WO2000058704A1

WO2000058704A1 - Torque and speed sensor

Info

Publication number: WO2000058704A1
Application number: PCT/GB2000/001163
Authority: WO
Inventors: Lutz Axel May; John Owsley
Original assignee: Fast Technology Ag.
Priority date: 1999-03-26
Filing date: 2000-03-27
Publication date: 2000-10-05
Also published as: EP1166069A1; JP2003523501A; IL145534A0; GB9907130D0; AU3447100A

Abstract

A magnetic-based torque transducer of the kind which emanates a magnetic field in dependence upon torque in a rotatable shaft is provided with means to perturbate the otherwise constant field in order to provide speed and/or position measurement. A magnetoelastic, circumferentially magnetised transducer element (122) forming an integral portion of a shaft (120) may be provided with adjacent indentations (124, 126) or projections (102a, 102b) or a ring of magnetic elements (102e) to modulate the emanated magnetic flux sensed by detector (136). A single perturbating member may be provided or a ring of such members. In the latter case two defectors (140, 142) may be provided offset by a half-pitch phase difference. The detector signals are combined to provide torque and speed outputs. Also described are embodiments of longitudinal and radially spaced magnetisations to which the same field perturbation technique are applicable.

Description

Title: Torque and Speed Sensor

FIELD OF THE INVENTION

This invention relates to a torque transducer arrangement for use in sensing a torque and to a sensor system incorporating such an arrangement. The invention has particular, though not exclusive, concern with the sensing of speed and/or angular position of a rotatable shaft .

The invention will be particularly described in relation to transducer elements which are of magnetoelastic material and which are circumferentially magnetised, that is are of an annular form, e.g. circular form, which is magnetised in a closed loop around the annulus . However, the invention has wider application to other magnetic-based transducer elements which need not necessarily utilise the phenomenon of magnetoelasticity in generating a torque-dependent or force-dependent measurement flux. Examples of this more general class of elements are what will be called herein "longitudinal magnetisation" and "radially-spaced magnetisation" .

Longitudinal magnetisation provides an annulus of magnetisation, on a torque-transmitting shaft for example, in which the magnetisation extends in an axial direction at the surface over a defined length and acts to provide a closed loop of magnetic flux within the shaft. This may be visualised as a torus of magnetic flux. This torus of flux is distorted under torque to provide a torque- dependent tangential component of magnetic field, that is a component normal to the radial direction. Radially-spaced magnetisation is particularly applicable to disc-like parts subject to torque about the disc axis. The disc-like part is of relatively short axial thickness and has two radially-spaced annular zones, e.g. circular in the most common form, which in the limit may be contiguous. The pair of spaced zones are each longitudinally magnetised in the axial direction or each circumferentially magnetised in a closed loop about the axis. In each case a torque-dependent field is generated in a direction which is circumferential to the two zones, that is a field component that is tangential or normal to the radial direction. Transducer elements based on longitudinal magnetisation and radially-spaced magnetisations also provide an output measuring field which is zero at zero applied torque.

Longitudinal magnetisation and radially-spaced magnetisations are described further below. As already indicated, the present invention will be described particularly with reference to the known art of circumferential magnetisation transducer technology as applied to the measurement of torque. BACKGROUND TO THE INVENTION

Magnetoelastic torque sensors have been described in which a transducer element in the form of a ring or torus of magnetoelastic material is secured to rotate with a shaft rotating about its longitudinal axis. The ring is circumferentially magnetised and torque transmitted from the shaft to the ring causes the ring to emanate an external flux which is proportional to the torque. The external flux is essentially zero at zero torque. The sensor also comprises an assembly of one or more magnetic field sensing devices mounted in a non-contacting manner adjacent the transducer ring to respond to the emanated magnetic flux. Examples of this form of ring transducer element are disclosed in U.S. patents 5,351,555, 5,465,625 and 5,520,059 (all in the name of Garshelis and assigned to Magnetoelastic Devices, Inc.). Patent 5,520,059 also discloses transducer elements using more than one zone of circumferential magnetisation, in which adjacent zones are of opposite polarity, and means for establishing circumferential fields in transducer elements. One disadvantage of the use of a ring type transducer element lies in the need to securely attach it to the shaft to ensure that torque generated in the shaft is transmitted to the ring, and the attendant complexity and cost of special measures to this end.

Another proposal for a torque transducer element is to provide it as an integral or unitary portion of the rotating shaft as is described in International Patent application PCT/GB99/00736 filed 11th March, 1999, published under the number O99/56099. A circumferential field is established in a portion of a shaft of a material exhibiting magnetoelastic properties without the need for the special measures previously proposed.

Examples of shafts incorporating integral transducer elements are illustrated in Figs, la, lb, lc and Id of the accompanying drawings .

Fig. la shows a solid shaft 10 of a material exhibiting magnetoelasticity and having a portion 12 that has been circumferentially magnetised. Portion 12 is shaded for clarity of illustration. It is integral with the remainder of the shaft, i.e. it is homogeneous with at least the adjoining portions of the shaft. The arrow M indicates the direction of circumferential magnetisation. It will be appreciated that two opposite polarities of magnetisation are possible. The shaft 10 is rotatable about its longitudinal axis A-A. In the absence of torque, the circumferential field is contained within the portion 12. A non-contacting sensor 14 (which diagrammatically represents an assembly of one or more sensor devices arranged as desired) is mounted non- contactingly adjacent the transducer element provided by portion 12. It will detect no field in the absence of torque. If the shaft is rotated about its axis A-A, the resultant torque causes the emanation of magnetic field from the transducer element in proportion to the torque. Thus the output of sensor 14 provides a measure of torque and is processed by signal-processing circuitry 16 to produce a signal T representing the sensed torque. The generally accepted theory of operation of circumferen- tially-magnetised, magnetoelastic transducer element is that under torque the internal field skews so that one side 18 of the element provides a North pole say and the other side 19 a South pole. The polarity depends on the polarity of the torque. An external flux linkage is established between the poles that can be sensed by an external sensing device.

