JP2008121582A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve improvement both in fuel economy and emission by executing ignition energy control and air fuel ratio control by appropriately using both of them as the situation demands. <P>SOLUTION: In a control unit (ECU60) for an internal combustion engine 1 provided with an air fuel ratio control means controlling air fuel ratio and an ignition energy control means controlling ignition energy and constructed in such a manner that lean burn operation is available, air fuel ratio control or ignition energy control of spark plugs are selected and executed according to torque fluctuation to inhibit fluctuation in lean burn operation. The fluctuation is inhibited by ignition energy control in a normal condition where torque fluctuation is a predetermined value or less, and torque fluctuation is inhibited by air fuel ratio control in a condition where torque fluctuation exceeds the predetermined value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine that includes an air-fuel ratio control unit that controls an air-fuel ratio and an ignition energy control unit that controls ignition energy, and is configured to be capable of lean burn operation. The present invention relates to a control device for an internal combustion engine that can achieve both improvement in fuel consumption and emission by appropriately performing air-fuel ratio control.

  In recent years, in order to further improve the fuel consumption of an internal combustion engine, various techniques for reducing the energy used for an actuator for controlling the internal combustion engine have been proposed. A technique for changing the ignition energy is well known.

  That is, for example, when a fluctuation in the rotational speed of an internal combustion engine is detected, a technique has been proposed that includes ignition correction means that corrects the ignition start timing and ignition energization time (ignition energy) according to the rotational speed (for example, , See Patent Document 1).

  Further, a technique has been proposed in which the ignition timing and the primary current energization time of the ignition coil are controlled according to the rotational fluctuation when the rotational fluctuation of the internal combustion engine is large (see, for example, Patent Document 2).

  In addition, in order to give ignition energy sufficient for complete combustion of the air-fuel mixture, the fluctuation rate of the time or angle during which the ionic current continues is calculated, and the fluctuation rate is set in advance according to the operating state of the internal combustion engine. A technique for controlling the number of times of multiple ignition (ignition energy) so as to achieve a variation rate has been proposed (see, for example, Patent Document 3).

  Further, the temperature of the ignition coil disposed in the cylinder of the internal combustion engine is estimated in order to control the energization time to the ignition coil without adding a current control element or the like for switching or adjusting the energization amount to the ignition coil. And the technique which controls the electricity supply time is proposed (for example, refer patent document 4).

JP 2004-324418 A JP 2006-83797 A JP 2002-180948 A Japanese Patent No. 3518563

  An internal combustion engine capable of lean burn operation aimed at improving fuel efficiency has a problem of requiring excessive ignition energy in order to ensure combustion stability. In other words, even if a spark plug product whose generated energy is at the lower limit level is used due to electrode wear due to aging and variations in the ignition coil, the engine is ignited and operated with more energy than necessary so that the internal combustion engine can burn stably. The fact is that it must be.

  In order to ensure combustion stability, various techniques for suppressing torque fluctuation by enriching the air-fuel ratio have been proposed and known. However, fuel economy and emissions may deteriorate due to enrichment of the air-fuel ratio.

  Accordingly, it has been desired to provide a control device for an internal combustion engine that can achieve both improvement in fuel consumption and emission by appropriately performing ignition energy control and air-fuel ratio control.

  The present invention has been made in view of the above, and provides a control device for an internal combustion engine that can achieve both improvement in fuel consumption and emission by appropriately using ignition energy control and air-fuel ratio control. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, a control apparatus for an internal combustion engine according to claim 1 of the present invention includes an air-fuel ratio control means for controlling an air-fuel ratio, an ignition energy control means for controlling ignition energy, and In the control apparatus for an internal combustion engine configured to be capable of lean burn operation, during the lean burn operation of the internal combustion engine, the ignition energy control means or the air-fuel ratio control means by the ignition energy control means according to fluctuations in torque or ignition timing The air-fuel ratio control is selected and executed to suppress the fluctuation. When the fluctuation is within a predetermined range, the fluctuation is suppressed by the ignition energy control, and the fluctuation exceeds a predetermined value. Is characterized by suppressing the fluctuation by the air-fuel ratio control.

  According to a second aspect of the present invention, there is provided a control apparatus for an internal combustion engine according to the first aspect, wherein the ignition energy is fixed to a predetermined upper limit value and the air-fuel ratio control is executed. Is.

