BEARING ASSEMBLY INCLUDING A SENSOR ROLLER

Technical Field

The invention relates to a sensor roller and to a bearing assembly including such a sensor roller. Technical Background

It is known to provide bearings with various sensors for load sensing and measuring temperature, rotating speed, noise etc.. In some cases, sensors are arranged together with wireless transmitters inside of rollers and need to be supplied with energy. One solution for this problem is to use a battery. However, the battery lifetime has turned out to fall short of the bearing lifetime in important fields of application and exchanging the batteries is inconvenient.

The document EP 0637 734 A1 discloses a device for load measurement in roller bearings whereby the measurement is carried out by means of sensors arranged to measure forces applied on the bearing. The sensors communicate with means for recording, processing and evaluation of signals emitted from the sensors, which are representative of the bearing load. At least one roller body per roller body row is provided with a bore in which is provided at least one sensor, as well as means for amplification and transmission of signals emitted from said sensor to a receiver. The receiver is provided at the nonrotating bearing ring of the bearing. The signals received by the receiver are forwarded to further external means for signal processing. The energy supply of the transmission and amplification means is achieved by means of a small coil mounted in connection to the amplifier/transmitter in the bore of the roller and the end thereof protrudes outside the end of the roller. This coil is arranged in the sensor roller so as to communicate with a large, stationary coil provided at the stationary bearing ring. The stationary coil provides the coil arranged in the roller with energy, and the coil arranged in the bore sends continuous load data, in the form of strain values from the sensors.

The solution of EP 0637 734 A1 has drawbacks in that the amount of energy which can be supplied to the small coil is limited, in particular in the case of low rotation speeds of the bearing. The document DE69828236 T2 teaches a bearing assembly with a roller having a bore, wherein a generator and a gearbox is provided inside of the bore. The gearbox is connected to a cage of the bearing with an elastic coupling member.

The solution proposed in the DE69828236 T2 has drawbacks in terms of robustness and lifetime of the elastic coupling member. Further, the elastic connection does not allow for overlooking or slippage protecting the internal parts of the roller from damages in the case of shocks or excessively high rotation speeds and the elastic properties of the elastic coupling member are sensitive to temperature changes and subject to ageing.

Summary of the Invention

It is an object of the invention to provide a sensor roller with integrated generator assembly with reduced maintenance costs, long lifetime and potential for miniaturi- zation.

The invention starts from a bearing assembly including an inner ring, an outer ring, a plurality of rollers including at least one sensor roller arranged in a cage between the inner ring and the outer ring, wherein the sensor roller is provided with a bore accommodating a sensor unit and at least a first part of a generator assembly.

It is proposed that the generator assembly comprises a second part provided by or arranged on the cage, wherein at least one magnetic circuit of the generator assembly is at least partially opened and closed by said second part as a function of a relative rotation between the cage and the sensor roller, wherein said first part of the generator assembly is configured to interact with said second part of the generator assembly in order to generate energy out of a relative rotation between the cage and the sensor roller. The distribution of the generator assembly over the sensor roller and the cage opens miniaturization potential such that generators may be provided even for rollers with small bore volume. Moving elements inside the bore may be avoided and, as a consequence, the robustness and the lifetime of the assembly can be further improved.

The use of a magnetic coupling instead of an elastic coupling element enables a practically wear-free operation and long lifetime. The magnetic properties are less susceptible to external influences than elastic properties of an elastic coupling member. Further, the magnetic interaction may be easily generated with permanent magnets and may contribute to the magnetic flux circuits used by the generator.

The invention is applicable to large-size roller bearings such as bearings for wind turbines which need to be monitored. Limitations are imposed by the maximum degree of miniaturization available for the generator assembly to be fitted into the bore of the roller and the amount of power that is to be generated at a certain rotational speed. The bearings may be single- or multiple-row roller bearings and may be equipped with one or more sensor rollers per row.

The sensor unit may comprise strain sensors, temperature sensors, vibration sensors or other sensors desired.

It is further proposed that the second part of the generator assembly includes at least one coil encompassing a magnetic flux of the magnetic circuit. The AC voltage induced in the coil can be used to generate energy.

In one embodiment of the invention, the generator assembly comprises a brushless DC generator, wherein the first part of the generator assembly is the stator part of the brushless DC generator and the second part of the generator assembly is the rotor part of the brushless DC generator. Preferably, the second part of the generator assembly comprises at least two permanent magnets arranged in positions symmetric to a rotation axis of the sensor roller connected by a metal plate with high magnetic permeability. In this case, it is preferred that the first part of the generator assembly comprises at least one U-shaped magnetic core provided with at least one coil.

