Exhaust purification system

Abstract

To provide an exhaust emission control system capable of preventing clogging of a nozzle hole of an injection valve and reducing the size of a dispersion device to the minimum necessary.SOLUTION: An exhaust emission control system 1 includes: an injection valve 2 for injecting reaction liquid toward a direction intersecting with an exhaust gas flowing direction; a dispersion device 3 having a collision surface 3a with which the reaction fluid (fuel) injected from the injection valve 2 is caused to collide; a pressure-feeding pump 6 for adjusting injection pressure that is pressure of the reaction liquid (fuel) injected from the injection valve 2; an integrated type oxidation catalyst 8; and a control device 4 for controlling the injection valve 2 and the pressure-feeding pump 6. The control device acquires an exhaust gas flow rate that is a flow rate of exhaust gas on the basis of an operating state of the internal combustion engine 11, and controls the pressure-feeding pump 6 in accordance with the exhaust gas flow rate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an exhaust gas purification system that injects a reactive liquid into an exhaust pipe of an internal combustion engine, mixes the injected reactive liquid with exhaust gas, and causes the exhaust gas to flow into an aftertreatment device to purify the exhaust gas.

[0002] Conventionally, when increasing the exhaust gas temperature to promote catalyst activation or regenerate a particulate filter, it is known that fuel is injected into the exhaust pipe from an injection valve installed in the exhaust pipe and reacted in an oxidation catalyst. When injecting fuel, it is desirable to uniformly disperse the fuel in the exhaust gas before allowing it to flow into the oxidation catalyst. Therefore, a dispersion device is installed upstream of the oxidation catalyst, and fuel is injected from the injection valve toward the dispersion device, and the injected fuel is collided with the dispersion device to atomize and disperse the fuel (see Patent Document 1).

[0003] The flow rate of exhaust gas flowing through the exhaust pipe is not always constant, but fluctuates depending on the load of the internal combustion engine. Therefore, in order to ensure that the fuel injected from the injection valve hits the dispersion device, it is not enough to simply aim the injection hole toward the dispersion device, but it is also necessary to consider that the fuel injected from the injection hole and flying through the air may be carried away by the exhaust gas. For example, if the dispersion device is made longer toward the downstream side of the exhaust gas, the injected fuel can be surely hit the dispersion device even if it is carried away by the exhaust gas. Alternatively, if the injection pressure of the injection valve is increased to increase the penetration force of the injected fuel, it is possible to suppress the fuel from being carried away by the exhaust gas, and therefore the fuel can be surely hit the dispersion device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2011 / 114388 Summary of the Invention [Problem to be solved by the invention]

[0005] However, making the dispersion device larger than necessary is undesirable because it increases the pressure loss in the exhaust system, leading to a deterioration in fuel efficiency and a decrease in maximum output.On the other hand, if the injection pressure of the injection valve is increased, for example, when the flow rate of exhaust gas is low, the fuel that collides with the dispersion device and rebounds may adhere to the fuel injection valve and become a deposit, which may cause clogging of the injection hole, which is undesirable.

[0006] The present invention aims to provide an exhaust purification system in which a reactive liquid is injected from an injection valve toward a dispersion device arranged in an exhaust pipe and dispersed, which does not cause clogging of the injection valve's nozzle hole and can minimize the size of the dispersion device. [Means for solving the problem]

[0007] According to one feature of the present disclosure, an exhaust purification system is an exhaust purification system that injects a reactive liquid into an exhaust pipe of an internal combustion engine, mixes the injected reactive liquid with exhaust gas, and flows the mixed liquid into an aftertreatment device to purify the exhaust gas, the exhaust purification system having an injection valve that injects the reactive liquid in a direction intersecting the flow direction of the exhaust gas, a dispersion device having a collision surface against which the reactive liquid sprayed from the injection valve collides, an injection pressure adjustment device that adjusts the injection pressure, which is the pressure of the reactive liquid sprayed from the injection valve, the aftertreatment device, and a control device that controls the injection valve and the injection pressure adjustment device, the control device having an exhaust gas flow rate acquisition unit that acquires an exhaust gas flow rate, which is the flow rate of the exhaust gas, based on the operating state of the internal combustion engine, and an injection pressure adjustment unit that controls the injection pressure adjustment device in accordance with the exhaust gas flow rate acquired by the exhaust gas flow rate acquisition unit.

