Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2002-03-20
2004-09-07
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S751000, C318S753000, C318S783000, C318S784000, C318S785000, C318S786000
Reexamination Certificate
active
06788023
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a motor starter circuit, particularly for refrigerator compressors, having improved characteristics. More particularly, the invention relates to a starter circuit for asynchronous motors, particularly but not exclusively suitable for refrigerator compressor motors.
It is known that in a refrigerator the compressor is operated cyclically so as to pump the refrigerant in the coils of the refrigerator.
This activation of the compressor occurs when the internal temperature of the refrigerator rises above a preset threshold. Accordingly, a heat-sensitive element detects the internal temperature of the refrigerator and when said temperature rises above the set threshold it sends an activation signal to a compressor starter circuit.
The starter circuit comprises a starter device and a device for protecting the motor of the compressor.
The starter device is constituted by a heat-sensitive element in which the flow of current increases the temperature, and such temperature increase causes the element to behave like a resistor of very high value, thus preventing the flow of current through it in order to reach the starter winding of the compressor motor.
However, although the heat-sensitive element is effective from the point of view of intermittent activation of the single-phase asynchronous motor of the compressor, it has the drawback of entailing a continuous, albeit low, consumption of power throughout the operation of the motor.
U.S. Ser. No. 09/526,508 by the same Applicant discloses a starter circuit which overcomes the above-cited drawbacks.
In practice, the starter circuit according to the above-cited patent application comprises means for generating pulses which decrease over time and are adapted to drive switching means (for example a triac) which are connected to the motor of the compressor to be started; the pulse generation means are supplied with AC power.
The description of the above-cited patent application is assumed to be fully included herein by reference.
However, the solution proposed in the above-cited patent application, while being highly efficient from the point of view of current consumption, is affected by a drawback described hereafter.
Generally, a motor for refrigerator compressors is a motor of the asynchronous type in which there are two windings: a steady-state winding, which is permanently powered, and a starter winding, which must be powered for a short time only upon motor startup and must then be disconnected.
FIG. 1
is a schematic view of the principle of insertion of the starter device according to the above-cited patent application for the actuation of an asynchronous motor.
The reference numeral
1
designates the starter device according to the above-cited patent application; the reference numeral
2
designates the starter winding; and the reference numeral
3
designates the steady-state winding, which is connected to the phase line
4
and to the neutral line
5
.
The operation of the circuit shown in
FIG. 1
is as follows. When voltage is supplied to the line, the starter
1
closes the circuit, supplying power to the starter winding
2
. After a preset time, the starter device
1
opens the switch that it contains (for example, as mentioned, a triac) and disengages the starter winding
2
.
In order to improve the efficiency of the motor, some models of compressor have a capacitor
6
, known as steady-state capacitor, shown in dashed lines in FIG.
1
.
The steady-state capacitor
6
is parallel-connected to the starter device
1
.
During starting, the capacitor
6
is charged periodically to significant voltages and discharges in very short times over the switch (triac) of the starter device
1
. These discharge currents are very high and damage the triac irreparably.
The problem of the coexistence of the triac and the capacitor is universally known and occurs not only in the field of refrigerator compressors but in every field in which a triac is used and there is, in the vicinity, a capacitor whose discharge current can damage the triac.
Accordingly, the circuit shown in
FIG. 1
has reliability problems caused by the presence of the capacitor
6
which discharges suddenly on the triac that is present in the starter device
1
.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a starter circuit for motors, particularly for refrigerator compressors, in which the capacitor that is provided in parallel to the starting configuration has no negative effect, with its discharge, on the switch of the starter device.
Within this aim, an object of the present invention is to provide a starter circuit for motors, particularly for refrigerator compressors, in which the discharge current that arrives from the capacitor connected in parallel to the starter device is highly limited, so that it remains within acceptable limits and can be withstood by the switch of the starter device.
Another object of the present invention is to provide a starter circuit for motors, particularly for refrigerator compressors, in which the operation of the motor is not affected by the presence of the circuit according to the invention.
Another object of the present invention is to provide a starter circuit for motors, particularly for refrigerator compressors, which is highly reliable, relatively simple to manufacture and at competitive costs.
This aim and these and other objects which will become better apparent hereinafter are achieved by a starter circuit for motors, particularly for refrigerator compressors, comprising a starter device which is adapted to be connected to the starter winding and to the steady-state winding of an asynchronous motor, said windings being in turn connected to the power supply line, a capacitor being connected in parallel to said starter device, the starter circuit further comprising a resistive element which is adapted to be connected between said starter device and said capacitor, in order to limit the discharge current of said capacitor on said starter device.
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patent: 4399394 (1983-08-01), Ballman
patent: 4672284 (1987-06-01), Ward
patent: 4761601 (1988-08-01), Zaderej
patent: 4806838 (1989-02-01), Weber
patent: 4843295 (1989-06-01), Thompson et al.
patent: 5103154 (1992-04-01), Dropps et al.
patent: 5650697 (1997-07-01), Imagi et al.
patent: 6051952 (2000-04-01), Moreira et al.
patent: A-0 049 870 (1982-04-01), None
patent: A-0 319 404 (1989-06-01), None
patent: A-0 542 955 (1993-05-01), None
patent: A-1 045 510 (2000-10-01), None
patent: A-2 092 401 (1982-08-01), None
patent: A-2000 308380 (2000-11-01), None
Pinotti Ermanno
Puppin Ezio
Josif Albert
Leykin Rita
Minu S.p.A.
Modiano Guido
O'Byrne Daniel
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