JP2007218123A - 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 keeping 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 air fuel ratio detected by an air fuel ratio sensor provided on an exhaust pipe from target air fuel ratio, a second fuel condition determination means determining fuel concentration purged from the canister under a condition where a purge control valve is closed, and an air fuel ratio control means controlling fuel injection quantity to the internal combustion engine to keep air fuel ratio at the target air fuel ratio based on fuel concentration purged from the canister. The air fuel ratio control means uses fuel concentration determined by the second fuel condition determination means as fuel concentration used for determining fuel injection quantity at the time of purge start or re-start, and uses fuel concentration determined by the first fuel condition determination means during purging after that. Consequently, purge ratio can be kept large from purge start or restart. <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 evaporated 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 evaporated fuel is detached from the adsorbent, the adsorbing 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 a fuel state of the air-fuel mixture purged from the canister while the purge control valve is closed; the air-fuel ratio control means for controlling the fuel injection amount; Switching between using the fuel state determined by the first fuel state determining means or the fuel state determined by the second fuel state determining means as the fuel state to be used is based on the vehicle operating state. And

  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, the period during which the fuel state cannot be determined decreases. 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 this case, the air-fuel ratio control means uses the fuel state determined by the second fuel state determination means when the vehicle operating state is before the purge start, as in claim 2. It is preferable to determine the fuel injection amount.

  This is because, as described above, the fuel state cannot be determined by the first fuel state determination unit before the purge is started, while the second fuel state determination unit can determine the fuel state. Therefore, according to the second 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 3, 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 third aspect, the fuel injection amount during the purge can be set to an appropriate value.

  Further, as described in claim 4, 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 fourth aspect of the present invention, 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 5, 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 interruption, the air-fuel ratio control unit Preferably, the fuel injection amount at the time of resuming the purge is determined based on the fuel state determined by the first fuel state determining means immediately before the purge is interrupted.

Further, in the second fuel state determination means, in order to determine the fuel state with the purge control valve closed, the configuration according to claim 6 can be adopted. That is, the invention according to claim 6 is the evaporative fuel processing apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein the measurement passage having a throttle in the middle and the gas flow passing through the restriction in the measurement passage are provided. A gas flow generating means to be generated; a pressure measuring means for measuring a pressure drop caused by the throttle when the gas flow generating means generates a gas flow; and Measurement switching between a first measurement state in which the gas flowing in the passage is air and a second measurement state in which the measurement passage is connected to the canister and the gas flowing in the measurement passage is an air-fuel mixture containing evaporated fuel from the canister Further comprising a passage switching means,
The second fuel state determination means includes a first pressure measured by the pressure measurement means in the first measurement state, and a second pressure measured by the pressure measurement means in the second measurement state. Based on the above, the fuel state is 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.

The invention according to claim 7 is the evaporative fuel processing apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the first fuel state determination means is compared with the target air-fuel ratio as a fuel state. To determine the relative evaporative fuel state of the mixture,
A state conversion means for converting the fuel state determined by the second fuel state determination means into a relative evaporated fuel state of the air-fuel mixture compared with the target air-fuel ratio;
The air-fuel ratio control means uses the fuel state converted by the state conversion means as the fuel state determined by the second fuel state determination means.

  In this way, the fuel state determined by the first fuel state determination unit and the fuel state after conversion by the state conversion unit become the relative evaporated fuel state compared with the same target air-fuel ratio. Whether the fuel state determined by the first fuel state determination unit or the fuel state after conversion by the state conversion unit is used in the fuel ratio control unit, the fuel injection amount is determined based on the same arithmetic expression. can do. Therefore, it becomes easy to switch which fuel state is used based on the operation state.

  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.

  In the canister 13, a partition plate 14 a is provided inside the canister 13 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 absorbed 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. 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. 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. " 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 of the air-fuel ratio control routine, which is executed at every constant cam angle.

In step 201, 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.

When an affirmative determination is made at step 201, the routine proceeds to step 202. In step 202, the output voltage V _OX of the air-fuel ratio sensor 6 is read. In step 203, 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, 0.45 V). If the determination in step 203 is affirmative, the air-fuel ratio of the exhaust gas is lean and the routine proceeds to step 204 where the air-fuel ratio flag XOX is set to “0”.

