Patent Abstract:
A cathodic protection system has electrodes disposed in a coolant passage of an engine filled with a conductive coolant. The electrodes are electrically insulated from the engine. A power supply device provides for a protective electric current to form from the electrodes to the engine through the coolant. The cathodic protection system reduces engine manufacturing and maintenance costs and provides an anticorrosive effect without increasing the size of the engine.

Full Description:
RELATED APPLICATIONS 
     The present application is based on and claims priority under 35 U.S.C. § 119(a)-(d) to Japanese Patent Application No. 2005-085522, filed on Mar. 24, 2005, the entire contents of which are hereby expressly incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an impressed current cathodic protection system for a marine engine. Preferably, the protection system provides a protective current flow through a coolant passage. 
     2. Description of the Related Art 
     A conventional outboard motor engine often uses seawater as a coolant and may be subject to cathodic corrosion due to the seawater contacting the inner wall of its coolant passages. In order to inhibit cathodic corrosion, an anticorrosive coating commonly is applied to an inner surface of at least some of the coolant passages within the engine. The anticorrosive coating may be applied by painting the coating on an inner wall of the coolant passage. The anticorrosive coating applied within the coolant passages may come off after the engine has been in service for a long period of time. Once the coating comes off, the coating no longer inhibits corrosion. 
     In some outboard motors, a cathodic protection system is used to inhibit electrolytic corrosion. For example, a corrosion protection system may use a sacrificial electrode or anode in the shape of a bar. The anode may be detachable from a cylinder head with its electrode facing an internal space of the coolant passage. 
     At least two types of sacrificial anodes often are used for conventional outboard motor engines. The first type of anode is externally attached to/detached from the engine while the other type of anode is internally attached to/detached from the engine. Self-corrosion of the anode produces a protective current which causes the anode to be consumed. The consumption of the anode creates a need for replacement before the anode is completely consumed. 
     The residual current of the anode is measured periodically or at the time of engine maintenance and, if necessary, the anode is replaced. The anode can also be visually inspected to determine whether replacement is required. To visually inspect the residual anode, the anode is removed from the engine or the engine is disassembled. 
     A disadvantage of this system is that part of the internal space of the coolant passage is used for setting the anodes. For anodes designed to be externally attached to/detached from the engine, a dedicated mounting seat on the external surface of the engine also must be provided. In addition, each anode is only effective over a limited area, and thus multiple anodes may be required for complete protection. An engine equipped with a cathodic prevention system that uses the aforementioned anodes tends to be larger. The extra assembly step of attaching the anode also increases manufacturing costs. Further, the measurement of the residual anode current and the replacement of the anodes increase maintenance costs. 
     Known impressed cathodic protection systems utilize an anticorrosive electrode in the coolant passage and more specifically on the upstream side of the engine. See, e.g. Japanese Publication No. 06-299377, dated Oct. 25, 1994. The anticorrosive electrode provides an anticorrosive effect to an area adjacent to the anticorrosive electrode; the anticorrosive effect is limited for other areas of the coolant passages through the engine, especially at the more narrow passages. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is directed toward addressing one or more of these problems and provides a cathodic protection system that has an anticorrosive effect without increasing the engine size and that can reduce engine manufacturing and maintenance costs. Preferably, the impressed current cathodic protection system has a plurality of electrodes disposed in a coolant passage of the engine filled with a conductive coolant. The electrodes are electrically insulated from the engine and power is supplied to the electrodes by a power supply device. The powered electrodes provide a protective current to the engine through the coolant. 
     Another aspect is an impressed current cathodic protection system for a marine engine having a coolant passage, the coolant passage being configured to receive a conductive coolant. The system comprises a plurality of electrodes disposed in the coolant passage, each electrode being electrically insulated from the engine and a power supply configured to provide a protective current between the plurality of electrodes and the engine via the conductive coolant. 
     Another aspect is a marine engine that comprises a coolant passage configured to receive a conductive coolant, a plurality of electrodes disposed in the coolant passage and electrically insulated from the engine, and a power supply configured to supply an electric potential to the plurality of electrodes and the engine. 
