Control device for internal combustion engines

Abstract

To effectively protect the exhaust catalytic converter when the catalyst temperature rises. [Solution] The control device 100 for the internal combustion engine includes a temperature calculation unit 41 that acquires information on the temperature of the exhaust catalytic converter in the exhaust passage, a throttle actuator 35 that adjusts the amount of intake air drawn into the engine, and a controller 40 that controls the throttle actuator 35 according to the load. The controller 40 has an intake limiting unit that limits the amount of intake air according to the catalytic converter temperature acquired by the temperature calculation unit 41, and the intake limiting unit starts limiting the amount of intake air earlier the greater the rise in catalytic converter temperature.

Description

Technical Field

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

Background Art

[0002] In recent years, efforts aimed at mitigating or reducing the impact of climate change have continued, and research and development related to emission improvement have been conducted to achieve this. As a technology related to this type of device, conventionally, when the exhaust temperature is being operated at high load, in order to protect the catalyst, a device that enriches and injects fuel has been known (see, for example, Patent Document 1). In the device described in Patent Document 1, when the decrease in the exhaust temperature is insufficient only by enriching the fuel, the amount of air sucked into the internal combustion engine is decreased.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=3 and]]However, due to a delay in the decrease in the amount of air sucked into the internal combustion engine, there is a risk that the exhaust temperature will overshoot and the catalyst will be damaged, and countermeasures for this point are necessary.

Means for Solving the Problems

[0005] A control device for an internal combustion engine according to an aspect of the present invention includes a temperature acquisition unit that acquires information on the catalyst temperature in an exhaust catalyst device provided in an exhaust passage of the internal combustion engine, an intake adjustment unit that adjusts the intake air amount sucked into the internal combustion engine, and a control unit that controls the intake adjustment unit according to the load. The control unit has an intake restriction unit that restricts the intake air amount according to the catalyst temperature acquired by the temperature acquisition unit, and the intake restriction unit starts restricting the intake air amount earlier as the degree of increase in the catalyst temperature is greater. [[ID= and]] [Effects of the Invention]

[0006] According to the present invention, the exhaust catalytic converter can be effectively protected when the catalyst temperature rises. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing the main components of an engine to which a control device for an internal combustion engine according to an embodiment of the present invention is applied. [Figure 2] A block diagram showing the main components of a control device for an internal combustion engine according to an embodiment of the present invention. [Figure 3A] This diagram shows the relationship between the load acting on the engine and the estimated temperature, which is an estimated value of the catalyst temperature. [Figure 3B] A diagram showing the relationship between estimated temperature and the set values ​​for intake control start and end. [Figure 4] A time chart showing an example of how catalyst temperature and estimated temperature change over time. [Figure 5] A flowchart showing an example of the process executed by the controller in Figure 2. [Figure 6] A time chart showing an example of changes in catalyst temperature and intake air volume. [Figure 7] A diagram illustrating an example of calculating catalyst temperature based on estimated temperature. [Modes for carrying out the invention]

[0008] An embodiment of the present invention will be described below with reference to Figures 1 to 7. The control device for an internal combustion engine according to the embodiment of the present invention is applied to a vehicle equipped with a gasoline engine as an internal combustion engine. That is, it is applied to an engine vehicle that runs using only the engine as a power source and a hybrid vehicle that runs using both the engine and the motor as power sources.

[0009] Figure 1 is a schematic diagram showing the main components of engine 1, which is an internal combustion engine to which the control device according to this embodiment is applied. Engine 1 is a spark-ignition type internal combustion engine that obtains power by igniting a mixture of fuel and air supplied to the combustion chamber, and is a four-stroke engine that goes through four strokes: intake, compression, expansion, and exhaust during the operating cycle. Engine 1 has multiple cylinders with the same configuration. Figure 1 shows the configuration of a single cylinder.

[0010] As shown in Figure 1, the engine 1 has a cylinder 2 formed in a cylinder block, a piston 3 slidably positioned inside the cylinder 2, and a combustion chamber 4 formed between the piston 3 and the cylinder head. The piston 3 is connected to the crankshaft 6 via a connecting rod 5, and the crankshaft 6 rotates as the piston 3 reciprocates along the inner wall of the cylinder 2.

[0011] The cylinder head is provided with an intake port 11 and an exhaust port 12. The combustion chamber 4 is connected to an intake passage 13 via the intake port 11, and to an exhaust passage 14 via the exhaust port 12. The intake port 11 is opened and closed by an intake valve 15, and the exhaust port 12 is opened and closed by an exhaust valve 16. A throttle valve 17 is provided in the intake passage 13 upstream of the intake valve 15.

[0012] The throttle valve 17 is configured, for example, as a butterfly valve, and the amount of intake air flowing into the combustion chamber 4 is adjusted by the throttle valve 17. The throttle valve 17 is driven by a throttle actuator, such as an electric motor, in response to the operation of the accelerator pedal. The intake valve 15 and the exhaust valve 16 are driven to open and close at predetermined timings synchronized with the rotation of the crankshaft 6 by a valve train mechanism (not shown). The opening and closing timing of the valves 15 and 16 can be changed as appropriate.

