GB1604581A - Latching mechanisms - Google Patents

Description

(54) IMPROVEMENTS RELATING TO LATCHING MECHANISMS (71) We, SERVIS DOMESTIC APPLIANCES LIMITED, a British Company of Darlaston Road, Kings Hill, Wednesbury, West Midlands WS10 7TE, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a latching mechanism.

The invention has been developed primarily but not exclusively for application to a washing machine comprising a body including a washing chamber having an opening for the loading and unloading of the articles to undergo washing into and out of the chamber, a door movable relatively to said opening between open and closed positions respectively to permit of and to prevent said loading and unloading operations, and a sealing means operative between the door and the body around said opening, said sealing means being of a form or construction to undergo elastic stressing when the door is in its closed position whereby it exerts a reactive force on the door tending to move the door to its open position and which requires to be resisted by the latching mechanism.

In order to ensure a satisfactory liquid-tight seal between the door and the body, the force required to effect the requisite elastic deformation of the sealing means cannot be reduced conveniently below a certain minimum value and this creates problems in effecting easy or reliable release of the latching mechanism.

If the latching mechanism is to be released by a manually operable member such as a push-button, the force required to be applied to the push-button is dependent upon the reactive force tending to open the door and the resulting pressure required to be exerted on the push-button may be higher than is acceptable to certain users. Alternatively the latching mechanism may require to be operated by electrically energised means, especially where the washing machine includes a control means for determining the programme of operation, such control means being electrical in character or electro-mechanical.

One of the most convenient forms of electrically energised means for operating a latching mechanism is an electrical solenoid. The size of the solenoid has to be increased resulting in appreciable increase in cost as the force which it is required to exert increases, and both from this point of view and from the point of view of maintaining such operating means in a reasonably compact form it is desirable that the latch mechanism shall be capable of being released with the exertion of no more than moderate force.

While the invention has been developed to meet the requirement which arises in relation to washing machines (both for washing articles of clothing and dishes) of the kind above referred to, it will be understood that it is generally applicable to latching mechanisms, more especially but not exclusively where there is requirement for release of the latching mechanism by the use of electrically energised cooperating means or manually in circumstances in which there is an appreciable reactive force exerted against the door when in its closed position due to the presence of elastically stressed sealing means or otherwise.

In the following description reference is made to a body and a door but it is to be understood that this is for convenience only and the latching mechanism in accordance with the invention may be applied to control relative movement between any two members which are required alternatively to be held in a latched position or released for relative separation from each other.

According to the invention we provide a latch mechanism comprising: a. a first latch having latch elements movable relatively to each other between a latching position and a releasing position respectively preventing and permitting of relative separation of the latch elements, b. a second latch having latch elements movable relatively to each other between a latching position and a releasing position respectively preventing and permitting of relative separation of these latch elements, c. electrically operable operating means adapted to produce a relative movement of the latching elements of the second latch towards their releasing position, d. biasing means adapted to cause movement between the latch elements of the first latch from their latching position to their releasing position; the arrangement being such that the elements of the first latch are held against relative movement to the releasing position while the elements of the second latch remain in their latched position and, on movement of the second latch elements to their releasing position, said biasing means produces movement of the latch elements of the first latch to their releasing position.

In one form of latched mechanism in accordance with the invention as above defined, a. the latch elements of the first latch cooperate with each other to hold the latch in its latching position through mutually engaging abutment faces which are slidable when the latch elements are subjected to said relative movement out of overlapping relation with each other, thereby releasing the latching elements for separation, b. the latch elements of the second latch cooperate with each other to hold the second latch in its latching position through mutually engaging abutment faces which, when subject to said relative movement, can slide out of overlapping relation and thereby release the latch elements of the second latch for separating movement; the arrangement being such that sliding movement of the latching elements of the first latch towards the releasing position is produced in response to separating movement of the latching elements of the second latch.

The biasing means preferably comprises mechanical energy storage means arranged to be charged during movement of the latch mechanism into its latching position, the stored energy being maintained by the latching of the elements of the second latch and released by the releasing of the elements of the second latch to permit such energy to be applied to the first latch for bringing about relative movement of the latching elements of the first latch to the releasing position.

The energy storage means may comprise: a. first spring means arranged to be charged in response to latching of the latching elements of the first latch and held in the charged condition by the elements of the second latch when in their latched position, b. a second spring means also arranged to be charged by latching of the elements of the first latch and held in this condition by these elements when latched; the arrangement being such that release of the second latch serves to release the charge of the first spring means to produce relative movement of the latching elements of the first latch to their released positions, and release of the charge of the second spring means, occurring in response to separating movement of the latching elements of the first latch, produces reversal of the relative movement of these latching elements towards the position in which they can again become latched when no longer separated.

Preferably the electrically operable operating means for the second latch comprises a solenoid.

