WO2009054640A2

WO2009054640A2 - Reciprocating compressor

Info

Publication number: WO2009054640A2
Application number: PCT/KR2008/006019
Authority: WO
Inventors: Yang-Jun Kang; Young-Hoan Jeon
Original assignee: Lg Electronics, Inc.
Priority date: 2007-10-26
Filing date: 2008-10-13
Publication date: 2009-04-30
Also published as: CN101836354A; WO2009054640A3; KR20090042563A; KR101316194B1; CN101836354B

Abstract

The present invention relates to a reciprocating compressor in which a piston is linearly reciprocated inside a cylinder, for sucking a refrigerant into a compression space, and compressing and discharging the refrigerant, and more particularly, to a reciprocating compressor which includes a power supply apparatus whose circuit unit is simplified due to a reduction in the number of inverter switches. A reciprocating compressor, which comprises a piston, a cylinder, a coil section provided in the cylinder and linearly reciprocating the piston, and a power supply apparatus for supplying power to the coil section, comprises: a rectifier section for rectifying an AC voltage supplied from an AC power supply unit; a DC link section for stabilizing the amplitude of the rectified voltage; and an inverter switch unit consisting of a pair of inverter switches connected to the DC link section, for applying the stabilized voltage to the coil section, both ends of the coil section being connected between the DC link section and the pair of inverter switches to allow the coil section to directly receive power from the DC link section, thus reducing the numnber of inverter switches.

Description

RECIPROCATING COMPRESSOR

Technical Field

[1] The present invention relates to a reciprocating compressor in which a piston is linearly reciprocated inside a cylinder, for sucking a refrigerant into a compression space, and compressing and discharging the refrigerant, and more particularly, to a reciprocating compressor which includes a power supply apparatus whose circuit unit is simplified due to a reduction in the number of inverter switches. Background Art

[2] In general, a compressor is a mechanical apparatus for compressing the air, refrigerant or other various operation gases and raising a pressure thereof, by receiving power from a power generation apparatus such as an electric motor or turbine. The compressor has been widely used for an electric home appliance such as a refrigerator and an air conditioner, or in the whole industry.

[3] The compressors are roughly classified into a reciprocating compressor in which a compression space for sucking or discharging an operation gas is formed between a piston and a cylinder, and the piston is linearly reciprocated inside the cylinder, for compressing a refrigerant, a rotary compressor in which a compression space for sucking or discharging an operation gas is formed between an eccentrically -rotated roller and a cylinder, and the roller is eccentrically rotated along the inner wall of the cylinder, for compressing a refrigerant, and a scroll compressor in which a compression space for sucking or discharging an operation gas is formed between an orbiting scroll and a fixed scroll, and the orbiting scroll is rotated along the fixed scroll, for compressing a refrigerant.

[4] Recently, a linear compressor which can improve compression efficiency and simplify the whole structure without a mechanical loss resulting from motion conversion by connecting a piston directly to a linearly -reciprocated driving motor has been popularly developed among the reciprocating compressors.

[5] Fig. 1 is a view illustrating a conventional power supply apparatus applied to a reciprocating compressor. There is a DC power supply unit 22 for rectifying an AC power (not shown) for home use or industrial use and converting it into a DC, and a separate control unit (not shown) controls inverter switches S 1 to S4 in a pulse width modulation (PWM) fashion to supply an AC power Vm to a linear motor. Although the DC power supply unit 22 includes a rectifier section for rectifying an AC power and a DC link section, the illustration and explanation thereof are omitted because they are generally known. The DC power controlled through the rectifier section (not shown) and the DC link section (not shown) is converted into an AC power Vm having an appropriate amplitude and frequency through the inverter switches Sl to S4, and the AC power Vm is applied to the linear motor (more precisely, a coil of the motor).

[6] Since such a conventional power supply apparatus have to employ four inverter switchces in order to apply an AC power to the linear motor, the on/off control and circuit configuration of the inverter switches are considerably complicated, and the reaction time of the inverter switches differs from each other, thus making it unable to apply a desired AC power to the lineari motor. Further, the manufacturing cost rises according to the applications of a plurality of inverter switches. Disclosure of Invention Technical Problem

[7] Accordingly, it is an object of the present invention to provide a reciprocating compressor which supplies a desired AC power to a linear motor even if the number of required inverter switches is reduced.

[8] It is another object of the present invention to provide a reciprocating compressor which makes it easy to control an inverter switch unit and simplifies the circuit configuration.

