Motor unit of electric bicycle and electric bicycle

Abstract

The present invention addresses the problem of providing a motor unit and an electric bicycle which achieve weight reduction and which make it easy to dissipate heat generated by a motor. A motor unit (2) comprises a case (3), a motor (4), a rotation shaft unit (5), and a transmission mechanism (6). The motor (4) is accommodated in the case (3). The rotation shaft unit (5) penetrates the case (3), is rotatably disposed, and has a pedal connected thereto via a crank arm. The transmission mechanism (6) transmits, to the rotation shaft unit (5), force from the motor (4). The case (3) has a first case part (3a) which has disposed therein a rotor (41) and a stator (42), and a second case part (3b). The first case part (3a) is formed from a material which has higher thermal conductivity than that of the second case part (3b). The second case part (3b) is formed from a material which has a lower specific gravity than that of the first case part (3a).

Description

Motor unit for electric bicycle and electric bicycle

[0001] The present disclosure relates to a motor unit for an electric bicycle and an electric bicycle.

[0002] Patent Document 1 describes a motor unit for an electric bicycle. The case of this motor unit is made of metal for the parts that require sufficient strength, such as the part that receives the bearing of the crankshaft, and other parts are made of resin for lighter weight.

[0003] However, in this motor unit, the case that covers the electric motor is made of resin. Therefore, although this motor unit can be made lighter, it has the problem of making it difficult to dissipate heat generated by the electric motor.

[0004] Japanese Patent Publication No. 2003-219603

[0005] An object of the present disclosure is to provide a motor unit for an electric bicycle that is lightweight and that easily dissipates heat generated by the motor, and an electric bicycle.

[0006] A motor unit for an electric bicycle according to one aspect of the present disclosure comprises a case, a motor, and a rotating shaft unit. The motor is housed within the case and has a rotor and a stator. The rotating shaft unit passes through the case and is arranged to be rotatable around the axis of the rotating shaft unit. Pedals are connected to the rotating shaft unit via crank arms. The motor unit further comprises a transmission mechanism. The transmission mechanism is housed within the case and transmits force from the motor to the rotating shaft unit. The case has a first case portion and a second case portion. The first case portion constitutes a part of the case, and the rotor and stator are arranged inside. The second case portion constitutes the other part of the case. The first case portion is formed of a material with a higher thermal conductivity than the second case portion. The second case portion is formed of a material with a lower specific gravity than the first case portion.

[0007] An electric bicycle according to one aspect of the present disclosure includes the motor unit and a frame, the frame having the motor unit attached to a lower portion thereof and supporting a rider.

[0008] Fig. 1 is a schematic side view showing an electric bicycle according to one embodiment of the present disclosure. Fig. 2 is a side view showing a bracket, a motor unit, and a cover provided on the electric bicycle. Fig. 3 is a perspective view showing the motor unit. Fig. 4 is a cross-sectional view showing a cross section of the motor unit at a portion corresponding to line A-A in Fig. 2. Fig. 5 is a cross-sectional view showing an enlarged view of portion B in Fig. 4. Fig. 6 is a cross-sectional view taken along line C-C in Fig. 2.

[0009] (One Embodiment) 1. Overview A motor unit 2 (hereinafter simply referred to as the "motor unit 2") of an electric bicycle 1 according to one embodiment shown in FIGS. 1 to 4 includes a case 3 and a motor 4. The motor 4 is housed within the case 3 and has a rotor 41 and a stator 42. The motor unit 2 further includes a rotating shaft unit 5 and a transmission mechanism 6. The rotating shaft unit 5 passes through the case 3 and is rotatable about the axis of the rotating shaft unit 5. Pedals 180 are connected to the rotating shaft unit 5 via crank arms 18. The transmission mechanism 6 is housed within the case 3 and transmits power from the motor 4 to the rotating shaft unit 5. The case 3 includes a first case portion 3a and a second case portion 3b. The first case portion 3a constitutes a portion of the case 3, and the rotor 41 and stator 42 are disposed inside the second case portion 3b, which constitutes the other portion of the case 3. The first case portion 3a is made of a material with a higher thermal conductivity than the second case portion 3b. The second case portion 3b is formed of a material having a lower specific gravity than the first case portion 3a.

[0010] The electric bicycle 1 of one embodiment includes a motor unit 2 and a frame 10. The motor unit 2 is attached to the lower part of the frame 10, and supports the rider.

[0011] In one embodiment of the electric bicycle 1 and motor unit 2 having the above configuration, the first case portion 3a of the case 3, on which the heat-generating parts of the motor 4 (i.e., the rotor 41 and stator 42) are located, is made of a material with a higher thermal conductivity than the second case portion 3b. As a result, the electric bicycle 1 and motor unit 2 of one embodiment easily dissipates heat generated by the motor 4. Also, in one embodiment of the electric bicycle 1 and motor unit 2, the second case portion 3b, which constitutes the other part of the case 3, is made of a material with a lower specific gravity than the first case portion 3a, making it easier to reduce the weight of the case 3. As a result, the electric bicycle 1 and motor unit 2 of one embodiment easily dissipates heat generated by the motor 4 while achieving a lighter weight.

[0012] 2. Details Next, the electric bicycle 1 and motor unit 2 of one embodiment shown in Figures 1 to 6 will be described in more detail with reference to the drawings. In this embodiment, the electric bicycle 1 is an electrically assisted bicycle that adds auxiliary driving force from the motor 4 to the driving force of the rider. The electric bicycle 1 may also be an electric motorcycle that runs solely on the driving force of the motor 4.

[0013] 1, the electric bicycle 1 includes a frame 10, wheels 11, a motor unit 2, and a cover 12. In the following description, the direction of travel of the electric bicycle 1 is defined as the forward direction, the opposite direction is defined as the rearward direction, and the left and right directions are defined based on the direction as seen by a rider riding the electric bicycle 1.