[0008] According to this, the injection pressure of the injection valve is adjusted according to the change in the flow rate of the exhaust gas. Therefore, for example, when the exhaust gas flow rate is low, the importance is placed on preventing the nozzle hole from being clogged due to the rebound of the fuel, and the injection pressure is lowered, and the speed of the fuel injected from the nozzle hole and flying through the air is made relatively slow. As a result, the particulate fuel that is rebounded and atomized by the dispersion device does not have the kinetic energy to reach the injection valve, and the particulate fuel does not adhere to the injection valve. Moreover, even if the penetration force of the fuel during injection is weakened, the exhaust gas flow rate is low to begin with, so the collision point of the injected fuel does not deviate significantly from the initially targeted position. Also, for example, when the exhaust gas flow rate is high, the importance is placed on preventing the collision point from being shifted, and the injection pressure is increased to increase the penetration force of the fuel, and the speed at which the fuel is injected from the nozzle hole and flying through the air is made relatively fast. As a result, the collision point of the fuel does not deviate significantly from the initially targeted position. Moreover, the fuel particles that bounce off the dispersion device and are atomized lose speed and their penetration is weakened as they are swept away by the exhaust gas, so the fuel particles that bounce off the dispersion device do not adhere to the fuel injector. And regardless of changes in the exhaust gas flow rate, the collision point of the fuel does not shift significantly from the originally targeted position. Therefore, the nozzle hole of the injection valve is not clogged, and the size of the dispersion device can be minimized.

[0009] According to another feature of the present invention, in the exhaust purification system, the injection pressure adjustment device has a pressure-feed pump that pressure-feeds the reaction liquid to the injection valve, and the control device has a target injection pressure acquisition unit that acquires a target injection pressure corresponding to the exhaust gas flow rate acquired by the exhaust gas flow rate acquisition unit, and the injection pressure adjustment unit drives the pressure-feed pump so that the injection pressure becomes the target injection pressure acquired by the target injection pressure acquisition unit.

[0010] According to this, since the fuel pressure is controlled by providing a pressure pump dedicated to the exhaust gas purification system according to the present invention, the injection pressure of the injection valve can be made to approach the target injection pressure with high accuracy.

[0011] According to another feature of the present invention, in the exhaust purification system, the injection pressure adjustment device has a fuel piping that guides fuel from a common rail that stores fuel at a predetermined pressure to be supplied to an injector that injects fuel into the internal combustion engine, to the injection valve, and a pressure adjustment valve that adjusts the pressure of fuel in the fuel piping connected to the injection valve, and the control device has a target injection pressure acquisition unit that acquires a target injection pressure according to the exhaust gas flow rate acquired by the exhaust gas flow rate acquisition unit, and the injection pressure adjustment unit drives the pressure adjustment valve so that the injection pressure becomes the target injection pressure acquired by the target injection pressure acquisition unit.

[0012] With this, there is no need to provide space for installing a pressure pump dedicated to the exhaust purification system of the present invention, and fuel is supplied to the fuel injection valve using the existing common rail, making it possible to reduce the size of the injection pressure adjustment device compared to the case where a pressure pump is installed.

[0013] According to another feature of the present invention, in an exhaust purification system, the target injection pressure is set to a higher value as the exhaust gas flow rate increases, and is set to a higher value as the exhaust gas temperature increases.

[0014] This allows the fuel injected from the nozzle hole to reach the collision surface reliably without being carried away by the exhaust gas, regardless of the flow rate or temperature of the exhaust gas, and without vaporizing before colliding with the collision surface of the dispersion device, thereby causing the fuel to be atomized and dispersed into the exhaust gas. [Brief description of the drawings]

[0015] [Figure 1] 1 is a diagram showing an overall configuration of an internal combustion engine system equipped with an exhaust purification system of the present invention. [Diagram 2] 11 is a flowchart illustrating an example of a processing procedure of an "injection pressure adjustment process." [Diagram 3] FIG. 4 is a diagram illustrating an example of exhaust gas flow rate vs. target injection pressure characteristics. [Figure 4] FIG. 4 is a diagram illustrating an example of target injection pressure vs. pump rotation speed characteristics. [Diagram 5] 10A and 10B are diagrams for explaining fuel injected when the exhaust gas flow rate is low, and fuel atomized by colliding with a dispersion plate. [Figure 6] 10A and 10B are diagrams for explaining fuel injected when the exhaust gas flow rate is high, and fuel atomized by colliding with a dispersion plate. [Figure 7] 13 is a flowchart illustrating an example of a processing procedure of an “injection pressure adjustment process” according to another embodiment. [Figure 8] FIG. 13 is a diagram showing the overall configuration of an internal combustion engine system equipped with an exhaust purification system according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] [Overall configuration of the internal combustion engine system 10 (Figure 1)] The overall configuration of an internal combustion engine system 10 equipped with an exhaust purification system 1 according to the present invention will be described with reference to Fig. 1. Fig. 1 is a diagram showing the overall configuration of an internal combustion engine system 10 equipped with an exhaust purification system 1 according to the present invention. Note that an internal combustion engine 11 in Fig. 1 is, for example, a diesel engine, and exhaust gas containing particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), etc. will be discharged from the internal combustion engine 11. The internal combustion engine system 10 shown in Fig. 1 will be described below in order from the intake side to the exhaust side.

