JP4715630B2 - Evaporative fuel processing equipment - Google Patents

Description

  The present invention relates to an apparatus for treating evaporated fuel generated from a fuel tank.

  The engine temporarily adsorbs the evaporated fuel generated in the fuel tank when the engine is stopped to the activated carbon of the canister, and removes the fuel adsorbed on the activated carbon using the suction negative pressure under the predetermined operating conditions after engine startup. There is provided an evaporative fuel processing device that separates (purge processing) and conducts combustion processing by guiding it to the intake pipe downstream of the throttle valve.

During the purge process, the fuel desorbed from the canister is sucked into the engine and the air-fuel ratio becomes rich. Therefore, in Patent Document 1, the amount of fuel desorption from the canister is estimated using a canister model, and the fuel is injected by reducing that amount.
JP 2004-60483 A

  However, since the canister model calculates the current value using the previous calculated value, the error is accumulated.

  The present invention has been made paying attention to such conventional problems, and provides an evaporative fuel processing apparatus that can appropriately calibrate a canister model (calibration process) and perform precise evaporative fuel processing. The purpose is to do.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

The present invention opens and closes a canister (10) that adsorbs evaporated fuel generated in a fuel tank (20), and a pipe (22) that connects the canister (10) and an intake passage (31) of an engine (30). An evaporative fuel processing apparatus having a purge valve (14), wherein an adsorbed amount of evaporated fuel adsorbed on the canister (10) is calculated based on a previous value of the fuel desorption amount, and based on the calculated fuel adsorbed amount The canister model (step S7) for calculating the current value of the amount of fuel desorbed from the canister (10), the purge valve (14) is opened at the time of purging, and the fuel desorption calculated by the canister model is used. Purge control means (steps S8 and S9) for reducing the amount of separation from the fuel supplied to the engine (30), and the canister model (step S7) A calibration value calculating means for calculating a calibration value of the fuel adsorption amount (step S2), and the weighted average processing means for weighted averaging calibration value (step S3), and holds the calibration conditions, further calibration interval limit And calibration means (step S6) for calibrating the fuel adsorption amount of the canister model (step S7) using the calibration value subjected to the weighted average processing when the weighted average processing is not performed .

  According to the present invention, the calibration value of the fuel adsorption amount of the canister model is calculated, and the calibration value is subjected to a weighted average process. When the calibration condition is satisfied, the weighted average processed calibration value is used to calculate the fuel of the canister model. Since the adsorption amount is calibrated, accurate calibration is possible.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. FIG. 1 is an overall configuration diagram of an engine including an evaporated fuel processing apparatus according to the present invention.

  A fuel injection valve 34 for each cylinder is provided in the intake passage 31 of the engine 30 downstream of the intake throttle valve 33. The exhaust passage 35 is provided with a three-way catalyst (not shown). The three-way catalyst exhibits maximum conversion efficiency when the air-fuel ratio in the exhaust gas is in a narrow range centered on the stoichiometric air-fuel ratio, reduces nitrogen oxide NOx in the exhaust gas, and produces hydrocarbon HC and monoxide. Carbon CO is oxidized.

  Therefore, the controller 100 inputs an intake air flow rate signal from the air flow meter 32, a signal from the crank angle sensor 37, an engine cooling water temperature signal from the water temperature sensor 38, etc., and the basic air-fuel ratio (theoretical) based on these signals. The basic injection pulse width Tp for obtaining an air / fuel mixture is calculated. The controller 100 calculates an air-fuel ratio feedback correction coefficient α based on the output signal of the oxygen sensor (O2 sensor) 36, and the basic injection pulse width Tp (engine) is calculated by the air-fuel ratio feedback correction coefficient α (air-fuel ratio feedback correction amount). The fuel injection pulse width Ti is obtained by correcting the basic amount of fuel supplied to the fuel, and the fuel injection valve 34 is controlled to open. By doing so, the air-fuel ratio in the exhaust gas matches the stoichiometric air-fuel ratio, and the three-way catalyst can exhibit the maximum conversion efficiency.

  The evaporative fuel processing apparatus 1 includes a canister 10, a bypass valve 11, a vacuum cut valve 12, a drain cut valve 13, and a purge valve 14, and these valves are controlled to be opened and closed by a controller 100, and a fuel tank of the engine 30. The evaporated fuel generated at 20 is processed.

