JP6098658B2 - 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, which is air containing evaporated fuel, is introduced into a passage.

  Conventionally, evaporated 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 that a first passage having a DUTY control valve (a valve whose opening is changed by changing the DUTY ratio) between a canister and an intake passage, an orifice and an ON / OFF in order from the upstream side. The thing provided with the 2nd channel | path provided with the OFF valve (valve switched only to a full close and full open) is disclosed. In the device of Patent Document 1, under a driving condition in which the throttle valve is closed such as during idling, a small amount of purge gas (air containing evaporated fuel) is introduced into the intake passage through the second passage, In other normal operating conditions, the purge gas is introduced into the intake passage via the first passage, whereby an amount of purge gas corresponding to the operation condition is introduced into the intake passage by the DUTY control valve.

Japanese Patent Laid-Open No. 5-280434

  Here, as in Patent Document 1, when the DUTY control valve is provided between the canister and the intake passage and the flow rate of the purge gas is changed by the DUTY control valve, the DUTY ratio of the DUTY control valve is changed. Thus, the flow rate of the purge gas can be controlled to an amount corresponding to the operating conditions. However, in this configuration, if intake pulsation occurs in the intake passage due to the closing timing of the intake valve being set at a relatively late time such that the intake air blows back into the intake passage from within the cylinder, the DUTY control valve There is a problem that the flow rate of the purge gas passing through the DUTY control valve, that is, the amount of the evaporated fuel introduced into the intake passage and the cylinder varies depending on the valve opening timing. Further, since the flow resistance of the DUTY control valve is relatively large, there is a problem that the introduction of the purge gas through the DUTY control valve reduces the maximum flow rate of the purge gas.

  The present invention has been made in view of the circumstances as described above, and is capable of introducing an appropriate amount of purge gas and evaporated fuel into the intake passage while increasing the maximum flow rate of the purge gas. An object is to provide an apparatus.

  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, which is an air containing evaporative fuel, is introduced from the canister into an intake passage, wherein the canister and the intake passage communicate with each other. Two passages, a first opening / closing valve provided in the first passage for opening and closing the first passage, and an upstream portion provided in a portion of the first passage downstream of the first opening / closing valve. A nozzle including a throttle portion having a smaller flow area, a second on-off valve provided in the second passage for opening and closing the second passage, and each portion including the first on-off valve and the second on-off valve Control to control The first on-off valve is a DUTY control valve whose opening degree is changed by changing the DUTY ratio, and the second on-off valve is an ON / OFF valve that is changed to fully closed and fully open. And the control means closes the second on-off valve and opens the first on-off valve when the required purge amount, which is a required value of the purge gas flow rate, is lower than a preset reference flow rate. When the required purge amount is equal to or greater than the reference flow rate, the second on-off valve is opened and the first on-off valve is closed (Claim 1).

  According to the present invention, the purge gas and the evaporated fuel contained therein can be introduced into the intake passage more appropriately while suppressing the influence of the intake pulsation on the flow rate of the purge gas while increasing the maximum flow rate of the purge gas. .

  Specifically, in the present invention, under the operating condition where the required purge amount is lower than the reference flow rate, the second on-off valve is closed and the first on-off valve, which is a DUTY control valve, is opened, and the DUTY control valve The purge gas is introduced from the canister into the intake passage through the nozzle. Therefore, by changing the DUTY ratio of the first on-off valve, the flow rate of the purge gas can be accurately controlled to the required low flow rate, the purge gas flow rate can be stabilized by the nozzle, and the required purge amount is low. Under operating conditions in which intake pulsation tends to have a large influence on the flow rate of purge gas, fluctuations in the amount of purge gas and evaporated fuel supplied to the intake passage can be suppressed.

