JP5050903B2 - Engine supercharger - Google Patents

Description

  The present invention is provided in an exhaust turbocharger and an exhaust passage, and stores NOx when the air-fuel ratio of the exhaust gas of the engine is lean and stores the NOx by enriching the air-fuel ratio of the exhaust gas. The present invention belongs to a technical field related to a supercharger for an engine provided with a NOx catalyst that reduces NOx.

Conventionally, there is a case where the air-fuel ratio is leaner than the stoichiometric air-fuel ratio for the purpose of improving engine fuel consumption, etc., but since such operation increases the amount of NOx components in the exhaust gas, In order to purify the exhaust gas, a NOx purification device is disposed in the exhaust passage. This NOx purification device has a NOx catalyst (NOx occlusion reduction type catalyst), stores NOx in the exhaust gas in the lean operation state, and operates at a stoichiometric air fuel ratio or an air fuel ratio richer than the stoichiometric air fuel ratio. In this state, NOx is reduced and released. When the stored NOx amount exceeds a predetermined amount, the air-fuel ratio is changed from lean to the stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio (rich spike) to forcibly reduce NOx. It is made to discharge | release (for example, refer patent document 1).
Japanese Patent No. 2,586,739

  Incidentally, the enrichment of the air-fuel ratio for reducing and purifying NOx stored in the NOx catalyst changes the opening degree of the intake throttle valve disposed in the intake passage in the closing direction, for example, in the case of a diesel engine. By doing.

  However, when the air-fuel ratio is enriched by closing the intake throttle valve, the intake air amount and the exhaust amount are reduced, so that the rotational speed of the turbine of the exhaust turbocharger is reduced. When an occupant of a vehicle equipped with an engine requests acceleration, it takes time until the turbine rotation speed reaches a predetermined level, and there is a problem that acceleration response is deteriorated.

  The present invention has been made in view of such points, and an object of the present invention is to provide an engine supercharging device including an exhaust turbocharger and a NOx catalyst that stores and reduces NOx. To reduce the NOx stored in the NOx catalyst, the air-fuel ratio can be enriched, and the acceleration response can be improved when NOx is reduced or when acceleration is requested immediately after completion of the reduction. It is in.

To achieve the above object, according to the present invention, when the engine load is a low load equal to or lower than a predetermined load, the intake bypass valve disposed in the intake bypass passage that bypasses the compressor of the first exhaust turbocharger is provided. The opening is larger than the intake bypass valve opening set in accordance with the operating state of the engine, and the first exhaust bypass passage that bypasses the turbine of the first exhaust turbocharger is disposed in the first exhaust bypass passage . By making the opening degree of the exhaust bypass valve equal to or less than the opening degree of the first exhaust bypass valve set according to the operating state of the engine, the air-fuel ratio of the exhaust gas is enriched and stored in the NOx catalyst. was NOx was reduced, the engine load is in the high load greater than the predetermined load, the second exhaust turbocharger turbine (the first exhaust turbocharger in the exhaust passage The opening of the second exhaust bypass valve disposed in the second exhaust bypass passage that bypasses the engine and the NOx catalyst) is set according to the operating state of the engine. By making it larger, the air-fuel ratio of the exhaust gas is enriched to reduce the NOx stored in the NOx catalyst .

Specifically, according to the first aspect of the present invention, a first exhaust turbocharger having a compressor disposed in an intake passage of an engine and a turbine disposed in an exhaust passage targeting an engine supercharging device. An intake bypass passage that bypasses the compressor of the first exhaust turbocharger, an intake bypass valve disposed in the intake bypass passage, and a first exhaust that bypasses the turbine of the first exhaust turbocharger The opening of the bypass passage, the first exhaust bypass valve disposed in the exhaust bypass passage, and the intake bypass valve and the first exhaust bypass valve are controlled to the openings set according to the operating state of the engine. A bypass valve control means that is disposed downstream of the turbine in the exhaust passage, and absorbs NOx when the air-fuel ratio of the exhaust gas of the engine is lean. And when the amount of NOx occluded in the NOx catalyst becomes a predetermined amount or more when the NOx catalyst occludes the NOx occluded by the enrichment of the air-fuel ratio of the exhaust gas. The air-fuel ratio control means for reducing the NOx occluded in the NOx catalyst, the compressor disposed on the upstream side of the compressor of the first exhaust turbocharger in the intake passage, and the exhaust passage A second exhaust turbocharger having a turbine of the first exhaust turbocharger and a turbine disposed between the NOx catalyst, and a second exhaust bypass for bypassing the turbine of the second exhaust turbocharger And a second exhaust bypass valve disposed in the second exhaust bypass passage, wherein the bypass valve control means includes the intake bypass valve and the first exhaust bypass valve. In addition to the opening of the valve, the opening of the second exhaust bypass valve is intended to control the opening degree set according to the operating state of the engine, the air-fuel ratio control means, the engine load is given When the load is lower than the load, the opening of the intake bypass valve is made larger than the intake bypass valve opening set by the bypass valve control means, and the opening of the first exhaust bypass valve is controlled by the bypass valve control. By making it equal to or less than the first exhaust bypass valve opening set by the means, the air-fuel ratio of the exhaust gas is enriched, the NOx stored in the NOx catalyst is reduced, and the engine load is When the load is higher than a predetermined load, the opening degree of the second exhaust bypass valve is set larger than the second exhaust bypass valve opening degree set by the bypass valve control means. It is assumed that the air-fuel ratio of the exhaust gas is enriched to reduce the NOx stored in the NOx catalyst .

