JP2002332891A - Exhaust emission gas control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission gas control device for an internal combustion engine, capable of reducing NOx in exhaust gas and minimizing worsening of durability and of fuel consumption of the internal combustion engine. SOLUTION: The exhaust emission gas control device 1 comprises a catalyst controller 20 for controlling air/fuel ratio, in such a manner that a NOx storage and reduction catalyst device 10 stores NOx before the passage of a first preset time and then when a diesel engine 2 becomes a lower-load condition, the air/ fuel ratio of the exhaust gas flowing into the NOx storage and reduction catalyst device 10 is changed close to theoretical air/fuel ratio, to cause the release of the NOx from the NOx storage and reduction catalyst device 10. Therefore, in the low-load condition, since pressure and temperature in the cylinder 31 become lower than in high-load condition, after the NOx storage and reduction catalyst device 10 stores the NOx to some degree, the stored NOx can be made to release from the NOx storage and reduction catalyst device 10 to minimize the worsening of the durability of the diesel engine 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to storing NOx when exhaust gas having a lean air-fuel ratio flows in, and storing it when the oxygen concentration of the flowing exhaust gas decreases. The present invention relates to an exhaust gas purification device for an internal combustion engine provided with a NOx storage reduction catalyst device that releases NOx.

[0002]

2. Description of the Related Art It has been known that an internal combustion engine is provided with an exhaust gas purifying device in order to reduce NOx in exhaust gas discharged from an internal combustion engine (for example, a diesel engine or the like). This exhaust gas purifying device includes a NOx storage reduction catalyst device that stores NOx when an exhaust gas having a lean air-fuel ratio flows in and releases the stored NOx when the oxygen concentration of the flowing exhaust gas decreases. The catalyst device is installed in the exhaust passage of the internal combustion engine.

[0003] As such an exhaust gas purifying device, one described in Japanese Patent No. 2,586,739 is known. This exhaust gas purifying device includes the above-described NOx storage reduction catalyst device, NOx amount estimation means for estimating the amount of NOx stored in the NOx storage reduction catalyst device,
A release unit that releases NOx from the NOx storage reduction catalyst device when the NOx amount estimated by the Ox amount estimation unit exceeds a predetermined value. Among them, the discharging means increases the amount of fuel supplied to the cylinder of the internal combustion engine so that the exhaust gas is near the stoichiometric air-fuel ratio.
By reducing the oxygen concentration of the exhaust gas flowing into the Ox storage reduction catalyst device, the NOx storage reduction catalyst device
Has been released.

[0004]

By the way, in the exhaust gas purifying apparatus as described above, the NOx amount estimated to be stored in the NOx storing and reducing catalyst device is uniform regardless of the load state of the internal combustion engine. When the amount exceeds the predetermined amount, the NOx is released from the NOx storage reduction catalyst device by increasing the fuel supply amount to the cylinder by the release means. That is, regardless of whether the load state of the internal combustion engine is low load or high load, the fuel supply amount to the cylinder is increased on the same basis in all load ranges.

However, when the load condition of the internal combustion engine is high, the pressure and temperature in the cylinder are high. If the amount of fuel supplied to such a cylinder is increased, the pressure inside the cylinder becomes considerably high and high. For this reason, when the internal combustion engine is under a high load, if the fuel supply amount to the cylinders is frequently increased, there is a possibility that the durability of the internal combustion engine itself may be deteriorated. In particular, in the case of an internal combustion engine equipped with a supercharger, since the amount of air supplied to the cylinder is large, the temperature inside the cylinder becomes higher and the problem of durability is more worried. In addition, since the amount of air discharged from the cylinder also increases, it is necessary to supply a large amount of fuel to the cylinder in order to bring the air-fuel ratio of the exhaust gas close to the stoichiometric air-fuel ratio.

It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine which can reduce NOx in exhaust gas and minimize deterioration of durability and fuel efficiency of the internal combustion engine.

[0007]

Means for Solving the Problems and Effects The NOx is stored when exhaust gas having a lean air-fuel ratio is disposed in the exhaust passage of the internal combustion engine, and is stored when the oxygen concentration of the flowing exhaust gas decreases. An exhaust gas purifying apparatus for an internal combustion engine including a NOx storage reduction catalyst device for releasing NOx, wherein load detection means for detecting a load state of the internal combustion engine, and the internal combustion engine flowing into the NOx storage reduction catalyst device Air-fuel ratio changing means for changing the air-fuel ratio of the exhaust gas to near or slightly stoichiometric air-fuel ratio, and control means for controlling the operation of the air-fuel ratio changing means, the control means,
After a lapse of a first predetermined time, if the load state of the internal combustion engine detected by the load detecting means is low, the air-fuel ratio changing means is operated.

According to the present invention, the NOx in the exhaust gas is stored by the NOx storage reduction catalyst device, and the air-fuel ratio of the exhaust gas is changed to near the stoichiometric air-fuel ratio or slightly rich by the air-fuel ratio changing means. By reducing the oxygen concentration of the gas and releasing the NOx stored in the NOx storage reduction catalyst device, that is, releasing the stored NOx as N ₂ , the amount of NOx discharged to the outside is reduced. Here, the air-fuel ratio changing unit is controlled by the control unit, and the control unit operates the air-fuel ratio changing unit when the load state of the internal combustion engine is low after the first predetermined time has elapsed. From the NOx storage reduction catalyst device to N
Ox is being released. That is, at least until the first predetermined time elapses, the NOx storage reduction catalyst
Ox is stored, and thereafter, when the load state of the internal combustion engine becomes low, for example, by increasing the amount of fuel supplied to the cylinder of the internal combustion engine or decreasing the amount of intake air to the cylinder, The air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst device is changed to near the stoichiometric air-fuel ratio or slightly rich, and NOx is released from the NOx storage reduction catalyst device. As described above, the NOx storage reduction catalyst device
After the Ox is stored, the NOx stored and released from the NOx storage reduction catalyst device is released when the pressure and temperature in the cylinder are low and the load is low as compared with the high load, so that the durability of the internal combustion engine is deteriorated. Can be minimized. Further, if the exhaust gas purifying apparatus of the present invention is adopted for an internal combustion engine with a supercharger, the air-fuel ratio at high load where a large amount of air is supplied into the cylinder (that is, the air-fuel ratio of the exhaust It is possible to change the air-fuel ratio at low load while avoiding changing the fuel-fuel ratio to near or slightly rich), so that the amount of fuel for changing the air-fuel ratio of exhaust gas to near the stoichiometric air-fuel ratio or slightly rich is small. It is possible to minimize fuel consumption deterioration.