[0014] The frame 10 supports a rider who drives the electric bicycle 1. The weight of the frame 10 and the rider is supported on the ground via a front wheel 110 and a rear wheel 111 that constitute the wheels 11.

[0015] The frame 10 has a head pipe 101, an upper pipe 102, a lower pipe 103, a vertical pipe 104, a seat stay 105, a chain stay 106, and a bracket 107. The frame 10 is formed from a metal such as aluminum or stainless steel, but may contain a non-metallic material in part. Alternatively, the entire frame 10 may be formed from a non-metallic material. There are no particular limitations on the material of the frame 10.

[0016] The head pipe 101 is a cylindrical member. A handle post 13 is inserted through the head pipe 101. The handle post 13 is inserted into the head pipe 101 so as to be rotatable around the axis of the head pipe 101. A front fork 14 is formed at the lower end of the handle post 13. A front wheel 110 is rotatably attached to the front fork 14. A handle bar 15 is fixed to the upper end of the handle post 13. The handle bar 15 is provided with a hand operation unit for turning the electric power on and off, and a gear change operation unit for changing the speed using a gear change mechanism provided in the rear wheel 111.

[0017] The upper pipe 102 is a cylindrical member that extends diagonally downward and rearward from the head pipe 101. The front end of the upper pipe 102 is fixed to the rear side wall of the head pipe 101 by welding or the like. The rear end of the upper pipe 102 is fixed to the stand pipe 104.

[0018] The standpipe 104 is a tubular member extending in the vertical direction. The rear end of the upper pipe 102 is fixed to the front sidewall of the standpipe 104 near its upper end (in other words, its upper part) by welding or the like. A shaft 160 extending downward from the saddle 16 is inserted into an opening at the upper end of the standpipe 104. The shaft 160 is fixed to the standpipe 104, thereby fixing the saddle 16 to the standpipe 104. A bracket 107 is fixed to the lower end of the standpipe 104.

[0019] The lower pipe 103 is a cylindrical member that extends diagonally downward and rearward from the head pipe 101. The front end of the lower pipe 103 is fixed by welding or the like to a portion of the rear side wall of the head pipe 101 that is lower than the portion to which the upper pipe 102 is fixed. A bracket 107 is fixed to the rear end of the lower pipe 103.

[0020] The bracket 107 is a part of the frame 10, and the motor unit 2 is attached to the bracket 107. The bracket 107 has insertion holes 1070 (see FIG. 2) through which screws 20 are inserted to fix the bracket 107 to the motor unit 2. In this embodiment, the bracket 107 is formed by combining a first bracket 107a and a second bracket 107b (see FIG. 6) that are aligned in the left-right direction.

[0021] The first bracket 107a located on the left side has three insertion holes 1070. Similarly, the second bracket 107b located on the right side has three insertion holes 1070. The three insertion holes 1070 of the first bracket 107a and the three insertion holes 1070 of the second bracket 107b are aligned one-to-one in the left-right direction.

[0022] The motor unit 2 is attached to the underside of the bracket 107. A space is formed between the inner surface of the bracket 107 and the outer surface of the motor unit 2 to allow wiring to pass through.

[0023] The front ends of the seat stays 105 are fixed to the rear end of the upper pipe 102 by welding or the like. The seat stays 105 are two hollow members that extend diagonally rearward and downward from near the upper end of the stand pipe 104 (in other words, from the upper part). The rear ends of the seat stays 105 are fixed to the rear ends of the chain stays 106. A rear wheel 111 is rotatably attached to the rear ends of the seat stays 105 and chain stays 106.

[0024] A battery 17 for supplying power to the motor unit 2 is detachably attached to the bracket 107 and the lower pipe 103 .

[0025] A gear shift wire or a brake wire is passed through the internal space of the down pipe 103 and the bracket 107. The gear shift wire connects a gear shift operation unit provided on the handlebar 15 to a gear shift mechanism of the rear wheel 111.

[0026] As shown in FIG. 2 , the cover 12 includes a lower cover 120, a first side cover 121, and a second side cover 122. The lower cover 120 covers the motor unit 2 from below. The first side cover 121 and the second side cover 122 cover the motor unit 2 from the left side. Each of the covers 120, 121, and 122 is formed from a flame-retardant and weather-resistant resin. The lower cover 120 is screwed to the bracket 107. The first side cover 121 is disk-shaped and is engaged with the motor unit 2. The second side cover 122 has an opening 1220 inside which the first side cover 121 is disposed. The second side cover 122 is screwed to the motor unit 2 and supports the first side cover 121 at the periphery of the opening 1220. The covers 120, 121, and 122 may all be formed from a material with high thermal conductivity, such as aluminum.

[0027] As shown in Figure 1, the electric bicycle 1 further includes a crank arm 18 and pedals 180. One end of the crank arm 18 is fixed to the rotary shaft unit 5 of the motor unit 2. The pedals 180 are rotatably attached to the other end of the crank arm 18. By pedaling the pedals 180, the rider of the electric bicycle 1 can transmit human power to the rotary shaft unit 5.

[0028] The electric bicycle 1 further includes a front sprocket (not shown) fixed to the rotating shaft unit 5 (more specifically, the output body 8), a rear sprocket 19 fixed to the hub of the rear wheel 111, and a chain 190 looped around the front sprocket and the rear sprocket 19.

[0029] (Motor Unit) As shown in FIGS. 3 and 4 , the motor unit 2 includes a case 3 , a motor 4 , a rotary shaft unit 5 , and a transmission mechanism 6 .

[0030] The case 3 forms the outer shell of the motor unit 2. The case 3 houses devices such as the motor 4, the rotary shaft unit 5, and the transmission mechanism 6 in an accommodation space formed inside. The case 3 has a first case portion 3a that forms a part of the case 3 and a second case portion 3b that forms the other part of the case 3. The rotor 41 and stator 42 of the motor 4 are disposed inside the first case portion 3a. The first case portion 3a is formed of a material with a higher thermal conductivity than the second case portion 3b, and the second case portion 3b is formed of a material with a lower specific gravity than the first case portion 3a.

[0031] In this embodiment, the case 3 has a first segment 30 and a second segment 31. The first segment 30 and the second segment 31 are aligned in the axial direction (i.e., the left-right direction) along the axis of the rotating shaft unit 5 and combined with each other. The first segment 30 and the second segment 31 each include an axial hole 300, 310 through which the rotating shaft unit 5 is inserted. The first segment 30 located on the left side is the first case portion 3a, and the second segment 31 located on the right side is the second case portion 3b. The case 3 is formed by combining the first segment 30 and the second segment 31.

[0032] The first division body 30 is formed of a material having a higher thermal conductivity than the second division body 31. The first division body 30 is formed of, for example, aluminum. The second division body 31 is formed of a material having a lower specific gravity than the first division body 30. The second division body 31 is formed of, for example, magnesium.

[0033] As shown in Figure 4, the internal storage space of the first division 30 on the left side is open to the right. The internal storage space of the second division 31 on the right side is open to the left. The first division 30 and the second division 31 are fitted together from the left and right so that the storage space of the first division 30 and the storage space of the second division 31 are continuous. The first division 30 and the second division 31 are fixed to each other with fastening members made of bolts.

[0034] The first divided body 30 has a first mounting portion 301 that is fixed to the bracket 107 with a screw 20 (see FIG. 1). The second divided body 31 has a second mounting portion 311 that is fixed to the bracket 107 with a screw 20 (not shown).

[0035] 3 , the first division 30 has three first mounting portions 301. One first mounting portion 301 protrudes forward from the first division 30, one first mounting portion 301 protrudes upward from the first division 30, and one first mounting portion 301 protrudes rearward from the first division 30.

[0036] The second divided body 31 has three second mounting portions 311. Similar to the three first mounting portions 301, the three second mounting portions 311 protrude forward, upward, and rearward from the second divided body 31. The three first mounting portions 301 and the three second mounting portions 311 are arranged one-to-one at intervals in the left-right direction.

[0037] A cylindrical member 21 is attached to the first attachment portion 301. The cylindrical member 21 can advance and retreat toward the bracket 107, and a screw 20 can be screwed into the inside of the cylindrical member 21. In this embodiment, a cylindrical member 21 is attached to each of the three first attachment portions 301.

[0038] 6 , the first mounting portion 301 is provided with a mounting hole 302 into which the cylindrical member 21 is mounted so as to be movable forward and backward. The second mounting portion 311 is provided with a fixing hole 312 into which the screw 20 is fixed. The mounting hole 302 has a larger diameter than the fixing hole 312.

[0039] A tubular member 21 forming a left-handed thread is screwed into the mounting hole 302. The tubular member 21 has a cylindrical main body 210 and a flange 211 protruding from one axial end (the left end in this embodiment) of the main body 210. Threads forming the left-handed thread are provided on the outer peripheral surface of the main body 210. A threaded hole 212 is formed on the inner peripheral surface of the main body 210. A thread groove is provided in the threaded hole 212 for threading in a screw 20 forming a right-handed thread. The threaded hole 212 has the same diameter as the fixing hole 312 of the second mounting portion 311.

[0040] In this embodiment, the motor unit 2 is attached to the bracket 107 as follows.

[0041] First, the second mounting portion 311 of the second divided body 31 is placed against the inner surface of the right-side second bracket 107b, and in this state, the screw 20 is inserted from the outside (i.e., the right side) into the insertion hole 1070 of the right-side second bracket 107b. At this time, the screw 20 is threaded into the fixing hole 312 of the second mounting portion 311, and the second bracket 107b and the second mounting portion 311 are fixed together by the screw 20.

[0042] Next, the tip of a tool is inserted into the insertion hole 1070 of the left-side first bracket 107a from the outside (i.e., the left side), and the tip of the tool is inserted into the inside of the main body 210 of the tubular member 21 of the first mounting part 301, and the tubular member 21 is rotated clockwise with the tool. This allows the tubular member 21 to be pulled out of the first mounting part 301 (i.e., moved to the left), and the flange part 211 to come into contact with the inner surface of the first bracket 107a.

[0043] Next, the tool is removed from the main body 210 of the tubular member 21 and the insertion hole 1070 of the left-side first bracket 107a. Next, the screw 20 is inserted from the outside into the insertion hole 1070 of the first bracket 107a and threaded into the threaded hole 212 on the inner surface of the main body 210 of the tubular member 21, thereby fixing the first bracket 107a and the first mounting portion 301 via the tubular member 21. Because the tubular member 21 is left-handed, even if the right-handed screw 20 is threaded into the threaded hole 212 of the tubular member 21, the tubular member 21 does not move relative to the first mounting portion 301. Therefore, the gap between the first mounting portion 301 and the first bracket 107a can be maintained filled by the tubular member 21. As a result, when the screw 20 is threaded into the first bracket 107a and the tubular member 21, a force is unlikely to act on the first mounting portion 301 in a direction away from the second mounting portion 311. Therefore, it is possible to prevent a gap from occurring at the joint between the first division 30 and the second division 31, and to prevent a decrease in the airtightness of the case 3.

[0044] In the electric bicycle 1 of this embodiment, the mating surfaces of the first bracket 107a and the second bracket 107b and the mating surfaces of the first divided body 30 and the second divided body 31 are aligned in the axial direction (i.e., left-right direction) of the rotating shaft unit 5.

[0045] As shown in Fig. 4, the motor 4 is attached to the case 3. The motor 4 has a rotating shaft 40, a rotor 41 that rotates integrally with the rotating shaft 40, and a stator 42. A portion of the rotating shaft 40, the rotor 41, and the stator 42 are disposed inside the first divided body 30.

