GB2154036A - Thermal alarm - Google Patents

Abstract

A self-contained portable thermal alarm device comprising, in combination: a permanent magnet adapted to cling magnetically to an external surface region of apparatus to be kept under surveillance; temperature-sensing means thermally conductively connected to said permanent magnet; and alarm means activatable when said temperature-sensing means reaches a predetermined threshold to thereby complete an electrical circuit which includes said alarm means and also a source of electrical energy. A test button 4 may be arranged to bridge the terminals 16 of the sensing means 3 (Fig. 3). <IMAGE>

Description

SPECIFICATION Thermal alarm This invention relates to what may be termed thermal alarms, and more particularly to such an alarm for the purpose of giving early, and preferably audible, warning of the over-heating of engines, especially internal combustion engines, or similar machines which are either artificially cooled or which must be prevented from operating above certain specified temperature limits.

In the operation of motor vehicles, for instance, it is often difficult to effectively monitor the coolant temperature. For example, it might easily not be realised that a radiator filler cap had been left off or insufficiently secured, with the consequence that the coolant's boiling point at atmospheric pressure is a mere 100" Celsius instead of being safely raised as high as 160 Celsius or more if the radiator were pressurized to, say, 6 atmospheres.Also, a pre-occupied driver perhaps in hazardous or heavy traffic conditions-may not even notice that a conventional warning device had been actuated when such simple faults as ruptured radiator hoses, or, in older vehicles, failed welch plugs, resulted in loss of coolant, Even the onset of boiling of the coolant may well be overlooked because drops of water impinging on a windscreen or window from condensed vapour derived from the coolant could be mistaken for rain; the absence of the characteristic smell of overheating being hardly suprising when the occupants of an air-conditioned vehicle are insulated from outside intrusions by closed windows.

In the event of the undetected overheating of an engine, or of a failure to detect such overheating within suffient time, expensive repairs such as re-bores can cost as much as $2,000 at present rates, or even up to $ 11 ,000 for such large commercial vehicles as semi-trailer prime-movers.

Attempts have been made to overcome such problems by fitting vehicles with various warning devices such as red indicator lights and/or electrical meters with indicator dials, but all these have been relatively expensive and, more importantly, also inherently unreliable, because their temperature-sensing means-usually a copper wire/iron wire thermocouple-is located substantially permanently in a hostile environment somewhere within the engine block, where a relentless cycle of large temperature changes is undergone, with inevitable eventual expansion and corrosion problems.

Furthermore, virtually all the prior-art temperature-sensing means are adapted to measure the temperature of the coolant contained in an engines's cooling system and thus when coolant is rapidly lost-as in the case of the previously mentioned radiator hose rupture or welch plug failurecontact with the sensor of the temperature-sensing means ceases, and all too often the indicator light or dial shows the dangerous temperature too late to prevent damage to the engine. In other words, when a sensor does finally "sense" that the temperature of the plenum is higher than the temperature of the lost coolant should have been, the engine will be already near the point of seizing.

From the foregoing it will be realized that the inventive device is essentially what may be said to be an "early warning" device; and with this in mind it is therefore an object of the present invention to provide a constructionally simple and inexpensive, preferably audible, early warning device capable of being easily and rapidly attached to an external surface region of an engine or the like by even the most inexpert and "unhandy" person, without the use of special tools of any kind, to enable a driver to stop an engine quickly and within sufficient time to prevent damage from incipient overheating.

Thus, according to the invention, a selfcontained, portable thermal alarm device may comprise, in combination: a permanent magnet adapted to cling magnetically to an external surface region of apparatus to be kept under surveillance; temperature-sensing means thermally conductively connected to the permanent magnet; and alarm signal means activatable when the temperature-sensing means reaches a predetermined threshold to thereby complete an electrical circuit which includes said alarm signal means and also a source of electrical energy.

The permanent magnet may be substantially of squat, right-cylindrical configuration and has therein a recess accommodating a bimetallic strip which constitutes the said temperature-sensing means, this bimetallic strip curving, when the predetermined threshold has been reached, so as to close a pair of electrical contacts to thereby complete the electrical circuit. (Alternatively, of course, such curvature of a bimetallic strip could act to separate a pair of electrical contacts so as to open a suitably modified circuit).

