Abstract:
An exhaust purifying system includes: a catalytic device supplied with electric power from a power supply unit; a first connecting unit connecting one end of the catalytic device to a negative electrode node of the power supply unit; a second connecting unit connecting the other end of the catalytic device to a positive electrode node of the power supply unit; a leak detecting unit detecting leak from the power supply unit; and a control unit controlling opening and closing of each of the first and second connecting units. When leak is not detected by the leak detecting unit in a leak check state where one of the first and second connecting units is closed and the other is opened, the control unit closes the other and applies current through the catalytic device, and when leak is detected in the leak check state, the control unit does not apply the current through the catalytic device.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a National Stage International Application No. PCT/JP2011/053220 filed Feb. 16, 2011, the contents of all of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to an exhaust purifying system for a hybrid vehicle and a control method therefor, and particularly to an exhaust purifying system for a hybrid vehicle including a catalytic device supplied with electric power and heated, and a control method therefor. 
     BACKGROUND ART 
     Generally, in a vehicle having an internal combustion engine mounted thereon, a catalytic device is provided to purify exhaust gas. Since this catalytic device does not produce any effect unless the temperature rises to some extent, the catalytic device is arranged close to the internal combustion engine such that the temperature rises immediately. 
     The purification effect is not perfect, however, immediately after startup of the internal combustion engine, that is, when the catalytic device has not yet been warmed. In addition, in a hybrid vehicle capable of running using only a motor, the internal combustion engine is operated as necessary. The catalytic device, however, is not always warmed by exhaust gas at the time of startup of the internal combustion engine. Therefore, warming the catalytic device in advance using electric power before startup of the internal combustion engine is under consideration. Such a catalytic device is called “Electrical Heated Catalyst” (hereinafter also referred to as “EHC”). The EHC generates heat by passing current through the catalytic device itself. Japanese Patent Laying-Open No. 2010-223159 (PTL 1) discloses a technique of preventing leak at the time of passing current through an EHC and suppressing deterioration in emission in a vehicle having the EHC mounted thereon. According to this technique, in a plug-in hybrid vehicle, an ECU first executes low-voltage driving of restraining driving voltage to 50 V when requesting passage of the current through the EHC, and detects the existence of occurrence of the leak caused by dew condensation of condensate in the EHC based on a resistance value of the EHC. As a result, when it is determined that the leak is occurring, passage of the current through the EHC is prohibited. On the other hand, when it is determined that the leak is not occurring, the driving voltage is boosted to 200 V in ordinary driving, and catalytic warming-up by the EHC is executed. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Laying-Open No. 2010-223159 
         PTL 2: Japanese Patent Laying-Open No. 2002-21541 
         PTL 3: Japanese Patent Laying-Open No. 2003-278528 
         PTL 4: Japanese Patent Laying-Open No. 6-17697 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     According to the above technique, upon sensing the leak and the like when a high-voltage power supply and the EHC are connected with an EHC driving device interposed therebetween, passage of the current through the EHC is interrupted. Therefore, there is a possibility that the high-voltage power supply is not protected sufficiently. Detection of the leak in the EHC has room for improvement in terms of protection of the high-voltage power supply. 
     An object of the present invention is to provide an exhaust purifying system for a hybrid vehicle in which greater protection is provided to a high-voltage power supply when leak occurs, and a control method therefor. 
     Solution to Problem 
     In summary, the present invention is directed to an exhaust purifying system for a hybrid vehicle including a power supply unit, a motor receiving electric power from the power supply unit, and an internal combustion engine used with the motor, the exhaust purifying system including: a catalytic device supplied with electric power from the power supply unit and heated; a first connecting unit connecting one end of the catalytic device to a negative electrode node of the power supply unit; a second connecting unit connecting the other end of the catalytic device to a positive electrode node of the power supply unit; a leak detecting unit detecting leak from the power supply unit; and a control unit controlling opening and closing of each of the first connecting unit and the second connecting unit. When leak is not detected by the leak detecting unit in a leak check state where one of the first connecting unit and the second connecting unit is closed and the other is opened, the control unit closes the other and applies current through the catalytic device, and when leak is detected in the leak check state, the control unit does not apply the current through the catalytic device. 
