EP2193341A1

EP2193341A1 - Device for detecting rotation and instrumented bearing fitted with such a device

Info

Publication number: EP2193341A1
Application number: EP08804612A
Authority: EP
Inventors: Franck Landrieve; Sylvain Chaussat
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2007-09-24
Filing date: 2008-09-23
Publication date: 2010-06-09
Also published as: FR2921481A1; WO2009040345A1; FR2921481B1

Abstract

Device for detecting rotation and instrumented bearing fitted with such a device A device for detecting the rotationofa revolving element of the type comprising a multiple-pole magnetic coder ring (1), fitted on the revolving element and a non-revolving sensor assembly (2) sensitive to the magnetic fields, fitted closeto the coder ring, the sensor assembly (2) comprising a flexible plate switch (5) linked by two terminals (8) to connecting wires and concentrator elements (11) positioned between said terminals (8) and the coder ring (1).

Description

Device for detecting rotation and instrumented bearing fitted with such a device

The present invention relates to devices for detecting proximity or passage of a revolving element, making it possible to determine at least one rotation parameter of the revolving element. The invention also relates to the applications of such devices to instrumented rolling bearings for measuring at least one rotation parameter of a wheel or a displacement parameter of a vehicle fitted with such a wheel. There are known devices for detecting rotation of a revolving element which comprise a multiple-pole magnetic coder ring fitted on the revolving element and associated with a non-revolving sensor assembly sensitive to the magnetic fields. The magnetic field variations resulting from the passage of the different poles of the coder ring in front of the fixed sensor assembly generate a signal, which can be interpreted to measure the parameters sought.

For the sensors, Hall-effect sensors can be used, but these do, however, present the drawback of requiring an electrical supply current. It is also possible to use sensors comprising a flexible plate commutator or switch (ILS), also called "Reed relay". These are devices sensitive to the magnetic fields that can occupy two positions, open or closed, depending on the magnetic field to which the commutator is subjected. A flexible plate switch generally comprises a glass capsule inside which two flexible plates forming the switch are fitted. The two plates are prolonged outside the capsule where they form connecting terminals via which the switch is connected to an associated measuring circuit. When such a flexible plate switch is subjected to the action of a magnetic field with field lines oriented in the general direction of the flexible plates, the relay closes. In the otherwise, it remains open.

Such a flexible plate switch can be housed in a casing o f synthetic material or even embedded in synthetic resin in order to form a magnetism-sensitive sensor assembly able to react to the presence o f magnetic fields and to supply a signal when the field lines are oriented in a certain way.

This type of sensor presents certain advantages which make its use particularly interesting in certain applications. Indeed, its cost is relatively low and it consumes no electrical current for its operation, unlike the case with Hall-effect cells.

For the control of a flexible plate switch by a simple magnet, a magnetic bar or a bipolar ring, positions of the magnet and of the flexible plate switch are adapted so as to obtain an opening and closing control according to relative motion of the magnet in relation to the sensor. This type of sensor is often used to detect the rotation o f a bicycle wheel or roller skates. The flexible plate switch is then associated with a magnet fixed on the wheel. The switch opens and closes on each passage of the magnet, which makes it possible, by sensing pulses in a given time interval, to deduce therefrom the speed of rotation of the wheel and the distance travelled.

It is difficult, however, to use sensors of this type in association with a rotating multiple-pole ring because of the excessive size of the sensor relative to the dimensions of the poles of the coder ring. Indeed, below critical dimensions of the poles relative to the dimensions of the flexible plate switch, the latter is simultaneously subjected to the magnetic fields produced by several pairs of poles, so that it is no longer possible to obtain a reaction to the passage of a determined pair of poles in front of the sensor. The flexible plate switches are in fact normally 200 times larger than the sensitive area of a Hall-effect cell which is often used in association with such a rotating multiple-pole ring.

