Control device for internal combustion engine

Abstract

To enable fuel vapor stagnated in a canister to be early purged while curbing disturbance in an air-fuel ratio of mixed gas.SOLUTION: A control device controls an internal combustion engine attached with a fuel vapor gas discharge inhibiting device which comprises: a connection passage which is connected to a fuel tank; a canister which traps fuel vapor generated in the fuel tank and flowing through the connection passage; an introduction passage which is connected to the canister and capable of introducing air; a purge gas flow passage which communicates the canister with an intake passage connected to a cylinder of the internal combustion engine and allows purge gas containing the fuel vapor trapped in the canister to be discharged into an intake passage; and a control valve which opens and closes the purge gas flow passage. The control device is adapted to set an enlarged amount per unit time of an opening of the control valve in a certain period since when the closed control valve is started to open to be smaller than the same in a period after the lapse of the certain period.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a control device for controlling the operation of an internal combustion engine mounted on a vehicle or the like. [Background technology]

[0002] Internal combustion engines have traditionally been equipped with a fuel evaporative emission control device that captures fuel vapor that has evaporated in the fuel tank (see, for example, the following patent document). A common fuel evaporative emission control device is called a charcoal canister, which captures the generated fuel vapor by adsorbing it in 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.

[0003] The canister is connected to a recovery passage for recovering fuel vapor from the fuel tank, 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 the fuel vapor adsorbed in the canister, a control valve provided in the purge gas passage is opened, and the intake negative pressure generated downstream of the throttle valve is used to draw outside air into the canister while drawing the fuel vapor into the intake passage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-044669 Summary of the Invention [Problem to be solved by the invention]

[0005] In a situation where 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 as much purge gas as possible to the intake passage.

[0006] However, purging the canister of fuel vapor also means sending pre-fueled air into the cylinder, which results in a richer air-fuel mixture being filled into the cylinder.

[0007] Generally, during operation of an internal combustion engine, the air-fuel ratio of gases discharged from the cylinders is sensed, and feedback control is performed to increase or decrease the fuel injection amount so that the measured air-fuel ratio tracks a 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 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.

[0008] This problem is particularly pronounced when using a control valve with a large flow rate (maximum flow rate). Control valves with a large flow rate tend to have a coarse resolution when controlling the flow rate, i.e., the minimum amount of change that can be made to precisely adjust the flow rate tends to be large. With such control valves, it is difficult to precisely control the amount of fuel vapor mixed into the intake air through valve opening adjustment, and purging the fuel vapor can result in the air-fuel ratio of the mixture becoming excessively rich.

[0009] The present invention has been made in light of the above points, and has as its intended object to enable early purging of fuel vapor remaining in the canister while suppressing disturbances in the air-fuel ratio of the mixture. [Means for solving the problem]

[0010] In the present invention, a control device for controlling an internal combustion engine equipped with a fuel evaporative emission control device is configured, which includes 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, and 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 that was closed begins to open to be smaller than the amount of increase per unit time in the opening degree of the control valve after the period has elapsed.

[0011] In essence, the present invention involves opening the control valve slowly at the beginning of the fuel vapor purge process, and then opening the control valve more quickly thereafter if possible.

[0012] In a device 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 an operation to open the control valve that was closed is performed, after the lapse of the period, the measured air-fuel ratio has switched from being leaner than the target air-fuel ratio to being richer than the target air-fuel ratio, and / or the measured air-fuel ratio has become richer than the target air-fuel ratio. rich from a state where the air-fuel ratio is lower than the target air-fuel ratio Lean It is conceivable to make the amount of expansion of the opening of the control valve per unit time larger than that during the aforementioned period, assuming that the number or frequency of switching to the aforementioned state exceeds a threshold as a necessary condition. R .

