KR100332079B1 - Apparatus for catalytic exhaust gas cleaning - Google Patents

Abstract

A first three-stage catalytic converter 4 disposed upstream of the engine 1, a hydrocarbon trap 7 disposed at a predetermined distance from a point immediately downstream of the three-stage catalytic converter 4, And a second catalytic converter (9) arranged in relation to the first catalytic converter (7). According to the present invention, since the time t _d elapsing from the start of the engine 1 to the start of the departure from the hydrocarbon trap 7 is equal to the time t _d from the start of the engine 1 to the first catalytic converter 4 (X) between the first catalytic converter (4) and the hydrocarbon trap (7) is selected to be equal to or greater than the time (t _ign ) that elapses until the temperature is ignited.

Description

TECHNICAL FIELD [0001] The present invention relates to a catalytic exhaust gas purifying apparatus,

Modern vehicles often incorporate catalytic converters for exhaust gas purification of vehicles. In general, modern catalytic converters can not fully exhibit their purifying capability during cold start of the vehicle. Thus, such an electric converter can be additionally provided with an electric-heated converter, that is, a starter converter disposed upstream of the regular converter. By electrically heating the starter converter during start-up of the engine, the warming time of the regular converter is reduced, and as a result, the purification effect is improved. This kind of device is disclosed in Swedish Patent Application No. 9100541-3.

From the contaminants (mainly HC-based, NO _x type, CO-based contaminants) discharged from an engine, there are many, especially emissions of HC-based contaminants immediately after engine starting. For this reason, it is known to use so-called " hydrocarbon traps " that can be placed in the exhaust system between the engine and the regular catalytic converter. The hydrocarbon traps, which may be made of zeolite material, can adsorb, or " recover, " HC-based contaminants discharged from the engine until the normal converter reaches its normal operating temperature and is capable of full purification capability.

If the temperature of the exhaust stream and the temperature in the resulting hydrocarbon trap exceeds a predetermined limit, the hydrocarbon trap will release (desorb) the HC compound recovered earlier. In this way, the emission of harmful HC-based compounds can be reduced even in the preheating stage, in which the temperature of the subsequent converter is too low to achieve optimal purification performance. A typical three-way catalytic converter is disposed downstream of the hydrocarbon trap to remove desorbed HC-based compounds.

The present invention relates to a catalytic converter comprising a first three-way catalytic converter disposed in the downstream of an internal combustion engine and a hydrocarbon trap disposed at a predetermined distance from a downstream point immediately after the first three- the present invention relates to a catalytic exhaust gas purification apparatus for an internal combustion engine having a hydrocarbon trap.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a preferred embodiment of an apparatus according to the present invention; FIG.

The present invention is particularly directed to a catalytic converter connected to a vehicle, termed a "tail conduit", comprising a conventional three-way catalytic converter in combination with an electrically heated starter converter and a hydrocarbon trap Respectively. A device in which a three-way catalytic converter is disposed downstream of the engine has already been disclosed in European Patent No. 48517 (see Fig. 1 (e), page 5, lines 41-48). Exhaust gas from the engine is passed through the converter to the electrically heated start converter. A second catalytic converter in the direction of Fig. 3 is disposed along the downstream in the exhaust system.

One disadvantage of the device according to EP 485179 is that it does not take into account the fact that the hydrocarbon trap should be placed at the optimum position for the regular catalytic converter so that sufficient purge capability is achieved in the exhaust system. If the distance between the regular catalytic converter and the hydrocarbon trap is short, the hydrocarbon trap is heated too rapidly to the threshold temperature at which the desorption begins. Thus, there is a risk that the regular converter will begin to desorb from the hydrocarbon trap before it is ignited (typically about 100 seconds after engine start-up), in which case HC-based compounds that are not cleaned in the normal converter nor adsorbed in the hydrocarbon trap are released.

On the other hand, if the distance between the normal converter and the hydrocarbon trap is too long, the hydrocarbon trap will reach the critical temperature very slowly. This may mean that desorption in the hydrocarbon trap occurs in an uncontrollable state.

