Patent Publication Number: US-10315722-B2

Title: Flow path control device and vehicle height adjustment apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from Japanese Patent Application No. 2016-071269 filed on Mar. 31, 2016, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a flow path control device and a vehicle height adjustment apparatus that adjusts the vehicle height of a motorcycle. 
     Related Art 
     In recent years, there is proposed an apparatus that increases the vehicle height of a motorcycle while traveling and decreases the vehicle height in order for a driver to easily get on and off the motorcycle at a stop. 
     For example, a vehicle height adjustment apparatus disclosed in JP-B-H08-22680 automatically changes the vehicle height of a motorcycle in response to the vehicle speed of the motorcycle. The vehicle height adjustment apparatus automatically raises the vehicle height when the vehicle speed reaches a set speed, and automatically lowers the vehicle height when the vehicle speed reaches a vehicle speed which is lower than or equal to the set speed. More specifically, when a switch is automatically turned on when the vehicle speed reaches the set speed and an electromagnetic actuator operates, when the vehicle speed reaches the above-described vehicle speed, an adjustment valve body is pushed out, and according to this, communication between a secondary side oil chamber and a primary side oil chamber which communicate with an oil chamber of a cylinder is blocked, and thus, discharge oil from a pump is pressurized from the primary side oil chamber to a working oil chamber via a through oil path. Due to this, a spring seat is pushed down, and according to this, the vehicle height is raised. In addition, when the switch is automatically turned off when the vehicle speed reaches a vehicle speed which is equal to or lower than the set speed, the adjustment valve body is attracted, the primary side oil chamber communicates with the secondary side oil chamber, and thus, working oil in a working oil chamber returns to the oil chamber of the cylinder via the primary side oil chamber and a passage, and the vehicle height is lowered. 
     SUMMARY 
     In a case where a valve which switches a flow path of a fluid, such as oil (working oil), is used, it is desirable to control the valve to be operated with high accuracy. 
     The invention provides an apparatus which can operate the valve with high accuracy. 
     According to an aspect of the invention, a flow path control device includes a first valve and a second valve. The first valve transitions between a closed state where a first flow path in which a fluid is oriented from a first chamber toward a second chamber is closed and an open state where the first flow path is open by moving toward a third chamber from the closed state. The first valve is formed with a communication path that communicates with the first flow path and the third chamber. In the closed state, a first pressure-receiving area which receives a pressure of the first chamber is smaller than a second pressure-receiving area which receives a pressure of the third chamber. The second valve is provided in the third chamber on a second flow path. The second flow path is oriented from the first chamber toward the second chamber through the communication path of the first valve. The second valve transitions between a first state where the communication path is closed and an inflow path oriented toward the third chamber from the first chamber is open and a second state where the inflow path is closed and the communication path is open. 
     According to another aspect of the invention, a vehicle height adjustment apparatus includes a spring, a changing device, a first valve, and a second valve. The spring has one end supported on a vehicle body side, and the other end supported on a wheel side. The changing device changes a length of the spring in accordance with an amount of fluid in an accommodation chamber that accommodates the fluid. The first valve transitions between a closed state where a first flow path oriented from the accommodation chamber toward a storage chamber that stores the fluid is closed and an open state where the first flow path is open by moving from the closed state toward a back pressure chamber in which a pressure in the direction of being closed is generated. The first vale is formed with a communication path that communicates with the first flow path and the back pressure chamber. In the closed state, a first pressure-receiving area which receives a pressure of the accommodation chamber is smaller than a second pressure-receiving area which receives a pressure of the back pressure chamber. The second valve is provided in the back pressure chamber on a second flow path. The second flow path is oriented from the accommodation chamber toward the storage chamber through the communication path of the first valve. The second valve transitions between a first state where the communication path is closed and an inflow path that reaches the back pressure chamber from the accommodation chamber is open and a second state where the inflow path is closed and the communication path is open. 
     According to the invention, it is possible to operate the valve with high accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a schematic configuration of a motorcycle according to an embodiment. 
         FIG. 2  is a sectional view of a front fork according to the embodiment. 
         FIG. 3A  is a view schematically illustrating an open and closed state of a flow path in a case where a front wheel side flow path switching unit is in a first switch state. 
         FIG. 3B  is a view schematically illustrating an open and closed state of the flow path in a case where the front wheel side flow path switching unit is in a second switch state. 
         FIG. 3C  is a view schematically illustrating an open and closed state of the flow path in case where the front wheel side flow path switching unit is in a third switch state. 
         FIG. 3D  is a view schematically illustrating an open and closed state of the flow path in case where the front wheel side flow path switching unit is in a fourth switch state. 
         FIG. 4  is an enlarged view of a portion IV in  FIG. 2 . 
         FIG. 5  is an enlarged view of a portion V in  FIG. 4 . 
         FIG. 6  is a perspective view of an upper end side columnar portion of a unit main body. 
         FIG. 7A  is a view illustrating a state where a position of a groove of a control valve in an axial direction and a position of a first radial communication hole overlap each other. 
         FIG. 7B  is a view illustrating a state where the position of the groove of the control valve in the axial direction and the position of the first radial communication hole do not overlap each other. 
         FIG. 8  is a view illustrating an operation of a front fork during a compression stroke. 
         FIG. 9  is a view illustrating the operation of the front fork during an extension stroke. 
         FIG. 10  is a view illustrating a flow state of oil in a case where the front wheel side flow path switching unit is in the first switch state. 
         FIG. 11  is a view illustrating a flow state of oil in a case where the front wheel side flow path switching unit is in the second switch state. 
         FIG. 12  is a view illustrating a flow state of oil in a case where the front wheel side flow path switching unit is in the third switch state. 
         FIG. 13  is a view illustrating a flow state of oil in a case where the front wheel side flow path switching unit is in the fourth switch state. 
         FIG. 14  is a view illustrating a positional relationship between an outer circumferential surface of the control valve and an opening portion of a first radial communication hole in a case where the groove is at a position which does not communicate with a side recess portion and the first radial communication hole. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a view illustrating the schematic view of a motorcycle  1  according to the embodiment. 
     The motorcycle  1  includes a front wheel  2  that is a wheel on a front side; a rear wheel  3  that is a wheel on a rear side; and a vehicle main body  10  that has a vehicle body frame  11  which is a frame of the motorcycle  1 , a handle bar  12 , an engine  13 , a seat  19 , and the like. 
     In addition, the motorcycle  1  has a front fork  21  as an example of a suspension apparatus which links the front wheel  2  to the vehicle main body  10 . In addition, the motorcycle  1  has a rear suspension  22  which links the rear wheel  3  to the vehicle main body  10 . In addition, the front fork  21  and the rear suspension  22  are an example of a changing device which changes a relative position of the vehicle main body  10  and axles of the front wheel  2  and the rear wheel  3 . 
     The motorcycle  1  includes two brackets  14  and a shaft  15 . The brackets  14  hold the front fork  21  disposed on the right side of the front wheel  2  and the front fork  21  disposed on the left side of the front wheel  2 , and the shaft  15  is disposed between the two brackets  14 . The shaft  15  is rotatably supported by the vehicle body frame  11 . 
     The motorcycle  1  includes a control device  70  that controls the vehicle height of the motorcycle  1  by controlling a front wheel side flow path switching unit  300  that will be described later of the front fork  21 . 
     Configuration of Front Fork  21   
     Hereinafter, the front fork  21  will be described in detail. 
       FIG. 2  is a sectional view of the front fork  21  according to the embodiment. 
     The front fork  21  according to the embodiment is a so-called upright front fork that is disposed between the vehicle main body  10  and the front wheel  2  of the motorcycle  1 , and supports the front wheel  2  side, and in which an outer member  110  (which will be described later) is disposed close to the front wheel  2 , and an inner tube  210  is disposed close to the vehicle main body  10  side. 
     The front fork  21  includes an axle side unit  100  and a main body side unit  200 . The axle side unit  100  has the outer member  110 , and is attached to the axle of the front wheel  2 , and the main body side unit  200  has the inner tube  210 , and is attached to the vehicle main body  10 . The front fork  21  includes a front wheel side spring  500  which is disposed between the axle side unit  100  and the main body side unit  200  such that the front wheel side spring  500  absorbs vibration which is applied to the front wheel  2  due to roughness of a road surface. 
     The outer member  110  and the inner tube  210  are cylindrical members which are coaxially disposed, and hereinafter, a direction (axial direction) of a center line of this circular cylinder may be referred to as a “vertical direction”. In the embodiment, an “upper” side represents a region in which the vehicle main body  10  is disposed, and a “lower” side represents a region in which the front wheel  2  is disposed. The axle side unit  100  and the main body side unit  200  move relatively to each other in the vertical direction (axial direction) such that the front fork  21  absorbs and suppresses vibration induced by roughness of a road surface while supporting the front wheel  2 . 
     Configuration of Axle Side Unit  100   
     The axle side unit  100  includes the outer member  110  that is attached to the axle of the front wheel  2 ; a damping force generation unit  130  that generates a damping force using the viscous resistance of oil which is an example of the fluid; a rod  150  that holds the damping force generation unit  130 ; and a rod holding member  160  that holds a lower end portion of the rod  150 . 
     The axle side unit  100  includes a spherical ball  166  that is inserted into an axial recess portion  161   a  (which will be described later) of the rod holding member  160 , and a restricting member  167  that restricts a movement of the ball  166 . 
     The axle side unit  100  includes a spring support member  170  that supports a lower end portion of the front wheel side spring  500 ; a support-member holding member  180  that holds the spring support member  170 ; and a guide member  190  that guides an axial movement of the inner tube  210 . 
     Configuration of Outer Member  110   
     The outer member  110  has a cylindrical portion  111  having a cylindrical shape into which the inner tube  210  is inserted, and an axle bracket portion  112  to which the axle of the front wheel  2  can be attached. 
     The cylindrical portion  111  has an oil seal  113  and a slide bush  114  in an upper end portion thereof. The oil seal  113  seals a gap between the outer circumferential surface of the inner tube  210  and the cylindrical portion  111 , and the slide bush  114  helps the cylindrical portion to smoothly slide against the outer circumferential surface of the inner tube  210 . 
     An axial through-hole  112   a  and an axle mounting hole  112   b  are formed in the axle bracket portion  112 . The rod holding member  160  is inserted into the axial through-hole  112   a  in the axial direction, and the axle of the front wheel  2  can pass through in the direction which intersects with the axial direction and be attached to the axle mounting hole  112   b.    
     Configuration of Damping Force Generation Unit  130   
     The damping force generation unit  130  includes a piston  131  that partitions off a working oil chamber  50  which is formed in the internal space of a cylinder  230  (which will be described later); an upper end side valve  136  that is provided at an upper end of the piston  131 ; and a lower end side valve  137  that is provided on a lower end side of the piston  131 . The damping force generation unit  130  includes a piston bolt  140  that supports the piston  131 , the upper end side valve  136 , the lower end side valve  137 , and the like, and a nut  145  that positions the piston  131 , the upper end side valve  136 , the lower end side valve  137 , and the like by being tightened to the piston bolt  140 . 
     The piston  131  is a cylindrical member, and a seal member for sealing the gap between the cylinder  230  and the piston  131  is provided on the outer circumferential surface of the piston  131 . The piston  131  is formed with a first through-hole  132  and a second through-hole  133  which are axial through-holes. The piston  131  is formed with a first radial communication path  134  and a second radial communication path  135 . The first radial communication path  134  is formed in an upper end portion of the piston  131  in such a way as to extend in a radial direction, and communicates with the first through-hole  132 . The second radial communication path  135  is formed in a lower end portion of the piston  131  in such a way as to extend in the radial direction, and communicates with the second through-hole  133 . A plurality of (for example, three) the first through-holes  132  and a plurality of (for example, three) the second through-holes  133  are formed in a circumferential direction, and the first radial communication path  134  and the second radial communication path  135  are positioned so as to correspond to the first through-hole  132  and the second through-hole  133 , respectively. 
     The upper end side valve  136  is configured with a single disk-shaped metal plate or a plurality of disk-shaped metal plates which are stacked. A through-hole is formed at the center of each of the metal plates of the upper end side valve  136 , and a shaft portion  141  (which will be described later) of the piston bolt  140  passes through the through-holes. The upper end side valve  136  blocks the second through-hole  133 , and opens the first through-hole  132 . 
     The lower end side valve  137  is formed by stacking a plurality of disk-shaped metal plates. A through-hole is formed at the center of each of the metal plates of the lower end side valve  137 , and the shaft portion  141  (which will be described later) of the piston bolt  140  passes through the through-holes. The lower end side valve  137  blocks the first through-hole  132 , and opens the second through-hole  133 . 
     The piston bolt  140  has a columnar shaft portion  141  that is provided at an upper end of the piston bolt  140 , and a columnar base portion  142  that is provided on a lower end side of the piston bolt  140 , and has a radius which is greater than the radius of the shaft portion  141 . The piston bolt  140  is formed with a recess portion  143  that is recessed from a lower end surface of the base portion  142  toward the shaft portion  141 . In addition, the base portion  142  of the piston bolt  140  may have, for example, a shape of a hexagonal column or a shape of a prism. 
     An upper end portion of the shaft portion  141  is formed with a male screw that is tightened to a female screw formed on the nut  145 . 
     The inner circumferential surface of a lower end portion of the recess portion  143  is formed with a female screw that is tightened to a male screw formed on an upper end portion of the rod  150 . A radial through-hole  144  is radially formed in an upper end portion of the recess portion  143  so that the outer side of the shaft portion  141  can communicate with the recess portion  143 . 