[0017] The intake air flow rate detection device 9a is, for example, an intake air flow rate sensor, and is provided in the intake passage 13 of the internal combustion engine 11 to output a detection signal corresponding to the flow rate of air taken in by the internal combustion engine 11 to the control device 4. The accelerator opening detection device 9b (for example, an accelerator opening sensor) outputs a detection signal corresponding to the opening of the accelerator operated by the driver (i.e., the load required by the driver) to the control device 4. The rotation detection device 9c is, for example, a rotation sensor, and outputs a detection signal corresponding to the rotation speed of the crankshaft of the internal combustion engine 11 (i.e., the engine rotation speed) to the control device 4.

[0018] The internal combustion engine 11 has a plurality of cylinders, and injectors 12a-12d are provided for each cylinder. Fuel is supplied to the injectors 12a-12d via a common rail 7 and fuel pipes 7a-7d, and the injectors 12a-12d are driven by control signals from the control device 4 to inject fuel into each cylinder. The common rail 7 is provided with a fuel pressure detection means 7e, and is filled with fuel adjusted to a target fuel pressure by a fuel pump 7f. The fuel pump 7f pumps up fuel 7h stored in a fuel tank 7g and pumps it to the common rail 7. The control device 4 controls the fuel pump 7f so that the fuel pressure detected by the fuel pressure detection means 7e approaches the target fuel pressure.

[0019] Exhaust gas from the internal combustion engine 11 is exhausted to an exhaust pipe 5 connected to the internal combustion engine 11. The exhaust gas flows downstream from the internal combustion engine 11 through the exhaust pipe 5a, the integrated oxidation catalyst 8, the exhaust pipe 5b, the selective reduction catalyst 16, and the exhaust pipe 5c in this order.

[0020] The exhaust pipe 5 is provided with an injector 2 driven by the control device 4, a dispersion device 3, and an exhaust temperature detection device 9d from the upstream side. The injector 2 is provided in the exhaust pipe 5a so as to inject fuel (reaction liquid) in a direction intersecting the flow direction of the exhaust gas. The injector 2 is driven by the control device 4 and injects fuel in the exhaust gas toward the dispersion device 3 provided upstream of the oxidation catalyst 8a. The injector 2 is connected to a fuel tank 7g via a fuel supply pipe 2b and a pressure pump 6, and fuel is supplied from the fuel tank 7g. The pressure pump 6 pressure-feeds fuel to the injector 2 via the fuel supply pipe 2b. The injector 2 is provided with a fuel pressure sensor 2a, which detects the pressure of the fuel supplied to the injector 2 and outputs a detection signal according to the fuel pressure to the control device 4.

[0021] The dispersion device 3 is provided in the exhaust pipe 5a upstream of the oxidation catalyst 8a. The dispersion device 3 atomizes the fuel injected from the injector 2 and colliding with it, disperses the fuel in the exhaust gas, and mixes it with the exhaust gas. The dispersion device 3 has a collision surface 3a against which the fuel injected from the injector 2 collides.

[0022] The integrated oxidation catalyst 8 includes an oxidation catalyst 8a (DOC: Diesel Oxidation Catalyst), an exhaust temperature detector 9e, a DPF 8c (Diesel Particulate Filter) which is a particulate matter removal filter, and a differential pressure sensor 9h.

[0023] The oxidation catalyst 8a is made of a ceramic cellular cylinder formed into a cylindrical shape or the like, with many through holes formed in the axial direction, and the inner surface of each through hole is coated with a precious metal catalyst such as platinum (Pt). By passing exhaust gas through the many through holes at a predetermined temperature, the oxidation catalyst 8a oxidizes and removes carbon monoxide (CO), hydrocarbons (HC), and the like contained in the exhaust gas.