[9] It is still another object of the present invention to provide a reciprocating compressor which simplifies the circuit configuration by constructing an AC power supply path to the linear motor by a DC link section and inverter switches. Technical Solution

[10] A reciprocating compressor according to the present invention, which comprises a piston, a cylinder, a coil section provided in the cylinder and linearly reciprocating the piston, and a power supply apparatus for supplying power to the coil section, comprises: a rectifier section for rectifying an AC voltage supplied from an AC power supply unit; a DC link section for stabilizing the amplitude of the rectified voltage; and an inverter switch unit consisting of a pair of inverter switches connected to the DC link section, for applying the stabilized voltage to the coil section, both ends of the coil section being connected between the DC link section and the pair of inverter switches to allow the coil section to directly receive power from the DC link section, thus reducing the numnber of inverter switches.

[11] Preferably, the rectifier section consists of full-bridge diodes.

[12] Preferably, the DC link section consists of a first capacitor and a second capacitor connected in series, both ends of the inverter switch unit are connected to both ends of the DC link section, and a connecting point of the first capacitor and the second capacitor is grounded.

[13] Preferably, the grounding portion of the AC power supply unit is connected to a connecting point of the first capacitor and the second capacitor. [14] Preferably, the pair of inverter switches is alternately turned on/off.

Advantageous Effects

[15] Consequently, the present invention can supply a desired AC power to a linear motor to drive the reciprocating compressor even if the number of required inverter switches is reduced. [16] Furthermore, the present invention makes it easy to control the inverter switch unit and simplifies the circuit configuration. [17] Furthermore, the present invention can simplify the circuit configuration and apply the maximum power to the linear motor by constructing an AC power supply path to the linear motor by a DC link section and inverter switches.

Brief Description of the Drawings

[18] Fig. 1 is a view illustrating a conventional power supply apparatus applied to a reciprocating compressor;

[19] Fig. 2 is a cross sectional view of a reciprocating compressor to which a power supply apparatus is applied according to the present invention; and

[20] Figs. 3 and 4 are views illustrating first and second embodiments of a power supply apparatus applied to the reciprocating compressor according to the present invention. Mode for the Invention

[21] Hereinafter, the present invention will be described in detail based upon the embodiments of the present invention and the attached drawings.

[22] Fig. 2 is a cross sectional view of a reciprocating compressor to which a power supply apparatus is applied according to the present invention.

[23] In the reciprocating compressor of Fig. 2, an inlet tube 2a and an outlet tube 2b through which refrigerants are sucked and discharged are installed at one side of a closed vessel 2, a cylinder 4 is fixedly installed inside the closed vessel 2, a piston 6 is installed inside the cylinder 4 to be linearly reciprocated to compress the refrigerants sucked into a compression space P in the cylinder 4, and various springs are installed to be elastically supported in the motion direction of the piston 6. Here, the piston 6 is connected to a reciprocating motor 10 for generating a linear reciprocation driving force.

[24] In addition, a suction valve 22 is installed at one end of the piston 6 contacting the compression space P, and a discharge valve assembly 24 is installed at one end of the cylinder 4 contacting the compression space P. The suction valve 22 and the discharge valve assembly 24 are automatically controlled to be opened or closed according to the inside pressure of the compression space P, respectively.

[25] The top and bottom shells of the closed vessel 2 are coupled to hermetically seal the closed vessel 2. The inlet tube 2a through which the refrigerants are sucked and the outlet tube 2b through which the refrigerants are discharged are installed at one side of the closed vessel 2. The piston 6 is installed inside the cylinder 4 to be elastically supported in the motion direction to perform the linear reciprocation. The reciprocating motor 10 is connected to a frame 18 outside the cylinder 4. The cylinder 4, the piston 6 and the linear motor 10 compose an assembly. The assembly is installed on the inside bottom surface of the closed vessel 2 to be elastically supported by a support spring 29.

[26] The inside bottom surface of the closed vessel 2 contains oil, an oil supply device 30 for pumping the oil is installed at the lower end of the assembly, and an oil supply tube 18a for supplying the oil between the piston 6 and the cylinder 4 is formed inside the frame 18 at the lower side of the assembly. Accordingly, the oil supply device 30 is operated by vibrations generated by the linear reciprocation of the piston 6, for pumping the oil, and the oil is supplied to the gap between the piston 6 and the cylinder 4 along the oil supply tube 18a, for cooling and lubrication.

[27] The cylinder 4 is formed in a hollow shape so that the piston 6 can perform the linear reciprocation, and has the compression space P at its one side. Preferably, the cylinder 4 is installed on the same straight line with the inlet tube 2a in a state where one end of the cylinder 4 is adjacent to the inside portion of the inlet tube 2a.

