FIELD OF THE INVENTION

The present invention relates to a sensor mounting device and is more particularly directed to a device that enables a sensor to be mounted to a curved component surface.

BACKGROUND

There are many applications where it is desirable that a machine component is equipped with one or more sensors for sensing one or more operational parameters. High-speed passenger trains, for example, are typically equipped with a traction control system and, to avoid skidding and locking during braking, are further equipped with a wheel slide protection system. These systems require realtime data on wheel speed and direction of rotation. The data is generally provided by a speed sensor that is integrated in the bearing unit which supports the wheel axle in the axle box. The speed sensor may comprise e.g. a hall element which faces a magnetic pulse ring that is rotationally connected to the bearing inner ring. The hall element may be encased in a sensor housing, part of which is received in an aperture in an annular sealing cover, mounted to the bearing outer ring.

Such an arrangement is disclosed in US 7014368, which relates to a bearing apparatus comprising a sensor unit. In addition to a rotational speed sensor, the sensor unit is further provided with a temperature sensor and/or an accelerometer for monitoring bearing condition. To facilitate the mounting of the sensor unit to the annular sealing cover, the outer circumference of the cover has a flat section in which the aperture is provided, and the sensor unit has a mount flange with a flat underside. The sensor unit is attached to the flat section of the cover, via the mount flange, by means of bolts. In the example of US 7014368, the sensor unit/sensor housing is attached directly to a specially adapted sealing cover. As will be understood, such a sealing cover is more expensive to manufacture than a standard cover. Alternatively, it is possible to execute an attachment part of the sensor housing with a radius of curvature that matches the curvature of the sealing cover. This helps ensure a tight fit between the two components and allows the use of a standard sealing cover, but the manufacture of the sensor housing becomes more complex. Furthermore, it is generally the case that sensors and the sensor housings used on rail vehicles must be certified by an inspection body. Sealing covers come in a range of diameters and designs, depending on the size and design of the bearing. A range of sensor housings with different curvatures would therefore be necessary for different bearing applications, and each housing would have to go through a certification process.

The above drawbacks are solved by attaching the sensor housing indirectly to the sealing cover via an intermediate element. This allows the use of a standard sealing cover and a standard (already certified) sensor housing. An example of an intermediate element is disclosed in US 6179471 , which relates to a device for mounting a sensor to a railway axle bearing unit having an annular sealing insert. The device comprises a mounting element of substantially annular shape adapted for mounting to an outer cylindrical surface of the annular sealing insert. The mounting element supports a sensor to be positioned at the upper half of the annular insert and a connector block located at the lower half, in electrical connection with the sensor. In one embodiment, the sensor is a rotational speed sensor.

There is still room for improvement, however. DISCLOSURE OF THE INVENTION

It is an object of the present invention to define a mounting device for attaching a sensor to a curved surface, which is easy and inexpensive to manufacture.

A further object is to define a mounting device, which enables a robust connection of the sensor to the mounting device.

A still further object is to define a mounting device, which enables an airtight seal to be maintained between the sensor and the mounting device for a long duration. The above objects are achieved according to the invention by means of a sensor mounting device as defined in claim 1. Specifically, the mounting device has a first side at which the sensor is attached and a second side which is curved, so that the device can be mounted to e.g. an outer circumference of an annular shield. Further, the mounting device has an aperture that is shaped to receive an insert part of the sensor, and a first sealing element is provided around the aperture, at the first side of the device. According to the invention, the first sealing element is provided on a first recessed surface of the mounting device, which surface is defined between a first upstanding rim and a second upstanding rim. The first and second rims extend in a circumferential direction of the device and provide a contact surface for an attachment part of the sensor. In addition, the first and second rims retain the first sealing element in both axial directions. The sealing element is typically made from an elastomeric material and has longitudinal edges which surround the aperture in a circumferential direction and lateral edges which surround the aperture in axial direction. It has been found that under the influence of temperature variations and loading, the longitudinal edges of the sealing element can drift, particularly in axial direction. Thus, the first and second rims ensure a durable seal by preventing the longitudinal edges of the first sealing element from movement.

Suitably, the first sealing element has a thickness which is sufficient for it to protrude above the first and second rims. When the sensor is attached, the first sealing element is compressed until the sensor makes contact with a radially outer surface of the first and second rims. The sensor attachment part is typically made of a metal material and at least the upstanding rims of the mounting device are preferably made of a metal material. The result is an airtight, metal-to-metal connection that can withstand forces without movement.

