JP2932828B2 - Diesel engine emission control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust control system for a diesel engine.

[0002]

2. Description of the Related Art In order to reduce NOx emitted from a diesel engine, an exhaust gas recirculation device (EGR device) for recirculating a part of exhaust gas from an exhaust passage into intake air is provided. Then, it is not always enough to reduce NOx.

[0003] On the other hand, a catalyst capable of reducing NOx even in an exhaust atmosphere containing oxygen, such as a diesel engine, has been developed.
There has been reported a method of improving the NOx reduction rate by injecting fuel into exhaust gas and using fuel (HC) as a reducing agent (see Nikkan Kogyo Shimbun, published on September 20, 1990, etc.).

[0004]

However, even if such a catalyst is used, a fuel injection device is provided in an exhaust pipe in addition to the engine in this case, and fuel is directly injected into exhaust gas.
The system becomes complicated and the cost increases significantly.

In addition, fuel consumption is deteriorated by the consumption of fuel as a reducing agent, and fuel is injected into exhaust gas.
The exhaust pipe becomes hot and thermal degradation is inevitable.

An object of the present invention is to reduce NOx accurately by controlling exhaust gas without causing such a problem.

[0007]

According to a first aspect of the present invention, there is provided a means for detecting operating conditions of an engine as shown in FIG. 1, and an exhaust gas recirculation passage for recirculating a part of exhaust gas from an exhaust passage of the engine to an intake system. And the exhaust gas recirculation control means 1 based on the operating conditions of the engine.
In a diesel engine 1 for controlling the amount of exhaust gas recirculated from an exhaust gas recirculation passage, a catalyst 12 capable of reducing NOx in the exhaust atmosphere of the diesel engine is interposed downstream of the exhaust passage, and means 13 for detecting the catalyst temperature Exhaust concentration estimating means 14 for estimating the concentration of HC and NOx in the exhaust from the operating conditions of the engine; and the concentration of HC / NOx in the exhaust based on the estimation result when the catalyst temperature is equal to or higher than a predetermined value. ratio
Exhaust gas recirculation correction control means 1 for increasing and correcting the amount of exhaust gas recirculated from the exhaust gas recirculation passage so that the value falls within the range of 0.5 to 3.
5 is provided.

According to a second aspect of the present invention, as shown in FIG. 2, means 20 for detecting the operating conditions of the engine, injection timing control means 21 for controlling the fuel injection timing of the fuel injection pump based on the operating conditions of the engine, and an engine A diesel engine comprising: an exhaust gas recirculation passage that recirculates part of exhaust gas from the exhaust gas passage to an intake system; and an exhaust gas recirculation control unit 22 that controls an amount of exhaust gas recirculated from the exhaust gas recirculation passage based on operating conditions of the engine. Means 2 for interposing a catalyst 23 capable of reducing NOx in an exhaust atmosphere of a diesel engine downstream of the exhaust passage and detecting the catalyst temperature
4 and the concentration of HC and NOx in the exhaust gas based on the operating conditions of the engine.
Exhaust concentration estimating means 25 for estimating the concentration of NOx and delaying the fuel injection timing of the fuel injection pump so that the concentration ratio of HC and NOx in the exhaust gas becomes equal to or higher than a predetermined value when the catalyst temperature is equal to or higher than a predetermined value. And an injection timing correction control means for correcting the angle.

According to a third aspect of the present invention, as shown in FIG. 3, means 30 for detecting the operating condition of the engine, injection timing control means 31 for controlling the fuel injection timing of the fuel injection pump based on the operating condition of the engine, An injection rate variable mechanism 32, an exhaust recirculation passage for recirculating a part of the exhaust gas from the exhaust passage of the engine to the intake system,
An exhaust gas recirculation control means 33 for controlling the amount of exhaust gas recirculated from the exhaust gas recirculation passage based on the operating conditions of the engine, a catalyst capable of reducing NOx in the exhaust atmosphere of the diesel engine downstream of the exhaust passage. 34, a means 35 for detecting the catalyst temperature, an exhaust concentration estimating means 36 for estimating the concentration of HC and NOx in the exhaust gas from the operating conditions of the engine, and a case where the catalyst temperature is a predetermined value or more. Injection correction control means 3 for delay-correcting the fuel injection timing of the fuel injection pump and reducing and reducing the fuel injection rate so that the concentration ratio of HC and NOx in the exhaust gas becomes a predetermined value or more.
7 is provided.

[0010]

[Operation] The generation of NOx is suppressed by the recirculation of exhaust gas.
When the exhaust gas recirculation is increased, HC increases. Further, HC is increased by retarding the fuel injection timing or by decreasing the fuel injection rate.

