Electric heating – Metal heating – By arc
Reexamination Certificate
2001-06-15
2003-08-05
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C290S04000F
Reexamination Certificate
active
06603097
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to engine driven welding generators. More specifically, it relates to a method and apparatus for controlling the engine speed of a welding generator.
BACKGROUND OF THE INVENTION
Engine driven generators are commonly used in welding. These welding generators are used extensively in connection with welding operations performed at remote locations where access to conventional utility power is limited or unavailable. Generators are also used by those who perform welding operations at multiple locations because they allow for portability without the need for access to utility power. In addition to a welding output, an auxiliary output (e.g., 120 or 240 volts 60 Hz ac for example) is also typically provided from the welding generator to run power tools, lights, etc . . . .
Engine driven welding generators include an engine (e.g, gasoline, diesel, propane, etc . . . ) and a generator. The term generator, as used herein, may include one or more generator stages or welding power supply stages. The generator stages are driven by the engine. A single generator stage may supply both the welding output and the auxiliary power. In other welding generators, two generator stages are provided, one supplying the welding power and the other supplying the auxiliary power. Both generator stages are driven by the engine. In yet another configuration, one generator stage provides auxiliary power and power to a welding power supply stage. The welding power supply stage receives the power from the generator stage and converts it into a welding output in a similar manner to the way a conventional welding power supply converts utility power into a welding output.
The engine of an engine driven welding generator is typically configured to operate at two speeds. It should be understood, however, that some engine driven welding generators have engines that operate at more than two speeds such as three or more speeds. The lower of the two speeds is referred to as the idle speed. The higher of the two speeds is referred to as the run speed.
The idle speed is the speed at which the engine normally operates when the welding generator is not supplying rated welding output power or auxiliary power. Although some welding generators are configured to provide output power when idling, these generators also operate at the idle speed when not providing output power. The term output power, as used herein in regards to a welding generator, includes both weld power and auxiliary power.
The actual speed at which an engine idles is typically chosen to be at or near the minimum speed required in order to maintain weld integrity when welding first begins (before the engine has a chance to switch to the run speed). Idle speeds for welding generators typically range between 900-2700 rpms with the vast majority of welding generators idling somewhere between 2200-2600 rpms. 1500 and 1800 rpms are also common idle speeds because 50 Hz and 60 Hz auxiliary output power are easily generated at these speeds using a four pole rotor.
Welding generally is performed with the engine operating at run speed. This is because most generators are configured to provide maximum horsepower at run speed. Auxiliary power is also typically provided with engines operating at run speed. Run speed, therefore, is typically the engine speed that will provide the maximum rated welding output power from the generator as well as auxiliary power at the desired frequency directly from the generator (e.g., 50 Hz or 60 Hz for example).
Engine run speeds typically range between approximately 1800-1900 rpms or 3600-3700 rpms. 3000 rpms is also a common engine speed, for example, because 50 Hz auxiliary output power is easily generated at this speed using a two pole rotor. Likewise, 3600 rpms is a common engine speed for providing 60 Hz auxiliary output power.
Prior art engine driven welding generators are configured to sense either a load current or the output power (either at the weld output or the auxiliary output of the generator). If the sensed load current or output power level exceeds a predetermined threshold, the engine automatically switches from idle speed to run speed to meet the demand for output power. The threshold level is generally set at a level that will reliably indicate whether welding is taking place or whether a device connected to the auxiliary output is demanding power. Once the threshold is exceeded, the engine will remain at run speed until the demand for output power stops (e.g, the load current or output power drop below the threshold.
Many prior art welding generators are configured to maintain the engine speed of the engine at the run speed even after the demand for weld power or auxiliary power ceases to exist (e.g., after the load current or output power drop below the threshold). This is because most welds are not made as one long continuous weld, but rather are made up of numerous short repetitive welds. It is common, therefore, for the user of a welding generator to cease welding for a brief period of time to make adjustments to the weld or the welding equipment (e.g., replace a welding electrode). Likewise, the user of a device connected to the auxiliary output may stop using the device briefly to make adjustments. These activities result in a momentary interruption in the demand for output power from the generator. In each of these cases however, a renewed demand for output power from the generator will typically be made within a short period of time.
To prevent the engine from switching back and forth between run speed and idle speed when a brief interruption in the demand for output power occurs, prior art welding generators provide a time delay before the engine slows to idle speed when the demand for output power terminates or is interrupted. Prior art welding generators use the same time delay regardless of the type of welding being performed and regardless of whether it is weld power or auxiliary power that is being provided.
The use of a single time delay can be problematic, however. This is because different types of welding typically require different types of adjustments, some of which may take longer to perform than others. Stick welding, for example, typically requires more adjustments to be made during the welding operation than does MIG or TIG welding. During stick welding, the operator repeatedly stops the welding process to replace the stick electrode and to chip away the slag material that forms on the weld. Electrode replacement and slag removal is generally not required during MIG or TIG welding.
To balance on the one hand the desire for an adequate time delay for each of the various welding types with on the other hand, the desire to not have the engine operate at run speed unnecessarily, prior art welding generators have incorporated a time delay that is a compromise between what is desirable for stick welding and what is desirable for MIG or TIG welding. As a result, prior art welding generators typically incorporate a single time delay of 12-14 seconds which provides a workable compromise. This means, however, that the time delay provided for the operator to perform the necessary adjustments when performing stick welding is shorter than is generally required and the time delay provided for those performing MIG and TIG welding is longer than is generally required.
It is desirable, therefore to have a welding generator that incorporates different length time delays for different types of welding. Preferably, the welding generator will provide a 10-12 second time delay for MIG and/or TIG welding while a 18-20 second time delay will be provided for stick welding. It is also desirable to have a welding generator that incorporates a variable time delay. Preferably, the operator of the welding generator will be able to set the duration of the time delay to meet his or her needs.
Engines used in welding generators typically require a short period of “warm-up time” after they are first started before they can sustain operation at idle speed. This is
Fosbinder Daniel C.
Leisner John C.
Illinois Tool Works Inc.
Shaw Clifford C.
Ziolkowski Patent Solutions Group LLC
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