[0046] The first divided body 30 has a motor housing portion 303 that houses the rotor 41 and stator 42 of the motor 4. The motor housing portion 303 is cylindrical and has a bottom. A heat insulating film 304 is provided on the outer surface of the motor housing portion 303 (specifically, the left surface and outer peripheral surface of the motor housing portion 303). The heat insulating film 304 is formed of a material that has lower thermal conductivity than the first divided body 30. The heat insulating film 304 is formed of, for example, resin or rubber. The heat insulating film 304 may be formed by painting or coating. The heat insulating film 304 may be attached to the outer surface of the motor housing portion 303.

[0047] The rotating shaft 40 is rotatably housed within the case 3 so that the axial direction of the rotating shaft 40 faces the left-right direction. The rotating shaft 40 protrudes to one side (specifically, to the right) from the stator 42, and teeth 400 that mesh with the transmission mechanism 6 are formed on the outer surface of the protruding portion. The right end of the rotating shaft 40 is supported by a rotating shaft support bearing 32 disposed in the second division body 31. The left end of the rotating shaft 40 does not protrude leftward from the stator 42, and is supported by a rotating shaft support bearing 33 disposed in the first division body 30.

[0048] The rotary shaft unit 5 has an input shaft 7 , an output body 8 , and an input body 9 .

[0049] The input shaft 7 passes through the case 3 in the left-right direction and is arranged to be rotatable about its own axis. In this embodiment, the input shaft 7 is cylindrical. The input shaft 7 may also be a solid round bar. One end of a crank arm 18 (see FIG. 1) is fixed to both ends of the input shaft 7 in the axial direction along the axis.

[0050] The first split body 30 of the case 3 has a first bearing 34 rotatably supporting the input shaft 7, at one end side (more specifically, the left end side) in the axial direction of the input shaft 7. A shaft hole 300 through which the input shaft 7 passes is formed in the first split body 30, and the first bearing 34 is disposed inside this shaft hole 300. In this embodiment, the first bearing 34 is configured as a ball bearing. The first bearing 34 may be various other bearings such as a roller bearing, and is not limited to a ball bearing. An O-ring (not shown) is provided between the outer circumferential surface of the first bearing 34 and the first split body 30.

[0051] The case 3 has a second bearing 35, which rotatably supports the input shaft 7, at the other end side (more specifically, the right end side) in the axial direction of the input shaft 7. A shaft hole 310 through which the input shaft 7 passes is formed in the second divided body 31, and the second bearing 35 is disposed inside this shaft hole 310. In this embodiment, the input shaft 7 is indirectly supported by the second bearing 35 via the output body 8. The second bearing 35 is configured by a ball bearing. The second bearing 35 is not limited to a ball bearing and may be various other bearings such as a roller bearing. A cover member 23 is attached to the shaft hole 310.

[0052] An input body 9 is disposed on the outer peripheral surface of the input shaft 7. The input body 9 rotates integrally with the input shaft 7. The input body 9 is a cylindrical member. The input body 9 is disposed concentrically with the input shaft 7, with its axial direction along the axis of the input body 9 facing the left-right direction. In other words, the axis of the input shaft 7 and the axis of the input body 9 coincide with each other, and the axial direction of the input shaft 7 and the axial direction of the input body 9 are the same. The length of the input body 9 in the left-right direction is shorter than the length of the input shaft 7 in the left-right direction. The input body 9 and the input shaft 7 have mating portions 900, 70 in part of their respective axial directions. The mating portions 900, 70 are mated with each other so as to be unable to rotate relatively around the axis of the input shaft 7. In this embodiment, the mating portions 900, 70, which are formed of a spline portion, serration portion, or the like, are formed on the left end of the input body 9 and on a part of the input shaft 7 corresponding to this portion. The mating portions 900 and 70 may be configured to be mated with male and female threads.

[0053] The input body 9 is divided into a first input body 90 and a second input body 91. The first input body 90 is connected to the input shaft 7. The first input body 90 is disposed on the outer peripheral surface of the left portion of the input shaft 7 and is housed within the first divided body 30. A fitting portion 900 that fits with the input shaft 7 is formed at the left end of the first input body 90. A gap S1 is formed between the first input body 90 and the input shaft 7 in a portion to the right of the fitting portion 900 at the left end of the first input body 90. This makes it easier to insert the input shaft 7 into the cylindrical first input body 90.

[0054] The second input body 91 is located at a different position from the first input body 90 in the axial direction of the input shaft 7 (specifically, to the right of the first input body 90) and is connected to the first input body 90. The second input body 91 transmits the rotational force of the input shaft 7 to the output body 8. The left end of the second input body 91 is located radially outward of the right end of the first input body 90. The input bodies 90, 91 partially overlap radially in the axial direction of the input shaft 7. The first input body 90 and the second input body 91 have mating portions 901, 910. The mating portions 901, 910 are mated with each other so as to be relatively unrotatable around the axis of the input shaft 7. In this embodiment, the mating portions 901, 910, which are formed of a spline portion, a serration portion, or the like, are formed at the right end of the first input body 90 and the left end of the second input body 91. In the present disclosure, "overlapping in the radial direction" refers to a state in which at least a portion of each object overlaps when viewed in the radial direction.

[0055] The output body 8 is disposed along the outer peripheral surface of the input shaft 7 so as to be rotatable around the axis of the input shaft 7 and receives a rotational force from the input body 9. The output body 8 is cylindrical. The output body 8 is disposed concentrically with the input shaft 7, with its axial direction aligned with the left-right direction. In other words, the axis of the input shaft 7 and the axis of the output body 8 coincide with each other, and the axial direction of the input shaft 7 and the axial direction of the output body 8 are the same. The left-right length of the output body 8 is shorter than the left-right length of the input shaft 7. The right end of the output body 8 protrudes outside the case 3 through a shaft hole 310 formed in the second divided body 31. The output body 8 is supported by a second bearing 35 disposed in the second divided body 31. The rotating shaft unit 5 described above is supported by the case 3 via the first bearing 34 and the second bearing 35.

