Exhaust gas control device and exhaust gas control method

Abstract

To control exhaust gas so as to obtain an appropriate NOx emission amount and ammonia outflow amount.SOLUTION: An exhaust gas control device 50 includes: an acquisition section 521 that acquires load information on a load of an engine, an intake air amount of the engine and an oxygen concentration downstream of a catalyst provided in an exhaust passage in which exhaust gas flows; a setting section 522 that sets a first range of an air-fuel ratio of an air-fuel mixture generated in the engine and a second range of the oxygen concentration on the basis of the load information, and sets updating times of the first range and the second range on the basis of the intake air amount of the engine; and a determination section 523 that determines the air-fuel ratio of the air-fuel mixture from the air-fuel ratio included in the first range so that the oxygen concentration is included in the second range. The setting section 522 resets the first range and the second range on the basis of the load information acquired by the acquisition section each time the updating time elapses from a time when the updating time is set previously, and resets the updating time on the basis of the intake air amount acquired by the acquisition section 521.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an exhaust control device and an exhaust control method. [Background technology]

[0002] The exhaust purification device of Patent Document 1 determines a target value for the amount of ammonia to be adsorbed onto the catalyst so that the amount of NOx (nitrogen oxides) emissions and the amount of ammonia outflow are within a predetermined range, and performs a rich spike to make the air-fuel ratio a predetermined rich air-fuel ratio until the amount of ammonia reaches the target value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-36700 A Summary of the Invention [Problem to be solved by the invention]

[0004] The air-fuel ratio suitable for keeping the NOx emissions and the ammonia outflow amount within the predetermined range varies depending on the engine load. Therefore, if the air-fuel ratio when performing a rich spike is not suitable for the engine load, there is a problem that the NOx emissions exceed the predetermined emission range before the ammonia outflow amount falls within the predetermined outflow range.

[0005] The present invention has been made in consideration of these points, and has an object to control exhaust gas so as to achieve appropriate NOx emissions and appropriate ammonia outflow amounts. [Means for solving the problem]

[0006] An exhaust control device according to a first aspect of the present invention has an acquisition unit that acquires load information related to an engine load, an intake air volume of the engine, and an oxygen concentration downstream of a catalyst provided in an exhaust passage through which exhaust gas flows; a setting unit that sets a first range of an air-fuel ratio of a mixture generated in the engine and a second range of the oxygen concentration based on the load information, and sets update times for the first range and the second range based on the intake air volume of the engine; and a determination unit that determines an air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that the oxygen concentration is included in the second range, and each time the update time has elapsed from the time when the update time was previously set, the setting unit resets the first range and the second range based on the load information acquired by the acquisition unit at the time when the update time has elapsed, and resets the update time based on the intake air volume acquired by the acquisition unit at the time when the update time has elapsed.

[0007] The setting unit may set the first range so that the first range is included in the second range corresponding to a load of the engine indicated by the load information acquired by the acquisition unit at a predetermined time, and the determination unit may determine the air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that an average value of the oxygen concentration acquired by the acquisition unit from a time before the predetermined time before the current time to the current time is included in the second range.

[0008] The setting unit may set the first range such that the proportion of oxygen indicated by the air-fuel ratio included in the first range increases as a load of the engine increases.

[0009] The setting unit may set the second range such that the oxygen concentration included in the second range decreases as the load of the engine increases.

[0010] The setting unit may set the update time to be shorter as the intake air amount increases.

[0011] The acquisition unit may acquire the load information including a rotation speed of the engine and a fuel injection amount per stroke of the engine.

[0012] The engine may further include a memory unit that stores the first ranges and the second ranges corresponding to each rotation range obtained by dividing the engine speed by a predetermined first number and each injection amount range obtained by dividing the fuel injection amount per engine stroke by a predetermined second number, and the setting unit may set the first ranges and the second ranges corresponding to the rotation range to which the engine speed included in the load information belongs and the injection amount range to which the fuel injection amount included in the load information belongs by referring to the memory unit.

[0013] The control device may further include a memory unit that stores the update time corresponding to each air volume range obtained by dividing the intake air volume by a predetermined third number, and the setting unit may set the update time corresponding to the air volume range to which the intake air volume acquired by the acquisition unit belongs.

