Double v topology for high-speed high-torque traction application

Abstract

A sleeveless rotor 100 for a high-speed electric machine for a vehicle, the rotor having a set of first magnets 110A arranged at a first angle 150A and defined by an equation wherein the number of po

Description

TECHNICAL FIELD The present disclosure relates to a double V topology for high-speed high-torque traction application. Aspects of the invention relate to a rotor, to an electric machine, to a drive system, and to a vehicle BACKGROUND 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 of the invention are defined in the appended claims. 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 illustrates a rotor with first and second magnets configured to achieve high rotational speeds; Figure 2 illustrates an outer circumferential lobe profile and an inner circumferential lobe profile of the rotor; Figure 3 illustrates a first radial lobe profile and a second radial lobe profile of the rotor; and Figure 4 shows a vehicle in accordance with an embodiment of the invention. DETAILED DESCRIPTION A rotor in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 1. As shown in Figure 6, the rotor is installed in a vehicle 600. In interior permanent magnet motors, magnets are typically arranged to concentrate the permanent magnet flux, which interacts with the stator flux to generate torque. The placement of the magnets in the rotor significantly influences the permanent magnet flux that interacts with the stator, thereby affecting the maximum torque that the rotor can generate. Therefore, optimising the placement of the magnets within the motor is required to achieve maximum torque. Maximising torque will also increase peak power in the motor at maximum speed. Moreover, it is crucial for the rotor to maintain structural integrity at higher speeds. Thus, the stresses applied to the rotor lamination must be managed, a requirement that is particularly critical for sleeveless rotors. Some flux lines make shorting flux paths within the rotor and do not contribute to torque production. To best utilize the permanent magnet flux within the rotor, the shorting flux paths can be blocked by reducing rotor lamination width perpendicular to the path of the shorting flux lines, this leads to saturation of the rotor lamination and lowers the permeability in the region, thereby breaking flux loops. However, reducing the rotor lamination width leads to an increase in stress in the region. Therefore, the minimum width and the profile of such a region must be adjusted for acceptable or good stress whilst maximizing torque. Shorting flux paths are typically near the ends of magnets within the rotor. Removing the rotor lamination at the ends of the magnets helps remove the shorting flux paths and creates a lobe profile which has a shape defined by the remaining rotor lamination at the ends of the magnets. The shape of the lobe profile can be adjusted for 1 acceptable or good structural integrity whilst maintaining high levels of torque at high speeds. The rotor lamination may be formed from a type of steel, such as electrical steel. Electrical steel provides excellent magnetic properties which make it highly efficient for converting electrical energy into magnetic energy and vice versa, however electrical steel is typically of a lower mechanical strength than alternatives such as high carbon steel. High-strength electrical steel may be used for a higher cost, but to remain cost effective standard electrical steel can be used in combination with a specific rotor configuration to maintain the structural integrity of the rotor at high speeds. Figure 1 illustrates a rotor section 100 designed for electric machines, such as high-speed electric motors, wherein rotor section 100 is a part view of a sleeveless rotor showing a single pole. Reference line R serves as a line of symmetry, wherein one side of line R is a mirror image of the other. The rotor section 100 comprises first magnet(s) 110A and second magnet(s) 110B which are placed at specific angles with respect to reference line R, herein described as V angles. AV angle 150A of the first magnet 110A is defined in Equation 1 below: Wherein 0, defines the V angle 150A of the first magnet 110 A, P defines the number of poles in the rotor, and k4 and k2 are constants. V angle 150 A is calculated using Equation 1, wherein the value of k4 is from 1.3 to 1.5, and in some instances specifically 1.5, and the value of k2 is from 1.7 to 1.9, and in some instances specifically 1.7. A V angle (150B) of the second magnet (150B) is defined 02 in Equation 2 below: n n k3p<02<k4p (2) Wherein 02 defines the V angle 150B of the second magnet 110 A, P defines the number of poles in the rotor, and k3 and k4 are constants. V angle 150B is calculated using Equation 2, wherein the value of k3 is from 1.6 to 1.83, and in some instances specifically 1.8, and the value of k4 is from 2 to 2.2, and in some instances specifically 2. A ratio of an area of the first magnet(s) to an area of the second magnet(s) is defined in Equation 3 below: p <AT^^-FirstMag p ATeClsecondMag (3) Wherein AreaFirstMag is defined as the area of