EP-4738655-A1 - ELECTRIC MOTOR AND VEHICLE COMPRISING THE ELECTRIC MOTOR

EP4738655A1EP 4738655 A1EP4738655 A1EP 4738655A1EP-4738655-A1

Abstract

An electric motor (1) comprising a rotor (2) rotatably arranged about a central axis (A) of the electric motor (1) and a stator (3) coaxial with the rotor (2). The stator (3) comprises a stator core (4) having a radially outer surface (10) comprising a plurality of ribs (8, 8') distributed circumferentially and extending longitudinally between axial ends (4a, 4b) of the stator core (4). The electric motor (1) further comprises a housing (12) arranged radially outside the stator (3) such that a substantially annular gap (14) is formed between the outer surface (10) of the stator core (4) and an inner wall of the housing (12). Moreover, the electric motor (1) comprises a cooling system (20) configured to create a circumferential flow (F) of a cooling liquid in the substantially annular gap (14). A vehicle (100) comprising the electric motor (1) is also disclosed.

Inventors

AFRIDI, Usman
BIRKESTAD, Per
NESS, CHRISTIAN
Engström, Jörgen
LANDEMOO, Viktor

Assignees

Traton AB

Dates

Publication Date: 20260506
Application Date: 20241101

Claims (13)

An electric motor (1) having a central axis (A) and comprising: a rotor (2) rotatably arranged about the central axis (A), a stator (3) coaxial with the rotor (2), the stator (3) comprising a stator core (4) having a radially outer surface (10) comprising a plurality of ribs (8, 8') distributed circumferentially and extending longitudinally between axial ends (4a, 4b) of the stator core (4), a housing (12) arranged radially outside the stator (3) such that a substantially annular gap (14) is formed between the outer surface (10) of the stator core (4) and an inner wall of the housing (12), and a cooling system (20) configured to create a circumferential flow (F) of a cooling liquid in the substantially annular gap (14).
The electric motor (1) according to claim 1, wherein each of the plurality of ribs (8, 8') has a cross section, perpendicular to the central axis (A), that is tapered.
The electric motor (1) according to claim 2, wherein said cross section comprises angled flanks (33, 34) connected via a rounded tip (31).
The electric motor (1) according to any one of the preceding claims, wherein each of the plurality of ribs (8, 8') has a downstream flank (33) and an upstream flank (34), relative to the circumferential flow (F) of cooling liquid, and wherein said upstream flank (34) is angled with an angle (α) of from 20° to 60°, relative to a stator core radius (R) at an outermost part (32) of a tip (31) of the rib (8, 8'); preferably with an angle (α) of from 25° to 45°.
The electric motor (1) according to any one of the preceding claims, wherein each of the plurality of ribs (8, 8') has a cross section, perpendicular to the central axis (A), which is symmetric about a radius (R) of the stator.
The electric motor (1) according to any one of the preceding claims, wherein a distance (D) between tips (31) of two adjacently arranged ribs (8, 8') of said plurality of ribs (8, 8') is from 1 to 3 times a width of a base of each of said two adjacently arranged ribs (8, 8').
The electric motor (1) according to any one of the preceding claims, wherein each of the plurality of ribs (8, 8') has a rounded tip (31) having a radius of curvature (r) that is from 0.4 to 0.8 times the radial height (h) of said rib (8, 8'); preferably from 0.5 to 0.7 times the radial height (h) of said rib (8, 8').
The electric motor (1) according to any one of the preceding claims, wherein a ratio of radial height (h) of each of the plurality of ribs (8, 8') to a maximum radial distance between the radially outer surface (10) of the stator core (4) and the inner wall of the housing (12) is from 0.4 to 0.7; preferably from 0.50 to 0.65.
The electric motor (1) according to any one of the preceding claims, wherein each of the plurality of ribs (8) extend longitudinally in parallel with the central axis (A).
The electric motor (1) according to any one of claims 1 to 8, wherein the plurality of ribs (8, 8') are helical ribs (8') having a helix angle (β) of equal to or less than 20 degrees; preferably equal to or less than 10 degrees.
The electric motor (1) according to any one of the preceding claims, wherein the cooling system (20) is configured to create a circumferential flow (F) in a substantially counter-gravity direction.
The electric motor (1) according to any one of the preceding claims, wherein the outer surface of the stator core, in addition to the plurality of ribs (8, 8'), further comprises a plurality of surface features configured to increase a surface area of the outer surface of the stator core.
A vehicle (100) comprising the electric motor (1) according to any one of the preceding claims.