On the other hand, in an exhaust atmosphere where oxygen is present, NO
The catalyst capable of reducing x is activated when the temperature is high, and becomes NO when the HC / NOx concentration ratio in the exhaust gas is equal to or higher than a predetermined value.
The reduction rate of x increases.

That is, in the first invention, the generation of NOx is suppressed by performing exhaust gas recirculation, and the HC / NOx concentration ratio in exhaust gas is increased to a predetermined value or more by increasing the amount of exhaust gas recirculation when the catalyst temperature is high. To obtain a high reduction rate of NOx on the catalyst.

In the second aspect of the present invention, the exhaust gas recirculation
By suppressing the generation of x and delaying the fuel injection timing of the fuel injection pump, the HC / NOx concentration ratio in the exhaust gas is maintained at a predetermined value or more, and a high reduction rate of NOx in the catalyst is obtained.

In the third aspect of the present invention, the generation of NOx is similarly suppressed by the recirculation of the exhaust gas, the fuel injection timing of the fuel injection pump is retarded, and the fuel injection rate is reduced, so that the HC / NOx concentration ratio in the exhaust gas is set to a predetermined value. Value and keep the N
Obtain high reduction of Ox.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 4 and 5 show an exhaust gas recirculation device 50 and a catalyst (such as a zeolite catalyst) 51 capable of reducing NOx in an exhaust atmosphere containing oxygen.

Reference numeral 52 denotes an exhaust passage of the engine, 53 denotes an intake passage of the engine, 54 denotes an exhaust recirculation passage which branches the exhaust passage 52 and connects to the intake passage 53, and 55 denotes an exhaust gas interposed in the exhaust recirculation passage 54. A recirculation valve, 56 is a negative pressure control valve for controlling the operation negative pressure of the exhaust gas recirculation valve 55, and 57 is an intake throttle valve provided in the intake passage 53 upstream of the junction of the exhaust gas recirculation passage 54.

The negative pressure control valve 56 has a lower diaphragm valve portion 58 for performing basic negative pressure control according to the exhaust pressure, and an upper diaphragm valve as a variable control mechanism for further changing the control characteristics to desired characteristics. It is roughly divided into a step motor 59.

The diaphragm valve portion 58 includes a casing 60.
Mainly the diaphragm 61 arranged inside,
The exhaust pressure chamber 62 is formed below the diaphragm 61 by the
The intake pressure chambers 63 are separated from each other at the upper part.

A predetermined set load is applied to the diaphragm 61 by a set spring 64 disposed in a compressed state in the exhaust pressure chamber 62, and a valve body 65 is mounted on the intake pressure chamber 63 side. .

The intake pressure chamber 63 communicates with the intake passage 53 upstream of the intake throttle valve 57 via an intake pressure passage 66. The intake pressure chamber 63 has an intake introduction port 6 opposed to the valve body 65.
7 is formed, and the intake introduction port 67 is connected to the negative pressure passage 6.
8 is connected.

The step motor 59 includes a pair of stators 70 fixed to a casing 69 and bearings 71 and 7.
2 and a rotor 73 rotatably supported through the rotor 2. In this step motor 59, the rotation angle is controlled in a stepwise manner by applying a predetermined pulse signal to the coil of the stator 70.
3 is configured to make one rotation. The rotor 73 has a cylindrical shape, and a female screw 74 is formed on an inner peripheral surface thereof.

Reference numeral 75 denotes a guide member fixed to the inner peripheral side of the bearing 72 of the casing 69. Reference numeral 76 denotes a plunger guided by the guide member 75 so as to be non-rotatable and slidable in the axial direction. 77 is formed, and this is screwed with the female screw 74 of the rotor 73.

The plunger 76 is provided with the step motor 5
9 is configured to linearly move in the axial direction according to the rotation angle of 9, and is located on the center line of the diaphragm 61. A disc-shaped spring seat 78 is provided below the plunger 76.
Is fixed, and the tip of the plunger 76 penetrates through the spring seat 78 and projects downward by a predetermined amount.

Reference numeral 79 denotes an intermediate member for transmitting the operation of the plunger 76 to the diaphragm 61. The intermediate member 79 includes a disc-shaped spring seat portion 79a and a push rod portion 79b extending from one side of the spring seat portion 79a in the axial direction of the plunger 76. The push rod portion 79b is connected to the intake pressure chamber of the casing 60. 63 is provided through the upper surface portion.

An auxiliary spring 80 is disposed in a compressed state between the spring seat portion 79a and the spring seat 78, and the tip of the push rod portion 79a of the intermediate member 79 is moved to the retainer 81 on the diaphragm 61 by this urging force. We are in pressure contact.

The urging force of the auxiliary spring 80 becomes weaker when the step motor 59 rotates and the spring seat 78 moves upward, and conversely becomes stronger when the spring seat 78 moves downward. FIG. 6 shows the relationship between the number of steps of the step motor 59 and the set load of the auxiliary spring 80.