     Preferably, the control unit controls the first connecting unit and the second connecting unit such that the first connecting unit is closed and the second connecting unit is opened in the leak check state. 
     Preferably, the leak detecting unit detects both leak from the power supply unit and leak from the catalytic device. 
     Preferably, the leak detecting unit detects leak from the power supply unit with the first connecting unit and the second connecting unit open, and thereafter, the first connecting unit and the second connecting unit are controlled such that the first connecting unit is closed and the second connecting unit is opened in the leak check state, and the leak detecting unit detects leak from the catalytic device. 
     According to another aspect, the present invention is directed to a hybrid vehicle including any one of the above-mentioned exhaust purifying systems. 
     According to still another aspect, the present invention is directed to a control method for an exhaust purifying system for a hybrid vehicle including a power supply unit including a power storage device, a motor driven by the power supply unit, and an internal combustion engine used with the motor. The exhaust purifying system includes: a catalytic device supplied with electric power from the power supply unit and heated; a first connecting unit connecting one end of the catalytic device to a negative electrode node of the power supply unit; a second connecting unit connecting the other end of the catalytic device to a positive electrode node of the power supply unit; a leak detecting unit detecting leak from the power supply unit; and a control unit controlling opening and closing of each of the first connecting unit and the second connecting unit. The control method includes the steps of: setting the exhaust purifying system to a leak check state where one of the first connecting unit and the second connecting unit is closed and the other is opened; detecting leak by the leak detecting unit; and controlling the first connecting unit and the second connecting unit to close the other and apply current through the catalytic device when leak is not detected in the step of detecting leak, and not to apply the current through the catalytic device when leak is detected. 
     Advantageous Effects of Invention 
     According to the present invention, there is provided an exhaust purifying system for a hybrid vehicle in which greater protection is provided to a high-voltage power supply when leak occurs, and a control method therefor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an overall block diagram of a hybrid vehicle to which an exhaust purifying system according to an embodiment of the present invention is applied. 
         FIG. 2  is a cross-sectional view showing a schematic configuration of an EHC  140  taken along a direction in which an exhaust pipe in  FIG. 1  extends. 
         FIG. 3  is a diagram for describing occurrence of leak in the EHC and a short circuit in a high-voltage power supply. 
         FIG. 4  is a circuit diagram showing a configuration of a leak detecting unit  80  in  FIG. 3 . 
         FIG. 5  is a flowchart for describing a leak detection sequence described with reference to  FIG. 3 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention will be described in detail hereinafter with reference to the drawings, in which the same or corresponding portions are denoted with the same reference characters and a description thereof will not be repeated. 
       FIG. 1  is an overall block diagram of a hybrid vehicle to which an exhaust purifying system according to an embodiment of the present invention is applied. 
     Referring to  FIG. 1 , a hybrid vehicle  1  includes an engine  10 , a motor generator MG 1 , a motor generator MG 2 , a power split device  40 , a decelerator  50 , and a driving wheel  55 . 
     Engine  10  is an internal combustion engine generating driving force for rotating a crankshaft by combustion energy generated during combustion of an air-fuel mixture taken into a combustion chamber. Motor generator MG 1  and motor generator MG 2  are AC motors, and are three-phase AC synchronous motors, for example. 
     Hybrid vehicle  1  runs using the driving force outputted from at least one of engine  10  and motor generator MG 2 . The driving force generated by engine  10  is split by power split device  40  into two paths, that is, the path through which the driving force is transmitted to driving wheel  55  via decelerator  50 , and the path through which the driving force is transmitted to motor generator MG 1 . 
     Power split device  40  includes a planetary gear formed of a sun gear, a pinion gear, a carrier, and a ring gear. The pinion gear engages with the sun gear and the ring gear. The carrier supports the pinion gear to allow rotation on its axis, and is coupled to the crankshaft of engine  10 . The sun gear is coupled to a rotation shaft of motor generator MG 1 . The ring gear is coupled to a rotation shaft of motor generator MG 2  and decelerator  50 . 
     Engine  10 , motor generator MG 1  and motor generator MG 2  are coupled with power split device  40  interposed thereamong, and thereby rotation speeds of engine  10 , motor generator MG 1  and motor generator MG 2  have such a relationship that they are linearly connected with one another in a collinear chart. 
