JP2007218148A - Evaporated fuel treatment device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaporated fuel treatment device for an internal combustion engine capable of making purge quantity sufficiently large. <P>SOLUTION: This device is provided with a first fuel condition determination means determining fuel concentration purged from a canister based on slippage quantity of actually measured air fuel ratio from target air fuel ratio, a second fuel condition determination means determining fuel concentration under a condition where a purge control valve is open, an abnormality detection means detecting abnormality of the second fuel condition determination means, and an air fuel ratio control means controlling fuel injection quantity based on fuel concentration. If the abnormality detection means does not detect abnormality, the air fuel ratio control means uses fuel concentration determined by the second fuel condition determination means at a time of purge start or re-start, and uses fuel concentration determined by the first fuel condition determination means during purging. Consequently, purge ratio can be kept large from the time of purge start or re-start. However, fuel concentration determined by the first fuel condition determination means is always used during abnormality diagnosis by the second fuel condition determination means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an evaporated fuel processing apparatus for an internal combustion engine.

  The evaporative fuel treatment device is used to prevent the evaporative fuel generated in the fuel tank from being released into the atmosphere. The evaporative fuel in the fuel tank is introduced into the canister containing the adsorbent and temporarily adsorbed. Adsorb to the material. The vapor fuel adsorbed by the adsorbent is separated from the adsorbent by the negative pressure generated in the intake pipe during operation of the internal combustion engine, and is discharged (purged) to the intake pipe of the internal combustion engine through the purge pipe. In this way, when the vapor fuel is desorbed from the adsorbent, the adsorption capacity of the adsorbent is recovered.

  Even when the evaporated fuel is purged, it is necessary to control the air-fuel ratio of the air-fuel mixture introduced to the internal combustion engine to be close to the target air-fuel ratio (generally the theoretical air-fuel ratio). Therefore, an air-fuel ratio sensor that measures the air-fuel ratio is provided in the exhaust pipe of the internal combustion engine, and feedback control is performed based on the amount of deviation of the air-fuel ratio measured by the air-fuel ratio sensor from the target air-fuel ratio. A technique for controlling the fuel injection amount so that the air-fuel ratio of the introduced air-fuel mixture becomes the target air-fuel ratio has been proposed (for example, Patent Document 1).

In the apparatus of Patent Document 1, first, the evaporated fuel concentration state of the air-fuel mixture including the evaporated fuel purged from the canister is determined based on the amount of deviation of the air / fuel ratio measured from the air / fuel ratio sensor from the target air / fuel ratio. Yes. The fuel vapor concentration is a kind of fuel state. Then, based on the determined evaporated fuel concentration (that is, the fuel state), the fuel injection fee is controlled so that the air-fuel ratio becomes the target air-fuel ratio.
JP-A-7-269419

  When the air-fuel ratio is measured by an air-fuel ratio sensor and the amount of deviation of the measured air-fuel ratio with respect to the target air-fuel ratio is determined as in Patent Document 1, the fuel injection amount is determined unless purging is performed. Cannot be determined.

  Therefore, at the start of the purge, it is necessary to gradually increase the purge rate as a purge rate that is so small that the air-fuel ratio fluctuation does not occur so much. Similarly, when restarting after a purge interruption, it is necessary to decrease the initial purge rate and gradually increase it. Therefore, there is a problem that the purge amount cannot be made sufficiently large.

  The present invention has been made based on this situation, and an object of the present invention is to provide an evaporative fuel processing apparatus for an internal combustion engine that can sufficiently increase the purge amount.

In order to achieve the object, a first aspect of the present invention provides a canister that temporarily adsorbs evaporated fuel generated from a fuel tank, and a purge pipe that guides the evaporated fuel purged from the canister to an intake pipe of an internal combustion engine. A purge control valve installed in the purge pipe for controlling the purge flow rate from the purge pipe to the intake pipe, an air-fuel ratio sensor provided in the exhaust pipe of the internal combustion engine for measuring the air-fuel ratio, and the purge control valve opened. A first fuel state determination for determining a fuel state of an air-fuel mixture including evaporated fuel purged from the canister based on a deviation amount of the air-fuel ratio detected by the air-fuel ratio sensor from the target air-fuel ratio. And an air-fuel ratio control for controlling the fuel injection amount to the internal combustion engine so that the air-fuel ratio becomes the target air-fuel ratio based on the fuel state of the air-fuel mixture purged from the canister. In the evaporative fuel processing apparatus for an internal combustion engine and means,
A second fuel state determining means for determining an evaporated fuel state of the air-fuel mixture by purging the air-fuel mixture containing the evaporated fuel from the canister while the purge control valve is closed; and a second fuel state determining means An abnormality detection means for detecting an abnormality,
The air-fuel ratio control means uses the fuel state determined by the first fuel state determination means or the fuel determined by the second fuel state determination means when no abnormality is detected by the abnormality detection means. Whether or not the state is used is switched based on the vehicle operating state, but when an abnormality is detected by the abnormality detecting means, the fuel state used for controlling the fuel injection amount regardless of the vehicle operating state The fuel state determined by the first fuel state determining means is used.

  The first fuel state determination means determines the fuel state based on the air-fuel ratio detected by the air-fuel ratio sensor when the purge control valve is open, and therefore determines the fuel state if purge is not actually performed. I can't. On the other hand, the second fuel state determination means determines the fuel state with the purge control valve closed. Therefore, by providing the first and second fuel state determination means, the period during which the fuel state cannot be determined is reduced.

  In the air-fuel ratio control means, the fuel state determined by the first fuel state determination means is used as the fuel state used for determining the fuel injection amount, or the fuel state determined by the second fuel state determination means is used. Since whether to use is switched based on the vehicle operating state, the period during which the fuel injection amount cannot be determined based on the fuel state is reduced. Accordingly, the number of purges can be increased because the state in which the purge rate must be made small enough not to affect the air-fuel ratio is reduced. In addition, when the abnormality of the second fuel state determination unit is detected by the abnormality detection unit, the fuel state determined by the first fuel state determination unit is used regardless of the vehicle operating state. It is also possible to suppress the fuel injection amount from being controlled based on the above.

