WO2026019449A1

WO2026019449A1 - A stator with an integrated drive circuit for an axial flux brushless dc motor

Info

Publication number: WO2026019449A1
Application number: PCT/US2025/012509
Authority: WO
Inventors: David Michael Hugh Matthews
Original assignee: Power Integrations Inc
Current assignee: Power Integrations Inc
Priority date: 2024-07-17
Filing date: 2025-01-22
Publication date: 2026-01-22
Anticipated expiration: 2027-01-17

Abstract

Examples of a stator for an axial flux motor, and axial flux motors, are described that integrate a drive circuit on the same physical substrate as the motor windings. The stator comprises a multilayer PCB substrate including one or more conductive coils proximate to an outer edge and spaced apart from an inner opening of the substrate. A drive circuit is coupled to the conductive coils and located on at least one surface of the substrate proximate to the inner opening. The drive circuit comprises at least one half-bridge module and an input smoothing capacitance. The stator may be mounted within a housing proximate to a rotor comprising a rotor shaft coupled to a rotor frame, wherein one or more permanent magnets are coupled to the rotor frame and wherein the rotor is mounted such that it is free to rotate about a central axis of the rotor shaft.

Description

A STATOR WITH AN INTEGRATED DRIVE CIRCUIT FOR AN AXIAL FLUX

BRUSHLESS DC MOTOR

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63/672,583, filed July 17, 2024, which is incorporated by reference in its entirety.

BACKGROUND

Field of the Disclosure

[0002] The present disclosure relates generally to electric motors and motor drivers and, more specifically, to stator assemblies with integrated motor drive circuits, for use in axial flux, brushless DC (BLDC) motors.

Discussion of the Related Art

[0003] Household and industrial appliances such as ventilation fans, cooling systems, refrigerators, dishwasher, washer/dryer machines, and many other products typically utilize electric motors that transfer energy from an electrical source to a mechanical load. BLDC motors, which are known for their higher reliability and efficiency, are becoming a popular choice in the market, replacing brushed DC and AC motors.

[0004] Electrical energy for driving the electric motor is provided through a drive system, which draws electrical energy from an electrical source (e.g., from an AC low frequency source). The electrical energy received from the electrical source is processed through a power converter, referred to as an inverter or drive circuit, and converted to a desired form of electrical energy that is supplied to the motor to achieve the desired mechanical output. The desired mechanical output of the motor may be, for example, the speed of the motor, the torque, or the position of a motor shaft.

[0005] A BLDC motor typically includes a stator, which includes windings of wire receiving signals from the drive circuit, and a rotor that houses permanent magnets. Varying electrical signals in the stator windings generate magnetic fields that may interact with the permanent magnets, inducing rotational motion of the rotor, to achieve the desired mechanical output.

[0006] One form of BLDC motor is an axial flux motor. An axial flux motor typically includes a planar stator that is fixed in place, a rotatably mounted rotor including permanent magnets mounted thereon and a drive circuit. In an axial flux motor, the stator and rotor are arranged such that the gap between the rotor and stator, and therefore the direction of magnetic flux between the two, is aligned parallel with the axis of rotation. SUMMARY OF THE DISCLOSURE

[0007] The present disclosure provides examples of a stator for use in an axial flux motor, and axial flux motors, that integrate a complete drive circuit on the same physical substrate as the motor windings.

[0008] In traditional motors, the windings are positioned very close to the motor laminations (which form a good magnetic path for magnetic flux in the motor) and therefore are very well capacitively coupled to the body of the motor. This means that, when the power switches in the drive circuit switch ON and OFF, they create large capacitive currents through the body of the motor which creates electromagnetic interference (“EMI”). Furthermore, because of the physical arrangement of the stator and the size of traditional drive circuit components, the drive circuit of the motor is usually either positioned completely outside the motor housing or in an added portion to the motor housing away from the main motor windings. The length of the conductors from the drive circuit power switches to the motor windings is therefore long and can be a source of radiated electrical noise and conducted electrical noise during switching of the power switches.

[0009] To limit the EMI generated and limit the size and cost of EMI filtering components, it is therefore typical to slow down the turn ON and OFF of the power switches (often also referred to as slew rate control of the switches) of the drive circuit. This reduced switching speed of the power switches in the drive circuit, however, adds switching losses to those switches, reducing the system efficiency.

[0010] In the disclosed examples, the stator is constructed of a multi-layer printed circuit board (“PCB”) referred to herein as a substrate. The disclosed examples may be described as planar axial motors with air cored stators. The stator windings (in this case the multi-layer PCB windings) are not wound around ferromagnetic material which would normally be the case in a traditional motor. Therefore, the stator windings may be considered to be wound around an air core within the stator.

[0011] In the disclosed examples, the stator windings are arranged substantially around the periphery of the substrate, while the drive circuit components are arranged substantially toward the center axis of the substrate. In the disclosed examples, the close proximity of the drive circuit to the motor windings on the same substrate reduces the length of the conductors from the drive circuit to the motor windings to a practical minimum, thus reducing their capacity to create radiated and conducted noise during switching. In addition, the windings are not wound on laminations and, as with other air cored designs, are therefore naturally poorly capacitively coupled to the motor housing. [0012] Both the poor capacitive coupling from motor winding to the motor housing and the very short conductor connections between the drive circuit and the motor windings, mean that the switches in the drive circuit can be driven at higher speeds than with typical BLDC motors, but with minimal impact on the EMI generated and with the advantage of reducing switching losses in the switches, enhancing motor efficiency.

[0013] Further, combining the drive circuit components on the same substrate as the motor windings provides significant design flexibility and enables more compact motor assemblies. Further combining the drive circuity components on the same substrate as the motor windings also saves an additional PCB which would normally be necessary along with the means to provide connections between those PCBs such a cables and connectors both of which compromise reliability and take space.

