Rotor for an electrical machine, in particular for an electric motor

Abstract

The invention provides a rotor (10) for an electric machine, in particular for an electric motor, the rotor (10) having a rotor shaft (12) and a plurality of rotor plates (16) mounted on the rotor shaft (12), the rotor plates (16) having recesses (30) which form coolant channels (24) extending axially through the stack formed by the rotor plates (16), the rotor shaft (12) having an axial coolant opening (22), a plurality of radial coolant openings (27; 36) which connect the axial cooling opening (22) in the rotor shaft (12) to the cooling channels (24) in the stack of rotor plates (16), the rotor (10) further having an end plate (18; 19, 50; 64) which forms a radial end for the radial cooling openings (27).

Description

Title of the invention: Rotor for an electric machine, in particular for an electric motor

[0001] The invention relates to a rotor for an electric machine, in particular for an electric motor of the type used for driving vehicles. The vehicles may in particular be utility vehicles or passenger cars operating either entirely on electric power or hybrid vehicles. The invention also relates to an electric machine comprising such a rotor.

[0002] It is known that electrical machines used for the propulsion of vehicles must be cooled in order to prevent the residual heat generated during operation from causing excessively high temperatures. It is known to guide a coolant (e.g. oil) through certain parts of the electrical machines so as to transport the waste heat to an external heat exchanger where it is discharged to the environment.

[0003] Many designs of coolant paths are known in the prior art. The object of the invention is to provide a rotor for an electrical machine in which the coolant path can be formed in a simple manner.

[0004] In order to solve this object, the invention provides a rotor for an electrical machine, in particular for an electric motor, the rotor having a rotor shaft and a plurality of rotor plates mounted on the rotor shaft, the rotor plates having cutouts which form cooling channels extending in an axial direction through the stack formed by the rotor plates, the rotor shaft having an axial cooling opening, a plurality of radial cooling openings being provided which connect the axial cooling opening in the rotor shaft to the cooling channels in the stack of rotor plates, the rotor further having at least one end plate which forms a radial end for the radial cooling openings. The rotor end plates are generally of sufficient thickness for mechanical reasons, in particular to compress the rotor plates mounted in the rotor shaft.The volume of the end plates can be used to extend or terminate a coolant path formed in the rotor shaft. No additional mechanical elements are required for this purpose. In addition, the end plate can be easily machined to the required configuration.

[0005] Preferably, the end plate has a solid contact surface for abutting the stack of rotor plates so that all of the rotor plates are uniformly supported or compressed in an axial direction.

[0006] In one embodiment, the rotor shaft has a radially enlarged end portion forming a shoulder against which the stack of rotor plates abuts in an axial direction, the radial cooling openings extending through the end portion to an outer circumference thereof. The enlarged end portion allows axial loads to be directly absorbed at the radially inner portion of the rotor plates and provides sufficient space to accommodate the radial cooling openings.

[0007] For reasons of ease of manufacture, the end portion preferably comprises at least one connecting opening for connecting the cooling channels formed in the stack of rotor plates to the radial cooling openings of the end portion.

[0008] The connection opening can be easily generated by machining so as to form an annular groove in the end portion on the side facing the rotor plate stack.

[0009] In order to preserve a larger support surface at the enlarged end portion, the connection opening may be formed by a plurality of axially extending openings which connect the cooling channels in the rotor plate stack to the radial cooling openings.

[0010] In one embodiment, the end plate has an annular groove at its radially inner end, on the side facing the rotor plate stack, allowing the end plate to be machined by rotation.

[0011] In another embodiment, the end plate has a plurality of radial recesses at its radially inner end on the side facing the rotor plate stack, thereby maintaining greater resistance to bending loads compared to an embodiment that uses an annular groove.

[0012] In one embodiment of the invention, the rotor shaft has a radially widened end portion which forms a shoulder against which the end plate abuts in an axial direction, the radial cooling openings being formed axially inwardly from the end portion. This design is advantageous in that only short openings for the coolant are required in the rotor shaft, the deflection of the coolant path to the rotor plates being provided by the end plate.

