WO2014094826A1

WO2014094826A1 - Torque shaft

Info

Publication number: WO2014094826A1
Application number: PCT/EP2012/075959
Authority: WO
Inventors: Pascal EHRET; Adam V.C. Reedman
Original assignee: Aktiebolaget Skf
Priority date: 2012-12-18
Filing date: 2012-12-18
Publication date: 2014-06-26

Abstract

A torque shaft (100) for transmitting torque by rotation including a coupling part (110) for coupling to a rotating part and a composite tubular body (120) attached to the coupling part (110). The composite tubular body (120) embeds a torque sensing fibre (130) for measuring the torque transmitted by the torque shaft (100). By embedding the torque sensing fibre (130) in the composite tubular body (120) a compact design of the torque shaft (100) is obtained.

Description

TORQUE SHAFT

FIELD OF THE INVENTION

The invention relates to a torque shaft comprising a tube made fibre composite material, with means for sensing a torque applied on the shaft.

BACKGROUND ART

Torque shafts are known in the art. Torque shafts are mechanical components suitable for transmitting torque between a first rotating part to a second rotating part. Conventional methods of measuring torque employ a torque sensor, made of strain gauges mounted to a torque shaft to measure the shear strain caused by the torque. One of the disadvantages to this approach is that multiple and different strain gauges may be needed and glued around the torque shaft. These gauges all need calibration with a known reference standard. These major disadvantages increase the complexity of said torque shafts. There is a need for improvements in the field of torque shafts.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least diminish the disadvantages of the known torque shafts.

According to the invention, this object is achieved by a torque shaft for transmitting torque by rotation comprising:

- a coupling part for coupling to a rotating part,

- a composite tubular body elongated along a longitudinal axis between a first end and a second end, the second end being attached to the coupling part, and

- a torque sensing fibre embedded in the composite tubular body comprising at least one sensor for measuring the torque transmitted by the torque shaft.

By embedding a torque sensing fibre in the composite tubular body, a compact design of the torque shaft and the accompanying torque sensing fibre is obtained. In a particular embodiment of the torque shaft, the torque sensing fibre comprises multiple sensors. By embedding multiple sensors in the same torque sensing fibre, errors in the measurement of the torque may be compensated. In another particular embodiment, the composite tubular body of the torque shaft comprises protrusions extending along a longitudinal axis of the composite tubular body towards a coupling part. The torque shaft further comprises attachment means for attaching the composite tubular body to the coupling part at an attachment area. The torque sensing fibre partially surrounds the attachment area and is embedded in the protrusions in a zone between the attachment means and a portion of the protrusions extending along the longitudinal axis towards the coupling part. In this embodiment, the torque sensing fibre measures the torque on the composite tubular body during rotation. By having the torque sensing fibre partially surrounding the attachment area and embedded in the protrusions in a zone between the attachment means and a portion of the protrusions extending along the longitudinal axis towards the coupling part, the torque sensing fibre predominantly sustains elongational deformation when torque is applied to the composite tubular body.

In another particular embodiment, the attachment means are pins. Further to that the attachment area and the coupling part are provided with evenly distributed openings along a perimeter of the composite tubular body for receiving radially the pins. The pins provide a strong mechanical coupling between the composite tubular body and the coupling part. A further advantage of this embodiment is that the torque shaft and in particular the composite tubular body of the torque shaft is more robust and reliable.

In further particular embodiments according to the invention the torque sensing fibre comprises multiple sensors with a least one optical fibre Bragg grating or one piezoelectric fibre. In these specific embodiments the torque sensing fibre may be well integrated in the composite tubular body during the manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawing, Fig. 1 shows an embodiment of a torque shaft according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows an example of a torque shaft according to the invention. The torque shaft 100 includes a coupling part 1 10 which may be coupled to a rotating part (not shown in the figure) and a composite tubular body 120 elongated along a longitudinal axis X102 between a first end 104 and a second end 106. In this example, the composite tubular body is made of a carbon-fibre-reinforced polymer. The composite tubular body 120 comprises protrusions 140 having the same composite material as the composite tubular body 120 and extending along the longitudinal axis X102 towards the coupling part 1 10. A torque sensing fibre 130 is embedded in the protrusions 140 at an attachment area 145 of the protrusions 140. The protrusions 140 are attached to the coupling part 1 10 by means of pins 150. The torque sensing fibre 130 is partially surrounding the attachment area 145 where the pins 150 are located and follows a path that includes an area of the protrusions 140 delimited between the attachment area 145 of the pins 150 and a portion of the protrusions 140 extending in the direction of the longitudinal axis X102 towards the coupling part 1 10. The torque sensing fibre 130 measures the torque transmitted by the torque shaft 100.