[0014] The fact that the winding is air cored as described above (the windings are not wound around a ferromagnetic material) means that the rotor magnets are faced with a magnetic circuit that is constant regardless of the rotor position. As such the rotor will rotate very smoothly. In motors where the windings are wound around ferromagnetic material, the magnets have preferred positions where they align with the ferromagnetic materials around which the windings are wound. This creates a ripple torque as the rotor rotates (often referred to as cogging torque). This ripple torque can lead to acoustic noise during motor operation. The fact that the motor described in this disclosure is air cored results in substantially zero cogging torque and therefore lower acoustic noise during operation which can be an advantage in applications where acceptable acoustic noise is limited.

[0015] Finally, having the drive components so close to the motor internal structure provides the benefit that the rotation of the motor rotor (that has the permanent magnets mounted on it), will naturally generate localized air circulation that will provide a very efficient way to cool the drive circuit components without needing expensive and bulky heatsinks. The magnets can also be arranged with small gaps between them to enhance this effect.

BRIEF DESCRIPTION OF DRAWINGS

[0016] Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. Corresponding reference characters indicate corresponding components throughout the several views of the figures. [0017] FIG. 1 illustrates an example implementation of system level blocks for a multiphase motor drive system and motor windings according to the teachings of the present disclosure.

[0018] FIGs. 2a, 2b, 2c and 2d illustrate plan views of an example configuration for motor windings arranged on multiple layers of a substrate according to the teachings of the present disclosure.

[0019] FIGs. 3a and 3b illustrate plan views of an example arrangement of the components of an example drive circuit on one surface of a multilayer substrate according to the teachings of the present disclosure.

[0020] FIG. 4 illustrates a plan view of an example configuration for a portion of a rotor assembly according to the teachings of the present disclosure.

[0021] FIGs. 5a, 5b and 5c illustrate sectional views of an example configuration for an axial flux motor according to the teachings of the present disclosure.

[0022] FIG. 6 illustrates a sectional view of another example configuration for an axial flux motor according to the teachings of the present disclosure.

[0023] FIG. 7 illustrates a sectional view of yet another example configuration for an axial flux motor according to the teachings of the present disclosure.

DETAILED DESCRIPTION

[0024] FIG. 1 illustrates an example implementation of a multiphase motor drive system and motor windings according to the teachings of the present disclosure.

[0025] The example implementation of FIG. 1 includes three half-bridge inverter modules (110, 120, 130) coupled individually to a high voltage (HV) bus 102 and controlled with a single system controller 150 to drive a multiphase motor, such as for example, a 3 -phase motor 190. Half-bridge inverter modules 110, 120 and 130 may be implemented using commercially available integrated circuit devices, such as the BridgeSwitch™ series of products from Power Integrations, Inc.

[0026] Power to the HV bus 102 is provided from a power source external to the illustrated motor drive system. In an example implementation, as illustrated below, this power may be provided though wires or cables coupled between the components of the drive circuit 100 and the external power source. It will be appreciated that although the example of FIG. 1 shows a 3-phase drive circuit, other configurations implementing other types of drive circuits, for example, a single phase, 2-phase, 4-phase or others, may be implemented according to the teachings of the present disclosure. It will also be appreciated that even though, in the example FIG. 1, the system controller is depicted as a microcontroller pC 150, other options such as a digital signal processor (DSP) controller, or microprocessor, may be applicable in different applications in accordance with the teachings of the present disclosure.

[0027] As shown in FIG. 1, each switching block 115 of each half-bridge inverter module includes a high side (HS) switch in series with a low side (LS) switch, which are coupled between HV bus 102 and ground 101. In general, the high side switch refers to the switch coupled to the HV bus 102 while the low side switch refers to the switch coupled to ground 101. The mid-point terminals, HB1 116 in half-bridge inverter module 110, HB2 in half-bridge inverter module 120, and HB3 in half-bridge inverter module 130, are coupled between the respective high side switch and low side switch of each half-bridge inverter module 110, 120, and 130, and are coupled to generate controlled AC voltages that are coupled to the respective phase terminals A 161, B 162 and C 163 of the multiphase motor 190.

[0028] As shown in FIG. 1, multiphase motor 190 is represented as including motor windings 171, 172 and 173, coupled to phase terminals 161 A, 162 B and 163 C, respectively. Motor windings 171, 172 and 173 are also all coupled together to a node 164 that provides a path to the common return node 101. Motor windings 171, 172, and 173, will be discussed in more detail below in the context of FIGs. 2a-2d.

[0029] Low side and high side control blocks 111 and 112 in half-bridge inverter module 110, control the corresponding LS and HS switches. Substantially similar low side and hide side control blocks are included in half-bridge inverter module 120 and 130, which control their corresponding LS and HS switches. Low side control blocks 111 may communicate with their corresponding high side control blocks 112 to share control and status information. Control signals 114, 124, and 134, which are coupled to half-bridge inverter modules 110, 120 and 130, respectively, communicate the feedback and function information with controller, pC 150. For example, controller pC 150 may provide on/off signals to the half-bridge inverter modules and may receive phase current information from them. Fault terminals on half-bridge inverter modules 110, 120 and 130, respectively, communicate fault and status report information through a single-wire fault bus 140 to the system controller, pC 150. Fault information may include, for example, the existence of over-voltage or over-current fault conditions. It will be appreciated that fault communication between the system controller pC 150 and the half-bridge inverter modules may be implemented in other ways consistent with the teaching of the present disclosure. It will also be appreciated that there may be additional terminals on each halfbridge inverter module to implement additional functionality. [0030] Input bulk capacitor 103, which may also be referred to as an input voltage smoothing capacitance, is coupled between HV bus 102 and half-bridge inverter modules 110, 120 and 130. Input bulk capacitor 103 provides energy storage sufficient to provide a substantially DC voltage to the half-bridge inverter modules. Input bulk capacitor 203 further provides a filtering function to filter transient current flowing in the HV bus 101 and prevent those current transients being supplied by other capacitors in the system but which are farther away from the inverter. Large currents flowing from external capacitors will tend to generate more EMI since transient currents will be flowing in larger loops.

[0031] It will be appreciated that, although the example shown in FIG.l includes a representation of the essential components for implementing a motor driver system, additional components, including passive components such as resistors, capacitors, and/or diodes, may be required to implement a fully functional motor drive system.

