JP2009275522A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control device of an internal combustion engine capable of improving drivability of the internal combustion engine even before completion of learning of alcohol concentration. <P>SOLUTION: The internal combustion engine 10 is provided with an air-fuel ratio sensor 19 which is raised in temperature by a heater 19a when engine temperature is within a predetermined temperature range. The control device 22 performs air-fuel ratio feedback control based on an output value of the air-fuel ratio sensor 19, performs a concentration learning process for estimating the alcohol concentration of fuel in a fuel tank 30 based on a correction value of a fuel injection quantity calculated in the air-fuel feedback control and corrects the fuel injection quantity according to the estimated alcohol concentration. The control device 22 forcibly energizes the heater 19a when the concentration learning process is not completed even if the engine temperature is equal to or lower than the predetermined temperature range, and corrects the fuel injection quantity so that a difference between an actual air-fuel ratio detected by the air-fuel ratio sensor 19 activated by the forcible energization and a target air-fuel ratio is settled within a predetermined range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel injection control device for an internal combustion engine.

  In an internal combustion engine, air-fuel ratio feedback control is performed to correct the fuel injection amount in accordance with the actual air-fuel ratio detected by the air-fuel ratio sensor in order to control the air-fuel ratio of the air-fuel mixture to an optimal air-fuel ratio according to the engine operating state. Is done. The air-fuel ratio sensor can detect the actual air-fuel ratio when its temperature (more specifically, the temperature of the detection element) is equal to or higher than the activation temperature. Therefore, the air-fuel ratio sensor is provided with a heater that is energized when the engine temperature is within a predetermined temperature range, and the air-fuel ratio sensor is activated early by this heater.

  On the other hand, in an internal combustion engine that can use alcohol fuel, the fuel injection amount corresponding to the optimum air-fuel ratio changes according to the alcohol concentration in the fuel. Since such alcohol concentration correlates with the correction value of the fuel injection amount calculated by the air-fuel ratio feedback control, concentration learning processing is executed to estimate the alcohol concentration from such correction value, and the alcohol concentration is determined according to the estimated alcohol concentration. Thus, the fuel injection amount is corrected.

  Here, when fuel is supplied to the fuel tank, there is a possibility that the alcohol concentration in the fuel has changed, and it is necessary to learn the alcohol concentration again. However, immediately after starting the engine in a low temperature environment, the engine temperature is excessively low and the exhaust gas temperature is also low. Therefore, even if air-fuel ratio feedback control is performed, exhaust purification by the catalyst cannot be expected so much. Therefore, immediately after the engine is started in a low temperature environment, the energization of the heater of the air-fuel ratio sensor and the execution of the air-fuel ratio feedback control are suspended until the engine temperature rises to some extent. As described above, under the situation where the execution of the air-fuel ratio feedback control is suspended for a while, the concentration learning process as described above cannot be performed, and the alcohol concentration remains unknown.

In order to correct the fuel injection amount even when the concentration learning process is not completed, for example, the apparatus described in Patent Document 1 performs the following process. That is, until the concentration learning process is completed, a value near a concentration that is approximately between the alcohol concentration of the fuel with the highest alcohol concentration and the alcohol concentration of the fuel with the lowest alcohol concentration of fuel that may be refueled. The fuel injection amount is corrected based on the fixed temporary alcohol concentration fixed value.
JP 2004-293491 A

  When the alcohol concentration of the fuel is set to a preset fixed value until the concentration learning process is completed as described in the above-mentioned document 1, a deviation occurs from the actual alcohol concentration, and the fuel injection amount is changed to the alcohol concentration. Accordingly, the correction accuracy at the time of correction is reduced. For this reason, the actual air-fuel ratio also deviates from the ideal air-fuel ratio, and the combustion state of the air-fuel mixture deteriorates, so that the drivability of the internal combustion engine decreases.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a fuel injection control device for an internal combustion engine that can improve the drivability of the internal combustion engine even before learning of the alcohol concentration is completed. It is to provide.

In the following, means for achieving the above object and its effects are described.
The invention according to claim 1 includes an air-fuel ratio sensor that is activated by being heated by a heater when the engine temperature is within a predetermined temperature range, and is based on the output value of the air-fuel ratio sensor. The feedback control is executed, and the concentration learning process for estimating the alcohol concentration of the fuel stored in the fuel tank is executed based on the correction value of the fuel injection amount calculated by the air-fuel ratio feedback control. In a fuel injection control device for an internal combustion engine that corrects a fuel injection amount in accordance with an alcohol concentration, a forced energization is performed to the heater when the concentration learning process is not completed even when the engine temperature is equal to or lower than the temperature range. The deviation between the air-fuel ratio detected by the energizing means and the air-fuel ratio sensor activated by the forced energization and the target air-fuel ratio falls within a predetermined range. As its gist in that it comprises an injection amount correction means for correcting the fuel injection quantity so that.