     An upper end portion of the nut  145  is formed with a female screw  146  to which a male screw of the piston bolt  140  is tightened, and a columnar recess portion  147  is recessed from a lower end surface of the nut  145 , is formed below the female screw  146 , and has a radius which is greater than the minor radius of the female screw  146 . In addition, the nut  145  is formed with an inclination direction through-hole  148 . The inclination direction through-hole  148  penetrates in the direction of being inclined in the axial direction to communicate with the outer portion of the nut  145  and the recess portion  147 . In addition, a plate valve  149  which covers an opening portion in the inclination direction through-hole  148  is provided on a lower end side of the nut  145 . 
     The damping force generation unit  130  configured as described above is held by the rod  150  by tightening the male screw formed on the upper end portion of the rod  150  to the female screw formed on the recess portion  143  of the piston bolt  140 . The piston  131  is in contact with the inner circumferential surface of the cylinder  230  via the seal member that is provided on the outer circumferential surface of the piston  131 , and the piston  131  partitions off the internal space of the cylinder  230  into a first oil chamber  51  (which is disposed above the piston  131 ) and a second oil chamber  52  (which is disposed below the piston). 
     Configuration of Rod  150   
     The rod  150  is a cylindrical member, and male screws are respectively formed on the outer circumferential surfaces of the upper end portion and the lower end portions of the rod  150 . The male screw formed on the upper end portion is tightened to the piston bolt  140  of the damping force generation unit  130 , and the male screw formed on the lower end portion is tightened to a female screw  161   d  that is formed on an upper end side columnar portion  161  of the rod holding member  160 . A lock nut  155  is tightened to the male screw that is formed on the lower end portion such that the rod  150  is fixed to the rod holding member  160 . 
     A female screw may be formed on the inner circumferential surface of the lower end portion of the rod  150 . 
     Configuration of Rod Holding Member  160   
     The rod holding member  160  has a plurality of columnar portions which have different diameters, and specifically, the rod holding member  160  has the upper end side columnar portion  161  that is an upper end portion, a lower end side columnar portion  162  that is a lower end portion, and an intermediate columnar portion  163  that is disposed between the upper end side columnar portion  161  and the lower end side columnar portion  162 . 
     The upper end side columnar portion  161  is formed with the axial recess portion  161   a , a radial recess portion  161   b , and a radial through-hole  161   c . The axial recess portion  161   a  is axially recessed from the upper end surface of the upper end side columnar portion  161 . The radial recess portion  161   b  is radially recessed from the outer circumferential surface of the upper end side columnar portion  161  across the entire circumference thereof. The radial through-hole  161   c  radially penetrates the axial recess portion  161   a  and the radial recess portion  161   b.    
     The axial recess portion  161   a  is formed with the female screw  161   d  that is tightened to the male screw formed on the lower end portion of the rod  150 . The axial recess portion  161   a  is formed with an inclined surface  161   e  which is inclined with respect to the axial direction such that the inner diameter of the axial recess portion  161   a  decreases gradually toward the lower side. 
     A lower end portion of the upper end side columnar portion  161  is formed with a male screw  161   f  that is tightened to a female screw  181  (which will be described later) which is formed on the support-member holding member  180 . 
     The intermediate columnar portion  163  has a diameter that is smaller than the inner diameter of the axial through-hole  112   a  which is formed in the outer member  110 , and the intermediate columnar portion  163  is fitted into the axial through-hole  112   a  of the outer member  110 . 
     A male screw  162   a  is formed on the outer circumferential surface of the lower end side columnar portion  162 . 
     The male screw  162   a  formed on the lower end side columnar portion  162  is tightened to a nut  165  which is inserted into the axial through-hole  112   a  of the outer member  110 , and thus, the rod holding member  160  is fixed to the outer member  110 . 
     Configuration of Restricting Member  167   
     The restricting member  167  is a stepped member which is formed in the cylindrical shape. A male screw is formed on the outer circumferential surface of an upper end portion of the restricting member  167 . A female screw formed on the inner circumferential surface of the lower end portion of the rod  150  is tightened to this male screw such that the restricting member  167  is fixed to the rod  150 . A lower end portion of the restricting member  167  restricts a movement of the ball  166  that is inserted into the axial recess portion  161   a  of the rod holding member  160 . 
     Configuration of Spring Support Member  170   
     The spring support member  170  is a cylindrical member, and is fixed to an upper end portion of the support-member holding member  180 . Fixing by welding, press-fitting, or using a stopper ring can be used as a fixing method. 
     Configuration of Support-member Holding Member  180   
     The support-member holding member  180  is a cylindrical member. The lower end portion of the support-member holding member  180  is formed with the female screw  181  that is tightened to the male screw  161   f  which is formed on the rod holding member  160 . The male screw  161   f  formed on the rod holding member  160  is tightened to the female screw  181  such that the support-member holding member  180  is fixed to the rod holding member  160 . In addition, the support-member holding member  180  and the rod holding member  160  may be fixed by using the stopper ring. 
     A communication hole  182  is formed in the support-member holding member  180  such that the inside and the outside of the support-member holding member  180  communicate with each other, and the communication hole  182  is disposed at an axial position which correspond to the position of the radial recess portion  161   b  of the rod holding member  160 . 
     Configuration of Guide Member  190   
     The guide member  190  has a cylindrical portion  191  having a cylindrical shape, and an inward portion  192  that is formed to be radially oriented toward the inner side from a lower end portion of the cylindrical portion  191 . 
     The inward portion  192  is interposed between the rod holding member  160  and the outer member  110  such that the guide member  190  is fixed between the rod holding member  160  and the outer member  110 . 
     A chamfer is formed in a lower end portion of the inward portion  192 , and a seal member  195 , such as an O-ring, is fitted into a space which is formed between the chamfer and the rod holding member  160 . The seal member  195  seals the gap between the guide member  190 , the rod holding member  160 , and the outer member  110 . Accordingly, the inner space of the cylindrical portion  111  of the outer member  110  is held in a liquid tight manner. 
     In the axle side unit  100  configured as described above, a reservoir chamber  40  is formed between (i) the inner circumferential surface of the outer member  110  and (ii) the outer circumferential surfaces of the rod  150  and the support-member holding member  180 . The reservoir chamber  40  stores oil that is sealed in the front fork  21 . 
     Configuration of Main Body Side Unit  200   
     The main body side unit  200  includes the cylindrical inner tube  210 , both ends of which are opened, and a cap  220  that is attached to an upper end portion of the inner tube  210 . 
     The main body side unit  200  includes the cylinder  230  having a cylindrical shape, and a seal member  240  that is attached to a lower end portion of the cylinder  230 , and seals the inner space of the cylinder  230 . 
     The main body side unit  200  includes a front wheel side spring-length changing unit  250  and the front wheel side flow path switching unit  300 . The front wheel side spring-length changing unit  250  supports an upper end portion of the front wheel side spring  500 , and adjusts (changes) the length of the front wheel side spring  500 , and the front wheel side flow path switching unit  300  is attached to an upper end portion of the cylinder  230 , and switches a flow path of oil as an example of a fluid. 
     Configuration of Inner Tube  210   
     The inner tube  210  is a cylindrical member. 
     The inner tube  210  includes a cylindrical slide bush  211  which helps the inner tube  210  to smoothly slide against the inner circumferential surface of the cylindrical portion  111  of the outer member  110  in the lower end portion. 
     The upper end portion of the inner tube  210  is formed with a female screw  213  which is tightened to a male screw  221  (which will be described later) that is formed on the cap  220 . 
     Configuration of Cap  220   
     The cap  220  is a substantially cylindrical member. The outer circumferential surface of the cap  220  is formed with the male screw  221  that is tightened to the female screw  213  which is formed on the inner tube  210 , and the inner circumferential surface of the cap  220  is formed with a female screw which is tightened to male screw that is formed on the front wheel side spring-length changing unit  250  or the front wheel side flow path switching unit  300 . The cap  220  is attached to the inner tube  210 , and holds the front wheel side spring-length changing unit  250  and the front wheel side flow path switching unit  300 . 
     The cap  220  has a seal member  222 , such as an O-ring, that holds the inner space of the inner tube  210  in a liquid tight manner. 
     Configuration of Cylinder  230   
     The cylinder  230  is a cylindrical member. The outer circumferential surface of the upper end portion of the cylinder  230  is formed with a female screw that is tightened to a male screw formed on the front wheel side flow path switching unit  300 , and the inner circumferential surface of the lower end portion of the cylinder  230  is formed with a female screw that is tightened to a male screw which is formed on the seal member  240 . 
     Configuration of Seal Member  240   
     The seal member  240  is a cylindrical member. The outer circumferential surface of the seal member  240  is formed with a male screw that is tightened to the female screw formed on the inner circumferential surface of the lower end portion of the cylinder  230 . The female screw formed on the inner circumferential surface of the lower end portion of the cylinder  230  is tightened to this male screw such that the seal member  240  is held by the cylinder  230 . 
     The seal member  240  has a slide bush  245  on the inner circumference, and the slide bush  245  helps the outer circumferential surface of the rod  150  to smoothly slide against the seal member  240 . The seal member  240  has a seal member  246 , such as an O-ring, that is disposed between the seal member  240  and the outer circumferential surface of the rod  150 , and a seal member  247 , such as an O-ring, that is disposed between the seal member  240  and the inner circumferential surface of the cylinder  230 , and as a result, the inner space of the cylinder  230  is held in a liquid tight manner. 
     A shock absorbing member  248  is attached to an upper end portion of the seal member  240 , and absorbs shock that is applied when the damping force generation unit  130  comes into contact with the shock absorbing member  248 . The shock absorbing member  248  can be formed as an elastic member made of resin or rubber. 
     Configuration of Front Wheel Side Spring-length Changing Unit  250   
     The front wheel side spring-length changing unit  250  includes a base member  260  and an upper end portion support member  270 . The base member  260  is fixed to the cap  220 , and the upper end portion support member  270  supports the upper end portion of the front wheel side spring  500 , and changes the length of the front wheel side spring  500  by moving relatively to the base member  260  in the axial direction. 
     The base member  260  is a substantially cylindrical member. A protrusion portion  260   a  is formed in an upper end portion of the base member  260 . The protrusion portion  260   a  is fixed to the cap  220 . 
     However, the upper end portion of the base member  260  is formed with a protrusion portion  260   b  of which a part in the circumferential direction protrudes in the radial direction. The upper end portion of the base member  260  forms a flow path  41  for discharging oil in the cylinder  230  to the reservoir chamber  40  between the inner surface of the protrusion portion  260   b  and the outer circumferential surface of a lower end portion of a support member  400  (which will be described later). 
     The base member  260  has a cylindrical slide bush  261  and a seal member  262 , such as an O-ring, in a lower end portion of the base member  260 . The slide bush  261  is fitted to the outer circumference of the base member  260 , and helps the base member  260  to smoothly slide against the inner circumferential surface of the upper end portion support member  270 , and the O-ring is provided inside the slide bush  261 . An annular flow path  61  is formed between the inner circumferential surface of the base member  260  and the outer circumferential surface of the cylinder  230 . 
     The upper end portion support member  270  has a cylindrical portion  271  having a cylindrical shape, and an inward portion  272  that is formed to be radially oriented toward the inner side from a lower end portion of the cylindrical portion  271 . The upper end portion support member  270  forms a jack chamber  60  in a space between the outer circumferential surface of the cylinder  230  and the lower end portion of the base member  260 , and the jack chamber  60  accommodates oil used to change the position of the upper end portion support member  270  with respect to the base member  260 . 
     The inner diameter of the cylindrical portion  271  is set to be smaller than the outer diameter of the slide bush  261  that is fitted to the base member  260 . A radial through-hole  273  is radially formed in the cylindrical portion  271  so that the inside and the outside of the cylindrical portion  271  communicate with each other. Oil is discharged from the jack chamber  60  to the reservoir chamber  40  via the radial through-hole  273  such that the amount of movement of the upper end portion support member  270  with respect to the base member  260  is restricted. 
     A seal member  274 , such as an O-ring, is provided on the inner circumference side of the inward portion  272 , and holds the jack chamber  60  in a liquid tight manner by sealing the gap between the inward portion  272  and the outer circumferential surface of the cylinder  230 . 
     Oil in the cylinder  230  is supplied to the jack chamber  60  via the annular flow path  61  that is formed between the inner circumferential surface of the base member  260  and the outer circumferential surface of the cylinder  230 . A detailed description thereof will be given later. 
     Configuration of Front Wheel Side Flow Path Switching Unit  300   
       FIG. 3A  is a view schematically illustrating an open and closed state of the flow path in a case where the front wheel side flow path switching unit  300  is in a first switch state (which will be described later).  FIG. 3B  is a view schematically illustrating an open and closed state of the flow path in a case where the front wheel side flow path switching unit  300  is in a second switch state (which will be described later).  FIG. 3C  is a view schematically illustrating an open and closed state of the flow path in case where the front wheel side flow path switching unit  300  is in a third switch state (which will be described later).  FIG. 3D  is a view schematically illustrating an open and closed state of the flow path in case where the front wheel side flow path switching unit  300  is in a fourth switch state (which will be described later). 
     The front wheel side flow path switching unit  300  is a device which switches supply of oil discharged by a pump  600  (which will be described later) to the reservoir chamber  40 , supply of oil discharged by the pump  600  to the jack chamber  60 , or supply of oil accommodated in the jack chamber  60  to the reservoir chamber  40 . 
     The front wheel side flow path switching unit  300  is formed with a first communication path R 1  which communicates with the inside of the cylinder  230  and the reservoir chamber  40 , a second communication path R 2  which communicates with the inside of the cylinder  230  and the jack chamber  60 , and a third communication path R 3  and a fourth communication path R 4  which communicate with the jack chamber  60  and the reservoir chamber  40 . 
     In addition, the front wheel side flow path switching unit  300  includes a first on-off valve  301  which opens and closes the first communication path R 1 , a second on-off valve  302  which opens and closes the second communication path R 2 , a third on-off valve  303  which opens and closes the third communication path R 3 , and a fourth on-off valve  304  which opens and closes the fourth communication path R 4 . 
