JP4240136B2 - Exhaust heat exchanger - Google Patents

Description

  The present invention relates to an exhaust heat exchanger that exchanges heat between exhaust gas discharged from a heat engine and cooling water, and in particular, cools exhaust gas used in an exhaust gas recirculation device (hereinafter referred to as EGR). This is effective for application to a gas cooler (hereinafter referred to as an EGR cooler).

  As an exhaust heat exchanger, for example, there is a diesel-type engine EGR cooler. A conventional EGR cooler is installed in the middle of an exhaust gas recirculation pipe that recirculates a part of the exhaust of the engine directly to the intake side of the engine (see, for example, Patent Document 1).

  In addition, the conventional EGR cooler has a structure in which a plurality of tubes are stacked and inner fins are arranged in the tubes, and by exchanging heat between the exhaust flowing through the tubes and the cooling water flowing outside the tubes, Exhaust gas is cooled (see, for example, Patent Document 1). Note that straight fins are used as the inner fins.

By the way, as a kind of inner fin, the offset fin used for the use different from EGR coolers, such as an intercooler other than a straight fin and a wave fin, is known (for example, refer patent document 2).
JP 2004-77024 A Japanese Patent No. 3766914

  As described below, the EGR cooler 10 and the intercooler are different in cooling method, required performance, specification environment, etc., so each of the fin pitch fp, fin height fh, segment length L, etc. of the offset fins About the dimension of a site | part, the specification of offset fins conventionally used, such as an offset fin for intercoolers, cannot be applied as it is.

  For example, the cooling system is different between the intercooler and the EGR cooler, that is, the air cooling type is generally used for the intercooler, whereas the water cooling type is generally used for the EGR cooler. The degree of contribution to is different.

  Further, the temperature of the cooling target gas is different between the intercooler and the EGR cooler, that is, the intercooler has a temperature of, for example, 170 ° C., whereas the EGR cooler has a temperature of, for example, 400 ° C.

  Intercooler and EGR cooler are made of different materials. Intercooler is generally made of aluminum, whereas EGR cooler is exposed to corrosive environment due to high temperature oxidation and condensed water. From the viewpoint of ensuring the quality, it is necessary to use stainless steel as the material.

  As another example, the oil cooler and the EGR cooler have different physical properties of the fluid to be cooled. In other words, the oil cooler cools oil with high viscosity and density, such as for engines and automatic transmissions, while the EGR cooler cools exhaust gas with low viscosity and density. The degree of contribution is different.

  The specifications of the offset fin are determined so that the heat exchange performance is the highest depending on the cooling method, the temperature of the cooling target gas, the material of the inner fin, etc. As the specifications of the offset fin for the EGR cooler If the specification for the intercooler is simply applied, the heat exchange performance of the EGR cooler may be lowered.

  Further, as described above, the exhaust gas recirculation apparatus shown in FIG. 1 is required to have a small pressure loss in the EGR cooler 10 in order to secure a flow rate at a high load. In the fin specification (fin pitch fp = 2 mm), the pressure loss in the tube becomes too large.

  The above-mentioned problem is not limited to the EGR cooler, and is also a problem that occurs in other types of exhaust heat exchangers that are water-cooled and made of stainless steel.

  In view of the above points, the present invention provides an exhaust heat exchanger having a structure having a tube and an inner fin. When an offset fin is used as the inner fin, the exhaust gas is obtained by obtaining various conditions for a fin that can obtain high performance. The purpose is to improve the performance of the heat exchanger.

In order to achieve the above object, according to the first aspect of the present invention, heat exchange is performed between the exhaust gas containing particulate matter generated by combustion in the engine (1) and the cooling water for cooling the exhaust gas. At the same time, in the exhaust heat exchanger that discharges the exhaust gas after heat exchange to the engine (1) side, a stainless steel tube (21) in which the exhaust gas flows inside and the cooling water flows in the outside is arranged in the tube. And an inner fin (22) made of stainless steel that promotes heat exchange between the exhaust gas and the cooling water, and the inner fin (22) has a cross-sectional shape substantially perpendicular to the flow direction of the exhaust gas. An offset fin having a wave shape that bends (31) alternately on one side and the other side and is partially raised in a direction parallel to the flow direction of the exhaust gas. And In the cross-sectional shape, the size of the fin pitch, which is the distance between the centers of the convex portions adjacent on the same side of one side and the other side, is fp, and the convexes adjacent on the same side of the one side and the other side. The equivalent circular diameter of the region surrounded by the fin between the part and the convex part is de, the length in the exhaust flow direction of the cut and raised part is L, and the convex part on the other side from the convex part on one side in the cross-sectional shape When the fin height, which is the distance to the part, is fh, the size of the fin pitch is
2 <fp ≦ 12 (unit: mm)
The length L in the exhaust flow direction of the cut and raised portion is
When fh <7 and fp ≦ 5, 0.5 <L ≦ 7 (unit: mm),
When fh <7, 5 <fp, 0.5 <L ≦ 1 (unit: mm),
When 7 ≦ fh and fp ≦ 5, 0.5 <L ≦ 4.5 (unit: mm), or
When 7 ≦ fh and 5 <fp, 0.5 <L ≦ 1.5 (unit: mm)
And furthermore,
When X = de × L ^0.14 / fh ^0.18 ,
In order to suppress the equivalent circular diameter de and the length L of the cut-and-raised portion in the exhaust flow direction from accumulating particulate matter on the inner fin (22),
1.1 ≦ X ≦ 4.3
It is a size that satisfies the requirements.

