Diesel engine

Abstract

Provided is a diesel engine in which exhaust gas can be purified by an SCR catalyst during no-load or low-load operation without using large power. The diesel engine is configured so as to start the temperature raising process of the SCR catalyst when a start condition is satisfied that the SCR inlet-side exhaust temperature (T4) of the SCR catalyst is equal to or less than a predetermined low-temperature determination temperature (TA) by the control of the electronic control device. The diesel engine is configured in such a manner that when an end condition is satisfied in which an SCR inlet-side exhaust gas temperature (T4) of the SCR catalyst is equal to or greater than a predetermined SCR temperature increase end determination temperature (TC), the temperature increase process of the SCR catalyst is ended, and when a start condition is satisfied again, the temperature increase process of the SCR catalyst is restarted, and in the temperature increase process of the SCR catalyst, the SCR inlet-side exhaust gas temperature (T4) of the SCR catalyst is not less than the predetermined SCR temperature increase end determination temperature (TC). The opening degree of the exhaust throttle valve is reduced, and when the valve upstream exhaust temperature (T0) of the exhaust throttle valve is equal to or greater than a predetermined post-injection permissible temperature (TB), post-injection from the fuel injector is started.

Description

Technical Field

[0001] The present invention relates to a diesel engine, and more particularly, to a diesel engine that can purify exhaust gas by an SCR catalyst during no-load or low-load operation without using a large amount of electricity. Background Art

[0002] Conventionally, there has been an engine that activates an SCR catalyst by heating with an electric heater when the exhaust gas temperature is low, and purifies the exhaust gas by the SCR catalyst (for example, refer to Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-148068 (refer to Figure 1 ) Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] <Problem> A large amount of electricity is required.

[0008] In the engine of Patent Document 1, when operating at no-load or low-load with a low exhaust gas temperature, it is necessary to activate the SCR catalyst by heating with an electric heater, which requires a large amount of electricity.

[0009] In this case, problems such as poor control of the engine ECU due to rapid consumption of the battery and voltage drop of the battery may occur.

[0010] An object of the present invention is to provide a diesel engine that can purify exhaust gas by an SCR catalyst during no-load or low-load operation without using a large amount of electricity.

[0011] Technical Means for Solving the Problem

[0012] The main structure of the present invention is described as follows.

[0013] As Figure 3 shown, this diesel engine is configured such that, under the control of an electronic control device (7), when the start condition that the exhaust gas temperature (T4) on the SCR inlet side of the SCR catalyst (3) is equal to or lower than a specified low-temperature determination temperature (TA) is satisfied, the temperature-raising process of the SCR catalyst (3) is started, and when the end condition that the exhaust gas temperature (T4) on the SCR inlet side of the SCR catalyst (3) is equal to or higher than a specified SCR temperature-raising end determination temperature (TC) is satisfied, the temperature-raising process of the SCR catalyst (3) is ended, and when the start condition is satisfied again, the temperature-raising process of the SCR catalyst (3) is restarted.

[0014] This diesel engine is characterized in that during the temperature-raising treatment of the SCR catalyst (3), the opening degree of the exhaust throttle valve (4) is reduced (S2), and when the exhaust temperature (T0) on the upstream side of the valve of the exhaust throttle valve (4) is equal to or higher than a specified post-injection allowable temperature (TB), post-injection from the fuel injector (6) is started (S5).

[0015] Advantages of the Invention

[0016] The invention of the present application has the following advantages.

[0017] <<Advantage 1>> Exhaust gas can be purified by the SCR catalyst (3) even during no-load or low-load operation.

[0018] As Figure 3 illustrated by way of example, in this engine, through the control of the electronic control device (7), when the exhaust temperature (T4) on the SCR inlet side of the SCR catalyst (3) is equal to or lower than a specified low-temperature determination temperature (TA), the SCR temperature-raising treatment is started, the exhaust temperature rises, and the temperature of the SCR catalyst (3) also rises. Since the SCR catalyst (3) can be activated, exhaust gas can be purified by the SCR catalyst (3) even during no-load or low-load operation.

[0019] <<Advantage 2>> No large amount of electric power is required for the activation of the SCR catalyst (3).

[0020] As Figure 3 illustrated by way of example, during the SCR temperature-raising treatment, the opening degree of the exhaust throttle valve (4) is reduced (S2) and post-injection is performed. Since the exhaust temperature rises due to the increase in exhaust pressure and the combustion of the post-injected fuel, no large amount of electric power is required for the activation of the SCR catalyst (3). Brief Description of the Drawings

[0021] Figure 1 is a schematic diagram of the engine according to the first embodiment of the present invention.

[0022] Figure 2 is Figure 1 a schematic diagram of the exhaust gas discharge path of the engine.

[0023] Figure 3 is Figure 1 a flowchart of the SCR catalyst temperature-raising treatment of the engine.

