Abstract:
The present invention provides a control system for controlling the load bearing capacity of a reciprocating compressor system such as the type used in commercial and industrial refrigeration systems. The capacity control system includes a controller section having a microprocessor that stores and executes software that embodies commands for causing elements within a mechanical section of the invention to facilitate loading and unloading of any number of compressor cylinders as required for efficient operation of the compressor system under varying load conditions. The mechanical section includes a plurality of solenoid valves that are controllable by the controller section such that required loading and unloading of the cylinders is effective as required to maintain efficient load bearing capacity of the compressor system under changing load requirements.

Description:
RELATED APPLICATION  
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Serial No. 60/434,781 filed Dec. 18, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to control devices for compressor systems and more particularly to a control system kit for regulating the capacity and efficiency of a compressor system under varying load conditions.  
         BACKGROUND OF THE INVENTION  
         [0003]    In many cases, fluid compressors are designed to operate at a substantially consistent speed. Hence, when the load on the compressor system varies, the compressor operates inefficiently unless the capacity of the compressor can be varied directly with the load conditions. As such, there are devices suitable for use in regulating the capacity of compressor systems under varying loads.  
           [0004]    U.S. Pat. No. 3,844,686 discloses a control device for regulating the capacity of a reciprocating compressor system that includes a solenoid disposed within the outer walls of the compressor. The solenoid is in mechanical communication with a cable having a plurality of forked members disposed thereon. The fork members are for contacting an undersurface of the suction valve of the compressor to lift the valve off its seat when it is desired to unload the compressor fluid from the cylinder of the compressor and to move away from the undersurface of the valve when it is desired for the cylinder of the compressor to return to a loaded condition.  
           [0005]    Although the above means provided for varying the capacity of the compressor under varying load conditions is relatively simple, it requires that portions of the control device be disposed in an outer wall of the compressor crankcase. This requires that such a control device be manufactured as part of the original compressor unit at an increased cost relative to conventional compressors. Additionally, such a design presents an additional failure mode within the compressor unit.  
           [0006]    The present invention seeks to overcome the disadvantages associated with mounting control devices within the compressor unit as according to the above-described device by providing a capacity control kit which can be adapted to control the load bearing capacity of a conventional reciprocal compressor system without affecting the design and structure of the compressor itself.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a capacity control system for regulating the load bearing capacity of a compressor system under varying load conditions.  
           [0008]    The capacity control system includes a mechanical section having a plurality of solenoid valves adapted to facilitate the transference of compressor fluid between cylinders of the compressor, a fluid pump, and the compressor crankcase such that loading and unloading of the compressor cylinders can be accomplished under a changing load.  
           [0009]    Each solenoid valve of the mechanical section includes a plurality of fluid ports wherein a first fluid port is in fluid communication with the fluid pump of the compressor system, a second fluid port of each solenoid is in fluid communication with at least one cylinder of the compressor unit, and a third fluid port is in fluid communication with the crankcase for the compressor.  
           [0010]    A control section is provided that includes a controller in electrical communication with the plurality of solenoid valves disposed in the mechanical section of the capacity control system. The controller is operative to cause at least one of the plurality of solenoid valves to actuate in response to receiving at least one pressure signal from the compressor system.  
           [0011]    In response to a first pressure signal received from the compressor system, the controller is operative to actuate at least one of the solenoid valves to effect fluid communication between the first and second fluid ports of the solenoid such that fluid flow is permitted between the fluid pump and at least one cylinder of the compressor system. In response to a second pressure signal received from the compressor system, the controller is operative to actuate the solenoid to effect fluid communication between the second and third fluid ports such that fluid flow is permitted between the at least one cylinder of the compressor system and the compressor crankcase. In this fashion the capacity control system of the present invention allows for the load bearing capacity of a compressor system to be varied in accordance with a varying load connected thereto. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawings in which like parts are given like reference numerals and wherein:  
         [0013]    [0013]FIG. 1 illustrates a block diagram of a capacity control system according to the invention having a microprocessor based controller section;  
         [0014]    [0014]FIG. 2 illustrates an alternative embodiment of a capacity control system as according to the invention having an electromechanical controller; and  
         [0015]    [0015]FIGS. 3A and 3B illustrate diagrammatic top and side views of the mechanical section of the capacity control system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    The capacity control system as according to the present invention provides a reliable and efficient means of regulating the load bearing capacity of reciprocating compressor systems such as the type used in commercial and industrial refrigeration systems.  
