Catalyst temperature estimation device

Abstract

Provided is a catalyst temperature estimation device that estimates a catalyst temperature of an exhaust catalyst device (20) provided in an exhaust passage (14) of an internal combustion engine (1) having a fuel injection portion (19) that injects fuel and having a fuel cut function that cuts fuel injection from the fuel injection portion (19) during vehicle travel, the catalyst temperature estimation device including an operation state acquisition portion (41) that acquires a parameter indicating an operation state of the internal combustion engine (1), and a temperature estimation portion (44) that estimates a catalyst temperature based on the parameter acquired by the operation state acquisition portion (41). The temperature estimation portion (44) maintains the estimated value at the start of fuel cut until the operation state after fuel cut becomes a prescribed operation state when fuel cut is performed.

Description

Technical Field

[0001] This invention relates to a catalyst temperature estimation device for estimating the temperature of an exhaust gas catalyst device. Background Technology

[0002] In recent years, continuous efforts have been made to mitigate climate change or reduce its impacts, leading to research and development of exhaust gas purification devices. As a technology related to such exhaust gas purification devices, devices for estimating the temperature of the exhaust gas catalyst (catalyst temperature) during fuel cutoff are known. Such a device is described, for example, in Patent Document 1. In the device described in Patent Document 1, the catalyst temperature is estimated based on the amount of air entering the engine and the engine speed during both fuel cutoff and non-fuel cutoff.

[0003] However, as with the device described in Patent Document 1, if the catalyst temperature is estimated based on the amount of air entering and the engine speed, it is difficult to estimate the catalyst temperature after fuel cut-off with high accuracy.

[0004] Existing technical documents

[0005] Patent documents Patent document 1: Japanese Patent Application Publication No. 2003-278583 (JP2003-278583A). Summary of the Invention

[0006] One technical solution of the present invention is a catalyst temperature estimation device for estimating the catalyst temperature of an exhaust gas catalytic converter. This device is installed in the exhaust passage of an internal combustion engine having a fuel injection section that injects fuel and a fuel cutoff function that cuts off fuel injection from the fuel injection section during vehicle operation. The catalyst temperature estimation device includes: an operating state acquisition unit that acquires parameters representing the operating state of the internal combustion engine; and a temperature estimation unit that calculates an estimated value of the catalyst temperature based on the parameters acquired by the operating state acquisition unit. When fuel cutoff is performed, the temperature estimation unit maintains the estimated value at the start of fuel cutoff until the operating state after fuel cutoff reaches a predetermined operating state. Attached Figure Description

[0007] The objectives, features, and advantages of the present invention are further illustrated by the following description of embodiments in conjunction with the accompanying drawings.

[0008] Figure 1 This is a diagram that schematically illustrates the main structural components of an engine using a catalyst temperature estimation device according to an embodiment of the present invention; Figure 2 This is a block diagram showing the main structural components of the control device for an internal combustion engine, including the catalyst temperature estimation device according to an embodiment of the present invention. Figure 3 It is a graph showing the relationship between the engine's cumulative intake air volume and the correction factor; Figure 4 This is a time-series diagram illustrating an example of the change in catalyst temperature versus cumulative intake air volume after fuel cut-off; Figure 5 This is a time series diagram illustrating an example of the change in catalyst temperature after fuel cut-off corresponding to different operating conditions; Figure 6 It is shown by Figure 2 A flowchart of an example of the processing performed by the controller; Figure 7 This is a time-series diagram illustrating an example of the change in catalyst temperature corresponding to different cumulative intake volumes before fuel cutoff. Detailed Implementation

[0009] The following is for reference Figures 1 to 7 An embodiment of the present invention will be described. The internal combustion engine control device of this embodiment is applied to vehicles equipped with a gasoline engine, which is an internal combustion engine. That is, it is applied to engine vehicles that operate solely using the engine as a drive source and hybrid vehicles that operate using both an engine and an electric motor as drive sources.

[0010] Figure 1 This diagram schematically illustrates the main structural components of the internal combustion engine, i.e., engine 1, to which the control device of this embodiment is applied. Engine 1 is a spark-ignition type internal combustion engine with a fuel cut-off function that stops fuel supply to multiple cylinders when the vehicle decelerates, and is a four-stroke engine that undergoes four strokes during its working cycle: intake, compression, expansion, and exhaust. Engine 1 has multiple cylinders with the same structure. Figure 1 The structure of a single cylinder is shown.

[0011] like Figure 1 As shown, the engine 1 has a cylinder block 2 formed on the cylinder block, a piston 3 slidably disposed inside the cylinder block 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 block 2.

[0012] An intake port 11 and an exhaust port 12 are provided in the cylinder head. The combustion chamber 4 is connected to the intake passage 13 via the intake port 11, and to the 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.

[0013] Throttle valve 17, for example, is a butterfly valve, and regulates the intake air volume flowing to combustion chamber 4. Throttle valve 17 is driven by a throttle actuator such as an electric motor, depending on the operation of the accelerator pedal. Intake valve 15 and exhaust valve 16 are opened and closed by a valve mechanism (not shown) at predetermined times synchronized with the rotation of crankshaft 6. The opening and closing timing of valves 15 and 16 can be appropriately changed.

[0014] A spark plug 18 and a direct injection injector 19 are respectively installed in either the cylinder head or the cylinder block (e.g., the cylinder head) facing the combustion chamber 4 of the cylinder block 2. The spark plug 18 is positioned between the intake port 11 and the exhaust port 12, and is electrically powered to generate a spark, igniting the fuel-air mixture in the combustion chamber 4. The injector 19 is positioned next to the intake valve 15, and is electrically driven to inject fuel into the combustion chamber 4 in a downward and oblique direction. The configuration of the injector 19 is not limited to this; it can also be positioned next to the spark plug 18.

