The Applicant is not aware of any prior art suggesting that a doubly-
salient pole machine should have either rotor or stator poles which are tilted or inclined relative to the direction radial to them from the shaft axis, apart that is from the Applicant's own copending GB Patent Application No. 9513855.8 filed on July 7, 1995, the priority of which is claimed in connection with this subject application. That prior application discloses a tilted form of stator pole construction formed by electrical sheet steel laminations which are each separate pole pieces providing flux bridging paths between rotor sections spaced along the machine spindle and the tilt is there aimed at providing a shaded-pole action obstructing passage of leakage flux through the related pole sides as rotor and stator poles separate.
Indeed, it was the findings in experimental work on such a machine that inspired the subject invention, which is entirely different in its is 3 function and is in no way obvious from orthodox design principles. The invention to be described has been implemented in an operable electric motor and performance data are provided in the later description.
BRIEF STATEMENT OF INVENTION According to the invention, a ferromagnetic rotor-stator configuration for a doubly-salient pole electrical machine in which, in addition to the pole interface across a small radial air gap when the poles of rotor and stator are in register, the profile as between rotor and stator provides an asymmetric interfacing association across the much larger air gap between pole faces and the pole sides when the poles are not in register, characterized in that the asymmetry feature of the configuration as applicable to any rotor pole when in near-register with a stator pole is between surfaces subtending an acute angle on one side of a pole and between surfaces subtending an obtuse angle on the other side of that pole.
Electrodynamic machines incorporating such rotor-stator configurations have a preferred direction of rotation which thereby determines which are the 'leading' and 'trailing' side edges of the rotor poles.
According to a feature of the invention, the ferromagnetic rotor stator configuration for a doubly-salient pole electrical machine is such that the rotor poles have a tilt, whereby the leading side edges of the rotor poles are inclined at an acute angle to the pole face of an interfacing stator pole and the trailing side edge is inclined at an obtuse angle to the pole face of the interfacing stator pole.
According to another feature of the invention, the ferromagnetic rotor-stator configuration for a doubly-salient pole electrical machine is 4 such that the stator poles have a tilt, whereby the side edges of the stator poles facing the leading edges of the rotor poles are inclined to them at an acute angle and the side edges of the stator poles facing the trailing side edges of the rotor poles are inclined to them at an obtuse 5 angle.
According to a further feature of the invention, the ferromagnetic rotorstator configuration is such that the acute angle is between 400 and 0 Other features of the invention relate to the salient poles of both the rotor and stator pole-bearing components having an equal angular pitch at the rotor perimeter that is also equal to the angular spacing between the poles at that perimeter and features such as the rotor and stator poles having flat side surfaces at least over half their length nearest to the pole face and from the tooth root.
BRIEF DESCRIPTION OF THE DRAWINGS Figs. I and 2 show in outline diagram form two alternative relative positions of a single stator pole and a set of rotor poles drawn as if in linear motion, the poles having configurations as suggested by this invention.
Fig. 3 shows a square-tooth pole arrangement having standard symmetry.
Fig. 4 shows a symmetrical pole arrangement of conventional form, shaped to locate magnetizing windings.
Fig. 5 shows an embodiment of the invention as a pair of interacting rotor and stator electrical sheet steel laminations suitable for assembly into a machine.
Fig. 6 is a geometric representation of the magnetic flux traversal across the acute angle of the tilted pole configuration.
