US 3198893 A
Description (OCR text may contain errors)
Aug. 3, 1965 G. c. MAPELSDEN SWITCH HAVING AN ARC PREVENTING CAM ARRANGEMENT Filed Oct. 26, 1962 s Sheets-Shet 1 fW kor: flea/ya C/VqW/s d9); ,9 VW 62 M Alta/"17 Aug. 3, 1965 G. c. MAPELSDEN SWITCH HAVING AN ARC PREVENTING CAM ARRANGEMENT Filed Oct. 26, 1962 3 Sheets-Sheet 2 L 9 a: w
MED/UM fax/6176021 Geo/ye C/VS/ULE/S dP/z by vii-M0 CZ.
Aug. 3, 1965 MAPELSDEN SWITCH HAVING AN ARC PREVENTING CAM ARRANGEMENT Filed Oct. 26. 1962 3 Sheets-Sheet 3 www 93 United States Patent 3,198,893 SWITCH HAVING AN ARC PREVENTING CAM ARRANGEMENT George C. Mapeisden, Easton, (1011111., assignor to General Electric Company, a corporation of New York Filed Oct. 26, 1962, Ser. No. 233,270 3 Claims. (Cl. 2006) The present invention relates to switches and in particular to rotary switches of the type which are used to control .alternating current circuits for such applications as electric ranges, etc.
The present invention is concerned with eliminating the possibility of flashover in rotary switches for electric ranges that operate on a three-wire 115/230 volt system. A flashover is defined as an electrical discharge or are between conducting portions of the switch of differing line potentials and is, therefore, a short circuit established through the are. This are may be of low current mag nitude and/or short time duration, in which case no damage is done to the switch. If, however, the current magnitude of the arc and/or the time duration are such as to cause melting of the current carrying switch parts due to high temperatures, the switch itself thereby may be destroyed or a fire may result. This phenomenon of fiashover may occur in any switching action in which a movable contact connected to a common load is transferred very rapidly from a contact of one potential to a contact of ground or opposite potential.
In a switch used to control the heating of an electric range, fiashover is most likely to occur when switching rapidly from a maximum heat position, with the range heating element across a 230 volt line, to a lower heat position, with the element across the 115 volt line. One typical rotary switch used for certain electric range applications is an 8-position switch, wherein seven different heating conditions are provided. For such a range application, each heating element usually includes two resistance units which are connected in various single, series, and parallel circuits operating at either 115 or 230 volts to give the different levels of heat desired for cocking. In the three higher heat positions of the switch, one or both of the resistance units are connected across the 230 volt line from one 115 volt terminal to the other of opposite polarity. In the next three lower heat positions, one or both of the resistance units are connected across the 115 volt line from one 115 volt terminal to neutral. in switching from any of the three higher heat positions to any of the next three lower heat positions, the load connection is transferred from one of the 115 volt line terminals to the neutral terminal. If the switching is done sufficiently rapidly, the are at the 115 volt terminal may not have been interrupted prior to the switch blade having closed on the neutral terminal, and a short circuit is established through the are between the 115 volt line and neutral, causing a flashover. Depending on the severity of the flashover, the temperature of the arc may be of such high intensity that it will weld the contacts together, destroying the usefulness of the switch.
The are established between the contacts of a switch of this type operating in an alternating current circuit may be interrupted in one of two ways: first, by opening the contacts far enough so that the arc is extinguished, and secondly, in certain instances, by the alternating current of the are going through a current zero as occurs at each half cycle. There is a practical limit to which the contacts can be separated to establish a long gap, thereby extinguishing the are. This limit is imposed by factors of 3,198,893 Patented Aug. 3, 1965 size and cost of materials of the switch. It is therefore preferable to interrupt the are by having the current reach a zero value on the sine curve of the alternating current. If the contact to be closed can be kept from closing for a full half cycle after the contact being interrupted is first opened, then flashover cannot occur since there is no arc to sustain the short circuit. As a practical matter, the contact transfer time can be considerably less than a half cycle since the available gap does help to interrupt the arc, and since flashover that occur late in the half cycle are of such short duration and of such low magnitudes of instantaneous current that the heat of the arc is not sufiicient to cause damage.