Various types of sensing devices are employable, for example, magnetic field sensitive elements such as Hall effect devices, magnetoresistive devices, magnetometers, and saturable inductors whose point of saturation is a function of the external field. An example of a saturable inductor type of circuit is disclosed in International Patent Application PCT/GB98/01357 published as O98/52063.

Fig. lb shows a modification of the Fig. la arrangement in which the rotatable shaft 10 is provided with two circumferentially magnetised portions 20 and 22 respectively of opposite polarity. They are contiguous or closely adjacent but spaced. A sensor arrangement 24 includes devices responsive to the respective fields emanated by the transducer elements 20 and 22. Such an arrangement may be used in" compensating for an external magnetic field, such as the Earth's field, in the environment in which the shaft is employed. Another example of the use of multiple circumferential fields is shown in Fig. lc. In this case three adjacent circumferentially magnetised zones 26, 28 and 30 are applied to the rotatable shaft 10. The inner region 28 acts as the transducer element and is bounded by the regions 26 and 30 of opposite polarity which act as guard zones enhancing the emanation of torque-dependent flux from the inner transducer element 28. It will be understood that in Figs, lb and lc, the lines indicating a demarcation of the multiple circumferentially-magnetised regions are notional and provided for clarity of illustration. Fig. Id shows another embodiment in which a shaft 34 is shaped by machining, casting or otherwise to provide an integral annular zone 36 projecting beyond the remainder of the shaft profile 38. This annular zone 36 is circumferentially magnetised (M) to provide the transducer element. The annular zone is thus integral with the solid shaft as indicated by cut-away 37 and is homogeneous with the magnetoelastic material of the shaft. The raised profile of the transducer element has sides 39 and 40

(which may be sloped) that enhance the emanation of torque-dependent flux for sensing by the non-contacting sensor arrangement 14.

For brevity the kind of profile configuration illustrated in Fig. Id may be referred to as the raised profile configuration, and the configurations of Figs, la- lc may be referred to as the flat profile configuration. All the above embodiments la-Id are further described and explained in above-mentioned publication W099/56099.

In the proposals described above, the output signal from the magnetic field sensor device is essentially constant at constant torque. The field does not vary significantly around the circumference of the shaft. In various circumstances, the need arises to provide rotational speed data for the rotating shaft and possibly also position data.

Proposals to meet this requirement have been described in "A Single Transducer for Non-Contact Measurement of the Power, Torque and Speed of a Rotary Shaft", I. J. Garshelis, C.R. Conto and W. S. Fiegel, SAE Technical Paper Series No. 950536 published 1995 by the Society of Automotive Engineers, Inc. Reference may also be made to U.S. patent 5,708,216 (Ivan J. Garshelis) . The proposals in both the above-reference and paper are concerned with the provision of speed sensing with a magnetoelastic transducer means which is specifically described as being of the separate ring type. SUMMARY OF THE INVENTION

The present invention provides means for obtaining speed and/or position data for a rotating shaft to which is applied a magnetic-based torque sensor arrangement. This may use one or more circumferentially magnetised transducer elements of the kind integral with the shaft, longitudinally magnetised transducer elements of the kind mentioned above, or radially-spaced magnetised transducer elements of the kind mentioned above. The present invention will initially be further described in relation to embodiments of the circumferentially magnetised integral torque-transducer element kind. Broadly stated, in one aspect of the invention there is provided a torque transducer arrangement as set forth in Claim 1. This may be implemented using circumferential magnetisation as set forth in Claims 2 and 3 , longitudinal magnetisation as set forth in Claim 4, or radially spaced magnetisation as set forth in Claim 8. In another aspect the invention provides a torque transducer system as set forth in Claims 24 or Claim 29. BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its practice will be further described with reference to Figs. 2a-19 of the accompanying drawings, in which:

Figs, la to Id illustrate the four earlier proposals for torque transducer elements that are integral with a shaft rotating about its axis;

Figs. 2a and 2b are longitudinal and cross-sections respectively of one embodiment of the present invention; Figs. 3a and 3b are longitudinal and cross-sections of another embodiment of the present invention;

Figs. 4a and 4b show the typical emanated flux output with the embodiments of Figs. 2a, 2b and 3a, 3b respectively;

Fig. 5 shows a block diagram circuit for a sensor system and usable with the embodiments of Figs. 2a, 2b and Figs. 3a, 3b;

Fig. 6 is a perspective view of a shaft having a number of sections showing different arrangements of rings of members for producing multiple perturbations in the output magnetic field for each rotation of the shaft;

Fig. 7 is a typical signal waveform obtained from a magnetic field sensor device when the transducer element is implemented with one of the sections of Fig. 6; Figs. 8a and 8b show perspective views of shafts provided with a respective ring of flux-perturbating indentations to each side of the transducer element;

Fig. 9 shows a perspective view, similar to Fig. 8b, of an embodiment having rings of projections;

Fig. 10 shows a perspective view of a shaft provided with a ring of flux-perturbating magnets to each side of the transducer element;

Fig. 11 shows a shaft section showing placement of a pair of sensor devices to provide out-of-phase signals;

Fig. 12 is a block diagram of a circuit for processing the signals from the pair of sensor devices of Fig. 11;

Figs. 13a to 13d illustrate perspective views of shafts having multiple circumferentially magnetised regions with flux-perturbating rings of members; and

Fig. 14 illustrates another embodiment for the implementation of a ring of magnetic flux-modulating members ; Fig. 15 shows the creation of a zone of longitudinal magnetisation in a portion of a shaft;

