Drive unit for a vehicle wheel

Abstract

Drive unit (3) for a vehicle wheel (1), wherein the drive unit (3) comprises an electric machine with a stator (12) and a rotor (7), a central shaft (9), at least one first wheel bearing (8) and at least one brake device, wherein the stator (12) is arranged coaxially to the central shaft (9) and is mounted on it, wherein the rotor (7) is mounted coaxially to the central shaft (9) and rotatably around the stator (12) by means of the at least first wheel bearing (8), wherein the rotor (8) has a rotor housing (21), wherein on a first section (22) of the rotor housing (21) in the circumferential direction of the rotor (7) 2p means for generating a magnetic field with alternating polarity are arranged, wherein a second section (23) of the rotor housing (21) is designed as a braking surface cooperating with the braking device, wherein the electric machine is a DC machine and the first and second sections (22, 23) of the rotor housing (21) are mechanically connected to each other by means of a third section (28), wherein the third section (28) prevents or reduces heat transfer between the second and the first section (22, 23), wherein the third section (28) is designed as a corrugated tube.

Description

[0001] The invention relates to a drive unit for a vehicle wheel, a vehicle wheel and a method for driving a vehicle wheel.

[0002] Wheel hub drives have long been known as a type of (decentralized) vehicle drive. In wheel hub drives, a drive unit that generates the mechanical driving force is essentially integrated into a vehicle wheel, particularly into the wheel rim.

[0003] DE 693 09 066 T2 discloses an electric motor / wheel unit comprising a hollow shaft with a first opening at one end and a second opening at the other, the first opening being capable of receiving supply conductors from outside the motor / wheel unit. The electric motor / wheel unit further comprises a stator coaxial with and attached to the shaft, the stator having a hollow section and windings. The electric motor / wheel unit also includes a rotor coaxial with and rotatably mounted around the stator, as well as a converter for converting an electrical input voltage and current into an electrical output voltage and current, the output current being a variable alternating current.The conversion element comprises power electronics with input terminals for receiving the electrical input current and output terminals for generating the variable alternating current, which, during operation, feeds the stator windings. Furthermore, power electronics are mounted within the hollow section. The supply conductors are connected so directly to the input terminals of the power electronics located within the hollow section that the conductors housed in the first opening of the hollow shaft can be of a relatively small diameter, even when the motor is required to generate a relatively high torque.

[0004] DE 44 04 926 A1 discloses an electric drive system for a DC-powered vehicle with a drive electric motor comprising a stator equipped with conductors and a rotor equipped with permanent magnets. The electric drive system further includes a sensor that reacts to a rotational movement of the rotor and an electronic control unit that responds to an output signal from the sensor and applies a pulsed voltage signal to the conductors. The control unit includes a speed measuring device that reacts to the sensor's output signal to generate a speed signal corresponding to the rotor's rotational speed. The control unit also includes a voltage control device that generates a voltage and winding control signal dependent on the speed signal.Furthermore, the control device has a pulse generation device that generates a pulse signal for the current conductors, the amplitude and phase angle of which is variable relative to the position of the rotor depending on the voltage and winding control signal.

[0005] With regard to a design of electrical machines, in particular external rotor machines, DE 10 2005 052 783 A1 discloses a stator for an electrical machine comprising a stator support and an outer stator part, wherein the stator support includes at least one meandering channel. A fluid can be guided in the meandering channel.

[0006] DE 10 2006 008 241 A1 discloses a generator-electric motor combination, in particular an electric transmission, with a first rotor of an input shaft and a second rotor of an output shaft, each having permanent magnets of alternating polarity mounted circumferentially. The generator-electric motor combination further comprises at least one stator, on the circumferential side of which, facing the permanent magnets, alternating slots for receiving at least one stator winding and stator teeth are formed, the circumferential tooth surfaces of which face the permanent magnets. Furthermore, during rotor rotation, the total area formed by the tooth surfaces covered by the respective permanent magnet remains essentially constant, regardless of the rotor rotation angle.

[0007] From JP H10 - 285 891 A, a drive unit for a vehicle wheel is known, wherein the drive unit comprises an electric machine with a stator and a rotor, a central shaft, at least one wheel bearing, and at least one braking device. The stator is arranged coaxially to the central shaft and mounted on it. Furthermore, the rotor is coaxially mounted to the central shaft and rotatably mounted around the stator by means of the at least first wheel bearing, the rotor having a rotor housing. On a first section of the rotor housing, two means for generating a magnetic field with alternating polarity are arranged circumferentially around the rotor, with a further section of the rotor housing being designed as a braking surface that interacts with the braking device. The electric machine is designed as a synchronous machine.The first and second sections are mechanically connected by a third section which has fins for heat dissipation due to iron losses.

