JP2001140701A - Egr device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform normal EGR as soon as possible by promoting a temperature rise of engine cooling water of an engine immediately after starting the engine. SOLUTION: An EGR passage 5 makes a part of exhaust circulate, which exhaust is made to flow from an exhaust passage 4 to an intake passage 2 of an engine 1. An EGR cooler 7 is arranged on the EGR passage 5 for cooling EGR gas by utilizing engine cooling water. A heat accumulator 12 is arranged on the way of a cooling water introduction passage 8 which introduces the engine cooling water to the EGR cooler 7, for keeping the cooling water under heat accumulation during stopping the engine. A bypass passage 10 and a changeover valve 11 are arranged for making at least a part of the engine cooling water bypass the EGR cooler 7 immediately after starting the engine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an EGR for an engine.
The present invention relates to an (exhaust gas recirculation) device, and more particularly to an improvement for promoting warm-up of an engine.

[0002]

2. Description of the Related Art As a conventional measure for promoting warming-up of an engine, as disclosed in JP-A-6-294327, in a diesel engine, immediately after starting, a supercharger is set to a full load state, and the engine is increased with an increase in exhaust pressure. In some cases, white smoke is reduced by rapidly performing warm-up.

[0003]

However, originally,
Immediately after start-up, the amount of EGR must be reduced as compared with that after completion of warm-up, and there is also a rise in exhaust pressure.
There was a problem that the emission amount deteriorated.

The present invention has been made in view of the above circumstances, and has as its object to solve the above-described problems by promoting the temperature rise of the engine cooling water without increasing the exhaust pressure and performing the normal EGR promptly. I do.

[0005]

According to the present invention, there is provided an EGR passage for recirculating a part of exhaust gas from an exhaust passage of an engine to an intake passage, and engine cooling water interposed in the EGR passage. EGR gas that cools EGR gas
In an EGR device for an engine including a cooler, a regenerator capable of storing high-temperature engine cooling water during engine operation in an engine cooling water passage in a heat storage state while the engine is stopped, and an engine cooling water immediately after the engine starts. A bypass passage and a switching valve capable of at least partially bypassing the EGR cooler are provided.

[0006] In the invention according to claim 2, the heat accumulator includes:
The cooling water introduction passage for introducing the engine cooling water to the EGR cooler is provided at a position upstream of a branch to the bypass passage.

[0007] In the invention according to claim 3, the heat accumulator is:
The switching valve is provided in the middle of the bypass passage, and the opening of the switching valve to the bypass passage is controlled in accordance with the temperature rise rate of the engine coolant.

The invention according to claim 4 is characterized in that the opening degree of the switching valve to the bypass passage is controlled based on the temperature difference between the engine cooling water and the cooling water in the EGR cooler.
In the invention according to claim 5, based on the temperature of the cooling water in the EGR cooler, the temperature rise rate, or the water pressure in the EGR cooler, the total amount of the cooling water is set under the condition that the boiling of the cooling water in the EGR cooler should be prevented. A bypass stop means for forcibly switching the switching valve so as to supply the EGR cooler to the EGR cooler.

In the invention according to claim 6, when the EGR valve is fully closed, a part of the exhaust gas is circulated to the EGR cooler.
An exhaust return passage for returning exhaust gas from the outlet side of the GR cooler to the exhaust passage is provided.

[0010] The invention according to claim 7 is characterized in that a correction means for correcting the opening control value of the EGR valve based on the gas temperature at the outlet side of the EGR cooler is provided.

[0011]

According to the first aspect of the present invention, the high-temperature engine cooling water during the operation of the engine in the engine cooling water passage is stored in the heat storage state while the engine is stopped by the heat storage device.
Immediately after the start of the engine, high-temperature engine cooling water is supplied from the regenerator and at least a part of the engine cooling water is bypassed to the EGR cooler, so that the temperature rise of the engine cooling water can be promoted.

