JP4909399B2 - Canister purge control method for internal combustion engine - Google Patents

Description

The present invention is Ru engages the canister purge control method for an internal combustion engine.

  In general, some internal combustion engines perform not only fuel supply by a fuel injection valve but also vapor purge processing for releasing and supplying evaporated fuel (evaporative gas) generated in a fuel tank to an intake system. In the evaporative purge process, it is known that after the evaporative gas is collected and adsorbed by the canister, the outside air is introduced into the canister and then released to the intake system.

  In this case, since it is necessary to perform air-fuel ratio control in which the fuel from the fuel injection valve and the fuel from the evaporation purge process are combined, various technologies relating to the canister purge control device in consideration of the HC concentration of the evaporation gas have been proposed. .

  In order to suppress fluctuations in the air-fuel ratio due to the evaporation purge process, the purge flow rate is set as a purge rate with respect to the intake air amount to the engine. By controlling, the purge flow rate is controlled to be a constant ratio (purge rate) of the amount of air passing through the throttle valve, thereby preventing adverse effects on the air-fuel ratio feedback.

  In addition, the purge concentration is estimated from the deviation of the air-fuel ratio feedback correction coefficient during purging from the air-fuel ratio feedback correction coefficient during purging and the purge rate, and the fuel vapor being purged is estimated from the concentration value and the purge rate. By calculating the increase and correcting the fuel injection valve output value for opening the fuel injection valve (evaporation correction), the amount of fuel vapor that is being purged is calculated from the fuel supplied by normal fuel control during the purge stop. By subtracting the increment, stable air-fuel ratio control is realized by controlling the air-fuel ratio feedback correction coefficient to a median value (Patent Document 1).

JP 2003-65165 A

However, when the concentrated evaporative gas desorbed from the canister is introduced at the beginning of the purge, the evaporative gas concentration is constant. Since it is proportional to the amount of air, fluctuations in the air-fuel ratio can be suppressed by subtracting the fuel corresponding to the increase in fuel vapor gas. However, after the purge has progressed sufficiently, there is a difference between the fresh air used for purging that has not been measured by the air flow meter and the fuel subtraction correction value for the fuel vapor gas increase, and the air-fuel ratio is There has been a problem of adverse effects such as deteriorating lean and worsening exhaust emissions.

The present invention was made in view of such problems, and an object is that the purge to prevent air-fuel ratio lean caused by fresh air after sufficiently proceed.

To achieve the above object, a canister purge control method for an internal combustion engine of the present invention includes a fuel vapor recovery means for recovering the evaporated fuel in the fuel tank, purging the fuel that has been recovered in the fuel vapor recovery means into the combustion chamber a method of controlling a canister purge internal combustion engine having a collecting fuel purge means, for, after the purge condition is satisfied, when changing stepwise the purge rate to the purge rate for the first time, than the previous purge air when more of this purge air-fuel ratio becomes rich, it is characterized in that make increase the purge rate.

Also, when the purge air-fuel ratio of this time is leaner than the previous purge air-fuel ratio and fuel vapor gas is generated by the purge, the purge rate is set to a fixed value, and when the generation of the vapor gas stops, the purge period is set. It is characterized by termination .

The first purge is performed at a predetermined purge rate, and the next and subsequent purge rates are determined based on the previous purge rate.

Further, the increase in the purge rate is determined based on the increase rate of the fuel vapor gas.

Further, after the purge period is completed, after a predetermined purge stop time has elapsed, characterized in that to resume the purging.

  The present invention can prevent the deterioration of the air-fuel ratio by increasing the purge rate in a state where the increase rate of the fuel vapor gas is proportional to the purge rate and subtracting the fuel injection amount accompanying the increase in the fuel vapor gas. Since purge can be performed at a high purge rate when the purge concentration is high and purge can be performed at a low purge rate when the purge concentration is low, deterioration in operability and exhaust gas emission is suppressed, and efficient purge is performed. Thereby, the transpiration prevention performance of fuel vapor gas can be improved.

1 is an overall configuration diagram of an engine system including a canister purge control device for an internal combustion engine according to an embodiment. The internal block diagram of the control unit provided with the canister purge control apparatus. The control block diagram of the canister purge control apparatus of this embodiment. The flowchart which shows the control operation in the air fuel ratio learning period in the canister purge control apparatus of this embodiment. The flowchart which shows the control operation | movement of the purge period in the canister purge control apparatus of this embodiment. 6 is a flowchart showing a control operation for calculating a purge air-fuel ratio in the canister purge control device of the present embodiment. Explanatory drawing of target purge rate calculation of the purge period by the purge rate calculation means in the canister purge control apparatus of this embodiment. The maximum purge rate map of the purge period by a purge rate calculation means. The flowchart of the air fuel ratio feedback value calculation by the air fuel ratio feedback means in the canister purge control apparatus of this embodiment. The flowchart of the air fuel ratio learning value calculation by the air fuel ratio learning means in the canister purge control apparatus of this embodiment. The flowchart of the fuel-injection correction value calculation by the fuel-injection correction | amendment means in the canister purge control apparatus of this embodiment.