  The second fuel state determination means can be configured as described in claim 2. That is, the second fuel state determination means includes a measurement passage having a restriction in the middle thereof, a pump that generates a gas flow that passes through the restriction in the measurement passage, and the restriction by the restriction when the pump generates a gas flow. A pressure measuring means for measuring the amount of pressure drop generated; a first measuring state in which the measuring passage is opened to the atmosphere and the gas flowing in the measuring passage is air; and the measuring passage with the purge control valve closed. And a measurement passage switching means for switching the gas flowing in the measurement passage to a second measurement state in which the gas flowing in the measurement passage is made into an air-fuel mixture containing evaporated fuel, and in the first measurement state, Based on the first pressure measured by the pressure measuring means and the second pressure measured by the pressure measuring means in the second measurement state, the fuel state Determined.

  When a gas flow is generated in a measurement passage having a restriction, the amount of pressure drop caused by the restriction increases as the density of the gas flowing through the restriction increases. Therefore, the first pressure is measured using the gas flowing in the measurement passage as air. The second pressure is measured by using the gas flowing in the measurement passage as a gas mixture, and the fuel state can be determined from the first pressure and the second pressure.

  In this way, when the second fuel state determination means includes the measurement passage, the pump, the pressure measurement means, and the measurement passage switching means, the abnormality detection means includes the abnormality detection means according to claim 2. And detecting at least one abnormality of the measurement passage, the pump, the pressure measurement means, and the measurement passage switching means.

  Further, when the second state detection means is configured as described in claim 2, the abnormality of the second state determination means can be detected as in claim 3. According to a third aspect of the present invention, there is provided a closed space forming valve for making at least a part of a fuel state detection system including the measurement passage, the pump, the pressure measurement means, and the measurement passage switching means into a closed space; Leakage inspection passage that is opened and provided with a reference throttle in the middle thereof, pressure application means that pressurizes or depressurizes the closed space and the inside of the leak inspection passage, and the closed space that is pressurized or depressurized by the pressure application means Or a pressure measuring means for measuring the pressure in the leak inspection passage, and a pressure application range pressurized or depressurized by the pressure application means, including at least one of the closed space and the leak inspection passage, and Pressure application range switching means for switching to any one of two types of leak measurement states having different pressure application ranges, and the abnormality detection means is configured to perform the abnormality detection in the two types of leak measurement states. Based on the comparison of the two pressures measured respectively by the force measuring means is for detecting an abnormality of the fuel state detection system.

  In this way, in claim 3, at least a part of the fuel state detection system is a closed space, and includes at least one of the closed space and the leak inspection passage provided with the reference throttle, and the pressure application ranges are different from each other. The pressure is measured in each of two types of leak measurement states. In this case, if there is a leak hole somewhere in the closed space, or if the measurement path switching means is abnormal and switching of the measurement path is insufficient, the two pressures detected in the two types of leak measurement states respectively. Since the difference is different from the case where the fuel state detection system is normal, the abnormality of the fuel state detection system can be detected based on the comparison of the two pressures.

  Here, since the measurement passage has a throttle in the middle, it is preferable to use the measurement passage as a leakage inspection passage. In this way, the device configuration can be simplified and the cost can be reduced.

  In addition, since the measurement passage switching means switches the flow path including the measurement passage, when the measurement passage is a leak inspection passage as described in claim 4, the measurement passage, that is, the leakage inspection passage is included. The pressure application range can be switched by the measurement passage switching means. Therefore, as described in claim 5, the measurement passage switching means can be used as the pressure application range switching means. By doing so, the device configuration can be further simplified and the cost can be further reduced.

  Moreover, it is preferable to use a pump for generating a gas flow in the measurement passage as the pressure applying means. Also by doing so, the apparatus configuration can be simplified and the cost can be reduced.

  The air-fuel ratio control means, as defined in claim 7, when the abnormality is not detected by the abnormality detection means and the vehicle operating state is before the start of purge, the second fuel state determination means. The fuel state determined by is used.

  This is because the fuel state cannot be determined by the first fuel state determination means before the purge is started, while the second fuel state determination means can determine the fuel state. Therefore, according to the seventh aspect, since the purge rate at the start of the purge can be increased, a large amount of evaporated fuel can be processed from the start of the purge.

  Further, as described in claim 8, the air-fuel ratio control means, when the vehicle operating state is after the start of purging and is not in the purge interruption state, the fuel state determined by the first fuel state determining means It is preferable to control the fuel injection amount by using.

  This is because the first fuel state determination means can determine the fuel state during the purge. Therefore, according to the eighth aspect, the fuel injection amount during the purge can be set to an appropriate value.

  Further, as described in claim 9, the air-fuel ratio control means uses the fuel state determined by the second fuel state determination means when the vehicle operating state is in the purge interruption, and at the time of restarting the purge. It is preferable to determine the fuel injection amount.

  This is because the fuel state can be determined by the second fuel state determination means because the purge control valve is closed during the purge interruption. According to the ninth aspect, since the purge rate at the time of restarting the purge can be increased, a large amount of evaporated fuel can be processed from the time of restarting the purge.

  Further, when the purge interruption time is short, it may be considered that the fuel state cannot be determined by the second fuel state determination means during the purge interruption. Therefore, as described in claim 10, when the vehicle operation state is the purge interruption, and the determination of the fuel state by the second fuel state determination unit is not completed, the air-fuel ratio control unit is It is preferable to use the fuel state determined by the first fuel state determination unit immediately before the purge is interrupted.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 is a configuration diagram showing a configuration of a fuel vapor processing apparatus according to an embodiment of the present invention. The evaporative fuel processing 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 a steam introduction passage.

  The canister 13 is filled with an adsorbent 14, and the evaporated fuel 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 that is a purge control valve, and the canister 13 and the intake pipe 2 communicate with each other when the purge valve 15 is opened.

  Inside the canister 13, partition plates 14a and 14b are provided. The partition plate 14 a is provided between the connection position of the evaporation line 12 and the connection position of the purge line 15, and the evaporated fuel introduced from the evaporation line 12 is discharged from the purge line 15 without being adsorbed by the adsorbent 14. Is prevented.

  As will be described later, the atmospheric line 17 is also connected to the canister 13, and the other partition plate 14 b has a filling depth of the adsorbent 14 between the connection position of the atmospheric line 17 and the connection position of the purge line 15. They are provided at approximately the same depth. As a result, the combustion steam introduced from the evaporation line 12 is prevented from being released from the atmospheric line 17.

  The purge valve 16 is an electromagnetic valve, and the opening degree is adjusted by an electronic control unit (not shown) that controls each part of the engine 1. The flow rate of the air-fuel mixture including the evaporated fuel 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, the air-fuel mixture containing the evaporated fuel 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. The switching valve 18 is in a first position where the canister 13 communicates with the atmospheric line 17 when not driven by the electronic control unit, and is switched to a second position where the canister 13 communicates with the suction side of the pump 26 when driven. .

