GB2538624A

GB2538624A - Power generator and railway bearing unit

Info

Publication number: GB2538624A
Application number: GB1607392.6A
Authority: GB
Inventors: Selvan Tamil; Clemens Van Der Ham Andreas
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2015-05-05
Filing date: 2016-04-28
Publication date: 2016-11-23
Anticipated expiration: 2036-04-28
Also published as: CN106151295A; DE102016207678A1; CN106151295B; GB201607392D0; GB2538624B

Abstract

A power generator for use in sensor package 12 of a railway bearing units, comprising a generally E-shaped generator core 28 having a yoke portion and three limbs protruding from the yoke portion so as to form a gap with a rotating tooth wheel 26, the limbs including at least one central limb 34b and two lateral limbs34a,34c, the lateral limb carrying permanent magnets 40a,40b for generating a magnetic flux in the generator core. A single coil 38 or multiple coils 38a,38b,38c are fitted over the central limb and the lateral limbs are have their ends shaped so as to approach the central limb to allow more coil space. The cross section of the central limb may be smaller than the lateral limbs and the ends of the lateral limbs may be provided with pole shoes such that the air gap has a uniform width. The width of the magnets may be greater than that the rest of the limbs so as to overlap at least one coil and the magnets may protrude from the lateral limbs towards the central limb.

Description

Power Generator and Railway Bearing Unit

Background of the Invention

It is known to provide railway axlebox bearings with toothed target wheels for wheel speed measurements. A sensor package is attached to a bearing housing and interacts with the toothed target wheel. The frequency of the sensor signals is proportional to the speed of rotation of the wheel.

The present day railway system use Hall based speed sensors for wheel speed measurement, which needs external power and cabling. The infrastructure cost and complexity is inhibiting. This project work is aimed at developing a speed sensor based on the variable reluctance principle and at the same time develops its own power.

Energy harvesting is known from other fields of

application and is the process of capturing minute amounts of energy from one or more of naturally-occurring energy sources, accumulating them and storing them for later use. Energy-harvesting devices efficiently and effectively capture, accumulate, store, condition and 25 manage this energy and supply it in a form that can be used to perform a helpful task. Similarly, an Energy Harvesting Module is an electronic device that can perform all these functions to power a variety of sensor and control circuitry for intermittent duty applications. 30 Energy-harvesting devices may be based on generators having at least one coil and a magnetic core. Oscillating magnetic fluxes in the magnetic core induce voltage in the coil which can then be transformed into usable energy. A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic fields in electrical and electromechanical devices such as transformers motors and generators. It is made of ferromagnetic metal such as iron, or ferromagnetic compounds such as ferrites. The high permeability, relative to the surrounding air, causes the magnetic field lines to be concentrated in the core material. The magnetic field is often created by a coil of wire around the core that carries a current or by a permanent magnet. The presence of the core can increase the magnetic field of a coil by a factor of several thousand over what it would be without the core.

The use of a magnetic core can enormously concentrate the strength and increase the effect of magnetic fields produced by electric currents and permanent magnets. The properties of a device will depend crucially on the following factors: -the geometry of the magnetic core, -the amount of air gap in the magnetic circuit, -the properties of the core material (especially permeability), -the operating temperature of the core, and -solid or laminated steel.

The documents GB 2 321 788 A and WO 2010/028417 Al disclose generator assemblies for use in railroad vehicle bearing assemblies.

It is an objective if the invention is to develop and select the concept for a variable reluctance generator which will produce a minimum of 2.0 V (Open clamp) and 10mW output power for the typical target wheel speed of trains, air gap and operating conditions. The design should also be able to fit into the existing sensor housing with easy scalability for the different target wheel dimensions.

Summary of the Invention

The invention relates to a power generator for use in sensor package of a railway bearing units, comprising a generally E-shaped generator core having a yoke portion and at least three limbs protruding from the yoke portion so as to form a gap with a rotating tooth wheel. The end faces of the limbs facing the toothed target wheel have a spacing essentially correspond to an integer multiple of a period length of the toothed target wheel such that a magnetic circuit is closed via the gap when the teeth are aligned with the end faces of the limbs and that the magnetic circuit is essentially open when they are not. In other words, the reluctance of the circuit is oscillating. The limbs include at least one central limb and two lateral limbs, and at least two permanent magnets for generating a magnetic flux in the generator core is provided. The oscillating reluctance leads to an oscillating flux through the coil such that an alternating current is induced in the coil, which can be rectified, stored in a capacitance or battery or used immediately.

The invention proposes that the coil is fitted over the central limb of the generator core, wherein two permanent magnets are provided in the lateral limbs of the generator core in order to generate a magnetic flux. The configuration of the enables adding a large magnetic load, i.e. large and strong permanent magnets in combination with a large inductive load, i.e. a coil with a high number of windings in a small building space such that a highly effective energy harvesting can be achieved meeting the output requirements even within the dimensions of existing sensor housings.

