JP6107862B2 - Evaporative fuel control device for internal combustion engine - Google Patents

Description

  The present invention includes a cylinder, an intake passage for introducing air into the cylinder, a fuel tank in which fuel is stored, and a canister that detachably adsorbs evaporated fuel generated in the fuel tank, and intake air from the canister The present invention relates to an evaporated fuel control device for an internal combustion engine in which purge gas containing evaporated fuel is introduced into a passage.

  Conventionally, evaporative fuel generated in a fuel tank is introduced into an intake passage via a canister and burned in a cylinder.

  For example, Patent Document 1 discloses a device including a purge passage that communicates a canister and an intake passage, an ON / OFF type on-off valve that opens and closes the purge passage, and a pump. In the device of Patent Document 1, the pressure difference between the upstream end and the downstream end of the purge passage is changed by changing the rotation speed of the pump while the on-off valve is opened, and is thereby introduced from the canister into the intake passage. The amount of purge gas is changed.

JP 2007-177727 A

  Here, since there is a response delay in the pump, it takes time until the rotational speed of the pump changes to the predetermined rotational speed. For this reason, the apparatus of Patent Document 1 has a problem that the amount of purge gas cannot be set to an appropriate amount until the pump changes to a predetermined rotational speed. In addition, since an appropriate amount of the evaporated fuel contained in the purge gas is not supplied into the cylinder, the air-fuel ratio in the cylinder may deviate from the target value, thereby deteriorating exhaust performance and the like.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an evaporated fuel control device for an internal combustion engine that can supply an appropriate amount of evaporated fuel to an intake passage more reliably. To do.

  In order to solve the above problems, the present invention provides a cylinder, an intake passage for introducing air into the cylinder, a fuel tank in which fuel is stored, and an evaporated fuel generated in the fuel tank so as to be detachable. An evaporative fuel control apparatus for an internal combustion engine, wherein a purge gas containing evaporative fuel desorbed from the canister is introduced into an intake passage, the purge passage communicating the canister and the intake passage, and the purge A purge valve provided in the passage for opening and closing the passage, a rotary pump provided in the purge passage for increasing the pressure difference between the upstream end and the downstream end of the purge passage as the rotational speed increases, and the purge valve And a control means for controlling the opening degree and the rotation speed of the pump. The control means has a required purge amount, which is a required purge gas amount, of a predetermined reference value. In the low flow rate region where the amount is less than the maximum amount, the opening degree of the purge valve is controlled to an intermediate opening degree between the fully closed state and the fully opened state, and the rotation speed of the pump is set to a preset low flow side target pump speed. In a high flow rate region where the required purge amount is equal to or greater than the reference purge amount, the opening of the purge valve is controlled to be fully open and the pump rotational speed is set to a preset high flow side target pump rotational speed. The higher flow rate target pump speed is set higher as the required purge amount is larger, and the minimum value of the higher flow rate target pump speed is the maximum of the lower flow rate target pump speed. It is set to a value smaller than the value (Claim 1).

  According to the present invention, the minimum value of the target pump speed in the high flow area is set smaller than the maximum value of the target pump speed in the low flow area, and the higher the required purge amount, the higher the target pump speed. The number is set to be high, and the target pump rotation speed ranges in the low flow rate region and the high flow rate region are set to overlap at least partially. Therefore, at the time of transition between the high flow rate region and the low flow rate region, the amount of change in the target pump rotational speed can be kept small, and the deviation of the pump rotational speed from the target pump rotational speed due to the pump response delay can be kept small. . Therefore, the amount of purge gas introduced into the intake passage can be controlled to the required amount at an earlier stage, and the evaporated fuel can be more reliably introduced into the appropriate amount of intake passage.

  In the present invention, the lower flow rate target pump speed is higher as the required purge amount is larger, and the increase rate with respect to the required purge amount is higher than the required flow rate with respect to the required purge amount. It is preferable that the intermediate opening is set to the open side as the required purge amount increases (Claim 2).

  In this way, the overlapping range of the target pump speed in the low flow rate region and the target pump speed in the high flow rate region can be made larger, so that the target value of the pump speed generated at the time of transition to these regions from the target value. The shift can be suppressed more reliably.

  Further, in the present invention, the low flow rate target pump speed is set to a constant value throughout the low flow rate region, and the intermediate opening is set to open as the required purge amount increases. (Claim 3).

  In this way, when the operating condition (required purge amount) changes in the low flow rate region, it is possible to suppress the amount of evaporated fuel supplied to the intake passage from deviating from an appropriate amount due to a delay in response of the pump. it can.