     In a case where the front wheel side flow path switching unit  300  is in the first switch state, as illustrated in  FIG. 3A , the first on-off valve  301  is open and the third on-off valve  303  and the fourth on-off valve  304  are closed, and thus, the oil discharged by the pump  600  reaches the reservoir chamber  40  via the first communication path R 1 . In this case, since the pressure of the oil discharged by the pump  600  is not as high as the second on-off valve  302  is opened, the oil does not circulate in the second communication path R 2 . In other words, since the first on-off valve  301  is open, the second on-off valve  302  is closed. In addition, in the first switch state, an amount of oil in the jack chamber  60  neither increases nor decreases. 
     In a case where the front wheel side flow path switching unit  300  is in the second switch state, as illustrated in  FIG. 3B , the first on-off valve  301 , the third on-off valve  303 , the fourth on-off valve  304  are closed, and thus, the oil discharged by the pump  600  opens the second on-off valve  302  and reaches the jack chamber  60  via the second communication path R 2 . In the second switch state, the amount of oil in the jack chamber  60  increases. Therefore, the jack chamber  60  extends. 
     In a case where the front wheel side flow path switching unit  300  is in the third switch state, as illustrated in  FIG. 3C , the first on-off valve  301  and the fourth on-off valve  304  are closed, the third on-off valve  303  is open, and thus, the oil in the jack chamber  60  reaches the reservoir chamber  40  via the third communication path R 3 . In the third switch state, an amount of oil in the jack chamber  60  decreases. Therefore, the jack chamber  60  contracts. 
     In a case where the front wheel side flow path switching unit  300  is in the fourth switch state, as illustrated in  FIG. 3D , the first on-off valve  301  and the third on-off valve  303  are closed, the fourth on-off valve  304  is open, and thus, the oil in the jack chamber  60  reaches the reservoir chamber  40  via the fourth communication path R 4 . As will be described later, a flow path area of the fourth communication path R 4  is wider than a flow path area of the third communication path R 3 , in the fourth switch state, an amount of oil in the jack chamber  60  decreases faster than that of the third switch state. Therefore, the jack chamber  60  rapidly contracts. 
     Specific Configuration of Front Wheel Side Flow Path Switching Unit  300   
       FIG. 4  is an enlarged view of a portion IV in  FIG. 2 . 
       FIG. 5  is an enlarged view of a portion V in  FIG. 4 . 
     The front wheel side flow path switching unit  300  includes a first coil spring  311  which gives a force in the direction in which the first communication path R 1  is closed with respect to the first on-off valve  301 , a second coil spring  312  which gives a force in the direction in which the second communication path R 2  is closed with respect to the second on-off valve  302 , and a third coil spring  313  which gives a force in the direction in which the third communication path R 3  is closed with respect to the third on-off valve  303 . 
     In addition, the front wheel side flow path switching unit  300  includes a control valve  305  which controls opening and closing of the first on-off valve  301 , a control valve coil spring  315  which is provided below the control valve  305 , and a front wheel side solenoid  320  which moves the control valve  305  downward against a spring force of the control valve coil spring  315 . 
     In addition, the front wheel side flow path switching unit  300  includes a push rod  316  which moves the third on-off valve  303  downward against a spring force of the third coil spring  313  provided below the third on-off valve  303 . The push rod  316  moves downward being pushed by the control valve  305 . 
     In addition, the front wheel side flow path switching unit  300  includes a unit main body  330  and a second on-off valve support member  370  which is mounted on the unit main body  330  and supports the second on-off valve  302 . In addition, the front wheel side flow path switching unit  300  includes a fourth on-off valve support member  380  which supports the fourth on-off valve  304 , and a cover member  395  which covers an opening portion of the fourth on-off valve support member  380 . In addition, the front wheel side flow path switching unit  300  includes a coil spring support member  388  and a leaf spring  389  which are disposed between the second on-off valve support member  370  and an inward portion  382  (which will be described later) of the fourth on-off valve support member  380 , and support an upper end portion of the second coil spring  312 . 
     Regarding First On-off Valve  301   
     The first on-off valve  301  includes a cylindrical portion  301   a  having a cylindrical shape and a conical portion  301   b  having a conical shape and having an inclined surface  301   c  which is inclined with respect to the axial direction such that the outer diameter thereof gradually decreases toward the lower side. 
     A seal member  306 , such as an O-ring, is fitted to a space between an outer circumferential surface  301   d  of the cylindrical portion  301   a  and an upper end side columnar portion  340  (which will be described later) of the unit main body  330 . 
     A through-hole  301   e  in the axial direction is formed in a center portion of the conical portion  301   b . The through-hole  301   e  communicates with the inner portion of the cylindrical portion  301   a  and the outer portion of the conical portion  301   b . The through-hole  301   e  communicates with an axial communication hole  351  (which will be described later) of the unit main body  330 , and a space (hereinafter, referred to as “first on-off valve back pressure chamber B 1 ”) in which the oil that gives a downward force with respect to the first on-off valve  301  exists. In addition, the first on-off valve back pressure chamber B 1  is a space surrounded by a lower end surface of a case  325  of the front wheel side solenoid  320  which will be described later, a spring support member  307 , a center protrusion  347  of the unit main body  330 , or the like. 
     The first coil spring  311  is disposed on an inner side of the cylindrical portion  301   a  of the first on-off valve  301 , and the lower end portion is supported on an upper end surface of the conical portion  301   b  of the first on-off valve  301 . 
     The front wheel side flow path switching unit  300  includes a spring support member  307  which supports an upper end portion of the first coil spring  311 , and a retaining ring  308  which suppresses upward movement of the seal member  306 . 
     The retaining ring  308  has a cylindrical shape, and an inner diameter thereof is greater than an outer diameter of the cylindrical portion  301   a  of the first on-off valve  301 . An outer diameter of the retaining ring  308  is greater than an inner diameter of a first columnar recess portion  346   a  of the upper end side columnar portion  340  (which will be described later) of the unit main body  330 , and is pressurized to the first columnar recess portion  346   a . In addition, the retaining ring  308  suppresses the upward movement of the seal member  306 . In addition, the retaining ring  308  may be formed to be integrated with the upper end side columnar portion  340 . 
     The spring support member  307  is a doughnut-shaped thin plate a center portion of which is formed with a through-hole having a diameter that is greater than an outer diameter of the center protrusion  347  (which will be described later) of the unit main body  330 . The spring support member  307  is disposed above the first on-off valve  301 , the first coil spring  311 , the seal member  306 , and the retaining ring  308 , and suppresses upward movement of the first on-off valve  301  and the first coil spring  311 . 
     Configuration of Fourth On-off Valve  304   
     The fourth on-off valve  304  includes a first columnar portion  391  and a second columnar portion  392  which have columnar shapes and which have different diameters from each other. A diameter of the first columnar portion  391  is smaller than a diameter of the second columnar portion  392 . 
     In addition, an axial through-hole  393  which penetrates in the axial direction is formed in the fourth on-off valve  304 . The axial through-hole  393  includes a first through-hole  393   a  and a second through-hole  393   b  which have a columnar shape and have different diameters from each other. A hole diameter d 1  of the first through-hole  393   a  is greater than a hole diameter d 2  of the second through-hole  393   b . The hole diameter d 2  of the second through-hole  393   b  is greater than a diameter of a second shaft portion  318  (which will be described later) of the push rod  316 , and the hole diameter d 1  of the first through-hole  393   a  is greater than a diameter of a third shaft portion  319  (which will be described later) of the push rod  316  such that the push rod  316  passes through the inside of the axial through-hole  393 . However, in order to suppress the downward movement of the push rod  316 , the hole diameter d 2  of the second through-hole  393   b  is greater than the diameter of the third shaft portion  319  of the push rod  316 . 
     The second columnar portion  392  is formed with a lower end side recess portion  392   a  which is recessed from the lower end surface. In an opening portion of the second through-hole  393   b  in the lower end side recess portion  392   a , a recess portion which is along a shape of the upper end portion of the spherical third on-off valve  303  is formed. 
     Configuration of Control Valve  305   
     The control valve  305  is a columnar member. A groove  305   a  which is recessed across the entire circumference thereof is formed on an outer circumferential surface of the control valve  305 . In addition, the control valve  305  is formed with an upper end side recess portion  305   b  and an inclined hole  305   c . The upper end side recess portion  305   b  is recessed from the upper end surface in the axial direction. The inclined hole  305   c  is inclined with respect to the axial direction to communicate with the upper end side recess portion  305   b  and a lower part of the control valve  305 . 
     The control valve  305  moves downward against a spring force of the control valve coil spring  315  by being pressed downward by an operation rod  324  of the front wheel side solenoid  320  inserted into the upper end side recess portion  305   b . Meanwhile, in a case where the operation rod  324  moves upward, the control valve  305  moves upward by the spring force of the control valve coil spring  315 . 
     Configuration of Push Rod  316   
     As illustrated in  FIG. 4 , the push rod  316  includes a columnar first shaft portion  317  which is positioned on the upper end portion side, the columnar second shaft portion  318  which is positioned on the lower end portion side, and the columnar third shaft portion  319  which is positioned between the first shaft portion  317  and the second shaft portion  318 . The diameter of the third shaft portion  319  is greater than the diameters of the first shaft portion  317  and the second shaft portion  318 . In addition, the third on-off valve  303  and the push rod  316  may be integrated with each other. 
     Configuration of Front Wheel Side Solenoid  320   
     The front wheel side solenoid  320  is a proportional solenoid including a coil  321 , a core  322  which is disposed on an inner side of the coil  321 , a plunger  323  which is guided into the core  322 , and the operation rod  324  which is linked to the plunger  323 . 
     In addition, the front wheel side solenoid  320  includes the case  325  which accommodates the coil  321 , the core  322 , the plunger  323  and the like, and a cover  326  which covers an opening portion of the case  325 . 
     The operation rod  324  is hollow, an upper end portion thereof is accommodated on the inside of the case  325 , and a lower end portion thereof protrudes from the case  325 . 
     The case  325  includes a cylindrical portion  325   a  having a cylindrical shape and an inward portion  325   b  which is formed to be oriented toward the inner side in the radial direction from the lower end portion in the cylindrical portion  325   a . The inward portion  325   b  is formed with a through-hole which passes through the operation rod  324 . A guide bush  325   c  which guides the movement of the operation rod  324  is fitted to the inward portion  325   b.    
     A front wheel side solenoid  320  configured as described above is energized to the coil  321  via a connector mounted on the cap  220  and a lead line, and an axial thrust force is generated in the plunger  323  in accordance with an energization current. In addition, the operation rod  324  which is linked to the plunger  323  moves in the axial direction by the thrust force of the plunger  323 . In the front wheel side solenoid  320  according to the embodiment, the axial thrust force is generated in the plunger  323  such that an amount of protrusion of the operation rod  324  from the case  325  increases as the energization current to the coil  321  increases. 
     In addition, an energization amount to the coil  321  is controlled by the control device  70 . 
     Configuration of Unit Main Body  330   
     The unit main body  330  includes the columnar upper end side columnar portion  340  which is provided on the upper end side, and a first cylindrical portion  350  and a second cylindrical portion  360  which are provided below the upper end side columnar portion  340 , have cylindrical shapes and have different outer diameters from each other. 
     An outer diameter of the upper end side columnar portion  340  is substantially the same as an outer diameter of the first cylindrical portion  350 , and an outer diameter of the first cylindrical portion  350  is greater than an outer diameter of the second cylindrical portion  360 . 
     An upper end side center recess portion  342 , a lower end side center recess portion  344 , a center communication hole  345  are formed in a center portion of the upper end side columnar portion  340 . The upper end side center recess portion  342  is recessed downward from an upper end surface  341 . The lower end side center recess portion  344  is recessed in the upward direction from a lower end surface  343 . The center communication hole  345  communicates with the upper end side center recess portion  342  and the lower end side center recess portion  344 . 
       FIG. 6  is a perspective view of the upper end side columnar portion  340  of a unit main body  330 . 
     The upper end side center recess portion  342  includes an accommodation portion  342   a  which accommodates the control valve  305  to be movable. In addition, the upper end side center recess portion  342  includes a side recess portion  342   b  which is recessed in the axial direction from an upper end surface of the center protrusion  347  (which will be described later) further to a part below a lower limit of a moving range of the control valve  305  so as to be continuous to the accommodation portion  342   a  in the radial direction which intersects with the axial direction. 
     In the upper end side columnar portion  340 , an upper end side intermediate recess portion  346  is formed between the upper end side center recess portion  342  and the outer circumferential surface. The upper end side intermediate recess portion  346  is recessed downward from the upper end surface  341 . The upper end side intermediate recess portion  346  includes three columnar recess portions including a first columnar recess portion  346   a , a second columnar recess portion  346   b , and a third columnar recess portion  346   c  which have columnar shapes and have different diameters from each other. In addition, the upper end side columnar portion  340  is formed with an intersecting-direction communication hole  346   d  which is a hole that communicates with the second columnar recess portion  346   b  and the outer portion in the direction which intersects with the axial direction. 
     In addition, in the center portion of the upper end side columnar portion  340 , the center protrusion  347  which protrudes upward from the upper end surface  341  is provided around the upper end side center recess portion  342 . 
     In addition, the upper end side columnar portion  340  includes a flange portion  348  which is oriented toward the outer side in the radial direction from the upper end portion. The flange portion  348  is formed with a cut-out portion  348   a  of which a part in the circumferential direction is cut out. 
     In addition, the upper end side columnar portion  340  is formed with a first radial communication hole  349   a  and a second radial communication hole  349   b . The first radial communication hole  349   a  is a through-hole in the radial direction that communicates with the upper end side center recess portion  342  and the cut-out portion  348   a . The second radial communication hole  349   b  is a through-hole in the radial direction that communicates with the lower end side center recess portion  344  and the outer portion. 
