US3514734A - Thermal sensing pressure switch - Google Patents

Description

May 26, 1970 J. K. GARRETT THERMAL SENSING PRESSURE SWITCH Filed Nov. 28, 1967 s: s- Ev Q; I 3 42 ;E r 5 30 did/5 A. 6416957 7' 1 INVENT'OR. 7%

United States Patent 3,514,734 THERMAL SENSING PRESSURE SWITCH James K. Garrett, Inkster, Mich., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Nov. 28, 1967, Ser. No. 686,153 Int. Cl. H0111 37/40 US. Cl. 337320 3 Claims ABSTRACT OF THE DISCLOSURE A thermo-sensing pressure switch for sensing air temperature in an engine compartment having a chamber which expands and responds to increased temperature thereby causing a diaphragm to flex against a piston which is slidably mounted in the switch housing. A piston which is biased against the diaphragm is caused to move so as to contact a micro-switch mounted within the switch housing thereby completing an electrical circuit and energizing a warning light in the drivers compartment.

This invention relates to a thermo-sensing pressure Switch. More particularly, this invention relates to a switch which is actuated in response to thermal conditions in internal combustion engine compartments. Thermally responsive switches have been known in the prior art, however, these switches were not compact and the response was not sufficiently predictable under any given environment. Prior art sensing switches were of a snap action type which were fast acting type in response to a relatively small change in temperature once a plateau temperature was reached. The present switch provides for a smooth operating switch which can operate in a relatively warm environment. Prior art devices have a limited range and have relatively high response. The present invention provides for a switch which can operate in a relatively high temperature while still requiring a relatively large change in temperature to energize or deenergize a switch.

The present invention, therefore, provides for a thermal sensing pressure switch having a two piece housing, diaphragm, piston, spring, and a micro-switch. Ambient air at some initial pressure is trapped in a sensing cavity formed in the housing. This pressure creates a force on the effective area of the diaphragm which is counteracted by the force of the spring. As the air temperature rises, the pressure within the sensing cavity also rises. This results in an increased load on the diaphragm. When this load exceeds the force of the spring, motion of the piston and diaphragm occurs. At some increased pressure, piston contact is made with the micro-switch resulting in closure of an electrical circuit.

It is, accordingly, an object of the present invention to overcome the above mentioned defects in prior art warning systems for overheated engine compartments.

It is another object of the present invention to provide a thermal sensing pressure switch for sensing air temperature in engine compartments.

It is yet another object of the present invention to provide a thermal sensing pressure switch which is utilized to provide a monitor signal responsive to an increase in temperature in the engine compartment.

It is yet another object of the present invention to provide a thermal sensing pressure switch which is fully automatic and does not require crew member actuation.

Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art by the following description when considered in relation to the accompanying drawing of which the sole figure is a cross-sectional view of the switch according to the invention.

Referring now to the drawing, the main casing for the switch is indicated at 10 having flanges 30 extending about the lower edge. Diaphragm 26 is mounted on a receptacle 12 and clamped between flange 32 of receptacle 12 and flange 30 of casing 10. A retainer 14 having a bore 18 extending therethrough is conveniently located within casing 10. Flange 16 is provided on one end of retainer 14 in abutting relation with shoulder 20' which is former in casing 10. A snap ring 24 secures flange 16 against shoulder 20 and prevents movement of the retainer 14.

Diaphragm 26 is formed of an elastomer and has a U-shaped told as shown at 28 secured therein. This fold permits pressure to increase on only one side of the diaphragm. Utilization of the U-shaped fold also eliminates the necessity of a seal between the piston 38 and the bore of casing 10. The disadvantage of using a seal is in thelfact that excess friction is created by the use of such sea s.

