US3801944A - Temperature-compensated, thermal-activated time delay switch - Google Patents

Temperature-compensated, thermal-activated time delay switch Download PDF

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Publication number
US3801944A
US3801944A US00292971A US3801944DA US3801944A US 3801944 A US3801944 A US 3801944A US 00292971 A US00292971 A US 00292971A US 3801944D A US3801944D A US 3801944DA US 3801944 A US3801944 A US 3801944A
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Prior art keywords
blade
strip
switch
bimetallic
switch structure
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Expired - Lifetime
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US00292971A
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English (en)
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R Brown
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TRI MEN Manufacturing Inc
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TRI MEN Manufacturing Inc
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H61/00—Electrothermal relays
    • H01H61/02—Electrothermal relays wherein the thermally-sensitive member is heated indirectly, e.g. resistively, inductively

Definitions

  • 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 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
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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,
  • 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.
  • 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.
  • 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.
  • the upper limit of flexure of the bimetallic actuator 40 is controlled by a stop means in the form of a positioning screw 61,
  • 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.
  • 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.
  • 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.
  • 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.
  • switch S 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.
  • 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
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the invention provides for adjustable means to limit the upward travel of the actuator 41.
  • adjustable screw 61 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.
  • 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.
  • this adjustment can be considered a standardizing setting.
  • 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.
  • 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.
  • switch S can be adapted for use in any of the above environments and the time delay period set as desired.
  • 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.
  • 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.
  • 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.

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  • Thermally Actuated Switches (AREA)
US00292971A 1972-09-28 1972-09-28 Temperature-compensated, thermal-activated time delay switch Expired - Lifetime US3801944A (en)

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US29297172A 1972-09-28 1972-09-28

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US (1) US3801944A (de)
JP (1) JPS4992565A (de)
CA (1) CA977806A (de)
DE (1) DE2348954A1 (de)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4495481A (en) * 1982-06-30 1985-01-22 Trigometer, Inc. Thermostat with bimetal compensating element
US6018286A (en) * 1998-11-20 2000-01-25 Therm-O-Disc, Incorporated Thermal switch
US6069551A (en) * 1997-05-02 2000-05-30 Therm-O-Disc, Incorporated Thermal switch assembly
US6140903A (en) * 1997-11-24 2000-10-31 Therm-O-Disc, Incorporated Thermal switch
US6191679B1 (en) 1997-05-02 2001-02-20 Thermo-O-Disc, Incorporated Thermal switch assembly
US6239686B1 (en) 1999-08-06 2001-05-29 Therm-O-Disc, Incorporated Temperature responsive switch with shape memory actuator
US6342826B1 (en) 1999-08-11 2002-01-29 Therm-O-Disc, Incorporated Pressure and temperature responsive switch assembly
US20060273876A1 (en) * 2005-06-02 2006-12-07 Pachla Timothy E Over-temperature protection devices, applications and circuits

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
HU184008B (en) * 1982-07-29 1984-06-28 Huetoegepgyar Bimetal switch particularly for protecting compressor motors of refrigerators

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2237705A (en) * 1938-06-21 1941-04-08 Everard F Kohl Snap-acting device
US3358095A (en) * 1966-04-04 1967-12-12 Norwalk Thermostat Company Reset mechanism for a stack switch which avoids closed circuit condition when a tripping condition prevails
US3533039A (en) * 1969-04-14 1970-10-06 Hold Heet Products Corp Thermostatic switch and safety circuit therefor

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2237705A (en) * 1938-06-21 1941-04-08 Everard F Kohl Snap-acting device
US3358095A (en) * 1966-04-04 1967-12-12 Norwalk Thermostat Company Reset mechanism for a stack switch which avoids closed circuit condition when a tripping condition prevails
US3533039A (en) * 1969-04-14 1970-10-06 Hold Heet Products Corp Thermostatic switch and safety circuit therefor

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4495481A (en) * 1982-06-30 1985-01-22 Trigometer, Inc. Thermostat with bimetal compensating element
US6069551A (en) * 1997-05-02 2000-05-30 Therm-O-Disc, Incorporated Thermal switch assembly
US6191679B1 (en) 1997-05-02 2001-02-20 Thermo-O-Disc, Incorporated Thermal switch assembly
US6294977B1 (en) 1997-05-02 2001-09-25 Therm-O-Disc, Incorporated Thermal switch assembly
US6140903A (en) * 1997-11-24 2000-10-31 Therm-O-Disc, Incorporated Thermal switch
US6018286A (en) * 1998-11-20 2000-01-25 Therm-O-Disc, Incorporated Thermal switch
US6078244A (en) * 1998-11-20 2000-06-20 Therm-O-Disc, Incorporated Thermal switch
US6239686B1 (en) 1999-08-06 2001-05-29 Therm-O-Disc, Incorporated Temperature responsive switch with shape memory actuator
US6342826B1 (en) 1999-08-11 2002-01-29 Therm-O-Disc, Incorporated Pressure and temperature responsive switch assembly
US20060273876A1 (en) * 2005-06-02 2006-12-07 Pachla Timothy E Over-temperature protection devices, applications and circuits

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Publication number Publication date
CA977806A (en) 1975-11-11
JPS4992565A (de) 1974-09-04
DE2348954A1 (de) 1974-04-11

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