Electric motor with cooling system

Abstract

An electric motor (1) comprising a stator (3), a rotor (2), a housing (20), a cooling system (4), and a motor drive system comprising a circuit board (6) and a plurality of power semiconductors (12), wherein the housing (20) comprises a stator housing section (21) including a peripheral wall (22a) surrounding the stator (3), and a drive system housing section (25) including a base wall (26) located at the axial end of the stator housing section (21), and the circuit board (6) is mounted on the base wall (26). The cooling system comprises a cooling channel (9) for circulating a coolant, the cooling channel being bounded by a wall portion including part of the peripheral wall (22a) and part of the base wall (26), and configured such that the liquid in the cooling channel cools both the stator and the motor drive system simultaneously.

Description

Technical Field

[0001] The present invention relates to an electric motor provided with a cooling system.

Background Art

[0002] It is well known in the art that some of the components of a powerful electric motor generate heat during operation and cooling is often required to avoid damage due to overheating. For example, the stator and the power semiconductors of an inverter are often cooled in a powerful electric motor. For example, a metal oxide semiconductor field effect transistor can be used as the power semiconductor of an inverter. In some motors, the electronics required to operate the motor including the inverter are integrated into the motor.

[0003] In some prior art solutions, the stator and power electronics are cooled in two separate independent cooling circuits. In other prior art solutions, the stator and power electronics are cooled in one cooling circuit having a relatively complex path through the motor housing.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In view of the above, an object of the present invention is to provide an electric motor including a highly reliable and efficient cooling system.

[0005] It is advantageous to provide an electric motor provided with a cooling system that is highly reliable, efficient and economical to manufacture.

[0006] It is advantageous to provide an electric motor provided with a compact cooling system.

Means for Solving the Problems

[0007] The object of the present invention is achieved by the electric motor described in the independent claim. The dependent claims illustrate embodiments of the present invention.

[0008] Disclosed herein is an electric motor comprising a stator, a rotor, a housing, a cooling system, and a motor drive system comprising a circuit board and a plurality of power semiconductors, wherein the housing comprises a stator housing section surrounding the stator and a drive system housing section including a base wall located at the axial end of the stator housing section, and the circuit board is mounted on the base wall.

[0009] The stator housing section and the drive system housing section are separate parts assembled and fixed together. The stator housing section includes an inner circumferential wall and an outer circumferential wall, the inner circumferential wall being joined to the outer circumferential wall at a first axial end, the inner and outer circumferential walls both extending to an assembly interface at a second axial end, and the base wall being assembled in contact with the second axial ends of the inner and outer circumferential walls. The cooling system includes cooling channels for circulating coolant, which are formed and bounded between the inner circumferential wall, the outer circumferential wall and the base wall, and are configured so that the fluid in the cooling channels cools both the stator and the motor drive system simultaneously.

[0010] In an advantageous embodiment, the seal is fitted within the assembly interface between the stator housing section and the base wall, and the base wall is assembled in a sealed state in contact with the second axial ends of the inner and outer circumferential walls.

[0011] In an advantageous embodiment, the cooling system includes a single inlet for the coolant flow to enter the cooling channel and a single outlet for the coolant flow to exit the cooling channel.

[0012] In an advantageous embodiment, the cooling channel completely encloses the stator, except for the separation wall between the inlet and outlet.

[0013] In a favorable embodiment, the separation wall between the inlet and outlet has a small tolerance gap, configured such that less than 5% of the overall coolant flow leaks directly across the separation wall from the inlet to the outlet.

[0014] In an advantageous embodiment, multiple power semiconductors are mounted on the circuit board in a position that overlaps the cooling channel axially.

[0015] In an advantageous embodiment, the base wall of the drive system housing section includes at least one heat transfer reinforcing structure, such as a rib, fin, support, projection, groove, or recess, within the cooling channel.

[0016] In an advantageous embodiment, the cooling channel has an axial portion and a radial portion, the axial portion extending along the circumferential wall and the radial portion extending on the base wall.

[0017] In an advantageous embodiment, the axial portion overlaps the stator for a length exceeding 50% of the stator's axial length.

[0018] In an advantageous embodiment, the axial and radial portions of the cooling channel together form a single unconstricted channel.

[0019] In an advantageous embodiment, the axial and radial portions of the cooling channel form a constricted portion that is fluidly interconnected by restricted fluid interconnection passages.

