Patent Publication Number: US-11027811-B2

Title: Outboard motor lifting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority to Japanese patent application No. 2019-057060, filed on Mar. 25, 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an outboard motor lifting device. 
     BACKGROUND ART 
     In a full field, there has been known an outboard motor lifting device including a tilt cylinder mainly serving for lifting an outboard motor up above water or lifting the outboard motor down below the water, and a trim cylinder mainly serving for changing an angle of the outboard motor below the water (for example, JP-T-S58-028159 and JP-A-H2-99494). 
     The outboard motor lifting device is preferable to suitably retain and lift up and down the outboard motor. 
     An object of the present invention is to provide an outboard motor lifting device which can retain and lift up and down an outboard motor suitably. 
     According to an aspect of the present invention, there is provided an outboard motor lifting device configured to lift up and down an outboard motor. The outboard motor lifting device includes: one or more tilt cylinders, each including a piston that partitions the tilt cylinder into a first chamber and a second chamber, and a rod that is connected to the piston and penetrates the first chamber of the tilt cylinder; one or more trim cylinders, each including a piston that partitions the trim cylinder into a first chamber and a second chamber, and a rod that is connected to the piston and penetrates the first chamber of the trim cylinder; a hydraulic power source; a first oil channel that connects the hydraulic power source with the second chamber of the one or more tilt cylinders; a second oil channel that connects the first oil channel with the second chamber of the one or more trim cylinders; a third oil channel that connects the hydraulic power source with the first chamber of the one or more tilt cylinders; a check valve that is provided on the first oil channel between the second chamber of the one or more tilt cylinders and a connection position between the first oil channel and the second oil channel, and that is configured to prohibit hydraulic oil from flowing out of the second chamber of the one or more tilt cylinders; a fourth oil channel that is connected to the third oil channel; and a switch valve that is provided on the second oil channel and to which the fourth oil channel is connected. A connection state of the switch valve includes: a first connection state in which communication between the first oil channel and the second chamber of the one or more trim cylinders is in a closed state, and communication between the fourth oil channel and the second chamber of the one or more trim cylinders is in an open state. 
     According to another aspect of the present invention, there is provided an outboard motor lifting device configured to lift up and down an outboard motor. The outboard motor lifting device includes: one or more tilt cylinders, each including a piston that partitions the tilt cylinder into a first chamber and a second chamber, and a rod that is connected to the piston and penetrates the first chamber of the tilt cylinder; one or more trim cylinders, each including a piston that partitions the trim cylinder into a first chamber and a second chamber, and a rod that is connected to the piston and penetrates the first chamber of the trim cylinder; a hydraulic power source; a first oil channel that connects the hydraulic power source with the first chamber of the one or more tilt cylinders; a second oil channel that connects the hydraulic power source with the second chamber of the one or more tilt cylinders; a first pump port that includes a first shuttle chamber connected to the first oil channel, and a second shuttle chamber connected to the second oil channel; a second pump port that includes a third shuttle chamber connected to the first shuttle chamber, and a fourth shuttle chamber connected to the second shuttle chamber; a third oil channel that connects the first oil channel with the second chamber of the one or more trim cylinders; a fourth oil channel that connects the fourth shuttle chamber with the second chamber of the one or more trim cylinders; a first switch valve that is provided on the third oil channel; and a second switch valve that is provided on the fourth oil channel. 
     According to the above configuration, an outboard motor lifting device can be provided which can retain and lift up and down an outboard motor suitably. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view showing a usage example of an outboard motor lifting device according to Embodiment 1. 
         FIG. 2  is a view showing a schematic internal configuration of an outboard motor according to Embodiment 1. 
         FIG. 3  is a front view showing an example of the configuration of the outboard motor lifting device according to Embodiment 1. 
         FIG. 4  is a sectional side view of the outboard motor lifting device according to Embodiment 1. 
         FIG. 5  is a diagram showing the configuration of an oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 1. 
         FIG. 6  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 1. 
         FIG. 7  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 1. 
         FIG. 8  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 1. 
         FIG. 9  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 1. 
         FIG. 10  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 1. 
         FIG. 11  is a diagram showing the configuration of an oil-hydraulic circuit of an outboard motor lifting device according to Embodiment 2. 
         FIG. 12  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 2. 
         FIG. 13  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 2. 
         FIG. 14  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 2. 
         FIG. 15  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 2. 
         FIG. 16  is a diagram showing a flow of hydraulic oil of the oil-hydraulic circuit of the outboard motor lifting device according to Embodiment 2. 
         FIG. 17  is a diagram showing an oil-hydraulic circuit of an outboard motor lifting device according to Embodiment 3 together with a control section (controller). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     An outboard motor lifting device  1  according to Embodiment 1 of the present invention will be described below with reference to  FIGS. 1 to 10 . 
     The outboard motor lifting device  1  is configured to lift up and down an outboard motor  300 .  FIG. 1  is a view showing a usage example of the outboard motor lifting device  1 . The outboard motor lifting device  1  shown in  FIG. 1  is attached to a rear portion of a hull (body)  200  and the outboard motor  300 . A solid line in  FIG. 1  illustrates a state in which the outboard motor  300  is lifted down. A broken line in  FIG. 1  illustrates a state in which the outboard motor  300  is lifted up.  FIG. 2  is an outline view schematically showing an internal configuration of the outboard motor  300 . As shown in  FIG. 2 , the outboard motor  300  includes an engine  301 , a propeller  303 , and a power transmission mechanism  302  which transmits motive power from the engine  301  to the propeller  303 . Here, the power transmission mechanism includes, for example, a shaft and a gear. 
       FIG. 3  is a front view showing an example of the configuration of the outboard motor lifting device  1 .  FIG. 4  is a sectional side view of the outboard motor lifting device  1 . As shown in  FIG. 3 , the outboard motor lifting device  1  includes a cylinder unit  10 , a pair of stern brackets  70 , and a swivel bracket  80 . The pair of stern brackets  70  are attached to the rear portion of the hull  200 . The swivel bracket  80  is attached to the outboard motor  300 . 
     As shown in  FIG. 3 , the cylinder unit  10  includes, for example, two trim cylinders  12 , one tilt cylinder  14 , a motor  16 , a tank  18 , an upper portion joint  22 , and a base portion  24 . The trim cylinders  12  and the tilt cylinder  14  are provided relatively immovably to the base portion  24 . 
     Incidentally, the number of trim cylinders  12  and the number of tilt cylinders  14  provided to the cylinder unit  10  are not limited to those of the present embodiment. A cylinder unit  10  including one or more trim cylinders  12  and one or more tilt cylinders  14  may be also within the present embodiment. Moreover, the following description can be also applied to such a cylinder unit  10  having any number of trim cylinders  12  and any number of tilt cylinders  14 . 
     Each of the trim cylinders  12  includes a cylinder  12   a , a piston  12   c  (see  FIG. 5 ), and a piston rod  12   b . The piston  12   c  is provided slidably inside the cylinder  12   a . The piston rod  12   b  is fixed to the piston  12   c . The tilt cylinder  14  includes a cylinder  14   a , a piston  14   c  (see  FIG. 5 ) and a piston rod  14   b . The piston  14   c  is provided slidably inside the cylinder  14   a . The piston rod  14   b  is fixed to the piston  14   c.    
     As shown in  FIG. 3 , through holes are respectively formed in the base portion  24  and the stern brackets  70 , and the base portion  24  and the stern brackets  70  are connected to each other relatively rotatably through an undershaft  26  penetrating the through holes. 