[0056] A front sprocket (not shown) is fixed to a portion of the output body 8 that protrudes outside the case 3. The front sprocket rotates integrally with the output body 8.

[0057] A one-way clutch (not shown) is disposed between the input body 9 and the output body 8. When a rotational force is applied to the input body 9 in a direction that accelerates the electric bicycle 1 in the traveling direction (hereinafter referred to as the acceleration direction), the one-way clutch transmits this rotational force to the output body 8. When a rotational force is applied to the input body 9 in a direction opposite to the acceleration direction, the one-way clutch does not transmit this rotational force to the output body 8. When a rotational force in the acceleration direction is applied to the output body 8 via the transmission mechanism 6, the one-way clutch does not transmit this rotational force to the input body 9. In this embodiment, the one-way clutch has a ratchet and is supplied with grease. Various one-way clutches can be used as appropriate. For example, a roller-type one-way clutch or a sprag-type one-way clutch may be used as the one-way clutch.

[0058] The output body 8 has a web 80 and a rim 81 on the outer peripheral surface side of the output body 8 at a portion overlapping with the input body 9 in the axial direction of the input shaft 7. The web 80 protrudes radially outward from the output body 8. The rim 81 is continuous with the outer end of the web 80 in the radial direction. In the axial direction of the input shaft 7, the rim 81 is longer than the web 80. The rim 81 has teeth 810 on its outer peripheral surface that mesh with the transmission mechanism 6.

[0059] The transmission mechanism 6 is housed in the case 3 and transmits the rotation of the motor 4 to the rotary shaft unit 5 (more specifically, the output body 8). The transmission mechanism 6 has a first transmission gear 60 and a second transmission gear 61. The first transmission gear 60 rotates by the rotational force of the rotary shaft 40 of the motor 4. In this embodiment, the first transmission gear 60 is formed of a cylindrical member. A toothed portion 600 that meshes with a toothed portion 400 formed on the rotary shaft 40 of the motor 4 is formed on the outer circumferential surface of the first transmission gear 60. The first transmission gear 60 is arranged along the outer circumferential surface of a rotary transmission shaft 62 of the transmission mechanism 6.

[0060] The transmission rotation shaft 62 is rotatably housed in the case 3 so that the axial direction of the transmission rotation shaft 62 faces the left-right direction. The transmission rotation shaft 62 is located rearward of the rotation shaft 40 of the motor 4, and is arranged in approximately the same position in the left-right direction as the portion of the rotation shaft 40 that protrudes rightward from the stator 42. The right end of the transmission rotation shaft 62 is supported by a transmission rotation shaft support bearing (not shown) arranged in the second division body 31.

[0061] The first transmission gear 60 is connected to the transmission rotation shaft 62 via a one-way clutch (not shown). When a rotational force in the acceleration direction is applied to the first transmission gear 60, the one-way clutch transmits this rotational force to the transmission rotation shaft 62. When a rotational force in the direction opposite to the acceleration direction is applied to the first transmission gear 60, the one-way clutch does not transmit this rotational force to the transmission rotation shaft 62. Furthermore, when a rotational force in the acceleration direction is applied to the transmission rotation shaft 62, the one-way clutch does not transmit this rotational force to the first transmission gear 60.

[0062] A second transmission gear 61 is fixed to the right side of the portion of the transmission rotation shaft 62 to which the one-way clutch is fixed so as to rotate integrally with the transmission rotation shaft 62. The second transmission gear 61 transmits the rotational force received from the first transmission gear 60 via the transmission rotation shaft 62 to a toothed portion 810 of the output body 8. The second transmission gear 61 has teeth on its outer circumferential surface that mesh with the toothed portion 810 of the rim 81 of the output body 8. The transmission mechanism 6 transmits the rotation of the motor 4 to the output body 8 at a reduced speed via the first transmission gear 60 and the second transmission gear 61. That is, the transmission mechanism 6 in this embodiment is a reduction mechanism.

[0063] When the rider pedals 180 (see FIG. 1 ) of the electric bicycle 1, a rotational force in the acceleration direction is applied to the input shaft 7. When the input shaft 7 rotates, the first input body 90 and the second input body 91 rotate integrally with the input shaft 7. The rotational force in the acceleration direction of the second input body 91 is applied to the output body 8 via the one-way clutch, causing the output body 8 and the front sprocket to rotate in the acceleration direction. When the front sprocket rotates in the acceleration direction, a rotational force in the acceleration direction is applied to the rear sprocket 19 via the chain 190, causing the rear sprocket 19 and rear wheel 111 to rotate in the acceleration direction. This causes the electric bicycle 1 to move forward in the forward direction.

[0064] While the electric bicycle 1 is moving forward under human power, the rotational force from the motor 4 can be applied to the output body 8 as an auxiliary force. When the rotating shaft 40 of the motor 4 rotates in the acceleration direction, the first transmission gear 60 that meshes with the rotating shaft 40 of the motor 4 rotates in the acceleration direction. The rotational force of the first transmission gear 60 in the acceleration direction is transmitted to the transmission rotating shaft 62 and the second transmission gear 61 via the one-way clutch, causing the second transmission gear 61 to rotate in the acceleration direction. The rotational force of the second transmission gear 61 in the acceleration direction is transmitted to the output body 8 that meshes with the second transmission gear 61. In other words, the output body 8 functions as a force combiner that combines the rotational force of human power from the input body 9 and the rotational force from the motor 4. The motor unit 2 in this embodiment is a so-called single-shaft motor unit 2.

[0065] When the motor 4 is not driven while the electric bicycle 1 is moving forward under human power, it operates as follows. In this case, the output body 8 is rotating in the acceleration direction, so the second transmission gear 61 and the transmission rotation shaft 62 that mesh with the output body 8 rotate in the acceleration direction, but the rotational force of the transmission rotation shaft 62 in the acceleration direction is not transmitted to the first transmission gear 60 by the one-way clutch. As a result, when the motor 4 is not driven, the rotation shaft 40 and the rotor 41 are prevented from rotating.