[28] The piston 6 is installed inside one end of the cylinder 4 adjacent to the inlet tube 2a to perform linear reciprocation, and the discharge valve assembly 24 is installed at one end of the cylinder 4 in the opposite direction to the inlet tube 2a.

[29] Here, the discharge valve assembly 24 includes a discharge cover 24a for forming a predetermined discharge space at one end of the cylinder 4, a discharge valve 24b for opening or closing one end of the cylinder 4 near the compression space P, and a valve spring 24c which is a kind of coil spring for applying an elastic force between the discharge cover 24a and the discharge valve 24b in the axial direction. An O-ring R is inserted onto the inside circumferential surface of one end of the cylinder 4, so that the discharge valve 24a can be closely adhered to one end of the cylinder 4.

[30] An indented loop pipe 28 is installed between one side of the discharge cover 24a and the outlet tube 2b, for guiding the compressed refrigerants to be externally discharged, and preventing vibrations generated by interactions of the cylinder 4, the piston 6 and the reciprocating motor 10 from being applied to the whole closed vessel 2.

[31] Therefore, when the piston 6 is linearly reciprocated inside the cylinder 4, if the pressure of the compression space P is over a predetermined discharge pressure, the valve spring 24c is compressed to open the discharge valve 24b, and the refrigerants are discharged from the compression space P, and then externally discharged along the loop pipe 28 and the outlet tube 2b. [32] A refrigerant passage 6a through which the refrigerants supplied from the inlet tube

2a flows is formed at the center of the piston 6. The reciprocating motor 10 is directly connected to one end of the piston 6 adjacent to the inlet tube 2a by a connection member 17, and the suction valve 22 is installed at one end of the piston 6 in the opposite direction to the inlet tube 2a. The piston 6 is elastically supported in the motion direction.

[33] The suction valve 22 is formed in a thin plate shape. The center of the suction valve

22 is partially cut to open or close the refrigerant passage 6a of the piston 6, and one side of the suction valve 22 is fixed to one end of the piston 6a by screws.

[34] Accordingly, when the piston 6 is linearly reciprocated inside the cylinder 4, if the pressure of the compression space P is below a predetermined suction pressure lower than the discharge pressure, the suction valve 22 is opened so that the refrigerants can be sucked into the compression space P, and if the pressure of the compression space P is over the predetermined suction pressure, the refrigerants of the compression space P are compressed in the close state of the suction valve 22.

[35] Especially, the piston 6 is installed to be elastically supported in the motion direction.

In detail, a piston flange 6b protruded in the radial direction from one end of the piston 6 adjacent to the inlet tube 2a is elastically supported in the motion direction of the piston 6 by mechanical springs 8a and 8b such as coil springs. The refrigerants included in the compression space P in the opposite direction to the inlet tube 2a are operated as gas spring due to an elastic force, thereby elastically supporting the piston 6.

[36] Here, the mechanical springs 8a and 8b have constant mechanical spring constants K m regardless of the load, and are preferably installed side by side with a support frame 26 fixed to the reciprocating motor 10 and the cylinder 4 in the axial direction from the piston flange 6b. Also, preferably, the mechanical spring 8a supported by the support frame 26 and the mechanical spring 8a installed on the cylinder 4 have the same mechanical spring constant K_m.

[37] The driving means 10 comprises coil sections 12 and 14 and a magnet 16. When a magnetic field is generated by the application of power to the coil sections, the magnet receives a force resulting from the magnetic field, and such a force results in a motive force for moving the piston 6.

[38] The reciprocating motor 10 includes an inner stator 12 formed by stacking a plurality of laminations 12a in the circumferential direction, and fixedly installed outside the cylinder 4 by the frame 18, an outer stator 14 formed by stacking a plurality of laminations 14b at the periphery of a coil wound body 14a in the circumferential direction, and installed outside the cylinder 4 by the frame 18 with a predetermined gap from the inner stator 12, and a permanent magnet 16 positioned at the gap between the inner stator 12 and the outer stator 14, and connected to the piston 6 by the connection member 17. Here, the coil wound body 14a can be fixedly installed outside the inner stator 12.

[39] In the reciprocating motor 10, when a current is applied to the coil wound body 14a to generate an electromagnetic force, the permanent magnet 16 is linearly reciprocated by interactions between the electromagnetic force and the permanent magnet 16, and the piston 6 connected to the permanent magnet 16 is linearly reciprocated inside the cylinder 4.

[40] Figs. 3 and 4 are views illustrating first and second embodiments of a power supply apparatus applied to the reciprocating compressor according to the present invention.