  Hereinafter, an embodiment of a canister purge control device for an internal combustion engine according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows an overall configuration of an engine system provided with a canister purge control device of this embodiment. The internal combustion engine 1 is a V-type 6-cylinder engine and includes a cylinder group having three cylinders for one bank. The cylinder groups 27a and 27b of the banks A and B are provided with intake manifolds 11a and 11b and exhaust manifolds 21a and 21b. The intake manifolds 11a and 11b are configured as branched intake pipes.

  The intake manifolds 11 a and 11 b are connected to the air cleaner 2 via a surge tank 9 and a throttle body 5, and the air sucked from the inlet 3 of the air cleaner 2 passes through the intake duct 4 and the throttle body 5. to go into. The intake duct 4 has an air flow meter (AFM) 7 for detecting the amount of intake air, the throttle body 5 has a throttle valve 6 for controlling the air flow rate, and the opening of the throttle valve 6 is measured. A throttle sensor 8 is installed at each appropriate position. Further, the throttle body 5 is provided with an auxiliary air valve (ISC valve) 10 that bypasses the throttle valve 6, and the air amount is controlled so that the idling speed is kept constant. The air that has passed through the throttle body 5 enters the surge tank 9, is distributed by the intake manifolds 11a and 11b, and enters the cylinder groups 27a and 27b.

  On the other hand, the fuel in the fuel tank 13 is sucked and pressurized by the fuel pump 26, passes through the fuel filter 15, is installed in the intake manifolds 11 a and 11 b, and is a fuel injection that is an aspect of a means for injecting fuel into the combustion chamber. It is supplied to the valves (injectors) 12a, 12b.

  Here, the evaporated fuel (evaporative gas) generated in the fuel tank 13 is adsorbed by the canister 40 which is one mode of the fuel vapor recovery means for recovering the evaporated fuel through the pipe 46 and is temporarily recovered. The canister 40 is provided with an air introduction port 45 for introducing outside air. During the operation of the internal combustion engine 1, the recovered fuel passes through a pipe 47 and a canister purge valve 41, which is one embodiment of a recovered fuel purge unit that discharges fuel into the combustion chamber, together with the air from the air inlet 45, and then surges. After being led to the tank 9, it is supplied to the cylinders 27a and 27b, and the exhaust gas is prevented from being discharged to the outside. One purge valve 41 is arranged at a position equidistant from the intake manifolds 11a and 11b. A negative pressure is introduced by energizing the purge valve 41, and the purge flow rate is adjusted and controlled. The purge flow rate is controlled as a purge rate that is proportional to the amount of intake air to the internal combustion engine 1, and prevents adverse effects on air-fuel ratio feedback, as will be described later.

The air-fuel mixture in the cylinder groups 27a and 27b is ignited and burned by the spark plugs 18a and 18b, then sent to the exhaust manifolds 21a and 21b, and purified by the front catalysts 23a and 23b and the main catalyst 24, and then the muffler 25 It is discharged via. At appropriate positions of the exhaust manifolds 21a and 21b, O ₂ sensors 22a and 22b, which are one mode of means for detecting the engine air-fuel ratio, are arranged.

Cam angle sensor 17, air flow meter (AFM) 7, throttle sensor 8, O ₂ sensors 22 a and 22 b, and temperature of internal combustion engine 1, which are basic signals for detecting engine speed, controlling fuel injection timing and ignition timing A signal indicating the engine state such as the water temperature sensor 20 for detecting the engine temperature is input to the engine control device (control unit) 30 including the purge control device 30a. Based on these signals, the control unit 30 performs predetermined arithmetic processing to perform various controls such as air-fuel ratio control, and outputs each drive signal to the injectors 12a, 12b,..., The ISC valve 10, the canister purge valve 41, etc. To do.

FIG. 2 shows the internal configuration of the control unit 30. The control unit 30 includes an MPU 31, a read / write RAM 32, a read-only ROM 33, and an I / O LSI 34 that controls input / output, and is connected to each other via buses 35, 36, and 37, and exchanges data. Specifically, the MPU 31 indicates the engine state such as the cam angle sensor 17, the air flow meter (air flow meter) 7, the throttle sensor 8, the O ₂ sensors 22 a and 22 b, and the water temperature sensor 20 that detects the temperature of the internal combustion engine 1. Signals to be received are received from the I / OLSI 34 through the bus 37, the processing contents stored in the ROM 33 are sequentially called to perform predetermined processing, stored in the RAM 32, and then again from the I / OLSI 34 to the six injectors 12a,. Each drive signal is output to the purge valve 41 and the like.

  FIG. 3 is a control block diagram of the purge control device 30a. The purge control device 30a switches between a base air-fuel ratio learning process due to variations in the internal combustion engine 1 itself performed for each bank A and B and a purge process for releasing the evaporated gas adsorbed by the canister 40 to the intake system. Processing is in progress.