  According to the control device for an internal combustion engine according to the present invention (Claim 1), the ignition energy control or the air-fuel ratio control is selected and executed in consideration of the influence on the emission and the fuel consumption according to the operation state of the internal combustion engine. Can improve fuel efficiency and emissions. That is, at the time when the fluctuation is less than or equal to a predetermined value, by executing ignition energy control that has less influence on emissions and fuel consumption than air-fuel ratio control (air-fuel ratio enrichment control), both emission and fuel efficiency can be improved. However, torque fluctuation can be suppressed. When the fluctuation exceeds a predetermined value, combustion can be stabilized at an early stage by giving priority to air-fuel ratio control over ignition energy control.

  According to the control device for an internal combustion engine according to the present invention (Claim 2), the ignition energy is fixed to a predetermined upper limit value, thereby suppressing the deterioration of combustion due to the shortage of ignition energy during air-fuel ratio control. can do.

  Embodiments of an internal combustion engine control apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a block diagram showing a system to which a control device for an internal combustion engine according to an embodiment of the present invention is applied. Although the internal combustion engine 1 has a plurality of cylinders 2, for convenience of explanation, only one cylinder is shown in FIG.

  The internal combustion engine 1 includes a cylinder block 6 having a piston 4 therein. The cylinder block 6 is provided with a cooling water temperature sensor 7 for detecting the cooling water temperature. The piston 4 is connected to the crankshaft 8 via a crank mechanism, and a crank angle sensor 9 that detects the rotation angle of the crankshaft 8 is provided in the vicinity of the crankshaft 8.

  A cylinder head 10 is assembled to the upper part of the cylinder block 6, and a combustion chamber 12 is formed in the space from the upper surface of the piston 4 to the cylinder head 10. The cylinder head 10 is provided with an injector 14 that directly injects fuel into the combustion chamber 12.

  The cylinder head 10 is provided with two spark plugs (ignition energy control means) 16 and 18 for igniting the air-fuel mixture in the combustion chamber 12. The first spark plug 16 is disposed on the upper portion of the combustion chamber 12, and the second spark plug 18 is disposed on the side wall of the combustion chamber 12.

  The cylinder head 10 includes an intake port 20 that communicates with the combustion chamber 12. An intake valve 22 is provided at a connection portion between the intake port 20 and the combustion chamber 12. An intake passage 24 is connected to the intake port 20. A surge tank 26 is provided in the middle of the intake passage 24.

  A throttle valve 28 is provided upstream of the surge tank 26. The throttle valve 28 is an electronically controlled valve that is driven by a throttle motor 29, and is driven based on an accelerator opening AA detected by an accelerator opening sensor 30.

  A throttle opening sensor 31 that detects the throttle opening TA is provided in the vicinity of the throttle valve 28. Further, an air flow meter 32 for detecting the intake air amount Ga is provided upstream of the throttle valve 28. An air cleaner 34 is provided upstream of the air flow meter 32.

  Further, the cylinder head 10 includes an exhaust port 36 that communicates with the combustion chamber 12. An exhaust valve 38 is provided at a connection portion between the exhaust port 36 and the combustion chamber 12. An exhaust passage 40 is connected to the exhaust port 36.

  The exhaust passage 40 is provided with a catalyst 42 for purifying exhaust gas. An air-fuel ratio sensor 44 that detects the exhaust air-fuel ratio is provided upstream of the catalyst 42. The catalyst 42 is provided with a catalyst bed temperature sensor 46 that detects the catalyst bed temperature.

  In addition, the system according to the present embodiment includes an ECU 60 that is an electronic control device. On the output side of the ECU 60, an injector 14, spark plugs 16 and 18, a throttle motor 29, and the like are connected.

  Further, on the input side of the ECU 60, a coolant temperature sensor 7, a crank angle sensor 9, an accelerator opening sensor 30, a throttle opening sensor 31, an air flow meter 32, an air-fuel ratio sensor (air-fuel ratio control means) 44, a catalyst bed temperature sensor. 46 etc. are connected.

  The ECU 60 executes overall control of the internal combustion engine 1 such as air-fuel ratio feedback control and ignition energy feedback control based on the output of each sensor. That is, the ECU 60 functions as an air-fuel ratio control unit and an ignition energy control unit. Further, the ECU 60 calculates the engine speed NE based on the output of the crank angle sensor 9.

  Further, the ECU 60 controls at least one of the ignition time and the energy density of the spark plugs 16 and 18 by controlling the number of ignitions according to the operating state and controlling the electric signal input to the spark plugs 16 and 18. . Thereby, the ignition energy of the spark plugs 16 and 18 is controlled.

