ENGINE CONTROL DEVICE

Abstract

Internal combustion engine control device comprising a controller which in turn comprises an output fluctuation value calculation unit (100) which calculates an output fluctuation value for each cylinder (10) at least on the basis of a detection result obtained by a detection unit for a physical quantity which detects a physical quantity which causes fluctuations in the engine torque of the internal combustion engine, and a state determination unit which determines whether the internal combustion engine is in a non-stationary operating state or a stationary operating state on the basis of a difference or ratio between a first output fluctuation value of a given first cylinder and a second output fluctuation value of a second cylinder which is different from the first cylinder, calculated by the output fluctuation value calculation unit (100).

Description

Technical area

[0001] The present invention relates to an internal combustion engine control device, and more particularly to an internal combustion engine control device that controls a control parameter of the internal combustion engine by determining a combustion state of an air-fuel mixture in a combustion chamber. Technical background

[0002] In recent years, regulations regarding the amount of fuel consumed (fuel consumption) and harmful exhaust components of vehicles, such as motor vehicles, have been tightened, and there is a trend for such regulations to become even more stringent in the future. Fuel consumption regulations, in particular, are of great interest due to issues such as recent increases in fuel prices, the impact of global warming, and the depletion of energy resources.

[0003] Under such circumstances, for example, in the automotive industry, various technical developments have been promoted for the purpose of improving the fuel efficiency and exhaust gas purification performance of vehicles. For example, as described in Japanese Patent Application Laid-Open No. JP H10-196429 A (Abstract) (Patent Literature 1), it is known that a combustion pressure sensor that detects the combustion pressure generated by the combustion of the air-fuel mixture in a combustion chamber is provided, a torque fluctuation amount is calculated based on the combustion pressure change in each torque generation cycle of a given cylinder detected during a sampling period of the combustion pressure sensor, and a control parameter of the internal combustion engine, e.g.,a fuel injection amount and an ignition timing, is adjusted so that the calculated torque fluctuation amount converges to a target torque fluctuation amount. List of citationsPatent literature

[0004] PTL1: JP H10 - 196 429 A (Abstract) Summary of the inventionTechnical problem

[0005] Many internal combustion engines operate while alternating between a steady-state operating state in which engine torque (which can be read as an engine output) hardly changes on a time axis (e.g., a state in which an accelerator pedal depression amount is almost constant) and a non-steady-state operating state in which engine torque is increased or decreased on a time axis (e.g., a state in which an accelerator pedal depression amount is increased or decreased). The internal combustion engine control device described in Patent Literature 1 detects the combustion instability of an air-fuel mixture as a torque fluctuation amount and stabilizes combustion by adjusting a control parameter of the internal combustion engine.

[0006] However, the amount of temporal fluctuation of the engine torque is large in the non-steady-state operating state of the internal combustion engine. Therefore, in a case where the amount of torque fluctuation is calculated based on the combustion pressure change in each torque generation cycle (combustion cycle) of a given cylinder, as described in Patent Literature 1, the calculated amount of torque fluctuation includes the amount of torque fluctuation in the steady-state operating state and the torque fluctuation of the engine torque itself resulting from the non-steady-state operating state.

[0007] For this reason, in the non-steady-state operating condition, there is a possibility that combustion may be erroneously determined to be unstable even though the combustion of the air-fuel mixture is stable. This creates a new problem that the fuel efficiency, output, and exhaust gas purification performance of the internal combustion engine deteriorate as a result of unnecessary adjustment of the control parameters.

[0008] It is an object of the present invention to provide a novel internal combustion engine control device that can accurately determine a combustion state of an air-fuel mixture in a combustion chamber even when the operation is switched between a steady-state operation state and a non-steady-state operation state. Solution to the problem

[0009] The present invention is characterized by including an output fluctuation value calculation unit that calculates an output fluctuation value for each cylinder based on a detection result obtained by a physical quantity detection unit that detects a physical quantity that causes fluctuations in engine torque of an internal combustion engine, and a state determination unit that determines whether the internal combustion engine is in a non-steady state or a steady state based on a difference or a ratio between a first output fluctuation value of a predetermined first cylinder and a second output fluctuation value of a second cylinder different from the first cylinder, which are calculated by the output fluctuation value calculation unit.

