| JP3756700 | THERMAL PROTECTOR |
| JP2754335 | MANUFACTURE OF FUSE SPRING BUILT-IN THERMOSTAT |
| WO/1990/009672 | IMMERSION HEATERS |
MARGARYAN, Hayk (Mananjyan Str, 1-17 Yerevan, 0006, AM)
Claims
1. Bimetallic thermal relay comprising a housing with metallic cup-shaped bottom part and electrically insulating cover, including two fixed contacts attached to ends of electrodes with current-taking terminals secured in the cover body symmetrically to the cover center and at equal distances, a support member either secured in the central part of cover or manufactured as an integral part of the cover and consisting of a guiding part and an aligning part arranged in a general axis and adjacent to each-other, forming a support area normal to the general axis, implemented for example as a cylinder with a protrusion normal to the internal surface of cover, a current-conducting contact bridge, having a central port and carrying elements in the peripheral part of the side opposite to contacts, a thermally sensitive bimetallic snap-action disk having a hole in the dome center and a compression spring implemented as a member with a supportive central part and a peripheral part pressing the contact bridge to the fixed contacts, with the guiding part of support member passing through the central port of the contact bridge, positioned in a way allowing translation motion, the aligning part of support member passing through a hole in the dome of the thermally sensitive bimetallic snap-action disk, mounted in a way allowing free positioning in the space bounded by the carrying elements, contact bridge and support area, characterized by that the spring is mounted between the contact bridge and thermally sensitive element, with the central part of the compression spring being secured on the support area of support member. 2. Bimetallic thermal relay of claim 1 characterized by that the aligning part of the support member is implemented as a rod aligned and attached to the guiding part, the rod having a cylinder head securing the central part of the compression spring to the support area. |
Bimetallic thermal relay
Technical Field
The present invention relates generally to electrical engineering, and more particularly to development of miniature bimetallic thermal relays. The invention may be used, for example, for protection against overheating of windings in motors, transformers, and other electrical devices. Known are bimetallic thermal relays in which bimetallic plates are used as thermally sensitive elements for temperature control inside the electrical devices, by enacting a switching mechanism which opens the circuit supplying power to the said devices when their temperature exceeds the admissible value, or closes the same circuit after cooling. Background Art Known are small bimetallic thermal relays with central position of contacts [1-10], contained in a housing with a metallic cup-shaped bottom part used as a current conductor to a movable contact, and a cover having a fixed contact secured in the center thereon. The bottom part and the cover are fastened together through an electrical insulator, forming thus a housing inside which the thermally sensitive switching mechanism is mounted. The thermally sensitive switching mechanism comprises a movable contact attached to the end part of a motion-transfer element, having a snap-action thermally sensitive bimetallic disk mounted thereon and one, or two compression springs (like in [2]), pressing the movable contact against the fixed contact and providing electrical connection of housing and movable contact.
The main disadvantage of the prior art is non-observance of the electrical safety regulation by using the housing as a current conductor to a movable contact. Various caps made of dielectric materials, when used for insulation, affect the operation characteristics of the thermal relays. A relay becomes more inertial, creating a permanent delay of the switching action when the critical temperature is reached in the controlled device. The attempts to remove this defect by applying various thermal bridges made in form of current-shunting resistors, complicate the relay structure, manufacturing of its parts and overall assembly, as well as critical temperature setup.
Known are miniature bimetallic thermal relays [11- 13] having two fixed contacts symmetrically positioned relative to the cover center and secured thereon, The interaction between the contacts is provided by an electrically conductive contact bridge pressed against the
fixed contacts by the central part of a compression spring the peripheral part of which is secured to the housing. The compression spring and the contact bridge are fastened together by a carrier element, supporting the dome of bimetallic thermal disk and allowing its free positioning.
Known thermal relays possess a number of shortcomings, such as complicated design, assembly and adjustment procedures. These complications arise in high-accuracy manufacturing of the housing hollowness, fixation of the compression spring periphery in the housing, with observance of the designed dimensional chains and provision of the required contact gap. Also the housing in the prior art [11] stays alive in the closed state of the contacts.
The closest prior art is the bimetallic thermal relay [14] selected as a prototype to the present invention.
