(a) Field of the Invention
This invention relates to the control of DC generators used in arc welding operations, the generators being driven by internal combustion engines.
(B) Description of the Prior Art
In U.S. Pat. No. 2,135,046 issued on Nov. 1, 1938 is described a controller for a motor-generator arc welding set. This patent describes a motor powered by a three-phase electric main. The motor drives an A/C generator which supplies current to an arc welder circuit. A saturable transformer 65 has a primary winding 66 connected in series circuit relation with the welding cable and a secondary winding 64 connected in series with the coil of a relay which controls the main switch of the three phase main. The relay has a pair of contacts which are coupled to a timer 35 for the purpose of disconnecting the motor from the main after a predetermined interval of time following the cessation of welding operations.
In many arc welding machines, especially those used in the construction field wherein no electric energy is readily available, DC generators are used which are driven by internal combustion engines.
The problems associated with controlling a DC generator of a welding machine driven by an internal combustion engine are totally different from those encountered in connection with controlling an A/C generator driven by an A/C motor. In fact, the problems were compounded by the fact that the running or stopping of an internal combustion engine does not, in and by itself, produce an electric phenomenon which can be electrically monitored.
Also, the very high surge currents resulting from switching a DC welding generator into a short circuit condition discouraged workers in the art from developing a controller for DC arc welding machines, since the switching mechanism received in the welding circuit to implement the remote starting function becomes very easily damaged when such surge currents are allowed to flow during the switch closure. For these and other well-known reasons, no practical controller for remotely controlling the DC generator of an arc welder driven by an internal combustion engine has been introduced on the market, even though there is a great and pressing need for such a controller, especially since almost 40 years ago said U.S. Pat. No. 2,135,046 had described certain desirable features which such a controller might possess.
The present invention provides what is believed to be by applicants, the first practical, reliable and relatively inexpensive controller for arc welding machines whose DC generators are driven by internal combustion engines. This invention couples a vacuum-actuated device to the intake manifold of the engine for the purpose of carrying out switching operations. Also, applicants have discovered practical means for protecting the controller from the surge currents in the welding circuit.