JP4367147B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine including an exhaust gas recirculation device that recirculates part of exhaust gas to an intake system.

  For example, in an internal combustion engine for a vehicle, an exhaust gas recirculation device that recirculates a part of exhaust gas to an intake system in order to reduce NOx has been known. However, in recent years, not only NOx reduction but also pumping loss of the internal combustion engine is known. It is known as one of the fuel efficiency improvement techniques to perform a large amount of exhaust gas recirculation under wider operating conditions for the purpose of reduction.

Patent Document 1 discloses a control device for an internal combustion engine equipped with such an exhaust gas recirculation device, which is configured to correct the exhaust gas recirculation amount to a reduced amount when accelerating the internal combustion engine when the driver depresses the accelerator pedal. It is disclosed. By reducing the exhaust gas recirculation amount during acceleration in this way, the ratio of fresh air in the intake air introduced into the combustion chamber is increased, and acceleration response is improved.
JP 2000-205004 A

  However, if the exhaust gas recirculation amount is always reduced during acceleration regardless of the operating conditions at that time, the effect of improving the fuel efficiency due to exhaust gas recirculation is greatly reduced. In other words, in order to improve fuel efficiency, it is desirable to perform exhaust gas recirculation as much as possible even during acceleration.

  On the other hand, if the exhaust gas recirculation is performed at the time of acceleration as in the steady state, it is not preferable from the viewpoint of improving the fuel efficiency as well as the acceleration response, particularly when accelerating from a relatively high load range. In other words, when the driver depresses the accelerator pedal for acceleration, if the exhaust gas recirculation is still performed, the torque rises slowly, so the driver unconsciously further depresses the accelerator pedal. And the operating condition of the internal combustion engine enters a high load side fuel consumption deterioration region where the fuel consumption is extremely deteriorated.

The present invention includes an exhaust gas recirculation device that recirculates a part of exhaust gas to an intake system, and controls the exhaust gas recirculation device so as to achieve a predetermined exhaust gas recirculation rate in accordance with operating conditions of the internal combustion engine. And means for detecting the driver's acceleration request and means for determining the amount of margin from the operating condition of the internal combustion engine when the acceleration request is detected to a predetermined fuel consumption deterioration region on the high load side. The exhaust gas recirculation by the exhaust gas recirculation device is stopped when the margin is small, and the exhaust gas recirculation device is controlled so that a predetermined exhaust gas recirculation rate is obtained according to the operating conditions otherwise .

  That is, when there is an acceleration request by the driver, if the operating condition of the internal combustion engine is on a relatively low load side and there is a large margin to the fuel consumption deterioration region, the exhaust gas recirculation is not particularly stopped, Exhaust gas recirculation is performed according to operating conditions. On the other hand, when the margin to the fuel consumption deterioration region is small, exhaust gas recirculation is forcibly stopped. As a result, the torque rises quickly, an unnecessary increase in the accelerator opening by the driver, that is, an increase in the accelerator pedal, is avoided, and the driving in the fuel efficiency deterioration region is suppressed.

  The fuel efficiency deterioration region means a region on the high load side where the fuel consumption is greatly deteriorated, and can be appropriately set as necessary. For example, in the low and medium load regions, the target air fuel ratio of the internal combustion engine is set to the stoichiometric air fuel ratio. Under the air-fuel ratio control in which the target air-fuel ratio is a rich air-fuel ratio that is less than or equal to the stoichiometric air-fuel ratio in the high load region, in general, the fuel consumption rate in the operating region where the target air-fuel ratio is less than the stoichiometric air-fuel ratio, that is, the fuel increase region Since the fuel consumption increases rapidly, this fuel increase region can be regarded as the fuel consumption deterioration region. Since the fuel consumption rate is further influenced by the ignition timing and the like, the fuel consumption deterioration region may be determined based on the characteristics of the actual fuel consumption rate considering these factors.

  The magnitude of the above margin is, for example, the torque of the internal combustion engine when an acceleration request is detected or a parameter that is a substitute for the torque, such as the intake air amount, the fuel injection amount, the throttle opening, the intake pressure in the intake collector, Or the like based on the above.