[0013] A spark plug 18 and a direct-injection injector 19 are mounted on either the cylinder head or the cylinder block (for example, the cylinder head), facing the combustion chamber 4 of cylinder 2. The spark plug 18 is positioned between the intake port 11 and the exhaust port 12, and generates a spark using electrical energy to ignite the fuel-air mixture in the combustion chamber 4. The injector 19 is positioned near the intake valve 15, and is driven by electrical energy to inject fuel diagonally downward into the combustion chamber 4. The position of the injector 19 is not limited to this, and it can also be positioned near the spark plug 18. The injector 19 may be a port-injection type that injects fuel into the intake port, either in place of or in addition to direct injection.

[0014] An exhaust catalytic converter 20 is installed in the exhaust passage 14 to purify the exhaust gas. The exhaust catalytic converter 20 is a three-way catalyst that removes and purifies HC, CO, and NOx contained in the exhaust gas through oxidation and reduction. Other exhaust catalytic converters, such as oxidation catalysts that oxidize CO and HC in the exhaust gas, can also be used. When the temperature of the catalyst contained in the exhaust catalytic converter 20 (catalyst temperature Tc) rises, the catalyst is activated, and the exhaust gas purification effect of the exhaust catalytic converter 20 is enhanced. However, if the catalyst temperature Tc becomes too high, the exhaust catalytic converter 20 will be damaged, so it is necessary to keep the catalyst temperature Tc below a predetermined temperature (upper limit temperature T1).

[0015] Furthermore, engine 1 is equipped with an exhaust gas recirculation device 25. The exhaust gas recirculation device 25 has an EGR passage 26 and an EGR valve 27 located in the EGR passage 26. One end of the EGR passage 26 is connected downstream of the exhaust catalytic converter 20 in the exhaust passage 14, and the other end is connected upstream of the throttle valve 17 in the intake passage 13. The exhaust gas that has flowed through the exhaust passage 14 can be recirculated to the intake passage 13 via the EGR passage 21 and the EGR valve 27. The EGR valve 27 is driven by an EGR actuator such as an electric motor and is configured to allow adjustment of its opening. The exhaust gas recirculation device 25 can also be omitted.

[0016] In such an engine 1, when the accelerator pedal is depressed, the throttle valve 17 is opened and the intake air amount increases. As a result, the exhaust temperature rises, and accordingly, the catalyst temperature Tc rises. The engine 1 needs to be configured so that the catalyst temperature Tc does not exceed the upper limit temperature T1. In order to suppress the catalyst temperature Tc, it is conceivable to relatively increase the fuel injection amount from the injector 19 to enrich the air-fuel ratio. However, in this case, since the fuel injection amount increases, it is accompanied by deterioration of fuel consumption and deterioration of emissions. Therefore, in the present embodiment, the control device of the internal combustion engine is configured to reduce the intake air amount below the target intake air amount according to the operation of the accelerator pedal, thereby suppressing the rise of the exhaust temperature and suppressing the catalyst temperature Tc below the upper limit temperature T1.

[0017] By the way, it takes some time for the intake air passing through the throttle valve 17 to reach the exhaust catalyst device 20. For this reason, when the accelerator pedal is depressed, the opening degree of the throttle valve 17 increases and the intake air amount increases, but the exhaust temperature does not immediately rise, and there is a delay in the rise of the catalyst temperature Tc. This is called the response delay of the catalyst temperature Tc due to the delay of the intake air. The response delay of the catalyst temperature Tc is caused by a delay corresponding to the length of the intake passage and the exhaust passage until the air reaches the exhaust catalyst device 20, and a delay in heat transfer from the air to the catalyst. Therefore, when the catalyst temperature Tc is detected (or calculated) and the intake air amount restriction is started when the catalyst temperature Tc reaches a predetermined value (restriction start temperature), the catalyst temperature Tc may overshoot due to the response delay and exceed the upper limit temperature T1.

[0018] In this regard, if the restriction start temperature is set low, even with a response delay, excessive rise of the catalyst temperature Tc can be suppressed. However, in this case, when the depression amount of the accelerator pedal is small and the rising speed of the exhaust temperature is slow, the intake air amount may be restricted more than necessary, and torque generation may be suppressed. Therefore, in the present embodiment, the control device of the internal combustion engine is configured as follows so that the catalyst temperature Tc is below the upper limit temperature T1 while optimally suppressing the intake air amount according to the operating state.

[0019] FIG. 2 is a block diagram showing a main configuration of a control device 100 for an internal combustion engine according to the present embodiment, mainly showing a configuration related to intake air amount control. As shown in FIG. 2, the control device 100 is configured around a controller 40 for engine control, and includes an input unit 31, an intake air amount sensor 32, a rotational speed sensor 33, and an actuator 35, which are connected to the controller 40.

