JP2011231624A - Purge control device and purge control method for dual injection engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for a dual injection engine which appropriately limits a purge rate according to a minimum injection amount of an injector even in a dual injection engine having two injectors.SOLUTION: An electronic control unit 19 limits a vapor purge rate based on the minimum injection amount of a port injector 8 when only port injection is performed, while the unit limits the vapor purge rate based on the minimum infection amount of a cylinder injector 9 when only cylinder injection is performed.

Description

  The present invention relates to a purge control device and a purge control method for a dual injection engine capable of performing fuel injection by two injection methods of port injection and in-cylinder injection.

  Injectors employed in in-vehicle engines, etc., the linear relationship between the injection amount and the injection amount is broken in the low injection region. Therefore, the minimum injection amount is set within a range in which the linear relationship can be maintained, and when the injection amount less than that is required, the fuel injection is performed with the minimum injection amount.

  On the other hand, some on-vehicle engines include a vapor processing device that collects fuel vapor (vapor) generated in a fuel tank in a canister and purges the collected vapor into intake air for processing. In an engine equipped with such a vapor processing device, the fuel injection amount is reduced by the amount of vapor purged during intake, thereby preventing air-fuel ratio disturbances associated with vapor purge.

  Here, as a result of the reduction of the fuel injection amount in accordance with the vapor purge, the injection amount of the injector may fall below the minimum injection amount. In such a case, since the injection amount of the injector cannot be made less than the minimum injection amount, there is a problem that more fuel than is originally required is supplied into the cylinder. Therefore, conventionally, the purge control device described in Patent Literature 1 attempts to solve the above problem by limiting the vapor purge rate so that the injection amount of the injector does not become less than the minimum injection amount.

JP-A-2005-351216

  By the way, in recent years, a dual injection engine capable of performing fuel injection by two injection methods of port injection and in-cylinder injection has been put into practical use. Even when vapor purge is performed in such a dual injection engine, it is necessary to limit the purge rate in accordance with the minimum injection amount of the injector. However, in such an engine, there are two injectors, and it is not clear which of the injectors should take into account the minimum injection amount when limiting the purge rate.

  The present invention has been made in view of such circumstances, and the problem to be solved is to accurately limit the purge rate in accordance with the minimum injection amount of the injector even in a dual injection engine having two injectors. It is an object of the present invention to provide a control device for a dual injection engine.

  In order to solve the above problems, a dual injection engine that is applied to a dual injection engine that can perform fuel injection by two injection methods of port injection and in-cylinder injection, and controls the purge rate of fuel vapor into the intake air. According to the first aspect of the invention as the purge control device, when performing only the port injection, the purge rate of the fuel vapor is limited based on the minimum injection amount of the port injection, and when performing only the in-cylinder injection, The purge rate of the fuel vapor is limited based on the minimum injection amount of the injection.

  In the above configuration, when performing only the port injection, the purge rate of the fuel vapor is limited based on the minimum injection amount of the port injection, and when performing only the in-cylinder injection, the fuel vapor purge rate is based on the minimum injection amount of the in-cylinder injection. The purge rate is limited. Therefore, even in a dual injection engine having two injectors, it is possible to accurately limit the purge rate in accordance with the minimum injection amount of the injector.

  In-cylinder injection, which requires fuel to be injected into a high-pressure cylinder, requires a higher fuel pressure than port injection. Usually, the injection amount of fuel per unit time of in-cylinder injection, that is, the injection rate Is greater than the injection rate of port injection. Therefore, in general, the minimum injection amount of in-cylinder injection is larger than the minimum injection amount of port injection, and in many cases, the injection amount of in-cylinder injection is earlier than the injection amount of port injection reaches the minimum injection time. The injection amount reaches the minimum injection amount. Therefore, as described in claim 2, when performing both port injection and in-cylinder injection, it is preferable to limit the purge rate of fuel vapor based on the minimum injection amount of in-cylinder injection.

  On the other hand, when performing both port injection and in-cylinder injection, it is conceivable to limit the purge rate in consideration of both the minimum injection amount of in-cylinder injection and the minimum injection amount of port injection. In such a case, as described in claim 3, the upper limit value of the purge rate calculated based on the minimum injection amount of port injection, and the upper limit value of the purge rate calculated based on the minimum injection amount of in-cylinder injection, The minimum value of the three values of the target purge rate calculated according to the engine operating state may be set as the final target purge rate when both port injection and in-cylinder injection are performed.