With the above configuration, the supercharging efficiency is lowered by making the opening degree of the intake bypass valve larger than the intake bypass valve opening degree set by the bypass valve control means (intake bypass valve opening degree during non-reduction). This reduces the amount of air supplied to the engine. As a result, the air-fuel ratio of the exhaust gas can be enriched, and NOx stored in the NOx catalyst can be reduced. Moreover, by making the opening degree of the first exhaust bypass valve equal to or less than the first exhaust bypass valve opening degree ( first exhaust bypass valve opening degree during non-reduction) set by the bypass valve control means, The turbine of the first exhaust turbocharger will continue to rotate even during reduction, and when the occupant depresses the accelerator pedal and makes an acceleration request immediately after NOx reduction or after completion of reduction, the turbine is already rotating, As a result, for example, by setting the opening of the intake bypass valve to the intake bypass valve opening at the time of non-reduction, it is possible to immediately perform appropriate supercharging and obtain a high acceleration response.

When two exhaust turbochargers are used, the amount of air supplied to the engine is reduced while rotating the turbine of the first exhaust turbocharger as described above, particularly at low loads where acceleration response is a problem. The air-fuel ratio can be enriched by reducing the NOx, so that NOx occluded in the NOx catalyst can be reduced, and a high acceleration response can be obtained when acceleration is requested.

  The first exhaust turbocharger is normally operated at the time of non-reduction at a low load so that an appropriate supercharging pressure can be obtained. For this reason, the intake bypass valve and the first exhaust bypass valve are in a state other than full open. On the other hand, the second exhaust turbocharger is operated almost fully at the time of low load both at the time of non-regeneration and at the time of regeneration (the second exhaust bypass valve is in a fully closed state or an opening degree close thereto). Is preferred. In this way, a certain degree of supercharging pressure can be stably obtained at the time of low load and reduction, and at the time of acceleration request, the turbines of the two exhaust turbochargers are already rotating, so that high acceleration is achieved. A response is obtained. In particular, the turbine of the second exhaust turbocharger is usually larger in size and has a larger inertia than the turbine of the first exhaust turbocharger. By always rotating at times, a high acceleration response can be reliably obtained.

Here, when the first exhaust turbocharger is operated at high load , exhaust resistance is caused instead. Therefore, the intake bypass valve and the first exhaust bypass valve are normally fully opened, and the second exhaust bypass valve is fully closed. Set the opening to a state close to that (opening that can prevent over-rotation). For this reason, at the time of high load, the opening degree of the intake bypass valve at the time of reduction cannot be made larger than the opening degree of the intake bypass valve at the time of non-reduction as in the case of low load. Further, when the opening of the first exhaust bypass valve is made smaller than the first exhaust bypass valve opening at the time of non-reduction at the time of high load when the acceleration response is not a big problem compared to that at the time of low load, it becomes exhaust resistance. Therefore, it is preferable not to do that. Therefore, at the time of high load, the opening of the second exhaust bypass valve is larger than the second exhaust bypass valve opening (second exhaust bypass valve opening at the time of non-reduction ) set according to the operating state of the engine. To do. On the other hand, the intake bypass valve and the first exhaust bypass valve maintain the same fully open state as during non-reduction. As a result, even when the first exhaust turbocharger is not operated at high load, the amount of air supplied to the engine can be reduced by increasing the opening of the second exhaust bypass valve, and the air-fuel ratio can be reduced. Can be enriched.