  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 the first position where the air supply line 20 is connected to the measurement line 22 by the electronic control unit described above, either the air supply line 20 or the branch line 19 with respect to the measurement line 22. It is possible to switch to either the second position where communication with the second line is blocked or the third 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 formed by orifices. The pump 26, which 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, and the on / off of the driving and the rotation speed are controlled by the electronic control unit. When the pump 26 is driven, the electronic control unit controls the rotation speed to be constant at a predetermined value set in advance.

  Therefore, when the electronic control unit drives the pump 26 with the switching valve 18 in the first position and the three-position valve 21 in the first position, the “first measurement state” in which air flows through the measurement line 22. It becomes. Further, when the pump 26 is driven with the three-position valve 21 in the third position, the air is supplied through the atmospheric line 17, the canister 13, a part of the purge line 15 up to the branch line 19, and the branch line 19. The air-fuel mixture containing the evaporated fuel 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 electronic control unit.

  The electronic control unit is a detection value that is detected by various sensors such as the opening degree of the throttle valve 3 provided in the intake pipe 2 and adjusting the intake air amount, the fuel injection amount from the injector 4, the opening degree of the purge valve 16, and the like. Control based on. For example, an intake air amount detected by an air flow sensor (not shown) provided in the intake pipe 2 and an intake pressure detected by an intake pressure sensor (not shown), and an air-fuel ratio sensor 6 provided in the exhaust pipe 5 are detected. In addition to the air / fuel ratio, the throttle opening, the fuel injection amount, the opening of the purge valve 16 and the like are controlled based on the ignition signal, engine speed, engine coolant temperature, accelerator opening, and the like.

  Next, the control of the electronic control unit according to the present invention will be described in detail. FIG. 2 is a flowchart showing abnormality diagnosis control for diagnosing abnormality of the fuel concentration detection system, together with leakage diagnosis of the evaporated fuel processing apparatus. Here, the fuel concentration detection system means a path and an apparatus through which gas flows in FIG. 7 (fuel concentration detection routine based on pressure measurement) described later. In the present embodiment, the processing shown in FIG. 2 corresponds to the abnormality detection means. In this processing, the three-position valve 21 and the switching valve 18 function as a closed space forming valve and a pressure application range switching means, and the measurement line 22 functions as a leak inspection passage, and the pump 26 functions as a pressure applying means.

  In step 21, it is determined whether or not an abnormality diagnosis execution condition is satisfied. The abnormality diagnosis execution condition (that is, the leakage diagnosis execution condition) is satisfied when the vehicle operation time continues for a certain time or when the outside air temperature is a certain value or more. If step 21 is negative, this routine is terminated. If the determination is affirmative, it is determined in step 22 whether or not the key is off. When this step 22 is negative determination, step 22 is repeated and it waits for key-off.

  If step 22 for determining whether or not the key is off is an affirmative determination, the process proceeds to step 23 to determine whether or not a predetermined time has elapsed since the key-off. In step 23, immediately after the key-off, the pressure in the evaporative fuel processing apparatus is unstable due to the fuel in the fuel tank 11 shaking or the fuel temperature being unstable. This is a process for making the diagnosis non-executable. The predetermined time is a time until the state in the evaporative fuel processing apparatus is stabilized from an unstable state immediately after key-off to a level at which leakage diagnosis can be accurately performed, and is set in advance. If step 23 is a negative determination, step 23 is repeated. If a predetermined time has elapsed and step 23 is affirmative, an abnormality diagnosis is executed in step 24, and then this flow ends.

  FIG. 3 shows an abnormality diagnosis execution routine. At the start of the abnormality diagnosis execution routine, the three-position valve 21 is in the first position, and the switching valve 18 is also in the first position. At this time, the pressure detected by the pressure sensor 24 which is a differential pressure sensor is zero.

  In step 241, the pump 26 is turned on. The gas distribution state at this time is shown in FIG. The state shown in FIG. 4 is the same as the first measurement state described above. As shown in FIG. 4, in the state of step 241, since the three-position valve 21 is in the first position, the air supply line 20 communicating with the atmosphere communicates with the measurement line 22, and the switching valve Since 18 is in the first position, the canister 13 and the pump 26 are not in communication. Therefore, the air flow is in a state where air flows through the measurement line 22, and the pressure detected by the pressure sensor 24 is a pressure drop amount due to the air restriction 23.

  In step 242, the variable i is set to zero. In the subsequent step 243, the pressure detected by the pressure sensor 24 is measured as the pressure P (i). In step 244, the change P (i-1) -P (i) from the immediately preceding measured pressure P (i-1) to the current measured pressure P (i) is compared with the threshold value Pa, and P (i-1 ) -P (i) <Pa is determined.

  If step 244 is negative, the variable i is incremented by 1 in step 245 and the process returns to step 243. If step 244 is affirmative, the process proceeds to step 246. That is, the measured pressure changes greatly with the rise of the pump 26, and then gradually converges to a pressure value defined by the passage cross-sectional area of the throttle 23, so that the measured pressure is sufficiently converged. This is to wait and execute the processing after step 246.

  In step 246, P (i) is substituted for the reference pressure P1. In step 247, a leak measurement state is set. This leakage measurement state is the state shown in FIG. 5, in which the three-position valve 21 is set to the second position and the switching valve 18 is set to the second position. Note that the purge valve 16 is also closed because the key is off when the abnormality diagnosis is executed.

  In this leakage measurement state, the fuel tank 11, the evaporation line 12, the canister 13, the purge line 15, the branch line 19, and the path from the canister 13 to the pump 26 via the switching valve 18 are closed spaces. Therefore, the gas in the closed space is released to the atmosphere by the pump 26, and the pressure in the closed space is reduced.

  Steps 248 to 255 are processes for determining whether there is an abnormality in the closed space by comparing the measured pressure with the reference pressure P1. In this closed space abnormality, when there is a leak hole in the closed space, that is, not only the abnormality of the line included in the closed space, but also the abnormality of other devices included in the closed space, such as the three-position valve 21 or A switching failure of the switching valve 18 is also included. The pressure at which the internal pressure of the closed space converges in a reduced pressure state is defined by the opening area of the throttle 23 if there is no abnormality in the closed space, but when there is a leak hole in the closed space, the three-position valve 21 or the switching valve 18. This is because the pressure does not reach the reference pressure P <b> 1 because a completely closed space is not formed when the switch is defective.

