JPH02125954A - Exhaust gas recirculation control device of diesel engine - Google Patents

Abstract

PURPOSE:To reduce the exhaust amount of NOx by controlling an EGR (exhaust gas recirculation) valve to open delaying to the opening of an exhaust gas throttle valve when the exhaust throttle valve is opened, while closing the EGR valve when the exhaust throttle valve is closed even in the exhaust gas recirculation area. CONSTITUTION:While an exhaust throttle valve 21 is provided on the way of an exhaust gas passage 16, an EGR valve 33 is provided on the way of an EGR passage 3 linking between the exhaust gas passage 16 at the upper stream of the valve 21 and an intake passage 15, and the valves 21 and 33 are opened and closed by actuators 22 and 34 of a diagraph system respectively. The negative pressure chambers 22a and 34a of the actuators 22 and 34 are connected to the outlets 7a and 8a of three-way switching valves 7 and 8 through delay valves 5 and 6, and the negative pressure chambers 22a and 34a are made to enable to connect to a vacuum pump 43 or to the atmosphere by the switching valves 7 and 8. And the switching valve 8 is controlled to close the EGR valve 33 in a specific amount when the exhaust throttle valve 21 is closed even in the exhaust gas recirculation area.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust gas recirculation control device for a diesel engine.

[Conventional technology]

Traditionally, diesel engines have been equipped with an exhaust recirculation system (
A type of engine equipped with an EGR device (EGR device) is known.

This exhaust gas recirculation system, as is generally well known,
It consists of an exhaust gas recirculation passage that communicates the intake passage and the exhaust passage, and an exhaust recirculation valve that communicates and blocks the exhaust gas recirculation passage. When the exhaust gas recirculation valve is opened, part of the exhaust gas passes through the exhaust recirculation passage and enters the intake passage. By recirculating the exhaust gas and supplying the recirculated exhaust gas together with intake air to the combustion chamber again, combustion is suppressed and NOxl in the exhaust gas is reduced.

A diesel engine having the above configuration is also disclosed in Japanese Utility Model Application No. 59-65968. In addition to the above configuration, the diesel engine disclosed in this publication is provided with an exhaust throttle valve for controlling the exhaust gas recirculation downstream of the exhaust gas recirculation outlet in the exhaust passage, so that the exhaust recirculation valve opens. By controlling the exhaust throttle valve so that the exhaust throttle valve waits for a predetermined period when the exhaust gas recirculates, the amount of exhaust gas recirculated at the start of exhaust gas recirculation can be increased, and a sufficient NOXI reduction effect can be obtained even during that period. I'm trying to make it possible.

By the way, unlike the diesel engine shown in the above publication, a diesel engine equipped with an exhaust gas recirculation device is one in which an exhaust throttle valve is provided downstream of the exhaust gas recirculation outlet in the exhaust passage for the purpose of promoting warm-up. be.

This diesel engine controls the exhaust throttle valve so that it is closed when the engine is cold at low speeds and low load. The amount of fuel is reduced to increase the load on the engine and promote warm-up.

[Problem to be solved by the invention]

However, if a diesel engine is provided with both a structure for reducing NOx@ and a structure for promoting warm-up as described above, the following problems occur.

Figure 5 shows the above NOx! This figure shows the relationship between region A (region in which the exhaust throttle valve is closed when cold) of a conventional diesel engine that aims to reduce engine temperature and promote engine warming (region where the exhaust throttle valve is closed when cold) and region B in which exhaust gas recirculation is performed.

As shown in the figure, when the engine is cold, area A where warm-up is promoted is set to the low-speed, low-load side, area B where exhaust gas recirculation is performed is set to the high-speed, high-load side, and area A where warm-up is promoted is set. and region B where exhaust gas recirculation is performed partially overlap. In region β, where region A for promoting warm-up and region B for exhaust gas recirculation overlap, the exhaust throttle valve is closed and the exhaust recirculation valve is opened, so that most of the exhaust gas escaping into the exhaust passage is exhausted. The exhaust gas is led to the recirculation passage, and the amount of exhaust gas recirculated increases excessively, resulting in extremely suppressed combustion. Therefore, it was not possible to obtain a sufficient warm-up promotion effect in this region β. However, if acceleration is performed when the engine is cold, that is, if the region β is changed to the region γ where only exhaust gas recirculation is performed, sufficient engine output cannot be obtained when transitioning from the region β to the region γ. The problem was that sufficient acceleration could not be obtained.

