Thru-axle with integrated heat pipe for improved cooling of hub motors

Abstract

A drive shaft (100) for improving the cooling of a vehicle hub motor is presented. The drive shaft has a base body (102) and a cavity (104). A heat pipe (106) is either installed in this cavity (104) or the cavity (104) itself serves as a heat pipe (106). The heat pipe (104) transfers heat from a central region (118) of the drive shaft (100) to at least one end region (112) of the drive shaft (100).

Description

Technical field

[0001] The present invention relates to a thru-axle with an integrated heat pipe for improved cooling of hub motors. State of the art

[0002] Hub motors are a well-known technology and are used, for example, in electric bicycles. A known problem with these motors is insufficient heat dissipation, especially during extended uphill rides with correspondingly high continuous power output. To prevent overheating, the motor power is reduced in such cases.

[0003] Since hub motors are typically external rotors, dissipating heat from the interior is difficult. The main heat sources—the windings of the internal stator and the power electronics—are separated from the rotor by a circumferential air gap, which acts like thermal insulation. Effective cooling can therefore only occur via heat conduction along the shaft.

[0004] Patent NL2004509 C2 discloses a hub motor for a bicycle in which a heat pipe is integrated into the hub motor's axle. The axle is a threaded axle, meaning it is an integral part of the motor and has external threads at both ends. When installed in the wheel, the axle is inserted into the open dropouts and then secured with two nuts. The heat pipe dissipates heat to the end of the threaded axle, with at least one end of the axle located outside the hub housing.

[0005] However, screw-in axles are rarely used today. High-quality mountain bikes and e-bikes now mostly use thru-axle systems. In this system, the wheel hub or hub motor has a hollow axle through which a thru-axle is inserted for mounting. Thru-axles provide improved stiffness, especially on suspension forks and when using disc brakes. Since the position is fixed by the thru-axle, the wheel does not need to be trued.

[0006] From CN 1 281 282 A, an auxiliary motor for electric vehicles is known in which the drive force is transmitted to the wheel smoothly and with low vibration via a special connection technology. The document describes in particular an overrunning one-way clutch that enables quiet operation when reversing. Furthermore, the document discloses that the wheel shaft through which the overspeed freewheel clutch is guided can be provided with several grooves. A heat pipe can be embedded in these grooves (see claim 8).

[0007] From CN 1 245 362 A, a wheel hub motor is known in which an electric motor is arranged directly in the wheel rim of a vehicle to increase the efficiency of power transmission and reduce assembly costs. The document further discloses that the motor shaft can be hollow, so that a heat pipe or similar heat-conducting elements can be inserted into the inner wall of the hollow shaft. Description of the invention

[0008] The object of the present invention is to improve the cooling of hub motors, in particular the internal winding of the stator and the power electronics. This allows the continuous power output of the motor to be increased and / or the temperature of the motor and the power electronics to be reduced. A lower temperature of the electric motor and the power electronics leads to an improvement in the efficiency and service life of the drive.

[0009] The problem is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are specified in the dependent claims, the description, and the accompanying figures. In particular, the independent claims of one claim category may also be further developed analogously to the dependent claims of another claim category.

[0010] The invention relates to a thru-axle for improving the cooling of a vehicle hub motor. The thru-axle has a base body. The base body has an elongated cavity. Either a heat pipe is integrated into this cavity, or the cavity itself is designed as a heat pipe. Designed as a heat pipe means that the cavity of the thru-axle itself serves as a heat pipe. The heat pipe serves to transfer heat from a central region of the thru-axle to at least one end region of the thru-axle. From this end region, the heat can then be dissipated to other components of the vehicle, for example, to the dropouts of the frame in the case of electric bicycles.

[0011] The heat pipe thus serves to improve heat conduction between the heat sources, especially the winding and the power electronics (e.g. MOSFETs) and the heat sinks, such as the dropouts of a bicycle frame.

[0012] When using a thru-axle according to the invention on an electric bicycle, heat dissipation towards the right-hand dropout (in the direction of travel) can be increased. This can be attributed, among other things, to the design of the hub motor. Furthermore, the chain or drive belt is located on the right side, while a disc brake is typically located on the left side, which introduces additional heat into the system during operation.

[0013] A heat pipe is an efficient heat transfer device that transports heat through the evaporation and condensation of a working fluid. It typically consists of a closed tube lined internally with capillary mesh and containing a liquid working fluid. At hot points within the heat pipe, the working fluid evaporates, absorbing heat. The resulting vapor travels through the tube to a cooler area, where it condenses and releases the absorbed heat. The condensed working fluid is then transported back through the capillary mesh inside the tube to the hot area, where the cycle begins again. A heat pipe is also known as a heat tube.

[0014] The term "dropout" can refer to the axle mount of a bicycle or other two-track vehicle. The rear axle mount can be part of a bicycle frame or a suspension system. It can also be a separate component that is permanently attached to the bicycle frame or suspension system (e.g., by means of a bolted connection).

