以下，根據圖所示之實施方式，說明本發明。如圖1及圖2所示般，一個實施方式之後緩衝單元RCU，具備：缸1；活塞2，可移動地***缸1內以將缸1內區隔成填充有液體的伸側室R1和壓側室R2；活塞桿3，可移動地***缸1內並且連結於活塞2；槽4，用於儲存液體；第1通路P1及第2通路P2，分別並列且將伸側室R1和壓側室R2連通；第3通路P3，將壓側室R2和槽4連通；伸側抑振力調整通路P4，設置於缸1的外側且將伸側室R1和壓側室R2連通；伸側抑振閥5，設置於第1通路P1並對於從伸側室R1朝向壓側室R2的液體流動給予阻力；壓側止回閥6，設置於第2通路P2並僅容許從壓側室R2朝向伸側室R1的液體流動；以及伸側抑振力調整閥EV，設置於伸側抑振力調整通路P4且可藉由來自於外側的操作而變更流路面積。
而且，此後緩衝單元RCU，如圖2所示般，介設於摩托車等的跨騎型車輛M的車體F和後輪W之間使用，以抑制車體F及後輪W的振動。
以下，針對後緩衝單元RCU的各部進行詳細說明。如圖1所示般，在本實施方式的後緩衝單元RCU中，具備配置於缸1的外周側且包覆缸1的外筒15。在缸1和外筒15之間，設置有形成伸側抑振力調整通路P4之環狀的間隙。
在缸1和外筒15的圖1中上端，裝設上部蓋11，缸1和外筒15的上端的開口藉由上部蓋11閉塞。
另外，在缸1的圖1中下端，嵌合環狀的桿導件7。桿導件7，具備：嵌合於外筒15的內周之環狀的本體7a、以及從本體7a的圖1中上端突出且嵌合於缸1的內周的凸部7b。另外，在桿導件7，從凸部7b的外周到本體7a形成凹槽7c。當將桿導件7嵌合於外筒15及缸1時，凸部7b嵌合於缸1的內周但通過凹槽7c而缸1內與形成於缸1和外筒15之間的伸側抑振力調整通路P4連通。
另外，在環狀的密封構件8及環狀的板9重疊於環狀的桿導件7的下方的狀態，***於外筒15的圖1中下端的內周。而且，***外筒15內的缸1、桿導件7、密封構件8及板9，藉由將外筒15的下端緊固所形成的緊固部15a和上部蓋11來夾住，以固定成相對於外筒15不動。此外，對於缸1、桿導件7、密封構件8及板9的外筒15的固定手段，可以任意設計變更。
另外，於上端裝設活塞2的活塞桿3，可移動地***缸1內。活塞桿3滑動自如地插穿密封構件8的內周及桿導件7的內周且***於缸1內，藉由桿導件7導引朝軸方向的移動。密封構件8是滑接於活塞桿3的外周且將活塞桿3的外周密封而將缸1內密閉。
缸1內藉由活塞2，區隔成填充有液體的伸側室R1和壓側室R2。所以，伸側抑振力調整通路P4，通過桿導件7的凹槽7c與伸側室R1連通。此外，液體，在本實施方式中，設定為液壓油，但液壓油以外，也可以使用例如水、水溶液這類液體。
在活塞桿3的圖1中下端，安裝有可與保持跨騎型車輛M之後輪W的擺臂SA連結的支架B1，另外，筒狀的凸緣緩衝墊14裝設在圖1中下端附近的外周。
凸緣緩衝墊14當在後緩衝單元RCU最收縮時與固定於外筒15的下端內周的板9抵接而被壓縮時，發揮反彈力來緩和後緩衝單元RCU的最收縮時的衝撃。
在活塞2，設置分別並列且將伸側室R1和壓側室R2連通的第1通路P1及第2通路P2。並且，在活塞2，設置：伸側抑振閥，可將第1通路P1開閉並對於從伸側室R1朝向壓側室R2的液體流動給予阻力；以及壓側止回閥6，可將第2通路P2開閉並僅容許從壓側室R2朝向伸側室R1的液體流動。
伸側抑振閥5，只要是對於從伸側室R1朝向壓側室R2的液壓油流動給予阻力，在後緩衝單元RCU的伸長作動時可以發揮妨礙後緩衝單元RCU的伸長的抑振力的閥的話即可。此外，具體來說，伸側抑振閥5，例如，設定成將環狀板複數片積層於活塞2的圖1中上端所構成且藉由伸側室R1的壓力彎曲時將第1通路P1開放的疊片閥等的話即可。
另外，壓側止回閥6，只要是可以容許在後緩衝單元RCU的收縮作動時僅對於從壓側室R2朝向伸側室R1的液壓油流動不給予太大阻力地的閥的話即可。此外，具體來說，壓側止回閥6，例如，設定成由重疊於活塞2的圖1中下端的環狀板和將該環狀板緊壓的彈簧常數較小的彈簧所構成且藉由壓側室R2的壓力而將第2通路P2開放的閥等的話即可。
在本實施方式中，上部蓋11，具備：蓋11a，裝設於缸1的圖1中上端；槽保持部11b，用於保持槽4；連接部11c，從蓋部11a的側方延伸而連接於槽保持部11b並且包含第3通路P3；筒狀的第1閥箱11d，設置於蓋11a且形成收容伸側抑振力調整閥EV的第1閥孔h1；以及筒狀的第2閥箱11e，形成收容設置於第3通路P3之途中的閥單元V的第2閥孔h2。
蓋11a嵌合於缸1的圖3中上端並且在外周螺紋結合於外筒15，而將缸1及外筒15的上端閉塞，並且於圖3中上方具備可連結於跨騎型車輛M之車體F的支架B2。另外，連接部11c，從蓋11a的側方突出且朝向圖3中下方彎曲而連接於插座狀的槽保持部11b。此外，在上部蓋11之蓋11a和外筒15的外周，嵌合筒狀的彈簧支座16。在彈簧支座16和活塞桿3的下端的支架B1之間，介設由螺旋彈簧所成的懸吊彈簧S。懸吊彈簧S，始終使活塞桿3朝從缸1突出的方向，換言之，朝使後緩衝單元RCU伸長的方向彈壓，當將後緩衝單元RCU介裝於跨騎型車輛M的車體F和後輪W之間時，將車體F彈性地支撐。
槽保持部11b，為有頂筒狀且上端一體連接於連接部11c的下端，在下端外周具備螺紋部11b1。而且，筒狀的槽4螺接於槽保持部11b的下端外周的螺紋部11b1。
在本實施方式中，槽4是圓筒狀且螺接於槽保持部11b。而且，在槽4內，***隔膜12，槽4內藉由隔膜12區隔成填充有液體的液室L、以及填充有氣體的氣室G。此外，在氣室G，以在後緩衝單元RCU的最伸長時至少氣室G內的壓力成為大氣壓以上的方式封入氣體。此外，槽4內的液室L和氣室G的區劃，除了利用隔膜12以外，也可以利用自由活塞及氣囊等。
