Patent Publication Number: US-9850860-B2

Title: Oil removal apparatus

Description:
BACKGROUND 
     Technical Field 
     The present disclosure relates to an oil removal apparatus that removes oil particles (e.g., oil mist) contained in blow-by gas in an internal combustion engine. 
     Description of the Related Art 
     In a conventional technique employed in an internal combustion engine, blow-by gas is recirculated to an intake system from a crank case through a blow-by gas passage. An oil removal apparatus that removes oil particles contained in the blow-by gas is provided in the blow-by gas passage. Japanese Patent Application Publication No. 2005-334876, for example, discloses an electrostatic precipitator having a collector electrode that collects ionized oil mist within an electric field created by a pulse-driven high voltage corona discharge electrode. 
     Further, Japanese Patent Application Publication No. S61-133155 discloses an electrostatic purification apparatus that removes microparticulate matter contained in engine oil. The electrostatic purification apparatus is structured such that an insulating filter is provided between electrodes. 
     Furthermore, Japan Association of Aerosol Science and Technology vol. 14 No. 4, 338-347 (1999) discloses a microparticle removal unit used in a clean elevator of a clean room. This removal unit mainly removes microparticles believed to originate from oil using a dielectric filter method. The removal unit is structured such that a nonwoven fabric serving as a dielectric fiber layer is filled between an anode and a cathode of a parallel plate electrode. Dielectric polarization is generated in the nonwoven fabric by applying a voltage to the electrodes, and microparticles are collected in the nonwoven fabric using a dielectric polarization force that acts between the fibers and the microparticles in addition to Coulomb force acting on charged particles. 
     SUMMARY 
     When a method of using dielectric polarization of a filter is employed in an oil removal apparatus that removes oil particles contained in blow-by gas flowing through a blow-by gas passage of an internal combustion engine, the oil removal apparatus is configured such that a filter formed from an insulator is disposed between an anode and a cathode extending in a flow direction of the blow-by gas of a bipolar electrode. With this configuration, dielectric polarization is generated in the filter by applying a voltage to the bipolar electrode such that dielectric polarization force acts on the oil particles flowing through the filter. Further, many of the oil particles contained in the blow-by gas are charged, and therefore, when a voltage is applied to the bipolar electrode, Coulomb force acts on the charged oil particles in addition to the dielectric polarization force. As a result, the oil particles are collected in the filter and thereby removed from the blow-by gas. 
     Here, the blow-by gas contains moisture, and therefore condensed water may be generated in the oil removal apparatus when the moisture in the blow-by gas condenses. When condensed water is generated in the oil removal apparatus configured as described above, the condensed water may spread through the filter such that conduction occurs between the anode and the cathode. When conduction occurs between the anode and the cathode due to the condensed water, power consumption may increase. 
     Embodiments of the present disclosure have been designed in consideration of the problem described above. The embodiments may suppress conduction between an anode and a cathode of a bipolar electrode caused by condensed water in an oil removal apparatus in which oil particles are collected in a filter disposed between the anode and the cathode. 
     In an oil removal apparatus according to some embodiments, an insulating layer that has an insulating property and prevents condensed water from connecting an anode and a cathode of a bipolar electrode is provided either between a filter and at least one of the anode and the cathode of the bipolar electrode or within the filter. 
     In some embodiments, an oil removal apparatus removes oil particles contained in blow-by gas flowing through a blow-by gas passage of an internal combustion engine, and includes: 
     a bipolar electrode having an anode and a cathode that extend in a flow direction of the blow-by gas; 
     a voltage applicator that applies a voltage to the bipolar electrode; 
     a filter disposed between the anode and the cathode of the bipolar electrode, in which dielectric polarization occurs when the voltage applicator applies a voltage to the bipolar electrode; and 
     an insulating layer that is sandwiched either between the filter and at least one of the anode and the cathode of the bipolar electrode or within the filter so as to extend in the flow direction of the blow-by gas, and that has an insulating property so as to prevent condensed water generated when moisture in the blow-by gas condenses from connecting the anode and the cathode of the bipolar electrode. 
