US-20260128626-A1 - ELECTRIC MACHINE IN-SLOT COOLING CHANNELS

US20260128626A1US 20260128626 A1US20260128626 A1US 20260128626A1US-20260128626-A1

Abstract

A cooling manifold for an electric machine is proposed with a hollow bolt feed solution that takes advantage of an existing bolt structure and interface to a housing of the electric machine to create a fluid passage for routing coolant to internal portions of a stator of the electric machine. The hollow bolt creates a sealed fluid interface without the need to add an additional seal, thereby reducing manufacturing complexity of the electric machine. In-slot cooling with the manifold, or with a plurality of the manifolds, may eliminate a reliance on slot liners and varnish for limiting relative motion of end windings of the stator and providing electrical isolation, while also cooling the hottest part of the electric machine, significantly influencing the machine's thermally limited capability.

Inventors

Nicholas Chase
Wenbo Liu
Myung Ki SUNG
Seth Avery
Alfredo R. Munoz

Assignees

FORD GLOBAL TECHNOLOGIES, LLC

Dates

Publication Date: 20260507
Application Date: 20241105

Claims (20)

1 . A cooling system for an electric machine having a stator and a housing, the cooling system comprising: a cooling manifold positioned at an axial center of the stator and aligned coaxially with a central axis of the stator; and a bolt clamping the stator to the housing, the bolt including a hollow section comprising a fluid inlet and a fluid outlet configured to transfer a coolant from the hollow section into a plurality of passages of the cooling manifold.
2 . The cooling system of claim 1 , wherein the hollow section includes a first portion that extends into the housing, and a second portion that extends into a stator core of the electric machine, the second portion including one or more radial holes positioned around a circumference of sides of the hollow section, the one or more radial holes positioned to allow the coolant to flow from a center passage of the hollow section to a passage between a stator core ear hole of the electric machine and an outer circumference of the hollow section.
3 . The cooling system of claim 2 , wherein the passage is sealed to a head of the bolt and the housing by a clamping force of the bolt, and the bolt includes a lip around an outer circumference of the bolt that seals the passage at an interface between the housing and the stator core.
4 . The electric machine of claim 2 , wherein the plurality of passages of the cooling manifold are sealed against laminations of the stator core axially by a compression of a plurality of bolts including the bolt.
5 . The cooling system of claim 2 , wherein the cooling manifold is in fluid communication with the fluid outlet, and the cooling manifold comprises a partially open compression limiting eyelet of a bolt hole through which coolant is transferred from the fluid outlet of the hollow section into a radial inlet of the cooling manifold.
6 . The cooling system of claim 5 , wherein the compression limiting eyelet includes dowel features that extend partially into portions of a plurality of stator core slots that align the cooling manifold to the plurality of stator core slots.
7 . The cooling system of claim 6 , wherein the cooling manifold extends radially and inwardly into the plurality of stator core slots to form an interference fit to windings of the stator.
8 . The cooling system of claim 7 , wherein the cooling manifold is made from injection molded plastic, and further comprises: a first circumferential section that distributes the coolant circumferentially around the stator to the plurality of stator core slots at an outer circumference of the cooling manifold; a second circumferential section that distributes the coolant circumferentially around the stator to the plurality of stator core slots at an inner circumference of the cooling manifold; and a center circumferential section including a plurality of radial ribs, each radial rib a mechanical retention feature that connects the first circumferential section to the second circumferential section such that the cooling manifold is molded as a single part.
9 . The cooling system of claim 8 , wherein: the center circumferential section has an interference fit to the windings to provide mechanical support needed to prevent an outer enamel coating of the windings from rubbing on the stator core, and features of the cooling manifold that interface to the windings are made of an over-molded material softer than a material of the cooling manifold.
10 . The cooling system of claim 1 , wherein the cooling manifold is made of electrical steel or aluminum, and further comprises two laminated sub stacks that include alternating and connected circumferential pockets to allow the coolant to be distributed circumferentially while still maintaining a continuous lamination.
11 . The electric machine of claim 2 , further comprising a first cooling manifold positioned at a first end of the stator core, and a second cooling manifold positioned at a second end of the stator core, wherein the coolant is flowed alternately to passages of the first cooling manifold and the second cooling manifold, such that each slot of the stator core is fed by one of the first cooling manifold and the second cooling manifold.
12 . A system, comprising: an electric machine including a stator; a cooling system configured to flow a coolant from a coolant pump to the stator; and a bolt coupling the cooling system to the electric machine, the bolt including a hollow section having one or more radial holes positioned around an outer circumference of the hollow section, the one or more radial holes positioned to allow the coolant to flow from the hollow section to a cooling manifold of the electric machine via a passage between a stator core ear hole of the electric machine and an outer circumference of the hollow section.
13 . The system of claim 12 , wherein the cooling manifold comprises a partially open compression limiting eyelet of a bolt hole through which coolant is transferred from the passage into a radial inlet of the cooling manifold.
14 . The system of claim 12 , wherein the cooling manifold extends radially and inwardly into a plurality of stator core slots of the stator to form an interference fit to windings of the stator.
15 . The system of claim 12 , further comprising a seal sleeve positioned at an inner diameter of the stator to seal in-slot fluid passages of the cooling manifold from leaking coolant into a machine air gap between the stator and a rotor of the electric machine.
16 . The system of claim 15 , further comprising a plurality of end rings positioned at end windings of the stator to provide mechanical fixation for the end windings via an interference fit to limit relative motion of the end windings, the plurality of end rings including orifices to control pressure in the in-slot fluid passages and distribute the coolant to the end windings.
17 . The system of claim 12 , wherein the cooling manifold comprises two laminated sub stacks that include alternating and connected circumferential pockets that distribute the coolant circumferentially throughout the cooling manifold while maintaining a continuous lamination.
18 . The system of claim 12 , wherein the electric machine comprises a first cooling manifold positioned at a first end of a stator core of the stator, and a second cooling manifold positioned at a second end of the stator core, and the coolant is flowed alternately to passages of the first cooling manifold and the second cooling manifold, such that each slot of the stator core is fed by either the first cooling manifold or the second cooling manifold.
19 . A method for cooling an electric machine, the method comprising: flowing a coolant to a plurality of circumferential and radial passages of a cooling manifold positioned at an axial center of a stator of the electric machine and aligned coaxially with a central axis of the stator, via a hollow section of a bolt clamping the stator to a housing of the electric machine, the cooling manifold extending radially and inwardly into a plurality of slots of a stator core of the electric machine to form an interference fit to windings of the stator.
20 . The method of claim 19 , further comprising: flowing the coolant from the hollow section to a passage between a stator core ear hole of the electric machine and an outer circumference of the hollow section via one or more radial holes positioned around a circumference of sides of the hollow section, the passage sealed to a head of the bolt and the housing by a clamping force of the bolt; and flowing the coolant from the passage to a radial inlet of the cooling manifold via a partially open compression limiting eyelet of a bolt hole of the cooling manifold.

