GB2203245A

GB2203245A - A bimetallic circuit element for a lock

Info

Publication number: GB2203245A
Application number: GB08806688A
Authority: GB
Inventors: Karl-Heinz Buttner; Kurt Raschkowski; Hermann Petlinski; Hermann A Bartels
Original assignee: Ymos AG Industrieprodukte
Current assignee: Ymos AG Industrieprodukte
Priority date: 1987-03-24
Filing date: 1988-03-21
Publication date: 1988-10-12
Anticipated expiration: 2008-03-21
Also published as: FR2613124B1; DE3709660C2; IT1216178B; FR2613124A1; GB2203245B; DE3709660A1; IT8819882A0; GB8806688D0

Description

4 1 1 A BIMETALLIC CIRCUIT ELEMENT AND A LOCK INCORPORATING SUCH AN

ELEMENT 2203245 This invention relates to a bimetallic circuit element and to a lock incorporating such an element.

Bimetallic strip elements are known which normally comprise two metal strips with different coefficients of heat expansion (e.g. steel and brass) which are welded together. When they are heated the two metal strips expand to a different extent, so that the element curves towards the side of the metal strip which has least expansion. This curving movement is used e.g. to control electric contac ts, so bimetallic strip elements are is employed in many different types of temperature controls or used as bimetallic releases in protective switches of electric motors or as switching members for blinker switches and the like.

A disadvantage of bimetallic strip elements is that they only change shape slowly because they are heated gradually. Hence no abrupt switching process is possible. To obtain quick switching operations with a bimetallic strip element it is further known to combine bimetallic strips with elastic springs or magnets which produce a switching jump when a defined change in the shape of the bimetallic strip element is reached.

The use of such springs or magnets results in more complication and there is thus a need for a generally improved bimetallic circuit element which does not use such springs or magnets but which provides adequate switching forces.

According to one aspect of the present invention there is provided a bimetallic circuit element having a bimetallic catch portion of slightly curved cross-section made from bimetallic material and at least one rigid arm portion joined to the catch portion.

When the bimetallic catch portion is heated or cooled it first moves slowly but then suddenly jumps out of one stable position into a second, similarly stable position according to the temperature. The arm portion joined to the catch portion is rigid, so that the force released when the catch portion changes its shape can be transmitted to the maximum extent.

The length of the arm- portion influences the effective switching path, particularly if the free end of the arm portion also acts as a switching contact.

4 A^ 2 In order to suppress the slow or creeping movement which takes place to a slight extent before the switching jump, means may be provided to limit the path of the rigid arm portion, e.g. in the f orm of stops.

The catch and arm portions preferably are made integrally of bimetallic material, and the arm portion preferably has a shaped non- linear cross-section, is elongated in form with a longitudinal rib therealong andlor has angled lateral edge regions, so as to have the required rigidity to prevent the temperature change in the bimetallic material from causing changes in the shape of the arm portion. Instead of the catch and arm portions being made integrally, it is also possible for them to be produced from a bimetallic catch portion and a separate rigid arm portion.

According to another aspect of the present invention there is provided a lock for an electrical appliance, which lock includes a lock housing securable to one part of the appliance, a closure member securable to another part of the appliance for releasable engagement with the lock housing via a movable retaining elemeht in the lock housing, and a bimetallic circuit element as hereinbefore described, wherein the rigid arm portion of the bimetallic circuit element acts as a drive for a movable securing element which is movable into and out of the path of movement of the movable retaining element engageable by the closure member, and wherein the bimetallic circuit element is operable, when the lock is operatively attached to an electrical appliance, to control an electric circuit of said appliance.

For a better u6derstanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings. in which:

Figure 1 is a plan view to an enlarged scale of a bimetallic circuit element of the invention, Figure 2 is a side elevational view of the bimetallic circuit element of Figure 1.

Figure 3 is a plan view of an open lock for a washing machine with bimetallic circuit element of Figures 1 and 2 in the OPEN position, Figure 4 is a view similar to that of Figure 3 but on a smaller scale and in the CLOSED position, Figure 5 is a sectional view taken along the line V-V in Figure 4, Figure 6 is a plan view of a detail of a lock according to a different v 1 1 3 is embodiment of the invention, and Figure 7 is a plan view of a detail of a further form of lock.

As shown in the accompanying drawings a bimetallic circuit element 1 of the invention has a bimetallic catch portion 2 of slightly curved crosssection material, and at least one rigid arm portion 3 joined to the catch portion 2.

As shown in Figures 1 and 2, the catch portion 2 and arm portion 3 are preferably made integrally of the same bimetallic material. The catch portion 2 is slightly concave, as can be seen particularly from Figure 2.

The elongated arm portion 3 has a profiled or shaped, non-planar cross section andlor a longitudinal rib 4 therealong to give it the necessary rigidity for an integral construction. The arm portion 3 should desirably be longer than the curved catch portion 2, and it may have a substantially rectangular or otherwise shaped outline. For many cases it is sufficient for the lateral edge regions 5, 6 of the arm portion 3 to be angled in order to give the necessary rigidity.

The circuit element 1 has retaining apertures 7, 8 in or in the region of the catch portion 2, to fix it to a machine. These apertures may, for example, be near the corners of the catch portion 2 remote from the arm portion 3.

Figure 3 shows an application of the bimetallic circuit element 1, in a lock 11 for an electrical appliance such as a household washing machine.

The lock 11 has a lock housing 13 securable to the one of the machine body or door and a closure member 12 securable to the other of the machine body or door. The member 12 is held in the closed position by mechanical and electrical switching and securing elements of the lock 11.

As can be seen from Figure 3, the lock 11 for the washing machine comprises the housing 13 in which a retaining element in the form of a detent slide 14 is movable andlor displaceable under the biassing action of a compression spring 15, preferably in the opening direction. A securing element in the form of a blocking slide 16 is movable transversely into the path of the detent slide 14. The slide 16 is controlled by the bimetallic circuit element 1, which is connected to it by its arm portion 3. For this purpose the blocking slide 16 has two blades 17 and 18, with the free end 19 of the arm portion 3 of the element 1 being located between the blades 17 and 18.

A 4 When the bimetallic circuit element 1 is switched over, the free end of the arm portion 3 moves the blocking slide 16 from the open position in Figure 3 to the locked position in Figure 4. In this embodiment the arm portion displaces the slide 16 into a recess 20 in the detent slide 14, thereby arresting it. The bimetallic element 1 swings into the Iccking position when current flows through it and through a PTC resistor 21 attached to it, thus heating the element 1. The use of a PTC resistor 21, with an electrical resistance which varies with temperature, is particularly appropriate for heating the catch portion 2 of the element 1 as in the embodiment of Figure 3. The resistor 21 is heated by current flowing from a contact lug 20a, first through the catch portion 2, then through the resistor 21 on the catch portion 2, and finally through a contact lug 22. When the current is switched off and the bimetallic element has cooled, it moves back into the Figure 3 open position, pulling the blocking slide 16 out of the position in which it was securing the detent slide 14.

Current can further flow for a limited time from the catch portion 2 through the arm portion 3 and, via a contact stud 23a on the arm 3 and a contact 23, to a further contact lug 24. The contact 23 is mounted rigidly, and the flow of current to the contact 23 is interrupted when the circuit element 1 is heated and springs out of its open Figure 3 position into the other position. The contact stud 23a on the arm portion 3 of the element 1 is then separated from the contact 23 and the flow of current at that point is interrupted. Another live connection is established simultaneously between another rigidly mounted contact 25 and a movable contact element 26, also connected -to the live contact lug 20a. The contact 25 also has a lug 27.

Switching over of the movable contact element 26 'takes place simultaneously with the separation of the arm portion 3 of the element 1 from the contact 23 and the displacement of the blocking slide 16 by the element 1. A forked projection 28 on the slide 16 engages round the free end of the movable contact 26 and swings it into its two operative positions.

In the open position shown in Figure 3 the washing programme of the washing machine may for example still be de-energized so that the machine cannot carry out any washing functions. Only when the slide 16 assumes its Figure 4 securing or closed position and the detent slide can no longer be moved manually into its open position does the operating current flow through the movable contact element 26 to the contact 25 and from there to -2 7 t the contact lug 27.

As soon as the washing operation is over and no more heating current is flowing through the contact lug 20a and thus through the PTC resistor 21, the catch portion 2 cools down and springs back de-energized into the inoperative position shown in Figure 3. It thus moves the blocking slide 16 to its open position and also opens the contact 25, so that incorrect manual switching measures will have no effect.

The PTC heating resistor 21 cools gradually when the current has been disconnected, In the bimetallic element 1 this produces a time lag for the switching and control process (the switching jump) after the time when the current is disconnected. The element 1 therefore only pulls the blocking slide 16 into the clearing position considerably later, i.e. with a time Jag. This delay function of the element 1 can also be affected by various parameters, e.g. the thickness of the bimetallic material, the degree of concavity of the catch portion or the nature of the PTC resistor 21 and its mass, so that the switching process can optionally be delayed several seconds after the time when the current is disconnected.

The blade 18 which is in contact with the free end 19 of the arm portion 3 of the element 1 is part of the forked projection 28 which swings the movable contact element 26. The blade 18 also acts as an insulator between the free end 19 of the arm portion 3 and the movable contact element 26.

The lock housing 13 is closed by a cover 30 shown in Figure 5. The closing member 12 engages through an opening 31 in the cover 30. The shape of the member 12 and detent slide 14 ensure that the member 12 cannot get out of the opening 31 when the detent slide 14 is locked by the blocking slide 16.

The two locks 11 shown in Figures 6 and 7 have one adjusting cam 33 (Figure 6) or two adjusting cams 33, 34 (Figure 7) in addition to the arrangement shown in Figure 4. The- cams 33 and 34 are respectively provided so that the bearing 35 of the element 1 and the position of the fixed contact 25 can be adjusted and fixed. The cams are rotatably mounted components with slotted heads, so that they can be adjusted in position with a screw driver.

The invention is not restricted to the examples illustrated in the drawings and other embodiments are possible.It may for example be t 6 appropriate to limit the path of the element 1 so that the creeping movement does not come into effect at the arm portion 3 which is used for switching. This limitation can be obtained by making the distance between the stationary contact 23 and the stationary contact 25 less than the maximum possible deflection or jump of the free end 19 of the arm portion 3.

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Claims

1. A bimetallic circuit element having a bimetallic catch portion of slightly curved cross-section made from bimetallic material and at least one rigid arm portion joined to the catch portion.

2. A circuit element accor.ding to Claim 1, wherein the catch portion and arm portion are integral and made from the same bimetallic material.

3. A circuit element according to Claim 1 or Claim 2 wherein the arm portion has a shaped non-planar cross-section.

4. A circuit element according to any one of Claims 1 to 3, wherein the arm portion is enlongated in form with a longitudinal rib therealong.

5. A circuit element according to any one of Claims 1 to 4, wherein the arm portion has angled lateral edge regions.

6. A bimetallic circuit element substantially as hereinbefore described and as illustrated in the accompanying drawings.

7. A lock for an electrical appliance, which lock includes a lock housing securable to one part of the appliance, a closure member securable to another part of the appliance for releasable engagement with the lock housing via a movable retaining element in the lock housing, and a bimetallic circuit element according to any one of claims 1 to 6, wherein the rigid arm portion of the bimetallic circuit element acts as a drive for a movable securing element which is movable into and out of the path of movement of the movable retaining element engageable by the closure member, and wherein the bimetallic circuit element is operable, when the lock is operatively attached to an electrical appliance, to control an electric circuit of said appliance.

8. A lock according to claim 7, wherein the retaining element is a detent slide and that the securing element is a blocking slide movable transversely to the detent slide.

a

9. A lock according to Claim 8, wherein the blocking slide is connected to the arm portion of the bimetallic circuit element.

10. A lock according to Claim 9, including a heating resistor with a positive temperature coefficient (PTC) on the catch portion of the bimetallic circuit element.

11. A 1 ock. according to Claim 10, wherein the arm portion of the bimetallic circuit element and a movable contact member are connected to 10 the blocking slide and wherein two stationary spaced apart contacts are provided for contact by the contact member.

12. A lock according to Claim 11, wherein the path of a free end of the arm portion of the bimetaMic circuit element is limited.

13. A lock according to claim 12, wherein the path limiting means is the two stationary contacts the distance between which contacts is less than the maximum possible deflection or jump of the free end of the arm portion.

14. A lock according to claim 10, wherein the heating re sistor on the catch portion is operable to provide a delayed switching process with gradual cooling of the bimetallic circuit element.

15. A lock for Ein electrical appliance substantially as hereinbefore 25 described with reference to Figures 3 to 5, Figure 6 or Figure 7 of the accompanying drawings.

Publithed 1988 at The Patent Office, State House. C6N1 HoIbom Iondon W01B 4TP. Purther copies may be obtained &om The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BRS 3RD. Printed by Multiplex techniques ltd St Mary, Kent, Con- 1187.