US3774130A

US3774130A - Limit apparatus

Info

Publication number: US3774130A
Application number: US00301302A
Authority: US
Inventors: A Teichert
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1972-10-27
Filing date: 1972-10-27
Publication date: 1973-11-20
Anticipated expiration: 1990-11-20

Abstract

Limit apparatus including a housing having switch means mounted thereon and connected with drive means which is operative in response to a predetermined parameter exceeding a selected magnitude to close the switch means. A cutoff device is coupled with the switch means and includes a lever arm carried pivotally from the housing and biased to a cutoff positon holding said switch means open but normally maintained in an inoperative position by means of electromagnetic means which selectively attracts a ferromagnetic keeper carried on such lever arm to maintain such lever arm pivoted against the bias of such biasing means. Limit control means is connected in circuit with the electromagnetic means and is responsive to a selected parameter to de-energize such electromagnetic means to release the keeper to enable the lever arm to rotate under the influence of the biasing means to thus open the switch means.

Description

United States Patent Teichert 1 5] Nov. 20, 1973 LIMIT APPARATUS Primary Examiner-Harold Broomc [75] Inventor: Allen L. Teichert, Placentia, Calif. Atwmey vem Schools) at [73] Assignee: Robertshaw Controls Company,

Richmond, Va. [57] ABSTRACT Limit apparatus including a housing having switch [22] 1972 means mounted thereon and connected with drive [21] Appl. No.: 301,302 means which is operative in response to a predetermined parameter exceeding a selected magnitude to close the switch means. A cutoff device is coupled [52] ;g; f with the switch means and includes a lever arm car- 51 I t Cl 24 ried pivotally from the housing and biased to a cutoff positon holding said switch means open but normally 1 o g "I I l7 f maintained in an inoperative position by means of 3 ll 1 3 f electromagnetic means which selectively attracts a fer- 3 l romagnetic keeper carried on such lever arm to maintain such lever arm pivoted against the bias of such bi- [56] References cued asing means. Limit control means is connected in cir- UNITED STATES PATENTS cuit with the electromagnetic means and is responsive 2,635,154 4/1953 Zuckerman 335/126 to a selected parameter to de-energize such electro- 2,658,123 11/1953 SlOeSer 126 magnetic means to release the keeper to enable the 3,109,906 11/1963 Abefldmth 335/l70 lever arm to rotate under the influence of the biasing 3,648,204 3/1972 Davies et al. 335/170 means to thus openthe Switch means 3,655,932 4/1972 Tabares et al. 200/5 C 10 Claims, 9 Drawing Figures 7 1 4 7 i I u I s4 if i 53 75 77 54 5/ E O 52 l w U Q l Q Q 4 3i v 1 O I i w s .5 59 w a LIMIT APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The limit apparatus of the present invention relates to a device for overriding a switch control means to selectively open such switch.

2. Description of the Prior Art Applicant is unaware of any prior art limit apparatuses which incorporate a pivotable lever arm biased to an override position engaging a switch means to open such switch means but normally held in an operative position by means of an electromagnet which is connected in circuit with limit control means and is operative in response to sensing a selected parameter to deenergize such magnet. I

The objects and advantages of the present invention will become apparent froma consideration of the following detailed description when taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 are transverse sectional views of a limit apparatus embodying the present invention and depicting such apparatus in different modes of operation;

FIGS. 4, and 6 are longitudinal sectional views taken along the lines 4-4, 5-5 and 6-6 of the respective FIGS. 1, 2 and 3; and

FIGS. 7, 8 and 9 are partial longitudinal sectional views taken along the respective lines 7-7, 8-8 and 9-9 of the respective FIGS. 1, 2 and 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT The limit apparatus of the present invention includes, generally, a housing 11 having a plurality of switches 13 mounted therein and opened by means of axially shiftable drive camshaft 15 coupled with a drive linkage 19 which incorporates a thermostatic control rod 21 that is selectively heated to effect shifting of such cam and closure of the respective switches. A cutoff cam bar 23 is disposed adjacent the drive camshaft 15 (FIG. 7) and has one end thereof coupled with one end of a lever arm 27 included in a cutoff device 25, such arm being biased counter-clockwise by means of a tension spring 29 which urges such lever arm to the cutoff position shown in FIG. 9. The opposite end of such lever arm 27 carries a ferromagnetic keeper 33 which is disposed adjacent an electromagnet 35 having a control switch 37 connected in circuit therewith. Consequently, when a predetermined parameter of a selected magnitude is sensed, the thermostatic rod control 21 will be heated to shift the drive camshaft 15 to the left to enable the switches 13 to assume their closed position shown in FIG. 2. However, sensing of a limit parameter will result in opening of the limit switch 37 thus de-energizing the electromagnet 35 to free the lever arm 27 for rotation counter-clockwise'to the cutoff position shown in FIG. 9 thus shifting the limit cam 23 axially to the left to assume the position shown in FIG. 3 thus opening the respective switches 13.

