GB1559333A

GB1559333A - Laundry washing machine and control circuit therefor

Info

Publication number: GB1559333A
Application number: GB29275/76A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1975-07-17
Filing date: 1976-07-14
Publication date: 1980-01-16
Also published as: JPS5212778A; FR2318260B1; IT1067462B; DE2630131A1; FR2318260A1

Description

(54) LAUNDRY WASHING MACHINE AND CONTROL CIRCUIT THEREFOR (71) We, N.V. PHILIPS' GLOEILAM PENFABRIEKEN, a limited liability Com- pany, organised and established under the laws of the Kingdom of the Netherlands, of Emmasingel 29, Eindhoven, - the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a laundry washing machine including means for stopping rotation of a washing drum of the machine, said drum being rotatably driven by a d.c. motor which is energized from an a.c. mains supply via a power supply circuit including a semiconductor rectifier bridge.

From Patent Specification No. 1195 179, a washing machine is known which is driven by a d.c. motor energized from an a.c., mains supply via a rectifier bridge and connected in series with a heating resistor. By means of a switch, the motor power supply can be interrupted and said motor can be connected to the terminals of the heating resistor which then functions as a braking resistor.

This known apparatus does not allow for the fact that an interruption of an inductive d.c. circuit can produce switching sparks of comparatively long duration, which allows the passage of high short-circuit currents in the braking resistor.

If the rectifier bridge includes semiconductor devices, these devices have reaction times which are negligible in comparison with the switching times of electromechanical switches, and the semiconductor devices can frequently be damaged by such shortcircuiting currents.

French Patent Specification 2,096,691 discloses apparatus including a semiconductor rectifier bridge which has protection for the semiconductor devices when the motor is switched to the braking resistor. In this apparatus, protection is provided by the braking resistor itself which is connected in parallel with the motor terminals and which has a value calculated so that the maximum current passing through any semiconductor device is below the permitted current rating of the device.

Such apparatus provides effective protection but it has the disadvantage that in order to minimize the time in which rotation will cease it requires the use of a resistor of low value. However, the lower the resistance, the greater the current will be, and it will then be necessary to use semiconductor devices with a high current tolerance and thus with a high cost price. It is an object of the invention to provide a washing machine which allows the use of semiconductor devices with normal characteristics and electromechanical switches which have undergone only simple modifications.

According to the invention, there is provided a laundry washing machine including means for stopping rotation of a washing drum of the machine, said drum being rotatably driven by a d.c. motor which is energized from an a.c. mains supply via a power supply circuit including a semiconductor rectifier bridge, which machine comprises the said washing drum, motor, power supply circuit, rectifier bridge and a switch connected for switching said motor from the power supply circuit to an electric braking circuit, the switch having break and make contacts for said circuits, the contacts being coupled to a time delay device which is arranged such that the braking circuit contact is closed with a time delay relative to the moment of opening of the power supply circuit contact.

A means opening the power supply circuit contact may actuate the time delay device.

The braking circuit contact of the switch may be directly connected to a terminal of the motor.

Preferably, the switch includes a movable member, which is located between contacts for the power supply circuit and the braking circuit, in which said movable member actuates the time delay device operation of which is initiated when said movable member is displaced from the contacts of the power supply circuit towards the contacts of the braking circuit. Preferably, the time delay device is of the fluid friction-damped type.

The description and accompanying drawing of an embodiment are given hereinafter by way of example and will enable the invention to be more fully understood. In the drawing: Figure 1 is a circuit diagram of a laundry washing machine motor power supply, giving the direct current polarities at different points in the circuit, and Figure 2 is a schematic sectional view of a switch having a suitable contact arrangement for the washing machine of the invention.

In the embodiment shown the invention is applied to a washing machine which comprises a tub in which a washing drum is rotatably driven by a permanent magnet d.c.

motor 1 (Figure 1). The motor 1 is energized from an a.c. mains supply source via a semiconductor rectifier bridge which comprises two diodes 2 and 3 and two thyristors 4 and 5.

The thyristors 4 and 5 are controlled by an electronic device 6.

An immersion heater of the washing machine is provided by an electrical resistance heater 7 capable of a power dissipation of 2000 watts and which operates at the main voltage and also serves as a voltage dropping resistor for the motor 1.

The wiring arrangement shown in this Fig- ure also allows the use of the heater 7 as a braking resistor for the motor. The braking resistor will come into operation by the closure of the contactors 8 and 9 during any interruption of the motor power supply.

The motor power supply and immersion heater circuit, is controlled by contactors 10 and 11 which are actuated either by a washing machine programme timer as in the present embodiment or by a manually operable push button. Thus, at the end of each spindrying operation of a washing programme, the timer interrupts the power supply circuit via the contactors 10 and 11 and'connects the motor to the resistor 7 by closing the contactors 8 and 9. It is evident that this braking operation can be effected after each spindrying operation following a rinsing operation.

However, braking is in particular effected for safety purposes at the end of the washing programme, the user being inclined to open the tub once spindrying is finished and the drum still rotates at a high speed under the influence of the inertia of the rotating mass including the load of laundry.

By means of the circuit diagram shown in Figure 1 the polarity at the terminals of the various contactors can be determined during their operation.

In the case that at the instant t a negative half cycle appears at the closed contactor 10, the thyristor 5 is conductive and the thyristor 4 is cut off.

The contactor 11 then carries an opposite half cycle which is positive. The positive half cycle appears at contact 81 of the open contactor 8.

At the switching instant t, the contactors 10 and 11 open and 8 and 9 close.

If this switching operation is fast and the closures of contactors 8 and 9 occur whilst a switching arc is present at the contactors 10 and 11, there will be a short circuit that will possibly damage the diode 2. If the arc persists, the diode 3 may also be damaged.

The thyristors 4 and 5 are protected against short-circuit currents by the impedance of the motor 1 and by the presence of the resistor 7.

At the switching instant t plus a few milliseconds the arcs at the contactors 10 and 11 will have been extinguished so that the transient state will have passed.

Short-circuits are most damaging when the circuit to be switched is inductive, when the current is high and when the semiconductor devices have a low transfer impedance.

In the circuit diagram of Figure 1, only the contactor 8 which has the same polarity at its contact 81 as the contactor 11 is dangerous during switching. In order to avoid the previously described problems, it is necessary to close the braking circuit only when the transient condition has terminated. This is achieved by introducing a time delay between the opening of the power supply circuit contactors 10 and 11 and the closure of the braking circuit contactors 8 and 9. The instant that the motor is switched to the braking circuit is thus delayed relative to the moment of interruption of the power supply circuit.

This switching method is carried out by a switching contactor having combined break and make contact pairs which is schematically shown in Figure 2. The contactor comprises a movable member 12 which is located between a normally-open set of contacts 81 82 and a normally-closed set of contacts 111112 under the influence of a cam on a disc 13 which is a part of the washing machine prog- ramme timer mechanism. Between the movable member 12 and a housing of the contactor a time delay device 14 is mounted, which in this example is a fluid friction-damped type of delay device. The delay device comes into operation when the cam displaces the movable member 12 and interrupts the continuity between the contacts 111 and 112.

The continuity between the contacts 81 and 82 is not immediately closed but such closure takes place after a time delay sufficient to allow any switching sparks at the contacts 111 and 112 to be extinguished. The delay device 14 can provide a time delay of the order of ten milliseconds.

WHAT WE CLAIM IS: 1. A laundry washing machine including means for stopping rotation of a washing drum of the machine, said drum being rotatably driven by a d.c. motor which is energized from an a.c. mains supply via a power supply circuit including a semiconductor rectifier bridge, which machine comprises the said washing drum, motor, power supply circuit, rectifier bridge and a switch connected for switching said motor from the power supply circuit to an electric braking circuit, switch having break and make contacts for said circuits, the contacts being coupled to a time delay device which is arranged such that the braking circuit contact is closed with a time delay relative to the moment of opening of the power supply circuit contact.

2. A washing machine as claimed in Claim 1, in which means opening the power supply circuit contact actuates the time delay device.

3. A washing machine as claimed in Claim 2, in which the braking circuit contact of the switch is directly connected to a terminal of the motor.

4. A washing machine as claimed in Claim 2 or 3 in which the switch includes a movable member, which is located between contacts for the power supply circuit and the braking circuit, in which said movable member actuates the time delay device operation of which is initiated when said movable member is displaced from the contacts of the power supply circuit towards the contacts of the braking circuit.

5. A washing machine as claimed in Claim 4, characterized in that the time delay device is of the fluid friction-damped type.

6. A laundry washing machine substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

111 and 112 to be extinguished. The delay device 14 can provide a time delay of the order of ten milliseconds.

WHAT WE CLAIM IS: 1. A laundry washing machine including means for stopping rotation of a washing drum of the machine, said drum being rotatably driven by a d.c. motor which is energized from an a.c. mains supply via a power supply circuit including a semiconductor rectifier bridge, which machine comprises the said washing drum, motor, power supply circuit, rectifier bridge and a switch connected for switching said motor from the power supply circuit to an electric braking circuit, switch having break and make contacts for said circuits, the contacts being coupled to a time delay device which is arranged such that the braking circuit contact is closed with a time delay relative to the moment of opening of the power supply circuit contact.
2. A washing machine as claimed in Claim 1, in which means opening the power supply circuit contact actuates the time delay device.
3. A washing machine as claimed in Claim 2, in which the braking circuit contact of the switch is directly connected to a terminal of the motor.
4. A washing machine as claimed in Claim 2 or 3 in which the switch includes a movable member, which is located between contacts for the power supply circuit and the braking circuit, in which said movable member actuates the time delay device operation of which is initiated when said movable member is displaced from the contacts of the power supply circuit towards the contacts of the braking circuit.
5. A washing machine as claimed in Claim 4, characterized in that the time delay device is of the fluid friction-damped type.
6. A laundry washing machine substantially as hereinbefore described with reference to the accompanying drawing.