In view of the above circumstances, the present invention aims to provide an exhaust recirculation control device for a diesel engine that is capable of reducing NOx emissions and promoting warm-up, as well as improving acceleration performance when cold. It is something to do.

[Means to solve the problem]

The exhaust recirculation control device for a diesel engine according to the present invention includes: an exhaust throttle valve provided in an exhaust passage; an exhaust recirculation passage in which an exhaust recirculation outlet is provided in the exhaust passage upstream of the exhaust throttle valve; In a diesel engine equipped with an exhaust gas recirculation valve that opens and closes a passage, an exhaust gas recirculation valve operation control means that closes the exhaust gas recirculation valve for a predetermined period when the exhaust throttle valve is closed even in a region where exhaust gas recirculation is performed. and an exhaust recirculation valve opening delay means for delaying the opening operation of the exhaust gas recirculation valve relative to the opening operation of the exhaust throttle valve when the exhaust throttle valve is opened in a region where exhaust gas recirculation is performed. This is what I did.

[Effect]

According to the above configuration, even in a region where exhaust gas is recirculated by the exhaust gas recirculation valve operation control means, when the exhaust throttle valve is closed, the exhaust gas recirculation valve is closed for a predetermined period (or completely closed). Therefore, as the exhaust throttle valve closes, the scavenging efficiency in the cylinder decreases only in this state within the region where exhaust gas recirculation occurs, and the amount of exhaust gas that is returned directly into the cylinder from the exhaust passage (internal exhaust gas gas recirculation amount) increases, and even if the exhaust recirculation valve is not completely opened, N
0xl can be sufficiently reduced, and the amount of exhaust recirculated gas is prevented from increasing excessively, resulting in relatively stable combustion, and as a result, warm-up promotion properties are improved. Further, when the exhaust gas recirculation valve opening operation delaying means opens the exhaust gas throttle valve in a region where exhaust gas is recirculated, the exhaust gas recirculation valve opens with a delay with respect to the opening operation of the exhaust gas throttle valve. Therefore, when the region where the warm-up promotion region and the exhaust gas recirculation region overlap during cold acceleration moves to the region where only exhaust gas recirculation is performed, the exhaust throttle valve is opened while the exhaust recirculation valve is closed. As a result, combustion is no longer suppressed and acceleration is improved.

〔Example〕

FIG. 1 shows an embodiment of an exhaust gas recirculation control device for a diesel engine according to the present invention. In the figure, 1 is a diesel engine, which includes a cylinder block 11, a cylinder head 12, and a piston 13. The combustion chamber 14 formed by the cylinder block 11, the cylinder head 12, and the piston 13 is connected to an intake passage 15 and an exhaust passage 16 that pass through the cylinder head 12, respectively, and the opening of the combustion chamber 14 of the intake passage 15 and the exhaust An intake valve 17 is provided at each opening of the combustion chamber 14 in the passage 16.
and an exhaust valve 18 are provided.

An exhaust throttle valve 21 for restricting the amount of exhaust gas is provided in the middle of the exhaust passage 16, and the exhaust throttle valve 21 is opened and closed by a diaphragm type exhaust throttle valve actuator 22.

An exhaust recirculation gas outlet 31 is formed in the middle of the intake passage 15, and an exhaust recirculation gas outlet 32 is formed in the exhaust passage 16 upstream of the exhaust throttle valve 21. The exhaust gas recirculation gas outlet 31 is communicated with the exhaust gas recirculation passage 3 . In the middle of this exhaust gas recirculation passage 3, there is an exhaust gas recirculation valve 33 that opens and closes this exhaust gas recirculation passage 3.
The exhaust gas recirculation valve 33 is opened and closed by a diaphragm type exhaust gas recirculation valve actuator 34.