  In this configuration, the heater provided in the air-fuel ratio sensor is energized when the engine temperature is within a predetermined temperature range. Here, according to the configuration, when the engine temperature is equal to or lower than the above temperature range, that is, in an excessively low temperature environment where the heater is not normally energized, a concentration learning process for learning the alcohol concentration of the fuel. When the process is not completed, the heater is forcibly energized so that the air-fuel ratio can be detected by the air-fuel ratio sensor. Then, the fuel injection amount is corrected so that the difference between the air-fuel ratio detected by the air-fuel ratio sensor activated by forced energization of the heater and the target air-fuel ratio falls within a predetermined range. Therefore, even before the learning of the alcohol concentration is completed, the actual air-fuel ratio can be brought close to the ideal air-fuel ratio, that is, the target air-fuel ratio, and the combustion state of the air-fuel mixture is maintained in a good state. be able to. Therefore, according to the configuration, drivability of the internal combustion engine can be improved even before the learning of the alcohol concentration is completed. As the engine temperature, the coolant temperature, oil temperature, etc. of the engine can be used as substitute values.

  According to a second aspect of the present invention, in the fuel injection control device for an internal combustion engine according to the first aspect, the target air-fuel ratio is greater than the stoichiometric air-fuel ratio until the engine temperature rises from the temperature range to a predetermined temperature. The gist of this is that the value is also set to a rich value.

  Immediately after starting the engine in a low-temperature environment where the engine temperature is likely to be below the above temperature range, it is difficult to promote the vaporization of the fuel contained in the mixture, so the air-fuel ratio of the mixture becomes substantially lean, and the combustion of the mixture Tends to be unstable. Therefore, in this configuration, the target air-fuel ratio is set to a richer value than the stoichiometric air-fuel ratio until the engine temperature rises from the temperature range below the predetermined temperature to a predetermined temperature. Insufficient fuel vaporization immediately after engine startup is compensated. Here, according to the configuration, immediately after the engine is started, the actual air-fuel ratio can be brought close to the target air-fuel ratio by the forced energization means and the injection amount correction means. The combustion state of the air-fuel mixture can be suitably stabilized.

  According to a third aspect of the present invention, in the fuel injection control device for an internal combustion engine according to the second aspect, the first determination value set to a richer side than the stoichiometric air-fuel ratio and a richer than the first determination value. The fuel injection amount is set when the air-fuel ratio detected by the air-fuel ratio sensor is leaner than the first determination value. The main point is to correct the fuel injection amount by decreasing the fuel injection amount when the air-fuel ratio detected by the air-fuel ratio sensor becomes richer than the second determination value.

  According to the same configuration, the actual air-fuel ratio falls within the range between the first determination value and the second determination value. Therefore, the actual air-fuel ratio can be maintained on the rich side in accordance with the target air-fuel ratio set to a value on the rich side with respect to the theoretical air-fuel ratio.

  According to a fourth aspect of the present invention, in the fuel injection control device for an internal combustion engine according to any one of the first to third aspects, the air-fuel ratio feedback control is performed by using an air-fuel ratio detected by the air-fuel ratio sensor and a target. This is control for calculating, as the correction value, a value composed of a correction term that is constantly updated according to the deviation from the air-fuel ratio and a learning term that is updated when the correction term exceeds a predetermined range. The gist of the concentration learning process is a process of estimating the alcohol concentration based on the learning term.

  In this configuration, the correction value of the fuel injection amount calculated by the air-fuel ratio feedback control is a constant that is constantly updated according to the amount of deviation between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio, The learning term is updated when the correction term exceeds a predetermined range. Here, the correction value including the correction term fluctuates in accordance with the engine operating state at that time. Therefore, if the alcohol concentration is estimated directly from such a correction value, the estimated alcohol concentration also fluctuates. On the other hand, the learning term updated when the correction term exceeds a predetermined range is a value with relatively little fluctuation, and the value reflects the setting tendency of the correction term that changes according to the alcohol concentration. The Therefore, it is possible to estimate the alcohol concentration based on the learning term. Therefore, in the same configuration, the alcohol concentration is estimated based on the learning term, so that the estimated value of the alcohol concentration can be stabilized. Here, since the learning term is updated after the correction term is changed to some extent, in the concentration learning processing using the learning term, when the alcohol concentration of the fuel changes, the corresponding concentration learning processing that has changed. It takes some time to complete.

  In this respect, according to the same configuration, the actual air-fuel ratio can be brought close to the target air-fuel ratio by the forced energization means and the injection amount correction means until the concentration learning process is completed. Even when the concentration learning process that takes a certain amount of time is executed, the drivability of the internal combustion engine before the completion of the execution of the concentration learning process can be improved.

  As the execution condition of the concentration learning process, as in the invention according to claim 5, it is determined whether or not the fuel tank has been refueled, and the concentration learning process is performed when it is determined that refueling is present. A configuration such as can be adopted. Note that the fuel supply to the fuel tank can be determined based on a change in the fuel gauge or the like.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying a fuel injection control device for an internal combustion engine according to the present invention will be described below with reference to FIGS.
FIG. 1 shows a schematic configuration of an internal combustion engine 10 to which the fuel injection control device according to the present embodiment is applied.

