Reserve tank

Abstract

To provide a reserve tank capable of reducing a flow speed of cooling water flowing from an internal flow path to a gas-liquid separation chamber without increasing a size of a tank case, while preventing the cooling water flowing from the internal flow path into the gas-liquid separation chamber from easily entraining bubbles in the gas-liquid separation chamber.SOLUTION: The reserve tank includes: tank cases 21, 51 each having an outer shape including a pair of short side parts and a pair of long side parts perpendicular to the short side parts; a first flow path 77 provided inside the tank case so as to be located below an indication 73 provided on the tank case for indicating a minimum storage amount; a second flow path 78 provided inside the tank case so as to be located below the indication and having a larger cross section area perpendicular to a distributing direction of cooling water than the first flow path; a connection end 78E as the downstream side end of the second flow path, in which a position in a direction along the long side part coincides with a center part of the long side part; and a gas-liquid separation chamber 79 provided inside the tank case so that an upper end is located above the indication.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a reserve tank. [Background technology]

[0002] Patent Document 1 below discloses a reserve tank that stores cooling water flowing through a flow path of a water-cooled cooling device. This reserve tank has an internal flow path and a gas-liquid separation chamber provided within the reserve tank. The cooling water that flows from the flow path into the reserve tank flows through the internal flow path to the gas-liquid separation chamber, and then flows from the gas-liquid separation chamber back into the flow path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-159318 Summary of the Invention [Problem to be solved by the invention]

[0004] If the overall length of the internal flow path is short, the flow rate of the cooling water may increase as it flows from the internal flow path to the gas-liquid separation chamber. In this case, the cooling water flowing from the internal flow path to the gas-liquid separation chamber is likely to entrain air bubbles (air) mixed in the cooling water in the gas-liquid separation chamber. If the cooling water flowing through the flow path contains a large number of air bubbles, the cooling effect of the cooling water on the object being cooled is reduced. To prevent air bubbles from being entrained in the cooling water, the internal flow path of the reserve tank can be lengthened to reduce the flow rate of the cooling water. However, the reserve tank of Patent Document 1 above is likely to become large when the internal flow path is lengthened.

[0005] In the reserve tank of Patent Document 1, a wall is provided between the internal flow path and the gas-liquid separation chamber, and the cooling water flows from the internal flow path to the gas-liquid separation chamber through a window provided in this wall. However, because the area of ​​the window is smaller than the cross-sectional area of ​​the internal flow path, the flow rate of the cooling water is unlikely to decrease when it flows from the internal flow path to the gas-liquid separation chamber.

[0006] Furthermore, when the reserve tank of Patent Document 1 tilts, the cooling water flowing from the internal flow path to the gas-liquid separation chamber is likely to entrain air bubbles mixed in the cooling water in the gas-liquid separation chamber.

[0007] In consideration of the above, the present invention aims to provide a reserve tank that can reduce the flow rate of cooling water flowing from the internal flow path to the gas-liquid separation chamber without increasing the size of the tank case, and that is less likely to trap air bubbles in the gas-liquid separation chamber when the tank is tilted. [Means for solving the problem]

[0008] The reserve tank of claim 1 comprises: a tank case having an outer shape including a pair of short sides parallel to each other when viewed in the vertical direction and a pair of long sides perpendicular to the short sides; an inlet port and an outlet port connected to the tank case and connected to a flow path through which cooling water flows; a first flow path located inside the tank case below a mark indicating the minimum storage capacity provided on the tank case and extending along the short sides, and connected to the downstream end of the inlet port; a second flow path located inside the tank case below the marking, extending along the long sides and connected to the downstream end of the first flow path, and having a cross-sectional area perpendicular to the flow direction in which the cooling water flows that is larger than that of the first flow path; a connection end that is the downstream end of the second flow path and whose position in the direction along the long sides coincides with the center of the long sides; and a gas-liquid separation chamber located inside the tank case so that its upper end is located above the marking and connected to the connection end and the upstream end of the outlet port.