[0024] Figure 4 is Figure 1 a flowchart of the DPF regeneration treatment of the engine.

[0025] Figure 5 is a schematic diagram of the exhaust gas discharge path of the engine according to another embodiment of the present invention,Figure 5 is a diagram of the second embodiment of (A). Figure 5 is a diagram of the third embodiment of (B).

[0026] Figure 6 is a schematic diagram of the exhaust gas discharge path of the engine according to another embodiment of the present invention. Figure 6 is a diagram of the fourth embodiment of (A). Figure 6 is a diagram of the fifth embodiment of (B). Detailed Embodiments

[0027] Figures 1 to 6 is a diagram of the engine illustrating each embodiment of the present invention. In each embodiment, a vertical in-line multi-cylinder (4-cylinder) diesel engine is described.

[0028] For Figure 1 , Figure 2 the first embodiment shown is described.

[0029] As Figure 1 shown, the engine has an intake device, a fuel supply device, and an exhaust device.

[0030] The intake device has an intake introduction passage (11) and an intake manifold (12) connected to the terminal of the intake introduction passage (11). The intake introduction passage (11) has a filter (13), an intake air flow meter (14), the air compressor (15a) of a supercharger (15), an intercooler (16), and an intake throttle valve (17) in order from the intake upstream side to the side closer to the intake downstream side.

[0031] The fuel supply device is a common rail type device and has a common rail (6a) and a fuel injector (6) that injects the fuel accumulated in the common rail (6a) into each combustion chamber (5).

[0032] As Figure 1 shown, the exhaust device has: an exhaust manifold (18); an exhaust turbine (15b) of a supercharger (15), connected to the exhaust confluence outlet (18a) of the exhaust manifold (18); an EGR passage (19), led out from between the exhaust manifold (18) and the exhaust turbine (15b); and an exhaust discharge path (1), led out from the exhaust outlet of the exhaust turbine (15b).

[0033] The EGR passage (19) has an EGR cooler (20) and an EGR valve (21) in order from the EGR upstream side to the side closer to the EGR downstream side. The leading end of the EGR passage (19) is connected to the intake introduction passage (11) on the intake downstream side of the intake throttle valve (17).

[0034] EGR is the abbreviation of exhaust gas recirculation.

[0035] As Figure 1 , Figure 2 shown, the engine is configured to have an exhaust gas discharge path (1), the exhaust gas discharge path (1) having an aqueous urea injector (2) and an SCR catalyst (3), and using the aqueous urea (2a) added to the exhaust gas (1a), the nitrogen oxides in the exhaust gas (1a) are purified by the SCR catalyst (3).

[0036] As Figure 1 shown, the engine has: an exhaust throttle valve (4) disposed in the exhaust gas discharge path (1), a fuel injector (6) that injects fuel into the combustion chamber (5), and an electronic control unit (7) that controls the opening and closing of the exhaust throttle valve (4) and the fuel injection from the fuel injector (6).

[0037] The SCR catalyst is the abbreviation of a Selective Catalytic Reduction type catalyst. In the SCR catalyst (3), a catalyst in which a catalyst component is supported on a flow-through honeycomb type catalyst carrier having a plurality of cells arranged in a penetrating manner along the axial length direction inside is used.

[0038] From Figure 1 , Figure 2 the aqueous urea (2a) injected into the exhaust gas (1a) from the aqueous urea injector (2) shown is hydrolyzed at a high temperature to become ammonia gas. By the catalytic action of the SCR catalyst (3), ammonia reacts with the nitrogen oxides (NO X ) in the exhaust gas (1a), and the nitrogen oxides (NO X ) are reduced to nitrogen (N2), and exhaust gas purification is performed.

[0039] The electronic control unit (7) uses an engine ECU (7a).

[0040] The ECU is the abbreviation of an electronic control unit and uses a microcomputer.

[0041] As Figure 3 shown, it is configured such that, by the control of the electronic control unit (7), when the start condition that the exhaust gas temperature (T4) on the SCR inlet side of the SCR catalyst (3) is below a specified low temperature determination temperature (TA) is satisfied, the temperature increase process of the SCR catalyst (3) is started, and when the end condition that the exhaust gas temperature (T4) on the SCR inlet side of the SCR catalyst (3) is above a specified SCR temperature increase end determination temperature (TC) is satisfied, the temperature increase process of the SCR catalyst (3) is ended, and when the start condition is satisfied again, the temperature increase process of the SCR catalyst (3) is restarted.

[0042] It is configured such that during the temperature-raising process of the SCR catalyst (3), the opening of the exhaust throttle valve (4) is reduced (S2), and when the exhaust temperature (T0) on the upstream side of the valve of the exhaust throttle valve (4) is equal to or higher than a specified post-injection allowable temperature (TB), post-injection from the fuel injector (6) is started (S5).