  In order to solve the above-mentioned problem, in the invention according to claim 4 as a purge control method of a dual injection engine, during the intake in a dual injection engine capable of performing fuel injection by two injection methods of port injection and in-cylinder injection. Is a method for controlling the purge rate of fuel vapor to the port, and when performing only port injection, the purge rate of fuel vapor is limited based on the minimum injection amount of port injection, and when performing only in-cylinder injection, The purge rate of the fuel vapor is limited based on the minimum injection amount of the internal injection.

  In the above method, when only port injection is performed, the purge rate of fuel vapor is limited based on the minimum injection amount of port injection, and when only in-cylinder injection is performed, the fuel vapor purge rate is based on the minimum injection amount of in-cylinder injection. The purge rate is limited. Therefore, even in a dual injection engine having two injectors, it is possible to accurately limit the purge rate in accordance with the minimum injection amount of the injector.

  In-cylinder injection, which requires fuel to be injected into a high-pressure cylinder, requires a higher fuel pressure than port injection. Usually, the injection amount of fuel per unit time of in-cylinder injection, that is, the injection rate Is greater than the injection rate of port injection. Therefore, in general, the minimum injection amount of in-cylinder injection is larger than the minimum injection amount of port injection, and in many cases, the injection amount of in-cylinder injection is earlier than the injection amount of port injection reaches the minimum injection time. The injection amount reaches the minimum injection amount. Therefore, as described in claim 5, when both port injection and in-cylinder injection are performed, the purge rate of fuel vapor is preferably limited based on the minimum injection amount of in-cylinder injection.

  On the other hand, when performing both port injection and in-cylinder injection, it is conceivable to limit the purge rate in consideration of both the minimum injection amount of in-cylinder injection and the minimum injection amount of port injection. In such a case, as described in claim 6, the first step of calculating the upper limit value of the purge rate based on the minimum injection amount of the port injection and the purge rate based on the minimum injection amount of the in-cylinder injection. A second step for calculating an upper limit value, a third step for calculating a target purge rate according to the engine operating state, two upper limit values calculated in the first and second steps, and a third step. A target purge rate when performing both port injection and in-cylinder injection is set through a fourth step of setting the minimum value of the three values of the calculated target purge rate as the final target purge rate. It is good to do so.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows typically the whole structure of the control apparatus of the dual injection engine which concerns on 1st Embodiment of this invention. The flowchart which shows the process sequence of the target purge rate setting routine employ | adopted as the same embodiment. The flowchart which shows the process sequence of the target purge rate setting routine at the time of injection division employ | adopted as 2nd Embodiment of this invention.

Hereinafter, an embodiment embodying a purge control apparatus and purge control method for a dual injection engine of the present invention will be described in detail with reference to FIGS. 1 and 2.
FIG. 1 shows a configuration of a dual injection engine to which the present embodiment is applied. As shown in the figure, this dual injection engine capable of performing fuel injection by two injection methods of port injection and in-cylinder injection includes an intake passage 1, a combustion chamber 2, and an exhaust passage 3.

  A throttle valve 4 for adjusting the flow rate of intake air is installed in the intake passage 1, and a surge tank 5 provided for suppressing intake pulsation and intake air interference is provided downstream thereof. The intake passage 1 is connected to the combustion chamber 2 via an intake port 6 and an intake valve 7 downstream of the surge tank 5.

  The engine configured as a dual injection engine is provided with two injectors: a port injection injector 8 for injecting fuel into the intake port 6 and an in-cylinder injector 9 for injecting fuel directly into the combustion chamber 2. It has been.

  The combustion chamber 2 of such a dual injection engine is provided with a spark plug 10 that ignites an air-fuel mixture introduced into the combustion chamber 2. The combustion chamber 2 is connected to the exhaust passage 3 via an exhaust valve 11 and an exhaust port 12.

  The dual injection engine is provided with a vapor processing system for processing fuel vapor (vapor) generated in the fuel tank 13. The vapor processing system includes a vapor passage 14 connected to the fuel tank 13, a canister 15 connected to the vapor passage 14, a purge passage 16 connecting the intake passage 1 downstream of the throttle valve 4 and the canister 15, and a canister 15. An air introduction passage 17 for introducing external air into the inside is provided. The canister 15 is configured to collect the vapor introduced through the vapor passage 14 by being adsorbed by an adsorbent such as activated carbon provided therein. Further, a purge valve 18 is provided in the purge passage 16, and the amount of vapor purged into the intake air is adjusted by adjusting the opening of the purge valve 18.