  Specifically, the purge control device 30a includes a purge period / air-fuel ratio learning period switching means 30A, air-fuel ratio feedback means 30Ba, 30Bb on the bank A side or bank B side, and means 30a1 for performing fuel purge flow rate control. Evaporative correction calculation means 30Ia, 30Ib on the bank A side and bank B side, air-fuel ratio learning means 30Da, 30Db on the bank A side or bank B side, and fuel injection correction means 30Ga, 30Gb on the bank A side or bank B side The fuel purge flow rate control means 30a1 includes the bank A side or bank B side purge air / fuel ratio estimation means 30Ca, 30Cb, purge air / fuel ratio comparison / adjustment means 30E, and control purge rate calculation means 30F. Consists of.

As will be described later, the purge period / air-fuel ratio learning period switching means 30A determines whether or not predetermined conditions such as an air-fuel ratio learning condition and a purge condition are satisfied based on output signals from the O ₂ sensors 22a and 22b. Then, the period of the air-fuel ratio learning process by the air-fuel ratio learning means 30Da, 30Db on the bank A side or the bank B side, and the purge air-fuel ratio estimation means 30Ca, 30Cb on the bank A side or bank B side of the means 30a1 for performing the purge flow rate control The period of the purge process by is switched.

The air-fuel ratio feedback means 30Ba, 30Bb on the bank A side or the bank B side is arranged so that the actual air-fuel ratio of the exhaust gas discharged from the combustion chamber by the O ₂ sensors 22a, 22b becomes the target air-fuel ratio. Air-fuel ratio feedback control is performed for each B, air-fuel ratio feedback values αa and αb are calculated, and the purge air-fuel ratio estimating means 30Ca and 30Cb on the bank A side or the bank B side, and the air on the bank A side or the bank B side are calculated. Output to the fuel ratio learning means 30Da, 30Db and the fuel injection correction means 30Ga, 30Gb on the bank A side or bank B side.

  The air-fuel ratio learning means 30Da, 30Db on the bank A side or the bank B side is set so that the correction amount by the air-fuel ratio feedback means 30Ba, 30Bb on the bank A side or the bank B side becomes a predetermined value in order to perform air-fuel ratio feedback control. The learning correction values αma and αmb are calculated based on the air-fuel ratio feedback values αa and αb, and are output to the fuel injection correction means 30Ga and 30Gb on the bank A side or the bank B side.

  The means 30a1 for performing the purge flow rate control of the fuel has the above-described configuration. As will be described later, when the air-fuel ratio feedback control by the air-fuel ratio feedback means 30Ba, 30Bb on the bank A side or the bank B side is stopped, The control of the purge valve 41 is stopped.

  The purge air-fuel ratio estimating means 30Ca and 30Cb on the bank A side and the bank B side estimate the purge air-fuel ratio AFevp based on the air-fuel ratio feedback values αa and αb and the purge rate Kevp, and the purge air-fuel ratio comparison adjusting means 30E and the evaporator It outputs to correction | amendment calculation means 30Ia and 30Ib. As will be described later, the purge air-fuel ratio AFevp is a basis for calculating the estimated value PDEN of the evaporation concentration. Hereinafter, the PDEN will be described as being equivalent to the purge air-fuel ratio.

  The purge air-fuel ratio comparison and adjustment means 30E compares the purge air-fuel ratios AFevp of the banks calculated by the purge air-fuel ratio estimation means 30Ca and 30Cb on the bank A side and the bank B side, and as will be described later, The maximum value of the deviation from the fuel ratio, more specifically, the maximum value of the absolute value of the deviation is output to the control purge rate calculation means 30F.

  Based on the purge air-fuel ratio AFevp calculated by the purge air-fuel ratio comparison adjusting means 30E, the air flow rate Qtvo of the throttle valve 6, and the purge flow rate Qevp of the canister 40, the control purge rate calculation means 30F The control purge rate Kevp is calculated and a drive signal is output to the canister purge valve 41 to release the evaporated gas to the cylinder groups 27a and 27b. Further, the calculated control purge rate Kevp is output to the evaporation correction calculating means 30Ia and 30Ib.

  The evaporation correction calculation means 30Ia and 30Ib on the bank A side and the bank B side include the purge air-fuel ratio AFevp of each bank calculated by the purge air-fuel ratio estimation means 30Ca and 30Cb on the bank A side and the bank B side, and the control purge rate. The evaporation correction values KLMNTCA and KLMNTCB are calculated based on the control purge rate Kevp calculated by the calculation means 30F, and output to the fuel injection correction means 30Ga and 30Gb on the bank A side or the bank B side.

The fuel injection correction means 30Ga and 30Gb on the bank A side or the bank B side correct the basic fuel injection amount based on the engine speed Ne and the intake air amount Qa, and the air-fuel ratio feedback on the bank A side and the bank B side. Air-fuel ratio feedback values αa, αb by means 30Ba, 30Bb, learning correction values αma, αmb by air-fuel ratio learning means 30Da, 30Db on bank A side and bank B side, and evaporation correction calculation on bank A side and bank B side The basic fuel injection amount is corrected based on the evaporation correction values KLMNTCA and KLMNTCB by means 30Ia and 30Ib, etc., and output to the injectors 12a, 12b.