Fig. 16a illustrates the toroidal form of magnetic flux in the longitudinal magnetised zone;

Fig. 16b illustrates the toroidal form of magnetic flux established by a two-step magnetisation process;

Figs. 17a and 17b illustrate the generation of a torque-dependent magnetic field vector component with a longitudinally magnetised transducer element in the absence of pre-torquing in accord with the invention, with the element under zero torque and under torque respectively and Fig. 17c is a magnetic vector diagram;

Figs. 18a and 18b show a torque-transmitting disc to which the invention is applicable, Fig. 18a showing a view of one face of the disc and Fig. 18b showing an axial section to which is added the magnetising arrangement for establishing radially-spaced annular zones of magnetisation and Fig. 18c is a magnetic vector diagram; and

Fig. 19 shows a view of one face of a modification of the disc arrangement of Figs. 18a and 18b for circumferentially-magnetised annular zones. DESCRIPTION OF PREFERRED CIRCUMFERENTIAL MAGNETISATION EMBODIMENTS

The embodiments to be initially described will assume a single transducer element, circumferentially magnetised as described, for example, with reference to Fig. la. For clarity of illustration the provision of flux-enhancing measures, such as the guard rings of Fig. lc are not shown. In these embodiments means are introduced into the circumferentially magnetised region or zone to produce at least one perturbation in the field as the shaft rotates. This may be done in various ways. Fig. 2a shows a solid shaft 80 of circular cylindrical form having a region 82 of circumferential magnetisation M providing a torque-sensitive transducer element. The element here is of the flat profile kind. The shaft is rotatable about its longitudinal axis. The otherwise smooth circumference of region 82 is provided with an indentation 84 interrupting the smooth circumference as seen in the cross-section of Fig. 2b taken through the region 82. This shaping feature provides a perturbation in the detected torque-dependent magnetic flux as the shaft rotates. Figs. 3a and 3b show the shaping feature in the region 82 being a projection 86 to produce the perturbation of the field as the shaft rotates.

It is to be noted that the shape feature 84 or 86 does not have to extend the whole axial width of the magnetised region 82, on the other hand it may extend further. The effect of the indentation 84 or projection 86 is illustrated in Figs. 4a and 4b, respectively. It is assumed that the shaft 80 is rotating and thus is under torque. The figures show the variation of external detectable field (flux) with shaft angle θ for each full 360° rotation of the shaft. The field is at a level F that is proportional to the torque. The effect of the shape feature is to produce a perturbation in the level F that is a downward pulse 88 for an indentation and an upward pulse 90 for a projection. These field pulses are thus reproduced in the output of the sensor device arrangement. This can be exemplified by the single field sensing device 14 in Fig. la.

Fig. 5 shows a processing circuit 92 for the signals from sensor device 14. The signal from the sensor device 14 is processed to separate the flux level component F from the perturbation pulse component 88 or 90 in units 94 and 96 which process the respective components. Conse- quently, the unit 94 is operable to effectively ignore the perturbation pulses to provide an output signal T representing torque and unit 96 is operable to detect and time successive perturbation pulses as the shaft rotates to provide a rotational speed output S. This signal processing may be done by analogue or digital hardware or implemented entirely in a software routine.

Consideration can now be given to more complex arrangements for producing output field perturbations. In particular it may be desirable to produce a number of pulses for each rotation of the shaft.

Referring to Fig. 6, there is shown a variety of means for inducing perturbations in the flux emanated by a magnetoelastic transducer element. For simplicity of illustration, all the measures proposed are shown in a single shaft though it will be understood that each measure illustrated is independently employable. All the proposals to be now discussed provide a plurality of perturbation-inducing features arranged uniformly around the circumference of the shaft . Thus at a constant rotation speed a constant pulse rate is generated proportional to the speed.

Shaft 100 in Fig. 6 illustrates the following sections. Sections 102a and 102b each show a ring of regular (uniformly spaced in the circumferential direction) projections, these being of a rectangular and round shape respectively. Sections 102c and 102d conversely show a ring of regular indentations of rectangular and round shape respectively. The indentations or projections in a ring are all identical.

Another possibility is to incorporate active magnetic poles as seen in Section 102e. Here a ring of alternate North and South poles 104 and 106 respectively are formed around the shaft circumference. This ring of magnetic poles modulates the external flux emanating from the transducer element. The poles 104 and 106 may be formed on a strip of thin tape, e.g. magnetic tape, affixed to the shaft. Individual poles 104 and 106 may be individual NS magnets in the radial direction or they may be formed from circumferentially extending magnets having north (N) poles adjacent and south (S) poles adjacent in alternation.

Another way of implementing the kind of ring structures illustrated and further discussed below is seen in Fig. 14 to which further reference is made later.

The rings of members of the various sections 102a- 102e may be located within a circumferentially magnetised region such as 82 in Fig. 2a or Fig. 3a providing multiple perturbations per rotation rather than just one. Alternatively, these rings of members may be applied to be located adjacent the magnetised transducer region as will appear from embodiments of the invention described below. The measures illustrated in Fig. 6 have the advantage of a greater pulse rate per rotation to assist in speed measurement techniques. It is also possible to introduce a means of indexing the actual angular position of the shaft from which actual position can be measured by counting the numbers of pulses. The index point could, for example, be marked by an indentation in a ring of projections or vice versa, by adding an extra indentation or projection into a regular ring of indentations or projections respectively and/or an irregularity or offset in the positioning of the individual members of a ring of projections, indentations or magnetic poles to provide a position-based index as the shaft rotates, or by having an amplitude variation introduced by a larger or smaller member of the ring.