  In step 248, the variable i is set to zero. In step 249, the pressure P (i) is measured. In step 250, the measured pressure P (i) is compared with the reference pressure P1, and it is determined whether P (i) <P1. If a positive determination is made, the process proceeds to step 253, and if a negative determination is made, the process proceeds to step 254. At the beginning of switching to the leakage measurement state, the measurement pressure P (i) usually does not reach the reference pressure P1, and step 250 is a negative determination.

  If step 250 is negative, the process proceeds to step 251. Steps 251 and 252 have the same purpose as steps 244 and 245. In step 251, the change P (i−1) −P () from the immediately preceding measurement pressure P (i−1) to the current measurement pressure P (i). i) is compared with the threshold value Pa to determine whether P (i-1) -P (i) <Pa. If a negative determination is made, the variable i is incremented by 1 in step 252 and the process returns to step 249. If step 251 is affirmative, the process proceeds to step 254. Similar to step 244, step 251 waits for the measured pressure P (i) to converge.

  In step 253, it is determined that the closed space is normal. In step 254, it is determined that there is an abnormality in the closed space. If there is a leak hole larger than the throttle 23 in the closed space, an abnormality is determined. However, not only when there is a leak hole, but the closed space is formed by the switching failure of the three-position valve 21 or the switching valve 18. Even if there is not, it is judged as abnormal.

  If step 253 is executed to determine normality, the process proceeds to step 256 as it is. On the other hand, if it is determined that an abnormality has occurred by executing step 254, the process proceeds to step 256 after executing step 255 for operating the warning means. The warning means is, for example, an indicator provided on the instrument panel of the vehicle.

  In step 256, the pump 26 is turned off, and both the three-position valve 21 and the switching valve 18 are set to the first position to return to the state before the abnormality diagnosis is executed.

  FIG. 6 is a flowchart showing a fuel concentration determination routine for determining the evaporated fuel concentration in the purge gas purged from the canister 13 and is executed every predetermined short period.

  In step 601, it is determined whether or not the ignition switch is ON. If this determination is negative, the engine 1 has not been started, and therefore purge control is not performed. Therefore, in step 606, it is determined that concentration detection based on pressure measurement (FIG. 7) is prohibited, and this routine is executed. finish.

  On the other hand, if step 601 is affirmative, step 602 is executed to further determine whether or not an abnormality has been diagnosed in the above-described abnormality diagnosis control (FIG. 2). If the determination in step 602 is affirmative, that is, if an abnormality is detected in the closed space shown in FIG. 5, step 606 is executed to perform concentration detection based on pressure measurement (FIG. 7). Ban.

  This is because the pressure drop amount (mixed airflow pressure P1) due to the throttle 23 of the air-fuel mixture purged from the canister 13 is measured in step 702 of FIG. Therefore, in step 702 of FIG. 7, the purge valve 16 is closed. If there is a leak hole in the evaporation line 15, the branch line 19, or the like, outside air flows from the leak hole and the fuel concentration of the mixture gas This makes it difficult to accurately detect the fuel concentration. In addition, when an abnormality is detected in the closed space, such as when the air-fuel mixture is not correctly guided to the throttle 23 even when the three-position valve 21 is not properly switched, the air flow pressure P1 in step 702 cannot be accurately measured. Since the possibility is high, concentration detection based on pressure measurement (FIG. 7) is prohibited.

  If step 602 is negative, that is, if it is diagnosed that the fuel concentration detection system is normal, the routine proceeds to step 603. In step 603, it is further determined whether or not the fuel concentration detection based on the previous pressure measurement, that is, the elapsed time from the fuel concentration detection based on FIG. If step 603 is negative, step 606 described above is executed.

  If the determination in step 603 is affirmative, it is further determined in step 604 whether the purge valve 16 is off, that is, is fully closed. Even when this step 604 is negative, that is, when the purge valve 16 is open, the above-described step 606 is executed.

  If step 604 is affirmative, in step 605 it is determined to start fuel concentration detection based on pressure measurement, and the process proceeds to FIG.

  FIG. 7 is a flowchart showing a concentration detection routine for detecting the fuel concentration based on pressure measurement. Before the execution of this concentration detection routine, 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 connected to the air supply line 20. The first position is connected 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.

  In step 701, the pressure P <b> 0 is measured by the pressure sensor 24 in a state where air flows as a gas flow through the measurement line 22. This state corresponds to the “first measurement state”. The pressure P0 due to the air flow is measured 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.

  Next, in step 702, the pressure P1 is measured in a state where an air-fuel mixture containing evaporative fuel is made to flow through the measurement line 22 as a gas flow. 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, the measurement line 22 is supplied with the air line 17, the canister 13, a part of the purge line 15 up to the branch line 19, and an air-fuel mixture containing evaporated fuel supplied via the branch line 19. That is, the air introduced from the atmospheric line 17 flows in the canister 13 to become a mixture of evaporated fuel and air, and is supplied to the measurement line 22 through a part of the purge line 15 and the branch line 19. . Therefore, when the pressure is measured by the mixed airflow, the pressure sensor 24 detects the amount of pressure drop when the air-fuel mixture containing the evaporated fuel passes through the restriction 23 of the measurement line 22.

  In step 703, the fuel concentration C is calculated and stored based on the pressures P0 and P1 measured in steps 701 and 702.

The fuel concentration C is calculated by calculating the pressure ratio RP between the pressures P0 and P1 according to the equation (1), and calculating the fuel concentration C according to the equation (2) based on the pressure ratio RP. In the formula (2), k1 is a constant previously adapted by experiments or the like.
RP = P1 / P0 (1)
C = k1 * (RP-1) (= (P1-P0) / P0) (2)

  Since evaporative fuel is heavier than air, the density increases when the purge gas contains evaporative fuel. 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 Expression (2). The fuel concentration C obtained in this way represents the concentration of the evaporated fuel in the purge gas as a mass ratio.

  In the next step 704, 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, and the three-position valve 21 is a first position where the air supply line 20 is connected to the measurement line 22.

  FIG. 8 is a flowchart of an air-fuel ratio control routine. This routine is executed every fixed cam angle.

In step 801, 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 allowed when all the conditions for completing the air-fuel ratio sensor activation are satisfied, and the air-fuel ratio feedback control is not allowed when any one of the conditions is not satisfied.

