Control device for internal combustion engine

Abstract

To suppress a rise in catalyst temperature while executing fuel cut.SOLUTION: A control device 70 for an internal combustion engine includes a fuel injector 51 for injecting fuel, a throttle valve 34 for adjusting an intake amount supplied to the internal combustion engine, a variable valve timing mechanism 24 for changing valve operation characteristics of at least one of an intake valve 19 and an exhaust valve 20, and a catalyst 43 for purifying exhaust gas discharged from a combustion chamber 13. When the catalyst temperature of the catalyst 43 is equal to or higher than the predetermined temperature at the timing when the fuel is not injected by the fuel injector 51, the control device 70 increases the throttle opening degree of the throttle valve 34 as compared with the case where the catalyst temperature is not equal to or higher than the predetermined temperature, and controls the variable valve timing mechanism 24 to increase the valve overlap amount between the intake valve 19 and the exhaust valve 20.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a control device for an internal combustion engine. [Background technology]

[0002] Conventionally, internal combustion engines equipped with catalysts that purify exhaust gases generated by the combustion of a mixture of fuel and intake air have been widely known. In an internal combustion engine equipped with a catalyst, when fuel cut (F / C) is performed while the mixture is being burned, oxygen reacts with unburned components at the time of combustion in the catalyst, resulting in so-called afterburning. If afterburning continues, the catalyst temperature rises, causing the catalyst to deteriorate.

[0003] Patent Document 1 discloses a device that estimates catalyst temperature during repeated acceleration and deceleration. This device performs catalyst protection control, such as executing fuel increase control to increase the amount of fuel supplied to the engine when the estimated catalyst temperature reaches a first temperature or higher, and executing fuel cut prohibition control to prohibit engine fuel cut when the estimated catalyst temperature reaches a second temperature or higher. This type of catalyst protection control aims to lower the catalyst temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-32090 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the device of Patent Document 1 has a problem in that fuel consumption deteriorates when fuel increase control is executed and when fuel cut prohibition control is executed, and also has a problem in that drivability deteriorates when fuel cut prohibition control is executed in cases where fuel would normally be cut.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has as its object to suppress an increase in catalyst temperature while a fuel cut is being executed. [Means for solving the problem]

[0007] The present invention provides a control device for an internal combustion engine comprising: a fuel injector that injects fuel; a throttle valve that adjusts the amount of intake air supplied to the internal combustion engine; an intake valve that allows the intake air to flow into a combustion chamber of the internal combustion engine; an exhaust valve that discharges exhaust gas generated by the combustion of a mixture of intake air and fuel from the combustion chamber; a variable valve timing mechanism that changes the valve operating characteristics of at least one of the intake valve and the exhaust valve; and a catalyst that purifies the exhaust gas discharged from the combustion chamber, wherein the control device is characterized in that, at a timing when fuel is not injected by the fuel injector, when the catalyst temperature of the catalyst is equal to or higher than a predetermined temperature, the control device increases the throttle opening of the throttle valve more than when the catalyst temperature is not equal to or higher than the predetermined temperature, and controls the variable valve timing mechanism to increase the valve overlap amount between the intake valve and the exhaust valve. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress an increase in catalyst temperature while a fuel cut is being executed. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of a schematic configuration of a vehicle. [Figure 2] 10 is a flowchart illustrating an example of a temperature suppression process. [Figure 3] 4 is a timing chart of the temperature suppression process according to the first embodiment. [Figure 4] 10 is a timing chart of the temperature suppression process according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention is a control device 70 for an internal combustion engine that includes a fuel injector 51 that injects fuel, a throttle valve 34 that adjusts the amount of intake air supplied to the internal combustion engine, an intake valve 19 that introduces intake air into a combustion chamber 13 of the internal combustion engine, an exhaust valve 20 that discharges exhaust gas generated by combustion of a mixture of intake air and fuel from the combustion chamber 13, a variable valve timing mechanism 24 that changes the valve operating characteristics of at least one of the intake valve 19 and the exhaust valve 20, and a catalyst 43 that purifies the exhaust gas discharged from the combustion chamber 13. When the catalyst temperature of the catalyst 43 is equal to or higher than a predetermined temperature, the control device 70 increases the throttle opening of the throttle valve 34 more than when the catalyst temperature is not equal to or higher than the predetermined temperature, and controls the variable valve timing mechanism 24 to increase the valve overlap between the intake valve 19 and the exhaust valve 20 when fuel is not injected by the fuel injector 51. This makes it possible to suppress an increase in catalyst temperature while maintaining a fuel cut. [Example]

[0011] <First Example> Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a diagram showing a schematic configuration of a vehicle 1 equipped with a control device 70 for an internal combustion engine according to this embodiment. Note that Fig. 1 is simplified for the sake of convenience in explaining this embodiment, and components that are normally included in a vehicle are assumed to be included even if they are not shown in the figure.