[0008] From CN 1 01 312 305 A a wheel hub motor is known, wherein part of a fluid-based cooling system is arranged parallel to an outer surface of a section of the rotor housing at a predetermined distance.

[0009] The technical problem is to create a drive unit for a vehicle wheel, a vehicle wheel and a method for driving a vehicle wheel that are optimized with regard to robustness, mass, installation space requirements, design effort and performance parameters (continuous drive torques, braking torques).

[0010] The solution to the technical problem is achieved by the objects having the features of claims 1, 9 and 10. Further advantageous embodiments of the invention are set forth in the dependent claims.

[0011] A drive unit for a vehicle wheel is proposed. This drive unit comprises an electric motor with a stator and a rotor, a central shaft, at least one wheel bearing, and at least one brake device. The electric motor can be operated in either motor or generator mode. The stator is arranged coaxially with the central shaft and mounted on it. Thus, the stator is mechanically connected to the central shaft and is not rotatably mounted. Furthermore, the rotor is coaxial with the central shaft and rotatably mounted around the stator by means of the at least one wheel bearing. Coaxiality here means that a central longitudinal axis of the central shaft coincides with a central longitudinal axis of the stator and a central longitudinal axis of the rotor. The central longitudinal axis of the central shaft is simultaneously an axis of rotation of the rotor and thus of a vehicle wheel mechanically connected to the rotor.

[0012] The stator is located inside the rotor. Therefore, this electric machine can be described as an external rotor electric machine.

[0013] The rotor has a rotor housing. On a first section of the rotor housing, circumferentially arranged 2p means for generating a magnetic field with alternating polarity, these means produce a so-called rotor field. The means for generating a magnetic field can be permanent magnets, preferably rare-earth permanent magnets. Here, p denotes the number of pole pairs. The number of pole pairs should be chosen to be as high as possible. In particular, the number of pole pairs can be in the range between 10 and 20; preferably, the number of pole pairs is 15. This advantageously results in low rotor field feedback within the rotor housing. The means for generating a magnetic field preferably produce a trapezoidal rotor field with the steepest possible flanks.

[0014] The stator can have alternating slots and teeth on its outer surface facing the first section of the rotor housing. Stator windings can be arranged in these slots. When a current flows through the stator windings, they generate a magnetic field, known as the stator field. During motor operation, the current flow through the stator windings is controlled to generate a stator field that rotates relative to the central longitudinal axis. Since the stator field interacts with the rotor field, this can cause the rotor to rotate.The arrangement and design of the rotor-side means for generating a magnetic field, the arrangement and design of the stator windings, and the control of the current flow (current direction, current intensity) must be selected such that, during motor operation, the highest possible induction is achieved in the air gap between the stator and rotor at the time of current flow. In this context, a magnetic flux density driven to saturation in the rotor-side return material (rotor housing) belonging to the magnetic circuit can also be accepted.

[0015] A high number of stator winding strands is recommended. Furthermore, various types of stator windings can be selected; preferably, the stator windings are arranged in a wave configuration. This advantageously allows for a short conductor length in the so-called winding head and thus low ohmic losses. Preferably, the number of stator winding strands is 6 to 12, more preferably 8.

[0016] According to the invention, a second section of the rotor housing is designed as a braking surface that interacts with the braking device (rotor-side braking surface). The braking device can be, for example, a disc brake or a drum brake. The braking device is mechanically connected to the central shaft, either directly or indirectly, and is therefore not rotatably mounted on the central shaft. In a mechanical braking process, a stator-side braking surface, e.g., a brake shoe, is pressed against the rotor-side braking surface. The resulting frictional forces generate a braking torque. During such a braking process, the rotor's kinetic energy is converted into thermal energy.

[0017] Furthermore, it is of course possible to decelerate the rotor in generator mode of the electric machine. In this process, the rotor's kinetic energy is converted into electrical energy primarily through induction. This electrical energy can then be used, for example, to charge a storage unit (accumulator, battery), a process known as regenerative braking.

