JP3259379B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for purifying NO _X in the exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art As a means for purifying NO _X in the gas discharged from an internal combustion engine such as a gasoline engine or a diesel engine, the reduction catalyst is known to be effective. These reducing catalyst has a temperature and the exhaust gas, the property of purifying ability of the NO _X changes with the content of the hydrocarbon to be added as a reducing agent (HC). Conventionally, this change in the purification rate is described as showing a mountain-shaped curve in a certain temperature range of the exhaust gas temperature. Therefore, an apparatus for controlling the exhaust gas temperature in this temperature range has been proposed. For example, Japanese Utility Model Laid-Open No. 3-49312 and Japanese Utility Model Laid-Open No. 4-769.
No. 22 discloses an apparatus for adjusting the exhaust gas temperature by providing a bypass passage in an exhaust pipe on the inlet side of a reduction catalyst.

However, it has been confirmed by various experiments that the purification characteristics of the reduction catalyst do not change with a simple mountain-shaped curve. Figure 7 is the temperature of the exhaust gas to the horizontal axis, the graph of the time taken to purification rate of the NO _X in the vertical axis, the change in the case of using one of the reduction catalyst, represented by the curve C1. That is, the region where the exhaust gas temperature is low (T ₁ )
In can be achieved relatively high purification rate, the exhaust gas temperature is entering the region T ₂ and rises, the purification rate drops indicate the trough of the curve, the area T ₃ further exhaust gas temperature rises and When this happens, the purification rate increases and shows a mountain-like curve. Then, in the higher temperature region T _4, it tends to decrease again purification rate. That is, the purification rate shows two peaks. In general, NO _X is composed of NO and NO ₂ , and it is said that most of it is NO.
The ratio of ₂ is relatively large (20-30%). 4-cylinder diesel engine provided with a NO _X catalyst, HC as a reducing agent
(Fuel / light oil) is introduced into the intake system, and NO, NO ₂ , N
As a result of measuring the purification rate of O _x (NO + NO ₂ ), 100 ° C.
It was found that even at a very low temperature (idle), a relatively high NO _x purification rate was exhibited. It is considered that this is because NO _{2 in} NO _X is decomposed or reduced, and most of the NO _X is changed to N ₂ and part of the NO is changed to NO, and the overall NO _X purification rate becomes relatively high. As the temperature rises, reduce the NO ₂ proportion in the NO _X, increasing the proportion of NO ₂ is changed to NO, 200
In the vicinity of ° C., only the increase of NO proceeds, and the total NO _X purification rate also decreases. When the temperature further rises, the majority of NO _X is occupied by NO and the NO reduction reaction proceeds, so that the total NO _X purification rate rises and reaches a maximum near 350 ° C.

[0004]

SUMMARY OF THE INVENTION Based on the above knowledge, the present invention provides a purification apparatus having a high purification rate over a wide temperature range of exhaust gas.

[0005]

An exhaust gas purifying apparatus according to the present invention comprises a first pipe and a second pipe formed by branching a catalyst provided in an exhaust pipe and an exhaust pipe upstream of the catalyst. A cooler provided in the first pipe, a first valve and a second valve provided in the first pipe and the second pipe, and an opening of the first valve and the second valve. It has a control unit to control the degree.

[0006]

The control unit controls the temperature of the exhaust gas flowing into the catalyst in accordance with the temperature of the exhaust gas and the operating condition of the internal combustion engine to optimize the purification rate.

[0007]

FIG. 1 is an explanatory view showing an embodiment of the present invention.
The internal combustion engine 10 has an intake pipe 12 and an exhaust pipe 14 and discharges combustion gas to the exhaust pipe 14 side. An intake pipe 12 is provided with an injector 200 for adding a reducing agent to the intake air.
H as a reducing agent via a pump 210 and a line 220
Receive C supply. The control unit 100 receives information on the engine speed Ne via the line 114 and information on the engine load L via the line 113, and outputs the information to the line 230 based on the information to output the reducing agent of the injector 200. Control the amount added.

The exhaust pipe 14 branches into two pipes 20 and 22. The first pipe 20 is provided with a first valve 51,
A cooler 70 is provided in a pipe on the outlet side of the first valve 51. The cooler cools the exhaust gas introduced by heat exchange. A second valve 61 is provided in the middle of the second conduit 22. The two pipes 20 and 22 are gathered again into one pipe 26, and a reduction catalyst 40 is provided in the pipe 26. The first valve 51 is operated by an actuator 52, and the actuator 52 is driven by a negative pressure supplied from a vacuum source 80 via an electromagnetic valve 53. Similarly, the second valve 61 is operated by an actuator 62, and the actuator 62 is driven by a negative pressure from a vacuum source 80 communicated via an electromagnetic valve 63. A temperature sensor 110 is provided in the conduit 26 at the inlet of the catalyst 40, detects the temperature of exhaust gas at the inlet of the catalyst 40, and sends the detected temperature to the control unit 100 via the line 112. The control unit 100 outputs to the lines 121 and 122 according to the exhaust gas temperature, and controls the opening and closing of the first valve 51 and the second valve 61 as shown in FIG. That, in the temperature range of T ₁ closes the first valve 51, opens the second valve 61. As a result, the exhaust gas is sent to the catalyst 40 without being cooled, and
Receive a reduction of O _X.

When the temperature of the exhaust gas rises to the region T _{2, the} region becomes a region where the purification rate of the catalyst is reduced.
1 is opened and the second valve 61 is controlled to close. Thus, the exhaust gas also flows to the cooler 70 and is cooled.
Therefore, the temperature of the exhaust gas sent to the catalyst 40 is kept low, and a region where the purification rate of the catalyst is high is used.