  Next, at step 205, 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 205, it is assumed that the lean state is continuing, and in step 206, 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 205, it is assumed that the rich state has been reversed to the lean state, and the routine proceeds to step 207 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 208, the state maintenance flag XOXO is reset and the routine is terminated.

  If a negative determination is made in step 203, the air-fuel ratio of the exhaust gas is rich and the routine proceeds to step 209, where the air-fuel ratio flag XOX is set to “1”. In step 210, it is determined whether or not the air-fuel ratio flag XOX and the state maintenance flag XOXO match. If an affirmative determination is made in step 210, it is assumed that the rich state continues, and in step 211, the air-fuel ratio correction coefficient FAF is decreased by the rich integration amount “b”, and this routine is terminated. On the other hand, when a negative determination is made in step 210, it is determined that the lean state is reversed to the rich state, and the routine proceeds to step 212, 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 213, the state maintenance flag XOXO is set to "b" and this routine is finished. When a negative determination is made at step 201, the routine proceeds to step 214, the air-fuel ratio correction coefficient FAF is set to “1.0”, and this routine is ended.

  FIG. 3 is a flowchart showing a fuel concentration determination routine for determining the evaporated fuel concentration in the purge gas purged from the canister 13. This routine is executed in parallel with the routine of FIG.

  In step 301, 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 305, it is determined that concentration detection based on pressure measurement is prohibited, and this routine is terminated.

  On the other hand, if the determination in step 301 is affirmative, it is determined in step 302 whether the elapsed time from the fuel concentration detection based on the previous pressure measurement, that is, the fuel concentration detection based on FIG. Determine further. If step 302 is negative, step 305 described above is executed.

  If the determination in step 302 is affirmative, it is further determined in step 303 whether the purge valve 16 is off, that is, is fully closed. If this step 303 is negative, that is, if the purge valve 16 is open, the above-described step 305 is also executed.

  If step 303 is affirmative, in step 304 it is determined to start fuel concentration detection based on pressure measurement, and the process proceeds to FIG.

  FIG. 4 is a flowchart showing a concentration detection routine for detecting the fuel concentration based on the pressure measurement. The second means for determining the fuel concentration, which is a kind of the fuel state, that is, the second fuel state determination means. It is. 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 401, the pressure P0 is measured by the pressure sensor 24 in a state where air is made to flow through the measurement line 22 as a gas flow. 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 402, the pressure P1 is measured in a state where an air-fuel mixture containing evaporated fuel is flowed 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, 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 403, the fuel concentration C is calculated and stored based on the pressures P0 and P1 measured in steps 401 and 402.

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 404, 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.

  FIG. 5 is a flowchart of the purge rate control routine. In step 501, it is determined whether or not the fuel concentration detection based on the pressure measurement shown in FIG. 4 is completed. If step 501 is affirmative, step 503 is executed after the pressure concentration detection completion flag XIPRGHC is set to 1 in step 502. On the other hand, if step 501 is negative, step 503 is directly executed.

  In step 503, it is determined whether air-fuel ratio feedback control is being performed. If an affirmative determination is made in step 503, the process proceeds to step 504 to determine whether or not a fuel cut is in progress.

  If a negative determination is made in step 504, the process proceeds to step 505. After performing normal purge rate control, the process proceeds to step 506. In step 506, the purge stop flag XIPGR is reset (set to 0), and then in step 507, the fuel cut counter Ccut is reset and this routine is ended.

  When an affirmative determination is made at step 504, the routine proceeds to step 508, where a restart correction purge rate is calculated. Then, at step 509, the purge stop flag XIPGR is set to "1" and this routine is terminated.

  Further, when a negative determination is made at step 503, the routine proceeds to step 510, where the purge rate PGR is reset (set to 0), and then at step 511, the purge stop flag XIPGR is set to “1” and this routine is executed. finish.

  FIG. 6 is a flowchart of the normal purge rate control process executed in step 505 of the purge rate control routine shown in FIG. First, in step 5051, 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 5052.

  FIG. 7 shows the details of the purge rate initial value determination routine. First, in steps 50521 and 50522, a purge flow allowable upper limit value is set. That is, in step 50521, an engine operating state is detected, and in step 50522, 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 50523, a current intake pipe pressure Pi is detected by an intake pressure sensor (not shown), and in step 50524, 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. 8 shows an example of the reference flow rate map.