[0015] An exhaust catalyst device 20 for purifying exhaust gases is installed in the exhaust passage 14. The exhaust catalyst device 20 is a three-way catalyst that removes and purifies HC, CO, and NOx contained in the exhaust gases through oxidation-reduction reactions. The catalyst can be a precious metal such as platinum. Other exhaust catalyst devices, such as oxidation catalysts that oxidize CO and HC in the exhaust gases, can also be used. When the temperature of the catalyst in the exhaust catalyst device 20 (catalyst temperature Tc) increases, the catalyst is activated, and the purification effect of the exhaust catalyst device 20 on the exhaust gases is enhanced. However, if the catalyst temperature Tc is too high, the exhaust catalyst device 20 will be damaged; therefore, the catalyst temperature Tc needs to be suppressed below a specified temperature (upper limit temperature T1).

[0016] Engine 1 also includes an exhaust gas recirculation (EGR) device 25. The EGR device 25 has an EGR passage 26 and an EGR valve 27 disposed on the EGR passage 26. One end of the EGR passage 26 is connected downstream of the exhaust catalyst device 20 in the exhaust passage 14, and the other end is connected upstream of the throttle valve 17 in the intake passage 13. Exhaust gas flowing through the exhaust passage 14 can be recirculated back 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 adjust its opening. The exhaust gas recirculation device 25 can also be omitted.

[0017] Engine 1 has a fuel cut-off function (fuel cut-off function) aimed at improving fuel efficiency. When a predetermined fuel cut-off condition is met while the engine is running, fuel injection from injector 19 is stopped. That is, when the fuel cut-off condition is met, fuel injection is stopped by entering a fuel cut-off mode (called F / C mode). For example, the fuel cut-off condition is met when the accelerator pedal operation (accelerator opening) is below a predetermined value, the crankshaft speed (engine speed) is above a predetermined value, and the vehicle speed is above a predetermined value. For example, the fuel cut-off condition is met during deceleration. The fuel cut-off conditions are not limited to those described above.

[0018] In F / C mode, throttle valve 17 is almost fully closed, but to suppress combustion instability caused by insufficient air intake when resuming from F / C mode, and to suppress the impact caused by the rapid change in air intake, air continues to enter most of the cylinder 2. Therefore, even in F / C mode, the cumulative air intake (F / C cumulative air intake) described later increases.

[0019] In this engine 1, when the accelerator pedal is depressed and the accelerator opening increases, the throttle valve 17 opens, increasing the intake air volume. This causes the exhaust temperature to rise, and consequently, the catalyst temperature Tc rises. To prevent damage to the exhaust catalyst assembly 20, engine 1 needs to be configured such that the catalyst temperature Tc does not exceed the upper limit temperature T1. Therefore, it is necessary to accurately estimate the catalyst temperature Tc. Thus, in this embodiment, a catalyst temperature estimation device is configured as follows.

[0020] Figure 2 This is a block diagram showing the main structural components of the control device 100 for engine 1. The control device 100 includes the catalyst temperature estimation device of this embodiment. Figure 2 As shown, the control device 100 is configured with the controller 40 as the center, and includes an accelerator opening sensor 31, a vehicle speed sensor 32, a crankshaft angle sensor 33, an intake air volume sensor 34, a spark plug 18, an injector 19, and an actuator 35, all of which are connected to the controller 40. Although not shown in the figure, the controller 50 is also connected to an air-fuel ratio sensor for detecting the actual air-fuel ratio, an intake air pressure sensor for detecting the intake air pressure, and other sensors.

[0021] An accelerator pedal (not shown) is installed on the accelerator pedal of the vehicle to detect the amount of accelerator pedal operation (accelerator opening). The target torque of the engine 1 is indicated based on the detection value of the accelerator pedal. That is, the torque command value is output by the accelerator pedal. The control device for the internal combustion engine of this embodiment can also be applied to vehicles with driver assistance functions or autonomous vehicles, in which case the vehicle control system outputs a torque command value to the controller 40.

[0022] Vehicle speed sensor 32 detects vehicle speed. Crankshaft angle sensor 33 is installed on crankshaft 6 and is configured to output pulse signals as crankshaft 6 rotates. Controller 40 determines the rotation angle (crankshaft angle) of crankshaft 6 based on the pulse signals from crankshaft angle sensor 33, using the position of top dead center (TDC) at the start of piston 3's intake stroke as a reference, and calculates the engine speed. Therefore, crankshaft angle sensor 33 also functions as an engine speed sensor. Hereinafter, for convenience, crankshaft angle sensor 33 will be treated as a device for detecting engine speed.

[0023] The intake air volume sensor 34 is a sensor that detects the amount of air entering the cylinder 2, and is, for example, constituted by an air flow meter disposed in the intake passage 13 (more specifically, upstream of the throttle valve 17). The controller 50 calculates the target injection quantity of the injector 19 based on the signal from the intake air volume sensor 34. The intake air volume detected by the intake air volume sensor 34 is correlated with the output torque of the engine 1. Therefore, the intake air volume sensor 34 also functions as a sensor for detecting engine load. The engine load (engine output torque) is calculated by the controller 40, but for convenience, the intake air volume sensor 34 will be treated as a device for detecting engine load below.

