JP5915856B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine including an EGR device that recirculates a part of the exhaust gas of the internal combustion engine to intake air.

  As a technique for reducing nitrogen oxide (NOx) contained in exhaust gas of an internal combustion engine (engine), an exhaust gas recirculation (EGR) device that introduces part of the exhaust gas into the intake air is known (see Patent Document 1). ). In recent years, exhaust gas regulations have become stricter, and NOx reduction during high-load operation (for example, during acceleration of high load and high acceleration) has been demanded.

  The exhaust passage is equipped with a NOx purification catalyst that purifies NOx. However, during high load operation, smoke may deteriorate unless a large amount of air is introduced into the combustion chamber. It is common not to break. For this reason, at the time of high load operation, the flow rate of the exhaust gas increases, the purification efficiency of the NOx purification catalyst decreases, and there is a possibility that NOx cannot be sufficiently purified. In particular, since the diesel engine has a large exhaust gas flow rate, the current situation is that the NOx purification performance tends to deteriorate during high-load operation.

  In addition, although the purification efficiency of the NOx purification catalyst can be maintained by suppressing the exhaust gas flow rate, if the control for suppressing the exhaust gas flow rate is performed, in a vehicle equipped with a supercharger, the supercharger is Exhaust gas amount for sufficient operation will be insufficient. For this reason, supercharging of intake air (pushing in fresh air) becomes insufficient, and there is a problem that smoke is deteriorated due to insufficient supply of air to the combustion chamber.

JP 2008-175100 A

  The present invention has been made in view of the above situation, and an object of the present invention is to provide an internal combustion engine exhaust gas purification device capable of reducing the flow rate of exhaust gas while ensuring a sufficient intake air amount during high load operation. And

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to a first aspect of the present invention comprises a supercharging means for supercharging intake air in an intake passage by exhausting an exhaust passage of the internal combustion engine, and more than the supercharging means. A NOx purification catalyst that is provided in the exhaust passage on the downstream side and purifies NOx in the exhaust, the intake passage on the upstream side of the supercharging means, and the NOx purification catalyst on the downstream side of the supercharging means A low pressure EGR passage communicating with the exhaust passage on the upstream side of the exhaust passage, and a low pressure EGR passage in the vicinity of a communicating portion with the exhaust passage, and opening and closing the low pressure EGR passage to open the intake passage from the exhaust passage a low pressure EGR valve for controlling the flow of exhaust gas to the downstream the intake passage than the supercharging means, and comprises a high-pressure EGR passage connecting the exhaust passage upstream of the supercharging means, Serial comprising a high-pressure EGR unit that recirculates into the intake passage by introducing a part of the exhaust gas in the exhaust passage to the high-pressure EGR passage, the low-pressure EGR valve, and control means for controlling the operation of the high-pressure EGR device, The control means includes a low-load, low-rotation high-pressure EGR introduction region, a higher load than the high-pressure EGR introduction region, a high-rotation low-pressure EGR introduction region, a higher load than the low-pressure EGR introduction region, and a high-rotation EGR non-introduction region The control means is provided on the condition that the low pressure EGR valve is closed in the operation region of the EGR non-introduction region and at the time of shifting to a high load and high rotation state. The low-pressure EGR valve is opened to shift to a high-load, high-rotation operation region, while the low-pressure EGR is shifted from the high-pressure EGR introduction region to the EGR non-introduction region. On the condition that the lube has been closed, characterized in that the transition from open the low-pressure EGR valve to the EGR untransfected region.

In the present invention according to claim 1, since a part of the exhaust gas in the exhaust passage is introduced into the low pressure EGR passage during the EGR non-introduction operation region where the internal combustion engine is in a high load state, the exhaust gas to the NOx purification catalyst The amount of inflow can be suppressed. Further, since the intake air amount is not affected, the amount of air supplied to the combustion chamber does not decrease.
At the time of transition from the low load operation region where the exhaust gas is recirculated by the high pressure EGR means to the EGR non-introduction operation region where the internal combustion engine is in a high load state, the low pressure EGR valve is opened to recycle the exhaust gas. The EGR can be brought into a non-introduced state after a temporary circulation.

  For this reason, the exhaust gas flow rate can be reduced and the purification performance of the NOx purification catalyst can be maintained in a state in which the intake amount is sufficiently secured during high load operation.