  4 and 5 are operation flowcharts from the purge period / air-fuel ratio learning period switching means 30A. FIG. 4 shows the operation during the air-fuel ratio learning period. In step 100, it is determined whether or not the air-fuel ratio feedback conditions of the banks A and B are satisfied after the engine is started. If the air-fuel ratio feedback state is not in the fuel cut state or the load is stable, that is, if YES, the routine proceeds to step 101. On the other hand, when the air-fuel ratio feedback condition is not satisfied, this determination operation is repeated.

  In step 101, it is determined whether or not the air-fuel ratio learning conditions of the banks A and B are satisfied. If the air-fuel ratio learning state is in effect, for example, the load is stable, that is, if YES, the process proceeds to step 102. On the other hand, this determination operation is repeated when the air-fuel ratio learning condition is not satisfied.

  In step 102, it is determined whether or not the initial base air-fuel ratio learning for the banks A and B has been completed. If not, that is, if NO, the process proceeds to step 103 as the base air-fuel ratio learning period, and the process proceeds to step 104. move on. In step 104, when the air-fuel ratio learning is performed, the learning number counter KLCONTA of the corresponding area is incremented by 1, and the process proceeds to step 105. On the other hand, when the base air-fuel ratio learning is completed, that is, when the determination is YES, the routine proceeds to step 108.

  In step 105, it is determined whether or not the learning number counter has reached the predetermined number KLCNT. If the learning number counter has reached the predetermined number KLCNT, that is, if YES, it is determined in step 106 that the initial base air-fuel ratio learning has ended, and the process proceeds to step 107. Proceed to complete a series of operations. On the other hand, when the cumulative number of air-fuel ratio learning is smaller than KLCNT in step 105, the air-fuel ratio learning period has not ended yet, so the routine proceeds to step 103 and the above operations are repeated. The air-fuel ratio learning period is set to a period proportional to the rich and lean cycles.

  On the other hand, when the initial base air-fuel ratio learning of the banks A and B is completed in step 102, it is determined in step 108 whether or not the purge period has ended. If the purge period has ended, that is, if YES, the routine proceeds to step 109 as the base air-fuel ratio learning period, and then proceeds to step 110. However, when the purge period has not ended, the process proceeds to step 111 as the purge period.

In step 110, the air-fuel ratio feedback means 30Ba, 30Bb determines whether the rich and lean cycles of the O ₂ sensors 22a, 22b have reached the predetermined number of times LRNCNT. Sometimes, the base air-fuel ratio learning period ends and the routine proceeds to step 107. On the other hand, if the predetermined number of times LRNCNT has not been reached, that is, if NO, the base air-fuel ratio learning period is set.

  FIG. 5 shows the operation during the purge period. In step 200, it is determined whether or not the air-fuel ratio learning of the bank A is completed. If this is completed, that is, if YES, the process proceeds to step 201. On the other hand, when not finished, the air-fuel ratio learning period is continued. In step 201, it is determined whether or not the air-fuel ratio learning of the bank B is completed. If this is completed, that is, if YES, the process proceeds to step 202. On the other hand, when not finished, the air-fuel ratio learning period is continued.

  In step 202, it is determined whether purge conditions such as the elapsed time after engine start, the engine coolant temperature, and the load are satisfied. If these conditions are satisfied, that is, if YES, the routine proceeds to step 203 as the purge period. This operation is repeated until this condition is satisfied.

  When the purge period is reached in step 203, the base air-fuel ratio learning is prohibited in step 204. In step 205, it is determined whether it is the first purge period before the evaporation concentration that is the basis of the purge air-fuel ratio estimation is determined. If the purge period is YES, that is, if YES, the routine proceeds to step 206 where the canister purge valve 41 is opened at a predetermined fixed purge rate, and the routine proceeds to step 207.

  Thus, immediately after the internal combustion engine 1 is started, learning of the air-fuel ratio is started, and when the learning of the air-fuel ratio has been performed a predetermined number of times or when the learning value has converged, Transfer to control. The target purge rate will be described later.

  In step 207, the purge air-fuel ratios PDENA and PDENB of the banks A and B are estimated by the purge air-fuel ratio estimating means 30Ca and 30Cb, and the process proceeds to step 208. A method for estimating the purge air-fuel ratio will be described later.

  In step 208, evaporation correction values KLMNTCA and KLMNTCB for the banks A and B are calculated from the control purge rate CTRTCTL and the purge air-fuel ratios PDENA and PDENB, and the process proceeds to step 209. In step 209, the fuel injection pulses TiA and TiB of the banks A and B are corrected by the evaporation correction values KLMNTCA and KLMNTCB.