[0014] An exhaust control method according to a second aspect of the present invention includes an acquisition step executed by a computer to acquire load information related to an engine load, an intake air amount of the engine, and an oxygen concentration downstream of a catalyst provided in an exhaust passage through which exhaust gas flows; a setting step to set a first range of an air-fuel ratio of a mixture generated in the engine and a second range of the oxygen concentration based on the load information, and to set update times for the first range and the second range based on the intake air amount of the engine; and a determination step to determine an air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that the oxygen concentration is included in the second range, wherein in the setting step, each time the update time has elapsed from the time when the update time was previously set, the first range and the second range are reset based on the load information acquired in the acquisition step at the time when the update time has elapsed, and the update time is reset based on the intake air amount acquired in the acquisition step at the time when the update time has elapsed. Effect of the Invention

[0015] The present invention has the effect of controlling exhaust so as to achieve appropriate NOx emissions and appropriate ammonia outflow amounts. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram for explaining an overview of an exhaust control system S according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram showing NH3 concentration and NOx concentration corresponding to air-fuel ratio. [Diagram 3] The operation when the update time is constant is shown. [Figure 4] The operation when the update time is changed according to the load on the engine 10 will be described. [Diagram 5] FIG. 2 is a diagram showing the configuration of an exhaust control device 50. [Figure 6] 4 is a diagram showing a processing sequence in the exhaust control device 50. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <Outline of the exhaust control system S> FIG. 1 is a diagram for explaining an outline of an exhaust control system S according to this embodiment. The exhaust control system S shown in FIG. 1 includes an engine 10, a turbocharger 11, an injector 12, an air cleaner 13, an intake pressure sensor 14, an intake passage 20, an exhaust passage 21, a purification device 30, a catalyst 31, an air-fuel ratio sensor 40, an O2 sensor 41, and an exhaust control device 50. The exhaust control system S has a function of determining the air-fuel ratio of the mixture generated inside the engine 10 based on the load of the engine 10. As an example, the load of the engine 10 is the rotation speed of the engine 10 and the fuel injection amount per stroke of the engine 10.

[0018] The engine 10 is, for example, a CNG (Compressed Natural Gas) engine, and is an internal combustion engine that burns and expands a mixture of fuel and intake air (air) to generate power. The supercharger 11 is, for example, a turbocharger, and uses the exhaust flow to increase the density of the intake air. The supercharger 11 has a compressor C provided in the intake passage 20 and a turbine T provided in the exhaust passage 21. The turbine T rotates by receiving the exhaust gas flowing through the exhaust passage 21. The compressor C is connected to the turbine T via a connecting shaft, and compresses the intake air by rotating together with the turbine T.

[0019] The injector 12 injects fuel in a fuel tank (not shown) into a combustion chamber in the engine 10. The air cleaner 13 is a filter that purifies the air supplied to the engine 10 by removing foreign matter such as dust and dirt contained in the air, and is provided upstream of an intake passage 20. The intake passage 20 is a passage through which the air supplied to the engine 10 (intake air) flows, and the exhaust passage 21 is a passage through which the exhaust gas from the engine 10 flows. The intake pressure sensor 14 is provided in the intake passage 20 and detects the air pressure of the air supplied to the engine 10 (intake pressure).

[0020] The purification device 30 is a device for purifying the exhaust gas of the engine 10, and contains a catalyst 31. The catalyst 31 is, for example, a three-way catalyst, and purifies hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the exhaust gas of the engine 10. Specifically, the catalyst 31 oxidizes hydrocarbons to water and carbon dioxide, oxidizes carbon monoxide to carbon dioxide, and reduces nitrogen oxides to nitrogen. In addition, the catalyst 31 generates ammonia when reducing nitrogen oxides to nitrogen.

[0021] The air-fuel ratio sensor 40 is provided downstream of the engine 10 and upstream of the catalyst 31 in the exhaust passage 21, and detects the air-fuel ratio of the mixture generated in the engine 10. The air-fuel ratio sensor 40 includes, for example, either an O2 sensor that detects the oxygen concentration contained in the exhaust gas of the engine 10, or an airflow sensor that measures the amount of air taken in by the engine 10. The O2 sensor 41 is provided downstream of the catalyst 31, and detects the oxygen concentration (hereinafter referred to as "O2 concentration") contained in the exhaust gas of the engine 10. The O2 sensor 41 outputs a voltage value corresponding to the O2 concentration. For example, the higher the O2 concentration, the lower the voltage value that the O2 sensor 41 outputs, and the lower the O2 concentration, the higher the voltage value that the O2 sensor 41 outputs.

[0022] The exhaust control device 50 is a housing including electronic components or a printed circuit board on which electronic components are mounted. The exhaust control device 50 executes processing to make the concentration of ammonia (hereinafter referred to as "NH3 concentration") and the concentration of nitrogen oxides (hereinafter referred to as "NOx concentration") contained in the exhaust gas discharged by the exhaust control system S fall within a predetermined range (e.g., less than 10 ppm). For example, the exhaust control device 50 determines an air-fuel ratio so that the NH3 concentration and the NOx concentration fall within the predetermined range, and causes the injector 12 to inject fuel based on the fuel injection amount corresponding to the air-fuel ratio.