Description

TECHNICAL FIELD The present disclosure relates in general to an electric motor. The present disclosure further relates in general to a vehicle comprising the electric motor. BACKGROUND The ongoing electrification of vehicles, in particular heavy-duty or medium-duty vehicles, has led to demands for electric motors with higher power densities. Electric motors comprise a rotor and a stator, which in turn comprises a stator core and windings. To reduce energy losses and improve efficiency, the stator core is typically formed of a large number of thin laminated sheets (typically having a sheet thickness of about 0.2-0.5 mm) that are stacked together in the axial direction of the stator core. These thin sheets are typically stamped or laser cut from a steel sheet in a shaped desired for the stator core, and thereafter stacked next to each other to build up the stator core in the axial direction thereof. Increasing power density requirements for electric motors necessitate enhanced cooling efficiency to allow meeting the demand. Electric motors generate heat, for example due to electrical losses in windings, core losses (resulting from hysteresis and eddy currents), and mechanical friction. Efficient cooling of electric motors is therefore essential, for example, to prevent overheating and avoid efficiency drops. More specifically, the lifespan and efficiency of an electric motor is constrained by temperature of the hot spots, which may often be located within a mid-stack region of the stator core. An electric motor may be cooled in several ways, using various types of cooling media. For example, an electric motor may be cooled by force air cooling. Forced air cooling is a simple and cost effective solution but is typically not sufficient for high-power applications, such as in heavy-duty vehicles. Another example is water cooling in which the coolant circulates through channels around or within the electric motor and transfers the heat to a heat exchanger, where it typically is cooled down by air. Water cooling is significantly more efficient than forced air cooling, but is a considerably more complex alternative. Water cooling may for example be achieved by using a water jacket that surrounds the housing of the electric motor. Yet another example is oil cooling. Oil cooling is particularly effective because oil has a higher heat capacity than air or water, and is therefore often desired for electrical motors intended to be used in, for example, heavy-duty vehicles. Oil cooling may for example be achieved through arranging various oil channels inside the electric motor, such as axial oil channels in the stator and/or the rotor, to further improve heat dissipation from the electric motor. SUMMARY The object of the present invention is to improve cooling capacity of an electric motor to, for example, enable meeting increasing power density demands. The object is achieved by the subject-matter of the appended independent claim(s). The present disclosure relates to an electric motor having a central axis. The electric motor comprises a rotor rotatably arranged about the central axis. The electric motor further comprises a stator coaxial with the rotor, the stator comprising a stator core having a radially outer surface comprising a plurality of ribs distributed circumferentially and extending longitudinally between axial ends of the stator core. The electric motor also comprises a housing arranged radially outside the stator such that a substantially annular gap is formed between the outer surface of the stator core and an inner wall of the housing. Furthermore, the electric motor comprises a cooling system configured to create a circumferential flow of a cooling liquid in the substantially annular gap. In the electric motor according to the present disclosure, direct cooling of the stator core may be achieved by means of a flow of cooling liquid in direct contact with the radially outer surface of the stator core. Furthermore, cooling capacity of the stator core, and thus also of the electric motor as such, is improved by the combination of the presence of a plurality of ribs, extending longitudinally between axial ends of the stator core, with a circumferential flow of cooling liquid. The plurality of ribs increase the surface area of the radially outer surface of the stator core and thus also the possible heat transfer surface between the stator core and the cooling liquid flowing outside of the stator core. A circumferential flow of cooling liquid, as created by the cooling system, leads to an efficient cooling of the most critical regions of the stator core (typically in the mid-stack region) as well as a consistent cooling effect across the stator core outer surface. Furthermore, for typical design dimensions of today's electrical motors for vehicles (which often have a considerably greater circumference of the stator core compared to the axial extension of the stator core), a circumferential flow of the coolin