US2446029A - Thermal time-delay switch - Google Patents

Description

July 27, 1948- v. N. TRAMoN-rlNl 2,446,029

THERMAL TIME DELAY SWITCH Filed sept. 14, 194ev O-E @7L-d' 70 i l az] 50 3 7g] y Y w/ 54/ y;

Patented July 27, 1948 UNITED STATES PATENT OFFICE THERMAL TIME-DELAY SWITCH Application September 14, 1946, Serial No. 697,128 1 claim. (cl'. 175-320) The present invention relates to time delay switches and more particularly is concerned with a time delay switch of the type adapted to be used in an electric safety circuit such that after a given time interval the switch operates to perform some useful function. Although the switch of the present invention has other uses, primarily it is intended as a. safety device to shut off the flow of fuel to a vehicle heater of the combustion type in the event that the heater fails to function properly within a predeterminedI time interval after being turned on.

It is common practice to provide vehicles with liquid fuel consuming heaters, the fuel usually being gasoline, of a type such that the fuel to the heater is turned on or off remotely through the agency of a magnetic valve. Such a heater is shown in the copending application of George W. Allen and Vernon N. Tramontini for Heaters filed June 14, 1946, Serial No. 676,776. The particular heater shown in this copending application is provided with a magnetic valve which permits fuel to flow through the heater when the magnetic valve is energized and interrupts the flow of fuel whenever the valve is de-energized. Under some conditions the flow of fuel to the heater even if the heater is not operating properly is not particularly objectionable inasmuch as the quantity of fuel which may collect in the heater and thereafter flow from the exhaust pipe is not very great. Under other conditions, however, it is quite desirable to provide an automatic device which will shut off the fiow of fuel to the heater in the event that the heater does not start within a matter of two or three minutes after the heater has been turned on.

In the past, time delay switches have been proposed for heater control purposes. Such switches usually depend upon the rate of heating of a bimetal strip by an electric resistance element to determine the interval from the time the heater is turned on until the fuel supply is automatically turned off in the event that the heater does not start meanwhile. The difficulty with such schemes when applied to automobile or other vehicle heaters is that the voltage atV the heater may vary all the way from approximately four volts to over eight volts and therefore the rate of heating of the thermosensitive element of such time delay switches will not be even approximately constant under different voltage conditions. For instance, a high voltage source will cause the thermosensitive element to heat up quickly and to turn oif the heater within a comparatively short time interval whereas low voltages will require a longer time for operation and under some conditions the switch may never operate at all because the heat loss from the thermosensitive element may balance the heat gain from the electric resistance heater before the thermosensitive element has deected enough to operate the switch. It is, therefore, one of the objects of the present invention to provide a novel time delay switch of the electrically heated bimetal type which will have a substantially constant time of operation even though the voltage supplied thereto may vary throughout a wide range.

Another object is to provide an improved voltage compensated electrically operated time delay switch which can be manufactured at low cost.

Still another object is to provide an improved vehicle heater electrical circuit which will interrupt the flow of fuel to the heater in the event that the heater does not start within a short period, even though the voltage at the heater may fluctuate considerably.

Yet another object is to provide a device as called for above which may be manufactured as two separate elements which may be located remotely with respect to each other, the two elements simply being connected by electrical wiring.

Other objects and advantages will become apparent from the following description of4 a preferred embodiment of my invention which is illustrated in the accompanying drawings.

In the drawings: f

Fig. 1 is a somewhat diagrammatic top view of a portion of my device;

Fig. 2 is a side view thereof; and

Fig. 3 is an electrical circuit diagram showing the complete device including an electric circuit suitable for the use of the device in a vehicle heater installation.

A heater suitable for use with the device of the present invention is described in the previously referred to copending application. For the purpose of understanding the present invention it is suflicient to consider that such a heater is provided with an electrical igniter of the hot wire type, indicated in Fig. 3 by the numeral I0, which is energized at the time of starting of the heater. This igniter quickly heats to ignition temperature and normally starts combustion within the heater in a matter of ten to twenty seconds, although under some conditions ignition may be delayed for a period of an additional half minute or so, particularly if the ambient temperature is low or the voltage is low so that considerable time is required to bring the igniter to operating temperature.

A magnetic valve, indicated by the numeral I2, is located in the fuel line to the heater and is normally in closed position. When this valve is energized electrically, it opens and permits fuel to flow until de-energized.

Thus, the ow of fuel to the heater can be controlled by energizing or cle-energizing the magnetic valve I2. The igniter I8 is energized by way of a relay I4 under the control of an igniter switch I6. The switch I6 is normally closed whenever the heater is cold so that as soon as the master switch I8 is closed the coil 20 of lthe relay I4 will be energized, thereby closing relay I4 and energizing the igniter I8. If the heater starts .promptly as it should, the increase in temperature of the igniter switch I6 which is norl.

mally located so as to be sensitive either to the temperature of the air ow from the heater or to the temperature of some portion of the heater, will cause this switch to interrupt the circuit to the coil 28 of the relay, thereby permitting the relay to -drop open and deenergize the igniter I8.

The switch of the present invention operates in conjunction with the igniter circuit and functions to interrupt the supply of fuel to the heater in the event that the igniter circuit remains energized after a period of, say, three minutes. Referring to Fig. 3 of the drawings, it will be seen that the switch of the present invention is comprised of two main elements. That indicated generally by the numeral 22 may be considered as an impulse sending device while the portlonindicated generally by the numeral 24 may properly be considered as the unit having direct control over the magnetic valve I2. The rst of these elements. that is, the unit 22, is comprised of a bimetal blade 26 anchored at one end while the opposite end is provided with a contact 28 which operats in conjunction with a second contact 38 which may be considered as rigidlyor adjustably mounted with respect to the contact 28. In other words, under normal conditions, the contact 38 does not move excepting for the purpose of adjusting the device. An electric resistance heating element 32 is associated with the bimetal blade 26 so that whenever the element 32 is energized the temperature of the blade 26 will be elevated above ambient.

As shown in Figs, 1 and 2, the bimetal strip 26 is preferably fof the ambient temperature compensatcd type. That is, it is formed of a U-shaped piece of bimetal strip anchored at one end by screws 34 which extend into an insulating block 36. The opposite end of the .bimetal strip-is equipped with a contact 28 which moves upwardly and downwardly whenever one leg of the U-shaped bimetal element is curved'more than the other. Ambient temperatures have little or no effect upon the position of the contact 28, since an increase in temperature in the device caused by an increase in ambient temperature causes the bimetal strip to curve so that its upper face is concave. Inasmuch as one end of the U-shaped strip is anchored, the contact will remain in a fixed position, since any curvature of one leg of the U will be offset by an equal amount of curvature in the other. The electric resistance heating element 32 pre lfiously referred to is formed by wrapping a single layer of resistance wire around 'he leg of the U-shaped bimetal strip which caries the contact 28. Whenever this resistance elenent is energized, it will raise the temperature of its leg of the bimetal strip carrying the contact 38,

thereby causing the fcontact 28 to be raised. When both legs of the thermosensitive element are at substantially the same temperature, the contact 28 rests against and makes contact with the ,previously referred to contact 38 which, in Fig. 2, is shown as mounted upon the end of a manually adjustable thumb screw 48 threaded through a .bushing 42 molded in the insulating block 36.

The second portion of the device, indicated at 24, may be considered as essentially the same as the portion 22 just described excepting that instead of the bimetal strip 26 carrying the contact 28 directly, the similar strip 44 in the control unit 24 yis enabled to move an appreciable distance before taking up suicient lost motion to catch beneath a hook 46 formed at the end of a flexible strip 48 which in turn is provided with a contact 58. As in the case of bimetal strip 26, the similar strip 44 is equipped with an electric heating element 54 of the resistance type. Il desired, the bimetal element 44 of the controller 24 may also be of the temperature compensated type, although this is not so necessary in order to obtain close regulation as it is in the case of the impulse sending unit 22. Also, the strip 44 and heater 54 should beinsulated or otherwise arranged so that the cooling rate thereof will be slower than for the strip 26.

The deviceis connected and operates in the following manner. The automobile or similar battery 68 is grounded at one side while the other side is connected through the previously referred to master switch to one side of an overheat switch 62. This overheat switch is of the thermostatic type and is sensitive to the temperature of the heater or the temperature of the air leaving the heater in'such manner that any malfunctioning of the heater which causes an abnormally high temperature will result in the switch x62 opening, thereby turning oif the heater. The lead which extends from the overheat switch 62 is connected by a wire 64 to one of the contacts 66 of the relay -I4. Also, this same lead 64 is connected through one end of each of the two electric resistance heaters 32 and 54, this connection being made by a lead 12. In each instance, the opposite ends of the electric heating elements 32 and 54 are grounded.

The stationary contact 52 of the controller 24 is directly connected by a lead 14 to coil I6 of the magnetic fuel control valve I2, the other end of the coil being grounded while the movable contact 58 is connected by way of the exible strip 48 and lead 18 to the dead contact of the overheat switch 62.

Before the heater is placed in operation, the master switch I8 will be open, the overheat switch will be closed as will the igniter switch I6, while the relay contacts 66 and 68 will be open. Also, contacts 28 and 38 will be together as will contacts 58 and 52. If, under such conditions, the master switch I8 is closed, the battery energizes the relay coil 28 by way 'of lead 64 and the contact of the igniter switch I6. The relay I4 is therefore closed so as to energize the igniter I8 by way of the contacts 66 and 68 and lead '18. The temperature of the igniter therefore begins to rise. Meanwhile, current also flows from the lead 10 by way of contacts 30 vand 28 and bimetal strip 25 to the lead 'l2 and thence through the two electric heating elements 32 and 54 to ground. The temperature of these two resistance elements therefore begins to rise and they in turn begin to raise the temperature of the bimetal strips 2G and 44. During this period current also flows through the overheat switch 52 and lead 18 to contact 50 and thence by way of contact 52 and lead 14 to the coil 15 of the fuel valve l2. The valve therefore opens, permitting fuel to flow to the heater.

If the heater starts in a normal length of time the temperature of the heater or of the air passing therethrough will rise suiciently to open the switch I5, thereby de-energizing the relay coil 20 and permitting the contacts 56 and 58 to separate. The lead 'l0 is therefore de-energized with the result that the igniter i begins to cool as do the resistance heaters 32 and 54. The result therefore is that contacts 52 and 50 never separate, since movement of the bimetal strip 44 under the influence of heater 54 has never been suflicient to close the lost motion gap which exists between the free end of the strip 44 and the hook 45. The coil 'l5 of the fuel valve I2 therefore remains energized and the heater continues to receive fuel.

If, on the other hand, the heater does not A start within a reasonable time, the relay I4 remains closed, since the switch I has not been heated to operating temperature. The result is that heating elements 32 and 54 continue to be energized until the temperature of the strip 25 rises sufciently so that upward fiexure of the free end of this strip separates the contact 28 from the contact 30. As soon as this occurs the heating element 32 and the heating element 54 will both be de-energized. since both these heating elements are energized by way of the contacts 25 and 3l. Both heating elements 32 and 54 therefore begin to cool until the contacts 28 and l0 re-engage so as to repeat the cycle. The heater 54 for the bimetal element 44 therefore receives current in impulses. Eventually, these impulses heat the bimetal element 44 sufficiently so that the free end is deflected upwardly enough to lift the hook 45 and separate the contacts 55 and 52, thereby de-energizing the coil 'I5 of the fuel valve I2.

If the voltage at the battery 50 is high, then upon closing of the contacts 28 and 30 the resistance element 32 will quickly supply enough heat to the bimetal element 25 to separate the contacts 20 and Il. On the other hand, it will require approximately the same cooling time before the contacts 28 and 3l reclose regardlessvof how rapidly they have been heated to the separating point. Conversely, if the voltage at the battery Il is low, the contacts 2B and 30 will remain closed a longer time interval before the heating element 32 has dissipated enough energy to heat the strip 25 to the point where the contact 2l is separated from the contact 30. In general, the amount of energy dissipated by the heating element I2 in separating the contacts 25 and 2l will remain approximately the same regardless of whether it accomplishes this quickly at high voltage or slowly at low voltage.

Inasmuch as the heating element 54 is in parallel with the heating element 32, it will be seen that the energy dissipated by the heating element 54 will remain constant over any time interval long enough to average the electrical impulses from the contacts 28 and Il. Thus, the amount of energy supplied to the bimetal strip 44 over a period of, say, three minutes will remain substantially constant at all voltages within the range of operation of the device even though under some conditions power may be supplied to the heating element 54 by short duration impulses at high voltage or at other times by long duration impulses at low voltage. Thus,

even though the voltage at the battery 5l may fluctuate widely, the time required for the separation of contact 50 from the contact 52 will remain substantially constant.

As has been pointed out previously, the bimetal strip 44 and heater 54 should be insulated or otherwise arranged so that the cooling rate r plished by providing less ventilation for the` bimetal strip 44 or by covering the strip and heating element with an insulating wrapping, or by providing a heating element of lower resistance so that more energy is dissipated during each on cycle in the heating element 54 than in the similar element 32.

Having described my invention, what I claim as new and useful and desire to secure by Letters Patent of the United States is:

A voltage compensated time delay switch comprising a pair of contacts, a bimetal element arranged to separate said contacts when heated to a predetermined temperature, an electric heating element in heat transfer relation to said bimetal element, a second set of contacts, a second bimetal element arranged to separate the last said contacts when heated to a predetermined temperature, a second electric heating element in heat transfer relation to the last said bimetal element, and circuit means connecting both of said heating elements in parallel and for energizing both of said heating elements by way of the said second set of contacts, the characteristics of the heating elements and the bimetal elements being such that simultaneous energization of both heating elements will cause separation of the second set of contacts before the first set of contacts has separated while simultaneous de-energlzation of both heating elements will cause closing" of the second set of contacts before the relationship of the first set of contacts has been substantially disturbed.

VERNON N. TRAMONTINI.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,743,053 Traver Jan. 7, 1930 1,816,451 Wallace July 28, 1931 1,920,806 Rich Aug. 1, 1933 2,060,494 Gamel Nov. 10, 1936 2,329,119

Jacobs Sept. 7, 1943

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