These difficulties are further aggravated by the fact that it is necessary, for reasons of mechanical integration, to normally provide a distance of several millimetres between the flexible plate switch and the coder element. The result of this is a reduction in the resolution which makes the use of this type of sensor practically impossible.

The object of the present invention is to resolve these difficulties and make it possible to use this type of sensor with conventional multiple-pole coder rings, even in the case where the latter have a multitude of poles of very small dimensions.

In one embodiment, a device for detecting the rotation of a revolving element of the type comprises a multiple-pole magnetic coder ring, fitted on the revolving element and a non-revolving sensor assembly sensitive to the magnetic fields, fitted close to the coder ring. The sensor assembly comprises a flexible plate switch linked by two terminals to connecting wires. Concentrator elements are positioned between said terminals and the coder ring.

The presence of these concentrator elements makes it possible to obtain a satisfactory response even if the dimensions of the flexible plate switch remain very much greater than those of the poles of the multiple-pole ring. Preferably, each concentrator element comprises a detection portion positioned facing the poles of the coder ring and a transmission portion in contact with one of the terminals of the flexible plate switch.

Each detection portion advantageously extends, in the circumferential direction, over a length substantially less than or equal to the circumferential length of a pole of the coder ring.

The detection portions of the concentrator elements preferably present ends that are mutually facing each other and separated by a distance equal to the circumferential length of a pair of poles of the coder ring.

In an advantageous embodiment variant, a screen of magnetic material is also positioned between the flexible plate switch and the multiple-pole coder ring. In this way, the field lines that are capable of acting on the control of the flexible plate switch are exclusively those that originate from the poles facing detection portions of the concentrator elements.

The screen preferably extends, in the circumferential direction, over a length slightly greater than the circumferential length of a pole and less than the circumferential length of a pair of poles of the coder ring.

In one embodiment, the detection portions are maintained separated from the facing surface of the coder ring, which defines an appropriate air gap. In some cases, however, it is difficult to maintain the sensor in such a precise separated position. It is then possible to provide on the coder ring a thin layer or a coating of amagnetic material. The detection portions are maintained in friction contact with this amagnetic layer that is integral to the coder ring, which also produces an appropriate air gap as previously.

In order to ensure a good friction contact and a controlled separation of the sensor relative to the coder ring, the transmission portions are preferably elastic and the sensor assembly is pressed towards the coder ring. The sensor assembly can be fitted with an air gap that is radial in relation to the coder ring or with an air gap that is axial in relation to the coder ring, depending on the applications.

Another aspect of the invention relates to an instrumented rolling bearing for measuring at least one rotation parameter of a wheel or a displacement parameter of a vehicle fitted with such a wheel. Such a bearing comprises a revolving ring, a non-revolving ring and at least one row of revolving elements positioned between the revolving and non-revolving rings. The bearing comprises a device as mentioned above, the coder ring being fitted on the revolving ring. The invention will be better understood by studying a few embodiments described as nonlimiting examples and illustrated by the appended drawings, in which:

Figure 1 diagrammatically illustrates the main units of a detection device according to the invention, the flexible plate switch being represented in the closed position;

Figure 2 is a partial view identical to Figure 1 , showing the flexible plate switch in the open position; Figure 3 is a view similar to Figure 1 of a second embodiment; and

Figure 4 is a cross-sectional view of an instrumented bearing equipped with a detection device according to the invention. As illustrated in Figures 1 and 2, a detection device according to the invention comprises a multiple-pole magnetic coder ring 1 fitted to rotate on a revolving element not shown in the figure and a non- revolving sensor assembly referenced 2 overall, fitted close to the periphery of the coder ring 1. The coder ring 1 has a plurality of magnetic poles around its periphery, each of the north poles 3 (marked N in Figure 1 ) being paired with a south pole 4 (denoted S in Figure 1 ) so as to form a pair of poles NS, the pairs of poles following each other side by side around the entire periphery of the coder ring 1. The sensor assembly 2 comprises a flexible plate switch 5 with an oblong glass bulb 6, inside which are fitted two flexible plates 7 capable of making an electrical contact depending on the orientation of the field lines of a magnetic field located nearby. The two plates 7 are prolonged outside the glass bulb 6 in the form of connecting terminals 8 at each end of said bulb 6. Connecting wires 9 are fixed, for example by soldering, to the terminals 8 and linked to connecting cables 10 capable of transmitting a signal to a measuring device not represented in the figure.