  Next, a control method will be described with reference to FIGS. The following control is executed by the ECU 60 every predetermined time. Here, FIG. 2 is a flowchart showing a main routine of the control method according to the present embodiment, and feedback control is abbreviated as “F / B”.

  FIG. 3 is a flowchart showing a torque fluctuation suppression control method by air-fuel ratio feedback control (air-fuel ratio control), and is a subroutine related to step S140 shown in FIG. FIG. 4 is a flowchart showing a torque fluctuation suppression control method based on ignition energy feedback control (ignition energy control), and is a subroutine related to step S170 shown in FIG.

  As shown in FIG. 2, first, it is determined whether or not the internal combustion engine 1 is currently in the lean burn operation (step S100). If the lean burn operation is not in progress (No at Step S100), the control is terminated because it is out of the scope of this control.

  If the lean burn operation is being performed (Yes at Step S100), the torque fluctuation value as the combustion fluctuation value is measured (Step S110). This torque fluctuation value can be calculated by measuring the fluctuation amount of the engine speed NE or by measuring the fluctuation amount of the maximum in-cylinder pressure (combustion pressure).

  Next, it is determined whether or not the torque fluctuation value measured in step S110 exceeds a predetermined value t1 (step S120). This predetermined value t1 is a value that cannot suppress torque fluctuation at the current air-fuel ratio even if the ignition energy is maximized, and is a threshold value that indicates that combustion is extremely poor and drivability is deteriorated. The predetermined value t1 is obtained in advance by an experiment or the like, and is stored in the ECU 60 as a constant.

  If the torque fluctuation value exceeds the predetermined value t1 (Yes in Step S120), the air-fuel ratio feedback control described later is not executed, and the ignition energy is fixed to the maximum value (an upper limit that can be designed) (Step S130). Suppresses combustion deterioration due to lack of ignition energy.

  That is, if this predetermined value t1 is exceeded, it can be determined that the mixture formation has deteriorated (combustion instability), and is improved so that the target torque fluctuation value (below the predetermined value t1) is obtained. It is necessary to enrich the air-fuel ratio.

  Therefore, torque fluctuation suppression control by air-fuel ratio feedback control described later is executed so that the torque fluctuation value becomes the target torque fluctuation value (step S140), and the control is terminated. When this air-fuel ratio feedback control is being executed, ignition energy feedback control, which will be described later, is stopped in order to avoid control interference.

  For the torque fluctuation suppression control by the air-fuel ratio feedback control, since a known control method can be adopted, detailed description is omitted. For example, as shown in a subroutine of FIG. A predetermined value t1 is set, and a difference between the target torque fluctuation value and the torque fluctuation value measured in step S110 is calculated (step S141).

  Next, the air-fuel ratio control amount is calculated by multiplying the difference between the torque fluctuation values calculated in step S141 by a predetermined gain (step S142). In order to suppress overshoot (abrupt change) of torque fluctuation, a guard value is provided for the control amount of one process (step S143), and the process returns to the main routine. In this guard process, for example, the increase in fuel injection may be made 10% or less.

  As described above, when the torque fluctuation value is larger than the predetermined value t1 (Yes at step S120), in order to give the highest priority to combustion stability, air-fuel ratio enrichment control (step) is performed while taking fuel efficiency and emissions into consideration. S140) is performed.

  On the other hand, if the torque fluctuation value measured in step S110 does not exceed the predetermined value t1 (No in step S120), it is determined whether the torque fluctuation value exceeds the predetermined value t2 and is equal to or less than the predetermined value t1. (Step S150).

  This predetermined value t2 is a threshold at which torque fluctuation can be compensated for by increasing ignition energy during lean burn operation, but vibration of the internal combustion engine 1 is felt uncomfortable due to torque fluctuation and the torque fluctuation needs to be improved. This predetermined value t2 is also determined in advance by an experiment or the like, and is stored in the ECU 60 as a constant.

  If the torque fluctuation value exceeds the predetermined value t2 and is not equal to or less than the predetermined value t1 (No in step S150), the torque fluctuation value is within the allowable range of the target torque fluctuation value (predetermined value t2 or less), and the torque fluctuation is suppressed. Since it can be determined that it is not necessary, the control is terminated.

