Patent Publication Number: US-2015061558-A1

Title: Electric compressor

Description:
This nonprovisional application is based on Japanese Patent Application No. 2013-182250 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 disclosure relates to an electric compressor, in particular, an electric compressor in which a driving circuit for driving an electric motor is incorporated. 
     2. Description of the Background Art 
     In recent years, as a compressor provided in a vehicle such as a hybrid vehicle, an electric vehicle, a fuel cell vehicle or the like, there has been developed an electric compressor in which a driving circuit for driving an electric motor is incorporated for size reduction. In such an electric compressor, an inverter unit is attached to a housing with the electric motor and a compressor mechanism. 
     When a vehicle such as an automobile collides with an obstacle or the like and large force is applied to the electric compressor, the driving circuit for driving the electric motor accommodated in the inverter unit may be damaged to result in electrical leakage from a capacitor having a relatively large amount of electric charges stored therein. Therefore, a technique to prevent the electrical leakage is disclosed. 
     For example, Japanese Patent Laying-Open No. 2010-148296 discloses an electric compressor in which a compressor mechanism and a motor for driving the compressor mechanism are accommodated in a housing and an inverter for controlling driving of the motor is provided in a portion of the housing. In the electric compressor, the inverter including at least one capacitor and other electrical components which are mounted on a circuit board is accommodated in an inverter case fixed to the housing. In the electric compressor, an electrically discharging member is disposed to face the capacitor with a space between the electrically discharging member and the capacitor. 
     However, when a vehicle collides with an obstacle or the like, there are many forms of collisions and it is difficult to predict direction and angle of an impact applied to the electric compressor. According to the technique disclosed in Japanese Patent Laying-Open No. 2010-148296, the electrically discharging member may not come into the capacitor properly depending on forms of collision. Therefore, the technique may cause problems such that the electric charges of the capacitor are not discharged or it takes a long time until discharging of the electric charges completes, and the like. 
     SUMMARY OF THE INVENTION 
     The present disclosure has been made to solve the aforementioned problems, and one object in an aspect thereof is to provide an electric compressor capable of discharging electric charges of a capacitor surely and quickly in the event of an impact. 
     An electric compressor in accordance with an embodiment includes: a compressing unit; an electric motor for rotating the compressing unit; a driving circuit for driving the electric motor; a housing for accommodating the compressing unit and the electric motor; and an inverter cover for accommodating the driving circuit. An outline of the electric compressor is formed by the housing and the inverter cover. The driving circuit includes: an inverter circuit for receiving electric power from a power supply line; a capacitor connected between the power supply line and a ground line; and an electrically discharging circuit, connected to the capacitor, for discharging electric charges accumulated in the capacitor. The electric compressor further includes a capacitor cover, disposed inside the inverter cover, for encompassing and accommodating at least the capacitor and the electrically discharging circuit. 
     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  is a schematic diagram showing an entire configuration of an electric compressor according to the present embodiment. 
         FIG. 2  is a circuit diagram of a driving circuit that drives an electric compressor motor. 
         FIG. 3  shows a lamination structure within an inverter unit. 
         FIG. 4  is a schematic cross sectional view of a VI-VI portion in  FIG. 3 . 
         FIG. 5  is another example of the schematic cross sectional view of the VI-VI portion in  FIG. 3 . 
         FIG. 6A  illustrates a position of a cutting line α formed on a circuit board. 
         FIG. 6B  illustrates the position of the cutting line α formed on the circuit board. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following describes the present embodiment in detail with reference to figures. It should be noted that the same or corresponding portions in the figures are given the same reference characters and are not described repeatedly. 
     Referring to  FIG. 1 , an entire configuration of an electric compressor according to the present embodiment is described. As shown in  FIG. 1 , the electric compressor  110  includes: a housing formed by joining a 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 . An outline of the electric compressor  110  is formed by the housing and an inverter cover  144  of the inverter unit  140 . 
     A suction port (not shown) is formed at the bottom portion side of the circumferential wall of the suction housing  112 . An external coolant circuit (not shown) is connected to the suction port. A discharge port  114  is formed at the cover side of the discharge housing  111 . The discharge port  114  is connected to the external coolant circuit. Accommodated in the suction housing  112  are: the compressing unit  115  for compressing coolant; 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. 
