WO2001001430A1

WO2001001430A1 - Switch mechanism with snap acting spring

Info

Publication number: WO2001001430A1
Application number: PCT/US2000/017261
Authority: WO
Inventors: Edward L. Stern; Brian D. Speldrich; Adam M. Ward; Harry C. Lantau
Original assignee: Honeywell Inc.
Priority date: 1999-06-25
Filing date: 2000-06-22
Publication date: 2001-01-04

Abstract

A snap action spring assembly for use in a switch is disclosed. The spring assembly includes first terminal and a flexible, electrically conductive flat spring. The flat spring has a fixed end attached to the first terminal and a free end defining a movable contact operable between normal and actuated positions. The flat spring includes an actuation point adapted to engage a mechanical actuator associated with the switch. An intermediate support is positioned between the fixed and free ends of the flat spring, and a second electrically conductive terminal defines a first stationary contact positioned to engage the movable contact in the actuated position. A third electrically conductive terminal defines a second stationary contact spaced from the first stationary contact and positioned to engage the moveable contact in the normal position. A bent spring has a base end engaging the intermediate support and an actuating end engaging the free end of the flat spring. The bent spring aids movement of the flat spring from the normal position to the actuated position as the mechanical actuator engages the actuation point.

Description

SWITCH MECHANISM WITH SNAP ACTING SPRING

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit under 35 U.S.C. § 119(e) of U.S. provisional patent application Serial No. 60/141 ,180 filed June 25, 1999, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION The present invention generally relates to switches and, more particularly, to spring assemblies providing moveable contacts in switches.

BACKGROUND OF THE INVENTION Switches using flat springs as the moveable contact are generally known in the art. Such springs typically have a fixed end that is attached to a stationary support and a free end moveable between first and second stationary contacts. The flat spring is made of a conductive material so that current supplied to the stationary support flows through the spring. The first and second stationary contacts are formed as part of first and second terminals. The free end of the flat spring has a normal position, in which the free end engages the first stationary contact. The flat spring is moveable from the normal position to an actuated position, in which the free end engages the second stationary contact. The flat spring has an actuation point disposed between the fixed and free ends positioned to engage a plunger or other actuating device which selectively applies force against the actuating point to drive the spring from the normal to the actuated position.

It is desirable to minimize the amount of force needed to actuate the moveable contact. It is generally known that the actuation force must overcome the resistance of the flat spring. In addition, when a current load is applied to the switch, small welds may develop between the moveable and stationary contacts, and, therefore, the holding force of any such welds must also be overcome. As the current load increases, the size and strength of the welds also increase, thereby requiring a greater force to actuate the switch. For applications in which a current load of 10 amps is applied, the force required to actuate the switch is typically on the order of 54 to 72 grams.

In addition, the welds formed in conventional switches are relatively strong due to the geometry of the components in the switch and the materials that are used. Conventional switches typically use a relatively rigid spring intended to increase the amount of actuation force transferred to the free end of the spring. As a result, the same area of the moveable contact consistently engages the stationary contact, thereby creating a relatively strong weld. Other switches attempt to decrease activation force by adding a lever to the actuation system, resulting in a more complicated and expensive switch.

In addition, it is desirable to minimize the amount of travel and force differential required to actuate and return the flat spring. Travel differential is determined by comparing the position of the plunger when the flat spring moves to the actuated position to the position of the plunger when the flat spring returns to the normal position. As the travel differential is reduced, the plunger stroke required to actuate and return the flat spring is also reduced.

Force differential is determined by measuring the amount of plunger force needed to actuate the flat spring to the actuated position and the amount of plunger force needed to return the flat spring to the normal position. The difference between the actuate and return forces determines the force differential for the spring. By minimizing force differential, a smaller plunger force is needed to trigger the switch. In diaphragm switches, for example, process pressure is applied against a first surface of a diaphragm. A counter spring is often applied to a second, opposite diaphragm surface to substantially balance the diaphragm against a baseline process pressure. As a result, the force differential determines how much force is needed to trigger the spring. In view of the foregoing, there is a need for a high current switch having a low actuation force, low travel differential, and low force differential.

SUMMARY OF THE INVENTION The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

In accordance with certain aspects of the present invention, a snap action switch is provided for use with a mechanical actuator. The snap action switch comprises a first electrically conductive terminal and a flexible, electrically conductive flat spring having a fixed end attached to the first terminal and a free end. The free end defines a movable contact operable between normal and actuated positions, and the flat spring includes an actuation point adapted to engage the mechanical actuator. An intermediate support is positioned between the fixed and free ends of the flat spring. A second electrically conductive terminal defines a first stationary contact positioned to engage the movable contact in the actuated position, and a third electrically conductive terminal defines a second stationary contact spaced from the first stationary contact and positioned to engage the moveable contact in the normal position. A bent spring is provided having a base end engaging the intermediate support and an actuating end engaging the free end of the flat spring. The bent spring aids movement of the flat spring from the normal position to the actuated position as the mechanical actuator engages the actuation point.