It is an object of the present invention to improve the exhaust gas purifying ability of a vehicle by purifying a large amount of contaminants coming out of the vehicle at a time when the normal converter does not reach the normal operating temperature, particularly in connection with the room temperature starting of the vehicle. This object is achieved by a catalytic converter comprising a first catalytic converter and a second catalytic converter such that the time elapsed from the start of the engine to the occurrence of desorption to the hydrocarbon trap is greater than or equal to the time elapsed from the start of the engine until the first catalytic converter is ignited to its normal operating temperature. The distances between the traps can be selected by the device described in the introduction.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described with reference to the accompanying drawings and preferred embodiments, which show an apparatus according to the invention. The gas exhausted from the internal combustion engine 1 is led to the exhaust pipe 3 via the main pipe 2. The exhaust pipe 3 is preferably connected to the first three-way catalytic converter 4 in the normal direction.

The first catalytic converter 4 may be provided with a separate electrically-heated first starting converter 5 assembled around a support disposed within the metal casing, which is connected to a heating power source (not shown) Which acts as a resistive load. A starter converter suitable for use in the present invention is disclosed in Swedish Patent Application No. 9100541-3.

The first catalytic converter 4 reaches the normal operating temperature (" ignition temperature ") after the lapse of the predetermined time t _ign from the starting time of the internal combustion engine 1, and exhibits the optimum purifying ability. Usually, this time t _ign is about 100 seconds.

The exhaust system of the vehicle also includes a conventional muffler 6.

In addition, a hydrocarbon trap (7) with a zeolite adsorbent is disposed in the exhaust system. In connection with the hydrocarbon trap, a second start-up converter 8, which is electrically heated by a power source not shown according to the first start-up converter 5, is arranged. Downstream of the second start-up converter 8, there is disposed a second catalytic converter 9 which can be formed in the usual three directions or at least capable of removing HC-based contaminants.

The hydrocarbon trap 7 is arranged at a predetermined distance x measured along the extension of the exhaust pipe from the downstream point just after the first catalytic converter 4. [ The selection of the optimal position of the hydrocarbon trap 7, i.e. the distance x, is determined based on information relating to the temperature change in the exhaust after the internal combustion engine 1 has started. Therefore, the exhaust device is configured such that the temperature in the hydrocarbon trap 7, which rises after starting the internal combustion engine 1 by heat supply by the exhaust gas and heats the converter, is ignited by the first catalytic converter 4, The dimensions are determined on the basis of the volume and the length at which the temperature reaches the temperature at which the desorption starts, either at the moment when the operating temperature is reached or at the beginning of the desorption.

When the internal combustion engine 1 is started up and still at room temperature, the content of the HC-based compound in the exhaust gas is relatively high. Since the first catalytic converter 4 has not yet reached its normal operating temperature (which means that the initially released HC-based compound has not been removed), at this point the hydrocarbon trap 7 will release the HC- It is necessary to adsorb, or " recover "

After startup of the internal combustion engine 1, the high-temperature exhaust flow gradually increases the temperature of the exhaust system. When the temperature of the hydrocarbon trap 7 reaches a predetermined limit temperature T _d , the detachment in the hydrocarbon trap 7 starts. The critical temperature T _d depends on the material parameters of the hydrocarbon trap 7 and the engine's technical parameters such as engine temperature and exhaust flow rate. The critical temperature (T _d ) is usually about 75 ° C. If the hydrocarbon trap 7 reaches the limit temperature T _d by placing the hydrocarbon trap 7 farther from the first catalytic converter 4 (i.e., if the value of the distance x is greater) It takes a longer time.

Therefore, when the predetermined time t _d elapses after starting the internal combustion engine 1, desorption starts, and the time t _d mainly depends on the limit temperature T _d and the distance x.

When the HC-based compound starts to be desorbed from the hydrocarbon trap 7, the first catalytic converter 4 must reach the normal operating temperature and be able to purify the exhaust gas discharged thereafter by the internal combustion engine 1 do. This is because the HC-based compound discharged thereafter by the internal combustion engine 1 is not adsorbed by the hydrocarbon trap 7 (since the hydrocarbon trap 7 has already reached the limit temperature T _d to be).

The time t _ign which elapses after the start of the internal combustion engine 1 until the first catalytic converter 4 reaches the normal operating temperature is obtained as the distance x Is selected to be substantially equal to the time (t _d ) that elapses until the hydrocarbon trap (7) reaches its limit temperature (T _d ). In fact, since the first catalytic converter 4 has already started operating at this time, the time t _d may be somewhat longer than the time t _ign .