[41] The power supply unit comprises a rectifier section 202 for rectifying an AC power supplied from an AC power supply unit 201, a DC link section 203 for stabilizing the rectified power, and an inverter switch unit 204 for controlling power applied to the coil section 205. The AC power is typically supplied from the outside through the AC power supply unit 201, such as power wires, cables, etc. The rectifier section 202 functions to rectify an AC power so as to make it flow only in one direction, and the DC link section 203 functions to reduce a variation in the amplitude of a rectified power (functions to stabilize). Since the purpose of the rectifier section 202 and DC link section 203 is to convert an AC power into a stable DC power, the two sections can be combined into a power conversion unit. The inverter switch unit 204 controls an applied power through switches. The controlled power is converted into an AC power having an appropriate amplitude and frequency through the inverter switch unit 204, and the AC power is applied to the coil section 205 (corresponding to the coil wound body 14a of Fig. 2).

[42] Fig. 3 is a view illustrating a first embodiment of a power supply unit applied to the reciprocating compressor according to the present invention.

[43] Although the rectifier section 202 functions to rectify an AC power, and, in Fig. 3, is composed by connecting four diodes in a full-bridge configuration, the configuration of the rectifier section is a well-known art, and therefore, anything that functions to rectify an AC power so as to make it flow in only one direction is available.

[44] The DC link section 203 functions to reduce the width of variation of the rectified voltage for stabilization. As shown in Fig. 3, if rectification is implemented by connecting diodes in a full-bridge configuration, even though power is applied in only one direction but the amplitude thereof is part of a sine wave, thereby resulting in serious variations (e.g., ripples). In order to reduce such variations, the DC link section 203 is provided to stabilize power. Concretely, in Fig. 6, for instance, the DC link section 203 is comprised of a first capacitor Cl and a second capacitor C2. The first capacitor Cl and the second capacitor C2 are serially connected to each other, and their connecting point is separately grounded to a grounding portion of the AC power supply section 201.

[45] If the first capacitor Cl and the second capacitor C2 have a large capacitance, the both end voltage V/2 of the first capacitor Cl and second capacitor C2 is not affected much even if a voltage with a wide variation is applied from the rectifier section 202. If the absolute value of a voltage of the first or second capacitor Cl or C2 is smaller than the absolute value of the power passed through the rectifier section 202, the diodes of the rectifier section 202 are closed, and the voltage of the DC link section 203 is applied to the inverter switch unit 204. Otherwise, if the absolute value of a voltage of the first or second capacitor C or C2 is larger than the absolute value of the power passed through the rectifier section 202, the diodes of the rectifier section 202 are closed, and the voltage of the DC link section 203 is affected by the power passed through the rectifier section 202 and thus the voltage passed through the rectifier section 202 is applied to the inverter switch unit 204. By this process, the width of variation of the voltage can be reduced.

[46] The inverter switch unit 204 consists of a first switch (or first inverter switch) Sl and a second switch (or second inverter switch) S2 which are for applying power to the coil section 205. Both ends of the inverter switch unit 204 are connected to both ends of the DC link section 203. That is, one ends of the first switch Sl and second switch S2 are connected to the respective capacitors Cl and C2 of the DC link section 203, and the other ends thereof are connected to the coil section 205. The coil section 205 is connected between the connecting point of the first capacitor Cl and second capacitor C2 and the connecting point of the first switch S 1 and second switch S2.

[47] The power controlled through the first switch Sl and second switch S2 is converted into an AC power having an appropriate amplitude and frequency, and the AC power is applied to the coil section 205. The coil section 205 of Fig. 3 is a brief illustration of the coil section 14a. In controlling the inverter switch unit 204, a control unit (not shown) of the reciprocating compressor alternately turns on/off the first switch Sl and the second switch S2 to thus apply power from the DC link section 203 to the coil section 205, whereby a suction stroke, compression stroke, discharge stroke, and re- expansion stroke of the reciprocating compressor are sequentially implemented. For instance, when the first switch Sl is in the on state or in the on operation, and the second switch S2 is in the off state or in the off operation, a voltage +V/2 is applied to the coil section 205 to thus sequentially implement the re-expansion stroke and suction stroke, and when the first switch S 1 is in the off operation or in the off state and the second switch S2 is in the on operation or in the on state, a voltage -V/2 is applied to the coil section 205 to thus sequentially implement the compression stroke and discharge stroke. [48] By this configuration, the same function as in the conventional art can be provided in spite that the number of inverter switches is reduced to two from four. Even if the AC power supply unit 201 applies a voltage having an amplitude of V through the rectifier section 202, if the first or second switch Sl or S2 is in the on state or in the on operation, a voltage applied to the first and second capacitors Cl and C2 from the DC link section 203 is decreased to V/2, i.e., a half thereof, thereby reducing efficiency. To solve this problem, a second embodiment is disclosed.