It will be appreciated that the techniques described with reference to flat profile shafts can be equally applied within the transducer elements of raised profile shafts of the kind illustrated in Fig. Id, and to separate ring transducer elements attached to shafts.

Referring again to the various sections shown in Fig. 6, it will be seen that adjacent members of a ring, whether they are indentations, projections or magnets are separated by portions of the cylindrical shaft surface 108. Thus in each section shown, it can be considered that there are portions 108 of locally unmodified shaft surface alternating with portions of locally modified shaft surface. Remembering that these sections are to be provided within a circumferentially magnetised region, such as 82 in Figs. 2a, 2b and Figs. 3a, 3b, it is presently preferred that the proportion of the shaft circumference constituted by modified surface should not exceed 50 per cent of the total circumference. This leaves at least an equal circumferential amount of unmodified shaft surface available for emanation of the torque-dependent flux.

Fig. 7 shows a typical output obtainable by employing one of the sections 102a-102e of Fig. 6 in the transducer element region . The output from the external magnetic field sensing device, e.g. device 14, becomes a series of pulses 110, processable to obtain the shaft rotation rate, while an average level 112 of the detected field represents the torque applied to the shaft. In many uses of a shaft, the rotational speed would increase with torque but this is not necessarily the case. In driving an increased load, the opposite may well be true.

As an alternative to providing a speed indicating means within the circumferentially magnetised region, such means can be provided adjacent one or both of the axially- spaced sides of the transducer element, which it will be recalled, provides the flux-emanating poles (Fig. la) at the axially spaced sides thereof. These pole-adjacent configurations modulate the flux detected by the external sensor arrangement . They preferably do not impinge to a significant extent on the surface of the region containing the circumferential magnetic field. Figs. 8a and 8b show examples of this. In Fig. 8a a circumferentially magnetised region 122 of a solid shaft 120 of magnetoelastic material is bounded by a respective ring 124, 126 of spaced indentations to each side of region 122 (shown in darker colour for clarity of illustration) . While indentations could be provided to only one side of region 122, it is preferred to use a respective ring of indentations to each side, the rings being identical with their indentations aligned. While Fig. 8a shows a flat profile embodiment, Fig. 8b shows a similar arrangement for an embodiment having a transducer element in the form of a raised profile ring 122' as described with reference to Fig. Id. In both of these embodiments the complete transducer system can use one or more magnetic field sensor devices adjacent the transducer element 122 or 122' similarly to Fig. la.

In the embodiments of Figs . 8a and 8b the indentations 124, 126 are replaceable by rings of projections, e.g. sections 102a, 102b of Fig. 6. One such variation is shown in Fig. 9 applied to a raised profile transducer element 122' in which the indentations are replaced by rings of projections 128, 130. Fig. 10 shows a flat profile embodiment in which the sides of the transducer element are bounded by respective magnet rings 132, 134 each of the kind shown at section 102e in Fig. 6. It is equally applicable to a raised profile transducer element .

In the embodiments of Figs. 8a, 8b and 9 the rings of members adjacent the sides of the transducer region together provide a series of aligned pairs of members . thus each pair has a localized perturbating effect on the flux emanated by the transducer region and linking in a generally axially direction between the opposite polarity sides of the region. Thus there will be a ripple effect in the magnitude of the detectable emanated flux around the circumference of the transducer region. The localised effect of each pair of members may be to enhance or reduce the magnetic field with respect to the field in the unmodified portions of the transducer region. For example, it is theorised that the indentations may provide additional surface area at the transducer region poles to enhance flux emanation while the projections may provide additional material to shunt flux into the shaft.

It is possible to combine two different types of members in each ring. For example a series of flux enhancing members interleaved with a series of flux reducing members providing a greater ripple effect (modulation) .

The rings of magnetic members such as illustrated in Fig. 10 is applied to provide the same localised enhancement or reduction of the detectable external flux involving a local distortion of the field emanated by the transducer. In this respect, a single ring of magnetic members may be sufficient. However a pair of rings may be used with a setting of the degree of offset of the axial alignment of the poles to adjust the degree of modulation detected on the torque-dependent field.

The provision of the or each ring of magnetic members can be done in various ways . The ring may be a sequence of alternating north and south poles formed on an adhesive magnetic tape as indicated in Section 102e of Fig. 6. In this case the individual magnets are radial . Alternatively the individual magnets can lie in the circumferential direction with like poles adjacent. Other possibilities include small magnets inserted into the shaft. Another possibility is the use of magnetic, but not necessarily magnetised, material to perturbate the emanated flux. Thus a series of areas of a magnetic material could be painted or coated onto the shaft to provide a ring of magnetic members. Another approach is to provide a ring of members in the form of a ring modified surface areas of the shaft. For example, locally applying a heat-shock to spaced areas around the shaft as by a laser in order to locally modify the permeability of the shaft. Such a result may also be achieved by a particle bombardment of the shaft at the required areas causing a local hardening of the shaft.

The magnetic field sensing arrangement can be implemented in various ways for the embodiments of Figs . 8a, 8b, 9 and 10. For example as shown in Fig. 8a a single sensor device 136 is mounted adjacent circumferential region 122. The flux linking the flux- emanating poles and externally bridging the region 122 for sensing by device 136 is modulated by the indentations (or projections or magnets) and thus a modulated waveform is obtained from the device from which both torque and speed measurement can be derived in a processing circuit 138 in a manner similar to the signal of Fig. 7. Although for simplicity Fig. 8a shows one sensor device, the sensor arrangement may comprise a plurality of such devices spaced uniformly or non-uniformly around the circumference .