     Hybrid vehicle  1  further includes an inverter  60  and a power supply unit  75 . Power supply unit  75  includes a smoothing capacitor C 1 , a voltage converter  90 , a system main relay  72 , and a power storage device  70 . 
     Inverter  60  controls driving of motor generator MG 1  and motor generator MG 2 . Motor generator MG 1  generates electric power using motive power of engine  10  split by power split device  40 . The electric power generated by motor generator MG 1  is converted from AC to DC by inverter  60  and is stored in power storage device  70 . 
     Motor generator MG 2  generates driving force using at least one of the electric power stored in power storage device  70  and the electric power generated by motor generator MG 1 . The driving force of motor generator MG 2  is transmitted to driving wheel  55  via decelerator  50 . Although driving wheel  55  is shown as a front wheel in  FIG. 1 , a rear wheel may be driven by motor generator MG 2  instead of or together with the front wheel. 
     It is to be noted that at the time of braking the vehicle and the like, motor generator MG 2  is driven by driving wheel  55  via decelerator  50  and operates as a generator. As a result, motor generator MG 2  also functions as a regenerative brake converting kinetic energy of the vehicle to electric power. The electric power generated by motor generator MG 2  is stored in power storage device  70 . 
     A secondary battery such as a lead storage battery, a nickel-metal hydride battery and a lithium ion battery, a large-capacitance capacitor such as an electrical double layer capacitor, or the like can be used, for example, as power storage device  70 . 
     Inverter  60  includes an inverter  60 - 1  and an inverter  60 - 2 . Inverter  60 - 1  and inverter  60 - 2  are connected to voltage converter  90  in parallel with each other. 
     Inverter  60 - 1  is provided between voltage converter  90  and motor generator MG 1 . Inverter  60 - 1  controls driving of motor generator MG 1  based on a control signal S 1  from an electronic control unit (hereinafter referred to as “ECU”)  150 . 
     Inverter  60 - 2  is provided between voltage converter  90  and motor generator MG 2 . Inverter  60 - 2  controls driving of motor generator MG 2  based on a control signal S 2  from ECU  150 . 
     Voltage converter  90  makes a voltage conversion between power storage device  70  and inverter  60 . Voltage converter  90  boosts a voltage of power storage device  70  (more precisely, a voltage between a positive electrode line PL 0  and a negative electrode line GL 0 ) to a target voltage value indicated by a control signal S 3  from ECU  150 , and outputs the boosted voltage to inverter  60 . As a result, a voltage between a positive electrode line PL 1  and negative electrode line GL 1  (hereinafter also referred to as “high-voltage-side DC voltage VH” or simply as “voltage VH”) is controlled to attain the target voltage value indicated by control signal S 3 . 
     Smoothing capacitor C 1  is connected between positive electrode line PL 1  and a negative electrode line GL 1 . It is to be noted that negative electrode line GL 1  and negative electrode line GL 0  are connected inside voltage converter  90 . Smoothing capacitor C 1  smoothes high-voltage-side DC voltage VH. 
     Hybrid vehicle  1  further includes a current sensor  120 , a voltage sensor  121 , rotation speed sensors  122 ,  123  and  124 , and a temperature sensor  125 . 
     Voltage sensor  121  measures a voltage VB across terminals of power storage device  70 . Current sensor  120  senses a current IB flowing to power storage device  70 , in order to monitor a state of charge (SOC) of power storage device  70  together with voltage sensor  121 . 
     Rotation speed sensors  122 ,  123  and  124  detect a rotation speed Ne of engine  10 , a rotation speed Nm 1  of motor generator MG 1 , and a rotation speed Nm 2  of motor generator MG 2 , respectively. Temperature sensor  125  detects a temperature Tehc of an EHC  140 . Each of these sensors transmits a result of detection to ECU  150 . 
     ECU  150  has a not-shown CPU (Central Processing Unit) and a not-shown memory built therein, and is configured to execute predetermined operation processing based on a map and a program stored in the memory. Alternatively, at least a part of ECU  150  may be configured to execute predetermined numerical and logical operation processing using hardware such as an electronic circuit. 