[0013] To achieve the desired axial compression of the rotor plates and to ensure that a refrigerant path formed in an axial direction through the rotor plate stack is essentially leak-free, a clamping element is arranged on the rotor shaft for axially clamping the rotor plate stack, in particular a nut tightening.

[0014] The invention will be described with reference to embodiments illustrated in the accompanying drawings. In the drawings,

[0015] [Fig. 1] shows a schematic cross-section of a rotor according to a first embodiment of the invention,

[0016] [Fig.2] shows a plan view of a portion of a rotor plate used in the rotor of [Fig.l],

[0017] [Fig.3] shows a schematic cross-section of the rotor of [Fig.l] along plane III-III,

[0018] [Fig.4] shows a cross-section along plane IV-IV of [Fig.l],

[0019] [Fig.5] shows a schematic cross-section along plane VV of [Fig.l],

[0020] [Fig.6] schematically illustrates a second embodiment of the invention,

[0021] [Fig.7] schematically shows a top view of an end plate of a variant of the second embodiment,

[0022] [Fig.8] schematically illustrates a third embodiment of the invention.

[0023] [Fig.9] schematically shows a fourth embodiment of the invention.

[0024] In [Fig.l], a rotor 10 is seen used in an electrical machine such as an electric motor. The motor may in particular be used to drive a vehicle such as a car or a truck, the vehicle being either entirely powered by electrical energy or a hybrid vehicle.

[0025] The rotor 10 comprises a rotor shaft 12, a stack 14 of rotor plates 16, and two end plates 18, 19. The stack 14 of rotor plates 16 is held axially clamped between the end plates 18, 19.

[0026] Each rotor plate 16 has a plurality of recesses 20 which, together with the recesses of the axially adjacent rotor plates 16, form pockets for receiving magnets. The magnets are permanent magnets made from rare earth materials. It is also possible to use ferrite magnets.

[0027] In a manner known per se, the magnets are grouped into segments, the angular position of the magnets in one segment being slightly different from the angular position of the magnets in an adjacent segment. This is advantageous with regard to torque ripples and noise reduction.

[0028] The rotor 10 is provided with a cooling path which consists mainly of an inlet channel 22, a plurality of cooling passages 24 and a plurality of outlet channels 26. The coolant path is closed in that the coolant flow admitted into the inlet channel 22 exits through the outlet channels 26. No coolant (except for a potential leakage flow very minor) is discharged from the rotor 10, except for the entire flow of coolant exiting through the outlet channels 26.

[0029] The inlet channel 22 is formed by an axial bore that extends through the majority of the rotor shaft 12. As can be seen in [Fig.l], the inlet channel 22 extends from an axial end of the rotor shaft 12 through the rotor shaft 12 to a position that is rearward of the end of the axial end of the stack 14 that is opposite the side where the inlet channel 22 opens. In other words, the inlet channel 22 is a blind hole extending approximately to the axial position where the left end plate 18 of [Fig.l] is disposed.

[0030] Near the axial end of the inlet channel 22, a plurality of radially extending cooling openings 27 are provided in the rotor shaft 12. The cooling openings 27 open on the outer circumferential surface of the rotor shaft 12 and are disposed inwardly of a shoulder formed by a radially widened end portion of the rotor shaft 12 on which the end plate 18 abuts.

[0031] The end plate 18 has a plurality of recesses 28 extending radially around its inner circumference. The position and spacing of the recesses 28 approximately coincide with the position of the radial cooling openings 27.

[0032] The recesses 28 do not extend over the entire end plate 18, 19. In other words, the depth of each recess, viewed in an axial direction, is less than the thickness of the respective end plate 18, 19.

[0033] The recesses 28 serve to connect the radially outer end of the cooling openings 27 to the cooling passages 24 formed in the stack 14 of rotor plates 16. The cooling passages 24 are formed from a plurality of cutouts 30 formed in each rotor plate 16.