[0009] The reserve tank of claim 1 has a first flow path and a second flow path provided inside the tank case. The first flow path extends along the short side of the tank case, and the second flow path extends along the long side of the tank case. Therefore, even if the internal flow paths (first flow path, second flow path) are lengthened, the tank case (reserve tank) is unlikely to become larger. Furthermore, in the reserve tank of claim 1, the cross-sectional area perpendicular to the flow direction of the connecting end (second flow path) connected to the gas-liquid separation chamber is larger than that of the first flow path. Therefore, when the cooling water flows from the connecting end (second flow path) to the gas-liquid separation chamber, the flow rate of the cooling water tends to decrease. Therefore, the reserve tank of claim 1 can reduce the flow rate of the cooling water flowing from the internal flow paths (first flow path, second flow path) to the gas-liquid separation chamber without increasing the size of the tank case.

[0010] Furthermore, the position of the connecting end of the second flow path of the reserve tank in the direction along the long side coincides with the center of the long side. Therefore, when the reserve tank is tilted, the connecting end is unlikely to move up and down by a large amount. Therefore, when the reserve tank is tilted, the cooling water flowing from the internal flow paths (first flow path, second flow path) to the gas-liquid separation chamber is unlikely to entrain air bubbles in the gas-liquid separation chamber.

[0011] The reserve tank of claim 2 is the same as claim 1, wherein the downstream end of the first flow path and the upstream end of the second flow path are directly connected to each other.

[0012] In the reserve tank of claim 2, the downstream end of the first flow path and the upstream end of the second flow path are directly connected. In other words, no wall with a through hole is provided between the downstream end of the first flow path and the upstream end of the second flow path. Therefore, when the cooling water flows between the downstream end of the first flow path and the upstream end of the second flow path, the cross-sectional area of ​​the cooling water flow path does not change abruptly. Therefore, when the cooling water flows from the downstream end of the first flow path to the upstream end of the second flow path, the pipe resistance from the first flow path and the second flow path to the cooling water is unlikely to increase. [Effects of the Invention]

[0013] As described above, the reserve tank of the present invention has the excellent effect of reducing the flow rate of the cooling water flowing from the internal flow path to the gas-liquid separation chamber without increasing the size of the tank case, and further, when the tank is tilted, the cooling water flowing from the internal flow path to the gas-liquid separation chamber is less likely to entrain air bubbles in the gas-liquid separation chamber. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a side view of the reserve tank according to the embodiment. [Figure 2] FIG. 2 is a perspective view of the reserve tank as viewed from above. [Figure 3] FIG. 2 is a perspective view showing a cross section of a portion of the reserve tank. [Figure 4] FIG. [Figure 5] FIG. 2 is a perspective view of the upper tank as viewed from below. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of a reserve tank 10 according to the present invention will be described with reference to the accompanying drawings. A first direction indicated by an arrow DR1 in the drawings is a direction parallel to the vertical direction of the vehicle. A second direction indicated by an arrow DR2 is a direction perpendicular to the first direction DR1, and a third direction indicated by an arrow DR3 is a direction perpendicular to the first direction DR1 and the second direction DR2.

[0016] The reserve tank 10 of this embodiment is mounted on, for example, a hybrid vehicle. The reserve tank 10 constitutes part of a cooling system that has a cooling flow path (not shown) that passes through an object to be cooled. The object to be cooled is, for example, a traction motor-generator, which is an electric motor, a power generation motor-generator, or a power control unit (PCU) that electrically controls these. The reserve tank 10 has a lower tank 20 and an upper tank 50. The lower tank 20 and the upper tank 50 are integrally molded from resin.

[0017] As shown in FIGS. 2 to 4, the lower tank 20 includes a case body (tank case) 21, which is a box-shaped member with an open top. As shown in FIG. 4, the planar shape of the case body 21 is substantially rectangular. The upper end surface 22 of the case body 21 is a plane perpendicular to the up-down direction. The upper end surface 22 includes a pair of short side portions 23, 24 that are substantially parallel to the third direction DR3, and a pair of long side portions 25, 26 that are substantially parallel to the second direction DR2. The long side portions 25, 26 are longer than the short side portions 23, 24. An annular flange 28 is provided on the upper outer peripheral surface of the case body 21, and is located below the upper end surface 22.

