JP5293279B2 - Exhaust pipe direct fuel injection system and exhaust gas purification system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust pipe direct fuel injection system capable of making the pressure of fuel supplied to a fuel injection valve always constant and necessary pressure even if fuel pressure is instantaneously changed by fluctuation in engine speed, in the exhaust pipe fuel direct injection of an internal combustion engine. <P>SOLUTION: A fuel pressure fluctuation suppression mechanism 20 is arranged at a fuel supply pipe 12 to the fuel injection valve 11 in series. In the fuel pressure fluctuation suppression mechanism 20, a first accumulator 22 is arranged at a fuel inlet 21 side and a second accumulator 24 is arranged at a fuel outlet 23 side, first check valves 25, 25A are arranged between a fuel inlet 21 and the first accumulator 22, and a second check valve 26 is arranged between the first accumulator 22 and the second accumulator 24 to allow a flow from the fuel inlet 21 side to the fuel outlet 23 side. The first accumulator 22 is provided with a pressure-regulating valve 27 for discharging fuel f when internal combustion pressure becomes higher than preset pressure. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention directly injects fuel into an exhaust pipe during an NOx regeneration process, a desulfurization process, a PM regeneration process, or the like for an exhaust gas purification device such as a NOx storage reduction catalyst or a diesel particulate filter (DPF). The present invention relates to an exhaust pipe direct fuel injection system and an exhaust gas purification system.

  In order to purify the exhaust gas of an internal combustion engine mounted on an automobile or the like using light oil or gasoline as fuel, an exhaust gas purification device (post-treatment device) is provided in the exhaust passage of the internal combustion engine to purify the exhaust gas. As this exhaust gas purification device, an oxidation catalyst (DOC) such as a three-way catalyst, a NOx storage reduction catalyst (LNT), a diesel particulate filter (DPF), a DPF with catalyst (CSF), or the like is used.

An oxidation catalyst such as a three-way catalyst oxidizes unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) by catalytic action. NOx occlusion reduction type catalyst carries alkali or alkaline earth metal together with noble metal, and the exhaust gas air-fuel ratio is lean and oxidizes nitric oxide (NO) to nitrogen dioxide (NO ₂ ), which is then nitrated on the catalyst. It adsorbs and purifies NOx, releases the adsorbed NOx when the air-fuel ratio of the exhaust gas is rich, and reduces the released NOx.

  The DPF with catalyst collects PM when the exhaust gas temperature or the catalyst temperature is equal to or lower than the PM combustion start temperature, purifies the exhaust gas, and PM burns the DPF with catalyst when the collected PM accumulates to some extent. The temperature is raised above the start temperature and the combustion is removed, thereby purifying the exhaust gas.

  In this NOx occlusion reduction type catalyst, before the NOx occlusion capacity reaches saturation, the air-fuel ratio of the exhaust gas is switched from the lean state to the rich state to release NOx from the NOx occlusion reduction type catalyst, and the released NOx Reduce and purify. This process for recovering the NOx storage capacity is called NOx regeneration process. In this NOx regeneration process, the NOx occlusion capacity is recovered while periodically repeating the process of reducing the λ (excess air ratio) of the exhaust gas entering the catalyst to a value smaller than 1.

  Further, in the NOx occlusion reduction type catalyst, the sulfur component is contained in the fuel of the internal combustion engine, and this sulfur component is adsorbed on the catalyst as a sulfate, so that the NOx occlusion capacity of the NOx occlusion material is lowered. There is a problem of sulfur poisoning. In order to regenerate the NOx occlusion material from this sulfur poisoning, the NOx occlusion material is desulfurized by raising the temperature of the catalyst to about 700 ° C. and maintaining the temperature to make the exhaust gas rich.

  Also, in the DPF device for collecting PM, a DPF with a catalyst that supports an oxidation catalyst or a PM oxidation catalyst and lowers the combustion start temperature of the PM collected by the DPF is used. Even in the DPF, in order to avoid an increase in exhaust pressure due to clogging, when the amount of collected PM increased to some extent, the DPF with catalyst was heated to about 550 ° C. by the temperature rise of the exhaust gas and collected. A PM regeneration process for burning and removing PM is performed. In this NOx regeneration process, desulfurization process, and PM regeneration process, in order to raise the catalyst temperature in a short time or to make the exhaust gas rich in the air-fuel ratio, post-injection by cylinder fuel injection control and In-pipe fuel direct injection, in which fuel is directly injected into the exhaust pipe, is performed.

  In this direct fuel injection in the exhaust pipe, the primary supply pressure of the fuel supply pump is used to pressurize the fuel injected into the exhaust pipe and supply it to the fuel injection valve. In this method, the fuel pressure depends on the engine speed. Therefore, the map data indicating the fuel pressure corresponding to the engine speed is created, and the fuel injection amount is controlled using the fuel injection time corresponding to the fuel pressure calculated from the map data.

