Throttle control for small engines and other applications

• US 6,118,186 A
• Filed: 07/03/1997
• Issued: 09/12/2000
• Est. Priority Date: 09/14/1994
• Status: Expired due to Fees

• Current Assignee: Pramac America LLC
• Original Assignee: Coleman Company Incorporated (Newell Brands Inc.)
• Inventors: Anderson, William J., Scott, Harold C., Sun, Chiping, Pandya, Kandarp I.
• Primary Examiner(s): Ramirez, Nestor
• Assistant Examiner(s): Ponomarenko, Nicholas
• Application Number:
  US08/887,908
• Time in Patent Office: 1,167 Days
• Field of Search: 290/1 A, 290/2, 290/40 A, 290/41, 290/40 B, 290/51, 322/1, 322/7, 322/8, 322/14, 322/15, 322/16, 322/25, 322/17
• US Class Current: 290/40.00B
• CPC Class Codes: F02D 11/10 of the electric type
• CPC Class Codes: F02D 11/105 characterised by the function converting demand to actuation, e.g. a map indicating relations between an accelerator pedal position and throttle valve opening or target engine torque
• CPC Class Codes: F02D 11/107 Safety-related aspects
• CPC Class Codes: F02D 2011/101 characterised by the means for actuating the throttles
• CPC Class Codes: F02D 2011/102 at least one throttle being moved only by an electric actuator
• CPC Class Codes: F02D 2200/0404 Throttle position
• CPC Class Codes: F02D 9/1065 Mechanical control linkage between an actuator and the flap, e.g. including levers, gears, springs, clutches, limit stops of the like
• CPC Class Codes: H02P 2101/45 for motor vehicles, e.g. car alternators
• CPC Class Codes: H02P 9/04 Control effected upon non-electric prime mover and dependent upon electric output value of the generator

Abstract

The throttle of an engine in an engine driven generator system operating under an intermittently heavy load, as in supplying current to a welder, is controlled such that successive control signals sent to a throttle actuator for adjusting the engine throttle position are inhibited until at least a predetermined time has elapsed since the last preceding adjustment to the throttle. This procedure ensures that, as to each incremental adjustment to the throttle, the engine has sufficient time to respond, thereby preventing over-speeding or stalling the engine. The throttle actuator may be a stepper motor which is stepped by throttle position change signals from a processor which monitors engine speed and generator load to determine whether the throttle should be adjusted and, if so, in which direct. Alternatively, the throttle actuator may be a solenoid pulling against a spring in accordance with the average current through the solenoid coil. In this embodiment, the processor causes pulse width modulated signals to be applied across the solenoid coil with throttle position changes being reflected in changes to the width of the pulses, such changes in the pulse width being delayed for at least the predetermined time since the last preceding adjustment to the throttle.

Claims

1. A method of controlling the throttle setting of an engine, the engine including a throttle and an actuator, the engine operating at a speed in accordance with the setting of the throttle, the actuator, responsive to control signals applied thereto, controlling the setting of the throttle, the method comprising the steps of:

selectively generating control signals to the actuator to selectively adjust the setting of the throttle; and

inhibiting adjustment of the throttle setting until at least a predetermined time has elapsed since the last preceding adjustment to the throttle;

wherein the actuator comprises a stepping motor including;

a plurality of stator coils;

a rotor having magnetic components; and

an output shaft cooperating with the rotor, and mechanically coupled to the throttle; and

the step of generating control signals to said actuator to selectively adjust the setting of the throttle comprisies selectively effecting current paths through the stator coils.

2. The method of claim 1 wherein the stator coils have stator poles associated therewith, and the step of selectively generating signals to said stepping motor to effect incremental rotation of the stepping motor output shaft comprises:

generating signals to said stepper motor to effect pairs of current paths in adjacent coils, in sequence, to incrementally advance the shaft by a full step, at full torque, from midpoint between adjacent stator polls to midpoint between a next successive pair of stator poles.

3. The method of claim 1 wherein current paths through the stator coils are effected in accordance with a predetermined sequence of coil activation states, and the method further comprises the step of dithering between respective coil activation states.

