Patent Publication Number: US-6663351-B2

Title: Piezoelectric actuated elastic membrane for a compressor and method for controlling the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application Nos. 2001-13300, filed Mar. 15, 2001 and 2002-5068, filed Jan. 29, 2002, in the Korean Industrial Property Office, the disclosures of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to compressors, and more particularly, to a compressor having a driving mechanism for linearly reciprocating a piston and a method for controlling the same. 
     2. Description of the Prior Art 
     In general, compressors are used to suck, compress and discharge a gas such as a vaporized refrigerant in apparatuses utilizing a refrigeration cycle, such as refrigerators and air conditioners. The compressors can be classified into linear compressors, reciprocating compressors, and rotary compressors. The linear compressors equipped with linear motors as their driving mechanisms have relatively high energy efficiencies due to a low energy loss in their driving mechanisms. 
     FIG. 1 shows the interior construction of a conventional linear compressor. The conventional linear compressor comprises a driving mechanism  3  which generates power in an airtight container  1  and a compressing mechanism  2  which sucks and compresses a refrigerant using the power transmitted from the driving mechanism  3 . 
     The compressing mechanism  2  includes a cylinder block  2   b  provided with a compression chamber  2   a  therein, and a cylinder head  2   c  coupled to the upper portion of the cylinder block  2   b  so as to guide the refrigerant being sucked and discharged. Additionally, a piston  2   d  which linearly reciprocates in response to an operation of the driving mechanism  3  is arranged in the compression chamber  2   a.    
     The driving mechanism  3 , which is a kind of a linear motor, includes a tubular back iron  3   d  arranged outside of the cylinder block  2   b , a core  3   b  spaced apart from the tubular back iron  3   d  having a wound coil  3   a  which forms a magnetic field in response to an applied power, and a magnet  3   c  arranged between the core  3   b  and the tubular back iron  3   d  which moves up and down. 
     The core  3   b  is composed of a plurality of layered electrical steel sheets, whose upper and lower portions are supported by a first frame  2   e  which outwardly extends from the upper portion of the cylinder block  2   b  and a second frame  2   f  fixed to the first frame  2   e  by bolts  4 , respectively. The magnet  3   c  linearly reciprocates through interaction with the magnetic field formed by the core  3   b , and is connected to the piston  2   d  through a connection rod  5 . The piston  2   d  reciprocates in the compression chamber  2   a  by the reciprocating movement of the magnet  3   c.    
     The compressing mechanism  2  and the driving mechanism  3  are supported by coil springs  6  and a resonance spring  7  that elastically support the cylinder block  2   b  in the lower portion of the interior of the airtight container  1 . That is, the coil springs  6  which elastically support the cylinder block  2   b  in the lower portion of the interior of the airtight container  1  are arranged under spacers  8  placed under the second frame  2   f  so as to position the piston  2   d.    
     The resonance spring  7  is a kind of a leaf spring, whose peripheral portions are attached to the spacers  8  and whose center portion is connected to the piston  2   d . The resonance spring  7  enhances the power to reciprocate the piston  2   d  and oscillates with the piston  2   d  in upward and downward directions (directions indicated by the arrows of FIG.  1 ). 
     However, the driving mechanism  3  which linearly reciprocates the piston  2   d  comprises a linear motor that requires a considerable-sized core and magnet to obtain a desired output. Furthermore, the structure of the linear motor is complicated. 
     Accordingly, the overall size of the conventional linear compressor is large and hinders the compressor from being mounted within apparatuses such as refrigerators. Additionally, the manufacturing process of a driving mechanism for a conventional linear compressor is complicated, making the performance of the compressor dependent on the complicated manufacturing process of the driving mechanism. 
     In addition, the piston  2   d  of the conventional linear compressor is operated to desired displacements by phase-controlling the driving mechanism  3  comprises a linear motor. For such an operation, the linear motor requires additional displacement sensors (not shown) to sense the displacements of the magnet  3   c  and the piston  2   d . As a result, the linear compressor is problematic in that other portions of the compressor are restricted to a narrow installation space due to the displacement sensors being mounted in the airtight container  1 . Moreover, the displacement sensors may undergo an integer variation due to temperature, and it is difficult to control the integer variation. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a compressor with an improved driving mechanism which linearly operates a piston, and allows the compressor to be miniaturized and easily manufactured. 
     It is another object of the present invention to provide a method of controlling a compressor provided with an improved driving mechanism for linearly operating a piston, which is capable of allowing the driving mechanism to be easily controlled. 
