JP6011461B2 - Combustion state diagnostic device - Google Patents

Description

  The present invention relates to a combustion state diagnostic apparatus for diagnosing the combustion state of an internal combustion engine.

  Conventionally, a method for predicting the occurrence of an engine stall (hereinafter also referred to as an engine stall) when the engine speed has decreased to a predetermined speed or when the number of times the engine speed has decreased below a threshold value has reached a predetermined number. It has been known.

  However, the engine stall is greatly influenced by the combustion fluctuations that change the state of combustion of the air-fuel mixture in the cylinder for each cycle. Therefore, the engine stalls are simply generated based on the engine speed. In the method for predicting, there is a possibility that sufficient prediction accuracy may not be obtained.

  Therefore, for example, in Patent Document 1, when the minimum value of the indicated torque calculated based on the in-cylinder pressure is smaller than the threshold value, it is determined that there is a possibility of engine stall, and the actual value of the intake air amount is set as “no fear of engine stall”. A technique for changing to a target value of the intake air amount so that the above determination can be obtained is disclosed.

JP 2007-211172 A

  By the way, in the thing of the said patent document 1, an air-fuel ratio, the residual amount of the burnt gas of the last cycle, the flow state of the air-fuel mixture in a cylinder, etc. are illustrated as a cause of the combustion fluctuation which affects the engine stall. ing. Moreover, in the thing of the said patent document 1, when the minimum value of an illustration torque is smaller than a threshold value, it determines with there exists a possibility of engine stall.

  However, in addition to those exemplified, there are various causes of engine stalls such as a decrease in fuel supply amount and variations between cylinders. Thus, depending on the cause of the occurrence of engine stall, a parameter may show a certain tendency in a plurality of cycles as a sign of engine stall occurrence.

  In other words, the signs of occurrence of engine stall vary depending on the cause of engine stall occurrence, and even if a certain parameter does not exceed the upper limit or lower limit in one cycle, the parameter tends to be constant in multiple cycles. In some cases, the occurrence of engine stall can be predicted. Therefore, it can be said that there is much room for improvement in the diagnosis of the combustion state of the internal combustion engine, including the prediction of engine stall.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a technique for improving the prediction accuracy of engine stall occurrence in a combustion state diagnostic apparatus for diagnosing the combustion state of an internal combustion engine. .

  In order to achieve the above object, the combustion state diagnosis apparatus according to the present invention monitors not only the combustion state in a single cycle, but also fluctuations in the combustion state between cycles.

  Specifically, the present invention is directed to a combustion state diagnostic apparatus that diagnoses the combustion state of an internal combustion engine.

Then, the combustion state diagnostic device acquires the first threshold value on the upper limit side and the second threshold value on the lower limit side set for the parameter relating to the heat generation rate waveform in the cycle, and the actual heat generation rate of each cycle. In the steady state, in the same cylinder, the parameter related to the actual heat generation rate in the n-1th cycle (n is an integer of 2 or more) exceeds the first threshold, and the actual heat generation in the nth cycle. When the parameter related to the rate falls below the second threshold, or the parameter related to the actual heat generation rate in the n-1th cycle falls below the second threshold and the actual heat generation in the nth cycle If the above parameters according to the rates exceeds the first threshold value, along with determined that there is an indication of the engine stall occurrence, in the steady state, a predetermined times of the same cylinder Of the cycle, the number of times the parameter related to the actual heat generation rate exceeds the first threshold value, or the number of times the parameter related to the actual heat generation rate falls below the second threshold value is equal to or greater than a predetermined reference number. In this case, it is also determined that there is an indication that an engine stall has occurred .

  In the present invention, the “first threshold value on the upper limit side” is set to be smaller than the upper limit value (threshold value that can be considered that an engine stall will surely occur if the parameter related to the actual heat generation rate waveform exceeds that value). Value. Further, the “second threshold on the lower limit side” is a value that is set to be larger than the lower limit (threshold that can be considered that an engine stall will surely occur if the parameter related to the actual heat generation rate waveform falls below that value). The “steady state” refers to an engine operating state in which, for example, the fluctuation range of the engine load and the engine speed within a predetermined time is within a predetermined value, and includes a steady state during idling of the internal combustion engine.

  If combustion is stable in one cylinder, the variation in the actual heat generation rate between cycles is small, and the parameter related to the actual heat generation rate waveform in each cycle (hereinafter also referred to as the actual parameter) is the first threshold value on the upper limit side. And easily falls within a region between the lower limit side second threshold value. In other words, if the actual parameter in each cycle exceeds the first threshold value or falls below the second threshold value, combustion is not stable in the cylinder, and it can be said that the possibility of engine stall is high. .

  However, if the actual parameter exceeds the first threshold value set to be smaller than the upper limit even once, it may be erroneously determined if it is determined that there is an indication that engine stall has occurred. On the other hand, if there is no sign of occurrence of engine stall until the actual parameter exceeds the upper limit value, the determination may be delayed. This also applies to the relationship between the lower limit value and the second threshold value.

Therefore, in the present invention, in a steady state, in the same cylinder, when the actual parameter of the (n-1) th cycle exceeds the first threshold value and the actual parameter of the nth cycle falls below the second threshold value, in other words, , it is determined that in the case of small scale combustion has occurred in the following large-scale combustion, there are signs of engine stall occurs. In the present invention, in a steady state, in the same cylinder, when the actual parameter of the (n-1) th cycle is lower than the second threshold value and the actual parameter of the nth cycle is higher than the first threshold value, in other words, , it is determined that if the large-scale combustion took place in the following small-scale combustion also, there are signs of engine stall occurs.

  Thus, when the combustion in which the actual parameter exceeds the first threshold value (large-scale combustion) and the combustion in which the actual parameter falls below the second threshold value (small-scale combustion) occur alternately, the cycle-to-cycle variation is large. For this reason, the possibility of occurrence of engine stalls is dramatically increased as compared with the case where these occur once. In addition, when the large-scale combustion and the small-scale combustion occur alternately even once, it is determined that there is a sign of the occurrence of the engine stall, so that the possibility of engine stall can be recognized at an early stage.

  In particular, in large-scale combustion after small-scale combustion in the same cylinder, the effective spray amount is reduced due to deposits, alcohol content, etc. in the n-1th cycle, and unburned spray is supplied to the nth cycle, resulting in large combustion. Since there is a high probability of the occurrence of mist, it can be regarded as combustion after the occurrence of a misfire cycle. Therefore, when large-scale combustion occurs after small-scale combustion in the same cylinder, it is possible to specify the cause of engine stalling as a decrease in the amount of fuel supply, and to reliably predict engine stalling.

  As described above, according to the present invention, the possibility of the occurrence of engine stall can be recognized at an early stage, and the prediction accuracy of engine stall occurrence can be improved.

