JP4415864B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly, to a control technique for preventing a rapid decrease in engine speed during idling.

As described in Patent Document 1, during idling of the internal combustion engine, feedback control of the intake air amount is performed in accordance with the difference between the target idle speed and the actual speed in order to keep the engine speed constant. In the prior art described in Patent Document 1, when the engine speed rapidly decreases due to any cause, the intake air amount is increased by opening the throttle valve, and the engine stall caused by the decrease in engine speed. Try to prevent.
JP 59-110443 A JP 2002-147287 A

  However, if the throttle valve is opened and the intake air amount is increased as in the prior art, the fuel injection amount is also increased accordingly. This is because the fuel injection amount is determined according to the intake air amount so that the air-fuel ratio becomes constant (for example, the theoretical air-fuel ratio). Although it is necessary to prevent engine stalls during idling, there is also a demand for minimizing excess fuel consumption.

  The present invention has been made to solve the above-described problems, and provides an internal combustion engine control device capable of preventing a rapid decrease in engine speed during idling without increasing fuel consumption. The purpose is to do.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
A throttle valve arranged in the intake passage;
An EGR amount adjusting means for adjusting the EGR amount;
A rotational speed detecting means for detecting an actual rotational speed of the internal combustion engine at idling;
A comparison means for comparing the detected actual rotational speed with a predetermined reference rotational speed set lower than the target rotational speed at idling;
When the actual rotational speed falls below the reference rotational speed, the operating amount of the EGR amount adjusting means is increased, and the opening of the throttle valve is adjusted to the EGR amount so that the actual rotational speed returns to the target rotational speed. Control means for controlling according to the operating amount of the adjusting means;
It is characterized by having.

A second invention is the EGR valve according to the first invention, wherein the EGR amount adjusting means adjusts an amount of exhaust gas recirculated from an exhaust passage to the intake passage.
The control means opens the EGR valve so as to reduce the negative pressure in the intake passage by increasing the recirculation amount of the exhaust gas, and reduces the amount of new gas that decreases as the EGR valve opens. The opening degree of the throttle valve is controlled in accordance with the opening degree of the EGR valve so as to compensate the intake amount.

In a third aspect based on the first aspect, the EGR amount adjusting means adjusts an exhaust gas blow-back amount from the exhaust passage to the intake passage by changing an overlap period of the exhaust valve and the intake valve. Valve timing variable mechanism
The control means operates the valve timing variable mechanism so as to decrease the negative pressure in the intake passage by increasing the exhaust gas blow-back amount, and decreases as the valve timing variable mechanism operates. The opening degree of the throttle valve is controlled in accordance with the overlap period so as to compensate the gas intake amount.

  According to a fourth invention, in any one of the first to third inventions, when the actual rotational speed is lower than the reference rotational speed, the target air-fuel ratio is set to a predetermined rich air-fuel ratio that is richer than stoichiometric. A target air-fuel ratio setting means for setting is further provided.

  According to the first invention, when the actual rotational speed is lower than the reference rotational speed, the EGR amount is increased by increasing the operation amount of the EGR amount adjusting means. When the EGR amount increases, the negative pressure in the intake passage decreases and the pumping loss of the internal combustion engine is reduced. As the pumping loss is reduced in this way, the net torque of the internal combustion engine is improved, so the amount of intake of new gas required to return the actual rotational speed to the target rotational speed is reduced, and the fuel consumption is reduced. Extra consumption is also suppressed. That is, according to the first aspect of the invention, it is possible to prevent a rapid decrease in the engine speed during idling without increasing the fuel consumption.

  In particular, according to the second invention, the negative pressure in the intake passage can be reduced by increasing the amount of exhaust gas recirculated from the exhaust passage to the intake passage, thereby reducing the pumping loss of the internal combustion engine. Further, according to the third aspect of the present invention, the negative pressure in the intake passage can be reduced by increasing the amount of exhaust gas blown back from the exhaust passage to the intake passage, thereby reducing the pumping loss of the internal combustion engine.