  As shown in FIG. 1, the intake passage 11 of the internal combustion engine 10 is provided with a throttle valve 15 whose passage area is variable, and the amount of air taken in through the air cleaner 14 is adjusted by opening degree control. Is done. The amount of inhaled air (intake air amount) is detected by the air flow meter 16. An injector 17 that injects fuel is provided downstream of the throttle valve 15, and fuel in the fuel tank 30 is supplied to the injector 17 via a fuel supply system 31. The fuel tank 30 is supplied with alcohol fuel in addition to gasoline fuel. That is, the internal combustion engine 10 is an engine that can use not only gasoline fuel but also alcohol fuel or a mixed fuel of gasoline fuel and alcohol fuel.

The air sucked into the intake passage 11 is mixed with the fuel injected from the injector 17 and then sent to the combustion chamber of the internal combustion engine 10 for combustion.
On the other hand, an exhaust gas purification catalyst 18 for purifying components in the exhaust gas is provided in the exhaust gas passage 13 through which exhaust gas generated by combustion in the combustion chamber is sent. The catalyst 18 has an action of purifying the exhaust gas by oxidizing HC and CO in the exhaust gas and reducing NOx in the exhaust gas in a state where combustion is performed in the vicinity of the theoretical air-fuel ratio (= 14.7). is doing.

  An air-fuel ratio sensor 19 is provided upstream of the catalyst 18. The air-fuel ratio sensor 19 is a well-known limiting current type oxygen sensor. This limiting current type oxygen sensor is a sensor that provides an output current according to the oxygen concentration in the exhaust gas by providing a ceramic layer called a diffusion rate limiting layer in the detection part of the concentration cell type oxygen sensor, and the oxygen concentration in the exhaust gas When the air-fuel ratio of the air-fuel mixture that is closely related to the stoichiometric air-fuel ratio is the stoichiometric air-fuel ratio, the output current is “0”. Further, the output current increases in the negative direction as the air-fuel ratio becomes rich, and the output current increases in the positive direction as the air-fuel ratio becomes lean. Therefore, the actual air-fuel ratio AFr of the air-fuel mixture is detected based on the output value of the air-fuel ratio sensor 19. The air-fuel ratio sensor 19 can detect the air-fuel ratio when its temperature (more specifically, the temperature of the detection element) is equal to or higher than the activation temperature. Here, if the engine warm-up progresses to some extent, the air-fuel ratio sensor 19 is activated by exhaust, but it is difficult to raise the temperature by exhaust immediately after the engine is started in a low temperature environment. Therefore, the air-fuel ratio sensor 19 is provided with a heater 19a that is energized when the engine temperature is within a predetermined temperature range, and the air-fuel ratio sensor 19 can be activated early by the heater 19a. ing.

  The catalyst 18 efficiently removes all of the main harmful components (HC, CO, NOx) in the exhaust gas by an oxidation-reduction reaction only when the air-fuel ratio of the air-fuel mixture to be burned is in a narrow range (window) near the stoichiometric air-fuel ratio. Purify. In order for such a catalyst 18 to function effectively, strict air-fuel ratio control is required in which the air-fuel ratio of the air-fuel mixture is adjusted to the center of the window.

  Such control of the air-fuel ratio is performed by the control device 22. The control device 22 includes the air flow meter 16, the air-fuel ratio sensor 19, a water temperature sensor 20 that detects the coolant temperature THW of the internal combustion engine 10, an accelerator sensor that detects the amount of depression of the accelerator pedal, and a rotational speed that detects the engine rotational speed. Detection signals of various sensors including a sensor or a fuel gauge 32 for detecting the fuel amount F in the fuel tank 30 are input. Then, the air-fuel ratio control is performed by drivingly controlling the throttle valve 15 and the injector 17 according to the operation status of the internal combustion engine 10 and the vehicle grasped by the detection signals of these sensors. The outline of the air-fuel ratio control by such a control device 22 is as follows.

  First, the control device 22 obtains the required amount of intake air that is grasped according to the amount of depression of the accelerator pedal, the engine speed, etc., and the opening of the throttle valve 15 is adjusted so that the intake air amount corresponding to that is obtained. adjust.