         [0017]    The capacity control system provided herein is operative to communicate with, and to control, a compressor system having multiple cylinders and/or multiple stages of compression. The system to be controlled by the present invention may also include a control panel in communication with the compressor system whereby a user may selectively choose between manual control of the compressor system operation, via interfacing relays and switches, or automatic control of the compressor system through enabling the capacity control system as according to the invention.  
         [0018]    With reference to FIG. 1, the capacity control system  10  is provided in the form of a kit having a controller section and a mechanical section operative to be disposed in mechanical and electrical communication with a reciprocating compressor system that lacks facility to vary its load bearing capacity in response to a varying load.  
         [0019]    As shown in FIG. 1, a controller section  12  of the capacity control system  10  is placed in electrical communication with at least one pressure sensor/transmitter device that is operative to communicate pressure information received from the compressor system to the controller section  12 . It is appreciated that the pressure sensor/transmitter may be hardwired to the controller section  12  or be adapted to communicate over a wireless link. The controller section  12  is also placed in communication with a compressor control panel  18  which permits a user to selectably choose between manual or automatic control of the compressor system as desired. Accordingly, the compressor control panel  18  communicates directly with the compressor  20  such that manual control can be facilitated. It is appreciated that the required mechanical and electrical connections between the capacity control system  10  and the compressor system are provided via conventional materials such as fluid piping or tubing, electrical cabling and other conventional mechanical and electrical communication interfaces suitable for such purpose.  
         [0020]    In a preferred embodiment of the capacity control system  10 , the pressure sensor/transmitter  16  receives at least one pressure signal from the compressor system suction pipe and/or manifold and thereafter transmits the signal to the controller section  16  of the system. When the capacity control system  10  is selected over manual control, the controller section  12  receives the pressure signal and then determines whether a loading or unloading command should be sent to the mechanical section  14  of the capacity control system  10 .  
         [0021]    Referring now to FIGS. 3A and 3B, the mechanical section  14  of the capacity control system  10  includes a plurality of solenoid valves  30 ,  32 ,  34 ,  36  each including a plurality of fluid ports  40 ,  42  and  44 . As illustrated here, the preferred embodiment uses solenoid valves having 3 fluid ports. A first fluid port  40  is in fluid communication with a fluid pump  50  that operates to pump compressor fluid into the compressor system under increased load conditions. A second fluid port  42  is provided in fluid communication with at least one cylinder of the compressor unit, and a third fluid port is in communication with a crankcase  54  of the compressor.  
         [0022]    Disposed between the cylinders  52  of the compressor, the fluid pump, and the compressor crankcase are a plurality of corresponding un-loader power elements which cooperate with the solenoid valves for loading and unloading the cylinders of the compressor to accomplish variable load bearing capacity of the compressor system in response to the varying load.  
         [0023]    Referring again to FIG. 1, the mechanical section  14  of the capacity control system  10  is in electrical communication with a controller section  12  and is operative to cause at least one of the plurality of solenoid valves  30 ,  32 ,  34  and  36  to actuate in response to receiving at least one pressure signal from the compressor system. In the preferred embodiment, the controller section  12  includes a microprocessor-based controller having a plurality of analog and digital input/output modules for facilitating communication with the various components of the compressor system and the mechanical section  14  of the capacity control system  10 .  