[0015] The heat pipe can extend over more than 80% of the thru-axle's length to transfer heat from a central area to both ends of the axle. This allows heat to be transported from the heat source to two heat sinks (e.g., the left and right dropouts of a bicycle frame).

[0016] The main body of the thru-axle can be made of steel, or of an aluminum or titanium alloy, for example.

[0017] In one embodiment, the heat pipe can be made of copper and inserted, glued or pressed into the hollow body of the base body.

[0018] In one embodiment, the heat pipe can be made of copper and inserted, glued or pressed into the hollow body of the base body, which is made of an aluminum alloy.

[0019] In one embodiment, the heat pipe can be made of steel or aluminum or an aluminum alloy and can be inserted, glued or pressed into the hollow body of the base body.

[0020] In one embodiment, the cavity of the base body can be designed directly as a heat pipe and the base body can be made of an aluminum alloy.

[0021] The thru-axle can have a screw head at one end and an external thread at the other. The external thread might, for example, have dimensions of M12 x 1.75 mm. The screw head can have a drive type, such as a hex socket. The thru-axle could, for example, be a so-called Boost thru-axle with a 148 mm installation width for the rear wheel of an e-bike. The installation width of the thru-axle can conform to common standards, i.e., it could be designed for an installation width of 142 mm (non-Boost), 148 mm (Boost), or 157 mm (Super Boost Plus).

[0022] A hub motor according to the invention comprises a variant of a plug-in axle described above. The hub motor can be designed as an external rotor and include a stator and power electronics, with the power electronics being mounted on the stator. The hub motor can be a direct-drive motor, i.e., it does not have a gearbox.

[0023] A vehicle according to the invention comprises a variant of a hub motor as described above. The vehicle can be an electric bicycle. An electric bicycle is a bicycle with an electric auxiliary motor. The electric bicycle can also be called an e-bike or pedelec. It can also be an S-pedelec with electric assistance up to 45 km / h. The hub motor can be installed in the rear wheel of the electric bicycle.

[0024] The invention comprises the use of a variant of the above-described drive shaft to improve the cooling of a vehicle hub motor. During installation, the drive shaft can be coated with an assembly paste. This improves heat transfer between the hollow shaft of the hub motor and the drive shaft. Simultaneously, the assembly paste serves as corrosion protection. The assembly paste can also be referred to as a hot-screw compound. For example, it could be a ceramic paste. Brief character description

[0025] The inventive idea will be described in more detail below with reference to the figures. However, the following description should be considered purely exemplary. The invention is defined solely by the subject matter of the claims. Advantageous embodiments of the invention are explained below with reference to the accompanying figures. The same reference numerals are used for identical or equivalent elements. Furthermore, for the sake of readability and identifiability, reference numerals are also used for features that are not shown in the described figure. Similarly, not all reference numerals are always drawn in comparable figures if these features are already clearly identified in the preceding figures. The figures show: Fig. 1 - 4 a stub axle according to an embodiment of the present invention; Fig. 5 - 6 a hub motor with a stub axle according to an embodiment of the present invention; and Fig. 7 a vehicle with a hub motor according to an embodiment of the present invention. Detailed character description and description of the invention

[0026] Fig. Figure 1 shows a drive shaft 100 with a base body 102, a heat pipe 106, and a protective element 107. The base body 102 has a cavity 104. The heat pipe 106 is installed in the cavity 104. The drive shaft 100 has a central section 118 and end sections 112. The end sections 112 are located at the two opposite ends of the drive shaft 100, with the central section 118 in between. The end sections 112 consist of a first end section 114 and a second end section 116. The drive shaft 100 has a screw head 110 with an internal hexagon socket 111 at the first end section 114 and an external thread 108 at the second end section 116. The heat pipe 106 has a common geometry for such a component. To protect against damage from tools when tightening the stub axle 100 via the internal hexagon 111, an additional protective element 107 is located in the cavity 104.

[0027] Fig. Figure 2 shows a plug-in axle 100 with a base body 102 and a heat pipe 106. The base body 102 has a cavity 104. The heat pipe is installed in the cavity 104. The plug-in axle 100 has a middle section 118 and end sections 112. The end sections 112 consist of a first end section 114 and a second end section 116. The plug-in axle 100 has a screw head 110 with an internal hexagon socket 111 at the first end section 114 and an external thread 108 at the second end section 116. In contrast to Fig. However, in 1, the heat pipe 106 is installed in the opposite direction. This allows access to the in Fig. The protective element 107 shown in Figure 1 can be omitted, and the effective area of ​​the heat pipe 106 extends closer to the screw head 110. In this embodiment, the heat pipe 106 is also longer than the base body 102, so that the heat pipe 106 protrudes from the base body 102.

