JP5257777B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine that controls ignition timing using the pressure in a combustion chamber detected by an in-cylinder pressure sensor.

  Patent Document 1 detects the in-cylinder pressure of an internal combustion engine, calculates a state quantity reflecting the combustion state at each time point in the combustion chamber based on the detected value, and determines torque fluctuation or misfire based on the state quantity. A technique is disclosed in which at least one of the ratio determinations is performed, and the internal combustion engine is controlled by changing the ignition timing based on the determination result.

  Further, Patent Document 2 detects the in-cylinder pressure in the combustion chamber in each combustion cycle of the internal combustion engine, and at each time point with respect to the total heat generation amount generated from the start of combustion to the end of combustion based on this in-cylinder pressure. A technique is disclosed in which a combustion rate (MFB) composed of a rate of heat generation is calculated, and operating conditions such as ignition timing are changed so that the combustion rate at a predetermined crank angle becomes a target value.

  In order to execute precise ignition timing control in the combustion stroke as described above, the performance of the spark plug that greatly affects the stability of combustion is important. As the wear deterioration of the spark plug progresses, it is difficult to stabilize the combustion, which may cause misfire.

  For this reason, in order to realize precise ignition timing control or the like, a technique for detecting deterioration of the spark plug on board is important.

Patent Document 3 discloses that the in-cylinder pressure P and the in-cylinder volume V when the in-cylinder pressure P is detected are raised to a predetermined index at measurement points determined in a predetermined period from the start of combustion to after the start of combustion. and to calculate the product P · V ^kappa and value, calculates a difference [Delta] P · V ^kappa of P · V ^kappa between two points of these, when the integrated value exceeds a predetermined value, misfire Disclosed is a technique for determining that it has occurred.

JP 2007-285194 A JP 2006-220139 A JP 2006-70885 A

  However, even if the misfire determination technique as described above is used, it cannot be specified whether the cause of the misfire is due to wear deterioration of the spark plug.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a control device for an internal combustion engine that can detect deterioration of a spark plug and can perform precise ignition timing control.

  The control apparatus for an internal combustion engine according to the present invention is based on the in-cylinder pressure detected by the in-cylinder pressure sensor provided in the cylinder of the internal combustion engine at each time point with respect to the total heat generation amount generated from the start of combustion to the end of combustion. A control device for an internal combustion engine having an ignition timing control means for calculating a combustion ratio, which is a ratio of a heat generation amount, and controlling an ignition timing of the internal combustion engine based on the combustion ratio, and executing the ignition timing control means Based on the change rate calculation means for calculating the rate of change of the combustion rate near the crank angle when the combustion rate reaches a predetermined value during the combustion stroke, and the change over time of the rate of change of the combustion rate, And a spark plug deterioration determining means for determining deterioration of a spark plug provided in the cylinder.

  In the above-described configuration, the ignition plug deterioration determining means is configured to end the combustion of the state quantity reflecting the change over time in the change rate of the combustion ratio and the amount of heat generated in the cylinder used when calculating the combustion ratio. A configuration in which deterioration of a spark plug provided in the cylinder is determined based on a value near the hour can be adopted.

  In the above configuration, when the spark plug deterioration determining means determines that the spark plug provided in the cylinder has not deteriorated based on the value of the state quantity near the end of combustion, the in-cylinder pressure sensor It is possible to adopt a configuration in which it is determined that the sensitivity in the high pressure region is abnormal.

  According to the present invention, the deterioration of the spark plug can be detected, and the ignition timing control of the internal combustion engine using the in-cylinder pressure can be executed more precisely.

