US2165801A - Switch - Google Patents

Description

' y 11, 1939- c. G. KRONMILLER 2,165,801

SWITCH Filed Aug. 6, 1956 2 Shee'ts-Sheet 1 'lllllllllllllllllll L A'EM 3% 85 1911242111101 L Car? GJfronmz'ller Aftorweg ucu APR ,8 1941 Patented July 11, 1939 UNITED STATES SWITCH Carl G. Kronmiller, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Com- }pany; Minneapolis, Minn., a corporation of Delaware Application August 6, 1936, Serial No. 94,529

8 Claims.

My invention relates to a switch and more particularly to a switch controlled by a condition responsive means.

It is common to employ for various control purposes a switch which will remain in closed position only when some controlling position has a desired value. A particularly common use for such a switch is in a safety pilot in a fluid fuel burner control system when the switch will remain closed only when the pilot is burning. In certain 01 such switches employing an electromagnetic holding means, a manual operating means is provided which is effective to initially close the switch, the switch remaining closed only if the holding means is energized. In prior art devices of this type, it has been possible to close the switch momentarily by the operating means before the electromagnetic means is energized. In other words, each time the operating means is actuated the switch is temporarily closed during such attempt to permanently close the switch. This may have a very definite disadvantages For instance, in the use just disclosed, wherein the switch operates as a safety pilot, the closing of this switch may under certain circumstances admit fluid to a fuel burner which fuel,

by reason of the fact that the pilot is unignited,

will itself not be ignited. The result is that each actuation of the operating means admits a certain amount of unignited fuel to the burner which, when the pilot is finally ignited, may lead to disastrous results.

Moreover, in certain cases where an attempt has been made in switches employing other types of holding means to prevent the operating means from changing the circuit controlling position of the switch until the holding means is effective, no means has been-provided for preventing the circuit controlling position of the switch being changed again upon an accidental actuation of the operating means after the holding means is effective. Thus, referring again to the use of the switch as a safety pilot, if it is possible to open the switch by actuating the operating means after the burner has been started, the result will be that theburner is extinguished momentarily and if at the same time the pilot burner is extinguished the release of the operating means will cause gas to be admitted to the main burner until the device responsive to the pilot flame has cooled off sufficiently to permanently open the safety pilot switch.

An object of the present invention is'to provide a switch controlled by an electromagnet and an operating means for the switch which is effective to move the switch to a desired controlling position only when the electromagnet is energized.

A further object of the present invention is to provide a switch of the type set forth in the previous object in which the electromagnet is energized by a thermocouple.

A further object of the present invention is to provide a switch having an actuating means which is eiIective to move the switch to a desired controlling position only when a desired condition exists and is ineffective to move said switch from said position.

Other objects of the present invention will be apparent from a consideration of the specification, claims and drawings, of which Figure 1 is a sectional view of one form of my improved switch.

Figure 2 is a. view of the contact blade structure and the insulating base supporting said blade structure, said view being taken along the line 2-2 of Figure l.

Figure 3 is a view of the portion of the switch apparatus during an intermediate stage of the operation thereof.

Figure 4 is a view of the switch mechanism in its switch-closed position.

Figure 5 is a detail view taken along the line 5-5 of Figure 4.

Figure 6 is a schematic view of one application of the improved switch.

Figure 7 is a section view of a modified form of the switch, the section being taken along the line 'l'l of Figure 9.

Figure 8 is a sectional view of the switch shown in Figure '7, the section being taken along the line 8-3 of Figure 7. t

Figure 9 is a sectional view of the modified switch along the line 99 of Figure 7.

Figure 10 is a detail view of two of the contact carrying members, and

Figure 11 is a detailed view of a portion of the switch operating mechanism with the switch members in a position assumed when the contacts are in a second circuit controlling position, the section being taken along the line H--ll of Figure 9.

Referring to Figure l of the drawings, the switch is mounted in a housing Hi to which is secured an insulating plate it. Mounted on insulating plate I! are contact carrying arms l2 and i3, which are secured thereto by terminal posts It and i5 respectively.

As best shown in Figures 3 and. 4-, the contact carrying arm 32 extends diagonally upwardly from the base and then horizontally. Secured to the horizontal portion thereof is a contact H. The outer end of the arm i2 is bent to form a U-shaped portion having a base i8 and an outer leg 19. The arm is of resilient material and by reason of the resiliency thereof is biased downwardly.

