Patent Publication Number: US-2023155448-A1

Title: Inverter device, motor, and motor unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is the U.S. national stage of application No. PCT/JP2020/034639, filed on Sep. 14, 2020, and priority under 35 U.S.C. § 119 (a) and 35 U.S.C. § 365(b) is claimed from Japanese Patent Application No. 2020-023048, filed on Feb. 14, 2020. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an inverter device, a motor, and a motor unit. 
     BACKGROUND 
     In an electronic control device mounted on a vehicle or the like, a configuration in which a honeycomb-shaped rib is included in a part of a case that accommodates a circuit board is known. 
     In a motor unit having a structure in which an inverter case accommodating an inverter is continuous to a motor housing accommodating a motor, membrane resonance of the inverter case is liable to be excited by motor vibration generated when the motor is driven. Installation of a rib is effective for suppressing membrane resonance. However, when a closed annular rib in such as a honeycomb shape is arranged on the upper surface of the inverter case, water having entered a recess surrounded by the rib is less likely to be discharged. 
     SUMMARY 
     According to one exemplary aspect of the present invention, there is provided an inverter device including an inverter and an inverter case that accommodates the inverter inside the inverter case. The inverter case has a top wall covering the inverter from above. The top wall includes a first inclined surface descending from a top part on an upper surface of the top wall toward a first end part of the top wall, and a plurality of first rod-shaped ribs extending from the top part toward the first end part. The first rod-shaped rib has a site where a protrusion height from the inclined surface increases toward the first end part. 
     The above and other elements, features, steps, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic configuration view of a motor unit according to an embodiment; 
         FIG.  2    is a perspective view of the motor unit according to the embodiment; 
         FIG.  3    is a schematic cross-sectional view of an inverter device according to the embodiment; 
         FIG.  4    is a plan view of an inverter cover according to the embodiment as viewed from above; 
         FIG.  5    is a plan view of the inverter cover according to the embodiment as viewed from below; and 
         FIG.  6    is a perspective view of the inverter cover according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description will be made with the direction of gravity being defined on the basis of positional relationships in the case where a motor unit  1  is mounted in a vehicle on a horizontal road surface. In the drawings, an XYZ coordinate system is shown appropriately as a three-dimensional orthogonal coordinate system. In the XYZ coordinate system, a Z-axis direction corresponds to a vertical direction (i.e., an up-down direction), and a +Z direction points upward (i.e., in a direction opposite to the direction of gravity), while a −Z direction points downward (i.e., in the direction of gravity). An X-axis direction corresponds to a front-rear direction of the vehicle in which the motor unit  1  is mounted, and is a direction orthogonal to the Z-axis direction, and a +X direction points forward of the vehicle, while a −X direction points rearward of the vehicle. 
     However, the +X direction and the −X direction may point rearward and forward, respectively, of the vehicle. A Y-axis direction is a direction orthogonal to both the X-axis direction and the Z-axis direction and indicates a width direction (left-right direction) of the vehicle, and a +Y direction points leftward of the vehicle, while a −Y direction points rightward of the vehicle. However, when the +X direction points rearward of the vehicle, the +Y direction may point rightward of the vehicle, and the −Y direction may point leftward of the vehicle. That is, the +Y direction simply points to one side in the left-right direction of the vehicle, and the −Y direction points to the other side in the left-right direction of the vehicle, regardless of the direction of the X-axis. 
     In description below, unless otherwise specified, a direction (that is, the Y-axis direction) parallel to a motor axis J 2  of a motor  2  will be simply referred to by the term “axial direction”, “axial”, or “axially”, radial directions around the motor axis J 2  will be simply referred to by the term “radial direction”, “radial”, or “radially”, and a circumferential direction around the motor axis J 2 , that is, a circumferential direction about the motor axis J 2 , will be simply referred to by the term “circumferential direction”, “circumferential”, or “circumferentially”. However, the term “parallel” as used above includes both “parallel” and “substantially parallel”. 
