Electronically commutated motor

• US 4,169,990 A
• Filed: 06/01/1977
• Issued: 10/02/1979
• Est. Priority Date: 06/24/1974
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Lerdman, David M.
• Primary Examiner(s): Rubinson, Gene Z.
• Application Number:
  US05/802,484
• Time in Patent Office: 853 Days
• Field of Search: 318/138, 318/254, 318/331, 318/439
• US Class Current: 318/400.41
• CPC Class Codes: F23N 2233/04 with variable speed
• CPC Class Codes: F23N 3/082 using electronic means
• CPC Class Codes: F25B 2600/021 Inverters therefor
• CPC Class Codes: H02K 29/10 using light effect devices
• CPC Class Codes: H02P 2209/07 Trapezoidal waveform
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position

Abstract

A brushless DC motor is constructed with photosensitive device for detecting rotor shaft position. Arcuate permanent magnets on the rotor provide a DC flux field while distributed stationary armature windings, each spanning a fixed number of slots in the armature assembly, provide mutually perpendicular magnetic fields. A logic circuit comprising NOR gates and transistor switches and drivers activated in response to signals from the shaft position sensors are utilized to control current switching in the armature windings of the motor. A light interrupting shutter mounted to the rotor cooperates with the light sensitive devices which are mounted to a supporting bracket fixed to the stationary armature assembly in a manner to selectively preset advancement of commutation of the armature windings. Variations on permanent magnet rotor construction and novel applications of a brushless DC motor are also disclosed as is a novel approach for dispensing with the mechanism for detecting the shaft position. In this last respect a commutating circuit is disclosed for a brushless DC motor, including a detecting circuit responsive to the electromotive force (emf) of the brushless DC motor to provide a simulated signal indicative of the rotation of the motor'"'"'s shaft and a logic circuit responds to the output of the shaft position detecting circuit to control the application of driving signals through the armature windings of the DC brushless motor.

Claims

1. A DC motor comprising a stationary armature having a core and at least two winding stages each comprising at least one effective winding;

each winding comprising at least two coils of winding turns accommodated by the core and arranged to establish a predetermined number of magnetic poles, and the winding turns of each winding having a number of sets of axially extending conductor portions with such member being equal in number to the predetermined number of poles;

the axially extending conductor portions within each given set being comprised generally of about one half of the conductor side turn portions of at least two different coils, and such conductors being disposed to conduct current instantaneously in the same axial direction along the core thereby contributing to the establishment of magnetic poles when the winding containing such given set is energized;

the arcuate spread of any given set of axially extending conductors being less than about 120 electrical degrees;

a rotor having constant magnetic polarity polar regions equal in number to the predetermined number of poles, said rotor being adapted to rotate relative to the armature in response to the magnetic poles established by the winding turns; and

commutation means for energizing the windings in a predetermined manner to establish the magnetic poles on said armature for causing rotational movement of the rotor.

2. A DC motor as set forth in claim 1 wherein the arcuate spread of each set of axially extending conductors is in a preferred range of from about 30 electrical degrees to about 120 electrical degrees.

3. A DC motor as set forth in claim 1 wherein the windings are arranged in winding coil pairs and each winding coil is formed of bifilar strands that share common armature slots.

4. A DC motor as set forth in claim 1 wherein said windings are connected in a half bridge configuration.

5. A DC motor as set forth in claim 1 wherein the constant magnetic polarity polar regions established by said rotor are created by permanent magnets disposed on the rotor.

6. A DC motor as set forth in claim 1 wherein the commutation means includes a light source, a light sensitive device, and a light interrupting shutter mounted to the rotor for rotation therewith to block the light pathway between the light source and light sensitive device for at least a portion of each revolution of the rotor.

7. A DC motor as set forth in claim 1 wherein the commutation means includes detector circuit means responsive to the current flow in the windings to provide an output signal indicative of rotor speed, and energizing circuit means responsive to the output of said detector circuit means for providing a plurality of armature winding energizing signals displaced in a predetermined temporal sequence.