[0028] Fig. Figure 3 shows a plug-in axle 100 with a base body 102 and a heat pipe 106. The base body 102 has a cavity 104. The heat pipe 106 is installed in the cavity 104. The plug-in axle 100 has a middle section 118 and end sections 112. The end sections 112 consist of a first end section 114 and a second end section 116. The plug-in axle 100 has a screw head 110 with an internal hexagon socket 111 at the first end section 114 and an external thread 108 at the second end section 116. In contrast to Fig. 1 and Fig. 2. The heat pipe 106 is a specially shaped design. This allows for the use of the in Fig. The protective element 107 shown in Figure 1 can be omitted, and the effective area of ​​the heat pipe 106 extends closer to the screw head 110. In contrast to Fig. 2. The heat pipe 106 does not protrude from the base body 102.

[0029] Fig. Figure 4 shows a plug-in axle 100 with a base body 102 and a heat pipe 106. The base body 102 has a cavity 104. The heat pipe 106 is installed in the cavity 104. The plug-in axle 100 has a middle section 118 and end sections 112. The end sections 112 consist of a first end section 114 and a second end section 116. The plug-in axle 100 has a screw head 110 with an internal hexagon socket 111 at the first end section 114 and an external thread 108 at the second end section 116. In contrast to the Fig. 1, Fig. 2 to Fig. In this embodiment, the heat pipe 106 is not a separate component, but rather the cavity 104 of the base body 102 serves directly as the heat pipe 106. This eliminates any material doubling in the area of ​​the external thread 108, thus providing more material for the external thread 108 within the base body 102. Compared to the Fig. 1, Fig. 2 to Fig. Therefore, an external thread 108 with a larger pitch is possible.

[0030] Fig. Figure 5 shows a hub motor 200 in an installation situation on a single-track vehicle such as an electric bicycle or motorcycle. The axle 100 is the axle 100 from the embodiment shown in Figure 5. Fig. 4. The hub motor 200 has an external rotor 206 with permanent magnets 208 and a stator 202 with power electronics 204. The rotor 206 is mounted on the hollow shaft 214. The drive shaft 100 is inserted through the hollow shaft 214 and screwed into the dropout 210. The heat flow is shown by arrows. Heat is conducted from the main heat sources, stator 202 and power electronics 204, to the central section 118 of the drive shaft 100 by thermal conduction. The heat is then conducted through the heat tube 106 to both end sections 112 of the heat tube 106 by the liquid evaporating in the central section 118 and condensing in the end sections 112. From the end sections 112 of the drive shaft 100, the heat is conducted to the dropouts 210 and 212. The dropouts 210 and 212 possess a certain heat capacity and can thus serve as a heat buffer. Furthermore, the heat from dropouts 210 and 212 can be dissipated to the ambient air.

[0031] Fig. Figure 6 shows a hub motor 200 installed on a multi-track vehicle, such as a light vehicle. In this case, the connection is made on one side to a wheel carrier 216. As in Fig. Figure 5 shows the heat flow with arrows. In this application example, the heat is conducted from a central area to the first end area 114 of the axle 100 and from there into the wheel suspension 216.

[0032] Fig. Figure 7 shows a vehicle 300 with a hub motor 200. The installation situation corresponds to that in Fig. 5. Design shown for single-track vehicles. Reference symbol list 100 thru axle 102 Basic bodies 104 Cavity 106 Heat pipe 107 Protective element 108 external threads 110 screw head 112 End range 114 first end range 116 second end range 118 middle range 200 hub motor 202 Stator 204 Power Electronics 206 Rotor 208 permanent magnets 210, 212 End of breakdown 214 Hollow axle 216 bike carriers 300 vehicles

Claims

A stub axle (100) for improving the cooling of a hub motor of a vehicle, wherein a base body (102) of the stub axle (100) has a cavity (104), wherein a heat pipe (106) is installed in the cavity (104), or the cavity (104) is directly designed as a heat pipe (106) to transfer heat from a central area (118) of the stub axle (100) to at least one end area (112) of the stub axle (100). The plug-in shaft (100) according to claim 1, wherein the heat pipe (106) extends over a length of more than 80% of the length of the plug-in shaft (100) in order to transfer the heat from a central region (118) to both end regions (112) of the plug-in shaft (100). A stub axle (100) according to one of the preceding claims, wherein the cavity (104) is directly designed as a heat pipe (106) and the base body (102) is made of an aluminum alloy. A thru-axle (100) according to one of the preceding claims, wherein the thru-axle (100) has a screw head (110) at a first end region (112, 114) and an external thread (108) at a second end region (112, 116). Hub motor (200) comprising a thru-axle (100) according to one of the preceding claims. Hub motor (200) according to claim 5, wherein the hub motor (200) is designed as an external rotor, and wherein the hub motor (200) comprises a stator (202) and power electronics (204), and wherein the power electronics (204) is mounted on the stator (202). Vehicle comprising a hub motor (200) according to one of claims 5 or 6. Vehicle according to claim 7, wherein the vehicle is an electric bicycle. Use of a thru-axle (100) according to one of claims 1 to 4 for improving the cooling of a hub motor (200) of a vehicle.

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