  As described above, in the present invention, when large-scale combustion and small-scale combustion occur alternately, it is determined that there is an indication of the occurrence of engine stall. Combustion and small-scale combustion do not always occur alternately. For example, large-scale combustion or small-scale combustion may occur several times in succession, or large-scale combustion and small-scale combustion may frequently occur with normal combustion in between. In other words, signs of engine stalling may appear in the form of small-scale combustion or increased frequency of large-scale combustion.

Therefore, in the combustion state diagnostic device, in a steady state, the number of times that the parameter related to the actual heat generation rate exceeds the first threshold in a predetermined number of cycles in the same cylinder, or the actual heat generation rate. number of times the parameter falls below said second threshold value, even when equal to or more than the predetermined reference number of times, and the so determined that there is an indication of engine stalling.

Thus, since it is determined that there is an indication of occurrence of engine stall even when the actual parameter has a frequency that is higher than the first threshold value or a frequency that is lower than the second threshold value, small-scale combustion and large-scale combustion can be performed. Even when it does not occur alternately, occurrence of engine stall can be reliably predicted. Thereby, since the recognition failure when the sign of the occurrence of the engine stall appears as much as possible, the prediction accuracy of the engine stall occurrence can be further improved.

  Further, in the combustion state diagnostic device, a third threshold value that is set for a parameter related to a heat release rate waveform in a cycle and that is an upper limit side further than the first threshold value and a lower limit side value that is further lower than the second threshold value. 4 threshold values are obtained, and it is determined that engine stall occurs when the parameter related to the actual heat generation rate exceeds the third threshold value or falls below the fourth threshold value in a steady state. It is preferable.

  In the present invention, the “third threshold value on the upper limit side” is a threshold value that can be considered that an engine stall will surely occur if the parameter related to the actual heat generation rate waveform exceeds that value. The “four threshold values” are threshold values that can be regarded as surely generating an engine stall if the parameter relating to the actual heat generation rate waveform falls below that value.

  According to this configuration, even if the actual parameter is once, if it exceeds the third threshold value or falls below the fourth threshold value, it is determined that an engine stall occurs, so the engine stall can be reliably suppressed. . Thus, the combination of such a configuration and the above-described configuration makes it possible to monitor the occurrence of the engine stall and its signs in a multifaceted manner, such as on a one-off, alternating, and frequency basis. Therefore, the prediction accuracy of engine stall can be improved more reliably.

  In the combustion state diagnosis apparatus, it is preferable that the parameter includes at least one of a peak value of the waveform, a phase of the waveform, a gradient of the waveform, and an area of the waveform.

  According to this configuration, for example, whether or not the peak value of the actual heat generation rate waveform is within the peak width between the first threshold value and the second threshold value, and for example, the area surrounded by the actual heat generation rate waveform is By determining whether or not the value falls within the numerical value determined by the first threshold value and the second threshold value, the sign of the occurrence of engine stall can be easily predicted.

  By the way, the gasoline engine has many restrictions from the viewpoint of fuel consumption and emission reduction, and the combustion tends to become unstable compared to the diesel engine, so the peak value, phase, gradient, area, etc. of the actual heat generation rate waveform are limited. It is originally assumed that it fluctuates within a certain range. For this reason, in a gasoline engine, even if the combustion state is good, the actual parameter may exceed the first threshold (below the second threshold) due to disturbance or the like. Therefore, in a gasoline engine, although the combustion state is good, there is a higher possibility that an erroneous determination that there is a sign of the occurrence of engine stall occurs compared to a diesel engine.

  Therefore, in the combustion state diagnostic device, in a steady state, the average value of the parameters related to the actual heat generation rate waveform in a predetermined cycle in the same cylinder is acquired every time the cycle is performed, and the average of the acquired parameters is also obtained. By comparing the values, the tendency of the combustion state in the same cylinder is estimated, and when the combustion state tends to deteriorate each time the cycle is performed, the first threshold value is lowered and the second threshold value is raised, while the cycle When the combustion state tends to be improved every time this is performed, it is preferable to raise the first threshold and lower the second threshold.

  In this configuration, after obtaining the average value of the actual heat generation rate in a predetermined cycle in the same cylinder in a steady state, the moving average value of the actual heat generation rate is acquired every time the cycle is performed. By comparing the moving average values of the actual heat generation rates acquired in this way, it is estimated whether the combustion state in the same cylinder tends to deteriorate or improve every time the cycle is performed can do.

  Thus, when the combustion state tends to deteriorate each time the cycle is performed, the upper limit side first threshold value is lowered and the lower limit side second threshold value is raised in order to tighten the determination criteria, for example, Reduce the peak width. On the other hand, when the combustion state tends to be improved every time the cycle is performed, the first threshold value on the upper limit side is raised and the second threshold value on the lower limit side is lowered, for example, to loosen the determination criterion. Increase the width.

  In this way, when the combustion state tends to deteriorate each time the cycle is performed, the peak width and the like are set narrow, so that it can be determined that there is a sign of engine stall at an early stage. On the other hand, when the combustion state tends to improve every time the cycle is performed, the peak width is widened, so there is a sign of occurrence of engine stall in the gasoline engine even though the combustion state is good. It is possible to suppress the occurrence of erroneous determination.

  Further, in the combustion state diagnostic device, in a transient state, the average value of the parameter relating to the actual heat generation rate waveform in a predetermined cycle is acquired for each cylinder, and the acquired average value of the parameter is compared between the cylinders. Thus, it is preferable to determine the variation between cylinders.

  The “transient state” means a state in which a high output is required, such as during acceleration or climbing, and the engine speed or engine load is changing to the increasing side, or the engine speed is in deceleration. This is the state where the number and engine load are changing to the decreasing side.

  In the transient state, unlike the steady state, it is difficult to grasp the combustion state only by comparing combustion fluctuations between cycles in one cylinder. In this regard, according to this configuration, for example, a cylinder having a good combustion state in a steady state is set as a standard cylinder, and an average value of actual parameters of the standard cylinder is compared with an average value of actual parameters of other cylinders. Even in the transient state, it is possible to easily identify the cylinder in which the combustion state is deteriorated among the plurality of cylinders.

  Furthermore, in the above-described combustion state diagnosis device, it is preferable to reduce the EGR amount in the cylinder when it is determined that there is an engine stall occurrence or an indication of engine stall occurrence.

  According to this configuration, by reducing the EGR amount in the cylinder, it is possible to improve combustion stability and suppress the occurrence of engine stall.

  Note that the presence of EGR gas in the cylinder means that a part of the exhaust gas passing through the exhaust system is recirculated to the intake system, the exhaust gas after combustion remains in the cylinder, or is once discharged into the exhaust system. This can be realized by re-inhaling the exhausted gas into the cylinder.