     In some embodiments, the insulating layer, which differs from the filter, is provided either between the filter and the anode or cathode of the bipolar electrode, or within the filter. The insulating layer is configured to prevent condensed water from connecting the anode and the cathode of the bipolar electrode. Hence, even when condensed water spreads through the filter, spreading of the condensed water between the anode and the cathode is blocked by the insulating layer. According to the present disclosure, therefore, conduction between the anode and the cathode caused by the condensed water can be suppressed. 
     In the present disclosure, the anode and the cathode of the bipolar electrode may be arranged in a gravitational direction (e.g., vertical direction) when the oil removal apparatus is installed in a vehicle. Likewise in this example, the filter is disposed between the anode and the cathode. Further, in this example, the insulating layer may be a space layer that is positioned between the filter and either the anode or the cathode, and formed from a space through which the blow-by gas flows. Alternatively, the filter may be divided into an anode side filter positioned on the anode side and a cathode side filter positioned on the cathode side, and the insulating layer may be a space layer that is positioned between the anode side filter and the cathode side filter, and formed from a space through which the blow-by gas flows. With these configurations, even when condensed water spreads through the filter, the condensed water does not spread to the anode or the cathode. Further, in situations where the oil removal apparatus is installed in a vehicle, droplets of the condensed water may drip downward through the space layer in the gravitational direction. However, in this case, the droplets of condensed water do not remain in the space layer. Hence, the space layer may prevent spreading of the condensed water between the anode and the cathode. As a result, conduction between the anode and the cathode due to the condensed water can be suppressed by the space layer. 
     Further, in the examples described above, the filter may be a fibrous filter, and hydrophobic treatment may be implemented on a surface of fiber forming the fibrous filter. In this example, condensed water on the surface of the fiber forming the filter is more likely to form droplets and less likely to infiltrate the fiber. The condensed water is therefore less likely to spread through the filter. Moreover, the droplets of condensed water are more likely to drip downward in the gravitational direction. According to this configuration, therefore, the condensed water is less likely to spread through the filter, and as a result, conduction between the anode and the cathode caused by the condensed water can be suppressed more reliably. 
     Furthermore, in the examples described above, when the space layer is formed between the filter and a lower electrode, which is a bipolar electrode, from among the anode and the cathode of the bipolar electrode, that is positioned below the filter in the gravitational direction when the oil removal apparatus is installed in a vehicle, hydrophilic treatment may be implemented on a surface of the lower electrode that contacts the space layer. According to this configuration, droplets of condensed water dripping onto the lower electrode are less likely to remain in droplet form on the lower electrode, and are therefore more likely to spread thinly over the surface of the lower electrode. Hence, conduction between the anode and the cathode caused by the condensed water can be suppressed even when the space layer is reduced in thickness. Moreover, by reducing the thickness of the space layer, a reduction in an oil particle collection ratio (a ratio of an amount of collected oil particles relative to an amount of inflowing oil particles) of the oil removal apparatus can be suppressed. 
     In embodiments, the insulating layer may be a water blocking layer that is formed from an insulator and is less permeable than the filter. With this configuration, condensed water is unlikely to infiltrate the water blocking layer. Therefore, even when condensed water spreads through the filter, spreading of the condensed water between the anode and the cathode is prevented by the water blocking layer. Hence, conduction between the anode and the cathode due to the condensed water can be suppressed by the water blocking layer. Furthermore, with this configuration, dielectric polarization occurs likewise in the water blocking layer when a voltage is applied to the bipolar electrode. Therefore, a reduction in the oil particle collection ratio is unlikely to occur likewise when the water blocking layer is provided as the insulating layer. 
     In the examples described above, the water blocking layer may be formed from a flat plate-shaped water blocking plate that extends in the flow direction of the blow-by gas. Further, the water blocking layer may be a coating layer covering a surface of the anode or the cathode. In this case, the water blocking layer can be formed by coating the surface of the anode or the cathode with an insulating material having low permeability. 
     In some embodiments, in an oil removal apparatus that collects oil particles in a filter disposed between an anode and a cathode of a bipolar electrode, conduction between the anode and the cathode caused by condensed water can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a configuration of an internal combustion engine, and an intake/exhaust system thereof, according to an embodiment; 
         FIG. 2  is a schematic view showing a configuration of an oil removal apparatus according to a first embodiment; 
         FIG. 3  is a graph showing an oil particle collection ratio of the oil removal apparatus; 
         FIG. 4  is a schematic view showing a configuration of an oil removal apparatus according to a modified example of the first embodiment; 
         FIGS. 5A and 5B  are image views showing condensed water on a lower electrode according to the first embodiment and a modified example thereof, respectively; 
         FIG. 6  is a schematic view showing a configuration of an oil removal apparatus according to a second embodiment; 
         FIG. 7  is a view showing an arrangement of electrodes in an oil removal apparatus according to a modified example of the second embodiment; and 
         FIG. 8  is a schematic view showing a configuration of an oil removal apparatus according to a modified example of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Specific embodiments of the present disclosure will be described below on the basis of the drawings. Unless specified otherwise, the technical scope of the present disclosure is not limited to the dimensions, materials, shapes, relative arrangements, and so on of constituent components described for the embodiments. 
     First Embodiment 
     An embodiment in which the oil removal apparatus according to the present disclosure is applied to a diesel engine will be described. Note that the oil removal apparatus according to the present disclosure is not limited to a diesel engine, and may be employed in another engine that uses oil (lubricating oil), such as a gasoline engine. 
     [Configuration of Internal Combustion Engine and Intake/Exhaust System Thereof] 
       FIG. 1  is a schematic view showing a configuration of the internal combustion engine and an intake/exhaust system thereof according to this embodiment. An internal combustion engine  1  is a diesel engine installed in a vehicle. An intake passage  2  and an exhaust passage  3  are connected to the internal combustion engine  1 . A compressor  4   a  of a turbocharger  4  is provided midway in the intake passage  2 . A turbine  4   b  of the turbocharger  4  is provided midway in the exhaust passage  3 . 
     An electronic control unit (ECU)  10  is provided alongside the internal combustion engine  1 . A crank position sensor  11  and an accelerator operation amount sensor  12  are electrically connected to the ECU  10 . The crank position sensor  11  detects a rotation position of an output shaft (a crankshaft) of the internal combustion engine  1 . The accelerator operation amount sensor  12  detects an accelerator operation amount of the vehicle in which the internal combustion engine  1  is installed. Output signals from the respective sensors are input into the ECU  10 . The ECU  10  calculates an engine load of the internal combustion engine  1  on the basis of an output value from the accelerator operation amount sensor  12 . Further, the ECU  10  calculates an engine rotation speed of the internal combustion engine  1  on the basis of an output value from the crank position sensor  11 . 
     The internal combustion engine  1  is further provided with a blow-by gas passage  5 . One end of the blow-by gas passage  5  communicates with a crank case of the internal combustion engine  1 . The blow-by gas passage  5  extends through a cylinder head cover of the internal combustion engine  1  such that the other end thereof is connected to the intake passage  2  on an upstream side of the compressor  4   a . Blow-by gas is recirculated to the intake passage  2  from the crank case through the blow-by gas passage  5 . 
     The blow-by gas contains oil particles (e.g., oil mist) generated when oil is scattered in the internal combustion engine  1 . Hence, an oil removal apparatus  6  is provided in the blow-by gas passage  5  within the cylinder head of the internal combustion engine  1  in order to remove the oil particles contained in the blow-by gas. 
     [Configuration of Oil Removal Apparatus] 
       FIG. 2  is a schematic view showing a configuration of the oil removal apparatus according to this embodiment. Note that upper and lower sides of  FIG. 2  correspond to upper and lower sides in a gravitational direction when the oil removal apparatus  6  is installed in a vehicle. Further, black-outlined arrows in  FIG. 2  denote the flow of the blow-by gas. 
     A first bipolar electrode  61 , a second bipolar electrode  62 , and a filter  63  are provided in a case  64  of the oil removal apparatus  6 . An upstream side (crank case side) blow-by gas passage  5   a  is connected to a gas inlet  64   a  of the case  64 . The blow-by gas flows into the case  64  from the blow-by gas passage  5   a  through the gas inlet  64   a . A downstream side (intake passage side) blow-by gas passage  5   b  is connected to a gas outlet  64   b  of the case  64 . The blow-by gas flows out of the case  64  into the blow-by gas passage  5   b  through the gas outlet  64   b.    