[0012] The vehicle 1 of this embodiment includes an engine 10 as an internal combustion engine, a control device 70, and the like. The engine 10 has an engine body 11, an intake system 30 that takes in intake air for combustion in the engine body 11, an exhaust system 40 that discharges exhaust gas from the engine body 11 to the outside, a fuel system 50 that supplies fuel to the engine body 11, and a sensor system that detects the state of the vehicle 1, etc.

[0013] Engine body 11 performs a series of strokes consisting of an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. Engine body 11 has a combustion chamber 13 in which a piston 12 is housed so that it can reciprocate, a crank chamber 15 in which a crankshaft 14 is housed so that it can rotate, an intake port 16 which is an inlet for intake air for combustion, and an exhaust port 17 which is an outlet for exhaust gas. Engine body 11 also has an ignition plug 18 arranged so that its tip is located within combustion chamber 13, an intake valve 19 located between combustion chamber 13 and intake port 16, and an exhaust valve 20 located between combustion chamber 13 and exhaust port 17.

[0014] During the intake stroke, the piston 12 descends from top dead center to bottom dead center, the intake valve 19 opens, and the exhaust valve 20 closes. As the piston 12 descends, a mixture of intake air and fuel flows from the intake system 30 into the combustion chamber 13. During the compression stroke, the piston 12 moves upward from the bottom dead center toward the top dead center, and the intake valve 19 and the exhaust valve 20 close. As the piston 12 moves upward, the air-fuel mixture is compressed.

[0015] During the combustion stroke, the compressed air-fuel mixture is ignited by the spark plug 18 and combusted, pushing the piston 12 downward from top dead center to bottom dead center. During the exhaust stroke, the piston 12 rises from bottom dead center to top dead center, the intake valve 19 closes, and the exhaust valve 20 opens. As the piston 12 rises, exhaust gases generated during the combustion stroke are discharged into the exhaust system 40.

[0016] The engine body 11 also has a valve actuation system. The valve actuation system has an intake cam 21 that opens and closes the intake valve 19, an exhaust cam 22 that opens and closes the exhaust valve 20, and a variable valve timing mechanism (VVT mechanism) 24. The camshaft of the intake cam 21 and the camshaft of the exhaust cam 22 are connected to the crankshaft 14 via a cam chain and rotate in conjunction with the rotation of the crankshaft 14.

[0017] The intake valve 19 and the exhaust valve 20 are opened by being pressed by the intake cam 21 and the exhaust cam 22, respectively, against the force of the valve spring 23. On the other hand, the intake valve 19 and the exhaust valve 20 are closed by being released from the pressure by the intake cam 21 and the exhaust cam 22, respectively, and being returned to their original positions by the force of the valve spring 23. Operation by such a valve actuation system controls the opening and closing timing (opening and closing timing) of the intake valve 19 and the exhaust valve 20 during the intake stroke, compression stroke, combustion stroke, and exhaust stroke of the engine body 11.

[0018] The variable valve timing mechanism 24 changes the valve actuation characteristics of at least one of the intake valve 19 and the exhaust valve 20. The variable valve timing mechanism 24 has an intake VVT ​​mechanism 25 and an exhaust VVT mechanism 26. The intake VVT ​​mechanism 25 varies the opening / closing timing and duration of the intake valve 19 based on control by the control device 70. The exhaust VVT mechanism 26 also varies the opening / closing timing and duration of the exhaust valve 20 based on control by the control device 70.

[0019] The engine body 11 repeats a series of processes, thereby transmitting driving force from the engine body 11 to the drive wheels via the crankshaft 14, causing the vehicle to run. The configuration of the engine body 11 is not particularly limited, and various known engines can be applied. The engine body 11 may be either a gasoline engine or a diesel engine.

