JP2007321681A - Air fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air fuel ratio control device for an internal combustion engine capable of simultaneously performing air fuel ratio learning and purging. <P>SOLUTION: An air fuel ratio learning routine calculates deviation quantity of air fuel ratio between target air fuel ratio and air fuel ratio detected by an air fuel ratio sensor 6 by using fuel evaporation concentration C detected in a concentration detection routine (step S 309) if the engine is under purging (step S302), and calculates learning correction value flaf for correcting the calculated air fuel ratio deviation quantity (step S310). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

Conventionally, according to the technique described in Patent Document 1, for example, when the learning completion condition for air-fuel ratio learning is not established for a certain period, the air-fuel ratio learning is temporarily stopped and the purge is forcibly executed. As a result, when the purge is stopped for a long time, the adsorption amount of the canister reaches a saturated state so that the subsequent adsorption is not impossible.
Japanese Patent No. 3,404,872

  In the above-described prior art, when purging is performed during learning of the air-fuel ratio, the amount of deviation of the air-fuel ratio between the air-fuel ratio detected by the air-fuel ratio sensor or the like and the target air-fuel ratio is due to the purging, or other than that Since it cannot be distinguished whether it is caused by a factor (for example, individual difference of injectors, etc.), the air-fuel ratio learning is temporarily stopped and the purge is forcibly executed.

  However, if it is possible to discriminate whether the air-fuel ratio deviation amount is due to purging or other factors, the air-fuel ratio learning is performed without temporarily stopping the air-fuel ratio learning. Purge can be performed. That is, the air-fuel ratio learning and the purge can be performed simultaneously.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can simultaneously perform air-fuel ratio learning and purge.

An air-fuel ratio control apparatus for an internal combustion engine according to claim 1,
A canister having an adsorbent for temporarily adsorbing fuel vapor introduced from the inside of the fuel tank through the introduction passage;
A fuel state detecting means for detecting a fuel state in the mixture when the fuel vapor adsorbed on the adsorbent is separated from the adsorbent and becomes a mixture;
A purge pipe connecting the canister and the intake pipe of the internal combustion engine;
A purge execution means for purging from the purge pipe to the intake pipe;
An air-fuel ratio sensor provided in an exhaust pipe of the internal combustion engine for detecting an air-fuel ratio of exhaust gas discharged from the internal combustion engine;
Air-fuel ratio learning means for performing air-fuel ratio learning for correcting the air-fuel ratio deviation amount between the air-fuel ratio and the target air-fuel ratio by the air-fuel ratio sensor;
An air-fuel ratio control means for controlling the fuel injection amount to the internal combustion engine based on the learning correction value of the air-fuel ratio learning means so that the air-fuel ratio by the air-fuel ratio sensor becomes the target air-fuel ratio,
The fuel state detection means
A measuring passage with a restriction,
Gas flow generating means for generating a gas flow in the measurement passage;
A pressure measuring means for measuring a pressure generated by the throttle when the gas flow generating means generates a gas flow; and
A first measurement state in which the measurement passage is opened to the atmosphere and the gas flowing in the measurement passage is air; and the gas mixture that includes the fuel vapor from the canister is connected to the measurement passage through the measurement passage. Measuring passage switching means for switching to the second measurement state
Fuel in the air-fuel mixture based on the first pressure measured by the pressure measuring means in the first measurement state and the second pressure measured by the pressure measurement means in the second measurement state Fuel state calculation means for calculating the state,
The air-fuel ratio learning means performs air-fuel ratio learning using the fuel state detected by the fuel state detection means when the purge execution means is performing the purge.

  Thus, the present invention enables learning of the air-fuel ratio using the fuel state detected by the fuel state detection means even during the purge. In other words, if the fuel state in the air-fuel mixture is detected by the fuel state detection means, even if purging is performed after the detection, the air-fuel ratio deviation amount between the air-fuel ratio and the target air-fuel ratio by the air-fuel ratio sensor is purged. Or due to factors other than purging (for example, individual differences in injectors that inject fuel into the internal combustion engine, etc.). Therefore, unlike the prior art, the purge can be performed while performing the air-fuel ratio learning (in other words, the air-fuel ratio learning and the purge are performed simultaneously) without temporarily stopping the air-fuel ratio learning.

According to the air-fuel ratio control apparatus for an internal combustion engine according to claim 2,
The air-fuel ratio learning means is
A learning card value setting means for setting a learning guard value for the learning correction value when the purge execution means is performing the purge, based on the learning correction value of the air-fuel ratio learning means when the purge execution means is not purged. Prepared,
When the purge execution unit is performing the purge, the learning card value set by the learning guard value setting unit is used to perform air-fuel ratio learning.

  For example, if a crack occurs in the purge pipe or the pressure measuring means temporarily fails, the fuel state detecting means will erroneously detect the fuel state in the mixture, but the air-fuel ratio learning means Since the air / fuel ratio learning is performed using the fuel state detected by the fuel state detecting means, the air / fuel ratio is erroneously learned due to erroneous detection of the fuel state.

  Therefore, the learning guard value is set based on the learning correction value of the air-fuel ratio learning means when purging has not been performed so that the air-fuel ratio learning means does not mislearn. When purge control is being performed, air-fuel ratio learning is performed using the learning guard value that has been set. As a result, the air-fuel ratio learning unit is not easily affected by the detection accuracy of the fuel state by the fuel state detection unit.

According to the air-fuel ratio control apparatus for an internal combustion engine according to claim 3,
The air-fuel ratio learning means includes a determination means for determining a sticking tendency of the learning correction value with respect to the learning guard value when the purge execution means is performing the purge,
When it is determined by the determination means that the learning correction value is sticking to or prone to sticking to the learning guard value, the purge execution means prohibits the purge execution, and the fuel state detection means prohibits the purge execution. In this case, the fuel state in the air-fuel mixture is detected again.