  However, in the direct fuel injection in the exhaust pipe, there are problems such as the following changes in the fuel pressure due to the engine speed and a temporary increase in the fuel pressure when the fuel injection is stopped.

  In other words, when the engine speed changes and the fuel pressure changes instantaneously, a difference is likely to occur between the fuel pressure value used when determining the injection amount by control and the actual fuel pressure value. When this occurs, the fuel injection amount actually injected becomes excessive or too small relative to the target fuel injection amount for control.

  Further, in the exhaust gas purification device (post-treatment device) using the NOx occlusion reduction type catalyst, the NOx regeneration process for recovery of the NOx purification capacity is performed with respect to the target fuel injection amount at the time of direct fuel injection in the exhaust pipe. If the actual fuel injection amount becomes excessive, excess fuel that has not been used for NOx reduction will be released into the atmosphere, making it difficult to satisfy exhaust gas regulations by increasing HC emissions. There is a fear. Further, when the actual fuel injection amount is too small with respect to the target fuel injection amount, NOx stored on the catalyst cannot be completely reduced, and NOx is released into the atmosphere. Since the purification performance is reduced, it may be difficult to satisfy the exhaust gas regulations regarding NOx even in this case.

  Further, during the desulfurization (sulfur desorption) process in the NOx occlusion reduction type catalyst, the excess air ratio λ corresponding to the air-fuel ratio of the ratio of the fuel injection amount and the air in the exhaust gas is about 0.1 than 1. It is necessary to maintain the catalyst temperature at about 0.9 and decrease the catalyst temperature to around 700 ° C. In this case, if the actual fuel injection amount decreases due to a change in fuel pressure, the catalyst temperature As the temperature decreases, the excess air ratio λ is less likely to be less than 1. On the other hand, when the actual fuel injection amount increases, the excess air ratio λ becomes a value smaller than 0.9, and the ratio of oxygen decreases, so the oxidation reaction rate decreases, so the catalyst temperature decreases. Will end up.

  Furthermore, when the fuel injection is stopped after injecting the fuel with the fuel injection valve (injector) for a certain period of time, the fuel is rapidly throttled during this injection stop process, so the pressure of the fuel flowing into the fuel injection valve is temporarily increased. Let If this increased fuel pressure is detected by the fuel pressure sensor, when calculating the fuel injection time corresponding to the fuel injection amount in the next direct fuel injection in the exhaust pipe, the fuel pressure for calculation is used as the actual fuel pressure. Since it is misrecognized as a value higher than the pressure and the injection time is reduced from the required injection time, the actual fuel injection amount is reduced from the target fuel injection amount.

In relation to this, regarding the reducing agent addition valve that injects the fuel component into the exhaust pipe provided with the exhaust gas purification device, the pulsation that suppresses the pressure fluctuation of the fuel generated in the addition system as the reducing agent addition valve opens and closes. An exhaust gas purification device including a suppression member has been proposed (see, for example, Patent Document 1). This pulsation suppressing member is composed of a container member that divides the main chamber and the sub chamber, and a sub chamber (buffer chamber) is provided in communication with the main chamber connected to the reducing material addition valve, and the pressure generated in the main chamber The wave is reflected in the sub chamber whose other end is opened or closed, and the pressure wave is suppressed by causing the reflected wave and the pressure wave to interfere with each other in the main chamber.

  However, in this pulsation suppressing member, the pressure pulsation suppressing effect is not increased unless the phase of the pressure wave in the main chamber and the sub chamber is reversed, and each of the main chamber and the sub chamber is appropriately dimensioned with respect to the pressure wave. It seems difficult to do.

JP 2006-200511 A

  The present invention has been made in view of the above-described situation, and an object of the present invention is to perform fuel injection even in an instantaneous change in fuel pressure due to fluctuations in engine speed in direct injection of fuel in an exhaust pipe of an internal combustion engine. It is an object of the present invention to provide a direct fuel injection system in an exhaust pipe that can always make the pressure of fuel supplied to a valve constant and necessary.

  Another object is to calculate the fuel injection amount by controlling the fuel injection in the direct fuel injection in the exhaust pipe of the internal combustion engine, against the temporary increase in fuel pressure when the fuel injection is stopped. An object of the present invention is to provide a direct fuel injection system in an exhaust pipe that can accurately calculate a target fuel injection amount without being detected by a fuel pressure sensor that detects a fuel pressure to be used.

A further object is to perform direct injection of fuel in the exhaust pipe with an accurate fuel injection amount at a stable fuel pressure that does not depend on the engine speed, etc., and increase during NOx regeneration processing, desulfurization processing, and PM regeneration processing. An object of the present invention is to provide an exhaust gas purification system that can make the conditions of the temperature and the air-fuel ratio (or the excess air ratio) of the exhaust gas appropriate and can sufficiently ensure the exhaust gas performance.

