JPH10196464A - Egr device with egr cooler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the dew condensation in an EGR cooler by providing the EGR cooler and an EGR valve in an EGR passage and connecting a section between the EGR cooler and the EGR valve with a section between an exhaust passage which is provided more downstream than an EGR gas inlet part of the EGR passage and it by means of an exhaust air return passage having a flow rate control valve. SOLUTION: An exhaust passage 2 is connected with a suction passage 8 by means of an EGR passage 6, and an EGR cooler 5 and an EGR valve 4 are provided in this EGR passage 6. Moreover, a section between the EGR cooler 5 and the EGR valve 4 is connected with a section between the exhaust passage 2 which is provided more downstream than an EGR gas inlet part 21 of the EGR passage 6 and it by means of an exhaust air passage 9, and a flow rate control valve 10 is provided in this exhaust air return passage 9. The flow rate control valve 10 is linked to the EGR valve 4. By opening the flow rate control valve 10 when EGR valve 4 is opened, exhaust gas Gc(=Ge+Gb) which passes the EGR cooler 54 is kept at such flow rate that its dew condensation does not occur, and exhaust gas Gb other then EGR gas Ge used in EGR is returned into the exhaust passage 2 through the exhaust air return passage 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an EGR for an engine.
In the above, the EGR cooler is used to lower the temperature of the EGR gas to improve the air intake efficiency, keep the combustion of the engine good, and lower the combustion temperature to reduce the N in the exhaust gas.
The present invention relates to an EGR device with an EGR cooler that reduces Ox.

[0002]

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

In this EGR device, for example, FIG.
As shown in FIG. 3, an EGR passage 6 for diverting exhaust gas from the exhaust passage 2 of the engine 1 is connected to the intake passage 8 side to
The EGR is performed while adjusting the EGR gas amount by the EGR valve 4 provided in the R passage 6. However, when the high-temperature EGR gas is circulated to the intake side as it is, the high-temperature expanded EGR gas is supplied to the intake manifold 3, so that the ratio of the EGR gas in the cylinder at the time of intake increases. There is a problem that the amount of air entering the cylinder is reduced.

For this purpose, for example, a water-cooled EGR cooler 5 is provided in the middle of the EGR passage 6, and engine cooling water is circulated through the cooling water passage 7, and the EGR is cooled by the cooling water.
After the gas is cooled and the volume is reduced, the gas is supplied to the intake manifold 3 to secure the amount of air supplied into the cylinder.

[0005]

However, the exhaust gas of the engine contains moisture generated by combustion,
EGR cooler 5 as in winter or immediately after engine start
When the EGR gas is cold or when the operation is performed at a low EGR rate with a small amount of the EGR gas, the EGR gas is supercooled, and water vapor in the EGR gas condenses in the EGR cooler 5.

Therefore, carbon in the EGR gas is captured by the dew water generated in the EGR cooler 5,
This adheres to heat transfer tubes and forms a heat transfer resistance layer,
The efficiency of the EGR cooler 5 is reduced,
The sulfur oxides in the R gas are dissolved in the dew water to form sulfuric acid, and the EGR cooler 5, the EGR passage 6, and the engine 1
There is a problem of corrosion inside.

Further, since the dew water dissolves in the lubricating oil during the intake stroke and oxidizes the lubricating oil, there is a problem that the lubricating performance is reduced and the wear of each part is promoted. To solve this problem, JP-A-55-131556 and JP-A-55-131557 have been proposed.
Japanese Patent Application Publication No. JP-A-2005-64131 proposes a method of controlling the amount of cooling water circulating to an EGR cooler to keep the EGR gas temperature within a certain temperature range. However, since the specific heat of water is significantly larger than the specific heat of the gas, It is very difficult to precisely control the cooling temperature of the EGR gas by controlling the flow rate of water, and the temperature of the EGR gas after cooling fluctuates. Therefore, the EGR gas cooled to an appropriate temperature while preventing dew condensation in the EGR cooler. There is a problem that it is difficult to stably supply the gas into the cylinder.

