Electrical machine rotor with coolant guiding ribs

Abstract

A rotor (100) for an electric machine (170) is described. The rotor (100) comprises a hollow rotor shaft (110) of a first diameter (D1); a rotor core (140) attached to the hollow rotor shaft (110); a rotor insert (130) arranged in the rotor core (140) such that an annular gap (150) configured to guide a coolant is provided between an inside of the rotor core (140) and an outside of the rotor insert (130); and a first plurality of guiding ribs (210a), configured to guide a coolant flow of a coolant, flowing radially from the hollow rotor shaft (110), along a first axial ending (135a) of the rotor insert (130) to the annular gap (150) of a second diameter (D2), which second diameter (D2) is larger than the first diameter (D1). An electric machine (170) and a vehicle (500) are also described.

Description

[0001] ELECTRICAL MACHINE ROTOR WITH COOLANT GUIDING RIBS

[0002] TECHNICAL FIELD

[0003] This document discloses rotor for an electric machine according to the appended patent claims. This document further relates to an electric machine and a vehicle comprising an electric machine.

[0004] BACKGROUND

[0005] Electric machines such as electric motors, generators and / or alternators comprise a stationary stator and a rotor configured to rotate in relation to the stator. The rotor is coaxially arranged to rotate within the stator.

[0006] The stator comprises conductor coils designed as windings and an energization of the windings with alternating current generates magnetic fields which, together with magnets of the rotor, produce attractive and repulsive forces on the rotor for the purpose of achieving a rotational movement of the rotor.

[0007] Due to resistance in the windings and friction during the rotation of the rotor, heat is developed. In order to utilise electric machines of the above-mentioned kind in vehicle propulsion systems and similar industrial applications, it is crucial to reach a good continuous performance of the electric machine to guarantee continuous torque and power over long periods of time. To avoid overheating, efficient cooling is required.

[0008] Overheating of the rotor will decrease efficiency of electric machines, affecting performance and lifetime of the involved components. Insulation layers may melt, for example.

[0009] The rotor may be attached to a hollow rotor shaft, in which pressurised coolant may be supplied radially by a pump in order to cool an inside surface of a hollow rotor. Cooling of the rotor is thereby achieved; however cooling efficiency is restricted / insufficient. A large pressure drop seems to hamper efficiency of the cooling liquid.

[0010] It would be desired to find a solution addressing at least some of the above issues and improve cooling of the rotor in electric machines, thereby improving capacity of high continuous power and torque.

[0011] SUMMARY It is therefore an object of this invention to solve at least some of the above problems and improve cooling capacity of a rotor in an electric machine.

[0012] According to a first aspect of the invention, this objective is achieved by a rotor for an electric machine. The rotor comprises a hollow rotor shaft of a first diameter, and a rotor core attached to the hollow rotor shaft. The rotor also comprises a rotor insert arranged in the rotor core such that an annular gap configured to guide a coolant is provided between an inside of the rotor core and an outside of the rotor insert.

[0013] Also, the rotor comprises a first plurality of guiding ribs, configured to guide a coolant flow of a coolant, flowing radially from the hollow rotor shaft, along a first axial ending of the rotor insert, to the annular gap of a second diameter, which second diameter is larger than the first diameter.

[0014] Thanks to the introduced plurality of guiding ribs, the coolant is guided when flowing radially to the annular gap. The guiding ribs are thereby preventing tangential motion of the coolant caused by Coriolis forces in previously known solutions without the provided guiding ribs. The friction / energy losses of previously known solutions due to viscous tangential forces of the coolant are eliminated or at least radically reduced.

[0015] Thereby, several advantages are achieved, such as increased power output for a given configuration of the electric machine due to increased cooling. Also, reliability and life length of the electric machine of the given configuration are increased due to the increased cooling.

[0016] The increased cooling enabled by the provided solution also saves costs as materials with lower resistance to high temperatures than in previously known solutions, i.e. cheaper material could be used which saves costs.

[0017] An alternative advantage is that the pump system for circulating the coolant could be downsized in relation to the pump capacity applied in previously known solutions, when the same cooling rate is applied, which saves resources and money.

[0018] Optionally, the rotor may comprise a second plurality of guiding ribs. The second plurality of guiding ribs may be configured to guide the coolant flow of the coolant, flowing from the annular gap along a second axial ending of the rotor insert, to the hollow rotor shaft.

