Abstract:
A combination sight glass and optical sensor is provided in the housing of a hermetic compressor to provide effective visual inspection in addition to automatic sensing of the level of oil in an oil sump. A sight glass fitting is provided in the housing and has a first portion that extends outwardly from the housing and that is accessible from outside the compressor. An optical oil level sensing device is removably attached to the first portion of the sight glass with electrical leads extending outside the compressor for connection to a compressor controller. A prism or similar device is attached to the sight glass fitting intermediate the sump oil and the optical sensor. The sensing device includes a light source, a photosensitive detector, and an opaque member to prevent cross coupling between the light source and the detector. Should the oil level in the oil sump fall below a predetermined level, the optical sensor sends a low oil level signal to the controller which interrupts power to the compressor or generates an alarm or status signal. A technician may remove the optical sensor from the sight glass fitting and visually inspect the oil level by looking through the sight glass fitting and prism and into the interior of the compressor housing. One embodiment of the optical sensor will also provide a low oil level signal to the controller when the optical sensor is disengaged or removed from the sight glass.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the invention. 
     The present invention relates to devices for sensing the level of oil in oil sumps in hermetic refrigeration and air conditioning compressors, such as scroll, reciprocating or rotary types, and more particularly to devices for optically inspecting and automatically sensing the level of oil in sumps. One aspect of the present invention relates to sight glass type devices attached to the housing of a compressor for allowing a person to visually examine the interior of the compressor from outside the compressor housing to determine the level of oil in an oil sump or to examine the surface of oil in a sump. Another aspect of the present invention relates to automatic sensing devices that optically sense the presence or level of oil in an oil sump and perform some desired function, such as alarm or service indication or compressor shut down, in the event the oil level becomes critically low. 
     2. Description of the related art. 
     The most common form of oil level sensing device utilized today and in the past in hermetic compressors is the mechanical float switch. A float is supported by oil in the sump of a compressor and with the oil at an acceptable level the switch maintains contact between a power source and the compressor. Should the oil, and the float supported thereby, drop below a threshold level, then the switch interrupts the power supply to the compressor and thereby terminates operation. A problem associated with magnetic float switches is that they generally utilize a magnetic reed switch which attracts metallic debris that binds the float switch and causes the device to become inoperable resulting in unnecessary compressor shut down or the loss of compressor protection. This type of device is wholly mounted internal the compressor housing requiring costly compressor disassembly to replace a malfunctioning switch. 
     Sight glass instruments have been incorporated in hermetic compressors to permit visual inspection of the level or presence of oil in a sump. Such sight glass instruments require an operator to periodically examine the compressor to verify that an acceptable level of oil is present in the sump. A problem with such sight glass instruments is that usually compressors are mounted in the interior of an outer housing of other devices, such as refrigerators, air conditioners, automobiles, etc., and, even if positioned most favorably, are difficult to examine and may require some disassembly. Another problem with such devices is that in the event of sudden catastrophic loss of oil in a sump, no advance warning is given and damage occurs without the opportunity for remedial measures. 
     Automatic oil level sensing devices are known which are generally mounted wholly in the interior of a compressor housing and electrically connected to the compressor power source via electrical leads which extend from the interior of the housing to the outside of the housing through a hermetic outlet in the housing. Typically, the leads are connected to the power source external of the compressor housing. When the sensor determines that the level of oil in the sump has dropped below a critical threshold level, the sensor, via switching contacts, relay contacts, TTL logic, etc., automatically interrupts the delivery of power to the compressor and operation is terminated. One problem with such known sensors is that the only way to verify the existence of a fault condition is to disassemble the compressor, no visual inspection is provided. 
     Often it is the sensor that has failed and has erroneously terminated compressor operation when in fact a sufficient level of oil is present in the sump. Again, the only way to determine this is to disassemble the compressor unless a second device, such as a sight glass described above, is also incorporated in the compressor. However, if the sensor has in fact failed then it is still necessary to disassemble the compressor to replace the failed sensor. This is not an economically desirable option but the only other alternative is to electrically bypass the failed sensor and permit unprotected compressor operation. 