Fig. 11 shows a sensor arrangement in which two sensor devices are used. This figure shows a cross- section through a shaft 120 having a circumferential magnetised region (not shown) forming a transducer element of the flat profile kind with a respective ring of indentations to each side, e.g. as in Fig. 8a. The cross- section illustrates one of the rings 126. In contrast to Fig. 8a, the section of Fig. 11 shows first and second sensor devices 140 and 142 angularly offset about the axis of rotation by an amount that provides one half-pitch phase difference in the emanated magnetic field sensed (the indentations are assumed to be spaced at a uniform pitch) . The sensor devices will preferably be actually mounted over the region 122 as in Fig. 8a. One device 140 is shown at a position of the shaft where it is sensing the flux emanating from a pole where it is at the shaft surface, i.e. between indentations) . The other device 142 is offset by a multiple of the pitch of the indentations plus a half-pitch so as to be located to sense the flux at an indentation position. It will be appreciated that as the shaft rotates about its axis, the sensor devices each produce an output signal such as that shown in Fig. 7, but the two output signals are 180° out of phase. The combined signals from the sensor will be substantially uniform to provide a measure of flux and thus torque. On the other hand by simultaneously subtracting the output signals, the direct component (DC) of the flux is removed leaving the pulsating component for use in speed measurement. The signal processing may thus be implemented by combining the outputs of devices 140 and 142 in sum and difference circuits (or equivalent implementations) to obtain the torque and speed signals. This kind of sensor device arrangement, which enables the pulses to be enhanced from the DC flux, may have advantage in circumstances where speed measurement is particularly important at low shaft rotation speeds. Such offsets also have the benefit of assisting the detection of an adequate level of emanated flux where torque is being measured in a stationary shaft. Fig. 12 shows the block diagram of a suitable circuit in which the outputs of devices 140 and 142 are both applied to summing unit 144 and difference unit 146 from which the signals representing the direct and pulsed flux components are further processed in units 148 and 150 to obtain the torque and speed signals T and S.

The practice of the invention may be extended to shafts with more than one circumferentially magnetised region, whether of the flat profile or raised profile transducer element kind. Examples of embodiments with plural transducer elements and plural rings of indentations/projections are shown in Figs. 13a to 13d.

Fig. 13a shows a shaft 160 with a pair of spaced circumferentially magnetised regions 162, 164 with three bounding rings 166, 168, 170 of indentations, one, 168, of which is common to both transducer elements. In Fig. 13a each transducer element is provided with a respective pair of cooperating sensor devices 140, 142 and 140', 142' for use in the manner described with reference to Figs. 11 and 12. The transducer elements 162 and 164 will normally be of opposite polarity magnetisation providing the compensation mentioned in connection with Fig. lb.

Fig. 13b shows another similar transducer arrangement to Fig. 13a but the shaft 160 having rings 172, 174, 176 of projections rather than indentations and applied to a raised profile transducer elements 162', 164' rather than flat profile transducers. The arrangements of Figs. 13a and 13b may be practised using rings of magnets. Fig. 13c shows a shaft 160 having three axially- spaced, circumferentially-magnetised regions 180, 182, 184 of the flat profile type (and shown darker for clarity) , in which normally the two outer regions 180, 184 would be of opposite polarity magnetisation to the inner region 182. Two rings 186, 188 of indentations bound the inner region 182 from which the torqued/speed dependent flux emanated is sensed In Fig. 13c, by having the regions 180 and 184 of opposite circumferential magnetisation polarity to that of inner region 182, the outer regions act as guard regions for the inner region 182 which provides the transducer element as in Fig. lc. The embodiment of Fig. 13c can be practised with raised profile transducer elements and/or rings of projections or magnets .

Fig. 13d shows the same principle extended to a shaft 160 having four spaced circumferentially-magnetised regions 192, 194, 196, 198. There are rings 200, 202, 204 of indentations between the magnetised regions 192, 194, 196, 198 but not axially exterior to the outer magnetised regions 192 and 198. Only the two inner regions 194 and 196 are bounded on each side by a ring of indentations. The same techniques are applicable whether the magnetised regions are of the flat profile or raised profile kind and whether the rings are indentations or projections or rings of magnets as shown in Fig. 6.

Fig. 13d has the four regions 192, 194, 196 and 198 of alternate polarity of magnetisation. It can be used in the manner of Fig. 13a to which guard regions have been added. The regions 194 and 196 are used as transducer elements whose opposite polarity of circumferential magnetisation enables compensation for external fields to be achieved (Fig. lb) . Regions 192 and 196 act as opposite polarity regions to enhance flux emanation from region 194, and regions 194 and 198 act in the same manner with respect to region 196. The rings of members 200, 202, 204 are at each side of the transducer regions, ring 202 being common to both.

Although in the various embodiments described above where a ring of members is provided to one side (axially) of a transducer region in order to perturbate or modulate the emanated flux, it is possible just to use a single ring, it is preferred to use a respective ring to each side of the transducer element .

In many cases the rings may be manufactured as a separate entity to the shaft and attached thereto. Fig. 14 shows an example of how this may be done and incorporates yet another flux modulating structure. As shown, it is particularly designed to provide a ring to be mounted at one side of a transducer element. In Fig. 14, the ring is made in the form of a clip 210 having a small gap 212 to enable the clip to be fitted onto the shaft.

The clip is secured by any appropriate means. To one side it is toothed 214. This is the side in proximity to the transducer element. The clip is of a magnetic material - it could have magnetised teeth. The toothed structure modulates the flux in the manner described above.

The various techniques described for modulation of the emanated flux to provide speed/position indicative information, has particularly referred to adjacent circumferentially-magnetised regions of opposite polarity. However, the invention is applicable in cases where adjacent regions of the same polarity are employed.