  On the other hand, a basic fuel injection amount Qb sufficient to obtain a theoretical air-fuel ratio is obtained with respect to the intake air amount detected by the air flow meter 16. Further, the air-fuel ratio feedback correction amount FH is calculated based on the deviation amount between the actual air-fuel ratio AFr detected by the air-fuel ratio sensor 19 and the target air-fuel ratio AFp, that is, the theoretical air-fuel ratio. When the actual air-fuel ratio AFr is richer than the target air-fuel ratio AFp, the air-fuel ratio feedback correction amount FH is set such that the fuel injection amount is reduced according to the richness. On the other hand, when the actual air-fuel ratio AFr is leaner than the target air-fuel ratio AFp, the value is set so that the fuel injection amount is increased according to the lean degree. The injector is configured such that the final fuel injection amount Qf is obtained by correcting the basic fuel injection amount Qb by reducing or increasing the basic fuel injection amount Qb based on the air-fuel ratio feedback correction amount FH thus set, and that final fuel injection amount Qf is injected. The valve opening period of 17 is adjusted. Such air-fuel ratio feedback control ensures the required accuracy of air-fuel ratio control.

  The air-fuel ratio feedback correction amount FH is updated when the correction term FA that is constantly updated in accordance with the amount of deviation between the actual air-fuel ratio AFr and the target air-fuel ratio AFp, and when the correction term FA exceeds a preset range. And a learning term FB.

  More specifically, when the actual air-fuel ratio AFr is richer than the target air-fuel ratio AFp, the correction term FA is set to a negative value so that the fuel injection amount is reduced according to the rich degree. On the other hand, when the actual air-fuel ratio AFr is leaner than the target air-fuel ratio AFp, a positive value is set so that the fuel injection amount is increased according to the lean degree.

  The learning term FB is updated as follows. That is, when the correction term FA reaches a preset lower limit value FAL (FAL <0), the predetermined update amount FB1 is subtracted from the learning term FB, and the update amount FB1 is added to the correction term FA along with this subtraction. Is done. On the other hand, when the correction term FA reaches a preset upper limit value FAU (FAU> 0), a predetermined update amount FB2 is added to the learning term FB, and an update amount FB2 is added from the correction term FA along with this addition. Subtracted. By updating the learning term FB and correcting the correction term FA in conjunction with the update, an excessive increase in the absolute value of the correction term FA is suppressed, and the learning term FB has a setting tendency of the correction term FA, that is, The tendency of deviation of the actual air-fuel ratio is reflected.

  Note that immediately after the engine is started in a low-temperature environment, the fuel contained in the air-fuel mixture is less likely to be vaporized, so the air-fuel ratio of the air-fuel mixture becomes substantially lean and combustion of the air-fuel mixture tends to become unstable. Therefore, when starting the engine in a low-temperature environment, the target air-fuel ratio AFp is set to a richer value than the stoichiometric air-fuel ratio until the engine temperature rises to a predetermined temperature and fuel vaporization is promoted. Is set. More specifically, the low temperature increase correction is performed on the final fuel injection amount Qf until the coolant temperature THW reaches a preset warm-up determination temperature TD. This compensates for insufficient fuel vaporization immediately after the engine is started in a low-temperature environment, and the combustion of the air-fuel mixture becomes stable. By the way, when such low temperature increase correction is performed, the fuel injection amount is controlled by open loop control during the period in which the air / fuel ratio feedback control cannot be executed, and when the air / fuel ratio feedback control becomes executable, The open loop control is stopped, and the fuel injection amount is controlled by air-fuel ratio feedback control. Note that while the low temperature increase correction is being performed, the fuel injection amount may be always controlled by open loop control.

  On the other hand, in the internal combustion engine 10, not only gasoline fuel but also alcohol fuel is used. In such an internal combustion engine 10, the fuel injection amount corresponding to the optimum air-fuel ratio changes according to the alcohol concentration in the fuel. Basically, the fuel injection amount needs to be increased and corrected as the alcohol concentration increases. Since such alcohol concentration correlates with the correction value of the fuel injection amount calculated by the air-fuel ratio feedback control, concentration learning processing is executed to estimate the alcohol concentration from such correction value, and the alcohol concentration is determined according to the estimated alcohol concentration. Thus, the final fuel injection amount Qf is corrected.

  More specifically, since the actual air-fuel ratio AFr shifts to the lean side as the alcohol concentration increases, the correction value of the fuel injection amount calculated in the air-fuel ratio feedback control increases to the positive side, that is, to the rich correction side. Become. Accordingly, it is possible to estimate that the alcohol concentration is higher as the lean degree of the actual air-fuel ratio AFr is higher or as the correction value of the fuel injection amount is increased to the positive side. Here, the air-fuel ratio feedback correction amount FH, which is the correction value of the fuel injection amount, includes a correction term FA that is constantly updated in accordance with the amount of deviation between the actual air-fuel ratio AFr and the target air-fuel ratio AFp. Therefore, the value fluctuates according to the engine operating state at that time. Therefore, when the alcohol concentration is directly estimated from the air-fuel ratio feedback correction amount FH, the alcohol concentration in the fuel in the fuel tank 30 is estimated even though it should be originally a constant value according to the fuel supplied. The alcohol concentration to be changed will come to fluctuate. On the other hand, the learning term FB updated when the correction term FA exceeds a predetermined range is a value with relatively little fluctuation, and the value has a tendency to set the correction term FA that changes according to the alcohol concentration. Is reflected. Therefore, it is possible to estimate the alcohol concentration based on the learning term FB. Therefore, in the present embodiment, the alcohol concentration is estimated based on the learning term FB, whereby the estimated value of the alcohol concentration is stabilized, and the alcohol concentration in the fuel in the fuel tank 30 is estimated appropriately. Then, the concentration correction amount NH whose value is increased as the estimated alcohol concentration is higher is calculated, and the concentration correction amount NH is added to the final fuel injection amount Qf. The injection amount is corrected to increase.

