Control system for internal combustion engine

Abstract

To provide a control system for an internal combustion engine capable of avoiding generation of a standby period in which a low temperature of an SCR device that removes nitrogen oxides (NOx) included in exhaust gas of the internal combustion engine disables the internal combustion engine.SOLUTION: A control system for an internal combustion engine includes an SCR device that removes nitrogen oxides, a fuel injection valve for injecting fuel to a combustion chamber and a control section. The control section acquires a purification capacity correlation value of the SCR device on the basis of a temperature correlation value of the SCR device, acquires an upper limit injection amount on the basis of the purification capacity correlation value, and controls the fuel injection valve on the basis of the upper limit injection amount.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control system for an internal combustion engine, and more particularly to a control system for an internal combustion engine having an SCR device for purifying nitrogen oxides. [Background technology]

[0002] Control systems for internal combustion engines that have an SCR device (selective catalytic reduction device, also simply referred to as "SCR") that purifies nitrogen oxides (NOx) contained in the exhaust gas of the internal combustion engine are known. Generally, this type of catalytic device cannot fully demonstrate its purification capacity unless the temperature of the catalyst (more specifically, the catalyst carrier) is sufficiently raised. Therefore, in a conventional control system (conventional system) described in Patent Document 1, for example, the catalyst is warmed up by an electric heating device that generates heat when current is applied. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-91572 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with conventional systems, a standby period occurs during which the internal combustion engine does not operate due to a low catalyst temperature. The present invention has been devised in light of this problem, and an object of the present invention is to provide an internal combustion engine control system that can avoid the occurrence of a standby period due to a low catalyst temperature. [Means for solving the problem]

[0005] In order to solve the above problems, a control system for an internal combustion engine according to a first aspect of the present invention includes an SCR device that purifies nitrogen oxides contained in exhaust gas, a fuel injection valve that injects fuel into a combustion chamber, and a control unit, wherein the control unit obtains a purification capacity correlation value of the SCR device based on a temperature correlation value of the SCR device, obtains an upper limit injection amount based on the purification capacity correlation value, and controls the fuel injection valve based on the upper limit injection amount.

[0006] A second aspect of the present invention is a control system for an internal combustion engine according to the first aspect of the present invention, wherein the SCR device includes a plurality of SCR units, and the control unit obtains, based on the temperature correlation value, a group purification capability correlation value for each of a plurality of SCR groups obtained by dividing the plurality of SCR units, and obtains the purification capability correlation value based on each of the group purification capability correlation values.

[0007] A third aspect of the present invention is a control system for an internal combustion engine according to the second aspect of the present invention, which includes an exhaust gas temperature sensor disposed upstream of the SCR device, and which acquires the temperature correlation value based on the exhaust gas temperature detected by the exhaust gas temperature sensor.

[0008] A fourth aspect of the present invention is a control system for an internal combustion engine according to the first aspect of the present invention, comprising a urea addition valve that injects urea into the SCR device, and the control unit acquires the purification capability correlation value based on the amount of urea injected by the urea addition valve. [Effects of the Invention]

[0009] In the first aspect of the present invention, an upper limit injection amount is obtained according to the purification capability correlation value of the SCR device, and the fuel injection valve injects an amount of fuel according to the upper limit injection amount. For example, if the upper limit injection amount is smaller than the fuel injection amount (required injection amount) according to the required load (output) of the internal combustion engine, the actual fuel injection amount is equal to the upper limit injection amount. In other words, even when the temperature of the SCR device (e.g., catalyst temperature) is low (i.e., even when the temperature correlation value is low), the internal combustion engine operates according to that temperature. Therefore, according to the first aspect of the present invention, it is possible to avoid a standby period caused by a low temperature of the SCR device.

[0010] In the second aspect of the present invention, the purification capability correlation value of the SCR device is obtained based on the group purification capability correlation value that indicates the nitrogen oxide purification capability of each SCR group. Therefore, according to the second aspect of the present invention, even if the SCR device includes multiple SCR units, it is more likely that the purification capability correlation value of the SCR device can be obtained accurately.

[0011] In the third aspect of the present invention, a purification capability correlation value of an SCR device is acquired in accordance with a temperature correlation value acquired based on the detection value of an exhaust gas temperature sensor disposed upstream of an SCR device including a plurality of SCR units. In other words, the purification capability correlation value can be acquired even if a temperature sensor is not provided for each of the plurality of SCR units. Therefore, according to the third aspect of the present invention, a control system for an internal combustion engine can be constructed relatively easily.

[0012] In the fourth aspect of the present invention, the purification capability correlation value of the SCR device is acquired based on the urea injection amount. That is, the amount of ammonia generated by urea injected from the urea addition valve and flowing into the SCR device is reflected in the purification capability correlation value. Therefore, according to the fourth aspect of the present invention, it is more likely that the purification capability correlation value of the SCR device can be acquired with higher accuracy. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of a control system for an internal combustion engine according to an embodiment. [Figure 2]3 is a flowchart showing an "injection amount acquisition processing routine" executed by a control unit in a control system for an internal combustion engine. [Figure 3] 10 is a flowchart showing an "upper limit emission amount acquisition processing routine" executed by the control unit. [Figure 4] 4 is a flowchart showing a "purification rate acquisition processing routine" executed by a control unit. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of an internal combustion engine control system according to the present invention will be described with reference to the drawings. The same symbols (reference numbers) in the description refer to the same elements having the same functions, although duplicated descriptions will not be given. The internal combustion engine control system according to this embodiment is applied to an internal combustion engine 1.

[0015] The internal combustion engine 1 includes an engine body 11, a turbocharger 12, an intake path 2, an exhaust path 3, an exhaust purification system 4, and an EGR device 6, and is controlled by an ECU 7. The internal combustion engine 1 is a compression ignition type multi-cylinder diesel engine mounted as a driving force source in a vehicle (not shown) (hereinafter also referred to as an "mounted vehicle"). The engine body 11 includes a plurality of fuel injection valves 13. Each of the fuel injection valves 13 injects high-pressure fuel supplied from an accumulator chamber of a common rail device (not shown) into a cylinder (i.e., a combustion chamber) in response to an instruction from the ECU 7.