1 is a configuration diagram illustrating an example of an internal combustion engine to which a control device according to an embodiment of the present invention is applied. It is a graph which shows the example of a correlation with product value PV (kappa) and the amount of heat generation in a combustion chamber. It is a graph which shows the correlation example of the combustion rate calculated | required based on product value PV ( ^kappa) , and the combustion rate calculated ^| required based on a heat release rate. It is a figure for demonstrating the influence of deterioration of a spark plug with respect to the combustion rate MFB. It is a graph which shows an example of "burning speed" when a spark plug is normal and it deteriorates. It is a figure for demonstrating the calculation method of "burning speed." It is a flowchart which shows an example of the ignition plug deterioration detection process by ECU. It is a graph which shows a time-dependent change of "burning speed." It is a figure for demonstrating the sensitivity fall in the high pressure area | region of a cylinder pressure sensor. It is a graph which shows an example of the output of the in-cylinder pressure sensor in the vicinity of the combustion stroke when the in-cylinder pressure sensor is normal and abnormal. It is a graph which shows an example of the combustion ratio MFB in the normal time of a cylinder pressure sensor, and the time of abnormality. It is a graph which shows an example of the "combustion speed" in the normal time of a cylinder pressure sensor, and the time of abnormality. It is a graph which shows an example of PV (kappa) at the time of normal and deterioration of a spark plug. It is a graph which shows an example of PV (kappa) at the time of normal and deterioration of a cylinder pressure sensor. It is a flowchart which shows the other example of the spark plug deterioration detection process by ECU.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First Embodiment FIG. 1 is a schematic configuration diagram showing an example of an internal combustion engine to which a control device for an internal combustion engine according to an embodiment of the present invention is applied.

  This internal combustion engine generates power by burning a mixture of fuel and air in a combustion chamber 14 of a cylinder 12 formed in a main body 10 and reciprocating a piston 16 in the cylinder 12.

  An intake port formed in the cylinder head of the internal combustion engine and facing each combustion chamber 14 is connected to an intake pipe (including an intake manifold) 18. Further, the exhaust ports formed in the cylinder head and facing each combustion chamber 14 are connected to an exhaust pipe (including an exhaust manifold) 20 respectively. The cylinder head is provided with an intake valve Vi and an exhaust valve Ve. Each intake valve Vi opens and closes a corresponding intake port, and each exhaust valve Ve opens and closes a corresponding exhaust port. Each intake valve Vi and each exhaust valve Ve are operated by a variable valve mechanism, for example, a valve mechanism (not shown) having a variable valve timing function.

  The internal combustion engine includes spark plugs 22 and direct fuel injectors 36 corresponding to the number of cylinders, and the spark plugs 22 and direct fuel injectors 36 are disposed in the cylinder head so as to face the corresponding combustion chambers 14. Has been. The spark plug 22 is in response to a control command from an electronic control unit (ECU) 100, which will be described later, and the fuel / air mixture fuel direct injection injector 36 is charged with gasoline in the combustion chamber 14 in response to a control command from the ECU 100. Etc. Fuel is directly injected.

  The internal combustion engine of the present embodiment is a so-called direct injection internal combustion engine, but is not limited to this, and the present invention can also be applied to a so-called port injection type gasoline engine.

  The intake pipe 18 is connected to the surge tank 24. An air flow meter 30 is incorporated in the surge tank 24, and an air supply line (intake pipe) is connected to the surge tank 24. The air supply line is connected to an air intake port (not shown) via an air cleaner 26. . A throttle valve (in this embodiment, an electronically controlled throttle valve) 28 is provided midway in the air supply line (between the surge tank 24 and the air cleaner 26). On the other hand, the exhaust pipe 20 is provided with a catalyst device, and is provided with a front-stage catalyst device 32 including a three-way catalyst and a rear-stage catalyst device 34 including a NOx storage reduction catalyst.

  Each cylinder 12 of the internal combustion engine is provided with an in-cylinder pressure sensor 50. The in-cylinder pressure sensor 50 includes, for example, a semiconductor element, a piezoelectric element, an optical fiber detection element, and the like, generates an electrical signal corresponding to the pressure in the combustion chamber 14 (in-cylinder pressure), and outputs this to the ECU 100. The installation position of the in-cylinder pressure sensor 50 is not limited to the position shown in FIG.

  A crank angle sensor 42 for detecting a crank angle is provided in the crankcase portion of the main body 10.

  A knock sensor 40 for detecting the occurrence of knocking is provided on the wall surface defining the cylinder 12 of the main body 10.