[0043] As Figure 3 shown, in this engine, through the control of the electronic control unit (7), when the exhaust temperature (T4) on the SCR inlet side of the SCR catalyst (3) is equal to or lower than a specified low-temperature determination temperature (TA), the SCR temperature-raising process is started, the exhaust temperature rises, and the temperature of the SCR catalyst (3) also rises. Since the SCR catalyst (3) can be activated, exhaust gas purification can be performed by the SCR catalyst (3) even during no-load or low-load operation.

[0044] As Figure 3 shown, during the SCR temperature-raising process, the opening of the exhaust throttle valve (4) is reduced (S2) and post-injection is performed. Since the exhaust temperature rises due to the increase in exhaust pressure and the combustion of the post-injected fuel, a large amount of power is not required for the activation of the SCR catalyst (3).

[0045] In this engine, Figure 3 the shown low-temperature determination temperature (TA) is set to a temperature higher than the activation temperature of the SCR catalyst (3).

[0046] Therefore, in this engine, the exhaust temperature (T4) on the SCR inlet side can be maintained at a temperature higher than the activation temperature of the SCR catalyst (3), and interruption of exhaust gas purification due to deactivation of the SCR catalyst (3) is less likely to occur even during no-load or low-load operation.

[0047] The activation temperature of this SCR catalyst (3) is 180°C.

[0048] In this engine, after the engine is started and the exhaust temperature (T4) on the SCR inlet side of the SCR catalyst (3) exceeds the activation temperature of the SCR catalyst (3), through the control of the electronic control unit (7), the exhaust temperature (T4) on the SCR inlet side of the SCR catalyst (3) is maintained at a temperature exceeding the activation temperature of the SCR catalyst (3) until the engine stops.

[0049] Therefore, in this engine, exhaust gas purification by the SCR catalyst (3) can be performed during substantially the entire period of engine operation except after engine startup.

[0050] In this engine, Figure 3The shown low-temperature determination temperature (TA) is preferably set to a temperature that is 30°C to 70°C higher than the activation temperature of the SCR catalyst (3).

[0051] When the increase in the low-temperature determination temperature (TA) is less than 30°C of the activation temperature of the SCR catalyst (3), during no-load or low-load operation, the exhaust gas temperature (T4) on the SCR inlet side of the SCR catalyst (3) is lower than the activation temperature of the SCR catalyst (3), and interruption of exhaust gas purification may occur. When it exceeds 70°C, although the exhaust gas temperature (T4) on the SCR inlet side of the SCR catalyst (3) sufficiently exceeds the activation temperature of the SCR catalyst (3), unnecessary SCR temperature increase treatment may start.

[0052] In contrast, when the increase in the low-temperature determination temperature (TA) is 30°C to 70°C of the activation temperature of the SCR catalyst (3), interruption of exhaust gas purification or start of unnecessary SCR temperature increase treatment can be avoided.

[0053] When the activation temperature of the SCR catalyst (3) is 180°C, the preferred range of the low-temperature determination temperature (TA) is 210°C to 250°C.

[0054] In this engine, Figure 3 The shown SCR temperature increase end determination temperature (TC) is preferably set to a temperature that is 30°C to 70°C higher than the low-temperature determination temperature (TA).

[0055] When the increase in the SCR temperature increase end determination temperature (TC) is less than 30°C of the low-temperature determination temperature (TA), during no-load or low-load operation, due to excessive heat dissipation from the exhaust gas discharge path (1), the exhaust gas temperature (T4) on the SCR inlet side of the SCR catalyst (3) sometimes becomes lower than the activation temperature of the SCR catalyst (3), which may cause interruption of exhaust gas purification. When it exceeds 70°C, although the exhaust gas temperature (T4) on the SCR inlet side of the SCR catalyst (3) sufficiently exceeds the activation temperature of the SCR catalyst (3), unnecessary SCR temperature increase treatment may continue.

[0056] In contrast, when the increase in the SCR temperature increase end determination temperature (TC) is 30°C to 70°C of the low-temperature determination temperature (TA), interruption of exhaust gas purification or continuation of unnecessary SCR temperature increase treatment can be avoided.

[0057] When the preferred range of the low-temperature determination temperature (TA) is 210°C to 250°C, the preferred range of the SCR temperature increase end determination temperature (TC) is 240°C to 320°C.

[0058] As Figure 1 、Figure 2 As shown, in this engine, the exhaust throttle valve (4) is arranged at a position more upstream of the exhaust than the urea water injector (2) and the SCR catalyst (3).

[0059] Therefore, in this engine, due to the reduction in the opening degree of the exhaust throttle valve (4), the exhaust temperature of the small-volume part of the path upstream of the exhaust throttle valve (4) is rapidly increased, and the time for the exhaust temperature (T0) upstream of the valve to reach the post-injection allowable temperature (TB) is shortened.