In a preferred embodiment of the invention the central limb has a cross-section with a diameter smaller than the diameter of a cross section of the lateral limbs. The reduced cross-section of the central limb makes additional space available for the coil such that the number of windings thereof can be further increased.

Further, it is the lateral limbs are shaped so as to approach the central limb in the direction of their respective ends forming the gap. While the spacing between the ends forming the gap is limited and defined by the spacing of the teeth of the tooth wheel, the wider space in the parts remote from the gap can be used for providing larger coils in order to increase the inductivity. This shape will referred to as a "dovetail" design in the following.

In configurations where a space between the limbs is variable in a longitudinal direction of a limbs, i.e. in a radial direction of the toothed target wheel, it is advantageous to provide multiple coils with different diameter fitted over the central limb which can be adapted such that the available space is maximally filled. Preferably and in particular in the case of the dovetail design, the coils are arranged such that the coil diameter increases in the direction of the yoke portion.

The individual coils are preferably cylindrical for cost reasons. The central limb may have a cylindrical shape fitting into the central bore of a coil former for pre-manufactured coils.

In a preferred embodiment of the invention, the limbs of the generator core are provided with pole shoes designed such that an air gap with uniform width is formed.

It is further proposed that a width of the permanent magnets in a longitudinal direction of the yoke portion is larger than a width of other parts of the lateral limbs, said other parts being arranged so as to overlap with the axial length of the at least one coil. This design maximizes the room for the magnet while leaving sufficient space for the at least one coil, which is preferably the largest coil if multiple coils exist.

The size of the permanent magnets can be further increased if these protrude from the lateral limbs 25 towards the central limb, respectively.

A further aspect of the invention relates to a sensor unit for housings of train bearings comprising a sensor housing, at least one electronic circuit including a sensor and a power generator as described above, wherein the electronic circuit is driven by energy provided by the generator circuit. Preferably, the electronic circuit includes a wireless transmitter for transmitting the sensor signals to the outside. In a preferred embodiment of the invention, the sensor package includes at least one sensor interacting with the toothed target wheel, or the wheel speed is determined based on the frequency of the current induced in the generator coil.

Further, it is proposed to provide a train hub unit including a bearing housing and a sensor unit as described above. The invention overcomes the technical prejudice that energy harvesting devices are not sufficiently robust for this field of application. Due to the arrangement of the coil so as to be protected by the lateral limbs the generator assembly is very robust and damages upon assembling the sensor package and the hub unit are avoided.

The sensor/generator system according to the invention comprises a metallic toothed target wheel, a ferrous yoke with permanent magnet excitation with coil wound on it.

An important advantage of the invention is that the generator fits within the sensor's present housing dimensions while having higher power density. The operating air gap of the generator is preferably between 1 and 2 mm, in particular 1.5 mm, such that it is preferred to use a ferrous iron core design to close the magnetic circuit. The invention proposes possibilities to increase the power output either by having more electrical loading, magnetic loading (within the available space) or both. The output power also depends on ratio of the maximum to minimum reluctance of the magnetic circuit.

In a preferred embodiment of the invention, the magnet thickness is at least 2times more than the air gap length so that magnet will not demagnetize by itself. The use of a pole shoe fixed onto the core helps to distribute the magnetic flux uniformly across the air gap.

The invention preferably utilizes already existing toothed (gear) wheels for speed sensing to serve as a variable reluctance for the generator to generate enough power for wireless electronics. As the air gap is well controlled, the efficiency of the solution is higher than with an external system that depends on a larger tolerance chain.

The unit is compact enough to also house the wireless electronics in the same housing as the generator using the same sensor body housing as the original speed sensor unit now in service. The design of the generator is optimized to fit within the existing envelope and yet cover a wide range of toothed target wheels for the railway application.

The above embodiments of the invention as well as the appended claims and figures 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 specific needs.

Brief Description of the Figures

Fig. 1 is a schematic sketch of a railway bearing unit including a sensor package according to the invention; Fig. 2 is a view of a power generator according to a first embodiment of the invention in interaction with a toothed target wheel; Fig. 3 is a schematic view of a power generator according to a second embodiment of the invention; Fig 4 is a schematic view of a power generator according to a third embodiment of the invention; and Fig. 5 is a schematic view of a power generator according to a fourth embodiment of the invention.

Detailed Description of the Embodiments

Fig. 1 is a schematic sketch of a railway bearing unit including a bearing 10 provided with a sensor package 12 according to the invention. The bearing includes a double row tapered roller bearing 10 with an inner ring 14 mounted on an axle 16 and an outer ring 18 mounted in a bearing housing 20. The hub unit is protected by an outer cover 22 having a bore receiving the plug-shaped sensor package 12, which is fitted into the bore in a radial direction of the axle 16.