Next, various processes related to the density learning process will be described.
When the fuel tank 30 is refueled, the alcohol concentration in the fuel may have changed, and the alcohol concentration learned before refueling needs to be learned again. Therefore,
First, it is determined whether or not the density learning process is to be executed through the density learning completion flag off setting process shown in FIG. This process is repeatedly executed at predetermined intervals by the control device 22.

  When this process is started, it is first determined whether or not it is an engine start time (S100). Here, affirmative determination is made when the ignition switch is immediately after being changed from OFF to ON. If it is not when the engine is started (S100: NO), this process is temporarily terminated.

  On the other hand, when the engine is being started (S100: YES), it is determined whether or not the fuel supply determination flag FK is set to “ON” (S110). The fuel supply determination flag FK is set to “ON” on condition that the increase amount of the fuel amount F in the fuel tank 30 exceeds a predetermined fuel supply determination value. For example, if the fuel amount F immediately after the start of the current engine is increased with respect to the fuel amount F immediately after the previous engine stop, and the increase amount exceeds the fuel supply determination value, the fuel supply determination flag FK is “ON”. "Is set. If the refueling determination flag FK is set to “OFF” (S110: NO), this process is temporarily terminated.

  On the other hand, when the fuel supply determination flag FK is set to “ON” (S110: YES), fuel is being supplied to the fuel tank 30, and the alcohol concentration in the fuel in the fuel tank 30 is changing. Since there is a possibility, the density learning completion flag FF is set to “OFF” (S120), and this process is temporarily terminated. When the concentration learning completion flag FF is set to “OFF” in this way, the condition that the learning term FB is being updated while the air-fuel ratio feedback control is being executed is further satisfied. The concentration learning process is executed, and the alcohol concentration is estimated. When the concentration learning process is completed and the relearning of the alcohol concentration is completed, the concentration learning completion flag FF is set to “ON” and the fuel supply determination flag FK is set to “OFF”.

  By the way, immediately after the engine is started in a low temperature environment, the engine temperature is excessively low and the exhaust gas temperature is low. Therefore, even if air-fuel ratio feedback control is performed, exhaust purification by the catalyst 18 cannot be expected so much. Further, under such a low temperature environment, the low temperature increase correction as described above is performed when setting the fuel injection amount. For these reasons, immediately after starting the engine in a low temperature environment, etc., until the engine temperature rises to some extent (for example, the coolant temperature THW correlated with the engine temperature exceeds the first determination temperature T1 set to about 0 ° C. Until execution of the air-fuel ratio feedback control is suspended. Further, energization to the heater 19a involved in the activation of the air-fuel ratio sensor 19 essential for the execution of the air-fuel ratio feedback control is also continued until the engine temperature rises to some extent (for example, the coolant temperature THW correlated with the engine temperature is -3 °). The execution is suspended until the second judgment temperature T2 set to about C is exceeded. Thus, under the situation where the execution of the air-fuel ratio feedback control is suspended for a while, the concentration learning process as described above cannot be performed, and the alcohol concentration in the fuel remains unknown. Therefore, after the engine is started, the fuel injection amount cannot be corrected according to the alcohol concentration until the learning of the alcohol concentration is completed after the execution of the air-fuel ratio feedback control is started. The state deteriorates and the drivability of the internal combustion engine 10 decreases.

  Therefore, in the present embodiment, the drivability correction process shown in FIG. 3 is executed to improve the drivability of the internal combustion engine 10 before the completion of the alcohol concentration learning. This injection amount correction process is also repeatedly executed by the control device 22 at predetermined intervals. Further, this processing constitutes the forced energization means and the injection amount correction means.

  When this process is started, it is first determined whether or not the above-described density learning completion flag FF is set to “OFF” (S200). When the concentration learning completion flag FF is set to “ON” (S200: NO), the alcohol concentration learning is completed and the concentration correction amount NH can be calculated. It is possible to appropriately correct the fuel injection amount without performing the injection amount correction. Therefore, in this case, this process is temporarily terminated.

  On the other hand, when the concentration learning completion flag FF is set to “OFF” (S200: YES), it is next determined whether or not the ON condition of the heater 19a is satisfied (S210). As the ON condition, as described above, a condition that the engine temperature is within a predetermined temperature range is set. More specifically, the second determination temperature T2 is set as the lower limit value of the temperature range. Further, as an upper limit value of the temperature range, the cooling that can be determined that the engine temperature has risen to such an extent that the activated state of the air-fuel ratio sensor 19 is maintained by exhaust even when the energization to the heater 19a is stopped. A third determination temperature T3 corresponding to the water temperature is set.