[0060] As Figure 1 、 Figure 2 shown, in this engine, a DOC (8) is provided at a position more upstream of the exhaust than the urea water injector (2) and the SCR catalyst (3).

[0061] Therefore, in this engine, the ratio of NO and NO2 in the exhaust gas (1a) in the DOC (8) is optimized, and the exhaust gas purification efficiency in the SCR catalyst (3) is improved.

[0062] As Figure 1 , Figure 2 shown, in this engine, the DOC (8) has an upstream-side DOC (8a) of the valve arranged upstream of the exhaust of the exhaust throttle valve (4).

[0063] Therefore, in this engine, due to the reduction in the opening degree of the exhaust throttle valve (4), the exhaust temperature of the small-volume space upstream of the exhaust of the exhaust throttle valve (4) is rapidly increased, and the upstream-side DOC (8a) of the valve quickly reaches the activation temperature.

[0064] As Figure 1 、 Figure 2 shown, in this engine, the DOC (8) also has a downstream-side DOC (8b) of the valve arranged downstream of the exhaust of the exhaust throttle valve (4).

[0065] Therefore, in this engine, the DOC (8) is divided into an upstream-side DOC (8a) of the valve and a downstream-side DOC (8b) of the valve, enabling the upstream-side DOC (8a) of the valve to be miniaturized and quickly reach the activation temperature.

[0066] DOC is the abbreviation of diesel oxidation catalyst. In both the upstream-side DOC (8a) of the valve and the downstream-side DOC (8b) of the valve, a catalyst in which a catalyst component is carried on a flow-through honeycomb-type catalyst carrier having a plurality of cells arranged in a penetrating manner along the axial length direction inside is used.

[0067] The DOC (8a) on the upstream side of the valve and the DOC (8b) on the downstream side of the valve are made of the same material and have the same structure, but the volume of the DOC (8a) on the upstream side of the valve is smaller than that of the DOC (8b) on the downstream side of the valve, and the temperature rise rate is faster.

[0068] The activation temperature of the DOC (8a) on the upstream side of the valve and the DOC (8b) on the downstream side of the valve is 190 °C.

[0069] The exhaust gas discharge path (1) used in the engine of the first embodiment is of a basic type, and its overall structure is as described below.

[0070] As Figure 1 , Figure 2 shown, the exhaust gas discharge path (1) has various catalysts and various exhaust gas treatment components, and in the order from the upstream side of the exhaust gas to the side closer to the downstream side of the exhaust gas, it has a DOC (8a) on the upstream side of the valve, an exhaust throttle valve (4), a DOC (8b) on the downstream side of the valve, a DPF (9), a urea water injector (2), a mixer (22), an upstream side SCR catalyst (3a), a downstream side SCR catalyst (3b), and an ASC (23).

[0071] DPF is the abbreviation of diesel particulate filter, which is used to capture PM in the engine exhaust gas. PM is the abbreviation of particulate matter. The DPF (9) uses a wall-flow type ceramic honeycomb in which a plurality of cells along the axial length direction are arranged inside, and the inlets and outlets of adjacent cells are alternately sealed.

[0072] The mixer is a mixer that disperses urea water in the exhaust gas. Therefore, the mixer (22) is composed of a plurality of plates parallel to the exhaust gas direction. Urea water (2a) is injected into the inlet of the mixer (22) from the urea water injector (2).

[0073] The SCR catalyst (3) is composed of an upstream side SCR catalyst (3a) and a downstream side SCR catalyst (3b).

[0074] ASC is the abbreviation of ammonia slip catalyst, which is a catalyst for purifying ammonia escaped from the SCR catalyst. The ASC (23) uses a catalyst in which a plurality of cells along the axial length direction are arranged in a through shape inside on a flow-through honeycomb type catalyst carrier carrying the catalyst.

[0075] As Figure 1 shown, the valve actuator (4a) of the exhaust throttle valve (4) and the valve actuator (2b) of the solenoid valve of the urea water injector (2) are electrically connected to the engine ECU (7a) via an actuator harness (24) together with the valve actuator (17a) of the intake throttle valve (17), the actuator (6b) of the solenoid valve of the fuel injector (6), and the valve actuator (21a) of the EGR valve (21), and are powered from the battery (35).