     Yet another aspect has at least one electrode in a linear form and bent to conform to a shape of the coolant passage. Another aspect has at least one of the electrodes in a loop form with part of the electrode connected to the power supply device. Another aspect has the electrodes arranged side by side. Another aspect has a circuit that automatically shuts off one of the plurality of electrodes upon the occurrence of a short circuit to the one of the plurality of electrodes. Another aspect has a switch which disconnects power to the electrode when the engine is stopped. Another aspect has an abnormality detection circuit for detecting an abnormality in the power supply to the electrodes. Yet another aspect has an alarm for producing a visible and/or audible alarm in response to the detection of an abnormality. 
     In a preferred form, a protective current flows from electrodes disposed in the engine and through a wall of the coolant passage in the engine. The current can inhibit cathodic corrosion in the engine. Unlike a sacrificial electrode, the electrodes do not readily wear out, and thus are less likely need replacing. The service life of the electrode may be longer than the service life of a sacrificial electrode. This longer service life may reduce maintenance costs compared to a conventional cathodic protection system that employs sacrificial electrodes. 
     Because easy access to the electrodes of the present invention is not necessary, the electrodes may be installed within the engine. By installing the electrodes within the engine and not on the engine, the size of the engine is not increased. 
     An additional aspect of the invention is to disable the electrodes when an abnormality occurs to the electrodes. Another aspect is to reduce the flow of protective current without creating significant fluctuations in the protective current (current value) if an insulating coating is formed on the wall of the coolant passage. Under these conditions, any reduction in corrosion protection is minimized. 
     An aspect of the invention is to form the electrodes to approximately conform to the complicated shapes of the coolant passages in the engine. Thus, the coolant passages through which the electrodes pass are subject to a stable protective potential regardless of the shape of the passage. 
     A further aspect of the cathodic protection system employs a loop-type electrode. By keeping the loop energized, the reliability of the impressed current cathodic protection system is improved. Another aspect includes an anticorrosive electrode that is divided into two portions with both portions being connected to the power supply device. Conductivity tests on both portions determine whether a break may have occurred in the electrode. Another aspect of the cathodic protection system includes providing two side by side electrodes so that if one of the electrodes is not operational, the other electrode provides corrosion protection to the engine. 
     An aspect of the cathodic protection system includes a power supply that automatically stops providing a protective current to a short-circuited electrode while still providing the protective current to the other electrodes. The power supply minimizes the size of the region affected by the short circuit and improves the reliability of the impressed current cathodic protection system. 
     An additional aspect of the cathodic protection system is to provide redundant electrodes disposed at the same position so if a first electrode shorts out, the second electrode provides the protective current. 
     Another aspect of the cathodic protection system turns the power on and off depending on the operation of the engine. For example, when seawater is flowing within the coolant passages and the engine is on, the power supply is ON to the anticorrosive electrodes. When the engine stops and a majority of the coolant is drained out of the engine, the power supply to the anticorrosive electrodes is OFF and reduces power consumption. 
     The systems and methods of the invention have several features, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of the invention as expressed by the claims which follow, its more prominent features have been discussed briefly above. After considering this discussion, and particularly after reading the section entitled “Detailed Description of the Preferred Embodiments” one will understand how the features of the system and methods provide several advantages over conventional corrosion protection systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects and advantages of the present invention will now be described in connection with preferred embodiments of the invention, in reference to the accompanying drawings. The illustrated embodiments, however, are merely examples and are not intended to limit the invention. The following are brief descriptions of the drawings. 
         FIG. 1  is a schematic cross-section of an impressed current cathodic protection system according to the invention. 
         FIG. 2  illustrates various conditions, including failure conditions, which may occur for each of the three power supply methods. 
         FIG. 3  is a cross-section of another embodiment of an impressed current cathodic protection system. 
         FIG. 4  is a plan view of a marine engine having an impressed current cathodic protection system with linear electrodes. 
         FIG. 5(   a ) is a schematic, cross-section of another embodiment of an impressed current cathodic protection system that includes a loop-type electrode. 
         FIG. 5(   b ) is an enlarged view of a portion of the anticorrosive electrode from  FIG. 5(   a ). 
         FIG. 6  is a schematic, cross-section of another embodiment of an impressed current cathodic protection system that includes a loop-type electrode. 