Referring to FIGS. 4 6, the switches 13 are formed by upstandng resilient electrically conductive blades 41 and 43 having respective electrical contacts 45 and 47 mounted intermediately thereon and have their bases 2 projecting through the housing 11 to form respective plug prongs 49 and 51.

Referring to FIGS. 1, 7 and 4, the drive camshaft I3 is in the form of a semi-cylindrical shaft disposed between the free extremities of the respective switch blades 41 and 43 and formed with a plurality of dwell cams 52 axially therealong and each formed with wedge shaped cam surfaces 53, the symmetry of which provides for equal and opposite movement of the respective free ends of the blades 41 and 43 as such camshaft 15 is shifted axially to the left from the figure shown in FIG. 1 to the figure shown in FIG. 2 to thus permit the free extremities ofsuch blades to move rapidly inwardly toward one another with equal and opposite speeds to thus bring the respective contacts 45 and 47 into contact with one another at rates of equal and opposite speeds. The cams 52 are separated by minor diameter necks 56 of a sufficiently small diameter to permit the blades 41 and 43 to bring the contacts 45 and 47 together when disposed between such blades. In the preferred embodiment, the switches 13 are in- Referring to FIGS. 1 3, the drive camshaft 15 is formed on its right hand end with a side driver notch 51 which has the free end of an upstanding drive link 53 included in the drive linkage 19 disposed therein,

the opposite end of such link being mounted from a longitudinal mounting bracket 54 by means of a pivot pin 55. A secondary link 57 is mounted from the end of the mounting bracket 54 opposite the drive link 53 by means ofa pivot pin 59 and is arranged generally coextensive with the drive link 53. The free end of the secondary link 57 is pivotally connected with the base of the drive link 53 by means ofa diagonal link 61. The upper extremity of the drive line 53 is urged to the left by means ofa tension spring connected between the free extremities of the

links

53 and 57. Leftward movement of the free extremity of the secondary drive link 57 is controlled by means of the thermostatic rod 21, such rod being anchored on one end to a flange 67 and the opposite end of such rod projecting through a bore in the link 57 and having a nut 71 screwed thereonto. The intermediate portion of the control rod 21 is wrapped with a high resistance heat motor 72 which may be connected in circuit with a control element such as a thermostat.

Referring to FIGS. 1, 2 and 7, the cutoff cam bar 23 is arranged over and projects coaxially with the drive camshaft 15, such camshaft being formed with individual cams 75 which are formed on one end with oppositely disposed and oppositely angled cam surfaces 77 for engagement with the respective switch blades 41 and 43 to urge the free extremities thereof apart. When the drive camshaft 15 is in its switch-close position shown in FIG. 2 and the cutoff cam bar 23 is in its inoperative position as shown in FIG. 2, the enlarged-indiameter drive and

cutoff cams

52 and 75 of the respective camshaft and

rod

15 and 23 are aligned with one another so the minor diameters of the respective camshafts are disposed between the respective blades 41 and 43 to permit the free extremities of such blades to. move inwardly toward one another and carry the contacts 45 and 47 into engagement with one another as shown in FIG. 5.

Referring to FIG. 7, the cutoff device 25 is coupled with the common ends of the respective drive and cutoff camshaft and

rod

15 and 23, the upper extremity of the lever arm 27 being bifurcated to form a first prong 81 received in a cutout 83 formed in the end of the drive camshaft l5 and abutting such shaft. The second prong 85 formed in, the upper extremity of such lever 27 is received in a downwardly opening slot 87 formed in a downturned flange 88 at the right hand end of the cutoff cam bar 23.

