JP7743151B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device that controls the operation of an internal combustion engine mounted on a vehicle, etc.

Internal combustion engines have traditionally been equipped with fuel evaporative emission control devices that capture fuel vapors that evaporate within the fuel tank (see, for example, the following patent documents). A common fuel evaporative emission control device is called a charcoal canister, which captures the generated fuel vapor by adsorbing it into a canister filled with activated charcoal, and then sends the fuel vapor to the intake passage of the internal combustion engine at the appropriate time to mix with the intake air and combust it in the cylinders.

In addition to a recovery passage for recovering fuel vapor from within the fuel tank, the canister is connected to an atmosphere inlet passage open to the atmosphere, and a purge gas passage that connects the canister to the intake passage of the internal combustion engine downstream of the throttle valve. To purge fuel vapor adsorbed in the canister, a control valve installed in the purge gas passage is opened, and the intake vacuum generated downstream of the throttle valve is used to draw outside air into the canister while drawing fuel vapor into the intake passage.

Japanese Patent Application Laid-Open No. 2019-044669

When a large amount of fuel vapor is stored in the canister, such as after a cold start of an internal combustion engine, it is desirable to open the control valve as quickly as possible to send more purge gas into the intake passage.

However, purging the fuel vapor in the canister also means sending air that already contains fuel components into the cylinder. As a result, the air-fuel ratio of the mixture filling the cylinder becomes richer, causing a disturbance.

Generally, when an internal combustion engine is operating, the air-fuel ratio of the gases emitted from the cylinders is sensed, and feedback control is implemented to increase or decrease the amount of fuel injected so that the measured air-fuel ratio tracks the target value. Purging fuel vapors causes a disturbance to the air-fuel ratio feedback control. If the disturbance is large, there is a concern that even feedback control may not be able to quickly converge the air-fuel ratio to the target value. Deviation of the air-fuel ratio from the target value leads to an increase in the amount of harmful substances emitted from the internal combustion engine, which is undesirable.

This problem is particularly likely to become apparent when using a control valve with a large flow rate (maximum flow rate). Control valves with a large flow rate tend to have a coarser resolution when controlling flow rate, meaning the minimum amount of change that can accurately adjust the flow rate tends to be larger. With such control valves, it is difficult to precisely control the amount of fuel vapor mixed into the intake air through opening adjustment, and purging the fuel vapor can result in the air-fuel ratio of the mixture becoming excessively rich.

The present invention was developed with the above points in mind, and its intended purpose is to enable early purging of fuel vapors remaining in the canister while suppressing disturbances in the air-fuel ratio of the mixture.

The present invention provides a control device for an internal combustion engine equipped with a fuel evaporative emission control device, the control device comprising: a connecting passage connected to a fuel tank; a canister that captures fuel vapor generated in the fuel tank and flowing through the connecting passage; an inlet passage connected to the canister and capable of introducing air; a purge gas flow passage that connects the canister to an intake passage connected to the cylinders of the internal combustion engine and releases purge gas containing the fuel vapor captured in the canister into the intake passage; and a control valve that opens and closes the purge gas flow passage. The control device for an internal combustion engine is configured to set the amount of increase per unit time in the opening degree of the control valve during a certain period after the control valve begins to open from a closed state to be smaller than the amount of increase per unit time in the opening degree of the control valve after that period has elapsed.

In essence, the present invention involves opening the control valve slowly at the beginning of the fuel vapor purging process, and then opening the control valve more quickly thereafter if possible.

In a system that detects the air-fuel ratio of gas flowing through an exhaust passage of an internal combustion engine via an air-fuel ratio sensor and performs feedback control to converge the measured air-fuel ratio to a target air-fuel ratio, when opening the control valve that was closed, it is possible to increase the amount of increase in the opening of the control valve per unit time to be greater than that during the period, on the necessary condition that, after the period has elapsed, the measured air-fuel ratio has switched from a state where it is leaner than the target air-fuel ratio to a state where it is richer than the target air-fuel ratio, and/or the number or frequency of the measured air-fuel ratio switching from a state where it is richer than the target air-fuel ratio to a state where it is leaner than the target air-fuel ratio has exceeded a threshold value.

The control method of the present invention is a method for controlling an internal combustion engine equipped with a fuel evaporative emission control device, the method comprising: a connection passage connected to a fuel tank; a canister that captures fuel vapor generated in the fuel tank and flowing through the connection passage; an inlet passage connected to the canister and capable of introducing air; a purge gas flow passage that connects the canister to an intake passage connected to a cylinder of the internal combustion engine and releases purge gas containing the fuel vapor captured in the canister into the intake passage; and a control valve that opens and closes the purge gas flow passage, the method comprising: calculating an amount of increase per unit time in the opening degree of the control valve during a certain period from when the closed control valve began to be opened; the air-fuel ratio of the gas flowing through the exhaust passage of the internal combustion engine is detected via an air-fuel ratio sensor, and feedback control is performed to converge the measured air-fuel ratio to the target air-fuel ratio; when an operation to open the control valve that was closed is performed, the amount of expansion of the opening of the control valve per unit time is set to be larger than that during the period, on the necessary condition that, after the period has elapsed, the number or frequency of the measured air-fuel ratio switching from a state where it is leaner than the target air-fuel ratio to a state where it is richer than the target air-fuel ratio, or the number or frequency of the switching from a state where it is richer than the target air-fuel ratio to a state where it is leaner than the target air-fuel ratio, exceeds a threshold value .

This invention makes it possible to quickly purge fuel vapors remaining in the canister while suppressing disturbances in the air-fuel ratio of the mixture.

1 is a diagram showing a schematic configuration of a vehicle internal combustion engine and a control device according to an embodiment of the present invention; FIG. 4 is a timing diagram showing the content of air-fuel ratio feedback control, particularly the correction amount FAF, with reference to the output signal of an air-fuel ratio sensor upstream of the catalyst in the exhaust passage. FIG. 10 is a diagram illustrating the relationship between the correction amount FACF of the air-fuel ratio feedback control and the delay times TDR and TDL. FIG. 4 is a timing chart showing the content of air-fuel ratio feedback control with reference to the output signal of an air-fuel ratio sensor downstream of the catalyst in the exhaust passage; FIG. 3 is a flowchart showing an example of a processing procedure executed by the control device according to the embodiment in accordance with a program. FIG. 3 is a timing chart showing the contents of control by the control device of the embodiment.

One embodiment of the present invention will be described with reference to the drawings. Figure 1 shows an overview of a vehicle internal combustion engine according to this embodiment. The internal combustion engine according to this embodiment is a spark-ignition, four-stroke gasoline engine equipped with multiple cylinders 1 (one of which is shown in Figure 1). An injector 11 for injecting fuel is provided near the intake port of each cylinder 1. In addition, an ignition plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The ignition plug 12 receives an induced voltage generated by an ignition coil and generates a spark discharge between the center electrode and the ground electrode.

The intake passage 3 leads to the intake port of each cylinder 1, circulating air taken in from the outside toward each cylinder 1 and supplying it to the cylinder 1. Arranged in this order from upstream to downstream are an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 in the intake passage 3.

The internal combustion engine is equipped with a fuel evaporative emission control device 6. The fuel evaporative emission control device 6 captures fuel vapor that has evaporated in the fuel tank 7 by adsorbing it into a charcoal canister 61 filled with activated carbon, and then sends the fuel vapor to the intake passage 3 at the appropriate time to mix with the intake air and combust it in the cylinder 1.

The fuel tank 7 and the canister 61 are connected via a connection passage 62. Fuel vapor generated in the fuel tank 7 flows into the canister 61 through the connection passage 62. The canister 61 and the intake passage 3 (particularly the surge tank 33, intake manifold 34, or intake port) are connected via a purge gas passage 63. Fuel vapor captured by the canister 61 flows into the intake passage 3 through the purge gas passage 63. In addition, the canister 61 is provided with an air introduction passage 64 that is open to the atmosphere.

A purge VSV (Vacuum Switching Valve) 65, a control valve that opens and closes the purge gas flow path 63, is located in the purge gas flow path 63. The VSV 65 is a flow control valve whose opening can be increased or decreased by adjusting (particularly, PWM (Pulse Width Modulation) control) the magnitude of the current or voltage applied to the solenoid that drives the valve body. While the VSV 65 is open, the canister 61 and the intake passage 3 are connected via the purge gas flow path 63. Then, due to the intake negative pressure generated downstream of the throttle valve 32 in the intake passage 3, fuel vapor in the canister 61 is drawn into the intake passage 3. At this time, air, i.e., outside air, is taken into the canister 61 through the inlet passage 64.

The exhaust passage 4 starts at the exhaust port of each cylinder 1 and guides the combustion gas generated as a result of burning fuel in each cylinder 1 to the outside. An exhaust manifold 42 and a three-way catalyst 41 for purifying exhaust gas are arranged in the exhaust passage 4. The catalyst 41 induces an oxidation/reduction reaction of harmful substances such as HC, CO, and _NOx , thereby rendering them harmless.

Air-fuel ratio sensors 43, 44 are installed upstream and downstream of the catalyst 41 in the exhaust passage 4 to detect the air-fuel ratio of the gas flowing through the exhaust passage 4. Each of the air-fuel ratio sensors 43, 44 may be an _O2 sensor with a nonlinear output characteristic relative to the air-fuel ratio of the exhaust gas, or a linear A/F sensor with an output characteristic proportional to the air-fuel ratio of the exhaust gas. The output voltage of the _O2 sensor decreases as the air-fuel ratio of the gas flowing out of the catalyst 41 becomes leaner. In particular, the output voltage exhibits a steeper rate of change with respect to the air-fuel ratio within a certain range near the stoichiometric air-fuel ratio. The output voltage of the linear A/F sensor asymptotically approaches a lower saturation value in regions where the air-fuel ratio is leaner than that and approaches a higher saturation value in regions where the air-fuel ratio is richer than that, forming a so-called Z-characteristic curve. The output voltage of the linear A/F sensor increases as the air-fuel ratio of the gas flowing into the catalyst 41 becomes leaner. In this embodiment, the air-fuel ratio sensor 43 upstream of the catalyst 41 and the air-fuel ratio sensor 44 downstream of the catalyst 41 are assumed to be O ₂ sensors.

As an aside, further exhaust purification catalysts, filters, etc. (not shown) may be installed downstream of the catalyst 41 and air-fuel ratio sensor 44 in the exhaust passage 4.

The exhaust gas recirculation device 2 comprises an external EGR passage 21 connecting the exhaust passage 4 and the intake passage 3, an EGR cooler 22 installed in the EGR passage 21, and an EGR valve 23 that opens and closes the EGR passage 21 to control the flow rate of EGR gas flowing through the EGR passage 21. The inlet of the EGR passage 21 is connected to a location downstream of the catalyst 41 in the exhaust passage 4. The outlet of the EGR passage 21 is connected to a location downstream of the throttle valve 32 in the intake passage 3 (in particular, the surge tank 33 or intake manifold 34).

The ECU (Electronic Control Unit) 0, which is the control device for the internal combustion engine in this embodiment, is a microcomputer system having a processor, memory, input interface, output interface, etc. The ECU 0 may be composed of multiple ECUs or controllers connected to each other so that they can communicate with each other via electrical communication lines such as a CAN (Controller Area Network).

The input interface of the ECU 0 receives a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crankshaft of the internal combustion engine and the engine speed, an accelerator opening signal c output from a sensor that detects the amount of accelerator pedal depression by the driver or the opening of the throttle valve 32 as the accelerator opening (in other words, the engine torque or engine load factor required by the internal combustion engine), and a signal from a sensor downstream of the throttle valve 32 in the intake passage 3 (particularly, a signal from the surge tank 33 or the intake manifold 34). The signals input to the exhaust passage 4 include an intake air temperature/intake pressure signal d output from a temperature/pressure sensor that detects the intake air temperature and intake pressure of the internal combustion engine, a coolant temperature signal e output from a water temperature sensor that detects the coolant temperature of the internal combustion engine, an air-fuel ratio signal (voltage signal) f output from an air-fuel ratio sensor 43 that detects the air-fuel ratio of the exhaust gas upstream of the catalyst 41 in the exhaust passage 4, an air-fuel ratio signal (voltage signal) g output from an air-fuel ratio sensor 44 that detects the air-fuel ratio of the exhaust gas downstream of the catalyst 41, an atmospheric pressure signal h output from an atmospheric pressure sensor that detects atmospheric pressure, and an outside air temperature signal o output from an outside air temperature sensor that detects the outside air temperature.

The output interface of ECU0 outputs an ignition signal i to the igniter 13 of the spark plug 12, a fuel injection signal j to the injector 11, an opening operation signal k to the throttle valve 32, an opening operation signal l to the EGR valve 23, an opening operation signal n to the VSV 65, etc.

The processor of ECU0 interprets and executes programs pre-stored in memory, calculating operating parameters and controlling the operation of the internal combustion engine. ECU0 acquires various pieces of information a, b, c, d, e, f, g, h, and o required for controlling the operation of the internal combustion engine via the input interface, determines the engine speed, and estimates the amount of air (fresh air) to be drawn into cylinder 1. Then, based on the engine speed and intake air volume, it determines various operating parameters such as the required fuel injection amount, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, required EGR rate (or EGR gas amount), and ignition timing (including the number of spark ignitions per combustion). ECU0 applies various control signals i, j, k, l, and n corresponding to the operating parameters via the output interface.

When determining the amount of fuel to be injected from the injector 11, the ECU 0 first calculates the amount of air taken into the cylinder 1 and determines a basic amount of fuel injection TP that is proportional to that amount of intake air (enables the stoichiometric air-fuel ratio or an air-fuel ratio close to it to be achieved depending on the amount of intake air). The intake amount is estimated based on the current engine speed and intake pressure (in the surge tank 33 or intake manifold 34), etc. The estimated intake amount may be corrected based on the current intake temperature, atmospheric pressure, etc. This method of estimating the intake amount is well known.

Next, this basic injection amount TP is corrected by a feedback correction coefficient FAF corresponding to the deviation between the air-fuel ratio of the gas flowing into the catalyst 41 and its target value, and various correction coefficients K determined according to environmental conditions and the like. The feedback correction coefficients FAF and K are each positive numbers that increase or decrease around 1. Furthermore, the final fuel injection time T, i.e., the time for opening the injector 11, is calculated taking into account the invalid injection time TAUV during which fuel is not injected even when the injector 11 is opened. The fuel injection time T is calculated as follows:
T=TP×FAF×K+TAUV
The ECU 0 inputs a signal j to the injector 11 for the fuel injection time T, and opens the valve of the injector 11 to inject fuel.

Air-fuel ratio feedback control converges the air-fuel ratio of the mixture filling cylinder 1, and ultimately the air-fuel ratio of the exhaust gas discharged from cylinder 1 and directed to catalyst 41, to a desired target air-fuel ratio, thereby maximizing the purification efficiency of harmful substances in catalyst 41. The air-fuel ratio feedback correction coefficient FAF is determined based on the output signal f of air-fuel ratio sensor 43 upstream of catalyst 41. As shown in Figure 2, ECU 0 compares the output voltage f of air-fuel ratio sensor 43, which detects the air-fuel ratio of gas upstream of catalyst 41, with a judgment voltage value corresponding to the target air-fuel ratio. If the output voltage f is higher than the judgment voltage value, the air-fuel ratio is determined to be lean, and if the output voltage f is lower than the judgment voltage value, the air-fuel ratio is determined to be rich. ECU 0 then adjusts the feedback correction coefficient FAF up or down based on the result of the judgment of the air-fuel ratio of gas upstream of catalyst 41.

Specifically, when the determined air-fuel ratio of the gas upstream of the catalyst 41 changes from lean to rich (after the delay time TDR described below has elapsed), the feedback correction coefficient FAF is decreased by the skip value RSM. Additionally, while the air-fuel ratio is determined to be rich, the feedback correction coefficient FAF is gradually decreased by the lean integral value KIM per calculation cycle (control cycle). The period of the calculation cycle is equal to the period in which each cylinder 1 of the internal combustion engine enters a new cycle (a series of intake stroke - compression stroke - expansion stroke - exhaust stroke). It is also possible to increase the absolute value of the lean integral value KIM the larger the absolute value of the difference or ratio between the determination voltage value and the output voltage value f of the air-fuel ratio sensor 43.

On the other hand, when the result of the determination of the air-fuel ratio of the gas upstream of the catalyst 41 reverses from rich to lean (when the delay time TDL described below has elapsed), the feedback correction coefficient FAF is increased by the skip value RSP. In addition, while the air-fuel ratio is determined to be lean, the feedback correction coefficient FAF is gradually increased by the rich integral value KIP per calculation cycle. Note that it is also possible to increase the absolute value of the rich integral value KIP the larger the absolute value of the difference or ratio between the output voltage value f of the air-fuel ratio sensor 43 and the determination voltage value.

When the feedback correction coefficient FAF, which is multiplied by the basic injection amount TP, decreases, the amount of fuel injected by the injector 11 is reduced, and the air-fuel ratio of the mixture moves toward a leaner mixture. When the feedback correction coefficient FAF increases, the amount of fuel injected by the injector 11 is increased, and the air-fuel ratio of the mixture moves toward a richer mixture.

However, when the output voltage f of the air-fuel ratio sensor 43 fluctuates so as to cross the judgment voltage value, the judgment result of the air-fuel ratio of the gas upstream of the catalyst 41 is not immediately inverted, but rather the judgment result is inverted after the delay times TDL and TDR have elapsed. That is, when the output voltage f of the air-fuel ratio sensor 43 switches from rich to lean (falls below the judgment voltage value), it is determined that the air-fuel ratio has inverted from rich to lean after the lean judgment delay time TDL has elapsed. Conversely, when the output voltage f of the air-fuel ratio sensor 43 switches from lean to rich (exceeds the judgment voltage value), it is determined that the air-fuel ratio has inverted from lean to rich after the rich judgment delay time TDR has elapsed.

The lean determination delay time TDL and rich determination delay time TDR are provided to prevent chattering, which occurs when noise is mixed into the output signal f of the air-fuel ratio sensor 43, causing the lean/rich air-fuel ratio determination result to reverse multiple times in a short period of time, causing the fuel injection amount to fluctuate.

The delay times TDL and TDR increase or decrease depending on the correction amount FACF. Figure 3 illustrates the relationship between the correction amount FACF and the delay times TDL and TDR. In Figure 3, the lean determination delay time TDL is represented by a dashed line, and the rich determination delay time TDR is represented by a solid line. As the correction amount FACF increases, the lean determination delay time TDL is shortened and the rich determination delay time TDR is extended. This delays the time when the feedback correction coefficient FAF changes from increasing to decreasing, and accelerates the time when it changes from decreasing to increasing. As a result, the fuel injection amount increases on average, and the target air-fuel ratio of the gas flowing into the catalyst 41, which should be converged by air-fuel ratio feedback control, shifts to the rich side.

Conversely, the smaller the correction amount FACF, the longer the lean determination delay time TDL and the shorter the rich determination delay time TDR. This means that the feedback correction coefficient FAF changes from increasing to decreasing earlier, and the time it changes from decreasing to increasing later. As a result, the fuel injection amount decreases on average, and the target air-fuel ratio of the gas flowing into the catalyst 41 shifts toward the lean side.

During air-fuel ratio feedback control, ECU0 also calculates the above-mentioned correction amount FACF. As shown in FIG. 4, when calculating the correction amount FACF, ECU0 compares the output voltage g of the air-fuel ratio sensor 44, which detects the air-fuel ratio of the gas downstream of the catalyst 41, with a judgment voltage value corresponding to the stoichiometric air-fuel ratio or a target air-fuel ratio close to the stoichiometric air-fuel ratio, and determines that the air-fuel ratio is rich if it is higher than the judgment voltage value, and lean if it is lower than the judgment voltage value. This judgment voltage value does not necessarily match the judgment voltage value compared with the output signal f of the air-fuel ratio sensor 43. Based on this, ECU0 adjusts the correction amount FACF up or down based on the result of the judgment of the air-fuel ratio of the gas downstream of the catalyst 41.

Specifically, while the air-fuel ratio of the gas downstream of the catalyst 41 is determined to be rich, the correction amount FACF is gradually decreased by the lean integral value FACFKIM per calculation cycle, while while the air-fuel ratio is determined to be lean, the correction amount FACF is gradually increased by the rich integral value FACFKIP per calculation cycle. The absolute value of the lean integral value FACFKIM may be increased as the absolute value of the difference or ratio between the determination voltage value and the output voltage value g of the air-fuel ratio sensor 44 increases, and the absolute value of the rich integral value FACFKIP may be increased as the absolute value of the difference or ratio between the output voltage g of the air-fuel ratio sensor 44 and the determination voltage value increases. As already mentioned, when the correction amount FACF decreases, the target air-fuel ratio of the gas flowing into the catalyst 41 moves toward leaner, and when the correction amount FACF increases, the target air-fuel ratio of the gas flowing into the catalyst 41 moves toward richer.

Fuel vapor that evaporates in the fuel tank 7 while the internal combustion engine is stopped is collected in the canister 61 of the fuel evaporative emission control device 6. After starting the stopped internal combustion engine (particularly during a cold start), the ECU 0 opens the VSV 65 at the appropriate time to purge the fuel vapor that has accumulated in the canister 61. That is, the fuel vapor is released into the intake passage 3 via the purge gas flow path 63 and combusted in the cylinder 1.

However, depending on the concentration of fuel contained in the purge gas that flows into the intake passage 3 due to the fuel vapor purging process, this could cause significant disturbances in the air-fuel ratio of the mixture filled into cylinder 1. When ECU 0 calculates the basic injection amount TP, it does not generally take fuel vapor purging into consideration, and determines the injection amount TP from injector 11 on the assumption that the intake air flowing through the intake passage 3 toward cylinder 1 does not contain unburned fuel components. However, because purge gas contains unburned fuel components, it is possible that the air-fuel ratio of the mixture filled into cylinder 1 will become richer than the target air-fuel ratio, even if only temporarily.

Disturbances in the air-fuel ratio of the mixture are usually suppressed by air-fuel ratio feedback control. However, if the concentration of unburned fuel components in the purge gas is very high, even feedback control may not be able to quickly converge the air-fuel ratio to the target value, which could result in an increase in the amount of harmful substances emitted from the internal combustion engine. Therefore, it is never desirable to perform fuel vapor purging processing without any restrictions.

As shown in FIG. 5, when the ECU 0 of this embodiment is permitted to open the VSV 65 and purge the fuel vapor captured in the canister 61 (step S1), it opens the VSV 65, which was closed (steps S2 and S5), and opens the purge gas flow path 63.

The conditions for permitting execution of the purge process in step S1 include the following: the flow rate (which can be estimated based on the current engine speed and the intake pressure (in the surge tank 33 or intake manifold 34), etc.) of intake air (purged gas, i.e., intake air that does not contain unburned fuel components) flowing through the intake passage 3 toward the cylinder 1 is greater than a predetermined amount; the cooling water temperature of the internal combustion engine is greater than a predetermined value (warm-up has already been completed to a certain extent); the estimated value of the purge gas concentration (which can be estimated by a known method) is greater than a predetermined value (purging of fuel vapor is necessary);
When the execution of the purge process is permitted and the closed VSV 65 starts to open, the speed at which the VSV 65 opens is slowed down (step S2), i.e., the amount of increase per unit time in the opening of the VSV 65 is set small. This is a measure to prevent the air-fuel ratio of the mixture from becoming suddenly rich, which would occur if purge gas containing unburned fuel were mixed with the intake air and drawn into the cylinder 1.

Then, ECU0 opens the VSV 65 more quickly (step S5), i.e., sets the opening amount of the VSV 65 per unit time to a larger amount than before, assuming that a predetermined period of time has elapsed since the VSV 65 began to open (step S3) and that the air-fuel ratio of the mixture filled into cylinder 1 is being stably controlled by air-fuel ratio feedback control (step S4).

In step S5, for example, the number of times that the result of the air-fuel ratio determination, which references the output signal f of the _O2 sensor 43 upstream of the catalyst 41 in the exhaust passage 4, has reversed from lean to rich and/or the number of times that the result of the air-fuel ratio determination has reversed from rich to lean, is counted. Then, when the counted number exceeds a threshold value, or when the number of times counted within a certain period of time (i.e., the frequency of reversals) exceeds the threshold value, it is determined that the air-fuel ratio of the air-fuel mixture is being stably controlled. If the number or frequency is greater than or equal to the threshold value, it suggests that the air-fuel ratio of the air-fuel mixture has remained within a certain range of the target air-fuel ratio due to air-fuel ratio feedback control for a certain period of time or more.

In a system that has a linear air-fuel ratio sensor 43 installed upstream of the catalyst 41, the condition of step S4 may be determined to be met if the absolute value of the deviation between the air-fuel ratio actually measured via the air-fuel ratio sensor 43 and the target air-fuel ratio remains below a predetermined value for a certain period of time or longer.

6 shows the control of the purge process by the ECU 0 of this embodiment. In FIG. 6, _t0 is the time when the permission condition in step S1 is met, _t1 is the time when the predetermined period in step S3 has elapsed, and _t2 is the time when the stability of the air-fuel ratio control in step S4 has been confirmed. The opening speed of the VSV 65 after time _t2 is faster than that before time _t2 . In other words, the amount of increase in the opening of the VSV 65 per unit time becomes greater after time _t2 .

Incidentally, the ECU 0 can also adjust the amount of fuel injected from the injector 11 according to the estimated concentration and flow rate of the purge gas flowing into the intake passage 3 (or the opening degree of the VSV 65, the differential pressure between atmospheric pressure and the intake pressure (in the surge tank 33 or intake manifold 34), etc.). If the concentration of the fuel components in the purge gas is high or the amount of purge gas flowing in is large, the correction coefficient K is decreased accordingly, and the fuel injection amount T is corrected downward. If the concentration of the fuel components in the purge gas is low or the amount of purge gas flowing in is small, the correction coefficient K is increased accordingly, and the fuel injection amount T is corrected upward.

In this embodiment, an internal combustion engine equipped with a fuel evaporative emission control device 6 is controlled, the device comprising: a connection passage 62 connecting to a fuel tank 7; a canister 61 that captures fuel vapor generated in the fuel tank 7 and flowing through the connection passage 62; an inlet passage 64 connected to the canister 61 and capable of introducing air; a purge gas flow passage 63 that connects the canister 61 to an intake passage 3 connected to a cylinder 1 of the internal combustion engine and releases purge gas containing the fuel vapor captured in the canister 61 into the intake passage 3; and a control valve 65 that opens and closes the purge gas flow passage 63. The control device 0 for the internal combustion engine is configured to set the amount of increase per unit time in the opening degree of the control valve 65 during a certain period of time after the control valve 65 begins to open from a closed state to be smaller than the amount of increase per unit time in the opening degree of the control valve 65 after that period has elapsed.

According to this embodiment, fuel component vapors captured in the canister 61 can be released into the intake passage 3 as quickly as possible while the internal combustion engine is stopped, without significantly disturbing the air-fuel ratio of the mixture filled in the cylinder 1. Actively purging fuel vapors also helps to suppress deterioration of the canister 61.

The fuel vapor released from the canister 61 into the intake passage 3 is burned in the cylinder 1. This allows the amount of fuel injection to be reduced, which is expected to improve practical fuel economy.

Note that the present invention is not limited to the embodiment described above. The specific configuration of each component and processing procedures can be modified in various ways without departing from the spirit of the present invention.

The present invention can be applied to the control of internal combustion engines installed in vehicles, etc.

0...Control unit (ECU)
REFERENCE SIGNS LIST 1 cylinder 11 injector 3 intake passage 32 throttle valve 4 exhaust passage 41 catalyst 6 fuel evaporative emission control device 61 canister 62 connection passage 63 purge gas flow passage 64 introduction passage 65 control valve (purge VSV)
7...Fuel tank b...Crank angle signal c...Accelerator opening signal f, g...Air-fuel ratio signal h...Atmospheric pressure signal o...Outside air temperature signal j...Fuel injection signal k...Throttle valve opening operation signal n...Control valve opening operation signal

Claims (2)

A control device for controlling an internal combustion engine equipped with a fuel evaporative emission control device, the control device comprising: a connecting passage connected to a fuel tank; a canister for capturing fuel vapor generated in the fuel tank and flowing through the connecting passage; an introduction passage connected to the canister and capable of introducing air; a purge gas flow passage that connects the canister to an intake passage connected to a cylinder of the internal combustion engine and releases purge gas containing the fuel vapor captured in the canister into the intake passage; and a control valve that opens and closes the purge gas flow passage,
The amount of increase in the opening of the control valve per unit time during a certain period from when the closed control valve starts to be opened is set to be smaller than the amount of increase in the opening of the control valve per unit time after the period has elapsed,
The air-fuel ratio of gas flowing through an exhaust passage of an internal combustion engine is detected via an air-fuel ratio sensor, and feedback control is performed to converge the measured air-fuel ratio to a target air-fuel ratio.
A control device for an internal combustion engine, which, when opening the control valve that has been closed, sets the amount of increase in the opening of the control valve per unit time to be greater than that during the period, on the condition that, after the period has elapsed, the number or frequency of the measured air-fuel ratio switching from a state leaner than the target air-fuel ratio to a state richer than the target air-fuel ratio, or the number or frequency of the measured air-fuel ratio switching from a state richer than the target air-fuel ratio to a state leaner than the target air-fuel ratio, exceeds a threshold value . A method for controlling an internal combustion engine equipped with a fuel evaporative emission control device, the method comprising: a connecting passage connected to a fuel tank; a canister for capturing fuel vapor generated in the fuel tank and flowing through the connecting passage; an introduction passage connected to the canister and capable of introducing air; a purge gas flow passage that connects the canister to an intake passage connected to a cylinder of the internal combustion engine and releases purge gas containing the fuel vapor captured in the canister into the intake passage; and a control valve that opens and closes the purge gas flow passage,
The amount of increase in the opening of the control valve per unit time during a certain period from when the closed control valve starts to be opened is set to be smaller than the amount of increase in the opening of the control valve per unit time after the period has elapsed,
The air-fuel ratio of gas flowing through an exhaust passage of an internal combustion engine is detected via an air-fuel ratio sensor, and feedback control is performed to converge the measured air-fuel ratio to a target air-fuel ratio.
A control method for an internal combustion engine, in which, when opening the control valve that was closed, the amount of increase in the opening of the control valve per unit time is made larger than that during the period, on the condition that, after the period has elapsed, the number or frequency of the measured air-fuel ratio switching from a state leaner than the target air-fuel ratio to a state richer than the target air-fuel ratio, or the number or frequency of the measured air-fuel ratio switching from a state richer than the target air-fuel ratio to a state leaner than the target air-fuel ratio, exceeds a threshold value .