DETAILED DESCRIPTION OF THE INVENTION Arising from a long standing research interest in magnetization processes in electrical sheet steels and the associated energy anomalies the Applicant has declined reliance on the above-referenced virtual work principle, for the simple reason that it fails to take account of thermodynamic processes that occur in association with the setting up magnetic fields. The reality is that in energizing a magnetic field in a pole gap, whether by feeding current to an electromagnet or pulling a permanent magnet away from a soft iron former, the work actually done goes into heat which is dissipated. However, there is a polarized condition in the field which affects the orientation of reactive spins in the charges which populate the field medium and account for what form the physical basis for Maxwell-type displacement currents, and these reaction currents exist even in a steady-state field reaction to the presence of a steady magnetic field. In effect the thermal equilibrium inherent to the field medium, with its randomly directed spins, is affected as those reacting spins, which are really microcurrent loops, come partially into line to oppose the applied field action, the existing base-equffibrium heat energy serving to sustain that reacting motion. Some quantum physicists refer to this as 'zero-point field energy' without relating it to magnetic inductance, which is its primary contribution in observable phenomenological processes.
What we see then is the setting up of a magnetic potential in the pole gap, even though the energy used has been lost as heat. The poles are attracted to one another owing to that magnetic potential and, if 6 allowed to come together, they will deliver mechanical energy and shed that magnetic potential. The energy supplied really comes from that partially ordered spin reaction in the field medium, which virtually acts as a powered primary winding waiting to deliver inductance energy back from the pole gap as it recovers its random state when the field is removed or thr gap closed. This process involves cooling, which accounts for the energy balance.
In summary, therefore, contrary to accepted teachings in electrical science, there are thermodynamic effects which cannot be ignored if we are to progress technologically and exploit what underlies the process of magnetic inductance.
Although the Applicant has understood this for several decades, since his Ph.D. research (1950-53) on magnetization energy anomalies, it is only now that a technological consequence has emerged by a chance research finding in experimenting with the shaded-pole motor mentioned above.
In fact, rotors with forward tilted poles complementing the forward tilt of the bridging stator pole pieces were incorporated in a test machine and, instead of having a preference for forward rotation, as had been found with a square-toothed rotor, it had an over-riding preference for rotation in the opposite direction. This meant that the rotor pole stagger was far more effective than the shaded-pole effect and, in turn, this meant that the shaded-pole feature was best removed to focus onward development on a form of stator using electrical sheet steel laminations coplanar with the rotor laminations, but retaining the tilt of the stator poles.
7 This introduces the description of the subject invention which includes some test data on a machine which has been constructed using rotor and stator Jaminati ns cut with special profiles by laser technology.
It is important to understand that the lines of magnetic force acting between pole faces and across the intervening pole gap do not run at right angles to the pole face. They develop at a small angle to directions normal to the pole face and, if they did not, the strong magnetic attraction would merely pull the poles radially with respect to the machine axis and no torque would be developed. The forces acting radially across the small radial gap between the pole faces can be extremely strong but only a small component resolved in the rotational sense develops the machine torque.
In comparison there is only a relatively weak passage of flux by leakage between pole surfaces other than at the pole interface but this flux acts at a much more effective angle in setting up forces on the those other pole surfaces. A weaker flux but at a more effective angle can add significantly to the machine drive torque.
At the International Symposium on EM Fields in Electrical Engineering held at the University of Southampton (September 18-20, 1991), there was a paper by M. R. Harris and J. K. Sykulski, both of the Department of Electrical Engineering at that university. It concerned the peak torque of a switched reluctance motor and explained how the tractive force between two slightly overlapped teeth exhibits anomalous force behaviour for which 'a theoretical explanation is not readily available'.
The paper explains how, in experiments on doubly-salient pole interactions, as the level of magnetization increases to near saturation at the pole edges, 'a factor of advantage of 21 is seen and it is stated that 8 the subject has been widely discussed and that measurements on a test rig have confirmed that enhancement of force does occur in practice.
The tests reported were based on square-shaped pole profiles, which means that, by symmetry, there is a stronger force one way as poles close and an equally strong force the other way as the poles separate. Evenso, the reluctance machine, duly controlled so as to have MMF switching, will run with better performance owing to this effect, but the lack of insight into the underlying thermodynamic implications has eluded those researching this field and so made way for this invention.