     As shown in  FIG. 3 , the upper portion joint  22  is provided in a front end of the piston rod  14   b , and support members  28  are fixed to the swivel bracket  80 . Through holes are respectively formed in the upper portion joint  22  and the support members  28 , and the upper portion joint  22  and the swivel bracket  80  are connected to each other relatively rotatably through an upper shaft  23  penetrating the through holes. 
     Through holes are respectively formed in one ends of upper portions of the stern brackets  70  and the swivel bracket  80 . As shown in  FIG. 4 , the stern brackets  70  and the swivel bracket  80  are connected to each other relatively rotatably through a support shaft  32  penetrating the through holes. 
     (Trim Region and Tilt Region) 
     As the piston rod  14   b  of the tilt cylinder  14  goes up and down, the swivel bracket  80  goes up and down. Accordingly, the outboard motor  300  is lifted up and down. 
     An angle region of the outboard motor  300  adjusted by up and down of the piston rod  14   b  of the tilt cylinder  14  includes a trim region and a tilt region shown in  FIG. 1 . The tilt region is an angle region where distal ends of the piston rods  12   b  of the trim cylinders  12  cannot abut against the swivel bracket  80 . An angle of the outboard motor  300  in the tilt region is adjusted by the piston rod  14   b  of the tilt cylinder  14 . 
     On the other hand, the trim region is an angle region where the distal ends of the piston rods  12   b  of the trim cylinders  12  can abut against the swivel bracket  80 . An angle of the outboard motor  300  in the trim region can be adjusted by both the piston rods  12   b  of the trim cylinders  12  and the piston rod  14   b  of the tilt cylinder  14 . However, as will be described later, the angle of the outboard motor  300  may be adjusted by only the piston rod  14   b  of the tilt cylinder  14  also in the trim region in the present embodiment. 
     (Oil-Hydraulic Circuit) 
     Next, an oil-hydraulic circuit of the outboard motor lifting device  1  will be described with reference to  FIG. 5 . In the following description, members similar to or the same as the above-described members will be referred to by the same signs correspondingly and respectively while description about the members will be omitted. 
     As shown in  FIG. 5 , the outboard motor lifting device  1  include the motor  16 , a pump  42  (which will be also referred to as hydraulic power source), the tilt cylinder  14 , the trim cylinders  12 , a switch valve  60 , a first check valve  44   a , a second check valve  44   b , a main valve  48  (which will be also referred to as pump port), a third check valve  51 , a fourth check valve  52 , a manual valve  53 , a thermal valve  54 , an upblow valve  55 , an upper chamber oil supply valve  56 , a first orifice  45 , a second orifice  46 , the tank  18 , filters F 1  to F 3 , and a first flow channel C 1  to a thirteenth flow channel C 13 . 
     The pump  42  serving as a hydraulic power source driven by the motor  16  is a normal/reverse rotation type hydraulic power source including a first discharge port and a second discharge port. The pump  42  performs one of a “normal rotation”, a “reverse rotation” and a “stop” in accordance with control performed by a user. Hydraulic oil is stored in the tank  18 . 
     As shown in  FIG. 5 , the main valve  48  includes a spool  48   a , a first check valve  48   b , and a second check valve  48   c . The main valve  48  is partitioned by the spool  48   a  into a first shuttle chamber  48   d  on the first check valve  48   b  side and a second shuttle chamber  48   e  on the second check valve  48   c  side. 
     The first flow channel C 1  connects the first discharge port of the pump  42  with the first shuttle chamber  48   d , and connects the first discharge port of the pump  42  with the first check valve  44   a . The second flow channel C 2  connects the second discharge port of the pump  42  with the second shuttle chamber  48   e , and connects the second discharge port of the pump  42  with the second check valve  44   b.    
     The tilt cylinder  14  is partitioned by the piston  14   c  into an upper chamber  14   f  and a lower chamber  14   g . As shown in  FIG. 5 , the piston  14   c  of the tilt cylinder  14  includes a shock blow valve  14   d  and a return valve  14   e.    
     Incidentally, in the description of the present invention, the terms “upper” and “lower” in the “upper chamber” and the “lower chamber” are terms merely used for distinguishing those from each other. It does not have to always mean that the upper chamber is positioned on a vertically upper side than the lower chamber. Therefore, the “upper chamber” may be expressed as, among a first chamber and a second chamber into which the cylinder is partitioned by the piston, the first chamber which is penetrated by the rod connected to the piston, and the “lower chamber” may be expressed as, among the first chamber and the second chamber into which the cylinder is partitioned by the piston, the second chamber which is not penetrated by the rod connected to the piston. 
     Each of the trim cylinders  12  is partitioned by the piston  12   c  into an upper chamber  12   f  and a lower chamber  12   g.    
     The first check valve  48   b  is connected with the lower chamber  14   g  of the tilt cylinder  14  through the third flow channel C 3 . The second check valve  48   c  is connected with the upper chamber  14   f  of the tilt cylinder  14  through the fourth flow channel C 4 . As shown in  FIG. 5 , the upper chamber oil supply valve  56  is connected to the fourth flow channel C 4 . 
     The manual valve  53  and the thermal valve  54  are connected to the fifth flow channel C 5  connecting the third flow channel C 3  with the fourth flow channel C 4 . As shown in  FIG. 5 , the first office  45  is disposed on the fourth flow channel C 4  between a connection position with the upper chamber oil supply valve  56  and a connection position with the fifth flow channel C 5 . 
     Incidentally, the first flow channel C 1  and the third flow channel C 3  which connect the first discharge port of the pump  42  with the lower chamber  14   g  of the tilt cylinder  14  through the main valve  48  will be also collectively referred to as first oil channel. The second flow channel C 2  and the fourth flow channel C 4  which connect the second discharge port of the pump  42  with the upper chamber  14   f  of the tilt cylinder  14  through the main valve  48  will be also collectively referred to as third oil channel. 
     The tenth flow channel C 10  (which will be also referred to as second oil channel) connects the third flow channel C 3  with the lower chambers  12   g  of the trim cylinders  12 . The switch valve  60  is disposed on the tenth flow channel C 10 . 
     The eleventh flow channel C 11  (which will be also referred to as fourth flow channel) connects the second flow channel C 2  with the tenth flow channel C 10  through the switch valve  60 . Incidentally, the eleventh flow channel C 11  may connect the fourth flow channel C 4  between the second shuttle chamber  48   e  and a connection position with the fifth flow channel C 5 , with the tenth flow channel C 10  through the switch valve  60 . 
     The third check valve  51  is disposed on the third flow channel C 3  between the lower chamber  14   g  of the tilt cylinder  14  and a connection position with the tenth flow channel C 10 . When hydraulic oil is pumped from the second discharge port of the pump  42 , the third check valve  51  opens the third flow channel C 3 . Otherwise, the third check valve  51  closes the third flow channel C 3 . Specifically, the third check valve  51  closes the third flow channel C 3  when hydraulic oil is pumped from the first discharge port of the pump  42  or when pumping of hydraulic oil from the pump  42  is stopped. 