  In the present invention, it is preferable that the low flow rate region is set in a region where the compressed self-ignition combustion of the air-fuel mixture having an air-fuel ratio larger than 1 is performed in the cylinder.

  As described above, in the present invention, the amount of evaporated fuel introduced into the intake passage can be appropriately controlled, so that the air-fuel ratio of the air-fuel mixture in the cylinder can be controlled more accurately. Therefore, according to this configuration, it is possible to realize appropriate compression self-ignition combustion while making the air-fuel ratio leaner than 1 more reliably.

  In the above configuration, when the control means shifts from the high flow rate region to the low flow rate region, the deviation between the pump rotation speed and the low flow side target pump rotation speed is greater than or equal to a predetermined reference deviation. Until the deviation becomes less than the reference deviation, the opening of the purge valve is set to the required purge amount and the rotation speed of the pump so that the amount of purge gas introduced into the intake passage becomes the required purge amount. It is preferable to correct accordingly.

  In this way, at the time of transition from the high flow rate region to the low flow rate region, the required purge gas amount is purged by correcting the opening of the purge valve until the pump rotational speed reaches the target pump rotational speed. The amount can be controlled. Accordingly, it is possible to suppress the deviation from the required amount of the purge gas amount and the evaporated fuel amount introduced into the intake passage and the deviation of the air-fuel ratio in the cylinder due to the pump response delay.

  As described above, according to the evaporated fuel control apparatus for an internal combustion engine of the present invention, an appropriate amount of evaporated fuel can be more reliably supplied to the intake passage.

It is a figure showing composition of an engine system concerning one embodiment of the present invention. It is the figure which showed the operation area | region which concerns on a combustion form. It is the flowchart which showed the flow of control of purge amount. It is the figure which showed the relationship between request | requirement purge amount and target pump rotation speed. It is the figure which showed the relationship between request | requirement purge amount and DUTY ratio of a purge valve. It is a figure for demonstrating the change of the target pump rotation speed at the time of area | region transfer. It is the figure which showed the change of each parameter when a request | requirement purge amount reduces. It is the figure which showed the other example of the relationship between request | requirement purge amount and target pump rotation speed.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing a configuration of an engine system to which an evaporated fuel control device for an internal combustion engine according to an embodiment of the present invention is applied. The engine system of this embodiment includes a four-stroke engine main body 1, an intake passage 20 for introducing combustion air (intake air) into the engine main body 1, and an exhaust for discharging exhaust from the engine main body 1 to the outside. A passage 31 and a purge system 40 for introducing evaporated fuel generated in the fuel tank 41 into the engine body 1 are provided. The engine body 1 is, for example, a four-cylinder engine having four cylinders 2a arranged in a direction orthogonal to the paper surface of FIG.

  Here, the case where the engine body 1 is a gasoline engine mainly using gasoline as a fuel will be described.

  The engine body 1 includes a cylinder block 2 in which a cylinder 2a is formed, a cylinder head 3 provided on the upper surface of the cylinder block 2, and a piston 4 inserted into the cylinder 2a so as to be slidable back and forth. Yes.

  A combustion chamber 5 is formed above the piston 4. Fuel is injected from the injector 10 into the combustion chamber 5. The injected fuel / air mixture is combusted in the combustion chamber 5, and the piston 4 is pushed down by the expansion force generated by the combustion and reciprocates up and down.

  The piston 4 is connected to the crankshaft 15 via a connecting rod, and the crankshaft 15 rotates around the central axis according to the reciprocating motion of the piston 4.

  The cylinder block 2 is provided with an engine speed sensor SW1 that detects the speed of the crankshaft 15 as the engine speed.

  The cylinder head 3 is provided with a pair of injectors 10 and spark plugs 11 for igniting a mixture of fuel and air injected from the injectors 10 by spark discharge for each cylinder 2a.

  The injector 10 has a plurality of injection holes serving as fuel injection ports at the tip, and is provided so as to face the combustion chamber 5 of each cylinder 2a from the side on the intake side. The fuel stored in the fuel tank 41 is supplied to the injector 10 through a filter or the like.

  The spark plug 11 has an electrode for discharging sparks at the tip, and is provided so as to face the combustion chamber 5 of each cylinder 2a from above.

  The engine body 1 of the present embodiment has a geometric compression ratio (ratio between the combustion chamber volume when the piston 4 is at bottom dead center and the combustion chamber volume when the piston 4 is at top dead center). The engine is set to a relatively high value. The reason for setting such a high geometric compression ratio is to improve the theoretical thermal efficiency and to ensure the ignitability in CI combustion (compression self-ignition combustion) described later.

