WO2020128843A1

WO2020128843A1 - Method for assembling a stator for an electric motor or generator

Info

Publication number: WO2020128843A1
Application number: PCT/IB2019/060935
Authority: WO
Inventors: Chris TIMS; Jamie Bell; Neil VANSTONE-REED
Original assignee: Protean Electric Limited
Priority date: 2018-12-18
Filing date: 2019-12-17
Publication date: 2020-06-25
Also published as: GB2573185A; GB2573185B; GB201820598D0

Abstract

A method for assembling a stator for an electric motor or generator, the method comprising providing an annular support having an inner diameter, wherein the annular component includes a lead frame having a plurality of circuit board layers, a first flexible printed circuit board having a first section and a second section, wherein the first section is mounted between a first surface of the lead frame and the annular support, wherein the second section extends through an aperture formed in the lead frame; placing a rigid sleeve over the second section of the flexible printed circuit board that extends through the lead frame; attaching the rigid sleeve to the lead frame; providing a heat sink, wherein the heat sink includes a mounting section having a circumferential outer wall and a flange section that extends around the mounting section and includes an aperture; heating the annular support to expand the inner diameter of the annular support; sliding the inner diameter of the circumferential support over the outer wall of the heat sink mounting section and the rigid sleeve and second section of the flexible printed circuit board through the aperture formed in the heat sink flange section; cooling the annular support to reduce the inner diameter of the circumferential support such that the inner wall of the circumferential support presses against the outer wall of the heat sink; removing the rigid sleeve from the lead frame.

Description

METHOD FOR ASSEMBLING A STATOR FOR AN ELECTRIC MOTOR OR GENERATOR

The present invention relates to a method for assembling a stator, in particular a method for assembling a stator for an electric motor or generator.

With increased interest being placed in environmentally friendly vehicles there has been a corresponding increase in interest in the use of electric motors for providing drive torque for vehicles.

Electric motor systems typically include an electric motor, with a control unit arranged to control the power of the electric motor. Examples of known types of electric motor include the induction motor, synchronous brushless permanent magnet motor, switched reluctance motor and linear motor.

Due to the high torque demands required for driving a

vehicle, the most common kind of electric motor used for this use is a three phase electric motor.

A three phase electric motor typically includes three coil sets, where each coil set is arranged to generate a magnetic field associated with one of the three phases of an

alternating voltage.

To increase the number of magnetic poles formed within an electric motor, each coil set will typically have a number of coil sub-sets that are distributed around the periphery of the electric motor, which are driven to produce a

rotating magnetic field.

By way of illustration, Figure 1 shows a typical three phase electric motor 10 having three coil sets 14, 16, 18. Each coil set consists of four coil sub-sets that are connected in series, where for a given coil set the magnetic field generated by the respective coil sub-sets will have a common phase .

The three coil sets of a three phase electric motor are typically configured in either a delta or wye configuration.

A control unit for a three phase electric motor having a DC power supply will typically include a three phase bridge inverter that generates a three phase voltage supply for driving the electric motor. Each of the respective voltage phases is applied to a respective coil set of the electric motor .

A three phase bridge inverter includes a number of switching devices, for example power electronic switches such as Insulated Gate Bipolar Transistor (IGBT) switches, which are used to generate an alternating voltage from a DC voltage supply.

In the context of an electric vehicle motor, a drive design that is becoming increasing popular is an integrated in wheel electric motor design in which an electric motor and its associated control system are integrated within a wheel of a vehicle.

To provide cooling to both the coil sets and the associated control system, typically a heat sink is attached to the electric motor, where a commonly used technique for

attaching the heat sink to the electric motor is via the use of a hot drop process. However, as a hot drop process typically requires various electric motor components to be heated to a specified temperature, the use of a hot drop process can result in other design constraints being imposed on the electric motor.

It is desirable to improve this situation.

In accordance with an aspect of the present invention there is provided a method for assembling a stator for an electric motor or generator according to the accompanying claims.

The present invention provides the advantage of allowing a flexible printed circuit board to be used as both a mounting element for an electric motor sensor and for allowing the sensor to be directly electrically connected to a control device for monitoring sensor readings without a risk of damage occurring to the flexible printed circuit board during the assembling of the stator to which the sensor is to be mounted.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which :

Figure 1 illustrates a prior art three phase electric motor;

Figure 2 illustrates an exploded view of a motor embodying the present invention;

Figure 3 illustrates a schematic representation of a control device;

Figure 4 illustrate the electrical connections provided by a lead frame according to an embodiment of the present invention; Figure 5 illustrates a lead frame according to an embodiment of the present invention;

Figure 6 illustrates a lead frame arrangement according to an embodiment of the present invention;

Figure 7 illustrates a lead frame according to an embodiment of the present invention;

Figure 8 illustrates a lead frame arrangement according to an embodiment of the present invention;

Figure 9 illustrates a conductive layer on a circuit board layer of a lead frame according to an embodiment of the present invention;

Figure 10 illustrates a lead frame according to a lead frame according to an embodiment of the present invention;

Figure 11 illustrates a conductive layer on a circuit board layer of a lead frame according to an embodiment of the present invention;

Figure 12 illustrates a conductive layer on a circuit board layer of a lead frame according to an embodiment of the present invention;

Figure 13 illustrates a conductive layer on a circuit board layer of a lead frame according to an embodiment of the present invention

Figure 14 illustrates a conductive layer on a circuit board layer of a lead frame according to an embodiment of the present invention; Figure 15 illustrates a lead frame according to an

embodiment of the present invention;

Figure 16 illustrates a flexible printed circuit board according to an embodiment of the present invention;

Figure 17 illustrates an exploded view of a stator according to an embodiment of the present invention;

Figure 18 illustrates a cross-sectional plan view of a stator according to an embodiment of the present invention;

Figure 19 illustrates an sectional view of a stator

according to an embodiment of the present invention;

Figure 20 illustrates an exploded view of a motor embodying the present invention;

Figure 21 illustrates an electric motor according to an embodiment of the present invention;

Figure 22 illustrates a stator back iron, coil windings and a lead frame according to an embodiment of the present invention;

Figure 23 illustrates a stator back iron and heat sink according to an embodiment of the present invention;

Figure 24 illustrates a stator back iron and heat sink according to an embodiment of the present invention;

Figure 25 illustrates a stator back iron according to an embodiment of the present invention; Figure 26 illustrates a rigid sleeve according to an

embodiment of the present invention;

Figure 27 illustrates a rigid sleeve according to an

embodiment of the present invention;

Figure 28 illustrates a stator according to an embodiment of the present invention.

The embodiment of the invention described is for a method for assembling a stator for an electric motor or generator stator. Preferably the electric motor is for use in a wheel of a vehicle. However if the electric motor is located within a vehicle it may be located anywhere within the vehicle. The motor is of the type having a set of coils being part of the stator for attachment to a vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel. For the avoidance of doubt, the various aspects of the invention are equally applicable to an electric generator having the same arrangement. As such, the definition of electric motor is intended to include electric generator. As would be appreciated by a person skilled in the art, the present invention is applicable for use with other types of electric motors.

For the purposes of the present embodiment, as illustrated in Figure 2, the in-wheel electric motor includes a stator 252 comprising a circumferential support 253 that acts as a heat sink, multiple coils 254, two control devices (not shown) mounted on the circumferential support 253 on a rear portion of the stator for driving the coils, and an annular capacitor (not shown) , otherwise known as a DC link

capacitor, a lead frame 255 mounted between an axial edge of the coils and an axial flange formed on the circumferential support for coupling the control devices to the coils, and a flexible printed circuit board 260 having an integrated temperature sensor, described below, mounted between the lead frame 255 and the coils 254. The flexible printed circuit board 260 includes a first section 261 that is mounted between the lead frame 255 and the coils 254 and a second section 262 arranged to extend through an aperture formed in the lead frame 255.

For the purposes of the embodiment shown in Figure 2, the electric motor includes two semi circumferential flexible printed circuit boards 260 mounted between a respective lead frame 255 and the coils 254, however a single flexible printed circuit board may be used.

