Patent Publication Number: US-2023145779-A1

Title: Cooling Device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2020-063569 filed on Mar. 31, 2020, the entire contents of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a cooling device for cooling a device to be cooled. 
     BACKGROUND 
     JP 2020-014278 A discloses an inverter module including a flow path for cooling water (a cooling device) formed between a power module and a capacitor body. 
     SUMMARY 
     However, in the cooling device of JP 2020-014278 A, a heat exchange area with the cooling water is increased by forming fins on a lower surface of the power module, but no study has been made on how the cooling water flows in the flow path. 
     An object of the present invention is to improve heat exchange efficiency between a device to be cooled and a fluid depending on how the fluid flows through a flow path. 
     According to an aspect of the present invention, a cooling device that has a first wide surface and a second wide surface facing the first wide surface, and cools a device to be cooled with a fluid flowing through a flat flow path formed between the first wide surface and the second wide surface, wherein the second wide surface has a plurality of protrusion portions protruding into the flow path, the protrusion portions extending in a flow path width direction, the protrusion portions being arranged side by side in a fluid flow direction, the first wide surface is not provided with the protrusion portions, the protrusion portions each include: a first inclined surface inclined to come close to the first wide surface from upstream to downstream in the fluid flow direction; and a second inclined surface disposed alternately with the first inclined surface in the fluid flow direction and inclined to be distanced from the first wide surface from upstream to downstream in the fluid flow direction, and the protrusion portions each are formed such that, in a cross section taken along the fluid flow direction, a virtual first circle is inscribed at three points on the first wide surface, the second inclined surface, and the first inclined surface adjacent to the second inclined surface downstream in the fluid flow direction. 
     According to the above aspect, in a cross section taken along a fluid flow direction, protrusion portions each are formed such that a virtual first circle is inscribed at three points on a first wide surface, a second inclined surface, and a first inclined surface adjacent to and downstream of the second inclined surface in the fluid flow direction. Therefore, when a fluid flows from the first inclined surface to the second inclined surface adjacent to and downstream of the first inclined surface in the fluid flow direction, a longitudinal vortex is generated and flows along the second inclined surface, and a large longitudinal vortex is generated in a space in which the virtual first circle is inscribed at the three points. Therefore, it is possible to improve heat exchange efficiency between a device to be cooled and the fluid in the space in which the virtual first circle is inscribed at the three points. Therefore, the heat exchange efficiency between the device to be cooled and the fluid can be improved depending on how the fluid flows through a flow path. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view of a cooling device according to an embodiment of the present invention as viewed from above; 
         FIG.  2    is an exploded perspective view of the cooling device as viewed from below; 
         FIG.  3    is a cross-sectional view taken along a line III-III in  FIG.  2   , and is a cross-sectional view of protrusion portions of the cooling device taken along a cooling water flow direction; 
         FIG.  4    is a bottom view showing a part of a second wide surface of the cooling device; 
         FIG.  5    is a cross-sectional view of the cooling device taken along a fluid flow direction and shows only a part of the cooling device in the fluid flow direction; 
         FIG.  6    is a bottom view schematically showing flow of a fluid in the protrusion portion; 
         FIG.  7    is a cross-sectional view of a side surface schematically showing the flow of the fluid in the protrusion portion; 
         FIG.  8    is a graph showing a ratio of a heat transfer coefficient with respect to Rm 1 ×P/Dv, where Rm 1  is a radius of a first circle C 1 , P is a pitch between peak portions adjacent to each other in the fluid flow direction, and Dv is a distance between a peak portion and a first wide surface; 
         FIG.  9    shows a value of Rm 1 ×P/Dv for each shape when an inclination angle θt, the pitch P, the distance Dv, and the radius Rm 1  are changed; 
         FIG.  10    is a graph showing upper and lower limit values of the inclination angle θt and an upper limit value of the distance Dv; 
         FIG.  11    is a graph showing a relation between the inclination angle θt and resistance ΔP; 
         FIG.  12    is a graph showing a relation between the pitch P and the heat transfer coefficient; 
         FIG.  13    is a graph showing a relation between the pitch P and the resistance ΔP; 
         FIG.  14    is a graph showing a ratio of a heat transfer coefficient with respect to Rm 1 ×P/Dv for a fluid having different Reynolds numbers; 
         FIG.  15    is a perspective view illustrating a flow path according to a first modification of the embodiment of the present invention; 
         FIG.  16    is a bottom view illustrating flow of a fluid in the first modification shown in  FIG.  15   ; 
         FIG.  17    is a perspective view illustrating a flow path according to a second modification of the embodiment of the present invention; 
         FIG.  18    is a perspective view illustrating a flow path according to a third modification of the embodiment of the present invention; 
         FIG.  19    is a perspective view illustrating a flow path according to a fourth modification of the embodiment of the present invention; 
         FIG.  20    is a perspective view illustrating a flow path according to a fifth modification of the embodiment of the present invention; 
         FIG.  21    is a perspective view illustrating a flow path according to a sixth modification of the embodiment of the present invention; 
         FIG.  22    is a perspective view illustrating a flow path according to a seventh modification of the embodiment of the present invention; and 
         FIG.  23    is a perspective view illustrating a flow path according to an eighth modification of the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a cooling device  1  according to an embodiment of the present invention will be described with reference to the drawings. 
     First, an overall configuration of the cooling device  1  will be described with reference to  FIGS.  1  to  5   . 
