Control system, method of operating an electronically commutated motor, and laundering apparatus

• US 4,654,566 A
• Filed: 02/02/1983
• Issued: 03/31/1987
• Est. Priority Date: 06/24/1974
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Erdman, David M.
• Primary Examiner(s): Miller, Charles D.
• Assistant Examiner(s): Ro, Bentsu
• Application Number:
  US06/463,147
• Time in Patent Office: 1,518 Days
• Field of Search: 318/138, 318/254, 318/254 A, 318/439, 318/599, 318/811
• US Class Current: 318/400.01
• 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 6/08 Arrangements for controlling the speed or torque of a single motor H02P6/10, H02P6/28 take precedence
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position
• CPC Class Codes: H02P 6/182 using back-emf in windings
• CPC Class Codes: H02P 6/187 using the star point voltage

Abstract

A control system for an electronically commutated DC motor having a rotatable assembly and a stationary assembly with a plurality of winding stages. The application of a DC voltage to the winding stages is controlled to provide an effective voltage thereto by commutating the winding stages to apply the DC voltage thereto in sequence to cause rotation of the rotatable assembly. A neutral conductor voltage of the motor is approximated and compared with the back emf of one of the winding stages to obtain an output representing the angular position of the rotatable assembly. The winding stages are commutated in response to this output when a predetermined angular position is reached. The DC voltage applied to the winding stages is pulse width modulated by alternately pulse width modulating first and second drive circuits. The first drive circuit associated with a winding stage which remains on after commutation is pulse width modulated until a predetermined time after commutation and then there is a shift to pulse width modulate the second drive circuit associated with the winding stage which will remain on after the next commutation.

A method of operating an electronically commutated motor and a laundering apparatus are also disclosed.

Claims

1. A control system for an electronically commutated motor having a rotatable assembly and a stationary assembly with a plurality of winding stages having respective terminals, the control system comprising:

controlling means for controlling the application of a DC voltage to provide a resultant effective voltage to the winding stages, said controlling means including commutating means for commutating the winding stages by applying the DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

approximating means for approximating a neutral conductor voltage for the motor wherein said approximating means has outputs corresponding to each of a plurality of pairs of the winding stages, the voltage on each output being a function of the sum of the terminal voltages of its corresponding pair of winding stages; and

comparing means for comparing the approximated neutral conductor voltage with the terminal voltage of one of the winding stages which is unenergized, the output of said comparing means representing the angular position of the rotatable assembly;

said controlling means being responsive to the output of said comparing means to cause said commutating means to commutate the winding stages when the rotatable assembly reaches a predetermined angular position.

2. The control system as set forth in claim 1 wherein the effective voltage is provided to less than all the winding stages at a time, the terminal voltage for said comparing means being obtained from a winding stage not having the effective voltage applied to it at that time, said approximating means including summing means for summing the terminal voltages of at least two of the winding stages to which the effective voltage is being provided at that time.

3. The control system as set forth in claim 2 wherein the motor has three winding stages, the effective voltage being provided to only two of the stages at a time, the third stage providing the terminal voltage for said comparing means, said summing means including means for summing the terminal voltages of the two stages to which the effective voltage is being provided at that time.

4. The control system as set forth in claim 1 further comprising electronically controlled switch means for connecting the outputs of said approximating means to a selected one of two inputs of said comparing means, said electronically controlled switch means being responsive to said controlling means to connect said selected one input of said comparing means at a particular time only to that output of said approximating means associated with the pair of winding stages to which the effective voltage is being provided at that time.

5. The control system as set forth in claim 4 wherein the back emf of each of the winding stages has different polarities relative to neutral upon different commutations, and further comprising second electronically controlled switch means responsive to said controlling means for selectively connecting to said winding stages the other of said two inputs of said comparing means, thereby to maintain the same polarity of the back emf relative to neutral across said two inputs of said comparing means upon different commutations.

6. The control system as set forth in claim 1 further comprising electronically controlled switch means for connecting the outputs of said approximating means to one input of said comparing means, said electronically controlled switch means being responsive to said controlling means to connect to said comparing means at a particular time only an output of said approximating means associated with a pair of winding stages to which the effective voltage is being provided at that time.

7. The control system as set forth in claim 6 further comprising a set of back emf outputs, one for each winding stage, the voltage on each back emf output being a function of the terminal voltage of its associated winding stage at that particular time, and second electronically controlled switch means for connecting a second input of said comparing means to the back emf outputs, said second electronically controlled switch means being responsive to said controlling means to connect said comparing means at a particular time only to a back emf output associated with a winding stage to which the effective voltage is not being provided at that time.

8. The control system as set forth in claim 7 wherein the motor has three winding stages, the effective voltage being provided to only two of the stages at a time, and said second electronically controlled switch means being responsive to said controlling means for connecting the second input of said comparing means to the back emf output associated with the third winding stage.

9. The control system as set forth in claim 1 wherein

said comparing means includes

integrator means for integrating the back emf of the winding stage to which the effective voltage is not being provided at a given time relative to the approximated neutral conductor voltage, and

commutation signal generating means for generating a commutation signal when the integrating reaches a predetermined level, the commutation signal being the output of said comparing means.

10. The control system as set forth in claim 9 further comprising means connected to said commutation signal generating means for providing respective signals for inhibiting the operation of said integrator means for first lengths of time in response to corresponding ones of the commutation signals, so that the first lengths of time are approximately a predetermined fraction of respective varying lengths of time between successive commutations.

11. A control system for an electronically commutated motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the control system comprising:

commutating means for commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

pulse width modulating means connected to said commutating means for pulse width modulating the DC voltage so that the DC voltage is applied by said commutating means in voltage pulses having a predetermined maximum duty cycle; and

means integrating connected to said pulse width modulating means for repeatedly integrating the DC voltage over the width of each of the voltage pulses and truncating each of the voltage pulses upon the integration reaching a predetermined level, said integrating means being reset before each voltage pulse.

12. The control system as set forth in claim 11 wherein the winding stages have an IR voltage drop when current passes through them, the control system further comprising means for sensing the current passing through the winding stages and effectively adjusting the predetermined level of said means for repeatedly integrating the DC voltage by an amount proportional to the current sensed, whereby voltage regulation for compensation of the IR voltage drop is achieved.

14. The control system as set forth in claim 11 wherein each winding stage of the motor has at least two terminals, one of which is commonly connected to one terminal of each of the other winding stages and the DC voltage is applied by said commutating means to pairs of other terminals of the winding stages in at least one preselected sequence and said pulse width modulating means includes:

logic means responsive to a signal representative of the angular position of the rotatable assembly for supplying a set of control signals to said commutating means in a sequence in which for each commutation one of the winding stages which was energized before commutation remains energized after commutation and the other winding stage which was energized before commutation becomes deenergized after commutation, each winding stage remaining energized through two successive commutations unique to it and then becoming deenergized, the direction of current flow in the winding stage which remains energized after commutation being the same as the direction of current flow in that winding stage before commutation; and

means for width modulating upon commutation the control signal associated with the winding stage which remained energized.

15. A control system for an electronically commutated motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the control system comprising:

commutating means responsive to a set of control signals for commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

commutation signal producing means responsive to a back emf signal indicative of the back emf condition of at least one winding stage for producing a commutation signal indicative of a predetermined angular position of the rotatable assembly; and

control signal means responsive to the commutation signal for providing the set of control signals to said commutating means to commutate the winding stages when the rotatable assembly reaches the predetermined angular position;

said control signal means including inhibiting means for inhibiting the operation of said commutation signal producing means for first lengths of time after corresponding occurrences of the commutation signal so that the first lengths of time are approximately a predetermined fraction of respective varying lengths of time between successive commutations, whereby commutation currents are prevented from affecting said commutation signal producing means.

13. The control system as set forth in claim 17 further comprising:

means for sensing a back emf signal indicative of the back emf condition of at least one winding stage;

commutation pulse generating means responsive to the back emf signal for generating a commutation pulse when the back emf signal indicates that a predetermined angular position of the rotatable assembly has been reached; and

means connected to the commutation pulse generating means for generating a set of control signals for said commutating means in response to receipt of a pulse to commutate the winding stages.

16. The control system as set forth in claim 15 wherein said control signal means further includes digital resetting means for resetting said commutation signal producing means each time the winding stages are commutated, said digital resetting means including an electronically controlled switch responsive to the commutation signal to reset said commutation signal producing means.

17. The control system as set forth in claim 15 wherein the predetermined fraction is approximately one-third whereby the first lengths of time correspond to approximately twenty electrical degrees of rotation of the rotatable assembly.

18. The control system as set forth in claim 15 wherein said inhibiting means includes means for repeatedly causing an electrical signal to increase at a first rate until the commutation signal occurs and then to decrease from a value so attained at a faster rate until a predetermined electrical value is reached and then to increase again at the first rate until the next commutation signal occurs, and means for disabling the operation of said commutation signal producing means while the electrical signal is changing at the faster rate, thereby defining the first lengths of time.

19. The control system as set forth in claim 15 wherein said inhibiting means includes means for generating sets of clock pulses having a first rate and a second faster rate, counting means for counting the clock pulses, means for causing said counting means to count the clock pulses at the first rate until the commutation signal occurs and then to count in reverse at the faster rate until a predetermined count is reached and then to resume counting the clock pulses at the first rate until the next commutation signal occurs, and means for preventing the operation of said commutation signal producing means while the counting is reversed, thereby defining the first lengths of time.

20. The control system as set forth in claim 15 further comprising resettable digital timer means for providing a starting pulse to said control signal means to initiate rotation of the rotatable assembly, said timer means providing the pulse to said control signal means unless the commutation signal occurs before the expiration of a predetermined time interval.

21. The control system as set forth in claim 15 wherein the commutation signal producing means comprising intergrating means for integrating a portion of the back emf signal.

22. The control system as set forth in claim 21 wherein the motor is a two-speed motor, said control system further including time constant providing means responsive to a speed control signal for providing two different time constants for said integrating means corresponding to the two speeds of the motor.

23. The control system as set forth in claim 22 wherein said time constant providing means includes a pair of electronically controlled switches and logic circuitry for preventing both switches from being closed as the same time.

24. The control system as set forth in claim 15 wherein said commutating means includes regulating means for regulating the magnitude of the applied DC voltage, said control system further including pulse width modulating means connected to said regulating means for pulse width modulating the set of control signals, whereby a resultant effective voltage is provided to the winding stages, said pulse width modulating means being responsive to an integral of the applied voltage above a predetermined level to reduce the duty cycle of the pulses applied to the winding stages.

25. The control system as set forth in claim 15 further comprising second inhibiting means for inhibiting the control signal means to prevent the generation of the set of control signals when the motor current exceeds a predetermined maximum value, said second inhibiting means maintaining the inhibition of said control signal means until it is manually reset.

26. A control system for an electronically commutated motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the control system comprising:

commutating means responsive to a set of control signals for commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

position sensing and providing means for sensing the angular position of the rotatable assembly and for providing a commutation signal indicative of a predetermined angular position of the rotatable assembly;

control signal means responsive to said position sensing and providing means for generating the set of control signals for said commutating means to commutate the winding stages when the rotatable assembly reaches the predetermined angular position; and

inhibiting means including means for comparing the motor current with a predetermined maximum value and actuable means connected to said comparing means for inhibiting the control signal means to prevent the generation of the set of control signals when the motor current exceeds the predetermined maximum value, said actuable means having input means for receiving a resetting signal and including means for maintaining the inhibition of said control signal means until a resetting signal appears at the input means.

27. The control system as set forth in claim 26 wherein said inhibiting means includes temporary inhibiting means for temporarily inhibiting fewer than all the control signals when the motor current exceeds a second predetermined value, said second predetermined current value being less than the predetermined maximum current value.

28. The control system as set forth in claim 27 wherein the motor has three winding stages, said control signal means including at least six logic gates, only three of which are inhibited when the motor current exceeds the second predetermined value.

29. The control system as set forth in claim 27 wherein the motor is a two-speed motor, said inhibiting means including means responsive to a speed control signal for providing two different predetermined second current values corresponding to the two speeds of the motor.

30. The control system as set forth in claim 27 further comprising means for sensing the voltage applied to the winding stages, said temporary inhibiting means being responsive to an integral of the DC voltage exceeding a predetermined voltage level to temporarily inhibit all the control signals but one to reduce the effective voltage applied to the winding stages.

31. The control system as set forth in claim 26 wherein the set of control signals are produced at the outputs of a set of logic gates and wherein said actuable means has an inhibit signal output for providing an inhibit signal when the predetermined maximum current value is exceeded, each of said logic gates having inputs connected to the inhibit signal output of said actuable means to receive the inhibit signal.

32. A control system for an electronically commutated motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, said control system comprising:

commutating means responsive to a set of control signals for commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly, each winding stage having at least two terminals, one of which is commonly connected to one terminal of each of the other winding stages and the DC voltage is applied to pairs of other terminals of the winding stages in at least one preselected sequence;

logic means responsive to a signal representative of the angular position of the rotatable assembly for supplying the control signals to said commutating means in a sequence in which for each commutation one of the winding stages which was energized before commutation remains energized after commutation and the other winding stage which was energized before commutation becomes deenergized after commutation, each winding stage remaining energized through two successive commutations unique to it and then becoming deenergized, the direction of current flow in the winding stage which remains energized after commutation being the same as the direction of current flow in that winding stage before commutation; and

pulse width modulating means for pulse width modulating the control signal associated with the winding stage which was commutated on until a time after commutation and for shifting at that time to pulse width modulate the control signal associated with the winding stage which will be deenergized after the next commutation.

