JPH1193781A - EGR device with EGR cooler - Google Patents

Abstract

[PROBLEMS] To provide a durable EGR by scavenging the inside of an EGR cooler when EGR is not operating, preventing dew condensation, adhesion of soot and the like, sulfuric acid corrosion, etc., and maintaining a cooling performance. E with cooler
A GR device is provided. In an EGR device of a supercharged engine capable of diluting EGR gas with fresh air before passing through an EGR cooler, an EGR valve for adjusting an EGR gas amount when shifting from an EGR operation state to an EGR non-operation state is provided. Close the valve, open the flow control valve for adjusting the fresh air amount for dilution, and partially remove the intake throttle provided between the branch portion of the branch passage for dilution of the intake passage and the junction of the EGR passage. When opened, fresh air sucked into the EGR cooler flows when the EGR is not operated to scavenge and clean.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an EGR for an engine.
The present invention relates to an EGR device with an EGR cooler that lowers the temperature of EGR gas by an EGR cooler to improve the air intake efficiency and maintain good engine combustion, and also lowers the combustion temperature to reduce NOx in exhaust gas. Things.

[0002]

2. Description of the Related Art In exhaust gas countermeasures for diesel engines and the like, in order to reduce the amount of NOx emission in exhaust gas, a part of the exhaust gas is recirculated to intake air to suppress the combustion temperature and reduce NOx emission. EGR to suppress generation
(Exhaust gas recirculation) is known to be effective, and is widely used.

In this EGR device, an EGR passage for dividing exhaust gas from an exhaust passage of an engine is connected to an intake passage side, and EGR is performed while adjusting a flow rate of the EGR gas by an EGR valve provided in the EGR passage. I have. However, if the EGR gas expanded at a high temperature is circulated to the intake side as it is, the proportion occupied by the EGR gas in the cylinder at the time of intake increases, and the amount of air entering the cylinder decreases. An EGR cooler of a water-cooled type or the like is provided to cool the EGR gas to reduce its volume, and then supply it to the intake manifold to secure the amount of air supplied into the cylinder.

However, since the exhaust gas of the engine contains moisture generated by combustion, when the EGR cooler is cold, such as in winter or immediately after the start of the engine, water vapor in the EGR gas in the EGR cooler is reduced. Condensation causes problems such as adhesion of soot in the EGR gas to the heat transfer tube and sulfuric acid corrosion due to sulfur content such as sulfur oxide. In order to solve this problem, as shown in FIG. 1, the present inventor supplies a portion Ab of fresh air to the upstream side of the EGR cooler 5 via the branching passage 9 for dilution to supply E to the upstream side of the EGR cooler 5.
An EGR device has been developed which dilutes the GR gas Ge, reduces the concentration of water vapor in the EGR gas (Ge + Ab) supplied to the EGR cooler 5, lowers the dew point temperature, and prevents dew condensation in the EGR cooler 5.

In this EGR device, EGR gas G
e, the EGR valve 4 for adjusting the amount of e, the flow rate adjusting valve 10 for adjusting the amount of the fresh air Ab for dilution, the branch passage 9 for dilution, and the EGR passage 6
The operation of each valve of the intake throttle 11 for adjusting the pressure is performed as shown in Table 1 for each operation region in FIG. In the area A where the operating state of the engine is low load, EGR is performed.
Since the exhaust gas temperature is low, the inlet temperature of the EGR cooler 5 becomes relatively low. On the other hand, EGR cooler 5
Since the temperature of the cooling water supplied to the EGR gas is substantially constant irrespective of the operating state of the engine, dew condensation due to supercooling of the EGR gas Ge is likely to occur.