Description

FIELD The present description relates generally to methods and systems for cooling an electric motor of a vehicle. BACKGROUND/SUMMARY During operation, an electric machine generates electromagnetic losses in the form of heat, which in most cases are focused in a stator of the electric machine. Furthermore, sustained performance of an electric machine is governed by an ability to remove heat coupled with component material temperature limits. Overheating of the electric machine can lead to degraded performance capability, and eventually, degradation of the electric machine. The inventors herein have developed systems and methods to at least partially address overheating of the electric machine. In particular, the hottest part of the electric machine (e.g., the thermally limiting hot spot) is the windings at the center of the stator, which may not directly receive coolant supplied by the existing cooling solutions. Directly cooling the hot spot may allow for higher power density and may increase continuous performance, as compared with the existing cooling solutions. In one example, the direct cooling of the windings may be accomplished by a cooling system for an electric machine having a stator and a housing, the cooling system comprising a cooling manifold positioned at an axial center of the stator and aligned coaxially with a central axis of stator; and a bolt clamping the stator to the housing, the bolt including a hollow section comprising a fluid inlet and a fluid outlet configured to transfer a coolant from the hollow section into a plurality of passages of the cooling manifold. The coolant may be flowed from the housing to the cooling manifold through the hollow section, and subsequently directed to end windings of the stator via radial passages that extend into winding slots of the stator. The coolant may also circulate from an inlet of the cooling manifold to all the radial passages via circumferential passages within the manifold. In other words, a plurality of passages may be incorporated into the stator that allow the coolant to flow between the stator core and windings, for direct hot spot cooling while meeting mechanical retention demands. In an electric machine, mechanical retention between a stator core and a housing of the electric machine may be relied on to provide reaction torque. Two common methods for stator retention are using bolts (through ears located outside of a stator yoke) and an interference fit (between the stator core and housing), in which no bolts are used. While interference fits are beneficial for noise, vibration, and harshness (NVH) and creating fluid interfaces to the stator core, bolts are often preferred due to increased core losses caused by compressive stresses of an interference fit. Thus, while using bolts for stator retention to minimize core losses, the hollow bolt presents a novel interface for introducing the coolant to the center of the electric machine. In this way, one or more fluid manifold(s) with hollow bolt feeds take advantage of an existing bolt and interface to the housing to create a fluid passage to the windings of the stator. The hollow bolt creates a sealed fluid interface without having to add an additional seal, thereby reducing manufacturing complexity of the electric machine. Mechanical retention is also used within the slots between the stator windings and the stator core to prevent relative motion that can lead to insulation degradation. Slot liners and varnish may be used to limit this relative motion and provide electrical isolation. As a result, in-slot cooling with the manifold(s) may eliminate the use of slot liners and varnish, while still reducing relative motion and cooling the hottest spot of the machine, reducing manufacturing resources and complexity while increasing the machine's thermally limited capability. The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS The advantages described herein will be more fully understood by reading an example of an embodiment, referred to herein as the Detailed Description, when taken alone or with reference to the drawings, where: FIG. 1 is a first perspective view of a portion of an exemplary electric machine including a hollow bolt and a cooling manifold; FIG. 2 is a cross-sectional view of the electric machine