In-wheel motor

Abstract

The purpose of the present invention is to improve a heat radiation performance by using the flow of wind due to traveling wind in an in-wheel motor.　In order to achieve the above purpose, an in-wheel motor according to the present invention is housed in a wheel, the in-wheel motor being characterized in that the wheel comprises: a tire mounting portion on which a tire is to be mounted; and an annular fin that is formed on an outer surface of the in-wheel motor in the circumferential direction and forms a flow path through which air flows between the annular fin and the tire mounting portion.

Description

In-wheel motor

[0001] The present invention relates to an in-wheel motor.

[0002] Japanese Patent Laid-Open Publication No. 2014-177167 (Patent Document 1) describes an outer rotor in-wheel motor (Abstract and paragraph 0008). This in-wheel motor includes a circular rotor core, a magnet fixed to the inner peripheral surface of the rotor core, and a case covering the outer periphery of the rotor core. The case has radially extending fins on the outer surface of its bottom. When the in-wheel motor is placed inside the wheel, the bottom of the case faces the front of the wheel, and a flow path connecting a front space and a rear space of the in-wheel motor is formed between the inner peripheral surface of the wheel and the outer peripheral surface of the case.

[0003] The fins on the case not only function as a heat sink, but also as a centrifugal fan. Furthermore, the case covers the outer periphery of the rotor core and has a flow path connecting the front and rear spaces of the in-wheel motor. This centrifugal fan action creates an airflow that draws air from outside the wheel past the outer periphery of the case and the wheel. This airflow constantly introduces fresh air between the fins, enhancing the heat dissipation effect of the fins (paragraph 0009).

[0004] JP 2014-177167 A

[0005] However, the cooling structure of Patent Document 1 cools the wheels by the flow caused by the centrifugal fan effect when the wheels rotate, and does not take into consideration the influence of wind caused by running.

[0006] An object of the present invention is to improve the heat dissipation performance of an in-wheel motor by utilizing the flow of wind caused by running wind.

[0007] In order to achieve the above object, the in-wheel motor of the present invention is an in-wheel motor housed within a wheel, the wheel having a tire mounting portion on which a tire is mounted, and an annular fin formed on the circumferential outer surface of the in-wheel motor to form a flow path for air to flow between the wheel and the tire mounting portion.

[0008] According to the present invention, it is possible to improve the heat dissipation performance of an in-wheel motor by utilizing the flow of wind caused by running wind.

[0009] FIG. 1 is a cross-sectional image diagram of an in-wheel motor according to an embodiment of the present invention, as seen from the vehicle's traveling direction. FIG. 2 is a perspective cross-sectional view of an in-wheel motor according to an embodiment of the present invention. FIG. 3 is an enlarged cross-sectional view of an annular fin according to an embodiment of the present invention. FIG. 4 is an image diagram explaining wind received by a tire whose rotation axis moves in the traveling direction. FIG. 5 is a perspective view showing the structure of annular fins and radial fins according to an embodiment of the present invention, and the flow of wind during traveling. FIG. 6 is an explanatory diagram explaining the flow of wind in the traveling direction in an annular flow path. FIG. 7 is an example of analysis of wind flow around a housing. FIG. 8 is a modified example of radial fins. FIG. 9 is a modified example of radial fins. FIG. 10 is a modified example of radial fins. FIG. 11 is an image diagram showing installation on a motorcycle. FIG. 12 is an enlarged cross-sectional view of an annular fin according to an embodiment of the present invention.

[0010] In the following description, the configuration according to the present invention and the configuration according to a comparative example will be described, but similar configurations will be assigned the same reference numerals to avoid duplication of similar explanations. Furthermore, if there are differences between the configurations assigned the same reference numerals, the differences will be explained.

[0011] An in-wheel motor 1 according to an embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional image diagram of the in-wheel motor 1 according to an embodiment of the present invention as seen from the direction of vehicle travel. Figure 2 is a perspective cross-sectional view of the in-wheel motor 1 according to an embodiment of the present invention.

[0012] The in-wheel motor 1 includes a stator 2, a rotor 3, and a rotor housing 4 as components. Although a power converter (not shown) may be disposed inside the rotor housing 4, in this embodiment, the power converter is mounted on the vehicle body. The stator 2 includes a stator core 21 and a coil 22, and the rotor 3 includes a rotor core 31 and a magnet 32. In this embodiment, the rotor core 31 is disposed on the outer periphery of the stator core 21 so that its inner periphery faces the inner periphery of the stator core 21. The stator core 21 is supported from its inner diameter side by a stator housing (not shown). In other words, the inner periphery of the stator core 21 is covered by the stator housing. A coil 22 is wound around the stator core 21. The coil 22 may be wound in any manner, including concentrated winding, distributed winding, or alpha winding. The wires may be round or rectangular.

