JP3689929B2 - Engine evaporative fuel processing system - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an evaporative fuel processing apparatus for an engine which collects evaporative fuel in a canister so that the evaporative fuel generated in the fuel tank is not released into the atmosphere, and causes the engine to inhale during combustion to perform combustion processing. About.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an evaporative fuel processing apparatus for an engine includes a canister that adsorbs evaporative fuel from a fuel tank, and a purge gas containing evaporative fuel that has been desorbed by introducing fresh air into the canister. A purge control valve interposed in the purge passage leading downstream, and the opening degree of the purge control valve is made constant, for example, in accordance with the operating conditions of the engine (purge rate (ratio of purge gas flow rate to intake air flow rate)) What is controlled is known.
[0003]
Further, as disclosed in Japanese Patent Laid-Open No. 63-297757, the amount of evaporated fuel generated during the stop is predicted based on the internal pressure of the fuel tank when the engine is stopped, and the opening of the purge control valve is accordingly increased at the next start. Some of them are corrected so as to be small.
Also, as disclosed in Japanese Patent Laid-Open No. 63-111277, the purge rate is reduced for a while after starting on the assumption that the canister filling rate is high when fuel is replenished. Further, there is also a technique that subtracts the fuel injection amount instead of the purge rate (Japanese Patent Laid-Open No. 1-211661).
[0004]
[Problems to be solved by the invention]
However, such a conventional engine evaporative fuel processing apparatus has the following problems.
Considering the prior art of Japanese Patent Laid-Open No. 63-297757, the fuel tank is not hermetically sealed, and a pipe is provided and connected to the canister, and the generated evaporated fuel is adsorbed by the canister through the pipe. Therefore, the internal pressure does not actually increase up to the vapor pressure of gasoline at that temperature. When a check valve is provided in the line, the valve opening pressure increases, but it is still usually about several mmHg.
[0005]
Therefore, it is not actually possible to predict the amount of evaporated fuel generated from the internal pressure of the fuel tank when the engine is stopped. Even if the fuel tank is sealed and the vapor pressure at that temperature is measured, if it is sealed, the evaporated fuel will not come out, so the amount generated is zero, contradicting the original meaning. Resulting in.
Even if the fresh air inlet of the canister is closed and the purge control valve is sealed, the evaporated fuel from the fuel tank is adsorbed by the canister until the canister is full. Rather than predicting the generated amount from the internal pressure that has risen since it was full, the canister is already full (that is, the adsorbed amount is constant), and the amount generated after that is not necessarily further adsorbed. There is no meaning to do.
[0006]
In addition, in the conventional control such as Japanese Patent Laid-Open No. 63-297757 and Japanese Patent Laid-Open No. 63-111277, the purge rate is reduced in order to prevent a rich error on the assumption that the purge gas is rich. However, this limits the amount of purge at the beginning of operation, so if you want to purge a large amount of the canister near a full time in a short time, or if the purge frequency is low due to repeated short-time operation (start → stop) However, there is a problem that the required purge amount cannot be earned and the evaporated fuel easily leaks out of the fuel tank because it accumulates in the canister.
[0007]
In actual use environment, when a large amount of evaporated fuel is generated due to parking in the middle of summer or continuously for a long time, when the purge concentration changes to 0 or lighter due to disconnection or clogging of the purge pipe, or because of a failure, etc. It is conceivable that the purge concentration is changed to 0 by replacing it with a new one, and the conventional technique is insufficient to cope with any of these cases.
[0008]
In addition, this point has a learned value of the fuel concentration in the purge gas, updates the concentration learned value from the change in the air-fuel ratio feedback correction coefficient before and after the purge, and from the obtained concentration learned value, the actually purged purge The same applies to the control method in which the fuel flow rate and purge air flow rate are obtained, subtracted from the fuel injection amount, and added to the intake air flow rate, respectively.
[0009]
This is because the concentration learning value that was updated and retained when the engine was stopped last time must be corrected for the concentration change during the stop even if the concentration learning value was backed up at the first purge after the next start. This is because the same problem remains as to “how many initial values should be started?”.
[0010]
The present invention has been made paying attention to such conventional problems, and the first purge after start-up is performed by narrowing the purge rate, and even if there is a deviation, the fuel concentration in the purge gas under the condition that the air-fuel ratio error is small. As soon as re-learning (correction for changes during engine stop) is completed, the air-fuel ratio error after engine startup becomes as small as possible, and as soon as possible, the transition to a large amount of purge is as fast as possible. The purpose is to enable a large amount of purging. .
[0011]
[Means for Solving the Problems]
For this reason, the invention according to claim 1 is provided with a fuel injection valve that injects and supplies fuel to the engine, while a canister that adsorbs the evaporated fuel from the fuel tank, and desorption by introducing fresh air into the canister. A purge control valve for controlling the purge gas flow rate interposed in the purge passage for guiding the purge gas containing the evaporated fuel downstream of the throttle valve in the engine intake passage, and a purge for controlling the purge gas flow rate by controlling the opening of the purge control valve As shown in FIG. 1, the engine evaporative fuel processing apparatus having the control means has the following means.
[0012]
That is, a basic fuel injection amount calculation means for calculating a basic fuel injection amount based on engine operating conditions, and an air-fuel ratio feedback correction for correcting the fuel injection amount based on a signal from an air-fuel ratio sensor provided in the exhaust passage. An air-fuel ratio feedback correction coefficient setting means for setting a coefficient; a purge fuel concentration learning means for learning the fuel concentration in the purge gas based on a change in the air-fuel ratio feedback correction coefficient; and learning of the purge gas flow rate and fuel concentration by the purge control means Purge fuel flow rate calculating means for calculating the purge fuel flow rate based on the value, and subtracting the purge fuel flow amount subtracting the basic fuel injection amount by subtracting the purge fuel flow rate amount from the basic fuel injection amount Based on the calculating means, the purge fuel subtraction basic fuel injection amount and the air-fuel ratio feedback correction coefficient, the fuel And the fuel injection amount calculating means for calculating an amount of fuel injection by events, the provision.
