Patent Publication Number: US-3874187-A

Title: Refrigerant compressor with overload protector

Description:
United States Patent [191 Anderson [11] 3,874,187 451 Apr. 1, 1975 REF RIGERANT COMPRESSOR WITH OVERLOAD PROTECTOR [75] Inventor: Thomas J. Anderson, North Brunswick, NJ.  
 [73] Assignee: Fedders Corporation, Edison, NJ.  
 Primary Examiner-Meyer Perlin Anorney, Agent, or FirmRyder, McAulay, Fields, Fisher &amp; Goldstein [57] ABSTRACT A compressor having a sealed housing provided with a bottom compressor unit compartment and an upper motor compartment. A compressor unit is received in the bottom compartment and a motor is received in the motor compartment for driving the unit. The motor comprises a rotor and a stator having a winding the bottom portion of which is positioned adjacent to the bottom of the motor compartment. Connected to the compressor unit is an inlet for the flow of low pressure refrigerant gas discharged from the refrigerator system. A desuperheating coil provides a conduit for the flow of compressed refrigerant gas from the compressor unit back to the housing where the cooled gas enters at a point adjacent to the bottom of the motor compartment. Mounted on the bottom portion of the stator winding and positioned in the path of flow of the gas from the desuperheating coil is a thermostatic switch which is serially connected with the motor and its source of energy. The switch is operable to disconnect the motor from its energy source when the switch senses a combined temperature and current above a preselected value indicative of a motor overload.  
 6 Claims, 2 Drawing Figures REFRIGERANT COMPRESSOR WITI-I OVERLOAD PROTECTOR This invention relates generally to a refrigerant compressor and, more particularly, pertains to a refrigerant compressor having an improved overload protector whereby faster and more accurate responses to overload conditions are obtained.  
  Motors used to drive compressor units in hermetically sealed refrigerant compressors are peculiarly subject to thermal overloads which might well damage the motor winding insulation, thereby resulting in short circuits. When such damage occurs, the compressor must be replaced and the cost of such replacement is usually expensive since a great deal of labor is required to replace a compressor in addition to the cost of the compressor per se.  
  Accordingly, various overload protection arrangements have been used to protect motors from thermal overloads of the type under consideration. In one arrangement typically referred to as a rotary compressor, the motor windings are cooled by positioning the windings in the path of the refrigerant gas as the gas flows from the compressor unit to the refrigerating system. While this arrangement provides the requisite cooling when the motor is operating properly, a problem is presented if the motor stops operating as, for example, when the rotor locks. The motor will then quickly overheat with consequent damage to the winding insulation.  
  Another arrangement commonly used is to provide a thermal cut-out or thermal overload protection device in the form of a thermostatic switch of conventional construction that is connected in series with the motor. The switch is operable to disconnect the motor from its source of energy when the temperature in the housing rises above a preselected level corresponding to an overload condition. However, these thermal protection devices have proved to be inefficient in the past particularly in the case of a so-called non-start condition because ofthe long interval required for the ambient temperature to reach the overload temperature. Therefore, an overload condition may be permitted to exist for a substantial time before the device operates.  
  To be more specific, since the normal operating temperature of a rotary compressor is relatively high, the temperature at which the thermal protection device is set to cut-out is likewise correspondingly in excess of such normal operating temperature. When the compressor is initially energized it is at substantially the temperature of the environment. If a non-start condition is encountered (ie. the motor fails to operate), the temperature within the housing will increase. However, since the thermal protection device cut-out point is set relatively high, the motor will be subjected to excessive elevated temperatures for a relatively long period of time. It is obvious that continued repetition of this sequence of events will have a destructive effect on the motor windings over a period of time.  