     The motor unit  1  of the present embodiment is mounted on a vehicle using a motor as a power source, such as a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHV), or an electric vehicle (EV), and is used as the power source. 
     As illustrated in  FIG.  1   , the motor unit  1  includes the motor  2 , a transmission mechanism  3 , a housing  6 , oil O accommodated in the housing  6 , an oil cooler  9 , and an inverter device  110 . 
     The motor  2  includes a rotor  20  that rotates about the motor axis J 2  extending in the horizontal direction, and a stator  30  located radially outside the rotor  20 . 
     The housing  6  includes a motor housing  60  that accommodates the motor  2 , a motor cover  61  that closes an end part on one side (−Y side) of the motor housing  60 , and a gear housing  62  that is located at an end part on the other side (+Y side) of the motor housing  60  and accommodates the transmission mechanism  3 . 
     The motor  2  is an inner rotor type motor. The rotor  20  is arranged radially inside the stator  30 . The rotor  20  includes a shaft  21 , a rotor core  24 , and a rotor magnet (not illustrated). The motor  2  may be an outer rotor type motor. 
     The shaft  21  is arranged about the motor axis J 2  extending in a horizontal direction and in a width direction of a vehicle. The shaft  21  is a hollow shaft having a hollow part  22  inside. The shaft  21  protrudes from the motor housing  60  into the gear housing  62 . An end part of the shaft  21  protruding to the gear housing  62  is coupled to the transmission mechanism  3 . Specifically, the shaft  21  is coupled to a first gear  41  of the transmission mechanism  3 . 
     The stator  30  encloses the rotor  20  from radially outside. The stator  30  includes a stator core  32 , a coil  31 , and an insulator (not illustrated) interposed between the stator core  32  and the coil  31 . The stator  30  is held by the motor housing  60 . The coil  31  is connected to the inverter device  110  directly or via a bus bar (not illustrated). 
     The transmission mechanism  3  is accommodated in the gear housing  62 . The transmission mechanism  3  is connected to the shaft  21  on one side in the axial direction of the motor axis J 2 . The transmission mechanism  3  includes a reduction gear  4  and a differential gear  5 . Torque output from the motor  2  is transmitted to the differential gear  5  through the reduction gear  4 . 
     The reduction gear  4  is connected to the shaft  21  of the motor  2 . The reduction gear  4  has the first gear  41 , a second gear  42 , a third gear  43 , and an intermediate shaft  45 . The first gear  41  is coupled to the shaft  21  of the motor  2 . The intermediate shaft  45  extends along an intermediate axis J 4  parallel to the motor axis J 2 . The second gear  42  and the third gear  43  are fixed to both ends of the intermediate shaft  45 . The second gear  42  and the third gear  43  are connected to each other via the intermediate shaft  45 . The second gear  42  meshes with the first gear  41 . The third gear  43  meshes with a ring gear  51  of the differential gear  5 . 
     Torque output from the motor  2  is transmitted to the ring gear  51  of the differential gear  5  through the shaft  21  of the motor  2 , the first gear  41 , the second gear  42 , the intermediate shaft  45 , and the third gear  43 . A gear ratio of each gear, the number of gears, and the like can be modified in various manners in accordance with a required reduction ratio. The reduction gear  4  is a speed reducer of a parallel-axis gearing type, in which axis centers of gears are arranged in parallel with one another. 
     The differential gear  5  transmits torque output from the motor  2  to an axle of a vehicle. The differential gear  5  transmits the torque to axles  55  of both the left and right wheels while absorbing the speed difference between the left and right wheels when the vehicle turns. The differential gear  5  includes a gear housing, a pinion gear, a pinion shaft, and a side gear (all not illustrated) in addition to the ring gear  51  meshing with the third gear of the reduction gear  4 . 
     A lower region in the gear housing  62  is provided with an oil reservoir P in which the oil O accumulates. In the present embodiment, a bottom part of the motor housing  60  is located at a higher level than a bottom part of the gear housing  62 . With this configuration, the oil O after the motor  2  is cooled can be easily collected from a lower region of the motor housing  60  to the oil reservoir P of the gear housing  62 . 