[0023] FIG. 2 is a diagram showing the NH3 concentration and NOx concentration corresponding to the air-fuel ratio. FIG. 2(a) shows the NOx concentration corresponding to the air-fuel ratio, and FIG. 2(b) shows the NH3 concentration corresponding to the air-fuel ratio. FIG. 2(c) also shows the O2 concentration corresponding to the air-fuel ratio. The horizontal axis of FIG. 2 shows the air-fuel ratio detected by the air-fuel ratio sensor 40. The vertical axis of FIG. 2(a) shows the NOx concentration of the exhaust gas discharged by the exhaust control system S, the vertical axis of FIG. 2(b) shows the NH3 concentration of the exhaust gas, and the vertical axis of FIG. 2(c) shows the O2 concentration detected by the O2 sensor 41. In FIG. 2, the load of the engine 10 corresponding to the broken line shown by the solid line (hereinafter referred to as "low load") is lower than the load of the engine 10 corresponding to the broken line shown by the dashed line (hereinafter referred to as "high load").

[0024] As shown in FIG. 2(a), the NOx concentration increases as the air-fuel ratio becomes leaner (i.e., the ratio of fuel contained in the mixture is smaller). On the other hand, as shown in FIG. 2(b), the NH3 concentration decreases as the air-fuel ratio becomes leaner. Therefore, the exhaust control device 50 specifies a first range of the air-fuel ratio and a second range of the O2 concentration for setting the NOx concentration and the NH3 concentration within a predetermined range, and determines the air-fuel ratio so that the O2 concentration falls within the second range from the air-fuel ratio included in the first range. Specifically, when the engine 10 is at a low load, the exhaust control device 50 specifies the first range from the air-fuel ratio λ1 to the air-fuel ratio λ2 by referring to FIG. 2(a) and FIG. 2(b), and specifies the second range from the concentration P1 to the concentration P2 by referring to FIG. 2(c).

[0025] In this way, the exhaust control device 50 specifies the first and second ranges, and thus, when the engine 10 is at a low load, it is possible to determine the air-fuel ratio for keeping the NOx concentration and the NH3 concentration within the predetermined range. However, when the engine 10 is at a high load, the first range for keeping the NOx concentration and the NH3 concentration within the predetermined range is from the air-fuel ratio λ3 to the air-fuel ratio λ4, and the second range is from the concentration P3 to the concentration P4. Since these ranges deviate from the first and second ranges specified when the engine 10 is at a low load, if the ranges specified when the engine 10 is at a low load are continued to be used, it is not possible to keep the NOx concentration and the NH3 concentration within the predetermined range.

[0026] Therefore, the exhaust control device 50 resets the first range of the air-fuel ratio and the second range of the O2 concentration based on the load of the engine 10 every time a predetermined time (hereinafter referred to as the "update time") has elapsed. Specifically, if the engine 10 is at a low load at the time the update time has elapsed, the first range is reset from the air-fuel ratio λ1 to the air-fuel ratio λ2, and the second range is reset from the concentration P1 to the concentration P2. On the other hand, if the engine 10 is at a high load, the first range is reset from the air-fuel ratio λ3 to the air-fuel ratio λ4, and the second range is reset from the concentration P3 to the concentration P4. In this way, by resetting the first and second ranges based on the load of the engine 10 every time the update time has elapsed, the NOx concentration and NH3 concentration contained in the exhaust gas can be set within the predetermined ranges.

[0027] Incidentally, the catalyst 31 adsorbs oxygen generated when reducing NOx. The time required for the catalyst 31 to adsorb oxygen up to the amount of oxygen that it can adsorb (so-called O2 storage amount) is shorter as the amount of air supplied to the engine 10 is larger. That is, the time required for the first range of the air-fuel ratio to set the NOx concentration within a predetermined range, which corresponds to the O2 concentration detected by the O2 sensor 41, is applicable is shorter as the intake air amount of the engine 10 is larger (the load of the engine 10 is higher). For this reason, when the update time is constant, the higher the load of the engine 10 is, the shorter the time required for the catalyst 31 to adsorb oxygen becomes compared to the time required to reset the first range, and the catalyst 31 will discharge NOx without being able to reduce it.