The coupling part 1 10 as well as the pins 150 may for example be made of any suitable metal such as steel, aluminum, etc. The composite tubular body 120 may be made of any type of fibre-reinforced polymer. Suitable materials for the fibres include carbon fibre, glass fibre and aramid fibre. The pins 150 may be slugs, screws, nails, clips, clasps, etc. or any suitable means for attaching the coupling part 1 10 to the composite tubular body 120. The composite tubular body 120 may or may not comprise protrusions 140. Additionally the composite tubular body 120 may or may not be attached to the coupling part 1 10 by means of pins 150. When pins 150 are not used for attaching the two parts, glue could for example be used. When the composite tubular body 120 contains protrusions 140 attached to the coupling part 1 10 by means of pins 150, the carbon fibres used for manufacturing the composite tubular body 120 may be placed to surround the pins 150. A placement of the carbon fibres may continue around the composite tubular body 120 and around the pins 150 until a combined structure formed by the coupling part 1 10 and the composite tubular body 120 is strong enough to transmit the torque during rotation of the torque shaft 100. The placement of the carbon fibres is obtained by, for example, winding the fibres around the tubular body 120 and by encircling all the pins 150 with the fibres. This process may be used at both extremities of the torque shaft 100 if a similar coupling part (not shown in Fig. 1 ) to the coupling part 1 10 is attached to the composite tubular body 120 by means of pins 150 at the first end 104 of the composite tubular body 120.

During rotation, a transmission of torque to the torque shaft 100 results in a generation of equal forces on each of the pins 150. The forces generated by the torque on the pins 150 have a direction parallel to a circumference of the composite tubular body 120. This force produces a contact force at the attachment area 145 between the pins 150 and the composite material of the composite tubular body 120. The forces acting on the attachment area 145 generate a small circumferential displacement on the composite tubular body 120 of the torque shaft 100. The circumferential displacement of the composite tubular body 120 results in a longitudinal displacement along the longitudinal axis X102 of the carbon fibres of the composite tubular body 120, due to the placement around the pins. Therefore, the carbon fibres are predominantly stressed in a longitudinal direction during rotation. This effect is more pronounced in the proximity of the attachment area 145 where the pins 150 contact the composite material of the composite tubular body 120.

The same effect is achieved in the torque sensing fibre 130 when the torque sensing fibre 130 is embedded in the protrusions 140 along a path that includes an area of the protrusions 140 delimited between the attachment area 145 and the portion of the protrusions extending along the longitudinal axis X102 towards the coupling part 1 10. This special arrangement of the torque sensing fibre 130 has two simultaneous advantageous effects. The first already described effect is that the torque sensing fibre 130 is mainly stressed in a longitudinal direction along the longitudinal axis X102. In this way the torque sensing fibre 130 predominantly sustains elongational deformation, to which it is most sensitive. The second effect of this embodiment is that the torque sensing fibre 130 operates at a location of maximal stress on the composite tubular body 120, thus furthering increasing the measurement sensitivity.

The torque sensing fibre 130 is small in size and can therefore be readily integrated in the composite tubular body 120 or alternatively in the protrusions 140 of the composite tubular body 120 (i.e. without the need of extra bulky equipment such as slip rings, rotary transformers, etc.).

It should also be noted that the protrusions 140 may have any other suitable shape than the sine or wavy shape shown in Fig. 1 . This shape could for example be a saw tooth shape or a series of squares or triangles or rectangles or a combination of any of these shapes. The protrusions 140 may be mounted on the outside of the coupling part 1 10 (as in Fig. 1 ).

The torque sensing fibre 130 may comprise at least one sensor using an optical fibre Bragg grating for measuring the torque transmitted by the shaft. Optical fibre Bragg gratings are optical fibres sensitive to stress because they reflect selectively certain wavelengths of light according to a particular amount of stress. If the composite tubular body 120 is for example made of carbon fibre reinforced materials, the use of optical fibre Bragg gratings is particularly advantageous. Optical fibre Bragg gratings match in fact quite well with new composite materials like carbon fibre reinforced materials. They may be integrated into composites or can be fixed directly on the surface of the composite tubular body 120. They may be advantageously used also for their relative lightness, immunity to electromagnetic interference and because of their geometrical flexibility they bend in curved or round shaped surfaces. Optical fibre Bragg gratings are also intrinsically passive (no electrical power necessary) and therefore may be used in harsh environments such as high voltage and potentially explosive atmosphere areas. Further to that, the actual data collection from Bragg grating torque sensors may take place at great distance from the spot of sensing.