  In addition, since the low pressure EGR valve is opened and a part of the exhaust gas is introduced into the low pressure EGR passage on the condition that a predetermined time has passed since the low pressure EGR valve provided in the vicinity of the communication portion with the exhaust passage is closed. The exhaust gas does not newly enter the low pressure EGR passage for a predetermined time, and the exhaust gas concentration in the low pressure EGR passage gradually decreases during that period. Therefore, a part of the exhaust gas in the exhaust passage can be introduced into the low-pressure EGR passage when shifting to the EGR non-introduction operation region during the high load operation regardless of the operation region before the transition, and the exhaust gas to the NOx purification catalyst can be introduced. The amount of gas inflow can be suppressed.

According to a second aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the first aspect of the present invention, wherein the low pressure EGR valve is closed and the exhaust gas is not recirculated. Sometimes, air introduction means for introducing air into the low pressure EGR passage is provided.

In the present invention according to claim 2 , when the exhaust gas is not recirculated, air can be introduced into the low-pressure EGR passage by the air introduction means, and a part of the exhaust gas in the exhaust passage is supplied to the low-pressure EGR. When the air is introduced into the passage, a sufficient amount of air is secured until the air inside the low-pressure EGR passage is supplied to the combustion chamber, and the problem of smoke does not occur.

According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the second aspect of the present invention, wherein the air introducing means converts a part of the intake air in the intake passage to the low pressure EGR. It is a means introduced into the passage.

In the present invention according to claim 3 , since a part of the intake air in the intake passage is introduced into the low pressure EGR passage by the air introduction means, when a part of the exhaust gas in the exhaust passage is introduced into the low pressure EGR passage, the air cleaner The intake air that has passed through can be supplied to the combustion chamber.

According to a fourth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the third aspect , wherein the air introduction means is upstream of an air flow sensor provided in the intake passage. Further, a part of the intake air is introduced into the low pressure EGR passage.

In the present invention according to claim 4 , since a part of the intake air is introduced into the low pressure EGR passage from the upstream side of the air flow sensor, there is no deviation between the detected value of the air flow sensor and the actual intake air amount.

An internal combustion engine exhaust gas purification apparatus according to a fifth aspect of the present invention is the internal combustion engine exhaust gas purification apparatus according to any one of the second to fourth aspects, wherein the air introducing means is the low pressure EGR. Air is introduced into the low pressure EGR passage near the valve and closer to the intake passage than the low pressure EGR valve.

In the present invention according to claim 5 , since air is introduced into the low pressure EGR passage closer to the intake passage than the low pressure EGR valve, the entire low pressure EGR passage can be scavenged.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention can reduce the flow rate of the exhaust gas while ensuring a sufficient intake amount during high load operation.

1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment of the present invention. It is a map showing an EGR area. It is a schematic block diagram explaining the flow of gas. It is a schematic block diagram explaining the flow of gas. It is a schematic block diagram explaining the flow of gas. It is a schematic block diagram of the exhaust gas purification apparatus of the internal combustion engine which concerns on 2nd Example of this invention. It is a schematic block diagram of the exhaust gas purification apparatus of the internal combustion engine which concerns on 3rd Example of this invention.

  The configuration of the exhaust gas purification apparatus for an internal combustion engine will be described with reference to FIGS. FIG. 1 shows a schematic configuration representing the system of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention, and FIG. 2 shows a map representing the EGR region by the relationship between the load and the engine speed.

  As shown in FIG. 1, an exhaust purification device 3 is provided in an exhaust pipe 2 of a multi-cylinder diesel engine (engine) 1 as an internal combustion engine mounted on a vehicle. A piston 5 is provided in the bore of the cylinder block 4 of the engine 1 so as to be able to reciprocate. A combustion chamber 7 is formed between the piston 5 and the cylinder head 6. The piston 5 is connected to the crankshaft 9 via a connecting rod 8, and the crankshaft 9 is driven by the reciprocating motion of the piston 5.

  An intake pipe (intake passage) 12 including an intake manifold 11 is connected to the cylinder head 6 via an intake port. The intake port is opened and closed by an intake valve. Further, an exhaust pipe (exhaust passage) 2 including an exhaust manifold 13 is connected to the cylinder head 6 through an exhaust port. The exhaust port is opened and closed by an exhaust valve.