     A part of the differential gear  5  soaks in the oil reservoir P. The oil O accumulated in the oil reservoir P is scraped up by operation of the differential gear  5 . A part of the scraped oil O is supplied into the shaft  21 . Another part of the oil O is diffused into the gear housing  62  and supplied to each gear of the reduction gear  4  and the differential gear  5 . The oil O used for lubrication of the reduction gear  4  and the differential gear  5  is dropped and collected in the oil reservoir P located on the lower side of the gear housing  62 . 
     The inverter device  110  includes an inverter  110   a  electrically connected to the motor  2  and an inverter case  120  accommodating the inverter  110   a . The inverter  110   a  controls current to be supplied to the motor  2 . The inverter case  120  is fixed to the motor housing  60 . A cooling water pipe  95  extending from a radiator of the vehicle is connected to the inverter device  110 . The cooling water pipe  95  extends to the oil cooler  9  via the inverter device  110 . 
     The oil cooler  9  is located on a side surface of the motor housing  60 . The cooling water pipe  95  extending from the inverter device  110  is connected to the oil cooler  9 . The oil  0  discharged from an electric oil pump  10  is supplied to the oil cooler  9 . The oil O passing through the inside of the oil cooler  9  is cooled through heat exchange with cooling water passing through the cooling water pipe  95 . 
     The oil O cooled by the oil cooler  9  is supplied to the motor  2 . 
     The electric oil pump  10  is an oil pump driven by a pump motor  10   a . The electric oil pump  10  sucks up the oil O from the oil reservoir P and supplies the oil O to the oil cooler  9 . The pump motor  10   a  rotates a pump mechanism of the electric oil pump  10 . In the motor unit  1 , a rotation axis J 6  of the pump motor  10   a  is parallel to the motor axis J 2 . The electric oil pump  10  having the pump motor  10   a  tends to become long in a direction in which the rotation axis J 6  extends. By making the rotation axis J 6  of the pump motor  10   a  parallel to the motor axis J 2 , the electric oil pump  10  becomes less likely to protrude in the radial direction of the motor unit  1 . This makes it possible to reduce the radial dimension of the motor unit  1 . 
     As illustrated in  FIG.  1   , the oil O circulates in an oil passage  90  provided in the housing  6 . The oil passage  90  is a path of the oil O for supplying the oil O from the oil reservoir P to the motor  2 . 
     The oil O circulating in the oil passage  90  is used as lubricating oil for the reduction gear  4  and the differential gear  5  and as cooling oil for the motor  2 . The oil O accumulates in the oil reservoir P in a lower part of the gear housing  62 . Oil equivalent to automatic transmission fluid (ATF) having a low viscosity is preferably used as the oil O so that the oil O can perform functions of lubricating oil and cooling oil. 
     As illustrated in  FIG.  1   , the oil passage  90  is a path of the oil O that is guided from the oil reservoir Pon the lower side of the motor  2  to the oil reservoir P on the lower side of the motor  2  again via the motor  2 . The oil passage  90  includes a first oil passage  91  passing through the inside of the motor  2  and a second oil passage  92  passing through the outside of the motor  2 . The oil O cools the motor  2  from the inside and the outside through the first oil passage  91  and the second oil passage  92 . 
     The oil O is scraped up by the differential gear  5  from the oil reservoir P, and is guided into an interior of the rotor  20  through the first oil passage  91 . The oil O is sprayed from the rotor  20  toward the coil  31  to cool the stator  30 . The oil  0  having cooled the stator  30  moves to the oil reservoir P of the gear housing  62  via the lower region of the motor housing  60 . 
     In the second oil passage  92 , the oil O is pumped up from the oil reservoir P by the electric oil pump  10 . The oil O is pumped up to an upper part of the motor  2  via the oil cooler  9  and is supplied to the motor  2  from the upper side of the motor  2 . The oil O having cooled the motor  2  moves to the oil reservoir P of the gear housing  62  via the lower region of the motor housing  60 . 
