Patent Application
20190024800
The present invention relates to a rotary seal having at least one axial sealing lip that bears against an axially oriented counterface. More specifically, the invention relates to a grease-lubricated seal of this kind, whereby the seal is adapted for improved lubrication of a contact interface between the axial sealing lip and the counterface.
An example of a rotary seal with an axial sealing lip is known from US 2010/0066030. This document describes a sealing device for a wheel bearing arrangement that is adapted for rotation of the bearing inner ring. The device comprises an elastomeric sealing element, mounted to a stationary part of the bearing arrangement, and a metal slinger, mounted to a rotational part of the bearing arrangement. The elastomeric element has a radial lip that bears against a cylindrical surface of the slinger and further has an axial lip that bears against a flange surface of the slinger. The primary function of the axial lip is to prevent the entry of contaminants into the bearing. A wheel bearing must operate in an environment where grit and moisture are heavily present, and the axial lip is therefore in tight contact with the flange surface of the slinger, to ensure that no ingress occurs. Under dynamic conditions, the resulting sliding contact generates friction and heat, meaning that lubrication is essential for preventing early failure of the seal.
In US 2010/0066030, a solution is proposed for improving the lubrication of the axial contact interface. The seal is provided with a grease lubricant and a non-contact part of the axial lip comprises a grease holding portion for holding grease that is to be supplied to a contact part of the lip. The grease holding portion may be provided in the form of concavities on the surface of the non-contact part, or annular or radial grooves.
Grease is a semi-solid substance that typically comprises a base oil that is held within a thickener matrix. Under hydrodynamic lubrication conditions, it is base oil from the grease that forms a lubricant film for preventing direct contact between the elastomeric lip and the metal counterface. When grease is supplied to a sliding contact interface, as taught by the above document, the grease will be sheared. This shearing mechanism is one of the mechanisms by which base oil is released from grease, but it also has the effect of increasing frictional losses.
Consequently, there is room for improvement.
The present invention is based on an improved understanding of grease lubrication in rotary seals.
In grease lubricated seals, the lubrication condition, or film thickness, is assumed to be determined by the availability of lubricant near the sealing contact. The present inventor has found that the available lubricant predominantly stems from grease that is present on a rotating part of the seal. Over time, the grease on the rotating part loses its base oil and eventually becomes incapable of providing an oil film thickness that adequately separates the sealing contact. The time at which this inadequate film thickness occurs can therefore be extended by increasing the amount of grease on the rotating part of the seal.
Thus, the present invention resides in a rotary seal comprising a first part having an axial sealing lip and a second part having an axial counterface against which the axial sealing lip bears, whereby one of the first and second parts is rotational with respect to the other of the first and second parts. According to the invention, the rotational part is provided with a reservoir for retaining a volume of grease at a location radially inward of the axial sealing lip. The reservoir is designed such that the movement of grease under the action of centrifugal force is prevented, while the movement of base oil, which bleeds from the volume of grease retained in the reservoir, is allowed. As a result, the supply of base oil to the sealing contact takes place for a longer period of time, which extends the life of the seal.
In a first embodiment of the invention, the second part of the seal is rotational. The second part may be a slinger comprising a cylindrical part and a radial flange part. In one example, the reservoir is formed by a bend in the flange part, which creates a retention surface for retaining the volume of grease in a radial direction. Suitably, the retention surface extends in an axial direction at an angle of less than 40 degrees relative to a rotation axis of the seal. The angle of the retention surface may be adapted depending on the operating speed of the rotational part (i.e. the magnitude of the centrifugal force acting on the grease volume). For example, in low-speed applications, an angle of between 20 and 40 degrees may be used. In high-speed applications, an angle of less than 20 degrees is preferable. As a result, an axial component of the centrifugal force acting on the volume of grease is insufficient to cause sideways movement of the grease, but is sufficient to allow side-flow of base oil. In some applications, to prevent movement of the grease, the retention surface may be parallel to the axis of rotation, so that the axial component of the centrifugal force is zero. In such applications, a pressure differential created within the rotating grease is sufficient to cause side flow of the base oil.
In a second example of the first embodiment, the reservoir comprises an overhanging lip, so that the volume of grease is retained in a radial direction and in an axial direction. The reservoir may be a separate part that is moulded to or adhesively fixed to the second part of the seal. To allow the movement of base oil, the reservoir further comprises channels. The channels may be grooves provided in the lip, which allow side-flow of oil out of the reservoir. The channels may also be through-holes provided in the reservoir which allow base oil to flow in a radially outward direction. In a still further embodiment, the reservoir is made of a porous material, whereby the pores in the reservoir act as channels for the base oil. Preferably, the channels have a width of less than 1 mm, so that grease cannot escape from the reservoir via the channels. The number of channels and the size of the channels is selected depending on the volume of base oil that is advantageously supplied to the sealing contact.
In a second embodiment of a seal according to the invention, the first part of the seal is rotational. The reservoir is then suitably moulded into an elastomeric element on which the axial sealing lip is provided. The reservoir may comprise an overhanging lip and further comprise channels, as described above. Alternatively, the reservoir may be formed by a roughened retention surface on the elastomeric element. Again, the roughened retention surface preferably extends in an axial direction at an angle of less than 40 degrees relative to the rotation axis. In high speed applications, the angle is preferably less than 20 degrees.