  As a result, the pressure loss of the exhaust gas flowing inside the tube and the flow resistance of the cooling water flowing outside the tube can be kept low, clogging inside the tube can be suppressed, and an exhaust heat exchanger having high heat dissipation performance can get.

  As a result, a high-performance exhaust heat exchanger in which the magnitude of the gas density, which is an index considering both cooling performance and pressure loss, is 93% or more of the maximum value can be obtained.

In the invention according to claim 2 , the equivalent circular diameter and the length of the cut and raised portion in the exhaust flow direction are:
It is a feature that is sized to satisfy 1.2 ≦ X ≦ 3.9.

  Thereby, a higher performance exhaust heat exchanger having a gas density of 95% or more of the maximum value can be obtained.

In the invention according to claim 3 , the equivalent circular diameter and the length of the cut and raised portion in the exhaust flow direction are:
It is a feature that is sized to satisfy 1.3 ≦ X ≦ 3.5.

  As a result, a higher performance exhaust heat exchanger can be obtained in which the magnitude of gas density, which is an index considering both cooling performance and pressure loss, is 97% or more of the maximum value.

Na us, reference numerals in parentheses of each means described in the scope and the field of claims is an example showing the correspondence with specific means described in embodiments described later.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments shown in the drawings will be described below. The fourth embodiment described below is an embodiment of the invention described in the claims. The first embodiment is a premise of the present invention, and the second, third, and fifth embodiments are It is shown as a reference example.
(First embodiment)
In this embodiment, an example in which the present invention is applied to an EGR cooler will be described. FIG. 1 shows a schematic diagram of an exhaust gas recirculation device in which an EGR cooler is used. In the exhaust gas recirculation device shown in FIG. 1, for example, an air cleaner 3, a variable turbo actuator 4, an intercooler 5, and an intake manifold 6 are arranged in the middle of the intake path 2 of the engine 1. The variable turbo actuator 4 and the DPF (diesel particulate filter) 8 are arranged, and the first exhaust recirculation pipe 9 is connected to the exhaust flow downstream side of the DPF 8 and the intake flow upstream side of the variable turbo actuator 4. In the middle of the first exhaust gas recirculation pipe 9, an EGR cooler 10 and an EGR valve 11 are arranged. The first exhaust gas recirculation pipe 9 is a pipe that recirculates a part of the exhaust gas that has passed through the DPF 8 to the intake side of the engine.

  As described above, in the exhaust gas recirculation device shown in FIG. 1, exhaust gas from which PM (particulate matter) has been removed by the DPF 8 is introduced into the EGR cooler 10, so that the exhaust gas introduced into the EGR cooler 10 The amount of soot is reduced.

  In addition, the exhaust gas recirculation device shown in FIG. 1 is arranged in the middle of the second exhaust gas recirculation pipe 12 that recirculates part of the exhaust gas of the engine directly to the intake side of the engine before passing it through the DPF 8. EGR valve 13 is provided. Comparing the first exhaust gas recirculation pipe 9 and the second exhaust gas recirculation pipe 12, the pressure of the exhaust gas flowing through the first exhaust gas recirculation pipe 9 is lower than that in the second exhaust gas recirculation pipe 12. . Therefore, the exhaust gas recirculation device shown in FIG. 1 is called a low-pressure EGR system, and this system has an advantage that the EGR can be operated even when the engine is heavily loaded.

  2 shows a side view of the EGR cooler of the present embodiment, FIG. 3 shows a cross-sectional view of the EGR cooler in the direction of arrows AA, and FIG. 4 shows a cross-sectional view of the EGR cooler in the direction of arrows BB. Show.

  The EGR cooler 10 is an exhaust heat exchanger that cools the exhaust gas generated by combustion in the engine 1 to the engine 1 with the cooling water of the engine 1, as shown in FIGS. As shown, a plurality of tubes 21, inner fins 22, a water side tank 23, and a gas side tank 24 are mainly provided. These members 21 to 44 are made of stainless steel, and are joined by brazing, welding, or the like.

  As shown in FIGS. 3 and 4, the tube 21 is a tube constituting an exhaust passage 21a through which exhaust gas flows, and the exhaust gas flows inside. Further, the cooling water flows outside the tube 21, and the exhaust gas and the cooling water are heat-exchanged through the tube 21. As cooling water, what is used for engine cooling water is employable, for example.

  Specifically, as shown in FIG. 3, the cross-sectional shape when viewed from the exhaust flow direction of the tube 21 is a flat shape having a long side 21c and a short side 21d, and a flat surface 21c on the long side 21c side. A plurality of tubes 21 are stacked in a direction perpendicular to the vertical direction (vertical direction in the figure). As shown in FIGS. 3 and 4, in this embodiment, a cooling water passage 21 b through which cooling water flows between the adjacent tubes 21 is basically configured by the outer wall of the adjacent tubes 21.