[0024] Actuator 35 is a throttle actuator, such as an electric motor, used to adjust the opening of throttle valve 17. Actuator 35 is driven according to a torque command value, and by driving actuator 35, the throttle opening is adjusted, thereby controlling the intake air volume. That is, the intake air volume can be controlled to a target intake air volume corresponding to the torque command value or to a limited intake air volume lower than the target intake air volume. It can also guide EGR gas into the intake passage via exhaust gas recirculation device 25 to limit the intake air volume (amount of fresh air). In this case, actuator 35 consists of a throttle actuator and an EGR actuator.

[0025] When the intake air volume is controlled to a limited level, it is sometimes predicted that the catalyst temperature Tc will exceed the upper limit temperature T1. In this case, by limiting the intake air volume, the rise in exhaust temperature is suppressed, thereby controlling the catalyst temperature Tc below the upper limit temperature T1. Alternatively, the air-fuel ratio can be enriched by relatively increasing the fuel injection quantity from injector 19, either by limiting the intake air volume or by doing so, thereby suppressing the rise in exhaust temperature and limiting the catalyst temperature Tc below the upper limit temperature T1.

[0026] The controller 40 is composed of an electronic control unit (ECU), which includes an arithmetic unit such as a CPU (central processing unit), a storage unit such as ROM (read-only memory) and RAM (random access memory), and other peripheral circuits, forming a computer-like structure. The controller 40 has an information acquisition unit 41, an injector control unit 42, a spark plug control unit 43, a temperature estimation unit 44, an output unit 45, and a storage unit 46, forming a functional structure. Various mappings, thresholds, control programs, etc., are pre-stored in the storage unit 46.

[0027] The information acquisition unit 41 reads signals from the accelerator opening sensor 31, vehicle speed sensor 32, crankshaft angle sensor 33, intake air volume sensor 34, etc. In other words, the information acquisition unit 41 acquires information (accelerator opening, vehicle speed, intake air volume, engine speed) represented by signals from these sensors 31 to 34. This information consists of parameters representing the operating state of the engine 1, and these parameters can be used to determine the operating point of the engine 1 on the control map, such as the operating point determined by the engine speed and engine load.

[0028] The injector control unit 42 performs feedback control, such that the actual air-fuel ratio detected by the air-fuel ratio sensor becomes the target air-fuel ratio (e.g., stoichiometric air-fuel ratio), while calculating the target injection quantity for each cycle based on the intake air quantity detected by the intake air quantity sensor 34. Then, based on the predetermined crankshaft angle detected by the crankshaft angle sensor 33, it controls the injector 19 to inject the target injection quantity of fuel in each cycle. This fuel injection mode is referred to as the conventional injection mode.

[0029] Furthermore, the injector control unit 42 determines whether the fuel cut-off condition is met. For example, when the accelerator pedal operation amount (accelerator opening) detected by the accelerator opening sensor 31 is below a predetermined value, the engine speed detected by the crankshaft angle sensor 33 is above a predetermined value, and the vehicle speed detected by the vehicle speed sensor 32 is above a predetermined value, the fuel cut-off condition is met. For example, the fuel cut-off condition is met during deceleration. When the injector control unit 42 determines that the fuel cut-off condition is met, it controls the injector 19 to stop fuel injection. The fuel injection mode in this situation is called the F / C mode. Therefore, when the fuel cut-off condition is met during normal injection mode operation, the injector control unit 42 switches the fuel injection mode from the normal injection mode to the F / C mode.

[0030] When operating in F / C mode, the injector control unit 42 determines whether the fuel cut-off recovery condition is met. The fuel cut-off recovery condition is met, for example, when the accelerator pedal is depressed as detected by the accelerator opening sensor 31, or when the engine speed drops below a predetermined value as detected by the crankshaft angle sensor 33. When the injector control unit 42 determines that the fuel cut-off recovery condition is met, it switches the fuel injection mode from F / C mode to normal mode and controls the injector 19 to resume fuel injection.

[0031] The spark plug control unit 43 uses a pre-stored mapping representing the relationship between engine speed and engine load to determine the target ignition timing corresponding to the engine speed detected by the crankshaft angle sensor 33 and the engine load (intake volume) detected by the intake volume sensor 34. Then, it controls the spark plug 18 to ignite at the target ignition timing.

[0032] The temperature estimation unit 44 estimates the catalyst temperature Tc in both conventional injection mode and F / C mode based on parameters representing the operating state of the engine 1 obtained by the information acquisition unit 41. In conventional injection mode, the temperature estimation unit 44 calculates the catalyst temperature Tc based on the engine speed detected by the crankshaft angle sensor 33 and the intake air volume detected by the intake air volume sensor 34. For example, it calculates the catalyst temperature Tc with engine speed and intake air volume as parameters using a pre-stored mapping or a prescribed calculation formula. The higher the engine speed and the greater the intake air volume, the higher the catalyst temperature Tc.

[0033] In conventional injection mode, the temperature estimation unit 44, in addition to estimating the catalyst temperature Tc, also calculates the cumulative intake air volume (referred to as the cumulative combustion intake air volume) G0, which is the intake air volume detected by the intake air volume sensor 34 since the start of conventional injection mode. The cumulative combustion intake air volume G0 is frequently updated and gradually increases as time passes after the start of conventional injection mode. Furthermore, when switching from fuel injection mode to F / C mode, the temperature estimation unit 44 calculates a correction coefficient α based on the cumulative combustion intake air volume G0, and multiplies the correction coefficient α by a specified intake air volume Gα to calculate a threshold G1. The specified intake air volume Gα is a reference value of the cumulative intake air volume pre-stored in the storage unit 46. This specified intake air volume Gα is obtained in advance through experiments and analysis.

