US 3801944 A
A temperature-compensated thermal-activated time delay switch comprising a base plate on which is mounted a current conducting bimetallic blade, a second current carrying blade supported by the base plate in spaced relation to the bimetallic blade, a bimetallic actuator strip carrying an electrical resistance heating element supported above the second blade and adapted to actuate said second blade through the medium of a spring member; whereby the two blades are normally in current conductive contact, but by reason of heat from the resistance element causing flexure of the bimetallic strip, they may be caused to separate with irreversible snap action, and reset means for bringing the blades again into contacting condition after the strip has cooled; additional means are provided for adjusting the position of the bimetallic strip in its unheated condition and further means are provided for adjusting the position of the bimetallic blade, whereby the time delay period for snap action of the switch is controlled within accurate limits in all ranges of ambient operational temperatures.
Claims available in
Description (OCR text may contain errors)
United States Patent [1 1 Brown TEMPERATURE-COMPENSATED,
THERMAL-ACTIVATED TIME DELAY SWITCH-  Inventor: Richard J. Brown, Mentor, Ohio  Assignee: Tri-Men Manufacturing, Inc.,
Painesville, Ohio 22 Filed: Sept. 28, 1972 211 Appl. No.: 292,971
 US. Cl 337/103, 337/107, 337/367, 337/370  Field of Search H0lh/6l/02; 337/100, 103, 337/102, 107, 367, 341, 370, 88
PrimafyExaminer-Bernard A. Gilheany Assistant Examiner-F. E. Bell Attorney, Agent, or Fi rm-Ge orge B. Kasik Apr. 2, 1974  ABSTRACT A temperature-compensated thermal-activated time delay switch comprising a base plate on which is mounted a current conducting bimetallic blade, a second current carrying blade supported by the base plate in spaced relation to the bimetallic blade, a bimetallic actuator strip carrying an electrical resistance heating element supported above the second blade and adapted to actuate said second blade through the medium of a spring member; whereby the two blades are normally in current conductive contact, but by reason of heat from the resistance element causing flexure of the bimetallic strip, they may be caused to separate with irreversible snap action, and reset means for bringing the blades again into contacting condition after the strip has cooled; additional means are provided for adjusting the position of the bimetallic strip in its unheated condition and further means are provided for adjusting the position of the bimetallic blade, whereby the time delay period for snap action of the switch is controlled within accurate limits in all ranges of ambient operational temperatures.
' 10 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION In the operation of heating equipment for vehicles, as for example, space heating equipment for mobile homes, it is necessary to provide safety controls to assure precise and reliable operation of the heating apparatus. Involved in such controls are time-delay devices that monitor the operating sequences of the apparatus and provide for safe shut down in the event of failure of the apparatus. Such failure may include non-ignition (due to malfunction of the control circuit or to lack of fuel), blower motor failure or insufficient voltage at the power (battery) supply. The time delay device of this application is one which is designed to open a circuit to a fail safe condition, after a precise time period during the start up operation or later in the running illustrates, in phantom, the means for re-setting the switch and also the throw of the lower'temperature compensated blade of the switch.
FIG. 4 is a schematic view of the switch as it may be employed in a circuit involving a control for a heater, wherein the load may comprise blower motor, ignition system and other switching apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENT Switch S comprises a stack of parts sandwiched between a base plate 1 and a cover plate.60 and held together by pins 70 and 71; the working parts of this switch are separated by a series of insulating spacers II and shims 30, as will be noted in the detailed description which follows. Referring to FIGS. 1 and 2, base plate 1 supports a first switch blade of generally operation, if defects in the system noted above should I occur. It is an object of the invention to provide a device that will operate in the desired manner within a very precise time period, regardless of the ambient temperature conditions under which it operates.
It is a further object of the invention to provide a safety switch which requires very little current for its operation and thereby reduces to a minimum the current draw on the power source (usually a wet storage battery).
It is a further object of the invention to provide a switch which is relatively unaffected by substantial variation in the voltage condition of the power source.
A further and important object of the invention is to provide a switch of this sort that moves to a locked out (i.e., open circuit) condition, requiring manual reset before it can be cycled again; this feature eliminates the possibility of recycling when such action might lead to a dangerous condition in the apparatus being controlled.
In the design of vehicular equipment, space requirements are a continual consideration and every effort is made to reduce the size of equipment used therewith to a minimum and at the same'time assure proper and safeperformance. To this end the switch of this invention is designed for compactness and reliability and to be operable under adverse conditions of vibration, wide ambient temperature fluctuations and other rugged usage conditions.