4. The method of claim 2 wherein the stator coils have stator poles associated therewith, and the step of selectively generating signals to said stepping motor to effect incremental rotation of the stepping motor output shaft comprises generating signals to said stepping motor to effect current flow through single coils, in sequence, to incrementally advance the shaft by a full step, from stator pole to stator pole.

5. The method of claim 2 wherein the stator coils have stator poles associated therewith, and the step of selectively generating signals to said stepping motor to effect incremental rotation of the stepping motor output shaft comprises:

generating signals to said stepping motor to effect pairs of current paths in adjacent coils, in sequence, to incrementally advance the shaft by a full step, at full torque, from midpoint between adjacent stator poles to midpoint between next successive pair of stator poles.

6. The method of claim 2 wherein the stator coils have stator poles associated therewith, and the step of selectively generating signals to said stepping motor to effect incremental rotation of the stepping motor output shaft comprises:

generating signals to energize a single coil, to bring the rotor into alignment with the stator pole associated with the coil, then generating signals to energize a pair of coils, to bring the rotor into alignment with the midpoint between that stator pole and the next successive stator pole.

7. The method of claim 2 wherein the step of selectively generating signals to said stepping motor to effect incremental rotation of the stepping motor output shaft comprises:

generating signals to said stepping motor to effect pairs of current paths in adjacent coils, in sequence, and effecting currents of different magnitudes through the respective coils.

8. The method of claim 2 wherein current paths through the stator coils are effected in accordance with a predetermined sequence of coil activation states, and the method further comprises the step of dithering between respective coil activation states.

9. The method of claim 8 wherein:

the engine has a mechanical response time associated therewith;

the actuator stator coils have an inductive rise time associated therewith; and

dithering between respective coil actuation states is effected at a rate faster than the mechanical response time of the engine but less than the inductive rise time of the actuator stator coils.

10. The method of claim 1 wherein:

current flow through the stator coils of the actuator generates magnetic fields of interct with the magnetic components of the rotor, and tends to cause the rotor to assume a predetermined alignment with said fields, and the step of generating control signals to said actuator to selectively adjust the setting of the throttle by a predetermined increment comprises the steps of;

(a) effecting, for a first predetermined time period, a first activation state in which current paths are effected through a first coil activation set, including at least one stator coil portion and tending to cause the rotor to assume a first predetermined alignment;

(b) the effecting, for a second predetermined time period, a second activation state in which current paths are effected through a second coil activation set, including at least one stator coil portion and tending to cause the rotor to assume a second predetermined alignment; and

(c) repeating steps (a) and (b).

11. The method of claim 8 wherein dithering between respective coil actuation states is effected at a rate sufficient to permit the throttle to assume a desired static position intermediate the positions associated the respective coil actuation states.

12. The method of claim 8 wherein dithering between respective coil actuation states is effected at a frequency that is equal to the lowest frequency that permits the throttle to assume a desired static position intermediate the positions associated the respective coil actuation states.

13. The method of claim 8 wherein the first and second coil activation states are maintained for different relative time periods.

14. The method of claim 1 wherein:

current flow through the stator coils generates magnetic fields to interact with the magnetic components of the rotor and tends to cause the rotor to assume a predetermined alignment with said fields; and

the throttle is adjusted in a first direction by effecting a predetermined sequence of activation states, in each activation state current paths being effected through a corresponding coil activation set, such set including at least one stator coil portion, tending to cause the rotor to assume a corresponding predetermined alignment.

15. The method of claim 1 wherein:

the actuator comprises a stepping motor including;

a plurality of stator coils;

a rotor having magnetic components; and

an output shaft cooperating with the rotor, and mechanically coupled to the throttle, current flow through the stator coils generating magnetic fields to interact with the magnetic components of the rotor, and tending to cause the rotor to assume a predetermined alignment with said fields, and the step of generating control signals to said actuator to selectively adjust the setting of the throttle by a predetermined increment comprises the steps of;

(a) effecting, for a first predetermined time period, a first activation state in which current paths are effected through a first coil activation set, including at least one stator coil portion and tending to cause the rotor to assume a first predetermined alignment;

(b) then effecting, for a second predetermined time period, a second activation state in which current paths are effected through a second coil activation set, including at least one stator coil portion and tending to cause the rotor to assume a second predetermined alignment; and

(c) repeating steps (a) and (b).