For a common load, the contact transfer time or switching interval between opening a first pair of switch contacts connected to a line of one potential and closing a'second pair of switch contacts connected to a line of neutral or opposite potential is a function of the speed of rotation of the switch actuating member that controls the positioning of the movable contact blades. The speed of angular rotation of .this switch operating member may be affected by such factors as the dexterity and vigor of the operator of the switch, the size of the manually operable knob which is used by the operator, friction, detent action, and the coaction between the movable contact blade(s) of the switch and the switch operating member. The present invention is principally concerned with the protection of a rotary switch from flashover by controlling the coaction between a switch operating cam and a movable contact member in order to maximize the contact transfer time taken between opening one circuit and closing another circuit.
An important object of this invention is to provide an improved switch with a novel means for protecting certain contacts thereof from fiashover.
Another object of the present invention is to provide an improved rotary switch structurally adapted to maximize the transfer time for movement of a cam operated contact from one position to another position in order to protect the switch from flashover.
A further object of this invention is to provide a new and improved rotary switch wherein flashover protection is expeditiously achieved by coaction between a switch operating cam and one or more movable cont-act blades.
In carrying out the present invention in one form thereof, I have provided an improved rotary switch which includes a novel means for protecting certain of its contacts from flashover. This switch includes a suitable hollow housing wherein there is located a contact means including at least one single-pole double-throw switch, and a rotatable cam for actuating this switch. The single-pole double-throw switch includes a movable contact blade having a cam follower portion between its ends and a double contact at its free ends for engagement with a fixed line contact and a fixed neutral contact. In accordance with the present invention, the switch operating cam includes an annular cam track with an improved actuating portion arranged .to transfer the movable contact blade between the fixed line contact and the fixed neutral contact. In particular, this actuating portion comprises a first abrupt slope which acts upon the follower portion of the movable contact blade to rapidly engage or disengage the movable contact blade and the fixed line contact, and a second abrupt slope inclined in the same direction as the first slope, which acts upon the follower portion of the movable contact blade to rapidly engage or disengage the movable contact blade and the fixed neutral contact.
Interposed between the two slopes of the cam track actuating portion there is also formed a step. This step connects adjacent ends of the first and second slopes and acts upon the follower portion of the movable contact blade to maintain it in disengagement with both of its associated fixed contacts for a relatively long contact transfer time. With such an arrangement, by utilizing a cam actuating portion having a pair of abrupt slope-s and an intermediate step therebetween, a maximal contact transfer time is achieved, thereby protecting the single-pole double-throw switch from fiashover and enhancing its efiiciency of operation.
Further aspects of my invention will become apparent hereinafter, and the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which I regard as my invention. The invention, however, as to organization and method of utilization, together with further objects and advantages thereof, may best be understood by reference to the following description when taken in conjunction with accompanying drawings in which:
FIG. 1 is a top view of a completely assembled rotary switch embodying my invention;
FIG. 2 is a side elevational view of the switch of F IG. 1;
FIG. 3 is a bottom view of the switch of FIG. 1;
FIG. 4 is a top view partially broken away of the rotary switch of FIG. 1;
FIG. 5 is a fragmentary view of the switch of FIG. 4, showing the detent arrangement for controlling the rot-ar movement of the cam;
FIG. 6 is a perspective View of one of the movable contact blades of the switch of FIG. 1;
FIG. 7 is a face view of the switch actuating side of the rotary cam;
FIG. 8 is a fragmentary perspective view of the cam of FIG. 7, showing an improved cam track in accordance with the present invention, and a movable contact blade operated thereby;
FIG. 9 is a layout of the various annular cam track surfaces of .the switch actuating cam of FIGS. 7 and 8; and
FIG. 9a is a table illustrating the angular position of the switch cam in FIG. 9 relative to the circuit condition of the switch;
FIG. 10 represents typical circuit diagrams for each of the eight positions of the switch of FIG. 1.
