US-20260128652-A1 - LOW IMPEDENCE GROUNDING FOR ELECTRIC MOTORS

Abstract

An electric motor grounding system includes a hollow cylinder packed with an electrically conductive media. Rotating seals are connected on the hollow cylinder on opposed ends of the hollow cylinder to retain the conductive media within the hollow cylinder. A rotor shaft is positioned within an electric motor, the rotor shaft having a hollow center internally receiving the hollow cylinder. A metal tube is connected to an electric ground. The metal tube is slidably inserted through the hollow center of the hollow cylinder, the rotor shaft being conductively connected to the electric ground through the metal tube and the conductive media.

Inventors

• Alireza Fatemi
• Zachary Strand
• Sen Jiang Zhou
• Jack M. Gayney
• John Patrick Spicer

Assignees

• GM Global Technology Operations LLC

Dates

Publication Date

20260507

Application Date

20241101

Claims (20)

1. 1 . An electric motor grounding mechanism, comprising: a hollow cylinder packed with a conductive media; rotating seals connected on the hollow cylinder on opposed ends of the hollow cylinder to retain the conductive media within the hollow cylinder; a rotor shaft positioned within an electric motor, the rotor shaft having a hollow center internally receiving the hollow cylinder; and a metal tube connected to an electric ground, the metal tube slidably inserted through the hollow center of the hollow cylinder, the rotor shaft being conductively connected to the electric ground through the metal tube and the conductive media.
2. 2 . The electric motor grounding mechanism of claim 1 , wherein the electric motor includes a housing defining the electric ground, the metal tube being fixedly connected to the housing.
3. 3 . The electric motor grounding mechanism of claim 2 , wherein the rotor shaft rotates with respect to a longitudinal axial centerline of the rotor shaft, the rotor shaft extending through the housing and induced to rotate by passing an electric current through a winding.
4. 4 . The electric motor grounding mechanism of claim 1 , wherein the metal tube is stationary during operation of the electric motor with the hollow cylinder being fixed to and corotating with the rotor shaft.
5. 5 . The electric motor grounding mechanism of claim 1 , including a biasing member defining one of a spring and a garter spring positioned behind a sealing lip acting in one of side compression and vertical compression, the biasing member providing one of an axial force and a radial force to maintain contact between the sealing lip and a shaft surface of the rotor shaft.
6. 6 . The electric motor grounding mechanism of claim 1 , including flexible spring-loaded tips used to maintain contact with the hollow cylinder and to compensate for cylinder surface irregularities.
7. 7 . The electric motor grounding mechanism of claim 1 , wherein the hollow cylinder is formed as first and second cylinder pieces and includes hermetic seals between the first and second cylinder pieces mitigating against ingress of contaminants and moisture into the grounding mechanism.
8. 8 . The electric motor grounding mechanism of claim 1 , including slots on at least one of a cylinder surface of the hollow cylinder and an inner diameter surface of the hollow cylinder, the slots directing passage of air into the rotor shaft to enhance ventilation and cooling for the electric motor during operation.
9. 9 . The electric motor grounding mechanism of claim 1 , including passages created in the hollow cylinder directing passage of an oil to enable cooling of the rotor and the conductive media.
10. 10 . The electric motor grounding mechanism of claim 1 , including surface features extending from the metal tube defining fins, the fins enhancing contact with the conductive media, the conductive media defining a conductive grease.
11. 11 . An electric motor grounding system, comprising: a vehicle having an electric motor positioned in a housing; a rotor shaft of the electric motor axially rotating within the housing, the rotor shaft having a hollow center; a hollow cylinder having a cylinder cavity in communication with the hollow center of the rotor shaft; multiple rotary seals connected to the hollow cylinder; and an electric ground created between the rotor shaft, the hollow cylinder and the housing to dissipate a parasitic voltage generated by rotation of the rotor shaft.
12. 12 . The electric motor grounding system of claim 11 , including a cartridge assembly having: a conductive grease packed within the hollow cylinder; and the multiple rotary seals are connected in the hollow cylinder on opposed ends of the hollow cylinder to retain the conductive grease within the hollow cylinder.
13. 13 . The electric motor grounding system of claim 12 , including a metal tube connected to the housing defining the electric ground, the metal tube slidably inserted through the rotary seals and the hollow center of the hollow cylinder and extending into and making contact with the conductive grease, the rotor shaft being conductively connected to the electric ground through the metal tube and the conductive grease internally receiving the hollow cylinder, and wherein during operation of the electric motor the metal tube remains stationary and the hollow cylinder co-rotating with the rotor shaft.
14. 14 . The electric motor grounding system of claim 13 , wherein the hollow cylinder is created in two pieces including an inner piece and an outer piece, with a hermetic seal and multiple air channels present between the inner piece and outer piece.
15. 15 . The electric motor grounding system of claim 13 , wherein the rotor shaft includes slots on a rotor surface to direct air into the rotor shaft, the slots formed on an inner diameter surface of the rotor shaft.
16. 16 . The electric motor grounding system of claim 11 , including: a first one of the rotary seals fixed at a first end of the hollow cylinder and a second one of the rotary seals fixed at a second end of the hollow cylinder opposite to the first one of the rotary seals; a first tube supplying a coolant to the cylinder cavity having a third one of the rotary seals connecting the first tube to the first one of the rotary seals; and a second tube directing the coolant out of the cylinder cavity and having a fourth one of the rotary seals connecting the second tube to the second one of the rotary seals; and wherein to remove the parasitic voltage from the hollow cylinder, the first one of the rotary seals, the second one of the rotary seals, the third one of the rotary seals and the fourth one of the rotary seals define a conductive sealing material.
17. 17 . The electric motor grounding system of claim 16 , wherein: the third one of the rotary seals is biased in a first sealing direction into sealing contact with the first one of the rotary seals; and the fourth one of the rotary seals is biased in a second sealing direction opposite to the first sealing direction into sealing contact with the third one of the rotary seals.
18. 18 . A method for forming an electric motor grounding mechanism, comprising: filling a portion of a longitudinal cavity of a hollow cylinder with a conductive media; sealing the hollow cylinder hermetically using rotating seals positioned at opposed ends of the portion of the longitudinal cavity of the hollow cylinder and sealing tapes to retain the conductive media within the hollow cylinder; inserting the hollow cylinder into a hollow bore of a rotor shaft of an electric motor; inserting a metal tube into the hollow bore of the rotor shaft and through the conductive media; providing surface features on the metal tube including tilted fins to enhance contact of the metal tube with the conductive media; and connecting the metal tube to an electric ground to electrically ground the rotor shaft through the metal tube and the conductive media.
19. 19 . The method of claim 18 , further including configuring the metal tube as a hollow tube directing passage of lubrication oil through the metal tube into the hollow bore of the rotor shaft.
20. 20 . The method of claim 18 , further including forming air passage features on one of an outer surface of the metal tube and an inner surface of the rotor shaft.

