Abstract:
A scroll compressor is provided with a reverse rotation detection circuit that monitors the temperature adjacent the suction tube. An elevated temperature at the suction tube is indicative of reverse rotation, and if the temperature exceeds a predetermined maximum, then a determination is made that reverse rotation is occurring. Once this determination is made, the rotation of the motor is stopped, or corrected.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to monitoring of the suction temperature of a scroll compressor to make a determination of when the compressor is running in reverse. 
     Scroll compressors are becoming widely utilized in many compression applications. Scroll compressors have high efficiency, and thus are becoming very popular. However, there are many challenges during scroll compressor operation. 
     Essentially, a scroll compressor includes a pair of interfitting scroll wraps each connected to a planar base. One of the wraps is fixed and the other wrap orbits relative to the fixed wrap. The wraps are in contact with each other and define compression chambers for an entrapped fluid. As the orbiting scroll moves relative to the fixed scroll, the size of the compression chambers change to compress the gas. 
     Scroll compressors are designed to operate in one direction. If there is orbiting movement of the orbiting scroll in the opposed direction, then the scroll compressor is not operating properly. There is unwanted noise, and increased heat in the compressor system. This is undesirable. 
     One main cause of reverse rotation in scroll compressors is miswiring of the motors. Often, scroll compressors are driven by three phase motors. The three phase motors typically include three power input lines leading from a power supply to the motor. If the lines are misconnected to the motor, then an improper phasing of the voltage may be supplied and the motor may run in reverse. As mentioned above, if a scroll compressor is ran in reverse, the results are undesirable. 
     SUMMARY OF THE INVENTION 
     When a scroll compressor is ran in reverse, there is noise and increased temperatures at many locations in the system. One location is the suction tube. Gas is no longer being drawn into the compressor. In fact, applicant has determined that a small quantity of gas passes out of the compressor and through the suction tube. When this occurs, the suction tube quickly reaches an elevated temperature. The housing around the tube also reaches an increased temperature. 
     The present invention monitors the temperature at or adjacent the suction tube. If a predetermined maximum suction temperature is exceeded, then a determination is made that reverse rotation is occurring. Once the determination is made, the motor is shut down. The motor may be shut down by a control directly to the motor, or the control may communicate to the power supply. As an example, phase reversing circuits are known wherein the phase of two of the three wires is changed. These circuits would result in proper wiring of the three phase motor should an improper connection be initially made. The phase circuits are activated by the temperature sensor. 
     In the preferred embodiment, the temperature sensor is one which moves from a monitoring position to an actuated position once a particular temperature is reached. As one example, the sensor may include a fusible element which melts when the target temperature is reached. As another example, the sensor may include a member which moves between one of two positions once the temperature is reached, such as a bi-metal snap disk. The sensor may include a manual reset, an automatic reset, or may be one which must be replaced after one actuation. The temperature in the suction tube or adjacent to the suction tube upon reverse rotation may approximate 300° F. The normal operating temperature should not exceed approximately 120° F. Thus, it is quite easy to design an element which will only be actuated upon reverse rotation. 
     In several embodiments, the sensor may be placed on the suction tube, or on the housing adjacent to the suction tube. Either location will be sufficient for identifying when reverse rotation is occurring. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a first embodiment of the present invention. 
     FIG. 2 shows a second embodiment of the present invention. 
     FIG. 3 shows a third embodiment of the present invention. 
     FIG. 4 shows a feature of the present invention. 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1, a compressor  20  incorporates a container housing  21  enclosing a motor  22  (shown schematically) and a pump unit  24 . As shown, the pump unit is preferably a scroll compressor. 
     A suction tube  26  leads into the container  21 . As known, an outlet tube  27  leaves the container at another location. The container seals the suction tube  26  from the outlet  27 . A temperature sensor  28  is mounted on suction tube  26  and monitors the temperature in the suction line  26 . The sensor may be mounted at various locations along tube  26 . A power supply  30  supplies three phase power  32  to motor  22 . 
     Should the three phase power supply be miswired, then it is possible that the motor  22  will be driven in reverse. This would result in noise and elevated temperatures within compressor  22 . One location of elevated temperature would be at the suction tube  26 . A small quantity of fluid may leave tube  26  from the compressor  20  when motor  22  is driven in reverse. This will raise the temperature adjacent tube  26 . 
     When temperature sensor  28  senses an elevated temperature that is above a predetermined maximum, a signal is sent to control  34  that reverse rotation is occurring. In the FIG. 1 embodiment, control  34  shuts down motor  22  by some means. As an example, control  34  might blow a fuse to stop the motor  22 . Other means of stopping the motor  22  may be used. 
     FIG. 2 shows a second embodiment wherein control  38  is operable to break at least one of the three phase lines  36  from supply  30  to the motor  22  if it is determined that reverse rotation is occurring. The structure for breaking a line could be a structure similar to a circuit breaker or other known elements. 
     FIG. 3 shows an automatic correction of reverse rotation. In FIG. 3, the control  40  responds to the determination of reverse rotation by acting in conjunction with a phase reversing circuit  42  to reverse the phase of at least two of the three wires  44  leading to the motor from the power supply  30 . By reversing the phase of two of the lines, the control reverses the overall power being supplied to the compressor and will reverse the rotation. Since the motor was rotating in the wrong direction, it will now be rotating in the proper direction. Phase reversing circuits are known and have been used to cause reverse rotation in other type systems, however, they have not been used to correct for improper wiring in scroll compressors. 
     FIG. 4 shows another embodiment  50  wherein the sensor includes two lines  52  and  54  connected in a fusible portion  56  connected to the housing  21 . Lines  52  and  54  lead to the control element. As compared to the FIG. 1 embodiment, the sensor is now mounted on the housing adjacent, rather than directly on, the suction tube  26 . The housing adjacent to the suction tube will still be at an sufficiently elevated temperature to actuate the sensor. 
     If the target temperature is reached, fusible element  56  melts breaking the circuit between lines  52  and  54 . The control interprets the break as an indication of reverse rotation. As an alternative to the fusible link, a bi-metal snap disk which actuates at a particular temperature may be utilized. 
     The fusible link may be one available from Elcot, of Osaka, Japan. The bi-metal snap disk switch may be one known as a fixed temperature thermostat, and available from Texas Instruments. The sensors may be manually reset, automatically reset, or may be of sort which must be replaced after one use. 
     The invention recognizes that the temperature in the suction tube or adjacent to the suction tube during reverse rotation can be on the order of 300° F. The temperature in the same location during normal operation typically does not exceed 120° F. Thus, there is a very large temperature range which allows this invention to be easily achieved, and appropriate sensors to be designed. 
     The present invention identifies reverse rotation by monitoring suction temperature, and responding to a determination of an elevated temperature by stopping the reverse rotation. Thus, a very simple approach to detecting and correcting reverse rotation is disclosed. 
     Although the specific disclosure is to a three-phase motor, reverse rotation can occur in a single phase motor, and this invention will correct for such reverse rotation. Also, although only three phase lines are shown, it should be understood that the type of three phase power supply having four wires also comes within the scope of this invention. 
     Preferred embodiments of this invention have been disclosed, however, a worker of ordinary skill in the art would recognize that certain modifications will come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.