[0032] FIG. 2a illustrates a plan view of a first layer 281 of a multilayer substrate 200. First layer 281 of substrate 200 includes an inner opening 206 and an outer edge 207. Inner opening 206 is provided to allow mounting of the substrate within a motor housing. Inner opening 206 is shown has having a generally circular shape but it will be appreciated that other shapes are possible. In an example substrate 200, inner opening 206 may have a diameter in the range of about 7 mm to 40 mm or more and substrate 200 may have an overall diameter in the range of about 100 mm to 130 mm or more.

[0033] First layer 281 may be formed of an insulating or dialectric material. Example materials for the insulation or dielectric material include resined glass, polysilicon, ceramic or prepreg materials to be cured at a later time.

[0034] Motor winding 271 is formed on a surface of first layer 281. As shown in FIG. 2a, motor winding 271, which is one example of motor winding 171 shown in FIG. 1, is formed on a top surface of first layer 281. Motor winding 271 may be formed of any conductive material and is preferably a metal, such as copper. Motor winding 271 may also be referred to as a conductive coil. Motor winding 271 may be formed on the surface of first layer 281 using any conventional means of forming metallic traces on the surface of a PCB, as will be understood by those of skill in the art.

[0035] In the example shown in FIG. 2a, motor winding 271 is shown as being formed of four segments, 271a, 271b, 271c and 27 Id. Each segment of motor winding 271 may also be referred to as a conductive coil. Motor winding 271 may be formed of more or less segments depending on the number of phases of the motor, the size of the substrate, or the placement of the drive circuit components, among other considerations. In the example shown, segment 271a is coupled to a node 261 which in one example, corresponds with node A 161 of FIG. 1, and provides for electrical contact with the drive circuit as will be illustrated further below.

[0036] Segments 271a, 271b, 271c, and 271d are coupled together in series with linking traces 205a. Linking traces 205a are formed of a conducting material on the surface of a layer of multilayer substrate 200. In one example, linking traces 205a may be formed on layer 281. In another example, linking traces 205a may be formed on a surface of an adjacent layer of the multilayer substrate. In the example of FIG. 2a, linking traces 205a are formed on a layer adjacent to layer 281. The linking traces 205a are shown as superimposed with the winding segments on FIG. 2a to provide an example of their relative positioning, but it will be understood they are formed on an adjacent layer. As will also be understood, segments 271a, 271b, 271c, and 271d may be electrically connected to linking traces 205a through vias.

[0037] As can be seen in FIG. 2a, there may be areas of first layer 281 and/or the adjacent layer including linking traces 205a that are unused for windings or linking traces. In such a case, the unused areas may include additional conducting material that can be used as a heatsink to extract heat from components in the drive circuit, including the power switches of the half-bridge inverter modules. Additional layers may be added to the multilayer substrate if additional heat sinking is desired.

[0038] In the example shown, segment 27 Id includes a node 204 for providing a connection point for coupling to a common node (corresponding to node 164 of FIG. 1) for the motor windings 271, 272 and 273. As can be seen in FIG. 2a, segments 271a, 271b, 271c, and 27 Id of motor winding 271 are formed adjacent to outer edge 207. Segments 271a-d are also formed so they are spaced apart from inner opening 206. While motor winding segments 271a, 271b, 271c, and 27 Id are shown as being formed in a truncated wedge shape, other shapes for the winding segments are possible.

[0039] Although motor winding segments 271a, 271b, 271c, and 271d are shown as each being made up of 4 turns of conducting material, other numbers of turns are possible. The shape and/or number of turns of the winding segments may be chosen to optimize the magnetic coupling between the winding and the magnets of an associated rotor and may depend on considerations such as the size and shape of the substrate, the number, size and placement of the components of the drive circuit and the physical gap between a surface of substrate 200 and the surface of the magnets of an associated rotor.

[0040] FIG. 2b illustrates a plan view of a second layer 282 of a multilayer substrate 200. As shown in FIG. 2b, second layer 282 includes the inner opening 206 and the outer edge 207. The inner opening 206 and the outer edge 207 of all the layers of multilayer substrate 200 are substantially coextensive. Second layer 272 may be formed of the same or a similar material as first layer 271.

[0041] Motor winding 272, which is one example of motor winding 172 shown in FIG. 1, is formed on a surface of second layer 282. Motor winding 272 shares many of the same characteristics as that of motor winding 271 discussed above with regard to FIG. 2a. For example, motor winding 272 is shown as divided into four winding segments 272a, 272b, 272c and 272d, each having a truncated wedge shape and four turns of conductive material. Windings segments 272a, 272b, 272c and 272d are also shown as coupled in series using linking traces 205b and vias. Motor winding 272 may form part of a separate phase of a multiphase motor system from that of motor winding 271.

[0042] Although segments 272a, 272b, 272c and 272d of motor winding 272 are represented with dashed lines, this is simply to visually distinguish between the representations of other motor windings. As will be understood, the segments 272a, 272b, 272c and 272d of motor winding 271 are formed of continuous traces of conductive material.

[0043] As shown in FIG. 2b, segment 272a is coupled to node 262 which, in one example, corresponds with node B 162 of FIG. 1, and provides for electrical contact with the drive circuit as will be illustrated further below. Segment 272d includes a terminating node, similar to node 204 of winding segment 27 Id, for providing a connection point for coupling to a common node (corresponding to node 164 of FIG. 1) for the motor windings 271, 272 and 273.

[0044] FIG. 2c illustrates a plan view of a third layer 283 of a multilayer substrate 200. As shown in FIG. 2c, third layer 283 includes the inner opening 206 and the outer edge 207. The inner opening 206 and the outer edge 207 of all the layers of multilayer substrate 200 are substantially coextensive. Third layer 273 may be formed of the same or a similar material as first layer 271.