If an affirmative determination is made in step 801, the process proceeds to step 802. In step 802, the output voltage V _OX of the air-fuel ratio sensor 6 is read. In step 803, it is determined whether or not the output voltage V _OX is equal to or lower than a predetermined reference voltage V _R (eg, 0.45 V). If an affirmative determination is made in step 803, the air-fuel ratio of the exhaust gas is lean and the routine proceeds to step 804, where the air-fuel ratio flag XOX is set to “0”.

  Next, at step 805, 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 805, it is assumed that the lean state continues, and in step 806, the air-fuel ratio correction coefficient FAF is increased by the lean integral amount “a”, and this routine is terminated. On the other hand, if a negative determination is made in step 805, it is assumed that the rich state is reversed to the lean state, and the routine proceeds to step 807, where the air-fuel ratio correction coefficient FAF is increased by the lean skip amount “A”. The lean skip amount “A” is set sufficiently larger than the lean integral amount “a”. In step 808, the state maintenance flag XOXO is reset and this routine is terminated.

  If a negative determination is made in step 803, it is determined that the air-fuel ratio of the exhaust gas is rich, the process proceeds to step 809, and the air-fuel ratio flag XOX is set to “1”. In step 810, 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 810, it is assumed that the rich state is continuing, and in step 811 the air-fuel ratio correction coefficient FAF is decreased by the rich integration amount “b”, and this routine is ended. On the other hand, if a negative determination is made in step 810, it is assumed that the lean state has been reversed to the rich state, and the routine proceeds to step 812, 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”.

  Next, at step 813, the state maintenance flag XOXO is set to "b", and this routine is finished. If a negative determination is made in step 801, the routine proceeds to step 814, where the air-fuel ratio correction coefficient FAF is set to “1.0”, and this routine is ended.

  FIG. 9 is a flowchart of a purge rate control routine. In step 901, it is determined whether or not the fuel concentration detection based on the pressure measurement shown in FIG. 7 is completed. If the determination in step 901 is affirmative, the pressure concentration detection completion flag XIPRGHC is set to 1 in step 902, and then step 903 is executed. On the other hand, if step 901 is negative, step 903 is directly executed.

  In step 903, it is determined whether air-fuel ratio feedback control is being performed. When an affirmative determination is made in step 903, the process proceeds to step 904 to determine whether or not the fuel is being cut.

  If a negative determination is made in step 904, the process proceeds to step 905, after normal purge rate control is performed, the process proceeds to step 906. In step 906, the purge stop flag XIPGR is reset (set to 0). Next, in step 907, the fuel cut counter Ccut is reset, and this routine is terminated.

  When an affirmative determination is made at step 904, the routine proceeds to step 908, where the correction purge rate at restart is calculated, and then, at step 909, the purge stop flag XIPGR is set to “1”, and this routine is terminated.

  If a negative determination is made in step 903, the process proceeds to step 910, the purge rate PGR is reset (set to 0), and then the purge stop flag XIPGR is set to “1” in step 911, and this routine is executed. finish.

  FIG. 10 is a flowchart of the normal purge rate control process executed in step 905 of the purge rate control routine shown in FIG. First, in step 9051, it is determined whether or not the pressure concentration detection completion flag XIPRGHC is 1. If this determination is affirmative, a purge rate initial value determination routine is executed in step 9052.

  FIG. 11 shows the details of the purge rate initial value determination routine. First, in steps 90521 and 90522, the purge flow allowable upper limit value is set. That is, in step 90521, an engine operating state is detected, and in step 90522, an allowable purge fuel vapor flow rate allowable value Fm is calculated based on the detected engine operating state. The purge fuel vapor flow rate allowable value Fm is calculated based on the fuel injection amount required under the engine operating state such as the current throttle opening, the lower limit value of the fuel injection amount controllable by the injector 4, and the like. When 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 90523, a current intake pipe pressure Pi is detected by an intake pressure sensor (not shown), and in step 90524, 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%. The calculation is performed according to the reference flow rate map. FIG. 12 shows an example of the reference flow rate map.

In step 90525, the expected flow rate Qc of the purge mixture is calculated according to equation (3) based on the fuel concentration C detected by the fuel concentration detection routine (FIG. 7). 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. 13 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 so, due to the law of energy conservation, the flow rate is reduced compared to when the purge gas is 100% air. The straight line in the figure is equivalent to equation (3). In equation (3), A is a constant and is stored in advance in the ROM of the electronic control unit together with the control program and the like.
Qc = Q100 × (1−A × C) (3)

In step 90526, 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 when the purge gas of the current fuel concentration C flows through the purge line 15 (hereinafter referred to as appropriate). Fc is calculated according to the equation (4).
Fc = Qc × C (4)

  Steps 90527 to 50529 set the purge valve opening x. In step 90527, 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 90528 to set the purge valve opening x 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 90527 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 90529. 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 90528 and 50529, the purge valve 16 is controlled to the opening.

  After execution of steps 90528 and 50529, the pressure concentration detection completion flag XIPRGHC is reset (set to 0) in step 90530 and the restart correction purge rate PGRcomp is set to 0. By resetting the pressure concentration detection completion flag XIPRGHC in step 90530, step 9051 in FIG. 10 is negatively determined and step 9053 and subsequent steps are executed.

  In step 9053, it is determined in which region the air-fuel ratio correction coefficient FAF is present. FIG. 14 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. 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 9053 that the region belongs to the region I, the process proceeds to step 9054, the purge rate PGR is increased by a predetermined purge rate increase amount D, and the process proceeds to step 9056. If it is determined in step 9053 that the region belongs to the region III, the process proceeds to step 9055, the purge rate PGR is decreased by a predetermined purge rate down amount E, and the procedure proceeds to step 9056. If it is determined in step 9053 that the image belongs to area II, the process directly proceeds to step 9056.

  In Step 9056, a restart correction purge rate PGRcomp, which will be described later, is subtracted from the purge rate PGR, and the flow proceeds to Step 9057. In step 9057, a predetermined fixed value F is subtracted from the resuming correction purge rate PGRcomp. In step 9058, it is determined whether or not the resuming correction purge rate PGRcomp is positive.

  If a negative determination is made in step 9058, the restart correction purge rate PGRcomp is set to the lower limit “0” in step 9059, and the process proceeds to step 9060. When an affirmative determination is made at step 9058, the routine directly proceeds to step 9060, where the upper and lower limits of the purge rate PGR are checked, and this routine is terminated.