Referring in detail to the drawings, and in particular to FIGS. 14, there is shown a rotary switch 1%) wherein my invention has been advantageously employed. The housing 12 for switch It) comprises a rectangularly configured recessed base 14 of molded phenolic or other suitable insulating material, and a cover plate 16. To facilirtate the convenient attachment of these two housing members together, the plate 16 includes a bent over section 18 at the center of its upper end (viewing FIG. 1) and two bent over sections 20 near the corners of its lower end (viewing FIG. 1). The section 18 is wrapped around the right end of base 14 (as shown in FIG. 2) and the sections 20 are wrapped around the left end of base 14 (as shown in FIG. 2) so that curled over extremities 18a and 20a of the sections 18 and 29 respectively (FIG. 3) cooperate with molded steps 22 of the base 14. The engagement of extremities 18a and 26a with molded steps 22 thus securely attaches the plate 16 to base 14 in a simple manner for holding the switch parts in their assembled positions.
For selectively operating the various circuits controlled by switch 10, a shaft 24 is rotatably mounted within housing 12 (see FIG. 2). Shaft 24 extends outwardly from the housing 12 through a suitable bearing aperture, and has a handle 26 secured to its slotted outer end (FIG. 2). The inner end of shaft 24 (FIG. 8) is suitably connected to a switch operating rotary cam 28 (FIGS. 7 and 8) which may be rotated in either direction for operating the switching elements. The structure and mode of operation of the cam 28 forms an important aspect of the present invention, as shall become apparent thereinafter.
Turning now to a further consideration of the interior of switch If), as shown in FIG. 4, the-re are three movable spring contacts 32, 34 and $6. The contact 32 is arranged on one side of shaft 24 and contacts 34 and 36 are arranged on the opposite side of shaft 24.
The three spring contacts 32, 34 and 36 are all fixed in the switch housing 12 at the upper end of base 14 (viewing FIG. 4). This mounting arrangement provides each spring contact with a cantilever act-ion, while the force or load applied to the cantilever is determined by the cam 28 engaging a cam follower 37 on each contact adjacent the center thereof. The fixed contacts are arranged at the lower end of the base 14 (viewing FIG. 4) opposite the fixed ends of the spring contacts. There are three fixed contacts in all, namely contacts 38, 3%, and 4%. Contacts 38 and 39 are arranged on the inner side of bottom wall 14a of base 14 and are engaged by contact buttons formed on the free ends of contacts 34, 36, and 32 respectively. The third fixed contact 443 is arranged above the free ends of the two inner spring contacts 32 and 34 (FIG. 4) and engaged by the cont-act buttons thereof. Hence, the outermost spring contact 36 is a single throw con-tact of a single-pole single-throw switch, while the innermost contacts 32 and 34 are double throw contacts of respective single-pole double-throw switches.
For a further explanation of the structure of the movable spring contacts 32, 34 and 36, attention is now directed to FIG. 6. As shown therein, each movable contact includes a spring blade 42, a fixed intermediate portion 44, and an integral tab type terminal 46. The free end, or end 48, opposite the fixed portion 44 of the contact carriers a silver contact button 59 which is adapted to make engagement with silver slugs 52 on the fixed contacts (FIG. 4). The cam fol-lower 37, mentioned previously, is merely a tab that extends from one side edge of the blade 42 and is upwardly directed (viewing FIG. 6) to engage with one of the cam tracks of cam 28 (FIG. 8). The end of the spring blade 42 that is remote from the silver contact button 59 is bent downwardly at a right angle as at 54, and the tab terminal 46 is an extension of one side edge of the portion 54. Actually, the terminal 46 is connected to the portion 54 by a right angle bend 56 so that the terminal 4 3 is perpendicular to the plane of the spring blade 42, while being generally parallel with one side edge of the blade. The spring contacts are assembled in the base 14 by inserting the terminals through suitable slots, (as shown in FIG. 3), and the fixed portion 44 is staked therein by forming over the edges as at 6%.