In step 210, the purge air-fuel ratio estimated in step 207 is compared with the previous purge air-fuel ratio. If the current purge air-fuel ratio is not leaner than the previous time, that is, if NO, the purge rate and the fuel vapor The increase rate of the gas maintains a proportional relationship, and the process proceeds to step 211 to further increase the purge rate. If the current purge air-fuel ratio is leaner than the previous time in step 210, that is, if YES, the increase rate of the fuel vapor gas is low, and the purge rate and the increase rate of the fuel vapor gas maintain a proportional relationship. If not, go to step 212.
In a state where the concentration of the evaporation gas is high, if the purge rate is set to a large value, the evaporation gas with a high concentration is drawn into the engine all at once. Therefore, it is necessary to set the purge rate small when the concentration is high. However, in this case, since a large amount of purge processing cannot be performed, the evaporation gas leaks, and there is a problem that it is difficult to improve the evaporation prevention performance of the evaporation gas. With the above-described configuration, it is possible to increase the purge rate even when high-concentration fuel vapor gas is generated, and to improve the evaporation gas evaporation prevention performance.

  In step 212, if the generation of fuel vapor gas based on the purge air-fuel ratio is NO, that is, if the evaporation gas is purged, the air-fuel ratio can be made rich and the fuel injection amount can be reduced. The rate is fixed at the previous purge rate. This is repeated until the generation of fuel vapor gas at the current purge air-fuel ratio becomes 0 or less at step 212. When the generation of fuel vapor gas at the current purge air-fuel ratio becomes 0 or less, the routine proceeds to step 214, where a series of operations are performed. Exit.

In step 215, the purge stop time is measured, and the process proceeds to step 216. In step 216, the purge stop time is measured. If the predetermined purge stop time has elapsed, that is, if YES, the process proceeds to step 217, and the purge is restarted (proceed to step 203). On the other hand, if NO in step 216, the measurement of the purge stop time is repeated until a predetermined purge stop time elapses.
As described above, according to this embodiment, when the purge rate at the purge after the purge introduction is proportional to the increase rate of the fuel vapor gas based on the purge air-fuel ratio with respect to the purge rate at the purge introduction, the purge rate is set. While increasing in steps, the basic fuel injection amount is corrected based on the purge air-fuel ratio, so the purge rate can be increased without the air-fuel ratio deviating richly, and the purge amount while maintaining the air-fuel ratio appropriately Therefore, the evaporation gas can be prevented from leaking and the evaporation prevention performance of the evaporation gas can be improved.

  FIG. 6 is an operation flowchart for calculating the purge air-fuel ratio PDEN. In step 300, it is determined whether or not the bank A is performing air-fuel ratio feedback. If feedback is being performed, that is, if YES, the process proceeds to step 301. If not, this operation is repeated.

In step 301, it is determined whether the bank B is performing air-fuel ratio feedback. If feedback is in progress, that is, if YES, the process proceeds to step 302. If not, the process returns to step 300. That is, when the air-fuel ratio feedback control by any of the air-fuel ratio feedback control means 30Ba, 30Bb based on any one output signal of the O ₂ sensors 22a, 22b is stopped, the control of the purge valve 41 is stopped. .

  In step 302, it is determined whether the purge period is in progress. If the purge period is YES, that is, if YES, the process proceeds to step 303, and if not in the purge period, this operation is repeated.

  In step 303, the purge air-fuel ratio estimating means 30Ca, 30Cb calculates the purge air-fuel ratios PDENA, PDENB described above, and in step 304, the maximum values of the purge air-fuel ratios PDENA, PDENB in bank A and bank B, more specifically. Is calculated as the purge air-fuel ratio PDEN.

  7 and 8 are explanatory diagrams of the control purge rate calculation means 30F of the means 30a1 for controlling the purge flow rate. The purge rate calculation means 30F first determines a target purge rate, and then calculates a control purge rate. As shown in FIG. 7, the target purge rate is purged at a predetermined purge rate for the first time, and the purge rate for the second time is determined by the purge air-fuel ratio calculated at the initial purge rate. For the second and subsequent times, the purge rate is determined by the rate of increase in the fuel vapor gas with the purge air-fuel ratio. That is, when the purge air-fuel ratio estimated when purging with the predetermined purge rate for the first time is rich and the increase rate of the fuel vapor gas is large, the purge rate is increased larger than the initial purge rate for purging.

  Next, the control purge rate is calculated by the ratio (Qevp / Qa) of the purge flow rate Qevp to the intake air amount Qa of the internal combustion engine 1, thereby obtaining the purge control amount. Here, while the intake air amount Qa varies greatly depending on the running state, the purge flow rate Qevp is limited to the maximum flow rate of the canister purge valve 41, so the control purge rate decreases as the intake air amount Qa increases. Since the purge flow rate Qevp decreases when the suction pipe negative pressure approaches atmospheric pressure, the control purge rate is not maintained constant even in this case. Therefore, as shown in FIG. 8, the control purge rate when the canister purge valve 41 is fully opened (valve DUTY 100%) is set in advance with reference to the maximum purge rate map obtained from the engine speed and the engine load. Is kept constant.