[0013]
Also, normal purge gas flow rate is set based on engine operating conditions Therefore, the target purge rate is set as the ratio of the purge gas flow rate to the intake air flow rate so that the purge gas flow rate corresponds to the intake air flow rate. Normal purge gas flow rate setting means (Target purge rate setting means) And set the initial purge gas flow rate smaller than the normal purge gas flow rate for the first time after engine startup. Accordingly, a fixed initial purge rate smaller than the target purge rate, or an initial purge rate obtained by multiplying the target purge rate by a predetermined correction rate so as to be smaller than the target purge rate is set. Initial purge gas flow rate setting means (Initial purge rate setting means) A learning progress degree determining means for determining a progress degree of fuel concentration learning by the purge fuel concentration learning means, and a purge gas flow rate controlled by the purge control means until the fuel concentration learning progresses after the engine is started. There is provided switching means for switching to the normal purge gas flow rate set by the normal purge gas flow rate setting unit after the progress of fuel concentration learning, with the initial purge gas flow rate set by the flow rate setting unit.
[0015]
Claim 2 In the invention according to the present invention, the learning progress degree determining means determines the learning progress degree based on whether or not the update increase / decrease direction of the fuel concentration learning value has been reversed a predetermined number of times or more.
Claim 3 The invention according to the present invention is characterized in that learning initialization means for initializing a learned value of the fuel concentration by the purged fuel concentration learning means at every engine start is provided (shown by a dotted line in FIG. 1).
[0016]
[Action]
In the first aspect of the invention, the basic fuel injection amount is calculated by the basic fuel injection amount calculation means based on the engine operating conditions. The air-fuel ratio feedback correction coefficient setting means sets the air-fuel ratio feedback correction coefficient based on the signal from the air-fuel ratio sensor.
[0017]
Here, the purge fuel concentration learning means learns the fuel concentration in the purge gas based on the change in the air-fuel ratio feedback correction coefficient. Specifically, the concentration is learned by updating the learning value so that the air-fuel ratio feedback correction coefficient before and after the purge becomes the same.
Then, the purge fuel flow rate calculation means calculates the purge fuel flow rate based on the purge gas flow rate by the purge control means and the learned value of the fuel concentration, and the purge fuel fraction subtraction basic fuel injection amount calculation means calculates from the basic fuel injection amount. The purge fuel flow amount is subtracted to calculate the purge fuel subtraction basic fuel injection amount.
[0018]
Then, the final fuel injection amount is calculated by the fuel injection amount calculation means based on the purge fuel subtraction basic fuel injection amount and the air-fuel ratio feedback correction coefficient.
On the other hand, the normal purge gas flow rate setting means sets the normal purge gas flow rate based on the engine operating conditions, but the initial purge gas flow rate setting means sets the initial purge gas flow rate smaller than the normal purge gas flow rate for the first time after engine startup. Set. This initial purge gas flow rate is such a value that the influence on emission and drivability can be reduced even if there is a difference between the actual fuel concentration and the learned value.
[0019]
Thus, at the first purge after the engine is started, the purge gas flow rate controlled by the purge control means is set as the initial purge gas flow rate.
That is, at the time of the first purge after the engine start, the purge gas flow rate is reduced, and even if there is a difference between the actual fuel concentration and the learned value, the purge is performed under a condition with a small air-fuel ratio error. The learning means learns the fuel concentration in the purge gas.
[0020]
Then, the progress of fuel concentration learning is determined by the learning progress degree determining means, and when the fuel concentration learning progresses, the switching means switches the purge gas flow rate controlled by the purge control means to the normal purge gas flow rate.
As described above, as soon as the learning of the fuel concentration (correction for changes during engine stop) is completed, the normal purge gas flow rate is switched to quickly shift to a large amount of purge.
[0021]
Therefore, even if there is a discrepancy between the actual fuel concentration when the engine is started and the previously learned value, the purge gas flow rate can be kept lower than the normal value until the discrepancy is corrected. When the deviation of the fuel concentration is corrected and the shift to the normal large-scale purge is quickly performed, it is possible to achieve both the prevention of deterioration of emission and operability and the large-scale purge.
[0022]
Also, The purge rate is controlled so that the purge gas flow rate corresponds to the intake air flow rate, and is smaller than the normal target purge rate at the first purge after startup. Obtained by multiplying the normal target purge rate by a predetermined correction factor so as to be smaller than the fixed initial purge rate or the normal target purge rate By setting the initial purge rate, the purge gas flow rate can be made to correspond to the intake air flow rate also at this time.
Claim 2 In the invention according to the above, the learning convergence state can be accurately grasped by determining the degree of learning progress based on whether or not the update increase / decrease direction of the fuel concentration learning value is reversed a predetermined number of times or more.
[0023]
Claim 3 In the invention according to the present invention, the learning value of the fuel concentration is initialized every time the engine is started by the learning initialization means, and the relearning of the fuel concentration always starts from a predetermined value. It is possible to suppress the variation of.
[0024]
【Example】
An embodiment of the present invention will be described below.
FIG. 2 shows a system configuration.