[0009] In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the control means may switch the second exhaust gas after the elapse of the first predetermined time.
Until the predetermined time is reached, if the load state of the internal combustion engine detected by the load detection means is low load,
It is desirable that the air-fuel ratio changing means be operated, and that the air-fuel ratio changing means be operated after the second predetermined time has elapsed, regardless of the load state of the internal combustion engine. In such a configuration, after the first predetermined time has elapsed, the second
Until the predetermined time is reached, NOx is released from the NOx storage reduction catalyst device when the load state of the internal combustion engine is low. Therefore, until the second predetermined time is reached, for example, the NOx storage reduction catalyst NO
Wait until the load condition of the internal combustion engine becomes a low load until the NOx is stored near the x storage capacity, and when the load becomes low, change the air-fuel ratio to near the stoichiometric air-fuel ratio or slightly rich. Therefore, the operation of the air-fuel ratio changing means in a high load region of the internal combustion engine can be avoided as much as possible, and deterioration of durability and fuel efficiency of the internal combustion engine can be minimized. On the other hand, after the lapse of the second predetermined time, regardless of the load state of the internal combustion engine, the NOx storage reduction catalyst device
By releasing Ox, the stored NOx amount becomes NOx
Before exceeding the NOx storage capacity of the storage reduction catalyst device,
NOx is released from the NOx storage reduction catalyst device.
As a result, even if the internal combustion engine continues to operate at a high load, N
NOx can be reliably released from the Ox storage reduction catalyst device, and the NOx storage reduction catalyst device can always have free space for storing NOx in the exhaust gas.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, it is preferable that the length of the second predetermined time is 1.5 to 2 times the length of the first predetermined time. With this configuration, the period during which the NOx storage reduction catalyst device releases NOx when the internal combustion engine is under a low load, that is, the period from the lapse of the first predetermined time to the arrival of the second predetermined time, can be made somewhat longer. Therefore, the probability that the load state of the internal combustion engine becomes low during the period is increased. Therefore, when the load is low, the probability of releasing NOx increases, so that the release of NOx under a high load can be avoided as much as possible, and deterioration of the durability of the internal combustion engine can be minimized.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the length of the second predetermined time is a length of time required for the NOx storage reduction catalyst to store NOx up to the vicinity of the NOx storable capacity. It is desirable that By doing so, the N occluded in the NOx occlusion reduction catalyst device
Until the Ox amount reaches the vicinity of the NOx storable capacity, it is possible to wait until the load state of the internal combustion engine becomes low, and the period for monitoring the load state of the internal combustion engine can be lengthened. Therefore, the probability that the load becomes low during the load monitoring period increases, and the probability that NOx can be released at the time when the load is low increases. Therefore, deterioration of the durability of the internal combustion engine can be minimized.

[0012] In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the length of the first predetermined time and / or the second predetermined time is determined according to the type of the vehicle equipped with the internal combustion engine and the work mode of the vehicle. It is desirable to set according to at least one of them. Thus, the type of vehicle,
That is, if the length of the first predetermined time and / or the second predetermined time is set depending on the type of vehicle, for example, the displacement and the rated output, the exhaust of the vehicle changes according to the displacement and the rated output. The first and / or second predetermined time can be set to an appropriate length according to the amount of NOx contained in the gas. On the other hand, depending on a work mode of the vehicle, for example, in a hydraulic shovel, a work mode in which a load change such as performing normal traveling is small, or a work mode in which a load change such as performing excavation work is large, the first and / or the second. If the second predetermined time is set, the first and / or the second predetermined time can be appropriately set in accordance with the timing of the load change that differs for each work mode, and the first predetermined time and the second predetermined time can be set between the first predetermined time and the second predetermined time. The probability that the internal combustion engine becomes a low load can be increased.

[0013] In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the control means may control the air-fuel ratio in accordance with a length of time from when the first predetermined time elapses to when the operation of the air-fuel ratio changing means is started. It is desirable to set the length of the period during which the fuel ratio changing means is operated. With this configuration, when the time until the operation of the air-fuel ratio changing means is started after the first predetermined time has elapsed, that is, the time until the start of NOx release is short and the amount of stored NOx is small, the exhaust gas When the air-fuel ratio is close to the stoichiometric air-fuel ratio or slightly rich (a period during which the air-fuel ratio changing means is operated), the time until the start of NOx release is long and the stored NOx amount is large. Since the period for operating the air-fuel ratio changing means can be made longer, the length of time for releasing NOx can be appropriately set according to the amount of NOx stored in the NOx storage reduction catalyst device.

Further, in the exhaust gas purifying apparatus for an internal combustion engine of the present invention, there is provided NOx amount calculating means for calculating the amount of NOx stored and accumulated in the NOx storing and reducing catalyst device, and the control means comprises the NOx storing means. The length of the period during which the air-fuel ratio changing means is operated may be set according to the amount of NOx stored in the reduction catalyst device. According to this configuration, the length of time during which NOx is released can be appropriately set in accordance with the amount of NOx stored in the NOx storage reduction catalyst device. Even if the air-fuel ratio is released, it is possible to prevent a problem that the operation at the air-fuel ratio near the stoichiometric air-fuel ratio or a slightly rich air-fuel ratio continues.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a system according to an embodiment of the present invention. The system includes an exhaust gas purification device 1 and a diesel engine 2 as an internal combustion engine to which the exhaust gas purification device 1 is mounted. First, an outline of the system will be described. The exhaust gas purification device 1 includes a NOx storage reduction catalyst device 10 installed in the exhaust system 50 of the diesel engine 2 and the NOx storage reduction catalyst device 10.
A catalyst controller 20 is provided as control means for controlling storage and release of NOx in the storage reduction catalyst device 10. The diesel engine 2 is an internal combustion engine that generates a driving force by injecting fuel into compressed high-temperature air and self-igniting, and includes a plurality of cylinders 31 (only one cylinder 31 is illustrated in FIG. An engine body 30 having other cylinders is omitted), an intake system 40 for performing intake to the cylinder 31, an exhaust system 50 for performing exhaust of the cylinder 31, a compressor 61 and a turbine 62. A supercharger 60 and an exhaust gas recirculation device (EG which extracts a part of the exhaust gas and recirculates it to the intake side)
R device) 71.

Next, details of the system will be described.
In the engine body 30 of the diesel engine 2, a combustion chamber 31A in the cylinder 31 is provided above each cylinder 31.
Each of the cylinder heads 32 is provided with an intake valve 33, an exhaust valve 34, and a fuel injection nozzle 35. Each cylinder 31 has a cylinder head 32
Are connected to each other via an intake passage 41 constituting the intake system 40 and an exhaust passage 51 constituting the exhaust system 50. The intake valve 33 and the exhaust valve 34 move up and down, so that the intake and exhaust in the cylinder 31 is reduced. Is being done. The fuel injection nozzle 35 is for injecting / supplying fuel pressurized by a fuel injection pump (not shown) into the cylinder 31. In the present embodiment, a fuel injection device having the above-described fuel injection nozzle 35 and a fuel injection pump (not shown) is employed as the fuel injection device for the diesel engine 2. The fuel injection amount and the fuel injection time from the fuel injection nozzle 35 are determined by the operation of the fuel injection pump, and the operation of the fuel injection pump is controlled by the engine controller 80. The engine controller 80 will be described later in detail.