As described above, according to the engine supercharging device of the present invention, when the engine load is a low load equal to or lower than a predetermined load , the opening degree of the intake bypass valve is set according to the operating state of the engine. By making the opening of the first exhaust bypass valve larger than the valve opening and making the opening of the first exhaust bypass valve equal to or less than the first exhaust bypass valve opening set according to the operating state of the engine, the air-fuel ratio of the exhaust gas The NOx stored in the NOx catalyst is reduced, and when the engine load is higher than the predetermined load, the opening degree of the second exhaust bypass valve is set according to the operating state of the engine. to be larger than the second exhaust bypass valve opening which is, by enriching the air-fuel ratio of the exhaust gas, by which is adapted to reduce the NOx occluded in the NOx catalyst, in particular an acceleration Suponsu made at low load and a problem, it is possible to perform the reduction of the NOx, when the acceleration request immediately reduced during or reduction completion of NOx, it is possible to improve the acceleration response. In addition, even at high loads, by increasing the opening of the second exhaust bypass valve, the amount of air supplied to the engine can be reduced, and the air-fuel ratio can be enriched.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration of an engine 1 employing a supercharging device according to an embodiment of the present invention. The engine 1 is a diesel engine mounted on a vehicle, and includes a cylinder block 3 provided with a plurality of cylinders 2 (only one is shown), a cylinder head 4 disposed on the cylinder block 3, An oil pan 9 is provided below the cylinder block 3 and stores lubricating oil. In each cylinder 2 of the engine 1, pistons 5 are fitted so as to be able to reciprocate. A deep dish-shaped combustion chamber 6 is formed on the top surface of the piston 5. The piston 5 is connected to the crankshaft 8 via a connecting rod 7.

  In the cylinder head 4, an intake port 12 and an exhaust port 13 are formed for each cylinder 2, and an intake valve 14 and an exhaust valve that open and close the opening of the intake port 12 and the exhaust port 13 on the combustion chamber 6 side. 15 are arranged respectively.

  The cylinder head 4 is provided with an injector 20 for injecting fuel, and a glow plug 25 for warming intake air and improving fuel ignitability when the engine 1 is cold. The injector 20 is arranged so that its fuel injection port faces the combustion chamber 6 from the ceiling surface of the combustion chamber 6 so that fuel is directly injected and supplied to the combustion chamber 6 near the top dead center of the compression stroke. It has become. The injector 20 is connected to a common rail (not shown) via a fuel supply pipe 21 and is configured so that fuel is supplied from a fuel tank (not shown) via the fuel supply pipe 21 and the common rail. . Excess fuel is returned to the fuel tank through the return pipe 22.

  An intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 12 of each cylinder 2. An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30, and the intake air filtered by the air cleaner 31 passes through the intake passage 30 and the intake port 12 and is a combustion chamber of each cylinder 2. 6 is supplied.

  An air flow sensor 32 for detecting the flow rate of intake air is disposed in the intake passage 30 near the downstream side of the air cleaner 31. A surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 downstream of the surge tank 33 is an independent passage branched for each cylinder 2, and the downstream end of each independent passage is connected to the intake port 12 of each cylinder 2.

  Further, a compressor 61 a of the first exhaust turbocharger 61 and a compressor 62 a of the second exhaust turbocharger 62 are disposed between the air flow sensor 32 and the surge tank 33 in the intake passage 30. The compressor 61a of the first exhaust turbocharger 61 is located downstream of the compressor 62a of the second exhaust turbocharger 62. The intake air is supercharged by the operation of both the compressors 61a and 62a. The intake passage 30 is connected to an intake bypass passage 64 that bypasses the compressor 61a of the first exhaust turbocharger 61. The intake bypass passage 64 adjusts the amount of air flowing to the intake bypass passage 64. An intake bypass valve 65 is provided. In the present embodiment, a bypass passage that bypasses the compressor 62a of the second exhaust turbocharger 62 is not provided. However, such a bypass passage is provided, and the bypass passage is similar to the intake bypass valve 65. This valve may be provided.

  Furthermore, between the compressor 61a and the surge tank 33 of the first exhaust turbocharger 61 in the intake passage 30, an intercooler that cools the air compressed by the compressors 61a and 62a in order from the upstream side. 35, an intake pressure sensor 36 for detecting the pressure of the air compressed by the compressors 61a and 62a, and an intake throttle valve 37 for adjusting the amount of intake air into the combustion chamber 6 of each cylinder 2 are provided. Yes. The intake throttle valve 37 is basically fully opened, but when the filter 43b described later is regenerated, the intake throttle valve 37 is changed from the fully opened state to the closing direction to have a predetermined opening degree. The intake throttle valve 37 is fully closed so that no shock occurs when the engine 1 is stopped.

  An exhaust passage 40 for discharging burned gas (exhaust gas) from the combustion chamber 6 of each cylinder 2 is connected to the other side of the engine 1. The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold having an independent passage branched for each cylinder 2 and connected to the outer end of the exhaust port 13 and a collecting portion where the independent passages gather. Yes. A turbine 61b of the first exhaust turbocharger 61 and a turbine 62b of the second exhaust turbocharger 62 are disposed in the exhaust passage 40 on the downstream side of the exhaust manifold. The turbine 61b of the charger 61 is positioned upstream of the turbine 62b of the second exhaust turbocharger 62. The turbines 61b and 62b are rotated by the exhaust gas flow, and the compressors 61a and 62a connected to the turbines 61b and 62b are operated by the rotation of the turbines 61b and 62b, respectively.