  The ECU 100 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a backup memory such as an EEPROM (Electronically Erasable and Programmable Read Only Memory), an A / D converter, a buffer, and the like. It comprises hardware including an output interface circuit including an input interface circuit, a drive circuit, etc., and necessary software. The ECU 100 receives signals from the air flow meter 30, knock sensor 40, crank angle sensor 42, and in-cylinder pressure sensor 50, and based on these signals, the spark plug 22, the throttle valve 28, and the direct fuel injector 36 are supplied to the ECU 100. By giving a control command, ignition timing control, fuel injection control, air-fuel ratio control, etc. can be executed.

  Further, the internal combustion engine 10 has a number of in-cylinder pressure sensors 50 including semiconductor elements, piezoelectric elements, optical fiber detection elements, and the like corresponding to the number of cylinders. Each in-cylinder pressure sensor 50 is disposed on the cylinder head so that the pressure receiving surface faces the corresponding combustion chamber 14, and is electrically connected to the ECU 38. Each in-cylinder pressure sensor 50 gives a sensor output signal corresponding to the detected value to the ECU 38 so as to detect the in-cylinder pressure (relative pressure) in the corresponding combustion chamber 14. Sensor output signals from the in-cylinder pressure sensors 50 are sequentially given to the ECU 38 at predetermined time intervals (predetermined crank angles) and converted into detection values that are absolute pressure values, for example, and then a predetermined storage area (buffer) of the ECU 38. Is stored and held by a predetermined amount. The in-cylinder pressure detection means includes an in-cylinder pressure sensor 50 as a detection unit and a part of the ECU 38 as a calculation unit.

  Next, an example of ignition timing control by the ECU 100 will be described with reference to FIGS.

  Here, the cylinder pressure detected or estimated by the cylinder pressure sensor 50 at the timing when the crank angle is θ is P (θ), and the timing when the crank angle is θ (when the cylinder pressure P (θ) is detected). Alternatively, the in-cylinder volume at the time of estimation is V (θ), and the specific heat ratio is κ. A product value P (θ) · Vκ (θ) (hereinafter, referred to as a value V (θ) obtained by raising the in-cylinder pressure P (θ) and the in-cylinder volume V (θ) to a power of a specific heat ratio (predetermined index) κ. The combustion ratio is calculated by paying attention to “PVκ” as appropriate. This PVκ is a state quantity that reflects the amount of heat generated in the cylinder.

  The change pattern of the heat generation amount Q in the combustion chamber of the internal combustion engine with respect to the crank angle and the change pattern of the product value PVκ with respect to the crank angle are, for example, as shown in FIG. It is known to have a correlation. In FIG. 2, the solid line shows the in-cylinder pressure detected at predetermined minute crank angles in a predetermined model cylinder, and the value obtained by raising the in-cylinder volume at the time of detection of the in-cylinder pressure by a predetermined specific heat ratio κ. The product value PVκ is plotted. In FIG. 2, the broken line indicates the heat generation amount Q in the model cylinder based on the following equation (1):

As calculated and plotted. In either case, for simplicity, κ = 1.32. In FIG. 2, −360 °, 0 ° and 360 ° are top dead centers (when the piston is located at the top dead center), and −180 ° and 180 ° are bottom dead centers (the piston is located at the bottom dead center). Corresponding to).

  As can be seen from the results shown in FIG. 2, the change pattern of the heat generation amount Q with respect to the crank angle and the change pattern of the product value PVκ with respect to the crank angle substantially coincide (similar). In particular, before and after the start of combustion of the air-fuel mixture in the cylinder (at the time of spark ignition for a gasoline engine, and at the time of compression ignition for a diesel engine) (for example, a range from about -180 ° to about 135 ° in FIG. 2), FIG. It is understood that both patterns match very well.

  Based on the product value PVκ of the in-cylinder pressure detected by the in-cylinder pressure sensor 50 and the in-cylinder volume at the time of detection of the in-cylinder pressure, using the correlation between the heat generation amount Q in the combustion chamber and the product value PVκ. Thus, a combustion ratio MFB that is a ratio of the heat generation amount between the two points up to a predetermined timing (heat generation amount ratio) with respect to the total heat generation amount between the two points is obtained (measured). Here, if the combustion ratio in the combustion chamber is calculated based on the product value PVκ, the combustion ratio in the combustion chamber can be obtained with high accuracy without requiring high-load calculation processing. That is, as shown in FIG. 3, the combustion rate obtained based on the product value PVκ (see the solid line in the figure) substantially matches the combustion rate obtained based on the heat generation rate (see the broken line in the figure).