The intake system 40 includes the intake passage 41 described above.
And a pre-cleaner 42 and an air cleaner 43 provided in the middle of the intake passage 41. The pre-cleaner 42 is connected to the upstream side of the air cleaner 43, and is used for an engine of a vehicle or a machine (for example, an engine of a construction machine) used in a place having a bad working environment such as a large amount of dust, and air taken in from outside. Is removed before entering the air cleaner 43. The precleaner 42 may not be provided depending on the working environment of the diesel engine 2. Air cleaner 43
Is for removing dust and dirt from the air that has passed through the pre-cleaner 42. The compressor 61 of the supercharger 60 is disposed between the air cleaner 43 in the intake passage 41 and the cylinder 31.

The exhaust system 50 includes the exhaust passage 51 described above.
And a catalyst housing 52 and an exhaust muffler 53 provided in the middle of the exhaust passage 51. The catalyst housing 52 is connected to an upstream side of the exhaust muffler 53. The catalyst housing 52 holds the NOx storage reduction catalyst device 10 of the exhaust gas purification device 1 therein, and the exhaust gas flowing from the inlet 52A of the catalyst housing 52 passes through the NOx storage reduction catalyst device 10 and exits. 52B. The exhaust muffler 53 is provided for silencing the exhaust gas that has passed through the NOx storage reduction catalyst device 10, for lowering the temperature of the exhaust gas, and the like. In the exhaust passage 51 of the exhaust system 50, a turbine 62 of a supercharger 60 is disposed between the catalyst housing 52 and the cylinder 31.

The exhaust gas recirculation device 71 connects the intake passage 41 and the exhaust passage 51 of the diesel engine 2 to the recirculation passage 7.
11, an EGR valve 712 for adjusting the degree of opening of the conduit of the return path 711, and an intake throttle valve 713 disposed in the middle of the intake passage 41. The return path 711 is
One end is connected to the intake passage 41 downstream of the intake throttle valve 713, and the other end is connected to the exhaust passage 51 upstream of the turbine 62. The EGR valve 712 adjusts the degree of opening of the pipeline by, for example, appropriately rotating a disk disposed in the recirculation passage 711, and thereby the exhaust passage 5
The amount of exhaust gas to be recirculated from 1 to the intake passage 41 can be adjusted. The intake throttle valve 713 is connected to the intake passage 4.
1, it is disposed downstream of the compressor 61 and upstream of a connection point between the intake passage 41 and the recirculation passage 711. The intake throttle valve 713 is connected to the EGR valve 71.
2 has the same configuration as that of the intake passage 41, for example.
The degree of opening of the conduit is adjusted by appropriately rotating the disk disposed therein, whereby the flow rate of intake air to the cylinder 31 can be adjusted.

The EGR valve 712 and the intake throttle valve 713 are connected to the EGR valve actuator 7 respectively.
14 and an intake throttle valve actuator 715.
The operations of 14, 715 are controlled by the engine controller 80. The engine controller 80 will be described later in detail. The exhaust gas recirculation device 71 having such a configuration operates by restricting the intake passage 41 with the intake throttle valve 713 to make the intake pressure negative with respect to the exhaust pressure, that is, so that the exhaust gas can be recirculated. Has become.

In the exhaust gas purifying apparatus 1, the NOx storage reduction catalyst device 10 stores NOx when exhaust gas having a lean air-fuel ratio flows in, and stores NOx as N ₂ when the oxygen concentration of the flowing exhaust gas decreases. A catalyst device that releases and releases. In the present embodiment, such NO
The control of the storage and release of NOx of the x storage reduction catalyst device 10 is performed by controlling the air-fuel ratio of the exhaust gas discharged from the diesel engine 2, and the air-fuel ratio control of the diesel engine 2 will be described below. This is performed by the catalyst controller 20 of the exhaust gas purification device 1.

The catalyst controller 20 supplies the amount of exhaust gas recirculated by the exhaust gas recirculation device 71 and the cylinder 31 according to the operating condition of the diesel engine 2 and the amount of NOx stored in the NOx storage reduction catalyst device 10. The fuel amount and the intake amount are controlled, and thereby the air-fuel ratio of the exhaust gas of the diesel engine 2 is controlled. here,
The catalyst controller 20 includes a governor provided in a fuel injection pump for injecting fuel into the cylinder 31 and an exhaust gas recirculation device 7 for detecting an operation state of the diesel engine 2.
It is electrically connected to the engine controller 80 that controls the EGR valve actuator 714, the intake throttle valve actuator 715, and the like. As a result, the catalyst controller 20 outputs an engine speed signal indicating the rotation speed of the diesel engine 2 and a fuel injection amount signal indicating the amount of fuel injected and supplied into the cylinder 31, which are output from the engine controller 80. A work mode signal indicating a work mode of the vehicle equipped with the diesel engine 2 is input.

In order to obtain the above-described engine speed signal and fuel injection amount signal, the diesel engine 2 has a speed sensor for detecting the speed and a fuel injected into the cylinder 31 (not shown). A fuel injection amount sensor is provided as load detection means for detecting the amount. The rotation speed sensor outputs to the engine controller 80 a signal corresponding to the rotation speed (rotation speed) of a crankshaft, a flywheel, or the like provided on the engine main body 30 of the diesel engine 2.

The fuel injection amount sensor detects the position of a control rack slidably provided with respect to the plunger in order to adjust the amount of fuel injected from the fuel injection pump. A signal corresponding to the position of the control rack is output to the engine controller 80. When a high-pressure fuel injection device including a common rail and an injector is used as the fuel injection device for the diesel engine 2, the fuel injection amount sensor detects the fuel injection amount determined by the injector opening time and the fuel pressure in the common rail. The output signal is output to the engine controller 80.

The work mode of the vehicle indicated by the work mode signal is, for example, when the vehicle equipped with the diesel engine 2 is a wheel loader,
There are shape loading (or cross drive loading), leveling work to level the ground, normal running, and idling. In these work modes, the load on the diesel engine 2 changes in a substantially constant cycle. For example, in the case of V-shape loading, when a work object such as soil is scooped into a bucket, a high load is applied. When the work object is loaded on a truck or the like, a low load is applied. It will be repeated in a cycle. For example, the driver operates a switch for selecting a work mode, and a signal output from the switch is input to the engine controller 80. May be used for recognizing which work mode is used. In addition, the state of the rotational speed and load of the diesel engine 2 may be detected and applied to the cycle pattern of the rotational speed and load state of various work modes. Thus, the operation mode may be recognized.

In the diesel engine 2, the oxygen concentration near the inlet 52A of the catalyst housing 52 is measured.
An O ₂ sensor 72 that outputs a signal corresponding to the oxygen concentration is provided. The catalyst controller 20 is adapted to the O ₂ sensor 72 is electrically connected to the oxygen concentration signal indicating the concentration of oxygen in the exhaust gas output from the O ₂ sensor 72 are inputted.

