US3373257A - Fluid damped electric switch actuator - Google Patents

Description

March 1968 H. MAT'IY'HIAS ETAL 3,373,257

FLUID DAMPED ELECTRIC SWITCH ACTUATOR Filed Sept. 2, 1966 ,2 FIG. 2.

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United States Patent 3,373,257 FLUID DAMPED ELECTRIC SWITCH ACTUATOR Lynn H. Matthias, Fox Point Village, and Roy E. Wilson, Miiwaukee, Wis., assignors to Allen-Bradley Company, Milwaukee, Wis., a corporation of Wisconsin Filed Sept. 2, 1966, Ser. No. 577,038 9 Claims. (Cl. 200-166) ABSTRACT OF THE DISCLOSURE An electric switch having a switch contact actuator and a fluid chamber and fluid adjacent to the actuator so that the fluid will damp actuator motion.

This invention pertains to damping the motion of the actuator means in an electrical switch. More particularly, the invention is directed to the damping of actuator motion in electrical switches through friction caused by a fluid such as a damping fluid.

It is many times important that motion of the electrical switch actuator with respect to the switch contact be controlled so that the switch contacts will perform in a desired manner. Of special concern is the need to prevent excess operation of the switch actuator caused by momentum, which excess operation causes the switch contacts to unacceptably change their relative position. This contact change many times leads to false switch operation and consequential injury or damage to the device being controlled by the switch.

An example of the conditions described above is to be found in the electrical limit switch which switch has a biased actuator means such as a lever arm and attached shaft having a normal condition corresponding to a first contact position and alternate conditions corresponding to separate contact positions distinct from those of the first contact position and, possibly, distinct one from the other. If the lever arm of this limit switch is allowed to fly back to the normal position under the influence of a biasing spring, the momentum of the arm and/or that structure connecting the arm to the electrical contacts can carry it beyond the normal condition or the corresponding first contact position. As the lever arm is carried past this normal condition, it approaches and very likely reaches a point at which the contacts change their position. This subsequent change in contact position leads to the above mentioned false operation or the unacceptable conditions. The fluid damping of this invention as applied to the switch actuator prevents this false operation of the switch cont-acts.

It is an object, then, of this invention to provide for damping the actuator motion of an electric switch through fluid damping.

It is a further object of this invention to provide a simple but effective fluid damping construction for electric switches; which construction permits adaptation in existing devices with a minimum of change.

It is a still further object of this invention to provide damping of actuator motion in an electric switch to control motion of the actuator and thereby control switch contact position. This damping thereby prevents false operation of associated contacts caused by the switch actuator being carried beyond the permissible limits of a desired actuator condition.

These and other objects will become apparent from the following description of an illustrative form of the invention. The particular structure used to illustrate the damping structure is a limit switch; but the invention is not limited to such an application. The reader is directed to the appended claims which set forth the scope of the invention.

In the drawings:

FIGURE 1 is the partial, cross-sectional view of the invention as applied to the head portion of a limit switch housing and taken along the line 1-1 of FIGURE 3.

FIGURE 2 is the front view of a limit switch incorporating the invention including the switch head from FIG- URE 1 and showing the switch contact portion in crosssection.

FIGURE 3 is the partial, cross-sectional view of the limit switch in FIGURES 1 and 2 but used here to illustrate the relative conditions of the actuator including lever arm as well as the relationship between a particular arm condition and a corresponding switch position.

FIGURE 4 is a partial, cross-sectional view of the switch shown in FIGURE 3 but with the lever arm shown in a condition distinct from that of FIGURE 3 and the switch contacts shown in a correspondingly different position.

The fluid damping construction of this invention is shown in FIGURE 1 as applied to the head portion of a limit switch housing. While the limit switch is used 'as illustrative of an application for the damping structure of this invention, the details of this limit switch will be found in US. Patent 2,796,487. Accordingly, a minimum of detail regarding the switch will be described below including only those details necessary for an understanding of the switch damping.

The housing 1 of the limit switch includes a head portion 2 and a base portion 3. An external operating force is applied to an actuator means such as lever arm 6 and attached shaft 7. This rotary motion of the actuator means at the shaft 7 is transformed into reciprocal motion at the plunger 8 through connector structure such as the link 9 which is located in the bore 14 of the head 2 and is operatively connected to the shaft 7. A flat portion 11 of shaft 7 abuts the cross-bar 12 which is integral to link 9. The particular relationship between the shaft 7 and cross-bar 12 so as to establish the reciprocal motion is accomplished through the flat portion 11 of shaft 7 raising and lowering the crossbar 12 'with rotation of the former. Compression spring 15, abutting against the crossbar 12, biases the shaft 7 to a normal condition as will be described later, and therefore urges the shaft 7 and lever arm 6 to return to this normal condition when external actuating forces are removed from the arm 6.

