Patent Publication Number: US-2015061421-A1

Title: Electric compressor

Description:
This nonprovisional application is based on Japanese Patent Application No. 2013-182045 filed on Sep. 3, 2013, with the Japan Patent Office, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electric compressor, in particular, an electric compressor provided with a filter circuit in a power supply input portion. 
     2. Description of the Background Art 
     As electric compressors for vehicles, there has been developed an electric compressor in which a driving circuit for driving a motor is incorporated for size reduction. If switching noise of the driving circuit of the electric compressor is leaked to outside, an adverse effect may be provided on a radio of the vehicle or the like. To address such a case, a filter circuit is generally provided in a power supply input portion thereof. 
     Japanese Patent Laying-Open No. 2010-48103 has discussed to dispose a low-pass filter circuit between a battery and an inverter circuit in order to suppress high-frequency noise in an output voltage of the battery from being generated due to an operation of the inverter circuit. 
     SUMMARY OF THE INVENTION 
     For such a low-pass filter circuit, an LC filter is usually used. However, the use of the LC filter results in resonance by L (reactance) of a coil and C (capacitance) of a capacitor at a specific frequency. 
     In order to avoid such resonance, an element constant is changed or the switching frequency of the inverter circuit is changed when the switching frequency of the inverter circuit is around the resonance frequency. 
     In the case where the element constant is changed, a damping resistor is provided in the filter circuit to let a DC component flow in the coil and let an AC component flow in the resistor, thereby lowering the resonance level. 
     The damping resistor thus added to the filter circuit receives a ripple current flowing from the system power supply side not only when starting an operation of the compressor but also when stopping the operation of the compressor. This may result in heat generation. 
     In such a case, in order to avoid the temperature of the damping resistor from being increased to reach or exceed the heat resistant temperature, the damping resistor needs to be effectively cooled also when stopping the operation of the compressor. 
     The present invention has an object to provide an electric compressor capable of effectively cooling a damping resistor of a filter circuit. 
     To summarize, the present invention provides an electric compressor including: a compressing unit; an electric motor that rotates the compressing unit; and a driving circuit that drives the electric motor. The driving circuit includes a filter circuit inserted in a power supply line, an inverter circuit that receives electric power from the power supply line via the filter circuit, and a circuit board on which the inverter circuit is disposed. The filter circuit includes a coil, and a damping resistor. The damping resistor is cooled by suctioned refrigerant suctioned in the electric compressor. 
     According to the present invention, the damping resistor is effectively cooled to improve reliability of the electric compressor. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an entire configuration of an electric compressor of the present embodiment. 
         FIG. 2  is a circuit diagram of a driving circuit that drives an electric compressor motor. 
         FIG. 3  is a perspective view showing an external appearance of an inverter unit. 
         FIG. 4  shows a lamination structure within the inverter unit. 
         FIG. 5  is a perspective view showing the shape of an aluminum base. 
         FIG. 6  is a cross sectional view of a VI-VI portion in  FIG. 5 . 
         FIG. 7  illustrates a first modification. 
         FIG. 8  illustrates a second modification. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following describes an embodiment of the present invention in detail with reference to figures. It should be noted that the same or corresponding portions in figures are given the same reference characters and are not described repeatedly. 
       FIG. 1  shows an entire configuration of an electric compressor of the present embodiment. Referring to  FIG. 1 , the electric compressor  110  includes: a housing formed by joining an discharge housing  111 , which has a cover-like shape and is made of aluminum (metal material), to a suction housing  112 , which has a shape of cylinder with a bottom and is made of aluminum (metal material); a compressing unit  115  and an electric motor  116 , which are accommodated in the suction housing  112 ; and an inverter unit  140  attached to the suction housing  112  such that the inverter unit  140  is incorporated with the suction housing  112 . 
     A suction port not shown in the figure is formed at the bottom portion side of the circumferential wall of the suction housing  112 . Connected to the suction port is an external refrigerant circuit not shown in the figure. A discharge port  114  is formed at the cover side of the discharge housing  111 . The discharge port  114  is connected to the external refrigerant circuit. Accommodated in the suction housing  112  are: the compressing unit  115  for compressing refrigerant; and the electric motor  116  for driving the compressing unit  115 . Although not shown in the figure, for example, the compressing unit  115  is configured to include a fixed scroll fixed in the suction housing  112  and a movable scroll disposed to face the fixed scroll. 