     One first radial communication hole  349   a  is formed at a position at which the side recess portion  342   b  of the upper end side center recess portion  342  is not formed, in the circumferential direction. In the embodiment, as illustrated in  FIG. 6 , the first radial communication hole  349   a  and the side recess portion  342   b  are formed on sides opposite to each other across a center line. The first radial communication hole  349   a  is a columnar hole, and an example in which a hole diameter thereof is the same as that of the groove  305   a  of the control valve  305  in the axial direction can be employed. 
     One or a plurality of the second radial communication holes  349   b  are formed at a part at which the upper end side intermediate recess portion  346  is not formed in the circumferential direction. 
     The axial communication hole  351  is formed in the first cylindrical portion  350 . The axial communication hole  351  is a through-hole in the axial direction that communicates with (i) a space that is below the first cylindrical portion  350  and that is formed between the outer circumferential surface of the second cylindrical portion  360  and the inner circumferential surface of the cylinder  230  and (ii) the upper end side intermediate recess portion  346 . One or a plurality of the axial communication holes  351  are formed in the circumferential direction. 
     A first radial recess portion  352 , a second radial recess portion  353 , and a male screw  354  are formed on the outer circumferential surface of the first cylindrical portion  350 . The first radial recess portion  352  and the second radial recess portion  353  are recessed in the radial direction across the entire circumference thereof. The male screw  354  is tightened to a female screw formed in the upper end portion of the cylinder  230 . 
     A seal member  355 , such as an O-ring, which seals a gap between the first radial recess portion  352  and the base member  260  of the front wheel side spring-length changing unit  250  is fitted to the first radial recess portion  352 . 
     A seal member  356 , such as an O-ring, which seals a gap between the second radial recess portion  353  and the cylinder  230 , is fitted to the second radial recess portion  353 . 
     In addition, the first cylindrical portion  350  is formed with a third radial communication hole  357  which is a through-hole in the radial direction that communicates with the inner portion and the outer portion. A position in the radial direction of the third radial communication hole  357  is between the first radial recess portion  352  and the second radial recess portion  353 . 
     A female screw  361  is formed in the lower end portion of the inner circumferential surface of the second cylindrical portion  360 . A male screw  373   a  (which will be described later) formed on the outer circumferential surface of the second on-off valve support member  370  is tightened to the female screw  361 . 
     Configuration of Second On-off Valve Support Member  370   
     The second on-off valve support member  370  includes an upper end side cylindrical portion  371  which has a cylindrical shape and is positioned on the upper end portion side, a columnar portion  372  which is positioned in the center portion, and a lower end side cylindrical portion  373  which is positioned on the lower end portion side. 
     An outer diameter of the upper end side cylindrical portion  371  is smaller than the diameter of the inner circumferential surface of the first cylindrical portion  350  of the unit main body  330 , and the upper end side cylindrical portion  371  is inserted into the first cylindrical portion  350  of the unit main body  330 . 
     The columnar portion  372  is formed with a plurality of (three in the embodiment) axial through-holes  372   a  which penetrate in the axial direction at an equivalent interval in the circumferential direction around the center line. The opening portion on the upper end side in each of the axial through-holes  372   a  is formed with a recess portion which is along the shape of the lower end portion of the spherical second on-off valve  302 . A groove  372   b  is formed on the outer circumferential surface of the columnar portion  372  across the entire circumference thereof. A seal member  374 , such as an O-ring, which seals a gap between the groove  372   b  and the unit main body  330  is fitted to the groove  372   b.    
     An inner circumferential surface of the lower end side cylindrical portion  373  is positioned on an outer side, in the radial direction, of the axial through-hole  372   a  formed in the columnar portion  372 . The male screw  373   a  is formed on an outer circumferential surface of the lower end side cylindrical portion  373 . The male screw  373   a  is tightened to the female screw formed in the lower end portion of the unit main body  330 . A collecting member  375  is provided on an inner side of the lower end side cylindrical portion  373 . The collecting member  375  collects dust of oil discharged by the pump  600  (which will be described later). 
     The second on-off valve support member  370  is mounted on the unit main body  330  as the male screw  373   a  formed on the outer circumferential surface of the lower end side cylindrical portion  373  is tightened to the female screw  361  formed in the unit main body  330 . In addition, on the inner side of the upper end side cylindrical portion  371 , three second on-off valves  302  which are disposed at an equivalent interval in the circumferential direction, and a second on-off valve pressing member  378  which presses the second coil spring  312  and three second on-off valves  302 , are accommodated. The second on-off valve  302  blocks the axial through-hole  372   a  by seating in the opening portion on the upper end side in the axial through-hole  372   a  formed in the columnar portion  372 . 
     Configuration of Collecting Member  375   
     The collecting member  375  includes a disk-shaped net  376  and a cylindrical holding member  377  which has a cylindrical shape and holds the net  376  on the inside thereof. The collecting member  375  is mounted on the lower end side cylindrical portion  373  as the holding member  377  is pressurized to the lower end side cylindrical portion  373 . In addition, the collecting member  375  may be configured only of the net  376  that is directly attached to the lower end side cylindrical portion  373  of the second on-off valve support member  370 , for example, by an adhesive. In addition, the collecting member  375  and the lower end side cylindrical portion  373  may be fixed by using the stopper ring. 
     Configuration of Second On-off Valve Pressing Member  378   
     The second on-off valve pressing member  378  includes two cylindrical portions including a first cylindrical portion  378   a  and a second cylindrical portion  378   b  which have cylindrical shapes and have the same inner diameter and different outer diameters from each other. An inner diameter of the second on-off valve pressing member  378  is slightly greater than an outer diameter of a columnar portion  383  of the fourth on-off valve support member  380 . The second on-off valve pressing member  378  moves in the axial direction while being supported by the columnar portion  383  of the fourth on-off valve support member  380 . 
     An outer diameter of the first cylindrical portion  378   a  is smaller than an inner diameter of the second coil spring  312 . 
     An outer diameter of the second cylindrical portion  378   b  is greater than the inner diameter of the second coil spring  312 , and is smaller than an inner diameter of the upper end side cylindrical portion  371  of the second on-off valve support member  370 . The second cylindrical portion  378   b  supports the lower end portion of the second coil spring  312  on the upper end surface. 
     A downward biasing force from the second coil spring  312  is applied to the second on-off valve pressing member  378 , and the second on-off valve pressing member  378  is positioned at a position at which the lower end surface of the second cylindrical portion  378   b  comes into contact with three second on-off valves  302 . 
     Configuration of Fourth On-off Valve Support Member  380   
     The fourth on-off valve support member  380  includes a cylindrical portion  381  having a cylindrical shape, an inward portion  382  which is formed to be oriented toward the inner side in the radial direction from the lower end portion in the cylindrical portion  381 , and a columnar portion  383  which is oriented downward from the lower end portion in the inward portion  382 . 
     The fourth on-off valve support member  380  is formed with an axial through-hole  384  which penetrates the inward portion  382  and the columnar portion  383  in the axial direction. An inner portion of the cylindrical portion  381  and a part below the columnar portion  383  communicate with each other via the axial through-hole  384 . 
     The fourth on-off valve support member  380  is formed with a radial communication hole  385  which is a through-hole in the radial direction that communicates with the cylindrical portion  381  and an outer side of the fourth on-off valve support member  380 . A plurality of radial communication holes  385  are formed at an equivalent interval in the circumferential direction. 
     In the inward portion  382 , a protrusion  382   a  which protrudes to an upper part in the axial direction from the upper end surface is provided. An opening portion of the axial through-hole  384  in the protrusion  382   a  is formed with a recess portion which is along the shape of the lower end portion of the third on-off valve  303 . 
     In the cylindrical portion  381  of the fourth on-off valve support member  380 , the fourth on-off valve  304 , the third on-off valve  303 , the third coil spring  313 , a support member  386  which supports the upper end portion of the third coil spring  313 , and a suppressing member  387  which suppresses the movement of the third on-off valve  303  in the radial direction, are accommodated. 
     The support member  386  is a doughnut-shaped thin plate a center portion of which is formed with a through-hole having a diameter that is smaller than a diameter of the third on-off valve  303 . The support member  386  supports the upper end portion of the third coil spring  313  as a periphery of the through-hole of the center portion comes into contact with the upper end portion of the third coil spring  313 . The downward movement of the third on-off valve  303  is suppressed by being fitted to the through-hole of the center portion of the support member  386 . At a position at which a force which is generated to the support member  386  and moves the third on-off valve  303  downward and an upward force given from the third coil spring  313  are balanced, a position of the support member  386  is determined. In the embodiment, in a case where the third on-off valve  303  is not pressed from the push rod  316 , the spring force of the third coil spring  313  is set such that the third on-off valve  303  blocks the opening portion of the second through-hole  393   b  of the fourth on-off valve  304 . Meanwhile, in a case where the third on-off valve  303  is strongly pressed from the push rod  316 , the spring force of the third coil spring  313  is set such that the third on-off valve  303  is mounted on the protrusion  382   a  of the inward portion  382  of the fourth on-off valve support member  380 , and blocks the opening portion on the upper side of the axial through-hole  384  formed in the fourth on-off valve support member  380 . 
     The suppressing member  387  is a doughnut-shaped thin plate a center portion of which is formed with a center through-hole  387   a  having a diameter that is greater than the diameter of the third on-off valve  303  in the center portion. As the third on-off valve  303  is disposed on an inner side of the center through-hole  387   a  of the suppressing member  387 , the movement of the third on-off valve  303  in the radial direction is suppressed. In addition, a plurality of periphery through-holes  387   b  are formed at an equivalent interval in the circumferential direction on the periphery of the center through-hole  387   a  in the suppressing member  387 , and the oil circulates in the axial direction via the plurality of through-holes. 
     Configuration of Cover Member  395   
     The cover member  395  includes three cylindrical portions including a first cylindrical portion  396 , a second cylindrical portion  397 , and a third cylindrical portion  398  which have cylindrical shapes and have the same inner diameters and different outer diameters from each other. 
     The outer diameter of the first cylindrical portion  396  is smaller than the diameter of the inner circumferential surface of the first cylindrical portion  350  of the unit main body  330 , and is greater than the inner diameter of the cylindrical portion  381  of the fourth on-off valve support member  380 . As the upper end surface of the cylindrical portion  381  of the fourth on-off valve support member  380  abuts against the lower end surface of the first cylindrical portion  396 , the upward movement of the fourth on-off valve support member  380  is suppressed. In addition, a groove  396   a  is formed on the outer circumferential surface of the first cylindrical portion  396 . The groove  396   a  is recessed across the entire circumference of the outer circumferential surface of the first cylindrical portion  396 . A seal member  399 , such as an O-ring, which seals a gap between the groove  396   a  and the unit main body  330  is fitted to the groove  396   a . In addition, the cover member  395  may be formed to be integrated with the unit main body  330 . 
     The outer diameter of the second cylindrical portion  397  is substantially the same as the inner diameter of the cylindrical portion  381  of the fourth on-off valve support member  380 . The second cylindrical portion  397  is fitted to the inner side of the cylindrical portion  381  of the fourth on-off valve support member  380 . 
     The outer diameter of the third cylindrical portion  398  is smaller than the inner diameter of the cylindrical portion  381  of the fourth on-off valve support member  380 . A seal member  314  which is an elastic member, such as a doughnut-shaped resin or rubber is pressurized to a space between the third cylindrical portion  398  and the cylindrical portion  381  of the fourth on-off valve support member  380 . By reducing size of the third cylindrical portion  398  in the axial direction to be smaller than the size of the seal member  314 , and by bringing the fourth on-off valve  304  into contact with the seal member  314 , the flow path between the fourth on-off valve  304  and the seal member  314  is sealed. 
     The inner diameter of the cover member  395  is greater than the diameter of the third shaft portion  319  of the push rod  316 , and the push rod  316  is disposed on the inner side of the cover member  395 . 
     Configuration of Coil Spring Support Member  388   
     The coil spring support member  388  is a cross-shaped thin plate a center portion of which is formed with a through-hole having a diameter which is greater than the outer diameter of the columnar portion  383  of the fourth on-off valve support member  380 . The thin plate has a cross shape when viewed in the axial direction. The coil spring support member  388  supports the upper end portion of the second coil spring  312  on the lower end surface. 
     The size in the radial direction from the center of the through-hole in the coil spring support member  388  is greater than a radius of the inner circumferential surface of the upper end side cylindrical portion  371  of the second on-off valve support member  370 . 
     As the coil spring support member  388  abuts against the upper end surface of the upper end side cylindrical portion  371  of the second on-off valve support member  370 , the downward movement thereof is suppressed. 
     The coil spring support member  388  is positioned at a position at which the downward biasing force applied from the leaf spring  389  and the upward biasing force applied from the second coil spring  312  are balanced. 
     Configuration of Support Member  400   
     As illustrated in  FIG. 4 , the support member  400  has a cylindrical portion  401  having a cylindrical shape, and an inward portion  402  that is formed to be radially oriented toward the inner side from a lower end portion of the cylindrical portion  401 . 
     The outer circumferential surface of an upper end portion of the cylindrical portion  401  is formed with a male screw  403  that is tightened to a female screw formed on the cap  220 . The male screw  403  formed on the outer circumferential surface of the cylindrical portion  401  is tightened to the female screw formed on the cap  220  such that the support member  400  is held by the cap  220 . The flange portion of the fourth on-off valve support member  380  and the flange portion of the unit main body  330  are interposed between the inward portion  402  and the front wheel side solenoid  320  such that the support member  400  holds the fourth on-off valve support member  380  and the unit main body  330 . 