In step 50525, the expected flow rate Qc of the purge mixture is calculated according to the equation (3) based on the fuel concentration C detected by the fuel 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. 9 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). When the fuel concentration C increases, the purge gas density 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 50526, 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 50527 to 50529 set the purge valve opening x. In step 50527, 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 50528 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 a negative determination is made in step 50527 for determining whether or not Fc ≦ Fm, 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 flow proceeds to step 50529. 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 50528 and 50529, the purge valve 16 is controlled to the opening.

  After execution of steps 50528 and 50529, the pressure concentration detection completion flag XIPRGHC is reset (set to 0) in step 50530 and the restart correction purge rate PGRcomp is set to 0. By resetting the pressure concentration detection completion flag XIPRGHC in step 50530, step 5051 in FIG. 6 is negatively determined, and step 5053 and subsequent steps are executed.

  In step 5053, it is determined in which region the air-fuel ratio correction coefficient FAF is present. FIG. 10 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 5053 that the region belongs to region I, the process proceeds to step 5054, the purge rate PGR is increased by a predetermined purge rate increase amount D, and the process proceeds to step 5056. If it is determined in step 5053 that the region belongs to the region III, the process proceeds to step 5055, the purge rate PGR is decreased by a predetermined purge rate down amount E, and the process proceeds to step 5056. If it is determined in step 5053 that the image belongs to area II, the process directly proceeds to step 5056.

  In step 5056, a restart correction purge rate PGRcomp, which will be described later, is subtracted from the purge rate PGR, and the flow proceeds to step 5057. In step 5057, a predetermined correction value F is subtracted from the restart-time corrected purge rate PGRcomp. In step 5058, it is determined whether the restart-time corrected purge rate PGRcomp is positive.

  If a negative determination is made in step 5058, the restart correction purge rate PGRcomp is set to the lower limit “0” in step 5059, and the process proceeds to step 5060. When an affirmative determination is made at step 5058, the routine directly proceeds to step 5060, where the upper and lower limits of the purge rate PGR are checked, and this routine is terminated.

  FIG. 11 is a flowchart of the correction purge rate calculation at restart executed in step 508 of the purge rate control routine shown in FIG. First, in step 5081, a 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 5082, the fuel cut counter Ccut is incremented and the routine proceeds to step 5083. The fuel cut counter Ccut represents the duration of the fuel cut state. In step 5083, 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 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. The evaporated fuel amount VAPOR can be obtained by the following equation that multiplies.
VAPOR = α (PT) ・ Ccut

In step 5084, a restart correction purge rate PGRcomp is determined as a function of the evaporated fuel amount VAPOR and the intake air amount GA detected by the air flow sensor.
PGRcomp = β · VAPOR / GA
Where β is a coefficient

  FIG. 12 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 121 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 122 the duty ratio Duty is set to “0”. Exit.

If a negative determination is made in step 121, it is determined that purging is in progress, and the routine proceeds to step 123, where the duty ratio Duty is calculated based on the following equation.
Duty = γ · PGR / PGR ₁₀₀ + δ
Here, PGR ₁₀₀ is a fully opened purge rate, and represents a purge amount when the purge valve 16 is fully opened. The fully open purge rate PGR ₁₀₀ is set in advance as a map of the engine speed Ne and the throttle valve opening TA. FIG. 13 is a setting example of a map for determining the fully open purge rate PGR ₁₀₀ . γ and δ are correction coefficients determined by the battery voltage and the atmospheric pressure.

FIG. 14 is a flowchart of a fuel concentration learning routine for calculating the fuel concentration FGPG. In step 1401, it is determined whether or not the pressure concentration detection completion flag XIPRGHC is 1. If step 1401 is affirmative, step 1402 corresponding to density conversion means is executed. In step 1402, by substituting the fuel concentration C determined in FIG. 4 into the following equation, the fuel concentration C is compared with the theoretical air fuel ratio (= 14.6) that 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 1402, the process proceeds to step 1410 described later.

  If the aforementioned step 1401 is negative, the process proceeds to step 1404, where it is determined whether or not the purge stop flag XIPGR is “1”. End the routine.