As shown in FIG. 2, the catalyst controller 20 has an input section 21 to which various signals output from the engine controller 80 and an oxygen concentration signal output from the O ₂ sensor 72 are input. An arithmetic processing unit 22 for performing arithmetic processing based on a signal from the CPU, a storage unit 23 in which information necessary for the arithmetic processing performed by the arithmetic processing unit 22 is stored, and an arithmetic processing unit And an output unit 24 for outputting a predetermined signal to the engine controller 80.

Here, the NOx storage-reduction catalyst device 10 provided in the diesel engine 2 stores and releases NOx based on the load state of the diesel engine 2 and the length of time during which NOx is stored. Is controlled by the catalyst controller 20. More specifically, as shown in FIG. 3, the NOx storage reduction catalyst device 10 starts storing NOx until the first predetermined time T1 has elapsed, regardless of the load state of the diesel engine 2. 2 is controlled to occlude NOx in the exhaust gas. On the other hand, the first predetermined time T1
During the period from the elapse to the time when the second predetermined time T2 is reached, when the diesel engine 2 is in a load region other than the low load, control is performed so as to store NOx in the exhaust gas, and the load state of the diesel engine 2 is controlled. Is controlled to release the NOx stored in the NOx storage reduction catalyst device 10 when the load becomes low. Then, the second predetermined time T
After the lapse of 2, the NOx stored in the NOx storage reduction catalyst device 10 is controlled to be released regardless of the load state of the diesel engine 2.

For the diesel engine 2 equipped with such a NOx storage reduction catalyst device 10, the arithmetic processing unit 22 of the catalyst controller 20 controls the NOx storage reduction catalyst device 10
Does not output a signal to the engine controller 80 until the first predetermined time T1 has elapsed since the start of storing NOx, the fuel injection amount into the cylinder 31 and the intake throttle valve 713.
The adjustment of the opening of the EGR valve 712 and the opening of the EGR valve 712 are controlled by the engine controller 80. That is, the air-fuel ratio control of the exhaust gas in the diesel engine 2 is performed by the engine controller 80. Here, in the present embodiment, the engine controller 80 is usually
Is controlled so that the air-fuel ratio becomes lean, and NOx in the exhaust gas is reduced by the NOx storage reduction catalyst device 10.
Is occluded.

In the period from the lapse of the first predetermined time T1 to the lapse of the second predetermined time T2, the arithmetic processing unit 22
Does not output a signal to the engine controller 80 when the diesel engine 2 is in a load region other than the low load, the air-fuel ratio control of the exhaust gas in the diesel engine 2 is continuously performed by the engine controller 80,
NOx in the exhaust gas continues to be stored in the NOx storage reduction catalyst device 10. On the other hand, when the load state of the diesel engine 2 becomes low, the arithmetic processing unit 22 outputs a signal to the engine controller 80 and controls the air-fuel ratio of the diesel engine 2 via the engine controller 80. ing. That is, the amount of fuel injected into the cylinder 31, the opening of the intake throttle valve 713, and the opening of the EGR valve 712 are adjusted to make the diesel engine 2
The air-fuel ratio of exhaust gas discharged from the NOx is changed to near the stoichiometric air-fuel ratio or slightly rich, and NOx stored in the NOx storage reduction catalyst device 10 is released to the outside.

After the second predetermined time T2 has elapsed, the arithmetic processing unit 22 determines whether the fuel injection amount into the cylinder 31 or the intake throttle valve 713 via the engine controller 80 regardless of the load state of the diesel engine 2. And the opening of the EGR valve 712 is adjusted to change the air-fuel ratio of the exhaust gas discharged from the diesel engine 2 to a value close to the stoichiometric air-fuel ratio or slightly rich, so that the NOx storage-reduction catalyst device 10 stores the exhaust gas. NOx is released to the outside. The air-fuel ratio changing means of the present invention includes a fuel injection device (a device having a fuel injection nozzle 35, a fuel injection pump, a governor, etc.) for injecting / supplying fuel into the cylinder 31, an exhaust gas recirculation device 71, and an engine controller 80. It is comprised including.

The specific configuration of the arithmetic processing unit 22 will be described below. Returning to FIG. 2, in order to control the NOx storage and release of the NOx storage reduction catalyst device 10, the arithmetic processing unit 22 includes a load calculation unit 22 </ b> A that detects a load state of the diesel engine 2, and a NOx storage reduction catalyst device. NOx for calculating the amount of NOx stored in the fuel cell 10
Quantity calculating means 22B and first predetermined time setting means 2 for setting the first and second predetermined times T1 and T2, respectively.
2C and a second predetermined time setting means 22D, and a first and second predetermined time T1 and T2 for counting the set first and second predetermined times T1 and T2.
When the timer 22E and the NOx storage reduction catalyst device 10
NOx release timing determining means 22F for determining the timing for releasing x, intake throttle valve opening setting means 22G for setting the opening of intake throttle valve 713, and EGR valve opening setting for setting the opening of EGR valve 712 Means 22H, fuel injection amount setting means 22I for setting the amount of fuel injected / supplied into the cylinder 31, and theory for setting the length of time for changing the air-fuel ratio of the exhaust gas of the diesel engine 2 to near the stoichiometric air-fuel ratio. Air-fuel ratio operation time setting means 22J, and a second timer 22K for counting the set theoretical air-fuel ratio operation time
And an air-fuel ratio calculation unit 22L that calculates the air-fuel ratio of the exhaust gas discharged from the diesel engine 2.

The load calculating means 22A detects whether the load state of the diesel engine 2 is low or in a load range other than the low load, based on the fuel injection amount signal output from the engine controller 80. . The load calculation means 22A receives a fuel injection amount signal at predetermined time intervals. Each time the fuel injection amount signal is input, the load calculation means 22A changes the load state of the diesel engine 2. It has been calculated.

The NOx amount calculating means 22B is based on the engine speed signal output from the engine controller 80, the load information of the diesel engine 2 output from the load calculating means 22A, and the information of the graph shown in FIG.
The NOx storage amount stored in the NOx storage reduction catalyst device 10 is calculated. Here, the NOx amount discharged from the diesel engine 2 is determined by the NOx storage reduction catalyst device 10.
It is estimated as the amount of NOx occluded and stored inside. The graph of FIG. 4 shows the NO emitted per unit time per unit of horsepower obtained from the engine test of the diesel engine 2.
The relationship between the x amount, the engine load (vertical axis) and the engine speed (horizontal axis) is shown, and each curve shown in the graph shows the same NOx amount. In the present embodiment, this graph is stored in the storage unit 23 of the catalyst controller 20 as a map. In the NOx amount calculating means 22B,
An engine speed signal from the engine controller 80,
When the engine load information is input from the load calculator 22A, the map is read from the storage unit 23, and the operating point (point on the graph determined by the engine speed and the engine load) in the graph of FIG. 4 is obtained. When this operating point is known, the amount of NOx emitted per unit time per unit horsepower can be determined based on the map. Then, the NOx amount calculating means 22B
The amount of NOx emitted from the diesel engine 2 is calculated by measuring how many hours the diesel engine 2 has been operated at various operating points and integrating the amount of NOx emitted as a result of operating at each operating point, This calculation result is estimated as the NOx storage amount of the NOx storage reduction catalyst device 10.