  Further, in the above-described combustion state diagnostic device, it is preferable to advance the ignition timing when it is determined that there is an engine stall occurrence or an indication of engine stall occurrence.

  According to this configuration, for example, when the ignition timing is retarded from the base ignition timing in order to suppress the occurrence of knocking, the torque can be increased to suppress the occurrence of the engine stall.

  As described above, according to the combustion state diagnosis apparatus according to the present invention, the possibility of occurrence of engine stall can be recognized at an early stage, and the prediction accuracy of engine stall generation can be improved.

It is a schematic block diagram which shows an example of the engine which concerns on embodiment of this invention, and its control system. It is a block diagram which shows the structure of control systems, such as ECU. It is a figure which shows typically the specific example of the parameter regarding a heat release rate waveform. It is a figure which shows typically the relationship between an upper limit and a lower limit, 1st and 2nd threshold value, and an actual heat generation rate. It is a figure which shows typically an example of the actual heat generation rate in the continuous cycle of the same cylinder, The figure (a) and (b) is a figure which shows the case where small-scale combustion occurs after large-scale combustion. FIGS. 3C and 3D are diagrams showing a case where large-scale combustion occurs after small-scale combustion. It is a flowchart which shows an example of a combustion state diagnosis. FIG. 4A is a diagram schematically showing an example when the combustion state tends to deteriorate, and FIG. 4B schematically shows an example when the combustion state tends to improve. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. This embodiment demonstrates the case where this invention is applied to the cylinder direct injection type gasoline engine 1 mounted in the motor vehicle.

-Engine configuration-
First, a schematic configuration of a gasoline engine (hereinafter also simply referred to as an engine) 1 according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram showing an example of an engine 1 and its control system according to the present embodiment. FIG. 1 shows only the configuration of one of the four cylinders of the engine 1.

  As shown in FIG. 1, a cylinder block 1c constituting a part of the engine 1 is formed with a cylindrical cylinder bore 1e. A piston 1b is accommodated in each cylinder bore 1e so as to be slidable in the vertical direction. The piston 1 b is connected to the crankshaft 15 via a connecting rod 16. The reciprocating motion of the piston 1b in the cylinder bore 1e is converted into the rotation of the crankshaft 15 by the connecting rod 16, so that the engine output can be obtained.

  A signal rotor 17 having a plurality of protrusions (teeth) 17 a on the outer peripheral surface is attached to the crankshaft 15. A crank position sensor (engine speed sensor) 25 is disposed near the side of the signal rotor 17. The crank position sensor 25 is, for example, an electromagnetic pickup, and outputs a detection signal (pulse) corresponding to the protrusion 17a of the signal rotor 17 each time the crankshaft 15 rotates.

  A water temperature sensor 21 that detects the coolant temperature of the engine 1 and a knock sensor 22 that detects engine vibration transmitted to the cylinder block 1 c of the engine 1 are disposed in the cylinder block 1 c of the engine 1. The water temperature sensor 21 outputs a detection signal corresponding to the cooling water temperature of the engine 1. The knock sensor 22 used in this example is a flat sensor (non-resonant knock sensor), for example, and has a substantially flat output characteristic over a wide frequency range of engine vibration.

  A combustion chamber 1a is formed above the top surface of the piston 1b. More specifically, the combustion chamber 1a is defined by the lower surface of the cylinder head 1d attached to the upper part of the cylinder block 1c, the inner wall surface of the cylinder bore 1e, and the top surface of the piston 1b.

  The cylinder head 1d is formed with an intake port 11a for introducing air into the combustion chamber 1a and an exhaust port 12a for discharging exhaust gas from the combustion chamber 1a. Further, an intake valve 13 and an exhaust valve 14 that open and close the intake port 11a and the exhaust port 12a, respectively, are opposed to the cylinder head 1d with the cylinder center line interposed therebetween. The opening / closing drive of the intake valve 13 and the exhaust valve 14 is performed by each rotation of an intake camshaft (not shown) and an exhaust camshaft (not shown) to which the rotation of the crankshaft 15 is transmitted.

  A spark plug 3 is disposed on the cylinder head 1d so that the tip of the cylinder head 1d faces the combustion chamber 1a. The ignition timing of the spark plug 3 is adjusted by the igniter 4. The igniter 4 is controlled by an ECU (Electronic Control Unit) 200. In addition, an in-cylinder pressure sensor 30 for detecting pressure in the combustion chamber 1a (hereinafter also referred to as in-cylinder pressure) is provided in the vicinity of the spark plug 3 in the cylinder head 1d.

  Further, an injector 2 for fuel injection is disposed in the cylinder head 1d. Fuel of a predetermined pressure is supplied to the injector 2 from a fuel tank (not shown) by a fuel pump (not shown), and the fuel is directly injected into the cylinder. This injected fuel is mixed with the intake air in the combustion chamber 1a, and is ignited by the spark plug 3 to burn and explode. The piston 1b reciprocates due to combustion / explosion of the air-fuel mixture in the combustion chamber 1a, and the crankshaft 15 rotates. The operation state of the engine 1 is controlled by the ECU 200.

  An intake passage 11 and an exhaust passage 12 are connected to the combustion chamber 1 a of the engine 1. The intake passage 11 includes an intake port 11a, an intake manifold 11b connected to the intake port 11a, an intake pipe 11c connected to the intake manifold 11b, and the like. In this intake passage 11, an air cleaner 7, a hot-wire air flow meter 23 that detects the intake air amount, an intake air temperature sensor 24 (built in the air flow meter 23), and an intake air amount of the engine 1 are adjusted in order from the upstream side. An electronically controlled throttle valve 5 is arranged. In addition, a surge tank 11 d is provided on the downstream side of the throttle valve 5 in the intake passage 11. The air flow meter 23 outputs an electrical signal corresponding to the amount of air flowing into the intake passage 11 via the air cleaner 7. The throttle valve 5 is driven by a throttle motor 6. The opening degree of the throttle valve 5 is detected by a throttle opening degree sensor 26.

  On the other hand, the exhaust passage 12 includes an exhaust port 12a, an exhaust manifold 12b connected to the exhaust port 12a, an exhaust pipe 12c connected to the exhaust manifold 12b, and the like. A three-way catalyst 8 is disposed in the exhaust passage 12. The three-way catalyst 8 has an oxygen storage capacity, adsorbs excess oxygen when the air-fuel ratio of the exhaust gas is lean, and releases insufficient oxygen when the air-fuel ratio of the exhaust gas is rich. Thus, carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) contained in the exhaust gas discharged from the combustion chamber 1a are purified.