  If the torque fluctuation value exceeds the predetermined value t2 and is equal to or less than the predetermined value t1 (Yes in step S150), the air-fuel ratio enrichment control (step S140) that has a relatively large effect on fuel consumption and emission is not executed. It is assumed that torque fluctuation suppression control by ignition energy feedback control, which will be described later, which has little influence on these, is executed, and prior to this, the air-fuel ratio is fixed to the current value (step S160).

  Then, torque fluctuation suppression control by ignition energy feedback control described later is executed so that the torque fluctuation value becomes the target torque fluctuation value (predetermined value t2 or less) (step S170), and the control is terminated.

  As described above, when the torque fluctuation value is equal to or less than the predetermined value t1 and within the predetermined range, the adverse effect on the emission and fuel consumption can be reduced by executing the ignition energy feedback control before the air-fuel ratio feedback control. .

  For torque fluctuation suppression control by the ignition energy feedback control, a known control method can be adopted and detailed description thereof is omitted. For example, as shown in a subroutine of FIG. Is the predetermined value t2, and the difference between the target torque fluctuation value and the torque fluctuation value measured in step S110 is calculated (step S171).

  Next, the ignition energy control amount is calculated by multiplying the difference between the torque fluctuation values calculated in step S171 by a predetermined gain (step S172). In order to suppress overshoot (abrupt change) of torque fluctuation, a guard value is provided for the control amount of one process (step S173), and the process returns to the main routine. In this guard process, for example, the amount of increase in ignition energy may be set to 10% or less.

  As described above, if the torque fluctuation value exceeds the predetermined value t2 and is equal to or less than the predetermined value t1 (Yes in step S150), the ignition energy feedback control has less influence on the emission and fuel consumption than the air-fuel ratio enrichment control. By executing the above, torque fluctuation can be suppressed, and both emission and fuel consumption can be improved.

  As described above, according to the control apparatus for an internal combustion engine according to this embodiment, both the improvement of fuel consumption and emission can be achieved by appropriately using the ignition energy control and the air-fuel ratio control according to the torque fluctuation state. can do.

  In the above embodiment, the torque fluctuation suppression control by the air-fuel ratio feedback control and the torque fluctuation suppression control by the ignition energy feedback control are selectively used based on the torque fluctuation value. However, the present invention is not limited to this. The above control can be selectively used based on the ignition timing fluctuation value. In this case as well, the same effect as in the above embodiment can be obtained.

  Further, in the above embodiment, the internal combustion engine 1 provided with two ignition plugs 16 and 18 for each cylinder has been described. However, the present invention is not limited to this, and for example, an internal combustion engine provided with three or more ignition plugs for each cylinder. The present invention can also be applied to. In this case as well, the same effect as in the above embodiment can be obtained.

  As described above, the control apparatus for an internal combustion engine according to the present invention includes an air-fuel ratio control unit that controls the air-fuel ratio and an ignition energy control unit that controls ignition energy. This is useful, and is particularly suitable for an internal combustion engine that aims to achieve both improvement in fuel consumption and emission by appropriately performing ignition energy control and air-fuel ratio control.

1 is a block diagram showing a system to which a control device for an internal combustion engine according to an embodiment of the present invention is applied. FIG. It is a flowchart which shows the main routine of the control method which concerns on a present Example. It is a flowchart which shows the torque fluctuation suppression control method by air fuel ratio feedback control. It is a flowchart which shows the torque fluctuation suppression control method by ignition energy feedback control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 9 Crank angle sensor 12 Combustion chamber 14 Injector 16 1st spark plug (ignition energy control means)
18 Second spark plug (ignition energy control means)
44 Air-fuel ratio sensor (air-fuel ratio control means)
60 ECU (air-fuel ratio control means, ignition energy control means, control device)
t1 predetermined value t2 predetermined value

Claims (2)

In a control apparatus for an internal combustion engine comprising an air-fuel ratio control means for controlling an air-fuel ratio and an ignition energy control means for controlling ignition energy, and configured to be capable of lean burn operation,
At the time of lean burn operation of the internal combustion engine, the ignition energy control by the ignition energy control means or the air-fuel ratio control by the air-fuel ratio control means is selected and executed according to fluctuations in torque or ignition timing to suppress the fluctuations And
At the normal time when the fluctuation is below a predetermined value, the fluctuation is suppressed by the ignition energy control,
The control apparatus for an internal combustion engine, wherein the fluctuation is suppressed by the air-fuel ratio control when the fluctuation exceeds a predetermined value.   The control device for an internal combustion engine according to claim 1, wherein the ignition energy is fixed to a predetermined upper limit value, and the air-fuel ratio control is executed.

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