         FIG. 7  is a schematic, cross-section of another embodiment of an impressed current cathodic protection system that includes two linear electrodes. 
         FIG. 8  is a block diagram illustrating another embodiment of the impressed current cathodic protection system that includes redundant or plural electrodes. 
         FIG. 9  is a schematic, cross-section of the impressed current cathodic protection system illustrated in  FIG. 8 . 
         FIG. 10  is a circuit diagram of the controller illustrated in  FIG. 9 . 
         FIG. 11  is a circuit diagram of a controller employing a constant-voltage method with the power supply. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following detailed description is now directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different systems and methods. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. 
       FIG. 1  is a schematic cross-section of an impressed current cathodic protection system  11  for use with a marine engine  2 . While the protection system  11  is described in connection with a marine engine, the protection system  11  also may be used with other types of engines. 
     The engine  2  includes a cylinder body  3  and a coolant passage  1  disposed within the cylinder body  3 . The cylinder body  3  may be made from an aluminum alloy. The coolant passage  1  may be designed for seawater coolant. 
     The impressed current cathodic protection system  11  includes electrodes  12 ,  13 ,  14 ,  15  attached through insulating support members  16  to a wall  4  of the coolant passage  1 . The impressed current cathodic protection system  11  further includes a power supply device  17  configured to apply a protective current to the coolant flowing in the internal space of the coolant passage  1  via the electrodes  12 ,  13 ,  14 ,  15 . The power supply device  17  includes a controller  18  and a battery  19  for supplying power to the controller  18 . The power supply device  17  illustrated in  FIG. 1  employs a potential control method. 
     The electrodes  12  to  15  may have a cylindrical shape and be connected to the controller  18  through lead wires  20 . The electrodes  13  to  15  are spaced at a specified distance from each other along the wall  4 . Support members  16  support the electrodes  12  to  15  and may comprise rubber or plastic. Preferably, the rubber or plastic has heat resistance and insulation properties. 
     The electrode  12  positioned leftmost in  FIG. 1  is a reference electrode for the controller  18 . The other anticorrosive electrodes  13  to  15  are configured to apply a protective current to the coolant in the internal space of the coolant passage  1  such that a value of the protective current generally corresponds to a potential measured by the reference electrode  12 . The anticorrosive electrodes  13  to  15  are disposed with specified gaps so that any area of the internal space in the coolant passage  1  receives an anticorrosive effect. A broken line A indicates that the anticorrosive effect is available throughout the internal space in the coolant passage  1 . 
     In the impressed current cathodic protection system  11  illustrated in  FIG. 1 , a protective current flows from the anticorrosive electrodes  13  to  15  disposed in the internal space of the coolant passage  1  and through the inner wall  4  of the cylinder body  3  to protect the engine  2  from cathodic corrosion. 
     Unlike conventional sacrificial electrodes, the anticorrosive electrodes  12  to  15  only provide a protective current and therefore do not readily wear out. Thus, the anticorrosive electrodes  13  to  15  may not need to be replaced. The service life for the electrodes  12  to  15  may be longer than the service life of sacrificial electrodes. 
     As described above, the anticorrosive electrodes  13  to  15  may not need to be replaced. Unlike electrodes  12  to  15 , conventional sacrificial electrodes are attached externally to the engine  2  to allow the sacrificial electrodes to be easily replaced. Thus, an engine  2  employing the cathodic protection system  11  does not increase in size even if the cathodic protection system  11  includes a plurality of anticorrosive electrodes since the electrodes may be installed internal to the engine  2 . 
       FIG. 2  illustrates various conditions, including a failed electrode  21 , which may occur for three different power supply methods. The three control methods are arranged in columns with the different abnormities arranged in rows. Instead of the potential control method employed by the power supply device  17  illustrated in  FIG. 1 , the cathodic protection system  11  may use a constant-voltage control method or a constant-current control method to energize the electrodes  13  to  15 . A cathodic protection system  11  using the constant-voltage control method or the constant-current control method does not require a reference electrode  12 . 
     When using the constant-voltage control method, a malfunctioning electrode  13  to  15  may cause insignificant fluctuations in the current value of the protective current and reduce the area subject to the protective current. The malfunction of an electrode  13  to  15  may be caused by the formation of an insulating coating  22 , such as aluminum oxide film, on the inner wall of the coolant passage  1 . 