       FIG.  1    is a perspective view of the cooling device  1  as viewed from above.  FIG.  2    is an exploded perspective view of the cooling device  1  as viewed from below.  FIG.  3    is a cross-sectional view taken along a line III-III in  FIG.  2   , and is a cross-sectional view of protrusion portions  30  of the cooling device  1  taken along a cooling water flow direction.  FIG.  4    is a bottom view showing a part of a second wide surface  12  on which the protrusion portions  30  are formed.  FIG.  5    is a cross-sectional view of the cooling device  1  taken along the cooling water flow direction, and shows only a part of the cooling device  1  in the cooling water flow direction. 
     As shown in  FIG.  1   , the cooling device  1  includes an inlet flow path  2 , an outlet flow path  3 , and a main body portion  10  that forms a flow path  20  (see  FIG.  2   ). Here, the cooling device  1  cools an inverter module  8  as a device to be cooled by heat exchange with cooling water as a fluid flowing through the flow path  20 . 
     The inverter module  8  controls, for example, a driving motor (not shown) of a vehicle. As shown in  FIG.  2   , the inverter module  8  includes three switching elements  9  along a flow direction of the cooling water in the flow path  20 . The inverter module  8  converts direct current power and alternating current power to each other by switching ON/OFF of the switching elements  9 . 
     The switching elements  9  corresponds to a U phase, a V phase, and a W phase of the inverter module  8 , respectively. The switching elements  9  are switched between ON and OFF at high speed to generate heat. The switching elements  9  that have generated the heat are cooled by exchanging heat with the cooling water in the flow path  20 . 
     As shown in  FIG.  1   , the inlet flow path  2  is a flow path for supplying the cooling water to the flat flow path  20  (see  FIG.  2   ) formed in the main body portion  10 . The inlet flow path  2  is provided to protrude from the main body portion  10 . The inlet flow path  2  is formed to be inclined with respect to the main body portion  10  so as to supply the cooling water along the cooling water flow direction in the flow path  20 . 
     The outlet flow path  3  is a flow path for draining the cooling water from the flow path  20 . The outlet flow path  3  is provided to protrude from the main body portion  10 . The outlet flow path  3  is formed to be inclined with respect to the main body portion  10  so as to guide the drained cooling water along the cooling water flow direction in the flow path  20 . 
     As shown in  FIG.  2   , the main body portion  10  includes the second wide surface  12 , a first side surface  13 , and a second side surface  14 . The inverter module  8  has a first wide surface  11 . The flow path  20  is formed flat by the first wide surface  11 , the second wide surface  12 , the first side surface  13 , and the second side surface  14 . 
     In the present embodiment, the first wide surface  11  is formed by a bottom surface of the inverter module  8 . That is, the cooling device  1  includes the main body portion  10  and the inverter module  8 . In this case, the heat exchange efficiency can be improved by bringing the cooling water into direct contact with the inverter module  8 . 
     Alternatively, the main body portion  10  may be formed to have the first wide surface  11 , and the inverter module  8  may be brought into contact with the outside of the first wide surface  11 . In this case, the cooling device  1  includes only the main body portion  10 . 
     Here, a direction in which the cooling water flows through the flow path  20  is referred to as the “cooling water flow direction” (a fluid flow direction), a direction perpendicular to the cooling water flow direction and parallel to the first wide surface  11  and the second wide surface  12  is referred to as a “flow path width direction”, and a direction perpendicular to the cooling water flow direction and parallel to the first side surface  13  and the second side surface  14  is referred to as a “flow path height direction”. The “cooling water flow direction” is not a local flow direction of the cooling water in which a traveling direction has changed due to an influence of the protrusion portions  30 , but is a flow direction of the cooling water when the flow path  20  as a whole is viewed. 
     The first wide surface  11  is formed in a planar shape extending linearly in the cooling water flow direction and also extending linearly in the flow path width direction orthogonal to the cooling water flow direction. The first wide surface  11  cools the inverter module  8  with the cooling water flowing through the flow path  20 . The first wide surface  11  is not provided with the protrusion portions  30  to be described later. 
     The second wide surface  12  faces the first wide surface  11  in the flow path height direction with a space corresponding to a flow path height. Accordingly, the flat flow path  20  is formed between the first wide surface  11  and the second wide surface  12 . Here, a flow path height of a narrowest portion of the flow path  20 , that is, a distance Dv (see  FIG.  5   ) between a peak portion  33  to be described later and the first wide surface  11  is 0.1 to 10 [mm]. The second wide surface  12  has the protrusion portions  30  protruding into the flow path  20  and extending in the flow path width direction. 
     A plurality of protrusion portions  30  are arranged side by side in parallel with the cooling water flow direction. The protrusion portions  30  are formed over an entire width of the flow path  20  in the flow path width direction. When there is a portion where the protrusion portions  30  are not formed, the cooling water may bypass the portion, but the protrusion portions  30  are formed over the entire width in the flow path width direction, and thus it is possible to prevent a decrease in heat exchange efficiency. 
     As shown in  FIG.  3   , the protrusion portions  30  each include a first inclined surface  31 , a second inclined surface  32 , the peak portion  33 , and a valley portion  34 . 
     The first inclined surface  31  is inclined to come close to the first wide surface  11  from upstream to downstream in the cooling water flow direction. The first inclined surface  31  is formed in a planar shape. The first inclined surface  31  is inclined at an inclination angle θt with respect to the second wide surface  12 . The inclination angle θt is preferably 15[°] to 45 [°], and is 30 [°] here. A thickness t of the second wide surface  12  is 1 [mm]. 
     The second inclined surface  32  is alternately arranged with the first inclined surface  31  in the cooling water flow direction, and is inclined to be distanced from the first wide surface  11  from upstream to downstream in the cooling water flow direction. The second inclined surface  32  is formed in a planar shape. Similarly, the second inclined surface  32  is inclined at the inclination angle θt with respect to the second wide surface  12 . 
