GB2050623A

GB2050623A - Torque sensing apparatus

Info

Publication number: GB2050623A
Application number: GB8015454A
Authority: GB
Original assignee: Sangamo Weston Ltd; Sangamo Weston Inc
Current assignee: Sangamo Weston Ltd; Atos Origin IT Services Inc
Priority date: 1979-05-16
Filing date: 1980-05-09
Publication date: 1981-01-07

Abstract

A shaft torquemeter 10 comprises first and second rotors coaxially secured to the shaft 12 at axially spaced apart points, one of the rotors being attached to the shaft via a torque tube 20. The first rotor 14 has radially outwardly projecting teeth 16, and the second rotor coaxially surrounds and is coplanar with tile first rotor and has radially inwardly projecting teeth 22 which project into the spaces between the teeth of the first rotor to define gaps 24. A single inductive sensor 30 is positioned adjacent the teeth and gaps, and produces a pulse signal in which the pulse spacing varies with the width of the gaps circumferentially of the rotors and therefore with torque. In alternative embodiments, only one of the rotors has radially projecting teeth, the other having axially projecting teeth. The inductive sensor 30 may further be replaced by electro-optical means. <IMAGE>

Description

SPECIFICATION Torque sensing apparatus This invention relates to torque sensing apparatus, and is more particularly but not exclusively concerned with torque sensing apparatus for sensing torque applied to a shaft of a gas turbine engine. One known form of torque sensing apparatus, described for example in US Patent No. 3 548 649, comprises two axially spaced apart toothed wheels secured to respective longitudinally spaced points on a shaft for which the applied torque is to be sensed. Each toothed wheel has axially projecting teeth, which project from its periphery towardslthe other toothed wheel and into the spaces between the teeth thereof. The respective teeth of the two axially spaced wheels are thus interlaced, and define therebetween gaps whose widths vary with changes in the torque applied to the shaft.

This known apparatus has the advantage that only a single sensing device, normally inductive and responsive to the widths of the gaps, is required, so that only a single channel of electronic circuitry is required to process the output signal produced by the sensing device.

However, the known apparatus suffers from the disadvantage that the toothed wheels, by virtue of their axially projecting teeth, are relatively difficult and expensive to manufacture. For the same reason, the toothed wheels have significant axial extent around the whole circumference of the shaft, which can be inconvenient in some applications.

It is an object of the present invention to provide torque sensing apparatus which retains the single sensing device and single signal processing channel advantage of the abovementioned known apparatus, while alleviating at least some of the disadvantages.

According to one aspect of the present invention, there is provided torque sensing apparatus for producing an electrical output signal representative of the torque applied to a shaft, the apparatus comprising: first and second toothed rotor members secured to said shaft at axially spaced apart positions thereon, the teeth on one rotor member projecting into the spaces between the teeth on the other rotor member to define therewith gaps whose respective widths, circumferentially of the rotor members, vary with changes in the torque applied to said shaft; and means responsive to the respective widths of at least alternate ones of said gaps to produce said output signal; wherein the teeth of at least one of the rotor members are radially projecting teeth which project radially into the spaces between the teeth of the other rotor member.

According to another aspect of the present invention, there is provided torque sensing apparatus for producing an electrical output signal representative of the torque applied to a shaft, the apparatus comprising first and second toothed rotor members secured to said shaft at axially spaced apart positions thereon, and means responsive to the relative angular positions of said rotors to produce said output signal; wherein said first rotor member has radially outwardly projecting teeth, and said second rotor member is annular and arranged to coaxially surround said first rotor member, and has radially inwardly projecting teeth which project into the spaces between the teeth of the first rotor member to define therewith gaps whose respective widths, circumferentially of the rotor members, vary with changes in the torque applied to said shaft; and wherein said angular position responsive means comprises means responsive to the respective widths of at least alteranate ones of said gaps.

The invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a somewhat diagrammatic perspective view of a first embodiment of shaft torque sensing apparatus in accordance with the present invention; Figure 2 is a sectional view of the apparatus of Figure 1; Figure 3 is an end view of part of the apparatus of Figure 1; Figure 4 is a much simplified block diagram of circuitry forming part of the apparatus of Figure 1; Figure 5 is a somewhat diagrammatic sectional view of a second embodiment of shaft torque sensing apparatus in accordance with the present invention; Figure 6 is an end view of part of the apparatus of Figure 5; Figure 7 is a somewhat diagrammatic sectional view of a third embodiment of shaft torque sensing apparatus in accordance with the present invention; and Figure 8 is an end view of part of the apparatus of Figure 7.

The shaft torque sensing apparatus of Figures 1 to 4 is indicated generally at 10, and is arranged to sense the torque applied to a shaft 12 eg of a gas turbine engine.

The apparatus 10 comprises a first (or inner) rotor 14, which is secured to and therefore rotates with the shaft 12. The rotor 14 is relatively thin axially, and has a plurality of equiangularly spaced-apart, radially outwardly projecting teeth 16.