In a further embodiment of the invention, the generator assembly comprises a variable reluctance generator, wherein the first part of the generator assembly is the stator part of the variable reluctance generator and the second part of the generator assembly is the rotor part of the variable reluctance generator.

In this case, it is preferred that first part of the generator assembly comprises at least two permanent magnets arranged in positions symmetric to a rotation axis of the sensor roller connected to a magnetic core.

In the further embodiment of the invention, it is preferred that the second part of the generator assembly comprises at least one metal plate with high magnetic permeability arranged so as to face an axial end face of a body of the sensor roller with an air gap.

The AC-DC converter and energy storage module can be a simple rectifier with voltage output regulator (buck/boost), or a voltage multiplier circuit and a voltage regulator or battery charger circuit. The person skilled in the art will select the type of storage cell dependent on the intended usage profile in combination with the roller speed profile. E.g. for bearing defects detection, it only makes sense to measure when the bearing is moving. For static measurements: temperature, strain, angle, etc., it is necessary to rely on the energy storage capacity of the module. The type of energy storage means depends on the usage (measurement and transmission) profile in combination with the rotational speed profile. Strategies can be developed to only measure and transmit when there is enough power from the generator and that the data is backed up in non-volatile memory during conditions where the power is insufficient. In that case a small storage cell, e.g. a capacitor can be used to cover the energy request while the data is backed up. Further, it is proposed that said sensor unit comprises a wireless transmitter unit for transmitting sensor signals to a receiving unit.

Though the invention is applicable to other types of rollers such as toroidal rollers or conical rollers, the widest applicability can be achieved with cylindrical rollers.

Preferably, the sensor unit and the part of the generator assembly received in the bore are encapsulated, preferably using a PUR potting compound in order to avoid corrosion by aggressive ingredients of lubricants used for the roller.

Preferably, the width of the air gap in the magnetic circuit separating the first and the second part of the generator assembly is 1 mm or less. Larger gaps will lead to insufficient efficiency of the generator assembly.

The above description of the invention as well as the appended claims, figures and the following description of preferred embodiments show multiple characterizing features of the invention in specific combinations. The skilled person will easily be able to consider further combinations or sub-combinations of these features in order to adapt the invention as defined in the claims to his or her specific needs.

Brief Description of the Drawings

Fig. 1 is a schematic view of a roller bearing including a sensor roller according to the invention.

Fig. 2 is a schematic sectional view of the sensor roller of the bearing of Fig. 1. Fig. 3 is a schematic sectional view of the sensor roller of a bearing according to a second embodiment of the invention.

Fig. 4a - 4c show various configurations of a generator assembly of the bearing according to the invention corresponding to relative rotation positions of the sensor roller and the cage. Detailed Description of the Embodiments Fig. 1 is a schematic view of a roller bearing including a sensor roller 10a according to the invention.

The bearing is a single-row roller bearing including one sensor roller 10a communicating in a wireless way with a remote receiver unit 12, which may be fixed e.g. to the stationary ring 14 of the bearing or to a housing or shaft retaining the stationary ring 14. The receiver unit 12 may have integrated data processing means or an interface for forwarding the received data to a further control- and monitoring unit (not shown) which processes the sensor data as desired. The bearing includes an inner ring 16, an outer ring 14 and a plurality of cylindrical rollers 10 including the sensor roller 10a. In the case of this embodiment, the outer ring 14 is the stationary ring.

The rollers 10 are arranged in a cage 18 between the inner ring 16 and the outer ring 14. At the position of the sensor roller 10a, the cage 18 is provided with metal plate 42 having two magnets 30a, 30b (Fig. 2) attached thereto.

Fig. 2 is a schematic sectional view of the sensor roller 10a of the bearing of Fig. 1. The sensor roller 10a is provided with a bore 24 accommodating a sensor unit 26 and at least a first part 28a of a generator assembly 28. The first part 28a of the generator assembly 28 integrated in the sensor roller 10a is configured to interact with the cage 18 in order to generate energy out of a relative rotation between the cage 18 and the sensor roller 10a.

The generator assembly 28 comprises a second part 28b arranged on the cage 18, wherein at least one magnetic circuit of the generator assembly 28 is at least partially opened and closed by the second part 28b as a function of a relative rotation between the cage 18 and the sensor roller 10a. As a consequence, the reluctance of the magnetic circuit oscillates with a frequency proportional to the frequency of the relative rotation between the roller 10a and the cage 18. Preferably, at least one permanent magnet is arranged in the magnetic circuit so as to generate a magnetic flux, which will be oscillating in response to the oscillations of the reluctance of the magnetic circuit. The first part 28a comprises a pair of

coils 44a, 44b wound around a magnetic core 46 guiding the magnetic flux and the oscillating voltage induced in the coils 44a, 44b is used to generate electric energy. In this way, the first part 28a of the generator assembly 28 in the bore configured to interact with the second part 28b of the generator assembly 28 on the cage 18 in order to generate energy out of a relative rotation between the cage 18 and the sensor roller 10a.