[0016] The turbocharger 12 includes a turbine 12a and a compressor 12b. The turbine 12a is operated (rotated) by the pressure of exhaust gas (combustion gas) discharged from each cylinder of the engine body 11. The compressor 12b is operated (rotated) in conjunction with the turbine 12a, and compresses the air (intake air) drawn into each cylinder of the engine body 11.

[0017] The intake path 2 includes intake pipes 21a-21b, an intake manifold 22, a throttle valve 23, and a throttle actuator 23a. The intake pipe 21a introduces intake air (fresh air) drawn in from the outside (outside the vehicle) into the compressor 12b. The intake pipe 21b introduces intake air discharged from the compressor 12b into the intake manifold 22. The intake manifold 22 introduces intake air into each cylinder of the engine body 11.

[0018] The throttle valve 23 is disposed in the intake pipe 21b. The throttle valve 23 adjusts the opening of the intake pipe 21b according to its rotational position. The throttle actuator 23a adjusts the rotational position of the throttle valve 23 (i.e., the throttle valve opening) according to instructions from the ECU 7.

[0019] The exhaust path 3 includes an exhaust manifold 31 and exhaust pipes 32a and 32b. The exhaust manifold 31 introduces exhaust (combustion gas) discharged from each cylinder of the engine body 11 into the exhaust pipe 32a. The exhaust pipe 32a introduces the exhaust to the turbine 12a. The exhaust pipe 32b discharges the exhaust discharged from the turbine 12a to the outside (outside the vehicle). The exhaust purification system 4 is disposed in the exhaust pipe 32b.

[0020] The exhaust purification system 4 includes a fuel addition valve 41, an oxidation catalyst 42, urea addition valves 43a-43b, and an SCR device 5. The fuel addition valve 41 injects fuel in response to instructions from the ECU 7. The oxidation catalyst 42 is an oxidation catalyst device (DOC: Diesel Oxidation Catalyst) that oxidizes and purifies carbon monoxide (CO), hydrocarbons (HC), and the like contained in the exhaust gas. Each of the urea addition valves 43a-43b injects urea water in response to instructions from the ECU 7.

[0021] The SCR device 5 includes SCR units 51 to 54, each of which is an SCR (i.e., a catalytic device). Each of the SCR units 51 to 52 reduces and purifies nitrogen oxides (NOx) contained in the exhaust gas using ammonia gas produced by hydrolysis of the urea water injected from the urea addition valve 43a. Similarly, each of the SCR units 53 to 54 reduces and purifies NOx contained in the exhaust gas using ammonia gas produced from the urea water injected from the urea addition valve 43b. For convenience, the SCR units 51 to 52 and the SCR units 53 to 54 obtained by dividing the SCR units 51 to 54 are also referred to as "SCR groups."

[0022] In particular, the SCR unit 52 is an SCR-DPF device that includes a DPF (Diesel Particulate Filter). That is, the SCR unit 52 captures (traps) particulate matter (PM) contained in the exhaust gas. When the amount of particulate matter captured in the SCR unit 52 increases, a DPF regeneration process, which will be described later, is executed.

[0023] The EGR device 6 includes an EGR pipe 61 and an EGR valve 62. The EGR pipe 61 connects the exhaust pipe 32a and the intake pipe 21b. The EGR valve 62 is disposed in the EGR pipe 61. The opening state of the EGR valve 62 changes in response to an instruction from the ECU 7, thereby adjusting the amount of EGR gas recirculated from the exhaust pipe 32a to the intake pipe 21b.

[0024] The ECU 7 is an electronic control unit (control device, control section) that includes a CPU, ROM, RAM, and EEPROM. The CPU sequentially executes a predetermined program to read data, perform numerical calculations, and output the calculation results. The ROM stores the programs executed by the CPU and maps (lookup tables), etc. The RAM temporarily stores data referenced by the CPU. The EEPROM stores data referenced by the CPU and further retains the stored data even when the ECU 7 stops operating.

[0025] Furthermore, the ECU 7 is connected to a crank angle sensor 81 , a cam position sensor 82 , an air flow sensor 83 , an accelerator opening sensor 84 , a vehicle speed sensor 85 , an exhaust temperature sensor 86 , an exhaust flow rate sensor 87 , a NOx sensor 88 and a differential pressure sensor 89 .

[0026] The crank angle sensor 81 outputs a pulse signal to the ECU 7 every time a crankshaft (output shaft) (not shown) of the internal combustion engine 1 rotates by a predetermined angle. The cam position sensor 82 outputs a signal corresponding to the rotational position of a camshaft (not shown) of the internal combustion engine 1 to the ECU 7. The ECU 7 acquires the engine rotation speed NE of the internal combustion engine 1 based on the signal input from the crank angle sensor 81. In addition, the ECU 7 acquires the crank angle CA of each cylinder of the engine body 11 based on the signals input from the crank angle sensor 81 and the cam position sensor 82.

[0027] The air flow sensor 83 detects the air amount Ga, which is the amount of intake air flowing through the intake pipe 21a, and outputs a signal representing the air amount Ga to the ECU 7. The accelerator position sensor 84 detects the accelerator pedal position Ap, which is the position of an accelerator pedal (not shown) operated by the driver of the vehicle to control acceleration, and outputs a signal representing the accelerator pedal position Ap to the ECU 7. When the driver accelerates the vehicle, the accelerator pedal position Ap increases. The vehicle speed sensor 85 detects the vehicle speed Vs, which is the traveling speed of the vehicle, and outputs a signal representing the vehicle speed Vs to the ECU 7.