  When the learning correction value is stuck to or tends to stick to the learning guard value set by the learning card value setting means (in other words, the learning correction value is closer to the learning guard value than the predetermined value), the fuel It is considered that the fuel state and the learning guard value detected by the state detecting means indicate abnormal values. In such a case, execution of the purge is prohibited, and the fuel state in the air-fuel mixture when the purge is not executed is detected again. As a result, the fuel state and the learning guard value are reset, and then the air-fuel ratio learning is performed again, so that a certain level of controllability is always ensured.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 is a configuration diagram showing a configuration of an air-fuel ratio control apparatus according to an embodiment of the present invention. The air-fuel ratio control apparatus according to this embodiment is applied to, for example, an automobile engine, and a fuel tank 11 of an engine 1 that is an internal combustion engine is connected to a canister 13 via an evaporation line 12 that is an introduction passage.

  The canister 13 is filled with an adsorbent 14, and the fuel vapor generated in the fuel tank 11 is temporarily adsorbed by the adsorbent 14. The canister 13 is connected to the intake pipe 2 of the engine 1 via a purge line 15 that is a purge pipe. The purge line 15 is provided with a purge valve 16 as a purge control valve, and the canister 13 and the intake pipe 2 communicate with each other when the purge valve 15 is opened.

  In addition, a partition plate 14 a is provided in the canister 13 between the connection position of the evaporation line 12 and the connection position of the purge line 15 in the canister 13, and the fuel vapor introduced from the evaporation line 12 flows into the adsorbent 14. It is prevented from being discharged from the purge line 15 without being adsorbed. An atmospheric line 17 is also connected to the canister 13 as will be described later. A partition plate 14 b having a depth substantially equal to the filling depth of the adsorbent 14 is provided inside the canister 13 between the connection position of the atmospheric line 17 and the connection position of the purge line 15. This prevents fuel vapor introduced from the evaporation line 12 from being released from the atmospheric line.

  The purge valve 16 is an electromagnetic valve, and its opening degree is adjusted by an electronic control unit (ECU 30) that controls each part of the engine 1. The flow rate of the air-fuel mixture containing fuel vapor flowing through the purge line 15 is controlled by the opening degree of the purge valve 16, and the air-fuel mixture whose flow rate is controlled is taken in by the negative pressure in the intake pipe 2 generated by the throttle valve 3. The gas is purged into the pipe 2 and burned together with the fuel injected from the injector 4 (hereinafter, an air-fuel mixture containing fuel vapor to be purged is referred to as purge gas as appropriate).

  Connected to the canister 13 is an atmospheric line 17 whose tip is opened to the atmosphere via a filter. The atmospheric line 17 is provided with a switching valve 18 that allows the canister 13 to communicate with either the atmospheric line 17 or the suction side of the pump 26. When the ECU 30 is not driven, the switching valve 18 is in a first position where the canister 13 communicates with the atmospheric line 17, and when driven, the switching valve 18 is switched to a second position where the canister 13 communicates with the suction side of the pump 26.

  A branch line 19 branched from the purge line 15 is connected to one input port of the three-position valve 21. The other input port of the three-position valve 21 is connected to an air supply line 20 that branches from a discharge line 27 of a pump 26 that is opened to the atmosphere via a filter. A measurement line 22 that is a measurement passage is connected to the output port of the three-position valve 21.

  The three-position valve 21 is a measurement passage switching means, and is a first position where the ECU 30 connects the air supply line 20 to the measurement line 22, and the communication between the air supply line 20 and the branch line 19 with respect to the measurement line 22 is interrupted. To the second position where the branch line 19 is connected to the measurement line 22. The three-position valve 21 is configured to be in the first position when not driven.

  The measurement line 22 is provided with a throttle 23 and a pump 26. The pump 26 that is a gas flow generating means is an electric pump, and causes the gas to flow through the measurement line 22 with the throttle 23 side as the suction side during driving. The driving ON / OFF and the rotation speed are controlled by the ECU 30. When driving the pump 26, the ECU 30 controls the rotational speed to be constant at a predetermined value set in advance.

  Accordingly, as shown in FIG. 2, when the ECU 30 drives the pump 26 with the switching valve 18 in the first position and the three-position valve 21 in the first position, air flows through the measurement line 22. The first measurement state is set. As shown in FIG. 3, when the pump 26 is driven with the three-position valve 21 in the third position, the atmospheric line 17, the canister 13, a part of the purge line 15 up to the branch line 19, and the branch line The air-fuel mixture containing the fuel vapor supplied via 19 enters the “second measurement state” in which the measurement line 22 flows.

  In addition, one end of a pressure sensor 24 that is a pressure measuring unit is connected to the measurement line 22 downstream of the throttle 23, that is, between the throttle 23 and the pump 26. The other end of the pressure sensor 24 is open to the atmosphere, and the pressure sensor 24 detects the differential pressure between the atmospheric pressure and the pressure downstream of the throttle 23 of the measurement line 22. The pressure measured by the pressure sensor 24 is output to the ECU 30.

  The ECU 30 is provided in the intake pipe 2 and adjusts the intake air amount, based on the detected values detected by various sensors such as the opening of the throttle valve 3, the fuel injection amount from the injector 4, the opening of the purge valve 16, and the like. Control. For example, the intake air amount detected by the air flow sensor 31 provided in the intake pipe 2, the intake pressure detected by the intake pressure sensor (not shown), the air-fuel ratio detected by the air-fuel ratio sensor 6 provided in the exhaust pipe 5. In addition, the throttle opening, the fuel injection amount, the opening of the purge valve 16 and the like are controlled based on the ignition signal, the engine speed, the engine coolant temperature, the accelerator opening, and the like.

