Patent Grant
8756925
This application claims priority to Japanese Patent Application No. 2010-290944 filed on Dec. 27, 2010, which is incorporated herein by reference in its entirety including the specification, drawings and abstract.
1. Field of the Invention
The invention relates to an exhaust pipe, and in particular to an exhaust pipe of an internal combustion engine.
2. Description of Related Art
A catalyst for purifying (controlling) exhaust gas is provided in an exhaust passage of an internal combustion engine. The exhaust gas purification (control) function of such a catalyst can not be sufficiently used unless the temperature of the catalyst is equal to its activation temperature or higher. Thus, normally, the catalyst is warmed up using the heat of exhaust gas until the temperature of the catalyst reaches the activation temperature or higher. To accelerate the warming-up of the catalyst, the temperature of exhaust gas is increased by reducing the heat loss of an exhaust pipe. For example, Japanese Patent Application Publication No. 2003-286841 describes a technology in which a double pipe is used as an exhaust pipe to reduce the radiation of heat of exhaust gas flowing in the exhaust pipe and thereby increase the exhaust gas temperature.
According to the technology described in Japanese Patent Application Publication No. 2003-286841, however, there is a possibility that the catalyst may be excessively heated due to the exhaust gas heat when the exhaust gas temperature is sufficiently high after the catalyst has been warmed up, and this may cause degradation of the exhaust gas purification (control) performance of the catalyst.
The invention provides an exhaust pipe that is capable of promoting warming-up of a catalyst, and is capable of restricting the catalyst from being excessively heated when the exhaust gas temperature is high.
The first aspect of the invention relates to an exhaust pipe. An exhaust port of an internal combustion engine and a catalyst for purifying an exhaust gas of the internal combustion engine are connected to each other through the exhaust pipe. The exhaust pipe has a porous portion that is provided on at least a part of an inner peripheral face of the exhaust pipe. A thermal conductivity that the porous portion exhibits in a high temperature state where a temperature of the exhaust gas is as high as it is required to radiate a heat of the exhaust gas through the exhaust pipe is at least ten times higher than a thermal conductivity that the porous portion exhibits in a low temperature state where the temperature of the exhaust gas is as low as it is required to warm the catalyst up.
According to the first aspect of the invention, when the exhaust gas temperature is low, the porous portion reduces the heat conduction through it, thus suppressing radiation, through the exhaust pipe, of the heat of the exhaust gas in the exhaust pipe. As such, the warming-up of the catalyst can be promoted. When the exhaust gas temperature is high, on the other hand, the porous portion enhances the heat conduction through it, thereby restricting the catalyst from being heated excessively.
The exhaust pipe of the first aspect of the invention may be such that a porosity of the porous portion is set such that the thermal conductivity of the porous portion in the high temperature state is at least ten times higher than the thermal conductivity of the porous portion in the low temperature state. According to this structure, the thermal conductivity of the porous portion in the high temperature state can be easily made at least ten times higher than the thermal conductivity of the porous portion in the low temperature state, as compared to the case where a desired thermal conductivity of the porous portion is achieved by adjusting an element(s) other than the porosity of the porous portion.
Further, in this structure, a cooler that cools a portion, at which the porous portion is provided, of a wall of the exhaust pipe may be provided. According to this structure, when the exhaust gas temperature is high and therefore the porous portion enhances the heat conduction through it, the heat of exhaust gas in the exhaust pipe can be conducted away through the porous portion and the wall of the exhaust pipe that is cooled by the cooler. Thus, the catalyst can be more effectively restricted from being heated excessively. Further, since the porous portion reduces the heat conduction through it when the exhaust gas temperature is low, even if the wall of the exhaust pipe is cooled by the cooler when the exhaust gas temperature is low, the radiation of the exhaust gas heat is suppressed by the porous portion, and thus the warming-up of the catalyst is not impeded.