     The peak portion  33  is formed between the first inclined surface  31  and the second inclined surface  32  adjacent to and downstream of the first inclined surface  31  in the cooling water flow direction. Here, a pitch P between adjacent peak portions  33  is 11 [mm]. The peak portion  33  is formed at a top portion where the first inclined surface  31  and the second inclined surface  32  abut each other. Alternatively, the peak portion  33  may be formed by a curved surface that gently connects the first inclined surface  31  and the second inclined surface  32 , or the peak portion  33  may be formed by a flat surface that connects the first inclined surface  31  and the second inclined surface  32 . 
     The valley portion  34  is formed between the second inclined surface  32  and the first inclined surface  31  adjacent to and downstream of the second inclined surface  32  in the cooling water flow direction. The valley portion  34  is formed in a bottom portion where the second inclined surface  32  and the first inclined surface  31  abut each other. Alternatively, the valley portion  34  may be formed by a curved surface that gently connects the second inclined surface  32  and the first inclined surface  31 , or the valley portion  34  may be formed by a flat surface that connects the second inclined surface  32  and the first inclined surface  31 . 
     When the cooling water passes through the flow path  20  between the peak portion  33  and the first wide surface  11 , the cooling water tends to flow in a direction nearly perpendicular to a ridge line of the peak portion  33  so as to reduce resistance. On the other hand, when the cooling water passes through the flow path  20  between the valley portion  34  and the first wide surface  11 , the cooling water tends to flow in a direction along a ridge line of the valley portion  34  having low resistance. In this way, the cooling water alternately passes through the peak portion  33  and the valley portion  34 , and thus a strong swirling flow (a longitudinal vortex) is generated in the valley portion  34  sandwiched between a pair of peak portions  33 . Therefore, the longitudinal vortex can be efficiently generated. 
     As shown in  FIG.  4   , the protrusion portions  30  adjacent to each other in the flow path width direction are inclined in opposite directions so as to alternate in the cooling water flow direction. An inclination angle θw of each of the protrusion portions  30  in the flow path width direction with respect to the cooling water flow direction is preferably 15 [°] to 40 [°], and is 30 [°] here. 
     Although  FIG.  4    shows only a pair of protrusion portions  30  adjacent to each other in the flow path width direction, the protrusion portions  30  are further provided side by side in the flow path width direction. That is, the protrusion portions  30  adjacent to each other in the flow path width direction are formed so that a V shape is continuous in the flow path width direction. Here, a size W in the flow path width direction of the pair of protrusion portions  30  adjacent to each other in the flow path width direction is 12.7 [mm]. 
     Ridge lines of the peak portions  33  adjacent to each other in the flow path width direction are continuously formed. Ridge lines of the valley portions  34  adjacent to each other in the flow path width direction are formed continuously. Accordingly, it is possible to improve a temperature distribution of the cooling water in the flow path  20 . The protrusion portions  30  have a connection portion  35  formed between the peak portions  33  that are continuous in the flow path width direction, and a top portion  36  of the connection portion  35  that protrudes downstream in the cooling water flow direction. 
     As shown in  FIG.  5   , the protrusion portions  30  each are formed such that, in a cross section taken along the cooling water flow direction, a virtual first circle C 1  is inscribed at three points on the first wide surface  11 , the second inclined surface  32 , and the first inclined surface  31  adjacent to and downstream of the second inclined surface  32  in the cooling water flow direction. Further, the protrusion portion  30  is formed such that the valley portion  34  does not fall within the first circle C 1 . 
     Similarly, the protrusion portions  30  each are formed such that, in a cross section taken along the cooling water flow direction, a virtual second circle C 2  is inscribed at three points on the first inclined surface  31  upstream of the peak portion  33 , the second inclined surface  32  downstream of the peak portion  33 , and a virtual facing surface S facing the first wide surface  11  and in which the valley portion  34  is located. Further, the protrusion portion  30  is formed such that the peak portion  33  does not fall within the second circle C 2 . Accordingly, the heat exchange efficiency can be improved without unnecessary increase in resistance. 
     Here, as shown in  FIG.  5   , a radius of the first circle C 1  is denoted by Rm 1 , a radius of the second circle C 2  is denoted by Rm 2 , a pitch between the peak portions  33  adjacent to each other in the cooling water flow direction is denoted by P, and a distance between the peak portion  33  and the first wide surface  11  is denoted by Dv. A shape of the protrusion portion  30  is determined when the radius Rm 1  of the first circle C 1 , the pitch P between the peak portions  33 , and the distance Dv are known. 
     At this time, sizes of the first circle C 1  and the second circle C 2  have a relation of Rm 1 &gt;Rm 2 . 
     In this way, by setting Rm 1 &gt;Rm 2 , it is possible to sufficiently secure a flow path cross-sectional area of the flow path  20  between the peak portion  33  and the first wide surface  11 . 
     Next, an operation of the cooling device  1  will be described with reference to  FIGS.  5  to  14   . 
       FIG.  6    is a plan view schematically showing flow of the cooling water in the protrusion portions  30 .  FIG.  7    is a cross-sectional view of a side surface schematically showing the flow of the cooling water in the protrusion portion  30 .  FIG.  8    is a graph showing a ratio of a heat transfer coefficient with respect to Rm 1 ×P/Dv, where Rm 1  is the radius of the first circle C 1 , P is the pitch between the peak portions  33  adjacent to each other in the cooling water flow direction, and Dv is the distance between the peak portion  33  and the first wide surface  11 .  FIG.  9    shows a value of Rm 1 ×P/Dv for each shape when the inclination angle θt, the pitch P, the distance Dv, and the radius Rm 1  are changed.  FIG.  10    is a graph showing upper and lower limit values of the inclination angle θt and an upper limit value of the distance Dv.  FIG.  11    is a graph showing a relation between the inclination angle θt and resistance ΔP [Pa].  FIG.  12    is a graph showing a relation between the pitch P and the heat transfer coefficient.  FIG.  13    is a graph showing a relation between the pitch P and the resistance ΔP.  FIG.  14    is a graph showing a ratio of a heat transfer coefficient with respect to Rm 1 ×P/Dv for a fluid having different Reynolds numbers Re. 