A front O ₂ sensor (main O ₂ sensor) 28 is disposed in the exhaust passage 12 upstream of the three-way catalyst 8. The front O ₂ sensor 28 is a sensor that exhibits linear characteristics with respect to the air-fuel ratio. A rear O ₂ sensor (sub O ₂ sensor) 29 is disposed in the exhaust passage 12 on the downstream side of the three-way catalyst 8. The rear O ₂ sensor 29 generates an electromotive force according to the oxygen concentration in the exhaust gas. When the output is higher than a voltage (comparison voltage) corresponding to the theoretical air-fuel ratio, the rear O ₂ sensor 29 determines that the output is rich. When the output is lower than the comparison voltage, it is determined as lean.

  Further, the engine 1 is provided with an exhaust gas recirculation passage (EGR passage) 18 that connects the intake passage 11 and the exhaust passage 12. The EGR passage 18 recirculates a part of the exhaust gas (hereinafter also referred to as EGR gas) to the intake passage 11 and supplies it again to the combustion chamber 1a to lower the combustion temperature, thereby reducing the amount of NOx generated. Is. The EGR passage 18 is opened and closed steplessly by electronic control, and an EGR valve 19 that can freely adjust an exhaust flow rate flowing through the passage, and an exhaust for passing (refluxing) the EGR passage 18 is cooled. An EGR cooler 20 is provided.

-ECU-
As shown in FIG. 2, the ECU 200 includes a CPU 201, a ROM 202, a RAM 203, a backup RAM 204, and the like.

  The ROM 202 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 201 executes various arithmetic processes based on various control programs and maps stored in the ROM 202. The RAM 203 is a memory for temporarily storing calculation results in the CPU 201, data input from each sensor, and the like. The backup RAM 204 is a non-volatile storage for storing data to be saved when the engine 1 is stopped, for example. Memory.

  The CPU 201, ROM 202, RAM 203, and backup RAM 204 are connected to each other via a bus 207, and are connected to an input interface 205 and an output interface 206.

The input interface 205 includes a water temperature sensor 21, a knock sensor 22, an air flow meter 23, an intake air temperature sensor 24, a crank position sensor 25, a throttle opening sensor 26, and a detection signal corresponding to the amount of depression of an accelerator pedal (not shown). An accelerator opening sensor 27, a front O ₂ sensor 28, a rear O ₂ sensor 29, an in-cylinder pressure sensor 30, and the like that output an accelerator ON / OFF detection signal) are connected.

  To the output interface 206, the injector 2, the igniter 4 of the spark plug 3, the throttle motor 6 of the throttle valve 5, the EGR valve 19, and the like are connected.

  The ECU 200 executes various controls of the engine 1 based on the detection signals of the various sensors described above.

For example, the main air-fuel ratio feedback control is executed based on the output of the front O ₂ sensor 28 disposed in the exhaust passage 12 (upstream of the three-way catalyst 8) of the engine 1. Further, the sub air-fuel ratio feedback control is executed based on the output of the rear O ₂ sensor 29 arranged in the exhaust passage 12 (downstream of the three-way catalyst 8) of the engine 1.

In the main air-fuel ratio feedback control, the amount of fuel injected from the injector 2 into the cylinder is controlled so that the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 8 matches the control target air-fuel ratio. Further, in the sub air-fuel ratio feedback control, more specifically, the rear disposed on the downstream side of the three-way catalyst 8 so that the air-fuel ratio of the exhaust gas flowing out downstream of the three-way catalyst 8 becomes the stoichiometric air-fuel ratio. The content of the main air-fuel ratio feedback control is corrected so that the output of the O ₂ sensor 29 becomes stoichiometric. By executing these air-fuel ratio feedback control, the air-fuel ratio on the downstream side of the three-way catalyst 8 can be accurately maintained at a value close to the stoichiometric air-fuel ratio, and excellent emission characteristics can be realized.

  The ECU 200 executes ignition timing control of the engine 1 including KCS learning control. The KCS learning control is a control that suppresses the occurrence of knocking of the engine 1, and determines whether or not knocking has occurred based on the output signal of the knock sensor 22, and delays the ignition timing from the base ignition timing based on the determination result. In addition, the ignition timing is retarded (KCS learning value).

  Specifically, based on the engine speed obtained from the output signal of the crank position sensor 25 and the intake air amount obtained from the output signal of the air flow meter 23, the base ignition timing is calculated with reference to a preset map. At the same time, the peak value of the knock signal from knock sensor 22 is compared with the knock determination level to determine whether knock has occurred or not. When it is determined that knocking has occurred, the ignition timing is retarded from the base ignition timing, thereby reducing the combustion speed of the air-fuel mixture and keeping the maximum combustion pressure low, thereby suppressing the occurrence of knocking. Further, the retard amount of the ignition timing is learned as a KCS learning value and stored in the RAM 203 or the backup RAM 204. In this KCS learning control, the retard amount is learned so that the ignition timing is retarded when knocking occurs, and the ignition timing is gradually advanced when knocking does not occur. The amount to be learned.

  Here, the base ignition timing is the most advanced ignition timing that does not cause knocking under standard environmental conditions based on the operating state of the engine 1 such as the engine speed and load. The load of the engine 1 is a required load (requested torque) obtained from an accelerator opening, an air conditioner load, an electric load, and the like. For example, based on an intake air amount obtained from an output signal of the air flow meter 23. Calculate with reference to the map. The load on the engine 1 may be calculated based on the intake air amount and the engine speed.

-Engine combustion condition diagnosis-
In the engine 1 of this embodiment, as described above, the EGR gas is introduced into the combustion chamber 1a to lower the combustion temperature, thereby reducing the amount of NOx generated. Further, by introducing EGR gas into the combustion chamber 1a, the cooling loss and the pumping loss are reduced, so that the fuel consumption can be improved. However, if the EGR rate of intake air becomes excessively high, combustion may become unstable, and problems such as misfire and torque fluctuation may occur.

  Further, in the engine 1, even in a steady state, the combustion fluctuation in which the state of combustion of the air-fuel mixture in the cylinder changes every combustion cycle occurs, and such combustion fluctuation occurs when the combustion is unstable. It is known to occur. Thus, the combustion fluctuation is reflected in the in-cylinder pressure (combustion pressure). When a large amount of EGR gas is introduced into the combustion chamber 1a in a state where the combustion pressure is not sufficient, the combustion becomes further unstable, and the engine There is a risk that the torque will decrease and engine stall (hereinafter also referred to as engine stall) will occur.

  For this reason, the ECU (combustion state diagnosis device) 200 is configured to diagnose the combustion state of the engine 1 in order to suppress the occurrence of engine stall. Specifically, the ECU 200 sets an upper limit value (third threshold value) UB and a lower limit value (fourth threshold value) LB that are set for a parameter relating to a heat release rate waveform in a combustion cycle (hereinafter also simply referred to as a cycle), The actual heat generation rate of each cycle is acquired, and it is determined that engine stall occurs when the parameter related to the actual heat generation rate exceeds the upper limit value UB or falls below the lower limit value LB in a steady state. It is configured (first combustion state diagnosis). Hereinafter, the first combustion state diagnosis will be described.

