JPH10238418A - Egr device with egr cooler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR device with an EGR cooler which has good durability and can prevent generation of HC white smoke, biting of sulphuric acid, and a dewing in an EGR cooler which cause deposition of carbon by preventing supercooling of EGR gas. SOLUTION: An EGR cooler 1 is disposed in an EGR passage 14 of an engine 11 provided with an EGR device. A cooling system of the EGR cooler 1 is constituted such that a pump 4 which is turned ON or OFF based on temperature of cooling water of the engine 11 and supplies the EGR cooler 1 with a refrigerant, a reserve tank 2 which can store whole of the refrigerant in the EGR cooler 1, and a heat exchanger 3 for cooling the refrigerant are provided, and the refrigerant in the EGR cooler 1 moves to the reserve tank 3 when the pump 4 stops.

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, an EGR passage for diverting exhaust gas from an engine exhaust passage is connected to an intake passage side, and EGR is performed while adjusting an EGR gas amount by an EGR valve provided in the EGR passage. . 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. There is a problem that the amount of air entering the interior is reduced.

[0004] Therefore, for example, a water-cooled EGR cooler is provided in the middle of the EGR passage so that engine cooling water is circulated through the cooling water passage. By supplying the air to the manifold, the amount of air supplied to the cylinder is secured.

[0005]

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

Therefore, the carbon in the EGR gas is captured by the dew water generated in the EGR cooler, and adheres to a heat transfer tube to form a heat transfer resistance layer.
The efficiency of the R cooler is reduced, and the sulfur oxides in the EGR gas dissolve in the dew condensation water to produce sulfuric acid.
There is a problem that the GR cooler, the EGR passage and the inside of the engine are corroded.

When the corrosion progresses and the heat transfer pipe of the EGR cooler is damaged, the cooling water leaks to the EGR gas side,
When sucked into the cylinder and mixed with the lubricating oil, poor lubrication may occur, or when a large amount of leakage occurs, the worst case may be damage to the engine by a water hammer. In addition, since dew condensation water is mixed into the lubricating oil during the intake stroke to oxidize the lubricating oil, there is a problem that the lubricating performance is reduced and wear of various parts is accelerated. When the gas is cooled, there is also a problem that the combustion temperature is lowered and a large amount of HC white smoke is generated.

In order to solve these problems, Japanese Patent Laid-Open No.
JP-131556 and JP-A-55-131557 disclose EGR.
A method has been proposed in which the amount of cooling water circulated to the cooler is controlled to keep the EGR gas temperature within a certain temperature range. However, since the cooling water is always filled in the EGR cooler, it is necessary to avoid cooling during startup. Therefore, there is a problem that dew condensation and generation of HC white smoke in the EGR cooler cannot be prevented.

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 EGR device for an engine that can control the cooling of EGR gas with high accuracy.
EGR even when the engine coolant temperature is low, such as when starting
An EG with an EGR cooler with good durability that can prevent supercooling of gas and prevent dew condensation inside the EGR cooler which causes HC white smoke, sulfuric acid corrosion and carbon adhesion.
R device.

[0010]

In order to achieve the above object, an EGR device with an EGR cooler is provided with an EGR cooler in an EGR passage of an engine provided with the EGR device. ON / OFF operation based on the cooling water temperature of the EG
A pump for supplying a refrigerant to the R cooler, a reserve tank capable of storing all of the refrigerant in the EGR cooler, and a heat exchanger for cooling the refrigerant, wherein when the pump stops, the inside of the EGR cooler is The refrigerant is configured to move to the reserve tank.
The temperature of the EGR gas passing through the R cooler can be adjusted according to the state of the engine.

[0011] Further, by providing a branch passage for the refrigerant bypassing the heat exchanger and providing a thermostat or a switching valve which switches according to the refrigerant temperature at the branch point,
More precise adjustment of the exhaust gas temperature becomes possible. Further, the rotation speed of the pump is controlled so that the temperature of the refrigerant passing through the EGR cooler is constant, so that the EGR gas temperature can be adjusted more precisely.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, an exhaust passage 12 such as an exhaust manifold and an exhaust pipe of an engine 11 and an intake passage 13 are provided.
Are connected by an EGR passage 14, and EG is connected to the EGR passage 14.
The R cooler 1 and the EGR valve 15 are provided in series.