  The cylinder head 3 includes an intake port 6 for introducing air supplied from the intake passage 20 into the combustion chamber 5 of each cylinder 2a, an intake valve 8 for opening and closing the intake port 6, and the combustion chamber 5 of each cylinder 2a. Are provided with an exhaust port 7 for leading the exhaust gas generated in step 1 to the exhaust passage 31 and an exhaust valve 9 for opening and closing the exhaust port 7.

  The intake passage 20 has a single intake pipe 23 and a plurality of (four) independent intake passages 24 (perpendicular to the plane of FIG. 1) for individually connecting the intake pipe 23 and the intake port 6 of each cylinder 2a. Are arranged in the direction). A surge tank 22 having a predetermined volume is provided at the downstream end of the intake pipe 23, and an independent intake passage 24 extends from the surge tank 22 to each intake port 6.

  A throttle valve 25 capable of opening and closing the passage of the intake pipe 23 and an air flow sensor SW2 for detecting the flow rate of air (intake) taken into the engine body 1 are provided in the middle of the intake pipe 23. . In the present embodiment, the throttle valve 25 has an opening that is almost always fully open except when the fuel injection is stopped, in order to keep the pumping loss small.

  The exhaust passage 31 includes a single exhaust pipe and a plurality of (four) independent intake passages that individually connect the exhaust pipe and the exhaust port 7 of each cylinder 2a. The exhaust passage 31 is provided with a catalytic converter 39 in which a catalyst such as a three-way catalyst is incorporated. Further, the exhaust passage 31 is provided with an A / F sensor SW3 for detecting the air-fuel ratio (ratio of air to fuel) of the exhaust gas, and thus the air-fuel mixture in the cylinder 2a.

  For example, for the purpose of increasing the temperature in the cylinder 2a or keeping the combustion temperature low, the exhaust passage 31 and the intake pipe 23 are connected, and a part of the exhaust is recirculated to the intake pipe 23. An EGR system may be provided.

  The purge system 40 includes a canister 42 that detachably adsorbs the evaporated fuel evaporated in the fuel tank 41, a purge air pipe 49 that introduces air into the canister 42, and a purge pipe (purge) that connects the canister 42 and the intake pipe 23. Passage) 43.

  The evaporated fuel adsorbed on the canister 42 is desorbed from the canister 42 by the air introduced from the purge air pipe 49. The evaporated fuel desorbed from the canister 42 is introduced into the intake pipe 23 through the purge pipe 43 together with air. Hereinafter, this gas composed of evaporated fuel and air is referred to as purge gas.

  The purge pipe 43 is connected to a portion of the intake pipe 23 that is downstream of the throttle valve 25. In the present embodiment, the purge pipe 43 is connected to the surge tank 22.

  The purge pipe 43 is provided with an air pump (pump) 44 that changes the differential pressure between the upstream end (connection portion with the canister 42) and the downstream end (connection portion with the intake pipe 23) of the purge pipe 43. The air pump 44 is driven to rotate by a pump motor (not shown) to pressurize the gas in the purge pipe 43. The higher the number of revolutions, the higher the pressure of the purge pipe 43 where the air pump 44 is installed. Increase the differential pressure. The air pump 44 is provided with a pump rotation speed sensor SW4 for detecting the rotation speed (hereinafter, appropriately referred to as pump rotation speed).

  In addition, a purge valve 45 that opens and closes the purge pipe 43 is provided at a portion downstream of the air pump 44 of the purge pipe 43 (on the intake pipe 23 side). The purge valve 45 is a DUTY control valve that repeatedly opens and closes, and the opening degree is changed by changing the DUTY ratio, which is the ratio of the valve opening period to the unit period that combines one valve opening period and the valve closing period. It is what is done. The purge valve 45 is an electromagnetic valve, and the DUTY ratio is the ratio of the energization period to the unit period including one energization period and one non-energization period. The purge valve 45 comprising the DUTY control valve is fully closed when the DUTY ratio is 0% and fully opened when 100%. Further, the opening degree, that is, the gas flow rate that passes through the valve in the unit period is changed almost in proportion to the DUTY ratio. More specifically, in the purge valve 45 according to the present embodiment, the DUTY ratio and the opening degree are not proportional to each other in the vicinity of the fully closed state and the fully opened state. For example, the DUTY ratio and the opening degree are proportional to each other between 5% and 95%. To do. Further, even if the DUTY ratio is not 100%, the valve opening is fully open at a value close to 100% (for example, a value of 95% or more).

(2) Control system Next, the control system of the engine system will be described. The engine system of this embodiment is mounted on a vehicle such as an automobile, and is controlled by an ECU (engine control unit) 60 provided in the vehicle. As is well known, the ECU 60 is a microprocessor including a CPU, a ROM, a RAM, an I / F, and the like, and corresponds to a control unit according to the present invention.

