Method of assembling stator assembly

Abstract

A method and apparatus for assembling a stator assembly (2, fig 5), the method comprising the steps of providing a stator core S1 and hairpins (3, fig 2A); inserting the hairpins S2 through the core s

Description

TECHNICAL FIELD The present disclosure relates to a method of and apparatus for assembling a stator assembly, to a stator assembly formed by such a method, to an electrical machine comprising such a stator assembly, and to a vehicle comprising such a stator assembly or electrical machine. BACKGROUND An electrical machine comprises a stator. The stator may comprise a stator core, and a plurality of hairpins (electrical elements, generally copper, having two long parallel members joined at one end by a shorter member, or head) which extend through the stator core and are electrically connected to form stator windings. To assemble this structure, the hairpins are inserted through holes or slots in the stator core so that the free ends of the hairpins (hairpin ends) extend out of the stator core. The free ends are then manipulated into desired positions (by widening and / or twisting), prior to being electrically connected. The process for widening and twisting hairpins within a stator assembly is well known. However, at present validating the positions of the hairpins after the process is carried out by means of a go / no go gauge. If the go / no go gauge indicates that the hairpin ends are not correctly positioned, an operator adjusts offsets for the apparatus carrying out the hairpin end manipulation in accordance with their best judgement, and the process is repeated (trial and error). This continues until the correct settings are found and the go / no go gauge indicates correct alignment of the hairpin ends. This process is very time consuming, and leads to wasted parts (the hairpin ends at least cannot easily be reused). It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a method of and apparatus for assembling a stator assembly, to a stator assembly formed by such a method, to an electrical machine comprising such a stator assembly, and to a vehicle comprising such a stator assembly or electrical machine as claimed in the appended claims. According to an aspect of the present invention there is provided a method of assembling a stator assembly, the method comprising the steps of: providing a stator core and a plurality of hairpins; inserting the hairpins through the stator core so that the ends of the hairpins extend from the stator core; manipulating the hairpin ends into pre-specified radial and angular positions with respect to the stator core using one or more tools; measuring an actual position of each manipulated hairpin end, and outputting a signal indicative of an amount of radial and / or angular deviation ofthe actual manipulated position from a desired position for each hairpin end. By way of these measuring and outputting steps, it is possible to enable a single adjustment step (or at least a reduced number of adjustment steps) in setting up an assembly apparatus to carry out a next iteration of assembling the stator. In this way, it is possible to validate the hairpin positions after the widen and twist process by applying angular and diameter tolerances to each individual hairpin end. In contrast with this, existing techniques do not measure the actual position of the hairpin ends, but instead merely offer up a template to identify whether the pin ends are correctly placed, and which are not. This only gives a window in which the hairpins can sit and, if a fault is found, offers no incremental values which can then be used within the machine offsets to alter and address the error. The method may comprise adjusting one or more parameters of at least one of the one or more tools in dependence on the outputted signal. The parameters may include an angular amount by which particular hairpin ends are rotated by a gripper tool, and / or a radial distance by which groups of hairpin ends are moved by a crown tool. The method may comprise comparing, for each hairpin end, a radial position of the hairpin end with a desired radial position of that hairpin end and / or an angular position of the hairpin end with a desired angular position of that hairpin end, and determining the amount of radial and / or angular deviation from the result of the comparison (s). The manipulation may comprise modifying a radial position of one or more of the hairpin ends by a predetermined radial distance, and modifying an angular position of all hairpin ends at a particular radial position by a predetermined angle. While these steps could be carried out in either order, preferably the radial position is modified for selected hairpin ends, and then the angular position is modified. The method may comprise defining, for each hairpin end, a label based on a radial and angular position at which it resides following radial manipulation and prior to angular manipulation, and identifying, for each hairpin end, an angular position with respect to a fixed datum on the stator to which each hairpin end is to be manipulated. The method may comprise generating and displaying a table of hairpin end positions following manipulation, wherein table entries for hairpin ends which deviate from a desired position by more than a threshold amount are visually distinguished from table entries for hairpin ends which do not deviate from a desired position by more than the threshold amount. The method may comprise generating an image representing the manipulated hairpin ends, wherein the image comprises an indication of hairpin ends which deviate from a desired position by more than a threshold amount. These represent possible “outputs” of the method - in each case an easy-to-follow display of information indicative of how the tools need adjusting. The step of measuring may comprise scanning or imaging the pin ends of the stator to generate a point cloud, and then calculating a position for each hairpin end from the point cloud. According to another aspect of the invention, there is provided an electrical machine comprising a stator assembled by a method according to the above. According to another aspect of the invention, there is provided a vehicle comprising an electrical machine according to the above. According to another aspect of the invention, there is provided an apparatus for assembling a stator assembly from a stator core and a plurality of hairpins inserted through the stator core so that the ends of the hairpins extend from the stator core, comprising: one or more tools for manipulating the hairpin ends into pre-specified radial and angular positions with respect to the stator core; a measurement device for measuring an actual position of each manipulated hairpin end, and a controller for outputting a signal indicative of an amount of radial and / or angular deviation of the actual manipulated position from a desired position for each hairpin end. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in anyway and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic illustration of a vehicle having an electric drive unit comprising a stator assembled according to the present technique; Figures 2A and 2B show a partially assembled stator with hairpins inserted; Figure 3 shows a schematic view of a slot and ring configuration of hairpin ends within a stator; Figure 4 is a table indicating a mapping of hairpin ends to slots following a naming convention and twisting of the hairpin ends; Figure 5 shows a schematic illustration of an apparatus for assembling and verifying the stator; and Figure 6 shows a schematic flow diagram of the method. DETAILED DESCRIPTION Referring to Figure 1, a vehicle 1 is shown which comprises two electric drive units 10, one at a front axle of the vehicle 1 and one at a rear axle of the vehicle 1. The electric drive units 10 are electrically connected to, and powered by, a vehicle battery 15. In alternative embodiments a single electric drive unit 10 may be provided, driving either or both of the front axle and the rear axle, or alternatively each wheel of the vehicle may be provided with its own electric drive unit 10. In the example shown, the vehicle 1 is a battery electric vehicle propelled electrically, and lacking an internal combustion engine. However, the vehicle 1 could alternatively be a hybrid electric vehicle comprising both one or more electric drive units 10 and an internal combustion engine. The or each electric drive unit 10 comprises an electric motor powered by the vehicle battery 15, and an output shaft (not shown) for conveying propulsion torque to a driveline (not shown) of the vehicle 1. Each electric motor comprises a stator and a rotor. The present application is concerned with the assembly of the stator. A stator is formed of a stator core, often constructed of a plurality of steel laminations stacked together with slots provided to receive copper hairpins, which are configured and manipulated to form windings. The hairpins are formed of copper flat wire, which is bent into a hairpin shape of two long parallel parts joined at one end by a shorter part (head). The free ends of the hairpin are inserted through slots in the stator core, to emerge (extend from) the opposite side of the stator core. The free ends are then manipulated into pre-specified radial and angular positions with respect to the stator core using one or more tools. In particular, at least some of the hairpins ends are first widened (moved outwardly from a radial axis of the core) and then the hairpin ends are twisted (rotated with respect to the radial axis of the stator core) into final position. This position is required to allow further processing of the stator and to create installation space for fitment into the electric drive unit. Referring to Figures 2A and 2E3, Figure 2A shows a stator core 2 with hairpins 3 inserted. The heads of the hairpins 3 can be seen to one side (upper) of the stator 2, while the free ends of the hairpins 3 can be seen to the other side (lower) of the stator 2. In Figure 2B, the hairpin ends can be seen to have been widened and twisted into a desired configuration. The present technique provides a measurement strategy which can be used as a method of validating the final pin end position and reduce both machine set up time and downtime in the result of an NOK (not ok) part. The first stage in the measurement strategy is to produce a naming convention for each pin end based on the slot number and ring in which it sits within the lamination core. Figure 3 shows a pin end layout after widening (that is, in the widened state), but prior to twisting. In Figure 3 there are 8 rings (radial distances), each made up of 48 angular positions (slots). Some angular positions of some rings are unoccupied by a pin end. The rings are labelled R1 through R8, starting with the outermost ring. Only some of the pin ends are widened (from slot 2 into slot 1, and from slot 7 into slot 8), whereas all pin ends of each slot (1 to 8) are to be rotated (each slot position I ring is adjusted by a different angle / direction). This naming convention is then used within the final output in the measurement programme. Referring to Figure 4, this is a table showing, for the first 24 slots and the 8 ring positions (R1-R8) for each of those slots, the pin end as identified within the naming convention intended to occupy that slot and ring position. For example, the position of slot 1, ring 2 is expected to be occupied by the pin end previously present (before twisting) in slot 4, ring 2. It can be seen from Figure 4 that rings R1, R3, R5, R7 and R8 include pin ends which have been rotated anticlockwise, while the pin ends of the other rings have been rotated clockwise. Within Figure 4, each pin end is assigned an angle on which it must sit in relation to a specified datum feature on the stator assembly (represented by the dashed vertical line at the top of Figure 3). Each angle references back to this datum feature. The angle is taken from the centre of the datum feature to the centre line of each pin end. Each ring of pins labelled from R1 to R8 is assigned a radial dimension on which they must sit in reference to the centre point of each individual stator assembly. Therefore each pin end has a defined angular and radial position e.g. S4R2 = A3.75°, R97.047mm. By having this defined, it means machine offsets can be altered precisely based on the error calculated. For instance, if S4R2 after measurement = A4.75° R98.047mm, an operator knows to alter the angular offset by -1 ° and the radius offset by -1 mm. In this way, it will be seen that the naming convention defines, for each hairpin end, a label based on a radial and angular position at which it resides following radial manipulation and prior to angular manipulation, and identifies, for each hairpin end, an angular position with respect to a fixed datum on the stator to which each hairpin end is to be manipulated. Using this measurement strategy substantially reduces machine downtime and scrap parts. Only single offset adjustment should be required based on output error. In contrast, a traditional go / no-go method would mean repeating offset adjustment multiple times until correct