     On the inner circumferential surface of the suction housing  112 , a stator  117  is fixed. The stator  117  is configured to include: a stator core  117   a  fixed to the inner circumferential surface of the suction housing  112 ; and coils  117   b  wound around teeth (not shown) of the stator core  117   a.    
     In the suction housing  112 , a rotating shaft  119 , which is inserted in the stator  117 , is rotatably supported. To this rotating shaft  119 , a rotor  118  is fixed. 
     The inverter unit  140  is provided on the suction housing  112  at its external surface opposite to the discharge housing  111 . The inverter unit  140  includes an aluminum base  142 , a circuit board  146 , and an inverter cover  144 . 
     The inverter cover  144  covers the circuit board  146  to protect it from contamination, humidity, and the like. The inverter cover  144  is preferably formed of a resin for weight reduction. More preferably, the inverter cover  144  is formed by disposing a metal plate in the resin so as to suppress emission of generated electromagnetic noise from the circuit board  146  to outside. The inverter cover  144  is fixed to the suction housing  112  by screws  152 ,  154  at both sides with legs  156 ,  158  interposed therebetween. The legs  156 ,  158  are formed in the bottom plate  161  of the aluminum base  142 . In the inverter cover  144 , a power supply input port  143  having a cylindrical shape is formed to be supplied with a DC power supply voltage from outside. 
     The circuit board  146  is accommodated in an accommodation space between the inverter cover  144  and the aluminum base  142  such that the mounting surface of the circuit board  146  is orthogonal to the axial direction of the rotating shaft  119 . In the present embodiment, the compressing unit  115 , the electric motor  116 , and the inverter unit  140  are arranged side by side in this order in the axial direction of the rotating shaft  119 . 
     The aluminum base  142  is fastened to the suction housing  112  using the screws  152 ,  154 . The aluminum base  142  and the suction housing  112  are each made of metal having good heat conductivity and are in close contact with each other. Hence, the aluminum base  142  serves to dissipate heat from the inverter unit  140  by conducting the heat in the inverter unit  140  to the suction housing  112 . 
     The circuit board  146  is fixed by the screws  148 ,  150  to the legs  160 ,  162  formed in the bottom plate  161  of the aluminum base  142 , with a space between the circuit board  146  and the bottom plate  161 . In the space therebetween, a driving control circuit (inverter circuit) for the electric motor  116  as well as an electromagnetic coil L 1  and a capacitor circuit  4 , which form a below-described filter circuit shown in  FIG. 4 , are accommodated. The driving control circuit, the electromagnetic coil L 1  and the capacitor circuit  4  are mounted on the circuit board  146 . 
     The electric power controlled by the inverter unit  140  is supplied to the electric motor  116 , thereby rotating the rotor  118  and the rotating shaft  119  at a controlled rotational speed. By this rotation, the compressing unit  115  is driven. By driving the compressing unit  115 , the refrigerant is suctioned from the external refrigerant circuit into the suction housing  112  via the suction port, the refrigerant thus suctioned into the suction housing  112  is compressed by the compressing unit  115 , and the compressed refrigerant is discharged to the external refrigerant circuit via the discharge port  114 . 
       FIG. 2  is a circuit diagram of the driving circuit that drives the electric compressor motor. Referring to  FIG. 2 , the driving circuit  100  includes: the electromagnetic coil L 1  and the capacitor circuit  4 ; an inverter circuit  14 ; a bleeder resistance circuit  6 ; an internal power supply voltage generating unit  8 ; a resistance circuit  10 ; and a control circuit  30 . 
     The inverter circuit  14  includes a U phase arm  15 , a V phase arm  16 , and a W phase arm  17 , each of which is connected between a positive electrode bus PL and a negative electrode bus SL. 
     The U phase arm  15  includes: transistors Q 3 , Q 4  connected in series between the positive electrode bus PL and the negative electrode bus SL; and diodes D 3 , D 4  respectively connected in anti-parallel with the transistors Q 3 , Q 4 . A connection node of the transistors Q 3 , Q 4  is connected to one end of the U phase coil of the stator of the electric motor  116 . 
     The V phase arm  16  includes: transistors Q 5 , Q 6  connected in series between the positive electrode bus PL and the negative electrode bus SL; and diodes D 5 , D 6  respectively connected in anti-parallel with the transistors Q 5 , Q 6 . A connection node of the transistors Q 5 , Q 6  is connected to one end of the V phase coil of the stator of the electric motor  116 . 