  Hereinafter, the control process of the ECU 30 of the present embodiment will be described in detail. FIG. 4 is a flowchart showing a concentration detection routine for detecting the fuel concentration (fuel state) in the purge gas purged from the canister 13. This routine is executed by a time interruption every predetermined time by the ECU 30.

  In step S101 shown in FIG. 4, it is determined whether density detection has not been performed. That is, it is determined whether or not the concentration detection completion flag XIPRGHC is “0” (not implemented). If this determination is negative, that is, if the concentration detection completion flag XIPRGHC is “1” (concentration detection completion), the process proceeds to step S103. If the determination is affirmative, the process proceeds to step S102. Proceed.

  In step S102, it is determined whether or not the purge valve 16 is “closed”. If this determination in step S102 is negative, that is, if the purge valve 16 is open, it is determined in step S104 that concentration detection based on pressure measurement is prohibited, and this routine is terminated. On the other hand, if the determination in step S102 is affirmative, it is determined to start concentration detection based on pressure measurement, and the process proceeds to step S105.

  In step S103, it is determined whether a predetermined time or more has elapsed since the completion of concentration detection based on the previous pressure measurement. When this step S103 is negative determination, the above-mentioned step S104 is executed, and when it is positive determination, the process proceeds to step S102.

  In step S <b> 105, the pressure P <b> 0 is measured by the pressure sensor 24 in a state where air is flowed as a gas flow through the measurement line 22. This state corresponds to the “first measurement state”. Prior to the execution of the process of step S105, the purge valve 16 is closed, the switching valve 18 is in the first position where the canister 13 is communicated with the atmospheric line 17, and the three-position valve 21 is the air supply line 20. Is the first position to connect to the measurement line 22. For this reason, in the initial state, the pressure detected by the pressure sensor 24 is substantially the same as the atmospheric pressure.

  The measurement of the pressure P0 due to the air flow in step S105 is performed by driving the pump 26 while the three-position valve 21 is held at the first position. In this case, air is supplied to the measurement line 22 via the air supply line 20. The upstream side of the throttle 23 of the air supply line 20 has the same atmospheric pressure as one end of the pressure sensor 24, and the other side of the pressure sensor 24 is connected to the downstream side of the throttle 23 of the air supply line 20. A pressure drop when the air passes through the throttle 23 is detected by the pressure sensor 24.

  In step S106, the pressure P1 is measured in a state in which an air-fuel mixture containing fuel vapor flows as a gas flow through the measurement line 22. This state corresponds to a “second measurement state”. Measurement of the pressure P1 by the mixed airflow is performed by driving the pump 26 while switching the three-position valve 21 to the third position.

  In this case, an air-fuel mixture containing fuel vapor supplied via the branch line 19 is supplied to the measurement line 22 from the atmospheric line 17, the canister 13, a part of the purge line 15 up to the branch line 19. That is, the air introduced from the atmospheric line 17 flows in the canister 13 to become a mixture of fuel vapor and air, and is supplied to the measurement line 22 via a part of the purge line 15 and the branch line 19. . Therefore, at the time of pressure measurement by the mixed air flow, the pressure sensor 24 detects the amount of pressure drop when the air-fuel mixture containing fuel vapor passes through the restriction 23 of the measurement line 22.

  In step S107, the fuel concentration C is calculated and stored based on the pressures P0 and P1 measured in steps S105 and S106. In calculating the fuel concentration C, the pressure ratio RP between the pressures P0 and P1 is calculated according to Equation 1, and the fuel concentration C is calculated according to Equation 2 based on the pressure ratio RP. In Equation 2, k1 is a constant previously adapted by experiments or the like.

(Equation 1)
RP = P1 / P0
(Equation 2)
C = k1 * (RP-1) (= (P1-P0) / P0)
Since the fuel vapor is heavier than air, the density increases if the purge gas contains the fuel vapor. If the rotation speed of the pump 26 is the same and the flow velocity (flow rate) of the measurement line 22 is the same, the pressure difference on both sides of the throttle 23 increases as the density increases according to the law of energy conservation. Therefore, as the fuel concentration C increases, the pressure ratio RP increases, and the relationship between the fuel concentration C and the pressure ratio RP becomes a linear relationship as shown in Equation 2. The fuel concentration C obtained in this way represents the concentration of the fuel vapor in the purge gas as a mass ratio.

  In step S108, each unit is returned to the initial state. That is, the switching valve 18 is a first position where the canister 13 and the atmospheric line 17 communicate with each other, and the three-position valve 21 is a first position where the air supply line 20 is connected to the measurement line 22. In step S109, the concentration detection completion flag XIPRGHC is set to “1”, and this routine ends.

  FIG. 5 is a flowchart of an air-fuel ratio feedback (F / B) control routine. This routine is executed in the ECU 30 at every constant cam angle. In this routine, the output voltage from the air-fuel ratio sensor 6 is input, and the rich / lean determination of the air-fuel mixture is performed. Then, when the state is reversed from the rich state to the lean state and when the state is reversed from the lean state to the rich state, the air-fuel ratio correction coefficient FAF is changed (skipped) stepwise to increase or decrease the fuel injection amount, and the rich state or the lean state In this case, the air-fuel ratio correction coefficient FAF is gradually increased or decreased.

