JP4539466B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust purification system used for an internal combustion engine mounted on a vehicle such as an automobile.

  For example, in an internal combustion engine such as a diesel engine, particulate matter (PM) or nitrogen oxides in exhaust gas are reduced because the temperature of the combustion chamber becomes low during low speed and low load operation such as during start operation. The amount of (NOx) is likely to increase.

  Exhaust gas is normally purified by a catalytic converter installed in the exhaust passage, but the purification capability is reduced when the catalyst bed temperature is low.

  Here, in an in-cylinder direct injection type lean combustion engine, when the exhaust gas temperature is low, in addition to performing main injection into the combustion chamber in an excess air state, sub-injection is performed after main injection to increase the combustion amount. It has been considered that an exhaust control valve is provided in the exhaust passage and is substantially fully closed to reduce the amount of unburned HC generated (see Patent Document 1).

  The temperature rise state of the exhaust gas is monitored based on the output of the exhaust gas temperature sensor and the exhaust pressure sensor arranged upstream of the catalytic converter. When sub-combustion is performed in addition to main injection, unburned HC generated during combustion by main injection (hereinafter referred to as “main combustion”) in the combustion chamber is combustion by sub-injection (hereinafter referred to as “sub-combustion”). Since it is burned, the amount of unburned HC itself generated is greatly reduced. Moreover, the unburned HC generated during the main combustion is combusted together with the auxiliary fuel, resulting in an increase in the amount of combustion, which inevitably increases the exhaust temperature and raises the catalyst bed temperature of the catalytic converter, thereby purifying the catalytic converter. Will improve.

  Further, an exhaust control valve is disposed downstream of the catalytic converter disposed in the exhaust passage of the internal combustion engine, and the exhaust control valve is closed until the temperature downstream of the catalytic converter reaches a predetermined temperature, thereby the catalyst bed temperature of the catalytic converter. Has been considered to raise the temperature to the activation temperature (see Patent Document 2).

Note that the exhaust control valve is operated based on the output of a temperature sensor disposed downstream of the catalytic converter.
JP 2001-123870 A JP 2001-59414 A

  Each of the above conventional examples is considered to be effective in positively activating the catalytic converter, but there is room for improvement in the following points.

  First, in the conventional example according to Patent Document 1, since the exhaust control valve is controlled to be opened and closed in addition to performing fuel injection in two stages, the configuration and operation control become complicated, and the equipment cost increases. In addition, the exhaust pressure sensor and the exhaust temperature sensor monitor the exhaust temperature upstream of the catalytic converter, and if a general static pressure sensor is used as the exhaust pressure sensor, the influence of the dynamic pressure component of the exhaust Therefore, it is considered that such an exhaust pressure sensor and an exhaust temperature sensor are insufficient to be used for estimating the catalyst bed temperature of the catalytic converter affected by the exhaust flow rate.

  Moreover, in the conventional example which concerns on patent document 2, since the exhaust control valve is controlled based on the output from the temperature sensor arrange | positioned downstream of the catalytic converter, when the catalyst bed temperature of a catalytic converter is controlled accurately, I can't say that.

  The present invention relates to an exhaust purification system that purifies exhaust gas discharged from an internal combustion engine by a catalytic converter provided in an exhaust passage, and enables the catalytic converter to be quickly and appropriately heated to an activation temperature as necessary. It is aimed.

  An exhaust purification system for an internal combustion engine according to the present invention includes a catalytic converter that is provided in an exhaust passage through which exhaust gas is exhausted from the internal combustion engine and purifies the exhaust gas, and is disposed downstream of the catalytic converter in the exhaust passage. An exhaust throttle valve that adjusts the flow rate, a dynamic pressure sensor that is arranged between the exhaust throttle valve and the catalytic converter or upstream of the catalytic converter and detects the fluctuating pressure or absolute pressure of the exhaust gas, and the temperature of the catalytic converter And a control device that performs catalyst temperature rise control for activating the catalytic converter, and the control device estimates the exhaust flow rate based on the output of the dynamic pressure sensor as necessary. In addition, catalyst bed temperature estimating means for estimating the catalyst bed temperature of the catalytic converter based on the estimated exhaust flow rate and the output of the temperature sensor, and a catalyst bed The target exhaust pressure setting means for setting the target exhaust pressure in consideration of the driving situation when the degree is lower than the predetermined reference value, and after setting the target exhaust pressure, the current exhaust pressure is determined based on at least the output of the dynamic pressure sensor. Exhaust pressure estimating means for estimating, and valve control means for controlling the opening of the exhaust throttle valve based on the difference between the estimated current exhaust pressure and the target exhaust pressure.