As described above, the hydrocarbon trap 7 may be disposed adjacent to the second starting converter 8. The second catalytic converter 9 is disposed adjacent to the second starting converter 8 and the HC-based compound desorbed from the hydrocarbon trap 7 after the start of desorption from the hydrocarbon trap 7 _x system and CO system pollutants). Thus, when the hydrocarbon trap 7 reaches the limit temperature T _d , the second catalytic converter 9 is necessarily ignited or, optionally, ignited as soon as possible. A temperature sensor 10 may be arranged immediately upstream of the hydrocarbon trap 7 to record the start of desorption of the hydrocarbon trap 7, which may be a thermocouple, a resistive sensing element or a bimetallic sensing element Lt; / RTI > The temperature sensor 10 can record the temperature of the exhaust flow and send inspection data in a signal format, preferably in a time relay format, to a control unit (not shown). The control unit is connected to a power source (not shown), whereby the second start converter 8 is activated when the hydrocarbon trap 7 reaches the limit temperature T _d .

The temperature sensor 10 may be disposed further upstream than the upstream point immediately before the hydrocarbon trap 7 in the exhaust system. In this case, the temperature value at which the temperature sensor 10 provides a signal to activate the second start-up converter 8 should be adjusted to a value somewhat higher than the normal limit temperature T _d . This correction is because the temperature upstream of the exhaust system is higher than the temperature at the upstream point immediately after the hydrocarbon trap 7. The advantage of this arrangement is that the temperature sensor 10 need not be connected directly to the hydrocarbon trap 7. [ Even if a temperature sensor is arranged at a predetermined distance upstream of the hydrocarbon trap 7, the same limit temperature T _d as that arranged adjacent to the hydrocarbon trap 7 can be specified. One advantage of this is that the second starter converter 8 and the second catalytic converter 9 have already been activated and the hydrocarbon trap 7 is already operating when the hydrocarbon trap 7 reaches the limit temperature T _d , When the detachment starts, it is already operating normally.

By actual experiment, it is possible to determine the hydrocarbon trap (7) is the limit temperature calculated value (t _dd) the estimated time to reach the (T _d) from the starting point of the internal combustion engine (1). T (the time _dd ), The second start-up converter 8 is operated. In this case, a separate temperature sensor 10 is not required.

Finally, in relation to the odor of hydrogen sulfide that can occur due to the chemical bonding of sulfur in the engine fuel in a three-way catalytic converter, the present invention achieves a beneficial effect. For example, during maximum throttle acceleration (when the amount of mixed fuel supplied to the internal combustion engine is relatively high), the hydrogen released in the combustion process combines with the sulfur present in the converter to form hydrogen sulfide (H ₂ S) can do. This problem can be solved by the present invention, which is properly assembled around a " pleated catalyst " composed of the other three-way second catalytic converter 9. [ In the second catalytic converter 9, the H ₂ S-based compound is reduced to SO ₂ , which is less odor than the H ₂ S-based compound.

Claims (4)

A first catalytic converter 4 in three directions located downstream of the internal combustion engine 1 and a hydrocarbon trap disposed at a predetermined distance x from a downstream point immediately after the first catalytic converter 4 in these three directions And a second catalytic converter (9) connected to the hydrocarbon trap (7), characterized in that the first catalytic converter (4) and the second catalytic converter first from the start-up of the hydrocarbon trap (7), the distance (x) is an internal combustion engine (1) a hydrocarbon trap (7) time (t _d) and the internal combustion engine (1) that elapses until it encounters removable from the from the start-up of between the Is longer than or equal to a time (t _ign ) that elapses from when the catalytic converter (4) is ignited at the normal operating temperature to the ignition timing. 2. A catalytic converter according to claim 1, characterized in that the electrically heated starter converter (8) is located downstream of the hydrocarbon trap (7), the three-way second catalytic converter (9) is located downstream of the starter converter And the converter (8) is arranged to be activated when detachment occurs in the hydrocarbon trap (7). 3. A method according to claim 2, characterized in that the temperature sensor (10) is arranged upstream of the hydrocarbon trap (7) and the starting converter (8) is closed when the temperature reaches a predetermined limit temperature (T _d ) corresponding to the desorption at the hydrocarbon trap (7) And a control signal for operating the catalytic exhaust gas purifier. The catalytic exhaust gas purifying apparatus according to any one of claims 1 to 3, wherein the electrically heated start converter (5) is disposed upstream of the first catalytic converter (4) in three directions.

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