JP2002276479A - Evaporated fuel processing device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set a best purge rate for performing large quantity of purging without deteriorating engine combustion stability and exhaust emission. SOLUTION: This evaporated fuel processing device for an engine 10 is provided with a canister 4 for adsorbing evaporated fuel generated in a fuel tank 1 and a purge valve 11 for opening and closing a pipe for communicating the canister 4 with an intake passage of the engine 10. At the time of purge disposal, a controller 21 sets a maximum purge rate under a present operation condition and sets a changed amount limit value of the purge rate based on a purge air-fuel ratio and air-fuel ratio fluctuation of the engine 10 generated by a change of the purge rate. A target purge rate for following the maximum purge rate is set by a changed amount of the below the purge rate changed amount limit value, and the purge valve 11 is driven so as to realize the target purge rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vapor treatment system for an engine.

[0002]

2. Description of the Related Art In an engine, fuel vapor generated in a fuel tank while the engine is stopped is temporarily adsorbed on activated carbon in a canister, and the activated carbon is converted into activated carbon by utilizing a suction negative pressure under predetermined operating conditions after the engine is started. An evaporative fuel processing device is provided for desorbing the adsorbed fuel, guiding it to the intake pipe downstream of the throttle valve, and performing combustion processing.

Japanese Patent Application Laid-Open No. Hei 6-264832 discloses a technique for setting a purge rate in accordance with an integrated purge flow rate as means for setting an efficient purge rate and securing a large purge flow rate in such an evaporative fuel processing apparatus. Is disclosed. Specifically, there is disclosed a technique of setting a purge rate according to a suction state of a canister by increasing a purge rate, which is a ratio between a purge flow rate and an intake air flow rate, in accordance with an increase in an integrated value of a purge flow rate. .

[0004]

[Problems to be solved by the invention]
In the above prior art, in order to prevent oversupply of fuel vapor due to purge, the purge rate with respect to the accumulated purge flow rate is set to an optimal value in a state where fuel is adsorbed to the maximum capacity of the canister (full charge state). Was. Therefore, the optimal purge rate can be set when the canister is in the fully charged state, but the optimal purge rate cannot be set when the amount of adsorption of the canister is small. For example, when the canister suction amount is small, a larger purge rate can be actually set, but in the above-described related art, a small purge rate based on the state of full charge is set.
Further, since a fixed purge rate is always set for the integrated purge flow rate, it is not possible to cope with a case where a purge having a concentration higher than expected is supplied.

The present invention has been made in view of the technical problems of the above-mentioned conventional fuel vapor processing apparatus, and in the fuel vapor processing apparatus, a large amount of purge can be performed without deteriorating the combustion stability of the engine and the exhaust emission. It is an object of the present invention to be able to set the best purge rate for performing.

[0006]

According to a first aspect of the present invention, there is provided an evaporative fuel processing apparatus for an engine, comprising: a canister for adsorbing evaporative fuel generated in a fuel tank; and a pipe for communicating the canister with an intake passage of the engine. A purge valve that opens and closes, a means for setting a maximum purge rate under the current operating conditions, an air-fuel ratio of the purge gas, and a change rate limit value of the purge rate based on an air-fuel ratio change of the engine caused by the change of the purge rate. Setting means; means for calculating a target purge rate that follows the maximum purge rate with a change amount equal to or less than the purge rate change amount limit value; and means for driving the purge valve so that the purge rate becomes the target purge rate. And characterized in that:

In a second aspect based on the first aspect, the means for setting the maximum purge rate sets the maximum purge rate to be equal to or less than an upper limit of the purge rate defined by the size of the purge valve. Things.

In a third aspect based on the first or second aspect, the means for setting the maximum purge rate is such that the maximum purge rate is set to be equal to or less than an upper limit of the purge rate defined by the performance of the fuel injection valve. It is characterized by the following.

In a fourth aspect based on the first to third aspects, the means for setting the maximum purge rate assumes all operating ranges which can be shifted from the current operating range, and sets the maximum operating rate in the assumed operating range. Is set, and the maximum purge rate is set to be equal to or less than the purge rate upper limit value calculated from the minimum purge rate and the purge rate change amount limit value.

According to a fifth aspect of the present invention, in the first to fourth aspects, the means for setting the maximum purge rate is equal to or less than a purge rate upper limit value defined such that the air-fuel ratio feedback correction coefficient is equal to or greater than the processing limit value. It is characterized in that the maximum purge rate is set.

In a sixth aspect based on the first to fifth aspects, the means for setting the variation limit value of the purge rate is such that the air-fuel ratio variation caused by the variation of the purge rate does not deteriorate the emission of the engine. The variation rate limit value of the purge rate is set so as to fall within the range.

According to a seventh aspect of the present invention, in the first to sixth aspects of the present invention, at least (a) based on a previous value of a fuel amount adsorbed on the canister and a previous value of a fuel amount desorbed from the canister. (B) calculating the amount of fuel desorbed from the canister based on the adsorption amount arithmetic expression for calculating the amount of fuel adsorbed on the canister, and (b) the adsorption amount calculated by the adsorption amount arithmetic expression, and the target purge rate. And a means for calculating the air-fuel ratio of the purge gas based on the amount of desorbed fuel calculated using the canister model. Things.

In an eighth aspect based on the seventh aspect, the means for calculating the error in the air-fuel ratio of the purge gas calculated based on the intake air flow rate, and the calculation based on the error in the air-fuel ratio calculated in the purge gas. And means for correcting the air-fuel ratio of the purge gas.

According to a ninth aspect, in the seventh or eighth aspect, means for calculating an error in the calculated air-fuel ratio of the purge gas based on the target purge rate; and an error in the calculated air-fuel ratio of the purge gas. Means for correcting the calculated air-fuel ratio of the purge gas based on the above.

[0015]

Therefore, in the evaporative fuel treatment apparatus according to the present invention, the evaporative fuel adsorbed by the canister is introduced into the engine and processed by utilizing the negative pressure in the intake passage as in the prior art. According to the first aspect, the target purge rate at the time of the purge processing is set to the maximum purge rate possible under the current operating conditions determined by physical restrictions and the like, by the air-fuel ratio of the purge gas (hereinafter, purge air-fuel ratio) and the like. The purge rate is set so as to follow the change amount equal to or less than the change amount limit value of the purge rate.