FIG. 15 is a flowchart of the restart correction purge rate calculation executed in step 908 of the purge rate control routine shown in FIG. First, in step 9081, 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. Therefore, 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 instead of the fuel tank internal pressure _PT to express the degree of fuel evaporation. However, when the fuel tank internal pressure _PT is used as a parameter, the influence of changes in atmospheric pressure or the like is canceled out, so that more accurate detection can be easily performed.

In the next step 9082, the fuel cut counter Ccut is incremented and the routine proceeds to step 9083. The fuel cut counter Ccut represents the duration of the fuel cut state. In step 9083, the evaporated fuel amount VAPOR (PT, Ccut) adsorbed by the canister 14 during the fuel cut is obtained as a function of the fuel tank internal 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, it is possible to determine the fuel evaporation amount per unit as a function time of the fuel tank pressure P _T α (PT), the count of the fuel cut counter Ccut corresponding to the elapsed time fuel evaporation quantity per unit time alpha The evaporated fuel amount VAPOR can be obtained by the following equation that multiplies the values.
VAPOR = α (PT) ・ Ccut

In step 9084, the restart-time corrected purge rate PGRcomp is determined as a function of the evaporated fuel amount VAPOR and the intake air amount GA detected by the airflow sensor.
PGRcomp = β · VAPOR / GA
Where β is a coefficient

  FIG. 16 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 161 whether or not the purge stop flag XIPGR is “1”. If the determination is affirmative, it is determined that the purge is stopped, and in step 162 the duty ratio Duty is set to “0”. Exit.

If a negative determination is made in step 161, it is determined that purging is in progress, and the routine proceeds to step 163, where the duty ratio Duty is calculated based on the following equation.
Duty = γ · PGR / PGR100 + δ
Here, PGR100 is a fully open 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. 17 is a map setting example for determining the fully open purge rate. γ and δ are correction coefficients determined by the battery voltage and the atmospheric pressure.

FIG. 18 is a flowchart of a fuel concentration learning routine for calculating the fuel concentration FGPG. In step 1801, it is determined whether or not the pressure concentration detection completion flag XIPRGHC is 1. If step 1801 is affirmative, step 1802 corresponding to density conversion means is executed. In step 1802, by substituting the fuel concentration C determined in FIG. 7 into the following equation, the fuel concentration C is compared with the theoretical air fuel ratio (= 14.6), which is the target air fuel ratio, and the relative evaporated fuel concentration of the purge gas is determined. It converts into the fuel concentration FGPG to represent.
FGPG = (1-C) − (14.6 × C × evaporated fuel density / air density)
The density of the evaporated fuel and the density of the air may be a predetermined constant value or may be determined based on the temperature.

  The fuel concentration FGPG becomes 0 when the ratio of the evaporated fuel in the purge gas is the same as the stoichiometric air-fuel ratio, and becomes negative when the ratio of the evaporated fuel exceeds the stoichiometric air-fuel ratio. Moreover, it becomes positive when the ratio of the evaporated fuel is smaller than the theoretical air-fuel ratio, and becomes 1 when no evaporated fuel 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. After execution of step 1802, the process proceeds to step 1810 described later.

  If the above step 1801 is negative, the process proceeds to step 1804 to determine whether or not the purge stop flag XIPGR is “1”. End the routine.

If an affirmative determination is made in step 1804, the process proceeds to step 1805 to determine whether or not a fuel concentration learning condition is satisfied. (1) During air-fuel ratio feedback control, (2) Coolant temperature ≧ 80 ° C., (3) Fuel increase at start-up = 0, (4) Warm-up fuel increase = 0
Learning is executed when all of the conditions are satisfied, and learning is not performed when any of the conditions is not satisfied.

  When a negative determination is made at step 1805, that is, when learning is not performed, this routine is directly terminated. When an affirmative determination is made in step 1805, that is, when learning is performed, the process proceeds to step 1806. In step 1806, the temporal average value FAFAV of the air-fuel ratio correction coefficient FAF calculated in the air-fuel ratio control routine of FIG. 8 is calculated, and the process proceeds to step 1807.

  In step 1807, it is determined whether the average value FAFAV is in the range of “0.98” or less, “0.98” and less than “1.02”, or “1.02” or more. When it is determined that the average value FAFAV is “0.98” or less, the process proceeds to step 1808, the fuel concentration FGPG is decreased by a predetermined amount “Q” (for example, 0.4%), and the process proceeds to step 1810.

  If it is determined that the value is “1.02” or more, the process proceeds to step 1809, the fuel concentration FGPG is increased by a predetermined amount “P” (for example, 0.4%), and the process proceeds to step 1810. If it exceeds “0.98” and is less than “1.02”, the process proceeds directly to Step 1810 without updating the fuel concentration FGPG. The fuel concentration FGPG determined in steps 1806 to 1809 corresponds to the first fuel concentration, that is, the first fuel state, and the electronic control unit that executes steps 1806 to 1809 corresponds to the first fuel state determination means.

  If the evaporated fuel concentration in the purge gas is “0”, the fuel concentration FGPG determined by executing step 1808 or step 1809 is set to “1”, and the fuel concentration increases as the fuel concentration increases. It is a certain value. In step 1810, the fuel concentration FGPG is limited to a value within a predetermined upper and lower limit value, and this routine is terminated.

FIG. 19 is a flowchart of an injector control routine. First, in step 1901, the basic fuel injection time Tp is obtained as a function of the engine speed Ne and the intake air amount GA.
Tp = Tp (Ne, GA)

In the next step 1902, a purge correction coefficient FPG is calculated based on the purge rate PGR and the fuel concentration FGPG determined in FIG.
FPG = FGPG · PGR

In step 1903, the injector valve opening time TAU is determined by the following equation using the air-fuel ratio correction coefficient FAF calculated in the air-fuel ratio control routine shown in FIG. 8 and the purge correction coefficient FPG.
TAU = α · Tp · (FAF + FPG) + β
Here, α and β are correction coefficients including a warm-up increase, a start increase, and the like.

  In step 1904, the injector valve opening time TAU is output, and this routine is terminated.

  FIG. 20 is a timing chart illustrating the purge timing in the present embodiment. FIG. 20 is a timing chart during engine start. When an abnormality diagnosis condition is satisfied while the engine is stopped, abnormality diagnosis control (FIG. 2) is executed in advance. An example of a time chart when the diagnosis result is an abnormality diagnosis is the time chart at the time of abnormality diagnosis shown in FIG. 20, and an example of a time chart when the diagnosis result is a normal diagnosis is at the time of normal diagnosis shown in FIG. It is a time chart.

