System for adjusting resonance frequencies in a linear compressor

Abstract

A system for adjusting resonant frequencies in a linear compressor comprising, in the interior of a shell: a linear motor: a cylinder; a piston reciprocating inside the cylinder; and an actuating means operatively coupling the piston to the linear motor, said system comprising: a detecting means to detect a load imposed to the linear motor, in an operational condition of the latter related to the gas pressure in the discharge thereof; and a frequency adjusting means operatively associated with the detecting means and with the resonant assembly, in order to define, as a function of said operational condition, a frequency adjustment, by varying at least one of the values related to the mass of the resonant assembly and to the average stroke of the piston, to a value of the mechanical resonance frequency corresponding to the electrical supply frequency.

1 . A system for adjusting resonant frequencies in a linear compressor comprising, in the interior of a shell: a linear motor supplied by an AC electrical current presenting a predetermined electrical supply frequency; a cylinder within which is defined a compression chamber closed by a valve plate; a piston reciprocating inside the cylinder in consecutive suction and compression strokes; and an actuating means operatively coupling the piston to the linear motor, said piston and actuating means forming part of a resonant assembly, comprising: 
 a detecting means to detect a load imposed to the linear motor of the compressor, in an operational condition of the latter related to the gas pressure in the discharge thereof; and    a frequency adjusting means operatively associated with the detecting means and with the resonant assembly, in order to define, as a function of the operational condition detected for the gas in the discharge of the compressor, a frequency adjustment by varying at least one of the values related to the mass of the resonant assembly and to the average stroke of the piston, to a value of the mechanical resonance frequency of the resonant assembly corresponding to the electrical supply frequency, maintaining unaltered the minimum distance between the piston and the valve plate at the end of each compression stroke.    
   
   
       2 . A system, as set forth in  claim 1 , wherein the detecting means detects at least one of the conditions of: pressure and temperature of the gas compressed in the discharge of the compressor, and operational electrical current of the linear motor.  
   
   
       3 . A system, as set forth in  claim 2 , wherein it comprises a control unit operatively connected to both the detecting means and the adjusting means, in order to receive, from the former, information about one of the operational conditions of: pressure and temperature of the gas in the discharge of the compressor, and operational electrical current of the linear motor, and to instruct the adjusting means to provide one of the operations of varying the average stroke of the piston and varying the mass of the resonant assembly.  
   
   
       4 . A system, as set forth in  claim 3 , wherein the variation of the mass of the resonant assembly is achieved by modifying the mass of at least one of the parts defined by the actuating means and the piston.  
   
   
       5 . A system, as set forth in  claim 4 , wherein each part of the resonant assembly, to have its mass modified, comprises an internal chamber containing an equalizing fluid and being maintained in fluid communication with an equalizing fluid reservoir defined in the interior of the compressor shell, the variation of the mass of the resonant assembly being achieved by modifying the mass of the fluid inside the internal chamber.  
   
   
       6 . A system, as set forth in  claim 5 , wherein the internal chamber of the piston presents a constant volume, and being maintained in fluid communication with an equalizing fluid impelling means provided in the interior of the shell in fluid communication with the equalizing fluid reservoir, in order to selectively pump said equalizing fluid into and out from said internal chamber.  
   
   
       7 . A system, as set forth in  claim 6 , wherein the equalizing fluid is defined by the lubricant oil of the compressor provided in an oil reservoir defined at the bottom of the compressor shell.  
   
   
       8 . A system, as set forth in  claim 2 , wherein the variation of the operational stroke of the piston is obtained by modifying the dead point of the piston at the end of the suction stroke.  
   
   
       9 . A system, as set forth in  claim 8 , wherein the modification of the dead point of the piston at the end of the suction stroke is achieved by an adjusting means in the form of an impeller, which is operatively coupled to the resonant assembly and to the control unit, so as to be driven by the latter between an inoperative condition, in which it does not produce any alteration in the stroke of the piston, and an operative condition, in which it modifies the stroke of the piston for adjusting the mechanical resonance frequency of the resonant assembly to the electrical supply resonance frequency.  
   
   
       10 . A system, as set forth in  claim 9 , wherein the impeller is one of the devices defined by an hydraulic actuator, a pneumatic actuator, and a mechanical actuator.  
   