  In addition, under operating conditions where the required purge amount is equal to or higher than the reference flow rate, the second on-off valve consisting of an ON / OFF valve having a smaller flow path resistance than the DUTY control valve is opened and the first on-off valve is closed, Purge gas is introduced from the canister into the intake passage via the second on-off valve. Therefore, a larger amount of purge gas can be introduced into the intake passage, and the maximum flow rate of the purge gas can be increased.

  In the present invention, it is provided with a pump provided in a passage between the nozzle and the intake passage to reduce the pressure in the passage by rotating, and the control means has the required purge amount higher than the reference flow rate. If it is lower, it is preferable to control the rotational speed of the pump to a rotational speed at which the flow rate of the purge gas passing through the throttle portion is constant regardless of the pressure downstream of the nozzle.

  According to this configuration, even when the intake pulsation occurs, that is, when the pressure on the downstream side of the nozzle fluctuates, the flow rate of the purge gas passing through the nozzle is constant regardless of the pressure on the downstream side. Thus, fluctuations in the purge gas flow rate associated with the intake pulsation can be more reliably suppressed.

  The said structure WHEREIN: The said 1st channel | path and the said 2nd channel | path are merged in the downstream rather than the said nozzle and the said 2nd on-off valve, and the said pump joins the said 1st channel | path and the said 2nd channel | path. The control means controls the flow rate of the purge gas by changing the rotational speed of the pump when the required purge amount is equal to or higher than the reference flow rate. (Claim 3).

  In this way, when the required purge amount is higher than the reference flow rate, the amount of purge gas and evaporated fuel supplied to the intake passage can be controlled to an appropriate amount according to the operating conditions by changing the pump speed. it can.

  In the above configuration, when the required purge amount is switched from an amount lower than the reference flow rate to an amount equal to or higher than the reference flow rate, the control means sets the rotation speed of the pump to the required purge amount after the switching. If the rotation speed is higher than the corresponding rotation speed, the rotation speed of the pump is changed to the rotation speed corresponding to the required purge amount after switching, and then the first on-off valve is closed and the second on-off valve is opened. It is preferable to make it valve (Claim 4).

  In this way, it is possible to avoid opening the second on-off valve in a state where the rotational speed of the pump is higher than the rotational speed corresponding to the required purge amount after switching due to a response delay. Therefore, by opening the second on-off valve with the pump rotating at a high speed, it is possible to avoid introducing a larger amount of purge gas than the required purge amount into the intake passage and the cylinder. The deviation from the required value of the air-fuel ratio in the cylinder due to the introduction of a larger amount of fuel than the required amount of evaporated fuel into the cylinder can be suppressed.

  As described above, according to the evaporated fuel control apparatus for an internal combustion engine of the present invention, the purge gas and the evaporated fuel are more appropriately controlled while suppressing the influence of the intake pulsation on the purge gas flow rate while increasing the maximum flow rate of the purge gas. Can be introduced into 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 required purge amount and DUTY ratio of the 1st purge valve. It is a figure for demonstrating the relationship between an intake pulsation and purge amount.

(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 43 that connects the canister 42 and the intake pipe 23. It has.

  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.

  In the middle of the purge pipe 43, the purge pipe 43 is divided into a bifurcated portion, a low flow purge pipe (first passage) 43a and a high flow purge pipe (second passage) 43b. Specifically, the purge pipe 43 branches into the low flow purge pipe 43a and the high flow purge pipe 43b on the way from the upstream side (canister 42 side) to the intake pipe 23, and then joins at the junction 43c. Then, it becomes a single passage again and is connected to the intake pipe 23.

  Among the purge pipes 43, the gas in the passage 43d is sucked into the passage 43d between the joining portion 43c where the low flow purge pipe 43a and the high flow purge pipe 43b join and the intake pipe 23. An air pump (pump) 44 for reducing the internal pressure is provided. The air pump 44 is driven to rotate by a pump motor (not shown) to suck gas, and the pressure in the passage 43d is further decreased as the rotational speed is higher. The air pump 44 is provided with a pump rotation speed sensor SW4 that detects the rotation speed.