Referring to Fig. I a sequence of tilted pole teeth I is shown in the upper part to represent a stator pole system and a sequence of tilted pole teeth 2 is shown in the lower part of the figure to represent a rotor moving to the left, as indicated by the arrow. In the relative positions shown the stray flux between the rotor and stator poles is concentrated in two regions and indicated by the broken lines. It pulls the poles into register, augmenting the main effect of pole overlap between interface surfaces separated by the small pole gap.
As the poles separate to the position shown in Fig. 2, there are three stray flux regions effective. Those closest to the main pole faces are similar in surface extent to the two regions mentioned by reference to Fig. 1, but the flux path length is so much longer, which means, in spite of the more acute angle of incidence of the flux in acting on the rotor, that the resulting braking effect here is weaker than the driving effect for the regions in Fig. 1. Moreover, in Fig. 2 there is the third region developing pull between the following rotor pole and the stator.
By providing the tilted pole feature, the asymmetry has led to there being stronger magnetic forces pulling the rotor to the left than the 9 forces trying to pull it to the right, when the action is integrated or averaged over the whole cycle of pole passage.
Accordingly, a machine incorporating rotor and stator laminations having tilted poles as suggested, will have characteristics giving more efficiency than conventional machines with symmetrical poles, providing rotation is, in the main, in the preferred angular direction as determined by the pole configuration.
Note, by reference to Fig. 3, that a square pole profile has symmetry and whatever the forces are on one side of a rotor pole, as averaged over the full movement, so they are the same in the opposite direction.
The same applies to Fig. 4, where a typical tooth profile is shown, the pole shoe area being enlarged and the main pole section being of smaller cross-section. This allows magnetizing windings to fit snuggly into the recesses formed, but the basic symmetry means that there is no scope for developing additional torque from the shaping of the teeth forming the poles.
Fig. 5 shows an embodiment of the invention in the form of coplanar rotor laminations 3 and stator laminations 4 having an 8-pole configuration, with the tilted feature.
It is not necessary to describe a machine, because it is self-evident to those skilled in the art of assembling electric motors how these laminations can be incorporated in a motor or a generator. Ideally, the machine employing this invention will use both the rotor and stator with the poles tilted in the same directions as shown but there can be a partial benefit from using either paired with a stator or rotor having symmetrical teeth as poles.
Essentially, therefore, the invention is simply the provision of a specially configured form of rotor and stator combination for use in an electric motor or generator which is of doubly-salient pole form.
An angle of pole tilt of 45" has been found to be satisfactory from a constructional and operational point of view, bearing in mind that control windings require adequate slots and the pole teeth have to be rigid enough to sustain the mechanical force. This, however, is a compromise because the more acute the angle, the stronger the differential force effect, but the magnetic flux path cannot be too restricted and the mechanical stresses when operating at speed need to be considered along with the need for seating the magnetizing windings. The results presented below apply to a machine built using rotor and stator laminations having this 45 angle as the acute angle effective at pole approach in the arrangement shown in Fig. 5, when the rotor lamination turns anticlockwise. A 40 to 50" range of angle could be deemed a practical range suited to the invention, but the functional effect of variation of the angle can be judged from the brief analysis appended below.
The test data to be presented applies to a machine in which the magnetomotive force was that set up by a magnetizing winding arrangement on the stator, which caused magnetic flux to circulate around magnetic paths each including two adjacent poles on both the stator and the rotor. The machine tested had both rotor and stator poles as teeth with an angular pitch equal to the slot width or spacing between teeth, that is somewhat different from the form shown in Fig. 5, where the slots are wider.
11 This latter point is important in understanding the experimental data because also, and not an optimum magnetization timing control, the magnetization in this experiment was switched on as the rotor and stator poles began to overlap and switched off as soon as they were in fun register. This was controlled by a mosfet circuit operated by an 8-vane Hall Effect sensing device, there being 8 poles on the stator and rotor laminations. The timing here was especially determined so that the experiment could verify the difference between clockwise and anticlockwise rotation under corresponding pole overlap conditions, without altering the time-phasing of the current switching.
The experimental data presented below serves merely to show that, absent any load on the machine and any factor which could set up more friction for clockwise motion versus anticlockwise motion, the performance obtained arises solely from the asymmetrical configuration of the poles of the rotor and stator.
For the machine rotating clockwise in the above sense, that is moving as if the tilted rotor poles and tilted stator poles are pulled into a common tilted line by magnetism flowing directly and with an attractive force between the rotor and the stator, the summary test data relating 2 0 the d. c. power supply and the resulting motor speed was:
volts amps watts rpm 5.0 0.49 2.45 270 6.0 0.56 3.36 360 7.o 0.64 4.48 450 8.0 0.73 5.84 580 For the machine rotating anticlockwise, that is moving now in a direction that this inventor originally thought might be less favoured by 12 the rotor-stator configuration, with the planar pole sides and pole faces of the rotor and stator coming together at an acute angle of 45", the following corresponding measurements were made:
volts amps watts rpm 5.0 0.45 2.25 370 6.0 0.52 3.12 7.0 0.59 4.13 8.0 0.68 5.44 450 570 670 9.0 0.77 6.93 760 What these data show is that the anticlockwise rotation had a 40% power advantage over clockwise rotation and, implicit in the figures, taking account of the resistance of the motor winding and the estimated current pulse duration, is the fact that almost all the power supplied is dissipated as J2 R loss in that winding.
is This is the essence of this invention, a surprising result, indeed a discovery that has seemingly no logic according to standard teaching in the electrical engineering art, but yet a simple technological innovation having very significant and far reaching implications.
Appendix Regarding the angle between the pole faces and the sides of the converging poles as E), this being 45" in the above account, one sees that this angle represents the mutual inclination of two surfaces between which it is assumed that the force contributing to this interaction is balanced, being equal and opposite as between rotor and stator.
If one now tries to use standard physics, embracing field curvature in space, one is left wondering about pressure in the field itself and 13 unbalanced reaction forces exerted on the aether, a medium which is not supposed to exist anyway because it is replaced by the mathematics of 'four-space'. One leaves technology behind once entrapped by a physicist's interpretation of how energy might deploy itself in the presumed non-aetherial field in an air gap between interfacing magnets.
What follows below is, therefore, an imperfect but yet adequate approximation giving some insight into how the magnitude of the pole interaction forces is affected by the pole tilt.
By symmetry, if we are to avoid regarding the field itself as mechanical structure rigidly attached to the machine, then to keep force balance between rotor and stator, the lines of magnetic force need to act at right angles to the line bisecting the angle e and they will act on the rotor pole face with a force component that is cos(E)/2) times the direct pull along the lines of force.
Denote x as distance from the intersecting junction in the pole gap formed by the side planar surfaces of the stator pole and the surface plane of the rotor pole.
The reluctance of an element of space in the region 5 under consideration at x will be its length 2xsin(8/2) divided by its area normal to the lines of force. The flux density B will be proportional to MMF, the magnetomotive force, divided by that length 2xsin(e/2).
From this, the force acting on unit area of pole face at x in the directional sense needed to produce torque is proportional to B 2 times sin(8/2) times the contracted projection of that unit pole face area as seen from the direction of the lines of force, this being a reduction proportional to cos(8/2).
14 The resulting force component per unit width and unit depth of pole in the axial direction is therefore proportional to: cot (e 12) (MMF) 2 /4X2 From the geometry of the gap region it can be then be argued that the minimum value of x is g[cote + tan(e/2)], where g is the air gap between the pole faces. Integrating 1 / x 2 in expression (1) with respect to x. one obtains 1/x, where x is at its minimum, less 1/x where x is at its maximum, some 10 or so times g at the moment the pole gap begins to close. For E) = 45", the minimal x is 1.414g so one can see that the integral I/x has a value which is approximately (0.6)1g. Thisreduces progressively as the pole sweeps across the pole face and to calculate instantaneous force one needs to take an average based on a log.x factor. However, the effect is dominated by the action near the pole gap and this average involves only a moderate reduction in the value just calculated.
