AN ELECTRIC MOTOR

[0001] The present invention relates to an electric motor wherein a thermal protector is utilized against overheating.

[0002] In a household appliance, for example in a washing machine, thermal protectors are utilized for the protection of electric motors against overheating and high currents that arise under conditions like the locking of the rotor. The most preferred thermal protectors are the bimetal type comprising stationary and movable parts. The bimetal thermal protector functions like an electric switch, wherein the stationary part is in contact with the movable part during normal operation of the electric motor, and when the electric motor is overheated due to overloading, the movable part is deformed with the effect of heat, losing contact with the stationary part and not allowing the flow of electric current. The thermal protector can be situated on the motor windings or anywhere the heat can be detected and is connected in series to the motor windings to stop the operation of the electric motor by cutting off the electricity in conditions of overheating and/or excessive rise in the current.

[0003] In an electric motor driven by DC current, if the thermal protector sensitive to high current and overheating is connected in series to the circuit wherein the DC current flows, for example to the motor windings, it will malfunction in a short period of time and will not be able to serve since it will be subjected to continuous high current, therefore it cannot be connected to the motor windings through which the DC current flows.

[0004] In order to solve this problem, in a brushless DC electric motor as cited in the Great Britain Patent No GB2249441 , the AC supply delivered to the motor control circuit is changed to DC through a rectifier and the thermal protector is connected in series to the AC voltage line but not to the motor windings wherein the DC current flows.

[0005] The aim of the present invention is the realization of an electric motor wherein the thermal protector is prevented from damage through being affected by high currents.

[0006] The electric motor realized in order to attain the aim of the present

invention is explicated in the claims.

[0007] A thermal protector, situated close to the windings or in the vicinity of the windings, is utilized for protecting the electric motor from overheating. When the temperature of the electric motor exceeds the predetermined limit value, the thermal protector cuts off the current passing through it by becoming an open circuit, maintaining to cut off the current delivered to the electric motor and to halt thereof.

[0008] The electric motor is driven by AC or DC current and is used in a household appliance like a washer/dryer. A switched mode power supply is provided in the electronic circuit controlling the electric motor which produces low value DC voltages, for example like 5V or 15V, required for operation of the electronic units in the circuit.

[0009] Single contact or double contact type phase relays connected to motor windings are used for actuating, halting or changing the direction of operation of the electric motor. The electronic units comprising the relay have to be energized for the phase relays to be operated and a low level DC voltage is sufficient for this process. The low DC voltages for energizing the relays are also received from the switched mode power supply.

[0010] In the electric motor of the present invention, the thermal protector terminals providing electrical connections of the thermal protector are connected in series to the feeder circuit that delivers the low DC feed voltages produced in the switched mode power supply to the relays in order to prevent damaging of the thermal protector by being subjected to high currents while functioning to detect the temperature.

[0011] Since the electric current passing through the thermal protector on the feeder circuit is at a low level, the thermal protector is prevented from damage. Since the thermal protector is connected in series to the relays that directly control the motor motion electrically, functions like a relay while operating, that is, at the moment it turns off the current, the relays to which it is connected change to passive mode and halt the motor.

[0012] Since the thermal protector is connected in series to the feeder circuit between the switched mode power supply and the relays, it can be easily

implemented in both the three-phase brushless direct current motor and also the single phase AC or DC current electric motors that have comparatively lower costs than the brushless direct current motor.

[0013] The electric motor realized in order to attain the aim of the present invention is illustrated in the attached figures, where:

[0014] Figure 1 - is the schematic view of an electric motor.

[0015] Figure 2 - is the circuit diagram of a three-phase brushless direct current motor.

[0016] Figure 3 - is the schematic view of the relay connection in a three-phase brushless direct current motor.

[0017] Figure 4 - is the circuit diagram of a single phase AC electric motor.

[0018] Figure 5 - is the circuit diagram of a single phase AC electric motor.

[0019] The elements illustrated in the figures are numbered as follows:

[0020] 1 - Electric motor

[0021] 2 - Winding

[0022] 3 - Thermal protector

[0023] 4 - Switched mode power supply

[0024] 5 - Feeder circuit

[0025] 6 - Control circuit

[0026] 7 - Relay

[0027] 8 - Rectifier

[0028] 9 - Inverter

[0029] The electric motor (1) utilized in household appliances like a washer/dryer, comprises a stator, a rotor, one or more windings (2) formed of isolated copper wire, the diameter and number of coils determined according to the desired power and rpm, a thermal protector (3) situated adjacent to the winding (2) or in the vicinity of the winding (2), having two thermal protector terminals (T1 , T2) maintaining the electrical connection thereof, that cuts off the current passing through it by becoming an open circuit when the temperature exceeds a predetermined limit value and a switched mode power supply (SMPS) (4) connected to the AC main power supply, that produces more than one low value DC feeder voltages (like 5V or 15V) for energizing the electronic units.

[0030] The electric motor (1) furthermore comprises one or more feeder circuits (5) that delivers the low DC feeding voltages generated in the switched mode power supply (4) to the electronic units for energizing, one or more control circuits (6) that delivers the control signals generated by the switched mode power supply (4) to the electronic circuits by means of a microprocessor for triggering the elements such as for example the transistor, triac etc., one or more relays (7) that are energized by the low rate DC voltage received from the feeder line (5) and the control signals received from the control circuit (6)and changes to the active - passive mode for actuating, halting or changing the operational direction of the electric motor (1).

[0031] The relays (7) get ready to operate by being energized with the low DC voltage delivered from the feeder circuit (5) and change to the appropriate modes by being triggered with the signals delivered from the control circuit (6).

[0032] The electric motor (1) of the present invention, comprises a thermal protector (3) situated between the switched mode power supply (4) and the relays (7) and is connected by means of thermal protector terminals (T1 , T2) to the feeder circuit (5) that delivers the low DC feeding voltages produced in the switched mode power supply (4) to the relays (7) and thus controls the operation of the relays (7) by being connected in series to the relays (7).

[0033] During the normal operation of the electric motor (1), the thermal protector (3) behaves as a short circuit and allows the current to flow through it. When the electric motor (1) temperature exceeds the limit value, the thermal protector (3) opens, not allowing the current to flow through it, thus interrupts the DC feeding current delivered from the feeder circuit (5) to which it is connected in series and prevents the DC feeding current from reaching the relays (7).

[0034] The relay (7) is in the active mode when energy is delivered and provides the electric motor (1) to operate. During the normal operation of the electric motor (1), current continues to flow normally from the feeder circuit (5) that the thermal protector (3) is connected in series and the relay (7)

drives the electric motor (1) according to the signals conning from the control unit (6). The relay (7) immediately changes to the passive mode when de-energized, and does not operate the electric motor (1). In the embodiment of the present invention, when the relay (7) is energized by means of the feeder circuit (5) to which the thermal protector (3) is connected in series, that is when current is delivered from the feeder circuit (5), changes to the active mode and controls the operation of the electric motor (1) according to the relay (7) driving signals (control signals) coming from the control circuit (6). When the thermal protector (3) cuts off the DC current delivered from the feeder circuit (5) due to excessive temperature, the relay (7) changes to the passive mode by being de-energized, even though the control signals continue to be delivered from the control circuit (6), does not deliver current to the windings (2) and the electric motor (1) is not operated.

[0035] In an embodiment of the present invention, the electric motor (1) is a three-phase brushless direct current motor (BLDC) (Figure 2). In this embodiment, the electric motor (1) comprises a rectifier diode bridge (8) that converts the AC main power supply voltage to DC voltage, an inverter (9) that delivers three different phase currents, to the windings (2) on the three phases (F) of the electric motor (1) and a double contact relay (7) that separates two of the inverter (9) outlets and two phases (F) of the electric motor (1). When the thermal protector (3) becomes open circuit, the double contact relay (7) cannot be fed from the feeder circuit (5) and becomes de-energized.

[0036] Since the double contact relay (7) controls the windings (2) on the two phases (F) of the electric motor (1), when it is de-energized and changes to the passive mode, current cannot be delivered to these windings (2) and the electric motor (1) cannot be operated.

[0037] In another embodiment of the present invention, the electric motor (1) is a single phase DC motor (Figure 4). In this embodiment, the electric motor (1) comprises a rectifier diode bridge (8) that converts the AC main power supply voltage to DC voltage, a triac (T) that controls the AC voltage received from the main power supply, two single contact directional relays

(7) connected in series to the stator windings (2) and the rotor windings (2) for rotating the rotor clockwise or counterclockwise by changing the current direction of the stator and rotor. When the thermal protector (3) becomes open circuit, the series connected directional relays (7) cannot be fed from the feeder circuit (5) and become de-energized. When the directional relays (7) are de-energized, they change to the mode of not operating the electric motor (1).

[0038] In another embodiment of the present invention, the electric motor (1) is a single phase AC electric motor (1) (Figure 3). In this embodiment, the electric motor (1) is directly driven directly by AC main power supply voltage and a triac (T) that controls the AC voltage is provided in the control circuit (6). In this embodiment as in the DC electric motor (1) of the preceding embodiment, the electric motor (1) comprises two single contact directional relays (7) connected in series to the stator windings (2) and the rotor windings (2) for rotating the rotor clockwise or counterclockwise by changing the current direction of the stator and rotor. When energy is not delivered from the feeder circuit (5) due to overheating and opening of the thermal protector (3), the relays (7) change to the passive mode and do not operate the electric motor (1).

[0039] By means of the embodiment of the present invention, particularly in places where the voltage received from the main power supply is irregular, the thermal protector (3) is not fed by the AC voltage and by the high value DC voltage delivering lines feeding the electric motor (1), instead is fed by the feeder line (5) delivering energy from the switched mode power supply (4) to the relays (7), is not subjected to high currents and current fluctuations, hence damage is prevented and a longer service life is provided.