Bearing with conductive medium

A bearing assembly having a conductive medium. The bearing unit is mountable on a shaft and includes a bearing unit including a radially inner bearing ring including a radially inner race, wherein the radially inner bearing ring is rotatable with the shaft. The bearing unit further includes a radially outer bearing rings including a radially outer race, wherein the radially outer bearing ring is stationary with respect to the shaft; and a plurality of rolling elements supported to roll between the radially inner race of the radially inner bearing ring and the radially outer race of the radially outer bearing ring. An annular chamber body is disposed adjacent the bearing unit. A conductive medium is disposed within the chamber body.

TECHNICAL FIELD

This disclosure is generally directed to a bearing technology, and in particular, although not exclusively, for a bearing assembly including a conductive medium.

BACKGROUND

The use of rolling bearings in electric motors can lead to the passage of current. Pulses from inverters can cause tensions between the bearing rings of the roller bearings. The currents can lead to electrical continuity damage to the rolling elements and bearing raceways from spark or electrical erosion. Electrical erosion may cause damage, such as removal of material, to contact surfaces from the passage of electric currents. As a result, the bearing can fail significantly prematurely and cause the failure of the entire machine. This leads to repair costs and costs due to failure.

Known solutions include hybrid bearings, coated bearing and insulated bushing. Also, separate grounding rings are often used, for example, wave grounding systems such as spring loaded graphite brush and carbon fiber rings. The grounding rings are used to protect the rolling bearings from damage. These are separate components that are often attached by crimping or screwing on the housing. These work with brushes and are only partially designed for life. Partly due to contamination in the machine to failure. These systems always have additional installation effort and space requirements and costs. Brushes add friction and contamination as brushes degrade, and also limit speed.

DETAILED DESCRIPTION

A bearing assembly in accordance with this disclosure is suitable for bearing units, in particular rolling bearings. The exemplary embodiments disclosed herein are suitable in particular, although not exclusively, for bearing units of electric motors such as automotive traction motors, said bearing units being provided on a shaft.

Exemplary embodiments disclosed herein reduce wear particles and friction, which extends the life of the bearing unit. Exemplary embodiments may also run at higher speeds due to the reduced friction.

Purely by way of a non-limiting example, inventive concepts of exemplary embodiments will now be described with reference to a bearing assembly on a rotating shaft. Exemplary embodiments create electrical conductivity between the rotating parts and the non-rotating parts.

With reference toFIG. 1, a bearing assembly in accordance with exemplary embodiments is denoted overall by10and includes a bearing unit12mounted on a rotatable shaft14. In the whole of the present description and in the claims, the terms and expressions indicating positions and orientations such as “radial” and “axial” are understood as referring to the central axis of rotation X of bearing unit12and shaft14. The figure shows a detail of the configuration provided by way of example.

Bearing unit12has a radially inner bearing ring16which is mounted on and rotatable with shaft14. Bearing unit12further comprises a radially outer bearing ring18which is stationary relative to inner bearing ring16and shaft14. Radially inner bearing ring16includes a radially inner raceway20and radially outer bearing ring18includes a radially outer raceway22. A plurality of rolling elements24are supported to roll between radially inner raceway20and radially outer raceway22. Rolling elements24may be stainless steel balls or the like. A first seal member26and a second seal member27are fixed to or unitary with radially inner bearing ring16and extend radially outwardly from radially inner bearing ring16towards radially outer bearing ring18on either side of radially inner raceway20and radially outer raceway22. Alternatively, first seal member26and second seal member27may be fixed to or unitary with radially outer bearing ring18and extend radially inwardly from radially outer bearing ring18towards radially inner bearing ring16.

The embodiment ofFIG. 1further includes an annular cassette28which is mountable on shaft14adjacent to bearing unit12. Cassette28has an interior chamber having a chamber body formed by a cassette shell30which is stationary with respect to shaft14. Shell30may include a first body portion32and a second body portion38which are configured to be attached to each other by openable locking elements31which allow first body portion32and second body portion38to be releasably attached to each other. First body portion32has a first radial wall portion34and a first axial wall portion36, and second body portion38has a second radial wall portion40and a second axial portion42. Second radial wall portion40may be configured to have a fitting portion44which is configured to be press fit to radially inner bearing ring16and radially outer bearing ring18so that it is stationary with radially outer bearing ring18. The entire bearing assembly10including bearing unit12and cassette28may be pressed onto shaft14as a unit after shell30is press fit to bearing assembly10or may be press fit separately onto shaft14. Shell30may be made from any suitable material including electrically conductive material such as stainless steel, steel and aluminum.