The flexible plate switch 5 which comprises the bulb 6, the two plates 7 and the connecting terminals 8 associated with the connecting wires 9, is fitted close to the periphery of the rotating multiple-pole ring 1 with two concentrator elements 1 1 interposed. Each of the concentrator elements 1 1 comprises a detection portion 12 positioned facing the poles of the ring 1 and a transmission portion 13 linking the detection portion 12 to one of the terminals 8 of the flexible plate switch 5. In the illustrated example, each transmission portion 13 is substantially radial in relation to the axis of rotation of the ring 1 and presents an extension section 13a which is in electrical contact with a terminal 8, to which it is fixed, for example by soldering. In the example illustrated in Figures 1 and 2, the two detection portions 12 have a substantially cylindrical form which corresponds to the general cylindrical form of the revolving multiple-pole ring 1 . An air gap is left between the two detection portions 12 and the external cylindrical surface facing the multiple-pole ring 1. The relative positioning of the flexible plate switch 5 and of the multiple-pole ring 1 is thus radial, the sensor assembly 2 being positioned radially outside the multiple-pole ring 1.

The two detection portions 12 present end edges 12a mutually facing each other and separated from each other by a distance roughly equal to the circumferential length of a pair of poles NS of the coder ring 1. Furthermore, each detection portion 12 extends, in the circumferential direction, over a length substantially equal to the circumferential length of an N or S pole of the coder ring 1. This length could also be slightly less than the length of one of the poles.

As a variant, the end edges 12a could be directed in opposite directions.

To enhance the quality of the signal, there is also provided in the example illustrated in Figures 1 and 2 a screen 14 made o f magnetic material and positioned between the flexible plate switch 5 and the multiple-pole coder ring 1 and between the two facing ends 12a of the two detection portions 12. The circumferential length of the screen 14 is slightly greater than the circumferential length of a pole of the coder ring 1 , as can be seen in Figure 2. However, it remains less than the circumferential length of a pair of poles so that the edges of the screen 14 remain separated from the end edges 12a facing two detection portions 12.

The assembly formed by the flexible plate switch 5 fitted with the connecting terminals 8 and connecting wires 9 and the two concentrator elements 1 1 and the screen 14, is included in a mass o f synthetic material 15 to ensure the spatial cohesion of the different elements of the sensor assembly 2 and which facilitates maintaining it in a precise position separated by an air gap mentioned above in relation to the multiple-pole ring 1 . All that appears outside the synthetic material are the surfaces of the detection portions 12 and o f the screen 14.

The interposing, between the terminals 8 of the flexible plate switch 5 and the poles 3 , 4 of the multiple-pole ring 1 , of the concentrators 1 1 , makes it possible to concentrate the flow of the field lines resulting from the magnetic field generated by the poles N, S o f the multiple-pole ring 1. The field lines are in effect channelled towards the two terminals 8 by the two concentrator elements 1 1. More specifically, the detection portions 12 sense the magnetic field lines which are then channelled by the transmission portions 13 as far as the terminals 8 of the flexible plate switch 5.

The dimensions of the detection portions 12 are chosen so as to accommodate a maximum of magnetic field lines, which is the case in the example illustrated in Figures 1 and 2, when the circumferential length of the detection portions 12 is substantially equal to the circumferential length of the poles to be detected 3 or 4.

It is thus possible to use flexible plate switches with multiple- pole coder rings of the type of that illustrated in Figures 1 and 2 with a pole pitch that can be less than 5 mm. The concentrators 1 1 are produced in a magnetic material capable of channelling the magnetic field lines, for example a ferromagnetic material such as steel.

