Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1987-04-16
1989-10-10
Salce, Patrick R.
Electrical generator or motor structure
Dynamoelectric
Rotary
310177, 318439, 318138, H02K 2316
Patent
active
048734632
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a d.c. motor.
D.C. motors require commutation i.e. the process of reversing the current in each armature coil. This is carried out while the commutator segments to which the coil is connected are short-circuited by a brush. Very high rates of change of current are involved, which change is opposed in conventional d.c. motors by the inductive e.m.f. induced in the coil. If the reversal is not completed by the time that the short-circuit is removed, then sparking will occur with consequential damage to the brushes and the commutator itself.
It is known to assist commutation by the provision of extra poles (or compoles) located between the main poles of the stator. These compoles are arranged so as to induce an e.m.f. in the short-circuited coils which opposes, and therefore acts in a direction to neutralise, the induced e.m.f. Even with the aid of compoles, sparkless commutation cannot be achieved in conventional d.c. motors unless the inductive e.m.f. is limited to about 10 volts per coil and the mean voltage between adjacent commutator segments does not exceed about 20 volts. These factors impose considerable limitations on the design of conventional d.c. motors.
Shunt connected d.c. motors produce a relatively low torque and series connected d.c. motors are used for high torque. However, series connected motors suffer from very poor speed regulation and reduced efficiency owing to the increased I.sup.2 R losses in the series field coils.
An object of the present invention is to provide a d.c. motor in which the above problems associated with commutation are overcome and which will provide high torque with good speed regulation.
In accordance with this invention as seen from one aspect there is provided a d.c. motor comprising a cylindrical stator, a rotor journalled on a shaft for rotation within the stator with a uniform gap between the rotor and stator as the rotor rotates, armature windings inserted in slots in a cylindrical surface on one of the stator and rotor and being divided into similar coils mutually spaced around the shaft axis, field generating means located on the other of said stator and rotor for forming poles mutually spaced around the shaft axis, and switching means adapted to connect said armature coils to a d.c. source in timed synchronism with rotation of the rotor such that switching of the d.c. to each armature coil occurs when a pole generated by that coil is substantially in alignment with a rotor (or stator) pole of opposite polarity and such that immediately before switching the e.m.f. induced in that armature coil is approaching maximum value and opposes the applied e.m.f. and immediately after switching those poles are of like polarity and the induced e.m.f. assists the applied e.m.f.
In accordance with this invention as seen from another aspect there is provided a d.c. motor comprising a cylindrical stator, a rotor journalled on a shaft for rotation within the stator with a uniform gap between the rotor and stator as the rotor rotates, armature windings inserted in slots in a cylindrical surface of the stator and being divided into similar coils mutually spaced around the shaft axis, field generating means located on the rotor for forming poles mutually spaced around the shaft axis, and switching means adapted to connect said armature coils to a d.c. source in timed synchronism with rotation of the rotor so as to generate a rotating field which is in arrear of and oposes the rotor field to exert a repelling force on the rotor poles.
The switched windings may be provided on the stator or on the rotor, i.e. either the stator or the rotor forms the armature. The field generating means may comprise windings divided into similar coils forming the field poles mutually spaced around the rotor (if the stator is the armature), or around the stator (if the rotor is the armature). Instead, the field generating means may comprise a permanent magnet.
In the motor in accordance with this invention, the induced e.m.f. due to relative movement of the field is
REFERENCES:
patent: 3631273 (1971-12-01), Stein
patent: 3786287 (1974-01-01), Stein
patent: 4135107 (1979-01-01), Kamerbeck et al.
patent: 4321494 (1982-03-01), MacNab
Jones Judson H.
Salce Patrick R.
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