  The exhaust passage 40 includes a first exhaust bypass passage 67 that bypasses the turbine 61 b of the first exhaust turbocharger 61 and a second exhaust bypass passage 69 that bypasses the turbine 62 b of the second exhaust turbocharger 62. And are connected. The first exhaust bypass passage 67 is provided with a regulating valve 68 (first exhaust bypass valve) for adjusting the amount of exhaust flowing to the first exhaust bypass passage 67, and the second exhaust bypass passage 69 includes A waste gate valve 70 (second exhaust bypass valve) for adjusting the amount of exhaust flowing to the second exhaust bypass passage 69 is provided.

  An exhaust gas purification device 43 that purifies harmful components in the exhaust gas is disposed downstream of the turbine 62b of the second exhaust turbocharger 62 in the exhaust passage 40. The exhaust purification device 43 includes an oxidation catalyst unit 43a, a diesel particulate filter (hereinafter referred to as a filter) 43b, and a lean NOx catalyst unit 43c, which are arranged in this order from the upstream side. The oxidation catalyst portion 43a and the filter 43b are accommodated in one case, and the lean NOx catalyst portion 43c is accommodated in a case different from the case that accommodates the oxidation catalyst portion 43a and the filter 43b. A silencer 48 is provided at the downstream end of the exhaust passage 40 (downstream of the lean NOx catalyst portion 43c).

The oxidation catalyst unit 43a has an oxidation catalyst supporting platinum or platinum added with palladium, etc., and performs a reaction in which CO and HC in the exhaust gas are oxidized to produce CO ₂ and H ₂ O. It is a thing to encourage. The filter 43b collects particulates such as soot contained in the exhaust gas of the engine 1. The filter 43b may be coated with an oxidation catalyst.

  The lean NOx catalyst unit 43c has a NOx occlusion reduction type catalyst (corresponding to the NOx catalyst of the present invention) that occludes NOx in exhaust gas to reduce and purify, for example, barium as a main component, potassium, A NOx occlusion material in which an alkali metal such as magnesium, strontium, or lanthanum, an alkaline earth metal, or a rare earth, and a noble metal having a chemical reaction catalytic action such as platinum is supported. The lean NOx catalyst 43c stores NOx in the exhaust gas in a state where the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. The NOx is released and subjected to an oxidation-reduction reaction with CO and HC in the exhaust gas to be decomposed into oxygen and nitrogen. Further, when the air-fuel ratio of the exhaust gas is in the vicinity of the stoichiometric air-fuel ratio, HC, CO and NOx are substantially completely purified.

  Since the engine 1 of this embodiment is a diesel engine, a lean operation is performed in which the air-fuel ratio is larger than the stoichiometric air-fuel ratio (λ> 1) in the entire operation region. If this lean operation is continued, the amount of NOx occluded in the lean NOx catalyst portion 43c increases, eventually becoming saturated, and the NOx purification capacity decreases. In order to prevent this, the air-fuel ratio is enriched so that the stored NOx is decomposed and released into oxygen and nitrogen to restore the NOx storage capacity. Specifically, the NOx amount occluded in the lean NOx catalyst unit 43c can be estimated from a NOx amount discharge map created in advance based on the operating state of the engine 1 such as the engine speed and engine load. The estimated integrated value of the NOx amount is estimated as the NOx amount occluded in the lean NOx catalyst portion 43c, and when the occluded NOx amount becomes equal to or greater than a predetermined amount α, the air-fuel ratio of the exhaust gas is set as described later. Richer than the air-fuel ratio at the time of lean operation (for example, the stoichiometric air-fuel ratio is set or richer than that).

  In the exhaust purification device 43, upstream and downstream pressure detectors 45 and 46 for detecting the pressure of the exhaust gas immediately before and after flowing into the filter 43b are provided on the upstream and downstream sides of the filter 43b, respectively. The upstream and downstream pressure detectors 45 and 46 are connected to a differential pressure sensor 47 that detects a differential pressure between the pressure detectors 45 and 46. This differential pressure corresponds to the amount of fine particles collected by the filter 43b (that is, the collected amount), and the larger the differential pressure, the larger the collected amount. When the collected amount increases, the filter 43b is clogged, and in order to prevent this, when the collected amount becomes a preset amount (for example, 70% of the maximum collected amount) or more. Then, the filter 43b is regenerated by burning the fine particles. In order to regenerate the filter 43b, unburned fuel is supplied to the oxidation catalyst unit 43a of the exhaust purification device 43, and the temperature of the filter 43b is increased by the oxidation reaction heat of the unburned fuel, and is collected in the filter 43b. Burn off the fine particles. The unburned fuel is supplied to the oxidation catalyst unit 43a at a time (expansion stroke or exhaust stroke) delayed from the main injection for injecting fuel near the top dead center of the compression stroke, intended for combustion in the combustion chamber 6. This is done by post-injection. The post injection is preferably divided injection divided into a plurality of times. When performing the post injection, the opening degree of the intake throttle valve 37 is changed from the fully opened state to the closing direction in order to increase the pump loss of the engine 1 and increase the exhaust heat energy. Further, it is preferable that an exhaust gas recirculation valve 51, which will be described later, be fully closed so that fuel by post injection does not flow into the intake passage 30.