Returning to FIG. 2, the first and second predetermined time setting means 22C and 22D set the lengths of the first and second predetermined times T1 and T2, respectively. The length is set to 1.5 to the length of the first predetermined time T1.
It is set to double. As a result, the interval between the first predetermined time T1 and the second predetermined time T2 can be lengthened to some extent, and the probability that the load state of the diesel engine 2 becomes low during the period increases, and the low load At the time of N
The probability of releasing Ox increases. In the second predetermined time setting means 22C, the length of the second predetermined time T2 is NO
The length of time required for the x storage reduction catalyst device 10 to store NOx to the vicinity of the NOx storable capacity is set to be substantially the same as the length of time. Accordingly, it is possible to wait until the load state of the diesel engine 2 becomes low until the amount of NOx stored in the NOx storage reduction catalyst device 10 reaches the vicinity of the NOx storable capacity. Monitoring period can be extended. Therefore, the probability that the load becomes low during the load monitoring period increases, and the probability that NOx can be released during the low load increases.

Further, the first and second predetermined time setting means 22C and 22D respectively determine the first and second predetermined time based on the work mode signal of the vehicle output from the engine controller 80 and the type of the vehicle on which the diesel engine 2 is mounted.
And the lengths of the second predetermined times T1 and T2.
Based on the work mode, the first and second predetermined times T1,
If T2 is set, for example, when the cycle of the engine load in the work mode at that time is a cycle of working for a fixed time at a low load and then working for a fixed time at a high load, the low load work is performed at the first predetermined time. The time can be set so as to be between the time T1 and the second predetermined time T2, and N is set between the first predetermined time T1 and the second predetermined time T2.
The NOx stored in the Ox storage reduction catalyst device 10 can be reliably released.

Furthermore, if the first and second predetermined times T1 and T2 are set based on vehicle type information, for example, the displacement and rated output of the vehicle, the vehicle changes according to the displacement and output. The first and second predetermined times T1 and T2 can be set in accordance with the amount of NOx contained in the exhaust gas. Note that such vehicle type information is stored in the storage unit 23 in advance.

In the first timer 22E, after the first and second predetermined times T1 are set by the first and second predetermined time setting means 22C and 22D as described above, the timer is started. Has become.

In the NOx release timing determining means 22F, the first
Timing for changing the air-fuel ratio of the exhaust gas to near the stoichiometric air-fuel ratio based on the time Ta counted by the timer 22E and the load information of the diesel engine 2 input from the load calculating means 22A, that is, the NOx storage reduction catalyst device 10 Is determined when NOx is released. At approximately the same time as the determined timing, the NOx release timing determining means 22F sets the intake throttle valve opening degree setting means 22F.
G, a predetermined signal is output to the EGR valve opening setting means 22H and the fuel injection amount setting means 22I. Specifically, the NOx release timing determination means 22F
The count time Ta of the first timer 22E is between the first predetermined time T1 and the second predetermined time T2, and the load calculating means 22
A predetermined signal is sent to the intake throttle valve opening degree setting means 2 when the load state calculated by A is low and when the count time Ta of the first timer 22E exceeds the second predetermined time T2.
2G, the output to the EGR valve opening setting means 22H and the fuel injection amount setting means 22I.

Intake throttle valve opening setting means 22G, EGR valve opening setting means 22H, fuel injection amount setting means 22I
When the predetermined signal output from the NOx release timing determining means 22F is input, the opening degree of the intake throttle valve 713, the opening degree of the EGR valve 712, and the fuel injection amount into the cylinder 31 are changed. In addition, a predetermined signal is output to the engine controller 80 almost simultaneously via the second timer 22K. Here, each setting means 2
2G, 22H and 22I are NOx release timing determining means 22
When the signal from F is input, the opening degree of the intake throttle valve 713, the opening degree of the EGR valve 712, and the fuel injection amount are
A predetermined numerical value stored in the storage unit 23 in advance is set. The predetermined numerical value is a numerical value at which the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio, and such a numerical value is obtained in advance by experiments, calculations, and the like. When the signals from the setting units 22G, 22H, and 22I are input, the engine controller 80 controls the governor and the exhaust gas recirculation device 71 provided in the fuel injection pump that injects fuel into the cylinder 31 based on the signals. The operations of the EGR valve actuator 714 and the intake throttle valve actuator 715 are controlled to adjust the amount of fuel injected into the cylinder 31, the opening of the intake throttle valve 713, and the opening of the EGR valve 712. .

The stoichiometric air-fuel ratio operation time setting means 22J is for setting the length of a period during which the diesel engine 2 operates in the vicinity of the stoichiometric air-fuel ratio (hereinafter referred to as stoichiometric air-fuel ratio operation time Tt). The setting is made based on the information from the calculating means 22B. NOx amount calculating means 22B
If the stoichiometric air-fuel ratio operation time Tt is set on the basis of the NOx storage amount information from the NOx storage time, when the amount of NOx stored in the NOx storage reduction catalyst device 10 is small, it takes no time to release the stoichiometric air-fuel ratio. If Tt can be set short, and if the amount of stored NOx is large, it takes a long time to release, so that the stoichiometric air-fuel ratio operation time Tt can be set long. Information on the stoichiometric air-fuel ratio operation time Tt set in this way is output to the second timer 22K.

The second timer 22K starts timing when signals output from the intake throttle valve opening setting means 22G, the EGR valve opening setting means 22H, and the fuel injection amount setting means 22I are input. Until the count time Tb of the second timer 22K reaches the stoichiometric air-fuel ratio operation time Tt, the engine controller 80 outputs a predetermined signal so that the diesel engine 2 continues to operate near the stoichiometric air-fuel ratio. On the other hand, when the count time Tb exceeds the stoichiometric air-fuel ratio operation time Tt, the output of the predetermined signal to the engine controller 80 ends.

In the air-fuel ratio calculating means 22L, the O ₂ sensor 7
The air-fuel ratio of the exhaust gas is calculated on the basis of the oxygen concentration information from No. 2 and the calculation result is compared with the value of the stoichiometric air-fuel ratio. When the operation of the diesel engine 2 is changed to an operation near the stoichiometric air-fuel ratio by the catalyst controller 20 and the value of the air-fuel ratio calculated by the air-fuel ratio calculating means 22L is not near the stoichiometric air-fuel ratio, the air-fuel ratio calculating means 22L In order to correct the air-fuel ratio, the intake throttle valve opening degree setting means 22G,
A signal is output to the EGR valve opening setting means 22H and the fuel injection amount setting means 22I. Each setting means 22G, 22H,
When a signal is input from the air-fuel ratio calculating means 22L, the air-fuel ratio of the exhaust gas is calculated based on comparison information between the value of the air-fuel ratio calculated by the air-fuel ratio calculating means 22L and the value of the stoichiometric air-fuel ratio. So that the intake air throttle valve 7 is close to the stoichiometric air-fuel ratio.
13, the value of the opening and the value of the fuel injection amount are newly set, and a new predetermined signal is output to the engine controller 80 via the second timer 22K.