[0019] By arranging guiding ribs not only on the coolant inflow side of the rotor, but also on the coolant outflow side, the cooling efficiency is additionally increased, thereby enhancing the above-mentioned advantages.

[0020] Optionally, each guiding rib of the rotor may have a radial extension, extending between the hollow rotor shaft and the annular gap.

[0021] Optionally, each guiding rib of the rotor may have a straight shape, extending in a substantially radial direction.

[0022] Optionally, each guiding rib of the rotor may have an angular displacement in radial direction.

[0023] Optionally, the first plurality of guiding ribs and / or second plurality of guiding ribs may be symmetrically distributed around a common centre of the coaxially arranged rotor shaft, rotor core, and rotor insert.

[0024] Optionally, the first plurality of guiding ribs of the rotor may be arranged on the first axial ending of the rotor insert.

[0025] Optionally, the second plurality of guiding ribs of the rotor may be arranged on the second axial ending of the rotor insert.

[0026] Optionally, the first plurality of guiding ribs may be arranged on a first separate guiding entity situated between the first axial ending of the rotor insert and a section of the rotor shaft opposing the first axial ending of the rotor insert.

[0027] Optionally, the second plurality of guiding ribs may be arranged on a second separate guiding entity situated between the second axial ending of the rotor insert, and a section of the rotor shaft opposing the second axial ending of the rotor insert.

[0028] Optionally, the first plurality of guiding ribs may be arranged on a first section of the rotor shaft opposing the first axial ending of the rotor insert.

[0029] Optionally, the second plurality of guiding ribs may be arranged on a second section of the rotor shaft opposing the second axial ending of the rotor insert.

[0030] Optionally, some guiding ribs of the first plurality of guiding ribs are arranged in the first axial ending of the rotor insert and some guiding ribs are arranged in the first section of the rotor shaft opposing the first axial ending of the rotor insert.

[0031] Optionally, some guiding ribs of the first plurality of guiding ribs may be extending radially between the hollow rotor shaft and the annular gap and some other guiding ribs may be extending radially only along a subset of the distance between the hollow rotor shaft and the annular gap, in connection with the annular gap.

[0032] There are several possible design options of the guiding ribs, all achieving advantages concerning cooling efficiency.

[0033] According to a second aspect of the invention, this objective is achieved by an electric machine. The electric machine comprises a stator with a stator winding, and a rotor according to the first aspect. The rotor is configured to operate coaxially inside the stator.

[0034] Reduced heat development, thanks to the improved cooling effect, leads to a lower gap between peak and continuous performance, thereby enabling higher continuous power density and torque of the electric machine.

[0035] According to a third aspect of the invention, this objective is achieved by a vehicle. The vehicle comprises an electrical machine according to the second aspect of the invention.

[0036] Other advantages and additional novel features will become apparent from the subsequent detailed description.

[0037] FIGURES

[0038] Embodiments of the invention will now be described in further detail with reference to the accompanying figures, in which:

[0039] Figure 1A illustrates a cross section of a rotor according to an embodiment.

[0040] Figure 1B illustrates a cross section of an electrical machine according to an embodiment.

[0041] Figure 2A illustrates an embodiment of a rotor insert comprising guiding ribs.

[0042] Figure 2B illustrates an embodiment of a rotor insert and a separate guiding entity comprising guiding ribs.

[0043] Figure 3 illustrates guiding ribs according to an embodiment of the invention.

[0044] Figure 4 illustrates guiding ribs according to an embodiment of the invention. Figure 5 illustrates a vehicle comprising an electric machine with a rotor comprising guiding ribs, according to an embodiment of the invention.

[0045] DETAILED DESCRIPTION

[0046] Embodiments of the invention described herein are defined as a rotor, an electric machine and a vehicle comprising the electric machine which may be put into practice in the embodiments described below. These embodiments may, however, be exemplified and realised in many different forms and are not to be limited to the examples set forth herein; rather, these illustrative examples of embodiments are provided so that this disclosure will be thorough and complete.

[0047] Still other objects and features may become apparent from the following detailed description, considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the herein disclosed embodiments, for which reference is to be made to the appended claims. Further, the drawings are not necessarily drawn to scale and, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

[0048] Figure 1A illustrates an example of a rotor 100 for an electric machine. The rotor 100 comprises a hollow rotor shaft 110 and a rotor core 140 attached to the hollow rotor shaft 110. The rotor core 140 is also hollow and a rotor insert 130 is arranged in the cavity created in the rotor core 140. The rotor insert 130 may be made in plastic or in metal such as aluminium in different embodiments. The rotor insert 130 may in turn also be hollow in some embodiments, or solid in other embodiments.