[0013] 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, wherein the amount of increase per unit time in the opening degree of the control valve during a certain period from when the closed control valve begins to open is set to be smaller than the amount of increase per unit time in the opening degree of the control valve 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. When opening the closed control valve, the amount of increase in the opening of the control valve per unit time is increased to be greater than that during the period, on the condition that, after the period has elapsed, the number of times or frequency at which the measured air-fuel ratio has switched from a state leaner than the target air-fuel ratio to a state richer than the target air-fuel ratio, or the number of times or frequency at which the measured air-fuel ratio has switched from a state richer than the target air-fuel ratio to a state leaner than the target air-fuel ratio, exceeds a threshold value. It is characterized by: [Effects of the Invention]

[0014] According to the present invention, fuel vapor remaining in the canister can be purged early while suppressing disturbances in the air-fuel ratio of the air-fuel mixture. [Brief explanation of the drawings]

[0015] [Figure 1] 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; [Figure 2] 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. [Figure 3] FIG. 4 is a diagram illustrating the relationship between the correction amount FACF of air-fuel ratio feedback control and delay times TDR and TDL. [Figure 4] 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; [Figure 5] FIG. 3 is a flowchart showing an example of a procedure of a process executed by the control device according to the embodiment in accordance with a program. [Figure 6] FIG. 3 is a timing chart showing the contents of control by the control device of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle according to this embodiment. The internal combustion engine according to this embodiment is a spark-ignition four-stroke gasoline engine having a plurality of cylinders 1 (one of which is shown in FIG. 1). An injector 11 for injecting fuel is provided near the intake port of each cylinder 1. 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 a center electrode and a ground electrode.

[0017] The intake passage 3 leads to the intake port of each cylinder 1, and circulates air taken in from the outside toward each cylinder 1, supplying it to the cylinder 1. In the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from upstream.

[0018] The internal combustion engine is equipped with a fuel evaporative emission control device 6. The fuel evaporative emission control device 6 captures fuel vapor evaporated in a fuel tank 7 by adsorbing it in a charcoal canister 61 filled with activated carbon, and sends the fuel vapor to the intake passage 3 at appropriate times to mix with the intake air and combust it in the cylinder 1.

[0019] 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, the intake manifold 34, or the intake port) are connected via a purge gas passage 63. The 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.

[0020] A purge VSV (Vacuum Switching Valve) 65, which is a control valve that opens and closes the purge gas passage 63, is located on the purge gas passage 63. The VSV 65 is a flow control valve that can adjust (particularly, PWM (Pulse Width Modulation) control) the magnitude of the current or voltage applied to a solenoid that drives a valve element to increase or decrease its opening. While the VSV 65 is open, the canister 61 and the intake passage 3 are connected via the purge gas passage 63. Then, fuel vapor in the canister 61 is drawn into the intake passage 3 by the intake negative pressure generated downstream of the throttle valve 32 in the intake passage 3. At this time, air, i.e., outside air, is taken into the canister 61 through an inlet passage 64.

[0021] The exhaust passage 4 starts from 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 on the exhaust passage 4. The catalyst 41 removes harmful substances such as HC, CO, and NO. x This induces an oxidation / reduction reaction, rendering these substances harmless.

[0022] 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 having a nonlinear output characteristic with respect to the air-fuel ratio of the exhaust gas, or a linear A / F sensor having 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 exhibits a steeper rate of change with respect to the air-fuel ratio within a certain range near the stoichiometric air-fuel ratio, and 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 O2 sensors.

[0023] Incidentally, downstream of the catalyst 41 and the air-fuel ratio sensor 44 in the exhaust passage 4, a catalyst, a filter, etc. (not shown) for purifying exhaust gas may be further provided.

[0024] The exhaust gas recirculation device 2 includes, as its elements, an external EGR passage 21 that connects the exhaust passage 4 and the intake passage 3, an EGR cooler 22 provided on 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, a surge tank 33 or an intake manifold 34).

[0025] 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, a memory, an input interface, an output interface, etc. The ECU 0 may be configured by connecting a plurality of ECUs or controllers to each other so that they can communicate with each other via an electric communication line such as a CAN (Controller Area Network).

[0026] 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 depression of the accelerator pedal 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 for the internal combustion engine), and a signal from a downstream of the throttle valve 32 in the intake passage 3 (particularly, a surge tank 33 or an 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.

[0027] 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.

[0028] The processor of ECU0 interprets and executes programs stored in memory in advance, calculates operating parameters, and controls 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 an 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 amount, etc., 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 an output interface.

[0029] When determining the amount of fuel injected from the injector 11, the ECU 0 first calculates the amount of air taken into the cylinder 1, and then determines a basic amount TP of fuel injection that is proportional to the amount of intake air (so that the theoretical air-fuel ratio or an air-fuel ratio close to it can 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 value of the intake amount may be corrected according to the current intake temperature, atmospheric pressure, etc. This method of estimating the intake amount is well known.

[0030] 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.

[0031] Air-fuel ratio feedback control converges the air-fuel ratio of the mixture filled in cylinder 1, and ultimately the air-fuel ratio of the exhaust gas discharged from cylinder 1 and guided to catalyst 41, to a desired target air-fuel ratio, thereby maximizing the purification efficiency of harmful substances in the catalyst 41. The air-fuel ratio feedback correction coefficient FAF is determined based on the output signal f of an air-fuel ratio sensor 43 upstream of the catalyst 41. As shown in FIG. 2, the ECU0 compares the output voltage f of the air-fuel ratio sensor 43, which detects the air-fuel ratio of gas upstream of the catalyst 41, with a determination voltage value corresponding to the target air-fuel ratio, and determines the air-fuel ratio to be lean if the output voltage f is higher than the determination voltage value, and rich if the output voltage f is lower than the determination voltage value. The ECU0 then increases or decreases the feedback correction coefficient FAF based on the determination result of the air-fuel ratio of the gas upstream of the catalyst 41.

[0032] Specifically, when the determination result of the air-fuel ratio of the gas upstream of the catalyst 41 changes from lean to rich (when the delay time TDR described below has elapsed), the feedback correction coefficient FAF is decreased by the skip value RSM. In addition, 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 as 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 increases.

[0033] On the other hand, when the determination result 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 as 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 increases.

[0034] 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 becomes leaner. 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 becomes richer.

[0035] 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 reversed, but rather the judgment result is reversed 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 (below the judgment voltage value), it is determined that the air-fuel ratio has reversed 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 reversed from lean to rich after the rich judgment delay time TDR has elapsed.

[0036] The lean determination delay time TDL and the rich determination delay time TDR are provided in order 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 be reversed multiple times in a short period of time, causing the fuel injection amount to fluctuate.

[0037] The delay times TDL and TDR increase or decrease depending on the correction amount FACF. FIG. 3 illustrates the relationship between the correction amount FACF and the delay times TDL and TDR. In FIG. 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.

[0038] Conversely, as the correction amount FACF becomes smaller, the lean determination delay time TDL becomes longer and the rich determination delay time TDR becomes shorter. This means that the timing at which the feedback correction coefficient FAF changes from increasing to decreasing is earlier and the timing at which it changes from decreasing to increasing is delayed. As a result, the fuel injection amount is reduced on average, and the target air-fuel ratio of the gas flowing into the catalyst 41 shifts to the lean side.

[0039] During air-fuel ratio feedback control, the ECU0 also calculates the above-mentioned correction amount FACF. As shown in Fig. 4, when calculating the correction amount FACF, the ECU0 compares the output voltage g of the air-fuel ratio sensor 44, which detects the air-fuel ratio of gas downstream of the catalyst 41, with a determination 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 determination voltage value, and lean if it is lower than the determination voltage value. This determination voltage value does not necessarily coincide with the determination voltage value compared with the output signal f of the air-fuel ratio sensor 43. Then, the correction amount FACF is increased or decreased based on the determination result of the air-fuel ratio of the gas downstream of the catalyst 41.

[0040] 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, whereas 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. Note that 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 described above, 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.

[0041] Fuel vapor that has evaporated 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 an 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 is burned in the cylinder 1.

[0042] 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 may cause a significant disturbance in the air-fuel ratio of the mixture filled into the cylinder 1. When the ECU 0 calculates the basic injection amount TP, it basically does not take the fuel vapor purging process into consideration, and determines the injection amount TP from the injector 11 on the assumption that the intake air flowing through the intake passage 3 toward the cylinder 1 does not contain unburned fuel components. However, because the purge gas contains unburned fuel components, it is possible that the air-fuel ratio of the mixture filled into the cylinder 1 will become richer than the target air-fuel ratio, even if only temporarily.

[0043] 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, feedback control may not be able to quickly converge the air-fuel ratio to the target value, which may increase the amount of harmful substances emitted from the internal combustion engine. Therefore, it is not desirable to perform fuel vapor purging without any restrictions.

[0044] As shown in FIG. 5, when the ECU0 of this embodiment is permitted to open the VSV 65 and purge the fuel vapor collected 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.

[0045] 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 execution of the purge process is permitted and the closed VSV 65 begins to open, the speed at which the VSV 65 opens is slowed down (step S2), that is, the amount of increase in the opening of the VSV 65 per unit time 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 cylinder 1.

[0046] Then, ECU0 opens VSV 65 more quickly (step S5), i.e., sets the opening amount of VSV 65 per unit time to be larger 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 can be stably controlled by air-fuel ratio feedback control (step S4).

[0047] In step S5, for example, the number of times that the determination result of the air-fuel ratio, 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 determination result of the air-fuel ratio 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.

[0048] In a system in which a linear air-fuel ratio sensor 43 is installed upstream of the catalyst 41, it may be determined that the condition of step S4 is 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 more.

[0049] 6 shows the control of the purge process by the ECU0 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. That is, the amount of increase in the opening of the VSV 65 per unit time becomes greater after time t2.

[0050] Incidentally, the ECU 0 can also adjust the amount of fuel injected from the injector 11 depending on 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 inflow of purge gas 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 inflow of purge gas is small, the correction coefficient K is increased accordingly, and the fuel injection amount T is corrected upward.

[0051] In this embodiment, the control device 0 controls an internal combustion engine equipped with a fuel evaporative emission control device 6, which includes a connection passage 62 connected to a fuel tank 7, a canister 61 that captures fuel vapor generated in the fuel tank 7 and flows 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 controls an internal combustion engine in which the amount of increase per unit time in the opening degree of the control valve 65 during a certain period from when the closed control valve 65 begins to open is set to be smaller than the amount of increase per unit time in the opening degree of the control valve 65 after the period has elapsed.

[0052] According to this embodiment, the vapor of the fuel components trapped in the canister 61 while the internal combustion engine is stopped can be released as quickly as possible into the intake passage 3 without significantly disturbing the air-fuel ratio of the mixture filled in the cylinder 1. Actively purging the fuel vapor also helps to suppress deterioration of the canister 61.

[0053] 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 accordingly, and improvement in practical fuel economy can be expected.

[0054] The present invention is not limited to the above-described embodiment, and various modifications can be made to the specific configurations of the various components and processing procedures without departing from the spirit of the present invention. [Industrial Applicability]

[0055] The present invention can be applied to the control of an internal combustion engine mounted on a vehicle or the like. [Explanation of symbols]

[0056] 0...Control unit (ECU) 1...cylinder 11...Injector 3...Intake passage 32...Throttle valve 4...Exhaust passage 41...Catalyst 6...Fuel evaporative emission control device 61...Canister 62...Connecting road 63...Purge gas flow path 64...Introduction path 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 temperature signal j…Fuel injection signal k...Throttle valve opening operation signal n...Control valve opening operation signal

Claims

1. 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.

2. 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.

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