     As illustrated in  FIGS.  1  to  3   , the inverter device  110  includes the inverter  110   a  and the inverter case  120  accommodating the inverter  110   a  inside the inverter case  120 . The inverter case  120  includes a box-shaped case body  121  that opens upward, and a cover  122  that closes an opening of the case body  121  from above. 
     As illustrated in  FIG.  2   , the case body  121  is continuous to the outer peripheral surface of the motor housing  60 . The case body  121  is located on the vehicle front side (+X side) of the motor housing  60 . In the motor unit  1 , the case body  121  and the motor housing  60  are a part of a single die casting member. 
     The cover  122  is a plate-like member that covers the inverter  110   a  from above. The cover  122  constitutes a top wall of the inverter case  120 . In the present embodiment, the inverter case  120  has a configuration including the box-shaped case body  121  that opens upward and the plate-shaped cover  122 , but other configurations can be adopted. For example, a configuration in which the case body  121  is opened in the axial direction (Y-axis direction), a configuration in which the case body  121  is opened to the vehicle front side (+X side), or a configuration in which the case body  121  is opened to the lower side (-Z side) maybe adopted. In these cases, the wall located at the upper end of the case body  121  is a top wall covering the inverter  110   a  from above. 
     In the present embodiment, the inverter  110   a  is fixed to the lower surface of the cover  122  as illustrated in  FIG.  3   . According to this configuration, since the cover  122  and the inverter  110   a  can be unitized, the manufacturing process can be made efficient. The inverter device  110  may have a configuration in which the inverter  110   a  is fixed to the case body  121 . 
     As illustrated in  FIGS.  2  to  4   , the cover  122  has a first inclined surface  131  descending from a top part  130  on the upper surface of the cover  122  toward a first end part  122   a  of the cover  122 , and a second inclined surface  132  descending from the top part  130  toward a second end part  122   b  different from the first end part  122   a.    
     The first end part  122   a  of the cover  122  is an end part on the vehicle rear side (−X side) in the motor unit  1 . The second end part  122   b  is an end part on the vehicle front side (+X side) of the motor unit  1 . The top part  130  is located midway between the first end part  122   a  and the second end part  122   b  in the vehicle front-rear direction (X-axis direction). 
     The top part  130  is a belt-shaped region extending along the vehicle left-right direction (Y-axis direction) when the motor unit  1  is viewed from above. From both end parts in the width direction of the top part  130 , the first inclined surface  131  and the second inclined surface  132  expand toward the first end part  122   a  and the second end part  122   b , respectively. In the present embodiment, the top part  130  is a topmost part located at the uppermost side on the upper surface of the cover  122 . The top part  130  may exist at a plurality of places on the upper surface of the cover  122 . 
     The top part  130  means an upper end part of a planar part facing upward in the upper surface of the cover  122 , and does not include a site locally protruding from the upper surface of the cover  122 . Examples of the site locally protruding from the upper surface of the cover  122  include a screw fixing boss, a screw head, or a first rod-shaped rib  141 , a second rod-shaped rib  142 , a first coupling rib  151 , and a second coupling rib  152 , which will be described later. 
     The first inclined surface  131  and the second inclined surface  132  may be inclined toward end parts of the cover  122  different from each other. The inclination direction of the first inclined surface  131  and the inclination direction of the second inclined surface  132  maybe directions that are parallel to each other or may be directions that intersect each other. For example, the inclination direction of the first inclined surface  131  and the inclination direction of the second inclined surface  132  may be configured to be orthogonal to each other. 
     The cover  122  has a plurality of the first rod-shaped ribs  141  extending from the top part  130  toward the first end part  122   a . As illustrated in  FIGS.  3  and  6   , the first rod-shaped rib  141  has a site where a protrusion height from the first inclined surface  131  increases toward the first end part  122   a.    