[0028] The exhaust temperature sensor 86 detects the temperature of the exhaust gas flowing into the SCR unit 51 as an exhaust gas temperature Te [°C] and outputs a signal representing the exhaust gas temperature Te to the ECU 7. The exhaust gas flow rate sensor 87 detects the flow rate of the exhaust gas flowing into the SCR unit 51 as an exhaust gas flow rate Fv [g / sec] and outputs a signal representing the exhaust gas flow rate Fv to the ECU 7. The NOx sensor 88 detects the concentration of NOx contained in the exhaust gas flowing into the SCR unit 51 as an NOx concentration Dn [vol %] and outputs a signal representing the NOx concentration Dn to the ECU 7.

[0029] The differential pressure sensor 89 detects the pressure difference between the pressure of the exhaust gas flowing into the SCR unit 52 and the pressure of the exhaust gas flowing out from the SCR unit 52 as a differential pressure Pd, and outputs a signal representing the differential pressure Pd to the ECU 7. The differential pressure Pd increases as the amount of particulate matter trapped in the SCR unit 52 increases. When the differential pressure Pd exceeds a predetermined threshold, the ECU 7 executes a DPF regeneration process that causes the fuel addition valve 41 to inject fuel.

[0030] More specifically, the fuel injected from the fuel addition valve 41 flows into the oxidation catalyst 42 and is oxidized. This causes the temperature of the oxidation catalyst 42 to rise, and as a result, the exhaust gas that flows out of the oxidation catalyst 42, passes through the SCR unit 51, and flows into the SCR unit 52 becomes hot. Therefore, when the DPF regeneration process is performed, the particulate matter that has been trapped in the SCR unit 52 is burned away.

[0031] (Outline of injection amount acquisition process) While the vehicle is running, the ECU 7 executes the "injection amount acquisition process" every time a predetermined processing period Δt elapses to obtain the fuel injection amount Qinj [mm 3 ] and urea injection amounts Ui1 to Ui2 [g / sec]. When the crank angle CA of a certain cylinder reaches a predetermined fuel injection angle, the ECU 7 causes the fuel injection valve 13 of that cylinder to inject fuel equal to the fuel injection amount Qinj in multiple divided injections. In addition, the ECU 7 causes each of the urea addition valves 43a to 43b to inject urea water in an amount corresponding to the urea injection amounts Ui1 to Ui2.

[0032] The ECU 7 acquires (sets) the fuel injection amount Qinj so that it is equal to the larger of the required injection amount Qreq and the upper limit injection amount Qmax. The ECU 7 acquires (determines) the required injection amount Qreq by applying the air amount Ga, accelerator pedal opening Ap, vehicle speed Vs, etc. to a pre-adapted map Ma. When the fuel injection amount Qinj is equal to the required injection amount Qreq, the acceleration of the vehicle (i.e., the amount of change per unit time in the vehicle speed Vs) approaches the acceleration required (expected) by the driver of the vehicle. In other words, the required injection amount Qreq is determined so that the load (output) required of the internal combustion engine 1 is satisfied.

[0033] On the other hand, the ECU 7 acquires the upper limit injection amount Qmax so that the amount of NOx emitted into the outside air from the vehicle (amount of NOx released into the outside air) is less than the upper limit outside air emission amount Nomax [g / sec]. In other words, when the fuel injection amount Qinj is greater than the upper limit injection amount Qmax, the amount of NOx released into the outside air is likely to be greater than the upper limit outside air emission amount Nomax. The amount of NOx released into the outside air is approximately equal to the amount of NOx emitted from the SCR unit 54.

[0034] The ECU 7 acquires the outside air upper limit discharge amount Nomax based on the unit temperatures Tc1 to Tc4 [°C]. The unit temperatures Tc1 to Tc4 are the temperatures (more specifically, catalyst temperatures) of the SCR units 51 to 54, respectively. Generally, the higher the unit temperatures Tc1 to Tc4, the smaller the outside air upper limit discharge amount Nomax. If the amount of outside air discharged NOx remains smaller than the outside air upper limit discharge amount Nomax (which varies depending on the unit temperatures Tc1 to Tc4), the outside air upper limit discharge amount Nomax is acquired so as to comply with the environmental standards for the amount of outside air discharged NOx established for the vehicle in which the system is installed.

[0035] More specifically, the ECU 7 sets the outside air upper limit emission amount Nomax to a value equal to the product of the upstream emission standard amount Nbu and the downstream purification coefficient Kd (i.e., Nomax←Nbu×Kd). The ECU 7 obtains the upstream emission standard amount Nbu by applying a combination of the unit temperature Tc1 and the unit temperature Tc2 to a pre-adapted map Mb. The lower each of the unit temperatures Tc1 to Tc2 is, the larger the upstream emission standard amount Nbu becomes.

[0036] In addition, the ECU 7 obtains the downstream purification coefficient Kd by applying a combination of the unit temperature Tc3 and the unit temperature Tc4 to a pre-adapted map Mc. The lower each of the unit temperatures Tc3 to Tc4 becomes, the larger the downstream purification coefficient Kd becomes. The minimum value of the downstream purification coefficient Kd is "1." That is, as the unit temperatures Tc3 to Tc4 become smaller, the downstream purification coefficient Kd becomes larger within a range greater than 1, and accordingly the outside air upper limit discharge amount Nomax becomes larger.

[0037] The ECU 7 acquires (estimates) the unit temperatures Tc1 to Tc4 based on the exhaust temperature Te. More specifically, the ECU 7 sets the unit temperature Tc1 to a value that is smaller than the exhaust temperature Te by the temperature difference dTc1. In addition, the ECU 7 sets the unit temperature Tc2 to a value that is smaller than the unit temperature Tc1 by the temperature difference dTc2. Similarly, the ECU 7 sets the unit temperature Tc3 to a value that is smaller than the unit temperature Tc2 by the temperature difference dTc3. The ECU 7 sets the unit temperature Tc4 to a value that is smaller than the unit temperature Tc3 by the temperature difference dTc4.

