AUTOMATIC WASHING MACHINE WITH ROTATING DRUM

Abstract: Described is a washing machine comprising a drum rotated by a motor for carrying out a laundering cycle during which the laundry is soaked with a laundering liquid and the motor operates at a reduced speed, with at least one spin-drying period during this laundering cycle. Control means are provided for detecting the rotational speed of the motor and for deenergizing the motor when the spin-dry­ ing speed exceeds a predetermined value.

Description: The present invention relates to a program operated washing machine according to the precharacterizing clause of claim 1. A washing machine of this general type is known from EP-A1-0090716. EP-A1-0090716 describes a washing machine which includes a control circuit to compare a signal related to the nominal speed of the drum with a tachygraph signal which indicates the actual speed of the drum. A difference in the signals due to slowing of the drum by an overload is converted to a phase angle differential which upon reaching a certain value operates upon a switch circuit to stop the motor. GB-A-656 439 describes a laundry washing machine in which the dry spinning cycle following a washing cycle is interrupted after a predetermined time interval before it has reached its full operating speed. After this interruption of the dry spinning cycle, the drain pump is kept operative to draw suds from the space between the spin basket and the tub. Only for the next dry spinning cycle may the spinning speed obtain its full value. Modern washing machines use dry spinning cycles between successive washing cycles which permit considerable saving of water, detergents and electric energy. Since, however, in such a spin drying cycle the water is heavily loaded with detergent, so much foam may be formed that the machine is totally filled up and foam may even escape through the detergent distributor. It is an object of the invention to obviate undue foam formation in a washing machine which carries out dry spinning cylces between successive washing cycles. This object is solved by the characterizing features of claim 1. The sub-claims include advantageous improvements. With reference to the drawings an embodiment of the invention is described in detail: Fig. 1 shows a block digram of a preferred embodiment of a control circuit for the motor rotating the drum of the washing machine according to the invention, and Fig. 2 shows the variations of the rotational speed of the drum of the washing machine of fig. 1 during the laundry washing phase. With reference to fig. 1, the washing machine according to the invention comprises as an essential component an electric motor 3, for example of the universal type, for rotating the laundering drum (not shown) of the machine. Motor 3 is energized through a normally closed controlled breaker switch 4 from the two output terminals 5 and 6 of a control unit 7. The latter is adapted to control the speed of motor 3, for example by varying the phase or frequency of the voltage appearing at output terminals 5 and 6, in response to a first control signal applied to a first input terminal 8 by a program unit 9 of the machine, and to a second control signal applied to a second input terminal 10. Control unit 7 has two additional terminals 11 and 12 connected to the electric supply mains, and is of a substantially conventional type comprising for instance an integrated circuit TDA 1085 supplied by Motorola Inc.. Program unit 9 is similarly of a conventional type, and the controlled breaker switch 4 may for instance be of the TRIAC type. Associated to motor 3 is a device, preferably a tachymetric generator 13, adapted to generate at an output terminal 14 a DC or AC voltage in proportion to the rotational speed of the motor. Output terminal 14 is connected to input terminal 10 of control unit 7, and in addition to the inverting input of a comparator 15 (for instance an operational amplifyer) the non-inverting input of which has a reference voltage V applied thereto. The output terminal of comparator 15 is connected to the control input terminal of breaker switch 4 for causing the latter to open in the per se known manner when the voltage at output terminal 14 of tachymetric generator 13 is higher than the reference voltage V. According to an aspect of the invention, the reference voltage is calculated so as to represent a predetermined rotational speed of motor 3 and thus, taking into consideration the transmission ratio, a predetermined spin-drying speed of the drum of the machine. With regard to the operation of the machine, reference is made to the sequence of a laundering cycle as diagrammatically shown in fig. 2. In accordance with the program stored in program unit 9, control unit 7 generates at its output terminals 5 and 6 a voltage of a phase or frequency causing motor 3 to rotate at a speed corresponding to a rotational speed of the washing drum of for example 50 rpm, with the conventional inversions of the sense of rotation of the drum and intervening rest periods, the tub of the machine containing a laundering liquid during this period. In other words, the drum of the washing machine rotates at the laundering speed in one direction for a period t0 - t1, and after a rest period t1-t2, in the opposite sense for a period t2-t3. At the end of a further rest period t3-t4, control unit 7 energizes motor 3 to operate at the spin-drying speed for a preselected duration t4-t7. Rotation of the drum is thus started at t4 with a relatively low acceleration for uniform distribution of the laundry within the drum. The spin-drying phase proper is initiated at t5 with a sudden increase of the speed of the drum so as to attain a predetermined rotational speed n2 of for instance 400 rpm at t6 (after about two min.). As explained before, at the rotational speed n2 of the drum the tachymetric generator 13 generates at its output terminal 14 a voltage identical to reference voltage V. As a result, comparator 15 generates an output control signal adapted not only to terminate the spin-drying phase by the action of control unit 7 in a per se known manner, but also to cause breaker switch 4 to open immediately. At t6 motor 3 is thus abruptly deenergized, so that its rotational speed drops to approximately zero at t7. The laundering cycle then proceeds in the previously described manner, with further phases of rotation of the drum at the speed n1, interrupted by rest periods. It is also possible to provide further periodically recurring spin-drying cycles as described with referecne to the period t4-t7. In the course of each of the periodic spin-drying phases the extraction of sufficient amount of the laundering liquid from the laundry is ensured, without however giving rise to the excessive formation of foam in the laundering tub. This effect is obtained by the use of the electronic components 4 and 15 operable to terminate the spin-drying phase at the proper time independently of any variables and tolerances which might give rise to an excessive formation of foam. The automatic washing machine according to the invention may of course undergo numerous modifications without thereby leaving the scope of the invention. Motor 3, comparator 5 and/or controlled breaker switch 4 may thus be of a different type; in addition, the periods of rotation and the rest periods of the drum during a laundering cycle may be variously modified, it being also possible to provide any number of periodic spin-drying phases analogous to the period t4-t7. A further modification may consist in the provision that the output of comparator 15 may be applied to a corresponding input of control unit 7, as will be readily evident to one skilled in the art. In this case the operation of breaker switch 4 is directly controlled by control unit 7. The control means 13, 14, 15 and breaker switch 4 may finally be employed for limiting the maximum rotational speed of the drum during the final spin-drying cycle when there is no detergent in the laundering tub.

Claims: Program operated laundry washing machine, comprising a tub with a rotatable drum, an electric motor (3) to drive the drum, detection means (13) to detect the actual rotational speed, and control means (4,7,15) to drive the motor (3) with selectable speed values, namely, a normal washing speed to be used in laundry washing cycles and an elevated spin-drying speed to be used at spin-drying cycles, characterized in that the machine carries out at least one spin drying cycle between two successive washing phases in a washing cycle, the spin drying cycle has a predetermined time duration, the detection and control means (4,13,14,15) are adapted to deenergize the motor (3) for the remaining time duration of the spin-drying cycle, when a rotational speed is detected within the spin-drying cycle which is beyond a predetermined speed value (n2). Laundry washing machine according to claim 1, characterized in that the motor (3) is connected to a control power supply (5,6) through a normally closed controlled switch (4) which is further connected to the control means (15) to be opened when the predetermined speed value (n2) is detected by the detection means (13). Laundry washing machine according to claim 1 or 2, characterized in that the detection means comprises a tachymetric generator (13) driven by the motor (3) which generates a control signal proportional to the rotational speed of the motor (3), the output of which controls a switch (4).

Inventors: NODASSI, FRANCESCO
Applicants: INDUSTRIE ZANUSSI S.P.A.
Application year: 1986
Main classification: D06F37
IPC codes: D06F37