  In such a vapor processing system, the vapor generated in the fuel tank 13 is introduced into the canister 15 through the vapor passage 14. The vapor introduced into the canister 15 is once adsorbed by the adsorbent inside. Thereafter, when the purge valve 18 is opened, the atmosphere is introduced into the canister 15 through the atmosphere introduction passage 17, and the vapor adsorbed by the adsorbent is separated by the flow force. The purge gas in which the separated vapor and air are mixed is discharged into the intake passage 1 through the purge passage 16. The purge gas thus discharged into the intake passage 1 is combusted in the combustion chamber 2 together with the air-fuel mixture of the intake air introduced through the intake passage 1 and the fuel injected from the port injector 8 or the in-cylinder injector 9. Become so.

  The dual injection engine provided with such a vapor processing system is controlled by an electronic control unit 19. The electronic control unit 19 includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output port (I / O). Here, the CPU performs various arithmetic processes for engine control, and the ROM stores a program and data for engine control. The RAM temporarily stores the calculation results of the CPU and the detection results of the sensors, and the I / O functions as an interface for exchanging signals with the outside.

  The electronic control unit 19 instructs the port injector 8 and the in-cylinder injector 9 to control fuel injection from each injector. The electronic control unit 19 adjusts the purge rate by controlling the purge valve 18 so as to obtain a target purge rate to be described later.

  In the dual injection engine configured as described above, the vapor generated in the fuel tank 13 is purged during the operation. During the purge process, vapor contained in the purge gas purged during the intake air is introduced into the combustion chamber 2 in addition to the fuel injected from the port injector 8 and the in-cylinder injector 9. Therefore, in this dual injection engine, the fuel injection amount from the port injector 8 and the in-cylinder injector 9 is corrected by reducing the amount of vapor contained in the purge gas, thereby avoiding air-fuel ratio disturbance associated with the purge process of the vapor. Like to do.

  On the other hand, in this dual injection engine, the fuel injection amount of the port injector 8 and the in-cylinder injector 9 is managed by the fuel injection time of each injector. This injection amount management is based on the premise that a linear relationship is shown between the fuel injection time [μsec] and the injection amount [mg]. However, in a region where the injection time is shorter than a certain level, such a linear relationship is lost. Therefore, a minimum injection amount is set for each injector within a range in which such a linear relationship can be maintained, and when an injection amount less than that is required, fuel injection is performed with the minimum injection amount.

  However, as a result of the reduction correction associated with the purge process as described above, the injection amount of each injector may fall below such a minimum injection amount. Even in such a case, since the injection amount of the injector cannot be less than the minimum injection amount, more fuel than is originally required is supplied into the cylinder. Therefore, by restricting the vapor purge rate so that the injection amount of the injector does not become less than the minimum injection amount, an unnecessary fuel supply into the cylinder is avoided.

  However, in the dual injection engine as described above, there are two injectors, and the minimum injection amounts are different. Therefore, in such a dual injection engine, there is a problem of which injector's minimum injection amount should be taken into consideration when limiting the purge rate. In the present embodiment, by limiting the purge rate in the following manner, the purge rate can be accurately limited even in such a dual injection engine.

  That is, in the present embodiment, when only port injection is performed, the vapor purge rate is limited based on the minimum injection amount of the port injection injector 8. More specifically, at this time, the vapor purge rate is limited so that the amount of vapor purged is equal to or less than the difference between the required injection amount and the minimum injection amount of the port injection injector 8.

  On the other hand, when only in-cylinder injection is performed, the vapor purge rate is limited based on the minimum injection amount of the in-cylinder injector 9. That is, at this time, the vapor purge rate is limited so that the amount of vapor purged is equal to or less than the difference between the required injection amount and the minimum injection amount of the in-cylinder injector 9.

  In the present embodiment, when both port injection and in-cylinder injection are performed, the vapor purge rate is limited based on the minimum injection amount of the in-cylinder injector 9. This is due to the following reason.