As a result, a target purge rate that cannot be achieved is set, and the target purge rate and the actual purge rate are deviated, so that the combustion stability and exhaust emission of the engine are deteriorated, or the target purge rate is followed. However, it is possible to prevent the change in the purge rate from being too large and to deteriorate the exhaust emission and the like, and to set the best purge rate for performing a large amount of purge.

In setting the maximum purge rate, an upper limit of the purge rate defined by the size of the purge valve and an upper limit of the purge rate defined by the performance of the fuel injector (minimum fuel injection pulse width) are assumed. The purge rate upper limit calculated from the minimum purge rate and the purge rate change amount limit value, and the purge rate upper limit specified so that the air-fuel ratio feedback correction coefficient is equal to or greater than the processing limit value are considered (second to fourth). Fifth invention).

Considering the upper limit of the purge rate defined by the size of the purge valve is that if a target purge rate that cannot be realized even if the opening of the purge valve is maximized is set, the target purge rate and the actual purge rate are compared. This is because a gap occurs, which causes deterioration of exhaust emission and deterioration of engine combustion stability.

The upper limit value of the purge rate defined from the fuel injection valve performance (minimum fuel injection pulse width) is considered as follows.
When the purge rate is set to a large value, the amount of fuel supplied to the engine by the purge process increases, and the fuel injection amount (injection pulse width) is corrected to decrease accordingly, but the fuel injection pulse width is defined to ensure injection accuracy. This is because it cannot be reduced below the minimum injection pulse width.

Considering the upper limit of the purge rate calculated from the assumed minimum purge rate and the limit value of the change in the purge rate, the target purge rate is determined in response to a sudden change in the operating range such as sudden acceleration when the accelerator is fully opened. This is because, when the rate suddenly decreases, if a too large target purge rate is set immediately before the change, it becomes impossible to follow a newly set small target purge rate without delay. Since the responsiveness of the purge rate is determined according to the magnitude of the purge rate change amount limit value, whether or not the expected minimum purge rate can be followed without delay is determined by the assumed minimum purge rate and the purge rate change amount limit value. Is determined based on

Further, the upper limit of the purge rate, which is defined so that the air-fuel ratio feedback correction coefficient is equal to or more than a predetermined value, is considered because the air-fuel ratio feedback correction coefficient is controlled near the predetermined value (for example, 80%). In such a case, the air-fuel ratio feedback correction coefficient is easily deviated from the control range (for example, α is within 100 ± 25%) due to disturbances other than the purge. This is because it is necessary to return to a value higher than the value.

On the other hand, the change rate limit value of the purge rate is set so as to fall within a predetermined range in which a change in the air-fuel ratio due to a change in the purge rate does not deteriorate the emission (a range that can be absorbed by the air-fuel ratio feedback control). (6th
Invention). Therefore, if the target purge rate is set so that the change amount of the target purge rate is equal to or less than the change amount limit value, the air-fuel ratio fluctuation due to the change of the purge rate is absorbed by the air-fuel ratio feedback control, and the exhaust emission Deterioration will be prevented.

Although the air-fuel ratio of the purge gas can be detected using an HC sensor, if the air-fuel ratio of the purge gas is obtained based on the amount of fuel desorbed from the canister calculated using a canister model, The purge air-fuel ratio used when setting the target purge rate can be calculated at low cost and accurately (seventh invention).

Further, since the error of the calculated purge air-fuel ratio increases as the intake air flow rate decreases and the purge rate decreases, the purge air-fuel ratio is corrected according to the intake air flow rate and the purge rate. This makes it possible to calculate a more accurate purge air-fuel ratio (eighth,
Ninth invention).

[0025]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the overall configuration of the fuel vapor processing apparatus according to the present invention.

This evaporative fuel processing apparatus is for processing the evaporative fuel generated in the fuel tank 1 of the engine 10 and includes a canister 4, a canister 4 and the fuel tank 1.
And a pipe 6 that communicates between the canister 4 and an intake passage 8 downstream of the throttle valve 7 of the engine 10.

The pipe 2 is provided with a vacuum cut valve 3 and a bypass valve 14 which are opened in parallel when the pressure in the passage on the side of the fuel tank 1 becomes lower than the atmospheric pressure, and the pipe 6 is provided with a bypass valve 14 in the canister 4. Fuel adsorbent (activated carbon) 4a
Purge valve 11 which is opened when desorbing fuel adsorbed on the pipe, and pressure sensor 13 which measures the pressure in the pipe
Is provided. Further, the canister 4 has an atmosphere opening port 5, which is opened and closed by a drain cut valve 12.

The fuel vapor generated in the fuel tank 1 is guided to the canister 4 through the pipe 2, and only the fuel component is adsorbed on the activated carbon 4 a in the canister 4, and the remaining air is discharged to the outside through the atmosphere release port 5. Is done. And this activated carbon 4
In order to process the fuel adsorbed on the purge valve 11 a
Is opened, and fresh air is introduced into the canister 4 from the air release port 5 using the suction negative pressure developed downstream of the throttle valve 7. As a result, the fuel adsorbed on the activated carbon 4a by the fresh air is desorbed and introduced together with the fresh air into the intake passage 8 of the engine 10 via the pipe 6 (hereinafter, this process is referred to as "purge process").

The controller 21 injects fuel with a pulse width corresponding to the amount of fuel required to achieve a target air-fuel ratio (generally, a stoichiometric air-fuel ratio) in accordance with the amount of intake air detected by the air flow meter 9. The valve 15 is driven. At this time, the controller 21 detects the post-combustion air-fuel ratio by the oxygen concentration sensor 18 attached to the exhaust passage 17 and corrects the fuel injection amount in accordance with the deviation from the target air-fuel ratio (hereinafter, “air-fuel ratio”). Fuel ratio feedback control "). In the air-fuel ratio feedback control, the difference between the target air-fuel ratio and the actual air-fuel ratio detected by the oxygen concentration sensor 18 is reflected on the air-fuel ratio feedback correction coefficient α.