     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. 
     To achieve the above and other objects of the present invention there is provided a compressor comprising a cylinder block having a compression chamber, a piston arranged in the compression chamber which reciprocates up and down, and a driving mechanism which drives the piston and comprises an elastic member whose peripheral portions are fixed to the cylinder block so as to allow the elastic member to oscillate up and down and whose center portion is attached to the piston, and one or more piezoelectric actuators arranged on the elastic member which repeatedly deform in response to a power and apply an exciting power to the elastic member. 
     To achieve the above and other objects of the present invention there is provided a method of controlling a compressor comprising a cylinder block having a compression chamber, a piston positioned in the compression chamber which reciprocates up and down through the compression chamber, an elastic member whose peripheral portions are fixed to the cylinder block so as to allow the elastic member to oscillate up and down and whose center portion is attached to the piston, and one or more piezoelectric actuators arranged on the elastic member which repeatedly deform in response to a power and apply an exciting power to the elastic member, the method comprising sensing a displacement of the elastic member through deformations of the piezoelectric actuators and controlling the displacement of the elastic member by adjusting an amount and/or frequency of an electric voltage applied to the piezoelectric actuators. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects, features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIG. 1 is a sectional view showing the interior construction of a conventional linear compressor; 
     FIG. 2 is a sectional view showing the interior construction of a compressor according to an embodiment of the present invention; 
     FIG. 3 is a plan view showing an elastic member of the compressor shown in FIG. 2 according to an aspect of the present invention; 
     FIGS. 4 and 5 are sectional views showing a driving operation of the compressor shown in FIG. 2; 
     FIG. 6 is a partial sectional view showing an elastic member of the compressor shown in FIG. 2 according to another aspect of the present invention; 
     FIG. 7 is a sectional view showing the interior construction of a compressor according to another embodiment of the present invention, 
     FIG. 8 a sectional views showing the interior construction of a compressor according to yet another embodiment of the present invention; and 
     FIG. 9 is a sectional view showing the interior construction of a compressor according to still another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals to like elements throughout. 
     FIG. 2 shows the interior construction of a compressor according to an embodiment of the present invention. As shown in FIG. 2, the compressor of the present invention includes a compressing mechanism  20 , a driving mechanism  30 , and an airtight container  10 . The compressing mechanism  20  sucks a refrigerant (not shown) completely evaporated in a refrigeration cycle, forming a closed circuit, and compresses and discharges the sucked refrigerant. The driving mechanism  30  generates a driving power with electricity supplied from the outside. The airtight container  10  encloses the driving mechanism  30  and the compressing mechanism  20  therein. 
     The compressing mechanism  20  is arranged in an upper portion of the interior of the airtight container  10 . The compressing mechanism includes a cylinder block  21  having a compression chamber  21   a , and a cylinder head  22  arranged on the top of the cylinder block  21  which guides the refrigerant being sucked and discharged. The compression chamber  21   a  is axially formed through the cylinder block  21 . A piston  23 , which reciprocates up and down by the driving mechanism  30 , is arranged in the compression chamber  21   a . The cylinder head  22  is provided therein with a suction chamber  22   a  which guides the refrigerant being sucked into the compression chamber  21   a , and a discharge chamber  22   b  which accommodates the refrigerant discharged from the compression chamber  21   a . Additionally, a valve plate  24 , a suction valve  25  and a discharge valve  26  are arranged between the cylinder head  22  and the cylinder block  21 . A suction hole  24   a  and a discharge hole  24   b  are formed through the valve plate  24 . The suction valve  25  and the discharge valve  26  selectively open and close the suction hole  24   a  and the discharge hole  24   b , respectively, according to upward and downward movements of the piston  23 . While the piston  23  moves toward its bottom dead center, the suction valve  25  is opened and the refrigerant in the suction chamber  22   a  is sucked into the compression chamber  21   a  through the suction hole  24   a . On the other hand, while the piston  23  moves toward its top dead center, the discharge valve  26  is opened and the refrigerant in the compression chamber  21   a  is compressed and discharged to the discharge chamber  22   b  through the discharge hole  24   b.    
     The driving mechanism  30 , which reciprocates the piston  23  up and down, comprises an elastic member  31  and one or more of piezoelectric actuators  32 . The driving mechanism  30  of the present invention has a simpler construction and can easily be miniaturized as compared to the conventional driving mechanisms shown in FIG.  1 . In the present embodiment, peripheral portions of the elastic member  31  are connected to the cylinder block  21 , and a center portion of the elastic member  31  supports the piston  23 . The piezoelectric actuators  32  are used to oscillate the elastic member  31  up and down. 