  The above problem is compounded by the fact that under operating conditions a temperature gradient exists within the housing with the higher temperature at the top of the housing and a lower temperature at the bottom. Thermal protection devices of the prior art, such as shown in US. Pat. No. 2,946,203, are positioned at the top of the housing and, therefore, must be .set at a relatively high cutout or operate temperature top of the housing otherwise the motor will be prematurely disconnected from the source of energy. As a result, the reaction time of the switch for a non-start condition or the like is correspondingly increased.  
  Accordingly, an object of this invention is to provide an improved overload protector for a refrigerant compressor motor.  
  A more specific object of the present invention is to provide an overload protector for a compressor that reacts relatively quickly to overload conditions.  
  Another object of the invention is a provision of an overload protector for a compressor that is highly sensitive to the temperature of the motor windings to be protected.  
  A further object of the invention resides in the novel details of construction that provide an overload protector of the type described for a refrigerant compressor that permits operation of the motor at lower terminal voltages than systems used heretofore.  
  In accordance with the present invention, a compressor is provided that comprises a sealed housing having a compressor unit disposed within a lower compressor unit compartment and a motor positioned above the compressor unit in an upper motor compartment and connected in driving relationship therewith. The motor includes a rotor and a stator provided with a winding having a bottom portion which is positioned adjacent to the bottom of the motor compartment. A compressor inlet is provided for introducing low pressure refrigerant gas from the refrigerating system into the compressor unit and conduit means provides for the flow of compressed refrigerant gas from the compressor unit into the motor compartment. A housing outlet provides a path for the discharge of the compressed refrigerant gas from the housing back to the refrigeration system. Thermally responsive switch means is mounted adjacent to the bottom of the motor compartment and is connected in electric circuit with the motor for disconnecting the motor from a source of potential when the switch means senses a temperature above a preselected value, thereby to protect the motor from damage due to overload conditions.  
  Other features and advantages of the present invention will become more apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawing, in which:  
  FIG. 1 is a front elevational view, partially in crosssection and partially in diagrammatic form, of a refrigerant compressor constructed according to the present invention; and  
  FIG. 2 is a schematic circuit wiring diagram of the compressor motor and overload protector.  
  A refrigerant compressor constructed according to the present invention is designated generally by the reference character 10 in FIG. 1 and comprises a hermetically sealed housing designated generally by the reference charcter 12. The housing 12 comprises a cylindrical intermediate section 14, a bottom dome section 16 and a top dome section 18. Peripheral portions adjacent to the bottom edges of the dome sections 16 and 18 are received within the cylindrical section 14 and are welded thereto so that the interior of the housing 12 is heremetically sealed from the external environment.  
  A mounting bracket 20 extends across the interior of the housing 12 and divides the housing into a lower compressor unit compartment 2.2 and an upper motor compartment 24. As shown in FIG. 1, the mounting bracket is spaced from the bottom of the housing 12 by a distance approximately equal to one-quarter of the overall height of the intermediate section 14. Mounted on the bottom surface of the bracket and received within the compressor unit compartment 22 in the bottom of the housing is a compressor unit 26. The compressor unit 26 is conventional in construction and is operable to compress refrigerant gas discharged from the refrigerating system.  
  Received within the motor compartment is a motor, illustrated diagrammatically at 28, which includes a rotor 30 and a stator windings 34. Connected to the rotor 30 is an output shaft 36 which connects with the compressor unit 26 to drive the unit. The stator windings 34 include a top portion 38 and a bottom portion 40 which is positioned adjacent to the bracket 20 at the bottom of the motor compartment 24.  
  An inlet tube 42 extends through the wall of the housing 12 into the compressor unit 26 and provides a path for the discharge of low pressure refrigerant gas from the refrigeration system (not shown) to the compr-essor unit. Compressed refrigerant gas from the compressor unit 26 is discharged through a conduit 44, which extends through the wall of the housing 12, into an inlet tube 46 of a desuperheater coil 48. The compressed refrigerant gas flows through the desuperheater coil 48 and is discharged from a desuperheater coil outlet tube 50 into the motor compartment 24 of the housing 12 through a wall passage 52. As shown in FIG. 1 the discharge opening of the passage 52 is positioned near the bottom ofthe motor compartment adjacent to the bottom portion 40 of the stator winding 34. The desuperheater coil 48 is conventional in construction and is operable to cool the refrigerant gas passing therethrough. For example, in an actualponstruction, the desuperheater coil has cooled compressed refrigerant gas flowing into the inlet tube 46 at a temperature of 235F. to 160F. as the gas flows out of the outlet tube 50. I  
  The gas flowing into the motor compartment 24 through the passage 52 flows upwardly across the motor 28 therby cooling the motor. Centrally positioned in the top dome 18 of the housing 12 is a discharge tube&#39;54 that provides a path for the discharge of the compressed refrigerant gas from the motor compartment 24 to the refrigeration system. The compressed refrigerant gas flows through the refrigeration system to provide cooling and is discharged back to the compressor unit 26 through the inlet tube 42 in the conventional manner. I  
  As&#39;not&#39;ed hereinabove, a temperature gradient exists within the motor compartment 24. The highest temperature exists at the top of the compartment and the lowest temperature is at the bottom of the compartment. Heretofore, overload protectors have been positioned adjacent to the top ofthe motor compartment and must therefore operate at elevated temperatures. In order to sense a thermal overload, the cut-out point or point of operation of the overload protector must be set relatively high. As a result, the response of the protection device has been relatively slow&#39;since a substantial interval of time exists before the ambient temperature of the device rises to the overload temperature point, particularly with regard to a non-start condition (at the initiation of a cycle of operation).  
  In accordance with the present invention, an overload protector or overload protection device 56 is provided which is located adjacent to the bottom of the motor compartment 24. The overload protector may be any of the well known types of thermal protection devices which are now on the market and which are operable to open a switch when the ambient temperature due to the motor current flowing through the device and the temperature of the motor windings reach a preset cutout point or temperature level. The switch is usually serially connected between the motor source of energy and the motor so that the device effectively disconnects the motor from its source of energy when the protection device operates.  
  More specifically, the overload protector 56 is mounted on the bottom portion 40 of the stator winding 34 as shown in FIG. 1. By so positioning the overload protector 56, a number of advantages are obtained. In the first place, by placing the overload protector directly on the stator winding 34, the sensitivity of the overload protector to winding temperature is increased. That is, since the overload protector is in direct heat exchanging relationship with the winding 34, the protector immediately senses the winding temperature.  
  Additionally, by locating the overload protector 56 in the bottom portion of the motor compartment 24, the cut-out point of the overload protector may be set for a lower temperature than if the protector were located in the upper portion of the compartment. That is, since a temperature gradient exists from the top to the bottom of the motor compartment 24, the temperature at the bottom of the compartment due to an overload condition will be lower than the corresponding temperature at the top of the compartment.  
  Moreover, in addition to locating the thermal protector 56 at the bottom of the motor compartment, the protector 56 is also positioned adjacent to the discharge opening of the passage 52. In other words, the protector is located directly in the path of the cooled compressed refrigerant gas from the desuperheater coil 48 which further serves to lower the ambient temperature of the protector 56. Accordingly, since the protector 56 is cooled by gas from the desuperheater coil and it is positioned in the lower (and cooler) portion of the motor compartment, the cut-out temperature may be set relatively low. Thus, if the flow of compressed refrigerant gas decreases or stops due to a locked rotor condition or a nonstart condition for example, the temperature of the stator winding 34 will immediately begin to rise. Since the cutout temperature point of the protector 56 is set relatively low and the compressed refrigerant gas from the desuperheater coil 48 is no longer cooling the protector, the protector will operate in a minimum amount of time to disconnect the motor from the power source, as noted in greater detail below.  
  The overload protector 56 is normally connected in series with the motor 28 and its energizing source as noted above. More specifically, as shown in FIG. 2, the motor 28 is connected between a pair of input terminals 58 and 60 which, in turn, are connected to the respective terminals of a source of energy 62. The overload protector 56 is connected between one terminal of the motor 28 and the input terminal 58. Accordingly, the motor current flows through the overload protector 56. The overload protector 56 operates on an additive basis (i.e., it senses heat generated by the motor current flowing through it as well as the heat generated by the winding) so that it monitors the current flowing through the motor 28 in addition to the ambient temperature of the protector 56. Hence, the overload protector will operate to disconnect the motor from the energizing source if the current drawn by the motor exceeds an overload value or if the temperature of the protector (and, therefore, the winding 34) rise to an overload point or any combination of the two.  
  As a result of positioning the overload protector 56 adjacent to the discharge end of the desuperheater coil 48 and adjacent to the bottom of the motor compartment 24, the ambient temperature of the overload protector 56 will be relatively low, as noted above. Therefore, the current drawn by the motor 28 may be increased above normal without causing the overload protector to operate as long as the current does not generate heat in excess of that which would cause the overload protector to operate. Thus, the motor 28 can run at lower terminal voltages since larger currents can be tolerated by the system. Hence, the compressor having the overload protector of the present invention is ideally suited for use during brown-out periods, when the terminal voltage is decreased. This is an extremely important consideration since brown-outs lie, decreased terminal voltage) most likely occur during summer months. However, this is precisely when the maximum demands are placed on refrigeration systems of the type under consideration. The pres ent invention therefore provides ideal protection for the compressor since it permits substantial low voltage operation at high load without taking the refrigeration system out of service.  
  Accordingly, a refrigerant compressor with an overload protector has been provided which has a faster response to overload conditions and which permits the compressor to operate at high load and relatively low voltage conditions.  
  While a preferred embodiment of the invention has been shown and described herein, it will be obvious that numerous omissions, changes and additions may be made in such embodiment without departing from the spirit and scope of the present invention.  
 What is claimed is:  
  l. A compressor for a refrigeration system comprising:  
 a. a sealed housing having a compressor unit compartment in the lower portion and a motor compartment in the upper portion thereof;  
 b. a compressor unit disposed within said compressor unit compartment of said housing;  
 c. a motor disposed in said motor compartment of said housing and connected in driving relation ship with said compressor unit;  
 , i. said motor comprising a rotor,  
 ii. and a stator provided with a winding having a bottom portion positioned adjacent to the bottom of said motor compartment;  
 d. a compressor inlet for introducing refrigerant gas discharged from the refrigeration system into said compressor unit;  
 e. conduit means for providing a path for the flow of compressed refrigerant gas from said compressor unit into said motor compartment;  
 f. a housing outlet providing for the discharge of compressed refrigerant gas from said housing back to said refrigeration system;  
 g. and thermally operated switch means mounted adjacent to the bottom of said motor compartment and connected in electric circuit with said motor for disconnecting said motor from a source of potential when said switch means senses a temperature above a preselected value.  
  2. A compressor as in claim 1, in which said switch means is mounted on the bottom portion of said stator winding in heat exchanging relationship therewith.  
  3. A compressor as in claim 2, in which said conduit means comprises a desuperheater coil having an inlet opening connected with said compressor unit and an outlet opening positioned adjacent to said bottom portion of said stator winding.  
  4. A compressor as in claim 3, in which said switch means comprises a thermostatic switch positioned in the path of flow of compressed refrigerant gas from said desuperheater coil outlet opening.  
  5. A compressor as in claim 4, in which said housing comprises a discharge tube in the upper portion of said housing for discharging compressed refrigerant gas back into the refrigeration system, whereby compressed refrigerant gas flows upwardly over said motor.  
  6. A compressor as in claim 1, in which said switch means generates heat in accordance with the motor current flowing therethrough, and said switch means senses temperatures due to the heat generated by the current flowing therethrough and the heat of said stator winding.