Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
A SEAL ASSEMBLY AS WELL AS A METHOD FOR MONITORING A RING-SHAPED SEAL
Document Type and Number:
WIPO Patent Application WO/2016/091561
Kind Code:
A1
Abstract:
A seal assembly (1) comprises a ring-shaped seal (3) and means to monitor the seal. The seal comprises a wear layer (7, 16) provided with a first element (8) of conductive material and a second element (11, 17) of dielectric material. Opposite ends (9, 10) of the first element are connected to each other by the second element of dielectric material to form a ring-shaped sensing circuit (12). The seal assembly further comprises a transceiver (13) said transceiver comprising a transmitter and a receiver, said transmitter for wirelessly powering the sensing circuit, and said receiver for wirelessly receiving a response of the sensing circuit when being powered.

Inventors:
LANG, Defeng (Haya van Somerenstraat 12, Hp Delft, NL-2614 Hp, NL)
DE WIT, Frank (Noordzijde 100A, PL Noordeloos, NL-4225 PL, NL)
Application Number:
EP2015/077318
Publication Date:
June 16, 2016
Filing Date:
November 23, 2015
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
AKTIEBOLAGET SKF (S- Göteborg, S-41550, SE)
International Classes:
F16J15/3296
Domestic Patent References:
WO2013152807A12013-10-17
Foreign References:
US6615639B12003-09-09
US20100283208A12010-11-11
EP1621863A22006-02-01
Attorney, Agent or Firm:
TWEEDLIE, Diane (Skf B.v, Kelvinbaan 16, MT Nieuwegein, NL-3439MT, NL)
Download PDF:
Claims:
CLAIMS

1. A seal assembly (l) comprising a ring-shaped seal (3) and means to monitor the seal (3), characterized in that tne seal comprises a wear layer (7, 16) provided with a first element (8) of conductive material and a second element (ll, 17) of dielectric material, wherein opposite ends (9. IO) of tne first element (8) are connected to each other by the second element (ll, 17) of dielectric material to form a ring-shaped sensing circuit (l2), which seal assembly (l) further comprises a transmitter for wirelessly powering the sensing circuit as well as a receiver for wirelessly receiving a response of the sensing circuit (l2) when being powered.

2. A seal assembly (l) according to claim 1, characterized in that the conductive material of the first element (8) is rubber or a polymer.

3. A seal assembly (l) according to claim 1 or 2, characterized in that the dielectric properties of the second element (ll, 17) are temperature dependent.

4. A seal assembly (l) according to one of the preceding claims, characterized in that the seal assembly (l) comprises a transceiver (l2) provided with the transmitter and the receiver.

5. A seal assembly (l) according to claim 4, characterized in that the transceiver (l2) is ring-shaped with an inner diameter (Dl) which is larger than the inner diameter (D2) of the ring-shaped seal (3).

6. A method for monitoring a ring-shaped seal (l), characterized in that the seal (3) comprises a wear layer (7, 16) provided with a first element (8) of conductive material and an second element (ll, 17) of dielectric material, wherein opposite ends (9, IO) of the first element (8) are connected to each other by the second element (ll, 17) of dielectric material to form a ring-shaped sensing circuit (l2), which sensing circuit (l2) is being wirelessly powered by means of a transmitter, whereby a response of the sensing circuit is being wirelessly received by a receiver.

7. A method according to claim 6, characterized in that the sensing circuit (l2) is being wirelessly powered over a range of frequencies, whereby based on the response wirelessly received by the receiver, the amount of energy absorbed by the sensing circuit (l2) at each frequency is being determined.

8. A method according to claim 7, cnaracterized in that a warning signal is provided if the change in the amount of energy absorbed by the sensing circuit (12) exceeds a predetermined threshold.

9. A method according to claim 7 or 8, characterized in that the frequency at which a maximum or minimum amount of energy is absorbed by the sensing circuit (12) is the resonant frequency of the sensing circuit (12), which resonant frequency changes when the wear layer (7) wears.

10. A method according to one of the preceding claims, characterized in that the dielectric properties of the second element (ll, 17) of dielectric material is temperature dependent, whereby based on the response received by the receiver from the sensing circuit (12), the temperature of the seal (3) is being determined.

Description:
A seal assembly as well as a method for monitoring a ring-shaped seal

FIELD OF THE INVENTION

Tne invention relates to a seal assembly comprising a ring-shaped seal and means to monitor the seal.