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 allow an EGR device of an engine to flow an amount of non-condensing EGR cooler, that is, a larger amount of exhaust gas than the amount of EGR gas. Accordingly, it is an object of the present invention to provide an EGR cooler and an EGR device with an EGR cooler that can improve the durability of an EGR passage and, further, the engine by preventing dew condensation in the EGR cooler which causes sulfuric acid corrosion and carbon adhesion. .

[0009]

An EGR device with an EGR cooler for achieving the above object is provided with an EGR cooler and an EGR valve in series from an upstream in an EGR passage of an engine having the EGR device, The EGR
E between the cooler and the EGR valve and the EGR passage.
An EGR device in which an exhaust gas return passage having a flow rate control valve is connected between the exhaust gas passage downstream of a GR gas inlet and an exhaust gas return passage, the amount of which can maintain an exhaust gas temperature downstream of the EGR cooler at a dew point temperature or more during EGR. Opening and closing the flow control valve in cooperation with the EGR valve so that exhaust gas passes through the EGR cooler and exhaust gas other than EGR gas for EGR is returned to the exhaust passage via the exhaust return passage. The flow rate control valve adjusts the amount of EGR gas passing through the EGR cooler, and the EGR rate can be adjusted by the EGR valve.

Further, exhaust gas temperature detecting means is provided downstream of the EGR cooler, and the flow rate control valve is controlled by the detected temperature of the detecting means, thereby enabling more precise adjustment of the exhaust gas temperature. . Further, an exhaust throttle valve is provided between an EGR gas inlet of the EGR passage and a junction of the exhaust return passage to the exhaust passage, and a pressure difference between the EGR gas inlet and the junction is reduced. The exhaust gas is made larger so as to promote the return of the exhaust gas in the exhaust return passage.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, an exhaust passage 2 such as an exhaust manifold 2a or an exhaust pipe 2b of the engine 1 and an intake passage 8 are connected by an EGR passage 6, and the EGR cooler 5 and the EGR valve are sequentially connected to the EGR passage 6 from the upstream. 4 are provided in series. This EGR cooler 5 has a cooling water passage 7
Is provided to circulate the cooling water of the engine 1 to cool the exhaust gas.

An exhaust return passage 9 connects between the EGR cooler 5 and the EGR valve 4 and the exhaust passage 2 downstream of the EGR gas inlet 21 of the EGR passage 6. A flow control valve 10 is provided. When the flow rate control valve 10 is linked with the EGR valve 4, the flow rate control valve 10 is opened when the EGR valve 4 is opened, so that the exhaust gas Gc (= Ge + Gb) passing through the EGR cooler 5 is increased to a flow rate that does not always cause dew condensation. While keeping the EGR gas Ge used for EGR
The exhaust gas Gb is supplied to the intake passage 8 through the R valve 4, and the other exhaust gas Gb is returned to the exhaust passage 2 via the exhaust return passage 9.

Further, the EGR on the downstream side of the EGR cooler 5
A temperature detecting means 15 using a temperature sensor such as a thermocouple for detecting the gas temperature is provided near the outlet of the EGR cooler 5 or in the EGR passage 6 on the downstream side.
The flow control valve 10 is configured to open and close according to the gas temperature to adjust the valve opening. The control of the flow rate control valve 10 based on the exhaust gas temperature is performed, for example, when the EGR gas temperature downstream of the EGR cooler 5 is a predetermined set value which is a temperature at which dew condensation can be prevented by experiment, measurement, calculation, or the like. The control can be performed by increasing the opening and, if it is larger than the set value, reducing the valve opening.

An exhaust throttle valve 11 is provided between an EGR gas inlet 21 where the EGR passage 6 branches from the exhaust passage 2 and a junction 22 where the exhaust return passage 9 joins the exhaust passage 2.
The pressure difference between the EGR gas inlet 21 and the junction 22 is increased so that the return exhaust gas Gb in the exhaust return passage 2 flows smoothly toward the exhaust passage 2. According to the EGR device with an EGR cooler having such a configuration, the following effects can be obtained.