[0034] Figure 3 It is a graph pre-stored in the storage unit 46, showing the relationship between the cumulative combustion intake volume G0 and the correction coefficient α. (Example) Figure 3 As shown, when the cumulative combustion intake air volume G0 is less than the specified value G01, the correction coefficient α is 0. When the cumulative combustion intake air volume G0 becomes the specified value G01 or higher, the correction coefficient α gradually increases with the increase of the cumulative combustion intake air volume G0. When the cumulative combustion intake air volume G0 becomes the specified value G02 or higher, the correction coefficient α is 1. The temperature estimation unit 44 is used... Figure 3 After calculating the correction coefficient α based on the relationship, the specified intake air volume Gα is multiplied by the correction coefficient α to calculate the threshold G1. The cumulative intake air volume G0 is reset to 0 at the end of each regular injection mode.

[0035] In F / C mode, the temperature estimation unit 44 estimates the catalyst temperature Tc in a manner different from that in conventional injection mode. Figure 4 This graph shows the estimated value of the catalyst temperature Tc and the change in cumulative intake air volume over time from the time point t0 when switching to F / C mode. Characteristic f1 (solid line) in the graph represents the catalyst temperature Tc estimated by the temperature estimation unit 44, and characteristic f2 (dashed line) represents the catalyst temperature Tc as a reference example. The catalyst temperature Tc used as the reference example was calculated using the same method as in the conventional injection mode. Characteristic f3 (double-dotted line) in the graph corresponds to the actual catalyst temperature Tc obtained through further experiments and analysis.

[0036] like Figure 4 As shown, in this embodiment, it is assumed that the catalyst temperature Tc is constant (Tc0) from the start of F / C mode until time t1 when the specified conditions are met. That is, after fuel cut-off, the catalyst itself is in a state of maintaining heat. In addition, from time t0 to t1, there is heat generated by the catalyst reaction due to the intake delay caused by the throttle valve 17 being closed after the start of F / C mode. Therefore, the actual catalyst temperature Tc (double-dotted line) does not drop immediately after the start of fuel cut-off, but remains constant or approximately constant. Taking this into consideration, the temperature estimation unit 44 maintains the catalyst temperature Tc0 at the time of fuel cut-off as the estimated value of catalyst temperature Tc until the specified conditions are met.

[0037] When the temperature estimation unit 44 is in F / C mode, it calculates the cumulative intake volume (called F / C cumulative intake volume) G2, which is the intake volume detected by the intake volume sensor 34 since the start of F / C mode. Figure 4 Characteristic f4 (solid line) represents the cumulative intake air volume G2 for the F / C mode. The cumulative intake air volume G2 is constantly updated, increasing as time passes since the start of F / C mode. More specifically, the cumulative intake air volume G2 is 0 before starting F / C mode, and gradually increases over time. The rate of increase in the cumulative intake air volume G2 (the slope of characteristic f4) is larger immediately after switching to F / C mode, and gradually decreases over time. The cumulative intake air volume G2 is reset to 0 at the end of each F / C mode session.

[0038] exist Figure 4The example shown is one where the specified conditions are met at time t1. The specified conditions refer to the cumulative intake air volume G2 of the fuel / c mixture being greater than or equal to the threshold G1. When the fuel / c mixture mode starts, the temperature estimation unit 44 determines whether G2 ≥ G1 is true. If G2 < G1, the catalyst temperature Tc0 at the time of fuel cut-off is directly used as the catalyst temperature Tc (time points t0 to t1).

[0039] When the temperature estimation unit 44 determines that G2 ≥ G1, it calculates the catalyst temperature Tc (time point t1) based on the engine speed detected by the crankshaft angle sensor 33 and the intake air volume detected by the intake air volume sensor 34. For example, it calculates the catalyst temperature Tc with engine speed and intake air volume as parameters using a pre-stored image or a prescribed formula. The lower the engine speed and the higher the intake air volume, the lower the catalyst temperature Tc. After the prescribed conditions are met, the catalyst temperature Tc gradually decreases.

[0040] Figure 5 This graph shows the change of catalyst temperature Tc, estimated by temperature estimation unit 44, over time after the specified conditions are met at point t1. Characteristics f11 to f13 (dashed lines) represent the characteristics of the catalyst's reach temperature Te corresponding to different operating states, while characteristics f21 to f23 (solid lines) represent the characteristics of catalyst temperature Tc. Reach temperature Te refers to the estimated catalyst temperature Tc that is expected to be reached when the specified operating state (intake air volume, engine speed) continues after fuel cut-off; it is equivalent to the convergence value when catalyst temperature Tc converges over time.

[0041] For example, Figure 5 Characteristic f11 is the arrival temperature Te1 corresponding to the first intake air volume, characteristic f12 is the arrival temperature Te2 corresponding to the second intake air volume which is less than the first intake air volume, and characteristic f13 is the arrival temperature Te3 corresponding to the third intake air volume which is less than the second intake air volume. Characteristic f21 is the catalyst temperature Tc1 corresponding to the first intake air volume, characteristic f22 is the catalyst temperature Tc2 corresponding to the second intake air volume, and characteristic f23 is the catalyst temperature Tc3 corresponding to the third intake air volume. The first, second, and third intake air volumes are the intake air volumes detected by the intake air volume sensor 34 when the fuel is cut off.