A further object is to provide a time delay switch in which the time interval for the switching action may be varied and set within close limits.
A still further object is to provide a switch that will operate with accuracy regardless of the ambient temperature in which it is located and that is not affected by changes in ambient temperature.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, wherein like parts are designated by like reference characters throughout the several views:
FIG. 1 is an exploded view (in two parts) of the subject switch, showing the specific form of each element and its relation to' other elements,
FIG. 2 is a longitudinal view, partially in section, showing the switch in its open or locked out condition.
FIG. 3 is a similar fragmentary view of the switch, illustrating the normally closed condition; this view also rectangular shape; this first blade is fabricated from current conductive bimetallic strip and is supported at one end with its other endfree to flex in response to temperature changes. An electrical contact point 12 is carried by this balde at its flexing end. An insulator block 11 spaces the blade 10, from the plate 1. In the embodiment shown, a terminal leaf 20, having an ear 20a with a electrical connection point 20b is interposed in the stack abutting the lower face of blade 10 and thus forms a means for conducting electrical current to the blade 10 from an outside source. Whereas, this construction is preferred for the present embodiment, it will be noted that the blade 10 could be constructed with a projecting tang to which electrical connection could be had for the same purpose; this same comment is applicable to the structure of the second blade 15 and its associated terminal leaf 23, described infra,
One end of a second flexible current-carrying blade 15 is held in fixed position above the blade 10 and spaced therefrom by means of an insulator block 11a, similar to block 11. This blade is of resilient currentcarrying metal and has a central cutout portion 16. The free end of blade 15 carries a switch contact 18, which is positioned to meet electrical contact 12, carried by blade 10, as will appear. Electrical connection to blade 15, is had through terminal 23, bearing ear 230, that is mounted in the pack between insulator block and adjacent said blade. A further terminal leaf 22, having a turned down tab 22a, is mounted between insulator 11a and blade 10, but separated therefrom, by an insulating shim 30, the purpose of this terminal leaf will appear below.
A T-shaped bimetallic actuator 40, is mounted above the blade 15, with its stem portion 41 extending above the opening 16, in the blade. This actuator may be fabricated from bimetal known as Chase 2400." The end of stem 41, terminates in a tab portion 42. A similar tab 17, projects inwardly from the front edge of the cutout 16 and these two tabs enter slots 47 and 48, respectively, in the arms of a U-shaped trigger spring 49 (preferably fabricated of thin, resilient berylium base alloy). The actuator 40 is wound along its stem with electrical resistance wire 43; electrical-insulating paper 44 separates the winding from the metal stem 41, but allows heat from the winding to reach the stem. The ends 45 and 46 of the winding are connected, respectively, to terminal strips 22 and 24 at 22a and 24a, as shown best in FIG. 2. When electric current is passed through winding 43, heat is generated and bimetal actuator 40 is caused to deflect downward through the opening 16 reset spring 50. This reset spring is generally rectangular in form and similar in dimension to the blade 15, and carries at the free end an insulated button 51, positioned to engage the contact button 18, at the end of blade' 15. A reset pin 55 is supported in a guide 58, carried by cover plate 60, which forms the upper end of the switch assembly. An insulating shim 30b, spaces cover 60, from reset spring 50 and allows clearance for flexure of the latter. Depression of pin 55 causes the reset spring 50 to move down against blade 15, as best seen in dotted outline in FIG. 3; upon release of pin 55, reset spring 50 returns to normal (horizontal) position.
The entire assembly is clamped between base plate I and cover member 60, by means of two like pins 70 rent-carrying parts from the rest of the assembly and these pins are swaged over at their ends 76 (FIG. 2) to tightly clamp the assembly together.
Base plate 1, also has a threaded opening 2, into which an adjusting screw 3 is turned that cooperates with insulating pad 4, carried by switch blade 10. This blade is designed to move downward with increasing temperature (as will appear from the following description) and the screw 3 is employed to set the at rest) position of the blade 10. In like manner, the upper limit of flexure of the bimetallic actuator 40 is controlled by a stop means in the form of a positioning screw 61,
' threaded through an opening 62, in cover plate 60.
This screw extends downward and its end can be brought to bear against the stem 41 at the free end thereof. Since the stem 41 moves downward with increase in temperature (including ambient) the said screw 61 can be set to limit the upward limit of travel of stem 41, in its normal unheated condition. An insulating pad 63, on the tip of screw 61, prevents passage of current into the cover plate 60.