[0015] E at an EGR rate corresponding to the operating condition of the engine.
When performing GR, the amount of EGR gas G fed into the intake passage 8
Since e can be adjusted by the EGR valve 4 and the amount of exhaust gas Gb returning to the exhaust return passage 9 can be adjusted by the flow control valve 10, the EGR cooler 5 is controlled by controlling the flow control valve 10 in cooperation with the EGR valve 4. G of exhaust gas passing through
Since c = Ge + Gb can be adjusted independently of the EGR rate, the exhaust gas amount Gc that can maintain the exhaust gas temperature after passing through the EGR cooler 5 at or above the dew point temperature can flow to the EGR cooler 5.

That is, even when the EGR is performed at a low EGR rate, that is, in an operation region where the EGR gas is supercooled and dew condensation is likely to occur, the valve opening of the flow control valve 10 is increased and the EGR is performed.
By increasing the amount of exhaust gas Gc passing through the cooler 5, the temperature of the exhaust gas inside and downstream of the EGR cooler 5 can be increased and maintained at or above its dew point temperature. Therefore,
Since the condensation of water vapor in the exhaust gas in the EGR cooler 5 and on the downstream side can be prevented, sulfuric acid corrosion generated by dissolving sulfur oxides in the exhaust gas in the condensed water can also be prevented.
The durability of the R cooler 5, the EGR passage 6, and the engine 1 can be improved. Further, since it is possible to prevent the dew condensation water from capturing the carbon in the exhaust gas and attaching the carbon to the heat transfer tube in the EGR cooler 5 to form a heat transfer resistance layer, it is possible to prevent a decrease in cooling efficiency.

In particular, when applied to a diesel engine, due to the nature of the fuel oil, moisture and sulfur contents are inevitable and sulfuric acid corrosion and generation of carbon during combustion are large, which is more effective. Also, regarding the warm-up of the engine, the water-cooled E
If the cooling water temperature of the GR cooler 5 is too low to suspend EGR, the EGR valve 4 is closed and the exhaust throttle valve is closed.
When the exhaust gas Gc passes through the EGR cooler 5 and the cooling water can be warmed by opening the flow rate control valve 10 by restricting the throttle 11, the warm-up of the engine can be promoted.

Further, even when the temperature of the cooling water rises and EGR is performed, the amount of exhaust gas G passing through the EGR cooler 5 is increased.
By increasing c in the normal operation and increasing the EGR gas temperature on the downstream side of the EGR cooler 5 in the normal operation, the engine parts such as the intake manifold 3 and the cylinder head and the piston, whose temperature has not yet increased, are warmed. Therefore, the warm-up performance can be further improved.

Further, by controlling the flow rate control valve 10 by employing feedback control or the like using the exhaust gas temperature as an input, the amount of the returned exhaust gas is accurately adjusted, and the temperature of the exhaust gas after passing through the EGR cooler 5 is adjusted. Can be adjusted accurately, and EGR gas cooled to an appropriate temperature can be supplied while preventing dew condensation of exhaust gas. Besides, EG
Since the exhaust throttle valve 11 is provided between the EGR gas inlet 21 of the R passage 6 and the junction 22 where the exhaust return passage 9 joins, the E
The pressure difference between the GR gas inlet 21 and the junction 22 can be increased, and the flow of the return exhaust gas Gb in the exhaust return passage 2 can flow smoothly toward the exhaust passage 2.

As shown in FIG. 2, when the present invention is applied to the turbocharged engine 1, there is a large pressure difference between the upstream and downstream of the turbine 12. Since there is no need to generate a pressure difference, the exhaust throttle valve 11 becomes unnecessary. Also, the exhaust throttle valve 11
Instead of providing the exhaust return passage 9 as shown in FIG.
Is formed by a nozzle 13 opened downstream in the exhaust passage 2, and the exhaust gas G is returned by the gas flow in the exhaust passage 2.
4, a venturi 14 is provided on the exhaust passage 2 side of the junction 22 where the exhaust return passage 9 joins as shown in FIG. 4, and the return exhaust gas Gb is sucked at a low pressure portion generated by the venturi 14. The flow of returning the return exhaust gas Gb to the exhaust passage 2 may be promoted by using a structure that can perform the return.

[0021]

EGR with EGR cooler according to the present invention
According to the device, the following effects can be obtained.
Since the exhaust gas return passage is provided and a part of the exhaust gas passing through the EGR cooler is returned to the exhaust passage side, an amount by which the temperature of the exhaust gas after passing through the EGR cooler can be maintained at the dew point temperature or higher, that is, EGR Since an amount of exhaust gas larger than the amount of gas can flow to the EGR cooler, dew condensation can be prevented. Therefore, sulfuric acid corrosion due to dew condensation and carbon adhesion to the heat transfer tube can be prevented, so that the durability of the EGR cooler and the like can be improved, and a decrease in cooling efficiency can be prevented.

Next, when the engine is warmed up, the EGR
Since the cooling water can be warmed by passing the amount of exhaust gas through the EGR cooler before the start, and each part of the engine can be warmed immediately after the start of EGR by passing a larger amount of exhaust gas than during normal operation. Warm-up performance can be improved. Further, by configuring the flow rate control valve 10 to be controlled at the exhaust gas temperature on the downstream side of the EGR cooler 5, it is possible to accurately adjust the flow rates of the return exhaust gas and the exhaust gas passing through the EGR cooler. EGR gas cooled to an appropriate temperature can be supplied while preventing dew condensation, and low NOx and good engine combustion can be performed.

By providing an exhaust throttle valve between the EGR gas inlet of the EGR passage and the junction of the exhaust return passage to the exhaust passage, the pressure difference between the EGR gas inlet and the junction is increased. Therefore, the return exhaust gas in the exhaust return passage can be promoted to flow toward the exhaust passage.

[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 configuration diagram of an EGR device when the present invention is applied to a turbocharged engine.

FIG. 3 is a view E showing an example of a junction of an exhaust return passage according to the present invention;
FIG. 2 is a partial view of a configuration of a GR device.

FIG. 4 is a partial view of the configuration of an EGR device showing another example of the junction of the exhaust return passage of the present invention.

FIG. 5 is a configuration diagram of an EGR device showing a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Exhaust passage 2a ... Exhaust manifold 2b ... Exhaust pipe 3 ... Intake manifold 4 ... EGR valve 5 ... EGR cooler 6 ... EGR passage 7 ... Cooling water passage 8 ... Intake passage 9 ... Exhaust return passage 10 ... Flow control valve 11 ... exhaust throttle valve 12 ... turbine 13 ... nozzle 14 ... venturi 15 ... temperature detecting means (temperature sensor) 21 ... EGR gas inlet 22 ... junction A ... fresh air G ... exhaust gas Gc ... exhaust gas passing through the EGR cooler Gb ... Return exhaust gas Ge: EGR exhaust gas

Claims (3)

[Claims] An EGR cooler and an EGR valve are provided in series in an EGR passage of an engine having an EGR device in order from an upstream, and between an EGR cooler and the EGR valve and from an EGR gas inlet of the EGR passage. An EGR device connected to the downstream exhaust passage by an exhaust return passage having a flow control valve, the exhaust gas being supplied to the EGR in such an amount that the exhaust gas temperature downstream of the EGR cooler can be maintained at a dew point temperature or higher during EGR. Let it pass through the cooler and
An EGR device with an EGR cooler that controls opening and closing of the flow control valve in cooperation with the EGR valve so that exhaust gas other than EGR gas for GR is returned to the exhaust passage via the exhaust return passage. 2. An EGR device with an EGR cooler according to claim 1, wherein exhaust gas temperature detecting means is provided downstream of said EGR cooler, and said flow rate control valve is controlled by a temperature detected by said detecting means. 3. An EGR gas inlet portion of the EGR passage,
An exhaust throttle valve is provided between the exhaust passage and a junction of the exhaust return passage, and a pressure difference between the EGR gas inlet and the junction is increased to reduce exhaust gas in the exhaust return passage. 3. The method as claimed in claim 1, wherein the return of the air is promoted.
An EGR device with an EGR cooler as described.