In order to achieve the above object, an exhaust pipe direct fuel injection system according to the present invention is an exhaust pipe direct fuel injection system in which fuel is injected into an exhaust pipe of an internal combustion engine by direct fuel injection into the exhaust pipe. A fuel pressure fluctuation suppression mechanism is arranged in series in a fuel supply pipe that supplies fuel to a fuel injection valve to be injected, and the fuel pressure fluctuation suppression mechanism is divided into a first pressure accumulation chamber on the fuel inlet side and a second pressure accumulation chamber on the fuel outlet side. A first check valve between the fuel inlet and the first pressure accumulation chamber, a second check valve between the first pressure accumulation chamber and the second pressure accumulation chamber, and a fuel from the fuel inlet side. Each of the first pressure accumulation chambers is configured to permit the flow to the outlet side and stop the opposite flow, and when the internal fuel pressure becomes higher than a preset pressure , the fuel is supplied to the first pressure accumulation chamber. Provided with a pressure adjustment valve that discharges to the outside of the accumulator That.

  According to this configuration, the fluctuation of the fuel pressure on the fuel supply pump side can be buffered in the first pressure accumulating chamber, and when the pressure in the first pressure accumulating chamber rises above a necessary value, the pressure regulating valve The high pressure fuel can be returned to the fuel tank or the like, and even if the fuel pressure in the fuel supply pipe connected to the fuel inlet side that supplies the fuel to the first pressure accumulating chamber decreases, the fuel is reduced by the first check valve. Since it is possible to prevent the fuel pressure in the first pressure accumulating chamber from flowing down to the fuel inlet side, fuel injection is always performed at a constant and necessary fuel pressure, i.e., a preset pressure, without depending on the engine speed. Can do.

In the exhaust pipe direct fuel injection system, a fuel pressure sensor for detecting a fuel pressure at the time of direct fuel injection in the exhaust pipe is provided in the first pressure accumulation chamber. According to this configuration, the temporary increase in fuel pressure after the fuel is injected into the exhaust pipe for a certain period of time is buffered in the second pressure accumulation chamber and the fuel flows from the second pressure accumulation chamber into the first pressure accumulation chamber. Since it can be blocked by the 2 check valve, it is possible to prevent the fuel pressure in the first pressure accumulation chamber from increasing. Therefore, the fuel pressure sensor detects the fuel pressure temporarily increased when direct fuel injection in the exhaust pipe is stopped, and the fuel pressure at the time of direct fuel injection in the exhaust pipe is higher than the pressure at which the fuel is actually injected. It is possible to prevent injection control.

  In the exhaust pipe fuel direct injection system, the first check valve is formed of a variable operating pressure check valve capable of changing the operating pressure. According to this configuration, since the fuel injection pressure can be changed by changing the operating pressure of the first check valve, the fuel injection speed is changed in accordance with the temperature of the catalyst and the degree of deterioration of the catalyst. Fuel injection becomes possible.

  In the exhaust pipe direct fuel injection system, the pressure regulating valve is formed of a variable working pressure type pressure regulating valve capable of changing the working pressure. According to this configuration, since the fuel injection pressure can be changed by changing the operating pressure of the pressure regulating valve, the fuel injection speed is changed according to the temperature of the catalyst and the degree of deterioration of the catalyst. become able to. In the exhaust pipe direct fuel injection system, a fuel temperature sensor for detecting a temperature of fuel is provided in the first pressure accumulation chamber or the second pressure accumulation chamber. According to this configuration, the temperature of the fuel stored in the first pressure accumulation chamber or the second pressure accumulation chamber is measured so that the fuel whose density varies with the fuel temperature becomes the control target fuel flow rate (mass flow rate). While correcting the fuel density and correcting the volume flow rate of the fuel, the fuel can be injected with higher accuracy.

  In addition, an exhaust gas purification system of the present invention for achieving the above object supplies fuel to an exhaust gas purification device provided in an exhaust passage of an internal combustion engine using the above-described fuel direct injection system in an exhaust pipe. Composed.

According to this configuration, the fuel pressure fluctuation suppressing mechanism suppresses a change in the fuel pressure supplied to the fuel injection valve and can supply the fuel to the fuel injection valve under a stable fuel pressure. This fuel injection amount can be prevented from deviating from the control target fuel injection amount. Therefore, it very effective to reduce emissions of NOx due to too little of emissions and exhaust pipe fuel injection amount of the unburned HC of the exhaust pipe fuel injection amount of excess in the NOx regeneration process, also, during the desulfurization process and the PM regeneration processing Therefore, the exhaust gas performance can be sufficiently ensured because the conditions of the temperature rise and the air-fuel ratio (or excess air ratio) of the exhaust gas can be satisfied.

According to the exhaust pipe fuel direct injection system of the present invention, the first pressure accumulation chamber can buffer the fuel pressure depending on the engine speed, and the pressure accumulation valve is provided in the first pressure accumulation chamber. When the pressure rises above a necessary value, the high-pressure fuel can be returned to the fuel tank or the like, and when the fuel pressure in the fuel supply pipe connected to the fuel inlet decreases, the first check valve Therefore, it is possible to prevent the fuel from returning to the fuel inlet side and reducing the fuel pressure in the first pressure accumulating chamber, so that the fuel can be always injected at a constant and necessary fuel pressure without depending on the engine speed. .

Further, after the fuel is injected into the exhaust pipe for a certain period of time, the fuel is rapidly throttled when the injection is stopped, but the temporary increase in fuel pressure generated by this rapid throttle is buffered in the second pressure accumulation chamber. At the same time, since the second check valve can prevent the fuel from flowing from the second pressure accumulation chamber into the first pressure accumulation chamber, an increase in the fuel pressure in the first pressure accumulation chamber can be prevented. Therefore, the fuel pressure sensor detects the fuel pressure temporarily increased when direct fuel injection in the exhaust pipe is stopped, and the fuel pressure at the time of direct fuel injection in the exhaust pipe is higher than the pressure at which the fuel is actually injected. It is possible to prevent injection control.

Further, according to the exhaust gas purification system of the present invention, the fuel pressure fluctuation suppressing mechanism can supply fuel to the fuel injection valve under a stable fuel pressure. Regardless of the number, the pressure can always be constant and necessary. Therefore, even when the engine speed changes transiently, direct fuel injection in the exhaust pipe can be performed with a precise fuel injection amount based on a stable fuel pressure.

  Therefore, the difference between the actual fuel injection amount into the exhaust pipe and the control target fuel injection amount is reduced, the temperature rise during the NOx regeneration process, the desulfurization process and the PM regeneration process, the air-fuel ratio (or the excess air ratio) of the exhaust gas. ) Can be satisfied, and exhaust gas performance can be sufficiently secured.

It is the figure which showed the structure of the exhaust-gas purification system of embodiment of this invention. It is the figure which showed the structure of the fuel pressure fluctuation suppression mechanism of embodiment of this invention. It is the figure which showed the structure of the fuel pressure fluctuation suppression mechanism at the time of forming a 1st check valve with a check valve of a working pressure variable type. It is the figure which showed the structure of the operating pressure variable type check valve. It is the figure which showed an example of the control flow for control of the fuel pressure fluctuation suppression mechanism of a pressure accumulation chamber.

  Hereinafter, an exhaust pipe direct fuel injection system and an exhaust gas purification system according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, a direct fuel injection system 10 in an exhaust pipe according to an embodiment of the present invention includes a fuel injection valve 11 that injects fuel f into an exhaust pipe (exhaust passage) 5 and supplies the fuel f to an exhaust gas purification device 6. A fuel pressure fluctuation suppression mechanism 20 is arranged in series with a fuel supply pipe 12 that supplies fuel. The fuel pressure fluctuation suppression mechanism 20 receives fuel f such as light oil from the fuel tank 15 via the fuel supply pipe 14. The fuel supply pump 13 is configured to be pressurized and supplied. The fuel supply pump 13 is driven by the rotational force of the crankshaft of the engine 2. Further, the fuel f from the fuel pressure fluctuation suppressing mechanism 20 is returned to the fuel tank 15 through the return pipe 16. The fuel injection valve 11, the fuel pressure fluctuation suppressing mechanism 20, the fuel supply pipe 12, the fuel supply pump 13, the control device 30 a that controls these, and the like constitute the direct fuel injection system 10 in the exhaust pipe.

  As shown in FIG. 2, the fuel pressure fluctuation suppressing mechanism 20 is formed to have a first pressure accumulation chamber 22 on the fuel inlet 21 side and a second pressure accumulation chamber 24 on the fuel outlet 23 side. A first check valve 25 is provided between the first pressure accumulating chamber 22 and the first check valve 25 so as to allow the flow from the fuel inlet 21 side to the first pressure accumulating chamber 22 side, that is, the fuel outlet 23 side, and stop the opposite flow. Further, a second check valve 26 is provided between the first pressure accumulation chamber 22 and the second pressure accumulation chamber 24 to flow from the first pressure accumulation chamber 22 side to the second pressure accumulation chamber 24 side, that is, from the fuel inlet 21 side to the fuel. It is provided to allow the flow toward the outlet 22 and stop the opposite flow.

  As a result, the engine speed is temporarily reduced, the supply pressure of the fuel supply pump 13 is temporarily reduced, and the fuel supply pipe 12 connected to the fuel inlet 21 side for supplying the fuel f to the first pressure accumulating chamber 22 is provided. Even when the fuel pressure decreases, the first check valve 25 can prevent the fuel f from flowing out to the fuel inlet 21 side and the fuel pressure in the first pressure accumulating chamber 22 from decreasing.

Further, a temporary increase in fuel pressure after fuel is injected into the exhaust pipe for a certain period of time is buffered in the second pressure accumulation chamber 24, and the second check valve 26 changes the second pressure accumulation chamber 24 to the first pressure accumulation chamber 22. Since the fuel f can be prevented from flowing in, an increase in the fuel pressure in the first pressure accumulating chamber 22 can be prevented.

Further, a pressure regulating valve 27 is provided in the first pressure accumulation chamber 22 so that the fuel f is returned to the fuel tank 15 when the fuel pressure inside the first pressure accumulation chamber 22 becomes higher than a preset pressure. . With this pressure regulating valve 27, the upper limit of the fuel pressure inside the first pressure accumulating chamber 22 can be maintained at a preset pressure.

Further, a fuel pressure sensor 28 for detecting the fuel pressure at the time of direct injection of fuel in the exhaust pipe is provided in the first pressure accumulation chamber 22. As a result, a temporary increase in fuel pressure after fuel is injected into the exhaust pipe for a certain period of time is buffered in the second pressure accumulation chamber 24 and the fuel f flows from the second pressure accumulation chamber 24 into the first pressure accumulation chamber 22. Since it is blocked by the second check valve 26, this temporary increase in fuel pressure is not transmitted to the fuel pressure sensor 28 provided in the first pressure accumulation chamber 22.

  Therefore, the fuel pressure sensor 28 detects the fuel pressure temporarily increased when the direct fuel injection in the exhaust pipe is stopped, and the fuel pressure at the time of direct fuel injection in the exhaust pipe is higher than the pressure at which the fuel is actually injected. Controlling fuel injection can be prevented.

  A fuel temperature sensor 29 that detects the temperature of the fuel f is provided in the first pressure accumulation chamber 22 or the second pressure accumulation chamber 24. The fuel flow is corrected by correcting the fuel density so that the fuel whose density changes according to the fuel temperature detected by the fuel temperature sensor 29 becomes the control target fuel flow rate (mass flow rate). However, the fuel can be injected with higher accuracy.

  With the fuel pressure fluctuation suppressing mechanism 20 having the above-described configuration, the fuel pressure change can be suppressed when the engine speed changes transiently in the direct fuel injection in the exhaust pipe, and the fuel pressure temporarily increased when the injection is stopped. Since the fuel pressure sensor 28 is disposed so that the fuel pressure sensor 28 does not detect the fuel pressure sensor 28, accurate fuel injection amount control can be performed under a stable fuel pressure. Accordingly, fuel can be injected into the exhaust pipe 5 at a constant and necessary fuel pressure, that is, a preset pressure, regardless of the engine speed. Thereby, the deviation between the fuel injection amount to the exhaust pipe and the target fuel injection amount can be reduced.

  Further, as shown in FIG. 3, the first check valve 25 is formed of a variable operating pressure check valve 25A capable of changing the operating pressure. As shown in FIG. 4, this variable operating pressure check valve 25A is connected to a fuel inlet 21 connected to the fuel supply pipe 12, and is a spherical valve body 25Aa for opening and closing the check valve 25A. A check operating pressure adjusting spring 25Ab that presses the valve body 25Aa against the fuel inlet 21, a spring displacement adjusting bar 25Ac that adjusts the base position of the check operating pressure adjusting spring 25Ab, and the spring displacement adjusting bar 25Ac It has an adjustment bar position control cam 25Ad to be moved.

  In this variable operating pressure type check valve 25A, the rotation position of the adjustment bar position control cam 25Ad is adjusted by adjusting the spring displacement of the adjustment bar position control cam 25Ad by controlling the rotation of the adjustment bar position control cam 25Ad with a step motor or the like. When the bar 25Ac is changed in the pushing direction, the spring displacement adjusting bar 25Ac pushes the base side position of the check operating pressure adjusting spring 25Ab toward the valve body 25Aa, so that the valve body 25Aa is pushed toward the fuel inlet 21 side. Since the urging force of the check operating pressure adjusting spring 25Ab increases, the set pressure when the check valve 25A is opened can be increased.

  Further, when the rotational position of the adjustment bar position control cam 25Ad is changed in the direction in which the adjustment bar position control cam 25Ad pulls out the spring displacement adjustment bar 25Ac, the biasing force of the check operating pressure adjustment spring 25Ab decreases, so the check The set pressure when the valve 25A is opened can be lowered.

  By using this variable operating pressure check valve 25A, the fuel injection pressure can be changed by changing the operating pressure of the first check valve 25A, so that it depends on the temperature of the catalyst and the degree of deterioration of the catalyst. Thus, fuel injection can be performed by changing the fuel injection speed.

  Next, an exhaust gas purification system according to an embodiment of the present invention will be described. In this exhaust gas purification system, the fuel f is supplied to the exhaust gas purification device 6 provided in the exhaust pipe (exhaust passage) 5 of the engine (internal combustion engine) 2 using the fuel direct injection system 10 in the exhaust pipe. Composed.

  As shown in FIG. 1, this exhaust gas purification system 1 includes an air cooler (not shown), an intake flow rate sensor (MAF sensor) (from the upstream side) to an intake passage 3 connected to an intake manifold 2a of an engine (internal combustion engine) 2. (Not shown), a compressor 4a of the turbocharger 4, an intercooler (not shown), and an intake valve (intake throttle) (not shown) are provided so that fresh air A can be supplied to a cylinder (cylinder) of the engine 2. The

  Further, the exhaust pipe 5 connected to the exhaust manifold 2b includes a turbine 4b of the turbocharger 4, a fuel injection valve (injector) 11 for direct fuel injection in the exhaust pipe, and an exhaust gas purification device 6 from the upstream side.

  In the configuration shown in FIG. 4, the exhaust gas purification device 6 includes an oxidation catalyst device (DOC) 6a, a NOx occlusion reduction type catalyst device (LNT) 6b, and a filter device with catalyst (CSF) 6c.

  The oxidation catalyst device 6a is formed by supporting an oxidation catalyst such as platinum on a porous ceramic honeycomb structure support. This oxidation catalyst is used for purifying exhaust gas by oxidizing HC and CO in the exhaust gas, for NOx regeneration for recovering NOx storage capacity of the NOx storage reduction catalyst, and for recovery from sulfur poisoning. During the desulfurization process of the catalyst and the PM regeneration process of the filter with catalyst, the fuel f supplied to the exhaust pipe 5 is partly oxidized to raise the temperature of the exhaust gas G. .

  The NOx occlusion reduction type catalyst device 6b 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 is lean air-fuel ratio, and releases the stored NOx when the exhaust gas is rich air-fuel ratio, and reduces the released NOx in a reducing atmosphere. To reduce. In this rich air-fuel ratio control for NOx release, the fuel f is directly supplied into the exhaust pipe 5.

  Further, in the NOx occlusion reduction type catalyst, the sulfur component is contained in the fuel of the engine 2, and this sulfur component is adsorbed on the catalyst as a sulfate, so that the NOx occlusion capacity of the NOx occlusion material is lowered. There is a problem of sulfur poisoning. In order to regenerate the NOx occlusion material from this sulfur poisoning, the fuel f is injected into the exhaust pipe 5 and the temperature of the exhaust gas is increased by oxidizing the fuel f with an oxidation catalyst, so that the catalyst is heated to about 700 ° C. The NOx occlusion material needs to be desulfurized by raising the temperature and maintaining the temperature to make the exhaust gas rich.

  The catalyst-equipped filter device 6c 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 amount of collected PM increases, the fuel f is injected into the exhaust pipe 5 and the temperature of the exhaust gas is increased by oxidizing the fuel f with the oxidation catalyst. 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 processing of the DPF with catalyst.

  Further, in order to measure the temperature Tg of the exhaust gas G, an exhaust gas temperature sensor 7a at the inlet of the exhaust gas purification device 6, and a catalyst temperature sensor 7b for measuring the catalyst temperature of the exhaust gas purification device 6, An excess air ratio sensor (λ sensor) 7c for measuring the excess air ratio (λ) or oxygen concentration in the exhaust gas is provided.

  An engine control device that performs exhaust gas purification control and regeneration control of the exhaust gas purification system 1 by inputting measured values of these sensors 7a, 7b, 7c, etc., the operation state of the engine 2, and data necessary for operation control of the engine 2. 30 is provided. The engine control device 30 is a control device called an ECU (engine control unit). The control device 30 a of the exhaust pipe direct fuel injection system 10 is provided in a form included in the engine control device (ECU) 30. The engine control device 30 is configured to control the intake valve (not shown), the fuel supply pump 13, the fuel injection valve 11, and the EGR passage 8 based on data from the engine 2 and detection values of an intake air amount sensor (not shown). The EGR valve 9 and the like are controlled.

  In the exhaust gas purification system 1, the fuel f boosted by the fuel supply pump 13 in the direct fuel injection in the exhaust pipe 5 such as NOx regeneration processing, desulfurization processing, and PM regeneration processing using the fuel injection system 10 in the exhaust pipe. The fuel pressure at the time of direct injection by the fuel pressure fluctuation suppressing mechanism 20 is set to a constant and necessary fuel pressure, and the fuel f is injected from the fuel injection valve 11.

  The exhaust pipe fuel injection in the exhaust gas purification system 1 is performed according to a control flow as shown in the control flow for direct exhaust pipe fuel injection as shown in FIG.

  In this control flow, the engine is started and called from the advanced control flow. When this control flow starts, it is determined in step S10 whether or not direct injection of fuel in the exhaust pipe is in progress. If it is not in the state where direct exhaust pipe fuel injection is performed in this determination, a predetermined determination time (a time related to an interval for determining whether direct exhaust pipe fuel injection is performed) Δt1 has elapsed, and then the process returns to step S10. .