  The low-flow purge pipe 43a is provided with a first purge valve (first on-off valve) 45 and a sonic nozzle (nozzle) 46 in order from the upstream side.

  The first purge valve 45 is a valve that opens and closes a passage in the low flow purge pipe 43a. The first purge valve 45 is a DUTY control valve (DUTY control valve), and is repeatedly opened and closed, and the DUTY ratio, which is the ratio of the valve opening period to the unit period including one valve opening period and the valve closing period, is changed. Thus, the opening degree is changed. The first 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 first purge valve 45 comprising this 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. Specifically, there are cases where 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%.

  The sonic nozzle 46 is a nozzle having a throat portion (throttle portion) 46b whose flow area is smaller than that of the upstream portion. In this embodiment, as shown in FIG. 1, the sonic nozzle 46 includes an upstream end portion of the nozzle 46, and the flow passage area is substantially constant in the upstream and downstream directions, and the flow passage is more than the entrance portion 46 a. The throat portion 46b has a reduced area, and the diffuser portion 46c has a flow passage area that gradually increases from the throat portion 46b toward the downstream side. With this configuration, the speed of the gas passing through the sonic nozzle 46 is increased when flowing into the throat portion 46b from the inlet portion 46a, and after passing through the throat portion 46b at the maximum flow velocity, the gas gradually passes through the diffuser portion 46c. Pressure is restored.

  Further, the sonic nozzle 46 has a flow rate of gas passing through the throat portion 46b when a pressure ratio (downstream pressure / upstream pressure), which is a ratio between the upstream pressure and the downstream pressure, is equal to or lower than a predetermined critical pressure ratio. This is a so-called critical nozzle (or sonic nozzle) that is configured so that the flow becomes choked at the speed of sound. Therefore, if the pressure ratio is equal to or lower than the critical pressure ratio, the flow velocity of the gas passing through the throat portion 46b is maintained at the sonic speed regardless of the downstream pressure.

  On the other hand, the high flow purge pipe 43b is provided with a second purge valve (second open / close valve) 47 for opening and closing the high flow purge pipe 43b. The second purge valve 47 is an ON / OFF valve that can be switched only between full closing and full opening.

(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). The first purge valve 45 (the drive mechanism that drives the first purge valve 45), the second purge valve 47 (the drive mechanism that drives the second purge valve 47), and the like. Based on the result of the above, a drive control signal is output to each of these devices.

(I) Control of engine body An outline of control of the engine body 1 will be described.

  FIG. 2 is a diagram conceptually showing a control map according 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.

  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 the present embodiment, in the first operating region A1, particularly in the region where the engine load is low, the opening / closing timing of the intake valve 8 is set to the retard side, and the exhaust valve 9 is closed before the intake valve 8 is closed. Open the valve. That is, a negative overlap period in which the valve opening timings of these valves 8 and 9 do not overlap is provided between the exhaust valve 9 closing and the intake valve 8 opening.

  The intake / exhaust valves 8 and 9 are controlled in this way in order to realize stable CI combustion. That is, in an operation region where the engine load is low, misfire may occur due to the low temperature in the combustion chamber 5. On the other hand, when a negative overlap period is provided in the intake stroke, the burned gas remaining in the combustion chamber 5 must be expanded during the negative overlap period, and the pumping loss increases. If the pumping loss increases in this way, the fuel amount can be increased by the pumping loss with respect to the required engine output, and the temperature of the combustion chamber 5 and the air-fuel mixture can be increased to achieve stable CI combustion. realizable.

  On the other hand, in the operation region where the engine load is relatively high and the ignitability is high in the first operation region A1, the intake valve 8 is opened before the closing timing of the exhaust valve 9, and the valves 8, 9 are opened. Overlapping valve timing. As a result, high-temperature exhaust gas remains in the combustion chamber 5 to achieve stable CI combustion.

  Note that, as described above, in the present embodiment, the throttle valve 25 is almost always fully opened.