The invention will now be described, by way of example, with reference to the accompanying drawings wherein: Figure I is a plan view, partly in section, of one embodiment of latch mechanism in accordance with the invention as applied to the body and door of a washing machine: Figure 2 is a view in front elevation of the mechanism also partly in cross-section; Figure 3 is a diagrammatic view illustrating the principle and mode of operation of the latching mechanism.

It is convenient, firstly, to refer to Figure 3. The latch mechanism comprises a first latch 10 which includes one latching element in the form of a pawl 11 which can be attached to the movable member such as the door to be controlled, the latter being assumed to be in the plane of the paper when closed and movable outwardly at right angles to the plane of the paper when opened. The first latch further comprises a latching element in the form of a sliding frame 12. In section A of Figure 3 the pawl 11 is shown in the process of becoming latched behind the frame 12 with the nose or leading end lia of the pawl moving past the opposed edge 12a of the frame 12. During this movement the pawl would be displaced against a pawl spring (not shown in Figure 3) so that it moves to the left and, when having moved past the frame 12, the pawl would move to the right and latch behind the frame 12 as shown in section B of Figure 3.

The latch mechanism comprises a second latch 13 which also includes a pawl 14 movable by an operating means such as a solenoid 15 having a plunger 16 pivotally connected to the pawl 14. The pawl forms one of the latching elements of the second latch.

The second latch includes a lug 17 on the frame 12 forming the further or cooperative latching element of the second latch. The pawl 14, when in its latching position, prevents the frame 12 moving to the right and when the pawl 14 is raised, as seen in section C of Figure 3, relatively to the lug 17, it permits the frame 12 to move to the right.

The latch mechanism further comprises a plunger 18 slidable from left to right as seen in Figure 3 relatively to the frame. Both the plunger 18 and the frame are guided in suitable guideways in a body of the latch mechanism (not shown in Figure 39.

The plunger 18 has a crosspiece 19 located within the aperture 20 of the frame and between this crosspiece and the further end of the frame is disposed a first spring means comprising compression springs 21 urging the crosspiece 19 against the end member 22 of the frame. At one end the plunger has an extension 23 which can come into contact with the face 1 lea of the pawl and at its opposite end the plunger has a ramp 24 which cooperates with the operating member 25 of a microswitch 26 controlling energisation of the solenoid 15.

Also, the plunger 18 is urged to the left by a second spring means in the form of a spring 27 acting between the plunger 18 and a fixed abutment 28 on the body. For convenience in Figure 3 parts 27 and 28 are shown at the end of the plunger 18, whereas in the constructional embodiment of Figures 1 and 2 these parts are adjacent to the aperture 20 and springs 21.

Starting with the parts in the position shown in section A of Figure 3, the pawl 11, as mentioned, has been deflected to the left by contact with the edge 12a of the frame 12, the latter being held by the second latch against displacement to the right. At this stage the pawl spring will have been stressed.

When the pawl 11 passes beyond, i.e. to the rear, of the frame 12 it will then be free to move to the right under the influence of the pawl spring (not shown) and take up the position shown in section B. In this position its edge 1 lea is brought into contact with the end of the extension piece 23 of the plunger 18 and causes the plunger 18 to move to the right further compressing both of the springs 21, the force exerted by the pawl spring being greater than the force exerted by springs 21 and spring 27. Also the ramp of the plunger cooperates with the operating member 25 of the microswitch and causes the microswitch to close, and to prepare a circuit allowing the solenoid 15 to be energised by means such as a push-button switch (not shown). Simultaneously the second spring means 27 is charged by compression of the spring.

During this operation the door to which the pawl 11 is attached will have been moved into its closed position and will have compressed elastic sealing ring or other elastically deformable sealing means provided between the door and the body surrounding the loading opening which is closed by closure of the door. The force required to deform the sealing ring may be appreciable, e.g. 5 Ibs. and when closure pressure is no longer exerted against the door, the reactive force exerted by the sealing ring will be borne entirely by the front face of the pawl bearing against the rear face of the frame 11. The force required, therefore, to move the frame 11 to the right for the purpose of releasing the cooperative elements of the first latch will depend upon the magnitude of this reactive force and the coefficient of friction between the frame and the pawl. The springs 21 have characteristics selected to provide a sufficient force (when in the position shown in section B of Figure 3) to be able to move the frame 12 to the right against the frictional force created between the pawl 11 and the frame 12.

Section B of Figure 3 represents the normally closed position of the door and latched position of the latch mechanism as a whole with the elements of both the first and second latches in their latched positions. In this position the first spring means, namely the springs 21, will have been charged to provide the energy for release of the first latch when required and the second spring means 27 will have been charged to provide the energy for returning the frame 12 to its original position preparatory to relatching of the elements of the first latch when the door is moved from its open to its closed position. The second spring means 27 need exert only a small force to return frame 12 since it requires to overcome only the sliding friction between the frame and the body under no load conditions, i.e. seal not compressed.

With the microswitch 26 closed, as shown in section B of Figure 3, a circuit through the solenoid 15 is prepared for energisation which can take place when appropriate conditions are established. A control circuit may be provided for determining these conditions as more fully disclosed in our co-pending application No. 827/78 (Serial No 1604582) dated 10th January 1978.

When the solenoid 15 is energised the pawl 14 is moved against the loading of a spring 14a to its releasing position as shown in section C of Figure 3. This allows the frame 12 to move to the right under the influence of springs 21 so that the edge 12a of the frame is then in non-overlapping relation with the face of the pawl 11. The pawl 11 which has not itself been moved is thus released from control with the frame 12 and the door to which it is attached can, therefore, move towards its open position. During this movement there is, of course, separation between the pawl 11 and the frame 12 due to the opening of the door while the frame 12 remains in a plane determined by the body of the machine to which the body of the latch mechanism as a whole is attached.

When the pawl 11 is clear of the frame 12, the latter is then free to undergo movement to the left under the influence of the second spring means 27. Such spring means acts through the plunger 18 and in particular its crosspiece 19 which will bear on the left-hand end of the frame. As seen in section D, the frame 12 returns to the position shown in section A ready for relatching with the pawl 11 when the door is closed. Return of the operating member 25 of the microswitch 26 to its original position causes the solenoid 15 to become de-energised and hence the pawl 14 can return to its latched position as shown.

One of the principal advantages of this arrangement is that the force required to move the frame 12 to the right in the stages represented between section B and section C is determined substantially by the reactive force, caused by the compression of the elastic sealing ring, exerted by the pawl 11 on the frame 12. This creates a friction force between the Pawl 11 and the frame 12 and to some extent between the frame 12 and guideways on the body, but the magnitude of this frictional resistance force is determined primarily by the reactive force applied by the pawl 12 multiplied by the average coefficient of friction between the abutting faces of the pawl 11 and frame 12 and the faces of the frame 12 and the guideways of the body.

Since the coefficient of friction can, by appropriate choice of materials, be kept quite low, it follows that the springs 21 in their charged condition shown in section B need exert only moderate preponderance of force over these frictional forces to be certain of being able to move the frame 12 to its releasing position. In turn this means that the reactive force between the lug 17 and pawl 14 can be less than the reactive force between the pawl 11 and frame 12, and consequently the force needed to be exerted by the solenoid to overcome friction between the abutting faces of the pawl 14 and lug 17 is substantially reduced compared with that necessary to move the frame 12.

In effect, this reduction results from the term (coefficient of friction) 2 in the expression for deriving the requisite operating force which the solenoid 15 has to exert.

The body, frame 11, pawl 12, pawl 14, lug 17 and plunger 18 may be made of a plastics material selected to provide a low coefficient of friction, e.g. a acetal copolymer such as that sold under the Registered Trade Mark HOSTAFORM "C".

It would, of course, be possible still further to reduce the initial operating force required to be exerted by the solenoid 15 by providing a lost motion connection between the solenoid plunger 16 and the pawl 14 so that the plunger 16, together with any elements attached thereto, achieves a certain kinetic energy fore any withdrawal force is applied to the pawl 14 and lug 17 relatively from overlapped to non-overlapped relation.

An approximate analysis of the conditions of operation is set out in the following equations.

Fo = reaction force exerted on door and loading first latch.

Mi force required to release sliding element of first latch from pawl 11.

= = coefficient of friction between sliding latch element 12 and pawl 11.

F2 = force exerted on sliding latch element 12 by pawl 11 when first latch fully engaged.

F3 = force exerted by each spring 22 when in released state.

F31 = force exerted by each spring 22 when in fully compressed state, i.e. with first latch fully engaged.

F4 = force exerted by spring 27 when in released state.

F41 = force exerted by spring 27 when in fully compressed state, i.e. with first latch fully engaged.

F5 = reaction force against pawl 13 of second latch with first latch full engaged.

F6 = force required to release pawl of second latch from sliding element of first latch.

> 2 = coefficient of friction between pawl of second latch and sliding element of first latch.

F6 2 C4? F5 (1) to ensure release of second latch.

F5 = 2F31 (2) 2F31 B F1 = Fo ij 1 (3) to ensure that springs are able to release first latch.

therefore F6 3 p1 112 F0 (4) F1 111 F0 force to release second latch is less than force to release first latch.

F2 2F31 + F41 (5) determines magnitude of F2 Referring to the constructional embodiment illustrated in Figures 1 and 2, parts corresponding to those of the diagrammatic representation of Figure 3 bear the same references and the preceding description is to be deemed to apply.

As seen in Figure 1, the pawl 11 is pivotally mounted on a vertical pin lib on the door 9 of the machine. The door is shown in its closed position with respect to the opening afforded in the chamber 8 of the machine, the body 7 of the latch mechanism being mounted inside a portion 6 of the body of the washing machine defining the chamber.

In the embodiment shown in Figures 1 and 2 the spring 27 acts directly between the frame 12 and an abutment 30 of the body 7 of the latch mechanism. When the latch elements of the first latch are in their latching position the spring 27 therefore will not be further stressed as is the case in the diagrammatic arrangement shown in Figure 3. The springs 21 however will be stressed exactly as shown in the arrangement of Figure 3.

On release of the latching elements of the second latch 13 the frame 12, biased by the springs 21, will move to the right thus releasing the elements of the first latch 10.

Relative movement between the frame 12 and the plunger 18, caused by the biasing force of the springs 21, releases the energy stored in the spring 21, until the overriding force on the frame 12 and plunger 18 is the compressed spring 27 which returns the frame 12 and plunger 18 to a position in which the second latch 13 re-engages and in which re-engagement of the first latch 10 is possible.

It will, of course, be understood that other electrically energised devices may be employed if desired to effect release of the second latch, e.g. a bimetal or other thermo-motive device energised electrically.

Claims (11)

WHAT WE CLAIM IS:

1. A latch mechanism comprising: a. a first latch having latch elements movable relatively to each other between a latching position and a releasing position respectively preventing and permitting of relative separation of the latch elements, b. a second latch having latch elements movable relatively to each other between a latching position and a releasing position respectively preventing and permitting of relative separation of these latch elements, c. electrically operable operating means adapted to produce a relative movement of the latching elements of the second latch towards their releasing position, d. biasing means adapted to cause movement between the latch elements of the first latch from their latching position to their releasing position; the arrangement being such that the elements of the first latch are held against relative movement to the releasing position while the elements of the second latch remain in their latched position and, on movement of the second latch elements to their releasing position, said biasing means produces movement of the latch elements of the first latch to their releasing position.

2. A latch mechanism as claimed in Claim 1 wherein: a. the latch elements of the first latch cooperate with each other to hold the latch in its latching position through mutually engaging abutment faces which are slidable when the latch elements are subjected to said relative movement out of overlapping relation with each other, thereby releasing the latching elements for separation, b. the latch elements of the second latch cooperate with each other to hold the second latch in its latching position through mutually engaging abutment faces which, when subject to said relative movement, can slide out of overlapping relation and thereby release the latch elements of the second latch for separating movement; the arrangement being such that sliding movement of the latching element of the first latch towards the releasing position is produced in response to separating movement of the latching elements of the second latch.

3. A latching mechanism as claimed in claim 1 or claim 2 wherein said biasing means comprises mechanical energy storage means adapted to be charged during relative movement of the latch elements towards their latching position, the stored energy being maintained by the latching of the elements of the second latch and released by the releasing of the elements of the second latch to permit such energy to be applied to the first latch for bringing about relative movement of the latching elements of the first latch to the releasing position.

4. A latching mechanism as claimed in any one of the preceding claims wherein the latch elements of the second latch are biased by mechanical energy storage means adapted to be charged during movement of the latch elements of the second latch towards their releasing position, the stored energy being applied in a direction to cause relative movement of the latch elements of the second latch to a latching position.

5. A latching mechanism as claimed in claim 3 wherein the energy storing means comprises: a. first spring means arranged to be charged in response to latching of the latching elements of the first latch and held in the charged condition by the elements of the second latch when in their latched position, b. a second spring means also arranged to be charged by latching of the elements of the first latch and held in this condition by these elements when latched; the arrangement being such that release of the second latch serves to release the charge of the first spring means to produce relative movement of the latching elements of the first latch to their released positions, and release of the charge of the second spring means, occuring in response to separating movement of the latching elements of the first latch, produces reversal of the relative movement of these latching elements toward the position in which they can again become latched when no longer separated.

6. A latching mechanism as claimed in any one of the preceding claims wherein electrically operable operating means comprises a solenoid.

7. A latching mechanism as claimed in any one of the preceding claims wherein said operating means when energised is adapted to maintain the energy storage means of the second latch in a stored state.

8. A latching mechanism as claimed in any one of the preceding claims wherein one of the latch elements of the first latch is adapted to cooperate with switch means enabling a circuit to be completed to the electrically operable operating means.

9. A latching mechanism as claimed in any one of the preceding claims wherein the latch elements of the first latch and/or the latch elements of the second latch are constructed from a material having a low coefficient of friction.

10. A latching mechanism as claimed in any one of the preceding claims wherein one of the latch elements of the first latch is connected to the door of a washing machine, the other latch elements of the first latch being connected to the body of a washing machine.

11. The latching mechanism substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.