  A portion of the intake passage 30 between the surge tank 33 and the intake throttle valve 37 (that is, a portion on the downstream side of the compressor 61a of the first exhaust turbocharger 61), the exhaust manifold and the first exhaust passage 40 in the exhaust passage 40. A portion between the first exhaust turbocharger 61 and the turbine 61b (that is, a portion upstream of the turbine 61b of the first exhaust turbocharger 61) is for returning a part of the exhaust gas to the intake passage 30. The exhaust gas recirculation passage 50 is connected. The exhaust gas recirculation passage 50 is provided with an exhaust gas recirculation valve 51 for adjusting the recirculation amount of the exhaust gas to the intake passage 30 and an EGR cooler 52 for cooling the exhaust gas with engine cooling water. ing.

  The first exhaust turbocharger 61 is small, and the second exhaust turbocharger 62 is large. That is, the inertia of the turbine 62 b of the second exhaust turbocharger 62 is larger than that of the turbine 61 b of the first exhaust turbocharger 61. Here, the T / C efficiency map of the first exhaust turbocharger 61 (showing how much the rotational energy of the turbine 61b can be converted into a pressure increase by the compressor 61a) is shown by a solid line in FIG. A T / C efficiency map of the exhaust turbocharger 62 is shown by a broken line in FIG. In FIG. 2, the “air flow rate” on the horizontal axis is the amount of air detected by the air flow sensor 32, and the “pressure ratio” on the vertical axis is the air pressure immediately after flowing out from the compressor with respect to the air pressure just before flowing into the compressor. Ratio. A plurality of annular lines drawn for each exhaust turbocharger are the efficiency obtained from the relationship between the air flow rate and the pressure ratio, and the efficiency increases as the line on the center side. As can be seen from FIG. 2, the large second exhaust turbocharger 62 has a wider area of high efficiency.

  As shown in FIG. 3, signals of detected values by the air flow sensor 32, the intake pressure sensor 36 and the differential pressure sensor 47 are input to an engine control unit (hereinafter referred to as ECU) 81 that controls the engine 1. In addition to these components, the ECU 81 includes an engine speed sensor 73 that detects the speed of the engine 1, a crank angle sensor 74 that detects the crank angle, a coolant temperature sensor 75 that detects the temperature of the engine coolant, and an accelerator. Signals of respective detection values such as an accelerator opening sensor 76 for detecting the opening are inputted, and based on these input signals, the injector 20, the intake throttle valve 37, the exhaust gas recirculation valve 51, the intake bypass valve 65, the regulating valve. 68 and the wastegate valve 70 are controlled. That is, the ECU 81 constitutes bypass valve control means for controlling the opening degree of the intake bypass valve 65, the regulating valve 68 and the waste gate valve 70.

  The ECU 81 controls the openings of the intake bypass valve 65, the regulator valve 68 and the waste gate valve 70 to the openings set according to the operating state of the engine 1. In the present embodiment, the low load and low rotation side region A (the engine load is smaller than the predetermined load (the smaller the engine rotation speed is larger)) in the map having the engine rotation speed and the engine load as parameters shown in FIG. In the region), both the first and second exhaust turbochargers 61 and 62 are operated, and in order to do so, the intake bypass valve 65 and the regulating valve 68 are set to openings other than fully open, and the wastegate valve 70 is a fully closed state. On the other hand, in the high load and high rotation side region B (region in which the engine load is larger than the predetermined load), the first exhaust turbocharger 61 becomes exhaust resistance, so that only the second exhaust turbocharger 62 is used. In order to operate and do this, the intake bypass valve 65 and the regulating valve 68 are fully opened, and the wastegate valve 70 is set to an opening close to the fully closed state. The waste gate valve 70 may be always fully closed (or the second exhaust bypass passage 69 and the waste gate valve 70 may be eliminated). However, in order to prevent over-rotation, the waste gate valve 70 is slightly opened in the region B. I'm offended.

  The opening degree of the intake bypass valve 65 in the region A is determined by the target intake pressure set by the operating state of the engine 1 and the accelerator opening degree. Further, as shown in FIG. 5, the regulating valve 68 gradually increases the opening as the load becomes high (high torque). In FIG. 5, the higher torque side of the line with the opening degree of 100% is an area corresponding to the area B, and the opening degree is 100% in this area. Furthermore, the opening degree of the waste gate valve 70 is as shown in FIG. In FIG. 6, the lower torque side of the line with the opening degree of 10% is an area corresponding to the area A, and the opening degree is 0% in this area. The solid line in FIGS. 5 and 6 is the maximum torque line generated in the engine 1.

