Electric power unit

Abstract

To provide an electrically-driven power unit capable of improving the rigidity of a housing and keeping low a noise level caused by resonance of the housing.SOLUTION: The present invention relates to an electrically-driven power unit 1 in which at least an electric motor is stored in a housing 2. Polygonal rib regions S1 and S2 in which polygonal ribs 8 are formed are provided on at least two surfaces of outer peripheral surfaces of the housing, and the polygonal rib regions S1 and S2 are connected with each other by a circumferential direction rib 9. Here, a first axial direction rib 6 and a second axial direction rib 7 extending in parallel in an axial direction are formed on the outer peripheral surfaces of the housing 2, and the polygonal rib regions are provided in a portion held between the first axial direction rib 6 and the second axial direction rib 7. The circumferential direction rib 9 is formed over the entire circumferential direction of the polygonal rib regions. The polygonal ribs are honeycomb ribs.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an electric power unit that uses an electric motor as a drive source. [Background technology]

[0002] In recent years, there has been active development of electric vehicles (EVs) that use electric motors as their drive source, replacing vehicles that use engines that emit exhaust gases as their drive source.Electric vehicles are equipped with an electric power unit that includes, integrated into a housing, an electric motor (AC motor) as its drive source, an inverter that converts DC current from a DC power source such as a battery into AC current and supplies it to the electric motor, a reduction mechanism that slows down the rotation of the electric motor (increases the torque), and a differential mechanism that imparts a difference in rotation between the left and right output shafts from the reduction mechanism.

[0003] However, when the vibration of the electric power unit containing the electric motor, which is the vibration source, is large, it causes unpleasant vibration and noise to the occupants, so it is desirable to keep the vibration and noise of the electric power unit low.

[0004] Known methods for reducing the vibration of electric motors include a method in which the magnetic structure of the electric motor is used to change the air gap distance at the tip of each tooth of the stator core, thereby canceling out specific electromagnetic excitation force components generated in the stator core and reducing vibration (see Patent Document 1), and a method in which current control is used to cancel out electromagnetic forces generated in the stator core, thereby reducing vibrations of specific orders (see Patent Document 2).

[0005] There are also known methods for suppressing vibration and noise in a motor housing by increasing the rigidity of the motor housing that houses the electric motor. For example, Patent Document 3 proposes a configuration in which the number of reinforcing ribs on the flange of the motor housing is set to a number that is not a divisor or multiple of the number of slots in the stator, and is also set to a number that is not a divisor or multiple of the number of poles in the rotor.

[0006] Furthermore, Patent Document 4 proposes a configuration in which a rubber mount that supports a power plant including an engine on a vehicle frame is joined to the power plant via an engine-side mounting bracket, and the movement of the rubber mount is restrained by a restraint device consisting of an electromagnet joined to the engine-side mounting bracket and the vehicle-frame-side mounting bracket via a support, thereby increasing the spring rigidity of the rubber mount and reducing vibrations of the power plant that occur when the engine is started and stopped. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-166710 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-057935 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-096845 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-023136 Summary of the Invention [Problem to be solved by the invention]

[0008] However, electric power units have a problem in that the housing resonates due to the rotational vibration of the electric motor and the vibration caused by meshing gears, becoming a source of noise and increasing the noise level.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric power unit that can increase the rigidity of the housing and reduce the noise level caused by resonance of the housing. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention is characterized in that, in an electric power unit that accommodates at least an electric motor within a housing, polygonal rib areas in which polygonal ribs are formed are provided on at least two outer surfaces of the housing, and the polygonal rib areas are connected to each other by circumferential ribs. [Effects of the Invention]