According to the second aspect of the invention, the regenerator is
By providing the cooling water introduction passage for introducing engine cooling water to the EGR cooler in the middle of the cooling water introduction passage from the branch to the bypass passage, the capacity of the cooling water passage from the heat accumulator to the engine is relatively large, and the internal combustion engine is provided with It is possible to suppress a thermal shock due to a sudden change in cooling water temperature, and to supply high-temperature engine cooling water from a heat storage unit independently of switching valve control.

According to the third aspect of the present invention, the regenerator is provided in the middle of the bypass passage, and the opening degree of the switching valve to the bypass passage is controlled in accordance with the temperature rise rate of the engine cooling water. By allowing the cooling water in the EGR cooler to flow by an amount necessary for the cooling water temperature to stably increase, it is possible to stably increase the cooling water temperature and prevent thermal shock. Further, since the temperature of the cooling water in the EGR cooler also rises faster than in the case where the entire amount is bypassed, it is possible to suppress an increase in the exhaust-side PM discharge amount that occurs when the temperature of the cooling water in the EGR cooler is low.

According to the fourth aspect of the present invention, the degree of opening of the switching valve to the bypass passage is controlled based on the temperature difference between the engine cooling water and the cooling water in the EGR cooler, so that the EGR is performed.
A sudden change in gas temperature can be suppressed, and the jerky feeling of combustion can be reduced.

According to the fifth aspect of the invention, the temperature of the cooling water in the EGR cooler, the rate of the temperature rise, or the EGR
On the basis of the water pressure in the cooler, the bypass is stopped under conditions that should prevent the boiling of the cooling water in the EGR cooler, and the entire cooling water is switched to be supplied to the EGR cooler. Boiling of residual water due to an excessive temperature rise can be reliably prevented.

According to the sixth aspect of the present invention, an exhaust return passage for returning exhaust gas from the outlet side of the EGR cooler to the exhaust passage is provided so that a part of the exhaust gas flows through the EGR cooler when the EGR valve is fully closed. Therefore, even when the EGR is not performed at the extremely low water temperature, a part of the exhaust gas is caused to flow to the EGR cooler, whereby the temperature of the cooling water in the EGR cooler is increased by heat exchange with the exhaust gas, and then mixed with the engine cooling water. Thereby, it is possible to further promote warm-up.

According to the seventh aspect of the invention, by correcting the opening control value (EGR rate) of the EGR valve based on the gas temperature at the exit side of the EGR cooler, if the warm-up is not completed, the total amount or the one Since the cooling water of the section bypasses the EGR cooler, even if a temperature difference occurs between the cooling water remaining in the EGR cooler and the cooling water circulating in the engine, a more appropriate EGR
It can be performed.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of an EGR device for a diesel engine showing a first embodiment of the present invention.

In the intake passage 2 of the diesel engine 1,
The supercharger 3, more specifically, the exhaust turbine 3a on the exhaust passage 4 side
An intake compressor 3b driven by the compressor is interposed. This supercharger 3 has a variable nozzle mechanism on the exhaust turbine 3a side, and by adjusting the nozzle opening degree,
It is possible to control to any boost pressure.

An EGR passage 5 is provided from the exhaust passage 4 to the intake passage 2 to recirculate a part of the exhaust gas (EGR gas). The EGR passage 5 controls an EGR amount.
Valve 6 is interposed.

An EGR cooler 7 is provided upstream of the EGR valve 6 in the EGR passage 5. EGR cooler 7
Guides engine cooling water from a cooling water outlet of the engine 1 through a cooling water introduction passage 8, cools the EGR gas with the engine cooling water, and supplies the engine cooling water to a cooling water inlet side of the engine 1 through a cooling water return passage 9. To return to.

Here, a bypass passage 10 for bypassing the EGR cooler 7 is provided from the middle of the cooling water introduction passage 8 to the middle of the cooling water return passage 9.
A switching valve 11 is provided on the inlet side of the EGR cooler 7, that is, at a branch point between a cooling water introduction passage 8 toward the EGR cooler 7 and a bypass passage 10 that bypasses the EGR cooler 7. The switching valve 11 can adjust not only the flow path but also each flow rate by controlling the opening degree.