  Further, according to the fourth invention, when the actual rotational speed is lower than the reference rotational speed, the target air-fuel ratio is changed to a rich air-fuel ratio that has a combustion speed faster than the stoichiometric speed, so that combustion fluctuations can be suppressed. Thus, it is possible to more reliably prevent the engine speed from decreasing.

Embodiment 1 FIG.
Hereinafter, the first embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a diagram showing a schematic configuration of an engine system to which an internal combustion engine control apparatus according to Embodiment 1 of the present invention is applied. An internal combustion engine (hereinafter simply referred to as an engine) according to this embodiment includes a cylinder block 6 in which a piston 8 is disposed, and a cylinder head 4 assembled to the cylinder block 6. A space from the upper surface of the piston 8 to the cylinder head 4 forms a combustion chamber 10, and an intake port 18 and an exhaust port 20 are formed in the cylinder head 4 so as to communicate with the combustion chamber 10. An intake valve 12 for controlling the communication state between the intake port 18 and the combustion chamber 10 is provided at a connection portion between the intake port 18 and the combustion chamber 10, and an exhaust gas is provided at a connection portion between the exhaust port 20 and the combustion chamber 10. An exhaust valve 14 for controlling the communication state between the port 20 and the combustion chamber 10 is provided. The intake valve 12 is provided with a variable valve timing mechanism (VVT) 70 for changing the valve timing. A spark plug 16 is attached to the cylinder head 4 so as to protrude from the top of the combustion chamber 10 into the combustion chamber 10.

  An intake passage 30 for introducing new gas into the combustion chamber 10 is connected to the intake port 18 of the cylinder head 4. An air cleaner 32 is provided at the upstream end of the intake passage 30, and new gas is taken into the intake passage 30 via the air cleaner 32. An air flow meter 56 for detecting the intake amount of new gas is disposed downstream of the air cleaner 32. A downstream portion of the intake passage 30 is branched for each cylinder (for each intake port 18), and a surge tank 34 is provided at the branched portion. An electronically controlled throttle valve 36 is disposed upstream of the surge tank 34 in the intake passage 30. The throttle valve 36 is provided with a throttle sensor 54 for detecting the opening degree. In addition, an injector 38 for injecting fuel is provided for each cylinder in the vicinity of the intake port 18 of the intake passage 30.

  On the other hand, the exhaust port 20 of the cylinder head 4 is connected to an exhaust passage 40 for discharging combustion gas generated by combustion in the combustion chamber 10 as exhaust gas. A catalyst 42 for purifying exhaust gas is provided in the exhaust passage 40. Further, an EGR passage 60 for diverting exhaust gas from the exhaust passage 40 is connected to the exhaust passage 40. The other end of the EGR passage 60 is connected upstream of the surge tank 34 in the intake passage 30. An EGR valve 62 that controls the communication state between the EGR passage 60 and the intake passage 30 is provided at a connection portion between the EGR passage 60 and the intake passage 30. A part of the exhaust gas is supplied into the intake passage 30 through the EGR passage 60 and recirculated to the combustion chamber 10. The exhaust gas recirculation amount (EGR amount) is adjusted by the opening degree of the EGR valve 62.

  Further, the internal combustion engine includes an ECU (Electronic Control Unit) 50 as its control device. Various devices such as the injector 38, the throttle valve 36, the spark plug 16, the EGR valve 62, and the valve timing variable mechanism 70 are connected to the output side of the ECU 50. In addition to the air flow meter 56 and the throttle sensor 54 described above, various sensors such as a crank angle sensor 52 that detects the rotation angle of the crankshaft 24 are connected to the input side of the ECU 50. The ECU 50 drives each device according to a predetermined control program based on the output of each sensor.

