Patent Publication Number: US-9849956-B2

Title: Pump device and ship propulsion machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-043764 filed on Mar. 5, 2015, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pump device and a ship propulsion machine. 
     2. Description of the Related Art 
     There has been proposed a device that causes a cylinder device coupled between a ship body and a ship propulsion machine main body to expand and contract to change an angle of the ship propulsion machine main body with respect to the ship body. 
     For example, Japanese Patent Application Laid-Open No. 2012-71683 describes an electric corrosion preventing structure of a ship propulsion machine in which a cylinder is integrally formed with a cylinder block, an electric coupling section is provided in a portion where a rod guide is fixed to the cylinder, an electric coupling section is provided in a portion where a piston is fixed to a rod on the inside of the cylinder, and, when the rod is extended most to project from the cylinder, the piston fixed to the rod collides with the rod guide in an electrically coupled state. 
     Japanese Patent Application Laid-Open No. H4-5190 describes a corrosion preventing mechanism of an outboard motor in which a swivel case is axially supported on a stern bracket fixed to a ship body to be capable of swinging up and down, an outboard motor main body is rotatably supported on the swivel case, and a tilt cylinder device is interposed between the stern bracket and the swivel case. A first galvanic anode is attached to a lower part of the outboard motor main body, a second galvanic anode is attached to a submerging portion of the stern bracket, and the first and second galvanic anodes are coupled by a first electric coupling circuit. A second electric coupling circuit is divided from the first electric coupling circuit. The second electric coupling circuit is coupled to the tilt cylinder device. 
     Japanese Patent Application Laid-Open No. 2012-71683 
     Japanese Patent Application Laid-Open No. H4-5190 
     For example, when a ship propulsion machine is used in the sea, electro-corrosion easily occurs in which metal used in the ship propulsion machine is ionized by the seawater and dissolves. 
     Therefore, in some case, a sacrificial anode made of more easily ionized metal is attached, the sacrificial anode and portions of the ship propulsion machine are electrically coupled, and the sacrificial anode is preferentially electro-corroded to suppress the electro-corrosion from occurring in the other portions. 
     However, among members configuring the ship propulsion machine, it is difficult to electrically couple a member including an insulating section, which interrupts electric coupling, in a portion pressed against the other members to the sacrificial anode. Electro-corrosion easily occurs in a rod member. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a pump device and the like in which electric coupling to a sacrificial anode is secured by a simple configuration and electro-corrosion less easily occurs. 
     In order to attain the object, the present invention provides a pump device including: a first case having a channel in which hydraulic fluid flows; a second case provided in contact with the first case; and a sacrificial anode coupled to one of the first case and the second case and suppressing corrosion of the first case and the second case. At least one of the first case and the second case includes an insulating section that interrupts electric coupling between the first case and the second case. The pump device includes a valve member which is provided in the channel, controls the flow of the hydraulic fluid flowing in the channel and electrically couples the first case and the second case. 
     The valve member may include a valve main body pressed against one of the first case and the second case, and a pressing member that presses the valve main body. 
     The valve main body may be pressed against a portion of one of the first case and the second case wherein the insulating section is not formed at the portion. The pressing member may press the valve main body while being supported by a portion of other of the first case and the second case wherein the insulating section is not formed at the portion. 
     From another viewpoint, the present invention provides a pump device including: a first case having a first channel in which hydraulic fluid flows; a second case provided in contact with the first case and having a second channel that is connected to the first channel; and a sacrificial anode coupled to one of the first case and the second case and suppressing corrosion of the first case and the second case. At least one of the first case and the second case includes, in a portion in contact with the other one, an insulating section that interrupts electric coupling to the other one. The pump device includes a conductive member provided at an inside of at least one of the first channel and the second channel and electrically coupling the first case and the second case. 
     In the first channel, an electrically connectable first conductive section may be formed. An electrically connectable second conductive section is formed in the second channel. The conductive member may be a valve member including a valve main body and a pressing member that presses the valve main body. One of the valve main body and the pressing member may be in contact with the first conductive member and other of the valve main body and the pressing member may be in contact with the second conductive section. 