The exhaust gas recirculation valve 55 provided in the middle of the exhaust gas recirculation passage 54 is a diaphragm type valve, and has a negative pressure chamber 82.
, A signal negative pressure, for example, a negative pressure from a vacuum tank of the engine is introduced through a negative pressure passage 83.

The negative pressure passage 83 is connected to the negative pressure passage 68 of the negative pressure control valve 56. The negative pressure control valve 56 appropriately introduces intake air to dilute the signal negative pressure, thereby providing an exhaust gas recirculation valve. 55 is controlled.

The exhaust gas recirculation passage 54 downstream of the exhaust gas recirculation valve 55
Is provided with an orifice 84 on the merging side of the intake passage 53 (intake manifold), and the exhaust pressure between the exhaust recirculation valve 55 and the orifice 84 is reduced by the exhaust pressure of the negative pressure control valve 56 via the exhaust pressure passage 85. It is introduced into the chamber 62.

The intake throttle valve 57 of the intake passage 53 controls a large amount of exhaust gas recirculation by reducing the area of the intake passage, and its opening is controlled by a step motor 86.

The negative pressure control valve 56 shown in FIG. 5 shows a state in which the number of steps of the step motor 59 is at an appropriate intermediate value. The differential pressure between the exhaust pressure and the intake pressure acts on the diaphragm 61, It is urged in the closing direction by the set spring 64 and urged in the opening direction by the auxiliary spring 80.

When the urging force of the auxiliary spring 80 is weakened, the valve body 65 moves to the closing side of the intake port 67, and the amount of intake air from the intake port 67 to the negative pressure passage 83 is reduced. When the opening degree of the recirculation valve 55 decreases and the urging force of the auxiliary spring 80 is increased, the valve body 65 moves to the opening side of the intake port 67, and the amount of intake air from the intake port 67 to the negative pressure passage 83 decreases. With the increase, the opening degree of the exhaust gas recirculation valve 55 increases.

That is, the step motor 5 of the negative pressure control valve 56
The opening / closing characteristics of the exhaust gas recirculation valve 55 can be controlled by the rotation angle control of No. 9, whereby the opening degree control of the intake throttle valve 57 via the step motor 86 and the rotation angle control of the step motor 59 of the negative pressure control valve 56 can be controlled. The exhaust gas recirculation characteristics can be obtained.

When the exhaust pressure rises for some reason or the like, the valve body 65 of the negative pressure control valve 56 moves to the closing side of the intake port 67 and the opening of the exhaust gas recirculation valve 55 decreases. The amount of reflux does not become excessive. Also,
Since the intake pressure is guided to the negative pressure control valve 56, the exhaust recirculation valve 55 can be controlled even in an engine with a supercharger, and predetermined exhaust gas recirculation can be performed.

A catalyst 51 capable of reducing NOx in an exhaust gas atmosphere in which oxygen is present is provided in an exhaust gas passage 52 downstream of a branch portion of an exhaust gas recirculation passage 54.

The catalyst 51 maintains a high NOx reduction rate when the HC / NOx concentration ratio in the exhaust gas is equal to or higher than a predetermined value. Specifically, as shown in FIG. 32, HC / NO at which a required value of about 10% is obtained as the NOx reduction rate
The x-concentration ratio is 0.5, and when it is higher than this, the reduction rate is improved up to HC / NOx concentration ratio = 3 or less. HC / NO
If the x-concentration ratio exceeds 3, the operability of the engine becomes poor, so that by controlling the HC / NOx concentration ratio between 0.5 and 3, a high NOx reduction rate is maintained.

FIG. 7 shows an in-line type fuel injection pump 90 for injecting fuel into the engine. The plunger 92 moves up and down by rotation of a cam 91 driven by the engine, and the fuel in the pressurizing chamber 93 passes through a fuel valve 94. And feeds it to the injection nozzle 100 under pressure.

A control sleeve 9 is provided around the plunger 92.
5 is mounted, and the position of the sleeve 95 determines the start timing of fuel pumping.

The sleeve 95 opens and closes an opening of the passage 97 provided in the plunger 92 communicating between the fuel chamber 96 into which the fuel is fed and the pressurizing chamber 93 toward the fuel chamber, and the plunger 92 rises. When the opening of the passage 97 is closed by the lower end of the sleeve 95, the communication with the fuel chamber 96 is cut off, the pressure in the pressurizing chamber 93 starts to increase, and the pumping of the fuel is started.

When the port 97a branched from the passage 97 communicates with the through-hole 95a provided in the middle of the sleeve 95 due to the rise of the plunger 92, the pressurizing chamber 93 is returned to the fuel chamber 96.
And the fuel pumping is terminated.

By moving the position of the sleeve 95 up and down by the position control mechanism 98, it is possible to advance or delay the fuel feeding start timing.