     For an engine  2  employing the constant-voltage control method on a lake, the increase in coolant resistance decreases the protective current and the anticorrosive effect. However, the fresh water in the lake inhibits cathodic corrosion. Accordingly, the reduced anticorrosive effect has limited impact on the engine  2 . For the aforementioned failures, the constant-voltage control method may minimize any adverse impact on the corrosion protection provided by the cathodic protection system  11 . 
     When using the constant-current control method, a malfunctioning electrode  13  to  15  may reduce the area subject to the protective current and the corrosion protection. The formation of an insulating coating  22  on the inner wall of the coolant passage  1  may concentrate an excessive amount of protective current at the remaining uncovered regions  23 . The inner wall  4  of the coolant passage  1  may become subjected to corrosion. In the constant-current control method, an increase in the resistance of the coolant prevents the protective current from flowing and the corrosion protection. 
     When using the potential control method, the corrosion control does not work when the reference electrode  12  or the anticorrosive electrodes  13  to  15  malfunction  21  as illustrated in  FIG. 2 . 
       FIG. 3  is a cross-section of another embodiment of an impressed current cathodic protection system  11  having a linear electrode  31 . The linear electrode  31  is in a linear form and may include a coated electrode wire. The electrode wire may have a platinum electrode or a flexible copper wire as a core. The electrode wire may be made by applying a protective coating of titanium, niobium or tantalum to the flexible copper wire, and then plating platinum to the external surface of the protective coating. Platinum, a principal component of the platinum plating, has high conductivity and is insoluble in an electrolyte. Application of the platinum plating to the core wire results in the electrode wire having high anticorrosive properties. 
     The coating may be formed by twisting a plastic string, which has both heat resistance and insulation properties, to create an elongated cylinder in the shape of a bag. The coating may be made of fluoro-plastics. The electrode wire passes through the cylindrical coating. The twisted string inhibits direct contact between the electrode coated wire and the engine  2  so as to prevent a short circuit from occurring when the electrode wire is in contact with the coolant. 
       FIG. 4  is a plan view of a marine engine  2  having an impressed current cathodic protection system  11  according to  FIG. 3  with a plurality of linear electrodes  31   a ,  31   b ,  31   c . The cylinder body  3  is a four-cylinder engine having first, second and third coolant passages  32 ,  33 ,  34 . The first coolant passage  32  surrounds the bores  35  of the cylinder body  3 . The second coolant passage  33  is defined between the cylinder bores  35  and exhaust ports  36 . The third coolant passage  34  surrounds the exhaust ports  36  externally. The linear anticorrosive electrodes  31   a ,  31   b ,  31   b  pass through the first, second and third coolant passage  32 ,  33 ,  34 , respectively. 
     A mating face  37  of the cylinder body  3  is configured to mate with a cylinder head (not shown). The coolant passages  32  to  34  are open in a direction toward the cylinder head. Coolant passages in the cylinder head connect with the coolant passages  32  to  34  of the cylinder body  3  when the cylinder head is fixed to the cylinder body  3 . 
     The first anticorrosive electrode  31   a  passes through the first coolant passage  32  surrounding the cylinder bores  35 . The shape of the electrode  31   a  may be selected to conform to the shape of the internal space within the first coolant passage  32 . The anticorrosive electrode  31   a  may be formed in one stroke so as to thoroughly enclose the opening edge of the first coolant passage  32 . 
     The second coolant passage  33  extends in a direction that is parallel to the cylinder bores  35 . As illustrated in  FIG. 4 , the anticorrosive electrode  31   b  extends through the second coolant passage  33 . 
     The third coolant passage  34  surrounds the exhaust ports  36 . The shape of the anticorrosive electrode  31   c  may be selected to conform to the shape of the opening edge of the third coolant passage  34 . 
     As shown in  FIG. 4 , the ends of the first, second, and third anticorrosive electrodes  31   a ,  31   b ,  31   c  extend through the cylinder body  3  and outside of the engine  2 . The external ends of the electrodes  31   a ,  31   b ,  31   c  are connected to the controller  18  for receiving power from the battery  19 . As shown in  FIG. 3 , support members  16  hold the anticorrosive electrodes  31   a ,  31   b ,  31   c  within the coolant passage  1 . The lead wire  20  may extend through the support member  16  and connects to the controller  18 . 