In a preferred embodiment of the device, the first sealing element has a width which is slightly less than a width of the first recessed surface, such that a small gap exists between the first and second rims and the adjacent longitudinal edges of first sealing element. The small gap ensures that when the first sealing element is compressed and as a result becomes wider, direct contact is made between an underside of the sensor attachment part and an upper side of the first and second rims.

In a particularly preferred embodiment, the mounting device has upstanding rims which extend in a circumferential direction only. This design is sufficient to ensure a robust and durably airtight connection between the sensor and mounting device, and is simple to manufacture.

Suitably, the second side of the mounting device describes an arc of between 10 and 60 degrees, depending on the diameter of the annular component to which the device is attached. The first side of the device is shaped to receive the attachment part of the sensor. Preferably, the sensor has a flat attachment part and the first side of the device is also flat, but other geometries are of course possible.

In a further development of the invention, the second side of the mounting device comprises a third upstanding rim and a fourth upstanding rim which extend in the circumferential direction. A second recessed surface is defined between these rims and a second sealing element is provided on the second recessed surface, around the aperture. The advantage of this development is that a robust and durably airtight connection can be achieved between the mounting device and the component to which it is attached. As described for the first sealing element, the second sealing element preferably has a width that is slightly less than the width of the second recessed surface.

The second sealing element is made of a compressible material, which is also sufficiently flexible to follow the radius of curvature of the second recessed surface. In one embodiment, the second sealing element has an essentially uniform thickness that is somewhat greater (e.g. by around 20%) than a height of the third and fourth rims relative to the second recessed surface. In this embodiment, the mounting device is adapted to be mounted to a surface with a radius of curvature that is essentially equal to the radius of curvature of the second side.

In a further development, the second sealing element has a non-uniform thickness. Specifically, a central portion of the second sealing element may be 50 - 100% thicker than the height of the third and fourth rims, while at each lateral edge, the thickness is greater than the rim height by around 20%. The thickness may taper towards each lateral edge such that viewed in axial direction after mounting, the second sealing element resembles a banana in shape. The advantage of this development is that the device can be mounted to surfaces with a larger radius of curvature than the second side of the device. The material of the second sealing element fills any gaps between the component surface and the mounting device, which enables the device to be mounted to annular components with a range of outside diameters.

The present invention further relates to a combination of a sensor and a sensor mounting device as previously described. The sensor is provided with one or more sensing elements for sensing one or more parameters. For example, a Hall element or GMR sensor to detect movement of a magnetized ring. The sensor may also comprise a capacitive or inductive sensor for measuring a gap to the surface of a component e.g. a bearing ring. Measured displacements are indicative of bearing load. The sensor may also comprise an accelerometer for sensing vibration and/or a thermocouple for sensing temperature. Many other possibilities exist.

A suitable application for the sensor and sensor mounting device according to the invention is for monitoring operating parameters of a rolling element bearing, such as a traction motor bearing unit. In one embodiment, the sensor plus mounting device is attached to an outer circumference of a sheet metal annual shield. In a further embodiment, the sensor plus mounting device is provided on an elongation of a bearing outer ring. The invention is not restricted to bearing applications, however, and may be used in any application where a sensor needs to be attached to a curved component surface and a strong and airtight connection is important. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be now be described in greater detail in the following, with reference to the embodiments that are shown in the attached drawings, in which Fig. 1 is a partial cross-sectional view of an application of a sensor and sensor mounting device according to the invention;

Fig. 2 is a perspective view of a sensor housing of the sensor in Fig. 1 ;

Fig. 3a is a top view of the mounting device shown in Fig. 1 (without seals). Fig. 3b is a cross-section though line B-B on Fig. 3a, shown after the first seal has been provided. An attachment part of the sensor is also shown.

Fig. 3c is a cross-section though line A-A on Fig. 3a, shown after the first and second seals have been provided.