  The cylinder head 6 is provided with an electronically controlled fuel injection valve 10 that directly injects fuel into the combustion chamber 7 of each cylinder. The fuel injection valve 10 is supplied with fuel from a common rail (not shown). In the common rail, the fuel is adjusted to a predetermined fuel pressure, and high pressure fuel controlled to the predetermined fuel pressure is supplied to the fuel injection valve 10.

  A turbocharger 15 is provided in the middle of the intake pipe 12 and the exhaust pipe 2 as a supercharger. The turbocharger 15 is provided with a turbine on the exhaust pipe 14 side, and a compressor connected to the turbine is provided on the intake pipe 12 side. It has been. When the exhaust gas of the engine 1 is sent from the exhaust pipe 14 to the turbocharger 15, the turbine is rotated by the flow of the exhaust gas, and the compressor rotates with the rotation of the turbine to supercharge the intake air in the intake pipe 12. .

  An intercooler 16 is disposed in the intake pipe 12 on the downstream side of the turbocharger 15, and the supercharged intake air is cooled by the intercooler 16 and sent to the combustion chamber 7. The intake pipe 12 on the downstream side of the intercooler 16 includes a throttle valve 17 that opens and closes the intake pipe 12 from the upstream side, an intake temperature sensor 18 that detects the temperature of intake air, and an intake manifold pressure sensor 19 that detects the pressure in the intake manifold 11. Is provided.

The exhaust pipe 2 on the downstream side of the turbocharger 15 includes a diesel oxidation catalyst (oxidation catalyst) 21 and an exhaust purification diesel particulate filter (DPF: Diesel Particulate Filter) 22 as an exhaust purification device 3. A device 23 is provided. When exhaust gas flows into the oxidation catalyst 21, nitrogen monoxide (NO) in the exhaust gas is oxidized to generate nitrogen dioxide (NO ₂ ). Further, particulate matter (PM) in the exhaust gas is collected by the filter 22.

PM collected by the filter 22 is oxidized (combusted) by NO ₂ in the exhaust gas and discharged as CO ₂ , and NO ₂ remaining in the filter 22 is decomposed into N ₂ and discharged. That is, in the purification device 23, the exhaust gas is purified and the exhaust amount of PM and NOx can be greatly reduced.

The exhaust pipe 2 on the downstream side of the purification device 23 is provided with a NOx trap catalyst 24 as the exhaust purification device 3. The NOx trap catalyst 24 once traps NOx in an oxidizing atmosphere, and releases the trapped NOx in a reducing atmosphere containing, for example, carbon monoxide (CO), hydrocarbon (HC), etc., and nitrogen (N ₂ ) or the like. It is a purification device that reduces to That is, NO ₂ generated by the oxidation catalyst 21 and NO remaining in the exhaust gas without being oxidized by the oxidation catalyst 21 are once captured, and the captured NOx is released and reduced to nitrogen (N ₂ ) or the like. .

  Instead of the NOx trap catalyst 24 that once captures NOx and releases NOx in a reducing atmosphere, it is possible to use a removal device (catalyst) that purifies NOx by another reaction or the like.

  An exhaust gas temperature sensor 25 is provided on the inlet side of the NOx trap catalyst 24, and the exhaust gas temperature sensor 25 detects the temperature of the exhaust gas at the inlet of the NOx trap catalyst 24, that is, the temperature of the exhaust gas discharged from the purification device 23. The A linear A / F sensor 26 is provided on the inlet side of the NOx trap catalyst 24, and the exhaust air-fuel ratio is detected by the linear A / F sensor 26.

  One end of a high-pressure EGR pipe 31 is connected to the exhaust pipe 14 on the upstream side of the turbocharger 15 as a high-pressure EGR passage, and the other end of the high-pressure EGR pipe 31 is intake air on the downstream side of the throttle valve 17 (downstream side of the turbocharger 15). It communicates with the tube 12. A high pressure EGR cooler 32 is provided in the high pressure EGR pipe 31, and a high pressure EGR valve 33 is provided in a connection portion of the high pressure EGR pipe 31 with the intake pipe 12.