[0066] In the electric bicycle 1, the rotational force from the motor 4 is controlled in accordance with the torque applied to the input shaft 7 and the number of rotations per unit time of the input shaft 7. The torque applied to the input shaft 7 is detected by a torque detection unit 36. The number of rotations per unit time of the input shaft 7 is detected by a rotation detection unit (not shown). The rotation detection unit is disposed within a partial range in the axial direction of the rotating shaft unit 5 so as to follow the outer peripheral surface of the rotating shaft unit 5.

[0067] A control board 22 having a control unit that controls the motor 4 is disposed within the case 3. The control unit has, for example, a microcomputer. The control unit controls the operation of each element by executing a program stored in a storage unit such as a ROM (Read Only Memory). Various types of control units can be used as appropriate, and detailed description thereof will be omitted. The control unit controls the rotational force from the motor 4 based on the torque detected by the torque detection unit and the rotation speed detected by the rotation detection unit.

[0068] The motor unit 2 has a third bearing 37 located between the first bearing 34 and the second bearing 35 in the axial direction of the input shaft 7. The third bearing 37 rotatably supports the input body 9. In the present embodiment, the third bearing 37 is configured by a ball bearing. The third bearing 37 may be various other bearings such as a roller bearing, and is not limited to a ball bearing.

[0069] The cover member 23 is provided to cover the gap between the axial hole 310 of the second divided body 31 of the case 3 and the output body 8. In this embodiment, the cover member 23 is made of rubber. The cover member 23 has an annular (more specifically, circular) shape when viewed in the axial direction of the input shaft 7.

[0070] 5 , the cover member 23 has an attachment portion 230 and a first contact portion 231. The attachment portion 230 is attached to the shaft hole 310 of the second divided body 31. The first contact portion 231 protrudes from the attachment portion 230 toward the rotating shaft unit 5 and comes into contact with the rotating shaft unit 5. The cover member 23 further has a second contact portion 232. The second contact portion 232 protrudes toward the rotating shaft unit 5 from a portion of the attachment portion 230 that is deeper than the first contact portion 231.

[0071] The mounting portion 230 is provided so as to sandwich the inner peripheral edge of the axial hole 310 of the second segment 31. The mounting portion 230 has a U-shaped cross section perpendicular to the circumferential direction of the cover member 23. A first contact portion 231 protrudes from the inner peripheral edge of the inner surface (left side in this embodiment) of the mounting portion 230, and a second contact portion 232 protrudes from the outer periphery of the inner surface of the mounting portion 230. Each of the first contact portion 231 and the second contact portion 232 is annular (more specifically, circular) when viewed in the left-right direction and protrudes toward the center of the mounting portion 230. In this embodiment, the first contact portion 231 and the second contact portion 232 are fin-shaped and are tapered toward the tip in the protruding direction.

[0072] The contact portions 231, 232 are configured so that, when the mounting portion 230 is attached to the axial hole 310 of the second segment 31, the first contact portion 231 comes into contact with the output body 8 and the second contact portion 232 comes into contact with a raceway 350 on the inner circumferential side of the second bearing 35. The raceway 350 on the inner circumferential side of the second bearing 35 is a portion of the second bearing 35 that supports the output body 8, and is located more inner than the rolling elements (i.e., balls 351). The second contact portion 232 may be configured to come into contact with a portion of the output body 8 that is closer to the second bearing 35 than the contact portion of the first contact portion 231.

[0073] In this way, the first contact portion 231 abuts against the output body 8, and the second contact portion 232 abuts against the raceway ring 350 on the inner periphery of the second bearing 35. As a result, the contact portions 231, 232 can doubly prevent foreign matter such as mud or sand from penetrating through the axial hole 310 to the rolling elements (i.e., balls 351) of the second bearing 35.

[0074] 3. Effects In the motor unit 2 of the present embodiment described above, the portion of the case 3 inside which the rotor 41 and stator 42 of the motor 4 are disposed (i.e., the motor housing portion 303) is formed from a material with high thermal conductivity. Therefore, in the motor unit 2 of the present embodiment, heat generated by the motor 4 is easily dissipated through the case 3.

[0075] In the motor unit 2 of this embodiment, the first divided body 30, which constitutes approximately half of the case 3 in the axial direction of the rotating shaft unit 5, is made of a material with high thermal conductivity. Therefore, in the motor unit 2 of this embodiment, the first divided body 30 has a large surface area, making it easy to dissipate heat generated by the motor 4.

[0076] Furthermore, in the motor unit 2 of this embodiment, the second divided body 31 of the case 3, which constitutes approximately half of the axial direction of the rotary shaft unit 5, is made of a material with a low specific gravity. Therefore, in the motor unit 2 of this embodiment, it is easy to reduce the overall weight of the case 3. As a result, in the motor unit 2 of this embodiment, it is easy to reduce the weight of the case 3, and therefore the motor unit 2.

[0077] Furthermore, in the motor unit 2 of this embodiment, the outer surface of the portion of the case 3 where the rotor 41 and stator 42 of the motor 4 are disposed is covered with a heat insulating film 304. Therefore, in the motor unit 2 of this embodiment, it is possible to prevent the driver from directly contacting the portion of the case 3 that is particularly susceptible to becoming hot. Furthermore, in the motor unit 2 of this embodiment, covering a portion of the case 3 with the heat insulating film 304 can also improve the design.

[0078] Furthermore, in the motor unit 2 of this embodiment, the first divided body 30 is covered with the cover 12, so that direct contact of the driver with the first divided body 30 can be prevented.

[0079] Furthermore, in the motor unit 2 of this embodiment, the tubular member 21 protrudes from the first mounting portion 301 of the first divided body 30, and the first mounting portion 301 is not in direct contact with the bracket 107. Therefore, in the motor unit 2 of this embodiment, heat from the first divided body 30 is not easily transferred to the bracket 107.

