JP5151959B2 - Exhaust gas purification system and exhaust gas purification method - Google Patents

Description

  The present invention relates to an exhaust gas purification system and an exhaust gas purification method for directly injecting fuel into an exhaust pipe with respect to an exhaust gas purification device such as a NOx storage reduction catalyst or a diesel particulate filter (DPF).

  One device for purifying exhaust gas from an internal combustion engine is a NOx purification catalyst device for purifying NOx (nitrogen oxide) in the exhaust gas. In one of these NOx purification catalyst devices, an alkali metal or alkaline earth metal is supported together with a noble metal, NO (nitrogen monoxide) in exhaust gas containing excess oxygen is oxidized and adsorbed on the catalyst as a nitrate, There is an apparatus carrying a NOx occlusion reduction type catalyst for purifying NOx.

  This NOx occlusion reduction type catalyst occludes NOx when the exhaust gas is in a lean air-fuel ratio state in which the oxygen is excessive, and releases NOx occluded in a rich air-fuel ratio state where the oxygen concentration is low or the excess air ratio is less than 1. At the same time, the released NOx is reduced in a reducing atmosphere to reduce NOx.

  In this NOx occlusion reduction type catalyst, when the lean air-fuel ratio state as in the normal operation of the diesel engine continues, most of the alkali metal or alkaline earth metal that is the NOx occlusion material changes to nitrate and is adsorbed on the catalyst. If the amount of nitrate exceeds a certain amount, the NOx occlusion function is lost, and the NOx purification performance decreases. Therefore, in order to maintain the NOx purification performance, before the NOx occlusion capacity reaches saturation, the reducing gas concentration derived from the fuel is increased with respect to the oxygen concentration, and the oxygen concentration in the exhaust gas is lowered to temporarily air. The regeneration process for releasing NOx from the NOx occlusion material is performed so that the excess ratio λ becomes a rich air-fuel ratio state of 1 or less. This regeneration process is performed at regular time intervals or when the accumulated amount of NOx occlusion is monitored and the NOx occlusion capacity approaches saturation.

  Moreover, since the sulfur component is contained in the fuel of the internal combustion engine, this sulfur component is adsorbed on the catalyst as a sulfate, so that there is a problem of sulfur poisoning that the NOx occlusion capacity of the NOx occlusion material is lowered. is there. In order to regenerate the NOx storage material from this sulfur poisoning, the temperature of the catalyst is raised to about 700 ° C., and while maintaining this temperature, a state in which oxygen is insufficient with respect to the amount of fuel contained in the exhaust gas is created. NOx storage material is desulfurized.

  In the control for these regeneration processes and desulfurization processes, it is necessary to create a state where oxygen in the exhaust gas is insufficient with respect to the amount of fuel contained in the exhaust gas while maintaining the catalyst temperature at an appropriate temperature. Increasing the amount of fuel supplied with a constant concentration of oxygen (intake air) results in a state where oxygen is insufficient (rich air-fuel ratio state), but if this state continues, the oxidation reaction rate of the fuel decreases, The calorific value per hour decreases, and the catalyst temperature decreases. Therefore, it is necessary to control to periodically decrease the fuel supply amount and increase the oxygen concentration in the exhaust gas.

  In these controls for regeneration and desulfurization, in addition to intake control that reduces the oxygen concentration by reducing the amount of air flowing into the cylinder to the extent that the engine output does not decrease, part of the exhaust gas is burned again. EGR (exhaust gas recirculation) control to return to the room is performed. Further, when it is necessary to further reduce the oxygen concentration in the exhaust gas flowing into the NOx purification catalyst, in the cylinder fuel injection control of the engine, post-injection control for adding fuel in the piston expansion stroke, NOx For example, direct fuel injection control in the exhaust pipe is performed so that the fuel is directly injected into the exhaust passage on the upstream side of the purification catalyst to make the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst rich.