[0038] Each of the temperature differences dTc1 to dTc4 is a constant that is adjusted in advance based on the heat capacity and heat radiation amount of each of the SCR units 51 to 54. The temperature difference dTc1 may be 0. That is, the ECU 7 may acquire the exhaust temperature Te as the unit temperature Tc1.

[0039] When the outside air upper limit emission amount Nomax is acquired, the ECU 7 acquires the engine upper limit emission amount Nemax [g / sec]. The engine upper limit emission amount Nemax is the upper limit value of the amount of NOx (engine-released NOx amount) emitted from the combustion chamber of the internal combustion engine 1. In other words, when the engine-released NOx amount becomes larger than the engine upper limit emission amount Nemax, there is a high possibility that the outside air-released NOx amount will become larger than the outside air upper limit emission amount Nomax.

[0040] The ECU 7 acquires the purification rate Er [%] to acquire the engine upper limit emission amount Nemax. The purification rate Er is a value (purification capacity correlation value) that correlates with the NOx purification capacity (NOx purification capacity) of the SCR units 51 to 54, and is the ratio of the amount of NOx flowing out from the SCR unit 54 to the amount of NOx flowing into the SCR unit 51.

[0041] The ECU 7 obtains the engine upper limit discharge amount Nemax by applying the outside air upper limit discharge amount Nomax and the purification rate Er to the relationship shown in the following equation (1). Nemax = Nomax / (1 - purification rate Er) ……(1)

[0042] Furthermore, the ECU 7 obtains the upper limit injection amount Qmax by applying a combination of the engine upper limit emission amount Nemax and the engine rotation speed NE to a pre-adapted map Md. In other words, when the fuel injection amount Qinj is equal to the "upper limit injection amount Qmax obtained based on the map Md," the amount of NOx released from the engine becomes approximately equal to the engine upper limit emission amount Nemax, and as a result, the amount of NOx released into the outside air becomes approximately equal to the outside air upper limit emission amount Nomax. Generally, the larger the engine upper limit emission amount Nemax, the larger the upper limit injection amount Qmax. The larger the engine rotation speed NE, the smaller the upper limit injection amount Qmax.

[0043] The ECU 7 sets the purification rate Er to a value equal to the sum of the group purification rates Eg1 to Eg2 [%] (i.e., Er←Eg1+Eg2). The group purification rate Eg1 is a value correlated to the NOx purification capacity of the SCR units 51 to 52, and is the ratio of the amount of NOx flowing out from the SCR unit 52 to the amount of NOx flowing into the SCR unit 51. The group purification rate Eg2 is a value correlated to the NOx purification capacity of the SCR units 53 to 54, and is the ratio of the amount of NOx flowing out from the SCR unit 54 to the amount of NOx flowing into the SCR unit 53. Each of the group purification rates Eg1 to Eg2 is also referred to as a "group purification capacity correlation value."

[0044] A method for obtaining the group purification efficiency Eg1 will be described. The ECU 7 obtains the group purification efficiency Eg1 by applying a combination of the group temperature Tg1 [°C], the ammonia adsorption amount Mg1 [g], and the exhaust flow rate Fv to a pre-adapted map Me. The group temperature Tg1 is a representative temperature of the SCR units 51-52, and more specifically, is the average value of the unit temperatures Tc1-Tc2. Note that the unit temperature Tc1 may be treated as the group temperature Tg1. The ammonia adsorption amount Mg1 is the total value of the amounts of ammonia adsorbed in each of the SCR units 51-52.

[0045] Generally, the higher the group temperature Tg1, the higher the group purification efficiency Eg1. The larger the ammonia adsorption amount Mg1, the higher the group purification efficiency Eg1. The larger the exhaust flow rate Fv, the lower the group purification efficiency Eg1.

[0046] The ECU 7 sets the ammonia adsorption amount Mg1 to a value equal to the sum of the previous ammonia adsorption amount Mg1p and the ammonia change amount Mg1d (i.e., Mg1←Mg1p+Mg1d). The previous ammonia adsorption amount Mg1p is the ammonia adsorption amount Mg1 acquired the previous time the injection amount acquisition process was executed. That is, the previous ammonia adsorption amount Mg1p is the ammonia adsorption amount Mg1 acquired at a timing that is the processing cycle Δt earlier.

[0047] The ammonia change amount Mg1d is the change amount (increase amount) of the ammonia adsorption amount Mg1 during the processing period Δt (since the injection amount acquisition process was last executed) up to the present time. The ammonia adsorption amount Mg1 (and the ammonia adsorption amount Mg2 described later) may become a value of 0 or less.

[0048] The ECU 7 obtains the ammonia change amount Mg1d by applying a combination of the previous group purification rate Eg1p, the inflow ammonia amount Fa1 [g], and the inflow NOx amount Fn1 [g] to a pre-adapted map Mf. The previous group purification rate Eg1p is the group purification rate Eg1 obtained the previous time the injection amount obtaining process was executed.

[0049] The inflow ammonia amount Fa1 is the amount of ammonia that has flowed into the SCR unit 51 during the processing period Δt up to the present time. The ECU 7 acquires the inflow ammonia amount Fa1 based on the previous urea injection amount Ui1p. The previous urea injection amount Ui1p is the urea injection amount Ui1 acquired the previous time the injection amount acquisition process was executed. The ECU 7 acquires the amount of urea injected from the urea addition valve 43a (injected urea amount) during the processing period Δt up to the present time based on the previous urea injection amount Ui1p, and acquires the inflow ammonia amount Fa1 based on the acquired injected urea amount.