[0020] The input unit 31 outputs a signal for commanding the target torque of the engine 1. The input unit 31 is constituted by, for example, an accelerator opening sensor that detects the operation amount of an accelerator pedal. A torque command value is input to the controller 40 by the input unit 31. The control device for the internal combustion engine according to the present embodiment can also be applied to a vehicle having a driving support function or an autonomous driving vehicle. In that case, a vehicle control system serves as the input unit 31, and a torque command value is input to the controller 40.

[0021] The intake air amount sensor 32 is a sensor that detects the intake air amount (mass flow rate). The intake air amount sensor 32 is constituted by, for example, an air flow meter disposed in the intake passage 13 (more specifically, upstream of the throttle valve 17). The intake air amount corresponds to a physical quantity having a correlation with the load of the engine 1. The load of the engine 1 can be calculated using not only the intake air amount sensor 32 but also detection values of an accelerator opening sensor (input unit 31) or a pressure sensor that detects the intake pressure downstream of the throttle valve 17.

[0022] The rotational speed sensor 33 is a sensor that detects the rotational speed of the engine 1, and is constituted by, for example, a crank angle sensor provided in the vicinity of the crankshaft 6. The crank angle sensor is configured to output a pulse signal (crank signal) as the crankshaft 6 rotates. That is, a crank signal is output each time the crankshaft rotates by a predetermined angle, and the engine rotational speed can be detected based on the crank signal. The operating state of the engine 1, that is, the operating point, can be specified mainly based on signals from the intake air amount sensor 32 and the rotational speed sensor 33.

[0023] Actuator 35 is a throttle actuator that adjusts the opening degree of the throttle valve 17. Actuator 35 is driven according to the torque command value, and by adjusting the throttle opening degree through the drive of actuator 35, the intake air volume can be controlled. That is, the intake air volume can be controlled to a target intake air volume according to the torque command value, or to a limited intake air volume that is restricted from the target intake air volume. Regarding the control of intake air volume, controlling to a target intake air volume according to the torque command value is called normal intake air control, and controlling to a limited intake air volume that is restricted from the target intake air volume is called limited intake air control.

[0024] The intake air volume (amount of fresh air) can also be limited by guiding EGR gas into the intake passage via the exhaust gas recirculation device 25. In this case, the actuator 35 consists of a throttle actuator and an EGR actuator.

[0025] The controller 40 is comprised of an electronic control unit (ECU). More specifically, the controller 40 includes a computer with a CPU, ROM, RAM, and other peripheral circuits such as an I / O interface. Based on signals from the input unit 31, the intake air volume sensor 32, and the rotational speed sensor 33, the controller 40 outputs a control signal to the actuator 35.

[0026] The controller 40 has a functional configuration comprising a temperature calculation unit 41, a temperature estimation unit 42, a setting unit 43, an output unit 44, and a storage unit 45. The storage unit 45 stores various maps, thresholds, control programs, etc. in advance. Figures 3A and 3B show examples of maps stored in the storage unit 45.

[0027] Figure 3A shows the relationship between the load acting on engine 1 and the estimated catalyst temperature Tc. The estimated catalyst temperature Tc (estimated temperature Te) is the catalyst temperature Tc corresponding to a given load, estimated assuming that a predetermined load is continuously acting on engine 1, and corresponds to the converged value when the catalyst temperature Tc converges over time. The characteristic f1 in Figure 3A can be determined in advance by experiment or analysis. As shown in Figure 3A, the estimated temperature Te increases with increasing load. In the region where the load is above a predetermined value, the estimated temperature Te becomes above the upper limit temperature T1. As mentioned above, the load corresponds to the throttle opening, intake air volume, and intake pressure. Therefore, the characteristic f1 in Figure 3A can be replaced with, for example, the relationship between the throttle opening (torque command value) and the estimated temperature Te. The estimated temperature Te can also be determined by a calculation formula with the load as a parameter, without using a map.

[0028] Characteristic f2 in Figure 3B shows the relationship between the estimated temperature Te and the setpoint Ta, and characteristic f3 shows the relationship between the estimated temperature Te and the setpoint Tb. The setpoint Ta is the setpoint for the catalyst temperature at which intake air restriction (restricted intake control) begins, i.e., the restriction start setpoint. The setpoint Tb is the setpoint for the catalyst temperature at which restricted intake control ends after it has started, i.e., the restriction end setpoint. Characteristic f2 and f3 in Figure 3B can be determined in advance by experiment or analysis. As shown in Figure 3B, both the restriction start setpoint Ta and the restriction end setpoint Tb decrease as the estimated temperature Te increases.