The EGR cooler 1 is provided with a dedicated cooling system independent of the cooling water of the engine 11,
The EGR gas flowing in the R cooler 1 is cooled. This cooling system controls the temperature of the engine 11 according to the cooling water temperature TW.
Pump 4 for supplying cooling water as a coolant to GR cooler 1
A reserve tank 2 for storing cooling water in the EGR cooler 1 while the pump 4 is stopped, and a heat exchanger 3 for cooling the cooling water. The pump 4 is configured to enter the reserve tank 2 via the EGR cooler 1, and further from the reserve tank 2 via the heat exchanger 3 to return to the pump 4.

That is, while the water pump 4 is operating, as shown in FIG. 2, the cooling water, which is the refrigerant of the EGR cooler 1, is drawn from the reserve tank 2 into the pipe 23 by the operation of the water pump 4 and heat exchange is performed. After being supplied to the radiator 3 and cooled, the water passes through the water pump 4 in the X direction via the pipe 24 and is supplied from the lower part of the EGR cooler 1 by the pipe 25 to cool the EGR gas. The air is discharged from the upper part of the cooler 1 to the pipe 26 and returns to the reserve tank 2. The piping is configured to repeat this circulation.

The pump 4 has a gap such that, for example, a vane pump, when stopped, allows water to easily move from the discharge side to the suction side due to gravity.
When the operation of the pump 4 is stopped, as shown in FIG. 3, all the cooling water in the water passage in the EGR cooler 1 flows in the Y direction through a gap such as a vane of the pump 4 by gravity and flows into the reserve tank 2. As you enter, EGR cooler 1
Is disposed above the water level 21 when the cooling water returns to the reserve tank 2, and the pump 4 is always filled with the cooling water so that the pump 4 is always filled with the water level 22 during the cooling water circulation. Arranged below.

If it is difficult for the cooling water to pass through the pump 4 and return depending on the type of the pump 4, a bypass passage connecting the EGR cooler 1 having an on-off valve (not shown) to the reserve tank 2 is provided. It is configured to return the water to the reserve tank 2 or to provide another pump that operates temporarily when the pump 4 is stopped to return the cooling water inside the EGR cooler 1 to the reserve tank 2. Is also good. In short, it is sufficient that the entire cooling water inside the EGR cooler 1 can be moved to the reserve tank 2 when the pump 4 stops, and it is not always necessary to arrange the EGR cooler 1, the reserve tank 2, and the pump 4 in order from the top. Absent.

The reserve tank 2 is provided with a pressure regulating valve 5 attached to a radiator of the engine to pressurize the inside of the cooling system to prevent boiling of the cooling water. Then, for controlling the water pump 4, the cooling water temperature TW of the engine 11 is controlled.
An engine cooling water temperature sensor 16 for measuring the temperature of the engine is provided in a cooling water passage of the engine, and its output is provided by an ECU (engine control unit) 17 which is a controller of the engine.
And the water pump 4 is controlled in accordance with the input value.

Further, in order to adjust the cooling of the EGR gas in accordance with the operating state of the engine 11, a configuration as shown in any of FIGS. In the configuration of FIG.
A branch passage 32 of a refrigerant for bypassing the cooling water is provided, and a thermostat 31 is provided at the branch point to flow cooling water to the bypass passage 32 at a low water temperature, so that the temperature TC of the cooling water passing through the EGR cooler can be controlled to be constant. With such a configuration, the heat release amount in the EGR cooler 1 is controlled. In FIG. 4, the thermostat 31 is provided at the upstream branch point of the heat exchanger 3, but may be provided at the downstream branch point.

In the configuration of FIG. 5, a switching valve 34 is provided in place of the thermostat 31 so that the value of the water temperature sensor 33 is set within a certain range within the vertical width ΔTCS of the target temperature TWA. Control the EGR cooler 1 or through the branch passage 32
The cooling water temperature TC is configured to be controlled to the target temperature TWA, and the heat release amount in the EGR cooler 1 is controlled.

In the configuration shown in FIG. 6, the rotation speed of the water pump 4 is controlled so that the temperature of the cooling water passing through the EGR cooler 1 becomes constant. A water temperature sensor 33 or 36 is provided to control the rotation speed of the water pump 4, that is, the discharge amount, so that the detection value falls within a certain range within the vertical width ΔTCS of the target temperature TWA. The temperature TC is set to the target temperature TWA, and the heat release amount in the EGR cooler 1 is controlled.

Further, as shown in FIG.
May be controlled based on the EGR gas temperature by directly measuring the EGR gas temperature by providing a gas temperature sensor 35 at the outlet side of the EGR cooler 1 instead of controlling the cooling water temperature. The operation control of the EGR device configured as described above is performed as follows. As shown in FIG. 7A, in a state A in which the engine coolant temperature TW is lower than a predetermined EGR start temperature TW1, such as immediately after engine start, the combustion temperature is low because the exhaust gas temperature is also low. Therefore, in this operation region, when EGR is performed, the combustion temperature further decreases, and a large amount of HC white smoke is generated.
Do not do.