  The water-side tank 23 mainly distributes and supplies the cooling water flowing into the EGR cooler in one water-side tank 23 to each tube 21, and collects and collects the cooling water from each tube 21 in the other water-side tank 23. Is. As shown in FIGS. 2 and 4, the water-side tank 23 is provided around the stacked tubes 21 in the vicinity of both ends of the tube 21 in the gas flow direction, and includes a cooling water inlet or a cooling water outlet 23 a. Yes.

  As shown in FIGS. 2 and 4, the gas side tanks 24 are respectively disposed at both ends of the tube 21 in the gas flow direction. Both gas side tanks 24 are connected to the first exhaust gas recirculation pipe 9, one gas side tank 24 distributes and supplies exhaust gas to each tube, and the other gas side tank 24 finishes heat exchange. The exhaust gas is collected and collected from each tube 21.

  The inner fin 22 is disposed in each tube 21, promotes heat exchange between the exhaust gas and the cooling water, and is fixed to the inner wall surface of the tube 21. Hereinafter, the details of the inner fin 22 will be described.

  FIG. 5 shows a perspective view of the inner fin, and FIG. 6 shows a partially enlarged view of the inner fin when viewed from the exhaust gas flow direction.

  As shown in FIGS. 5 and 6, the inner fin 22 has a cross-sectional shape that is substantially perpendicular to the flow direction of the exhaust gas, that is, a cross-sectional shape when viewed from the flow direction of the exhaust gas. A wavy shape that is alternately positioned on the side and bends, and includes a cut-and-raised portion 32 that is partially cut and raised in the flow direction of the exhaust gas, and the cut-and-raised portion when viewed from the flow direction of the exhaust gas The corrugated portion formed by 32 is an offset fin that is offset with respect to the corrugated portion adjacent in the exhaust gas flow direction. In the offset fin 22, the convex portion 31 is in contact with the inner wall surface on the long side 21 c side of the tube 21.

  As shown in FIG. 3, the offset fin 22 divides the inside of the tube 21 into a plurality of flow paths in a direction parallel to the long side 21 c of the tube 21 (in other words, a partition). The flow paths divided into a plurality of are partially offset in the exhaust flow direction. That is, as shown in FIG. 5, the wall part 33 which divides | segments the inside of the tube 21 into a some flow path is arrange | positioned in zigzag form along the flow direction of exhaust gas. Further, when the offset fins 22 are viewed in the exhaust flow direction, the convex portions 31 on the same side, such as one side and the other side, are adjacent to each other in the exhaust flow direction. Has been.

  At this time, as shown in FIG. 6, the offset distance s is preferably set to about half the gas passage height u so that the heat transfer coefficient is high and the gas resistance is small. Here, the offset distance s is a wave-shaped portion where the wave-shaped portion formed by the cut-and-raised portion 32 of the offset fin 22 is adjacent in the flow direction of the exhaust gas when viewed from the flow direction of the exhaust gas. In contrast, in the direction in which the convex portions 31 adjacent on the same side are arranged in a cross-sectional shape substantially perpendicular to the flow direction of the exhaust gas, it is the shift length when they are shifted, in other words, one side adjacent to each other In the direction parallel to the long side 21c of the tube 21 between the wall portion 33 positioned between the convex portion 31 on the other side and the wall portion 33 of the cut-and-raised portion 32 that is displaced with respect to the wall portion 33. It is an interval.

  The cross-sectional shape of the offset fin 22 in the exhaust gas flow direction may be either a shape including a linear portion at the apex of the convex portion 31 or a shape not including it.

  The offset fins 22 are manufactured by bending a flat plate into a wave shape by press working, and by raising a portion that becomes the cut and raised portion 32 by press working. In addition, as a method of raising the part which becomes the cut-and-raised part 32, before raising, a method of making a slit in advance before corrugating or cutting and raising by pressing both sides of the plate with a press machine. You may do it at the same time. The fins may be formed by roller processing, or a combination of both roller processing and press processing.

  In the offset fin 22 having such a structure, as shown in FIGS. 5 and 6, the cross-sectional shape viewed from the flow direction of the exhaust gas has one side and the other side, like one side or the other side. On the same side, the specifications such as the fin pitch fp which is the distance between the centers of the adjacent convex portions 31 and the size of the fin height fh which is the distance from the convex portion on one side to the convex portion on the other side, The performance of the EGR cooler 10 is determined. The fin height fh is a distance in a direction perpendicular to the inner wall surface of the tube 21 with which the offset fins 22 are in contact, and is equivalent to the inner diameter of the tube 21 in the stacking direction of the tubes 21.