[0024] The particulate matter removal filter (hereinafter referred to as "DPF") 8c is formed into a cylindrical shape or the like from a porous member made of a ceramic material or the like. The porous DPF 8c captures particulate matter (PM) by passing the inflowing exhaust gas through it, and removes the PM from the exhaust gas. As particulate matter (PM) accumulates in the DPF 8c, it becomes more difficult for the exhaust gas to pass through the DPF 8c, and the collection function decreases.

[0025] The exhaust gas temperature detection device 9d is, for example, an exhaust gas temperature sensor, and outputs a detection signal corresponding to the temperature of the exhaust gas upstream of the oxidation catalyst 8a to the control device 4. The exhaust gas temperature detection device 9e is, for example, an exhaust gas temperature sensor, and outputs a detection signal corresponding to the temperature of the exhaust gas downstream of the oxidation catalyst 8a (and upstream of the DPF 8c) to the control device 4.

[0026] The differential pressure sensor 9h outputs a detection signal corresponding to the differential pressure (pressure difference) between the exhaust pressure (exhaust pipe pressure) downstream of the oxidation catalyst 8a and upstream of the DPF 8c, and the exhaust pipe pressure downstream of the DPF 8c, to the control device 4. Here, the differential pressure (pressure difference) changes when a large amount of particulate matter (PM) accumulates in the DPF 8c. The control device 4 can estimate, based on the detection signal output by the differential pressure sensor 9h, whether a large amount of particulate matter (PM) has accumulated in the DPF 8c, making it difficult for exhaust gas to pass through the DPF 8c, and whether it is necessary to remove the particulate matter (PM) accumulated in the DPF 8c and restore (regenerate) the DPF 8c.

[0027] When the control device 4 estimates that the DPF 8c needs to be restored (regenerated), it causes the injector 2 to inject fuel (reaction liquid) into the exhaust gas in order to remove particulate matter (PM) accumulated in the DPF 8c. The fuel injected from the injector 2 collides with the collision surface 3a of the dispersion device 3 and is dispersed into the exhaust gas (see Figs. 5 and 6). The mixture of exhaust gas and fuel flows into the integrated oxidation catalyst 8 and is guided to the inlet end surface 8b of the oxidation catalyst 8a of the integrated oxidation catalyst 8.

[0028] The fuel is oxidized by the oxygen remaining in the exhaust gas in the oxidation catalyst 8a. The heat generated by the oxidation raises the temperature of the exhaust gas, and the exhaust gas becomes hot. The hot exhaust gas raises the bed temperature of the DPF 8c. When the bed temperature reaches a predetermined temperature or higher (for example, 590°C or higher), the particulate matter (PM) accumulated in the DPF 8c is burned and incinerated, and the collection function of the DPF 8c is restored (regenerated).

[0029] The integrated oxidation catalyst 8 is a type of exhaust purification device into which a mixture of exhaust gas and fuel (reaction liquid) injected into the exhaust gas flows and reacts with the fuel (reaction liquid).

[0030] The exhaust pipe 5b is connected to the downstream side of the DPF 8c, and is provided with an exhaust temperature detection device 9f, a NOx sensor 9i, and a urea water addition valve .

[0031] The exhaust gas temperature detection device 9f is, for example, an exhaust gas temperature sensor, and outputs a detection signal corresponding to the temperature of the exhaust gas downstream of the DPF 8c to the control device 4. The NOx sensor 9i outputs a detection signal corresponding to the concentration of NOx in the exhaust gas upstream of the catalyst 17 to the control device 4.

[0032] The urea water addition valve (liquid addition valve) 14 is provided in the exhaust pipe 5b upstream of the dispersion plate 15. The urea water addition valve 14 is driven by the control device 4 to inject (discharge, add) urea water (reaction liquid) in the exhaust gas toward the dispersion plate 15 provided upstream of the selective reduction catalyst 16. The urea water addition valve 14 is connected to a urea water tank via a urea water supply pipe and a urea water pump (not shown), and urea water is supplied from the urea water tank.

[0033] The dispersion plate 15 is provided in the exhaust pipe 5b upstream of the selective reduction catalyst 16. The dispersion plate 15 atomizes the urea water (reaction liquid) injected from the urea water addition valve 14, disperses the urea water in the exhaust gas, and mixes with the exhaust gas.

[0034] The selective reduction catalyst 16 is formed in a cylindrical shape and is provided with a columnar catalyst 17 inside. The selective reduction catalyst 16 is provided between the exhaust pipe 5b and the exhaust pipe 5c, and is a type of exhaust purification device into which a mixture of urea water (reaction liquid) injected into the exhaust gas and exhaust gas flows in, causing the urea water (reaction liquid) to react with the exhaust gas.

[0035] The particulate urea water reaches the inlet end surface 18 of the catalyst 17 from the dispersion plate 15, and is reformed into ammonia by the heat of the exhaust gas. The catalyst 17 is a catalyst that purifies the exhaust gas by reacting nitrogen oxides (NOx) in the exhaust gas with ammonia (by reducing the NOx). The exhaust gas purified by the catalyst 17 flows into the exhaust pipe 5c through the selective reduction catalyst 16.

[0036] The exhaust pipe 5c is connected to the downstream side of the selective reduction catalyst 16, and an exhaust temperature detection device 9g and a NOx sensor 9j are provided in the exhaust pipe 5c. The exhaust temperature detection device 9g is, for example, an exhaust temperature sensor, and outputs a detection signal corresponding to the temperature of the exhaust gas downstream of the selective reduction catalyst 16 to the control device 4. The NOx sensor 9j outputs a detection signal corresponding to the concentration of NOx in the exhaust gas downstream of the selective reduction catalyst 16 to the control device 4.

[0037] The control device 4 includes a CPU 41, a RAM 42, a storage device 43, a timer 44, and the like. Detection signals from the various detection means described above are input to the control device 4 (CPU 41). The control device 4 (CPU 41) outputs control signals to the various actuators described above. The inputs and outputs of the control device 4 are not limited to the detection means and actuators described above. The temperature and pressure of each part may be calculated by estimation without mounting a sensor. The control device 4 detects the operating state of the internal combustion engine 11 based on detection signals from various detection means including the detection means described above, and controls various actuators including the actuators described above. The storage device 43 is, for example, a storage device such as a Flash-ROM, and stores programs and data for executing control and self-diagnosis of the internal combustion engine. The control device 4 (CPU 41) also includes an exhaust gas flow rate acquisition unit 4a, a target injection pressure acquisition unit 4b, an injection pressure adjustment unit 4c, and the like, the details of which will be described later.

[0038] Hereinafter, an example of an exhaust gas purification system in which fuel (corresponding to a reaction liquid) is injected from an injection valve 2 toward a collision surface 3a of a dispersion device 3 to an oxidation catalyst 8a (corresponding to an aftertreatment device) will be described.

[0039] [Processing procedure of the control device 4 in the first embodiment (FIG. 2)] The exhaust purification system 1 in the internal combustion engine system 10 has an injection valve 2, a fuel supply pipe 2b, a distribution device 3, a pressure pump 6, a fuel tank 7g, and a control device 4, and performs the following process to ensure that fuel hits the distribution device 3.

[0040] The control device 4 (CPU 41) starts the "injection pressure adjustment process" shown in FIG. 2 at a predetermined time interval (several [ms] to several tens of [ms]), for example, and advances the process to step S110.

[0041] In step S110, the control device 4 calculates the current exhaust gas flow rate, and proceeds to step S120. The control device 4 detects the operating state of the internal combustion engine 11 based on detection signals from, for example, the intake air flow rate detection device 9a, the accelerator opening detection device 9b, the rotation detection device 9c, the exhaust temperature detection device 9d, etc., and obtains the exhaust gas flow rate based on the operating state.

[0042] In step S120, the control device 4 obtains the target injection pressure based on the calculated exhaust gas flow rate, and proceeds to step S130. The exhaust gas flow rate vs. target injection pressure characteristic shown in Fig. 3 is stored in the storage device 43 of the control device 4, and the control device 4 obtains the target injection pressure based on the exhaust gas flow rate vs. target injection pressure characteristic and the exhaust gas flow rate.

[0043] In step S130, the control device 4 obtains a target rotation speed of the pressure feed pump 6 based on the obtained target injection pressure, and proceeds to step S140. The target injection pressure-target rotation speed characteristic shown in Fig. 4 is stored in the memory device 43 of the control device 4, and the control device 4 obtains the target rotation speed based on the target injection pressure-target rotation speed characteristic and the target injection pressure.

[0044] In step S140, the control device 4 instructs the obtained target rotation speed to the pressure pump 6, and ends the process shown in Fig. 2. When performing the above process, the fuel pressure sensor 2a may be omitted.

[0045] The control device 4 (CPU 41) executing the process of step S110 corresponds to an exhaust gas flow rate acquisition unit 4a (see FIG. 1) that acquires an exhaust gas flow rate, which is the flow rate of the exhaust gas, based on the operating state of the internal combustion engine.

[0046] In addition, the control device 4 (CPU 41) executing the process of step S120 corresponds to a target injection pressure acquisition unit 4b (see FIG. 1) that acquires a target injection pressure according to the exhaust gas flow rate acquired by the exhaust gas flow rate acquisition unit.

[0047] The control device 4 (CPU 41) executing the process of step S140 corresponds to the injection pressure adjustment unit 4c (see FIG. 1) that drives the pressure pump so that the injection pressure of the fuel injection valve becomes the target injection pressure acquired by the target injection pressure acquisition unit.

[0048] ●[Actions and effects of the reaction mixture system (Figures 5 and 6)] FIG. 5 is a diagram for explaining fuel injected when the exhaust gas flow rate is low and fuel atomized by colliding with the dispersion plate. As shown in FIG. 5, the injection valve 2 has, for example, two nozzle holes 2e, 2f at the tip. The dispersion device 3 is provided in the exhaust pipe 5a so as to be located below the nozzle holes 2e, 2f and so that the collision surface 3a is parallel to the flow direction of the exhaust gas. The fuel F1 is injected from the nozzle holes 2e, 2f in a direction intersecting the flow direction of the exhaust gas. The nozzle holes 2e, 2f are directed toward the collision surface 3a of the dispersion device 3, and each of them is aimed at one point on the collision surface 3a. The number of the nozzle holes 2e, 2f is not limited to two, and may be one or three or more.

[0049] According to the exhaust gas purification system 1 of the present invention, when the flow rate of the exhaust gas flowing through the exhaust pipe 5a is low, the rotation speed of the pressure pump 6 is accordingly reduced. As a result, the injection pressure of the injection valve 2 is also reduced. The fuel F1 injected from the injection valve 2 with a low injection pressure is ejected from the nozzle holes 2e and 2f and flies through the air at a relatively slow speed. Therefore, the fuel that bounces off the collision surface 3a of the dispersion device 3 and is atomized does not have enough kinetic energy to reach the nozzle holes 2e and 2f of the injection valve 2. For example, when focusing on one particle of fuel F2, the fuel F2 bounces in a direction that reaches the nozzle hole 2f in the shortest distance, but the speed in that direction immediately drops, so it does not reach the nozzle hole 2f and does not adhere to it. Moreover, advantageously, although the penetration force of the injected fuel F1 (the force that crosses without being affected by the flow of exhaust gas) is weak, the exhaust gas flow rate is low to begin with, so the collision point of the fuel F1 does not deviate significantly from the position originally aimed at the collision surface 3a of the dispersion device 3.

[0050] FIG. 6 is a diagram for explaining the fuel injected when the exhaust gas flow rate is high and the fuel atomized by colliding with the dispersion plate. When the exhaust gas flow rate is high as shown in FIG. 6, the rotation speed of the pressure pump 6 increases accordingly. As a result, the injection pressure of the injection valve 2 also increases. The fuel F3 injected from the injection valve 2 with a high injection pressure is injected from the nozzle holes 2e and 2f and flies through the air at a relatively high speed and has a strong penetrating force. Therefore, it collides with the collision surface 3a of the dispersion device 3 at a position almost as originally intended without being washed away by the exhaust gas. Moreover, conveniently, the particulate fuel F4 that bounces off the collision surface 3a of the dispersion device 3 and is atomized is washed away by the exhaust gas because its speed decreases and its penetrating force is weakened. For example, if one particulate fuel F4 is focused on, the fuel F4 bounces in a direction that reaches the nozzle hole 2e in the shortest distance, but is washed away by the exhaust gas and does not adhere to the nozzle hole 2f. Therefore, it does not reach the nozzle hole 2e of the injection valve 2 and adhere to it. And since the fuel injected from the injector 2 collides with the collision surface 3a at a substantially targeted position regardless of the change in the exhaust gas flow rate, there is no need to enlarge the dispersion device 3 to account for deviations. Thus, clogging of the injection hole of the injector 2 does not occur, and the size of the dispersion device 3 can be minimized.

[0051] Incidentally, in order to prevent clogging of the nozzle holes 2e and 2f due to the rebound of fuel, it is possible to provide the dispersion device 3 downstream of the injection valve 2, for example, rather than below the nozzle holes 2e and 2f, and to point the tip of the injection valve 2 toward the dispersion device 3 located downstream accordingly. In this way, the fuel rebounded from the collision surface 3a is scattered almost downstream, and does not fly toward the injection valve 2 located upstream. However, a large collision surface 3a is required to receive the fuel injected from the nozzle holes 2e and 2f of such an injection valve 2. Therefore, it is desirable to position the dispersion device 3 as far below the nozzle holes 2e and 2f as possible.

[0052] The exhaust gas purification system of the present invention is not limited to the appearance, configuration, structure, etc. described in this embodiment, and various changes, additions, and deletions are possible within the scope of the present invention. For example, in this embodiment, so-called open loop control is performed as the injection pressure adjustment process, but feedback control may be performed using the fuel pressure sensor 2a to bring the actual injection pressure of the injector 2 closer to the target injection pressure. Figure 7 is a flowchart explaining an example of the processing procedure of the [injection pressure adjustment process] according to another embodiment when feedback control is performed.

[0053] [Processing procedure of the control device 4 in another embodiment (FIG. 7)] In the above embodiment, the fuel pressure sensor 2a may be omitted, but in this embodiment, the fuel pressure sensor 2a is required. The control device 4 (CPU 41) starts the "injection pressure adjustment process" shown in Fig. 2 at a predetermined time interval (several [ms] to several tens of [ms]), for example, and proceeds to step S210.

[0054] In step S210, the control device 4 calculates the current exhaust gas flow rate, and proceeds to step S220. The control device 4 detects the operating state of the internal combustion engine 11 based on detection signals from, for example, the intake air flow rate detection device 9a, the accelerator opening detection device 9b, the rotation detection device 9c, the exhaust temperature detection device 9d, etc., and obtains the exhaust gas flow rate based on the operating state.

[0055] In step S220, the control device 4 acquires the target injection pressure based on the calculated exhaust gas flow rate, and proceeds to step S230. The exhaust gas flow rate vs. target injection pressure characteristic shown in Fig. 3 is stored in the memory device 43 of the control device 4, and the control device 4 acquires the target injection pressure based on the exhaust gas flow rate vs. target injection pressure characteristic and the exhaust gas flow rate. In the exhaust gas flow rate vs. target injection pressure characteristic shown in Fig. 3, the higher the exhaust gas flow rate, the higher the target injection pressure that is acquired.

[0056] In step S230, the control device 4 feedback controls the rotation speed of the pressure feed pump 6 so that the pressure detected by the fuel pressure sensor 2a approaches the acquired target injection pressure, and then ends the process shown in FIG.

[0057] The control device 4 (CPU 41) executing the process of step S230 corresponds to the injection pressure adjustment unit 4c (see FIG. 1) that drives the pressure pump so that the injection pressure of the fuel injection valve becomes the target injection pressure acquired by the target injection pressure acquisition unit.

[0058] [Exhaust gas purification system 21 according to another embodiment (FIG. 8)] In the present embodiment, the injection pressure adjusting device for adjusting the injection pressure of the injection valve 2 has been described as having a fuel tank 7g, a fuel supply pipe 2b, and a pressure pump 6. However, as shown in FIG. 8, the injection pressure adjusting device may have a common rail 7, a fuel supply pipe 2c, and a pressure adjustment valve 2d. The fuel supply pipe 2c guides fuel from the common rail 7 to the injection valve 2. The fuel supply pipe 2c is provided with a pressure adjustment valve 2d, and the control device 4 adjusts the pressure of fuel in the fuel supply pipe 2c connected to the injection valve 2 by driving the pressure adjustment valve 2d.

[0059] In this case, for example, the process shown in FIG. 7 is performed, and in the process of step S230, the opening degree of the pressure regulating valve 2d or the opening time per predetermined period in the PWM control is feedback controlled so that the pressure detected by the fuel pressure sensor 2a approaches the target injection pressure.

[0060] In this embodiment, the exhaust gas purification system according to the present invention is applied to the injector 2 and the dispersion device 3, but it may be applied to the urea water addition valve 14 (corresponding to the injector) and the dispersion plate 15 (corresponding to the dispersion device). In this case, the selective reduction catalyst 16 corresponds to the aftertreatment device, the urea water corresponds to the reaction liquid, and a pressure pump (not shown) that pressure-feeds the urea water is controlled.