position found to pass gauge resulting in longer downtime and increased scrap rate. Figure 5 schematically illustrates a generalised form of the apparatus for carrying out the assembly of the stator. The stator 2 is held in a seat 22. This may be any mechanical or robotic part for holding the stator 2, and potentially moving it around. A manipulator 24 (which may include one or more grippers, crowns or other tools for gripping the hairpin ends and moving them radially and / or rotationally) is provided, which is movable with respect to the seat 22. An imaging (measurement) device 26 is provided, for imaging the pin ends following the manipulation process. A controller 28, which may be a general-purpose computer or other electronic device, receives the image data and determines / measures the actual position of the pin ends, and identifies if they are correctly positioned. The controller 28 is configured to output a signal indicative of an amount of radial and / or angular deviation of the actual manipulated position from a desired position for each hairpin end. The controller 28 is able to send commands to the manipulator 24 to adjust parameters thereof for use in a subsequent manipulation of hairpin ends based on the output signal. For example, adjusting the parameters may have the effect of modifying a radial position of one or more of the hairpin ends by a predetermined radial distance in a subsequent operation of the manipulator 24, and / or modifying an angular position of all hairpin ends at a particular radial position by a predetermined angle in a subsequent operation of the manipulator 24. A user interface 29 is provided, for providing a visual indication of the hairpin end positions and / or their deviation from an intended position to an operator, and for receiving user inputs from the operator. The user interface 29, under control of the controller 29, may generate and display a table of hairpin end positions following manipulation, in which table entries for hairpin ends which deviate from a desired position by more than a threshold amount are visually distinguished from table entries for hairpin ends which do not deviate from a desired position by more than the threshold amount. This could be achieved with specific colouring or other visual indicia. The user interface 29, under control of the controller 28, may also generate an image representing the manipulated hairpin ends, wherein the image comprises an indication of hairpin ends which deviate from a desired position by more than a threshold amount, again using colouring or other visual indicia. The commands provided from the controller 28 to the manipulator 24 may be generated and sent either automatically or in response to user input via the user interface 29 (which may be made by the operator in response to the table or image referred to above). The imaging device 26 takes a 3D scan of the stator using a series of lasers which generate a point cloud of the hairpin ends. Measuring the positions of the hairpin ends then comprises calculating a position for each hairpin end from the point cloud. Software running on the controller 28 then computes the dataset calculating the position of each hairpin end and converts into absolute angular and radial values. For each hairpin end, a radial position of the hairpin end is compared with a desired radial position of that hairpin end and / or an angular position of the hairpin end is compared with a desired angular position of that hairpin end, and the amount of radial and / or angular deviation is determined from the result of the comparison(s). The present technique therefore uses a measurement strategy to address the problems described above, and which gives the operator accurate values for the position of each hairpin end, both angular and diametrically which can in turn be used to adjust the machine offsets (of the manipulator 24) precisely. By having a single measurement which the operator can use to adjust values using tangible figures it is possible to significantly reduce the time it takes to rework components. Figure 6 describes the method of the present technique, in general terms. At a step S1, a stator core and a set of hairpins are provided. At a step S2, the hairpins are inserted into and through slots in the stator core, in a desired configuration. At a step S3, a subset of the hairpin ends are manipulated to a different diameter position (ring) with respect to a rotational axis of the stator. At a step S4, all hairpin ends in a particular ring are rotated in a predetermined rotational direction, and by a predetermined angle. At a step S5, the hairpin ends are imaged. At a step S6, the position of each of the hairpin ends is determined from the image generated at the step S5. At a step S7, the determined position of each hairpin end is compared with an intended position for that hairpin end. At a step S8 it is determined, for each hairpin end, whether its position is within an acceptable error range with respect to the intended position. If this is the case for all hairpin ends, it is determined that the hairpin ends have been successfully manipulated, and the process ends at a step S9 (or more specifically, the assembly process continues with that part, for example by welding the hairpin ends together to form a completed winding). If however one or more hairpin ends deviated from their intended position by more than the acceptable error range, then at a step S10 one or more parameters of the apparatus for modifying the position of the hairpin ends are adjusted, based on the amount and type of deviation (for example the diameter deviation and the angular deviation). The process then returns to the step S1, in which the adjusted parameters are used for the steps S3 and / or S4. It will be appreciated that the stator core in this case may be the same stator core as for the first iteration (with the hairpins removed), or an entirely new stator core having the same dimensions as the first. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A method of assembling a stator assembly, the method comprising the steps of: providing a stator core and a plurality of hairpins;inserting the hairpins through the stator core so that the ends of the hairpins extend from the stator core;manipulating the hairpin ends into pre-specified radial and angular positions with respect to the stator core using one or more tools;measuring an actual position of each manipulated hairpin end, andoutputting a signal indicative of an amount of radial and / or angular deviation ofthe actual manipulated position from a desired position for each hairpin end.