[0018] According to the invention, the electric machine is designed as a DC machine. Furthermore, the first and second sections of the rotor housing are mechanically connected to each other by means of a third section, which is designed as a corrugated tube. The third section prevents or reduces heat transfer between the second and first sections. In particular, the third section prevents or reduces heat conduction between the second and first sections. For this purpose, the third section can be made, at least partially, of a material with a predetermined, in particular low, thermal conductivity. Furthermore, the third section can have a predetermined, in particular large, outer surface area by means of which heat can be transferred to a flowing fluid, in particular air, via thermal convection. The third section can also be made of a material with a predetermined, in particular high, emissivity, e.g.,It must have an emissivity greater than 0.5. This allows heat dissipation from the third section to occur via thermal radiation.

[0019] The drive unit according to the invention thus enables a compact arrangement of a braking device and a DC motor in external rotor design, whereby heat transfer between the thermal energy generated in a mechanical braking process and the rotor-side means for generating a magnetic field is prevented or reduced. Since properties, especially of permanent magnets, are strongly temperature-dependent, this advantageously avoids or reduces changes in the properties of the rotor field (field strength, pattern) due to heat transfer, which would negatively affect the operation of the drive unit.

[0020] In this design, a rim, in particular a wheel flange, a wheel ring, or an outer ring of the rim, can be attached to the rotor housing. The rim is mechanically coupled to the rotor via this connection.

[0021] In a further embodiment, the stator has sections for fluid-based cooling. In particular, the stator can have elements for cooling with cooling water or a cooling liquid. These can, for example, be designed as cooling channels. As described in DE 10 2005 052 783 A1, the stator can, for example, have an outer stator part, wherein the aforementioned grooves and stator teeth are formed on an outer surface of the outer stator part. Furthermore, the stator can have a so-called stator carrier, wherein the stator carrier is arranged within the outer stator part. Cooling channels can be formed within the stator carrier. Preferably, the cooling channels are designed as meandering cooling channels. For example, the stator carrier can be formed from an outer stator carrier part and an inner stator carrier part, which are welded together by means of a weld.Here, the meandering cooling channels can be formed by meandering grooves on the inside of the outer stator support part, with each meandering groove being covered by the outside of the inner stator support part. The other embodiments of a stator disclosed in DE 10 2005 052 783 A1 can also be part of the invention. Sections for fluid-based cooling advantageously enable a higher cooling capacity of the stator and, as described below, also of the rotor. Such improved cooling allows, in particular, the cooling of a lamination or laminations and the stator windings. This makes a higher field strength of the stator field achievable, thereby increasing the maximum driving torque or braking torque.

[0022] In a further embodiment, at least a portion of an outer surface of the fluid-based cooling section is arranged parallel to an outer surface of the second section of the rotor housing at a predetermined distance from it. If, for example, the stator-side portion of an outer surface of the fluid-based cooling section has a (partially) circular profile with a first radius in a cross-section perpendicular to the central longitudinal axis, then an outer surface of the rotor-side second section of the rotor housing can have a (partially) circular profile with a second radius in the same cross-section, the second radius being larger than the first radius by the predetermined distance. Alternatively and / or additionally, a portion of an outer surface of the fluid-based cooling section can be arranged in a plane perpendicular to the central longitudinal axis.Here, a rotor-side outer surface of the second section of the rotor housing can be arranged in a plane perpendicular to the central longitudinal axis, with the planes spaced apart from each other at a predetermined distance. Of course, other arrangements of the stator-side portion of an outer surface of the fluid-based cooling section and the rotor-side portion of an outer surface of the second section of the rotor housing are also possible, provided that rotation of the rotor is ensured. The predetermined distance should be chosen to be as small as possible, but it must allow safe rotation of the rotor around the stator. This advantageously enables cooling of the second section by means of the fluid-based cooling elements, while preventing the transport of fluids by, for example, the stator.The heat energy generated during braking is transferred via thermal radiation from the second section to the fluid-based cooling element. To improve this heat transfer, for example, part of the outer surface of the rotor-side second section of the rotor housing can be made of a material with a high emissivity, such as an emissivity greater than 0.5. For instance, the outer surface can be painted black or anodized black. This advantageously results in improved cooling of the second section of the rotor housing and thus improved dissipation of braking heat, as well as a further reduction in the heating of the magnetic field generation elements, which are also attached to the rotor housing.