     A problem with externally mounted sensors is that the sensor continues to sense an acceptable oil level after having fallen off or been removed from the sight glass. This situation may lead to damage to the compressor if the oil level does become low. 
     SUMMARY OF THE INVENTION 
     The present invention provides a combination oil sight glass and optical sensor for determining the level of oil in a sump of a hermetic refrigeration compressor. An oil sight glass is disposed in the bottom portion of the housing of a compressor at approximately the lowest acceptable level of the oil in the sump. The sight glass fitting is generally hollow and is hermetically sealed to the compressor housing. The hollow sight glass has a first end portion adjacent the oil sump and an opposite second end portion which preferably extends outwardly from the side of the housing external of the compressor. A prism, or other such device, is disposed in the sight glass at a first end portion of the sight glass and is optically accessible via the hollow sight glass from outside the compressor. The prism part may be placed anywhere along the length of the sight glass fitting, but is preferably located outside the compressor housing at a position most easily viewed by a person maintaining the compressor. With the sight glass placed in the housing of a compressor, an individual may visually examine the level of oil in the sump by looking through the sight glass and prism and into the interior of the compressor. 
     In combination with the prism, an optical sensor is removably disposed in, on, or about the sight glass. The optical sensor, through the separate prism of the sight glass, automatically senses the level of oil in the sump and generates a signal or trips a switch or otherwise breaks contacts when the level becomes critically low or exceeds a predetermined operating range. Electrical leads extend outwardly from the optical sensor external of the compressor and are connected to the electrical connections of the compressor or other devices so as to achieve a desired function. 
     For example, the leads of the optical sensor, which may be a combination sensor and switch, may be placed in series with the compressor power source, directly or via the contacts of a relay, to automatically terminate compressor operation in the event a critically low oil level is sensed. This prevents the compressor from becoming damaged due to insufficient lubrication. Alternatively, the leads of the sensor may be connected to a compressor controller, an alarming device, or some electronic protection circuit, for automatically generating a fault indication alarm upon the occurrence of a predetermined condition. The alarm, which may take the form of a flashing light, a horn, a remote indication, etc., gains the attention of an operator who may then visually verify the existence of a fault condition via the sight glass by removing the optical sensor and looking through the sight glass and prism and into the interior of the compressor housing. The signal generated by the sensor may be input to a facility management control system to provide enhanced maintenance capabilities and reporting. 
     In this manner, the present invention provides an automatic sensing device which may be removed from the compressor from outside of the compressor and which has electrical leads that may be disconnected from the compressor from outside the compressor. Accordingly, the present invention provides a simplified method of replacing a failed sensor without disassembling the compressor. The present invention further provides an integral sight glass that permits visual examination of the oil level in the sump to confirm a low oil level fault condition as sensed by the optical sensor. 
     The sight glass and sensor combination of the present invention may be used in reciprocating compressors, scroll compressors, and rotary compressors, such as disclosed in U.S. Pat. Nos. 5,266,015, 5,306,126, and 5,236,318, respectively, which are incorporated herein by reference. 
     The invention comprises, in one form thereof, a hermetic compressor comprising a housing, a motor receiving power through a controller from a power source, a compressor mechanism driven by said motor, an oil sump in said housing for holding lubricating oil therein, and an oil level sensing and viewing device. The oil level sensing and viewing device comprises a sight glass hermetically attached to said housing and an optical sensor removably mounted on said sight glass and electrically connected to the controller. The optical sensor may be removed from the sight glass from outside the housing. The optical sensor includes a light source, a photosensitive detector, and an opaque cylinder and adapted to sense the level of oil in the oil sump. The opaque cylinder includes a pair of bores. The light source and the detector are disposed within the bores preventing cross coupling between the light source and the detector. With the optical sensor removed from the sight glass a person may visually examine the level of oil in the oil sump by looking through the sight glass. With the optical sensor disposed on the sight glass and sensing a low oil level in the oil sump, the optical sensor sends a low oil level signal to the controller that interrupts the power to the motor thereby terminating compressor operation. 