  First, the “parameter relating to the heat release rate waveform” means a parameter characterizing the heat release rate waveform. Specifically, the “parameter regarding the heat generation rate waveform” includes the peak value of the heat generation rate waveform as shown in FIG. 3A and the phase of the heat generation rate waveform as shown in FIG. 3), the slope of the heat generation rate waveform as shown in FIG. 3C (change rate of the heat generation rate), and the area (integrated value) surrounded by the heat generation rate waveform as shown in FIG. Including at least one. Hereinafter, a case where the peak value of the heat generation rate waveform is adopted as the “parameter regarding the heat generation rate waveform” will be described.

  Thus, the “upper limit value UB set for the parameter related to the heat release rate waveform” is a threshold value that can be regarded as surely generating an engine stall if the parameter related to the actual heat release rate waveform exceeds the upper limit value UB. (See FIG. 4). On the other hand, the “lower limit value LB set for the parameter related to the heat release rate waveform” is a threshold value that can be regarded as surely generating an engine stall if the parameter related to the actual heat release rate waveform falls below the lower limit value LB. (See FIG. 4). The upper limit value UB and the lower limit value LB can be obtained based on, for example, experience, experiments, simulation results, and the like. The upper limit value UB and the lower limit value LB corresponding to the amount of fuel to be injected are stored in the ROM 202 in advance. Is remembered. Thus, the CPU 201 refers to (acquires) the upper limit value UB and the lower limit value LB as necessary.

  Since there is a correlation between the heat generation rate and the in-cylinder pressure, the ECU 200 estimates (acquires) the actual heat generation rate of each cycle for each cylinder based on the in-cylinder pressure detected by the in-cylinder pressure sensor 30. The in-cylinder pressure data detected by the in-cylinder pressure sensor 30 includes electrical noise, noise due to air column vibration generated between the in-cylinder pressure sensor 30 and the combustion chamber 1a due to a change in the in-cylinder pressure, and the like. There is a risk of errors due to. Therefore, after analyzing the in-cylinder pressure data using the fast Fourier transform and obtaining the in-cylinder pressure spectrum of each frequency band, it is necessary to estimate the actual heat generation rate by removing the band that causes noise by a filter. It is also possible to extract only a small band, filter this by inverse fast Fourier transform, and calculate the actual heat generation rate from the filtered in-cylinder pressure data.

  When the actual heat generation rate of each cycle is obtained, ECU 200 determines whether or not the peak value (hereinafter also referred to as actual peak value) Pt of the actual heat generation rate waveform of each cycle is equal to or lower than upper limit value UB and lower limit value LB. That is, it is confirmed whether or not the peak width is defined by the upper limit value UB and the lower limit value LB. Then, when the actual peak value Pt exceeds the upper limit value UB (see the broken line in FIG. 4), or when the actual peak value Pt falls below the lower limit value LB (see the thin solid line in FIG. 4), the ECU 200 judge.

  Thus, ECU 200 predicts the occurrence of engine stall when actual peak value Pt in a single cycle exceeds upper limit value UB or lower limit value LB, but depending on the cause of engine stall occurrence, As an indication of the occurrence of engine stall, the actual peak value Pt may show a constant tendency in a plurality of cycles. In other words, the signs of the occurrence of engine stall vary depending on the cause of engine stall occurrence, and even if the actual peak value Pt does not exceed the upper limit value UB or the lower limit value LB in one cycle, the actual peak value in a plurality of cycles. If Pt shows a certain tendency, the occurrence of engine stall may be predicted.

Therefore, the ECU 200 acquires the first threshold value T ₁ on the upper limit side and the second threshold value T ₂ on the lower limit side set for the peak value of the heat generation rate waveform in the cycle, and the actual heat generation rate of each cycle. . Thus, in a steady state, the ECU 200 causes the actual peak value Pt in the previous cycle to exceed the first threshold value T ₁ and the actual peak value Pt in the current cycle to fall below the second threshold value T ₂ in the same cylinder. If the actual peak value Pt in the previous cycle falls below the second threshold value T ₂ and the actual peak value Pt in the current cycle exceeds the first threshold value T ₁ , there is an indication that engine stall has occurred. It is configured to determine that there is (second combustion state diagnosis). The “previous cycle” corresponds to the “n−1th cycle” (n is an integer of 2 or more) in the present invention, and the “current cycle” corresponds to the “nth cycle” in the present invention. .

Here, the “first threshold value T ₁ on the upper limit side” is a value set smaller than the upper limit value UB (see FIG. 4). Unlike the upper limit value UB, the first threshold value T ₁ is not determined that an engine stall will occur even if the actual peak value Pt exceeds the first threshold value T ₁ , but the actual peak value Pt if it exceeds the first threshold T _1, which is a value to regarded as significant combustion occurring than normal combustion (normal combustion).

On the other hand, the “second threshold T ₂ on the lower limit side” is a value set larger than the lower limit LB (see FIG. 4). Unlike the lower limit value LB, the second threshold T ₂ is not determined that an engine stall will occur even if the actual peak value Pt falls below the second threshold T ₂ , but the actual peak value Pt if falls below a second threshold value T _2, the value to regarded as a small combustion occurs than normal combustion.

The first threshold value T ₁ and the second threshold value T ₂ are, for example experiences or experiments and, it is possible to determine on the basis of such simulation results, the first threshold value corresponding to the fuel quantity injected T ₁ and second A threshold value T ₂ is stored in the ROM 202 in advance. Thus, the CPU 201 refers (acquires) as necessary.

As a specific method of setting the first threshold value T ₁ and the second threshold value T ₂ , for example, the actual heat generation rate and the peak value of the waveform in a plurality of consecutive cycles in the same cylinder are calculated, A reference peak value is calculated from an average waveform or an ideal waveform of a plurality of actual heat generation rates. Then, the plurality of actual peak values Pt are divided into an actual peak value Pt that is greater than or equal to the reference peak value and an actual peak value Pt that is less than the reference peak value, and an average value of the actual peak values Pt that are greater than or equal to the reference peak value is The first threshold value T ₁ may be used, and the average value of the actual peak values Pt less than the reference peak value may be set as the second threshold value T ₂ . In addition, when the phase of the heat release rate waveform is adopted as a parameter related to the heat release rate waveform, the actual phase (including the same phase as the reference phase) on the advance side of the reference phase (the phase of the actual heat release rate waveform) ) May be the first threshold value T _1, and the average value of the actual phase retarded from the reference phase may be the second threshold value T ₂ .