the first magnet, AreaSecondMag is defined as the area of the second magnet and k5 and k6 are constants. The ratio of the area of the first magnet(s) to the area of the second magnet(s) is calculated using Equation 3, wherein the value of k5 is from 2.4 to 2.7, and in some instances specifically 2.7, and the value of k6 is from 3.2 to 3.5, and in some instances specifically 3.2. The placement of the first magnet(s) 110A and second magnet(s) 110B at particular angles significantly impacts the performance of the motor as the mass distribution within the rotor section 100 changes stress distribution of the rotor section 100. For the rotor to operate at high torques, such as 329 Nm, and at desirable 2 high speeds above 20,000 RPM, such as 25,000 RPM, the V angles of the first magnet(s) 110A and second magnet(s) 110B and the ratio of the area of the first magnet(s) 110Ato the area of the second magnet(s) 110B are adjusted as demonstrated in Equations 1 to 3. Furthermore, the weight of the second magnet(s) 110B should be approximately equal to one third of the weight of the first magnet(s) 110A. Shorting flux paths at the ends of first magnet(s) 110A and second magnet(s) 110B can be reduced by reducing bridge thickness and adjusting the shape of the lobe profiles at the ends of the first magnet(s) 110A and second magnet(s) 110B. First magnet(s) 110A comprises a first radial bridge 130C, which partly encompasses a first radial lobe 132C, and an outer circumferential bridge 120A, which partly encompasses an outer circumferential lobe 122A. Second magnet(s) 110B comprises a second radial bridge 130D, which partly encompasses a second radial lobe 132D, and an inner circumferential bridge 120B, which partly encompasses an inner circumferential lobe 122B. The outer circumferential bridge is radially outboard of the inner circumferential bridge with respect to reference line R. The thickness of each of the outer circumferential bridge 120A, the inner circumferential bridge 120B, the first radial bridge 130C, and the second radial bridge 130D can be adjusted for acceptable or good structural integrity and torque whilst achieving high speeds such as 25,000RPM. The shape of the outer 122A and inner 122B circumferential lobes as well as the shape of the first 132C and second 132D radial lobes can also be adjusted to enhance performance in a similar way. Figure 2 illustrates an outer circumferential lobe profile A and an inner circumferential lobe profile B of the rotor section 100. Outer circumferential lobe profile A comprises the outer circumferential bridge 120A, the outer circumferential lobe 122A, and the first magnet(s) 110A. First magnet(s) 110A has an inner end and an outer end and first and second sides extending between the inner end and the outer end, wherein the outer end is radially outbound of the inner end and the first end is radially outbound of the second end with respect to reference line R. Further, a width of the first magnet(s) 110A is defined by the distance between the first and second sides of the first magnet(s) 110A and a length of the first magnet(s) 110A is defined by the distance between the inner end and the outer end of the first magnet(s) 110A. Similarly, second magnet(s) 110B has an inner end and an outer end and first and second sides extending between the inner end and the outer end, wherein the outer end is radially outbound of the inner end and the first end is radially outbound of the second end with respect to reference line R. Further, a width of the second magnet(s) 110B is defined by the distance between the first and second sides of the first magnet(s) 110B and a length of the second magnet(s) 110B is defined by the distance between the inner end and the outer end of the second magnet(s) 110B. Protrusion 125A defines a protrusion of the rotor lamination into the outer circumferential lobe 122A, wherein the protrusion 125A overlaps the outer end of the first magnet(s) 110A and the overlap ranges from 30 per cent to 40 per cent of the width of the first magnet(s) 110A in the plane of the drawing. The protrusion 125A helps keep first magnet(s) 110A in place. Further, the protrusion 125A is adjacent to a first recess or part of the outer circumferential lobe 122A which is axially and radially outboard to the protrusion 125A with respect to the central axis of the first magnet(s) 110A. A second recess 127 or part of the outer circumferential lobe 3 122A overlaps the second side of the first magnet(s) 110A and the overlap ranges from 50 per cent to 60 per cent of the width of the first magnet(s) 110A in the plane of the drawing. The extent of this overlap is shown by the arrow 1270. Inner circumferential lobe profile B comprises the same configuration as the outer circumferential lobe profile A but does not have an equivalent to the second recess 127. Circumferential bridge thickness is defined by Equation 4 below: (pouter ^inner) Crouter dinner') (4) 7 — tbridgeC — 7 K7 Kg Wherein tbridgeC is circumferential bridge thickness, r01lter is the outer radius of the rotor lamination, rinner is the inner radius of the rotor lamination, and k7 and k8 are constants. Outer circumferential