     As shown in  FIGS.  6  and  7   , when the cooling water flows from the first inclined surface  31  to the second inclined surface  32  adjacent to and downstream of the first inclined surface  31  in the cooling water flow direction, the longitudinal vortex is generated and flows along the second inclined surface  32 . Then, a large longitudinal vortex is formed in a space (see  FIG.  5   ) in which the virtual first circle C 1  is inscribed at the three points. Therefore, it is possible to improve heat exchange efficiency between the inverter module  8  and the cooling water in the space in which the virtual first circle C 1  is inscribed at the three points. Therefore, the heat exchange efficiency between the inverter module  8  and the cooling water can be improved depending on how the cooling water flows through the flow path  20 . 
     A horizontal axis of  FIG.  8    is Rm 1 ×P/Dv (Rm 1  is the radius of the first circle C 1 , P is the pitch between the peak portions  33  (or between the valley portions  34 ), and Dv is the distance between the peak portion  33  and the first wide surface  11 ). A vertical axis of  FIG.  8    is a ratio of a heat transfer coefficient to a case of a flat flow path in which the protrusion portions  30  are not formed. 
     Here, in the cooling device  1 , while the swirling flow is generated toward the valley portion  34 , the swirling flow is contracted between the peak portion  33  and the first wide surface  11  (a portion of the distance Dv), and thus a temperature boundary layer is thinned and the heat exchange efficiency is improved. The radius Rm 1 , the pitch P, and the distance Dv are parameters that are related to each other in order to generate a series of flows. Specifically, the radius Rm 1  has an inverse correlation in which the ratio is relatively large as the distance Dv is small, and the pitch P has an inverse correlation in which the ratio is relatively large as the distance Dv is small. In this way, there is a geometric correlation among the radius Rm 1 , the pitch P, and the distance Dv. Therefore, since the geometric correlation affects the flow, a peak can be indicated by a value of Rm 1 ×P/Dv. 
       FIG.  8    shows, as an example, a case where Re=1640 in a range of the Reynolds number Re that is frequently used in the cooling device  1 . Each plot in  FIG.  8    shows a case of each shape shown in  FIG.  9   . In  FIG.  8   , a plot of a triangle (▴) is a case where the distance Dv is 0.6 [mm], a plot of a circle (●) is a case where the distance Dv is 1.0 [mm], and a plot of a square (▪) is a case where the distance Dv is 1.4 [mm]. 
     Referring to  FIG.  8   , when the distance Dv is 1.0 [mm], a value of an inflection point, that is, when Rm 1 ×P/Dv is 40, is set as an upper limit, and a lower limit value is set to 4 based on the ratio of the heat transfer coefficient to the case of the flat flow path at that time. Therefore, it can be seen that performance of the cooling device  1  is improved when Rm 1 ×P/Dv is in a range of 4 to 40. Therefore, by setting Rm 1 ×P/Dv in the range of 4 to 40, the heat transfer coefficient can be improved, that is, a performance improvement margin can be increased. It can be seen that the performance of the cooling device  1  is similarly improved when the distance Dv is in a range of 0.6 to 1.4 [mm] based on the case where the distance Dv is 1.0 [mm]. 
     Subsequently, upper and lower limit values of each parameter in Rm 1 ×P/Dv will be described with reference to  FIGS.  10  to  14   . 
     In  FIG.  10   , a horizontal axis represents the inclination angle θt, and a vertical axis represents the heat transfer coefficient [W/m 2 K]. In  FIG.  10   , a plot of a triangle (▴) is a case where the distance Dv is 0.6 [mm], a plot of a circle (●) is a case where the distance Dv is 1.0 [mm], and a plot of a square (▪) is a case where the distance Dv is 1.4 [mm]. 
     As shown in  FIG.  10   , when the distance Dv is 1.4 [mm], a change in a magnitude of the heat transfer coefficient in a range of the inclination angle θt of 10° to 45° is less than 5%. Therefore, based on  FIG.  10   , the upper limit value of the distance Dv is 1.4 [mm], a lower limit value of the inclination angle θt is 10 [°], and an upper limit value of the inclination angle θt is 45 [°]. 
     In  FIG.  11   , a horizontal axis represents the inclination angle θt, and a vertical axis represents the resistance ΔP [Pa]. In  FIG.  11   , a plot of a triangle (▴) is a case where the distance Dv is 0.6 [mm], a plot of a circle (●) is a case where the distance Dv is 1.0 [mm], and a plot of a square (▪) is a case where the distance Dv is 1.4 [mm]. 
     As shown in  FIG.  11   , when the distance Dv is 0.6 [mm], the resistance ΔP is five times or more the resistance ΔP when the distance Dv is 1.4 [mm]. Therefore, the lower limit value of the distance Dv is 0.6 [mm]. 
     In  FIG.  12   , a horizontal axis represents the pitch P [mm], and the vertical axis represents the heat transfer coefficient [W/m 2 K]. In  FIG.  13   , a horizontal axis represents the pitch P [mm], and a vertical axis represents the resistance ΔP [kPa]. In  FIGS.  12  and  13   , a plot of a triangle (▴) is a case where the distance Dv is 0.6 [mm], a plot of a circle (●) is a case where the distance Dv is 1.0 [mm], and a plot of a square (▪) is a case where the distance Dv is 1.4 [mm]. 