As another method of setting the first threshold T ₁ and the second threshold T ₂ , for example, a reference peak value is calculated from an average waveform or an ideal waveform of a plurality of actual heat generation rates, and the reference peak value the 0.6 to 0.7 times the value second as a threshold value T _2, a 1.5-1.6 times the value of the reference peak value may be used as the first threshold value T _1.

Then, after the actual peak value Pt exceeds the first threshold value T ₁ (or after the second threshold value T ₂ falls below) in the same cylinder, the ECU 200 sets the actual peak value Pt to the second threshold value in the next cycle. If it falls below T ₂ (or exceeds the first threshold value T ₁ ), it is determined that there is a sign of the occurrence of engine stall. This determination is made for the following reason.

That is, if combustion is stable in one cylinder, the variation in the actual heat generation rate between cycles is small, and the actual peak value Pt in each cycle is defined by the first threshold value T ₁ and the second threshold value T _2. Easily fit within the peak width. In other words, if the actual peak value Pt in each cycle exceeds the first threshold value T ₁ or falls below the second threshold value T ₂ , combustion is not stable in the cylinder, and engine stall occurs. It is highly possible.

However, if the actual peak value Pt exceeds the first threshold value T ₁ even once (or if it falls below the second threshold value T ₂ once), it may be erroneously determined if it is determined that there is a sign of the occurrence of engine stall. There is. On the other hand, if there is no sign of the occurrence of engine stall until the actual peak value Pt exceeds the upper limit value UB (or falls below the lower limit value LB), the determination may be delayed.

Therefore, as shown in FIGS. 5A and 5B, the ECU 200 causes the actual peak value Pt of the previous cycle to exceed the first threshold value T ₁ and the actual peak value Pt of the current cycle in the same cylinder. If but it falls below the second threshold value T _2, in other words, when the small-scale combustion occurs in the following large-scale combustion, and is configured to determine that there is an indication of engine stall occurs. Similarly, as shown in FIGS. 5C and 5D, the ECU 200 determines that the actual peak value Pt of the previous cycle is less than the second threshold T ₂ and the actual peak value of the current cycle in the same cylinder. If Pt exceeds the first threshold value T _1, in other words, when a large-scale combustion happened next small-scale combustion, and is configured to determine that there is an indication of engine stall occurs.

Thus, combustion in which the actual peak value Pt exceeds the first threshold value T ₁ (large-scale combustion) (see the one-dot chain line in FIG. 4) and combustion in which the actual peak value Pt is less than the second threshold value T ₂ (small-scale combustion). (See the two-dot chain line in FIG. 4) occur alternately, the fluctuations between cycles are large, so the possibility of engine stalling is dramatically greater than when these occur only once. Rise. In addition, when the large-scale combustion and the small-scale combustion occur alternately even once, it is determined that there is a sign of the occurrence of the engine stall, so that the possibility of engine stall can be recognized at an early stage.

  In particular, large-scale combustion after small-scale combustion in the same cylinder can be regarded as combustion after the occurrence of a misfire cycle for the following reasons, and the cause of engine stall can be specified as a decrease in fuel supply amount. It becomes possible. That is, deposits, which are incomplete combustion products of fuel and engine oil, tend to accumulate inside the engine 1, and when such deposits accumulate on the nozzles of the injector 2, the effective spray amount decreases (fuel supply amount decreases). There is a case. Also, since alcohol is generally difficult to vaporize at low temperatures, when using gasoline containing alcohol, the effective spray amount may decrease. Thus, if the effective spray amount decreases due to deposits, alcohol content, or the like, there is a high possibility that misfire will occur, and if misfire occurs, small-scale combustion with a low peak value of actual heat generation rate will occur. In this embodiment, not only when the air-fuel mixture is not ignited or when the air-fuel mixture is ignited but without flame propagation without extinguishing the flame, the flame propagation is performed but the air-fuel mixture remains a lot. Also included in “misfire” when the flame disappears.

Thus, when misfire occurs in the previous cycle, in this cycle, in addition to newly supplied fuel (spray), unburned spray with high ignitability is also supplied, so the peak of actual heat generation rate Large scale combustion with high value is likely to occur. In other words, the fact that a large combustion in current cycles has occurred, rather than the combustion state is good, high probability of the previous cycle misfire has occurred, moreover, the cause of the misfire is valid There is a high probability that the spray amount is reduced (fuel supply amount is reduced). In the first combustion state diagnosis, when the actual peak value Pt exceeds the upper limit value UB, it is determined that engine stall occurs for the same reason.

Thus, ECU 200, when the actual peak value Pt is a combustion above a first threshold value T _1, the combustion actual peak value Pt is less than the second threshold value T ₂ occurs in an alternating manner, the sign of the engine stall occurrence However, the opposite phenomenon is not always true. That is, even if there is an indication of the occurrence of engine stall, combustion in which the actual peak value Pt exceeds the first threshold value T ₁ and combustion in which the actual peak value Pt is less than the second threshold value T ₂ always occur alternately. Instead, for example, large-scale combustion or small-scale combustion may occur continuously several times, or large-scale combustion and small-scale combustion may frequently occur with normal combustion (normal combustion) interposed therebetween.

Therefore, the ECU 200 determines the number of times that the actual peak value Pt exceeds the first threshold value T ₁ or the number of times that the actual peak value Pt falls below the second threshold value T ₂ in a predetermined number of cycles in the same cylinder. When the reference number of times is exceeded, it is determined that there is a sign of the occurrence of engine stall (third combustion state diagnosis).

According to the third combustion state diagnosis, engine stall occurs when the frequency at which the actual parameter exceeds the first threshold value T ₁ or the frequency at which the actual parameter falls below the second threshold value T ₂ exceeds a predetermined frequency in the same cylinder. Since it is determined that there is a sign, even when small-scale combustion and large-scale combustion do not occur alternately, a recognition failure when a sign of occurrence of engine stall appears can be suppressed as much as possible.

  As described above, according to the present embodiment, a single (first combustion state diagnosis), an alternating (second combustion state diagnosis), and a frequency (third combustion state diagnosis) are used. Since it becomes possible to monitor the occurrence of engine stalls and their signs from various angles, the prediction accuracy of engine stall occurrence can be reliably improved.

-Specific control after the occurrence of engine stall or its signs-
When it is determined by the first to third combustion state diagnoses that engine stall has occurred or there is an indication thereof, the ECU 200 decreases the EGR amount in the cylinder or decreases the EGR amount in the cylinder. , Advance the ignition timing.

  Specifically, if the ECU 200 is in a rough idle state (for example, when it is determined that there is a sign of the occurrence of engine stall in the second or third combustion state diagnosis), the EGR valve 19 is throttled (controlled to the closed side). As a result, the amount of EGR gas introduced into the combustion chamber 1a is reduced.

