sensor is known to the public. The glow plug integrated type in-cylinder pressure sensor comprises a pressure receiving section which displaces in an axial direction with an in-cylinder pressure fraction. The pressure receiving section is also configured to work as a heating section of the glow plug. 
     JP 2010-071197 A discloses a control device which is configured to control a diesel engine equipped with the glow plug integrated type in-cylinder pressure sensor. The control device is configured to calculate a correction coefficient based on a pressure difference between a reference in-cylinder pressure and an actual in-cylinder pressure when the diesel engine is in a motoring state. The control device is further configured to correct an actual in-cylinder pressure when the diesel engine is in a non-motoring state based on the calculated correction coefficient. 
     When deposits adhere to and accumulate on a periphery of the pressure receiving section, a displacement amount of the pressure receiving section changes, and hysteresis occurs to the actual in-cylinder pressure. In this regard, according to the control device, the correction coefficient can be calculated based on the pressure difference in the motoring state, and therefore, the actual in-cylinder pressure in the non-motoring state can be corrected. 
     However, according to further verification of the present inventor, it has been found out that there exists a crank angle region where the pressure difference in the non-motoring state becomes difficult to observe in the motoring state. Consequently, in the control device which is configured to correct the correction coefficient by the pressure difference in the motoring state, precision of correction of the actual in-cylinder pressure in the non-motoring state is likely to be reduced. 
     The present application addresses the above-described problem and has an object to restrain reduction in precision of correction of an actual in-cylinder pressure in a non-motoring state, which is performed based on an actual in-cylinder pressure in a motoring state, in a diesel engine including a glow plug integrated type in-cylinder pressure sensor. 
     SUMMARY 
     A control device for a diesel engine according to one or more embodiments of the present application is a control device which is configured to control a diesel engine including a glow plug integrated type in-cylinder pressure sensor, 
     wherein the control device is also configured to: 
     determine a crank angle at which a difference, which is obtained by subtracting a reference in-cylinder pressure at a crank angle at which an actual in-cylinder pressure is detected, from the actual in-cylinder pressure detected by the in-cylinder pressure sensor at each of predetermined crank angles in a cycle in which the diesel engine is in a motoring state, changes from negative to positive; 
     calculate a rate of change of a pressure difference between the actual in-cylinder pressure and the reference in-cylinder pressure in a predetermined crank angle region at a retardation side from the crank angle at which the difference changes from negative to positive; and 
     correct the actual in-cylinder pressure detected at each of the predetermined crank angles in the cycle in which the diesel engine is in the non-motoring state, based on a crank angle interval from the crank angle at which the actual in-cylinder pressure is detected to the crank angle at which the difference changes from negative to positive, and the rate of change. 
     In the control device according to one or more embodiments of the present application, the crank angle at which the difference changes from negative to positive may be a crank angle at a retardation side from a compression top dead center. 
     The control device may also be configured to correct the rate of change by relating the rate of change to an amount of fuel that is injected into a cylinder of the diesel engine. The rate of change may be corrected to a smaller value as the amount of fuel is larger. 
     The control device may also be configured to correct the rate of change by relating the rate of change to an engine speed in the motoring state. 
     The control device may also be configured to before calculating the difference: 
     correct data of the actual in-cylinder pressure so that a maximum value of the actual in-cylinder pressure detected by the in-cylinder pressure sensor at each of the predetermined crank angles in the cycle in which the diesel engine is in the motoring state becomes equal to a maximum value of the reference in-cylinder pressure; and 
     correct the data of the actual in-cylinder pressure so that a crank angle showing the maximum value corresponds to a top dead center. 
     The control device may also be configured to correct the actual in-cylinder pressure detected at each of the predetermined crank angles in the cycle in which the diesel engine is in the non-motoring state, based on equation (1) as follows: 
       Correction value of actual in-cylinder pressure-value  P   n  of actual in-cylinder pressure×(detection crank angle θ n −hysteresis zero angle  H   0 )×correction coefficient η  (1),
 
     in equation (1), the value P n  of the actual in-cylinder pressure means the actual in-cylinder pressure detected at each of the predetermined crank angles in the cycle in which the diesel engine is in the non-motoring state, the detection crank angle θ n  means the crank angle at which the value P n  of the actual in-cylinder pressure is detected, the hysteresis zero angle H 0  means the crank angle at which the difference changes from negative to positive, and the correction coefficient η means the rate of change. 
     The control device may also be configured to correct the actual in-cylinder pressure detected at each of the predetermined crank angles in the cycle in which the diesel engine is in the non-motoring state, based on equation (2) as follows: 
       Correction value  P   n  of actual in-cylinder pressure=value  P   n  of actual in-cylinder pressure×(detection crank angle θ n −hysteresis zero angle  H   0 )×correction coefficient η/100  (2),
 
     in equation (2), the value P n  of the actual in-cylinder pressure means the actual in-cylinder pressure detected at each of the predetermined crank angles in the cycle in which the diesel engine is in the non-motoring state, the detection crank angle θ n  means the crank angle at which the value P n  of the actual in-cylinder pressure is detected, the hysteresis zero angle H 0  means the crank angle at which the difference changes from negative to positive, and the correction coefficient η means a percentage of a value obtained by dividing the rate of change by the reference in-cylinder pressure. 