     The cover  122  has a plurality of the second rod-shaped ribs  142  extending from the top part  130  toward the second end part  122   b . The second rod-shaped rib  142  has a site where a protrusion height from the second inclined surface  132  increases toward the second end part  122   b.    
     According to the above configuration, since both the first inclined surface  131  and the second inclined surface  132  of the cover  122  go down from the top part  130  toward the end part of the cover  122 , even when water falls on the upper surface of the inverter device  110 , the water on the upper surface of the cover  122  flows down along the first inclined surface  131  or the second inclined surface  132  to the first end part  122   a  or the second end part  122   b . This makes it difficult for water to accumulate on the inverter device  110 . 
     Since the first rod-shaped rib  141  extends along the first inclined surface  131  and the second rod-shaped rib  142  extends along the second inclined surface  132 , water flowing on the first inclined surface  131  and the second inclined surface  132  smoothly flows to the end part of the cover  122  without being obstructed by the first rod-shaped rib  141  and the second rod-shaped rib  142 , and is discharged to the outside of the cover  122 . 
     Since the first inclined surface  131  and the second inclined surface  132  have the first rod-shaped rib  141  and the second rod-shaped rib  142 , membrane resonance is suppressed on both of the first inclined surface  131  and the second inclined surface  132 . Therefore, generation of noise in the motor unit  1  can be suppressed. 
     The protrusion height of the first rod-shaped rib  141  from the first inclined surface  131  increases toward the first end part  122   a , and the protrusion height of the second rod-shaped rib  142  from the second inclined surface  132  increases toward the second end part  122   b . According to this configuration, since the protrusion heights of the first rod-shaped rib  141  and the second rod-shaped rib  142  in the vicinity of the top part  130  are suppressed, it is possible to suppress the thickness of the cover - 122  from becoming excessively large. On the other hand, since the first rod-shaped rib  141  and the second rod-shaped rib  142  can secure the required protrusion height at the end part of the cover  122 , it is easy to secure the rigidity with which the noise suppression effect can be obtained. 
     In the present embodiment, both the first rod-shaped rib  141  and the second rod-shaped rib  142  are configured to extend in the vehicle front-rear direction (X-axis direction), but any one or both of the first rod-shaped rib  141  and the second rod-shaped rib  142  may be configured to extend in a direction intersecting the vehicle front-rear direction (X-axis direction). 
     As in the present embodiment, when the direction from the top part  130  toward the first end part  122   a  is the vehicle front-rear direction, the direction in which the first rod-shaped rib  141  extends can be a direction intersecting the vehicle front-rear direction within a range of less than ±45°. The same applies to the second rod-shaped rib  142 . By setting the intersection angle to the above range, it is possible to suppress the flow of water along the first inclined surface  131  and the second inclined surface  132  from being obstructed by the first rod-shaped rib  141  and the second rod-shaped rib  142 . 
     In the present embodiment, the cover  122  is configured to have the first inclined surface  131  and the second inclined surface  132 , but the cover  122  may be configured to only have any one of the first inclined surface  131  and the second inclined surface  132 . For example, even in a case where the cover  122  has only the first inclined surface  131 , the water having fallen on the upper surface of the inverter device  110  flows down on the first inclined surface  131  located between the plurality of first rod-shaped ribs  141  from the top part  130  toward the first end part  122   a . This makes it possible to suppress water from accumulating on the upper surface of the inverter device  110 . 
     The cover  122  may be configured to have three or more inclined surfaces. Also in this case, by making the three or more inclined surfaces inclined surfaces descending from the top part  130  toward the peripheral edge part of the cover  122 , it is possible to achieve a configuration in which water is less likely to accumulate on the upper surface of the cover  122 . 
     The cover  122  has a plurality of the first coupling ribs  151  that couple two of the first rod-shaped ribs  141  arranged next to each other . In the case of the present embodiment, two or three of the first coupling ribs  151  are bridged between the two of the first rod-shaped ribs  141  arranged next to each other. 