[0020] The intake system 30 includes an intake passage 31, an air cleaner 33, and a throttle valve 34. The intake passage 31 is a passage that guides intake air taken in from outside the vehicle 1 to the combustion chamber 13 via the intake port 16. The intake passage 31 is mainly composed of an intake pipe 32. The air cleaner 33 is disposed in the intake passage 31 and purifies the intake air by removing foreign matter such as dust and dirt contained in the intake air. The throttle valve 34 is disposed in the intake passage 31 and adjusts the flow rate of the intake air by opening and closing. The throttle valve 34 adjusts the flow rate of the intake air based on the control of the control device 70.

[0021] The exhaust system 40 includes an exhaust passage 41 and a catalyst (catalytic converter) 43. The exhaust passage 41 is a passage through which exhaust gas burned in the combustion chamber 13 is exhausted to the outside of the vehicle 1 via the exhaust port 17. The exhaust passage 41 is mainly composed of an exhaust pipe 42. The catalyst 43 purifies harmful substances contained in the exhaust gas. For example, various known three-way catalysts or the like can be used as the catalyst 43.

[0022] The fuel system 50 supplies fuel to the engine body 11. The fuel system 50 includes a fuel tank, a fuel pump, and a fuel injector 51. The fuel pump supplies fuel stored in the fuel tank to the fuel injector 51. The fuel injector 51 injects the fuel supplied from the fuel tank into the intake passage 31. The fuel injector 51 adjusts the amount of fuel injected based on the control of the control device 70. Furthermore, the fuel injector 51 is not limited to injecting fuel into the intake passage 31, and may be configured to inject fuel into the combustion chamber 13 or the intake port 16.

[0023] The sensor system detects the state of the vehicle 1 and transmits the detected results to the control device 70. The sensor system includes a crank angle sensor 61, a vehicle speed sensor 62, an exhaust pressure sensor 63, an air-fuel ratio sensor 64, an outside air temperature sensor 65, a throttle valve opening sensor 66, an accelerator opening sensor 67, a catalyst temperature sensor 68, and an exhaust temperature sensor 69. The sensor system also includes sensors that are normally included in the vehicle 1, such as an intake pressure sensor, an air flow meter, and an engine rotation speed sensor.

[0024] The crank angle sensor 61 detects the crank angle (the rotation angle of the crankshaft 14) and transmits information about the detected crank angle to the control device 70. The control device 70 controls the ignition timing of the spark plug 18 based on the information about the crank angle detected by the crank angle sensor 61.

[0025] The vehicle speed sensor 62 detects the speed of the vehicle 1 and transmits information on the detected vehicle speed to the control device 70. The exhaust pressure sensor 63 detects the pressure of the exhaust gas and transmits information on the detected exhaust gas pressure to the control device 70 .

[0026] The air-fuel ratio sensor 64 detects the air-fuel ratio of the exhaust gas and transmits information on the detected air-fuel ratio of the exhaust gas to the control device 70. The outside air temperature sensor 65 detects the outside air temperature and transmits information about the detected outside air temperature to the control device 70.

[0027] The throttle valve opening sensor 66 detects the throttle opening of the throttle valve 34 and transmits information on the detected throttle opening of the throttle valve 34 to the control device 70 . The accelerator opening sensor 67 detects the stroke of the accelerator pedal and transmits information about the detected stroke of the accelerator pedal to the control device 70.

[0028] The catalyst temperature sensor 68 detects the catalyst temperature of the catalyst 43 and transmits information on the detected catalyst temperature of the catalyst 43 to the control device 70 . The exhaust gas temperature sensor 69 detects the temperature of the exhaust gas and transmits information on the detected exhaust gas temperature to the control device 70 .

[0029] The control device 70 controls the entire vehicle 1 and the engine 10. For example, an ECU (Electronic Control Unit) can be used as the control device 70. The control device 70 has a CPU, ROM, RAM, etc. as its hardware configuration. The ROM stores programs and predetermined information for controlling the vehicle 1, the engine 10, etc. The RAM is a work memory that temporarily stores programs and data. The CPU reads out programs stored in the ROM, expands them into the RAM, and executes them to control the vehicle 1, the engine 10, etc.

[0030] The control device 70 drives the engine 10 by controlling the timing and amount of fuel injection from the fuel injector 51, the ignition timing of the spark plug 18, the amount of intake air taken in by the intake system 30, etc., in accordance with the amount of accelerator pedal stroke detected by the accelerator opening sensor 67.