The negative pressure chamber 22a of the exhaust throttle valve actuator 22 and the negative pressure chamber 34a of the exhaust recirculation valve actuator 34 are connected to the delay valve (exhaust throttle valve closing operation delay means) 5 and the delay valve (exhaust recirculation valve opening operation delay means) through pipes 41a and 42a, respectively. Operation delay means) 6 second baud h5b, 6b
connected to each first boat 5a of the delay valve 5.6.
, 6a are connected to the respective first outlet lowers a, 8a of the three-way switching valve 7.8 by pipes 41b, 42b, respectively. Note that the negative pressure chamber 2 of the exhaust throttle valve actuator 22
The volume of the exhaust gas recirculation valve 2a is equal to the volume of the negative pressure chamber 34a of the exhaust gas recirculation valve actuator 34.

The delay valve 5.6 includes a one-way valve 51.61 that allows air to flow only from the first boats 5a, 6a to the second boats 5b, 6b, and a small-diameter throttle 52.62. 51.61 and the small diameter aperture 52.62, the first boats 5a, 5a to the second boats 5b, 6
A large amount of air is allowed to flow from the second boat 5b, 6b to the first boat 5a, 5a at a time.

Each second outlet lower b, 8b of the three-way switching valves 7, 8 is connected to the pipe 4.
1c and 42c to the vacuum pump 43, and each third output lower C8C of the three-way switching valve 7.8 is open to the atmosphere. The three-way switching valve 7゜8 is configured to switch in response to a control signal from the -control unit 9, thereby controlling the first output lower a, 8a and the second output lower b.
, Bb, or first output lower a, 8a and third output lower C9
8C is connected. When the first output lower a and the second output lower b of the three-way switching valve 7 are connected, the negative pressure chamber 22a of the exhaust throttle valve actuator 22 and the vacuum pump 43 are connected, and the exhaust throttle valve actuator The air in the negative pressure chamber 22a of 22 is pulled by the vacuum pump 43, the exhaust throttle valve 21 is closed, and the first output lower a and the third output lower C of the three-way switching valve 7 are connected. Then, the negative pressure chamber 22a of the exhaust throttle valve actuator 22
Exhaust throttle valve actuator 22 combines popularity with
Atmospheric air is introduced into the negative pressure chamber 22a, and the exhaust throttle valve 21 is opened. Further, when the first outlet 8a and the second outlet 8b of the three-way switching valve 8 are connected, the negative pressure chamber 34a of the exhaust recirculation valve actuator 34 and the vacuum pump 43 are connected, and the exhaust recirculation valve actuator 34 Negative pressure v3
4a is pulled by the vacuum pump 43 to open the exhaust recirculation valve 33, and when the first outlet 8a and the third outlet 8C of the three-way switching valve 8 are connected, the exhaust recirculation valve 33 is opened. The negative pressure chamber 34a of the actuator 34 is connected to the atmosphere,
Atmospheric air is introduced into the negative pressure chamber 34a of the exhaust gas recirculation valve actuator 34, and the exhaust gas recirculation valve 33 is closed.

The control unit 9 includes an engine rotation speed detection means 9a for detecting the engine rotation speed, an accelerator opening detection means 9b for detecting the accelerator opening degree, and an engine water temperature detection means 9C for detecting the engine water temperature. The signal is now being input. The control unit 9 includes a region determining means 91, an exhaust throttle valve operation control means 92, and an exhaust recirculation valve operation control means 93.

The area determining means 91 is the engine rotation speed detecting means 9a.
, opens the exhaust gas recirculation valve 33 based on the detection signals from the accelerator opening detection means 9b and the engine coolant temperature detection means 9C, that is, determines whether or not the exhaust gas recirculation is performed, and closes the exhaust throttle valve 21. That is, it is determined whether or not the warm-up promotion is to be performed (at a predetermined temperature or lower and in a predetermined range). Exhaust throttle valve operation control means 9
2 outputs a connection signal to connect the first output lower a and the second output lower b to the three-way switching valve 7 when the area determination means 91 determines that the warm-up promotion is to be performed. When the region determining means 91 determines that the promotion is not in the state, a connection signal is output to the three-way switching valve 7 to connect the first output lower a and the third output lower C. Further, the exhaust gas recirculation valve operation control means 93 has a region where exhaust gas recirculation is performed.
When the region determining means 91 determines that the warm-up promotion is not performed, a connection signal is output to the three-way switching valve 8 to connect the first outlet 8a and the second outlet 8b, and the region is outside the region where exhaust gas recirculation is performed. Or, if the region determining means 91 determines that the warm-up promotion is to be performed (the state in which the exhaust throttle valve 21 should be closed) even in the region where exhaust gas recirculation is performed, the three-way switching valve 8 is connected to the first outlet 8a. A connection signal is output to connect the terminal and the third outlet 8C.