Further, in the middle of the cooling water introduction passage 8, upstream of the branch (switching valve 11) to the bypass passage 10,
2 is provided, and this regenerator 12 can store high-temperature engine cooling water during engine operation in a heat-storage state while the engine is stopped.

The EGR cooler 7 is provided with a relief valve 13 in a cooling water passage inside the EGR cooler 7.
When the pressure of the cooling water in the inside becomes equal to or higher than a predetermined value, the relief valve 13 is opened, and the cooling water in the inside of the
It can be made to escape to the cooling water return passage 9 more.

The EGR cooler 7 in the EGR passage 5 and E
An exhaust return passage 15 communicating with the GR valve 6 and communicating with the exhaust passage 4 downstream of the exhaust turbine 3 a is provided. The exhaust return passage 15 is provided with an exhaust throttle valve 16.

The operations of the EGR valve 6, the switching valve 11, and the exhaust throttle valve 16 are controlled by an engine control unit 20.
For these controls, in addition to information on the engine speed and load, an engine cooling water temperature sensor 21 such as a thermocouple that detects the engine cooling water temperature Tw upstream of the cooling water introduction passage 8 (upstream of the regenerator 12), A cooling water temperature sensor 22 in the cooler such as a thermocouple for detecting a cooling water temperature (cooling water temperature in the cooler) Tcool in the EGR cooler 7 and the EGR cooler 7
Outlet side EGR gas temperature (cooler outlet gas temperature) Tgas
A detection signal is input from a cooler outlet gas temperature sensor 23 such as a thermocouple for detecting the temperature.

Here, the engine control unit 20 operates according to the flow chart of FIG.
1 is controlled. Step 1 (referred to as S1 in the figure).
In the following, the engine coolant temperature Tw and the cooler internal coolant temperature Tcool are read.

In step 2, the amount of change in the engine coolant temperature per unit time (temperature rise rate) ΔT is calculated from the current value Tw (n) and the previous value Tw (n-1) of the engine coolant temperature.
Calculate w = Tw (n) -Tw (n-1).

In step 3, the engine cooling water temperature Tw
Difference ΔT between the cooling water temperature in the cooler Tcool and Twool
Calculate cool. In step 4, it is determined whether or not the temperature increase rate ΔTw of the engine coolant temperature is equal to or greater than a predetermined value DTW1 #.

Generally, the temperature of the engine cooling water changes as shown in FIG. 3 depending on the elapsed time from the start of the engine. The temperature rise rate immediately after the start is large, and becomes small from around 60 ° C. In consideration of the tendency of the engine cooling water temperature to rise, there are a case where the temperature rising rate ΔTw of the engine cooling water is equal to or more than a predetermined value DTW1 # (for example, 0.05 ° C./sec) and a case where it is less than the predetermined value DTW1 #. Perform different controls.

If ΔTw ≧ DTW1 #, step 5
And the bypass amount is controlled by the switching valve 11 to
In order to control the amount of cooling water to the GR cooler 7, the engine cooling water temperature Tw and the cooling water temperature T in the cooler are controlled as shown in FIG.
The switching valve opening KVO to the EGR cooler 7 is set in accordance with the temperature difference ΔT from cool.

Here, when the temperature difference ΔT is on the minus side, that is, when the cooling water temperature Tcool in the cooler is higher, the switching valve opening KVO to the EGR cooler 7 is set to the maximum value K
VOmax is set so that the entire cooling water amount passes through the EGR cooler 7.

When the temperature difference ΔT is on the plus side, that is, when the engine cooling water temperature Tw is higher, as the temperature difference ΔT becomes smaller, the switching valve opening KVO to the EGR cooler 7 is increased. Thus, while reducing the bypass amount, the amount of cooling water to the EGR cooler 7 is increased.

If ΔTw <DTW1 #, step 6
In order to supply the total cooling water amount to the EGR cooler 7,
The switching valve opening KVO to the EGR cooler 7 is set to the maximum value KVO.
It is set to max, and the bypass amount = 0.

The switching valve opening KVO set in step 5 or 6 is output to the switching valve 11 after being converted into a duty Duty in step 7. Next, the operation and effect of the present embodiment will be described.