[0028] Therefore, the exhaust control device 50 resets the update time based on the amount of air supplied to the engine 10, which is determined by integrating the intake pressure detected by the intake pressure sensor 14 and the update time, every time the update time elapses. FIGS. 3 and 4 are diagrams for explaining the operation of resetting the first range every time the update time elapses. FIG. 3 shows the operation when the update time is constant, and FIG. 4 shows the operation when the update time is changed according to the load of the engine 10. The horizontal axis of FIG. 3 indicates time. The vertical axis of FIG. 3(a) indicates the NH3 concentration and the O2 sensor output value (i.e., the voltage value output by the O2 sensor 41). For ease of explanation, the vertical axis of FIG. 3(b) indicates the median value of the first range. The vertical axis of FIG. 3(c) indicates the NOx concentration H when the engine 10 is under high load, and the NOx concentration L when the engine 10 is under low load. The horizontal and vertical axes in Fig. 4 are different from those in Fig. 3 in that the vertical axis in Fig. 4(b) indicates the median value H2 of the first range when the engine 10 is under high load and the median value L2 of the first range when the engine 10 is under low load, but are otherwise the same. In Fig. 3(c) and Fig. 4(c), the broken solid lines indicate the case when the engine 10 is under low load (i.e., when the amount of intake air of the engine 10 is small), and the broken dashed lines indicate the case when the engine 10 is under high load (i.e., when the amount of intake air of the engine 10 is large).

[0029] As shown in FIG. 3(a) and FIG. 3(b), the exhaust control device 50 reduces the NH3 concentration by resetting the first range from time 0 to time T3. Then, as shown in FIG. 3(a) and FIG. 3(c), when the engine 10 is at a low load, the exhaust control device 50 achieves an NH3 concentration lower than the target value A and an NOx concentration L lower than the target value N at a time after time T3. However, when the engine 10 is at a high load, the exhaust control device 50 discharges exhaust with a NOx concentration H higher than the target value N from time T3 to time T4 as shown in FIG. 3(c). Therefore, as shown in FIG. 4(b), when the intake air amount of the engine 10 is large, the exhaust control device 50 determines that the engine 10 is at a high load and shortens the update time of the first range. As a result, as shown in FIG. 4(c), even when the engine 10 is at a high load, exhaust with a NOx concentration H lower than the target value N can be discharged from time T3 to time T4.

[0030] As described above, the exhaust control device 50 resets the first range of the air-fuel ratio and the second range of the O2 concentration based on the load of the engine 10 each time the update time elapses, and resets the update time based on the intake air amount of the engine 10, thereby controlling the exhaust to achieve appropriate NOx emissions and NH3 emissions. 2, 3, and 4, for ease of explanation, the load of the engine 10 is divided into two (high load, low load) and the intake air amount of the engine 10 is divided into two (the intake air amount corresponding to the high load, and the intake air amount corresponding to the low load), but this is not limited to this. The exhaust control device 50 may divide the engine load into three or more and reset the first range and the second range corresponding to each divided load range. The exhaust control device 50 may divide the intake air amount of the engine 10 into three or more and reset the update time corresponding to each divided intake air amount range. The configuration and operation of the exhaust control device 50 will be described in detail below.

[0031] <Configuration of the exhaust control device 50> 5 is a diagram showing a configuration of the exhaust control device 50. The exhaust control device 50 has a storage unit 51 and a control unit 52. The control unit 52 has an acquisition unit 521, a setting unit 522, and a determination unit 523.

[0032] The storage unit 51 includes a storage medium such as a read only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), a solid state drive (SSD), etc. The storage unit 51 stores a program executed by the control unit 52.

[0033] The storage unit 51 stores various information for the control unit 52 to determine the air-fuel ratio of the mixture generated in the engine 10. The storage unit 51 stores, for example, a first range of the air-fuel ratio and a second range of the O2 concentration corresponding to each rotation range obtained by dividing the rotation speed of the engine 10 by a predetermined first number and each injection amount range obtained by dividing the fuel injection amount per stroke of the engine by a predetermined second number. The storage unit 51 stores, for example, an update time corresponding to each air amount range obtained by dividing the intake air amount of the engine 10 by a predetermined third number. The predetermined first number, the predetermined second number, and the predetermined third number are, for example, numbers from 8 to 16. The first range, the second range, and the update time stored in the storage unit 51 are data determined by an experiment or a simulation.

[0034] The control unit 52 is, for example, a processor such as a CPU (Central Processing Unit) or an ECU (Electronic Control Unit). The control unit 52 executes a program stored in the storage unit 51 to function as an acquisition unit 521, a setting unit 522, and a determination unit 523. The control unit 52 may be configured with one processor, or may be configured with multiple processors or a combination of one or more processors and an electronic circuit. The configuration of each unit realized by the control unit 52 will be described below.