Further, since the branch port 97a is opened as an inclined groove around the plunger, when the rotation position of the plunger 92 around the axis is changed by the rotation control mechanism 99, the communication timing with the communication port 95a changes. The fuel pumping end time can be changed.

That is, the rotation control mechanism 99 controls the fuel injection timing, and the position control mechanism 98 controls the fuel injection amount.

FIGS. 8 and 9 show a variable mechanism 101 for changing the oil supply rate (fuel injection rate) by advancing and retarding the phase of the cam 91 of the fuel injection pump 90. FIG.

This is interposed at the connection between the pump shaft (cam shaft) 90a of the fuel injection pump 90 and the rotating body 102 to which the engine rotation is transmitted, so that the transmission phase of the engine rotation to the pump shaft 90a can be changed. adjust.

Rotating disk 1 coaxially coupled to pump shaft 90a
The rotating body 102 is freely rotatable with the shaft 103 of the
Is supported.

Then, in order to impart a phase difference to the rotation transmitted from the rotating body 102 to the rotating disk 104 as necessary,
As a mechanism for connecting the rotating disk 104 and the rotating body 102 so as to be relatively displaceable in the rotational (circumferential) direction, first, the rotating disk 104 is provided with a pair of circular holes 104a at equidistant positions from the center of rotation.
Is opened, and the first eccentric cam 105 is inserted therein. Also, a circular hole 105a provided in the eccentric cam 105
Is inserted with the second eccentric cam 106.

The eccentric pin 106b of the second eccentric cam 106
Penetrates the rotating body 102 from the side, and the eccentric pin 105b of the first eccentric cam 105 is connected to the piston 107a housed in the cylinder 107.

The cylinder 107 is integrally mounted on the turntable 104 in the radial direction of the shaft 103, and has an oil chamber 107b.
The pressure oil supplied through the inner peripheral passage 103a of the shaft portion 103 is guided to the shaft. The piston 107a moves to a position where the supply pressure and the return spring 107c balance.

Accordingly, the first eccentric cam 105 is rotated by the eccentric pin 105b in accordance with the position of the piston 107a, whereby the second eccentric cam 106 is rotated by the rotating disk 104.
, The phase of the rotating body 102 and the rotating disk 104 connected via the eccentric pin 106b is changed in the rotational direction.

As a result, the pump shaft 90a of the fuel injection pump 90, that is, the rotation phase of the cam 91 changes with respect to the engine rotation, and the fuel feed rate changes according to the lift characteristics of the cam 91.

The oil pressure from the oil pump 109 guided to the oil chamber 107b of the cylinder 107 changes according to the opening of the control valve 108. When the opening of the control valve 108 increases, the oil pressure decreases and the rotation phase of the cam 91 changes. When the control valve opening decreases, the hydraulic pressure increases and the rotation phase of the cam 91 advances.

That is, when the opening degree of the control valve 108 is increased, the oil supply rate and the injection rate are reduced, and when the opening degree is decreased, the oil supply rate and the injection rate are increased.

FIG. 10 shows exhaust gas recirculation control means, exhaust gas concentration estimating means, exhaust gas recirculation correction control means (first invention), injection timing control means, exhaust gas recirculation control means, exhaust gas concentration estimating means, injection timing correction control means (first embodiment). Invention of 2), injection timing control means,
Control unit 120 as exhaust gas recirculation control means, exhaust concentration estimation means, injection correction control means (third invention)
FIG.

The control unit 120 includes a central processing unit (CPU) 121 and a read only memory (RO).
M) 122, random access memory (RAM) 12
3. It comprises an input / output circuit (I / O) 124.

The I / O 124 includes an engine speed sensor 125, an accelerator opening sensor 126, an intake air temperature sensor 12
7, outputs of an exhaust temperature sensor 128, an intake pressure sensor 129, a water temperature sensor 130 for detecting a cooling water temperature, a fuel temperature sensor 131, a catalyst temperature sensor 132 for detecting the temperature of the catalyst 51, and the like are input.

The CPU 121 fetches information from the I / O 124 in accordance with a program stored in the ROM 122, performs arithmetic processing, and calculates a fuel injection pump 90 for controlling a fuel injection amount, a fuel injection timing, a fuel injection rate, and an exhaust gas recirculation amount. Data as a control amount for controlling the intake throttle valve 57 and the negative pressure control valve 56 to be controlled is set in the I / O 124. The RAM 123 is used to temporarily save data related to the arithmetic processing of the CPU 121.

The I / O 124 controls the fuel injection pump 90 (position control mechanism 98,
Each actuator of the rotation control mechanism 99, the variable mechanism 101
Control valve 108), intake throttle valve 57 (step motor 8
6) Output a control signal to the negative pressure control valve 56 (step motor 59).