Referring to FIGS. 7 and 9, the lever arm 27 itself is carried in a housing aperture 89 which forms a fulcrum. Mounted adjacent the intermediate portion of such lever arm 27 is a reset switch, generally designated 91, such switch including a stationary contact 93 and a movable contact 95. Still referring to FIG. 7, an upstanding mounting bracket 107 is affixedto the housing 11 and has an electrical insulator 96 projecting therefrom to mount a pair of downwardly projecting electrically

conductive blades

97 and 99 which mount the

contacts

93 and 95 on the respective extremities thereof. The blade 99 is resilient and is formed to normally assume the bent position shown in FIG. 9 maintaining the movable contact 95 spaced from the stationary contact 93. The

blades

97 and 99 of the reset switch 91 are connected in series with the thermostatic control rod 21 by means ofleads 101 and 103, the purpose of such connection appearing hereinafter.

The electromagnet 35 is mounted from the mounting bracket 107 carried on the housing 11 and has its coil connected in series with a switch 37 formed by a thermostatic blade which is responsive to a predetermined temperature to open.

In operation, the limit apparatus of the present invention may conveniently be utilized in a control system for controlling a furnace to prevent overheating thereof. In such arrangements, the switches 13 may be connected in circuit with respective heating elements of a multiple heating elementfurnace, it being appreciated that the switch 13 shown at the far left in FIG. 1 may be connected with the blower of such furnace and that due to the staggered relationship of the cam elements 52 with respect to the contact mounting blades 41 and 43, the switch 13 will be the first switch closed as the drive camshaft 15 is shifted to the left thus assuring energization of such blower prior to the time any of the heating elements are energized to prevent overheating of such element before air is circulated thereover. Further, it will be appreciated that the cutoff cam bar 23 does not incorporate a cam 73 for interposition between the blades 41 and 43 of the switch 13 thus resulting in such switch remaining closed when the drive camshaft I5 is in its switch actuating position shown in FIGS. 2 and 3, even though such cam bar 23 has been shifted to its cutoff position shown in FIG. 3. This assures that the blower will continue to operate thus pre venting overheating of the furnace heating elements even after the circuits to such elements have been opened as a result of opening of the remaining switches 13.

The leads leading from the opposite end of the heat motor 72 may then be connected in circuit with a thermostat sensing the temperature of the room of which the temperature is to be controlled. The thermostatic limit switch 37 may then be placed in the plenum chamber of the furnace adjacent the heating elements, the overheating of which is to be prevented.

Thereafter, if the temperature of such room falls below the target temperature, the thermostat will actuate to close the circuit through the heat motor 72 thus energizing such motor to heat the thermostatic control rod 21 causing such rod to grow in length thus permitting the free extremity of the secondary link 57 to rotate to the left as viewed in FIGS. 1 3 under the influence of the biasing spring 65 acting through the drive linkage 19. Such shifting to the left of the free extremity of the secondary link 57 permits the free extremity of the primary link 53 to shift to the left thus shifting the drive camshaft 15 to the left resulting in the respective cams 52 being moved out of alignment with the respective switch blades 41 and 43 to permit such switch blades to draw inwardly toward one another on opposite sides of the necks 54 thus carrying the electrical contacts 45 and 47 into engagement with one another. It will be appreciated that the staggered relationship of the respective cams 52 with respect to the respective blades 41 and 43 causes the cams 52 on the left hand end of such camshaft 15 to first clear the respective blades 41 and 43 to thus close the left-most switches 13 first. The remaining switches 13 are then sequentially closed thus resulting in sequential energization of the control furnace heating elements thus preventing placing the entire furnace load instantaneously on the power source to thus avoid overloading of such power source.

If during heating of the room the furnace malfunctions resulting in overheating of the heating elements and raising the temperature of the limit switch 37 above a selected level, such limit switch will be over-- heated thus causing its thermostatic blade to warp to the position shown in FIG. 9 thus opening the circuit to the electromagnet 35 and discontinuing the magnetic attraction on the ferromagnetic keeper 33. Consequently, the upper extremity of the lever arm 27 will be drawn counter-clockwise under the influence of the biasing spring 29 to thus shift the cutoff camshaft 23 positively and rapidly to the left thus shifting the cutoff cam elements into alignment between the respective blades 41 and 43 of the respective switches 13 thus spreading the free extremities of such blades apart to the position shown in FIG. 6 and separating the contacts 45 and 47. It will be appreciated that the wedge shaped slope of the respective cutoff cam elements 55 provides for wedging of such elements between the blades 41 and 43 to thus force such blades apart and provide for the breaking of any relatively minor welding that may have taken place between the contacts 45 and 47.