  According to the present invention, the exhaust gas recirculation is allowed when the allowance to the fuel consumption deterioration region is large even during acceleration, so that the fuel consumption improvement by the exhaust gas recirculation can be further increased. In addition, exhaust gas recirculation is stopped when accelerating from a condition where the margin to the fuel efficiency deterioration area is small, and an unnecessary increase in the accelerator opening is avoided by the driver. Can do.

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

  FIG. 1 is an explanatory diagram showing a system configuration of a control device according to the present invention. An internal combustion engine 1 which is a spark ignition gasoline engine includes an ignition plug 2 at the center of a combustion chamber, an intake valve 3 and an exhaust gas. A crank angle sensor 5 that includes a valve 4 and detects rotation of the crankshaft is provided.

  The exhaust passage 6 includes a catalytic converter 7 and a silencer 8, and an air-fuel ratio sensor 9 that detects an exhaust air-fuel ratio is provided at an upstream position of the catalytic converter 7. An exhaust gas recirculation passage 12 extending from the exhaust passage 6 to the intake air passage 11 is provided as the exhaust gas recirculation device 10, and a step motor type exhaust gas recirculation control valve 13 for variably controlling the exhaust gas recirculation amount is provided. It is interposed in the passage 12.

  A fuel injection valve 15 that injects fuel toward each intake port is disposed at an intake port inlet of each cylinder, which is a downstream portion of the intake passage 11. The intake passage 11 of each cylinder is gathered in an intake collector 16, and an electronically controlled throttle valve 17 is provided in the intake passage 11 on the inlet side of the intake collector 16. The electronically controlled throttle valve 17 includes an actuator formed of an electric motor, and its opening degree is controlled by a control signal supplied from an engine control module (ECM) 19. Note that a sensor (not shown) that detects the actual opening of the throttle valve 17 is integrally provided, and the throttle valve opening is closed-loop controlled to the target opening based on the detection signal. An air flow meter 18 for detecting the air flow rate is provided upstream of the throttle valve 17.

  Further, an accelerator opening sensor 20 for detecting the amount of depression of the accelerator pedal (accelerator pedal opening APO) operated by the driver is provided, and the detection signal thereof is the crank angle sensor 5 or the air-fuel ratio sensor 9 described above. Along with the detection signal from the air flow meter 18 and the like, it is input to the engine control module 19. Based on these detection signals, the engine control module 19 controls the injection amount and injection timing of the fuel injection valve 15, the ignition timing by the spark plug 2, the opening of the throttle valve 17, and the like.

  The internal combustion engine 1 drives the drive wheels of a vehicle via a belt type continuously variable transmission (so-called CVT) (not shown). The gear ratio of the continuously variable transmission is continuously controlled based on the driving state of the vehicle, mainly the accelerator pedal opening APO and the vehicle speed.

  Next, the exhaust gas recirculation control in the configuration of the above embodiment will be described.

  First, basic exhaust gas recirculation control, air-fuel ratio control, and fuel consumption characteristics will be described. FIG. 2 is a characteristic diagram showing the operating conditions of the internal combustion engine 1 using the engine torque and the engine speed (engine speed) as parameters, and, as is well known, the uppermost part shown as “WOT”. The line represents the fully open characteristic when the throttle valve 17 is fully open. Here, as the air-fuel ratio control of the internal combustion engine 1, in the high-load side region, specifically, in the high-load side region (fuel increase region) from the line shown as the “theoretical air-fuel ratio limit”, the theoretical air-fuel ratio control. Operation is performed with an air-fuel ratio richer than the fuel ratio, and operation is performed with the stoichiometric air-fuel ratio as the target air-fuel ratio in the low-medium load region (theoretical air-fuel ratio region) below the “theoretical air-fuel ratio limit” line. That is, in the low and medium load region, the fuel injection amount of the fuel injection valve 15 is corrected by the feedback control by the air-fuel ratio sensor 9 and is accurately maintained at the theoretical air-fuel ratio. On the other hand, in the fuel increase region on the high load side, the feedback control of the fuel injection amount is stopped, and the fuel injection amount is increased so that a predetermined target air-fuel ratio richer than the stoichiometric air-fuel ratio is obtained.

