Engine-driven generator

• US 5,504,417 A
• Filed: 07/27/1994
• Issued: 04/02/1996
• Est. Priority Date: 06/11/1992
• Status: Expired due to Fees

• Current Assignee: Generac Power Systems Incorporated (Generac Holdings Incorporated)
• Original Assignee: Generac Corporation
• Inventors: McLean, Graham W., Wheeley, Michael R., Kastner, Mark, Kern, Robert, Hoenisch, Herb, Ruehlow, Gerald, Wedel, Frank, Sarder, Mark J.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Ponomarenko, Nicholas
• Application Number:
  US08/282,514
• Time in Patent Office: 615 Days
• Field of Search: 322/14, 322/15, 322/29, 322/32, 363/160
• US Class Current: 322/32
• CPC Class Codes: F02B 63/04 for electric generators
• CPC Class Codes: F02B 63/042 Rotating electric generators
• CPC Class Codes: H02P 9/04 Control effected upon non-electric prime mover and dependent upon electric output value of the generator

Abstract

An engine-driven generator includes an internal combustion engine, a permanent magnet alternator and an AC to AC converter. The output frequency and voltage of the permanent magnet alternator are largely dependent on engine speed and the alternator load. The AC to AC converter converts the speed-dependent alternating potential developed by the alternator to another alternating potential whose frequency and voltage are largely independent of engine speed. Voltage regulation is provided by varying the engine speed in accordance with the load current. Frequency regulation is provided by frequency dividing the alternator output by an integer divisor that varies in accordance with engine speed. Additional voltage regulation is provided by deleting selected cycles of the alternator output current as needed to maintain the RMS output voltage within predetermined limits. A stepper motor coupled to the throttle of the internal combustion engine controls the speed of the engine in accordance with commands received from an electronic system control.

Claims

1. An engine-driven generator comprising:

an internal combustion engine including a throttle;

an altemator coupled to said engine and operable to develop a first alternating potential having a frequency and no-load voltage dependent on the speed of said engine;

switching means for converting said first alternating potential into a second alternating potential wherein said second alternating potential is of a lower frequency than said first alternating potential and wherein said second alternating potential comprises a predetermined number of positive polarity half cycles of said first alternating potential followed by an equal number of negative polarity half cycles of said first alternating potential;

frequency regulating means for increasing or decreasing said predetermined number in accordance with the frequency of said first alternating potential so as to maintain the frequency of said second alternating potential between pre-established upper and lower frequency limits; and

speed regulating means for operating said internal combustion engine at a desired speed, said speed regulating means comprising;

a stepper motor coupled to said throttle of said internal combustion engine for controlling the position of said throttle; and

feedback means responsive to the voltage of said second alternating potential for generating and applying to said stepper motor a control signal operable to actuate said stepper motor to move said throttle and thereby change the speed of said internal combustion engine so as to maintain the voltage of said second alternating potential within a pre-established voltage range.

2. An engine-driven generator as defined in claim 1 wherein said predetermined number of said positive and negative polarity half-cycles is an integer.

3. An engine-driven generator as defined in claim 2 wherein said switching means includes electronic power switching devices.

5. An engine-driven generator as defined in claim 1 wherein said feedback means further includes means for maintaining the speed of said intemal combustion engine between pre-established upper and lower speed limits regardless of the voltage of said second alternating potential.

6. An engine-driven generator as defined in claim 1 further comprising means for deleting from said second alternating potential selected ones of said positive polarity and said negative polarity half-cycles during acceleration of said internal combustion engine so as to reduce the torque required to accelerate said alternator.

7. An engine-driven generator as defined in claim 6 wherein the number of said positive polarity and said negative polarity half pulses deleted from said second alternating potential increases at increased engine speeds.

4. An engine-driven generator as defmed in claim 4 wherein said electronic power switching devices are triacs.

8. An engine-driven generator comprising:

an internal combustion engine including a throttle;

an alternator coupled to said engine operable to develop a first alternating potential having a frequency and no-load voltage dependent on the speed of said engine;

converter means for converting said first alternating potential to a second alternating potential of a lower frequency than said first alternating potential;

a stepper motor having an output shaft rotatable to predetermined angular positions in accordance with externally applied input commands;

a cam operatively coupled to said output shaft of said stepper motor; and

a cam follower engaging said cam and coupled to the throttle of said engine so that movement of said cam in response to movement of said output shaft results in movement of the throttle to vary engine speed.

9. An engine-driven generator as defined in claim 8 wherein said cam is shaped so that the ratio of change in engine power to change in angular position of said output shaft is substantially constant.

10. An engine-driven generator as defined in claim 8 wherein said externally applied input commands are developed by an electronic system control.

11. An engine-driven generator as defined in claim 10 wherein said electronic system control senses the voltage of said second alternating potential and generates an input command to open said throttle and thereby increase the speed of said internal combustion engine when said voltage is less than a predetermined reference and wherein said electronic control system generates an input command to close said throttle and thereby reduce the speed of said internal combustion engine when said voltage exceeds said predetermined reference.

12. An engine-driven generator as defined in claim 11 wherein said electronic control circuit further includes means for maintaining the speed of said internal combustion engine within predetermined maximum and minimum speed limits regardless of the voltage of said second alternating potential.

13. An engine-driven generator as defined in claim 12 wherein said electronic control circuit comprises a microprocessor-based circuit.

14. An engine-driven generator comprising:

an internal combustion engine of the type having a movable throttle for changing engine power and speed, wherein the relationship between the change in engine power and speed and the change in throttle position is non-linear;

an alternator coupled to said engine operable to develop a first alternating potential having a frequency and no-load voltage dependent on the speed of said engine;

converter means for converting said first alternating potential into a second alternating potential of lower frequency than said first alternating potential;

a stepper motor responsive to an applied input cormnand and having an output shaft, the angular position of said output shaft being determined by the applied input command;

a cam coupled to said output shaft of said stepper motor for angular movement so that the angular position of said cam changes in direct proportion to changes in the angular position of said output shaft; and

a cam follower engaging said cam and coupled to said throttle so that a change in the angular position of said cam results in movement of the throttle to effect a change in the engine speed and power;

said cam being shaped so that the relationship between the change in the angular position of said cam and the change in the position of the throttle is non-linear and substantially compensates for the non-linear relationship between throttle position and engine speed and power so as to provide a predetermined relationship between changes in the angular position of said stepper motor output shaft and the resulting changes in engine speed and power.

15. An engine-driven generator as defined in claim 14 wherein said predetermined relationship comprises a substantially linear relationship between changes in the angular position of said stepper motor output shaft and said resulting changes in engine speed and power.