US3617665A

US3617665A - Snap-action pressure-sensitive switch with safety feature responsive to contact welding

Info

Publication number: US3617665A
Application number: US882140A
Authority: US
Inventors: Johannes J Berson; Joseph Pilet
Original assignee: Controls Company of America
Current assignee: Eaton Corp
Priority date: 1968-12-13
Filing date: 1969-12-04
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02
Also published as: DE1962486A1; AU460986B2; GB1228400A; AU1623670A; DE1962486B2

Abstract

The pressure switch comprises a toggle switch in which a flexible switch tongue is moved by a pressure-actuated diaphragm against the force of a return spring, and a contact-carrying flexible switch blade, connected to the blade tongue, through an overcenter spring, is moved by snap-action in one direction as the blade tongue moves through the overcenter position in the opposite direction: To effect a safety function; a contact is movable by the switch tongue to engage a stationary contact after a predetermined movement of the switch tongue past the overcenter position, the switch tongue being movable despite the possibility of welding of the toggle switch contacts. Closure of the safety switch by the switch tongue in this way can be used to energize a pump in the event of failure of a water valve to close or to energize a water valve otherwise prevented from energization by welding of two of the toggle switch contacts.

Description

United States Patent [54] SNAP-ACTION PRESSURE-SENSITIVE SWITCH WITH SAFETY FEATURE RESPONSIVE TO CONTACT WELDING 7 Claims, 5 Drawing Figs.

[52] US. Cl 200/83 R, 200/83 P, 337/311, 200/62 [51] Int. Cl. H0lh 35/34 [50] Field of Search 200/83 WM, 83 P, 83 R, 146, 67 D, 62;337/86, 103, 309, 311, 318; 335/107, 106, 127

[56] References Cited UNITED STATES PATENTS 2,484,112 10/1949 Moorhead 335/107 X 2,792,466 5/1957 Raney 20 /83 P Primary Examiner-H. 0. Jones Assistant Examiner-Robert A. Vanderhye Attorneys-John W. Michael, Gerrit D. Foster, Bayard H.

Michael, Paul R. Puerner, Joseph A. Gemignani, Andrew 0. Riteris, Daniel Van Dyke and Spencer B. Michael ABSTRACT: The pressure switch comprises a toggle switch in which a flexible switch tongue is moved by a pressure-actuated diaphragm against the force of a return spring, and a contact-carrying flexible switch blade, connected to the blade tongue, through an overcenter spring, is moved by snap-action in one direction as the blade tongue moves through the overcenter position in the opposite direction: To effect a safety function; a contact is movable by the switch tongue to engage a stationary contact after a predetermined movement of the switch tongue past the overcenter position, the switch tongue being movable despite the possibility of welding of the toggle switch contacts. Closure of the safety switch by the switch tongue in this way can be used to energize a pump in the event of failure of a water valve to close or to energize a water valve otherwise prevented from energization by welding of two of the toggle switch contacts.

SNAP-ACTION PRESSURE-SENSITIVE SWITCH WITH SAFETY FEATURE RESPONSIVE TO CONTACT WELDING BACKGROUND OF THE INVENTION This invention relates to pressure-sensitive switch devices (normally referred to as pressure switches), in particular for use in washing machines to control the level of water in the washtub or to control other functions in dependence upon such level. i a g A conventional pressure switch for a washing machine comprises a casing housing a switch blade and a switch tongue anchored at a common point, the outer end of the switch tongue being connected through a toggle or overcenter spring to the outer end portion of the switch blade so that movement of the switch tongue in either direction through an overcenter position snaps the switch blade in the opposite directions, the switch blade being movable between a stationary trip contact and a stationary reset contact. The switch tongue is biased in one direction by a variable force-calibrating spring and in the opposite direction by a pressure-sensitive diaphragm.

The reset contact of the switch is connected to a solenoidoperated water valve so that when the water level, and hence the pressure on the diaphragm, increases to a predetermined value, the switch blade is tripped off the reset contact to deenergize and thus close the water valve. Engagement of the switch blade with the trip contact can be used to energize and electric water heater. Conversely when the water level has fallen to a predetermined value, the switch blade is tripped out of engagement with the trip contact and on to the reset contact thereby opening the water valve.

In practice, the pressure switch can incorporate two or more separate switch assemblies with? separate trip and reset contacts, each switch assembly being operable independently by the diaphragm to switch over at different pressure levels. Thus two level, or even three level, switches can be made by varying the number of switch assemblies.