[0034] The end plate 18 thus serves as a radial end for the radial cooling openings formed from the radial cooling openings 27 in the rotor shaft 12 and from the recesses 28.

[0035] Each cutout 30 has a drop-shaped cross-section (see in particular [Fig. 2]), the contour of each cutout 30 having two straight portions 32 and one curved portion 34. The straight portions 32 are provided to interact with a mounting tool which defines the angular or circumferential position of each rotor plate 16 on the rotor shaft 12. In order to achieve the slight angular offset of the pockets for the magnets on the stack 14 of rotor plates, the angular position of the cutouts 30 differs slightly between the different types of rotor plates. Given the ability of the cutouts 30 to form the coolant passage 24, the cutouts 30 have a relatively large cross-section.

[0036] Furthermore, cutouts 30 are arranged between the adjacent recesses 20 which form the pockets for receiving the magnets, so that the waste heat generated in this part of the rotor can be very efficiently discharged to the coolant circulating in the cooling passages 24. The distance between the pocket formed by the recesses 20 and the coolant passage 24 formed by the cutouts 30 is designated in [Fig. 2] by the arrow A.

[0037] The dotted line L shows that the radially outer end of the cutouts 30 overlaps the radially inner ends of the recesses 20, which allows residual heat to be dissipated very efficiently.

[0038] As can be seen in [Fig.l] and [Fig.4], the end plate 19 disposed at the end of the stack 14 of rotor plates 16 which is adjacent the open end of the inlet channel 22, is provided with recesses 28 in a similar manner to the end plate 18 disposed at the opposite end.

[0039] At the location of the recesses 28 in the end plate 19, the rotor shaft 12 is provided with a plurality of radial cooling openings 36 which connect the cooling passages 24 (via the recesses 28) to the outlet channels 26. In this way, a closed cooling path is formed by the inlet channel 22, the radial cooling openings 27, the recesses 28, the cooling passages 24, the recesses 28, the radial cooling openings 36 and the outlet channels 26.

[0040] Similar to the end plate 18, the end plate 19 also serves as the radial end of the refrigerant passage formed by the recesses 28 and the refrigerant openings 36.

[0041] As can be seen in Figures 4 and 5, the recesses 28 are wider than the cooling passages 24. It is therefore possible to use standardized end plates 18, 19 which do not necessarily have to correspond perfectly, with their recesses 28, to the circumferential position of the cooling passages 24. The slight angular offset does not have a negative impact on the section available for the flow of the coolant.

[0042] In order to reduce coolant leakage, seals may be used to seal between the end plate 18 and a radially enlarged end portion 13 on the rotor shaft 12, between the end plate 18 and the adjacent rotor plate 16, between the adjacent rotor plates, between the end plate 19 and the adjacent rotor plate 16, and between the end plate 19 and the rotor shaft 12. Reference numeral 40 is used to designate potential positions of a seal or sealing material.

[0043] [Fig. 6] shows a second embodiment. For the known elements of the first embodiment, the same reference numbers are used, and it is made reference to the comments above.

[0044] In the embodiment of [Fig. 6], the inlet of the coolant path is formed by a combination of coolant openings 27 extending radially in the rotor shaft 12 and an end plate 50. The end plate 50 is similar to the end plate 19 in that it is held axially in the rotor shaft 12 by a nut (not shown in [Fig. 6]). Thus, the end plate 50 (more precisely: the radially outer ends of the recesses 28) forms a radial end for the radially extending portion of the coolant path so that the coolant path is diverted from a radial direction to an axial direction in the cutouts of the rotor plates.

[0045] A gasket 40 is used to prevent leakage of the coolant.

[0046] An alternative to the second embodiment is illustrated in [Fig. 7]. Instead of a plurality of separate recesses, an annular groove 52 is provided at the radially inner end of the end plate 50 on the side facing the rotor plates 16, the radially outer surface 54 of the groove 52 serving as the radial end of the cooling openings.

[0047] [Fig. 8] shows a third embodiment. For the known elements of the first and second embodiments, the same reference numbers are used, and reference is made to the above comments.

