EP0736625A1

EP0736625A1 - Improvement in the unbalance-preventing means of a top-loading clothes washing machine

Info

Publication number: EP0736625A1
Application number: EP96103921A
Authority: EP
Inventors: Silvio Battistella; Silvano Cimetta
Original assignee: Electrolux Zanussi Elettrodomestici SpA
Current assignee: Electrolux Zanussi SpA
Priority date: 1995-04-06
Filing date: 1996-03-13
Publication date: 1996-10-09
Anticipated expiration: 2016-03-13
Also published as: ITPN950021A1; EP0736625B1; ES2141409T3; DE69605073T2; ITPN950021A0; DE69605073D1; IT1282416B1

Abstract

Clothes washing machine, typically a top-loading one, provided with a washing tub, a cylindrical drum (2) adapted to hold the washload (1) which is loaded thereinto through a lid (3) closing an aperture provided in a portion of the surface of the drum, a plurality of rib-like elevators (4) arranged on the inner surface of said drum, the latter having no mass-balance weight for balancing the weight of the lid.

The machine is provided with means adapted to identify the position of the loading lid, to allow the drum to go on rotating for a pre-determined period of time at an adequately low revolution speed so as to allow the washload to collect on the bottom of the drum and to allow said drum to start spinning when said means indicate that the loading lid has reached its upper position.

A variant thereto consists in preceding spin-extraction with a phase in which the drum is allowed to rotate at a speed which, although generally low, is adequately high to enable the washload to distribute along the inner periphery of the drum, while starting the spin-extraction phase as soon as unbalance is detected to lie at a value which is lower than a pre-determined one.