  Further, if the combustion fluctuation is in a steep state (for example, when it is determined that engine stall occurs in the first combustion state diagnosis), the ECU 200 reduces the EGR amount in the cylinder in order to quickly stabilize the combustion. When the ignition timing is retarded from the base ignition timing by the KCS learning control, the KCS learning control is temporarily stopped and a command is issued to the igniter 4 to advance the ignition timing.

  Note that these are merely examples, and when it is determined that engine stall has occurred or there is an indication thereof, the amount of fuel injection may be increased to increase torque, and the closing timing of the exhaust valve 14 may be set. The amount of EGR remaining in the cylinder may be decreased by retarding the angle.

-Combustion state diagnosis routine-
Next, the combustion state diagnosis procedure according to this embodiment will be described with reference to the flowchart of FIG.

  First, in step S1, the ECU 200 estimates the actual heat generation rate of the current cycle based on the in-cylinder pressure detected by the in-cylinder pressure sensor 30, and acquires the actual peak value Pt of the current cycle.

  In the next step S2, the ECU 200 refers to the upper limit value UB and the lower limit value LB stored in the ROM 202, and determines whether or not the actual peak value Pt of the current cycle is not less than the lower limit value LB and not more than the upper limit value UB. Determine. If the determination in step S2 is NO, that is, if the actual peak value Pt exceeds the upper limit value UB or falls below the lower limit value LB, the process proceeds to step S8, where the ECU 200 determines that an engine stall occurs. After predicting the occurrence of engine stall, return. On the other hand, if the determination in step S2 is yes, the process proceeds to step S3.

In the next step S3, ECU 200 references the second threshold value T ₂ stored in the ROM 202, the actual peak value Pt of the current cycle is determined whether a second threshold value T ₂ or more. When the determination of step S3 is NO, i.e., when the actual peak value Pt is below the second threshold value T ₂ are, the process proceeds to step S6.

In the next step S6, ECU 200 references the actual peak value Pl and the first threshold value T ₁ of the previous cycle stored in the ROM 202, above the actual peak value Pl of the previous cycle of the first thresholds T ₁ It is determined whether it has been. If the determination in step S6 is YES, that is, if large-scale combustion has occurred in the previous cycle and small-scale combustion has occurred in the current cycle (negative determination in step S3), the process proceeds to step S9, and ECU 200 However, after determining that there is a sign of the occurrence of engine stall (predicting the sign of engine stall occurrence), the process returns. On the other hand, if the determination in step S6 is no, the process proceeds to step S7.

In contrast, when the determination in step S3 is YES, the process proceeds to step S4, ECU 200 determines whether the actual peak value Pt of the current cycle exceeds the first threshold value T _1. If the determination of step S4 is NO, the actual peak value Pt of the current cycle, since it falls within the peak width defined by the first thresholds T ₁ and the second threshold value T _2, the routine returns . On the other hand, if the determination in step S4 is yes, the process proceeds to step S5.

In the next step S5, ECU 200 determines whether the actual peak value Pl of the previous cycle was below the second threshold T _2. If the determination in step S5 is YES, that is, if small-scale combustion has occurred in the previous cycle and large-scale combustion has occurred in the current cycle (affirmative determination in step S4), the process proceeds to step S9 and the ECU 200 However, it returns after determining that there is an indication that an engine stall has occurred. On the other hand, if the determination in step S5 is no, the process proceeds to step S7. That is, to step S7, small-scale combustion or large-scale combustion occurred in this cycle in step S3 → step S6 or step S4 → step S5, but small-scale combustion and large-scale combustion occurred in the previous cycle and this cycle. The process proceeds when scale combustion does not occur alternately.

In the next step S7, ECU 200 is, by adding the result of comparison between first thresholds T ₁ or the second threshold value T ₂ and the actual peak value Pt of the current cycle, small combustion or large combustion in predetermined cycles It is determined whether or not the number of occurrences has exceeded the reference number. If the determination in step S7 is YES, that is, if the frequency of occurrence of small-scale combustion or large-scale combustion is equal to or higher than the reference value, the process proceeds to step S9, and the ECU 200 determines that there is an indication that engine stall has occurred. Then return. On the other hand, if the determination in step S7 is no, the process directly returns.

(Modification 1)
In the embodiment described above, the second combustion state diagnosis and the third combustion state diagnosis are performed using the first threshold value T ₁ and the second threshold value T ₂ stored in advance in the ROM 202 as they are. In this modification, the initial control, pre ROM202 to the first threshold value T ₁ and the second threshold value T ₂ the use is stored, the first threshold value T ₁ and while reflecting the combustion state in accordance with the cycle is performed Control to update the second threshold T ₂ is performed.

In the gasoline engine 1 of the present embodiment, as described above, in order to improve the fuel efficiency by reducing the amount of NOx generated, cooling loss and pumping loss, the EGR gas is introduced into the combustion chamber 1a and the air-fuel ratio is reduced. Must be controlled. Thus, since the gasoline engine 1 has many restrictions, combustion tends to be unstable as compared with a diesel engine. Further, as described above, the in-cylinder pressure data detected by the in-cylinder pressure sensor 30 includes an air column generated between the in-cylinder pressure sensor 30 and the combustion chamber 1a due to electrical noise or a change in the in-cylinder pressure. There may be errors due to noise caused by vibration. For this reason, in the gasoline engine 1, even if the combustion state is good, it may exceed the first threshold T ₁ or fall below the second threshold T _2. There is a risk of erroneous determination that there is a sign of the occurrence of engine stall.

Therefore, the ECU 200 acquires the average value of the actual peak value Pt in a predetermined cycle every time the cycle is performed, and compares the acquired average value of the actual peak value Pt to thereby tend to indicate the combustion state in the same cylinder. Is estimated. Thus, when the combustion state tends to deteriorate each time the cycle is performed, the first threshold value T ₁ is decreased and the second threshold value T ₂ is increased, while the combustion state is improved every time the cycle is performed. If there is a tendency, the first threshold value T ₁ is raised and the second threshold value T ₂ is lowered.

  For example, when the average value of the actual peak value Pt in the m-th (predetermined) cycle from the first time to the m-th time is obtained with l and m being positive integers, To obtain the average value of the actual peak value Pt in m cycles from m to m + 1, and when the (m + 1) th cycle is performed, the actual peak value Pt in m cycles from the (l + 1) th time to the (m + 1) th time is obtained. The moving average value of the actual peak value Pt is acquired every time the cycle is performed, for example, the average value is acquired. By comparing the moving average values of the actual peak values Pt acquired in this way, it is estimated whether the combustion state in the same cylinder tends to deteriorate every time a cycle is performed or tends to improve. To do.