The air introduced into the engine 1 from the air cleaner 2 and controlled by the throttle valve 3 is sucked through the intake manifold 4. The intake manifold 4 is provided with a fuel injection valve 5 for each cylinder, and an amount of fuel corresponding to the intake air is injected and supplied. As a result, an air-fuel mixture is generated and combusted in each cylinder of the engine 1, and the exhaust gas is introduced into a three-way catalyst (not shown) through the exhaust passage 6.
[0025]
The fuel injection valve 5 is energized by a drive pulse signal output at a predetermined timing in synchronization with the rotation of the engine 1 from a control unit 7 with a built-in microcomputer. It is a fuel injection valve, and the fuel injection amount is controlled by the pulse width of the drive pulse signal.
The control unit 7 includes an air flow meter 8, a crank angle sensor 9, an air-fuel ratio sensor (O ₂ Sensor) 10 is receiving a signal. The air flow meter 8 is provided upstream of the throttle valve 3 in the intake passage and detects the intake air flow rate QA (intake air flow rate detection means). The crank angle sensor 9 outputs a reference signal REF at every predetermined crank angle (720 ° / number of cylinders) in synchronization with the rotation of the engine 1, and can detect the engine speed NE from the cycle of the reference signal REF. . O ₂ The sensor 10 is provided in the exhaust passage 6 and has an exhaust composition (O ₂ The air / fuel ratio (rich / lean) of the air-fuel mixture supplied to the engine 1 is detected from the concentration. In addition, the control unit 7 receives signals such as throttle valve opening TVO and vehicle speed VSP from various sensors, as well as ON / OFF signals of various switches.
[0026]
Further, an auxiliary air passage 11 that bypasses the throttle valve 3 is provided in the intake passage, and an idle control valve 12 for controlling the idle speed that is duty-controlled is interposed in the auxiliary air passage 11. This idle control valve 12 is also controlled by the control unit 7.
On the other hand, a canister 14 is provided to process the evaporated fuel generated from the fuel tank 13.
[0027]
The canister 14 is a container filled with an adsorbent 14a such as activated carbon, and an evaporative fuel introduction pipe 15 from the fuel tank 13 is connected to the upper space side. Accordingly, the evaporated fuel generated in the fuel tank 13 while the engine 1 is stopped is guided to the canister 14 through the evaporated fuel introduction pipe 15 and adsorbed thereto.
The canister 14 is also formed with a fresh air inlet 16 on the lower space side, and a purge passage 17 is led out from the upper space side. The purge passage 17 is connected to the intake passage downstream of the throttle valve 3 (intake manifold 4) via a purge control valve 18.
[0028]
The purge control valve 18 is opened by a signal output from the control unit 7 under a predetermined condition during operation of the engine 1 and the opening degree is duty-controlled. Accordingly, if the purge ON permission condition is satisfied during the subsequent operation of the engine 1, the purge control valve 18 is opened, and the intake negative pressure of the engine 1 acts on the canister 14, so that it is introduced from the fresh air inlet 16. The evaporated fuel adsorbed on the adsorbent 14a of the canister 14 is desorbed by the air that is discharged, and the purge gas containing the desorbed evaporated fuel is sucked into the intake manifold 4 through the purge passage 17, and then the engine Combustion processing is performed in one cylinder.
[0029]
The control of the purge control valve 18 by the control unit 7, and further the control of the fuel injection valve 5 and the idle control valve 12 are performed according to the flowcharts shown in FIG. 3 to FIG. I will explain.
FIG. 3 is a job for calculating the purge rate (the ratio of the purge gas flow rate passing through the purge control valve to the intake air flow rate QA) and determining the purge ON permission condition, and is executed as a background job.
[0030]
First, in step 101, various sensors (air flow meter, O ₂ It is checked whether the sensor, throttle sensor, etc.) is NG. If there is an NG sensor, the purge rate PAGERT = NGPGRT # (constant rate) is determined in step 102.
If the sensor is not NG, the process proceeds to step 103 and branches to FIG. 5 which is a subroutine for calculating the purge rate.
[0031]
In step 201 in FIG. 5, a target purge rate TPAGERT is calculated. The target purge rate TPAGERT is the ratio of the target purge gas flow rate to the intake air flow rate QA, and is set to a fixed value or high according to the concentration learning value (learning value of the fuel concentration in the purge gas) WC as shown in FIG. Set so that the concentration decreases.
Next, in step 202, has the fuel concentration learning progressed after the engine start, that is, whether the correction of the deviation between the actual fuel concentration in the purge gas after the engine start and the concentration learned value (initial concentration deviation) has been completed? If the correction is not completed by looking at the flag #FSWCOK (if # FSWCOK = 0), the process proceeds to step 203.
[0032]
In step 203, the purge rate PAGERT is set not to the target purge rate TPAGERT but to an initial purge rate (fixed value) smaller than the target purge rate set for the first purge after engine startup.
This is because you want to correct (relearn) the change in concentration (deviation from the learning hold value) that occurs due to the generation of fuel vapor or canister replacement while the engine is stopped. This is because the process is performed within the conditions that do not affect the fuel ratio and the operability, so that the target purge rate to be originally flowed is set to a low value.
[0033]
The initial purge rate may be calculated as a target purge rate * GAIN # instead of a fixed value. Here, GAIN # is a correction factor of 1 or less.
Even during this time, the learning / updating of the density learning value WC is performed by the rotation synchronization job shown in FIGS.
Next, in step 204, it is checked whether the update increase / decrease direction of the density learning value WC is reversed three times or more. This is to determine whether the correction of the deviation between the actual fuel concentration and the concentration learning value has been completed.If the concentration learning value update increase / decrease direction is reversed in the purge performed after the start and its concentration learning, Judge that the actual value has been caught up. The reason why the number of times of determination is three times is to increase the accuracy in consideration of the overshoot of the control, although it may originally be one time.