     ECU  150  generates above-mentioned control signals S 0  to S 4  based on information from each sensor and the like, and outputs generated control signals S 0  to S 4  to each device. For example, ECU  150  sets a torque command value Tgcom of motor generator MG 1  and a torque command value Tmcom of motor generator MG 2  based on the information from each sensor and the like, generates control signal S 1  for matching torque Tg of motor generator MG 1  with torque command value Tgcom as well as control signal S 2  for matching torque Tm of motor generator MG 2  with torque command value Tmcom, and outputs control signal S 1  and control signal S 2  to inverter  60 - 1  and inverter  60 - 2 , respectively. In addition, ECU  150  sets a command value of an amount of fuel injected by engine  10 , based on the information from each sensor and the like, generates control signal S 4  for matching the actual amount of fuel injected by engine  10  with the command value, and outputs control signal S 4  to engine  10 . 
     In addition, ECU  150  also controls passage of current through electrical heated catalyst (EHC)  140  based on a control signal S 5 . Exhaust gas discharged from engine  10  is discharged through an exhaust passage  130  to the air. EHC  140  is provided in exhaust passage  130 . 
     EHC  140  is configured to be capable of electrically heating a catalyst for purifying the exhaust gas. EHC  140  is connected to power storage device  70  with a junction box  100 , voltage converter  90  and system main relay  72  interposed therebetween, and heats the catalyst using supplied electric power. Since the catalyst provided in EHC  140  is heated, the purification performance is enhanced. It is to be noted that various known EHCs can be applied as EHC  140 . 
     ON/OFF of system main relay  72  can be switched based on control signal S 0 . Junction box  100  can switch whether or not to supply electric power to EHC  140 , based on control signal S 5 . As described later with reference to  FIG. 3 , junction box  100  is configured to be capable of controlling connection to positive electrode line PL 1  and connection to negative electrode line GL 1  independently, using relays SW 1  and SW 2 . It is to be noted that a source of power to EHC  140  may be positive electrode line PLO and negative electrode line GL 0 , instead of positive electrode line PL 1  and negative electrode line GL 1 . 
       FIG. 2  is a cross-sectional view showing a schematic configuration of EHC  140  taken along a direction in which an exhaust pipe in  FIG. 1  extends. 
     Referring to  FIG. 2 , EHC  140  is configured to include a case  410 , an insulating member  420 , an EHC carrier  430 , temperature sensors  125 A and  125 B, a positive electrode  450 , a positive electrode coating unit  460 , a negative electrode  470 , and a negative electrode coating unit  480 . EHC  140  is one example of an electrical heated catalytic device. 
     Case  410  is a housing for EHC  140  made of a metallic material such as, for example, stainless, and is connected to exhaust passage  130  in  FIG. 1  by coupling members (not shown) at ends of case  410  on the upstream and downstream sides. 
     Insulating member  420  is placed to cover an inner circumferential surface of case  410 , and has the heat insulation property and the electrical insulation property. An insulating material such as, for example, alumina is used as insulating member  420 . 
     EHC carrier  430  is a conductive catalyst carrier whose cross section orthogonal to the exhaust direction forms a honeycomb structure. It is to be noted that the carrier refers to a substance serving as a base for fixing (carrying) a substance exhibiting adsorption and catalytic activity. EHC carrier  430  carries a not-shown oxidized catalyst and is configured to be capable of purifying as appropriate the exhaust gas passing through EHC carrier  430 . It is to be noted that the catalyst carried by EHC carrier  430  may be a three-way catalyst. 
     Positive electrode  450  is an electrode for applying a positive voltage, which has one end fixed to a portion near an end on the exhaust upstream side of EHC carrier  430 . The other end of positive electrode  450  is connected to relay SW 2  in  FIG. 1 . It is to be noted that a part of positive electrode  450  is covered with positive electrode coating unit  460  made of a resin and having the electrical insulation property to keep the electrical insulation state between case  410  and positive electrode  450 . 
     Upstream temperature sensor  125 A is a sensor arranged in the exhaust pipe upstream of EHC carrier  430  and configured to be capable of detecting a temperature of a portion near EHC carrier  430 . Upstream temperature sensor  125 A is electrically connected to ECU  150  in  FIG. 1 , and the detected temperature is referred to by ECU  150  at a constant or inconstant cycle. 
