Electrical switches using push button or plunger type switch actuators have many applications including use in automobile car doors, ignition circuits, refrigerator doors, home appliances and the like. These push button switches are either normally open or normally closed. The push button switch in a refrigerator door, for example, is open when the plunger is forced inward by contact with the refrigerator door. When the door opens, the push button moves to a closed state causing a switch wiper element to bridge the switch contacts and turn the refrigerator light on.
One prior art switch assembly includes spaced apart metal contacts which are selectively bridged by a leaf spring wiper member. In a normally open switch, inward movement of the push button causes the leaf spring to bridge the switch contacts. This also compresses the leaf spring to assure positive engagement of leaf spring contact regions against the two metal switch contacts. In a normally closed switch the push button moves the leaf spring contact regions out of contact with the switch contacts.
Use of the leaf spring as the switch wiper element has certain disadvantages. Prior art leaf spring switch wipers known to applicant are stamped from sheet metal. Stamping the leaf spring is a relatively costly manufacturing step. A V-shaped leaf spring opens and closes in response to push button actuator movement. During the life of the switch, the V-shaped leaf spring is flexed many times and during these flexings, stress forces are concentrated at the apex of the V. This concentration of forces tends to reduce the switch life since prior art leafs tend to fracture over time.
Prior art leaf spring wiper elements must have a certain length to achieve sufficient biasing of the wiper element contact region against the switch contacts. As the leaf spring is repeatedly flexed during the life of the switch, the force of engagement between the leaf spring and the switch contacts tends to diminish so that a margin must be built into the design of the leaf spring. This results in an even longer leaf spring than would be necessary if this degradation with time did not occur.
Some prior art leaf spring contact regions have small extensions or bumps that increase the force of engagement between the metal switch contacts and the leaf spring. This makes the switch more reliable but makes the leaf spring more complex and therefore more expensive.
If the leaf spring bridges the gap between metal switch contacts and currents beyond the rated value of the switch are experienced, the leaf spring may actually be welded to the switch contacts so that the switch can fail in a closed condition. This may be acceptable if the switch is a normally closed switch, but creates a problem if the switch is normally opened and fails in the closed position.
USPTO Backgrounds
USPTO Backgrounds