JP2006266120A - HC adsorption catalyst system - Google Patents

Abstract

【Task】
Without arranging an exhaust pipe or heat capacity body having a high heat mass between the upstream HC catalyst and the downstream HC catalyst, the efficiency of the exhaust purification system is improved while maintaining a catalyst layout free and low cost.
[Solution]
The exhaust passage of the internal combustion engine is provided with at least two HC adsorption catalysts for adsorbing and purifying HC discharged from the internal combustion engine, and the temperature rise rate of each HC adsorption catalyst is in the temperature rise rate range in which the adsorption HC purification performance is within the range. An adsorption catalyst system, a temperature rising rate of an upstream HC adsorption catalyst installed on the upstream side close to the internal combustion engine is set to a rapid temperature increase rate range 401, and a downstream HC adsorption catalyst installed downstream of the upstream HC adsorption catalyst Is set to a slow temperature increase rate range 402.
[Selection] Figure 4

Description

  The present invention relates to an HC adsorption catalyst system for exhaust purification of an internal combustion engine.

In recent years, in consideration of the environment, it is required to further increase the purification efficiency of HC contained in the exhaust gas of an internal combustion engine mounted on an automobile or the like.

As a conventional exhaust gas purification system for an internal combustion engine, a heat capacity body is disposed between an upstream HC catalyst disposed closer to the internal combustion engine and a downstream HC catalyst disposed downstream of the upstream HC catalyst. There is a thing (for example, patent document 1).

  This utilizes the properties of the HC catalyst in which there are an adsorption stage, a desorption stage, and a purification stage for HC discharged from the internal combustion engine as the temperature inside the HC catalyst rises. That is, by disposing a heat capacity body between the upstream HC catalyst and the downstream HC catalyst, the downstream HC maintains the adsorption stage until the upstream HC catalyst reaches the purification stage, and the HC desorbed from the upstream side is removed. It is intended to improve the efficiency of the exhaust purification system by adsorbing and purifying on the downstream side.

JP 2003-201832 A

  However, in the above technique, in order to maintain the downstream HC in the adsorption stage until the upstream HC catalyst reaches the purification stage, the heat capacity body or the exhaust gas having a high heat mass installed between the upstream HC catalyst and the downstream HC catalyst is used. The pipe had to be designed according to the length of the exhaust pipe, the temperature characteristics of the HC catalyst, the type of engine, the operating environment (outside temperature, etc.), and the like. For this reason, there has been a problem of restriction of the catalyst layout of the entire exhaust purification system and further cost increase.

  The object of the present invention is to improve the efficiency of the exhaust purification system while maintaining the catalyst layout free and low cost without disposing an exhaust pipe or heat capacity body having a high heat mass between the upstream HC catalyst and the downstream HC catalyst. It is to plan.

  In the present invention, a plurality of HC adsorption catalysts are provided in the exhaust passage of the internal combustion engine, the temperature rising rate of the upstream HC adsorption catalyst installed on the upstream side close to the internal combustion engine, and the downstream of the upstream HC adsorption catalyst. The temperature increase rate of the downstream HC adsorption catalyst is set to an appropriate speed range by paying attention to the HC purification rate, or the material, structure, etc. are selected and designed so as to be within such an appropriate speed range. is there.

  According to the present invention, the efficiency of the exhaust purification system can be improved while maintaining catalyst layout free and low cost.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of an HC catalyst system of the present invention, in which two HC catalysts 103 and 104 are arranged in series from an internal combustion engine main body 101 in the middle of an exhaust pipe 102 including a manifold.

  In the present embodiment, the HC catalyst closer to the internal combustion engine 101 is the upstream HC catalyst 103, and the upstream HC catalyst 103 is disposed immediately after the exhaust manifold of the internal combustion engine 101. Further, the HC catalyst downstream from the upstream HC catalyst 103 is used as the downstream HC catalyst 104, and the downstream HC catalyst 104 is disposed at a position separated from the upstream HC catalyst 103 by 600 mm or more.

Here, as shown in FIG. 2, an HC catalyst having a small heat mass is used as the upstream HC catalyst 103 as an upstream / downstream HC catalyst, and an HC catalyst having a large heat mass is used as the downstream HC catalyst 104. In general, the temperature increase in the catalyst per unit time of the HC catalyst (hereinafter referred to as the rate of temperature increase) is inversely proportional to the heat mass of the HC catalyst itself. Therefore, the upstream side HC catalyst 104 is closer to the internal combustion engine 101 than the downstream side HC catalyst 103, and the heat mass is small, so that the rate of temperature increase is increased. On the other hand, the downstream side HC catalyst 104 is farther from the internal combustion engine 101 than the upstream side HC catalyst 103 and the heat mass is large, so the rate of temperature increase is small.

  The above heat mass setting is realized by the difference in the number of cells as shown in FIG. 3, for example, 900 cells of HC catalysts are arranged on the upstream side, and 300 cells of HC catalysts are arranged on the downstream side.

  Next, the relationship between the purification rate of adsorbed HC and the rate of temperature rise will be described in detail.

As shown in FIG. 5, the HC adsorption combustion catalyst has HC adsorption, HC desorption,
It goes through the HC purification stage.

  As the internal combustion engine 101 starts, HC is discharged from the internal combustion engine 101. Immediately after the internal combustion engine 101 is started, both the upstream HC catalyst 103 and the downstream HC catalyst 104 are in a low temperature state. Therefore, the upstream HC catalyst 103 and the downstream HC catalyst 104 are in the HC adsorption stage, and HC is adsorbed by the upstream and downstream HC catalysts.

  When the HC catalyst reaches the HC desorption start temperature, the HC adsorbed in the HC adsorption stage is desorbed. The amount of HC desorption is affected by the temperature increase rate of the HC catalyst. This will be described in detail later with reference to FIG.

  The adsorbed HC is purified by the activation of the HC catalyst. The purification efficiency characteristic of the adsorbed HC with respect to the temperature rising rate at that time is as shown in FIG. The horizontal axis represents the rate of temperature rise of the HC catalyst, and the vertical axis represents the ratio of HC that can purify HC adsorbed in the HC adsorption stage in the HC purification stage (HC purification efficiency characteristics). The purification efficiency E of the adsorbed HC is expressed as (Equation 1).

(M0−M1) × 100 / M0 = E (%) (Formula 1)
M0: HC amount adsorbed in HC adsorption stage (g)
M1: HC amount desorbed in HC desorption step (g)

  The purification efficiency E of the adsorbed HC includes a measurement error of ± 5% from the true value.

  When the purification performance characteristic of the HC catalyst is considered with the temperature increase rate of the catalyst as a parameter, the purification efficiency of the adsorbed HC decreases as the temperature increase rate of the HC catalyst increases, and almost reaches a boundary at a predetermined temperature increase rate Ts. 0 (zero). However, the inventors have found through experimentation that the purification efficiency of adsorbed HC increases again at a certain predetermined temperature increase rate Tl as the temperature increase rate of the HC catalyst is further increased.

  Here, the temperature increase rate range (temperature increase rate Ts or less) in which the purification efficiency of the adsorbed HC increases as the temperature increase rate is set to be small is set as the slow temperature increase rate range, and the adsorption HC is purified as the temperature increase rate is set to be large. A temperature increase rate range in which efficiency increases (a temperature increase rate Tl or more) is defined as a rapid temperature increase rate range. Here, in the range where the temperature rising rate is larger than Ts and smaller than Tl, the adsorption HC purification performance is lower than the adsorption HC purification performance in the rapid temperature rise rate range or the slow temperature rise rate range, and is almost 0 (zero). ing. This range is the low purification rate temperature increase rate range.

HC adsorbed on the HC catalyst has a property of being more easily desorbed from the HC catalyst as the thermal energy per unit time supplied to the HC catalyst from the outside such as exhaust gas increases. Here, in the slow temperature increase rate range, the HC desorption period of the HC catalyst becomes longer than the HC desorption period of the HC catalyst at the temperature increase rate Ts. However, since the thermal energy per unit time supplied to the HC catalyst is small, the amount of HC desorbed per unit time is smaller than the HC desorption period of the HC catalyst at the temperature increase rate Ts. Therefore, the slow temperature increase rate range is the time until the activation temperature of the HC catalyst is reached.
It can also be defined as a temperature rise range in which HC trapped by the HC catalyst can be purified.