[0048] The third embodiment corresponds largely to the first embodiment, with the difference that the widened end portion 13 of the rotor shaft 12 and the end plate 18 abutting against the shoulder formed by the widened end portion 13, are here arranged on the "coolant inlet side" of the rotor shaft 12.

[0049] Similar to the variant illustrated in [Fig. 7], the end plate 18 may be provided with an annular groove instead of a plurality of separate radial recesses. In any case, the outer radial end of the respective configuration (either the circumferential wall of the groove or the outer end of each recess) forms the radial end of the opening for the coolant and marks the deflection of the coolant from a radial flow direction to an axial flow direction.

[0050] [Fig. 9] shows a fourth embodiment. For elements known from previous embodiments, the same reference numbers are used, and reference is made to the above comments.

[0051] The difference between the fourth embodiment and the previous embodiments is that, in the fourth embodiment, the axial support of the stack or rotor plates 16 is composed of a shoulder 60 on a ra- end portion dially enlarged 62 of the rotor shaft 12, and an end plate 64 which is disposed on the outer circumference of the end portion 62.

[0052] The cooling openings 27 extend through the enlarged end portion 62 and terminate at the outer circumferential surface of the end portion 62. There, they are closed by the inner circumferential surface of the end plate 64.

[0053] The widened end portion 62 is provided, on its side facing the rotor plates 16, with a plurality of connecting openings 66 which connect the radial cooling openings 27 to the cooling passages 24.

[0054] As an alternative to the separate connection openings 66, a circumferential groove could be used in the shoulder 60 on the side facing the rotor plates 16.

Claims

Claims

1. Rotor (10) for an electric machine, in particular for an electric motor, the rotor (10) having a rotor shaft (12) and a plurality of rotor plates (16) mounted on the rotor shaft (12), the rotor plates (16) having recesses (30) which form coolant channels (24) extending in the axial direction through the stack formed by the rotor plates (16), the rotor shaft (12) having an axial coolant opening (22), a plurality of radial coolant openings (27; 36) which connect the axial cooling opening (22) in the rotor shaft (12) to the cooling channels (24) in the stack of rotor plates (16), the rotor (10) further having an end plate (18; 19, 50;64) which forms a radial end for the radial cooling openings (27) wherein the rotor shaft (12) has a radially enlarged end portion (62) forming a shoulder (60) on which the rotor plate stack (16) abuts in an axial direction, the radial cooling openings (27) extending through the end portion (62) to an outer circumference thereof.;

2. The rotor (10) of claim 1, wherein the end plate (64) has a solid contact surface for abutting the rotor plate stack (16).

3. The rotor (10) of claim 1, wherein the end portion (62) has at least one connecting opening (66) for connecting the cooling channels (24) formed in the rotor plate stack (16) to the radial cooling openings (27) in the end portion.

4. The rotor (10) of claim 3, wherein the connection opening (66) is formed by an annular groove in the end portion on the side facing the rotor plate stack (16).

5. The rotor (10) of claim 3, wherein the connecting opening (66) is formed by a plurality of axially extending openings that connect the cooling channels (24) in the rotor plate stack (16) to the radial cooling openings (27).

6. The rotor (10) of claim 1, wherein the end plate (50) has an annular groove (52) at its radially inner end on the side facing the stack of rotor plates (16).

7. The rotor (10) of claim 1, wherein the end plate (18; 19; 50; 62) has a plurality of radial recesses (28) at its radially inner end on the side facing the rotor plate stack (16).

8. A rotor according to claim 6 or claim 7, wherein the rotor shaft (12) has a radially enlarged end portion (13) forming a shoulder at which the end plate (18) abuts in an axial direction, the radial cooling openings (27) being formed axially inwardly from the end portion (13).

9. Rotor (10) according to claim 6 or claim 7, wherein a clamping element is arranged on the rotor shaft (12) for axially clamping the rotor plate stack (16), in particular a clamping nut.

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