Patent Publication Number: US-2003231963-A1

Title: Apparatus and method to control a linear compressor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] This application claims the benefit of Korean Application No. 2002-33820, filed Jun. 17, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates generally to an apparatus and method to control a linear compressor, and more particularly, to an apparatus and method which controls the opening/closing of a discharge passage that is a passage through which refrigerant discharged from the linear compressor passes.  
       [0004] 2. Description of the Related Art  
       [0005] In general, a linear compressor is used in various kinds of refrigerating machines, and refers to a compressor that produces and discharges high-pressure refrigerant through a linear compression process, differently from a rotary compressor.  
       [0006] Hereinafter, a conventional method of controlling a conventional linear compressor is described with reference to FIGS. 1 and 2.  
       [0007]FIG. 1 is a sectional view illustrating the conventional linear compressor. FIG. 2 is a block diagram illustrating the conventional linear compressor control method.  
       [0008] Referring to the FIG. 1, the linear compressor generally comprises a sealed casing  101 , a compression chamber that sucks and compresses refrigerant and then discharges the refrigerant, and a drive unit that generates power.  
       [0009] In more detail, the compression chamber comprises a cylinder  103 , a cylinder head  109 , and a piston  107 . The cylinder  103  is provided with a compression chamber  100 . The cylinder head  109  is equipped with suction and discharge valves to guide the suction and discharge of the refrigerant, and is combined with the upper part of the cylinder  103 . The piston  107  is provided in the cylinder  103  to perform linear reciprocal movement.  
       [0010] The drive unit comprises a cylindrically shaped inner core  105 , an outer core  104  and a permanent magnet  102   a . The cylindrically shaped inner core  105  is located around the cylinder  103 . The outer core  104  is located to be spaced apart from the inner core  105  by a certain distance, and equipped with a coil  106  wound around the inner core  105  to generate a magnetic field when current is applied to the coil  106 . The permanent magnet  102   a  is located between the inner core  105  and the outer core  104 . The permanent magnet  102   a  is fixedly supported by a mover  102 , and the piston  107  is also fixedly supported by the mover  102 . The lower part of the mover  102  is extended to form an extension part  112 . The movement of the extension part  112  is sensed by a moving distance sensor  113 . That is, the moving distance sensor  113  can sense the moving distance of the piston  107  by sensing the moving distance of the extension part  112 .  
       [0011] Hereinafter, the operation of the linear compressor is described. When a magnetic field is generated around the coil  106  by applying current to the coil  106 , a certain amount of magnetic force formed by magnetic fields generated by the current application to the coil  106  and the permanent magnet  102   a  acts upon the permanent magnet  102   a . However, since the current applied to the coil  106  is Alternating Current (AC), the directions of the magnetic poles of the magnetic field generated by the coil  106  vary periodically, so the permanent magnet  102   a  periodically performs reciprocal movement. In this case, the mover  102  that fixedly supports the permanent magnet  102   a  is moved together with the permanent magnet  102   a , and the piston  107  fixedly supported by the mover  102  is reciprocally moved by the mover  102 , thus achieving the suction and compression operations of the linear compressor.  
       [0012] A reference numeral  108  designates a resonant spring that resonates in up and down directions along with the piston  107 , and doubles the reciprocal movement of the piston  107 . A reference numeral  111  designates a suction muffler that decreases a suction noise when low-pressure refrigerant is sucked to the linear compressor during the suction operation of the linear compressor. A reference numeral  111   a  designates a suction pipe that forms a passage through which the low-pressure refrigerant is moved and flows into the linear compressor during the suction operation of the linear compressor. A reference numeral  110  designates a discharge muffler that decreases a discharge noise when high-pressure refrigerant, compressed in a compression chamber during the suction operation of the linear compressor, is discharged outside of the linear compressor. A reference numeral  110   a  designates a discharge pipe that forms a discharge passage through which high-pressure refrigerant compressed in the compression chamber during the suction operation of the linear compressor is sucked and moved.  
       [0013] Next, a conventional method of controlling the conventional linear compressor is described with reference to FIG. 2.  