If it is determined in step S10 that direct fuel injection in the exhaust pipe is performed, the process proceeds to the next step S11. In step S11, it is determined whether or not the catalyst temperature Tc of the exhaust gas purification device 6 to be subjected to direct fuel injection in the exhaust pipe is in the temperature regions R1, R2, and R3 for performing the respective processes.

This temperature range is a first temperature range R1 of 200 ° C. to 300 ° C. (200 ° C. ≦ Tc <300 ° C.) in the NOx regeneration process, and 300 ° C. to 500 ° C. (300 ° C. ≦ Tc <500) in the PM regeneration process. Second temperature region R2 of 500 ° C. to 700 ° C. (500 ° C. ≦ Tc <700 ° C.) in the desulfurization process.

If it is determined in step S11 that the temperature range of the catalyst temperature is not in the temperature ranges R1, R2, and R3 of the direct fuel injection in each exhaust pipe, the process proceeds to step S12, and the direct fuel injection in the exhaust pipe is not performed. Alternatively, if injection has been performed, the injection is stopped, and after a predetermined time (time related to the catalyst temperature determination time interval) Δt2, the process returns to step S11.

If it is determined in step S11 that the temperature range of the catalyst temperature is in each of the exhaust pipe fuel direct injection temperature ranges R1, R2, and R3, the process proceeds to step S13, and the fuel pressure when direct exhaust pipe fuel injection is performed. Is adjusted to the optimum fuel pressure.

In this adjustment, when the temperature range of the catalyst temperature is in the first temperature range R1 of the NOx regeneration process, the adjustment bar position control cam 25Ad of the fuel pressure fluctuation suppression mechanism 20 is rotationally controlled by a step motor or the like. The position of the spring displacement adjustment bar 25Ac corresponding to the catalyst temperature Tc is moved to a preset position Li, and the fuel pressure Pi corresponding to this position Li is set.

When the temperature range of the catalyst temperature is in the second temperature range R2 of the PM regeneration process, the catalyst temperature is controlled by rotating the adjustment bar position control cam 25Ad of the fuel pressure fluctuation suppression mechanism 20 with a step motor or the like. The position of the spring displacement adjustment bar 25Ac corresponding to Tc is moved to a preset position Lj, and the fuel pressure Pj corresponding to this position Lj is set. Further, when the temperature range of the catalyst temperature is in the third temperature range R3 of the desulfurization process, the catalyst temperature Tc is controlled by rotating the adjustment bar position control cam 25Ad of the fuel pressure fluctuation suppressing mechanism 20 with a step motor or the like. The position of the spring displacement adjustment bar 25Ac corresponding to is moved to a preset position Lk, and the fuel pressure Pk corresponding to this position Lk is set.

In step S14, the fuel pressure setting value is determined to determine whether or not the fuel pressure detection value Pm is greater than the lower limit threshold value P1. If the detected value Pm of the fuel pressure is not larger than the lower limit threshold value P1 in this determination, the process returns to step S10 after a predetermined time (time related to the determination time interval of the detected value of the fuel pressure) Δt3. .

  If it is determined in step S14 that the detected fuel pressure value Pm is larger than the lower limit threshold value P1, it is determined in step S15 whether the detected fuel pressure value Pm is smaller than the upper limit threshold value P2. In this determination, if the detected value Pm of the fuel pressure is not smaller than the upper limit threshold P2, the pressure regulating valve 27 is opened in step S16, and the fuel pressure in the first pressure accumulating chamber 22 is lowered for a predetermined time (fuel). After a lapse of Δt4 (time related to the pressure detection value determination time interval), the process returns to step S15.

  If the detected value Pm of the fuel pressure is smaller than the upper limit threshold value P2 in the determination in step S15, the process goes to step S17 to calculate the fuel injection amount corresponding to each process that is the target of direct fuel injection in each exhaust pipe, The fuel temperature Tf detected by the fuel temperature sensor 29 is read, and the correction considering the fuel density is performed based on the detected fuel temperature Tf. Further, the fuel injection time is calculated based on the reference fuel pressure, the fuel pressure Pm detected by the fuel pressure sensor 28 is read, and the fuel injection amount in the direct fuel injection in the exhaust pipe is corrected by the fuel pressure Pm. Set the injection time.

  In the next step 18, the fuel injection valve 11 is instructed to open so that the direct fuel injection in the exhaust pipe is performed during the set fuel injection time. After performing this valve opening instruction and direct fuel injection in the exhaust pipe, the process returns to step S10.

When the engine operation is stopped, an interruption occurs, and in step S19, the exhaust pipe direct fuel injection control end operation is performed, the process returns to the upper control flow, and the exhaust pipe direct fuel injection control is controlled. finish.