  The canister 10 communicates with the fuel tank 20 via a pipe 21 and communicates with an intake passage 31 downstream of the throttle valve 33 of the engine 30 via a pipe 22. The canister 10 has a fuel adsorbent (activated carbon) 10a inside. The canister 10 includes an air release port 10b. The air release port 10 b is opened and closed by a drain cut valve 13.

  The bypass valve 11 and the vacuum cut valve 12 are provided in parallel with the pipe 21. The vacuum cut valve 12 opens when the internal pressure of the fuel tank 20 becomes lower than the atmospheric pressure.

  The purge valve 14 is provided in the pipe 22. The purge valve 14 is opened when the fuel adsorbed on the fuel adsorbent (activated carbon) 10a of the canister 10 is desorbed. The pipe 22 is provided with a pressure sensor 23 that measures the pressure in the pipe.

  The evaporated fuel generated in the fuel tank 20 is guided to the canister 10 through the pipe 21, only the fuel component is adsorbed by the activated carbon 10a of the canister 10, and the remaining air is released to the outside from the atmosphere opening 10b.

  When processing the fuel adsorbed on the activated carbon 10a, the purge valve 14 is opened, and fresh air is introduced into the canister 10 from the air release port 10b by the suction negative pressure developed downstream of the throttle valve 33. As a result, the fuel adsorbed on the activated carbon 10a is desorbed and sucked into the intake passage 31 of the engine 30 through the pipe 22 together with fresh air (hereinafter, this process is referred to as “purge process”).

  During the purge process, the controller 100 sets a target purge rate (a ratio of the purge flow rate to the intake air flow rate) as high as possible within a range not deteriorating engine combustion stability and exhaust emission, and realizes the target purge rate. The purge valve 14 is driven. Further, during the purge process, the fuel and air in the purge gas are supplied to the engine. Therefore, the fuel injection amount is corrected according to the purge rate and the purge concentration, and the air-fuel ratio fluctuation of the engine 30 is changed. Suppress.

  Therefore, the controller 100 estimates a desorbed fuel amount Dg from the canister 10 using a canister model described later, and calculates a purge correction coefficient FHOS based on the desorbed fuel amount Dg, the target purge rate, and the intake air mass. The basic injection pulse width Tp is corrected with the purge correction coefficient FHOS. By doing so, the effect of the purge on the exhaust air / fuel ratio is compensated by the purge correction coefficient FHOS, and the air / fuel ratio feedback correction coefficient α behaves in the same manner as when there is no purge. Therefore, the air-fuel ratio feedback correction coefficient α does not have to consider the influence on the disturbance due to the purge.

  By the way, the canister model can express the desorption characteristics of the canister 10 with high accuracy. However, since the canister model is an approximate model to the last, the values (desorption amount, adsorption amount, etc.) calculated using this can be calculated from actual values. Slip. Further, since the canister model calculates the amount of fuel newly desorbed from the canister 10 using the previous calculation result as will be described later, the error is integrated as the model operation time becomes longer, and the calculated value and the actual value are calculated. The deviation increases. Therefore, the controller 100 performs calibration (calibration) when the condition is satisfied so as to calibrate the deviation and maintain high calculation accuracy of the model.

  Specifically, the air-fuel ratio fluctuation (when absorbed by the air-fuel ratio feedback control and appears as the fluctuation of the air-fuel ratio feedback correction coefficient α) is satisfied when the condition that almost all can be regarded as the purge is satisfied. The amount of adsorption is calculated backward based on the amount of fuel desorbed from the canister 10 estimated based on (the fluctuation of the air-fuel ratio feedback correction coefficient α). The value of the amount of adsorption that the canister model has is calibrated with this value. In addition, the strength against disturbance is increased by always calculating the amount of adsorption and performing weighted averaging.

  Below, the concrete control logic of the controller 100 is demonstrated along a flowchart.

  FIG. 2 is a main flowchart for explaining the operation of the evaporated fuel processing apparatus according to the present invention.

  In step S1, the controller 100 sets a target purge rate. A specific setting method will be described later.

  In step S2, the controller 100 calculates the adsorption amount Yα based on the air-fuel ratio feedback correction coefficient α. A specific calculation method will be described later.

  In step S3, the controller 100 calculates a weighted average value Yαave of the adsorption amount Yα.

  In step S4, the controller 100 determines whether or not the calibration execution condition is satisfied. Until it is established, the process proceeds to step S7, and when established, the process proceeds to step S5. A specific determination method will be described later.