[0010] Furthermore, the present invention is characterized by including a combustion determination region setting unit that sets a portion of the steady-state operating state as a combustion determination region in a case where the state determination unit determines that the state is the steady-state operating state, and a combustion disturbance determination unit that determines that the first cylinder or the second cylinder has a combustion disturbance in a case where an output fluctuation value of the first cylinder or the second cylinder calculated by the output fluctuation value calculation unit is equal to or greater than a setting value in the combustion determination region set by the combustion determination region setting unit. Advantageous effects of the invention

[0011] According to the present invention, since the combustion disturbance determination is carried out in a section determined as the steady-state operation state, it is possible to accurately determine a combustion disturbance state of an air-fuel mixture of a cylinder even in a case where the operation is switched between the steady-state operation state and the non-steady-state operation state. Short description of the drawing Fig. 1 is a cross-sectional view illustrating a configuration of an internal combustion engine to which the present invention is applied. Fig. 2 is a plan view of the internal combustion engine viewed from above, which is shown in Fig. 1 is illustrated. Fig. 3 is an explanatory view for explaining a determination result of combustion stability based on the temporal changes of the specified average working pressures and output fluctuation rates of two conventional cylinders in a case where the operation is switched between a steady-state operation state and a non-steady-state operation state. Fig. 4 is a flowchart illustrating a procedure of determining combustion stability and control parameter correction control according to the first embodiment of the present invention. Fig. 5 is a flowchart showing a procedure for determining a steady-state operating state or a non-steady-state operating state in the Fig. 4 illustrated step S103. Fig. 6 is an explanatory view for explaining a determination result of combustion stability based on the temporal changes of the indicated average working pressures and output fluctuation rates of two cylinders according to the first embodiment in a case where the operation is switched between a steady-state operation state and a non-steady-state operation state. Fig. 7 is a map showing an example of a Fig. 5 with respect to an engine speed, an engine torque, an oil temperature, and a water temperature. Fig. 8 is a flowchart illustrating a procedure for determining a steady state operation or a non-steady state operation in the second embodiment of the present invention. Fig. 9 is an explanatory view for explaining a determination result of combustion stability based on the temporal changes of the indicated average working pressures and output fluctuation rates of two cylinders according to the second embodiment in a case where the operation is switched between a steady-state operation state and a non-steady-state operation state. Fig. 10 is a flowchart illustrating a procedure for determining a steady state or a non-steady state and the correction control executed on all cylinders according to the third embodiment of the present invention. Description of the embodiments

[0012] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and various modifications and applications are included within the technical concept of the present invention. Embodiment 1

[0013] Fig. 1 illustrates a cross section of an internal combustion engine according to a first embodiment of the present invention. An internal combustion engine IC is a spark-ignition 4-stroke gasoline internal combustion engine and has a combustion chamber formed by an engine head, a cylinder 10, a piston 11, an intake valve 12, and an exhaust valve 13. A fuel injection valve 14 is provided in the engine head, and an injection nozzle of the fuel injection valve 14 enters a combustion chamber (hereinafter referred to as a cylinder). This constitutes a direct injection internal combustion engine. The cylinder head is further provided with a spark plug 15. Combustion air is drawn into the cylinder through an air cleaner 16, a throttle valve 17, and an intake port 18. The exhaust gas after combustion is discharged to the atmosphere through an exhaust port 19 and an exhaust gas purification catalyst 20.

[0014] The amount of air drawn into the cylinder is detected by an air flow sensor 21. The pressure in the cylinder is detected by an in-cylinder pressure sensor 22 provided in the cylinder head. Furthermore, the engine speed is detected by a crank angle sensor 23, while the degree of throttle opening is detected by a throttle opening sensor 24. The values ​​detected by these sensors are input to a control unit 100 and used for state detection and operation control of the internal combustion engine IC.

[0015] Further, the control unit 100 outputs the opening degree of the throttle valve 17, an injection start timing and an injection end timing of the fuel injection valve 14, an ignition timing of the spark plug 15, and the like, thereby controlling the internal combustion engine IC to a predetermined operating state.

[0016] Although only a single cylinder in Fig. 1 to illustrate the configuration of the combustion chamber of the internal combustion engine, the internal combustion engine according to the embodiment of the present invention is a multi-cylinder internal combustion engine formed by two or more cylinders. A four-cylinder internal combustion engine will be described below as an example, wherein Fig. 2 illustrates a floor plan viewed from above.

[0017] The in-cylinder pressure sensor 22 is provided in each cylinder, and the control unit 100 can independently detect the in-cylinder pressure of each cylinder. Furthermore, the control unit 100 can independently control the injection start and end timing of the fuel injection valve 14 and the ignition timing of the spark plug 15 for each cylinder.

[0018] The control unit 100 receives a value of the in-cylinder pressure detected by the in-cylinder pressure sensor 22 at every constant crank angle dCA (e.g., every crank angle 1°), and calculates an indicated average working pressure (Pi) from the following equation (1) using a sample value of the in-cylinder pressure within one combustion cycle from an intake stroke to an exhaust stroke of the internal combustion engine. [Equation 1] Pi=∫(P−Pa)VdV

[0019] In equation (1), “P” is a sampled value of the pressure in the cylinder, “Pa” is an atmospheric pressure, dV is an amount of volume fluctuation in the cylinder during a dCA period, and V is a stroke volume of the cylinder.