The coils 254 are formed on stator tooth laminations to form coil windings. A stator cover 256 is mounted on the rear portion of the stator 252, enclosing the control devices and annular capacitor to form the stator 252, which may then be fixed to a vehicle and does not rotate relative to the vehicle during use.

As schematically represented in Figure 3, each control device 300 includes an inverter 310 with one of the control devices including control logic 320, which in the present embodiment includes a processor, for controlling the operation of both inverters 310. Each inverter is coupled to three sets of coil windings, arranged electrically in parallel, to form a set of three sub motors, as described below .

The annular capacitor is coupled between the inverters 310 and the electric motor' s DC power source for reducing voltage ripple on the electric motor's power supply line, otherwise known as the DC busbar, and for reducing voltage overshoots during operation of the electric motor. For reduced inductance the capacitor is preferably mounted adjacent to the control devices 300.

A rotor 240 comprises a front portion 220 and a cylindrical portion 221 forming a cover, which substantially surrounds the stator 252. The rotor includes a plurality of permanent magnets 242 arranged around the inside of the cylindrical portion 221. For the purposes of the present embodiment 32 magnet pairs are mounted on the inside of the cylindrical portion 221. However, any number of magnet pairs may be used.

The magnets are in close proximity to the coil windings on the stator 252 so that magnetic fields generated by the coils interact with the magnets 242 arranged around the inside of the cylindrical portion 221 of the rotor 240 to cause the rotor 240 to rotate. As the permanent magnets 242 are utilized to generate a drive torque for driving the electric motor, the permanent magnets are typically called drive magnets.

The rotor 240 is attached to the stator 252 by a bearing block (not shown) . The bearing block can be a standard bearing block as would be used in a vehicle to which this motor assembly is to be fitted. The bearing block comprises two parts, a first part fixed to the stator and a second part fixed to the rotor. The bearing block is fixed to a central portion of the wall of the stator 252 and also to a central portion of the housing wall 220 of the rotor 240.

The rotor 240 is thus rotationally fixed to the vehicle with which it is to be used via the bearing block at the central portion of the rotor 240. This has an advantage in that a wheel rim and tyre can then be fixed to the rotor 240 at the central portion using the normal wheel bolts to fix the wheel rim to the central portion of the rotor and

consequently firmly onto the rotatable side of the bearing block. The wheel bolts may be fitted through the central portion of the rotor through into the bearing block itself. With both the rotor 240 and the wheel being mounted to the bearing block there is a one to one correspondence between the angle of rotation of the rotor and the wheel.

The rotor also includes a set of magnets (not shown) for position sensing, otherwise known as commutation magnets, which in conjunction with sensors mounted on the stator allows for a rotor flux angle to be estimated. The rotor flux angle defines the positional relationship of the drive magnets to the coil windings. Alternatively, in place of a set of separate magnets the rotor may include a ring of magnetic material that has multiple poles that act as a set of separate magnets.

In the present embodiment the electric motor includes six coil sets with each coil set having three coil sub-sets that are coupled in a wye configuration to form a three phase sub-motor, resulting in the motor having six three phase sub-motors, where as stated above the respective coils of the six coil sets are wound on individual stator teeth, which form part of the stator. The operation of the

respective sub-motors is controlled via one of two control devices 300, as described below. Although the present embodiment describes an electric motor having six coil sets (i.e. six sub motors) the motor may equally have one or more coil sets with associated control devices. Equally, each coil set may have any number of coil sub-sets, thereby allowing each sub-motor to have two or more phases.

Figure 3 illustrates the connections between the respective coil sets 60 and the control devices 300, where three coil sets 60 are connected to a respective three phase inverter 310 included on a control device 300. As is well known to a person skilled in the art, a three phase inverter contains six switches, where a three phase alternating voltage may be generated by the controlled operation of the six switches. However, the number of switches will depend upon the number of voltage phases to be applied to the respective sub motors, where the sub motors can be constructed to have any number of phases. Each control device 300 is arranged to communicate with the other control device 300 via a

communication bus 330.

Preferably, the control devices 300 are of a modular construction. In a preferred embodiment each control device, otherwise known as a power module, includes a power printed circuit board on which is mounted a control printed circuit board, two power source busbars for connecting to a DC battery via the DC link capacitor, three phase winding busbars for connecting to respective coil windings via the lead frame, and a power substrate assembly, which includes an inverter.

The power printed circuit board includes a variety of other components that include drivers for the inverter switches formed on the power substrate assembly, where the drivers are used to convert control signals from the control printed circuit board into a suitable form for operating switches mounted on the power printed circuit board, however these components will not be discussed in any further detail. One of the control devices 300 includes a processor 320. The processor 320 is configured to control the operation of the electric motor, which includes monitoring temperature readings received from a temperature sensor mounted on the flexible printed circuit board 260, for determining whether the electric motor is operating within an acceptable temperature range, and for controlling the operation of the inverter switches in both control devices 300. Additionally, each control device 300 includes an interface arrangement to allow communication between the respective control devices 300 via a communication bus 330 with one control device 300 being arranged to communicate with a vehicle controller mounted external to the electric motor.

The processor 320 in the respective control device 300 is arranged to control the operation of the inverter switches mounted within each control device 300 to allow each of the electric motor coil sets 60 to be supplied with a three phase voltage supply, thereby allowing the respective coil sub-sets to generate a rotating magnetic field. As stated above, although the present embodiment describes each coil set 60 as having three coil sub-sets, the present invention is not limited by this and it would be appreciated that each coil set 60 may have one or more coil sub-sets.

Under the control of the processor, each three phase bridge inverter 310 is arranged to provide PWM voltage control across the respective coil sub-sets, thereby generating a current flow in the respective coil sub-sets for providing a required torque by the respective sub-motors.

PWM control works by using the motor inductance to average out an applied pulse voltage to drive the required current into the motor coils. Using PWM control an applied voltage is switched across the motor windings. During the period when voltage is switched across the motor coils, the current rises in the motor coils at a rate dictated by their inductance and the applied voltage. The PWM voltage control is switched off before the current has increased beyond a required value, thereby allowing precise control of the current to be achieved.

For a given coil set 60 the three phase bridge inverter 310 switches are arranged to apply a single voltage phase across each of the coil sub-sets.

Using PWM switching, the plurality of switches are arranged to apply an alternating voltage across the respective coil sub-sets. The voltage envelope and phase angle of the electrical signals is determined by the modulating voltage pulses .

The inverter switches can include semiconductor devices such as MOSFETs or IGBTs. In the present example, the switches comprise IGBTs. However, any suitable known switching circuit can be employed for controlling the current. One well known example of such a switching circuit is the three phase bridge circuit having six switches configured to drive a three phase electric motor. The six switches are

configured as three parallel sets of two switches, where each pair of switches is placed in series and form a leg of the three phase bridge circuit. A single phase inverter will have two pairs of switches arranged in series to form two legs of an inverter.

The inverter formed on the power assembly in one control device is coupled to three coil sets, to form a first set of three sub motors, with the inverter formed on the power assembly in the other control device being coupled to the other coil sets, to form a second set of three sub motors.

Both inverters are coupled to the respective coil sets via the lead frame, where each leg of the respective inverters is coupled to the lead frame via a respective phase winding busbar. For the purposes of the present embodiment, the different voltage phases generated by each inverter leg are designated W, V and U.

The coil windings are coupled to the lead frame 255, as described below, to allow current to flow from the DC power source via the respective inverters in the control devices to the coil windings to allow drive torque to be generated by the electric motor.

Figure 4 illustrates the electrical connections that the lead frame 255 provides between the phase winding busbars for one of the control devices and coil windings mounted on the stator, where the lead frame 255 is arranged to couple the phase windings for the respective coil sub-sets in a wye configuration. However, the lead frame 255 can be configured to couple the phase windings for the respective coil subsets in different configurations. As described above, each coil sub-set includes three coil windings (i.e. phase windings) to form a three phase sub motor.

Although, each coil winding/phase winding within each respective coil subset may be configured as a single, independent, coil winding, the coil winding may comprise two or more separate coils that are serially connected. For the purposes of the present embodiment, each of the coil windings that form a coil sub-set is formed from three separately wound coils that are coupled via a circuit board layer of the lead frame, as described below.