[0020] Further objectives and advantageous features of the present invention will become apparent from the claims, detailed description, and accompanying drawings. [Brief explanation of the drawing]

[0021] [Figure 1] This is a perspective view of an electric motor according to a first embodiment of the present invention. [Figure 2a]Exploded perspective view of the base portion of the stator housing of the electric motor and the motor drive system housing according to the first embodiment of the present invention. [Figure 2b] Exploded perspective view of the base portion of the stator housing of the electric motor and the motor drive system housing according to the first embodiment of the present invention. [Figure 3a] Cross-sectional view of the electric motor according to the first embodiment of the present invention. [Figure 3b] Partial perspective cross-sectional view of the electric motor according to the first embodiment of the present invention. [Figure 4] Perspective view of the motor drive system housing of the electric motor according to the first embodiment of the present invention. [Figure 5] Perspective view of the motor drive system housing of the electric motor according to a modified example of the first embodiment of the present invention. [Figure 6] Perspective view of the stator and stator housing of the electric motor according to the first embodiment of the present invention. [Figure 7] Perspective view of the electric motor according to the second embodiment of the present invention. [Figure 8] Perspective cross-sectional view of the electric motor according to the second embodiment of the present invention.

Mode for Carrying Out the Invention

[0022] Referring to the drawings, an electric motor 1 according to an embodiment of the present invention includes a rotor 2, a stator 3, a motor drive system, and a housing 20 in which the rotor, stator, and motor drive system are mounted.

[0023] The electric motor 1 further includes a cooling system 4 including a cooling channel 9 formed in the housing 20, and a coolant is received in the cooling channel and flows through the cooling channel.

[0024] The motor drive system includes a circuit board 6 and electronic components mounted on the circuit board, including at least one inverter containing a power semiconductor 12. The inverter supplies drive current to the electrical phase of the electric motor, so that a motor with multiple phases has multiple corresponding inverters.

[0025] The power semiconductor of the inverter can take the form of a bipolar transistor, an insulated-gate bipolar transistor (IGBT), a metal-oxide-semiconductor field-effect transistor (MOSFET) based on, for example, Si, SiC, or GaN, which are well known in the field of inverters for electric motors, or a high electron-mobility transistor (HEMT) based on, for example, GaN.

[0026] In certain embodiments, the electric motor 1 can be a high-voltage electric motor with a nominal DC voltage exceeding 850V, particularly exceeding 1000V, and especially exceeding 1500V.

[0027] The housing 20 includes a stator housing section 21 that houses the stator 3, and a drive system housing section 25 that houses a circuit board 6 of the motor drive system, which includes electronic components including power semiconductors 12. The drive system housing section 25 is advantageously positioned at the axial end of the stator housing section 21, thereby positioning the circuit board 6 of the motor drive system adjacent to the axial end of the stator 3, where axial is defined herein as the direction of the rotation axis of the rotor 2. Mounting the motor drive system on the axial end of the stator 3 advantageously results in a compact configuration and allows for efficient cooling of both the stator and the electronic components of the motor drive system, as will be described in more detail below.

[0028] The stator housing section 21 includes an inner circumferential wall 22a that surrounds and contacts the stator 3. This inner circumferential wall also forms the boundary of the cooling channel 9 on the side opposite to the side in contact with the stator, and the heat generated in the stator is mainly discharged into the cooling fluid flowing through the cooling channel by conduction via the inner circumferential wall 22a. The inner circumferential wall 22a continues to an end wall 23 via a bend, and the axial end of the stator 3 is located in contact with this end wall 23.

[0029] The drive system housing section 25 includes a base wall 26 positioned axially between the stator 3 and the circuit board 6, which houses the electronic components of the motor drive system. The base wall 26 also has a portion on the side opposite to the side in contact with the motor drive system that forms the boundary of the cooling channel 9, thereby allowing heat generated within the motor drive system, and more specifically heat generated by the power semiconductors of the motor drive system, to be discharged into the cooling fluid flowing through the cooling channel 9, primarily by conduction through the base wall 26.

[0030] Therefore, the cooling channel 9 is bounded by a wall portion that includes a part of the inner circumferential wall 22a surrounding the stator 3 and a part of the base wall 26 to which the motor drive system is mounted. As a result, the coolant flowing through the cooling channel serves to cool both the stator and the motor drive system simultaneously. The outer circumferential wall 22b of the stator housing section 21 forms the radially outer boundary of the cooling channel, closing it off. The outer circumferential wall 22b is in contact with the surrounding environment and helps dissipate heat through convection.