Cassette28further includes an annular flinger ring46disposed within shell30and configured to have an L-shaped cross-section having an axial flinger ring portion48and a radial flinger ring portion50. Axial flinger ring portion48is configured to be press fit on to shaft14so that flinger ring46is rotatable with shaft14. Flinger ring46further has two seal lips52which extend at an angle from opposite sides of radial flinger ring portion50. Seal lips52may be made from any suitable material such as vulcanized rubber and may be attached to radial flinger ring portion50by overmolding or gluing. Seal lips52may also be made of suitable polymers depending on the performance specifications. For example, seal lips52may be made from nitril rubber (NBR) and hydrogenated nitril rubber (HNBR) for lower performance (low speed/low temperature—125° C.); fluoroelastomers or fluorocarbons (FKM) for high performance (high speed/high temperature—150° C.); and polytetrafluoroethylene (PTFE) for very high performance (very high speed and temperature—175° C.).

Cassette28is configured to hold a conductive medium58. Conductive medium58may be a conductive paste, fluid, grease, granules, gel or other medium. Conductive medium58may further be an ionic liquid, conductive fat, or oil based matrix. Conductive material may as a poor lubricant while good lubricants typically have low conductivity. Thus, a balance may be achieved by using a non-conductive material with conductive particles dispersed throughout. Conductive medium58is kept inside cassette28by seal lips52and is disposed above seal lips52.

Referring toFIG. 2, another exemplary embodiment of a bearing assembly110is shown. For the sake of simplicity, like or similar elements in alternative embodiments will be referenced by the same reference numeral as earlier embodiments advanced by multiples of one hundred. A cassette128is integrally formed with bearing unit112. Cassette128includes a cassette shell130which is stationary with respect to shaft114. Shell130may include a first body portion132and a second body portion138. First body portion132has a first radial wall portion134and a first axial wall portion136, and second body portion138has a second radial wall portion140and a second axial portion142. First radial wall portion134may be configured to have a fitting portion145which is configured to be press fit to radially outer bearing ring118so that it is stationary with radially outer bearing ring118. The entire bearing assembly110may be pressed onto shaft114as a unit. A first seal member126is fixed to or unitary with radially inner bearing ring116. A second seal member is not provided. Cassette128further includes an annular flinger ring146, sealing lips152and a conductive medium158as before.

Referring toFIG. 3, another exemplary embodiment of a bearing assembly210is shown on a shaft214. In this embodiment, a bearing assembly210includes a sealed chamber body228integrally formed with a bearing unit212wherein the cassette is separated from bearing unit212by a seal227. Sealed chamber body228is an annular chamber at least partially filled with a conductive medium258.

Referring toFIG. 4, another exemplary embodiment of a bearing assembly310is shown. Bearing assembly310includes a sealed chamber body328integrally formed with a bearing unit312wherein 328 is an annular chamber at least partially filled with a conductive medium358. Sealed chamber body328further includes an internal annular ring347which rotates with shaft314.

In the embodiments ofFIGS. 3 and 4, no space for further components is needed so bearing assemblies210and310may be used in tight spaces. Sealed chambers228and328may be sealed to keep in conductive medium258,358. An additional seal229,329may be utilized to coat the interior walls231,331of sealed chambers228and328. Additional seal229,329may also include a conductive medium such as copper, aluminium or silver to provide additional conductivity.

Referring toFIG. 5, another exemplary embodiment of a bearing assembly410is shown. Bearing assembly410includes a sealed chamber body428integrally formed with a bearing unit412wherein sealed chamber body428is separated from bearing unit412by a seal427and may include an additional seal such as that described with respect toFIGS. 3 and 4. A disk-shaped device such a disk-shaped laminar grounding brush460similar to a ground ring is provided within sealed chamber body428and rotatable with shaft414. Grounding brush460may include conductive brush filaments462sandwiched between conductive rings464and may be of the type disclosed in U.S. Pat. No. 9,790,995 entitled Bearing Seal with Integrated Grounding Brush, the disclosure of which is incorporated by reference herein. Alternatively, sealed chamber body428may be filled with a kind of metal wool of conductive metal such as copper wool or silver wool which ensures an electrically conductive connection between rotating and station parts of bearing unit412. To increase the conductivity of the bearing unit, the bearing unit rotating and station parts can still be coated with conductive material, for example silver.

Further preferred and/or particularly advantageous of exemplary embodiments of inventive concepts are described in accordance with the characteristic features indicated in the attached dependent claims.