     The sixth flow channel C 6  connects the third flow channel C 3  between the lower chamber  14   g  of the tilt cylinder  14  and the third check valve  51 , with the third flow channel C 3  between the third check valve  51  and the first shuttle chamber  48   d . The fourth check valve  52  is disposed on the sixth flow channel C 6 . When hydraulic oil is pumped from the first discharge port of the pump  42 , the fourth check valve  52  opens the sixth flow channel C 6 . When hydraulic oil is pumped from the second discharge port of the pump  42 , the fourth check valve  52  closes the sixth flow channel C 6 . 
     Incidentally, the third check valve  51  and the fourth check valve  52  will be also collectively referred to as a check valve. The oil-hydraulic circuit according to the present embodiment uses the check valve to prohibit hydraulic oil from flowing out of the lower chamber  14   g  of the tilt cylinder  14 . 
     The seventh flow channel C 7  connects the first check valve  44   a  and the second check valve  44   b  with the tank  18  through the filter F 1 . 
     The eighth flow channel C 8  connects the first flow channel C 1  with the tank  18  through the upblow valve  55 . 
     The ninth flow channel C 9  connects the second flow channel C 2  with the tank  18  through the filter F 2  and the filter F 3 . As shown in  FIG. 5 , the second orifice  46  is disposed on the ninth flow channel C 9  between the filter F 2  and the filter F 3 . 
     The twelfth flow channel C 12  connects the upper flow channels  12   f  of the trim cylinders  12  to each other. Due to the presence of the twelfth flow channel C 12 , pressures in the upper chambers  12   f  of the trim cylinders  12  are equalized to each other. 
     The thirteenth flow channel C 13  connects one of the upper chambers  12   f  of the trim cylinders  12  with the tank  18 . 
     The first check valve  44   a  supplies hydraulic oil from the tank  18  to the pump  42  when the pump  42  still recovers hydraulic oil even in a state in which the trim cylinders  12  and the tilt cylinder  14  have retracted completely. 
     When the tilt cylinder  14  extends, the second check valve  44   b  supplies hydraulic oil corresponding to a leave volume of the piston rod  14   b , from the tank  18  to the pump  42 . When the trim cylinders  12  extend, the second check valve  44   b  supplies hydraulic oil corresponding to leave volumes of the piston rods  12 , from the tank  18  to the pump  42 . 
     The manual valve  53  can be opened and closed manually. As the manual valve  53  is changed to an open state during maintenance or the like of the outboard motor lifting device  1 , hydraulic oil can be returned from the lower chamber  14   g  of the tilt cylinder  14  to the tank  18 . Thus, the tilt cylinder  14  can be retracted manually. 
     When the volume of the hydraulic oil increases due to an increase of temperature, the thermal valve  54  returns excess hydraulic oil to the tank  18 . 
     When the pump  42  still pumps hydraulic oil even in a state in which the trim cylinders  12  and the tilt cylinder  14  have extended completely, the upblow valve  55  returns excess hydraulic oil to the tank  18 . 
     (Switch Valve  60 ) 
     As shown in  FIG. 5 , the switch valve  60  provided on the tenth flow channel C 10  includes a solenoid  61 , and a plunger  62  which is driven by the solenoid  61  to switch a connection state of the switch valve  60 . The solenoid  61  switches the connection state of the switch valve  60  in accordance with control performed by a user. 
     The connection state of the switch valve  60  includes a first connection state, a second connection state and a third connection state. In the first connection state, the switch valve  60  closes communication between the third flow channel C 3  and the lower chambers  12   g  of the trim cylinders  12 , but opens communication between the eleventh flow channel C 11  and the lower chambers  12   g  of the trim cylinders  12 . In the second connection state, the switch valve  60  closes communication between the third flow channel C 3  and the lower chambers  12   g  of the trim cylinders  12 , and closes communication between the eleventh flow channel C 11  and the lower chambers  12   g  of the trim cylinders  12 . In the third connection state, the switch valve  60  opens communication between the third flow channel C 3  and the lower chambers  12   g  of the trim cylinders  12 , but closes communication between the eleventh flow channel C 11  and the lower chambers  12   g  of the trim cylinders  12 . 
     Incidentally, in the present embodiment, the plunger  62  includes a first protective valve  66  for preventing an excessive increase of oil pressure in each of the lower chambers  12   g  of the trim cylinders  12  in the first connection state. Further, the plunger  62  includes a second protective valve  65  for preventing an excessive increase of oil pressure in each of the lower chambers  12   g  of the trim cylinders  12  in the second connection state. Still further, the plunger  62  includes a third protective valve  64  and a fourth protective valve  63  for preventing an excessive increase of oil pressure in each of the lower chambers  12   g  of the trim cylinders  12  in the third connection state. 
     (Operation Example of Outboard Motor Lifting Device  1 ) 
     Next, an operation example of the outboard motor lifting device  1  will be described with reference to  FIGS. 5 to 10 . 
     (First Lifting Up Operation) 
     A flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting up operation of the outboard motor  300  by means of only the tilt cylinder  14  (which will be referred to as first lifting up operation) will be described below with reference to  FIG. 6 . 
     As shown in  FIG. 6 , the lifting up operation of the outboard motor  300  is performed by means of only the tilt cylinder  14  as follows. First, the switch valve  60  is switched to the second connection state. That is, the switch valve  60  closes communication between the third flow channel C 3  and the lower chambers  12   g  of the trim cylinders  12 , and closes communication between the eleventh flow channel C 11  and the lower chambers  12   g  of the trim cylinders  12 . 
     Next, when the pump  42  rotates in a normal direction, hydraulic oil is pumped from the first discharge port of the pump  42  into the first shuttle chamber  48   d  of the main valve  48  through the first flow channel C 1 . Thus, the first check valve  48   b  is opened, and the spool  48   a  moves toward the second check valve  48   c  to open the second check valve  48   c.    
     Here, when the hydraulic oil is pumped from the first discharge port of the pump  42  as described above, the third check valve  51  closes the third flow channel C 3 , and the fourth check valve  52  opens the sixth flow channel C 6 . Therefore, when the first check valve  48   b  is open, the hydraulic oil pumped into the first shuttle chamber  48   d  of the main valve  48  is supplied to the lower chamber  14   g  of the tilt cylinder  14  via the third flow channel C 3  and the sixth flow channel C 6 . As the hydraulic oil is supplied to the lower chamber  14   g  of the tilt cylinder  14 , the piston  14   c  of the tilt cylinder  14  slides toward the upper chamber  14   f  of the tilt cylinder  14 , and the piston rod  14   b  of the tilt cylinder  14  goes up. 
     The hydraulic oil pumped by the sliding of the piston  14   c  of the tilt cylinder  14  is supplied from the upper chamber  14   f  of the tilt cylinder  14  to the second shuttle chamber  48   e  of the main valve  48  via the fourth flow channel C 4 . The hydraulic oil supplied to the second shuttle chamber  48   e  of the main valve  48  is supplied to the pump  42  via the second flow channel C 2 . 
     Thus, while the switch valve  60  is in the second connection state, as the pump  42  is rotated in the normal direction, the tilt cylinder  14  can extend suitably. 
     (First Lifting Down Operation) 
     A flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the outboard motor  300  by means of only the tilt cylinder  14  (which will be referred to as first lifting down operation) will be described below with reference to  FIG. 7 . 
     As shown in  FIG. 7 , the lifting down operation of the outboard motor  300  is performed by means of only the tilt cylinder  14  as follows. First, the switch valve  60  is switched to the second connection state. That is, the switch valve  60  closes communication between the third flow channel C 3  and the lower chambers  12   g  of the trim cylinders  12 , and closes communication between the eleventh flow channel C 11  and the lower chambers  12   g  of the trim cylinders  12 . Incidentally, the trim cylinders  12  are in a retracted state in the first lifting down operation. 