As referred to above, the subject switch was designed to accommodate the control of a burner used to furnish heat to vehicles, although it has other important applications, and it will be described herein, in connection with such a control. Referring to FIG. 4, the switch is shown in schematic form as used in a control circuit. A source of power 80, which may be a vehicular storage battery, has one lead 81, connected to temperaturecompensated switch blade 10 (through terminal b) and also, to the input side of an electrical control system 82. Conductor 83 leads fromcontrol 82 to one side 45, of the bimetal actuator winding 43 through terminal leaf 22; the other side 46 of this winding is electrically connected to the other side of the power source 80 through terminal 24 and conductor 87. The other side of the switch, namely blade 15, is electrically con- 4 control 82 and that the energization of the load 85, is principally under the control of the switch S and depends primarily on the open (FIG. 2) or closed (FIG. 3) condition of said switch. In the embodiment nected to the load 85, via conductor 84, extending shown, switch S is designed to monitor the early (start up) period of operation of the system so that, if failure of any of certain components of the system occurs, in a preselected time period, switch S is designed to open and disconnect the load 85, from the source of energization 80, to thereby prevent the system from reaching a possibly dangerous condition. If there is a malfunction in the burner system and switch S has performed its protective function, it is desirable that it lock out, i.e., remain in a stable, open circuit condition to prevent recycling and/or continual consumption of power from the source 80. Preferably, and in the present embodiment, the opening of switch S, also, de-energizes the actuator winding 43 through the operation of control 82, so that no power is thereafter consumed by the switch. 7
DISCUSSION OF PRINCIPLE AND DETAILS OF OPERATION In the application herein described, the switch is employed to deliver current to certain parts of the load for a closely determined period of time (for example, the time required to allow a burner to light and attain the run condition) and, if there is failure, in the burner or other parts, to open the circuit to the load and remain in open-circuit condition (known as lockout) until manually reset at which time, the operator manually, resetting the switch will presumably make corrections in the load that caused lock-out. Thus the switch S is nonnally in closed condition as illustrated in FIG. 3, and moves to open circuit, or lock-out condition as illustrated in FIG. 2 under certain conditions. In the system for which the subject switch was designed, the time from first energization of the switch to lock-out is about 35 seconds; as will be shown, this delay period may be regulated within limits by adjustment screw 3.
The detailed operation of the switch S can be understood best from a study of FIGS. 2 and 3. The principle of operation is to move the end of the bimetallic actuator acutator 41 through a limited arc, which causes trigger spring 49 to throw the upper switch blade 15 from its normal contact-making position with blade 10 (as shown in FIG. 3), to an open circuit position (as shown in FIG. 2) out of contact with blade 10 and into an upper position, where said blade 15 is held until manually reset. Heat generated by the passage of electrical current through winding 43 causes the bimetal stem 41 to warp downwardly, passing into and through the opening 16 in blade 15, until tab 42 squeezes past tang 17 and spring 49 snaps blade 15 upward and out of contact with blade 10. This switching action interrupts the current flow through winding 43 (by virtue of the action of control 82, as explained above) and the actuator 40 cools and tends to return to its normal condition. However, the trigger'spring 49 holds blade 15 in its open circuit position and prevents actuator stem 41 from returning to its at rest starting position. In other words, blade 15 is held irreversibly in open circuit condition, 'as shown in FIG. 3. Whereas, the nominal move ment of actuator tip 41 (due to heating warpage of the stem) may be only l/l6 inch, action of spring 49 increases this throw and assures lock-out condition. In
resetting the switch, pin 55 is depressed, spring leaf S0 bears against blade 15 and forces it downward toward blade this squeezes trigger spring 49 and allows blade to slip past stem 41 (which is now cooling or has cooled and moved upward to its starting position). Thereafter, spring 49 acts to hold blade 15 firmly in contact with blade 10 to assure a low resistance path for the succeeding flow of current through the switch blades 10 and 15, across the contacts 12 and 18 thereof.
Switch blade 10 is fabricated from bimetal to compensate for changes in ambient and operating temperatures. Thus at low ambient, this blade tends to warp upwardly toward the blade 15 and assists the trigger action (closes the distance stem 40. has to travel). Bearing in mind that at low temperatures the heating effect of winding 43 is less (greater heat loss increases the time delay action) this upward warping of blade 10 is in the proper direction and tends to keep the time delay period constant. Conversely, however, at higher operating temperatures (which may develop when the control is located in a region of tight enclosure, or when it is near the heating apparatus, etc.) it is desirable to have this blade flex downwardly to compensate for the more rapid heating of the bimetal 40, in the Wanner environs.
Although a rise in temperature of the ambient has a similar effect on bimetal 40, it is not so pronounced,
because the length of blade 10 is greater than that of bimetal 40, so that the effect of higher ambient temperature is to increase the distance between the tip 41 and the tang 17. This results in a tendency toward the lengthening of the time delay period and overcomes the shortening effect of faster heating (in the higher ambient) of the bimetal 40. The net result is a constant time period for the trip action, as desired.
The screw adjustment means screw 3 is used to set the length of the time delay period. Closing the distance between blade 10 and the bimetal actuator 40, by turning in screw 3 and raising blade 10, reduces the time delay period. As stated above, this period may be adjusted in the present embodiment from 20 seconds to 120 seconds. This adjustment is also used to compensate for differences in the physical characteristics of the bimetal material from which blade 10 is fabricated.
Normally, bimetal actuator 40 would lie flat at a normal ambient temperature of 70 F. (it is not preformed prior to assembly into the switch), but due to the action of trigger spring 49, it is caused to bend upwardly, as shown in FIG. 3, when the switch blade 15 has been reset and is in its downward closed position. The amount of this upward flexure is determined by the amount of spring (bending) action in the spring 49. Furthermore, as the ambient temperature decreases, there is a tendency for bimetal actuator 40 to curl upwardly and away from blade 15. Both of these added displacements have to be overcome before the trigger action takes place and, therefore, affect the time delay period of the switch. To compensate for this effect, the invention provides for adjustable means to limit the upward travel of the actuator 41. This is in the form of adjustable screw 61 that can be set to keep the throw of the actuator 41 at a constant value by positioning the upper point of travel of the stem end of said actuator. Thus when the screw 61 is adjusted properly, the heating action of winding 43 will move the end of bimetal 41 through the same are distance regardless of ambient temperature and the time delay period is accustal tiqn.tema gt rq the g; m y reach F rately controlled. In other words, this adjustment can be considered a standardizing setting.
As referred to above, the subject switch S may be employed in environments that have widely different tem peratures. This may be due to the climatic temperature differences of geographical locations (arctic vs. temperate zone, herein called the ambient range) or to the variations in ambient temperature at a given location of the equipment (herein described as the ambient limits of temperature), over which it must operate at that given location. For example, the switch S may be employed in a northern installation where the ambient temperature is 10 F but due to the nature of the in- '9 in this instance, the switch must be adjustable t o F. ambient and operate over a F. temperature rise. By proper and coordinated adjustment of the screw means 3 and 61, switch S can be adapted for use in any of the above environments and the time delay period set as desired. Furthermore, such adjustment means are capable of correcting for variations in the operating charecteristics of the bimetals employed and variables encountered in the physical characteristics of the trigger spring 49. 1t will be seen that the subject switch is adaptable to fine line operation within the expected limits of temperature over a wide ambient range.
The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
1. A switch structure comprising a base plate and a cover plate between which a first and a second rectangular shaped switch blade are clamped at their one end in spaced apart relation, having their free ends in normally contact-making condition to provide a principal current conducting circuit through the first blade across the contact point and thence through the second blade, a relatively low mass bimetallic actuator strip shorter than either blade and having one end supported proximate to and above the second blade, electrical means, having a source of energization, carried by the actuator strip to produce heat at said strip to cause the unsupported end thereof to flex, spring means for coupling the unsupported end of the strip with the corresponding end of the second switch blade, whereby limited flexure of the bimetallic strip causes the second blade to move irreversibly out of contact with the first blade, and means electrically independent of the principal current conducting circuit for manually overriding the spring means to allow the second blade to'return to a position in contact with the first blade, when the bimetallic strip has been allowed to come to substantially ambient temperature.
2. A switch structure as described in claim 1, wherein said first blade is a bimetallic strip responsive to change in ambient temperature.
3. A switch structure as described in claim 2, wherein said second blade has a central cutout portion into the area of which the unsupported end of the actuator strip is free to move with respect to the said blade.
4. A switch structure as described in claim 2, including adjustment means carried by the base plate for positioning the free end of the first blade.
5. The switch structure described in claim 4 wherein the adjusting means is in the form of a screw threaded said electrical heating means comprises resistance wire wound around the strip in heat conducting relation thereto.
9. A switch structure as described in claim 1, wherein said over-ride means includes a tongue mounted above and spaced from the second blade that cooperates with a manually depressible pin mounted on the cover plate and by which said tongue can be flexed downwardly against the said blade to over-ride the spring action and bring said second blade into contact with the first blade. 7
10. A switch structure as described in claim 3, wherein electrical terminal means are provided at the fixed ends of the first and second blades as part of the principal circuit and like terminal means are provided for the ends of the winding of resistance wire.