  In FIG. 3, the solid line represents the combustion ratio at the timing when the crank angle = θ in the model cylinder described above, according to the following equation (2) and based on the detected in-cylinder pressure P (θ), It is a plot. However, for simplicity, κ = 1.32. In FIG. 3, the broken line indicates the in-cylinder pressure P (θ) in accordance with the above equation (1) and the following equation (3) and the combustion ratio at the timing when the crank angle = θ in the above model cylinder. Calculated based on the above and plotted. Also in this case, for simplicity, κ = 1.32.

  Here, an example in which two timings of 120 ° before compression top dead center (simply −120 ° in equation (2)) and 120 ° after compression top dead center (simply 120 ° in equation (2)) are adopted. The calculation of the combustion ratio focused on PVκ was explained. However, they may be at other timings, such as 60 ° before compression top dead center to eliminate the effects of ignition noise, and 60 ° after compression top dead center to cover all combustion modes. Can be °.

  The ECU 100 calculates the above-described combustion ratio MFB at every sampling time, and uses this to calculate the spark ignition timing of the air-fuel mixture in the combustion chamber of the internal combustion engine at an optimal timing (MBT: Ignition timing control of the spark plug 22 for setting to “Minimum advance for Best Torque” is executed. Specifically, the ECU 100 controls the ignition timing of the spark plug 22 so that the combustion ratio MFB at a predetermined crank angle (for example, 10 degrees) becomes a target value (for example, 50%). Hereinafter, this ignition timing control is referred to as MBT control.

  Next, the deterioration detection principle of the spark plug according to the present embodiment will be described with reference to FIGS.

  Here, FIG. 4 is a diagram for explaining the influence of the deterioration of the spark plug on the combustion rate MFB, and FIG. 5 is an example of the change rate (burning rate) of the combustion rate when the spark plug is normal and when the spark plug is deteriorated. FIG. 6 is a diagram for explaining a method for calculating the rate of change of the combustion ratio (combustion speed).

  As shown in FIG. 4, when the spark plug 22 is normal (1) and when the ignition characteristics are deteriorated due to electrode wear or the like (2), the slope of the rise of the combustion ratio MFB during the combustion stroke is compared. It can be seen that the case (2) becomes smaller than the case (1) where the deterioration is normal. In FIG. 4, the crank angle θc is a crank angle at the combustion center G where the value of the combustion ratio MFB is 50%.

  FIG. 5 is a value obtained by differentiating the combustion rate MFB with respect to θ when the spark plug 22 is normal (1) and when it is deteriorated (2) shown in FIG. 4, that is, the change rate of the combustion rate MFB. is there. Hereinafter, the rate of change of the combustion rate MFB is referred to as “burning rate”. For example, the combustion speed CS near the crank angle θc is calculated by the equation (A) shown in FIG.

In FIG. 5, CS ₀ is an initial value of the combustion speed CS at which the spark plug 22 is normal, and CS _n is a combustion speed CS at which the spark plug 22 has deteriorated after n-trip travel. Comparing these, it can be seen that when the spark plug 22 deteriorates, the value of the combustion rate CS decreases.

  In the present invention, when the spark plug 22 is deteriorated, the combustion rate MFB is a rate of change of the combustion rate MFB in the vicinity of the crank angle θc when the combustion rate MFB during the combustion stroke reaches a predetermined value (for example, 50%). The deterioration of the spark plug 22 is determined on the basis of the change.

The time-dependent change in the value of the combustion speed CS is, for example, that the value of the combustion speed CS in the vicinity of the crank angle θc is calculated every trip for a predetermined period or a predetermined distance (for example, 10,000 kilometers), and the initial value CS ₀ is calculated. In contrast, it means how much the value of the current combustion rate CS has changed.

Therefore, for example, based on how much the value of the current combustion speed CS has decreased with respect to the initial value CS ₀ or the previously calculated combustion speed CS, it is determined whether or not the spark plug 22 has deteriorated. Judgment can be made. This is the ignition plug deterioration detection principle in the present invention.