[0023] In a further embodiment, the rotor is additionally rotatably mounted around the stator by means of a second wheel bearing, the second wheel bearing being arranged offset from the first wheel bearing along a central axis of the central shaft. This advantageously achieves improved mechanical support of the rotor on the central shaft. Simultaneously, the mounting with an additional, second wheel bearing reduces the rotor's tilting play. This allows for a smaller air gap between the stator and rotor compared to a mounting with only one wheel bearing. A reduced air gap results in higher performance of the wheel hub drive, particularly higher drive and braking torque.In this invention, a sealing means, in particular a sealing ring, can be arranged adjacent to the second wheel bearing on the central shaft to seal an interior enclosed by the rotor housing. The sealing ring can be centered by the second, additional wheel bearing. According to the invention, the second wheel bearing is arranged offset from the first wheel bearing along the central longitudinal axis. For example, the first wheel bearing can be located on the outer side of the wheel and the second wheel bearing on the inner side of the wheel on the central shaft. This advantageously allows a rotor housing to enclose an interior space located between the first and second wheel bearings, effectively protecting it from, for example, moisture and dirt.

[0024] In a further embodiment, the central shaft is designed as a hollow shaft, wherein the hollow shaft comprises means for supplying a cooling fluid and / or means for supplying electrical conductors. This advantageously results in the supply of utilities, in particular, for example, a cooling fluid and / or electrical energy, to the drive unit according to the invention being effected through the central hollow shaft and thus being better protected against external influences.

[0025] In a further embodiment, an outer surface of the stator facing the first section of the rotor housing has alternating slots and stator teeth, wherein the total area formed by the tooth surfaces covered by the respective means for generating a magnetic field remains constant regardless of the rotor rotation angle or changes only by a predetermined amount. The predetermined amount is to be chosen to be small, in particular less than 5% of a maximum total area. This advantageously reduces cogging torques during operation of the drive unit, whereby cogging torques arise when, during rotation of the rotor, the sum of the stator teeth superimposed on or influenced by the respective rotor field does not remain constant but varies.

[0026] In another embodiment, the width of the means for generating a magnetic field in the circumferential direction of the rotor is one or more times the sum of the slot width and the tooth width. Alternatively or cumulatively, the magnetic spacing between the means for generating a magnetic field adjacent in the circumferential direction of the rotor is one or more times the sum of the slot width and the tooth width. Preferably, the magnetic spacing is simply the sum of the slot width and the tooth width. More preferably, the magnetic spacing is chosen to be smaller than the width of the means for generating a magnetic field; for example, the width of the means for generating a magnetic field can be four times the sum of the slot width and the tooth width. A minimal magnetic spacing advantageously results in the steepest possible transition between alternating polarities of the rotor field.This allows for the advantageous generation of an approximately rectangular, i.e., ideal, rotor field.

[0027] Reference is expressly made here to DE 10 2006 008 241 A1, the content of which is also to be part of this disclosure.

[0028] It should be taken into account that the highest possible moment can be achieved by using the largest possible width of the means for generating a magnetic field perpendicular to the circumferential direction, i.e., in the direction of the central longitudinal axis. For this purpose, the winding head should be dimensioned as small as possible.

[0029] A large air gap diameter, i.e., the diameter of the circular cross-section of the surface facing the central longitudinal axis of the means for generating a magnetic field, also serves to achieve the highest possible torque. This requires a thin rotor wall.

[0030] In a further embodiment, the stator forms a cavity in which elements for controlling and / or supplying power to the DC machine are arranged. This cavity can also be part of an interior space of the rotor enclosed by the rotor housing. This advantageously protects the control and / or power supply elements from external influences, particularly from contamination or moisture. Power supply elements include, for example, a DC / DC converter. Control elements include, for example, a control unit. Power supply elements can also include elements for commutation of the existing windings. Furthermore, the drive unit can include at least one means for sensing the rotor field, in particular for detecting the field strength and / or polarity of the rotor field.Preferably, such a means for sensing the rotor field is arranged in each slot of the stator. This allows, for example, the control element to determine whether a north or south pole of the rotor-side means for generating a magnetic field is present at any given time. Depending on the desired direction of rotation of the rotor, the control element can, for example, switch the commutation electronics assigned to the respective strand, such as an H-bridge, to conduct or non-conduct. For example, the control element can switch the commutation element assigned to a strand to non-conduct if the means for generating a magnetic field located above the respective strand moves out of a region above a stator tooth due to rotation.Subsequently, for example, the element associated with the next strand, which is located in the next slot, can be switched to conduction for commutation. In this process, energy I stored in the inductance when a strand is switched to non-conduction can be released. 2The current x L / 2 can be directed both into another, currently conducting, strand and into a capacitor. The switch-on time (the point at which the current is switched on) and the switch-off time (the point at which the current is switched off) determine the current profile in the respective strand. A rectangular or trapezoidal profile is desirable, preferably adapted to the profile of the rotor field. By controlling the current profile in the respective strands in this way using the control element, a high torque density can advantageously be achieved, which is not possible, for example, with sinusoidal fields and / or currents.