[0011] According to the present invention, the rigidity of the housing is increased by the polygonal ribs, so that membrane vibration caused by resonance of the housing is kept low, and the noise level generated by this membrane vibration is also kept low. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a vertical cross-sectional view seen from the rear of a vehicle, schematically showing the overall configuration of an electric power unit according to the present invention. [Figure 2] 1 is a perspective view of an electric power unit according to the present invention, seen from diagonally rear right. [Figure 3] FIG. 2 is a right side view of the electric power unit according to the present invention. [Figure 4] 1 is a perspective view of an electric power unit according to the present invention, viewed diagonally forward to the right from the bottom side. FIG. [Figure 5] 1 is a front view of an electric power unit according to the present invention, as viewed from the front. [Figure 6] FIG. 2 is a bottom view of the electric power unit according to the present invention. [Figure 7] FIG. 10 is a diagram showing the relationship between the motor rotation speed and noise level of the electric power unit according to the present invention in comparison with that of a conventional electric power unit. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0014] [Basic structure and function of electric power units] 1 is a longitudinal cross-sectional view seen from the rear of a vehicle, showing a schematic diagram of the overall configuration of an electric power unit according to the present invention, and the illustrated electric power unit 1 is mounted on an electric vehicle (EV). Note that in FIG. 1, the arrow directions indicate the "up and down" and "left and right" directions (vehicle width directions), respectively, as shown.

[0015] In the electric power unit 1 according to this embodiment, an electric motor 10 serving as a drive source is housed in a motor housing section (motor chamber) Sm formed in the right half of an aluminum die-cast housing 2, and a reduction gear mechanism 20 and a differential mechanism 30 are housed in a gear housing section (gear chamber) Sg formed in the left half of the housing 2. An inverter (not shown) is housed in an inverter housing section Si formed in the upper part of the housing 2. The inverter converts direct current (DC) from a battery (not shown) serving as a DC power source into alternating current (AC) and supplies the AC current to the electric motor 10, and is configured to include control elements such as IGBTs.

[0016] Here, the electric motor 10 is a three-phase AC motor and includes a rotor 12 that rotates together with a hollow shaft (motor shaft) 11 that passes through the center of the motor, and a cylindrical stator 13 that is fixed to the periphery of the rotor 12. Here, the shaft 11 is arranged horizontally along the left-right direction (vehicle width direction) in FIG. 1, and the rotor 12 that is fixed to the outer periphery of the shaft 11 includes a rotor core 12a and a permanent magnet (not shown) embedded in the rotor core 12a. The stator 13 also includes a stator core 13a and a coil 13b, and the coil 13b is electrically connected to an inverter.

[0017] Within the gear housing Sg, a countershaft 21 and left and right output shafts 22L, 22R are arranged parallel to the shaft 11, and the reduction gear mechanism 20 is made up of a first gear 23 attached to the outer periphery of the left end of the shaft 11 facing the gear housing Sg, a second gear 24 and a third gear 25 of different diameters attached to the countershaft 21, and a large-diameter ring gear 26 attached to a differential case 31 of the differential mechanism 30. Here, the first gear 23 and the second gear 24 mesh with each other, and the third gear 25 and the ring gear 26 mesh with each other.

[0018] The differential mechanism 30 functions to absorb the difference in rotation between the left and right drive wheels when the vehicle is cornering, etc., and transmits power to the left and right output shafts 22L, 22R, respectively. Since its configuration is well known, detailed description will be omitted here. However, a pair of pinion gears and side gears meshing with the pinion gears are housed within the differential case 31. An oil pan P is provided at the bottom of the gear housing portion Sg of the housing 2, and a predetermined amount of oil is stored in this oil pan P. A portion (outer periphery) of the ring gear 26 is immersed in the oil stored in this oil pan P.

[0019] In the electric power unit 1 according to this embodiment, an oil pump 40 and an oil cooler 50, which are auxiliary machines, are attached to the housing 2. The oil pump 40 is rotated by a pump motor 41, which is a drive source. A cooling water pipe 51 extending from a radiator (not shown) and passing through the inverter housing portion Si is connected to the oil cooler 50, and the oil is cooled in the oil cooler 50 by heat exchange with the cooling water. The cooling water used to cool the oil in the oil cooler 50 is returned from the cooling water pipe 51 to the radiator (not shown). In this way, the cooling water cools the inverter (not shown) and the oil housed in the inverter housing portion Si by continuously circulating through the closed circuit.