     To facilitate connecting the internal anticorrosive electrodes  31  to the controller  18 , an electrode lead-out member (not shown) may be employed in the cylinder body  3  or cylinder head. One or more of the electrodes  31  passes through the electrode lead-out members between the inside and outside of the engine  2 . A sealing member between the electrode  31  and the lead-out member may be employed to prevent coolant from leaking through the lead-out member. The embodiment of the cathodic protection system  11  illustrated in  FIGS. 3 and 4  may employ any one of the three power supply methods described above with reference to  FIG. 2 . 
     In the impressed current cathodic protection system  11  illustrated in  FIGS. 3 and 4 , the linear anticorrosive electrodes  31   a  to  31   c  are formed so as to approximately conform to the complicated shapes of the coolant passages  1 ,  32 ,  33 ,  34  and inhibit corrosion of the engine  2 . Thus, the coolant passages through which the anticorrosive electrodes  31   a  to  31   c  pass experience a stable protective potential regardless of the shape of the coolant passage. 
     Each linear anticorrosive electrode  31   a ,  31   b ,  31   c  may be held in place at one or more locations along the electrode. For conventional cathodic protection systems, the bar-shaped sacrificial electrodes require additional space for their attachment to the engine  2 . The cathodic protection system  11  illustrated in  FIGS. 3 and 4  uses fewer anticorrosive electrodes  31  ( 31   a  to  31   c ) as compared to a conventional cathodic protection system of bar-shaped sacrificial electrodes. 
     The linear anticorrosive electrodes  31  may be used in combination with the cylindrical anticorrosive electrodes  13  to  15  illustrated in  FIG. 1  or with conventional sacrificial electrodes. The combination of electrode types may provide more complete protection to the engine  2  or add coverage for regions of the coolant passages that the linear electrodes  31  have little effect. These regions may include any gaps between the cylinders on the coolant passage in the cylinder head and an internal portion of a coolant passage cover (not shown) on the cylinder body  3 . 
       FIG. 5(   a ) is a schematic, cross-section of another embodiment of an impressed current cathodic protection system  11  having an anticorrosive electrode  31  in a loop form.  FIG. 5(   b ) is an enlarged view of the anticorrosive electrode  31  illustrated in  FIG. 5(   a ). The anticorrosive electrode  31  shown in  FIGS. 5(   a ) and  5 ( b ) is a linear electrode similar to the linear electrode described above with reference to  FIGS. 3 and 4  except that the linear electrode illustrated in  FIGS. 5(   a ) and  5 ( b ) is in a loop form. The anticorrosive electrode  31  shown in  FIGS. 5(   a ) and  5 ( b ) passes through the coolant passage  1  with part of the electrode  31  being connected to the power supply device  17 . The coolant passage  1  surrounds the cylinder bores  35 . 
     A portion of the anticorrosive electrode  31  shown in  FIGS. 5(   a ) and  5 ( b ) is external to the engine  2  and includes a dividing terminal  41 . The power supply device  17  supplies power to the anticorrosive electrode  31  through a lead wire  42  connected to the dividing terminal  41 . 
     As illustrated in  FIG. 5(   b ), the dividing terminal  41  divides the anticorrosive electrode  31  into two portions: a first terminal  41  and a second terminal  41 . To determine whether a break has occurred in the anticorrosive electrode  31 , contacts  45  are provided to attach a conductive measurement tester (not shown) to the first and second terminals  41 . With the terminals  41  external to the engine  2 , the conductive measurement may advantageously be performed without disassembling the engine  2 . 
       FIG. 6  is a schematic, cross-section of an impressed current cathodic protection system  11  that includes a loop-type anticorrosive electrode  31 . The anticorrosive electrode  31  of  FIG. 6  is a loop-type electrode similar to the loop-type electrodes illustrated in  FIGS. 5(   a ) and  5 ( b ). The electrode  31  illustrated in  FIG. 6  has a linear electrode body  43  passing through the coolant passage  1  and a lead wire  44  for connecting together both ends of the electrode body  43 . The lead wire  44  is provided with a dividing terminal (not shown) that is equivalent to the dividing terminal  41  shown in  FIGS. 5(   a ) and  5 ( b ). 