[0049] Between the coaxially arranged rotor core 140 and the therein comprised rotor insert 130 is an annular gap 150 created.

[0050] The hollow rotor shaft 110 has an internal diameter D1 and the rotor insert 130 has an external diameter D2, wherein D2 is larger than D1.

[0051] Coolant is provided axially in a flow in the hollow rotor shaft 110 in the direction of the arrows in Figure 1A. The coolant flow enters a first axial ending 135a of the rotor insert 130. The rotor insert 130 redirects the coolant flow to the annular gap 150 between the rotor insert 130 and the rotor core 140. At a second axial ending 135b of the rotor insert 130, the coolant is guided to the hollow rotor shaft 110 at the second axial ending 135b of the rotor insert 130. The coolant is circulated through a pump system, creating a fluid pressure, for continuously circulating the coolant through the hollow rotor shaft 110 and the annular gap 150 between the rotor insert 130 and the rotor core 140 and back to the hollow rotor shaft 110 at the opposite axial ending 135b of the rotor insert 130. The inlet and the outlet of the coolant are made on opposite axial endings 135a, 135b of the rotor insert 130 and the rotor core 140, for an efficient cooling.

[0052] The coolant may then be brought to a heat exchanger or similar arrangement where heat from the heated fluid is dissipated, before forwarding the coolant back to the hollow rotor shaft 110.

[0053] The temperature of the rotor 100 is thereby reduced, in order to counteract the heat created by friction when the rotor 100 rotates in relation to a stator of the electric machine.

[0054] The coolant is a cooling fluid which may comprise for example oil, water, or a mixture of water and glycol. Oil has several advantages as coolant, before water. Oil has a higher boiling point than water and can be used for cooling the electric machine, even if water cooling also may exceed 100 degrees Celsius when pressurised. Oil is also an electrical insulator, why an accidental leak of cooling fluid does not cause any hazard, besides, the interruption / disturbance in cooling.

[0055] A first plurality of guiding ribs is configured to guide the coolant flow of the coolant, flowing in radial direction from the hollow rotor shaft 110, along the first axial ending 135a of the rotor insert 130, to the annular gap 150.

[0056] By guiding the coolant in radial direction from the interior 120 of the hollow rotor shaft 110, to the annular gap 150 radially, an efficient coolant flow with low losses is achieved.

[0057] The rotor 100 may form part of an electric machine 170 as illustrated in Figure 1 B. The rotor 100 may be arranged to operate coaxially inside a stator 160.

[0058] The rotor 100 is rotatably disposed on an inward side of the stator 160 with an air gap distance between the rotor surface and the stator 160, creating a radial clearance distance between the rotor 100 and the stator 160. Thus, the rotor 100 forms a rotating part of the electric machine 170 while the stator 160 forms a stationary part thereof. The electric machine 170 may be configured for converting electrical energy into mechanical energy thereby operating as an electric motor. The electric machine 170 may also, or alternatively comprise an electric generator, which has the same configuration as an electric motor but operates with a reversed flow of power, converting mechanical energy into electrical energy.

[0059] The stator 160 may comprise conductor coils designed as windings and an energization of the windings may generate magnetic fields which, together with magnets of the rotor 100, produce attractive and repulsive forces on the rotor 100, due to induction according to Faradays Law. This rotating magnetic field is cooperating with the permanent magnetic field of the magnets situated in the rotor 100, thereby causing the rotor 100 to rotate. The electric machine 170 thereby operates in motor mode.

[0060] The electric machine 170 may be comprised in a vehicle and be configured to propel the vehicle while driving thereby operating as an electric motor. In case the vehicle is driving down-hill and / or braking, the electric machine 100 instead may operate as an electric generator, generating electricity which may be stored in a battery.

[0061] A typical rotating speed of the rotor 100 during electric machine operation in motor mode may be about 4000 rpm, with maximum speeds of up to 12 000 rpm in some embodiments.

[0062] The guiding ribs may be physically situated on the axial end section 135a of the rotor insert 130, as illustrated in Figure 2A, in a separate guiding entity as illustrated in Figure 2B, or in the rotor shaft 110. In some embodiments, some guiding ribs may be arranged in the rotor insert 130 and some guiding ribs may be arranged in a section 115 of the rotor shaft 110 opposing the axial ending 135 of the rotor insert 130, as illustrated il Figure 4.