  According to this configuration, when the catalyst bed temperature of the catalytic converter is low, that is, when the purification capacity of the catalytic converter is low, the exhaust pressure can be increased by controlling the exhaust throttle valve to the closed side. Become.

  As a result, exhaust heat can be retained in and around the catalytic converter in the exhaust passage, so that the catalytic converter is quickly and appropriately heated to the activation temperature, and its purification capability is improved. Become.

  In addition, since a dynamic pressure sensor that can accurately detect pressure fluctuations and absolute pressure due to exhaust pulsation is used, the reliability of the output of the dynamic pressure sensor is increased, and the exhaust gas estimated based on the output of the dynamic pressure sensor is increased. The reliability of the flow rate is also increased. Since the catalyst bed temperature is estimated based on the estimated exhaust flow rate and the output of the temperature sensor, the catalyst bed temperature can be accurately grasped. Therefore, the target exhaust pressure can be set to an ideal hard upper limit pressure with a small margin in the catalyst temperature increase control.

  Therefore, in the catalyst temperature increase control, the exhaust throttle valve can be controlled so as to increase the exhaust pressure to an ideal hard upper limit pressure according to the operating condition, and the catalytic converter can be effectively utilized over the entire operating condition. .

  Note that the hard upper limit pressure means that, for example, when the exhaust throttle valve is closed in the exhaust stroke of the internal combustion engine, the pressure of the exhaust port increases, the oil seal of the valve stem falls off, or the exhaust valve (not shown) It is the upper limit pressure for avoiding the occurrence of mechanical operation problems such as interference with a piston (not shown). Since this hard upper limit pressure is determined at the time of structural design of the internal combustion engine, the target exhaust pressure in the catalyst temperature rise control is generally set to a value that allows for a predetermined margin in the design hard upper limit pressure. is there.

  The exhaust purification system further includes a rotational speed detection means for detecting the rotational speed of the internal combustion engine, and the exhaust pressure estimation means of the control device is configured to output the output from the rotational speed detection means and the load of the internal combustion engine to the current exhaust gas. It can be in addition to the atmospheric pressure estimation requirements.

  In this configuration, considering the fact that the relative relationship between the opening of the exhaust throttle valve and the exhaust pressure varies depending on the engine speed and load of the internal combustion engine, the engine speed and load of the internal combustion engine are the conditions for controlling the exhaust throttle valve. Therefore, it becomes possible to appropriately control the exhaust throttle valve in accordance with the target exhaust pressure.

  The dynamic pressure sensor of the exhaust purification system may be arranged at a resonance abdomen in the exhaust passage.

  According to this configuration, since the arrangement of the dynamic pressure sensors is made appropriate, the detection accuracy of the dynamic pressure sensor can be increased, and the reliability of the detection output of the dynamic pressure sensor is improved.

  In the exhaust gas purification system, the downstream area of the exhaust gas passage in the exhaust passage is formed with a smaller diameter than the catalytic converter, and the outlet portion of the catalytic converter is gradually reduced in diameter toward the small diameter area. The dynamic pressure sensor is arranged between the minimum diameter position of the outlet portion and the arrangement position of the exhaust throttle valve in the small-diameter region and at the abdomen of exhaust resonance in the exhaust passage. be able to.

  According to this configuration, the detection accuracy of the dynamic pressure sensor can be further increased, and the reliability of the detection output of the dynamic pressure sensor is further improved.

  The dynamic pressure sensor of the exhaust purification system may be attached in a state of protruding from the outer diameter side to the inner diameter side of the pipe forming the exhaust passage.