       [0014] In general, the method of controlling the conventional linear compressor  200  is carried out by sensing the movement of the piston  107  using the moving distance sensor  113  of FIG. 1, recognizing and evaluating the movement of the piston  107  using a control unit  201 , and controlling a power switch  202  using the control unit  201  if excessive movement of the piston  107  occurs. Accordingly, current applied to the coil  106  is cut off and passed by cutting off and passing power supplied to the linear compressor  200 , respectively, thereby controlling the operation of the linear compressor. Alternatively, the conventional method of controlling the conventional linear compressor  200  can be carried out by sensing the intensity of current using a current sensor that senses the intensity of the current applied to the linear compressor  200 , recognizing and determining the intensity of current using the control unit  201 , and cutting off power supplied from a power supply by controlling the power switch  202  if excessive current is applied to the linear compressor  200 .  
       [0015] However, the moving distance of the piston  107  described above does not have a fixed displacement value but a free displacement value. Accordingly, if excessive current is applied to the linear compressor  200 , a generated magnetic field is intensified and, therefore, a magnetic field acting on the permanent magnet  102   a  is increased, so there occurs a problem in that the piston  107  collides with the cylinder head  109  of the linear compressor. Additionally, the conventional linear compressor control method that was proposed to solve this problem is carried out by sensing the moving distance of the piston or the intensity of the current flowing through the coil, and stopping the operation of the linear compressor by cutting off the current that passes through the coil of the linear compressor if the value of the moving distance or current intensity exceeds a certain value, thereby resulting in the deterioration of reliability on the linear compressor due to the frequent ON/OFF operations of the linear compressor.  
       SUMMARY OF THE INVENTION  
       [0016] Accordingly, it is an object of the present invention to provide an apparatus and method to control a linear compressor in accordance with the present invention, which is capable of preventing collisions between a piston and a cylinder head caused by the excessive movement of the piston by controlling the operation of the linear compressor, thereby extending the life-span of the linear compressor, improving reliability on products and preventing the occurrence of abnormalities caused by the frequent ON/OFF operations of the compressor  
       [0017] Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
       [0018] The foregoing and other objects of the present invention are achieved by providing an apparatus to control a linear compressor having a discharge passage opening/closing control unit to control an opening/closing rate of a discharge passage through which high-pressure refrigerant generated by a compression operation of the linear compressor is discharged and moved. Additionally, the discharge passage opening/closing control means preferably includes an automatic control valve that opens or closes the discharge passage, an opening/closing control switch that directs the opening/closing of the automatic control valve, a sensor that senses the operating state of the linear compressor, and a control unit to recognize and evaluate information sensed by the sensor, and controls the automatic control valve or the opening/closing control switch.  
       [0019] The foregoing and other objects of the present invention are also achieved by providing a method to control a linear compressor, comprising: sensing an operating state of the linear compressor; comparing the sensed information with a preset value and determining whether the operating state of the linear compressor is abnormal; and controlling a discharge passage of the linear compressor if the operating state of the linear compressor is abnormal, wherein the sensing of the operating state of the linear compressor is carried out by sensing a moving distance of a piston in the linear compressor or the intensity of current applied to the linear compressor. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0020] These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
     [0021]FIG. 1 is a sectional view illustrating a conventional linear compressor;  
     [0022]FIG. 2 is a block diagram that is used to describe a conventional method of controlling the conventional linear compressor;  
     [0023]FIG. 3 is a view illustrating an apparatus to control a linear compressor according to an embodiment of the present invention;  
     [0024]FIG. 4 is a view illustrating another apparatus to control a linear compressor according to another embodiment of the present invention;  
     [0025]FIGS. 5A and 5B are schematic views illustrating the movement of a piston and the direction of force applied to the piston according to the embodiments of FIGS. 3 and 4, respectively; and  
     [0026]FIG. 6 is a flowchart illustrating a method of controlling a linear compressor according to an embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0027] Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
     [0028] Hereinafter, the embodiments according to the present invention are described with reference to the accompanying drawings.  