     The W phase arm  17  includes: transistors Q 7 , Q 8  connected in series between the positive electrode bus PL and the negative electrode bus SL; and diodes D 7 , D 8  respectively connected in anti-parallel with the transistors Q 7 , Q 8 . A connection node of the transistors Q 7 , Q 8  is connected to one end of the W phase coil of the stator of the electric motor  116 . 
     The other end of each of the U phase coil, the V phase coil, and the W phase coil of the stator of the electric motor  116  is connected to a neutral point. 
     Examples of the transistors Q 3  to Q 8  used herein include semiconductor transistors such as insulated gate bipolar transistors and electric field effect transistors. 
     By controlling switching of the transistors Q 3  to Q 8 , a three-phase alternating current is output from the inverter circuit  14  to the stator coils of the electric motor  116 . 
     The inverter circuit  14  is supplied with a DC voltage from a DC power supply B via relays RY 1 , RY 2  and a low-pass filter circuit  2 . 
     The electromagnetic coil L 1 , the capacitor circuit  4 , and the damping resistor R 1  are included in the low-pass filter circuit  2 . The low-pass filter circuit  2  suppresses passage of high-frequency component of the voltage from the DC power supply B to the inverter circuit  14 , and suppresses passage of high-frequency component of the voltage from the inverter circuit  14  to the DC power supply B side. The high-frequency component of the voltage refers to a voltage component having a frequency equal to or higher than a predetermined value. The predetermined value is a cutoff frequency determined from the electromagnetic coil L 1 , the capacitor circuit  4 , and the damping resistor R 1 . 
     The electromagnetic coil L 1  is connected between the positive electrode of the DC power supply B and the positive electrode bus PL. The damping resistor R 1  is connected between the positive electrode of the DC power supply B and the positive electrode bus PL and is connected in parallel with the electromagnetic coil L 1 . The capacitor circuit  4  is connected between the positive electrode bus PL and the negative electrode bus SL. 
     The capacitor circuit  4  includes capacitors C 1  and C 2  connected in series between the positive electrode bus PL and the negative electrode bus SL. 
     The bleeder resistance circuit  6  is provided to suppress variation in a ratio between voltages held by the capacitors C 1 , C 2 . The bleeder resistance circuit  6  includes resistors R 2 , R 3  and a Zener diode D 1  connected in series between the positive electrode bus PL and the negative electrode bus SL. A connection node of the resistors R 2 , R 3  is connected to the connection node of the capacitors C 1 , C 2 . 
     The internal power supply voltage generating unit  8  generates an internal power supply voltage used in the control circuit  30 . The resistance circuit  10  divides the voltage using resistance elements connected in series between the positive electrode bus PL and the negative electrode bus SL so as to decrease it to a voltage that can be monitored by the control circuit  30 , and outputs the divided voltage to the control circuit  30 . 
     A current sensor  24  detects a current flowing in the negative electrode bus SL. The current flowing in the negative electrode bus SL is obtained by superimposing a W phase current, a V phase current, and a U phase current. The W phase current is a current flowing in the W phase coil. The V phase current is a current flowing in the V phase coil. The U phase current is a current flowing in the U phase coil. 
     The control circuit  30  is configured to include a CPU (Central Processing Unit) and the like and executes a computer program that controls driving of the electric motor  116 . 
     It should be noted that the DC power supply B in the present embodiment may supply electric power to a three-phase drive motor in addition to the electric motor  116 . The three-phase drive motor performs a power running operation for driving driving wheels of a hybrid vehicle or an electric vehicle, and a regenerative operation for generating electric power using rotational force of the driving wheels. 
       FIG. 3  is a perspective view showing an external appearance of the inverter unit.  FIG. 4  shows a lamination structure within the inverter unit.  FIG. 5  is a perspective view showing a shape of the aluminum base. Referring to  FIG. 3  to  FIG. 5 , the inverter cover  144  covers the circuit board  146 , which is fixed above the aluminum base  142 , to protect the circuit board  146 . Onto the circuit board  146 , each of leads of the electromagnetic coil L 1 , the capacitor circuit  4 , and the damping resistor R 1  included in the filter circuit  2  is soldered, thereby mounting the electromagnetic coil L 1 , the capacitor circuit  4 , and the damping resistor R 1  thereon. 