Next, the operation of the present embodiment will be described with reference to the flowchart of FIG. When the diesel engine 2 is started, the catalyst controller 20 and the engine controller 80 start. The activated catalyst controller 20
First, in step S11, first and second predetermined times T1 and T2 are set, and the process proceeds to step S12. In step S12, the first timer 22E starts measuring time, and proceeds to step S13. In step S13, it is determined whether or not the count time Ta of the first timer 22E has exceeded a first predetermined time T1, and until the count time Ta reaches the first predetermined time T1, the diesel engine 2 is controlled by the engine controller 80. The air-fuel ratio control is performed, and the air-fuel ratio is normally operated in a lean state. On the other hand, when the count time Ta exceeds the first predetermined time T1, step S
Proceed to 14. In step S14, it is determined whether or not the count time Ta has passed a second predetermined time. If the count time Ta has not reached the second predetermined time T2, the process proceeds to step S15. On the other hand, when the count time T has passed the second predetermined time T2, the process proceeds to step S16. Step S
At 15, it is determined whether or not the load state of the diesel engine 2 is low. If the load is not low, the air-fuel ratio control of the diesel engine 2 by the engine controller 80 is continuously performed. On the other hand, when the load state of the diesel engine 2 becomes low, the process proceeds to step S16. In step S16, the count by the first timer 22E ends, the first timer 22E is reset, and the process proceeds to step S17.

In step S17, the catalyst controller 2
0, the air-fuel ratio control of the diesel engine 2 is started, the opening degree of the intake throttle valve and the EGR valve 712, the fuel injection amount into the cylinder 31 are adjusted by the catalyst controller 20, and the diesel engine near the stoichiometric air-fuel ratio is adjusted. When the operation of No. 2 is performed and the operation near the stoichiometric air-fuel ratio ends, the process proceeds to step S18. Here, the operation near the stoichiometric air-fuel ratio by the catalyst controller 20 is performed as shown in FIG.
Is performed according to the flowchart shown in FIG. First, in step S21, the counting of the stoichiometric air-fuel ratio operation time Tt by the second timer 22K is started substantially simultaneously with the start of the operation near the stoichiometric air-fuel ratio, and the process proceeds to step S22. Note that the stoichiometric air-fuel ratio operation time Tt is set before starting the operation near the stoichiometric air-fuel ratio.
It is set by the stoichiometric air-fuel ratio operation time setting means 22J. In step S22, the air-fuel ratio calculation means 22L calculates
The air-fuel ratio of the exhaust gas of the diesel engine 2 is obtained based on the information from the O ₂ sensor 72, and the process proceeds to step S23. In step S23, it is confirmed whether or not the value of the air-fuel ratio obtained by the air-fuel ratio calculation means 22L is near the stoichiometric air-fuel ratio. If not, the process proceeds to step S24, where the value is near the stoichiometric air-fuel ratio. In this case, the process proceeds to step S25.

In step S24, the catalyst controller determines the opening degree of the intake throttle valve 713 and the EGR valve 712, the cylinder, based on the information of the air-fuel ratio value obtained by the air-fuel ratio calculating means 22L and the stoichiometric air-fuel ratio value. By re-adjusting the fuel injection amount into the diesel engine 2, the diesel engine 2
The air-fuel ratio of the exhaust gas is corrected so as to be close to the stoichiometric air-fuel ratio, and the process proceeds to step S25. In step S25, it is confirmed whether or not the count time Tb by the second timer 22K has reached the stoichiometric air-fuel ratio operation time Tt. If the count time Tb has not reached the stoichiometric air-fuel ratio operation time Tt,
The operation of the diesel engine 2 near the stoichiometric air-fuel ratio is continuously performed, and the series of steps starting from step S22 described above is repeated many times. On the other hand, when the count time Tb reaches the stoichiometric air-fuel ratio operation time Tt, the process proceeds to step S26. In step S26, the air-fuel ratio control of the diesel engine 2 by the catalyst controller 20 ends, that is,
The operation near the stoichiometric air-fuel ratio ends, and the air-fuel ratio control of the diesel engine 2 by the engine controller 80 is started again.

In step S18, it is checked whether or not the diesel engine 2 is operating. If the diesel engine 2 is stopped, the process ends because the catalyst controller 20 is also stopped. On the other hand, if the diesel engine 2 continues to operate, the process returns to step S11, and the series of steps starting from step 1 described above is repeated many times until the diesel engine 2 stops.

According to the above-described embodiment, the following effects can be obtained. In the present embodiment, the NOx storage reduction catalyst device 10 stores NOx in the exhaust gas, and the catalyst controller 20 adjusts the opening degree of the intake throttle valve 713 and the EGR valve 712 and the amount of fuel injected into the cylinder 31. By changing the air-fuel ratio of the exhaust gas to near the stoichiometric air-fuel ratio, the oxygen concentration of the exhaust gas is reduced,
NOx storage reduction catalyst device 10 in occluded have been NOx emissions, i.e., since the occluded have the NOx is detached as N _2, it is possible to reduce the amount of NOx discharged to the outside.

In this embodiment, the catalyst controller 2
0 indicates that NOx is stored in the NOx storage reduction catalyst device 10 via the engine controller 80 at least until the first predetermined time T1 has elapsed, and thereafter the load state of the diesel engine 2 becomes low. In such a case, the amount of fuel supplied into the cylinder 31 of the diesel engine 2 or the amount of exhaust gas to be recirculated is increased, the amount of intake air to the cylinder 31 is reduced, and the like.
The NOx storage / reduction catalyst device 10 is configured to change the air-fuel ratio of the exhaust gas flowing into the fuel cell to near the stoichiometric air-fuel ratio and to release NOx from the NOx storage-reduction catalyst device 10.
Release control. As described above, after the NOx storage reduction catalyst device 10 has absorbed NOx to some extent, the NOx stored and reduced from the NOx storage reduction catalyst device 10 when the pressure and temperature in the cylinder 31 are low and the load is low compared to the high load.
Since x is released, deterioration of the durability of the diesel engine 2 can be minimized.

Since the exhaust gas purifying device 1 is employed in the diesel engine 2 with the supercharger 60, the cylinder 31
The air-fuel ratio can be changed at a low load while avoiding a change in the air-fuel ratio at a high load in which a large amount of air is supplied (that is, changing the air-fuel ratio of the exhaust gas to near the stoichiometric air-fuel ratio). Therefore, the amount of fuel for changing the air-fuel ratio of the exhaust gas to near the stoichiometric air-fuel ratio can be reduced, and deterioration of fuel efficiency can be minimized.