(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, it is determined whether or not the required purge amount is equal to or greater than a preset reference purge amount (reference flow rate) Qp1. In the present embodiment, the reference purge amount Qp1 is set to an amount equal to or less than a value corresponding to the required fuel amount when the engine load becomes the switching load T1 (a constant ratio amount of the required fuel amount). Therefore, if the determination in step S6 is NO, the engine load is less than the switching load T1 and the engine is operating in the region included in the first operation region A1, and CI combustion is performed.

  When the determination in step S6 is NO, the process proceeds to step S7, and the second purge valve 47 is closed (when the valve is already closed, the valve is kept closed). In step S8, the pump rotation speed, which is the rotation speed of the air pump 44, is set to a preset low flow rate rotation speed N1, and in step S9, the first purge valve 45 is set according to the required purge amount calculated in step S5. Change the DUTY ratio.

  Thus, when the determination in step S6 is NO and the required purge amount is less than the reference purge amount Qp1, the second purge valve 47 is closed to set the DUTY ratio of the first purge valve 45 to a predetermined value, and for low flow rate Purge gas is introduced into the intake pipe 23 through the purge pipe 43a.

  The low flow rate N1 is set to a constant value regardless of the required purge amount. Further, when the air pump 44 is rotated at the low flow rate N1, the low flow rate N1 is the pressure downstream of the sonic nozzle 46 (the air pump 44 and the sonic nozzle 46 in the low flow rate purge pipe 43a). And the pressure on the upstream side of the sonic nozzle 46 (the pressure between the first purge valve 45 and the sonic nozzle 46 in the low flow rate purge pipe 43a) The number of rotations is equal to or lower than the critical pressure ratio, and is set in advance by experiments or the like.

  Here, as described above, in the present embodiment, the first purge valve 45 is provided on the upstream side of the sonic nozzle 46, and the gas whose flow rate is increased by the first purge valve 45 flows into the sonic nozzle 46. That is, pressure loss occurs in the first purge valve 45, and accordingly, the gas flow velocity is increased when the first purge valve 45 passes through. Therefore, in this embodiment, the downstream pressure necessary for increasing the gas velocity to the sonic velocity at the throat portion 46b of the sonic nozzle 46 is relatively low (when the first purge valve 45 is provided downstream of the sonic nozzle 46). The low flow rate N1 is set to a relatively high value.

  By controlling the pump rotational speed to the low flow rate rotational speed N1 set as described above, the speed of the purge gas passing through the throat portion 46b of the sonic nozzle 46 is maintained at the sonic speed. Therefore, the flow rate of the purge gas introduced into the intake pipe 23 and the cylinder 2 a is proportional to the opening of the first purge valve 45.

  Therefore, in step S9, as shown in FIG. 5, the DUTY ratio of the first purge valve 45 is changed in proportion to the required purge amount. Specifically, as described above, there is a possibility that the DUTY ratio and the opening degree of the first purge valve 45 are not completely proportional in the vicinity of the fully closed position and the fully open position. Therefore, the DUTY ratio is changed within a range (range from Dmin to Dmax) that is proportional to the opening of the first purge valve 45 and thus the flow rate of the purge gas that passes through the first purge valve 45.

  On the other hand, if the determination in step S6 is YES and the required purge amount is equal to or greater than the reference purge amount Qp1, the process proceeds to step S10.

  In step S10, a target pump speed Npo, which is a target value of the speed of the air pump 44, is set based on the required purge amount calculated in step S5.