[0076] In addition, Figure 1 , Figure 2 the exhaust gas discharge path (1) shown has various sensors, and in the order from the upstream side of the exhaust gas to the side closer to the downstream side of the exhaust gas, it has: an upstream side exhaust gas temperature sensor (25) and an upstream side exhaust gas pressure sensor (26) arranged between the DOC (8a) on the upstream side of the valve and the exhaust gas throttle valve (4); a downstream side DOC inlet side exhaust gas temperature sensor (27) arranged between the exhaust gas throttle valve (4) and the DOC (8b) on the downstream side of the valve; a DPF inlet side exhaust gas temperature sensor (28) arranged between the DOC (8b) on the downstream side of the valve and the DPF (9); a differential pressure sensor (29) spanning the inlet side and the outlet side of the DPF (9); a DPF outlet side exhaust gas temperature sensor (30) arranged between the DPF (9) and the urea water injector (2); an SCR inlet side exhaust gas temperature sensor (31) and an SCR upstream side NO X sensor (32) arranged between the mixer (22) and the upstream side SCR catalyst (3a); and an SCR downstream side NO X sensor (33) arranged on the outlet side of the ASC (23).

[0077] The above various sensors are electrically connected to the engine ECU (7a) via a sensor harness (34) together with the intake air flow meter (14).

[0078] As Figure 2 shown, in the upstream side exhaust gas temperature sensor (25), the upstream side exhaust gas temperature (T0) of the exhaust gas throttle valve (4) is detected; in the upstream side exhaust gas pressure sensor (26), the upstream side exhaust gas pressure (P0) is detected; in the downstream side DOC inlet side exhaust gas temperature sensor (27), the downstream side DOC inlet side exhaust gas temperature (T1) is detected; in the DPF inlet side exhaust gas temperature sensor (28), the DPF inlet side exhaust gas temperature (T2) is detected; in the differential pressure sensor (29), the differential pressure (ΔP) between the DPF inlet side and the DPF outlet side is detected; and in the DPF outlet side exhaust gas temperature sensor (30), the DPF outlet side exhaust gas temperature (T3) is detected.

[0079] In addition, in the SCR inlet side exhaust gas temperature sensor (31), the SCR inlet side exhaust gas temperature (T4) is detected; in the SCR upstream side NO X sensor (32), the SCR upstream side NO X concentration (NO X 1) is detected; and in the SCR downstream side NO X sensor (33), the SCR downstream side NO X concentration (NO X 2) is detected.

[0080] InFigure 3 In the flowchart, the control steps of the SCR warm-up process performed by the engine ECU (7a) are described.

[0081] In step (S1), it is determined whether the SCR inlet-side exhaust gas temperature (T4) which is the start condition of the SCR warm-up process is below the low-temperature determination temperature (TA). If the determination is negative, the determination in step (S1) is repeated. If the determination is positive, in step (S2), the opening of the intake throttle valve (17) is reduced and the opening of the exhaust throttle valve (4) is reduced, and then step (S3) is entered.

[0082] In step (S3), it is determined whether the exhaust gas pressure (P0) upstream of the valve is below the exhaust gas pressure upper limit value (Pmax). If the determination is positive, step (S4) is entered. If the determination is negative, after increasing the opening of the exhaust throttle valve (4) in step (S3-2), step (S4) is entered.

[0083] In step (S4), it is determined whether the exhaust gas temperature (T0) upstream of the valve is above the post-injection allowable temperature (TB). If the determination is negative, the determination in step (S4) is repeated. If the determination is positive, post-injection is started in step (S5), and then step (S6) is entered. The post-injection allowable temperature (TB) is set to a temperature lower than the low-temperature determination temperature (TA), for example, 150 °C.

[0084] In step (S6), it is determined whether the SCR inlet-side exhaust gas temperature (T4) which is the end condition of the SCR warm-up process is above the SCR warm-up end determination temperature (TC). If the determination is negative, the determination in step (S6) is repeated. If the determination is positive, post-injection is ended in step (S7), and then step (S8) is entered.

[0085] In step (S08), the intake throttle valve (17) is fully opened and reset, and the exhaust throttle valve (4) is fully opened and reset, and then it returns to step (S1).

[0086] In addition, in the exhaust gas purification process performed by the SCR catalyst (3), the engine ECU (7a) allocates the injection amount of the aqueous urea (2a) from the aqueous urea injector (2) according to the NOx purification rate.

[0087] The NOx purification rate is estimated by the engine ECU (7a) based on the NO X concentration (NO X 1) on the upstream side of the SCR and the NO X concentration (NO X 2) on the downstream side of the SCR.

[0088] Next, for Figure 4The control steps of the DPF regeneration process performed by the engine ECU (7a) in the flowchart will be described.

[0089] In step (S9), it is determined whether the estimated value of PM accumulation (APM) in the DPF (9), which is the start condition of the DPF regeneration process, is equal to or higher than the start determination value (RSJ) of the regeneration process. If the determination is negative, the determination in step (S9) is repeated. If the determination in step (S9) is positive, the process proceeds to step (S10).

[0090] The estimated value of PM accumulation (APM) in step (S9) is estimated by the engine ECU (7a) based on the differential pressure (ΔP) detected by the differential pressure sensor (29) between the DPF inlet side and the DPF outlet side.