[0029] The limit end setting value Tb is lower than the limit start setting value Ta. The rate of decrease in the limit start setting value Ta as the estimated temperature Te increases (slope of characteristic f2) is equal to the rate of decrease in the limit end setting value Tb (slope of characteristic f3). The rate of decrease in the limit start setting value Ta may differ from the rate of decrease in the limit end setting value Tb. The setting values ​​Ta and Tb can also be determined by a calculation formula with the estimated temperature Te as a parameter, without using a map.

[0030] The temperature calculation unit 41 calculates the catalyst temperature Tc according to the operating state of the engine 1. Specifically, the temperature calculation unit 41 calculates the current catalyst temperature Tc using a predetermined map or a calculation formula based on signals from the intake air volume sensor 32 and the rotational speed sensor 33. The higher the intake air volume and the higher the engine speed, the higher the calculated catalyst temperature Tc. The temperature calculation unit 41 may also use a value obtained by adding a predetermined margin to the calculated catalyst temperature as the catalyst temperature Tc. That is, the catalyst temperature Tc may be set to a value that is higher than the actual catalyst temperature by a predetermined margin.

[0031] Instead of calculating the catalyst temperature Tc based on the intake air volume and engine speed, the catalyst temperature Tc may be detected by a sensor. For example, the catalyst temperature Tc may be directly detected by a temperature sensor. Alternatively, the temperature of other parts that have a correlation with the catalyst temperature Tc may be detected, and the temperature calculation unit 41 may calculate the catalyst temperature based on the detected value. For example, the temperature of the combustion chamber 4 or its vicinity may be detected by a temperature sensor, and the catalyst temperature Tc may be calculated based on the temperature of the combustion chamber 4. Alternatively, the exhaust temperature may be detected by a temperature sensor, and the catalyst temperature Tc may be calculated based on the exhaust temperature.

[0032] The temperature estimation unit 42 calculates the estimated temperature Te corresponding to the load of the engine 1 using the characteristic f1 in Figure 3A. Specifically, the temperature estimation unit 42 considers the torque command value input by the input unit 31 as the load and calculates the estimated temperature Te according to the load. Alternatively, the load of the engine 1 may be detected by a pressure sensor that detects the intake pressure downstream of the throttle valve 17, and the temperature estimation unit 42 may calculate the estimated temperature Te according to the value detected by the pressure sensor.

[0033] Figure 4 is a time chart showing an example of the changes in catalyst temperature Tc and estimated temperature Te over time. The horizontal axis of Figure 4 represents the elapsed time t from the moment the accelerator pedal is pressed, i.e., from the moment the torque increase command is input. The solid lines f11 to f13 in the figure represent the characteristics showing the change in catalyst temperature Tc, and the dotted lines f21 to f23 represent the characteristics showing the change in estimated temperature Te. The estimated temperature Te is the target temperature of the catalyst, such as the target set temperature or target temperature set value.

[0034] Characteristics f11 and f21 correspond to the first load L1, characteristics f12 and f22 correspond to the second load L2, and characteristics f13 and f23 correspond to the third load L3. The first load L1 is greater than the second load L2, and the second load L2 is greater than the third load L3 (L1 > L2 > L3). The first load L1 may be called the high load, the second load L2 the medium load, and the third load L3 the low load to distinguish them.

[0035] As shown in Figure 4, when the accelerator pedal is pressed at time t0, the estimated temperature Te estimated by the temperature estimation unit 42 rises. The estimated temperature Te is higher with increasing load (Figure 3A), and the estimated temperatures Te corresponding to the first load L1, second load L2, and third load L3 are Te1, Te2, and Te3, respectively. There is a relationship Te1 > Te2 > Te3 among these estimated temperatures Te1, Te2, and Te3. In Figure 4, the estimated temperatures Te1, Te2, and Te3 all decrease over time, which is because the intake air volume is restricted and the load decreases (Figure 3A).

[0036] When the accelerator pedal is depressed at time t0, the catalyst temperature Tc calculated by the temperature calculation unit 41 also rises. The rate of increase of the catalyst temperature Tc (the amount of temperature increase per unit time), that is, the slopes of characteristics f11 to f13, are larger as the load is larger. If the rates of increase of the catalyst temperatures Tc1, Tc2, and Tc3 corresponding to the first load L1, the second load L2, and the third load L3 are ΔTc1, ΔTc2, and ΔTc3, there is a relationship of ΔTc1 > ΔTc2 > ΔTc3 among these ΔTc1, ΔTc2, and ΔTc3. However, the rate of increase of the catalyst temperature Tc is smaller than the rate of increase of the estimated temperature Te. Therefore, immediately after the accelerator pedal is depressed, the estimated temperature Te is higher than the catalyst temperature Tc.

[0037] The setting unit 43 in FIG. 2 sets a set value corresponding to the estimated temperature Te, that is, a limit start set value Ta, based on the characteristic f2 in FIG. 3B. For example, when the estimated temperature Te is any one of the estimated temperatures Te1, Te2, and Te3 in FIG. 4, the limit start set values Ta1, Ta2, and Ta3 corresponding to any one of the estimated temperatures Te1, Te2, and Te3 are set. There is a relationship of Ta1 < Ta2 < Ta3 among the limit start set values Ta1, Ta2, and Ta3, and the higher the estimated temperature Te, the lower the limit start set value Ta.