33. The control system as set forth in claim 32 wherein said commutating means includes first drive means associated with each winding stage for allowing the flow of current through its associated winding stage in a first direction in response to a first one of the control signals and second drive means associated with each winding stage for allowing the flow of current through its associated winding stage in the opposite direction in response to a second one of the control signals.

34. The control system as set forth in claim 33 further comprising inhibiting means responsive to a signal indicative of motor current for inhibiting said logic means to prevent the generation of the set of control signals when the motor current exceeds a predetermined maximum value, thereby turning off said first and second drive means for all the winding stages, said inhibiting means preventing the generation of control signal until it is manually reset.

35. The control system as set forth in claim 34 wherein said inhibiting means includes temporary inhibiting means for temporarily inhibiting all but one of the control signals when the motor current exceeds a second predetermined value, the second predetermined current value being less than the predetermined maximum current value, whereby one of said first and second drive means is left on to allow circulation of the winding currents.

36. The control system as set forth in claim 35 wherein the motor is a two-speed motor, said inhibiting means including means responsive to a speed control signal and to an applied voltage exceeding a predetermined level to reduce the effective voltage applied to the winding stages.

37. The control system as set forth in claim 35 further comprising means for sensing the voltage applied to the winding stages, said temporary inhibiting means being responsive to an applied voltage exceeding a predetermined level to temporarily inhibit all the control signals but one to reduce the effective voltage applied to the winding stages.

38. The control system as set forth in claim 33 wherein said pulse width modulating means includes means for modulating the control signals for said first drive means and the control signals for said second drive means substantially equal amounts.

39. The control system as set forth in claim 38 further comprising means for generating a drive selection signal which changes state every commutation, said pulse width modulating means being responsive to a first state of the drive selection signal to shift from modulating the control signals for said first drive means to modulating the control signals for said second drive means upon the expiration of said time after commutation and being responsive to a second state of the drive selection signal to shift from modulating the control signals for said second drive means to modulating the control signals for said first drive means upon the expiration of said time after commutation.

40. The control system as set forth in claim 32 further comprising inhibiting means responsive to a signal indicative of motor current for inhibiting the logic means to prevent the generation of the set of control signals when the motor current exceeds a predetermined maximum value, thereby deenergizaing the winding stages, said inhibiting means preventing the generation of control signals until it is manually reset.

41. The control system as set forth in claim 40 wherein said inhibiting means includes temporary inhibiting means for temporarily inhibiting all but one of the control signals when the motor current exceeds a second predetermined value, the second predetermined current value being less than the predetermined maximum current value, whereby one of the winding stages is left on to allow circulation of the winding currents.

42. The control system as set forth in claim 41 wherein the motor is a two-speed motor, said inhibiting means including means responsive to a speed control signal and to an applied voltage exceeding a predetermined level to reduce the effective voltage applied to the winding stages.

43. The control system as set forth in claim 41 further comprising means for sensing the voltage applied to the winding stages, said temporary inhibiting means being responsive to an applied voltage exceeding a predetermined level to temporarily inhibit all the control signals but one to reduce the effective voltage applied to the winding stages.

44. The control system as set forth in claim 32 further comprising means for sensing a back emf signal indicative of the back emf condition of at least one winding stage, integrating means for integrating a portion of the back emf signal to produce an output indicative of the angular position of the rotatable assembly, and commutation signal generating means responsive to the output of said integrating means for generating a commutation signal when said integrating means output reaches a predetermined level, the commutation signal being the signal representative of the angular position of the rotatable assembly to which said logic means is responsive.

45. The control system as set forth in claim 44 further comprising digital resetting means for resetting said integrating means each time the winding stages are commutated, said digital resetting means including an electronically controlled switch responsive to the commutation signal to reset said integrating means.

46. The control system as set forth in claim 45 wherein said digital resetting means include digital delay means for inhibiting the operation of said integrating means for said time after commutation, whereby commutation currents are prevented from being integrated by said integrating means, said pulse width modulating means being responsive to said digital delay means to shift after said time after commutation to pulse width modulate the control signal associated with the winding stage which will be deenergized after the next commutation.

47. A control system for an electronically commutated motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, said control system comprising:

commutating means responsive to a set of control signals for commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly, each winding stage having at least two terminals, one of which is commonly connected to one terminal of each of the other winding stages and the DC voltage is applied to pairs of other terminals of the winding stages in at least one preselected sequence, said commutating means including first drive means associated with each winding stage for allowing the flow of current through its associated winding stage in a first direction in response to a first one of the control signals and second drive means associated with each winding stage for allowing the flow of current through its associated winding stage in the opposite direction in response to a second one of the control signals;

logic means responsive to a signal representative of the angular position of the rotatable assembly for supplying the control signals to said commutating means in a sequence in which for each commutation one of the winding stages which was energized before commutation remains energized after commutation and the other winding stage which was energized before commutation becomes deenergized after commutation, each winding stage remaining energized through two successive commutations unique to it and then becoming deenergized, the direction of current flow in the winding stage which remains energized after commutation being the same as the direction of current flow in that winding stage before commutation; and

pulse width modulating means responsive to respective successive commutations for pulse width modulating the control signals for said first drive means, then shifting to pulse width modulate the control signals for said second drive means upon the expiration of a first time period after one commutation and subsequently shifting back to pulse width modulate the control signals for said first drive means upon the expiration of a second time period after the next commutation.

48. The control system as set forth in claim 47 further comprising inhibiting means responsive to a signal indicative of motor current for inhibiting said logic means to prevent the generation of the set of control signals when the motor current exceeds a predetermined maximum value, thereby turning off said first and second drive means for all the winding stages, said inhibiting means preventing the generation of control signals until it is manually reset.

49. The control system as set forth in claim 48 wherein said inhibiting means includes temporary inhibiting means for temporarily inhibiting all but one of the control signals when the motor current exceeds a second predetermined value, the second predetermined current value being less than the predetermined maximum current value, whereby one of said first and second drive means is left on to allow circulation of the winding currents.

50. The control system as set forth in claim 49 wherein the motor is a two-speed motor, said inhibiting means including means responsive to a speed control signal and to an applied voltage exceeding a predetermined level to reduce the effective voltage applied to the winding stages.

51. The control system as set forth in claim 49 further comprising means for sensing the voltage applied to the winding stages, said temporary inhibiting means being responsive to an applied voltage exceeding a predetermined level to temporarily inhibit all the control signals but one to reduce the effective voltage applied to the winding stages.

52. The control system as set forth in claim 47 further comprising means for sensing a back emf signal indicative of the back emf condition of at least one winding stage, integrating means for integrating a portion of the back emf signal to produce an output indicative of the angular position of the rotatable assembly, and commutation signal generating means responsive to the output of said integrating means for generating a commutation signal when said integrating means output reaches a predetermined level, the commutation signal being the signal representative of the angular position of the rotatable assembly to which said logic means is responsive.

53. The control system as set forth in claim 52 further comprising digital resetting means for resetting said integrating means each time the winding stages are commutated, said digital resetting means including an electronically controlled switch responsive to the commutation signal to reset said integrating means.

54. The control system as set forth in claim 53 wherein said digital resetting means includes digital delay means for inhibiting the operation of said integrating means for the time periods after commutations, whereby commutation currents are prevented from being integrated by said integrating means, said pulse width modulating means being responsive to said digital delay means to shift upon the expiration of the time periods after commutations.

55. A control system for an electronically commutated motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, said control system comprising:

commutating means responsive to a set of control signals for commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly, each winding stage having at least two terminals, one of which is commonly connected to one terminal of each of the other winding stages and the DC voltage is applied to pairs of other terminals of the winding stages in at least one preselected sequence;

logic means responsive to a signal representative of the angular position of the rotatable assembly for supplying the control signals to said commutating means in a sequence in which for each commutation one of the winding stages which was energized before commutation remains energized after commutation and the other winding stage which was energized before commutation becomes deenergized after commutation, each winding stage remaining energized through two successive commutations unique to it and then becoming deenergized, the direction of current flow in the winding stage which remains energized after commutation being the same as the direction of current flow in that winding stage before commutation;

pulse width modulating means for pulse width modulating the control signals; and

means responsive to a commutation selection signal for controlling said pulse width modulating means when the commutation selection signal is in a first state to pulse width modulate the control signal associated with the winding stage which is commutated on until a time after commutation and for shifting at that time to pulse width modulate the control signal associated with the winding stage which will be deenergized after the next commutation and for controlling said pulse width modulating means when the commutation selection signal is in a second state to pulse width modulate upon commutation the control signal associated with the winding stage which remained on.

56. The control system as set forth in claim 55 wherein said commutating means includes first drive means associated with each winding stage for allowing the flow of current through its associated winding stage in a first direction in response to a first one of the control signals and second drive means associated with each winding stage for allowing the flow of current through its associated winding stage in the opposite direction in response to a second one of the control signals.

57. The control system as set forth in claim 56 further comprising inhibiting means responsive to a signal indicative of motor current for inhibiting said logic means to prevent the generation of the set of control signals when the motor current exceeds a predetermined maximum value, thereby turning off said first and second drive means for all the winding stages, said inhibiting means preventing the generation of control signals until it is manually reset.

58. The control system as set forth in claim 57 wherein said inhibiting means includes temporary inhibiting means for temporarily inhibiting all but one of the control signals when the motor current exceeds a second predetermined value, the second predetermined current value being less than the predetermined maximum current value, whereby one of said first and second drive means is left on to allow circulation of the winding currents.

59. The control system as set forth in claim 58 wherein the motor is a two-speed motor, said inhibiting means including means responsive to a speed control signal and to an applied voltage exceeding a predetermined level to reduce the effective voltage applied to the winding stages.

60. The control system as set forth in claim 58 further comprising means for sensing the voltage applied to the winding stages, said temporary inhibiting means being responsive to an applied voltage exceeding a predetermined level to temporarily inhibit all the control signals but one to reduce the effective voltage applied to the winding stages.

61. The control system as set forth in claim 56 further comprising means for generating a drive selection signal every other commutation, said pulse width modulating means being responsive to a first state of the drive selection signal to shift from modulating the control signals for said first drive means to modulating the control signals for said second drive means and being responsive to a second state of the drive selection signal to shift from modulating the control signals for said second drive means to modulating the control signals for said first drive means, the second and first states of the commutation selection signal respectively determining whether the shifting occurs upon commutation or at said time after commutation.

62. A control system for an electronically commutated motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, said control system comprising:

commutating means responsive to a set of control signals for commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly, each winding stage having at least two terminals, one of which is commonly connected to one terminal of each of the other winding stages and the DC voltage is applied to pairs of other terminals of the winding stages in at least one preselected sequence, said commutating means including first drive means associated with each winding stage for allowing the flow of current through its associated winding stage in a first direction in response to a first one of the control signals and second drive means associated with each winding stage for allowing the flow of current through its associated winding stage in the opposite direction in response to a second one of the control signals;

logic means responsive to a signal representative of the angular position of the rotatable assembly for supplying the control signals to said commutating means in a sequence in which for each commutation one of the winding stages which was energized before commutation remains energized after commutation and the other winding stage which was energized before commutation becomes deenergized after commutation, each winding stage remaining energized through two successive commutations unique to it and then becoming deenergized, the direction of current flow in the winding stage which remains energized after commutation being the same as the direction of current flow in that winding stage before commutation;

means for generating a drive selection signal which changes state every commutation; and

means responsive to the drive selection signal for pulse width modulating the control signals for said first drive means and then shifting to pulse width modulate the control signals for said second drive means when the drive selection signal changes state upon commutation and subsequently shifting back to pulse width modulate the control signals for said first drive means when the drive selection signal again changes state upon the next commutation.

63. The control system as set forth in claim 62 further comprising inhibiting means responsive to a signal indicative of motor current for inhibiting said logic means to prevent the generation of the set of control signals when the motor current exceeds a predetermined maximum value, thereby turning off said first and second drive means for all the winding stages, said inhibiting means preventing the generation of control signals until it is manually reset.

64. The control system as set forth in claim 63 wherein said inhibiting means includes temporary inhibiting means for temporarily inhibiting all but one of the control signals when the motor current exceeds a second predetermined value, the second predetermined current value being less than the predetermined maximum current value, whereby one of said first and second drive means is left on to allow circulation of the winding currents.

65. The control system as set forth in claim 64 wherein the motor is a two-speed motor, said inhibiting means including means responsive to a speed control signal and to an applied voltage exceeding a predetermined levl to reduce the effective voltage applied to the winding stages.

66. The control system as set forth in claim 64 further comprising means for sensing the voltage applied to the winding stages, said temporary inhibiting means being responsive to an integral of the applied voltage exceeding a predetermined level to temporarily inhibit all the control signals but one to reduce the effective voltage applied to the winding stages.

67. A control system for an electronically commutated, two-speed motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the control system comprising:

commutating means responsive to a set of control signals for commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

back emf sensing means for sensing a back emf signal indicative of the back emf condition of at least one winding

integrating means for integrating a portion of the back emf signal and for producing a commutation signal indicative of a predetermined angular position of the rotatable assembly;

control signal means responsive to the commutation signal for providing the set of control signals to said commutating means to commutate the winding stages when the rotatable assembly reaches the predetermined angular position; and

time constant providing means responsive to a speed control signal for providing two different time constants for said integrating means corresponding to the two speeds of the motor.

68. The control system as set forth in claim 67 further comprising digital delay means for inhibiting the operation of said integrating means for a predetermined interval of time after the occurrence of the commutation signal whereby commutation currents are prevented from being integrated by said integrating means.

69. The control system as set forth in claim 67 wherein the winding stages have respective terminals, the control system further comprising means for approximating a neutral conductor voltage for the motor and wherein said back emf sensing means includes means for comparing the approximated neutral conductor voltage with the terminal voltage of one of the winding stages.

70. The control system as set forth in claim 67 wherein said time constant providing means includes a pair of electronically controlled switches responsive to the commutation signal to inhibit integration by said integrating means.

71. The control system as set forth in claim 67 wherein said time constant providing means includes a pair of electronically controlled switches and logic circuitry for preventing both switches from being closed at the same time.

72. A laundering apparatus comprising in combination:

a rotatable component;

an electronically commutated motor, said motor comprising rotatable assembly means for driving the rotatable component and a stationary assembly with a plurality of winding stages;

a control system connected to said motor; and

means for applying a DC voltage to said control system;

said control system including controlling means for controlling the application of the DC voltage to provide a resultant effective voltage to said winding stages, said controlling means including commutating means for commutating said winding stages by applying the DC voltage thereto in at least one preselected sequence to cause rotation of said rotatable assembly means, thereby to cause rotation of said rotatable component;

approximating means for approximating a neutral conductor voltage for said motor wherein said approximating means has outputs for each of a plurality of pairs of said winding stages, the voltage on each output being a function of the sum of the terminal voltages of its associated pair of winding stages; and

comparing means for comparing the approximated neutral conductor voltage with the terminal voltage of one of said winding stages, the output of said comparing means representing the angular position of said rotatable assembly means;

said controlling means further including means responsive to the output of said comparing means to cause said commutating means to commutate said winding stages when said rotatable assembly means reaches a predetermined angular position.

73. The laundering apparatus as set forth in claim 72 wherein the back emf of each of the winding stages has different polarities relative to neutral upon different commutations, and further comprising first electronically controlled switch means for connecting the outputs of said approximating means to a selected one of two inputs of said comparing means, said first electronically controlled switch means being responsive to said controlling means to connect to said selected one input of said comparing means at a particular time only that output of said approximating means associated with the pair of winding stages to which the effective voltage is being provided at that time, and second electronically controlled switch means responsive to said controlling means for selectively connecting said winding stages to the other of said two inputs of said comparing means, thereby to maintain the same polarity of the back emf relative to neutral across said two inputs of said comparing means upon different commutations.

74. The laundering apparatus as set forth in claim 72 further comprising electronically controlled switch means for connecting the outputs of said approximating means to said comparing means, said electronically controlled switch means being responsive to said controlling means to connect said comparing means at a particular time only to that output of the approximating means associated with said pair of winding stages to which the effective voltage is being provided at that time.

75. The laundering apparatus as set forth in claim 72 wherein

said comparing means for comparing the approximated neutral conductor voltage with the terminal voltage of one of said winding stages includes

integrator means for integrating the back emf of one of said winding stages to which the effective voltage is not being provided at a given time relative to the approximated neutral conductor voltage, and

means for generating a commutation signal when said integrator means output reaches a predetermined level, the commutation signal being the output of said comparing means.

76. A laundering apparatus comprising in combination:

a rotatable component;

an electronically commutated DC motor, said motor comprising rotatable assembly means for driving the rotatable component and a stationary assembly with a plurality of winding stages;

a control system connected to said motor; and

means for applying a DC voltage to said control system;

said control system commutating including means responsive to a set of control signals for commutating said winding stages by applying the DC voltage thereto in at least one preselected sequence to cause rotation of said rotatable assembly means;

integrating means for integrating a portion of a back emf signal indicative of the back emf condition of at least one of said winding stages to produce an output indicative of the angular position of said rotatable assembly means;

first pulse generating means responsive to the output of said integrating means for generating a pulse when said integrating means output reaches a predetermined level;

control signal means connected to said first pulse generating means for providing the set of control signals to said commutating means in response to receipt of a pulse to commutate said winding stages, said control signal means including inhibiting means for inhibiting the operation of said integrating means for first lengths of time after corresponding occurrences of the pulse from said first pulse generating means so that the first lengths of time are approximately a predetermined fraction of respective varying lengths of time between successive commutations, whereby commutation currents are prevented from affecting said integrating means.

77. The laundering apparatus as set forth in claim 76 wherein said inhibiting means includes means for generating sets of clock pulses having a first rate and a second faster rate counting means for counting the clock pulses, means for causing said counting means to count the clock pulses at the first rate until a pulse from said first pulse generating means occurs, and then to count in reverse at the second rate until a predetermined count is reached and then to resume counting the clock pulses at the first rate until the nest pulse occurs, and means for disabling the operation of said integrating means while the counting is reversed, thereby defining the first lengths of time.

78. A laundering apparatus comprising a combination:

a rotatable component;

an electronically commutated motor, said motor comprising rotatable assembly means for driving the rotatable component and a stationary assembly with a plurality of winding stages;

a control system connected to said motor; and

means for supplying a DC voltage to said control system;

said control system including commutating means responsive to a set of control signals for commutating said winding stages by applying the DC voltage thereto in at least one preselected sequence to cause rotation of said rotatable assembly means, each winding stage having at least two terminals, one of which is commonly connected to one terminal of each of the other winding stages and the DC voltage is applied to pairs of other terminals of said winding stages in at least one preselected sequence;

logic means responsive to a signal representative of the angular position of said rotatable assembly means for supplying the control signals to said commutating means in a sequence in which for each communtation one of said winding stages which was energized before commutation remains energized after commutation and another winding stage which was energized before commutation becomes deenergized after commutation, each winding stage remaining energized through two successive commutations unique to it and then becoming deenergized, the direction of current flow in said winding stage which remains energized after commutation being the same as the direction of current flow in that winding stage before commutation; and

pulse width modulating means for pulse width modulating the control signal associated with said winding stage which was commutated on until a time after commutation and for shifting at that time a pulse width modulate the control signal associated with said winding stage which will be deenergized after the next commutation.

79. The laundering apparatus as set forth in claim 78 wherein said commutating means includes first drive means associated with each winding stage for allowing the flow of current through its associated winding stage in a first direction in response to a first one of the control signals and second drive means associated with each winding stage for allowing the flow of current through its associated winding stage in the opposite direction in response to a second one of the control signals.

80. The laundering apparatus as set forth in claim 79 further comprising inhibiting means responsive to a signal indicative of motor current for inhibiting said logic means to prevent the generation of the set of control signals when the motor current exceeds a predetermined maximum value, thereby turning off said first and second drive means for all said winding stages, said inhibiting means preventing the generation of control signals until it is manually reset.

81. The laundering apparatus as set forth in claim 80 wherein said inhibiting means includes temporary inhibiting means for temporarily inhibiting all but one of the control signals when the motor current exceeds a second predetermined value, the second predetermined current value being less than the predetermined maximum current value, whereby one of said first and second drive means is left on to allow circulation of the winding currents.

82. The laundering apparatus as set forth in claim 81 wherein said motor is a two-speed motor, said inhibiting means including means responsive to a speed control signal for providing two different predetermined second current values corresponding to the two speeds of said motor.

83. The laundering apparatus as set forth in claim 81 further comprising means for sensing the voltage applied to said winding stages said temporary inhibiting means being responsive to an integral of the applied voltage exceeding a predetermined level to temporarily inhibit all the control signals but one to reduce the effective voltage applied to said winding stages.

84. The laundering apparatus as set forth in claim 79 wherein said pulse width modulating means includes means for modulating the control signals for said first drive means and the control signals for said second drive means substantially equal amounts.

85. The laundering apparatus as set forth in claim 84 further comprising means for generating a drive selection signal every other commutation, said pulse width modulating means being responsive to a first state of the drive selection signal to shift from modulating the control signals for said first drive means to modulating the control signals for said second drive means upon the expiration of said time after commutation and being responsive to a second state of the drive selection signal to shift from modulating the control signals for said second drive means to modulating the control signals for said first drive means upon the expiration of said time after commutation.

86. The laundering apparatus as set forth in claim 78 further comprising means for sensing a back emf signal indicative of the back emf condition of at least one winding stage, intergrating means for integrating a portion of the back emf signal to produce an output indicative of the angular position of said rotatable assembly means, and pulse generating means responsive to the output of said integrating means for generating a commutation pulse when said intergrating means output reaches a predetermined level, the pulse being the signal representative of the angular position of said rotatable assembly means to which said logic means is responsive.

87. The laundering apparatus as set forth in claim 86 further comprising digital resetting means for resetting said integrating means each time said winding stages are commutated, said digital resetting means including an electronically controlled switch responsive to the commutation pulse to reset said integrating means.

88. The laundering apparatus as set forth in claim 87 wherein said digital resetting means includes digital delay means for inhibiting the operation of said integrating means for said time after commutation, whereby commutation currents are prevented from being integrated by said integrating means, said pulse width modulating means being responsive to said digital delay means to shift after said time after commutation.

89. The laundering apparatus as set forth in claim 87 wherein said motor is a two-speed motor, said control system further including means responsive to a speed control signal for providing two different time constants for said integrating means corresponding to the two speeds of said motor.

90. A laundering apparatus comprising in combination:

a rotatable component;

an electronically commutated motor, said motor comprising rotatable assembly means for driving the rotatable component and a stationary assembly with a plurality of winding stages;

a control system connected to said motor; and

means for applying a DC voltage to said control system;

said control system including commutating means for commutating said winding stages by applying the DC voltage thereto in at least one preselected sequence to cause rotation of said rotatable assembly means;

pulse width modulating means connected to said commutating means for pulse width modulating the DC voltage so that the DC voltage is applied by said commutating means in voltage pulses having a predetermined maximum duty cycle; and

integrating means connected to said pulse width modulating means for repeatedly integrating the DC voltage over the width of each of the voltage pulses and truncating each of the voltage pulses upon the integration reaching a predetermined level, said integrating means being reset before each voltage pulse.

91. The laundering apparatus as set forth in claim 90 wherein said winding stages have low and high speed connections and have an IR voltage drop depending on which of the low or high speed connections is energized when current passes through said winding stages, said control system further comprising means responsive to a speed control signal indicative of which connection is energized, for sensing the current passing through said winding stages and effectively adjusting the predetermined level of said means for repeatedly integrating the DC voltage by an amount dependent upon the current sensed and said speed control signal, whereby voltage regulation for compensation of the IR voltage drop on both the low and high speed connections is achieved.

92. A laundering apparatus comprising in combination:

a rotatable component;

an electronically commutated motor, said motor comprising rotatable assembly means for driving the rotatable component and a stationary assembly with a plurality of winding stages;

a control system connected to said motor; and

means for supplying a DC voltage to said control system;

said control means including commutating means responsive to a set of control signals for commutating said winding stages by applying the DC voltage thereto in at least one preselected sequence to cause rotation of said rotatable assembly means, each winding stage having at least two terminals, one of which is commonly connected to one terminal of each of the other winding stages and the DC voltage is applied to pairs of other terminals of said winding stages in at least one preselected sequence, said commutating means including first drive means associated with each winding stage for allowing the flow of current through its associated winding stage in a first direction in response to a first one of the control signals and second drive means associated with each winding stage for allowng the flow of current through its associated winding stage in the opposite direction in response to a second one of the control signals;

logic means responsive to a signal representative of the angular position of said rotatable assembly means for supplying the control signals to said commutating means in a sequence in which for each commutation one of said winding stages which was energized before commutation remains energized after commutation and another winding stage which was energized before commutation becomes deenergized after commutation, each winding stage remaining energized through two successive commutations unique to it and then becoming deenergized, the direction of current flow in said winding stage which remains energized after commutation being the same as the direction of current flow in that winding stage before commutation; and

pulse width modulating means responsive to respective successive commutations for pulse width modulating the control signals for said first drive means, then shifting to pulse width modulate the control signals for said second drive means upon the expiration of a first time period after one commutation and subsequently shifting back to pulse width modulate the control signals for the first drive means upon the expiration of a second time period after the next commutation.

93. The laundering apparatus as set forth in claim 92 further comprising inhibiting means responsive to a signal indicative of motor current for inhibiting said logic means to prevent the generation of the set of control signals when the motor current exceeds a predetermined maximum value, thereby turning off said first and second drive means for all said winding stages, said inhibiting means preventing the generation of control signals until it is manually reset.

94. The laundering apparatus as set forth in claim 93 wherein said inhibiting means includes temporary inhibiting means for temporarily inhibiting all but one of the control signals when the motor current exceeds a second predetermined value, the second predetermined current value being less than the predetermined maximum current value, whereby one of said first and second drive means is left on to allow circulation of the winding currents.

95. The laundering apparatus as set forth in claim 94 wherein said motor is a two-speed motor, said inhibiting means including means responsive to a speed control signal for providing two different predetermined second current values corresponding to the two speeds of said motor.

96. The laundering apparatus as set forth in claim 94 further comprising means for sensing the voltage applied to said winding stages, said temporary inhibiting means being responsive to an integral of the applied voltage exceeding a predetermined level to temporarily inhibit all the control signals but one to reduce the effective voltage applied to said winding stages.

97. The laundering apparatus as set forth in claim 92 further comprising means for sensing a back emf signal indicative of the back emf condition of at least one winding stage, intergrating means for integrating a portion of the back emf signal to produce an output indicative of the angular position of said rotatable assembly means, and pulse generating means responsive to the output of said integrating means for generating a commutation pulse when said intergrating means output reaches a predetermined level, the pulse being the signal representative of the angular position of said rotatable assembly means to which said logic means is responsive.

98. The laundering apparatus as set forth in claim 97 further comprising digital resetting means for resetting said integrating means each time said winding stages are commutated, said digital resetting means including an electronically controlled switch responsive to the commutation pulse to reset said integrating means.

99. The laundering apparatus as set forth in claim 98 wherein said digital resetting means includes digital delay means for inhibiting the operation of said integrating means for said time periods after commutations, whereby commutation currents are prevented from being integrated by said integrating means, said pulse width modulating means being responsive to said digital delay means to shift upon the expiration of said time periods after commutations.

100. The laundering apparatus as set forth in claim 98 wherein said motor is a two-speed DC motor, said control system further including means responsive to a speed control signal for providing two different time constants for said integrating means corresponding to the two speeds of said motor.

101. A laundering apparatus comprising in combination:

a rotatable component;

an electronically commutated, two-speed motor, said motor comprising rotatable assembly means for driving the rotatable component and a stationary assembly with a plurality of winding stages;

a control system connected to said motor; and

means for applying a DC voltage to said control system;

said control system including commutating means responsive to a set of control signals for commutating said winding stages by applying the DC voltage thereto in at least one preselected sequence to cause rotation of said rotatable assembly means;

back emf sensing means for sensing a back emf signal indicative of the back emf condition of at least one winding stage;

integrating means for integrating a portion of the back emf signal and for producing a commutation signal indicative of a predetermined angular position of said rotatable assembly means; and

control signal means responsive to the commutation signal for providing the set of control signals to said commutating means to commutate said winding stages when said rotatable assembly means reaches the predetermined angular position; and

means responsive to a speed control signal for providing two different time constants for said integrating means corresponding to the two speeds of said motor.

102. The laundering apparatus as set forth in claim 101 further comprising digital delay means for inhibiting the operation of said integrating means for an interval of time after the occurrence of the commutation signal whereby commutation currents are prevented from being integrated by said integrating means.

103. The laundering apparatus as set forth in claim 101 wherein said winding stages have respective terminals, the laundering apparatus further comprising means for approximating a neutral conductor voltage for said motor and wherein said back emf sensing means includes means for comparing the approximated neutral conductor voltage with the terminal voltage of one of said winding stages.

104. A method of operating an electronically commutated motor with the motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the method comprising the steps of:

commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

approximating a neutral conductor voltage for the motor at outputs corresponding to each of a plurality of pairs of the winding stages, the voltage on each of the outputs being a function of the sum of the terminal voltages of its corresponding pair of winding stages; and

comparing the approximated neutral conductor voltage with the terminal voltage of one of the winding stages, the result of the comparison representing the angular position of the rotatable assembly;

the commutation of the winding stages occurring when the rotatable assembly reaches a predetermined angular position.

105. The method as set forth in claim 104 wherein the motor has three winding stages, the effective voltage being provided to only two of the stages at a time, the approximating step including summing the terminal voltages of the two stages to which the effective voltage is being provided at that time.

106. The method as set forth in claim 104 wherein the comparing step includes the steps of:

integrating the back emf of one of the winding stages relative to the approximated neutral conductor voltage to provide a signal representing the angular position of the rotatable assembly; and

generating a commutation signal when the integration result reaches a predetermined level.

107. The method as set forth in claim 106 including the further step of inhibiting the integrating step for respective intervals of time after occurrences of the commutation signal so that the intervals of time are approximately a predetermined fraction of respective varying lengths of time between successive occurrences of the commutation signal.

108. The method as set forth in claim 104 wherein the DC voltage is provided to fewer than all the winding stages at a time, the terminal voltage for the comparison being obtained from a winding stage not having the DC voltage applied to it at that time, and the approximating step including summing the terminal voltages of at least two of the winding stages to which the effective voltage is being provided at that time.

109. The method as set forth in claim 104 further including selectively switching to said winding stages and to the outputs for said approximated neutral voltage to maintain the same polarity of back emf relative to neutral upon different commutations for use in said comparing step.

110. A method of operating an electronically commutated motor with the motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the method comprising the steps of:

commutating the winding stages in response to a set of control signals by applying the DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

sensing a back emf signal indicative of the back emf condition of at least one winding stage;

producing a commutation signal indicative of a predetermined angular position of the rotatable assembly in response to the sensed back emf signal;

providing the set of control signals in response to the commutation signal to commutate the winding stages when the rotatable assembly reaches the predetermined angular position; and

inhibiting the sensing step for respective intervals of time after occurrences of the commutation signal so that the intervals of time are approximately a predetermined fraction of respective varying lengths of time between successive occurrences of the commutation signal, whereby commutation currents are prevented from being sensed.

111. The method as set forth in claim 110 wherein the respective intervals of time correspond to approximately twenty electrical degrees of rotation of the rotatable assembly.

112. The method as set forth in claim 110 wherein the inhibiting step includes repeatedly causing an electrical signal to increase at a first rate until the commutation signal occurs and then to decrease from a value so attained at a faster rate until a predetermined electrical value is reached and then to increase again at the first rate until the next commutation signal occurs, thereby defining the respective intervals of time when the electrical signal is changing at the faster rate.

113. The method as set forth in claim 110 wherein the inhibiting step includes generating sets of clock pulses having a first rate and a second faster rate;

counting the clock pulses at the first rate until the commutation signal occurs and then counting in reverse at the faster rate until a predetermined count is reached and then resuming counting the clock pulses at the first rate until the next commutation signal occurs; and

preventing the sensing while the counting is reversed, thereby defining the respective intervals of time.

114. The method as set forth in claim 110 further including the step of digitally providing a starting pulse to initiate rotation of the rotatable assembly unless the commutation signal occurs before the expiration of a predetermined time interval.

115. The method as set forth in claim 110 wherein the motor is a two-speed motor, and the commutation signal producing step including integrating at a first rate in response to one state of a speed control signal and integrating at a second rate in response to a second state of the speed control signal, the two states of the speed control signal corresponding to the two speeds of the motor.