In step S201 shown in FIG. 5, it is determined whether air-fuel ratio feedback control is permitted. That is,
(1) Not when starting (2) Not cutting fuel (3) Cooling water temperature (THW) ≥ 0 ° C
(4) The air-fuel ratio feedback control is permitted when all the conditions (hereinafter referred to as F / B conditions) that the air-fuel ratio sensor 6 is in the active state are satisfied, and the air-fuel ratio is satisfied when any one of the conditions is not satisfied. Feedback control is not allowed.

If a positive determination is made in step S201, the process proceeds to step S202. In step S202, the output voltage V _OX of the air-fuel ratio sensor 6 is read. In step S203, it is determined whether or not the output voltage V _OX is equal to or lower than a predetermined reference voltage V _R (for example, 0.45V). If an affirmative determination is made in step S203, it is determined that the air-fuel ratio of the exhaust gas is lean, the process proceeds to step S204, and the air-fuel ratio flag XOX is set to “0”.

  Next, in step S205, it is determined whether the air-fuel ratio flag XOX and the state maintenance flag XOXO match. If an affirmative determination is made in step S205, it is assumed that the lean state is continuing, and in step S206, the air-fuel ratio correction coefficient FAF is increased by the lean integral amount “a”, and this routine is ended. On the other hand, if a negative determination is made in step S205, the air-fuel ratio correction coefficient FAF is increased by the lean skip amount “A” in step S207, assuming that the rich state is reversed to the lean state. The lean skip amount “A” is set sufficiently larger than the lean integral amount “a”. In step S208, the state maintenance flag XOXO is reset and this routine is terminated.

  If a negative determination is made in step S203, it is determined that the air-fuel ratio of the exhaust gas is rich, the process proceeds to step S209, and the air-fuel ratio flag XOX is set to “1”. In step S210, it is determined whether or not the air-fuel ratio flag XOX matches the state maintenance flag XOXO. If an affirmative determination is made in step S210, it is assumed that the rich state continues, and in step S211, the air-fuel ratio correction coefficient FAF is reduced by the rich integration amount “b”, and this routine is ended. On the other hand, if a negative determination is made in step S210, it is assumed that the lean state has been reversed to the rich state, and the flow proceeds to step S212, where the air-fuel ratio correction coefficient FAF is reduced by the rich skip amount “B”. The rich skip amount “B” is set sufficiently larger than the rich integration amount “b”.

  In step S213, the state maintenance flag XOXO is set to “1”, and this routine ends. If a negative determination is made in step S201, the process proceeds to step S214, the air-fuel ratio correction coefficient FAF is set to “1.0”, and this routine is ended.

  FIG. 6 is a flowchart showing an air-fuel ratio learning routine as a base routine by the ECU 30. In step S301 shown in FIG. 6, it is determined whether the air-fuel ratio learning start condition is satisfied. The air-fuel ratio learning start condition includes the aforementioned F / B condition, cooling water temperature condition (THW> 80 ° C.), concentration detection completion condition (concentration detection completion flag XIPRGHC = 1), and the like.

  If an affirmative determination is made in step S301, the process proceeds to step S302. If a negative determination is made, the process waits until the air-fuel ratio learning start condition is satisfied. When the air-fuel ratio learning start condition is satisfied, it is determined in step S302 whether or not the purge stop flag XIPGR is “1” (purging is not performed). Here, if an affirmative determination is made, the processing after step S303 is executed, and if a negative determination is made, the processing after step S308 is executed.

  In step S303, learning guard values (upper limit value AFGmax and lower limit value AFGmin) for a learning correction value flaf, which will be described later, are set as in Expression 3 and Expression 4. Note that the values of kMAX1 and kMIN1 in Equation 3 and Equation 4 are set in advance.

(Equation 3)
AFGmax = kMAX1
(Equation 4)
AFGmin = kMIN1
In step S304, the air-fuel ratio deviation amount between the air-fuel ratio by the air-fuel ratio sensor 6 and the target air-fuel ratio (theoretical air-fuel ratio) is calculated. In step S305, a learning correction value flaf for correcting the air-fuel ratio deviation amount calculated in step S304 is calculated, and the learning correction value flaf is stored in a RAM (not shown) of the ECU 30.

  In step S306, the learning correction base value flaf calculated in step S304 when purge is not performed is used for setting a learning guard value when purge is being performed (step S308 described later). Is set to the learning correction value flaf.

  In step S307, it is determined whether an air-fuel ratio learning completion condition is satisfied. The air / fuel ratio learning completion condition is the deviation (ΔFAF) (= | FAF−) of the air / fuel ratio correction coefficient FAF indicating the absolute value of the difference between the air / fuel ratio correction coefficient FAF and the reference value (= 1) of the air / fuel ratio correction coefficient. 1 |) indicates that a predetermined number of skips of the air-fuel ratio correction coefficient FAF has been completed in a state where the value is stable within 2%. If a negative determination is made in step S307, the process proceeds to step S304, and air-fuel ratio learning is repeatedly executed. On the other hand, if an affirmative determination is made, this routine ends.

  If it is determined in step S302 that the purge is being performed, the processing after step S308 is executed. In step S308, the learning guard value (upper limit value) for the learning correction value when purging is being performed with reference to the learning guard base value flabse (= learning correction value flaf when purging has not been performed) set in step S306. AFGmax and lower limit value AFGmin) are set as in Equation 5 and Equation 6. Note that the values of kMAX2 and kMIN2 in Equation 5 and Equation 6 are set in advance.

