JP5769402B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine that stores evaporated fuel in a canister and discharges it into an intake system in accordance with an operating state.

  Conventionally, the evaporated fuel generated in the fuel tank is stored in a canister, and the evaporated fuel is discharged into the intake system, that is, purged according to the operating state. This prevents the evaporated fuel from being released into the atmosphere and improves the emission characteristics of the internal combustion engine. The canister captures the fuel vapor even at the time of a purge cut where the purge is not performed, for example, at the time of fuel cut or supercharging. Then, in order to avoid over-richness of the air-fuel ratio due to the fuel vapor trapped in the canister being temporarily released to the intake system more than expected, the air-fuel ratio control can be made in time by gradually increasing the purge control amount. The technique of making is proposed. In order to increase the purge amount, there has also been proposed a control in which the purge control amount at the time of restarting the purge is restarted immediately from the purge control amount at the previous purge cut (see, for example, Patent Document 1).

  However, when the operating state, for example, the ratio of fuel cut or supercharging is large and the frequency of purging is low, the purge cannot be performed for a sufficient time, and the purge amount cannot be secured sufficiently. End up.

  On the other hand, in the control described in Patent Document 1, if the purge cut time is long, the concentration of the fuel vapor in the purge may be high. There is a risk of causing a problem that the fuel ratio becomes excessively rich.

Japanese Patent No. 2789908

  The present invention pays attention to such a problem, and an object of the present invention is to provide a control device for an internal combustion engine that can secure a necessary purge flow rate even when the frequency of purging is low.

  In order to achieve such an object, the present invention takes the following measures.

That is, the control device for an internal combustion engine according to the present invention has a function of purging the evaporated fuel adsorbed by the canister into the intake passage, and controls the purge flow rate so that the purge flow rate becomes the target purge control amount. cut the purge conditions, during restart of the purge from the purge cut, it is to increase the gradually increasing rate of the purge control amount for increasing the purge flow rate as the purge cut time is short.

  In such a case, when the purge cut time is short, the state in the canister at the time of restarting the purge is not greatly changed from the start of the purge cut, so the purge control is quickly performed by increasing the increase rate of the purge control amount. The purge can be effectively secured as the amount at the start of the purge cut, and when the purge cut time is long, the purge gas concentration is high, so the problem that the air-fuel ratio becomes excessively rich when restarting the purge is effective Can be avoided. Thereby, even when the frequency of purging is low, a necessary purge flow rate can be ensured.

In the present invention , the control to increase the purge control amount increase rate as the purge cut time is shorter is controlled until the purge control amount reaches the purge control amount at the start of the purge cut , and the purge control amount is the previous control amount. Until the purge control amount at the start of the purge cut is reached, and if the purge control amount exceeds that at the start of the previous purge cut, the value is equal to or less than the increase rate of the purge control amount until then. And In this way , the purge is rapidly increased to the purge control amount that has been set before the purge cut, in other words, the actual purge control amount that has been set. As a result, even when the increase rate of the purge control amount is increased, the problem that the air-fuel ratio becomes excessively rich can be avoided more effectively.

  According to the present invention, a necessary purge flow rate can be ensured even when the frequency of purging is low.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic structure explanatory drawing of the engine which concerns on one Embodiment of this invention. FIG. 3 is a schematic configuration explanatory diagram of the electronic control device of the embodiment. FIG. 6 is a schematic explanatory view showing a purge control amount according to the embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  An engine 100 that is an internal combustion engine schematically shown in FIG. 1 is a three-cylinder engine having, for example, three cylinders 1, an intake passage 2 for supplying intake air to each cylinder 1, and exhaust gas. An exhaust passage 3 for discharging, and a turbocharger 4 having a turbine 5 disposed on the exhaust passage 3 and a compressor 6 disposed on the intake passage 2 are provided. In the intake passage 2, an air cleaner 7, an intake throttle valve 8, a compressor 6, an intercooler 9, and an electronically controlled throttle valve (hereinafter referred to as a throttle valve 10) are arranged in this order from the upstream. In the present embodiment, an intercooler bypass passage 11a that communicates the upstream portion and the downstream portion of the intercooler 9 and an intercooler bypass valve 11b provided in the intercooler bypass passage 11a are provided. Has been established. In addition, in the present embodiment, a fresh air bypass passage 12a communicating between a portion upstream of the intake throttle valve 8 and a portion downstream of the throttle valve 10, and a new air provided in the fresh air bypass passage 12a. An air bypass valve 12b is provided. During deceleration, a continuously variable valve timing mechanism (VVT 29), which will be described later, is controlled to minimize internal EGR, and at the same time, fresh air is introduced from the fresh air bypass passage 12a, thereby preventing misfire due to excessive EGR. Like to do. The throttle valve 10 opens and closes according to the amount of operation of an accelerator pedal (not shown).

  In the present embodiment, the fuel vapor generated in the fuel tank 42 is adsorbed by the canister 13 and is introduced into the intake passage 2 via the purge vacuum switching valve 14 (purge VSV) after the engine 100 is started. However, the manner in which the fuel vapor is introduced into the intake passage 2 by the purge VSV 14 will be described in detail later.

  Each cylinder 1 is provided with a spark plug 15 and a fuel injection valve 16. The fuel injection valve 16 is connected to a high-pressure fuel pump 18 via a delivery pipe 17. The cylinder 1 is provided with swirl control valves (SCV) 19a, 19b, and 19c at the intake port so as to generate a swirling flow when fuel is injected from the fuel injection valve 16.

On the exhaust passage 3, a turbine 5, a three-way catalyst 20, and an exhaust muffler (not shown) are arranged in this order from the upstream. On the upstream side of the three-way catalyst 20, an air-fuel ratio sensor 21 is provided that outputs an output signal corresponding to the air-fuel ratio or oxygen concentration upstream of the three-way catalyst 20 to an electronic control unit (hereinafter referred to as ECU 33). On the other hand, a rear O ₂ sensor 22 that outputs a signal corresponding to the oxygen concentration in the three-way catalyst 20 to the ECU 33 is provided downstream of the three-way catalyst 20.

  The turbocharger 4 can use a well-known one in this field, and includes an exhaust bypass passage 23a that enables communication between the upstream and downstream of the turbine 5 in order to control the supercharging pressure. A waste gate valve 23b for opening and closing the exhaust bypass passage 23a is provided. The waste gate valve 23b is closed so as to supercharge more fresh air into the cylinder 1 by introducing more exhaust gas to the turbine 5 during low-speed traveling, and supercharging during medium-high speed traveling. Opened to prevent knocking from occurring. A turbocharging pressure bypass mechanism 24 that bypasses the compressor 6 is provided on the compressor 6 side of the turbocharger 4. The supercharging pressure bypass mechanism 24 includes an intake bypass passage 24a that enables communication between the upstream and downstream of the compressor 6, and an ABV 24b (air bypass valve) that is an intake bypass valve that opens and closes the intake bypass passage 24a. . During deceleration, the supercharging pressure is lowered and the EGR rate is lowered to prevent misfire.

  In the present embodiment, an EGR device 25 for mixing exhaust gas with fresh air flowing into the intake passage 2 via the air cleaner 7 is provided in communication between the intake passage 2 and the exhaust passage 3. . That is, the EGR device 25 is provided in the exhaust gas recirculation pipeline (hereinafter referred to as the EGR pipeline 26) in which the intake passage 2 and the exhaust passage 3 are selectively communicated with each other and the EGR pipeline 26. An exhaust gas recirculation control valve (hereinafter referred to as an EGR valve 27) that controls the amount of exhaust gas (EGR gas) that passes through or is recirculated through the pipe line 26, and an EGR provided upstream of the EGR valve 27 An EGR cooler 28 that cools the gas with water is provided. The EGR pipe line 26 communicates a portion of the exhaust passage 3 downstream of the three-way catalyst 20 and a portion of the intake passage 2 downstream of the intake throttle valve 8 and upstream of the compressor 6. The EGR valve 27 is controlled by the ECU 33. Furthermore, in this embodiment, a continuously variable valve timing mechanism (hereinafter referred to as VVT 29) is provided. The VVT 29 changes the valve timing of the intake valve while constantly opening and closing the exhaust valve with respect to the rotation of the crankshaft (not shown), so that the relative position between the valve timing of the exhaust valve and the valve timing of the intake valve is changed. The phase difference can be freely changed within a predetermined angle range. The ECU 33 controls the VVT 29. In the present embodiment, a blow-by gas recirculation device 30 for sending blow-by gas generated in the crank chamber in the crank case of the engine 100 and the cam chamber in the cylinder head cover to the intake passage 2 is also provided. The blow-by gas recirculation device 30 includes a PCV passage 31 and a blow-by passage 32 as elements. Specifically, one end of the blow-by passage 32 is connected to a predetermined location on the upstream side of the compressor 6 in the intake passage 2, more precisely on the upstream side of the intake throttle valve 8.

  In the present embodiment, as described above, the fuel vapor generated in the fuel tank 42 is adsorbed by the canister 13 and is introduced into the intake passage 2 via the purge VSV 14 after the engine 100 is started. . Specifically, the canister 13 has a fuel vapor chamber 13b and an atmospheric chamber 13c on both sides of the activated carbon 13a. The fuel vapor chamber 13b is connected on the one hand to the fuel tank 42 and on the other hand to the intake passage 2 side. The fuel vapor generated in the fuel tank 42 is sent into the canister 13 and adsorbed on the activated carbon 13a. When the purge VSV 14 is opened, intake negative pressure is introduced to the canister 13. By such negative intake pressure, air is sent from the atmospheric chamber 13c through the activated carbon 13a to the intake passage 2 side. When the air passes through the activated carbon 13a, the fuel vapor adsorbed on the activated carbon 13a is desorbed from the activated carbon 13a, and thus air containing the fuel vapor, that is, vapor is purged to the intake passage 2 side. In this way, the fuel vapor in the fuel tank 42 is guided to the intake passage 2 side without being released to the atmosphere.

As schematically shown in FIG. 2, the ECU 33 is a microcomputer system including a CPU 33a, a RAM 33b, a ROM 33c, a flash memory 33d, an I / O interface 33e, and the like. The I / O interface 33e includes an air flow rate signal a output from the air flow meter 34 for detecting the air flow rate, a vehicle speed signal b output from the vehicle speed sensor 35 for detecting the vehicle speed, and a rotational speed for detecting the engine speed. The rotation speed signal c output from the sensor 36, the throttle opening signal d output from the throttle position sensor 37 that detects the throttle valve opening, and the pressure sensor 38 that detects the intake pressure (supercharging pressure) in the intake passage 2. , An intake air temperature signal f output from an intake air temperature sensor 39 for detecting the intake air temperature in the intake passage 2, a water temperature signal g output from a water temperature sensor 40 for detecting a cooling water temperature, and a fuel pressure. fuel pressure signal h which is output from the fuel pressure sensor 41 for detecting the air-fuel ratio signal i output from the air-fuel ratio sensor 21, is output from the rear O ₂ sensor 22 Voltage signal j, and the like are input. From the I / O interface 33e, a fuel injection signal p for the fuel injection valve 16, an ignition signal q for the ignition plug 15 (ignition coil thereof), and an opening / closing timing signal for the VVT 29 (oil control valve thereof). r, and the evaporation purge duty signal s and the like are output to the purge VSV 14 described above.

  Various control programs are stored in the ROM 33c or the flash memory 33d, and the programs are read into the RAM 33b and decoded by the CPU 33a. The CPU 33a acquires various signals a, b, c, d, e, f, g, h, i, j necessary for operation control of the engine 100 via the I / O interface 33e, and uses the information indicated by these signals. Based on the intake air amount, the required fuel injection amount, the ignition timing, the opening / closing valve timing, the opening degree of the EGR valve 25b, and the like. Then, various control signals p, q, r, and s corresponding to the calculation result are applied through the I / O interface 33e.

  Therefore, in the present embodiment, the ECU 33 cuts the purge under a predetermined condition, and when the purge is resumed from the purge cut, the ECU 33 increases the purge control amount increasing rate θ gradually, as the purge cut time Δt is shorter. Try to make it bigger.

  Next, control of the purge control amount at the time of fuel cut will be described with reference to FIG.

  Purge is executed when the value of the purge execution condition OK flag xprgig and the value of the purge execution flag xprg are 1. When the fuel is cut or supercharged during operation, the value of the purge execution condition OK flag xprgig and the value of the purge execution flag xprg are 0. In such a case, the ECU 33 performs the purge cut by closing the purge VSV 14 by applying the evaporation purge duty signal s via the I / O interface 33e.

  Here, in the air-fuel ratio feedback control performed in the present embodiment, when the air-fuel ratio becomes rich when purge is introduced, the ECU 33 applies the fuel injection signal p via the I / O interface 33e to reduce the fuel injection amount. I have to. In addition, the purge introduction amount is temporarily reduced when the air-fuel ratio at the time of purge introduction becomes richer than a predetermined value and the control is not in time. In other words, it is necessary to temporarily prevent excessive fuel vapor from being introduced during purge introduction. In this embodiment, the purge flow rate is estimated in consideration of not only the valve opening of the purge VSV 14 but also the intake pressure based on the intake pressure signal e output from the pressure sensor 38. This is because the amount of purge sent to the intake passage 2 side varies depending on the level of the intake negative pressure leading from the canister 13 to the intake passage 2. In the present embodiment, if the amount of fuel vapor in the purge gas exceeds a certain value, the responsiveness of the air-fuel ratio feedback control is likely to be lost. Therefore, the maximum value of the purge supply amount is set to a predetermined value in advance. ing.