8. A DC motor comprising a stationary armature having a core and at least two winding stages each comprising at least one effective winding;

each winding comprising concentric winding turns accommodated by said core and arranged to establish a predetermined number of magnetic poles and the winding turns of each winding having a number of sets of axially extending conductor portions with such number equal to the predetermined number of magnetic poles;

the axially extending conductor portions within each set being disposed in said armature to conduct current instantaneously in the same axial direction along the core thereby contributing to the establishment of magnetic poles when the winding containing the given set is energized;

the arcuate spread of any given set of axially extending conductors being less than about 120 electrical degrees;

a rotor having constant magnetic polar regions equal in number to the predetermined number of poles, said rotor being adapted to rotate in response to the magnetic poles established by the winding turns; and

a commutation circuit for energizing the windings in a predetermined manner wherein said commutation circuit includes a detector circuit for sensing a back emf signal indicative of the back emf condition of at least one winding, position determining circuit means for conditioning the back emf signal sensed by the detector circuit and for producing a simulated relative position output that is indicative of the relative angular position of the rotor and armature, with such relative position output determined by the back emf condition of a winding, and circuit means interconnected with the position determining circuit means for supplying an output signal for energizing a selected one of the windings.

9. The DC motor circuit of claim 8 wherein the position determining circuit means of the commutation circuit includes a circuit for producing a signal as a measure of flux in a winding not then being energized and for producing said simulated relative position output.

10. The DC motor of claim 8 wherein the position determining circuit is operative to cause advancement of commutation of the windings by an angle alpha of from about five to about thirty electrical degrees to aid the build up of current when the windings are energized during running condition.

11. The DC motor of claim 10 wherein the position determining circuit includes means to vary the advancement of commutation angle alpha.

12. The DC motor of claim 8 wherein the position determining circuit means of the commutation circuit includes an integration means for integrating the back emf signal from said detector circuit to a predetermined value of volt-seconds whereupon the position determining circuit means produces an output signal to the circuit means.

13. The DC motor of claim 12 wherein the predetermined value of volt-seconds attained by said position determining circuit means occurs at an angular rotor position relative to the armature corresponding to an advancement of commutation angle alpha.

14. The DC motor of claim 8 wherein the position determining circuit means of the commutation circuit comprises a voltage controlled oscillator responsive to the output of said detector circuit, for producing output pulses at a frequency indicative of said detector output signal and a counter means responsive to the oscillator for producing an output signal after a predetermined number of pulses have been counted.

15. The DC motor of claim 8 wherein the detector circuit of the commutation circuit senses the back emf of only one winding at a time and wherein the circuit further comprises switching means that sequentially gate back emf signals from the different windings to the detector circuit.

16. The DC motor of claim 8, wherein the back emf condition sensed by the detector circuit of the commutation circuit includes a characteristic signal generated by means for aiding starting and wherein the characteristic signal is associated with the emf condition of the motor at low motor speed.

17. The DC motor of claim 8 wherein the commutation circuit further includes means for resetting the position determining circuit means after the simulated relative position output is produced.

18. The DC motor of claim 8 wherein the circuit means of the commutation circuit includes logic circuit means responsive to the output of the position determining circuit means for the purpose of selecting an energization sequence for the windings.

19. The DC motor of claim 8, wherein the circuit means of commutation circuit comprises indexing means responsive to the output of the position determining circuit means for producing an energization sequence for the windings.

20. The DC motor of claim 8, wherein the circuit means of the commutation circuit comprises first and second flip-flops, the input of said first flip-flop being coupled to the output of the position determining circuit means to provide first and second complementary signals, said second flip-flop having an input coupled to one of the outputs of said first flip-flop for providing third and fourth complementary signals.

21. The DC motor circuit of claim 8 wherein the commutation circuit further includes protection means operative to prevent damage to the commutation circuit and motor due to reverse polarity of a direct current source supplying power to the commutation circuit and motor.