[0042] The storage unit 46 stores in advance the relationship between the operating state of the engine 1 after fuel cutoff (intake air volume, engine speed) and the reached temperature Te. The catalyst is cooled by the intake air; therefore, the higher the intake air volume, the greater the cooling effect on the catalyst. Furthermore, the lower the engine speed, the better the catalyst temperature rise caused by compression heat is suppressed. Considering this, the storage unit 46 stores a relationship that the higher the intake air volume and the lower the engine speed, the lower the reached temperature Te. This relationship can be obtained in advance through experiments and analysis. The temperature estimation unit 44 uses this relationship stored in the storage unit 46 to calculate the reached temperature Te (Te1 to Te3) corresponding to the operating state.

[0043] The actual catalyst temperature Tc does not reach the target temperature Te immediately after fuel cut-off, but gradually approaches the target temperature Te over time. Therefore, the temperature estimation unit 44 performs a easing process on the target temperature Te to calculate the catalyst temperature Tc. More specifically, the catalyst temperature Tc is calculated by easing the rate of decrease in catalyst temperature Tc as the target temperature Te is lower (i.e., the higher the intake air volume and the lower the engine speed). When ΔTc1, ΔTc2, and ΔTc3 represent the rate of decrease in catalyst temperature Tc1 to Tc3 for characteristics f21 to f23 respectively, as follows: Figure 5 As shown, the relationship ΔTc1>ΔTc2>ΔTc3 holds true.

[0044] The output unit 45 outputs a control signal to the actuator 35, causing the catalyst temperature Tc estimated by the temperature estimation unit 44 to be below the upper limit temperature T1. For example, when the catalyst temperature Tc reaches or exceeds a predetermined value, the actuator 35 is controlled to make the intake air volume a limited intake air volume that is smaller than the target intake air volume corresponding to the accelerator opening (torque command value). This suppresses the rise in catalyst temperature Tc, keeping it below the upper limit temperature T1. When the catalyst temperature Tc reaches or exceeds a predetermined value, the output unit 45 can also output a control signal to the injector 19, relatively increasing the fuel injection quantity and enriching the air-fuel ratio. Not only the intake air volume is controlled, but the rise in catalyst temperature Tc can also be suppressed by controlling the fuel injection quantity.

[0045] Figure 6 This is a flowchart illustrating an example of the processing performed by the CPU of the controller 40, particularly an example of the processing related to the estimation of the catalyst temperature Tc by the temperature estimation unit 44. The processing shown in this flowchart begins, for example, when the engine ignition switch is turned on, and is repeated at a predetermined cycle.

[0046] like Figure 6As shown, in step S1 (S: processing step), the controller 40 first reads signals from the crankshaft angle sensor 33 and the intake air volume sensor 34. Additionally, the controller 40 reads a signal from the injector control unit 42, which indicates the switching of the fuel injection mode. Next, in step S2, the controller 40 determines whether the F / C flag is 1. The F / C flag is set to 1 in F / C mode and to 0 in normal injection mode.

[0047] When S2 is negative (S2), proceed to S3, where the controller 40 calculates the catalyst temperature Tc based on the engine speed detected by the crankshaft angle sensor 33 and the intake air volume detected by the intake air volume sensor 34. Then, in S4, the controller 40 calculates the cumulative combustion intake air volume G0, accumulated from the intake air volume detected by the intake air volume sensor 34 since the start of the normal injection mode.

[0048] Next, in S5, the controller 40 determines whether the fuel injection mode has switched from the conventional injection mode to the F / C mode based on the signal from the injector control unit 42. When S5 is negative (S5: No), the process proceeds to S6, where the controller 40 sets the flag to 0 and ends the process.

[0049] When S5 is affirmative (S5: Yes), proceed to S7, where controller 40 sets the flag to 1. Then, in S8, controller 40... Figure 3 Based on the characteristics of the data, the controller 40 calculates a correction coefficient α corresponding to the cumulative combustion intake volume G0 calculated in S4. Then, the controller 40 multiplies the specified intake volume Gα by the correction coefficient α to calculate a threshold G1, stores the threshold G1 in the storage unit 46, and ends the process. When calculating the threshold G1, the controller 40 resets the cumulative combustion intake volume G0.

[0050] In S2, when the F / C flag is determined to be 1, the process proceeds to S10, where the controller calculates the cumulative F / C intake volume G2, which is the intake volume detected by the intake volume sensor 34 since the start of F / C mode. Then, in S11, the controller 40 determines whether the cumulative F / C intake volume G2 is above the threshold G1.

[0051] When S11 is negative (S11: No), proceed to S12. The controller 40 maintains the latest catalyst temperature Tc0 calculated in S3, which is the catalyst temperature Tc0 when the fuel injection mode is switched to F / C mode, as the catalyst temperature Tc. Then, in S13, the flag is set to 1, and the process ends.

[0052] On the other hand, when S11 is affirmative (S11: Yes), the process proceeds to S14, where the controller 40 calculates the arrival temperature Te corresponding to the operating state of the engine 1 after fuel cut-off. That is, it calculates the arrival temperature Te corresponding to the intake air volume detected by the intake air volume sensor 34 and the engine speed calculated by the crankshaft angle sensor 33. Furthermore, the controller 40 performs a gradual process, such as the catalyst temperature Tc gradually approaching the arrival temperature Te over time, and calculates the catalyst temperature Tc.

[0053] Next, in S15, the controller 40 determines whether the fuel injection mode has switched from F / C mode to conventional injection mode based on the signal from the injector control unit 42. If S15 is negative (S15: No), proceed to S13; if it is positive (S15: Yes), proceed to S16. In S16, the controller 40 sets the flag to 0 and ends the process. At this time, the controller 40 resets the F / C cumulative intake air volume G2.

[0054] The operation of the catalyst temperature estimation device in this embodiment is summarized below. In the normal injection mode, the catalyst temperature Tc (S3) is calculated based on the operating state of engine 1 (engine speed, intake air volume). Figure 7 This is an example graph showing the estimated value of catalyst temperature Tc and the cumulative F / C intake flow rate G2 over time. Figure 7 At time point t0, when the fuel injection mode is switched to F / C mode, the estimated value of catalyst temperature Tc remains the catalyst temperature Tc0 at time point t0 when switching to F / C mode.

[0055] That is, after the fuel cut-off is complete, the catalyst itself remains in a state of heat retention. Furthermore, in the exhaust catalyst unit 20, there is heat generated by the catalyst reaction due to the intake delay after the throttle valve 17 is closed. Therefore, after the fuel cut-off is complete, when calculating the catalyst temperature Tc based on the engine 1's operating state, the calculated catalyst temperature Tc is lower than the actual catalyst temperature Tc, resulting in a deterioration in the accuracy of the temperature estimation. In this embodiment, after the fuel cut-off is complete, the catalyst temperature Tc is kept constant (Tc0), thus enabling a high-accuracy estimation of the catalyst temperature Tc.

[0056] The time for which the catalyst temperature Tc is kept constant is determined by the threshold G1 before fuel cutoff. At the threshold G1... Figure 7 When the specified value G1a is reached, as shown by characteristic f1a (solid line), the catalyst temperature Tc is gradually reduced starting at time point t1a, and the estimated value of the catalyst temperature Tc gradually decreases (S14). On the other hand, the threshold G1 is... Figure 7When the specified value G1b is reached, as shown by characteristic f1b (dashed line), the easing treatment of catalyst temperature Tc begins at time t1b, which is later than time t1a. That is, the larger the threshold G1, the later the easing treatment begins, and the longer the catalyst temperature Tc remains constant.

[0057] The threshold G1 affects the heating state of the catalyst; the larger the threshold G1, the more difficult it is for the catalyst temperature Tc to decrease. The threshold G1 is calculated by multiplying a specified intake air volume Gα by a correction factor α. However, the greater the cumulative intake air volume G0 before fuel cutoff, the larger the correction factor α. Figure 3 Therefore, by considering the heating state of the catalyst before fuel cut-off, the catalyst temperature Tc can be calculated, thus enabling a high-precision estimation of the catalyst temperature Tc.

[0058] The catalyst temperature Tc easing treatment is a treatment that, based on the operating conditions of engine 1, results in a greater decrease in catalyst temperature Tc due to the lower the reached temperature Te of catalyst temperature Tc. Figure 5 Therefore, the greater the intake air volume after fuel cutoff and the lower the engine speed, the lower the temperature Te, and the greater the percentage decrease in the calculated catalyst temperature Tc. Thus, this applies not only immediately after fuel cutoff but also after meeting specified conditions following fuel cutoff (…). Figure 7 (After time points t1a and t1b), the catalyst temperature Tc can also be estimated with high accuracy.

[0059] The following effects can be achieved by adopting this implementation method.

[0060] (1) The catalyst temperature estimation device is configured to estimate the catalyst temperature Tc of the exhaust catalyst device 20. The exhaust catalyst device 20 is installed in the exhaust passage 14 of the engine 1, which has an injector 19 that injects fuel and has a fuel cut-off function that cuts off fuel injection from the injector 19 during vehicle operation. Figure 1 The catalyst temperature estimation device includes: an information acquisition unit 41 that acquires parameters representing the operating state of the engine 1 (intake volume, engine speed, etc.); and a temperature estimation unit 44 that calculates an estimated value of the catalyst temperature Tc based on the parameters acquired by the information acquisition unit 41. Figure 2 When fuel cutoff is performed, the temperature estimation unit 44 maintains the estimated value (Tc0) at the start of fuel cutoff until the operating state after fuel cutoff becomes a specified operating state (until the specified conditions are met), specifically, until the cumulative F / C intake air volume G2 becomes above the threshold G1. Figure 4 , Figure 6 ).

[0061] Therefore, the catalyst temperature Tc after fuel cut-off can be estimated with high accuracy. That is, immediately after fuel cut-off, the catalyst itself is in a state of retaining heat, and there is also heat generated by the catalyst reaction due to the supply of air to the exhaust catalyst unit 20. Therefore, if the catalyst temperature Tc is calculated using the same method after fuel cut-off as before fuel cut-off, it is difficult to calculate the catalyst temperature Tc with high accuracy. In this embodiment, this is addressed by maintaining the estimated value of the catalyst temperature Tc at the start of fuel cut-off until predetermined conditions are met after fuel cut-off, such as... Figure 4 As shown, the catalyst temperature Tc (characteristic f1) can be estimated with high accuracy by matching the catalyst temperature Tc (characteristic f1) with the actual catalyst temperature (characteristic f3).

[0062] (2) The information acquisition unit 41 acquires information about the intake air volume of the engine 1 detected by the intake air volume sensor 34. Figure 2 The temperature estimation unit 44 calculates the cumulative value of the intake air volume since the start of fuel cut-off, i.e., the cumulative F / C intake air volume G2, based on the intake air volume information obtained by the information acquisition unit 41, and maintains the estimated value (Tc0) at the start of fuel cut-off until the cumulative F / C intake air volume G2 reaches the threshold G1. Figure 4 , Figure 6 After fuel cutoff, the catalyst is cooled by the intake air, but the temperature drop is small under low intake air conditions. Taking this into account, the catalyst temperature Tc is estimated, thus enabling a high-precision estimation of the catalyst temperature Tc after fuel cutoff.