To enable each of the movable contacts 32, 34 and 36 to be operated by the switch operating cam 28, each of these contacts has the aforementioned cam follower 37 which is directed toward the cam from the general plane of the blade 42 (FIGS. 4- and 8). The cam follower 37 of each of the movable contact blades 32, 34 and 36 overlies an associated cam track and rides thereupon for selective actuation of its appropriate switch in response to the angular position of the switch operating cam 23. The illustrated switch 119 includes three circular cam tracks 62, 64, and 66 (FIG. 7), one for operating each of the movable spring contacts 32, 34, and 36 respectively. Thus, more particularly, as shown illust-ratively in FIG. 8, the cam follower 37 of the movable contact blade 32 is, in general, operated by the sloped interruptions formed upon its associated cam track 62 and moves in a direction parallel to the axis of cam 28 to open and close into engagement with fixed contacts 39 and 40. It will be understood further from viewing the cam track layouts of FIG. 9, and studying FIGS. 4 and 7 that the cam followers of blades 34 and 36 operate their associated switches in response to sloped interruptions of cam tracks 64 and 6-6.
To protect the contacts 32, 3% and 4d of switch 13 from the possibility of fiashover, the present invention provides ("greases an improved camming means for maximizing the contact transfer time involved in operating movable contact 32 between its two closed positions. The reason why it is important to provide such protection for contacts 32, 39, and 40 shall be better under-stood after a study is made of the circuit diagrams of FIG. 10. The diagrams of FIG. show the various heating conditions which may be typically and selectively operated by my switch 10.
As shown in FIG. 10, the movable spring blades 32, 34 and 36 have terminal ends which are represented, respectively, as load terminals A, B, and C of the switch. The fixed contact 39 has its terminal end represented as line terminal L1; fixed contacts 40a and 49b of arm 49 have their terminal end represented as neutral terminal N; and fixed contacts 38a and 38b have their terminal ends represented as line terminal L2. The circuits of FIG. 10 are labeled in the order of decreasing temperature from off, as high, 3, 4, medium, 5, 6, and simmer. The switch 10 is supplied with a voltage of 115/230 from three conductors (not shown) that are joined to the load terminals L1, N and L2. Accordingly, any circuit across one of the line terminals L1 or L2 and the neutral terminal N would be operating at a voltage of 115 volts, while a circuit across the two line terminals L1 and L2 would be at a potential of 230 volts. The heating element that is to be controlled by the subject switch comprises two resistance heaters 80 and 82 which are used alone or together in series or in parallel circuits across either the low orthe high voltages to provide a wide range of available cooking temperatures.
In the high position, heating elements 83 and 82 are connected in parallel across the two line terminals L1 and L2 at a potential of 230 volts. For the position 3 of switch 10, as shown in the circuit immediately to the right of the high position circuit, resistance heater 80 is energized, and it is connected across the line terminals L1 and L2 at a potential of 230 volts. At position 4, only the resistance element 82 is energized and it is connected across the line terminals L1 and L2 at a potential of 230 volts. For the medium heat position of switch 10, the two resistance heaters 80 and 82 are again connected in parallel, as in the high heat position, but they are then across the line L2 and neutral N at a potential of 115 volts. At position 5, the heater 89 is the only element that is energized and it is operated at the low voltage of 115 volts. For position 6, only the resistance heater 82 is energized and it is across the line L2 and neutral N to provide it with 115 volts. Lastly, for the simmer position the resistance heaters 80 and 82 are connected in series across the line L2 and neutral N at 115 volts.