     The aluminum base  142  includes the bottom plate  161  and the legs  156 ,  158 ,  160 ,  162  provided in the bottom plate  161 . The circuit board  146  is attached to the legs  160 ,  162  by the screws  148 ,  150 . The inverter cover  144  is attached to the legs  156 ,  158  by screws not shown in the figure. 
     In the bottom plate  161  of the aluminum base  142 , the depressions  182 ,  184  are formed in conformity with the shapes of the electromagnetic coil L 1  and the capacitor circuit  4 . By providing the depressions in the aluminum base  142  in this way, the electromagnetic coil L 1  and the capacitor circuit  4  can be brought into close contact with the aluminum base  142 . Accordingly, heat generated in the filter circuit  2  can be dissipated from the aluminum base to the housing. 
     Further, in the present embodiment, it is designed such that the damping resistor R 1  can be also readily in the close contact with the aluminum base. 
     In the present embodiment, the damping resistor R 1  is not surface-mounted on the circuit board  146 . Rather, the damping resistor R 1  employed herein is a package attached thereto by soldering at a lead  183  with the damping resistor R 1  standing from the circuit board  146 . Also, the damping resistor R 1  is attached to the side surface portion of the aluminum base  142  in close contact with each other by a screw  172 . 
       FIG. 6  is a cross sectional view of a VI-VI portion in  FIG. 5 . Referring to  FIG. 5  and  FIG. 6 , the aluminum base  142  includes: the bottom plate  161 ; and a wall portion  174  formed to stand from the bottom plate  161  toward the circuit board  146  and in abutment with the damping resistor R 1 . 
     To the circuit board  146 , the damping resistor R 1  and the capacitor  4  are respectively soldered at portions of the leads  183 ,  184 . Further, the capacitor  4  is positioned by a resin holder  187  disposed at the circuit board  146 . The resin holder  187  has an opening opposite to the circuit board  146 , and the capacitor  4  and the aluminum base  142  are in abutment with each other such that heat conduction is good therebetween. 
     The aluminum base  142  is provided with a recess at a portion provided with the wall portion  174 . In the recess, the damping resistor R 1  is disposed. The side portion  180  of the damping resistor R 1  abuts the aluminum base  142 . 
     The bottom plate  161  of the aluminum base  142  is attached to the suction housing  112  such that heat conduction is good therebetween. The aluminum base  142  is attached at a position away from the compressing unit  115  in  FIG. 1  and close to the suction port via which the refrigerant is suctioned. 
     Referring to  FIG. 1  again, in the electric compressor  110 , the refrigerant is suctioned via the suction port. The temperature of the suctioned refrigerant is low, so that the suction housing  112  of the electric compressor  110  is cooled by the suctioned refrigerant. The suctioned refrigerant passes through the motor  116 , and is compressed by the compressing unit  115  to become a discharged gas having a high temperature and a high pressure, which is then discharged from the discharge port  114  to the external refrigerant circuit. 
     As shown in  FIG. 6 , the suctioned refrigerant is circulated at the inner surface of the suction housing  112 . To the external surface of the suction housing  112 , the aluminum base  142 , the damping resistor R 1 , and the capacitor  4  are fixed. The position at which the aluminum base  142  is attached in the suction housing  112  is cooled by the suctioned refrigerant flowing as indicated by arrows A 1 , A 2 . Accordingly, the aluminum base  142  in contact with this portion is also cooled by the suctioned refrigerant, whereby the damping resistor R 1  and the capacitor  4  are also cooled by the suctioned refrigerant. 
     Further, the wall portion  174  is provided to stand and the wall portion  174  and the side portion  180  of the damping resistor R 1  are in abutment with each other, thereby providing a wide area at which the aluminum base  142  is in close contact with the damping resistor R 1 . This leads to good heat dissipation. 
     Further, in  FIG. 6 , the bottom portion  181  of the damping resistor R 1  is directly in abutment with the suction housing  112 . Therefore, the heat of the damping resistor R 1  is also dissipated from the bottom portion  181  to the suction housing  112 , whereby the damping resistor R 1  is cooled more. 
       FIG. 7  illustrates a first modification. Each of  FIG. 1  and  FIG. 6  has illustrated the embodiment in which the aluminum base  142  is attached to the suction housing  112  and the damping resistor R 1  is in abutment with the aluminum base  142 .  FIG. 7  illustrates an embodiment in which a portion of the suction housing  112  is changed into a shape corresponding to the aluminum base  142 . 