The catalyst controller 20 controls the NOx so as to release NOx when the load state of the diesel engine 2 is low during a period from the lapse of the first predetermined time T1 to the arrival of the second predetermined time T2. The storage reduction catalyst device 10 is controlled. Therefore, until the second predetermined time T2 is reached, for example, the NOx storage reduction catalyst device 1
Wait until the load state of the diesel engine 2 becomes low until the NOx is stored near the NOx storage capacity of 0, and when the load becomes low, the air-fuel ratio is changed to near the stoichiometric air-fuel ratio. Therefore, the operation of the air-fuel ratio changing means in the high load region of the diesel engine 2 can be avoided as much as possible, and deterioration of the durability and fuel efficiency of the diesel engine 2 can be minimized. On the other hand, after the lapse of the second predetermined time T2, the NOx storage reduction catalyst device 10
By releasing x, NOx is released from the NOx storage reduction catalyst device 10 before the stored NOx amount exceeds the NOx storage capacity of the NOx storage reduction catalyst device 10. Accordingly, even if the operation of the diesel engine 2 at a high load continues, the NOx storage reduction catalyst device 10
Ox can be reliably released, and N
The NOx storage reduction catalyst device 10 can always have a free space for storing Ox.

In the exhaust gas purifying apparatus 1 of the diesel engine 2, the length of the second predetermined time T2 is changed to the first predetermined time T1.
Is set to 1.5 to 2 times the length of the NOx storage reduction catalyst device 10 when the diesel engine 2 is under a low load, that is, the first predetermined time T1
Since a certain period can be taken after the lapse of time until the second predetermined time T2 is reached, the probability that the load state of the diesel engine 2 becomes low during the period increases, and when the load is low, NOx Is increased, the emission of NOx under a high load can be avoided as much as possible, and deterioration of the durability of the diesel engine 2 can be minimized.

In the exhaust gas purifying apparatus 1, the second predetermined time T
2, the length of the NOx storage reduction catalyst device 10
Since the length of time required to occlude NOx to the vicinity of the storable capacity is set, the load state of the diesel engine 2 is maintained until the amount of NOx stored in the NOx occluding and reducing catalyst device 10 reaches the vicinity of the NOx storable capacity. Can be waited for a low load, and the period for monitoring the load state of the diesel engine 2 can be extended. Therefore, the probability that the load becomes low during the load monitoring period increases, and the probability that NOx can be released during the low load also increases.
Deterioration of the durability of the diesel engine 2 can be minimized.

In the present embodiment, the length of the first predetermined time T1 and the length of the second predetermined time T2 are set according to the displacement, the rated output, and the like that differ depending on the type of the vehicle, that is, the type of the diesel engine 2. NOx contained in the exhaust gas of the vehicle, which varies according to the displacement, rated output, etc.
The first and second predetermined times T1 and T2 can be set to appropriate lengths according to the amount. In addition, since the first and second predetermined times T1 and T2 are set according to the work mode of the vehicle, the first and second predetermined times T1 and T2 are set corresponding to different load fluctuation cycles for each work mode. T2 can be set appropriately, and the probability that the diesel engine 2 will have a low load between the first predetermined time T1 and the second predetermined time T2 can be increased.

The catalyst controller 20 sets the length of the period during which the operation near the stoichiometric air-fuel ratio is performed according to the length of time from the elapse of the first predetermined time T1 to the start of the operation near the stoichiometric air-fuel ratio. When the time from the start of storing NOx to the start of release is short and the amount of stored NOx is small, the period in which the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio can be shortened, and the NOx can be stored. When the amount of NOx occluded is long because the time from the start of the release to the start of the release is long, the period for keeping the air-fuel ratio of the exhaust gas close to the stoichiometric air-fuel ratio can be made longer, so that the NOx storage reduction catalyst device 10 The length of time during which NOx is released can be appropriately set according to the amount of NOx stored in the inside. Therefore, NOx
Can be prevented from being released almost completely, or the problem that the operation near the stoichiometric air-fuel ratio is continued even after all the NOx has been released can be prevented.

In this embodiment, the intake throttle valve 713 for reducing the amount of intake air into the cylinder 31 is used as stoichiometric air-fuel ratio changing means for changing the air-fuel ratio of the diesel engine 2 to near the stoichiometric air-fuel ratio. When the air-fuel ratio is changed to a value close to the stoichiometric air-fuel ratio, the amount of fuel to be increased (the amount of fuel injected into the cylinder 31) can be minimized, and deterioration of fuel efficiency can be minimized.

[0057] Further, in the present embodiment, a theoretical air-fuel ratio changing means for changing the air-fuel ratio of the diesel engine 2 to near the stoichiometric air-fuel ratio, using the exhaust gas recirculation system 71, to reflux the exhaust gas, the O ₂ Since the air-fuel ratio is changed to near the stoichiometric air-fuel ratio by supplying a part of the small exhaust gas into the cylinder 31, the fuel amount and the intake throttle amount to be increased when the air-fuel ratio is changed to near the stoichiometric air-fuel ratio are increased. Fuel consumption and durability can be minimized.

It should be noted that the present invention is not limited to the above embodiment, and modifications and improvements as long as the object of the present invention can be achieved are included in the present invention. For example,
As the exhaust gas recirculation device 71 of the above-described embodiment, instead of the intake throttle valve 713, an exhaust throttle valve installed in an exhaust passage, or an exhaust throttle 51 installed in the middle of the recirculation passage 711 and
It may be provided with a blowing means for blowing a part of the exhaust gas from the side to the intake passage 41 side.

The first predetermined time and the second predetermined time are not limited to those set in accordance with information such as a vehicle type and a work mode, but may be set based on any one of these pieces of information. Or a predetermined time set in advance. Further, the length of the second predetermined time does not necessarily have to be 1.5 to 2 times the length of the first predetermined time, and the NOx storage reduction catalyst device stores NOx up to near the NOx storageable capacity. The time may be shorter than the length of time required to perform.

The period during which the air-fuel ratio changing means is operated (the stoichiometric air-fuel ratio operation time Tt) is not limited to the period set in accordance with the amount of NOx stored in the NOx storage reduction catalyst device. It may be set in accordance with the length of time from when the first predetermined time has elapsed to when the operation of the air-fuel ratio changing means is started. In such a case,
When the time until the operation of the air-fuel ratio changing means is started after the first predetermined time has elapsed, that is, the time until the start of NOx release is short and the amount of stored NOx is small, the air-fuel ratio of the exhaust gas is changed to the stoichiometric air-fuel ratio. The period in which the air-fuel ratio changing means is close to or slightly rich (the period in which the air-fuel ratio changing means is operated) can be shortened. Since the operation period can be made longer, the length of time for releasing NOx can be appropriately set according to the amount of NOx stored in the NOx storage reduction catalyst device. Further, the period during which the air-fuel ratio changing unit is operated may be a predetermined time set similarly to the first and second predetermined times.
In the above-described embodiment, the stoichiometric air-fuel ratio operation time setting unit 22J is configured to set the stoichiometric air-fuel ratio operation time Tt based on the NOx storage amount calculated by the NOx amount calculation unit. As described above, the stoichiometric air-fuel ratio operation time Tt does not need to be set based on the NOx storage amount. In such a case, the catalyst controller 20 does not need to include the NOx amount calculation means 22B.