With reference to Figure 4, coils 401 form a first phase winding of a first sub motor 411, coils 402 form a second phase winding of the first sub motor 411, and coils 403 form a third phase winding of the first sub motor 411. With respect to the second sub motor 412, coils 404 form a first phase winding of the second sub motor 412, coils 405 form a second phase winding of the second sub motor 412, and coils 406 form a third phase winding of the second sub motor 412. With respect to the third sub motor 413, coils 407 form a first phase winding of the third sub motor 413, coils 408 form a second phase winding of the third sub motor 413, and coils 409 form a third phase winding of the third sub motor 413.

Each coil 400 illustrated in Figure 4 corresponds to a coil wound on a single stator tooth, where the end sections of each coil are arranged to be coupled to the lead frame 255 to allow the coils to be coupled in the configuration shown in Figure 4.

The lead frame 255 is arranged to connect the W phase inverter busbar to the first coil 400 of the first phase winding 401 of the first sub motor 411, the first phase winding 404 of the second sub motor 412 and the first phase winding 407 of the third sub motor 413.

The lead frame also connects the V phase inverter busbar to the first coil 400 of the second phase winding 402 of the first sub motor 411, the second phase winding 405 of the second sub motor 412 and the second phase winding 408 of the third sub motor 413 and connects the U phase inverter busbar to the first coil 400 of the third phase winding 403 of the first sub motor 411, the third phase winding 406 of the second sub motor 412 and the third phase winding 409 of the third sub motor 413.

As illustrated in Figure 4, the lead frame 255 connects the last coil 400 of the first phase winding 401 of the first sub motor 411 to the last coil 400 of the second phase winding 402 and third phase winding 403 of the first sub motor 411. Similarly, the lead frame 255 also connects the last coil 400 of the first phase winding 404 of the second sub motor 412 to the last coil 400 of the second phase winding 405 and third phase winding 406 of the second sub motor 412 and connects the last coil 400 of the first phase winding 407 of the third sub motor 413 to the last coil of the second phase winding 408 and third phase winding 409 of the third sub motor 413. These connections acts as the star point for each of the respective sub motors.

Additionally, the lead frame 255 is arranged to electrically connect the respective coils 400 for each phase winding to form a serial connection between the respective coils 400 for each phase winding.

Accordingly, the lead frame provides the electrical

connections between the W, V, U phase inverter busbars and the respective coils 400 to form three sub motors driven by a single inverter 310, where the coil windings of the respective sub motors are coupled in a wye configuration.

Similarly, the lead frame 255 also couples the phase winding busbars for the inverter 310 for the other control device 300 and coils mounted on the stator in the same manner to form three further sub motors driven by the inverter 310 in the second control device 300.

The configuration of the lead frame 255 will now be

described, where in a first embodiment a single,

substantially, circumferential lead frame, as illustrated in Figure 5, is used for providing current from both control devices to the respective coil sets. As illustrated in Figure 6 the substantially circumferential lead frame 255 is mounted to an axial mounting surface of a stator back-iron 600, which forms part of the stator 252, adjacent to the coils, where coils are wound on stator teeth formed on the stator back-iron 600.

The lead frame 255 includes a first set of three apertures 610 for receiving a respective busbar lead frame pin for coupling the lead frame 255 to an inverter 310 in the first control device 300 and a second set of three apertures 620 for receiving a respective busbar lead frame pin for coupling the lead frame 255 to an inverter 310 in the second control device 300, as described below. Additionally, the lead frame 255 includes two apertures 670, where each aperture 670 is arranged to receive a second section of a respective flexible printed circuit board, as described below.

The lead frame 255 is mounted to the stator back-iron 600 via the use of heat stakes 630 attached to the stator back- iron 600 at predetermined locations that are arranged to extend through apertures formed in the lead frame 255. Once the lead frame 255 is mounted on the stator back-iron 600 with the respective heat stakes 630 extending through a respective aperture formed in the lead frame 255, the heat stakes 630 are melted, thereby retaining the lead frame 255 to the stator back-iron 600. However, any suitable means for attaching the lead frame to the stator back-iron may be used.

As also illustrated in Figure 6, the lead frame 255 includes a plurality of recesses 640 formed on both the inner and outer radial edges of the lead frame 255 for receiving the end sections of the coils wound on the stator teeth for coupling the coils 400 to the lead frame 255, as described below, where for each coil wound on a stator tooth, one end section is mounted in a recess 640 formed on the inner radial edge of the lead frame and the other end section is mounted in a recess 640 formed on the outer radial edge of the lead frame 255.

Figure 7 illustrates a second embodiment of the lead frame, where the lead frame comprises a first lead frame section 701 and a second lead frame section (not shown), where preferably both the first lead frame section 701 and the second lead frame section are semi-circumferential such that when mounted on the stator 252 the first lead frame section 701 and the second lead frame section form a substantially circumferential lead frame arrangement. As illustrated in Figure 8 each lead frame section 701 is mounted to an axial mounting surface of a stator back-iron 600, which forms part of the stator 252, adjacent to the coils, where coils are wound on stator teeth formed on the stator back-iron 600.

Both the first lead frame section and the second lead frame section includes a set of three apertures 801 for receiving a respective busbar lead frame pin for coupling the first lead frame section 701 and the second lead frame section 701 to an inverter 310 in the first control device 300 and the second control device 300 respectively. Additionally, each lead frame 255 includes apertures 810, where each aperture 810 is arranged to receive a second section of a respective flexible printed circuit board, as described below.

The first lead frame section 701 and the second lead frame section 701 are mounted to the stator back-iron 600 via the use of heat stakes 630 attached to the stator back-iron 600 at predetermined locations that are arranged to extend through apertures formed in the first lead frame section 701 and the second lead frame section 701. Once the first lead frame section 701 and the second lead frame section 701 are mounted on the stator back-iron 600 with the respective heat stakes 630 extending through respective apertures formed in the first lead frame section 701 and the second lead frame section 701, the heat stakes 630 are melted, thereby retaining the first lead frame section 701 and the second lead frame section 701 to the stator back-iron 600. However, any suitable means for attaching the first lead frame section 701 and the second lead frame section 701 to the stator back-iron 600 may be used.

As also illustrated in Figure 8, the first lead frame section 701 and the second lead frame section 701 includes a plurality of recesses 640 formed on both the inner and outer radial edges of the first lead frame section 701 and the second lead frame section 701 for receiving the end sections of the coils 400 wound on the stator teeth for coupling the coil 400 to the first lead frame section 701 and the second lead frame section 701 respectively, as described below. For each coil wound on a stator tooth, one end section is mounted in a recess 640 formed on the inner radial edge of the first lead frame section 701 or the second lead frame section 701 and the other end section is mounted in a recess 640 formed on the outer radial edge of the corresponding lead frame section 701.

In accordance with the first embodiment of the lead frame 255, as stated above, a single circumferential lead frame is used as a current path from the respective inverters 310 within the control devices 300 to the respective coil windings, where the lead frame 255 is a substantially circumferential printed circuit board having a plurality of circuit board layers having a conductive layer printed on each circuit board layer. Within this embodiment, for each circuit board layer, a printed conductive layer formed on a first half of the surface area provides the electrical connections for one of the control devices 300 and coil windings mounted on the stator, and a printed conductive layer formed on a second half of the surface area provides the electrical connections for the other control device 300 and coil windings mounted on the stator. In other words, one half of the circumference of the lead frame printed circuit board is allocated for coupling a first control device 300 to one set of coil windings to form a first set of three sub motors and a second half of the circumference of the lead frame printed circuit board is allocated for coupling a second control device 300 to a second set of coil windings to form a second set of three sub motors.

The plurality of circuit board layers are separated by a respective insulating substrate.

The printed circuit board substrate material is made of substances that do not conduct electric currents. Typically the substrate material functions as a laminated electrical insulator for the conductive layers formed on the printed circuit board. Materials that serve as effective substrates include fibreglass, Teflon, ceramics and certain polymers, where one of the most popular substrate is FR-4. FR-4 is a fibreglass- epoxy laminate that is affordable, a good electrical insulator and is more flame-resistant than fibreglass-only boards. However, other insulating substrates may be used.