  According to this structure, since the detection part of a dynamic pressure sensor is arrange | positioned in the optimal place, the reliability of the detection output of a dynamic pressure sensor comes to improve further.

  According to the exhaust gas purification system for an internal combustion engine according to the present invention, it is possible to quickly and appropriately raise the catalytic converter to the activation temperature as necessary, so that the exhaust gas of the internal combustion engine can be efficiently purified.

  An embodiment of the present invention will be described below with reference to FIGS.

  Prior to the description of the exhaust purification system according to the present invention, a schematic configuration of an internal combustion engine to be used will be described with reference to FIG.

  An internal combustion engine 1 shown in FIG. 1 is an in-line four-cylinder diesel engine, and basically mixes air supplied from an intake system and fuel supplied from a fuel supply system at an appropriate air-fuel ratio. After the air-fuel mixture is injected into the combustion chamber 2 and combusted, the exhaust gas in the combustion chamber 2 is released into the atmosphere through the exhaust system.

  In the intake system, an air cleaner 23, an air flow meter 24, and a throttle valve 25 are arranged in this order from the upstream side in an intake passage formed by connecting an intake pipe 22 to an intake manifold 21 connected to an intake port 3 of a cylinder head. It is. The air flow meter 24 outputs an electrical signal corresponding to the amount of air flowing into the intake pipe 22 via the air cleaner 23.

  The fuel supply system has a configuration in which a fuel tank 32, a supply pump 33, a common rail 34, a plurality of injectors 35,... The fuel in the fuel tank 32 is sucked out by the supply pump 33, supplied to the common rail 34, and injected from the common rail 34 to the combustion chamber 2 through the injectors 35. The supply pump 33 is driven by a crankshaft (not shown) of the internal combustion engine 1.

  The exhaust system includes an exhaust passage configured by connecting a muffler 42 to an exhaust manifold 41 connected to the exhaust port 4 of the cylinder head.

  The internal combustion engine 1 exemplified in this embodiment is equipped with a turbocharger 5, an intercooler 6, an EGR device 7 as an exhaust gas recirculation device, and a catalytic converter 8, and will be described below.

  The turbocharger 5 boosts intake air using exhaust gas, and includes a compressor 5a and a turbine 5b. The compressor 5 a is disposed downstream of the air flow meter 24 in the intake pipe 22, and the turbine 5 b is disposed between the collection portion of the exhaust manifold 41 and the muffler 42.

  The intercooler 6 cools the intake air whose pressure has been increased by the turbocharger 5, and is disposed between the compressor 5 a of the turbocharger 5 and the throttle valve 25.

  The EGR device 7 reduces NOx by returning a part of the exhaust gas (EGR gas) to the intake system and supplying the exhaust gas again to the combustion chamber 2, and enters the EGR passage 7a from the upstream side to the EGR catalytic converter 7b, The cooler 7c and the EGR valve 7d are arranged.

  The EGR passage 7a includes a bypass passage that bypasses the combustion chamber 2 and is connected from the exhaust system to the intake system. The EGR catalytic converter 7b purifies the exhaust gas flowing into the EGR passage 7a. The EGR cooler 7c includes a heat exchanger that lowers the temperature of the EGR gas by exchanging heat between the EGR gas and the coolant of the internal combustion engine 1, for example. The EGR valve 7d controls the amount of exhaust gas flowing in the EGR passage 7a from the exhaust system side to the intake system side.

  The catalytic converter 8 is interposed between an exhaust manifold 41 and a muffler 42 that constitute an exhaust passage. In this embodiment, the catalytic converter 8 is called a DPNR (Diesel Paticulate-Nox Reduction system).

The catalytic converter 8 made of DPNR reduces both particulate matter (PM) and nitrogen oxide (NOx) in the exhaust gas. As shown in FIG. 2, a honeycomb structure is formed in the case 8a. The body 8b is housed and arranged.

  The middle part of the case 8a has a cylindrical shape, and one end part (entrance) and the other end part (exit) thereof have a tapered shape in which the diameter gradually decreases toward the end edge. A honeycomb structure 8b is disposed in an intermediate portion of the case 8a.