  Further, in the regeneration process of the particulate filter that collects PM (particulate matter) in the exhaust gas, when the bed temperature of the particulate filter is equal to or higher than the first temperature, the fuel addition means in the combustion chamber is used. If the exhaust passage temperature is equal to or higher than the second temperature and the particulate bed temperature is equal to or higher than the third temperature, an exhaust gas purification apparatus and method for an internal combustion engine using fuel addition means in the exhaust passage has been proposed (for example, Patent Document 1).

  In relation to this, when regenerating the catalyst regeneration type particulate filter, the fuel injection from the fuel injector is heated to evaporate fuel, and the mixed gas is ignited while being sent into the exhaust pipe. An exhaust gas purification device that supplies the gas to the upstream side of the particulate filter has been proposed (see, for example, Patent Document 2).

  In these direct fuel injections in the exhaust pipe, a fuel injection valve (injector) that can inject fuel at a high pressure is used to atomize the light oil fuel, which is a liquid, into fine droplets and evaporate and vaporize it in a short time. I use it. In this fuel injection valve, highly accurate injection amount control is required to maintain the temperature of the catalyst and to control the ratio of fuel and oxygen in accordance with the control target value.

However, when a fuel injection valve using fuel boosted by a fuel supply pump for supplying fuel into the cylinder (inside the cylinder) of the internal combustion engine is used, there are the following problems. In other words, when fuel is supplied directly to the exhaust passage, the fuel pressure changes depending on the engine speed related to the speed of the fuel supply pump. Therefore, if the engine speed is low or fluctuates significantly, the fuel pressure Not set pressure.

  That is, when running using a vehicle equipped with an exhaust gas purification system, the engine speed is not always a constant speed and may vary. If the engine speed changes abruptly from 1200 rpm to 2000 rpm during the gear shift process of the transmission, for example, the fuel pressure increases and decreases in proportion to the engine speed. If this happens, the fuel pressure will fluctuate. If the time for injecting the fuel is short (for example, 1 second), this problem can be reduced considerably. However, the particulate matter (PM) trapped in the particulate filter (DPF) is removed by combustion or the NOx occlusion reduction type. In the desulfurization treatment for removing sulfur adsorbed on the catalyst (LNT catalyst), fuel may be continuously injected into the exhaust pipe for several seconds to several hundred seconds. In such a case, the rotational speed varies during injection. The fuel pressure during injection is not fixed.

When the fuel is injected in a state where the fuel pressure is lower than the set pressure, the fuel injection amount becomes smaller than the necessary amount (control target amount), and the exhaust gas temperature and the catalyst temperature are difficult to rise. Conversely, when fuel is injected in a state where the fuel pressure is higher than the set pressure, the amount of fuel injection becomes too large, and the exhaust gas temperature rises too much, and white smoke is likely to be generated. It becomes.
JP 2003-148132 A JP 2005-61249 A

  The present invention has been made in view of the above situation, and its purpose is to directly supply fuel to the exhaust passage with high-precision flow rate adjustment even when the engine speed of the internal combustion engine is low and the fuel pressure is low. It is an object to provide an exhaust gas purification system and an exhaust gas purification method that can be supplied.

In order to achieve the above object, an exhaust gas purification system of the present invention is a first exhaust that injects fuel directly into an exhaust pipe by using fuel pressure for in-cylinder fuel injection in order from an upstream side into an exhaust passage of an internal combustion engine. In an exhaust gas purification system provided with an in-pipe direct fuel supply device and an exhaust gas purification device, the supply capacity is smaller than that in the first exhaust pipe direct fuel supply device and the fuel pressure for in-cylinder fuel injection is not used. A direct fuel supply device is provided, and the second direct fuel supply device in the exhaust pipe is sucked into the bypass passage from the fuel storage portion by the negative pressure of the bypass passage provided in the exhaust passage, and is passed through the bypass passage. The exhaust gas purifier is configured to be supplied to the exhaust passage on the upstream side, and a throttling portion is provided in the exhaust passage downstream of the branch portion of the bypass passage from the exhaust passage. Rutotomoni be constituted by providing an exhaust throttle valve to the merging portion between the bypass passage of the exhaust passage.