     As shown in  FIGS.  12  and  13   , when the pitch is 16.5 [mm], the heat transfer coefficient decreases and the resistance ΔP increases. Therefore, the upper limit value of the pitch P is 16.5 [mm]. On the other hand, when the pitch P is 5.5 [mm], an increase in heat transfer coefficient from the pitch P of 11.0 [mm] is 10%, while the resistance ΔP is increased by 37%. It can be expected that the resistance ΔP increases quadratically when the pitch P is smaller than 5.5 [mm]. Therefore, the lower limit value of the pitch P is 5.5 [mm]. 
     A size of the radius Rm 1  is determined by the inclination angle θt, the distance Dv, and the pitch P. Thus, a range of the size of the radius Rm 1  can be obtained as follows based on upper and lower limit values of the inclination angle θt, the distance Dv, and the pitch P. A lower limit value of the radius Rm 1  is a value when the inclination angle θt is 10 [° ], the distance Dv is 0.6 [mm], and the pitch P is 5.5 [mm], and is 0.54 [mm] here. An upper limit value of the radius Rm 1  is a value when the inclination angle θtis 45 [°], the distance Dv is 1.4 [mm], and the pitch P is 16.5 [mm], and is 3.61 [mm] here. 
       FIG.  14    adds a case where the Reynolds numbers Re of the fluid are different when the distance Dv is 1.0 [mm] in the graph of  FIG.  8   . In  FIG.  14   , a plot of a circle (●) is a case where the Reynolds number Re of the fluid is 1640, a plot of a square (▪) is a case where the Reynolds number Re of the fluid is 1230, and a plot of a triangle (▴) is a case where the Reynolds number Re of the fluid is 820. 
     As shown in  FIG.  14   , when the Reynolds number Re of the fluid is small, a peak of a peak value is low and gentle, and is offset to a lower side. However, it can be seen that even if the Reynolds number Re of the fluid is changed, an overall tendency is the same. 
     Hereinafter, first to eighth modifications of the embodiment of the present invention will be described with reference to  FIGS.  15  to  23   . 
     First, a first modification and a second modification of the embodiment of the present invention will be described with reference to  FIGS.  15  to  17   . 
       FIG.  15    is a perspective view illustrating the flow path  20  according to the first modification of the embodiment of the present invention.  FIG.  16    is a plan view illustrating flow of cooling water in the first modification shown in  FIG.  15   .  FIG.  17    is a perspective view illustrating the flow path  20  according to the second modification of the embodiment of the present invention. 
     As shown in  FIG.  15   , the flow path  20  includes a central flow path  21 , a side flow path  22 , and a turn flow path  23 . 
     The central flow path  21  is formed at a position in a flow path width direction corresponding to a central portion of the inverter module  8  having a large heat generation amount. The central flow path  21  is provided with the protrusion portions  30 . Therefore, the central portion of the inverter module  8  can be preferentially cooled by cooling water flowing through the central flow path  21 . 
     The side flow path  22  is provided outside the central flow path  21  in the flow path width direction. The side flow path  22  is provided with the protrusion portions  30 . Therefore, a portion of the inverter module  8  having a relatively small heat generation amount can be further cooled by the cooling water whose temperature has risen due to heat exchange with the inverter module  8  in the central flow path  21 . 
     The turn flow path  23  turns the cooling water back from the central flow path  21  toward the side flow path  22 . As shown in  FIG.  16   , the cooling water turned back in the turn flow path  23  passes through the side flow path  22  and is drained from the outlet flow path  3 . 
     As described above, since the central portion of the inverter module  8  in the flow path width direction has a large heat generation amount, the inverter module  8  can be efficiently cooled by providing the protrusion portions  30  in the central flow path  21  that cools the central portion. The cooling water turned back via the turn flow path  23  flows through the side flow path  22 , and thus it is possible to further cool the portion of the inverter module  8  having a relatively small heat generation amount. 
     Since the protrusion portions  30  are formed not only in the central flow path  21  but also in the side flow path  22 , the heat exchange efficiency of the inverter module  8  can be further improved. 
     As in the second modification shown in  FIG.  17   , the protrusion portions  30  may not be formed in the side flow path  22  depending on the heat generation amount of the inverter module  8 . In this case, resistance of the cooling water can be reduced by not forming the protrusion portions  30  in the side flow path  22 . 
     Next, a third modification of the embodiment of the present invention will be described with reference to  FIG.  18   . 
       FIG.  18    is a perspective view illustrating the flow path  20  according to the third modification of the embodiment of the present invention. 
     As shown in  FIG.  18   , the protrusion portion  30  each further includes a rectifying fin  37  extending downstream in the cooling water flow direction from the top portion  36  protruding downstream in the cooling water flow direction in the connection portion  35  between the peak portions  33  continuous in the flow path width direction. 
     The rectifying fin  37  is formed downstream in the cooling water flow direction from the peak portion  33 . The rectifying fin  37  is formed to have a length to the valley portion  34  along the second inclined surface  32 . 
     In this way, since the flow path  20  is partitioned in the flow path width direction by providing the rectifying fin  37 , it is possible to prevent interference between longitudinal vortices of the cooling water on both sides of the rectifying fin  37 . Therefore, it is possible to improve cooling performance while preventing an increase in resistance of the cooling water. 
     Next, a fourth modification of the embodiment of the present invention will be described with reference to  FIG.  19   . 
       FIG.  19    is a perspective view illustrating the flow path  20  according to the fourth modification of the embodiment of the present invention. 
