JP2010242708A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain the occurrence of a misfire, even when an error is caused in the estimate air-fuel ratio, in air-fuel ratio control of an internal combustion engine. <P>SOLUTION: In the air-fuel ratio control of the internal combustion engine, an upper limit value and a lower limit value of the takable air-fuel ratio are determined, and an air-fuel ratio range is determined by these upper limit value and lower limit value. The ignition timing is set in the timing of not causing the misfire even if the actual air-fuel ratio is any air-fuel ratio in a predetermined air-fuel ratio range. For example, when starting the internal combustion engine, a starting time air-fuel ratio range is set so that when fuel is heavy fuel, the air-fuel ratio measured when starting is set as the upper limit value, and when the fuel is light fuel, the air-fuel ratio measured when starting is set as the lower limit value. When starting the internal combustion engine, in any air-fuel ratio in the starting time air-fuel ratio range, the ignition timing is advanced to a range of not causing the misfire, and the ignition timing is delayed after starting ignition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine.

  For example, Patent Document 1 discloses a technique for controlling the air-fuel ratio of an internal combustion engine. Specifically, in the air-fuel ratio control of the internal combustion engine of this technique, the upper limit value and the lower limit value of the normal air-fuel ratio of the internal combustion engine are set. Then, a time period when the air-fuel ratio exceeds the upper limit value and a time period when the air-fuel ratio falls below the lower limit value are measured between a cycle where the air-fuel ratio is deep and a light cycle. Thereafter, by comparing both time periods, it is determined whether the air-fuel ratio is in a rich state or a thin state, and the air-fuel ratio is adjusted based on this determination.

JP-A-4-269348 JP 2000-234550 A JP 2008-115802 A JP 09-217640 A JP 2005-120886 A

  However, the estimated value of the air-fuel ratio calculated in the feedback control of the air-fuel ratio of the internal combustion engine includes errors due to an intake air amount estimation error, an engine rotational speed detection error, an engine friction estimation error, and the like. included. For this reason, when the fuel injection amount and the ignition timing are determined and controlled based on the estimated air-fuel ratio, the actual air-fuel ratio differs from the required air-fuel ratio, for example, causing a lean misfire. obtain.

  Accordingly, in order to solve the above problems, the present invention provides an air-fuel ratio control apparatus for an internal combustion engine that is improved so as to suppress the occurrence of misfire even when an error occurs in an estimated air-fuel ratio.

In order to achieve the above object, a first invention is an air-fuel ratio control apparatus for an internal combustion engine,
An air-fuel ratio range estimating means for estimating an air-fuel ratio range which is a possible range of the air-fuel ratio of the internal combustion engine;
Ignition timing setting means for setting the ignition timing so as not to cause misfire at any air-fuel ratio within the air-fuel ratio range;
It is characterized by providing.

According to a second invention, in the first invention,
When starting the internal combustion engine, when the fuel is heavy fuel, the upper limit is the air-fuel ratio measured at the start, and when the fuel is light fuel, the air-fuel ratio measured at the start is the lower limit. , Further comprising a starting air-fuel ratio range setting means for setting the starting air-fuel ratio range,
The ignition timing setting means includes
At the start of the internal combustion engine, at any air-fuel ratio within the starting air-fuel ratio range, the ignition timing is advanced to a range that does not cause misfire,
After ignition in each cylinder is started, the ignition timing is retarded to the maximum within a range in which no misfire occurs at any air-fuel ratio within the air-fuel ratio range estimated by the air-fuel ratio range estimation means. Features.

  According to the first aspect of the invention, when the air-fuel ratio is estimated in the air-fuel ratio control, the value that the air-fuel ratio can take is estimated as a range. In addition, the ignition timing is set so that misfire does not occur at any air-fuel ratio within this air-fuel ratio range. Therefore, it is possible to suppress misfire due to an error in the estimated value of the air-fuel ratio. In addition, since the air-fuel ratio can be estimated as a range and control can be performed so as not to cause misfire according to the entire air-fuel ratio range, there is no need to switch the control for each fuel evaporation characteristic, and the control process is reduced. Can be reduced.

  According to the second aspect of the invention, the range of the air-fuel ratio range can be set in advance by the upper limit value and the lower limit value in consideration of the fuel properties at the start, and control can be performed so as not to cause misfire within this range. Thereby, the control according to the fuel property at the time of starting can be made unnecessary. In addition, after the start of ignition in the cylinder, the ignition timing is retarded to the maximum in a range where no misfire occurs in the air-fuel ratio range. Thereby, the discharge amount of HC can be reduced.