  Next, an example of the deterioration detection process of the spark plug 22 by the ECU 100 will be described with reference to a flowchart shown in FIG. Note that the deterioration detection routine 1 of the spark plug 22 shown in FIG. 7 is executed, for example, every predetermined time.

  Next, it is determined whether the current trip distance T has reached a predetermined distance n (step S1). Note that n is, for example, 0, 1, 2, 3,. . . It is set as [10,000 km].

  Next, the MBT control is turned on, ignition timing control based on the combustion ratio MFB is executed (step S2), the valve overlap of the variable valve mechanism is made zero (step S3), and a part of the exhaust gas is reintroduced into the intake system. The EGR valve of the EGR system to be circulated is closed (step S4). Note that the processing in steps S3 and S4 is for performing MBT control under operating conditions where combustion does not slow down in order to calculate the combustion rate CS.

Next, the combustion rate CS _n is calculated (step S5). The combustion rate CS _n is calculated from the equation (A) described with reference to FIG. The initial value CS ₀ is calculated and stored when the processing routine is first executed.

Next, it is determined whether the ratio (CS _n / CS ₀ ) between the combustion speed CS _n and the initial value CS ₀ is equal to or less than a predetermined value α (step S6). That is, as shown in FIG. 8, when the spark plug 22 is normal, the ratio (CS _n / CS ₀ ) is close to 1, but decreases as the deterioration of the spark plug 22 proceeds. When the ratio (CS _n / CS ₀ ) falls below a predetermined value α (a predetermined value from 0 to 1), it is determined that the spark plug 22 has deteriorated (step S7). If the ratio (CS _n / CS ₀ ) is greater than the predetermined value α, it is determined that the spark plug 22 has not deteriorated, and the process is terminated.

The in- cylinder pressure sensor 50 used for the second embodiment MBT control, for example, as shown in FIG. 9, is less susceptible to lowering of sensitivity in a region where the in-cylinder pressure is relatively low, but the sensitivity deteriorates over time as the in-cylinder pressure increases. There is a tendency to decrease. If the sensor sensitivity decreases in the high pressure region, it becomes difficult to perform precise ignition timing control in the combustion stroke.

When the sensor sensitivity decreases in the high pressure region of the in-cylinder pressure sensor 50, for example, as shown in FIG. 10, the peak value of the in-cylinder pressure in the combustion stroke is decreased. When such a decrease in sensitivity occurs in the high pressure region, the combustion ratio MFB has a small gradient near the combustion center of gravity G, as shown in FIG. Accordingly, as shown in FIG. 12, the combustion speed at the crank angle θc decreases from CS ₀ at normal time (1) to CS _n at abnormal sensitivity (2). That is, the combustion ratio MFB and the combustion speed CS when the sensor sensitivity is reduced in the high pressure region of the in-cylinder pressure sensor 50 have the same tendency as when the spark plug 22 is deteriorated. Therefore, when the above-described spark plug deterioration detection method is used, when the sensor sensitivity is abnormal in the high pressure region of the in-cylinder pressure sensor 50, the spark plug 22 is deteriorated even though the spark plug 22 is normal. May be mistakenly determined to be.

Here, in the present embodiment, the case where the sensitivity is abnormal in the high pressure region of the in-cylinder pressure sensor 50 and the case where the spark plug 22 is deteriorated are near the calculation end point of the combustion ratio MFB, that is, in the combustion stroke. A distinction is made based on the value of PV ^κ near the end of combustion.

Here, FIG. 13 is a graph showing an example of a PV ^kappa during degradation and normal of the spark plug 22, FIG. 14 is a graph showing an example of a PV ^kappa during degradation and normal in-cylinder pressure sensor.

In FIG. 13, it can be seen that PV ^κ near the calculation end point of the combustion ratio MFB, that is, near the end of combustion in the combustion stroke, takes a larger value at the time of deterioration (2) than at the time of normal (1). This is because when the ignition plug 22 is deteriorated, the combustion in the cylinder becomes slow and the combustion time becomes long, so that the accumulated heat amount (ΔPV ^κ ) generated in the cylinder becomes relatively large.