     As shown in  FIG.  19   , the flow path  20  includes a wide portion  25 , a width reducing portion  26 , and a narrow portion  27 . The flow path  20  is formed such that a downstream side in the cooling water flow direction is narrower in the flow path width direction than an upstream side in the cooling water flow direction. 
     The wide portion  25  is formed such that the cooling water cools the entire inverter module  8  in the flow path width direction. The wide portion  25  is formed at a portion into which the cooling water flows from the inlet flow path  2 . Therefore, the cooling water having a relatively low temperature flows through the wide portion  25 . Therefore, the wide portion  25  is formed, and thus it is possible to widely cool the inverter module  8  while preventing a flow velocity of the cooling water. 
     The width reducing portion  26  gradually reduces a flow path width from the wide portion  25  toward the narrow portion  27 . The width reducing portion  26  is formed along the ridge line of the valley portion  34 . Therefore, the flow path width can be reduced so as not to hinder the flow of the longitudinal vortex formed by the protrusion portions  30 , and thus an increase in resistance can be prevented. 
     The narrow portion  27  is formed to be narrower than the wide portion  25  in the flow path width direction. The narrow portion  27  is formed at a position in the flow path width direction corresponding to the central portion of the inverter module  8  having a large heat generation amount. The cooling water flowing through the narrow portion  27  has a higher flow velocity than the cooling water flowing through the wide portion  25 . Therefore, even when the inverter module  8  is cooled at the wide portion  25  and the width reducing portion  26  and the temperature of the cooling water is increased, the inverter module  8  can be cooled at the narrow portion  27  by increasing the flow velocity. 
     Next, fifth to eighth modifications of the embodiment of the present invention will be described with reference to  FIGS.  20  to  23   . 
       FIG.  20    is a perspective view illustrating the flow path  20  according to a fifth modification of the embodiment of the present invention.  FIG.  21    is a perspective view illustrating the flow path  20  according to a sixth modification of the embodiment of the present invention.  FIG.  22    is a perspective view illustrating the flow path  20  according to a seventh modification of the embodiment of the present invention.  FIG.  23    is a perspective view illustrating the flow path  20  according to an eighth modification of the embodiment of the present invention. 
       FIGS.  20  to  23    show a state in which a part of an outer cylinder  5  or an inner cylinder  6  is cut off so that a shape of the protrusion portion  30  can be seen. In each of the modifications shown in  FIGS.  20  to  23   , an electric motor (driving motor)  80  having a cylindrical outer shape is applied as the device to be cooled instead of the inverter module  8 . 
     In the fifth modification shown in  FIG.  20   , the cooling device  1  includes a tubular outer cylinder  5  and a tubular inner cylinder  6  that is provided at an interval on an inner periphery of the outer cylinder  5  and accommodates the electric motor  80  on the inner periphery. An inner diameter of the outer cylinder  5  is formed to be larger than an outer diameter of the inner cylinder  6 . The first wide surface  11  is formed on the inner periphery of the outer cylinder  5 , and the second wide surface  12  is formed on an outer periphery of the inner cylinder  6 . 
     The flow path  20  is formed in an annular shape between the outer cylinder  5  and the inner cylinder  6 . The cooling water flows through the flow path  20  in a central axis direction. That is, the first wide surface  11  and the second wide surface  12  linearly extend in the cooling water flow direction, and are circularly curved in a direction orthogonal to the cooling water flow direction. 
     The protrusion portions  30  protrude from an outer periphery of the second wide surface  12  into the flow path  20  and extend in the flow path width direction, and are arranged side by side in the central axis direction of the flow path  20 , which is the cooling water flow direction. The protrusion portions  30  are not provided on the first wide surface  11 . 
     In the sixth modification shown in  FIG.  21   , the cooling device  1  includes a tubular outer cylinder  5  and a tubular inner cylinder  6  that is provided at an interval on an inner periphery of the outer cylinder  5  and accommodates the electric motor  80  on the inner periphery. An inner diameter of the outer cylinder  5  is formed to be larger than an outer diameter of the inner cylinder  6 . The first wide surface  11  is formed on the inner periphery of the outer cylinder  5 , and the second wide surface  12  is formed on an outer periphery of the inner cylinder  6 . 
     The flow path  20  is formed in an annular shape between the outer cylinder  5  and the inner cylinder  6 . The cooling water flows through the flow path  20  in a circumferential direction. That is, the first wide surface  11  and the second wide surface  12  are circularly curved in the cooling water flow direction, and linearly extend in a direction orthogonal to the cooling water flow direction. 
     The protrusion portions  30  protrude from an outer periphery of the second wide surface  12  into the flow path  20  and extend in the flow path width direction, and are arranged side by side in the circumferential direction of the flow path  20 , which is the cooling water flow direction. The protrusion portions  30  are not provided on the first wide surface  11 . 
     In the seventh modification shown in  FIG.  22   , the cooling device  1  includes a tubular outer cylinder  5  and a tubular inner cylinder  6  that is provided at an interval on an inner periphery of the outer cylinder  5  and accommodates the electric motor  80  on the inner periphery. An inner diameter of the outer cylinder  5  is formed to be larger than an outer diameter of the inner cylinder  6 . The second wide surface  12  is formed on the inner periphery of the outer cylinder  5 , and the first wide surface  11  is formed on an outer periphery of the inner cylinder  6 . 
     The flow path  20  is formed in an annular shape between the outer cylinder  5  and the inner cylinder  6 . The cooling water flows through the flow path  20  in a central axis direction. That is, the first wide surface  11  and the second wide surface  12  linearly extend in the cooling water flow direction, and are circularly curved in a direction orthogonal to the cooling water flow direction. 
     The protrusion portions  30  protrude from an inner periphery of the second wide surface  12  into the flow path  20  and extend in the flow path width direction, and are arranged side by side in the central axis direction of the flow path  20 , which is the cooling water flow direction. The protrusion portions  30  are not provided on the first wide surface  11 . 
     In the eighth modification shown in  FIG.  23   , the cooling device  1  includes a tubular outer cylinder  5  and a tubular inner cylinder  6  that is provided at an interval on an inner periphery of the outer cylinder  5  and accommodates the electric motor  80  on the inner periphery. An inner diameter of the outer cylinder  5  is formed to be larger than an outer diameter of the inner cylinder  6 . The second wide surface  12  is formed on the inner periphery of the outer cylinder  5 , and the first wide surface  11  is formed on an outer periphery of the inner cylinder  6 . 
     The flow path  20  is formed in an annular shape between the outer cylinder  5  and the inner cylinder  6 . The cooling water flows through the flow path  20  in a circumferential direction. That is, the first wide surface  11  and the second wide surface  12  are circularly curved in the cooling water flow direction, and linearly extend in a direction orthogonal to the cooling water flow direction. 
     The protrusion portions  30  protrude from an inner periphery of the second wide surface  12  into the flow path  20  and extend in the flow path width direction, and are arranged side by side in the circumferential direction of the flow path  20 , which is the cooling water flow direction. The protrusion portions  30  are not provided on the first wide surface  11 . 
     As described above, in the fifth to eighth modifications, the first wide surface  11  and the second wide surface  12  extend linearly in one direction of the cooling water flow direction and the direction orthogonal to the cooling water flow direction, and extend linearly or are circularly curved in the other direction. In this way, the flat flow path  20  may be formed not only in a geometric planar shape including two straight lines but also in a curved surface shape. Specifically, the flow path  20  is formed between the outer cylinder  5  and the inner cylinder  6  formed in a tubular shape, and may be circularly curved in the cooling water flow direction or may be circularly curved in the direction orthogonal to the cooling water flow direction. 
     In this way, not only in a case where the first wide surface  11  and the second wide surface  12  are formed in a planar shape, but also in a case where the flow path  20  is formed in the circumferential direction or in a case where the flow path  20  is circularly curved in the width direction, similarly, by providing the protrusion portions  30 , the heat exchange efficiency between the electric motor  80  as the device to be cooled and the cooling water can be improved depending on how the cooling water flows through the flow path  20 . 
     According to the above embodiment, the following effects are exerted. 
     In a cooling device  1  that has a first wide surface  11  and a second wide surface  12  facing the first wide surface  11 , and cools an inverter module  8  with cooling water flowing through a flat flow path  20  formed between the first wide surface  11  and the second wide surface  12 , the first wide surface  11  cools the inverter module  8  with the cooling water, the second wide surface  12  has a plurality of protrusion portions  30  protruding into the flow path  20 , extending in a flow path width direction, the protrusion portions  30  being arranged side by side in a cooling water flow direction, the first wide surface  11  is not provided with the protrusion portions  30 , the protrusion portions  30  each have a first inclined surface  31  inclined to come close to the first wide surface  11  from upstream to downstream in the cooling water flow direction, and a second inclined surface  32  disposed alternately with the first inclined surface  31  in the cooling water flow direction and inclined to be distanced from the first wide surface  11  from upstream to downstream in the cooling water flow direction, and the protrusion portions  30  each are formed such that, in a cross section taken along the cooling water flow direction, a virtual first circle C 1  is inscribed at three points on the first wide surface  11 , the second inclined surface  32 , and the first inclined surface  31  adjacent to the second inclined surface  32  downstream in the cooling water flow direction. 
     According to the configuration, the protrusion portions  30  each are formed such that, in the cross section taken along the cooling water flow direction, the virtual first circle C 1  is inscribed at three points on the first wide surface  11 , the second inclined surface  32 , and the first inclined surface  31  adjacent to and downstream of the second inclined surface  32  in the cooling water flow direction. Therefore, when the cooling water flows from the first inclined surface  31  to the second inclined surface  32  adjacent to and downstream of the first inclined surface  31  in the cooling water flow direction, a longitudinal vortex is generated and flows along the second inclined surface  32 , and a large longitudinal vortex is generated in a space in which the virtual first circle C 1  is inscribed at the three points. Therefore, it is possible to improve heat exchange efficiency between the inverter module  8  and the cooling water in a space in which the virtual first circle C 1  is inscribed at the three points. Therefore, the heat exchange efficiency between the inverter module  8  and the cooling water can be improved depending on how the cooling water flows through the flow path  20 . 
     The protrusion portions  30  each include a peak portion  33  formed between the first inclined surface  31  and the second inclined surface  32  adjacent to the first inclined surface  31  downstream in the cooling water flow direction, and a valley portion  34  formed between the second inclined surface  32  and the first inclined surface  31  adjacent to the second inclined surface  32  downstream in the cooling water flow direction, and the protrusion portions  30  each is formed such that, in a cross section taken along the cooling water flow direction, a virtual second circle C 2  is inscribed at three points on the first inclined surface  31  upstream of the peak portion  33 , the second inclined surface  32  downstream of the peak portion  33 , and a virtual facing surface S facing the first wide surface  11  and in which the valley portion  34  is located, and the peak portion  33  does not fall within the second circle C 2 . 