[0091] In step (S10), it is determined whether the exhaust temperature (T0) on the upstream side of the valve is equal to or higher than the post-injection allowable temperature (TP). If the determination is negative, the determination in step (S10) is repeated. If the determination is positive, the process proceeds to step (S11).

[0092] The post-injection allowable temperature (TP) exceeds the post-injection allowable temperature (TB) and reaches a temperature equal to or higher than the activation temperature of the oxidation catalyst (8), for example, 200°C.

[0093] In step (S11), post-injection starts.

[0094] The post-injection is set such that the exhaust temperature (T1) at the DOC inlet side on the downstream side of the valve is maintained at 400°C or higher and 700°C or lower, and the exhaust temperature (T2) at the DPF inlet side is maintained at 550°C or higher and 700°C or lower. In particular, in order to prevent abnormal combustion of the accumulated PM, the exhaust temperature (T2) at the DPF inlet side is preferably set to 700°C or lower.

[0095] During the post-injection, the post-injection fuel injected into the combustion chamber during the expansion stroke or the exhaust stroke burns in the catalysts of the DOC (8a) on the upstream side of the valve and the DOC (8b) on the downstream side of the valve, the exhaust gas (1a) is heated, and the PM accumulated in the DPF (9) is burned and removed.

[0096] In step (S12) after step (S11), it is determined whether the estimated value of PM accumulation (APM) in the DPF (9), which is the end condition of the DPF regeneration process, is equal to or lower than the end determination value (REJ) of the regeneration process. If the determination is negative, the determination in step (S12) is repeated. If the determination in step (S12) is positive, the process proceeds to step (S13).

[0097] In step (S13), the post-injection ends, and the process returns to step (S9).

[0098] The end determination value (REJ) of step (S12) is estimated by the engine ECU (7a) based on the differential pressure (ΔP) between the DPF inlet side and the DPF outlet side detected by the differential pressure sensor (29).

[0099] In addition, Figure 4 The post-injection allowable temperature (TP) shown is the determination temperature for the exhaust gas temperature (T0) on the upstream side of the valve detected by the exhaust gas temperature sensor (25) on the upstream side of the valve, as Figure 2 shown, the exhaust gas temperature (T0) on the upstream side of the valve is detected by the exhaust gas temperature sensor (25) on the upstream side of the valve and is controlled by the engine ECU (7a).

[0100] The exhaust gas temperature (T1) at the DOC inlet side on the downstream side of the valve is controlled by adjusting the injection timing and the fuel injection amount performed by the engine ECU (7a) through the exhaust gas temperature (T0) on the upstream side of the valve detected by the exhaust gas temperature sensor (25) on the upstream side of the valve.

[0101] The exhaust gas temperature (T2) on the DPF inlet side is detected by the DPF inlet side exhaust gas temperature sensor (28) and is controlled by adjusting the injection timing and the fuel injection amount performed by the engine ECU (7a).

[0102] In addition, when the exhaust gas temperature (T3) on the DPF outlet side detected by the DPF outlet side exhaust gas temperature sensor (30) is a temperature equal to or higher than a specified upper limit temperature, the post-injection or post-supplemental injection is emergently stopped through the control of the engine ECU (7a).

[0103] Among the injection types performed by the fuel injector (6) in one combustion cycle, there are pre-injection (pilot injection), main injection, post-injection, and post-supplemental injection.

[0104] One combustion cycle in a four-cycle engine consists of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke.

[0105] Pre-injection (pilot injection) is an injection for suppressing the ignition delay of the main injection fuel and starts during the intake stroke or the compression stroke.

[0106] Main injection is the main injection for obtaining output and starts before top dead center of compression.

[0107] Post-injection is an injection for raising the temperature of the exhaust gas and starts during the expansion stroke after the main injection.

[0108] Post-supplemental injection is an injection for raising the temperature of the exhaust gas and starts during the expansion stroke after the post-injection. The post-supplemental injection can also start during the exhaust stroke.

[0109] Next, for Figure 5The second embodiment shown in (A) Figure 5 and the exhaust gas discharge path (1) of the third embodiment shown in (B) will be described.

[0110] The exhaust gas discharge paths (1) of both the second and third embodiments are valve-downstream-DOC-free types obtained by removing the downstream-DOC (8b) on the valve downstream side from Figure 2 the basic type. The DOC (8) does not have a downstream-DOC (8b) disposed on the exhaust gas downstream side of the exhaust gas throttle valve (4), nor does it have a downstream-DOC inlet-side exhaust gas temperature sensor (27).

[0111] In the second and third embodiments, since there is no downstream-DOC (8b) on the valve side, the exhaust gas discharge path (1) is shortened and is shorter than that of the first embodiment.

