JPH06173666A - Exhaust gas purifying device of internal combustion engine - Google Patents

Abstract

PURPOSE:To improve a purifying rate by providing a valve and a catalyst in first and second passages respectively, and providing a pipe passage for connecting the inlet part of the catalyst of the first pipe passage to the outlet part of the catalyst of the second passage, and selectively opening/closing two valves and serially and parallelly forming the two catalyst. CONSTITUTION:An exhaust pipe 14 is branched into first and second pipe passages 20, 22, and a first valve 51, a first catalyst 41, a third valve 61 are provided on the pipe passage 20, and a second catalyst 42 and a second valve 71 are provided on the pipe passage 22, and then the upstream side of the first catalyst 41 and the downstream side of the second catalyst 42 are connected to each other by the pipe passage 28. The valve 51 is closed, the valve 61 is opened and the valve 71 is closed by a control unit 100 when a temperature of exhaust gas is known by the signal of a temperature sensor 110, and the catalysts 42, 41 are connected together is series. When the temperature of the exhaust gas is high, the valve 51, is opened, the valve 61 is opened and the valve 71 is opened and then the catalysts 41, 49 are connected together in parallel. Consequently, the pipe passage of the catalyst is changed over in response to the temperature of the exhaust gas, and the purifying rate is improved and then deterioration of the catalyst is prevented.

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 It is known that a reducing catalyst is effective as a means for purifying NO _X in gas discharged from an internal combustion engine such as a gasoline engine or a diesel engine. These reduction catalysts have the characteristic that the NO _x purification capacity changes depending on the temperature of the exhaust gas and the content ratio of hydrocarbon (HC) added as a reducing agent. Conventionally, it has been described that the change of the purification rate shows a mountain-shaped curve in a certain temperature range of the exhaust gas temperature, and therefore, a device for controlling the exhaust gas temperature in this temperature range has been proposed. For example, Japanese Unexamined Patent Publication No. 60-198318 discloses a device for adjusting an exhaust gas temperature by providing a bypass passage in an exhaust pipe on an inlet side of a reduction catalyst, and Japanese Unexamined Patent Publication No. 4-175416 discloses a device in which catalysts are arranged in parallel. An apparatus has been proposed in which the catalyst is used alternately when the exhaust gas temperature is high. However, it has been confirmed by various experiments that the purification characteristics of the reduction catalyst do not change with a simple mountain curve. In FIG. 3, the horizontal axis indicates the temperature of exhaust gas and the vertical axis indicates N.
In the graph when taking purification rate of O _X, the change in the case of using one of the reduction catalyst, represented by the curve C _1. That is, although a relatively high purification rate can be achieved in the region where the exhaust gas temperature is low (T ₁ ), the exhaust gas temperature rises and the region T ₂ increases.
When it enters, the purification rate decreases to show a valley curve, and when the exhaust gas temperature rises to the region T ₃ , the purification rate increases and shows a mountain curve. Then, in the temperature region T ₄ higher than that, the purification rate tends to decrease again. Figure 3
Curve C ₂ shows the change in the purification rate when two catalysts are arranged in series. That is, in the regions T ₁ , T ₂ and T ₃ where the exhaust gas temperature is low or medium, the purification rate is higher when two catalysts are used in series than when one is used in series, but in the high temperature region T _On the contrary, in the case of ₄ , the purification rate of one catalyst is higher. This in exhaust gas contacts with prolonged catalyst at a high temperature, a reaction of NO _X. NO → N ₂ + O ₂ (reduction) (1) NO ← NO ₂ (repetition of oxidation / reduction) Among (2), the proportion of (2) increases at high temperature and the purification rate rather decreases. it is conceivable that.

[0004]

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

[0005]

An exhaust gas purifying apparatus of the present invention is provided with a first valve and a first catalyst provided in a first pipe branching into an exhaust pipe, and a second pipe. A second catalyst and a second valve, a pipe line connecting the inlet of the first catalyst and the outlet of the second catalyst, and two valves are selectively opened and closed to connect the two catalysts in series or A control unit formed in parallel is provided.

[0006]

The control unit optimizes the purification rate by using the catalysts in series or in parallel according to the exhaust gas temperature and the operating condition of the internal combustion engine.

[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. The exhaust pipe 14 branches into two pipe lines 20 and 22. A first valve 51 is provided in the first conduit 20, and a first catalyst 41 is provided in the conduit 24 on the outlet side of the first valve 51. A third valve 61 is provided in the conduit 30 leading to the outlet of the first catalyst 41,
The outlet side of the valve 61 communicates with the atmosphere side. Second conduit 22
The second catalyst 42 is provided in the middle of the
A second valve 71 is provided in the conduit 26 on the outlet side of the. The outlet side of the second valve 71 communicates with the atmosphere side.