  Therefore, the present inventor examined the optimum specification of the offset fin 22. In the present embodiment, the EGR cooler 10 having the above-described structure in which the fin pitch fp and the fin height fh have various sizes is manufactured, and the exhaust gas flowing inside the tube 21 when the gas and the cooling water are flowed under predetermined conditions. Evaluate the magnitude of the gas pressure loss, the resistance of the cooling water flowing outside the tube 21, the clogging inside the tube 21, and the heat dissipation performance of the EGR cooler. It was determined. The predetermined conditions are gas inlet temperature Tg1: 400 ° C., gas flow rate: 30 g / s, gas inlet pressure Pg 1: 50 kPa, cooling water inlet temperature Tw 1: 80 ° C., cooling water flow rate: 10 L / min.

  FIG. 7 shows the relationship between the fin height fh and the pressure loss ratio (ΔPg ratio). The pressure loss ΔPg is the difference between the gas pressure Pg1 at the gas inlet of the gas side tank 14 and the gas pressure Pg2 at the gas outlet, and the ΔPg ratio is the pressure loss ΔPg in each condition The ratio (%) when the maximum value is the reference value 100.

  The conditions of the offset fins 22 used at this time are as follows: the plate thickness t of the offset fins 22: 0.2 mm, the fin pitch fp: 5 mm, 7 mm, the length L of the cut and raised portion 32 in the exhaust flow direction: 1 mm, 5 mm The radius of curvature R is 0.2 mm. Hereinafter, the length L of the cut and raised portion 32 in the exhaust flow direction is referred to as a segment length L. In addition, fp5 and fp7 in FIG. 7 indicate fp = 5 mm and fp = 7 mm, respectively, L1 and L5 indicate L = 1 mm and L = 5 mm, respectively. The following numbers indicate the length. The same applies to other drawings.

  As shown in FIG. 7, the physique of the cooler is fixed, that is, the sizes of the water side tank 23 and the gas side tank 24 are fixed, and the fin pitch fp and the segment length L are also fp = 5 mm, L = 1mm, when the fin height fh is changed to a smaller side, the inclination changes when the fin height fh is 3.5 mm, as in fp5 and L1 in the figure. It became an inflection point, and it was found that the rate of increase in pressure loss increased when the fin height fh was 3.5 mm or less compared to when it was larger than 3.5 mm.

  Similarly, when fixed at fp = 5 mm and L = 5 mm as in fp5 and L5 in the figure and the fin height fh is changed to a smaller side, or as in fp7 and L5 in the figure , Fp = 7 mm, L = 5 mm, and even when the fin height fh is changed to a smaller side, the inflection point is when the fin height fh is 3.5 mm, and fh = 3. The rate of increase in pressure loss was different at 5 mm.

  From this result, when the physique of the cooler is fixed and fp and L are the same, when fh is 3.5 mm or less, the pressure loss is relatively large, and when fh is larger than 3.5 mm, the pressure loss is compared. It can be said that it is small. Therefore, it can be said that the fin height fh is preferably larger than 3.5 mm.

  Next, FIG. 8 shows the relationship between the fin height fh and the water flow resistance ΔPw. The water flow resistance ΔPw is the difference between the water pressure at the cooling water inlet of the water side tank and the water pressure at the cooling water outlet. The conditions of the offset fins 22 used at this time are the same as in FIG.

  As shown in FIG. 8, when the physique of the cooler is fixed and the interval between the tubes 21 serving as the width of the cooling water passage 21b is constant, the water flow is changed as the fin height fh is changed to the larger side. Resistance ΔPw tends to increase. And from the viewpoint of cooling performance, if the water flow resistance ΔPw is 3 to 3.2 kPa or more, a high-performance water pump is required to secure the cooling water flow rate, leading to an increase in cost. Therefore, the fin height fh is preferably 12 mm or less, and more preferably 10 mm or less.

  Further, as a result of investigating the presence or absence of clogging, as the fin pitch fp is decreased, the offset distance s is decreased. When the fin thickness t is 0.2 mm or less, the offset is obtained when the fin pitch fp is 2 mm or less. The distance s became too small, and clogging occurred due to soot in the exhaust gas. Therefore, it can be said that the fin pitch fp is preferably larger than 2 mm from the viewpoint of suppressing the occurrence of clogging.

  Further, by shortening the segment length L, the heat dissipation performance of the offset fins 22 can be enhanced. Therefore, the relationship between the fin pitch fp and the heat dissipation performance of the EGR cooler when the range of the segment length L is 1 ≦ L ≦ 10 mm and the range of the fin height fh is 3.5 <fh ≦ 12 was examined. The result is shown in FIG. FIG. 9 shows the results when the fin height fh is 3.6 mm or 12 mm and the segment length L is 1 mm or 10 mm.

  As can be seen from FIG. 9, regardless of the fin height fh, when the segment length L is 1 mm, the heat dissipation performance of the EGR cooler is higher, the fin height fh is 12 mm, and the segment length When the length L is 10 mm, as can be seen from fh12-L10 in FIG. 9, when the fin pitch fp is larger than 12 mm, the heat dissipation performance required for the EGR cooler in the market is 5.5 kw / L. However, if the fin pitch fp is 12 mm or less, the heat dissipation performance required in the market is satisfied.

  Therefore, when the range of the fin height fh is 3.5 <fh ≦ 12, it can be said that the fin pitch fp is preferably 12 mm or less.

From the above examination results, the size of the fin pitch fp and the fin height fh
3.5 <fh ≦ 12
2 <fp ≦ 12
It can be said that it is preferable to make the size satisfy.

  Thereby, the pressure loss of the exhaust gas flowing through the tube 21 and the flow resistance of the cooling water flowing outside the tube 21 can be kept low, clogging inside the tube 21 can be suppressed, and high heat dissipation performance can be obtained. .

(Second Embodiment)
In the present embodiment, a case will be described in which the optimum specification of the offset fin 22 is determined based on parameters and criteria different from those in the first embodiment. Note that the basic structure of the EGR cooler 10 is the same as that of the first embodiment, and thus the description thereof is omitted.

  In the present embodiment, the optimum specification of the offset fin 22 is determined based on the relationship between the equivalent circular diameter de and the EGR gas density ratio ρ.

  Here, as shown in FIG. 6, the equivalent circular diameter de is adjacent on the same side, such as one side and the other side, in a cross-sectional shape substantially perpendicular to the exhaust gas flow direction of the offset fin 22. It means the diameter (unit: mm) when the hatched area C surrounded by the fins 22 and the tube 21 between the convex portion 31 and the convex portion 31 is converted into a circle, and is expressed by the following formula.

de = 4 × S / l
Note, S is a gas passage sectional area (corresponding to the diameter of a circle in cross-sectional area [pi] D ^2/4 of the circle when a D). In addition, l is a wetting edge length (corresponding to a circumference πD when the diameter of the circle is D), and the length of the inner wall surface of one gas flow passage formed by the fins 22 and the tubes 21 (the inner wall and The length of the portion in contact with the gas).

  A method for calculating the equivalent circle diameter de will be described. FIG. 10 shows a partial cross-sectional view of the offset fin 22 when the offset fin 22 is cut in a direction substantially perpendicular to the exhaust gas flow direction.

  As shown in FIG. 10, by dividing the wetting edge length l / 2 corresponding to the right half of the hatched area C in FIG. 6 into five line segments (1) to (5), When the straight line length is 0 or more, the wetting edge length l can be expressed by using the fin pitch fp, the fin height fh, the plate thickness t, and the curvature radius R of the curved portion as in the following equation. Further, by dividing the gas passage cross-sectional area corresponding to the right half of the hatched region C in FIG. 6 into four regions a to d, the gas passage cross-sectional area S is expressed by the fin pitch fp, It can be expressed using the fin height fh, the plate thickness t, and the curvature radius R of the curved portion.

l / 2 = fp / 2− (fp / 2− (2R + t)) / 2 (1)
+ Π (R + t) / 2 (2)
+ Fh-2 (R + t) (3)
+ ΠR / 2 (4)
+ (Fp / 2− (2R + t)) / 2 (5)
S / 2 = (fh−t) (fp / 2− (2R + t)) / 2... A
+ (Fh- (R + t)) R ... b
+ ΠR2 / 4 ... c
+ (R + t) 2- [pi] (R + t) 2/4 ... d
Therefore, the equivalent circular diameter de is determined by the fin pitch fp, the fin height fh, the plate thickness t, and the curvature radius R of the curved portion.

On the other hand, the EGR gas density ρ is an index that considers both the cooling performance of the EGR cooler and the magnitude of pressure loss, and the EGR gas density ρ [kg / m ³ ] is expressed by the following equation, where ρ is The larger the ratio, the higher the EGR gas filling rate and the higher the EGR rate.

ρ = Pg2 / (R · Tg2)
Pg2 is the gas outlet absolute pressure (Pa), R is the gas constant = 287.05 J / kg · K, and Tg2 is the gas outlet temperature (K).

  FIG. 11 shows the relationship between the equivalent circular diameter de and the EGR gas density ρ ratio. The EGR gas density ρ ratio is a ratio when the maximum value of the EGR gas density ρ is 100%. In FIG. 11, the measurement conditions are as follows: gas inlet temperature Tg 1: 400 ° C., gas flow rate: 30 g / s, gas inlet pressure Pg 1: 50 kPa, cooling water inlet temperature Tw 1: 80 ° C., cooling water flow rate: 10 L / min. This is a calculation result based on the measurement results when the fin thickness t is 0.2 mm, the fin height fh is 9 mm, and the curvature radius R is 0.2 mm.

  Moreover, the curve (a) in FIG. 11 is a measurement result when the segment length L is 1 mm, and the curve (b) in FIG. 11 is a result when L is 5 mm. When the range of L is 0 <L <5, the result is the same as the curve (a) in FIG. 11, and when 5 ≦ L ≦ 15, the result is the same as the curve (b) in FIG. .

  Therefore, from the curve (a) in FIG. 11, when 0 <L <5, the size of the equivalent circle diameter de is set to 1.2 ≦ de ≦ 6.1, so that the ρ ratio is 93% or more. By making 1.3 ≦ de ≦ 5.3, the ρ ratio can be made 95% or more, and by making 1.5 ≦ de ≦ 4.5, the ρ ratio is 97 It turns out that it can be made into% or more.