[0112] Furthermore, Figure 5 the exhaust gas discharge path (1) of the third embodiment shown in (B) is a DPF-cumulative-SCR-catalyst type in which the DPF (9) also serves as an upstream-side SCR catalyst (3a). An SCR catalyst component is supported on the DPF (9) disposed on the exhaust gas downstream side of the urea aqueous solution injector (2), and the DPF (9) also serves as an SCR catalyst (3).

[0113] In this third embodiment, since the DPF (9) also serves as an upstream-side SCR catalyst (3a), the exhaust gas discharge path (1) is shortened and is shorter than that of the second embodiment.

[0114] In addition, in this third embodiment, the DPF inlet-side exhaust gas temperature sensor (28) also serves as an SCR inlet-side exhaust gas temperature sensor (31). During the SCR catalyst heating process, the SCR inlet-side exhaust gas temperature (T4) is detected as the SCR inlet-side exhaust gas temperature sensor (31), and during the DPF generation process, the DPF inlet-side exhaust gas temperature (T2) is detected as the DPF inlet-side exhaust gas temperature sensor (28).

[0115] Next, Figure 6 the exhaust gas discharge path (1) of the fourth embodiment shown in (A) Figure 6 and the exhaust gas discharge path (1) of the fifth embodiment shown in (B) will be described.

[0116] The exhaust gas discharge paths (1) of both the fourth and fifth embodiments are throttle-valve-farthest-downstream types in which the exhaust gas throttle valve (4) is moved from Figure 2 the basic type to the farthest downstream side, and the exhaust gas throttle valve (4) is disposed on the exhaust gas outlet side of the ASC (23).

[0117] In the fourth and fifth embodiments, the increase in the exhaust pressure caused by the throttling of the exhaust throttle valve (4) promotes the temperature rise of the SCR catalyst (3).

[0118] Furthermore, in Figure 6 In the fourth embodiment shown in (A) of, the exhaust throttle valve (4) of the exhaust gas discharge path (1) of the basic example moves from between the upstream-side DOC (8a) and the downstream-side DOC (8b) to the most downstream position, so the upstream-side DOC (8a) and the downstream-side DOC (8b) of the basic example become the upstream-side DOC (8a)' and the downstream-side DOC (8b)', and the exhaust gas temperature (T1) at the inlet side of the downstream-side DOC becomes the exhaust gas temperature (T1)' at the inlet side of the downstream-side DOC.

[0119] In this fourth embodiment, the upstream-side exhaust gas temperature sensor (25) also serves as the downstream-side DOC inlet-side exhaust gas temperature sensor (27)'. Before the post-injection or the post-compensatory injection, the upstream-side exhaust gas temperature (T0) is detected by the upstream-side exhaust gas temperature sensor (25). After the post-compensatory injection, the downstream-side DOC inlet-side exhaust gas temperature (T1)' is detected by the downstream-side DOC inlet-side exhaust gas temperature sensor (27)'.

[0120] Figure 6 The exhaust gas discharge path (1) of the fifth embodiment shown in (B) of has a structure of a mixer-integrated urea decomposition catalyst type in which a urea decomposition catalyst (10) that also serves as a mixer (22) for dispersing the urea water (2a) in the exhaust gas (1a) is provided between the urea water injector (2) and the SCR catalyst (3).

[0121] In this fifth embodiment, the hydrolysis of urea is promoted, and the exhaust gas purification by the SCR catalyst (3) is promoted.

[0122] The mixer (22) uses a flow-through honeycomb type structure in which a plurality of cells along the axial length direction are arranged in a penetrating manner inside.

[0123] In the exhaust gas discharge path (1) of the fifth embodiment, the DOC (8) uses a single unit that is not divided into an upstream side and a downstream side, and the exhaust gas temperature (T1) at the inlet side of the downstream-side DOC of the basic example becomes the exhaust gas temperature (T1)'' at the inlet side of the DOC.

[0124] In this fifth embodiment, the upstream-side exhaust gas temperature sensor (25) also serves as the DOC inlet-side exhaust gas temperature sensor (27)''. Before the post-injection or the post-compensatory injection, the upstream-side exhaust gas temperature (T0) is detected by the upstream-side exhaust gas temperature sensor (25). After the post-compensatory injection, the DOC inlet-side exhaust gas temperature (T1)'' is detected by the DOC inlet-side exhaust gas temperature sensor (27)''.

[0125] Figure 5 of (A) and (B), Figure 6 For the exhaust gas discharge paths (1) of the second to fifth embodiments shown in (A) and (B) of Figure 6 , except for the differences from the basic example of the above-described first embodiment, they have the same structure as the basic example and are controlled according to the flowchart of the basic example and the steps described according thereto. Except for the functional differences caused by the structural differences from the basic example, they have the same functions as the basic example.

[0126] In Figure 5 of (A) and (B), Figure 6 in (A) and (B) of Figure 6 , for the elements identical to Figure 2 the same, the same reference numerals as Figure 2 are assigned.