  In the rapid temperature increase rate range, the heat energy per unit time supplied to the HC catalyst is large. Therefore, the amount of HC desorbed per unit time is larger than the HC desorption period of the HC catalyst having the temperature increase rate Tl. However, the HC desorption period of the HC catalyst is shorter than the HC desorption period of the HC catalyst having the temperature increase rate Tl. Therefore, the rapid temperature increase rate range can also be defined as a temperature increase range in which the residual HC of the HC catalyst until the activation temperature of the HC catalyst is reached can be purified.

  The low purification rate temperature increase rate range is defined as a temperature increase rate range in which the amount of HC trapped in the HC adsorption stage of the HC adsorption catalyst is almost equal to the amount of HC desorbed in the HC desorption stage of the HC adsorption catalyst. You can also That is, the amount of HC trapped in the HC adsorption stage is a temperature rise range in which almost all is desorbed in the HC desorption stage. However, since the measurement error includes ± 5%, the temperature increase rate range where the purification efficiency is about 5% can be defined as the low purification rate temperature increase rate range.

  In the exhaust gas purification system using two conventional HC catalysts, a three-way catalyst serving as a heat capacity body is installed between the internal combustion engine and the upstream HC catalyst, and between the upstream HC catalyst and the downstream HC catalyst. Since the exhaust pipe and heat capacity body having a high heat mass were installed in the HC catalyst, the HC catalyst itself was not designed to have a rapid temperature increase rate range. In particular, although the upstream HC catalyst is close to the internal combustion engine and is exposed to a relatively high temperature exhaust gas, it does not reach the rapid temperature increase rate range in the present application, and the purification performance of the upstream HC catalyst is not so much exhibited. It was.

  From the above, the most efficient combination of the temperature rising rates of the HC catalyst is that the temperature rising rate of the upstream HC catalyst 103 close to the internal combustion engine 101 is in the rapid temperature rising rate range and the temperature rising rate of the downstream HC catalyst 104 is slow. It is to set the temperature increase rate range. The reason is that the exhaust temperature in the exhaust pipe 102 is high immediately after exhaust, and the thermal energy of the exhaust gas is absorbed by the catalyst or the like as it goes downstream, and the temperature of the exhaust gas decreases.

  As described above, in this embodiment, the upstream HC catalyst is suddenly changed by changing the heat mass of the upstream HC catalyst itself without installing a three-way catalyst serving as a heat capacity body between the internal combustion engine and the upstream HC catalyst. The temperature increase rate range. On the other hand, the temperature of the downstream HC catalyst is increased slowly by changing the heat mass of the downstream HC catalyst itself without installing an exhaust pipe or heat capacity body having a high heat mass between the upstream HC catalyst and the downstream HC catalyst. The range.

  Note that the temperature increase rates Tl and Ts in FIG. 4 are average temperature increase rates until the exhaust temperature immediately after the upstream and downstream HC catalysts reaches 300 ° C. during the LA-4 mode traveling. When the V6 type 2500cc engine was used as the internal combustion engine 101, Tl = 6 ° C./second and Ts = 2 ° C./second.

Next, FIG. 5 shows the temperature rise characteristics when the number of cells of the upstream HC catalyst 103 is 900 cells and the number of cells of the downstream HC catalyst 104 is 300 cells. The upstream side HC catalyst 103 and the downstream side HC catalyst 104 have temperature rise characteristics as shown in FIG. As a result, the upstream HC catalyst 103 has a temperature increase rate of 10 ° C./second, and the downstream HC catalyst 104 has a temperature increase of 1.5 ° C./second, which is larger than the aforementioned Tl = 6 ° C./second and Ts = 2 ° C./second. I confirmed that it was getting smaller.