     Negative electrode  470  is an electrode for supplying a reference potential, which has one end fixed to a portion near an end on the exhaust downstream side of EHC carrier  430 . The other end of negative electrode  470  is connected to relay SW 1  in  FIG. 1 . It is to be noted that a part of negative electrode  470  is covered with negative electrode coating unit  480  made of a resin and having the electrical insulation property to keep the electrical insulation state between case  410  and negative electrode  470 . 
     Downstream temperature sensor  125 B is a sensor arranged in the exhaust pipe downstream of EHC carrier  430  and configured to be capable of detecting a temperature of a portion near EHC carrier  430 . Downstream temperature sensor  125 B is electrically connected to ECU  150 , and the detected temperature is referred to by ECU  150  at a constant or inconstant cycle. 
     In EHC  140  having the above-mentioned configuration, when the positive voltage is applied to positive electrode  450  with respect to the potential of negative electrode  470 , current flows through conductive EHC carrier  430  and EHC carrier  430  generates heat. This heat generation promotes a rise in the temperature of the oxidized catalyst carried by EHC carrier  430 , and EHC  140  moves to the catalytically active state quickly. 
     It is to be noted that the above-mentioned configuration of EHC  140  is merely one example. The configuration of the EHC carrier, arrangement of each electrode, the manner of control and the like, for example, may have various known manners. 
     In order to sufficiently maintain the heat capacity of EHC  140 , a material having a relatively large electrical resistance (e.g., ceramics) is used as EHC carrier  430 . 
     A DC driving voltage Vehc is supplied between positive electrode  450  and negative electrode  470 . A driving current Iehc corresponding to this DC driving voltage Vehc is generated in EHC carrier  430 , and EHC carrier  430  generates heat in accordance with the amount of heat generated based on this driving current Iehc and an electrical resistance Rehc of EHC carrier  430 . 
       FIG. 3  is a diagram for describing occurrence of leak in the EHC and a short circuit in the high-voltage power supply. 
     Referring to  FIG. 3 , a capacitor  83  and a leak detecting unit  80  are serially connected between a negative electrode of power storage device  70  and a ground node (body earth). 
     Junction box  100  includes relay SW 2  connecting positive electrode line PL 1  to positive electrode  450  of EHC  140 , relay SW 1  connecting negative electrode line GL 1  to negative electrode  470  of EHC  140 , and a fuse Fl serially connected to relay SW 2 . 
     Assume that leak occurs at a point P 1  in EHC  140 , leak also occurs at a point P 2 , and connection to the body earth is provided at a point P 3 . At this time, if both relay SW 1  and relay SW 2  are connected simultaneously, a short circuit occurs in positive electrode line PL 1  and negative electrode line GL 1  due to the case without passing through a resistor of EHC  140 . Then, excessive current may flow through power storage device  70 , and thus, power storage device  70  must be protected. In addition, since the case is connected to the body earth, the high voltage of power storage device  70  may be applied to the body earth as well. 
     Provision of another leak detecting unit in the EHC  140  portion separately from leak detecting unit  80 , however, leads to an increase in circuits, which causes an increase in vehicle manufacturing cost. 
     Thus, in the exhaust purifying system according to the present embodiment, leak detecting unit  80  carries out leak detection with relay SW 1  closed and relay SW 2  opened. When leak detection is carried out in this state, current never flows from power storage device  70  because the high voltage is not applied to positive electrode  450 . In other words, even when leak occurs at both points P 1  and P 2 , a current path from the positive electrode to the negative electrode of power storage device  70  is not formed because relay SW 2  is open, and thus, current never flows from power storage device  70 . In addition, since leak detecting unit  80  can also detect leak occurring in EHC  140 , it is not necessary to provide a new leak detecting unit. 
       FIG. 4  is a circuit diagram showing a configuration of leak detecting unit  80  in  FIG. 3 . 
     Referring to  FIG. 4 , a circuit system  200  indicates the vehicle system shown in  FIG. 1  by one functional block. In addition, a ground node shown in  FIG. 4  corresponds to the body earth (vehicle body) in the vehicle. 
     Leak detecting unit  80  includes an oscillation circuit  81  serving as a signal generating unit, a detection resistance  82 , a bandpass filter (BPF)  84 , a circuit block  85  formed of an offset circuit and an amplification circuit, an overvoltage protection diode  87 , a resistance  86 , a capacitor  88 , and a control circuit  110 . 