Although not shown in detail, the honeycomb structure 8b has a configuration in which, for example, a NOx occlusion reduction type three-way catalyst is supported on a porous ceramic base material. When flowing in as shown by the arrows in FIG. 3, PM is trapped in the micropores of the porous ceramic substrate, NOx is occluded when passing through the micropores of the porous ceramic substrate, and N ₂ and CO ₂ are discharged. It is like that.

Usually, the catalyst bed of the catalytic converter 8 absorbs NOx when the air-fuel ratio of the exhaust gas (hereinafter referred to as the exhaust air-fuel ratio) is leaner than the stoichiometric air-fuel ratio, and the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or higher. NOx absorbed is released as NO ₂ or NO when the oxygen concentration in the inflowing exhaust gas decreases due to the richness. N discharged from the catalyst bed of the catalytic converter 8
Ox (NO ₂ or NO) immediately reacts with unburned HC and CO in the exhaust gas and is reduced to N ₂ .

The control device 9 is an ECU (Electronic Control Unit), and is composed of a central processing unit (CPU), a program memory (ROM), a data memory (RAM) and the like connected to each other by a bidirectional bus as is well known. Yes.

  The control device 9 controls various operations of the internal combustion engine 1, but the description of the operation is omitted here.

  In general, PM trapped in the catalytic converter 8 is basically burned and removed when the catalyst bed temperature of the catalytic converter 8 becomes the activation temperature.

  However, for example, when operating conditions such as cold operation, start operation, or low speed and low load operation of the internal combustion engine 1, the catalyst bed temperature of the catalytic converter 8 tends to be low, so that PM tends to remain without being burned, The purification capacity of the catalytic converter 8 tends to decrease. If the operation under such operating conditions is continued for a long time, the PM trapping ability in the catalytic converter 8 can be saturated.

  In such a case, it is desirable to activate the catalytic converter 8 by increasing the catalyst bed temperature of the catalytic converter 8 and the ambient temperature around it.

  Therefore, in this embodiment, the controller 9 is devised so as to perform the catalyst temperature increase control to raise the catalyst bed temperature of the catalytic converter 8 to the activation temperature as necessary, and will be described in detail below. .

  First, as shown in FIG. 1, an exhaust throttle valve 10 for adjusting the exhaust flow rate is installed on the downstream side of the catalytic converter 8 in the muffler 42, and between the exhaust throttle valve 10 and the catalytic converter 8. A dynamic pressure sensor 11 capable of measuring the fluctuating pressure and the absolute pressure of the exhaust gas is installed.

  Specifically, the exhaust throttle valve 10 is installed in the muffler 42 downstream from the catalytic converter 8 and is driven to open and close by the control device 9.

The dynamic pressure sensor 11 extends from the minimum diameter portion 8c of the downstream end portion in the exhaust passage direction in the case 8a of the catalytic converter 8 to the arrangement portion of the exhaust throttle valve 10 in the muffler 42, and in the phantom line of FIG. The abdominal part (dynamic pressure generating part) X ₁ or X _{2 of the} in-tube resonance as shown is output to the control device 9 with an electrical signal corresponding to the detected pressure.

The dynamic pressure sensor 11 is attached in a state of protruding a predetermined amount from the outer diameter side to the inner diameter side of the muffler 42. The amount of protrusion of the dynamic pressure sensor 11 is appropriately set so as to make it difficult to become exhaust resistance while being close to the center of the abdomen X ₁ or X _{2 of the} in-pipe resonance.

  If the arrangement and attachment state of the dynamic pressure sensor 11 are specified in this way, it is advantageous in increasing the detection accuracy of the dynamic pressure sensor 11.

  A static pressure sensor 12 is provided upstream of the catalytic converter 8 in the muffler 42. In the catalytic converter 8, a temperature sensor 13 is provided substantially at the center in the exhaust gas passage direction.

  An intake air pressure sensor 14 is provided between the compressor 5 a of the turbocharger 5 and the intercooler 6 in the intake pipe 22. Further, the engine 1 is provided with a crank rotation sensor 15 that detects the rotation speed of a crankshaft (not shown).