[0020] Furthermore, a standard deviation (CPi) of a specified mean working pressure (Pi) for a given combustion cycle (e.g., 100 combustion cycles) is calculated from the following equation (2). Hereinafter, this is defined as an output fluctuation rate (CPi). [Equation 2] CPi=1n∑k(Pki−Pim)2Pim

[0021] In equation 2, “n” is the number of combustion cycles, “P k i " is a specified average working pressure in any combustion cycle, and "Pim" is an average value of the specified average working pressures. In the present embodiment, an output fluctuation rate (CPi) is calculated independently for each cylinder because the in-cylinder pressure sensor 22 is provided in each cylinder.

[0022] In a spark-ignition internal combustion engine, lean combustion (lean burn) or large-volume exhaust gas recirculation (EGR) combustion is known as a method for improving the fuel efficiency of the internal combustion engine. According to these methods, pumping loss and cooling loss at part load can be reduced by diluting the air-fuel mixture with air or exhaust gas. To achieve higher fuel efficiency, it is effective to increase the dilution rate by increasing the amount of air or exhaust gas.

[0023] However, lean combustion and EGR combustion tend to be unstable. In particular, in a multi-cylinder internal combustion engine, a difference in combustion stability occurs between cylinders. This causes a problem in that a dilution rate boundary is depressed to a low level by a cylinder exhibiting low combustion stability (poor combustion stability). Therefore, if a cylinder exhibiting low combustion stability is detected and corrective control (e.g., correction of a fuel injection amount or ignition timing) is performed to improve combustion stability for that cylinder, the internal combustion engine as a whole operates at a high dilution rate. This makes it possible to maximize fuel efficiency.

[0024] To determine combustion stability, generally, the above output fluctuation rate (CPi) is compared with a predetermined fluctuation rate determination threshold, and if the output fluctuation rate (CPi) is greater than this fluctuation rate determination threshold, it is determined that combustion is unstable. However, when the internal combustion engine is in a non-steady state, the output fluctuation rate (CPi) includes a torque fluctuation component resulting from the combustion instability that is necessary, and a torque fluctuation component resulting from the shift of the engine torque to a target engine torque that occurs while experiencing a predetermined non-steady state. This may undesirably lead to an erroneous determination of whether combustion stability is good or poor.

[0025] Next, a specific example of an erroneous determination of whether the combustion stability is good or bad is presented with respect to Fig. 3 described. Fig. 3 illustrates the changes in the indicated mean working pressures (Pi) and the output fluctuation rates (CPi) of a given cylinder 1 and a given cylinder 2 different from the given cylinder 1 in a case where a multi-cylinder internal combustion engine is operated in such a manner that the engine torque includes a steady-state operating condition and a non-steady-state operating condition.

[0026] In Fig. 3, the engine torque is controlled by the control unit 100 such that a period of 5 to 10 seconds is a steady-state operating condition, a period of 10 to 20 seconds is a non-steady-state operating condition (the engine torque decreases), a period of 20 to 30 seconds is a steady-state operating condition, a period of 30 to 35 seconds is a non-steady-state operating condition (the engine torque increases), and a period of 35 to 45 seconds is a steady-state operating condition.

[0027] Cylinder 1 is a cylinder with high combustion stability and has a specified mean working pressure (Pi) that follows a given output value without oscillation. On the other hand, cylinder 2 is a cylinder with low combustion stability and has a specified mean working pressure (Pi) that experiences a short-cycle cyclic fluctuation.

[0028] When comparing the output fluctuation rate (CPi) of cylinder 1 and the output fluctuation rate (CPi) of cylinder 2, in a section where the engine torque is in the steady-state operating state, the output fluctuation rate (CPi) of cylinder 2, indicated by the solid line, is significantly larger than the output fluctuation rate (CPi) of cylinder 1, indicated by the dashed line. Therefore, in the steady-state operating state, by comparing the output fluctuation rate (CPi) with a fluctuation rate determination threshold (CPi SL), which is a suitable "combustion determination threshold" indicated by a line with alternating long and short dashes, it can be correctly determined that the combustion stability of cylinder 1 is high and the combustion stability of cylinder 2 is low. It is stated that an experimentally calculated experimental value can be used as the fluctuation rate determination threshold (CPi SL ) is used.