[0034]
If it is not reversed three times or more, this subroutine is terminated as it is, but if it is reversed three or more times, the fuel concentration learning proceeds and the correction of the “initial concentration deviation” is completed (the actual concentration is learned). It is determined that the value has caught up, and the process proceeds to step 205.
In step 205, the purge rate PAGERT = the target purge rate TPAGERT. That is, the purge rate that has been kept low until now is switched to the target purge rate.
[0035]
Next, at step 206, the fuel concentration learning progresses and a flag #FSWCOK indicating that the correction of the “initial concentration deviation” has been completed is set (# FSWCOK = 1), and this subroutine is terminated.
Returning to the original state, if the correction of “initial density deviation” has been completed in the determination in step 202 (if # FSWCOK = 1), the process proceeds to step 207, where purge rate PAGERT = target purge rate TPAGERT This subroutine ends. Thereafter, this operation is repeated.
[0036]
As described above, in this subroutine, the actual fuel concentration in the purge gas and the concentration learning value shift due to the evaporated fuel generated while the engine is stopped. In order to avoid going out, the first purge after start-up is always kept at a low purge rate (initial purge rate), and the concentration deviation is corrected (re-learning) under conditions that have little influence, and after the correction is completed, it is desired to immediately flow Since it is configured to shift to a large amount of purge, even if there is a deviation between the actual concentration and the learned value during the first barge after startup, the purge gas flow rate will be smaller than the normal value until the deviation is corrected. Therefore, it is possible to satisfy both the prevention of deterioration of operability and emission and the securing of a large amount of purge.
[0037]
Here, this subroutine corresponds to the purge control means, in particular, steps 201 and 207 correspond to the normal purge gas flow rate setting means (target purge rate setting means), and step 203 corresponds to the initial purge gas flow rate setting means (initial purge rate). The steps 204 and 206 correspond to the learning progress degree determination means, and the step 202 corresponds to the switching means.
[0038]
Returning to FIG. 3, the description will be continued.
In steps 104 to 112, the purge ON permission condition is determined.
That is, in steps 104 to 108, it is determined whether or not the ignition switch is OFF, the engine is stalled, the starter switch is ON, the engine is idling (idle switch ON), and the vehicle speed VSP is low. Proceeding to FIG. 4 (step 125), purging is prohibited.
[0039]
In step 109, the purge permission lower limit basic fuel injection amount (purge permission lower limit TP) TPCPC is obtained from the engine speed NE with reference to the characteristic table shown in FIG. In step 110, the actual basic fuel injection amount TP is compared with the purge permission lower limit basic fuel injection amount TPCPC. If TP <TPCPC (load is too small), purge is similarly prohibited.
[0040]
In step 111, the intake air flow rate QH0 obtained from the throttle valve opening TVO and the engine speed NE is compared with a predetermined upper limit value EVPCGH. If QH0> EVPCGH (the load is too large), the same applies. Purging is prohibited.
Further, in step 112, it is checked whether the air-fuel ratio feedback control (ramcon) is being clamped. If clamped, purge is similarly prohibited.
[0041]
If all of the determinations at steps 104 to 112 are NO, the purge ON permission condition is satisfied, and the routine proceeds to FIG. 4 (step 113), where purge ON is permitted.
FIG. 4 is a job executed subsequent to FIG. 3, and calculation of the purge gas flow rate (herein referred to as purge valve flow rate) passing through the purge control valve and the ON duty of the purge control valve (herein referred to as purge valve duty); Concentration learning is permitted.
[0042]
The case where the purge ON permission condition is satisfied and the case where it is not satisfied will be described separately.
[When the purge ON permission condition is satisfied]
In step 113, purge ON is permitted.
Next, at step 114, the pressure difference correction rate KPVQH for the purge valve flow rate is obtained from the intake air flow rate QH0 obtained from the throttle valve opening TVO and the engine speed NE with reference to the characteristic table shown in FIG. This differential pressure correction rate KPVQH is a correction rate for changing the flow rate due to the differential pressure before and after the purge valve flow path area is constant.
[0043]
It should be noted that the basic fuel injection amount TP is closer to the purge valve differential pressure than QH0 in terms of phase during transition, and it is better to use TP, but TP is related to the purge valve differential pressure at atmospheric pressure and intake air temperature. Here, QH0 was used.
Next, at step 115, the voltage correction factor KPVVB of the purge valve flow rate is obtained from the battery voltage VB with reference to the characteristic table shown in FIG. This voltage correction factor KPVVB is a correction factor corresponding to the purge valve duty / flow rate relationship that varies depending on the purge valve applied voltage, and of course varies depending on the valve type.
[0044]
Next, at step 116, the target purge valve flow rate QPV is calculated by the following equation.
QPV = (QA * PAGERT) / (KPVQH * KPVQH)
That is, the purge valve flow rate QPV is obtained by multiplying the intake air flow rate QA by the purge rate PAGERT and further correcting with the differential pressure correction rate KPVQH and the voltage correction rate KPVQH. Next, at step 117, the purge valve duty (basic DUTY) EVAP necessary for actually flowing the purge valve flow rate QPV is obtained with reference to the characteristic table shown in FIG.
[0045]
Then, the obtained purge valve duty EVAP is compared with a predetermined upper limit value EVPMAX # (step 118), and if EVAP> EVPMAX #, the purge valve duty EVAP is limited to the upper limit value EVPMAX # (step 119).
Next, at step 120, the purge fuel flow rate QEF is calculated by the following equation.