Since cot(22.5") is 2.414, we find that the average is somewhat less than 0.36(MMF)2/g, say, 0.3 times (MMF)2/g, this latter expression representing the corresponding force action asserted by the pole interaction in the pole gap.
In other words, we expect from this theoretical analysis to find that a 45" acute angle between the rotor pole face and the stator pole side edge should increase the motor torque by 30%. However, there are two such interfacing pole regions as the side of the rotor pole also interacts across an acute angle of 45' with the stator pole face. Therefore, a 60% additional torque factor is to be expected.
This has to be compared with the square or 90 pole profile as reference. Putting this angle as e, the additional torque is of the order of one third that just calculated and, if we had used the obtuse angle 135' is to calculate the brake torque in the Fig. 2 position the result would be very much smaller.
Therefore, there is good theoretical reason to suspect that a 40% gain in motor torque may result from the side forces on the poles, provided the magnetic excitation is powered as the poles presenting the 45' interfaces close together.
This power gain has been observed in the experiment reported above and the anticlockwise direction of rotation does correspond with the condition just analyzed.
16 CLAIMS I. A ferromagnetic rotor-stator configuration for a doubly-salient pole electrical machine in which, in addition to the pole interface across a small radial air gap when the poles of rotor and stator are in register, the profile as between rotor and stator provides an asymmetric interfacing association across the much larger air gap between pole faces and the pole sides when the poles are not in register, characterized in that the asymmetry feature of the configuration as applicable to any rotor pole when in near-register with a stator pole is between surfaces subtending an acute angle on one side of a pole and between surfaces subtending an obtuse angle on the other side of that pole. 2. A ferromagnetic rotor- stator configuration for a doubly-salient pole electrical machine according to claim 1, in which the rotor poles have a tilt, whereby the leading side edges of the rotor poles are inclined at an acute angle to the pole face of an interfacing stator pole and the trailing side edge is inclined at an obtuse angle to the pole face of the interfacing stator pole. 3. A ferromagnetic rotor-stator configuration for a doubly-salient pole electrical machine according to claim 2, in which the stator poles have a tilt, whereby the side edges of the stator poles facing the leading edges of the rotor poles are inclined to them at an acute angle and the side edges of the stator poles facing the trailing side edges of the rotor poles are inclined to them at an obtuse angle. 4. A ferromagnetic rotor- stator configuration according to claim 1, wherein the acute angle is between 40 and 50". 5. A ferromagnetic rotor- stator configuration according to claim 1, wherein the salient poles of both the rotor and stator components have an 17 equal angular pitch at the rotor perimeter that is also equal to the angular spacing between the poles at that perimeter. 6. A ferromagnetic rotor-stator configuration according to claim 2, wherein the rotor poles have flat side surfaces at least over half their length nearest to the pole face and from the tooth root. 7. A ferromagnetic rotor-stator configuration according to claim 3, wherein the stator poles have flat side surfaces at least over half their length nearest to the pole face and from the tooth root.
V Amendments to the claims have been filed as follows Is CLAIMS 1. A ferromagnetic rotor-stator configuration for a doubly-salient pole electrical machine in which the pole faces of both the rotor and stator are concentric so as to provide a small and uniform radial air gap and the pole profile of the stator provides an asymmetric interfacing association across a much larger air gap between rotor pole faces and stator pole sides when the poles are not in register, which, for a given machine magnetization, sets up a differential attraction acting on the rotor from the sides, as opposed to the faces, of the stator poles, which differential attraction supplements the magnetic attraction across said radial air gap, the stator poles all having the same asymmetrical shape and the rotor poles all having the same asymmetrical shape with the sides of both rotor and stator poles being inclined at between 40' and 50' to the radial direction from the rotor axis.