[0020] In the electric power unit 1 configured as described above, when a DC current is output from a battery (not shown), this DC current is converted into an AC current by an inverter (not shown), and when this AC current is supplied to the electric motor 10, the electric motor 10 is rotationally driven by electromagnetic induction. That is, the rotor 12 and shaft 11 of the electric motor 10 are rotationally driven at a predetermined speed, and this rotation is reduced at a predetermined reduction ratio by the reduction mechanism 20 and transmitted to the differential mechanism 30. The rotation transmitted to the differential mechanism 30 is then distributed to the left and right by the differential mechanism 30 and transmitted to the left and right output shafts 22L, 22R, respectively, so that both output shafts 22L, 22R rotate at a predetermined speed.

[0021] Although not shown, the left and right output shafts 22L, 22R are connected to left and right axles, respectively, and left and right drive wheels are attached to the ends of the left and right axles. Therefore, when the left and right output shafts 22L, 22R rotate as described above, the drive wheels (not shown) attached to both axles are rotated and driven, respectively, and the vehicle travels at a predetermined speed.

[0022] When the electric power unit 1 is driven as described above, the oil pump 40 is driven by the pump motor 41, and the cooling water is circulated in a closed circuit by a cooling water pump (not shown).

[0023] As described above, a portion (outer periphery) of the ring gear 26 is immersed in oil stored in the oil pan P provided at the bottom of the gear accommodating portion Sg of the housing 2, and therefore, the rotation of the ring gear 26 scoops up the oil in the oil pan P. Some of the oil scooped up passes through the shaft 11 and is supplied to each part of the electric motor 10 to lubricate and cool each part, as shown by the arrows in FIG. 1. The oil that has been used to lubricate and cool each part of the electric motor 10 then falls into the oil pan P and is collected, as shown by the arrows in FIG. 1.

[0024] Another portion of the oil scooped up by the ring gear 26 is used to lubricate and cool the reduction gear mechanism 20 and the differential mechanism 30, and then drops into the oil pan P to be collected. Then, as shown by the arrow in FIG. 1, some of the oil in the oil pan P is sent to the oil cooler 50 by the oil pump 40, where it is cooled by heat exchange with the cooling water flowing through the cooling water pipe 51. Then, as shown by the arrow in FIG. 1, the cooled oil is sent to a tray T disposed above the electric motor 10, and oil that overflows from this tray T drops onto the electric motor 10 to lubricate and cool various parts of the electric motor 10. The oil that has thus been used to lubricate and cool various parts of the electric motor 10 is returned to the oil pan P at the bottom of the gear housing Sg and collected.

[0025] [Specific configuration of the electric power unit] Next, a specific configuration of the electric power unit 1 according to the present invention will be described below with reference to FIGS.

[0026] Fig. 2 is a perspective view of the electric power unit according to the present invention as seen from the right rear, Fig. 3 is a right side view of the electric power unit, Fig. 4 is a perspective view of the electric power unit as seen from the bottom side as seen diagonally forward to the right, Fig. 5 is a front view of the electric power unit as seen from the front, and Fig. 6 is a bottom view of the electric power unit. Note that in Figs. 2 to 6, the directions of the arrows indicate the "front-rear", "left-right" and "up-down" directions, respectively, as shown.

[0027] As shown in Fig. 1, an electric motor 10 is accommodated in the right half of a housing 2 of the electric power unit 1, and a reduction gear mechanism 20 and a differential mechanism 30 are accommodated in the left half. Openings (not shown) are formed on the left and right sides of the housing 2. Flange portions 2a, 2b are formed around the peripheries of the left and right openings of the housing 2, as shown in Fig. 2. A motor cover 3 is detachably attached to the right flange portion 2a with a plurality of bolts (not shown), and a gear cover 4 is detachably attached to the left flange portion 2b with a plurality of bolts (not shown). In other words, the right opening of the housing 2 is closed by the motor cover 3, and the left opening is closed by the gear cover 4.