16. The method of claim 15 wherein the first and second time periods are equal.

17. The method of claim 15 wherein the first time period is a predetermined multiple of the second time period.

18. The method of claim 15 wherein the second time period is a predetermined multiple of the first time period.

19. The method of claim 1 wherein:

the actuator comprises a stepping motor including;

a plurality of stator coils;

a rotor having magnetic components; and

an output shaft cooperating with the rotor, and mechanically coupled to the throttle, current flow through the stator coils generating magnetic fields to interact with the magnetic components of the rotor, and tending to cause the rotor to assume a predetermined alignment with said fields;

and the throttle is adjusted in a first direction by effecting a predetermined sequence of activation states, in each activation state current paths being effected through a corresponding coil activation set, such set including at least one stator coil portion, tending to cause the rotor to assume a corresponding predetermined alignment.

20. The method of claim 19 wherein the first time period is three times the second time period.

21. The method of claim 20 wherein in at least some of the activation states current paths of the same polarity are effected through coils on adjacent stator poles.

22. The method of claim 19 wherein in at least some of the activation states current paths of the same polarity are effected through coils on adjacent stator poles.

23. The method of claim 19 wherein the throttle is adjusted in a second direction, opposite the first direction, by effecting the predetermined sequence of activation states in reverse order.

24. The method of claim 19 wherein the predetermined sequence of activation states includes a first activation state tending to cause the rotor to assume a first predetermined alignment and a second activation state tending to cause the rotor to assume a second predetermined alignment, and at least a first intermediate activation state, the throttle being advanced from a setting corresponding to the first activation state to a setting corresponding to the second activation state through at least a first intermediate setting between the setting corresponding to the first activation state and the setting corresponding to the second activation state, by a sequence comprising the steps of:

(a) effecting, for a first predetermined time period, the first activation state;

(b) then effecting, for a second predetermined time period, the second activation state; and

(c) for so long as the first intermediate activation state is maintained, repeating steps (a) and (b).

25. The method of claim 24 wherein the first and second time periods are equal.

26. The method of claim 24 wherein the intermediate setting is effectively midway between the setting corresponding to the first activation state and the setting corresponding to the second activation state.

27. The method of claim 24 wherein the first time period is a predetermined multiple of the second time period.

28. The method of claim 24 wherein the second time period is a predetermined multiple of the first time period.

29. The method of claim 24 wherein the throttle is advanced from a setting corresponding to the first activation state to a setting corresponding to the second activation state through at least a second setting intermediate the setting corresponding to the first activation state and the setting corresponding to the second activation state, and the sequence further comprises the steps of

(a) effecting, for said second predetermined time period, said first activation state;

(b) then effecting, for said first predetermined time period, said second activation state; and

(c) for so long as the second intermediate activation state is maintained, repeating steps (a) and (b).

30. The method of claim 29 wherein the first time period is a predetermined multiple of the second time period.

31. The method of claim 30 wherein the first time period is three times the second time period.

32. The method of claim 29 wherein the throttle is advanced from a setting corresponding to the first activation state to a setting corresponding to the second activation state through at least a third setting intermediate the setting corresponding to the first activation state and the setting corresponding to the second activation state, and the sequence further comprises the steps of

(a) effecting, for a third predetermined time period, said first activation state;

(b) then effecting, for said third predetermined time period, said second activation state; and

(c) for so long as the third intermediate activation state is maintained, repeating steps (a) and (b).