[0038] When the estimated temperature Te is constant, the setting unit 43 calculates the limit start set value Ta as a constant value. Therefore, during the periods from time t0 to t1, from time t0 to t2, and from time t0 to t3 in FIG. 4, the limit start set values Ta1, Ta2, and Ta3 are constant respectively. After time t1, after time t2, or after time t3, when the estimated temperature Te decreases, the limit start set value Ta (dashed-dotted line) set by the setting unit 43 increases accordingly (FIG. 3B).

[0039] The output unit 44 determines the magnitude relationship between the catalyst temperature Tc calculated by the temperature calculation unit 41 and the limit start setting value Ta set by the setting unit 43. More specifically, the output unit 44 determines whether the catalyst temperature Tc is greater than or equal to the limit start setting value Ta. Then, according to the determination result, a control signal is output to the throttle actuator 35. For example, when it is determined that Tc < Ta, the output unit 44 controls the actuator 35 according to the torque command value input by the input unit 31 (normal intake control). Thereby, the throttle opening becomes the target throttle opening corresponding to the depression of the accelerator pedal, and the intake air amount becomes the target intake air amount corresponding to the torque command value.

[0040] On the other hand, when it is determined that Tc ≥ Ta, the output unit 44 restricts the throttle opening from the target throttle opening (restricted intake control). Thereby, the increase in the intake air amount can be suppressed, the rise of the catalyst temperature Tc can be suppressed, and the catalyst temperature Tc can be suppressed below the upper limit temperature T1. The output unit 44 can perform the restriction of the intake air amount in various modes in the restricted intake control. For example, the output unit 44 controls the actuator 35 so that the intake air amount becomes a value obtained by multiplying the target intake air amount by a predetermined coefficient less than 1 in normal intake control. As another example, in the restricted intake control, the output unit 44 may restrict the throttle opening to a predetermined opening regardless of the target intake air amount.

[0041] After the restricted intake control is started, the setting unit 43 sets a setting value corresponding to the estimated temperature Te, that is, a limit end setting value Tb, based on the characteristic f3 in FIG. 3B. After the start of the restricted intake control, the output unit 44 determines the magnitude relationship between the catalyst temperature Tc calculated by the temperature calculation unit 41 and the limit end setting value Tb set by the setting unit 43. More specifically, the output unit 44 determines whether the catalyst temperature Tc is less than or equal to the limit end setting value Tb. When the output unit 44 determines that Tc > Tb, the restriction of the intake air by the restricted intake control continues. When the output unit 44 determines that Tc ≤ Tb, the restricted intake control is terminated, and the actuator 35 is controlled according to the torque command value input by the input unit 31 (normal intake control).

[0042] As described above, the controller 40 functions as an intake limiting unit that limits the intake air volume according to the catalyst temperature Tc, and a limit release unit that releases the intake air volume limit according to the catalyst temperature Tc after the intake limiting unit has started. The intake limiting unit and the limit release unit can be configured by a setting unit 43 and an output unit 44.

[0043] Figure 5 is a flowchart showing an example of processing performed by the CPU of the controller 40 in Figure 2, particularly an example of processing related to intake control (normal intake control, limited intake control). The processing shown in this flowchart is started, for example, when the engine key switch is turned on, and is repeated at predetermined intervals.

[0044] As shown in Figure 5, the controller 40 first reads signals from the input unit (e.g., accelerator opening sensor) 31, intake air volume sensor 32, and rotational speed sensor 33 in step S1. Next, in step S2, the controller 40 (temperature calculation unit 41) calculates the current catalyst temperature Tc based on the signals from the intake air volume sensor 32 and rotational speed sensor 33, using a predetermined map or calculation formula. Next, in step S3, the controller 40 (temperature estimation unit 42) calculates an estimated temperature Te corresponding to the load of the engine 1 using the characteristic f1 in Figure 3A. For example, the temperature estimation unit 42 considers the torque command value input by the input unit 31 as the load and calculates an estimated temperature Te corresponding to the torque command value.

[0045] Next, in step S4, the controller 40 (setting unit 43) determines whether the intake flag is 1 or not. The intake flag is 0 in the initial state and is set to 1 when intake restriction control is started. If it is determined in step S4 that the intake flag is not 1, that is, that intake restriction control is not in progress, the process proceeds to step S5. In step S5, the controller 40 (setting unit 43) sets the restriction start setting value Ta corresponding to the estimated temperature Te, based on the characteristic f2 in Figure 3B.