Coaxially surrounding the rotor 14 is an annular second (or outer) rotor 18, which is secured to the shaft 12, at a point significantly axially spaced from the rotor 14, by means of a stepped torque tube 20. The rotor 1 8 also is relatively thin axially, and has a plurality of radially inwardly projecting teeth 22 whose angular spacing is the same as that of the teeth 1 6 and which projects into the spaces between the teeth 1 6 to define therewith gaps 24.

The rotors 14 and 1 8 are typically made from a ferromagnetic material such as mild steel, either directly by stamping, or by stamping followed by an erosion technique such as spark erosion (applied to the outer periphery of an annular disc for the rotor 14, to form the teeth 1 6, and to the inner periphery of an annular disc for the rotor 18, to form the teeth 22). The securing of the rotors 14, 18 to the shaft 12 is effected by welding, typically electron beam welding.

The apparatus 10 further includes an inductive sensing device 30, which is positioned adjacent the rotors 14 and 1 8 and secured to a fixed structure 31 of the engine or other machine in which the apparatus 10 is being used. The sensing device 30 comprises an approximately E-shaped ferromagnetic member 32, of which the two outer projecting limbs 34 and 36 are formed by permanent magnets and extend parallel to the axes of, and into proximity with, the rotors 14 and 1 8 respectively.The limbs 34, 36 are magnetically coupled together by the main (or "upright") limb 38 of the member 32, which is made of soft iron and extends radially of the rotors 14, 1 8. The middle projecting limb 40 of the member 32 also extends parallel to the axes of the rotors 14, 1 8, but into close proximity with the teeth 16, 22 and the gaps 24 defined therebetween. The limb 40 is constituted by a soft iron core which is secured to the main limb 38 and around which is wound a coil 42.

The output of the coil 42 is coupled via an input buffer amplifier 44 to the input of a squaring amplifier 46, whose output is coupled to the clock input of a bistable circuit 48, connected for example as a divide-by-two frequency divider. The output of the bistable circuit 48 is connected to digital timing circuitry 50, of any convenient form, arranged to produce a digital output signal representative of the mark-space ratio of the output singnal produced by the bistable circuit 48, and/or to a moving coil measuring and indicating instrument 52.

In operation, changes in the torque applied to the shaft 12 vary the relative angular positions of the rotors 14 and 18, and thus vary the widths, circumferentially of the rotors, of the gaps 24 defined between the teeth 16,22: it will be appreciated that as the torque increases, one set of alternate gaps 24 increases in with, while the other set decreases in width, and vice versa. The output signal produced by the coil 42 therefore effectively comprises a composite signal made up of two interleaved sets of alternate pulses, each pulse of one set corresponding to the passage of a tooth 1 6 past the magnet 40 of each pulse of the other set corresponding to the passage of a tooth 22 past the magnet 40: both sets of pulses have the same frequency, and their phase difference is dependent upon the torque applied to the shaft 12.

The pulses are amplified and squared in the amplifiers 44 and 46, and then applied to and frequency-divided by the bistable circuit 48. The bistable circuit 48 thus produces a square wave type output signal whose mark-space ratio is a measure of the aforementioned phase difference, and therefore of the torque applied to the shaft 12.

and whose amplitude is accurately predetermined.

The square wave type output signal of the bistable circuit 48 is processed to determine its markspace ratio in the circuitry 50, which produces a torque representative output signal usabie for display and/or control purposes, and also directly drives the instrument 52, which is calibrated to produce a torque indication.

The torque sensing apparatus 10 described above has a number of significant adavantages over the apparatus described in the aforementioned US patent For example, the rotors 14 and 1 8 can be made with relatively high tooth accuracy using relatively simple manufacturing techniques. Additionally a larger radius of active tooth area, and a more effectively coupled magnetic circuit, are achievable, both of which contribute to a high level of output signal from the coil 42 and therefore to a better singal-to-noise raltio. Finally, the use of thin single plane rotors reduces the mass secured tooth shaft 12 and also reduces the possibility of shaft alignment errors (which would lead to mark-space errors).

A number of modifications can be made to the torque sensing apparatus 10. For example, and as shown in Figures 5 and 6, the rotors 14 and 18 can be provided with axially extending annular portions 60 and 62 respectively, which are arranged to define smali radial air gaps with the outer limbs 34, 36 respectively of the E-shaped member 32 and thus enhance the magnetic coupling between the memer 32 and the rotors 14, 1 8. Alternatively, the inductive sensing device 30 can be replaced by an optical sensing device, for example formed by a combined solid state light source and light dectector postioned to direct light through the gaps 24 between the teeth 1 6, 22 and to receive light reflected from a reflecting surface provided on the inside 64 of the radiallyextending stepped portion 66 of the torque tube 20: the light detector thus produces an output signal analogous to that produced by the coil.