槽4之液室L，經由設置於連接部11c的內部的埠11c1而連通於第2閥箱11e內。另外，第2閥箱11e內經由設置於蓋11a的埠11a2而連通於壓側室R2。所以，液室L，經由埠11c1、第2閥箱11e內及埠11a2而連通於壓側室R2。
第1閥箱11d和第2閥箱11e，為蓋11a的側部且隔著連接部11c被設置於連接部11c的兩側。具體來說，如圖4所示般，第1閥箱11d為筒狀，配置於連接部11c的右側並以使自身的軸線L1正交於缸1的軸線LC的方式，設置於蓋11a。第2閥箱11e為筒狀，配置於連接部11c的左側並以使自身的軸線L2正交於缸1的軸線LC的方式，設置於蓋11a。此外，第1閥箱11d和第2閥箱11e相對於蓋11a的安裝位置，不限於前述的位置，可變更設計。The present invention is described below according to the embodiment shown in the figure. As shown in Figures 1 and 2, in one embodiment, the rear buffer unit RCU comprises: a cylinder 1; a piston 2, which is movably inserted into the cylinder 1 to divide the cylinder 1 into an extension chamber R1 and a pressure chamber R2 filled with liquid; a piston rod 3, which is movably inserted into the cylinder 1 and connected to the piston 2; a groove 4 for storing liquid; a first passage P1 and a second passage P2, which are respectively parallel and connect the extension chamber R1 and the pressure chamber R2; a third passage P3, which connects the pressure chamber R2 and the groove 4; an extension vibration damping device; a second passage P1 and a second passage P2, which are respectively parallel and connect the extension chamber R1 and the pressure chamber R2; a third passage P3, which connects the pressure chamber R2 and the groove 4; an extension vibration damping device; a second passage P2 and a second passage P3, which connect the pressure chamber R2 and the groove 4; a second passage P1 and a second passage P2, which are parallel and connect the extension chamber R1 and the pressure chamber R2; a third passage P3, which connects the pressure chamber R2 and the groove 4; a second passage P1 and a second passage P2, which ... The force adjustment passage P4 is provided on the outside of the cylinder 1 and connects the extension chamber R1 and the pressure chamber R2; the extension vibration damping valve 5 is provided on the first passage P1 and provides resistance to the flow of liquid from the extension chamber R1 to the pressure chamber R2; the pressure check valve 6 is provided on the second passage P2 and only allows the flow of liquid from the pressure chamber R2 to the extension chamber R1; and the extension vibration damping force adjustment valve EV is provided on the extension vibration damping force adjustment passage P4 and can change the flow area by operation from the outside.