  Then, as shown in the figure, when the value of the purge execution condition OK flag xprgig and the value of the purge execution flag xprg becomes 1 again due to the completion of the fuel cut or the like, the purge is resumed.

  When the purge is resumed, the purge amount is gradually increased based on the purge control amount increase rate θ determined according to the purge cut time Δt. That is, when the purge cut time is the shortest Δta, the purge control amount increase rate θ is set to the largest θa as shown in the figure. This is because the amount of fuel vapor adsorbed on the canister 13 is expected to be relatively small, and even if the increase rate θ of the purge control amount is increased, the air-fuel ratio is unlikely to become rich. On the other hand, when the purge cut time is the longest Δtc, the amount of fuel vapor adsorbed on the canister 13 is expected to be relatively large, so the rate of increase in the purge control amount is lower than θa. It is effectively avoided that the air-fuel ratio becomes excessively rich as θc. Further, in this embodiment, when the purge cut time Δt is Δtb which is intermediate between the above Δta and Δtc, the purge control amount increase rate is also set between θa and θc. The change in the increase rate θ of the purge control amount with the length of the purge cut time Δt may be stepwise or stepless.

  Thereafter, when the purge flow rate reaches the purge cut amount by restarting the purge, the purge control amount increase rate θ is equal to a predetermined value regardless of whether the purge cut time Δt is Δta, Δtb, or Δtc. The increase rate of the purge control amount is set to θd. In the figure, as an example, the increase rate θd of the predetermined purge control amount is set to the same increase rate as θc. Thus, particularly when the purge cut time Δt is Δta or Δtb, it is possible to effectively avoid over-riching of the air-fuel ratio due to excessive introduction of the evaporated fuel into the intake passage side 2 from the purge cut time. Yes.

  With this configuration, in this embodiment, when the purge is restarted from the purge cut, the purge control amount increase rate θ that gradually increases the purge flow rate is increased as the purge cut time Δt is shorter. Therefore, when the purge cut time Δt is short, the state in the canister 13 at the time of restarting the purge is not significantly changed from the start of the purge cut, so the purge control amount can be quickly increased by increasing the increase rate θ of the purge control amount. The purge can be effectively ensured as a state at the start of the purge cut, and when the purge cut time Δt is long, the purge gas concentration, that is, the amount of evaporated fuel in the purge is high. It is possible to effectively avoid the problem that becomes. Thereby, even when the frequency of purging is low, it is possible to ensure the necessary purge flow rate while avoiding the air-fuel ratio from becoming excessively rich.

  Further, in the present embodiment, the control for increasing the purge control amount increase rate θ as the purge cut time Δt is shortened until the purge control amount reaches the purge control amount at the start of the previous purge cut. If it exceeds that at the start of the previous purge cut, then the purge control amounts increase rates θa, θb and θc below that value, and more specifically θd, which is equal to θc. As a result, the increase rate θ of the purge control amount is increased to effectively avoid the problem that the air-fuel ratio becomes excessively rich after the purge is rapidly increased to the purge control amount already set before the purge cut.

  Although the embodiment of the present invention has been described above, the specific configuration of each unit is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the above-described embodiment, a mode in which the present invention is applied to an engine equipped with a supercharger, that is, a turbocharger is disclosed, but of course, an engine not equipped with a turbocharger may be used. The specific mode of air-fuel ratio control and the specific estimation method of the purge control amount are not limited to those of the above embodiment, and various modes including the existing ones can be applied. .

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be used as a control device for an internal combustion engine that stores evaporated fuel in a canister and discharges it into an intake system according to an operating state.

100: Internal combustion engine (engine)
13 ... Canister 2 ... Intake passage

Claims (1)

It has a function to purge the evaporated fuel adsorbed by the canister into the intake passage, and the purge flow rate is controlled so that the purge flow rate becomes the target purge control amount, and the purge is cut under a predetermined condition. When the purge is restarted, the rate of increase in the purge control amount that gradually increases the purge flow rate is increased as the purge cut time is shorter ,
Until the purge flow reaches the purge flow at the start of the purge cut, the purge control amount reaches the purge control amount at the start of the previous purge cut. A control apparatus for an internal combustion engine, characterized in that if the purge control amount exceeds that at the start of the previous purge cut, the value is equal to or less than the rate of increase of the purge control amount so far .

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