QEF = QPV * WC
That is, the purge fuel flow rate QEF is obtained by multiplying the purge valve flow rate (purge gas flow rate) QPV by the concentration learning value (learning value of the fuel concentration in the purge gas) WC. This portion corresponds to the purge fuel flow rate calculation means.
[0046]
Next, at step 121, the purge air flow rate QEA is calculated by the following equation.
QEA = QPV-QEF
This is because the remainder obtained by subtracting the purge fuel flow rate QEF from the purge valve flow rate (purge gas flow rate) QPV corresponds to the purge air flow rate QEA. This portion corresponds to the purge air flow rate calculation means.
[0047]
Next, in step 122, it is checked whether the routine has been passed through the previous time. If it is the first time, in step 123, the flag that has been passed once is set (step 123), and then in step 124, concentration learning (WC learning) is performed. Is allowed (# FWCGKOK = 1). If it is not the first time, this job is terminated.
[When the purge ON permission condition is not satisfied]
In step 125, purging is prohibited.
[0048]
In step 126, the purge valve duty EVAP = 0. As a result, the purge valve duty EVAP output from the control unit in the process of FIG. 9 described later also becomes 0, and the purge control valve is controlled to be closed.
Accordingly, in steps 127 and 128, the purge fuel flow rate QEF and the purge air flow rate QEA are both set to zero. When the purge control valve is closed, the purge fuel flowing into the intake manifold becomes zero. However, since this purge fuel is diffused in the intake manifold and is delayed in phase, the purge fuel drawn into the cylinder is purged. Fuel does not immediately go to zero. Therefore, the calculation for this point is performed in FIG. 9 as described later.
[0049]
Further, in step 129, the permission of density learning is canceled along with purge OFF (# FWCGKOK = 0), and this job is terminated.
FIG. 6 is a job for determining the start and end of density learning (WC learning), and is executed as a rotation synchronization job.
First, in step 301, it is checked whether the various sensors are NG. If there is an NG sensor, in step 302, after the concentration learning value WC = NGWC #, the WC learning flag and RAM are initialized. (Step 310), this job is finished.
[0050]
If the sensor is not NG, the process proceeds to step 303, where it is checked whether WC learning is permitted (# FWCGKOK = 1). If WC learning is not permitted, the job is terminated as it is.
If WC learning is permitted, the learning start permission condition is determined in steps 304 to 306.
[0051]
That is, in step 304, it is checked whether the air-fuel ratio feedback control (ramcon) is being clamped. In step 305, the purge valve duty EVAP is compared with a predetermined lower limit WCGDTY # to check whether EVAP <WCGDTY # (the purge valve duty is too low). In step 306, the intake air flow rate QH0 obtained from the throttle valve opening TVO and the engine speed NE is compared with a predetermined upper limit value WCGQH # to check whether QH0> WCGQH # (the load is too high). .
[0052]
If YES in any of these determinations, WC learning is disabled and the WC learning flag and RAM are initialized (step 310), and the job is terminated.
If all the determinations in steps 304 to 306 are NO, learning starts as the WC learning condition OK. First, in step 307, “end determination” of WC learning is performed. That is, it is checked whether or not the step amount ± PWC of the update amount of the density learning value WC has been added NSSWCGK # times or more.
[0053]
If NSWCCGK has been added more than # times, a flag (# FWC1KAI) indicating that WC learning has been performed once is set in step 308, and the concentration learning value WC is The update is clamped to the average value of WC immediately before the addition of the number of steps.
WC = (OLDWC1 + OLDWC2) / 2
Subsequently, after the WC learning flag and RAM are initialized (step 310), this job is terminated.
[0054]
If it is determined in step 307 that the step ± PWC of the update amount of the concentration learning value WC has not been added NSSWCGK # times or more, the process branches to FIG.
FIG. 7 is a job executed subsequent to FIG. 6 and is a main job of concentration learning (WC learning), and corresponds to purge fuel concentration learning means.
A branch to this job occurs when purge is ON, the WC learning condition is OK, and the step number ± PWC of the update amount of the concentration learning value WC is less than NSWCCG #.
[0055]
First, in step 311, it is checked whether it is the first time after entering WC learning. If it is the first time, in step 312, the average value ALPAV of the air-fuel ratio feedback correction coefficient α calculated by the job of FIG. Store in the starting holding RAM = ALPST to prepare for learning.
Next, in step 313, referring to the characteristic table shown in FIG. 18, an integrated amount IWC of the update amount of the density learning value WC is obtained from the current density learning value WC.
[0056]
Here, the concentration learning value WC is used for calculating the integral amount IWC of the update amount. When the fuel concentration in the purge gas is high, the change in the actual concentration decreases rapidly, so that it is constant regardless of the fuel concentration ( In this case, the update amount of the concentration learning value does not catch up, and the concentration learning value remains shifted to a value larger than the actual concentration, and the fuel injection amount This is to prevent a lean error from occurring due to an excessive reduction correction amount. On the contrary, in the thinned region, the renewal amount is too large with respect to the change in the actual concentration, so that the control amount overshoots and hunting occurs in the air-fuel ratio control.
[0057]
That is, the update amount of the concentration learning value WC is solved by referring to the concentration learning value WC that can predict the change rate of the fuel concentration.
As a result, the update amount of the concentration learning value WC corresponding to the actual change rate of the fuel concentration accompanying the progress of the canister purge can be obtained from the initial stage of the purge.
[0058]
Next, at step 314, a change amount (change amount from the start of learning) Δα of the air-fuel ratio feedback correction coefficient α is calculated by the following equation.