[0045] Motor winding 273 is formed on a surface of third layer 283. Motor winding 273 shares many of the same characteristics as that of motor winding 271 discussed above with regard to FIG. 2a. For example, motor winding 273 is shown as divided into four winding segments 273a, 273b, 273c, and 273d, each having a truncated wedge shape and four turns of conductive material. Windings segments 273a, 273b, 273c, and 273d are also shown as coupled in series using linking traces 205c and vias. Motor winding 273 may form part of a separate phase of a multiphase motor system from that of motor winding 271 and motor winding 272. [0046] Although segments 273 a, 273b, 273 c, and 273 d of motor winding 273 are represented with small dashed lines, this is simply to visually distinguish between the representations of other motor windings. As will be understood, the segments 273a, 273b, 273 c, and 273 d of motor winding 273 are formed of continuous traces of conductive material.

[0047] As shown in FIG. 2c, segment 273a is coupled to a node 263 which, in one example, corresponds with node C 163 of FIG. 1, and provides for electrical contact with the drive circuit as will be illustrated further below. Segment 273d includes a terminating node, similar to node 204 of winding segment 27 Id, for providing a connection point for coupling to a common node (corresponding to node 164 of FIG. 1) for the motor windings 271, 272 and 273.

[0048] FIG. 2d shows a composite plan view to represent an example configuration of motor windings 271, 272 and 273. In the composite view of FIG. 2d, only the motor windings are shown, in relation to a single underlying layer of the substrate, to illustrate the relative locations of the motor windings to one another.

[0049] As shown in FIG. 2d, substrate 200 includes an inner opening 206 and an outer edge 206 that correspond to the similarly numbered elements of FIGs. 2a, 2b, and 2c. As shown in FIG. 2d, each motor winding is subdivided into four segments, and the individual segments of motor windings 271, 272 and 273 partially overlap with one another. This may be because, as explained in relation to FIGs. 2a, 2b, and 2c, each winding is formed on a different layer of multilayer substrate 200. In other configurations, there may be different numbers of segments of the motor windings and/or the segments may not overlap at all.

[0050] As shown and discussed previously, motor windings 271, 272 and 273 form part of a three-phase motor configuration. Although a specific winding configuration is shown, other winding configuration could be used depending on the drive circuit and motor design. For example, in other examples, a single-phase winding/driver could be used or a 4-phase winding/driver could be implemented.

[0051] Although not shown in FIG. 2d, when combined together into a multi-layer substrate, the insulating material of each layer will provide electrical insulation between the motor winding formed on that layer and motor windings formed on nearby or adjacent layers. In an example, multilayer substrate 200 may have an overall thickness in a range of about 3 mm to 6 mm or more. [0052] FIGs. 3a and 3b illustrate plan views of an example arrangement of the components of an example drive circuit on one surface of a multilayer substrate according to the teachings of the present disclosure.

[0053] FIG. 3a shows a plan view of the top surface of an example substrate 300. Substrate 300 includes an inner opening 306 and an outer edge 307 which are similar to the corresponding features of substrate 200 discussed with regard to FIGs. 2a-d. FIG. 3a shows a dotted line 308. Line 308 represents the boundary of an area of a central region inside the annulus of the magnets of a rotor that may be used in combination with substrate 300 to form an axial flux motor, as will be described in more detail below in the discussion of FIGs 5a-7.

[0054] FIG. 3a shows an example arrangement of the components of an example drive circuit 360 that corresponds to the drive circuit 100 illustrated in FIG. 1. The components of the drive circuit 360 are placed on the surface of substrate 300 so that they are within the area defined by line 308. As shown, drive circuit 360 includes integrated circuit half-bridge inverter modules 310, 320 and 330, each one of which drives one phase of a three-phase drive circuit arrangement. Half-bridge inverter modules 310, 320 and 330 are one example of half-bridge inverter modules 110, 120 and 130 of FIG. 1.

[0055] Drive circuit 360 also includes system controller 350, which is one example of system controller pC 150. Drive circuit 360 also includes connector 302, which is one example of HV bus 102, for electrically connecting an external source of power to drive circuit 360. Drive circuit 360 may also include additional components, including capacitors Cl, C2 and C3, resistors R1 through R5, and optional sensors, for example Hall sensors 365.

[0056] As will be understood, the components of drive circuit 360 may be interconnected with one another with conductive traces on the top surface of substrate 300. Alternatively, or in addition to traces on the top surface, components of drive circuit 360 may be interconnected with conductive traces on other layers of substrate 300 and by employing vias through the insulating layers. Although as shown in the example of FIG. 3a the components of drive circuit 360 are placed on the top surface of substrate 300 within the area defined by line 308, the components of drive circuit 360 may be placed on the bottom surface of substrate 300 within the corresponding inner area, or components may be placed on both the top and bottom surfaces of substrate 300.

[0057] As will be explained and illustrated in more detail below, when implementing a drive circuit with components located on both surfaces of a substrate, one surface will include an exclusion zone proximate to the inner opening wherein no components may be placed. The exclusion zone provides an area wherein the substrate may include attachment features to allow mechanical connections to secure the substrate within a motor housing. The size of the exclusion zone and the number and characteristics of the attachment features may vary based on the design of the motor.

[0058] FIG. 3a represents a single example of the possible arrangement of the components of a drive circuit. Many other arrangements are possible and will depend on the specific design of the drive circuit and motor. What will be common is that the components will be arranged substantially within a central area of the substrate, proximate to the inner opening and spaced apart from the outer edge. The particular arrangement will need to accommodate the available space to place the drive circuit components without interfering with the movement of any associated rotor when implementing a complete motor.

[0059] FIG. 3b shows a composite plan view to represent an example configuration of motor windings 371, 372 and 373 in relation to the components of drive circuit 360. In the composite view of FIG. 3b, the locations of the motor windings are shown, in relation to a single underlying layer of the substrate 300, to illustrate the relative locations of the motor windings to one another and to the components of drive circuit 360.

[0060] Fig. 3b shows a configuration of three motor windings (371, 372, 373) in a 3- phase configuration substantially similar to that shown in FIG. 2d. It can be seen that, in the example configuration, some of the components of drive circuit 360 overlap with one or more segments of the motor windings. This is possible because the windings can occupy layers of the multilayer substrate 300 other than the surface layer on which the drive circuit components are placed. Because the components of drive circuit 360 are integrated on the same multilayer substrate as the motor windings, careful consideration of the layout of these components can minimize the length of the conductive traces from the mid-point terminals of the half-bridge inverter modules to their associated motor windings.