With this configuration, in the low engine speed range where the fuel pressure does not reach the set pressure, the fuel supply pressure that depends on the engine speed does not depend on the fuel pressure depending on the engine speed, and the direct fuel supply device in the second exhaust pipe can provide a precise supply amount in the exhaust pipe A small amount of fuel can be supplied to the vehicle. Further, in the high engine speed region where the fuel pressure reaches the set pressure, the fuel can be directly supplied into the exhaust pipe at the set pressure with an accurate supply amount by the second exhaust pipe direct fuel supply device. it can. Further, in the second direct exhaust pipe fuel supply device, since the fuel is sucked, a very small amount of fuel can be supplied. A small amount of fuel can be sucked by the direct fuel supply device in the second exhaust pipe with the bypass passage having a negative pressure by the throttle of the exhaust throttle valve.

  In the above exhaust gas purification system, an exhaust gas amount adjusting device is further provided in the bypass passage in order to adjust the fuel supply amount from the second direct exhaust pipe fuel supply device. According to this configuration, the fuel supply amount can be minutely adjusted by the exhaust gas amount adjusting device.

  Alternatively, in the above exhaust gas purification system, in order to adjust the fuel supply amount from the second direct exhaust pipe direct fuel supply device, the exhaust passage is joined from the bypass passage to the exhaust passage downstream from the joining portion. An exhaust gas amount adjusting passage is provided, and an exhaust gas amount adjusting device is provided in the exhaust gas amount adjusting passage. According to this configuration, the fuel supply amount can be minutely adjusted by the exhaust gas amount adjusting device.

In addition, the exhaust gas purification method of the present invention for achieving the above object is the above exhaust gas purification system, wherein when the engine speed is equal to or less than a preset engine speed threshold, the direct fuel in the second exhaust pipe the fuel from the supply device is supplied to the exhaust passage, and wherein the engine speed is the case the engine is greater than the rotational speed threshold value, to supply the fuel from the first exhaust pipe direct fuel supply device to the exhaust passage It is a method to do.

  The engine speed threshold is lower than the set pressure when the engine speed is equal to or lower than the engine speed threshold, and varies depending on the engine speed. When the engine speed is greater than the engine speed threshold, fuel supply is performed. The engine speed is stabilized when the fuel pressure by the pump becomes equal to or higher than the set pressure.

  By this method, in a low engine speed region where the fuel pressure does not reach the set pressure, a small amount of fuel can be accurately supplied by a small-capacity direct fuel supply device in the second exhaust pipe regardless of the fuel pressure depending on the engine speed. The fuel can be supplied. In addition, in the high engine speed region where the fuel pressure reaches the set pressure, the fuel can be supplied at an accurate supply amount at the set pressure with the second exhaust pipe direct fuel supply device.

In the exhaust gas purification system or the exhaust gas purification method, the fuel supply from the second direct exhaust pipe fuel supply device generates a negative pressure in the bypass passage by restricting the exhaust throttle valve. To do. According to this method, in the second direct exhaust pipe fuel supply device, the fuel is sucked by the generated negative pressure, so that a very small amount of fuel can be supplied.

In the exhaust gas purification system, fuel is supplied from both the first exhaust pipe direct fuel supply device and the second exhaust pipe direct fuel supply device within an engine speed range in which the engine speed is set in advance. . Alternatively, in the exhaust gas purification system, the fuel supply from the second direct exhaust pipe fuel supply device is performed by generating a negative pressure in the bypass passage by restricting the exhaust throttle valve , and the engine speed In the engine speed range set in advance, fuel is supplied from both the first exhaust pipe direct fuel supply device and the second exhaust pipe direct fuel supply device.
According to these methods, when the engine speed is within a preset engine speed range and the fuel pressure is relatively stable, the basic fuel supply amount is set by the first exhaust pipe direct fuel supply device. Since the supply and fine adjustment of the supply amount can be performed by adjusting the fuel supply from the direct fuel supply device in the second exhaust pipe, the fuel can be supplied with high accuracy.