[0063] Figure 2A illustrates a rotor insert 130, comprising a first plurality of guiding ribs 210a, configured to guide a coolant flow of a coolant, flowing radially from the hollow rotor shaft 110, along a first axial ending 135a of the rotor insert 130, to the annular gap 150.

[0064] The rotor insert 130 may also comprise a second plurality of guiding ribs 210b, configured to guide the coolant flow of the coolant, flowing from the annular gap 150 along a second axial ending 135b of the rotor insert 130, to the hollow rotor shaft 110.

[0065] Each guiding rib 210a, 210b may have a radial extension, extending between the hollow rotor shaft 110 and the annular gap 150. Thereby, each guiding rib 210a, 210b may have a straight shape, extending in a substantially radial direction.

[0066] The guiding rib 210a, 210b may have equal sizes, or varying length, thickness, and / or angle in different embodiments.

[0067] In some embodiments, each of the guiding ribs 210a, 210b may have an angular displacement in radial direction. This may be an advantage in embodiments wherein the rotor 100 is only rotating in one direction.

[0068] The first plurality of guiding ribs 210a and / or the second plurality of guiding ribs 210b may be symmetrically distributed around a common centre 101 of the coaxially arranged rotor shaft 110, rotor core 140, and rotor insert 130.

[0069] The first plurality of guiding ribs 210a may be arranged on the first axial ending 135a of the rotor insert 130. Also, in some embodiments, the second plurality of guiding ribs 210b may be arranged on the second axial ending 135b of the rotor insert 130.

[0070] The first plurality of guiding ribs 210a may be arranged on a first separate guiding entity 220a situated between the first axial ending 135a of the rotor insert 130 and a section 115 of the rotor shaft 110 opposing the first axial ending 135a of the rotor insert 130, as illustrated in Figure 2B.

[0071] In some embodiments, the second plurality of guiding ribs 210b may be arranged on a second separate guiding entity 220b situated between the second axial ending 135b of the rotor insert 130 and a section 115b of the rotor shaft 110 opposing the second axial ending 135b of the rotor insert 130.

[0072] In yet some alternative embodiments, some guiding ribs 210a of the first plurality of guiding ribs 210a may be extending radially between the hollow rotor shaft 110 and the annular gap 150 and some other guiding ribs 211a may be extending radially only along a subset of the distance between the hollow rotor shaft 110 and the annular gap 150, in connection with the annular gap 150, as illustrated in Figure 3.

[0073] In alternative embodiments, the first plurality of guiding ribs 210a may be arranged on a first section 115a of the rotor shaft 110 opposing the first axial ending 135a of the rotor insert 130. Also, or in addition, the second plurality of guiding ribs 210b may be arranged on a second section 115b of the rotor shaft 110 opposing the second axial ending 135b of the rotor insert 130.

[0074] In yet some embodiments, some guiding ribs 210a of the first plurality of guiding ribs 210a may be arranged in the first axial ending 135a of the rotor insert 130 and some guiding ribs 211a may be arranged in the first section 115a of the rotor shaft 110 opposing the first axial ending 135a of the rotor insert 130, as illustrated in Figure 4.

[0075] Figure 5 illustrates a vehicle 500 comprising an electric machine 170 with a rotor 100 and a stator 160 according to any above-described embodiment.

[0076] The vehicle 500 may be driver controlled or driverless autonomously controlled in different embodiments. The vehicle 500 may comprise a means for transportation in broad sense such as e.g., a truck, a car, a motorcycle, a trailer, a bus, a bike, a train, a tram, an aircraft, a watercraft, an unmanned underwater vehicle, a drone, a humanoid service robot, a spacecraft, or other similar manned or unmanned means of conveyance running e.g., on wheels, rails, air, water, or similar media.

[0077] The vehicle 500 may be an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, etc., wherein the electric machine 170 is configured for propelling the vehicle 500 and / or for generating electrical energy for the vehicle 500 to use, depending on mode: motor mode or generator mode.