When an affirmative determination is made at step 1404, the routine proceeds to step 1405, where it is determined 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 1405, that is, when learning is not performed, this routine is directly terminated. When an affirmative determination is made in step 1405, that is, when learning is performed, the process proceeds to step 1406. In step 1406, the temporal average value FAFAV of the air-fuel ratio correction coefficient FAF calculated in the air-fuel ratio control routine of FIG. 2 is calculated, and the process proceeds to step 1407.

  In step 1407, it is determined whether the average value FAFAV is in a range of “0.98” or less, exceeding “0.98”, 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 1408, the fuel concentration FGPG is decreased by a predetermined amount “Q” (for example, 0.4%), and the process proceeds to step 1410.

  If it is determined that the value is “1.02” or more, the process proceeds to step 1409, the fuel concentration FGPG is increased by a predetermined amount “P” (for example, 0.4%), and the process proceeds to step 1410. When it exceeds “0.98” and is less than “1.02”, the process directly proceeds to step 1410 without updating the fuel concentration FGPG. Steps 1406 to 1409 correspond to first means for determining the fuel concentration, which is a kind of fuel state, that is, first fuel state determination means.

  If the evaporated fuel concentration in the purge gas is “0”, the fuel concentration FGPG determined by executing Step 1408 or Step 1409 is set to “1”, and the fuel concentration becomes smaller as “1” as the fuel concentration increases. It is a certain value. In step 1410, the fuel concentration FGPG is limited to a value within a predetermined upper and lower limit value, and this routine is terminated.

FIG. 15 is a flowchart of an injector control routine. First, in step 1501, a 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 1502, 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 1503, 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. 2 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 1504, the injector valve opening time TAU is output, and this routine is terminated.

  FIG. 16 is a timing chart comparing the purge timings of this embodiment and the prior art described in Patent Document 1 described above.

  The fuel concentration detection (FIG. 4) based on the pressure measurement is started when the steps 301 to 303 in FIG. 3 are affirmed, such as when the ignition switch is turned on (time t1). When the concentration detection in FIG. 4 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 1402 in FIG. Further, the pressure concentration detection completion flag XIPRGHC is set to 1, and the purge rate PGR is set to the maximum target purge rate (for example, set to 10 to 20%) in step 5052 of FIG. 6, so that the purge valve 16 is fully opened. Purge is started (time t2).

  On the other hand, in the conventional technique described in Patent Document 1, since the fuel concentration FGPG cannot be known unless the purge is started, the purge must be 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 set to the maximum target purge rate is predicted with the small purge rate PGR. Furthermore, from the time when the prediction is completed (time t4), the purge valve 16 must be gradually opened while repeating the learning of the fuel concentration FGPG based on the predicted value in order to suppress the disturbance of the air-fuel ratio. The purge rate PGR can be set to the maximum target purge rate at time t5.

  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, in this embodiment, all the steps 301 to 303 in FIG. The density 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 502 of FIG. 5, and the fuel concentration FGPG is calculated in step 1402 of FIG.

  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 1402 of FIG. The purge can be restarted with the purge rate PGR as the maximum target purge rate.

  On the other hand, in the prior art described in Patent Document 1, the purge rate PGR can be increased to some extent by accumulating the fuel cut-on state period, but the purge rate PGR is set to the maximum target purge rate. In order not to disturb the air-fuel ratio, it is necessary to increase the purge rate PGR while repeatedly learning 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, this embodiment In the same manner as in the prior art described in Patent Document 1, the purge is resumed at the purge rate PGR determined by integrating the periods of the fuel cut-on state.

  As described above, when comparing the operation of the present embodiment with the operation of the prior art described in Patent Document 1, first, in the prior art described in Patent Document 1, the initial purge rate PGR is set to the air-fuel ratio at the initial stage of purging. The value must be small enough not to affect it. In contrast, in the present embodiment, the purge rate PGR can be set to the maximum target purge rate from the purge start time (time t2), so that the purge amount can be increased in the present embodiment.