According to the exhaust gas purification system 1 having the above configuration, the fuel f can be supplied to the fuel injection valve 11 under a stable fuel pressure by the fuel pressure fluctuation suppressing mechanism 20, so that the fuel f injected into the exhaust pipe 5 can be supplied. The pressure can be always constant and necessary without depending on the engine speed. Therefore, even when the engine speed changes transiently, direct fuel injection in the exhaust pipe can be performed with a precise fuel injection amount based on a stable fuel pressure.

  Accordingly, the difference between the actual fuel injection amount into the exhaust pipe 5 and the control target fuel injection amount is reduced, the temperature rise during the NOx regeneration process, the desulfurization process and the PM regeneration process, and the air-fuel ratio (or air) of the exhaust gas. Excess ratio) can be satisfied, and exhaust gas performance can be sufficiently secured.

  In the exhaust pipe direct fuel injection system of the present invention, in the fuel direct injection in the exhaust pipe, the fuel pressure fluctuation suppression mechanism can supply the fuel to the fuel injection valve under a stable fuel pressure, so that the fuel injected into the exhaust pipe can be supplied. The fuel can be injected at a constant and necessary pressure without depending on the engine speed, and the difference between the fuel injection amount to the exhaust pipe and the target fuel injection amount can be reduced. The present invention can be used as an exhaust pipe fuel direct injection system in an exhaust gas purification system of an internal combustion engine mounted on an automobile.

  Further, the exhaust gas purification system of the present invention reduces the difference between the actual fuel injection amount into the exhaust pipe and the control target fuel injection amount, and increases the temperature and exhaust gas during NOx regeneration processing, desulfurization processing, and PM regeneration processing. As an exhaust gas purification system and an exhaust gas purification method in an exhaust pipe of an internal combustion engine or the like mounted on an automobile can be satisfied because exhaust gas performance can be sufficiently ensured by satisfying the conditions of gas air-fuel ratio (or excess air ratio). Available.

1 Exhaust gas purification system 2 Engine (internal combustion engine)
3 Intake passage 5 Exhaust pipe (exhaust passage)
6 Exhaust gas purification device 6a Oxidation catalyst device (DOC)
6b NOx occlusion reduction catalyst device (LNT)
6c Filter device with catalyst (CSF)
10 Fuel direct injection system in exhaust pipe 11 Fuel injection valve (injector)
DESCRIPTION OF SYMBOLS 12 Fuel supply piping 13 Fuel supply pump 14 Fuel supply piping 15 Fuel tank 20 Fuel pressure fluctuation suppression mechanism 21 Fuel inlet 22 First pressure accumulation chamber 23 Fuel outlet 24 Second pressure accumulation chamber 25 First check valve 25A Reverse of operation pressure variable type Stop valve 26 Second check valve 27 Pressure adjustment valve 28 Fuel pressure sensor 30 Engine control device 30a Control device f Fuel

Claims (6)

In an exhaust pipe direct fuel injection system for injecting fuel into an exhaust pipe of an internal combustion engine by direct fuel injection in an exhaust pipe, a fuel pressure fluctuation suppression mechanism for a fuel supply pipe for supplying fuel to a fuel injection valve for injecting fuel into the exhaust pipe Are arranged in series, and the fuel pressure fluctuation suppressing mechanism is provided with a first pressure accumulation chamber on the fuel inlet side and a second pressure accumulation chamber on the fuel outlet side, and a first reverse is provided between the fuel inlet and the first pressure accumulation chamber. A stop valve is provided between the first pressure accumulation chamber and the second pressure accumulation chamber so that a second check valve is allowed to flow from the fuel inlet side to the fuel outlet side, and the opposite flow is stopped. The fuel in the exhaust pipe is characterized in that the first pressure accumulating chamber is provided with a pressure adjusting valve that discharges fuel to the outside of the first pressure accumulating chamber when the internal fuel pressure becomes higher than a preset pressure. Direct injection system . 2. The exhaust pipe direct fuel injection system according to claim 1, wherein a fuel pressure sensor for detecting a fuel pressure at the time of direct fuel injection in the exhaust pipe is provided in the first pressure accumulation chamber. 3. The exhaust pipe direct fuel injection system according to claim 1, wherein the first check valve is formed of a variable operating pressure check valve capable of changing an operating pressure. The direct fuel injection system in an exhaust pipe according to claim 1, 2 or 3, wherein the pressure regulating valve is formed of a variable pressure regulating valve capable of changing an operating pressure.   5. The fuel direct injection system in the exhaust pipe according to claim 1, wherein a fuel temperature sensor for detecting a temperature of fuel is provided in the first pressure accumulation chamber or the second pressure accumulation chamber. The fuel direct injection system in an exhaust pipe as described. An exhaust gas purification system for supplying fuel to an exhaust gas purification device provided in an exhaust passage of an internal combustion engine using the fuel direct injection system in an exhaust pipe according to any one of claims 1 to 5. .

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