[0061] More specifically, as shown in FIG. 3b, half-bridge inverter module 310 may be placed very close to, or even overlap, the input node of motor winding 371. Accordingly, the length of the conductor needed to couple half-bridge inverter module 310 with motor winding 371 can be minimized. Similarly, the positioning of half-bridge inverter modules 320 and 330, relative to the input nodes of their associated motor windings 372 and 373, respectively, may also be accomplished to minimize the lengths of their respective connecting traces. Examples of input nodes include nodes 261, 262, and 263 shown in FIG. 2a, 2b, and 2c.

[0062] Together, multilayer substrate 300, the motor windings (371, 372, 373) and drive circuit 360 form an integrated stator for use in implementing an axial flux motor. Although, as shown, the components of drive circuit 360 may overlap the motor windings to some extent, the components of drive circuit 360 must still be placed within the area defined by the central annulus of the rotor with which the stator is to be paired, as will be discussed and illustrated in more detail below.

[0063] FIG. 4 illustrates a plan view of an example configuration for a portion of a rotor assembly according to the teachings of the present disclosure. An axial flux motor typically includes a rotor which includes permanent magnets mounted thereon and is rotatably mounted within a motor housing.

[0064] FIG. 4 shows an example portion of a rotor assembly 400 for illustrative purposes. In the example of FIG. 4, eight permanent magnets are rigidly mounted within a frame 401. Frame 401 includes a portion configured to mount the frame to a rotor shaft for rotation within motor housing. Frame 401 also includes portions configured to hold one or more permanent magnets in place and provide structural support to maintain the magnets in place within the rotor when the rotor is in motion. The example frame 401 may be constructed of aluminum or similar rigid material.

[0065] In the example shown in FIG. 4, four of the magnets 403 are oriented so that their positive pole is adjacent to the top surface shown in the figure. Magnets 403 are shown in diagonal fill. The other four magnets 404 are oriented so that their negative pole is adjacent to the top surface shown in the figure. Magnets 404 are shown in dotted fill. The magnets are arranged such that each magnet 403 has magnets 404 oriented in the opposite polarity immediately adjacent on each side. In the example of FIG. 4, the magnets may be constructed of neodymiun iron boron (NdFeB), samarium colbalt, be ferrite magnets or be constructed of other similar magnetic material.

[0066] In the example of FIG. 4, the magnets are shaped such that their boundaries closest to the center of the rotor assembly collectively form an inner annulus 408 of the rotor assembly. In an example rotor assembly 400, the inner annulus 408 may have a diameter in the range of about 40 mm to 70 mm. As will be explained and illustrated in more detail below, the inner annulus 408 defines the outer limits of the area of the stator available for placement of drive circuit components. In one example, the boundary of inner annulus 408 corresponds to line 308 of the plan view shown in FIG. 3a. [0067] Although the example of FIG. 4 is shown with eight magnets, as will be understood, the number, shape, size and arrangement of the magnets may vary depending on the design of the stator, drive circuit and motor.

[0068] FIGs. 5a, 5b and 5c illustrate sectional views of an example configuration for an axial flux motor according to the teachings of the present disclosure. FIG 5a shows a sectional view of an axial flux motor 500 showing only portions of the motor assembly for illustrative purposes.

[0069] FIG. 5a shows an axial flux motor 500 including a housing 590. Housing 590 forms an enclosure around motor 500. Housing 590 may be constructed of aluminum or other material of similar rigidity. As will be understood, housing 590 provides structural support for the components of motor 500 as well as protection for the components from external and environmental influences or contaminants. The specific size, shape and configuration of housing 590 will depend on the overall motor design as well as requirements for its output and intended application.

[0070] FIG. 5a shows an example multilayer substrate 570 located within, and rigidly mounted to housing 590. In one example, substrate 570 may include an arrangement of motor windings similar to that discussed with reference to FIGs. 2a-2d. Substrate 570 may also include components of an integrated drive circuit as discussed in more detail below.

[0071] Support member 518 includes a cap portion 518b and provides a structure for affixing substrate 570 to housing 590. Substrate 570 may be affixed, for example, using one or more screws 517, as in the illustrated example. As will be understood, other means for rigidly mounting substrate 570, including other mechanical means such as bolts, or appropriate adhesives, may be used in other examples. As shown in the example of FIG. 5a, cap portion 518a overlaps an exclusion area 516 on one surface of substrate 570 where no drive circuit components are placed. This exclusion area 516 facilitates a robust mechanical attachment between substrate 570 and housing 590 through support member 518.

[0072] In the example shown in FIG. 5a, support member 518 extends from one wall of housing 590 and through the inner opening of substrate 570. In an example, support member 518 may include an inner, hollow channel and provide a means to pass wires 502 to carry power from an external source to the drive circuit components integrated on substrate 570. In the example of FIG. 5a, the length of support member 518 is chosen to locate substrate 570 off center within housing 590. In the example of FIG. 5a, substrate 570 is offset left-of-center as viewed from the perspective of the figure. The length and location of support member 18 is also chosen to ensure that outer edge 507 of substrate 570 is properly located within and does not obstruct the movement of the associated rotor. The relative location of substrate 570 within housing 590 will depend on the design of the associated rotor, as will be explained in more detail below.

[0073] In the example of FIG. 5a, the components of the drive circuit are mounted to both a first and a second surface of substrate 570. In one example, as shown, integrated half-bridge inverter modules 510 and 520 and discrete resistors R1 and R2 may be mounted on the first surface of substrate 570. Although not shown in the view of FIG. 5a, other low-profile components of a drive circuit, such as additional half-bridge inverter modules, a system controller, or other discrete components may also be mounted on the first surface of substrate 570.

[0074] In one example, larger or bulkier components, such as capacitors Cl, C2 and C3, and optional sensor 565 may be mounted to the second surface of substrate 570. The choice of mounting location for the components of the drive circuit will depend on the overall design of the substrate, drive circuit and motor. As will be seen below, integrating the drive circuit components on the stator substrate provides significant flexibility in the design of motor 500.