Flashover is known to occur in rotary switches of previous designs when the movable contact transfers from one side of the line to neutral in a time of less than onehalf cycle (i.e., 0.0083 second for 60 cycle AC.) so that the unextinguished arc is drawn across the gap and continues as a short circuit. In prior art switches of the general nature described, when the rotary switch is operated from the 4 position to the medium position, such as by changing the ultimate switch setting eitherfrom the high, 3 or 4 heat positions to either the medium, 5 or 6 heat positions, the occurrence of flashover has presented a problem. In particular, attention is drawn to the fact that in the 4 heat position, the contacts 32, 39 are closed between line L1 and load A, while the contacts 32, 40a are open between the neutral terminal N and load A. However, in the medium position, the contacts 32, 39 are open while the contacts 32, 48a are closed. Hence, it will be seen that if the circuit is closed by the contacts 32, 48a before the are is extinguished in the gap formed by the opening of contacts 32, 39, a short circuit through the arc will develop as the switch mechanism performs its switching operation from the 230 volt settings to the 115 volt settings, or from the high to the low voltage condition. However, if a suificient transfer time is given for the opening of the contacts 32, 39 before the contacts 6 32, 40a are closed, the arc in the air gap will be extinguished automatically.
To protect the contacts 32, 39 and 40a from the possibility of fiashover, my invention provides a simplified and effective camming structure for maximizing the contact transfer time involved in operating the movable contact blade 32 from its line L1 to its neutral N positions. As previously mentioned, the movable spring contact 32 has its positioning controlled by means of the coaction of cam track 52 of the cam 28 with the follower 37 of the contact. As shown in FIG. 9 by the sectional layout or profile illustration of cam track 62, the camming surface of the track 62 includes a specially constructed actuating portion 92 (see also FIG. 8). The portion 92 is adapted to transfer the follower section 37 of movable contact 32 between upper surface 94 (viewing FIG. 9), where the blade 32 is cammed into engagement with fixed contact 39 (FIG. 8), and lower recessed surface 96 (FIG. 9), where the contact 32 is allowed to move by its internal biasing force into engagement with fixed contact 40:: (FIG. 8).
To describe the actuating portion 92 of cam track 62 in greater detail, it comprises a first abrupt slope 98 which extends downwardly and to the right from horizontal upper surface 94 (viewing FIG. 9) and is conterminous at its lower end with an intermediate step 100. The slope 98 is preferably disposed at an angle of 45 degrees with the horizontal upper surface 94, and the intermediate step 190 is in parallel relationship with upper and lower surfaces 4 and 96. The right end of intermediate step 100 (viewing FIG. 9) is conterminous with a second abrupt slope 182 which extends downwardly and to the right, being conterrninous at its lower end with horizontal lower surface 96. Abrupt slope 182 is also preferably disposed at a 45 degree angle relative to upper surface 94 and lower surface 95, and is therefore parallel to slope 98.
From a study of FIG. 9, it will be noted that the special actuating portion 92 is located on cam track 62 between the degree and degree reference positions, or in other words, between the 4 position and the medium position. The upper end of slope 98 (viewing FIG. 9) is spaced approximately 4 degrees from the 135 degree position of cam 28, and the lower end of slope 102 (viewing FIG. 9) is spaced approximately 4 degrees from the 180 degree position of the cam 28. With this arrangement, it will be further understood that the cam track 62 rotates in either direction relative to the follower section 37 of the movable switch contact 32.