  In-cylinder injection, which requires fuel to be injected into a high-pressure cylinder, requires a higher fuel pressure than port injection. Usually, the amount of fuel injected per unit time of in-cylinder injection, that is, the injection rate Is greater than the injection rate of port injection. For this reason, the minimum injection amount of in-cylinder injection is larger than the minimum injection amount of port injection, and in many cases, the injection amount of in-cylinder injection is earlier than the injection amount of port injection reaches the minimum injection time. Reaches the minimum injection amount. Therefore, if the vapor purge rate is limited based on the minimum in-cylinder injection amount, an appropriate air-fuel ratio can be maintained even when both port injection and in-cylinder injection are performed.

  FIG. 2 shows a flowchart of a target purge rate setting routine employed in this embodiment. The processing of this routine is periodically and repeatedly executed by the electronic control unit 19 during operation of the dual injection engine. The electronic control unit 19 adjusts the opening of the purge valve 18 so that the target purge rate set through the processing of this routine is obtained.

  When this routine is started, it is first determined in step S100 whether or not the port injection ratio is 100%. That is, it is determined here whether the operation state is in which only the port injection is performed, whether only the in-cylinder injection is performed, or the operation state in which both the port injection and the in-cylinder injection are performed.

  Here, when it is determined that the ratio of port injection is 100% (S100: YES), a predetermined constant α [μs] is added to the minimum injection amount τminP [μs] of the port injection injector 8 in step S101. The value is calculated as the limit injection amount pgtau [μs]. On the other hand, when it is determined that the ratio of port injection is not 100% (S100: NO), a value obtained by adding a predetermined constant β [μs] to the minimum injection amount τminD [μs] of the in-cylinder injector 9 in step S102. , Calculated as the limit injection amount pgtau [μs].

  When the limit injection amount pgtau is calculated in this manner, in the subsequent step S103, it is determined whether or not the calculated limit injection amount pgtau is larger than the required injection amount t_tau. If the limit injection amount pgtau is equal to or less than the required injection amount t_tau (S103: NO), the normal target purge rate [%] is set to the final target purge rate [%] in step S104, and then the current target purge rate [%] is set. The routine processing is terminated.

  On the other hand, if the limit injection amount pgtau is larger than the required injection amount t_tau (S103: YES), in step S105, the limit purge rate fpglmt [%] is calculated from the following equation (1). In the following formula (1), “efpg” represents the current purge correction amount [%]. Incidentally, the purge correction amount efpg is a correction factor of the air-fuel ratio A / F according to the purge.

fpglmt
← efpg- (1.0− (pgtau / t_tau)) × 100 (1)

In step S105, a value obtained by dividing the limit purge rate fpglmt calculated by the above equation (1) by the current purge concentration learning value efgppg [% /%] is calculated as the purge rate limit [%]. The purge concentration learning value efgpg indicates an A / F correction rate per 1% of the purge rate.

  Furthermore, in step S105, the purge rate limit is compared with the normal target purge rate, the larger value is set as the final purge rate, and then the processing of this routine is terminated.

According to the purge control device for a dual injection engine of the present embodiment described above, the following effects can be obtained.
(1) In this embodiment, when only port injection is performed, the vapor purge rate is limited based on the minimum injection amount τminP of port injection, and when only in-cylinder injection is performed, the minimum injection amount τminD of in-cylinder injection is set. Based on this, the vapor purge rate is limited. Therefore, even in a dual injection engine having two injectors, it is possible to accurately limit the purge rate in accordance with the minimum injection amount of the injector.

  (2) In the present embodiment, when both port injection and in-cylinder injection are performed, the vapor purge rate is limited based on the minimum injection amount τminD of in-cylinder injection. In-cylinder injection, which requires fuel to be injected into a high-pressure cylinder, requires a higher fuel pressure than port injection. Usually, the injection amount of fuel per unit time of in-cylinder injection, that is, the injection rate Is greater than the injection rate of port injection. Therefore, if the vapor purge rate is limited based on the minimum injection amount of the in-cylinder injection, the purge rate can be accurately limited even when the port injection and the in-cylinder injection are performed separately. become.

(Second Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to FIG. In the present embodiment, the same components as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the first embodiment, the vapor purge rate is limited based on the minimum injection amount τminD of the in-cylinder injection at the time of the injection that performs both the port injection and the in-cylinder injection. However, in order to more strictly limit the purge rate at the time of separate injection, it is desirable to consider the minimum injection amounts of both port injection and in-cylinder injection.