[0078] As used herein, the term “and / or” comprises any and all combinations of one or more of the associated listed items. The term “or” as used herein, is to be interpreted as a mathematical OR, i.e. , as an inclusive disjunction; not as a mathematical exclusive OR (XOR), unless expressly stated otherwise. In addition, the singular forms “a”, “an” and “the” are to be interpreted as “at least one”, thus also possibly comprising a plurality of entities of the same kind, unless expressly stated otherwise. It will be further understood that the terms “includes”, “comprises”, “including” and / or “comprising”, specifies the presence of stated features, actions, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, actions, integers, steps, operations, elements, components, and / or groups thereof. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

PATENT CLAIMS1. A rotor (100) for an electric machine (170), the rotor (100) comprising a hollow rotor shaft (110) of a first diameter (D1); a rotor core (140) attached to the hollow rotor shaft (110); a rotor insert (130) arranged in the rotor core (140) such that an annular gap (150) configured to guide a coolant is provided between an inside of the rotor core (140) and an outside of the rotor insert (130); and a first plurality of guiding ribs (210a), configured to guide a coolant flow of a coolant, flowing radially from the hollow rotor shaft (110), along a first axial ending (135a) of the rotor insert (130) to the annular gap (150) of a second diameter (D2), which second diameter (D2) is larger than the first diameter (D1).

2. The rotor (100) according to claim 1 , comprising a second plurality of guiding ribs (210b), configured to guide the coolant flow of the coolant, flowing from the annular gap (150) along a second axial ending (135b) of the rotor insert (130); to the hollow rotor shaft (110).

3. The rotor (100) according to any one of the preceding claims, wherein each guiding rib (210) has a radial extension, extending between the hollow rotor shaft (110) and the annular gap (150).

4. The rotor (100) according to any one of the preceding claims, wherein each guiding rib (210) has a straight shape, extending in a substantially radial direction.

5. The rotor (100) according to any one of the claims 1-3, wherein each guiding rib (210) has an angular displacement in radial direction.

6. The rotor (100) according to any one of the preceding claims, wherein the first plurality of guiding ribs (210a) and / or second plurality of guiding ribs (210b) is / are symmetrically distributed around a common centre (101) of the coaxially arranged rotor shaft (110), rotor core (140), and rotor insert (130).

7. The rotor (100) according to any one of the preceding claims, wherein the first plurality of guiding ribs (210a) is arranged on the first axial ending (135a) of the rotor insert (130).

8. The rotor (100) according to any one of the claims 2-7, wherein the second plurality of guiding ribs (210b) is arranged on the second axial ending (135b) of the rotor insert (130).

9. The rotor (100) according to any one of the claims 1-6, wherein the first plurality of guiding ribs (210a) is arranged on a first separate guiding entity (220a) situated between the first axial ending (135a) of the rotor insert (130) and a section (115) of the rotor shaft (110) opposing the first axial ending (135a) of the rotor insert (130).

10. The rotor (100) according to any one of the claims 2-6 or 9, wherein the second plurality of guiding ribs (210b) is arranged on a second separate guiding entity (220b) situated between the second axial ending (135b) of the rotor insert (130) and a section (115) of the rotor shaft (110) opposing the second axial ending (135b) of the rotor insert (130).

11. The rotor (100) according to any one of the claims 1-6, wherein the first plurality of guiding ribs (210a) is arranged on a first section (115a) of the rotor shaft (110) opposing the first axial ending (135a) of the rotor insert (130).

12. The rotor (100) according to any one of the claims 2-6 or 11 , wherein the second plurality of guiding ribs (210b) is arranged on a second section (115b) of the rotor shaft (110) opposing the second axial ending (135b) of the rotor insert (130).

13. The rotor (100) according to any one of the preceding claims, wherein some guiding ribs (210) of the first plurality of guiding ribs (210a) are arranged in the first axial ending (135a) of the rotor insert (130) and some guiding ribs (210) are arranged in the first section (115a) of the rotor shaft (110) opposing the first axial ending (135a) of the rotor insert (130).

14. The rotor (100) according to any one of the preceding claims, wherein some guiding ribs (210) of the first plurality of guiding ribs (210a) are extending radially between the hollow rotor shaft (110) and the annular gap (150) and some other guiding ribs (211) are extending radially only along a subset of the distance between the hollow rotor shaft (110) and the annular gap (150), in connection with the annular gap (150).

15. An electric machine (170), comprising:a stator (160) comprising a stator winding; a rotor (100) according to any one of the preceding claims, configured to operate coaxially inside the stator (160).

16. A vehicle (500) comprising an electric machine (170) according to claim 15.

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