  In the region including the line indicated by the broken line in FIG. 4 and the lower load and lower rotation side (including the region A), the exhaust gas recirculation valve 51 is opened, and a part of the exhaust gas enters the intake passage 30. It is designed to be refluxed. Hereinafter, this region is referred to as an EGR region. The opening degree of the exhaust gas recirculation valve 51 in this EGR region is set according to the operating state of the engine 1. On the other hand, the exhaust gas recirculation valve 51 is fully closed at a higher load and higher rotation side than the above line, and the recirculation of the exhaust gas to the intake passage 30 is not performed.

  The region A for operating both the first and second exhaust turbochargers 61 and 62, the region B for operating only the second exhaust turbocharger, and the EGR region are shown in FIG. The T / C efficiency map may be used for setting. That is, the area corresponding to the area A is an area surrounded by a thick line in FIG. 7A, the area corresponding to the area B is an area surrounded by a thick line in FIG. 7B, and the EGR area The corresponding area is an area surrounded by a thick line in FIG. Thereby, from the relationship between the amount of air detected by the air flow sensor 32 and the ratio of the air pressure immediately after flowing out of the compressor to the air pressure immediately before flowing into the compressor, the first and second exhaust turbochargers 61, It is determined whether or not both of 62 are operated, only the second exhaust turbocharger 62 is operated, or the exhaust gas is recirculated to the intake passage 30.

  Inside the ECU 81, when the amount of NOx occluded in the lean NOx catalyst portion 43c becomes equal to or greater than the predetermined amount α, the lean NOx catalyst portion 43c is occluded by the enrichment of the air-fuel ratio of the exhaust gas. An air-fuel ratio control unit 81a that functions as air-fuel ratio control means for reducing NOx is provided, and the air-fuel ratio control unit 81a enriches the air-fuel ratio.

  Specifically, in the region A, the air-fuel ratio control unit 81a sets the opening degree of the intake bypass valve 65 according to the operating state of the engine 1 (the intake bypass valve when not reducing). And the opening of the regulating valve 68 is equal to or less than the regulating valve opening set according to the operating state of the engine 1 (the regulating valve opening during non-reduction). As a result, the air-fuel ratio of the exhaust gas is enriched, and the NOx occluded in the lean NOx catalyst portion 43c is reduced and purified. At this time, the waste gate valve 70 is in the fully closed state as in non-reduction.

  Thus, by making the opening degree of the intake bypass valve 65 larger than the intake bypass valve opening degree at the time of non-reduction, the supercharging efficiency is lowered, and the amount of air supplied to the engine is reduced. The air-fuel ratio of the gas can be enriched, and the NOx stored in the lean NOx catalyst unit 43c can be reduced and purified.

  Further, by making the opening degree of the regulating valve 68 equal to or less than the opening degree of the regulating valve at the time of non-reduction, the turbine 61b of the first exhaust turbocharger 61 continues to rotate. When the occupant depresses the accelerator pedal to make an acceleration request, that is, when the rate of change of the accelerator opening detected by the accelerator opening sensor 76 is greater than or equal to a predetermined value, the turbine 61b is already rotating, so the intake bypass valve By setting the opening of 65 to the intake bypass valve opening at the time of non-reduction, appropriate supercharging can be performed immediately, and a high acceleration response can be obtained.

  The opening degree of the regulating valve 68 at the time of reduction is within the range equal to or smaller than the opening degree of the regulating valve at the time of non-reduction, and the air-fuel ratio is appropriately adjusted in relation to the opening degree of the intake bypass valve 65. Although it may be set as appropriate from the viewpoint of being able to be enriched and obtaining a high acceleration response, it is preferable to set the opening so that the turbine 61b of the first exhaust turbocharger 61 rotates at a rotational speed equal to or higher than a predetermined rotational speed. . From this, the opening degree of the regulating valve 68 at the time of reduction is preferably larger as the engine load is larger, like the regulating valve opening degree at the time of non-reducing. In this embodiment, if the regulating valve 68 is fully closed during non-reduction, it is also fully closed during reduction. If the regulating valve 68 is not fully closed during non-reduction, the regulating valve 68 is used during reduction. Is reduced by a certain percentage with respect to the regulating valve opening at the time of non-reduction.