[0035] The acquisition unit 521 acquires load information related to the load of the engine 10. The load information includes the rotation speed of the engine 10 and the fuel injection amount per stroke of the engine 10. The acquisition unit 521 acquires the rotation speed of the engine 10, for example, from a rotation speed sensor (not shown) provided on a flywheel, a camshaft, or a crank pulley of the engine 10. The acquisition unit 521 acquires the fuel injection amount per stroke of the engine 10 by calculating the fuel injection amount based on, for example, the displacement, the number of cylinders, the charging efficiency, and the air-fuel ratio of the engine 10. Hereinafter, the fuel injection amount per stroke of the engine 10 may be simply referred to as the "fuel injection amount".

[0036] The acquisition unit 521 acquires the intake air amount of the engine 10. For example, the acquisition unit 521 acquires the intake air amount by integrating the average value of the air pressure of the air supplied to the engine 10 detected by the intake pressure sensor 14 at the update time by the update time. The acquisition unit 521 also acquires the O2 concentration downstream of the catalyst 31 provided in the exhaust passage 21 through which the exhaust gas flows, from the O2 sensor 41. For example, the acquisition unit 521 acquires the O2 concentration by identifying the O2 concentration corresponding to the voltage value output by the O2 sensor 41. The acquisition unit 521 may acquire the air-fuel ratio of the mixture generated in the engine 10 from the air-fuel ratio sensor 40.

[0037] The setting unit 522 sets a first range of the air-fuel ratio of the mixture generated in the engine 10 and a second range of the O2 concentration based on the load information acquired by the acquisition unit 521, and sets update times for the first and second ranges based on the intake air amount acquired by the acquisition unit 521. The operation of setting the first range, the second range, and the update time will be described in detail later. By operating the setting unit 522 in this manner, the determination unit 523 can determine an air-fuel ratio suitable for the load of the engine 10 from the air-fuel ratio included in the first range so that the NOx concentration and the NH3 concentration are within the predetermined range.

[0038] The setting unit 522 sets the first range so as to be included in the second range corresponding to the load of the engine 10 indicated by the load information acquired by the acquisition unit 521 at a predetermined time, for example. The predetermined time is the time from the time when the update time was previously set to the time when the update time has elapsed. For example, the setting unit 522 specifies that the load of the engine 10 at the predetermined time is high by specifying the average value of the rotation speed of the engine 10 and the average value of the fuel injection amount per stroke of the engine 10 based on the multiple load information acquired by the acquisition unit 521 at the predetermined time. Having specified that the load of the engine 10 is high, the setting unit 522 sets the concentration P3 to the concentration P4 shown in FIG. 2(c) as the second range, and sets the air-fuel ratio λ3 to the air-fuel ratio λ4 shown in FIG. 2(c) as the first range.

[0039] For example, the setting unit 522 sets the first range so that the ratio of oxygen indicated by the air-fuel ratio included in the first range increases as the load of the engine 10 increases. For example, the setting unit 522 sets the air-fuel ratio included in the first range so that the air-fuel ratio included in the first range becomes leaner as the average value of the engine 10 rotation speed and the average value of the fuel injection amount of the engine 10 in a predetermined time increase. By operating the setting unit 522 in this manner, it is possible to easily suppress the concentration of NH3 contained in the exhaust gas.

[0040] For example, the setting unit 522 sets the second range such that the O2 concentration included in the second range decreases as the load of the engine 10 increases. For example, the setting unit 522 sets the second range such that the O2 concentration included in the second range decreases as the average value of the engine 10 rotation speed and the average value of the fuel injection amount of the engine 10 in a predetermined time increase. By operating in this manner, the setting unit 522 can set the first range according to the load of the engine 10. As a result, even if the load of the engine 10 changes, the NOx concentration and NH3 concentration of the exhaust can be kept within a predetermined range (for example, less than 10 ppm).

[0041] For example, the larger the intake air amount of the engine 10, the shorter the update time is set by the setting unit 522. Specifically, when the intake air amount of the engine 10 at a predetermined time is equal to or greater than a predetermined amount, the setting unit 522 determines that the engine 10 is in a high load state, and sets the update time to 2 seconds. On the other hand, when the intake air amount of the engine 10 is less than the predetermined amount, the setting unit 522 determines that the engine 10 is in a low load state, and sets the update time to 5 seconds. By operating the setting unit 522 in this manner, it is possible to prevent the amount of oxygen adsorbed by the catalyst 31 from reaching the maximum amount of oxygen that can be adsorbed before the update time has elapsed. As a result, it is possible to easily suppress the concentration of NOx contained in the exhaust gas.