  FIG. 2 is a flowchart showing the contents of engine control executed by the ECU 50 in the present embodiment. The routine shown in FIG. 2 is periodically executed at every constant crank angle. In the first step 100 of this routine, it is determined whether or not the ignition switch is on. If the ignition switch is still off, this routine is not started. Further, when the ignition switch is turned off during execution of this routine, this routine ends.

  If it is determined in step 100 that the ignition switch is on, it is determined in step 102 whether or not the engine is in an idle state. Whether or not the engine is in the idle state can be determined by turning on / off an idle switch (not shown). When the engine is in an idle state, the routine proceeds to step 104, where the engine speed (the number of revolutions per minute) Ne is acquired. The engine speed Ne can be calculated by processing the crank angle signal from the crank angle sensor 52.

  In the next step 106, it is determined whether or not the acquired engine rotational speed Ne is smaller than a predetermined reference rotational speed Necr. The reference rotational speed Necr is a rotational speed that is determined to be likely to cause an engine stall if the engine rotational speed Ne is lower than this. Naturally, the rotational speed is set lower than the target rotational speed Net at idling. When the engine speed Ne is equal to or higher than the reference speed Necr, the routine proceeds to step 200 where normal idle control is executed. That is, feedback control of the opening degree of the throttle valve 36 is performed according to the difference between the target rotational speed Net and the engine rotational speed Ne.

  On the other hand, if it is determined in step 106 that the engine speed Ne is lower than the reference rotational speed Necr, the processing after step 108 is executed. First, at step 108, the current engine load factor KL is acquired. The load factor KL is obtained from the intake air amount detected by the air flow meter 56. In step 110, the throttle opening degree TA detected by the throttle sensor 54 is acquired.

  In the next step 112, the target air-fuel ratio AFt is changed to a predetermined air-fuel ratio (around 12.5) slightly richer than the stoichiometric air-fuel ratio set during normal idle control. The combustion speed of the air-fuel mixture in the combustion chamber 10 is the fastest when the air-fuel ratio is around 12.5, and the combustion fluctuation is also reduced. Therefore, by changing the target air-fuel ratio AFt as described above, it is possible to suppress the rapid decrease in the engine speed Ne to some extent by improving the combustion.

  In the next step 114, the EGR valve 62 is opened to a predetermined opening. During normal idle control, the EGR valve 62 is closed, and exhaust gas (EGR gas) is not introduced into the intake passage 30. In this step, the negative pressure in the intake passage 30 is reduced by opening the EGR valve 62 and introducing EGR gas into the intake passage 30. The pumping loss of the engine is reduced by reducing the negative pressure in the intake passage 30.

  However, when the EGR gas is introduced into the intake passage 30, the amount of new gas sucked into the combustion chamber 10 is reduced accordingly. Since the decrease in the intake amount of the new gas reduces the torque generated by the engine, the engine speed Ne cannot be returned to the target speed Net only by reducing the pumping loss by introducing the EGR gas. Therefore, in the next step 116, an increment ΔTA1 of the throttle opening degree TA necessary for returning the engine speed Ne to the target speed Net is calculated. The throttle opening increment ΔTA1 changes using the engine speed Ne, the load factor KL, the throttle opening TA, the difference between the target speed Net and the engine speed Ne, and the opening of the EGR valve 62 as parameters. The relationship between the throttle opening increment ΔTA1 and each parameter is obtained in advance by calculation or the like, and stored as a multidimensional map with each parameter as an axis. In step 116, the engine speed Ne acquired in step 104, the load factor KL acquired in step 108, the throttle opening TA acquired in step 110, the difference between the target speed Net and the engine speed Ne, and A throttle opening increment ΔTA1 corresponding to the opening of the EGR valve 62 set in step 114 is acquired from the multidimensional map.

  In the next step 118, the throttle valve 36 is driven in accordance with the throttle opening increment ΔTA1 calculated in step 116. As a result, the intake amount of the new gas into the intake passage 30 is increased, and the intake amount of the new gas that decreases with the introduction of the EGR gas is compensated. At the same time, the negative pressure decreases due to an increase in the amount of new gas sucked into the intake passage 30, and the pumping loss of the engine is further reduced. As a result, the generated torque (net torque) of the engine is improved, and the engine speed Ne is recovered to the target speed Net.

  According to the routine described above, when the engine speed Ne is lower than the reference speed Necr, the EGR gas is introduced into the intake passage 30 by opening the EGR valve 62, thereby reducing the pumping loss of the engine. . As the pumping loss is reduced, the net torque of the engine will be improved. Therefore, the increase in the amount of new gas intake required to return the engine speed Ne to the target speed Net can be reduced. Extra consumption is also suppressed. That is, by performing the engine control according to the above routine, it is possible to prevent a sudden decrease in the engine speed during idling without increasing the fuel consumption and to avoid engine stall.

  In the above-described embodiment, the “rotation speed detecting means” of the first invention is realized by the execution of the process of step 104 by the ECU 50, and the “ "Comparison means" is realized. Further, the “control means” according to the first and second aspects of the present invention is realized by the execution of the processing of steps 114, 116, and 118 by the ECU 50.

Embodiment 2.
Hereinafter, Embodiment 2 of the present invention will be described with reference to FIGS. 1 and 3.
The control apparatus for an internal combustion engine of the present embodiment can be realized by causing the ECU 50 to execute the routine of FIG. 3 in the engine system having the configuration shown in FIG. FIG. 3 is a flowchart showing the contents of engine control executed by the ECU 50 in the present embodiment. Of the processes executed in the routine shown in FIG. 3, the same processes as those executed in the routine according to the first embodiment (see FIG. 2) are denoted by the same step numbers.

  In this routine, the process of step 114-2 is executed instead of the process of step 114 according to the first embodiment, and the process of step 116-2 is executed instead of the process of step 116. In step 114-2 of this routine, the variable valve timing mechanism 70 is driven in a direction in which the valve overlap period of the intake valve 12 and the exhaust valve 14 increases. As the valve overlap period increases, the amount of exhaust gas (internal EGR gas) blown back from the exhaust passage 40 to the intake passage 30 increases. As a result, similarly to when the opening degree of the EGR valve 62 is increased, the negative pressure in the intake passage 30 is reduced due to the increase of the internal EGR gas, and the pumping loss of the engine is reduced.

  Further, the amount of new gas sucked into the combustion chamber 10 decreases as the internal EGR gas increases. For this reason, in step 116-2, an increment ΔTA2 of the throttle opening degree TA necessary to return the engine speed Ne to the target speed Net is calculated. The throttle opening increment ΔTA2 changes using the engine speed Ne, the load factor KL, the throttle opening TA, the difference between the target speed Net and the engine speed Ne, and the valve overlap period as parameters. The relationship between the throttle opening increment ΔTA2 and each parameter described above is obtained in advance by calculation or the like, and is stored as a multidimensional map with each parameter as an axis. In Step 116-2, the engine speed Ne acquired in Step 104, the load factor KL acquired in Step 108, the throttle opening degree TA acquired in Step 110, the difference between the target speed Net and the engine speed Ne. , And the throttle opening increment ΔTA2 corresponding to the valve overlap period set in step 114-2 is acquired from the multidimensional map.

  In the next step 118, the throttle valve 36 is driven in accordance with the throttle opening increment ΔTA2 calculated in step 116-2. As a result, the decrease in the new gas intake amount accompanying the increase in the internal EGR gas is compensated for by the increase in the new gas intake amount into the intake passage 30. At the same time, the negative pressure decreases due to an increase in the amount of new gas sucked into the intake passage 30, and the pumping loss of the engine is further reduced. As a result, the net torque of the engine is improved, and the engine speed Ne is restored to the target speed Net.