     FIG. 3 shows the construction of the driving mechanism  30 . Referring to FIGS. 2 and 3, the elastic member  31  comprises a leaf spring. Two peripheral portions  31   a  and  31   b  of the elastic member  31  are fixed by fastening means such as bolts  33  to a pair of fixing members  27  downwardly extended from both sides of the cylinder block  21 . A center portion  31   c  of the elastic member  31  is fixed to a bottom of the piston  23  also by fastening means such as the bolt  33 . Fixing holes  31   d  are formed through the peripheral portions  31   a  and  31   b  and the center portion  31   c  of the elastic member  31  so as to accommodate the bolts  33  therein. The elastic member  31 , fixed to the piston  23 , oscillates up and down in response to an operation of the piezoelectric actuators  32 . 
     As a positive voltage and a negative voltage are alternately applied to the piezoelectric actuators  32 , the piezoelectric actuators  32  repeatedly deform up and down, resulting in an exciting force applied to the elastic member  31 . In response to the exciting force, the elastic member  31  oscillates up and down. 
     According to an embodiment of the present invention, the piezoelectric actuators  32  are attached to the peripheral portions  31   a  and  31   b  of an upper surface of the elastic member  31 , on the opposite sides of the piston  23 . The piezoelectric actuators  32  include intelligent type elements, such as piezoelectric elements, piezoelectric ceramics and shape memory alloys, which oscillate the elastic member  31  and sense the position of the elastic member  31 . In response to an electrical energy, the intelligent type elements convert the applied electrical energy into a mechanical quantity, such as a force or a deformation. In response to a physical force, the intelligent type elements convert the physical force into a converted electrical energy. 
     According to an aspect of the present invention, piezoelectric elements are implemented as the piezoelectric actuators  32 . 
     According to another aspect of the present invention, a controller  40  is constructed to sense the displacement of the elastic member  31  by using deformations of the piezoelectric elements. 
     FIG. 4 shows the controller  40  which controls the operation of the compressor in the airtight container  10 . The controller  40  includes a detection unit  41 , a comparison unit  42 , and an exciting unit  43 . The detection unit  41  is electrically connected to the piezoelectric actuators  32 , and senses the displacement of the elastic member  31  using the deformations of the piezoelectric actuators  32 . The comparison unit  42  compares a displacement value sensed by the detection unit  41  with a preset reference value. The exciting unit  43  controls an electrical energy applied to the piezoelectric actuators  32  according to a comparison result obtained from the comparison unit  42 . 
     Hereinafter, the operation of the compressor of the present invention is described in detail. 
     In absence of power, FIG. 2 shows that the piezoelectric actuators  32  are not deformed and the elastic member  31  maintains its flat state. 
     In response to a positive voltage, FIG. 4 shows that the piezoelectric actuators  32  are deformed downward. Accordingly, the center portion  31   c  (FIG. 3) of the elastic member  31  is deformed downward, thereby allowing the piston  23  to move toward its bottom dead center (in a direction indicated by an arrow A of FIG.  4 ). The piezoelectric actuators  32  are attached to the opposite peripheral portions  31   a  and  31   b  (FIG. 3) of the fixed elastic member  31 , such that the movable center portion  31   c  of the elastic member  31  is predominantly moved downward. 
     In response to a negative voltage, FIG. 5 shows that the piezoelectric actuators  32  are deformed upward. Therefore, the center portion  31   c  of the elastic member  31  is also deformed upward, thereby allowing the piston  23  to move toward its top dead center (in a direction indicated by an arrow B of FIG.  5 ). 
     The controller  40  senses the movement of the piston  23  through the deformations of the piezoelectric actuators  32 , and reciprocates the piston  23  up and down by applying a power to the piezoelectric actuators  32  until a desired output is achieved. As a result, the piston  23  is linearly reciprocated up and down through the compression chamber  21   a  by its own weight and an exciting power of the elastic member  31 . Accordingly, the refrigerant in the suction chamber  22   a  is sucked into the compression chamber  21  through the suction hole  24   a  to be compressed. Thereafter, the sucked refrigerant is compressed, the compressed refrigerant is discharged to the discharge chamber  22   b  through the discharge hole  24   b , and the discharged refrigerant is returned to the freezing cycle. 