  Information from various sensors is input to the ECU 60. For example, the ECU 60 is electrically connected to an engine speed sensor SW1, an air flow sensor SW2, an A / F sensor SW3, and a pump speed sensor SW4, and input signals (engine speed, intake air flow rate) from these sensors. Information, the air-fuel ratio of the air-fuel mixture in the cylinder 2a, and the rotation speed of the air pump 44). Further, the vehicle is provided with an accelerator opening sensor SW5 for detecting the opening degree of the accelerator pedal 70 operated by the driver, a vehicle speed sensor SW6 for detecting the vehicle speed, and a shift stage sensor SW7 for detecting the shift stage. Detection signals from these sensors SW5 to SW7 are also input to the ECU 60. Note that the gear position may be calculated based on the vehicle speed detected by the vehicle speed sensor SW6 and the engine speed detected by the engine speed sensor SW1.

  ECU60 controls each part of an engine system, performing various calculations etc. based on the input signal from each sensor (SW1-SW7 grade | etc.,). That is, the ECU 60 includes the injector 10, the spark plug 11, the throttle valve 25, the intake valve 8 (a drive mechanism that drives the intake valve 8), the exhaust valve 9 (the drive mechanism that drives the exhaust valve 9), and the air pump 44 (the air pump 44). And a purge valve 45 (a drive mechanism for driving the purge valve 45) and the like, and outputs a control signal for driving to each of these devices based on the result of the calculation.

(I) Control of Engine Body FIG. 2 is a diagram conceptually showing a control map related to the combustion mode referred to by the ECU 60 during operation of the engine.

  In the present embodiment, as shown in this control map, in the first operation region A1 from the lowest load of the engine to the switching load T1, the air-fuel mixture is heated to a high temperature and pressure by the compression action of the piston 4, and near the compression top dead center. CI combustion for self-ignition (compression self-ignition combustion) is performed, and in the second operation region A2 from the switching load T1 to the maximum load, the air-fuel mixture is burned by flame propagation triggered by forced ignition by spark discharge from the spark plug 11 SI combustion (spark ignition combustion) is performed.

  In the present embodiment, in the first operating region A1, the air-fuel ratio of the air-fuel mixture in the cylinder 2a is made larger than 1, and lean CI combustion is performed.

  The ECU 60 sequentially determines in which operating region the engine is operating in the map of FIG. 2 from each value of the load (engine required torque based on the accelerator opening) and the engine speed during operation of the engine. The injector 10 and the like are controlled according to the area.

  Specifically, in the first operation region A1, ignition by the spark plug 11 is stopped and fuel is injected into the combustion chamber by the injector 10 during the intake stroke. On the other hand, in the second operation region A2, ignition by the spark plug 11 is performed.

  In this embodiment, as described above, the ECU 60 almost always sets the throttle valve 25 to an opening degree near the fully open position.

(Ii) Purge Control Next, control of purge gas introduced from the canister 42 into the intake pipe 23 will be described.

  First, the concentration learning of the evaporated fuel contained in the purge gas will be briefly described.

  In the present embodiment, based on the air-fuel ratio of the air-fuel mixture in the cylinder 2a detected by the A / F sensor SW3 and the amount of air introduced into the cylinder 2a estimated from the detection value of the airflow sensor SW2, etc. The amount of fuel supplied to 2a is estimated. Then, the amount of evaporated fuel supplied to the cylinder 2a is estimated by subtracting the amount of fuel injected from the injector 10 into the cylinder 2a from this amount of fuel. Then, the concentration of the evaporated fuel contained in the purge gas is estimated and learned from the required purge amount described later and the estimated evaporated fuel amount.

  In this embodiment, the concentration learning of the evaporated fuel is performed almost constantly during operation of the engine and is constantly updated. If the concentration learning has not yet been performed at the time of starting, etc., first, a small amount of purge gas is supplied to the intake pipe 23 under operating conditions with a low engine load such as idle operation. The concentration of the evaporated fuel is estimated based on the detected value of the A / F sensor SW3.

  Next, the purge gas flow rate control performed by the ECU 60 will be described with reference to the flowchart of FIG. The flowchart of FIG. 3 shows a control procedure after the evaporative fuel concentration learning is performed at least once.

  First, in step S1, the detected value (vehicle speed) of the vehicle speed sensor SW6, the detected value of the accelerator opening sensor SW5 (accelerator opening), the detected value of the shift speed sensor SW7 (shift speed), and the detection of the pump speed sensor SW4. Read the value (pump speed Np).