[0127] Description of Reference Numerals

[0128] (1): Exhaust gas discharge path, (1a): Exhaust gas, (2): Urea water injector, (2a): Urea water, (3): SCR catalyst, (3a): Upstream SCR catalyst, (3b): Downstream SCR catalyst, (4): Exhaust throttle valve, (5): Combustion chamber, (6): Fuel injector, (7): Electronic control unit, (8): DOC, (8a): DOC upstream of the valve, (8b): DOC downstream of the valve, (9): DPF, (10): Urea decomposition catalyst.

Claims

1. A diesel engine configured to have an exhaust gas discharge path (1), the exhaust gas discharge path (1) having an aqueous urea injector (2) and an SCR catalyst (3), and using the aqueous urea (2a) added to the exhaust gas (1a) to purify nitrogen oxides in the exhaust gas (1a) by the SCR catalyst (3), wherein the diesel engine is characterized in that it has: an exhaust throttle valve (4) of the exhaust gas discharge path (1), a fuel injector (6) for injecting fuel into the combustion chamber (5), and an electronic control unit (7) for controlling the opening and closing of the exhaust throttle valve (4) and the fuel injection from the fuel injector (6); the diesel engine is configured such that: through the control of the electronic control unit (7), when the start condition that the SCR inlet side exhaust gas temperature (T4) of the SCR catalyst (3) is equal to or lower than a specified low temperature determination temperature (TA) is satisfied, the temperature increase treatment of the SCR catalyst (3) is started, and when the end condition that the SCR inlet side exhaust gas temperature (T4) of the SCR catalyst (3) is equal to or higher than a specified SCR temperature increase end determination temperature (TC) is satisfied, the temperature increase treatment of the SCR catalyst (3) is ended, and when the start condition is satisfied again, the temperature increase treatment of the SCR catalyst (3) is restarted; the diesel engine is configured such that: during the temperature increase treatment of the SCR catalyst (3), the opening of the exhaust throttle valve (4) is reduced (S2), and when the exhaust gas temperature (T0) on the upstream side of the valve of the exhaust throttle valve (4) is equal to or higher than a specified post-injection allowable temperature (TB), post-injection (S5) from the fuel injector (6) is started.

2. The diesel engine according to claim 1, characterized in that the low temperature determination temperature (TA) is set to a temperature higher than the activation temperature of the SCR catalyst (3).

3. The diesel engine according to claim 2, characterized in that after the engine is started and the SCR inlet side exhaust gas temperature (T4) of the SCR catalyst (3) exceeds the activation temperature of the SCR catalyst (3), through the control of the electronic control unit (7), the SCR inlet side exhaust gas temperature (T4) of the SCR catalyst (3) is maintained at a temperature exceeding the activation temperature of the SCR catalyst (3) until the engine stops.

4. The diesel engine according to claim 2, characterized in that the low temperature determination temperature (TA) is set to a temperature 30°C to 70°C higher than the activation temperature of the SCR catalyst (3).

5. The diesel engine according to claim 4, characterized in that the SCR temperature increase end determination temperature (TC) is set to a temperature 30°C to 70°C higher than the low temperature determination temperature (TA).

6. The diesel engine according to any one of claims 1 to 5, characterized in that the exhaust throttle valve (4) is arranged at a position more upstream of the exhaust gas than the aqueous urea injector (2) and the SCR catalyst (3).

7. The diesel engine according to claim 6, characterized in that a DOC (8) is provided at a position more upstream of the exhaust gas than the aqueous urea injector (2) and the SCR catalyst (3).

8. The diesel engine according to claim 7, characterized in that the DOC (8) has an upstream-of-valve DOC (8a) disposed on the upstream side of the exhaust of the exhaust throttle valve (4).

9. The diesel engine according to claim 8, characterized in that the DOC (8) further has a downstream-of-valve DOC (8b) disposed on the downstream side of the exhaust of the exhaust throttle valve (4).

10. The diesel engine according to claim 8, characterized in that the DOC (8) does not have a downstream-of-valve DOC (8b) disposed on the downstream side of the exhaust of the exhaust throttle valve (4).

11. The diesel engine according to any one of claims 1 to 5, characterized in that the DPF (9) disposed at a position more downstream of the exhaust than the urea water injector (2) carries an SCR catalyst component, and the DPF (9) also serves as an SCR catalyst (3).

12. The diesel engine according to any one of claims 1 to 5, characterized in that the exhaust throttle valve (4) is disposed at a position more downstream of the exhaust than the SCR catalyst (3).

13. The diesel engine according to claim 12, characterized in that a urea decomposition catalyst (10) that also serves as a mixer (22) for dispersing the urea water (2a) in the exhaust gas (1a) is provided between the urea water injector (2) and the SCR catalyst (3).

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