  By opening the high pressure EGR valve 33, a part of the exhaust gas flowing through the exhaust pipe 14 upstream of the turbocharger 15 is introduced into the high pressure EGR pipe 31, and the exhaust gas introduced into the high pressure EGR pipe 31 is the high pressure EGR cooler 32. And is supplied to the intake pipe 12 on the downstream side of the turbocharger 15 (high pressure EGR means).

  One end of a low-pressure EGR pipe 35 is connected as a low-pressure EGR passage to the exhaust pipe 14 downstream of the purification device 23 and upstream of the NOx trap catalyst 24 (downstream of the turbocharger 15). It communicates with the intake pipe 12 on the upstream side of the turbocharger 15. The low-pressure EGR pipe 35 is provided with a low-pressure EGR cooler 36, and a low-pressure EGR valve 37 is provided in the vicinity of the connection portion between the low-pressure EGR pipe 35 and the exhaust pipe 14.

By opening the low pressure EGR valve 37, a part of the exhaust gas flowing through the exhaust pipe 14 on the downstream side of the turbocharger 15 is introduced into the low pressure EGR pipe 35, and the exhaust gas introduced into the low pressure EGR pipe 35 is the low pressure EGR cooler 36. And is supplied to the intake pipe 12 upstream of the turbocharger 15.

  By recirculating a part of the exhaust gas to the intake air by the high pressure EGR means and the low pressure EGR means, the combustion temperature in the combustion chamber 7 of the engine 1 can be lowered, and the amount of NOx emission can be reduced. Since the high-pressure EGR means circulates a part of the exhaust gas upstream of the turbocharger 15, in the operation state where the turbocharger 15 needs to be sufficiently charged (the operation state where it is necessary to secure the air amount), NOx emissions are reduced using low pressure EGR means.

  That is, as shown by slanted lines with a narrow pitch in FIG. 2, a high-pressure EGR region in which the high-pressure EGR means is used in a region where the load (torque) is small and the engine rotational speed is low is shown in FIG. As described above, the low pressure EGR region (the operation region in which the air amount needs to be ensured) is used in the region where the load (torque) is larger than the high pressure EGR region and the engine rotational speed is high.

  A low pressure throttle valve 38 is provided in the intake pipe 12 upstream of the connection portion with the low pressure EGR pipe 35, and an air cleaner 39 is provided in the intake pipe 12 upstream of the low pressure throttle valve 38. The flow rate of the intake air that has passed through the air cleaner 39 is detected by an air flow sensor (with a temperature sensor) 30.

  The vehicle is provided with an electronic control unit (ECU) 41 as control means, and the ECU 41 is provided with an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, timers and counters. Yes. Information from the above-described sensors (the intake temperature sensor 18, the intake manifold pressure sensor 19, the exhaust temperature sensor 25, the linear A / F sensor 26, the airflow sensor 30, etc.) is input to the ECU 41, and exhaust is performed based on the sensor information. The ECU 41 performs overall control of the engine 1 including the purification device 3, the high pressure EGR means, and the low pressure EGR means.

  As shown in FIG. 2, the engine 1 equipped with the exhaust purification device described above has a high pressure EGR region in which the high pressure EGR means is used and a low pressure EGR region in which the low pressure EGR means is used depending on the relationship between the load (torque) and the engine speed. An EGR non-introduction operation region (indicated by a mesh line in the figure) in which the engine 1 is in a high load state is set. A region where the engine 1 is in a high load state at the time of acceleration or the like is a region where the EGR means is not used, and there is a concern that the exhaust gas flow rate increases and the purification efficiency of the NOx trap catalyst 24 decreases.

  Therefore, in the EGR non-introduction operation region where the engine 1 is in a high load state, a part of the exhaust gas upstream of the NOx trap catalyst 24 is introduced into the low pressure EGR pipe 35, and the exhaust gas to the NOx trap catalyst 24 is introduced. The amount of inflow is controlled.

  For example, at the time of transition from an operation region (EGR non-introduction operation region) in which exhaust gas is not recirculated by the low-pressure EGR means to an EGR non-introduction operation region where the load is higher than that state, that is, an arrow in FIG. As shown by A and arrow B, when the operating state changes in a state where it crosses over the NOx amount line (indicated by the alternate long and short dash line in the figure) in the EGR non-introducing operating region, the NOx trap catalyst 24 is placed in the low pressure EGR pipe 35. Control for introducing a part of the exhaust gas on the upstream side is performed, and then a predetermined operation state is set.