  On the other hand, from the curve (b) in FIG. 11, when 5 ≦ L ≦ 15, the equivalent circle diameter de is set to 1.0 ≦ de ≦ 4.3, whereby the ρ ratio is 93% or more. By making 1.1 ≦ de ≦ 4.0, the ρ ratio can be made 95% or more, and by making 1.3 ≦ de ≦ 3.5, the ρ ratio is 97 It turns out that it can be made into% or more. The unit of L and de described above is mm.

  The results in FIG. 11 are the results when the plate thickness t and the curvature radius R of the fin are 0.2 mm, respectively, but when the plate thickness t and the curvature radius of the fin are slightly changed within a feasible range. The same result is obtained for. For example, the same result is obtained when the plate thickness t and the radius of curvature of the fin are each changed by 0.1 to 0.2 mm.

(Third embodiment)
In the present embodiment, a case will be described in which the optimum specification of the offset fin 22 is determined based on parameters and criteria different from those of the above-described embodiment. Note that the basic structure of the EGR cooler 10 is the same as that of the first embodiment, and thus the description thereof is omitted.

  In the present embodiment, the optimum specification of the offset fin 22 is determined based on the relationship between the segment length L and the EGR gas density ratio ρ.

  FIG. 12 shows the relationship between the segment length L and the EGR gas density ρ ratio. The EGR gas density ρ ratio is a ratio when the maximum value of the EGR gas density ρ is 100%. In addition, FIG. 12 is the result calculated based on the measurement result on the same measurement conditions as the time of FIG. However, the fin height fh and the segment length L are different from those in FIG.

  A curve (a) in FIG. 12 is a calculation result when fh <7 and fp ≦ 5. For example, the curve (a) is a calculation result when fh = 4.6 and fp = 4.5. At this time, by setting the segment length L to 0.5 <L ≦ 65, the ρ ratio can be 95% or more, and by setting 0.5 <L ≦ 25, the ρ ratio is 97 %, And by making 0.5 <L ≦ 7, the ρ ratio can be 99% or more.

  A curve (b) in FIG. 12 is a calculation result when fh <7, 5 <fp, for example, a calculation result when fh = 4.6 and fp = 5.5. At this time, by setting the segment length L to 0.5 <L ≦ 20, the ρ ratio can be 95% or more, and by setting 0.5 <L ≦ 8, the ρ ratio is 97 %, And by making 0.5 <L ≦ 1, the ρ ratio can be 99% or more.

  A curve (c) in FIG. 12 is a calculation result when 7 ≦ fh and fp ≦ 5, and is a calculation result when fh = 9 and fp = 4.5, for example. At this time, by setting the segment length L to 0.5 <L ≦ 50, the ρ ratio can be 95% or more. By setting 0.5 <L ≦ 15, the ρ ratio is 97 %, And by making 0.5 <L ≦ 4.5, the ρ ratio can be 99% or more.

  A curve (d) in FIG. 12 is a calculation result when 7 ≦ fh and 5 <fp, for example, a calculation result when fh = 9 and fp = 5.5. At this time, by setting the segment length L to 0.5 <L ≦ 15, the ρ ratio can be 95% or more, and by setting 0.5 <L ≦ 6, the ρ ratio is 97 %, And by making 0.5 <L ≦ 1.5, the ρ ratio can be 99% or more.

  The unit of fh, fp, and L described above is mm. Further, the results of FIG. 12 are the results when the plate thickness t and the curvature radius R of the fin are 0.2 mm, respectively, but when the plate thickness t and the curvature radius of the fin are slightly changed within a feasible range. The same result is obtained for. For example, the same result is obtained when the plate thickness t and the radius of curvature of the fin are each changed by 0.1 to 0.2 mm.

(Fourth embodiment)
In the present embodiment, a case will be described in which the optimum specification of the offset fin 22 is determined based on parameters and criteria different from those of the above-described embodiment. Note that the basic structure of the EGR cooler 10 is the same as that of the first embodiment, and thus the description thereof is omitted.

  In the present embodiment, the optimum specification of the offset fin 22 is determined based on the relationship between the function X using the equivalent circular diameter de, the segment length L, and the fin height fh and the EGR gas density ratio ρ.

  FIG. 13 shows the relationship between the function X and the EGR gas density ratio ρ. This function X is expressed by the following equation.

X = de × L ^0.14 / fh ^0.18
FIG. 13 shows calculation results of the EGR gas density ratio ρ when the fin pitch fp, the fin height fh, and the segment length L are various sizes. Each curve in the figure is obtained by plotting the EGR gas density ratio for each size of fp, with fh and L being fixed, fp being an arbitrary size. As the value on the horizontal axis increases, fp increases. As an example, in FIG. 13, fp of each curve is indicated as fp12 and fp14 at positions of 12 mm and 14 mm, respectively. Specifically, the fin pitch fp is any of 1.5 to 14 mm, the fin height fh is any of 4.6, 5.6, 7, 9, and 12 mm, and the segment length L is 1 mm. Or 10 mm. Other measurement conditions are the same as those in FIGS.

  From the results shown in FIG. 13, it can be seen that the curve indicating the relationship between the function X and the EGR gas density ratio ρ shows the same tendency under each condition.