[0029] On the other hand, in a section where the internal combustion engine is in a non-stationary operating state, both the output fluctuation rate (CPi) of cylinder 1 and the output fluctuation rate (CPi) of cylinder 2 are large. This is because the output fluctuation rate (CPi) includes a torque fluctuation component for each combustion cycle resulting from combustion instability and a torque fluctuation component of the engine torque itself resulting from a predetermined non-stationary change. When the output fluctuation rate (CPi) in the section where the internal combustion engine is in the non-stationary operating state is compared with the fluctuation rate determination threshold (CPi SL ), it may therefore be erroneously determined that cylinder 1, which has high combustion stability, has low combustion stability in addition to cylinder 2.

[0030] Therefore, in the present embodiment, the combustion stability of each cylinder is determined as shown in Fig. 4, wherein a control parameter correction control is performed on a cylinder having low combustion stability. Fig. 4 illustrates a control processing flow executed by the control unit 100.

[0031] In Fig. 4, in step S10, an output fluctuation rate (CPi) of each cylinder is calculated from equations (1) and (2) using a sample of the detection output of the in-cylinder pressure sensor 22 of each cylinder. In step S11, a maximum value (CPimax) of an output fluctuation rate is determined among the output fluctuation rates (CPi) of the respective cylinders, and their cylinder number (Nmax) is determined.

[0032] Subsequently, in step S12, it is determined whether the internal combustion engine is in a steady-state operating state or in a non-steady-state operating state. This determination process is carried out with respect to Fig. 5. In a case where it is determined that the internal combustion engine is in a non-stationary operating state, the processing ends, waiting for the next activation time.

[0033] On the other hand, in a case where it is determined that the internal combustion engine is in a steady state operation, the processing proceeds to step S13, where the maximum value (CPimax) of the output fluctuation rate is compared with a predetermined fluctuation rate determination threshold value (CPi SL) is compared. One reason why the maximum value (CPimax) is compared is that the other cylinders have an output fluctuation rate (CPi) that is smaller than the maximum value (CPimax) (have stable combustion). In a case where the maximum value (CPimax) is smaller than the fluctuation rate determination threshold (CPi SL ), it is determined that there is no problem with combustion stability, and processing ends and waits for the next activation time.

[0034] On the other hand, in a case where the maximum value (CPimax) is larger than the fluctuation rate determination threshold (CPi SL), it is determined that combustion stability is poor, and processing proceeds to step S14. In step S14, correction control for stabilizing combustion is executed for the cylinder (Nmax) exhibiting the maximum output fluctuation rate. The correction control for stabilizing combustion refers, for example, to increasing a fuel injection amount of the cylinder determined to have unstable combustion compared to the other cylinders, or advancing or retarding a fuel injection timing and an ignition timing compared to the other cylinders.

[0035] In other words, increasing the fuel injection amount makes the air-fuel ratio richer. This improves ignitability and flame propagation characteristics, thereby stabilizing combustion. Furthermore, changing the fuel injection timing optimizes the air-fuel mixture distribution and turbulence intensity of the air-fuel mixture in the cylinder, thereby stabilizing combustion. Furthermore, changing the ignition timing optimizes the heat generation center in the cylinder, thereby stabilizing combustion.

[0036] It should be noted that which type of correction control should be executed can be appropriately selected in accordance with the internal combustion engine system, further explanation being omitted, but at least one of the fuel injection amount, the fuel injection timing, and the ignition timing simply needs to be corrected next.

[0037] Next, a method for determining a steady-state operating state and a non-steady-state operating state of the internal combustion engine with respect to Fig. 5 described. Fig. 5 illustrates the details of the Fig. 4 illustrated step S12 for determining the stationary / non-stationary operating state.

[0038] In step S12a, a minimum value (CPimin) of an output fluctuation rate is determined from the output fluctuation rates (CPi) of the respective cylinders. In step S12b, a fluctuation rate difference value (ΔCPi) between the maximum value (CPimax) and the minimum value (CPimin) of the output fluctuation rate is obtained by calculating "ΔCPi = CPimax - CPimin."

[0039] Subsequently, in step S12c, the fluctuation rate difference value (ΔCPi) is compared with a difference value determination threshold value (ΔCPi SL), which is a predetermined “condition determination threshold value”, and in a case where the fluctuation rate difference value (ΔCPi) is greater than the difference value determination threshold value (ΔCPi SL ), it is determined that the internal combustion engine is in a steady-state operating state, and the processing proceeds to step S13. On the other hand, in a case where the fluctuation rate difference value (ΔCPi) is smaller than the difference value determination threshold (ΔCPi SL ), it is determined that the internal combustion engine is in a non-stationary operating state, and the combustion stability determination processing sequence ends and waits for a next activation time.