[0013] The stator 2 and rotor 3 are configured so that the outer peripheral surface of the rotor core 31 faces the inner peripheral surface of the stator core 21, that is, an inner rotor is outside the scope of the present invention.

[0014] The power conversion device performs switching operations to convert DC power supplied from a battery (not shown) into three-phase AC power. This three-phase AC power is supplied to the stator windings of the stator 2, which generates a rotating magnetic field in the stator 2. The rotating magnetic field generated in the stator 2 drives the rotor 3 to rotate.

[0015] The in-wheel motor 1 is housed inside the wheel 5 and is connected to the wheel 5 via a rotor housing 4. The wheel 5 has a tire mounting portion 51 and a central portion 52. In this embodiment, the outer peripheral surface of the rotor core 31 is fixed to the inner peripheral surface of the central portion 52 by shrink fitting, adhesive, leaf springs, bolts, or the like.

[0016] The wheel 5 is manufactured by press molding or drawing of steel-based materials, or by casting, die-casting, forging, or machining of light metals such as aluminum. It may be constructed as a single unit, or may be divided into two or three parts along the axial direction and assembled after molding. Unlike conventional wheels, there are no spokes to support the vehicle weight and transmit rotation; the rotor housing 4 also serves as the spokes.

[0017] A tire 6 is mounted on the wheel 5. The tire 6 is selected from commercially available conventional tires to match the rim diameter and rim width of the wheel.

[0018] The rotor housing 4 is manufactured using a light metal such as aluminum by casting, die-casting, forging, or machining. While it can also be manufactured using press molding or drawing of steel-based materials, casting or die-casting of light metal is preferable due to the difficulty of constructing the cooling fins described below. Because it serves as the boundary between the interior of the in-wheel motor 1 and the atmosphere and provides dustproof and waterproof functions, a one-piece construction is desirable. In this embodiment, heat is expected to be dissipated from the outer surface of the rotor housing 4 into the atmosphere, so the material for the rotor housing 4 must have high thermal conductivity. While highly thermally conductive resins are also candidates, metal is preferable from the perspective of thermal conductivity. For example, the thermal conductivity of highly thermally conductive resins is approximately 5 W / (m·K) at most, while the thermal conductivity of aluminum is approximately 240 W / (m·K).

[0019] The rotor housing 4 seals the space between the wheel 5 and the axle (not shown) and is made up of a cylindrical portion 41 and a side plate portion 42, with annular fins 43 formed on the cylindrical portion 41 and multiple radial fins 44 formed on the side plate portion 42. Heat is transferred from heat-generating parts of the motor, such as the core and coil, to the cylindrical portion 41 or the side plate portion 42 and is ultimately dissipated into the atmosphere via the fins. From the perspective of heat conduction, therefore, it is desirable that the annular fins 43 and the radial fins 44 be molded integrally with the cylindrical portion 41 and the side plate portion 42.

[0020] The annular area surrounded by three surfaces of the annular fin 43, the tire mounting portion 51 of the wheel 5, and the cylindrical portion 41 is the annular flow path 431. In a structure in which the rotating shaft is stationary and the vehicle is rotating in place, no air flows into the annular flow path 431, and the cooling effect is weak. However, in the case of an object that moves in the direction of vehicle travel while rotating, such as a tire, the airflow from the vehicle flows into the flow path, increasing the cooling effect.

[0021] The radial area surrounded by two adjacent radial fins 44 and three surfaces of the side plate portion 42 is the radial flow path 441. A radial flow 451 is generated by the centrifugal fan. When the rotor housing 4 rotates, centrifugal force pushes the air in the radial flow paths 441 outward, and new air flows into the radial flow paths 441 from the inner periphery. This air flow is called the centrifugal fan effect, and heat is transferred from the radial fins 44 to the air in the radial flow paths 441. In a structure in which the rotating shaft is stationary and the air rotates in place, the air velocity and heat dissipation amount are the same in all radial flow paths 441. However, in the case of an object such as a tire that rotates while moving in the direction of vehicle travel, the flow in the radial flow paths and the airflow due to travel are opposite directions, resulting in a slower air velocity in front of the tire. Details will be described later using Figure 4.

[0022] Although not shown in Figures 1 and 2, the rotor 3 is provided with a rotating shaft. In the following description, the direction along the axis of the rotating shaft will be referred to as the "axial direction." Furthermore, the terms "circumferential direction" and "radial direction" refer to the "circumferential direction" and "radial direction" of the in-wheel motor 1 (stator core, rotor core) unless otherwise specified.