  In the above example, since the temperature increase rate of the upstream HC catalyst 103 is in the rapid temperature increase rate range, the time from the start of the internal combustion engine 101 to the activation temperature of the HC catalyst is within 30 seconds, short. In addition, the upstream HC catalyst has a high temperature rising rate within a rapid heating rate range of purification efficiency, and most of the HC discharged within 30 seconds from the start of the internal combustion engine 101 is also adsorbed and purified by the upstream HC catalyst. Is done. Furthermore, HC desorbed from the upstream HC catalyst is adsorbed and purified by the downstream HC catalyst 104 in the slow temperature increase rate range, so that both the upstream and downstream HC catalysts can be used with high efficiency.

  As described above, when a plurality of HC catalysts are arranged in the middle of the exhaust pipe 102, the HC catalyst capable of setting the temperature rising rate within the rapid temperature rising rate range and the HC catalyst capable of setting the temperature rising rate within the slow temperature rising rate range are combined. As a result, an optimum combination is obtained for the HC adsorption catalyst system. Furthermore, since the upstream HC catalyst 103 can be activated earlier than in the prior art, the amount of exhaust components such as CO and NOx discharged before activation can be reduced.

  Further, when both the upstream and downstream HC catalysts are in the rapid temperature increase rate range, the HC desorption period of the entire catalyst can be shortened, so that exhaust of exhaust components other than HC can be achieved while exhibiting high HC purification performance. Purification performance can also be improved. For example, this is a case where the heat mass is reduced so that the number of cells of the upstream and downstream HC catalysts is 900 or more. Hereinafter, a method different from the method of changing the number of cells described above as a method of adjusting the heat mass will be described with reference to the drawings.

  FIG. 6 shows that the volume of the upstream HC catalyst 103 is smaller than the volume of the downstream HC catalyst 104. Thereby, the heat mass of the upstream HC catalyst 103 can be made smaller than the heat mass of the downstream HC catalyst 104. Furthermore, since the volume of the upstream HC catalyst 103 is small, it is possible to save space in the engine room.

FIG. 7 shows that the catalyst inner wall of the upstream HC catalyst 103 is thinner than the catalyst inner wall of the downstream HC catalyst 104. Thereby, the heat mass of the upstream HC catalyst 103 can be made smaller than the heat mass of the downstream HC catalyst 104. Furthermore, by reducing the inner wall of the catalyst, exhaust ventilation resistance can be reduced.

  FIG. 8 shows that the mass of the upstream HC catalyst 103 is smaller than the mass of the downstream HC catalyst 104. Thereby, the heat mass of the upstream HC catalyst 103 can be made smaller than the heat mass of the downstream HC catalyst 104. Further, the cost can be reduced by reducing the amount of noble metal, adsorbent, and catalyst carrier constituting the HC catalyst.

FIG. 9 shows that the surface area of the upstream HC catalyst 103 is larger than the surface area of the downstream HC catalyst 104. Thereby, the heat mass of the upstream HC catalyst 103 can be made smaller than the heat mass of the downstream HC catalyst 104. Further, the large surface area improves the durability by improving the HC adsorption performance and highly dispersing the catalyst metal. .

  FIG. 10 shows that a material having a specific heat smaller than that of the downstream HC catalyst 104 is used for the upstream HC catalyst 103. Thereby, the heat mass of the upstream HC catalyst 103 can be made smaller than that of the downstream HC catalyst 104. Furthermore, when a metal or the like is used as a material having a small specific heat, the structural strength and heat resistance of the upstream HC catalyst 103 are improved, and the temperature can be increased more rapidly.

  The number of cells is changed by adjusting the heat mass by the method as described above, and setting the temperature increase rate of the upstream HC catalyst 103 to the rapid temperature increase rate range and the temperature increase rate of the downstream HC catalyst 104 to the moderate temperature increase rate range. The same effect as the case can be obtained. Two or more of the above examples may be combined. However, in consideration of the positional relationship between the upstream and downstream HC catalysts and the internal combustion engine and the exhaust temperature gradient in the exhaust pipe, the temperature of both the upstream and downstream HC catalysts can be increased within a rapid temperature increase rate range, or the upstream HC catalyst Depending on circumstances, the combination may be properly used, such as increasing the temperature within a slow temperature increase rate range and increasing the temperature of the downstream HC catalyst within a rapid temperature increase rate range.