It is a figure for demonstrating the relationship between the air fuel ratio and ignition timing in Embodiment 1 of this invention. It is a figure for demonstrating the relationship between the air fuel ratio and ignition timing in Embodiment 2 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment 1 FIG.
[Calculation method of estimated air-fuel ratio range]
The output torque of the internal combustion engine is determined based on the in-cylinder air amount, the ignition timing, and the engine speed, as shown in the following equation (1). Here, the in-cylinder air amount is an estimated value calculated according to another model formula.
Torque = f (In-cylinder air amount, ignition timing, estimated A / F, engine speed) (1)

Further, the output torque of the internal combustion engine can also be calculated based on the engine rotational fluctuation and the internal combustion engine friction as in the following equation (2).
J ・ dω / dt = Torque-Friction (2)
In equation (2), J is the moment of inertia of the internal combustion engine, dω / dt is the angular acceleration, and is calculated from the engine speed fluctuation of the internal combustion engine. Friction is an estimated value calculated from water temperature and engine speed.

From the above equations (1) and (2), the air-fuel ratio (estimated A / F) is estimated as follows.
Estimated A / F = f ^-1 (J ・ dω / dt + friction, cylinder air quantity, ignition timing, engine speed) (3)

  By the way, it is considered that an error α occurs in the estimated A / F calculated according to the above equation (3) due to the angular acceleration dω / dt, the friction, and the in-cylinder air amount. That is, it is considered that there is a difference in error α between the estimated A / F and the actual A / F.

  Therefore, for example, although the actual A / F is 16, the estimated A / F may be calculated as 14.7. When the estimated A / F indicates the target air-fuel ratio as in this example, the fuel injection amount is not corrected. Therefore, in actuality, the fuel is supplied with the amount of A / F being 16. On the other hand, even when the fuel injection amount is actually an amount corresponding to A / F of 16, the ignition timing is controlled as it is when the A / F is 14.7. . As a result, a lean misfire may occur.

  Therefore, in the first embodiment, instead of calculating the estimated A / F, the entire range (A / F range) of the in-cylinder air-fuel ratio (that is, the value that the actual A / F can take) is calculated. In addition, the ignition timing is set to a timing that does not cause misfire for the entire A / F range. This suppresses the occurrence of misfire regardless of the value of the actual A / F within the A / F range.

[A / F range calculation method]
The A / F range is calculated by calculating an upper limit value (upper limit A / F) and a lower limit value (lower limit A / F) of the estimated A / F due to the error of the variable in the above equation (3). Specifically, the in-cylinder air amount calculated by the model equation and friction are likely to include a relatively large error in equation (3). The actual A / F is increased when the actual torque is small. In this case, there is a physical characteristic that the in-cylinder air amount is large. Therefore, in Equation (3), the estimated A / F is the largest when the actual friction is the lowest value in the error range, and the actual in-cylinder air amount is within the error range. This is considered to be the maximum value. From the above, the upper limit A / F can be obtained by setting the friction as friction−Δfriction and the in-cylinder air amount as in-cylinder air amount + Δair amount in equation (3).

  Similarly, the estimated A / F is the smallest when the actual friction is the maximum value within the error range, and when the in-cylinder air amount is the minimum value within the error range. It is believed that there is. Therefore, the lower limit A / F is calculated by setting the friction as friction + Δfriction and the in-cylinder air amount as in-cylinder air amount−Δair amount in the equation (3).

  Note that the terms of Δ (that is, Δ friction and Δ air amount) are both estimated amounts of estimated value errors, and are obtained in advance and stored in the control device. These values are set with a certain margin.

[Method of Air-Fuel Ratio Control of Embodiment 1]
FIG. 1 is a diagram for illustrating the relationship between in-cylinder air-fuel ratio and ignition timing in Embodiment 1 of the present invention. In FIG. 1, the horizontal axis represents the in-cylinder air-fuel ratio, and the vertical axis represents the ignition timing. In FIG. 1, the calculated A / F range is represented by a straight line (A).

  Further, the in-cylinder air-fuel ratio and the limit value of the ignition timing with which it does not misfire are represented by a one-dot chain line (B) and a broken line (C). A region where the ignition timing is advanced from the alternate long and short dash line (B) is a misfire region, and similarly, a region where the ignition timing is retarded from the broken line (C) is a misfire region. An alternate long and short dash line (D) represents a region (knock region) where knocking is expected to occur.

  In the system of the first embodiment, the entire calculated A / F range (straight line (A)) falls within the area (ignition area) surrounded by the alternate long and short dash lines (B), (C), and (D). Control ignition timing. More specifically, when the upper limit A / F or the lower limit A / F is outside this ignition region, the ignition timing is set to the MBT side so that the upper limit A / F and the lower limit A / F are within the ignition region. Control to be closer to.