  Since the EGR non-introduction operation region is a region where the low pressure EGR valve 37 is closed, the control for introducing a part of the exhaust gas upstream of the NOx trap catalyst 24 into the low pressure EGR pipe 35 is performed by the low pressure EGR valve 37. It is implemented on the condition that a predetermined time has passed since the closing.

  Further, during a transition from the high pressure EGR region where exhaust gas recirculation is performed by the high pressure EGR means to the EGR non-introduction operation region, that is, as indicated by an arrow C in FIG. When the operating state changes so as to increase the speed, control for temporarily introducing a part of the exhaust gas upstream of the NOx trap catalyst 24 into the low-pressure EGR pipe 35 is temporarily performed, and then the EGR non-introducing operation region It will be in the driving state at.

  Since the high pressure EGR region is a region where the low pressure EGR valve 37 is closed, the control for introducing a part of the exhaust gas upstream of the NOx trap catalyst 24 into the low pressure EGR pipe 35 is performed by closing the low pressure EGR valve 37. It is carried out on condition that a predetermined time has passed since then.

  For this reason, a part of the exhaust gas in the exhaust pipe 14 can be introduced into the low-pressure EGR pipe 35 when shifting to the EGR non-introduction operation area during high load operation regardless of the operation area before the transition, and the NOx trap. The amount of exhaust gas flowing into the catalyst 24 can be suppressed. For this reason, it is possible to reduce the flow rate of the exhaust gas while maintaining a sufficient intake amount during high-load operation, and to suppress the reduction in the purification performance of the NOx trap catalyst 24 due to the increase in the exhaust gas flow rate.

  The gas flow of the engine 1 equipped with the exhaust emission control device of this embodiment will be specifically described with reference to FIGS.

  Fig. 3 shows the status of gas in the system before high load operation (before acceleration), Fig. 4 shows the status of gas in the system at the start of acceleration, and Fig. 5 shows the status of gas in the system during acceleration. Is shown.

  As shown in FIG. 3, in the state before acceleration, air is present in the intake pipe 12 leading to the combustion chamber 7 (in a white state in the figure), and from the combustion chamber 7 to the downstream side of the NOx trap catalyst 24. Exhaust gas having a low NOx concentration is present in the exhaust pipe 14 (light colored mesh state in the figure). And the exhaust gas at the time of the last recirculation exists in the low pressure EGR pipe 35 (shaded state in the figure).

  As shown in FIG. 4, when acceleration is started, the low-pressure EGR valve 37 is opened, and a part of the exhaust gas starts to flow to the low-pressure EGR pipe 35, and the exhaust gas flowing to the NOx trap catalyst 24 decreases. At the same time, the exhaust gas at the time of the previous recirculation flows into the intake pipe 12, and the exhaust gas 14 having a high NOx concentration (black state in the figure) exists in the exhaust pipe 14 from the combustion chamber 7 to the purification device 23. During the response delay of the low pressure EGR means, the exhaust gas (hatched state in the figure) at the previous recirculation does not reach the combustion chamber 7 and a state where a sufficient amount of air is secured is maintained.

  As a result, even during acceleration, part of the exhaust gas is introduced into the low pressure EGR pipe 35, and the flow rate of the exhaust gas flowing through the NOx trap catalyst 24 is reduced to suppress the deterioration of the purification performance of the NOx trap catalyst 24. be able to. At the start of acceleration, the exhaust gas from the low pressure EGR pipe 35 does not reach the combustion chamber 7 due to a response delay of the low pressure EGR means, so that a sufficient amount of air is secured and no smoke problem occurs.

  Since the exhaust gas existing in the exhaust pipe 14 at the start of acceleration is an exhaust gas having a low NOx concentration (light-colored mesh state in the figure), the purification efficiency of the NOx trap catalyst 24 can be improved without reducing the flow rate of the exhaust gas. Even in a low state, the amount of NOx released to the atmosphere is small. For this reason, it is possible to open the low pressure EGR valve 37 in accordance with the timing at which the exhaust gas having a high NOx concentration after starting acceleration (black state in the figure) reaches the connection position of the low pressure EGR pipe 35.