[0031] In order to suppress an increase in the catalyst temperature of the catalyst 43, the control device 70 of this embodiment executes a temperature suppression process when the catalyst temperature is equal to or higher than a predetermined temperature at a timing when fuel is not injected by the fuel injector 51. Here, the temperature suppression process is a process of increasing the throttle opening of the throttle valve 34 more than usual and increasing the valve overlap amount between the intake valve 19 and the exhaust valve 20. In this embodiment, a case will be described in which the timing when fuel is not injected by the fuel injector 51 is a fuel cut (F / C) timing.

[0032] Fig. 2 is a flowchart showing an example of a temperature suppression process performed by the control device 70. The flowchart in Fig. 2 is implemented, for example, by the ECU, which is the control device 70, executing a program. The flowchart in Fig. 2 is initiated when the engine 10 is started.

[0033] In S10, the control device 70 determines whether or not fuel is being cut (F / C). Specifically, the control device 70 determines that fuel is being cut when fuel injection from the fuel injector 51 is stopped. If fuel is being cut, the process proceeds to S11. On the other hand, if fuel is not being cut, the process returns to S10 without executing the temperature suppression process of S13, which will be described later.

[0034] In S11, the control device 70 determines whether the catalyst temperature is equal to or higher than a predetermined temperature (first threshold temperature Th). Specifically, the control device 70 makes this determination by comparing the catalyst temperature detected by the catalyst temperature sensor 68 with the first threshold temperature Th. Information about the first threshold temperature Th is stored in the control device 70. The first threshold temperature is set, for example, to a temperature at which the catalyst 43 may melt and deteriorate if the temperature continues to rise. If it is determined that the catalyst temperature is equal to or higher than the predetermined temperature, the process proceeds to S12. On the other hand, if it is determined that the catalyst temperature is not equal to or higher than the predetermined temperature, the catalyst 43 is unlikely to deteriorate, so the process returns to S10 without executing the temperature suppression process of S13, which will be described later.

[0035] In S12, the control device 70 determines that the conditions for executing the temperature suppression process are met to suppress the catalyst temperature of the catalyst 43. Specifically, the control device 70 stores the execution flag for the temperature suppression process so that it is turned on.

[0036] In S13, in response to the fact that the execution flag for the temperature suppression process is on, the control device 70 executes the temperature suppression process for the catalyst 43. There are two types of temperature suppression process. First, as a first process, the control device 70 controls the throttle valve 34 so that the throttle opening is increased when fuel is cut (F / C) compared to when the catalyst temperature is not equal to or higher than the predetermined temperature.

[0037] Since this is the timing of fuel cut (F / C), no intake air is required to generate an air-fuel mixture, and so normally (in normal engine control), the throttle valve 34 would be controlled to be fully closed or nearly fully closed. However, in this embodiment, by increasing the throttle opening of the throttle valve 34 during fuel cut (F / C), low-temperature intake air can be allowed to flow through the throttle valve 34 to the catalyst 43. Therefore, the catalyst temperature of the catalyst 43 can be lowered by the low-temperature intake air.

[0038] Next, as a second process, the control device 70 controls the variable valve timing mechanism 24 so as to increase the valve overlap between the intake valve 19 and the exhaust valve 20 during fuel cut (F / C) compared to when the catalyst temperature is not equal to or higher than a predetermined temperature. Specifically, the control device 70 increases the valve overlap by controlling the intake VVT ​​mechanism 25 to advance the intake valve 19 and the exhaust VVT mechanism 26 to retard the exhaust valve 20.

[0039] Since this is the timing of fuel cut (F / C), there is no need to consider the intake air charging efficiency, and so normally (in normal engine control), the valve overlap amount would be controlled to be 0 or approximately 0. On the other hand, in this embodiment, by increasing the valve overlap amount between the intake valve 19 and the exhaust valve 20 at the timing of fuel cut (F / C), low-temperature intake air can be made to flow into the catalyst 43 at the timing when the intake valve 19 and the exhaust valve 20 overlap. Therefore, the catalyst temperature of the catalyst 43 can be lowered by the low-temperature intake air.

[0040] Information on the amount by which the throttle opening of the throttle valve 34 is increased and the amount by which the valve overlap is increased during fuel cut (F / C) is stored in the control device 70. The information on each amount of increase can be set by conducting experiments or simulations in advance to determine the throttle opening at which the amount of heat dissipation becomes greater than the amount of heat of reaction, based on the operating conditions (engine speed, exhaust temperature, vehicle speed, etc.). The amount by which the valve overlap is increased may be the maximum valve overlap that can be set by advancing the intake valve 19 to the maximum and retarding the exhaust valve 20 to the maximum.