(Equation 5)
AFGmax = flabse + kMAX2
(Equation 6)
AFGmin = flabse + kMIN2
In step S309, the air-fuel ratio deviation amount between the air-fuel ratio and the target air-fuel ratio by the air-fuel ratio sensor 6 is calculated using the fuel concentration C in the purge gas obtained in the concentration detection routine. Here, the air-fuel ratio detected by the air-fuel ratio sensor 6 indicates the weight ratio of fuel and air sucked into the cylinder during the intake stroke of the engine 1, and the concentration of fuel vapor in the purge gas is expressed by weight ratio. If the indicated fuel concentration C is detected when purging is not performed, whether the air-fuel ratio deviation between the air-fuel ratio and the target air-fuel ratio by the air-fuel ratio sensor 6 is due to purging even if purging is performed thereafter. Therefore, it is possible to distinguish whether it is due to factors other than the purge execution (for example, individual differences of the injector 4 or the like).

  Therefore, in step S309, the fuel concentration C is subtracted from the air-fuel ratio by the air-fuel ratio sensor 6, and the air-fuel ratio deviation amount between the subtraction result and the target air-fuel ratio is calculated. As a result, the purge can be performed while performing the air-fuel ratio learning (in other words, the air-fuel ratio learning and the purge are performed simultaneously) without temporarily stopping the air-fuel ratio learning as in the conventional technique described above. .

  In step S310, a learning correction value flaf for correcting the air-fuel ratio deviation amount calculated in step S309 is calculated, and the learning correction value flaf is stored in the RAM of the ECU 30.

  In step S311, it is determined whether the aforementioned air-fuel ratio learning completion condition is satisfied. If a positive determination is made in step S307, this routine is terminated. On the other hand, if a negative determination is made, the process proceeds to step S304, and air-fuel ratio learning is repeatedly executed.

  In step S312, the learning correction value flaf calculated in step S310 sticks to or tends to stick to the learning guard value (upper limit value AFGmax or lower limit value AFGmin) set in step S308 (for example, learning). It is determined whether the correction value flafg is closer to the upper limit value AFGmax or the lower limit value AFGmin by a predetermined value or more.

  If an affirmative determination is made in step S312, the process proceeds to step S313. If a negative determination is made, the process proceeds to step S309, and the above-described process is repeated.

  As described above, in the processing from step S308 to step S312, learning when purging is being performed using the learning guard base value flabse (= learning correction value flaf when purging has not been performed) set at step S306. A learning guard value (upper limit value AFGmax and lower limit value AFGmin) for the correction value is set, and air-fuel ratio learning is performed using the set learning card value. This is due to the following reason.

  For example, if the purge line 15 is cracked or the pressure sensor 24 is temporarily broken, the fuel concentration C is erroneously detected in the above-described concentration detection routine. In the case of implementation, since the air-fuel ratio learning is performed using the fuel concentration C detected in the concentration detection routine, the air-fuel ratio is erroneously learned due to erroneous detection of the fuel concentration C.

  Therefore, when purging is being performed, a learning guard value is set on the basis of the learning correction value when purging has not been performed so as not to be greatly mislearned in this air-fuel ratio learning routine, and this learning guard value thus set is used. To perform air-fuel ratio learning. Thereby, it becomes difficult to be influenced by the detection accuracy of the fuel concentration C by the concentration detection routine.

  If an affirmative determination is made in step S312, that is, if the upper limit value AFGmax or the lower limit value AFGmin is stuck or tends to stick, in step S313, the purge stop flag XIPGR is set to prohibit the purge operation. Set to 1 ”. As a result, the purge is stopped when the purge is being performed in the purge execution routine described later. In step S314, the concentration detection completion flag XIPRGHC is set to “0” (not implemented), and this routine ends. As a result, since the above-described concentration detection routine is started, the fuel concentration C when the purge is stopped is detected again.

  This is because, in step S312, when the learning correction value flaf is stuck to the learning guard value (upper limit value AFGmax or lower limit value AFGmin) or tends to stick, the fuel concentration C and the learning guard value flaf indicate abnormal values. This is because purging is prohibited and the fuel concentration C is detected again to reset the fuel concentration C and the learning guard value flaf, and then perform air-fuel ratio learning again. Then, if air-fuel ratio learning is performed again, a certain level of controllability is always ensured.

  FIG. 7 is a flowchart of the purge execution routine. This routine is executed in parallel with the aforementioned air-fuel ratio F / B control routine. In step S401, it is determined whether air-fuel ratio feedback control is being performed. When an affirmative determination is made in step S401, the process proceeds to step S402 to determine whether or not a fuel cut is in progress.

  When a negative determination is made in step S402, the process proceeds to step S403, and after performing normal purge rate control, the process proceeds to step S404. In step S404, the purge stop flag XIPGR is reset (set to 0), and then in step S405, the fuel cut counter Ccut is reset and the routine is terminated. On the other hand, when an affirmative determination is made in step S402, the process proceeds to step S406, a resuming correction purge rate is calculated, and then in step S407, the purge stop flag XIPGR is set to “1”, and this routine is ended.

  If a negative determination is made in step S401, the process proceeds to step S408, the purge rate PGR is reset (set to 0), and then the purge stop flag XIPGR is set to “1” in step S409, and this routine is executed. finish.

  FIG. 8 is a flowchart of the normal purge rate control process executed in step S403 of the purge rate control routine shown in FIG. First, in step S4031, it is determined whether or not the concentration detection completion flag XIPRGHC is 1. If this determination is affirmative, a purge rate initial value determination routine is executed in step S4032.