The invention also relates to a method for monitoring such a seal.

BACKGROUND OF THE INVENTION

By such a seal assembly, which is known from EP1956275A1, the sealing element is of an electrically conductive sealing material, which is in contact with an electrically conductive carrier body. On the electrically conductive sealing material an electrically non- conductive second sealing material is applied, which comes into sealing contact with an electrically conductive counterbody. Upon abrasion of the second sealing material an electric circuit is closed to indicate the wear limit.

A disadvantage of this known seal assembly is that only two wear values can be measured, one wear value when the electric circuit is being open and the sealing element still comprises electrically non-conductive second sealing material and one wear value when the electric circuit is closed and the electrically non-conductive second sealing material of the sealing element has been worn. No intermediate wear values are available

Another disadvantage of this known seal assembly is that, because of the wiring, it cannot be allowed to rotate, thus limiting the possible applications.

SUMMARY OF THE INVENTION

One of the objects of the invention is to provide seal assembly whereby the seal can easily be monitored during its lifetime.

This object is achieved by the seal assembly according to the invention in that the seal comprises a wear layer provided with a first element of conductive material and a second element of dielectric material, wherein opposite ends of the first element are connected to each other by the second element to form a ring-shaped sensing circuit, which seal assembly further comprises a transmitter for wirelessly powering the sensing circuit as well as a receiver for wirelessly receiving a response of the sensing circuit when being powered.

The opposite ends of the first element may be directed towards each other in circumferential direction or may overlap. When the ends of the first element overlap, a first end of the first element will be located at a larger radius than the second end of the first element.

Tne first element forms a resistance R, the second element a capacitance C and the interconnected first and second elements forms an inductance L, whereby the sensing circuit forms an RLC series electric circuit.

By wirelessly powering the sensing circuit by means of the transmitter, the sensing circuit will absorb at least a part of the energy emitted by the transmitter. The receiver will wirelessly receive a response of the sensing circuit when being powered. Based on this response the amount of energy absorbed by the sensing circuit and the corresponding frequency or frequencies at which the energy is absorbed can be determined. Since the contact with the transmitter as well as with the receiver is wireless, no direct physical electric contact needs to be made with the wear layer.

If for example, the wear layer wears and becomes thinner, the values of the resistance R, capacitance C and inductance L will change, due to which the amount of absorbed energy will change. Based on the amount of energy absorbed by the sensing circuit and the corresponding frequency range, the wear of the wear layer of the seal can continuously be determined.

I for example, the amount of energy absorbed by the sensing circuit exceeds a predetermined threshold, a warning signal may be provided to warn that the seal needs to be replaced. Meanwhile the seal can still remain functional for a period on the remaining material before the seal fully fails. In case that the running time of the seal is monitored till the alarm has been given, an estimation for the remaining service life of the seal can be provided till the remaining seal is fully worn out.

The seal can be a dynamic seal which can be used in or in combination with a bearing, for example. The wear layer can also be used by static seals.

The wear layer can be positioned at different locations in or on the seal. In one embodiment a seal lip of the seal comprises the wear layer. In another embodiment the wear layer is located inside the seal, whereby only after a first part of the seal has been worn, the wear layer will start to wear. In a further embodiment the wear layer can be located parallel to a seal lip of the seal and only act as a wear indicator. In the latter configuration the wear layer will not provide a sealing function and the the seal lip need not to be conductive.

An embodiment of the seal assembly according to the invention is characterized in that the conductive material of the first element is rubber or a polymer.

Such a rubber or polymer can easily be made electrically conductive, whereas these materials also provides sufficient sealing effect. Because of wear the thickness of the wear layer material will decrease and the resistance R will increase. This has a direct influence on the energy absorption, wherein tne change of absorbed energy will be observed by means of the receiver.

Another embodiment of the seal assembly according to the invention is characterized in that the dielectric properties of the second element of dielectric material are temperature dependent.

When the temperature changes, the capacitance C of the second element changes. In the short run, the wear can be neglected and the change of the capacitance C will only be due to a change of temperature. The change in capacitance C will cause a change in the frequency at which the energy will be absorbed. In the long run wear occurs causing a permanent change in amongst others the capacitance C, so a new calibration has to be done for temperature measurement.

An example of dielectric material could be Barium Titanate or even water.

Another embodiment of the seal assembly according to the invention is characterized in that the seal assembly comprises a transceiver provided with the transmitter and the receiver.

