Prime-mover dynamo plants – Electric control – Engine control
Reexamination Certificate
1999-03-30
2002-04-02
Enad, Elvin (Department: 2834)
Prime-mover dynamo plants
Electric control
Engine control
C290S04000F, C290S04000F, C290S04000F, C290S04000F, C290S04000F
Reexamination Certificate
active
06365982
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to internal combustion engines and, more particularly, to engine speed control.
BACKGROUND OF THE INVENTION
Many applications which use an internal combustion engine as the prime mover require that engine speed be held relatively constant. One example is a mobile machine such as a concrete mixer where the work output function, i.e., rotating the mixing drum, is hydraulically powered. The hydraulic pump is engine-driven at constant speed and speed control of the work function is effected by hydraulic valves rather than by controlling engine speed.
Another exemplary application is a walk-behind lawn mower. Particularly on less-expensive mower models, the engine runs at substantially constant speed.
Still another example is an engine-driven electrical generator. As is well known, generator output voltage and frequency are, as a general matter, a function of the rotational speed at which the generator is driven. It is desirable to hold both voltage and frequency within relatively narrow limits.
Very commonly, regulation of engine speed in such applications is by using a mechanical governor of the type known as a flyweight or centrifugal governor. Such a governor has a mechanical lever or linkage coupled to the carburetor butterfly valve. A spring applies force to the linkage in a direction to urge the valve open (and run the engine faster) and the flyweight governor applies force to such linkage in a direction to urge the valve closed. At the nominal regulated speed, the effects of the spring and the flyweight governor balance one another and the engine runs at that speed so long as the load remains unchanged.
But in applications like those described above, engine load routinely changes. For example, a lawn mower encounters grass of differing height or density and the resulting changing load causes engine speed to change. And more or less electrical power will be demanded from a generator and changes in engine speed will result.
A common flyweight governor functions in such a way that engine speed is highest when the engine is at no load or is lightly loaded and decreases as engine load increases. Engine speed at full load may be 12-15% lower than engine speed at no load. This phenomenon is often referred to as speed “droop.” When engine speed decreases, so does the available engine horsepower. And if the engine is driving a generator, the generator frequency also declines with decreasing engine speed.
A known approach to engine-generator control (and particularly engine speed control) involves monitoring generator voltage. Since a decrease in such voltage means that engine speed is decreasing, the generator field current is increased to bring the voltage back to some norm. But the resulting increased load often kills the engine. A remedial measure involves reducing field current to reduce the voltage but substantially maintain (or at least prevent a significant decrease in) generator frequency.
Often, an application for a speed-regulated internal combustion engine will exhibit a characteristic loading pattern. The on-board, engine-driven electrical generator installed in many recreational vehicles (RVs) is an example. It is estimated that a high percentage, e.g. 80% or so, of the running time of an RV generator is at or below 50% of rated load. Such a generator may be nearly fully loaded only when most or all of the RV electrical equipment, probably including an air conditioning compressor, is operating simultaneously.
Given the foregoing characteristics of a flyweight governor, this means that in an RV generator, lightly loaded during much of its running time, the engine spends much of its life running at or near its highest speed. This has at least three unfavorable implications.
One is that higher engine operating speed results in reduced engine life. Another is that high engine speed produces a sound level which must either be deadened by installing extra insulation—at additional cost—at the time of manufacture or simply be tolerated by the occupants of the RV. Yet another is that, undesirably, the engine output horsepower declines precisely during the times that maximum or near-maximum horsepower is required.
In view of the invention, none of these eventualities need occur, either at all or at least not nearly to the degree required by earlier engine speed regulation arrangements. The new apparatus and method represent an important advance in the field of engine speed regulation for generator applications.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a new apparatus and method for positioning an engine throttle which address some of the problems and shortcomings of the prior art.
Another object of the invention is to provide a new apparatus and method for positioning an engine throttle which are particularly applicable to engine-driven generators used on recreational vehicles.
Another object of the invention is to provide such a new apparatus and method which reduce engine sound levels at lighter engine loads.
Yet another object of the invention is to provide such a new apparatus and method which help reduce engine wear and extend engine life.
Another object of the invention is to provide such a new apparatus and method which obtain incrementally greater horsepower from the engine.
Another object of the invention is to provide such a new apparatus and method which substantially avoid engine stalling.
Still another object of the invention is to provide such a new apparatus and method which incrementally increase generator frequency with increasing engine load.
Another object of the invention is to provide such a new apparatus and method which generally “match” the engine output horsepower with horsepower demand. How these and other objects are accomplished will become apparent from the following descriptions and from the drawings.
SUMMARY OF THE INVENTION
Aspects of the invention involve a method for controlling the speed of an engine driving a generator which supplies electrical current to a load. The method includes monitoring the magnitude of the current to the load, increasing the speed when the current increases and decreasing the speed when the current decreases. The increasing step includes increasing the speed to a maximum speed when the current increases to a predetermined value such as rated generator full load current. The decreasing step includes decreasing the speed to a minimum speed, e.g., engine idle speed or thereabouts, when the current decreases to a predetermined value, e.g., zero amperes or near zero.
More specifically, the method involves an AC generator, the output current of which has a frequency. For geographical areas where commercial power is at 60 Hz (and clocks and other products are configured in anticipation of such frequency), the frequency at the maximum speed is not in excess of about 65 Hz. And the frequency at the minimum speed is not less than about 55 Hz. In a highly preferred method, the frequencies at maximum and minimum speeds are about 63 Hz and 57 Hz, respectively. And where commercial power is at 50 Hz, the frequency at the maximum speed is not in excess of about 55 Hz and the frequency at the minimum speed is not less than about 45 Hz.
In other aspects of the method, the engine has a throttle valve controlling the rate of fuel flow to the engine. It also has a governor apparatus with a linkage arm coupled to the throttle valve. A force is applied to the linkage arm along a vector and the linkage arm and the vector define an included angle between them. The increasing step includes increasing the included angle and the decreasing step includes decreasing the included angle.
It is most preferable to equip the governor apparatus with a control arm coupled to a positioning motor. This “bell crank” arrangement, described in more detail below, is advantageously used when the positioning motor is very small and of low power. In this configuration, the force is applied by a spring extending between the linkage arm and the control arm. When a positioning motor
Iles Robert
Kern Robert D.
Orlikowski Michael T.
Ruehlow Gerald C.
Shi Bijun
Boyle Frederickson Newholm Stein & Gratz S.C.
Enad Elvin
Generac Power Systems, Inc.
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