US2793271A - Thermo-bimetal instantaneous switch in particular for flash signal apparatus and luminescence lamps - Google Patents

Description

May 21, 1957 C. F. 0. MULLER ETAL 2,793,271 THERMO-BIMETAL INSTANTANEOUS SWITCH IN PARTICULAR FOR FLASH s IGNAL APPARATUS AND LUMINESCENCE LAMPS Filed March 22, 1955 V 3 Sheets-Sheet l P 9 3 1 FIG.1 2

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May 21, 1957 c. F. o. MULLER ETAL 2,793,271

THERMO-BIMETAL INSTANTANEOUS SWITCH IN PARTICULAR FOR FLASH SIGNAL APPARATUS AND LUMINESCENCE LAMPS Filed March 22, 1955 3 Sheets-Sheet 2 4 I 13 Has 1 14 9 IN VE/VTORS an arm MULLER orro MULLER ATTORNEYS Filed March 22, 1955 y 1957 c. F. o. MULLER ETAL 2,793,271

7 THERMO-BIMETAL INSTANTANEOUS SWITCH IN PARTICULAR FOR FLASH SIGNAL APPARATUS AND LUMINESCENCE LAMPS 3 Sheets-Sheet 3 FIG. 80

FIG. 8b

FIG. 9

mvlvroRs 0.1? orro MUZLER orro MULLER United States Patent THERMQ-BINIETAL INFsTANTANEDUS. SWITCH IN PARTICULAR FOR FIASH- SIGNAL APPARATUS AND LUMINESCENCE LAMPS C. F. Otto Miiller and Qtto lviiiller, Frauenalb, Germany Application March 22,1955, Serial No. 496,015

Claims priority, application Germany March 24, 1954' 12 Claims. (Cl. 2tl0--138) This invention relates to a thermo-bimetal instantaneous switch, in particular for flash signal apparatus and luminescence lamps.

Ithas been known in the art to provide. electric warming pads with thermostats in order to prevent overheating. Mostly such thermostats consist of a strip of thermobimetal which under. the influence of heat bendsto one side so that-on reaching the desired maximum temperature the circuit is opened and closed again as soon as the warming pad is sufiiciently cooled down. The thermostat is connected in series with the winding of the warming pad. Such thermostats havingv a contact spring with an opposite contact whichspring is influenced by a thermo-bimetal strip may berproduced at a very low price and are therefore. preferred in use.

Since-withsuch thermostats the switching is effected gradually and the switching movement amounts to only fractions of millimeters thecontacts burn aftera short period of use. Consequently the thermostatis no longer able to switch off'correctly whereby numerousfire damages have been caused. Besides annoying radio interferences occur.

The present invention relates to a thermostat with a thermo-bimetal strip.

According'to the invention the'thermo-bimetal stripis formed in such a way that instantaneous switching; is effected and a relatively large switching movement is obtained so that the drawbacks mentioned above are obviated. Furthermore this new thermostat may be produced at the same low price as the known thermostats of the kind described above.

A further object of the invention consists in-using such thermo-bimetal strips for operating flash signal apparatus or for igniting and operating gas discharge lamps, especially low voltage luminescence lamps.

It has already been known inv the art to use so-called Spenzerscheiben, i. e. vaulted plates of bimetal having a surface whichcannot be unrolled (spherical cap), the convexity of which jerkily vaults to the'other side as soon as a maximum temperature is reached and which returns in the same way by jerks to its initial position at a certainlow temperature, which Spenzerscheiben are used for rapid switching onand off electrical circuits.

Various alterations of such switching discs have been developed while maintaining the essential idea of the invention. Such devices serve especially for regulating the temperature of electric irons and similar apparatus in which the temperatures required for operating such switching discs, being always beyond 100 degrees centigrade, occur, and in which sufiicient space is provided toarrange the mentioned discs which cannot be produced below a certain diameter. The production of such switching discs is rather difiicult.