  In the exhaust gas purification method, an exhaust gas amount adjusting device may be provided in the bypass passage in order to adjust the fuel supply amount from the second direct fuel supply device in the exhaust pipe, or the second In order to adjust the fuel supply amount from the direct fuel supply device in the exhaust pipe, an exhaust gas amount adjusting passage that joins the exhaust passage from the bypass passage to the downstream side of the joining portion is provided, and the exhaust gas amount adjustment When the exhaust gas amount adjusting device is provided in the passage, the amount of fuel supplied from the second direct exhaust pipe fuel supply device is adjusted by adjusting the amount of exhaust gas passing through the bypass passage. . According to this method, it is possible to adjust the fuel supply amount by the exhaust gas amount adjusting device.

  Also, when the fuel required for heating the catalyst is supplied by direct fuel injection in the exhaust pipe so that the temperature of the catalyst can be raised in a short time at the time of engine start or low exhaust temperature such as low power operation, the catalyst temperature Responding to changes, the supply of fuel and the amount of air necessary for combustion are controlled and supplied with high-accuracy flow control, thereby suppressing the discharge of unburned fuel (HC) to the downstream side of the exhaust gas purification device can do.

  In addition, a decrease in exhaust gas temperature is detected from the amount of fuel supplied to the cylinder of the internal combustion engine and the engine speed, and the amount of fuel and air supplied to the upstream side of the exhaust gas purification device (oxygen amount) is highly accurate. By controlling at, it is possible to suppress the catalyst temperature from deviating to a lower temperature side than the activation temperature range.

  Also, in the desulfurization process (sulfur desorption process) for recovery from sulfur poisoning, fuel and air are supplied to the exhaust gas flowing into the catalyst of the exhaust gas purification device with high-accuracy flow adjustment. By burning the catalyst, it is possible to heat the catalyst to a high temperature and keep the reducing atmosphere at a desulfurizable temperature (around 700 ° C.) while preventing deterioration of fuel consumption.

  According to the exhaust gas purification system and the exhaust gas purification method of the present invention, even when the engine speed of the internal combustion engine is low, fuel can be directly supplied to the exhaust passage with high-precision flow rate adjustment. In other words, even in an engine operating region where the fuel injection pressure at the fuel injection valve changes depending on the engine speed, it is possible to perform highly accurate flow rate adjustment control of the fuel injection amount in accordance with the exhaust gas flow rate. be able to. Further, the fuel can be atomized and mixed with the exhaust gas regardless of the fuel injection pressure.

  Furthermore, by supplying the fuel with high accuracy, it is possible to suppress an increase in the exhaust gas flow rate, and it is possible to suppress heat dissipation from the exhaust gas purification device disposed downstream of the direct fuel supply device in the exhaust pipe to the exhaust gas. . Therefore, it is possible to improve the heat retention of the exhaust gas purification device during transient operation where the engine speed is unstable.

  Hereinafter, an exhaust gas purification system and an exhaust gas purification method according to embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of an exhaust gas purification system 1 according to an embodiment of the present invention. This exhaust gas purification system 1 injects fuel f1 directly into an exhaust pipe (exhaust passage) 16 using an in-cylinder fuel injection fuel pressure Pf in order from the upstream side into an exhaust passage 16 of an engine (internal combustion engine) 10. The first exhaust pipe direct fuel supply device 17 and the exhaust gas purification device 18 are configured.

  The engine 10 of the exhaust gas purification system 1 includes an intake air amount sensor 12 (MAF sensor), a compressor 13a of a turbocharger 13, an intercooler 14, and an intake valve (intake throttle) 15 in an intake passage 11 connected to an intake manifold 10a. It has. Further, a turbine 13b of the turbocharger 13, a first in-pipe direct fuel supply device 17 and an exhaust gas purification device 18 for directly injecting fuel into the exhaust passage 16 are connected to the exhaust passage 16 connected to the exhaust manifold 10b. I have. The first exhaust pipe direct fuel supply device 17 is constituted by a fuel injection valve that uses a fuel pressure Pf for in-cylinder fuel injection. Further, the EGR passage 19 connecting the exhaust manifold 10b and the intake manifold 10a is provided with an EGR cooler 20 and an EGR valve 21.

  In the configuration of FIG. 1, the exhaust gas purification device 18 includes an oxidation catalyst device (DOC) 18a, a NOx occlusion reduction type catalyst device (LNT) 18b, and a filter device with catalyst (CSF) 18c.

The oxidation catalyst device 18a is formed by supporting an oxidation catalyst such as platinum on a porous ceramic honeycomb structure support. This oxidation catalyst serves to purify the exhaust gas by oxidizing HC and CO in the exhaust gas, and at the time of NOx regeneration for recovering the NOx storage capacity of the NOx storage reduction catalyst and PM regeneration of the filter 18c with catalyst. At this time, a part of the fuel supplied into the exhaust passage 16 is oxidized to raise the temperature of the exhaust gas G. The NOx occlusion reduction type catalyst device 18b is formed by supporting an alkali metal or an alkaline earth metal together with a noble metal, and oxidizes NO in exhaust gas containing excess oxygen and adsorbs it as a nitrate on the catalyst to purify NOx. . The NOx occlusion reduction type catalyst stores NOx when the exhaust gas G is lean, and releases the stored NOx when the exhaust gas G is rich, and reduces the released NOx in a reducing atmosphere. Reduce. In this rich air-fuel ratio control for NOx release, fuel is directly supplied into the exhaust passage 16.

  The catalyst-equipped filter device 18c is composed of a DPF with a catalyst provided with a diesel particulate filter (DPF) for collecting particulate matter (PM) in the exhaust gas. The catalyst-attached DPF is formed of a monolith honeycomb wall flow type filter or the like in which the inlet and outlet of a porous ceramic honeycomb channel are alternately plugged. A catalyst such as platinum or cerium oxide is supported on the filter.

By this DPF with catalyst, PM in the exhaust gas is collected by the porous ceramic wall. When the trapped amount of the PM is increased, by injecting fuel into the exhaust passage 16, to increase the temperature of the exhaust gas G The fuel is oxidized by the oxidation catalyst, catalyzed by the high temperature exhaust gas G The attached DPF is raised to the combustion start temperature of PM, and the collected PM is forcibly burned and removed to perform PM regeneration of the DPF with catalyst.

  Further, in order to measure the temperature of the exhaust gas G, a first temperature sensor 22 is provided at the inlet of the exhaust gas purification device 18, and a second temperature sensor 23 and a λ (excess air ratio) sensor 24 are provided at the outlet of the exhaust gas purification device 18. Is disposed.

  A control device for inputting the measurement values of these sensors 22, 23, 24 and the like and data necessary for operation control of the engine 10 to perform the operation state of the engine 10 and the exhaust gas purification control and regeneration control of the exhaust gas purification system 1 ( (Not shown) is provided. This control device is a control device called an ECU (engine control unit), and based on the data from the engine 10 and the detected value of the intake air amount sensor 12 and the like, the intake valve 15, the first exhaust pipe direct fuel supply device 17, The EGR valve 22 and the like, a second exhaust pipe direct fuel supply device 30 and an exhaust throttle valve 16b, which will be described later, are controlled.

Further, in the present invention, the second exhaust pipe direct fuel supply device 30 that has a smaller supply capacity than the first exhaust pipe direct fuel supply device 17 and does not use the fuel pressure for in-cylinder fuel injection is provided. . As shown in FIG. 2, the second direct fuel supply device 30 in the exhaust pipe draws the fuel f <b> 2 from the fuel storage portion 32 by setting the bypass passage 31 provided in the exhaust passage 16 to a negative pressure, thereby bypassing the bypass passage 31. The exhaust gas purification device 18 is configured to be supplied to the exhaust passage 16 on the upstream side of the exhaust gas purification device 18 via 31. In the second direct exhaust pipe fuel supply device 30, the fuel f2 is supplied to the exhaust passage 16 by suction, so that the flow rate can be adjusted with a small amount with high accuracy.