bridge thickness 120A tbridge0C is calculated using Equation 4, wherein k7 is from 26.75 to 29.43, and in some instances specifically 26.75, and k8 is from 10.53 to 11.7, and in some instances specifically 11.7. Inner circumferential bridge thickness 120B tbridgeIC is calculated using Equation 4, wherein k7 is from 26.75 to 29.72, and in some instances specifically 29.72, and k8 is from 22.37 to 24.85, and in some instances specifically 24.85. Outer / inner circumferential bridge 120A / 120B sustains the structural integrity of the rotor section 100 by providing a robust framework that supports the first / second magnet(s) 110A / 110B and maintains alignment during high-speed rotation. The thickness of the outer / inner circumferential bridge 120A / 120B is adjusted to the range set out in Equation 4 to ensure that the rotor section 100 can manage the stress applied to it at high speeds and high torque without compromising on structural integrity. This is especially important in the application of sleeveless rotors where no rotor sleeve is used to aid in managing the stress applied to the rotor lamination. The outer / inner circumferential lobe 122A / 122B is designed to facilitate efficient magnetic flux distribution, contributing to improved torque and reduced energy loss. The size and shape of the outer / inner circumferential lobe 122A / 122B has an impact on the amount of rotor lamination removed from the rotor section 100 at the outer end of first / second magnet(s) 110A / 110B, which in turn affects the number of shorting flux paths present at the outer end of the first / second magnet(s) 110A / 110B. Removing more rotor lamination from the outer end of first / second magnet(s) 110A / 110B will reduce the number of shorting flux paths at the outer end of the first / second magnet(s) 110A / 110B, which will in turn improve the efficiency of the rotor section 100 when interacting with the stator, thus maximising the torque and power output of the rotor. An additional advantage of increasing the size of the outer / inner circumferential lobe 122A / 122B is that the mass of rotor section 100 will be reduced, which will reduce the amount of radial force and stress experienced by rotor section 100 when operating at maximum speed. Both the thickness of the outer / inner circumferential bridge 120A / 120B and the size and shape of the outer / inner circumferential lobe 122A / 122B are adjusted to ensure the rotor can operate at maximum speed and torque and minimum stress. Figure 3 illustrates a first radial lobe profile C and a second radial lobe profile D. First radial lobe profile C comprises the first radial bridge 130C, the first radial lobe 132C, and the first magnet(s) 110A. Protrusion 135C defines a protrusion of the rotor lamination into the first radial lobe 132C, wherein the protrusion 135C overlaps the inner end of the first magnet(s) 110A and the overlap ranges from 30 per cent to 40 per cent of the width of the first magnet(s) 110A in the plane of the drawing. The protrusion 135C helps keep first magnet(s) 110A in place. Further, the protrusion 135C is adjacent to a first recess or part of the first radial lobe 132C which is axially outboard, and radially outboard away from the protrusion 135C, both with respect to the central axis of the first magnet(s) 110A. A second recess 137 or part of the first radial lobe 132C overlaps the second side of the first magnet(s) 110A and the overlap ranges from 50 per cent to 60 per cent of the width of the first magnet(s) 110A in the plane of the drawing. The extent of this overlap is shown by the arrow 1370. Second radial profile D comprises the same configuration as the first radial profile C but does not have an equivalent to the second recess 137. A protrusion 135D overlaps the inner end of second magnet(s) 110B with a range from 25 per cent to 35 per cent of the width of the second magnet(s) 110B in the plane of the drawing. Radial bridge thickness is defined by Equation 5 below: . ^mean,bridge . ^mean,bridge (5) ^9 * “ — '-bridgeR — ^10 * ~ 'outer 'outer Wherein tbridgeR is radial bridge thickness, router is the outer radius of the rotor lamination, rmeanbridge is a mean radius at which the first radial bridge of the rotor lamination lies, and k9 and k10 are constants. First radial bridge thickness 130C tbridgeFR is calculated using Equation 5, wherein k9 is from 4.34 to 4.82, and in some instances specifically 4.82, and k10 is from 5.89 to 6.48, and in some instances specifically 5.89. Second radial bridge thickness 130D tbridgeSR is calculated using Equation 5, wherein k9 is from 0.95 to 1.05, and in some instances specifically 1.05, and k10 is from 2.16 to 2.38, and in some instances specifically 2.16. First / second radial bridge 130C / 130D sustains the structural integrity of the rotor section 100 by providing a robust framework that supports the first / second magnet(s) 110A / 110B and maintains alignment during highspeed rotation. The thickness of the first / second radial bridge 130C / 130D is adjusted to the range set out in Equation 5 to ensure that the rotor section 100 can manage the stress applied to it at high speeds and high