In certain countries there are prescriptions for the manufacture of electric warming pads. The warming pads have to be switched off at a temperature of 80 to 90degrees centigrade which cannot be obtained in using the above mentioned discs.

The difierence between the 2,793,271 Patented May 21, 1957 temperature for switching on and off such discs is so large that the latter are not suitable for many switching operations, respectively switching devices, as for instance the thermostats of. warming pads.

Extensive experiments have revealed that the critical temperature at which the' vaulting is reversed from the initial position to the opposite side is only below degrees centigrade if the thickness of material of the thermo-birnetalsis the smallest possible to be produced, namely: from about 0.0610- 0.08 millimeters, respectively to 0.15 millimeters at.-the-most, and if further the mentioned spherical caps have a diameter of only a few millimeters and a slight,vh'ardly perceptible vault, that is to say that-the ball pcrtaining to' the spherical caps is of extremely long radius.

Our invention will be-still, better. understood from the description thereofi given hereinafter; in. connection with the accompanying, drawings in which Figure 1 is atop viewof, an embodiment of, a bimetal member according; to the invention.

'Figure; 2 isaa; cross-sectional'view thereof along line 2.2, of Figure: 1.

Figure 3 illustrates a longitudinal section along line 3-:-3 in Figure 1.

Figure 4 shows an arrangement, comprising two circuits-to be switched: on and otf by means-of the bimetal switch according to the invention.

Figure; 5 showsa circuit comprising an incandescent lamp, which circuit is controlled by a bimetal switch according to-the invention;

Figure-6 illustrates aZClI'CUltUSC d-Wlih.(lllCCtlCvH indicaters forvehicles; which circuit comprises a switch according torthe invention.

Figure 7' shows acomplete lamp circuit'conrprising a bimetal switch accordingto the invention.

Figure: 8a. shows a' starting; device provided'with the bimetal strip according: to'thefinvention, in which said switchmakes contact.

Figure 8b shows the same arrangement as 'in'Figure 8a with contact interrupted; and

Figure 9 illustratesyet another arrangement ofza' bimetal switch according to the invention and a thermistor.

According to the invention for instance .a strip consisting of very thin thermo-bimetal of the mentioned thicknesses. and a'width'r of only about 6 to'8 millimeters (see Fig. 1) is stamped in such a-waythat a hardly perceptible indent 2' in the shapeofraxspherical cap of at least the diameter of the thermo-bimetal strip 1 is formed. By theprocess of stamping an'edge is'provided'about which the sheet-metal jerks intotanother shape. By this transformation a jolting of thesheet-metal is caused which is restricted to a tolerable extent by means of a hole 3 of any desired shape.

In order to prevent the parts (4 and 5) of the bimetalstrip adjoining the spherical cap 2"on both sides from slowly bending to one side when heated it is necessary to provide part 4 having a fixing hole 6with-for instance two: indentations 8 and 9 in the form of lines or grooves, preferably cxtendingfrom the edges to the centre of the hole 3 and to provide part 5 having a contact plate 7 with an indentation Ill-likewise in the form of a line or groove. According .t0Fig.'2 showing a cross-section of part 5 (Fig. l) the said part 5 is thereby slightly angularly folded in such a way that the two surfaces being angularly folded gradually pass into the indent 2 in the form of a spherical cap (see Fig. 1). The same applies'to the two indentationsof part4 (Fig; 1).

In practice it has'proved useful according to Fig. 3, showing a longitudinal section through the centre of the bimetalstrip according to Fig. l, to support the latter at the side where it is'fixedby a narrow tongue 11 placed underneath and extending approximately to the centre strip e. g. 8 millimeters wide will have a most favorable length of about 20 to 24 millimeters. Thus thermostats of small dimensions as desired for electric warming pads or for mounting in the windings of motors or transformers to prevent the latter from being overheated may be produced without difliculties. It is now possible to manufacture thermostats using the described bimetal strips which thermostats respond for instance at a temperature of 80 degrees centigrade already. They suddenly open the circuit as soon as the critical temperature is reached at a switching movement of at least 1 millimeter. It is, however, possible to reach even larger switching movements.

Strips of thermo-bimetal as described above provided with suitable heating windings may also be employed in manufacturing switching devices for switching on and off incandescent lamps or for controlling other switching processes whereas it is easily possible to obtain switching frequencies of e. g. 3 to 6 seconds on and 3'to 6 seconds off as often required for flash light, and whereat a relatively large switching movement and an instantaneous contact are desired.

The present invention represents an important progress in the field of thermo-bimetal switches over the known constructions with sliding contact. It was, for instance, impossible, owing to the distance of fractions of millimeters covered by the contact side of the bimetal spring, to control two circuits by means of such a bimetal switch, i. e. to open a circuit at a certain temperature and simultaneously to close a second circuit. This control is however-easily to be obtained when using thermo-bimetal strips according to the present invention.

In Fig. 4 an arrangement is shown by way of example in which two circuits are alternately switched on and off. The thermo-bimetal strip 1 according to the present invention is provided with a heating winding 12 which is connected in parallel with the incandescent lamp 13; On switching on a current flows across the contact 14 and simultaneously across the incandescent lamp 13 and the heating winding 12. As soonas the critical temperature of the bimetal strip is reached the contact 15 is suddenly closed, the contact 14 is interrupted, and the incandescent lamp 16 is switched on. The heating winding now being currentless cools down whereupon the whole process is repeated. f

Since a relatively weak current is required, when using thermo-bimetal strips according to the invention, to heat the same up to the critical temperature by the current of the object to be switched it is also possible to switch on and off an incandescent lamp of suflicient power consump tion according to Fig. immediately by means of such a thermo-bimetal strip. The current flows from the source across the bimetal strip 1 to the contact 14, to the incandescent lamp 13, and back to the source. If the power consumption of the incandescent lamp or any other object to be switched is insufficient it is possible, in cases where the amount of power consumption is of no concern, to provide a resistor 17 parallel to the object to be switched, said resistor having such dimensions that the total current intensity now being produced is adequate to heat the thermo-bimetal strip sufliciently. Such an arrangement 'which may be manufactured at a'low price and in very small dimensions is, for instance, suitable for the production of flash light in direction indicators of motor vehicles. A further advantage of this arrangement is the fact that owing to the considerable initial tension of the bimetal strip such switching devices are practically insensible against normally occurring vibrations. Inthis A arrangement the instantaneous contact and the relatively large switching movement also prevent the contacts from being prematurely burnt.

Fig. 6 shows by way of example the instantaneous switch described above used in connection with a direction indicator for vehicles consisting of flash signal lamps. In the illustration reference B indicates the bimetal strip which actuates a rest contact K1 and a working contact K2. Reference S indicates the commutator switch in its neutral position. The lamps L1, L2, R1 and R2 are to indicate the change in direction by giving flash signals. KL is a control lamp. When turning the switch S to position K1 the current flows from plus via B and K1 to L1 and L2, and from thereon to minus whereby the bimetal strip B is heated and changes from position K1 to position K2. The lamps L1 and L2 go out and the control lamp KL flashes up. The current flowing across the control lamp is weaker than that flowing across the direction indicator lamps L1 and L2 and is not suflicient to maintain the bending of the bimetal. The bimetal returns to its initial position, the lamps L1 and L2 flash up whereas the control lamp KL goes out. The process is then repeated.

The bimetal conducting the current may also be replaced by a bimetal strip heated by an additional winding. Instead of using two direction indicating lamps in each case one or several lamps may be employed. If the bimetal switch is used as flash signal apparatus employing a control lamp this control lamp fails to flash up .or its flash period is distinctly altered in case the arrangement is disturbed.

In the same way as the flash signal apparatus for vehicles described above such flash signal apparatus may also be used for other purposes, e. g. for advertising and warning flash signals, etc.

A further preferred field of application are devices for igniting and operating gas discharge lamps, particularly low voltage luminescence lamps. Gas discharge tubes, above all low voltage luminescence lamps, are mainly ignited by so-called glow starting devices. The disadvantages of such starting devices as, for instance, flickering when switching on, cold starting of the lamps, short duration, etc. are well known. Therefore a considerable number of other kinds of starting devices have been developed working either electro-magnetically or thermically which, however, have proved to be unsatisfactory, partly because of the high costs of manufacture, partly because the fitting-in of a special choking coil with tapping or auxiliary winding is necessary. When using thermoelectric starting devices with a sliding contact a relatively rapid burning of the contacts and thereby a shortening of the duration is caused.

According to the invention the starting device is controlled by the thermo-bimetal switch in such a way that the above-mentioned drawbacks are avoided. This starting device as well as a glow starting device can be inserted in any arrangement which has so far been operated by glow starting devices. An additional permanent power consumption amounts to only about 0.5 watt which is of no importance when using, for instance, a 40-watt lamp. A very simple construction having only one switching device in the form of a snap contact guarantees long duration at very low cost of production.

The working manner of the starting device is to be seen from Figures 7-9. Fig. 7 shows the complete switching of a lamp circuit. The line voltage, e. g. 220 volt, is connected to the terminals 21 and 22. The starting device is in the position as illustrated. A current flows across the choking coil 23, the two heating spiral filaments 24 and 25 of the gas discharge lamp '26 at contacts 2-7 and 28 of the starting device 29. 'The contact 32/33 is open. The high-ohmic winding 35 of the normal non-snapping bimetal spring which is to be formed in a suitable way is supplied with almost the complete line voltage. The spring 34 of thermobimetal is heated and bends out in the direction as illustrated. Thereby the pre-loaded thermo-bimetal spring 31 in the form of a snap spring is released. The contact 32/33 is closed and a strong current flows through the low-ohmic heating winding 30. The electrodes 24 and 25 are heated. During this period the drag spring 34 cools down since the voltage between 27 and 28 has decreased to a few volts due to the flow of current across the low-ohmic winding 30. The spring then bends back to its initial position according to Fig. 8a. The bimetal snap spring 31 now heated returns to its initial position according to Figs. 7 and 8!; simultaneously interrupting the contact 32/33 whereby the heating winding 30 becomes currentless. The rush of induction current being formed in the choking coil 23 ignites the pre-heated lamp in the known manner.

The bimetal drag spring (bolt) prevents the cooleddown snap spring 31 from snapping back. The ignited lamp having a line voltage of e. g. 220 volts is supplied with a voltage of about 100-110 volts which is not sufficient to heat the drag spring 34 to such an extent that the snap spring 31 is released. The output at the winding 35 amounts to only A of the output being formed at 220 volts. In case of a wrong start the high-ohmic winding 35 is provided again with the full voltage and heats the spring 34 to such an extent that the spring 31 is again released. The contact 32/33 is closed and the process is repeated.

Fig. 8a shows the starting device the contact 32/33 being closed. The bimetal spring 31 is heated.

The arrangement of the individual constructional members may be varied. Stopping and adjusting devices may also be arranged if necessary.

Fig. 9 shows a different arrangement in which the low-ohmic winding 30 is arranged not on top of but near the snap spring 31 whereas the high-ohmic winding 35 of the drag spring 34 consists of a carbon layer resistor or a resistor of any other suitable material. In this case it is of advantage to employ a so-called thermistor.

An interference protection condenser is to be provided in the known manner.

The drag spring 34 may also be controlled by the lamp current and a tapped choking coil respectively an auxiliary winding is required for this purpose.

The drag spring 34 may also be controlled electromagnetically by lamp current or voltage. The bimetal spring 31 might be replaced according to the invention by an electromagnetically acting switching device working with retardation which is locked by the spring 34 as described above. The construction with thermo-bimetal springs being cheaper and taking up less room will, however, be preferred in practice.

The whole arrangement is to be placed in a suitable housing and may easily be arranged in such a way that a housing of conventional construction employed with glow starting devices and comprising the usual contact parts may be used.

With; all electrical switches suflicient contact-point pressure is required which is guaranteed by the shaping of the bimetal strip even when using metal strips of the minimum thickness mentioned above.

What we claim is:

1. A thermobimetal instantaneous switch for flash sig nal apparatus and luminescence lamps, and adapted to serve as a thermostat in electric warming pads, comprising an elongated, flat thermo-bimetal strip adapted to be fastened at one end and having one flat surface developed as contact surface at the other end of said strip, contact means mounted on said thermo-bimetal strip at the fiat surface opposed to said contact surface and adjacent said other end, said bimetal strip having a shallow recess in the form of a flat spherical cap in the central region of said strip, the diameter of said recess being at least equal to the width of the strip, the portion of the strip between said recess and the fastened strip end being provided with two folds extending from the corners at the fastened end of said strip toward the center of said recess, and the portion of said strip between said recess and the contact end of said strip being provided with a central fold in longitudinal direction, said strip being provided with a central hole at the center of said recess.

2. An instantaneous switch as described in claim 1 wherein the thickness of said bimetal strip is below 0.15 millimeter.

3. An instantaneous switch as described in claim 1 further comprising a narrow tongue mounted at the portion of said bimetal strip between its fixed end and said recess, said tongue extending from said fixed end approximately to the center of said central hole.

4. Instantaneous switch according to claim 1, characterized in the provision of a resistor connected in parallel to the incandescent lamp or any other electrical apparatus from which resistor a current required for heating the bimetal strip to its critical temperature results.

5. Instantaneous switch according to claim 1, characterized in that two circuits are switched alternately by this switch.

6. Instantaneous switch according to claim 1, in particular for flash signal apparatus, characterized in that a working and a rest contact are provided whereby flash signals and a control light are switched on alternately and the control lamp fails to flash up or its flash period is distinctly altered in case the arrangement is disturbed.

7. Instantaneous switch according to claim 6, characterized in that the bimetal strip is provided with a particular heating winding.

8. Instantaneous switch according to claim 1, especially for igniting and operating gas discharge lamps, in particular low voltage luminescence lamps, characterized in that the said witch is provided with a pre-loaded bimetal snap spring having a heating winding and contact plates and is stopped in its open position or its rest position by a bolt which on closing the circuit releases the pre-loaded bimetal snap spring so that the electrodes of the gas discharge lamp are preheated by the contact now closed, and after heating of the electrodes the heating current is interrupted by the bimetal snap contact whereby the lamp is ignited.

9. Instantaneous switch according to claim 1, characterized in that the bolt consists of a thermo-bimetal spring with a mounted-on heating winding to which practically the full line voltage is supplied when the lamp is not ignited and by which the bimetal spring is heated to such an extent that the latter bends out and releases the pre-loaded bimetal snap spring thus closing the contact and maintaining the bolting when the lamp is ignited.

10. Instantaneous switch according to claim 1, characterized in that the bolt is heated by a high-ohmic resistor, e. g. a carbon layer resistor or a thermistor.

11. Instantaneous switch according to claim 1, characterized in that an electromagnetically controlled bolt is used the control of which is preferably effected by the voltage at the gas discharge lamp.

l2. Instantaneous switch according to claim 1, characterized in that the bimetal snap spring may be replaced by an electromagnetically acting switching device working with retardation which device is locked by a bolt.

References Cited in the file of this patent UNITED STATES PATENTS 2,266,537 Elmer Dec. 16, 1941 2,528,756 Kaser Nov. 7, 1950 2,707,216 Farison Apr. 26, 1955 2,715,168 Mertler Aug. 9, 1955

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