  In FIG. 2, an isofuel curve is drawn in contour lines, and the center of the contour line is the driving condition with the best fuel economy. In other words, the best fuel economy can be obtained in terms of medium speed and medium load. From this point, the fuel efficiency gradually deteriorates toward the high load side or the low load side, and similarly, gradually toward the low speed side or the high speed side. However, fuel consumption deteriorates. In particular, in the fuel increase region on the high load side described above, since the air-fuel ratio becomes rich, fuel consumption is greatly deteriorated. Therefore, in this embodiment, the fuel increase area is defined as a fuel consumption deterioration area. Note that the fuel efficiency depends on the ignition timing and the like, so the isofuel curve and the “theoretical air-fuel ratio limit” line have slightly different characteristics.

  Further, in FIG. 2, the characteristics of the target exhaust gas recirculation rate in the exhaust gas recirculation control are shown as contour lines by three lines “EGR1” to “EGR3”. In the figure, the center portion of the contour line surrounded by the line “EGR1” has the highest exhaust gas recirculation rate. Further, outside the outermost “EGR3” line, the exhaust gas recirculation rate is 0, that is, exhaust gas recirculation is not performed. As shown in this figure, in this embodiment, a relatively large amount of exhaust gas recirculation is performed over a wide range of operating conditions. In the exhaust gas recirculation control that is generally performed in the past, exhaust gas recirculation is performed only in a narrow region on the low-speed and low-load side indicated by three contour lines “EGR11” to “EGR13”. The value itself is also lower than the exhaust gas recirculation rate of this embodiment. In other words, in the present embodiment, as much exhaust gas recirculation as possible is performed in most of the theoretical air-fuel ratio region in order to improve fuel efficiency by reducing pumping loss. Therefore, it frequently occurs that the driver requires acceleration while exhaust gas recirculation is being performed.

  Next, the relationship with the gear ratio of the continuously variable transmission will be described based on FIG. The characteristic diagram of FIG. 3 shows the same fuel efficiency curve as in FIG. 2, and in addition to this, the characteristics of the engine torque and the engine speed with respect to the running resistance when running on a flat road, that is, the road load (R / R). L) Curves are shown. As is apparent from this figure, in this embodiment, in order to improve fuel efficiency, the gear ratio of the continuously variable transmission is controlled so that the R / L curve passes through the best fuel efficiency point of the contoured isofuel consumption curve. The In the conventional general gear ratio control, the R / L curve is on the lower load side than the fuel efficiency best point as shown as “conventional” in the figure. Further, in a stepped automatic transmission, an R / L curve is located on the lower load side as shown as “AT R / L line” in the figure. Therefore, in this embodiment, the internal combustion engine 1 is operated with a relatively high load in order to improve fuel efficiency. Therefore, for example, when accelerating while traveling on a flat road, the margin torque to the fuel increase range is relatively small, and the frequency of operation in the fuel increase range with poor fuel consumption tends to increase. In order to improve the actual fuel consumption, it is important to avoid driving in an unnecessary fuel increase region.

  In particular, when accelerating from a region where exhaust gas recirculation is performed, if the margin torque to the fuel increase region is small, the fuel increase region is likely to be used. This will be described with reference to FIG. For example, if the driver attempts to accelerate by depressing the accelerator pedal in a state where the internal combustion engine 1 is operated at a point d that has a small margin torque up to the fuel increase range and is within the exhaust gas recirculation region, the exhaust gas recirculation is reduced. Since the amount of fresh air flowing into the combustion chamber is small in the state in which it is being performed, the torque rises slowly even if the throttle valve 17 is opened. For this reason, the driver trying to accelerate (particularly sudden acceleration) tends to unconsciously increase the accelerator pedal, and as a result, the operating condition of the internal combustion engine 1 changes as shown by the arrow A in FIG. The fuel increase area may be used unnecessarily.

  On the other hand, in this embodiment, when there is little margin torque up to the fuel increase range, exhaust recirculation is stopped when there is an acceleration request that can be regarded as rapid acceleration. When the exhaust gas recirculation is stopped in this way, the amount of fresh air flowing into the combustion chamber increases, and the torque quickly increases as the opening of the throttle valve 17 increases, so that an unnecessary accelerator pedal depression by the driver is prevented. Avoided. Therefore, the operating condition of the internal combustion engine 1 changes as indicated by the arrow B from the point d, and the operation in the fuel increase region is avoided.

  Further, in this embodiment, when the acceleration is slow, the exhaust gas recirculation is not stopped when the acceleration is slow or when the surplus torque at the time when the acceleration is requested is large, and the exhaust gas recirculation rate as shown in FIG. Exhaust gas recirculation is performed in accordance with a characteristic control map (target EGR map). Therefore, the fuel efficiency improvement effect by reducing the pumping loss can be obtained to the maximum.

  FIG. 5 is a flowchart showing the main part of the exhaust gas recirculation control in the above embodiment, and it is determined in step 1 and step 2 whether a predetermined sudden acceleration is requested. Specifically, in Step 1, it is determined whether or not the change speed VAPO of the accelerator pedal opening APO is larger than a predetermined value VAPOa. In step 2, it is determined whether or not the value of the accelerator pedal opening APO is larger than a predetermined value APOa. That is, when the accelerator pedal is stepped on rapidly and largely, it is determined that the acceleration is requested. If NO in step 1 or step 2, the routine proceeds to step 4 where normal exhaust gas recirculation is performed with reference to the target EGR map. Note that in the region where the target exhaust gas recirculation rate is 0, exhaust gas recirculation is not actually performed.

  If it is determined that there is a sudden acceleration request, in step 3, the magnitude of the surplus torque up to the fuel increase range is determined based on the engine operating condition at that time. A specific method for this determination will be described later. If it is determined that the margin torque is large, the process proceeds to step 4 described above, and normal exhaust gas recirculation is performed with reference to the target EGR map. On the other hand, when it is determined that the margin torque is small, the process proceeds to step 5 and the exhaust gas recirculation rate is set to zero. That is, exhaust gas recirculation is stopped.

  FIG. 6 is a time chart showing the action at the time of sudden acceleration of the above-described embodiment. In order from the top, the accelerator pedal opening APO, the accelerator pedal opening changing speed VAPO, the required driving force P, the throttle valve opening TVO, An intake negative pressure boost, an exhaust gas recirculation rate EGR, an engine torque Te, and an actually generated driving force in the intake collector 16 are shown. In this example, as shown in the figure, when the accelerator pedal opening APO exceeds a predetermined value APOa and the accelerator pedal opening change speed VAPO is larger than the predetermined value APOa, it is determined that the rapid acceleration is requested. The required driving force P is a driving force (a product of torque and rotational speed) required for the driver's acceleration request, and is considered to be basically equal to the change in the accelerator pedal opening APO here. ing. Then, the throttle valve opening TVO is controlled according to the required driving force P. The intake negative pressure boost changes as the throttle valve opening TVO changes.

  Regarding the three components of the exhaust gas recirculation rate EGR, the engine torque Te, and the actually generated driving force, the conventional characteristics are indicated by broken lines, and the characteristics of the above-described embodiment are indicated by solid lines. That is, in the conventional system, as shown by the broken line as the exhaust gas recirculation rate EGR, the exhaust gas recirculation is continued even during acceleration. Become slow. As a result, the accelerator pedal described above tends to increase. On the other hand, in this embodiment, the exhaust gas recirculation rate EGR becomes 0 when the rapid acceleration is requested as indicated by the solid line, and the exhaust gas recirculation is stopped. Therefore, as shown by the solid line, the engine torque Te rises quickly, and the actual driving force is obtained along the required driving force P. In the example of FIG. 6, the exhaust gas recirculation rate EGR is set to 0 until the accelerator pedal opening APO becomes equal to or less than the predetermined value APOa after the determination of the rapid acceleration. Since it is important, for example, the exhaust gas recirculation may be stopped for a certain time from the sudden acceleration determination, and thereafter the exhaust gas recirculation may be resumed.

  Next, a specific method for determining the magnitude of the surplus torque in step 3 will be described.

  FIG. 7 shows the first embodiment. Each engine speed is lower by a certain ratio (A% in the figure) when the torque value at the theoretical air-fuel ratio limit is 100%. The torque value is set as a threshold Ta for magnitude determination, and if the torque at the time of a sudden acceleration request is in a region on the lower load side than the threshold Ta, it is determined that the surplus torque is large, and in a region on the higher load side than the threshold Ta. If so, it is determined that the margin torque is small.