     Next, when the pump  42  rotates in a reverse direction, hydraulic oil is pumped from the second discharge port of the pump  42  into the second shuttle chamber  48   e  of the main valve  48  via the second flow channel C 2 . Thus, the second check valve  48   c  is opened, and the spool  48   a  moves toward the first check valve  48   b  to open the first check valve  48   b.    
     When the second check valve  48   c  is opened, the hydraulic oil pumped into the second shuttle chamber  48   e  of the main valve  48  is supplied to the upper chamber  14   f  of the tilt cylinder  14  via the fourth flow channel C 4 . As the hydraulic oil is supplied to the upper chamber  14   f  of the tilt cylinder  14 , the piston  14   c  of the tilt cylinder  14  slides toward the lower chamber  14   g  of the tilt cylinder  14 , and the piston rod  14   b  of the tilt cylinder  14  goes down. 
     Here, when the hydraulic oil is pumped from the second discharge port of the pump  42  as described above, the third check valve  51  opens the third flow channel C 3 , and the fourth check valve  52  closes the sixth flow channel C 6 . Therefore, the hydraulic oil pumped by the sliding of the piston  14   c  of the tilt cylinder  14  is supplied from the lower chamber  14   g  of the tilt cylinder  14  to the first shuttle chamber  48   d  of the main valve  48  via the third flow channel C 3 . The hydraulic oil supplied to the first shuttle chamber  48   d  of the main valve  48  is supplied to the pump  42  via the first flow channel C 1 . 
     Thus, while the switch valve  60  is in the second connection state, as the pump  42  is rotated in the reverse direction, the tilt cylinder  14  can retract suitably. 
     (Retention Operation of Tilt Cylinder  14 ) 
     A retention operation of the tilt cylinder  14  will be described below with reference to  FIG. 5 . 
     When the pump  42  is stopped to retain the tilt cylinder  14 , the connection state of the switch valve  60  may be any of the first to third connection states. 
     When the pump  42  is stopped, the third check valve  51  closes the third flow channel C 3 , and the fourth check valve  52  closes the sixth flow channel C 6 , as described above. Thus, the third check valve  51  and the fourth check valve  52  prohibit hydraulic oil from flowing out of the lower chamber  14   g  of the tilt cylinder  14 . Thus, as the tilt cylinder  14  is retained, the outboard motor  300  can be prevented from lifting down. Accordingly, the outboard motor  300  can be retained suitably. 
     (Second Lifting Up Operation) 
     A flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting up operation of the outboard motor  300  by means of the tilt cylinder  14  and the trim cylinders  12  (which will be referred to as second lifting up operation) will be described below with reference to  FIG. 8 . Here, a flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting up operation of the tilt cylinder  14  is similar to the first lifting up operation. Therefore, only a flow of hydraulic oil for performing a lifting up operation of the trim cylinders  12  will be described below while description about the flow of the hydraulic oil for performing the lifting up operation of the tilt cylinder  14  will be omitted. 
     As shown in  FIG. 8 , the lifting up operation of the outboard motor  300  is performed by means of the tilt cylinder  14  and the trim cylinders  12  as follows. First, the switch valve  60  is switched to the third connection state. That is, the switch valve  60  opens communication between the third flow channel C 3  and the lower chambers  12   g  of the trim cylinders  12 , but closes communication between the eleventh flow channel C 11  and the lower chambers  12   g  of the trim cylinders  12 . 
     Next, when the pump  42  rotates in a normal direction, hydraulic oil is pumped from the first discharge port of the pump  42  into the first shuttle chamber  48   d  of the main valve  48  via the first flow channel C 1 . Thus, the first check valve  48   b  is opened, and the spool  48   a  moves toward the second check valve  48   c  to open the second check valve  48   c.    
     Next, when the first check valve  48   b  is opened, the hydraulic oil pumped into the first shuttle chamber  48   d  of the main valve  48  is supplied to the lower chambers  12   g  of the trim cylinders  12  through the third flow channel C 3  and the tenth flow channel C 10 . As the hydraulic oil is supplied to the lower chambers  12   g  of the trim cylinders  12 , the pistons  12   c  of the trim cylinders  12  slide toward the upper chambers  12   f  of the trim cylinders  12 , and the piston rods  12   b  of the trim cylinders  12  go up. 
     Thus, while the switch valve  60  is in the third connection state, as the pump  42  is rotated in the normal direction, the trim cylinders  12  can extend suitably. 
     (Second Lifting Down Operation) 
     A flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the outboard motor  300  by means of the tilt cylinder  14  and the trim cylinders  12  (which will be referred to as second lifting down operation) will be described below with reference to  FIG. 9 . Here, a flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the tilt cylinder  14  is similar to the first lifting down operation. Therefore, only a flow of hydraulic oil for performing a lifting down operation of the trim cylinders  12  will be described below while description about the flow of the hydraulic oil for performing the lifting down operation of the tilt cylinder  14  will be omitted. 
     As shown in  FIG. 9 , the lifting down operation of the outboard motor  300  is performed by means of the tilt cylinder  14  and the trim cylinders  12  as follows. First, the switch valve  60  is switched to the third connection state. That is, the switch valve  60  opens communication between the third flow channel C 3  and the lower chambers  12   g  of the trim cylinders  12 , but closes communication between the eleventh flow channel C 11  and the lower chambers  12   g  of the trim cylinders  12 . Incidentally, the trim cylinders  12  are in an extended state in the second lifting down operation. 
     When the pump  42  rotates in a reverse direction, hydraulic oil in the lower chambers  12   g  of the trim cylinders  12  is supplied to the first shuttle chamber  48   d  of the main valve  48  through the tenth flow channel C 10  and the third flow channel C 3 . The hydraulic oil supplied to the first shuttle chamber  48   d  of the main valve  48  is supplied to the pump  42  through the first flow channel C 1 . As the hydraulic oil is supplied from the lower chambers  12   g  of the trim cylinders  12 , the pistons  12   c  of the trim cylinders  12  slide toward the lower chambers  12   g  of the trim cylinders  12 , and the piston rods  12   b  of the trim cylinders  12  goes down. 
     Thus, while the switch valve  60  is in the third connection state, as the pump  42  is rotated in the reverse direction, the trim cylinders  12  can retract suitably. 
     (Third Lifting Down Operation) 
     A flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the outboard motor  300  by means of the tilt cylinder  14  and extending the trim cylinders  12  (which will be referred to as third lifting down operation) will be described below with reference to  FIG. 10 . Here, a flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the tilt cylinder  14  is similar to the first lifting down operation. Therefore, only a flow of hydraulic oil for extending the trim cylinders  12  will be described below while description about the flow of the hydraulic oil for performing the lifting down operation of the tilt cylinder  14  will be omitted. 
     As shown in  FIG. 10 , the lifting down operation of the outboard motor  300  is performed by means of the tilt cylinder  14  and the trim cylinders  12  are extended as follows. First, the switch valve  60  is switched to the first connection state. That is, the switch valve  60  closes communication between the third flow channel C 3  and the lower chambers  12   g  of the trim cylinders  12 , but opens communication between the eleventh flow channel C 11  and the lower chambers  12   g  of the trim cylinders  12 . 