     The first bipolar electrode  61  is a parallel plate electrode including an anode  61   a  and a cathode  61   b  that extend in a flow direction of the blow-by gas. The second bipolar electrode  62  is a parallel plate electrode including an anode  62   a  and a cathode  62   b  that extend in the flow direction of the blow-by gas, and is provided between the anode  61   a  and the cathode  61   b  of the first bipolar electrode  61 . Further, when the oil removal apparatus  6  is installed in the vehicle, the anode  61   a  and cathode  61   b  of the first bipolar electrode  61  and the anode  62   a  and cathode  62   b  of the second bipolar electrode  62  are arranged in the gravitational direction. Furthermore, the anode  62   a  of the second bipolar electrode  62  is positioned on the side of the cathode  61   b  of the first bipolar electrode  61 , while the cathode  62   b  of the second bipolar electrode  62  is positioned on the side of the anode  61   a  of the first bipolar electrode  61 . In other words, the respective electrodes are disposed such that the anode  62   a  and the cathode  62   b  of the second bipolar electrode  62  face each other, the anode  61   a  of the first bipolar electrode  61  and the cathode  62   b  of the second bipolar electrode  62  face each other, and the cathode  61   b  of the first bipolar electrode  61  and the anode  62   a  of the second bipolar electrode  62  face each other. 
     The filter  63  is provided between the anode  61   a  of the first bipolar electrode  61  and the cathode  62   b  of the second bipolar electrode  62 , between the cathode  62   b  of the second bipolar electrode  62  and the anode  62   a  of the second bipolar electrode  62 , and between the anode  62   a  of the second bipolar electrode  62  and the cathode  61   b  of the first bipolar electrode  61 . The filter  63  is a fibrous filter formed from insulating fiber such as polyethylene terephthalate (PET) or glass fiber. Further, to reduce pressure loss, a filter having a small filling factor (a filling factor of approximately 0.014 (1.4%), for example) is employed as the filter  63 . Moreover, space layers  70  are provided between the filters  63  and the respective electrodes  61   a ,  61   b ,  62   a ,  62   b . The space layer  70  will be described in detail below. Note that the filters  63  do not necessarily have to be provided over an entire region the anode and the cathode from an upstream end to a downstream end of the electrodes. 
     Furthermore, a drain passage  66  is connected to a lower side of the case  64  on a downstream side of the part in which the bipolar electrodes  61 ,  62  and the filters  63  are disposed. The drain passage  66  communicates with the interior of the cylinder head of the internal combustion engine  1 . Recovered oil collected by the filters  63  is returned to the internal combustion engine  1  through the drain passage  66 . To enable the recovered oil to flow into the drain passage  66  more easily, the oil removal apparatus  6  may be disposed in the cylinder head of the internal combustion engine  1  at an incline so that the gas outlet  64   b  of the case  64  is positioned below the gas inlet  64   a . Further, a lower wall surface of the case  64  may be formed as an inclined surface such that the gas outlet  64   b  side of the case  64  is positioned below the gas inlet  64   a  side. Moreover, a guide passage for guiding the recovered oil to the drain passage  66  may be provided in the lower wall surface of the case  64 . Furthermore, the respective electrodes may be constituted by lattice-shaped lattice electrodes so that the oil collected by the filters  63  can reach the lower wall surface of the case  64  through the filters  63 . 
     The respective bipolar electrodes  61 ,  62  are electrically connected to a power supply  65  that applies a voltage to the bipolar electrodes  61 ,  62 . The power supply  65  is electrically connected to the ECU  10 . Voltage application to the respective bipolar electrodes  61 ,  62  is controlled by the ECU  10 . 
     Note that in the oil removal apparatus according to this embodiment, a configuration employing two bipolar electrode sets, namely the first and second bipolar electrodes  61 ,  62 , is employed. However, the oil removal apparatus according to the present disclosure is not limited to this electrode configuration, and a configuration having a single bipolar electrode set or a configuration having three or more bipolar electrode sets may be employed instead. 
     [Mechanism for Collecting Oil Particles] 
     A mechanism by which the oil particles contained in the blow-by gas are collected in the oil removal apparatus according to this embodiment will now be described. In the oil removal apparatus  6 , as described above, the filling factor of the filter  63  is small, and therefore, when no voltage is applied to the bipolar electrodes  61 ,  62 , substantially none of the oil particles contained in the blow-by gas are collected in the filters  63 . When a voltage is applied to the bipolar electrodes  61 ,  62 , however, dielectric polarization force and Coulomb force act on the oil particles, and as a result, the oil particles are collected in the filters  63 . 