     Further, from still another viewpoint, the present invention provides a ship propulsion machine including: a ship propulsion machine main body including a propeller; and a tilt-trim device including a cylinder, a cylinder device including a piston that divides the inside of the cylinder into a first chamber and a second chamber and a piston rod, an end portion of which is fixed to the piston and which extends from the cylinder, and a pump device supplying hydraulic fluid to the inside of the cylinder device to thereby cause the cylinder device to expand and contract. The pump device includes: a first case having a channel in which hydraulic fluid flows; a second case provided in contact with the first case; and a sacrificial anode coupled to one of the first case and the second case and suppressing corrosion of the first case and the second case. At least one of the first case and the second case includes an insulating section that interrupts electric coupling between the first case and the second case. The pump device includes a valve member which is provided in the channel, controls the flow of the hydraulic fluid flowing in the channel and electrically couples the first case and the second case. 
     According to the present invention, it is possible to provide a pump device and the like in which electric coupling to a sacrificial anode is secured by a simple configuration and electro-corrosion less easily occurs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration diagram of an outboard motor applied with a tilt-trim device according to an embodiment of the present invention; 
         FIG. 2  is an external view of the tilt-trim device; 
         FIG. 3  is a partial sectional view of the tilt-trim device; 
         FIG. 4  is a hydraulic circuit of a pump device; 
         FIG. 5  is a diagram showing the structure of a relief valve; 
         FIGS. 6A and 6B  are diagrams for explaining an exposed section; and 
         FIGS. 7A, 7B and 7C  are diagrams for explaining modifications. 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1  Tilt-trim device 
           5  Outboard motor 
           5   a  Outboard motor main body 
           51  Cylinder 
           51   k  Exposed section 
           181  Housing 
           181   c  Exposed section 
           300  Relief valve 
           301  Check ball 
           303  Coil spring 
       
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention is explained in detail below with reference to the accompanying drawings. 
       FIG. 1  is a schematic configuration diagram of an outboard motor  5  applied to a tilt-trim device  1  according to the embodiment of the present invention. 
     The outboard motor  5  includes an outboard motor main body  5   a  that generates a propulsion force to a ship body  2  of a ship and a tilt-trim device  1  that adjusts an inclination angle θ of the outboard motor main body  5   a  with respect to the ship body  2 . 
     Schematic Configuration of the Outboard Motor Main Body  5   a    
     The outboard motor main body  5   a  includes an engine (not shown in the figure) placed such that the axial direction of a crankshaft (not shown in the figure) faces the vertical direction (in  FIG. 1 , the up-down direction) with respect to a water surface and a driveshaft (not shown in the figure) rotatably integrally coupled to the lower end of the crankshaft and extending vertically downward. Further, the outboard motor main body  5   a  includes a propeller shaft  11  coupled to the driveshaft via a bevel gear mechanism and a propeller  12  attached to the rear end of the propeller shaft  11 . 
     The outboard motor main body  5   a  includes a swivel shaft (not shown in the figure) provided in the vertical direction (in  FIG. 1 , the up-down direction) with respect to the water surface, a horizontal shaft  14  provided in the horizontal direction with respect to the water surface, and a swivel case  15  in which the swivel shaft is rotatably housed. The swivel case  15  is coupled to a pin hole  53   a  of a piston rod  53  of a cylinder explained below of the tilt-trim device  1  by a pin (not shown in the figure). 
     The inclination angle θ adjusted by the tilt-trim device  1  includes a trim region and a tilt region. 
     In the trim region (θ 0  to θ 1 ), the inclination angle θ of the outboard motor main body  5   a  is adjusted according to the posture of the ship. Further, when the speed of the ship increases, the bow rises and the propeller  12  faces the downward direction. In this case, efficiency of the propulsion generated by the outboard motor main body  5   a  decreases. Therefore, the inclination angle θ of the outboard motor main body  5   a  is adjusted in the trim region to direct the propeller  12  in the horizontal direction with respect to the water surface and suppress the efficiency of the propulsion from decreasing. 
