Magnetic seal system

A magnetic seal system adapted for use between a support structure and a rotatable shaft. The seal system includes a rotating annular seal assembly surrounding the shaft and rotating therewith, which includes an annular seal, and a non-rotating biasing assembly sealingly mounted to the support structure around the shaft and axially engaging the annular seal assembly. The biasing assembly includes an annular magnet unit axially displaceable relative to the shaft and supported surrounding the shaft. The annular magnet unit exerting an attracting force on the annular seal assembly to biasingly displace the annular magnet unit towards the annular seal. A bias member unit is also provided for non-magnetically biasing the annular magnet unit axially relative to the shaft towards the annular seal. Adjacent contacting surfaces between the annular seal and the annular magnet unit biasingly contact one another to form a sealing interface therebetween.

TECHNICAL FIELD

The application relates generally to magnetic seals of the type used to seal a rotating shaft.

BACKGROUND OF THE ART

Magnetic seals may be used for sealing compartments in rotating systems like gas turbine engines. These magnetic seals can include a magnet and a seal mounted on a shaft. In some instances, a high magnetic attraction between the magnet and the seal may be required to maintain the sealing integrity of the magnetic seal. Therefore, to provide a rotary seal in such magnetic seals, a preformed packing of the seal is required to transmit rotating motion between the shaft and seal. The preformed packing can require a higher than normal amount of packing squeeze to prevent slippage between the seal and the shaft which can result in a difficult installation as well as variability in the face load of the carbon seal. A high packing squeeze can also prevent the seal from properly tracking axial movements of the shaft. Room for improvement exists.

SUMMARY

In one aspect, there is provided a magnetic seal system adapted for use between a support structure and a rotatable shaft, the seal system comprising a rotating annular seal assembly configured to be surrounding the shaft to rotate therewith, the annular seal assembly including an annular seal; and a non-rotating biasing assembly configured to be sealingly mounted to the support structure around the shaft and axially engaging the annular seal assembly, the biasing assembly including an annular magnet unit configured to be axially displaceable relative to the shaft and to be supported surrounding the shaft, the annular magnet unit exerting an attracting force on the annular seal assembly to biasingly displace the annular magnet unit towards the annular seal, and a bias member unit non-magnetically biasing the annular magnet unit axially relative to the shaft towards the annular seal, wherein adjacent contacting surfaces between the annular seal and the annular magnet unit biasingly contact one another to form a sealing interface therebetween.

In another aspect, there is provided an engine assembly comprising an engine core including at least one internal combustion engine; a rotatable shaft operatively engaged with the engine core; a support structure mounted around the shaft, the support structure housing at least a section of the shaft; a magnetic seal system connected to the support structure, the magnetic seal system including a rotating annular seal assembly surrounding the shaft to rotate therewith, the annular seal assembly including an annular seal; and a non-rotating biasing assembly sealingly mounted to the support structure around the shaft and axially engaging the annular seal assembly, the biasing assembly including an annular magnet unit configured to be axially displaceable relative to the shaft and to be supported surrounding the shaft, the annular magnet unit exerting an attracting force on the annular seal assembly to biasingly displace the annular magnet unit towards the annular seal, and a bias member unit non-magnetically biasing the annular magnet unit axially relative to the shaft towards the annular seal, wherein adjacent contacting surfaces between the annular seal and the annular magnet unit biasingly contact one another to form a sealing interface therebetween.

In a further aspect, there is provided a method of sealing a space surrounding a rotatable shaft mounted within a support structure and including an annular seal assembly and an annular magnet unit, the method comprising magnetically biasing the annular magnet unit towards an annular seal via an attracting force between the annular seal assembly and the annular magnet unit; non-magnetically biasing the annular magnet unit towards the annular seal via a bias force produced by a bias member unit; and sealing adjacent contacting surfaces between the annular magnet unit and the annular seal.

DETAILED DESCRIPTION

Referring toFIG. 2, a magnetic seal system in accordance with the present disclosure is generally shown at30, for instance of the type used in the accessory gearbox19(FIG. 1) of the gas turbine engine10(FIG. 1). It is also contemplated to use the magnetic seal system30in other applications as well. For example, the magnetic seal system30can be used as an output shaft seal on a turboshaft and turboprop engines, as well as a bearing cavity seal on engine mainshafts. The magnetic seal system30is used to seal a space A between a shaft20and a support structure21(i.e., a structure of the apparatus using the magnetic seal system30, a housing thereof, etc), to block fluid passage through the space A by forming a sealing interface31. In the illustrated embodiment, the space A is an annular space. The support structure21can be any rigid housing or casing surrounding the shaft20and enclosing the space A. In a particular embodiment, the support structure21houses a section or a portion of the shaft20. Alternately, the support structure21substantially houses the shaft20.