  FIG. 9 shows the details of the purge rate initial value determination routine. First, in steps S40321 and S40322, the purge flow allowable upper limit value is set. That is, in step S40321, the operating state of the engine 1 is detected, and in step S40322, an allowable purge fuel vapor flow rate allowable value Fm is calculated based on the detected operating state. The permissible purge fuel vapor flow rate Fm is calculated based on the fuel injection amount required under the operating state of the engine 1 such as the current throttle opening, the lower limit value of the fuel injection amount that can be controlled by the injector 4, and the like. The If the fuel injection amount is large, the ratio of the purge fuel vapor flow rate to the fuel injection amount acts in the direction of decreasing, so the purge fuel vapor flow rate allowable value Fm is allowed to a large value.

  In step S40323, a current intake pipe pressure Pi is detected by an intake pressure sensor (not shown), and in step S40324, a reference flow rate Q100 is calculated based on the intake pipe pressure Pi. The reference flow rate Q100 is the flow rate of the gas flowing through the purge line 15 when the gas flowing through the purge line 15 is 100% air and the opening degree of the purge valve 16 (hereinafter referred to as the purge valve opening degree as appropriate) is 100%. Calculated according to the flow map. FIG. 10 shows an example of the reference flow rate map.

  In step S40325, the expected flow rate Qc of the purge mixture is calculated according to Equation 7 based on the fuel concentration C detected by the concentration detection routine. The expected flow rate Qc is an expected value of the purge gas flow rate when a purge gas having a current fuel concentration C flows through the purge line 15 with the purge valve opening being 100%. FIG. 11 shows the relationship between the fuel concentration C and the ratio of the expected flow rate Qc to the reference flow rate Q100 (Qc / Q100). As the fuel concentration C increases, the density of the purge gas increases and the intake pipe pressure Pi is the same. Even if it exists, according to the law of energy conservation, flow volume will decrease compared with when purge gas is 100% of air. The straight line in the figure is equivalent to Equation 7. In Equation 7, A is a constant and is stored in advance in a ROM (not shown) of the ECU 30 together with a control program and the like.

(Equation 7)
Qc = Q100 * (1-A * C)
In step S40326, based on the fuel concentration C and the expected flow rate Qc, the purge valve opening is set to 100%, and the purge fuel vapor expected flow rate (hereinafter referred to as appropriate) when the purge gas of the current fuel concentration C flows through the purge line 15. Fc) (referred to as an expected purge fuel vapor flow rate) is calculated according to Equation 8.

(Equation 8)
Fc = Qc × C
In steps S40327 to S40329, the purge valve opening x is set. In step S40327, the expected purge fuel vapor flow rate Fc is compared with the purge fuel vapor flow rate allowable value Fm, and it is determined whether or not Fc ≦ Fm. If an affirmative determination is made, the process proceeds to step S40328, and the purge valve opening x is set to 100%. This is because even if the purge valve opening x is set to 100%, there is a margin to the allowable purge fuel vapor flow rate allowable value Fm. If the determination in step S40327 for determining whether or not Fc ≦ Fm is negative, it is determined that if the purge valve opening x is 100%, the air-fuel ratio control cannot be normally performed due to excessive fuel vapor, and the process proceeds to step S40329. Then, the purge valve opening x is set to (Fm / Fc) × 100%. This is because the maximum purge flow rate at which proper air-fuel ratio control is guaranteed under Fc> Fm is the purge fuel vapor flow rate allowable value Fm.

  By calculating the purge valve opening x in steps S40328 and S40329, the purge valve 16 is controlled to the opening. After execution of steps S40328 and S40329, the concentration detection completion flag XIPRGHC is reset (set to “0”) in step S40330, and the restart correction purge rate PGRcomp is set to “0”. By resetting the concentration detection completion flag XIPRGHC in step S40330, step S4031 in FIG. 8 is negatively determined, and step S4033 and subsequent steps are executed.

  In step S4033 in FIG. 8, it is determined in which region the air-fuel ratio correction coefficient FAF is located. FIG. 12 is a graph showing the region of the air-fuel ratio correction coefficient FAF. When it is within 1 ± F, it is in region I, and when it is between 1 ± F and 1 ± G, it is in region II. If it is outside, it is determined that it belongs to region III. Note that 0 <F <G.

  If it is determined in step S4033 that it belongs to the region I, the process proceeds to step S4034, the purge rate PGR is increased by a predetermined purge rate increase amount D, and the process proceeds to step S4036. If it is determined in step S4033 that it belongs to region III, the process proceeds to step S4035, the purge rate PGR is decreased by a predetermined purge rate down amount E, and the process proceeds to step S4036. If it is determined in step S4033 that it belongs to region II, the process directly proceeds to step S4036.

  In step S4036, a restart correction purge rate PGRcomp, which will be described later, is subtracted from the purge rate PGR, and the flow proceeds to step S4037. In step S4037, a predetermined fixed value F is subtracted from the resuming correction purge rate PGRcomp. In step S4038, it is determined whether or not the resuming correction purge rate PGRcomp is positive.

  If a negative determination is made in step S4038, the restart correction purge rate PGRcomp is set to the lower limit value “0” in step S4039, and the process proceeds to step S4040. If an affirmative determination is made in step S4038, the process proceeds directly to step S4040, where the upper and lower limits of the purge rate PGR are checked, and this routine is terminated.

  FIG. 13 is a flowchart of the correction purge rate calculation at restart executed in step S406 of the purge execution routine shown in FIG. First, in step S4061, the fuel tank internal pressure PT is detected by a pressure sensor (not shown) provided in the fuel tank 11. The fuel tank internal pressure PT is a function of the amount of evaporated fuel in the fuel tank 11, and the amount of evaporated fuel in the fuel tank 11 represents an equilibrium state such as evaporation of fuel, discharge to the canister 13, and liquefaction of evaporated fuel. The fuel tank internal pressure PT represents the degree of fuel evaporation in the fuel tank 11. Since the degree of fuel evaporation is substantially determined by the fuel temperature and the pressure acting on the fuel surface, the fuel temperature may be used in place of the fuel tank pressure PT as an indication of the degree of fuel evaporation. However, when the fuel tank internal pressure PT is used as a parameter, an influence such as a change in atmospheric pressure is offset, so that more accurate detection can be easily performed.