Therefore, in the region A, the EGR valve 4 and the flow control valve 10 are opened, and the intake throttle 11 is half-opened and throttled.
The EGR gas Ge is supplied to the cooler 5 to dilute the EGR gas Ge so as to lower the partial pressure of steam to prevent dew condensation due to supercooling. Next, in the area B of the medium load, since there is a margin in the amount of air,
The GR valve 4 is opened halfway, the flow control valve 10 is closed, and the intake throttle is closed.
11 is opened, and low EGR is performed. In this area B,
Since the exhaust gas temperature is high, the inlet temperature of the EGR cooler 5 is also relatively high, so that the heat release amount of the EGR cooler 5 must be set appropriately so that the EGR gas Ge is not overcooled. Thereby, occurrence of dew condensation can be prevented.

In the high-load region C, the amount of combustion injection is large, and if EGR is performed, the amount of fresh air is insufficient and smoke is deteriorated. Therefore, the EGR valve 4 and the flow control valve 10 are closed, and the intake throttle 11 is closed. Is opened and EGR is not performed. The area D is in a no-injection engine braking state, and does not perform EGR similarly to the area C.

[0008]

[Table 1]

[0009]

However, in the EGR device shown in FIG. 1, when the EGR is stopped, the EGR gas Ge and fresh air Ab are stored in the EGR cooler 5.
Does not pass through, so that EG
The R gas Ge will stay. For this reason, the retained EGR gas Ge is cooled to a temperature close to the temperature of the cooling water, so that even the diluted mixed gas Ge + Ab generates dew.

When the dew condensation occurs when the EGR is not operated, soot in the EGR gas Ge is captured by the dew condensation water and adheres to and accumulates on the inner surface of the EGR cooler 5 to deteriorate the heat transfer coefficient. There is a problem that the heat radiation amount of the cooler 5 is reduced and the performance is deteriorated. Further, since sulfur such as sulfur oxides contained in the EGR gas Ge is dissolved in the dew condensation water to generate sulfuric acid, there is a problem that a cooling pipe of the EGR cooler 5 is corroded with sulfuric acid and damaged.

As one of the measures for preventing contamination of the EGR cooler when the EGR gas is stopped, Japanese Patent Application Laid-Open No. 8-135517 discloses a method in which a heat exchanger passage is provided in a part of the intake pipe.
At the time of GR, the passage valve to the heat exchanger (EGR cooler) in the heat exchanger passage is closed, and the EGR entering the intake pipe is closed.
An EGR device has been proposed in which gas is introduced into the heat exchanger to cool it, and when the EGR is stopped, the heat exchanger passage is opened to flow intake air into the heat exchanger to remove dirt such as soot.

However, in this device, the flow rate of the fresh air in the intake pipe changes depending on the operating state of the engine, so that a flow rate sufficient to remove dirt from the heat exchanger cannot be obtained. There is a problem that cleaning of the inside of the vessel becomes insufficient. In other words, the passage cross-sectional area of the intake passage is
Since the engine is formed so as to have a sufficient area with respect to the intake air amount required at the time of rated operation of the engine, for example, at the time of operation at 50% of the rated speed, the flow velocity in the intake passage is 50% of the rated operation. However, since the heat exchanger has flow resistance and more intake air flows into the side of the intake passage, the flow velocity of the intake air flowing through the heat exchanger becomes very low, It is not possible to obtain a flow rate sufficient to remove the dirt.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide an EG when the EGR is not operating.
Sulfur generated by scavenging the inside of the R cooler to prevent the occurrence of dew condensation, adhesion of soot and the like, which causes a decrease in the heat transfer coefficient of the cooling pipe, and sulfur components such as sulfur oxides in the EGR gas being dissolved in the dew condensation water Corrosion can be prevented, and cooling performance can be maintained by cleaning the inside of the EGR cooler with fresh air.
An object of the present invention is to provide an EGR device with an EGR cooler that can improve durability performance.

Further, the present invention prevents smoke and excessive EGR which are likely to be generated when operating a valve for flowing intake air to the EGR cooler when the EGR is stopped.

