Torque limiter

Abstract

A torque limiter device includes an input shaft having a first contact surface and an output shaft having a second contact surface. The input and output shafts are operable in an engaged position wherein the contact surfaces are brought into mechanical engagement, and a disengaged position wherein the contact surfaces are separated. A biasing mechanism provides a bias force that mechanically biases the input and output shafts in one of the positions and sets a threshold torque. An electromagnet is arranged to selectively provide an electromagnetic force that opposes the bias force when an activation current is supplied. A rotation sensor arrangement measures a respective rotation of the input shaft and of the output shaft. A controller determines a difference in rotations of the shafts and selectively supply the activation current to the electromagnet so as to disengage the input and output shafts when the rotation difference exceeds a threshold.

Claims

1. A torque limiter device comprising: an input shaft arranged to be driven by an externally applied torque such that it rotates around a first axis, said input shaft comprising a first contact surface; an output shaft rotatable around a second axis, wherein the second axis is substantially coaxial with the first axis, said output shaft comprising a second contact surface that faces the first contact surface, and wherein the input and output shafts are operable in an engaged position wherein the first and second contact surfaces are brought into mechanical engagement, and a disengaged position wherein the first and second contact surfaces are separated; a biasing mechanism arranged to provide a bias force that biases the input and output shafts in one of the positions; an electromagnet arranged to provide an electromagnetic force that opposes said bias force when an activation current is passed through a coil of said electromagnet, thereby operating the input and output shafts in the other of said positions; a rotation sensor arrangement arranged to measure a rotation of the input shaft and a rotation of the output shaft; and a controller arranged to determine a difference between the rotation of the input shaft and the rotation of the output shaft, said controller being further arranged to selectively supply the activation current to the coil of the electromagnet such that the input and output shafts are operated in the disengaged position when the difference exceeds a threshold.

2. The torque limiter device as claimed in claim 1, wherein the first and second contact surfaces are brought into direct contact in the engaged position.

3. The torque limiter device as claimed in claim 1, wherein the torque limiter device further comprises a friction plate having first and second friction plate surfaces on opposite sides thereof, wherein the first and second contact surfaces are brought into contact with the first and second friction plate surfaces respectively in the engaged position.

4. The torque limiter device as claimed in claim 1, wherein at least one of the contact surfaces is moveable along the axis of its respective shaft, thereby providing movement between the engaged and disengaged positions.

5. The torque limiter device as claimed in claim 4, wherein the second contact surface is axially moveable along the second axis, thereby providing movement between the engaged and disengaged positions.

6. The torque limiter device as claimed in claim 1, wherein the biasing mechanism comprises a resilient member, wherein the bias force is supplied by said resilient member.

7. The torque limiter device as claimed in claim 6, wherein the resilient member comprises a spring.

8. The torque limiter device as claimed in claim 7, wherein the spring comprises a Belleville washer.

9. The torque limiter device as claimed in claim 1, wherein the bias force biases the input and output shafts to the engaged position, wherein the electromagnetic force that opposes the bias force when an activation current is passed through the coil of said electromagnet operates the input and output shafts in the disengaged position.

10. The torque limiter device as claimed in claim 1, wherein the rotation sensor is arranged to determine a difference between a rotation frequency of the input shaft and a rotation frequency of the output shaft.

11. The torque limiter device as claimed in claim 1, wherein the rotation sensor is arranged to determine a difference between a rotation phase of the input shaft and a rotation phase of the output shaft.

12. The torque limiter device as claimed in claim 11, wherein the rotation sensor is arranged to determine a rate of change of said difference.

13. The torque limiter device as claimed in claim 1, wherein at least one of the input and output shafts comprises a toothed arrangement, wherein the rotation sensor detects a motion of the toothed arrangement to determine the rotation of the shaft.

14. The torque limiter device as claimed in claim 13, wherein the rotation sensor comprises a Hall effect sensor arranged to determine the rotation of the toothed arrangement.

15. The torque limiter device as claimed in claim 13, wherein the input and output shafts each comprise a respective toothed arrangement.

16. A thrust reversal actuation system or high-lift system comprising the torque limiter device as claimed in claim 1.

17. The torque limiter device as claimed in claim 1 wherein the controller is arranged to apply the activation current such that the bias force retains the input and output shafts in the engaged position if the difference does not exceed the threshold.

18. A method of operating a torque limiter device, the method comprising: monitoring a difference in rotation between an input shaft and an output shaft; selectively supplying current to an electromagnet, thereby moving one of the input shaft and the output shafts relative to the other against a biasing force; determining when the difference in rotation exceeds a threshold; and disengaging the input shaft from the output shaft when the difference in rotation exceeds the threshold.

