Control method and control device for internal combustion engine

Abstract

When the amount of fuel is increased to suppress the exhaust gas temperature, if the fuel injection timing is set to the output required injection timing, unburned HC will increase. In an internal combustion engine in which a fuel injection valve injects fuel toward an intake port, if air-fuel ratio feedback control is in progress, the fuel injection timing is set to an exhaust-demand injection timing that ends before intake top dead center (S1, S2). When the accelerator opening APO is equal to or greater than a predetermined opening APO1 that is close to full throttle and the exhaust system temperature TEMP is equal to or greater than a first threshold temperature TEMP1, the amount of fuel is increased. Even after the fuel increase begins, the exhaust-demand injection timing is maintained until the exhaust system temperature TEMP falls to a second threshold temperature TEMP2 (S3, S4, S5, S2). When the exhaust system temperature TEMP falls to the second threshold temperature TEMP2, the output-demand injection timing is set so that part of the injection period overlaps with the intake stroke (S5, S6).

Description

[Technical Field]

[0001] The present invention relates to control of an internal combustion engine in which the amount of fuel is increased to suppress the exhaust temperature when the exhaust system temperature becomes excessively high in a high load range, and in particular to control of the fuel injection timing when the amount of fuel is increased. [Background technology]

[0002] Patent Document 1 describes a technology in which the temperature of exhaust system components is estimated, and when this estimated temperature becomes higher than a predetermined temperature, the amount of fuel is increased to suppress the exhaust temperature by the heat of vaporization of the fuel.

[0003] Patent Document 1 exemplifies an internal combustion engine equipped with a direct-injection fuel injection system that injects fuel into a cylinder, but in the case of a port-injection fuel injection system that injects fuel into an intake port, injecting fuel near the intake top dead center is advantageous in order to ensure output when the required output is high, such as when the engine is fully open, while in the partial load range, it is advantageous to end injection before the intake top dead center from the perspective of exhaust composition. Therefore, in port-injection fuel injection systems, the fuel injection timing setting is often changed depending on the required output. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-066934 Summary of the Invention [Problem to be solved by the invention]

[0005] Under conditions where the temperature of exhaust system components is high and the amount of fuel is increased to suppress the exhaust temperature, the required output is basically large, and in order to ensure output, it is advantageous to inject the fuel near the intake top dead center. However, if the increased amount of fuel is injected toward the intake port near the intake top dead center, more fuel will flow into the cylinder without being sufficiently atomized, which increases the amount of unburned hydrocarbon emissions, which is undesirable. [Means for solving the problem]

[0006] The present invention relates to a spark ignition internal combustion engine equipped with a port injection type fuel injection device that injects fuel into an intake port, and a control method for the internal combustion engine, which sets the fuel injection timing to an exhaust request injection timing in which injection ends before intake top dead center during air-fuel ratio feedback control, and sets the output request injection timing in which at least a part of the injection period overlaps with the intake stroke during fuel increase, When the accelerator opening is equal to or greater than a predetermined opening and the exhaust system temperature reaches a predetermined first threshold temperature, the amount of fuel is increased to suppress the exhaust temperature; For a predetermined period from the start of the fuel increase, the exhaust request injection timing is set as described above. [Effects of the Invention]

[0007] In the present invention, for example, when a driver accelerates with the accelerator fully open, the exhaust required injection timing is maintained so that injection ends before intake top dead center during the initial period after the increase in amount, i.e., for a predetermined period, thereby suppressing deterioration of the exhaust composition. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an explanatory diagram showing the configuration of an internal combustion engine that performs an increasing control according to an embodiment; [Figure 2] 6 is a flowchart showing a process for switching the fuel injection timing setting in accordance with the amount increase control. [Figure 3] 4 is a time chart showing an example of the operation of an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of an internal combustion engine 1 according to one embodiment of the present invention. The internal combustion engine 1 according to the embodiment is a four-stroke, spark-ignition internal combustion engine (a so-called gasoline engine) used to drive a vehicle, and each cylinder is provided with an intake valve 2, an exhaust valve 3, and a spark plug 4. The internal combustion engine 1 is equipped with a port-injection fuel injection system, and each cylinder is provided with a fuel injection valve 5 that injects fuel toward the intake port 6 of the cylinder. The fuel injection valve 5 injects fuel adjusted to a predetermined fuel pressure by lifting a needle valve through the operation of a solenoid or piezoelectric element, and the amount of fuel injected is basically proportional to the pulse width of a drive pulse signal applied to the solenoid or piezoelectric element.