Connecting the link 9 to the plunger 8 is plate 16 to which the plunger 9 is attached. The diaphragm 17 is secured between the plate 16 and the plunger 8 so as to move therewith while being secured at its periphery to the housing 1.

The plunger 8 in turn operates 'a second plunger 20 which is operatively connected to a contact carrier 21. A contact blade 22 with movable contacts 23 thereon responds to the motion of the contact carrier 21 to move the movable contacts 23 between the fixed contact illustrated as paired fixed contacts 26 and the paired fixed contacts 27. Each of the fixed contacts 26 and 27 is :appnopriately connected to terminals 28 while compression spring 29 biases the plunger 20.

Returning to the head 2 and the particular damping structure therein. A rotor 36 is attached to the shaft through knurling on the shaft with the rotor 36 having a general cylindrical shape. At one end of the rotor 36 is a beveled portion 37 while the other end of the rotor 36 consists of flange means 38. A damping fluid 40 surrounds the rotor 36 with this damping fluid 4i retained in a fluid chamber formed by the walls of the bore 41 in the head 2 along with sealing means such as the front seal 42. This seal 42 is shaped so as to conform with the shape of the rotor especially along the beveled portion 37. A resilient material such as rubber is used for the front seal 42 as the shaft 7 must rotate within the front seal 42 while n3 maintaining a seal therebetween. This seal between the rotating shaft 7 and the fixed front seal 42 is insured through the use of groove means 45 molded or cut into the front seal 42 which provide ridges therebetween to abut the shaft 7 and establish a tighter fit therebetween. Through the use of the groove 46 in the bore 41 of head 2 and the ridge 47 in the front seal 42, the front seal is positively located with respect to the head 2. End cap 48 encloses the head 2. Further, the grooves 45 provide the needed resiliency to permit entry of a filling tool between it and the shaft 7; which filling tool conducts damping fluid 40 into the fluid chamber. Thus, both sealing and filling functions have been accomplished with a simple and economic construction.

The shaft 7 is rotatingly located within the head 2 by means of the front sleeve bearing 59 and the rear bearing 51; the shaft 7 being appropriately shaped at those points adjacent the bearings 50 and 51 so as to positively locate same in the head 2. A ring seal 53 is located in the groove 54 of shaft 7 and maintains a sealing relationship with the bearing 59 so as to contain the damping fluid in its cavity defined by the bore 41 and the front seal 42.

Damping the motion of the electrical switch actuator means, or in this case the rotary motion of the lever arm 6 and shaft 7, is established through frictional force between the moving actuator, here the rotor 36, and the damping fluid 40. The amount of frictional force is primarily a function of the viscosity of the damping fluid 40 although the characteristics of the material used to contact the damping fluid 40, in this case the rotor 36, also plays an important role in the amount of frictional force. The distance between the moving actuator and the walls of the fluid chamber also influence the frictional force, viz distance is a function of damping fluid viscosity. Research indicates that criticality of the damping fluid viscosity increases as this distance between actuator and wall increases or decreases from an optimum distance determined in part by characteristics of materials involved.

One additional factor in determining the frictional force is the amount of moving surface which the damping fluid 40 contacts. The rotor 36 is designed with flanges 38 and beveled surface 37 so as to provide the maximum practical contact surface for the damping fluid 40 while at the same time permitting use of the desired distance between rotor 36 and the fluid chamber walls as disclosed above. Significant results have been achieved through the use of relatively high viscosityfluids such as a silicone fluid or a grease for the damping fluid 40 and a rotor 36 made from nylon.

FIGURES 3 and 4 of the drawing help to illustrate the significant advantages which come from using the fluid damping of this invention. The actuator means including lever arm 6 is illustrated to have three conditions, viz the normal condition illustrated by 1H and the two alternate positions illustrated by I and II. In the normal condition III, the movable contacts 23 establish a first position, that is contact with the fixed contacts 26 as shown in FIGURE 3, while the conditions -I and II show the movable contacts 23 in a distinct position, i.e. in contact with the fixed contacts 27. When the lever arm 6 is moved by an external force from its normal condition 111 to either of the alternate conditions I or II the movable contacts 23 move with snap action from the position of FIGURE 3 to that of FIGURE 4 and the biasing spring in the head 2 is compressed so as to provide potential energy to urge the lever arm 6 back to the normal condition III. That is, the conditions I and II are unstable.

Should the external force on the lever arm 6 be suddenly removed, the lever arm 6 will fly back to the condition III due to the biased force in the head 2, e.g. the spring 15. During this return of the lever arm 6 to the condition III, the movable contacts 23 change their position. However, sufficient momentum can be established in the lever arm 6 and/or that structure connecting the arm 6 to the movable contacts 23 such that the r turn travel will take the lever arm 6 beyond the condition III and very likely to that point between the condition 111 and condition I or II at which the movable contacts 23 will once again change their position, for example, to that of FIGURE 4. The final return movement of the lever arm 6 will establish the condition III at which the movable contacts 23 will again return to their corresponding position, e.g. FIGURE 3; but the unacceptable momentary additional change in the position of the movable contact 23 has occurred. That is, the movable contacts 23 have momentarily closedwith fixed contacts when contact opening, only, is desired. This momentary contact closing can easily cause a false switch operation and the varied consequences attached thereto such as injury and damage resulting from unexpected operation of the device being controlled. The use of the fluid damper of this invention with the damping fluid 40 damping the motion of the switch actuator means through the rotor 36 sufllciently retards this return motion to the condition III such that the momentum is not great enough to provide the undesirable overtravel of the lever arm 6.

The above description with reference to the limit switch of the drawings, illustrates how the fluid damper resolves a critical problem in this particular switch. Since this problem is to be found in a variety of electrical switches, the fluid damper invention cannot be limited to this particular application.

We claim: g

1. An electric switch comprising:

(a) a housing with fixed and movable contacts therein,

(b) actuator means extending into said housing,

(c) connector means connecting said movable contacts to said actuator so as to move said movable contacts between open and closed positions in response to motion of said actuator means,

(d) a fluid chamber surrounding said actuator means,

and

(e) fluid in said fluid chamber in contact with said actuator means and thereby damp the motion of said actuator means.

2. In the electric switch of claim 1:

(a) said actuator means providing rotary motion (b) said fluid thereby damping rotary motion.

3. In the electric switch of claim 2:

(a) said rotating actuator means including a rotor (b) said fluid contacting said actuator at said rotor.

4. In the electric switch of claim 3:

(a) said actuator means have at least three conditions corresponding to separate said positions for the movable contacts with two of said conditions locating said contact in one of said contact positions and the third condition being intermediate said two conditions during which said contacts are in the alternate ofsaid contact positions (b) biasing means urging said actuator means to said third condition from said two conditions (0) said actuator means damped by said fluid so that said bias means can move said actuator means directly from said two conditions to said third condition only and thereby move said contacts directly from said first contact position to said second contact position only.

5. In the electric switch of claim 3, said rotor is of F cylindrical shape. E)

6. In the electric switch of claim 5:

(a) said fluid chamber located in a bore of said housing, (b) a seal closing said bore to confine said fluid in said chamber, (c) said seal having a beveled surface adjacent said chamber, 7

(d) said rotor having a beveled surface corresponding to said sealed beveled surface and separated therefrom by said damping fluid.

7. In the electric switch of claim 5:

(a) said rotor having a flange means at least at one end of said cylinder.

8. In the electric switch of claim 1:

(a) said fluid chamber located in the bore of said housing,

(b) sealing means closing said bore to confine said fluid in said chamber and abutting said actuator to establish a seal therewith.

9. In the electric switch of claim 8 said sealing means including groove means at said abutment with said 10 actuator.

References Cited UNITED STATES PATENTS Dehn 200-67 Ray 335-277 Dobes 200-168 Loken 20034 Nielsen 200168 ROBERT K. SCI-IAEFER, Primary Examiner.

H. O. I ONES, Assistant Examiner.

Disclaimer 3,373,257.-Lynn H. Matthias, Fox Point Village, and Roy E. Wilson, Milwaukee Wis. FLUID DAMPED ELECTRIC SWITCH ACTUA- TOR. 1 mm dated Mar. 12, 1968. Disclaimer filed Jan. 29, 1971, by the assignee Allen-Bradley Company. Hereby enters this disclaimer to claims 1, 2, 3, 4 and 5 of said patent.

[Oflicz'al Gazette September 28, 1971.]

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