Preferably, it is envisaged that the electrical circuit could well be powered by the battery of the vehicle in which the thermal alarm system is installed, but in those particular applications in which there is no battery, one or more dry cell batteries may be employed.

Ideally, the alarm signal means may be constituted by a small reverse-flow screamer of the piezo-ceramic kind.

The permanent magnet may well incorporate a test push-button assembly, whereby finger pressure applied to the button causes the temperature-sensing means to short out, thus activating the alarm signal means irrespective of the temperature.

Advantageously, a potentiometer may be incorporated in the electrical circuit to provide an adjustable temperature threshold.

In order that the reader may gain a better understanding of the present invention, hereinafter will be described a preferred embodiment thereof, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a permanent magnet/temperature-sensing means assembly according to the present invention.

Figure 2 shows a typical alarm signal means: Figure 3 is a vertical section through a permanent magnet component of the invention; Figure 4 shows the device of the invention installed on an internal combustion engine; and Figure 5 is a diagram of the electrical circuit.

Figure 1 shows an inventive permanent magnet/temperature-sensing means assembly which is composed of a permanent magnet 1 adapted to cling magnetically to an external surface region of an engine or the like to be kept under surveillance, indicated at 2. Permanent magnet 1 is substantially of squat, right-cylindrical configuration and has within it a recess designed to accommodate a temperature-sensing means 3. Also incorporated in permanent magnet 1 is a test push-buttom assembly, the finger button of which is referenced 4. The construction and mechanism of this permanent magnet/temperature-sensing assembly will be more fully described hereinafter with reference to Figure 3.

Permanent magnet 1 and temperature-sensing means 3 are two components of the novel combination of the present invention, the third essential component being an alarm signal means shown in Figure 2.

This alarm signal means is preferably constituted by a reverse-flow "screamer" of the piezo-ceramic kind commonly used in smokedetector alarm systems. Such a screamer may well be housed in a 30mm diameter, squat, right-cylindrical plastic case 5. Case 5 accom modates a ceramic disc which, in known manner, bends and produces a shrill sound when a current is applied to it; hence the qualifying term "reverse-flow" which arizes from the standard definition of "piezo-elec tric":- "becoming electrically polarized under pressure", the inverse being also true. Case 5 has an aperture 6 through which may extend the electrical conductor 7 and an opposed pair of lugs 8 by means of which the screamer may be secured to a support such as the instrument panel of a motor vehicle.

Turning now to Figure 3, the permanent magnet 1, having interior recess 9 therein, will be seen to include a centrally-located test push-button assembly extending downwardly through an appropriate bore 10 in the top wall of permanent magnet 1, through which can pass a spindle or shaft 11. The protruding end of shaft 11 has a finger-button 4 (as also shown in Figure 1) while at its other end is a washer 1 2 dimensioned to retain captive the shaft 11 in co-operating bore 10. Button 4 and shaft 11 are urged into an "upward" position by a helical spring 1 3 which surrounds shaft 11.

The lower element of Figure 3 represents the temperature-sensing means 3, as also to be glimpsed in Figure 1, but shown in side elevation in contrast to the sectioned upper element of the drawing. Means 3 has a squat, right-cylindrical plastic case 14 having an electrically-conducting cap 1 5. Case 14 is provided with a pair of external contacts 16, by means of which temperature-sensing means 3 may be connected into the electrical circuitry, and a pair of internal contacts 1 7 by way of which it may be shorted out as later explained herein.

Temperature-sensing means 3 has, within the case 14, a sensor comprising a bimetallic strip type of thermostat. Ideally, this bimetallic strip may be of the copper-or-brass/iron-ormild-steel kind, the strip assuming a curve, when a predetermined temperature threshold has been reached, so as to "close" the exter nal electrical contact pair 1 6 to thereby com plete the electrical circuit. On completion of this circuit, the ceramic disc in the screamer is caused to be bent because of its reverse flow characteristic--to thereby activate the alarm signal. If the engine is cut in response to this alarm signal, the bimetallic strip returns to its initial position as cooling occurs, and the contacts open to thereby break the circuit and stop the alarm signal.

In Figure 3, for the sake of clarity, temperature-sensing means 3 is shown rotated through 90 ; in use, means 3 is a snug "push-fit" up into recess 9, the metal cap 1 5 conductively connecting means 3 to magnet 1. Contacts 1 6 project through lateral exten sions 1 8 of recess 9 -ne of which is shown in Figure 1-so as to be able to be connected into the circuit between electrical wires 1 9.

It would clearly be of advantage if the alarm could be tested when necessary or desired.

An obvious way would be to switch on the ignition of the vehicle (after installation of the device, of course), lift the magnet off the engine block, head etc., and short-out the circuit by bridging the sensor contacts with the blade of a screwdriver or a piece of wire.

A much easier and more elegant way of testing, however, is by use of the test push button assembly as in Figure 3. When the sensor is in position in the recess in the permanent magnet, there is an air-gap be tween metal washer 3 and internal contacts 1 7. When button 4 is depressed by the finger, shaft 11 is forced downwardly through bore 10, washer 1 2 comes into contact with the internal contacts 17, the sensor is thus shorted out to complete the circuit and to cause current to be applied to the ceramic disc of the piezo-ceramic screamer so that it bends and emits an audible alarm signal.

In use, the permanent magnet/temperaturesensing device assembly may be speedily attached to an engine, on the block thereof or on the head, perhaps after cleaning a suitable small area thereof with petrol, kerosene or the like, and hence left in place. In the case of a conventional cast steel block and head, almost any flat region would suffice for attachment, but in the case of aluminium alloy engines, some auxilliary steel component should be employed as an attachment base. For example, such means as a steel disc could be adhered to the aluminium with a heat-resistant bonding material, and the magnet could be placed upon this disc.

In this connection, attention is now drawn to Figure 4 which shows, in broken line, a schematically-drawn internal combustion engine. For clarity, the particular engine depicted, generally referenced 20, is a simple vintage 8-cylinder single overhead camshaft engine and in this regard it should be stated that the alarm device of the present invention has particular application to vintage and veteran motdr vehicles, since an engine which has seized or is otherwise seriously damaged may be irreplaceable or, at least, extremely expensive to repair.In Figure 4, the magnet 1 clings to the flat upper surface of the head 21 while one wire 1 9 from the sensor runs to the vehicle's battery as indicated by arrow A, and the other wire 1 9 goes to the screamer located, say, on the vehicie's instrument panel, indicated by arrow B.

Now, while installation of the alarm device as described above is within the capacity of almost any person to undertake, nevertheless a typical circuit diagram is illustrated in Figure 5. In this circuit, plugs, such as say, banana plugs, or so-called splice connectors, are referenced 22; such connectors providing for a series of extensions for different applications.

The circuit includes alarm signal means 23, temperature-sensing means 24 and a battery 25, which latter may either be the battery of the vehicle itself or may be one or more dry cell batteries. For simplicity a completely wired circuit is shown, but in practice one side of the battery would be earthed in the usual manner, and the vehicle itself would be used as an earth return. The wiring, needless to say, will be the neater for being collected in bundles with such devices as cable ties or suitable clips. "Limbs" 27 and 28 of the wiring may terminate in battery clips such as are used on so-called jumper leads.

While a range of the inventive alarm devices having differing thresholds may be offered for specific usages, it is envisaged that it may be provided with an adjustable temperature threshold, for example by incorporating a suitable potentiometer in the circuit, as referenced 26.

An appropriate temperature threshold for the engine in question is ascertained and a concommitant sensor is employed in the installation. It is noteworthy that the permanent magnet would conceivably never reach the very high temperatures at which iron demagnetizes (i.e. at "cherry-red" heat, about 700 C+in which case the magnet would simply fall off the block-because such temperatures are never likely to be reached, except in the case of total destruction by fire. In any case, it is not necessary to actually measure the relatively high temperature of the engine block, it being sufficient to know the lower temperature of some mass which is associated with the engine, and to calibrate the device accordingly to give a reading which is proportional to the temperature of the block.

Although the temperature-sensing means has up to now been described in terms of a bimetallic strip, it is also contemplated that its place could be taken by a mercury/glass thermometer, such a thermometer having at least one electrically-conductive probe penetrating the bore of the glass tube, whereby expansion of the mercury within the bore, beyond a pre-set limit, would complete the circuit which is connected to the probe. The glass tube of the thermometer may be attached to the magnet either by certain of the well-known metal cements presently commercially available, or by the previously-mentioned heat-resistant bonding material.

A further embodiment could take the form of a mercury contact having the form of a small mercury-containing vessel with a probe incorporated in its cover dome or top wall.

The device of the present invention will be seen to possess a number of advantages; for example, it is self-contained and portable, and is rapidly demountable from one engine and instantly available for transfer to another. The device is light in weight and inexpensive.

Although the inventive device may, needless to say, be initially supplied by the vendor of the vehicle, it could also be readily offered as a retrofit item for the accessories market.

There again, it is contemplated that the device could well be retailed in kit form, bubblepackaged on a card, in a format making it suitable for all applications.

However, the device is not confined to use just upon a motor vehicle engine but may be applied to any apparatus or machine where overheating can result in damage, destruction or danger. For instance, it has particular application to large agricultural implements where the operator may be more than, say 7 metres from the prime mover. The preferred bimetallic strip embodiment is especially useful, also, in the field of food-processing, for example in jam-making, while refrigerating plant would cl'early be the better for the employment of the device. There again, grain and fodder silos can spontaneously combust under certain conditons of damp storage and would benefit from the fitting of the device of the present invention. Other applications spring rapidly to mind---outboard motors, copying machines, air-conditioners, pumps, generators, electric motors, bearing housings and the like being typical.

From the abovegoing, the reader will readily appreciate that self-contained, portable thermal alarm devices made in accordance with the present invention will provide the public with a new or much-improved article or, at the very least, offer to it a useful and attractive choice.

Claims (9)

1. A self-contained portable thermal alarm device comprising, in combination: a permanent magnet adapted to cling magnetically to an external surface region of apparatus to be kept under surveillance; temperature-sensing means thermally conductively connected to said permanent magnet; and alarm signal means activatable when said temperature-sensing means reaches a predetermined threshold to thereby complete an electrical circuit which includes said alarm signal means and also a source of electrical energy.

2. The self-contained, portable thermal alarm device as claimed in Claim 1, wherein said permanent magnet is substantially of squat, right-cylindrical configuration and has therein a recess accommodating a bimetallic strip which constitutes said temperature-sensing means, said bimetallic strip curving, when said predetermined threshold has been reached, to close a pair of electrical contacts to thereby complete said circuit.

3. The self-contained portable thermal alarm device as claimed in Claim 1 or Claim 2, wherein said apparatus is the engine of a vehicle.

4. The self-contained, portable thermal alarm device as claimed in Claim 1 or Claim 2, wherein said electrical circuit is powered by the battery of the vehicle in which the said thermal alarm device is installed.

5. The self-contained portable thermal alarm device as claimed in any one of Claims 1 to 3, wherein said electrical circuit is powered by one or more dry cell batteries.

6. The self-contained portable thermal alarm device as claimed in any one of the preceding Claims, wherein said alarm signal means is constituted by a piezo-ceramic, re verse-flow screamer.

7. The self-contained portable thermal alarm device as claimed in any one of the preceding Claims, wherein said permanent magnet incorporates a test push-button assembly, finger pressure applied to said button causing said temperature-sensing means to be shorted-circuited to thereby activate said alarm signal means.

8. The self-contained portable thermal alarm device as claimed in any one of the preceding claims, wherein a potentiometer is incorporated in said electrical circuit to provide an adjustable termperature threshold.

9. A self-contained portable thermal alarm device, substantially as hereinbefore described with reference to the accompanying drawings.