  In step S5, the controller 100 determines whether or not the calibration interval is being limited. If so, the process proceeds to step S7; otherwise, the process proceeds to step S6. A specific determination method will be described later.

  In step S6, the controller 100 sets the weighted average value Yαave to the previous value Yz of the adsorption amount.

  In step S7, the controller 100 calculates the amount of desorption by the canister model. A specific calculation method will be described later.

  In step S8, the controller 100 calculates the fuel injection amount. A specific calculation method will be described later.

  In step S <b> 9, the controller 100 controls the purge valve 14 and the fuel injection valve 34.

  FIG. 3 is a flowchart for explaining the contents of the target purge rate setting routine.

  In step S11, the controller 100 determines whether or not the current purge control is the first control. That is, the previous value of the target purge rate is required to set the target purge rate based on the adsorption state of the canister 10. However, since there is no previous value at the time of initial control, the target purge rate must be set without being based on the adsorption state of the canister 10 at that time. Therefore, it is determined whether or not the current control is the initial control. When it is the initial control, the process proceeds to step S12, and when it is not the initial control, the process proceeds to step S13.

  In step S <b> 12, the controller 100 sets a target purge rate that is not based on the adsorption state of the canister 10. A specific setting method will be described later.

  In step S <b> 13, the controller 100 sets a target purge rate based on the adsorption state of the canister 10. A specific setting method will be described later.

  FIG. 4 is a flowchart for explaining the contents of a target purge rate setting routine that is not based on the adsorption state of the canister.

  In step S121, the controller 100 calculates an integrated purge flow rate (total purge flow rate after starting the purge). The integrated purge flow rate is zero as an initial value at the start of the purge. After the purge starts, the purge flow rate is obtained from the previously calculated target purge rate and intake air flow rate, and the integrated purge flow rate is updated.

  In step S122, the controller 100 determines whether or not the integrated purge flow rate is larger than the purge pipe volume (the volume of the pipe from the canister 10 to the purge valve 14). If the integrated purge flow rate is larger than the purge pipe volume, the process proceeds to step S124; otherwise, the process proceeds to step S123.

  In step S123, the controller 100 sets the initial purge rate (a small value of 1% or less) as the target purge rate. This small value is set for the following reason. That is, if the purge is started when the integrated purge flow rate has not reached the purge pipe volume, the low concentration purge gas present in the purge pipe is supplied to the engine. Even in such a case, if the target purge rate is set as shown in and after step S124, the air-fuel ratio fluctuation due to the low-concentration purge gas is small, so it is determined that a large amount of purge is possible and a large purge rate is set. There is a risk. However, when a large purge rate is set in this way, a large amount of desorbed fuel is suddenly supplied, so that the combustion stability of the engine 10 is deteriorated. Therefore, when the integrated purge flow rate does not reach the purge pipe volume, the target purge rate is set and the initial purge rate (a small value of 1% or less) is set.

  In step S124, the controller 100 calculates a difference between the target air-fuel ratio feedback deviation and the actual air-fuel ratio feedback deviation (hereinafter referred to as “air-fuel ratio feedback deviation difference”). The target air-fuel ratio feedback deviation is a deviation (= | tα-100 |%) of the target value tα of the air-fuel ratio feedback correction coefficient with respect to the reference value (100%) of the air-fuel ratio feedback correction coefficient. The actual air-fuel ratio feedback deviation is a deviation (= | α-100 |%) of the actual air-fuel ratio feedback correction coefficient α with respect to the reference value (100%) of the air-fuel ratio feedback correction coefficient. For example, when the target value tα of the air-fuel ratio feedback correction coefficient is set to 80% for the purpose of ensuring a large purge flow rate within a range in which air-fuel ratio fluctuation due to purge can be sufficiently absorbed by the air-fuel ratio feedback control, The air-fuel ratio feedback deviation is set to 20%.

  In step S125, the controller 100 searches the characteristic table shown in FIG. 5 stored in advance in the ROM to obtain the purge rate change amount according to the difference in the air-fuel ratio feedback deviation. The absolute value of the purge rate change amount increases as the absolute value of the difference in the air-fuel ratio feedback deviation increases, thereby improving the convergence to the target value. However, even if the absolute value of the difference in the air-fuel ratio feedback deviation is the same, the absolute value of the purge rate change amount differs depending on whether it is positive or negative. As for the absolute value of the purge rate change amount, the negative value is larger than the positive value. This characteristic is obtained when the difference in air-fuel ratio feedback deviation is shifted to the negative side, the air-fuel ratio feedback correction coefficient α is smaller than the target 80%, and on the opposite positive side. This is because the engine stability and emission are likely to be deteriorated by disturbances other than purge, as compared with the case of deviation, which is disadvantageous. In other words, changing the characteristics of the purge change amount according to the sign of the difference in the air-fuel ratio feedback deviation is to quickly return the control point to the safe side in order to improve engine combustion stability and prevent emissions from deteriorating. Because.