  Next, in step S2, the engine required torque is calculated based on the vehicle speed, accelerator opening, and gear position read in step S1.

  Next, in step S3, a required fuel amount that is a target value of the fuel amount to be supplied into the cylinder 2a is calculated based on the engine required torque calculated in step S2.

  Next, in step S4, based on the required fuel amount calculated in step S3, a required evaporated fuel amount that is the amount of evaporated fuel introduced into the cylinder 2a and the intake pipe 23 is calculated. Specifically, a certain amount of the required fuel amount is calculated as the required evaporated fuel amount. Thus, in the present embodiment, the required fuel amount, that is, the engine load and the required evaporated fuel amount are proportional.

  Next, in step S5, based on the required evaporated fuel amount calculated in step S4, the target purge gas amount per unit time introduced into the intake pipe 23, that is, the purge gas flow rate (hereinafter sometimes referred to as the purge amount). Calculate the requested purge amount that is the value. Specifically, the amount of purge gas including the required evaporated fuel amount is calculated as the required purge amount from the required evaporated fuel amount and the learned concentration of evaporated fuel.

  Next, in step S6, based on the required purge amount calculated in step S5, the target pump speed Npo, which is the target value of the speed of the air pump 44, and the basic DUTY, which is the basic value of the DUTY ratio of the purge valve 45, Set the ratio.

  In the present embodiment, the target pump speed Npo is set as shown by the solid line in FIG.

  Specifically, in the low flow rate region B1 where the required purge amount is less than the preset reference purge amount Qp1, the target pump rotation speed Npo is set to the low flow rate first rotation speed N1_min and the low flow rate second rotation speed. N1_max is set so as to increase as the required purge amount increases. That is, the lower flow rate side target pump rotation speed, which is the target pump rotation speed Npo in the low flow area B1, is higher as the required purge amount increases between the low flow rate first rotation speed N1_min and the lower flow rate second rotation speed N1_max. It is set to be. In the present embodiment, in the low flow rate region B1, the target pump speed Npo is increased in proportion to the required purge amount.

  The reference purge amount Qp1 is set to a value equal to or less than a certain percentage of the required fuel amount when the engine load becomes the switching load T1, and the low flow region B1 is a first operation region A1 in which lean CI combustion is performed. Included.

  On the other hand, in the high flow rate region B2 where the required purge amount is equal to or greater than the reference purge amount Qp1, the target pump rotational speed Npo is set to increase in proportion to the required purge amount from the high flow rate first rotational speed N2_min. That is, the high flow rate side target pump rotational speed which is the target pump rotational speed Npo in the high flow rate region B2 is set so as to increase in proportion to the required purge amount from the high flow rate first rotational speed N2_min.

  The high flow first rotation speed N2_min, which is the minimum value of the target pump speed Npo (high flow side target pump speed) in the high flow area B2, is the target pump speed Npo (low flow side target pump speed) in the low flow area B1. Number) is set to a value smaller than the low flow rate second rotation speed N1_max. Accordingly, the range of the target pump speed Npo in the high flow rate region B2 and the range of the target pump speed Npo in the low flow rate region B1 overlap. In this embodiment, the low flow rate first rotation speed N1_min and the high flow rate first rotation speed N2_min are set to the same value, and the entire range of the target pump rotation speed Npo in the low flow area B1 is the target in the high flow area B2. It overlaps the range of the pump speed Npo.

  The target pump speed Npo in the low flow rate region B1 is set such that the increase rate with respect to the required purge amount is smaller than the increase rate with respect to the required purge amount of the target pump speed Npo in the high flow rate region B2. That is, in FIG. 4, the line L1 indicating the target pump speed Npo in the low flow rate region B1 is gentler than the line L2 having the same inclination as the target pump speed Npo in the high flow rate region B2.

  Further, the basic DUTY ratio is set as shown in FIG.

  Specifically, in the low flow rate region B1, the basic DUTY ratio is between 0% and 100% so that the basic opening of the purge valve 45 is an intermediate opening between fully closed and fully opened. Set to an intermediate value. In this embodiment, the basic DUTY ratio is set within a range in which the valve opening degree and the DUTY ratio are proportional (for example, between 5% and 95%). In this embodiment, in the low flow rate region B1, the basic DUTY ratio increases between 0% and 100% as the required purge amount increases and increases in proportion to the required purge amount. Is set to

  On the other hand, in the high flow rate region B2, the basic DUTY ratio is set to 100%, and the basic opening of the purge valve 45 is fully opened.