     In the tilt region (θ 1  to θ 2 ), the outboard motor main body  5   a  can be lifted above the water surface (e.g., a state indicated by an alternate long and two short dashes line in the figure, an inclination angle of which is θ 2 ) by inclining the outboard motor main body  5   a . Consequently, it is possible to suppress shellfish and the like from adhering to the outboard motor main body  5   a  during anchorage of the ship and prevent the outboard motor main body  5   a  from being easily damaged. 
     Schematic Configuration of the Tilt-Trim Device  1   
       FIG. 2  is an external view of the tilt-trim device  1 . 
       FIG. 3  is a partial sectional view of the tilt-trim device  1 . 
     The tilt-trim device  1  includes, as shown in  FIGS. 2 and 3 , a cylinder device  50  that expands and contracts according to supply and discharge of oil, a pump device  10  that ejects the oil, and a motor  70  that drives the pump device  10 . 
     The tilt-trim device  1  includes a stern bracket  16  (see  FIG. 1 ) that connects the swivel case  15  of the outboard motor main body  5   a  to the ship body  2 . The stern bracket  16  is coupled to a pin hole  51   b  of a cylinder  51  explained below by a pin (not shown in the figure). 
     The tilt-trim device  1  includes a sacrificial anode  27  (see  FIG. 1 ), which is an example of a sacrificial anode of the present invention, made of metal in which electro-corrosion easily occurs. In this embodiment, the sacrificial anode  27  is provided in a lower part of the stern bracket  16  (see  FIG. 1 ) and bolted to the stern bracket  16 . 
     In the tilt-trim device  1 , a large number of components made of metals such as iron, aluminum, and an aluminum alloy are used. Therefore, in particular, when the tilt-trim device  1  is used in the sea, an electric current flows via the seawater according to a potential difference generated among metals. As a result, electro-corrosion easily occurs in which the metals are ionized and dissolve into the seawater. 
     Therefore, in this embodiment, the sacrificial anode  27  made of metal more easily ionized than these metals is provided. The components made of the metals and the sacrificial anode  27  are electrically coupled to preferentially electro-corrode the sacrificial anode  27 . Consequently, the electro-corrosion is suppressed from occurring in the other components. 
     Examples of the metal that can be used in the sacrificial anode  27  include zinc (Zn), a zinc alloy, magnesium (Mg), and a magnesium alloy. 
     Cylinder Device  50   
     The cylinder device  50  includes, as shown in  FIG. 3 , a cylinder  51  extending in an axis CL direction and a piston  52  disposed on the inside of the cylinder  51  and divides an internal space of the cylinder  51  into a first chamber Y 1  and a second chamber Y 2 . The cylinder device  50  includes a piston rod  53  that holds the piston  52  at one end portion in the axis CL direction and moves in the axis CL direction with respect to the cylinder  51  together with the piston  52 . Further, the cylinder device  50  includes a relief valve  300  (explained below) that allows oil in the first chamber Y 1  to escape. 
     In the following explanation, when a direction in the axis CL direction of the cylinder  51  is indicated, downward in  FIG. 3  is sometimes referred to as “downward” and upward in  FIG. 3  is sometimes referred to as “upward”. 
     The cylinder device  50  contracts when the oil is supplied to the first chamber Y 1  and expands when the oil is supplied to the second chamber Y 2 . When the cylinder device  50  expands, the cylinder device  50  discharges the oil from the first chamber Y 1 . When the cylinder device  50  contracts, the cylinder device  50  discharges the oil from the second chamber Y 2 . 
     The cylinder device  50  includes a projecting section  51   a  in below the cylinder  51 . In the projecting section  51   a , a pin hole  51   b  into which a pin (not shown in the figure) for connection to the stern bracket  16  (see  FIG. 1 ) of the outboard motor main body  5   a  is inserted is formed. At the upper end of the piston rod  53 , a pin hole  53   a  into which a pin (not shown in the figure) for connection to the swivel case  15  (see  FIG. 1 ) of the outboard motor main body  5   a  is inserted is formed. 
     In a state in which the cylinder device  50  is coupled to the stern bracket  16  via the pin hole  51   b  formed below the cylinder  51  and the cylinder device  50  is coupled to the swivel case  15  via the pin hole  53   a  formed in the piston rod  53 , when the cylinder device  50  expands and contracts, the distance between the stern bracket  16  and the swivel case  15  changes. When the distance between the stern bracket  16  and the swivel case  15  changes, the inclination angle θ of the outboard motor main body  5   a  with respect to the ship body  2  changes. 
     Pump Device  10   
     The pump device  10  includes a tank  180  that stores oil and a pump  200  that is disposed in the tank  180  and ejects the oil stored in the tank  180 . 
     Tank  180   
     The tank  180  includes, as shown in  FIG. 3 , a housing  181  and a tank chamber  182 , which is a space surrounded by the housing  181  and the motor  70 . 
     The housing  181  in an example shown in  FIG. 3  is formed in a bottomed cylindrical shape opened upward. Holes (not shown in the figure) configuring a first channel  111  and a second channel  112  explained below are formed between the cylinder  51  and the housing  181 . 
     As shown in  FIG. 3 , the motor  70  is fixed above the housing  181  to liquid-tightly close the upward opening. A drive shaft  71  of the motor  70  is coupled to the pump  200  disposed in the tank chamber  182 . The motor  70  drives to rotate the drive shaft  71  to drive to rotate the pump  200 . 
     The housing  181 , which is an example of the first case of the present invention, is provided separately from the cylinder  51 , which is an example of the second case of the present invention. In the example shown in the figure, the housing  181  is fixed to the cylinder  51  via a bolt  183 . The housing  181  and the cylinder  51  press each other and are disposed to in direct contact with each other. A surface on the housing  181  side in a contact region of the housing  181  and the cylinder  51  is referred to as housing surface  181   a . A surface on the cylinder  51  side is referred to as cylinder surface  51   c.    
     The housing  181  and the cylinder  51  are respectively formed of, for example, aluminum. Surface treatment (alumite treatment) is applied to the respective outer circumferential surfaces of the housing  181  and the cylinder  51  in order to suppress electro-corrosion from occurring. In the example shown in the figure, as examples of the insulating section, the housing  181  includes a treated section  181   s  (see  FIG. 5  referred to below), which is a portion applied with the outer circumferential surface treatment and the cylinder  51  includes a treated section  51   s  (see  FIG. 5  referred to below), which is a portion applied with the outer circumferential surface treatment. Since such surface treatment is applied, in a region where the housing  181  and the cylinder  51  are in direct contact with each other, the housing  181  and the cylinder  51  are not electrically coupled. 
     Note that, in this embodiment, the surface treatment is also applied to the bolt  183  that fixes the housing  181  and the cylinder  51 . That is, the housing  181  and the cylinder  51  are not electrically coupled via the bolt  183 . 
     In this embodiment, a relief valve  300  (details are explained below) is provided in the region where the housing  181  and the cylinder  51  are in direct contact with each other. The relief valve  300  is located below the tank chamber  182  and above the bolt  183 . Further, the bolt  183  shown in the figure is a member located at the bottom among members that bind the housing  181  and the cylinder  51 . 
       FIG. 4  shows a hydraulic circuit of the pump device  10 . 
     Pump  200   
     The pump  200  includes, as shown in  FIG. 4 , a first pump  201  including a first ejecting section  201   a  and a second ejecting section  201   b  that respectively eject oil stored in the tank  180  and a second pump  203  including a third ejecting section  203   a  and a fourth ejecting section  203   b  that respectively eject the oil. 
     When the motor  70  normally rotates, the pump  200  ejects the oil from the first ejecting section  201   a  of the first pump  201  and the third ejecting section  203   a  of the second pump  203 . On the other hand, when the motor  70  reversely rotates, the pump  200  ejects the oil from the second ejecting section  201   b  of the first pump  201  and the fourth ejecting section  203   b  of the second pump  203 . 