The basic fuel injection amount, fuel injection timing, exhaust gas recirculation amount, and intake throttle valve 57 for obtaining the exhaust gas recirculation amount
The characteristics of the basic opening degree and the basic step number of the step motor 59 of the negative pressure control valve 56 are shown in FIGS.

Next, the control contents of the control unit 120 will be described with reference to flowcharts.

FIG. 16 corresponds to the first invention. First, in step 100, various data of operating conditions such as the engine speed Ne, the accelerator opening Acc, the cooling water temperature Tw, the catalyst temperature Tt, etc. are read.

In step 110, based on the data read in step 100, the basic injection amount QN and the basic injection timing I
TN, basic opening degree WN of intake throttle valve 57, negative pressure control valve 56
The basic step number STEPN of the step motor 59 is calculated.

The basic injection amount QN and the basic injection timing ITN are calculated from the data shown in FIGS. 11 and 12 based on the basic opening W of the intake throttle valve 57.
N, the basic step number STEPN of the step motor 59 of the negative pressure control valve 56 is obtained by reading the data of FIGS.
2 and read it.

Next, in step 120, step 100
Then, it is determined whether or not the catalyst temperature Tt read in is equal to or higher than a predetermined value (activation temperature, for example, 350 ° C.).

If it is determined in step 120 that the catalyst temperature is lower than the predetermined value, in step 130 , the corrected opening degree ΔW of the intake throttle valve 57 and the number of steps ΔSTEP of the step motor 59 of the negative pressure control valve 56 are set to 0. That is, the process proceeds to step 150 while the basic exhaust gas recirculation amount is maintained.

[0067] On the other hand, when the catalyst temperature is determined to be equal to or greater than the predetermined value in step 120, HC concentration in the exhaust gas from the operating condition at step 140, to estimate the NOx concentration, this
Takes a value within a predetermined range described later.
Thus, the correction opening ΔW of the intake throttle valve 57 and the negative pressure control valve 5
In step 6, the number of correction steps ΔSTEP of the step motor 59 is calculated, that is, the increased amount of exhaust gas recirculation is set.

The correction opening ΔW of the intake throttle valve 57 and the correction step number ΔSTE of the step motor 59 of the negative pressure control valve 56
P is based on the engine speed Ne and the basic injection amount QN in FIG.
7. The data as shown in FIG. 18 is stored in the ROM 122 and read.

Then, in step 150, QN, IT
From N, WN + ΔW, STEPN + ΔSTEP, the fuel injection amount Q, the injection timing IT, the opening degree W of the intake throttle valve 57, the number of steps of the step motor 59 of the negative pressure control valve 56, STEP
And output.

With this configuration, when the catalyst 51 has not reached the activation temperature, it is necessary to secure a flow rate of exhaust gas to the catalyst 51 in order to promote the activity of the catalyst 51.
The intake throttle valve 57 and the exhaust gas recirculation valve 55 are set to the basic opening based on the operating conditions of the engine, and the exhaust gas is recirculated with the basic exhaust gas recirculation amount.

For this reason, the generation of NOx is suppressed by the recirculation of exhaust gas, and in this case, the amount of generation is small.
Is sufficiently reduced.

On the other hand, when the catalyst 51 is at the activation temperature,
The degrees of opening of the intake throttle valve 57 and the exhaust gas recirculation valve 55 are corrected, and the HC / NOx concentration ratio in the exhaust gas falls within a predetermined range .
The exhaust gas recirculation amount is controlled.

Specifically, the exhaust gas recirculation amount is determined by the HC /
The NOx concentration ratio is in the range of 0.5 to 3 as shown in FIG.
Is controlled so as to be within.
A high reduction rate of Ox is obtained.

As the exhaust gas recirculation amount is changed, the NOx concentration and the HC concentration are increased and decreased with the characteristics shown in FIGS. 19 and 20, and by changing the exhaust gas recirculation amount, the exhaust gas recirculation amount is changed as shown in FIG.
The HC / NOx concentration ratio is arbitrarily set with a characteristic like 1.

That is, the engine speed Ne and the basic injection amount Q
The opening degree of the intake throttle valve 57 and the exhaust gas recirculation valve 55 is controlled based on N to control the amount of exhaust gas recirculation.
The HC concentration and the NOx concentration in the exhaust gas are estimated from the basic injection amount QN, and an increase in the exhaust gas recirculation amount is obtained. Therefore, the intake throttle valve 5 is determined based on the engine speed Ne and the basic injection amount QN.
7. By correcting the opening degree of the exhaust gas recirculation valve 55, HC /
The NOx concentration ratio is controlled within a predetermined range .

As a result, generation of NOx due to exhaust gas recirculation is suppressed, and a high reduction rate of NOx in the catalyst 51 is maintained, so that NOx is significantly reduced.