  In the region B, as described above, the intake bypass valve 65 and the regulating valve 68 are fully opened at the time of non-reduction, and the first exhaust turbocharger 61 is not operated. You cannot change the direction to open. Further, in the region B in which the acceleration response is not a big problem compared to the region A, if the opening degree of the regulating valve 68 is made smaller than the regulating valve opening degree in the non-reducing state at the time of reduction, exhaust resistance is caused. It is better not to do anything. Therefore, the air-fuel ratio control unit 81a, in the region B, sets the opening of the waste gate valve 70 according to the operating state of the engine 1 (the waste gate valve opening during non-reduction). ), The air-fuel ratio of the exhaust gas is enriched, and the NOx occluded in the lean NOx catalyst portion 43c is reduced and purified. On the other hand, the opening degree of the intake bypass valve 65 and the regulating valve 68 at the time of reduction in the region B is set to the fully open state at the time of non-reduction. By doing so, the amount of air supplied to the combustion chamber 6 can be reduced by increasing the opening degree of the wastegate valve 70 even at a high load when the first exhaust turbocharger 61 is not operated. The air-fuel ratio can be enriched.

  Further, the ECU 81 reduces the opening of the exhaust gas recirculation valve 51 to a smaller side when the opening of the intake bypass valve 65 is larger than the intake bypass valve opening during non-reduction as described above. To correct. That is, it is made smaller than the exhaust gas recirculation valve opening degree set according to the operating state of the engine 1. This suppresses the exhaust gas recirculation amount from becoming excessive due to the decrease in the supercharging pressure.

  Here, control operations of the exhaust gas recirculation valve 51, the intake bypass valve 65, the regulating valve 68, and the wastegate valve 70 in the ECU 81 will be described based on the flowchart of FIG.

  In the first step S1, input signals from various sensors are read. In the next step S2, the target intake pressure and the target opening of the exhaust gas recirculation valve 51, the intake bypass valve 65, the regulating valve 68 and the wastegate valve 70 ( The opening degree at the time of non-reduction) is set.

  In the next step S3, it is determined whether or not the operating state of the engine 1 is in the EGR region. If the determination in step S3 is YES, the process proceeds to step S4, and the exhaust gas recirculation valve 51 (in FIG. 8). The opening of the EGR valve is set to an opening corresponding to the operating state of the engine 1 (the set target opening), and then the process proceeds to step S6. On the other hand, when the determination in step S3 is NO, the process proceeds to step S5, the exhaust gas recirculation valve 51 is fully closed, and then the process proceeds to step S6.

  In step S6, the amount of NOx occluded in the lean NOx catalyst portion 43c as described above is estimated, and in the next step S7, it is determined whether or not the NOx amount is equal to or greater than the predetermined amount α. If the determination in step S7 is NO, the process directly returns. On the other hand, if the determination in step S7 is YES, the process proceeds to step S8.

  In step S8, it is determined whether or not the operating state of the engine 1 is in the region A. When the determination in step S8 is NO, that is, when the operating state of the engine 1 is in the region B, the process proceeds to step S9. In the air-fuel ratio control unit 81a, the opening degree of the waste gate valve 70 is changed to the larger side (opening direction) with respect to the waste gate valve opening degree set in step S2, and then the process returns.

  On the other hand, when the determination in step S8 is YES, the process proceeds to step S10, and in the air-fuel ratio controller 81a, the opening of the intake bypass valve 65 is larger than the intake bypass valve opening set in step S2. And the opening degree of the regulating valve 68 is changed to a smaller side (closing direction) by a certain percentage with respect to the regulating valve opening degree set in step S2 (step S2). When the regulating valve opening set in step 0 is 0, it is set to 0 as it is). However, the target intake pressure is kept constant.

  In the next step S11 following step S10, the opening degree of the exhaust gas recirculation valve 51 is corrected to the smaller side (closed direction), and in the next step S12, the change in the accelerator opening degree detected by the accelerator opening degree sensor 76 is corrected. Whether the rate (the value obtained by subtracting the accelerator opening detected last time from the accelerator opening detected this time divided by the detection time interval) is greater than or equal to a predetermined value, that is, whether the passenger is requesting acceleration Determine.

  If the determination in step S12 is NO, the process returns as it is. If the determination in step S12 is YES, the process proceeds to step S13, and the opening of the intake bypass valve 65 is changed to the opening at the time of non-reduction. In the next step S14, the correction of the closing direction of the exhaust gas recirculation valve 51 is stopped, and then the process returns.

  Therefore, in this embodiment, the opening degree of the intake bypass valve 65 is set according to the operating state of the engine 1 in order to reduce NOx occluded in the lean NOx catalyst unit 43c when the engine load is a low load equal to or lower than a predetermined load. Is set to a value larger than the intake bypass valve opening (the intake bypass valve opening at the time of non-reduction) and the opening of the regulating valve 68 is set according to the operating state of the engine 1 (non-reducing) The amount of air supplied to the combustion chamber 6 can be reduced and the air-fuel ratio of the exhaust gas can be made rich by reducing the supercharging efficiency. Thus, the NOx occluded in the lean NOx catalyst unit 43c can be reduced and purified, and the acceleration response when the acceleration is requested can be improved.