     Regarding Positional Relationship Between Side Recess Portion  342   b  and First Radial Communication Hole  349   a  which are Formed in Upper End Side Columnar Portion  340  of Unit Main Body  330   
       FIGS. 7A and 7B  are sectional views on a surface which is perpendicular in the axial direction and passes through the hole center of the first radial communication hole  349   a  of the upper end side columnar portion  340  of the unit main body  330 .  FIG. 7A  is a view illustrating a state where a position of the groove  305   a  of the control valve  305  in the axial direction and a position of the first radial communication hole  349   a  overlap each other.  FIG. 7B  is a view illustrating a state where the position of the groove  305   a  of the control valve  305  in the axial direction and the position of the first radial communication hole  349   a  do not overlap each other. 
     In the front wheel side flow path switching unit  300  configured as described above, in a case where the energization to the coil  321  of the front wheel side solenoid  320  is stopped or a current which is less than a first reference current set in advance is supplied, the amount of protrusion of the operation rod  324  which protrudes from the case  325  becomes less than a first reference amount set in advance. In the embodiment, in a case where the amount of protrusion of the operation rod  324  is less than the first reference amount, the position in the axial direction of the groove  305   a  of the control valve  305  overlaps the first radial communication hole  349   a  formed in the upper end side columnar portion  340  of the unit main body  330 . For example, in a case where the energization to the coil  321  of the front wheel side solenoid  320  is stopped and the amount of protrusion of the operation rod  324  is an initial amount, the control valve  305  is positioned at an initial position. In a case where the control valve  305  is at the initial position, the center position in the axial direction of the groove  305   a  of the control valve  305  and the position of the hole center of the first radial communication hole  349   a  become the same as each other, and the groove  305   a  and the first radial communication hole  349   a  overlap each other. In addition, at this time, as illustrated in  FIG. 7A , the side recess portion  342   b  and the first radial communication hole  349   a  which are formed in the upper end side columnar portion  340  of the unit main body  330  communicate with each other via the groove  305   a  of the control valve  305  and the first on-off valve back pressure chamber B 1  and the reservoir chamber  40  communicate with each other via the groove  305   a  of the control valve  305 . 
     In a case where the current which is equal to or greater than the first reference current is supplied to the coil  321  of the front wheel side solenoid  320 , the amount of protrusion of the operation rod  324  from the case  325  becomes equal to or greater than the first reference amount. In a case where the amount of protrusion of the operation rod  324  is equal to or greater than the first reference amount, the control valve  305  is pushed down by the operation rod  324  such that the position in the axial direction of the groove  305   a  of the control valve  305  becomes a position below the first radial communication hole  349   a  formed in the upper end side columnar portion  340  of the unit main body  330 . In other words, in a case where the amount of protrusion from the case  325  is equal to or greater than the first reference amount, the operation rod  324  pushes down the control valve  305  until the position in the axial direction of the groove  305   a  of the control valve  305  is positioned below the first radial communication hole  349   a  formed in the upper end side columnar portion  340  of the unit main body  330 . In a case where the groove  305   a  of the control valve  305  is positioned below the first radial communication hole  349   a , the position in the axial direction of the groove  305   a  of the control valve  305  do not overlap the position of the first radial communication hole  349   a . In addition, at this time, as illustrated in  FIG. 7B , the side recess portion  342   b  and the first radial communication hole  349   a  which are formed in the upper end side columnar portion  340  of the unit main body  330  do not communicate with each other via the groove  305   a  of the control valve  305 , and the first on-off valve back pressure chamber B 1  and the reservoir chamber  40  do not communicate with each other via the groove  305   a  of the control valve  305 . 
     In addition, an example in which the first reference amount of the amount of protrusion from the case  325  is half of a hole diameter of the first radial communication hole  349   a  formed in the upper end side columnar portion  340  of the unit main body  330  can be employed. 
     In a case where the current which is equal to or greater than a second reference current set in advance to be a value that is greater than the first reference current is supplied to the coil  321  of the front wheel side solenoid  320 , the operation rod  324  moves further downward, and the amount of protrusion of the operation rod  324  from the case  325  becomes equal to or greater than a second reference amount set in advance to be a value that is greater than the first reference amount. In a case where the amount of protrusion of the operation rod  324  is equal to or greater than the second reference amount, the control valve  305  comes into contact with the push rod  316  and comes into contact with the third on-off valve  303 , and the push rod  316  is placed in a state of being interposed between the control valve  305  and the third on-off valve  303 . 
     In a case where the current which is equal to or greater than a third reference current set in advance to be a value that is greater than the second reference current is supplied to the coil  321  of the front wheel side solenoid  320 , the amount of protrusion of the operation rod  324  from the case  325  becomes equal to or greater than a third reference amount set in advance to be a value that is greater than the second reference amount. When the amount of protrusion of the operation rod  324  from the case  325  becomes greater than the second reference amount, the push rod  316  is pushed downward via the control valve  305 . The push rod  316  which has moved downward pushes down the third on-off valve  303 , and the third on-off valve  303  is separated from the opening portion of the second through-hole  393   b  of the fourth on-off valve  304 . In other words, the push rod  316  is pushed by the control valve  305  in a case where the amount of protrusion of the operation rod  324  from the case  325  is greater than the second reference amount, the third on-off valve  303  is pushed such that the third on-off valve  303  is separated from the opening portion of the second through-hole  393   b  of the fourth on-off valve  304 . The third reference amount will be described later. 
     In a case where the current which is equal to or greater than a fourth reference current set in advance to be a value that is greater than the third reference current is supplied to the coil  321  of the front wheel side solenoid  320 , the amount of protrusion of the operation rod  324  from the case  325  becomes equal to or greater than a fourth reference amount set in advance to be a value that is greater than the third reference amount. In a case where the amount of protrusion of the operation rod  324  is equal to or greater than the fourth reference amount, the third on-off valve  303  which is pushed down by the push rod  316  is mounted on the protrusion  382   a  of the inward portion  382  of the fourth on-off valve support member  380 , and blocks the opening portion on the upper side of the axial through-hole  384 . In other words, in a case where the amount of protrusion of the operation rod  324  from the case  325  is equal to or greater than the fourth reference amount, the push rod  316  pushes the third on-off valve  303  to block the opening portion on the upper side of the axial through-hole  384  formed in the fourth on-off valve support member  380 . 
     Hereinafter, a state where the energization to the coil  321  is stopped or the current which is less than the first reference current is supplied, the position in the axial direction of the groove  305   a  of the control valve  305  overlaps the first radial communication hole  349   a  formed in the upper end side columnar portion  340  of the unit main body  330 , and the first on-off valve back pressure chamber B 1  and the reservoir chamber  40  communicate with each other via the groove  305   a  of the control valve  305 , is referred to as a first switch state. 
     In addition, a state where the current which is equal to or greater than the first reference current and is equal to or lower than the second reference current is supplied to the coil  321 , the operation rod  324  pushes down the control valve  305  to the position at which the groove  305   a  of the control valve  305  does not overlap the first radial communication hole  349   a  of the unit main body  330 , the first on-off valve back pressure chamber B 1  and the reservoir chamber  40  do not communicate with each other via the groove  305   a  of the control valve  305 , and the third on-off valve  303  blocks the opening portion of the second through-hole  393   b  of the fourth on-off valve  304 , is referred to as a second switch state. 
     In addition, a state where the current which is greater than the second reference current is supplied to the coil  321 , the first on-off valve back pressure chamber B 1  and the reservoir chamber  40  do not communicate with each other via the groove  305   a  of the control valve  305 , and the third on-off valve  303  does not block both of the opening portion of the second through-hole  393   b  of the fourth on-off valve  304  and the opening portion of the axial through-hole  384  of the fourth on-off valve support member  380 , is referred to as a third switch state. 
     In addition, a state where the current which is equal to or greater than the fourth reference current is supplied to the coil  321 , the first on-off valve back pressure chamber B 1  and the reservoir chamber  40  do not communicate with each other via the groove  305   a  of the control valve  305 , the third on-off valve  303  blocks the opening portion of the axial through-hole  384  of the fourth on-off valve support member  380 , is referred to as a fourth switch state. In the fourth switch state, as will be described later, the fourth on-off valve  304  is separated from the seal member  314 . 
     Operation of Front Fork  21   
     In the front fork  21  configured as described above, the front wheel side spring  500  supports weight of the motorcycle  1  and absorbs shock, and the damping force generation unit  130  damps vibration of the front wheel side spring  500 . 
       FIG. 8  is a view illustrating the operation of the front fork  21  during a compression stroke. 
     When the front fork  21  undergoes the compression stroke, the piston  131  of the damping force generation unit  130  moves upward with respect to the cylinder  230  as illustrated by the white arrow, and due to the movement of the piston  131 , oil in the first oil chamber  51  is pressed, and oil pressure increases. As a result, the first through-hole  132  is blocked, the lower end side valve  137  is opened, and the oil flows into the second oil chamber  52  via the first through-hole  132  (refer to arrow C 1 ). The flow of the oil from the first oil chamber  51  to the second oil chamber  52  is restricted by the first through-hole  132  and the lower end side valve  137  such that a damping force is obtained during the compression stroke. 
     Since the rod  150  enters the cylinder  230  during the compression stroke, a volume of oil corresponding to the extent of the entry of the rod is supplied to the jack chamber  60  or the reservoir chamber  40  in accordance with a switch state of the front wheel side flow path switching unit  300  (refer to arrow C 2 ). The supply of oil to either of the jack chamber  60  and the reservoir chamber  40  in accordance with a switch state of the front wheel side flow path switching unit  300  will be described later. The damping force generation unit  130 , the rod  150 , the cylinder  230 , and the like work as a pump that supplies the oil in the cylinder  230  to the jack chamber  60  or the reservoir chamber  40 . Hereinafter, this pump may be referred to as a “pump  600 ”. 
       FIG. 9  is a view illustrating the operation of the front fork  21  during an extension stroke. 
     When the front fork  21  undergoes the extension stroke, the piston  131  of the damping force generation unit  130  moves downward with respect to the cylinder  230  as illustrated by the white arrow, and due to the movement of the piston  131 , oil in the second oil chamber  52  is pressed, and oil pressure increases. As a result, the second through-hole  133  is blocked, the upper end side valve  136  is opened, and the oil flows into the first oil chamber  51  via the second through-hole  133  (refer to arrow T 1 ). The flow of the oil from the second oil chamber  52  to the first oil chamber  51  is restricted by the second through-hole  133  and the upper end side valve  136  such that a damping force is obtained during the extension stroke. 
     Since the rod  150  is pulled out of the cylinder  230  during the extension stroke, a volume of oil corresponding to the extent of the rod being pulled out is supplied from the reservoir chamber  40  to the first oil chamber  51 . That is, oil in the reservoir chamber  40  enters the first oil chamber  51  the pressure of which has become low due to the downward movement of the piston  131 . That is, the oil in the reservoir chamber  40  enters the axial recess portion  161   a  of the rod holding member  160  via the communication hole  182  of the support-member holding member  180 , and the radial through-hole  161   c  of the rod holding member  160 , moves the ball  166  upward, and then enters the inside of the rod  150  (refer to arrow T 2 ). The oil, which has entered the inside of the rod  150 , reaches the first oil chamber  51  via the recess portion  143  and the radial through-hole  144  of the piston bolt  140 , and the inclination direction through-hole  148  of the nut  145  (refer to arrow T 3 ). In addition, since the plate valve  149  which covers the opening portion of the inclination direction through-hole  148  is provided on the lower end side of the nut  145 , it is prevented that the oil flows back to the inside of the rod  150  from the first oil chamber  51 . 
     In this manner, the communication hole  182  of the support-member holding member  180 , the radial through-hole  161   c  of the rod holding member  160 , the axial recess portion  161   a  of the rod holding member  160 , the inner portion of the rod  150 , the recess portion  143  of the piston bolt  140 , the radial through-hole  144 , and the inclination direction through-hole  148  of the nut  145  function as a suction passage which suctions the oil to the inside of the cylinder  230  (first oil chamber  51 ) from the reservoir chamber  40 . In addition, the ball  166  functions as a check valve that allows inflow of the oil to the inside of the rod  150  from the reservoir chamber  40  and suppresses discharge of the oil to the reservoir chamber  40  from the inside of the rod  150 . Hereinafter, the ball  166  is referred to as a “suction side check valve Vc”. 
     Flow State of Oil in Accordance with Switch State of Front Wheel Side Flow Path Switching Unit  300   
       FIG. 10  is a view illustrating a flow state of oil in a case where the front wheel side flow path switching unit  300  is in the first switch state. 
     In a case where the front wheel side flow path switching unit  300  is in the first switch state during the compression stroke of the front fork  21 , as illustrated by arrow P 1  in  FIG. 10 , oil discharged by the pump  600  which is configured with the damping force generation unit  130 , the rod  150 , the cylinder  230 , and the like flows upward through an axial communication hole  351  formed in the unit main body  330 . As illustrated in  FIG. 7A , the oil of the first on-off valve back pressure chamber B 1  is discharged to the outside of the unit main body  330  through the side recess portion  342   b  of the unit main body  330 , the groove  305   a  of the control valve  305 , and the first radial communication hole  349   a  of the unit main body  330 . In addition, as illustrated by an arrow P 1  in  FIG. 10 , the oil discharged to the outside of the unit main body  330  is oriented toward the reservoir chamber  40  through the gap between the cut-out portion  348   a  of the unit main body  330  and the support member  400 , that is, through the flow path  41  formed between the protrusion portion  260   b  of the base member  260  and the lower end portion of the support member  400 . 