Such an integrated combination of the transmitter and the receiver provides a device for transmitting and receiving energy. The transceiver can be, as an example, independently located outside the seal, or located in a frame of the seal. At least the receiver comprising for example an antenna needs to be located close enough to the seal to be able to receive information from the seal.

Another embodiment of the seal assembly according to the invention is characterized in that the transceiver is ring-shaped with an inner diameter which is larger than the inner diameter of the ring-shaped seal.

The inner diameter of the seal will be in contact with an axle, for example. In axial direction the transceiver is located next to the seal. Since the inner diameter of the transceiver is larger than the inner diameter of the seal, contact between the axle and the transceiver is easily being prevented.

The invention also relates to a method for monitoring a ring-shaped seal, wherein the seal comprises a wear layer provided with a first element of conductive material and a second element of dielectric material, wherein opposite ends of the first element are connected to each other by the second element of dielectric material to form a ring-shaped sensing circuit, which sensing circuit is being wirelessly powered by means of a transmitter, whereby a response of the sensing circuit is being received by a receiver.

As described above, based on the response the status of the seal can be determined. With such a method the status of the seal can easily be monitored.

An embodiment of the method according to the invention is characterized in that the sensing circuit is being wirelessly powered over a range of frequencies, whereby based on the response wirelessly received by tne receiver, tne amount of energy absorbed by the sensing circuit at each frequency is being determined.

When the wear layer becomes thinner due to wear, the amount of energy absorbed by the sensing circuit at, at least, most of the induced frequencies changes. Based on these changes the amount of wear can be determined.

Another embodiment of the method according to the invention is characterized in that a warning signal is provided if the change in the amount of energy absorbed by the sensing circuit exceeds a predetermined threshold.

By providing such a warning signal the operator knows that he needs to replace the seal. Preferably such warning signal is being given timely before the seal stops functioning so that the operator has sufficient time to replace the seal.

Another embodiment of the method according to the invention is characterized in that the frequency at which a maximum or minimum amount of energy is absorbed by the sensing circuit is the resonant frequency of the sensing circuit, which resonant frequency changes when the wear layer wears.

The resonant frequency is a measure for C/L. Since the inductance L being dependent on the diameter of the seal lip, which diameter doesn't change or doesn't change much during wear compared to the other components, the inductance L is mostly constant. So the resonant frequency provides information about the capacitance C. As this value is dependent on the remaining material of the second element, wear will normally reduce the C-value and increase the resonant frequency. However, the same principle applies when the resonant frequency will decrease when the wear layer wears.

The slow, long-term, trend in the wear related change in the capacitance C can be separated from the fast, short term change in the capacitance C caused by temperature, for example by the fact that the resisance R, so the quality Q does not change significantly in the short term where R does change significantly with C in the long term.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic cross section of a first embodiment of a seal assembly according to the invention,

figure 2A and 2B are a perspective schematic view and a front view of a first embodiment of a wear layer of the seal assembly as shown in figure 1

figure 3 is an electrical diagram of the seal assembly according to the invention as shown in the figures 1 and 2A-2B,

figure 4 is a front view of a second embodiment of a wear layer of a seal assembly according to the invention, figure 5 is a graph snowing a value for tne absorbed energy relating to the frequency.

In the drawings, like reference numerals refer to like elements.

DESCRIPTION OF THE FIGURES

Figure 1 shows a first embodiment of a seal assembly 1 according to the invention mounted on a shaft 2. The shaft 2 may be rotatable in which case the seal assembly 1 is a dynamic seal assembly 1. In case that the shaft 2 is stationary, the seal assembly 1 forms a static seal assembly 1.

The seal assembly 1 comprises a ring-shaped seal 3· The seal 3 comprises a metal housing 4 , a seal lip 5 connected to the housing 4 and a garter spring 6 pressing the seal lip 5 in abutment with the shaft 2 to prevent for example a fluid to flow from a left side of the seal 3 to the right side or vice versa. Such a seal 3 is known in the art.

According to the invention the seal 3 comprises a wear layer 7· The whole seal lip 5 may act as a wear layer 7 or only a part of the seal lip 5 located against the shaft can be used as a wear layer 7·

As can best be seen in figures 2A and 2B the wear layer 7 is provided with a ring-shaped first element 8 of conductive material. The conductive material of the first element 8 is rubber or a polymer.