  In addition, since the wastegate valve 70 is in a fully closed state at the time of the reduction at the low load, even if the opening degree of the intake bypass valve 65 is increased, a certain degree of supercharging pressure can be stably obtained. When acceleration is requested, the turbine 62b of the large second exhaust turbocharger 62 is already rotating, so that a high acceleration response can be obtained with certainty.

  Furthermore, when the engine load is higher than the predetermined load, the opening degree of the waste gate valve 70 is set according to the operating state of the engine 1 so as to reduce the NOx stored in the lean NOx catalyst unit 43c. Since the waste gate valve opening (the waste gate valve opening at the time of non-reduction) is made larger, the first exhaust turbocharger 61 is supplied to the engine 1 even at the time of high load. The amount of air can be reduced, and the air-fuel ratio can be enriched.

The present invention can be applied not only to a diesel engine but also to a gasoline engine.

The present invention includes two exhaust turbochargers are useful supercharging apparatus for an engine that includes a NOx catalyst for reducing and occludes NOx.

It is the schematic which shows the structure of the engine which employ | adopted the supercharging apparatus which concerns on embodiment of this invention. It is a T / C efficiency map of the 1st and 2nd exhaust turbocharger. It is a block diagram which shows schematic structure of a supercharging device. 3 is an operation map of first and second exhaust turbochargers and an exhaust gas recirculation valve. It is a map which shows the opening degree of a regulating valve. It is a map which shows the opening degree of a waste gate valve. FIG. 5 is an operation map different from FIG. 4 for the first and second exhaust turbochargers and the exhaust gas recirculation valve. It is a flowchart which shows control operation | movement of an exhaust-gas recirculation valve, an intake bypass valve, a regulating valve, and a wastegate valve in an engine control unit.

1 Engine 30 Intake passage 40 Exhaust passage 43 Exhaust purification device 43c Lean NOx catalyst unit 61 First exhaust turbocharger 61a Compressor 61b Turbine 62 Second exhaust turbocharger 62a Compressor 62b Turbine 64 Intake bypass passage 65 Intake bypass valve 67 First exhaust bypass passage 68 Regulating valve (first exhaust bypass valve)
69 Second exhaust bypass passage 70 Wastegate valve (second exhaust bypass valve)
81 Engine control unit (bypass valve control means)
(Exhaust gas recirculation valve control means)
81a Air-fuel ratio control unit (air-fuel ratio control means)

Claims (1)

A first exhaust turbocharger having a compressor disposed in an intake passage of the engine and a turbine disposed in an exhaust passage;
An intake bypass passage for bypassing the compressor of the first exhaust turbocharger;
An intake bypass valve disposed in the intake bypass passage;
A first exhaust bypass passage for bypassing the turbine of the first exhaust turbocharger;
A first exhaust bypass valve disposed in the exhaust bypass passage;
Bypass valve control means for controlling the openings of the intake bypass valve and the first exhaust bypass valve to openings set in accordance with the operating state of the engine;
It is disposed downstream of the turbine in the exhaust passage, and stores NOx when the air-fuel ratio of the exhaust gas of the engine is lean and reduces the stored NOx by enriching the air-fuel ratio of the exhaust gas. NOx catalyst to
An air-fuel ratio control means for reducing the NOx stored in the NOx catalyst by enriching the air-fuel ratio of the exhaust gas when the amount of NOx stored in the NOx catalyst exceeds a predetermined amount ;
The compressor is disposed upstream of the compressor of the first exhaust turbocharger in the intake passage, and is disposed between the turbine of the first exhaust turbocharger and the NOx catalyst in the exhaust passage. A second exhaust turbocharger having a turbine;
A second exhaust bypass passage for bypassing the turbine of the second exhaust turbocharger;
A second exhaust bypass valve disposed in the second exhaust bypass passage,
The bypass valve control means controls the opening of the second exhaust bypass valve to an opening set according to the operating state of the engine, in addition to the opening of the intake bypass valve and the first exhaust bypass valve. Is,
The air-fuel ratio control means makes the opening degree of the intake bypass valve larger than the intake bypass valve opening degree set by the bypass valve control means when the engine load is a low load equal to or lower than a predetermined load . By making the opening of one exhaust bypass valve equal to or less than the opening of the first exhaust bypass valve set by the bypass valve control means, the air-fuel ratio of the exhaust gas is enriched and stored in the NOx catalyst. When the engine load is high and the engine load is higher than the predetermined load, the opening degree of the second exhaust bypass valve is set to be larger than the second exhaust bypass valve opening degree set by the bypass valve control means. by also increasing, ene, characterized in that the air-fuel ratio of the exhaust gas is rich, and is configured to reduce NOx stored in the NOx catalyst Down of the supercharger.

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