GB2378737A

GB2378737A - Permanent magnet differential reluctance torque limiting clutch

Info

Publication number: GB2378737A
Application number: GB0116290A
Authority: GB
Inventors: Martin Boughtwood
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-06-30
Filing date: 2001-06-30
Publication date: 2003-02-19
Also published as: GB0116290D0

Abstract

A permanent magnet differential reluctance torque limiting clutch comprising a rotor with alternating high 5 and low 1 reluctance material and a stator with alternating high 5 and low 4 reluctance material and at least 1 permanent magnet 3. Detent torque is generated by reluctance differential of low reluctance and high reluctance segments. Energy consumption is reduced due to energy return action of negative torque from misaligned low reluctance rotor and stator sections during torque limiting action.

Description

PERMANENT MAGNET DIFFERENTIAL RELUCTANCE TORQUE LIMITING CLUTCH This invention relates to a permanent magnet differential reluctance torque limiting clutch.

Torque limiting clutches are well known devices used to limit the maximum torque within a rotating mechanical system. There are several forms of magnetic torque limiting clutch, one arrangement of which depends upon electromagnetism. Electromagnetic torque limiting clutches typically comprise a solenoid concentrically arranged with a moving plate and an interposing friction surface.

The magnetic path is such that by controlling the current to the solenoid a controlled force is applied between the solenoid body, the moving plate and the friction surface. The input torque is applied to either the solenoid body or the moving plate and the output torque is taken from either the moving plate or the solenoid body. Thus torque is limited by the friction established at the friction surface by the applied force.

Other arrangements of torque limiting clutch depend upon a permanent magnet or magnets to provide the force in a manner similar to the solenoid described above. The permanent magnet provides a fixed force and hence fixed torque depending upon the choice of friction material at the friction surface. In unit load

material handling conveyors where loads are required to accumulate, clutches of the above types are often incorporated into the rollers used to transport the load. Torque limiting clutches in use today suffer from one or both the disadvantages of: A) Energy consumption when limiting torque B) Wear when limiting torque According to a first aspect of the present invention there is provided a permanent magnet differential reluctance torque limiting clutch comprising a rotor constructed to form a pair or pairs of poles of a low reluctance magnetic circuit interspaced around a common rotation axis with higher reluctance sections, a stator constructed to form a pair or pairs of poles of a low reluctance magnetic circuit interspaced around the same common rotation axis with higher reluctance sections, and at least 1 permanent magnet incorporated into the low reluctance magnetic circuit.

According to a second aspect of the present invention there is provided an energy return action by way of magnetic attraction which presents a negative load to the input drive prime mover.

The invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows schematically a selection of radial configurations.

Figure 2 shows schematically an example axial configuration.

Referring to the drawing the permanent magnet differential reluctance torque limiting clutch comprises low reluctance rotor 1 axially and radially aligned with stator 2. Permanent magnet 3 is located within the rotor 1 stator 2 low reluctance circuit. When rotor and stator are aligned such that a low reluctance circuit is substantially complete the rotor and stator are magnetically attracted to one another. This magnetic attraction combined with adjacent higher reluctance 5 results in a detent torque which has to be overcome before relative rotation can occur.

When the detent torque is overcome the rotor is moved to align with a higher reluctance stator or rotor position 5 and detent torque drops to a low level, thus allowing relatively free rotation. During this phase of movement the next adjacent low reluctance section produces a magnetic attraction to pull the rotor into alignment.

This results in a negative or back-driving torque to the prime moving input which results in some energy being returned to the source. As the rotor stator alignment reaches another low reluctance position 4 detent torque rises tending to stop relative rotation. Torque limit can be raised by use of an increased number of permanent magnet pole pairs active at any one time. Torque can be further maximised by maintaining rotor stator air gap 6 at its minimum practical dimension. Drawings depict air as the higher reluctance material.

Claims

CLAIMS 1 A permanent magnet differential reluctance, torque limiting clutch, comprising a rotor constructed to form a pair or pairs of poles of a low reluctance magnetic material interspaced around a common rotation axis with higher reluctance sections, a stator constructed to form a pair or pairs of poles of a low reluctance magnetic material interspaced around the same common rotation axis with higher reluctance sections, and at least 1 permanent magnet incorporated into the low reluctance magnetic circuit.
2 A permanent magnet differential reluctance, torque limiting clutch, as claimed in Claim 1 wherein at any substantially common radius, the circumferential length of low reluctance material at any pole is no greater than the circumferential length of higher reluctance material interspaced between poles.
3 A permanent magnet differential reluctance, torque limiting clutch, as claimed in Claim 1 or Claim 2 wherein the rotor and stator are dimensioned and positioned to allow relative rotation whilst maintaining minimum gap between rotor and stator pole faces.

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4 A permanent magnet differential reluctance, torque limiting clutch, as claimed in Claim 2 or Claim 3 wherein the magnetic axes at the rotor stator interface are substantially radial to the common axis of rotation.
5 A permanent magnet differential reluctance, torque limiting clutch, as claimed in Claim 2 or Claim 3 wherein the magnetic axes at the rotor stator pole faces are substantially axial and parallel to the common axis of rotation.
6 A permanent magnet differential reluctance, torque limiting clutch, as claimed in Claim 4 or Claim 5 wherein the rotor is fixed and the stator rotates relative to the rotor.
7 A permanent magnet differential reluctance, torque limiting clutch, as claimed in Claim 4 or Claim 5 wherein the stator is fixed and the rotor rotates relative to the stator.
8 A permanent magnet differential reluctance, torque limiting clutch, as claimed in Claim 4 or Claim 5 wherein the stator is fixed relative to the rotor and both the rotor and stator rotate relative to ground.
9 A permanent magnet differential reluctance torque limiting clutch, as claimed in any preceding claim wherein energy is

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returned to the prime mover by means of magnetic attraction between non aligned rotor and stator, producing negative torque during relative motion of stator and rotor.
10 An accumulation conveyor roller comprising a permanent magnet differential reluctance, torque limiting clutch, as claimed in any preceding claim.