     The anticorrosive electrodes  31  of the impressed current cathodic protection systems  11  illustrated in  FIGS. 5(   a ),  5 ( b ), and  6  are loop-type electrodes. Part of the electrodes  31  are connected to the power supply device  17  so that the electrodes  31  are kept thoroughly energized in the event a part of the loop is broken. Thus, the embodiments illustrated in  FIGS. 5(   a ),  5 ( b ), and  6  may have improved reliability over a non-loop type electrode. 
     The embodiments of the impressed current cathodic protection systems  11  illustrated in  FIGS. 5(   a ),  5 ( b ), and  6  may employ any of the power supply methods described above with reference to  FIG. 2 . The loop-type anticorrosive electrode  31  may be made from a flexible linear-type anticorrosive electrode  31  or made using a rigid member to form the anticorrosive electrode into a loop shape. 
       FIG. 7  is a schematic, cross-section of another embodiment of an impressed current cathodic protection system  11  that includes two linear electrodes  31 . The two linear anticorrosive electrodes  31 ,  31  may be disposed at the same position in the internal space of the coolant passage  1 . The anticorrosive electrodes  31  attach to a cylinder body  3  via support members  16 . A controller  18  is connected to the ends of the electrodes  31  via lead wires  20 . 
     The two anticorrosive electrodes  31  provide redundant corrosion protection. In the event one of the anticorrosive electrodes  31  can not be energized, the other energized electrode  31  prevents corrosion. Thus, the impressed current cathodic protection system  11  illustrated in  FIG. 7  may have improved reliability. 
     In the event of a failure with the cathodic protection system  11  illustrated in  FIG. 7 , one of the linear, anticorrosive electrodes  31  may be used as a reference electrode to identify the cause of the failure. To identify the cause of the failure, a tester (not shown) may be connected to the lead wire  20  of the reference electrode  31  to measure the polarization potential. 
     To determine the cause of a failure for an engine having a conventional protection system, a mounting hole is drilled on the external wall of the cylinder body for receiving a reference electrode. In contrast, the cathodic protection system  11  illustrated in  FIG. 7  does not require any drilling since one of the remaining electrodes  31  may be used as a reference electrode. 
     With the plurality of anticorrosive electrodes  31  illustrated in  FIG. 7 , the cathodic protection system  11  may employ any of the three power supply methods described above with reference to  FIG. 2 . If the potential control method is selected, a tester may be connected to one of the anticorrosive electrodes  31  as the reference electrode  12  and also connected to one of the other anticorrosive electrode  31  to measure the polarization potential. 
       FIG. 8  is a block diagram illustrating another embodiment of an impressed current cathodic protection system  11  that includes redundant or plural electrodes  31 .  FIG. 9  is a schematic, cross-section of the impressed current cathodic protection system  11  illustrated in  FIG. 8 . 
     The embodiment illustrated in  FIGS. 8 through 10  includes a plurality of anticorrosive electrodes  31 . Protective current flows to each anticorrosive electrode  31  through the controller  18 . 
       FIG. 10  is a circuit diagram of the controller  18  illustrated in  FIG. 9 . As shown in  FIG. 10 , the controller  18  illustrated in  FIGS. 8 and 9  may include various circuits. In the illustrated embodiment, the controller  18  includes an abnormal current/voltage detecting circuit  51 , a power switch  54 , a filter circuit  55 , a current limiting circuit  56 , a comparator  57 , and an output control circuit  58 . The controller  18  may further include four output terminals  53  connected to the four anticorrosive electrodes  31 . Each output terminal  53  may correspond to a power supply circuit  52  and to an abnormal current/voltage detecting circuit  51 . 
     The abnormal current/voltage detecting circuit  51  automatically shuts-off the power supplying circuits to the anticorrosive electrodes  31  if a short circuit occurs. For example, a short circuit may occur if any of the electrodes  31  contacts the engine  2 . In this case, the abnormal current/voltage detecting circuit  51  automatically stops the supply of power to the short-circuited anticorrosive electrode  31 . The rest of the anticorrosive electrodes  31 ,  31  can thus continue to be supplied with a protective current despite the short circuit. The abnormal current/voltage detecting circuit  51  shuts-off the power supply circuits  52  to the anticorrosive electrodes  31  when a current flowing through the anticorrosive electrodes  31  exceeds a predetermined value. 
