EP1428926A2

EP1428926A2 - Washing machine with improved synchronous motor

Info

Publication number: EP1428926A2
Application number: EP03023702A
Authority: EP
Inventors: Ugo Favret; Silvano Cimetta
Original assignee: Electrolux Home Products Corp NV
Current assignee: Electrolux Home Products Corp NV
Priority date: 2002-12-10
Filing date: 2003-10-20
Publication date: 2004-06-16
Anticipated expiration: 2023-10-20
Also published as: DE60318932D1; ITPN20020096A1; EP1428926B1; ES2297086T3; ATE385269T1; DE60318932T2; EP1428926A3

Abstract

A washing machine is provided with a drain pump comprising a synchronous motor and an impeller (2); the shaft (1) of the motor is provided with an appropriate flywheel (33) and has an eccentric protrusion (4) at the extremity thereof, and said impeller, in its central zone where it is fitted onto said shaft, is provided with a ring-shaped (5) cavity extending circularly only along a definite arc portion (A) and adapted to accommodate said eccentric protrusion. This eccentric protrusion is in turn so sized with respect to said cavity as to be capable of freely rotating for a pre-definable arc (B) within said cavity.

Description

The present invention refers to an improved kind of machine, preferably of the type for use in households, for washing clothes or dishes, adapted to use in an advantageous manner an electric motor of the synchronous type used in a drain pump.
Generally known in the art is the fact that, during those cycle phases in which the washing or rinsing liquor is being let off the machine, the drainage sump, which is generally provided under the bottom of the tub or vessel containing the items to be washed, fills up with the liquor that was previously filling said tub or vessel; from such a drainage sump said liquor is then let off through the operation of an appropriate pump, whose impeller is situated inside said same drainage sump.
The motor used to drive such pump is usually an electric motor of the asynchronous type, the operation of which, apart from being well known in the art, does not give rise to any particular problems either in the starting phase or in the final pump-off phase in which the gradual reduction in the amount of liquor to be let off eventually causes decreasing amounts of water to come into contact with the pump impeller along with certain amounts of air being taken in from the interior of the tub or vessel via the drainage sump that is no longer full at this point.
However, asynchronous motors are also largely known to be rather expensive due to the considerable amounts of copper and ferromagnetic material required.
In view of reducing the costs implied by the use of said asynchronous motors, these are therefore being replaced by appropriate synchronous motors, which are much lower in costs than asynchronous motors, while being capable of performing the equivalent functions thereof without any serious drawback.
However, synchronous motors require that, during the starting phase, a resisting torque be created on the motor shaft that would enable the rotation of the same motor to be started in the first place. This resisting torque must be rather moderate, so as to avoid blocking the motion of the shaft, but at the same time it must not be too low, since it would in this case risk preventing said rotation from starting at all.
To this purpose, and with particular reference to the accompanying Figures 1 through to 5A, the practice is known in the art to create on the shaft 1 of the rotor 10 a protruding portion 4, which is eccentric with respect to the axis of the same motor and is adapted to be inserted in a ring-shaped cavity 5 extending circularly only along a definite arc portion A in the central zone of the impeller 2; in addition, said protruding portion 4 is annular and capable of being inserted in the cavity 5 so as to be able to rotate therewithin by a definable angle B, thereby floating between the two mutually opposing positions, as symbolically represented in Figures 3A and 4A and most clearly inferable from comparing the illustrations in said Figures with each other.
When correctly assembled, the devices noted and illustrated above make it possible for said shaft 1 to be coupled with said impeller, wherein such a coupling, however, is not a rigid one owing to the provision of the above-mentioned angle of rotation B.
As stated above, such angle of rotation allows for said shaft and said impeller to be at first practically uncoupled from each other, since they would otherwise make it in many cases impossible for the motor to be started, owing to the considerable resisting torque due to the mass of liquor surrounding the impeller. On the other hand, the presence of a moderate resisting torque is necessary in order to switch from a polarity to the other one during starting; to that purpose there is provided an cylindrical element 6 coaxially to and firmly joined with said shaft 1, in a position contiguous to said protrusion; then, in the corresponding position in the central zone of the impeller 2 there is provided a cavity 7 that is coaxial to said shaft and is sized so as to be capable of accommodating said cylindrical element 6 without any interference.
Finally, between said cavity 7 and said cylindrical element 6 there is arranged an elastic means 8, preferably sitting astride of said cylindrical element and adapted to generate friction when said cavity and said cylindrical element move rotatably relative to each other.
Because of said means 8, the mass of liquor acting on the impeller generates the required controlled amount of resisting torque on the shaft, which, when combined with the definite arc of rotation B, enables the motor to start.
This solution is generally effective in reaching the above-cited aim; however, it still has a drawback: in fact, when a progressively reduced amount of liquor towards the final phases of the draining operation causes a smaller amount of water to come into contact with the impeller along with greater amounts of air being taken in via the drain sump of the machine, the resisting torque on the impeller becomes irregular and, from time to time, almost nil. Owing to this, the synchronous motor, which provides a substantially constant driving torque under steady-state conditions, tends to first accelerate and, immediately thereafter, to brake in response to an abrupt drop in the resisting torque.
As a result, the impeller, shrink-fitted onto the motor shaft, finds itself being like rushed rotatably forwards with respect to the instant position of the motor shaft itself, this being in fact allowed by the presence of said angle B.
In other words, when the motor accelerates, said cavity is pushed by the entrainment, i.e. driving edge of said protrusion, which it was originally in contact with, and for a very short period of time, in an accelerating motion, it any way remains in contact with said edge, since it is the latter that drives it into its accelerating rotary motion. However, when the motor starts to slow down, owing to its being a synchronous motor that, therefore, tends to maintain synchronism, the inertia of the impeller tends to cause the same impeller to continue to rotate at the just acquired speed, which is faster than the slowed-down speed of the motor and the protrusion, so that, owing to them being scarcely hindered therefrom by the lower resisting torque provided by the liquor, the same impeller, along with the cavity associated thereto, tends to move away from said pushing edge of the protrusion.
Subsequently, as the resisting torque increases owing to an increasing mass of liquor re-establishing therearound, the impeller slows down in a sensible manner until it moves eventually back into its initial position in contact with said pushing edge of said protrusion.
However, it stands as a matter of fact that the braking speed will turn out as being greater than the rotating speed of the shaft, so that, owing to its own inertia, the impeller and, through it, said protrusion 4 move into impinging rather violently against the corresponding edge 13 of said cavity, thereby generating a perceivable rattling noise.
Such an occurrence tends to repeat itself at an extremely fast and persisting rate whenever a mass of water and emulsion (foam, air, etc.) is being let out, translating into a clearly perceivable rattling noise being issued which certainly proves quite annoying, and which is most frequently even mistaken for a sign of machine failure, leading to unnecessary service calls, when the machine is on the contrary operating in a fully regular manner.
Such phenomenon has been investigated quantitatively by measuring the noise emitted by a sample machine in the course of a number of test runs carried out during the final washing tub/vessel emptying phase. The following Table A, jointly with the related graph, sets out the noise values as detected by sampling the noise in 1/24 octave frequency band.
From both the table and the related graph it clearly appears that there is a frequency band ranging from approximately 800 to 2200 Hz, in which the noise turns out to have particularly high values, which can actually be ascribed to the afore-mentioned impingements.
In an effort to obviate this drawback, the practice has taken root of arranging shock-cushioning means, typically some kind of rubber pads, grommets or the like, between said protrusion 4 and said cavity 5, so as to eliminate a direct contact of the protrusion with the edges of the cavity and absorb the related shocks. However, this solution has proven to be scarcely effective due to both shocks anyway continuing to occur, although dampened by said cushioning means, and the durability of said cushioning means being rather unsatisfactory due to their thickness being actually too small if considered on the background of the intensive wear and tear they are subject to in use. As a matter of fact, for such a cushioning means to be able to perform its duty in an adequate manner, it should be provided with a considerable thickness, but this would again contrast the basic requirement of having anyway to provide a sufficient sliding length, or stroke, for said protrusion in said cavity. In addition, the particular kind of stress imposed to it by the protrusion repeatedly impinging against the cavity, causes the cushioning means to embrittle and, as a result, particles thereof to break loose. These particles end then up by fitting in the coupling between the cavity and the protrusion, thereby making the combined operation thereof uncertain.
It would therefore be desirable, and is actually a main purpose of the present invention, to provide a washing-rinsing machine that uses a drain pump driven by a synchronous motor, which does not give rise to the afore-described kind of noise.
Furthermore, according to another purpose of the present invention, such machine shall be able to be easily manufactured using existing, readily available materials and techniques, and be competitive in its construction; it shall additionally be able to incorporate the features of the present invention without suffering any alteration or reduction in the performance abilities and the reliability thereof.
According to the present invention, these aims are reached in a particular type of washing machine provided with a synchronous motor as described below by way of non-limiting example with reference to the accompanying drawings, in which:

Figure 1 is an exploded, partially see-through view of a rotor and related impeller according to the prior art;
Figure 2 is a schematical perspective view of a detail of the illustration appearing in Figure 1;
Figures 3, 3A, 4 and 4A, 5 and 5A are three cross-sectional views along the sectional plane extending parallel to the plane of the sheet of Figure 1, and passing through the axis of the motor, in three distinct operating dispositions, as well as three corresponding cross-sectional views along the sectional plane B - B of the respective Figures 3, 4 and 5;
Figures 6, 7, 7A and 8 are views of respective embodiments of a synchronous motor according to the present invention.

In order to do away with the afore-mentioned impingements, and the related rattling noise, it has been considered that a useful solution might lie in increasing the inertia available on the shaft 1 of the motor, so that the rotating speed thereof is subject to a smaller extent of variability due to variations of the resisting torque on the impeller, and so that it can be reasonably expected that, in this way, the separation of the cavity from the protrusion is significantly reduced in terms of both relative angle and relative angular speeds, so as to attenuate or, in the best case, even do totally away with said succession of impingements along with the related beating noise.
An appropriate flywheel 33 has therefore been fitted to said shaft 1 of the motor, so as symbolically illustrated in Figure 6, to the purpose of providing the desired increase in the inertia.
Related experiments have then been carried out under fully similar test conditions as the ones used to obtain the experimental results set forth in Table A. The results of these new experiments are set forth in Table B and the related graph: an easily made comparison of the data in these two Tables most readily and clearly emphasizes the quite considerable noise reduction obtained exactly in the frequency range where the turned out to be greater without the application of such flywheel.
In view of getting around possible constraints of a manufacturing-related or, more in general, technical nature, such flywheel 33 may be provided, further to the way in which this is illustrated in Figure 6, also between the rotor 10 of the motor and said impeller, as this is illustrated in Figure 7, or even attached to said cylindrical element 6, so as shown schematically in Figure 7A, or it may be split into two parts to be arranged on a side 33A and on the other side 33B of the rotor, as shown in Figure 8.
It will be readily appreciated, at this point, that the value of the moment of inertia to be adopted can be determined each time by anyone skilled in the art through easily performed experiments and tests, also on the basis of all other parameters affecting the overall result and, in particular, the size and geometry of said cavity 5 and said respective protrusion 4 with respect to each other.
It will also be readily appreciated that said protrusion and said respective cavity may exchange position with each other, i.e. the protrusion may change from the shaft to the impeller, and vice-versa, such design option being regarded and classifiable as a simple technical equivalent.
It should finally be noticed that the afore-described solution according to the present invention is effective in removing the problem directly at the root. In fact, while the prior-art solution based on the use of cushioning means substantially preserves the problem as such, and is merely directed at providing means aimed at reducing the inconveniences generated by the same, the present invention simply eliminates the problem itself by being effective upon the cause that generates such problem and doing away with that cause at the root thereof.

Claims

Washing machine, in particular for washing textiles or clothes, dishes or the like in water, comprising:

a stationary tub or vessel holding said items to be washed,

a drainage sump arranged below said tub or vessel, and accommodating appropriate water pump means to pump out said water, said pump means being driven by a synchronous electric motor, on the shaft (1) of which there id shrink-fitted an impeller (2),

a water discharge pipe connected to an extremity of said drainage sump and adapted to convey the water being pumped by said pump means outside the machine,

said machine being adapted to carry out a pre-set sequence of process phases comprising at least a water discharge phase,
characterized in that:

said shaft of said motor is provided with appropriate flywheel means (33),

at an extremity thereof, said shaft is provided with an eccentric protrusion (4),

said impeller, in its central zone where it is fitted onto said shaft, is provided with a ring-shaped cavity (5) extending circularly only along a definite arc portion (A) and adapted to accommodate said eccentric protrusion (4), the latter being so sized as to be capable of freely rotating for a pre-definable arc (B) within said cavity.
Washing machine according to claim 1, characterized in that said flywheel (33) is arranged, with respect to the rotor (10) of said motor, in the shaft portion that is opposite to said impeller (2).
Washing machine according to claim 1, characterized in that said flywheel (33) is arranged between the rotor (10) of said motor and said impeller.
Washing machine according to claim 1, characterized in that said flywheel (33) is split into two separate and distinct parts, a first one (33A) of which is arranged between said impeller and said rotor (10) of said motor, and the second one (33B) of which is arranged on the opposite side with respect to said rotor.
Washing machine according to any of the preceding claims,
characterized in that

there is provided a cylindrical element (6) coaxially with said shaft, and preferably in a position that is contiguous to said protrusion,

in said central zone of said impeller there is provided a cavity (7) coaxial with said shaft and so sized as to be able to accommodate said cylindrical element without any interference, and

between said cavity and said cylindrical element there is provided an elastic means adapted to generate friction between said cylindrical element (6) and said cavity (7) when they move relative to each other.
Washing machine according to claim 5, characterized in that said elastic means is a ring (8) arranged on a plane that is orthogonal to said shaft, coaxially therewith.
Washing machine according to claim 6, characterized in that said elastic ring (8) is applied firmly round said cylindrical element.