     [0029]FIG. 3 is a view illustrating an apparatus to control a linear compressor according to an embodiment of the present invention. FIG. 4 is a view illustrating another apparatus to control a linear compressor according to another embodiment of the present invention. FIGS. 5A and 5B are schematic views illustrating the movement of a piston and the direction of force applied to the piston according to an embodiment of the present invention, respectively.  
     [0030] Referring to FIG. 3, there is illustrated a linear compressor  300 . A suction pipe  305  is connected to a side of the linear compressor  300  and forms a passage through which a low-pressure refrigerant is moved during the suction operation of the linear compressor  300 . A discharge pipe  303  is connected to another side of the linear compressor  300  and forms a discharge passage through which compressed high-pressure refrigerant is sucked and moved during the suction operation of the linear compressor  300 . An automatic control valve  304  is positioned in the discharge pipe  303  and selectively opens and closes the discharge passage formed by the discharge pipe  303 . An opening/closing control unit  302  is connected to the automatic control valve  304  and directs the opening/closing of the automatic control valve  304 . A moving distance sensor  306  is connected to the linear compressor  300  and senses a moving distance through which the piston of the linear compressor  300  is moved. A control unit  301  recognizes and evaluates information sensed by the opening/closing control switch  302 , and commands the opening/closing control unit  302  to direct the automatic control valve  304  to selectively open and close the discharge passage.  
     [0031] Hereinafter, the above-described embodiment is described in detail.  
     [0032] When power is supplied to the linear compressor  300  and the linear compressor  300  is operated, the piston in the cylinder of the linear compressor  300  carries out suction and compression operations while regularly moving within a certain range. The low-pressure refrigerant flows into the linear compressor through the suction pipe  305  when the suction operation is carried out, while the high-pressure refrigerant compressed in the linear compressor  300  is discharged from the linear compressor and moved through the discharge pipe  303  when a discharge operation is carried out. When excessive current flows at a moment while carrying out such suction and compression operations, the moving distance of the piston is lengthened. An excessive moving distance of the piston is sensed by the moving distance sensor  306 , and sensed information is transmitted to the control unit  301 . The control unit  301  recognizes the sensed information, evaluates the operating state of the linear compressor  300  and commands the opening/closing control unit  302  to direct the automatic control valve  304  to block the discharge passage within a certain range corresponding to a distance by which the excessive moving distance of the piston exceeds the normal moving distance of the piston. Accordingly, the opening/closing control unit  302  directs the automatic control valve  304  to block the discharge passage within the certain range, and the automatic control valve  304  blocks the discharge passage within the directed certain range. The discharge passage is not required to be completely blocked. The reason for this is that if the blocking of the discharge passage is performed within the certain range, the discharge passage is blocked to the extent corresponding to the certain range and the movement of the high-pressure refrigerant is interrupted to the extent corresponding to the certain range. Accordingly, it is preferable that the range of the discharge passage able to be blocked by the automatic control valve  304  is preferably designed to be from 0% to 100%. 0% means the complete opening of the discharge passage, and 100% means the complete closing of the discharge passage. The reason why the above-described construction is used is that it is preferable to prevent the linear compressor from suddenly stopping or re-operating due to the fact that the compressor is forced to select complete opening or complete closing depending upon the extent of the abnormal operation of the linear compressor  300 , thus allowing smooth control to be implemented.  
     [0033]FIG. 4 illustrates another embodiment of the present invention, and the same reference numerals are used for the same components as in FIG. 3.  
     [0034] As illustrated in FIG. 4, a linear compressor  300  employs a current sensor  401  that senses the intensity of the current applied to the linear compressor  300 , instead of the moving distance sensor  306 , so as to determine the operating state of the linear compressor. Accordingly, the intensity of current is sensed by the current sensor  401 , and the sensed information is transmitted to the control unit  301 . Thereafter, the control unit  301  accordingly recognizes the intensity of current and determines whether the linear compressor  300  is in an abnormal state. Thereafter, the control unit  301  controls the blocking of the discharge passage to correspond to the extent of the abnormal state. Additionally, it is preferable that an opening/closing rate of the automatic control valve  304  ranges from 0% to 100% to complete the closing of the discharge passage.  