Another modification which can be made to the torque sensing apparatus 10 is illustrated in Figures 7 and 8, in which it can be seen that the outer rotor 1 8 of Figures 1 to 3 has been replaced by an annular rotor 70 having extending teeth 72.

The teeth 72 have the same angular spacing as the teeth 1 6 and project axially into the spaces between the teeth 16 to define therewith gaps 74 which serve the same purpose as as the gaps 24 of Figures 1 to 3. It will be appreciated that the teeth 1 6 can equally be regarded as projecting radially into the spaces between the teeth 72 to define therewith the gaps 74.

In the apparatus of Figures 7 and 8, the inductive sensing device 30 of Figures 1 and 2 has also been replaced, by å slightly different inductive sensing device 76. The device 76 comprises a ferromagnetic rod-like pole member 78, whose axis is aligned with the axially extending teeth 72 and upon which the coil 42 is wound. One end of the pole member 78 is disposed closely adjacent the teeth 1 6, 72 and the gaps 74, while the other end abuts a permanent magnet 80.

The operation of the apparatus of Figures 7 and 8 is completely analogous to the operation of the apparatus 10 as described hereinbefore.

In the apparatus of Figures 7 and 8, the respective radii of the rotor 14 at the roots and tips of the teeth 116 can be selected such that they are respectively just less than and just more than the radius of the torque tube 20, in which case the torque tube 20 need not be stepped, but can simply have the teeth 72 formed in one axial end thereof.

finally, if desired, the inner rotor 14 of Figures 1 to 3 can be modified to have axially projecting teeth Instead of radially outward projecting teeth, the radially inwardly projecting teeth 22 of the outer rotor 1 8 projecting radially into the spaces between these axially projecting teeth to define therewith gaps analogous to the gaps 24.

Claims

1. Torque sensing apparatus for producing an electrical output signal representative of the torque applied to a shaft, the apparatus comprising: first and second toothed rotor members secured to said shaft at axially spaced apart positions thereon, the teeth on one rotor member projecting into the spaces between the teeth on the other rotor member to define therewith gaps whose respective widths, circumferentially of the rotor members, vary with changes in the torque applied to said shaft; and means responsive to the respective widths of at least alternate ones of said gaps to produce said output signal; wherein the teeth of at least one of the rotor members are radially projecting teeth which project radially into the spaces between the teeth of the other rotor member.

2. Apparatus as claimed in claim 1, wherein the first rotor member has radially outwardly projecting teeth, and the second rotor member has radially inwardly projecting teeth.

3. Apparatus as claimed in claim 1, wherein the first rotor member has radially outwardly projecting teeth, and the second rotor member has axially projecting teeth.

4. Apparatus as claimed in claim 2 or claim 3, wherein the teeth of the first rotor member are substantially radially aligned with the position at which the first rotor member is secured to the shaft, and the second rotor member is secured to the shaft via a tube coaxial with the shaft.

5. Torque sensing apparatus for producing an electrical output signal representative of the torque applied to a shaft, this appartus comprising first and second toothed rotor members secured to said shaft at axially spaced apart positions thereon, and means responsive to the relative angular positions of said rotors to produce said output signal; wherein said first rotor member has radially outwardly projecting teeth, and said second rotor member is annular and arranged to coaxially surround said first rotor member, and has radially inwardly projecting teeth which project into the spaces between the teeth of the first rotor member to define therewith gaps whose respective widths, circumferentially of the rotor members, vary with changes in the torque applied to said shaft; and wherein said angular position responsive means comprises means responsive to the respective widths of at least alternate ones of said gaps.

6. Apparatus as claimed in any preceding claim, wherein the gap width responsive means is of the variable inductance type.

i. Apparatus as claimed in claim 6, wherein the gap width responsive means comprises an elongate ferromagnetic member having one end disposed adjacent the teeth and gaps and having a coil wound therearound.

8. Apparatus as claimed in claim 7, wherein the other end of said elongate member abuts a permanent magnet.

9. Apparatus as claimed in claim 2 or claim 5, wherein the gap width responsive means comprises an approximately E-shaped magnetic member of which the three projecting limbs extend substantially parallel to the axis of the rotors into proximity therewith, the respective ends of the outer ones of the projecting limbs being adjacent the first and second rotors respectively, and the middle projecting limb terminating adjacent the teeth and gaps and having a coil wound therearound.

10. Apparatus as claimed in claim 8, wherein said two outer limbs are permanent magnets, while the remainder of the magnetic member is made of a ferromagnetic material.

11. Torque sensing apparatus substantially as herein described with reference to Figures 1 to 4 of the accompanying drawings.

12. Torque sensing apparatus substantially as herein described with reference to Figures 1 to 4, as modified by Figures 5 and 6 of the accompanying drawings.

1 3. Torque sensing apparatus substantially as herein described with reference to Figures 1 to 4, as modified by Figures 7 and 8, of the accompanying drawings.