  FIG. 8 shows the second embodiment. For each engine speed, a torque value lower than the theoretical air-fuel ratio limit torque value by a certain torque (B [Nm] in the figure) is judged to be large or small. If the torque at the time of sudden acceleration request is in the region on the lower load side than the threshold Tb, it is determined that the margin torque is large, and if the torque is in the region on the higher load side than the threshold Tb, the margin torque is present. Judged to be small.

  FIG. 9 shows a third embodiment. A constant torque value (C [Nm] in the figure) is set as a magnitude determination threshold value Tc regardless of the engine speed, and a rapid acceleration request is made. If the current torque is in the region on the lower load side than the threshold value Tc, it is determined that the margin torque is large, and if it is in the region on the higher load side than the threshold value Tc, it is determined that the margin torque is small. In particular, the value of the torque value C serving as the threshold value Tc coincides with the minimum torque value at the theoretical air-fuel ratio limit that varies depending on the engine speed.

  It should be noted that when determining whether the margin to the theoretical air-fuel ratio limit, which is the fuel efficiency deterioration region, is substituted for engine torque, the intake air amount of the internal combustion engine 1, the fuel injection pulse width, the throttle valve opening TVO, the intake negative pressure boost, Other parameters corresponding to the torque can also be used.

1 is a system configuration diagram showing an embodiment of the present invention. The characteristic view which shows the characteristic of a fuel consumption, a fuel increase area, and an exhaust gas recirculation rate with respect to the driving | running condition of an internal combustion engine. The characteristic view which shows the characteristic of the gear ratio with respect to the driving | running condition of an internal combustion engine. The characteristic view which showed the change of the driving | running condition by sudden acceleration when a margin torque is small. 3 is a flowchart showing exhaust gas recirculation control according to the present invention. Time chart showing changes in various parameters when sudden acceleration is requested. The characteristic view which shows the 1st Example of magnitude determination of a surplus torque. The characteristic view which shows the 2nd Example of magnitude determination of a surplus torque. The characteristic view which shows the 3rd Example of the magnitude determination of a surplus torque.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 10 ... Exhaust gas recirculation device 19 ... Engine control module 20 ... Accelerator opening sensor

Claims (7)

In a control device for an internal combustion engine that includes an exhaust gas recirculation device that recirculates a part of exhaust gas to an intake system and controls the exhaust gas recirculation device so as to have a predetermined exhaust gas recirculation rate according to an operation condition of the internal combustion engine. Means for detecting the acceleration request, and means for discriminating the size of the margin from the operating condition of the internal combustion engine when the acceleration request is detected to a predetermined fuel consumption deterioration region on the high load side. A control device for an internal combustion engine, which stops exhaust gas recirculation by the exhaust gas recirculation device when small, and controls the exhaust gas recirculation device so that a predetermined exhaust gas recirculation rate is obtained according to operating conditions otherwise. .   2. The control apparatus for an internal combustion engine according to claim 1, wherein the fuel efficiency deterioration region is a fuel increase region in which a target air-fuel ratio of the internal combustion engine is equal to or less than a theoretical air-fuel ratio.   The control device for an internal combustion engine according to claim 1 or 2, wherein the magnitude of the margin is determined based on the torque of the internal combustion engine when an acceleration request is detected or a parameter that is a substitute for the torque.   When the difference between the torque of the internal combustion engine when the acceleration request is detected and the torque at the boundary of the fuel consumption deterioration region at the same rotational speed is smaller than a predetermined value, it is determined that the margin is small. The control apparatus for an internal combustion engine according to claim 3.   When the ratio of the torque of the internal combustion engine when the acceleration request is detected to the torque at the boundary of the fuel consumption deterioration region at the same rotational speed is a predetermined value or more, it is determined that the margin is small. The control device for an internal combustion engine according to claim 3.   4. The method according to claim 3, wherein the margin is determined to be small when the torque of the internal combustion engine when the acceleration request is detected is greater than the minimum value of the torque at the boundary of the fuel consumption deterioration region. The internal combustion engine control device described.   The control apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the internal combustion engine is combined with a continuously variable transmission whose speed ratio is variably controlled in accordance with a driving state of the vehicle.

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