[0041] After S13 is executed, the process returns to S10. Note that if S10 returns to S10 without proceeding to S11, or if S11 returns to S10 without proceeding to S12, the catalyst 43 is unlikely to deteriorate, so the control device 70 does not execute the temperature suppression process of S13. That is, when fuel is cut (F / C), the control device 70 performs normal engine control such that the throttle opening of the throttle valve 34 is fully or almost fully closed based on the accelerator opening sensor 67, and the valve overlap amount is zero or almost zero.

[0042] 3 is a timing chart showing the timing when the control device 70 performs the temperature suppression process in the first embodiment. Here, the explanation is given assuming that the driver alternately depresses and releases the accelerator pedal, repeatedly accelerating and decelerating. During this type of repeated acceleration and deceleration, oxygen reacts with unburned fuel in the catalyst 43, which tends to increase the catalyst temperature.

[0043] Figure 3(a) shows the change in accelerator pedal stroke (accelerator opening). Figure 3(b) shows the change in catalyst temperature of catalyst 43. Figure 3(c) shows the change in fuel cut (F / C) state. Figure 3(d) shows the determination of the execution conditions for temperature suppression processing. Figure 3(e) shows the state of throttle opening. Figure 3(f) shows the state of the opening and closing timing of intake valve 19 by intake VVT ​​mechanism 25. Figure 3(g) shows the state of the opening and closing timing of exhaust valve 20 by exhaust VVT mechanism 26.

[0044] Here, the driver alternately presses and releases the accelerator pedal, causing the accelerator pedal stroke shown in Figure 3(a) to alternate between fully closed and open. Therefore, as shown in Figure 3(c), fuel is cut off when the accelerator pedal stroke is fully closed, and fuel is not cut off when the accelerator pedal stroke is open. Furthermore, as shown in Figure 3(e), the throttle opening of throttle valve 34 is controlled to alternate between fully closed (or nearly fully closed) and open depending on the accelerator pedal stroke.

[0045] 3(b), repeated acceleration and deceleration causes oxygen and unburned fuel to react in the catalyst 43, gradually increasing the catalyst temperature, and at time T1 the catalyst temperature reaches or exceeds the first threshold temperature Th. Therefore, as shown in FIG. 3(d), the execution condition for the temperature suppression process is met at time T1.

[0046] In Figure 3(e), the change in throttle opening when the temperature suppression process is executed from time T1 to time T2 is shown by a solid line as an example, and the change in throttle opening when normal engine control is executed without executing the temperature suppression process is shown by a dashed line as a comparative example. As shown in Figure 3(e), in the example, the throttle opening is controlled to increase by an increment I when fuel is cut (F / C) compared to the comparative example. In this way, by increasing the throttle opening of the throttle valve 34, low-temperature intake air can be made to flow into the catalyst 43 through the throttle valve 34.

[0047] In Figure 3(f), the change in the opening / closing timing of the intake valve 19 when the temperature suppression process is executed from time T1 to time T2 is shown by a solid line as an example, and the change in the opening / closing timing of the intake valve 19 when normal engine control is executed without executing the temperature suppression process is shown by a dashed line as a comparative example. As shown in Figure 3(f), in the example, the intake VVT ​​mechanism 25 is controlled to advance the intake valve 19 at the timing when fuel is cut (F / C) compared to the comparative example.

[0048] In Figure 3(g), the change in the opening and closing timing of the exhaust valve 20 when the temperature suppression process is executed from time T1 to time T2 is shown by a solid line as an example, and the change in the opening and closing timing of the exhaust valve 20 when normal engine control is executed without executing the temperature suppression process is shown by a dashed line as a comparative example. As shown in Figure 3(g), in the example, the exhaust VVT mechanism 26 is controlled to retard the opening angle of the exhaust valve 20 at the timing when fuel is cut (F / C) compared to the comparative example.

[0049] In this way, by advancing the intake valve 19 and retarding the exhaust valve 20 to increase the valve overlap, both the intake valve 19 and the exhaust valve 20 are kept open, allowing low-temperature intake air to easily flow into the catalyst 43.

[0050] In Figure 3(b), the change in catalyst temperature when the temperature suppression process is executed after time T1 is shown by a solid line as an example, and the change in catalyst temperature when normal engine control is executed without executing the temperature suppression process is shown by a dashed line as a comparative example. As shown in Figure 3(b), in the example, the catalyst temperature gradually decreases compared to the comparative example because the catalyst 43 is cooled by the low-temperature intake air. Here, at time T2, the catalyst temperature of the catalyst 43 becomes equal to or lower than the second threshold temperature T1.

[0051] As shown in Figure 3(d), the control device 70 determines that the condition for executing the temperature suppression process is not met at time T2 when the catalyst temperature of the catalyst 43 becomes equal to or lower than the second threshold temperature Tl. Therefore, as shown in Figure 3(e), after time T2, the control device 70 ends the control for increasing the throttle opening degree when fuel is cut (F / C). Also, as shown in Figures 3(f) and 3(g), after time T2, the control device 70 ends the control for increasing the valve overlap amount when fuel is cut (F / C). In this case, by setting a difference between the first threshold temperature Th when the execution conditions for the temperature suppression process are met and the second threshold temperature Tl when the execution conditions for the temperature suppression process are not met, it is possible to prevent the temperature suppression process from being frequently executed and canceled.

[0052] As described above, according to this embodiment, the throttle opening of the throttle valve 34 is increased and the valve overlap between the intake valve 19 and the exhaust valve 20 is increased when fuel is not being injected by the fuel injector 51. Therefore, the amount of intake air flowing into the catalyst 43 can be increased, thereby lowering the catalyst temperature with lower temperature intake air. Since no additional device is required to increase the amount of intake air flowing into the catalyst 43, an increase in catalyst temperature can be suppressed while avoiding a complex structure for lowering the catalyst temperature. Furthermore, deterioration in fuel economy and drivability due to the fuel cut remaining in effect can be prevented.

[0053] <Second Example> In the first embodiment, a case was described in which the throttle opening was increased by a fixed amount and the valve overlap amount was increased by a fixed amount during the temperature suppression process. When the throttle opening is increased, the increased intake air may cause an increase in engine output when the engine returns from a fuel cut (when fuel is injected), which is known as tip-in shock. In the second embodiment, a case will be described in which tip-in shock is suppressed by adjusting the amount of increase when the throttle opening of the throttle valve 34 is increased and the amount of increase when the valve overlap amount is increased.

[0054] In this embodiment, the temperature suppression process in S13 of the flowchart in FIG. 2 can be changed to the following first temperature suppression process or second temperature suppression process. In the first temperature suppression process, the amount by which the throttle opening of the throttle valve 34 is increased and the amount by which the valve overlap is increased are adjusted based on the catalyst temperature. Specifically, association data that associates the amount by which the throttle opening is increased and the amount by which the valve overlap is increased with the current catalyst temperature and the trend of catalyst temperature change (whether it is increasing or decreasing) is stored in the control device 70. The association data stores amounts by which the throttle opening is increased and the valve overlap is increased, which are capable of reducing the catalyst temperature and suppressing tip-in shock. If the catalyst temperature is increasing, a larger amount of increase in the throttle opening and a larger amount of increase in the valve overlap are stored compared to when the catalyst temperature is decreasing, and if the catalyst temperature is decreasing, a smaller amount of increase in the throttle opening and a smaller amount of increase in the valve overlap are stored compared to when the catalyst temperature is increasing.

[0055] The control device 70 can determine the trend of catalyst temperature change (whether it is increasing or decreasing) based on the previous catalyst temperature detected by the catalyst temperature sensor 68 and the current catalyst temperature. Therefore, the control device 70 extracts information on the throttle opening increase amount and the valve overlap increase amount associated with the current catalyst temperature and the determined catalyst temperature change trend from the association data. Next, the control device 70 adjusts the amount of increase in throttle opening by controlling the throttle valve 34 so that the throttle opening increase amount is the extracted amount. The control device 70 also adjusts the amount of increase in valve overlap by controlling the intake VVT ​​mechanism 25 and the exhaust VVT mechanism 26 so that the valve overlap increase amount is the extracted amount. In this way, by not increasing the throttle opening increase amount or the valve overlap amount more than necessary, tip-in shock when returning from a fuel cut (when fuel is injected) can be suppressed, thereby improving drivability. The control device 70 may calculate the rate of change of the catalyst temperature based on the previous catalyst temperature and the current catalyst temperature, and adjust the amount of increase when increasing the throttle opening and the amount of increase when increasing the valve overlap amount by referring to association data that stores the rate of change of the catalyst temperature (rate of increase or rate of decrease) instead of the trend of change in the catalyst temperature.