[0018] 3 and 4, the bottom of the case body 21 includes a first bottom 30, a second bottom 31 located higher than the first bottom 30, and a third bottom 32 located higher than the second bottom 31. As shown in FIG. 4, the end of the bottom of the case body 21 on one side DR2A in the second direction DR2 is the second bottom 31, and the end of the bottom of the case body 21 on the other side DR2B in the second direction DR2 is the third bottom 32. Furthermore, an inclined wall 36 connecting the first bottom 30 and the second bottom 31 is provided between the end of one side DR2A of the first bottom 30 and the second bottom 31 (see FIGS. 3 and 4). Furthermore, a partition wall 33 having an L-shaped planar shape is provided on the bottom of the case body 21. The partition wall 33 includes a first wall portion 34 parallel to the short side portion 23 in a plan view and a second wall portion 35 parallel to the long side portion 25 in a plan view. One end of the first wall portion 34 is connected to the side wall 21A on the long side portion 26 side of the case body 21. The first wall portion 34 separates the second bottom portion 31 from the inclined wall 36. The other end of the first wall portion 34 is connected to one end of the second wall portion 35. The upper end surface 33A of the partition wall 33 is a plane perpendicular to the up-down direction and is located at the same height as the upper end surface 22. Furthermore, a guide wall 38 separate from the partition wall 33 is provided on the bottom surface of the first bottom portion 30. The end of the guide wall 38 on the long side portion 25 side is connected to the side wall 21B on the long side portion 25 side of the case body 21. Guide wall 38 includes an inclined portion 39 that is inclined relative to short side portion 23 and long side portion 25 in a plan view, and a tip portion 40 that is approximately parallel to short side portion 23 in a plan view. Upper end surface 38A of guide wall 38 is a plane that is perpendicular to the up-down direction and is located at the same height as upper end surfaces 22 and 33A.

[0019] The space surrounded by the side wall 21C on the short side 23 side of the case body 21, the second bottom 31, and the first wall 34 and parallel to the third direction DR3 in plan view is the first flow path forming portion 41A. The space surrounded by the side wall 21B, the first bottom 30, the second wall 35, and the guide wall 38 and parallel to the second direction DR2 in plan view is the second flow path forming portion 41B. The space surrounded by the side wall 21A, the side wall 21B, the first bottom 30, the third bottom 32, the partition wall 33, and the guide wall 38 and larger than the first flow path forming portion 41A and the second flow path forming portion 41B is the gas-liquid separation chamber forming portion 41C.

[0020] 4, a recess 30A that is approximately trapezoidal in plan view is provided at an end of one side DR3A in the third direction DR3 and the other side DR2B in the second direction DR2 of the first bottom portion 30. That is, a bottom surface 30A1 of the recess 30A is located below the first bottom portion 30. Furthermore, an inclined wall 42 that connects the first bottom portion 30 and the third bottom portion 32 is provided between the end of the other side DR2B of the first bottom portion 30 and the end of the one side DR2A of the third bottom portion 32.

[0021] As shown in Fig. 2, a through hole 44 is formed in the side wall 21C on the short side 23 side of the case body 21. Furthermore, one end of an inlet port 45 is watertightly connected to the through hole 44. As shown in Fig. 4, a through hole 47 is formed in the end of one side DR3A of the inclined wall 42. Furthermore, one end of an outlet port 48 is watertightly connected to the through hole 47.

[0022] As shown in Figures 2, 3, and 5, the upper tank 50 includes a case body (tank case) 51, which is a box-shaped member with an open bottom. The planar shape of the case body 51 is approximately rectangular. A lower end surface 52 of the case body 51 is a plane perpendicular to the up-down direction. The lower end surface 52 includes a pair of short sides 53, 54 that are approximately parallel to the third direction DR3, and a pair of long sides 55, 56 that are approximately parallel to the second direction DR2. The long sides 55, 56 are longer than the short sides 53, 54. An annular flange 58 is provided on the lower outer peripheral surface of the case body 51, located above the lower end surface 52.