In accordance with additional aspects of the present invention, a snap action spring assembly is provided for use in a switch having a first terminal, a first stationary contact, and a second stationary contact. The assembly comprises a flat spring having a fixed end adapted for attachment to the first terminal and a free end disposed between the first and second stationary contacts. The flat spring has an actuation point disposed between the fixed and free ends wherein an actuation force applied at the actuation point drives the flat spring from a normal position to an actuated position. An intermediate support is positioned between the fixed and free ends of the spring, and a movable contact is attached to the free end of the spring. The movable contact engages the first stationary contact when the flat spring is in the normal position and the second stationary contact when the flat spring is in the actuated position. A bent spring has a first end adapted for engagement with the intermediate support and a second end engaging the free end of the flat spring. The bent spring assists movement of the flat spring from the normal position to the actuated position in response to the actuation force.

In accordance with further aspects of the present invention, a switch is provided comprising at least one stationary contact and a current conducting spring, wherein the current conducting spring has first and second positions. The current conducting spring engages the stationary contact in the first position and does not engage the stationary contact in the second position. The assembly further includes a support and a bent spring having one end affixed to the support and a second end affixed to the current conducting spring. The bent spring assists the current conducting spring in snapping from one of the first and second positions to the other of the first and second positions in response to an actuation force applied to the current conducting spring.

The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention.

FIG. 1 is a side elevation view, in cross section, of a switch having a spring assembly in accordance with the teachings of the present invention. FIG. 2 is an exploded view of the switch shown in FIG. 1. FIG. 3 is a detailed view of the spring assembly of FIG. 1. FIG. 4 is a plan view of the spring assembly. FIGS. 5A and 5B are side and plan views, respectively, of a bent spring adapted for use in the spring assembly.

FIGS. 6A, 6B and 6C are side views of the spring assembly as it moves from the normal to the actuated position.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 , a switch 10 is shown having a spring assembly 12 in accordance with the teachings of the present invention. The switch 10 includes a housing 14 for enclosing the spring assembly 12. The housing 14 has an opening 16 for receiving a mechanical actuator such as a plunger (not shown).

A first electrically conductive terminal 18 is formed as an anchor 20 supported inside the housing 14. One end of the anchor 20 is formed as a tab 22, which extends outside the housing 14. The other end of the anchor 20 is disposed inside the housing 14 and extends upwardly to form an intermediate support 24. A slot 26 extends through the intermediate support 24.

A second electrically conductive terminal 28 is also secured inside the housing. The second electrically conductive terminal 28 also has an end formed as a tab 30 extending outside the housing 14. The opposite end of the second electrically conductive terminal 28 is formed as a lower stationary contact 32. A third electrically conductive terminal 34 is supported by the housing 14 and has a tab 36 (FIG. 2) extending outside the housing 14. The third electrically conductive terminal 34 also includes an upper stationary contact 38 spaced from the lower stationary contact 32.

As best shown in FIGs. 3 and 4, the spring assembly 12 includes a flat spring 40 having a fixed end 42 attached to the anchor 20. The flat spring 40 extends through the housing 14 so that an opposite or free end 44 is disposed between the lower and upper stationary contacts 32, 38. A contact insert 46 is preferably attached to the free end 44 and has lower and upper contact surfaces 48, 50 (FIG. 4) for engaging the lower and upper stationary contacts 32, 38, respectively. The flat spring 40 includes an aperture 51 as described in greater detail below. The flat spring 40 further includes a projection 52 which serves as an actuation point adapted for engagement by the plunger.

A bent spring 54 is provided for creating a snap action in the flat spring 40. The bent spring 54 includes a base end 56 having a tab 58 (FIG. 5B) adapted for insertion into the slot 26 formed in the intermediate support 24. An actuating end 62 engages the free end 44 of the flat spring 40. Between the base end 56 and the actuating end 62, a body 64 of the bent spring is formed with a general C-shape although other shapes are possible. As best understood with reference to FIGs. 1 and 2, the body 64 of the bent spring 54 passes through the aperture 51 of the flat spring 40 and bends back downward to engage an edge of the aperture 51 near the free end 44. The bent spring 54 is compressed as it is inserted into the aperture 51 so that the flat spring 40 is placed under tension.

The flat spring 40 serves as the main current carrying member of the spring assembly 12 and, therefore, is formed of an electrically conductive material. The material for the flat spring 40 is also flexible to allow the free end 44 of the flat spring 40 to move between normal and actuated positions. In the normal position, as shown in FIG. 6A, the bent spring 54 urges the free end 44 toward the upper stationary contact 38. When a sufficient downward force is applied at the projection 52, the bent spring 54 enhances the downward force to create a downward snap action. In the actuated position, therefore, the free end 44 engages the lower stationary contact 32.

In one position, as best shown in FIG. 6A, the free end 44 of the flat spring 40 engages the upper stationary contact 38. The bent spring 54 flexes the flat spring 40 into a downwardly-opening concave shape. As a result, an inner portion 66 of the contact insert 46 engages the upper stationary contact 38, while an outer portion 68 of the contact insert 46 is spaced from the upper stationary contact 38. As a downward pressure is applied to the projection 52, the flat spring 40 has a flatter shape as shown in FIG. 6B. With the flat spring 40 in this position, it will be appreciated that the contact insert 46 has rotated so that a center portion 70 of the contact insert 46 engages the upper stationary contact 38. While the bent-spring 54 also rotates, the point of contact of the actuating end 62 with the flat spring free end 44 remains above the base end 56 so that the flat spring 40 is subsequently returned to the normal position.

As it moves toward the actuated position, the flat spring is straightened so that the contact insert 46 slides outward (to the right in FIG. 6B). Both the rotation and sliding of the contact insert 46 serve to break any welds which may have developed while the flat spring 40 was in the normal position. When the force at the projection 52 further increases, the flat spring 40 snaps to the actuated position as best shown in FIG. 6C.

The compressive force provided by the bent spring 54 assists in the downward movement of the flat spring 40. The distance between the base end 56 and actuating end 62 of the bent spring 54 is shorter than that between the fixed end 42 and free end 44 of the flat spring 40. As a result, the bent spring 54 creates a force-balance type of action to achieve the snap-action. The force-balance action can be created by one of a variety of known mechanisms, such as an over-center type mechanism or a force-balance mechanism. The flat spring 40 is preferably formed of an electrically conductive material which is flexible to allow the bent spring 54 to create a curvature in the free end 44. In a preferred embodiment, the flat spring 40 is formed of 0.003 inch thick C17410HT beryllium copper. Other suitable materials include silver plating, gold flashing, or pure copper clad metal in combination with a spring base metal to form a laminated spring material. The particular material or combination of materials is selected according to desired electrical conductivity characteristics, and, thus, materials additional to those listed above are contemplated by the present invention. The flat spring 40 is also relatively long to increase the amount of curvature, thereby enhancing the sliding of the contact insert 46 along the upper stationary contact 38.

The bent spring 54 is preferably stamped from 0.003 inch thick C17200 half-hard beryllium copper, which is preferably rolled to temper or mill-hardened to increase strength and fatigue life. The operating characteristics of the bent spring 54 can be altered by using different materials and thickness or by punching a hole 72 in the middle of the springs apex, as best shown in FIGs. 2 and 5B.

The positions of the lower and upper stationary contacts 32, 38 and the thickness of the contact insert 46 determine an air gap "ag" through which the flat spring 40 should move between the normal and actuated positions. As best shown in FIG. 6A, the lower and upper stationary contacts 32, 38 are separated by a distance "d". The contact insert 46, which is positioned between the lower and upper contacts 32 and 38, has a thickness "t". The air gap "ag" is determined by subtracting the contact insert thickness "t" from the stationary contact distance "d". The air gap "ag" is preferably minimized to reduce the travel and force differentials. In a preferred embodiment, the air gap "ag" is on the order of approximately 0.006 inches.

When using the above preferred materials and thicknesses for the flat spring 40 and bent spring 54, the spring assembly 12 is capable of carrying a 15 amp load while requiring only 15 to 20 grams of force to operate from the normal to the actuated position. In preliminary testing, this embodiment has carried a 22.5 amp load through 62 consecutive actuations operating between 15 and 20 grams with no contact sticks. Accordingly, the snap action switch is suitable for a variety of applications, including use with a pressure- driven diaphragm that relies on air flow in a residential gas furnace to provide the mechanical force and travel needed to actuate the switch.

The embodiments and examples set forth herein are presented to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and utilize the invention. Those skilled in the art, however, will recognize that the foregoing description and examples have been presented for the purpose of illustration and example only. Other variations and modifications of the present invention will be apparent to those of skill in the art, and it is the intent of the appended claims that such variations and modifications be covered. The description as set forth is not intended to be exhaustive nor to limit the scope of the invention. Many modifications and variations are possible in light of the above teaching without departing from the spirit and scope of the following claims. It is contemplated that the use of the present invention can involve components having different characteristics. It is intended that the scope of the present invention be defined by the claims appended hereto, giving full cognizance to equivalents in all respects.

Claims

CLAIMS The embodiments of an invention in which an exclusive property or right is claimed are defined as follows:

1. A snap action switch for use with a mechanical actuator, the snap action switch comprising: a first electrically conductive terminal; a flexible, electrically conductive flat spring having a fixed end attached to the first terminal and a free end, the free end defining a movable contact operable between normal and actuated positions, the flat spring including an actuation point adapted to engage the mechanical actuator; an intermediate support positioned between the fixed and free ends of the flat spring; a second electrically conductive terminal defining a first stationary contact positioned to engage the movable contact in the actuated position; a third electrically conductive terminal defining a second stationary contact spaced from the first stationary contact and positioned to engage the moveable contact in the normal position; and a bent spring having a base end engaging the intermediate support and an actuating end engaging the free end of the flat spring; wherein the bent spring aids movement of the flat spring from the normal position to the actuated position as the mechanical actuator engages the actuation point.

2. The snap action switch of Claim 1 , in which the flat spring includes an aperture sized to receive the bent spring.

3. The snap action switch of Claim 1 , in which the bent spring has a C-shaped bend.

4. The snap action switch of Claim 3, in which the bent spring further comprises a hole formed at an apex of the C-shaped bend.

5. The snap action switch of Claim 1 , in which the movable contact comprises an insert having arcuate upper and lower contact surfaces.

6. The snap action switch of Claim 5, in which the bent spring creates a concave shape in the free end of the flat spring so that a first portion of the first contact surface engages the first stationary contact in the normal position.

7. The snap action switch of Claim 6, in which movement of the flat spring from the normal position to the actuated position rotates the free end of the flat spring so that a second portion of the first contact surface engages the first stationary contact.

8. The snap action switch of Claim 1 , in which the first and second stationary contacts are spaced by a distance "d", the movable contact has a thickness "t", and the movable contact travels through a gap as it moves between the normal and actuated positions, the gap being equal to the distance "d" subtracted by the thickness "t".

9. The snap action switch of Claim 8, in which the gap is equal to approximately 0.006 inches.

10. A snap action spring assembly for use in a switch having a first terminal, a first stationary contact, and a second stationary contact, the assembly comprising: a flat spring having a fixed end adapted for attachment to the first terminal and a free end disposed between the first and second stationary contacts, the flat spring having an actuation point disposed between the fixed and free ends wherein an actuation force applied at the actuation point drives the flat spring from a normal position to an actuated position; an intermediate support positioned between the fixed and free ends of the spring; a movable contact attached to the free end of the spring, the movable contact engaging the first stationary contact when the flat spring is in the normal position and the second stationary contact when the flat spring is in the actuated position; and a bent spring having a first end adapted for engagement with the intermediate support and a second end engaging the free end of the flat spring; wherein the bent spring assists movement of the flat spring from the normal position to the actuated position in response to the actuation force.

11. The assembly of Claim 10, in which the flat spring includes an aperture sized to receive the bent spring.

12. The assembly of Claim 10, in which the bent spring has a C-shaped bend.

13. The assembly of Claim 12, in which the bent spring further comprises a hole formed at an apex of the C-shaped bend.

14. The assembly of Claim 10, in which the movable contact comprises arcuate upper and lower contact surfaces.

15. The assembly of Claim 14, in which the bent spring creates a concave shape in the free end of the flat spring so that a first portion of the first contact surface engages the first stationary contact in the normal position.

16. The assembly of Claim 15, in which movement of the flat spring from the normal position to the actuated position rotates the free end of the flat spring so that a second portion of the first contact surface engages the first stationary contact.

17. The assembly of Claim 10, in which the first and second stationary contacts are spaced by a distance "d" and in which the movable contact has a thickness "t", wherein the movable contact travels through a gap as it moves between the normal and actuated positions, the gap being equal to the distance "d" subtracted by the thickness "t".

18. The assembly of Claim 17, in which the gap is equal to approximately 0.006 inches.

19. A switch comprising: at least one stationary contact; a current conducting spring, wherein the current conducting spring has first and second positions, wherein the current conducting spring engages the stationary contact in the first position, and wherein the current conducting spring does not engage the stationary contact in the second position; a support; and, a bent spring having one end affixed to the support and a second end affixed to the current conducting spring, wherein the bent spring assists the current conducting spring in snapping from one of the first and second positions to the other of the first and second positions in response to an actuation force applied to the current conducting spring.

20. The switch of Claim 19 wherein the current conducting spring has an aperture sized to receive the bent spring.

21. The switch of Claim 19 wherein the bent spring has a C-shaped bend.

22. The switch of Claim 21 wherein the bent spring further comprises a hole formed at an apex of the C-shaped bend.

23. The switch of Claim 19 wherein the current conducting spring comprises a curved contact surface that engages the stationary contact.

24. The switch of Claim 23 wherein the bent spring creates a concave shape in the current conducting spring so that a first portion of the arcuate contact surface engages the stationary contact in the first position.

25. The switch of Claim 24 wherein movement of the current conducting spring between the first and second positions moves the current conducting spring so that a second portion of the arcuate contact surface engages the stationary contact.