Further, in this structure, a controller that controls the cooler based on the temperature of the wall may be provided. According to this structure, the temperature of the wall can be more accurately adjusted. Further, in this structure, the controller may be adapted to control the cooler so as to bring the temperature of the wall to an activation temperature of the catalyst or lower.
Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:
First, an exhaust pipe of the first example embodiment of the invention will be described. In the following, an internal combustion engine system 5 incorporating the exhaust pipe of the first example embodiment will be first described, and then the exhaust pipe will be described.
The internal combustion engine 10 may be of any type. For example, it may be a gasoline engine, diesel engine, or the like. The internal combustion engine 10 is provided with a cylinder block 11, a cylinder head 12 mounted on the cylinder block 11, and pistons 13 disposed in the cylinder block 11. In the internal combustion engine 10, the cylinder block 11, the cylinder head 12, and the respective pistons 13 define combustion chambers 14. Intake ports 15 through which intake air is drawn into the respective combustion chambers 14 and exhaust ports 16 through which exhaust gas is discharged from the respective combustion chambers 14 are formed in the cylinder block 11.
The exhaust pipe 20 serves as a passage through which to discharge the exhaust gas of the internal combustion engine 10 to the outside of the internal combustion engine system 5. The upstream end of the exhaust pipe 20 is connected to the exhaust ports 16 of the internal combustion engine 10. The exhaust pipe 20 may be, for example, a metallic pipe. A porous portion 30 is provided between the exhaust ports 16 and the catalyst 40 in the exhaust pipe 20. The porous portion 30 has a number of pores. The material of the porous portion 30 is not limited to any specific material. In the first example embodiment, by way of example, the porous portion 30 is made of amorphous silica as the main component. The porous portion 30 will be described in more detail later. The porous portion 30 may be made of the amorphous.
In the first example embodiment, the exhaust pipe 20 has a first exhaust pipe 21 and a second exhaust pipe 22 that are connected to each other. The upstream end of the first exhaust pipe 21 is connected to the exhaust ports 16, and the upstream end of the second exhaust pipe 22 is connected to the downstream end of the first exhaust pipe 21. The porous portion 30 is provided in the first exhaust pipe 21, and the catalyst 40 is provided in the second exhaust pipe 22. It is to be noted that the porous portion 30 may be provided near or in proximity of the catalyst 40.
According to the structure described above, for example, the exhaust pipe 20 may be manufactured by setting the porous portion 30 in the first exhaust pipe 21, then setting the catalyst 40 in the second exhaust pipe 22, and then connecting the first exhaust pipe 21 and the second exhaust pipe 22 to each other. As such, the exhaust pipe 20 is constituted of the first exhaust pipe 21 and the second exhaust pipe 22 that are connected to each other, and therefore the exhaust pipe 20 in which the porous portion 30 and the catalyst 40 are provided can be easily manufactured.
In the meantime, the connection between the first exhaust pipe 21 and the second exhaust pipe 22 is not limited to any specific connection form or structure. For example, the first exhaust pipe 21 and the second exhaust pipe 22 may be connected using various known joints used for connecting two pipes or pipe-like members, such as flange joint and welded joint. Further, the structure of the exhaust pipe 20 is not limited to such a combination of the first exhaust pipe 21 and the second exhaust pipe 22 that are connected to each other. For example the exhaust pipe 20 may alternatively be a single exhaust pipe.
Any catalyst may be used as the catalyst 40 as long as it is capable of purifying (controlling) the exhaust gas as needed. For example, a three-way catalyst, or the like, may be used as the catalyst 40. The position of the catalyst 40 is not specifically limited. In the first example embodiment, by way of example, the catalyst 40 is arranged at the radially center portion of the interior of the second exhaust pipe 22 (i.e., a region having a specific volume and centered at the axis of the second exhaust pipe 22).
Meanwhile, referring to
Next, the structure of the porous portion 30 will be described in detail. However, before that, the reason why the exhaust pipe 20 has the porous portion 30 will be first explained in detail. The catalyst 40 is not sufficiently active until it is heated up to a given activation temperature or higher. If the catalyst 40 is not sufficiently active, its exhaust gas purification (control) function can not be sufficiently used, possibly failing to reduce the emissions as needed. Thus, required is a process for warming (heating) the catalyst 40 up to the activation temperature or higher (i.e., the catalyst 40 needs to be warmed up). The catalyst 40 is warmed up using the heat of exhaust gas.
Meanwhile, when heated up to a certain temperature (will hereinafter be referred to as “upper limit temperature”) or higher, the exhaust gas purification (control) performance of the catalyst 40 becomes low. Thus, in order to restrict the catalyst 40 from being heated up to the upper limit temperature or higher by the exhaust gas heat, it is necessary or desirable to suppress an increase in the exhaust gas temperature by enhancing the exhaust gas heat radiation through the exhaust pipe 20 when the exhaust gas temperature is high after the warming-up of the catalyst 40.
The graph of
The low temperature region is the region where the catalyst 40 is required to be warmed up. When the exhaust gas temperature is in the low temperature region, the warming-up of the catalyst 40 is promoted by suppressing the exhaust gas heat radiation through the exhaust pipe 20. That is, the low temperature region can be also deemed as the region where the exhaust gas heat radiation through the exhaust pipe 20 is required to be suppressed. The high temperature region, on the other hand, is the region where the exhaust gas heat is required to be radiated through the exhaust pipe 20. When the exhaust gas temperature is in the high temperature region, in order to restrict degradation of the exhaust gas purification (control) performance of the catalyst 40, the catalyst 40 is restricted from being heated up to the upper limit temperature or higher by promoting the exhaust gas heat radiation through the exhaust pipe 20. It is to be noted that the high temperature region also includes temperatures close to the upper limit value.
However, it is not easy to achieve both the promotion of warming-up of the catalyst 40 during the exhaust gas temperature being low and the restriction of excessive heating of the catalyst 40 during the exhaust gas temperature being high. For example, the warming-up of the catalyst 40 can be promoted by providing a thermal insulator in the exhaust pipe 20. This, however, increases the possibility that the exhaust gas temperature rise up to the upper limit temperature or higher after the warming-up of the catalyst 40. As such, the catalyst 40 is more likely to be heated up to the upper limit temperature or higher, that is, the possibility of degradation of the exhaust gas purification (control) performance of the catalyst 40 increases. To counter this, in the first example embodiment, the porous portion 30 is provided in the exhaust pipe 20 to achieve both the promotion of warming-up of the catalyst 40 during the exhaust gas temperature being low and the restriction of excessive heating of the catalyst 40 during the exhaust gas temperature being high.
Next, the thermal conductivity characteristic of the porous portion 30 will be described. The graph in
The equations (1) and (2) shown below are Hazen-Williams' equations used for calculating the thermal conductivities represented by the curves 102 and 103.
λ=(1−Φ)×λs+Φ+λg+(1−Φ)−1×λr (1)
λr=16σ×T3/(3Ke) (2)
In the equations (1) and (2), λ represents the thermal conductivity of the porous portion 30, and λs represents the thermal conductivity of the material of the porous portion 30. In the example illustrated in
As is evident from
That is, comparing the thermal conductivity of the porous portion 30 with that of the material of the porous portion 30, it is found that the thermal conductivity of the porous portion 30 is lower than that of the material of the porous portion 30 when the exhaust gas temperature is low, while the thermal conductivity of the porous portion 30 is higher than that of the material of the porous portion 30 when the exhaust gas temperature is high. As such, if the porous portion 30 is provided on the inner peripheral face of the exhaust pipe 20, the porous portion 30 serves as a member or portion for reducing the heat conduction when the exhaust gas temperature is low, and serves as a member or portion for enhancing the heat conduction when the exhaust gas temperature is high.
Next, the thermal conductivity of the porous portion 30 will be described. More specifically, in the following, a description will be made of, by way of example, a preferred thermal conductivity of the porous portion 30 for achieving both the promotion of warming-up of the catalyst 40 during the exhaust gas temperature being low and the restriction of excessive heating of the catalyst 40 during the exhaust gas temperature being high.
First, a relation between the exhaust gas temperature and the flux of heat traveling from the exhaust gas in the exhaust pipe 20 to the wall of the exhaust pipe 20 will be described. Table 1 shown below represents the relation between the exhaust gas temperature and the heat flux. In Table 1, the unit of the temperature is ° C., the unit of the thermal transfer coefficient is W/m2K, and the unit of the heat flux is kW/m2. In the example illustrated in Table 1, the heat flux in the low temperature region was calculated, by way of example, on the assumption that the exhaust gas temperature is 400° C., which is the example activation temperature of the catalyst 40, the wall temperature of the exhaust pipe 20 is 100° C., and the heat transfer coefficient of exhaust gas is 50 W/m2K. In the example illustrated in Table 1, the heat flux in the high temperature region was calculated, by way of example, on the assumption that the exhaust gas temperature is 900° C., which is the example upper limit temperature of the catalyst 40, the wall temperature of the exhaust pipe 20 is 100° C., and the heat transfer coefficient of exhaust gas is 250 W/m2K.
As is evident from Table 1, the heat flux achieved when the exhaust gas temperature is in the high temperature region is 200 kW/M2, that is, at least ten times larger than the heat flux achieved when the exhaust gas temperature is in the low temperature region (15 kW/M2). This shows that in order to keep the temperature of the catalyst 40 lower than the upper limit temperature when the exhaust gas temperature is high, preferably, the thermal conductivity that the porous portion 30 exhibits when the exhaust gas temperature is high is high enough to conduct a heat flux at least ten times larger than the heat flux conducted when the exhaust gas temperature is low.
In view of the above, in the first example embodiment, the thermal conductivity of the porous portion 30 is set such that the thermal conductivity that the porous portion 30 exhibits when the exhaust gas temperature is high is at least ten times higher than the thermal conductivity that the porous portion 30 exhibits when the exhaust gas temperature is low. Accordingly, when the exhaust gas temperature is high after the warming-up of the catalyst 40, the porous portion 30 enhances the heat conduction through it, restricting the exhaust gas temperature from reaching the upper limit temperature of the catalyst 40 or higher. As such, the catalyst 40 can be restricted from being heated up to the upper limit temperature or higher. On the other hand, when the exhaust gas temperature is low, the porous portion 30 reduces the heat conduction through it, allowing the catalyst 40 to be quickly heated up to the activation temperature or higher.
Next, a method for setting the thermal conductivity of the porous portion 30 will be described. As is evident from
The target value of the porosity of the porous portion 30, for example, can be calculated using the equations (1) and (2) described earlier. Described in the following is an example case where such a target value of the porosity of the porous portion 30 is calculated using the equations (1) and (2) on the assumption that the temperature of the low temperature exhaust gas is 400 K and the temperature of the high temperature exhaust gas is 1200 K. The thermal conductivity λ1 of the porous portion 30 during the exhaust gas temperature being low (T=400 K) is expressed by the following equation (3), which is obtained from the equations (1) and (2).
λ1=λs×(1−Φ)+19/((1−Φ)×Ke) (3)
On the other hand, the thermal conductivity λ2 of the porous portion 30 during the exhaust gas temperature being high (T=1200 K) is expressed by the following equation (4), which is obtained from the equations (1) and (2).
λ2=λs×(1−Φ)+420/((1−Φ))×Ke) (4)
Meanwhile, the following equation (5) needs to be satisfied to make the thermal conductivity λ2 at least ten times higher than the thermal conductivity λ1.
λ1/λ2=(λsλ(1−Φ)2+420/Ke)/(λs×(1−Φ)2+19/Ke)≧10 (5)
The porosity Φ for satisfying the equation (5) above is only required to satisfy the equation (6) below.
Φ≧1−(25/(λs×Ke))1/2 (6)
Thus, by calculating the porosity Φ using the equation (6) above, it is possible to calculate the porosity with which the thermal conductivity of the porous portion 30 during the exhaust gas temperature being high is at least ten times higher than the thermal conductivity of the porous portion 30 during the exhaust gas temperature being low. For example, in a case where the porous portion 30 is made of amorphous silica as the main component, λs is 1.38 W/mK, and Kc is 2100 m−1, and therefore the equation (6) gives the porosity Φ of 0.9 or more (Φ≧0.9). That is, in a case where the porous portion 30 is made of amorphous silica as the main component, the thermal conductivity of the porous portion 30 during the exhaust gas temperature being high is at least ten times higher than the thermal conductivity of the porous portion 30 during the exhaust gas temperature being low, if the porosity of the porous portion 30 is 90% or more.
According to the exhaust pipe 20 of the first example embodiment, as described above, the porous portion 30 is provided on at least a part of the inner peripheral face of the exhaust pipe 20 through which the exhaust ports 16 of the internal combustion engine 10 and the catalyst 40 are connected to each other, and the thermal conductivity of the porous portion 30 during the exhaust gas temperature being high is at least ten times higher than the thermal conductivity of the porous portion 30 during the exhaust gas temperature being low. As such, when the exhaust gas temperature is low, the porous portion 30 reduces the heat conduction through it, suppressing the radiation of the exhaust gas heat through the exhaust pipe 20, and thus promoting the warming-up of the catalyst 40. When the exhaust gas temperature is high, on the other hand, the porous portion 30 enhances the heat conduction through it, restricting the catalyst 40 from being heated excessively. More specifically, since the thermal conductivity of the porous portion 30 during the exhaust gas temperature being high is at least ten times higher than the thermal conductivity of the porous portion 30 during the exhaust gas temperature being low, the exhaust gas temperature is restricted from rising up to the upper limit temperature of the catalyst 40 or higher, and thus the catalyst 40 is restricted from being heated up to the upper limit temperature or higher. Accordingly, degradation of the exhaust gas purification (control) performance of the catalyst 40 can be restricted.
According to the exhaust pipe 20 of the first example embodiment, further, the thermal conductivity of the porous portion 30 during the exhaust gas temperature being high is made at least ten times higher than the thermal conductivity of the porous portion 30 during the exhaust gas temperature being low, by setting the porosity of the porous portion 30 to the target value. Thus, the thermal conductivity of the porous portion 30 during the exhaust gas temperature being high can be easily made at least ten times higher than the thermal conductivity of the porous portion 30 during the exhaust gas temperature being low, as compared to the case where a desired thermal conductivity of the porous portion 30 is achieved by adjusting an element(s) other than the porosity of the porous portion 30.
Next, an exhaust pipe 20a of the second example embodiment of the invention will be described.
The cooler 50 may be selected from among various types of coolers, as long as it is capable of cooling the wall 23. For example, the cooler 50 may either be a water-cooled cooler or an air-cooled cooler, or it may be a cooler combining a water-cooled cooling system and an air-cooled cooling system.
The cooler 50 shown in
A comparison between
On the other hand, a comparison between
Accordingly, due to the porous portion 30 and the cooler 50, the exhaust pipe 20a of the second example embodiment is capable of promoting the warming-up of the catalyst 40 when the exhaust gas temperature is low, and is capable of more effectively restricting the catalyst 40 from being heated excessively when the exhaust gas temperature is high.
The cooler 50a has fans 52 and fins 53. The fans 52 blow air toward the wall 23. Thus, the wall 23 is cooled by the fans 52 blowing air. The fans 52 are two in this modification example. It is to be noted that the number of the fans 52 is not specifically limited. The first fan 52 blows air toward one side of the exhaust pipe 20a, while the second fan 52 blows air toward the other side of the exhaust pipe 20a.
The fins 53 are provided on the outer peripheral face of the wall 23 of the exhaust pipe 20a. The fins 53 facilitate the heat radiation from the wall 23. As such, providing the exhaust pipe 20a with both the fans 52 and the fins 53 achieves a higher cooling effect on the wall 23 than when the fans 52 or the fins 53 are not provided.
As well as the exhaust pipe 20a shown in
Next, an exhaust pipe 20b of the third example embodiment of the invention will be described.
The controller 60 is a microcomputer incorporating a central processing unit (CPU) 61, a read-only memory (ROM) 62. and a random-access memory (RAM) 63. The CPU 61 operates on various programs, maps, and the like, stored in the ROM 62 while using the RAM 63 as a temporary data storage (memory); so that the cooler 50 serves as controlling means for controlling the cooler 50a.
More specifically, the controller 60 determines the temperature of the wall 23 and controls the cooler 50a based on the determined temperature of the wall 23. The method that the controller 60 uses to determine the temperature of the wall 23 is not limited specifically. The temperature of the wall 23 is correlative to the exhaust gas temperature, and the exhaust gas temperature is correlative to the operation state of the internal combustion engine 10. Therefore, for example, the controller 60 can determine the temperature of the wall 23 based on the operation state of the internal combustion engine 10. Alternatively, the temperature of the wall 23 may be determined based on the result of detection by, if any, a temperature sensor for detecting the temperature of the wall 23.
The controller 60 of the third example embodiment is adapted, by way of example, to determine the temperature of the wall 23 based on the operation state of the internal combustion engine 10. More specifically, the controller 60 determines the temperature of the wall 23 based on the load on the internal combustion engine 10 and the speed of the internal combustion engine 10. For this purpose, a result of detection by an engine load detection portion 70 that detects the load on the internal combustion engine 10 and an engine speed detection portion 71 that detects the speed of the internal combustion engine 10 are sent to the controller 60.
The load on the internal combustion engine 10 can be, for example, calculated based on the accelerator operation amount (e.g., the travel of the accelerator pedal), the fuel injection amount, and so on. Therefore, for example, the engine load detection portion 70 may be an electronic control unit (ECU) that calculates the load on the internal combustion engine 10 based on at least one of the accelerator operation amount and the fuel injection amount. The engine speed can be calculated based on the angle of the crankshaft (crank angle) of the internal combustion engine 10. Therefore, for example, the engine speed detection portion 71 may be an ECU that calculates the engine speed based on the crank angle.
Meanwhile, by way a example, a map specifying the temperature of the wall 23 in association with the load on the internal combustion engine 10 and the speed of the internal combustion engine 10 is prestored in the ROM 62 of the controller 60. In this case, the controller 60 determines the temperature of the wall 23 by applying to the map the results of detections by the engine load detection portion 70 and engine speed detection portion 71.
After determining the temperature of the wall 23, the controller 60 controls the cooler 50a in accordance with the determined temperature of the wall 23. In the third example embodiment, the controller 60 is adapted to control the cooler 50a so as to bring the temperature of the wall 23 to a predetermined temperature. More specifically, the controller 60 controls the airflow from the cooler 50a such that the temperature of the wall 23 becomes equal to or lower than the activation temperature of the catalyst 40.
More specifically, the controller 60 prestores therein a threshold (Tc) for the temperature of the wall 23, which is used as a reference value for determining whether to activate the fans 52 of the cooler 50a. The values of the threshold (Tc) prestored in the controller 60 are associated with the operation state of the internal combustion engine 10. The controller 60 determines the temperature of the wall 23 and the value of the threshold (Tc) based on the operation state of the internal combustion engine 10. If the temperature of the wall 23 is higher than the value of the threshold (Tc), the controller 60 activates the fans 52 of the cooler 50a to control the temperature of the wall 23 to be equal to or lower than the activation temperature of the catalyst 40. On the other hand, if the temperature of the wall 23 is equal to or lower than the value of the threshold (Tc), the controller 60 stops the fans 52 of the cooler 50a.