  A second embodiment of the present invention will be described with reference to the drawings.

  The arrangement of the internal combustion engine, the exhaust pipe, the catalyst, and the like are the same as those in the first embodiment, but any heat mass may be used for the upstream and downstream HC catalysts. FIG. 11 shows the temperature rise characteristic of the upstream HC catalyst 103 when the temperature rise control is performed on the exhaust gas of the internal combustion engine 101. Due to the effect of the temperature rise control, there is a difference in temperature characteristics until the HC catalyst is activated when temperature rise control is performed and when temperature rise control is not performed. When the temperature increase control is performed, the HC desorption period can be shortened compared to the case where the temperature increase control is not performed, and further, the HC catalyst is activated early so that exhaust components such as HC, CO, and NOx are also accelerated. It can be purified. Moreover, the effect similar to Example 1 can be acquired only by temperature rising control, without changing a heat mass by making the temperature rising rate of an upstream HC catalyst into the rapid temperature rising rate range by temperature rising control.

  Exhaust temperature raising control is performed by ignition timing control as shown in FIG. 12, for example. That is, immediately after the internal combustion engine 101 is started, the ignition timing is retarded and the temperature of the exhaust gas from the internal combustion engine 101 is increased. Thereby, the temperature increase rate of the upstream HC catalyst 103 is increased. After the upstream side HC catalyst 103 reaches the activation temperature, the exhaust gas temperature is lowered by the advance of the ignition timing and the temperature increase rate of the downstream side HC catalyst 104 is moderated while taking care not to become below that temperature. To. At this time, the temperature of the upstream side HC catalyst 103 is measured by a temperature sensor, or estimated from a water temperature, an engine speed, an engine load value, and the like. In addition, control is performed so that the ignition timing is gradually brought closer to the normal ignition timing from the advance side by the signal of the knock sensor or the water temperature so that knocking does not occur due to the advance angle. Alternatively, when knocking is detected, the ignition timing may be retarded and controlled to gradually approach the normal ignition timing.

  It should be noted that the advance of the ignition timing after the upstream HC catalyst 103 reaches the activation temperature does not have to be performed, such as when both the upstream HC catalyst 103 and the downstream HC catalyst 104 are in the rapid temperature increase rate range. There is a good case.

  Therefore, according to the second embodiment, in addition to the combination of the upstream and downstream HC catalysts in the first embodiment, the temperature increase rate of the upstream HC catalyst 103 is set within the rapid temperature increase rate range, and the temperature increase of the downstream HC catalyst 104 is increased. A temperature rate can be made into a moderate temperature increase rate range, and the purification performance of the HC adsorption catalyst system can be improved.

  In addition to the above, for example, as shown in FIG. 13, the temperature rise control can be performed by the valve timing. That is, immediately after the internal combustion engine 101 is started, the exhaust valve temperature is increased by advancing the opening timing of the exhaust valve. Thereby, the temperature increase rate of the upstream HC catalyst 103 is increased. After the upstream HC catalyst 103 reaches the activation temperature, the exhaust valve is opened at a slower timing and the temperature increase rate of the downstream HC catalyst 104 is moderated while taking care not to be below that temperature. To do. Also at this time, the temperature of the upstream side HC catalyst 103 is measured by a temperature sensor or estimated by a water temperature, an engine speed, an engine load value, and the like. In addition, in order to prevent knocking, control is performed so that the timing at which the exhaust valve opens gradually approaches the normal valve opening timing, depending on the signal from the knock sensor or the water temperature. Alternatively, when knocking is detected, the valve opening timing may be advanced to gradually approach the normal valve opening timing.

  On the other hand, immediately after the internal combustion engine 101 is started, the temperature increase rate of the HC catalyst can be set within the rapid temperature increase rate range by the electric heater using a battery, an alternator, or other power source. By forcibly heating the upstream HC catalyst 103, the rapid temperature increase rate range can be set faster than when the upstream HC catalyst 103 is not forcibly heated. Also, considering the heat resistance depending on the type of HC catalyst, the HC species to be adsorbed, etc., the downstream HC catalyst 104 is forcibly heated, the downstream HC catalyst 104 is in the rapid temperature increase rate range, and the upstream is the slow temperature increase rate. It is possible to make a combination of the heating rate of the HC catalyst so as to be in the range. In addition, by heating and cooling at the same time with a heater using the Peltier effect, either one of the upstream and downstream HC catalysts may be heated within a rapid temperature increase rate range. Or as a cooler, you may use only for either. Further, any one of the above may be used in combination with the heat mass adjusting means of the first embodiment.