[0080] Furthermore, in the motor unit 2 of this embodiment, the bracket 107 is fixed with the screw 20 to the tubular member 21 protruding from the first mounting portion 301, so that gaps are unlikely to occur between the first divided body 30 and the second divided body 31 that are combined with each other. Therefore, in the motor unit 2 of this embodiment, it is easy to ensure the airtightness of the case 3.

[0081] Furthermore, in the motor unit 2 of this embodiment, the cover member 23 that fills the gap between the shaft hole 310 of the second divided body 31 of the case 3 and the output body 8 of the rotary shaft unit 5 can provide a double seal with the first contact portion 231 and the second contact portion 232. Therefore, in the motor unit 2 of this embodiment, foreign matter such as mud and sand is less likely to enter the case 3 through the shaft hole 310.

[0082] 4. Modifications Next, we will explain modifications of the above-described motor unit 2 and electric bicycle 1. The modifications shown below can be combined as appropriate.

[0083] The case 3 is not limited to being formed by combining the first divided body 30 and the second divided body 31. The case 3 may be formed by combining three or more divided bodies. Furthermore, only a portion of the first divided body 30 may be the first case portion 3a. In other words, in the first divided body 30, only the motor accommodating portion 303 may have a higher thermal conductivity than the second case portion 3b. The remaining portion of the first divided body 30, excluding the motor accommodating portion 303, may have the same thermal conductivity as the second case portion 3b.

[0084] The outer surface of the portion of the first divided body 30 where the rotor 41 and the stator 42 are disposed (i.e., the motor accommodating portion 303 ) does not need to be covered with the heat insulating film 304 .

[0085] The cylindrical member 21, which can be advanced and retreated toward the bracket 107 and into which the screw 20 can be screwed, does not necessarily have to be attached to the first attachment portion 301. The gap between the first attachment portion 301 and the bracket 107 may be filled by other means.

[0086] The cover member 23 may have only one of the first contact portion 231 and the second contact portion 232. In addition, the motor unit 2 may have another structure that can fill the gap between the shaft hole 310 and the rotating shaft unit 5.

[0087] The transmission mechanism 6 is not limited to a reduction mechanism.

[0088] The arrangement and structure of the motor 4, the transmission mechanism 6, and the rotary shaft unit 5 within the case 3 are not limited to the arrangement and structure shown in FIG.

[0089] The first and second segments 30, 31 are not limited to a combination of aluminum and magnesium, and may be formed of other combinations of materials that satisfy certain conditions. For example, the second segment 31 may be formed of a non-metal such as resin. Furthermore, the first segment 30 may be formed by metal insert molding, with only the motor housing portion 303 being made of a material with high thermal conductivity such as aluminum, and the other portions being made of resin.

[0090] (Summary) As in the above-described embodiment and its modified example, the motor unit (2) of the first aspect has the following configuration.

[0091] The motor unit (2) of the first aspect includes a case (3), a motor (4), and a rotating shaft unit (5). The motor (4) is housed in the case (3) and has a rotor (41) and a stator (42). The rotating shaft unit (5) passes through the case (3) and is arranged to be rotatable around the axis of the rotating shaft unit (5). A pedal (180) is connected to the rotating shaft unit (5) via a crank arm (18). The motor unit (2) further includes a transmission mechanism (6). The transmission mechanism (6) is housed in the case (3) and transmits force from the motor (4) to the rotating shaft unit (5). The case (3) has a first case portion (3a) and a second case portion (3b). The first case portion (3a) constitutes a part of the case (3), and the rotor (41) and the stator (42) are arranged inside the first case portion (3a). The second case portion (3b) constitutes the other portion of the case (3). The first case portion (3a) is formed of a material having a higher thermal conductivity than the second case portion (3b), and the second case portion (3b) is formed of a material having a lower specific gravity than the first case portion (3a).

[0092] In the motor unit (2) of the first aspect having the above configuration, the first case portion (3a) of the case (3), on the inside of which the heat-generating parts of the motor (4) (i.e., the rotor 41 and the stator 42) are arranged, is formed of a material with high thermal conductivity. Therefore, in the motor unit (2) of the first aspect, it is easy to dissipate heat generated by the motor (4). Also, in the motor unit (2) of the first aspect, the second case portion (3b) constituting the other part of the case (3) is formed of a material with a low specific gravity. Therefore, in the motor unit (2) of the first aspect, it is easy to reduce the weight of the case (3). Therefore, in the motor unit (2) of the first aspect, it is easy to dissipate heat generated by the motor (4) while achieving a reduction in weight.

[0093] As in the above-described embodiment and its modified example, the motor unit (2) of the second aspect additionally includes the following configuration in addition to the configuration of the first aspect.

[0094] In the motor unit (2) of the second aspect, the case (3) has a first divided body (30) and a second divided body (31) that are combined with each other. The first divided body (30) and the second divided body (31) are aligned in the axial direction along the axis of the rotating shaft unit (5). The first divided body (30) and the second divided body (31) each include an axial hole (300, 310) through which the rotating shaft unit (5) is inserted. The first divided body (30) is the first case portion (3a). The second divided body (31) is the second case portion (3b).

[0095] In the second embodiment of the motor unit (2) having the above configuration, the first case portion (3a) and the second case portion (3b) can each be made relatively large, which makes it easier to improve the heat dissipation properties of the first case portion (3a) and to reduce the weight of the case (3).

[0096] As in the above-described embodiment and its modified example, the motor unit (2) of the third aspect additionally includes the following configuration in addition to the configuration of the second aspect.

[0097] In the motor unit (2) of the third aspect, the outer surface of the first divided body (30) in which the rotor (41) and the stator (42) are disposed is covered with a heat insulating film (304).

[0098] In the motor unit (2) of the third aspect having the above-described configuration, the outer surface of the portion of the first divided body (30) where the rotor (41) and the stator (42) are disposed inside and which is prone to become hot can be covered with the heat insulating film (304). Therefore, in the motor unit (2) of the third aspect, direct contact with the portion which is prone to become hot can be prevented.