22. The DC motor of claim 8 wherein the commutation circuit includes power driving means for applying power to the windings and unidirectional conducting means connected thereto for conducting stored energy from a winding after deenergization of the winding.

23. A DC motor comprising a stationary armature having a slotted core and at least two winding stages each comprising at least one effective winding;

each winding comprising at least one coil of winding turns accommodated in nonadjacent slots disposed around a bore of the core and arranged to establish a predetermined number of magnetic poles, and the winding turns of each winding having a number of sets of axially extending conductor portions with such number being equal in number to the predetermined number of poles;

the axially extending conductor portions within each given set being comprised generally of one half of the conductor portions of the at least one coil, and such conductors being disposed to conduct current instantaneously in the same axial direction along the core thereby contributing to the establishment of magnetic poles when the winding containing such given set is energized;

the arcuate spread of any given set of axially extending conductors being less than 120 electrical degrees;

a rotor having constant magentic polarity polar regions equal in number to the predetermined number of poles, said rotor being adapted to rotate relative to the armature in response to the magnetic poles established by the winding turns; and

commutation means for energizing the windings in a predetermined manner to establish the magnetic poles on said armature for causing rotational movement of the rotor.

24. A DC motor comprising a stationary armature having a core and at least two winding stages each comprising at least one effective winding;

each winding comprising concentric winding turns accommodated by the core and arranged to establish a predetermined number of magnetic poles, and the winding turns of each winding having a number of sets of axially extending conductor portions with such number being equl in number to the predetermined number of poles;

the side turn axially extending conductor portions within each given set being disposed to conduct current instantaneously in the same axial direction along the core thereby establishing a predetermined spread and contributing to the establishment of magnetic poles when the winding containing each given set is energized;

a rotor having a plurality of permanent magnet segments disposed thereon and adapted to rotate in response to the magnetic poles established by the armature;

a commutation circuit for energizing the windings in a predetermined manner and at a predetermined angle of advance α

; and

wherein each permanent magnet segment establishes a constant magnetic polar region about said rotor which is about equal in electrical degrees to the winding spread plus 180 (N-1)/N minus 2 α

where N equals the number of winding stages of the motor.

25. The DC motor as set forth in claim 24 wherein the preferred predetermined angle of advance α

is from about 5 electrical degrees to about 30 electrical degrees.

26. The DC motor of claim 24 wherein 180 (N-1)/N with N equal to the number of stages of the motor corresponds to the energization time in electrical degrees of each winding of the motor.

27. The DC motor of claim 24 wherein the preferred value of spread with all slots of the stationary armature being utilized and with no shared slots between windings being about equal to 180/N where N equals the number of winding stages of the motor.

28. A DC motor comprising a stationary armature comprising a core having a longitudinal axis and at least two different energizable windings each including concentrically disposed winding turns, the windings supported on said core to produce at least two spaced apart magnetic poles, a rotor having a predetermined number of constant polarity magnetic regions adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, commutation means for energizing said armature windings in a predetermined manner, at least two groups of winding turns each having a predetermined span of at least about 180 electrical degrees and wherein conductive turn segments in adjacent slots of the core arranged to carry current in the same relative axial direction have a predetermined spread less than 120 electrical degrees.

29. A brushless DC motor comprising a stationary armature having a core and at least two winding stages each comprising at least one effective winding, each winding comprising concentric winding turns accommodated by the core and arranged to produce a predetermined number of magnetic poles, a rotor adapted to rotate about said longitudinal axis in response to the magnetic poles established by said armature, and a commutation circuit for energizing the windings in a predetermined manner wherein said commutation circuit includes a detector circuit comprising:

means responsive to the current drawn by the armature windings to provide an output signal indicative thereof, means for scaling the output signal by a factor corresponding to the resistance of the armature windings, means for substracting the resulting scaled signal from the voltage applied to the armature windings to provide a signal indicative of the back emf of the brushless DC motor, and wherein the commutation circuit further includes a frequency circuit means responsive to the back emf signal for generating a signal of a frequency proportional thereto indicative of the rotor speed and with said frequency circuit means having a minimum frequency output signal to aid starting of the brushless DC motor.