  Thus, the control duty for the canister purge valve 41 can be obtained by dividing the control purge rate by the control purge rate calculation means 30F by the maximum purge rate. Since it is difficult to flow a purge flow rate equal to or higher than the maximum purge rate, the control purge rate by the control purge rate calculation means 30F is limited by the maximum purge rate.

FIG. 9 is a flowchart for calculating the air-fuel ratio feedback values αa and αb by the air-fuel ratio feedback means 30Ba and Bb. Since the air-fuel ratio feedback performs the same operation for the banks A and B, only one operation will be described below. In step 600, the output of the O ₂ sensor 22 is read. In step 601, the rich / lean determination of the O ₂ sensor 22 is performed. If the output is Rich, the process proceeds to step 602. If the output is Lean, the process proceeds to step 605. When Rich, that is, the engine air-fuel ratio is small, the output of the O ₂ sensor 22 is about 0.8 v. On the other hand, when Lean, that is, the engine air-fuel ratio is large, the output of the O ₂ sensor 22 is about 0.2 v. Therefore, Rich determination or Lean determination is made by comparing this output value with a predetermined value (0.5 v).

  In step 602, the previous processing state is checked. That is, it is determined whether or not the previous time was Rich. If the previous time was NO that is not Rich, that is, if the previous time was in the Lean state, the current state changed from the Lean to the Rich state. As shown in (5), proportional control (subtraction) is performed on the air-fuel ratio feedback value α, and the routine proceeds to step 608.

[Equation 1]
α = α-ARP ………… (5)

  Here, ARP is a proportional correction amount at the time of Rich, and data is stored in the ROM 33. On the other hand, if the previous time is the Rich state in step 602, that is, if YES, the process proceeds to step 604, where integral control (subtraction) is performed as shown in equation (6), and the process proceeds to step 608.

[Equation 2]
α = α-ARI ………… (6)

  Here, ARI is an integral correction amount at the time of Rich, and data is stored in the ROM 33. In step 605, the previous processing state is checked in the same manner as in step 602. That is, it is determined whether or not the previous time is Rich. If the previous time is Rich, that is, if YES, the state has changed from Rich to Lean at this time, so the process proceeds to Step 606 and is expressed by Equation (7). Then, proportional control (addition) is performed, and the process proceeds to Step 608.

[Equation 3]
α = α + ALP ………………………… （7）

  Here, ALP is a proportional correction for Lean time, and data is stored in the ROM 33. On the other hand, when the previous time is not the Rich state in step 605, the process proceeds to step 607, where integral control (addition) is performed as shown in equation (8), and the process proceeds to step 608.

[Equation 4]
α = α + ALI ………………………… (8)

  Here, ALI is an integral correction amount at Lean time, and data is stored in the ROM 33. In step 608, each air-fuel ratio feedback value α obtained in step 603, step 604, step 606 or step 607 is stored in the RAM 32, and the process proceeds to step 609. In step 609, the weighted average process is performed in this embodiment. Thus, αave after the averaging process of each air-fuel ratio feedback value α is obtained, and a series of operations is completed.

  Next, the purge air-fuel ratio estimating means 30Ca and 30Cb will be described. Regarding air-fuel ratio learning, the same operation is performed for banks A and B, and therefore only one operation will be described below. First, the effect of the evaporation gas on the air-fuel ratio to the internal combustion engine 1 will be described below. The engine air-fuel ratio AFcy1 due to the air-fuel mixture supplied into the cylinder group 27 is calculated as in equation (9).

[Equation 5]
AFcy1 = (Qtvo + qAevp) / (Qinj + qFevp) (9)

  Here, Qtvo is the amount of air passing through the throttle valve 6, Qinj is the amount of fuel injected by the injector 12, qAevp is fresh air passing through the canister 40, and qFevp is the amount of fuel leaving the canister 40. Further, the purge air-fuel ratio AFevp is calculated as shown in Expression (10).

[Equation 6]
AFevp = (qAevp / qFevp) (10)

  The purge flow rate Qevp that passes through the canister purge valve 41 is expressed by equation (11).

[Equation 7]
Qevp = qAevp + qFevp ……………………………… (11)

  Here, since the engine air-fuel ratio AFcy1 is controlled to be the stoichiometric air-fuel ratio 14.7 in the air-fuel ratio feedback on the system, when the air-fuel ratio feedback value α is set, the equation (12) is obtained.

[Equation 8]
14.7 = (Qtvo + qAevp) / (α × Qinj + qFevp) (12)
When Expression (12) is summarized by the air-fuel ratio feedback value α, Expression (13) is obtained.

[Equation 9]
α = (Qtvo + qAevp) / (14.7 × Qinj) − (qFevp / Qinj) (13)

  Since the fuel injection amount Qinj by the injector 12 is adjusted to be the stoichiometric air-fuel ratio 14.7, if the fuel injection amount Qinj (= Qtvo / 14.7) is deleted from the equation (13), the equation (14 ) Is obtained.

