Electricity: motive power systems – Induction motor systems – Reversing
Reexamination Certificate
1999-10-01
2001-01-16
Masih, Karen (Department: 2837)
Electricity: motive power systems
Induction motor systems
Reversing
C318S779000, C318S774000, C318S775000, C318S767000, C318S772000, C318S817000, C310S254100
Reexamination Certificate
active
06175208
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention generally relates to permanent split capacitor single phase induction motors and, particularly, to a permanent split capacitor motor having a full capacity mode and a modulated capacity mode for improving operating efficiency.
A permanent split capacitor (PSC) motor of the type described herein has a stator assembly forming a core of magnetic material. Typically, the core consists of a stack of laminations punched from sheet-like ferro-magnetic material. Each lamination has a plurality of teeth spaced around a central opening and extending radially inwardly. When the laminations are stacked, the central openings are coaxial and constitute a bore extending longitudinally through the core. The bore receives a rotor assembly (e.g., a squirrel cage rotor) made from a stack of rotor laminations. A slip between the rotation of the rotor and the rotation of a magnetic field created by the stator induces a current in the rotor. In turn, the induced current creates a magnetic field of the rotor in contrast to the magnetic field of the stator. These contrasting rotating magnetic fields cause rotating torque of the rotor. Such a motor is particularly useful for driving a compressor of a refrigeration or air conditioning system. In this instance, the rotor has a bore for receiving a hermetic compressor crankshaft that rotatably supports the rotor body within the stator bore.
The rising cost of energy, the heightened awareness of environmental issues and the attendant governmental regulations for appliances and the like have all tended to accentuate the ongoing need for efficient and economical motors. As described above, single phase induction motors, including PSC motors, are frequently used as part of refrigeration and air conditioning systems for driving hermetically sealed compressors. In such systems, proper sizing of the equipment seeks to improve efficiency for operation over a wide range of load conditions. However, it is difficult to provide ample capacity and efficient operation for peak load conditions while still operating efficiently at lighter load conditions.
In general, the efficiency of a compressor motor involves the ratio of running load torque to breakdown torque. A ratio of about 3.0 (breakdown torque/running load torque) is desired for a relatively high efficiency for running load while still meeting the low voltage run down loaded requirements. The Air conditioning and Refrigeration Institute (ARI) sets forth standard test procedures for evaluating compressor efficiency. The test procedures examine the compressor's performance at standard conditions of 45° F. evaporating and 130° F. condensing temperature. Present government guidelines for energy efficiency reference ARI standards. In addition, compressor performance may be measured at operating conditions more closely approximating the actual operating conditions of a high efficiency system. For example, Copeland Corporation evaluates the performance of its compressors according to a standard referred to as “CHEER.” The CHEER standard rates compressor performance at 45° F. evaporating, 100° F. condensing temperature; 85° F. liquid; 65° F. return gas. Since the CHEER rating conditions more closely approximate the conditions under which the compressor will operate most frequently, higher compressor efficiency at CHEER generally equates to lower operating cost.
One method for modulating the compressor of the refrigeration system involves operating the compressor at two distinct speeds. However, multiple speed motors often cost more than single speed motors and/or fail to provide sufficient operating torque at low speeds. As an example, distinct winding multiple speed motors require separate main and auxiliary windings for each motor speed, which can increase the cost of the motor and present problems with respect to slot fill.
Since the motor is enclosed and hermetically sealed within the compressor unit in such a system, the number of leads from the motor is another cost factor. Electrical connections are made through the shell of the compressor and special connectors are needed to preserve the hermetic seal. The use and insertion of the connectors in the shell add significantly to the cost of the compressor. Consequently, motors designed for use in hermetic compressors should incorporate a minimum number of leads so as to minimize construction problems and the cost inherent in making multiple electrical connector openings through the compressor shell.
For these reasons, a motor is desired for reducing breakdown torque and improving efficiency over a wide operating range from peak load conditions to lightly loaded conditions. Further, such a motor is desired that does not require a large number of leads.
Commonly assigned U.S. Pat. No. 4,322,665, U.S. Pat. No. 4,103,212 and U.S. Pat. No. 4,103,213, the entire disclosures of which are incorporated herein by reference, disclose single phase motors that may be used for driving compressors.
SUMMARY OF THE INVENTION
The invention meets the above needs and overcomes the deficiencies of the prior art by providing an improved PSC motor system. Among the several objects and features of the present invention may be noted the provision of such a motor system that permits high efficiency operation over a wide range of load conditions; the provision of such a motor system that permits operation in a full capacity mode and in a modulated capacity mode; the provision of such a motor system that permits reducing breakdown torque in a modulated capacity mode; the provision of such a motor system that permits electrical connections using a minimum number of leads; the provision of such a motor system that permits unidirectional rotation for driving a compressor; and the provision of such method that can be carried out efficiently and economically and such system that is economically feasible and commercially practical.
Briefly described, a permanent split capacitor motor embodying aspects of the invention is operable in a full mode and in a modulated mode. The motor includes a stator and a rotor in rotational relationship with the stator. The motor also includes first and second windings wound on the stator. The windings are in a magnetically coupled relationship with each other such that one of the windings is a main motor winding while the other is an auxiliary motor winding. The windings define an A-ratio as a function of turns in the main motor winding compared to turns in the auxiliary motor winding. The motor further includes a switching circuit for selectively energizing the first and second windings in a full mode configuration and in a modulated mode configuration based on motor load conditions. In a preferred embodiment, the A-ratio of the windings energized in the full mode configuration is greater than the A-ratio of the windings energized in the modulated mode configuration. In this manner, the motor is selectively operable in the full and modulated modes based on motor load conditions for improving efficiency.
In another embodiment, a permanent split capacitor having a stator and a rotor in rotational relationship with the stator is operable in a full mode and in a modulated mode. The motor includes first and second windings wound on the stator in a magnetically coupled relationship with each other. The first winding generates a first rotating main magnetic field and the second winding generates a first rotating auxiliary magnetic field when the windings are energized in a full mode configuration for rotating the rotor. On the other hand, the second winding generates a second rotating main magnetic field and the first winding generates a second rotating auxiliary magnetic field when the windings are energized in a modulated mode configuration different from the full mode configuration for rotating the rotor. The motor also includes a switching circuit for selectively energizing the windings in the full mode configuration and in the modulated mode configuration based on motor load conditions. In this manner, the motor is sel
Emerson Electric Co.
Masih Karen
Senniger Powers Leavitt & Roedel
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