A seal according to the invention can be used in any rotational application for sealing a gap between an outer component that is mounted coaxially around an inner component. The first part of the seal can comprise the reservoir according to the invention and can be mounted to the inner component or to the outer component, depending on which component is rotational in use. Similarly, the second part of the seal can comprise the reservoir and can be mounted to the inner component or to the outer component. As mentioned, the second part of the seal can be a slinger. The second part can also be an integral part of an assembly in which the first part is mounted. For example, in a wheel bearing unit adapted for inner ring rotation, the part having the counterface for the axial sealing lip can be a wheel mounting flange of the bearing unit. The wheel mounting flange then comprises the reservoir feature, which may be moulded on or adhesively attached. Alternatively, depending on the material of the wheel mounting flange, the reservoir feature may be cast into the flange, or machined into the flange after e.g. a metal forging process.
A seal according to the invention is provided with a grease lubricant. The grease may be provided in a cavity of the seal, in an amount greater than the volume of grease retained in the reservoir. In an advantageous development, the reservoir is specifically filled with grease, such that the retained volume of grease represents at least 80% of the total volume of grease in the seal. Since the grease in the reservoir is the main source of base oil for lubricating the sealing contact, the amount of grease used can be significantly reduced while, at the same time, seal life is extended.
Other advantages will become apparent from the following detailed description and accompanying drawings.
The seal shown in
The main purpose of the seal is to protect the functionality of the bearing unit. The seal both retains lubricant within the bearing cavity and prevents the ingress of contaminants such as moisture and grit. The axial sealing lip 115 is particularly important for preventing the entry of contaminants and is therefore generally in tight contact with the axial counterface 127. To ensure that tight contact is maintained, the first part of the seal may further comprise a garter spring 140. Friction is therefore generated when the slinger 120 is rotating. To reduce the friction, the seal 100 is provided with a grease lubricant 160 in a cavity 145 between the axial sealing lip 115 and the cylindrical part 122 of the slinger 120.
The lubrication of the sealing contact between the axial sealing lip 115 and the axial counterface 127 will now be discussed. Under rotational conditions, most of the grease 160 will be thrown onto the stationary elastomeric element 112 and a relatively small amount of grease 160 will remain on the slinger, as indicated in
The released oil forms an oil film under hydrodynamic lubrication conditions, which separates the axial sealing lip and the axial counterface. Over time, film thickness decreases due to loss of oil. When a feed rate of released oil becomes insufficient to replenish the sealing contact, the film thickness will reach a critical value at which the axial sealing lip and the axial counterface are no longer adequately separated. Wear and loss of sealing function will then soon take place.
The present inventor has found that the time until the critical thickness value is reached can be significantly lengthened by increasing the volume of grease on the rotating part of the seal which is available for supplying base oil to the sealing contact. As a result, seal life can be extended.
Thus, in a seal according to the invention, the rotating part of the seal comprises a reservoir feature for holding a volume of grease. The reservoir is adapted to prevent the movement of grease under the action of centrifugal force, but to allow the movement of base oil, which bleeds from the grease retained in the reservoir.
An example of a first embodiment of a seal according to the invention is shown in
In this example, the seal is filled with an amount of grease in a cavity 245 between the axial sealing lip 215 and the cylindrical part 222 of the slinger. Under the action of centrifugal force, much of the grease will be thrown onto the stationary elastomeric element 212. Some of the grease—the grease volume 260—will be thrown onto the overhanging retention surface 235 on the flange part 225 of the slinger. Suitably, the retention surface 235 extends at an angle α of less than 40 degrees relative to the rotational axis 250. In the example of
Comparing the inventive seal of
A further example of a seal according to the invention comprising a slinger with a reservoir feature is shown in
In the example depicted in
In the examples discussed thus far, the second part of the seal (the part comprising the axial counterface) has formed the rotating part of the seal. In a second embodiment, the first part of the seal forms the rotational part. A first example of such a seal according to the invention is shown in
The second part of the seal 400 is again formed by a slinger 420, which has an axially oriented counterface 427 on the flange part 425. The first part 410 of the seal comprises a metal casing element to which an elastomeric element 412 is bonded. The elastomeric element has an axial sealing lip 415, which is in sealing contact with the counterface 427. Further, the elastomeric element 412 comprises a reservoir 430 according to the invention, which retains a volume of grease 460 at a location radially inward of the sealing contact. The grease volume 460 in this example is specifically provided on the reservoir 430, and constitutes the large majority of the grease within the seal.
In this example, the reservoir 430 comprises a retention surface 435 which is roughened to promote the adhesion of grease. Part of the retention surface extends in an axial direction, essentially parallel to a rotational axis of the seal. The volume of grease 460 is therefore retained in a radial direction and will not move in a sideways direction under the action of centrifugal force. A pressure differential created within the grease under rotational conditions allows the side-flow of base oil, which will ultimately flow towards the sealing contact.
A second example of a seal according to the invention, whereby the first part of the seal 500 comprises a reservoir, is shown in
The grooves 537 extend from an axially inner side of the lip 532 to an axially outer side of the lip, thereby allowing the side flow of base oil, which will ultimately flow in a radially outward direction towards the sealing contact. Suitably, the grooves have a width of less than 1 mm, to that grease is unable to pass through.
The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/EP2011/064604 | Aug 2011 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14241022 | Apr 2014 | US |
| Child | 16122291 | US |