30. The brushless DC motor of claim 29 wherein said frequency circuit means comprises a voltage controlled oscillator for generating a signal of a frequency proportional thereto indicative of rotor speed and wherein the voltage controlled oscillator has a minimum frequency output signal to aid starting of the brushless DC motor.

31. The brushless DC motor of claim 29 wherein the commutation circuit further comprising means for selectively preventing the application of the detector circuit signal indicative of back emf to the frequency circuit means and means operative therewith for selectively substituting a signal proportional to motor load to be applied to the frequency circuit means.

32. The brushless DC motor of claim 31 wherein the means for substituting a signal proportional to motor load comprises means for sampling a first portion of the motor winding current, means for sampling a second portion of the motor winding current, means for comparing the first and second sampled portions, for modifying the frequency of the frequency circuit means output.

33. A commutation circuit for a brushless DC motor having a stationary armature with a longitudinal axis, a plurality of windings disposed on said armature to produce magnetic fields, a rotor adapted to rotate about said longitudinal axis in response to the magnetic fields established by the armature, said commutation circuit comprising:

a detector circuit for sensing the current drawn through the armature windings and for scaling the sensed current signal in accordance with the resistance of the windings, for sensing voltage applied to the winding, and for generating an output signal indicative of rotor speed;

an indexing means responsive to the detector circuit output signal for generating a plurality of output signals indicative of a relative position of said rotor with respect to said armature;

an energizing circuit means responsive to said plurality of output signals from said indexing means for energizing said windings in a predetermined sequence in accordance with the relative position of said rotor.

34. The commutation circuit as claimed in claim 33, wherein said detector circuit includes a voltage-controlled oscillator circuit for generating a signal of a frequency proportional to the rotor speed of the brushless DC motor.

35. A brushless DC motor having a stationary armature with at least two different energizable windings disposed thereon for producing spaced apart magnetic fields and a rotor adapted to rotate about a longitudinal axis in response to the magnetic fields, said motor further comprising:

a rotor position sensor for producing pulse output signals indicative of rotor position relative the stationary armature;

stepping logic circuitry responsive to the pulse output signals from the rotor position sensor for inhibiting continuous winding commutation in a predetermined sequence;

mode control circuitry responsive to the pulse output signals from the rotor position sensor, to rotational direction command signals, and to continuous and stepping operational command signals for producing an output for use in selecting a winding for energization;

a pulse modulating circuit responsive to the mode control circuitry for supplying an output signal for energizing a selected one of the windings; and

a current sensor responsive to the current flow through the windings of the motor for producing an output signal to said pulse modulating circuit for inhibiting the modulating circuit output signal for a predetermined period of time when the motor current exceeds a predetermined value so as to limit the magnitude of current supplied to the motor windings.

36. The brushless DC motor of claim 35 wherein the rotor position sensor includes stationary exciter and pick up coils and a rotating shutter supported by the rotor for sequentially coupling and decoupling the coils to produce output signals indicative of rotor position relative the stationary armature.

37. A brushless DC motor having a stationary armature with at least two different energizable windings for producing spaced apart magnetic fields in time sequence, a rotor adapted to rotate about a longitudinal axis in response to the magnetic fields, and a commutation circuit for controlling commutation of the windings wherein said commutation circuit comprises:

a position circuit for simulating rotor position in accordance with the back emf condition of at least one winding;

a circuit for energizing a selected one of the windings in accordance with the simulated rotor position; and

an under speed protection circuit operable to prevent the circuit for energizing a selected one of the windings from energizing any of the windings when the motor speed is less than a predetermined minimum value for a predetermined length of time.

38. The brushless DC motor of claim 37 wherein said under speed protection circuit includes means for varying said predetermined minimum value of motor speed.

39. The brushless DC motor of claim 37 wherein said under speed protection circuit includes reset means for allowing energization of the motor windings after a predetermined period of time.