     According to this configuration, the plurality of first coupling ribs  151  can reinforce the plurality of first rod-shaped ribs  141 . Membrane vibration of the first inclined surface  131  can be further suppressed by improving the strength of the rib supporting the first inclined surface  131 . Noise caused by membrane resonance of the first inclined surface  131  can be reduced. 
     In the cover  122 , as illustrated in  FIG.  3   , the individual first coupling ribs  151  have a protrusion height of a side surface  151   a  facing the top part  130  side from the first inclined surface  131  that is smaller than a protrusion height of a side surface  151   b  facing the first end part  122   a  side from the first inclined surface  131 . 
     According to this configuration, when water flows from the top part  130  side with respect to the first coupling rib  151 , since the side surface  151   a  on the top part  130  side is low, the water easily gets over the first coupling rib  151 . Therefore, it is possible to provide the inverter device  110  in which water is less likely to accumulate on the upper surface of the cover  122 . 
     An upper surface  151   c  of the first coupling rib  151  is preferably a flat surface expanding in the horizontal direction or a flat surface having an inclination of equal to or less than 10° with respect to the horizontal direction. According to this configuration, it becomes possible to easily secure the height of the first coupling rib  151  while causing water to easily flow on the first inclined surface  131 . It becomes easy to secure the rigidity of the first coupling rib  151 . 
     The upper surface  151   c  may be an inclined surface descending toward the first end part  122   a . According to this configuration, the water having flown onto the upper surface  151   c  easily flows to the first end part  122   a  side. 
     The cover  122  may have a coupling rib also on the second inclined surface  132  similar to that on the first inclined surface  131  side. That is, as illustrated in  FIGS.  3  and  4   , the cover  122  may be configured to have the plurality of second coupling ribs  152  that couple two of the second rod-shaped ribs  142  arranged next to each other, and the individual second coupling ribs  152  may have a configuration in which a protrusion height of a side surface facing the top part  130  side from the second inclined surface is smaller than a protrusion height of a side surface facing the second end part  122   b  side from the second inclined surface. According to this configuration, the strength of the ribs can be increased even on the second inclined surface  132 . Membrane resonance is less likely to occur on the second inclined surface  132 , and noise is reduced. 
     As illustrated in  FIGS.  3  and  4   , the cover  122  has a honeycomb-shaped lower surface rib  161  on the lower surface of the cover  122 . The lower surface rib  161  has a configuration in which regular hexagonal annular ribs are arranged without a gap on the lower surface of the cover  122 . The honeycomb-shaped lower surface rib  161  is excellent in flexural strength and compressive strength as compared with other polygonal ribs. Therefore, by providing the cover  122  with the honeycomb-shaped lower surface rib  161 , it is possible to increase the rigidity of the cover  122 , and it is possible to provide a thin, low-noise cover. 
     As illustrated in  FIGS.  3  and  5   , the cover  122  has a first back side inclined surface  171  following the first inclined surface  131  on the back side of the first inclined surface  131 . As illustrated in  FIG.  3   , the lower surface rib  161  located on the first back side inclined surface  171  has a larger protrusion height downward from the first back side inclined surface  171  toward the top part  130 . 
     On the upper surface of the cover  122 , the first rod-shaped rib  141  has a small protrusion height in the vicinity of the top part  130 . By making the protrusion height of the lower surface rib  161  relatively high in the vicinity of the top part  130 , it becomes easily to secure the rigidity of the entire top part  130 . Since the protrusion height of the first rod-shaped rib  141  can be reduced in the vicinity of the top part  130 , the upper surface of the inverter device  110  can be easily flattened, so that a space with components located around the motor unit  1  can be easily secured in the vehicle. 
     As illustrated in  FIGS.  3  to  5   , the cover  122  has through holes  124  and  125  penetrating the cover  122  in the up-down direction. The through hole  124  and the through hole  125  are, for example, access ports into which a tool for electrically connecting the inverter  110   a  and the stator  30  of the motor  2  is inserted. 