For an understanding of how the special actuating portion 92 of cam track 62 coacts with movable contact 32, attention is now directed to FIGS. 8, 9 and 10. When the cam follower section 37 of movable spring contact 32 is riding upon the horizontal upper surface 94 of the cam track 62, the contacts 32 and 39 are engaged or closed and current flows through load terminal A and line terminal L1 at a potential voltage of 230 volts. This is the condition of the contacts 32 and 39 for switch positions high, 3, and 4. When the cam 28 is rotated to its 135 degrees or 4 position, as shown schematically in FIG. 9, follower 37 of contact 32 is held upwardly or away from the actuating face of the cam against the internal biasing force of contact 32. After the came track 62 then moves rotatively relative to the follower 37 of blade 32 (i.e., in a direction from right to left viewing FIG. 9, and toward the 180 degrees or medium switch position) through a 4 degree arc, the follower then reaches the top of abrupt slope 98. The follower of contact 32 then rapidly drops to its open circuit position where contact '32 is disengaged from both of the fixed contacts 39 and 40 (FIG. 8). To be more specific, the biasing force of the blade section 42 of contact 32 normally urges it in a downward direction into on gagernent with cam track 62 (viewing FIG. 8). After the cam follower section 37 of the movable contact blade 32 has reached abrupt slope 98 of the actuating portion 92, the internal biasing force of the blade 32 causes it to ride downwardly along slope 98 (viewing FIGS. 8 and 9) are in response to further rotation of cam 28 (in a counterclockwise direction of rotation viewing PEG. 8) until follower 3? reaches intermediate step 10th.
When the cam 28 is then rotated further in the same direction, with the blade 32 riding upon the intermediate step 1%, it is in positive disengagement with its associated fixed contacts 39 and tea. The blade 32 remains in this position until the follower section 37 of the movable contact blade 32 reaches the top of abrupt slope 162 (viewing FIGS. 8 and 9), and rides thereupon to allow the contact 32 to rapidly drop toward lower surface 96. Blade 32, then closes into engagement with movable contact 4% and establishes a circuit connection from load terminal A to Neutral terminal. After further rotation (in the same direction) of cam 28 through a 4 degree arc, the switch is at the 180 degree or medium position.
By using such a configuration for the actuating portion 92 of the cam track 62, maximum advantage has been taken of a relatively small angle of rotation of the cam 23 (eg. 45 degrees) to control the movable contact 32 in an improved manner. Thus by subdividing the actuating portion 92 into two similar slopes 93 and N2 of a maximum practical steepness and separating these slopes by an elongated intermediate step 1% for positively holding the movable contact blade of a single-pole double-throw switch in its open position, a camming structure has been provided which very rapidly opens and closes the contacts and positively controls their separation. With such an a rangement, it has been found that the contact transfer time involved in movement of the movable contact blade 32 from its 4 position to its medium position is maxirnized, thereby effectively reducing fiashover to a level of high improbability.
For controlling or detenting the rotation of the switch actuating cam 28 of switch 1%, as shown in FIG. 5, a pair of elongated spring members 119 have been provided. Each of the members 119 is of elongated bladelike configuration and has a curved projection 112 facing sideways from between its ends. The members 1-14 are fitted into appropriate recesses of cover plate 15, with each member i 110 located on one side of shaft 24 and the projections 112 facing inwardly toward each other and toward the axis of the cam (as shown in FIG. 5). The back side 116 of cam 28 has an annular hub 113 integrally formed upon it. Hub 118 includes a radially arranged series of detent notches 12% formed on the periphery thereof. The opposed projections 112 of the members 1153 cooperate in spring-like fashion with the notches 12%, as shown in FIG. 5, to index or control the rotary movement of cam 23 as well as its associated shaft 24 and knob 26.
It will be understood from viewing the arrangement of the spring members 1-14) in FIG. 5, that the cam 25 is rotatable in either a clockwise or counterclockwise direction of rotation.
It will now therefore be seen that my new and improved switch arrangement as illustrated herein Provides a simplified and effective means for protectin a cam operated rotary switch from flashove'r. it will further be' understood that such an approach involves only a minimum number of parts and is relatively inexpensive to manufacture.
While in accordance with the patent statutes, I have described what at present is considered to be the preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from my invention and I, therefore, aim in the following claims to cover all such equivalent variations as fall within the true spirit and scope of this invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. A manually operated switch comprising a housing, a manually operable shaft extending into said housing, a rotatable cam in said housing and attached to said shaft for rotation thereby, detent means engaging said shaft to releasably hold said shaft in two spaced positions of rotation and to prevent said shaft from stopping between said positions, a movable contact operable between a first fixed contact and a second fixed contact, a follower section on said movable contact, said cam including at least one annular cam track formed on one surface thereof for operating said follower section between said two fixed contacts in a continuous operation controlled by said detent means, said cam track having a switching surface portion including a first abruptly sloped arcuate section arranged to coast with said follower section for rapidly disengaging said movable contact from said first fixed contact, an arcuate step section at the disengaging end of said first section for holding said movable contact in positive disengagement with said first and second contacts for a finite period and a second abruptly sloped arcuate section facing in the same general direction as said first slope at th opposite end of said step portion and arranged to coact with said follower section for rapidly engaging said movable contact with said second fixed contact, said cam being positioned on said shaft so that said switching surface portion moves quickly past said follower section as said shaft passes between the two spaced positions determined by said detent means, whereby a single switching action is performed and the fiow of arcing current between said first and second fixed contacts through said movable contact is prevented.
2. A manually operated switch comprising a housing, a manually operable shaft extending into said housing, a rotatable cam in said housing and attached to said shaft for rotation thereby, a rotatable detent indexing member attached to said shaft for rotation by said shaft to control bidirectional rotary movement of said cam, said detent member releasably holding said shaft in two spaced positions of rotation and preventing said shaft from stopping 1 etween said positions, a movable contact operable between a first fixed contact and a second fixed contact, a follower section on said movable contact, said cam including at least one annular cam track formed on one surface thereof for operating said follower section, said cam track having a switching surface portion including a first inclined arcuate section arranged to coact with said follower section for rapidly disengaging said movable contact from said first fixed contact, an arcuate step porticn at the disengaging end of said first section for holding said movable contact in positive disengagement with said first and second contacts, said step being disposed in a plane perpendicular to the axis of rotation of said cam, and a second inclined arcuate section inclined in the same general direction as said first slope at the opposite end of said step portion and arranged to coact with said follower section for rapidly engaging said movable contact with said second fixed contact, said cam being positioned on said shaft so that said switching surface portion moves quickly past said follower section in one continuous operation as said shaft passes between the two spaced positions determined by said detent means, whereby a single switching action is performed and the flow of arcing current between said first and second fixed contacts through said movable contact is prevented.
3. A manually operated switch for use in a control circuit wherein a common load terminal is selectively switched from a first power terminal of high potential to a second power terminal of ground potential, a movable cont-act connected to said load terminal, a first fixed contact connected to said first power terminal, a second fixed contact connected to said second power terminal, a cam, said cam including a cam track arranged thereon for operating said movable contact between said first and second fixed contacts, said cam track having a switching surface portion including a first abrupt slope coacting with said movable contact for rapidly disengaging said movable contact from said first fixed contact, a second abrupt slope inclined in the same direction as said first slope and coacting with said movable contact for rapidly engaging a,1es,ses
said movable contact with said second fixed contact, and a step interposed between said first and second slopes for transferring said movable contact between said first and second slopes and holding said movable contact in positive disengagement with said first and second fixed contacts, and a detent means connected to said cam to releasably hold said cam in two spaced positions of rotation and t-o prevent said cam from stopping between said positions, said switching surface portion of said cam coacting continuously with said movable contact as said cam passes between the two spaced positions determined and controlled by said detent means whereby a single switching action is performed and the flow of arcing current between said first and second fixed contacts through said movable contact is prevented.
References (Iited by the Examiner UNITED STATES PATENTS Dusinberre et a1 200-153 Frank 200-18 Crouch 200-153 X Frank et al 200-18 Guth 200-21 X Jones 200-6 Oberholzer 200-153 X Baehi 200-153 X Sweger 200-153 X Clapp et a1 200-153 X 15 BERNARD A. GILHEANY, Primary Examiner.