At this time, the reduction rate of NOx in the catalyst 51
Is, as described above, 0.5 ≦ HC / NOx concentration in exhaust gas.
By increasing the exhaust gas recirculation amount so as to satisfy the ratio ≦ 3 , a high reduction rate is secured.

The opening correction amounts ΔW and ΔSTEP of the intake throttle valve 57 and the exhaust gas recirculation valve 55 are smaller as the basic injection amount QN is smaller (FIGS. 17 and 18). This is because the basic exhaust gas recirculation amount is often increased (FIG. 13), and in this case, the shortage with respect to the predetermined HC / NOx concentration ratio is small.

Since the exhaust gas recirculation control is performed as described above, NO
The amount of HC can be increased while suppressing the generation of x, and there is a synergistic effect in setting the HC / NOx concentration ratio to a predetermined value. In addition, fuel consumption is hardly deteriorated as compared with the case where fuel is injected into exhaust gas, control can be performed using conventional components, the system is simplified, and there is no increase in cost.

Further, there is no problem in durability due to the fuel injection in the exhaust gas, and the HC / NOx concentration ratio can be controlled with high accuracy. By performing a large amount of exhaust gas recirculation, the amount of exhaust gas passing through the catalyst 51 is reduced, and
It is effective for raising the temperature.

FIG. 22 corresponds to the second aspect of the present invention, in which the fuel injection timing is retarded and the HC / NOx concentration ratio in the exhaust gas is set to a predetermined value or more.

First, at step 200, the engine speed N
e, accelerator opening Acc, cooling water temperature Tw, catalyst temperature Tt
Reads various data of operating conditions such as.

In step 210, based on the data read in step 200, the basic injection amount QN and the basic injection timing I
TN, basic opening degree WN of intake throttle valve 57, negative pressure control valve 56
The basic step number STEPN of the step motor 59 is calculated.

The basic injection amount QN and the basic injection timing ITN are based on the data shown in FIGS. 11 and 12, and the basic opening WN of the intake throttle valve 57 and the basic step number STEPN of the step motor 59 of the negative pressure control valve 56 are described above. 14 and FIG. 15 are stored in the ROM 122 and read.

Next, at step 220, step 200
Then, it is determined whether or not the catalyst temperature Tt read in is equal to or higher than a predetermined value (activation temperature, for example, 350 ° C.).

If it is determined in step 220 that the catalyst temperature is lower than the predetermined value, the process proceeds to step 240
Proceed to.

On the other hand, if it is determined in step 220 that the catalyst temperature is equal to or higher than the predetermined value, then in step 230, the HC concentration and NOx concentration in the exhaust are estimated from the operating conditions, and H
The correction injection timing opening ΔIT is calculated so that the C / NOx concentration ratio becomes equal to or more than a predetermined value, and the routine proceeds to step 240.

As the corrected injection timing opening ΔIT, data as shown in FIG. 23 is stored in the ROM 122 based on the engine speed Ne and the basic injection amount QN, and is read.

Then, in step 240, QN, ITN
From + ΔIT, WN, and STEPN, a fuel injection amount Q, an injection timing IT, an opening degree W of the intake throttle valve 57, and a step number STEP of the step motor 59 of the negative pressure control valve 56 are obtained and output.

That is, when the catalyst 51 is at the activation temperature while the generation of NOx is suppressed by the exhaust gas recirculation, the fuel injection timing is retarded so that the HC / NOx concentration ratio in the exhaust gas becomes a predetermined value or more. Is done.

As the fuel injection timing is changed, NOx
Since the concentration and the HC concentration are increased and decreased by the characteristics shown in FIGS. 24 and 25, by changing the fuel injection timing,
The HC / NOx concentration ratio is arbitrarily set with characteristics as shown in FIG.

For this reason, the retard amount of the fuel injection timing is obtained based on the engine speed Ne and the basic injection amount QN, and the fuel injection timing is corrected by the retard, so that the HC / NOx concentration ratio is equal to or more than a predetermined value. Is controlled.

As a result, generation of NOx due to exhaust gas recirculation is suppressed, and a high reduction rate of NOx in the catalyst 51 is maintained, so that NOx is significantly reduced.

FIG. 27 corresponds to the third aspect of the invention, in which the fuel injection timing is retarded while lowering the fuel injection rate to set the HC / NOx concentration ratio in the exhaust gas to a predetermined value or more.

First, at step 300, the engine speed N
e, accelerator opening Acc, cooling water temperature Tw, catalyst temperature Tt
Reads various data of operating conditions such as.

In step 310, based on the data read in step 300, the basic injection amount QN and the basic injection timing I
TN, basic opening degree WN of intake throttle valve 57, negative pressure control valve 56
Variable number mechanism 101 for obtaining basic step number STEPN and basic fuel injection rate of step motor 59 of FIG.
Of the basic cam phase DQN is calculated.