116. The method as set forth in claim 110 further including the steps of pulse width modulating the set of control signals and reducing the duty cycle of the pulses of the DC voltage thereby applied to the winding stages in response to an integration of the DC voltage reaching a predetermined level.

117. A method of operating an electronically commutated motor with the motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the method comprising the steps of:

commutating the winding stages by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

pulse width modulating the DC voltage so that the DC voltage is applied in said commutating step in voltage pulses having a predetermined maximum duty cycle; and

controlling said pulse width modulating by repeatedly integrating the DC voltage over the width of each of the voltage pulses, the integrating beginning from a value that is reset before each voltage pulse, and truncating each of the voltage pulses upon the integrating reaching a predetermined level.

118. A method of operating an electronically commutated motor with the motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the method comprising the steps of:

receiving a DC voltage for application to the motor;

commutating the winding stages in response to a set of control signals by applying the DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

sensing the angular position of the rotatable assembly and providing a commutation signal indicative of a predetermined angular position of the rotatable assembly;

providing the set of control signals to commutate the winding stages when the rotatable assembly reaches the predetermined angular position; and

inhibiting the generation of the set of control signals when the motor current exceeds a predetermined maximum value, the inhibition being maintained until it is manually overriden.

119. The method as set forth in claim 118 wherein the inhibiting step includes temporarily inhibiting less than all the control signals when the motor current exceeds a second predetermined value, the second predetermined current value being less than the predetermined maximum current value.

120. The method as set forth in claim 119 including sensing the DC voltage applied to the winding stages and temporarily inhibiting all the control signals but one to reduce the effective voltage applied to the winding stages when the integral of the DC voltage exceeds a predetermined level.

121. A method of operating an electronically commutated motor with the motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the method comprising the steps of:

commutating the winding stages in response to a set of control signals by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly, each winding stage having at least two terminals, one of which is commonly connected to one terminal of each of the other winding stages and the DC voltage is applied to pairs of other terminals of the winding stages in at least one preselected sequence;

supplying the control signals in a sequence in which for each commutation one of the winding stages which was energized before commutation remains energized after commutation and the other winding stage which was energized before commutation becomes deenergized after commutation, each winding stage remaining energized through two successive commutations unique to it and then becoming deenergized, the direction of current flow in the winding stage which remains energized after commutation being the same as the direction of current flow in that winding stage before commutation; and

pulse width modulating the control signal associated with the winding stage which was commutated on until a time after commutation and shifting at that time to pulse width modulate the control signal associated with the winding stage which will be deenergized after the next commutation.

122. The method as set forth in claim 121 wherein the winding stages have associated therewith drive means for selectively allowing the flow of current through at least one of the winding stages in a first direction in response to some of the control signals and second drive means for selectively allowing the flow of current through at least one of the winding stages in the opposite direction in response to others of the control signals, wherein the pulse width modulating step includes modulating the control signals for the first drive means and the control signals for the second drive means substantially equal amounts.

123. The method as set forth in claim 122 further including generating a drive selection signal every other commutation, and shifting in response to a first state of the drive selection signal from modulating the control signals for the first drive means to modulating the control signals for the second drive means upon the expiration of said time after commutation and shifting in response to a second state of the drive selection signal from modulating the control signals for the second drive means to modulating the control signals for the first drive means upon the expiration of said time after commutation.

124. The method as set forth in claim 121 further including sensing a back emf signal indicative of the back emf condition of at least one winding, integrating a portion of the back emf signal to produce an output indicative of the angular position of the rotatable assembly, and generating a commutation signal when the integration output reaches a predetermined level, the commutation signal representing the angular position of the rotatable assembly.

125. The method as set forth in claim 124 including inhibiting the integration between a commutation and said time after commutation, whereby commutation currents are prevented from being integrated by the integrating means.

126. A method of operating an electronically commutated motor with the motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the method comprising the steps of:

a commutating the winding stages in response to a set of control signals by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly, the winding stages being connected together at one end whereby the DC voltage is applied to a pair of winding stages at a time, and wherein each winding stage has associated therewith first drive means for allowing the flow of current through its associated winding stage in a first direction in response to a first one of the control signals and second drive means for allowing the flow of current through its associated winding stage in the opposite direction in response to a second one of the control signals;

supplying the control signals in a sequence in which for each commutation one of the winding stages which was energized before commutation remains energized after commutation and the other winding stage which was energized before commutation becomes deenergized after commutation, each winding stage remaining energized through two successive commutations unique to it and then becoming deenergized, the direction of current flow in the winding stage which remains energized after commutation being the same as the direction of current flow in that winding stage before commutation; and

pulse width modulating upon commutation the control signal associated with the winding stage which remains energized by generating a drive selection signal every other commutation and in response to a first state of the drive selection signal shifting from modulating the control signals for the first drive means to modulating the control signals for the second drive means upon commutation and in response to a second state of the drive selection signal shifting from modulating the control signals for the second drive means to modulating the control signals for the first drive means upon commutation.

127. The method as set forth in claim 126 further including sensing the motor current and inhibiting generation of the set of control signals when the motor current exceeds a predetermined maximum value, thereby turning off the first and second drive means for all the winding stages, said inhibiting preventing the generation of control signals until it is manually overridden.

128. The method as set forth in claim 127 including temporarily inhibiting all but one of the control signals when the motor current exceeds a second predetermined value, the second predetermined current value being less than the predetermined maximum current value, whereby one of the drive means is left on to allow circulation of the winding currents.

129. The method as set forth in claim 128 including sensing the voltage applied to the winding stages and, in response to an integral of the applied voltage exceeding a predetermined level, temporarily inhibiting all the control signals but one to reduce the effective voltage applied to the winding stages.

130. A method of operating an electronically commutated, two-speed motor with the motor having a rotatable assembly and a stationary assembly with a plurality of winding stages, the method comprising the steps of:

commutating the winding stages in response to a set of control signals by applying a DC voltage thereto in at least one preselected sequence to cause rotation of the rotatable assembly;

sensing a back emf signal indicative of the back emf condition of at least one winding;

integrating a portion of the back emf signal and producing a commutation signal indicative of a predetermined angular position of the rotatable assembly, the integration occurring at a first rate when the motor is being operated at one speed and occurring at a second rate when the motor is being operated at the second speed, the rate of integration being determined by a speed control signal; and

providing the set of control signals in response to the commutation signal to commutate the winding stages when the rotatable assembly reaches the predetermined angular position.

131. The method as set forth in claim 130 further including digitally inhibiting the integration for a time after the occurrence of the commutation signal, whereby commutation currents are prevented from being integrated by the integrating means.

132. The method as set forth in claim 130 wherein the winding stages have respective terminals, the method further including approximating a neutral conductor voltage for the motor and wherein the back emf sensing step includes comparing the approximated neutral conductor voltage with the terminal voltage of one of the winding stages.