A first and a second end 9, 10 of the first element 8 are located opposite each other and are connected to each other by a second element 11 of dielectric material. The dielectric properties of the second element 11 of dielectric material are temperature dependent.

The first and second element 8, 11 form a ring-shaped sensing circuit 12, wherein the first element 7 forms a resistance R, the second element 11 a capacitance C and the interconnected first and second elements 8, 11 forms a inductance L, whereby the sensing circuit 12 is a RLC series electric circuit.

The seal assembly 1 further comprises a ring-shaped transceiver 13 provided with a transmitter and a receiver. The transmitter is used for wirelessly powering the sensing circuit 12. The receiver is used for wirelessly receiving a response of the sensing circuit 12 when being powered.

The ring-shaped transceiver 13 is located around the shaft 2 at a distance of for example a couple of millimetres from the wear layer 7· The ring-shaped transceiver 12 has an inner diameter Dl which is larger than the inner diameter D2 of the shaft 2 and the ring- shaped seal 3· In this manner physical contact of the transmitter 12 with the shaft 2 is being prevented.

Figure 3 shows an electrical diagram of the seal assembly 1 according to the invention. The sensing circuit 12 of the wear layer 7 is a RLC series electric circuit.

By means of tne transceiver 13 tne sensing circuit 12 is wirelessly powered over a range of frequencies. When tne sensing circuit 12 is powered at its resonant frequency (also known as oscillation frequency) it absorbs another amount of energy than at other frequencies. The receiver wirelessly receives a response from the sensing circuit 12. Based on the response received by the receiver, the amount of energy absorbed by the sensing circuit 12 at each frequency can be determined. On the short run the capacitance C will change due to a change of temperature. This change of capacitance C will result in a change of the frequencies at which the different amounts of energy will be absorbed. On the long run the capacitance C as well as the resistance R will change due to wear.

The sensing circuit 12 acts as an energy sink at the frequency determined by the RLC values. The resonant frequency is determined by:

ω 0 = 2π fo with Q being the quality of the sensing circuit, f 0 being the resonant frequency in hertz and (X)Q being the resonant frequency in radians per second.

The resistance R has an influence on the quality Q of the sensing circuit. The higher the resistance R the smaller the bandwidth of resonance and the higher the internal damping.

The R, C and L depend amongst others on the material and design of the wear layer 7. The values can vary in a large range for different seal assemblies. The inductance L mainly depends on the diameter of the seal lip 5·

The frequency at which a maximum or minimum amount of energy is absorbed by the sensing circuit 12 is the resonant frequency f 0 of the sensing circuit 12. The resonant frequency f 0 changes, normally increases, when the wear layer 7 wears.

Based on the amount of energy absorbed by the sensing circuit 12 at each frequency also the change of the amount of energy absorbed by the sensing circuit 12 at each frequency during the lifetime of the seal 3 can be determined, for example by means of a computer. A warning signal may be provided by the computer if the change in the amount of energy absorbed by the sensing circuit 11 exceeds a predetermined threshold.

Figure 4 shows a second embodiment of a wear layer 16 wherein the ends 9, 10 of the first element 8 overlap and the second element 17 is located in radial direction between the first and second ends 9, 10. Such wear layer 16 can be used instead of the wear layer 7 wherein the second element 11 is located in circumferential direction between the first and second ends 9, 10.

Figure 5 shows a graph with on the Y-scale in dB reception level and the X-scale in MHz of a seal assembly according to the invention. The dB reception level is representative for the amount of absorbed energy, the lower the dB reception level the higher the amount of absorbed energy. As can be seen in the graph, the dB reception level is the lowest at ~32MHz. This frequency is the resonant frequency. When determining the resonant frequency continuously or at predetermined intervals when the seal assembly is being used, the change of the resonant frequency as well as the change in the dB reception level at the each frequency and especially at the resonant frequency can be determined.

It is also possible that the receiver and transmitter are formed by separate components. The receiver being an antenna, for example coil-shaped. The receiver needs to be located close to the seal. In case of a static seal, it can also be mounted inside the seal.

The person skilled in the art will realize that the present invention is by no means limited to the preferred embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does 30 not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the scope should not be construed as limiting the scope of the claims.

LIST OF REFERENCE SIGNS

1 seal assembly

2 shaft

3 ring-shaped sea

4 housing

5 seal lip

6 garter spring

7 wear layer first element

first end

second end

second element ring-snaped sensing circuit ring-snaped transceiver wear layer

second element