[Equation 10]
α = 1 + (qAevp / Qtvo) − ((14.7 × qFevp) / Qtvo) (14)

  Therefore, Expression (15) is obtained from Expressions (10), (11), and (14).

[Equation 11]
α = 1 + (Qevp / Qtvo) × ((AFevp−14.7) / (AFevp + 1)) (15)

  Therefore, it can be understood from the equation (15) that if the control purge rate (Qevp / Qtvo) can be controlled to be constant, the purge air-fuel ratio AFevp can be calculated based on the air-fuel ratio feedback value α, and the evaporation used for correcting the injection pulse can be calculated. In the correction value KLMNTC, the (AFevp-14.7) / (AFevp + 1) portion of the equation (15) is used as the estimated concentration PDEN of the evaporation concentration, and the deviation (α-1) of the air-fuel ratio feedback value α is controlled purge rate (Qevp Calculated by dividing by / Qa). Next, the correction to the fuel injection amount TI is performed as follows. First, the fuel amount TIEVP for the evaporation is calculated as shown in Expression (16).

[Equation 12]
TIEVP = (Qevp / Qtvo) × PDEN × TP × COEF (16)

Here, TP is a basic fuel pulse width, and COEF is a correction amount.
That is, since the deviation (α-1) of the air-fuel ratio feedback value α indicates the current excess / deficiency of the fuel, the deviation (α-1) is multiplied by the current fuel to be injected (TP × COEF). Thus, the fuel amount TIEVP for the evaporation is calculated. Therefore, it can be seen that even if the canister purge valve 41 is opened and the evaporation gas is discharged to the surge tank 9, the engine air-fuel ratio can be kept constant if the fuel amount TIEVP for the evaporation is reduced from the fuel injection amount TI. This can be expressed as equation (17), and if the base air-fuel ratio learning is accurately performed, the air-fuel ratio feedback value α is considered to converge to around 1.0. If it is arranged as 1.0, it will become like Formula (18). Then, when the evaporation correction value KLMNTTC, which is a correction value of the evaporation density, is used, Equation (19) is obtained.

[Equation 13]
TI = (TP × COEF × α) −TIEV
= (TP × COEF × α) − (Qevp / Qtvo) × PDEN × TP × COEF
= (TP × COEF) × (α− (Qevp / Qtvo) × PDEN) (17)
TI = (TP × COEF) × (1− (Qevp / Qtvo) × PDEN) (18)
TI = (TP × COEF) × (1-KLMNTC) ……………………… (19)
This KLMNTC is (Qevp / Qtvo) × PDEN.

  Therefore, if the fuel injection amount is corrected with the air-fuel ratio correction value KLMNTC obtained from the deviation (α-1) of the air-fuel ratio feedback value α on the basis of the equation (19), the influence of the evaporation can be absorbed. Variations in the air-fuel ratio can be prevented.

  FIG. 10 is a flowchart until the learning correction coefficient αm is updated by the air-fuel ratio learning means 30Da and 30Db. Regarding air-fuel ratio learning, the same operation is performed for banks A and B, and therefore only one operation will be described below. In step 700, the air-fuel ratio learning period by the air-fuel ratio learning unit 30D is confirmed, and the process proceeds to step 701.

  In step 701, the air-fuel ratio feedback means 30B reads the air-fuel ratio feedback value α and proceeds to step 702. In step 702, the air-fuel ratio learning means 30D updates the air-fuel ratio learning correction coefficient αm of the area and updates the series. End the operation.

  FIG. 11 is a flowchart for calculating the actual injection widths Tea and Teb by the fuel injection correction means 30Ga and 30Gb. Regarding the fuel injection setting, since the same operation is performed for each of the banks A and B, only one operation will be described below.

First, in step 800, the engine speed Ne is read and the process proceeds to step 801. In step 801, the intake air amount Qa is read and the process proceeds to step 802. In step 802, the basic fuel is expressed as shown in equation (20). The injection amount Tp is calculated and the routine proceeds to step 803.

[Formula 14]
Tp = Kinj × Qa / Ne ……………………………………………… (20)

  Here, Kinj is an injector injection amount coefficient. In step 803, after reading various correction coefficients COEF, the fuel injection width TIOUT is calculated as shown in equation (21), and the process proceeds to step 804.

[Equation 15]
TIOUT = Tp × COEF ………………………………………… (21)

  Next, in step 804, the air-fuel ratio feedback value α corresponding to the temporary calculated by the air-fuel ratio feedback means 30B is read, and the process proceeds to step 805. In step 805, the purge air-fuel ratio estimation means 30C calculated by the purge air-fuel ratio estimation means 30C. The evaporation correction value KLMNTC for the period is read and the routine proceeds to step 806. In step 806, the air-fuel ratio learning value αm for the learning period calculated by the air-fuel ratio learning means 30D is read and the fuel injection correction means 30G performs fuel injection. The width TIOUT is corrected, and the actual injection width Te is calculated as shown in Expression (22), and the series of operations is completed.