To allow for large currents to flow from the inverters 310 to the coil windings, and hence allow the electric motor to generate sufficient torque for driving a vehicle, the conductive layer on each circuit board is arranged to extend over a substantial portion of each circuit board where each conductive layer is arrange to correspond to a specific circuit path between the respective inverters 310 and the coil windings and between the different coil subsets that form the respective sub motors, as described below.

Consequently, each circuit board layer is optimised for current flow.

To achieve the circuit configuration illustrated in Figure 4, the configuration of the printed circuit board layers and conductive layers printed on the circuit board layers will now be described, where as the conductive layers printed on the circuit board layers for coupling one inverter 310 in one control device 300 to a first set of coil windings are, on each circuit board layer, a mirror image of the

conductive layers for coupling the other inverter 310 in the second control device 300 to a second set of coil windings, only the conductive layers for coupling one inverter to one set of coil windings will be described. Although each circuit board layer includes two sets of electrical connections for coupling three coil sub sets to one inverter and another three coil sub sets to another inverter, each circuit board layer may include any number of conductive layers based on the number of inverters. For example, if a single inverter were to be used to drive all the coil windings mounted on the stator the conductive layer printed on each circuit board layer would be arranged to form a specific circuit path between the inverter and the coil windings and between the different coil subsets that form the respective sub motors.

The printed circuit board includes a first circuit board layer having a first electrically conductive layer

illustrated in Figure 9 that extends over substantially a first semi-circumferential section of the circumferential circuit board that is arranged to be electrically coupled to the W phase inverter busbar and to the first coil of the first phase winding 401 of the first sub motor 411, the first coil of the first phase winding 404 of the second sub motor 412 and the first coil of the first phase winding 407 of the third sub motor 413. As stated above, an alternative electrically conductive layer extends over substantially a second semi-circumferential section of the circumferential circuit board that is arranged to be electrically coupled to the W phase inverter busbar of the second inverter and to corresponding coil windings mounted on the stator, where the alternative electrically conductive layer is electrically isolated from the first electrically conductive layer.

However as this arrangement, as with all the other circuit board layers, is a mirror image of the connections for the first inverter, the lead frame connections for coupling the second inverter to the coil windings will not be described further . The W phase inverter busbar is coupled to the first circuit board layer via a busbar lead frame pin 1010, as illustrated in Figure 10, which is a cylindrical conductive element coupled to the W phase inverter busbar, where the busbar lead frame pin extends through the relevant lead frame pin aperture 610 formed in the printed circuit board. The W busbar lead frame pin 1010 is arranged to be electrically coupled to the first conductive layer 900 at location 910.

To allow the first coil of the first phase winding 401 of the first sub motor 411, the first coil of the first phase winding 404 of the second sub motor 412 and the first coil of the first phase winding 405 of the third sub motor 413 to be coupled to the first conductive layer at locations 920, 930, 940, the end sections of the relevant coils are arranged to be mounted within the recesses 640 formed within the inner and outer radial edge of the lead frame 255, as described above, where the end section of the coil windings mounted within the recess formed within the inner radial edge of the lead frame at locations 920, 930, 940 and are electrically coupled to the first conductive layer 900. The other end sections of the first coils of the first phase windings for the first, second and third sub motor and the end sections of the remaining coil windings, which are mounted in respective recesses formed within the inner and outer radial edges of the lead frame, are electrically isolated from the first conductive layer.

The printed circuit board includes a second circuit board layer having a second electrically conductive layer 1100 illustrated in Figure 11 that extends over substantially a first semi-circumferential section of the circumferential circuit board that is arranged to be electrically coupled to the U phase inverter busbar and to the first coil of the second phase winding 402 of the first sub motor 411, first coil of the second phase winding 405 of the second sub motor 412 and first coil of the second phase winding 408 of the third sub motor 413. As stated above, an alternative electrically conductive layer extends over substantially a second semi-circumferential section of the circumferential circuit board that is arranged to be electrically coupled to the U phase inverter busbar of the second inverter and to corresponding coil windings mounted on the stator, where the alternative electrically conductive layer is electrically isolated from the second electrically conductive layer.

However as this arrangement, as with all the other circuit board layers, is a mirror image of the connections for the first inverter, the lead frame connections for coupling the second inverter to the coil windings will not be described further .

The U phase inverter busbar is coupled to the second circuit board layer via a busbar lead frame pin 1010, as illustrated in Figure 10, which is a cylindrical conductive element coupled to the U phase inverter busbar that extends through the relevant lead frame pin aperture 610 formed in the printed circuit board. The U busbar lead frame pin 1010 is arranged to be electrically coupled to the second conductive layer 1100 at location 1110. To allow the first coil of the second phase winding 402 of the first sub motor 411, the first coil of the second phase winding 405 of the second sub motor 412 and the first coil of the second phase winding 408 of the third sub motor 413 to be coupled to the second conductive layer at locations 1120, 1130, 1140 respectively, the end sections of the relevant coils are arranged to be mounted within the recesses 640 formed within the inner and outer radial edge of the lead frame 255, as described above, where the end section of the coil windings mounted within the recess formed within the inner radial edge of the lead frame 255 at locations 1120, 1130, 1140 are electrically coupled to the second conductive layer. The other end sections of the first coils of the second phase windings for the first, second and third sub motor and the end sections of the remaining coil windings, which are mounted in respective recesses formed within the inner and outer radial edges of the lead frame, are electrically isolated from the second conductive layer.

The printed circuit board includes a third circuit board layer having a third electrically conductive layer

illustrated in Figure 12 that extends over substantially a first semi-circumferential section of the circumferential circuit board that is arranged to be electrically coupled to the V phase inverter busbar and to the first coil of the third phase winding 403 of the first sub motor 411, first coil of the third phase winding 406 of the second sub motor 412 and first coil of the third phase winding 409 of the third sub motor 413. As stated above, an alternative electrically conductive layer extends over substantially a second semi-circumferential section of the circumferential circuit board that is arranged to be electrically coupled to the V phase inverter busbar of the second inverter and to corresponding coil windings mounted on the stator, where the alternative electrically conductive layer is electrically isolated from the second electrically conductive layer.

However as this arrangement, as with all the other circuit board layers, is a mirror image of the connections for the first inverter, the lead frame connections for coupling the second inverter to the coil windings will not be described further . The V phase inverter busbar is coupled to the third circuit board layer via a busbar lead frame pin 1010, as illustrated in Figure 10, which is a cylindrical conductive element coupled to the V phase inverter busbar that extends through the relevant lead frame pin aperture 610 formed in the printed circuit board. The V busbar lead frame pin 1010 is arranged to be electrically coupled to the third conductive layer 1200 at location 1210. To allow the first coil of the third phase winding 403 of the first sub motor 411, the first coil of the third phase winding 406 of the second sub motor 412 and the first coil of the third phase winding 409 of the third sub motor 413 to be coupled to the third conductive layer, the end sections of the relevant coils are arranged to be mounted within the recesses 640 formed within the inner and outer radial edge of the lead frame 255, as described above, where the end section of the coil windings mounted within the recess formed within the inner radial edge of the lead frame at locations 1220, 1230, 1240 are electrically coupled to the third conductive layer. The other end sections of the first coils of the third phase windings for the first, second and third sub motor and the end sections of the remaining coil windings, which are mounted in respective recesses formed within the inner and outer radial edges of the lead frame, are electrically isolated from the third conductive layer.

The printed circuit board includes a fourth circuit board layer having a fourth electrically conductive layer 1310, fifth electrically conductive layer 1320 and a sixth electrically conductive layer 1330, illustrated in Figure 13, where the fourth electrically conductive layer 1310, fifth electrically conductive layer 1320 and sixth

electrically conductive layer 1330 together extend over substantially a first semi-circumferential section of the circumferential circuit board. The fourth electrically conductive layer 1310, fifth electrically conductive layer 1320 and sixth electrically conductive layer 1330 are electrically isolated from each other.