  As described in the first embodiment, the fin pitch fp is preferably in a range satisfying 2 <fp ≦ 12. In this range, it can be seen from a straight line connecting points where fp in FIG. 13 is 12 mm. In addition, by setting the equivalent circle diameter de and the segment length L to a size that satisfies 1.1 ≦ X ≦ 4.3, and more preferably, a size that satisfies 1.1 ≦ X ≦ 3.5, The ρ ratio can be 93% or more. Similarly, by setting the equivalent circle diameter de and the segment length L to a size satisfying 1.2 ≦ X ≦ 3.9, more preferably 1.2 ≦ X ≦ 3.3. , The ρ ratio can be 95% or more, and a size satisfying 1.3 ≦ X ≦ 3.5, more preferably a size satisfying 1.3 ≦ X ≦ 2.9. The ρ ratio can be 97% or more.

  The unit of fp and X is mm. The results in FIG. 13 are the results when the plate thickness t and the radius of curvature R of the fin are 0.2 mm, respectively, but when the plate thickness t and the radius of curvature of the fin are slightly changed within a feasible range. The same result is obtained for. For example, the same result is obtained when the plate thickness t and the radius of curvature of the fin are changed within a range of 0.1 mm or more and less than 0.2 mm, respectively.

(Fifth embodiment)
In the first embodiment, the offset amount s illustrated in FIG. 6 has been described as being preferably set to a relative size that is approximately half the gas passage height u. However, in the present embodiment, The absolute size of the offset distance s will be described. In the following description, the basic structure of the EGR cooler 10 other than the offset distance s is the same as that of the first embodiment, and a description thereof will be omitted.

  FIG. 14A shows the accumulation of PM (particulate matter) such as soot in the exhaust gas that accumulates on the surface of the offset fin when the exhaust gas passes through the EGR cooler having the configuration described in the first embodiment. The result of investigating the relationship between thickness and time is shown. FIG. 14B is a cross-sectional view of the offset fin 22 when cut in a direction parallel to the exhaust gas flow and the long side 21 c of the tube 21. FIG. 14B shows the wall portions 33 of the offset fins 22 arranged in a staggered pattern along the exhaust gas flow direction, and the left-right direction of FIG. 14B is the exhaust gas flow direction. is there.

  As shown in FIG. 14B, when the exhaust gas passes through the EGR cooler, PM 41 is deposited on the surface of the offset fin 22. And as shown with the broken line in Fig.14 (a), as for PM41, average deposition thickness increases as time passes, and when 8 hours or more pass, the average deposition thickness of PM41 is about 0.00. It was found that the size was almost constant at a size of 25 mm.

  From this, when the offset distance s is set to 0.5 mm, the average of PM 41 deposited on the surface of the offset fins 22 as shown in FIG. The deposition thickness becomes 0.25 mm, and the exhaust gas passage is blocked near the boundary between the offset fins 22 adjacent to each other in the flow direction of the exhaust gas.

  Therefore, the offset distance s needs to be larger than 0.5 mm from the viewpoint of preventing clogging. In addition, this embodiment can be combined with the above-described first to fourth embodiments.

(Other embodiments)
(1) In the fifth embodiment described above, the magnitude of the offset distance s has been described. However, the fins 22 and the tubes 21 are surrounded by the convex portions 31 adjacent to each other on the same side in FIG. The optimum specification of the offset fin 22 can be determined using the ratio of the offset region D to the hatched region C as a parameter.

  That is, as shown in FIG. 6, when the offset fin 22 is viewed in the exhaust gas flow direction, a portion offset with respect to the convex portion 31 adjacent in the exhaust flow direction is referred to as an offset region D in FIG. When the ratio of the area of the offset region D to the area of the hatched region C is smaller than 25%, the gas resistance when the exhaust gas passes through the offset portion D is large, and the pressure loss becomes large. The ratio of D is preferably 25% or more.

  Further, in the case where the area ratio of the offset region D is to be made larger than 40%, for example, the offset fin 22 is bent into a corrugated shape by pressing to raise a portion that becomes the cut and raised portion 32. When manufactured, the length in the direction parallel to the fin pitch fp of the remaining portion that has been cut and raised becomes shorter, and the base portion of the cut and raised portion 32 is likely to be cut. 40% or less.

  Therefore, the area ratio of the offset region D to the hatched region C is preferably 25% or more and 40% or less. This embodiment can be combined with the above-described embodiments.

  In other words, the area of the offset region D described above is obtained by dividing the wave shape portion formed by the cut and raised portion 32 and the wave shape portion adjacent thereto in the exhaust gas flow direction as shown in FIG. 22 is an area of the exhaust gas passage portion surrounded by the wall portion 33 and the wall portion 33 of both portions when projected onto a plane substantially perpendicular to the flow direction of the exhaust gas 22.

  (2) FIG. 15 shows a schematic diagram of an exhaust gas recirculation device according to another embodiment of the present invention. In FIG. 15, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

  In each of the above-described embodiments, the example in which the present invention is applied to the EGR cooler 10 disposed in the middle of the first exhaust gas recirculation pipe 9 in the exhaust gas recirculation apparatus shown in FIG. 1 has been described. As shown in FIG. Furthermore, the present invention is applied to the EGR cooler 10 disposed in the middle of the second exhaust gas recirculation pipe 12 that recirculates part of the exhaust gas of the engine 1 directly to the intake side of the engine 1 before passing it through the DPF 8. Can also be applied.