  As a result, the timing at which the exhaust gas in the low-pressure EGR pipe 35 (hatched state in the figure) flows into the intake pipe 12 is delayed, and a state in which a sufficient amount of air is secured can be maintained for a long time. Will be advantageous.

  As shown in FIG. 5, during acceleration, exhaust gas having a high NOx concentration (black state in the figure) is introduced into the low pressure EGR pipe 35, and the flow rate of exhaust gas having a high NOx concentration flowing through the NOx trap catalyst 24 decreases. Yes. Since the air sucked into the intake pipe 12 and the exhaust gas flowing in from the low pressure EGR pipe 35 are introduced into the combustion chamber 7, the same gas flow rate as when a part of the exhaust gas is not introduced into the low pressure EGR pipe 35. Is secured.

  Therefore, the purification performance of the NOx trap catalyst 24 can be maintained even during acceleration. And the air quantity supplied to the combustion chamber 7 is ensured enough, and the problem of smoke does not arise.

  In the above-described embodiments, the NOx trap catalyst 24 that stores and releases NOx has been described as an example of the NOx purification catalyst. However, urea SCR (urea water addition selective reduction catalyst) and solid SCR (ammonia solid storage / direct addition) It is also possible to apply other NOx purification catalysts such as a selective reduction catalyst.

  It is also possible to install a fluid storage tank in the low pressure EGR pipe 35 on the downstream side of the low pressure EGR valve 37. In the illustrated embodiment, the low pressure EGR cooler 36 serves as a fluid storage tank. By providing the fluid storage tank, the time until a part of the exhaust gas introduced into the low pressure EGR pipe 35 reaches the combustion chamber 7 can be extended.

  Moreover, it is preferable that the cooling water system of the low pressure EGR cooler 36 is a system different from the engine cooling water system, and the cooling water is cooled by a dedicated heat exchanger. As a result, the cooling capacity of the low-pressure EGR cooler 36 can be increased, a part of the exhaust gas is introduced into the low-pressure EGR pipe 35 with a high load, and the outlet temperature of the compressor (the compressor of the turbocharger 15) becomes high. Even in this case, the temperature of the low-pressure EGR gas introduced into the compressor can be lowered, and the outlet temperature of the compressor does not exceed the allowable temperature.

  Further, in order to perform regeneration control of the DPF 22, the amount of PM accumulated in the DPF 22 is calculated. When accumulating the amount of accumulation, the amount of PM flowing into the DPF 22 relative to the engine speed and load (PM in exhaust gas) Amount) map value is integrated. As this map, a map dedicated to the control for introducing a part of the exhaust gas into the low-pressure EGR pipe 35 is applied separately from the normal operation. When the fully open acceleration state continues for a certain time or more and the exhaust gas from the low pressure EGR means is continuously introduced into the combustion chamber 7, it is expected that the PM deposition on the DPF 22 proceeds faster than usual. By applying a dedicated map, it is possible to perform control in consideration of the point where PM deposition proceeds quickly.

  Further, when the fully open acceleration state continues for a certain time or more and the exhaust gas from the low pressure EGR means is continuously introduced into the combustion chamber 7, additional fuel is injected after the main fuel injection according to the operating conditions, etc. Can suppress the generation of smoke.

  Another embodiment will be described with reference to FIGS.

  FIG. 6 is a schematic diagram showing a system of an exhaust gas purification apparatus for an internal combustion engine according to the second embodiment of the present invention, and FIG. 7 is a schematic diagram showing a system of an exhaust gas purification apparatus for an internal combustion engine according to the third embodiment of the present invention. The configuration is shown. The same members as those shown in FIG. Below, the part of a different structure is demonstrated.

  A second embodiment will be described.

  As shown in FIG. 6, an external air introduction pipe 51 is connected in the vicinity of the connection portion between the low pressure EGR pipe 35 and the exhaust pipe 14, and the external air introduction pipe 51 is provided with an open / close valve 52. By opening the opening / closing valve 52, air can be introduced into the low pressure EGR pipe 35.

  After using the low pressure EGR means, the on-off valve 52 is opened and air is introduced into the low pressure EGR pipe 35. After the predetermined time has elapsed, the open / close valve 52 is closed to fill the inside of the low pressure EGR pipe 35 with air. At least when the low pressure EGR valve 37 is opened, the open / close valve 52 is closed. Further, by restricting the low-pressure throttle valve 38, the intake pipe 12 becomes relatively low pressure (negative pressure) as compared with the external air introduction pipe 51, and air can be easily introduced into the low-pressure EGR pipe 35.

