JPS5865926A - Purifying system of exhaust gas - Google Patents

Abstract

PURPOSE:To largely improve purifying performance of HC and CO almost without worsening the purifying performance of Nox, by controlling air-fuel ratio of exhaust gas to a lean side from logical air-fuel ratio when the temperature of exhaust gas is less than a prescribed value. CONSTITUTION:A thermocouple 8 is provided to a catalytic inlet part of a catalytic converter 4 connected to an exhaust pipe 1, and temperature detected by the thermocouple 8 is also relayed by a temperature controller 80, then a signal is fed to a solenoid valve 7 provided in an air supply pipe 5, thus supply of air from an air pump 10 is on-off controlled. Fuel is fed to an engine 13 from a fuel injection valve 12 controlled by a computer 11. When temperature of exhaust gas is less than a prescribed value, the air-fuel ratio is controlled to a lean side from logical air-fuel ratio, while controlled to the logical air-fuel ratio when the temperature of exhaust gas is at prescribed temperature or more.

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to improve the exhaust gas purification performance in an automobile exhaust gas purification system using a three-way catalyst.

Catalytic converter and oxygen concentration detection device in exhaust gas passage? 't is provided and the air-fuel ratio is controlled to achieve HO and OQ.

Conventionally, in a three-way catalyst type exhaust gas purification system that simultaneously purifies the emission components of NOx, 7. Oxygen sensors such as rOz sensor, tie sensor, etc. detect the cumulative concentration of acid in the exhaust gas and feed the result to the intake system, changing the air-fuel ratio of the air-fuel mixture supplied to the engine into a false air-fuel ratio. Some methods are used to rich match the engine and introduce air into the exhaust gas using an air pump or air suction valve upstream of the catalyst to control the secondary air-fuel ratio to the stoichiometric air-fuel ratio. Ta.

In this way, in conventional systems, the catalyst is used in an atmosphere with a stoichiometric air-fuel ratio, but in this case, as shown in Figure 1, the purification temperature characteristics are Immediately before, the crystallinity was about 230-240"C, NOx purification started at about 210-220"C, and both were about 32"C.
Equilibrium is finally reached at 0°C, and the purification performance is low in wet discharge areas such as cold starts.

Recently, there has been a lot of concern about 3V in various countries regarding exhaust gas purification.
There is a demand for a purification system with improved purification performance.

In view of the above-mentioned circumstances, the inventors conducted a divine experiment with the aim of meeting the above-mentioned demands.

Figures 2 to 4 show He (Figure 2) when the air-fuel ratio of the mixture supplied to the engine is increased, that is, made lean.
, ao (Fig. 3, 1), and No. (Fig. 4). In the figure, the numbers attached to each performance curve indicate the air-fuel ratio. As can be seen from the figure, when the engine characteristics are tilted toward the lean side, the hot water purification performance for HOlOO is 8! This is significantly improved compared to the case of the stoichiometric air-fuel ratio (145 in this experiment). In addition, since NOx also oxidizes at low temperatures, the fan ffL of the catalyst itself increases, and the purification start temperature becomes lower than in the stoichiometric air/fuel situation. However, as the temperature rises, the purification performance of any emission component becomes better at the stoichiometric air-fuel ratio.

Next, from the 5th operator to the 7th figure, air is pumped in just before the catalyst.
j1 who gave the secondary sky light and lean the L hak! .

) HO (5th NM), ao (Fig. 6), NOX (
This shows the purification performance of No. 7f, i). When the engine characteristics were set to lean gamma, almost the same slope of ff was obtained by 1M, and the purification performance of rHo, 00, and NOx was better as the tank was raised.

So, what are the benefits in the low/crystalline region when in a lean state, and theory 2! Combining the merits of the fuel ratio in the high temperature range with the fuel ratio factor L7, we investigated this method for the furnace, and obtained the results shown in Figure 8.

The eighth river has a catalyst temperature of 300 °C! Under 'J, air is introduced into the exhaust passage (the air-fuel ratio is leaner than C (1
+16.0) K, 300'C or higher, the air width is stopped and the stoichiometric air-fuel ratio is achieved. This shows the purification rate of each emission component. Ho, the purification performance has been greatly improved at temperatures below 300°C, resulting in an overall purification performance Q! ' Ir has improved greatly.

NOx was slightly higher, but it decreased.

Next, in order not to reduce the NOx purification performance, the temperature at which air introduction is stopped +1- is set to 250"C, and below 250°C, air is introduced to reduce the air-fuel ratio to approximately 16, OK,
Above 250'C, the stoichiometric air-fuel ratio is set to ff (shown in Figure 9. When compared with the experimental results in Figure 8, Ho, 00 decreases once at around 260°C. However, as a whole, in the case of Figure 1 The purification performance is significantly better than that of the NO.
X is HO.

