Leonard v. Cutler-Hammer Mfg. Co.

168 F. 249, 93 C.C.A. 551, 1909 U.S. App. LEXIS 4450
CourtCourt of Appeals for the Second Circuit
DecidedFebruary 16, 1909
DocketNo. 114
StatusPublished
Cited by1 cases

This text of 168 F. 249 (Leonard v. Cutler-Hammer Mfg. Co.) is published on Counsel Stack Legal Research, covering Court of Appeals for the Second Circuit primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
Leonard v. Cutler-Hammer Mfg. Co., 168 F. 249, 93 C.C.A. 551, 1909 U.S. App. LEXIS 4450 (2d Cir. 1909).

Opinion

NOYES, Circuit Judge.

This is a suit in equity to restrain the alleged infringement of letters patent No. 673,274 granted to the complainant April 30, 1901, for an improvement in electric circuit-controllers.

The patentee thus states the principal object of his invention:

“The object of my invention is mainly to provide a circuit-controller of the character referred to, with an electro-responsive device responding to abnormal increases in current, hereinafter referred to as ‘overload-currents’; which will be effective at all times; that is, both while the controller is being operated by hand to adjust it to the normal position and after adjustment — the overload switch or controller operated or controlled by said electro-responsive device being operative to respond to an overload-current even while the switch-operating lever of the controller is being moved by the operator.”

It will be observed, therefore, at the outset, that, while the patent is said to relate to circuit-controllers, its main purpose is to provide automatic protection against excessive or “overload” currents, when a manually operated starter is employed in an electric circuit. And at the outset it should also be observed that, while the claims of the patent are not limited to shunt-wound motors, the devices which they describe-are in their useful application practically confined to the regulation of the flow of the current to motors of that character — as distinguished from series motors — and the case has been presented upon both sides as if the claims referred specifically to them.

Before examining the claims of the patent, therefore, it will be desirable to ascertain what shunt motors are, the difficulties and dangers attending their use, the early protective devices, and the situation existing when the complainant made his alleged invention.

Shunt motors are electric motors having a stationary field magnet and a revolving armature, both of which are wound with wire. The winding on the former is the field winding, and the winding on the latter is the armature winding. When the current traverses'" the two windings it magnetizes the field magnet and the armature magnet, and the former, by attracting and repelling the latter, causes the armature to rotate and enables it to do its work. The field winding and armature are connected in parallel branches or side by side between the electric mains instead of being in series. The current flowing through the field winding has only to magnetize the stationary element of the motor, and the winding is such that it is constant and small when compared [251]*251with that traversing the armature winding. The field magnet, therefore, has little need of protection. The armature winding, however, ordinarily offers little resistance to the current, and as the armature —the working part of the motor — has many different conditions to ’■meet, it would be liable to be injured were it not that when once started it is able to automatically adjust itself to the amount of current, and, consequently, to the amount of work to be done.

This automatic action is effected by means of what is technically called the “counter electromotive force” of the motor armature. When the armature rotates it produces, by dynamo action, a back voltage or force proportioned to the speed, which operates in opposition to the current flowing from the source of supply. Thus when the motor lias started and is running in normal operation, this counter force protects the armature from an excess of current and governs the flow when the. work to be done varies. When, however, the motor is not running, no counter electromotive force is generated, and, if in this condition the full current is permitted to enter and bear upon the armature, it is liable to bum it out. The problem is to start the motor gradually and give the armature opportunity to catch up with its back pressure.

This problem was met early in the art by the use of a hand-operated starting rheostat or gradual-resistance switch in the line of the flow c i the current to the motor. Such a switch usually consists of a serie? of resistance coils attached to adjacent contact segments which can be swept over by a pivoted switch arm. With such a switch the operator gradually cuts out the resistance sections, and as they are cut out the current in tiie armature tends to increase. But as they are being cut out the' speed of the armature also increases, and it regulates itself by generating the back pressure, so that when they are all cut out it ip running protected. Tiie starting rheostat, therefore, without other device, serves to protect the armature in the admission of the current during tiie period of starting.

But should the current be suddenly shut off at any time after the starting switch has been closed, it would remain in an “on” position. Then,' should the current lie resumed, there would be nothing to protect the armature from its sudden inflow. The danger would not lie in the “no voltage” condition, but in tiie resumption of the current. To meet this contingency it was old in tiie art to provide an arrangement called a “no voltage” or underload switch or cut out which would open the circuit and protect the armature in. case of the interruption of the current .supply and return the contact lever to an “off” position. This was accomplished in a prior Blades patent by a device in which the contact lever was held in an “on” position when the current was passing through by a retaining magnet in tiie circuit acting in opposition to a retracting spring, and which was carried to an “of” position by the force of tiie spring when the current was interrupted.

This underload cut out, however, afforded no protection in the case of an excessive current without antecedent “no voltage” conditions. To meet this danger it was old in the art to arrange the apparatus so that the switch which was opened in the case o [ “no voltage” was also opened in the case of excessive currents. Thus in one form of the Fiske device an overload magnet was so arranged as to de-energize the [252]*252underload or no voltage magnet, release the resistance switch, and open the circuit in case of an excessive current, while also permitting the latter magnet to open the switch when de-energized by the failure of current. In another form, a single magnet was made to open the^ switch in response to either an excess or interruption of the current. But in all these cases the underload and overload devices operated only upon one and the same switch.

Independent devices for opening circuits in the case of excessive currents — overload circuit breakers — were also old in the art at the time of the complainant’s alleged invention. At first fuses were provided which would carry the normal full-load current, but which would melt in the case of an overload and cut off the flow of the current before the motor could be injured. Fuses, however, were found to serve their purpose only imperfectly, and automatic overload circuit breakers came into use in electric circuits. In a common form of such a device a magnet was introduced into the circuit and became energized thereby. In case of an excessive current this magnet was so arranged as to actuate an iron core which, unlatched the overload switch lever and opened the circuit. Fuses were commonly used with shunt motors, but whether the automatic circuit breakers were so used is a question which we need not now determine. Certainly there is evidence of such use.

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Bluebook (online)
168 F. 249, 93 C.C.A. 551, 1909 U.S. App. LEXIS 4450, Counsel Stack Legal Research, https://law.counselstack.com/opinion/leonard-v-cutler-hammer-mfg-co-ca2-1909.