  In step S7 following step S6, the pump speed is controlled to the target pump speed Npo set in step S6. Specifically, the driving force of the pump motor is changed so that the pump rotation speed becomes the target pump rotation speed Npo.

  In step S8 following step S7, it is determined whether the requested purge amount calculated in step S5 is less than the reference purge amount Qp1. That is, it is determined whether or not the vehicle is operating in the low flow rate region B1.

  If the determination in step S8 is NO, the requested purge amount is equal to or greater than the reference purge amount Qp1, and the operation is performed in the high flow rate region B2, the process proceeds to step S10, and the DUTY ratio is controlled to the basic DUTY ratio. As described above, in the high flow rate region B2, the basic DUTY ratio is set to 100%, and in step S10, the DUTY ratio is set to 100% and the purge valve 45 is fully opened. After step S10, the process ends (returns to step S1).

  On the other hand, if the determination in step S8 is YES and the required purge amount is less than the reference purge amount Qp1, and the operation is performed in the low flow rate region B1, the process proceeds to step S11.

  In step S11, whether or not the deviation (absolute value of these differences) between the target pump speed Npo set in step S6 and the current pump speed Np detected in step S1 is less than a preset reference deviation. Determine whether. The reference deviation is set to a value close to 0, for example.

  When the determination in step S11 is YES and the absolute value of the difference between the target pump speed Npo and the pump speed Np is less than the standard deviation, the process proceeds to step S12, and the DUTY ratio is controlled to the basic DUTY ratio. . As described above, in the low flow rate region B1, the basic DUTY ratio is set to an intermediate value, and in step S12, the purge valve 45 is set to an intermediate opening. After step S12, the process ends (returns to step S1).

  On the other hand, if the determination in step S11 is NO and the pump rotational speed Np has not reached the rotational speed at which the deviation from the target pump rotational speed is less than the reference deviation, the process proceeds to step S13.

  In step S13, the DUTY ratio of the purge valve 45 is corrected based on the current pump speed Np (the pump speed Np detected in step S1) and the required purge amount set in step S5. Specifically, the DUTY ratio is corrected to a DUTY ratio that allows the purge amount to be the required purge amount at the current pump speed Np. In the present embodiment, the relationship among the pump rotational speed Np, the DUTY ratio, and the purge amount is obtained in advance by experiments or the like, and is stored in the ECU 60 as a map. The ECU 60 determines the required purge amount and the current pump rotation from this map. A DUTY ratio corresponding to the number Np is extracted. After step S13, the process ends (returns to step S1). In this embodiment, the DUTY ratio is corrected within a range in which the DUTY ratio and the valve opening are proportional.

(3) Operation, etc. As described above, in the present embodiment, the entire range of the target pump speed Npo in the low flow rate region B1 overlaps the range of the target pump speed Npo in the high flow rate region B2. Therefore, at the time of transition from the low flow rate region B1 to the high flow rate region B2 or from the high flow rate region B2 to the low flow rate region B1, the amount of change in the target pump speed Npo can be kept small, and the pump speed can be made earlier. It is possible to control the target pump speed Npo at the transfer destination.

  This will be specifically described with reference to FIG. In FIG. 6, the chain line simply indicates the case where the target pump speed Npo is increased in proportion to the required purge amount in the entire region (region including the low flow region B1 and the high flow region B2) (hereinafter referred to as a comparative example). The target pump speed Npo is shown, and the solid line shows the target pump speed Npo of this embodiment. As shown in FIG. 6, when the required purge amount changes between the first purge amount Qp_a included in the low flow region B1 and the second purge amount Qp_b included in the high flow region B2 due to acceleration / deceleration or the like. In this embodiment, the change amount ΔN1 of the target pump speed can be significantly reduced compared to the change amount ΔN1 ′ of the target pump speed in the comparative example.

  Therefore, in the present embodiment, during a transition such as acceleration / deceleration, the deviation of the pump speed from the target value (target pump speed Npo) due to the response delay of the air pump 44 can be suppressed to a small value, and the purge amount requested purge It is possible to suppress the deviation from the amount, and to introduce the purge gas and the evaporated fuel into the proper amount intake pipe 23 and the cylinder 2a more reliably.

  In particular, in the present embodiment, as described above, the low flow rate region B1 is included in the first operation region A1 where the lean CI combustion is performed. Therefore, if the air-fuel ratio of the air-fuel mixture deviates in this region B1 (A1), proper combustion cannot be realized, and the engine performance may be significantly deteriorated. For example, misfire may occur or exhaust performance may deteriorate. On the other hand, in this embodiment, since an appropriate amount of evaporated fuel can be supplied to the intake pipe 23 and the cylinder 2a in the low flow rate region B1 as described above, the air-fuel ratio of the air-fuel mixture in the cylinder 2a is set appropriately. Therefore, it is possible to achieve proper lean CI combustion while maintaining a good value, and to improve engine performance.