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 third valve 61 is also operated by the actuator 62, and the actuator 62 is driven by the negative pressure from the vacuum source 80 communicated via the electromagnetic valve 63. The second valve 71 is similarly operated by the actuator 72, and the actuator 72 is driven by the negative pressure from the vacuum source 80 communicated via the potential valve 73. Further, the pipeline 24 on the upstream side of the first catalyst 41 and the pipeline 26 on the downstream side of the second catalyst 42 are connected by a pipeline 28.

The control unit 100 receives the load information L of the internal combustion engine via the line 113 and the rotational speed information Ne of the internal combustion engine via the line 114. In addition, the temperature sensor 110 provided in the exhaust pipe 14 includes the catalysts 41, 42.
The exhaust gas temperature on the upstream side of is detected and sent to the control unit 100 via the line 112. The control unit 100 controls the solenoid valves 53, 63, 73 via the lines 121, 122, 123 to control the valves 51, 61,
Open and close 71.

Since this device is constructed as described above,
When the exhaust gas temperature detected by the temperature sensor 110 is lower than the region T ₃ , the control unit 100 makes the first
The valve 51 is closed, the third valve 61 is opened, and the second valve 71 is closed. Thereby, the exhaust gas of the exhaust pipe 14 is
It is sent from the conduit 22 along the flow paths of the second catalyst 42, the conduit 26, the conduit 28, the first catalyst 41, the conduit 30, and the second valve 61. Therefore, the exhaust gas is generated by the two catalysts 41, 4
It passes through 2 in series and undergoes reduction. Now, assuming that the purification rate of one catalyst is A%, the purification rate in the case of series is (A / 100) + ((1- (A / 100)) × A / 10
0 = (2A / 100) - is represented by (A ^2/10000).

As shown in FIG. 3, in a region where the exhaust gas temperature is lower than the temperature region T ₃ , using two catalysts in series results in a longer contact time between the gas and the catalyst, which promotes the reaction. Is like. Next, when the sensor 110 detects that the exhaust gas temperature has reached such a high temperature as to reach the region T ₄ , the control unit 100 opens the first valve 51, opens the third valve 61, and opens the second valve 61. The valve 71 is controlled to open. As a result, the exhaust gas flows in parallel with the first catalyst 41 and the second catalyst 42. At high temperatures, the contact time of the gas with the catalyst is shortened to prevent the catalyst from changing.

The purification rate at this time is (1/2) × (A / 100) + (1/2) × (A / 10
0) = A / 100. In addition to the exhaust gas temperature, as shown in FIG. 2, the engine speed Ne and the load L are plotted on the horizontal axis and the vertical axis. You may connect in series in a small area | region and in parallel in a high area | region. The third valve 61 and its drive mechanism can be omitted.

[0013]

As described above, according to the present invention, the exhaust pipe of the internal combustion engine is divided into two parts, the reduction catalyst is arranged in each branch pipe, and the valve provided in the pipe line is switched to use the catalyst in series. Or configured to be used in parallel. When the exhaust gas temperature is below the middle temperature, the catalyst is used in series to improve the purification rate. In a region where the gas temperature is high, the catalysts are used in parallel to shorten the contact time between the gas and the catalyst, prevent the catalyst from deteriorating, and mitigate the tendency of the purification rate to decrease.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing an operation.

FIG. 3 is a graph showing the effect.

[Explanation of symbols]

 10 Internal Combustion Engine 14 Exhaust Pipe 20 First Branch Pipe 22 Second Branch Pipe 41 First Catalyst 42 Second Catalyst 51 First Valve 61 Third Valve 71 Second Valve 80 Vacuum Source 100 Control Unit 110 Temperature sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location F01N 3/28 301 H

Claims (3)

[Claims] 1. A first valve and a first catalyst provided in a first conduit branched from an exhaust pipe, a second catalyst and a second valve provided in a second conduit, and a first valve. Internal combustion engine comprising: a pipe line connecting an inlet part of the catalyst and an outlet part of the second catalyst; and a control unit for selectively opening and closing two valves to form two catalysts in series or in parallel. Exhaust gas purification device. 2. An exhaust gas purification system for an internal combustion engine according to claim 1, further comprising a temperature sensor provided in the exhaust pipe, and a control unit which outputs a signal for operating each valve by using data from the temperature sensor as an input signal. apparatus. 3. The exhaust gas system for an internal combustion engine according to claim 1, further comprising a control unit which outputs a signal for operating each valve by using a rotation speed and a load of the internal combustion engine as input signals.