  In this embodiment, when the required purge amount is equal to or larger than the reference purge amount Qp1, basically, the first purge valve 45 is closed and the second purge valve 47 is fully opened, and the purge gas is sucked in via the high flow rate purge pipe 43b. The purge amount is controlled to the required purge amount by introducing it into the pipe 23 and changing the pump rotation speed. Here, as described above, the air pump 44 is configured to decrease the pressure in the passage 43d as the rotational speed increases. Accordingly, in step S10, the differential pressure between the upstream end and the downstream end of the high flow rate purge pipe 43b (the differential pressure between the canister 42 and the intake pipe 23) increases, and the flow rate of the purge gas passing through the high flow rate purge pipe 43b is reduced. The target pump speed Npo is set higher as the required purge amount increases so as to increase. Specifically, as shown in FIG. 4, when the required purge amount is equal to or greater than the reference purge amount Qp1, the target pump speed Npo is increased in proportion to the required purge amount.

  As shown in FIG. 4, in this embodiment, the pump rotation speed when the required purge amount becomes the reference purge amount Qp1 is set to the switching start rotation speed N2 lower than the low flow rate rotation speed N1. The target pump speed is increased as the required purge amount increases from the switching start speed N2.

  In step S11 following step S10, the pump speed is controlled to the target pump speed Npo set in step S10. Specifically, the driving force of the pump motor is changed according to the target pump speed Npo.

  In step S12 following step S11, the purge gas is being introduced into the intake pipe 23 via the low flow rate purge pipe 43a (the DUTY ratio of the first purge valve 45 is not 0%), and the current pump rotational speed Np is It is determined whether or not it is greater than the target pump speed Npo.

  If the determination in step S12 is YES, the process proceeds to step S13, where the DUTY ratio of the first purge valve 45 is set to 100% and the first purge valve 45 is fully opened.

  On the other hand, if the determination in step S12 is NO, that is, purge gas is being introduced into the intake pipe 23 via the high flow rate purge pipe 43b (the DUTY ratio of the first purge valve 45 is 0%), or the current pump rotation When the number Np is equal to or less than the target pump speed Npo, the process proceeds to step S14, where the DUTY ratio of the first purge valve 45 is set to 0% (when already 0%, the first purge valve 45 is maintained at 0%). In addition to closing, in step S15, the second purge valve 47 is opened (if the valve is already opened, the valve is kept open).

  That is, if the determination in step S6 is YES and the required purge amount is equal to or greater than the reference purge amount Qp1, basically, the first purge valve 45 is closed and the second purge valve 47 is fully opened, The purge amount is controlled to the required purge amount by introducing the purge gas into the intake pipe 23 via the purge pipe 43b and changing the pump rotation speed. However, when the required purge amount becomes equal to or higher than the reference purge amount Qp1 while the purge gas is introduced into the intake pipe 23 via the low flow rate purge pipe 43a, that is, the required purge amount is less than the reference purge amount Qp1 and is the reference purge amount. When switching to the amount Qp1 or more, while the pump rotational speed Np is higher than the target pump rotational speed Npo, the pump rotational speed Np is decreased toward the target pump rotational speed Npo, via the low flow rate purge pipe 43a. The purge gas is continued to be introduced into the intake pipe 23 and the first purge valve 45 is fully opened to increase the purge amount. When the pump rotation speed Np decreases to the target pump rotation speed Npo, the first purge valve 45 is closed, the second purge valve 47 is opened, and the purge gas is supplied to the intake pipe 23 via the high flow purge pipe 43b. .

  Thus, in this embodiment, when the required purge amount is less than the reference purge amount Qp1, the purge gas is introduced into the intake pipe 23 via the low flow purge pipe 43a. At this time, the rotation speed of the air pump 44 is maintained constant at the low flow rate N1, and the purge amount is controlled to the required purge amount by changing the DUTY ratio of the first purge valve 45.

  On the other hand, when the required purge amount is equal to or larger than the reference purge amount Qp1, purge gas is introduced into the intake pipe 23 via the high flow rate purge pipe 43b. Then, the purge amount is made the required purge amount by changing the rotation speed of the air pump 44. Further, when the required purge amount is switched from an amount less than the reference purge amount Qp1 to an amount equal to or more than the reference purge amount Qp1, the first purge valve 45 is fully opened until the pump rotational speed falls below the target pump rotational speed Then, the purge gas is supplied to the intake pipe 23 through the low flow rate purge pipe 43a.

(3) Operation As described above, in this embodiment, when the required purge amount is less than the reference purge amount Qp1 and a relatively small amount of purge gas is introduced into the intake pipe 23, the low-flow purge pipe 43a is used. Purge gas is introduced into the intake pipe 23, and the purge amount is controlled to the required purge amount by changing the DUTY ratio of the first purge valve 45. Therefore, the purge amount can be accurately controlled to a small required amount by changing the DUTY ratio. As a result, the air-fuel ratio in the cylinder 2a can be properly controlled. Further, when estimating and learning the concentration of the evaporated fuel by supplying a small amount of purge gas to the intake pipe 23 and the cylinder 2a as described above, this estimation and learning can be performed with higher accuracy.

  In addition, the low flow purge pipe 43a is provided with the sonic nozzle 46 configured as described above. When the purge gas is introduced into the intake pipe 23 via the sonic nozzle 46 (via the low flow rate purge pipe 43a), the rotation speed N1 of the low flow rate is set as described above. Thus, the speed at which the purge gas passes through the sonic nozzle 46 (throat portion 46b) is maintained at the speed of sound regardless of the pressure on the downstream side of the sonic nozzle 46. Accordingly, the flow rate of the purge gas supplied to the intake pipe 23 due to the intake air pulsation in the intake pipe 23 can be avoided while changing the flow rate of the purge gas depending on the DUTY ratio (opening degree) of the first purge valve 45. . Therefore, it is possible to avoid fluctuations in the amount of evaporated fuel introduced into the cylinder 2a and the air-fuel ratio in the cylinder 2a due to this intake pulsation, and to make the evaporated fuel amount and air-fuel ratio more appropriate values. Can do.

  This will be specifically described with reference to FIG. FIG. 6 is a schematic diagram showing temporal changes in the current supplied to the first purge valve 45 (first purge valve current flow), the pressure in the intake pipe 23 (intake pipe pressure), and the purge amount. In the purge amount of FIG. 6, the broken line indicates the change in the purge amount when the sonic nozzle 46 is omitted, and the solid line indicates the change in the purge amount of the present embodiment in which the sonic nozzle 46 is provided. As shown in FIG. 6, the pressure in the intake pipe 23 may pulsate in synchronization with the rotation of the engine. For example, in the present embodiment, the opening / closing timing of the intake valve 8 is set to the retard side in the region where the engine load is particularly low in the first operation region A1. Therefore, intake air blows back into the intake passage from the inside of the cylinder, and intake pulsation is caused accordingly.

  As described above, when the intake pulsation occurs in the intake pipe 23 and the sonic nozzle 46 is not provided, the purge amount varies depending on the opening timing of the first purge valve 45 as shown by the broken line in FIG. . When the purge amount varies in this manner, the amount of evaporated fuel supplied to the cylinder 2a varies and the air-fuel ratio in the cylinder 2a varies.

  In particular, as in this embodiment, when the throttle valve 25 is almost always fully open, the negative pressure generated in the intake pipe 23 is small, and the upstream end and the downstream end of the low flow purge pipe 43a are small. Since the differential pressure becomes small, the influence of the intake pulsation, that is, the pressure fluctuation in the intake pipe 23, on the differential pressure and thus the purge amount becomes large. Further, the influence of the fluctuation of the purge amount, that is, the fluctuation of the evaporated fuel amount, on the air-fuel ratio of the cylinder 2a, that is, the deviation from the required value of the air-fuel ratio due to the fluctuation of the evaporated fuel amount is the total The smaller the amount of fuel, the larger.

  In contrast, in this embodiment, as described above, when the required purge amount is less than the reference purge amount Qp1, the speed of the purge gas passing through the sonic nozzle 46 is the sonic velocity regardless of the pressure on the downstream side of the sonic nozzle 46. Maintained. That is, even when the pressure in the intake pipe 23 located on the downstream side of the sonic nozzle 46 fluctuates, the speed of the purge gas passing through the sonic nozzle 46 is maintained constant. Therefore, as shown by the solid line in FIG. 6, even when intake pulsation occurs, the purge amount can be made constant regardless of the opening timing of the first purge valve 45, and the fluctuation of the air-fuel ratio in the cylinder 2a is suppressed. be able to.

  In particular, since the required evaporated fuel amount and the required fuel amount are set to be proportional, when the required purge amount is less than the reference purge amount Qp1, the total fuel amount supplied to the cylinder 2a is relatively small. However, since the purge gas is supplied to the intake pipe 23 via the sonic nozzle 46 under such a condition that the total fuel amount is small, fluctuations in the purge amount and the evaporated fuel amount due to the intake pulsation are suppressed. Deviation from the required value of the air-fuel ratio can be effectively reduced.

  In the present embodiment, since the sonic nozzle 46 is provided on the downstream side of the first purge valve 45, the low flow rate N1 can be set to a relatively high value as described above. Therefore, while maintaining the purge gas speed at the sonic speed in the sonic nozzle 46, the driving force of the pump motor can be kept small, and the power consumption of the pump motor and hence the fuel efficiency can be improved.

  Further, in the present embodiment, when the required purge amount is equal to or larger than the reference purge amount Qp1, the purge gas is supplied to the intake pipe via the second purge valve 47, which is an ON / OFF valve with less pressure loss than the first purge valve 45, which is a DUTY control valve. 23. Therefore, more purge gas can be introduced into the intake pipe 23. Specifically, when the purge gas is supplied to the intake pipe 23 via the first purge valve 45, which is a DUTY control valve, the pressure loss at the first purge valve 45 is large. The purge valve 45 and the sonic nozzle 46 need to be enlarged. Alternatively, it is necessary to increase the rotational speed of the air pump 44 in order to lower the pressure on the downstream side of the low flow rate purge pipe 43a, and the fuel efficiency is deteriorated. In contrast, in the present embodiment, the maximum amount of purge gas supplied to the intake pipe 23 can be increased without increasing the size of the first purge valve 45 and the sonic nozzle 46 and deteriorating fuel consumption.

  In the present embodiment, the air pump 44 is provided in the passage 43d between the merging portion 43c where the low flow rate purge pipe 43a and the high flow rate purge pipe 43b merge and the intake pipe 23, and the required purge amount Is equal to or greater than the reference purge amount Qp1 and the purge gas is introduced into the intake pipe 23 via the high flow purge pipe 43b, the purge amount is controlled by changing the rotational speed of the air pump 44. Therefore, even when the required purge amount is equal to or greater than the reference purge amount Qp1, an appropriate amount of purge gas can be supplied to the intake pipe 23 according to the operating condition (required fuel amount).

  Further, in the present embodiment, when the required purge amount is switched from an amount less than the reference purge amount Qp1 to an amount equal to or more than the reference purge amount Qp1, the first pump rotation number is decreased until the rotation speed of the air pump 44 decreases below the target pump rotation number Npo. With the 1 purge valve 45 fully opened, purge gas is supplied to the intake pipe 23 through the low flow rate purge pipe 43a. Therefore, it is avoided that the second purge valve 47 is opened in a state where the pump rotational speed is higher than the target pump rotational speed corresponding to the required purge amount due to the response delay of the air pump 44. Here, if the second purge valve 47 is opened while the rotation speed of the air pump 44 is high, a larger amount of purge gas and evaporated fuel are introduced into the intake pipe 23 and the cylinder 2a, and the air-fuel ratio becomes excessive. Become. On the other hand, in this embodiment, it is possible to avoid the excessive evaporated fuel from being introduced into the intake pipe 23 and the cylinder 2a, and to set the air-fuel ratio to an appropriate value.

(4) Modified Example In the above embodiment, the air pump 44 is provided between the merging portion 43 c and the intake pipe 23 where the low flow purge pipe 43 a and the high flow purge pipe 43 b of the purge pipe 43 merge. Although the case has been described, the air pump 44 may be provided in a portion between the sonic nozzle 46 and the merging portion 43c in the low flow rate purge pipe 43a. However, if the air pump 44 is provided downstream of the merging portion 43c as in the above embodiment, the rotation of the air pump 44 is performed when the purge gas is introduced into the intake pipe 23 via the high flow purge pipe 43b. The purge amount can be controlled to the required purge amount by changing the number.

  Moreover, the sonic nozzle should just be a nozzle which has a throat part by which the flow-path area was made smaller than the upstream part, and the specific structure is not restricted above. For example, the inlet portion 46a of the sonic nozzle 46 may have a shape in which the channel area becomes smaller toward the downstream side. Moreover, it is comprised so that the flow-path area of the whole nozzle may become small toward the downstream, and a downstream end part may be made into the throat part.

1 Engine body 2a Cylinder 42 Canister 43a Low flow purge pipe (first passage)
43b High flow purge pipe (second passage)
44 Air pump (pump)
45 First purge valve (first on-off valve)
46 Sonic nozzle (nozzle)
46a Throat part (throttle part)
47 Second purge valve (second on-off valve)
60 ECU (control means)

Claims (4)

A cylinder, an intake passage for introducing air into the cylinder, a fuel tank in which fuel is stored, and a canister that adsorbs evaporated fuel generated in the fuel tank in a detachable manner. The evaporated fuel is supplied from the canister to the intake passage. An evaporative fuel control device for an internal combustion engine into which purge gas that is air is introduced,
A first passage and a second passage that respectively connect the canister and the intake passage;
A first on-off valve provided in the first passage for opening and closing the first passage;
A nozzle including a throttle portion provided in a portion of the first passage on the downstream side of the first on-off valve and having a flow path area smaller than that of the upstream portion;
A second on-off valve provided in the second passage for opening and closing the second passage;
Control means for controlling each part including the first on-off valve and the second on-off valve;
The first on-off valve is a DUTY control valve whose opening degree is changed by changing the DUTY ratio,
The second on-off valve is an ON / OFF valve that is changed between fully closed and fully open.
The control means closes the second on-off valve and opens the first on-off valve when a required purge amount, which is a required value of the purge gas flow rate, is lower than a preset reference flow rate. ,
An evaporative fuel control system for an internal combustion engine, wherein when the required purge amount is equal to or greater than the reference flow rate, the second on-off valve is opened and the first on-off valve is closed. An evaporative fuel control device for an internal combustion engine according to claim 1,
A pump provided in a passage between the nozzle and the intake passage to reduce the pressure in the passage by rotating;
When the required purge amount is lower than the reference flow rate, the control means sets the rotation speed of the pump at a constant flow rate of purge gas that passes through the throttle portion regardless of the pressure downstream of the nozzle. An evaporative fuel control device for an internal combustion engine, characterized by controlling the number of revolutions. An evaporative fuel control device for an internal combustion engine according to claim 2,
The first passage and the second passage are joined downstream of the nozzle and the second on-off valve,
The pump is provided in a passage between the joining portion of the first passage and the second passage and the intake passage;
An evaporative fuel control device for an internal combustion engine, wherein the control means controls the flow rate of the purge gas by changing the rotational speed of the pump when the required purge amount is equal to or greater than the reference flow rate. An evaporative fuel control device for an internal combustion engine according to claim 3,
When the required purge amount is switched from an amount lower than the reference flow rate to an amount equal to or higher than the reference flow rate, the control means is configured such that the rotational speed of the pump is higher than the rotational speed corresponding to the requested purge amount after the switching. If high, the pump speed is changed to a speed corresponding to the required purge amount after switching, and then the first on-off valve is closed and the second on-off valve is opened. An evaporative fuel control device for an internal combustion engine.

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