  Further, a throttle portion 16 a is provided in the exhaust passage 16 downstream of the branch portion 33 from the exhaust passage 16 of the bypass passage 31. At the same time, an exhaust throttle valve 16 b is provided at a joining portion 34 of the bypass passage 31 to the exhaust passage 16. By the throttle of the exhaust throttle valve 16b, the bypass passage 31 is set to a negative pressure and a small amount of fuel f2 is sucked. That is, by utilizing the phenomenon that the flow rate of the exhaust gas G increases and the pressure decreases at a place where the exhaust gas G is throttled, a negative pressure is generated in the bypass passage 31 with respect to the fuel storage portion 32 to generate a small amount of fuel. F2 is sucked and supplied to the exhaust passage 16. By adjusting the valve opening of the exhaust throttle valve 16b, the flow rate of the fuel f2 to be sucked can be adjusted.

Further, an exhaust gas amount adjusting passage (exhaust pipe injection) that joins the exhaust passage 16 downstream from the joining portion 34 from the bypass passage 31 in order to adjust the fuel supply amount from the second direct fuel supply device 30 in the exhaust pipe. And an exhaust gas amount adjusting device 36 formed of an adjustment cone or the like that can enter and exit the exhaust gas amount adjusting passage 35 is provided. With this exhaust gas amount adjusting device 36, for example, by adjusting the insertion amount of the adjustment cone, the fuel supply amount can be adjusted minutely. This prevents the fuel f2 that is greater than the required fuel from being supplied into the exhaust gas. It should be noted that an exhaust gas amount adjusting device may be provided in the bypass passage 31 without providing the exhaust gas amount adjusting passage 35. In this case, the fuel supply amount can be made completely zero.

  Next, an exhaust gas purification method in the exhaust gas purification system 1 will be described. In this exhaust gas purification method, in the exhaust gas purification system 1 described above, when the engine speed Ne is equal to or less than the preset engine speed threshold Ns, the fuel f2 is sent from the second exhaust pipe direct fuel supply device 30 to the exhaust passage 16. When the engine speed Ne is greater than a preset engine speed threshold Ns, the fuel f1 is supplied from the first exhaust pipe direct fuel supply device 17 into the exhaust passage 16.

  As shown in FIG. 3, when the engine speed Ne is equal to or lower than the engine speed threshold Ns, the fuel pressure Pf is lower than the set pressure Pfs and the engine speed threshold Ns varies depending on the engine speed Ne. Further, when the engine speed Ne is larger than the engine speed threshold value Ns, the fuel pressure Pf by the fuel supply pump becomes equal to or higher than the set pressure Pfs, and the engine speed is stable.

  Further, the above control can be performed based on, for example, control flows as shown in FIGS. 4 and 5, and these control flows are called when there is a demand for supplying fuel directly into the exhaust pipe. It is a flow and is repeatedly executed by being called by an advanced control flow until this request is completed.

The control flow in FIG. 4 is for determining whether or not to inject fuel into the exhaust pipe. When the temperature Tg of the exhaust gas temperature G is low, the fuel is exhausted even if fuel is supplied into the exhaust pipe. Even if it reaches the oxidation catalyst device 18a of the gas purification device 18, the catalytic oxidation reaction does not occur, and the supplied fuel flows to the downstream side of the exhaust gas purification device 18 in an unburned state. In order to prevent this, It is a control flow for supplying fuel after the exhaust gas temperature at which the oxidation reaction in the oxidation catalyst device 18a becomes possible.

  When the control flow in FIG. 4 starts, the operation of the exhaust throttle valve 16b is stopped (S14) while the temperature Tg of the exhaust gas G is equal to or lower than a preset temperature threshold Tg1 (for example, 250 ° C.) (NO in S12). After the temperature Tg of the exhaust gas G becomes higher than the temperature threshold Tg1 (YES in S12), the operation of the exhaust throttle valve 16b is started (S13). By this control, the throttle of the exhaust throttle valve 16b and the supply of the fuel f2 from the second exhaust pipe direct fuel supply device 30 into the exhaust passage 16 by this throttle are stopped until the temperature of the exhaust gas G becomes high. .