The sensor package 12 is fixed to the bearing housing 20 via the cover 22 and is therefore fastened to the non-rotating outer ring 18 of the bearing 10.

An end cap 24 is mounted on an axial end-face of the axle 16 and preloads the inner ring 14 of the bearing 10. A toothed target wheel 26 is mounted on the end cap 24 such that the teeth arranged at radially outer circumference of the toothed target wheel 26 face a radially inner face of the sensor package 12.

The sensor package includes a generator core 28 held by a housing 30 of the sensor package 12 so as to the teeth of the toothed target wheel 26. The target wheel 26 is rotatably fastened to the rotating inner ring 14 via the end cap 24 and the axle 16 and rotates with the inner ring 14 of the bearing 10 when a train including the bearing unit illustrated in Fig. 1 is driving. The sensor package further includes an electronic circuit 42, which includes further sensors 44, a microcomputer and a wireless transmitter unit 46 The configuration of the generator core 28 in relation to the target wheel 26 is illustrated in further detail in 25 Fig. 2.

The generator core 28 is generally E-shaped and has a yoke portion 32 and three limbs 34a, 34b, 34c protruding from the yoke portion 32 towards the teeth of the toothed target wheel 26. The end faces of the limbs 34a -34c have a spacing in a circumferential direction of the target wheel 26 essentially corresponding to a period length of the toothed target wheel 26 with a gap 36. The gap 36 has preferably a width between 1 and 2 mm. A central limb 34b has a coil 38 wound around it or fitted over it. The central limb 34b may be of cylindrical shape such that a cylindrical coil 38 can be used. The two 5 lateral limbs 34a, 34c are provided with permanent magnets 40a, 40b on their respective ends, wherein the magnetic polarity of the permanent magnets 40a, 40b is oriented parallel to the longitudinal direction of the limbs 34a, 34c and points in the same direction for the 10 two permanent magnets 40a, 40b.

The permanent magnets 40a, 40b create a magnetic flux illustrated with arrows in Fig. 2. When the teeth of the toothed target wheel 26 are aligned with the end faces of the limbs 34a -34c, a magnetic circuit is closed via the gap 36, whereas the magnetic circuit is essentially open when the ends of the limbs 34a to 34c is located between the teeth of the target wheel 26. More precisely, the reluctance of the magnetic circuit is oscillating with the frequency of the passing teeth of the toothed target wheel. The oscillating reluctance leads to an oscillating flux to the coil 38 such that an alternating current is induced in the coil 38. This current can be rectified and used for driving components of the electronic circuit 42.

Figs. 3 to 5 illustrate further embodiments of the generator core according to the invention. In order to avoid repetitions, the following description focuses on differences to the embodiment of Fig. 1, wherein similar features are indicated with the same reference numbers. For features which remain unchanged, the reader is referred to the above description of Figs. 1 and 2.

In the embodiment of Fig. 3, the central limb 34b has a cross-section with a diameter smaller than the diameter of a (rectangular) cross-section of the lateral limbs 34a, 34c. Due to the reduced diameter of the central limb 34b, the space for the coil 38 can be increased without modifying other components, in particular without increasing the envelope of the generator core 28, which therefore fits into a standard sensor housing 30.

Further, the ends of the lateral limbs 34a, 34c are provided with pole shoes 48a, 48b respectively, the shape of which is adapted to the curved envelope of the toothed target wheel 26 and ensure a uniform width of the gap 36.

In the third embodiment of the invention illustrated in Fig. 4, pole shoes 48a, 48b are provided similar to the embodiment of Fig. 3. In addition, the lateral limbs 34a, 34c are shaped as a dovetail so as to approach the central limb 34b when approaching the respected ends forming the gap 36.

The width of the yoke portion 32 in the circumferential direction of the target wheel 26 is larger than the distance between the circumferentially outer ends of the pole shoes 48a, 48b such that a radially outer part of the generator core 28 provides for a wider space for a large coil 38a. The generator core 28 is equipped with three coils 38a, 38b, 38c with different diameters, wherein the diameter of the coils 38a, 38b, 38c decreases in a direction approaching the ends of the limbs 34a to 34c. The coils are designed so as to fill the space available between the lateral limbs 34a, 34c as good as possible while avoiding non-cylindrical coils which are hardly available on the market as pre-manufactured components.

The width of the magnets 40a, 40b is larger than the width of the lateral limbs 34a, 34c in their main parts and the magnets 40a, 40b as well as a part of the limbs 34a, 34c on which the magnets 40a, 40b are fixed protrude inward in the direction of the central limb 34b. In comparison to the embodiment of Fig. 3, the embodiment of Fig. 4 does not only enable the provision of larger magnets 40a, 40b but also of the provision of larger coils 38a to 38c, e.g. the provision of multiple coils with a larger total number of windings.