During the purging process, the controller 21 sets the target purge rate (the ratio of the purge flow rate to the intake air flow rate) as high as possible without deteriorating the engine combustion stability and the exhaust emission. The purge valve 11 is driven so as to be realized. Further, when the purge process is being performed, the fuel and the air in the purge gas are supplied to the engine. Therefore, the fuel injection amount is corrected in accordance with the purge rate and the purge concentration, and the air-fuel ratio of the engine 10 is corrected. To fluctuate.

FIG. 2 is a block diagram showing an outline of a part related to the purge control in the control performed by the controller 21.

To explain each component, the target purge rate setting section B1 calculates the maximum purge rate that can be set in the current operation range based on the performance limit of parts related to the purge control, and follows the maximum purge rate. Set the target purge rate to perform However, a rapid change in the purge rate causes a change in the air-fuel ratio and causes deterioration of the emission. Therefore, the amount of change in the purge rate is equal to or less than a predetermined amount (purge rate change amount limit value) so that the purge rate is not rapidly changed. Is limited to The duty ratio calculator B2 calculates the duty ratio of the purge valve 11 required to achieve the target purge rate. The purge valve driver B3 uses the duty ratio calculated by the duty ratio calculator B2. 11 is a part for driving.

On the other hand, the desorption amount calculation unit B4 uses the physical model of the canister 4 (hereinafter, referred to as a canister model) to purge the fuel desorbed from the canister 4 when purging is performed at the target purge rate. The purge correction coefficient calculating unit B5 calculates the fuel injection pulse width correction coefficient FHOS based on the estimated desorption amount so that the air-fuel ratio fluctuation due to the purge is reduced. is there. The delay correction unit B6 performs a delay correction including a dead time correction and a smoothing process on the correction coefficient FHOS, and the fuel injection pulse width calculation unit B7 performs the delay with respect to the fuel injection pulse width set according to operation conditions. Correction coefficient FH after correction
This part corrects the fuel injection pulse width based on the OS.
The fuel injection valve driving section B8 is a portion that drives the fuel injection valve 15 with the fuel injection pulse width after delay correction and performs fuel injection.

Further, the canister model expresses the desorption characteristics of the canister with high accuracy. However, since it is an approximation model, the values (desorption amount, adsorption amount, etc.) calculated using this model are actually Is slightly deviated from the value of. Further, the canister model calculates the amount of fuel newly desorbed from the canister 4 using the previous calculation result, as described later, so that the error is integrated as the model operation time becomes longer, and the calculated value and the actual value are calculated. Deviation increases. Then, in order to calibrate this deviation and maintain the calculation accuracy of the model at a high level, the controller 21 determines that the calibration process can be executed by the calibration determination unit B9, and the suction of the canister 4 which is one of the internal variables of the canister model. The value of the quantity is calibrated (calibration unit B10).

Specifically, the calibration determination unit B9 determines that the air-fuel ratio fluctuation (absorbed by the air-fuel ratio feedback control and appears as a fluctuation of the air-fuel ratio feedback correction coefficient α) can be regarded as almost entirely due to the purge. Is satisfied, it is determined that the calibration process can be executed. If it is determined that the calibration process can be executed, the calibration unit B10 determines the amount of fuel from the canister 4 based on the air-fuel ratio fluctuation (fluctuation of the air-fuel ratio feedback correction coefficient α) at that time. The desorption amount is estimated, and the adsorption amount is calculated back from the estimated desorption amount. Then, the value of the adsorption amount of the canister model is calibrated with this value.

Hereinafter, the specific contents of the control performed by the controller 21 will be described.

FIG. 3 is a flowchart showing the contents of the purge process (model reference purge process) performed by the controller 21, and is repeatedly executed when the purge is executed. By this process, the fuel injection amount (fuel injection pulse width) is corrected in accordance with the amount of fuel supplied from the canister 4 to the engine 10 by the purge process, and the fluctuation of the air-fuel ratio due to the purge is suppressed.

First, in step S1, it is determined whether or not calibration of the value of the amount of adsorption, which is an internal variable of the canister model, can be performed. When the air-fuel ratio disturbance due to factors other than the purge is small and the effect of the purge on the air-fuel ratio feedback correction coefficient α is relatively large, that is, almost all the deviation of the air-fuel ratio feedback correction coefficient α from the target value is regarded as the effect of the purge. If the calibration process can be performed, it is determined that the calibration process can be executed.

Specifically, “steady-state conditions” shown in FIG.
When all of the “purge valve accuracy condition” and the “purge influence degree condition” are satisfied, it is determined that the calibration process can be executed. If none of these conditions is satisfied, it is determined that the calibration process cannot be executed. This determination process is performed by the calibration determination unit B in FIG.
9 corresponds to the processing in FIG.

As shown in FIG. 4, the "steady-state conditions" include a misfire condition (the engine 10 is not misfired), a fuel cut condition (the engine 10 is not fuel cut), and a blow-by condition. (No blow-by gas), EGR conditions (exhaust gas recirculation rate is constant), throttle opening area and engine speed conditions (throttle opening area and engine speed are constant), purge rate conditions (purge rate Is constant). When all these conditions are satisfied and it is determined that the air-fuel ratio disturbance other than the purge is small, it is determined that the steady-state condition is satisfied.

The "purge valve accuracy condition" is a purge flow condition (the purge flow must be a predetermined amount or more).
Is set. When the purge flow rate is small, the control accuracy of the purge flow rate is reduced, and the calculation accuracy in the calibration process described later is reduced. Therefore, when the purge flow rate is smaller than a predetermined amount, it is determined that the purge valve accuracy condition is not satisfied.

The "purge influence degree condition" includes a purge establishment condition (purging is performed), a purge concentration condition (purge gas concentration higher than a predetermined concentration, for example, α change per 1% purge rate). The amount is 1% or more), and the purge rate condition (the purge rate is a predetermined value or more, for example, the purge rate is 30% or more) is set. When all of these conditions are satisfied and it is determined that the effect of the purge on the air-fuel ratio is relatively large, it is determined that the purge influence degree condition is satisfied.