Description

INTRODUCTION The present disclosure relates to grounding of electric motors. During electric vehicle operation, one or more electric motors may be used for propulsion of the vehicle. The electric motors include a rotor which axially rotates and thereby via friction generates low impedance electrical charges that need to be dissipated. Providing a grounding path to the axially rotating motor rotor is complicated and may be provided using external grounding paths. Thus, while current systems and methods to discharge electrical charges from operating electric motors achieve their intended purpose, there is a need for a new and improved system and method to ground vehicle electric motor rotors. SUMMARY According to several aspects, an electric motor grounding system includes a hollow cylinder packed with a conductive media. Rotating seals are connected on the hollow cylinder on opposed ends of the hollow cylinder to retain the conductive media within the hollow cylinder. A rotor shaft is positioned within an electric motor, the rotor shaft having a hollow center internally receiving the hollow cylinder. A metal tube is connected to an electric ground. The metal tube is slidably inserted through the hollow center of the hollow cylinder, the rotor shaft being conductively connected to the electric ground through the metal tube and the conductive media. In another aspect of the present disclosure, the electric motor includes a housing defining the electric ground, the metal tube being fixedly connected to the housing. In another aspect of the present disclosure, the rotor shaft rotates with respect to a longitudinal axial centerline of the rotor shaft, the rotor shaft extending through the housing and induced to rotate by passing an electric current through a winding. In another aspect of the present disclosure, the metal tube is stationary during operation of the electric motor with the hollow cylinder being fixed to and corotating with the rotor shaft. In another aspect of the present disclosure, a biasing member defining one of a spring and a garter spring is positioned behind a sealing lip acting in one of side compression and vertical compression, the biasing member providing one of an axial force and a radial force to maintain contact between the sealing lip and a shaft surface of the rotor shaft. In another aspect of the present disclosure, flexible spring-loaded tips are used to maintain contact with the hollow cylinder and to compensate for cylinder surface irregularities. In another aspect of the present disclosure, the hollow cylinder is formed as first and second cylinder pieces and includes hermetic seals between the first and second cylinder pieces mitigating against ingress of contaminants and moisture into the grounding mechanism. In another aspect of the present disclosure, slots on at least one of a cylinder surface of the hollow cylinder and an inner diameter surface of the hollow cylinder, the slots directing passage of air into the rotor shaft to enhance ventilation and cooling for the electric motor during operation. In another aspect of the present disclosure, passages created in the hollow cylinder direct passage of an oil to enable cooling of the rotor and the conductive media. In another aspect of the present disclosure, surface features extending from the metal tube defining fins, the fins enhancing contact with the conductive media, the conductive media defining a conductive grease. According to several aspects, an electric motor grounding system includes a vehicle having an electric motor positioned in a housing. A rotor shaft of the electric motor axially rotating within the housing has a hollow center. A hollow cylinder has a cylinder cavity in communication with the hollow center of the rotor shaft. Multiple rotary seals are connected to the hollow cylinder. An electric ground is created between the rotor shaft, the hollow cylinder and the housing to dissipate a parasitic voltage generated by rotation of the rotor shaft. In another aspect of the present disclosure, a cartridge assembly includes: a conductive grease packed within the hollow cylinder; and the multiple rotary seals are connected in the hollow cylinder on opposed ends of the hollow cylinder to retain the conductive grease within the hollow cylinder. In another aspect of the present disclosure, a metal tube connected to the housing defining the electric ground, the metal tube slidably inserted through the rotary seals and the hollow center of the hollow cylinder and extending into and making contact with the conductive grease, the rotor shaft being conductively connected to the electric ground through the metal tube and the conductive grease internally receiving the hollow cylinder, and wherein during operation of the electric motor the metal tube remains stationary and the hollow cylinder co-rotates with the rotor shaft. In another aspect of the present disclosure, the hollow cylinder is created in two pieces including