The sensor assembly 2 can easily be encapsulated in a casing that can also comprise the connecting arrangements not illustrated in the figures. Given the relatively large dimensions of the flexible plate switch 5 relative to the different poles 3 , 4, it is advantageous to provide the screen 14 in magnetic material, for example steel. This screen 14 in effect forms a magnetic shield and short-circuits the field lines in order for them not to disturb the operation of the flexible plate switch 5. The screen 14 prevents the magnetic field lines originating from the poles remaining between the facing ends of the two detection portions 12 from influencing the flexible plate switch 5 and disturbing the detection.

In the position illustrated in Figure 1 , each of the detection portions 12 is facing a north pole 3 and respectively a south pole 4. A pair of north/south poles remains between the two end edges 12a facing the two detection portions 12. The screen 14 is positioned straddling, facing this pair of poles. In the position illustrated in Figure 1 , the flexible plate switch 5 senses almost all the field lines originating from the two north and south poles facing which there are two detection portions 12. The flexible plate switch 5 is therefore in the closed position.

In the position illustrated in Figure 2 where the multiple-pole ring 1 has revolved slightly, each of the detection portions 12 is positioned facing the junction zone between two north/south poles. In this case, the flexible plate switch 5 is in the open position given that the detection portions 12 do not transmit to the flexible plate switch 5 field lines oriented so as to provoke the closure of the flexible plates 7.

The embodiment illustrated in Figure 3 , in which the identical elements are given the same references, differs essentially from the embodiment illustrated in Figures 1 and 2 by the fact that an additional ring 16, of small thickness, forming a layer of amagnetic material, is positioned around the multiple-pole coder ring 1 in order to define an air gap between the coder ring 1 and the sensor assembly 2. Such a ring could be replaced by an amagnetic coating. The two detection portions 12 here come into friction contact with the external cylindrical surface of the amagnetic ring 16. Furthermore, transmission portions 13 , instead of being substantially radial as in the embodiment of Figures 1 and 2, present an inclined V section with a branch 13 f fixed by an extension section 13a to a terminal 8 and a branch 13c extending the detection portion 12. This shape gives each transmission portion 13 an elastic character. A bearing force exerted substantially radially to the sensor element 2 therefore makes it possible to elastically maintain the two detection portions 12 always in contact with the external periphery of the ring 16. The thickness of the ring 16 forming the abovementioned amagnetic layer thus accurately defines the air gap which is maintained between the detection portions 12 and the multiple-pole ring 1. Such an arrangement makes it possible to simplify the radial positioning of the sensor assembly 2 relative to the multiple-pole ring 1 by enhancing the accuracy of this positioning. Although no screen 14 is illustrated in Figure 3 , it will be understood that such a screen can also be provided in this embodiment, the screen then being able to be incorporated in the synthetic material 15 , between the flexible plate switch 5 and the multiple-pole ring 1.

Unlike the case in the embodiment of Figures 1 and 2 where the set of concentrator elements 1 1 and the screen 14 were included in the synthetic material 15 , in the embodiment of Figure 3 , an arrangement will advantageously be used in which the detection portions 12 and the branches 13c of the transmission portions 13 project outside the synthetic material 15 so as to guarantee the elasticity of the assembly.

Figure 4 illustrates an exemplary application of a detection device as illustrated in the preceding figures. In this application, a multiple-pole coder ring 1 is fitted by an annular support element 17 on the revolving internal ring 18 of a ball bearing 9. To this end, the element 17 comprises an annular portion 17a, fitted over the external cylindrical surface of the ring 18 and a radial end plate portion 17b with an annular fold 17c on which is fitted the multiple-pole ring 1.