Moreover, the rear buffer unit RCU is used between the body F and the rear wheel W of a straddle-type vehicle M such as a motorcycle as shown in FIG2 to suppress the vibration of the body F and the rear wheel W.
Below, each part of the rear buffer unit RCU is described in detail. As shown in FIG1, in the rear buffer unit RCU of the present embodiment, there is an outer cylinder 15 arranged on the outer peripheral side of the cylinder 1 and covering the cylinder 1. Between the cylinder 1 and the outer cylinder 15, there is provided an annular gap forming an extension side vibration suppression force adjustment passage P4.
At the upper end of the cylinder 1 and the outer cylinder 15 in FIG1, an upper cover 11 is installed, and the openings of the upper ends of the cylinder 1 and the outer cylinder 15 are closed by the upper cover 11.
In addition, an annular rod guide 7 is fitted at the lower end of the cylinder 1 in FIG1. The rod guide 7 has an annular main body 7a fitted in the inner periphery of the outer cylinder 15, and a convex portion 7b protruding from the upper end of the main body 7a in FIG1 and fitted in the inner periphery of the cylinder 1. In addition, a groove 7c is formed in the rod guide 7 from the outer periphery of the convex portion 7b to the main body 7a. When the rod guide 7 is fitted in the outer cylinder 15 and the cylinder 1, the convex portion 7b is fitted in the inner periphery of the cylinder 1, but the cylinder 1 communicates with the extension-side vibration-damping force adjustment passage P4 formed between the cylinder 1 and the outer cylinder 15 through the groove 7c.
In addition, in a state where the annular sealing member 8 and the annular plate 9 are overlapped below the annular rod guide 7, it is inserted into the inner periphery of the lower end of the outer cylinder 15 in FIG1. Furthermore, the cylinder 1, the rod guide 7, the sealing member 8 and the plate 9 inserted into the outer cylinder 15 are clamped by the fastening portion 15a formed by fastening the lower end of the outer cylinder 15 and the upper cover 11 to be fixed relative to the outer cylinder 15. In addition, the fixing means of the outer cylinder 15 of the cylinder 1, the rod guide 7, the sealing member 8 and the plate 9 can be arbitrarily designed and changed.
In addition, the piston rod 3 with the piston 2 installed at the upper end can be movably inserted into the cylinder 1. The piston rod 3 is inserted into the cylinder 1 while slidingly passing through the inner periphery of the sealing member 8 and the inner periphery of the rod guide 7, and is inserted into the cylinder 1, and the movement in the axial direction is guided by the rod guide 7. The sealing member 8 is slidably connected to the outer periphery of the piston rod 3 and seals the outer periphery of the piston rod 3 to seal the inside of the cylinder 1.
The cylinder 1 is divided into an extension chamber R1 and a compression chamber R2 filled with liquid by the piston 2. Therefore, the extension vibration damping force adjustment passage P4 is connected to the extension chamber R1 through the groove 7c of the rod guide 7. In addition, the liquid is set to hydraulic oil in this embodiment, but liquids such as water and aqueous solutions can also be used in addition to hydraulic oil.
At the lower end of the piston rod 3 in Figure 1, a bracket B1 that can be connected to the swing arm SA that holds the rear wheel W of the straddle-type vehicle M is installed, and a cylindrical flange buffer 14 is installed on the outer periphery near the lower end in Figure 1.
When the flange cushion 14 is compressed by contacting the plate 9 fixed to the inner circumference of the lower end of the outer cylinder 15 when the rear cushion unit RCU is most contracted, the rebound force is exerted to cushion the impact of the rear cushion unit RCU when it is most contracted.
In the piston 2, the first passage P1 and the second passage P2 are provided which are parallel and connect the extension chamber R1 and the compression chamber R2. Furthermore, the piston 2 is provided with: an extension-side vibration damping valve that can open and close the first passage P1 and provide resistance to the flow of liquid from the extension-side chamber R1 to the pressure-side chamber R2; and a pressure-side check valve 6 that can open and close the second passage P2 and only allow the flow of liquid from the pressure-side chamber R2 to the extension-side chamber R1.