The contact carrying arm 53 extends vertically upwardly from the base and then horizontally, terminating in a downwardly extending leg 2| which is bent at 22 to provide a portion lying under the contact ill of member 02. Secured to this portion is contact 223 which is adapted to cooperate with contact ill. zontal portion of arm. (lit is a relatively rigid strip M which extends beyond the strip [l3 to constitute a horizontal continuation of the same. arm it is of resilient material which resists movement of the arm from the position shown in Figure 1.

Also secured to insulating base it is a resilient strip 25 which has secured thereto a relatively rigid strip 26 which overlies the strip 20 and is adapted to cooperate with the same in a manner to be subsequently disclosed. Thestrip 25 tends to move upwardly by reason of its resilience.

A lever lid is pivotally secured to the insulating plate ii. A portion of this lever is channelshaped and is provided with side walls 3i and a base portion 32, which base portion extends beyond the side walls 36. The arm 3t is secured to plate 6 I! through a pivot pin which, as shown in Figure 5, is non-rotatably secured to plate ill! by a set screw M. A spring has one end extending through the pivot pin and has its other end engaging the base portion of arm 8ft so as to urge lever iiii in a counter-clockwise direction. A roller ii is secured between the two side portions 3i of lever Elli and cooperates with the base portion it of the U-shaped portion of contact carrying arm l2. Also mounted on pivot pin is a U- shaped arm 59 which is provided with an end por= tion Ml which is inclined in such a direction that when it lies under the strip 25 as shown in Figure 4, it is substantially parallel therewith. Arm 39 is provided with two ears (ll, as best shown in Figure 5. Two springs 33 are mounted on pivot pins 33 and cooperate with ears ill and with the side walls 3!] of lever 3t so as to urge ears ii] of member 39 into engagement with the upper edge of arm 38. The result is that a strain release connection between arm 39 and lever til is provided.

As shown in Figure l, a U-shaped bracket 65 is secured to the insulating plate ill through ears 56 which project through the plate ii and may be secured thereto by crimping or any other suitable manner. The bracket 35 is provided with a central portion 41 which is enlarged so as to have a cylindrical housing member 58 secured thereto. Located in this housing 48 is aypush button 49 which is provided with a collar 5t! intermediate its two ends. The push button 49 terminates in a reduced stem portion 5i which extends through an aperture in the portion ll of bracket 45. A sprin 52 is located between member 47 and collar 50 and serves to urge push button 49 outwardly. The push button is so located that the stem 5! is adapted to engage strip 26 upon the push button being moved inwardly. A cap 53 is threaded on housing 48 and is adapted to prevent the accidental displacement of push button 49. A cover 54 encloses the upper portion of the switch mechanism.

Associated with lever 30 is an armature 55 which is provided with a stem 51 extending through an aperture in the base portion 32 of arm 38. .A flange 58 is provided at theouter portion or stem 51 and a spring 59 is located between armature 55 and member 38 and normally serves to urge the armature 55 to the position relative to lever 30 shown in Figures 1 and 4. The spring 59 and flange 58 serve to provide a strain release connection between armature 55 and arm-32.

The armature 55 is 'designed to cooperate with an electromagnet 56 which comprises a core 6| Secured to the hori- The and a winding The core ti is preferably of material oi high magnetic permeability. The

windings (52 are energized by a thermocouple iii.

The thermocouple 66 is provided with the usual members it and it of different thermoelectric 5 characteristics which are jointed at V2 to provide the hot junction of the thermocouple. While members lit and ill may be of any suitable material having desired therinoelectric characteristics, it has been found particularly desirable to make 10 the outer member iii of a suitable stainless steel which will resist the heat of a pilot flame and the inner member of Constantan", an alloy consisting of approximately 50% nickel and 50% copper. ihe inner member iii is secured to a conductor 73 which is insulated as at M. The outer member id is connected to a copper reducing sleeve 75 which in turn is connected to a copper tubing it. The copper tubing it is electrically connected through a sleeve ill with one endtof the winding d2 of the 20 electromagnet. The sleeve ll also serves to secure tubing lit to the casing iii. The inner conductor it is secured to the other end of the winding 62 through a coupling sleeve til which is insulated from sleeve ill through a suitable insulating bush- 25 ing 8 i.