[0046] Next, in step S6, the controller 40 (output unit 44) determines whether the catalyst temperature Tc calculated in step S2 is greater than or equal to the limit start setting value Ta set in step S5. If this is not determined in step S6, the process proceeds to step S7, where the controller 40 (output unit 44) outputs a control signal to the actuator 35, controlling the throttle opening to a target throttle opening corresponding to the torque command value of the input unit 31. In this case, the intake volume is not limited (intake volume unlimited).

[0047] On the other hand, if the result in step S6 is affirmed, the process proceeds to step S8, where the controller 40 (output unit 44) outputs a control signal to the actuator 35 to limit the throttle opening. This causes the throttle opening to become smaller than the target throttle opening, limiting the intake air volume (intake volume limiting). Next, in step S9, the controller 40 sets the intake flag to 1 and terminates the process.

[0048] If the intake flag is determined to be 1 in step S4, the process proceeds to step S10. In step S10, the controller 40 (setting unit 43) sets the limit termination setting value Tb corresponding to the estimated temperature Te based on the characteristic f3 in Figure 3B. Next, in step S11, the controller 40 (output unit 44) determines whether the catalyst temperature Tc is less than or equal to the limit termination setting value Tb. If this is not determined in step S11, the process proceeds to step S8, where the controller 40 (output unit 44) outputs a control signal to the actuator 35 to continue throttle restriction (intake volume restriction).

[0049] On the other hand, if the result in step S11 is positive, the process proceeds to step S12, where the controller 40 (output unit 44) outputs a control signal to the actuator 35, controlling the throttle opening to a target throttle opening corresponding to the torque command value of the input unit 31, similar to step S7 (intake volume unrestricted). Then, in step S13, the controller 40 resets the intake flag to 0 and terminates the process.

[0050] The main operation of the control device 100 for the internal combustion engine according to this embodiment will now be described. For example, when the accelerator pedal is fully depressed at time t0 in Figure 4, a first load L1 acts on the engine 1. At this time, the estimated temperature Te, which is an estimated value of the catalyst temperature Tc (Tc1), rises rapidly, and the estimated temperature Te1 corresponding to the first load L1 exceeds the upper limit temperature T1 (characteristic f21). At this time, the actual catalyst temperature Tc1 rises more slowly than the estimated temperature Te (characteristic f11).

[0051] Subsequently, at time t1, when the catalyst temperature Tc1 reaches the limit start setting value Ta1 corresponding to the estimated temperature Te1 of the first load L1, the throttle opening is restricted, thereby limiting the intake air volume (step S8). As a result, the estimated temperature Te gradually decreases (characteristic f21), and the rate of increase ΔTc1 of the catalyst temperature Tc1 becomes gradual (characteristic f11). Therefore, the catalyst temperature Tc1 approaches the upper limit temperature T1 over time without overshooting, or with only a small degree of overshooting.

[0052] At time t0, when the accelerator pedal is depressed to a small extent, the load on engine 1 becomes the second load L2 or third load L3, which is less than the first load L1. In this case as well, the estimated temperature Te rises rapidly, but the estimated temperature Te2 corresponding to the second load L2 and the estimated temperature Te3 corresponding to the third load L3 are lower than the estimated temperature Te1 (characteristics f22, f23). Therefore, the limit start setting values ​​Ta2 and Ta3 are higher than the limit start setting value Ta1, and the throttle opening limit (intake volume limit) starts at time t2 or t3, which is later than time t1 (step S8).

[0053] As a result, the rate of increase in catalyst temperature Tc2 corresponding to the second load L2, ΔTc2, becomes gradual after time t2 (characteristic f12), and the rate of increase in catalyst temperature Tc3 corresponding to the third load L3, ΔTc3, becomes gradual after time t3 (characteristic f13). Thus, when the second load L2 or third load L3 acts on engine 1, the timing of the start of intake restriction is delayed compared to when the first load L1 acts. However, the rate of increase in catalyst temperatures Tc2 and Tc3 before the start of intake restriction, ΔTc2 and ΔTc3, is smaller than the rate of increase in catalyst temperature Tc1 before the start of intake restriction, ΔTc1. Therefore, catalyst temperatures Tc2 and Tc3 approach the upper limit temperature T1 over time without overshooting, or with only a small degree of overshooting.

[0054] Thus, in this embodiment, the smaller the load acting on the engine 1, the later the timing of the intake restriction start. As a result, when the load increases due to pressing the accelerator pedal, the catalyst temperature Tc does not exceed the upper limit temperature T1, and the reduction in torque can be minimized.

[0055] Figure 6 is a time chart showing an example of the changes in catalyst temperature Tc and intake air volume G from time t0 onward, and is, for example, a time chart corresponding to the first load L1. In the figure, characteristic f14 shows the change in catalyst temperature Tc, and characteristic f15 shows the change in intake air volume G. As shown in Figure 6, when the accelerator pedal is pressed at time t0, the catalyst temperature Tc (Tc1) gradually rises. At this time, the intake air volume G becomes the target intake air volume G1 corresponding to the torque command value.