The fourth electrically conductive layer 1310 is arranged to electrically couple the last coil of the first phase winding 401 of the first sub motor 411, last coil of the second phase winding 402 of the first sub motor 411 and last coil of the third phase winding 403 of the first sub motor 411 to form a neutral point (i.e. a star point) between the first coil winding 401, the second coil winding 402, and the third coil winding 403 of the first sub motor 411.

To allow the last coil of the first phase winding 401 of the first sub motor 411, the last coil of the second phase winding 402 of the first sub motor 411 and the last coil of the third phase winding 403 of the first sub motor 411 to be coupled, the end sections of the relevant coils are arranged to be mounted within the recesses 640 formed within the inner and outer radial edge of the lead frame 255, as described above, where the end section of the coil windings mounted within the recess formed within the outer radial edge of the lead frame at locations 1311, 1312, 1313 are electrically coupled to the fourth conductive layer 1310.

The other end sections of the last coil of the first phase winding 401 of the first sub motor 411, the last coil of the second phase winding 402 of the first sub motor 411 and the last coil of the third phase winding 403 of the first sub motor 411 and the end sections of the remaining coil windings, which are mounted in respective recesses formed within the inner and outer radial edges of the lead frame 255, are electrically isolated from the fourth conductive layer 1310. The fifth electrically conductive layer 1320 is arranged to electrically couple the last coil of the first phase winding 404 of the second sub motor 412, last coil of the second phase winding 405 of the second sub motor 412 and last coil of the third phase winding 406 of the second sub motor 412 to form a neutral point (i.e. a star point) between the first coil winding 404, the second coil winding 405, and the third coil winding 405of the second sub motor 412.

To allow the last coil of the first phase winding 404 of the second sub motor 412, the last coil of the second phase winding 405 of the second sub motor 412 and the last coil of the third phase winding 406 of the second sub motor 412 to be coupled, the end sections of the relevant coils are arranged to be mounted within the recesses 640 formed within the inner and outer radial edge of the lead frame 255, as described above, where the end section of the coil windings mounted within the recess formed within the outer radial edge of the lead frame at locations 1321, 1322, 1323 are electrically coupled to the fifth conductive layer 1320. The other end sections of the last coil of the first phase winding 404 of the second sub motor 412, the last coil of the second phase winding 405 of the second sub motor 412 and the last coil of the third phase winding 406 of the second sub motor 412 and the end sections of the remaining coil windings, which are mounted in respective recesses 640 formed within the inner and outer radial edges of the lead frame 255, are electrically isolated from the fifth

conductive layer 1320.

The sixth electrically conductive layer 1330 is arranged to electrically couple the last coil of the first phase winding 407 of the third sub motor 413, last coil of the second phase winding 408 of the third sub motor 413 and last coil of the third phase winding 409 of the third sub motor 413 to form a neutral point (i.e. a star point) between the first coil winding 407, the second coil winding 408, and the third coil winding 409 of the third sub motor 413.

To allow the last coil of the first phase winding 407 of the third sub motor 413, the last coil of the second phase winding 408 of the third sub motor 413 and the last coil of the third phase winding 409 of the third sub motor 413 to be coupled, the end sections of the relevant coils are arranged to be mounted within the recesses 640 formed within the inner and outer radial edge of the lead frame 255, as described above, where the end section of the coil windings mounted within the recess formed within the outer radial edge of the lead frame at locations 1331, 1332, 1333 are electrically coupled to the sixth conductive layer 1330. The other end sections of the last coil of the first phase winding 407 of the third sub motor 413, the last coil of the second phase winding 408 of the third sub motor 413 and the last coil of the third phase winding 409 of the third sub motor 413 and the end sections of the remaining coil windings, which are mounted in respective recesses 640 formed within the inner and outer radial edges of the lead frame 255, are electrically isolated from the sixth

conductive layer 1330.

The printed circuit board includes a fifth circuit board layer having a plurality of electrically conductive layers illustrated in Figure 14 for electrically coupling coils 400 that form the first phase winding 401 of the first sub motor 411, coils 400 that form the second phase winding 402 of the first sub motor 411, and coils 400 that form the third phase winding 402 of the first sub motor 411. With respect to the second sub motor, the plurality of electrically conductive layers are arranged to electrically couple coils 400 that form the first phase winding 404 of the second sub motor 412, coils 400 that form the second phase winding 405 of the second sub motor 412, and coils 400 that form the third phase winding 406 of the second sub motor 412. With respect to the third sub motor, the plurality of electrically conductive layers are arranged to electrically couple coils 400 that form the first phase winding 407 of the third sub motor 413, coils 400 that form the second phase winding 408 of the third sub motor 413, and coils 400 that form the third phase winding 409 of the third sub motor 413.

Preferably the plurality of electrically conductive layers on the fifth circuit board layer are arranged to allow the plurality of coils for each respective coil sub-set to be coupled such that each coil within a coil winding produces a magnetic field that is anti-parallel with its adjacent coil for a given direction of current flow while having a common phase .

Of the plurality of electrically conductive layers formed on the fifth printed circuit board layer, two electrically conductive layers 1501, 1502 are used for coupling coils 400 that form the first phase winding 401 of the first sub motor 411, two electrically conductive layers 1503, 1504 are used for coupling coils 400 that form the second phase winding 402 of the first sub motor 411, and two electrically conductive layers 1505, 1506 are used for coupling coils 400 that form the third phase winding 403 of the first sub motor 411. With respect to the second sub motor, two electrically conductive layers 1507, 1508 are used for coupling coils 400 that form the first phase winding 404 of the second sub motor 412, two electrically conductive layers 1509, 1510 are used for coupling coils 400 that form the second phase winding 405 of the second sub motor 412, and two

electrically conductive layers 1511, 1512 are used for coupling coils 400 that form the third phase winding 406 of the second sub motor 412. With respect to the third sub motor, two electrically conductive layers 1513, 1514 are used for coupling coils 400 that form the first phase winding 407 of the third sub motor 413, two electrically conductive layers 1515, 1516 are used for coupling coils 400 that form the second phase winding 408 of the third sub motor 413, and two electrically conductive layers 1517, 1518 are used for coupling coils 400 that form the third phase winding 409 of the third sub motor 413.

By way of illustration, the connections for coupling coils 400 will be described.

As stated above, one end section of the first coil that forms the set of coils that form the first phase winding 401 of the first sub motor 411 is mounted in a recess 640 formed on the inner radial edge of the lead frame 255 at location 920 and is electrically coupled to the first electrically conductive layer 900 formed on the first circuit board layer while being electrically isolated from any other

electrically conductive layers on the other circuit board layers. The other end of the first coil is mounted in an opposite recess formed on the outer radial edge of the lead frame at location 950 and is electrically coupled to electrically conductive layer 1502 on the fifth circuit board layer.

One end section of the second coil that forms the set of coils that form the first phase winding 401 of the first sub motor 411 is mounted in recess formed on the outer radial edge of the lead frame at location 951 and is electrically coupled to electrically conductive layer 1502 on the fifth circuit board layer, thereby electrically connecting the second coil to the W phase busbar pin via the first coil.

The other end of the second coil is mounted in an opposite recess formed on the inner radial edge of the lead frame at location 952 and is electrically coupled to electrically conductive layer 1501 on the fifth circuit board layer that is electrically isolated from electrically conductive layer 1502.

One end section of the third coil that forms the set of coils that form the first phase winding 401 of the first sub motor 411 is mounted in recess formed on the inner radial edge of the lead frame at location 953 and is electrically coupled to electrically conductive layer 1501 on the fifth circuit board layer, thereby electrically connecting the third coil to the W phase busbar pin via the first and second coils. The other end of the third coil is mounted in an opposite recess formed on the outer radial edge of the lead frame at location 954 and is electrically coupled to the fourth conductive layer 1310 on the fourth circuit board layer for coupling the third coil to the corresponding coil for the second phase winding 402 and the third phase winding 403 that form the first sub motor 411.