[0099] As in the above-described embodiment and its modified example, the motor unit (2) of the fourth aspect additionally includes the following configuration in addition to the configuration of the second or third aspect.

[0100] In the motor unit (2) of the fourth aspect, the first segment (30) has a first mounting portion (301) that is fixed with a screw (20) to a bracket (107) at the bottom of the frame (10) of the electric bicycle (1). The second segment (31) has a second mounting portion (311) that is fixed with a screw (20) to the bracket (107). A tubular member (21) is attached to the first mounting portion (301). The tubular member (21) can move forward and backward toward the bracket (107), and the screw (20) can be threaded into its inside.

[0101] In the motor unit (2) of the fourth aspect having the above configuration, the second mounting portion (311) of the second division (31) can be fixed to the bracket (107) with the screw (20). In the motor unit (2) of the fourth aspect, the tubular member (21) extending from the first mounting portion (301) of the first division (30) toward the bracket (107) can be fixed to the bracket (107) with the screw (20). Therefore, in the motor unit (2) of the fourth aspect, when the screw (20) is tightened, force is less likely to be applied to the first mounting portion (301) in a direction toward the bracket (107). As a result, the motor unit (2) of the fourth aspect can easily prevent a gap from occurring between the first division (30) and the second division (31) and thereby reduce the airtightness of the case (3).

[0102] As in the above-described embodiment and its modified example, the motor unit (2) of the fifth aspect additionally includes the following configuration in addition to the configuration of any one of the first to fourth aspects.

[0103] In a motor unit (2) of a fifth aspect, the case (3) has an axial hole (310) through which the rotating shaft unit (5) is inserted. A cover member (23) is attached to the axial hole (310) to fill the gap between the axial hole (310) and the rotating shaft unit (5). The cover member (23) has an attachment portion (230) attached to the axial hole (310) and a first contact portion (231) that protrudes from the attachment portion (230) toward the rotating shaft unit (5) and comes into contact with the rotating shaft unit (5). The cover member (23) further has a second contact portion (232) that protrudes toward the rotating shaft unit (5) from a portion of the attachment portion (230) that is deeper than the first contact portion (231).

[0104] In the fifth aspect of the motor unit (2) having the above-mentioned configuration, the contact portions (231, 232) of the cover member (23) can doubly prevent foreign matter such as mud and sand from entering the case (3) through the gap between the axial hole (310) of the case (3) and the rotating shaft unit (5).

[0105] As in the above-described embodiment and its variant, the electric bicycle (1) of the sixth aspect comprises a motor unit (2) of any one of the first to fifth aspects, and a frame (10) to which the motor unit (2) is attached at the bottom and which supports the rider.

[0106] In the electric bicycle (1) of the sixth aspect having the above configuration, the weight of the motor unit (2) can be reduced, which facilitates weight reduction of the electric bicycle (1). Also, in the electric bicycle (1) of the sixth aspect, heat generated in the motor (4) can be easily dissipated through the case (3), which facilitates improvement of the safety of the electric bicycle (1).

[0107] The present disclosure has been described above based on the embodiments shown in the accompanying drawings, but the present disclosure is not limited to the above embodiments, and appropriate design changes are possible within the intended scope of the present disclosure.

[0108] REFERENCE SIGNS LIST 1 Electric bicycle 2 Motor unit 3 Case 3a First case portion 3b Second case portion 30 First divided body 300 Shaft hole 304 Heat insulating film 31 Second divided body 310 Shaft hole 4 Motor 41 Rotor 42 Stator 5 Rotating shaft unit 6 Transmission mechanism 21 Cylindrical member 23 Cover member 230 Mounting portion 231 First contact portion 232 Second contact portion 10 Frame 107 Bracket

Claims

1. A motor unit for an electric bicycle comprising: a case; a motor housed within the case and having a rotor and a stator; a rotating shaft unit that passes through the case and is arranged to be rotatable around an axis, and to which pedals are connected via crank arms; and a transmission mechanism housed within the case and transmits power from the motor to the rotating shaft unit, wherein the case has: a first case section that forms part of the case and inside which the rotor and stator are arranged; and a second case section that forms the other part of the case, wherein the first case section is formed from a material with a higher thermal conductivity than the second case section, and the second case section is formed from a material with a lower specific gravity than the first case section.

2. A motor unit for an electric bicycle as described in claim 1, wherein the case has a first divided body and a second divided body that are aligned axially along the axis of the rotating shaft unit and combined with each other, each of the first divided body and the second divided body including an axial hole through which the rotating shaft unit is inserted, the first divided body being the first case portion, and the second divided body being the second case portion.

3. The motor unit for an electric bicycle according to claim 2, wherein the outer surface of the portion of the first divided body inside which the rotor and the stator are disposed is covered with a heat insulating film.

4. A motor unit for an electric bicycle as described in claim 2 or 3, wherein the first divided body has a first mounting portion that is fixed with a screw to a bracket at the bottom of a frame provided on the electric bicycle, the second divided body has a second mounting portion that is fixed with a screw to the bracket, and the first mounting portion has attached to it a tubular member that is movable toward and away from the bracket and into which the screw can be threaded.

5. A motor unit for an electric bicycle as described in any one of claims 1 to 4, wherein the case has an axle hole through which the rotating shaft unit is inserted, and a cover member is attached to the axle hole to fill the gap between the axle hole and the rotating shaft unit, and the cover member has: an attachment portion attached to the axle hole, a first contact portion that protrudes from the attachment portion towards the rotating shaft unit and comes into contact with the rotating shaft unit, and a second contact portion that protrudes towards the rotating shaft unit from a portion of the attachment portion that is further back than the first contact portion.

6. An electric bicycle comprising: a motor unit according to any one of claims 1 to 5; and a frame to which the motor unit is attached at a lower part and which supports a rider.

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