[0056] At time t1, if the catalyst temperature Tc1 exceeds the limit start setting value Ta1, the throttle opening is restricted and the intake air volume decreases (step S8). At this time, the controller 40 outputs a control signal to the actuator 35 to gradually reduce the throttle opening (times t1 to t4). This gradually reduces the intake air volume and suppresses shock (characteristic f31). When the intake air volume is restricted, the catalyst temperature Tc1 gradually decreases (characteristic f14). This prevents the catalyst temperature Tc1 from reaching the upper limit temperature T1.

[0057] Subsequently, at time t5, when the catalyst temperature Tc1 falls below the limit termination temperature Tb1, the intake restriction control ends, and the throttle opening returns to its pre-restriction value (step S12). This causes the intake air volume to gradually increase. In this way, when the catalyst temperature Tc falls below the limit termination set value Tb, the intake restriction is released, allowing for a quick release of the intake restriction and minimizing the reduction in torque. Furthermore, since the limit termination set value Tb is set lower than the limit start set value Ta, it is possible to prevent frequent repetition of the start and end of intake restriction when the catalyst temperature Tc changes.

[0058] This embodiment can produce the following effects and benefits. (1) The control device 100 for the internal combustion engine includes a temperature calculation unit 41 that calculates the catalyst temperature Tc in the exhaust catalytic converter 20 provided in the exhaust passage 14 of the engine 1, an actuator 35 for driving a throttle valve 17 that adjusts the amount of intake air drawn into the engine 1, and a controller 40 that controls the actuator 35 according to the load (Figure 2). The controller 40 has an intake limiting unit that limits the amount of intake air according to the catalyst temperature Tc calculated by the temperature calculation unit 41 (Figure 4). The intake limiting unit starts limiting the amount of intake air earlier the greater the rise in catalyst temperature Tc (Figure 4). In other words, when the rate of increase in catalyst temperature Tc is large (e.g., characteristic f11), intake limiting is started earlier than when the rate of increase is small (e.g., characteristic f13) (Figure 4). As a result, the timing of the start of intake limiting is variable, and the reduction in torque can be minimized while keeping the catalyst temperature Tc below the upper limit temperature T1.

[0059] (2) The controller 40 (intake limiting unit) calculates the estimated temperature Te, which is the temperature to be reached at the catalyst temperature Tc corresponding to the operating state of the engine 1, and starts limiting the intake volume earlier the higher the estimated temperature Te is (Figure 4). Since the rate of increase in catalyst temperature Tc is greater the higher the estimated temperature Te is, by starting to limit the intake volume earlier the higher the estimated temperature Te is, it is possible to reliably prevent the catalyst temperature Tc from exceeding the upper limit temperature T1 due to a delay in the response of catalyst temperature Tc caused by a delay in intake.

[0060] (3) The controller 40 (intake limiting unit) sets the intake volume limiting start setting value Ta lower the higher the estimated temperature Te is, and starts limiting the intake volume when the catalyst temperature Tc is equal to or higher than the limiting start setting value Ta (Figure 5). As a result, the higher the estimated temperature Te is, the earlier the intake volume limiting can be started.

[0061] (4) The controller 40 further includes a restriction release unit that releases the intake air volume restriction in accordance with the catalyst temperature Tc after initiating the intake air volume restriction (Figure 5). The restriction release unit sets a higher intake air volume restriction termination setting value Tb the lower the estimated temperature Te is, and releases the intake air volume restriction when the catalyst temperature Tc falls below the restriction termination setting value Tb (Figures 3B, 5). This allows the intake air restriction to be terminated earlier, minimizing the reduction in torque.

[0062] (5) The controller 40 (restriction release unit) sets the restriction end setting value Tb to a value lower than the restriction start setting value Ta (Figure 3B). This prevents the intake restriction from being started and stopped frequently when the catalyst temperature Tc changes.

[0063] In the above embodiment, the temperature calculation unit 41 calculates the catalyst temperature Tc based on signals from the intake air volume sensor 32 and the rotational speed sensor 33, but there is a correlation between the estimated temperature Te and the catalyst temperature Tc (Figure 4). For this reason, the catalyst temperature Tc may be calculated based on the estimated temperature Te. Figure 7 shows an example of calculating the catalyst temperature Tc based on the estimated temperature Te. The horizontal axis in the figure is time (elapsed time from the time t0 when the accelerator pedal is pressed), and the vertical axis shows the characteristics of the change in estimated temperature Te f25~f27 (dotted line) and the characteristics of the change in catalyst temperature Tc f15~f17 (solid line). Characteristics f25 and f15 correspond to the first load L1, characteristics f26 and f16 correspond to the second load L2, and characteristics f27 and f17 correspond to the third load L3.