[0031] Speed ​​and torque are controlled, as in a conventional DC motor, by preselecting the voltage and current. If, as is typical for electric vehicles, energy is drawn from a traction battery, the drive unit can include a DC / DC converter that converts the output voltage of the traction battery to a desired voltage for the drive unit. A separate DC / DC converter can be used for each wheel driven by a drive unit according to the invention. This advantageously results in maximum flexibility for generating driving dynamics effects for a vehicle driven by multiple drive units. However, it is also conceivable to provide only one DC / DC converter for a vehicle driven by multiple drive units according to the invention.Furthermore, it is possible to assign a DC converter to each group of drive units, for example a DC converter for the front wheels and a DC converter for the rear wheels.

[0032] The invention is explained in more detail using an exemplary embodiment. The figures show: Fig. 1 a cross-section of a wheel according to the invention, Fig. 2 a first perspective view of the in Fig. 1 wheel shown, Fig. 3 a second perspective view of the in Fig. 1 wheel shown, Fig. 4 a third perspective view of the in Fig. 1 of the depicted wheel 1 without rotor, Fig. 5 a perspective view of a rotor, Fig. 6 a perspective view of a stator and Fig. 7 a schematic block diagram of a control system for the wheel hub drive according to the invention.

[0033] In the following, identical reference symbols denote elements with the same or similar technical properties.

[0034] In Fig. Figure 1 shows a cross-section of a wheel 1 according to the invention. The wheel 1 is shown without a tire. The wheel 1 consists of a rim 2 and a drive unit 3 arranged within the wheel 1. The rim 2 has a rim hub 4, a rim flange (not shown), and an outer ring (also not shown). The drive unit 3 is arranged in a hollow or interior space enclosed by the outer ring. The rim 2 is rigidly mechanically coupled to a rotor 7 of the drive unit 3. The rotor 7 is rotatably mounted on a central shaft 9 by means of a first ball bearing 8. The first ball bearing 8 is located on the outside of the wheel on the central shaft 9. The central shaft 9 serves to attach the wheel 1, for example, to a wheel suspension of a vehicle (not shown). A central longitudinal axis 10 forms a central axis of rotation for the wheel 1 and the rotor 7.The drive unit 3 is rotationally symmetrical about the central longitudinal axis 10, with a center of gravity located on the central longitudinal axis 10. On the inside of the wheel, the central shaft 9 has a . Fig. The two illustrated openings 45 of fluid lines (not shown) are present; their function is explained in more detail below. The central shaft 9 also has openings or connections 11 on an inner side of the wheel 1 for power supply lines. This allows the drive unit to be supplied with energy.

[0035] A stator 12 is mechanically rigidly arranged on the central shaft 9. The stator 12 includes a stator support 13. Furthermore, the stator has meandering cooling channels 14, which are arranged as close as possible to a stator winding 15. The stator 12 also includes the stator winding 15 and in Fig. 4 stator teeth 16 shown, wherein the stator winding 15 is in a slot 46 (see Fig. 4) is arranged between the stator teeth 16. The fluid lines serve to supply and discharge fluid to the cooling channels 14. For this purpose, the fluid lines can, for example, have an L-shaped configuration. A first leg of the L-shaped configuration runs, for example, parallel to the central longitudinal axis 10, with this first leg also having the opening (not shown) towards the inside of the wheel 1. A second leg of the L-shaped fluid channel runs perpendicular to the central longitudinal axis 10 within the stator carrier 13 from the central shaft 9 towards the cooling channels 14.

[0036] The first ball bearing 8 has an inner ring 19 fixedly mounted on the central shaft and an outer ring 20 with a T-shaped cross-section. The outer ring has a crossbar parallel to the central longitudinal axis 10 and a base perpendicular to the central longitudinal axis 10. The rotor 7 is rigidly attached to a surface on the outer side of the base of the outer ring 20.

[0037] The stator 12, together with the outer ring 20 and the rotor 7, forms a cavity 17 which is, for example, sealed against moisture or dirt. Within this cavity 17, elements 18 for control, such as control units, and elements 18 for the power supply of the DC machine, such as DC-DC converters, are arranged, as shown schematically. These are mechanically fixed to the stator 12, for example, to the stator support 13.

[0038] Channels 57 are also shown, through which lines for power supply, introduced through openings or connections 11 into the stator 12, e.g. to Fig. The 3 elements shown can be used for control and energy supply.