DETAILED DESCRIPTION

Figure 1 shows a partial, cross-sectional view of an application comprising one example of a sensor and sensor mounting device according to the invention, provided on a traction motor bearing unit. The resulting sensorized bearing unit 100 has a flanged outer ring 110, an inner ring 115 and a row of cylindrical rollers 120 disposed between the outer and inner rings on opposing raceways. Further, to retain lubricant within the bearing and prevent the ingress of contaminants, the gap between the inner and outer rings at each axial side is covered by a first annular shield 125 and a second annular shield 135. The first and second annular shields 125, 135 are mounted to the flanged outer ring 110 and respectively comprise first and second cylindrical portions 126, 136 which extend in an axially inward direction. The first cylindrical portion 126 extends into a gap defined between a first labyrinth ring 130 and a first radially outer surface of the inner ring 115, thereby creating a labyrinth sealing. Similarly, the second cylindrical portion 36 extends into a gap between a second labyrinth ring 140 and second radially outer surface of the inner ring 115. For the purposes of traction control and/or wheel slide protection, the bearing unit is provided with a rotational speed sensor 180. The sensor 180 comprises a sensor housing, an example of which is shown in a perspective view in Figure 2. The housing 182 is made of a metal, such as aluminium, and has an attachment flange 183 that is preferably provided with one or more screw holes 184. The main body of the housing typically encases a PCB, electronic components and a sensing element. The sensing element is located in a first part 185 (an insert part) of the sensor housing; a second part 186 of the sensor housing comprises a hole 187 through which the sensor cabling is led by means of a cable gland to e.g. a processing unit.

Returning to the example of Figure 1 and also with reference to Figure 2, a magnetic ring 150 is mounted on the first labyrinth ring 130 and is therefore rotatable with the bearing inner ring 115. Movement of the magnetic ring 150 is sensed by a magnetic sensor - e.g. a Hall element or GMR sensor - which is mounted facing the ring 150 on the insert part 185 of the sensor housing 182. The insert part 185 protrudes though the first annular shield 125, and an outer circumference of the shield is provided with a suitable opening. In accordance with the invention, the sensor 180 is mounted to the first annular shield 125 via a sensor mounting device 170. The device 170 is made of a metal, such as an aluminium and copper alloy, and also comprises an aperture that is shaped to receive the insert part 185 of the sensor housing 182.

In the depicted application, the bearing and components attached thereto experience relatively large forces. It is important that the magnetic sensing element maintains a precise position relative to the magnetic ring 150, to ensure the accuracy of the real time data that is provided to e.g. the traction control system. It is therefore important to have a robust connection between the sensor 180 and the sensor mounting device 170, and between the sensor mounting device 170 and the first annular shield 125. This is best achieved by means of metal-to-metal connections, as these connections can withstand forces without movement. Furthermore, because the mounting device 170 and first annular shield 125 comprise openings for the insert part 185 of the sensor and because the bearing operates under severe environmental conditions, sealing is also very important.

Consequently, a first sealing element 191 is provided between the attachment flange 183 and the mounting device 170 and suitably a second sealing element 192 is provided between the mounting device 170 and the annular shield 125. According to the invention, the mounting device is adapted to enable direct contact with the attachment flange 183 of the sensor, while maintaining an airtight and durable seal of the aperture in the mounting device 170. Suitably, the mounting device is further adapted to enable direct contact with the outer circumference of the annular shield 125, while maintaining an airtight and durable seal of the opening in the annular shield.

This will be explained further with reference to Figures 3a - 3c. Figure 3a shows a top view of the sensor mounting device depicted in Figure 1. Figure 3b shows a cross-section of the device through the line B-B on Figure 3a, after the first sealing element has been provided and before the attachment flange of the sensor is connected to the device. Figure 3c shows a cross-section of the device through the line A-A on Figure 3a, after the first and second sealing elements have been mounted.

The sensor mounting device 170 has a first side 178 and a second side 179, whereby the first side 178 is the side at which the sensor is attached to the device and the second side 179 is the side at which the device is attached to the annular shield. Further, the device has an aperture 177 that is shaped to receive the insert part 185 of the sensor housing 182 (see Fig. 2). At the first side 178, the mounting device has a first rim 171 and a second rim 172 which extend in a circumferential direction of the device. The first and second rims 171 , 172 are preferably located at opposite longitudinal edges of the device and extend along the full length. Further, the first and second rims protrude above a first recessed surface 175a of the device by a height h.

The sensor attachment flange 183 has a width that is greater than an axial distance d between the two rims, meaning that a top surface of the first and second rims 171 , 172 serves as the contact surface with the attachment flange 183. Since the sensor housing 182 and the mounting device 170 are made of metal, a metal-to-metal contact is achieved. The sensor attachment flange 182 can be connected to the mounting device by mechanical means, e.g. a screw connection. Suitably, screw holes 176 are provided in the recessed surface 175 at a location in alignment with corresponding screw holes in the attachment flange 183 of the sensor housing

To seal the aperture 177 and create an airtight connection between the mounting device and the sensor attachment flange 183, a first sealing element 191 is provided on the first recessed surface 175a, around the aperture 177, so as to be axially retained between the first and second rims 171 , 172. In other words, longitudinal edges of the first sealing element are in contact with the first and second rims. The first sealing element 191 has an opening, which preferably has the same shape and size as the aperture 177 and may further comprise holes which line up with the screw holes 176 in the recessed surface 175a. The first sealing element 191 is made of a compressible material, such as an elastomer, and has a thickness t which is somewhat greater than the height h of the first and second rims. In the depicted example, the first sealing element 191 is approximately 20% thicker than the rim height. Therefore, when the attachment flange 183 of the sensor housing is screwed on, the first sealing element is compressed until metal-to-metal contact is achieved between the attachment flange and the first and second rims. The compressed sealing element creates an airtight seal.