When the temperature rise rate ΔTw of the engine cooling water is equal to or more than a predetermined value immediately after the engine is started, the switching valve 11 is moved to the bypass passage 10 so that at least a part of the engine cooling water bypasses the EGR cooler 7. Is switched. Therefore, part or all of the high-temperature engine cooling water stored in the regenerator 12 is supplied to the engine 1 from the bypass passage 10 without passing through the EGR cooler 7.

Thereafter, when the temperature rise rate ΔTw becomes less than a predetermined value due to an increase in the temperature of the engine cooling water, the switching valve 11 is switched to the EGR cooler 11 side, and the entire engine cooling water is supplied to the EGR cooler 7. The EGR gas is cooled.

According to this, the regenerator 12 capable of keeping the temperature of the engine cooling water is provided to keep the high temperature of the engine cooling water at the time of the previous operation and to promote the rise of the temperature of the engine cooling water at the time of restart. By doing so, it is possible to quickly shift to the normal EGR region shown in FIG. At that time, immediately after the start, the engine cooling water is circulated by bypassing the EGR cooler 7, so that the amount of cooling water circulated by the amount of water remaining in the EGR cooler 7 is reduced, and the engine cooling water temperature is further increased. Promoted.

When the regenerator 12 is installed on the outlet side of the EGR cooler 7, hot water is rapidly introduced into the engine 1 at the time of restart, so that a temperature difference occurs between the regenerator 12 and the engine body, and thermal shock occurs. In addition, it has an adverse effect on combustion and the like. Therefore, by installing the regenerator 12 on the inlet side of the EGR cooler 7, since the cooling water channel capacity exists from the regenerator 12 to the engine inlet, a rapid change in the cooling water temperature inside the engine 1 is suppressed, Shock can be suppressed.

In particular, by optimizing the capacity of the EGR cooling water passage from the heat accumulator 12 to the engine inlet so that the temperature rise is optimal, from the relationship between the capacity of the heat accumulator 12 and the amount of engine cooling water, As shown in FIG.
By providing the cooling water passage with a certain volume, a thermal shock generated when the EGR cooling water passage is relatively small can be suppressed, and a bad influence on combustion can also be suppressed.

Immediately after the start, the switching valve opening toward the bypass passage 10 (the switching valve opening KV toward the EGR cooler 7).
O) is the temperature difference Δ between the engine cooling water and the cooling water in the cooler.
By controlling based on T, a sudden change in the EGR gas temperature can be suppressed, the EGR gas at an appropriate temperature can be recirculated to the intake air, and the jerky feeling of combustion can be reduced.

In addition to the above, there are the following further operational effects. Since the introduction of the cooling water to the EGR cooler 7 is restricted at a low water temperature, the EGR cooler 7
, There is a possibility that a sharp rise in temperature may occur, and there is a possibility that residual water in the EGR cooler 7 will boil.

Therefore, as shown in the flowchart of FIG. 6, the cooling water temperature Tcool in the cooler is set to a predetermined value (for example, 90%).
° C) or the temperature rise rate ΔTcool is greater than or equal to a predetermined value (eg, 1.0 ° C / sec) (step 21). If YES, the switching is performed to prevent boiling of the residual water. The bypass by the valve 11 is stopped, and the total amount of cooling water is introduced into the EGR cooler 7 (step 23). Also, E
Even when the temperature distribution of the residual water in the GR cooler 7 becomes uneven and the temperature cannot be measured accurately, the EG due to boiling
In order to prevent the residual water pressure in the R cooler 7 from rising, a relief valve 13 is provided to forcibly release the pressure in the EGR cooler 7 and to operate the relief valve 13 (that is, increase the water pressure in the EGR cooler 7). In conjunction with this (step 22), the bypass by the switching valve 11 is stopped, and the total cooling water amount is reduced to EGR.
It is introduced into the cooler 7 (step 23). This flow is EG
It corresponds to a bypass stop means for preventing boiling of the cooling water in the R cooler 7.

