JP2006097588A - Control device for internal combustion engine and method for calculating air fuel ratio - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine and a method for calculating air fuel ratio capable of always calculating air fuel ratio in a combustion chamber irrespective of a type of the internal combustion engine and fuel supply timing. <P>SOLUTION: The internal combustion engine 1 burns mixture of fuel and air in the combustion chamber to generate power, and is provided with ECU 20 and a cylinder pressure sensor 15 for acquiring cylinder pressure in the combustion chamber 3. The ECU 20 calculates combustion time Tc from start of combustion in the combustion chamber 3 until substantial completion of combustion based on cylinder pressure acquired with using the cylinder pressure sensor 15 and reaches air fuel ratio AF in the combustion chamber 3 based on the calculated combustion time Tc. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control method and an air-fuel ratio calculation method for an internal combustion engine that generates power by burning a fuel / air mixture in a combustion chamber.

Conventionally, it is known that the compression stroke of an internal combustion engine follows a polytropic process, and that the polytropic index and the air-fuel ratio in the combustion chamber have a correlation with each other. Then, as a method for calculating the air-fuel ratio of the internal combustion engine using these points, a polytropic index n satisfying the relationship of P · V ⁿ = constant is obtained based on the in-cylinder pressure detected at two points during the compression stroke, and obtained. A technique for obtaining an air-fuel ratio corresponding to the obtained polytropic index n is known (for example, see Patent Document 1).

JP-A-3-23349

  However, the fuel supply timing to the combustion chamber differs depending on the type and operating conditions of the internal combustion engine, and the fuel required for a certain cycle (four strokes of intake, compression, expansion, and exhaust in the case of a four-stroke engine). Not all are supplied into the combustion chamber before the start of the compression stroke. For this reason, even if the in-cylinder pressure detected at two points during the compression stroke is used as in the conventional method, the air-fuel ratio in the combustion chamber cannot be obtained accurately. In particular, in a diesel engine or a so-called direct injection engine in which fuel is supplied to the combustion chamber after the intake stroke, there may be no fuel in the combustion chamber during the compression stroke, so the above-described conventional method is applied. That is practically difficult.

  Therefore, an object of the present invention is to provide an internal combustion engine control device and an air-fuel ratio calculation method that can always accurately calculate the air-fuel ratio in the combustion chamber regardless of the type of the internal combustion engine and the fuel supply timing.

  An internal combustion engine control apparatus according to the present invention includes an in-cylinder pressure detecting means for acquiring an in-cylinder pressure, an in-cylinder pressure in an internal combustion engine control apparatus for generating power by burning a mixture of fuel and air in a combustion chamber. Based on the in-cylinder pressure acquired using the detecting means, the combustion time calculating means for calculating the combustion time from the start of combustion in the combustion chamber until the combustion is substantially completed, and the combustion time calculating means And air-fuel ratio deriving means for deriving the air-fuel ratio in the combustion chamber based on the combustion time to be performed.

  In general, it is known that a predetermined correlation is recognized between the air-fuel ratio in the combustion chamber of the internal combustion engine and the combustion speed of the air-fuel mixture (fuel) in the combustion chamber. Further, the combustion speed of the air-fuel mixture in the combustion chamber is such that the combustion is substantially completed after the combustion is started in the combustion chamber (after the air-fuel mixture is spark-ignited or after the air-fuel mixture is compressed and ignited). It is closely related to the combustion time until. Therefore, if the correlation between the combustion speed and the air-fuel ratio is used, the correlation between the combustion time and the air-fuel ratio in the combustion chamber can be obtained. The combustion time is substantially the same after the combustion is started in the combustion chamber, regardless of the type of internal combustion engine and the fuel supply timing. It can be determined based on the in-cylinder pressure acquired until completion. Thus, as in the control device for the internal combustion engine, after determining the combustion time from the start of combustion to the substantial completion of combustion based on the in-cylinder pressure, the air-fuel ratio in the combustion chamber is calculated based on the obtained combustion time. As a result, the air-fuel ratio in the combustion chamber can always be accurately calculated regardless of the type of the internal combustion engine and the fuel supply timing.