In a washing machine incorporatingsuch a pressure switch, a fault in the water control circuit can lead to overflow of the washtub. This fault usually occurs as a result of the water valve failing to close when deenergized, but it can also result from the switch blade becoming welded to the reset contact preventing deenergization of the water valve.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pressure switch in which failure of the water control circuit to terminate the water supply when the water level has risen to predetermined value is counteracted.

Another object of the invention is to provide a pressure switch with a safety arrangement for preventing the water level in the tub from falling to such a low level that a waterheating electric element would no longer be immersed in water.

A conventional pressure switch is accordingly modified to providing a safety switch in the form of a contact on a member movable with the flexible switch tongue, and a stationary contact arranged to be engaged by the movable contact following a predetermined movement of the switch tongue past the overcenter position under or against the force of an additional spring. This force can be varied. Since movement of the switch tongue controls movement of the switch blade, but is only partly effected by movement of the switch blade, the switch tongue can move to close the safety switch despite welding of a stationary contact to the movable contact of the blade.

DESCRIPTION OF DRAWINGS FIG. 1 is a section through a pressui'e switch in accordance with the invention, for a washing machine, and

FIGS. 2, 3, 4 and 5 are diagrammatic illustrations of the moving parts of the switch of FIG. I in various operational positions.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in the drawing, the pressure switch comprises a housing 10 which is divided by a flexible diaphragm 11 into a pressure chamber 8 connected to the tub of a washing machine, and a switch chamber 9 for containing the switch mechanism.

In'the illustrated embodiment, two separate switch assemblies are provided only one of which is shown. This comprises a flexible switch blade 12 supporting a contact 31 for movement therewith between a stationary but adjustable reset contact 32 and a stationary trip contact 33, and a flexible switch tongue l3fixed at the same anchorage point as the switch blade and connected at its outer end to the switch blade through a toggle or overcenter spring 14. A switch-actuating lever 15, extending alongside the switch tongue and con nected to the switch tongue for movement therewith, is biased by an adjustable calibrating spring 16 in a sense to keep the switch blade on the reset contact 32. The movement of the diaphragm as a result of pressure variation is transmitted to the switch tongue and lever through a bridge 17 which is pivoted on a metal reinforcing plate 18 on the diaphragm, this bridge also transmitting the movement of the diaphragm to the second switch assembly referred to above but not illustrated.

Thus, in operation of the conventional pressure switch constructiondescribed so far, movement of the diaphragm under increasing fluid pressure moves the switch tongue 13 in a sense to compress the toggle spring 14 which holds the switch blade on the reset contact 32, this movement being opposed by the calibrating spring. When the toggle spring moves through the overcenter position, the switch blade is moved with a snap-action from the reset contact and toward the trip contact 33. If the reset contact is connected to a solenoidoperated water valve, the solenoid is 'deenergized and the valve permitted to close. (See FIGS. 2 and 3). If the trip contact is connected to an electric heater, for heating the water, engagement of the switch blade with the trip contact energizes the water heater.

The arrangement for overcoming the possibility of the water valve 6 failing to close (overflow safety control), or the switch blade becoming welded to the reset contact (heater safety control), comprises a pin 22 supported for longitudinal movement in the wall of the housing on a biasing spring 23, whose force is adjustable by a screw 24, the pin being aligned with an abutment 25 on the switch lever so that as the switch lever is moved toward the pin past the switch-tripping position, the abutment comes into engagement with the pin and commences to move the pin against the force of its biasing spring. In addition the switch lever supports at its outer end a safety switch contact 26 which is cooperable with a stationary safety switch contact 27 in the wall of the housing and connected to the water pump 7 of the machine. As increasing fluid pressure overcomes the force both of the calibrating spring 16 and of the pin-biasing spring 23, the movable safety switch contact engages thestationary safety switch contact to close the safety switch and thereby energize the pump for pumping water out of the washing machine tub (see FIG. 4).

Variation of the bias of the pin-biasing spring 23 varies the water level at which the safety switch energizes the pump to avoid overflow. This spring adjustment however does not affect the normal levels at which the pressure switch operates as determined by the position of trip and reset contacts. Moreover, the intermittent operation of the pump will serve as a warning signal.

If the movable contact of the overcenter switch assembly becomes welded to the trip contact 33, so that the movable contact cannot engage the reset contact 32 to open the water valve, there is a danger that the water heater will remain energized whilst the water level is low, and result in damage to the heater or to the whole machine. This is overcome by an arrangement so that when the switch lever 15 has moved in the trip direction past the overcenter position, another movable safety switch contact 28 on the lever 15 comes to rest on a second stationary safety switch contact 29 connected to the reset contact 32 of the overcenter switch assembly to ensure that a circuit is completed to a water valve 7 for opening the water valve. (See FIG.

Furthermore, such a pressure switch, even using only one overcenter switch assembly, provides three-level switch operation, i.e. trip level, reset level, and a safety level.

In a modification of the illustrated embodiment, it will be evident that by suitably shaping the switch tongue 13 and positioning the

contacts

27, 29, the switch tongue could engage the

contacts

27, 29 directly and so obviate the need for the separate switch-actuating lever 15.

Moreover, although

contacts

26, 27, 28 and 29 have been illustrated as actual contact buttons secured to the metal members on which they are supported, it will be apparent that since these contacts serve only an emergency function it is not necessary to provide contact buttons, and mere engagement between the metal members themselves will suffice to complete a circuit.

I claim:

1. in a pressure-sensitive switch device,

a toggle switch having a switch tongue movable through an overcenter position,

a pressure-sensitive device and a return spring biasing said switch tongue in opposite directions, and

a safety switch arranged to be closed by further movement of the switch tongue in the same direction after passing said overcenter position.

2. In a pressure-sensitive switch device,

a toggle switch having a switch blade movable to move a switch contact between a first stationary contact and a second stationary contact a switch tongue and a toggle spring connected between the switch tongue and the switch blade for moving the switch blade with a snapaction in one direction as the switch tongue moves in the opposite direction through an overcenter position;

a pressure-sensitive member operable to move the switch tongue against the force of a return spring,

a third stationary contact and a further movable contact movable by the switch tongue into engagement with said third stationary contact after said switch tongue has passed the overcenter position in a direction against the force of the return spring.

3. A switch device according to claim 2 wherein said further movable contact is mounted on a member connected for movement with said switch tongue.

4. A switch device according to claim 2 including a further spring for opposing movement of said further movable contact towards the third stationary contact and arranged to come into operation only after the switch tongue has passed said overcenter position.

5. A switch device according to claim 4 having means for varying the force of said further spring.

6. A switch device according to claim 2 wherein said further movable contact is movable, in response to increasing pressure, into contact with the third stationary contact despite the switch contact being welded to one of said first and second stationary contacts.

7. In a pressure-sensitive switch device,

a safety switch stationary contact and a safety switch movable contact movable by the switch tongue into engagement with said safety switch stationary contact after said switch tongue has passed the overcenter position, and in the event that said switch contact has failed to move in response to the overcenter movement of the switch tongue.

* t t It t

Claims

1. In a pressure-sensitive switch device, a toggle switch having a switch tongue movable through an overcenter position, a pressure-sensitive device and a return spring biasing said switch tongue in opposite directions, and a safety switch arranged to be closed by further movement of the switch tongue in the same direction after passing said overcenter position.

2. In a pressure-sensitive switch device, a toggle switch having a switch blade movable to move a switch contact between a first stationary contact and a second stationary contact a switch tongue and a toggle spring connected between the switch tongue and the switch blade for moving the switch blade with a snap-action in one direction as the switch tongue moves in the opposite direction through an overcenter position; a pressure-sensitive member operable to move the switch tongue against the force of a return spring, a third stationary contact and a further movable contact movable by the switch tongue into engagement with said third stationary contact after said switch tongue has passed the overcenter position in a direction against the force of the return spring.

7. In a pressure-sensitive switch device, a toggle switch having a switch blade movable to move a switch contact between a first stationary contact and a second stationary contact a switch tongue and a toggle spring connected between the switch tongue and the switch blade for moving the switch blade with a snap-action in one direction as the switch tongue moves in the opposite direction through an overcenter position; a pressure-sensitive member operable to move the switch tongue against the force of a return spring, a safety switch stationary contact and a safety switch movable contact movable by the switch tongue into engagement with said safety switch stationary contact after said switch tongue has passed the overcenter position, and in the event that said switch contact has failed to move in response to the overcenter movement of the switch tongue.