     When the pump  42  rotates in a reverse direction, hydraulic oil is pumped from the second discharge port of the pump  42  into the lower chambers  12   g  of the trim cylinders  12  through the eleventh flow channel C 11  and the tenth flow channel C 10 . As the hydraulic oil is pumped into the lower chambers  12   g  of the trim cylinders  12 , the pistons  12   c  of the trim cylinders  12  slide toward the upper chambers  12   f  of the trim cylinders  12 , and the piston rods  12   b  of the trim cylinders  12  goes up. 
     Thus, while the switch valve  60  is in the first connection state, as the pump  42  is rotated in the reverse direction, the trim cylinders  12  extend. In the oil-hydraulic circuit according to the present embodiment, the hydraulic oil can be pumped from the pump  42  into the lower chambers  12   g  of the trim cylinders  12 . Therefore, when the outboard motor  300  is lifted down, the trim cylinders  12  can be extended sufficiently in order to support the lifting down of the outboard motor  300 . Accordingly, lifting up and down of the outboard motor  300  can be performed suitably. 
     Incidentally, the outboard motor lifting device  1  according to the present embodiment may include a control section (not shown) such that the switch valve  60  can be switched based on control of the control section. 
     Embodiment 2 
     An outboard motor lifting device  2  according to Embodiment 2 will be described below with reference to  FIGS. 11 to 16 . 
     (Oil-Hydraulic Circuit) 
     An oil-hydraulic circuit of the outboard motor lifting device  2  will be described with reference to  FIG. 11 .  FIG. 11  is a diagram showing the oil-hydraulic circuit of the outboard motor lifting device  2 . In the following description, members similar to or the same as the above-described members will be referred to by the same signs correspondingly and respectively, and description thereof will be omitted. 
     As shown in  FIG. 11 , the outboard motor lifting device  2  includes a motor  16 , a pump  42 , a tilt cylinder  14 , trim cylinders  12 , a first switch valve  71 , a second switch valve  81 , a first check valve  44   a , a second check valve  44   b , a main valve  48  (which will be also referred to as first pump port), a second main valve  49  (which will be also referred to as second pump port), a manual valve  53 , a thermal valve  54 , an upblow valve  55 , an upper chamber oil supply valve  56 , a fifth check valve  57 , a sixth check valve  58 , a seventh check valve  59  (which will be also referred to as check valve), a first orifice  45 , a second orifice  46 , a tank  18 , a filter F 2 , and a first flow channel D 1  to a fourteenth flow channel D 14 . 
     The first flow channel D 1  connects a first discharge port of the pump  42  with a first shuttle chamber  48   d , and connects the first discharge port of the pump  42  with the first check valve  44   a . The second flow channel D 2  connects a second discharge port of the pump  42  with a second shuttle chamber  48   e , and connects the second discharge port of the pump  42  with the second check valve  44   b.    
     The third flow channel D 3  connects a first check valve  48   b  with a lower chamber  14   g  of the tilt cylinder  14 . The fourth flow channel D 4  connects a second check valve  48   c  with an upper chamber  14   f  of the tilt cylinder  14 . As shown in  FIG. 11 , the upper chamber oil supply valve  56  is connected to the fourth flow channel D 4 . 
     The manual valve  53  and the thermal valve  54  are connected to the fifth flow channel D 5  connecting the third flow channel D 3  with the fourth flow channel D 4 . As shown in  FIG. 11 , the first orifice  45  is disposed on the fourth flow channel D 4  between a connection position with the upper chamber oil supply valve  56  and a connection position with the fifth flow channel D 5 . 
     Incidentally, the first flow channel D 1  and the third flow channel D 3  which connect the first discharge port of the pump  42  with the lower chamber  14   g  of the tilt cylinder  14  through the main valve  48  will be also collectively referred to as a second oil channel. The second flow channel D 2  and the fourth flow channel D 4  which connect the second discharge port of the pump  42  with the upper chamber  14   f  of the tilt cylinder  14  through the main valve  48  will be also collectively referred to as first oil channel. 
     The sixth flow channel D 6  connects the first check valve  44   a  and the second check valve  44   b  with the tank  18 . 
     The seventh flow channel D 7  connects the first flow channel D 1  with the tank  18  through the upblow valve  55 . 
     The eighth flow channel D 8  connects the second flow channel D 2  with the tank  18  through the filter F 2 . As shown in  FIG. 11 , the second orifice  46  is disposed on the eighth flow channel D 8  between the filter F 2  and the tank  18 . 
     The ninth flow channel D 9  connects upper chambers  12   f  of the trim cylinders  12  to each other. Due to the presence of the ninth flow channel D 9 , pressures in the upper chambers  12   f  of the trim cylinders  12  are equalized to each other. 
     The tenth flow channel D 10  connects one of the upper chambers  12   f  of the trim cylinders  12  with the tank  18 . 
     As shown in  FIG. 11 , the second main valve  49  includes a spool  49   a  and a check valve  49   b . The second main valve  49  is partitioned by the spool  49   a  into a first shuttle chamber  49   d  (which will be also referred to as third shuttle chamber) on the check valve  49   b  side, and a second shuttle chamber  49   e  (which will be also referred to as fourth shuttle chamber) on an opposite side to the check valve  49   b  with respect to the spool  49   a.    
     The first shuttle chamber  49   d  in the second main valve  49  is also connected to the first shuttle chamber  48   d  in the main valve  48  through the eleventh flow channel D 11 . The second shuttle chamber  49   e  in the second main valve  49  is also connected to the second shuttle chamber  48   e  in the main valve  48  through the twelfth flow channel D 12 . 
     The thirteenth flow channel D 13  (which will be also referred to as third oil channel) connects the second flow channel D 2  with lower chambers  12   g  of the trim cylinders  12 . As shown in  FIG. 11 , the first switch valve  71  and the fifth check valve  57  are disposed on the thirteenth flow channel D 13 . 
     The fourteenth flow channel D 14  (which may be also referred to as fourth oil channel) connects the check valve  49   b  in the second main valve  49  with the lower chambers  12   g  of the trim cylinders  12 . In other words, the fourteenth flow channel  14  is connected to the first shuttle chamber  49   d  in the second main valve  49  through the check valve  49   b . As shown in  FIG. 11 , the second switch valve  81  and the sixth check valve  58  are disposed on the fourteenth flow channel D 14 . 
     As shown in  FIG. 11 , the fourteenth flow channel D 14  is also connected to the manual valve  53 . As shown in  FIG. 11 , the seventh check valve  59  is disposed on the fourteenth flow channel D 14  between the sixth check valve  58  and the lower chambers  12   g  of the trim cylinders  12 . The fourteenth flow channel D 14  is connected to the tank  18  through the seventh check valve  59 . 
     The fifth check valve  57  opens the thirteenth flow channel D 13  when hydraulic oil is supplied from the side of the second flow channel D 2 . The fifth check valve  57  closes the thirteenth flow channel D 13  when hydraulic oil is supplied from the sides of the lower chambers  12   g  of the trim cylinders  12 . 
     The sixth check valve  58  opens the fourteenth flow channel D 14  when hydraulic oil is supplied from the side of the second main valve  49 . The sixth check valve  58  closes the fourteenth flow channel D 14  when hydraulic oil is supplied from the sides of the lower chambers  12   g  of the trim cylinders  12 . 