[0031] The inner circumferential wall 22a is pressed against the outer diameter of the stator 3 to enable efficient heat transfer from the stator 3 to the cooling channel 9 via very low thermal resistance in the contact area. In one embodiment, the assembly between the outer diameter of the stator 3 and the inner diameter of the inner circumferential wall 22a may be performed by press-fitting, shrink-fitting, or thermal fitting to ensure pressing contact even when the housing is thermally expanded.

[0032] In the illustrated embodiment, the stator housing section 21 and the drive system housing section 25 are separate components that are assembled and fixed together. Seals 33a and 33b are fitted to the interface between the stator housing section 21 and the drive system housing section 25 to ensure the sealing of the cooling channel 9 and prevent liquid from leaking from the cooling channel at the interface between the housing sections 21 and 25.

[0033] The outer peripheral wall 22b is joined to the inner peripheral wall 22b at the first axial end 37a, and both the inner and outer peripheral walls extend from the first axial end to the second axial end 37b located at the assembly interface with the base wall 26. Seals 33a and 33b seal the base wall tightly to the second axial ends 37b of the respective inner and outer peripheral walls 22a and outer peripheral walls 22b, forming a cooling channel 9 between the inner and outer peripheral walls and the base wall. This configuration provides a compact and simple stator and cooling structure, enabling efficient cooling of both the stator and the electronics of the drive system.

[0034] The stator housing section 21 can be advantageously manufactured from a single block of material as a single, integrally formed part, for example, by molding, machining, or additive manufacturing techniques such as 3D printing.

[0035] The housing 20 may include a cap 24 that covers the end of the stator 3 opposite to the end where other components that fit onto the stator housing section 21, such as the drive system housing section 25, are positioned.

[0036] It should be noted that the output shaft 29 of the rotor 2 may extend axially from one side of the motor, as in the illustrated embodiment, or it may extend from both sides of the motor (an unillustrated embodiment). For example, in the latter modification, the cap may have an opening through which the rotor shaft extends.

[0037] The motor drive system may be positioned on the side of the stator 3 through which the rotor output shaft 29 extends, as in the first embodiment shown in Figures 1 to 6. In this embodiment, the circuit board 6 includes a hole 30 that allows the rotor shaft to extend through it.

[0038] In another embodiment, the motor drive system may be positioned on the side of the stator 3 through which the rotor output shaft 29 does not extend, as shown in Figures 7 and 8. In this embodiment, the circuit board 6 does not require holes, and the motor drive system may include a position sensor 36 mounted on the circuit board facing the axial end of the rotor shaft to detect the angular position and velocity of the rotor.

[0039] In the second embodiment, the advantage of mounting the motor drive system on the side without the output shaft is easy access to the electronic components of the drive system, which can be easily repaired or replaced.

[0040] The cooling system 4 includes an inlet 31 and an outlet 32 ​​that are fluid-connected to the cooling channel 9.

[0041] The cooling channel 9 has an axially extending portion 9a and a radially extending portion 9b, the axial portion 9a extending along the circumferential wall 22a and the radial portion 9b extending over the base wall 26.

[0042] Preferably, the axial portion 9a overlaps with the stator 3 over a length a1 that exceeds 50% of the axial length a2 of the stator 3.

[0043] The radial portion 9b may extend radially over a distance r1, thereby overlapping with the stator 3 and serving to cool the electronic components of the motor drive system located within the circumference of the motor, depending on the stator diameter.

[0044] In the illustrated embodiment, the cooling channel 9 substantially encloses the stator 3, except for a separation wall 34b between the inlet 31 and the outlet 32. The inlet and outlet include an inlet mouth and an outlet mouth, respectively. The inlet mouth and outlet mouth may be formed through the base wall 26 of the drive system housing section 25 as shown in Figures 1 to 6, or through the outer periphery wall 22 as shown in Figures 7 and 8. The inlet mouth and outlet mouth may be positioned adjacent to each other, so that the separation wall 34a, 34b is formed between the inlet mouth and the outlet mouth in the cooling channel 9 to ensure the flow of coolant from the inlet mouth, around the stator, and to the outlet mouth.

[0045] In a preferred embodiment, when the stator housing section 21 and the drive system housing section 25 are assembled, mechanical play 34c remains between the separation walls 34a and 34b. This mechanical play 34c, necessary for iso-constrained assembly, allows a small amount of coolant to leak through the separation wall between the inlet 31 and the outlet 32. The thickness of the mechanical play 34c may vary due to production variability and tolerances, but remains sufficiently small so that less than 5% of the overall coolant flow leaks directly across the separation walls 34a and 34b from the inlet 31 to the outlet 32.