     As illustrated in  FIGS.  3  and  5   , the cover  122  has a trapezoidal lower surface rib  162  located in the vicinity of the through holes  124  and  125  in the lower surface of the cover  122 . The lower surface rib  162  of the present embodiment has a configuration in which a plurality of trapezoidal annular ribs are arranged without a gap on the lower surface of the cover  122 . The lower surface rib  162  is located in a region surrounded by the through hole  124  and the through hole  125  and the outer peripheral edge of the cover  122 . 
     In the present embodiment, the “trapezoidal rib” is not limited to a geometrically accurate trapezoidal annular rib. The “trapezoidal rib” of the present embodiment may be an annular rib including at least two linear ribs parallel to each other and at least one linear rib bridged between the two linear ribs. 
     As illustrated in  FIG.  5   , the lower surface rib  162  includes more linear ribs than that of the honeycomb-shaped lower surface rib  161 . According to the lower surface rib  162 , it is easy to obtain higher rigidity than the honeycomb-shaped lower surface rib  161 . In the cover  122 , the sites where the through holes  124  and  125  are provided is liable to decrease in rigidity, and therefore, by arranging the trapezoidal lower surface rib  162  in the vicinity of the through holes  124  and  125 , it becomes easy to secure the rigidity of the cover  122 . 
     The shape of the lower surface rib  162  can also be described as a shape in which two vertices of the honeycomb-shaped rib are connected by a linear rib passing through the inside of the hexagon. By having the linear rib connecting the vertices of the honeycomb, the area of the region surrounded by the rib is smaller and the installation density of the ribs becomes larger than those of a simple honeycomb-shaped rib. This increase the rigidity of the lower surface rib  162 , and increases the noise reduction effect by the lower surface rib  162 . 
     As illustrated in  FIG.  3   , the cover  122  has a second back side inclined surface  172  following the second inclined surface  132  on the back side of the second inclined surface  132 . The lower surface rib  162  located on the second back side inclined surface  172  has a larger protrusion height from the second back side inclined surface  172  toward the top part  130 . 
     Also on the second inclined surface  132 , since the protrusion height of the second rod-shaped rib  142  is relatively low in the vicinity of the top part  130 , the rigidity of the entire top part  130  can be easily secured by making the protrusion height of the lower surface rib  162  relatively high in the vicinity of the top part  130 . Since the protrusion height of the second rod-shaped rib  142  can be reduced in the vicinity of the top part  130 , the upper surface of the inverter device  110  can be easily flattened, so that a space with components located around the motor unit  1  can be easily secured in the vehicle. 
     The cover  122  has a refrigerant flow path  123  in a central part when the cover  122  is viewed from below. The cooling water pipe  95  illustrated in  FIG.  1    is connected to the refrigerant flow path  123 . The inverter  110   a  attached to the lower surface of the cover  122  is cooled by the cooling water flowing through the refrigerant flow path  123 . The cover  122  may be configured not to include the refrigerant flow path  123 . 
     In the above embodiment, the motor unit  1  including the motor  2 , the transmission mechanism  3 , and the inverter device  110  has been described, but the motor unit  1  may be configured to include only the motor  2  and the inverter device  110 . 
     That is, the embodiment of the present invention can also be configured as a motor including the rotor  20 , the stator  30 , the motor housing  60  that accommodates the rotor  20  and the stator  30 , and the inverter device  110  arranged in contact with the motor housing  60 . 
     In the motor, the motor housing  60  and the inverter case  120  may be a part of a single die casting member similarly to the previous embodiment. Alternatively, the motor housing  60  and the inverter case  120  formed of separate members from each other may be included. Even if the inverter case  120  and the motor housing  60  are separate components, when they are arranged in contact with each other, vibration of the motor is transmitted to the inverter case  120 . Since the inverter device  110  includes the cover  112  of the embodiment, vibration of the inverter case  120  can be suppressed, and a puddle on the upper surface is less likely to occur. 
     Features of the above-described preferred embodiments and the modifications thereof may be combined appropriately as long as no conflict arises. 
     While preferred embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.