Δα = ALPAV−ALPST
That is, the current average value ALPAV of the air-fuel ratio feedback correction coefficient α is read, and the average value ALPST at the start of learning is subtracted therefrom to obtain the change amount Δα from the start of learning.
[0059]
Next, at step 315, it is checked whether ALPAV = ALPST has no change (Δα = 0). If there is no change, it is determined that the actual fuel concentration matches the learning value, and at step 316, concentration learning is performed. The value update amount ΔWC = 0.
If Δα = 0 is not satisfied, it is checked in step 317 whether Δα is positive or negative.
If Δα is negative, the air-fuel ratio changes to the rich side compared to before purging when purge is turned on, and α is reduced to compensate for it, so the actual fuel concentration is maintained at the current level. It can be determined that the value is “darker” than the value (the current concentration learning value is not enough to correct the injection amount).
[0060]
Therefore, if Δα is negative, the concentration learning value WC is increased. At this time, in step 318, it is checked whether the learning update direction is reversed with respect to the previous update. In step 319, + PWC, which is a large update amount step for accelerating learning convergence, is added as the update amount ΔWC (ΔWC = + PWC). If not inverted, in step 322, + IWC, which is an integral of a small update amount obtained according to the density change based on the density learning value WC, is added (ΔWC = + IWC).
[0061]
If Δα is positive, the air-fuel ratio is changed to the lean side when purging is turned on, and α is increased to correct it, so the actual fuel concentration is maintained at the current level. It can be judged that it is much thinner than the value.
Therefore, if Δα is positive, the concentration learning value WC is decreased. At this time, in step 323, it is determined whether the learning update direction is reversed with respect to the previous update. In step 324, -PWC, which is a large update amount step for accelerating learning convergence, is added as the update amount ΔWC (ΔWC = -PWC). If not inverted, in step 327, -IWC, which is an integral of a small update amount obtained according to the density change based on the density learning value WC, is added (ΔWC = -IWC).
[0062]
When adding step ± PWC, in step 320 or step 325, the WC immediately before the addition of the step is stored from the newest to the previous two (OLDWC1 to OLDWC2 and WC to OLDWC1). Then, in step 321 or step 326, the counter indicating the number of times of adding ± PWC for the step is incremented by 1. This counter is used for determining the end of WC learning in step 307 of FIG.
[0063]
Thereafter, this operation is repeated so that the value of the air-fuel ratio feedback correction coefficient α before and after the purge becomes the same, and the change in the fuel concentration as the purge proceeds so that the air-fuel ratio does not deviate even during the purge. The minutes are corrected sequentially.
Next, at step 328, the current value of the concentration learning value WC (WC _-1 ) Is added with the update amount ΔWC to update the density learning value WC.
[0064]
WC = WC _-1 + ΔWC
Next, in step 329, the updated density learning value WC is compared with a predetermined upper limit value and lower limit value. If these values are exceeded, the upper limit value and lower limit value are limited, and this job is terminated.
FIG. 8 is a job for calculating the average value ALPAV of the air-fuel ratio feedback correction coefficient α, and is executed as a REF synchronization job synchronized with the generation of the reference signal REF from the crank angle sensor.
[0065]
O ₂ In the air-fuel ratio feedback control using the sensor, the air-fuel ratio feedback correction coefficient α is controlled by a step (P) and an integral (I), and the fluctuation of α is large. The ALPAV is obtained by a simple average of α immediately before) and α when the previous P minutes are added (immediately before addition). This is a technique often used in basic air-fuel ratio learning control.
[0066]
Therefore, in step 401, it is determined whether the air-fuel ratio feedback control (ramcon) is clamped. If clamped, ALPAV = 1.0 and ALPOLD = 1.0 are set in step 402.
If it is not clamped, it is determined in step 403 whether P is added.
If P is added, in step 404, the peak-peak average value ALPAV of the air-fuel ratio feedback correction coefficient α is obtained by the following equation immediately before adding P.
[0067]
ALPAV = (α + ALPOLD) / 2
Next, the current α is held in ALPOLD to prepare for the next time.
Thereafter, in step 405, normal P component calculation is performed, and P component is added to the air-fuel ratio feedback correction coefficient α.
If the P component is not added, a normal I component calculation is performed at step 406 to add the I component to the air-fuel ratio feedback correction coefficient α.
[0068]
Here, steps 403 to 406 correspond to air-fuel ratio feedback correction coefficient setting means.
FIG. 9 is a job for calculating the cylinder intake purge fuel flow rate in consideration of the delay output to the purge control valve and the delay, and is executed as a REF synchronous job.
In step 501, the purge valve duty EVAP is output to the control unit / output port. As a result, the purge control valve is turned on and off. The output to the purge control valve is a pulse signal with a period of 6.4 ms, and the ON time ratio is controlled by the duty.
[0069]
Next, in step 502, the purge fuel flow rate QEF flows into the intake manifold from the purge control valve, and the calculation for approximating the amount of intake into the cylinder with diffusion and transfer delay in the intake manifold is performed as follows. ing.
First, assuming that the diffusion of fuel gas in the intake manifold is caused by a first-order lag, approximation is performed by applying a weighted average to QEF as in the following equation.
[0070]
QEF1 = QEF * EDMP # + QEF1 _-1 * (1-EDMP #)
Next, in order to approximate the dead time (simple time delay) in the intake manifold, the final cylinder intake purge fuel flow rate QEFC is obtained by bringing the QEF1 obtained by this job several REF before the memory operation as shown in the following equation. And
QWFC = number of QEF1 value before REF
Of course, since the QEF1 obtained this time is used after several REFs, it is stored in a considerable memory.