[0023] As shown in FIG. 5, the ceiling portion of the case body 51 includes a first ceiling portion 60, a second ceiling portion 61 located below the first ceiling portion 60, and a third ceiling portion 62 located below the first ceiling portion 60 and above the second ceiling portion 61. A through-hole 60A is provided in the first ceiling portion 60. Furthermore, as shown in FIGS. 1 and 2, a cylindrical refill protrusion 60B communicating with the through-hole 60A is provided on the upper end surface of the case body 51. A partition wall 63 having an L-shaped bottom surface is provided on the inner peripheral edge of the second ceiling portion 61. The partition wall 63 includes a first wall portion 64 parallel to the short side portion 53 in a plan view and a second wall portion 65 parallel to the long side portion 55 in a plan view. One end of the first wall portion 64 is connected to the side portion 51A on the long side 56 side of the lower end of the case body 51. The other end of the first wall portion 64 is connected to one end of the second wall portion 65. A lower end surface 63A of the partition wall 63 is a plane perpendicular to the up-down direction and is located at the same height as the lower end surface 52. Furthermore, a guide wall 68 separated from the partition wall 63 is provided on the second ceiling portion 61. An end of the guide wall 68 on the long side portion 55 side is connected to the side portion 51B on the long side portion 55 side of the lower end of the case main body 51. The guide wall 68 has an inclined portion 69 that is inclined with respect to the first wall portion 64 and the second wall portion 65 in a plan view, and a tip portion 70 that is approximately parallel to the first wall portion 64 in a bottom view. A lower end surface 68A of the guide wall 68 is a plane perpendicular to the up-down direction and is located at the same height as the lower end surface 52 and the lower end surface 63A.

[0024] The space surrounded by the side portion 51C on the short side portion 53 side of the lower end of the case body 51, the second ceiling portion 61, and the first wall portion 64 and parallel to the third direction DR3 in plan view is the first flow path forming portion 71A. The space surrounded by the side portion 51B, the second ceiling portion 61, the second wall portion 65, and the guide wall 68 and parallel to the second direction DR2 in plan view is the second flow path forming portion 71B. The space surrounded by the inner circumferential surface of the case body 51, the first ceiling portion 60, the third ceiling portion 62, the partition wall 63, and the guide wall 68 and larger than the first flow path forming portion 71A and the second flow path forming portion 71B is the gas-liquid separation chamber forming portion 71C.

[0025] As shown in FIGS. 1 and 2, a LOW line (indicating the minimum storage amount) 73 and a FULL line 75 are provided on the side of one side DR3A of the case body 51.

[0026] The lower tank 20 and upper tank 50 described above are joined together. Specifically, with the upper end surface 22 of the lower tank 20 and the lower end surface 52 of the upper tank 50 in contact with each other, the entire abutting portions of the upper end surface 22 and the lower end surface 52 are heat-welded. Furthermore, the entire abutting portion of the upper end surface 33A of the partition wall 33 of the lower tank 20 and the lower end surface 63A of the partition wall 63 of the upper tank 50 are heat-welded, and the entire abutting portion of the upper end surface 38A of the guide wall 38 and the lower end surface 68A of the guide wall 68 are heat-welded. When the reserve tank 10 is assembled in this manner, an internal flow path for coolant is formed inside the reserve tank 10. As shown in FIG. 3 , the internal flow path includes a first flow path 77 formed by the first flow path-constituting portion 41A and the first flow path-constituting portion 71A, and a second flow path 78 formed by the second flow path-constituting portion 41B and the second flow path-constituting portion 71B. Furthermore, a gas-liquid separation chamber 79 constituted by the gas-liquid separation chamber constituent portion 41C and the gas-liquid separation chamber constituent portion 71C is formed inside the reserve tank 10. As is clear from Figures 2 to 4, an outlet portion (connection end portion) 78E of the second flow path 78 is located in the center of the reserve tank 10 in the second direction DR2.

[0027] Furthermore, the cooling flow path is connected to the inlet port 45 and the outlet port 48 of the reserve tank 10. An electric pump (not shown) is provided in the cooling flow path, and the cooling water circulates through the cooling flow path by the force generated by the electric pump, and passes through the first flow path 77, the second flow path 78, and the gas-liquid separation chamber 79 of the reserve tank 10.

[0028] The LOW line 73 and the FULL line 75 indicate the appropriate amount of coolant stored in the reserve tank 10. When the operation of the object to be cooled is stopped and the temperature of the object to be cooled drops sufficiently, the temperature of the coolant drops. In this state, if the level of the coolant in the reserve tank 10 is above the LOW line 73 and below the FULL line 75, the amount of coolant in the reserve tank 10 is appropriate. If the level of the coolant is below the LOW line 73, coolant is poured into the reserve tank 10 via the refill protrusion 60B.