[0063] (3) The temperature estimation unit 44 also calculates the cumulative value of the intake air volume before fuel cutoff, i.e., the cumulative combustion intake air volume G0, and sets a threshold G1 based on the cumulative combustion intake air volume G0. Figure 3 Before fuel cutoff, the catalyst is heated by the exhaust gas, but under conditions of high exhaust volume, the catalyst retains a significant amount of heat. Because this is taken into account when estimating the catalyst temperature Tc, it is possible to accurately estimate the catalyst temperature Tc after fuel cutoff.

[0064] (4) The larger the cumulative intake air volume G0 of combustion, the larger the correction coefficient α of the temperature estimation unit 44, and the larger the threshold G1 is set to ( Figure 3 Therefore, the correction coefficient α for the threshold G1 used to calculate the cumulative intake air volume G2 of F / C can be appropriately set, and the estimation accuracy of the catalyst temperature Tc is improved.

[0065] (5) The temperature estimation unit 44 calculates the estimated arrival temperature Te, which is the catalyst temperature Tc, based on the parameters obtained by the information acquisition unit 41. Furthermore, after fuel cut-off, once the cumulative F / C intake air volume G2 reaches the threshold G1, the temperature estimation unit 44 performs a gradual process towards the arrival temperature Te, such that the lower the arrival temperature Te, the greater the temperature drop per unit time, and calculates the estimated value of the catalyst temperature Tc. Figure 5 Therefore, it is possible to accurately estimate the catalyst temperature Tc that will decrease after fuel cut-off.

[0066] (6) The information acquisition unit 41 acquires information on the intake air volume of the engine 1 detected by the intake sensor 34 and information on the engine speed of the engine 1 detected by the crankshaft angle sensor 33. Figure 2 After the cumulative intake air volume G2 reaches the threshold G1, the temperature estimation unit 44 performs a mitigation process, such as the larger the intake air volume contained in the information obtained by the information acquisition unit 41 and / or the smaller the engine speed contained in the information obtained by the information acquisition unit 41, the greater the temperature drop per unit time, and calculates the estimated value of the catalyst temperature Tc. Figure 5 The more air intake, the better the catalyst cooling effect. The lower the engine speed, the better the catalyst temperature rise caused by compression heat is suppressed. However, because this is taken into account and a mitigation process is implemented, the catalyst temperature Tc can be estimated with high accuracy through the mitigation process.

[0067] (7) The information acquisition unit 41 acquires information on the intake air volume of the engine 1 detected by the intake sensor 34 and information on the engine speed of the engine 1 detected by the crankshaft angle sensor 33. Figure 2 The temperature estimation unit 44 calculates the reached temperature Te in a manner that the larger the intake air volume contained in the information obtained by the information acquisition unit 41 and / or the smaller the engine speed contained in the information obtained by the information acquisition unit 41, the lower the reached temperature Te. Figure 5 Therefore, the peak temperature Te of the catalyst Tc can be calculated accurately, and the catalyst temperature for slack treatment can be estimated with high precision.

[0068] The above-described embodiments can be modified in various ways. The following describes some modifications. In the above-described embodiments, the injector 19, which serves as the fuel injection unit, is a direct injection type that injects fuel into the combustion chamber 4. However, it can also be a port injection type that injects fuel into the intake port, instead of a direct injection type. In the above-described embodiments, the engine 1 has a fuel cut-off function that cuts off the fuel injected from the injector 19 when a predetermined fuel cut-off condition is met during engine operation. However, the fuel cut-off condition is not limited to those described above, and the structure of an internal combustion engine with a fuel cut-off function is not limited to those described above.

[0069] In the above embodiment, the information acquisition unit 41 acquires parameters representing the operating state of the engine 1, such as intake air volume and engine speed. However, the structure of the operating state acquisition unit is not limited to the above description. That is, the operating state acquisition unit may be a component other than an intake air information acquisition unit that acquires intake air volume information and a speed information acquisition unit that acquires internal combustion engine speed information. In the above embodiment, when fuel cut-off is performed, the estimated value of the catalyst temperature Tc at the start of fuel cut-off is maintained until the cumulative value of the intake air volume since the start of fuel cut-off, i.e., the cumulative F / C intake air volume G2, reaches or exceeds the threshold G1. That is, the estimated value at the start of fuel cut-off is maintained until the predetermined condition G2≥G1 is met after fuel cut-off, but the predetermined condition is not limited to the above description. Therefore, as long as the estimated value at the start of fuel cut-off is maintained until the operating state after fuel cut-off becomes the predetermined operating state, the structure of the temperature estimation unit 44 can be any way.

[0070] In the above embodiment, the temperature estimation unit 44 calculates the cumulative value of the intake air volume before fuel cutoff, i.e., the cumulative combustion intake air volume G0 (cumulative value before fuel cutoff), and sets a threshold value G1 (prescribed value) based on this cumulative value. More specifically, the larger the cumulative combustion intake air volume G0, the larger the comparison object, i.e., the prescribed value, for the cumulative F / C intake air volume G2 is set, but the prescribed value is not limited to what has been described above. In the above embodiment, the arrival temperature Te, which is estimated to be reached by the catalyst temperature after fuel cutoff, is calculated, and the catalyst temperature Tc is estimated based on the arrival temperature Te. However, the catalyst temperature Tc may also be estimated without using the arrival temperature Te.

[0071] In the above embodiments, after fuel cutoff, a mitigation process is performed where a larger intake air volume and a lower engine speed result in a greater temperature drop per unit time after fuel cutoff. However, it is also possible that a larger intake air volume or a lower engine speed results in a greater temperature drop per unit time. In the above embodiments, a larger intake air volume and a lower engine speed result in a lower temperature Te. However, it is also possible that a larger intake air volume or a lower engine speed results in a lower temperature Te.