[0061] In this embodiment, the storage device 43 of the control device 4 stores an exhaust gas flow rate vs. target injection pressure characteristic in which the target injection pressure is obtained based on the exhaust gas flow rate, and one target injection pressure corresponding to one exhaust gas flow rate is obtained. However, the target injection pressure may be obtained based on two values, the exhaust gas flow rate and the exhaust gas temperature, taking into consideration the exhaust gas temperature in addition to the exhaust gas flow rate. The target injection pressure is set to a higher value as the exhaust gas flow rate increases, and is set to a higher value as the exhaust gas temperature increases. [Explanation of symbols]

[0062] 1, 21 Exhaust purification system 2 Injection valve 2a Fuel pressure sensor 2b, 2c fuel supply pipe 2d Pressure Regulating Valve 2e, 2f nozzle hole 3 Dispersion device 3a Collision surface 4. Control device 4a Exhaust gas flow rate acquisition unit 4b Target injection pressure acquisition unit 41 CPU 42 RAM 43 Storage device 44 Timer 5a~5c Exhaust pipe 6. Pressure pump 7 Common Rail 7a~7d Fuel piping 7e Fuel pressure detection means 7f Fuel Pump 7g Fuel Tank 7h fuel 8 Integrated oxidation catalyst 8a Oxidation catalyst 8b Inlet side end face 8c DPF 9a Intake air flow rate detection device 9b Accelerator opening detection device 9c Rotation detection device 9d~9g Exhaust temperature detector 9h Differential Pressure Sensor 10 Internal Combustion Engine System 11 Internal combustion engine 12a~12d Injectors 13 Intake passage 14 Urea solution addition valve 15 Dispersion plate 16 Selective reduction catalyst 17 Catalyst 18 Inlet side end face

Claims

1. An exhaust purification system that injects a reaction liquid into an exhaust pipe of an internal combustion engine, mixes the injected reaction liquid with exhaust gas, and causes the exhaust gas to flow into an aftertreatment device to purify the exhaust gas, The exhaust purification system includes: an injection valve that injects the reaction liquid in a direction intersecting a flow direction of the exhaust gas; a dispersion device having a collision surface on which the reaction liquid injected from the injection valve is collided; an injection pressure adjusting device for adjusting an injection pressure, which is the pressure of the reaction liquid injected from the injection valve; The post-treatment device; a control device for controlling the injection valve and the injection pressure adjusting device; It has The control device includes: an exhaust gas flow rate acquisition unit that acquires an exhaust gas flow rate, which is a flow rate of the exhaust gas, based on an operating state of the internal combustion engine; an injection pressure adjusting unit that controls the injection pressure adjusting device in accordance with the exhaust gas flow rate acquired by the exhaust gas flow rate acquiring unit; It has The injection pressure adjusting device is a fuel pipe for guiding fuel from a common rail that stores fuel at a predetermined pressure to be supplied to an injector that injects fuel into the internal combustion engine to the injection valve; a pressure regulating valve that adjusts the pressure of fuel in the fuel pipe connected to the injection valve; It has The control device includes: a target injection pressure acquisition unit that acquires a target injection pressure according to the exhaust gas flow rate acquired by the exhaust gas flow rate acquisition unit, the injection pressure adjusting unit drives the pressure adjusting valve so that the injection pressure becomes the target injection pressure acquired by the target injection pressure acquiring unit; Exhaust purification system.

2. An exhaust purification system which injects a reaction liquid into an exhaust pipe of an internal combustion engine, mixes the injected reaction liquid with exhaust gas, and causes the mixed gas to flow into an aftertreatment device to purify the exhaust gas, The exhaust purification system includes: an injection valve that injects the reaction liquid in a direction intersecting a flow direction of the exhaust gas; a dispersion device having a collision surface on which the reaction liquid injected from the injection valve is collided; an injection pressure adjusting device for adjusting an injection pressure, which is the pressure of the reaction liquid injected from the injection valve; The post-treatment device; a control device for controlling the injection valve and the injection pressure adjusting device; It has The control device includes: an exhaust gas flow rate acquisition unit that acquires an exhaust gas flow rate, which is a flow rate of the exhaust gas, based on an operating state of the internal combustion engine; an injection pressure adjusting unit that controls the injection pressure adjusting device in accordance with the exhaust gas flow rate acquired by the exhaust gas flow rate acquiring unit; It has The control device includes: a target injection pressure acquisition unit that acquires a target injection pressure according to the exhaust gas flow rate acquired by the exhaust gas flow rate acquisition unit, The injection pressure adjusting unit drives the injection pressure adjusting device so that the injection pressure becomes the target injection pressure acquired by the target injection pressure acquiring unit, The reaction liquid is a fuel, The target injection pressure is The larger the exhaust gas flow rate, the higher the value is set, and the higher the exhaust gas temperature, the higher the value is set. Exhaust purification system.

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