[0042] The setting unit 522 may set a first range and a second range corresponding to the rotation range to which the rotation speed of the engine 10 included in the load information belongs and the injection amount range to which the fuel injection amount included in the load information belongs, among the multiple rotation ranges and multiple injection amount ranges stored in the storage unit 51. The setting unit 522, for example, specifies the average value of the rotation speed of the engine 10 and the average value of the fuel injection amount of the engine 10 in a predetermined time. The setting unit 522 sets the first range and the second range corresponding to the rotation range to which the specified average value of the rotation speed belongs and the injection amount range to which the specified average value of the fuel injection amount belongs, by referring to the storage unit 51. By operating in this manner, the setting unit 522 can divide the rotation speed and the fuel injection amount of the engine 10 into multiple regions, and therefore can set the first range and the second range in detail. Furthermore, the setting unit 522 can quickly set the first range and the second range by referring to the storage unit 51.

[0043] Furthermore, the setting unit 522 may set an update time corresponding to an air volume range to which the intake air volume acquired by the acquisition unit 521 belongs, among a plurality of air volume ranges stored in the storage unit 51. The setting unit 522, for example, specifies an average value of the intake air volume of the engine 10 at a predetermined time. The setting unit 522 sets an update time corresponding to an air volume range to which the specified average value of the intake air volume belongs, by referring to the storage unit 51. By operating in this manner, the setting unit 522 can divide the intake air volume into a plurality of regions, and therefore can set the update time in detail. Furthermore, the setting unit 522 can quickly set the update time by referring to the storage unit 51.

[0044] Furthermore, each time an update time has elapsed since the time when the update time was previously set, the setting unit 522 resets the first range and the second range based on the load information acquired by the acquisition unit 521 at the time when the update time has elapsed, and resets the update time based on the intake air amount. The setting unit 522 resets the first range and the second range corresponding to the rotation speed and the fuel injection amount of the engine 10 included in the load information acquired by the acquisition unit 521 at the time when the update time has elapsed, for example, by referring to the storage unit 51. The setting unit 522 resets the update time based on the intake air amount acquired by the acquisition unit 521 at the time when the update time has elapsed. Then, the setting unit 522 further resets the first range, the second range, and the update time at the time when the reset update time has elapsed from the time when the update time was reset. By operating in this manner, even if the load of the engine 10 changes, the setting unit 522 can set the first range, the second range, and the update time suitable for the load.

[0045] The setting unit 522 may reset the first range and the second range based on a plurality of load information from the time when the update time was previously set to the time when the update time has elapsed. The setting unit 522 may reset the update time based on a plurality of intake air amounts from the time when the update time was previously set to the time when the update time has elapsed. For example, at the time when the update time has elapsed, the setting unit 522 specifies the average value of the rotation speed of the engine 10 and the average value of the fuel injection amount of the engine 10 based on the load information from the time when the update time was previously set to the time when the update time has elapsed. The setting unit 522 resets the first range and the second range corresponding to the specified average value of the rotation speed of the engine 10 and the average value of the fuel injection amount by referring to the storage unit 51. By operating in this manner, the setting unit 522 can specify the load of the engine 10 with high accuracy, and therefore the probability of erroneously setting the first range and the second range can be reduced.

[0046] For example, at the time when the update time has elapsed, the setting unit 522 specifies the average value of the intake air amount from the time when the update time was previously set to the time when the update time has elapsed. The setting unit 522 resets the update time corresponding to the specified average value of the intake air amount by referring to the storage unit 51. By operating in this manner, the setting unit 522 can specify the intake air amount of the engine 10 with high accuracy, and therefore the probability of erroneously setting the update time can be reduced.

[0047] The determination unit 523 determines the air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that the O2 concentration is included in the second range, and causes the injector 12 to inject fuel based on the fuel injection amount corresponding to the air-fuel ratio. The fuel injection amount corresponding to the air-fuel ratio is stored in the memory unit 51.

[0048] The determination unit 523 determines the air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that the average value of the O2 concentration acquired by the acquisition unit 521 from a time a predetermined time before the current time to the current time is included in the second range. The time a predetermined time before the current time is, for example, the time closest to the current time among the times at which the update time was previously set. The determination unit 523 specifies the average value of the O2 concentration based on a plurality of O2 concentrations acquired by the acquisition unit 521 from a time a predetermined time before the current time to the current time. The determination unit 523 specifies the load of the engine 10 based on the load information acquired by the acquisition unit 521 from a time a predetermined time before the current time to the current time. Then, the determination unit 523 determines the air-fuel ratio so that the average value of the specified O2 concentration is included in the second range corresponding to the specified load.