  A third embodiment of the present invention will be described with reference to the drawings. The arrangement of the internal combustion engine, the exhaust pipe, and the catalyst is the same as that of the first embodiment. However, as shown in FIG. 14, the upstream side HC catalyst 103 and the downstream side HC catalyst 104 are different in the structure of the adsorption layer. Yes.

  Next, the adsorption layer of the HC catalyst and the adsorption of HC to the adsorption layer will be described. The adsorption layer of the HC catalyst is provided on the surface of the catalyst carrier, and further, a ternary layer is provided on the surface of the adsorption layer. When the HC catalyst is heated to the catalyst activation temperature, HC desorbed from the lower adsorption layer is burned and removed in the upper ternary layer.

During operation of the internal combustion engine 101, various types of HC are generated and discharged by the combustion of fuel. The HC catalyst adsorbs the HC to the adsorption layer when cold, holds the HC until the HC catalyst is activated, and then purifies the HC. Therefore, the ability to hold the adsorbed HC (hereinafter referred to as HC holding performance) is an important factor for improving the HC purification efficiency of the HC catalyst, and the HC holding performance is between the adsorbate HC and the adsorption layer. Depends on the strength of the interaction (hereinafter referred to as adsorption force) acting on. Further, the adsorption force is generally determined by the compatibility with the composition and structure of the adsorbate and the composition and structure of the adsorbent. Therefore, in order to obtain a strong adsorption force, it is necessary to combine the adsorbate composition and structure and the adsorbent composition and structure so as to strengthen the interaction. However, since HC contained in the exhaust gas has a wide variety of compositions and structures, it is difficult to adsorb and hold all HC species with only one adsorbent as shown in FIG.

In addition to the above, the HC adsorption force of the HC catalyst is closely related to the temperature. Generally, the HC adsorption force is adsorbed at a high surface temperature in an atmosphere having a high temperature or a large temperature change. It has the property of becoming smaller for the material. Considering the above properties, high temperature exhaust gas flows into the upstream HC catalyst, the temperature of the adsorption layer is high, and the temperature change also increases. Therefore, HC that is not compatible with the adsorption layer continues to be retained even after adsorption. Is difficult. If these HCs are to be maintained, it is necessary to lower the temperature of the exhaust or to moderate the temperature change.

  Therefore, in this embodiment, different materials are used for the adsorption layers of the upstream HC catalyst 103 and the downstream HC catalyst 104. Further, the HC retention performance of the HC adsorption catalyst system is improved by using the main HC species desorbed from the upstream HC catalyst 103 and the adsorbent exhibiting a strong adsorption force for the downstream HC catalyst 104. It is.

According to the configuration of the present embodiment, as shown in FIG. 16, the HC species that exerts a strong adsorption force with the upstream HC catalyst 103 is adsorbed and purified by the upstream HC catalyst 103. On the other hand, since the adsorption layer of the downstream HC catalyst 104 exhibits a strong adsorption force with the main HC species desorbed from the upstream HC catalyst 103, these HCs are adsorbed and purified by the downstream HC catalyst 104.

Specifically, as shown in FIG. 17, for example, saturated hydrocarbons and linear hydrocarbons, which are generally known as the most difficult to hold HC, are adsorbed to the upstream HC catalyst 103. An adsorption layer for purification is provided, and the downstream HC catalyst 104 is provided with an adsorption layer for adsorbing and purifying linear hydrocarbons. In the present embodiment, desorption is promoted in a straight-chain hydrocarbon within a rapid temperature increase rate range as compared with a saturated hydrocarbon. Therefore, such a configuration is adopted so that the linear hydrocarbon is adsorbed and purified by the downstream HC catalyst in the slow temperature increase rate range.