Upon compression, the elastomeric sealing element 191 will become slightly wider. It may therefore have an uncompressed width w that is marginally less than the axial distance d between the first and second rims 171 , 172. Suitably, the compressed width of the first sealing element is equal to the axial distance d. This ensures that no elastomeric material intervenes in the contact between the first and second rims 171 , 172 and the attachment flange 183 of the sensor. As mentioned above, the first and second rims 171 , 172 not only provide a contact surface for the sensor attachment flange, but also locate the longitudinal edges of the first sealing element 191 in both axial directions. In use, the bearing unit experiences large temperature differences. These cause expansion and contraction of the first sealing element, which can lead to movement of the seal and loss of sealing function. The present inventors have found that it is sufficient to retain the sealing element only in the axial directions, in order to prevent movement. It would, of course, be possible to provide the mounting device with additional rims (at each lateral edge). This would also retain the sealing element in both circumferential directions, but would add to the cost of manufacturing the mounting device.

In the depicted example, the sensor housing has an attachment flange with a flat underside. The top surface of the first and second rims 171 , 172, the recessed surface 175a therebetween and the first sealing element 191 are therefore also flat. As will be understood, the first side 178 of the mounting device can be adapted to receive sensor attachment flanges with different geometries.

At the second side 179, the mounting device 170 has a curved surface. In the depicted example, the second side 179 has a radius of curvature that is essentially equal to the radius of curvature of the annular shield 125 (see Fig. 1 ). This facilitates a tight fit between the curved component surface and the mounting device. Further, the device is suitably provided at the second side 179 with a third rim 173 and a fourth rim 174. To ensure an airtight connection, a second sealing element 192 is provided around the aperture 177 on a second recessed surface 175b of the device, between the third and fourth rims 173, 174.

In this example, the second sealing element 192 has a thickness equal to that of the first sealing element 191 , and the third and fourth rims 173, 174 have a rim height equal to that of the first and second rims 171 , 172. Thus, when the device 170 is screwed to the annular shield, the second sealing element 192 is compressed until metal-to-metal contact is achieved between the third and fourth rims and the outer circumference of the shield. Again, the resulting connection is durably sealed and can withstand forces without movement. As described for the first sealing element, the second sealing element may have an uncompressed width that is slightly smaller than the axial spacing between the third and fourth rims. In a further embodiment of the invention, the mounting device is adapted to be mounted to surfaces with a larger radius of curvature than the radius of curvature of the second recessed surface 175b and the third and fourth rims 173, 174. The second sealing element is suitably executed with a non-uniform thickness. Viewed in axial direction, a central portion of the sealing element may have a thickness that is 50 - 100% larger than the height of the third and fourth rims 173, 174. Towards lateral edges of the seal, the thickness reduces in magnitude to approximately 20% greater than the rim height. The advantage of this embodiment is that the device may be attached in a robust and airtight manner to components with a range of outside diameters.

A number of aspects/embodiments of the invention have been described. It is to be understood that each aspect/embodiment may be combined with any other aspect/embodiment. The invention may thus be varied within the scope of the accompanying patent claims.

Reference numerals

100 Sensorized bearing unit

110 Bearing outer ring

115 Bearing inner ring

120 Cylindrical rollers

125 First annular shield

126 Cylindrical portion of first annular shield

130 First labyrinth ring

135 Second annular shield

136 Cylindrical portion of second annular shield

140 Second labyrinth ring

150 Magnetic ring

170 Sensor mounting device

171 First rim on device

172 Second rim

173 Third rim

174 Fourth rim

175a First recessed surface

175b Second recessed surface

176 Attachment hole

177 Aperture

178 First side of device

179 Second side of device

180 Sensor

182 Sensor housing

183 Sensor attachment flange

184 Mounting hole

185 First part (insert part) of sensor housing

186 Second part of sensor housing

187 Hole for cabling

191 First sealing element

192 Second sealing element d axial distance between first and second rims

w uncompressed width of first sealing element

h height of first and second rims relative to first recessed surface t thickness of first sealing element