       FIG. 3  is a graph showing an oil particle collection ratio of the oil removal apparatus. A solid line in  FIG. 3  shows the oil particle collection ratio when a voltage is applied to the electrodes of an oil removal apparatus configured such that a filter formed from an insulator and having a small filling factor, as in this embodiment, is provided between the anode and the cathode. Further, a dotted line in  FIG. 3  shows the oil particle collection ratio when a voltage is applied to the electrodes of an oil removal apparatus configured such that a filter is not provided between the anode and the cathode. The solid line and the dotted line in  FIG. 3  show the collection ratio in cases where an identical predetermined voltage is applied to the electrodes of both oil removal apparatuses. Note that in  FIG. 3 , the ordinate shows the oil particle collection ratio of the oil removal apparatus, and the abscissa shows a particle size of the oil particles. Furthermore, numerical values of the oil particle collection ratio in  FIG. 3  are numerical values obtained in a case where a distance between the anode and the cathode is set at a specific distance, and when the filter is provided (the solid line), the filling factor of the filter is set at a specific filling factor. In other words, the numerical values of the oil particle collection ratio shown in  FIG. 3  are merely examples, and these numerical values vary in accordance with the distance between the anode and the cathode. 
     As shown by the dotted line in  FIG. 3 , even with the configuration in which a filter is not provided between the anode and the cathode, when the predetermined voltage is applied to the electrodes, an oil particle collection ratio of at least 50% is obtained, regardless of the particle size of the oil particles. In other words, a part of the oil particles contained in the blow-by gas is collected by the electrodes even when a filter is not provided between the anode and the cathode. The reason for this is that when oil in respective operating parts of the internal combustion engine turns into mist, many of the oil particles are charged, and therefore many of the oil particles in the blow-by gas are charged. Hence, when a voltage is applied to the bipolar electrodes in the oil removal apparatus, Coulomb force acts on the charged oil particles. 
     Further, as shown by the solid line in  FIG. 3 , with the configuration in which the filter is provided between the anode and the cathode, the oil particle collection ratio of the oil removal apparatus improves in comparison with the configuration in which a filter is not provided between the anode and the cathode such that a collection ratio of approximately 90% is obtained. The reason for this is that when a voltage is applied to the bipolar electrodes, dielectric polarization occurs in the filter formed from an insulator (a dielectric), and therefore dielectric polarization force acts on the oil particles contained in the blow-by gas in addition to the Coulomb force, with the result that the oil particles are collected in the filter. The Coulomb force acts only on the charged oil particles, whereas the dielectric polarization force also acts between uncharged oil particles and the filter. Therefore, not only the charged oil particles but also the uncharged oil particles are collected in the filter. Furthermore, the force acting on the uncharged oil particles increases by applying the dielectric polarization force to the uncharged oil particles in addition to the Coulomb force. Hence, with the configuration in which the filter is provided between the anode and the cathode, even though the filter has such a small filling factor that substantially no oil particles are collected therein when no voltage is applied to the electrodes, the oil particle collection ratio of the oil removal apparatus is higher than with the configuration in which the filter is not provided between the anode and the cathode. 
     [Countermeasures Against Condensed Water] 
     The blow-by gas contains moisture. Hence, the moisture in the blow-by gas may condense inside the oil removal apparatus  6  so as to generate condensed water. When the condensed water spreads through the filter  63 , the condensed water may cause conduction to occur between the anode and the cathode of the bipolar electrode, which are provided to face each other on either side of the filter  63 , and as a result, power consumption may increase. In the oil removal apparatus  6 , therefore, the space layers  70  are provided to suppress conduction between the anode and the cathode caused by condensed water. The space layers  70  are formed from spaces positioned between the filter  63  and the respective electrodes  61   a ,  61   b ,  62   a ,  62   b , and through which the blow-by gas flows. In other words, surfaces of the respective electrodes  61   a ,  61   b ,  62   a ,  62   b  that oppose the filters  63  and surfaces of the filters  63  that oppose the electrodes  61   a ,  61   b ,  62   a ,  62   b  contact the space layers  70 . 