[0071]
FIG. 10 shows a job for calculating the cylinder intake air flow rate Q, which is executed every 4 ms, for example.
In step 601, the cylinder intake air flow rate Q used for fuel injection amount calculation is obtained by adding the purge air flow rate QEA to the intake air flow rate QA detected by the air flow meter, as shown in the following equation. This portion corresponds to cylinder intake air flow rate calculation means.
[0072]
Q = QA + QEA
By correcting the purge air component from the canister that is not measured by the air flow meter and sucked into the engine in this way, it is possible to prevent an air-fuel ratio lean error that increases particularly as desorption progresses.
FIG. 11 shows a correction of the fuel injection amount based on the WC learning result and an idling aiming at preventing deterioration of drivability due to a change in torque by increasing the intake air amount to the engine by the amount of purge air of the canister. This is a job for correcting the control valve opening, and is executed, for example, every 10 ms.
[0073]
First, at step 701, a normal basic fuel injection amount (basic injection pulse width) TP is obtained by the following equation from the cylinder intake air flow rate Q and the engine speed NE as usual. This portion corresponds to basic fuel injection amount calculation means.
TP0 = Q * KCONST # / NE
TP = TP0 * FLOAD + TP _-1 * (1-FLOAD)
Here, KCONST # is a proportional constant conventionally used, and FLOAD is a weighted average coefficient for phase matching of TP to the cylinder intake.
[0074]
Next, in step 702, the cylinder intake purge fuel flow rate QEFC obtained in FIG. 9 is converted into units corresponding to the injection pulse width by the following equation to obtain the purge fuel amount (a reduction correction amount corresponding to the cylinder intake purge fuel flow rate) TEFC.
TEFC = QEFC * KFQ ## * KCONST # / NE
Here, KFQ # is a correction coefficient for the purge gas specific gravity.
[0075]
Next, at step 703, as shown in the following formula, the purge fuel amount (decrease correction amount corresponding to the cylinder intake purge fuel flow rate) TEFC is subtracted from the basic fuel injection amount TP to eliminate the purge fuel component. A purge fuel subtraction basic fuel injection amount TPE which is an injection amount is obtained. This portion corresponds to the purge fuel subtraction basic fuel injection amount calculation means.
[0076]
TPE = TP-TEFC
Next, at step 704, based on the purged fuel subtraction basic fuel injection amount TPE, the target fuel / air ratio TFBYA, the air / fuel ratio feedback correction coefficient α, etc. are corrected as shown in the following equation to obtain the final fuel injection amount TI ( Sequential injection). This portion corresponds to the fuel injection amount calculation means.
[0077]
TI = TPE * TFBYA * α * 2 + TS
Here, TS is an invalid pulse width.
Thus, by using TPE instead of the conventional TP, it is possible to reduce the amount of purge fuel from the fuel injection amount, so that a large amount of purge can be performed without deteriorating the air-fuel ratio when the purge is turned on including transients. It becomes possible.
[0078]
Next, the calculation part (steps 705 and 706) of the idle speed control specification will be described.
This is because the duty correction amount ICEVP corresponding to the purge air flow rate QEA is subtracted during the purge from the duty (ISC duty) to the normal idle control valve, so that the difference in intake air amount when the purge is ON and OFF The purpose is to prevent the deterioration of drivability due to sudden changes in torque.
[0079]
In step 705, the duty correction amount ICEVP is calculated by converting the purge air flow rate QEA into the ISC duty for the idle control valve as in the following equation.
ICEVP = QEA * ISCEVG # / (KPVQH * KPVVB)
Here, ISCEVG # is a coefficient for converting the purge air flow rate QEA into an ISC duty. KPVQH and KPVVB are the above-described differential pressure correction rate and voltage correction rate.
[0080]
Next, at step 706, the duty correction amount ICEVP is subtracted from the normal ISC duty to obtain a calculated duty (ON duty) ISCON to the idle control valve, and this is output.
ISCON = (normal ISC duty) −ISCEVP
FIG. 12 shows an initialization job, which corresponds to learning initialization means, and is executed only once when the engine is started.
[0081]
In step 801, the density learning value WC is initialized by giving an initial value. The initial value here is 0% or a predetermined value. The predetermined value may be a lower limit value of the fuel concentration in the purge gas on the market or an intermediate value in the use range.
Next, the function and effect of the present embodiment will be described with reference to FIG.
If the fuel concentration becomes high due to evaporative fuel or the like generated while the engine is stopped, a deviation from the previously learned concentration learning value occurs. For this reason, at the time of the first purge at the next engine start, if a large amount of purge is performed, the deviation in concentration cannot be corrected, which adversely affects emissions and operability. That is, when the target purge rate is given from the beginning (conventional example 1), the concentration deviation is large * the high purge rate, and the air-fuel ratio error becomes large.
[0082]
Therefore, in the present invention, the initial purge rate after start-up is limited to a low purge rate (initial purge rate), and the concentration deviation is corrected (relearned) under conditions that have little influence. Then, after the correction is completed, that is, after the learned value catches up with the actual concentration, the purge rate is switched to the target purge rate, and a large-scale purge is performed. Therefore, it is possible to quickly shift to large-scale purge, and it is possible to achieve both prevention of deterioration of operability and emission and securing of large-scale purge.
[0083]
On the other hand, when the purge rate is initially reduced and gradually increased (conventional example 2), the air-fuel ratio error is small, but the purge amount is also reduced.