[0029] The LOW line 73 is located above the upper ends of the first flow path 77 and the second flow path 78. Therefore, when the amount of coolant in the reserve tank 10 is appropriate, the first flow path 77 and the second flow path 78 are substantially filled with coolant. On the other hand, the upper end of the gas-liquid separation chamber 79 is located above the FULL line 75. Even when the amount of coolant in the reserve tank 10 is appropriate, the upper part of the gas-liquid separation chamber 79 is filled with air. In other words, the space that is part of the gas-liquid separation chamber 79 formed in the upper tank 50 and that is located above the upper surface of the coolant is filled with air.

[0030] (Action and effect) Next, the operation and effects of this embodiment will be described.

[0031] When the cooling water flowing through the cooling flow path due to the force generated by the electric pump enters the first flow path 77 of the reserve tank 10 from the inlet port 45 (through-hole 44), the cooling water passes through the second flow path 78 and is sent to the gas-liquid separation chamber 79 (see arrows WD in Figures 3 and 4). The cooling water in the gas-liquid separation chamber 79 is then discharged into the cooling flow path through the through-hole 47 and the outlet port 48. The cooling object is then cooled by the cooling water flowing through the cooling flow path. However, if the cooling water flowing through the cooling flow path contains a large number of bubbles, the cooling effect of the cooling water on the cooling object is reduced. For this reason, it is preferable to minimize the amount of bubbles in the cooling water flowing through the cooling flow path.

[0032] When the flow velocity of the cooling water from the outlet 78E of the second flow path 78 toward the gas-liquid separation chamber 79 is high, the cooling water swirls in the gas-liquid separation chamber 79, easily entraining air bubbles in the gas-liquid separation chamber 79. Therefore, it is ideal to set the flow velocity of the cooling water when it reaches the outlet 78E to be sufficiently lower than the flow velocity of the cooling water when it enters the first flow path 77 from the inlet port 45. The reserve tank 10 of this embodiment has, as internal flow paths, the first flow path 77 parallel to the third direction DR3 and the second flow path 78 parallel to the second direction DR2. Therefore, the total length of the internal flow paths provided in the reserve tank 10 is sufficiently long. Therefore, the flow velocity of the cooling water is likely to decrease as it flows through the first flow path 77 and the second flow path 78. Furthermore, as is clear from FIG. 3 , the cross section of the second flow path 78 (outlet 78E) perpendicular to the flow direction WD of the cooling water is larger than the cross section of the first flow path 77 perpendicular to the flow direction WD, which is the direction in which the cooling water flows. Therefore, the flow rate of the cooling water when flowing through the second flow path 78 is likely to be lower than the flow rate of the cooling water when flowing through the first flow path 77. Furthermore, the first flow path 77 and the second flow path 78 are not formed as a single straight line, but are formed in an L-shape. Therefore, although the flow rate of the cooling water can be reduced by the first flow path 77 and the second flow path 78, it is difficult to increase the size of the reserve tank 10.

[0033] Incidentally, when the vehicle vibrates, for example, due to a sudden start or stop, the reserve tank 10 may tilt relative to the road surface on which the vehicle is traveling. In this case, the amount of vertical movement (vibration) of the center of the reserve tank 10 in the second direction DR2 tends to be smaller than the amount of vertical movement (vibration) of the end of the reserve tank 10 on one side DR2A and the end of the reserve tank 10 on the other side DR2B. In the reserve tank 10 of this embodiment, the outlet 78E of the second flow path 78 is located in the center of the reserve tank 10 in the second direction DR2. Therefore, there is little risk that the coolant flowing from the outlet 78E to the gas-liquid separation chamber 79 when the reserve tank 10 tilts will vibrate significantly in the vertical direction. Therefore, the coolant flowing from the outlet 78E to the gas-liquid separation chamber 79 when the reserve tank 10 tilts is less likely to swirl in the gas-liquid separation chamber 79, thereby less likely to entrain air bubbles.