  The combustion time calculation means obtains the theoretical heat generation amount during the combustion time based on the amount of fuel supplied to the combustion chamber, and based on the in-cylinder pressure acquired using the in-cylinder pressure detection means. It is preferable to obtain an assumed heat generation amount assumed to be generated during the combustion time, and calculate the combustion time based on the theoretical heat generation amount and the assumed heat generation amount.

  Thus, the theoretical heat generation amount during the combustion time theoretically determined based on the amount of fuel supplied to the combustion chamber, and the assumed heat generation amount during the combustion time determined based on the in-cylinder pressure, By comparing the above, it is possible to accurately obtain the combustion time.

  Further, the combustion time calculation means obtains the theoretical heat generation amount based on the previous fuel supply amount at a predetermined timing, and uses the in-cylinder pressure detection means between the start of the previous combustion and the substantial completion of the combustion. It is preferable to calculate the assumed heat generation amount based on the in-cylinder pressure acquired in this way.

  Thus, if the combustion time from when combustion is started in the combustion chamber until the combustion is substantially completed is calculated based on the previous fuel supply amount or the in-cylinder pressure acquired at the previous combustion, Well, this makes it possible to obtain a practically good air-fuel ratio in the combustion chamber.

  The control apparatus for an internal combustion engine according to the present invention corrects the air-fuel ratio closer to the target air-fuel ratio based on a deviation between the air-fuel ratio derived by the air-fuel ratio deriving means and a predetermined target air-fuel ratio. It is preferable that correction means for calculating the amount is further provided.

  As a result, the air-fuel ratio in the combustion chamber of the internal combustion engine can be controlled with high accuracy, and deviation from the target value of the air-fuel ratio at the time of transition can be satisfactorily suppressed.

An air-fuel ratio calculation method for an internal combustion engine according to the present invention includes an in-cylinder pressure detecting means for acquiring an in-cylinder pressure in a fuel chamber, and an internal combustion engine for generating power by burning a mixture of fuel and air in a combustion chamber. In the air-fuel ratio calculation method,
(A) calculating a combustion time from the start of combustion in the combustion chamber until the combustion is substantially completed based on the in-cylinder pressure acquired using the in-cylinder pressure detecting means;
And (b) deriving an air-fuel ratio in the combustion chamber based on the combustion time calculated in step (a).

  According to the present invention, it is possible to realize an internal combustion engine control apparatus and an air-fuel ratio calculation method that can always accurately calculate the air-fuel ratio in the combustion chamber regardless of the type of the internal combustion engine and the fuel supply timing.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an internal combustion engine to which a control device according to the present invention is applied. The internal combustion engine 1 shown in FIG. 1 generates power by burning a fuel / air mixture in a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. Is. Although only one cylinder is shown in FIG. 1, the internal combustion engine 1 is preferably configured as a multi-cylinder engine, and the internal combustion engine 1 of the present embodiment is configured as a four-cylinder engine, for example.

  The intake port of each combustion chamber 3 is connected to the intake pipe 5 via an intake manifold, and the exhaust port of each combustion chamber 3 is connected to the exhaust pipe 6 via an exhaust manifold. In addition, an intake valve Vi that opens and closes an intake port and an exhaust valve Ve that opens and closes an exhaust port are provided for each combustion chamber 3 in the cylinder head of the internal combustion engine 1. Each intake valve Vi and each exhaust valve Ve are opened and closed by a valve operating mechanism (not shown) having a variable valve timing function. Further, the internal combustion engine 1 has a number of spark plugs 7 corresponding to the number of cylinders, and the spark plugs 7 are disposed in the cylinder heads so as to face the corresponding combustion chambers 3.

  The intake pipe 5 is connected to a surge tank 8 as shown in FIG. An air supply pipe L1 is connected to the surge tank 8, and the air supply pipe L1 is connected to an air intake port (not shown) via an air cleaner 9. A throttle valve (electronically controlled throttle valve in this embodiment) 10 is incorporated in the middle of the supply pipe L1 (between the surge tank 8 and the air cleaner 9). On the other hand, as shown in FIG. 1, a front-stage catalyst device 11 a including a three-way catalyst and a rear-stage catalyst device 11 b including a NOx storage reduction catalyst are connected to the exhaust pipe 6.

  Further, as shown in FIG. 1, the internal combustion engine 1 has a plurality of injectors 12, and the injectors 12 are arranged in the cylinder head so as to face the corresponding combustion chambers 3. Each piston 4 of the internal combustion engine 1 is configured as a so-called deep dish top surface type, and a recess 4a is formed on the upper surface thereof. In the internal combustion engine 1, fuel such as gasoline is directly injected from each injector 12 toward the recess 4 a of the piston 4 in each combustion chamber 3 in a state where air is sucked into each combustion chamber 3. As a result, in the internal combustion engine 1, the fuel / air mixture layer is formed (stratified) in the vicinity of the spark plug 7 so as to be separated from the surrounding air layer. And stable stratified combustion can be performed.

  Each of the spark plugs 7, the throttle valve 10, the injectors 12, the valve operating mechanism and the like described above are electrically connected to an ECU 20 that functions as a control device for the internal combustion engine 1. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, etc., all not shown. Various sensors such as an air flow meter AFM for detecting the intake air amount are electrically connected to the ECU 20 via an A / D converter or the like. The ECU 20 uses the various maps stored in the storage device and the spark plug 7, the throttle valve 10, the injector 12, the valve operating mechanism, etc. so as to obtain a desired output based on the detection values of various sensors. To control.

  As shown in FIG. 1, the crank angle sensor 14 is included in the sensors connected to the ECU 20. The crank angle sensor 14 is a magnetic sensor or a photoelectric sensor including a rotor plate (signal plate) fixed to the crankshaft, and the like, and provides a pulse signal indicating the rotation angle of the crankshaft to the ECU 20 every minute time. Further, the internal combustion engine 1 has in-cylinder pressure sensors (in-cylinder pressure detecting means) 15 including a semiconductor element, a piezoelectric element, an optical fiber detection element, or the like, corresponding to the number of cylinders. Each in-cylinder pressure sensor 15 is disposed on the cylinder head so that the pressure receiving surface faces the corresponding combustion chamber 3, and is electrically connected to the ECU 20 via an A / D converter (not shown). . Each in-cylinder pressure sensor 15 outputs a voltage signal (a signal indicating a detection value) corresponding to the pressure (in-cylinder pressure) applied to the pressure receiving surface in the combustion chamber 3. The detection value of each in-cylinder pressure sensor 15 is sequentially given to the ECU 20 every predetermined time (predetermined crank angle), corrected to an absolute pressure, and stored and held in a predetermined storage area (buffer) of the ECU 20 by a predetermined amount. . In the present invention, the in-cylinder pressure sensor 15, the ECU 20, and the like constitute an air-fuel ratio calculation device that calculates the air-fuel ratio in the combustion chamber 3 of the internal combustion engine 1.

  Next, a procedure for calculating the air-fuel ratio in each combustion chamber 3 of the internal combustion engine 1 will be described with reference to FIGS.

When the internal combustion engine 1 is started and a predetermined number of cycles (four strokes of intake, compression, expansion, and exhaust) are completed, the ECU 20 starts executing the air-fuel ratio calculation routine shown in FIG. Calculate the air-fuel ratio. When this routine is started, the ECU 20 first determines whether or not the exhaust valve Ve is opened for each combustion chamber 3 (whether an exhaust stroke is started) (S10). When the ECU 20 determines that the exhaust valve Ve is opened in the combustion chamber 3 in S10, the ignition timing (crank angle corresponding to the previous ignition timing) θ _SA immediately before the exhaust valve Ve in the combustion chamber 3 is opened. , the fuel injection time of the immediately preceding the opening of the exhaust valve Ve reading the τ and previous target air-fuel ratio AF _T (fuel injection time last) from a predetermined storage area (S12).

After the process of S12, the ECU 20 generates theoretical heat, which is a theoretical value of the amount of heat generated in the combustion chamber 3 between the previous ignition and the substantial completion of combustion based on the acquired previous fuel injection time τ. to calculate the amount _{Q T} (S14). In this case, the theoretical heat generation amount Q _T is expressed as the following equation (1), where q is the lower heating value of the fuel and f is the fuel injection amount per unit time of the injector 12. However, in the formula (1), α is a coefficient considering loss, unburned fuel, and the like, and the value is obtained empirically and experimentally (for example, 70 to 80%).

When the theoretical heat generation amount Q _T is obtained, the ECU 20 starts from the predetermined storage area until the exhaust valve Ve is opened from the previous ignition timing θ _SA (the crank angle when the exhaust valve Ve is opened is θ _EVO ). ), P (θ _SA ),..., P (θ),..., P (θ _EVO ) indicating the in-cylinder pressure acquired during (). Furthermore, ECU 20 uses the following equation (2), calculates the heat generation rate dQ / d [theta] for theta each crank angle from the ignition timing theta _SA at every predetermined crank angle d [theta] (S18). However, in equation (2), κ is a specific heat ratio, and V (θ) is an in-cylinder volume when the crank angle becomes θ, and is calculated in advance for each crank angle and then stored in the storage device. Is remembered.

When the heat generation rate dQ / dθ is calculated for a certain crank angle in S18, the ECU 20 sequentially accumulates the calculated heat generation rates dQ / dθ, thereby assuming the assumed heat generated in the combustion chamber 3 after the previous ignition. determine the amount of generated Q _a (S20), whether the absolute value of the deviation of the calculated theoretical heat release amount Q _T and assumed heat generation amount Q _a at S14 is held below a predetermined threshold epsilon, i.e., assuming obtained It determines whether the heat generation amount _{Q a} is approximately equal to the theoretical heat generation amount _{Q T} calculated in S14 (S22). ECU20 until it determines that the assumed heat generation amount _{Q A} is approximately equal to the theoretical heat generation amount _{Q T} at S22, it repeats the processing of S18 and S20, at the stage of performing a positive determination in S22, assuming heat generation The crank angle θ _T at the time when the amount Q _A becomes substantially equal to the theoretical heat generation amount Q _T , that is, when combustion is substantially completed is obtained (S24). Then, ECU 20 includes a crank angle theta _T obtained in S24, based on the preceding ignition timing theta _SA acquired in S12, the burn time Tc is the time from the preceding ignition until substantial combustion completion Tc = θ _T −θ _SA
(S26).

  Incidentally, it is generally known that a correlation as shown in FIG. 3 is recognized between the air-fuel ratio in the combustion chamber of the internal combustion engine and the combustion speed of the air-fuel mixture (fuel) in the combustion chamber. The combustion speed of the air-fuel mixture in the combustion chamber is closely related to the combustion time Tc from the start of combustion in the combustion chamber until the combustion is substantially completed. Therefore, the correlation between the combustion time Tc and the air-fuel ratio AF in the combustion chamber can be experimentally obtained by utilizing the correlation between the combustion speed and the air-fuel ratio in FIG. In consideration of such points, in the internal combustion engine 1, an air-fuel ratio map that prescribes a correlation between the combustion time Tc and the air-fuel ratio AF in the combustion chamber as shown in FIG. Stored in Then, after the process of S24, the ECU 20 reads out the air-fuel ratio AF corresponding to the combustion time Tc obtained in S24 from the air-fuel ratio map (S28).

Here, the combustion time Tc from the start of combustion in the combustion chamber 3 by ignition of the spark plug 7 until the combustion is substantially completed is based on the previous fuel injection time τ as described above. Calculated based on the theoretical heat generation amount Q _T during the combustion time Tc theoretically obtained and the in-cylinder pressure obtained using the in-cylinder pressure sensor 15 between the previous ignition and the substantial completion of combustion. by comparing the assumed heat generation amount Q _a that, the form and the internal combustion engine such as gasoline engines and diesel engines, regardless of the fuel supply timing such intake stroke injection and after TDC injection, which can precisely obtain Is. Therefore, after obtaining the combustion time Tc based on the in-cylinder pressure by the processing from S12 to S26, and obtaining the air-fuel ratio AF corresponding to the combustion time Tc from the air-fuel ratio map, the type of the internal combustion engine and the fuel supply Regardless of the timing, the air-fuel ratio in the combustion chamber 3 can always be obtained with high accuracy.