[0049] The determination unit 523 determines an air-fuel ratio corresponding to the median of the second range (i.e., the median of the first range) from the air-fuel ratios included in the first range so that the average value of the O2 concentration becomes the median of the second range. For example, when the load of the engine 10 is high and the average value of the O2 concentration is concentration P3 shown in Fig. 2(c), the determination unit 523 determines the air-fuel ratio to be the median of air-fuel ratio λ3 and air-fuel ratio λ4 so that the average value of the O2 concentration approaches the median value of concentrations P3 and P4. By operating in this manner, the determination unit 523 can include the O2 concentration in the second range at a time later than the current time.

[0050] When the average value of the O2 concentration is lower or higher than the second range, the determination unit 523 determines the air-fuel ratio corresponding to the O2 concentration that has the smallest difference from the average value of the O2 concentration among the O2 concentrations included in the second range. For example, when the load of the engine 10 is high and the average value of the O2 concentration is lower than the concentration P3 shown in Fig. 2(c), the determination unit 523 determines the air-fuel ratio to be the air-fuel ratio λ3 corresponding to the concentration P3. By operating in this manner, the determination unit 523 can reduce the amount of change in the air-fuel ratio, so that the air-fuel ratio can be gradually converged to the target air-fuel ratio.

[0051] Furthermore, when the average value of the O2 concentration is lower or higher than the second range, the determination unit 523 may determine an air-fuel ratio corresponding to an O2 concentration that has the largest difference from the average value of the O2 concentration among the O2 concentrations included in the second range. For example, when the load of the engine 10 is high and the average value of the O2 concentration is lower than the concentration P3 shown in Fig. 2(c), the determination unit 523 determines the air-fuel ratio to be the air-fuel ratio λ4 corresponding to the concentration P4. By operating in this manner, the determination unit 523 can quickly converge to the target air-fuel ratio.

[0052] <Processing sequence in the exhaust control device 50> Fig. 6 is a diagram showing a processing sequence in the exhaust control device 50. The processing sequence shown in Fig. 6 shows an operation of the setting unit 522 to reset the first range, the second range, and the update time every time the update time elapses, and an operation of the determination unit 523 to determine the air-fuel ratio. Note that in Fig. 6, it is assumed that the update time is set to a time earlier than the current time.

[0053] The acquisition unit 521 acquires load information including the rotation speed of the engine 10 and the fuel injection amount per stroke of the engine 10 (S11). The acquisition unit 521 acquires the intake air amount of the engine 10 (S12). The acquisition unit 521 acquires the O2 concentration detected by the O2 sensor 41 (S13). The determination unit 523 identifies the average value of the O2 concentration acquired by the acquisition unit 521 from a time a predetermined time before the current time to the current time (S14).

[0054] If the update time has elapsed (YES in S15), the setting unit 522 specifies the rotation range to which the rotation speed of the engine 10 included in the load information acquired by the acquisition unit 521 belongs and the injection amount range to which the fuel injection amount included in the load information belongs. The setting unit 522 resets the second range (S16) and the first range (S17) corresponding to the specified rotation range and injection amount range by referring to the storage unit 51. The setting unit 522 resets the update time (S18) corresponding to the specified intake air amount by referring to the storage unit 51. If the update time has not elapsed (NO in S15), the setting unit 522 does not reset the first range, the second range, and the update time. That is, the exhaust control device 50 proceeds to the process of S19 without performing the processes of S16 to S18.

[0055] The determination unit 523 determines the air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that the identified average value of the O2 concentration is included in the second range reset by the setting unit 522 (S19). If an instruction to end the process has not been received (NO in S20), the exhaust control device 50 repeats the processes from S11 to S19. If an instruction to end the process has been received (YES in S20), the exhaust control device 50 ends the process.

[0056] <Modification> In the above description, the operation of the exhaust control system S having one catalyst has been exemplified, but is not limited to this. The exhaust control system S may be provided with a silencer (not shown) containing a catalyst different from the catalyst 31 downstream of the O2 sensor 41. The other catalyst is, for example, a three-way catalyst.

[0057] <Effects of the exhaust control device 50> As described above, the exhaust control device 50 includes a setting unit 522 that sets a first range of the air-fuel ratio of the mixture generated in the engine 10 and a second range of the O2 concentration based on the load information acquired by the acquisition unit 521, and sets update times for the first and second ranges based on the intake air amount of the engine 10 acquired by the acquisition unit 521, and a determination unit 523 that determines the air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that the O2 concentration falls within the second range. Then, each time an update time has elapsed since the time when the update time was previously set, the setting unit 522 resets the first and second ranges based on the load information acquired by the acquisition unit 521 at the time when the update time has elapsed, and resets the update time based on the intake air amount acquired by the acquisition unit 521 at the time when the update time has elapsed.