     In addition, in a case where the front wheel side flow path switching unit  300  is in the first switch state, since the pressure in the first on-off valve back pressure chamber B 1  is low, the oil which is discharged by the pump  600  and is oriented upward through the axial communication hole  351  formed in the unit main body  330  moves the first on-off valve  301  upward, and separates the inclined surface  301   c  of the first on-off valve  301  from the opening portion of the third columnar recess portion  346   c  of the unit main body  330 . In addition, the oil which flows through the gap between the inclined surface  301   c  of the first on-off valve  301  and the unit main body  330  passes through the intersecting-direction communication hole  346   d  formed in the unit main body  330 , and is oriented toward the reservoir chamber  40  through the flow path  41  formed between the protrusion portion  260   b  of the base member  260  and the lower end portion of the support member  400 . 
     In other words, in a case where the front wheel side flow path switching unit  300  is in the first switch state, the pressure in the first on-off valve back pressure chamber B 1  is not too high to make it difficult for the oil which is discharged by the pump  600  and is oriented upward through the axial communication hole  351  formed in the unit main body  330  to separate the first on-off valve  301  from the unit main body  330 . As a result, the oil discharged by the pump  600  is oriented toward the reservoir chamber  40 . 
     In this manner, the axial communication hole  351  of the unit main body  330 , the intersecting-direction communication hole  346   d , and the flow path  41  function as the first communication path R 1  (refer to  FIG. 3 ) which communicates with the inside of the cylinder  230  and the reservoir chamber  40 . 
     In addition, the axial communication hole  351  of the unit main body  330 , the through-hole  301   e  of the first on-off valve  301 , the side recess portion  342   b  of the unit main body  330 , the groove  305   a  of the control valve  305 , the first radial communication hole  349   a  of the unit main body  330 , and the flow path  41  function as a first communication path bypass path R 5  which communicates with the inside of the cylinder  230  and the reservoir chamber  40 . The control valve  305  functions as a valve which controls the opening and closing of the first on-off valve  301  by opening and closing the first communication path bypass path R 5 . 
     In addition, the side recess portion  342   b , the accommodation portion  342   a , and the first radial communication hole  349   a  which are formed in the unit main body  330  function as a discharge flow path through which the oil is oriented toward the reservoir chamber  40  from the first on-off valve back pressure chamber B 1 . The control valve  305  functions as a valve which controls the opening and closing of the first on-off valve  301  by opening and closing the discharge flow path. 
       FIG. 11  is a view illustrating a flow state of oil in a case where the front wheel side flow path switching unit  300  is in the second switch state. 
     In a case where the front wheel side flow path switching unit  300  is in the second switch state during the compression stroke of the front fork  21 , since the first on-off valve back pressure chamber B 1  and the reservoir chamber  40  do not communicate with each other via the groove  305   a  of the control valve  305 , the oil in the first on-off valve back pressure chamber B 1  is not oriented toward the reservoir chamber  40  through the groove  305   a  of the control valve  305 . Meanwhile, the axial communication hole  351  formed in the unit main body  330  and the first on-off valve back pressure chamber B 1  communicate with each other via the through-hole  301   e  of the first on-off valve  301 . 
     Therefore, in a case where the front wheel side flow path switching unit  300  is in the second switch state, the pressure in the first on-off valve back pressure chamber B 1  is not too high to make it difficult for the oil which is discharged by the pump  600  and is oriented upward through the axial communication hole  351  of the unit main body  330  to move the first on-off valve  301  upward (open the first on-off valve  301 ). 
     In this manner, in a case where the front wheel side flow path switching unit  300  is in the second switch state, since the first on-off valve  301  closes the first communication path R 1 , as illustrated by an arrow P 2  illustrated in  FIG. 11 , the oil discharged by the pump  600  is oriented toward the jack chamber  60 . In other words, the oil which is discharged by the pump  600  and passes through the axial through-hole  372   a  of the second on-off valve support member  370  pushes up the second on-off valve  302  against the biasing force of the second coil spring  312 , and is oriented upward through the gap between the outer circumferential surface of the fourth on-off valve support member  380  and the inner circumferential surface of the unit main body  330 . In addition, the oil which is oriented upward through the gap between the outer circumferential surface of the fourth on-off valve support member  380  and the inner circumferential surface of the unit main body  330  is oriented toward the outer side of the unit main body  330  through the third radial communication hole  357  of the unit main body  330 . After this, the oil which passes through the third radial communication hole  357  is oriented toward the jack chamber  60  through the annular flow path  61  formed between the outer circumferential surface of the cylinder  230  and the inner circumferential surface of the base member  260  of the front wheel side spring-length changing unit  250 . 
     In this manner, the axial through-hole  372   a  of the second on-off valve support member  370 , the gap between the outer circumferential surface of the fourth on-off valve support member  380  and the inner circumferential surface of the unit main body  330 , the third radial communication hole  357  of the unit main body  330 , and the annular flow path  61  function as the second communication path R 2  (refer to  FIG. 3 ) which communicates with the inside of the cylinder  230  and the jack chamber  60 . The second on-off valve  302  is also a check valve which allows the flow of the oil to the jack chamber  60  from the inside of the cylinder  230 , and which interrupts the flow of the oil to the inside of the cylinder  230  from the jack chamber  60 . 
     In addition, in a case where the front wheel side flow path switching unit  300  is in the second switch state, the third on-off valve  303  blocks the opening portion of the second through-hole  393   b  of the fourth on-off valve  304 . Therefore, a space S 1  surrounded by the inner circumferential surface of the cylindrical portion  381  of the fourth on-off valve support member  380 , the lower end surface of the second columnar portion  392  of the fourth on-off valve  304 , and the upper end surface of the inward portion  382  of the fourth on-off valve support member  380 , and the jack chamber  60  communicate with each other via the axial through-hole  384  of the fourth on-off valve support member  380  or a spherical gap between on second on-off valve  302  and the other second on-off valve  302 . 
     In addition, a space S 2  which is between the inner circumferential surface of the cylindrical portion  381  of the fourth on-off valve support member  380  and the outer circumferential surface of the first columnar portion  391  of the fourth on-off valve  304 , and the jack chamber  60  communicate with each other via the radial communication hole  385  of the fourth on-off valve support member  380 . 
     As a result, the pressure of the oil in the space S 1  which is oil that applies an upward force to the fourth on-off valve  304  is the same as the pressure of the oil in the space S 2  which is oil that applies a downward force to the fourth on-off valve  304 . In addition, in the fourth on-off valve  304 , since a pressure-receiving area A 1  (an area of the lower end surface of the second columnar portion  392 ) which receives the pressure of the oil in the space S 1  is greater than a pressure-receiving area A 2  (an area of the upper end surface of the second columnar portion  392 ) which receives the pressure of the oil in the space S 2 , the fourth on-off valve  304  is maintained to be in contact with the seal member  314 . 
       FIG. 12  is a view illustrating a flow state of oil in a case where the front wheel side flow path switching unit  300  is in the third switch state. 
     In a case where the front wheel side flow path switching unit  300  is in the third switch state, as illustrated by an arrow P 3  in  FIG. 12 , the oil in the jack chamber  60  is oriented toward the reservoir chamber  40 . In other words, the oil in the jack chamber  60  is oriented downward through the annular flow path  61  formed between the outer circumferential surface of the cylinder  230  and the inner circumferential surface of the base member  260  of the front wheel side spring-length changing unit  250 , the third radial communication hole  357  of the unit main body  330 , and the gap between the outer circumferential surface of the fourth on-off valve support member  380  and the inner circumferential surface of the unit main body  330 , and enters a gap G 1  between the inner circumferential surface of the upper end side cylindrical portion  371  of the second on-off valve support member  370  and the outer circumferential surface of the columnar portion  383  of the fourth on-off valve support member  380 . In addition, the oil in the gap G 1  is oriented upward through the spherical gap between one second on-off valve  302  and the other second on-off valve  302 , the axial through-hole  384  of the fourth on-off valve support member  380 , the gap between the third on-off valve  303  and the fourth on-off valve  304 , and the gap between the inner circumferential surface of the second through-hole  393   b  of the fourth on-off valve  304  and the outer circumferential surface of the push rod  316 . The oil which is oriented upward is oriented toward the reservoir chamber  40  through the second radial communication hole  349   b  of the unit main body  330 , and the flow path  41  formed between the protrusion portion  260   b  of the base member  260  and the lower end portion of the support member  400 . 
     In this manner, the annular flow path  61 , the third radial communication hole  357  of the unit main body  330 , the gap between the outer circumferential surface of the fourth on-off valve support member  380  and the inner circumferential surface of the unit main body  330 , the axial through-hole  384  of the fourth on-off valve support member  380 , the gap between the third on-off valve  303  and the fourth on-off valve  304 , the gap between the inner circumferential surface of the second through-hole  393   b  of the fourth on-off valve  304  and the outer circumferential surface of the push rod  316 , the second radial communication hole  349   b  of the unit main body  330 , and the flow path  41  function as the third communication path R 3  (refer to  FIG. 3 ) which communicates with the jack chamber  60  and the reservoir chamber  40 . In addition, the third on-off valve  303  opens and closes the third communication path R 3 . 
     In addition, the annular flow path  61 , the third radial communication hole  357  of the unit main body  330 , the gap between the outer circumferential surface of the fourth on-off valve support member  380  and the inner circumferential surface of the unit main body  330 , and the axial through-hole  384  of the fourth on-off valve support member  380  which are on the upstream side of the space S 1  in the third communication path R 3  function as an inflow path which is oriented toward the space S 1  from the jack chamber  60 . The third on-off valve  303  also opens and closes the inflow path. 
     In addition, in a case where the front wheel side flow path switching unit  300  is in the third switch state, the third on-off valve  303  is separated from the opening portion of the second through-hole  393   b  such that a gap G 2  between the third on-off valve  303  and the opening portion of the second through-hole  393   b  of the fourth on-off valve  304  becomes the smallest restriction portion in the third communication path R 3 . In a state where the third on-off valve  303  is separated from the opening portion of the second through-hole  393   b , the pressure of the oil in the space S 1  which applies the upward force to the fourth on-off valve  304  is smaller than the pressure of the oil in the space S 2  which is oil that applies the downward force to the fourth on-off valve  304 , but the pressure-receiving area A 1  is greater than the pressure-receiving area A 2 , and thus, the fourth on-off valve  304  is maintained to be in contact with the seal member  314  (pressure of oil in the space S 1 ×pressure-receiving area A 1 &gt;pressure of oil in the space S 2 ×pressure-receiving area A 2 ). 
     In other words, in a case where the front wheel side flow path switching unit  300  is in the third switch state, the fourth on-off valve  304  is set as follows to be maintained to be in contact with the seal member  314 . In other words, the third reference amount is set so that the gap G 2  becomes the smallest restriction portion by further reducing a flow path area formed by the gap G 2  to be smaller than a flow path area (the smallest area of the inflow path) of the axial through-hole  384  of the fourth on-off valve support member  380  or an area (the smallest area of the flow path downstream of the gap G 2 ) of the flow path formed by a gap G 3  between the outer circumferential surface of the second shaft portion  318  of the push rod  316  and the inner circumferential surface of the second through-hole  393   b  of the fourth on-off valve  304 . In addition, the third reference amount is set considering the pressure-receiving area A 1  and the pressure-receiving area A 2  so that a value obtained by multiplying the pressure of the oil in the space S 1  that becomes small as the third on-off valve  303  is open by the pressure-receiving area A 1  becomes greater than a value obtained by multiplying the pressure of the oil in the space S 2  by the pressure-receiving area A 2  (pressure of oil in the space S 1 ×pressure-receiving area A 1 &gt;pressure of oil in the space S 2 ×pressure-receiving area A 2 ). 
       FIG. 13  is a view illustrating a flow state of oil in a case where the front wheel side flow path switching unit  300  is in the fourth switch state. 
     In a case where the front wheel side flow path switching unit  300  is in the fourth switch state, since the third on-off valve  303  blocks the opening portion of the axial through-hole  384  of the fourth on-off valve support member  380 , the inflow of the oil into the space S 1  that applies the upward force to the fourth on-off valve  304  is small or the oil does not flow into the space S 1 . Therefore, even when the pressure of the oil in the space S 1  is smaller than that of a case where the front wheel side flow path switching unit  300  is in the third switch state and the pressure-receiving area A 1  is greater than the pressure-receiving area A 2 , the downward force applied to the fourth on-off valve  304  is greater than the upward force (pressure of oil in the space S 1 ×pressure-receiving area A 1 &lt;pressure of oil in the space S 2 ×pressure-receiving area A 2 ). As a result, the fourth on-off valve  304  is separated from the seal member  314 . In addition, as illustrated by an arrow P 4  in  FIG. 13 , the oil in the jack chamber  60  is oriented toward the reservoir chamber  40  through the gap between the fourth on-off valve  304  and the seal member  314 . In other words, the oil in the jack chamber  60  is oriented toward the reservoir chamber  40  through the annular flow path  61 , the third radial communication hole  357  of the unit main body  330 , the radial communication hole  385  of the fourth on-off valve support member  380 , the gap between the fourth on-off valve  304  and the seal member  314 , the second radial communication hole  349   b  of the unit main body  330 , the flow path  41  formed between the protrusion portion  260   b  of the base member  260  and the lower end portion of the support member  400 . 
     In this manner, the annular flow path  61 , the third radial communication hole  357  of the unit main body  330 , the radial communication hole  385  of the fourth on-off valve support member  380 , the gap between the fourth on-off valve  304  and the seal member  314 , the second radial communication hole  349   b  of the unit main body  330 , and the flow path  41  function as the fourth communication path R 4  (refer to  FIG. 3 ) which communicates with the jack chamber  60  and the reservoir chamber  40 . In addition, the fourth on-off valve  304  opens and closes the fourth communication path R 4 . 