Therefore, in the present embodiment, at the time of separate injection, the purge value calculated based on the purge rate upper limit value (purge rate limit P) calculated based on the port injection minimum injection amount τminP and the in-cylinder injection minimum injection amount τminD. An upper limit value of the rate (purge rate limit D) is obtained. The final target when performing both the port injection and the in-cylinder injection is made the minimum value of the three values of the two upper limit values obtained and the normal target purge rate calculated according to the engine operating state. The purge rate is set. That is, in the present embodiment, the final target purge rate at the time of spraying is set through the following steps.
A first step of calculating an upper limit value of purge rate (purge rate limit P) based on the minimum injection amount τminP of port injection.
A second step of calculating an upper limit value of purge rate (purge rate limit D) based on the minimum injection amount τminD of in-cylinder injection
A third step of calculating a normal target purge rate according to the engine operating state.
A fourth step of setting, as the final target purge rate, the minimum value of the three values of the two upper limit values calculated in the first and second steps and the target purge rate calculated in the third step.

  FIG. 3 shows a flowchart of the target purge rate setting routine at the time of spraying adopted in the present embodiment. The processing of this routine is periodically and repeatedly executed by the electronic control unit 19 during operation of the dual injection engine.

  When this routine is started, it is first determined in step S200 whether or not the port injection and the in-cylinder injection are being performed separately. If it is not at the time of spraying (S200: NO), the process of this routine is terminated as it is. If not (S200: YES), the process proceeds to step S201.

  In step S201, a value obtained by adding a predetermined constant α [μs] to the minimum injection amount τminP [μs] of the port injector 8 is calculated as the port injection limit injection amount pgtaup [μs]. In step 201, a value obtained by adding a predetermined constant β [μs] to the minimum injection amount τminD [μs] of the in-cylinder injector 9 is calculated as the in-cylinder injection limit injection amount pgtaud [μs].

  In the subsequent step S202, it is determined whether or not the port injection limit injection amount pgtaup calculated here is larger than the current injection amount etaubp of the port injection injector 8. If the port injection limit injection amount pgtaup is equal to or less than the injection amount etaubp (S202: NO), the purge rate limit P is set to the maximum value MAX (= 100%) in step S204.

  On the other hand, if the port injection limit injection amount pgtaup is larger than the injection amount etaubp (S202: YES), in step S203, the port injection limit purge rate fpglmtp [%] is calculated from the following equation (2). In step S203, a value obtained by dividing the port injection limit purge rate fpglmtp calculated by the following expression (2) by the current purge concentration learning value efpgpg [% /%] is calculated as the purge rate limit P [%]. .

fpglmtp
← efpg- (1.0- (pgtaup / etaubp)) × 100 (2)

When the purge rate limit P is calculated as described above, the process proceeds to step S205. In step S205, whether or not the in-cylinder injection limit injection amount pgtaud is larger than the current in-cylinder injection amount 9 of the in-cylinder injector 9. Is determined. If the in-cylinder injection limit injection amount pgtaud is equal to or less than the injection amount etaub (S205: NO), the purge rate limit D is set to the maximum value MAX (= 100%) in step S207.

  On the other hand, if in-cylinder injection limit injection amount pgtaud is larger than injection amount etaubd (S205: YES), in-cylinder injection limit purge rate fpglmtd [%] is calculated from the following equation (3) in step S206. In step S206, a value obtained by dividing the in-cylinder injection limit purge rate fpglmtd calculated by the following expression (3) by the current purge concentration learning value efpgpg [% /%] is calculated as the purge rate limit D [%]. The

fpglmtd
← efpg- (1.0− (pgtaud / etaubd)) × 100 (3)

When the purge rate limit P and the purge rate limit D are thus calculated, the process proceeds to step S208. In step S208, the minimum value among the three values of the purge rate limit P, the purge rate limit D, and the normal target purge rate is set as the final target purge rate.