         [0024]    The microprocessor controller includes software that causes at least one of the plurality of solenoids in the mechanical section to effect fluid communication between the first and second fluid ports such that fluid flow is permitted between the fluid pump and at least one cylinder when a first pressure signal is received from the compressor system. In this case, the load bearing capacity of the compressor system would be increased in response to an increased load.  
         [0025]    Additionally, the software is operative to effect fluid communication between the second and third fluid ports such that fluid flow is permitted between at least one cylinder of the compressor and the crankcase when a second pressure signal is received. In this case, an unloading of the compressor system is realized whereby the load bearing capacity of the system is reduced in response to a decreased load. Accordingly, the microprocessor-based controller is operative to detect pressure signals from the compressor system and to cause the solenoids of the mechanical section to actuate in a manner that facilitates the loading or unloading of corresponding cylinders of the compressor system to affect the loading bearing capacity such that efficient operation of the compressor system is maintained.  
         [0026]    Referring now to FIG. 2 an alternative embodiment  10 ′ is illustrated wherein the controller section  12 ′ has an electromechanical controller rather than a microprocessor-based controller. Here the capacity control system  10 ′ utilizes cylinder loading and unloading pressure switches that communicate the open and/or closed status of the switches to the electromechanical controller.  
         [0027]    The status of the pressure switches are used to control relays and timers within the electromechanical controller  12 ′ which actuate accordingly to cause the loading and unloading of cylinders of the compressor unit when the compressor system is operating at suction pressures outside of predetermined thresholds. As such, when a low pressure switch is closed a first pressure signal is received by the electromechanical controller to effect fluid communication between the first and second fluid ports of a corresponding solenoid such that fluid flow is permitted between the fluid pump and at least one cylinder of the compressor unit to increase the load bearing capacity.  
         [0028]    Similarly, an unloading pressure switch  62  causes a second pressure signal to be received by the electromechanical controller  12 ′ such that the solenoid is caused to effect fluid communication between the second and third fluid ports whereby fluid flow is permitted between the cylinder and the crankcase thereby decreasing the load bearing capacity of the compressor unit.  
         [0029]    Preferably, the controller section  12  of the capacity control system  10  includes an I/O module in communication with a device operative to allow for visual monitoring of the compressor system performance in addition to being in communication with a device for recording system performance as desired.  
         [0030]    Most preferably, the capacity control system  10  having the electromechanical controller is adapted to sequentially control the stages for loading and/or unloading of cylinders, and multiple compressors, within a minimum of 6-8 psi pressure differential. For the microprocessor-based controller embodiment, the capacity control system  10  is preferably operable to control the sequential loading and unloading of cylinders, and multiple compressors, with pressure differentials as low as practical and tolerable by the process, most preferably less than 6 psi.  
         [0031]    When multiple compressors are used, the microprocessor-based controller is preferably operable to periodically sequence the operation of each compressor in order to promote equal wear and tear among the units. Still further, the capacity control system  10  having the microprocessor-based controller is preferably operable to control condensing temperature by cycling and/or modulating fans and pumps of the compressor system and its corresponding condenser. In such case, the microprocessor-based controller section can be adapted to control efficient load bearing capacity as well as temperature modulation.  
         [0032]    It is appreciated that the electromechanical controller of the present invention may also be adapted to control the modulations of pumps and fans in relation to condensers of the compressor system. Each of the capacity control system embodiments is adapted to be integrated into a reciprocating compressor system to effect efficient load bearing capacity under varying load conditions. Each embodiment is adaptable to accommodate any number of loading and unloading stages per compressor and will also accommodate multiple compressors. Each system is operable with all types of coolant fluids including NH 3 , halocarbons, or the like.  
         [0033]    From the foregoing, it can be seen that the present invention provides a capacity control system for modulating the load bearing capacity of a compressor system under varying loads such that efficient operation of the compressor system is maintained. It is appreciated that one skilled in the art may realize changes and modifications to the present invention upon reading the specification that do not, however, depart from the spirit of the invention as defined by the scope of the appended claims.