[0010] An electronically controlled throttle valve 10, the opening of which is controlled by a control signal from an engine controller 9, is disposed upstream of a collector section 8 in an intake passage 7 connected to the intake port 6 of each cylinder. An air flow meter 11, which detects the amount of intake air, is disposed upstream of the throttle valve 10, and an air cleaner 12 is disposed further upstream.

[0011] The exhaust ports 13 of each cylinder are joined together to form a single exhaust passage 14, which is provided with an exhaust purification catalyst for purifying the exhaust, such as a three-way catalyst 15. The three-way catalyst 15 is, for example, a monolithic ceramic catalyst in which a catalyst layer containing catalytic metal is coated on the surface of a monolithic ceramic body having fine passages formed therein. The three-way catalyst 15 may also be configured to further include a downstream catalyst (a so-called underfloor catalyst) arranged in series.

[0012] An upstream air-fuel ratio sensor 19 for detecting the air-fuel ratio of exhaust gas discharged from the internal combustion engine 1 is disposed on the inlet side of the three-way catalyst 15 in the exhaust passage 14, i.e., on the upstream side of the three-way catalyst 15. This upstream air-fuel ratio sensor 19 is a so-called wide-range air-fuel ratio sensor that obtains an output corresponding to the exhaust air-fuel ratio. Furthermore, a downstream air-fuel ratio sensor 20 is disposed on the outlet side or downstream side of the three-way catalyst 15, that detects the air-fuel ratio of exhaust gas flowing out from the three-way catalyst 15. Like the upstream air-fuel ratio sensor 19, the downstream air-fuel ratio sensor 20 is a wide-range air-fuel ratio sensor that obtains an output corresponding to the exhaust air-fuel ratio. Note that the air-fuel ratio sensors 19, 20 may be so-called O2 sensors.

[0013] Detection signals from the air-fuel ratio sensors 19, 20 and the air flow meter 11 are input to the engine controller 9. Further detection signals from a number of sensors, such as a crank angle sensor 21 for detecting the engine speed, a water temperature sensor 22 for detecting the coolant temperature, and an accelerator position sensor 23 for detecting the amount of depression of the accelerator pedal operated by the driver (i.e., accelerator position APO), are input to the engine controller 9. Based on these input signals, the engine controller 9 optimally controls the amount and injection timing of fuel injection by the fuel injection valve 5, the ignition timing of the spark plug 4, the opening of the throttle valve 10, etc.

[0014] Next, the fuel increase for suppressing the exhaust gas temperature, which is a main part of the present invention, and the accompanying control of switching the fuel injection timing setting will be described.

[0015] The internal combustion engine 1 is basically operated with the stoichiometric air-fuel ratio as the target air-fuel ratio. That is, a basic fuel injection amount Tp is calculated as Tp = K·Qa / Ne (K is a constant) using the intake air amount Qa detected by the air flow meter 11 and the engine rotation speed Ne. The fuel injection amount Ti by the fuel injection valve 5 is calculated as Ti = Tp × TABYF × α × COEF. TABYF is the target equivalence ratio (the reciprocal of the excess air ratio) and is 1 at the stoichiometric air-fuel ratio. α is an air-fuel ratio feedback correction coefficient calculated by PID control or the like using the detection signals of the air-fuel ratio sensors 19 and 20 when the air-fuel ratio feedback control conditions are met. During open-loop control when the air-fuel ratio feedback control conditions are not met, α = 1. COEF indicates various correction coefficients. Under most operating points (combinations of rotation speed Ne and load Te) of the internal combustion engine 1, the engine is operated near the stoichiometric air-fuel ratio by air-fuel ratio feedback control so that the three-way catalyst 15 can purify the exhaust gas optimally.

[0016] On the other hand, when the accelerator opening APO detected by the accelerator opening sensor 23 is equal to or greater than a predetermined opening APO1 close to full throttle and the exhaust system temperature TEMP reaches a predetermined first threshold temperature TEMP1, the amount of fuel is increased to suppress the exhaust temperature in order to protect exhaust system components (such as the three-way catalyst 15). Note that the exhaust system temperature TEMP can be an appropriate value, such as an estimated temperature value of the three-way catalyst 15 as a representative point of the exhaust system. When the amount of fuel is increased to suppress the exhaust temperature, the air-fuel ratio control becomes open-loop control, and a target equivalence ratio KMRM during increase, which is greater than 1, is used as the target equivalence ratio TABYF. The value of the target equivalence ratio KMRM during increase is predetermined for each operating point determined by the engine speed Ne and the load Te; that is, it is obtained from a map using the engine speed Ne and the load Te as parameters.

[0017] By increasing the amount of fuel so that the air-fuel ratio is richer than the theoretical air-fuel ratio in this way, a cooling effect is obtained by the heat of vaporization of the fuel, and the exhaust temperature is reduced.