In order for the extremely small electro-motive force which is generated by the difference in temperature between the hot junction 72 and the cold junction, to produce a sufficient holding action in 30 the electromagnet, it is necessary that the resistance of the circuit energized by the thermocouple be extremely low. In order for this to be true it is necessary that conductors it, copper tubing 16 and the conductor constituting the winding 62, be 5 of a relatively large size so as to oiier little resistance to the flow of current.

As previously stated, one application for which the switch is particularly designed is that of a safety pilot in a fuel burner control system. Such 0 an application is shown schematically in Figure 6 of the drawings. Referring to said figure, a gas burner is supplied with gas through a pipe 86. The flow of gas through pipe ditto burner 85 is controlled by a valve 8? of any suitable electrically 45 operated type. For the purposes of illustration, the valve 8? may be of a motor operated type. A pilot burner 88 is associated with'the main gas burner 85 and it is desired that it be impossible to open the main gas valve 8? unless this pilot is 50 burning. The improved switch of the present invention is designated in its entirety in this figure by the reference numeral 99. The motor of valve 81 is under the joint control of this switch and a thermostatic switch ill of any suitable construc- 55' tion.

A stepdown transformer 92 supplies power for the operation of the valve. This transformer comprises a high voltage primary 93 connected to line wires 96 and a low voltage secondary 94. 99 The secondary 94 is connected through a conductor 98 with .a fixed contact of the thermostat 9|. Conductor 99 connects the other terminal of the thermostat with one terminal of switch and a conductor I00 leads from the other ter- 65 minal of the switch 98 to one terminal of a valve operating mechanism of valve 81, the other termine] of which is connected to secondary 94 by a conductor IOI. It will be readily apparent that when switch 98 is open it is impossible to 70 establish a circuit to the valve operating mecha* nism of valve 81 even though thermostat 9| be closed. It is accordingly imperative in order for the valve 81 to be opened that switch 90 be closed. For a'reason which will be more apparent from 76 the subsequent description of the operation of the switch, it is impossible to close switch 99 unless the pilot 66 is burning.

The switch is shown in Figure 1 in the position assumed when the pilot is extinguished. Under these conditions, the biasing action of spring 36 urges the lever 39 in a counter-clockwise direction and due to the action of roller 31 pressing against portion I9 of contact carrying arm I2,

20 the latter arm 'is held in the position shown' in Figure 1 against the action of its own resiliency, which tends'to urge it downwardly. The'contact arm I3 tends toassume the position shown in Figure 1 by reason of its inherent resiliency. The

15 resiliency of member 25 tends to hold the rigid strip 26 substantially in engagement with push button 49. Due to the fact that-the energization of the electromagnet by thermocouple 64 is relatively small, armature 55 will not be moved by the go magnet downwardly into engagement with the magnet from the position shown in Figure 1. It is necessary if there is to' be any co-action between the electromagnet 56 and armature 55 for these two members to be brought into engagement. The push button mechanism is for this purpose.

Upon push button 49 being moved inwardly with respect to plate II, the plate 26 will first engage plate 24 and will then urge arm I2 downwardly through its engagement with the outer leg I9 of arm I2. Due to the fact that the contact 23 is rigidly secured with respect to contact arm I3 .and that the spacing of contact carrying arms I2 and I3 is fixed when contact arm I3 is 35 being moved downwardly by reason of the leg' I9, the downward movement of these members by the actuation of push button 49 does not cause engagement or contacts I1 and 23. Upon push button 49 being moved completely inwardly'the 40 parts assume the position shown in Figure 3. It will be noted that the arm 39 has moved against the end of plate 26 where it is resiliently held by the action of springs 93 which, as previously stated, tend to urge ears 4I into engage- 5 ment with arm 39. It will be further noted that the downward movement of contact arm 39 has caused armature 65 to be moved into engagement with the core iii of electromagnet 56. As previously stated, the spring 59 functions to provide 59 a strain release connection between arm. 39 and armature 55 so as to insure a firm seating of armature 65 with core H of electromagnet 56.

If the pilot burner is not ignited so that electromagnet 56 is not energized, the release of push 55 button 49 will cause the parts to all return to the position shown in Figure 1. It will be noted that during this entire action, contacts I1 and 23 are maintained spaced so that it is impossible to even momentarily close the circuit to the gas so valve 81.