36. The method of claim 32 wherein the sum of the first and second periods equals twice the third period.

37. The method of claim 1 wherein:

the actuator comprises;

a stepping motor having a rotary output shaft and plurality of coils, rotational movement of the shaft being effected by selective application of current through the coils;

a drive circuit, responsive to control signals applied thereto for selectively effecting current flow through at least portions of the respective individual coils; and

a mechanical coupling between the stepping motor shaft and the engine throttle, such that rotary movement of the stepping motor shaft effects control of the throttle setting; and

the step of selectively generating control signals to said actuator to selectively adjust the setting of the throttle comprises;

selectively generating signals to said drive circuit to effect a selected one of a plurality of coil activation states, wherein, in each such activation state, current paths are effected through a corresponding predetermined activated coil set, each set comprising at least a portion of at least one stepping motor coil; and

effecting such activation states in predetermined sequences to cause the rotary shaft to move in predetermined increments.

38. The method of claim 37 wherein the step of generating signals to effect predetermined sequences of coil activation states comprises the steps of:

maintaining, for each activation state, indicia of the corresponding activated coil set; and

generating control signals to the coils in accordance with the desired activation state.

39. The method of claim 37 wherein the drive circuit comprises an unidirectional driver.

40. The method of claim 37 wherein:

the respective stepping motor coils each include a center tap; and

the drive circuit comprises respective switching devices, responsive to control signals applied thereto, each disposed to selectively complete a current path through an associated coil portion to a common node; and

the step of selectively generating signals to said drive circuit to effect a selected one of a plurality of coil activation states, comprises;

establishing a potential difference between the coil center taps and the common node; and

selectively providing control signals to the switching devices associated the corresponding activated coil set to selectively effect current paths from the center tap of the coils to the common node.

41. The method of claim 37 wherein the drive circuit comprises a bipolar driver.

42. The method of claim 37 wherein:

the drive circuit to effect a selected one of a plurality of coil activation states, comprises;

a first set of switching devices disposed to selectively effect connections between the respective ends of the stepping motor coils to a common node, and

a second set of switching devices disposed to selectively effect connections between the respective ends of the stepping motor coils and a positive potential relative to the common node; and

the step of selectively generating signals to the drive circuit comprises;

selectively providing control signals to the switching devices to selectively effect current flows of selected polarity through the coils in the corresponding activated coil set.

76. The method of claim 1 wherein:

the actuator comprises a stepping motor including;

a plurality of stator coils;

a rotor having magnetic components; and

an output shaft cooperating with the rotor, and mechanically coupled to the throttle, current flow through the stator coils generating magnetic fields to interact with the magnetic components of the rotor, and tending to cause the rotor to assume a predetermined alignment with said fields, in each activation state current paths being effected through a corresponding coil activation set, such set including at least one stator coil portion, tending to cause the rotor to assume a corresponding predetermined alignment.

77. The method of claim 76 wherein in at least some of the activation states a current path is effected through a single corresponding coil.

78. The method of claim 77 wherein in at least some of the activation states current paths of the same polarity are effected through coils on adjacent stator poles.

79. The method of claim 19 wherein in at least some of the activation states current paths of the same polarity are effected through coils on adjacent stator poles.

80. The method of claim 19 wherein the throttle is advanced in a first direction by effecting a predetermined sequence of activation states, and in a second direction, opposite the first direction, by effecting the predetermined sequence of activation states in reverse order.

33. The method of claim 33 wherein the first time period is a predetermined multiple of the second time period.

34. The method of claim 33 wherein the first time period is three times the second time period.

35. The method of claim 33 wherein the first, second and third intermediate settings are effectively 1/4, 3/4 and 1/2 of the way, respectively, between the setting corresponding to the first activation state and the setting corresponding to the second activation state.

43. A method of controlling the throttle setting of an engine, the engine including a throttle, and an actuator, the engine operating at a speed in accordance with the setting of the throttle, the actuator, responsive to control signals applied thereto and having a plurality of discrete activation states associated therewith, controlling the setting of the throttle, the method comprising the steps of:

selectively generating control signals to said actuator corresponding to a first activation state;

selectively generating control signals to said actuator corresponding to a second activation state; and

dithering between the respective activation states at a predetermined frequency.

44. The method of claim 43 wherein the engine has a mechanical response time associated therewith, and the actuator includes coils have an inductive rise time associated therewith;

and dithering between respective coil actuation states is effected at a rate faster than the mechanical response time of the engine but less than the inductive rise time of the actuator coils.