  Next, the catalyst temperature increase control by the control device 9 will be described with reference to the flowchart shown in FIG.

  The control device 9 periodically enters the flowchart shown in FIG. 6 during the operation of the internal combustion engine 1. First, in step S1, it is determined whether or not the exhaust pressure needs to be increased. In this determination, the catalyst bed temperature of the catalytic converter 8 is estimated, and the exhaust pressure is increased by comparing the estimated catalyst bed temperature with a predetermined reference value (activation temperature of the catalytic converter 8 to be used). Determine if it is necessary.

  In the first place, as shown in FIGS. 5A and 5B, the catalytic converter 8 has a different catalyst bed temperature distribution depending on the exhaust flow rate. That is, when the exhaust gas flow rate is large, as shown in FIG. 5A, the temperature spread from the upstream side to the downstream side is faster in the radially intermediate portion than in the outer diameter side portion. The temperature difference between the direction intermediate portion and the outer diameter side portion is increased. On the other hand, when the exhaust gas flow rate is small, as shown in FIG. 5B, the temperature spread from the upstream side to the downstream side is slightly faster at the radially intermediate portion than at the outer diameter side portion. Therefore, the temperature difference between the radially intermediate portion and the outer diameter side portion is slight.

  For this reason, in this embodiment, it is considered that it is not accurate to specify the catalyst bed temperature of the catalytic converter 8 only by the output of the temperature sensor 13, and the flow rate of exhaust gas passing through the catalytic converter 8 is determined by the catalytic converter 8. Estimated based on the output of the dynamic pressure sensor 11 disposed downstream, and utilizing the estimated exhaust flow rate, the output of the temperature sensor 13, the output of the intake air pressure sensor 14 and the output of the crank rotation sensor 15, the catalyst bed of the catalytic converter 8. The temperature is estimated. Since the output of the dynamic pressure sensor 11 is proportional to the exhaust gas flow rate, the exhaust flow rate can be estimated relatively easily and accurately.

  Here, first, when the catalyst bed temperature is equal to or higher than the reference value, a negative determination is made in step S1, and the process returns to the main flow relating to the operation control of the internal combustion engine 1 (not shown).

On the other hand, if the catalyst bed temperature is lower than the reference value, an affirmative determination is made in step S1, and the target exhaust pressure P ₁ is set in step S2, assuming that the purification capacity of the catalytic converter 8 is insufficient.

The target exhaust pressure P ₁ is set to a so-called hard upper limit pressure by grasping the operation state. Note that the hard upper limit pressure means that, for example, when the exhaust throttle valve is closed in the exhaust stroke of the internal combustion engine, the pressure of the exhaust port rises, the oil seal of the valve stem falls off, or the exhaust valve (not shown) This is the upper limit pressure for avoiding the occurrence of mechanical operation problems such as interference with (not shown). Since the hard upper limit pressure is determined at the time of structural design of the internal combustion engine 1, the target exhaust pressure P ₁ in the catalyst temperature increase control is set to a value that allows for a predetermined margin in the design hard upper limit pressure. It is common.

Here, if a general static pressure sensor is used as a pressure sensor for detecting the exhaust pressure downstream of the catalytic converter 8 as in the conventional example, the margin is considered in consideration of the range of pressure fluctuation due to exhaust pulsation. Must be as large as possible, and the target exhaust pressure P ₁ must be set lower than the ideal target exhaust pressure P ₀ (see, for example, the solid line in FIG. 7).

However, in this embodiment, since the catalyst bed temperature can be estimated with high accuracy as in step S1, the target exhaust pressure P ₁ is set to the ideal target exhaust pressure P ₀ with the margin set small. This makes it possible to approach the design hard upper limit pressure.

Thereafter, in steps S3 to S6, the output of the static pressure sensor 12, the output of the dynamic pressure sensor 11, the output of the intake air pressure sensor 14, and the output of the crank rotation sensor 15 are sequentially taken in. Then, in step S7, the above step S3 is performed. The current exhaust pressure P ₂ is obtained based on the various types of information captured in S6.