     Disposition of Channels and Valves of the Pump Device  10   
     As shown in  FIG. 4 , the pump device  10  includes a first channel  111  that connects the first chamber Y 1  of the cylinder device  50  and the first ejecting section  201   a  of the first pump  201  and a second channel  112  that connects the second chamber Y 2  of the cylinder device  50  and the second ejecting section  201   b  of the first pump  201 . 
     The pump device  10  includes a third channel  113  that connects the first chamber Y 1  of the cylinder device  50  and the third ejecting section  203   a  of the second pump  203  and a fourth channel  114  that connects the second chamber Y 2  of the cylinder device  50  and the fourth ejecting section  203   b  of the second pump  203 . 
     In an example shown in the figure, the third channel  113  is connected to the first chamber Y 1  of the cylinder device  50  via the first channel  111 . The fourth channel  114  is connected to the second chamber Y 2  of the cylinder device  50  via the second channel  112 . 
     The pump device  10  includes a first check valve  131  that is provided in the third channel  113  and allows a flow of the oil from the third ejecting section  203   a  of the second pump  203  to the first channel  111  and prevents a flow from the first channel  111  to the third ejecting section  203   a.    
     The pump device  10  includes a second check valve  132  that is provided in the fourth channel  114  and allows a flow of the oil from the fourth ejecting section  203   b  of the second pump  203  to the second channel  112  and prevents a flow from the second channel  112  to the fourth ejecting section  203   b.    
     The pump device  10  includes a first suction path  121  that connects the third channel  113  and the tank  180  and circulates the oil stored in the tank  180  to the third ejecting section  203   a.    
     The pump device  10  includes a second suction path  122  that connects the fourth channel  114  and the tank  180  and circulates the oil stored in the tank  180  to the fourth ejecting section  203   b.    
     The pump device  10  includes a third check valve  133  that is provided in the first suction path  121  and allows a flow of the oil from the tank  180  to the third ejecting section  203   a  of the second pump  203  and prevents a flow from the third ejecting section  203   a  to the tank  180 . 
     The pump device  10  includes a fourth check valve  134  that is provided in the second suction path  122  and allows a flow of the oil from the tank  180  to the fourth ejecting section  203   b  of the second pump  203  and prevents a flow from the fourth ejecting section  203   b  to the tank  180 . 
     The pump device  10  includes a fifth channel  115  that branches from the first channel  111  and is connected to the tank  180  and a fifth channel switch valve  141  that is provided in the fifth channel  115  and receives the pressure of a sixth channel  116  explained below and opens the fifth channel  115 . 
     The pump device  10  includes a sixth channel  116  that branches from the second channel  112  and is connected to the tank  180  and a sixth channel switch valve  142  that is provided in the sixth channel  116  and receives the pressure of the fifth channel  115  and opens the sixth channel  116 . 
     The pump device  10  includes a seventh channel  117  that branches from the first channel  111  and is connected to the tank  180  and an eighth channel  118  that branches from the second channel  112  and is connected to the tank  180 . 
     The pump device  10  includes a seventh channel switch valve  143  that is provided in the seventh channel  117  and opens when the pressure of the oil in the seventh channel  117  is higher than a seventh predetermined pressure set in advance and allows the oil in the first channel  111  to escape to the tank  180  via the seventh channel  117 . 
     The pump device  10  includes an eighth channel switch valve  144  that is provided in the eighth channel  118  and opens when the pressure of the oil in the eighth channel  118  is higher than an eighth predetermined pressure set in advance and allows the oil in the second channel  112  to escape to the tank  180  via the eighth channel  118 . 
     The pump device  10  includes a ninth channel  119  that branches from the third channel  113  and is connected to the tank  180  and a ninth channel switch valve  145  that is provided in the ninth channel  119  and receives the pressure of the second channel  112  and opens the ninth channel  119 . 
     The pump device  10  includes a tenth channel  120  that branches from the fourth channel  114  and is connected to the tank  180  and a tenth channel switch valve  146  that is provided in the tenth channel  120  and opens when the pressure of the oil in the tenth channel  120  is higher than a tenth predetermined pressure set in advance and allows the oil in the tenth channel  120  to escape to the tank  180 . 
     The pump device  10  includes a switching valve  150  that is connected to the first channel  111  and the second channel  112  and switches the direction of a flow of the oil ejected from the first pump  201 . 
     The switching valve  150  includes a first switch valve  160  provided on the first channel  111  and a second switch valve  170  provided on the second channel  112 . 
     A connection path  151  that allows the first switch valve  160  and the second switch valve  170  to be connected with each other is formed in the switching valve  150 . 
     The pump device  10  includes a relief path  123  that connects the first chamber Y 1  and the second chamber Y 2  of the cylinder device  50 . 
     The pump device  10  includes the relief valve  300  that is provided in the relief path  123  and opens when the pressure of the second chamber Y 2  of the cylinder device  50  is higher than an eleventh predetermined pressure set in advance, allows the oil in the second chamber Y 2  to escape, and prevents a flow of the oil from the first chamber Y 1  to the second chamber Y 2  and an orifice  55  that narrows a flow of the oil flowing from the second chamber Y 2  to the relief valve  300 . 
     Relief Valve  300   
       FIG. 5  is a diagram showing the structure of the relief valve  300 . 
     The structure of the relief valve  300  and the periphery of the relief valve  300  is explained with reference to  FIG. 5 . 
     The relief valve  300 , which is an example of the valve member of the present invention, includes a check ball  301 , which is an example of the valve main body of the present invention, and a coil spring  303 , which is an example of the pressing member of the present invention. The check ball  301  and the coil spring  303  are formed of a so-called conductive material such as metal or resin including copper, iron, or an alloy of copper and iron. Therefore, the valve main body and the pressing member can be electrically coupled by coming into contact with each other. 
     The relief valve  300  is provided in the relief path  123  as explained above. The relief path  123 , which is an example of the channel of the present invention, is explained. The relief path  123  includes a relief valve chamber  51   e  that is connected to the orifice  55  and houses the relief valve  300  and a connecting path  51   f  that connects the relief valve chamber  51   e  and the first chamber Y 1  (see  FIG. 3 ). The oil (hydraulic fluid) flowing from the orifice  55  into the relief valve chamber  51   e  flows to the first chamber Y 1  via the connecting path  51   f.    
     The relief valve chamber  51   e  is divided by a recess substantially circular in section opened in the cylinder surface  51   c , which is the outer circumferential surface of the cylinder  51 , a portion opened in the cylinder surface  51   c  is liquid-tightly closed by the housing surface  181   a  of the housing  181 . 
     Further, the relief valve chamber  51   e  includes a main body section  51   g , a small diameter section  51   h  provided on the opposite side (the orifice  55  side) of the cylinder surface  51   c  across the main body section  51   g , and a large diameter section  51   i  provided at a position further toward the side of the cylinder surface  51   c  than the main body section  51   g  and opened in the cylinder surface  51   c . Note that, on the respective surfaces of the main body section  51   g , the small diameter section  51   h , and the large diameter section  51   i , like the cylinder surface  51   c , the treated section  51   s  applied with the alumite treatment is formed. 
     The main body section  51   g  houses the relief valve  300  on the inside. The main body section  51   g  is contiguous to the connecting path  51   f  in the center in the axial direction of the main body section  51   g . Further, the axis of the main body section  51   g  and the axis of the connecting path  51   f  extend in directions orthogonal to each other. The oil flowing into the main body section  51   g  from the orifice  55  changes the direction thereof and flows out to the connecting path  51   f.    
     The main body section  51   g  includes, at an end portion on the small diameter section  51   h  in the axial direction, a taper section  51   j  inclined to be reduced in a diameter toward the small diameter section  51   h . The check ball  301  of the relief valve  300  is pressed against the taper section  51   j.    
     In the large diameter section  51   i , a sealing member  184  that seals the oil in the relief valve chamber  51   e  is housed. The sealing member  184  in an example shown in the figure is a substantially annular elastic member (so-called O-ring). The inner diameter of the sealing member  184  is larger than the outer diameter of the coil spring  303 . The sealing member  184  is provided to be pressed against the housing surface  181   a  of the housing  181 . 
     The configuration of the housing  181  that closes the relief valve chamber  51   e  is explained. As explained above, the housing surface  181   a  of the housing  181  includes the treated section  181   s  applied with the alumite treatment. The housing  181  includes a recess  181   b  in a portion opposed to the relief valve chamber  51   e  on the housing surface  181   a . The recess  181   b  is substantially circular in cross section and supports one end  303   a  of the coil spring  303 . That is, the recess  181   b  functions as a seat of the coil spring  303 . 
     In the relief valve  300  housed in the relief valve chamber  51   e , the one end  303   a  of the coil spring  303  is supported by the recess  181   b  and the check ball  301  is supported by the taper section  51   j . Consequently, the coil spring  303  is compressed. The elastic force of the compressed coil spring  303  urges the check ball  301  toward the taper section  51   j  side, whereby the pressure of the oil flowing into the relief valve chamber  51   e  from the orifice  55  is controlled. 
     Electric Coupling of the Cylinder  51  and the Housing  181   
       FIGS. 6A and 6B  are diagrams for explaining exposed sections  51   k  and  181   c .  FIG. 6A  is a cross section in VIa-VIa in  FIG. 5  and is a diagram showing the exposed section  51   k . Note that, in  FIG. 6A , the check ball  301  is omitted.  FIG. 6B  is a cross section in VIb-VIb in  FIG. 5  and is a diagram showing the exposed section  181   c.    
     Electric coupling of the cylinder  51  and the housing  181  is explained with reference to  FIG. 5  and  FIGS. 6A and 6B . 
     As explained with reference to  FIG. 1 , the sacrificial anode  27  is electrically coupled to the portions of the outboard motor  5 . In the pump device  10  shown in  FIG. 3 , the housing  181  is electrically coupled to the sacrificial anode  27 . The cylinder  51  and the housing  181  are disposed in contact with each other. However, the alumite treatment is applied to the outer circumferential surface of the cylinder and the housing  181 . Therefore, in a place where the cylinder  51  and the housing  181  are in direct contact with each other, the cylinder  51  and the housing  181  are not electrically coupled 
     Therefore, in this embodiment, a portion that enables electric coupling is provided in a part of a surface forming the relief valve chamber  51   e . The relief valve  300  formed of a conductive material is disposed in contact with the portion that enables electric coupling. Consequently, the cylinder  51  and the housing  181  are conducted (electrically coupled) via the relief valve  300 . 
     In the following explanation, a specific configuration for electrically coupling the cylinder  51  and the housing  181  is explained. 
     As shown in  FIGS. 5 and 6A , a portion (the exposed section)  51   k , which is not applied with the alumite treatment and in which aluminum used as a material is exposed, is formed in a part of the taper section  51   j  of the cylinder  51 . The exposed section  51   k , which is an example of the second conductive section of the present invention, is located in a region against which the check ball  301  is pressed in the taper section  51   j . Note that the exposed section  51   k  is an example of a portion where the insulating section is not formed. 
     As shown in  FIGS. 5 and 6B , similarly, a portion (the exposed section)  181   c , which is not applied with the alumite treatment and in which aluminum used as a material is exposed, is formed in the recess  181   b  of the housing  181 . The exposed section  181   c , which is an example of the first conductive section of the present invention, is located in a region against which the one end  303   a  of the coil spring  303  is pressed in the recess  181   b.    
     The exposed section  51   k  and the exposed section  181   c  are parts of a surface that divides the relief valve chamber  51   e . Oil is stored in the relief valve chamber  51   e . By the presence of the oil, the exposed section  51   k  and the exposed section  181   c  are suppressed from being corroded. 
     Further, as shown in  FIG. 5 , the exposed section  51   k  and the exposed section  181   c  are formed in regions further on the inner diameter side than the sealing member  184 . The outer circumferences of these portions are present in regions surrounded by the sealing member  184 . The regions are positions where the seawater entering from the outside less easily reaches. 
     With the configuration explained above, in a state in which the relief valve  300  is disposed in the relief valve chamber  51   e , the check ball  301  is pressed against the exposed section  51   k  of the cylinder  51  and the one end  303   a  of the coil spring  303  is pressed against the exposed section  181   c  of the housing  181 . The other end  303   b  of the coil spring  303  and the check ball  301  are pressed against each other. Consequently, the cylinder  51  and the housing  181  are electrically coupled via the relief valve  300 . 
     As explained above, the coil spring  303  is disposed in the relief valve chamber  51   e  in the compressed state. For example, even when the outboard motor  5  (see  FIG. 1 ) receives vibration from the outside, with the elastic force of the coil spring  303 , the check ball  301  is suppressed from being separated from the exposed section  51   k  or the one end  303   a  of the coil spring  303  is suppressed from being separated from the exposed section  181   c . As a result, electric coupling in the cylinder  51  and the housing  181  is secured. In addition, in this embodiment, since the relief valve  300  is used, a dedicated component for securing electric coupling of the cylinder  51  and the housing  181  is unnecessary. 
     The exposed section  51   k  and the exposed section  181   c  are respectively formed by applying masking, for example, when the cylinder  51  and the housing  181  are subjected to the alumite treatment. That is, unlike other regions, regions applied with the masking are regions remaining without being applied with the alumite treatment, that is, the exposed section  51   k  and the exposed section  181   c.    
     Note that, unlike this forming method, the exposed section  51   k  and the exposed section  181   c  may be formed by applying machining, for example, shaving parts of the surfaces of the cylinder  51  and the housing  181  after subjecting the entire outer circumferential surfaces of the cylinder  51  and the housing  181  to the alumite treatment. 
     Modifications 
       FIGS. 7A to 7C  are diagrams for explaining modifications. 
     In the above explanation referring to  FIG. 5 , the housing  181  includes the recess  181   b  in the portion opposed to the relief valve chamber  51   e . However, the present invention is not limited to this. 
     For example, as shown in  FIG. 7A , a portion opposed to a relief valve chamber  251   e  in a housing  281  may be flat and may not include the recess  181   b  (see  FIG. 5 ). 
     Further, a space (a recess) for housing a relief valve  400  may be provided in one of a cylinder  251  and the housing  281  or may be provided in both of the cylinder  251  and the housing  281 . 
     In the above explanation referring to  FIG. 5 , the relief valve  300  is provided in the relief valve chamber  51   e , that is, electric coupling is secured in a place where the oil flowing in from the orifice  55  changes the direction of the flow and flows out to the connecting path  51   f . However, the present invention is not limited to this. 
     For example, as shown in  FIG. 7B , a cylinder  351  and a housing  381  may be formed. That is, in a relief valve chamber  351   e  in which oil flowing in from an orifice  550  flows out to a connecting path  510   f  without changing the direction of the flow, a relief valve  500  may be provided. 
     In the explanation referring to  FIG. 5 , the electric coupling is secured by the relief valve  300 . However, the configuration explained above may be adopted in other valves. 
     Alternatively, a member other than a valve may be adopted as long as electric coupling is secured. For example, as shown in  FIG. 7C , a spring  501  in a compressed state may be disposed in a space in which oil flowing in from an orifice (a first channel)  650  flows out to a connecting path (a second channel)  610   f , that is, a space  451   f  sandwiched by a cylinder  451  and a housing  481 . In other words, the spring  501  may be in a stretched state in the space  451   f  and disposed in contact with an exposed section  451   k  of the cylinder (a first case)  451  and an exposed section  481   b  of the housing (a second case)  481 . 
     In the explanation referring to  FIG. 5 , the cylinder  51  and the housing  181  are disposed in direct contact with each other. However, the present invention is not limited to this. Other members may be interposed between the cylinder  51  and the housing  181  as long as the cylinder  51  and the housing  181  are electrically coupled by the relief valve  300  or the like. 
     The various embodiments and modifications are explained above. However, naturally, the embodiments and the modifications may be combined with one another. 
     This disclosure is not limited by the embodiments at all and can be carried out in various forms without departing from the spirit of this disclosure.