[0056] The second temperature suppression process adjusts the amount by which the throttle opening of the throttle valve 34 is increased and the amount by which the valve overlap amount is increased based on the difference between the amount of heat generated by catalytic reaction and the amount of heat dissipation of the catalyst 43. Specifically, association data is stored in advance in the control device 70, which associates the amount by which the throttle opening is increased and the amount by which the valve overlap amount is increased with the current catalyst temperature and the difference between the amount of heat generated by catalytic reaction and the amount of heat dissipation.

[0057] Here, the catalytic reaction heat quantity is the amount of heat generated by the reaction of oxygen with unburned fuel in the catalyst 43. The catalytic reaction heat quantity can be calculated based on the exhaust flow rate and the air-fuel ratio. The exhaust flow rate can be calculated from the exhaust pressure detected by the exhaust pressure sensor 63. For example, the control device 70 can calculate the catalytic reaction heat quantity based on the exhaust flow rate and the air-fuel ratio by referring to association data in which the catalytic reaction heat quantity is previously associated with the exhaust flow rate and the air-fuel ratio.

[0058] On the other hand, the heat radiation amount is the sum of the heat radiation amount from the outside air and the heat radiation amount from the exhaust gas. The amount of heat released by the outside air is the amount of heat released from the catalyst 43 due to the temperature difference with the outside air or the wind generated while the vehicle is running, and can be calculated based on the outside air temperature and the vehicle speed. For example, the control device 70 can calculate the amount of heat released by the outside air by referring to association data in which the amount of heat released by the outside air is previously associated with the outside air temperature and the vehicle speed. The amount of exhaust heat release is the amount of heat released from the catalyst 43 by the exhaust gas, and can be calculated based on the exhaust flow rate and the exhaust temperature. For example, the control device 70 can calculate the amount of exhaust heat release by referring to association data in which the amount of exhaust heat release is previously associated with the exhaust flow rate and the exhaust temperature.

[0059] Specifically, association data that associates in advance the increase in throttle opening and the increase in valve overlap amount with the difference between the catalytic reaction heat amount and the heat dissipation amount is stored in the control device 70. The association data stores the increase in throttle opening and the increase in valve overlap amount that can reduce the catalyst temperature and suppress tip-in shock. When the catalytic reaction heat amount is greater than the heat dissipation amount, a larger increase in throttle opening and a larger increase in valve overlap amount are stored compared to when the catalytic reaction heat amount is smaller than the heat dissipation amount, and when the catalytic reaction heat amount is smaller than the heat dissipation amount, a smaller increase in throttle opening and a smaller increase in valve overlap amount are stored compared to when the catalytic reaction heat amount is greater than the heat dissipation amount.

[0060] The control device 70 extracts information on the increase in throttle opening and the increase in valve overlap amount that are associated with the difference between the catalytic reaction heat amount and the heat radiation amount from the association data. The control device 70 can adjust the increase in throttle opening by controlling the throttle valve 34 so that the increase in throttle opening becomes the extracted increase in throttle opening. The control device 70 also adjusts the increase in valve overlap amount by controlling the intake VVT ​​mechanism 25 and the exhaust VVT mechanism 26 so that the increase in valve overlap becomes the extracted increase in valve overlap amount. Note that the association data may also associate the increase in throttle opening and the increase in valve overlap amount with the difference between the catalytic reaction heat amount and the heat radiation amount and the current catalyst temperature. In this case, the control device 70 extracts from the association data the difference between the catalytic reaction heat amount and the heat radiation amount, and information on the increase in throttle opening and increase in valve overlap amount associated with the catalyst temperature, and controls the throttle valve 34 so that the increase in throttle opening amount becomes the extracted amount, and controls the intake VVT ​​mechanism 25 and the exhaust VVT mechanism 26 so that the increase in valve overlap amount becomes the extracted amount.

[0061] 4A to 4D are timing charts showing the timings when the control device 70 performs the temperature suppression process in the second embodiment. The timing charts in Fig. 4A to 4D are the same as the timing charts in Fig. 3A to 3D, and therefore will not be described again. In Figure 4(e), the change in throttle opening when the temperature suppression process is executed from time T1 to time T2 is shown by a solid line as an example, and the change in throttle opening when normal engine control is executed without executing the temperature suppression process is shown by a dashed line as a comparative example. As shown in Figure 4(e), in the example, when fuel is cut (F / C), the increase in throttle opening is adjusted so that it is large when the catalyst temperature is rising and small when the catalyst temperature is falling.