Next, as shown in FIG. 7B, the engine coolant temperature TW is warmed up to a certain extent and the engine coolant temperature TW is higher than the EGR start temperature TW1, but is lower than the preset EGR gas cooling start temperature TW2. In the state B where
In this state B, if the EGR rate increases, the amount of HC white smoke increases, so the EGR rate is kept low. Also, cooling of the EGR gas lowers the combustion temperature and also causes an increase in HC white smoke. In addition, since the EGR rate is small and the effect of increasing the air intake efficiency by cooling the EGR gas is small, the cooling of the EGR gas is not performed. Not performed.

As shown in FIG. 7C, in a state C in which the engine has been sufficiently warmed up and the engine coolant temperature TW has become equal to or higher than the EGR gas cooling start temperature TW2, the control is performed after the engine is warmed up. In addition to increasing the rate, the water pump is turned on mainly to suppress smoke, and the cooling of the EGR gas is cooled to ensure a sufficient suction efficiency. Note that the EGR gas cooling start temperature TW2 is set to a temperature close to the cooling water temperature at which the thermostat starts operating by warming up.

FIG. 8 is a timing chart showing the operation as described above.
The transition of W indicates a state in which the water pump 4 is turned ON / OFF, and how the exhaust gas temperature and the EGR rate change over time. A, B, and C in the drawing are states A, B, and C in FIG.
Respectively. 9 and 10 show an embodiment of a flowchart for performing this control.

The flowchart of FIG.
When the engine is started, first, the water pump 4 is turned off in S1, and it is determined in next S2 whether the engine coolant temperature TW is equal to or higher than the set temperature TW2. And the water pump 4 is maintained in the OFF state. If it is the above, the process proceeds to S3, the water pump 4 is turned on, and the EGR gas is cooled with the cooling water.

FIG. 10 is an example of a flowchart relating to the control of the circulation amount of the cooling water for the EGR cooler 1, which is called repeatedly from the main control flow to control the rotation speed of the water pump. First, when started, data of the water temperature sensor is taken in S10. Next, if the difference between the cooling water temperature TC for the EGR cooler TC and the preset target temperature TCA is less than the allowable value ΔTCS in S11, the routine returns without changing the rotation speed of the water pump 4.

If it is determined in step S11 that the difference between the cooling water temperature TC and the set temperature TCA is equal to or more than the allowable value ΔTCS, the process proceeds to step S11.
Proceeding to 12, it is determined whether the cooling water temperature TC is lower or higher than the target temperature TCA. If the cooling water temperature TC is lower, the cooling water supply amount is reduced to prevent the EGR gas temperature from decreasing at S13. DOWN the number of rotations and return. On the other hand, if it is high, the number of revolutions of the water pump 4 is increased in S14 in order to prevent the rise of the EGR gas temperature by increasing the supply amount of the cooling water and return.

FIGS. 7 and 8 are schematic diagrams illustrating the concept of the basic control, and are actually more complicated because the exhaust gas temperature varies depending on the operation state. Although the control flowcharts of FIGS. 9 and 10 are also described as one of the embodiments, actually, the operation control of the engine is performed based on various data.
It becomes a complicated control flowchart.

The E with an EGR cooler having the above configuration
According to the GR device, the following effects can be obtained. When the cooling water of the engine is at a low water temperature during operation of the engine, when the pump 4 is stopped, the EGR cooler 1 and the reserve tank 2 are subjected to a pressure difference due to a vertical positional relationship between the EGR cooler 1 and the reserve tank 2.
Since all the cooling water in the water channel in the cooler 1 returns to the reserve tank 2 through the gap inside the pump 4, the inside of the EGR cooler 1 can be emptied.
R gas can be prevented from being supercooled, and sulfuric acid corrosion due to condensation of water vapor in the EGR gas 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 the cooling efficiency decreases. Can also be prevented.

In particular, when the present invention is applied to a diesel engine, it is more effective because of the nature of the fuel oil, the moisture and sulfur content are not lost, and sulfuric acid corrosion and carbon generation during combustion are large. In addition, since the cooling water of the EGR cooler 1 returns to the reserve tank 2 when the engine is stopped, even if the EGR cooler 1 is damaged, the cooling water may accumulate in the cylinder through the intake / exhaust passage while the engine is stopped. Therefore, a so-called water hammer, in which the engine is restarted with water remaining in the cylinder and the engine is damaged, can be prevented.