   
       11 . A system, as set forth in  claim 10 , wherein the hydraulic actuator is maintained in fluid communication with an equalizing fluid reservoir provided in the interior of the shell, said hydraulic actuator being defined in a non-resonant portion of the compressor.  
   
   
       12 . A system, as set forth in  claim 11  and in which the resonant assembly comprises a spring means coupling the resonant assembly to the non-resonant assembly of the compressor, wherein the hydraulic actuator is operatively coupled to the spring means.  
   
   
       13 . A system, as set forth in  claim 12  and in which in the bottom of the shell is defined a lubricant oil reservoir, wherein the equalizing fluid is defined by the lubricant oil of the compressor.  
   
   
       14 . A system, as set forth in  claim 10 , wherein the pneumatic actuator is maintained in fluid communication with a reservoir, for an equalizing fluid in the form of gas, provided in the interior of the shell, said pneumatic actuator being defined in a non-resonant portion of the compressor.  
   
   
       15 . A system, as set forth in  claim 14 , in which the resonant assembly comprises spring means coupling the resonant assembly to the non-resonant assembly of the compressor, wherein the pneumatic actuator is operatively coupled to the spring means.  
   
   
       16 . A system, as set forth in  claim 15 , wherein the pneumatic actuator has a cylinder incorporated to the non-resonant assembly and a plunger axially displaceable in the interior of the cylinder and which operates as a movable stop means onto which is seated the spring means of the resonant assembly.  
   
   
       17 . A system, as set forth in  claim 16 , wherein the pneumatic actuator is a bellows.  
   
   
       18 . A system, as set forth in  claim 10 , wherein the mechanical actuator is operatively coupled to the non-resonant assembly and to the spring means and operated by a driving means, which moves said mechanical actuator to different operational positions.  
   
   
       19 . A system, as set forth in  claim 18 , wherein the driving means is one of the devices defined by a motor, a hydraulic actuator, and a pneumatic actuator.  
   
   
       20 . A system, as set forth in  claim 19 , wherein the driving means is operatively connected to the control unit.  
   
   
       21 . A system, as set forth in  claim 18 , wherein the mechanical actuator comprises one of the elements defined by a cam of linear displacement and a rotary cam coupled to the non-resonant assembly of the compressor, as well as a slide defining a cam follower coupling one of said elements defined by the cam of linear displacement and the rotary cam to the spring means.  
   
   
       22 . A system, as set forth in  claim 21 , wherein the cam of linear displacement is provided with steps which are dimensioned so as to define different positions for the dead point of the piston at the end of the suction stroke.  
   
   
       23 . A system, as set forth in  claim 22 , wherein the slide associated with the cam of linear displacement carries a contact portion in a surface of said slide confronting with the cam of linear displacement.  
   
   
       24 . A system, as set forth in  claim 23 , wherein the contact portion is a convex surface portion incorporated to the surface of the slide confronting with the cam of linear displacement.  
   
   
       25 . A system, as set forth in  claim 21 , wherein the cam of linear displacement presents one ramp surface which is slidingly seated against a confronting inclined surface of the slide of axial displacement.  
   
   
       26 . A system, as set forth in  claim 21 , wherein the rotary cam is provided with a continuous ramp which is dimensioned so as to define, continuously, by actuating on the slide, different positions for the dead point of the piston at the end of the suction stroke.  
   
   
       27 . A system, as set forth in  claim 18 , wherein the mechanical actuator comprises a mechanical stop means threaded to the non-resonant assembly and which is operatively coupled to the resonant assembly in order to alter the dead point of the piston at the end of the suction stroke, when rotated around its longitudinal axis.  
   
   
       28 . A system, as set forth in  claim 10 , wherein the equalizing fluid is the refrigerant gas compressed by the compressor.  
   
   
       29 . A system, as set forth in  claim 28 , wherein it comprises a control valve maintained in fluid communication with the cylinder of the pneumatic actuator through at least one opening of said cylinder, a control valve lodging a sealing means which is selectively displaced between a closed position, a pressurization position and a depressurization position, in order to, selectively, block the opening of the cylinder upon discharge of the compressor and communicate the interior of the cylinder with the interior of the compressor shell.  
   
   
       30 . A system, as set forth in  claim 29 , wherein the sealing means is a slide provided with an internal passage and which is linearly displaceable in one and in the other direction, by the discharge gas pressure and by the return elastic means, in order to provide the alignment and disalignment of said internal passage in relation to the opening.