[0064] As shown in Figure 7, the temperature calculation unit 41 calculates the catalyst temperature Tc by applying an annealing process to the estimated temperature Te so that it gradually increases over time when the catalyst temperature Tc rises. More specifically, the higher the estimated temperature Te, the greater the rate (slope) of increase in the catalyst temperature Tc. Although not shown in the figure, the temperature calculation unit 41 calculates the catalyst temperature Tc by applying an annealing process not only when the catalyst temperature Tc rises, but also when it falls. More specifically, the lower the estimated temperature Te, the greater the rate (slope) of decrease in the catalyst temperature Tc.

[0065] In this way, the temperature calculation unit 41 calculates the catalyst temperature Tc by applying an annealing process to the estimated temperature Te such that the catalyst temperature Tc rises more rapidly when the estimated temperature Te is high, and falls more rapidly when the estimated temperature Te is low (Figure 7). This allows the catalyst temperature Tc to be calculated accurately according to the estimated temperature Te.

[0066] The above embodiment can be modified in various ways. Modifications are described below. In the above embodiment, the temperature calculation unit 41 acquires information on the catalyst temperature Tc, but the catalyst temperature Tc may be detected by a sensor and information on the catalyst temperature Tc may be acquired, and the configuration of the temperature acquisition unit is not limited to that described above. In the above embodiment, the intake air volume is adjusted by driving the throttle actuator 35, but the intake air volume can also be adjusted by driving the EGR valve 27, or by controlling the drive of the intake valve 15. Therefore, the configuration of the intake air adjustment unit is not limited to that described above.

[0067] In the above embodiment, the controller 40, acting as a control unit, controls the actuator 35 according to the load. Specifically, an estimated temperature Te (target temperature) is calculated as the temperature to be reached by the catalyst temperature Tc, and the higher the estimated temperature Te, the lower the intake air volume limit start setting value T (limit start temperature). However, any processing by the intake air limiting unit is acceptable as long as the intake air volume limiting starts earlier as the estimated temperature Te increases. If the intake air volume limiting starts earlier as the degree of rise in catalyst temperature Tc increases, the intake air limiting unit may perform intake air limiting without using the estimated temperature. For example, the degree of rise in catalyst temperature Tc (amount of rise in catalyst temperature Tc per unit time) may be detected by a sensor or calculated using a formula, and intake air volume limiting may be started based on this.

[0068] The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as the features of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above embodiments and modifications, and to combine modifications with each other. [Explanation of Symbols]

[0069] 1 Engine, 17 Throttle valve, 31 Input unit, 32 Intake volume sensor, 33 Rotation speed sensor, 35 Actuator, 40 Controller, 41 Temperature calculation unit, 42 Temperature estimation unit, 43 Setting unit, 44 Output unit, 100 Control device, Tc Catalyst temperature, Te Estimated temperature, Ta Limit start setting value, Tb Limit end setting value

Claims

1. A temperature acquisition unit that acquires information on the catalyst temperature in an exhaust catalytic converter installed in the exhaust passage of an internal combustion engine, An intake adjustment unit that adjusts the amount of intake air drawn into the internal combustion engine, It comprises a control unit that controls the intake adjustment unit according to the load, The control unit has an intake limiting unit that limits the intake amount according to the catalyst temperature obtained by the temperature acquisition unit, The control device for an internal combustion engine is characterized in that the intake limiting unit starts limiting the intake amount earlier the greater the degree of rise in the catalyst temperature.

2. In the control device for an internal combustion engine according to claim 1, The control device for an internal combustion engine is characterized in that the intake limiting unit estimates the temperature at which the catalyst temperature is expected to reach, corresponding to the operating state of the internal combustion engine, and the higher the estimated temperature at which the catalyst temperature is expected to reach, the earlier the intake limiting unit is initiated.

3. In the control device for an internal combustion engine according to claim 2, The control device for an internal combustion engine is characterized in that the intake limiting unit sets the intake volume limiting start temperature lower as the catalyst temperature reaches the target temperature, and starts limiting the intake volume when the catalyst temperature reaches or exceeds the limiting start temperature.

4. In the control device for an internal combustion engine according to claim 2 or 3, The control device for an internal combustion engine is characterized in that the temperature acquisition unit calculates the catalyst temperature by applying an annealing process to the target temperature such that the temperature rises more rapidly when the target temperature is high during an increase in the catalyst temperature, and decreases more rapidly when the target temperature is low during a decrease in the catalyst temperature.

5. In the control device for an internal combustion engine according to claim 3, The control unit further includes a restriction release unit that, after starting to restrict the intake air volume by the intake air limiting unit, releases the restriction on the intake air volume according to the catalyst temperature. The control device for an internal combustion engine is characterized in that the restriction release unit sets a higher intake air volume limit termination temperature as the catalyst temperature reaches a lower temperature, and releases the intake air volume restriction when the catalyst temperature falls below the limit termination temperature.

6. In the control device for an internal combustion engine according to claim 5, The control device for an internal combustion engine is characterized in that the restriction release unit sets the restriction termination temperature lower than the restriction start temperature.

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