Further, even when the EGR gas is not recirculated to the intake air at the extremely low coolant temperature (the EGR valve 6 is fully closed), a part of the exhaust gas flows to the EGR cooler 7 and then the exhaust gas downstream of the exhaust turbine 3a. By discharging to passage 4,
By increasing the temperature of the residual water in the EGR cooler 3 by heat exchange with the exhaust gas, and then mixing the residual water with the engine cooling water, it is possible to further promote warm-up.

At this time, in order to prevent all exhaust gas from passing through the exhaust return passage 15, an exhaust throttle valve 16 is provided in the exhaust return passage 15 to perform exhaust throttle. Since the throttle opening of the variable nozzle supercharger 3 and the throttle loss of the exhaust throttle valve 16 become the same, each opening (nozzle opening and exhaust throttle valve opening) has a one-to-one correspondence. A table as shown in FIG. 7 may be provided in advance, and the opening of the exhaust throttle valve 16 may be controlled according to the nozzle opening of the variable nozzle supercharger 3.

When the warm-up is not completed, the whole or a part of the cooling water bypasses the EGR cooler 7, and
A temperature difference occurs between the cooling water remaining in the cooler 7 and the cooling water circulating in the engine 1.

Therefore, in addition to the conventional correction of only the engine coolant temperature Tw, the EG is also obtained from the cooler outlet gas temperature Tgas.
Correct the R rate. That is, as shown in the flowchart of FIG. 8, the engine cooling water temperature Tw and the cooler outlet gas temperature Tgas are read (step 31), and based on these, the EGR rate correction coefficient is set from the map shown in FIG. 9 (step 31). 32). Specifically, as the engine coolant temperature Tw is lower and the cooler outlet gas temperature Tgas is lower, the EGR rate correction coefficient is made closer to 0 to reduce the EGR rate. As the temperature of the cooler outlet gas Tgas increases, the EGR rate correction coefficient approaches 1 to increase the EGR rate.
Return to R. As a result, the combustion state can be grasped more accurately,
Appropriate EGR can be performed. This flow corresponds to correction means for the opening control value of the EGR control valve 6.

Next, a second embodiment of the present invention will be described. In the first embodiment, in order to prevent thermal shock when mixing the cooling water in the regenerator and the engine cooling water, measures such as placing the regenerator on the cooling water outlet side of the engine and expanding the piping capacity are taken. This must be done, but simply placing the regenerator on the cooling water outlet side of the engine is not enough to prevent thermal shock, and expanding the piping capacity just to prevent thermal shock leads to an increase in the size of the piping. In addition, the cooling water capacity is increased, and the time until the completion of the warm-up is increased. Therefore, it is not necessarily efficient in terms of the early completion of the warm-up.

Therefore, the second embodiment is improved based on the above points. FIG. 10 is a system diagram of an EGR device for a diesel engine according to a second embodiment of the present invention, which is different from the first embodiment (FIG. 1) mainly in the switching valve 11.
And the arrangement of the heat accumulator 12 is different.

Here, from the middle of the cooling water introduction passage 8 to the EGR cooler 7 to the middle of the cooling water return passage 9, the EGR
A bypass passage 10 that bypasses the cooler 7 is provided.
The switching valve 11 is provided at the outlet side of the bypass passage 10, that is, at the junction of the cooling water return passage 9 from the EGR cooler 11 and the bypass passage 10 bypassing the EGR cooler 7.

A regenerator 12 is provided in the middle of the bypass passage 10. The regenerator 12 can store high-temperature engine cooling water during operation of the engine in a state of storing heat while the engine is stopped.

The engine cooling water temperature sensor 21
It is provided downstream of the cooling water return passage 9 (downstream of the switching valve 11). Here, the engine control unit 20 controls the switching valve 1 according to the flowchart of FIG.
1 is controlled.

Steps 1 to 4 are the same as in the first embodiment (FIG. 2). As a result of the determination in step 4, ΔTw
When ≧ DTW1 #, the amount of cooling water to the EGR cooler 7 is controlled by the bypass amount control by the switching valve 11,
Proceed to step 11 and subsequent steps.