Embodiments have been described in which the means to perturbate the emanated flux from a transducer region is provided in the region itself. In general, it is preferred to employ the kinds of embodiment in which the perturbation is provided by means adjacent to but outside the transducer region itself . Such arrangements are considered to be more conducive to the long-life of the circumferential magnetic field but circumstances of an individual application of the invention may dictate that the perturbation is provided in the transducer region.

It will be understood that the various measures in accord with the invention involving rings of field- perturbating members can be independently applied to separate transducer regions. For example, the shaft such as illustrated in Fig. 8a, 8b, 9 or 10 can have two axially-spaced transducer regions with entirely independent rings of members associated with them. The rings of members for one region do not have to have the same angular pitch as for the other, i.e. different numbers of members in the respective rings. Each can independently supply speed data but the different rate of modulation of the outputs of the two transducer regions can be used to provide angular position also, as by use of phase comparison techniques or by having the signals conform to a simple digital code. By using more circumferentially magnetised regions each having respective rings of different angular pitches to modulate the output a more complex code can be established, e.g. in accordance with a Gray code .

Other means of perturbating the magnetic field are also contemplated. For example, in a tubular structure, particularly a thin-walled tube, means that influence the emanated field may be mounted in the tube. A toothed element for example could be inserted in the tube. An alternative is to locally modify the interior wall of the tube as by laser treatment .

Local modification of the structure of a shaft at grain size level (as in alloys) or molecular level may be utilised to provide a local modification of the magnetic property of the material. There is an advantage of a procedure which can be applied to the shaft without special machining or forming of the shaft . For example a local working of the shaft material to alter its magnetic property may be achievable by a punching/striking type of operation. An alternative method of locally modifying the structure of the shaft material may be to treat the material with laser energy.

It will also be appreciated that punching or laser treatment operations may be applied not only to modify the structure of the material, without significant mechanical deformation, but to cause mechanical deformation such as the indentations previously described.

The measures described in the foregoing paragraph and those previously described have been described specifically in relation to circumferential magnetisation in which there is a single detectable field component from a transducer element . In the application of the invention to longitudinal magnetisation and some forms of radially- spaced magnetisations (as described further below) , there is a field component which is little or not torque dependent. The measures described can be applied to the perturbation of this non-torque dependent flux component. Heretofore, it has been the case that the external flux available from a transducer region has been essentially zero at zero torque which may cause signal-to- noise ratio problems in the near zero torque region. This will affect both torque and speed measurement. The provision of a real measurable value of emanated flux under zero torque is achieved by the measures disclosed in our copending PCT application PCT/GB00/ filed

March, 2000 (publication No. WO (Lloyd Wise, Tregear Case 44462) and claiming priority from British patent application 99/06735.7, filed 23rd March, 1999. Briefly the copending application proposes a technique known as pre-torquing in which a circumferential field is established in a transducer element while it is under a predetermined torque. When the element is relaxed to a zero-torque state, the "distortion" of the stored field produces a measurable magnetic field component at zero torque. The same technique can be applied in transducer elements employing longitudinal magnetisation or radially- spaced magnetisation referred to above. These forms of magnetisation will be now further described, assuming the material of the transducer element (s) is ferromagnetic. LONGITUDINAL MAGNETISATION EMBODIMENTS

The nature of longitudinal magnetisation has been outlined above. The techniques of the invention taught above for a circumferentially magnetised transducer element are also applicable to a longitudinally magnetised transducer element or a pair of such elements. Fig. 15 shows how an annulus of longitudinal magnetisation is applied to an integral portion of a shaft. The portion is to provide a transducer element and it at least is of magnetic material. In Fig. 9 a shaft 310 of magnetic material is rotated about its axis so that a portion 352 of it is magnetised by the axially-spaced north-south poles NS of a magnet arrangement 350. This may be conveniently an electromagnetic which enables the magnetisation to be readily controlled. The magnet system may be moved about the shaft. The result of this magnetisation is to produce an annular zone of surface magnetisation 354 as shown in Fig. 16a having NS poles as indicated. It extends as an annulus about the shaft axis having the remanent magnetisation of the same polarity around the axis of the shaft and axially-directed. As indicated, the annular magnetisation tends to form a closed flux path within the shaft interior to annulus 354 so that a toroid of magnetic flux is established about the shaft axis. What is important is the magnetic field detectable exteriorly of the shaft as will be shortly explained.

The toroidal flux concept can be enhanced as is shown in Fig. 16b which shows a surface adjacent annular magnetised zone 354 within which an interior annular magnetised zone 356 of opposite polarity is established. The two zones combine as shown to provide the torus of closed loop magnetic flux. The magnetisation is obtained by a two-step procedure. Firstly a deep annular region of the polarity of zone 356 is formed by the magnet 350. Then the surface adjacent zone 354 is formed by reversing the magnetisation polarity of the surface adjacent region of the deep region.

Turning to the practical utilisation of the resultant transducer element, reference is made to Fig. 17a which shows the magnetic field of zone 354 as seen at the surface of the shaft in the absence of torque. The arrow Mf indicates a fringing field which will extend generally in the axial direction between the poles of region 354 in the ambient medium usually air.

Fig. 17b shows the effect of putting the shaft, and thus transducer element portion 352, under torque in one direction about the axis of shaft 310. The longitudinal field in zone 354 is skewed as shown by the arrows (the skew is exaggerated for clarity of illustration) . The external fringing field is likewise skewed or deflected as represented by magnetic vector Mf ' (Fig. lie) . Also generated is a vector component Ms which in this embodiment extends circumferentially about the circumference of shaft 310. The component Ms is tangential to the shaft at any point, that is perpendicular to the local radius. It is the Ms component that provides the component for measuring torque by means of an appropriate oriented magnetic field sensor or group of sensors. Ms is a function of torque. If the torque is in the opposite direction the direction of Ms is reversed. At zero torque, Ms has a zero value. To overcome the difficulty of measurement at zero or near zero torque, the solution adopted is the same as that given above for circumferential magnetisation, namely that of pre-torquing the shaft portion 352 while establishing the magnetisation of it so that on allowing the shaft to relax to zero torque, the quiescent field is skewed with a detectable Ms component. This technique can be extended to more than two longitudinally magnetised regions .