[0040] Next, the operations and effects of the present embodiment will be explained with respect to Fig. 6 described. Fig. Figure 6 illustrates the changes in the specified mean working pressures (Pi), the output fluctuation rates (CPi), and the fluctuation rate difference values ​​(ΔCPi) of cylinder 1 and cylinder 2 in a case where a multi-cylinder internal combustion engine is operated such that the internal combustion engine includes a steady-state operating condition and a non-steady-state operating condition. The changes in the specified mean working pressures (Pi) and the output fluctuation rates (CPi) are the same as those according to Fig. 3.

[0041] As in Fig. As illustrated in Figure 6, the fluctuation rate difference value (ΔCPi) is large in a case where the internal combustion engine is in a steady-state operating state, while it is small in a case where the internal combustion engine is in a non-steady-state operating state. This is because the output fluctuation rate (CPi) in the steady-state operating state represents only a torque fluctuation component for each combustion cycle resulting from combustion instability, whereas the output fluctuation rate (CPi) in the non-steady-state operating state represents a sum of a torque fluctuation component for each combustion cycle resulting from combustion instability and a torque fluctuation component of the engine torque itself resulting from a predetermined non-steady-state change.Therefore, in the non-steady state, a ratio of the torque fluctuation component for each combustion cycle resulting from the combustion instability to the output fluctuation rate (CPi) decreases, and the fluctuation rate difference value (ΔCPi) becomes small in a cylinder with a low combustion stability compared to a cylinder with a high combustion stability.

[0042] In view of this, the combustion stability is only determined in a case where the fluctuation rate difference value (ΔCPi) is larger than the predetermined difference value determination threshold (ΔCPi SL) is determined from a value of the output fluctuation rate (CPi). That is, the combustion stability is determined only in a steady-state operating condition, and therefore, an erroneous determination of the combustion stability in a non-steady-state operating condition can be prevented. Because the combustion stability in the steady-state operating condition is accurately determined as described above, the control parameter correction control in a cylinder with a low combustion stability is Fig. 4, steps S13 and S14 are suitably carried out, whereby the fuel efficiency and exhaust gas purification performance of the internal combustion engine can be improved.

[0043] It is stated that the difference value determination threshold (ΔCPi SL) does not necessarily have to be a constant value, and may change depending on an engine speed, an engine torque, an oil temperature, a water temperature, and the like. In a case where the internal combustion engine is in a non-stationary operating state, the output fluctuation rate (CPi) includes a torque fluctuation component for each combustion cycle and a torque fluctuation component resulting from a non-stationary change. Accordingly, in a case where the torque fluctuation component for each combustion cycle is larger than the torque fluctuation component resulting from the non-stationary change, the fluctuation rate difference value (ΔCPi) becomes larger. This increases a risk of erroneously determining the non-stationary operating state as the steady-state operating state.

[0044] In view of this, it is desirable to set the difference value determination threshold (ΔCPi SL ) in a state where the engine speed is low, the engine torque is low, or the oil temperature or the water temperature is low, in which state an output fluctuation rate for each combustion cycle tends to be large, to increase as in Fig. 7. In this case, the difference value determination threshold (ΔCPi SL ) may be gradually reduced as indicated by characteristic curve A, and may be further reduced successively as indicated by characteristic curve B as the engine speed, engine torque, oil temperature or water temperature becomes higher.

[0045] Furthermore, under operating conditions where engine torque instability is very high, such as when the oil temperature or water temperature is very low, or immediately after restarting from an idle stop, there is a high risk of (1) erroneous determination of a steady-state operating state or a non-steady-state operating state and (2) erroneous determination of the combustion stability of the internal combustion engine. Therefore, in these conditions, it is desirable to stop (1) the determination of a steady-state operating state or a non-steady-state operating state and (2) the determination of the combustion stability of the internal combustion engine. Embodiment 2

[0046] Next, a second embodiment of the present invention will be described. The first embodiment proposes an example in which the determination of a steady-state operating state or a non-steady-state operating state of an internal combustion engine is performed using a fluctuation rate difference value (ΔCPi). On the other hand, the second embodiment proposes an example in which the determination is performed using a fluctuation rate ratio.

[0047] Fig. Figure 8 illustrates the details of step S12 in Fig. 4. In step S12a, a minimum value (CPimin) of an output fluctuation rate is determined among the output fluctuation rates (CPi) of the respective cylinders. In step S12d, a fluctuation rate ratio (RCPi) between a maximum value (CPimax) and the minimum value (CPimin) of the output fluctuation rate is obtained by calculating "RCPi = CPimax / CPimin".