[Equation 16]
Te = TIOUT × (α + αm + KLMNTC) + Ts (22)

  Here, Ts is the invalid pulse width of the injector 12. Then, the injector 12 is energized from the I / O LSI 34 based on the actual injection width Te, and fuel is injected. Actually, since the calculations described above are performed for the banks A and B, the injection pulse is expressed by the equation (23) for the bank A and the equation (24) for the bank B.

[Equation 17]
Tea = TIOUTa × (αa + αma + KLMNTCA) + Ts (23)
Teb = TIOUTb × (αb + αmb + KLMNTC) + Ts (24)

  Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and various changes in design can be made without departing from the spirit of the invention described in the claims. It can be done. For example, in this embodiment, when the current purge air-fuel ratio becomes leaner than the previous purge air-fuel ratio in step 210 in FIG. 5, the purge rate is fixed in step 213, but the fuel vapor gas increases. The purge rate may be controlled to decrease according to the rate. As the rate of increase in the fuel vapor gas decreases, the purge rate is gradually reduced, so that it is possible to reliably prevent fresh air from flowing into the intake system. There is no effect.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Air cleaner, 3 ... Air cleaner entrance part, 4 ... Intake duct, 5 ... Throttle body, 6 ... Throttle valve, 7 ... Air flow meter (AFM), 8 ... Throttle sensor, 9 ... Surge tank, 10 ... an auxiliary air valve (ISC valve), 11a ... an intake manifold on the bank A side, 11b ... an intake manifold on the bank B side, 12a ... an injector on the bank A side, 12b ... an injector on the bank B side, 13 ... a fuel tank, 15 ... Fuel filter, 17 ... Cam angle sensor, 18a ... Spark plug on bank A side, 18b ... Spark plug on bank B side, 20 ... Water temperature sensor, 21a ... Exhaust manifold on bank A side, 21b ... Exhaust manifold on bank B side, 22a: an air-fuel ratio sensor on the bank A side, 22b: an air-fuel ratio sensor on the bank B side, 2 3a ... Pre-catalyst on bank A side, 23b ... Pre-catalyst on bank B side, 24 ... Main catalyst, 25 ... Muffler, 26 ... Fuel pump, 27a ... Cylinder group on bank A side, 27b ... Cylinder group on bank B side, DESCRIPTION OF SYMBOLS 30 ... Engine control apparatus (control unit), 30a ... Canister purge control apparatus, 30a1 ... Means to control purge flow rate of fuel, 30A ... Means to switch between air-fuel ratio learning control and purge control, 30Ba ... Air-fuel ratio on bank A side Means for performing feedback control, 30Bb: means for performing air-fuel ratio feedback control on the bank B side, 30Ca: means for estimating the purge air-fuel ratio on the bank A side, 30Cb: means for estimating the purge air-fuel ratio on the bank B side, 30Da ... Means for learning control of the air-fuel ratio on the bank A side, 30Db: Hand for learning control of the air-fuel ratio on the bank B side 30E: means for comparing and adjusting the purge air-fuel ratio; 30F: means for calculating the control purge rate; 30Ga: means for correcting the fuel injection amount on the bank A side; 30Gb: means for correcting the fuel injection amount on the bank B side; 30Ia: Evaporation correction calculating means on bank A side, 30Ib: Evaporation correction calculating means on bank B side, 31 ... MPU, 32 ... RAM, 33 ... ROM, 34 ... I / OLSI, 35 ... bus, 40 ... canister, 41 ... Canister purge valve, 45 ... Air inlet, 46 ... Evaporative gas piping, 47 ... Evaporative gas piping

Claims (5)

Fuel vapor recovery means for recovering the fuel evaporated in the fuel tank;
Recovered fuel purge means for purging the fuel recovered by the fuel vapor recovery means into the combustion chamber ;
In a method for controlling a canister purge of an internal combustion engine comprising:
When the purge rate is changed in stages with respect to the initial purge rate after the purge condition is satisfied ,
A canister purge control method for an internal combustion engine, characterized in that when the current purge air-fuel ratio becomes richer than the previous purge air-fuel ratio , the purge rate is increased. When the current purge air-fuel ratio is leaner than the previous purge air-fuel ratio and fuel vapor gas is generated by the purge, the purge rate is set to a fixed value, and when the generation of the vapor gas stops, the purge period ends.
The canister purge control method for an internal combustion engine according to claim 1. To purge the first at a predetermined purge rate, the purge rate after the next time, a canister purge control method for an internal combustion engine according to claim 1 or claim 2, wherein the determining based on the previous purge ratio. Canister purge control method for an internal combustion engine according to any one of claims 1 to 3, characterized in that to determine the increase of the purge rate based on the rate of increase of fuel vapor gas. 5. The canister purge control method for an internal combustion engine according to claim 2 , wherein the purge is restarted after a predetermined purge stop time has elapsed after the purge period has ended .