     In the motoring state, there exists the crank angle at which a magnitude relation of the actual in-cylinder pressure detected by the in-cylinder pressure sensor, and the reference in-cylinder pressure in the crank angle at which the actual in-cylinder pressure is detected is reversed. In a crank angle region at an advance side from the crank angle at which the magnitude relation is reversed, the pressure difference between the actual in-cylinder pressure and the reference in-cylinder pressure is difficult to observe. 
     According to one or more embodiments of the present application, the crank angle at which the magnitude relation of the actual in-cylinder pressure and the reference in-cylinder pressure is reversed can be determined. Further, the rate of change of the pressure difference can be calculated based on the data of the pressure difference in the predetermined crank angle region at the retardation side from the determined crank angle. In other words, at the time of calculation of the rate of change of the pressure difference, the data of the pressure difference in the crank angle region at the advance side from the determined crank angle can be excluded. Consequently, the rate of change of the pressure difference can be calculated more accurately. Accordingly, precision of correction of the actual in-cylinder pressure in the non-motoring state can be enhanced. 
     In the motoring state, the pressure difference between the actual in-cylinder pressure and the reference in-cylinder pressure is observed stably in the crank angle region at the retardation side from the compression top dead center. 
     According to one or more embodiments of the present application, the crank angle at which the above described magnitude relation is reversed can be determined as the crank angle at the retardation side from the compression top dead center. Accordingly, precision of correction of the actual in-cylinder pressure in the non-motoring state can be enhanced. 
     When the amount of the fuel which is injected into the cylinder increases, the maximum value of the in-cylinder temperature at the time of combustion increases. When the maximum value of the in-cylinder temperature increases, viscosity of deposits that adhere to and accumulate on a periphery of a pressure receiving section of the in-cylinder pressure sensor reduces. When the viscosity of the deposits reduces, the pressure receiving section of the in-cylinder pressure sensor easily moves, so that the hysteresis which occurs to the actual in-cylinder pressure reduces. 
     According to one or more embodiments of the present application, the rate of change of the pressure difference can be corrected to a smaller value as the fuel injection amount in the non-motoring state is larger. Accordingly, precision of correction of the actual in-cylinder pressure in the non-motoring state can be further enhanced. 
     The engine speed in the motoring state may have an influence on the relation between the rate of change of the pressure difference and the fuel injection amount. 
     According to one or more embodiments of the present application, the rate of change of the pressure difference can be corrected by being related to the engine speed in the motoring state. Consequently, the influence which the engine speed in the motoring state gives can be reduced. 
     According to one or more embodiments of the present application, the difference can be accurately calculated, which is obtained by subtracting the reference in-cylinder pressure at the crank angle at which the actual in-cylinder pressure is detected, from the actual in-cylinder pressure detected by the in-cylinder pressure sensor at each of the predetermined crank angles in the cycle in which the diesel engine is in the motoring state. 
     According to one or more embodiments of the present application, the actual in-cylinder pressure in the non-motoring state can be corrected based on equation (1) described above. 
     According to one or more embodiments of the present application, the actual in-cylinder pressure in the non-motoring state can be corrected based on equation (2) described above. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram explaining a configuration of a diesel engine to which a control device according to a first embodiment of the present application is applied; 
         FIG. 2  is a functional block diagram of an ECU  20  as the control device according to the first embodiment of the present application; 
         FIG. 3  is a diagram explaining a problem in an in-cylinder pressure sensor  10 ; 
         FIG. 4  is a diagram explaining a problem in the in-cylinder pressure sensor  10 ; 
         FIG. 5  is a diagram illustrating processing images of data of actual in-cylinder pressures in a P max  correction section  46   a  and a TDC correction section  46   b  illustrated in  FIG. 2 ; 
         FIG. 6  is a diagram explaining hysteresis between a correction value P n ′ of an actual in-cylinder pressure in a motoring state, and a value PR n  of a reference in-cylinder pressure; 
         FIG. 7  is a diagram explaining details of the hysteresis between “reference values” and “sensor values” observed in  FIG. 4  and  FIG. 6 ; 
         FIG. 8  is a diagram explaining details of the hysteresis between the “reference values” and the “sensor values” observed in  FIG. 4  and  FIG. 6 ; 
         FIG. 9  is a diagram illustrating a processing image of a deviation Δh n  in a hysteresis zero angle determination section  46   c  and a gradient calculation section  46   d  illustrated in  FIG. 2 : 
         FIG. 10  is a diagram illustrating a processing image of data of an actual in-cylinder pressure in an in-cylinder pressure correction section  44  illustrated in  FIG. 2 ; 
         FIG. 11  is a flowchart illustrating one example of data processing of an actual in-cylinder pressure realized by a function of the ECU  20 ; 
         FIG. 12  is a functional block diagram of the ECU  20  as a control device according to a second embodiment of the present application: 
         FIG. 13  is a diagram explaining a method for relating a gradient d n  to a fuel injection amount; and 
         FIG. 14  is one example of a diagram illustrating the relationship illustrated in  FIG. 13  at each engine speed in the motoring state. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereunder, one or more embodiments of the present application will be described based on the drawings. Note that common elements in the respective drawings are assigned with the same reference signs, and redundant explanation will be omitted. Further, the present application is not limited by the one or more embodiments as follows. 
     First Embodiment 
     First of all, a first embodiment of the present application will be described with reference to  FIG. 1  to  FIG. 11 . 
       FIG. 1  is a schematic diagram explaining a configuration of a diesel engine to which a control device according to the first embodiment of the present application is applied. The diesel engine to which the control device according to the present embodiment is applied includes a glow plug integrated type in-cylinder pressure sensor  10 . The in-cylinder pressure sensor  10  includes a hollow housing  12 . In a shaft hole of the housing  12 , a pressure receiving section  14  that also functions as a heater rod is inserted. The pressure receiving section  14  is configured to be movable in an axial direction thereof. When a pressure in a cylinder changes, a magnitude of a load that is transmitted to a sensing section  16  via the pressure receiving section  14  changes. The change of the load is detected by the sensing section  16 , and thereby the pressure in the cylinder is detected. A seal member  18  is provided between the housing  12  and the pressure receiving section  14 . The seal member  18  is provided, and thereby leakage of gas in the cylinder to an outside is prevented. 
     The control device according to the present embodiment is realized as a part of a function of the ECU  20  that controls the diesel engine. The ECU  20  takes in and processes signals of various sensors installed in the diesel engine.  FIG. 2  illustrates various sensors that are connected to the ECU  20 . As illustrated in  FIG. 2 , the various sensors include at least an accelerator opening degree sensor  22 , a crank angle sensor  24 , a water temperature sensor  26  and an ignition switch  28 , besides the in-cylinder pressure sensor  10  illustrated in  FIG. 1 . 
     The accelerator opening degree sensor  22  detects a depressing amount on an accelerator pedal. The crank angle sensor  24  detects a rotation angle of a crankshaft. The water temperature sensor  26  detects a cooling water temperature of the diesel engine. The ignition switch  28  receives an instruction to supply/stop electric power to an electric power system of the diesel engine. 
     The ECU  20  processes the signals taken in from the aforementioned various sensors, and operates various actuators of a system in accordance with a predetermined control program.  FIG. 2  also illustrates various actuators that are connected to the ECU  20 . As illustrated in  FIG. 2 , the various actuators include at least an injector  30  that injects fuel into the cylinder of the diesel engine, besides a heater rod  10   a  of the in-cylinder pressure sensor  10 . 
       FIG. 2  illustrates functional blocks of the ECU  20  as the control device according to the present embodiment. As illustrated in  FIG. 2 , the ECU  20  includes an operation state determination section  32 , a glow plug drive control section  34 , a fuel injection amount setting section  36 , a fuel injection timing setting section  40  and an injector drive control section  38 . 
     The operation state determination section  32  determines an operation state of the diesel engine. The glow plug drive control section  34  performs energization (glow energization) to the heater rod  10   a  while a cooling water temperature that is detected by the water temperature sensor  26  is lower than a predetermined temperature at a time of a cold start of the diesel engine. The energization is started by an ON signal from the ignition switch  28 . Further, the energization is ended at a time point at which the cooling water temperature rises to a temperature higher than a predetermined temperature. The fuel injection amount setting section  36  sets a fuel injection amount corresponding to a depressing amount on the accelerator pedal based on the operation state determined by the operation state determination section  32 . The fuel injection amount setting section  36  also outputs the set fuel injection amount to the injector drive control section  38 . The fuel injection timing setting section  40  sets an injection mode, an injection timing and the like that correspond to the fuel injection amount which is set by the fuel injection amount setting section  36 . The fuel injection timing setting section  40  also outputs the injection mode, the injection timing and the like which are set, to the injector drive control section  38 . 
     The ECU  20  also includes a storage section  42 , an in-cylinder pressure correction section  44 , and a correction coefficient setting section  46 , as components for performing correction of the in-cylinder pressure detected by the in-cylinder pressure sensor  10 . 
     The storage section  42  stores a correction coefficient η for correcting a value P n  of the actual in-cylinder pressure, and a value PR n  of a reference in-cylinder pressure. The value P n  of the actual in-cylinder pressure is a value of an in-cylinder pressure which is detected at each predetermined crank angle θ 1  by the in-cylinder pressure sensor  10 . The value PR n  of the reference in-cylinder pressure is a value (an initial value) of an in-cylinder pressure at a time of the sensor being brand new, and in a motoring state. As the initial value, a value of an in-cylinder pressure that is obtained in advance by an in-cylinder pressure sensor having a configuration equivalent to the configuration of the in-cylinder pressure sensor  10  is usually used. 
     Here, the motoring state refers to an operation state in which the engine speed of the diesel engine is in a low speed region, the depressing amount on the accelerator pedal is zero and fuel is not injected from the injector  30 . A region of 3000 rpm or less is cited as an example of the low speed region, but it is needless to say that the low speed region should be properly changed in accordance with an engine system. The correction coefficient η is updated each time the correction coefficient η is set in the correction coefficient setting section  46 . Note that details of the correction coefficient η will be described later. Further, the storage section  42  is assumed to store data necessary to realize the function in the present embodiment in addition to the correction coefficient η. 
     Before explaining the in-cylinder pressure correction section  44  and the correction coefficient setting section  46 , a problem in the in-cylinder pressure sensor  10  will be described with reference to  FIGS. 3 and 4 . As illustrated in  FIG. 3 , a small gap exists between a sensor insertion hole  48  that is formed in the cylinder head, and the pressure receiving section  14 . When soot that is generated in the cylinder, unburned fuel, engine oil and the like enter the gap, and adhere to a wall surface of the sensor insertion hole  48  and a surface of the pressure receiving section  14 , the soot, unburned fuel, engine oil and the like may become deposits. When soot and the like further adhere to the deposits, or the deposits bond to deposits around them, the deposits accumulate. When deposits adhere to or accumulate on the surface of the pressure receiving section  14 , a movement characteristic in an axial direction of the pressure receiving section  14  changes. 
     When the movement characteristic in the axial direction of the pressure receiving section  14  changes, hysteresis occurs to the value P n  of the actual in-cylinder pressure.  FIG. 4  is a diagram explaining the hysteresis.  FIG. 4  is created when fuel is injected from the injector  30 , that is, when the diesel engine is in a non-motoring state. In  FIG. 4 , the value P n  of the actual in-cylinder pressure at a time of deposit adherence/accumulation is expressed by a “sensor value”, and the value P n  of the actual in-cylinder pressure at a time of a sensor being brand new is expressed by a “reference value”. As is understandable when tendencies of the “sensor value” and the “reference value” illustrated in  FIG. 4  are compared, hysteresis is observed between both of them. Describing in more detail, from 60° before a compression top dead center to a vicinity of 10° after the compression top dead center, the “reference value” is substantially larger than the “sensor value”. Contrary to the above, at a retardation side from the vicinity of 10° after the compression top dead center, the “reference value” is substantially smaller than the “sensor value”. 
     Returning to  FIG. 2 , explanation of the functions of the ECU  20  will be continued. The correction coefficient setting section  46  sets the correction coefficient η by using data of the reference in-cylinder pressure received from the storage section  42 , and data of the actual in-cylinder pressure in the motoring state. As components for setting the correction coefficient η, the correction coefficient setting section  46  includes a P max  correction section  46   a , a TDC correction section  46   b , a hysteresis zero angle determination section  46   c  and a gradient calculation section  46   d.    
     First, the P max  correction section  46   a  and the TDC correction section  46   b  will be described. In the P max  correction section  46   a  and the TDC correction section  46   b , preprocessing of the data of the actual in-cylinder pressure in the motoring state is performed. As already described, the actual in-cylinder pressure is detected at each of predetermined crank angles θ 1  (intervals of 10° as an example). Consequently, when the values P n  of the actual in-cylinder pressure from 60° before the compression top dead center to 60° after the compression top dead center are arranged in sequence of the detection crank angles, data (θ n , P n ) is expressed by (θ BTDC60° , P BTDC60° ), (θ BTDC60°+θ1 , P BTDC60°+θ1 ), . . . , (θ ATDC60°−θ1 , P ATDC60°−θ1 ), and (θ ATDC60° , P ATDC60° ). 
     The P max  correction section  46   a  corrects the data (θ n , P n ) so that a maximum value P n   _   max  of the actual in-cylinder pressure in the motoring state becomes equal to a maximum value PR n     —max    of the reference in-cylinder pressure. More specifically, the P max  correction section  46   a  firstly detects a pressure difference ΔP n   _   max  between the maximum value P n     —max    and the maximum value PR n   _   max . When the pressure difference ΔP n   _   max  is detected, the P max  correction section  46   a  corrects the value P n  of the actual in-cylinder pressure to increase the value P n  by the pressure difference ΔP n   _   max , or decrease the value P n  by ΔP n   _   max . 
     The TDC correction section  46   b  corrects the data (θ n , P n ) so that a crank angle showing the maximum value P n   _   max  of the actual in-cylinder pressure in the motoring state corresponds to a TDC. More specifically, the TDC correction section  46   b  firstly detects a phase difference Δθ of the crank angle showing the maximum value P n   _   max  and the TDC. When the phase difference Δθ is detected, the TDC correction section  46   b  corrects the value of a detection crank angle θ n  to a retardation side or an advance side by the phase difference Δθ. 
       FIG. 5  illustrates a processing image of the data (θ n , P n ) in the P max  correction section  46   a  and the TDC correction section  46   b . In  FIG. 5 , the maximum value PR n   _   max  is larger than the maximum value P n   _   max . Consequently, in the P max  correction section  46   a , the value P n  of the actual in-cylinder pressure is corrected to increase by an amount of the pressure difference ΔP n   _   max . Further, in  FIG. 5 , the crank angle showing the maximum value P n   _   max  is located at a retardation side from the TDC. Consequently, in the TDC correction section  46   b , the value of the detection crank angle θ n  is corrected to the advance side by the amount of the phase difference Δθ. 
     Next, the hysteresis zero angle determination section  46   c  and the gradient calculation section  46   d  will be described. The hysteresis zero angle determination section  46   c  calculates a deviation Δh h  of a correction value P n ′ of the actual in-cylinder pressure to the value of the reference in-cylinder pressure PR n  based on correction data (θ n ′, P n ′) of the actual in-cylinder pressure, and data (θ n , PR n ) of the values of the reference in-cylinder pressure PR n  arranged in sequence of the detection crank angles. The hysteresis zero angle determination section  46   c  determines a crank angle (hereinafter, also referred to as “a hysteresis zero angle H 0 ”) at which a value of the deviation Δh n  changes from negative to positive. The gradient calculation section  46   d  calculates a gradient d n  of the deviation Δh n  in a crank angle region at a retardation side from the hysteresis zero angle H 0 . 
       FIG. 6  is a diagram explaining hysteresis between the correction value P n ′ of the actual in-cylinder pressure in the motoring state, and the PR n  of the reference in-cylinder pressure. In  FIG. 6 , the correction value P n ′ of the actual in-cylinder pressure at a time of deposit adherence/accumulation is expressed by a “sensor value” and the value P n  of the actual in-cylinder pressure at the time of the sensor being brand new is expressed by a “reference value”. As is understandable when tendencies of the “sensor value” and the “reference value” illustrated in  FIG. 6  are compared, hysteresis is observed between both of them. Describing in more detail, the “reference value” becomes lower than the “sensor value” in a retardation side from a vicinity of 10° after the compression top dead center. However, as is understandable when  FIG. 6  is compared with  FIG. 4 ,  FIG. 6  illustrating the tendency in the motoring state, and  FIG. 4  illustrating the tendency in the non-motoring state differ in the crank angle region where hysteresis is observed. 
       FIGS. 7 and 8  are diagrams explaining details of the hysteresis of the “reference values” and the “sensor values” observed in  FIGS. 4 and 6 . The same diagram as in  FIG. 4  is illustrated on an upper tier of  FIG. 7 , and the deviation Δh n  of the “sensor value” to the “reference value” illustrated in  FIG. 4  is illustrated in a lower tier in  FIG. 7 . Further, the same diagram as in  FIG. 6  is drawn on an upper tier in  FIG. 8 , and the deviation Δh n  of the “sensor value” to the “reference value” illustrated in  FIG. 6  is illustrated in a lower tier in  FIG. 8 . The deviation Δh n  of the “sensor value” to the “reference value” is expressed as a percentage calculated by substituting the “reference value” and the “sensor value” at the same crank angle into equation (1) as follows. 
       Deviation Δ h   n  [%]=100×(sensor value−reference value)/reference value  (1)
 
     In the lower tier in  FIG. 7 , a gradient (that is, a rate of change of the deviation Δh n ) of the deviation Δh n  is substantially constant. In the lower tier in  FIG. 8 , a gradient of the deviation Δh n  becomes small in a crank region at an advance side from the vicinity of 10° after the compression top dead center. In particular, in the crank angle region from the a vicinity of 30° before the compression top dead center to the vicinity of 10° after the compression top dead center, the gradient of the deviation Δh n  becomes remarkably small. The cause of occurrence of such a difference is not certain. However, the present inventor surmises that the difference between the maximum value P n   _   max  and the minimum value P n   _   min  of the actual in-cylinder pressure is originally small because combustion is not performed in the motoring state, and therefore hysteresis is difficult to observe in the crank angle region at the advance side from the compression top dead center. 
     The hysteresis zero angle determination section  46   c  and the gradient calculation section  46   d  perform processing in which characteristics peculiar to the motoring state like this are taken into consideration.  FIG. 9  is a diagram illustrating a processing image of the deviation Δh n  in the hysteresis zero angle determination section  46   c  and the gradient calculation section  46   d .  FIG. 9  illustrates the deviation Δh n  illustrated in the lower tier in  FIG. 8 , which is in the vicinity of 10° after the compression top dead center. The hysteresis zero angle H 0  is determined as a crank angle at a time of the value of the deviation Δh n  illustrated by the solid line corresponds to zero. Further, from the value of the deviation Δh n  in the crank angle region at the retardation side from the hysteresis zero angle H 0 , a gradient d n  illustrated by a broken line is calculated. 
     In calculation of the gradient d n , data (θ n , Δh n ) of the deviation Δh n  at the retardation side from the hysteresis zero angle H 0 , and at an advance side from a predetermined crank angle (60° after the compression top dead center, as an example) is used. In other words, data (θ n , Δh n ) of the deviation Δh n  at an advance side from the hysteresis zero angle H 0 , and data (θ n , Δh n ) at a retardation side from the predetermined crank angle are not used in calculation of the gradient d n . 
     Calculation of the gradient d n  is performed by using data (θ n , Δh n ) of at least two deviations Δh n . 
     For example, when arbitrary two data (θ k+θ1 , Δh k+θ1 ) and (θ k−θ1 , Δh k−θ1 ) of the data (θ n , Δh n ) of the deviation Δh n  in the aforementioned crank angle region are used, the gradient d n  can be obtained by equation (4) as follows. 
       Gradient  d   n =gradient  d   k =(Δ h   k+1   −Δh   k−1 )/(θ k+1 −θ k−1 )  (4)
 
     Further, for example, when all the data (θ n , Δh n ) of the deviation Δh n  in the aforementioned crank angle region are used, the gradient d n  can be obtained by equation (5) as follows. 
       Gradient  d   n =average of gradient  d   k   =ave {(Δ h   n+θ1   −Δh   n−θ1 )/(θ n+θ1 −θ n−θ1 )}  (5)
 
     Further, for example, a plurality of gradients d k  obtained by equation (4) described above are obtained within the aforementioned crank angle region, and a maximum value of the plurality of gradients d k  can be used as the gradient d n  (refer to equation (6) as follows). 
       Gradient  d   n =maximum value of gradient  d   k =max{(Δ h   n+θ1   −Δh   n−θ1 )/(θ n+θ1 −θ n−θ1 )}  (6)
 
     The correction coefficient setting section  46  outputs the value of the hysteresis zero angle H 0  to the storage section  42 . In addition, the correction coefficient setting section  46  outputs the value of the gradient d n  to the storage section  42  as the correction coefficient η. 
     The in-cylinder pressure correction section  44  receives the correction coefficient η and the date of the hysteresis zero angle H 0  from the storage section  42 , and performs correction of the value P n  of the actual in-cylinder pressure in the non-motoring state. The value P n  of the actual in-cylinder pressure that configures the data (θ n , P n ) of the actual in-cylinder pressure in the non-motoring state is corrected by equation (7) as follows that uses a crank angle interval from the hysteresis zero angle H 0  to the detection crank angle θ n  for example, and the correction coefficient η. 
       Correction value  P   n  of actual in-cylinder pressure=value  P   n  of actual in-cylinder pressure×(detection crank angle θ n −hysteresis zero angle  H   0 )×correction coefficient η/100  (7)
 
       FIG. 10  is a diagram illustrating a processing image of data of the actual in-cylinder pressure in the in-cylinder pressure correction section  44 . As illustrated in  FIG. 10 , in the in-cylinder pressure correction section  44 , the value P n  of the actual in-cylinder pressure is corrected to an increase side, in the crank angle region at the advance side from the compression top dead center, when classifying roughly. Contrary to the above, in the crank angle region at the retardation side from the compression top dead center, the value P n  of the actual in-cylinder pressure is corrected to a decrease side. That is, the data of the actual in-cylinder pressure is corrected in a direction to eliminate the hysteresis of the “sensor value” and the “reference value” explained with  FIG. 4 . 
       FIG. 11  is a flowchart illustrating an example of data processing of the actual in-cylinder pressure which is realized by the function of the ECU  20  described above. Note that the routine illustrated in  FIG. 11  is repeatedly executed at each cycle after start of the diesel engine. 
     In the routine illustrated in  FIG. 11 , it is firstly determined whether the diesel engine is in a motoring state (step S 10 ). In the present step, processing as follows is performed. First, an engine speed is calculated based on a detection value of the crank angle sensor  24 . Further, a detection value of the accelerator opening degree sensor  22  is acquired. When the engine speed is less than a threshold value, and the detection value of the accelerator opening degree sensor  22  is equal to zero, it is determined that the diesel engine is in the motoring state. When the engine speed is the threshold value or more, or the detection value of the accelerator opening degree sensor  22  is not zero, it is determined that the diesel engine is in the non-motoring state. 
     When it is determined that the diesel engine is in the motoring state in step S 10 , the preprocessing of the data (θ n , P n ) of the actual in-cylinder pressure is performed (step S 12 ). In the present step, processing as follows is performed. First, the value PR n  of the reference in-cylinder pressure is read from the storage section  42 . Subsequently, the data (θ n , P n ) is corrected so that the maximum value PR n   _   max  of the reference in-cylinder pressure and the maximum value P n   _   max  of the actual in-cylinder pressure correspond to each other (refer to the P max  correction section  46   a  in  FIG. 2 ). Subsequently, the data (θ n , P n ) is further corrected so that the crank angle showing the maximum value P n   _   max  of the actual in-cylinder pressure corresponds to the TDC (refer to the TDC correction section  46   b  in  FIG. 2 ). 
     Subsequently to step S 12 , the hysteresis zero angle H 0  is determined (step S 14 ). In the present step, processing as follows is performed. First, the deviation Δh n  is calculated based on the correction data (θ n ′, P n ′) and the data of the reference in-cylinder pressure (θ n , PR n ). In calculation of the deviation Δh n , equation (1) described above is used. Subsequently, the crank angle at a time of the value of the deviation Δh n  changing from negative to positive is determined as the hysteresis zero angle H 0  (the hysteresis zero angle determination section  46   c  in  FIG. 2 ). Note that as explained with  FIG. 6 , the value of the deviation Δh n  changes from negative to positive at the retardation side from the compression top dead center. Consequently, determination of the crank angle described above may be performed after the crank angle region is narrowed down to the crank angle region at the retardation side from the compression top dead center. 
     Subsequently to step S 14 , the gradient d n  is calculated (step S 16 ). In the present step, the gradient d n  is calculated based on the data (θ n , Δh n ) of the deviation Δh n  at the retardation side from the hysteresis zero angle H 0  and at the advance side from the predetermined crank angle (refer to the gradient calculation section  46   d  in  FIG. 2 ). Any one of equations (4) to (6) described above is used in calculation of the gradient d n . 
     Subsequently to step S 16 , the correction coefficient η and the hysteresis zero angle H 0  are updated (step S 18 ). In the present step, the gradient d n  calculated in step S 16  is stored in the storage section  42  as the newest correction coefficient η. Further, the hysteresis zero angle H 0  determined in step S 14  is stored in the storage section  42  as the newest hysteresis zero angle H 0 . 
     When it is determined that the diesel engine is in the non-motoring state in step S 10 , the newest correction coefficient η and the hysteresis zero angle H 0  are read from the storage section  42  (step S 20 ). 
     Subsequently to step S 20 , the data (θ n , P n ) of the actual in-cylinder pressure is corrected (step S 22 ). In the present step, the data (θ n , P n ) of the actual in-cylinder pressure, the newest correction coefficient η and hysteresis zero angle H 0  are substituted into equation (7) as described above. 
     As above, according to the routine illustrated in  FIG. 11 , determination of the hysteresis zero angle H 0  and calculation of the gradient d n  can be performed from the data (θ n , P n ) of the actual in-cylinder pressure in the motoring state. Further, the data (θ n , P n ) of the actual in-cylinder pressure can be corrected by using the determined hysteresis zero angle H 0  and the calculated gradient d n  (that is, the correction coefficient η) in the non-motoring state. The hysteresis zero angle H 0  and the correction coefficient η that are used in the non-motoring state are determined or calculated in a latest motoring state. Accordingly, precision of correction of the data of the actual in-cylinder pressure in the non-motoring state can be enhanced, and precision of combustion control of the diesel engine using the data can be enhanced. 
     Incidentally, in the above described first embodiment, the value of the deviation Δh n  changes from negative to positive at the retardation side from the compression top dead center, and therefore, the crank angle at which the reversal occurs is determined as the hysteresis zero angle H 0 . However, since the cause of occurrence of difference in the gradient of the deviation Δh n  is not certain as described in explanation of comparison of the lower tier in  FIG. 7  and the lower tier in  FIG. 8 , there is a possibility that the crank angle at which the reversal of positive and negative of the value of the deviation Δh n  occurs corresponds to the compression top dead center, or is at the advance side from the compression top dead center. However, it is needless to say that even in the case like this, if the crank angle at which the reversal of positive and negative of the value of the deviation Δh n  occurs is determined as the hysteresis zero angle H 0 , the gradient d n  can be calculated as in the above described first embodiment. Note that the present modification example can be similarly applied to a second embodiment that will be described later. 
     Further, in the above described first embodiment, the hysteresis zero angle H 0  and the gradient d n  are calculated by using the value of the deviation Δh n  calculated in accordance with equation (1) described above. However, the hysteresis zero angle H 0  and the gradient d n  (that is, the rate of change of the pressure difference ΔP n ) may be calculated by using the value of the pressure difference ΔP n  that is calculated by equation (8) as follows that is obtained by simplifying equation (1) described above. 
       Pressure difference Δ P   n =value  P   n  of actual in-cylinder pressure-value  PR   n  of reference in-cylinder pressure  (8)
 
     In this connection, when the hysteresis zero angle H 0  which is determined from equation (8) described above is used, the value P n  of the actual in-cylinder pressure configuring the data (θ n , P n ) of the actual in-cylinder pressure in the non-motoring state is corrected by equation (9) as follows. 
       Correction value of actual in-cylinder pressure=value  P   n  of actual in-cylinder pressure×(detection crank angle θ n −hysteresis zero angle  H   0 )×correction coefficient η   (9)
 
     Note that the present modification example can be similarly applied to the second embodiment which will be described later. 
     Second Embodiment 
     Next, the second embodiment of the present application will be described with reference to  FIGS. 12 to 14 . 
     Note that a configuration of a diesel engine to which a control device according to the present embodiment is applied, and basic functions of the ECU  20  are common to the above described first embodiment, and therefore, explanation thereof will be omitted or simplified. 
       FIG. 12  is a functional block diagram of the ECU  20  as the control device according to the second embodiment of the present application. The basic functions of the ECU  20  are the same as the functions explained in  FIG. 2 . However, in  FIG. 12 , a gradient correction section  46   e  is provided. Further, in  FIG. 12 , the value Q of the fuel injection amount is outputted to not only the injector drive control section  38  but also the operation state determination section  32 . In  FIG. 12 , the value Q of the fuel injection amount outputted to the operation state determination section  32  is also outputted to the storage section  42 . 
     In the above described first embodiment, the gradient d n  calculated in the motoring state is set as the correction coefficient η, and the correction coefficient η is used in correction of the data (θ n , P n ) of the actual in-cylinder pressure in the non-motoring state. However, in the motoring state, the value Q of the fuel injection amount is zero, whereas in the cycle in the non-motoring state, the value Q of the fuel injection amount becomes larger than zero. Here, combustion is performed when the value Q of the fuel injection amount is larger than zero, and as the value Q of the fuel injection amount increases, a maximum value of the in-cylinder temperature at the time of combustion increases. When the maximum value of the in-cylinder temperature increases, viscosity of the deposits adhering to and accumulating on the periphery of the pressure receiving section of the in-cylinder pressure sensor  10  decreases. When the viscosity of the deposits decreases, the pressure receiving section  14  easily moves, and therefore the hysteresis that occurs to the value P n  of the actual in-cylinder pressure reduces. That is, the difference between the “sensor value” and the “reference value” explained in  FIG. 14  decreases. Therefore, the deviation Δh n  that is calculated in equation (1) described above, and the gradient d n  that is calculated in equations (4) to (6) described above decrease. 
     In the present embodiment, in order to take the characteristics by the fuel injection amount like this into consideration, correction that relates the gradient d n  calculated in the motoring state to the fuel injection amount is performed in the gradient correction section  46   e .  FIG. 13  is a diagram explaining a method for relating the gradient d n  to the fuel injection amount. The gradient d n  which is calculated in the motoring state can be said as the correction coefficient η at the time of the value Q of the fuel injection amount being zero, and therefore, the value of the gradient d n  is taken for an intercept of a vertical axis. When the fuel injection amount increases, the deviation Δh n  becomes small, and therefore, both the value Q and the value of the gradient d n  are related to each other so that as the value Q of the fuel injection amount becomes larger, the value of the gradient d 0  becomes smaller (refer to equation (10) as follows). 
       Gradient  d   n =constant  a ×value  Q  of fuel injection amount+gradient  d   n   _   Q=0   (10)
 
     Further, the correction coefficient setting section  46  of the present embodiment outputs data (Q, d n ) of the gradient to the storage section  42  as the correction coefficient η. When the storage section  42  receives data of the value Q of the fuel injection amount from the operation state determination section  32 , the storage section  42  outputs the data of the correction coefficient η corresponding to the data to the in-cylinder pressure correction section  44 . The in-cylinder pressure correction section  44  performs correction of the value P n  of the actual in-cylinder pressure in the non-motoring state by using the data of the correction coefficient η and the hysteresis zero angle H 0  which are received from the storage section  42 . The value P n  of the actual in-cylinder pressure in the non-motoring state is corrected by equation (7) described above. 
     According to the present embodiment described above, correction that relates the gradient d n  calculated in the motoring state to the fuel injection amount is performed. Accordingly, precision of correction of the data of the actual in-cylinder pressure in the non-motoring state can be enhanced more. 
     Incidentally, in the above described second embodiment, the gradient d n  calculated in the motoring state is related to the fuel injection amount. However, the gradient d n  may be related to not only the fuel injection amount but also the engine speed in the motoring state.  FIG. 14  is an example of a diagram illustrating the relationship illustrated in  FIG. 13  at each engine speed in the motoring state. In the example illustrated in  FIG. 14 , an influence which the fuel injection amount gives to the gradient d n  becomes smaller as the engine speed becomes higher. 
     In this case, the data (Q, Ne, d n ) of the gradient is outputted to the storage section  42  as the correction coefficient η. Subsequently, when the storage section  42  receives the data of the value Q of the fuel injection amount and data of a value Ne of the engine speed, the storage section  42  outputs the data of the correction coefficient η corresponding to the data to the in-cylinder pressure correction section  44 . The processing in the in-cylinder pressure correction section  44  which is performed hereinafter is the same as in the above described second embodiment. 
     From the above, when not only the fuel injection amount but also the engine speed in the motoring state influences the gradient d n , the engine speed is added to a basis of correction of the gradient d n , and thereby it becomes possible to enhance precision of correction of the data of the actual in-cylinder pressure in the non-motoring state more.