46. The method of claim 43 wherein dithering between respective coil actuation states is effected at a rate sufficient to permit the throttle to assume a desired static position intermediate the positions associated with the first and second coil actuation states.

47. The method of claim 43 wherein dithering between respective coil actuation states is effected at a frequency that is equal to the lowest frequency that permits the throttle to assume a desired static position intermediate the positions associated with the first and second coil actuation states.

48. The method of claim 43 the first and second coil activation states are maintained for different relative time periods.

49. The method claim 43 wherein the actuator comprises a stepping motor including:

a plurality of stator coils;

a rotor having magnetic components; and

an output shaft cooperating with the rotor, and mechanically coupled to the throttle; and

the control signals effect current paths through the stator coils are in accordance with a predetermined sequence of coil activation states.

50. The method of claim 49 wherein:

the engine has a mechanical response time associated therewith;

the actuator stator coils have an inductive rise time associated therewith; and

dithering between respective coil actuation states is effected at a rate faster than the mechanical response time of the engine but less than the inductive rise time of the actuator stator coils.

51. The method of claim 49 wherein:

the actuator stator coils have an inductive rise time associated therewith;

the actuator rotor has a mechanical response time associated therewith when coupled to the throttle; and

dithering between respective coil actuation states is effected at a rate faster than the mechanical response time of the actuator but less than the inductive rise time of the stator coils.

52. The method of claim 49 wherein dithering between respective coil actuation states is effected at a rate sufficient to permit the throttle to assume a desired static position intermediate the positions associated with the first and second coil actuation states.

53. The method of claim 49 wherein dithering between respective coil actuation states is effected at a rate sufficient to permit the throttle to assume a desired static position intermediate the positions associated with the first and second coil actuation states.

54. The method of claim 49 the first and second coil activation states are maintained for different relative time periods.

45. For apparatus including an engine having a throttle and an actuator, the engine

operating at a speed in accordance with the setting of the throttle, wherein the actuator is responsive to control signals applied thereto and has a plurality of discrete activation states associated therewith, a method of increasing control resolution whereby at least a first intermediate throttle setting is provided between throttle settings corresponding to first and second discrete activation states, the method comprising the steps of:

(a) generating, for a first predetermined time period, control signals corresponding to the first activation state;

(b) then generating, for a second predetermined time period, control signals corresponding to the second activation state; and

(c) for so long as the first intermediate activation state is maintained, repeating steps (a) and (b), dithering between the first and second activation states.

55. A method of controlling the throttle setting of an engine, the engine including a throttle, and an actuator, the engine operating at a speed in accordance with the setting of the throttle, the actuator, responsive to control signals applied thereto and having a plurality of discrete activation states associated therewith, controlling the setting of the throttle, the method comprising the steps of:

(a) generating, for a first predetermined time period, control signals corresponding to a first activation state;

(b) then generating, for a second predetermined time period, control signals corresponding to a second activation state; and

(c) repeating steps (a) and (b), thereby dithering between the first and second activation states.

56. The method of claim 55 wherein the first and second time periods are equal.

57. The method of claim 55 wherein the first time period is a predetermined multiple of the second time period.

58. The method of claim 55 wherein the second time period is a predetermined multiple of the first time period.

59. The method of claim 55, wherein the actuator comprises a stepping motor including:

a plurality of stator coils;

a rotor having magnetic components; and

an output shaft cooperating with the rotor, and mechanically coupled to the throttle, current flow through the stator coils generating magnetic fields to interact with the magnetic components of the rotor, and tending to cause the rotor to assume a predetermined alignment with said fields, and the method comprises the steps of;

(a) effecting, for a first predetermined time period, a first activation state in which current paths are effected through a first coil activation set, including at least one stator coil portion and tending to cause the rotor to assume a first predetermined alignment;

(b) then effecting, for a second predetermined time period, a second activation state in which current paths are effected through a second coil activation set, including at least one stator coil portion and tending to cause the rotor to assume a second predetermined alignment; and

(c) repeating steps (a) and (b).