The bimetallic thermal relay prototype comprises a housing with a cup-shaped bottom part fastened together with a cover made of electrically insulating material. The housing contains a thermally sensitive switching mechanism and two fixed contacts attached to the internal ends of electrodes secured in the cover body symmetrically and at equal distances from the center. The external ends of electrodes have current supply terminals attached thereon. The thermally sensitive switching mechanism comprises a support member, a conductive contact bridge with carrier elements provided thereon, on the side opposite to contacts, a bimetallic thermally sensitive snap-action disk, and a compression spring made in form of an element with supported central part and periphery pressing the contact bridge to the fixed contacts. The support member is positioned in the cover center, between the contacts, and consists of guiding and aligning parts arranged on the same axis and adjoining each other, forming thus a support area. A possible embodiment is in form of a cylinder with protrusion normal to the internal surface of cover. The current-conducting contact bridge together with carrying element is positioned on the guiding part of support member, allowing translation thέreon. The contact bridge with carrying elements has a preferred embodiment in form of a washer with two protrusions located on the opposite ends of diameter and bent inwards and normally to the washer surface. The aligning part of the support member passes through a hole in the dome of the thermally sensitive bimetallic disk, freely positioned in a space bounded by internal surfaces of carrying elements, contact bridge, and support area. The central part of the compression spring rests on the housing bottom, while the peripheral part interacts with the external surface of carrying elements, by pressing the contact bridge to the fixed contacts.
Prototype disadvantages are complicated structure and assembly technology, as well as absence of complete galvanic decoupling, which can cause electric shock.
The mentioned disadvantages are due the following structural approaches:
Reliable functioning of the relay is determined by the quality of translation motion of the external part of the contact bridge. Namely, the gap between the contacts and the bridge surface must be the same all the time, in order to escape the possible sticking, chatter and non-uniform wear of the contacts, which are able to cause the relay failure. In the prior art, the contact bridge is pressed to contacts by a spring interacting with the carrier elements surface, the number of such elements being usually two and which are located symmetrically to the cover center. Translation motion of the contact bridge external surface maintaining interaction with the surface of carrying elements is possible either by means of a special high-precision spring, or by increase of the carrying elements number. Both these options result in complicated structure of thermal relay, with the second additionally requiring accurate positioning of the bimetallic disk.
The prior art structure makes impossible step-by-step control and adjustment of parameters in process of assembly. Testing of the operation parameters is possible only after complete assembly and sealing of the relay housing. Therefore manufacturing of such relays is possible if high-precision parts and complex assembly procedure is used.
Since the compression spring is located between the contact bridge and the bottom part of the housing, the latter stays alive in the closed state of the contacts. Thus the galvanic decoupling is incomplete and electrical safety norms are violated. Disclosure of the Invention The objectives of the present invention are to simplify the thermal relay structure and assembly procedure, as well as provide electric safety.
In order to reach these objectives, the following modifications were introduced in the prior art thermal relay comprising a housing with a cup-shaped bottom part fastened together with a cover made of electrically insulating material, containing two fixed contacts attached to the internal ends of electrodes secured in the cover body symmetrically and at equal distances from the center, with the external ends of electrodes having current supply terminals attached thereon, and a thermally sensitive switching mechanism comprising a support member positioned in the central part of cover and consisting of the same-axis and adjacent guiding and aligning parts, shaped for example as a cylinder with protrusion normal to the internal surface of cover, a conductive contact bridge with carrier elements provided thereon, on the side opposite to contacts, positioned on the guiding part of support member and allowing translation motion thereon, a bimetallic thermally sensitive snap-action disk mounted in a way allowing its free positioning in the space bounded by internal surfaces of the carrying elements, contact bridge and support area surface, and retained inside the space by the aligning part of support member
passing through a hole in the disk dome, and a compression spring having a supporting central part and peripheral part pressing the contact bridge to fixed contacts, namely:
The compression spring is positioned between the internal surface of contact bridge and the thermally sensitive element, the central part being secured on the supporting area of the support member, while the peripheral part presses the contact bridge to the fixed contact by interacting with the internal surface of the contact bridge.
The proposed thermal relay is also characterized by that the aligning part of the support member is implemented in form of a rod with cylindrical head securing the central part of the supporting spring to the support area. Mounting of the spring having its central part secured to the support area of supporting member, while the peripheral part of the spring interacts with the internal surface of the contact bridge, between the contact bridge and the thermally sensitive elements, makes possible the following:
• Provides complete galvanic decoupling, i.e. electrical safety of the relay, because electrical contact of the housing with the current conducting elements has been eliminated;
• Makes simpler the relay structure, due to substitution of a special high-precision spring by a simple one. Indeed, in the preferred embodiment the peripheral part of the spring interacts with all internal surface of the contact bridge. As a result, the compression force is uniformly spread over all surface, providing translation motion of the contact bridge by acting at least in three selected areas of the surface. Therefore the simple spring in form of a washer with multiple symmetrically arranged petals solves the task;
• Makes simpler the assembly procedure, since in the preferred embodiment the relay housing has no mechanical connection with the thermally sensitive switching mechanism, being assembled as a separate module with a step-by-step control and adjustment of functional parameters and then secured to the cover.
The purpose of this invention is further explained by means of a preferred embodiment. Fig. 1 shows the bimetallic thermal relay according to the present invention in a sectioned side view, having its contacts in the closed state; Fig. 2 is a section along the I - I plane of the bimetallic thermal relay shown in Fig. 1 ; and Fig. 3 is the bimetallic thermal relay shown in Fig. 1, but having its contacts in the open state.
The bimetallic thermal relay comprises a housing having a cup-shaped bottom part 1 made of a metal, with a peripheral collar 2, and a cover part 3 made of an electrically insulating material, resting on the collar 2 and fastened to the bottom part 1 to form a housing. The housing includes two fixed contacts 4, a support member consisting of a guiding part 5 and an aligning part 6, a conductive contact bridge 7 with carrier elements 8, a bimetallic snap-action disk 9 and
a compression spring 10. The said fixed contacts 4 are attached to the internal ends of electrodes 11 secured in the body of cover 3 oppositely and at equal distances from its center. The external ends of electrodes 11 are attached to current-taking terminals 12. The said support member may be implemented as an integral part of the cover 3, representing a protrusion in the central part of the cover, shaped as a cylinder and having a collar thereon. The support member itself may be integral or composite. In this preferred embodiment, a composite support member is described. The guiding part 5 of support member is executed as a cylinder with an axial port is mounted in the central part of cover 3 (the guiding part 5 may be implemented as an integral part of the cover 3, in form of cylindrical protrusion in central part of cover 3. The aligning part 6 of the support member is executed as a cylinder having radius smaller than the radius of the guiding part cylinder 5 and attached to the latter by a rod 13. A contact bridge 7 is provided, shaped as a washer having two protrusions on the opposite ends of diameter bent inwards at a right angle and carrier elements 8, mounted on the guiding part 5 of support member allowing translation thereon. The compression spring 10 has its central part secured to the supporting area of the support member (the end face of cylinder of the guiding part 5) by a rod 13 passing through a port and by aligning part 6. The peripheral part of compression spring 11 presses the contact bridge 7 to fixed contacts by interacting with the internal surface (opposite to surface of contacts 4) of the contact bridge 7. The thermally sensitive bimetallic snap-action disk 9 is freely mounted inside a space bounded by the carrier elements 8, compression spring 10, and aligning part 6 passing through a port in the dome of thermally sensitive disk 9. The cover 3 is sealed by a compound 14.
Assembly of the relay shown in Fig. 1 includes the following operations. The contact bridge 7 is fitted over the guiding cylinder 5, executed as a protrusion of cover 3, in a position closing the contacts 4. The compression spring 10 is fitted over the end of guiding cylinder 5, so that the hole in the central support part of the spring 10 is aligned with the axial port of cylinder 5, while the peripheral part rests on the internal (opposite to contacts) surface of the contact bridge 7. The thermally sensitive bimetallic disk 9 is introduced between the two carrying elements 8 of contact bridge 7 and the compression spring 10 until the hole in the dome of disk 9 is aligned with the axial port of cylinder 5; in this case the periphery of disk 9 is located between two carrier elements 8. The rod 13 having a cylindrical head 6 is passed through the holes in the disk dome and spring, inserted in axial port of the cylinder 5 and deepened inside the port, up to complete fixation of the spring 10 support part by a cylindrical head 6, and fastened together with the cylinder 5. The assembled module is adjusted and tested for proper functional parameters. The ready module is inserted in the housing bottom part 1 and supported there by the collar 2. The cover 3 is expanded in the housing bottom part 1 sealed by a compound 14.
The assembly procedure is somewhat different in the case when the guiding part 5 and aligning part 6 of the support member are manufactured as an integral part. After mounting the contact bridge 7, the central support part of the spring 10 is secured upon the support area (the surface formed by the contacting end faces of guiding cylinder 5 and aligning cylinder 6), by any known method, e.g. glued upon, or sealed in the special groove. The contact bridge 7 is cleared off the contacts 4 for a distance required for passing of the thermally sensitive disk 9 over the end of aligning cylinder 6, until the hole in the disk 9 is coincident wit the end of aligning cylinder 6. Then the clearance is eliminated, resulting in that the spring 10 presses the contact bridge 7 to the contacts 4 while the aligning cylinder 6 is positioned inside the hole of the disk 9. This ends the module assembly.
The described assembly procedure is easy and it confirms the relation between the introduced characteristic features and embodiment of the invention.
The work process of the bimetallic thermal relay according to the present invention is as follows. The compression spring 10 presses the contact bridge 7 to the contacts 4 as the temperature is increased up to the critical value. During that process, the bimetallic snap-action disk 9 slowly changes its bending. Since the disk 9 is freely positioned in the space, the slow change of bending does not result in generation of interaction forces with the carrier elements 8 of the contact bridge 7. The spring 10 presses the contact bridge 7 to the contacts 4 with the same force as before. When the upper critical temperature is reached, the thermally sensitive disk 9 changes abruptly, with a snap, its shape to the opposite one. The dome of the disk 9 is pressed to the support part of the spring 10, while the peripheral part of disk 9 is pressed to the inside-bent parts of the carrier elements 8, generating thus the forces performing work against the pressure force of the spring 10. As a result, the contact bridge 7 is cleared off the contacts 4 disconnecting the latter. Further growth of the temperature does not affect the configuration of interacting members, so that the contacts preserve their disconnected state.
When the temperature goes down in cooling process, before the lower critical temperature is reached, the contacts remain open. As soon as the lower critical temperature is reached, the thermally sensitive bimetallic disk 9 abruptly inverts its shape with a snap. The dome of the disk 9 is cleared from the support surface, while its peripheral part does not press on the carrier elements 8. The thermally sensitive disk 9 is freely positioned in its location space. The compression spring 10 shifts the contact bridge 7 and presses it to the contacts 4 thus closing them.
References
1. German Patent JNb 2917482, Int. Cl. 7 H01H37/54; H01H71/16,1980.
2. German Patent JNb 3122899, Int. Cl. 7 H01H37/54,1982.
3. German Patent JNb 4142716, Int. Cl. 7 H01C7/02; H01H37/54; H02H3/08,1993.
4. German Patent JNb 4428226, Int. Cl. 7 H01H37/74; H01H37/54,1995.
5. German Patent JNb 19514853, Int. CL 7 H01H37/74,1996.
6. Russian Federation Patent JNb 2075790, Int. Cl. 7 H01H37/74,1997.
7. German Patent JNb 19545997, Int. Cl. 7 H01H37/02; H01H37/54; H01H37/04,1997.
8. German Patent JN-0 19545998, H01H37/54; Int. Cl. 7 H01H37/74, 1997.
9. German Patent JNb 19604939, Int. Cl. 7 H01H37/74; H01H37/54,1997.
10. German Patent JNb 19623570, Int. Cl. 7 H01H37/74; H01H37/54,1998.
11. German Patent JNb 2644411, Int. Cl. 7 H01H37/52,1978.
12. US Patent JNb 5973587, Int. Cl. 7 H01H37/14; H01H37/54,1999.
13. US Patent JNb 6100784, Int. Cl. 7 H01H37/74; H01H37/52; H01H37/54, 2000.
14. German Patent JNb 2143652, Int. Cl. 7 H01H37/54,1973.
Next Patent: LIQUID CONTAINER, ESPECIALLY FOR DRINKS OR MOUTHWASH