[0015]

An EGR device with an EGR cooler for achieving the above object connects an intake passage and an exhaust passage downstream of a compressor of a supercharged engine with an EGR passage. The EGR passage and the upstream side of the intake passage where the EGR passage joins are connected by a branch passage for dilution having a flow control valve, and an EGR valve is connected to an upstream side of the EGR passage connected to the branch passage for dilution. An EGR cooler provided on each downstream side, and an intake throttle provided between a branch portion of the dilution branch passage of the intake passage and a junction of the EGR passage.
The EGR valve is closed, the flow rate regulating valve is opened, the intake throttle is partially opened, and the EGR is performed when shifting from the EGR operation state to the EGR non-operation state.
It is configured to control the flow of fresh air sucked into the cooler, and when the EGR is not operated, the fresh air is flown to the EGR cooler to scavenge the EGR cooler,
This is to prevent dew condensation, adhesion of soot and the like, and sulfuric acid corrosion in the EGR cooler, and to clean the inside of the EGR cooler.

In the present invention, since the intake throttle is provided between the branch portion of the dilution branch passage of the intake passage and the junction of the EGR passage, the intake throttle is narrowed to reduce the EGR.
The amount of fresh air flowing to the cooler can be adjusted. Therefore, the flow rate of fresh air flowing through the EGR cooler can be maintained at a flow rate sufficient for cleaning the EGR cooler regardless of the operation state of the engine, so that high scavenging performance and high cleaning performance can be achieved.

Further, when shifting from the EGR operation state to the EGR non-operation state, the EGR valve is closed and then the flow control valve is opened, and after the flow control valve is opened, the intake throttle is partially closed. By opening the valve and controlling the intake air to flow to the EGR cooler, that is, by specifying the opening and closing sequence of the valve for flowing the intake air to the EGR cooler, E
Avoid discharge of smoke and excessive EGR, which are likely to occur when the intake air flows into the GR cooler.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. E with EGR cooler according to the present invention
The GR device is configured as shown in FIG. 1. In the supercharged engine 1, the exhaust passage 2 such as an exhaust manifold and an exhaust pipe and the intake passage 8 downstream of the compressor 15 are provided.
And are connected by an EGR passage 6. This EGR passage 6
And a portion 13 upstream of a junction 12 where the EGR passage 6 of the intake passage 8 joins with a branch passage 9 for dilution, and a flow control valve 10 for adjusting the amount of fresh air Ab is connected to the branch passage 9 for dilution. It is provided.

Further, a connecting portion to which the branch passage 9 for dilution is connected.
The EGR valve 4 for adjusting the flow rate of the EGR gas Ge is provided in the EGR passage 6 upstream of the EGR passage 14, and the EGR cooler 5 is provided in the EGR passage 6 downstream of the connection part 14. Next, a junction where the branch portion 13 where the dilution branch passage 9 branches and the EGR passage 6 merges.
An intake throttle 11 such as a throttle valve is provided in the intake passage 8 between the throttle valve 12 and the intake passage 11.

If necessary, an intercooler 16 for cooling the fresh air Am + Ab whose temperature has been raised by the pressure increase in the compressor 15 of the supercharger is connected to a branch portion 13 where the dilution branch passage 9 of the intake passage 6 branches. The EGR device is provided on the upstream side or on the downstream side. Then, when shifting from the EGR operation state to the EGR non-operation state, that is, when stopping the EGR, the EGR valve 4 is closed, the flow control valve 10 is opened, and the intake throttle 11 is partially moved. EG is opened
Control is performed so that intake air flows into the R cooler 5.

The operation of each of the valves 4, 10, and 11 such as the EGR valve 4 in the EGR device with the EGR cooler is performed by the operation shown in Table 2 in each operation state region shown in FIG. In FIG. 2, the region C in FIG.
The load is divided into C1 on the low load side and C2 on the high load side. When the EGR is stopped, that is, when the operating state changes from the area A to the area D or changes from the area B to the areas C1 and C2 after passing through the area C1, the EGR cooler 5 and the EGR passage In order to prevent the occurrence of dew condensation, the adhesion of soot and the corrosion of sulfuric acid, the EGR valve 4 is closed, the flow rate regulating valve 10 is opened, the intake throttle 11 is half-opened, and only a part of fresh air Ab is throttled. The gas is passed through the cooler 5 and scavenged.