In the embodiment illustrated in Fig. 2, the generator assembly 28 is formed as a brushless DC generator. The first part 28a of the generator assembly 28 plays the role the stator part of the brushless DC generator and the second part 28b of the generator assembly 28 plays the role of the rotor part of the brushless DC generator, wherein the expressions "stator" and "rotor" refer to a static position and rotation relative to a coordinate system rotating together with the body of the sensor roller 10a. The second part 28b of the generator assembly 28 comprises two permanent magnets 30a, 30b arranged in positions symmetric to a rotation axis of the sensor roller connected by the metal plate 42 with high magnetic permeability. The magnetization directions of the permanent magnets 30a, 30b are identical and oriented axially with respect to the rotation axis of the sensor roller 10a.

The first part 28a of the generator assembly 28 comprises at least one U-shaped magnetic core 46 provided with two coils 44a, 44b wound on the axially extending legs of the core 46. In the equilibrium position with minimum magnetic field energy, the axial end faces of the legs of the core 46 face one of the permanent magnets 30a, 30b respectively, wherein a small air gap is provided between the permanent magnets 30a, 30b and the end faces of the core 46.

The width of the air gap and the strength of the magnets 30a, 30b is chosen such that the magnetic flux is sufficiently strong to generate the required amount of energy, whereas slippage of the roller 10a due to excessive magnetic holding forces should of course be avoided.

The generator assembly 28 further includes an AC-DC and energy storage circuit 32 and a wireless monitoring node 34. The wireless monitoring node 34 includes the sensor unit 26 and a wireless transmitter unit 36 for transmitting the sensor signals to the receiver unit 12 in a wireless way.

The AC-DC and energy storage circuit 32 comprises a simple rectifier 38 with voltage output regulator (buck/boost) and the energy storage is achieved with a simple capacitor 40, wherein more complicated tasks may require more complicated energy storage solutions.

The wireless monitoring node 34 including the sensor unit 26 as well as the first part 28a of the generator assembly 28 in the bore 24 are encapsulated using a Polyurethane (PUR) potting compound in order to avoid corrosion by aggressive ingredients of lubricants used for the roller.

Figure 3 shows a further possible embodiment of the invention. In order to avoid repetitions, the following description focuses on differences to the embodiment of Figure 1 and 2 and the reader is referred to the description of Figures 1 and 2 for features which are similar or identical. In order to highlight the common function or concept, the same or similar reference numbers are employed for features having identical or very similar functions.

In the embodiment of Fig. 3, the generator assembly 28 comprises a variable reluctance generator, wherein the first part 28a of the generator assembly 28 is the stator part of the variable reluctance generator and the second part 28b of the generator assembly is the rotor part of the variable reluctance generator. Again, the expressions "stator" and "rotor" refer to a static position and rotation relative to a coordinate system rotating together with the body of the sensor roller 10a.

In this case, it the first part 28a of the generator assembly comprises two permanent magnets 30a, 30b arranged in positions symmetric to a rotation axis of the sensor roller 10a connected to a magnetic core 46. In the second embodiment of the invention, the second part 28b of the generator assembly comprises at least one metal plate 42 with high magnetic permeability arranged so as to face an axial end face of a body of the sensor roller 10a with an air gap. The magnetic flux illustrated with arrows is therefore guided through the body of the sensor roller 10a over the air gap to the metal plate 42, radially inward to the permanent magnets 30a, 30b, bundled in the magnetic core 46 provided with one single coil 44 and back into the body of the sensor roller 10a. The flux is maximum if the magnets 30a, 30b face the metal plate 42 as illustrated in Fig. 4a and is minimum of the lengthy metal plate 42 is oriented perpendicular to the symmetry axis of the permanent magnet arrangement as shown in Fig. 4c. An intermediate configuration is illustrated in Fig. 4b. Of course, this principle can be easily generalized to star-shaped magnet arrangements and metal plates if desired. In alternative embodiments of the invention, the cage 18 itself or parts thereof could be made of sufficiently magnetizable material such that the metal plate 42 could be dispensed with.

The invention according to both embodiments allows to dispense with an external power source and the power can be internally generated for the entire lifetime of the bearing. Compared to an embedded eccentric mass/pendulum type of solution, much more power can be generated due to the fact that the force that can be transmitted via the magnetic interaction between the cage 18 and the generator shaft 42 is rather high compared to the force generated by the eccentric mass.