The basic injection amount QN and the basic injection timing ITN are based on the data shown in FIGS. 11 and 12, and the basic opening degree WN of the intake throttle valve 57 and the basic step number STEPN of the step motor 59 of the negative pressure control valve 56 are described above. The data of FIG. 14 and FIG. 15 and the basic cam phase DQN
It is stored in M122 and read.

Next, at step 320, step 300
Then, it is determined whether or not the catalyst temperature Tt read in is equal to or higher than a predetermined value (activation temperature, for example, 350 ° C.).

If it is determined in step 320 that the catalyst temperature is lower than the predetermined value, the process proceeds to step 340 as it is.
Proceed to.

On the other hand, when it is determined in step 320 that the catalyst temperature is equal to or higher than the predetermined value, in step 330, the HC concentration and NOx concentration in the exhaust gas are estimated from the operating conditions, and H
The correction injection timing opening degree ΔIT and the correction cam phase ΔDQN of the oil supply rate variable mechanism 101 are calculated so that the C / NOx concentration ratio becomes a predetermined value or more, that is, the delay amount of the injection timing and the reduction amount of the injection rate are calculated. Set and go to step 340.

Corrected injection timing opening ΔIT, corrected cam phase Δ
The DQN stores data as shown in FIGS. 29 and 30 in the ROM 122 based on the engine speed Ne and the basic injection amount QN, and reads them.

Then, in step 340, QN, ITN
+ ΔIT, WN, STEPN, DQN + ΔDQN,
The fuel injection amount Q, the injection timing IT, the opening degree W of the intake throttle valve 57, the number of steps STEP of the step motor 59 of the negative pressure control valve 56, and the cam phase DQ of the oil supply rate variable mechanism 101 are obtained and output.

That is, when the catalyst 51 is at the activation temperature while the generation of NOx is suppressed by the exhaust gas recirculation, the fuel injection timing is retarded so that the HC / NOx concentration ratio in the exhaust gas becomes a predetermined value or more. At the same time, the fuel injection rate (oil feeding rate) is reduced.

When the fuel injection rate is reduced, the NO in the exhaust
The x concentration and the HC concentration are reduced as shown in FIG.

For this reason, H depends on the retardation of the fuel injection timing.
When setting the C / NOx concentration ratio to a predetermined value or more, the retard angle width can be reduced, and the fuel efficiency is improved.

In the cases of FIGS. 22 and 27, the exhaust gas recirculation amount may be increased.

[0107]

As described above, according to the present invention, in an exhaust gas control apparatus provided with a catalyst capable of reducing NOx in an exhaust gas atmosphere of a diesel engine, H under a temperature condition at which the activity of the catalyst increases.
A configuration is provided in which the exhaust gas recirculation amount is increased, the fuel injection timing is retarded, and the fuel injection rate is reduced so that the C / NOx concentration ratio is in the range of 0.5 to 3. Therefore, a high NOx reduction rate can be achieved by making full use of the catalyst ability in the active state, that is, NOx can be sufficiently reduced. In addition, the system is simple, there is no increase in cost, and there is no adverse effect such as deterioration of fuel efficiency.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of the present invention.

FIG. 2 is a configuration diagram of the present invention.

FIG. 3 is a configuration diagram of the present invention.

FIG. 4 is a configuration sectional view of an exhaust system.

FIG. 5 is a sectional view of a negative pressure control valve.

FIG. 6 is a characteristic diagram of a spring load.

FIG. 7 is a sectional view of a fuel injection pump.

FIG. 8 is a cross-sectional view of an oil feed rate variable mechanism.

FIG. 9 is a front view of a variable oil feed rate mechanism.

FIG. 10 is a block diagram of a control unit.

FIG. 11 is a characteristic diagram of control data.

FIG. 12 is a characteristic diagram of control data.

FIG. 13 is a characteristic diagram of control data.

FIG. 14 is a characteristic diagram of control data.

FIG. 15 is a characteristic diagram of control data.

FIG. 16 is a flowchart showing control contents.

FIG. 17 is a characteristic diagram of control data.

FIG. 18 is a characteristic diagram of control data.

FIG. 19 is a characteristic diagram of exhaust gas concentration.

FIG. 20 is a characteristic diagram of exhaust gas concentration.

FIG. 21 is a characteristic diagram of exhaust gas concentration.

FIG. 22 is a flowchart showing control contents.

FIG. 23 is a characteristic diagram of control data.

FIG. 24 is a characteristic diagram of exhaust gas concentration.

FIG. 25 is a characteristic diagram of exhaust gas concentration.

FIG. 26 is a characteristic diagram of exhaust gas concentration.

FIG. 27 is a flowchart showing control contents.