[0084]
【The invention's effect】
As described above, according to the first aspect of the present invention, even if there is a deviation between the actual fuel concentration and the learned value when the engine is started, the purge gas flow rate is smaller than the normal value until the deviation is corrected. Because it can be suppressed, the impact on emissions and operability can be avoided, and when the deviation in fuel concentration is corrected, it is possible to quickly shift to normal large-scale purge. The effect that both can be made compatible is obtained.
[0085]
Also, By setting an initial purge rate smaller than the normal target purge rate at the first purge after start-up, the purge gas flow rate can be made to correspond to the intake air flow rate at this time as well.
Claim 2 According to the present invention, the learning convergence state can be accurately grasped by determining the progress of learning based on whether or not the update increase / decrease direction of the fuel concentration learning value is reversed a predetermined number of times or more. can get.
[0086]
Claim 3 According to the invention, the learning value of the fuel concentration is initialized every time the engine is started, and the relearning of the fuel concentration is always started from a predetermined value. The effect that it can suppress is acquired.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing the configuration of the present invention.
FIG. 2 is a system diagram showing an embodiment of the present invention.
FIG. 3 is a flowchart of a job for calculating a purge rate and the like.
FIG. 4 is a flowchart of a job following FIG.
FIG. 5 is a flowchart of a purge rate calculation subroutine.
FIG. 6 is a flowchart of a job for determining the start and end of density learning.
FIG. 7 is a flowchart of a density learning main job following FIG.
FIG. 8 is a flowchart of an air-fuel ratio feedback control job.
FIG. 9 is a flowchart of a cylinder suction purge fuel flow rate calculation job.
FIG. 10 is a flowchart of a cylinder intake air flow rate calculation job.
FIG. 11 is a flowchart of a job for calculating a fuel injection amount and the like.
FIG. 12 is a flowchart of a job for calculating a weight loss correction rate.
FIG. 13 is a diagram showing an example of characteristics of a target purge rate calculation table
FIG. 14 is a diagram showing a characteristic example of a purge permission lower limit TP calculation table.
FIG. 15 is a diagram illustrating an example of characteristics of a differential pressure correction rate calculation table.
FIG. 16 is a diagram illustrating a characteristic example of a voltage correction factor calculation table.
FIG. 17 is a diagram showing a purge valve duty calculation table
FIG. 18 is a diagram illustrating an example of characteristics of an IWC calculation table.
FIG. 19 is a diagram showing the effect of the embodiment.
[Explanation of symbols]
1 engine
2 Air cleaner
3 Throttle valve
4 Intake manifold
5 Fuel injection valve
6 Exhaust passage
7 Control unit
8 Air flow meter
9 Crank angle sensor
10 O ₂ Sensor
11 Bypass passage
12 Idle control valve
13 Fuel tank
14 Canister
15 Evaporative fuel introduction pipe
16 Fresh air inlet
17 Purge passage
18 Purge control valve

Claims (3)

While equipped with a fuel injection valve that injects fuel into the engine,
A canister that adsorbs fuel vapor from the fuel tank;
A purge control valve for controlling the purge gas flow rate interposed in the purge passage for guiding the purge gas containing the evaporated fuel desorbed by introducing fresh air into the canister downstream of the throttle valve of the engine intake passage;
Purge control means for controlling the purge gas flow rate by controlling the opening of the purge control valve;
In an engine evaporative fuel processing apparatus comprising:
Basic fuel injection amount calculating means for calculating a basic fuel injection amount based on engine operating conditions;
Air-fuel ratio feedback correction coefficient setting means for setting an air-fuel ratio feedback correction coefficient for correcting the fuel injection amount based on a signal from an air-fuel ratio sensor provided in the exhaust passage;
Purge fuel concentration learning means for learning the fuel concentration in the purge gas based on a change in the air-fuel ratio feedback correction coefficient;
A purge fuel flow rate calculating means for calculating a purge fuel flow rate based on a purge gas flow rate by the purge control unit and a learned value of the fuel concentration;
A purge fuel subtraction basic fuel injection amount calculating means for subtracting the purge fuel flow amount from the basic fuel injection amount to calculate a purge fuel subtraction basic fuel injection amount;
A fuel injection amount calculating means for calculating a fuel injection amount by the fuel injection valve based on a purge fuel subtraction basic fuel injection amount and an air-fuel ratio feedback correction coefficient;
A normal purge gas flow rate setting means for setting a target purge rate as a ratio of the purge gas flow rate to the intake air flow rate so as to be a purge gas flow rate corresponding to the intake air flow rate in order to set a normal purge gas flow rate based on the operating state of the engine When,
In order to set an initial purge gas flow rate smaller than the normal purge gas flow rate for the first time after engine startup , the target purge rate is set to a fixed initial purge rate smaller than the target purge rate or smaller than the target purge rate. Initial purge gas flow rate setting means for setting an initial purge rate obtained by multiplying the rate by a predetermined correction rate ;
A learning progress degree determining means for determining a progress degree of fuel concentration learning by the purge fuel concentration learning means;
The purge gas flow rate controlled by the purge control unit is set as the initial purge gas flow rate set by the initial purge gas flow rate setting unit until the fuel concentration learning progresses after the engine is started, and the normal purge gas flow rate setting unit is set after the progress of fuel concentration learning. Switching means for switching to the normal purge gas flow rate set by
An evaporative fuel processing device for an engine characterized by comprising: 2. The engine evaporation according to claim 1, wherein the learning progress degree determining means is configured to determine the learning progress degree based on whether or not the update increase / decrease direction of the fuel concentration learning value is reversed a predetermined number of times or more. Fuel processor. 3. The evaporative fuel processing device for an engine according to claim 1 , further comprising learning initialization means for initializing a learned value of fuel concentration by said purge fuel concentration learning means every time the engine is started.

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