       FIG. 8  illustrates a second modification.  FIG. 1  has illustrated the example in which the inverter circuit and the filter circuit are accommodated in the same inverter unit  140 . In contrast,  FIG. 8  illustrates an embodiment in which the inverter circuit  14  and the filter circuit  2  are disposed at different positions in the suction housing  112 A. 
     Referring to  FIG. 8 , an electric compressor  110 A includes: an inverter circuit accommodating portion  14 A in which the inverter circuit  14  is accommodated; and a filter circuit accommodating portion  2 A in which the filter circuit  2  is accommodated. The inverter circuit accommodating portion  14 A and the filter circuit accommodating portion  2 A are provided at different positions in the suction housing  112 A. 
     In the inner surface  113 A of the suction housing  112 A, the motor  116  is accommodated and the suctioned refrigerant is distributed. The motor  116  includes the stator  117 , the rotor  118 , and the rotating shaft  119 . 
     There is no limitation as long as they are disposed at different positions, but as shown in  FIG. 8 , for example, the inverter circuit accommodating portion  14 A can be disposed at the external surface of the suction housing  112 A above the motor accommodating portion and the filter circuit accommodating portion  2 A can be disposed at the external surface of the suction housing  112 A lateral to the motor accommodating portion. 
     Finally, referring to the figures again, the present embodiment is summarized as follows. Referring to  FIG. 1 , an electric compressor  110  of the present embodiment includes: a compressing unit  115 ; an electric motor  116  that rotates the compressing unit  115 ; and a driving circuit  100  that drives the electric motor  116 . Referring to  FIG. 1  and  FIG. 2 , the driving circuit  100  includes a filter circuit  2  inserted in a power supply line PL, an inverter circuit  14  that receives electric power from the power supply line PL via the filter circuit  2 , and a circuit board  146  on which the inverter circuit  14  is disposed. The filter circuit  2  has an electromagnetic coil L 1 , and a damping resistor R 1 . The damping resistor R 1  is cooled by suctioned refrigerant for the electric compressor. 
     Preferably, the electric compressor  110  further includes a housing (the suction housing  112 ) that is made of metal and that accommodates the compressing unit  115  and the electric motor  116 . The damping resistor R 1  is fixed to an external surface of the housing  112 . 
     More preferably, the electric compressor  110  further includes a base member (the aluminum base  142 ) that is attached to the external surface of the housing  112 , that supports the circuit board  146 , and that is made of metal. The damping resistor R 1  is fixed to the aluminum base  142 . 
     Further preferably, as shown in  FIG. 5  and  FIG. 6 , the aluminum base  142  includes a leg  160 ,  162  onto which the circuit board  146  is attached, a bottom plate  161  in which the leg  160 ,  162  is formed, and a wall portion  174  formed to stand from the bottom plate  161  toward the circuit board  146  and in abutment with the damping resistor R 1 . The damping resistor R 1  abuts wall portion  174 . 
     Further preferably, as shown in  FIG. 5  and  FIG. 6 , in the aluminum base  142 , a recess is formed at a portion provided with the wall portion  174 , and the damping resistor R 1  is disposed in the recess and a side portion  180  of the damping resistor R 1  abuts the aluminum base  142 . 
     Further preferably, the damping resistor R 1  has a bottom portion  181  in abutment with the housing  112 . 
     Further preferably, as shown in  FIG. 8 , the electric compressor  110 A further includes: an inverter circuit accommodating portion  14 A in which the inverter circuit  14  is accommodated; and a filter circuit accommodating portion  2 A in which the filter circuit  2  is accommodated. The inverter circuit accommodating portion  14 A and the filter circuit accommodating portion  2 A are formed at different positions in the housing  112 A. 
     It should be noted that as shown in  FIG. 7 , by incorporating the aluminum base  142  into a portion of the suction housing  112 , the aluminum base  142  may be configured as a portion of the metal housing in which the compressing unit  115  and the electric motor  116  are accommodated. In this case, the circuit board  146  is attached to the external surface of the suction housing  112 . 
     In the present embodiment, the damping resistor R 1  is provided on the housing or the aluminum base so as to provide a structure capable of cooling the damping resistor R 1  also when stopping the operation of the compressor. 
     With such a structure, heat generated in the damping resistor is dissipated to the housing of the compressor, thereby reducing the temperature increase of the damping resistor. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims.