US2490020A - Electrical contact - Google Patents

Description

Dec. 6, 1949 P. R. ENZLER 2,490,020

ELECTRICAL CONTACT Filed Feb. 11, 1946 l8& '8 [9 a 19 33a 2 b3 7 ,#Q%%%%%% mwmmmm %W P16. 4 FKLS ffie.4a-

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ATTYB Patented Dec. 6, 1949 UNITED STATES PATENT OFFICE ELECTRICAL CONTACT Paul Robert Enzler, Freeport, Ill., asslgnor to First Industrial Corporation, Wilmington, Del., a corporation of Delaware Application February '11, 1946, Serial No. 646,900

4 Claims. 1

My invention relates to an electrical contact and more particularly to an improved contacting or engaging surface therefor.

In sensitive, precision type snap acting switches, for example, such as shown and described in the P. K. McGall Patent No. 1,960,020, issued May 22, 1934, the force tending to urge the movable contact against one of the stationary contacts may in some cases be quite small, resulting in high contact resistance, rapid temperature rise, and arcing or sizzle when inclusions of dirt hold the contact surfaces a minute distance apart.

One method of meeting this'problem' has been to reduce the actual contact area, thereby increasing the contact pressure, by knurling one of the contact surfaces in two or more directions whereby a number of continuous grooves are made to intersect one another in the contacting surface. This produces a number of independent and discontinuous high points adapted to bear against the surface of the opposed contact at relatively high localized stresses. An example of this type of construction is shown and described in Design Patent No. 133,641, issued to Vernon L. High, September 1, 1942.

The construction shown in the High patent represented an improvement over the art, which previously had used flat or rounded contacts, in that dirt inclusions could hold the conventional flat or rounded contacts apart to cause them to sizzlej while if one of the contacting surfaces were made in accordance with the High patent, such dirt inclusions would merely be displaced into an adjacent groove thereby not interfering with contact engagement at the peaks. However, I have found that this is not yet the complete answer to the problem, for, in time, the pattern of the multi-pointed contact will be transferred to the flat surface, either by material transfer or by the tendency of the peaks to dig in due to impact, furthermore, in switches where the movable contact is carried by a reed or leaf spring, as for instance in the above-referred-to'McGall switch, high speed camera studies reveal that as the contacts are snapped together, the reed will vibrate for a very short interval, alternately shortening and lengthening of the reed and rubbing the movable contacts against the stationary contact along an axis of movement parallel to the long 2 hollows, with the result that there will be slight momentary arcing at each contacting operation and cumulative roughening of the engaging surfaces.

Whether the limited rubbing action between the contacts is unintentional or whether it is purposeful to improve the intimacy of engagement by rubbing off the oxide film, I have found that the action of such a. switch may be substantially improved by forming one of the contacting surfaces with continuous serrations or ribs or ridges, all extending in the direction of the axis of the above-mentioned limited rubbing action. By such construction, the pattern of the ribs which may eventually be transferred to the face of the opposed contact will take the form of continuous grooves so that when the contact carrying member vibrates, the ribs of the one member will merely slide recip-rocably within the grooves in the other and there will be no tendency to disengage due to improper meshing of the opposed patterns. Even when the flat contact is made of suificiently hard material that the serrated or ribbed contact makes no appreciable impression in it, this construction is markedly superior in performing without objectionable sizzle.

Thus, a primary object of my invention is the provision of an electrical contact having a contact surface formed with a series of ribs or continuous high lines, as opposed to certain prior art constructions having a contact surface formed with a series of discontinuous high' points.

Another object is the provision of an electrical contact having improved length of life and freedom from objectionable arcing and sizzle.

Other objects and advantages of the invention will become apparent from the following description of a specific embodiment of the invention, which serves by way of example to illustrate the manner in which the invention may be constructed and used.

In the drawings:

Figure 1 is a longitudinal, sectional, elevational view of a complete snap switch embodying my present invention; 7

Fig. 2 is asection on the line 2-2 of Figure 1;

Fig. 3 is an enlarged view of the stationary and movable contacts shown in Figure 1;

Fig. 4 is a section taken on the line 4-4 of Fig. 3 and shows the contacting surfaces of my invention as applied to the movable contact;

Fig. 4a is a view similar to Fig. 4, showing a modified form of my contacting surface;

Fig. 5 is another modification of my invention showing, in a sectional view similar to Fig. 4, the

-' to the stationary contacts, and

6 'is a perspective view of the leaf spring coi i t ctcarrier illustrated in Figure 1 showing a perspective view. of the serrated contacting surface.

Like parts are designated by like referen characters throughout the figures;

Referring now to Figure 1 in more detail, the snap switch therein shown is illustrative of the above-mentioned McGall type of switch with which my invention may be used advantageously. Reference may be had to Patent No. 1,960,020 for details concerning this type of switch. Brief- 1y, it includes an insulating'case having a base It and acover ll; upper and lowerv stationary contacts or stops I3 and M, respectively, having" has been a previously employed method of serrating electrical contact faces, the limited rubhing movement induced by depression or vibration of the tension element 20 would cause the terminals l5 and I6; and movable contacts 18 and is carried by an overcenter snap spring member 25 which is connected at the opposite end to the terminal 24.

Thespring member 25 comprises a thin leaf tension elementor reed 20 which is connected in cantilever fashion to the terminal 24 by means of a screw 22. A pair of thin leaf compression elements 26 are joined to the tension element 20 at the movable contacts l8 and I9 and pivotally supported intermediate the ends of the tension element 20 where they bear against a support member 28. This support member 28 is cut out in the center so as to be left U-shaped to clear the tension member 20 and has a pair of notches 30 for receiving and pivotally supporting the compression elements 26. The operation is such that when the plunger 21 is depressed it will move the tension element 20 downward to a position in line with the pivots 3B. This position is the position or axis of maximum-stress for the spring member and further depression of the plunger 21 moving the tension element through this axis will cause the spring to move downwardly with a snap action, disengaging the contacts l8 and I3 and engaging contacts I9 and I4; conversely, when. the depressive force on the plunger 21 is released, the tension element 20 will move upwardly through the axis of maximum compression, and the spring will be caused to return by snap action to the normal position shown in Figure 1. While a returning type of switch is shown, my invention is equally applicable for use with a non-returning type of switch.

When the spring snaps upwardly against the stationary contact l3 there will be a very short following interval in which the tension element or reed 20 will vibrate between opposite bowed and shortened positions which are indicated by the numerals 3| in Fig. 3 and shown in broken lines. Up or down movement of the plunger 21 to initiate snap action movement of the spring member will likewise cause the tension element to bow and shorten in this manner. In passing between these shortened positions, which are very much exaggerated for purposes of illustration, the tension element will pass through its normal position of maximum length (shown in solid lines in Fig. 3). Thus, in alternately shortening and lengthening, the reed will rub the movable contact back and forth against the stationary contact through a limited degree of movement indicated by the letter A, this limited rubbing movement being in a direction substantially parallel to the axis of the spring 25. It will be obvious that if the contacting face of the movable contact l8, for instance, were formed with a number of independent high points or peaks, as

, contacting surfaces.

peaks to jump in and out of the pattern of corresponding hollows previously imprinted in the stationary contactsurface. This would result in momentary arcing and shortened contact life.

Figs. 2, 3, 4, 5 and; show the manner in which I prefer to serrate at least one of each pair of Notches 32 are formed in the contacting surface in any desired manner, for example, by a coining or cold pressing method. The notches should be'substantially parallel to one another and parallel to the axis of limited rubbing movement,'in this case being parallel to the longitudinal axis of the spring member 25. 'I'hustwhen the switch shown in Figure 1 is provided with serrated movable contacts l8 and I3, and when the spring member is snapped upwardly to the position shown in Figures 1 and 2, any indentation made in the stationary contact 13 by the impact of the movable contact I8 will be a series of continuous parallel lines or grooves corresponding to' the ribs 33 on the movable contact. Then, during the interval of limited rubbing movement (shownin Fig. 3) the ribs 33 will reciprocate within the previously transferred grooves, if any, or will reciprocate on the fiat part of the stationary contact between the grooves and remain in engagement to prevent sizzling.

Another important advantage of my invention, which results particularly when the serrations are applied to the movable contact, is that the contact is self-cleaning; that is, during the period of limited rubbing motion when the reed 20 is vibrating, dirt inclusions which will fall into the grooves from time to time will be worked to one end or the other of the grooves and will be thrown off the contact. Furthermore, in moving rapidly though limitedly through an arc, considerable centrifugal force is established tending to throw any dirt inclusions off the movable contact in a radially outward direction; and by serrating the movable contact parallel to the axis of the spring, removal of the dirt by centrifugal force is facilitated.

Instead of serrating the movable contact members l8 and I9, as I have shown in Fig. 4, the stationary contact members I 3 and I4 may be serrated, as shown in Fig. 5.

Under some conditions of service, where a high localized bearing stress is desired on a few of the serrations, one or the other of the contacting surfaces may be formed with a convex surface; for instance with a spherical or rounded surface as is the case with the movable contact l8w-l9a shown in Fig. 4a where the surface joining the ridges 33a may be either cylindrical or spherical. Obviously, for the same effect, the stationary contact surfaces may be similarly formed.

I claim:

1. An electrical contact for a precision snap acting switch having a relatively broad contact surface shaped to engage an opposed unitary solid contact having a smooth continuous contact face, said surface having a plurality of alternate elongated pointed ridges and grooves integrally formed thereon, said ridges and grooves extendin the full length of one dimension of said surface and alternately disposed across the entire surface of the contact in a direction perpendicular to the first dimension.

2. In a precision snap acting switch, a fixed contact and a movable contact shaped and positioned to engage said fixed contact, said contacts having relatively broad flat surfaces of substantially the same overall dimensions, one of said contacts having a plurality of alternately disposed continuous elongated sharply pointed ribs and grooves integrally formed on one of said flat surfaces, said sharply pointed ribs and grooves extending the full length of one of the dimensions of the contact surfaces and disposed alternately across the surface of the contact on which they are formed in a direction perpendicular to the first dimension.

3. In a precision snap acting switch, a fixed contact and a movable contact shaped and positioned to engage said fixed contact limitedly movable along an axis relative to said fixed contact, said contacts having contact surfaces of substantially the same overall dimensions, one of said contacts having a relatively smooth fiat surface, and one of said contacts having a plurality of alternately disposed elongated sharply pointed ribs and grooves integrally formed on the surface thereof, said sharply pointed ribs and grooves extending the full length of the dimension of the contact surface in the direction of said axis and disposed alternately across the entire surface of the contact in a direction perpendicular to said axis.

4. In a precision snap acting switch, a fixed contact and a movable contact shaped and positioned to engage said fixed contact, said contacts having broad contact surfaces of substantially the same overall dimensions, one of said contacts having a spherical surface, and the other contact having a smooth flat surface, one of said surfaces having a plurality of alternate elongated sharply pointed ribs and grooves integrally formed thereon, said ribs and grooves extending the full length of one dimension of the surface of the contact on which they are formed and alternately disposed across the entire surface of the contact said sharply pointed ribs engaging the opposed contact in a series of substantially parallel lines. I

PAUL ROBERT EN ZLER.

REFERENCES CITED The following references are of record in the file of this patent:

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