Referring to FIG. 9, it will be appreciated that the counter-clockwise rotation of the lever arm 27 resulted in opening of the reset switch 91 thus de-energizing the heat motor 72 to permit cooling thereof resulting in shrinkage of the thermostatic rod 21 thus pivoting the free extremity of the primary lever arm 53 to the right and shifting the drive camshaft 15 to the right, causing the right hand end thereof to engage the downwardly extending flange 88 of the cutoff camshaft 23 thus shifting such cutoff camshaft also to the right, it being appreciated that the shrinking of the thermostatic rod 21 (FIG. 1) provides sufficient force to overcome the bias of the cutoff spring 29 and biasing spring 65. Thus, the keeper 33 will be reseated on the relay coil 35 and upon cooling of the limit switch 37, such coil will again be energized. It will be appreciated that the reset switch I 91 is not critical to the present invention and may be eliminated thus resulting in the cutoff device failing to reset itself and alerting responsible personnel that there has been a malfunction.

However, assuming the cutoff device 25 has been reset, if the thermostat continues to call for heat, the heat motor 72 will reheat the thermostatic rod 21 to thus shift the camshaft again to the left thus closing the respective switches 13 and re-energizing the furnace heating elements. If the malfunction has been corrected, the limit switch 37 will not be heated above the normal temperature thus resulting in such switch remaining closed and avoiding reactuation of the cutoff device 25.

From the foregoing, it will be apparent that the limit apparatus of the present invention provides an eco nomical and highly effective control device for controlling an electrical switch and for overriding the control device to provide for positive opening thereof upon sensing of a cutoff signal.

What is claimed is:

1. Limit apparatus comprising:

a housing;

electrical switch means mounted on said housing;

drive means coupled with said switch means;

control means connected with said drive means and operative in response to a predetermined parameter exceeding a selected magnitude to actuate said drive means to open said switch means;

a cutoff device including a lever arm coupled with said switch means and carried pivotally from said housing, said lever being shiftable from an inoperative position to a cutoff position to open said switch means, cutoff biasing means urging said lever to its cutoff position, ferromagnetic keeper means mounted on said lever arm, electromagnetic means disposed adjacent said keeper means and operative upon energization thereof to draw said lever arm against the force of said biasing means to said cutoff position; and

limit control means connected with said electromagnetic means and responsive to a selected parameter to de-energize said electromagnetic means whereby sensing of said predetermined parameter of said selected magnitude by said drive means will actuate said drive means to open said switch means and sensing of said selected parameter by said limit control means will de-energize said electromagnetic means to cause said biasing means to shift said lever to its cutoff position.

2. Limit apparatus as set forth in claim 1 wherein:

said drive means includes drive cam means coupled with said switch means.

3. Limit apparatus as set forth in claim 1 wherein:

said cutoff device includes cutoff cam means engageable with said switch means.

4. Limit apparatus as set forth in claim 1 wherein:

said switch means includes a pair of substantially identical resilient blades mounted on their respective one ends from said housing and contacts mounted on the free ends of said blades.

5. Limit apparatus as set forth in claim 1 wherein:

said switch means includes a plurality of controlled switches;

said drive means includes drive camshaft means formed with individual cams engageable with said respective controlled switches and shiftable axially in one direction to a switch closed position to disengage said cams from said respective switches for closing thereof and shiftable in the opposite direction to a switch open position causing said switches to open;

said cutoff device includes cutoff bar means coextensive with said drive camshaft means and coupled with said lever arm, said cam bar means being formed with individual cutoff cams engageable with said switches, said cam bar means being ar ranged to be shifted axially in said one direction when said lever is shifted to said cutoff position to engage said cutoff cams with said respective switches to open said switches.