On the other hand, in FIG. 14, in the vicinity of the calculation end point of the combustion ratio MFB, that is, PV ^κ near the end of combustion in the combustion stroke, a sensitivity abnormality occurs in the high pressure region when the in-cylinder pressure sensor 50 is normal (1). In case (2), it is almost the same. This is because even if there is an abnormality in the sensitivity of the in-cylinder pressure sensor 50, the combustion time does not increase.

  In the present embodiment, the case where the sensitivity is abnormal in the high pressure region of the in-cylinder pressure sensor 50 is distinguished from the case where the spark plug 22 is deteriorated by utilizing the difference in characteristics shown in FIGS. 13 and 14. .

  Hereinafter, spark plug deterioration detection processing using this principle will be described with reference to the flowchart shown in FIG.

  In FIG. 15, the processing in steps S11 to S16 is the same as the processing in steps S1 to S6 described in the flowchart of FIG.

In step S17, ΔPV ^κ _n corresponding to the amount of heat generated from the start of combustion to the end of combustion, which is used in the denominator of equation (2), is acquired.

Then, the ratio of the initial value Pv ^kappa ₀ and Pv ^kappa _n of _{^{ΔPV κ (ΔPV κ n / ΔPV}} κ 0) is determined greater than the predetermined value beta (Step S18). The predetermined value β is a value larger than 1 and is set as appropriate.

When the spark plug 22 is deteriorated, the value of ΔPV ^κ _n is larger than the initial value ΔPV ^κ ₀ , so the ratio (ΔPV ^κ _n / ΔPV ^κ ₀ ) is larger than 1, and the predetermined value β is set. If exceeded, it is determined that the spark plug 22 has deteriorated (step S19).

On the other hand, when the sensitivity in the high pressure region of the in-cylinder pressure sensor 50 is abnormal, the value of ΔPV ^κ _n is substantially the same as the initial value ΔPV ^κ _0, and the ratio (ΔPV ^κ _n / ΔPV ^κ ₀ ) is a value in the vicinity of 1. Since the value is smaller than the predetermined value β, it is determined that the sensitivity in the high pressure region of the in-cylinder pressure sensor 50 is abnormal (step S20).

  In this embodiment, in step S16, it is determined whether or not the spark plug 22 has deteriorated. Further, in step S18, the deterioration of the spark plug 22 and the sensitivity abnormality in the high pressure region of the in-cylinder pressure sensor 50 are distinguished. 22 deterioration detection can be performed more accurately. In addition, an abnormality in sensitivity in the high pressure region of the in-cylinder pressure sensor 50 can be detected.

DESCRIPTION OF SYMBOLS 10 ... Main body 12 ... Cylinder 14 ... Combustion chamber 16 ... Piston 18 ... Intake pipe 20 ... Exhaust pipe Vi ... Intake valve Ve ... Exhaust valve 22 ... Spark plug 24 ... Surge tank 36 ... Direct fuel injection injector 50 ... In-cylinder pressure sensor 100 ... Electronic control unit (ECU)

Claims (3)

Based on the in-cylinder pressure detected by the in-cylinder pressure sensor provided in the cylinder of the internal combustion engine, the combustion ratio that is the ratio of the heat generation amount at each time point to the total heat generation amount generated from the start of combustion to the end of combustion is calculated. An internal combustion engine control device having ignition timing control means for controlling the ignition timing of the internal combustion engine based on the combustion ratio,
A change rate calculating means for calculating a change rate of the combustion ratio in the vicinity of a crank angle when the combustion ratio reaches a predetermined value during a combustion stroke during execution of the ignition timing control means;
A control device for an internal combustion engine, comprising: an ignition plug deterioration determination unit that determines deterioration of an ignition plug provided in the cylinder based on a change with time of the change rate of the combustion ratio. The spark plug deterioration determining means includes a change with time in the change rate of the combustion rate, and
Deterioration of a spark plug provided in the cylinder is determined based on a value in the vicinity of the end of combustion of a state quantity reflecting the amount of heat generated in the cylinder used when calculating the combustion ratio. The control apparatus for an internal combustion engine according to claim 1.   When the spark plug deterioration determining means determines that the spark plug provided in the cylinder has not deteriorated based on the value of the state quantity in the vicinity of the end of combustion, the spark plug deterioration determining means The control device for an internal combustion engine according to claim 2, wherein the sensitivity is determined to be abnormal.

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