The magnetic seal system30includes a rotating annular seal assembly40and a non-rotating biasing assembly50. For better clarity, elements relating to, or forming part of, the annular seal assembly40are referenced by numerals ranging between forty and fifty, whereas elements relating to, or forming part of, the non-rotating biasing assembly50are referenced by numerals ranging between fifty and sixty.

In the particular embodiment shown inFIG. 2, the non-rotating biasing assembly50is displaced towards the rotating annular seal assembly40to form the sealing interface31between the two assemblies40,50, thereby sealing the space A into two sealingly adjacent spaces A1, A2.

The rotating annular seal assembly40includes an annular member41. The annular member41typically consists of a structurally rigid material with a ferromagnetic content, such as a metal. The annular member41is mounted to the shaft20to rotate therewith via a connector42. The connector42blocks a relative rotation between the annular member41and the shaft20. The connector42may also limit or block axial displacement of the annular seal assembly40along the shaft20, for example, via one or more shoulders positioned along the shaft20to block the displacement of the annular seal assembly40. The connector42shown is an interlocking engagement between a protrusion of the annular member41and the shaft20. Other connector configurations are also possible.

A seal43is provided to seal off an interface between the annular member41and the shaft20. For instance, the seal43may be an O-ring, a gasket, etc, made of a material capable of withstanding the pressures and temperatures in the apparatus and/or ambient environment. Moreover, the material must be resistant to the nature of ambient fluids (e.g., oil).

The rotating annular seal assembly40also includes an annular seal44disposed adjacent to the annular member41. The annular seal44is connected to the annular member41to rotate therewith. In the embodiment shown, the annular member41defines a shoulder45that is configured to receive thereon the annular seal44. The shoulder45provides a pair of abutment surfaces for receiving the annular seal44to strengthen the connection between the annular seal44and the annular member41and to cause concurrent rotation between the annular seal44and the annular member41. Other arrangements are contemplated, such as an annular groove formed in the annular member41to accommodate a portion of the annular seal44. The annular seal44is made of a material that will wear off gradually, while forming a contact surface conforming to the component it will rub against, to create the dynamic seal interface31. For example, the annular seal44is made of carbon, or equivalent.

The non-rotating biasing assembly50is sealingly mounted to the support structure21around the shaft20. The non-rotating biasing assembly50includes an annular magnet unit51that can move axially in a direction X parallel or substantially parallel to the rotational axis of the shaft20. The annular magnet unit51can include one or more discrete annular magnets. In the illustrated embodiment, the annular magnet unit51includes one annular magnet52. The annular magnet52exerts an attracting force with respect to the annular member41, such that the annular magnet unit51is drawn toward the annular member41, as the annular magnet unit51is movable in the direction X. Although the annular magnet52is illustrated as a single monolithic magnet, numerous other arrangements are considered. For example, the annular magnet52may be constituted of a non-magnetic annular body supporting a plurality of discrete magnets, among other possibilities. The expression “annular magnet” encompasses this arrangement of discrete magnets in a support body, along with other arrangements.

In the illustrated embodiment, the annular magnet unit51may include a carrier53. The carrier53is a non-magnetic annular body supporting the annular magnet52. The carrier53defines a seat54for receiving the annular magnet52. A seal55is provided to seal off an interface between the annular magnet52and the carrier53. For instance, the seal55may be an O-ring, a gasket, etc, made of a material capable of withstanding the pressures and temperatures in the apparatus and/or ambient environment.

The non-rotating biasing assembly50also include a bias member unit56mounted to an annular housing57. In the illustrated embodiment, the bias member unit56is a spring mounted between the annular magnet unit51and an inner wall57A of the annular housing57. The bias member unit56can be any other device that can apply a force to its surrounding, for example a bellow, a tension spring, a pneumatic, hydraulic and/or electrical telescoping member or any equivalent thereof. The bias member unit56is positioned so that it displaces the annular magnet unit51away from the inner wall57A of the annular housing57towards the rotating annular seal assembly40. Other configurations of the bias member unit56are possible. The bias member unit56cooperates with the carrier53for biasing the annular magnet unit51towards the rotating annular seal assembly40.