19. The method of claim 18, wherein the input and output shafts are retained in an engaged position with the biasing force if the difference does not exceed the threshold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain examples of the present disclosure will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic diagram of a torque limiter device in the disengaged position in accordance with an example of the present disclosure;

(3) FIG. 2 is a schematic diagram of torque limiter device of FIG. 1 in the engaged position;

(4) FIG. 3 is a graph shows the torque Tlimited of the device of FIG. 1 compared to a prior art device;

(5) FIGS. 4A-C are schematic diagrams of a ball-and-ramp interface; and

(6) FIG. 5 is a schematic diagram of a yoke-and-solenoid arrangement.

DETAILED DESCRIPTION

(7) FIG. 1 is a schematic diagram of a torque limiter device 2 in the disengaged position in accordance with an example of the present disclosure. FIG. 2 is a schematic diagram of a torque limiter device 2 of FIG. 1 in the engaged position. The clutch mechanism 2 is positioned within a housing 3 that does not itself rotate.

(8) The torque limiter device 2 of FIGS. 1 and 2 comprises an input shaft 4 and an output shaft 6. The input shaft 4 is a ‘driving’ shaft and is arranged to be connected to a motor (not shown) or some other suitable driving means that imparts an externally applied torque on the input shaft 4, thereby causing it to rotate about its major axis 8. It will be appreciated that the ‘major axis’ of a shaft is along the axial direction, with the shaft considered a cylinder.

(9) The output shaft 6 is a ‘driven’ shaft, and rotates about its major axis 10 in response to a torque transferred from the input shaft 4 when in the engaged position, as outlined in further detail below with reference to FIG. 2. The shafts 4, 6 are coaxial with one another, i.e. their axes 8, 10 coincide. In the disengaged position, there is a gap between the contact surfaces 12, 14 as shown in FIG. 1 such that no such torque is transferred, thereby preventing power transmission.

(10) In the engaged position, a contact surface 12 of the input shaft 4 is brought into engagement with a contact surface 14 of the output shaft 6. While these contact surfaces 12, 14 could be brought directly into contact (which may involve providing the contact surfaces 12, 14 with suitable friction-enhancing coatings depending on the materials that the contact surfaces 12, 14 themselves are made from), in this example, a friction plate 16 is provided between the contact surfaces 12, 14.

(11) This friction plate 16 is of a disc-like construction and has opposing faces that are brought into contact with the contact surfaces 12, 14 in the engaged position, as shown in FIG. 2.

(12) A Belleville washer 18 is provided that, in this example, biases the second contact surface 14 (i.e. the contact surface of the output shaft 6) toward the contact surface 12 of the input shaft 4, and therefore into mechanical engagement with the friction plate 16, as shown in FIG. 2. This Belleville washer 18 therefore acts as a spring that applies a spring force that ‘urges’ the clutch into the engaged position in the absence of any sufficient opposing force.

(13) A nut 20 is provided on the output shaft 6, where adjusting this nut 20 varies the ‘preload’ spring force applied on the second contact surface 14 by the Belleville washer 18. The torque (T) that can be transmitted is a function of the biasing force between both (F), the contact surface average radius (R) and the coefficient of friction (f): T=F×R×f.

(14) Thus with appropriate choice of force F from the biasing portion, a threshold torque Tthreshold may be set, as can be seen in the graph of FIG. 3, where this threshold torque Tthreshold corresponds to the ‘slipping torque’ setting of the device 2. Specifically, the graph of FIG. 3 shows plots of the torque Tlimited of the device 2 according to the example of the present disclosure and the torque Tprior_art associated with a device without the torque limiter.

(15) In the disclosed device 2, when the torque exceeds the threshold torque Tthreshold, the input shaft 4 and output shaft 6 are immediately disengaged, leading to rapid reduction in torque and preventing transmission of power substantially immediately. Thus the torque is ‘clipped’ at the threshold value Tthreshold. This may help to prevent damage to other mechanical components that would occur as a result of the torque exceeding this value, as may occur with the prior art arrangement.

(16) An electromagnet 22 is arranged to provide an electromagnetic force that opposes the bias force from the Belleville washer 18 when an activation current is passed through a coil of the electromagnet 22. This current is supplied by a controller 24, the details of which are described in further detail below. The electromagnet 22 does not rotate, and is typically fixed to the housing 3.

(17) Each of the contact surfaces 12, 14 (or, more generally, the flange at the end of the shafts 4, 6, the ends of which form the contact surfaces 12, 14) is provided with a respective toothed arrangement 26, 28. These toothed arrangements 26, 28 are formed by etching grooves on the outer diameter of the contact surfaces 12, 14. A pair of rotation sensors 30, 32 are arranged in proximity to the toothed arrangements 26, 28. Specifically, the rotation sensors 30, 32 are Hall effect sensors, i.e. they detect variation in the ‘ferromagnetic mass’ in front of the sensor. These rotation sensors 30, 32 do not rotate, and are typically fixed to the housing 3.