[0028] 2, an oil cooler mounting portion 2c in the shape of a substantially rectangular block is integrally formed on the rear surface of the housing 2 in the center in the left-right direction (vehicle width direction), and an oil cooler 50 is attached to this oil cooler mounting portion 2c. A pump mounting portion 2d is integrally formed diagonally below and to the right of the oil cooler mounting portion 2c on the rear surface of the housing 2, and an oil pump 40 is attached to this pump mounting portion 2d. As shown in FIG. 2, a circular hole 2e is formed in the oil cooler mounting portion 2c along the left-right direction, and the left and right output shafts 22L, 22R (see FIG. 1) pass through it.

[0029] 2 and 3, a flange portion 2f is integrally formed on the upper rear surface of the housing 2, and the space surrounded by this flange portion 2f constitutes the inverter accommodating portion Si shown in Fig. 1. An inverter (not shown) is accommodated in this inverter accommodating portion Si.

[0030] The inverter accommodating section Si (see FIG. 1) has an open top surface, and this top opening is closed by an inverter cover 5 that is detachably attached to the flange section 2f with a plurality of bolts (not shown). The inverter cover 5 is also integrally formed by aluminum die casting.

[0031] 4 to 6, in the housing 2 of the electric power unit 1 according to this embodiment, first axial ribs 6 and second axial ribs 7 are provided on the front and bottom surfaces, respectively, extending parallel to the axial direction (left-right direction, i.e., vehicle width direction), and both axial ends of each of these first axial ribs 6 and second axial ribs 7 are connected to left and right flange portions 2a, 2b formed integrally with the housing 2. In this way, by connecting both axial ends of each of the first axial ribs 6 and second axial ribs 7 to the left and right flange portions 2a, 2b of the housing 2, which have high rigidity, the rigidity of these first axial ribs 6 and second axial ribs 7 is increased, and as a result, the rigidity of the housing 2 itself is increased.

[0032] The rectangular portions surrounded by the left and right flange portions 2a, 2b on the front and bottom surfaces of the housing 2 and the first axial rib 6 and second axial rib 7 are designated as polygonal rib regions S1, S2, and a plurality of polygonal ribs (hexagonal ribs in this embodiment, hereinafter referred to as "honeycomb ribs") 8 are formed in an orderly fashion in each of these polygonal rib regions S1, S2.

[0033] The polygonal rib regions S1, S2 formed on the front and bottom surfaces of the housing 2 are connected to each other by a plurality of (three in this embodiment) circumferential ribs 9 extending in the axis-perpendicular direction (circumferential direction). More specifically, in this embodiment, the three circumferential ribs 9 are formed parallel to each other at appropriate intervals along the left-right direction (vehicle width direction) and integrally over the entire circumferential direction of the two polygonal rib regions S1, S2, and each circumferential rib 9 passes through the center of the honeycomb rib 8. As shown in FIGS. 4 and 6, on the front surface of the housing 2, cylindrical bosses 2g, 2h are formed integrally with the longitudinal intermediate portions of the three circumferential ribs 9, respectively.

[0034] As described above, in the present embodiment, the polygonal rib regions S1, S2 defined by the first axial rib 6 and the second axial rib 7 on the front and bottom surfaces of the housing 2 and the left and right flange portions 2a, 2b each have a plurality of honeycomb ribs 8. This increases the rigidity of the front and bottom surfaces of the housing 2, thereby improving the rigidity of the entire housing 2. The two first axial ribs 6 and the two second axial ribs 7 defining each polygonal rib region S1, S2 are connected to the left and right flange portions 2a, 2b, which are relatively thick and rigid. The polygonal rib regions S1, S2 are connected to each other by three circumferential ribs 9, and each polygonal rib region S1, S2 has a plurality of honeycomb ribs 8. This increases the rigidity of the front and bottom surfaces of the housing 2 on which the polygonal rib regions S1, S2 are formed, thereby effectively improving the rigidity of the entire housing 2. In particular, in this embodiment, highly rigid bosses 2g, 2h are formed integrally with the three circumferential ribs 9 arranged in the polygonal rib region S1 on the front surface of the housing 2 at the longitudinal middle portions thereof, thereby increasing the rigidity of the circumferential ribs 9. Furthermore, in each of the polygonal rib regions S1, S2, the three circumferential ribs 9 are passed through the center of the honeycomb rib 8, thereby maintaining a good balance in the rigidity of the housing 2 in the left-right direction (vehicle width direction).