In a similar fashion, the next set of two conductive layers 1503, 1504 on the fifth circuit board layer are used to couple coils 400 that form the second phase winding 402 of the first sub motor 411 to the V phase busbar pin, and the next set of two conductive layers 1505, 1506 on the fifth circuit board layer are used to couple coils 400 that form the third phase winding 403 of the first sub motor 411 to the U phase busbar pin.

The next set of two conductive layers 1507, 1508 on the fifth circuit board layer are used to couple coils 400 that form the first phase winding 404 of the second sub motor 412 to the W phase busbar pin the next set of two conductive layers 1509, 1510 on the fifth circuit board layer are used to couple coils 400 that form the second phase winding 405 of the second sub motor 412 to the V phase busbar pin, and the next set of two conductive layers 1511, 1512 on the fifth circuit board layer are used to couple coils 400 that form the third phase winding 406 of the second sub motor 412 to the U phase busbar pin.

The next set of two conductive layers 1513, 1514 on the fifth circuit board layer are used to couple coils 400 that form the first phase winding 407 of the third sub motor 413 to the W phase busbar pin the next set of two conductive layers 1515, 1516 on the fifth circuit board layer are used to couple coils 400 that form the second phase winding 408 of the third sub motor 413 to the V phase busbar pin, and the next set of two conductive layers 1517, 1518 on the fifth circuit board layer are used to couple coils 400 that form the third phase winding 409 of the third sub motor 413 to the U phase busbar pin.

In a preferred embodiment, to allow for increased current flow, and consequently increase torque, one or more of the circuit board layers may be duplicated. Accordingly, the first circuit board layer may be replaced with two circuit board layers having the same configuration as the first circuit board layer, thereby doubling the conductive area provided by the first circuit board. Similarly, the second circuit board layer may be replaced with two circuit board layers having the same configuration as the second circuit board layer, the third circuit board layer may be replaced with two circuit board layers having the same configuration as the third circuit board layer, the fourth circuit board layer may be replaced with two circuit board layers having the same configuration as the fourth circuit board layer, and the fifth circuit board layer may be replaced with two circuit board layers having the same configuration as the fifth circuit board layer.

The electrical connection for coupling the W, U, V phase busbar pins and the respective coils to the lead frame will now be described.

With regard to the electrical connections for coupling the phase busbar pins 1010 to the respective conductive layers printed on the lead frame circuit board layers, an

electrically conductive sleeve 1600 is inserted into the respective apertures formed in the lead frame for the W, U,

V phase busbar pins 1010, as illustrated in Figure 15. When the W, U, V phase busbar pins are inserted into the

respective electrically conductive sleeves 1600 the phase busbar pins 1010 are arranged to be in electrical contact with the sleeves 1600. For improved electrical contact between the pins 1010 and the sleeve 1600, solder or other electrically conductive material may be used.

For any conductive layers formed on the respective circuit board layers that need to be electrically connected to a phase busbar pin 1010, the respective conductive layers are arranged to extend and be in electrical contact to the electrically conductive sleeve 1600. For any conductive layers formed on the respective circuit board layers that are electrically isolated from a phase busbar pin 1010, the respective conductive layers are arranged to be electrically isolated from the electrically conductive sleeve 1600.

For example, with reference to in Figure 15, the lead frame includes ten circuit board layers, where the first two circuit board layers 1611, 1612 correspond to the first circuit board layer described above for coupling the W busbar lead frame pin to the lead frame, the next two circuit board layers 1613, 1614 correspond to the second circuit board layer described above for coupling the U busbar lead frame pin to the lead frame, the next two circuit board layers 1615, 1616 correspond to the third circuit board layer described above for coupling the V busbar lead frame pin to the lead frame, the next two circuit board layers 1617, 1618 correspond to the fourth circuit board layer described above for coupling the first phase winding, the second phase winding and the third phase winding of the respective sub motors, with the next two circuit board layers 1619, 1620 corresponding to the fifth circuit board layer described above for coupling the coils for the respective phase windings. As illustrated in Figure 15, the first conductive layers on the first two circuit board layers 1611, 1612 are in contact with the electrically conductive sleeve for coupling the W busbar lead frame pin to these two conductive layers. In contrast the conductive layers printed on the other circuit board layers are electrically isolated from the electrically conductive sleeve . Although, the present embodiment uses an electrically conductive sleeve 1600 for electrically coupling a busbar lead frame pin 1010 to the lead frame 255, any mechanism may be used for coupling the respective inverter legs to the lead frame 255.

With regard to the end sections of the respective coils, a similar arrangement to that used for electrically coupling the phase busbar pins 1010 may be used for electrically coupling the respective end sections of the coils 400 to a required conductive layer printed on one or more of the circuit board layers, where a semicircular conductive sleeve is placed within the respective recesses formed in the inner and outer radial edges of the lead frame. Alternatively, the end sections of the respective coils 400 may be placed directly within the recess 640 formed in the inner and outer radial edges of the lead frame 255 with a conductive material placed between the end sections of the coils and the relevant conductive layers for improved conductivity between the end sections of the respective coils and the conductive layers with which they are intended to be electrically connected.

Embodiments of the flexible printed circuit board 260 mounting between the lead frame 255 and the coils 400 will now be described.

Typically, the flexible printed circuit board 260 will include a flexible plastic substrate such as polyimide, polyether ether ketone PEEK or transparent conductive polyester, as is well known to a person skilled in the art, with at least one temperature sensor 1610 mounted on the flexible plastic substrate. Figure 16 illustrates an embodiment of a flexible printed circuit board that is substantially semi circumferential; however, as discussed below, the flexible printed circuit board may take any shape .

As discussed above, the flexible printed circuit board 260 includes a first section 261 and a second section 262. The first section 261 is arranged to be mounted between the lead frame 255 and the coils 400. The second section 262 extends radially away from the first section 261 and is arranged to flex in a direction perpendicular to the first section 261, as illustrated in Figure 17.

As illustrated in Figure 17, when the second section 262 is flexed in a direction perpendicular to the first section 261, the second section 262 is configured to extend through the aperture 810 formed in the lead frame 255. Preferably, the first section 261 of the flexible printed circuit board 260 is substantially flat, where the surface of the flexible printed circuit board 260 adjacent to the lead frame 255 has a similar surface area configuration to that of the

corresponding surface of the lead frame 255.

When the second section 262 of the flexible printed circuit board 260 is flexed to extend perpendicular to the first section 261 and extends through the aperture 810 formed in the lead frame 255, the end portion of the second section of the flexible printed circuit board 262 is arranged to be coupled to a control device 400 mounted on the stator.

As illustrated in Figure 16, a conductive strip 1620 is formed on the flexible printed circuit board substrate, which extends from the temperature sensor 1610 to the end portion of the second section 262 of the flexible printed circuit board substrate, for allowing the control device 400 to monitor the temperature readings measured by the

temperature sensor 1610 mounted on the flexible printed circuit board substrate. For the purposes of the embodiment of the flexible printed circuit board illustrated in Figure 16, the flexible printed circuit board includes three temperature sensors with a conductive strip 1610 extending from each temperature sensor to the end portion of the second section of the flexible printed circuit board, however any number of temperature sensors may be used.

Preferably, the temperature sensor 1610 is arranged to be mounted on the first section 261 of the first flexible printed circuit board 260 on a side of the first section 261 adjacent to the first surface of the coil windings.

To allow the control device 400 to monitor the temperature readings measured by the temperature sensor mounted on the flexible printed circuit board substrate, the conductive strip 1610 formed on the flexible printed circuit board substrate that extends from the temperature sensor 1610 to an end portion of the second section 262 of flexible printed circuit board 260 is coupled to a control device 400 mounted adjacent to a second surface of the lead frame 255.

Preferably, the material of the flexible printed circuit board substrate is arranged to electrically isolate the coil windings from the lead frame 255.

In a first embodiment of a stator, the stator includes two flexible printed circuit boards 260, as illustrated in Figure 2, each flexible printed circuit board 260 is substantially semi circumferential in shape having three temperature sensors mounted on each flexible printed circuit board substrate. Each of the temperature sensors 1610 are located on the side of the first section of the flexible printed circuit board substrate adjacent to the coils.