(18) As the contact surfaces 12, 14 rotate with their corresponding shafts 4, 6, the respective rotation sensors 30, 32 will detect fluctuations in the ferromagnetic mass in front of the sensor 30, 32 as they are alternately presented with portions of the outer diameters of the contact surfaces 12, 14 having different heights due to the toothed arrangements 26, 28 (i.e. depending on whether it is a grooved portion of the outer diameter or not). Each rotation sensor 30, 32 generates a respective signal that is fed to the controller 24.

(19) The controller 24 determines whether slipping is occurring from a difference in rotation between the signals from the rotation sensors 30, 32. Slipping may be detected by comparing the respective frequencies of the signals from the rotation sensors 30, 32. The frequency of the signals from these sensors 30, 32 corresponds to the rotation speed (i.e. the angular rate) of the respective shaft 4, 6.

(20) Under normal operation, the respective speeds of the input and output shafts 4, 6 should be substantially equal. However, if the speeds of these shafts 4, 6 are not equal, there will be a difference in the rotation frequencies of the shafts. If this frequency difference is sufficiently large, this may indicate slippage between the shafts, e.g. due to a downstream jam. The controller 24 compares the frequency difference to a threshold value. If the frequency difference exceeds the threshold, the controller 24 supplies an activation current to the coil of the electromagnet 22, thereby giving rise to an attractive electromagnetic force that pulls the contact surface 14 of the output shaft 6 away from the contact surface 12 of the input shaft 4.

(21) The controller 24 also monitors the relative phases of the signals from the rotation sensors 30, 32. When the rotation speed of the input shaft 4 is equal to the rotation speed of the output shaft 6, the relative phase between the signals from their respective rotation sensors 30, 32 will remain constant. However, if the relative phase changes, or changes over time (i.e. there is a phase drift), this may indicate slipping. If the time difference between ‘rising fronts’ and/or ‘decreasing fronts’ of the signals from the rotation sensors 30, 32 varies over time, the controller 24 may determine that slipping is occurring and supply the activation current to the coil of the electromagnet 22 as outlined above.

(22) The controller is therefore arranged to selectively supply the activation current to the coil of the electromagnet 22 such that the input and output shafts 4, 6 are operated in the disengaged position as shown in FIG. 1 when slipping is detected. If the difference does not exceed the threshold, the activation current is not supplied, and thus the biasing force from the Belleville washer 18 retains the clutch in the engaged position as shown in FIG. 2.

(23) In the example described above, power is transmitted due to a frictional contact between the opposing faces of the contact surfaces on the input and output shafts. However, as described previously, a ball-and-ramp interface may be provided to improve mechanical engagement between these surfaces, as shown in FIGS. 4A-C. Many of the features of this arrangement are similar to those described above, where like reference numerals appended with a prime symbol (′) indicate like components.

(24) In this arrangement, each contact surface 12′, 14′ is provided with a respective groove 34, 36. Rotating members (e.g. ball bearings or rollers) are held in a ‘cage’ as shown in FIGS. 4A and 4C. In this example, the rotating members are ball bearings 38. These rotating members provide a mechanical interface between the contact surfaces 12′, 14′ in the engaged position as they sit between the grooves 34, 36 of the contact surfaces 12′, 14′. These ball bearings 38 provide for a rotating contact, rather than a sliding contact. In general, there may be a number of rotating members in the interface, and these may all be provided on one contact surface 12′, 14′, or each may have one or more.

(25) This ball-and-ramp arrangement may make use of a yoke-and-solenoid arrangement, an example of which is shown in FIG. 5. In this example, the electromagnet 22 of FIG. 1 is replaced with a yoke-and-solenoid, where a solenoid 40 (a type of electromagnet) drives motion of a yoke 42, which in turn pulls the contact surface 14′ into the disengaged position when excessive torque is detected as outlined above. This may be advantageous when motion of more than a couple of millimetres is required (i.e. for the grooves 34, 36 to sufficiently ‘clear’ the space occupied by the ball bearings 38) in order for the contact surfaces 12′, 14′ to mechanically disengage. It will be appreciated that greater motion under the influence of an electromagnet alone is possible, but will require a more powerful electromagnet. Alternative examples are envisioned in which a linear motor could be used in place of the solenoid.

(26) While specific examples of the disclosure have been described in detail, it will be appreciated by those skilled in the art that the examples described in detail are not limiting on the scope of the disclosure.