     In a second form, the present invention comprises a hermetic refrigeration compressor comprising a housing, a motor receiving power through a controller from a power source, a compressor mechanism driven by said motor, an oil sump in said housing for holding lubricating oil therein, and an oil level sensing and viewing device. The oil level sensing and viewing device comprises a sight glass hermetically attached to said housing and an optical sensor removably mounted on said sight glass and electrically connected to the controller. The optical sensor is adapted to sense the level of oil in the oil sump and includes a housing, a light source, a photosensitive detector and a blocking member. The blocking member has a first position and a second position within the sensor housing. The first position is disposed between the light source and the detector preventing optical cross coupling when the optical sensor is attached to the sight glass. The second position is disposed away from the light source and the detector allowing cross coupling when the optical sensor is removed from the sight glass. The optical sensor may be removed from the sight glass from outside the housing and will send a low oil level signal to the controller to terminate compressor operation when removed from the sight glass. With the optical sensor removed from the sight glass a person may visually examine the level of oil in the oil sump by looking through the sight glass. With the optical sensor disposed in the sight glass and sensing a low oil level in the oil sump, the optical sensor sends a low oil level signal to the controller that interrupts the power to the motor thereby terminating compressor operation. 
     An advantage of the present invention is the ability to easily replace a defective oil level sensor from outside the compressor housing without disassembling the compressor. 
     Another advantage is the ability to externally visually check the level of oil in an oil sump or to visually verify a sensed low level condition after an optical sensor has terminated compressor operation. 
     Another advantage is that with the sensing device located essentially outside of the compressor, it is not subjected to the harsh environmental conditions suffered by such devices mounted wholly inside the compressor. 
     Yet another advantage is that cross coupling between the LED and the phototransistor is prevented by the opaque portions. 
     A further advantage is that the optical sensor will not allow the compressor to operate when it is not disposed on the sight glass in a position to sense the oil level. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a sectional view of a reciprocating refrigeration compressor incorporating the combination sight glass and optical sensor of one form of the present invention. 
     FIG. 2 is a cross-sectional view of the combination sight glass and optical sensor of FIG. 1 shown mounted in the housing of the compressor. 
     FIG. 3 is a partial sectional view of the bottom portion of the compressor of FIG. 1 illustrating the combination sight glass and optical sensor with the optical sensor removed for visual inspection of the oil level in the oil sump via the sight glass. 
     FIGS. 4 and 5 show an alternative embodiment of the sight glass. 
     FIG. 6 is a cross-sectional view of an alternate preferred embodiment of the optical sensor. 
     FIG. 7 is a cross-sectional view of the optical sensor of FIG. 6 shown mounted on the sight glass in the housing of a compressor. 
     FIG. 8A is a top view of the slidable opaque member of the optical sensor shown in FIG.  6 . 
     FIG. 8B is a side view of the slidable opaque member of the optical sensor shown in FIG.  6 . 
     FIG. 9A is a side view of one of the halves of the shell of the optical sensor shown in FIG.  6 . 
     FIG. 9B is an end view of the shell member shown in FIG.  9 A. 
     FIG. 10 is a schematic diagram of the LED and phototransistor circuit in the optical sensor. 
     FIG. 11 is a schematic diagram of the interface circuitry on a controller that connects to the LED and phototransistor circuit shown in FIG.  10 . 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In an exemplary embodiment of the invention as shown in the drawings, and in particular by referring to FIG. 1, a compressor, referenced generally at  10 , is shown having a housing generally designated at  12 . Although a reciprocating type compressor is illustrated in the drawings, this embodiment is only provided as an example and the invention is not limited thereto, but rather is applicable to all hermetic compressor applications. Housing  12  is shown having upper housing portion  14  and lower housing portion  16  and is supported by mounting flange  18  which is welded to bottom portion  16  for mounting the compressor in a vertically upright position. Located within hermetically sealed housing  12  is an electric motor, generally designated at  20 , having stator  22  surrounding rotor  24 . Stator  22  is secured within housing  12  by an interference fit such as by shrink fitting, and is provided with windings  26 . Rotor  24  has central aperture  28  provided therein into which is secured crankshaft  30  such as by interference fit. A terminal cluster  32  is provided in housing  12  for connecting motor  20  to a source of electric power. 
     Compressor  10  also includes an oil sump  34  generally located in the bottom portion  16 . A centrifugal oil pick-up tube  36  is press fit into counter bore  38  in the lower end of crankshaft  30 . Oil pick-up tube  36  is of conventional construction and includes a vertical paddle (not shown) enclosed therein. An oil inlet end  40  of pick up tube  36  extends downwardly into the open end of a cylindrical oil cup  42 , which provides a quiet zone from which high quality, non-agitated oil is drawn. 
     Compressor  10  includes a lubrication system for lubricating the moving parts of the compressor, including a reciprocating compressor mechanism, referenced generally at  44 , crankshaft  30 , and crank mechanism, referenced generally at  46 . An axial oil passageway  48  is provided in crankshaft  30 , which communicates with tube  36  and extends upwardly along the central axis of crankshaft  30 . At a central location along the length of crankshaft  30 , an offset, radially divergent oil passageway  50  intersects passageway  48  and extends to an opening  52 . As crankshaft  30  rotates, oil pick-up tube  36  draws lubricating oil from oil sump  34  and causes oil to move upwardly through oil passageways  48  and  50 . Lubrication of bearing  54  and crank mechanism  46  is accomplished by means of flats formed in crankshaft  30 , located in the general vicinity of bearing  54  and crank mechanism  46 , and communicating with oil passageways  48  and  50  by means of radial passages  56 . 
     An oil level sensing and viewing device, referenced generally at  58 , is provided in lower housing portion  16  and is hermetically sealed thereto. The particular placement of oil sensing/viewing device  58  is dependent upon the desired minimum level of oil in oil sump  34 . The oil level sensing/viewing device should be mounted on lower housing portion  16  such that the middle of the device is at the lowest acceptable oil level in oil sump  34 . Oil level sensing/viewing device  58  includes sight glass fitting  60 , prism  62 , and optical sensing device  64 . Sight glass fitting  60  is received in an opening  65  formed in lower housing portion  16  and is hermetically sealed to the housing by means of projection welding or the like at joint  66  as shown in FIG.  2 . Fitting  60  is generally hollow and tubular in shape and includes inward end portion  68 , which is received in interior  70  of housing  12  and outward end portion  72  which extends outwardly from housing  12  and is exposed and readily accessible. 
     Inward end portion  68  is provided with a protruding annular collar  74  which engages inner surface  76  of lower housing portion  16 . Inward end portion  68  is further provided with an opening  78 , which receives prism  62 . Prism  62  is fixably attached to sight glass fitting  60  by means of an adhesive, a deflectable flange about opening  78 , or any other suitable means. Rear surface  80  of prism  62  extends to the outermost portion of outward end portion  72  of sight glass fitting  60 . Prism  62  includes face  79  that faces inwardly toward and perpendicular to the oil level in sump  34 . Face  79  is provided with an outwardly extending point  84  which establishes the low level threshold point of the oil in sump  34 . 
     Oil sensing/viewing device  58  should be mounted such that point  84  is maintained below the acceptable and expected oil level throughout all phases of compressor operation. More importantly, oil sensing/viewing device  58  should be mounted on housing  12  such that outwardly extending point  84  of prism  62  is at that level below which the volume of oil in sump  34  is unacceptable. For example, as shown in FIG. 1, oil level  86  is clearly above outwardly extending point  84  as desired for proper compressor lubrication. Oil level  88 , as shown in FIG. 3, is level with outwardly extending point  84  of prism  62  and therefore represents the lowest acceptable oil level to be permitted in sump  34 . Should oil level  88  recede below outwardly extending point  84 , then the oil level is unacceptable and the compressor is shut down. 
     Oil level sensing device  64  includes opaque cylinder  150 , LED  140 , and phototransistor  142  and is introduced around outward end portion  72  of sight glass fitting  60 . Opaque molded plastic cylinder  150  is provided with a cylindrical forward portion  196  which surrounds outward end portion  72  of sight glass fitting  60 . Outward end portion  72  provides a stop to limit the movement of oil level sensing device  64  in a direction toward housing  12  with surface  165  of opaque cylinder abutting rear surface  80  of prism  62 . Oil level sensing device  64  may be sealably attached to fitting  60  by  0 -rings or the like and is external to housing  12  and readily accessible from outside compressor  10 . Oil level sensing device  64  may be may be securedly attached to fitting  60  by means such that unintended de-coupling is prevented, or may be easily removable from fitting  60  to permit removal by unaided hand operation. 
     Opaque cylinder  150  includes a pair of bores  152 ,  154  for LED  140  and phototransistor  142 , respectively, such that cross coupling between LED  140  and phototransistor  142  is prevented from either sideways coupling or by refection from rear surface  80  of prism  62 . 
     As shown in FIG. 10, the anode of LED  140  is electrically connected to the emitter of phototransistor  142 , requiring only three electrical leads for operation of oil sensing device  64 . Electrical leads  144 ,  146 ,  148  extend from oil level sensing device  64  and are electrically connected to a compressor control circuit (FIG.  11 ). The compressor control circuit provides a half-wave rectified voltage to LED  140  on lead  146  and a ground to LED  140  and phototransistor  142  on lead  148 . The input AC voltage to the compressor control circuit is fed into transformer TX 1 , resulting in a 24 VAC output from transformer TX 1  which forms the basis for the system&#39;s DC power supply. The 24 VAC is conditioned by resistor R 1  and diode D 1  to the half-wave rectified voltage provided to LED  140  on lead  146 . Oil level sensing device  64  provides an oil level signal to the compressor control circuit on lead  144 , which is either an open circuit or oscillates between an open circuit and ground at the same rate as the supplied half-wave rectified voltage. Resistor R 2  and capacitor C 1  of the compressor control circuit filter the oil level signal to bilateral switch U 2 , thus converting the output on lead  144  to a DC level. Switch U 2  controls the operation of the compressor from a number of factors which are fed to switch U 2  through gate U 1  and by the oil level signal. 
     In operation, LED  140  emits a beam of light which passes through bore  152  and prism  62  and into oil sump  34 , and phototransistor  142  receives any light returned through prism  62  and bore  154 . The threshold point for a low level oil indication is outwardly extending point  84  of prism  62 . If the compressor oil level is above point  84 , then the beam of light from LED  140  passes into the oil and is not returned to phototransistor  142 . Phototransistor  142  remains off and lead  144  displays an open circuit, allowing gate U 1  to control switch U 2 . Gate U 1  receives compressor protection inputs that can shut down compressor  10 . If the compressor oil level falls below point  84 , then the beam of light from LED  140  refracts in prism  62  back through bore  154  to phototransistor  142  turning it on and providing an oscillating ground on lead  144  which is filtered to a low logic level for input to switch U 2 , allowing device  64  to control switch U 2  which shuts down compressor  10 . 
     A description of one method of operation of the present invention, with reference to FIGS. 2 and 3, may be instructional. In the event the oil level in sump  34  falls below threshold level  88 , oil level sensing device  64  will either shut down compressor operation or trigger an alarm indication, as discussed above, relating to the low oil level. Upon compressor shut down or alarm indication, a technician may remove oil level sensing device  64  from sight glass fitting  60  by grasping protruding portion  100  and pulling radially outward therefrom. The particular manner of removing oil level sensor  64  from sight glass fitting  60  is unimportant and many known methods may be implemented and are fully contemplated by the present invention. For example, cylinder forward end  196  may have an inner cylindrical surface which is threaded and outward end portion  72  of sight glass fitting  60  may have an outer cylindrical surface which is matingly threaded for rotatably receiving oil level sensor  64  onto sight glass fitting  60 . In any event, with oil level sensor  64  removed from sight glass fitting  60 , as shown in FIG. 3, a technician may visually inspect interior  70  of compressor  10  by looking through sight glass fitting  60  and prism  62  at opening  90 . In this manner, the technician may determine if in fact the oil level in interior  70  of housing  12  has dropped below the acceptable threshold level. 
     If the technician determines that the oil level has not dropped below the threshold level, then oil level sensor  64  should be inspected to determine if it is defective. If it is defective, then it is a simple manner to replace the defective sensor with a new or reconditioned sensor which may then be installed in sight glass fitting  60 . If sensor  64  is not defective, then the technician will know to look elsewhere for the source of the problem. If, after visually inspecting the oil level via sight glass fitting  60  the technician determines that the oil level has in fact dropped below the acceptable threshold level, then the technician knows to inspect the compressor and refrigerant system for sources of that problem. In this manner, the compressor is protected from risk of damage due to insufficient lubricating oil and a technician may easily and cost effectively troubleshoot the source of compressor shutdown without unnecessarily disassembling the compressor or associated equipment. 
     Referring to FIGS. 4 and 5, an alternative oil level sensing and viewing device, referenced generally at  110 , is provided in lower housing portion  16  and is hermetically sealed thereto. Oil level sensing/viewing device  110  includes alternative sight glass fitting  112  and prism  114 . Fitting  112  includes an outward end portion  120 , which extends outwardly from housing  12  and is exposed and readily accessible. Outward end portion  120  is provided with an annular shoulder  126 , which engages the outermost portions of rear surface  130  of prism  114 . Prism  114  includes outwardly extending point  134  which does not extend past inner surface  76  of lower housing portion  16 . 
     Referring to FIGS. 6 and 7, an alternative oil level sensing device, referenced generally at  160 , is provided on sight glass fitting  60 . Oil level sensing device  160  includes housing  162 , LED  198  and phototransistor  200  mounted on circuit board  170 , and opaque member  164 . Housing  162  is comprised of two identical halves attached together to form a cylinder. As shown in FIGS. 9A and 9B, each half of housing  162  includes annular grooves  176 ,  178  for gaskets  180 ,  182  indents  186  for opaque member  164 , and annular pocket  194  for circuit board  170 . Opaque member  164  includes bores  166 ,  168 , wide center portion  188 , narrow edge portion  190 , and tabs  192 . 
     Housing  162  is provided with cylindrical forward portions  172 ,  174  which surround outwardly extending portion  72  of sight glass fitting  60 . Outward end portion  72  provides a stop to limit the movement of oil level sensing device  160  in a direction toward housing  12  with surface  189  portion  188  of opaque member  164  abutting rear surface  80  of prism  62 . Opaque member  164  biased toward portions  172 ,  174  by springs  184  in indents  186  engaging tabs  192  is urged away from portions  172 ,  174  by portion  72  of fitting  60 , inserting LED  198  and phototransistor  200  into bores  168  and  166 , respectively. With opaque member  164  in this position, cross coupling between LED  198  and phototransistor  200  is prevented from either sideways coupling or by reflection from rear surface  80  of prism  62 . Oil level sensing device  64  may be sealably attached to fitting  60  by O-rings or the like and is external to housing  12  and readily accessible from outside compressor  10 . Oil level sensing device  64  may be may be securedly attached to fitting  60  by means such that unintended de-coupling is prevented, or may be easily removable from fitting  60  to permit removal by unaided hand operation. 
     Other devices can be used in place of opaque member  164  and springs  184  such as a foam compression device or other compressible devices which would function to prevent cross coupling between LED  198  and phototransistor  200  when compressed and to allow cross coupling when not compressed. 
     The electrical connections between LED  198 , phototransistor  200 , and the compressor control circuit are identical to that described above for oil sensing device  64 . The mounting of LED  198  and phototransistor  200  on circuit board  170  provides support for these items and a location to attach the three required electrical leads. 
     In operation, oil level sensing device  160  when installed on sight glass fitting  60  works in an identical manner as that of oil level sensing device  64 . However, should oil level sensing device  160  fall off or be removed from sight glass fitting  60 , opaque member  164  is urged off of LED  198  and phototransistor  200  by springs  184  (FIG.  6 ). With opaque member  164  removed and nothing between LED  198  and phototransistor  200 , sideways coupling occurs and light emitted from LED  198  is detected by phototransistor  200 , turning phototransistor  200  on. This provides a low logic level to switch U 2  which then shuts down compressor  10 . Therefore, oil level sensing device  160  will not allow compressor  10  to run when it is not on sight glass fitting  60  and in a position to detect the oil level in compressor  10 . 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.