During scavenging in the EGR cooler 5, the passing fresh air Ab is heated and expanded in the EGR cooler 5, so that the amount of fresh air supplied to the cylinder is reduced. For this reason, smoke is likely to occur in the high load periods C1 and C2, but scavenging is performed only in the region C1 where the supply air amount is still large, and in the high load region C2, the scavenging is stopped, thereby generating the smoke. Can be suppressed.

[0023]

[Table 2] Further, when the operating state changes from the area B to the area C1,
There is no problem if each of the valves 4, 10, 11 has a sufficiently fast response, but if the response is slow, the following problem occurs.

First, if the intake throttle 11 starts closing before the EGR valve 4 completes closing, the pressure at the junction 12 of the EGR passage 6 decreases and a large amount of EGR gas is sucked.
It becomes R. If the intake throttle 11 starts closing before the flow control valve 10 opens by a predetermined amount, the intake air is throttled, so that the amount of fresh air supplied to the cylinder is insufficient, and smoke is generated.

If the flow control valve 10 is opened before the EGR valve 4 is closed in a state where the intake throttle 11 is not closed, E
The GR gas Ge is supplied to the intake passage 3 side without being cooled through the flow control valve 10, and the amount of fresh air supplied to the cylinder becomes insufficient, and there is a possibility that smoke is generated. In order to avoid these phenomena, consider the response speed of each valve 4,10,11, determine the operation order of each valve 4,10,11 and provide a time lag, then close the EGR valve 4 The valves 4, 10, and 11 are controlled such that the flow control valve 10 is opened, and finally, the intake throttle 11 is partially opened.

That is, from region B to region C1, the EGR
As shown in FIG. 3, the EGR valve 4 is fully closed from half open, and then the flow rate regulating valve 10 is fully opened from half closed, as shown in FIG.
Finally, the intake throttle 11 is partially opened from full open to half closed. On the other hand, when changing from the area C1 to the area B, on the contrary, the intake throttle 11 is fully opened from half closed,
10 is fully closed from half open, and then the EGR valve 4 is changed from fully closed to half open.

According to the EGR device with an EGR cooler as described above, when shifting from the EGR operation state to the EGR non-operation state, the EGR valve 4 of the EGR passage 6 is closed and the flow rate of the dilution branch passage 9 is adjusted. By opening the valve 10 and partially opening the intake throttle 11 provided between the branch portion 13 of the dilution branch passage 9 of the intake passage 8 and the junction 12 of the EGR passage 6, the EGR is not activated. At times, fresh air can flow into the EGR cooler 5.

With the passage of the fresh air, the EGR cooler 5
Since the inside can be scavenged, the occurrence of dew condensation in the EGR cooler 5 when the EGR is not operated is prevented, so that the adhesion of soot and the like is prevented, and the sulfur content such as sulfur oxides in the EGR gas dissolves in the condensed water. The corrosion of the cooling pipe by sulfuric acid generated in the above can be prevented. Further, since the heat transfer tube and the EGR passage 6 in the EGR cooler 5 can be cleaned by the fresh air,
It is possible to prevent soot and the like from adhering to the heat transfer tube and prevent the heat transfer coefficient from deteriorating and the amount of heat radiation from decreasing, thereby maintaining the cooling performance of the EGR cooler.

Since the intake throttle 11 is provided between the branch portion 13 of the dilution branch passage 9 of the intake passage 8 and the junction 12 of the EGR passage 6, the intake throttle 11 is throttled to reduce the EG.
Since the fresh air Ab passing through the R cooler 5 can be increased, the flow rate of the fresh air passing through the EGR cooler 5 can be maintained high irrespective of the operation state of the engine, so that high scavenging performance and high cleaning can be achieved. Since the capacity is obtained and soot and the like in the heat transfer tube of the EGR cooler 5 generated during the EGR can be efficiently cleaned, a decrease in the heat transfer coefficient of the heat transfer tube can be prevented.

Accordingly, the cooling performance of the EGR cooler 5 can be maintained, and further, sulfuric acid corrosion can be prevented.
The durability of the EGR cooler 5 can be improved.
Further, after the EGR valve 4 is closed, the flow control valve 10 is closed.
And finally opening the intake throttle 11 partially, it is possible to prevent smoke and excessive EGR which are likely to be generated while the valves 4, 10, 11 are being operated.

[0031]

EGR with EGR cooler according to the present invention
According to the device, in an EGR device with an EGR cooler of a supercharged engine capable of mixing the fresh air sucked into the EGR gas before passing through the EGR cooler,
By operating a valve, a flow rate regulating valve for fresh air for dilution, and an intake throttle provided between a branch portion of the branch passage for dilution of the intake passage and a junction of the EGR passage, the engine is not operated when the EGR is not operated. A sufficient amount of fresh air can flow into the EGR cooler regardless of the rotation state.

Accordingly, since the inside of the EGR cooler is scavenged to prevent dew condensation and clean the inside of the heat transfer tube, it is possible to prevent the adhesion of soot and the like to the heat transfer tube, the deterioration of the heat transfer coefficient and the decrease in the amount of heat radiation due to the adhesion. , The cooling performance of the EGR cooler can be maintained. Further, since sulfuric acid corrosion generated by dissolution of sulfur components such as sulfur oxides contained in the EGR gas in the dew condensation water can be prevented, the durability of the EGR cooler, the EGR pipe, and the like can be improved. .

Further, from the EGR operating state, the EGR
By operating the EGR valve, the flow regulating valve, and the intake throttle in this order when the EGR is stopped to shift to the non-operating state, the EGR valve is operated.
It is possible to prevent the discharge of smoke and the occurrence of excessive EGR, which are likely to occur when the intake air flows into the cooler.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an EGR device showing an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a division of an operating state of an engine related to the present invention.

FIG. 3 is a timing chart showing an operation of a valve when EGR is stopped according to the present invention.

FIG. 4 is a schematic diagram showing a division of an operating state of an engine.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Exhaust passage 3 ... Intake manifold 4 ... EGR valve 5 ... EGR cooler 6 ... EGR passage 7 ... Cooling water passage 8 ... Intake passage 9 ... Branch passage for dilution 10 ... Flow control valve 11 ... Inlet throttle 12 ... Confluence Part 13… Branch part 14… Connection part 15… Compressor Am… Main part of fresh air Ab… Part of fresh air (for dilution) G… Exhaust gas Ge… EGR exhaust gas

Claims (2)

[Claims] An EGR passage (6) connects an intake passage (8) and an exhaust passage (2) downstream of a compressor (15) of a supercharged engine (1). And an upstream side of the intake passage (8) where the EGR passage (6) merges, through a dilution branch passage (9) having a flow control valve (10), and the dilution of the EGR passage (6) is performed. An EGR valve (4) is provided on the upstream side to which the branch passage (9) is connected, and an EGR cooler (5) is provided on the downstream side. Further, a branch portion of the dilution passage (9) of the intake passage (8) is provided. An intake throttle (11) is provided between (13) and the converging portion (12) of the EGR passage (6).
In the GR device, when shifting from the EGR operation state to the EGR non-operation state, the EGR valve (4) is closed, the flow control valve (10) is opened, and the intake throttle (11) is closed. An EGR device with an EGR cooler which is partially opened to control the flow of fresh air taken into the EGR cooler (5). 2. When shifting from an EGR operation state to an EGR non-operation state, the EGR valve (4) is closed, and then the flow control valve (10) is opened, and the flow control valve (10) is opened. The EGR device with an EGR cooler according to claim 1, wherein after the valve is opened, the intake throttle (11) is partially opened to control the flow of intake air to the EGR cooler (5).