40. A brushless DC motor having a stationary armature with at least two different energizable windings disposed on said armature and energizable from a voltage source for producing spaced apart magnetic fields in time sequence, a rotor adapted to rotate about a longitudinal axis in response to the magnetic fields and a commutation circuit for controlling commutation of the windings wherein said commutation circuit comprises:

a position circuit for simulating rotor position in accordance with the back emf condition of at least one winding;

a circuit for energizing a selected one of the windings with power from the voltage source in accordance with the simulated rotor position; and

an undervoltage protection circuit operable to prevent the circuit for energizing a selected one of the windings from energizing any of the windings when the voltage source output is less than a predetermined minimum value.

41. A brushless DC motor having a stationary armature with at least two different energizable windings disposed on said armature and energizable from a voltage source for producing spaced apart magnetic fields in time sequence, a rotor adapted to rotate about a longitudinal axis in response to the magnetic fields and a commutation circuit for controlling commutation of the windings wherein said commutation circuit comprises:

a position circuit for simulating rotor position in accordance with the back emf condition of at least one winding;

a circuit for energizing a selected one of the windings with power from the voltage source in accordance with the simulated rotor position; and

an overvoltage circuit operable to prevent the circuit for energizing a selected one of the windings from energizing any of the windings when the voltage source output is greater than a predetermined maximum value.

42. A commutation circuit for a brushless DC motor having a stationary armature with at least two energizable windings disposed on said armature for producing spaced apart magnetic fields in time sequence, a rotor adapted to rotate about a longitudinal axis in response to the magnetic fields established by the armature and a commutation circuit for controlling commutation of the windings at a predetermined angle of advancement and wherein said commutation circuit includes means for aiding starting of the motor by generating a characteristic signal that is associated with an emf condition of the motor at low motor speed and wherein the characteristic signal is substantially less in magnitude than emf associated with the motor at full operating speed.

43. A DC motor comprising a stationary armature having a core and at least two winding stages each comprising at least one effective winding;

each winding comprising concentric winding turns accommodated by said core and arranged to establish a predetermined number of magnetic poles and the winding turns of each winding having a number of sets of axially extending conductor portions with such number equal to the predetermined number of magnetic poles;

the axially extending conductor portions within each set being disposed in said armature to conduct current instantaneously in the same axial direction along the core thereby to establish a magnetic pole when the winding containing the given set is energized;

a rotor having constant magnetic polar regions equal in number to the predetermined number of poles, said rotor being adapted to rotate in response to the magnetic poles established by the winding turns; and

a commutation circuit for energizing the windings in a predetermined manner wherein said commutation circuit includes a detector circuit for sensing a back emf signal indicative of the back emf condition of at least one winding, position determining circuit means responsive to only a positive polarity portion of the emf signal from the detector circuit for integrating said positive polarity portion of the emf signal to a predetermined value of a volt-seconds whereupon the position determining circuit means produces a simulated relative position output for establishing a predetermined advancement of commutation angle alpha of from about 5 electrical degrees to about 30 electrical degrees, and a circuit means responsive to the simulated relative position output from the position determining circuit means for supplying an output signal for energizing a selected one of the windings.

44. A DC motor comprising a stationary armature comprising a core having a longitudinal axis and at least two windings disposed on said core to produce differently directed magnetic fields, a rotor adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, means for providing signals indicative of the relative rotational position of said rotor, and circuit means responsive to said signals for energizing said stator windings in a predetermined sequence, said means for providing being operative to cause advancement of commutation of the windings by an angle alpha of from about five to about twenty-five electrical degrees to aid the build-up of current when the windings are energized during running condition, wherein said means for providing signals indicative of the relative rotational position of said rotor includes a detector circuit for sensing a back emf signal indicative of the back emf condition of at least one winding and a means responsive to the back emf signal from the detector circuit for integrating the emf signal to a predetermined value of volt-seconds and for producing said signal indicative of the relative rotational position of the rotor.