A spring 44 is located about retainer 14 and is located between flange 16 and the bottom 39 of piston 38. Piston 38 has side walls 37 which are slidably engaged with the internal bore of casing 10. The tendency of the spring 44 is to force piston head 39 downwardly and cause diaphragm 26 to move towards receptacle 12. Mounted on the underside of diaphragm 26 is a stop, indicated generally at 47 comprised of plate 34, bolt 48 and nut 49. Plate 34 is held in engagement with diaphragm 26 to prevent downward movement thereof by spring 44. As can be seen in the drawing, flanges 36 are provided about the outer circumference of plate 34 to provide adequate support for the diaphragm 26. Bolt 48 passes through diaphragm 26 and is secured to piston head 39. Hence, piston head 39, diaphragm 26, nut 49, and bolt 48 move as a unit. If desired the bolt 48 and nut 49 may be adjustable so that plate 34 will permit increased movement of piston 38 in a downward direction.

The assemblage of parts including casing 10, diaphragm 26 and receptacle 12 has thus provided a sensing cavity 40. Air is trapped within the sensing cavity 40 which will expand or contract in response to the environmental temperature in which the pressure switch is located. If the environmental temperature increases, the air which is trapped within cavity 40 will expand, thus causing diaphragm 26 to flex upwardly. If however, the environmental temperature decreases, the diaphragm 26 will flex downward causing plate 34 and stop 47 to move downward until bolt 48 engages receptacle 12. The tension of the spring 44 may be adjusted such that the pressure of the entrapped gas within cavity 40 will be suflicient to overcome the force of spring 44 at some predetermined point.

Mounted within retainer 14 is a micro-switch which is shown schematically at 50. Leads 54 connect switch 50 in an electrical circuit containing an indicating light 56. At least one movable contact 52 is provided at the bottom of the micro-switch 50 which when depressed will engage another contact within switch 50 and thereby complete the electrical circuit in which the switch is located. Upon depression of contact 52, switch 50 will close thus completing the circuit and enabling power to flow thru leads 54 to the indicating light 56, thereby, indicating a desired sensed condition. The movement of the piston 38 is designed to actuate switch 50 which is supported in retainer 40.

As can be seen in the drawing relief ports 46 are provided in casing to permit escape of air entrapped in chamber 42. As piston 38 is caused to move upward against the force of spring 44, air will escape through ports 46 and thereby allowing diaphragm 26 to flex in an upward direction. If ports 46 were not so provided, the pressure of the air entrapped in sensing cavity 40 and chamber 42 on opposite sides of diaphragm 26 would tend to equalize in response to relatively identical environmental conditions. This would seriously limit the eflicacy of the sensing switch.

If desired, a mechanical fuse could be utilized in place of bolt 48, and nut 49. These types of fuses are known in the art and provide a mechanical force which would prevent movement of plate 34 and diaphragm 26 in an upward direction until the fuse is broken. These type of fuses commonly break when a predetermined temperature is reached, thereby melting the fuse link and permitting movement of the diaphragm. This feature would permit the present invention to incorporate the features of a snap action switch in addition to those features previously mentioned. The use of a fuse of this type, however, has the disadvantage that once the fuse is broken the support from plate 34 will be eliminated. If the switch is to be used in an environment where the temperature is at a relatively high base and/or if the temperature tends to fluctuate around the base reference temperature, this would cause the fuse to break and hence the use of such a fuse would be inadvisable.

In operation, the pressure switch is placed in an engine compartment for sensing air temperature and is mechanically fastened therein by any suitable manner. The spring member 44 is so adjusted that the resultant pressure exerted on piston 38 will normally retain stop member 47 in contact with receptacle 12 and thus the electrical circuit will be de-energized and the indicating light 56 in the crew compartment will be off. As the temperature within the engine compartment rises, the pressure of the air trapped within sensing cavity 40 increases. When pressure within sensing cavity 40 increases beyond a prede termined threshold pressure, piston 38 will slide upward against the force of spring 44 until piston head 39 depresses contact 52. As piston 38 slides upward, air entrapped in chamber 42 will escape through ports 46, thereby reducing the pressure on the upward side of the diaphragm 26. When contact 52 is depressed, micro-switch 50 will be closed, therefore the electrical circuit including the indicator light 56 will be completed. This will permit power to flow through leads 54 from any suitable source such as a vehicle battery to the indicator light. This will notify the vehicle operator to take necessary remedial steps to correct the abnormal temperature condition.

When the environmental temperature within the engine compartment decreases, the pressure of the entrapped air within sensing cavity 40 will decrease and thereby permit diaphragm 26 to regain its original position wherein stop member 47 will rest against receptacle 12. Piston 38 will also be forced downward against diaphragm 26 by the force of spring 44 pressing against piston head 39. When piston head 39 is thus lowered, micro-switch 50 will no longer be closed due to the removal of force on contact 52. The indicator light will then be de-energized, thereby indicating normal temperature operation.

While the thermo sensing pressure-switch has been indicated to have utility within an engine compartment, it will be evident that the switch will be operative within any environment in which an indication of change in temperature is useful and desirable.

While the switch has been described as being utilized to actuate an indicator light, it should be noted that the switch may be used to complete any electrical circuit.

What has been described therefore is a thermally responsive pressure switch which is compact, durable, and able to operate smoothly in an air environment which is both fluctuating and at a relatively high base temperature. The invention therefore further provides for a thermo sensing switch which has a range and response which is not known in the prior art. A switch according to the present invention has a response, which is sufficiently low to permit fluctuations in the environmental temperature without adversely affecting switch operation.

Since it is obvious that many changes and modifications can be made in the above described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not limited to said details except as set forth in the appended claims.

What I claim is:

1. A thermal sensing pressure switch comprising:

a casing having at least one movable contact forming a portion of a switch mounted therein and an internal bore;

a receptacle shaped so as to form a sensing cavity;

a diaphragm clamped between said casing and said receptacle;

a piston slideably mounted in and engaging said internal bore so that when the pressure increases in said cavity in response to increased environmental temperature, said switch is activated; and

at least one fixed contact located within a micro-switch;

said micro-switch secured in a retainer which is fixed in said housing and extends into said piston.

2. A thermal sensing switch in accordance with claim 1 wherein:

said diaphragm has a U-shaped fold positioned therein extending intermediate said piston and said casing so as to permit the diaphragm to flex toward said contact; and

a spring is mounted intermediate a portion of said retainer in said piston to bias said piston against said diaphragm.

3. A thermal sensing pressure switch comprising,

a casing,

a receptacle,

a diaphragm,

a piston,

a retainer,

a micro-switch,

a spring biasing means,

and a support means,

said diaphragm being clamped between said casing and said receptacle so as to form a sensing activity and an exhaust chamber,

said support means comprising a plate mounted within said sensing cavity and attached to said piston,

said retainer being mounted within said casing so as to form said exhaust chamber intermediate said retainer and said piston,

said piston having a piston head which is in engagement with said diaphragm and a side member which is slidably engaged with said casing,

said micro-switch being mounted within said retainer and having at least one movable contact,

said spring means being mounted intermediate said retainer and said piston whereby the pressure of gas which is trapped within said sensing cavity will inand cause said diaphragm to flex against said piston so as to permit said piston to slide and cause said piston head to engage said contact of said micro- 5 6 switch when the environmental temperature reaches 2,688,064 8/ 1954 Traver 337320 a predetermined threshold temperature. 3,324,262 6/ 1967 Noth 337-320 References Cited FOREIGN PATENTS 198,367 5/1923 Great Britain.

UNITED STATES PATENTS y 6t -1 *?2 BERNARD A. GILHEANY, Primary Examiner gf g g f 333:; DEWI'IT M. MORGAN, Assistant Examiner Starbird 337-315 Szwargulski 200-835 10 Mayo 337 320 20083.5, 83.91; 337-327 Coffin 337320

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