     Regarding Raising and Lowering Vehicle Height 
     In a case where the front wheel side flow path switching unit  300  is in the second switch state, during the compression stroke of the front fork  21  that operates as described above, the oil discharged by the pump  600  flows into the jack chamber  60 , and the amount of oil in the jack chamber  60  increases. Due to an increase in amount of oil in the jack chamber  60 , the upper end portion support member  270  moves downward with respect to the base member  260  of the front wheel side spring-length changing unit  250 . When the spring length of the front wheel side spring  500  decreases due to the downward movement of the upper end portion support member  270  with respect to the base member  260 , a spring force of the front wheel side spring  500  pushing the upper end portion support member  270  increases compared to that before the upper end portion support member  270  moves with respect to the base member  260 . As a result, even when a force acts on the front wheel  2  side from the vehicle body frame  11 , an initial set load (preload) at which relative positions both of the front wheel  2  and the vehicle body frame  11  are not changed, increases. In this case, in a case where the same force acts on the front wheel  2  from the vehicle body frame  11  (a seat  19 ) side in the axial direction, the amount of compression of the front fork  21  decreases. Therefore, when the spring length of the front wheel side spring  500  decreases due to the movement of the upper end portion support member  270  with respect to the base member  260 , the height of the seat  19  is raised (the vehicle height is raised) as compared to that before the upper end portion support member  270  moves with respect to the base member  260 . 
     On the other hand, in a case where the front wheel side flow path switching unit  300  is in the third switch state or in the fourth switch state, the amount of oil in the jack chamber  60  decreases. Thereby, the upper end portion support member  270  moves upward with respect to the base member  260  of the front wheel side spring-length changing unit  250 . When the spring length of the front wheel side spring  500  increases due to the upward movement of the upper end portion support member  270  with respect to the base member  260 , a spring force of the front wheel side spring  500  pushing the upper end portion support member  270  decreases as compared to that before the upper end portion support member  270  moves with respect to the base member  260 . In this case, the initial set load (preload) decreases, and in a case where the same force acts from the vehicle body frame  11  (the seat  19 ) in the axial direction, the amount of compression of the front fork  21  increases. Therefore, when the spring length of the front wheel side spring  500  increases due to the upward movement of the upper end portion support member  270  with respect to the base member  260 , the height of the seat  19  is lowered (the vehicle height is lowered) as compared to that before the upper end portion support member  270  moves with respect to the base member  260 . When the front wheel side flow path switching unit  300  is in the fourth switch state, the amount of oil in the jack chamber  60  decreases more quickly than that in a case of the third switch state, and thus, the vehicle height is lowered more quickly than in the third switch state. 
     In a case where the front wheel side flow path switching unit  300  is in the first switch state, the oil discharged by the pump  600  during the compression stroke flows into the reservoir chamber  40 , and thus, the amount of oil in the jack chamber  60  neither increases nor decreases. Hence, the height of the seat  19  is maintained (the vehicle height is maintained). 
     In this manner, the front wheel side flow path switching unit  300  according to the embodiment can open any communication path among the first communication path R 1 , the second communication path R 2 , and the third communication path R 3 , in accordance with the amount of supplied current. In other words, the front wheel side flow path switching unit  300  can raise the vehicle height, lower the vehicle height, or maintain the vehicle height by suppressing the axial movement amount of the operation rod  324  of the front wheel side solenoid  320 , in accordance with the amount of supplied current. In other words, the front wheel side flow path switching unit  300  configured as a single unit can control three control modes in accordance with the amount of current: a raising mode in which the vehicle height is raised; a lowering mode in which the vehicle height is lowered; and a maintaining mode in which the vehicle height is maintained. In addition, in the lowering mode, the front wheel side flow path switching unit  300  can realize a slow lowering mode in which the vehicle height can be slowly lowered; and a quick lowering mode in which the vehicle height is quickly lowered. 
     In addition, the front wheel side flow path switching unit  300  which realizes the above-described function is configured to be attached to the upper end portion of the cylinder  230  on the inner side of the inner tube  210 . In other words, the front wheel side flow path switching unit  300  is not disposed on the outer side of the inner tube  210 . In addition, the front wheel side flow path switching unit  300  does not require a plurality of electromagnetic actuators (solenoids or the like) so as to realize the three control modes. Hence, according to the front wheel side flow path switching unit  300  according to the embodiment, it is possible to reduce a mounting space by simplifying the configuration of the front fork  21 , and to realize the aforementioned function. In other words, the front fork  21  can switch between the three control modes without an increase in size by employing the front wheel side flow path switching unit  300  according to the embodiment to the front fork  21  which has a limited surrounding space. 
     The front wheel side flow path switching unit  300  according to the embodiment is placed in the maintaining mode in a case where the current to be supplied is less than the first reference current, the raising mode in a case where the current to be supplied is equal to or greater than the first reference current and is less than the second reference current, and the lowering mode in a case where the current to be supplied is equal to or greater than the second reference current. In other words, the front wheel side flow path switching unit  300  sequentially transitions from the maintaining mode, to the raising mode, and to the lowering mode in accordance with the increase in amount of current to be supplied. 
     In this manner, the front wheel side flow path switching unit  300  according to the embodiment does not sequentially transition from the maintaining mode, to the lowering mode, and to the raising mode in accordance with the increase in amount of current to be supplied. In a case where the front wheel side flow path switching unit  300  is configured to transition from the maintaining mode, to the lowering mode, and to the raising mode, when the amount of current is decreased so as to maintain a raised vehicle height, there is a concern that the amount of current is adjusted to the amount of current corresponding to the lower mode, and the vehicle height is lowered. 
     Meanwhile, since the front wheel side flow path switching unit  300  according to the embodiment sequentially transitions from the maintaining mode, to the raising mode, and to the lowering mode in accordance with the increase in the amount of current to be supplied, even when the amount of current is decreased so as to maintain a raised vehicle height, the vehicle height is not lowered. 
     The front wheel side flow path switching unit  300  which is an example of a flow path control device according to the embodiment as described above includes the first on-off valve  301  which is an example of a first valve, and the unit main body  330  which is an example of a flow path forming member. The first on-off valve  301  opens and closes the first communication path R 1  which is an example of a first flow path. In the first communication path R 1 , the supplied oil is oriented toward the reservoir chamber  40  which is an example of a first chamber. The unit main body  330  forms a discharge flow path which is an example of a second flow path that is oriented toward the reservoir chamber  40  from the first on-off valve back pressure chamber B 1  which is an example of a second chamber that accommodates the oil which applies the force in the direction in which the first on-off valve  301  is closed to the first on-off valve  301 . The unit main body  330  is formed with the accommodation portion  342   a , the first radial communication hole  349   a , and the side recess portion  342   b . The accommodation portion  342   a  is an example of a first recess portion and is recessed from the first on-off valve back pressure chamber B 1 . The first radial communication hole  349   a  is an example of a communication path and communicates with the accommodation portion  342   a  and the reservoir chamber  40 . The side recess portion  342   b  is an example of a second recess portion and is recessed from the first on-off valve back pressure chamber B 1  so as to be continuous to the accommodation portion  342   a  and not to be continuous to the first radial communication hole  349   a . The unit main body  330  forms the discharge flow path which is an example of a second flow path that is oriented toward the reservoir chamber  40  from the first on-off valve back pressure chamber B 1  via the first radial communication hole  349   a  and the side recess portion  342   b . Then, the front wheel side flow path switching unit  300  includes the control valve  305  which is an example of a second valve. The control valve  305  is formed with the groove  305   a  which is recessed from the outer surface. The control valve  305  is fitted to the accommodation portion  342   a  of the unit main body  330 . The control valve  305  opens and closes the discharge flow path which is an example of a second flow path by moving between (i) the position at which the groove  305   a  communicates with the side recess portion  342   b  and the first radial communication hole  349   a  and (ii) the position at which the groove  305   a  does not communicate with the side recess portion  342   b  and the first radial communication hole  349   a.    
     According to the front wheel side flow path switching unit  300  configured as described above, in a case where the control valve  305  is at the position at which the groove  305   a  communicates with the side recess portion  342   b  and the first radial communication hole  349   a , the pressure in the first on-off valve back pressure chamber B 1  decreases since the oil in the first on-off valve back pressure chamber B 1  is oriented toward the reservoir chamber  40 . As a result, the force in the direction in which the first on-off valve  301  is closed decreases, the first on-off valve  301  is open, and the oil supplied from the pump  600  is oriented toward the reservoir chamber  40 . 
     Meanwhile, in a case where the control valve  305  is positioned at a position at which the groove  305   a  does not communicate with the side recess portion  342   b  and the first radial communication hole  349   a , the pressure in the first on-off valve back pressure chamber B 1  is high since the oil in the first on-off valve back pressure chamber B 1  is unlikely to be oriented toward the reservoir chamber  40 . As a result, the force in the direction in which the first on-off valve  301  is closed increases, the first on-off valve  301  is closed, and the oil supplied from the pump  600  is unlikely to be oriented toward the reservoir chamber  40 . According to the front wheel side flow path switching unit  300  according to the embodiment, since it is possible to control the opening and closing of the first on-off valve  301  by suppressing the position of the control valve  305 , it is possible to control whether or not the oil supplied from the pump  600  is oriented toward the reservoir chamber  40  with high accuracy. Therefore, for example, even when a large amount of oil is discharged by the pump due to rapid vibration of the front wheel  2  by reducing the interval of roughness of a road surface or a large amplitude of vibration of the front wheel  2  by increasing roughness of a road surface, it is possible to control whether or not the oil supplied from the pump  600  is oriented toward the reservoir chamber  40  with high accuracy, and thus, it is possible to control the amount of oil in the jack chamber  60  with high accuracy. 
     Here, the side recess portion  342   b  of the unit main body  330  may be recessed in the same direction as the moving direction of the control valve  305 , and the first radial communication hole  349   a  may be formed in the direction intersecting with the moving direction of the control valve  305 . Accordingly, it is possible to easily control whether or not the side recess portion  342   b  and the first radial communication hole  349   a  communicate with each other by moving the control valve  305  with high accuracy. 
     In addition, in the moving direction of the control valve  305 , the side recess portion  342   b  and the first radial communication hole  349   a  may communicate with each other in a case where the groove  305   a  of the control valve  305  overlap the first radial communication hole  349   a  of the unit main body  330 , and the side recess portion  342   b  and the first radial communication hole  349   a  may not communicate with each other in a case where the groove  305   a  does not overlap the first radial communication hole  349   a . Accordingly, it is possible to easily control the opening and closing of the first on-off valve  301  according to whether or not the position of the groove  305   a  of the control valve  305  matches the position of the first radial communication hole  349   a  of the unit main body  330 . 
       FIG. 14  is a view illustrating a positional relationship between the outer circumferential surface of the control valve  305  and the opening portion of a first radial communication hole  349   a  in a case where the groove  305   a  is at a position which does not communicate with the side recess portion  342   b  and the first radial communication hole  349   a.    
     The control valve  305  may have a columnar shape and move in an axial direction of the columnar shape. When viewed in the moving direction of the control valve  305 , the first radial communication hole  349   a  of the unit main body  330  may be formed on the side opposite to the side recess portion  342   b  across the center of the control valve  305 . Accordingly, the force which is oriented toward the first radial communication hole  349   a  is applied to the control valve  305  by the oil in the side recess portion  342   b . As a result, in particular, in a case where the position of the control valve  305  in the moving direction is the position at which the groove  305   a  does not overlap the first radial communication hole  349   a , as illustrated in  FIG. 14 , the outer surface of the control valve  305  blocks the opening portion of the first radial communication hole  349   a . Therefore, for example, even in a case of a dimensional relationship in which the inner surface of the accommodation portion  342   a  is greater than the outer surface of the control valve  305  and a gap is generated between the outer surface of the control valve  305  and the inner surface of the accommodation portion  342   a , it is possible to maintain high pressure in the first on-off valve back pressure chamber B 1  since the oil in the first on-off valve back pressure chamber B 1  is unlikely to be oriented toward the reservoir chamber  40 . 
     In addition, when the force oriented toward first radial communication hole  349   a  is applied to the control valve  305  by the oil in the side recess portion  342   b , the first radial communication hole  349   a  and the side recess portion  342   b  may not be formed to be opposite to each other across the center of the control valve  305 . In addition, the control valve  305  may have a shape of a square column. 
     As described above, the front wheel side flow path switching unit  300  which is an example of a flow path control device according to the embodiment includes the fourth on-off valve  304  which is an example of a first valve. The fourth on-off valve  304  transitions from a closed state in which the fourth communication path R 4  which is an example of a first flow path and which is oriented from the jack chamber  60  which is an example of a first chamber toward the reservoir chamber  40  which is an example of a second chamber is closed to an open state in which the fourth communication path R 4  is open by moving from the closed state to the space S 1  which is an example of a third chamber. The fourth on-off valve  304  is formed with the axial through-hole  393  which is an example of a communication path and which communicates with the fourth communication path R 4  and the space S 1 . The pressure-receiving area A 1  which is an example of a first pressure-receiving area and to which the pressure in the jack chamber  60  is applied in the closed state is smaller than the pressure-receiving area A 2  which is an example of a second pressure-receiving area and to which the pressure in the space S 1  is applied. In addition, the front wheel side flow path switching unit  300  includes the third on-off valve  303  which is an example of a second valve. The third on-off valve  303  is provided in the space S 1  on the third communication path R 3  which is an example of the second flow path. The third communication path R 3  is oriented from the jack chamber  60  toward the reservoir chamber  40  through the axial through-hole  393  of the fourth on-off valve  304 . The third on-off valve  303  transitions between (i) a first state where the axial through-hole  393  is closed and the inflow path oriented from the jack chamber  60  toward the space S 1  is open and (ii) a second state where the inflow path is closed and the axial through-hole  393  is open. 