  If the ON condition of the heater 19a is satisfied (S210: YES), this process is temporarily terminated. In this case, since the actual air-fuel ratio AFr can be detected by the air-fuel ratio sensor 19 by energizing the heater 19a, according to the amount of deviation between the detected actual air-fuel ratio AFr and the target air-fuel ratio AFp. The basic fuel injection amount Qb is corrected, and thereby the fuel injection amount is appropriately corrected. The state in which the concentration learning completion flag FF is set to “OFF” and the concentration learning process is not completed occurs because the air-fuel ratio feedback control as described above is not executed. Therefore, the engine state at this time is such a state that the engine temperature is low enough that the air-fuel ratio feedback control cannot be executed, and the target air-fuel ratio AFp is set to a richer value than the stoichiometric air-fuel ratio as described above. .

  On the other hand, when it is determined in step S210 that the ON condition of the heater 19a is not satisfied (S210: NO), the learning of the alcohol concentration is incomplete, and furthermore, the actual air-fuel ratio AFr by the air-fuel ratio sensor 19 is determined. Since detection is impossible, it is necessary to correct the injection amount by this processing. Therefore, first, even when the ON condition of the heater 19a is not satisfied, the forced energization to the heater 19a is executed (S220).

  Then, it is determined whether the actual air-fuel ratio AFr detected by the air-fuel ratio sensor 19 activated by this forced energization is larger than the first determination value R1 (S230). The first determination value R1 is an air-fuel ratio that is richer than the stoichiometric air-fuel ratio and leaner than the target air-fuel ratio AFp, so that the combustion state of the air-fuel mixture can be stabilized at a low engine temperature. The air-fuel ratio is set. Further, the second determination value R2, which will be described later, is an air-fuel ratio richer than the first determination value R1 and the target air-fuel ratio AFp, and can stabilize the combustion state of the air-fuel mixture at a low engine temperature. The air / fuel ratio is set. Therefore, both the first determination value R1 and the second determination value R2 are richer than the stoichiometric air-fuel ratio, and the first determination value R1 is leaner than the target air-fuel ratio AFp. Second determination values R2 are set on the rich side with respect to AFp.

  When the actual air-fuel ratio AFr is larger than the first determination value R1 (S230: YES), the current actual air-fuel ratio AFr is leaned excessively than the target air-fuel ratio AFp, so the fuel injection amount is corrected to increase. (S260), and this process is temporarily terminated. In this embodiment, when the fuel injection amount is increased, a correction value FD obtained by multiplying the final fuel injection amount Qf by a fixed correction coefficient (for example, 0.02) is added. Amendments can be made with timely changes. Then, while an affirmative determination is made in step S230, the increase correction of the fuel injection amount is repeatedly executed, so that the actual air-fuel ratio AFr becomes smaller than the first determination value R1, and excessive leaning is eliminated. .

On the other hand, when the actual air-fuel ratio AFr is equal to or less than the first determination value R1 (S230: NO), it is determined whether the actual air-fuel ratio AFr is smaller than the second determination value R2 (S240). .
When the actual air-fuel ratio AFr is greater than or equal to the second determination value R2 (S240: NO), the actual air-fuel ratio AFr is an air-fuel ratio between the first determination value R1 and the second determination value R2. Since it can be determined that the combustion state of the air-fuel mixture is stable, the current correction amount FD with respect to the final fuel injection amount Qf is held, and this processing is temporarily terminated.

  On the other hand, when the actual air-fuel ratio AFr is smaller than the second determination value R2 (S240: YES), since the current actual air-fuel ratio AFr is excessively richer than the target air-fuel ratio AFp, the fuel injection amount is decreased. After the correction (S250), this process is temporarily terminated. In this embodiment, when the fuel injection amount is reduced, the correction value FD obtained by multiplying the final fuel injection amount Qf by a fixed correction coefficient (for example, 0.02) is subtracted. Amendments can be made with timely changes. Then, while an affirmative determination is made in step S240, the reduction correction of the fuel injection amount is repeatedly executed, so that the actual air-fuel ratio AFr becomes larger than the second determination value R2, and excessive enrichment is eliminated. .