[0048] Subsequently, in step S12e, the fluctuation rate ratio (RCPi) is compared with a predetermined fluctuation rate ratio determination threshold value (RCPi SL ), whereby in a case where the fluctuation rate ratio (RCPi) is greater than the fluctuation rate ratio determination threshold (RCPi SL ), it is determined that a state is a steady state operation state, and the processing proceeds to step S13. On the other hand, in a case where the fluctuation rate ratio (RCPi) is smaller than the fluctuation rate ratio determination threshold (RCPi SL ), determines that the condition is a non-stationary operating condition, and the combustion stability determination processing flow ends and waits for a next activation time.

[0049] It is stated that the above-described fluctuation rate ratio (RCPi) can be obtained by exchanging the denominator and the numerator as "RCPi = CPimin / CPimax." In this case, in step S12e, the fluctuation rate ratio (RCPi) is multiplied by a predetermined fluctuation rate ratio determination threshold value (RCPi SL ), whereby in a case where the fluctuation rate ratio (RCPi) is less than the fluctuation rate ratio determination threshold (RCPi SL ), it is determined that the state is a steady state operation state, and the processing proceeds to step S13.

[0050] Next, the operations and effects of the present embodiment will be explained with respect to Fig. 9 described. Fig. Figure 9 illustrates the changes in the specified mean working pressures (Pi), the output fluctuation rates (CPi), and the fluctuation rate ratios (RCPi) of cylinder 1 and cylinder 2 in a case where a multi-cylinder internal combustion engine is operated such that the internal combustion engine includes a steady-state operating condition and a non-steady-state operating condition. The fluctuation rate ratio (RCPi) is a value obtained by "RCPi = CPimax / CPimin." The changes in the specified mean working pressures (Pi) and the output fluctuation rates (CPi) are the same as those according to Fig. 3.

[0051] As in Fig. 9, the fluctuation rate ratio (RCPi) is large in a case where the internal combustion engine is in a steady-state operating state, while it is small in a case where the internal combustion engine is in a non-steady-state operating state. This is because the output fluctuation rate (CPi) in the steady-state operating state represents only a torque fluctuation component for each combustion cycle resulting from combustion instability, whereas the output fluctuation rate (CPi) in the non-steady-state operating state represents a sum of a torque fluctuation component for each combustion cycle resulting from combustion instability and a torque fluctuation component of the engine torque itself resulting from a predetermined non-steady-state change. Therefore, for the same reason as that explained with respect to Fig. 6, the fluctuation rate ratio (RCPi) in a cylinder with low combustion stability is small compared to a cylinder with high combustion stability.

[0052] In view of this, the combustion stability is only ensured in a case where the fluctuation rate ratio (RCPi) is larger than the predetermined fluctuation rate ratio determination threshold (RCPi SL ) is determined from a value of the output fluctuation rate (CPi). That is, the combustion stability is determined only in a steady-state operating condition, whereby an erroneous determination of the combustion stability in the non-steady-state operating condition can be prevented. Because the combustion stability in the steady-state operating condition is accurately determined as described above, the control parameter correction control on a cylinder having low combustion stability is Fig. 4, steps S13 and S14 are suitably carried out, whereby the combustion efficiency and the exhaust gas purification performance of the internal combustion engine can be improved.

[0053] In a case where the fluctuation rate ratio (RCPi) is obtained by “RCPi = CPimin / CPimax”, the changes in the fluctuation rate ratios (RCPi) are to be calculated as Fig. 9. Therefore, it is only necessary to determine the combustion stability from the output fluctuation rate (CPi) value when the fluctuation rate ratio (RCPi) is greater than the specified fluctuation rate ratio determination threshold (RCPi SL ) is.

[0054] Although a method for determining a steady-state operating condition or a non-steady-state operating condition using the in-cylinder pressures of at least two cylinders has been proposed in the above description, other parameters may also be used. For example, the temporal change rates of physical quantities related to engine output, such as a throttle opening degree, a fuel injection amount per unit cycle, an intake air amount per unit cycle, an intake pipe air pressure, an engine speed, and a maximum value Pmax of an in-cylinder pressure, are used.regularly monitored, wherein in a case where the time rates of change are equal to or less than a predetermined value, it can be determined that the condition is a steady-state operating condition, while in a case where the time rates of change are equal to or greater than the predetermined value, it can be determined that the condition is a non-steady-state operating condition.

[0055] It is noted that, however, in a case where a steady-state operation state or a non-steady-state operation state is determined using the output fluctuation rate (CPi) of a pressure in the cylinder as described in the above embodiment, the following specific operations and effects are produced.

[0056] In a case where the output fluctuation rate (CPi), which is used as an index value for determining combustion stability, is also used to determine a steady-state operating state of the engine or a non-steady-state operating state, the processing from the determination of (1) a steady-state operating state or a non-steady-state operating state to the determination of (2) combustion stability is simplified. This can reduce the computation load on the control unit 100.