     According to the front wheel side flow path switching unit  300  configured as described above, in a case of the first state where the third on-off valve  303  closes the axial through-hole  393  of the fourth on-off valve  304  and opens the inflow path that reaches the space S 1  from the jack chamber  60 , the jack chamber  60  and the space S 1  which is a back pressure chamber of the fourth on-off valve  304  have the same pressure. Then, since the pressure-receiving area A 1  of the fourth on-off valve  304  to which the pressure of the jack chamber  60  is applied in the closed state is smaller than the pressure-receiving area A 2  to which the pressure in the space S 1  is applied, the fourth on-off valve  304  is placed in the closed state. Since the third on-off valve  303  closes the axial through-hole  393  of the fourth on-off valve  304 , the third communication path R 3  is also closed. Therefore, the oil in the jack chamber  60  does not reach the reservoir chamber  40 . 
     On the other hand, in a case of the second state where the third on-off valve  303  closes the inflow path that reaches the space S 1  from the jack chamber  60  and opens the axial through-hole  393  of the fourth on-off valve  304 , the oil is not supplied to the space S 1  which is the back pressure chamber of the fourth on-off valve  304 . Thus, the pressure becomes lower than that of the jack chamber  60 . Therefore, the fourth on-off valve  304  is likely to move to the space S 1 , and the fourth on-off valve  304  is likely to be open. Then, in the front wheel side flow path switching unit  300  according to the embodiment, in a case where the third on-off valve  303  is in the second state, the fourth on-off valve  304  is set to be in the open state. As a result, the oil in the jack chamber  60  is likely to reach the reservoir chamber  40  through the fourth communication path R 4 . 
     With the front wheel side flow path switching unit  300  according to the embodiment, it is possible to control the opening and closing of the fourth on-off valve  304  by controlling the opening and closing of the third on-off valve  303 . Thus, it is possible to control whether or not the oil in the jack chamber  60  is oriented toward the reservoir chamber  40  with high accuracy. 
     Here, the third on-off valve  303  may transition to the third state where the axial through-hole  393  and the inflow path are open such that the gap G 2  between the third on-off valve  303  and the opening portion of the axial through-hole  393  of the fourth on-off valve  304  becomes the smallest restriction portion of the third communication path R 3 . In a case where the third on-off valve  303  is in the third state, the axial through-hole  393  of the fourth on-off valve  304  and the inflow path are open. Thus, the third communication path R 3  is open, and the oil in the jack chamber  60  reaches the reservoir chamber  40  through the third communication path R 3 . In addition, the pressure in the space S 1  which is the back pressure chamber of the fourth on-off valve  304  becomes lower than that of the jack chamber  60 . However, since the gap G 2  between the third on-off valve  303  and the opening portion of the axial through-hole  393  of the fourth on-off valve  304  is the smallest restriction portion of the third communication path R 3 , the pressure in the space S 1  is higher than that of the axial through-hole  393  of the fourth on-off valve  304 . Therefore, the position of the fourth on-off valve  304  is determined by the size of the pressure-receiving area A 1  of the fourth on-off valve  304  to which the pressure of the jack chamber  60  is applied in the closed state and the size of the pressure-receiving area A 2  to which the pressure in the space S 1  is applied. 
     Then, in a case where the third on-off valve  303  is in the third state, the pressure-receiving area A 2  of the fourth on-off valve  304  may be greater than the pressure-receiving area A 1  such that the fourth on-off valve  304  is closed. Accordingly, in a case where the third on-off valve  303  is in the third state, while the fourth on-off valve  304  is in the closed state, the oil in the jack chamber  60  can reach the reservoir chamber  40  only through the third communication path R 3 . Then, by reducing the flow path area of the third communication path R 3  to be smaller than the flow path area of the fourth communication path R 4 , it is possible to reduce the speed by which the oil in the jack chamber  60  reaches the reservoir chamber  40  in a case where the third on-off valve  303  is in the third state as compared with a case where the third on-off valve  303  is in the second state. In addition, as the fourth on-off valve  304  is in the closed state in a case where the third on-off valve  303  is in the third state, it is possible to more rapidly change from a state where the amount of oil in the jack chamber  60  is reduced and the vehicle height is low to a state where the amount of oil in the jack chamber  60  is maintained and the vehicle height is maintained, in a case where the third on-off valve  303  is in the third state as compared with a case where the fourth on-off valve  304  is in an open state. 
     The front fork  21  which is an example of a vehicle height adjustment apparatus according to embodiment as described above includes the spring  500 , the spring-length changing unit  250  which is an example of a changing device, the first on-off valve  301  which is an example of a first valve, the control valve  305  which is an example of a back pressure adjustment valve, and the second on-off valve  302 . One end of the spring  500  is supported on the vehicle body side. The other end of the spring  500  is supported on the wheel side. The spring-length changing unit  250  changes the length of the spring  500  in accordance with the amount of oil in the jack chamber  60  which is an example of the accommodation chamber that accommodates the oil. The first on-off valve  301  opens and closes the first communication path R 1  which is an example of a first flow path. In the first flow path, the oil supplied from the pump  600  is oriented toward the reservoir chamber  40  which is an example of a storage chamber. The control valve  305  opens and closes the discharge flow path oriented toward the reservoir chamber  40  from the first on-off valve back pressure chamber B 1  which is an example of a back pressure chamber. The first on-off valve back pressure chamber B 1  accommodates oil that applies the force in the direction in which the first on-off valve  301  is closed to the first on-off valve  301 . The second on-off valve  302  opens and closes the second communication path R 2  which is an example of a second flow path. In the second flow path, the oil supplied from the pump  600  is oriented toward the jack chamber  60  in a case where the first on-off valve  301  is in the closed state. 
     With the front fork  21  according to the embodiment configured as described above, in a case where the control valve  305  opens the discharge flow path oriented toward the reservoir chamber  40  from the first on-off valve back pressure chamber B 1 , the pressure in the first on-off valve back pressure chamber B 1  is low since the oil in the first on-off valve back pressure chamber B 1  is oriented toward the reservoir chamber  40 . As a result, the force in the direction in which the first on-off valve  301  is closed decreases, the first on-off valve  301  is open, and the oil supplied from the pump  600  is oriented toward the reservoir chamber  40 . Meanwhile, in a case where the control valve  305  closes the discharge flow path oriented toward the reservoir chamber  40  from the first on-off valve back pressure chamber B 1 , the pressure in the first on-off valve back pressure chamber B 1  is high since the oil in the first on-off valve back pressure chamber B 1  is unlikely to be oriented toward the reservoir chamber  40 . As a result, the force in the direction in which the first on-off valve  301  is closed increases, the first on-off valve  301  is unlikely to be open, and the oil supplied from the pump  600  is unlikely to be oriented toward the reservoir chamber  40 . Then, in the front fork  21  according to the embodiment, in a case where the first on-off valve  301  is closed, the second on-off valve  302  opens the second communication path R 2 . Thus, the oil supplied from the pump  600  is oriented toward the jack chamber  60  through the second communication path R 2 . With the front fork  21  according to the embodiment, it is possible to control the opening and closing of the first on-off valve  301  by controlling the position of the control valve  305 . Thus, it is possible to control whether the oil supplied from the pump  600  is oriented toward the reservoir chamber  40  or is oriented toward the jack chamber  60 , with high accuracy. Therefore, it is possible to control the length of the spring  500  with high accuracy by controlling the position of the control valve  305 , and to adjust the vehicle height with high accuracy. 
     Then, the front fork  21  may further include the unit main body  330  which is an example of a flow path forming member. The unit main body  330  forms the discharge flow path oriented toward the reservoir chamber  40  from the first on-off valve back pressure chamber B 1  via the upper end side center recess portion  342  which is an example of a recess portion that is recessed from the first on-off valve back pressure chamber B 1 . The control valve  305  may be fitted to the upper end side center recess portion  342  of the unit main body  330  to be movable between a position at which the discharge flow path is open and a position at which the discharge flow path is closed. Accordingly, it is possible to control the pressure in the first on-off valve back pressure chamber B 1  with high accuracy by controlling the position of the control valve  305 , and to control the opening and closing of the first on-off valve  301  with high accuracy. As a result, it is possible to adjust the vehicle height with high accuracy. 
     In addition, the front fork  21  may further include the third on-off valve  303  which is an example of a third valve. The third on-off valve  303  opens and closes the third communication path R 3  which is an example of a third flow path oriented toward the reservoir chamber  40  from the jack chamber  60  by moving in accordance with the position of the control valve  305 . Accordingly, it is possible to control the position of the third on-off valve  303  by controlling the position of the control valve  305 , and to control the opening and closing of the third communication path R 3  oriented toward the reservoir chamber  40  from the jack chamber  60  with high accuracy. Therefore, it is possible to control whether the amount of oil in the jack chamber  60  is reduced by allowing the oil in the jack chamber  60  to be oriented toward the reservoir chamber  40 , or the amount of oil in the jack chamber  60  is maintained with high accuracy, and to adjust the vehicle height with high accuracy. 
     In addition, the front fork  21  may further include the fourth on-off valve  304  which is an example of a fourth valve. The fourth on-off valve  304  opens and closes the fourth communication path R 4  which is an example of a fourth flow path, by moving in accordance with the position of the third on-off valve  303 . The fourth communication path R 4  is a flow path oriented toward the reservoir chamber  40  from the jack chamber  60 . The flow path area of the fourth communication path R 4  is greater than that of the third communication path R 3 . Accordingly, it is possible to control the position of the fourth on-off valve  304  by controlling the position of the control valve  305  that controls the position of the third on-off valve  303 , and to control the opening and closing of the fourth communication path R 4  oriented toward the reservoir chamber  40  from the jack chamber  60  with high accuracy. Therefore, it is possible to control whether the amount of oil in the jack chamber  60  rapidly decreases by allowing the oil in the jack chamber  60  to be oriented toward the reservoir chamber  40  through the fourth communication path R 4  having a large flow path area, or the amount of oil in the jack chamber  60  slowly decreases by allowing the oil in the jack chamber  60  to be oriented toward the reservoir chamber  40  through the third communication path R 3  having a small flow path area, and to adjust the vehicle height with high accuracy. 
     In addition, the third on-off valve  303  may be provided on the third communication path R 3  and in the space S 1  which is an example of a fourth valve back pressure chamber that accommodates oil which applies the force in the direction in which the fourth on-off valve  304  is closed to the fourth on-off valve  304 . The third on-off valve  303  may move between a position at which the inflow path that reaches the space S 1  from the jack chamber  60  is open and a position at which the inflow path is closed. In a case where the third on-off valve  303  is at a position at which the inflow path that reaches the space S 1  from the jack chamber  60  is closed, the oil is not supplied to the space S 1  which becomes the back pressure chamber of the fourth on-off valve  304 . Thus, the pressure becomes lower than that of the jack chamber  60 . Therefore, the fourth on-off valve  304  is likely to move to the space S 1 , and the fourth on-off valve  304  is likely to be open. Meanwhile, in a case where the third on-off valve  303  is at a position at which the inflow path is open, the oil is supplied to the space S 1  which becomes the back pressure chamber of the fourth on-off valve  304 . Thus, the pressure becomes lower than that in a case where the third on-off valve  303  is at a position at which the inflow path is closed. Therefore, the fourth on-off valve  304  is unlikely to move to the space S 1 , and the fourth on-off valve  304  is unlikely to be open. With the front fork  21  according to the embodiment, by controlling the position of the third on-off valve  303 , it is possible to control the open and closed state of the fourth on-off valve  304  with high accuracy. 
     Modification Example of Control Valve  305   
     In the control valve  305  according to the above-described embodiment, in order to perform sequential transition to the maintaining mode, the raising mode, and the lowering mode in order in accordance with the increase in amount of current to be supplied, a relationship between the amount of protrusion of the operation rod  324  and the position of the groove  305   a  of the control valve  305  is defined. In other words, in a case where the amount of protrusion of the operation rod  324  is less than the first reference amount, the position in the axial direction of the groove  305   a  of the control valve  305  overlaps the first radial communication hole  349   a  of the unit main body  330 , and in a case where the amount of protrusion of the operation rod  324  is equal to or greater than the first reference amount, the position in the axial direction of the groove  305   a  becomes a position below the first radial communication hole  349   a . Meanwhile, in a case where the amount of protrusion of the operation rod  324  is less than the first reference amount, the position in the axial direction of the groove  305   a  of the control valve  305  becomes the position above the first radial communication hole  349   a  of the unit main body  330 , and in a case where the amount of protrusion of the operation rod  324  is equal to or greater than the first reference amount, by forming the groove  305   a  such that the position in the axial direction of the groove  305   a  overlaps the first radial communication hole  349   a , sequential transition from the raising mode, to the maintaining mode, and to the lowering mode in accordance with the increase in amount of current to be supplied can be performed. In other words, only by changing the position of the groove  305   a  of the control valve  305 , it is possible to realize the front wheel side flow path switching unit  300  which sequentially transitions from the raising mode, to the maintaining mode, and to the lowering mode. 
     Modification Example of Front Wheel Side Flow Path Switching Unit  300   
     A front wheel side solenoid  310  according to the above-described embodiment generates an axial thrust force to a plunger  313  in such a way that the amount of protrusion of an operation rod  314  from the case  315  increases to the extent that energization current to a coil  311  increases; however, the invention is not particularly limited thereto. For example, the front wheel side solenoid  310  may generate an axial thrust force to the plunger  313  in such a way that the amount of protrusion of the operation rod  314  from the case  315  decreases to the extent that energization current to the coil  311  increases. The front wheel side flow path switching unit  300  with this configuration as a single unit can control the three control modes according to the amount of current: the raising mode in which the vehicle height is raised; the lowering mode in which the vehicle height is lowered; and the maintaining mode in which the vehicle height is maintained. 
     In addition, in the above-described embodiment, a configuration in which the front wheel side flow path switching unit  300  which can be switched to three control modes including the raising mode, the lowering mode, and the maintaining mode is employed in the front fork  21  is illustrated, but the invention is not particularly limited. The front wheel side flow path switching unit  300  according to the above-described embodiment may be employed in the rear suspension  22 .