  As an example of the structure of the adsorption layer that realizes the above, the upstream HC catalyst 103 is made of an adsorbent obtained by adding a noble metal such as silver or palladium to zeolite, and the downstream HC catalyst 104 is an A-type zeolite or ferrierite. , ZAM-5 or other zeolite with a small pore size is used as the adsorbent.

  The selection of the adsorbent for the upstream / downstream HC catalyst may be reversed in accordance with the use conditions such as the internal combustion engine to be used and the temperature increase rate of the upstream / downstream HC catalyst.

  As a result, it is possible to adsorb and purify almost all HCs including saturated hydrocarbons and linear hydrocarbons that are most easily desorbed. Therefore, according to the third example of the present embodiment, the retention performance of the HC adsorption catalyst system can be improved, and the HC purification efficiency can be improved.

  In addition to the above-described method of changing the configuration of the adsorbent with the upstream / downstream HC catalyst, the adsorbent may be used in combination with at least one of the above and the first embodiment or the second embodiment.

1 shows a schematic diagram of an HC catalyst system according to an embodiment of the present invention. FIG. The figure of the relationship between the upstream / downstream HC catalyst and the heat mass in FIG. 1 is shown. Sectional drawing of the upstream HC catalyst and downstream HC catalyst in FIG. 1 is shown. The figure of the purification efficiency characteristic of adsorption | suction HC with respect to a temperature increase rate is shown. The figure of the relationship between the number of cells of the upstream / downstream HC catalyst and the temperature rise characteristic in FIG. 1 is shown. The figure of the heat mass adjustment method by the volume change of the upstream / downstream HC catalyst in FIG. 1 is shown. The figure of the heat mass adjustment method by the change of the catalyst inner wall thickness of the upstream / downstream HC catalyst in FIG. 1 is shown. The figure of the heat mass adjustment method by the mass change of the upstream / downstream HC catalyst in FIG. 1 is shown. The figure of the heat mass adjustment method by the surface area change of the upstream / downstream HC catalyst in FIG. 1 is shown. The figure of the heat mass adjustment method by the specific heat change of the upstream and downstream HC catalyst in FIG. 1 is shown. FIG. 2 is a graph of temperature increase characteristics of an upstream HC catalyst when temperature increase control is applied to the exhaust gas of the internal combustion engine in FIG. 1. It is a figure which shows the temperature rising characteristic at the time of performing temperature rising control of exhaust_gas | exhaustion by ignition timing control in FIG. The figure of the temperature rising characteristic at the time of performing the temperature rising control of exhaust by the valve timing in FIG. 1 is shown. The block diagram of the adsorption layer of the upstream HC catalyst and downstream HC catalyst in FIG. 1 is shown. A diagram of HC adsorption and desorption when only one adsorbent is used is shown. The figure of HC adsorption | suction and desorption when the adsorbent of the upstream / downstream HC catalyst in FIG. 1 is changed is shown. FIG. 2 is a diagram showing the adsorption, desorption, and purification of upstream and downstream HC catalysts with respect to various HCs in FIG.

Explanation of symbols

401: Rapid temperature increase rate range, 402: Slow temperature increase rate range.

Claims (18)

A plurality of HC adsorption catalysts are provided in the exhaust passage of the internal combustion engine,
The temperature increase rate of the upstream HC adsorption catalyst installed on the upstream side close to the internal combustion engine is a rate in a temperature increase rate range in which the purification efficiency of the adsorbed HC increases as the temperature increase rate is set to be large,
The HC adsorption catalyst in which the temperature increase rate of the downstream HC adsorption catalyst installed downstream of the upstream HC adsorption catalyst is within a temperature increase rate range in which the purification efficiency of the adsorbed HC increases as the temperature increase rate is set smaller. system. A plurality of HC adsorption catalysts are provided in the exhaust passage of the internal combustion engine,
The temperature rising rate of the upstream HC adsorption catalyst installed on the upstream side near the internal combustion engine is such that the amount of HC captured in the HC adsorption stage of the HC adsorption catalyst and the HC desorbed in the HC desorption stage of the HC adsorption catalyst. The rate is higher than the low purification rate heating rate range in which the amount is almost equal,
An HC adsorption catalyst system in which a temperature increase rate of a downstream HC adsorption catalyst installed downstream of the upstream HC adsorption catalyst is lower than the low purification temperature increase rate range. A plurality of HC adsorption catalysts are provided in the exhaust passage of the internal combustion engine,
The temperature rising rate of the upstream HC adsorption catalyst installed on the upstream side close to the internal combustion engine is higher than the temperature rising temperature range in which the purification rate is substantially zero,
An HC adsorption catalyst system in which a temperature increase rate of a downstream HC adsorption catalyst installed downstream of the upstream HC adsorption catalyst is lower than a temperature increase temperature range in which a purification rate is substantially zero. A plurality of HC adsorption catalysts are provided in the exhaust passage of the internal combustion engine,
The temperature rising rate of the upstream HC adsorption catalyst installed on the upstream side close to the internal combustion engine is higher than 6 ° C./second,
An HC adsorption catalyst system in which a temperature increase rate of a downstream HC adsorption catalyst installed downstream of the upstream HC adsorption catalyst is lower than 2 ° C./second. The HC adsorption catalyst system according to any one of claims 1 to 4,
An HC adsorption catalyst system in which the heat mass of the upstream HC adsorption catalyst is smaller than the heat mass of the downstream HC adsorption catalyst. The HC adsorption catalyst system according to any one of claims 1 to 4,
An HC adsorption catalyst system in which the number of cells of the upstream HC adsorption catalyst is larger than the number of cells of the downstream HC adsorption catalyst. The HC adsorption catalyst system according to any one of claims 1 to 4,
An HC adsorption catalyst system in which the volume of the upstream HC adsorption catalyst is smaller than the volume of the downstream HC adsorption catalyst. The HC adsorption catalyst system according to any one of claims 1 to 4,
An HC adsorption catalyst system in which a surface area of the upstream HC adsorption catalyst is larger than a surface area of the downstream HC adsorption catalyst. The HC adsorption catalyst system according to any one of claims 1 to 4,
An HC adsorption catalyst system in which the upstream HC adsorption catalyst has a specific heat smaller than that of the downstream HC adsorption catalyst. The HC adsorption catalyst system according to any one of claims 1 to 9,
An HC adsorption catalyst system that controls the exhaust temperature by controlling the internal combustion engine. The HC adsorption catalyst system according to claim 10,
An HC adsorption catalyst system that controls exhaust gas temperature by controlling ignition timing control of the internal combustion engine. The HC adsorption catalyst system according to claim 10,
An HC adsorption catalyst system comprising means for measuring or estimating the temperature inside the upstream HC adsorption catalyst, and the ignition timing of the internal combustion engine is retarded until the upstream HC adsorption catalyst reaches a purification start temperature. The HC adsorption catalyst system according to claim 12,
An HC adsorption catalyst system in which the ignition timing of the internal combustion engine is advanced after the upstream HC adsorption combustion catalyst reaches the purification start temperature. The HC adsorption catalyst system according to claim 10,
An HC adsorption catalyst system for controlling the exhaust temperature by controlling the opening timing of the exhaust valve of the internal combustion engine. The HC adsorption catalyst system according to claim 14,
HC adsorption having a means for measuring or estimating the temperature inside the upstream HC adsorption catalyst, wherein the opening timing of the exhaust valve of the internal combustion engine is advanced until the upstream HC adsorption catalyst reaches the purification start temperature Catalyst system. The HC adsorption catalyst system according to claim 15,
An HC adsorption catalyst system in which the opening timing of the exhaust valve of the internal combustion engine is delayed after the upstream HC adsorption catalyst reaches the purification start temperature. The HC adsorption catalyst system according to any one of claims 1 to 4,
An HC adsorption catalyst system in which a component of the adsorption layer of the upstream HC adsorption catalyst is different from a component of the adsorption layer of the downstream HC adsorption catalyst. The HC adsorption catalyst system according to claim 19,
An HC adsorption catalyst system comprising an adsorption layer for adsorbing HC species desorbed from the upstream HC adsorption catalyst on the downstream HC adsorption catalyst.

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