Illinois Tool Works Inc.

John K McVey

Larry L Sharp

Bruce A Luxon

Edward W Wanatowicz

Stanley E Filipiak

A capacitive keyswitch is formed with a fixed horizontal plate that is imbedded in a horizontal printed circuit board below an overlaying dielectric layer and a moveable cantilever mounted plate that is hinged to the printed circuit board so as to project upwardly at an acute angle. When a plunger is actuated, a portion of it presses down on an overtravel mechanism that is formed from the moveable plate which causes the moveable plate to assume approximately a parallel position with respect to fixed horizontal plate, thereby changing the capacitance of the switch and actuating the switch. The overtravel mechanism consists of a tab cut out of a bent-up portion of the moveable plate so that the tab is bent along an intersection line formed by the intersection of the plane or moveable plate and the plane of the bent-up section.

Capacitive keyswitch with overtravel mechanism on moveable plate

A capacitive keyswitch is formed by a flat, horizontal capacitor plate that is covered by a dielectric layer on a printed circuit board and a moveable capacitor plate that is secured to the printed circuit board by a pair of tabs and is hinged so that it projects upwardly at an acute angle with respect to the horizontal printed circuit board. The plastic plunger for actuating the switch is formed with an integrally molded cantilever overtravel arm, which preferably is formed as a segment of the circumference of a circle. The arm has an integral transversely projecting cylindrical rod at its end which contacts the moveable capacitor plate during actuation of the keyswitch.

Capacitive keyswitch with overtravel plunger mechanism

A thermal switch is described which has a pair of axial leads, one of which is electrically insulated from the conductive outer housing and the other of which is in contact with the housing. An electrically-conductive temperature-sensing pellet which is made of solder, or other conductive material, is formed into a donut shape and rests on the bottom of the housing. A donut shaped insulator rests on top of the sensing pellet to protect the pellet from excessive force on it. A ring-shaped sliding contact is placed on top of a ceramic insulator and is bowed outwardly between the ceramic insulator and a conductive disc, which is in contact with the head of the insulated lead, so as to contact the conductive outer wall of the housing. When the temperature-sensing pellet melts, the solder flows allowing the contact to relax to its undeformed state and a spring that surrounds the insulated lead then forces the contact away from the head of the insulated lead. The solder repellent grease preferably surrounds the insulated lead so as to minimize the possibility of melted solder contacting this lead.

Thermal switch with electrically conductive thermal sensing pellet

The thermal switch of the present invention relates to thermal switches in which an organic pellet melts at a predetermined temperature which thereby allows the switch to change from a closed to an open state. More particularly, the switch is of the axial lead type wherein one of the leads is connected to the outside of a metallic housing for the device, and the other lead passes through an insulator into the interior of the housing. A thermally-sensitive pellet is positioned in the bottom of the metallic housing and a contact member is positioned in the gap between the pellet and the head of the insulated lead. A coiled spring encircles the insulated lead and forces the contact member toward the temperature-sensing pellet. The electrically conductive contact is formed with a bottom which either engages the pellet, or a wafer which is in contact with the pellet, and a top which is partially open and has a pair of inwardly bent ends that contact the head of the insulated lead at an angle. The contact is deformed due to the applied forces so as to engage the metallic housing of the switch. When the pellet melts, the spring forces the contact member away from the head of the insulated lead and the deformed condition of the contact is relaxed so that it is no longer in electrical contact with the metallic outer housing and thus the other lead of the switch.

Thermal switch with split ring construction

A temperature-responsive electrical switch is provided which has a pair of axial leads, one of which is connected to the cylindrically-shaped electrically conductive housing, and the other of which passes through an insulator into the interior of the housing. A cylindrical-shaped, slideable electrical contact which is open at one end is positioned in the housing. A coil spring is located inside the slideable contact between the bottom end of the contact and an enlarged section of the insulator. The contact has a plurality of spring fingers which are integrally formed from the bottom of the contact and which project upwardly from the bottom of the contact toward the head of the insulated lead. A thermally-sensitive pellet, which melts at a predetermined temperature and is formed to have a cavity in it, is positioned below the spring fingers. The pellet is dimensioned transversely so as to force the fingers into contact with the head of the insulated lead. Upon reaching the predetermined temperature the pellet melts and its liquid mass assumes a smaller transverse dimension, because of the original cavity in the solid pellet. This allows the spring to release its compressive force; and this, in turn, allows the slideable contact to move along the interior of the housing so as to thereby break electrical contact between the spring fingers and the head of the insulated lead.

Temperature-responsive electrical switch with sliding contact

The device described herein is useful in applications which formerly required both a thermal cut-off device and an electrical fuse. This device will open an electrical circuit in response to either an increase in ambient temperature or an increase in electrical current. A bracket is provided to support a radial lead thermal cut-off device. The bracket is of a general C-shaped configuration and has an extending lead bar that is crimped into electrical engagement with an input lead, and one radial lead of the thermal cut-off device is crimped into electrical engagement with the second input lead. A helical conductive coil has one end welded or otherwise secured to the C-shaped bracket, and the second lead of the thermal cut-off device is crimped to the other end of the helical coil which is positioned over the thermal cut-off device so as to surround it. Thus, an ambient temperature rise may cause the thermal cut-off device to open the electrical circuit; or alternately the heat generated by the I.sup.2 R loss in the coil due to excessive electrical current flow may cause the device to also open.

Combined thermal and electrical cut-off device

A thermal switch for automatically opening a circuit when the ambient temperature exceeds a predetermined level is disclosed which utilizes a sensing pellet formed of an organic-glass bead mixture. The organic-glass bead pellet retains a pair of leads in contact with each other when the ambient temperature is below the melting temperature of the organic material. The addition of the glass beads to the temperature sensing pellet allows the compressive strength that is needed to hold the leads together to be more reliably controlled. In the process of combining the organic material and the glass beads, to form the pellet, the organic material is first melted so as to flow around the beads. Manufacture of the thermal-sensing pellet in this manner eliminates the voids which occur in the pressed organic pellets that are conventionally used in thermal sensing devices. The elimination of these voids increases the strength of the otherwise relatively fragile pellet thereby improving reliability of thermal switches which utilize the improved pellet of the present invention.

Thermal switch with organic-glass bead mixture sensing pellet

A radial lead thermal cut-off device for opening an electrical circuit when a predetermined temperature is disclosed. Electrical connection between the radial leads is maintained by thin spring contact which is forced against the terminal heads of the leads of the device. The spring contact is forced into contact by a disc against the force of a coiled bias spring that engages the center of the spring contact. The disc is held in place by a temperature-sensing pellet of organic material which melts at a predetermined temperature and which preferably incorporates a multitude of spherical glass beads filling that greatly increase its strength. The pellet has a centrally located cavity so that when the organic material of the pellet melts the material fills a volume having a smaller transverse dimension. This allows the disc to move as the compression force of the coiled spring is relieved, which in turn opens the circuit between the contact members as the thin spring contact is forced away from the lead heads by the coiled spring.

Radial lead thermal cut-off device

A thermal switch device for automatically opening a circuit when the ambient temperature is increased to a predetermined level. A pair of conductor wires arranged in side by side fashion are spring loaded into contact with one another by inserting the contact regions into a cup-shaped pellet of heat-fusible material. The cup is structurally secured within a nonconductive tubular casing with a layer of insulative cement. The lead regions of the wires are also securely anchored within the casing with an insulative cement.

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Bensenville, IL, United States of America

John K McVey