[0057] Furthermore, because the output fluctuation rate (CPi) of the in-cylinder pressure is an index that directly represents the engine torque fluctuation of the internal combustion engine, a steady-state operating state or a non-steady-state operating state can be determined more accurately with less time delay compared with a case where an index that indirectly represents the engine output, such as a throttle opening degree, a fuel injection amount, or an air flow amount, is used. Embodiment 3

[0058] In a multi-cylinder internal combustion engine, there is a risk that the combustion stability of all cylinders may be reduced due to a significant change in ambient conditions and fuel properties, deterioration of mechanical parts, etc. In this case, even if corrective control is performed on a specific cylinder with lower combustion stability, it is difficult to maintain the fuel efficiency, output, and exhaust gas purification performance of the internal combustion engine.

[0059] In view of this, in a case where the combustion stability of all cylinders becomes low, it is desirable to detect this and perform appropriate control parameter correction control on all cylinders. Fig. Figure 10 illustrates an engine control procedure to achieve this. The procedure according to Fig. 10 is achieved by adding the control step S16 and the control step S17 between the step S12 for determining a steady-state operating state and a non-steady-state operating state and the step S13 for determining the combustion stability in the Fig. 4 illustrated internal combustion engine control processing flow.

[0060] In the Fig. 10, in a case where it is determined in step S12 that the state is a steady-state operation state, in step S16, a minimum value (CPimin) of an output fluctuation rate among the output fluctuation rates (CPi) of the respective cylinders is compared with a predetermined fluctuation rate determination threshold value (CPi SL) is compared. One reason why the minimum value (CPimin) is compared is that the other cylinders have a larger output fluctuation rate (CPi) (less stable combustion) than the minimum value (CPimin). In a case where the minimum value (CPimin) is larger than the fluctuation rate determination threshold (CPi SL ), it is determined that all cylinders have a combustion stability problem, and processing proceeds to step S17.

[0061] On the other hand, in a case where the output fluctuation rate minimum value (CPimin) is smaller than the fluctuation rate determination threshold value (CPi SL ), the processing to steps S13 and S14 as in Fig. 4 to execute the control parameter correction control on a cylinder having a maximum output fluctuation rate.

[0062] Because it is determined in step S16 that all cylinders exhibit low combustion stability, control parameter correction control is performed on all cylinders in step S17. This control is, for example, a correction such as reducing the air-fuel ratio of all cylinders (to a value close to the theoretical air-fuel ratio) or reducing the EGR rate of all cylinders and thereby reducing the dilution rate. Furthermore, in this case, it is desirable to give an operator a warning, for example, by illuminating a warning lamp.

[0063] In this way, even in a case where the combustion stability of all cylinders is low, correction control is performed to stabilize combustion in all cylinders, thereby maintaining the fuel efficiency, output, and exhaust gas purification performance of the internal combustion engine. In a case where the combustion stability of a specific cylinder is low, correction control is performed on that cylinder, thereby enabling the internal combustion engine as a whole to maintain high fuel efficiency.

[0064] As described above, the present invention is characterized by including an output fluctuation value calculation unit that calculates an output fluctuation value for each cylinder based on a detection result obtained by a physical quantity detection unit that detects a physical quantity that causes fluctuations in engine torque of an internal combustion engine; and a state determination unit that determines whether the internal combustion engine is in a non-steady state or a steady state based on a difference or a ratio between a first output fluctuation value of a predetermined first cylinder and a second output fluctuation value of a predetermined second cylinder calculated by the output fluctuation value calculation unit.

[0065] According to this configuration, even in a case where the operation is switched between the steady-state operation state and the non-steady-state operation state to perform combustion disturbance determination in a section that has been determined as the steady-state operation state, a combustion disturbance state of an air-fuel mixture of a cylinder can be accurately determined.

[0066] The present invention is not limited to the above embodiments and includes various modifications. For example, the above embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and they are not necessarily limited to one having all of the described elements. Furthermore, one or more elements of one embodiment may be replaced by an element of another embodiment. Furthermore, an element of one embodiment may be added to the elements of another embodiment. Moreover, the addition, deletion, or replacement of an element with respect to one or more elements of each embodiment is possible. List of reference symbols 10 Cylinder head and cylinder 11 pistons 12 Inlet valve 13 Exhaust valve 14 Fuel injection valve 15 Spark plug 16 air purifiers 17 Throttle valve 18 Inlet opening 19 Outlet opening 20 Exhaust gas purification catalyst 21 Air flow sensor 22 Pressure sensor in the cylinder 23 Crank angle sensor 24 Control unit

