AU710163B2 - Preventing unnecessary imbalance cutout during spin drying in a vertical axis clothes washing machine - Google Patents

Description

PREVENTING UNNECESSARY IMBALANCE CUTOUT DURING SPIN DRYING IN A VERTICAL AXIS CLOTHES WASHING MACHINE.

This invention relates to clothes washing machines, particularly vertical axis types which are loaded with clothes from the top. Designers of clothes washing machines have to repeatedly cope with certain design problems in the face of required styling changes, testing and adaptation of new materials and designs associated with the continual search for economy of manufacture and improvement in performance. There is required repeated judgment in designing machines to effectively wash the maximum load of clothes with the minimum water consumption whilst providing minimum wear and tear on clothes, thorough rinsing of residual soap and a thorough spin drying of the load. One perennial problem with which designers of such machines have to cope is controlling excessive vibration caused by out of balance of clothes loads during spin drying. This problem is manifested in the worst cases by the machine travelling laterally (during spin drying) across the support surface upon which it stands. At least one earlier patent document proposed tethering the washing machine to an adjacent wall to stop such lateral travel but this is not regarded as a generally acceptable solution.

The usual approach applicable to control excessive vibration in vertical axis type washing machines is to flexibly support from below or suspend from above the washing sub-assembly relative to the cabinet, which rests on the floor. The present invention is thought to be more applicable to the type known as a top suspension vertical axis type, described later in relation to Figures 1 and 2, where a particular problem associated with the vibration control aspect of the machine is that the cut-out switch provided to shut down an imbalanced spin dry cycle is inclined to act unnecessarily during a short acceleration phase of the bowl at the start of the spin drying cycle.

It is usual that in such washing machines, the damped motion of the mobile parts of the washing machine is so designed as to limit the transmission of rotary vibration or energy to the surrounding supporting cabinet, so limiting the tendency e* *to lateral motion or "walking". If, at the conclusion of a wash-water pump-out phase of a washing programme, the clothes are arranged around the axis in an unbalanced fashion, then during spin drying, the suspended parts will oscillate laterally to an extent determined by such factors as the unbalanced mass, its centre of gravity and the stiffness of the particular design of suspension.

Machines are generally designed to cope with as much out of balance as possible but, in extreme cases, where the need for human intervention would be preferable, the lateral motion of the suspended parts is detected by contact with a trip switch actuator which stops the spin-dry cycle to enable a person to manually re-arrange the load of clothes to reduce the out of balance.

A particular problem inclined to be observed in vertical axis type machines, particularly top suspension types, is that there may be one or more natural frequencies of vibration that are accentuated at low frequencies, typical of those that might be passed through during the acceleration of the spin-drying bowl up to its full spin drying rotational speed. The suspension is generally designed to encourage some lateral motion of the suspended parts of the machine such that the vertical axis remains vertical or close to vertical. To permit this motion there is some clearance space allowed between the suspended parts and the walls of the surrounding cabinet. Designing the suspensions such that lateral motion occurs with the vertical axis remaining vertical permits the generally desirable objective of minimising the external cabinet dimensions in relation to the clothes load capacity of the suspended machine sub-assembly.

If a natural frequency is passed through whilst the loaded bowl of wet clothes is accelerated up to full speed, a short period during which quite substantial lateral excursion takes place may be experienced, even although the out of balance in the load of clothes would not be too excessive for the vibration damping :performance of the suspension to cope at full spin dry speed.

The present invention seeks to provide a means to overcome the possibility of such excessive lateral motion so that the out-of-balance responsive trip-switch actuator is not activated in such an unnecessary circumstance as above described, but which does not prevent the trip-switch being activated in cases where the amount of unbalance of clothes in the bowl is truly sufficient to require shut-down of the machine once full rotational speed is reached.

The invention comprises means to prevent unnecessary cut out during start-up of spin drying rotation in a clothes washing machine of the vertical axis type, wherein the means is adapted to limit normal relative motion between suspended parts of the machine that are intended to move relative to a cabinet to which said parts are attached to enable vibration isolation of unbalanced clothes loads, said suspended parts including a collector tank housing a bowl rotatable about said axis wherein said means comprises at least one viscoelastic member occupying at least one clearance space between a collector tank and the cabinet, said viscoelastic member being adapted, by resisting compression and shear, to reduce start-up lateral excursion of the suspended parts during acceleration of the bowl to full spin speed to an extent that any such start-up lateral excursion prevents the collector tank from touching the overload cut-out trip switch actuator.

Preferably said viscoelastic member is a resilient cell foam.

One particularly preferred form of interposing the viscoelastic member in the clearance space is to attach a cube shaped block of such material to the external surface of the collector tank so that it is deformed both radially inwardly and tangentially during both lateral and angular excursion of the collector tank during 0;0*0the acceleration phase of the spin drying cycle.

o• The invention will be described more fully in relation to a presently preferred exemplary embodiment of it with reference to the accompanying illustrations in which: Figure 1 is a schematic upright sectional elevation of a vertical axis clothes .i washing machine according to the invention; and 2 i Figure 2 is a plan view of the machine in Fig 1.

*o oo* Fig 1 depicts a well known type of clothes washing machine 10 of the vertical axis type having a cabinet or shell 12 of cubical shape and square cross-section in plan view. The cabinet has four support feet 14 at the bottom corners with the usual adjustment to enable levelling of the machine regardless of uneven or nonlevel supports. Other general construction features entirely non-specific to this particular invention are a perforated bowl 16 to hold the clothes while being washed, the bowl being surrounded by a collector tank 18 which is provided with the usual connection to enable it to be filled to a desired level with water and to be emptied at required times of the washing cycle. Attached rigidly to the bottom of the collector tank 18 is a chassis 20 on which is mounted a drive motor 22, a gearbox 23 and a water pump 24. The motor in this instance is connected to the gearbox via a belt-drive Specific to the top suspension nature of the preferred embodiment here described, the sub-assembly of all the parts previously described are suspended to the cabinet by means of four suspension rods 26 connecting four part spherical plastic ball and socket supports 28 fixed to the top four corners of the cabinet.

The lower end of each suspension rod is connected to four lower lugs 30 integral with or rigidly attached to the collector tank at its lowermost point. Other means of attachment would be possible involving for example, somewhat different lengths of suspension rod.

*4o* As best seen with reference to figure 2, at rest or during steady state balanced operation of the machine whilst spin drying, the central axis of the cabinet and of the perforated bowl 16 are coincident. The washing machine sub-assembly is suspended in the cabinet with a clearance space C between the outside of the collector tank 16 and the inside of the cabinet 12.

During a washing cycle the agitator 31 oscillates rotationally about the central axis to cause the water in the bowl and the clothes being washed to move vigorously relative to one another. At the conclusion of the wash cycle the water in the tank is pumped out by the pump 24 and it is possible, indeed commonplace, for the clothes to rest in the bowl in a random unbalanced condition relative to the central vertical axis of the bowl. When, in usual fashion, the bowl is rotated unidirectionally up to a sufficiently high speed to centrifugally extract a substantial portion of the water wetting the clothes at the completion of the wash cycle, any slight out of balance around the central axis is manifested by the suspended subassembly twisting to some extent, perhaps in the order of 20 to 300, and oscillating laterally from side to side. In order to minimise the effect of an out of balance clothes load, a balance ring 36 is located around the top of the bowl, the balance ring being of the known type which is hollow and partly filled with water and containing a number of restrictors 38 or water dams to slow down the rate at which water swirls around inside the balance ring in order to counter-balance the imbalance of the clothing load.

Due to complex dynamic behaviour of the suspended sub-assembly under particular circumstances, a moderate degree of imbalance of the clothing load during rotational acceleration up to full spin speed may not be adequately compensated for by the flow of water in the balance ring due to the restrictors 38 to water flow in the balance ring delaying the time taken to reach optimal counter balance mode. During this transient period, the suspended sub-assembly might move laterally sufficiently so that the collector tank contacts the trip switch actuator 40 which is adapted to shut down the machine to enable the clothes to be re-arranged in a more balanced manner. However, it is common that the lateral oscillation of the suspended sub-assembly is greater during the early part 0* of acceleration than at steady full speed operation and so the mechanical trip switch actuator 40 receives a false signal by being touched by the outside of the collector tank, which indicates a greater than tolerable imbalance even although the balance ring has not had time to stabilise in its fully counter-balancing condition.

The invention is adapted to prevent this false signalling of the trip switch actuator and in the preferred form comprises four resilient vibration damping buffer pads 42 fixed to the outside of the collector tank at four points spaced 900 apart around the tank where the clearance between the outside diameter of the tank and the inside of the cabinet is at a minimum distance designated C in figure 2. The -7relative dimensions between the outside of the collector tank and the inside of the cabinet in figure 1 are not to scale as the diagram is schematic to illustrate the suspension rods.

During acceleration to speed of the bowl 16 during spin drying, the amplitude of combined rotational displacement of the collector tank and its lateral oscillations is resisted by both viscoelastic compression and shearing between the outside wall of the collector tank and the inside wall of the cabinet. A resiliently compressible open cell foam such as polyether (etherfoam) or polyurethane (esterfoam) is effective. There is a particular preference for polyether because of its relatively soft spring rate which ensures that, in a true imbalance situation justifying shutdown, that the compressibility of the buffers 42 is not so great as to prevent the trip switch from actuating given that a truly excessive balance remains present in the spinning bowl.

o .o -8- WHAT WE CLAIM IS: 1. In a clothes washing machine of the vertical axis type having a spin drying bowl moveably suspended in a water collector tank inside an outer cabinet; and a cutout trip switch adapted to interrupt a spin dry cycle in the event of a pre-determined excessive amount of vibration caused by out of balance of clothes in said bowl; an improvement comprising a visco-elastic damper occupying a portion of at least one clearance space between said collector tank and said cabinet, said damper being effective to limit lateral displacement of said collector tank with respect to said cabinet such that no displacement of said tank during an acceleration phase of said spin dry cycle actuates said trip switch unless a specific out-of-balance condition would be sufficient to cause a pre-determined maximum lateral displacement of the collector tank to be exceeded during a subsequent phase of the spin dry cycle during which phase the spin drying bowl rotates at a substantially uniform speed.

2. A clothes washing machine according to claim 1 in which the visco-elastic damper is a resilient cell foam.

3. A washing machine as claimed in claim 1 or claim 2 in which the viscoelastic damper is attached to the collector tank.

4. A washing machine as claimed in any one of the preceding claims in which the visco-elastic damper is in the shape of a rectangular prism.

A washing machine as claimed in claim 4 in which the visco-elastic damper is attached to a vertical wall of the collector tank.

S: 6. A washing machine as claimed in any preceding claim in which the viscoelastic damper comprises four separate rectangular prismatic shaped pieces attached circumferentially at spaced apart locations around the •collector tank.

Claims (4)

1. 7. A washing machine as claimed in any one of the preceding claims which is of the top suspension vertical axis type.
2. 8. A washing machine as claimed in any one of the preceding claims in which the visco-elastic damper consists of one of the group of polyether foam (etherfoam) and polyurethane foam (esterfoam).
3. 9. A washing machine substantially as described as herein with reference to Figs. 1 and 2. DATED: 11 December 1996 Southcorp Whitegoods Pty Ltd
4. 6533.<613> ABSTRACT PREVENTING UNNECESSARY IMBALANCE CUTOUT DURING SPIN DRYING IN A VERTICAL AXIS CLOTHES WASHING MACHINE. A vertical axis clothes washing machine having a spin drying bowl moveably suspended in a water collector tank connected to an outer cabinet and having a cutout trip switch to sense excessive vibration of the cabinet during spin dry cycles if clothes in the bowl are excessively out of balance. A cutout trip switch is provided to interrupt the spin dry cycle if necessary, the invention providing a visco-elastic damper, preferably polyether or polyurethane foam blocks attached to the water collector tank to prevent spurious triping of the trip switch during an acceleration phase of the spin dry cycle. S 6533 o