     The space layers  70  themselves function as insulating layers. Further, by providing the space layers  70 , even when condensed water spreads through the filters  63 , the condensed water does not spread to the anode or the cathode. Moreover, the space layers  70  have a predetermined thickness and are sandwiched between the filters  63  and the anode or the cathode in the gravitational direction, and therefore condensed water in the form of droplets may drip downward in the gravitational direction through the space layers  70 . In other words, droplets of condensed water formed in the filter  63  may drip through the space layer  70  onto the electrode positioned below the filter  63  in the gravitational direction. Furthermore, droplets of condensed water formed on the surface of the electrode may drip through the space layer  70  onto the filter  63  positioned below the electrode in the gravitational direction. Even in these cases, however, the droplets of condensed water do not remain in the space layers  70 . In other words, the droplets of condensed water pass through the space layers  70 , but since the space layers  70  have a predetermined thickness, the droplets of condensed water do not contact the surface of the filter  63  and the surface of the electrode at the same time. 
     According to this configuration, even when condensed water spreads through the filter  63 , the condensed water is prevented from connecting the anode and the cathode of the bipolar electrode, which oppose each other on either side of the filter  63 , by the space layer  70 . Hence, by providing the space layers  70 , conduction between the anode and the cathode caused by the condensed water can be suppressed. 
     First Modified Example 
     Note that in the configuration shown in  FIG. 2 , the space layer  70  is provided both between the filter  63  and the anode and between the filter  63  and the cathode. However, a configuration in which the space layer  70  is only provided either between the filter  63  and the anode or between the filter  63  and the cathode may be employed as the configuration of the oil removal apparatus  6 . Likewise in this case, the space layer  70  prevents condensed water from connecting the anode and the cathode of the bipolar electrode, which oppose each other on either side of the filter  63 . 
     Second Modified Example 
     Further, as shown in  FIG. 4 , a configuration in which the space layer  70  is provided within the filter  63  disposed between the anode and the cathode of the bipolar electrode may be employed as the configuration of the oil removal apparatus  6 . In this case, the filter  63  is divided by the space layer  70  into an anode side filter positioned on the anode side and a cathode side filter positioned on the cathode side. Hereafter, the filter positioned on the upper side in the gravitational direction, of the filter  63  divided by the space layer  70 , will be referred to as an upper filter  63   a , and the filter positioned on the lower side in the gravitational direction will be referred to as a lower filter  63   b.    
     In a case where the space layer  70  is provided between the upper filter  63   a  and the lower filter  63   b , even when condensed water spreads respectively through the upper filter  63   a  and the lower filter  63   b , the condensed water spreading through one of the filters does not reach the other filter. Further, droplets of condensed water formed in the upper filter  63   a  may drip into the lower filter  63   b  through the space layer  70 , but likewise in this case, the condensed water does not remain in the space layer  70 . In other words, the droplets of condensed water pass through the space layer  70 , but since the space layer  70  has a predetermined thickness, the droplets of condensed water do not contact a surface of the upper filter  63   a  and a surface of the lower filter  63   b  at the same time. Hence, likewise with a configuration in which the space layer  70  is provided within the filter  63 , the space layer  70  prevents condensed water from connecting the anode and the cathode of the bipolar electrode, which oppose each other on either side of the filter  63 . 
     Third Modified Example 
     Further, in a case where the space layers  70  are provided between the filters  63  and the electrodes (referred to hereafter as lower electrodes)  61   b ,  62   a ,  62   b  positioned respectively below the filters  63  in the gravitational direction, hydrophilic treatment may be implemented on the surfaces of the lower electrodes  61   b ,  62   a ,  62   b  that contact the space layers  70 . Processing for coating the surfaces of the electrodes with a substance containing a silanol group as a functional group may be cited as an example of hydrophilic treatment. 