[0039] The rotor 7 consists of a rotor housing 21, which in turn comprises a first section 22 and a second section 23. The first section 22 is essentially L-shaped, with a leg 24 located on the outside of the wheel extending essentially perpendicular to the central longitudinal axis 10. A leg 25 on the circumference of the wheel of the first section 22 extends parallel to the central longitudinal axis 10 and is spaced from it at a predetermined distance. The leg 25 on the circumference has permanent magnets 26 arranged on its inner surface. A surface of the permanent magnets 26 faces the stator windings 15 and stator teeth 16 and is separated from them by an air gap 27.The rotor field generated by the permanent magnets 26 and the stator field generated by the stator windings 15 interact through the air gap 27. At the inner end of the wheel-circumferential leg 25, the rotor housing has a third section 28, which connects the first section 22 and the second section 23. This third section 28 is designed as a corrugated tube and has an S-shaped cross-section. Fig. Figure 1 shows that the third section is formed as a single unit with the first section 22 and is mechanically connected to the second section 23 by means of a screw 29. Of course, it is also conceivable that the third section 28 could be formed as a separate component from the first and second sections 22, 23.

[0040] The second section 23 of the rotor housing 21 has a cross-section comprising a first L-shaped section and a second L-shaped section connected to it. A first leg 30 of the first section extends perpendicular to the central longitudinal axis 10, with a wheel-circumferential end of the first leg being mechanically connected to a wheel-inside end of the third section by means of the screw 29. A second leg 31 of the first section adjoins an end opposite the wheel-circumferential end of the first leg and extends parallel to the central longitudinal axis 10 from a wheel-inside 32 to a wheel-outside 33. A first leg 34 of the second section adjoins an end of the second leg 31 of the first section facing the wheel-outside and extends perpendicularly to the central longitudinal axis 10.To this first leg 34 a second leg 35 of the second part is attached, which runs parallel to the central longitudinal axis 10 towards the inside of the wheel 32.

[0041] Here, the second leg 35 is fixedly connected to an outer ring 40 of a second ball bearing 41. An inner ring 42 of the second ball bearing 41 is fixedly arranged on the central shaft 9, the second ball bearing 41 being spaced a predetermined distance along the central longitudinal axis 10 from a wheel outer side 33 to a wheel inner side 32 from the first ball bearing 8. It is shown that a sealing ring 43 is arranged adjacent to the second ball bearing 41 on the central shaft 9, the sealing ring 43 sealing an interior enclosed by the first ball bearing 8, the first, second, and third sections 21, 28, 23, and the second ball bearing 41, tightly against moisture and dirt. The stator 12 is arranged in this interior.

[0042] A wheel cover 37 is arranged on the inside of the wheel, which is mechanically rigidly connected to the central shaft 9, thus preventing rotation. The second leg 31 of the first part of the second section 23, the first leg 34 and the second leg 35 of the second part of the second section 23, and the wheel cover 37 enclose a cavity 38. A drum brake 39 is arranged in this cavity 38. The drum brake 39 has a brake shoe (not shown) which, during braking, is pressed against a surface of the second leg 31 of the first part of the second section 23 facing the central shaft 9.

[0043] The third section 28, the corrugated tube, prevents heat transfer from the thermal energy generated by braking in the second section 23 to the first section 21. For this purpose, the third section 28 is made of a material with low thermal conductivity. Due to its S-shaped profile, the third section 28 also has a large surface area for dissipating thermal energy via convection. In this process, the third section 28 releases a large portion of the thermal energy to the air.

[0044] The third section, however, not only serves to prevent heat transfer, but must also transmit a force or moment from the first section 22 to the second section 23 (drive) or from the second section 23 to the first section (brakes). Designing the third section 28 as a corrugated tube with an S-shaped cross-section advantageously enables a reliable mechanical coupling between the first and second sections 22, 23, and thus a reliable transmission of the desired forces / moments.

[0045] Furthermore, an outer surface of a part of the stator carrier 13, which has the meandering cooling channels 14, is arranged parallel to a part of the wheel-circumferential surface of the second leg 31 of the first part of the second section 23 and spaced at a predetermined distance from the wheel-circumferential surface. The outer surface(s) run parallel to the central longitudinal axis 9.

[0046] An outer surface of another stator part 44 of the stator 13, which is thermally coupled to the part of the stator carrier 13 having the meandering cooling channels 14, is also arranged parallel to a surface of the first leg 30 of the first part of the second section 23 facing the outer side 33 of the wheel and spaced at a predetermined distance from the surface of the first leg 30 facing the outer side 33 of the wheel. The outer surface is perpendicular to the parallel longitudinal axis 9.

