Patent Application
20090074338
The invention relates to a bearing system for rotary machinery, and more particularly to a rotary bearing system that has fail-safe functionality.
Rotating equipment is used in many relatively service-free applications, such as electric motors for fans, blowers and pumps. Although relatively service-free, bearings for such rotating machinery have a limited service life. Particularly in the case of such rotating machinery subject to unfavourable environments, such as those with ambient contamination or temperature extremes, and such machinery that employs sealed bearings, the service life of these bearings may at times be less than predicted. In such instances, the bearings may be subject to catastrophic failure whilst in service. Such failure may cause damage to the machinery and adversely affect ambient conditions, such as due to sparks, smoke, heat and odour.
For machinery comprising rotary components attached to at least one drive shaft, at least one rotary bearing to position the drive shaft with a rotational freedom of movement about a drive shaft axis and associated stationary components with at least one predetermined clearance from the rotary components, the invention generally comprises apparatus for preventing the rotary components from contacting the stationary components upon failure of the bearing, comprising: a rotary backup bearing sleeve attached to the drive shaft proximate the bearing comprising a rotary radial surface relative to the drive shaft axis and a rotary axial surface relative to the drive shaft axis; and a stationary backup bearing collar mounted proximate the rotary backup bearing sleeve comprising a stationary radial surface relative to the drive shaft axis proximate the rotary radial surface with a predetermined axial clearance and a stationary axial surface relative to the drive shaft axis proximate the rotary radial surface with a predetermined axial clearance; wherein the rotary backup bearing sleeve contacts the stationary backup bearing collar upon failure of the bearing and the predetermined axial and radial clearances limit deviation of the rotary components to less than the predetermined clearance from the stationary components.
Should one or both shaft bearings 14 fail whilst the fan 2 is in service, the drive shaft 10 may continue to rotate. In this case, the drive shaft 10 may no longer rotate about its normal axis of rotation 18, and instead it may wobble or drift off of the axis 18 to such an extent that the rotor 20 drifts more than the predetermined stator clearance 24 and rubs against the stator 22, the fan blade 8 drifts more than the predetermined wall clearance 26 and rubs against the inner wall 28 of the outer housing 4, or both. This condition may cause damage to any one of these components, as well as adversely affect ambient conditions, such as due to sparks, smoke, heat and odour.
Upon the occurrence of excessive wear or failure of one of the bearings 14, the backup sleeve 34 may start to make contact with the backup bearing collar 40 in its associated backup bearing assembly 32. The predetermined axial clearance 44 and the predetermined radial clearance 48 have values such that when the backup bearing sleeve 34 makes contact with the backup bearing collar 40 the backup bearing assembly 32 limits deviation of the fan blade 8 to less than its predetermined wall clearance 26 and likewise limits radial deviation of the rotor 20 to less than its predetermined stator clearance 24.
The contact surfaces of the backup bearing sleeve 34 and the backup bearing collar in each backup bearing 32 preferably comprise a high-temperature material that offers a moderate degree of friction. Using a high-temperature material prevents contamination of ambient conditions, such as by sparks, smoke, heat and odour. Using a material that offers a moderate degree of friction is useful to induce a motor overload condition that may conveniently trigger motor shutdown. Alternatively, such friction may induce sufficient heat in the backup bearing assembly 32 to trigger an associated bearing failure sensor 50.
The bearing failure sensor 50 may comprise any sort of contact-sensitive sensor or component for sensing contact of the backup bearing sleeve 34 and the backup bearing collar 40 that may transmit an electrical sensor signal or interrupt electrical power to the electrical motor 6. For example, the bearing sensor 50 may comprise a speed change-sensitive sensor or component, such as an accelerometer, that responds to speed change due to contact and transmits a sensor signal to a motor controller (not shown) that interrupts electrical power to the electrical motor 6 upon reaching a predetermined change in speed. Alternatively, the sensor 50 may comprise a sensor or component that responds to temperature change and that interrupts electrical power to the electrical motor 6 upon reaching a predetermined temperature. For instance, the sensor 50 may comprise a thermocouple that transmits a temperature signal to a motor controller (not shown) that interrupts electrical power to the electrical motor 6 if the temperature signal exceeds a predetermined value. Alternatively, the sensor 50 may comprise a bimetallic switch or fusible link to interrupt power to the electrical motor 6 if the temperature reaches or exceeds a predetermined value.
Although the apparatus hereinbefore described comprises an electric fan by way of example, the apparatus may be any machinery with rotating components. Likewise, the apparatus may have as little as a single bearing or more than two. It may also have multiple drive shafts, with as little as one bearing for each drive shaft. As little as one, or as many as all, of the bearings may have associated backup bearing assemblies according to the invention. The described embodiment of the invention is only an illustrative implementation of the invention wherein changes and substitutions of the various parts and arrangement thereof are within the scope of the invention as set forth in the attached claims.