     When oil pressure in each of the lower chambers  12   g  of the trim cylinders  12  increases excessively, the seventh check valve  59  opens itself to supply hydraulic oil to the tank  18 . As a result, the seventh check valve  59  releases the excessive oil pressure in the lower chamber  12   g  of the trim cylinder  12 . When, for example, piston rods  12   b  of the trim cylinders  12  are pushed inward by an outboard motor  300  which is lifted down, so that the oil pressure in each of the lower chambers  12   g  of the trim cylinders  12  increases excessively, the seventh check valve  59  opens itself to thereby release the excessive oil pressure in the lower chamber  12   g  of the trim cylinder  12 . 
     (First Switch Valve  71 ) 
     As shown in  FIG. 11 , the first switch valve  71  provided on the thirteenth flow channel D 13  includes a solenoid  72  and a plunger  74 . The plunger  74  is driven by the solenoid  72  to switch the thirteenth flow channel D 13  to a closed state or an open state. 
     The first switch valve  71  may be configured as a normally closed valve which turns to a closed state to thereby close the thirteenth flow channel D 13  when the solenoid  72  is OFF, and which turns to an open state to thereby open the thirteenth flow channel D 13  when the solenoid  72  is ON, or may be configured as a normally open valve which turns to an open state to thereby open the thirteenth flow channel D 13  when the solenoid  72  is OFF, and which turns to a closed state to thereby close the thirteenth flow channel D 13  when the solenoid  72  is ON. 
     Incidentally, in the present embodiment, the plunger  74  includes a protective valve  76  for preventing an excessive increase of oil pressure in each of the lower chambers  12   g  of the trim cylinders  12  in the closed state of the thirteenth flow channel D 13 . 
     (Second Switch Valve  81 ) 
     As shown in  FIG. 11 , the second switch valve  81  provided on the fourteenth flow channel D 14  includes a solenoid  82  and a plunger  84 . The plunger  84  is driven by the solenoid  82  to switch the fourteenth flow channel D 14  to a closed state or an open state. 
     The second switch valve  81  may be configured as a normally closed valve which turns to a closed state to thereby close the fourteenth flow channel D 14  when the solenoid  82  is OFF, and which turns to an open state to thereby open the fourteenth flow channel D 14  when the solenoid  82  is ON, or may be configured as a normally open valve which turns to an open state to thereby open the fourteenth flow channel D 14  when the solenoid  82  is OFF, and which turns to a closed state to thereby close the fourteenth flow channel D 14  when the solenoid  82  is ON. 
     Incidentally, in the present embodiment, the plunger  84  includes a protective valve  86  for preventing an excessive increase of oil pressure in each of the lower chambers  12   g  of the trim cylinders  12  in the closed state of the fourteenth flow channel D 14 . 
     (Connection State of Switch Valve) 
     A connection state of the first switch valve  71  and the second switch valve  81  includes a first connection state, a second connection state and a third connection state. In the first connection state, the first switch valve  71  switches the thirteenth flow channel D 13  to a closed state, and the second switch valve  81  switches the fourteenth flow channel D 14  to a closed state. In the second connection state, the first switch valve  71  switches the thirteenth flow channel D 13  to a closed state, and the second switch valve  81  switches the fourteenth flow channel D 14  to an open (communicable) state. In the third connection state, the first switch valve  71  switches the thirteenth flow channel D 13  to an open (communicable) state, and the second switch valve  81  switches the fourteenth flow channel D 14  to a closed state. 
     (Operation Example of Outboard Motor Lifting Device  2 ) 
     Next, an operation example of the outboard motor lifting device  2  will be described with reference to  FIGS. 11 to 16 . 
     (First Lifting Up Operation) 
     A flow of hydraulic oil of an oil-hydraulic circuit for performing a lifting up operation of the outboard motor  300  by means of only the tilt cylinder  14  (which will be referred to as first lifting up operation) will be described below with reference to  FIG. 12 . 
     As shown in  FIG. 12 , the lifting up operation of the outboard motor  300  is performed by means of only the tilt cylinder  14  as follows. First, the first switch valve  71  and the second switch valve  81  are switched to the first connection state. That is, the first switch valve  71  switches the thirteenth flow channel D 13  to the closed state, and the second switch valve  81  switches the fourteenth flow channel D 14  to the closed state. 
     Next, when the pump  42  rotates in a normal direction, hydraulic oil is pumped from the first discharge port of the pump  42  into the first shuttle chamber  48   d  of the main valve  48  through the first flow channel D 1 . Thus, the first check valve  48   b  is opened, and a spool  48   a  moves toward the second check valve  48   c  to open the second check valve  48   c.    
     When the first check valve  48   b  is opened, the hydraulic oil pumped into the first shuttle chamber  48   d  of the main valve  48  is supplied to the lower chamber  14   g  of the tilt cylinder  14  through the third flow channel D 3 . As the hydraulic oil is supplied to the lower chamber  14   g  of the tilt cylinder  14 , a piston  14   c  of the tilt cylinder  14  slides toward the upper chamber  14   f  of the tilt cylinder  14 , and a piston rod  14   b  of the tilt cylinder  14  goes up. 
     The hydraulic oil pumped by the sliding of the piston  14   c  of the tilt cylinder  14  is supplied from the upper chamber  14   f  of the tilt cylinder  14  to the second shuttle chamber  48   e  of the main valve  48  through the fourth flow channel D 4 . The hydraulic oil supplied to the second shuttle chamber  48   e  of the main valve  48  is supplied to the pump  42  through the second flow channel D 2 . 
     Thus, while the first switch valve  71  and the second switch valve  81  are in the first connection state, as the pump  42  is rotated in the normal direction, the tilt cylinder  14  can extend suitably. 
     (First Lifting Down Operation) 
     A flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the outboard motor  300  by means of only the tilt cylinder  14  (which will be referred to as first lifting down operation) will be described below with reference to  FIG. 13 . 
     As shown in  FIG. 13 , the lifting down operation of the outboard motor  300  is performed by means of only the tilt cylinder  14  as follows. First, the first switch valve  71  and the second switch valve  81  are switched to the first connection state. That is, the first switch valve  71  switches the thirteenth flow channel D 13  to the closed state, and the second switch valve  81  switches the fourteenth flow channel D 14  to the closed state. Incidentally, the trim cylinders  12  are in a retracted state in the first lifting down operation. 
     Next, when the pump  42  rotates in a reverse direction, hydraulic oil is pumped from the second discharge port of the pump  42  into the second shuttle chamber  48   e  of the main valve  48  through the second flow channel D 2 . Thus, the second check valve  48   c  is opened, and the spool  48   a  moves toward the first check valve  48   b  to open the first check valve  48   b.    
     When the second check valve  48   c  is opened, the hydraulic oil pumped into the second shuttle chamber  48   e  of the main valve  48  is supplied to the upper chamber  14   f  of the tilt cylinder  14  through the fourth flow channel D 4 . As the hydraulic oil supplied to the upper chamber  14   f  of the tilt cylinder  14 , the piston  14   c  of the tilt cylinder  14  slides toward the lower chamber  14   g  of the tilt cylinder  14 , and the piston rod  14   b  of the tilt cylinder  14  goes down. 
     The hydraulic oil pumped by the sliding of the piston  14   c  of the tilt cylinder  14  is supplied from the lower chamber  14   g  of the tilt cylinder  14  to the first shuttle chamber  48   d  of the main valve  48  through the third flow channel D 3 . The hydraulic oil supplied to the first shuttle chamber  48   d  of the main valve  48  is supplied to the pump  42  through the first flow channel D 1 . 