The various means for perturbating the emanating field described above can be adapted for longitudinal magnetisation embodiments. They may be applied to act on the torque-dependent component (Ms) or the fringe field component (Mr, Mr' ) . RADIALLY-SPACED MAGNETISATION The principles given above can be applied to radially-spaced magnetisations which find particular, though not exclusive, application in torque transmitting discs .

Figs. 18a and 18b show a face view and an axial section of a disc 410 which is mounted on a shaft 420 for rotation about its axis A-A and carries, for example, a gearing 424 at its outer periphery for enabling transmission of torque through the disc. Also shown is the provision of a magnet system comprising magnets 416 and 418 on opposite sides of the disc to establish two magnetised zones 412 and 414. Each zone is established as an annulus about the axis A-A, as by rotating the disc between the magnets. Each zone is longitudinally magnetised in that the magnetisation extends in the axial direction and the two zones 412 and 414 have opposite polarities of magnetisation. The two magnetised zones provide a transducer element 422 (the magnets 416, 418 being removed) which from face 411, say, appears as in the segment of the disc shown in Fig. 18a. At the surface 411 zone 412 provides an annular pole (N) of one polarity and zone 414 an annular pole (S) of the opposite polarity between which an exterior magnetic flux Mr (Fig. 18c) is established to link the poles. The exterior magnetic field vector is radial at any point around the annuli . Under torque the vector is deflected or skewed from the radial to a position Mr' to provide a circumferential or tangential component Ms which extends around the annulus. Ms is a function of torque having a zero value at zero torque unless pre-torquing is adopted. Thus as in the earlier described embodiments, the magnetised zones 412 and 414 are established while torque is applied (pre- torquing) so that a detectable value of Ms is generated when the disc is relaxed to a zero torque state.

Fig. 18a also shows sensors 228a-228d for detecting the circumferential component Ms and sensor 226a-226b for detecting the radial component Mr used as a reference. Fig. 19 illustrates how the disc-like torque transducer assembly can be adapted to work with circumferential magnetisation. Fig. 19 is a face view of a disc 550 through which torque is transmitted between a drive applied on the axis A and the periphery or vice versa as previously described. In this embodiment, there is a transducer region 552 which comprises an inner annular region 554 and an outer annular region 556. The regions 554 and 556 have opposite polarities of magnetisation as indicated by the respective arrows. The circumferential magnetisation may be applied through the face 558 using a magnet arrangement of the kind shown in above-mentioned WO99/56099 with reference to Fig. 14b.

In the absence of torque the circumferential fields in regions 554 and 556 will be trapped within the annular regions. However, under torque the fields become skewed in the manner well-known with prior art circumferential transducers, e.g. Garshelis U.S. patents 5,351,555, 5,520,059 and 5,465,627. The consequence is that at face 558 the regions 554 and 556 develop magnetic poles of opposite polarity. The polarity is dependent on the direction of torque.

A radial measurement field Ms is generated externally of the surface 558 between regions 554 and 556, the radial magnetic flux being a function of torque. The radial flux can be sensed by sensors disposed as for the radial (reference) flux in Fig. 18a, e.g. sensors 226a-d. In contrast to Fig. 18a it is seen that the detectable torque-dependent flux is radial, rather than circumferential, but there is no reference field component available .

The above modification also has a zero field Ms at zero torque unless the circumferential fields are established in regions 554 and 556 by pre-torquing the disc while establishing the fields in accord with the teaching given above.

The various means for perturbating the magnetic field described above in connection with the circumferential magnetisation embodiments can be adapted for radially- spaced magnetisation embodiments. In the case such as Figs. 18a-18c, the perturbation can be applied to either the torque-dependent component (Ms) or to the radial component (Mr, Mr' ) .

Claims

Claims :

1. A torque transducer arrangement comprising a region rotatable with the shaft about an axis and having an exterior annular surface and magnetised to emanate an external magnetic flux, and means associated with said region to cause at least one perturbation in the detectable external magnetic field as the shaft rotates.

2. A torque transducer arrangement as claimed in Claim

1 in which said region is an integral portion of a shaft, rotatable about an axis, and said exterior annular surface extends about said axis.

3. A torque transducer arrangement as claimed in Claim

2 in which said region is circumferentially magnetised.

4. A torque transducer arrangement as claimed in Claim 1 in which said exterior annular surface extends about an axis of rotation and is parallel to said axis, and said region is longitudinally magnetised in the axial direction.

5. A torque transducer arrangement as claimed in Claim 4 in which said region is an integral portion of a shaft rotatable about said axis.

6. A torque transducer arrangement as claimed in Claim 5 in which the perturbation causing means is located to provide at least one perturbation in a torque-dependent magnetic field at right angles to the axis of rotation as the region rotates.

7. A torque transducer as claimed in Claim 5 or 6 in which the perturbation causing means is located to provide at least one perturbation in an axially-directed magnetic field associated with said longitudinally-magnetised region .

8. A torque transducer arrangement as claimed in Claim 1 in which said exterior annular surface extends in a plane transverse to an axis of rotation, and said region comprises two radially spaced annular zones of magnetisation, the two zones being of opposite polarities of magnetisation.

9. A torque transducer arrangement as claimed in Claim 8 in which said plane is normal to the axis of rotation.

10. A torque transducer arrangement as claimed in Claim 8 or 9 in which said two radially spaced zones of magnetisation are each magnetised in an essentially axial direction to provide annular poles of opposite polarity at said surface .