[0035] As described above, the rigidity of the housing 2 is increased, and as a result, even if the housing 2 resonates due to vibrations caused by the driving of the electric motor 10, which is the vibration source, or vibrations caused by the meshing of the gears 23, 24, 25, and 26 of the reduction mechanism 20, the noise level associated with this resonance of the housing 2 is kept low.

[0036] FIG. 7 shows the relationship between the motor rotation speed and noise level of the electric power unit 1 according to the present invention in comparison with that of a conventional electric power unit. As shown by the solid line A in FIG. 7, the noise level of the electric power unit 1 according to the present invention was kept lower (specifically, about 4 dB lower) than the conventional noise level shown by the dashed line B in FIG. 7 over the entire range of motor rotation speed.

[0037] The natural frequency f that generates resonance is given by the following equation, where π is the constant of the circumference of a circle, m is the mass, and k is the spring constant (rigidity): f=1 / 2π·(k / m) 1 / 2 Therefore, when the stiffness (spring constant k) is increased, the first, second, third, etc. resonance points (points where noise level peaks appear) shift to the higher rotation speed side, as shown in Figure 7.

[0038] Although the above describes an embodiment in which the present invention is applied to an electric power unit mounted on an electric vehicle (EV), the present invention can also be applied to electric power units mounted on hybrid vehicles (HEV) and plug-in hybrid vehicles (PHV).

[0039] Furthermore, in the above embodiment, the polygonal rib regions S1, S2 are provided on two surfaces, the front and bottom surfaces, of the housing 2, but the polygonal rib regions can be provided on any surface of the housing 2. And, in the above embodiment, the polygonal ribs 8 formed in the polygonal rib regions S1, S2 are regular hexagonal honeycomb ribs, but the shape of the polygonal ribs is arbitrary, and any polygonal shape including triangles, rectangles, pentagons, etc. can be used.

[0040] Furthermore, in the above embodiment, the number of circumferential ribs 9 is three, but the number of circumferential ribs 9 is arbitrary and is not limited to three.

[0041] Furthermore, the present invention is not limited to the application of the above-described embodiments, and it goes without saying that various modifications are possible within the scope of the claims and the technical ideas described in the specification and drawings. [Explanation of symbols]

[0042] 1 Electric power unit 2. Housing 2a, 2b Housing flange 2g, 2h housing boss 6 First axial rib 7 Second axial rib 8 Honeycomb rib (polygonal rib) 9 Circumferential Rib 10 Electric motor 20 Reduction mechanism 30 Differential mechanism S1,S2 Polygonal rib area

Claims

1. An electric power unit that accommodates at least an electric motor in a housing, An electric power unit characterized in that a polygonal rib region in which a polygonal rib is formed is provided on each of two outer peripheral surfaces of the housing, the two polygonal rib regions are spaced a predetermined distance apart in the circumferential direction of the housing, the two polygonal rib regions are connected to each other by a circumferential rib, and the circumferential rib is not the polygonal rib.

2. 2. The electric power unit according to claim 1, wherein a first axial rib and a second axial rib extending parallel to the axial direction are further formed on each of two outer peripheral surfaces of the housing, and each of the polygonal rib regions is provided in a portion sandwiched between the first axial rib and the second axial rib.

3. 3. The electric power unit according to claim 1, wherein the circumferential rib extends into each of the polygonal rib regions and is formed over the entire circumferential direction of the polygonal rib region.

4. An electric power unit as described in Claim 3, characterized in that a boss is integrally formed at the longitudinal middle portion of the circumferential rib inside each of the polygonal rib regions.

5. 3. The electric power unit according to claim 2, wherein both axial ends of the first and second axial ribs are connected to flange portions formed on both axial ends of the housing.

6. 4. The electric power unit according to claim 3, wherein the circumferential rib passes through the center of the polygonal rib.

7. 7. The electric power unit according to claim 1, wherein the polygonal rib is a honeycomb rib.

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