  (3) In the above-described embodiments, the EGR gas cooler has been described as an example. However, the present invention can also be applied to other exhaust heat exchangers made of stainless steel. For example, the present invention can be applied to an exhaust heat recovery heat exchanger in which heat is exchanged between exhaust gas discharged to the outside air and cooling water to heat the cooling water.

It is a mimetic diagram of an exhaust gas recirculation device in which an exhaust heat exchanger in a 1st embodiment of the present invention is used. It is a whole side view of the EGR cooler as an exhaust heat exchanger in a 1st embodiment of the present invention. It is the sectional view on the AA line of the EGR cooler in FIG. It is the BB sectional view of the EGR cooler in FIG. It is a perspective view of the inner fin used for the EGR cooler in FIG. It is sectional drawing of the inner fin used for the EGR cooler in FIG. 2 when it sees from an exhaust gas flow direction. It is a figure which shows the relationship between the fin height fh of an offset fin, and a pressure loss ratio. It is a figure which shows the relationship between fin height fh of an offset fin, and water flow resistance (DELTA) Pw. It is a figure which shows the relationship between fin pitch fp and the thermal radiation performance of an EGR cooler. 3 is a partial cross-sectional view of the offset fin 22 when cut in a direction substantially perpendicular to the flow direction of the exhaust gas of the offset fin 22. FIG. It is a figure which shows the relationship between the equivalent circular diameter de of an offset fin, and EGR gas density (rho) ratio. It is a figure which shows the relationship between the segment length L of an offset fin, and EGR gas density (rho) ratio. It is a figure which shows the relationship between the function X using Equivalent circle diameter de of the offset fin, segment length L, and fin height fh, and EGR gas density (rho) ratio. (A) is a figure which shows the relationship between the deposition thickness of PM, such as soot in the exhaust gas deposited on the surface of an offset fin, and time, (b) is an exhaust gas flow and the long side 21c of the tube 21 is shown. It is sectional drawing of the offset fin 22 when it cut | disconnects in a parallel direction. It is a schematic diagram of the exhaust gas recirculation apparatus in other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine, 8 ... DPF, 9 ... 1st exhaust gas recirculation pipe, 10 ... EGR cooler,
21 ... Tube, 22 ... Offset type inner fin.

Claims (3)

Engine performs heat exchange with the cooling water for cooling the exhaust gas and the exhaust gas containing particulate matter generated by combustion in (1), wherein the exhaust gas after the heat exchange engine (1) In the exhaust heat exchanger flowing out to the side ,
Internal the exhaust gas flow, the stainless steel tubing through the external said cooling water (21),
Wherein arranged in the tube, and a stainless steel inner fin to promote heat exchange (22) between the said cooling water and the exhaust gas,
The inner fin (22) is approximately the cross-sectional shape perpendicular to the flow direction of the exhaust gas, a wave shape which bent by alternately positioned protrusions (31) on one side and the other side, the exhaust gas An offset fin comprising a cut-and-raised part (32) partially cut and raised in a direction parallel to the flow direction of
In the cross-sectional shape, the size of the fin pitch, which is the distance between the centers of the convex portions adjacent to each other on the same side of the one side and the other side , is fp , The equivalent circular diameter of the region surrounded by the fins between the convex portions adjacent to each other on the same side is de, the length of the cut-and-raised portion in the exhaust flow direction is L, and the cross-sectional shape is It said one fin height is the distance from the convex portion of the side to the convex portion of the other side is taken as fh,
The size of the fin pitch is
2 <fp ≦ 12 (unit: mm)
Is a size that satisfies
The length L of the cut and raised portion in the exhaust flow direction is
When fh <7 and fp ≦ 5, 0.5 <L ≦ 7 (unit: mm),
When fh <7, 5 <fp, 0.5 <L ≦ 1 (unit: mm),
When 7 ≦ fh and fp ≦ 5, 0.5 <L ≦ 4.5 (unit: mm), or
When 7 ≦ fh and 5 <fp, 0.5 <L ≦ 1.5 (unit: mm)
Because
further,
When X = de × L ^0.14 / fh ^0.18 ,
In order to suppress the equivalent circular diameter de and the length L of the cut and raised portion in the exhaust flow direction from being deposited on the inner fin (22),
1.1 ≦ X ≦ 4.3
Exhaust heat exchanger, characterized in has become sized Rukoto that satisfies. The equivalent circular diameter and the length of the cut and raised portion in the exhaust flow direction are:
1.2 ≦ X ≦ 3.9
The exhaust heat exchanger according to claim 1 , wherein the exhaust heat exchanger has a size satisfying. The equivalent circular diameter and the length of the cut and raised portion in the exhaust flow direction are:
1.3 ≦ X ≦ 3.5
The exhaust heat exchanger according to claim 1 , wherein the exhaust heat exchanger has a size satisfying.

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