In step 11, as shown in FIG.
The switching valve opening KVOC to the EGR cooler 7 as a required value on the regenerator 12 is set according to the temperature rise rate ΔTw of the engine cooling water.

Here, the temperature rise rate ΔTw is equal to the predetermined value DT.
The switching valve opening KVOC to the EGR cooler 7 side is increased as the value is larger than W1 # (0 → maximum value KVOCmax).
), An excessive increase in ΔTw due to supplying a larger amount of cooling water through the EGR cooler 7 and supplying high-temperature engine cooling water to the engine 1 from the regenerator 12 is suppressed.

In the next step 12, it is determined whether or not the temperature difference ΔT between the engine coolant temperature Tw and the cooler internal coolant temperature Tcool is less than a predetermined value DTW2 #. If the result of this determination is that ΔT <DTW2 #, the routine proceeds to step 13, where as shown in FIG. 13, EG is determined according to the temperature difference ΔT between the engine coolant temperature Tw and the cooler internal coolant temperature Tcool.
A switching valve opening KVOegr to the EGR cooler 7 as a required value for the R cooler 7 is set.

Here, when the temperature difference ΔT is on the minus side, that is, when the cooling water temperature Tcool in the cooler is higher, the switching valve opening KVOegr to the EGR cooler 7 is set to the maximum value KVOegrmax. More cooling water
It is made to pass through the GR cooler 7.

When the temperature difference ΔT is on the plus side, that is, when the engine cooling water temperature Tw is higher, the switching valve opening KVOegr to the EGR cooler 7 increases as the temperature difference ΔT decreases. By increasing the supply amount from the bypass passage 10 side (the regenerator 12 side), a larger amount of cooling water is supplied to the EGR cooler 7.

If ΔT ≧ DTW2 #, step 12
Then, the process proceeds to step 15, and the switching valve opening KVOegr to the EGR cooler 7 as the required value on the EGR cooler 7 side =
Set to 0.

At step 16, the switching valve opening KVOC to the EGR cooler 7, which is the required value of the regenerator 12, and E
The switching valve opening KVOegr to the EGR cooler 7 which is the required value of the GR cooler 7 is added to set the final switching valve opening KVO = KVOC + KVOegr to the EGR passage 7.

On the other hand, as a result of the determination in step 4, ΔTw
In the case of <DTW1 #, it is determined that no sudden change in the coolant temperature inside the engine 1 has occurred, and the routine proceeds to step 14, where the switching valve to the EGR cooler 7 as the required value of the regenerator 12 is opened. The degree KVOC is set to 0, and the routine proceeds to step 12. Also, as a result of the determination in step 12, ΔT ≧ DT
In the case of W2 #, the required value on the EGR cooler 7 side is EG
The switching valve opening KVOegr = 0 to the R cooler 7 is set to zero.

The switching valve opening KVO set in step 16 is converted to a duty Duty in step 17 and then output to the switching valve 11. Further, KVOCmax in FIG. 12 and KVOegrmax in FIG. 13 are values having the following relationship.

(1) KVOCmax + KVOegrmax = 1 (full opening) (2) 0 ≦ KVOCmax ≦ 1, 0 ≦ KVOegrmax ≦ 1 By setting these values, the heat storage unit 12 side or E
The required value can be weighted with respect to the switching valve opening on the GR cooler 7 side.

In the present embodiment, the regenerator 12 is provided in the middle of the bypass passage 10, and the switching valve opening to the bypass passage 10 (the opening to the EGR cooler 7) is changed in accordance with the temperature rise rate ΔTw of the engine cooling water. By controlling the switching valve opening degree KVO), the cooling water in the EGR cooler 7 is allowed to flow by an amount necessary for stably increasing the cooling water temperature, and the cooling water temperature as shown in FIG. Can be stably raised, and the occurrence of thermal shock can be prevented.

The temperature of the cooling water in the EGR cooler 7 is also
As it rises faster than bypassing the entire volume,
As shown in FIG. 5, the effect on the EGR gas cooling emission at the time of cold start can be suppressed from increasing the exhaust PM (particulate) emission, which occurs when the temperature of the cooling water in the cooler is low.