[0034] Furthermore, the downstream end of the first flow path 77 and the upstream end of the second flow path 78 are directly connected. In other words, no wall having a through hole with an opening area smaller than the cross-sectional areas of the first flow path 77 and the second flow path 78 is provided between the downstream end of the first flow path 77 and the upstream end of the second flow path 78. Furthermore, because the bottom surface of the upstream end of the second flow path 78 is formed by the inclined wall 36, the cross-sectional area of ​​the upstream end of the second flow path 78 gradually changes from the downstream end of the first flow path 77 toward the center of the second flow path 78. Therefore, when the cooling water flows between the downstream end of the first flow path 77 and the upstream end of the second flow path 78, the cross-sectional area of ​​the cooling water flow path does not change abruptly. Therefore, when the cooling water flows between the downstream end of the first flow path 77 and the upstream end of the second flow path 78, the pipe resistance from the first flow path 77 and the second flow path 78 to the cooling water is unlikely to increase. Therefore, it is not necessary to increase the output of the electric pump.

[0035] Furthermore, the cooling water flowing from the outlet 78E to the gas-liquid separation chamber 79 tends to flow toward the recess 30A, as shown in FIG. 4 . Furthermore, the flow of cooling water tends to separate into a flow toward the recess 30A (bottom surface 30A1) (hereinafter referred to as the downward flow) and a flow above the downward flow (hereinafter referred to as the upward flow). Air bubbles in the cooling water tend to move upward rather than downward. Therefore, if air bubbles are contained in the cooling water flowing from the outlet 78E toward the recess 30A (bottom surface 30A1), the air bubbles are likely to be contained in the cooling water flowing along the upward flow when the cooling water branches into two. Furthermore, the lower end of the through-hole 47 (outlet port 48) is located below the upper end (first bottom 30) of the recess 30A. Therefore, the cooling water flowing along the downward flow, which is less likely to contain air bubbles, tends to flow toward the through-hole 47 (outlet port 48). Therefore, it is difficult for the cooling water containing many bubbles to be sent to the object to be cooled through the cooling flow path.

[0036] The upper surfaces of the first flow path 77 and the second flow path 78 are blocked by the second bottom 61 and the partition wall 63. Therefore, there is no risk that the cooling water located at the top of the gas-liquid separation chamber 79 will fall from above the first flow path 77 and the second flow path 78 into the first flow path 77 and the second flow path 78, causing a vortex in the cooling water flowing through the first flow path 77 and the second flow path 78.

[0037] Furthermore, the inlet port 45 and the outlet port 48 protrude from the case body 21 in the second direction DR2, but do not protrude in the third direction DR3. Therefore, the inlet port 45 and the outlet port 48 do not increase the size of the reserve tank 10 in the third direction DR3.

[0038] The airflow control structure 60 according to the embodiment has been described above, but the design can be modified as appropriate within the scope of the gist of the present invention.

[0039] For example, the object to be cooled by the cooling water may be an internal combustion engine. [Explanation of symbols]

[0040] 10. Reserve Tank 21 Case body (tank case) 23 24 Short side 25 26 Long side 30A recess 45 inlet port 48 Exit Port 51 Case body (tank case) 53 54 Short side 55 56 Long side 73 LOW line (indicating minimum storage volume) 77 First Channel 78 Second Channel 78E Outlet (Connection End) 79 Gas-liquid separation chamber

Claims

1. a tank case having an outer shape including a pair of short sides parallel to each other when viewed in the up-down direction and a pair of long sides perpendicular to the short sides; an inlet port and an outlet port connected to the tank case and connected to a flow path through which cooling water flows; a first flow path provided inside the tank case so as to be located below a mark indicating a minimum storage capacity provided on the tank case and extending along the short side, the first flow path being connected to a downstream end of the inlet port; a second flow path that is provided inside the tank case so as to be positioned below the marking, extends along the long side portion, is connected to a downstream end of the first flow path, and has a cross-sectional area perpendicular to a flow direction in which the cooling water flows that is larger than that of the first flow path; a connection end portion that is a downstream end portion of the second flow path and whose position in a direction along the long side portion coincides with a center portion of the long side portion; a gas-liquid separation chamber provided inside the tank case such that an upper end thereof is located above the marking and connected to the connection end portion and an upstream end portion of the outlet port; A reserve tank equipped with

2. 2. The reserve tank according to claim 1, wherein the downstream end of the first flow passage and the upstream end of the second flow passage are directly connected to each other.

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