[0047] The predetermined distances must allow the rotor 7 to rotate safely around the stator 3, but should be chosen to be as small as possible.

[0048] Due to the small distances, heat convection can occur from the second section 23 to sections of the stator 3 that are cooled directly via the cooling channels or by means of thermal coupling. This enables improved cooling and dissipation of heat energy resulting from braking energy.

[0049] In Fig. 2 is a first perspective view of the in Fig. Figure 1 shows the wheel 1. In particular, the openings 45 of the central shaft 9 for fluid lines on an inner wheel side 32 are shown. For the sake of clarity, only the stator 3, the rotor 7, the first section 22, the second section 23, the third section 28, the screw 29, the inner wheel side 32, the outer wheel side 33, and the wheel cover 37 are labelled with reference numerals.

[0050] In Fig. 3 is a second perspective view of the in Fig. Figure 1 shows the wheel 1. In particular, the rim hub 4 and the control and power supply elements 18 are shown. For the sake of clarity, only the stator 3, the rotor 7, the rotor housing 21, the first section 22, the second section 23, the third section 28, the screw 29, the inner wheel surface 32, the outer wheel surface 33, and the wheel cover 37 are labelled with reference numerals.

[0051] In Fig. 4 is a third perspective view of the in Fig. Figure 1 shows the wheel 1 without the rotor. The stator teeth 16 and the grooves 46 formed between the stator teeth 16 are shown in particular. For the sake of clarity, only the stator 3, the central shaft 9, and the outer ring 20 of the first ball bearing 8 are shown (see Figure 1). Fig. 1), the elements 18 for control and energy supply, the inner wheel side 32 and the outer wheel side 33 are designated with reference numerals.

[0052] The in Fig. 1 to Fig. Figure 4 shows that all elements of the wheel hub drive according to the invention can be arranged as compactly as possible within a cavity enclosed by the rotor housing 21 and the wheel cover 37. In particular, the wheel hub drive has no elements protruding from this cavity that could, for example, collide with a curb when parking.

[0053] Fig. Figure 5 shows a perspective view of a rotor 7. A rotor housing 21 is shown with a first section 22 and a third section 28. The second section 23, which is e.g. in Fig. As shown in 1, is in Fig. Figure 5 is not shown. Permanent magnets 26 are shown. The permanent magnets have a width B1 in the circumferential direction of the rotor 7, which is a multiple of the sum of a slot width and a tooth width in the circumferential direction. Furthermore, a distance A1 between the permanent magnets 26 adjacent to each other in the circumferential direction of the rotor 7 is simply the sum of the slot width and the tooth width. A width B2 of the permanent magnets 26 perpendicular to the circumferential direction of the rotor 7 is also shown.

[0054] Fig. Figure 6 shows a perspective view of a stator 12. In particular, a stator support 12, a stator winding 15, meandering cooling channels 14, an outer wheel surface 33, an inner wheel surface 32, and channels 57 are shown. It is shown that only the stator support 13 has the meandering cooling channels 14. However, a further cooling channel 59 is formed by the stator support 13 and a stator section 58 arranged between the stator support 13 and the stator windings 15. This cooling channel 58 is formed at an inner wheel-side end of the stator support 13 and the stator section 58.