As described above, a diesel engine has been described as an embodiment of the present invention, but it is needless to say that the present invention can be applied to other engines such as a gasoline engine.

[Brief description of the drawings]

FIG. 1 is a system diagram of an EGR device for a diesel engine showing a first embodiment of the present invention.

FIG. 2 is a flowchart of switching valve control according to the first embodiment;

FIG. 3 is a diagram showing a change in engine coolant temperature after the engine is started;

FIG. 4 is a view showing a switching valve opening degree table;

FIG. 5 is a diagram comparing changes in cooling water temperature according to EGR cooling water channel volume;

FIG. 6 is a flowchart of control for preventing boiling of cooling water in an EGR cooler.

FIG. 7 is a diagram showing a relationship between a nozzle opening degree and an exhaust throttle valve opening degree of a variable nozzle type supercharger.

FIG. 8 is a flowchart of EGR rate correction control.

FIG. 9 is a diagram showing an EGR rate correction coefficient map;

FIG. 10 is a system diagram of an EGR device for a diesel engine showing a second embodiment of the present invention.

FIG. 11 is a flowchart of switching valve control according to a second embodiment.

FIG. 12 is a diagram showing a switching valve opening degree table according to a regenerator request;

FIG. 13 is a diagram showing a switching valve opening degree table according to an EGR cooler side request;

FIG. 14 is a diagram showing the effect of regenerator bypass control.

FIG. 15 is a diagram showing the effect of EGR gas cooling on emissions during a cold start.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 engine 2 intake passage 3 supercharger 4 exhaust passage 5 EGR passage 6 EGR valve 7 EGR cooler 8 cooling water introduction passage 9 cooling water return passage 10 bypass passage 11 switching valve 12 heat storage device 13 relief valve 14 relief passage 15 exhaust return passage 16 Exhaust throttle valve 20 Engine control unit 21 Engine cooling water temperature sensor 22 Cooler internal cooling water temperature sensor 23 Cooler outlet gas temperature sensor

Claims (7)

[Claims] An EGR passage for recirculating a part of exhaust gas from an exhaust passage of an engine to an intake passage, and an EGR disposed in the EGR passage for cooling EGR gas by engine cooling water.
An EGR device for an engine including a cooler, a regenerator capable of storing high-temperature engine cooling water during engine operation in an engine cooling water passage in a heat storage state while the engine is stopped, and an engine cooling water immediately after the engine starts. An EGR device for an engine, comprising: a bypass passage and a switching valve capable of at least partially bypassing an EGR cooler. 2. The engine according to claim 1, wherein said regenerator is provided in a cooling water introduction passage for introducing engine cooling water to an EGR cooler and upstream of a branch to a bypass passage. EGR device. 3. The regenerator is provided in the middle of a bypass passage, and the opening of the switching valve to the bypass passage is controlled in accordance with the rate of temperature rise of the engine coolant. The EGR device for an engine according to claim 1, wherein 4. An opening degree of a switching valve to a bypass passage is controlled based on a temperature difference between engine cooling water and cooling water in an EGR cooler. An EGR device for an engine according to any one of the preceding claims. 5. An EGR cooler according to claim 1, wherein the temperature of the cooling water in the EGR cooler, the rate of temperature rise thereof, or the water pressure in the EGR cooler.
A bypass stop means for forcibly switching a switching valve so as to supply a total amount of cooling water to the EGR cooler under a condition in which boiling of the cooling water in the GR cooler is to be prevented. Item 5. An EGR device for an engine according to any one of Items 4. 6. An exhaust return passage for returning exhaust gas from the outlet side of the EGR cooler to the exhaust passage so that a part of the exhaust gas flows to the EGR cooler when the EGR valve is fully closed. An EGR device for an engine according to any one of claims 1 to 5. 7. The apparatus according to claim 1, further comprising a correction means for correcting an EGR valve opening control value based on a gas temperature at an EGR cooler outlet side. Engine EGR device.