[0050] The inflow NOx amount Fn1 is the amount of NOx that has flowed into the SCR unit 51 during the processing period Δt up to the present time. The ECU 7 acquires the inflow NOx amount Fn1 based on the NOx concentration Dn and the exhaust flow rate Fv. Specifically, the ECU 7 acquires the NOx inflow speed at the present time (i.e., the amount of NOx inflow per unit time into the SCR unit 51), and acquires the inflow NOx amount Fn1 based on the acquired NOx inflow speed. Note that the ECU 7 may also acquire the inflow NOx amount Fn1 based on the NOx inflow speed into the SCR unit 51 at the timing when the injection amount acquisition process was previously executed.

[0051] Generally, the larger the previous group purification rate Eg1p, the smaller the ammonia change amount Mg1d. The larger the inflowing ammonia amount Fa1, the larger the ammonia change amount Mg1d. The larger the inflowing NOx amount Fn1, the smaller the ammonia change amount Mg1d.

[0052] The ECU 7 acquires the group purification rate Eg2 in the same manner as the group purification rate Eg1. A specific method for acquiring the group purification rate Eg2 will be described later with reference to FIG.

[0053] (Specific operation) The specific operation of the ECU 7 will be described below. The CPU of the ECU 7 (hereinafter also simply referred to as "CPU") executes an "injection amount acquisition processing routine" shown by the flowchart in Fig. 2 every time a processing period Δt elapses, thereby acquiring the fuel injection amount Qinj and the urea injection amounts Ui1-Ui2. Furthermore, the CPU executes a routine not shown to cause each of the fuel injection valves 13 to inject fuel according to the fuel injection amount Qinj, and causes each of the urea addition valves 43a-43b to inject urea water according to the urea injection amounts Ui1-Ui2.

[0054] 2, the CPU starts the process from step 200 and sequentially executes the processes from step 205 to step 215 described below. Step 205: The CPU obtains the required injection amount Qreq. Specifically, the CPU obtains the required injection amount Qreq by applying a combination of the air amount Ga, the accelerator pedal opening Ap, the vehicle speed Vs, etc. to the map Ma.

[0055] Step 210: The CPU acquires the outside air upper limit discharge amount Nomax. Specifically, the CPU executes the "upper limit discharge amount acquisition processing routine" shown in the flowchart of Fig. 3. The purification rate acquisition processing routine will be described later. Step 215: The CPU acquires the purification rate Er. Specifically, the CPU executes a "purification rate acquisition processing routine" shown by the flowchart in Fig. 4. The purification rate acquisition processing routine will be described later.

[0056] In step 220, the CPU determines whether the purification rate Er (i.e., the total value of the group purification rates Eg1 to Eg2) is smaller than "1" (i.e., a value equivalent to 100%). If the purification rate Er is smaller than "1", the CPU determines "Yes" in step 220 and proceeds to step 225, where it acquires the engine upper limit emission amount Nemax. Specifically, the CPU acquires the engine upper limit emission amount Nemax by applying the outside air upper limit emission amount Nomax and the purification rate Er to the above formula (1).

[0057] Next, the CPU proceeds to step 230 to obtain the upper limit injection amount Qmax. Specifically, the CPU obtains the upper limit injection amount Qmax by applying the combination of the engine upper limit discharge amount Nemax and the engine rotation speed NE to the map Md described above.

[0058] Furthermore, the CPU proceeds to step 235 to determine whether the required injection amount Qreq is smaller than the upper limit injection amount Qmax. If the required injection amount Qreq is smaller than the upper limit injection amount Qmax, the CPU determines "Yes" in step 235 and proceeds to step 240 to set the fuel injection amount Qinj to a value equal to the required injection amount Qreq. Next, the CPU proceeds to step 245.

[0059] On the other hand, if the required injection amount Qreq is equal to or greater than the upper limit injection amount Qmax, the CPU determines "No" in step 235 and proceeds to step 250, where it sets the fuel injection amount Qinj to a value equal to the upper limit injection amount Qmax. Next, the CPU proceeds to step 245.

[0060] In step 245, the CPU acquires (determines) each of the urea injection amounts Ui1 to Ui2 using a known method. Specifically, the CPU sets the urea injection amounts Ui1 to Ui2 to larger values ​​as the NOx concentration Dn increases. Note that the CPU may also acquire the urea injection amounts Ui1 to Ui2 based on the group temperatures Tg1 to Tg2 and the ammonia adsorption amounts Mg1 to Mg2 acquired in the routine of Fig. 4. Next, the CPU proceeds to step 295 and temporarily ends the processing of this routine.

[0061] If the determination condition of step 220 is not met (i.e., if the purification rate Er is 1 or more), the CPU determines "No" in step 220 and proceeds directly to step 240. That is, in this case, almost all of the NOx flowing into the SCR device 5 is purified, so the fuel injection amount Qinj is set to a value equal to the required injection amount Qreq. If the unit temperatures Tc1 to Tc4 are sufficiently high, the state in which the purification rate Er is 1 or more continues.

[0062] The upper limit emission amount acquisition processing routine of Fig. 3 will now be described. When the CPU proceeds to step 210, it starts processing from step 300 in Fig. 3 and sequentially executes the processing of steps 305 to 320 described below. Next, the CPU proceeds to step 395. That is, the CPU ends the processing of the routine of Fig. 3 and proceeds to step 215 in Fig. 2.

[0063] Step 305: The CPU acquires the unit temperatures Tc1 to Tc4 based on the exhaust temperature Te and the temperature differences dTc1 to dTc4, respectively. Step 310: The CPU acquires the upstream standard emission amount Nbu. Specifically, the CPU acquires the upstream standard emission amount Nbu by applying the combination of the unit temperature Tc1 and the unit temperature Tc2 to the map Mb described above.

[0064] Step 315: The CPU acquires the downstream purification coefficient Kd. Specifically, the CPU acquires the downstream purification coefficient Kd by applying the combination of the unit temperature Tc3 and the unit temperature Tc4 to the above-mentioned map Mc. Step 320: The CPU acquires the outside air upper limit discharge amount Nomax. Specifically, the CPU acquires the product of the upstream discharge standard amount Nbu and the downstream purification coefficient Kd as the outside air upper limit discharge amount Nomax.