FIG. 28 is a characteristic diagram of an example of control data.

FIG. 29 is a characteristic diagram of an example of control data.

FIG. 30 is a characteristic diagram of an example of control data.

FIG. 31 is a characteristic diagram of exhaust gas concentration.

FIG. 32 is a characteristic diagram showing the relationship between the HC / NOx concentration ratio and the NOx reduction rate.

[Explanation of symbols]

 Reference Signs List 50 exhaust recirculation device 51 catalyst 52 exhaust passage 53 intake passage 54 exhaust recirculation passage 55 exhaust recirculation valve 56 negative pressure control valve 57 intake throttle valve 59 step motor 61 diaphragm 62 exhaust pressure chamber 63 intake pressure chamber 64 set spring 65 valve body 67 intake Introduction port 80 Auxiliary spring 86 Step motor 90 Fuel injection pump 91 Cam 92 Plunger 95 Control sleeve 98 Position control mechanism 99 Rotation control mechanism 100 Injection nozzle 101 Variable oil feed rate mechanism 108 Control valve 120 Control unit 125 Engine speed sensor 126 Accelerator open Degree sensor 127 Intake temperature sensor 128 Exhaust temperature sensor 129 Intake pressure sensor 130 Water temperature sensor 131 Fuel temperature sensor 132 Catalyst temperature sensor

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code FI F02D 43/00 301 F02D 43/00 301J (56) References JP-A-3-74560 (JP, A) JP-A-2-99736 (JP, A) JP-A-3-253744 (JP, A) JP-A-3-54343 (JP, A) JP-A-4-209956 (JP, A) JP-A-3-74561 (JP, A) JP-A-2-95742 (JP, A) JP-A-62-7927 (JP, A) JP-A-61-93255 (JP, A) JP-A-61-53441 (JP, A) JP-A-55-164740 (JP, A) JP, A) JP-A-63-283727 (JP, A) Jpn. (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02M 25/07 F02D 41/00-45/00

Claims (3)

(57) [Claims] An exhaust gas recirculation passage that recirculates a part of exhaust gas from an exhaust passage of the engine to an intake system, wherein the exhaust gas recirculation control unit controls the exhaust gas recirculation based on the operating condition of the engine. In a diesel engine for controlling an exhaust gas recirculation amount from a recirculation passage, a catalyst capable of reducing NOx in an exhaust atmosphere of the diesel engine is interposed downstream of the exhaust passage,
Means for detecting the catalyst temperature; exhaust concentration estimating means for estimating the concentration of HC and NOx in the exhaust from the operating conditions of the engine; and, when the catalyst temperature is equal to or higher than a predetermined value, the exhaust gas based on the estimation result HC / NOx concentration ratio of 0.5 to 3
An exhaust gas recirculation correction control means for increasing and correcting the amount of exhaust gas recirculated from the exhaust gas recirculation passage so as to fall within the range of the exhaust gas recirculation passage. Means for detecting operating conditions of the engine, injection timing control means for controlling fuel injection timing of a fuel injection pump based on the operating conditions of the engine, and a part of exhaust gas from an exhaust passage of the engine to an intake system. A diesel engine comprising: an exhaust gas recirculation passage that recirculates exhaust gas; and exhaust gas recirculation control means that controls the amount of exhaust gas recirculated from the exhaust gas recirculation passage based on operating conditions of the engine. Means for detecting the catalyst temperature, exhaust gas concentration estimating means for estimating the concentration of HC in the exhaust gas and the concentration of NOx from the operating conditions of the engine. Injection timing correction control means for retarding the fuel injection timing of the fuel injection pump so that the concentration ratio between HC and NOx in the exhaust gas becomes equal to or higher than a predetermined value when the value is equal to or more than the predetermined value. Emission control device for diesel engines. 3. An engine operating condition detecting means, an injection timing control means for controlling a fuel injection timing of a fuel injection pump based on the engine operating condition, a variable fuel injection rate mechanism, and an exhaust passage of the engine. An exhaust gas recirculation passage that recirculates a part of exhaust gas to an intake system, and an exhaust gas recirculation control unit that controls an amount of exhaust gas recirculated from the exhaust gas recirculation passage based on operating conditions of the engine. Means for detecting the catalyst temperature by interposing a catalyst capable of reducing NOx in the exhaust atmosphere of the diesel engine downstream, and estimating the exhaust gas concentration to estimate the concentration of HC and NOx in the exhaust gas from the operating conditions of the engine Means for delaying the fuel injection timing of the fuel injection pump and lowering the fuel injection rate so that the concentration ratio of HC and NOx in the exhaust gas becomes equal to or higher than a predetermined value when the catalyst temperature is equal to or higher than a predetermined value. An exhaust control device for a diesel engine, comprising: injection correction control means for performing a decrement correction.