[0075] FIG. 5b shows a sectional view of axial flux motor 500 showing different portions of the motor assembly for illustrative purposes. FIG 5b shows a different view of axial flux motor 500, illustrating a different portion of the motor assembly within housing 590 from that shown in FIG 5a. In particular, FIG. 5b shows an example rotor assembly for motor 500 within housing 590.

[0076] In the example of FIG. 5b, a rotor assembly includes rotor frame 501, rotor backplate 501b, permanent magnets 503 and 504, rotor shaft 505 and bearings 509. Rotor frame 501 may be constructed of a lightweight rigid and durable material such as aluminum for the parts that do not need to conduct magnetic flux and mild steel where a high permeability is required.

[0077] In the example shown in FIG 5b, rotor frame 501 is illustrated as being constructed of multiple parts that are joined together. In other examples, rotor frame 501 may be constructed in a single, unitary structure. Rotor backplate 501b may be constructed of mild steel or other suitable material that provides sufficient structural support as well as magnetic permeability. Rotor shaft 505 is coupled to rotor backplate 501b and rotor frame 501. Rotor shaft 505 may be constructed of a lightweight rigid and durable material such as aluminum. [0078] In the example shown, rotor shaft 505 is mechanically coupled to rotor backplate 501b using screws 517b. As would be understood, other means of mechanical coupling, such as with bolts, adhesives, or other alternatives may be used to provide secure connection between rotor shaft 505 and the other portions of the rotor assembly.

[0079] Rotor shaft 505 extends from rotor backplate 501b and through housing 590 to its exterior. Rotor shaft 505 provides a means for transferring rotational energy from the rotor assembly to a load external to motor 500. The specific dimensions of rotor shaft 505 will vary based on the overall design of motor 500 and the needs of the intended application.

[0080] Permanent magnets 503 and 504 are mounted to rotor backplate 501b and contained within rotor frame 501. Permanent magnet 503 is shown in diagonal fill while permanent magnet 504 is shown in dotted fill. Permanent magnets 503 and 504 may be part of an arrangement such as the example depicted in FIG. 4. As discussed in the context of FIG. 4, other arrangements of permanent magnets may be used to implement motor 500.

[0081] As illustrated in FIG. 5b, the edges of magnets 503 and 504 closest to rotor shaft 505 form an inner annulus 508 of the rotor assembly. In one example, the boundary of inner annulus 508 corresponds to inner annulus 408 of FIG. 4 and/or to line 308 of the plan view shown in FIG. 3a. The area encompassed by the inner annulus 508 provides space for the components of a drive circuit to be placed on a stator substrate, as will be seen in more detail below with regard to FIG. 5c.

[0082] To facilitate smooth and reliable rotation of rotor frame 501 and rotor shaft 505, a collection of bearings 509a and 509b may be employed. Bearings 509a-b may be standard ball bearings used in motor constructions. In the example shown, bearings 509a are mounted within housing 590, proximate to rotor shaft 505, to facilitate rotation of rotor shaft 505. In addition, bearings 509b are mounted to rotor frame 501 to facilitate rotation of rotor frame 501 around support member 518. It will be appreciated that other configurations of bearings 509a and 509b may be used to facilitate reliable rotation of the complete rotor assembly within housing 590.

[0083] FIG 5c shows a sectional view of axial flux motor 500 including the components depicted in FIG. 5a and FIG. 5b arranged together within housing 590. FIG. 5c illustrates an example axial flux motor 500 including a stator substrate 570 having drive circuit components mounted thereon, located within housing 590 and surrounded by rotor frame 501. FIG. 5c combines the elements disclosed in FIGs. 5a and 5b, and it should be appreciated that similarly numbered elements couple and function as described above.

[0084] Substrate 570 is mounted to housing 590 through support member 518. Substrate 570 is mounted such that one of its surfaces is near to the adjacent surface of permanent magnets 503 and 504. Minimizing the gap between the surface of substrate 570 and that of magnets 503 and 504 promotes magnetic coupling between the stator and rotor. As can be seen, drive circuit components, for example, integrated half-bridge inverter modules 510 and 520 and capacitors Cl, C2 and C2, are mounted to substrate 570 within the space formed by inner annulus 508.

[0085] In the example of FIG. 5c, the length of support member 518 is chosen such that substrate 570 is mounted offset from the center of housing 590. In the example of FIG. 5c, substrate 570 is offset left-of-center as viewed from the perspective of the figure. Rotor frame 501 includes permanent magnets 503 and 504 opposite only one surface of substrate 570. In other examples, permanent magnets may be placed opposite both surfaces of substrate 570.

[0086] As can be seen, in the configuration of FIG. 5c, there is more space on one side of substrate 570 (the right side in the figure) than on the other. Accordingly, the larger or bulkier components, such as capacitors Cl, C2, and C3 may be mounted on the surface of substrate 570, where there is physical space to accommodate them while not interfering with the rotation of rotor frame 501 and magnets 503 and 504. In contrast, there is less space proximate to the other side of substrate 570 (the left side in the figure), but still enough space to accommodate low profile components such as, for example, integrated half-bridge inverter modules 510 and 520. In other examples, all of the drive circuit components may be mounted on only one surface of substrate 570.

[0087] As will be appreciated, in the configuration shown, rotor frame 501, rotor backplate 501b, permanent magnets 503 and 504 and rotor shaft 505 are free to rotate about the central axis of rotor shaft 505 without interference from substrate 570 or any drive circuit components. As explained above, smooth and reliable rotation of the rotor assembly is enhanced by bearings 509a and 509b. The diameter of substrate 570 is chosen such that the gap between outer edge 507 and rotor frame 501 is optimized to allow for as much overlap as practical between the magnets 503 and 504 and the windings (not shown) within substrate 570, to maximize magnetic coupling, while maintaining unimpeded rotation of rotor frame 501. The specific dimensions of rotor frame 501, rotor backplate 501a, the diameter and thickness of substrate 570 and the height and thickness of permanent magnets 403 and 404 may vary and will depend on the overall design of motor 500 and the needs of the intended application.

[0088] FIG. 6 illustrates a sectional view of another example configuration for an axial flux motor according to the teachings of the present disclosure. FIG. 6 shows an example axial flux motor 600 including a housing, a stator and a rotor. The example of FIG. 6 shares many aspects in common with the example of FIG. 5, and it should be appreciated that similarly numbered elements couple and function similarly as described above.

[0089] Motor 600 includes a housing 690. Within housing 690, motor 600 includes a stator substrate 670 having integrated motor windings (not shown) and drive circuit components mounted thereon. In one example, the motor windings of substrate 670 may be configured as shown in FIGs. 2a-2d. In the example of FIG. 6, substrate 670 is mounted to housing 690 through support member 618. In this example, the length of support member 618 is chosen such that substrate 670 is substantially centered within housing 690. More specifically, substrate 670 is substantially centered along an axis running left to right in the view of the figure through support member 618 and rotor shaft 605. As can be seen, the substantially central location of substrate 670 within housing 670, and within rotor frame 601, provides an area within the inner annulus formed by magnets 603 and 604 that has roughly equal height with respect to the first and second surface of substrate 670. In the example of FIG. 6, the location of substrate 670 allows for the flexible placement of components on either surface of substrate 670 to efficiently meet the design requirements of the drive circuit.

[0090] Motor 600 includes a rotor assembly, including rotor frame 601, rotor backplate 601b and rotor shaft 605. These components are similar to the corresponding components of motor 500 shown in FIGs. 5b-c, but they have some differences. As can be seen, the specific configuration of rotor frame 601 is different from rotor frame 501 and defines a different geometry of interior space to accommodate the placement of drive circuit components. Also, as can be seen, the configuration of rotor backplate 601b is different from that of rotor backplate 501b and provides for a different base to mount magnets 603 and 604, allowing for magnets of different thickness compared to magnets 503 and 504 of motor 500.

[0091] As explained above in the context of FIGs. 5a-5c, smooth and reliable rotation of the rotor assembly of motor 600 may be enhanced by use of bearings 609a and 609b.

[0092] FIG. 7 illustrates a sectional view of yet another example configuration for an axial flux motor according to the teachings of the present disclosure. FIG. 7 shows an example axial flux motor 700 including a housing, a stator and a rotor. The example of FIG. 7 shares many aspects in common with the examples of FIG. 5 and FIG. 6, and it should be appreciated that similarly numbered elements couple and function similarly as described above.

[0093] Motor 700 includes a housing 790. Within housing 790, motor 700 includes a stator substrate 770 having integrated motor windings (not shown) and drive circuit components mounted thereon. In one example, the motor windings of substrate 770 may be configured as shown in FIGs. 2a-2d.

[0094] In the example of FIG. 7, substrate 770 is mounted to housing 790 through support member 718. In this example, the length of support member 718 is chosen such that substrate 770 is offset from the center of housing 790. In this case, substrate 770 is offset to the right of center as seen in the figure. As can be seen, in this configuration, there is more space on one side of substrate 770 (the left side in the figure) than on the other. Accordingly, the larger or bulkier components, such as capacitors, may be mounted on the surface of substrate 770, where there is physical space to accommodate them while not interfering with the rotation of rotor frame 701 and magnets 703 and 704. In contrast, there is less space proximate to the other side of substrate 770 (the right side in the figure), but still enough space to accommodate low profile components such as, for example, resistors.

[0095] The offset configurations of FIG. 5a-c or FIG. 7 may be of use if, for example, there are taller components that cannot all be accommodated on one side of the substrate if the substrate were to be centered within the motor housing. As will be understood, if the overall size of the motor housing is unchanged, then the increased height to one side of the substrate is accompanied by a reduction in height to the other side of the substrate and the components on the short side of the substrate must therefore be designed appropriately. Further, the offset location of substrate 770 also allows for a rotor configuration that includes two sets of permanent magnets.

[0096] Motor 700 includes a rotor assembly including rotor frame 701, rotor backplate 701b, rotor backplate 701c, and rotor shaft 705. These components are similar to the corresponding components of the example motors shown in FIGs. 5b-c and FIG. 6, but they have some differences. As can be seen, the specific configuration of rotor frame 701 is different from rotor frame 501 and rotor frame 601 and defines a different geometry of interior space to accommodate the placement of drive circuit components. Also, as can be seen, the configuration of rotor backplate 701b is different from that of rotor backplates 50 lb/60 lb . Motor 700 further includes a second rotor backplate 701c. In motor 700, the combination of rotor frame 701 and rotor backplates 701b and 701c provides for the mounting of two sets of permanent magnets 703/704.

[0097] In the example of FIG. 7, motor 700 includes one set of permanent magnets 703/704 opposite one surface of substrate 770 and a second set of permanent magnets 703/704 opposite the second surface of substrate 770. In one example, each set of permanent magnets 703/704 may be configured as is shown in FIG. 4, although other configurations may be used in other examples.

[0098] The example configurations of FIG. 6 and FIG. 7 demonstrate that magnets can be placed on both or only one side of the stator substrate while still benefiting from the teachings of the present disclosure where the stator windings of the motor are on the same substrate as the drive circuit.

[0099] Numerous specific details are set forth above in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present invention. For example, skilled artisans will appreciate that elements in the previously described figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in the figures in order to facilitate a less obstructed view of these various embodiments of the present invention.

[0100] Reference throughout this specification to “one embodiment”, “an embodiment”, “one example” or “an example” means that a particular feature, structure or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, “one example” or “an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures or characteristics may be combined in any suitable combinations and/or subcombinations in one or more embodiments or examples.

[0101] The description of illustrated examples of the present invention, including what is described in the Abstract, are not intended to be exhaustive or to be a limitation to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible without departing from the broader spirit and scope of the present invention. Indeed, it is appreciated that any specific example values are provided for explanation purposes and that other values may also be employed in other embodiments and examples in accordance with the teachings of the present invention.

Claims

CLAIMS What is claimed is:

1. A stator assembly with an integrated drive circuit for use in an axial flux motor comprising: a multi-layer substrate having a first surface and a second surface, an inner opening and an outer edge; one or more conductive coils formed on one or more layers of the substrate, the coils formed proximate to the outer edge and spaced apart from the inner opening; and a drive circuit coupled to the one or more conductive coils, wherein the drive circuit is located on at least the first surface of the substrate proximate to the inner opening, and wherein the drive circuit comprises at least one half-bridge module and an input voltage smoothing capacitance.

2. The stator assembly of claim 1, wherein each of the one or more conductive coils is formed on a different layer of the substrate.

3. The stator assembly of claim 2, wherein each of the one or more conductive coils is formed of multiple segments.

4. The stator assembly of claim 3, wherein the multiple segments of each conductive coil are coupled together in series through linking traces formed on a different layer of the substrate from the multiple segments of each conductive coil.

5. The stator assembly of claim 1, wherein each of the one or more coils is driven by the drive circuit in a different phase.

6. The stator assembly of claim 1, wherein the substrate comprises at least two conductive coils and the drive circuit comprises at least two half-bridge modules, wherein an output of each half-bridge module is coupled to an input of one of the conductive coils and wherein the drive circuit drives the conductive coils in a multi-phase configuration.

7. The stator assembly of claim 6, wherein the at least two conductive coils are formed on different layers of the substrate and wherein the conductive coils at least partially overlap one another.

8. The stator assembly of claim 7, wherein each of the one or more conductive coils is formed of multiple segments.

9. The stator assembly of claim 8, wherein the multiple segments of each conductive coil are coupled together in series through linking traces formed on a different layer of the substrate from the multiple segments of each conductive coil.

10. The stator assembly of claim 6, wherein the two half-bridge modules are located on the first surface of the substrate and the input voltage smoothing capacitance is located on the second surface of the substrate.

11. The stator assembly of claim 6, wherein the half-bridge modules are arranged on the surface of the substrate such that the distance between the output of each half-bridge module and the input of the conductive coil to which it is coupled is minimized.

12. The stator assembly of claim 1, wherein the drive circuit is arranged such that no part of the drive circuit overlaps any portion of the conductive coils.

13. The stator assembly of claim 1, wherein the drive circuit is located on the first surface and the second surface of the substrate.

14. The stator assembly of claim 13, wherein the at least one half-bridge module is located on the first surface of the substrate and the input voltage smoothing capacitance is located on the second surface of the substrate.

15. The stator assembly of claim 1, wherein each of the one or more half-bridge modules is a packaged integrated circuit.

16. The stator assembly of claim 1, wherein at least one of the first surface and the second surface comprises an exclusion zone proximate to and around the inner opening and wherein no portion of the drive circuit is located within the exclusion zone.

17. The stator assembly of claim 16 wherein the exclusion zone comprises one or more through holes configured to allow mechanical attachment of the substrate to a motor housing.

18. The stator assembly of claim 17 wherein the stator assembly is substantially circular in shape and has a diameter from about 100 mm to 130 mm and wherein the inner opening is substantially circular in shape and has a diameter from about 7 mm to 40 mm.

19. An axial flux motor, comprising: a housing; a rotor, comprising a rotor shaft coupled to a rotor frame, wherein one or more permanent magnets are coupled to the rotor frame and wherein the rotor is mounted within the housing such that the rotor is free to rotate about a central axis of the rotor shaft; and a stator assembly rigidly mounted within the housing, the stator assembly comprising; a multi-layer substrate having a first surface and a second surface, an inner opening and an outer edge; one or more conductive coils formed on one or more layers of the substrate, the conductive coils formed proximate to the outer edge and spaced apart from the inner opening; a drive circuit coupled to the one or more conductive coils, wherein the drive circuit is located on at least the first surface of the substrate proximate to the inner opening, and wherein the drive circuit comprises at least one half-bridge module and an input voltage smoothing capacitance; wherein the stator assembly and the rotor are mounted within the housing such that the one or more permanent magnets are proximate to the outer edge of the substrate and are magnetically coupled to the one or more conductive coils.

20. The axial flux motor of claim 19, wherein the rotor is configured such that the permanent magnets are proximate to both the first and the second surface of the substrate.

21. The axial flux motor of claim 19, wherein the rotor comprises at least four permanent magnets; each magnet comprises a first surface with a positive magnetic pole and a second surface with a negative magnetic pole; and the magnets are arranged within the rotor such that each surface of each magnet has a magnetic pole that is opposite in polarity from the pole of the surface of the magnets immediately adjacent to it.

22. The axial flux motor of claim 19, wherein the housing is formed of aluminum.

23. The axial flux motor of claim 19, wherein each magnet is formed in a truncated wedge shape and the magnet surfaces facing toward the inner opening of the substrate form an inner annulus surrounding the drive circuit.

24. The axial flux motor of claim 23, wherein the inner annulus is substantially circular in shape and has a diameter from about 40 mm to 70 mm.

25. The axial flux motor of claim 19, wherein the substrate comprises at least two conductive coils and the drive circuit comprises at least two half-bridge modules, wherein an output of each half-bridge module is coupled to an input of one of the conductive coils and wherein the drive circuit drives the conductive coils in a multi-phase configuration.

26. The axial flux motor of claim 25, wherein the half-bridge modules are arranged on the surface of the substrate such that the distance between the output of each half-bridge module and the input of the conductive coil to which it is coupled is minimized.

27. The axial flux motor of claim 19, wherein at least one of the first surface and the second surface of the substrate comprises an exclusion zone proximate to and around the inner opening and wherein no portion of the drive circuit is located within the exclusion zone.

28. The axial flux motor of claim 27, wherein the exclusion zone comprises one or more through holes configured to allow mechanical attachment of the substrate to the housing.

29. The axial flux motor of claim 19, wherein the multilayer substrate is substantially circular in shape and has a diameter from about 100 mm to 130 mm and wherein the inner opening is substantially circular in shape and has a diameter from about 7 mm to 40 mm.