     Oscillation circuit  81  applies a pulse signal SIG changing at a predetermined frequency (predetermined cycle Tp) to a node NA. Detection resistance  82  is connected between node NA and a node N 1 . A coupling capacitor  83  is connected between node N 1  and power storage device  70  subjected to leak detection. Bandpass filter  84  has an input terminal connected to node N 1  and an output terminal connected to a node N 2 . The passband frequency of bandpass filter  84  is designed to correspond to the frequency of pulse signal SIG. 
     Circuit block  85  is connected between node N 2  and a node N 3 . Circuit block  85  amplifies a voltage change near a threshold voltage set at the time of detecting an insulation resistance, of the pulse signal that has passed through bandpass filter  84 . Overvoltage protection diode  87  has a cathode connected to a constant voltage node and an anode connected to a node NB, and removes a surge voltage (high voltage or negative voltage). Resistance  86  is connected between node N 3  and node NB. Capacitor  88  is connected between node NB and the ground node. Resistance  86  and capacitor  88  function as a filter removing noise of a signal outputted from circuit block  85 . 
     Control circuit  110  controls oscillation circuit  81 . In addition, control circuit  110  detects a voltage at node NB and detects a decrease in an insulation resistance Ri based on the detected voltage. Control circuit  110  includes an oscillation commanding unit  111 , an A/D converting unit  112  and a determining unit  113 . 
     Oscillation commanding unit  111  provides an instruction to generate pulse signal SIG to oscillation circuit  81 , and provides an instruction to change the duty ratio of pulse signal SIG. A/D converting unit  112  makes an A/D conversion of the voltage (detected voltage) at node NB detected at a predetermined sampling cycle Ts. Since sampling cycle Ts is sufficiently shorter than cycle Tp of pulse signal SIG, the maximum voltage (peak voltage Vp) and the minimum voltage at node NB can be detected. Determining unit  113  compares a value of peak voltage Vp obtained from A/D converting unit  112  with a threshold value. As a result, control circuit  110  detects whether insulation resistance Ri decreases or not. 
     Next, an operation for detecting the decrease in insulation resistance Ri will be described. Pulse signal SIG generated by oscillation circuit  81  is applied to a series circuit configured to include detection resistance  82 , coupling capacitor  83 , insulation resistance Ri, and bandpass filter  84 . As a result, at node N 1  corresponding to a point connecting detection resistance  82  and coupling capacitor  83 , a pulse voltage is generated, which takes, as a crest value, a value related to a product of a voltage division ratio of insulation resistance Ri and detection resistance  82  (resistance value Rd): Ri/(Rd+Ri) and an amplitude of pulse signal SIG (voltage that is a power supply voltage+B). It is to be noted that voltage+B may be, for example, a voltage of an auxiliary battery, although voltage+B is not limited thereto. 
     As for the pulse voltage generated at node N 1 , the components other than the frequency of pulse signal SIG is attenuated by bandpass filter  84 . Only voltage change near the threshold voltage, of pulse signal SIG that has passed through bandpass filter  84 , is amplified by circuit block  85 . The signal outputted from circuit block  85  is transmitted to node NB. When the signal is transmitted from node N 3  to node NB, the surge voltage is removed by overvoltage protection diode  87  and the noise is removed by resistance  86  and capacitor  88 . 
     When insulation resistance Ri is normal, Ri&gt;&gt;Rd. As Ri becomes higher, peak voltage Vp becomes almost equal to voltage+B. On the other hand, when insulation resistance Ri decreases, voltage division ratio: Ri/(Rd+Ri) decreases, and thus, peak voltage Vp decreases. Detection of the decrease in peak voltage Vp allows detection of occurrence of leak. 
       FIG. 5  is a flowchart for describing a leak detection sequence described with reference to  FIG. 3 . 
     Referring to  FIG. 5 , first, when processing starts, ECU  150  in  FIG. 1  detects in step ST 1  whether or not a signal IG has changed from the OFF state to the ON state as a result of driver&#39;s operation of a switch for starting up the vehicle. While the change from the OFF state to the ON state is not detected, the processing in step ST 1  is repeatedly performed. 
     If it is detected in step ST 1  that signal IG has changed from the OFF state to the ON state, the processing proceeds to step ST 2 . In step ST 2 , ECU  150  controls both relay SW 1  and relay SW 2  in  FIG. 3  to the OFF state. 
     Then, the processing proceeds to step ST 3 , and ECU  150  starts a sequence of connection of the system main relay (SMR). In this connection sequence, system main relay  72  is controlled such that connection through a limiting resistance is first made so as not to generate a spark at the time of charging capacitors C 0  and C 1 , and after capacitors C 0  and C 1  are charged using power storage device  70 , connection without the limiting resistance is made. 
     Preferably, when both relays SW 1  and SW 2  are open, leak detecting unit  80  may carry out leak detection in the portions other than EHC  140  during this connection sequence. For example, system main relay  72  is controlled such that GL 1  is first connected to the negative electrode of power storage device  70  through the limiting resistance and the positive electrode of power storage device  70  is opened, and leak detecting unit  80  may carry out leak detection in this state. Then, when leak is not detected, the positive electrode of power storage device  70  is connected to voltage converter  90 . 
     In step ST 4 , it is determined whether or not the processing of connection of system main relay  72  has completed. When charging of capacitors C 0  and C 1  is still insufficient in step ST 4 , the processing waits in step ST 4 . If it is determined in step ST 4  that the processing of connection of system main relay  72  has completed, the processing proceeds to step ST 5 . 
     In step ST 5 , relay SW 1  in  FIG. 3  is controlled from the OFF state to the ON state. Then, in step ST 6 , the leak detection sequence described with reference to  FIG. 4  starts. 
     Then, in step ST 7 , it is determined whether or not a result of the leak detection operation is that leak is occurring. If it is determined in step ST 7  that leak is not occurring, the processing proceeds to step ST 8 . In step ST 8 , relay SW 2  is also controlled from the OFF state to the ON state. Then, in step ST 9 , passage of current through the EHC becomes possible. 
     On the other hand, if it is determined in step ST 7  that leak is occurring, the processing proceeds to step ST 10 . In step ST 10 , relay SW 1  is controlled from the ON state to the OFF state. Then, in step ST 11 , passage of current through the EHC is prohibited. 
     Subsequently to the processing in step ST 9  or step ST 11 , the processing proceeds to step ST 12  and the control returns to the main routine. In the main routine, when leak is detected, a warning lamp and the like inform the driver of abnormality or a history of abnormality is stored. 
     With leak detection in accordance with the sequence as described above, leak detecting unit  80  of power storage device  70  can also be used to detect leak in the EHC without providing a special leak detecting unit in the EHC portion. As a result, an increase in cost can be avoided and the reliability of the vehicle can be increased. In addition, since leak detecting unit  80  detects leak in EHC  140  before positive electrode line PL 1  is connected to EHC  140 , a short circuit in positive electrode line PL 1  and negative electrode line GL 1  can be avoided and power storage device  70  can be protected. 
     It should be understood that the embodiment disclosed herein is illustrative and not limitative in any respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
       1  hybrid vehicle;  10  engine;  40  power split device;  50  decelerator;  55  driving wheel;  60  inverter;  70  power storage device;  72  system main relay;  75  power supply unit;  80  leak detecting unit;  81  oscillation circuit;  82  detection resistance;  83  coupling capacitor;  84  bandpass filter;  85  circuit block;  86  resistance;  87  overvoltage protection diode;  88 , C 0 , C 1  capacitor;  90  voltage converter;  100  junction box;  110  control circuit;  111  oscillation commanding unit;  112  A/D converting unit;  113  determining unit;  120  current sensor;  121  voltage sensor;  122 ,  123 ,  124  rotation speed sensor;  125 ,  125 A,  125 B temperature sensor;  130  exhaust passage;  200  circuit system;  410  case;  420  insulating member;  430  EHC carrier;  450  positive electrode;  460  positive electrode coating unit;  470  negative electrode;  480  negative electrode coating unit; C 1  smoothing capacitor; F 1  fuse; GL 0 , GL 1  negative electrode line; MG 1 , MG 2  motor generator; PL 0 , PL 1  positive electrode line; SW 1 , SW 2  relay