ROTARY ELECTRICAL MACHINES

Abstract: The machine has a stator winding 11 in which a voltage V is induced by permanent magnet pole pieces 31, 34 which are arranged circumferentially on respective rotor parts 30, 32. Rotor parts 30, 32 are driven by an input shaft 13 through respective epicyclic gear trains 14, 35, the gear train 14 being a differential gear responsive to rotation of a ring gear 17 by an actuator 21. With the ring gear 17 stationary the rotor parts 30, 32 are driven in the same direction and at the same speeds. Operation of the actuator 21 in response to varia­ tions in the voltage V thus varies the relative angular positions of the rotor parts 30, 32 and is arranged to maintain the voltage V substantially constant.

Description: This invention relates to rotary electrical machines having permanent magnet rotors. It is known to provide rotary electrical machines having permanent magnet rotors. In a generator the use of such rotors gives rise to difficulties in regulating output voltage under varying conditions of external loads and shaft speeds. In a motor there are corresponding difficulties in regulating the output speed. It has been proposed to provide regulation as aforesaid by modification of the field of the rotor, this modification being effected by relative movement between parts of the rotor. An electric machine having means for providing relative rotation betareen permanent magnet rotor parts is disclosed in US Patent 3,713,015. It is necessary that the aforesaid relative rotation is carried out lfhile the machine is in operation, and the rotor may therefore be turning at a high speed. The force required to effect this relative rotation correspond to the resulting change in the input or output poafer of the machine, and may therefore be considerable. tt has therefore been found necessary to effect relative rotation by means of a power actuator. In US Patent#3,713,O15 a linear actuator is coupled to one rotor part through a sliding collar and skew splines. Such an arrangement results in high frictional forces between the relatively moving parts. It has also been proposed, in UE Patent Application 2,051,496A, to incorporate a linear hydraulic actuator within the rotor and to apply a fluid pressure thereto through the rotor shaft. Such an arrangement introduces difficulties in making the required hydraulic connections to v shaft which may be rotating at high speed. It is an object of the present invention to provide a rotary electrical machine having a permanent magnet rotor, in which modification of the rotor field is effected by relative movement between parts of the rotor, and in which this relative movement can be induced by an actuator mounted on a relatively stationary part of the machine, the coupling between the actuator and the rotor being entirely rotary. According to the invention there is provided a permanent magnet rotary electrical machine comprising a rotor having a first permanent magnet pole structure and a second pole structure, a stator winding surrounding said rotor, a drive shaft, means for drivingly connecting one of said pole structures to said drive shaft, a differential gear having a first input element which is drivingly coupled to said drive shaft, a second input element and an output element which is drivingly coupled to the other end of said pole structures, and actuator means for rotating said second input element relative to said stator winding so as to vary the relative angular positions of said first and second pole structures. In a particular embodiment said differential gear is an epicyclic gear and said means for drivingly connecting said one pole structure to said shaft comprises a second epicyclic gear having a first input element drivingly coupled to said shaft, a reaction element and an output element drivingly coupled to said one pole structure, the velocity ratios of said first and second epicyclic gears being identical wfhen the second input element of said first differential gear is stationary. In one embodiment, said first and second pole structures each comprises a plurality of permanent magnets. In a further embodiment, said second pole structure comprises a plurality of first elements of a relatively high permeability and a plurality of second elements of a relatively lower permeability, said first and second pole structures being relatively annularly movable between a first relative position in lfllich said first elements provide substantially the arllole of a flux path between the poles of said first structure, and a second relative position in which said second elements lie in said flux path, lahereby in said second relative position flux from said first pole structure is directed eternally of said rotor. b#iibodiinents of the invention thrill novv be described by way of example only and with reference to the accompanying drawings, in which:- Figure 1 is a longitudinal half-section through an electric generator, and Figures 2 and 3 sholf transverse sections of an alternative form of rotor, in respective operating positions. The generator shown in Figure 1 has a fixed housing 10 which carries stator windings 11 on a former 12. A drive shaft 13 is journalled in the housing 10. A first differential epicyclic gear train 14 comprises a carrier 15 keyed to the shaft 13 and supporting a plurality of planet gears 16. The gears 16 engage both an external ring gear 17 and a sun gear 18 secured to a sleeve 19 which is rotatable on the shaft 13. The ring gear 17 is mounted on a bearing 20 and is rotatable relative to the housing 10 by means of a suitable actuator 21. In the particular embodiment the actuator 21 is a hydraulic piston and cylinder unit operable by a servo pressure in a line 22, the magnitude of this pressure being regulated by a control arrangement 23 which is responsive, inter alia, to the voltage V at an output terminal 24 of the generator. The servo pressure in line 22 is intermediate the pressure at the outlet of a positive displacement pump 25 which is driven by the shaft 13, and the pressure in a return line 26. In alternative embodiments the arrangement 23 may be responsive to the speed of the shaft 13, or to both voltage V and shaft speed. Secured to the sleeve 19 is a toroidal yoke 30 around the circumference of which are spaced a first plurality of samarium cobalt permanent magnet elements 31. A further toroidal yoke 32 is secured to a sleeve 33 which is rotatable on the shaft 13, the yoke 32 also carrying a plurality of circumferentially spaced permanent magnet elements 34. A second epicyclic gear train 35 comprises a sun gear 36 integral with the sleeve 33, a plurality of planet gears 37 mounted on a carrier 38 which is keyed to the shaft 13, and a ring reaction member 39 fixed to the housing 10. Sun gears 18, 36 have an identical number of teeth, as have the planet gears 16, 37 and the ring gears 17, 39. The arrangement is therefore such that with the ring gear 17 held stationary by the actuator 21, the yokes 30, 32 of the rotor are driven at identical speeds. If, however, the ring gear 17 is moved by the actuator 21 the yoke 30 will be rotated with respect to the yoke 32. Since the pitch circle diameter of the ring gear 17 is twice that of the sun gear 18, angular movement of the yoke 30 relative to the yoke 32 will be twice that of the gear 17. The permanent magnet elements 31, 34 are each arranged in heteropolar fashion such that with the shaft 13 at rest, lie poles of the elements 31, 34 are aligned, wdlereby combined flux from the elements 31, 34 passes externally of the rotor as a whole and induces a voltage in the stator winding 11. At predetermined levels of voltage in V or the speed of the shaft 13 the control arrangement 23 causes the servo pressure in line 22 to be sufficient to rotate the ring gear 17 and move the elements 31, 34 out of polar alignment. The actuator 21 is such that the elements 31 can be moved up to a maximum of one pitch relative to the elements 34, in which condition unlike poles of the elements 31, 34 are aligned and the flux from these elements is effectively shorted out. Intermediate relative positions of the elements 31, 34 under control of the arrangements 23, may thus be used to regulate the output voltage V in accordance with the speed of the shaft 13, to maintain the voltage V substantially constant. In the arrangement of Figure 1 the yokes 30,32 and elements 31, 34 provide two pole structures each of which includes permanent magnets. Figures 2 and 3 show an alternative form of rotor in which only an inner one of two pole structures comprises a samarium cobalt permanent magnet 40 sandlfiched betweell soft iron pole pieces 41, the assembly being mounted on, for example, the sleeve 33 in Figure 1. An outer pole structure closely surrounds the inner pole structure and is mounted on the other sleeve 19 for rotation relative to the inner pole structure. The outer pole structure comprises a composite tube consisting of two diametrally opposed soft iron pole pieces 42 and two non-magnetic steel sectors 43. For this embodiment it is necessary that the actuator 21 of Figure 1 shall be capable of rotating the outer pole structure through 900 from the position shown in Figure 2 to that sholfn in Figure 3. In the relative positions of the inner and outer pole structures shown in Figure 2, the flux from the magnet 40 passes through the soft iron elements 42 to coact with the stator windings. In the relative positions shown in Figure 3 the flux from the magnet 40 is shorted through the parts 42. The inner and outer pole structures may be moved to intermediate relative positions to control the output voltage V of the generator.