  In the next step S4062, the fuel cut counter Ccut is incremented, and the process proceeds to step S4063. The fuel cut counter Ccut represents the duration of the fuel cut state. In step S4063, the evaporated fuel amount VAPOR (PT, Ccut) adsorbed on the canister 14 during the fuel cut is obtained as a function of the fuel tank pressure PT and the fuel cut counter Ccut.

  As a function for obtaining the evaporated fuel amount VAPOR, for example, the following can be used. That is, since the fuel evaporation amount α (PT) per unit time can be determined as a function of the fuel tank internal pressure PT, the count value of the fuel cut counter Ccut corresponding to the elapsed time is equal to the fuel evaporation amount α per unit time. Evaporated fuel amount VAPOR can be obtained by Equation 9 that multiplies.

(Equation 9)
VAPOR = α (PT) × Ccut
In step S4064, a restart correction purge rate PGRcomp shown in Expression 10 is determined as a function of the evaporated fuel amount VAPOR and the intake air amount GA detected by the airflow sensor 31. In Equation 10, β is a coefficient.

(Equation 10)
PGRcomp = β × VAPOR / GA
FIG. 14 is a flowchart of the purge control valve drive routine, in which the opening degree of the purge valve 16 is controlled by so-called duty ratio control. That is, it is determined in step S501 whether or not the purge stop flag XIPGR is “1”. If the determination is affirmative, it is determined that purging has not been performed. In step S502, the duty ratio Duty is set to “0”. Exit.

  On the other hand, if a negative determination is made in step S501, purging is performed, so that the process proceeds to step S503, and the duty ratio Duty is calculated based on Equation 11.

(Equation 11)
Duty = γ × PGR / PGR ₁₀₀ + δ
Here, PGR ₁₀₀ is a fully opened purge rate, and represents the purge amount when the purge valve 16 is fully opened. This fully open purge rate is set in advance as a map of the engine speed Ne and the throttle valve opening TA. FIG. 15 is an example of setting a map for determining the fully open purge rate. γ and δ are correction coefficients determined by the battery voltage and the atmospheric pressure.

  FIG. 16 is a flowchart of a fuel concentration learning routine for calculating the fuel concentration FGPG. In step S601, it is determined whether the concentration detection completion flag XIPRGHC is 1. If step S601 is affirmative, step S602 is executed. In step S602, the fuel concentration C detected in FIG. 4 is calculated by substituting into the equation 12, so that the fuel concentration C is compared with the theoretical air-fuel ratio (= 14.6) that is the target air-fuel ratio. It converts into the fuel density | concentration FGPG showing a density | concentration. In Formula 12, the density of fuel vapor and the density of air may be fixed values determined in advance, or may be determined based on temperature.

(Equation 12)
FGPG = (1-C) − (14.6 × C × density of fuel vapor / air density)
The fuel concentration FGPG becomes 0 when the ratio of fuel vapor in the purge gas is the same as the stoichiometric air-fuel ratio mixture, and becomes negative when the ratio of fuel vapor exceeds the stoichiometric air-fuel ratio. Further, it becomes positive when the ratio of the fuel vapor is lower than the stoichiometric air-fuel ratio, and becomes 1 when no fuel vapor is contained. Therefore, it can be said that the fuel concentration FGPG represents the degree of deviation from the theoretical air-fuel ratio of the purge gas. And it progresses to step S609 mentioned later.

  If the determination in step S601 is negative, the process proceeds to step S603, where it is determined whether the purge stop flag XIPGR is “1”. If the determination is affirmative, this routine is terminated as the purge is stopped. .

When an affirmative determination is made in step S603, the process proceeds to step S604 to determine whether or not the concentration learning condition is satisfied. That is,
(1) During air-fuel ratio feedback control (2) Cooling water temperature (THW) ≧ 80 ° C
(3) Fuel increase at start-up = 0
(4) Increase in warm-up fuel = 0
Learning is executed when all the conditions are satisfied, and learning is not performed when any of the conditions is not satisfied.

  When a negative determination is made in step S604, that is, when learning is not performed, this routine is terminated. When an affirmative determination is made in step S604, that is, when learning is performed, the process proceeds to step S605. In step S605, the temporal average value FAFAV of the air-fuel ratio correction coefficient FAF calculated in the air-fuel ratio F / B control routine of FIG. 5 is calculated, and the process proceeds to step S606.

  In step S606, it is determined whether the average value FAFAV is “0.98” or less, exceeds “0.98”, is less than “1.02”, or is “1.02” or more. When it is determined that the average value FAFAV is “0.98” or less, the process proceeds to step S607, the fuel concentration FGPG is decreased by a predetermined amount “Q” (for example, 0.4%), and the process proceeds to step S609.

  If it is determined in step S606 that the value is “1.02” or more, the process proceeds to step S608, the fuel concentration FGPG is increased by a predetermined amount “P” (for example, 0.4%), and the process proceeds to step S609. If it is determined in step S606 that the value exceeds “0.98” and is less than “1.02”, the process proceeds to step S609 without updating the fuel concentration FGPG.

  If the fuel concentration in the purge gas is “0”, the fuel concentration FGPG determined by executing step S607 or step S608 is set to “1”, and the fuel concentration increases as the fuel concentration increases. Value. In step S609, the fuel concentration FGPG is limited to a value within a predetermined upper and lower limit value, and this routine is terminated.