     Thus, while the first switch valve  71  and the second switch valve  81  are in the first connection state, as the pump  42  is rotated in the reverse direction, the tilt cylinder  14  can retract suitably. 
     (Retention Operation of Tilt Cylinder  14 ) 
     A retention operation of the tilt cylinder  14  will be described below with reference to  FIG. 11 . 
     When the pump  42  is stopped to retain the tilt cylinder  14 , the connection state for the first switch valve  71  and the second switch valve  81  may be any of the first to third connection states. 
     In the oil-hydraulic circuit according to the present embodiment, the tilt cylinder  14  is connected to the main valve  48  through the third flow channel D 3 , and the trim cylinders  12  are connected to the second main valve  49  through the fourteenth flow channel D 14 , as described above. Thus, the oil-hydraulic circuit according to the present embodiment has the tilt cylinder  14  and the trim cylinders  12  connected to the different main valves respectively and correspondingly. With this configuration, the hydraulic oil can be prevented from flowing out of the lower chamber  14   g  of the tilt cylinder  14  when the pump  42  is stopped. Thus, when the tilt cylinder  14  is retained, the outboard motor  300  can be prevented from lifted down. Accordingly, the outboard motor  300  can be retained suitably. 
     (Second Lifting Up Operation) 
     A flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting up operation of the outboard motor  300  by means of the tilt cylinder  14  and the trim cylinders  12  (which will be referred to as second lifting up operation) will be described below with reference to  FIG. 14 . Here, a flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting up operation of the tilt cylinder  14  is similar to the first lifting up operation. Therefore, only a flow of hydraulic oil for performing a lifting up operation of the trim cylinders  12  will be described below while description about the flow of the hydraulic oil for performing the lifting up operation of the tilt cylinder  14  will be omitted. 
     As shown in  FIG. 14 , the lifting up operation of the outboard motor  300  is performed by means of the tilt cylinder  14  and the trim cylinders  12  as follows. First, the first switch valve  71  and the second switch valve  81  are switched to the second connection state. That is, the first switch valve  71  switches the thirteenth flow channel D 13  to the closed state, and the second switch valve  81  switches the fourteenth flow channel D 14  to the open (communicable) state. 
     Next, when the pump  42  rotates in the normal direction, hydraulic oil is pumped from the first discharge port of the pump  42  into the first shuttle chamber  48   d  of the main valve  48  through the first flow channel D 1 . The hydraulic oil pumped into the first shuttle chamber  48   d  of the main valve  48  is pumped into the first shuttle chamber  49   d  of the second main valve  49  through the eleventh flow channel D 11 . Thus, the check valve  49   b  of the second main valve  49  is opened. 
     When the check valve  49   b  is opened, the hydraulic oil pumped into the second main valve  49  is supplied to the lower chambers  12   g  of the trim cylinders  12  through the fourteenth flow channel D 14 . As the hydraulic oil is supplied to the lower chambers  12   g  of the trim cylinders  12 , pistons  12   c  of the trim cylinders  12  slide toward the upper chambers  12   f  of the trim cylinders  12 , and the piston rods  12   b  of the trim cylinders  12  goes up. 
     Thus, while the first switch valve  71  and the second switch valve  81  are in the second connection state, as the pump  42  is rotated in the normal direction, the trim cylinders  12  can extend suitably. 
     (Second Lifting Down Operation) 
     A flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the outboard motor  300  by means of the tilt cylinder  14  and the trim cylinders  12  (which will be referred to as second lifting down operation) will be described below with reference to  FIG. 15 . Here, a flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the tilt cylinder  14  is similar to the first lifting down operation. Therefore, only a flow of hydraulic oil for performing a lifting down operation of the trim cylinders  12  will be described below while description about the flow of hydraulic oil for performing the lifting down operation of the tilt cylinder  14  will be omitted. 
     As shown in  FIG. 15 , the lifting down operation of the outboard motor  300  is performed by means of the tilt cylinder  14  and the trim cylinders  12  as follows. First, the first switch valve  71  and the second switch valve  81  are switched to the second connection state. That is, the first switch valve  71  switches the thirteenth flow channel D 13  to the shut state, and the second switch valve  81  switches the fourteenth flow channel D 14  to the open (communicable) state. Incidentally, the trim cylinders  12  are in an extended state in the second lifting down operation. 
     The pump  42  rotates in a reverse direction so that the tilt cylinder  14  retracts. Accordingly, the outboard motor  300  is lifted down. When the outboard motor  300  is lifted down, the piston rods  12   b  of the trim cylinders  12  are pushed inward by the outboard motor  300 , so that the pistons  12   c  of the trim cylinders  12  slide toward the lower chambers  12   g  of the trim cylinders  12 . Thus, the piston rods  12   b  of the trim cylinders  12  goes down. Hydraulic oil pumped due to the sliding of the piston  12   c  of the trim cylinders  12  is supplied to the tank  18  through the seventh check valve  59 . 
     Thus, while the first switch valve  71  and the second switch valve  81  are in the first connection state and the trim cylinders  12  are in an extended state, as the pump  42  is rotated in the reverse direction, the trim cylinders  12  can retract suitably. 
     (Third Lifting Down Operation) 
     A flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the outboard motor  300  by means of the tilt cylinder  14  and extending the trim cylinders  12  (which will be referred to as third lifting down operation) will be described below with reference to  FIG. 16 . Here, a flow of hydraulic oil of the oil-hydraulic circuit for performing a lifting down operation of the tilt cylinder  14  is similar to the first lifting down operation. Therefore, only a flow of hydraulic oil for extending the trim cylinders  12  will be described below while description about the flow of hydraulic oil for performing the lifting down operation of the tilt cylinder  14  will be omitted. 
     As shown in  FIG. 16 , the lifting down operation of the outboard motor  300  is performed by means of the tilt cylinder  14  and the trim cylinders  12  are extended as follows. First, the first switch valve  71  and the second switch valve  81  are switched to the third connection state. That is, the first switch valve  71  switches the thirteenth flow channel D 13  to the open (communicable) state, and the second switch valve  81  switches the fourteenth flow channel D 14  to the closed state. 
     When the pump  42  rotates in a reverse direction, hydraulic oil is pumped from the second discharge port of the pump  42  into the lower chambers  12   g  of the trim cylinders  12  through the thirteenth flow channel D 13 . As the hydraulic oil is pumped into the lower chambers  12   g  of the trim cylinders  12 , the pistons  12   c  of the trim cylinders  12  slide toward the upper chambers  12   f  of the trim cylinders  12 , and the piston rods  12   b  of the trim cylinders  12  goes up. 
     Thus, while the first switch valve  71  and the second switch valve  81  are in the third connection state, as the pump  42  is rotated in the reverse direction, the trim cylinders  12  extend. In the oil-hydraulic circuit according to the present embodiment, the hydraulic oil can be pumped from the pump  42  into the lower chambers  12   g  of the trim cylinders  12 . Therefore, when the outboard motor  300  is lifted down, the trim cylinders  12  can be extended sufficiently in order to support the lifted down of the outboard motor  300 . Accordingly, lifting up and down of the outboard motor  300  can be performed suitably. 
     Embodiment 3 
     An outboard motor lifting device  3  according to Embodiment 3 will be described below with reference to  FIG. 17 . 