[0023] 3 and 13 are enlarged cross-sectional views of an annular fin 43 according to one embodiment of the present invention. The annular fin 43 is formed on the circumferential outer surface of the in-wheel motor 1, and defines an annular flow path 431, which is a flow path for air to flow between the annular fin 43 and the tire mounting portion 51. The radial fins 44 are formed radially on the axial outer surface of the in-wheel motor 1. In this embodiment, the radial fins 44 extend radially and are connected to the annular fin 43. That is, the radially outermost portion of the radial fin 44 is larger than the inner diameter of the annular fin 43 and smaller than the outer diameter thereof, and is configured to connect the radial fins 44 and the annular fin 43.

[0024] In this way, the radial fins 44 are connected to the annular fins 43, making them longer in the radial direction. This increases centrifugal force, improving the flow rate within the radial flow paths 441 and, consequently, improving the heat transfer coefficient from the radial fins 44 to the atmosphere. Furthermore, by connecting the annular fins 43, which improve the radial rigidity of the cylindrical portion 41, with the radial fins 44, which improve the axial rigidity of the side plate portions, when considered as a beam model, the support at the end of the side plate portions 42 changes from pin support to fixed support, improving rigidity. This leads to an improvement in the heat transfer coefficient of the radial fins 44 and an improvement in the rigidity around the connection between the cylindrical portion 41 and the side plate portions 42. This improves cooling efficiency, enables the use of different housing materials, and makes it possible to provide a lightweight, highly rigid rotor housing.

[0025] 3 , the annular fins 43 are arranged axially inward of the outermost periphery of the side plate portion 42 of the housing of the in-wheel motor 1. This, as above, lengthens the radial flow paths 441, which leads to an improvement in the heat transfer coefficient of the radial fins 44 and an improvement in the rigidity around the joint between the cylindrical portion 41 and the side plate portion 42.

[0026] 13, a sloped surface 42a is formed between the side plate 42 and the cylindrical portion 41. When air flows through the radial flow paths 441, the pressure is lower radially outside the sloped surface 42a, so the air flows along the sloped surface 42a. By making this portion sloped rather than at a right angle, the air flows along the sloped surface, and the heat transfer coefficient of the sloped surface also increases. If it were at a right angle, the air would not flow along the cylindrical portion 41 (the flow would not turn at a right angle), and the air would separate near the cylindrical portion 41, remaining at low pressure, and the improvement in the heat transfer coefficient of the cylindrical portion 41 would be minimal.

[0027] These inclined surfaces improve the heat transfer coefficient of the radial fins 44, leading to improved heat dissipation performance. The angle between the inclined surface 42a and the side plate 42 is preferably 45 degrees or less. A smaller angle reduces flow separation in the radial flow paths 441 (flow moving away from the wall, resulting in low pressure near the wall), further improving the heat transfer coefficient of the inclined surface 42a.

[0028] Figure 4 is an illustration of the wind a tire receives. In the case of something like a centrifugal fan, where the rotation axis does not move and the fan rotates in place, the flow rate and flow velocity in all radial flow paths are uniform. On the other hand, in the case of something like a tire that rotates while moving in the direction of vehicle travel, it receives a traveling wind (headwind) with a wind speed equal to the speed in the direction of travel, ignoring natural winds. As the tire rotates, the relative speed between the tire's outer periphery and the surrounding air becomes a circumferential speed T. Above the tire, the circumferential speed is in the same direction as the direction of travel, so the relative speed between the tire and the surrounding air is 2T, twice the circumferential speed T (= travel speed). Below the tire, the circumferential speed is in the opposite direction to the direction of travel, so the relative speed between the tire and the surrounding air is zero.

[0029] 5 is an image of the airflow near the in-wheel motor 1. As mentioned above, the airflow velocity from running is high above the rotor housing 4, which has a large effect on heat transfer, so by providing a circumferential flow path in this area, i.e., annular flow path 431, the flow velocity within the flow path can be increased and heat dissipation performance can be improved. On the other hand, from the front to the top, the airflow in the radial flow paths 441 and the running airflow oppose each other, so the cooling effect of the radial flow paths 441 decreases.

[0030] Behind the rotor housing 4, the air flow in the radial flow passages 441 and the running wind are in the same direction, so the influence of the radial flow due to the centrifugal fan effect is greater. Below the rotor housing 4, the relative speed in the direction of travel is low, so cooling by the running wind cannot be expected, but cooling by the radial flow is possible.

[0031] In this way, the area above the rotor housing 4, where the flow rate becomes relatively faster due to the movement of the tire, is cooled by the circumferential flow of the annular flow path 431, while the area behind the wheel, where the circumferential flow is weaker, is cooled by the radial flow of the radial flow path 441. As a result, the heat transfer coefficient is improved by the fins that follow the air flow, and the cooling effect is enhanced.