Claims

[1] An internal combustion engine control device comprising a controller comprising an output fluctuation value calculation unit (100) that calculates an output fluctuation value for each cylinder (10) based at least on a detection result obtained by a physical quantity detection unit that detects a physical quantity that causes fluctuations in engine torque of the internal combustion engine, and a state determination unit that determines whether the internal combustion engine is in a non-steady state or a steady state based on a difference or a ratio between a first output fluctuation value of a predetermined first cylinder and a second output fluctuation value of a second cylinder different from the first cylinder, which are calculated by the output fluctuation value calculation unit (100). [2] Internal combustion engine control device according to claim 1, wherein the state determination unit determines that the first cylinder and the second cylinder are in the steady-state operation state when the difference or ratio between the first output fluctuation value of the first cylinder and the second output fluctuation value of the second cylinder is equal to or greater than a state determination threshold; and the state determination unit determines that the first cylinder and the second cylinder are in the non-stationary operation state in a case where the difference or the ratio between the first output fluctuation value of the first cylinder and the second output fluctuation value of the second cylinder is smaller than the state determination threshold. [3] The internal combustion engine control device according to claim 1 or 2, wherein the state determination threshold is changed in accordance with at least one of an engine torque, an engine speed, an oil temperature, and a water temperature. [4] An internal combustion engine control device according to any one of claims 1 to 3, wherein the controller includes: a combustion determination region setting unit that, in a case where the state determination unit determines that the first cylinder and the second cylinder are in the steady-state operating state, sets a portion of the steady-state operating state as a combustion determination region, and a combustion disturbance determination unit that determines that the first cylinder or the second cylinder has a combustion disturbance in a case where an output fluctuation value of the first cylinder or the second cylinder calculated by the output fluctuation value calculation unit (100) is equal to or greater than a setting value in the fuel determination range set by the combustion determination range setting unit. [5] The internal combustion engine control device according to claim 4, wherein, in a case where the state determining unit determines that the first cylinder and the second cylinder are in the non-steady state, the combustion determination region setting unit sets a portion of the non-steady state as a combustion determination prohibition region. [6] An internal combustion engine control device according to any one of claims 1 to 3, wherein the controller includes: a combustion determination region setting unit that, in a case where the state determination unit determines that the first cylinder and the second cylinder are in the steady-state operating state, sets a portion of the steady-state operating state as a combustion determination region, and a control parameter correction unit that corrects a control parameter of the first cylinder or the second cylinder in a case where an output fluctuation value of the first cylinder or the second cylinder calculated by the output fluctuation value calculation unit (100) is equal to or greater than a setting value in the combustion determination range set by the combustion determination range setting unit. [7] The internal combustion engine control device according to claim 1, wherein the physical quantity detected by the physical quantity detecting unit is any one of a throttle opening degree, an intake air pressure, an air flow amount, a fuel injection amount, a maximum pressure in the cylinder, and a rotational speed. [8] An internal combustion engine control apparatus according to claim 2, wherein said physical quantity detecting unit detects an in-cylinder pressure based on a signal obtained from an in-cylinder pressure sensor (22) provided in each of said four or more cylinders. [9] Internal combustion engine control device according to claim 8, wherein the output fluctuation value calculation unit (100) calculates an output fluctuation rate which is a standard deviation of a specified mean working pressure for a predetermined combustion cycle of each of the cylinders (10), and calculates a difference or a ratio between a maximum value and a minimum value of the output fluctuation rate of each of the cylinders (10); and the state determination unit compares the difference or the ratio between the maximum value and the minimum value of the output fluctuation rate with a predetermined state determination threshold, and in a case where it is determined that the difference or the ratio between the maximum value and the minimum value of the output fluctuation rate is greater than the predetermined state determination threshold, determines that the state is the steady-state operation state, and in a case where it is determined that the difference or the ratio between the maximum value and the minimum value of the output fluctuation rate is smaller than the predetermined state determination threshold, determines that the state is the non-steady-state operation state. [10] An internal combustion engine control device according to claim 9, wherein the controller includes: a combustion determination region setting unit that, in a case where the state determination unit determines that the first cylinder and the second cylinder are in the steady-state operating state, sets a portion of the steady-state operating state as a combustion determination region, and a control parameter correction unit that corrects at least one of a fuel injection amount, a fuel injection timing, and an ignition timing of the first cylinder or the second cylinder in a case where the output fluctuation rate of the first cylinder or the second cylinder calculated by the output fluctuation value calculation unit (100) is equal to or greater than a predetermined combustion determination threshold in the combustion determination range set by the combustion range determination setting unit.

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