     (Oil-Hydraulic Circuit) 
     An oil-hydraulic circuit of the outboard motor lifting device  3  will be described with reference to  FIG. 17 .  FIG. 17  is a diagram showing the oil-hydraulic circuit of the outboard motor lifting device  3  together with a control section (controller). As shown in  FIG. 17 , the outboard motor lifting device  3  according to the present embodiment has a configuration in which a first switch valve  711  and a second switch valve  811  are provided in place of the first switch valve  71  and the second switch valve  81  in the outboard motor lifting device  2  according to Embodiment 2. In addition, the outboard motor lifting device  3  according to the present embodiment has a configuration in which a control section (controller)  100  is further provided in the outboard motor lifting device  2  according to Embodiment 2. In the following description, members similar to or the same as the aforementioned members will be referred to by the same signs correspondingly and respectively, and description thereof will be omitted. 
     (First Switch Valve  711 ) 
     The first switch valve  711  is provided on a thirteenth flow channel D 13 . As shown in  FIG. 17 , the first switch valve  711  includes a solenoid  712  and a plunger  714 . The plunger  714  is driven by the solenoid  712  to switch the thirteenth flow channel D 13  to a closed state or an open state. A connection state of the first switch valve  711  is controlled based on control of the control section  100  which will be described later. Specifically, a control signal SIG_CONT is provided from the control section  100  which will be describe later to the first switch valve  711 , and the solenoid  712  of the first switch valve  711  is switched between ON and OFF based on the control signal SIG_CONT. 
     The first switch valve  711  may be configured as a normally closed valve which turns to a closed state to thereby close the thirteenth flow channel D 13  when the solenoid  712  is OFF, and which turns to an open state to thereby open the thirteenth flow channel D 13  when the solenoid  712  is ON, or may be configured as a normally open valve which turns to an open state to thereby open the thirteenth flow channel D 13  when the solenoid  712  is OFF, and which turns to a closed state to thereby close the thirteenth flow channel D 13  when the solenoid  712  is ON. 
     Incidentally, in the present embodiment, the plunger  714  includes a protective valve  716  for preventing an excessive increase of oil pressure in each of lower chambers  12   g  of trim cylinders  12  in the closed state of the thirteenth flow channel D 13 . 
     (Second Switch Valve  811 ) 
     As shown in  FIG. 17 , the second switch valve  811  provided on a fourteenth flow channel D 14  includes a solenoid  812  and a plunger  814 . The plunger  814  is driven by the solenoid  812  to switch the fourteenth flow channel D 14  to a closed state or an open state. A connection state of the second switch valve  811  is controlled based on control of the control section  100  which will be described later. Specifically, a control signal SIG_CONT is provided from the control section  100  which will be described later to the second switch valve  811 , and the solenoid  812  of the second switch valve  811  is switched over between ON and OFF based on the control signal SIG_CONT. 
     The second switch valve  811  may be configured as a normally closed valve which turns to a closed state to thereby close the fourteenth flow channel D 14  when the solenoid  812  is OFF, and which turns to an open state to thereby open the fourteenth flow channel D 14  when the solenoid  812  is ON, or may be configured as a normally open valve which turns to an open state to thereby open the fourteenth flow channel D 14  when the solenoid  812  is OFF, and which turns to a closed state to thereby close the fourteenth flow channel D 14  when the solenoid  812  is ON. 
     Incidentally, in the present embodiment, the plunger  814  includes a protective valve  816  for preventing an excessive increase of oil pressure in each of the lower chambers  12   g  of the trim cylinders  12  in the closed state of the fourteenth flow channel D 14 . 
     (Control Section) 
     The control section  100  provides the control signal SIG_CONT to each of a motor  16 , the first switch valve  711  and the second switch valve  811  in accordance with lifting up and down control of an outboard motor  300  performed by a user. Thus, the control section  100  controls operation of the motor  16  and a connection state of the first switch valve  711  and the second switch valve  811 . 
     (Control Example of Control Section  100 ) 
     Next, a control example of the control section  100  for the operation of the outboard motor lifting device  3  will be described. 
     (First Lifting Up Operation) 
     To perform control on a first lifting up operation, the control section  100  controls the motor  16  to rotate a pump  42  in a normal direction, and controls the first switch valve  711  and the second switch valve  811  to be a first connection state. That is, the first switch valve  711  switches the thirteenth flow channel D 13  to a closed state, and the second switch valve  811  switches the fourteenth flow channel D 14  to a closed state. Thus, a tilt cylinder  14  can extend suitably, as described above in Embodiment 2. 
     (First Lifting Down Operation) 
     To perform control on a first lifting down operation, the control section  100  controls the motor  16  to rotate the pump  42  in a reverse direction, and controls the first switch valve  711  and the second switch valve  811  to be the first connection state. That is, the first switch valve  711  switches the thirteenth flow channel D 13  to the closed state, and the second switch valve  811  switches the fourteenth flow channel D 14  to the closed state. Thus, the tilt cylinder  14  can retract suitably, as described above in Embodiment 2. 
     (Retention Operation of Tilt Cylinder  14 ) 
     To perform control on a retention operation of the tilt cylinder  14 , the control section  100  controls the motor  16  to stop the pump  42 . Incidentally, to perform control on the retention operation of the tilt cylinder  14 , the control section  100  may control the connection state of the first switch valve  711  and the second switch valve  811  to any of first to third connection states. 
     (Second Lifting Up Operation) 
     To perform control on a second lifting up operation, the control section  100  controls the motor  16  to rotate the pump  42  in a normal direction, and controls the first switch valve  711  and the second switch valve  811  to be the second connection state. That is, the first switch valve  711  switches the thirteenth flow channel D 13  to a closed state, and the second switch valve  811  switches the fourteenth flow channel D 14  to an open (communicable) state. Thus, trim cylinders  12  can extend suitably, as described above in Embodiment 2. 
     (Second Lifting Down Operation) 
     To perform control on a second lifting down operation, the control section  100  controls the motor  16  to rotate the pump  42  in a reverse direction, and controls the first switch valve  711  and the second switch valve  811  to be the second connection state. That is, the first switch valve  711  switches the thirteenth flow channel D 13  to the closed state, and the second switch valve  811  switches the fourteenth flow channel D 14  to the open (communicable) state. Thus, the trim cylinders  12  can retract suitably, as described above in Embodiment 2. 
     (Third Lifting Down Operation) 
     To perform control on a third lifting down operation, the control section  100  controls the motor  16  to rotate the pump  42  in a reverse direction, and controls the first switch valve  711  and the second switch valve  811  to be the third connection state. That is, the first switch valve  711  switches the thirteenth flow channel D 13  to an open (communicable) state, and the second switch valve  811  switches the fourteenth flow channel D 14  to a closed state. Thus, when the outboard motor  300  is lifted down, the trim cylinders  12  can be extended sufficiently in order to support the lifting down of the outboard motor  300 , as described above in Embodiment 2. 
     The outboard motor lifting device  3  according to the present embodiment includes the control section  100 . Accordingly, when malfunction occurs in any of the motor, the switch valves or the like, the control section  100  can detect the malfunction to thereby reduce or prevent abnormal operation in the trim cylinders  12 , the tilt cylinder  14 , or the like. 
     The present invention is not limited to the above-described embodiments but may be changed variously within the inventive concept of the present invention. Any embodiment obtained by combining technical aspects disclosed respectively in different embodiments should be also included in the technical scope of the present invention.