[0018] The fuel injection amount Ti calculated as above corresponds to the required valve opening time of the fuel injection valve 5, i.e., the pulse width of the drive pulse signal, and is a real-time value. Therefore, in actual fuel injection control, the pulse width, which is the real time, is converted into a crank angle range, and the injection start timing (injection start crank angle) is calculated based on the crank angle range so that the injection end timing coincides with the target injection end crank angle. Then, when the crank angle reaches this injection start crank angle, fuel injection starts.

[0019] There are two modes for setting the fuel injection timing. One is exhaust demand injection timing, which prioritizes exhaust composition and ends injection before intake top dead center. For example, the target injection end crank angle is approximately 60° BTDC. During air-fuel ratio feedback control, the fuel injection timing is controlled by this exhaust demand injection timing. With this fuel injection timing setting, the fuel injected into the intake port 6 is sufficiently atomized and flows into the cylinder as a good air-fuel mixture, resulting in good exhaust composition.

[0020] The other is a power-demand injection timing that overlaps at least a portion of the injection period with the intake stroke. For example, the target injection end crank angle is approximately 30° ATDC to 110° ATDC. When the accelerator opening APO is equal to or greater than a predetermined opening APO1 near full throttle and fuel is being increased, the driver is requesting high power output, so the fuel injection timing is basically controlled by this power-demand injection timing. With this fuel injection timing setting, the injected fuel flows into the cylinder relatively early, and the cooling effect caused by the heat of vaporization in the cylinder increases the filling efficiency, which is advantageous for improving power output.

[0021] However, if the increased amount of fuel is injected toward the intake port 6 near the intake top dead center, more fuel will flow into the cylinder without being sufficiently atomized, which is undesirable as it increases the amount of unburned hydrocarbons emitted. Therefore, in the present invention, the exhaust requirement injection timing is used for a predetermined period from the start of the fuel increase, and after the predetermined period has elapsed, the injection timing is shifted to the output requirement injection timing.

[0022] In a preferred embodiment, the predetermined period is the period from the start of the fuel increase until the exhaust system temperature TEMP drops to a predetermined second threshold temperature TEMP2 that is lower than the first threshold temperature TEMP1.

[0023] 3 is a time chart showing an example of the operation of the above embodiment when the driver performs so-called full-throttle acceleration. From top to bottom, the chart shows (a) fuel injection timing setting (whether it is exhaust-request injection timing or output-request injection timing), (b) a fuel increase flag indicating that fuel is being increased, (c) exhaust system temperature TEMP, and (d) accelerator opening APO. In this time chart, before time t1, the accelerator opening APO reaches or exceeds a predetermined opening APO1 close to full throttle, and the exhaust system temperature TEMP is on an upward trend. At this time, the target equivalence ratio TABYF is still 1, and the fuel injection timing is set to the exhaust-request injection timing that prioritizes exhaust gas composition.

[0024] At time t1, the exhaust system temperature TEMP reaches the first threshold temperature TEMP1, and the fuel amount is increased. This fuel increase causes the exhaust system temperature TEMP to tend to decrease. Even after the fuel amount increase starts, the fuel injection timing setting is maintained at the exhaust required injection timing.

[0025] After that, at time t2, the exhaust system temperature TEMP drops to a predetermined second threshold temperature TEMP2. In the illustrated example, the exhaust system temperature TEMP, which had been on a downward trend, reaches a state of equilibrium around time t2. At this point in time t2, the fuel injection timing setting is switched to the output-request injection timing. After that, while the fuel increase continues, injection is performed at the output-request injection timing, and when the fuel increase ends, the timing is restored to the exhaust-request injection timing.

[0026] In this way, in the above embodiment, the fuel injection timing setting is maintained at the exhaust request injection timing from the start of fuel increase until the exhaust system temperature TEMP drops to the predetermined second threshold temperature TEMP2, thereby suppressing an increase in unburned HC due to switching to the output request injection timing. If full-throttle acceleration is completed in a relatively short time (before time t2), the injection timing does not switch to the output request injection timing, minimizing the deterioration of HC due to full-throttle acceleration. On the other hand, if the driver requests a long full-throttle acceleration, the injection timing switches to the output request injection timing at time t2, ensuring good output characteristics.

[0027] 2 is a flowchart showing the process of switching the fuel injection timing setting associated with the above-mentioned increase control. First, in step 1, it is determined whether or not air-fuel ratio feedback control is in progress. If air-fuel ratio feedback control is in progress, the process proceeds to step 2, where the exhaust request injection timing is selected as the fuel injection timing setting. If air-fuel ratio feedback control is not in progress, the process proceeds from step 1 to step 3, where it is determined whether the accelerator opening APO is equal to or greater than a predetermined opening APO1 that is close to full opening. If the answer is NO here, the process similarly proceeds to step 2, where the exhaust request injection timing is selected.