  FIG. 17 is a flowchart of an injector control routine. This routine is executed by a time interruption every predetermined time by the ECU 30. First, in step S701, as shown in Equation 13, a basic fuel injection time Tp is obtained as a function of the engine speed Ne and the intake air amount GA.

(Equation 13)
Tp = Tp (Ne, GA)
In step S702, a purge correction coefficient FPG shown in Equation 14 is calculated based on the purge rate PGR and the fuel concentration FGPG.

(Equation 14)
FPG = FGPG × PGR
In step 1503, the injector valve opening time TAU is determined by Equation 15 using the air-fuel ratio correction coefficient FAF, the purge correction coefficient FPG, and the learning correction value flaf obtained in the air-fuel ratio learning routine of FIG. Note that α and β in Equation 15 are correction coefficients including a warm-up increase, a start increase, and the like.

(Equation 15)
TAU = α × Tp × (FAF + FPG) × flaf + β
In step S704, the injector valve opening time TAU is output, and this routine is terminated.

  As described above, the air-fuel ratio control apparatus of the present embodiment uses the fuel concentration C in the purge gas obtained in the concentration detection routine in the air-fuel ratio learning routine in FIG. Learning was possible. Thus, it is possible to perform the purge while performing the air-fuel ratio learning (in other words, the air-fuel ratio learning and the purge are performed simultaneously) without temporarily stopping the air-fuel ratio learning as in the prior art.

It is a block diagram which shows the structure of the air fuel ratio control apparatus in embodiment of this invention. It is a figure for demonstrating a 1st measurement state. It is a figure for demonstrating a 2nd measurement state. It is a flowchart of a density | concentration detection routine. It is a flowchart of an air-fuel ratio F / B control routine. It is a flowchart of an air fuel ratio learning routine. It is a flowchart of a purge execution routine. It is a flowchart of a normal purge rate control process. It is a flowchart of a purge rate initial value determination routine. It is the figure which showed an example of the reference | standard flow volume map. It is the figure which showed the relationship with the ratio (Qc / Q100) of the prediction flow volume Qc. It is a graph which shows the area | region of the air fuel ratio correction coefficient FAF. It is a flowchart of correction purge rate calculation at the time of restart. It is a flowchart of a purge control valve drive routine. It is an example of the setting of the map for determining a full open purge rate. It is a flowchart of a fuel concentration learning routine. It is a flowchart of an injector control routine.

Explanation of symbols

5: Exhaust pipe 6: Air-fuel ratio sensor 11: Fuel tank 13: Canister 14: Adsorbent 15: Purge line (purge pipe)
16: Purge valve 21: 3-position valve (measurement passage switching means)
22: Measurement line (measurement passage)
23: Aperture 24: Pressure sensor (pressure measuring means)
26: Pump (gas flow generating means)
30: ECU

Claims (3)

A canister having an adsorbent for temporarily adsorbing fuel vapor introduced from the inside of the fuel tank through the introduction passage;
A fuel state detection means for detecting a fuel state in the mixture when the fuel vapor adsorbed on the adsorbent is separated from the adsorbent and becomes a mixture;
A purge pipe connecting the canister and an intake pipe of the internal combustion engine;
Purging means for purging from the purge pipe to the intake pipe;
An air-fuel ratio sensor provided in an exhaust pipe of the internal combustion engine for detecting an air-fuel ratio of exhaust gas discharged from the internal combustion engine;
Air-fuel ratio learning means for performing air-fuel ratio learning for correcting an air-fuel ratio deviation amount between the air-fuel ratio and the target air-fuel ratio by the air-fuel ratio sensor;
Air-fuel ratio control means for controlling the fuel injection amount to the internal combustion engine based on the learning correction value of the air-fuel ratio learning means so that the air-fuel ratio by the air-fuel ratio sensor becomes the target air-fuel ratio. In the fuel ratio control device,
The fuel state detecting means includes
A measuring passage with a restriction,
Gas flow generating means for generating a gas flow in the measurement passage;
Pressure measuring means for measuring a pressure generated by the throttle when the gas flow generating means generates a gas flow;
A first measurement state in which the measurement passage is opened to the atmosphere, and the gas flowing through the measurement passage is air, and the measurement passage is communicated with the canister, and the gas flowing through the measurement passage is sent to the fuel vapor from the canister. Measurement passage switching means for switching to a second measurement state with an air-fuel mixture containing
Based on the first pressure measured by the pressure measuring means in the first measuring state and the second pressure measured by the pressure measuring means in the second measuring state Fuel state calculating means for calculating the fuel state in the air,
An air-fuel ratio control apparatus for an internal combustion engine, wherein the air-fuel ratio learning means performs air-fuel ratio learning using the fuel state detected by the fuel state detection means when the purge execution means is performing a purge. The air-fuel ratio learning means includes
A learning card value for setting a learning guard value for a learning correction value when the purge execution unit is performing a purge, based on a learning correction value of the air-fuel ratio learning unit when the purge execution unit is not purging Comprising setting means,
2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein when the purge execution means is performing the purge, the air-fuel ratio learning is performed using the learning card value set by the learning guard value setting means. The air-fuel ratio learning unit includes a determination unit that determines a sticking tendency of the learning correction value with respect to the learning guard value when the purge execution unit is performing the purge,
When it is determined by the determination means that the learning correction value is attached to the learning guard value or is in a tendency to stick, the purge execution means prohibits the purge execution, and the fuel state detection means 3. The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein when the purge is prohibited, the fuel state in the air-fuel mixture is detected again.

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