In addition, when it is cold, the area that promotes warming up and the exhaust 3!
The relationship with the region where the flow occurs is not shown in FIG. 5 and is the same as in the case of a conventional diesel engine.

In the above configuration, a region α in which only warm-up promotion is performed when the engine is cold (for example, when the engine water temperature is 60° C. or lower) is changed to a region β in which region A in which warm-up promotion is performed and region 8 in which exhaust gas recirculation is performed overlap. The operation is shown when acceleration is performed so as to pass through the region γ where only exhaust gas recirculation is performed.

First, when it is in the region α, the region determining means 91 determines that it is not the region 8 where exhaust gas recirculation is performed, and furthermore, since it is cold and in the region A, it is determined that the state is in which warm-up promotion is performed. A connection signal is output from the exhaust throttle valve operation control means 92 to the three-way switching valve 7 to connect the first output lower a and the second output lower b, and the exhaust recirculation valve operation control means 93 outputs a connection signal to the three-way switching valve 8. A connection signal connecting the first outlet 8a and the third outlet 8C is output. Therefore, the negative pressure chamber 22a of the exhaust throttle valve actuator 22 is connected to the vacuum pump 43, the exhaust throttle valve 21 is closed, and the negative pressure chamber 34a of the exhaust recirculation valve actuator 34 is connected to the atmosphere. The exhaust gas recirculation valve 33 is closed. In region A where warm-up promotion is performed, the amount of fuel is increased between fuel injections. Therefore, in this region α, the internal exhaust gas recirculation amount increases due to the closing of the exhaust throttle valve 21, the load on the engine increases, and warm-up is promoted.

When moving from the area α to the area β, the area determination means 91
It is determined that the engine is in a state where warming-up is promoted and is in region B where exhaust gas recirculation is performed. In this case, since the exhaust throttle valve operation control means 92 is in a state of promoting warm-up, the first
A connection signal connecting the output lower a and the second output lower b is output.

Furthermore, from the exhaust gas recirculation valve operation control means 93, although it is region B where exhaust gas recirculation is performed, it is in a state where warm-up promotion is performed.
Similarly to the above region α, a connection signal is output to the three-way switching valve 8 to connect the first outlet 8a and the third outlet 8c. As a result, the same state as in the region α, that is, the state in which the exhaust throttle valve 21 is closed and the exhaust gas recirculation valve 33 is maintained, is maintained. Therefore, warm-up is promoted like in the above region α. Moreover, since the exhaust throttle valve 21 is closed and the amount of internal exhaust gas recirculated increases, the amount of NOx can be reduced even when the exhaust recirculation valve 33 is closed.

Thereafter, when the region β shifts to the region γ, the region determining means 91 determines that the warm-up promotion is not performed and the exhaust gas recirculation is performed in the region B, and the exhaust throttle valve operation control means 92 to the three-way switching valve 7 from the first output lower a
and the third outlet lower C is output, and the exhaust recirculation valve operation control means 93 outputs a connection signal connecting the first outlet 8a and the second outlet 8b to the three-way switching valve 8. become. As a result, the exhaust throttle valve actuator 2
The negative pressure chamber 22a of the exhaust throttle valve actuator 22 is connected to the atmosphere, and the atmosphere is introduced from the third output lower C of the three-way switching valve 7 through the delay valve 5. At the same time, the negative pressure chamber 34a of the exhaust gas recirculation valve actuator 34 is connected to the vacuum pump 43, so that the air in the negative pressure chamber 34a of the exhaust gas recirculation valve actuator 34 is drawn to the vacuum pump 43 via the delay valve 6. Become. At this time, the delay valve 5°6 moves from the first boat 5a, 6a to the second boat 1-5b.

A large amount of air flows to 6b at once, and the second boat 5b, 6
Since only a small amount of air can flow from b to the first boats 5a and 6a at a time, a large amount of air flows at once from the first boat 5a of the day valve 5 to the second boat 5b, and Exhaust gas recirculation valve actuator 34 flowing from the second boat 6b to the first boat 6a of No. 6
Only a small amount of air can flow in the negative pressure chamber 34a at a time. Therefore, the atmosphere is quickly introduced into the negative pressure chamber 22a of the exhaust throttle valve actuator 22, and the air in the negative pressure chamber 34a of the exhaust recirculation valve actuator 34 is slowly drawn out. As a result, the exhaust throttle valve 21 opens quickly, and the exhaust recirculation valve 33 opens later than the exhaust throttle valve 21.

Next, the operation when deceleration is performed so as to shift from the region γ to the region β in a cold state will be described.

When transitioning from region γ to region β, region B is a state in which warm-up promotion is performed by the region determination means 91 and in which exhaust gas recirculation is performed.
As a result, as described above, the negative pressure chamber 34a of the exhaust recirculation valve actuator 34 is connected to the atmosphere, and the negative pressure chamber 34a of the exhaust i-flow valve actuator 34 is connected to the atmosphere.
from the third outlet 8C of the three-way switching valve 8 to the delay valve 6.
At the same time, the negative pressure chamber 22a of the exhaust throttle valve actuator 22 is connected to the vacuum pump 43, and the air in the negative pressure chamber 22a of the exhaust throttle valve actuator 22 is supplied to the delay valve 5. It comes to be drawn by the vacuum pump 43 via. At this time, due to the action of the delay valve 5.6, a large amount of air flows at once from the first boat 6a of the delay valve 6 to the second boat 6b, and from the second boat 5b of the delay valve 5 to the first boat 5a. Since only a small amount of air in the negative pressure chamber 22a of the exhaust throttle valve actuator 22 flows at a time, the h pressure chamber 34 of the exhaust gas recirculation valve actuator 34
Atmospheric air is quickly introduced into a, and the air in the negative pressure chamber 22a of the exhaust throttle valve actuator 22 is slowly drawn out. As a result, the exhaust gas recirculation valve 33 closes quickly.
The exhaust throttle valve 21 closes later than the exhaust recirculation valve 33.

Note that when deceleration is performed to move from region β to region α, there is no change in the connection signals output from the exhaust throttle valve operation control means 92 and the exhaust recirculation valve operation control means 93 in each region. , even if we move from region β to region α,
The exhaust recirculation valve 33 and the exhaust throttle valve 21 are kept in the same state as in the region β, that is, both are kept closed.

FIG. 2 shows the first bow 1 of the delay valve 5 when moving from the region α through the region β to the region γ during the cold acceleration.
~5a and the pressure Pa, Pb of the second boat 5b, etc., to the first boat 1 of the Tilley valve 6 68 and the second boat 6b
Fig. 3 shows the temporal changes in the pressures Pc and Pd and the opening and closing states of the exhaust throttle valve 21 and the exhaust recirculation valve 33. The pressures Pa, Pb, Pc, Pd when shifting to α,
3 shows temporal changes in the open and closed states of the exhaust gas comparison valve 21 and the exhaust gas recirculation valve 33, respectively. In these figures,
ta and tb indicate the time of transition from area α to area β and the time of transition from area β to area γ during acceleration; tc,
It shows the time when td shifted from region γ to region β and the time when td shifted from region β to region α.

As shown in FIG. 2, in the configuration of the exhaust recirculation control device for this diesel engine, even in region B where exhaust gas recirculation is performed during cold acceleration, warm-up should be promoted, that is, the exhaust throttle valve 21 should be closed. In this state, the exhaust gas recirculation valve 33 is closed (between ta and tb). Moreover, when the transition from region β to region γ occurs during cold acceleration, the pressures pa and p of the first boats 5a and 5a of the delay valve 5.6
Even if the pressure Pd of the second boat 6b of the delay valve 6 changes at the same time, the pressure Pd of the second boat 5b of the delay valve 5 changes at the same time.
The pressure changes by a time Ta later than the pressure pb, and the exhaust gas recirculation valve 33 opens later than the opening timing of the exhaust throttle valve 21 by that amount. Therefore, during cold acceleration,
The exhaust gas recirculation valve 33 is opened when the exhaust throttle valve 21 is closed to perform exhaust gas recirculation, which eliminates the situation where combustion is extremely suppressed, and acceleration performance in cold conditions is improved.

Furthermore, as shown in Fig. 3, with the configuration of this diesel engine exhaust recirculation control device, even during cold deceleration,
If the exhaust gas recirculation is performed in the region 14B and the exhaust throttle valve 21 should be closed, the exhaust gas recirculation valve 33 is closed (t
(between c and td), and the pressure Pa of the first boats 5a, 5a of the delay valves 5, 6 when shifting from the region γ to the region β.

Even if Pc changes at the same time, the pressure Pb of the second boat 5b of the delay valve 5 will be the same as the pressure Pb of the second boat 6 of the delay valve 6.
The pressure changes at a time Tb slower than the pressure Pd at point b, and the exhaust throttle valve 21 closes later than the timing at which the exhaust recirculation valve 33 closes. Therefore, even during cold deceleration, the exhaust gas recirculation valve 33 is opened while the exhaust throttle valve 21 is closed, exhaust gas recirculation is performed, and combustion is not extremely suppressed, resulting in deterioration of combustibility. This can prevent deterioration in emission performance due to this.

FIG. 4 shows another embodiment. In this figure, the same reference numerals as in the above embodiment indicate the same parts as in the above embodiment, and the explanation thereof will be omitted. In this example,
The three-way switching valve 7 and the negative pressure chamber 22a1 of the exhaust throttle valve actuator 22 and the three-way switching valve 8 and the negative pressure chamber 22a of the exhaust throttle valve actuator 22 are connected to the pipe 41, respectively.
In place of the delay valve 6.5 of the embodiment described above, a delay timer 94.
95 is used. These delay timers 9
4.95 is between the exhaust recirculation valve operation control means 93 and the three-way switching valve 8, and the exhaust throttle valve operation control means 9.
2 and the three-way switching valve 7.

The delay timer 94 operates at a signal input section 94a when a connection signal for connecting the first outlet 8a and the third outlet 8C to the three-way switching valve 8 is output from the exhaust gas recirculation valve operation control means 93.
A signal is immediately transmitted from the exhaust recirculation valve operation control means 93 to the signal output section 94b to the three-way switching valve 8 at the first outlet 8a.
When a connection signal is output to connect the second outlet 8b and the second outlet 8b, the signal is transmitted from the signal input section 94a to the signal output section 94b after a predetermined period of time has elapsed. Further, the delay timer 95 outputs a signal from the signal input section 95a when the exhaust throttle valve operation control means 92 outputs a connection signal for connecting the first output lower a and the second output lower b to the three-way switching valve 7. When a connection signal is output from the exhaust throttle valve operation control means 92 to the three-way switching valve 7 to connect the first output lower a and the third output lower C, the signal is immediately transmitted to the signal input section 95b. The signal is transmitted to the signal output section 95b after a predetermined period of time has elapsed.

Therefore, during cold acceleration, there is a transition from region β to region γ,
From the exhaust throttle valve operation control means 92 to the first of the three-way switching valve 7
A connection signal connecting the output lower a and the third output lower C is output, and a connection signal connecting the first outlet 8a and the second outlet 8b of the three-way switching valve 8 is output from the exhaust recirculation valve operation control means 93. When the connection signal is transmitted to the three-way switching valve 7, the delay timers 94 and 95 are activated, and the timing at which the connection signal is transmitted to the three-way switching valve 8 is determined from the timing at which the connection signal is transmitted to the three-way switching valve 7. As a result, the exhaust throttle valve actuator 22
The time when the air in the negative pressure chamber 34a of the exhaust communication valve actuator 34 is drawn is delayed from the time when the atmosphere is introduced into the negative pressure chamber 22a of It starts to open.

Further, during cold deceleration, the transition from region γ to region β occurs, and a connection signal for connecting the first output lower a and the second output lower b of the three-way switching valve 7 is output from the exhaust throttle valve operation control means 92. is,
From the exhaust recirculation valve operation control means 93 to the first of the three-way switching valve 8
Even when the connection signal connecting the exit 8a and the third exit 8C is output, the delay timer 94.95
In this case, the timing at which the connection signal is transmitted to the three-way switching valve 7 is delayed from the timing at which the connection signal is transmitted to the three-way switching valve 8. As a result, the negative pressure chamber 22 of the exhaust throttle valve actuator 22 is
The timing at which the air in a is drawn out is delayed, and the exhaust throttle valve 21 closes later than the exhaust recirculation valve 33.

In this way, in the configuration of this embodiment as well, it is possible to differentiate the opening and closing operations of the exhaust gas recirculation valve 33 with respect to the exhaust throttle valve 21 during cold acceleration and deceleration, as in the previous embodiment. Moreover, in addition to this, the configuration of this embodiment is also provided with an exhaust recirculation valve operation control means 93 that functions in the same manner as in the previous embodiment, so that the exhaust throttle valve 21 can be closed even in the w414B that performs exhaust gas recirculation. Since the exhaust gas recirculation valve 33 is closed in this state, it is possible to obtain cold opening/closing operation characteristics of the exhaust throttle valve 21 and the exhaust gas recirculation valve 33 similar to those of the previous embodiment.

Note that the method of delaying the opening operation of the exhaust gas recirculation valve with respect to the opening operation of the exhaust throttle valve is not limited to the method according to the above embodiment. For example, this may be done by making the volume of the negative pressure chamber of the exhaust throttle valve actuator different from the volume of the negative pressure chamber of the exhaust flow valve actuator.

Further, in the above embodiment, the exhaust gas recirculation valve is fully closed in the region β, but it may be closed to a degree that does not significantly deteriorate the combustibility (exhaust gas leaks).

Furthermore, in a device in which the exhaust throttle valve is closed to increase engine resistance when the vehicle decelerates (at low load), the same control as that during cold deceleration shown in the above embodiment is performed. In this way, reduction of NOXI and stable combustion in a low engine speed range may be achieved.

〔Effect of the invention〕

In the exhaust gas recirculation control device for a diesel engine according to the present invention, the exhaust gas recirculation valve is closed when the exhaust throttle valve is closed even in the region where exhaust gas recirculation is performed, and the exhaust gas recirculation valve is opened in the region where the exhaust gas recirculation is performed. In some cases, the exhaust gas recirculation valve opens with a delay from the opening operation of the exhaust throttle valve. Therefore, in a region where the region where warm-up promotion is performed and the region where exhaust gas recirculation is performed have a small overlap, N0XI can be sufficiently reduced and warm-up can be sufficiently promoted.
When the region where the warm-up promotion region and the exhaust gas recirculation region overlap each other is shifted to the region where only the exhaust gas recirculation is performed, combustion is no longer suppressed and acceleration performance during cold conditions is not impaired. Therefore, according to the present invention, it is possible to efficiently promote warm-up and reduce the amount of NOx, and furthermore, it is possible to improve the acceleration performance when the engine is cold.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of the exhaust recirculation control device for a diesel engine according to the present invention, FIG. 2 is a time chart during acceleration, FIG. 3 is a time chart during deceleration, and FIG. 4 5 is a schematic configuration diagram showing another embodiment, and FIG. 5 is a graph showing the relationship between the region where warm-up promotion is performed and the region where exhaust gas recirculation is performed. 3... Exhaust communication passage, 6.94... Exhaust recirculation valve inter-operation delay means, 16... Exhaust passage, 21... Exhaust throttle valve 32... Exhaust recirculation outlet, 33... exhaust recirculation valve,
93... Exhaust recirculation valve operation control means, A... Area where the exhaust throttle valve is closed when cold, B... Area where exhaust gas recirculation is performed.

Claims (1)

[Claims] 1. A diesel engine comprising an exhaust throttle valve provided in an exhaust passage, an exhaust recirculation passage having an exhaust recirculation outlet provided in the exhaust passage upstream of the exhaust throttle valve, and an exhaust recirculation valve that opens and closes the exhaust recirculation passage. an exhaust recirculation valve operation control means for closing the exhaust gas recirculation valve by a predetermined amount in a state where the exhaust throttle valve is closed even in an area where exhaust gas recirculation is performed; Exhaust recirculation control for a diesel engine, characterized in that an exhaust recirculation valve opening operation delay means is provided for delaying the opening operation of the exhaust recirculation valve with respect to the opening operation of the exhaust throttle valve when the exhaust recirculation valve is opened. Device.