Thereafter, in step S8, by subtracting the current exhaust pressure P ₂ obtained in step S7 the target exhaust pressure P ₁ set in step S2, determines whether the result is equal to or greater than "0" To do. In short, in short, it is examined whether the current exhaust pressure P ₂ is lower or higher than the target exhaust pressure P ₁ .

Here, first, if P ₁ −P ₂ <0, that is, if the current exhaust pressure P ₂ exceeds the target exhaust pressure P ₁ , a negative determination is made in step S8, and the target exhaust pressure P ₁ is determined in step S9. On the basis of the difference between the current exhaust pressure P ₂ and the current exhaust pressure P ₂ , a process for controlling the exhaust throttle valve 10 to the open side so as to reach the target exhaust pressure P ₁ is executed. Return to flow.

  As a result, the exhaust resistance at the exhaust throttle valve 10 in the exhaust passage (exhaust manifold 41, muffler 42) is reduced, the exhaust pressure upstream of the exhaust throttle valve 10 is reduced, and the exhaust heat is transferred from within the catalytic converter 8. Since it comes out smoothly, the catalyst bed temperature of the catalytic converter 8 falls within an allowable range.

On the other hand, if P ₁ −P ₂ ≧ 0, that is, if the current exhaust pressure P ₂ is less than or equal to the target exhaust pressure P ₁ , an affirmative determination is made in step S8, and the target exhaust pressure P ₁ and the current exhaust pressure are determined in step S10. Based on the difference from the exhaust pressure P ₂ , the process of controlling the exhaust throttle valve 10 to the closed side so as to be the target exhaust pressure P ₁ is executed, and then the process returns to the main flow relating to the operation control of the internal combustion engine 1 not shown. .

  As a result, the exhaust resistance at the exhaust throttle valve 10 increases in the exhaust passage (exhaust manifold 41, muffler 42), the exhaust pressure upstream of the exhaust throttle valve 10 is increased, and the exhaust heat flows into the catalytic converter 8. Since it is retained, the catalytic converter 8 is heated.

In the first place, normally, as indicated by the phantom line in FIG. 7, the lower the number of revolutions of the internal combustion engine 1, that is, the smaller the exhaust flow rate, the more ideal exhaust pressure becomes even if the exhaust throttle valve 10 is closed. ₀
It becomes difficult to rise.

  In this way, in consideration of the fact that the relative relationship between the opening degree of the exhaust throttle valve 10 and the exhaust pressure varies depending on the rotational speed of the internal combustion engine 1, that is, the magnitude of the exhaust flow rate, in step S10, the exhaust throttle valve 10 Regarding the control conditions, not only the outputs of the dynamic pressure sensor 11 and the static pressure sensor 12, but also the outputs from the temperature sensor 13, the intake air pressure sensor 14, and the crank rotation sensor 15 are used.

Therefore, if the operation state of the internal combustion engine 1 is taken into consideration for the operation control of the exhaust throttle valve 10 in steps S9 and S10, the exhaust throttle valve 10 can be appropriately controlled in accordance with the target exhaust pressure P ₁ . As indicated by the solid line 7, the exhaust pressure corresponding to the ideal target exhaust pressure P ₀ can be secured with the control of the exhaust throttle valve 10.

  In step S10, it is preferable to set the opening so as to allow passage of a predetermined amount of exhaust gas and avoid exhaust clogging without setting the exhaust throttle valve 10 to a fully closed state.

  In such steps S9 and S10, when the catalyst bed temperature of the catalytic converter 8 reaches the activation temperature, the opening degree of the exhaust throttle valve 10 is returned to a predetermined opening degree.

  By the way, the control device 9 functions as a catalyst bed temperature estimation means in step S1, functions as a target exhaust pressure setting means in step S2, and exhaust pressure estimation means in steps S3 to S7 in the above-described catalyst temperature increase control process. And functions as valve control means in steps S8 to S10.