[0032] Figure 6 is a cross-sectional view taken along the arrow AA in Figure 5. Generally, the axial width of the tire 6 is greater than the axial width of the tire mounting portion 51. Therefore, when viewed from the front in the direction of travel, the annular flow path 431 is hidden by the tire 6 and cannot be seen. However, just like the wings of an airplane, the traveling wind flows along the tire 6 and wheel 5, as indicated by the arrows in the figure. This is because, if the traveling wind expanded by the axial width of the tire 6 flows rearward, the pressure becomes low near the annular fin 43 of the wheel 5, and this pressure difference causes the traveling wind to bend and flow along the contour. Looking at the cross-section of the tire 6, it is found to be streamlined, and the air flows into the annular flow path 431 without separation or other problems.

[0033] Figure 7 is an example of an analysis of wind flow at a speed of 30 km / h. The flow velocity streamlines are shown. From the front to the top, it can be seen that the flow in the annular channel is large, and the wind flows from the front into the annular channel 431 and continues upward. At the rear, it can be seen that there is almost no flow in the annular channel 431, and the flow velocity in the radial channels 441 is large. In this analysis example, only the tire and wheel are modeled, but the flow patterns in the annular channel 431 and the radial channels 441 do not change significantly even when factors such as fenders and suspension arms are taken into account.

[0034] 8 to 11 show modified examples of the radial fins 44. Fig. 8 shows an embodiment in which fins of the same length are arranged radially around the rotation axis.

[0035] 9 shows a modified example in which fins of different lengths are arranged alternately. This configuration allows the length of the fins 44a to be increased, leading to an increase in surface area and allowing them to function as reinforcing ribs on the inner diameter side, where structural strength is required. If all radial fins were made longer, the spacing between fins on the inner diameter side would be narrow, making it difficult to increase the number of fins. However, by combining short fins 44b, it is possible to increase the number of radial fins on the outer diameter side, which increases the centrifugal fan effect.

[0036] 10 shows a modified example in which the fins are arranged at an angle relative to the radial direction. By arranging the fins at an angle, the length of the fins can be increased, which leads to an increase in the surface area and also makes it difficult for the radial flow and the running wind to oppose each other in the region from the front to the top, which increases the flow speed of the radial flow paths 441 and improves heat dissipation performance.

[0037] 11 shows a modified example in which the outer diameter side of the radial fins is arc-shaped. This makes the air flow smoother near the outlet of the radial flow paths 441, leading to an improvement in flow velocity and a reduction in windage loss due to rotation.

[0038] 8 to 11 are examples of the embodiment and are not intended to limit the structure. Also, it is possible to configure the structure by combining each of them.

[0039] FIG. 12 shows an image of the in-wheel motor mounted on a motorcycle. As shown in the figure, the in-wheel motor 1 may be mounted on both the front and rear wheels, or only the front or rear wheel. The in-wheel motor 1 can be applied to vehicles other than motorcycles, as long as the rotor housing 4 is exposed on the outermost surface. For example, it can be applied to compact mobility vehicles. In the case of four-wheel in-wheel motors 1, it is common to cover the outside of the in-wheel motor 1 with a conventional wheel for maintenance and compatibility reasons, so it cannot be applied to structures that are not directly exposed to the wind from traveling. As described above, cooling performance can be improved by cooling the area above the wheel, where the flow speed becomes relatively faster due to the movement of the tire, with the circumferential flow of the annular flow path.

[0040] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the configurations. Furthermore, it is possible to add, delete, or replace part of the configuration of the embodiments with other configurations.

[0041] 1... In-wheel motor, 2... Stator, 3... Rotor, 4... Rotor housing, 6... Tire, 41... Cylindrical portion, 42... Side plate portion, 43... Annular fin, 431... Annular flow path, 44... Radial fin, 441... Radial flow path, 5... Wheel, 51... Tire mounting portion, 52... Central portion,

Claims

1. An in-wheel motor housed within a wheel, wherein the wheel comprises: a tire mounting portion on which a tire is mounted; and annular fins formed on the circumferential outer surface of the in-wheel motor and forming a flow path for air to flow between the tire mounting portion and the wheel.

2. An in-wheel motor as claimed in claim 1, further comprising radial fins formed radially on an outer surface of the in-wheel motor in the axial direction.

3. An in-wheel motor according to claim 2, characterized in that the radial fins and the annular fin are connected to each other.

4. An in-wheel motor as claimed in claim 3, characterized in that the annular fin is arranged axially inwardly of the outermost periphery of a side plate portion of a housing of the in-wheel motor.

5. An in-wheel motor as claimed in claim 4, comprising a cylindrical portion on which the annular fin is arranged, and a side plate portion on which the radial fins are arranged, and a slope portion is formed between the cylindrical portion and the side plate portion.

6. An in-wheel motor according to claim 5, wherein the inclined surface portion is configured to intersect with the side plate portion at an angle of 45 degrees or less.

7. An in-wheel motor according to any one of claims 3 to 6, wherein the outer diameter of the annular fin is larger than the outer diameter of the radial fins.

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