60. The method of claim 59 wherein the first and second time periods are equal.

61. The method of claim 59 wherein the first time period is a predetermined multiple of the second time period.

62. The method of claim 59 wherein the second time period is a predetermined multiple of the first time period.

63. For apparatus including an the engine having a throttle and an actuator, the engine operating at a speed in accordance with the setting of the throttle, wherein the actuator is responsive to control signals applied thereto and has a plurality of discrete activation states associated therewith, a method of increasing control resolution whereby at least a first intermediate throttle setting is provided between throttle settings corresponding to first and second discrete activation states, the method comprising the steps of:

(a) generating, for a first predetermined time period, control signals corresponding to the first activation state;

(b) then generating, for a second predetermined time period, control signals corresponding to the second activation state; and

(c) for so long as the first intermediate activation state is maintained, repeating steps (a) and (b), dithering between the first and second activation states.

64. The method of claim 63 wherein the first and second time periods are equal.

65. The method of claim 63 wherein the intermediate setting is effectively midway between the setting corresponding to the first activation state and the setting corresponding to the second activation state.

66. The method of claim 63 wherein the first time period is a predetermined multiple of the second time period.

67. The method of claim 63 wherein the second time period is a predetermined multiple of the first time period.

68. The method of claim 63 wherein the throttle is advanced from a setting corresponding to the first activation state to a setting corresponding to the second activation state through at least a second setting intermediate the setting corresponding to the first activation state and the setting corresponding to the second activation state, and the sequence further comprises the steps of

(a) effecting, for said second predetermined time period, said first activation state;

(b) then effecting, for said first predetermined time period, said second activation state; and

(c) for so long as the second intermediate activation state is maintained, repeating steps (a) and (b).

69. The method of claim 68 wherein the first time period is a predetermined multiple of the second time period.

70. The method of claim 69 wherein the first time period is three times the second time period.

71. The method of claim 68 wherein the throttle is advanced from a setting corresponding to the first activation state to a setting corresponding to the second activation state through at least a third setting intermediate the setting corresponding to the first activation state and the setting corresponding to the second activation state, and the sequence further comprises the steps of

(a) effecting, for a third predetermined time period, said first activation state;

(b) then effecting, for said third predetermined time period, said second activation state; and

(c) for so long as the third intermediate activation state is maintained, repeating steps (a) and (b).

75. The method of claim 71 wherein the sum of the first and second periods equals twice the third period.

72. The method of claim 72 wherein the first time period is a predetermined multiple of the second time period.

73. The method of claim 72 wherein the first time period is three times the second time period.

74. The method of claim 72 wherein the first, second and third intermediate settings are effectively 1/4, 3/4 and 1/2 of the way, respectively, between the setting corresponding to the first activation state and the setting corresponding to the second activation state.

81. Apparatus for controlling the throttle setting of an engine, comprising:

an actuator, responsive to control signals applied thereto, for controlling the setting of the throttle; and

a control circuit, for generating the control signals to the actuator;

wherein the actuator comprises;

a throttle lever arm adapted to cooperate with the throttle such that the throttle setting varies in accordance with the position of the throttle lever arm;

an elongated magnet, magnetized through the length thereof, a non-magnetic coupling between the magnet and throttle arm, such that movement of the magnet effects a corresponding movement of the throttle arm;

an electrical coil, receptive of a control signal applied thereto, and disposed such that current flow therethrough effects magnetic interaction with the magnet, causing the magnet to assume a position in accordance with the power through the coil, to control the position of the throttle arm.

82. The apparatus of claim 81 wherein the throttle control signal to the actuator coil is pulse width modulated and the width of the pulse determines the power of the electrical signal supplied to the coil.

83. The apparatus of claim 81, further comprising a fly-back diode provided across the coil.

84. The apparatus of claim 81, wherein the control circuit comprises a microcomputer.

85. The apparatus of claim 81, wherein the control circuit includes means for delaying adjustment of the throttle setting until at least a predetermined time has elapsed since the last preceding adjustment to the throttle.