When determining the air-fuel ratio AF in the combustion chamber 3 at S28, ECU 20 is the absolute value of the deviation between the air-fuel ratio AF determined by the target air-fuel ratio AF _T and S28 obtained in S12 is a predetermined tolerance δ above and or going on, i.e., it determines whether or not the air-fuel ratio AF determined deviates more than a predetermined amount from the target air-fuel ratio AF _T (S30). Injector ECU20 is in accordance with the deviation of the absolute value of the deviation between the target air-fuel ratio AF _T and the air-fuel ratio AF at S32, it is determined that the predetermined tolerance δ above, the target air-fuel ratio AF _T and the air-fuel ratio AF A correction amount of 12 fuel injection times is set (S32). This makes it possible to control the air-fuel ratio AF in the combustion chamber 3 of the internal combustion engine 1 with high accuracy, it is possible to favorably suppress the deviation from the target air-fuel ratio AF _T of the air-fuel ratio AF in the transient or the like. In S32, a correction amount for the opening degree of the throttle valve 10 may be set together with the fuel injection time correction amount or instead of the fuel injection time correction amount. After executing the process of S32 or making a negative determination in S30, the ECU 20 repeatedly executes the processes after S10.

  A plurality of air-fuel ratio maps used in S28 may be created according to the load of the internal combustion engine 1. As described above, when a plurality of air-fuel ratio maps corresponding to loads are used, the map is obtained after obtaining the load of the internal combustion engine 1 based on the opening degree of the throttle valve 10 and the like before S28 in FIG. The map corresponding to the loaded load may be read out. Moreover, although the internal combustion engine 1 of this embodiment was demonstrated as what is called a direct injection engine, it is not restricted to this, It cannot be overemphasized that this invention can be applied to an internal combustion engine of an intake pipe (port) injection type. Nor. Furthermore, it goes without saying that the present invention can be applied to a diesel engine.

It is a schematic block diagram which shows the internal combustion engine to which the control apparatus by this invention was applied. 2 is a flowchart for illustrating an air-fuel ratio calculation routine executed in the internal combustion engine of FIG. It is a graph which shows the correlation with the combustion speed of the air-fuel | gaseous mixture in a combustion chamber, and the air fuel ratio in a combustion chamber. It is a graph which shows the correlation of the combustion time after the combustion is started in a combustion chamber until the said combustion is substantially completed, and the air fuel ratio in a combustion chamber.

Explanation of symbols

1 Internal combustion engine 3 Combustion chamber 4 Piston 7 Spark plug 12 Injector 14 Crank angle sensor 15 In-cylinder pressure sensor 20 ECU
Ve Exhaust valve Vi Intake valve

Claims (5)

In a control device for an internal combustion engine that generates power by burning a mixture of fuel and air in a combustion chamber,
In-cylinder pressure detecting means for acquiring the in-cylinder pressure;
A combustion time calculating means for calculating a combustion time from when combustion is started in the combustion chamber until the combustion is substantially completed based on an in-cylinder pressure acquired using the in-cylinder pressure detecting means;
An internal combustion engine control device comprising: an air-fuel ratio deriving unit that derives an air-fuel ratio in the combustion chamber based on the combustion time calculated by the combustion time calculating unit.   The combustion time calculating means obtains the theoretical heat generation amount during the combustion time based on the amount of fuel supplied to the combustion chamber, and calculates the in-cylinder pressure obtained using the in-cylinder pressure detecting means. The calculated heat generation amount assumed to be generated during the combustion time is obtained based on the theoretical heat generation amount and the assumed heat generation amount, and the combustion time is calculated on the basis of the theoretical heat generation amount. Control device for internal combustion engine.   The combustion time calculating means obtains the theoretical heat generation amount based on the previous fuel supply amount at a predetermined timing, and the in-cylinder pressure detecting means between the start of the previous combustion and the substantial completion of the combustion. The control apparatus for an internal combustion engine according to claim 2, wherein the assumed heat generation amount is calculated based on the in-cylinder pressure acquired by using the in-cylinder pressure.   Further provided is a correction means for calculating a correction amount for bringing the air-fuel ratio closer to the target air-fuel ratio based on a deviation between the air-fuel ratio derived by the air-fuel ratio deriving means and a predetermined target air-fuel ratio. The control apparatus for an internal combustion engine according to any one of claims 1 to 3. In a method for calculating an air-fuel ratio of an internal combustion engine, comprising an in-cylinder pressure detecting means for acquiring an in-cylinder pressure in a fuel chamber, and generating a power by burning a fuel / air mixture in the combustion chamber,
(A) calculating a combustion time from the start of combustion in the combustion chamber until the combustion is substantially completed based on the in-cylinder pressure acquired using the in-cylinder pressure detecting means;
And (b) deriving an air-fuel ratio in the combustion chamber based on the combustion time calculated in step (a).

Images