A conductive strip 1620 extends from each temperature sensor 1610 to an end portion of the second section of the

respective flexible printed circuit board 260 to allow a control device 400 to monitor the temperature readings measured by each of the temperature sensors 1610 mounted on the respective flexible printed circuit board substrate.

Each of the temperature sensors 1610 are positioned on the flexible printed circuit board substrate for both flexible printed circuit boards 260 to measure temperature readings for a respective set of coil windings.

In a preferred embodiment, each temperature sensor 1610 is positioned substantially midway between the front and back of the coil windings and midway between two of the three coil windings that form a set of coil windings. Figure 18 illustrates the positioning of a temperature sensor between the front and back of the coil windings. Figure 19

illustrates the position of a temperature sensor between two of the three coils that form a set of coil windings.

Advantages of placing the temperature sensors substantially midway between the coil windings include improved electrical insulation from the coil windings and for obtaining an average temperature reading for the respective coil

windings .

In a second embodiment of a stator, the stator includes a single flexible printed circuit board 260, as illustrated in Figure 20, where the flexible printed circuit board 260 is substantially circumferential in shape, in other words substantially annular in shape. The flexible printed circuit board 260 includes six temperature sensors mounted on the flexible printed circuit board substrate.

A conductive strip extends from each temperature sensor to an end portion of the second section of the flexible printed circuit board to allow a control device 400 to monitor the temperature readings measured by each of the temperature sensor mounted on the flexible printed circuit board substrate .

Each of the temperature sensors are positioned on the flexible printed circuit board substrate for the flexible printed circuit board 260 to measure temperature readings for one of the six sets of coil windings.

In a preferred embodiment, each temperature sensor is positioned substantially midway between the front and back of the coil windings and midway between two of the three coil windings that form a set of coil windings, as

illustrated in Figure 18 and Figure 19.

Although the first embodiment and the second embodiment of the stator include two semi circumferential flexible printed circuit boards and a single circumferential flexible printed circuit board, respectively, any number of flexible printed circuit boards may be mounted between the lead frame 255 and the coils for measuring the temperature of the coils 400, where the flexible printed circuit boards 260 may take any shape that allows a temperature sensor to measure the temperature of coils 400.

A preferred process for assembling the stator, which includes attaching the flexible printed circuit board 260 and lead frame 255 to the stator back iron 600 and coil windings, mounting the end sections of the coils 400 in the inner and outer radial recesses 640 of the lead frame 255 and coupling the flexible printed circuit board 260 and lead frame 255 to a control device 300, will now be described.

Prior to the mounting of the flexible printed circuit board 260 and lead frame 255 to the stator back iron 600, the end sections of the coils are arranged to extend in a radial direction away from the stator back iron 600 in the same plane as the axial mounting surface of the stator back iron 600. In this configuration, the end section of a coil on the outer radial edge of the stator back iron 600 is arranged to extend in a radial direction away from the centre of the stator back iron 600 and the end section of the coil on the inner radial edge of the stator back iron 600 is arranged to extend in a radial direction towards the centre of the stator back iron 600.

As stated above, the flexible printed circuit board 260 and the lead frame 255 are then mounted on the axial mounting surface of the stator back iron 600, preferably via the use of heat stakes, where recesses formed in the inner and outer radial edges of the first section of the flexible printed circuit board and lead frame 255 are arranged to align with the end sections of the coils such that the respective recesses 640 formed in the inner and outer radial edges of the first section of the flexible printed circuit board and lead frame 255 are positioned over a respective end section of a coil, where Figure 21 illustrates one coil end section 2110 extending in a radial direction away from the stator back iron 600. The end sections of the respective coils are then rotated by ninety degrees to extend into a flexible printed circuit board recess and lead frame recess 640 positioned above the respective end sections of the

respective coils, thereby resulting in the coil end section 2120 extending in an axial direction. Any means may be used for rotating the end sections into the respective recess formed on the inner and outer radial edge of the lead frame.

With reference to Figure 21, the end section of a coil prior to being positioned within an axial recess 640 formed in the lead frame 255 is shown in solid, whereas the dashed version of the end section shown in Figure 21 represents the position of the end section of the coil once it has been rotated ninety degrees into the recess 640.

Figure 22 illustrates a section of the stator back iron showing seven coils 400 with their respective coil end sections extending into an inner and outer radial recess 640 formed in the lead frame 255 for coupling the respective coils to the lead frame 255, as described above. As stated above, for improved electrical contact between the end sections of the respective coils and the lead frame 255, solder, or some other electrically conductive material may be used to between the end section of the coils and the lead frame 255.

Once the lead frame 255 has been mounted on the stator back iron 600, with the flexible printed circuit board 260 sandwiched between the lead frame 255 and the coils 400, and the end sections of the coils have been coupled to the lead frame 255, the stator back iron 600 is arranged to be mounted to the stator heat sink 253.

As illustrated in Figures 23 and 24, the heat sink includes a circumferential support 253 having a circumferential mounting surface upon which the stator back iron 600 is arranged to be mounted. Extending radially away from the circumferential support 253 is a flange, where the

respective control devices are arranged to be mounted on the radial surface of the heat sink opposite to that upon which the circumferential support 253 is formed.

To allow the flexible printed circuit board 260 and lead frame 255 to be electrically coupled to a respective control device 300, an outer section of the radial flange 2300 of the heat sink includes a plurality of apertures 2310, 2320 arranged to receive the end sections of the flexible printed circuit boards, which extend through the lead frame 255, and the lead frame phase pin connections 2330.

Preferably, the stator back iron 600 is mounted on the stator heat sink 253 via a hot drop mechanism to create an interference fit between the stator back iron 600 and the stator heat sink 253, for example as described in Patent application GB1615255.5, where the inner radial surface of the stator back iron 600 is arranged to have the same or slightly smaller diameter than the circumferential mounting surface of the stator heat sink 253 when both the stator back iron 600 and the stator heat sink 253 are at the same temperature, which prevents the stator back iron 600 from fitting around the circumferential mounting surface of the stator heat sink 253 when both items are at the same temperature .

When producing the interference fit it is necessary to heat the stator back iron to cause expansion. The temperature to which the component is heated depends upon a number of factors including the degree of expansion required to generate a clearance, the thermal expansion coefficient of the material and the safe temperature to which the material can be heated.

Prior to the hot drop process, to protect the end sections of the flexible printed circuit boards 260 and ensure that they do not come into contact with the heat sink when being placed through the respective apertures 2310 formed in the heat sink flange 2300, a rigid sleeve 2340, otherwise known as a protective sleeve, is mounted over the sections of the flexible printed circuit boards 260 that extend through the lead frame 255, as illustrated in Figure 26, where Figure 25 illustrates the stator back iron prior to the protective sleeves 2340 being attached. This ensures that despite the flexible nature of the flexible printed circuit board 260 the end sections of the flexible printed circuit board extend perpendicularly away from the radial surface of the lead frame 255, thereby avoiding the end sections of the flexible printed circuit board 260 coming into contact with the inner radial flange surface of the heat sink 253 during the hot drop process.

Preferably, to avoid the protective sleeves 2340 coming away from the lead frame 255 during the hot drop process, the respective protective sleeves 2340 are mechanically attached to the lead frame 255.

For example, as illustrated in Figure 27, each of the protective sleeves 2340 includes one or more flanges 2700 that are arranged to engage with a corresponding aperture formed in the lead frame 255 to allow the protective sleeve 2340 to be attached to the lead frame 255 via a twist and lock action to allow the protective sleeve 2340 to be easily attached to the lead frame 255 prior to the hot drop process and detached from the lead frame after the hot drop process. However, any suitable means may be used for removably attaching the protective sleeve to the lead frame, for example a bayonet fitting, a spring tang fitting.

To allow the protective sleeves 2340 to protect the end sections of the flexible printed circuit board 260 and avoid the end sections of the flexible printed circuit boards 260 coming into contact with the heat sink flange 2300 the protective sleeves 2340 are preferably arranged to extend around the whole length of the sections of the flexible printed circuit boards 260 that extend through the lead frame 255. Preferably the outer form of the protective sleeves 2340 correspond to the apertures formed in the heat sink flange to allow the protective sleeve 2340 to extend through the respective apertures 2310 during the hot drop process .

To avoid the protective sleeves 2340 becoming deformed from the heat generated during hot drop process the protective sleeves are preferably made from a heat resistance material, for example a thermo resistant plastic, carbon fibre/glass fibre, silicone rubber, vulcanized rubber.

Once the stator back iron has been heated to the required temperature the inner diameter of the circumferential support is slid over the circumferential mounting surface of the stator heat sink 253, thereby causing the protective sleeve 2340 and end sections of the flexible printed circuit board 260 to extend through the respective apertures 2310 formed in the heat sink flange 2300. The stator back iron is then allowed to cool, thereby causing the inner diameter of the stator back to reduce such that the inner wall of the stator back iron presses against the outer circumferential wall of the heat sink 253, thereby creating an interference fit between the stator back iron and the heat sink 253. The protective sleeves 2340 are then removed from the lead frame 255.

The respective control devices are then mounted to the heat sink and electrically coupled to the flexible printed circuit boards and the lead frame phase pins.

During operation of the electric motor, to allow for cooling of the stator back iron 600, the coils 400, the flexible printed circuit board 260, and the lead frame 255, the stator head sink 253 has a cooling channel having a first section 1810 that is arranged to extend along the inner axial edge of the stator teeth and back iron 600, and a second section 1820 that is arranged to extend in a radially outward direction that is parallel to the axial mounting surface of stator back iron 600 on which the lead frame is mounted, as illustrated in a cross sectional view of the stator shown in Figure 28.

For improved thermal conductivity between the stator heat sink 253, the flexible printed circuit board 260 and the lead frame 255, potting material 1830 is placed between the heat sink 253 and the lead frame 255 and between the lead frame 255, the flexible printed circuit board 260 and the stator coils 400. Typically the potting material 1830 used is arranged to provide good thermal conductivity. One example of a suitable potting material is ceramic filled epoxy resin; however other types of potting material may be used.

With regard to the second embodiment of the lead frame, the lead frame configuration is the same as that described above with respect to the first embodiment other than two semi circular lead frame sections 701 having a plurality of printed circuit board layers are used for mounting the conductive layers for coupling an inverter 310 to a

plurality of coils. In other words, a first lead frame section 701 has a first set of printed circuit boards having conductive layers, as described above, for coupling a first inverter 310 to a first set of coils 400 to form a first set of three sub motors, with a second lead frame section 701 having a second set of printed circuit boards having conductive layers, as described above, for coupling a second inverter 310 to a second set of coils 400 to form a second set of three sub motors.

For this embodiment, as a result of each lead frame section 701 only forming a semi circular section, this has the advantage of reducing manufacturing costs for the overall lead frame arrangement compared to the manufacturing costs for a single circumferential lead frame.

In a further preferred embodiment of the lead frame, for improved current flow, if there are portions of a conductive layer on one or more printed circuit board layers, where current flow is not required, these sections of the

conductive layer can be isolated from the rest of the conductive layer and used as an additional current path for conductive layers on other printed circuit board layers. For example, as the right hand section of the conductive layer 900 on the first printed circuit board is not required for current flow between the W phase busbar pin and the first phase windings of the first sub motor, second sub motor and the third sub motor, this section of the conductive layer may be used to support current flow for other conductive layers. For the purposes of this embodiment, this section of the first conductive layer is electrically isolated from the rest of the first conductive layer and is used for support current flow in the sixth conductive layer on the fourth printed circuit board layer.

Claims

1. A method for assembling a stator for an electric motor or generator, the method comprising providing an annular support having an inner diameter, wherein the annular support includes a lead frame having a

plurality of circuit board layers, a first flexible printed circuit board having a first section and a second section, wherein the first section is mounted between a first surface of the lead frame and the annular support, wherein the second section extends through an aperture formed in the lead frame; placing a rigid sleeve over the second section of the flexible printed circuit board that extends through the lead frame; attaching the rigid sleeve to the lead frame; providing a heat sink, wherein the heat sink includes a mounting section having a circumferential outer wall and a flange section that extends around the mounting section and includes an aperture; heating the annular support to expand the inner diameter of the annular support; sliding the inner diameter of the annular support over the outer wall of the heat sink mounting section and the rigid sleeve and second section of the flexible printed circuit board through the aperture formed in the heat sink flange section; cooling the annular support to reduce the inner diameter of the annular support such that the inner wall of the annular support presses against the outer wall of the heat sink; removing the rigid sleeve from the lead frame.

2. A method according to claim 1, wherein the annular

support includes a plurality of teeth, wherein coil windings are mounted on a plurality of teeth.

3. A method according to claim 2, wherein a sensor is mounted on the first section of the first flexible printed circuit board on a side of the first section adjacent to a first surface of the coil windings.

4. A method according to claim 3, wherein the sensor is a temperature sensor.

5. A method according to any one of the preceding claims, further comprising coupling the coil windings to the plurality of circuit board layers to allow current to flow in the coil windings to allow the electric motor to generate a drive torque.

6. A method according to any one of claims 2 to 5, further comprising placing a potting material between the annular support, the coil windings, the flexible printed circuit board and the lead frame.

7. A method according to any one of the preceding claims, wherein an electrical connection extends from the sensor to the second section of the flexible printed circuit board.

8. A method according to any one of claims 4 to 7, further comprising mounting a control device adjacent to a second surface of the lead frame and coupling the second section of the flexible printed circuit board to the control device to allow the control device to monitor the temperature of the coil windings.

9. A method according to any one of the preceding claims, wherein the heat sink is arranged to providing cooling to the annular support

10. A method according to any one of the preceding claims, wherein the aperture formed in the lead frame extends in a direction substantially perpendicular to the first surface of the lead frame.

11. A method according to any one of claims 2 to 10,

wherein the first section of the flexible printed circuit board is substantially annular in shape and is arranged to extend around a first surface of the coil windings

12. A method according to any one of claims 2 to 10,

further comprising a second flexible printed circuit board having a first section and a second section, wherein the first section is mounted between the first surface of the lead frame and the first surface of the coil windings, wherein a temperature sensor is mounted on the first section of the second flexible printed circuit board on a side of the first section adjacent to the first surface of the coil windings, wherein the second section is arranged to extend through an aperture formed in the lead frame for coupling to a control device mounted adjacent to a second surface of the lead frame, wherein an electrical connection extends from the temperature sensor mounted on the first section to the second section to allow the control device to monitor the temperature of the coil windings .

13. A method according to claim 12, wherein the flexible printed circuit board and the second flexible printed circuit board are substantially semi-circumferential.

14. A method according to any one of claims 2 to 13,

wherein the sensor is positioned on the flexible printed circuit board substantially midway between two teeth mounted on the annular support.

15. A method according to any one claims 2 to 14, wherein the lead frame is arranged to electrically couple a first inverter having a plurality of inverter legs to a first set of coil windings of the electric motor or generator, the lead frame comprising a printed circuit board having a plurality of circuit board layers, wherein each circuit board layer includes an insulating substrate having an electrically conductive layer formed on the insulating substrate, wherein a first circuit board layer includes a first electrically conductive layer arranged to be coupled to a first coil winding of the first set of coil windings and a first leg of the first inverter, a second circuit board layer includes a second electrically conductive layer arranged to be coupled to a second coil winding of the first set of coil windings and a second leg of the first inverter, a third circuit board layer includes a third electrically conductive layer arranged to be coupled to a third coil winding of the first set of coil windings and a third leg of the first inverter; and a fourth circuit board layer includes a fourth electrically conductive layer arranged to be coupled to the first coil winding, the second coil winding, and the third coil winding to form a neutral point between the first coil winding, the second coil winding, and the third coil winding.

16. A method according to any one of the preceding claims, wherein the printed circuit board of the lead frame includes means for locating the lead frame the annular support in a predetermined location.

17. A method according to any one of claims 2 to 16,

wherein the printed circuit board of the lead frame includes a plurality of recesses formed in the inner and outer edge of the printed circuit board, wherein each recess is arranged to receive a respective coil winding for electrically coupling the coil winding to the printed circuit board.