[0046] The axial portion 9a and radial portion 9b of the cooling channel 9 may together form an essentially single non-constricted channel, as in the embodiments shown in Figures 1 to 6, or they may form constricted portions fluidly interconnected by a restricted fluid interconnection passage 9c. This restricted fluid interconnection passage 9c allows for the separation of most of the hydrodynamic coolant flow around the stator from most of the hydrodynamic coolant flow on the base wall 26 of the motor drive system, while having a single coolant circuit (with a single inlet and a single outlet) within the electric motor. The partially separated coolant flow allows for better coordination and optimization of the coolant flow for dissipating heat from the motor drive system and stator, according to the motor configuration and the heat generated by the respective motor drive system and stator.

[0047] The main source of heat generated within the motor drive system is the power semiconductor 12. The power semiconductor is positioned on the circuit board 6 and is preferably axially aligned with or overlapping with the cooling channel 9, particularly the radial portion 9b of the cooling channel. This allows the heat conduction path between the power semiconductor 12 and the coolant liquid to be advantageously very short.

[0048] Heat transfer between the material, e.g., metal, of the wall portions 22a, 26 that form the boundaries of the cooling channel 9 and the coolant liquid can be increased by providing heat transfer enhancing structures 35, such as ribs, pillars, fins, recesses, grooves, or other protrusions or structures, on the wall portions within the cooling channel 9. In an advantageous embodiment, the base wall 26 of the drive system housing section 25 includes at least one heat transfer enhancing structure 35 within the cooling channel 9. The base wall 26 of the drive system housing section 25 may include multiple heat transfer enhancing structures 35 of the same or different types within the cooling channel 9. Advantageously, the heat transfer enhancing structures 35 may be arranged to be in thermal contact with the power semiconductors via a stack of material layers, the stack of layers being thermally conductive but electrically insulated.

[0049] [List of illustrated feature parts] Electric motor 1 Rotor 2 Output shaft 29 Stator 3 Housing 20 Stator housing section 21 Inner peripheral wall 22a Outer wall 22b First axial end 37a second axial end 37b End wall 23 Cap 24 Fixed element 28a Drive system housing section 25 Base wall 26 Fixed element 28b Cooling system 4 Thermal interface layer 7 Heatsink 8 Cooling channel 9 Axial part 9a Radial part 9b Connection part 9c Entrance 31 exit 32 Seal part Inner sealing portion 33a Outer seal portion 33b Separation walls 34a, 34b Small gap 34c Heat transfer reinforced structure 35 For example, ribs, supports, grooves Motor drive system Circuit board 6 Electronic components Power semiconductor 12

[0050] [Implementation Method] (1) An electric motor (1) comprising a stator (3), a rotor (2), a housing (20), a cooling system (4), a motor drive system comprising a circuit board (6) and a plurality of power semiconductors (12), wherein the housing (20) comprises a stator housing section (21) surrounding the stator (3) and a drive system housing section (25) comprising a base wall (26), the circuit board (6) mounted on the base wall (26), and the stator housing section (21) and the drive system housing section (25) being separate components assembled and fixed together. An electric motor characterized in that the stator housing section (21) includes an inner circumferential wall (22a) and an outer circumferential wall (22b), the inner circumferential wall being joined to the outer circumferential wall at a first axial end (37a), both the inner circumferential wall and the outer circumferential wall extending from the first axial end to an assembly interface at a second axial end (37b), and the cooling system includes a cooling channel (9) for flowing a coolant through, the cooling channel being formed and bounded between the inner circumferential wall (22a), the outer circumferential wall (22b), and the base wall (26), and the fluid in the cooling channel being configured to cool both the stator and the motor drive system simultaneously. (2) The electric motor according to Embodiment 1, wherein seals (33a, 33b) are fitted within the assembly interface between the stator housing section and the base wall, and the base wall (26) is assembled in a sealed state in contact with the second axial ends of the inner and outer walls. (3) The electric motor according to Embodiment 1 or 2, wherein the cooling system (4) includes a single inlet (31) for the flow of the coolant to enter the cooling channel and a single outlet (32) for the flow of the coolant to exit the cooling channel. (4) An electric motor according to any one of embodiments 1 to 3, wherein the cooling channel (9) completely encloses the stator, except for the separation wall (34a, 34b) between the inlet (31) and the outlet (32). (5) The electric motor according to Embodiment 4, wherein the separation wall (34a, 34b) between the inlet (31) and the outlet (32) has a small tolerance gap (34c) configured such that less than 5% of the overall coolant flow leaks directly across the separation wall from the inlet to the outlet.

[0051] (6) The electric motor according to any one of embodiments 1 to 5, wherein the plurality of power semiconductors (12) are mounted on the circuit board in a position that overlaps the cooling channel in the axial direction. (7) An electric motor according to any one of embodiments 1 to 6, wherein the base wall (26) of the drive system housing section (25) includes at least one heat transfer reinforcing structure (35), such as a rib, fin, support, projection, groove, or recess, within the cooling channel (9). (8) The electric motor according to any one of embodiments 1 to 7, wherein the cooling channel (9) has an axial portion (9a) and a radial portion (9b), the axial portion extending along the circumferential wall (22a), the radial portion extending on the base wall (26), and the axial portion (9a) overlapping the stator (3) for a length (a1) exceeding 50% of the axial length (a2) of the stator. (9) The electric motor according to Embodiment 8, wherein the axial portion (9a) and the radial portion (9b) of the cooling channel together form a single non-constricted channel. (10) The electric motor according to embodiment 8 or 9, wherein the axial portion (9a) and the radial portion (9b) of the cooling channel form a constricted portion that is fluidly interconnected by a restricted fluid interconnection passage (9c).

[0052] (11) The electric motor according to any one of embodiments 1 to 10, wherein the stator housing section (21) is a single integrally formed part.

Claims

1. An electric motor (1) comprising a stator (3), a rotor (2), a housing (20), a cooling system (4), a motor drive system including a circuit board (6) and a plurality of power semiconductors (12), wherein the housing (20) comprises a stator housing section (21) surrounding the stator (3) and a drive system housing section (25) including a base wall (26), the circuit board (6) mounted on the base wall (26), and the stator housing section (21) and the drive system housing section (25) are separate components assembled and fixed together. An electric motor characterized in that the stator housing section (21) includes an inner circumferential wall (22a) and an outer circumferential wall (22b), the inner circumferential wall being joined to the outer circumferential wall at a first axial end (37a), both the inner circumferential wall and the outer circumferential wall extending from the first axial end to an assembly interface at a second axial end (37b), and the cooling system includes a cooling channel (9) for flowing a coolant through, the cooling channel being formed and bounded between the inner circumferential wall (22a), the outer circumferential wall (22b), and the base wall (26), and the fluid in the cooling channel being configured to cool both the stator and the motor drive system simultaneously.

2. The electric motor according to claim 1, wherein seals (33a, 33b) are fitted within the assembly interface between the stator housing section and the base wall, and the base wall (26) is assembled in a sealed state in contact with the second axial ends of the inner and outer circumferential walls.

3. The electric motor according to claim 1 or 2, wherein the cooling system (4) includes a single inlet (31) for the flow of the coolant to enter the cooling channel and a single outlet (32) for the flow of the coolant to exit the cooling channel.

4. The electric motor according to claim 1, wherein the cooling channel (9) completely encloses the stator, except for the separation wall (34a, 34b) between the inlet (31) and the outlet (32).

5. The electric motor according to claim 4, wherein the separation wall (34a, 34b) between the inlet (31) and the outlet (32) has a small tolerance gap (34c) configured such that less than 5% of the overall coolant flow leaks directly across the separation wall from the inlet to the outlet.

6. The electric motor according to claim 1, wherein the plurality of power semiconductors (12) are mounted on the circuit board in a position that overlaps the cooling channel in the axial direction.

7. The electric motor according to claim 1, wherein the base wall (26) of the drive system housing section (25) includes at least one heat transfer reinforcing structure (35), such as a rib, fin, support, projection, groove, or recess, within the cooling channel (9).

8. The electric motor according to claim 1, wherein the cooling channel (9) has an axial portion (9a) and a radial portion (9b), the axial portion extending along the circumferential wall (22a), the radial portion extending on the base wall (26), and the axial portion (9a) overlapping the stator (3) for a length (a1) exceeding 50% of the axial length (a2) of the stator.

9. The electric motor according to claim 8, wherein the axial portion (9a) and the radial portion (9b) of the cooling channel together form a single non-constricted channel.

10. The electric motor according to claim 8 or 9, wherein the axial portion (9a) and the radial portion (9b) of the cooling channel form a constricted portion that is fluidly interconnected by a restricted fluid interconnection passage (9c).

11. The electric motor according to claim 1, wherein the stator housing section (21) is a single, integrally formed part.

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