     According to the configuration, when the cooling water passes through the flow path  20  between the peak portion  33  and the first wide surface  11 , the cooling water tends to flow in a direction nearly perpendicular to a ridge line of the peak portion  33  so as to reduce resistance. On the other hand, when the cooling water passes through the flow path  20  between the valley portion  34  and the first wide surface  11 , the cooling water tends to flow in a direction along a ridge line of the valley portion  34  having low resistance. In this way, the cooling water alternately passes through the peak portion  33  and the valley portion  34 , and thus a strong swirling flow (a longitudinal vortex) is generated in the valley portion  34  sandwiched between a pair of peak portions  33 . Therefore, the longitudinal vortex can be efficiently generated. 
     Further, Rm 1 &gt;Rm 2 , wherein a radius of the first circle C 1  is Rm 1  and a radius of the second circle C 2  is Rm 2 . 
     According to the configuration, by setting Rm 1 &gt;Rm 2 , it is possible to sufficiently secure a flow path cross-sectional area of the flow path  20  between the peak portion  33  and the first wide surface  11 . 
     When P is a pitch between peak portions  33  adjacent to each other in the cooling water flow direction, and Dv is a distance between the peak portion  33  and the first wide surface  11 , Rm 1 ×P/Dv is 4 to 40. 
     According to the configuration, when Rm 1 ×P/Dv is in a range of 4 to 40, performance of the cooling device  1  is improved as compared with a flat flow path in which the protrusion portions  30  are not formed. Therefore, by setting Rm 1 ×P/Dv in the range of 4 to 40, a heat transfer coefficient can be improved, that is, a performance improvement margin can be increased. 
     The protrusion portions  30  adjacent to each other in the flow path width direction are inclined in opposite directions so as to alternate in the cooling water flow direction, ridge lines of the peak portions  33  adjacent to each other in the flow path width direction are continuously formed, and ridge lines of valley portions  34  adjacent to each other in the flow path width direction are continuously formed. 
     According to the configuration, it is possible to improve a temperature distribution of the cooling water in the flow path  20 . 
     The protrusion portions  30  are formed over an entire width in the flow path width direction. 
     According to the configuration, when there is a portion where the protrusion portions  30  are not formed, the cooling water may bypass the portion, but the protrusion portions  30  are formed over the entire width in the flow path width direction, and thus it is possible to prevent a decrease in heat exchange efficiency. 
     The flow path  20  includes a central flow path  21  provided with the protrusion portions  30 , a side flow path  22  provided outside the central flow path  21  in the flow path width direction, and a turn flow path  23  in which the cooling water is turned back from the central flow path  21  toward the side flow path  22 . 
     According to the configuration, since the central portion of the inverter module  8  in the flow path width direction has a large heat generation amount, the inverter module  8  can be efficiently cooled by providing the protrusion portions  30  in the central flow path  21  that cools the central portion. The cooling water turned back via the turn flow path  23  flows through the side flow path  22 , and thus it is possible to further cool a portion of the inverter module  8  having a relatively small heat generation amount. 
     The side flow path  22  is provided with the protrusion portions  30 . 
     According to the configuration, since the protrusion portions  30  are formed not only in the central flow path  21  but also in the side flow path  22 , the heat exchange efficiency of the inverter module  8  can be further improved. 
     The protrusion portions  30  may not be formed in the side flow path  22  depending on the heat generation amount of the inverter module  8 . In this case, resistance of the cooling water can be reduced by not forming the protrusion portions  30  in the side flow path  22 . 
     The flow path  20  is formed such that a downstream side in the cooling water flow direction is narrower in the flow path width direction than an upstream side in the cooling water flow direction. 
     According to the configuration, cooling water flowing through a narrow portion  27  has a higher flow velocity than cooling water flowing through a wide portion  25 . Therefore, even when the inverter module  8  is cooled at the wide portion  25  and the width reducing portion  26  and the temperature of the cooling water is increased, the inverter module  8  can be cooled at the narrow portion  27  by increasing the flow velocity. 
     The first wide surface  11  is formed by a bottom surface of the inverter module  8 . 
     According to the configuration, the heat exchange efficiency can be further improved by bringing the cooling water into direct contact with the inverter module  8 . 
     The protrusion portions  30  each include: the peak portion  33  formed between the first inclined surface  31  and the second inclined surface  32  adjacent to the first inclined surface  31  downstream in the cooling water flow direction; the valley portion  34  formed between the second inclined surface  32  and the first inclined surface  31  adjacent to the second inclined surface  32  downstream in the cooling water flow direction; and a rectifying fin  37  extending downstream in the cooling water flow direction from a top portion  36  protruding downstream in the cooling water flow direction in a connection portion  35  between the peak portions  33  continuous in the flow path width direction. 
     According to the configuration, since the flow path  20  is partitioned in the flow path width direction by providing the rectifying fin  37 , it is possible to prevent interference between longitudinal vortices of the cooling water on both sides of the rectifying fin  37 . Therefore, it is possible to improve cooling performance while preventing an increase in resistance of the cooling water. 
     The first wide surface  11  extends linearly in one direction of the cooling water flow direction and a direction orthogonal to the cooling water flow direction, and extends linearly or is circularly curved in the other direction. 
     According to the configuration, not only in a case where the first wide surface  11  is formed in a planar shape, but also in a case where the flow path  20  is formed in the circumferential direction or in a case where the flow path  20  is circularly curved in the width direction, similarly, by providing the protrusion portions  30 , the heat exchange efficiency between an electric motor  80  as the device to be cooled and the cooling water can be improved depending on how the cooling water flows through the flow path  20 . 
     Although the embodiments of the present invention have been described above, the above-mentioned embodiments are merely a part of application examples of the present invention, and do not mean that the technical scope of the present invention is limited to the specific configurations of the above-mentioned embodiments. 
     For example, in the above embodiment, the cooling device  1  cools the inverter module  8  or the electric motor  80 , but instead of these, the cooling device  1  may cool other devices to be cooled.