If, however, when the parts are moved to the -position shown in Figure 3 by reason of push button 49 being moved inwardly, the pilot burner is lighted so that electromagnet 56 is energized,

c5 armature 55 will be held in engagement with the electromagnet. Under these circumstances the arm 39 will not be permitted to return to the position shown in Figure 1 but will move in a counter-clockwise direction merely until the por- 70 tion 32 thereof engages the flange 59 as shown in Figure 4. 'Due to the fact that the switch arm I2 is biased downwardly by reason of its own resilience, its upper motion will terminate as soon as the portion 32 of lever 30 engages 75 flange 56. Arm I3 will, on the other hand, continue to travel upwardly by reason of being biased upwardly because of its resilience with the result that upon push button 49 reaching its uppermost position the various parts will be in the position shown in Figure 4, wherein contacts IT 5 and 23 are in engagement. It will be noted that the actuation of push button 49 results in contacts. I1 and 23 being brought into engagement only when the pilot is ignited.

Referring to Figure 4, it will be noted that the portion 40 of arm 39 lies underneath the strip 26. Referring to Figure 3 it will be noted that the only thing which tends to prevent arm 39 from rotating in a clockwise direction with respect to lever 39 is the engagement of this arm with the end of strip 26. When this strip moves upwardly due to the push button being released, springs 43 will be effective to move arm 39 to the pos tion shown in Figure 4. If it is now attempted to change the position of the switch by actuation of push button 49, rigid strip 26 will never be moved-into engagement with strip 24 due to the fact that it will first engage arm 40 and further downward movement of strip 26 will be prevented. The result is that it is impossible to even momentarily openthe circuit to the actuating means of gas valve 81. For the reasons previously pointed out, this is a considerable advantage over prior structures.

In Figures '7 to 11 of the drawings a modified 3@ form of the switch is shown. The principal difference between the modified switch and the one previously described is that this switch is partly adapted for the control of a three-wire circuit as distinguished from a two-wire circuit for which the previously described switch was adapted. There are also certain differences in construc-, tional detail which are of general applicability to either a two-wire or a three-wire type of switch. 4@

Referring to Figures 7 and 8, a base plate is designated by the reference numeral I93. Lo-=' cated above this plate I63 is an insulating plate I94 which is supported on base plate Hit by spacers I96. A bracket 666 of inverted U-shape is located upon the insulating plate I99 Screws Mil serve to connect plate I93, insulating plate 999 and bracket I66 to the spacers I95, and to secure these members together 'in assembled re lation. 5@

Also mounted upon insulating plate MM are contact carrying arms H9, Ill and H2. These contact carrying arms are, as best shown in Figures Qand 11, secured to the plate I96 through terminals H6, H5 and H6 respectively.

The contact carrying arm I iii is relatively rigid. This arm after leaving the terminal lit first extends vertically and then terminates in a hori= zontal portion H8. This horizontal portion is enlarged adjacent its midpoint and extending e through this enlarged portion is a circular opening H9. Secured at the outer end of horizontai portion M9 on the underside thereof is a con tact I29.

The contact arm iii is of more or less resilient a material and is so disposed that it tends to move downwardly by reason of its resiliency. This arm, as best shown in Figures 10 and 11, is provided with an ear portion I2I which lies under the circular opening H9. of contact carrying m member III). This ear portion I2I is provided with an aperture I29 therethrough which apertureis aligned with aperture II9. Arm IN! is further provided with a vertically extending portion I22 and extending from the last named pertion is an ear G23 parallel to ear 112i. Secured to the opposite sides of ear 023 are contacts 023- and 625 which are aligned in a vertical direction with contact M0. Contacts H and 026 are adapted to cooperate with each other and are shown in engagement in Figures 7 and 8.

The contact carrying arm M2 is also of re-- silient material and is so formed that the outer portion of this arm tends to move upwardly by reason of the resiliency of the arm. This arm is provided with a portion i215 which extends diagonally upwardlyand terminates in a horizontal portion to the upper side of which a contact B21 is secured. The horizontal portion is formed so as to provide an ear E28 which is adapted to be aligned with apertures M9 and E29.