When the temperature region enters T ₃ , the first valve 51 is closed and the second valve 61 is opened. Thus, the exhaust gas is directly sent to the catalyst 40 without passing through the cooler. The purification rate is high in this temperature range.

[0011] Once in the temperature range T _4, since the purification rate is reduced in accordance with the increase in the exhaust temperature, to open the first valve 51, the exhaust gas temperature by controlling the direction of closing the second valve 61 catalyst Maintain a high purification rate. FIG. 5 shows the first valve 51.
And curve V ₁ illustrating the opening and closing of, a curve G ₂ showing the opening and closing of the second valve 61, a high temperature of the exhaust gas of purification rate 2
Indicates that it is controlled by one area.

FIG. 2 shows another embodiment of the present invention. In this embodiment, the temperature sensor 1 provided at the entrance of the catalyst 40
10 and the exhaust pipe 14 at the outlet of the exhaust manifold.
And a second temperature sensor 130. The temperature sensor 130 detects the exhaust gas temperature at the exhaust manifold outlet and sends it to the control unit 100 via the line 132. The control unit 100 initializes the opening degrees of the first valve 51 and the second valve 61 based on the exhaust gas temperature at the exhaust manifold outlet detected by the second temperature sensor 130, and sets the first temperature sensor 110 The opening degree of the first valve 51 and the second valve 61 is controlled using the detected exhaust gas temperature at the inlet of the catalyst 40 as feedback data. With this configuration, highly responsive temperature control can be achieved.

FIG. 3 shows still another embodiment of the present invention. In the present apparatus, the temperature sensor 110 monitors the exhaust gas temperature at the inlet of the catalyst 40, and the control unit 100 receives data of the engine speed Ne from the line 114 and sends the engine load data L to the line 113. Receive through.

FIG. 4 shows the relationship between the engine speed Ne on the horizontal axis and the load L of the engine on the vertical axis. The exhaust temperature is shown by a curve. Therefore, based on these data, the controller 100 initializes the opening of the first valve 51 and the second valve 61 based on the current value of the engine speed Ne and the current value of the load L. Temperature sensor 110
Is fed back to control the opening of the two valves. Region A ₁ in the state of light load, such as during a low exhaust gas temperature e.g. idle, the purification rate of the catalyst in this state is relatively high. Therefore, the first valve 51 is closed and the second valve 61 is opened to send the exhaust gas to the catalyst 40 without cooling.
Engine rotational speed and the load is increased, when entered the region B ₁ represents, opening the first valve 51, the second valve 61 is closed to control the direction, maintaining the exhaust gas temperature to the temperature of the region A ₁ I do. In the area A _2, since the purification rate of the catalyst is in a high region, closing the first valve 51, directly sent to the catalyst 40 of the exhaust gas by opening the second valve 61. Once in region B _2,
The first valve 51 is opened and the second valve is controlled to close so that the exhaust gas temperature is cooled. FIG. 6 shows the load L on the horizontal axis,
Shows the curve when taking exhaust gas temperature and the purification rate in the vertical axis, the exhaust gas temperature G ₁ of the exhaust manifold outlet is in the catalyst inlet is controlled as indicated by the curve G _2. As a result, the purification rate curve C1 is improved to the state shown in the curve C2.

[0015]

According to the present invention as described above, of the NO _X catalyst N
O _X purification rate characteristics, focusing to a peak at two locations of the low temperature range (idle much) and high temperature range (about medium load), the low temperature region when the temperature range of the low-temperature or high-temperature or less, the high-temperature In the above case, the exhaust gas temperature is cooled to a high temperature range, thereby always achieving a high purification rate in the entire range. Since the low temperature range is a temperature near idle, there is no lower temperature below this. Also, just always cool the exhaust or let it flow,
There is no need to raise the temperature. In order to raise the temperature, a heater and a burner are required, and power consumption and system size and complexity are unrealistic. In the present invention, since the exhaust gas only needs to be cooled, for example, an aluminum pipe having a radiation fin alone is sufficiently effective. Therefore, the device can be simplified.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an embodiment of the present invention.

FIG. 3 is an explanatory view of an embodiment of the present invention.

FIG. 4 is a graph showing an operation.

FIG. 5 is a graph showing an operation.

FIG. 6 is a graph showing an operation.

FIG. 7 is a graph showing characteristics of a reduction catalyst.

[Explanation of symbols]

 Reference Signs List 10 internal combustion engine 14 exhaust pipe 20 first branch pipe 22 second branch pipe 40 catalyst 51 first valve 61 second valve 70 cooler 80 vacuum source 100 control unit 110 temperature sensor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F01N 3/08-3/24

Claims (1)

(57) [Claims] 1. A catalyst provided in an exhaust pipe, a first pipe and a second pipe formed by branching an exhaust pipe upstream of the catalyst, and a cooler provided in the first pipe. , a first valve and a second valve provided in the first conduit and the second conduit, touch
A temperature sensor provided in the conduit at the inlet of the medium and an engine
Engine speed, engine load and temperature sensor data.
There are, a control unit for controlling the opening of the first and second valves, the control unit ene
The first valve and the second valve based on the engine speed and the engine load.
The opening degree of the second valve is initially set, and the purification rate characteristic of the catalyst is the first.
Close the first valve in the peak exhaust temperature range
Opening the second valve, the exhaust gas temperature at which the purification rate characteristic of the catalyst decreases
In the area of, the first valve is opened and the second valve is closed to purify the catalyst.
In the region where the exhaust gas temperature is high where the
An exhaust gas purification device for an internal combustion engine that performs control to close a first valve and open a second valve .