11. A torque transducer arrangement as claimed in Claim 8 or 9 in which said two radially spaced zones of magnetisation are each magnetised in a circumferential direction, the circumferential magnetisations of the two zones as present at said surface being of opposite polarity.

12. A torque transducer arrangement as claimed in Claim 10 in which the perturbation causing means is located to provide at least one perturbation in a torque-dependent magnetic field at right angles to said annular zones .

13. A torque transducer arrangement as claimed in Claim 10 in which the perturbation causing means is located to provide at least one perturbation in an annular magnetic field extending between said annular poles of opposite polarity.

14. A torque transducer arrangement as claimed in Claim 11 in which the perturbation causing means is located to provide at least one perturbation in a torque-dependent field between said two zones.

15. A torque transducer arrangement as claimed in any one of Claims 8 to 14 comprising a disc-like or plate like member rotatable about said axis and through which rotational drive is transmitted between two rotational parts comprises a shaft rotatable about said axis and means carried by said disc-like or plate-like member located radially outward of said two magnetised zones whereby torque is generated in zones in response to the transmission of rotational drive through the member, said exterior annular surface being a surface of said disc-like or plate-like member.

16. A torque transducer arrangement as claimed in Claim 1 in which said region is a portion of a shaft rotatable about said axis.

17. A torque transducer arrangement as claimed in Claim 1 in which said region is a portion of a disc-like or plate-like member mounted to a shaft to rotate therewith and extending substantially radially therefrom, said member having annular means located outwardly of the shaft between which and the shaft torque is transmissible to or from the shaft, and said exterior annular surface comprising a substantially radially-extending surface of said member between said shaft and said outwardly located means, and said region comprising two radially-spaced annular zones of magnetisation extending to said exterior annular surface, said zones being of opposite magnetic polarity.

18. A torque transducer arrangement as claimed in Claim 17 wherein said two zones are oppositely magnetised in an axial direction to provide opposite poles.

19. A torque transducer arrangement as claimed in Claim 17 wherein said two zones are oppositely circumferentially magnetised.

20. A torque transducer arrangement as claimed in any preceding claim in which said perturbation-causing means comprises at least one indentation or projection at said exterior annular surface.

21. A torque transducer arrangement as claimed in any one of Claims 1 to 19 in which said perturbation-causing means comprises a plurality of indentations, a plurality of projections, or a plurality of indentations and projections arranged in a ring around said exterior annular surface, to provide a plurality of perturbations in the detectable external magnetic field for each revolution of the shaft.

22. A torque transducer arrangement as claimed in any one of Claims 1 to 19 in which said perturbation-causing means comprises at least one magnet at or adjacent said exterior annular surface.

23. A torque transducer arrangement as claimed in any one of Claims 1 to 19 in which said perturbation-causing means comprises a plurality of magnets arranged in a ring around or adjacent said exterior annular surface to provide a plurality of perturbations in the detectable external magnetic field for each revolution of the shaft.

24. A torque transducer system comprising a torque transducer arrangement as claimed in any one of Claims 1 to 23, a magnetic field sensor arrangement positioned adjacent said exterior annular surface to provide at least one signal representing the detected magnetic field, and signal processing means responsive to said at least one signal to generate therefrom a first output signal representing the torque in the shaft and a second output signal representing the speed of rotation of the shaft.

25. A torque transducer arrangement as claimed in any one of Claims 1 to 19 in which said perturbation-causing means comprises at least one indentation, projection or magnet to one side of said exterior annular surface and adjacent thereto.

26. A torque transducer arrangement as claimed in any one of Claims 1 to 19 in which said perturbation-causing means comprises a plurality of indentations, a plurality of projections, or a combination of indentations or projections, or a plurality of magnets arranged in a ring to one side of said exterior annular surface and adjacent thereto, to provide a plurality of perturbations in the detectable external magnetic field for each revolution of the shaft .

27. A torque transducer arrangement as claimed in any one of Claims 1 to 19 in which said perturbation-causing means comprises first and second pluralities of members, said members comprising projections, indentations, a combination of projections and indentations, or magnets, said first and second pluralities of members being arranged in respective rings to each side of said exterior annular surface, to provide a plurality of perturbations in the detectable external magnetic field for each resolution of the shaft.

28. A torque transducer arrangement as claimed in Claim 27 in which the members of said first plurality are aligned with the members of the second plurality in the axial direction of the shaft.

29. A torque transducer system comprising a torque transducer arrangement as claimed in any one of Claims 25 to 28, a magnetic field sensor arrangement positioned adjacent said exterior annular surface to provide at least one signal representing the detected magnetic field, and signal processing means responsive to said at least one signal to generate therefrom a first output signal representing torque in the shaft and a second output signal representing the speed of rotation of the shaft.

30. A torque transducer system as claimed in Claim 29 in which the members of the or each ring are spaced at a uniform pitch and in which said magnetic field sensor arrangement comprises first and second sensor devices offset about the axis of rotation by an odd number of half-pitches to provide respective signals that are 180° out-of -phase, and in which said signal processing means is operable to sum and difference said respective signals in obtaining said torque and speed output signals.

31. A torque transducer arrangement as claimed in any one of Claims 1 to 19 in which said perturbation-causing means comprises at least one member capable of affecting the external magnetic field.

32. A torque transducer arrangement as claimed in Claim

31 in which said perturbation-causing means comprises at least two members spaced apart in the circumferential direction.

33. A torque transducer arrangement as claimed in Claim 31 in which said perturbation-causing means comprises a plurality of members spaced apart in a circumferential ring.

34. A torque transducer arrangement as claimed in Claim

32 in which said plurality of members are spaced apart in a uniform manner.