Secured to the upper horizontal portion of bracket I06 is a cylindrical housing member H30. This member houses a push button H36 corresponding in function to push button 49 of the previously described species. Push button i3i is provided with a shoulder I32 and is threadedly connected to a cylindrical member 833 of insulating material whih is located on the opposite side of bracket I06 from the portion of push button I 3I which is manually operated. A spring E34 is located between member I00 and shoulder H2 and serves to bias the push button outwardly. The outward movement of push button I35 is limited by reason of the engagement of the cylindrical insulating member I33 with bracket I06. The cylindrical member I33 extends through opening H9 and is adapted to engage the ear I28 of contact carrying arm I I2.

Secured to the base plate I03 is an electromagnet housing I31. Located within this housing I31 is an electromagnet I38. A member I39 functions as a closure for the electromagnet housing, as a guide for the armature cooperating with the electromagnet, and as a spring bearing member. This member is provided with a collar I40 which is clamped betweena shoulder of housing I31 and the base plate I03. Extending downwardly from the central portion of member I39 are two spaced members I4I which function as guides for an armature I42 which is adapted to cooperate with the electromagnet I38. The armature I42 is secured to a stem I43 through a clip I44. Secured to the upper end of stem I43 is a cup-like member I 45 as best shown in Figure 11. An insulating stud I41 is threaded into the cup-like member I45 and a split ring I46 is located between these two members and serves to secure the same to stem I43. Insulating stud I41 is provided with a reduced portion I48 at its upper end which extends through the opening I29 in contact carrying member III. A spring I49 bears at one end against member I45 and at the other end against the base of a recessed portion 950 of member I39, which recessed portion serves as a bearing for spring I49. The spring I49 serves to bias member I45 and consequently stud 641 upwardly so as to maintain contact carrying member III in an upper position such as shown in Figure 7 wherein contacts I20 and I24 are in It is furthermore believed unneces- I tails of the electromagnet and the method of connecting the leads from the thermocouple to the electromagnet.

The various elements of the switch are shown in Figures 7 and 8 in the position which they assume when the electromagnet is deenergized due to the absence of a flame adjacent the thermocouple. In this position contacts till and I24 are in engagement. When it is desired to bring contacts H and I2'l into engagement, the push button 530 is pressed downwardly. The actuation of push button 63H causes insulating member I33 to move downwardly. The downward movement of insulating member I33 causes its engagement with ear I28 of contact carrying arm H2, causing the latter member to move downwardly. At the same time the downward motion of member I33 is transmitted through ear H28 to stud I41, causing the latter member to also move downwardly. As previously stated, contact carrying arm III is biased downwardly and is held in the position shown in Figure 11 only by reason of the biasing action of spring 849 acting through members I45 and I41 to move arm Ill upwardly. Upon the downward movement of member I41, contact carrying arm Ml is free to move downwardly, moving down substantially simultaneously with contact carrying arm I I2. As a result both members are shifted in position but contacts I25 and I21 are not allowed to move into engagement.

The downward movement of stem I 43 causes armature I42 to be moved into engagement with electromagnet I38. Due to the fact that armature I 42 is now in direct engagement with magnet I 38, the latter will be effective to hold the armature if the thermocouple is being heated. If the thermocouple is not being heated the release of push button I3I will restore the parts to the position shown in Figures 7 and 8, thus causing re-engagement of the contacts I20 and I24 without having at any time effected engagement of contacts I25 and I21. Due to the fact that in a normal use of this apparatus in three-wire circuits, the engagementof contacts I25 and I21 would effect the operation of the fuel supplying apparatus, it is highly important that these contacts not be engaged even momentarily for a reason similar to-that set forth in connection with the previously described species of the apparatus.

If, however, the pilot is burning properly and armature I44 is held in engagement with magnet I28, stud I 41 is held in its lowermost position as indicated at Figure 11. Due to the fact that as previously mentioned contact carrying arm III is biased downwardly, this arm will remain in its lowermost position as indicated in Figure 11.

Upon the release of push button I3I, arm 2 will be free to travel upwardly due to its natural bias and will cause contact I21 to move into engagement with contact I25.

It will be readily seen that as in the first de-.

scribed species, the engagement of the contacts which cause operation of fuel feeding means or which bring about a. normal running condition of the system being controlled, is not effected by operation of the initial resetting means unless the electromagnet is energized by reason of the existence of a desired condition such as the ignition of the pilot burner. Moreover. this object has been accomplished in both species with an extremely simple mechanism which has a minimum number of moving parts.