  For example, in Fig. 1, when the upper limit A / F is a misfire area, as in the A / F range (straight line (A)), the entire A / F range (A) is represented by a broken line (E). Correct the ignition timing to advance to the MBT side so that it is within the A / F range.

  In addition, the upper limit A / F and lower limit A / F side values of the A / F range may both be in the misfire region. In this case, the ignition timing range where the upper limit A / F falls within the ignition range and the ignition timing range where the lower limit A / F falls within the ignition range are obtained, and the ignition timing range (H) common to both ignition timing ranges is determined as the ignition timing range. Set as.

  As described above, according to the first embodiment, the range of possible air-fuel ratios is estimated, and by setting the ignition timing within which the entire A / F range falls within the ignition region, the deviation of the air-fuel ratio estimation can be achieved. The occurrence of misfire due to can be suppressed.

  Although the calculation method of the estimated A / F has been described in this embodiment, the calculation method of the estimated A / F is limited to that calculated by the model equations described in the above equations (1) to (3). is not. When calculating the estimated A / F by other methods, calculating the A / F range including the error that may occur, and placing this A / F range within the ignition region will similarly prevent misfires. Can be suppressed.

Embodiment 2. FIG.
FIG. 2 is a diagram for explaining the relationship between the in-cylinder air-fuel ratio and the ignition timing in the second embodiment of the present invention. In FIG. 1, the horizontal axis represents the in-cylinder air-fuel ratio, and the vertical axis represents the ignition timing.

  The system according to the second embodiment is different from the system according to the first embodiment in the control at the time of starting. Specifically, the fuel properties used in the internal combustion engine vary, and the evaporation characteristics differ depending on the fuel properties. For this reason, until the air-fuel ratio sensor is activated, the detected air-fuel ratio varies greatly depending on the fuel properties. Therefore, for example, if control is performed so that incomplete combustion such as misfire does not occur even in heavy fuel, HC discharged in light fuel increases. This complicates the control and increases the number of processes by tuning.

  Further, since ignition is not performed from the cranking to the start of combustion, the composition of the air-fuel mixture is unknown, and the torque cannot be calculated by the above equation (1). Therefore, the A / F range is set to a predetermined maximum width until ignition occurs. That is, here, the upper limit A / F is measured in advance for A / F in the case of heavy fuel, and the lower limit A / F is set in advance by measuring the A / F for light fuel.

  At the time of starting, as shown by the straight line (a) in FIG. 2, control is performed on the advance side so that the minimum value on the rich side is not less than a predetermined value. At this time, the set A / F upper limit can be ignited. The ignition timing is advanced to the most retarded amount within the ignition timing range.

  After that, after ignition has started and the air-fuel ratio monitor can be used, or after transition to a steady state and the A / F range has been reduced, as shown in the straight line (b) of FIG. Switch the control to a condition with good warm-up. Specifically, for example, the fuel injection amount is determined with the air-fuel ratio target value as the lean limit value (16 to 18), and the air-fuel ratio is controlled within this range. The ignition timing is retarded to the most retarded side (for example, about BDTC-10 or less) of the ignition range where the upper limit A / F ignites. Thereby, it can switch to the conditions with good warm-up property, reducing HC.

  In the above embodiment, when referring to the number of each element, quantity, quantity, range, etc., the reference is made unless otherwise specified or the number is clearly specified in principle. The invention is not limited to the numbers. Further, the structure and the like described in this embodiment are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

Claims (2)

An air-fuel ratio range estimating means for estimating an air-fuel ratio range which is a possible range of the air-fuel ratio of the internal combustion engine;
Ignition timing setting means for setting the ignition timing so as not to cause misfire at any air-fuel ratio within the air-fuel ratio range;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: At the start of the internal combustion engine, when the fuel is heavy fuel, the upper limit is the air-fuel ratio measured at the start, and when the fuel is light fuel, the air-fuel ratio measured at the start is the lower limit. A starting air-fuel ratio range setting means for setting a starting air-fuel ratio range, further comprising:
The ignition timing setting means includes
At the start of the internal combustion engine, at any air-fuel ratio within the starting air-fuel ratio range, the ignition timing is advanced to a range that does not cause misfire,
After ignition in each cylinder is started, the ignition timing is retarded to the maximum within a range in which no misfire occurs at any air-fuel ratio within the air-fuel ratio range estimated by the air-fuel ratio range estimation means. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein

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