The ball bearing 19 also comprises a non-revolving external ring 20 and a row of balls 21 fitted in a cage 22. On one side of the rolling bearing 19 there is fitted a lip seal 23. On the other side, there is positioned, around the multiple-pole ring 1 , an annular part 24 of synthetic material inside which is embedded the flexible plate switch

5 , as illustrated in Figure 1. The annular part 24 is snap fitted inside the non-revolving ring 20 by an annular fold 25 which cooperates with a groove 26 formed in the bore of the ring 20. A radial face 27 of the annular part 24 comes into contact with a front face of the ring 20. This makes it possible to accurately define the radial and axial positions of the detection portions 12 embedded in the part 24 relative to the multiple-pole ring 1 and therefore the remaining radial air gap.

The annular part 24 presents a radial end plate 28 ending in an annular fold 29 directed towards the ring 18 and with a small separation from it.

The part of the part 24 that includes the flexible plate switch 5 and the detection portions 12 forms, with the radial end plate 28 and the fold 29 a sort of cover enclosing the ring 1 and its annular support 17. This forms a sort of labyrinth seal for the bearing 19, on the side opposite to the lip seal 23. All of the assembly can, of course, be reversed, with a non-revolving internal ring and a revolving external ring.

The signals sent by the flexible plate switch 5 are transmitted by the connecting cable 10 to a processing device that is not represented.

Although all the examples illustrated have shown the sensor assembly fitted with an air gap that is radial in relation to the coder ring, it will be understood that it is also possible to fit the sensor assembly with an axial air gap on one side or the other of a multiple- pole coder ring.

The invention makes it possible to use flexible plate switches with multiple-pole coder rings comprising a plurality of poles of very small dimensions.

Claims

1. Device for detecting the rotation of a revolving element of the type comprising a multiple-pole magnetic coder ring ( 1 ), fitted on the revolving element and a non-revolving sensor assembly (2) sensitive to the magnetic fields, fitted close to the coder ring, characterized in that the sensor assembly (2) comprises a flexible plate switch (5) linked by two terminals (8) to connecting wires and concentrator elements ( 1 1 ) positioned between said terminals (8) and the coder ring ( 1 ).

2. Device according to Claim 1 , in which each concentrator element ( 1 1 ) comprises a detection portion ( 12) positioned facing the poles of the coder ring (1 ) and a transmission portion ( 13) in contact with one of the terminals (8) of the flexible plate switch (5).

3. Device according to one of the preceding claims, in which each detection portion (12) extends, in the circumferential direction, over a length less than or equal to the circumferential length of a pole of the coder ring.

4. Device according to one of the preceding claims, in which the detection portions ( 12) of the concentrator elements (1 1 ) present ends ( 12a) mutually facing each other and separated by a distance equal to the circumferential length of a pair of poles of the coder ring.

5. Device according to one of the preceding claims, in which a screen ( 14) of magnetic material is positioned between the flexible plate switch (5) and the multiple-pole coder ring ( 1 ).

6. Device according to Claim 5 , in which the screen ( 14) extends, in the circumferential direction, over a length greater than the circumferential length of a pole and less than the circumferential length of a pair of poles of the coder ring.

7. Device according to one of Claims 2 to 6, in which the detection portions (2) are maintained separated from the facing surface of the coder ring.

8. Device according to one of Claims 2 to 6, in which the detection portions ( 12) are maintained in friction contact with a layer ( 16) of amagnetic material integral with the coder ring ( 1 ).

9. Device according to Claim 8, in which the transmission portions ( 13) are elastic.

10. Device according to one of the preceding claims, in which the sensor assembly is fitted with an air gap that is radial relative to the coder ring.

1 1. Device according to one of Claims 1 to 9, in which the sensor assembly is fitted with an air gap that is axial relative to the coder ring.

12. Instrumented rolling bearing for measuring at least one rotation parameter of a wheel or a displacement parameter of an engine fitted with such a wheel, comprising a revolving ring ( 18), a non-revolving ring (20), at least one row of revolving elements (21 ) positioned between the revolving and non-revolving rings, characterized in that it comprises a device according to one of the preceding claims, the coder ring (1 , 17) being fitted on the revolving ring (18).