Claims: C L A I M s : 1. A permanent magnet rotary electrical machine comprising a rotor having a first, permanent magnet pole structure, and a second pole structure, a stator winding surrounding said rotor, a drive shaft and first and second driving connections between said shaft and the first and second pole structures respectively, said first driving connection includ¯=ng a device for varying the angular position of said first pole structure relative to said second pole structure, characterised in that saiddevice comprises a differential gear having a first input element drivingly coupled to said shaft, a second input element, and an output element which is drivingly coupled to one of said pole structures, and an actuator for rotating said second input element relative to said stator winding. 2. A machine as claimed in Claim 1, in which said differential gear comprises an epicycle gear train. 3. A machine as claimed in Claim 2, in which said second driving connection comprises a second epicyclic gear train having a first input element drivingly coupled to said shaft, a reaction element and an output element drivingly coupled to the other of said pole structures, the velocity ratios of said first and second epicyclic gear trains being identical when the second input element of said differential gear is stationary. 4. A machine as claimed in any preceding Claim, in which said actuator comprises a fluid pressure operated device. 5. A machine as claimed in Claim 3, 71lich includes a control device, responsive to an operating condition of the machine for regulating a control pressure for said pressure-operated device. 6. A machine as claimed in any preceding Claim, in which said first and second pole structures each comprises a plurality of permanent magnets. A -Amachine as claimed in any of Claims 1 to 5, in which one of said pole structures comprises a plurality of first elements of a relatively high permeability and a plurality of second elements of a relatively lower permeab lity, said first and second pole structures being relatively angularly movable between a first relative position in which said first elements provide substantially the whole of a flux path between the poles of the other of said structw ess and a second relative position in which said second elements lie in said flu=: path, whereby in said second relative position flux from said one pole structure is directed externally of said rotor. S. A permanent magnet rotary electrical machine, substantially as hereinbefore described with reference to Figure 1, or to Figure 1 as modified by Figures 2 and 3, of the accompanying drawings.

Inventors: HOWARD, JOHN REDMAN
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1982
Main classification: H02K21
IPC codes: H02K21, H02K7