  When a normal diagnosis is made, the fuel concentration detection (FIG. 7) based on the pressure measurement is started by making an affirmative determination in steps 601 to 603 of FIG. 6 such as turning on the ignition switch (at time t1). .

  When the concentration detection in FIG. 7 is completed and the fuel concentration C is obtained, the fuel concentration C can be converted into the relative evaporated fuel concentration, that is, the fuel concentration FGPG in step 1802 in FIG. Further, since the pressure concentration detection completion flag XIPRGHC becomes 1, the purge rate initial value determination process in step 5052 of FIG. 10 is executed. Therefore, the purge rate PGR is determined by executing the purge rate initial value determination process, and the purge is started (at time t2).

  On the other hand, at the time of abnormality diagnosis, the purge is started with a small purge rate PGR that does not affect the air-fuel ratio (at time t3). Then, the fuel concentration FGPG when the purge rate PGR is further increased with the small purge rate PGR is predicted. Further, from the time when the prediction is completed (time t4), the purge valve 16 is gradually opened while repeating learning of the fuel concentration FGPG based on the predicted value. The purge rate PGR reaches the maximum value at time t5. By doing so, even if the fuel concentration FGPG cannot be known before the purge starts, the purge can be performed while suppressing the disturbance of the air-fuel ratio.

  When the vehicle speed is decelerated and the fuel is cut off (at time t6), the purge rate PGR is 0, that is, the purge is interrupted with the purge valve 16 fully closed. Then, when a predetermined time has elapsed since the completion of the fuel concentration detection based on the previous pressure measurement in the purge interruption state, all the steps 601 to 604 in FIG. Detection is started again (at time t7). When the fuel concentration detection is completed at time t8, the pressure concentration detection completion flag is set to 1 in step 902 in FIG. 9, and the fuel concentration FGPG is calculated in step 1802 in FIG.

  Then, at time t9 after time t8, when the fuel cut-off state, that is, the state where the fuel cut is released, the fuel concentration FGPG is calculated in step 1802 of FIG. 18, so the purge is resumed (time t9). The purge is resumed at a large purge rate PGR.

  On the other hand, at the time of abnormality diagnosis, the purge is resumed at the purge rate PGR determined based on the period of the fuel cut-on state. By doing so, the purge can be resumed without disturbing the air-fuel ratio. After the purge is resumed, the purge rate PGR is increased while repeating the learning of the fuel concentration FGPG.

  Further, when the fuel cut-on state is reached at time t10 and concentration detection based on pressure measurement is started at time t11, but the concentration detection is not completed and the fuel cut-off state is returned at time t12, the normal diagnosis is performed. Even so, the purge is restarted at the purge rate PGR determined by integrating the fuel cut-on state periods as in the abnormality diagnosis.

  As described above, in the present embodiment, when the fuel concentration detection system is normal, the purge rate PGR can be maximized from the purge start time (time t2) and the purge can be started (t9). The purge rate PGR can also be maximized. Therefore, the purge amount can be made sufficiently large.

  Further, when the fuel concentration detection is not completed during the purge interruption, the purge rate PGR at the time of restarting the purge is determined based on the purge interruption time, so even if the fuel concentration detection is not completed during the purge interruption. The purge rate PGR when restarting the purge can be increased to some extent. This also makes it possible to increase the purge amount.

  In addition, when it is diagnosed that there is an abnormality in the fuel concentration detection system in the abnormality diagnosis control of FIG. 2, the fuel concentration detection by the fuel concentration detection system (FIG. 7) is not executed, regardless of the vehicle operating state. 8, since the fuel concentration FGPG (first fuel concentration) determined based on the amount of deviation of the air-fuel ratio from the target air-fuel ratio is used, the fuel injection amount is controlled on the basis of the abnormal fuel concentration. It can also be suppressed that the fuel ratio greatly deviates.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the above-described embodiment, the closed space formed for performing abnormality diagnosis is formed by the purge valve 16 being closed, the 3-position valve 21 being in the second position, and the switching valve 18 being in the second position. However, the closed space only needs to partially include a path through which the air-fuel mixture flows or a path communicating with the path in the fuel concentration detection based on pressure measurement (FIG. 7). In this case, when there is an abnormality in the closed space, it can be determined that there is a high possibility that the mixed airflow pressure P1 cannot be accurately measured. Therefore, for example, the purge valve 16 and the switching valve 18 remain in the above-described embodiment, but the closed space is reduced by setting the three-position valve 21 to the third position (position where the branch line 19 and the measurement line 22 communicate). It may be formed. Further, the three-position valve 21 is set to the second position (the position where the measurement line 22 does not communicate with either the air supply line 20 or the branch line 19), and the switching valve 18 is set to the first position (the measurement line 22 is the caster 13 or the standby line 17). The closed space may be formed by setting the position to be blocked with respect to.

  Further, in addition to the measurement of the pressure P in the closed space, the abnormality of the fuel concentration detection system may be diagnosed based on whether or not the pressure has decreased to a predetermined determination value or less. This is because, when the pressure P does not decrease below the determination value, it is considered that an abnormality such as a reduction in the capacity of the pump 26, a switching operation failure of the switching valve 18 or the three-position valve 21 and a leakage failure has occurred.

  Further, a position sensor that detects the position of the switching valve 18 or the three-position valve 21 may be provided, and an abnormality of the switching valve 18 or the three-position valve 21 may be diagnosed based on a signal from the position sensor.

  In the above-described embodiment, the pressure sensor 24 has one end connected to the downstream side of the throttle 23 and the other end opened to the atmosphere. The pressure difference before and after 23 may be detected.

  In the above-described embodiment, the three-position valve 21 is used. However, a switching operation corresponding to the first to third positions described above can be performed by combining a plurality of two-position valves. It is.