According to the purge control device for a dual injection engine of the present embodiment described above, the following effect can be further obtained in addition to the effect described in (1) above.
(3) In this embodiment, at the time of separate injection, it is calculated based on the upper limit value of purge rate (purge rate limit P) calculated based on the minimum injection amount τminP of port injection and the minimum injection amount τminD of in-cylinder injection. Further, an upper limit value of purge rate (purge rate limit D) is obtained. The final target when performing both the port injection and the in-cylinder injection is made the minimum value of the three values of the two upper limit values obtained and the normal target purge rate calculated according to the engine operating state. The purge rate is set. Therefore, the purge rate can be accurately limited even during spraying.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, the value obtained by adding the constant α to the minimum injection amount τminP is calculated as the port injection limit injection amount pgtaup, and the value obtained by adding the constant β to the minimum injection amount τminD is used as the in-cylinder injection limit injection amount pgtaud. I was trying to calculate. Thus, if the value obtained by adding a constant to the minimum injection amount is obtained as the limit injection amount, the region in which the injection time and the injection amount have a linear relationship regardless of the difference in individual injectors or the difference in the minimum injection amount due to changes over time It becomes possible to use only. However, if the difference in the minimum injection amount for each injector is small enough to be ignored, the minimum injection amount τminP and τminD are used as they are as the port injection limit injection amount pgtaup and the in-cylinder injection limit injection amount pgtaud. Also good.

In the above embodiment, the purge rate limit is calculated through the equations (1) to (3). The calculation formula for such purge rate limitation may be changed as appropriate.
-The dual injection applied in the above embodiment performs the injection of port injection and in-cylinder injection, but the present invention can also be applied to dual injection that does not perform such injection. it can. In such a case, when only the port injection is performed, the vapor purge rate is limited based on the minimum injection amount τminP of the port injector 8, and when only the in-cylinder injection is performed, the minimum injection amount τminD of the in-cylinder injector 9 is set. Therefore, the vapor purge rate is limited.

  DESCRIPTION OF SYMBOLS 1 ... Intake passage, 2 ... Combustion chamber, 3 ... Exhaust passage, 4 ... Throttle valve, 5 ... Surge tank 5, 6 ... Intake port, 7 ... Intake valve, 8 ... Port injection injector, 9 ... In-cylinder injection injector, 10 DESCRIPTION OF SYMBOLS ... Spark plug, 11 ... Exhaust valve, 12 ... Exhaust port, 13 ... Fuel tank, 14 ... Vapor passage, 15 ... Canister, 16 ... Purge passage, 17 ... Air introduction passage, 18 ... Purge valve, 19 ... Electronic control unit

Claims (6)

In a dual injection engine purge control device that is applied to a dual injection engine capable of performing fuel injection by two injection methods of port injection and in-cylinder injection and controls the purge rate of fuel vapor into the intake air,
When performing only the port injection, the purge rate of the fuel vapor is limited based on the minimum injection amount of the port injection, and when performing only the in-cylinder injection, the purge rate of the fuel vapor is based on the minimum injection amount of the in-cylinder injection. A purge control device for a dual injection engine characterized by The dual injection engine purge control device according to claim 1, wherein when performing both port injection and in-cylinder injection, the purge rate of the fuel vapor is limited based on a minimum injection amount of in-cylinder injection. The upper limit value of the purge rate calculated based on the minimum injection amount of port injection, the upper limit value of the purge rate calculated based on the minimum injection amount of in-cylinder injection, and the target purge rate calculated according to the engine operating state The purge control device for a dual injection engine according to claim 1, wherein a minimum value of the three values is set as a final target purge rate when both port injection and in-cylinder injection are performed. A method for controlling a purge rate of fuel vapor into intake air in a dual injection engine capable of performing fuel injection by two injection methods of port injection and in-cylinder injection,
When performing only the port injection, the purge rate of the fuel vapor is limited based on the minimum injection amount of the port injection, and when performing only the in-cylinder injection, the purging of the fuel vapor is performed based on the minimum injection amount of the in-cylinder injection. A purge control method for a dual injection engine characterized by limiting the rate. The dual injection engine purge control method according to claim 4, wherein when performing both port injection and in-cylinder injection, the purge rate of the fuel vapor is limited based on a minimum injection amount of in-cylinder injection. A first step of calculating an upper limit value of the purge rate based on the minimum injection amount of the port injection;
A second step of calculating an upper limit value of the purge rate based on the minimum injection amount of in-cylinder injection;
A third step of calculating a target purge rate according to the engine operating state;
A fourth value that sets a minimum value of three values of the two upper limit values calculated in the first and second steps and the target purge rate calculated in the third step as a final target purge rate. Steps,
The purge control method for a dual injection engine according to claim 4, wherein a target purge rate is set when both port injection and in-cylinder injection are performed.

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