torque without compromising on structural integrity. This is especially important in the application of sleeveless rotors where no rotor sleeve is used to aid in managing the stress applied to the rotor lamination. The first / second radial lobe 132C / 132D is designed to facilitate efficient magnetic flux distribution, contributing to improved torque and reduced energy loss. The size and shape of the first / second radial lobe 132C / 132D has an impact on the amount of rotor lamination removed from the rotor section 100 at the inner end of first / second magnet(s) 110A / 110B, which in turn affects the number of shorting flux paths present at the inner end of the first / second magnet(s) 110A / 110B. Removing more rotor lamination from the inner end of 5 first / second magnet(s) 110A / 110B will reduce the number of shorting flux paths at the inner end of the first / second magnet(s) 110A / 110B, which will in turn improve the efficiency of rotor section 100 when interacting with the stator, thus maximising the torque and power output of the rotor. An additional advantage of increasing the size of the first / second radial lobe 132C / 132D is that the mass of rotor section 100 will be reduced, which will reduce the amount of radial force and stress experienced by rotor section 100 when operating at maximum speed. Both the thickness of the first / second radial bridge 130C / 130D and the size and shape of the first / second radial lobe 132C / 132D are adjusted to ensure the rotor can operate at maximum speed and torque and minimum stress. Table 1 below shows the performance of the outer / inner circumferential lobe profiles A / B of Figure 2, and the first / second radial lobe profiles C / D of Figure 3. Profile A B C D Mass (gm) 4801 4801 4801 4801 Stress (MPa) 376 357 369 364 PEEQ 0.27% 0.17% 0.47% 0.37% Torque (Nm) 329.26 329.26 329.26 329.26 Ld (Low speed / High speed) 0.167 mH / 0.23 mH 0.167 mH / 0.23 mH Lq (Low speed / High speed) 0.284 mH / 0.66 mH 0.284 mH / 0.66 mH Peak Power (kW) 280 Peak Power (kW) at Max speed 219 As shown in Table 1, lobe profiles A to D facilitate the production of high levels of torque whilst maintaining manageable levels of stress and equivalent plastic strain (PEEQ) for a high-speed electric motor. Figure 4 illustrates a vehicle 400 according to an embodiment of the present invention. The vehicle 400 comprises a drive system 410. The drive system 410 comprises an electric machine comprising a sleeveless rotor having the rotor section 100, wherein rotor section 100 is illustrated in Figure 1. The drive system 410 of vehicle 400 is designed to benefit from the high-speed capabilities of a sleeveless rotor having the rotor section 100, which enhances the overall performance and efficiency of the electric machine and thus the drive system. The rotor lamination of rotor section 100 may be made using electrical steel. This configuration allows the vehicle to achieve improved acceleration and energy efficiency, making it suitable for modern electric or hybrid vehicles. The electric machine housing the rotor section 100, leverages the optimised magnet configurations and structural features to provide a robust and efficient power source for the vehicle. The absence of a rotor sleeve reduces weight and complexity, contributing to the vehicle's lightweight design and improved handling. 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 sleeveless rotor for a high-speed electric machine for a vehicle, the sleeveless rotor comprising: a set of first magnets configured at a first V angle, wherein the first V angle is defined by 1.3^ <0! <1.9^, wherein P specifies the number of poles in the sleeveless rotor;a set of second magnets configured at a second V angle, wherein the second V angle is defined by 1.6 <02 <2.2 , wherein P specifies the number of poles in the rotor; anda ratio of an area of the first magnet to an area of the second magnet being between 2.4 and 3.5.

2. The sleeveless rotor of claim 1, comprising:an outer circumferential bridge, wherein a thickness of the outer circumferential bridge is defined by <t <^outer-rinnerX andan inner circumferential bridge, wherein a thickness of the inner circumferential bridge is defined by <t eIC <^outer-rinner).wherein router is an outer radius of a rotor lamination of the sleeveless rotor and rinner is an inner radius of the rotor lamination of the sleeveless rotor.3.The sleeveless rotor of any preceding claim, comprising:a first radial bridge, wherein a thickness of the first radial bridge is defined by 4.34 *rmean,bridge router— ^bridgeFR —6.48 * androutera second radial bridge, wherein a thickness of the second radial bridge is defined by0.95 * rmean,bridge router— ^bridgeSR — 2.38 *rmean,bridge. routerwherein router is an outer radius of a rotor lamination of the sleeveless rotor, and rmeanbridgeis a mean radius at which the first radial bridge of the rotor lamination lies.

4. An electric machine comprising the sleeveless rotor of any preceding claim.

5. A drive system comprising the electric machine of claim 4.

6. A vehicle comprising the drive system of claim 5.

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