It is a block diagram which shows the structure of the evaporative fuel processing apparatus by embodiment of this invention. It is a flowchart which shows the abnormality diagnosis control which diagnoses the abnormality of a fuel concentration detection system with the leak diagnosis of an evaporative fuel processing apparatus. 3 is a flowchart showing an abnormality diagnosis execution routine executed in step 204 of FIG. It is a figure which shows the distribution | circulation state of the gas at the time of step 241 execution of FIG. It is a figure which shows the distribution | circulation state of the gas at the time of step 247 execution of FIG. 4 is a flowchart showing a fuel concentration determination routine for determining an evaporated fuel concentration in a purge gas purged from a canister. It is a flowchart which shows the density | concentration detection routine which detects a fuel density | concentration based on pressure measurement. It is a flowchart of an air fuel ratio control routine. It is a flowchart of a purge rate control routine. FIG. 10 is a flowchart of a normal purge rate control process executed in step 905 of the purge rate control routine shown in FIG. 9. FIG. FIG. 11 is a flowchart of a purge rate initial value determination routine executed in step 9052 of FIG. 10. FIG. It is a figure which shows an example of a reference | standard flow volume map. It is a figure which shows the relationship between the fuel density | concentration C and the ratio (Qc / Q100) of the estimated flow volume Qc with respect to the reference flow volume Q100. It is a graph which shows the area | region of the air fuel ratio correction coefficient FAF. FIG. 10 is a flowchart of resuming correction purge rate calculation executed in step 908 of the purge rate control routine shown in FIG. 9. FIG. 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 the fuel concentration learning routine for calculating the fuel concentration FGPG. It is a flowchart of an injector control routine. It is a timing chart which illustrates the purge timing in this embodiment.

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 (purge control valve)
18: Switching valve (closed space forming valve)
21: 3-position valve (measurement passage switching means, closed space forming valve, pressure application range switching means)
22: Measurement line (measurement passage, leak inspection passage)
23: Aperture (reference aperture)
24: Pressure sensor (pressure measuring means)
26: Pump (gas flow generating means, pressure applying means)
Step 1802: Concentration conversion means Steps 1901 to 1904: Air-fuel ratio control means

Claims (10)

A canister that temporarily adsorbs the evaporated fuel generated from the fuel tank;
A purge pipe for guiding the evaporated fuel purged from the canister to the intake pipe of the internal combustion engine;
A purge control valve that is installed in the purge pipe and controls a purge flow rate from the purge pipe to the intake pipe;
An air-fuel ratio sensor provided in an exhaust pipe of an internal combustion engine for measuring an air-fuel ratio;
When the purge control valve is open, the fuel state of the air-fuel mixture including the evaporated fuel purged from the canister is determined based on the amount of deviation of the air-fuel ratio detected from the air-fuel ratio sensor from the target air-fuel ratio. First fuel condition determining means for
Vaporized fuel for an internal combustion engine, comprising: air-fuel ratio control means for controlling the fuel injection amount to the internal combustion engine so that the air-fuel ratio becomes the target air-fuel ratio based on the fuel state of the air-fuel mixture purged from the canister In the processing device,
Second fuel state determining means for determining the fuel vapor state of the air-fuel mixture by purging the air-fuel mixture containing fuel vapor from the canister while the purge control valve is closed;
An abnormality detection means for detecting an abnormality of the second fuel state determination means,
The air-fuel ratio control means uses the fuel state determined by the first fuel state determination means or the fuel determined by the second fuel state determination means when no abnormality is detected by the abnormality detection means. Whether or not the state is used is switched based on the vehicle operating state, but when an abnormality is detected by the abnormality detecting means, the fuel state used for controlling the fuel injection amount regardless of the vehicle operating state An evaporative fuel processing apparatus for an internal combustion engine, wherein the fuel state determined by the first fuel state determination means is used. The second fuel state determining means includes
A measuring passage with a restriction in the middle,
A pump that generates a gas flow that passes through the restriction of the measurement passage;
Pressure measuring means for measuring a pressure drop caused by the throttle when the pump generates a gas flow;
The measurement passage is opened to the atmosphere, and the measurement passage is connected to the canister with the first measurement state in which the gas flowing through the measurement passage is air, and the purge control valve is closed. Measuring passage switching means for switching to a second measurement state in which the flowing gas is an air-fuel mixture containing evaporated fuel from the canister,
The fuel state is determined based on a first pressure measured by the pressure measuring unit in the first measurement state and a second pressure measured by the pressure measurement unit in the second measurement state. Is what
The evaporated fuel processing apparatus for an internal combustion engine according to claim 1, wherein the abnormality detection means detects at least one abnormality of the measurement passage, the pump, the pressure measurement means, and the measurement passage switching means. . A closed space forming valve for making at least a part of a fuel state detection system including the measurement passage, the pump, the pressure measurement means, and the measurement passage switching means into a closed space;
A leak inspection passage opened to the atmosphere at one end and provided with a reference throttle in the middle;
Pressure applying means for pressurizing or depressurizing the closed space and the inside of the leakage inspection passage;
Pressure measuring means for measuring the pressure in the closed space or the leak inspection passage pressurized or depressurized by the pressure applying means;
The pressure application range to be pressurized or depressurized by the pressure application means includes at least one of the closed space and the leak inspection passage, and is in one of two types of leak measurement states in which the pressure application range is different from each other. Pressure application range switching means for switching,
The abnormality detection means detects an abnormality of the fuel state detection system based on a comparison of two pressures respectively measured by the pressure measurement means in the two types of leak measurement states. The fuel vapor processing apparatus for an internal combustion engine according to claim 2.   The evaporative fuel processing device for an internal combustion engine according to claim 3, wherein the leak inspection passage is the measurement passage.   The evaporated fuel processing device for an internal combustion engine according to claim 4, wherein the pressure application range switching means is the measurement passage switching means.   6. The evaporative fuel processing apparatus for an internal combustion engine according to claim 3, wherein the pressure applying means is a pump that generates a gas flow in the measurement passage.   The air-fuel ratio control means uses the fuel state determined by the second fuel state determination means when no abnormality is detected by the abnormality detection means and the vehicle operating state is before the start of purging. The evaporative fuel processing apparatus of the internal combustion engine according to any one of claims 1 to 6.   The air-fuel ratio control means uses the fuel state determined by the first fuel state determination means when the vehicle operating state is after the start of purging and is not suspended. The evaporative fuel processing apparatus of the internal combustion engine in any one of 7.   The air-fuel ratio control means uses the fuel state determined by the second fuel state determination means when no abnormality is detected by the abnormality detection means and the vehicle operating state is suspended in the purge. An evaporative fuel processing apparatus for an internal combustion engine according to any one of claims 1 to 8.   If the determination of the fuel state by the second fuel state determination unit is not completed when the vehicle operation state is the purge suspension, the air-fuel ratio control unit is configured to perform the first fuel state immediately before the purge suspension. The fuel vapor processing apparatus for an internal combustion engine according to claim 9, wherein the fuel state determined by the determining means is used.

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