This is better than the case shown in Figure 8 because the CO is combusted in a curved manner. From the experimental results shown in FIGS. 8 and 9, it can be seen that a purification performance similar to a combination of the purification curve of the lean state and the purification curve of the stoichiometric air-fuel ratio can be obtained at the temperature at which the introduction of draft air is stopped.

Furthermore, Fig. 10 shows the outline of the exhaust system used in the above experiment, and the exhaust pipe consists of an exhaust pipe 1 that communicates with the engine and an exhaust pipe 2 whose length is variable. A catalytic converting pipe 6 provided with a catalyst 3 is attached. The air supply pipe 5 is provided with a solenoid valve 7, and the supply of secondary air y is controlled by a signal from a temperature sensor 8 installed upstream of the converter 4 with seven solenoid valves. An output sampling tube 9 is attached downstream of the converter 4. The purification rate in the above experiment was determined by input sampling.The absolute amount of the emission component detected by the exhaust gas analyzer row (not shown) connected to A1 output sampling pipe 9 was calculated by the input sampling test. (A-B)X when B is the absolute amount of the emission component detected by
It is 100/A (%). The experiment was conducted under engine conditions (rpm 3000 ram, intake angle -2 aommHg).
), the temperature immediately before the catalyst was changed by changing the length of the exhaust pipe 2, and the secondary air supply level was adjusted based on the signal from the temperature sensor 8.

Next, the results of running the purification system of the present invention in the US LA'4 mode on a chassis stand will be described. FIG. 11 shows the exhaust purification system used in the implementation, in which the temperature detected by a thermoelectric pair 8 installed at the catalyst inlet of the catalytic converter 4 connected to the exhaust IFL; 1 is relayed by a temperature controller 80. and a solenoid valve 7 provided in the air supply pipe 5.
Send a signal to air pump 10 (connected to 7 Umbert)
It is designed to turn on and off the air supply from the Fuel is supplied to the engine 13 by a solvent injection valve 12 controlled by a computer 11.

In the example, in a low temperature region where the catalyst input temperature is 350"C or less, air is introduced into the exhaust pipe using an air pump to control the secondary air-fuel ratio to 16,5,160,155,150, and 350°
When the temperature exceeded C, the air was cut and the air-fuel ratio was controlled to the stoichiometric air-fuel ratio.

Actual tuna example 2 In a low humidity region where the crystallinity of the catalyst is 300°C or less, air is introduced into the exhaust jn using an air pump to control the secondary air-fuel ratio to 165.16.0, 15.5.150, 30
When the temperature exceeded 0°C, air was cut to control the stoichiometric air-fuel ratio.

Example 3 In a low-temperature region where the catalyst population depletion is 250°C or less, air is introduced into the exhaust pipe using an air pump to bring the secondary air-fuel ratio to 1.
6.5.16.0.15.5.150, 250
When the temperature exceeded °C, air was added to control the stoichiometric air-fuel ratio.

The total emission values for each example are shown in the following table. For comparison, a reference example (air introduced below 370°C, 3
The stoichiometric air-fuel ratio at 70°C or higher) and the conventional example (stoichiometric air-fuel ratio regardless of temperature) are also listed.

From the results in the following table, when using the purification system of the present invention,
HOlo with almost no loss in NOx purification performance.
It can be seen that the purification performance of o can be greatly improved.

In addition, the sensor used in the system of the present invention may be a thermistor, an Io temperature sensor, a diode temperature sensor, etc. in addition to the butler pair, and the 141 catalysts are three-way catalysts, and their shape and composition may vary. is not particularly limited. Historically, a temperature of 350°C or higher for switching from the lean condition (1) to the stoichiometric air-fuel ratio is appropriate, but specifically, an appropriate temperature of 350°C or lower is selected depending on the vehicle environment. In addition, the purification performance nP can be further improved by controlling the lean state in the low and high ranges by appropriately changing the air-fuel ratio.

[Brief explanation of the drawing]

FIGS. 1 to 9 are diagrams showing experimental results regarding exhaust gas purification performance, and FIGS. 10 and 11 are system diagrams of an automobile exhaust system used in the first embodiment of the present invention, respectively. 1.2... Exhaust pipe 4... Catalytic converter 5... Air supply pipe 7... Solenoid valve 8... Temperature sensor -2・・・・・・
・Fuel injection arrangement 13...Engine 1 Figure 3 Figure 4 Figure 6

Claims (2)

[Claims] (1) A three-way catalytic converter provided in the exhaust gas passage of an automobile includes a means for detecting the degree of exhaust gas, a means for supplying air into the exhaust gas, and a means for detecting the air-fuel ratio of 1=I14 gas, When the air temperature is less than the specified value, Np
Exhaust gas purification system that controls air gas to leaner than the stoichiometric air-fuel ratio and at a predetermined temperature (↓ stoichiometry) (2) The pleasant air gas purification system according to claim 1, wherein the exhaust gas temperature at which the exhaust gas is switched from lean (TTL) to stoichiometric air is set to 350"C or lower.