In an alternative embodiment, the bias member unit56can include a bellow covering the spring and sealing an interface between the bias member unit56and a radially inner surface of the annular housing57. In yet another alternative embodiment, the bias member unit56includes a series of discrete bias elements, such as discrete springs, radially mounted on the inner wall57A and engaging the annular magnet unit51. In yet another alternative embodiment, a space A3can be pressurized by fluid to bias the annular magnet unit51towards the rotating annular seal assembly40.

The annular housing57is sealingly mounted to the support structure21in a non-contacting relationship around the shaft20and defining the annular space A3. The annular housing57houses the annular magnet unit51and the bias member unit56, and can be removed together with both units51,56from the support structure21. A seal58is provided to seal off an interface between the annular housing57and the support structure21. For instance, the seal58may be an O-ring, a gasket, etc, made of a material capable of withstanding the pressures and temperatures in the apparatus and/or ambient environment. Moreover, the material must be resistant to the nature of ambient fluids (e.g., oil).

Still referring toFIG. 2, the annular housing unit51includes a slot59A on a radially outer surface of the annular space A3. A protrusion59B of the annular magnet unit51is received within the slot59A preventing relative rotation between the annular magnet unit51and the annular housing57. The protrusion59B can be shaped and sized to snugly fit within the slot59A while still allowing an axial movement of the protrusion59B within the slot59A. The contact surfaces between the protrusion59B and the slot59A can be lubricated to reduce friction between them. This is one of numerous anti-rotation features contemplated.

A retaining ring59C is mounted to an end59D of the annular housing57. The end59D defines a shoulder that receives the retaining ring59C in a fixed position relative to the annular housing57. The retaining ring59C axially blocks the displacement of the annular magnet unit51upon contact between the annular magnet unit51and the retaining ring59C. The retaining ring59C also retains the annular magnet unit51and/or the bias member unit56within, or partially within, the annular housing57. Advantageously, the non-rotating biasing assembly50can be transported as a single unit retained within the annular housing57.

In use, the displaceable annular magnet unit51attracts the stationary annular member41. The attraction force biases the annular magnet unit51towards and against the annular seal44thereby forming the sealing interface31. The bias member unit56also biases, as illustrated through compression load, the annular magnet unit51towards and against the annular seal44thereby forming the sealing interface31. The annular contact interface between the annular seal44and a lateral surface of the annular magnet52is therefore the sealing interface31. The sealing interface31blocks fluid from passing through the space A, such as from space A1to space A2, or vice versa. Advantageously, the sealing interface31is achieved via cooperation and combination of both magnetic attraction load and non-magnetic load.

Although a configuration including the effect of gravity alone as a non-magnetic biasing force may be contemplated, it may not be useful nor practical. This configuration can be achieved, for example, when the magnetic seal system30is inclined such that a weight of the annular magnetic unit51biases the annular magnetic unit51towards the annular seal44. However, the configuration based on gravitational force alone is not effective, at least, when the magnetic seal system30is placed in a horizontal or substantially horizontal plane, or if the inclination of the magnetic seal system30is such that the weight of the annular magnetic unit51biases the annular magnetic unit51away from the annular seal44.

Accordingly, in a particular embodiment, the magnetic seal system30is used for magnetically biasing the annular magnet unit51towards the annular seal44via an attracting force between the annular seal assembly40and the annular magnet unit51, non-magnetically biasing the annular magnet unit51towards the annular seal44via a bias force produced by the bias member unit56, and sealing adjacent contacting surfaces between the annular magnet unit51and the annular seal44. The magnetic seal system30is also used for axially blocking the displacement of the annular magnet unit51upon contact between the annular magnet unit51and the retaining ring59C and receiving the protrusion59B of the annular magnet unit51into the annular housing57for blocking a rotation of the annular magnet unit51around the shaft20.

In the embodiment shown, non-magnetically biasing the annular magnet unit51includes mechanically biasing the annular magnet unit51towards the annular seal44via a spring56.

In an alternative embodiment, non-magnetically biasing the annular magnet unit51includes using fluid pressure to cause the annular magnet unit51to displace towards the annular seal44.