       FIGS. 5A and 5B  are image views showing condensed water on the lower electrode.  FIG. 5A  shows condensed water when hydrophilic treatment is not implemented on the surface of the lower electrode, and  FIG. 5B  shows condensed water when hydrophilic treatment is implemented on the surface of the lower electrode that contacts the space layer. As described above, droplets of condensed water formed in the filters  63  may drip through the space layers  70  onto the lower electrodes  61   b ,  62   a ,  62   b . If, at this time, hydrophilic treatment is not implemented on the surfaces of the lower electrodes  61   b ,  62   a ,  62   b , as shown in  FIG. 5A , the droplets of condensed water dripping onto the lower electrodes  61   b ,  62   a ,  62   b  are more likely to remain in droplet form on the lower electrodes  61   b ,  62   a ,  62   b . When the droplets of condensed water on the lower electrodes  61   b ,  62   a ,  62   b  contact the filters  63 , the condensed water may connect the lower electrodes  61   b ,  62   a ,  62   b  to the electrodes that oppose the lower electrodes  61   b ,  62   a ,  62   b  via the filters  63  (in other words, electrodes having an opposite polarity to the lower electrodes). Therefore, to suppress conduction between the anode and the cathode caused by the condensed water, a thickness ds of the space layer  70  may be made greater than a height of the droplets of condensed water existing on the lower electrodes  61   b ,  62   a ,  62   b . As the thickness ds of the space layer  70  is increased, however, a sectional area of the filter  63  between the anode and the cathode in a vertical direction decreases relative to the sectional area thereof in the flow direction of the blow-by gas, and as a result, the oil particle collection ratio of the oil removal apparatus  6  decreases. 
     When, on the other hand, hydrophilic treatment is implemented on the surfaces of the lower electrodes  61   b ,  62   a ,  62   b  that contact the space layers  70 , as shown in  FIG. 5B , the droplets of condensed water dripping onto the lower electrodes  61   b ,  62   a ,  62   b  are less likely to remain in droplet form on the lower electrodes  61   b ,  62   a ,  62   b , and therefore more likely to spread thinly over the surfaces of the lower electrodes  61   b ,  62   a ,  62   b . The condensed water on the lower electrodes  61   b ,  62   a ,  62   b  is therefore unlikely to contact the filter  63  even when the thickness ds of the space layer  70  is reduced. Hence, conduction between the anode and the cathode caused by the condensed water can be suppressed even when the thickness ds of the space layer  70  is reduced. By reducing the thickness ds of the space layer  70 , therefore, a reduction in the oil particle collection ratio of the oil removal apparatus  6  can be suppressed. 
     Fourth Modified Example 
     Further, hydrophobic treatment may be implemented on the surface of the fiber forming the filter  63 . Processing for coating the surface of the fiber with a substance containing a saturated fluoroalkyl group, an alkylsilyl group, a fluorosilyl group, or a long chain alkyl group as a functional group may be cited as an example of hydrophobic treatment. In this case, condensed water is more likely to form droplets on the surface of the fiber forming the filter  63  and less likely to infiltrate the fiber. Accordingly, the condensed water is less likely to spread through the filter  63 . Furthermore, the condensed water droplets are more likely to drip downward in the gravitational direction, and therefore the condensed water is less likely to remain in the filter  63 . Hence, by implementing hydrophobic treatment on the surface of the fiber forming the filter  63 , conduction between the anode and the cathode caused by the condensed water can be suppressed. 
     Second Embodiment 
     An internal combustion engine and an intake/exhaust system thereof according to a second embodiment are configured identically to the first embodiment. In an oil removal apparatus according to this embodiment, the configuration for suppressing conduction between the anode and the cathode caused by condensed water differs from the first embodiment.  FIG. 6  is a schematic view showing a configuration of the oil removal apparatus according to this embodiment. Note that upper and lower sides of  FIG. 6  correspond to the upper and lower sides in the gravitational direction when the oil removal apparatus  6  is installed in a vehicle. Further, black-outlined arrows in  FIG. 6  denote the flow of the blow-by gas. 