  When the engine speed Ne is equal to or less than the preset engine speed threshold Ns (NO in S22), the control flow in FIG. 5 is performed while maintaining the operation of the exhaust throttle valve 16b (S24) while direct fuel in the second exhaust pipe. The fuel f2 is supplied into the exhaust passage 16 only from the supply device 30 (S25), and when the engine speed Ne is higher than the preset engine speed threshold Ns (YES in S22), the first direct exhaust pipe fuel supply apparatus Fuel f1 is supplied into the exhaust passage 16 only from 17 (S23).

  With this method, in the low engine speed region (Ne ≦ Ns) where the fuel pressure Pf does not reach the set pressure Pfs, the direct fuel supply in the second exhaust pipe having a small capacity is performed regardless of the fuel pressure Pf depending on the engine speed Ne. The device 30 can supply a small amount of fuel with an accurate supply amount. Further, in the high engine speed region (Ne> Ns) where the fuel pressure Pf is the set pressure Pfs, the second exhaust pipe direct fuel supply device 17 can supply the fuel with an accurate supply amount at the set pressure Pfs. .

  In addition, the fuel supply from the second exhaust pipe direct fuel supply device 30 increases the flow rate of the exhaust gas G1 passing through the bypass passage 31 by restricting the exhaust throttle valve 16b, and generates a negative pressure in the bypass passage 31. To do. According to this method, in the second exhaust pipe direct fuel supply device 30, the fuel f2 is sucked by the generated negative pressure, so that a very small amount of fuel can be supplied. Further, the flow rate of the fuel f2 to be sucked can be adjusted by adjusting the valve opening degree of the exhaust throttle valve 16b.

  Further, the flow rate of the fuel f2 supplied from the second direct exhaust pipe fuel supply device 30 is adjusted by adjusting the flow rate of the exhaust gas G1 passing through the bypass passage 31 by the exhaust gas amount adjusting device 36. The exhaust gas amount adjusting device 36 can adjust the fuel supply amount by a minute amount.

  Normally, only one of the first exhaust pipe direct fuel supply device 17 and the second exhaust pipe direct fuel supply device 30 supplies fuel into the exhaust pipe, but both may be used at the same time. Good. In this case, the fuel is supplied from both the first exhaust pipe direct fuel supply device 17 and the second exhaust pipe direct fuel supply device 30 within the engine speed range in which the engine speed Ne is set in advance. According to this, when the engine speed Ne is within a preset engine speed range and the fuel pressure is relatively stable, the basic fuel supply amount is supplied by the first in-exhaust pipe direct injection device 17. In addition, since the fine adjustment of the supply amount can be performed by adjusting the fuel supply from the direct fuel supply device 30 in the second exhaust pipe, the fuel supply can be performed with high accuracy.

  Alternatively, the fuel is supplied from both the first exhaust pipe direct fuel supply device 17 and the second exhaust pipe direct fuel supply device 30 when the target fuel supply amount is within a preset supply amount range. According to this, fuel can be supplied from both even if the supply amount is insufficient in the second exhaust pipe direct fuel supply device 30 alone, so that fuel can be supplied with high accuracy.

  According to the exhaust gas purification system 1 and the exhaust gas purification method described above, even when the engine speed Ne of the engine 10 is low, fuel can be directly supplied to the exhaust passage 16 with high-precision flow rate adjustment. That is, even in the operating region of the engine 10 where the fuel injection pressure Pf at the fuel injection valve of the first direct exhaust pipe direct fuel injection device 17 varies depending on the engine speed Ne, the fuel injection pressure Pf is not affected. In addition, it is possible to perform highly accurate flow rate adjustment control of the fuel injection amount according to the flow rate of the exhaust gas G, and atomization of the fuel f2 and mixing with the exhaust gas G are possible.