  Furthermore, in the present embodiment, basically, in the low flow rate region B1, the DUTY ratio of the purge valve 45 is set to an intermediate value, and the opening degree of the purge valve 45 is maintained at the intermediate opening degree, while the pump rotational speed and the target pump rotation are maintained. When the difference from the number is equal to or larger than the reference deviation, the DUTY ratio is corrected so that the required purge amount is realized while the pump speed is changed toward the target pump speed. Therefore, when the required purge amount changes in the low flow rate region B1 and at the time of transition from the high flow rate region B2 to the low flow rate region B1, the required value of the purge amount (required purge amount) associated with the response delay of the air pump 44. Therefore, the amount of evaporated fuel introduced into the intake pipe 23 and thus the air-fuel ratio of the air-fuel mixture in the cylinder 2a can be more reliably set to an appropriate value.

  This will be specifically described with reference to FIG. FIG. 7 schematically shows temporal changes in the purge amount, the pump speed, and the DUTY ratio of the purge valve 45 when the required purge amount decreases from the second purge amount Qp_b shown in FIG. 6 to the first purge amount Qp_a due to deceleration or the like. FIG. In FIG. 7, a solid line indicates a state when the above control according to the present embodiment is performed, and a chain line indicates a state in the comparative example in which the control of steps S <b> 11 and S <b> 13 is omitted.

  When the required purge amount decreases rapidly at time t1, the target pump speed also decreases. However, since the rotation of the air pump 44 has a response delay, the pump rotation speed does not decrease immediately. Therefore, in the case of the comparative example, that is, when the DUTY ratio of the purge valve 45 is not corrected based on the pump rotational speed or the like (when the DUTY ratio is simply changed to the basic DUTY ratio), the purge amount is reduced only gradually. The deviation of the purge amount from the target value (required purge amount) becomes large. Then, the amount of evaporated fuel introduced into the intake pipe 23 is greatly deviated from the required amount of evaporated fuel (required evaporated fuel amount).

  On the other hand, in this embodiment, when the required purge amount decreases to a value in the low flow rate region B1 at time t1, the DUTY ratio of the purge valve 45 is corrected according to the current pump speed and the required purge amount. . In the example shown in FIG. 7, immediately after time t1, the DUTY ratio of the purge valve 45 is set to a value smaller than the basic DUTY ratio (the value of the comparative example indicated by the chain line), and the purge valve 45 is controlled to the closing side. Then, the DUTY ratio of the purge valve 45 is increased as the pump speed decreases. Therefore, the purge amount can be reduced to the required purge amount at an early stage and maintained at the required purge amount. Therefore, the air-fuel ratio of the air-fuel mixture in the cylinder 2a can be set to an appropriate value.

(4) Modifications In the above embodiment, the case where the entire range of the target pump speed Npo in the low flow rate region B1 is included in the range of the target pump speed Npo in the high flow rate region B2 has been described, but only a part thereof It may be duplicated. That is, in the above embodiment, the low flow rate first rotation speed (the minimum value of the target pump rotation speed in the low flow area B1) is the high flow rate first rotation speed (the minimum value of the target pump rotation speed in the high flow area B2) N2_min. May be smaller. Of course, the low flow rate first rotation speed N1_min may be larger than the high flow rate first rotation speed N2_min.

  In the above embodiment, the case where the target pump rotation speed Npo is increased in proportion to the required purge amount in the low flow rate region B1 has been described. However, as shown in the solid line in FIG. The rotation speed Npo may be constant regardless of the required purge amount. In this way, the entire range of the target pump speed Npo in the low flow rate region B1 can be included in the range of the target pump speed Npo in the high flow rate region B2. Further, when the operating condition (required purge amount) changes in the low flow rate region B1, the target pump speed Npo does not change. Therefore, it is possible to suppress a deviation from the target value of the pump rotation speed and the amount of evaporated fuel supplied to the intake pipe 23 at the time of transition between the low flow rate region B1 and the high flow rate region B2, and to operate in the low flow rate region B1. Even if the condition (required purge amount) changes, it is possible to prevent the amount of evaporated fuel supplied to the intake pipe 23 from deviating from the required amount due to the response delay of the air pump 44.