6. Limit apparatus as set forth in claim 5 wherein:

said cutoff bar means includes flange means formed with an abutment surface projecting into the path of said drive camshaft means and engageable thereby as said drive camshaft means is shifted from its switch closed position to its switch open position to carry said cutoff bar means to its inoperative position; and

said control means includes drive biasing means coupled with said drive camshaft means and having sufficient biasing force to overcome said cutoff biasing means to enable said drive camshaft means to engage said cutoff bar means and return said bar means to its inoperative position.

7. Limit apparatus as set forth in claim 5 wherein:

said cutoff means includes reset switch means connected in circuit with said control means and operative upon actuation of said cutoff device to render said control means inoperative.

8. Limit apparatus as set forth in claim 5 wherein:

said individual drive cams are arranged in staggered relationship with respect to said switches to cause said controlled switches to be closed sequentially when said control means is actuated.

9. Limit apparatus as set forth in claim 8 wherein:

said respective cutoff cams are spaced apart a distance corresponding with the spacing of said controlled switches to open said controlled switches simultaneously upon actuation of said cutoff device.

10. Limit apparatus as set forth in claim 9 wherein:

said drive camshaft means and cutoff bar means are linear and project parallel to one another.

Claims

1. Limit apparatus comprising: a housing; electrical switch means mounted on said housing; drive means coupled with said switch means; control means connected with said drive means and operative in response to a predetermined parameter exceeding a selected magnitude to actuate said drive means to open said switch means; a cutoff device including a lever arm coupled with said switch means and carried pivotally from said housing, said lever being shiftable from an inoperative position to a cutoff position to open said switch means, cutoff biasing means urging said lever to its cutoff position, ferromagnetic keeper means mounted on said lever arm, electromagnetic means disposed adjacent said keeper means and operative upon energization thereof to draw said lever arm against the force of said biasing means to said cutoff position; and limit control means connected with said electromagnetic means and responsive to a selected parameter to de-energize said electromagnetic means whereby sensing of said predetermined parameter of said selected magnitude by said drive means will actuate said drive means to open said switch means and sensing of said selected parameter by said limit control means will deenergize said electromagnetic means to cause said biasing means to shift said lever to its cutoff position.

2. Limit apparatus as set forth in claim 1 wherein: said drive means includes drive cam means coupled with said switch means.

3. Limit apparatus as set forth in claim 1 wherein: said cutoff device includes cutoff cam means engageable with said switch means.

4. Limit apparatus as set forth in claim 1 wherein: said switch means includes a pair of substantially identical resilient blades mounted on their respective one ends from said housing and contacts mounted on the free ends of said blades.

5. Limit apparatus as set forth in claim 1 wherein: said switch means includes a plurality of controlled switches; said drive means includes drive camshaft means formed with individual cams engageable with said respective controlled switches and shiftable axially in one direction to a switch closed position to disengage said cams from said respective switches for closing thereof and shiftable in the opposite direction to a switch open position causing said switches to open; said cutoff device includes cutoff bar means coextensive with said drive camshaft means and coupled with said lever arm, said cam bar means being formed with individual cutoff cams engageable with said switches, said cam bar means being arranged to be shifted axially in said one direction when said lever is shifted to said cutoff position to engage said cutoff cams with said respective switches to open said switches.

6. Limit apparatus as set forth in claim 5 wherein: said cutoff bar means includes flange means formed with an abutment surface projecting into the path of said drive camshaft means and engageable thereby as said drive camshaft means is shifted from its switch closed position to its switch open position to carry said cutoff bar means to its inoperative position; and said control means includes drive biasing means coupled with said drive camshaft means and having sufficient biasing force to overcome said cutoff biasing means to enable said drive camshaft means to engage said cutoff bar means and return said bar means to its inoperative position.

7. Limit apparatus as set forth in claim 5 wherein: said cutoff means includes reset switch means connected in circuit with said control means and operative upon actuation of said cutoff device to render said control means inoperative.

8. Limit apparatus as set forth in claim 5 wherein: said individual drive cams are arranged in staggered relationship with respect to said switches to cause said controlled switches to be closed sequentially when said control means is actuated.

9. Limit apparatus as set forth in claim 8 wherein: said respective cutoff cams are spaced apart a distance corresponding with the spacing of said controlled switches to open said controlled switches simultaneously upon actuation of said cutoff device.

10. Limit apparatus as set forth in claim 9 wherein: said drive camshaft means and cutoff bar means are linear and project parallel to one another.