[0055] Fig. Figure 7 shows a schematic block diagram of a control circuit for the wheel hub drive according to the invention. Two so-called H-circuits 47 are shown, each leg of which consists of two MOSFETs 48 connected in series, with freewheeling diodes 49 connected in parallel to the MOSFETs 48. The connecting part of the two legs is connected between the MOSFETs 48 and forms a phase 50 of the stator winding 15 (see Figure 7). Fig.1) A wheel-side computing unit 51 controls a wheel-side DC-DC converter 52. This converter transforms an output voltage from a vehicle battery 53, which is located on the vehicle side, into an intermediate circuit voltage applied to an intermediate circuit capacitor 54. A commutation computer 56 evaluates output signals from a Hall sensor 55, which detects the strength and direction of a rotor field above the respective strand 50. Depending on these output signals, the commutation computer 56 controls the MOSFET 48, thereby controlling the current flow through the strands 50. Only one Hall sensor 55 is shown here. From a rotational speed, which is detected, for example, by a speed sensor (not shown), and the geometry of the rotor and stator, the time period in which the rotor field detected by the Hall sensor moves across the subsequent strand 50 can be calculated.Thus, depending on this information, a current flow through the strand 50 not equipped with a Hall sensor 55 can be controlled. Reference symbol list 1 wheel 2 rim 3 Drive unit 4 rim hub 7 Rotor 8 first ball bearing 9 central wave 10 central longitudinal axis 11 connections 12 Stator 13 Stator carriers 14 cooling channels 15 Stator winding 16 stator teeth 17 Cavity 18 elements for control and power supply 19 inner ring 20 outer ring 21 Rotor housings 22 first section 23 second section 24 thighs 25 thighs 26 permanent magnets 27 air gap 28 third section 29 screw 30 first thigh 31 second thigh 32 inner wheel 33 Wheel outer side 34 first thigh 35 second thigh 37 Wheel cover 38 Cavity 39 Drum brake 40 outer ring 41 second ball bearing 42 inner ring 43 Sealing ring 44 additional stator part 45 openings 46 Nut 47 H-circuit 48 MOSFET 49 Freewheeling diode 50 strands 51 computing unit 52 DC converters 53 Vehicle battery 54 Intermediate circuit capacitor 55 Hall sensor 56 Commutation calculators 57 channels 58 Stator part 59 Cooling channel B1 width B2 width A1 distance

Claims

[1] Drive unit (3) for a vehicle wheel (1), wherein the drive unit (3) comprises an electric machine with a stator (12) and a rotor (7), a central shaft (9), at least one first wheel bearing (8) and at least one brake device, wherein the stator (12) is arranged coaxially to the central shaft (9) and is mounted on it, wherein the rotor (7) is mounted coaxially to the central shaft (9) and rotatably around the stator (12) by means of the at least first wheel bearing (8), wherein the rotor (8) has a rotor housing (21), wherein on a first section (22) of the rotor housing (21) in the circumferential direction of the rotor (7) 2p means for generating a magnetic field with alternating polarity are arranged, wherein a second section (23) of the rotor housing (21) is designed as a braking surface cooperating with the braking device, wherein the electric machine is a DC machine and the first and second sections (22, 23) of the rotor housing (21) are mechanically connected to each other by means of a third section (28), wherein the third section (28) prevents or reduces heat transfer between the second and the first section (22, 23), wherein the third section (28) is designed as a corrugated tube. [2] Drive unit (3) according to claim 1, characterized by , that the stator (12) has sections for fluid-based cooling. [3] Drive unit (3) according to claim 2, characterized by , that at least part of an outer surface of the section for fluid-based cooling is arranged parallel to an outer surface of the second section (23) of the rotor housing (21) at a predetermined distance. [4] Drive unit (3) according to any one of the preceding claims, characterized by , that the rotor (7) is additionally mounted rotatably about the stator (12) by means of a second wheel bearing (41), wherein the second wheel bearing (41) is arranged offset to the first wheel bearing (8) along a central longitudinal axis (10) of the central shaft (9). [5] Drive unit (3) according to any one of the preceding claims, characterized by , that the central shaft (9) is designed as a hollow shaft, wherein the hollow shaft comprises means for supplying a cooling fluid and / or means for supplying electrical conductors. [6] Drive unit (3) according to any of the preceding claims, characterized by, that an outer surface of the stator (12) facing the first section (22) of the rotor housing (21) has alternating slots (46) and stator teeth (16), wherein a total area formed by the tooth surfaces covered by the respective means for generating a magnetic field remains constant regardless of a rotor rotation angle or changes only by a predetermined amount. [7] Drive unit (3) according to claim 6, characterized by , that the width of the means for generating a magnetic field in the circumferential direction of the rotor (7) is one or more times the sum of a slot width and a tooth width in the circumferential direction and / or the magnetic distance between the means for generating a magnetic field adjacent in the circumferential direction of the rotor (7) is one or more times the sum of the slot width and the tooth width. [8] Drive unit (3) according to any of the preceding claims, characterized by, that the stator (12) forms a cavity (17) and in this cavity (17) elements (18) for controlling and / or supplying power to the DC machine are arranged. [9] vehicle wheel (1) wherein the vehicle wheel (1) comprises at least one rim (2), characterized by , that a drive unit (3) according to one of claims 1 to 8 is arranged completely within the rim interior, wherein the rotor (7) of the DC machine is mechanically connected to the rim (2). [10] Method for driving a vehicle wheel (1) by means of a drive unit (3) according to any one of claims 1 to 8, characterized by , that a control unit controls the DC machine, wherein the rotor (7) of the DC machine is mechanically connected to a rim (2) of the vehicle wheel (1).

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