[0058] By configuring the exhaust control device 50 in this manner, the air-fuel ratio that brings the concentrations of NOx and NH3 contained in the exhaust to predetermined concentrations (e.g., less than 10 ppm) can be determined according to the load of the engine 10 (e.g., the engine 10 revolution speed, fuel injection amount, and intake air amount). As a result, the exhaust control device 50 can control the exhaust to achieve appropriate NOx emission and NH3 emission amounts.

[0059] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination combines the effect of the original embodiment. [Explanation of symbols]

[0060] 10 Engine 11. Turbocharger 12 Injector 13 Air cleaner 14 Intake pressure sensor 20 Intake passage 21 Exhaust duct 30 Purification Equipment 31 Catalyst 40 Air-fuel ratio sensor 41 O2 sensor 50 Exhaust control device 51 Storage section 52 Control section 521 Acquisition Department 522 Settings 523 Decision Section

Claims

1. an acquisition unit that acquires load information related to a load of an engine, an intake air amount of the engine, and an oxygen concentration downstream of a catalyst provided in an exhaust passage through which exhaust gas flows; a setting unit that sets a first range of an air-fuel ratio of an air-fuel mixture generated in the engine and a second range of an oxygen concentration so as to make the concentrations of ammonia and nitrogen oxides contained in the exhaust gas less than predetermined concentrations based on the load information, and sets update times for the first range and the second range based on an intake air amount of the engine; a determination unit that determines an air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that the oxygen concentration is included in the second range; having the setting unit resets the first range and the second range based on the load information acquired by the acquisition unit at the time when the update time has elapsed, each time the update time has elapsed since the time when the update time was previously set, and resets the update time based on the intake air amount acquired by the acquisition unit at the time when the update time has elapsed. Exhaust control device.

2. the setting unit sets the first range so as to be included in the second range corresponding to a load of the engine indicated by the load information acquired by the acquisition unit at a predetermined time; The determination unit determines an air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that an average value of the oxygen concentration acquired by the acquisition unit from a time before the predetermined time from the current time to the current time is included in the second range. The exhaust control device according to claim 1 .

3. the setting unit sets the first range such that the ratio of oxygen indicated by the air-fuel ratio included in the first range increases as the load of the engine increases. The exhaust control device according to claim 2.

4. the setting unit sets the second range such that the oxygen concentration included in the second range becomes smaller as the load of the engine becomes larger. The exhaust control device according to claim 2.

5. The setting unit sets the update time to be shorter as the intake air amount is larger. The exhaust control device according to claim 1 .

6. The acquisition unit acquires the load information including a rotation speed of the engine and a fuel injection amount per stroke of the engine. The exhaust control device according to claim 1 .

7. a storage unit that stores a first range and a second range corresponding to each rotation range obtained by dividing the engine rotation speed by a predetermined first number and each injection amount range obtained by dividing the fuel injection amount per one stroke of the engine by a predetermined second number, the setting unit sets the first range and the second range corresponding to a rotation range to which the engine speed included in the load information belongs and an injection amount range to which the fuel injection amount included in the load information belongs, by referring to the storage unit. The exhaust control device according to claim 6.

8. a storage unit that stores the update time corresponding to each air amount range obtained by dividing the intake air amount by a predetermined third number, the setting unit sets the update time corresponding to an air amount range to which the intake air amount acquired by the acquisition unit belongs. The exhaust control device according to claim 1 .

9. The computer executes an acquisition step of acquiring load information related to an engine load, an intake air amount of the engine, and an oxygen concentration downstream of a catalyst provided in an exhaust passage through which exhaust gas flows; a setting step of setting a first range of an air-fuel ratio of the mixture generated in the engine and a second range of the oxygen concentration so as to make the respective concentrations of ammonia and nitrogen oxide contained in the exhaust gas less than predetermined concentrations based on the load information, and setting update times for the first range and the second range based on an intake air amount of the engine; determining an air-fuel ratio of the mixture from the air-fuel ratio included in the first range so that the oxygen concentration is included in the second range; having In the setting step, each time the update time elapses from a time when the update time was previously set, the first range and the second range are reset based on the load information acquired in the acquisition step at the time when the update time has elapsed, and the update time is reset based on the intake air amount acquired in the acquisition step at the time when the update time has elapsed. Emissions control methods.

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