  According to the exhaust purification system of the embodiment described above, the exhaust throttle valve 10 is controlled to the closed side when the control device 9 recognizes a situation where the catalyst bed temperature of the catalytic converter 8 is lower than the activation temperature. As a result, the catalyst bed temperature of the catalytic converter 8 is quickly raised to the activation temperature so that PM or the like collected in the catalytic converter 8 is combusted and the purification capability of the catalytic converter 8 is enhanced. Yes.

  As a result, even when the catalyst bed temperature of the catalytic converter 8 becomes low, such as when the internal combustion engine 1 is cold or at low speed and low load operation, the catalyst bed temperature of the catalytic converter 8 can be quickly and quickly increased. Since the activation temperature can be appropriately raised, combustion removal of PM and the like of the catalytic converter 8 can be efficiently performed, and the purification ability of the catalytic converter 8 can be sufficiently increased. It becomes possible to purify the exhaust gas discharged efficiently.

In particular, since the dynamic pressure sensor 11 that can detect the pressure fluctuation and absolute pressure due to the exhaust pulsation with high accuracy is used and disposed in an optimum place, the dynamic pressure is controlled in the catalyst temperature increase control as described above. The reliability of the output of the sensor 11 is increased, and the reliability of the exhaust flow rate estimated based on the output of the dynamic pressure sensor 11 is also increased. Since the catalyst bed temperature is estimated based on the estimated exhaust flow rate and the output of the temperature sensor 13, the catalyst bed temperature can be accurately grasped. Therefore, the target exhaust pressure P ₁ can be set to an ideal hard upper limit pressure with a small margin in the catalyst temperature increase control.

  Therefore, in the catalyst temperature increase control, the exhaust throttle valve 10 can be controlled so as to increase the exhaust pressure to an ideal hard upper limit pressure according to the operating condition, and the catalytic converter 8 can be effectively utilized over the entire operating condition. become.

Furthermore, considering that the relative relationship between the opening degree of the exhaust throttle valve 10 and the exhaust pressure varies depending on the rotational speed (exhaust flow rate) of the internal combustion engine 1 and the load, the exhaust throttle valve 10 is closed on the catalyst temperature increase control. when controlling the operating condition of the internal combustion engine 1, in particular the rotational speed the engine 1 (exhaust flow rate), because in consideration of load determines the degree of opening of the throttle valve 10 exhaust, according to the target exhaust pressure P ₁ Thus, the exhaust throttle valve 10 can be appropriately controlled, and the exhaust pressure corresponding to the target exhaust pressure P ₁ can be secured.

  Hereinafter, other embodiments of the present invention will be described.

(1) In the above embodiment, if necessary, an additive supply device that supplies an additive (fuel, for example, light oil in a diesel engine) to the exhaust system to recover the purification ability of the catalytic converter 8 can be provided. .

  An example is shown in FIG. In the embodiment shown in FIG. 8, in addition to the configuration shown in FIG. 1, an addition valve 51 that supplies an additive toward the assembly portion of the exhaust manifold 41 is attached outside the exhaust manifold 41. Is connected to the supply pump 33 via the additive supply path 52. Then, based on the output of the temperature sensor 13 installed in the catalytic converter 8 in the muffler 42, the control device 9 causes the additive valve 51 to open, for example, for a predetermined time to inject the additive toward the exhaust manifold 41. .

  The addition valve 51, the additive supply path 52, the supply pump 33, and the control device 9 described above constitute an additive supply device.

  (2) Although the diesel engine is illustrated as the internal combustion engine 1 in the above-described embodiment, the present invention is not limited to this and may be, for example, a direct combustion type lean combustion gasoline engine.

  (3) Although the internal combustion engine 1 exemplified in the above embodiment is exemplified by the one equipped with the turbocharger 5 and the EGR device 7, even if one or both of them are eliminated, the present invention. Can be applied.

  (4) The catalytic converter 8 can be, for example, a DPF (Diesel Paticulate Filter), a NOx storage reduction catalyst, an oxidation catalyst, or the like. Further, when the internal combustion engine is a lean combustion type gasoline engine, the catalytic converter 8 can be a three-way catalytic converter. Furthermore, in the above-described embodiment, an example in which the catalytic converter 8 is integrated is given, but the present invention can be applied to two or three combined converters. The types of the plurality of catalytic converters are not particularly limited, and various types of catalytic converters can be used as appropriate.