[49] Fig. 4 is a view illustrating a second embodiment of a power supply unit applied to the reciprocating compressor of the present invention.

[50] The connection and functions of the DC link section 203 and the inverter switch unit

204 are identical to those of Fig. 3, so a description thereof will be omitted. In the rectifier section 202, a second node 102 connected to an AC power source 201 is connected to a grounding portion of the DC link section 203, i.e., a connecting point of the first capacitor Cl and second capacitor C2. Therefore, the grounding portion of the DC link section 203 and the grounding portion of the AC power 201 are connected, and a voltage of the second node 102 is always zero. Except this, the configuration of the rectifier section is the same as that of the previous embodiment. Accordingly, the both end voltage of the first capacitor Cl and second capacitor C2 of the DC link section 203 rises to V, and the voltage V is applied to the coil section 205.

[51] In the second embodiment of Fig. 4, too, the first and second switches Sl and S2 are alternately turned on/off, thereby sequentially implementing a suction stroke, compression stroke, discharge stroke, and re-expansion stroke of the reciprocating compressor.

[52] If a voltage of the first node 101 is higher than that of the third node 103, power flows toward the third node to make the voltage of the third node equal to a voltage of the AC power source 201. If a voltage of the first node 101 is lower than that of the fourth node 104, power flows from the fourth node 104 to make the voltage of the fourth node 104 equal to the voltage of the AC power source 201. If the voltage of the first node 101 is between the voltage of the third node 103 and the voltage of the fourth node, all the diodes are closed. If the capacitance of the capacitors constituting the DC link section 203 is large, the voltage of the DC link section 203 does not almost change. By this process, the width of variation of the voltage applied to the inverter switch unit 204 through the DC link section 203 is decreased. A stabilized DC power is converted into an AC power Vm having an appropriate amplitude and frequency through the inverter switch unit 204, and the AC power Vm is applied to the coil section 205.

[53] In this specification, although the control unit for controlling the inverter switch unit

204 according to a PWM signal has not beeen described, the construction of such a control unit is well known to those skilled in the art.

[54] The present invention has been described in detail with reference to the embodiments and the attached drawings. However, the scope of the present invention is not limited to these embodiments and drawings, but defined by the appended claims.

Claims

[1] A reciprocating compressor, which comprises a piston, a cylinder, a coil section provided in the cylinder and linearly reciprocating the piston, and a power supply apparatus for supplying power to the coil section, comprises: a rectifier section for rectifying an AC voltage supplied from an AC power supply unit; a DC link section for stabilizing the amplitude of the rectified voltage; and an inverter switch unit consisting of a pair of inverter switches connected to the DC link section, for applying the stabilized voltage to the coil section, both ends of the coil section being connected between the DC link section and the pair of inverter switches.

[2] The reciprocating compressor of claim 1, wherein the rectifier section consists of full-bridge diodes.

[3] The reciprocating compressor of claim 1 or 2, wherein the DC link section consists of a first capacitor and a second capacitor connected in series, both ends of the inverter switch unit are connected to both ends of the DC link section, and a connecting point of the first capacitor and the second capacitor is grounded.

[4] The reciprocating compressor of claim 3, wherein the grounding portion of the

AC power supply unit is connected to the connecting point of the first capacitor and the second capacitor.

[5] The reciprocating compressor of any of claims 1 to 4, wherein the pair of inverter switches is alternately turned on/off.

[6] A reciprocating compressor, which comprises a piston, a cylinder, a coil section provided in the cylinder and linearly reciprocating the piston, and a power supply apparatus for supplying power to the coil section, comprises: a rectifier section for rectifying an AC voltage supplied from an AC power supply unit; a pair of capacitors for stabilizing the amplitude of the rectified voltage; and an inverter switch unit consisting of a pair of inverter switches connected to the DC link section, for applying the stabilized voltage to the coil section, both ends of the coil section being connected between a connecting point of the pair of capacitors and a connecting point of the pair of inverter switches.

[7] The reciprocating compressor of claim 6, wherein the connecting point of the pair of capacitors is grounded.

[8] The reciprocating compressor of claim 6, wherein a grounding portion of the pair of capacitors and a grounding portion of the AC power supply unit are connected to each other. [9] The reciprocating compressor of any of claims 6 to 8, wherein the rectifier section consists of full-bridge diodes. [10] The reciprocating compressor of any of claims 6 to 9, wherein the pair of inverter switches is alternately turned on/off.