A fourth embodiment of the invention is illustrated in Fig. 5. In contrast to the embodiment of Fig. 4, the lateral limbs 34a, 34c do not approach the central limb 34b continuously but in a sharp step. The resulting space for the coil 38 has an essentially rectangular cross-section such that a single large coil can be fitted in. For mounting the coils in the embodiments of Figs. 4 and 5, these can be fitted into the generator core from a lateral direction (perpendicular to the plane of the Figs. with a central limb 34b removed and the central limb 34b is then fixed to the yoke portion 32 by press-fitting, screwing or the like (not illustrated).

As in the previous embodiment, the width of the central limb 34b amounts to 1,65 mm and is therefore smaller than 30 the width of the lateral limbs 34a, 34c which amounts to 2 mm.

The thickness of the magnets 40a, 40c in a radial direction of the target wheel 26 amounts to 3 mm and is therefore the expected maximum width of the gap, wherein tolerances are accounted for.

The total width of the core 28 amounts to 24 mm and the height is about 15 mm.

For typical train applications, the target wheel is used for sensing the speed. The generator core according to the embodiments can be fitted into the sensor housing 30 in addition to the speed sensors interacting with the existing target wheel 26 or the speed can be measured using the frequency of the current reduced in the coils 38. In each of the embodiments, the generator core 28 can be formed as a laminated stack of ferrous steel, eventually with the exception of the central limb 34a, which can be massive for the sake of simplicity and with the exception of the permanent magnets 40a, 40b. The target wheels 26 in typical train applications have an outer diameter of 195mm and 80 equally spaced teeth and slots and the thickness of the target wheel is 6 mm.

Simulations have shown that the generators according to Figs. 1 to 5 are able to produce opened clamp voltages of 2 Volt or more and an output of 8.4 mW (in the embodiment of Fig. 2) up to 20 or even 30 mW in the other designs. This is sufficient for the intended use even when tolerances are accounted for, even when toothed target wheels with other diameters and different tooth pitch are used. The design is very robust and meets the requirements for train applications to be able to operate in temperature ranges from -40° C to 85° C with relative humidity up to 95 5.

Claims

Claims 1. Power generator for use in a sensor package of a railway bearing unit, comprising: a generally E-shaped generator core (28) having a yoke portion (32) and at least three limbs (34a, 34b, 34c) protruding from the yoke portion (32) so as to form a gap (36) with a rotating toothed target wheel (26), the limbs including at least one central limb (34b) and two lateral limbs (34a, 34c); and at least two permanent magnets (40a, 40h) provided in the generator core (28) for generating a magnetic flux in the generator core (28); characterized in that a coil (38) is fitted over the central limb (34b) of the generator core (28), wherein two permanent magnets (40a, 40b) are provided in the lateral limbs (34a, 34c) of the generator core (28) in order to generate a magnetic flux, wherein the lateral limbs (34a, 34c) are shaped so as to approach the central limb (34b) in the direction of their respective ends forming the gap (36).
2. Power generator according to claim 1, characterized in that the central limb (34b) has a cross-25 section with a diameter smaller than the diameter of a cross section of the lateral limbs (34a, 34c).
3. Power generator according one of the preceding claims, characterized by comprising multiple coils (38a, 38b, 30 38c) with different diameter fitted over the central limb (34b).
4. Power generator according to claim 3, characterized in that the coils (38a, 38b, 38b) are arranged such that the coil diameter increases in the direction of the yoke portion (32).
5. Power generator according one of the preceding claims, characterized in that the limbs (34a, 34c) of the generator core are provided with pole shoes (48a, 48b) designed such that the air gap (36) is formed with uniform width.
6. Power generator according to one of the preceding claims, characterized in that a width of the permanent magnets (40a, 40b) in a longitudinal direction of the yoke portion (32) is larger than a width of other parts of the lateral limbs (34a, 34c), said other parts being arranged so as to overlap with the axial length of the at least one coil (38).
7. Power generator according to one of the preceding claims, characterized in that the permanent magnets (40a, 40b) protrude from the lateral limbs (34a, 34c) towards the 25 central limb (34b) respectively.
8. Sensor unit for housings of train bearings comprising a sensor housing (30), at least one electronic circuit (42) including a sensor (44) and a power generator 30 according to one of the preceding claims, wherein the electronic circuit (43) is driven by energy provided by the generator circuit.
9. Sensor unit according to claim 8, wherein the electronic circuit includes a wireless transmitter unit (46).
10. Train hub unit including a bearing housing attached to a non-rotating ring, a metallic toothed target wheel mounted on a rotating ring and a sensor unit according to claim 8 or 9 mounted on the housing.