  However, when the target pump speed Npo in the low flow rate region B1 is constant regardless of the required purge amount, that is, the target pump speed Npo in the low flow rate region B1 is set as shown by the solid line in FIG. In this case, the target pump speed Npo is higher at least in the region where the required purge amount is smaller than in the above-described embodiment indicated by the chain line in FIG. 8, that is, when the target pump speed Npo is increased according to the required purge amount. . Therefore, in order to reduce the power consumption of the pump motor and improve the fuel efficiency, it is preferable to increase the target pump speed Npo according to the required purge amount.

  Further, in the above embodiment, the target pump speed Npo is increased in accordance with the required purge amount in the low flow rate region B1, and the increase rate of the target pump speed with respect to the required purge amount is higher in the low flow rate region than in the high flow rate region. However, the rate of increase may be the same or may be set to be larger in the low flow rate region. However, if the rate of increase of the target pump speed relative to the required purge amount is set to be smaller in the low flow rate region as in the above embodiment, the target pump speed range in the low flow rate region can be kept narrow. Therefore, the overlapping range of the target pump speeds in the low flow rate region and the high flow rate region can be further increased. Therefore, the deviation from the target value of the pump rotation speed and the deviation from the required value of the evaporated fuel amount supplied to the intake pipe 23 at the time of shifting to these regions can be further suppressed.

  In the above embodiment, the basic DUTY ratio in the low flow rate region B1 is set to increase in proportion to the required purge amount. However, the basic DUTY ratio in the low flow rate region B1 is 0% and 100%. It is not limited to the above as long as it is an intermediate value between. For example, in the low flow rate region B1, the basic DUTY ratio may be constant regardless of the required purge amount.

  Further, the combustion mode in the low flow rate region B1 is not limited to the above. However, when the lean CI combustion is performed in the region B1 as described above, appropriate combustion can be realized by appropriately controlling the air-fuel ratio, and a high effect can be obtained.

1 Engine body 2a Cylinder 23 Intake pipe (intake passage)
42 Canister 43 Purge pipe (Purge passage)
44 Air pump (pump)
45 Purge valve 60 ECU (control means)

Claims (5)

A cylinder, an intake passage for introducing air into the cylinder, a fuel tank in which fuel is stored, and a canister that detachably adsorbs the evaporated fuel generated in the fuel tank, and the evaporated fuel removed from the canister An internal combustion engine evaporative fuel control device in which a purge gas containing is introduced into an intake passage,
A purge passage communicating the canister and the intake passage;
A purge valve provided in the purge passage for opening and closing the passage;
A rotary pump that is provided in the purge passage and increases the pressure difference between the upstream end and the downstream end of the purge passage as the rotational speed increases;
Control means for controlling the opening of the purge valve and the rotational speed of the pump,
The control means includes
In a low flow rate region where the required purge amount, which is the amount of purge gas required, is less than a predetermined reference purge amount, the opening of the purge valve is controlled to an intermediate opening between its fully closed and fully opened, and the pump Is controlled to a preset low flow rate target pump speed,
In the high flow rate region where the required purge amount is equal to or greater than the reference purge amount, the purge valve opening is controlled to be fully opened, and the pump speed is controlled to a preset high flow rate side target pump speed,
The higher flow rate target pump speed is set higher as the required purge amount is larger,
The minimum value of the high flow rate side target pump speed is set to a value smaller than the maximum value of the low flow rate side target pump speed. An evaporative fuel control device for an internal combustion engine according to claim 1,
The lower flow rate target pump speed is higher as the required purge amount is larger, and the increase rate with respect to the required purge amount is smaller than the increase rate with respect to the required purge amount of the higher flow rate target pump speed. Is set,
The evaporative fuel control device for an internal combustion engine, wherein the intermediate opening is set to open as the required purge amount increases. An evaporative fuel control device for an internal combustion engine according to claim 1,
The low flow rate side target pump speed is set to a constant value throughout the low flow rate region,
The evaporative fuel control device for an internal combustion engine, wherein the intermediate opening is set to open as the required purge amount increases. An evaporative fuel control device for an internal combustion engine according to any one of claims 1 to 3,
An evaporative fuel control apparatus for an internal combustion engine, wherein the low flow rate region is set to a region where compressed self-ignition combustion of an air-fuel ratio greater than 1 is performed in a cylinder. An evaporative fuel control device for an internal combustion engine according to any one of claims 1 to 4,
When the deviation between the rotation speed of the pump and the target pump rotation speed on the low flow rate side is greater than or equal to a predetermined reference deviation at the time of transition from the high flow rate region to the low flow rate region, the control means The opening of the purge valve is corrected according to the required purge amount and the rotational speed of the pump so that the amount of purge gas introduced into the intake passage becomes the required purge amount until it becomes less than the reference deviation. An evaporative fuel control apparatus for an internal combustion engine characterized by the above.

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