Back to results
US 4,366,405 AGranted
Tachogenerator having stray flux cancelling output coils
AssigneePapst-Motoren GmbH & Co. KG
InventorFritz Schmider
Life of this patent
Estimating the term…
Loading patent…
Loading patent…
AssigneePapst-Motoren GmbH & Co. KG
InventorFritz Schmider
Estimating the term…
A tachogenerator mounted on the underside of a brushless d.c. motor having an external permanent magnet rotor 11 and ironless stator coils affixed to a return magnetic path plate has a first winding surrounded by a first magnetic circuit for producing an alternating voltage of a frequency dependent upon speed of rotation and a second winding for compensation of the effect of the alternating stray flux penetrating through the tachogenerator, the compensation being provided by superposing the output voltage of the second winding on the output voltage of the first winding. The second winding is arranged in a second magnetic circuit, such that upon revolution of the rotor, useful alternating flux is generated which is synchronous with that generated by the first magnetic circuit, but which is spatially in phase opposition thereto. A common rotor and a common source of magnetomotive force, such as a permanent magnet, are provided for both magnetic circuits, the magnet being an annular magnet with a large number of poles of alternating polarity, which cooperates with a toothed element of which the alternating recesses and projections are the same in number as the alternating poles of the magnet. The configuration is such that with relative movement, one part of the useful alternating magnetic flux generated flows around the winding of the first magnetic circuit in one sense, and another part of the same useful magnetic flux flows around the winding of the second magnetic circuit in the opposite sense. The ring magnet is preferably stationary and the toothed element is constituted by the outer portion of the rotor which revolves just inside the ring magnet. The second return path member carries at its center a bearing for the common shaft of the tachogenerator and the d.c. motor.
A tachogenerator having two toroidal magnetic circuits and a rotor forming part of both said magnetic circuits, each of said magnetic circuits passing through said rotor, having a source of magnetic flux and having an individual winding for pick up of induced current, the configurations of the source of magnetic flux, rotor and winding of each circuit being such as to induce current in the winding of each magnetic circuit which is of a frequency dependent on the rotational speed of the rotor, the frequency being the same for the currents induced in both windings, said windings being so wound that induced currents of said frequency in one winding are spatially in phase opposition to those in the other winding and so connected that the said currents of said frequency reinforce each other, while electromotive forces in said windings induced by alternating stray magnetic flux passing through the tachogenerator compensate each other so as to inhibit the inducing of disturbing current.
A tachogenerator having a first winding toroidally encircled by a first magnetic circuit which latter comprises a rotor (37) and a source of magnetic flux so as to produce in operation variations of magnetic flux (32) in said first magnetic circuit and to induce in said first winding a first alternating voltage having a frequency dependent on the rotational speed of said rotor, further having, in spatial proximity to said first magnetic circuit, a second winding toroidally encircled by a second magnetic circuit, the latter also comprising said rotor (37) and said source of magnetic flux (32) so as to produce in operation variations of magnetic flux in said second magnetic circuit having the same frequency as the flux variations in said first magnetic circuit but being oppositely directed, i.e. oppositely phased, with respect thereto, so as to induce a second alternating voltage in said second winding having the same frequency as that induced in the first winding, and means for additively superimposing said first and said second alternating voltages, whereby voltages induced by stray fluxes in said first and second windings are substantially cancelled out.
Dependencies are inferred from the claim text.