In the above embodiment, the catalyst controller 20
Has obtained various information for detecting the operation status of the diesel engine 2 via the engine controller 80 and has performed the air-fuel ratio control of the diesel engine 2. It may perform various types of information acquisition for detecting the operating status of the vehicle and control the air-fuel ratio of the diesel engine 2. In such a case, the catalyst controller 20 is replaced with various sensors, various actuators,
It is electrically connected to the governor of the fuel injection device.

As a method for detecting the load of the internal combustion engine,
The method is not limited to the method of detecting the amount of fuel injected into the cylinder based on a signal from a fuel injection amount sensor that detects the amount of fuel to be supplied to the cylinder. A method of detecting a load based on an output of a generator driven by an engine, a method of detecting a load based on an accelerator opening of a vehicle driven by an internal combustion engine of the present invention, and the like may be employed. It is.

The NOx amount calculating means calculates the NOx amount discharged from the internal combustion engine, that is, the NOx amount stored in the NOx storage reduction catalyst device, based on information on the engine speed and the engine load. For example, the NOx sensor is provided in the exhaust passage, measures a NOx concentration upstream of the NOx storage reduction catalyst device, and outputs a signal corresponding to the NOx concentration. The amount may be calculated.

As the air-fuel ratio changing means, the air-fuel ratio may be changed to a value close to the stoichiometric air-fuel ratio only by the intake throttle and the increase of the fuel injection amount supplied to the cylinder. The air-fuel ratio may be changed to near the stoichiometric air-fuel ratio by only one of the two means. In the above-described embodiment, the air-fuel ratio of the diesel engine 2 is changed to near the stoichiometric air-fuel ratio in order to release NOx from the NOx storage reduction catalyst device 10. However, the air-fuel ratio may be changed to a slightly richer one. Such cases are also included in the present invention.

In the above-described embodiment, the turbocharger driven by exhaust gas has been described as the supercharger. However, the supercharger according to the present invention is not limited to this and is provided exclusively. A mechanical drive type supercharger driven by a drive source such as an electric motor may be used. Further, the internal combustion engine is not limited to a compression ignition type diesel engine, but may be a spark ignition type internal combustion engine such as a gasoline engine, or may be a naturally aspirated type without supercharging.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a system according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a catalyst controller in the embodiment.

FIG. 3 is a diagram for explaining the operation of the embodiment.

FIG. 4 is a graph showing the amount of NOx emitted per unit time per unit horsepower from the diesel engine in the embodiment.

FIG. 5 is a flowchart for explaining the operation of the embodiment.

FIG. 6 is a flowchart for explaining the operation of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust gas purification apparatus 2 Diesel engine which is an internal combustion engine 10 NOx storage reduction catalyst device 20 Catalyst controller which is control means 22B NOx amount calculation means 51 Exhaust passage 71 Exhaust recirculation device (air-fuel ratio changing means) 80 Engine controller (air-fuel ratio changing) Means) T1 first predetermined time T2 second predetermined time

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/28 301 F01N 3/28 301C F02D 41/14 310 F02D 41/14 310A F-term (Reference) 3G091 AA02 AA05 AA10 AA11 AA18 AB06 BA01 BA14 CA24 CB02 CB07 CB08 DC03 EA01 EA03 EA04 EA08 EA30 EA34 FA13 FB11 3G301 HA02 HA11 HA13 JA02 JA15 JA25 KA08 LA03 LB14 MA01 ND03 ND12 ND15 NE14 NE23 PD17ZP04

Claims (7)

[Claims] 1. An exhaust gas disposed at an intermediate position in an exhaust passage (51) of an internal combustion engine (2) and having a lean air-fuel ratio absorbs NOx, and absorbs NOx when the oxygen concentration of the flowing exhaust gas decreases. NOx storage reduction catalyst device that releases NOx
An exhaust gas purifying apparatus (1) for an internal combustion engine (2) comprising (10) a load detecting means for detecting a load state of the internal combustion engine (2); and a NOx storage reduction catalyst device (10). Air-fuel ratio changing means for changing the air-fuel ratio of the exhaust gas of the internal combustion engine (2) flowing into the vicinity of the stoichiometric air-fuel ratio or slightly rich; and control means (20) for controlling the operation of the air-fuel ratio changing means, The control means (20) activates the air-fuel ratio changing means when the load state of the internal combustion engine (2) detected by the load detection means is low after the first predetermined time (T1) has elapsed. An exhaust gas purification device (1) for an internal combustion engine (2), characterized in that: 2. The exhaust gas purifying apparatus (1) for an internal combustion engine (2) according to claim 1, wherein the control means (20) is configured to execute a second predetermined time (T1) after a lapse of the first predetermined time (T1). Until T2), if the load state of the internal combustion engine (2) detected by the load detecting means is low, the air-fuel ratio changing means is activated, and the second predetermined time (T2) After the lapse, the internal combustion engine
An exhaust gas purifying apparatus (1) for an internal combustion engine (2), wherein the air-fuel ratio changing means is operated irrespective of the load state of (2). 3. The exhaust gas purifying apparatus (1) for an internal combustion engine (2) according to claim 2, wherein the length of the second predetermined time (T2) is equal to the first predetermined time.
(1) An exhaust gas purification device (1) for an internal combustion engine (2), wherein the length is 1.5 to 2 times the length of (T1). 4. The exhaust gas purifying apparatus (1) for an internal combustion engine (2) according to claim 2, wherein the length of the second predetermined time (T2) is equal to the length of the NOx storage reduction catalyst device (T2). 10) is NO up to the vicinity of the NOx storable capacity.
An exhaust gas purifying apparatus (1) for an internal combustion engine (2), characterized in that it is a length of time required to store x. 5. The exhaust gas purification device (1) for an internal combustion engine (2) according to claim 2, wherein the first predetermined time (T1) and / or the second predetermined time ( The length of T2) is set according to at least one of a type of a vehicle provided with the internal combustion engine (2) and a work mode of the vehicle.
Exhaust gas purifier (1). 6. The exhaust gas purifying apparatus (1) for an internal combustion engine (2) according to any one of claims 1 to 5, wherein the control means (20) determines that the first predetermined time (T1) has elapsed. An exhaust gas for an internal combustion engine (2), wherein the length of time during which the air-fuel ratio changing means is operated is set in accordance with the length of time until the operation of the air-fuel ratio changing means is started later. Purification device (1). 7. The exhaust gas purifying apparatus (1) for an internal combustion engine (2) according to claim 1, wherein NOx stored and accumulated in said NOx storage reduction catalyst device (10). A NOx amount calculating means (22B) for calculating the amount, wherein the control means (20) is provided with the NOx storage reduction catalyst device.
The exhaust gas purifying apparatus (1) for an internal combustion engine (2), wherein the length of the period during which the air-fuel ratio changing means is operated is set according to the amount of NOx stored in (10).