  Furthermore, by supplying the fuels f1 and f2 with high accuracy, it is possible to prevent the fuel more than the necessary fuel from being supplied into the exhaust gas, and to suppress an increase in the flow rate of the exhaust gas G. Heat dissipation from the exhaust gas purification device 18 disposed downstream of the direct supply devices 17 and 30 to the exhaust gas G can be suppressed. Accordingly, it is possible to improve the heat retention of the exhaust gas purifying device 18 during transient operation where the engine speed Ne is unstable.

It is a figure which shows the structure of the exhaust-gas purification system of embodiment of this invention. It is a figure which shows the structure of the 1st exhaust pipe direct fuel supply apparatus and the 2nd exhaust pipe direct fuel supply apparatus. It is a figure which shows the relationship between an engine speed and fuel pressure. It is a figure which shows an example of the control flow of an exhaust throttle valve. It is a figure which shows an example of the control flow of the direct fuel supply in an exhaust pipe.

Explanation of symbols

1 Exhaust gas purification system 10 Engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 11 Intake passage 16 Exhaust passage 16a Throttle part 16b Exhaust throttle valve 17 1st exhaust pipe direct fuel supply apparatus 18 Exhaust gas purification apparatus 30 2nd exhaust pipe direct fuel supply apparatus 31 Bypass path 32 Fuel storage part 33 Branch part 34 Merge part 35 Exhaust gas amount adjusting passage 36 Exhaust gas amount adjusting device f1, f2 Fuel G Exhaust gas G1 Bypass passage exhaust gas Ne Engine speed Ns Pre-set engine speed threshold value Pf Fuel pressure Pfs Set pressure Tg Exhaust gas temperature Tg1 Temperature Threshold

Claims (6)

An exhaust gas purification system provided with a first direct exhaust pipe fuel supply device and an exhaust gas purification device for injecting fuel directly into an exhaust pipe using a fuel pressure for in-cylinder fuel injection in order from the upstream side in an exhaust passage of an internal combustion engine In
A second exhaust pipe direct fuel supply device that has a smaller supply capacity than the first exhaust pipe direct fuel supply device and does not use fuel pressure for in-cylinder fuel injection ;
In the second exhaust pipe direct fuel supply device, the negative pressure of the bypass passage provided in the exhaust passage causes the fuel to be sucked into the bypass passage from the fuel storage portion, and the upstream side of the exhaust gas purification device via the bypass passage. Configured to supply to the exhaust passage,
In addition, a throttle portion is provided in the exhaust passage downstream of the branch passage from the exhaust passage of the bypass passage, and an exhaust throttle valve is provided in a joint portion of the exhaust passage with the bypass passage. Exhaust gas purification system. 2. The exhaust gas purification system according to claim 1, wherein when the engine speed is equal to or less than a preset engine speed threshold, fuel is supplied from the second exhaust pipe direct fuel supply device into the exhaust passage, and the engine speed is increased. When the number is larger than the engine speed threshold, the exhaust gas purification method is characterized in that fuel is supplied from the first exhaust pipe direct fuel supply device into the exhaust passage. 2. The exhaust gas purification system according to claim 1, wherein the fuel supply from the second direct exhaust pipe fuel supply device is performed by generating a negative pressure in the bypass passage by restricting the exhaust throttle valve. Exhaust gas purification method. 3. The exhaust gas purification method according to claim 2, wherein the fuel supply from the second direct exhaust pipe fuel supply device is performed by generating a negative pressure in the bypass passage by restricting the exhaust throttle valve. . 2. The exhaust gas purification system according to claim 1, wherein fuel is supplied from both of the first exhaust pipe direct fuel supply device and the second exhaust pipe direct fuel supply device within an engine speed range in which the engine speed is set in advance. Exhaust gas purification method characterized by performing . In the engine speed is the engine speed region previously set, according to claim 3, characterized in that the fuel is supplied from both of the first exhaust pipe direct fuel supply device and the second exhaust pipe direct fuel supply system Exhaust gas purification method.

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