Description

The present invention refers to a clothes washing machine provided with a cylindrical drum arranged to rotate about a horizontal axis and having an opening in its outer side mantle, and with improved means adapted to measure and balance unbalanced washloads in the drum of such clothes washing machines during the execution of spin-extraction phases, without any need arising to make use of permanent masses to counter-balance the weight of the lid.
It is widely known that, during the execution of each washing process or cycle, the clothes loaded into the drum for washing tend to distribute in a frequently irregular, uneven manner along the inner periphery of the drum, thereby originating unbalance moments that give rise to irregular mechanical stresses and vibrations which, should they reach intensities above certain pre-determined critical values, may cause the mechanical structure of the machine to suffer damages, particularly in the case in which the oscillations of the washing assembly, ie. the tub and drum unit, are so strong as to cause said assembly to strike against the outer casing of the machine.
In practice, in order to prevent such irregular conditions from arising, it is necessary for the level of the mechanical stresses that are brought about depending on the rotating speed of the drum to be instantaneously known in due advance, so as to be able to prevent the critical levels from being reached. This is generally obtained by appropriately modifying the rotating speed of the drum, ie. reducing it to such levels as to enable the washload in the drum to get more evenly and effectively distributed inside the same drum and at the same time determine a reduction in or the elimination of the unbalance condition of said washload.
A number of technical solutions are known in the art, which, although differing from each other, are invariably aimed at identifying the occurrence of excessive unbalance conditions and controlling the manner in which the rotating speed of the drum is increased, and adjusting the highest attainable rotating speed of the drum accordingly, in view of reaching the above indicated aims.
For instance, solutions are disclosed in the patent specifications DE 3822924-C, FR 2629484 and DE 3606819, in which the unbalance condition is detected on the basis of the oscillations of the current absorbed by the drum driving motor or the oscillations of the rotating speed of the same drum.
According to further solutions disclosed in the patent specifications DE 3605924, GB 2174564 and J 60137389, sensors of various kinds are used to measure oscillations in view of detecting the unbalance condition, whereas unbalance conditions are determined according to the patent specification J 6013 2598 by comparing the rotating speed of the drum against a pre-determined reference rotating speed profile that is stored in advance in the system's memory.
The Italian patent application PN91A000020 filed by the same applicant teaches that unbalance conditions can be detected on the basis of the phase difference between the current absorbed by and the voltage supplied to the motor.
All these solutions are to a varying extent effective in enabling the oscillations of the washing assembly within the outer casing of the machine to be detected and reduced. It should however be noticed that, in top-loading washing machines, a permanent unbalance factor is represented by the weight of the lid used to close the opening through which the washload is introduced in the drum, said lid being actually arranged on a portion of the cylindrical mantle, ie. the side wall of the drum.
As a matter of fact, said lid, along with the opening, locking and reinforcement means associated therewith, generates an additional mass whose weight can reasonably be considered to amount to approx. 500 to 600 gr.
The unbalance condition brought about by such a mass, if it is still acceptable in machines having relatively slow spin-extraction speeds, becomes fully unacceptable and dangerous in modern machines which can spin-extract at rotating speeds of up to 1500 rpm and more.
In order to balance such a mass, it is a commonly know expedient to arrange, within a rib-like clothes elevator provided inside the drum in a position which is possibly opposite to said lid, an appropriate counterweight, usually made of stainless steel. Such a solution, however, has substantially two drawbacks, the first of which derives from the cost of such a counterweight, which, due to the use of premium-priced material, is not so insignificant, considering especially the fact that it is used as a ballast and, therefore, performs a rather undemanding function.
The second drawback refers to the need arising to reinforce the lid. In fact, in the presence of a quite appropriately distributed, balanced washload, the latter tends to quite evenly distribute all along the inner periphery of the cylindrical mantle of the drum, and therefore also in corrispondence of the loading lid, which, as a consequence, must be able to withstand the centrifugal force imparted to the corresponding portion of washload and must therefore be strengthened accordingly in its various load-bearing elements, such as hinges, walls, pins, etc. Of course, this adds significantly to the manufacturing costs, too.
Nor shall the worsening effect be neglected which can be noticed to occur in the rotating drums, especially in those rotating at low speed and lacking said balancing masses, ie. the unbalance condition brought about by the weight of the lid which, under particular circumstances, may add to the unbalance effect caused by the washload, so that a really serious overall unbalance condition may ultimately occur.
It is therefore a purpose of the present invention to provide a clothes washing machine which is free from the above cited drawbacks thanks to some simple, reliable improvements, with the use of readily available techniques.
The invention will be more clearly understood from the description which is given below by way of non-limiting example with reference to the accompanying drawings, in which:

Figure 1 is a schematical view of the drum of a washing machine according to the present invention,
Figure 2 is a view of a traditional drum of a top-loading washing machine, and
Figure 3 illustrates the flow chart indicating the sequences of the spin-extraction starting process of a washing machine according to the present invention.

The general term "liquor", or even "water", will be used in the following description to indistinctly mean washing liquor and rinsing water. However, such a simplification will not affect the full and clear understandability of the same description, considering the context in which such terms are used, as anyone skilled in the art will readily appreciate.
The clothes washing machine being described comprises a drum 2 rotating within a washing tub (not shown) and adapted to hold the washload 1, a lid 3 that can be opened to introduce the washload into the drum, a pre-selectably variable-speed driving motor, a plurality of rib-like elevators 4 adapted to favour the agitation of the washload, means adapted to detect the unbalance condition of the washload in the drum and selectively compare it against a plurality of pre-defined unbalance levels, as well as selectively perform different operations in accordance with the outcome of such comparisons.
According to the presently used, prior-art technique (Figure 2), a balancing mass 8 is associated to the rib-like elevator arranged in the opposite position with respect to the lid. A machine arranged in such a manner is generally known, so that it will not be described here any longer.
According to a first variant of the present invention, the machine is provided with means (not shown) adapted to identify the rotational position of the drum with respect to the position of the lid, as well as control and actuation means adapted to receive and process the information concerning said position and generate corresponding control signals for the driving motor to start driving the drum at high spin-extraction speed. Such means for identifying the position of the lid may be anyone among the various devices available and currently used to such a purpose, such as for instance a proximity sensor installed in the machine and adapted to co-operate with a corresponding appendix rotating with the drum, or a photoelectric cell adapted to detect the passage of a corresponding opaque element rotating with the drum. Such elements defining the position of the rotating drum may also be mounted on means that rotate synchronically therewith, such as for instance the pulley associated therewith or the driving belt, provided that the position of the drum is in any case detected univocally.
Upon completion of the washing phase of the cycle, followed by the discharge of the liquor from the tub, and before starting the drum to rotate at high spin-extraction speed, the afore mentioned control and actuation means becomes activated to cause the drum to be driven for a pre-determined period at a sufficiently low speed of rotation, typically in the vicinity of 35 rpm, so as to prevent the washload items from getting distributed along the inner wall of the drum and enable them on the contrary to substantially collect on the bottom portion of the drum as they fall there by gravity and keep rolling there so as to maintain their lowest position.
At the end of such a period, the control means enables the position sensor to operate, so that when the latter conveys the signal indicating that the drum is in a position in which the lid is on top, this means that, at exactly that moment, the lid and the washload are positioned opposite to each other. As a result, in such a situation the washload acts as a lid-balancing mass, so that the overall unbalance is correspondingly reduced. And this is exactly the moment selected by the control means for actuating the driving motor so as to cause the drum to start rotating at high spin-extraction speed. Owing to the effect of a reduced overall unbalance, a spin-extraction operation, either an intermediate or final one, is therefore obtained, which gives rise to a much smaller extent of vibrations as compared to the situation in which the rotation at high spin-extraction speed of the drum is started randomly, ie. regardless of the actual position of the drum. Inversely, for the same extent of vibrations the spin-extraction speed of rotation of the drum can be increased correspondingly.
Under actual operating conditions, it has however been observed that, in practice, the drum only gradually manages to reach a spin-extraction speed of rotation which is sufficient to cause the washload item to keep sticking against the wall of the dum along the inner periphery thereof, so that a certain period of time, not very long indeed, but nevertheless quite appreciable, generally elapses from the moment in which the rotation at high spin-extraction speed is started, to the moment in which the washload items are actually sticking firmly against the wall of the drum.
As a result, the washload items keep still rolling loosely for a certain period of time before adhering firmly against the wall of the drum and this usually leads to a situation in which the final position taken by the washload will of course be somehow displaced backwards with respect to the position in which it is exactly opposite to the lid, thereby causing a worsening in the desired balance conditions.
In order to obviate such a problem, it is therefore necessary for the high-speed spin-extraction operation to be started before the lid reaches its upper position, so that the time needed by the lid to reach its upper position equals actually the time needed by the driving motor to accelerate the drum to the rotation speed required to cause the washload items to cease rolling and, as a consequence, the final position of the washload is actually the one lying opposite to the lid.
The extent of such an anticipated starting of the high-speed spin-extraction phase is of course variable in accordance with the various influential factors, such as in particular, but not solely, the washload, the motor starting torque, the overall inertia, the diameter of the drum, the dynamic resistances. For this reason, it is practically impossible to pre-define a generally applying optimum value, which can however be readily found by those skilled in the art for each individual machine and set of conditions.
The above described invention can be used to best advantage in machines with relatively low spin-extraction speeds of the drum. Unfortunately, however, the residual unbalance that remains in some cases may still prove excessive, ie. objectionable, in the presence of machines with drums rotating at high speeds during spin-extraction, so that an advantageous improvement of the same invention lies in combining the use of the well-known and currently applied unbalance detection technique and the elimination of the weight used to counterbalance the mass of the lid.
As a consequence, the washing machine is provided with means for detecting the unbalance condition, which are in turn associated to control and actuation means that, before any spin-extraction phase is started, activates the driving motor so as to cause the drum to rotate at a low speed V₁, typically at approx. 85 rpm, which is however sufficient to cause the washload items to distribute along the inner periphery of the drum. Immediately thereafter the unbalance detecting means are activated, which preferably operate on the basis of the current absorbed by the motor.
The unbalance measured in this way will obviously be the overall unbalance brought about by the distribution of the washload items, which is usually quite uneven, and the presence of the mass of the lid.
As a result, the afore cited control and actuation means are pre-arranged so as to be adapted to carry out the following sequence:

if the unbalance is detected to liw below a pre-determined level B_c1, corresponding to the value of the highest allowable unbalance, this means that the washload items have settled or distributed in such a manner with respect to the lid that the respective unbalance effects are mutually compensating in a generally acceptable way; in this case, the control and actuation means, after having ascertained the existence of such a situation, enable the subsequent spin-extraction phase to be regularly started;
should such a condition fail to occur, ie. to be detected, this means that the unbalance is still excessive for enabling a spin-extraction phase to be safely started.

In such a case, the sequence is returned to the starting point of the whole procedure, with the drum caused to slow down to a rotation speed V₀, in correspondence of which the washload falls on to the bottom of the drum and the above described sequence is then started again. Such a procedure of drum revolutions at low speed V₀, drum revolutions at a higher speed V₁ and drum load balance controls is repeated automatically until a value is reached which is lower than the pre-set level B_c1, or until a pre-determined maximum number of repetitions of the same procedure has been completed.

Claims

Clothes washing machine provided with:
- a washing tub,

- a cylindrical drum rotating about a horizontal axis within said tub and adapted to hold the washload which is loaded thereinto through a lid closing an aperture provided in a portion of the cylindrical surface of the drum,

- a motor adapted to rotatably drive said drum at variable and pre-selectable speeds,
characterized in that said drum is free of any mass for counterbalancing the weight of the loading lid, and that said machine is provided with means adapted to identify the position of the loading lid, enable the drum to go on rotating for a pre-determined period of time at an adequately low revolution speed so as to allow the washload to substantially collect on the bottom of the drum and keep rolling there so as to maintain such a position during said period of low-speed rotation of the drum, and enable said drum to start spinning when said means indicate that the loading lid has reached its upper position, so that said spin-extraction phase is started when said loading lid and said washload are positioned opposite to each other in the drum.
Clothes washing machine according to claim 1, characterized in that the drum is enabled to start rotating at high spin-extraction speed in advance of the moment at which the loading lid reaches its upper position.
Clothes washing machine provided with:
- a washing tub,

- a cylindrical drum rotating about a horizontal axis within said tub and adapted to hold the washload which is loaded thereinto through a lid closing an aperture provided in a portion of the cylindrical surface of the drum,

- a motor adapted to rotatably drive said drum at variable and pre-selectable speeds,

- means adapted to detect the unbalance condition of said drum,
characterized in that the spin-extraction phase is preceded by a phase in which the drum is allowed to rotate at a speed which, although generally low, is sufficiently high to cause the washload to distribute along the inner periphery of the drum, and that it is arranged to enable the spin-extraction phase to start if the unbalance is detected to lie at a value which is lower than a pre-determined highest allowable one.
Clothes washing machine according to claim 2, characterized in that if the detected unbalance does not lie below said pre-determined highest allowable value, the drum is caused to slow down to a rotation speed V₀, in correspondence of which the washload falls on to the bottom of the drum and an automatic sequence consisting of a plurality of drum revolutions at low speed V₀, drum revolutions at a higher speed V₁ and drum load balance controls is then started again and again until either a value is reached which is lower than the highest allowable level or a pre-determined maximum number of repetitions of the same sequence has been completed.
Clothes washing machine according to claim 3, characterized in that if said sequence is repeated for said pre-determined, maximum sustainable number of times without succeeding in reaching an unbalance condition which is less severe than the one corresponding to said pre-determined highest allowable level, the washing machine goes on operating regularly, however at a correspondingly reduced spin-extraction speed.
Clothes washing machine according to any of the preceding claims 2 to 4, characterized in that said unbalance condition is detected on the basis of the variation in the rotational speed of the drum.