When it is determined in step S1 that the calibration process can be executed, the process proceeds to step S3, where the calibration process is executed. In the calibration process, the amount of fuel desorbed from the canister 4 is estimated from the change in the air-fuel ratio feedback correction coefficient α, and the amount of fuel adsorbed on the canister 4 is calculated from the estimated amount of desorption by inverse calculation. The value of the amount of adsorption, which is an internal variable of the model, is calibrated to the value of the amount of adsorption determined by the inverse operation (the details will be described later).

On the other hand, if it is determined in step S1 that the calibration process cannot be executed, the process proceeds to step S2, where it is determined whether the calibration process has been executed in the past. Such a determination is made because the initial value (initial adsorption amount) required to operate the canister model does not yet exist if the calibration process has never been performed. This is to prevent the purging process based on. As a result of the determination, if the calibration process has been performed at least once in the past, the process proceeds to step S4, and if the calibration process has never been performed, the present routine ends.

If the calibration process has never been performed, purging is not necessarily performed, but the purging process is executed by a purging process (boot-up control shown in FIG. 15) that does not use a canister model described later.

In step S4, the amount of desorption from the canister 4 is calculated using the canister model. Specifically, the amount of fuel desorbed from the canister 4 is calculated according to the flow shown in FIG. 10 (details will be described later).

In step S5, a purge correction coefficient FHOS is calculated based on the desorption amount and the intake air flow rate. The purge correction coefficient FHOS is calculated in accordance with the air-fuel ratio fluctuation (change in the air-fuel ratio feedback correction coefficient α) expected when the desorption amount calculated by the canister model is supplied to the engine 10. Specifically, for example, when the amount of desorption from the canister 4 increases and the amount of fuel supplied to the engine 10 increases, the air-fuel ratio of the engine 10 shifts to the rich side, and the air-fuel ratio shifts to the original state. Since the fuel ratio feedback correction coefficient α is expected to change to a small side, a small value is calculated as the purge correction coefficient FHOS so that the fuel injection amount is reduced in advance correspondingly. The calculated correction coefficient FHOS is sequentially stored in a predetermined data storage location (see FIG. 8) in the controller 21.

In step S6, the purge correction coefficient FHOS is subjected to delay correction including dead time correction and smoothing processing. The reason for performing the dead time correction is that there is a delay according to the transfer speed of the purge gas and the distance between the purge valve 11 and the cylinder of the engine 10 between the time when the purge valve 11 is opened and the time when the purge gas reaches the cylinder of the engine 10. The reason why the annealing process is performed is that the fuel desorbed from the canister 4 diffuses before reaching the cylinder of the engine 10.

FIG. 5 is a flowchart showing the contents of the delay correction, and corresponds to the processing in the delay correction unit B6 in FIG.

This will be described in step S21.
Then, the intake air flow rate is detected from the output of the air flow meter 9, and in steps S22 and S23, the dead time and the smoothing coefficient are obtained with reference to the tables shown in FIGS. Since the intake flow velocity increases as the intake air flow rate increases, a small value is set for the dead time.In addition, when the intake air flow rate increases and the intake flow velocity increases, the speed at which the desorbed fuel diffuses also increases. A large value is set for the annealing coefficient.

In step S24, a value corresponding to the moving speed of the purge gas is calculated from the dead time. This purge gas moving speed equivalent value is calculated as the reciprocal of the dead time obtained in step S22.

In step S25, the purge correction coefficient FHOS stored in the data storage location (see FIG. 8) in the controller 21 corresponding to the distance between the purge valve 11 and the cylinder of the engine 10 is read, and step S2 is executed.
In step 6, the data is shifted toward the cylinder by the value corresponding to the moving speed of the purge gas. In step S27, the average value of the data overflowed from the data storage location due to the data shift is obtained.

In step S28, the average value of the overflow data obtained in step S27 is subjected to an averaging process using the averaging coefficient obtained in step S22. Note that the smoothing process is a smoothing process using a general first-order delay system, and the degree of smoothing increases as the smoothing coefficient decreases.

FIG. 8 is a diagram showing an outline of the dead time correction in the delay correction. In FIG. 8, black circles and white circles indicate data before the data shift and data after the data shift, respectively.

As shown, the memory of the controller 21 has a data storage location corresponding to the distance between the purge valve 11 and the cylinder of the engine 10.
The correction coefficient FHOS calculated according to the amount of fuel desorbed from the canister 4 is sequentially stored in the storage location. In the dead time correction, these data are shifted toward the cylinder by an amount equivalent to the transfer speed of the purge gas (the reciprocal of the dead time), and an overflow from the data storage location due to this data shift arrives in the cylinder and is supplied to the purge gas. Is a correction coefficient corresponding to. Then, a value obtained by performing a smoothing process on the average value of the overflowed data is used for correcting a fuel injection pulse width Ti described later. In this way, by combining the dead time correction and the smoothing process, the arrival delay of the purge gas can be accurately corrected.

Returning to FIG. 3, in step S7, the fuel injection pulse width (fuel injection valve drive pulse width) Ti is calculated. Specifically, the following equation (1), Ti = Tion × FHOS × α × K + TB (1) Tion: Reference pulse width FHOS: Purge correction coefficient (value after delay smoothing) α: Air-fuel ratio The reference pulse width Tion is corrected by the air-fuel ratio feedback correction coefficient α and the purge correction coefficient FHOS according to the feedback correction coefficient K: fuel injection valve coefficient TB: fuel injection valve invalid pulse width, and the injection pulse width Ti of the fuel injection valve 15 becomes Is calculated. Here, the reference pulse width Tion is set according to the intake air flow rate, the number of cylinders, and the like so that the target air-fuel ratio is achieved. The air-fuel ratio feedback correction coefficient α is set to 100% (= 1) when the target air-fuel ratio and the air-fuel ratio detected by the oxygen concentration sensor 18 match, but the detected air-fuel ratio is set to the target air-fuel ratio. A value less than 100% when it is richer than the fuel ratio,
100 when the detected air-fuel ratio is thinner than the target air-fuel ratio
%, And the fuel injection amount is corrected so that the actual air-fuel ratio approaches the target air-fuel ratio. Further, the fuel injection valve invalid pulse width TB is used to correct an operation delay until a drive voltage is applied to the fuel injection valve 15 to open the valve and fuel is injected.

Next, the contents of the calibration process performed in step S3 will be specifically described. FIG. 9 is a flowchart showing the contents of the calibration processing, and corresponds to the processing in the calibration unit B9 in FIG.

To describe this, first, in step S31, it is determined whether or not purging is being performed. The determination as to whether or not the purging is being performed is based on the assumption that the arithmetic processing in the subsequent steps S32 and S33 is performing the purging. Therefore, if these processings are performed when the purging is not performed, the correct calibration is performed. Is no longer possible. Therefore, if it is determined that the process is not being executed, the routine is terminated and the calibration process is not performed.

If it is determined that the purging is being performed, the process proceeds to the next step S32, in which the intake air weight, the purge rate and the purge correction coefficient FHOS, which are obtained from the intake air flow rate and the intake air temperature, etc.
From the air-fuel ratio feedback correction coefficient α, the following equation (2), Dg = K1 × (1−DLT + K2 × PR) × Qg (2) Dg: Desorption amount DLT: Total air-fuel ratio deviation (= α × FHOS / 100) PR: Purge rate K1: Coefficient (constant determined by properties of desorbed fuel) K2: Coefficient (constant determined by properties of air) Qg: Desorption amount (mass) is calculated from intake air weight. This equation (2) is
Air-fuel ratio deviation from reference value (first and second terms on right side)
And the equation for calculating the amount of fuel desorbed from the canister 4 from the purge rate (third term on the right side) and the intake air weight at that time. That is, all deviations of the air-fuel ratio feedback correction coefficient α from the reference value are regarded as being caused by the purge, and the desorption amount is estimated from the deviation of the air-fuel ratio.

Then, in step S33, step S
From the desorption amount and the purge flow rate calculated in 32, the following equation (3), Yr = KD × Dg ^ (1 / n (T)) (3) n (T): desorption index KD: desorption coefficient The adsorption amount Yr (mass) of the canister 4 is calculated from T: activated carbon temperature. Equation (3) is an inverse operation of equation (5), which is one of the equations constituting the canister model described later.

In step S34, the value Y of the adsorption amount used in calculating the desorption amount based on the canister model is replaced with the adsorption amount Yr calculated in step S33. Thereby, the value of the amount of adsorption used in the canister model can be calibrated to a correct value, and the calculation accuracy of the amount of desorption thereafter can be improved.

FIG. 10 shows the content of the desorption amount calculation process using the canister model in step S4 of FIG.
This will be described with reference to the flowchart shown in FIG. This processing corresponds to the processing in the desorption amount calculation unit B4 in FIG.

According to this, first, in step S41,
The current value Y of the amount of fuel adsorbed in the canister is calculated by the following equation (4).

[Adsorption amount calculation formula] Y = Yz-Dgz (4) Yz: Previous value of adsorption amount Dgz: Previous value of desorption amount This adsorption amount calculation formula is obtained from the previous value of adsorption amount Yz to the previous value. The present adsorption amount Y (mass) is calculated by subtracting the desorbed amount Dgz. However, when the calibration processing shown in FIG. 9 is executed, the calculation of Expression (4) is not performed, or the calculation of Expression (4) is not performed.
Is ignored, and in the subsequent calculations, the suction amount Yr calculated by the calibration process is used as the suction amount Y.

In step S42, the desorption amount Dgk at the reference purge flow rate is calculated by the following equation (5).

[Formula for Desorption at Reference Purge Flow Rate] Dgk = (Y / A) ^ n (T) (5) Y: adsorption amount A: desorption constant n (T): desorption index T: Activated carbon temperature This equation (5) describes the adsorption-desorption phenomenon (Freunlich (Freunrich)
dlich) is applied to the canister detachment phenomenon, whereby the fuel detachment characteristic from the canister 4 can be expressed almost exactly. The Freundlich equation is described in “Theory on Surfaces II” (Maruzen, Tsukada), p.25-p.27, p.108-p115.

In step S43, the desorption amount is calculated from the following equation (6).

[Detachment amount calculation formula according to purge flow rate] Dg = k × PQ × Dgk (6) K: constant PQ: purge flow rate (= purge rate × intake air flow rate) Dgk: desorption at reference flow rate Desorption amount The desorption amount calculation formula (6) according to the purge flow rate calculates the desorption amount Dg by linear approximation because the purge flow rate and the desorption amount are almost proportional. Here, equation (5)
The desorption amount at the reference flow rate is obtained by using the equation (6), and the desorption amount is calculated by multiplying the desorption amount by the purge flow rate in equation (6). However, the equations (5) and (6) can be combined into one equation. Good.

In step S44, the activated carbon temperature T is calculated by the following equation (7).

[Calculated equation of activated carbon temperature] T = Tz−Kt1 × (Yz2−Yz) + Kt2 × (Tz−Ta) (7) Tz: Previous value of activated carbon temperature Kt1: Endothermic coefficient Yz2: Adsorption amount Previous value Yz: Previous value of adsorption amount Kt2: Heat transfer component coefficient Ta: Canister ambient temperature This activated carbon temperature calculation formula is the past temperature (first term on the right side)
And a temperature decrease due to desorption (the second term on the right side) and a temperature increase due to heat transfer (the third term on the right side). The reason for calculating the activated carbon temperature T in this way is that the desorption index n (T) in the equation (5) is affected by the activated carbon temperature T. In particular, when the desorption amount is large, the amount of decrease in the activated carbon temperature T is reduced. This is because the influence on the fuel desorption characteristics of the canister 4 cannot be ignored.

Therefore, the canister model is composed of the four equations (4) to (7), and three equations when equations (5) and (6) are put together. FIG. 11 shows the canister model. The canister model is composed of an adsorption amount calculation unit B41, a reference desorption amount calculation unit B42, a flow rate equivalent desorption amount calculation unit B43, and an activated carbon temperature calculation unit B44. These correspond to equations (4) to (7), respectively.

Next, the process of setting the target purge rate will be described.

FIG. 12 is a flowchart showing the contents of the target purge rate setting processing, and corresponds to the processing in the target purge rate setting section B5 in FIG. The purge valve 11 is driven with a duty ratio that achieves the target purge rate set by this processing.

First, in step S51, the air-fuel ratio of the purge gas (purge air-fuel ratio) is calculated based on the desorption amount calculated based on the canister model and the purge flow rate. Although the purge air-fuel ratio may be detected by an HC sensor, the purge air-fuel ratio can be calculated at low cost and accurately by calculating the purge air-fuel ratio based on a desorption amount calculated based on a canister model.

In the next step S52, an error in the purge air-fuel ratio is estimated from operating conditions, for example, parameters such as engine speed, engine load, and intake air flow rate.
The estimation of the purge air-fuel ratio error is obtained with reference to, for example, a table shown in FIG. 13. The purge air-fuel ratio error increases as the intake air flow rate decreases and the purge rate decreases. Alternatively, the purge air-fuel ratio error may be obtained by referring to a table that defines the relationship between the purge air-fuel ratio and the purge air-fuel ratio error as shown in FIG. When the purge air-fuel ratio error is determined, the process proceeds to step S53, and the purge air-fuel ratio determined in step S51 is corrected based on the error.

In step S54, a purge rate change amount limit value is calculated based on the purge air-fuel ratio after error correction. When the purge rate changes, the air-fuel ratio of the engine 10 changes,
The purge rate change amount limit value is calculated such that the air-fuel ratio change of the engine 10 at this time falls within the allowable range. The allowable range of the air-fuel ratio fluctuation is set to a range that can be absorbed by the air-fuel ratio air-fuel ratio feedback control and does not deteriorate the emission.

In step S55, a purge rate upper limit value PVMX defined by the size of the purge valve 11 is calculated. The reason why the purge rate upper limit value PVMX is obtained is that if the target purge rate is set to a value larger than the purge rate obtained by setting the purge valve 11 to the maximum opening, a mismatch between the purge rate and the target purge rate occurs. , FHOS calculation error increases, and the air-fuel ratio fluctuation increases. This causes a problem such as emission deterioration. Specifically, when the purge valve size is constant, the larger the differential pressure across the purge valve, the larger the flow rate of the purge gas that can flow.Therefore, when the differential pressure across the purge valve is large, a large value is calculated as the purge rate upper limit value PVMX. You.

In step S56, the fuel injection valve 1 is determined based on the relationship between the minimum fuel injection pulse width determined according to the performance of the fuel injection valve 15, the previous value of the target purge rate, and the purge correction coefficient.
The purge rate upper limit value TINMMX based on the performance of No. 5 is calculated.
When the purge rate increases, the fuel amount supplied to the engine 10 increases due to the purge. Therefore, the fuel injection pulse width is corrected to be short so that the fuel injection amount from the fuel injection valve 15 is reduced by that amount. In order to ensure the injection accuracy of the valve 15, the injection pulse width must be larger than a predetermined minimum pulse width. In other words, in order to make the fuel injection pulse width larger than the minimum pulse width, the purge rate must be smaller than a certain value. For this reason, the upper limit of the purge rate is also determined by the injection performance of the fuel injection valve 15.

In step S57, all possible operating regions are assumed from the current operating region, the minimum purge rate in the operation region is predicted, and the purge rate is calculated from the minimum purge rate and the purge rate change limit value. Calculate the rate upper limit value PRMNMX. For example, when accelerating with the accelerator fully open, the target purge rate is set to a very small value, but if the target purge rate is set to a large value immediately before the accelerator is fully opened, the amount of change in the purge rate changes. Since the purge rate is limited to the amount limit value or less, the purge rate cannot follow the target purge rate. Since the following delay causes an increase in emission and the like, it is necessary to define the upper limit of the purge rate from the minimum purge rate that can be assumed so as not to cause such a delay.

In step S58, the air-fuel ratio feedback correction coefficient α is monitored. Is calculated as The reason for providing such an upper limit value ALPMX is that in the air-fuel ratio feedback control, the air-fuel ratio feedback correction coefficient α is controlled to be within 100 ± 25%, but the air-fuel ratio feedback correction coefficient α is set to the limit value (for example, 80%). %), When a large amount of purge is performed in the case where the control is performed in the vicinity, disturbances other than the purge are likely to cause a deviation from the control range.

In step S59, the above four upper limit values PVM
Select the smallest value from X, TINMMX, PRMNMX, ALPMX,
Set that value to the maximum purge rate.

In steps S60 and S61, the previous value of the target purge rate is compared with the maximum purge rate, and when the previous value of the target purge rate is equal to the maximum purge rate, the target purge rate is kept at the previous value (step S61). S63) If the previous value of the target purge rate is larger than the maximum purge rate, the target purge rate is set to a value obtained by subtracting the purge rate change amount limit value from the previous value (step S64), and the previous value of the target purge rate becomes the maximum. When the purge rate is smaller than the purge rate, the target purge rate is set to a value obtained by adding the purge rate change amount limit value to the previous value (step S6).
2).

Therefore, the target purge rate is set so as to follow the maximum purge rate within the range of the purge rate change amount limit value, and is the best for performing a large amount of purge without deteriorating the exhaust emission. Is set. Also, when setting the maximum purge rate, the upper limit values PVMX, TINMMX, AL
Not only PMX but also the upper limit value PRMNMX, which is determined so that the maximum purge rate in the operating area can be shifted to without delay even if the operating area changes, is considered. It is possible to set the best purge rate for performing a large amount of purge without using a large amount.

By the way, the purge process (model reference purge process) centering on the canister model is executed while the calibration process has not been executed yet and the initial value (initial suction amount) used in the above-described canister model does not exist. Can not do it. However, in order to realize a large amount of purge, it is necessary to execute a purge process even before the execution of the calibration process. So, until the calibration process is executed,
A purge rate is set by the following processing (boot-up control) shown in FIG. 15 instead of the above processing, and the purge processing is executed at the set purge rate. In the boot-up control, the air-fuel ratio fluctuation due to the purge is absorbed by the air-fuel ratio feedback control, and the fuel injection amount is not corrected.