     As described above, the reciprocating movement of the piston  23  is provided by one or more of piezoelectric actuators  32  being repeatedly deformed, so as to oscillate the elastic member  31  up and down according to the applied power. Therefore, the deformation of the elastic member  31  can be controlled by adjusting the amount and/or frequency of the power such as an electric voltage applied to the piezoelectric actuators  32 . That is, the deformation of the elastic member  31  is varied according to the amount of the electric voltage applied to the piezoelectric actuators  32 , thus enabling the displacement of the piston  23  to be easily controlled. In addition, the displacement of the piston  23  can be controlled by varying the frequency of the electric voltage (signal) so as to dynamically vary the applied electric voltage. 
     According to another embodiment of the present invention, the piezoelectric actuators  32  can be oppositely attached to upper and lower surfaces of the elastic member  31 . 
     According to yet another embodiment of the present invention, a number of piezoelectric actuators can be arranged to be spaced apart from each other throughout an entire surface of the elastic member  31 , so as to generate a greater exciting force to the elastic member  31 . 
     FIG. 6 shows still another embodiment of the present invention where one or more piezoelectric actuators  32   a  are contained in an elastic member  31   e  having a predetermined thickness. 
     FIG. 7 shows still yet another embodiment of the present invention where one or more piezoelectric actuators  32   b  are positioned between a piston  23  and an elastic member  31  in a layered fashion such that the actuators  32   b  can be expanded and contracted upward and downward. Accordingly, when a power is repeatedly applied to the piezoelectric actuators  32   b , the actuators  32   b  repeatedly undergo a cycle of expansion and contraction, thus allowing the piston  23  to be linearly reciprocated by the piezoelectric actuators  32   b.  The reciprocating movement of the piston  23  is further increased by the elastic member  31 . 
     FIG. 8 shows an additional embodiment of the present invention where a piezoelectric actuator  50  is placed between a piston  23  and an elastic member  31 . The piezoelectric actuator  50  comprises a first piezoelectric element  51  having its center portion bent in one direction, and a second piezoelectric element  52  having its center portion bent in the opposite direction of the center portion of the first piezoelectric element  51  and arranged symmetrically to the first piezoelectric element  51 . That is, the first and second piezoelectric elements  51  and  52  are each formed to be a leaf spring type. One end of each of the first and second piezoelectric elements  51  and  52  is fixed to a center portion of the elastic member  31 , and the other end is fixed to an end portion of the piston  23 . The first and second piezoelectric elements  51  and  52  are symmetrically arranged so as to not eccentrically operate the piston  23 . According to an aspect of this embodiment, the first and second piezoelectric elements  51  and  52  can be arranged to have a multi-fold structure so as to drive the piston  23  with a more powerful force. 
     Accordingly, as voltage is repeatedly applied to the first and second piezoelectric elements  51  and  52 , the first and second piezoelectric elements  51  and  52  repeatedly expand and contract along a vertical distance, while the center portions of the first and second piezoelectric elements  51  and  52  are bent. Therefore, the piston  23  is linearly reciprocated. At this time, the elastic member  31  also oscillates, thus increasing the reciprocating movement of the piston  23 . 
     FIG. 9 shows yet additional another embodiment of the present invention where a piezoelectric actuator  53  comprises first and second piezoelectric elements  54  and  55  which are alternately arranged side by side between a piston  23  and an elastic member  31 , wherein center portions of the first piezoelectric elements  54  are bent in the opposite direction of center portions of the second piezoelectric elements  55 . Accordingly, the exciting force of the piezoelectric actuator  53  and the elastic member  31  is increased, thus improving the efficiency of a compressor  10 . 
     As described above, the present invention provides a compressor and a method of controlling the compressor. According to an embodiment of the present invention, a driving mechanism which operates a piston includes an elastic member whose peripheral portions are fixed to a cylinder block so as to allow the elastic member to oscillate up and down and whose center portion is attached to a piston, and one or more of piezoelectric actuators arranged on the elastic member which deform and apply an exciting power to the elastic member in response to a power. Accordingly, a driving mechanism of the present invention can be miniaturized to reduce the overall size of the compressor. Furthermore, displacements of the piston can be sensed through the piezoelectric actuators to easily control the desired output of the compressor by controlling a voltage applied to the piezoelectric actuators. Therefore, the present invention does not require additional displacement sensors to sense the displacements of the piston and the elastic member. In addition, a variable-capacity compressor can be realized according to the present invention for desirably varying the capacity of the compressor. 
     Although a few preferred embodiments of the present invention have been shown and described, it would appreciated be 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.