While certain specific embodiments of the present invention have been shown and described, it

is to be understood that these are for purposes of illustration only and that my invention is to be limited only by the accompanying claims.

I claim as my invention:

1. In combination, a switch movable between first and second controlling positions and biased to a first position, holding means comprising an electromagnet for holding an element associated with said switch in a position wherein said switch is biased to said second controlling position, actuating means for moving said switch, without moving the same to said second controlling position, to a position wherein said element is held by said holding means if said electromagnet is energized, said biasing means being operative upon further movement of said actuating means to move said switch to said second controlling position, and means to prevent movement of said switch from said second circuit controlling position by said actuating means.

2. In combination, a switch movable between first and second controlling positions, means biasing said switch to said first position, holding means comprising an electromagnet for holding an element of said biasing means in a position wherein the latter is effective to bias said switch to said second controlling position, actuatingmeans for moving said element of said biasing means, without affecting the circuit controlling position of said switch, to a position wherein said holding means is effective if energized, and means efiective upon said switch being moved to said second controlling position to prevent movement of the same from said position by said actuating means.

3. In combination, a pair of resilient contact carrying members tending by reason of their own resilience to move to a first circuit controlling position, biasing means normally acting on said contact carrying members to urge the same against their resilience into a second circuit controlling position, holding means for retaining said biasing means in a position wherein said contactcarrying members are not effected thereby, actuating means operative upon movement thereof in one direction to move said biasing means while preventing said contact carrying members from moving to said first circuit controlling position, into a position wherein said biasing means may be retained by said holding means if effective, said members being operative upon further movement of said actuating means to move to said first circuit controlling position by reason of their own resilience.

4. In combination, a pair of resilient contact carrying members tending by reason of their own resilience to move to a first circuit controlling position, biasing means normally acting on said contact carrying members to urge the same against their resilience into a second circuit controlling position, holding means for retaining said biasing means in a position wherein said contact carrying members are not affected thereby, actuating means including a reciprocable member operative upon movement of said member in one direction to move said biasing means while preventing said contact carrying members from moving to said first circuit controlling position, into a position wherein said biasing means may be retained by said holding means if effective, said contact carrying'members being operative upon movement of said reciprocable member in the opposite direction to move to said first circuit controlling position by reason of their own resilience.

5. In combination, three contact carrying members, a first of which is substantially immovable and a second and third of which are movable, said second member being biased into a contact making position with respect to said first member, reciprocable means for moving said second and third contact carrying members without changing the relation of the contacts carried thereby, and means operable when said members are so moved by actuation of said reciprocable means in one direction to hold an element associated with one of said members so that upon actuation of said reciprocable means in the-opposite direction, only one of said two contact carrying members returns in the direction of its original position whereby the contacts carried by said second and third members are brought into engagement.

6. In combination, a switch normally resting in a predetermined circuit controlling position, means to move said switch back and forth with out changing its circuit controlling position, an electromagnet member and an armature member, one of said members being operated by said means to bring the same adjacent the other of said members, means to move said switch to another circuit controlling position when said members are held adjacent each other by reason of the energization of said electromagnet upon movement of said switch moving means to a position in which said members would otherwise be moved apart, and means to prevent further actuation of said switch moving means from changing the circuit controlling position of said switch.

- '7. In combination, a pair of resilient contact carrying members tending by reason of their own resilience to move to a first circuit controlling position, an element adapted to engage one of said contact carrying members and biased so as to hold said member out of said first controlling position with respect to said other contact carrying member, an armature secured to said element, an electromagnet adapted upon energization thereof to hold said armature when said members are positioned adjacent each other, reciprocable means operable upon movement in one direction to move said element so as to cause engagement of said armature and electromagnet while preventing movement of said contact carrying members to said firstv controlling position, said members being operable upon the armature being held by said electromagnet and upon movement of said reciprocable means in the other direction to move to said first controlling position.

8. In combination, a switch movable between first and second controlling positions and biased to a first position, selectively operable holding means ior holding an element associated with said switch in a position wherein said switch is biased to said second controlling position, actuating means for moving said switch, without moving the same to said second controlling position, to a position wherein said element is held by said holding means if operative, said biasing means being operative upon further movement of said actuating means to move said switch to said second controlling position, and means to prevent movement of said switch from said second circuit controlling position by said actuating means.

CARL q. KRONMILLER.

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