According to this embodiment described above, the following effects can be obtained.
(1) Even when the coolant temperature THW correlated with the engine temperature is equal to or lower than the second determination temperature T2, that is, under an excessively low temperature environment where the heater 19a of the air-fuel ratio sensor 19 is not normally energized, When the concentration learning process for learning the alcohol concentration of the fuel is not completed, the heater 19a is forcibly energized through the execution of the injection amount correction process. Such forced energization makes it possible to detect the actual air-fuel ratio AFr by the air-fuel ratio sensor 19 that cannot be detected. Through the execution of the injection amount correction process, the deviation between the actual air-fuel ratio AFr detected by the air-fuel ratio sensor 19 activated by forced energization of the heater 19a and the target air-fuel ratio AFp is within a predetermined range. The fuel injection amount is corrected. Therefore, even before the learning of the alcohol concentration is completed, the actual air-fuel ratio AFr can be brought close to the ideal air-fuel ratio, that is, the target air-fuel ratio AFp, and the combustion state of the air-fuel mixture can be improved. Can be maintained. Therefore, drivability of the internal combustion engine 10 can be improved even before learning of the alcohol concentration is completed.

  (2) Immediately after starting the engine in a low temperature environment where the coolant temperature THW correlated with the engine temperature is likely to be equal to or lower than the second determination temperature T2, vaporization of the fuel contained in the mixture is difficult to promote, so the air-fuel ratio of the mixture Becomes substantially lean, and the combustion of the air-fuel mixture tends to become unstable. Therefore, until the coolant temperature THW reaches the warm-up determination temperature TD, the target air-fuel ratio AFp is set to a richer value than the stoichiometric air-fuel ratio, thereby enriching the actual air-fuel ratio. Insufficient fuel vaporization immediately after engine startup in a low-temperature environment is compensated. Here, immediately after the engine is started in such a low temperature environment, the concentration learning process is difficult to execute, and the correction of the fuel injection amount based on the detection value of the air-fuel ratio sensor 19 is also difficult to execute. Therefore, the actual air-fuel ratio AFr may not be sufficiently enriched depending on the alcohol concentration in the fuel. In this respect, in the present embodiment, the actual air-fuel ratio AFr can be brought close to the target air-fuel ratio AFp set to the rich side by executing the injection amount correction process, so immediately after the engine is started in a low temperature environment. Thus, the combustion state of the air-fuel mixture can be suitably stabilized.

  (3) The first determination value R1 set on the rich side with respect to the stoichiometric air-fuel ratio and the second determination value R2 set on the rich side with respect to the first determination value R1 are set. When the actual air-fuel ratio AFr detected by the air-fuel ratio sensor 19 is leaner than the first determination value R1, the fuel injection amount is corrected to be increased, and the actual air-fuel ratio AFr is richer than the second determination value R2. When it becomes, the fuel injection amount is corrected to decrease. For this reason, the actual air-fuel ratio AFr falls within the range between the first determination value R1 and the second determination value R2, and the target that is set to a value on the richer side than the stoichiometric air-fuel ratio at the time of cold start. In accordance with the air-fuel ratio AFp, the actual air-fuel ratio AFr can be maintained on the rich side.

  (4) In the above air-fuel ratio feedback control, the correction term FA that is constantly updated in accordance with the amount of deviation between the actual air-fuel ratio AFr and the target air-fuel ratio AFp, and the correction term FA is updated when it exceeds a predetermined range. A value composed of the learning term FB is calculated as the air-fuel ratio feedback correction amount FH for the fuel injection amount. Such a learning term FB is a value with relatively little fluctuation because it is updated when the correction term FA exceeds a predetermined range, and the value is a setting of the correction term FA that changes according to the alcohol concentration. The trend is reflected. Therefore, in the concentration learning process, the alcohol concentration is estimated on the basis of such a learning term FB, so that the estimated value of the alcohol concentration can be stabilized.

  Here, since the learning term FB is a value that is updated after the correction term FA changes to some extent as described above, in the concentration learning process using the learning term FB, when the alcohol concentration of the fuel changes, It takes a certain amount of time to complete the changed concentration learning process.

  In this regard, according to the present embodiment, the actual air-fuel ratio AFr can be brought close to the target air-fuel ratio AFp through the execution of the injection amount correction process until the concentration learning process is completed. Therefore, even when the concentration learning process that takes a certain amount of time to complete the learning of the alcohol concentration is executed, the drivability of the internal combustion engine 10 before the completion of the execution of the concentration learning process can be improved.

In addition, the said embodiment can also be changed and implemented as follows.
・ Cooling water temperature THW was used as a value correlated with engine temperature. In addition, since the temperature of the lubricating oil of the internal combustion engine 10 tends to increase as the engine temperature increases, the oil temperature of the lubricating oil may be used as a value correlated with the engine temperature.

  In the injection amount correction process, the fuel injection amount is corrected to increase or decrease so that the actual air-fuel ratio AFr falls within the range between the first determination value R1 and the second determination value R2. In addition, the fuel injection amount may be corrected to increase or decrease in accordance with the amount of deviation between the actual air-fuel ratio AFr and the target air-fuel ratio AFp so that the actual air-fuel ratio AFr and the target air-fuel ratio AFp coincide.