     As shown in  FIG. 9 , with the plurality of electrodes  31  disposed at the same position in the coolant channel  1 , a redundant electrode  31  provides corrosion protection even the other electrode  31  fails. The remaining anticorrosive electrode  31  continues to flow the protective current through the short-circuited portion to provide protection to that portion. In this way, the area affected by the failed or short-circuited electrode  31  is minimized. 
     The power switch  54  switches the controller  18  ON/OFF and is operatively connected to an engine switch or main switch. During engine  2  operation with the coolant passage  1  supplied with seawater  59 , the power supply is ON for the anticorrosive electrodes  31 . When the engine  2  stops and a majority of the coolant is drained from the engine  2 , the power supply is OFF. By turning the impressed current cathodic protection system  11  off when the engine  2  is not in use, power consumption is reduced. 
     For embodiments of the controller  18  that include the abnormal current/voltage detecting circuit  51 , any of the three power supply methods described above with reference to  FIG. 2  may be employed. 
       FIG. 11  is a circuit diagram of a controller  18  employing a constant-voltage method for the power supply. The controller  18  illustrated in  FIG. 11  includes a constant-voltage control section  61 , an over current shut-off section  62 , a dual establishment mechanism  63 , an alarm display section  68 , a stabilized power supply filter  69 , and an output-side filter  70 . Terminal  71  is a connection location for the anticorrosive electrodes  31 . Reference electrode terminal  72  is a connection location for a reference electrode if a potential control method is selected. Terminal  73  is an adjustment terminal. Terminal  74  is a check terminal. 
     The constant-voltage control section  61  maintains a voltage applied to the anticorrosive electrodes  31 . The over-current shut-off section  62  stops the supply of power to the anticorrosive electrodes  31  when an over-current flows through the anticorrosive electrodes  31 . The dual establishment mechanism  63  monitors the supply of power to the anticorrosive electrodes  31 . 
     The alarm display section  68  may include a plurality of LEDs  64 ,  65 ,  66 ,  67  for notifying an operator of an alarm condition. The alarm section  68  may provide an audible alarm to the operator. For example, a circuit may light the LED  64  in response to a drop in the voltage applied to the anticorrosive electrodes  31  to a level below a predetermined minimum value. A circuit may light the LED  65  in response to a voltage exceeding a predetermined maximum value. A circuit may light the LED  66  in response to a drop in the current flowing through the anticorrosive electrodes  31  to a level below a predetermined minimum value. A circuit may light the LED  67  in response to the current exceeding a predetermined maximum value. 
     The controller  18  may further include an LED  75  and LED  76 . The LED  75  may be configured to light up when current is being supplied to the stabilized power supply filter  69 . The LED  76  may be configured to light up when the over-current shut-off section  62  stops the supply of power to the anticorrosive electrodes  31 . 
     When the voltage or current being supplied to the anticorrosive electrodes  31  excessively increases/decreases or is not within a normal range, the associated LED  64 ,  65 ,  66 ,  67  lights up so as to inform a driver of the occurrence of the abnormality. As described above, the designs of the cathodic protection system  11  allow preventive inspections and repairs to be performed on the cathodic protection system  11 . By designing the cathodic protection system  11  in this manner, these repairs and inspections may prevent additional corrosion from occurring after an abnormality is detected by the controller  18 . 
     An advantage of the cathodic protection system is less that space is needed to fix the electrodes to the engine as compared to fixing a conventional cathodic protection system that has a number of bar-shaped sacrificial electrodes. Moreover, the cathodic protection system of the invention uses fewer electrodes as compared to a conventional cathodic protection system that has bar-shaped sacrificial electrodes. The engine manufacturing costs for the cathodic protection system of the invention are less than the costs for assembling an engine employing a conventional cathodic protection system. 
     Although this invention has been disclosed in the context of a certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combine with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims.

Technology Classification (CPC): 5