The process shown in FIG. 15 will be described. First, in step S71, the accumulated purge flow rate (total purge flow rate after starting the purge) is compared with the purge pipe volume (the volume of the pipe from the canister 4 to the purge valve 11). If the accumulated purge flow rate exceeds the purge pipe volume, the process proceeds to step S72, and if not, the process proceeds to step S75.

In step S75, an initial purge rate (a small value of 1% or less) is set as the target purge rate. The reason for setting such a small value is that if the integrated purge flow rate does not reach the purge pipe volume, the gas in the purge pipe will be supplied to the engine 10 before the purge is started. This is because the air-fuel ratio of the gas is unknown, and if the target purge rate setting process shown in step S72 and thereafter is performed as it is, problems such as deterioration in combustion stability of the engine 10 will occur.

That is, at the start of the purge, a low-concentration purge gas existing in the purge pipe is supplied, and if the fluctuation in the air-fuel ratio is small, it is determined that a larger amount of purge is possible and a large purge rate is set. However, if a large purge rate is set in this way, a large amount of desorbed fuel is suddenly supplied when all low-concentration gases in the pipe are supplied and the original high purge gas is supplied. This causes the combustion stability and the like of the engine 10 to deteriorate.

If the accumulated purge flow rate exceeds the pipe volume, the process proceeds to step S72, where the difference between the actual air-fuel ratio feedback deviation and the target air-fuel ratio feedback deviation is calculated. Here, the target air-fuel ratio feedback deviation is a deviation (= | tα−1) between the target value tα of the air-fuel ratio feedback correction coefficient and the reference value (100%) of the air-fuel ratio feedback correction coefficient.
00 |%), and the actual air-fuel ratio feedback deviation is the deviation (= | α−100 |) between the actual air-fuel ratio feedback correction coefficient α and the reference value of the air-fuel ratio feedback correction coefficient.
%). For example, if the target value of the air-fuel ratio feedback correction coefficient α is set to 80% for the purpose of securing a large amount of purge flow within a range in which air-fuel ratio fluctuation due to purge can be sufficiently absorbed by the air-fuel ratio feedback control, The fuel ratio feedback deviation is set to 20%.

In step S73, the table shown in FIG. 16 is searched to determine the purge rate change amount according to the difference between the target air-fuel ratio feedback deviation and the actual air-fuel ratio feedback deviation. The purge rate change amount is set to a larger value as the absolute value of the difference between the target air-fuel ratio feedback deviation and the actual air-fuel ratio feedback deviation increases, and the convergence to the target value is enhanced. Depending on the sign of the difference in the actual air-fuel ratio feedback deviation, a different value is set even if the absolute value of the deviation is the same, and the purge change amount is larger when the difference in the air-fuel ratio feedback deviation is shifted to the negative side ( Absolute value) is set.

The reason why the purge change amount is made to have different characteristics depending on whether the air-fuel ratio feedback deviation is positive or negative is that the air-fuel ratio feedback correction coefficient α is a target when the air-fuel ratio feedback deviation is shifted to the negative side. This is because the value is smaller than%, and the engine stability and emission are more likely to be degraded by disturbances other than the purge, as compared with the case where the value is shifted to the opposite positive side. That is, the reason why the characteristic of the purge change amount is changed in accordance with the sign of the difference in the air-fuel ratio feedback deviation is to quickly return the control point to the safe side from the viewpoint of engine combustion stability and prevention of emission deterioration.

After the purge rate change amount is calculated as described above, the process proceeds to step S74, in which the purge rate change amount calculated in step S73 is added to the target purge rate obtained in the previous execution of this routine, and a new target purge rate is calculated. Is calculated. In step S76, the purge flow rate is obtained from the target purge rate and the intake air flow rate, and the value of the integrated purge flow rate is updated.

Therefore, according to this processing, an optimum purge rate can be set irrespective of the adsorption state of the canister 4, and even when a purge with a concentration higher than expected is supplied, the air-fuel ratio fluctuation Accordingly, the target purge rate is appropriately changed, and the optimum purge rate can always be set.

In this embodiment, the process shown in FIG. 15 is performed until the initial value of the canister model is calculated by the calibration process, and after the calibration process is performed, the purge process based on the canister model (model reference purge process). However, it is also possible to always perform purging by the processing shown in FIG.

Next, the overall operation of the above control will be described.

In the evaporative fuel treatment apparatus according to the present invention, the target purge rate is set as large as possible within a range that does not cause a decrease in engine combustion stability and an increase in emission during the purge processing, and this target purge rate is realized. Valve 11 is driven in such a manner.

During the purging process, the purge gas containing the fuel desorbed from the canister 4 is supplied to the engine 10. Therefore, the controller 21 estimates the amount of fuel desorbed from the canister 4 and supplies the purge gas by purging. The fuel injection valve 15 predicts the air-fuel ratio fluctuation of the engine 10 caused by the supplied fuel and suppresses the air-fuel ratio fluctuation.
To correct the fuel injection pulse width.

At this time, the amount of desorbed fuel from the canister 4 is estimated using the canister model represented by the equations (4) to (7), and the desorbed amount is accurately estimated in a short time. Here, the desorption amount or the like calculated based on the canister model includes an error. Since the error increases and increases as the operation time of the canister model increases, the controller 21 determines the change in the air-fuel ratio feedback correction coefficient α. Then, the amount of fuel desorbed from the canister 4 is estimated, and the value of the adsorbed amount, which is an internal variable of the canister model, is calibrated by the adsorbed amount reversed from the estimated desorbed amount. In this calibration process, the air-fuel ratio disturbance other than the purge is small, and the air-fuel ratio fluctuation (change in the air-fuel ratio feedback coefficient α) can be regarded as almost entirely due to the purge, and the effect of the purge on the air-fuel ratio is relatively large. When executed.

Further, there is a delay from when the purge valve 11 is opened to when the desorbed fuel reaches the cylinder of the engine 10, and there is a diffusion of the fuel before reaching the cylinder.
The correction of the fuel injection pulse width is performed in consideration of the delay and the smoothing action.