     [0035] Referring to FIGS. 5A and 5B in conjunction with the embodiment described with reference to FIG. 3, FIG. 5A illustrates a case where, during the normal operation of the linear compressor, high-pressure refrigerant is moved to the head part  503  in a forward direction and discharged by a stable compression operation in which the flow of high-pressure refrigerant in the compression chamber  501  does not exceed a preset displacement of the piston  502 . The high-pressure refrigerant moved to the head part  503  is normally moved along the suction pipe through the suction valve (not shown). In contrast, FIG. 5B illustrates a case where, as an abnormal movement, in which the piston  502  is moved an excessive distance more than the preset normal moving distance of the piston  502 , the discharge passage is blocked within a certain range corresponding to a distance by which the excessive moving distance of the piston exceeds the normal moving distance of the piston, and, accordingly, the high-pressure refrigerant not discharged from the compression chamber  501  of the linear compressor  300  exerts force in a reverse direction to hinder the piston  502  from moving to the head part  503 .  
     [0036] That is, when the discharge passage formed by the discharge pipe  303  is blocked within the certain range, the flow of the refrigerant discharged from the linear compressor  300  is interrupted by the automatic control valve  304  to an extent corresponding to the certain range during the discharge operation of the linear compressor, and high-pressure refrigerant not discharged from the compression chamber  501  remains in the compression chamber  501 . Since the remaining refrigerant applies hydraulic force in the direction opposite to the moving direction of the piston  502  during the compression operation, a collision between the piston  502  and the cylinder head part  503  due to the overload of the linear compressor  300  can be prevented. Of course, it will be easily appreciated that the above-described control method has an effect in which the moving distance of the piston  502  of the linear compressor  300 , having a free displacement, approximates the moving distance of a piston having a fixed displacement. Meanwhile, the same effect may be obtained by setting the intensity of current to a certain value instead of setting the preset displacement, and controlling the opening/closing of the automatic control valve  304  according to the set intensity of current.  
     [0037]FIG. 6 is a flowchart illustrating the method of controlling the linear compressor according to the above embodiment.  
     [0038] First, referring to FIG. 6, when the linear compressor  300  starts to operate, the moving distance of the piston  502  of the linear compressor  300  is sensed by the moving distance sensor  306  at S 601 . Thereafter, the control unit  301  compares the value of an actually sensed moving distance with the value of a preset displacement and determines whether the operating state of the linear compressor  300  is abnormal at S 602 . That is, it is determined whether the moving distance of the piston  502  is greater than the preset displacement. Thereafter, if it is determined that the operating state of the linear compressor  300  is normal on the basis of the determination, the operation in which the moving distance of the piston  502  is continuously sensed and compared with the preset displacement is repeated. In contrast, if it is determined that the operating state of the linear compressor  300  is abnormal on the basis of the information of the determination, that is, the moving distance of the piston  502  is greater than the preset displacement, the moving distance of the piston  502  is continuously sensed and compared with the preset displacement and the opening/closing control unit  302  is commanded to control the automatic control valve  304  at S 603 . Thereafter, the opening/closing control unit  302  transmits a certain electric signal to the automatic control valve  304  and the automatic control valve  304  is controlled to open or close the discharge passage in response to the electrical signal at S 604 . The operation of the linear compressor is smoothly carried out through the above-described process. Of course, the operating state of the linear compressor  300  can be sensed by the intensity of current actually applied to the linear compressor  300  at S 601 . Accordingly, in this case, the preset value of the intensity of current is compared with the intensity of current actually applied to the linear compressor  300 , and it is determined whether the operating state of the linear compressor  300  is normal at S 602 . Of course, the discharge passage is blocked in a range from 0% to 100% to complete the closing of the discharge passage.  
     [0039] As described above, the apparatus and method to control a linear compressor in accordance with the present invention is capable of preventing collisions between the piston and the cylinder head caused by the excessive movement of the piston by controlling the operation of the linear compressor, thereby extending the lifespan of the linear compressor, improving reliability on products and preventing the occurrence of abnormalities caused by the frequent ON/OFF operations of the compressor.  
     [0040] Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.