[0072] It is possible to combine one or more of the above-described embodiments and variations, and to combine the variations with each other.

[0073] Using this invention, the catalyst temperature after fuel cut-off can be estimated with high precision.

[0074] The present invention has been described above in conjunction with preferred embodiments, but those skilled in the art should understand that various modifications and changes can be made without departing from the scope of the claims.

Claims

1. A catalyst temperature estimation device, which is a catalyst temperature estimation device for estimating the catalyst temperature of an exhaust catalyst device (20), wherein the exhaust catalyst device (20) is provided in an exhaust passage (14) of an internal combustion engine (1) having a fuel injection section (19) for injecting fuel and having a fuel cut-off function for cutting off fuel injection from said fuel injection section (19) during vehicle operation, characterized in that, have: The operating status acquisition unit (41) acquires parameters representing the operating status of the internal combustion engine (1); and The temperature estimation unit (44) calculates an estimated value for the catalyst temperature based on the parameters obtained by the operating state acquisition unit (41). When the fuel cut-off is performed, the temperature estimation unit (44) maintains the estimated value at the start of the fuel cut-off until the operating state after the fuel cut-off becomes the specified operating state.

2. The catalyst temperature estimation device according to claim 1, characterized in that, The operating status acquisition unit (41) includes an intake information acquisition unit that acquires information about the intake air volume of the internal combustion engine (1). The temperature estimation unit (44) calculates the cumulative value of the intake air volume from the start of fuel cut-off based on the intake air volume information obtained by the intake air information acquisition unit, and maintains the estimated value at the start of fuel cut-off until the cumulative value reaches a predetermined value (G1).

3. The catalyst temperature estimation device according to claim 2, characterized in that, The temperature estimation unit (44) also calculates the cumulative value of the intake air volume before fuel cut-off, i.e., the cumulative value before fuel cut-off (G0), and sets the specified value (G1) based on the cumulative value before fuel cut-off (G0).

4. The catalyst temperature estimation device according to claim 3, characterized in that, The larger the cumulative value (G0) before fuel cut-off, the larger the temperature estimation unit (44) sets the specified value (G1) to.

5. The catalyst temperature estimation device according to claim 4, characterized in that, The temperature estimation unit (44) calculates the correction coefficient corresponding to the fuel cut-off cumulative value based on the characteristic that the relationship between the predetermined fuel cut-off cumulative value and the correction coefficient is such that the correction coefficient is 0 when the fuel cut-off cumulative value is less than a first predetermined value, gradually increases as the fuel cut-off cumulative value increases, and becomes 1 when the fuel cut-off cumulative value becomes a second predetermined value greater than the first predetermined value. The unit then multiplies the predetermined reference value (Gα) of the fuel cut-off cumulative value by the correction coefficient and sets the predetermined value (G1).

6. The catalyst temperature estimation device according to any one of claims 2 to 5, characterized in that, The temperature estimation unit (44) calculates the estimated temperature at which the catalyst temperature is expected to be reached when the predetermined operating state continues after fuel cut-off, based on the parameters obtained by the operating state acquisition unit. After the cumulative value reaches the predetermined value, it performs a mitigation process toward the estimated temperature in such a way that the lower the estimated temperature is, the greater the temperature drop per unit time, and obtains the estimated value of the catalyst temperature.

7. The catalyst temperature estimation device according to claim 6, characterized in that, The operating status acquisition unit also includes a speed information acquisition unit for acquiring information about the speed of the internal combustion engine. After the cumulative value reaches the predetermined value, the temperature estimation unit performs the mitigation process in such a way that the larger the intake volume contained in the information obtained by the intake information acquisition unit and / or the smaller the rotational speed contained in the information obtained by the rotational speed acquisition unit, the greater the proportion of temperature drop per unit time, and calculates the estimated value.

8. The catalyst temperature estimation device according to claim 6, characterized in that, The operating status acquisition unit also includes a speed information acquisition unit for acquiring information about the speed of the internal combustion engine. The temperature estimation unit calculates the arrival temperature in such a way that the larger the intake volume contained in the information obtained by the intake information acquisition unit and / or the smaller the rotational speed contained in the information obtained by the rotational speed acquisition unit, the lower the arrival temperature.

9. The catalyst temperature estimation device according to claim 1, characterized in that, It also has: Intake volume sensor (34), which detects the intake volume of the internal combustion engine; and A speed sensor (33) detects the speed of the internal combustion engine. The temperature estimation unit (44) calculates the estimated value of the catalyst temperature at the start of the fuel cut-off based on signals from the intake air volume sensor (34) and the speed sensor (33).

10. A control device for an internal combustion engine, comprising a fuel injection unit (19) for injecting fuel and a fuel cut-off function for cutting off fuel injection from the fuel injection unit (19) during vehicle operation, characterized in that, The internal combustion engine (1) also has an intake regulating unit (35) for regulating the intake air volume and an exhaust catalyst device (20) disposed in the exhaust passage (14). The control device for the internal combustion engine includes: The catalyst temperature estimation device according to claim 1; The control unit (40) controls the intake regulating unit (35) based on the estimated value of the catalyst temperature of the exhaust catalyst device (20) estimated by the catalyst temperature estimation device. When the control unit (40) determines that the estimated value of the catalyst temperature exceeds the specified value (T1), it limits the intake air volume relative to when it determines that the estimated value does not exceed the specified value (T1).

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