Further, the purging process using the canister model (model reference purging process) cannot exert its effect until the initial value of the adsorption amount is obtained by the calibration process, but the initial value of the canister model is calculated. Until the target air-fuel ratio feedback deviation and the actual air-fuel ratio feedback deviation, the target purge rate is set according to the difference,
The purge valve 11 is set so that the target purge rate is realized.
Is driven. Thereby, the purge process can be performed even before the initial value is calculated by the calibration process,
Effective purging can be performed in all regions.

Although the embodiments of the present invention have been described above, the configuration of the above embodiment is an example of the configuration to which the present invention is applied, and the scope of the present invention is not limited to the above configuration. Absent. As described above, in the above-described embodiment, the purge process shown in FIG. 15 is supplementarily executed until the purge process by the canister model becomes possible, but the purge process shown in FIG. 15 is continuously used. You may do so.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a fuel vapor processing apparatus according to the present invention.

FIG. 2 is a block diagram showing an outline of a purge process in a controller.

FIG. 3 is a flowchart showing the contents of a purge process.

FIG. 4 is a flowchart showing calibration processing possible conditions.

FIG. 5 is a flowchart showing the contents of a delay smoothing process.

FIG. 6 is a table defining a relationship between an intake air flow rate and a dead time.

FIG. 7 is a table defining a relationship between an intake air flow rate and a smoothing coefficient.

FIG. 8 is a diagram showing an outline of dead time processing in delay correction.

FIG. 9 is a flowchart showing the contents of a calibration process.

FIG. 10 is a flowchart showing the content of a calculation process of a desorption amount based on a canister model.

FIG. 11 is a block diagram showing a configuration of a canister model.

FIG. 12 is a flowchart showing the contents of a target purge rate setting process.

FIG. 13 is a map defining a relationship between a purge air-fuel ratio error with respect to an intake air flow rate and a purge rate.

FIG. 14 is a table defining a relationship between a purge air-fuel ratio and a purge air-fuel ratio error.

FIG. 15 is a flowchart showing a target purge rate setting process until the canister model is activated.

FIG. 16 is a difference in air-fuel ratio feedback deviation (= target air-fuel ratio feedback deviation−actual air-fuel ratio feedback deviation).
4 is a table that defines the relationship between the purge rate and the purge rate change amount.

FIG. 17 is a block diagram showing an outline of conventional air-fuel ratio feedback control.

[Explanation of symbols]

 Reference Signs List 1 fuel tank 2 pipe 4 canister 6 pipe 8 intake passage 9 air flow meter 10 engine 11 purge valve 15 fuel injection valve 17 exhaust passage 18 air-fuel ratio sensor 21 controller

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mari Kobayashi 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Prefecture Inside Nissan Motor Co., Ltd. In-house F term (reference) 3G044 AA04 BA03 BA08 DA02 EA04 EA19 EA23 EA32 EA35 EA40 EA50 EA62 FA02 FA08 FA18 FA20 FA27 FA28 FA38 GA22 3G301 HA13 HA14 JA04 JA21 MA12 NA08 NC02 ND01 ND41 NE17 PA01Z PA18Z PD02PD02

Claims (9)

[Claims] 1. A canister for adsorbing fuel vapor generated in a fuel tank, a purge valve for opening and closing a pipe communicating the canister with an intake passage of an engine, and means for setting a maximum purge rate under current operating conditions. Means for setting a limit value for a change in the purge rate based on the air-fuel ratio of the purge gas and a change in the air-fuel ratio of the engine caused by a change in the purge rate; and An evaporative fuel processing device for an engine, comprising: means for calculating a target purge rate that follows a purge rate; and means for driving the purge valve so that the purge rate becomes the target purge rate. 2. The fuel vapor processing according to claim 1, wherein said means for setting the maximum purge rate sets the maximum purge rate to be equal to or less than an upper limit of a purge rate defined by a size of the purge valve. apparatus. 3. The apparatus according to claim 1, wherein said means for setting the maximum purge rate sets the maximum purge rate to be equal to or less than an upper limit of a purge rate defined from the performance of a fuel injection valve. Evaporative fuel processing equipment. 4. A means for setting the maximum purge rate, assuming all operation areas which can be shifted from the current operation area, predicting a minimum purge rate in the assumed operation area, and setting the minimum purge rate. The evaporative fuel processing apparatus according to any one of claims 1 to 3, wherein the maximum purge rate is set to be equal to or less than a purge rate upper limit value calculated from the purge rate change amount limit value and the purge rate change amount limit value. 5. The means for setting the maximum purge rate sets the maximum purge rate below an upper limit of a purge rate defined so that an air-fuel ratio feedback correction coefficient becomes equal to or greater than a processing limit value. The evaporative fuel processing apparatus according to claim 1. 6. A means for setting the purge rate change amount limiting value, wherein the purge rate change amount limit value is set so that an air-fuel ratio change due to a change in the purge rate falls within a range that does not deteriorate the emission of the engine. The evaporative fuel treatment apparatus according to any one of claims 1 to 5, wherein a value is set. 7. An adsorption amount for calculating a fuel amount adsorbed on the canister based on at least a previous value of the amount of fuel adsorbed on the canister and a previous value of the amount of fuel desorbed from the canister. (B) a canister constituted by a desorption amount calculation expression for calculating an amount of fuel desorbed from the canister based on the adsorption amount calculated by the adsorption amount calculation expression and the target purge rate. The evaporation according to any one of claims 1 to 6, further comprising: a model; and means for calculating an air-fuel ratio of the purge gas based on a desorbed fuel amount calculated using the canister model. Fuel processor. 8. A means for calculating an error in the calculated air / fuel ratio of the purge gas based on the intake air flow rate, and a means for correcting the calculated air / fuel ratio in the purge gas based on the calculated error in the air / fuel ratio of the purge gas. The evaporated fuel processing apparatus according to claim 7, further comprising: 9. A means for calculating an error in the calculated air / fuel ratio of the purge gas based on the target purge rate, and correcting the calculated air / fuel ratio in the purge gas based on the calculated error in the air / fuel ratio of the purge gas. The evaporative fuel treatment apparatus according to claim 7 or 8, further comprising: