Control device for internal combustion engine

Abstract

To secure an opportunity to purge fuel vapor stagnated in a canister 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 allows the control valve to be opened under the requirement that a flow rate of air flowing through the intake passage toward the cylinder exceeds a threshold or closes the control valve if the requirement is not satisfied.SELECTED DRAWING: Figure 5

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] Opening the control valve to purge the fuel vapors adsorbed in the canister also means sending air containing fuel components into the cylinder, which results in a disturbance in the air-fuel ratio of the mixture filling the cylinder, making it richer.

[0006] 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.

[0007] 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.

[0008] The present invention has been made in light of the above points, and has as its intended object to ensure an opportunity to purge fuel vapor remaining in the canister while suppressing disturbances in the air-fuel ratio of the air-fuel mixture. [Means for solving the problem]

[0009] The present invention controls an internal combustion engine equipped with a fuel evaporative emission control device, which includes 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, and allows the control valve to open when the flow rate of air flowing through the intake passage toward the cylinder exceeds a threshold value as a necessary condition, and closes the control valve otherwise. The higher the estimated value of the current purge gas concentration, the larger the threshold value to be compared with the flow rate of air flowing through the intake passage toward the cylinder, and the lower the estimated value, the smaller the threshold value to be compared with the flow rate of air flowing through the intake passage toward the cylinder. Also, the larger the differential pressure between the current atmospheric pressure and the intake pressure downstream of the throttle valve in the intake passage, the smaller the opening degree when opening the control valve or the shorter the time for opening the control valve. A control device for an internal combustion engine was constructed.

[0010] The control method for an internal combustion engine according to the present invention controls an internal combustion engine equipped with a fuel evaporative emission control device, 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 leading 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 includes the steps of comparing the flow rate of air flowing through the intake passage toward the cylinders with a threshold value, and opening a closed control valve, provided that the flow rate of air exceeds the threshold value as a necessary condition. The threshold value is increased as the current estimated value of the purge gas concentration becomes higher, and decreased as the current estimated value of the purge gas concentration becomes lower. Also, the larger the pressure difference between the current atmospheric pressure and the intake pressure downstream of the throttle valve in the intake passage, the smaller the opening degree when the control valve is opened, or the shorter the opening time of the control valve. [Effects of the Invention]

[0011] According to the present invention, it is possible to ensure an opportunity to purge fuel vapor remaining in the canister while suppressing disturbances in the air-fuel ratio of the mixture. [Brief explanation of the drawings]

[0012] [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. 10 is a diagram illustrating the relationship between the flow rate of intake air flowing through the intake passage during fuel vapor purge gas processing and the degree of influence of the purge gas on air-fuel ratio feedback control. [Figure 7] FIG. 4 is a timing chart showing the relationship between the flow rate of intake air flowing through the intake passage and whether or not purge gas processing of fuel vapor is performed. [Figure 8] FIG. 10 is a diagram illustrating the relationship between the differential pressure between atmospheric pressure and intake pressure and the flow rate of purge gas when a control valve on a purge gas flow path is opened to a certain opening degree. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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 relative 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 in the rate of change relative 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.

[0020] 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.

[0021] 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).

[0022] 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).

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 5, the ECU0 of this embodiment first estimates (or learns) the concentration of fuel components contained in the purge gas that will flow through the purge gas flow path 63 and be released into the intake passage 3 as a result of opening the VSV 65 (step S1). In other words, the amount of fuel vapor currently stored in the canister 61 is estimated.

[0042] An example of a method for estimating the purge gas concentration in step S1 will be described. When the stopped internal combustion engine is started, the ECU 0 performs an initial estimation of the purge gas concentration. Specifically, the ECU 0 determines an initial value for the estimated concentration of the purge gas flowing through the purge gas flow path 63 immediately after the start of the internal combustion engine based on the length of time the internal combustion engine was stopped before starting and the temperature of the fuel tank or its surroundings while the internal combustion engine was stopped (or while the vehicle was parked). The length of time the internal combustion engine was stopped and the temperature of the fuel tank while the internal combustion engine was stopped both affect the amount of fuel vapor generated in the fuel tank 7 and collected in the canister 61 while the internal combustion engine was stopped. In principle, the longer the internal combustion engine was stopped, the greater the amount of fuel vapor collected in the canister 61, resulting in a higher concentration of the purge gas immediately after starting. Furthermore, the higher the temperature of the fuel tank 7 while the internal combustion engine was stopped, the greater the amount of fuel vapor collected in the canister 61, resulting in a higher concentration of the purge gas immediately after starting.

[0043] The memory of the ECU0 stores map data that defines the relationship between the length of time the internal combustion engine is stopped, values ​​that indicate the temperature of the fuel tank 7 or its surroundings while the internal combustion engine is stopped, and the initial value of the estimated concentration of purge gas immediately after the internal combustion engine is started. An example of a value that indicates the temperature of the fuel tank 7 or its surroundings while the internal combustion engine is stopped is the outside air temperature when the internal combustion engine is stopped or started. If the body ECU can actually measure the temperature of the vehicle body while the internal combustion engine is stopped, the actually measured temperature may be used as a value that indicates the temperature of the fuel tank 7 or its surroundings while the internal combustion engine is stopped. The ECU0 searches the map using the length of time the internal combustion engine is stopped and values ​​that indicate the temperature of the fuel tank 7 or its surroundings while the internal combustion engine is stopped as keys, and obtains the initial value of the estimated concentration of purge gas immediately after start.

[0044] Additionally, when the VSV 65 is used to perform a fuel vapor purge process while the internal combustion engine is running, the ECU 0 performs a calculation to gradually decrease and update the estimated fuel concentration of the purge gas flowing through the purge gas passage 63 from its initial value. When the VSV 65 is opened to perform the purge process, the amount of fuel vapor remaining in the canister 61 gradually decreases, eventually leading to a leaner purge gas concentration. The ECU 0 estimates the fuel concentration of the purge gas flowing through the purge gas passage 63 based on a correction coefficient FAF, which corrects the fuel injection amount TP through air-fuel ratio feedback control. If the VSV 65 is opened under conditions in which fuel is injected at an injection amount TP proportional to the amount of air taken into cylinder 1, and the air-fuel ratio of the gas flowing through the exhaust passage 4 becomes richer than the target air-fuel ratio, the purge gas flowing into the intake passage 3 is considered to be rich in fuel components. The concentration can be estimated to be higher as the feedback correction coefficient FAF decreases. Conversely, if the air-fuel ratio of the gas flowing through the exhaust passage 4 becomes leaner than the target air-fuel ratio, it is considered that the fuel component in the purge gas flowing into the intake passage 3 is lean. It can be estimated that the concentration becomes lower as the feedback correction coefficient FAF increases.

[0045] Incidentally, the ECU 0 can also adjust the amount of fuel injected from the injector 11 depending on the estimated purge gas concentration. If the concentration of the fuel component in the purge gas is high, the correction coefficient K is decreased accordingly, and the fuel injection amount T is corrected downward. If the concentration of the fuel component in the purge gas is low, the correction coefficient K is increased accordingly, and the fuel injection amount T is corrected upward.

[0046] Having estimated the concentration of fuel components in the purge gas flowing through the purge gas flow passage 63, the ECU0 sets a determination threshold (step S2) to be compared with the flow rate of intake air (or the flow rate of intake air including EGR gas) in step S3 (described later) depending on whether the estimated concentration is high or low. This threshold is one condition for determining whether or not it is permitted to open the VSV 65 and perform the fuel vapor purge process during firing operation of the internal combustion engine.

[0047] Figure 6 shows the relationship between the flow rate of intake air flowing through the intake passage 3 of the internal combustion engine toward the cylinder 1 and the magnitude of the effect on air-fuel ratio control of the purge gas that flows from the canister 61 into the intake passage 3 via the purge gas flow path 63 when the VSV 65 is opened to perform fuel vapor purging. In Figure 6, the solid line represents a case where the concentration of unburned fuel in the purge gas is relatively low, the dashed-dotted line represents a case where the concentration of unburned fuel in the purge gas is relatively high, and the dashed line represents a case somewhere between these two.

[0048] Even if the concentration of the purge gas flowing into the intake passage 3 due to the purging process is high, the air-fuel ratio of the mixture filled into the cylinder 1 will not be excessively rich as long as the flow rate of intake air flowing through the intake passage 3 is originally high. Conversely, if the flow rate of intake air flowing through the intake passage 3 is low, the fuel injected from the injector 11 will be added to the unburned fuel contained in the purge gas, which could cause the air-fuel ratio of the mixture to become excessively rich. The amount of change (absolute value) of the air-fuel ratio feedback correction coefficient FAF per unit time or per unit calculation cycle is limited to a finite value (otherwise the fuel injection amount and air-fuel ratio would hunt, oscillating up and down), making it difficult to immediately correct an excessively rich air-fuel ratio to the target value, which could result in increased emissions of harmful substances during that time.

[0049] Therefore, in this embodiment, the fuel vapor purge process is permitted only when the magnitude of the effect of the purge gas flowing into the intake passage 3 on the air-fuel ratio of the mixture is below the allowable upper limit. L , T M , T H If the condition is greater than or equal to the number of bytes, VSV65 is allowed to open; otherwise, VSV65 is forbidden to open and VSV65 is closed.

[0050] The determination threshold T to be compared with the intake air flow rate set in step S2 L , T M , T HThe higher the estimated value of the current purge gas concentration, the larger the value becomes, and the lower the estimated value becomes, the smaller the value becomes. L is the threshold value when the concentration of unburned fuel in the purge gas is relatively low, T H is the threshold value when the concentration of unburned fuel in the purge gas is relatively high, T M is a threshold value in the case where the concentration of unburned fuel contained in the purge gas is somewhere between these two.

[0051] Map data defining the relationship between the purge gas concentration and the determination threshold is stored in advance in the memory of the ECU 0. The ECU 0 searches the map using the current estimated value of the purge gas concentration as a key to determine the determination threshold to be compared with the intake air flow rate.

[0052] Then, the ECU0 compares the flow rate of intake air currently flowing through the intake passage 3 with the judgment threshold set in step S2 (step S3). The intake air flow rate can be estimated based on the current engine speed and the intake pressure (in the surge tank 33 or intake manifold 34), etc. In a system in which an air flow meter is installed in the intake passage 3, the intake air flow rate can also be actually measured via the air flow meter.

[0053] If the intake air flow rate is below the threshold, there is a concern that the purging of fuel vapor will significantly disrupt the air-fuel ratio of the mixture filled into cylinder 1, so the VSV 65 is closed and the purging process is not performed (step S6). On the other hand, if the intake air flow rate is above the threshold, the VSV 65 is opened and the purging process is performed (step S5) on the assumption that other required conditions are met (step S4). Specific examples of the other conditions referred to in step S4 include the internal combustion engine coolant temperature being higher than a predetermined value (warm-up has already been completed to a certain extent), the estimated value of the purge gas concentration being higher than a predetermined value (purging of fuel vapor is necessary), etc.

[0054] 7, at time t0, the intake air flow rate exceeds the determination threshold, permitting the fuel vapor purge process that involves opening the VSV 65. Then, at time t1, the intake air flow rate falls below the determination threshold, prohibiting the fuel vapor purge process that involves opening the VSV 65.

[0055] In the fuel vapor purging process of step S5, the opening degree of VSV 65 and / or the length of time for which VSV 65 is open may be adjusted depending on the estimated concentration of fuel components contained in the purge gas, the flow rate of intake air flowing through the intake passage 3 (in other words, the operating range of the internal combustion engine [engine speed, accelerator opening (or intake pressure in surge tank 33 or intake manifold 34), etc.]), the pressure difference between atmospheric pressure and the intake pressure (in surge tank 33 or intake manifold 34), etc.

[0056] 8, when the VSV 65 is opened to a fixed degree of opening, the flow rate of purge gas flowing through the purge gas passage 63 increases as the differential pressure (absolute value) between atmospheric pressure and intake pressure increases. In other words, the purge gas is more likely to be drawn in by the intake negative pressure generated downstream of the throttle valve 32 in the intake passage 3. Therefore, if the estimated concentration of purge gas and the flow rate of intake air are the same, the greater the differential pressure, the smaller the opening of the VSV 65 and / or the shorter the opening time of the VSV 65 may be.

[0057] In this embodiment, the control device 0 controls an internal combustion engine equipped with a fuel evaporative emission control device 6, which includes a connecting passage 62 connected to a fuel tank 7, a canister 61 that captures fuel vapor generated in the fuel tank 7 and flowing through the connecting 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 control valve 65 is allowed to open if the flow rate of air (or intake air, not containing unburned fuel components) flowing through the intake passage 3 toward the cylinder 1 exceeds a threshold value, as a necessary condition, and closes the control valve 65 otherwise.

[0058] In the control method for an internal combustion engine according to this embodiment, step S3 is executed to compare the flow rate of air flowing through the intake passage 3 toward the cylinder 1 with a threshold value, and step S5 is executed to open a closed control valve, provided that the flow rate of the air exceeds the threshold value as a necessary condition.

[0059] According to this embodiment, when there is no concern that the air-fuel ratio of the mixture filling the cylinder 1 will be significantly disturbed, the control valve 65 is opened to purge the vapor of the fuel components trapped in the canister 61, thereby suppressing an increase in the emission of harmful substances due to the purging process. On the other hand, when there is no concern that the air-fuel ratio of the mixture will be significantly disturbed, opportunities to purge the fuel vapor can be actively secured. Active purging of the fuel vapor also leads to suppression of deterioration of the canister 61.

[0060] 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.

[0061] The present invention is not limited to the above-described embodiment, and the specific configuration of each part and the processing procedure can be modified in various ways without departing from the spirit of the present invention. [Industrial Applicability]

[0062] The present invention can be applied to the control of an internal combustion engine mounted on a vehicle or the like. [Explanation of symbols]

[0063] 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. The control device controls 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 inlet passage connected to the canister and capable of introducing air; a purge gas flow passage that communicates the canister with 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 control valve is permitted to open only when the flow rate of air flowing through the intake passage toward the cylinder exceeds a threshold value, and the control valve is closed otherwise; a threshold value to be compared with the flow rate of air flowing through the intake passage toward the cylinder is set to be larger as the estimated value of the current purge gas concentration is higher, and set to be smaller as the estimated value of the current purge gas concentration is lower; Also, the control device for an internal combustion engine reduces the opening degree when opening the control valve or shortens the time for opening the control valve as the pressure difference between the current atmospheric pressure and the intake pressure downstream of the throttle valve in the intake passage increases.

2. The control device controls 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 inlet passage connected to the canister and capable of introducing air; a purge gas flow passage that communicates the canister with 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. a step of comparing a flow rate of air flowing through an intake passage toward a cylinder with a threshold value; opening a closed control valve on the condition that the air flow rate is greater than the threshold; and a threshold value to be compared with the flow rate of air flowing through the intake passage toward the cylinder is set to be larger as the estimated value of the current purge gas concentration is higher, and set to be smaller as the estimated value of the current purge gas concentration is lower; Also, the control method for an internal combustion engine reduces the opening degree of the control valve when it is opened or shortens the time for which the control valve is opened as the pressure difference between the current atmospheric pressure and the intake pressure downstream of the throttle valve in the intake passage increases.

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