[0001] The present invention refers to a method for controlling the rotational speed of
the drum of an automatic clothes washing machine in the spin-extraction phase of a
washing cycle.
[0002] Modern clothes washing machines are generally known to use small amounts of water
and, therefore, are quite easily subject to considerable sudsing, i.e. heavy foam
formation during clothes washing phases, owing for instance to the addition of an
excessive amount of detergent in the water or the use of a detergent product that
by its nature gives rise to excessive foaming.
[0003] Many such clothes washing machines are therefore provided with an anti-foaming arrangement
formed by a pressure or level-control switch, or the like, adapted to de-energize
the drum driving motor in response to an excessive formation of foam in the washing
tub of the machine.
[0004] It should furthermore be noticed that an excessive formation of foam in the washing
tub turns ultimately into a cause of inefficiency of the drain pump of the machine
during the phases in which the washing liquor is let off under spin-extraction conditions
of the clothes.
[0005] Ultimately, an excessive foaming in the washing tub brings about a whole set of disadvantages,
i.e.:
- the rotating drum is repeatedly started to rise to its spin-extraction speed and then
de-energized owing to the anti-foaming arrangement tripping, with a resulting sequence
of aborted, i.e. "false starts";
- as a result, off-balance conditions and displacements of the machine are most likely
to occur, along with considerable mechanical stresses imposed on the whole motion-transmission
system between vthe driving motor and the rotating drum;
- the time needed to complete the water discharge phase turns out to be undesirably
lengthened;
- the operating noise and the energy usage of the machine are increased.
[0006] It therefore is a main purpose of the present invention to provide a method for controlling
the rotational speed of the drum of an automatic clothes washing machine, in the spin-extraction
phase of the clothes, which is capable in doing away with the above-cited drawbacks.
[0007] In particular, it is a purpose of the present invention to provide a method of the
above cited kind, with which the water discharge phases carried out under spin-extraction
conditions of the clothes are substantially shortened and simplified, under resulting
reduction in both the mechanical stresses imparted to the machine parts and the energy
usage of the machine.
[0008] According to the present invention, these and further aims are reached in a method
for controlling the rotational speed of the drum of an automatic clothes washing machine,
in the spin-extraction phases of the clothes, incorporating the characteristics as
recited and defined in the appended claims.
[0009] Anyway, features and advantages of the present invention may be more readily understood
from the description that is given below by way of nonlimiting example with reference
to the accompanying drawings, in which:
- Figure 1 is a purely schematic view of a washing machine adapted to implement the
method according to the present invention; and
- Figure 2 is a diagrammatical view illustrating the variations in the rotational speed
of the drum of the washing machine during significant phases of the method according
to the present invention; and
- Figure 3 is a diagrammatical view illustrating the variations in the rotational speed
of the drum under optimum theoretical conditions.
[0010] With reference to the above-mentioned Figures, the method according to the present
invention may be implemented in a clothes washing machine featuring a substantially
traditional structure, with a washing tub 1 that houses a rotating drum 2 adapted
to hold the clothes and to be selectively driven rotatably at a low washing speed
(under cyclical reversal of the direction of rotation) and a high spin-extraction
speed by an electric motor 3 controlled by a programme sequence control unit 4.
[0011] A water discharge conduit 5, to which there is associated a drain pump 6, departs
from said washing tub 1.
[0012] Again in a substantially traditional manner, the clothes washing machine shall be
understood as being provided with a plurality of operational elements and parts controlled
by said programme sequence control unit 4, which is preferably of an electronic type,
to carry out a number of selectable operating cycles, at least one of which comprises
in particular a washing phase carried out with detergent-added water that is let into
the washing tub 1 up to a first operating level L1 and is preferably heated up. The
washing phase is concluded by at least a water discharge phase, in which the drain
pump 6 is energized by the programme sequence control unit 4 under the control of
an analogue pressure switch 7 (or a similar level-control switch or sensor).
[0013] In particular, the pressure switch 7 drives the programme sequence control unit 4
with a signal that is indicative of the pressure determined by the variations in the
level of the water (along with any possible foam in said water) in the washing tub
1. For reasons of greater simplicity, in the following description the assumption
is made that the pressure is directly proportional to the water level.
[0014] The programme sequence control unit 4 is set so as to be adapted to start the water
discharge phase, through the energization of the drain pump 6, under substantially
static conditions of the drum 2, in such a manner as to enable the foam that may be
present in the washing tub to be substantially abated.
[0015] The programme sequence control unit is further set so as to stop the drain pump 6
and start the driving motor 3, in view of bringing the drum 3 up to a maximum spin-extraction
speed Vs, when the water in the washing tub 1 lowers down to a minimum level L2 that
preferably corresponds to the minimum pressure value P2 that can be detected by the
pressure switch 7. In the example illustrated in Figure 2, this occurs at an instant
t1, after which the drum is accelerated into spin-extraction, so that the resulting
water released by the clothes causes the water level in the washing tub 1 to increase.
[0016] According to a further aspect of the present invention, the programme sequence control
unit 4 is set so as to energize again the drain pump 6 and stop the acceleration of
the driving motor 3, while keeping the instant speed thereof substantially constant,
upon the pressure switch 7 detecting a pre-determined maximum pressure value P3 that
substantially corresponds to a water level L3 that is greater than L2.
[0017] Preferably, said level L3 is lower than or equal to the level at the base 8 of the
rotating drum 2, in such a manner as to prevent any further foam from forming owing
to a contact of the rotating drum with the water containing sudsing, i.e. foaming
additives.
[0018] In all cases, the drain pump 6 is advantageously energized when the priming conditions
thereof are favourable, whereas the discontinuation in the acceleration of the rotating
drum 2 enables the clothes to go on being spin-dried, i.e. to further undergo spin-extraction,
while at the same time preventing the water in the washing tub from further increasing
to any excessive level.
[0019] With reference to the example illustrated in Figure 2, the operation of the clothes
washing machine shown schematically in Figure 1 with the method according to the present
invention is briefly summarized below.
[0020] Up to an instant t0, an operational washing or similar phase is carried out in the
machine with water let into the washing tub 1 up to the level L1 and, preferably,
under a sequence of alternate rotations of the drum 2, as indicated schematically
at A, at a rotating speed of approx. 50 rpm.
[0021] Upon reaching said instant t0, a water discharge phase is then triggered with the
drum 2 substantially at a standstill, until the pressure switch 7 then, i.e. at an
instant t1, detects a condition indicating that the minimum level L2 has been reached.
[0022] At this point, the drain pump 6 is de-energized and the drum 2 is driven to rotate
up to its spin-extraction speed Vs.
[0023] During such an acceleration in the rotating speed of the drum, should the pressure
switch 7 occur at an instant t2 to detect a condition indicative of a level L3 having
been reached, the instant speed Vi of the drum is kept substantially constant and
the pump 6 is energized again.
[0024] Upon the pressure switch 7 detecting again a level L2 of the water in the washing
tub, the drain pump is again de-energized and the drum is again accelerated up to
its pre-determined spin-extraction speed Vs.
[0025] The drum itself will reach said spin-extraction speed Vs thereof within a period
of time t1-t3 which is variable depending on and according to the actual operating
conditions (such as, in particular, the amount of foam generated in the suds or washing
bath). In particular, during the period of time t1-t3 in which the drum 2 is accelerated
into spin-extraction speed, a number of transients may possibly be experienced during
which, in the above described manner, the drum 2 is accelerated in a gradual, step-like
manner (as indicated schematically at B in Figure 2) up to said spin-extraction speed
Vs.
[0026] In any case, from the above description it clearly appears that such an acceleration
of the drum 2 takes always place in a gradual manner and under the most favourable
operating conditions. Unlike the prior-art solutions, in particular, in the method
according to the present invention the drum 2 reaches its spin-extraction speed Vs
without going through any "false start", so that the time t1-t3 is drastically reduced
and the mechanical stresses in the washing machine are kept down to a minimum.
[0027] As it may be noticed by comparing the curves in Figures 2 and 3, the actual speed
variations of the drum 2 do not deviate from the optimum theoretical ones to any substantial
extent.
[0028] After the instant t3, the operation of the washing machine can continue in a traditional
manner, possibly with a further time-controlled energization of the drain pump 6.
[0029] It shall be appreciated that the above described control method may be the subject
of a number of modifications without departing from the scope of the present invention.
[0030] For instance, the values of the water levels L1, L2 and L3 may be changed in accordance
to the requirements, and the means used to implement the control method (such as for
instance the pressure switch 7) may be of a different kind.
1. Method for controlling the rotational speed of the drum of a clothes washing machine
in the spin-extraction phase thereof, in which at the end of an operational phase
carried out with a first water level (L1) in the washing tub of the machine, the water
is let off the machine and the drum is driven into spin-extraction,
characterized in that:
- the water is first let off the tub (1) under substantially static conditions of
the drum (2);
- when the water in the tub (1) reaches down to a minimum level (L2), water discharge
is discontinued and the rotating drum (2) is rotatably accelerated up to a maximum
spin-extraction speed (Vs), in such a manner as to enable the clothes to release water
in the washing tub;
- if the water in the tub (1) rises again up to a pre-determined level (L3), it is
again let off the tub and the instant rotational speed of the drum (2) is kept substantially
constant;
- when the water lowers again down to the minimum level (L2), water discharge is interrupted
and the drum (2) is accelerated towards said highest spin-extraction speed (Vs) thereof.
2. Control method according to claim 1, characterized in that said water discharge phases and said actuations of the rotating drum (2) as a function
of said minimum water level (L2) and said pre-determined water level (L3) occur repeatedly
until the drum reaches said highest spin-extraction speed thereof.
3. Control method according to claim 1, characterized in that said pre-determined level (L3) is lower than or equal to the level of the base (8)
of the rotating drum (2).