  According to the routine described above, when the engine speed Ne is lower than the reference speed Necr, the internal EGR gas blown back from the exhaust passage 40 to the intake passage 40 due to the change of the valve overlap period by the valve timing variable mechanism 70. The amount of pumping is increased, thereby reducing the pumping loss of the engine. As the pumping loss is reduced, the net torque of the engine will be improved. Therefore, the increase in the amount of new gas intake required to return the engine speed Ne to the target speed Net can be reduced. Extra consumption is also suppressed. That is, by performing engine control according to the above routine, as in the first embodiment, it is possible to prevent a rapid decrease in the engine speed during idling without increasing the fuel consumption and to avoid engine stall. .

  In the above-described embodiment, the “control means” of the first and third aspects of the present invention is realized by the execution of the processing of steps 114-2, 116-2, 118 by the ECU 50.

Others.
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications can be made without departing from the spirit of the present invention. For example, the following modifications may be made.

  In the first embodiment, the opening when the EGR valve 62 is opened is fixed to a predetermined opening. However, the opening of the EGR valve 62 depends on the amount of decrease in the engine speed Ne from the target speed Net. May be changed. The same applies to the second embodiment, and the valve overlap period may be changed in accordance with the amount of decrease in the engine speed Ne from the target speed Net.

  In the above embodiment, the load factor KL of the engine is obtained from the intake air amount detected by the air flow meter 56, but an intake passage pressure sensor for detecting the pressure in the intake passage 30 (intake passage pressure) is provided. In this case, the intake passage pressure may be used instead of the load factor KL.

1 is a schematic configuration diagram of an engine system to which a control device for an internal combustion engine as Embodiment 1 of the present invention is applied. It is a flowchart of the engine control routine executed in the first embodiment of the present invention. It is a flowchart of the engine control routine performed in Embodiment 2 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Combustion chamber 12 Intake valve 14 Exhaust valve 16 Spark plug 18 Intake port 20 Exhaust port 24 Crankshaft 30 Intake passage 36 Throttle valve 38 Injector 40 Exhaust passage 50 ECU
52 Crank angle sensor 54 Throttle sensor 56 Air flow meter 60 EGR passage 62 EGR valve 70 Variable valve timing mechanism

Claims (4)

A throttle valve arranged in the intake passage;
An EGR amount adjusting means for adjusting the EGR amount;
A rotational speed detecting means for detecting an actual rotational speed of the internal combustion engine at idling;
A comparison means for comparing the detected actual rotational speed with a predetermined reference rotational speed set lower than the target rotational speed at idling;
When the actual rotational speed falls below the reference rotational speed, the operating amount of the EGR amount adjusting means is increased, and the opening of the throttle valve is adjusted to the EGR amount so that the actual rotational speed returns to the target rotational speed. Control means for controlling according to the operating amount of the adjusting means;
A control device for an internal combustion engine, comprising: The EGR amount adjusting means is an EGR valve that adjusts a recirculation amount of exhaust gas from an exhaust passage to the intake passage,
The control means opens the EGR valve so as to reduce the negative pressure in the intake passage by increasing the recirculation amount of the exhaust gas, and reduces the amount of new gas that decreases as the EGR valve opens. 2. The control apparatus for an internal combustion engine according to claim 1, wherein the opening degree of the throttle valve is controlled in accordance with the opening degree of the EGR valve so as to compensate the intake amount. The EGR amount adjusting means is a variable valve timing mechanism that adjusts an exhaust gas blowback amount from the exhaust passage to the intake passage by changing an overlap period of the exhaust valve and the intake valve.
The control means operates the valve timing variable mechanism so as to decrease the negative pressure in the intake passage by increasing the exhaust gas blow-back amount, and decreases as the valve timing variable mechanism operates. 2. The control device for an internal combustion engine according to claim 1, wherein the opening degree of the throttle valve is controlled in accordance with the overlap period so as to compensate for the gas intake amount. 4. A target air-fuel ratio setting means for setting the target air-fuel ratio to a predetermined rich air-fuel ratio that is richer than stoichiometric when the actual rotational speed falls below the reference rotational speed. The control device for an internal combustion engine according to any one of the above.

Images