[0028] If the accelerator opening APO is equal to or greater than the predetermined opening APO1, it is further determined in step 4 whether or not fuel is being increased to suppress the exhaust temperature. If the determination is NO here, the process proceeds to step 2, and the fuel injection timing is set to the exhaust request injection timing. Note that whether or not the fuel increase to suppress the exhaust temperature is necessary is determined by another routine (not shown), and if the fuel increase is to be performed, the increase target equivalence ratio KMRM is set according to the operating point, as described above.

[0029] If it is determined in step 4 that fuel is being increased to suppress the exhaust temperature, the process proceeds from step 4 to step 5, where it is determined whether the exhaust system temperature TEMP has dropped to a predetermined second threshold temperature TEMP2 after the fuel increase started. If the result is NO, the process proceeds to step 2, where the exhaust request injection timing is set. In other words, the exhaust request injection timing is maintained as the fuel injection timing setting from the start of the fuel increase until the exhaust system temperature TEMP drops to the predetermined second threshold temperature TEMP2.

[0030] If it is determined in step 5 that the exhaust system temperature TEMP has dropped to the predetermined second threshold temperature TEMP2, the process proceeds from step 5 to step 6, where the output required injection timing is selected as the fuel injection timing setting.

[0031] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the exhaust-request injection timing is maintained from the start of the fuel increase until time t2 when the exhaust system temperature TEMP falls to the predetermined second threshold temperature TEMP2. However, the exhaust-request injection timing may be maintained until the exhaust system temperature TEMP, which has been decreasing due to the start of the fuel increase, reaches a stable state, at which point the exhaust-request injection timing is switched to the output-request injection timing. Alternatively, a timer may be used to measure the elapsed time from the start of the fuel increase, and the exhaust-request injection timing may be maintained until a predetermined time has elapsed. Furthermore, although the above embodiment has been described using a naturally aspirated engine as an example, the present invention may also be applied to an internal combustion engine equipped with a supercharger such as a turbocharger. [Explanation of symbols]

[0032] 1...Internal combustion engine 5...Fuel injection valve 6...Intake port 9...Engine controller 15...Three-way catalyst 21...Crank angle sensor 23...Accelerator opening sensor

Claims

1. A control method for a spark ignition internal combustion engine equipped with a port injection type fuel injection device that injects fuel into an intake port, wherein the fuel injection timing is set to an exhaust required injection timing in which injection ends before intake top dead center during air-fuel ratio feedback control, and to an output required injection timing in which at least a part of the injection period overlaps with the intake stroke during fuel increase, When the accelerator opening is equal to or greater than a predetermined opening and the exhaust system temperature reaches a predetermined first threshold temperature, the amount of fuel is increased to suppress the exhaust temperature; The exhaust request injection timing is set as described above for a predetermined period from the start of the fuel increase. A method for controlling an internal combustion engine.

2. The predetermined period is a period from the start of the fuel increase until the exhaust system temperature decreases to a predetermined second threshold temperature.

2. The method for controlling an internal combustion engine according to claim 1.

3. the predetermined period is a period from the start of the fuel increase to the time when the exhaust system temperature, which decreases due to the fuel increase, reaches an equilibrium state.

2. The method for controlling an internal combustion engine according to claim 1.

4. The exhaust required injection timing is set such that the injection end target crank angle is set before the intake top dead center, and the output required injection timing is set such that the injection end target crank angle is set after the intake top dead center, and the injection start timing is controlled so that the injection ends at the target crank angle.

2. The method for controlling an internal combustion engine according to claim 1.

5. The degree of fuel increase for suppressing the exhaust gas temperature is set for each operating point determined by the rotation speed and load of the internal combustion engine.

2. The method for controlling an internal combustion engine according to claim 1.

6. A control device for an internal combustion engine, which is equipped with a port injection type fuel injection device that injects fuel into an intake port, and which sets the fuel injection timing to an exhaust required injection timing in which injection ends before intake top dead center during air-fuel ratio feedback control, and sets the output required injection timing in which at least a part of the injection period overlaps with the intake stroke during fuel increase, When the accelerator opening is equal to or greater than a predetermined opening and the exhaust system temperature reaches a predetermined first threshold temperature, the amount of fuel is increased to suppress the exhaust temperature; The exhaust request injection timing is set as described above for a predetermined period from the start of the fuel increase. Control device for internal combustion engines.

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