  Further, in the prior art in which the fuel concentration FGPG is determined from the deviation of the air-fuel ratio when the purge is actually performed, a change in the fuel concentration FGPG cannot be detected during the purge interruption. Therefore, when the purge is resumed after the fuel cut-on state and the purge is interrupted, the purge rate PGR at the time of restart must be made smaller than the maximum target purge rate, and the purge rate PGR must be gradually increased. On the other hand, in the present embodiment, the fuel concentration FGPG can be obtained during the purge interruption, so that the purge rate PGR at the time of restarting the purge (at time t9) can be set to the maximum target purge rate. Therefore, the amount of purge at the time of resuming purge can be increased in the present embodiment.

  In the present embodiment, 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 as in the conventional technique described in Patent Document 1. Therefore, even if the fuel concentration detection is not completed during the purge interruption, the purge amount is not reduced as compared with the conventional technique.

  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 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 of an air fuel ratio control routine. 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 a purge rate control routine. 6 is a flowchart of normal purge rate control processing executed in step 505 of the purge rate control routine shown in FIG. FIG. 7 is a flowchart of a purge rate initial value determination routine executed in step 5052 of FIG. 6. FIG. It is a figure which shows an example of a reference | standard flow volume map. It is a figure which shows the relationship with the ratio (Qc / Q100) of the prediction flow volume Qc with respect to fuel concentration C reference | standard flow volume Q100. It is a graph which shows the area | region of the air fuel ratio correction coefficient FAF. FIG. 6 is a flowchart of a correction purge rate calculation at restart executed in step 508 of the purge rate control routine shown in FIG. 5. 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. 5 is a timing chart comparing the purge timings of the present embodiment and the prior art described in Patent Document 1 described above.

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)
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)
Steps 401 to 404: Second fuel state determination means Step 1402: Concentration conversion means Steps 1406 to 1409: First fuel state determination means Steps 1501 to 1504: Air-fuel ratio control means

Claims (7)

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,
A second fuel state determining means for determining a fuel state of an air-fuel mixture purged from the canister while the purge control valve is closed;
The air-fuel ratio control means uses the fuel state determined by the first fuel state determination means as the fuel state used for controlling the fuel injection amount, or the fuel determined by the second fuel state determination means An evaporative fuel processing apparatus for an internal combustion engine, wherein the state is used is switched based on a vehicle operating state.   The air-fuel ratio control means determines the fuel injection amount at the start of purge using the fuel state determined by the second fuel state determination means when the vehicle operating state is before the purge start. The evaporative fuel processing apparatus of the internal combustion engine according to claim 1.   The air-fuel ratio control means controls the fuel injection amount using the fuel state determined by the first fuel state determination means when the vehicle operating state is after the purge is started and the purge is not suspended. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1 or 2.   The air-fuel ratio control means determines the fuel injection amount at the time of resuming the purge using the fuel state determined by the second fuel state determination means when the vehicle operating state is in the purge interruption. An evaporative fuel processing apparatus for an internal combustion engine according to any one of claims 1 to 3.   If the determination of the fuel state by the second fuel concentration 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. 5. An evaporative fuel processing apparatus for an internal combustion engine according to claim 4, wherein the fuel injection amount at the time of restarting the purge is determined based on the fuel state concentration determined by the determining means. A measuring passage with a restriction in the middle,
A gas flow generating means for generating a gas flow passing through the restriction of the measurement passage;
Pressure measuring means for measuring a pressure drop caused by the restriction 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 in the measurement passage is air, and the gas that flows through the measurement passage by connecting the measurement passage to the canister is mixed with fuel vaporized from the canister Measuring passage switching means for switching to the second measurement state of interest,
The second fuel state determination means includes a first pressure measured by the pressure measurement means in the first measurement state, and a second pressure measured by the pressure measurement means in the second measurement state. The fuel vapor processing apparatus for an internal combustion engine according to claim 1, wherein the fuel state is determined based on The first fuel state determining means determines a relative evaporated fuel state of the air-fuel mixture as compared with the target air-fuel ratio as a fuel state,
A state conversion means for converting the fuel state determined by the second fuel state determination means into a relative evaporated fuel state of the air-fuel mixture compared with the target air-fuel ratio;
7. The air-fuel ratio control unit uses a fuel state converted by the state conversion unit as the fuel state determined by the second fuel state determination unit. The evaporative fuel processing apparatus of the internal combustion engine of description.

Images