     A stator  117  is fixed on the inner circumferential surface of the suction housing  112 . The stator  117  includes: 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. A rotor  118  is fixed to the rotating shaft  119 . 
     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 the 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 screws  148 ,  150  to 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. 2 , are accommodated. The driving control circuit is 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 coolant is suctioned from the external coolant circuit into the suction housing  112  via the suction port, the coolant thus suctioned into the suction housing  112  is compressed by the compressing unit  115 , and the compressed coolant is discharged to the external coolant circuit via the discharge port  114 . 
     Referring to  FIG. 2 , the driving circuit that drives the electric compressor motor is described. As shown 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  and the capacitor circuit  4  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  and the capacitor circuit  4 . 
     The electromagnetic coil L 1  is connected between the positive electrode of the DC power supply B and the positive electrode bus PL. 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  includes 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 motor for traveling in addition to the electric motor  116 . The three-phase motor for traveling performs a power running operation for 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. 
     Referring to  FIG. 3 , a lamination structure within the inverter unit  140  is described. As shown to  FIG. 3 , 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  and the capacitor circuit  4  included in the filter circuit  2  is soldered and mounted. 
     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 bottom plate  161  of the aluminum base  142 , a depression is formed in conformity with the shape of the electromagnetic coil L 1  and a depression is formed in conformity with the shape of the capacitor cover  201  for the accommodating 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  142  to the housing. 
     The capacitor cover  201  accommodates the capacitor circuit  4  and an electrically discharging circuit described later in  FIG. 4 . Specifically, the capacitor cover  201  is a protective case for protecting these electrical components from external force. The capacitor cover  201  has fracture strength higher than that of the housing including the suction housing  112  and the discharge housing  111  shown in  FIG. 1 , and that of the inverter cover  144 . For example, the capacitor cover  201  is made of iron material. 
     Referring to  FIG. 4 , a schematic cross section of a VI-VI portion in  FIG. 3  is described. As shown in  FIG. 4 , the capacitor cover  201  accommodates the capacitor circuit  4  and the circuit board  202  on which the electrically discharging circuit is mounted to discharge the electric charges accumulated in the capacitor circuit  4 . For example, referring to  FIG. 2 , the electrically discharging circuit is the bleeder resistance circuit  6  connected in parallel with the capacitor circuit  4  and the inverter circuit  14 . In  FIG. 4 , it is noted that a lower side of the capacitor circuit  4  is in close contact with the aluminum base  142  and is not encompassed by the capacitor cover  201 , but the capacitor cover  201  may be formed to encompass the lower side of the capacitor circuit  4 . 
     To secure an insulation property between each of the circuit board  202  and the capacitor circuit  4  and the capacitor cover  201 , these circuits are fixed with a space between each circuit and a surface of the capacitor cover  201 . Alternatively, an insulation sheet for securing an insulation property may be bonded to the surface of the capacitor cover  201 . 
     It is noted that the capacitor cover  201  may encompass at least the capacitor circuit  4  and the electrically discharging circuit, and, for example, the capacitor cover  201  may encompass the electromagnetic coil L 1  included in the filter circuit  2  in addition to the capacitor circuit  4  and the electrically discharging circuit. 
     The circuit board  146  having the inverter circuit  14  mounted thereon is disposed outside the capacitor cover  201 . The inverter cover  144  is formed to cover the circuit board  146  having the inverter circuit  14  mounted thereon. Specifically, the inverter cover  144  accommodates the driving circuit  100  shown in  FIG. 2 . 
     The circuit board  202  and the circuit board  146  are electrically connected to each other via a bus bar  205  which is soldered thereon. The circuit board  202  and the capacitor circuit  4  are electrically connected to each other via a bus bar  203  which is soldered thereon. It is noted that the circuit board  202  and the circuit board  146  are electrically connected to each other via the bus bar  205 , and the circuit board  202  and the capacitor circuit  4  are electrically connected to each other via the bus bar  203 , but the electric connection between the circuit board  202  and the circuit board  146  and the electric connection between the circuit board  202  and the capacitor circuit  4  may be attained via lead wires, respectively. 
     Here, when a vehicle provided with the electric compressor  110  according to the present embodiment collides with an obstacle or the like, for example, a collision load is applied to the inverter unit  140  in the directions of arrows shown in  FIG. 4 . Even if the inverter cover  144  is thereby deformed or fractured, it is possible to prevent damage of the circuit board  202  and the capacitor circuit  4 , since the capacitor cover  201  has fracture strength higher than that of the inverter cover  144 . Also, preferably, the capacitor cover  201  is attached to the aluminum base  142 , and the capacitor cover  201  and the inverter cover  144  are disposed with a space therebetween. Thus, it is possible to further reduce an impact applied to the capacitor circuit  4  and the circuit board  202  which are accommodated in the capacitor cover  201 . 
     In the event of a collision, the relays RY 1 , RY 2  shown in  FIG. 2  function by receiving a collision detection signal from a collision sensor (not shown) provided in the vehicle, whereby electric power from the DC power supply B is not supplied to the driving circuit  100 . In such case, the capacitors C 1 , C 2  (hereinafter collectively referred to as “capacitor C”) have a relatively large amount of electric charges accumulated therein. Thus, from the perspective of safety, the capacitor C needs to be discharged until an applied voltage of the capacitor C reaches a desired voltage (e.g., 60 V) within a reference time (e.g., within 5 seconds). For example, it is noted that the collision sensor is a sensor used for the operation and the like for an airbag of the vehicle. 
     In the electric compressor  110  according to the present embodiment, since the circuit board  202  and the capacitor circuit  4  remain undamaged even in the event of such a collusion, the electric charges of the capacitor C can be surely discharged spontaneously by the electrically discharging circuit provided in the circuit board  202  as in a normal state (a state with no collusion). 
     It is noted that the electrically discharging circuit is the bleeder resistance circuit  6  as a specific example, but the electrically discharging circuit may further include the internal power supply voltage generating unit  8  and the resistance circuit  10  depending on a capacitance of the capacitor C. Specifically, when the capacitor C has a relatively small capacitance (e.g., when the capacitor C is a film capacitor), the bleeder resistance circuit  6  is mounted on the circuit board  202  as the electrically discharging circuit, since it takes a relatively short discharge time until the applied voltage of the capacitor C reaches the desired voltage. On the other hand, when the capacitor C has a relatively large capacitance (e.g., when the capacitor C is an electrolytic capacitor), the bleeder resistance circuit  6 , the internal power supply voltage generating unit  8 , and the resistance circuit  10  are mounted on the circuit board  202  as the electrically discharging circuit, since it requires a relatively long discharge time until the applied voltage of the capacitor C reaches the desired voltage. 
     However, it is necessary that the internal power supply voltage generating unit  8  generates internal power supply voltage in the control circuit  30  and the resistance circuit  10  outputs the divided voltage to the control circuit  30 . Therefore, in a circuit design, it may be difficult that the internal power supply voltage generating unit  8  and the resistance circuit  10  are mounted on the circuit board  202  which is different from the circuit board  146  having the control circuit  30  mounted thereon. 
     Thus, when the capacitor C has a relatively large capacitance, an electrically discharging resistor for adjusting the discharge time may be mounted on the circuit board  202  to reduce the discharge time. For example, in a circuit diagram shown in  FIG. 2 , the electrically discharging resistor is connected between the bleeder resistance circuit  6  and the internal power supply voltage generating unit  8  and in parallel with the bleeder resistance circuit  6 . 
     Thereby, in a circuit design, by using the bleeder resistance circuit  6  and the electrically discharging resistor which can readily be mounted on the circuit board  202 , it is possible to reduce the discharge time of the capacitor C. The resistance value of the electrically discharging resistor is determined depending on the desired discharge time. It is noted that the electrically discharging resistor may be a variable resistor capable of adjusting the resistance value. 
     Modification 
     As described above, when the vehicle collides with an obstacle, the relays RY 1 , RY 2  function by receiving the signal from the collision sensor (not shown) and electric power supply from the DC power supply B to the driving circuit  100  is cut off. However, when the power supply line PL is branched from other electrical components such as a PCU (Power Control Unit) provided on the vehicle and comes into the driving circuit  100 , the PCU and the driving circuit  100  are still electrically connected to each other even though the relays RY 1 , RY 2  function. Therefore, electric charges left in the PCU may flow into the driving circuit  100  via the power supply line PL. Since this is a factor that inhibits the discharge of the capacitor C, the driving circuit  100  is preferably electrically cut off from the other electrical components such as the PCU in the event of a collision. 
     Referring to  FIG. 5 , another example of the schematic cross section of the VI-VI portion in  FIG. 3  is described. Configurations of the inverter unit  140  shown in  FIG. 5  are different from those of the inverter unit  140  shown in  FIG. 4  in that protrusions  207 A,  207 B are provided on the inverter cover  144  and in that a cutting line α is formed on the circuit board  146 , and the other configurations of the inverter unit  140  shown in  FIG. 5  are identical to those of the inverter unit  140  shown in  FIG. 4 . Referring to  FIG. 6A  and  FIG. 6B , a position of the cutting line α formed on the circuit board  146  is described. Specifically, referring to  FIG. 6A , a position electrically cut off at the cutting line α is described using a circuit diagram of the driving circuit driving the electric compressor motor. Referring to  FIG. 6B , the position cut at the cutting line α in the circuit board  146  is described. 
     Referring to  FIG. 5 ,  FIG. 6A , and  FIG. 6B , in the circuit board  146 , the cutting line α is formed between a voltage input region  230  of the DC power supply B and a region  210  on which the bus bar  205  leading to the circuit board  202  is soldered. On the inverter cover  144 , the protrusions  207 A,  207 B are disposed at positions to face the cutting line α. The protrusions  207 A,  207 B are formed to project toward the circuit board  146 . The protrusions  207 A,  207 B are made of the same material as the material of the inverter cover  144  and formed integrally with the inverter cover  144 . It is noted that the protrusions  207 A,  207 B may be made of a material different from that of the inverter cover  144 . 
     When a collision load is applied to the inverter unit  140  shown in  FIG. 5  in the event of a collision of the vehicle with an obstacle, since the protrusions  207 A,  207 B are pressed downward and is brought into contact with the circuit board  146 , a stress is exerted near the cutting line α. Therefore, the circuit board  146  is cut from the cutting line α as a starting point. The circuit board  146  is supported by a region A of the aluminum base  142  or a region B of the capacitor cover  201 . Thereby, the stress exerted to the circuit board  146  is received and the circuit board  146  is surely cut along the cutting line α. For example, the cutting line α is a cutting line involving perforations with connection portions and is configured such that the connection portions can be cut sequentially. It is noted that the cutting line α may not be the cutting line involving perforations and may be a cutting line in the form of a groove. 
     Further, referring to  FIG. 6A  and  FIG. 6B , the circuit board  146  is cut to be separated into the voltage input region  230  and the region  210  at the cutting line α. Therefore, the capacitor circuit  4  and the voltage input region  230  are electrically cut off from each other. Thereby, since the driving circuit  100  and the PCU are electrically cut off from each other in the event of a collision, it is possible to prevent the electric charges from flowing from the PCU into the capacitor C. It is noted that the position of the cutting line α is not limited to the position shown in  FIG. 6B  and may be a position such that the circuit board  146  is separated into the voltage input region  230  and the region  210 . 
     Finally, referring to the figures again, the present embodiment is summarized as follows. Referring to  FIG. 1 , the electric compressor  110  of the present embodiment includes: the compressing unit  115 ; the electric motor  116  for rotating the compressing unit  115 ; the driving circuit  100  for driving the electric motor  116 ; the housing (the suction housing  112 ) for accommodating the compressing unit  115  and the electric motor  116 ; and the inverter cover  144  for accommodating the driving circuit  100 . An outline of the electric compressor  110  is formed by the housing and the inverter cover  144 . Referring to  FIGS. 1 and 2 , the driving circuit  100  includes: the inverter circuit  14  for receiving electric power from the power supply line PL; the capacitor circuit  4  connected between the power supply line PL and the ground line SL; and the electrically discharging circuit, connected to the capacitor circuit  4 , for discharging electric charge accumulated in the capacitor circuit  4 . Referring to  FIGS. 3 and 4 , the electric compressor  110  further includes the capacitor cover  201 , disposed inside the inverter cover  144 , for encompassing and accommodating at least the capacitor circuit  4  and the electrically discharging circuit. 
     According to the above configuration, it is possible to prevent damage of the capacitor circuit  4  and the electrically discharging circuit included in the electric compressor  110  even if the vehicle collides with an obstacle, regardless of forms of the collision. Therefore, it is possible to discharge the electric charges of the capacitor surely and quickly. 
     Preferably, the suction housing  112  is made of metal and the capacitor cover  201  has fracture strength higher than fracture strength of the suction housing  112 . 
     According to the above configuration, since the capacitor cover  201  has fracture strength higher than that of the housing, it is possible to prevent damage of the capacitor circuit  4  and the electrically discharging circuit even if a collision load to break the housing is applied thereto. 
     Preferably, referring to  FIG. 4 , the capacitor cover  201  and the inverter cover  144  are disposed with a space therebetween. 
     According to the above configuration, since the inverter cover  144  and the capacitor cover  201  do not contact each other, it is possible to reduce an impact applied to the capacitor circuit  4  and the electrically discharging circuit that are accommodated in the capacitor cover  201 . Therefore, it is possible to prevent the damage of the capacitor circuit  4  and the electrically discharging circuit caused by the impact more effectively. 
     Preferably, referring to  FIG. 4 , the electric compressor  110  further includes: the circuit board  146  provided with the inverter circuit  14 ; and the circuit board  202  provided with the electrically discharging circuit and electrically connected to the circuit board  146  via the bus bar  205 . The capacitor cover  201  is configured to accommodate the circuit board  202 , and the capacitor circuit  4  electrically connected to the circuit board  202  via the bus bar  203 . 
     According to the above configuration, since the electrically discharging circuit is provided in the circuit board  202  which is different from the circuit board  146  provided with the inverter circuit  14 , it is possible to accommodate the electrically discharging circuit and the capacitor circuit  4  readily in the capacitor cover  201 . 
     Preferably, referring to  FIGS. 2 ,  5 ,  6 A, and  6 B, the power supply line PL is supplied with the DC voltage from the DC power supply B. The cutting line α is formed in the circuit board  146  between the voltage input region  230  via which the DC voltage is input to the circuit board  146  and the region  210  to which the bus bar  205  is connected. The Inverter cover  144  includes the protrusions  207 A,  207 B disposed at positions to face the cutting line α formed in the circuit board  146 . 
     According to the above configuration, since the driving circuit  100  is electrically cut off from other electrical components such as a PCU and the like in the event of a collision of the vehicle, it is possible to discharge the capacitor surely. 
     Preferably, referring to  FIG. 5 , the protrusions  207 A,  207 B are formed integrally with the inverter cover  144 . 
     According to the above configuration, since the protrusions  207 A,  207 B are formed integrally with the inverter cover  144 , it is not necessary to additionally provide a process for forming the protrusions  207 A,  207 B on the inverter cover  144 . 
     Preferably, the capacitor cover  201  is made of iron material. 
     According to the above configuration, the capacitor cover  201  has high fracture strength and therefore can withstand a larger collision load, thereby preventing the damage of the capacitor circuit  4  and the electrically discharging circuit. 
     Preferably, the electrically discharging circuit includes the bleeder resistance circuit  6 . 
     According to the above configuration, a circuit design is facilitated by using the bleeder resistance circuit  6  as the electrically discharging circuit. 
     Preferably, the electrically discharging circuit further includes the electrically discharging resistor, connected in parallel with the bleeder resistance circuit  6 , for adjusting a discharge time of the capacitor circuit  4 . 
     According to the above configuration, by further providing the electrically discharging resistor capable of adjusting the discharge time as the electrically discharging circuit, it is possible to reduce the discharge time even when the capacitance of the capacitor is relatively large. 
     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.