  In step S126, the controller 100 calculates the current value of the target purge rate by adding the purge rate change calculated in step S125 to the previous value of the target purge rate.

  According to this process, an optimum purge rate can be set regardless of the adsorption state of the canister 10, and even when a purge with a concentration higher than expected is supplied, the target is received in response to fluctuations in the air / fuel ratio. The purge rate is changed as appropriate, and an optimal purge rate can always be set.

  FIG. 6 is a flowchart for explaining the contents of a target purge rate setting routine based on the adsorption state of the canister.

  In step S131, the controller 100 sets a purge change amount limit value. A specific setting method will be described later.

  In step S132, the controller 100 sets a maximum purge rate. A specific setting method will be described later.

  In step S133, the controller 100 determines whether or not the previous value of the target purge rate matches the maximum purge rate. If they match, the process proceeds to step S134; otherwise, the process proceeds to step S135.

  In step S134, the controller 100 sets the previous value of the target purge rate as the target purge rate as it is.

  In step S135, the controller 100 determines whether or not the previous value of the target purge rate is below the maximum purge rate. If it is lower, the process proceeds to step S136, and if not, the process proceeds to step S137.

  In step S136, the controller 100 sets the target purge rate by adding the purge rate change limit value to the previous value of the target purge rate.

  In step S137, the controller 100 sets the target purge rate by subtracting the purge rate change limit value from the previous value of the target purge rate.

  FIG. 7 is a flowchart for explaining the contents of the purge change amount limit value setting routine.

  In step S1311, the controller 100 calculates the purge gas air-fuel ratio (purge air-fuel ratio) based on the desorption amount and the purge flow rate calculated by the canister model. The purge air-fuel ratio may be detected using an HC sensor, but can be obtained inexpensively and accurately if calculated by calculation.

  In step S1312, the controller 100 estimates the purge air-fuel ratio error based on operating conditions, for example, parameters such as engine speed, engine load, and intake air flow rate. Specifically, for example, it is obtained with reference to a characteristic table shown in FIG. According to FIG. 8A, the purge air-fuel ratio error increases as the intake air flow rate decreases and the purge rate decreases. Further, it may be obtained with reference to a characteristic table shown in FIG. According to FIG. 8B, the purge air-fuel ratio error increases as the purge air-fuel ratio decreases.

  In step S1313, the controller 100 corrects the purge air-fuel ratio obtained in step S1311 based on the purge air-fuel ratio error.

  In step S1314, the controller 100 calculates a purge rate change amount limit value based on the corrected purge air-fuel ratio. The purge rate change limit value is a limit value for keeping the air-fuel ratio change of the engine 10 that occurs when the purge rate is changed within an air-fuel ratio fluctuation range that can be absorbed by air-fuel ratio feedback control without deteriorating emissions. It is.

  FIG. 9 is a flowchart for explaining the contents of the maximum purge rate setting routine.

  In step S1321, the controller 100 sets the purge rate upper limit PVMX based on the size of the purge valve 14. This purge rate upper limit PVMX is the purge rate when the purge valve 14 is at the maximum opening. If a target purge rate larger than the purge rate when the purge valve 14 is at the maximum opening is set, the purge rate cannot be matched with the target purge rate. For this reason, the calculation error of FHOS becomes large, the air-fuel ratio fluctuation becomes large, and emission deterioration occurs. The larger the purge valve size, the larger the purge gas flow rate. Therefore, the purge rate upper limit PVMX is set larger as the purge valve size is larger.

  In step S1322, the controller 100 determines the purge rate upper limit value based on the performance of the fuel injection valve 15 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. Set TIMNMX. When the purge rate increases, the amount of fuel supplied to the engine 10 by the purge increases, so it is necessary to reduce the fuel injection amount of the fuel injection valve 15 by the increase amount, but the injection accuracy of the fuel injection valve 15 is ensured. Requires a certain amount of fuel injection. Therefore, in order to ensure the injection accuracy of the fuel injection valve 15, an upper limit value TIMNMX is set for the purge rate.

  In step S1323, the controller 100 assumes all the operation regions that can be assumed from the current operation region, predicts the minimum purge rate in the operation region, and determines the purge rate upper limit from the minimum purge rate and the purge rate change limit value. Set the value PRMNMX. For example, when acceleration is performed 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 is The purge rate cannot be made to follow the target purge rate because it is limited to the change amount limit value or less. Since this follow-up delay causes an increase in emissions, the purge rate upper limit value PRMNMX is set based on the minimum purge rate that can be assumed so as not to cause such follow-up delay.

  In step S1324, the controller 100 monitors the air-fuel ratio feedback correction coefficient α, and if it is equal to or less than a predetermined value, sets the largest value among the purge rates at which the air-fuel ratio feedback correction coefficient α is equal to or greater than the predetermined value as the purge rate upper limit value ALPMX. To do. The upper limit value ALPMX is provided so that the air-fuel ratio feedback correction coefficient α is controlled to be within 100 ± 25% in the air-fuel ratio feedback control, but the air-fuel ratio feedback correction coefficient α is set to the limit value (for example, 80 %) In the case of being controlled in the vicinity, if a large amount of purging is performed, disturbances other than purging will occur and it will easily be out of the control range.

  In step S1325, the controller 100 selects the smallest value from the four upper limit values PVMX, TIMNMX, PRMNMX, and ALPMX, and sets that value as the maximum purge rate.

  In the target purge rate setting routine (S13) based on the adsorption state of the canister 10, the target purge rate is set so as to reach the maximum purge rate within the range of the purge rate change amount limit value, so that exhaust emission is not deteriorated. The best purge rate can be set when performing a large amount of purge. In addition to the upper limits PVMX, TIMNMX, and ALPMX that are determined by physical limits and the current operating range, the upper limit is determined so that even if the operating range changes, the maximum purge rate in that range can be shifted without delay. Since the maximum purge rate is set in consideration of the value PRMNMX, it is possible to set the best purge rate that enables a large-scale purge that does not deteriorate the exhaust emission even if the operating condition changes.

  FIG. 10 is a flowchart for explaining the contents of the adsorption amount calculation routine based on the air-fuel ratio feedback correction coefficient.

  In step S21, the controller 100 calculates the fuel desorption amount Dg (mass) of the canister 10 based on the air-fuel ratio feedback correction coefficient α. Specifically, it is obtained by the following formula (1).

  This equation (1) is desorbed from the canister 10 based on the deviation of the air-fuel ratio with respect to the reference value (first and second terms on the right side), the purge rate at that time (third term on the right side) and the intake air mass. It is a formula for calculating the amount of fuel. That is, the deviation of the air-fuel ratio feedback correction coefficient α with respect to the reference value is considered to be all due to the purge, and the desorption amount is estimated from the deviation of the air-fuel ratio.

  In step S22, the controller 100 calculates the adsorption amount Yα (mass) of the canister 10 based on the air-fuel ratio feedback correction coefficient α from the desorption amount and the purge flow rate calculated in step S21. Specifically, it is obtained by the following formula (2).

  This equation (2) is an inverse operation of equation (5), which is one of the equations constituting the canister model described later.

  FIG. 11 is an explanatory diagram of the calibration execution condition determination method in step S4.

  The controller 100 purges almost all deviations from the target value of the air-fuel ratio feedback correction coefficient α when the air-fuel ratio disturbance due to factors other than purge is small and the influence of the purge on the air-fuel ratio feedback correction coefficient α is relatively large. If it can be considered that the effect of the calibration is satisfied, it is determined whether the calibration execution condition is satisfied.

  Specifically, when all of the “steady condition”, “purge valve accuracy condition”, and “purge influence condition” conditions shown in FIG. 11 are satisfied, it is determined that the calibration execution condition is satisfied, and one of these conditions is determined. If none of them is established, it is determined that calibration cannot be performed.

  “Steady conditions” include, for example, misfire conditions (the engine 10 has not misfired), fuel cut conditions (the fuel cut of the engine 10 has not been performed), blow-by conditions (no blow-by gas), Conditions such as EGR condition (exhaust gas recirculation rate is constant), throttle opening area and engine rotation speed condition (throttle opening area and engine rotation speed are constant), purge rate condition (purge rate is constant) It is. When all these conditions are satisfied and the air-fuel ratio disturbance other than purge is small, it is determined that the steady condition is satisfied.

  The “purge valve accuracy condition” is, for example, a purge flow rate condition (the purge flow rate is a predetermined amount or more). When the purge flow rate is small, the control accuracy of the purge flow rate is lowered and the calculation accuracy in the calibration is lowered. Therefore, when the purge flow rate is smaller than the predetermined amount, it is determined that the purge valve accuracy condition is not satisfied.

  “Purge influence condition” refers to, for example, purge establishment condition (purging being performed), purge concentration condition (purge gas concentration is higher than a predetermined concentration, for example, α change amount per purge rate 1% is 1 % Or more), and a purge rate condition (the purge rate is a predetermined value or more, for example, the purge rate is 30% or more). When all of these conditions are satisfied and the influence of the purge on the air-fuel ratio is relatively large, it is determined whether the purge influence condition is satisfied.

  FIG. 12 is an explanatory diagram of a method for determining whether or not the calibration interval is being restricted in step S5.

  In the air-fuel ratio control, as described above, the output signal of the oxygen sensor (O2 sensor) 36 is fed back to control the injection amount of the fuel injection valve 34. Therefore, the next control is not executed until the combustion gas from the fuel controlled this time is detected. If the next control is executed before the combustion gas from the fuel controlled this time is detected, the feedback control will not be established. The speed from the current control to the next control is called the air-fuel ratio feedback control speed.

  Therefore, even if the calibration execution condition is satisfied, the calibration is executed at an interval time shorter than the air-fuel ratio feedback control described above, that is, the calibration is executed at a speed faster than the air-fuel ratio feedback control speed. Therefore, the purge control interferes with the air-fuel ratio feedback control and inhibits the accurate air-fuel ratio feedback control.

  Therefore, the speed (calibration speed) from the previous calibration to the current calibration is made slower than the air-fuel ratio feedback control speed.

  The air-fuel ratio feedback control speed increases as the intake air amount increases and the combustion gas flow rate increases. Therefore, the limit value of the calibration speed is preferably increased as the amount of intake air increases, as indicated by the broken line in FIG. As another method, as indicated by the alternate long and short dash line in FIG. 12, the speed obtained from the minimum value of the intake air amount may be used as the limit value.

  FIG. 13 is a flowchart for explaining the contents of a desorption amount calculation routine using a canister model.

  In step S71, the controller 100 calculates the current value Y of the amount of fuel adsorbed by the canister 10 according to the following equation (3).

  In step S72, the controller 100 calculates the activated carbon temperature T by the following equation (4).

  This activated carbon temperature calculation formula is composed of past temperature (right side first term), temperature drop due to desorption (right side second term), and temperature rise due to heat transfer (right side third term). The activated carbon temperature T is calculated in this way because the desorption index n (T) in the following equation (5) is affected by the activated carbon temperature T, and particularly when the desorption amount is large, the decrease in the activated carbon temperature T is calculated. This is because the influence of this on the fuel desorption characteristics in the canister 10 cannot be ignored.

  In step S73, the controller 100 calculates the desorption amount Dgk at the reference purge flow rate according to the following equation (5).

  This equation (5) applies the idea of the adsorption / desorption phenomenon (Freundlich's equation) to the canister 10 desorption phenomenon, thereby expressing the fuel desorption characteristics from the canister 10 almost accurately. be able to. The Freundlich equation is described in “Theory on the Surface II” (Maruzen, Tsukada), p.25-p.27, p.108-p115.

  In step S74, the controller 100 calculates the desorption amount by the following equation (6).

  The desorption amount calculation formula (6) corresponding to the purge flow rate calculates the desorption amount Dg by linear approximation since the purge flow rate and the desorption amount are substantially proportional. Here, the amount of desorption at the reference flow rate is obtained from equation (5), and the amount of desorption is calculated by multiplying this by the purge flow rate in equation (6), but equations (5), (6) May be combined into one expression.

  Therefore, the canister model is constituted by the above equations (3) to (6), and this canister model is shown in FIG. 14 as a control block diagram. The canister model includes an adsorption amount calculation unit B71, an activated carbon temperature calculation unit B72, a reference desorption amount calculation unit B73, and a flow rate equivalent desorption amount calculation unit B74, and each part corresponds to the equations (3) to (6), respectively. .

  FIG. 15 is a flowchart for explaining the contents of the fuel injection amount setting routine.

  In step S81, the controller 100 calculates the purge correction coefficient FHOS based on the estimated desorption amount and the intake air flow rate. When the amount of fuel desorbed from the canister 10 and sucked into the engine 10 increases, the air-fuel ratio of the engine 10 shifts to the rich side, and the air-fuel ratio feedback correction coefficient α changes to the small side in order to restore this. In order to prevent this, a coefficient for reducing the fuel injection amount in advance is a purge correction coefficient FHOS. Accordingly, 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 sucked into the engine 10. The calculated correction coefficient FHOS is sequentially stored in a predetermined data storage location (see FIG. 18) of the controller 21.

  In step S82, the controller 100 performs delay correction composed of dead time correction and smoothing processing on the purge correction coefficient FHOS. The dead time correction is performed because there is a delay according to the transition speed of the purge gas and the distance between the purge valve 14 and the cylinder of the engine 10 until the purge gas reaches the cylinder of the engine 10 after the purge valve 14 is opened. It is. The reason why the annealing process is performed is that there is fuel diffusion until the fuel desorbed from the canister 10 reaches the cylinder of the engine 10. A specific correction method will be described later.

  In step S83, the controller 100 obtains the fuel injection amount (fuel injection pulse width Ti) by correcting the reference pulse width Tion with the air-fuel ratio feedback correction coefficient α and the purge correction coefficient FHOS. Specifically, it is calculated by the following equation (7).

  The reference pulse width Tion is set according to the intake air flow rate, the number of cylinders, and the like so as to achieve a target air-fuel ratio.

  The air-fuel ratio feedback correction coefficient α is set to 100% (= 1) when the output of the oxygen sensor (O2 sensor) 36 is at the slice level (that is, the detected air-fuel ratio is the stoichiometric air-fuel ratio), and is less than the slice level. When it is large (ie, the detected air-fuel ratio is rich), it is set to a value smaller than 100%, and when it is smaller than the slice level (ie, the detected air-fuel ratio is lean), it is set to a value larger than 100%.

  The invalid pulse width TB is for correcting an operation delay until the valve is opened and fuel is injected when a drive voltage is applied to the fuel injection valve 15.

  FIG. 16 is a flowchart for explaining the contents of the delay correction processing routine.

  In step S <b> 821, the controller 100 detects the intake air flow rate from the output of the air flow meter 9.

  In step S822, the controller 100 refers to the characteristic table shown in FIG. As the intake air flow rate increases, the intake air flow rate increases and the dead time decreases.

  In step S823, the controller 100 refers to the characteristic table shown in FIG. As the intake air flow rate increases and the intake air flow rate increases, the rate at which the desorbed fuel diffuses also increases, so the smoothing coefficient increases.

  In step S824, the controller 100 calculates a purge gas moving speed equivalent value from the dead time. Specifically, it is calculated as the reciprocal of the dead time obtained in step S822.

  In step S825, the controller 100 reads the purge correction coefficient FHOS stored in the data storage location (see FIG. 18) of the controller 21 corresponding to the distance from the purge valve 14 to the cylinder of the engine 10.

  In step S826, the controller 100 shifts the data to the cylinder side by the value corresponding to the purge gas moving speed.

  In step S827, the controller 100 obtains an average value of the data overflowed from the data storage location due to the data shift.

  In step S828, the controller 100 performs an annealing process on the average value of the overflow data obtained in step S827 using the smoothing coefficient obtained in step S822. Note that the annealing process is a general first-order delay system, and the degree of annealing increases as the annealing coefficient decreases.

  FIG. 18 is an explanatory diagram of an outline of dead time correction in delay correction. In the figure, black circles indicate data before shifting, and white circles indicate data after shifting.

  As shown in FIG. 18, the memory of the controller 21 has a data storage location corresponding to the distance from the purge valve 14 to the cylinder of the engine 10.

  The correction coefficient FHOS calculated according to the amount of fuel desorbed from the canister 10 is sequentially stored in the data storage location. In the dead time correction, these data are shifted to the cylinder side by an amount corresponding to the purge gas transfer speed (reciprocal of the dead time). The data overflowed from the data storage location when shifted is the correction coefficient corresponding to the purge gas that has reached the cylinder. Then, using the value obtained by subjecting the average value of the overflowed data to the smoothing process, the fuel injection pulse width Ti is corrected in step S83. In this way, by combining the dead time correction and the annealing process, the arrival delay of the purge gas can be corrected accurately.

  According to the present embodiment, the calibration value of the fuel adsorption amount of the canister model is calculated based on the air-fuel ratio feedback correction coefficient α, the weighted average process is performed on the calibration value, and the weighted average process is performed when the calibration condition is satisfied. The amount of fuel adsorbed in the canister model was calibrated using the calibration value. The air-fuel ratio feedback correction coefficient α is set depending on whether the output of the oxygen sensor (O2 sensor) is larger or smaller than the slice level, but is easily affected by disturbance. Therefore, in this embodiment, the calibration value of the fuel adsorption amount of the canister model is always calculated based on the air-fuel ratio feedback correction coefficient α, and the calibration value is subjected to a weighted average process. By doing in this way, the intensity | strength with respect to a disturbance can be increased.

  If the calibration speed is set faster than the air-fuel ratio feedback control speed, the air-fuel ratio feedback control becomes inaccurate. Therefore, the calibration speed was set to be slower than the air-fuel ratio feedback control speed. If the calibration speed is set to be slower than the slowest speed of the air-fuel ratio feedback control speed, the adaptation man-hour becomes unnecessary.

  The present invention is not limited to the embodiment described above, and various modifications and changes can be made within the scope of the technical idea, and it is obvious that these are equivalent to the present invention.

It is a whole block diagram of an engine provided with the evaporative fuel processing apparatus by this invention. It is a main flowchart explaining operation | movement of the evaporative fuel processing apparatus by this invention. It is a flowchart explaining the content of the target purge rate setting routine. It is a flowchart explaining the content of the target purge rate setting routine which is not based on the adsorption state of a canister. It is a figure which shows the characteristic table for calculating | requiring the purge rate change amount according to the difference of an air fuel ratio feedback deviation. It is a flowchart explaining the content of the target purge rate setting routine based on the adsorption state of a canister. It is a flowchart explaining the content of the purge change amount limit value setting routine. It is a figure which shows the characteristic table for estimating the error of a purge air fuel ratio. It is a flowchart explaining the content of the maximum purge rate setting routine. It is a flowchart explaining the content of the adsorption amount calculation routine based on an air-fuel ratio feedback correction coefficient. It is explanatory drawing of the determination method of the calibration implementation condition in step S4. It is explanatory drawing of the determination method whether it is during the calibration interval restriction | limiting in step S5. It is a flowchart explaining the content of the desorption amount calculation routine by a canister model. It is a control block diagram which shows a canister model. It is a flowchart explaining the content of the fuel injection amount calculation routine. It is a flowchart explaining the content of a delay correction process routine. It is a figure which shows the characteristic table for calculating | requiring dead time and a smoothing coefficient. It is explanatory drawing of the outline | summary of the dead time correction | amendment in delay correction | amendment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Evaporated fuel processing apparatus 10 Canister 14 Purge valve 20 Fuel tank 22 Piping 30 Engine 31 Intake passage 100 Controller Step S2 Calibration value calculation means Step S3 Weighted average processing means Step S6 Calibration means Step S7 Canister model Steps S8 and S9 Purge control means

Claims (3)

A canister that adsorbs the evaporated fuel generated in the fuel tank;
A purge valve that opens and closes a pipe that communicates the canister and the intake passage of the engine;
An evaporative fuel processing apparatus comprising:
A canister that calculates an adsorption amount of evaporated fuel adsorbed to the canister based on the previous value of the fuel desorption amount, and calculates a current value of the fuel desorption amount desorbed from the canister based on the calculated fuel adsorption amount Model and
A purge control means for opening the purge valve at the time of purging, and reducing the fuel desorption amount calculated by the canister model from the fuel supplied to the engine;
Calibration value calculation means for calculating a calibration value of the fuel adsorption amount of the canister model;
A weighted average processing means for performing a weighted average processing on the calibration value;
A calibration means for calibrating the fuel adsorption amount of the canister model using the weighted average calibration value when the calibration condition is satisfied and the calibration interval is not limited ;
The evaporative fuel processing apparatus characterized by having. The calibration means limits the calibration interval when the speed from the previous calibration to the current calibration is faster than the speed of the air-fuel ratio feedback control.
The evaporative fuel processing apparatus according to claim 1 . The calibration means limits the calibration interval when the speed from the previous calibration to the current calibration is faster than the slowest speed of the air-fuel ratio feedback control speed,
The evaporative fuel processing apparatus according to claim 1 .

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