Thus, for example, as shown in FIG. 7 (a), the moving average of the actual peak value Pt decreases (or may increase) every time the cycle is performed, that is, the combustion state tends to deteriorate. In some cases, the peak width is narrowed by lowering the first threshold T ₁ and raising the second threshold T ₂ in order to tighten the criteria. On the other hand, as shown in FIG. 7B, for example, when the moving average of the actual peak value Pt approaches the intermediate value between the first threshold T ₁ and the second threshold T ₂ every time the cycle is performed, When the combustion state tends to improve, the peak width is widened by raising the first threshold T ₁ and lowering the second threshold T ₂ in order to loosen the criterion.

  In this way, when the combustion state tends to deteriorate each time the cycle is performed, the peak width is set to be narrow, so it can be determined that there is a sign of engine stall at an early stage. On the other hand, when the combustion state tends to be improved every time the cycle is performed, the peak width is widened. Therefore, in the gasoline engine 1 in which combustion is likely to be unstable compared to the diesel engine, the combustion state is Although it is good, it is possible to suppress erroneous determination that there is a sign of the occurrence of engine stall.

(Modification 2)
In the embodiment and the first modification described above, the combustion state in the same cylinder in the steady state is the object of diagnosis, but in this modification, the variation among the four cylinders in the transient state is detected.

  In the transient state, unlike the steady state, it is difficult to grasp the combustion state only by comparing combustion fluctuations between cycles in one cylinder. Accordingly, the ECU 200 acquires the average value of the actual peak value Pt in a predetermined cycle for each cylinder, and determines the variation between the cylinders by comparing the acquired average value of the actual peak value Pt between the cylinders. It is configured.

  More specifically, the ECU 200 performs the combustion state diagnosis according to the above-described embodiment and / or modification 1 to set one of the four cylinders with the best combustion state in the steady state as a standard cylinder. To do. Then, by comparing the average value of the actual peak value Pt of the standard cylinder with the average value of the actual peak value Pt of the other cylinders, in other words, with respect to the average value of the actual peak value Pt of the standard cylinder Thus, by detecting how far the average value of the actual peak values Pt in the other cylinders is, for example, a cylinder having a deteriorated combustion state among the plurality of cylinders is specified. Thereby, even in the transient state, it is possible to easily identify the cylinder in which the combustion state is deteriorated (or tends to deteriorate) among the four cylinders.

(Other embodiments)
The present invention is not limited to the embodiments, and can be implemented in various other forms without departing from the spirit or main features thereof.

  In the said embodiment, although this invention was applied to the cylinder direct injection type gasoline engine 1, it is applicable not only to this but a port injection type gasoline engine. The present invention can also be applied to a diesel engine.

  In the above embodiment, the EGR gas is recirculated to the intake passage 11 using the EGR passage 18 and supplied again to the combustion chamber 1a. However, the present invention is not limited to this, and the exhaust gas once discharged into the exhaust passage 12 is used. May be re-inhaled into the cylinder.

  Furthermore, in the above embodiment, the peak value of the waveform, the phase of the waveform, the gradient of the waveform, and the area surrounded by the waveform are given as the parameters related to the heat release rate waveform, but these are examples, and other parameters may be used. Good.

  In the above-described embodiment, whether or not small-scale combustion and large-scale combustion are alternately generated in the current cycle and the previous cycle is confirmed. Data may be extracted from the first cycle, and it may be confirmed whether small-scale combustion and large-scale combustion are alternately generated in the (n-1) th cycle and the nth cycle.

  As described above, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  According to the present invention, it is possible to improve the prediction accuracy of engine stall occurrence, which is extremely useful when applied to a combustion state diagnostic apparatus for diagnosing the combustion state of an internal combustion engine.

1 engine (internal combustion engine)
200 ECU (combustion state diagnosis device)

Claims (7)

A combustion state diagnostic device for diagnosing the combustion state of an internal combustion engine,
The first threshold value on the upper limit side and the second threshold value on the lower limit side set for the parameters related to the heat generation rate waveform in the cycle, and the actual heat generation rate of each cycle are acquired,
In a steady state, in the same cylinder, the parameter related to the actual heat generation rate in the (n-1) th cycle (n is an integer of 2 or more) exceeds the first threshold, and the actual heat generation rate in the nth cycle. Or when the parameter relating to the actual heat generation rate in the (n-1) th cycle falls below the second threshold value and the actual heat generation rate in the nth cycle. When the parameter according to the above exceeds the first threshold value, it is determined that there is an indication that an engine stall has occurred, and the parameter related to the actual heat generation rate in a predetermined number of cycles in the same cylinder in a steady state. The number of times that exceeded the first threshold or the number of times that the parameter related to the actual heat generation rate fell below the second threshold became equal to or greater than a predetermined reference number. Even if the combustion condition diagnosis apparatus characterized by determining that there is a sign of engine stalling. In the combustion state diagnostic device according to claim 1 ,
A third threshold value set on the upper limit side of the first threshold value and a fourth threshold value set on the lower limit side of the second threshold value, which are set for the parameters relating to the heat release rate waveform in the cycle,
A combustion state diagnosis characterized in that it is determined that an engine stall occurs when the parameter relating to the actual heat generation rate exceeds the third threshold value or falls below the fourth threshold value in a steady state. apparatus. In the combustion state diagnostic device according to claim 1 or 2 ,
The combustion state diagnosis apparatus, wherein the parameter includes at least one of a peak value of the waveform, a phase of the waveform, a gradient of the waveform, and an area of the waveform. In the combustion state diagnostic device according to any one of claims 1 to 3 ,
In a steady state, the average value of the parameter related to the actual heat generation rate waveform in a predetermined cycle in the same cylinder is acquired every time the cycle is performed, and the average value of the acquired parameter is compared with each other in the same cylinder Estimate the state of combustion in
If the combustion state tends to deteriorate each time the cycle is performed, the first threshold value is lowered and the second threshold value is raised, while the combustion state tends to improve every time the cycle is performed, A combustion state diagnosing device, wherein the first threshold value is raised and the second threshold value is lowered. In the combustion state diagnostic device according to any one of claims 1 to 4 ,
In the transient state, the average value of the parameter related to the actual heat generation rate waveform in a predetermined cycle is acquired for each cylinder, and the average value of the acquired parameter is compared between the cylinders to determine the variation between the cylinders. Combustion state diagnostic device characterized by the above. In the combustion state diagnostic device according to any one of claims 1 to 5 ,
A combustion state diagnosis device that reduces an EGR amount in a cylinder when it is determined that an engine stall has occurred or an indication of an engine stall has occurred. In the combustion state diagnosis apparatus according to claim 6 ,
A combustion state diagnosis apparatus that advances an ignition timing when it is determined that an engine stall has occurred or an indication of an engine stall has occurred.

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