86. The apparatus of claim 81 wherein the magnet is cylindrical.

87. The apparatus of claim 81 wherein the magnet is formed of Alnico.

88. The apparatus of claim 81 wherein the coupling comprises an elongated non-magnetic push rod, coupled to, and in general axial alignment with the magnet.

89. The apparatus of claim 81 wherein the actuator further comprises a spring disposed to bias the throttle arm into a designated idle position such that the magnet moves against the bias of the spring to control the position of the throttle arm.

90. Apparatus for controlling the throttle setting of an engine, the engine having a mechanical response time to throttle setting changes, comprising:

an actuator, responsive to control signals applied thereto, for controlling the setting of the throttle; and

a control circuit, for generating the control signals to the actuator;

wherein the actuator comprises;

a stepping motor having a rotor with magnetic components and plurality of stator coils, the stator coils having an inductive rise time associated therewith;

a drive circuit, responsive to control signals applied thereto, for selectively effecting current flow through designated coils, the stepping motor having a plurality of activation states associated therewith, each such activation state corresponding to current flow through a corresponding predetermined activated coil set, each set comprising at least a portion of at least one stepping motor coil, current flow through an activated coil set generating magnetic fields to interact with the magnetic components of the rotor, and tending to cause the rotor to assume a predetermined alignment with said fields;

a mechanical coupling between the stepping motor shaft and the engine throttle, such that rotary movement of the stepping motor shaft effects control of the throttle setting; and

wherein the control circuit selectively generates signals to the drive circuit to dither between successive coil actuation states, the engine has a mechanical response time associated therewith;

the actuator stator coils have an inductive rise time associated therewith; and

dithering between respective coil actuation states is effected at a rate faster than the mechanical response time of the engine but less than the inductive rise time of the actuator stator coils, the actuator stator coils have an inductive rise time associated therewith;

the actuator rotor has a mechanical response time associated therewith when coupled to the throttle; and

dithering between respective coil actuation states is effected at a rate faster than the mechanical response time of the actuator but less than the inductive rise time of the stator coils comprises a microcomputer selectively generates control signals to said drive circuit to effect current paths through at least portions of the respective stepping motor coils in predetermined sequences to cause the rotary shaft to move in predetermined increments.

91. The apparatus of claim 90 further including means for inhibiting adjustment of the throttle setting until at least a predetermined time has elapsed since the last preceding adjustment to the throttle.

92. The apparatus of claim 90 wherein the stator coils have stator poles associated therewith, and said activation coil sets comprise single coils, adjacent coils being activated in sequence, to incrementally advance the shaft by a full step, from stator pole to stator pole.

93. The apparatus of claim 90 wherein the stator coils have stator poles associated therewith, and said activation coil sets comprise pairs of adjacent coils, adjacent pairs of coils being acted in sequence, to incrementally advance the shaft by a full step, at full torque, from midpoint between adjacent stator poles to midpoint between next successive pair of stator poles.

94. The apparatus of claim 90 wherein the stator coils have stator poles associated therewith, and certain of said activation coil sets comprise, successively, a single coil and the single coil together with the next sucessive coil, said control circuit generating control signals to energize the single coil, to bring the rotor into alignment with the stator pole associated with the coil, and generating signals to energize the pair of coils, to bring the rotor into alignment with the midpoint between that stator pole and the next successive stator pole.

95. The apparatus of claim 90 wherein the control circuit comprises a microcomputer.

96. The apparatus of claim 90 wherein the drive circuit comprises an unidirectional driver.

97. The apparatus of claim 90 wherein:

the respective stepping motor coils each include a center tap; and

the drive circuit comprises respective switching devices, responsive to control signals applied thereto, disposed to selectively complete a current path through a portion of the coil, establishing current flow of a predetermined polarity.

98. The apparatus of claim 90 wherein the drive circuit comprises a bipolar driver.

99. The apparatus of claim 90 wherein the drive circuit comprises:

a first set of switching devices disposed to selectively effect connections between the respective ends of the stepping motor coils to a first potential, and

a second set of switching devices disposed to selectively effect connections between the respective ends of the stepping motor coils and a second potential; and

the control circuit provides control signals to the switching devices to selectively effect current flows of selected polarity through the coils.