In an embodiment according to the invention the torque shaft 100 comprises a further sensor 160 for measuring temperature. Optical fibre Bragg gratings show high temperature dependence. When the torque sensing fibre 130 includes an optical fibre Bragg grating, it is therefore preferable to measure the temperature with another sensor to compensate for temperature variations. The compensation may be performed by another optical fibre Bragg grating 160 which may also be easily embedded in the composite tubular body 120.

In a particular advantageous embodiment the torque sensing fibre 130 may comprise one or more sensors for measuring strain or other type of forces applied to the torque shaft 100 during rotation. Multiple sensors may be needed to compensate for a variety of errors in the measurement of the torque (e.g. for bending of the torque shaft 100 caused by misalignment between the coupling part 1 10 and the composite tubular body 120). For example by using differently spaced Bragg gratings in the same optical fibre, multiple sensors sensitive to varying levels of strain and temperature may be embedded in the same torque sensing fibre 130.

In another embodiment according to the invention the torque sensing fibre 130 may comprise multiple sensors using at least one piezoelectric fibre. Piezoelectric fibres have many advantages over the conventional bulky strain gauge sensors. Piezoelectric fibres are a good choice for continuously measuring the stress levels of composite structures like carbon fibres (e.g. the composite material with which the composite tubular body 120 described above may be made of). They are highly flexible, easily embeddable in composite materials and provide manufacturing flexibility. The torque sensing fibre 130 may also include any suitable sensor usable to measure stress and embeddable in the composite tubular body 120 different from the optical fibre Bragg gratings or piezoelectric fibres.

The torque sensing fibre 130 may be embedded at any location in the composite tubular body 120. When the torque sensing fibre 130 includes multiple sensors, these sensors may be placed at multiple locations in the composite tubular body 120. In this case the strain at different locations may be measured. The measurements at different locations may be used to compensate for errors in the measurement of the torque. For the sake of simplicity all electrical connections to power supplies or data processing apparatus and/or cabled or wireless systems used to transmit and receive data to and from the torque sensing fibre 130 and/or to and from the further sensor 160 are not shown in Fig. 1 .

Claims

CLAIMS:

1 . A torque shaft (100) for transmitting torque by rotation comprising:

a coupling part (1 10) for coupling to a rotating part,

a composite tubular body (120) elongated along a longitudinal axis (X102) between a first end (104) and a second end (106), the second end (106) being attached to the coupling part (1 10), and

a torque sensing fibre (130) embedded in the composite tubular body (120) comprising at least one sensor for measuring the torque transmitted by the torque shaft (100).

2. A torque shaft (100) according to claim 1 , wherein the torque sensing fibre (130) comprises multiple sensors.

3. A torque shaft (100) according to claim 1 or 2, wherein the second end (106) of the composite tubular body (120) comprises protrusions (140) extending along the longitudinal axis (X102) of the composite tubular body (120) towards the coupling part (1 10), further comprising attachment means arranged for attaching the protrusions (140) to the coupling part (1 10) at an attachment area (145) of the protrusions (140), and wherein the torque sensing fibre (130) is partially surrounding the attachment area (145) and embedded in the protrusions (140) along a path including an area delimited between the attachment area (145) and a portion of the protrusions (140) extending from the attachment area (145) towards the coupling part (1 10) along the longitudinal axis (X102).

4. A torque shaft (100) according to claim 3 wherein the attachments means are pins (150), and wherein the attachment area (145) and the coupling part (1 10) are provided with evenly distributed openings along a perimeter of the composite tubular body (120) for receiving radially the pins (150).

5. A torque shaft (100) according to claim 3 or 4, wherein the protrusions (140) are mounted on the outside of the first coupling part (1 10).

6. A torque shaft (100) according to claim 2, 3, 4 or 5, wherein the multiple sensors comprise at least one optical fibre Bragg grating.

7. A torque shaft (100) according to claim 2, 3, 4, 5 or 6, wherein the multiple sensors comprise at least one piezoelectric fibre.

8. A torque shaft (100) according to claim 1 , 2, 3, 4, 5, 6 or 7, further comprising a further sensor (160) for measuring temperature.