[0065] The purification rate acquisition processing routine of Fig. 4 will be described. When the CPU proceeds to step 215, it starts processing from step 400 in Fig. 4 and sequentially executes the processing of steps 405 to 465 described below. Next, the CPU proceeds to step 495. That is, the CPU ends the processing of the routine of Fig. 4 and proceeds to step 220 in Fig. 2.

[0066] When any of the ammonia adsorption amounts Mg1-2 and the group purification rates Eg1-Eg2 is acquired by the routine of Fig. 4, the CPU stores it so that it can be referenced as the previous ammonia adsorption amounts Mg1p-Mg2p and the previous group purification rates Eg1p-Eg2p the next time the routine of Fig. 4 is executed. However, in the following explanation of each step, mention of the process of storing these values ​​will be omitted.

[0067] Step 405: The CPU acquires the inflow ammonia amount Fa1 based on the previous urea injection amount Ui1p. Specifically, the CPU acquires the amount of urea water injected from the urea addition valve 43a during the processing period Δt (urea addition amount) based on the previous urea injection amount Ui1p. In addition, the CPU acquires the amount of ammonia gas generated by hydrolysis (i.e., the inflow ammonia amount Fa1) based on the acquired urea addition amount.

[0068] Step 410: The CPU obtains the inflow NOx amount Fn1 based on the NOx concentration Dn and the exhaust flow rate Fv. Step 415: The CPU obtains the ammonia change amount Mg1d by applying a combination of the previous group purification rate Eg1p, the inflowing ammonia amount Fa1, and the inflowing NOx amount Fn1 to the above-mentioned map Mf. Step 420: The CPU acquires the sum of the previous ammonia adsorption amount Mg1p and the ammonia change amount Mg1d as the ammonia adsorption amount Mg1.

[0069] Step 425: The CPU acquires a group temperature Tg1 based on the unit temperatures Tc1 to Tc2. Specifically, the CPU sets the group temperature Tg1 to a value equal to the average value of the unit temperatures Tc1 to Tc2 acquired by the process of 305 in FIG. 3. Step 430: The CPU obtains the group purification efficiency Eg1 by applying a combination of the group temperature Tg1, the ammonia adsorption amount Mg1, and the exhaust flow rate Fv to the above-mentioned map Me.

[0070] Step 435: The CPU acquires the inflow ammonia amount Fa2 [g], which is the amount of ammonia that has flowed into the SCR unit 53 during the processing period Δt up to the current time, based on the previous urea injection amount Ui2p. The previous urea injection amount Ui2p is the urea injection amount Ui2 acquired the previous time the injection amount acquisition process was executed. That is, the CPU executes the same process as step 405. Note that the CPU may acquire the amount of ammonia that has flowed out of the SCR unit 52 during the processing period Δt based on the previous urea injection amount Ui1p and the previous group purification rate Eg1p, and take the acquired outflow ammonia amount into consideration when acquiring the inflow ammonia amount Fa2.

[0071] Step 440: The CPU acquires the inflow NOx amount Fn2 [g], which is the amount of NOx that has flowed into the SCR unit 53 during the processing period Δt up to the current time, based on the NOx concentration Dn, the exhaust flow rate Fv, and the group purification rate Eg1. That is, the CPU acquires the amount of NOx that has flowed into the SCR units 51-52 during the processing period Δt and has not been purified by the SCR units 51-52 as the inflow NOx amount Fn2.

[0072] Specifically, similar to the inflow NOx amount Fn1, the CPU acquires the NOx inflow velocity of the SCR unit 53 at the current time, and acquires the inflow NOx amount Fn2 based on the acquired NOx inflow velocity. Note that the CPU may acquire the inflow NOx amount Fn2 based on the NOx inflow velocity of the SCR unit 53 at the timing when the injection amount acquisition process was previously executed (similar to the inflow NOx amount Fn1).

[0073] Step 445: The CPU acquires the ammonia change amount Mg2d. The ammonia change amount Mg2d is the change amount (increase) in the ammonia adsorption amount Mg2 [g] during the processing period Δt up to the current time point. The ammonia adsorption amount Mg2 is the total value of the amount of ammonia adsorbed in each of the SCR units 53 to 54. The CPU acquires the ammonia change amount Mg2d by applying a combination of the previous group purification rate Eg2p, the inflow ammonia amount Fa2, and the inflow NOx amount Fn2 to a pre-adapted map Mg (similar to the above-mentioned map Mf).

[0074] The previous group purification rate Eg2p is the group purification rate Eg2 acquired the previous time the injection amount acquisition process was performed. Generally, the larger the previous group purification rate Eg2p, the smaller the ammonia change amount Mg2d. The larger the inflowing ammonia amount Fa2, the larger the ammonia change amount Mg2d. The larger the inflowing NOx amount Fn2, the smaller the ammonia change amount Mg2d.

[0075] Step 450: The CPU acquires the sum of the previous ammonia adsorption amount Mg2p and the ammonia change amount Mg2d as the ammonia adsorption amount Mg2. The previous ammonia adsorption amount Mg2p is the ammonia adsorption amount Mg2 acquired the previous time the injection amount acquisition process was executed. Step 455: The CPU acquires a group temperature Tg2 based on the unit temperatures Tc3 to Tc4. Specifically, the CPU sets the group temperature Tg2 to a value equal to the average value of the unit temperatures Tc3 to Tc4 acquired by the process of 305 in Fig. 3. Note that the unit temperature Tc3 may also be treated as the group temperature Tg2.

[0076] Step 460: The CPU obtains the group purification efficiency Eg2 by applying a combination of the group temperature Tg2, the ammonia adsorption amount Mg2, and the exhaust flow rate Fv to a pre-adapted map Mh (similar to the map Me described above). Generally, the higher the group temperature Tg2, the higher the group purification efficiency Eg2. The higher the ammonia adsorption amount Mg2, the higher the group purification efficiency Eg2. The higher the exhaust flow rate Fv, the lower the group purification efficiency Eg2.

[0077] Step 465: The CPU acquires the total value of each of the group purification rates Eg1 to Eg2 [%] as the purification rate Er. The group temperatures Tg1 to Tg2 referenced when acquiring the group purification rates Eg1 to Eg2 correlate with the temperatures of the SCR units 51 to 54 (i.e., unit temperatures Tc1 to Tc4), and for convenience, are also referred to as "temperature correlation values." As described above, the higher the catalyst temperature of each of the SCR units 51 to 54, the higher the unit temperatures Tc1 to Tc4, and accordingly the group temperatures Tg1 to Tg2 increase.

[0078] As described above, the ECU 7 obtains the upper limit injection amount Qmax based on the purification rate Er of the SCR device 5 (i.e., SCR units 51 to 54), and controls the fuel injection valve 13 based on the fuel injection amount Qinj, which is set to the larger of the required injection amount Qreq and the upper limit injection amount Qmax. Therefore, even if the purification rate Er is small due to a low temperature of the SCR device 5 (specifically, the group temperatures Tg1 to Tg2), the fuel injection valve 13 injects fuel according to the upper limit injection amount Qmax. This prevents a standby period from occurring due to a low temperature of the SCR device 5. In other words, while the SCR device 5 is warming up (i.e., when the unit temperatures Tc1 to Tc4 are low), the NOx purification capacity of the SCR device 5 is relatively low, but it is possible to operate the internal combustion engine 1 according to the NOx purification capacity at that time.

[0079] Additionally, the ECU 7 obtains the purification efficiency Er based on the group purification efficiency Eg1-Eg2 obtained for each of a plurality of SCR groups (i.e., SCR units 51-52 and SCR units 53-54) obtained by dividing the SCR units 51-54. Furthermore, when obtaining the group purification efficiency Eg1-Eg2, the ECU 7 refers to the group temperatures Tg1-Tg2 of each SCR group. Therefore, even if the SCR device 5 includes a plurality of SCR units (i.e., SCR units 51-54), the purification efficiency Er (i.e., the NOx purification capacity of the SCR device 5) can be obtained with high accuracy.

[0080] Furthermore, the ECU 7 acquires each of the unit temperatures Tc1 to Tc4 based on the exhaust temperature Te detected by the exhaust temperature sensor 86. In other words, it is no longer necessary to provide a temperature sensor for each of the SCR units 51 to 54, and it is possible to relatively easily construct a control system for the internal combustion engine.

[0081] In addition, the ECU 7 also refers to the urea injection amounts Ui1 to Ui2 (more specifically, the inflow ammonia amounts Fa1 to Fa2) when obtaining the group purification rates Eg1 to Eg2, thereby making it possible to obtain the purification rate Er with even greater accuracy.

[0082] Furthermore, when the unit temperatures Tc1 to Tc4 are low, the outside air upper limit discharge amount Nomax becomes large, and therefore the engine upper limit discharge amount Nemax becomes large (compared to when the outside air upper limit discharge amount Nomax is small). Therefore, it is possible to avoid as much as possible the discomfort felt by the driver of the vehicle equipped with the engine due to the upper limit injection amount Qmax becoming small when the unit temperatures Tc1 to Tc4 are low.

[0083] Although the embodiments of the present invention have been described above with reference to the above structures, many modifications, improvements, and variations are possible without departing from the scope of the present invention. Therefore, the present invention includes all modifications, improvements, and variations that do not depart from the spirit and scope of the appended claims. The present invention is not limited to the specific structures described above, and modifications such as those described below are possible.

[0084] The ECU 7 obtained the purification rate Er based on the group purification rates Eg1 to Eg2. In other words, the SCR device 5 was divided into two groups: SCR units 51 to 52 and SCR units 53 to 54. Alternatively, the SCR device 5 may be divided into four groups. In this case, the ECU 7 may obtain the purification rate (i.e., four values) of each of the SCR units 51 to 54 and obtain the purification rate Er of the SCR device 5 based on these purification rates. Alternatively, the SCR device 5 may be divided into three groups. The division (i.e., grouping) of the multiple SCR units is performed, for example, so that multiple adjacent SCR units (e.g., SCR units 51 to 53) belong to the same SCR group.

[0085] Furthermore, the ECU 7 may obtain the purification rate Er without obtaining the purification rate for each of the plurality of SCR groups (i.e., group purification rates Eg1 to Eg2). In this case, the ECU 7 may obtain the purification rate Er (i.e., purification capability correlation value) based on the exhaust gas temperature Te (i.e., temperature correlation value), the total amount of ammonia adsorbed in each of the SCR units 51 to 54, and the exhaust gas flow rate Fv.

[0086] The ECU 7 acquired the purification rate Er as the purification capability correlation value. Instead of this, the ECU 7 may acquire the NOx purification amount [g / sec] as the purification capability correlation value related to the SCR device 5. For example, the ECU 7 may acquire the total value of the NOx purification amounts of the SCR units 51-52 and the SCR units 53-54 (i.e., the group NOx purification amount (group purification capability correlation value)) as the NOx purification amount related to the SCR device 5. More specifically, the ECU 7 may acquire the group NOx purification amount based on maps similar to the above-mentioned maps Me and Mh.

[0087] The ECU 7 acquired the unit temperatures Tc1 to Tc4 based on the exhaust gas temperature Te detected by the exhaust gas temperature sensor 86. Alternatively, the ECU 7 may acquire, as the unit temperatures Tc1 to Tc4, the detection values ​​of (plurality of) temperature sensors that directly detect the catalyst temperatures of the SCR units 51 to 54. Alternatively, the ECU 7 may acquire the exhaust gas temperature Te as the unit temperature Tc1, and acquire, as the unit temperatures Tc2 to Tc4, the detection values ​​of (plurality of) temperature sensors that directly detect the temperature of the exhaust gas flowing into the SCR units 52 to 54.

[0088] The upper limit injection amount Qmax has been treated as the upper limit of the fuel injection amount Qinj (i.e., the total amount of fuel injected by one of the fuel injection valves 13 in one cycle of the internal combustion engine 1). Instead of this, the upper limit injection amount Qmax acquired based on the purification rate Er may be treated as the upper limit of the fuel injected by the fuel injection valve 13 as the main injection (for example, the main injection amount obtained by subtracting the pilot injection amount from the total injection amount).

[0089] The exhaust purification system 4 includes the fuel addition valve 41, the oxidation catalyst 42, and the SCR device 5 (i.e., SCR units 51 to 54). In addition to these, the exhaust purification system 4 may further include a downstream oxidation catalyst that is disposed downstream of the SCR unit 54 and purifies the ammonia gas (i.e., excess ammonia) discharged from the SCR unit 54.

[0090] Alternatively, the exhaust purification system 4 may include an ASC (ammonia slip catalyst) device disposed downstream of the SCR unit 54. If this ASC device has the ability to purify NOx, the ECU 7 may obtain the NOx purification rate (ASC purification rate) of the ASC device and refer to the ASC purification rate when obtaining the purification rate Er.

[0091] On the other hand, the SCR device 5 may include only one SCR unit. Even in this case, the ECU 7 can obtain the purification efficiency Er based on the temperature of this SCR unit (i.e., the temperature correlation value).

[0092] The exhaust purification system 4 includes the urea addition valves 43a to 43b. Alternatively, the exhaust purification system 4 may include one urea addition valve disposed upstream of the SCR unit 51. Alternatively, the exhaust purification system 4 may include four urea addition valves disposed upstream of each of the SCR units 51 to 54. In either case, the ECU 7 can obtain the purification rate Er based on a correlation value of the amount of ammonia flowing into each of the SCR units 51 to 54.

[0093] The exhaust purification system 4 includes the NOx sensor 88 disposed upstream of the SCR unit 51. In addition, the exhaust purification system 4 may include a NOx sensor (downstream NOx sensor) disposed downstream of the SCR unit 54. In this case, the ECU 7 may obtain the purification rate Er based on the detection value of the NOx sensor 88 (i.e., the NOx concentration Dn) and the detection value of the downstream NOx sensor.

[0094] When the purification rate Er is smaller than a predetermined purification rate threshold, the ECU 7 may stop the operation of the internal combustion engine 1. In this case, when the purification rate Er becomes larger than the purification rate threshold, the operation of the internal combustion engine 1 is started, and the fuel injection amount Qinj is set in a range equal to or smaller than the upper limit injection amount Qmax (until the purification rate Er becomes 1 or larger). In other words, the operation of the internal combustion engine 1 is stopped only when the purification rate Er becomes smaller than the purification rate threshold due to an extremely low temperature of the SCR device 5.

[0095] The vehicle is equipped with the internal combustion engine 1 as a driving force source. In addition, the vehicle may be equipped with an electric motor as a driving force source. In this case, when the fuel injection amount Qinj is smaller than the required injection amount Qreq (i.e., when the fuel injection amount Qinj is equal to the upper limit injection amount Qmax), the ECU 7 may compensate for the insufficient driving force (i.e., the amount of reduction in the output of the internal combustion engine 1 corresponding to the difference between the fuel injection amount Qinj and the required injection amount Qreq) with the output of the electric motor. [Explanation of symbols]

[0096] 1...internal combustion engine, 11...engine body 12... turbocharger, 12a... turbine, 12b... compressor, 13... fuel injection valve 2...intake path, 21a-21b...intake pipe, 22...intake manifold 23... throttle valve, 23a... throttle actuator 3...exhaust path, 31...exhaust manifold, 32a to 32b...exhaust pipe 4...Exhaust gas purification system, 41...Fuel addition valve 42...oxidation catalyst, 43a to 43b...urea addition valve 5...SCR device, 51~54...SCR unit 6...EGR device, 61...EGR pipe, 62...EGR valve 7...ECU 81...Crank angle sensor, 82...Cam position sensor 83...Air flow sensor, 84...Accelerator opening sensor, 85...Vehicle speed sensor 86...Exhaust temperature sensor, 87...Exhaust flow rate sensor 88...NOx sensor, 89...differential pressure sensor

Claims

1. A control system for an internal combustion engine, comprising: an SCR device that purifies nitrogen oxides contained in exhaust gas; a fuel injection valve that injects fuel into a combustion chamber; a control unit; The control unit obtaining a purification capacity correlation value of the SCR device based on the temperature correlation value of the SCR device; acquiring an upper limit injection amount based on the purification capability correlation value; A control system for an internal combustion engine that controls the fuel injection valve based on the upper limit injection amount.

2. 2. The control system for an internal combustion engine according to claim 1, the SCR device includes a plurality of SCR units; The control unit obtaining a group purification capacity correlation value for each of a plurality of SCR groups obtained by dividing the plurality of SCR units based on the temperature correlation value; A control system for an internal combustion engine that obtains the purification ability correlation value based on each of the group purification ability correlation values.

3. 3. A control system for an internal combustion engine according to claim 2, an exhaust gas temperature sensor disposed upstream of the SCR device; A control system for an internal combustion engine that obtains the temperature correlation value based on the exhaust temperature detected by the exhaust temperature sensor.

4. 2. The control system for an internal combustion engine according to claim 1, a urea addition valve that injects urea into the SCR device; The control unit a control system for an internal combustion engine, the control system acquiring the purification ability correlation value based on the amount of urea injected by the urea addition valve;

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