  (5) In the above embodiment, the arrangement positions of the dynamic pressure sensor 11 and the static pressure sensor 12 may be reversed. Even in that case, it is preferable to arrange the dynamic pressure sensor 11 in the abdominal part of the intraductal resonance as in the above embodiment.

1 is a schematic configuration diagram showing an embodiment of an exhaust gas purification system for an internal combustion engine according to the present invention. It is a schematic block diagram which shows the catalytic converter of FIG. It is explanatory drawing which shows typically the purification principle by the catalytic converter of FIG. It is a principal part enlarged view of FIG. FIG. 2 is a schematic diagram showing a temperature distribution of the catalytic converter of FIG. 1, where (a) shows a case where the exhaust flow rate is large, and (b) shows a case where the exhaust flow rate is small. 2 is a flowchart used for explaining the operation of the exhaust purification system shown in FIG. 1. It is a graph which shows the change of the exhaust pressure with respect to the rotation speed of an internal combustion engine. FIG. 6 is a view corresponding to FIG. 1 in another embodiment of the exhaust gas purification system for an internal combustion engine according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Combustion chamber 4 Cylinder head exhaust port 8 Catalytic converter 9 Control device 10 Exhaust throttle valve 11 Dynamic pressure sensor 12 Static pressure sensor 13 Temperature sensor 14 Suction air pressure sensor 15 Crank rotation sensor 41 Exhaust manifold (exhaust passage)
42 Muffler (exhaust passage)

Claims (5)

A catalytic converter for purifying exhaust gas provided in an exhaust passage through which exhaust gas is discharged from the internal combustion engine, an exhaust throttle valve for adjusting an exhaust flow rate disposed downstream of the catalytic converter in the exhaust passage, and the exhaust throttle A dynamic pressure sensor disposed between the valve and the catalytic converter or upstream of the catalytic converter for detecting fluctuating pressure and absolute pressure of exhaust gas, a temperature sensor for detecting the temperature of the catalytic converter, and activating the catalytic converter And a control device that performs catalyst temperature rise control for
The controller is
Catalyst bed temperature estimating means for estimating the exhaust gas flow rate based on the output of the dynamic pressure sensor as necessary and estimating the catalyst bed temperature of the catalytic converter based on the estimated exhaust gas flow rate and the output of the temperature sensor; ,
A target exhaust pressure setting means for setting a target exhaust pressure in consideration of the operation state when the catalyst bed temperature is lower than a predetermined reference value;
Exhaust pressure estimating means for estimating the current exhaust pressure based on at least the output of the dynamic pressure sensor after setting the target exhaust pressure;
An exhaust gas purification system for an internal combustion engine, comprising: valve control means for controlling an opening degree of the exhaust throttle valve based on a difference between the estimated current exhaust pressure and the target exhaust pressure. A rotation number detecting means for detecting a rotation number of the internal combustion engine;
The exhaust purification system for an internal combustion engine according to claim 1, wherein the exhaust pressure estimation means adds the output from the rotation speed detection means and the load of the internal combustion engine to the current exhaust pressure estimation requirements.   The exhaust purification system for an internal combustion engine according to claim 1 or 2, wherein the dynamic pressure sensor is disposed at a resonance abdomen in the exhaust passage. A region downstream of the catalytic converter in the exhaust passage is formed with a smaller diameter than the catalytic converter, and an outlet portion of the catalytic converter has a shape gradually reduced in diameter toward the small diameter region,
The said dynamic pressure sensor is arrange | positioned from the minimum diameter position of the said exit part to the arrangement position of the said exhaust throttle valve in the said small diameter area | region, and is arrange | positioned in the abdominal part of the exhaust resonance in an exhaust passage. 3. An exhaust gas purification system for an internal combustion engine according to 1 or 2.   The exhaust gas purification of an internal combustion engine according to any one of claims 1 to 4, wherein the dynamic pressure sensor is attached in a state of protruding from an outer diameter side to an inner diameter side of a pipe forming the exhaust passage. system.

Images