[0062] 4(f) and 4(g), the solid lines show the change in the opening / closing timing of the intake valve 19 and the exhaust valve 20 when the temperature suppression process is executed from time T1 to time T2 as an example, and the dashed lines show the change in the opening / closing timing of the intake valve 19 and the exhaust valve 20 when normal engine control is executed without executing the temperature suppression process as a comparative example. As shown in FIG. 4(f), in the example, during fuel cut (F / C), the advance amount of the intake valve 19 is increased by a large amount when the catalyst temperature is rising, and decreased by a small amount when the catalyst temperature is falling. Also, as shown in FIG. 4(g), in the example, during fuel cut (F / C), the advance amount of the exhaust valve 20 is increased by a large amount when the catalyst temperature is rising, and decreased by a small amount when the catalyst temperature is falling. In other words, when fuel is cut (F / C), the valve overlap amount is increased by a large amount when the catalyst temperature is rising, and by a small amount when the catalyst temperature is falling.

[0063] In this way, according to this embodiment, by not increasing the throttle opening by more than necessary or by not increasing the valve overlap amount by more than necessary, it is possible to suppress tip-in shock when returning from a fuel cut (when fuel is injected), thereby improving drivability.

[0064] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications and the like are possible within the scope of the present invention. In the first and second embodiments described above, the timing at which fuel injector 51 does not inject fuel is the timing of fuel cut (F / C), but this is not limiting. For example, if vehicle 1 has a so-called idling stop function, the timing at which fuel injector 51 does not inject fuel can be the timing at which idling stop is performed. Also, for example, if vehicle 1 is a so-called hybrid vehicle, the timing at which fuel injector 51 does not inject fuel can be the timing at which the vehicle is not driven by the engine but by the motor.

[0065] In the first and second embodiments described above, the valve overlap between the intake valve 19 and the exhaust valve 20 is increased by advancing the intake valve 19 and retarding the exhaust valve 20. However, the valve overlap between the intake valve 19 and the exhaust valve 20 may be increased by varying the opening and closing timing of either the intake valve 19 or the exhaust valve 20.

[0066] In the second embodiment described above, both the amount by which the throttle opening of the throttle valve 34 is increased and the amount by which the valve overlap amount is increased are adjusted, but the present invention is not limited to this. That is, it is also possible to adjust either the amount by which the throttle opening of the throttle valve 34 is increased or the amount by which the valve overlap amount is increased. [Explanation of symbols]

[0067] 1: Vehicle 10: Engine (internal combustion engine) 11: Engine body 12: Piston 13: Combustion chamber 19: Intake valve 20: Exhaust valve 24: Variable valve timing mechanism 25: Intake VVT ​​mechanism 26: Exhaust VVT mechanism 30: Intake system 34: Throttle valve 40: Exhaust system 43: Catalyst 50: Fuel system 51: Fuel injector 61: Crank angle sensor 62: Vehicle speed sensor 63: Exhaust pressure sensor 64: Air-fuel ratio sensor 65: Outside air temperature sensor 66: Throttle valve opening sensor 67: Accelerator opening sensor 68: Catalyst temperature sensor 69: Exhaust temperature sensor 70: Control device

Claims

1. a fuel injector that injects fuel; a throttle valve that adjusts the amount of intake air supplied to the internal combustion engine; an intake valve that allows intake air to flow into a combustion chamber of the internal combustion engine; an exhaust valve that discharges exhaust gas generated by combustion of a mixture of intake air and fuel from the combustion chamber; a variable valve timing mechanism that changes the valve operating characteristics of at least one of the intake valve and the exhaust valve; a catalyst that purifies exhaust gas discharged from the combustion chamber, The control device At a timing when fuel is not injected by the fuel injector, a control device for an internal combustion engine, characterized in that, when a catalyst temperature of the catalyst is equal to or higher than a predetermined temperature, the throttle opening of the throttle valve is increased more than when the catalyst temperature is not equal to or higher than the predetermined temperature, and the variable valve timing mechanism is controlled to increase a valve overlap amount between the intake valve and the exhaust valve.

2. The control device 2. The control device for an internal combustion engine according to claim 1, wherein the amount of valve overlap between the intake valve and the exhaust valve is adjusted based on the catalyst temperature of the catalyst or based on the difference between the amount of catalytic reaction heat and the amount of heat radiation.

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