  In the above embodiment, the target air-fuel ratio AFp is set to a richer value than the stoichiometric air-fuel ratio at the time of cold start, but the present invention can be similarly applied even when such enrichment is not performed. . For example, when the target air-fuel ratio AFp is set to the stoichiometric air-fuel ratio, the first determination value R1 is set to an air-fuel ratio leaner than the stoichiometric air-fuel ratio, and the second determination value R2 is richer than the stoichiometric air-fuel ratio. The air-fuel ratio on the side may be set. Further, when the target air-fuel ratio AFp is set to a value leaner than the stoichiometric air-fuel ratio, the second determination value R2 is leaner than the stoichiometric air-fuel ratio and richer than the target air-fuel ratio AFp. The air-fuel ratio may be set, and the first determination value R1 may be set to an air-fuel ratio leaner than the second determination value R2 and the target air-fuel ratio AFp.

  Although the alcohol concentration is estimated by the learning term FB, the correction term FA is set so that the estimated alcohol concentration increases as the correction term FA increases or as the air-fuel ratio feedback correction amount FH increases. Alternatively, the alcohol concentration may be estimated based on the air-fuel ratio feedback correction amount FH. In this case, in order to suppress the fluctuation of the estimated alcohol concentration, the alcohol concentration is estimated based on the value obtained by gradually changing the correction term FA or the value obtained by gradually changing the air-fuel ratio feedback correction amount FH. It is desirable.

  In the above embodiment, the alcohol concentration is estimated. In addition, an alcohol sensor for detecting the alcohol concentration is provided to basically measure the alcohol concentration. However, the present invention is similarly applied to an apparatus in which the alcohol concentration is estimated in the above manner only when the concentration cannot be detected by the alcohol sensor (for example, when an abnormality occurs in the alcohol sensor). be able to.

  The fuel amount is determined to be present when the increase amount of the fuel amount F in the fuel tank 30 exceeds a preset determination value. However, the fuel supply determination may be performed in another manner. For example, a fuel supply pipe connected to the fuel tank 30 and a cap provided at the inlet thereof is opened or closed, a fuel lid provided in a vehicle is opened or closed, or a fuel supply nozzle is inserted into the fuel supply pipe. For example, various operations related to refueling may be detected, and the presence or absence of refueling may be determined based on the detection result.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the internal combustion engine to which this is applied, and its periphery structure about one Embodiment of the fuel-injection control apparatus of the internal combustion engine concerning this invention. 6 is a flowchart showing the procedure of density learning completion flag off setting processing in the embodiment. The flowchart which shows the procedure about the injection quantity correction process in the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Intake passage, 13 ... Exhaust passage, 14 ... Air cleaner, 15 ... Throttle valve, 16 ... Air flow meter, 17 ... Injector, 18 ... Catalyst, 19 ... Air-fuel ratio sensor, 19a ... Heater, 20 ... Water temperature Sensors, 22 ... control device, 30 ... fuel tank, 31 ... fuel supply system, 32 ... fuel gauge.

Claims (5)

An air-fuel ratio sensor that is activated when the engine temperature is within a predetermined temperature range is activated by raising the temperature with a heater, performs air-fuel ratio feedback control based on the output value of the air-fuel ratio sensor, and A concentration learning process is performed to estimate the alcohol concentration of the fuel stored in the fuel tank based on the correction value of the fuel injection amount calculated by the fuel ratio feedback control, and the fuel injection amount is determined according to the estimated alcohol concentration. In the fuel injection control device of the internal combustion engine to be corrected,
Forced energizing means for forcibly energizing the heater when the concentration learning process is not completed even when the engine temperature is equal to or lower than the temperature range;
Injection amount correction means for correcting the fuel injection amount so that the difference between the air-fuel ratio detected by the air-fuel ratio sensor activated by the forced energization and the target air-fuel ratio falls within a predetermined range. A fuel injection control device for an internal combustion engine. 2. The fuel injection control device for an internal combustion engine according to claim 1, wherein the target air-fuel ratio is set to a richer value than the stoichiometric air-fuel ratio until the engine temperature rises to a predetermined temperature from the temperature range or less. A first determination value set on the rich side of the theoretical air-fuel ratio and a second determination value set on the rich side of the first determination value are set;
The injection amount correcting means corrects the fuel injection amount to be increased when the air-fuel ratio detected by the air-fuel ratio sensor is leaner than the first determination value, and the air-fuel ratio detected by the air-fuel ratio sensor is The fuel injection control device for an internal combustion engine according to claim 2, wherein the fuel injection amount is corrected to decrease when it becomes richer than the second determination value. The air-fuel ratio feedback control is updated when the correction term is constantly updated according to the amount of deviation between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio, and when the correction term exceeds a predetermined range. And a control value for calculating a value composed of a learning term as the correction value,
The fuel injection control device for an internal combustion engine according to any one of claims 1 to 3, wherein the concentration learning process is a process of estimating the alcohol concentration based on the learning term. The fuel injection control device for an internal combustion engine according to any one of claims 1 to 4, wherein it is determined whether or not fuel has been supplied to the fuel tank, and the concentration learning process is executed when it is determined that fuel has been supplied.

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