  In the second embodiment, since the inside of the low pressure EGR pipe 35 can be filled with air before acceleration, the time during which the air inside the low pressure EGR pipe 35 is supplied to the intake pipe 12 and the air is supplied at the start of acceleration. Can be lengthened. For this reason, even when the fully open acceleration state continues for a long time, the time for the exhaust gas introduced into the low pressure EGR pipe 35 to reach the combustion chamber 7 is extended, and there is no problem of deterioration of smoke.

  When the high pressure EGR means is used, the open / close valve 52 is opened to introduce external air. Thereby, the driving | running condition which uses the low voltage | pressure EGR at the time of acceleration can be avoided.

  Further, while the open / close valve 52 is opened and external air is being introduced, the amount of air introduced into the low pressure EGR pipe 35 is estimated. The amount of air supplied to the combustion chamber 7 is the sum of the intake air amount measured by the air flow sensor 30 and the estimated air amount introduced into the low pressure EGR pipe 35. Thereby, when introducing the air in the low pressure EGR pipe 35 into the combustion chamber 7, there is no error between the amount of air measured by the air flow sensor 30 and the amount of air actually introduced into the combustion chamber 7. Control can be performed.

  A third embodiment will be described.

  As shown in FIG. 7, one end of the internal air introduction pipe 55 is connected in the vicinity of the connection portion of the low pressure EGR pipe 35 with the exhaust pipe 14, and the other end of the internal air introduction pipe 55 communicates with the air cleaner 39. Yes. An inflow opening / closing valve 56 is provided in the vicinity of the other end of the internal air introduction pipe 55. By opening the inflow opening / closing valve 56, the air downstream of the air cleaner 39 can be introduced into the low pressure EGR pipe 35.

  After using the low pressure EGR means, the inflow opening / closing valve 56 is opened, and the air that has passed through the air cleaner 39 is introduced into the low pressure EGR pipe 35. After the predetermined time has elapsed, the inflow opening / closing valve 56 is closed to fill the inside of the low pressure EGR pipe 35 with clean air. At least when the low pressure EGR valve 37 is opened, the inflow opening / closing valve 56 is closed.

  In the third embodiment, in addition to the second embodiment, clean air that has passed through the air cleaner 39 can be introduced into the low-pressure EGR pipe 35. Since the other end of the internal air introduction pipe 55 communicates with a portion of the air cleaner 39 on the upstream side of the air flow sensor 30, the amount of air measured by the air flow sensor 30 and combustion when air is introduced into the low pressure EGR pipe 35. There is no error between the amount of air actually introduced into the chamber 7.

  In the third embodiment, the other end of the internal air introduction pipe 55 communicates with the air cleaner 39 and the communication portion is located upstream of the air flow sensor 30. However, the internal air introduction pipe 55 is connected downstream of the air flow sensor 30. It is also possible to communicate the ends. At this time, the amount of air introduced into the low pressure EGR pipe 35 is estimated. The amount of air supplied to the combustion chamber 7 is the amount of air obtained by subtracting the estimated amount of air introduced into the low pressure EGR pipe 35 from the amount of intake air measured by the air flow sensor 30. When EGR is not introduced from the high-pressure EGR means (when high-pressure EGR is not introduced), the amount of air sucked into the combustion chamber 7 uses the amount of air measured by the intake manifold pressure sensor 19 of the intake manifold 11 as it is. .

  When estimating the amount of air introduced and stored in the low pressure EGR pipe 35, when EGR is not introduced from the high pressure EGR means (when high pressure EGR is not introduced), the amount of air measured by the air flow sensor 30; The difference from the air amount measured by the intake manifold pressure sensor 19 is used. This estimated amount is stored in the ECU 41, and when the low pressure EGR valve 37 is open (while the air in the low pressure EGR pipe 35 is being introduced into the intake pipe 12), the amount of air measured by the air flow sensor 30 is estimated and The obtained air amount in the low pressure EGR pipe 35 is added to obtain the air amount sucked into the combustion chamber 7.