By way of example, the threshold (Tc) may be a variable with which the temperature of the catalyst 40 can be kept equal to or lower than its activation temperature by activating the fans 52 of the cooler 50a in response to the temperature of the wall 23 reaching the value of the threshold (Tc). The values of the threshold (Tc) may be set in advance empirically or through simulations, for example, and then stored in the ROM 62, or the like.
The flowchart of
Then, the controller 60 determines whether the temperature of the wall 23 is higher than the value of the threshold (Tc) (step S2). If it is determined in step S2 that the temperature of the wall 23 is higher than the threshold (Tc), the controller 60 then activates the fans 52 of the cooler 50a (step S3). It is to be noted that the controller 60 may be adapted to control the airflow by adjusting the speed of the fans 52 in accordance with the operation state of the internal combustion engine 10. In this case, for example, the controller 60 may control the speed of the fans 52 such that it is higher when the load on the internal combustion engine 10 is larger than a predetermined value and the speed of the internal combustion engine 10 is higher than a predetermined value, than when the load on the internal combustion engine 10 is not larger than the predetermined value and the speed of the internal combustion engine 10 is not higher than the predetermined value. After step S3, the controller 60 executes step S1 again.
In contrast, if it is not determined in step S2 that the temperature of the wall 23 is higher than the value of the threshold (Tc), the controller 60 then stops the fans 52 of the cooler 50a (step S4), after which the controller 60 finishes the control routine.
Thus, due to the porous portion 30, the cooler 50a, and the controller 60, the exhaust pipe 20b of the third example embodiment provides the effect that the temperature of the wall 23 can be more accurately controlled, as well as the effects of the first and second example embodiments. More specifically, the exhaust pipe 20b is capable of controlling the temperature of the wall 23 to be equal to or lower than the activation temperature of the catalyst 40, and thus is capable of making the temperature of the catalyst 40 closer to the activation temperature.
While the cooler 50a in the third example embodiment is an air-cooled cooler, coolers of various other types may attentively be used. For example, the cooler 50a may be a water-cooled cooler. In this case, for example, the controller 60 is adapted to control the temperature of the wall 23 by controlling a pump for delivering the coolant for the cooler 50, a flowrate control valve for controlling the flowrate of the coolant, and so on. More specifically, if it is determined in step S2 in the control routine illustrated in
Next, an exhaust pipe of the fourth example embodiment of the invention (will hereinafter be referred to as “exhaust pipe 20c”) will be described. The exhaust pipe 20c of the fourth example embodiment is different from the exhaust pipes of the first to third example embodiments in that the average size of the pores of the porous portion 30 is equal to or smaller than the mean free path of air. Other structural features are the same as those in the first to third example embodiments, and therefore their descriptions will be omitted.
The graph of
The chart of
According to the exhaust pipe 20c of the fourth example embodiment, in contrast, the average size of the pores of the porous portion 30 is equal to or smaller than the mean free path of air, and therefore it is possible to suppress the heat conductions that may be caused by collisions between the molecules 80 of the air in the pores of the porous portion 30. As such, the exhaust pipe 20c of the fourth example embodiment provides the effect that the thermal conductivity of the porous portion 30 can be restricted from becoming higher than estimated, as well as the effects of the first to third example embodiments.
The invention has been described with reference to the example embodiments for illustrative purposes only. It should be understood that the description is not intended to be exhaustive or to limit form of the invention and that the invention may be adapted for use in other systems and applications. The scope of the invention embraces various modifications and equivalent arrangements that may be conceived by one skilled in the art.
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|---|---|---|---|
| 2010-290944 | Dec 2010 | JP | national |
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| 3238330 | Apr 1984 | DE |
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| Number | Date | Country | |
|---|---|---|---|
| 20120159936 A1 | Jun 2012 | US |