In addition, after the engine is warmed up, the pump 4 is driven to supply cooling water to the EGR cooler 1 so that EGR gas cooled to an appropriate temperature can be supplied. And good combustion can be obtained. Further, since the cooling water temperature of the EGR cooler 1 can be kept constant and the EGR gas at an appropriate temperature can be supplied, it is possible to perform EGR while keeping the air intake efficiency good, and to achieve low NOx and good performance. Engine combustion can be performed.

[0032]

EGR with EGR cooler according to the present invention
According to the device, the following effects can be obtained.
When the engine cooling water is at low water temperature while the engine is running,
Since the pump is stopped and the cooling water in the EGR cooler is temporarily returned to the reserve tank, and the cooling water in the EGR cooler is drained, it is possible to prevent the EGR gas from passing through and to prevent the EGR gas from being excessively cooled. It is possible to prevent sulfuric acid corrosion due to the condensation of water vapor in the EGR gas and carbon adhesion to the heat transfer tube, thereby improving the durability of the EGR cooler and the like and preventing a decrease in cooling efficiency.

Further, even when the engine is stopped, the pump is stopped and the cooling water of the EGR cooler is returned to the reserve tank so that the EG is cooled.
Since the cooling water of the R cooler is emptied, even if the EGR cooler is damaged, the cooling water is
The engine does not accumulate in the cylinder through the exhaust passage, and damage to the engine due to the water hammer can be prevented.

Further, after the engine is warmed up, the pump can be driven to supply cooling water to the EGR cooler to cool the EGR gas to an appropriate temperature, so that the efficiency of intake of air from the cylinder can be improved, and good results can be obtained. Combustion state can be maintained. In addition, since the cooling water temperature of the EGR cooler is configured to be kept within a certain range, an EGR gas having an appropriate temperature can be supplied, and EGR can be performed while maintaining good air intake efficiency. NOx can be reduced while performing combustion.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a state of a cooling water level when the water pump of the EGR cooler according to the embodiment of the present invention is stopped.

FIG. 3 is a diagram showing circulation of cooling water during operation of a water pump of the EGR cooler according to the embodiment of the present invention.

FIG. 4 is a partial configuration diagram showing a heat exchanger according to a second embodiment of the present invention.

FIG. 5 is a partial configuration diagram illustrating an EGR cooler according to a third embodiment of the present invention.

FIG. 6 is a partial configuration diagram illustrating a heat exchanger according to a fourth embodiment of the present invention.

FIGS. 7A and 7B are diagrams showing a relationship between a load, an engine speed, and an EGR rate. FIG. 7A shows a case where the engine coolant temperature is lower than TW1, and FIG. 7B shows a case where the engine coolant temperature is lower than TW2. And (c) the case where the engine coolant temperature is TW2 or more.

FIG. 8 is a timing chart showing an operation state of the water pump according to the embodiment of the present invention.

FIG. 9 is a flowchart showing on / off control of the water pump of the present invention.

FIG. 10 is a flowchart showing the control of the number of revolutions of the water pump of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... EGR cooler 2 ... Reserve tank 3 ... Heat exchanger 4 ... Water pump 5 ... Pressure regulating valve 11 ... Engine 12 ... Exhaust pipe 13 ... Intake pipe 14 ... EGR passage 15 ... EGR valve 16 ... Engine cooling water temperature sensor 17 ... ECU 21… Water level when the water pump is stopped 22… Water level when the water pump is running 31… Thermostat 32… Bypass passage 33… Water temperature sensor (EGR cooler inlet) 34… Switching valve 35… Gas temperature sensor 36… Water temperature sensor (EGR cooler outlet) G … Exhaust gas W… Cooling water

Claims (3)

[Claims] An EGR cooler is provided in an EGR passage of an engine equipped with an EGR device, and a cooling system of the EGR cooler is turned on / off based on a temperature of a cooling water of the engine to supply a refrigerant to the EGR cooler. Pump, a reserve tank capable of containing all of the refrigerant in the EGR cooler, and a heat exchanger for cooling the refrigerant, when the pump is stopped, the refrigerant in the EGR cooler is supplied to the reserve tank. An EGR device with an EGR cooler configured to move. 2. An EGR device with an EGR cooler according to claim 1, wherein a branch passage for the refrigerant bypassing the heat exchanger is provided, and a thermostat or a switching valve switched according to the refrigerant temperature is provided at the branch point. 3. The EGR cooler-equipped EGR device according to claim 1, wherein the rotation speed of the pump is controlled so that the temperature of the refrigerant passing through the EGR cooler becomes constant.