  Thereby, when introducing the air in the low pressure EGR pipe 35 into the combustion chamber 7, there is no error between the amount of air measured by the air flow sensor 30 and the amount of air actually introduced into the combustion chamber 7. Control can be performed.

  INDUSTRIAL APPLICABILITY The present invention can be used in the industrial field of an exhaust gas purification device for an internal combustion engine provided with an EGR device that recirculates part of the exhaust gas of the internal combustion engine to intake air.

DESCRIPTION OF SYMBOLS 1 Multi-cylinder diesel engine 2 Exhaust pipe 3 Exhaust gas purification device 4 Cylinder block 5 Piston 6 Cylinder head 7 Combustion chamber 8 Connecting rod 9 Crankshaft 10 Fuel injection valve 11 Intake manifold 12 Intake pipe 13 Exhaust manifold 14 Exhaust pipe 15 Turbocharger 16 Intercooler 17 Throttle valve 18 Intake air temperature sensor 19 Intake manifold pressure sensor 21 Diesel oxidation catalyst (oxidation catalyst)
22 Diesel particulate filter (DPF)
23 Purification device 24 NOx trap catalyst 25 Exhaust temperature sensor 26 Linear A / F sensor 30 Air flow sensor 31 High pressure EGR pipe 32 High pressure EGR cooler 33 High pressure EGR valve 35 Low pressure EGR pipe 36 Low pressure EGR cooler 37 Low pressure EGR valve 38 Low pressure throttle valve 39 Air cleaner 41 Electronic control unit (ECU)
51 External air introduction pipe 52 Open / close valve 55 Internal air introduction pipe 56 Inflow open / close valve

Claims (5)

Supercharging means for supercharging intake air in the intake passage by exhausting the exhaust passage of the internal combustion engine;
A NOx purification catalyst that is provided in the exhaust passage downstream of the supercharging means and purifies NOx in the exhaust;
A low-pressure EGR passage communicating with the intake passage upstream of the supercharging means, and the exhaust passage downstream of the supercharging means and upstream of the NOx purification catalyst;
A low pressure EGR valve that is provided in the low pressure EGR passage in the vicinity of the communication portion with the exhaust passage, and controls the flow of exhaust gas from the exhaust passage to the intake passage by opening and closing the low pressure EGR passage;
A high-pressure EGR passage communicating with the intake passage on the downstream side of the supercharging means and the exhaust passage on the upstream side of the supercharging means, and a part of the exhaust gas of the exhaust passage in the high-pressure EGR passage And high pressure EGR means for recirculating to the intake passage,
Control means for controlling the operation of the low pressure EGR valve and the high pressure EGR means ,
The control means includes
Low load, low rotation high pressure EGR introduction area,
High pressure EGR introduction area, high load, high speed low pressure EGR introduction area,
A control map having an EGR non-introduction region with higher load and higher rotation than the low-pressure EGR introduction region is provided.
The control means includes
Within the operation region of the EGR non-introduction region, the low pressure EGR valve is opened on the condition that the low pressure EGR valve is closed at the time of shifting to a high load, high rotation state. While moving to the rotation operating area,
When the transition from the high-pressure EGR introduction region to the EGR non-introduction region, the low-pressure EGR valve is opened on the condition that the low-pressure EGR valve is closed, and then the transition to the EGR non-introduction region is performed. An exhaust purification device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
An exhaust gas purification apparatus for an internal combustion engine, comprising: air introduction means for introducing air into the low pressure EGR passage when the low pressure EGR valve is closed and exhaust gas is not recirculated. The exhaust gas purification apparatus for an internal combustion engine according to claim 2 ,
The air introducing means is
An exhaust gas purifying apparatus for an internal combustion engine, characterized in that it is means for introducing part of the intake air in the intake passage into the low pressure EGR passage. The exhaust gas purification apparatus for an internal combustion engine according to claim 3,
The air introducing means is
A part of the intake air from the upstream side of the air flow sensor provided in the intake passage is transferred to the low pressure EGR.
An exhaust purification device for an internal combustion engine, characterized by being introduced into a passage. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 2 to 4 ,
The air introducing means is
An exhaust gas purification apparatus for an internal combustion engine, wherein air is introduced into the low pressure EGR passage in the vicinity of the low pressure EGR valve and closer to the intake passage than the low pressure EGR valve.

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