     In the oil removal apparatus according to this embodiment, a water blocking plate  80  is provided in place of the space layer  70  of the oil removal apparatus according to the first embodiment. The water blocking plate  80  takes the shape of a flat plate extending in the flow direction of the blow-by gas. The water blocking plate  80  is sandwiched within the filters  63  provided respectively between the anode  61   a  of the first bipolar electrode  61  and the cathode  62   b  of the second bipolar electrode  62 , between the cathode  62   b  and the anode  62   a  of the second bipolar electrode  62 , and between the anode  62   a  of the second bipolar electrode  62  and the cathode  61   b  of the first bipolar electrode  61 . In other words, the filter  63  is divided by the water blocking plate  80  into an anode side and a cathode side. Hereafter, the filter positioned on the upper side in the gravitational direction, of the filter  63  divided by the water blocking plate  80 , will be referred to as an upper filter  63   c , and the filter positioned on the lower side in the gravitational direction will be referred to as a lower filter  63   d.    
     The water blocking plate  80  is formed from an insulator, and is structured to be less permeable than the filter  63 . In other words, the water blocking plate  80  has a higher density than the filter  63  so that water is less likely to infiltrate. Glass epoxy resin may be cited as an example of a material of the water blocking plate  80 . Alternatively, a component obtained by implementing superhydrophobic treatment on a surface of a plate-shaped insulating material may be used as the water blocking plate. 
     With the configuration described above, condensed water is unlikely to infiltrate the water blocking plate  80 . Therefore, even when condensed water spreads respectively through the upper filter  63   c  and the lower filter  63   d , the condensed water spreading through one of the filters does not reach the other filter. In other words, the water blocking plate  80  prevents the condensed water from connecting the anode and the cathode of the bipolar electrode, which oppose each other on either side of the filter  63 . As a result, conduction between the anode and the cathode caused by the condensed water can be suppressed. 
     Moreover, with the configuration described above, dielectric polarization occurs likewise in the water blocking plates  80  when a voltage is applied to the bipolar electrodes  61 ,  62 . The dielectric polarization force generated as a result acts on the oil particles. Hence, when the water blocking plates  80  are provided to suppress conduction between the anode and the cathode caused by condensed water, a reduction in the oil particle collection ratio of the oil removal apparatus  6  is even less likely to occur than when the space layers  70  are provided, as in the configuration according to the first embodiment. 
     First Modified Example 
     Note that when the water blocking plates  80  are provided in the oil removal apparatus  6  to suppress conduction between the anode and the cathode caused by condensed water, in contrast to a case in which the space layers  70  are provided, as in the configuration according to the first embodiment, the anodes and the cathodes of the bipolar electrodes do not necessarily have to be arranged in the gravitational direction upon installation of the oil removal apparatus  6  in a vehicle. In other words, a configuration such as that shown in  FIG. 7 , in which the anodes  61   a ,  62   a  and cathodes  62   a ,  62   b  of the bipolar electrodes  61 ,  62  are arranged in a horizontal direction when the oil removal apparatus  6  is installed in a vehicle may be employed as the configuration of the oil removal apparatus  6  (upper and lower sides in  FIG. 7  correspond to the upper and lower sides in the gravitational direction when the oil removal apparatus  6  is installed in a vehicle). In this case, the respective water blocking plates  80  are also arranged in the horizontal direction. 
     Second Modified Example 
     Furthermore, the water blocking plates  80  do not necessarily have to be sandwiched within the filters  63 . In other words, a configuration in which the water blocking plate  80  is sandwiched between the filter  63  and the anode and/or between the filter  63  and the cathode may be employed as the configuration of the oil removal apparatus  6 . With this configuration, even when condensed water spreads through the filter  63 , the condensed water does not spread to the anode or the cathode. In other words, the water blocking plate  80  prevents the condensed water from connecting the anode and the cathode of the bipolar electrode, which oppose each other on either side of the filter  63 . 
     Third Modified Example 
     Further, a configuration such as that shown in  FIG. 8 , in which the surfaces of the anode and the cathode of bipolar electrode are covered with a water blocking coating layer  81  in place of the water blocking plates  80 , may be employed as the configuration of the oil removal apparatus  6 . In this case, the surfaces of the respective electrodes that contact the filter  63  are coated with an insulating material having a similarly low permeability to the material forming the water blocking plate  80 . Fluorine resin may be cited as an example of a coating material. In so doing, similar effects to that of a case in which the water blocking plate  80  is sandwiched between the electrode and the filter  63  can be obtained. Note that likewise with this configuration, the coating layer  81  does not necessarily have to be provided on both the anode and the cathode that oppose each other on either side of the filter  63 , and may be provided on only one thereof.