2. The method according to claim 1, comprising adjusting one or more parameters of at least one of the one or more tools in dependence on the outputted signal.

3. The method according to claim 1 or claim 2, comprising comparing, for each hairpin end, a radial position of the hairpin end from a desired radial position of that hairpin end and / or an angular position ofthe hairpin end from a desired angular position of that hairpin end, and determining the amount of radial and / or angular deviation from the result ofthe comparison(s).

4. The method according to any preceding claim, wherein the manipulation comprises modifying a radial position of one or more of the hairpin ends by a predetermined radial distance, and modifying an angular position of all hairpin ends at a particular radial position by a predetermined angle.

5. The method of claim 4, wherein the manipulation to modify the radial position is carried out before the manipulation to modify the angular position.

6. The method according to claim 4 or claim 5, comprising defining, for each hairpin end, a label based on a radial and angular position at which it resides following radial manipulation and prior to angular manipulation, and identifying, for each hairpin end, an angular position with respect to a fixed datum on the stator to which each hairpin end is to be manipulated.

7. The method according to any preceding claim, comprising generating and displaying a table of hairpin end positions following manipulation, wherein table entries for hairpin ends which deviate from a desired position by more than a threshold amount are visually distinguished from table entries for hairpin ends which do not deviate from a desired position by more than the threshold amount.

8. The method according to any preceding claim, comprising generating an image representing the manipulated hairpin ends, wherein the image comprises an indication of hairpin ends which deviate from a desired position by more than a threshold amount.

9. The method according to any preceding claim, wherein the step of measuring comprises scanning or imaging the pin ends of the stator to generate a point cloud, and then calculating a position for each hairpin end from the point cloud.5 10. An electrical machine comprising a stator assembled by a method according to any preceding claim.

11. A vehicle comprising an electrical machine according to claim 10.

12. An apparatus for assembling a stator assembly from a stator core and a plurality of hairpins inserted10 through the stator core so that the ends of the hairpins extend from the stator core, comprising:one or more tools for manipulating the hairpin ends into pre-specified radial and angular positions with respect to the stator core;a measurement device for measuring an actual position of each manipulated hairpin end, anda controller for outputting a signal indicative of an amount of radial and / or angular deviation of the15 actual manipulated position from a desired position for each hairpin end.10

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