The extension-side vibration damping valve 5 can be any valve that provides resistance to the flow of hydraulic oil from the extension-side chamber R1 to the pressure-side chamber R2 and can exert a vibration damping force that hinders the extension of the rear buffer unit RCU during the extension action of the rear buffer unit RCU. In addition, specifically, the extension side damping valve 5 may be, for example, a stacked valve formed by stacking a plurality of annular plates on the upper end of the piston 2 in FIG. 1 and opening the first passage P1 when the extension side chamber R1 is bent by the pressure.
In addition, the pressure side check valve 6 may be a valve that allows the hydraulic oil to flow from the pressure side chamber R2 toward the extension side chamber R1 without providing much resistance during the contraction of the rear buffer unit RCU. In addition, specifically, the pressure-side check valve 6 may be configured as a valve that is composed of, for example, an annular plate superimposed on the lower end of the piston 2 in FIG. 1 and a spring with a smaller spring constant that presses the annular plate, and opens the second passage P2 by the pressure of the pressure-side chamber R2.
In this embodiment, the upper cover 11 comprises: a cover 11a, which is mounted on the upper end of the cylinder 1 in FIG. 1; a groove holding portion 11b, which is used to hold the groove 4; a connecting portion 11c, which extends from the side of the cover 11a and is connected to the groove holding portion 11b and includes a third passage P3; a cylindrical first valve box 11d, which is arranged on the cover 11a and forms a first valve hole h1 for accommodating the extension-side vibration damping force adjustment valve EV; and a cylindrical second valve box 11e, which forms a second valve hole h2 for accommodating the valve unit V arranged in the middle of the third passage P3.
The cover 11a is fitted in the upper end of the cylinder 1 in FIG3 and is threadedly coupled to the outer cylinder 15 at the outer circumference, thereby closing the upper ends of the cylinder 1 and the outer cylinder 15, and a bracket B2 is provided at the upper end in FIG3 that can be connected to the body F of the straddle-type vehicle M. In addition, the connecting portion 11c protrudes from the side of the cover 11a and is bent downward in FIG3 to be connected to the socket-shaped groove holding portion 11b. In addition, a cylindrical spring support 16 is fitted in the outer circumference of the cover 11a and the outer cylinder 15 of the upper cover 11. A suspension spring S composed of a coil spring is interposed between the spring support 16 and the bracket B1 at the lower end of the piston rod 3. The suspension spring S always presses the piston rod 3 in the direction of protruding from the cylinder 1, in other words, in the direction of extending the rear shock absorber unit RCU, and elastically supports the body F when the rear shock absorber unit RCU is installed between the body F and the rear wheel W of the straddle-type vehicle M.
The groove retaining portion 11b is a top-cylindrical shape, and the upper end is integrally connected to the lower end of the connecting portion 11c, and a threaded portion 11b1 is provided on the outer periphery of the lower end. Moreover, the cylindrical groove 4 is screwed to the threaded portion 11b1 on the outer periphery of the lower end of the groove retaining portion 11b.
In this embodiment, the groove 4 is cylindrical and screwed to the groove retaining portion 11b. Furthermore, a diaphragm 12 is inserted into the groove 4, and the groove 4 is divided into a liquid chamber L filled with liquid and an air chamber G filled with gas by the diaphragm 12. In addition, in the air chamber G, gas is sealed in such a way that the pressure in at least the air chamber G becomes greater than atmospheric pressure when the rear cushion unit RCU is most extended. In addition, the division of the liquid chamber L and the air chamber G in the groove 4 can also be made by using a free piston and an air bag, in addition to the diaphragm 12.
The liquid chamber L of the groove 4 is connected to the second valve box 11e through the port 11c1 provided inside the connecting portion 11c. In addition, the second valve box 11e is connected to the pressure side chamber R2 through the port 11a2 provided on the cover 11a. Therefore, the liquid chamber L is connected to the pressure side chamber R2 through the port 11c1, the second valve box 11e and the port 11a2.
The first valve box 11d and the second valve box 11e are the side parts of the cover 11a and are arranged on both sides of the connecting part 11c across the connecting part 11c. Specifically, as shown in FIG. 4, the first valve box 11d is cylindrical, arranged on the right side of the connecting part 11c and arranged on the cover 11a in such a manner that its axis L1 is orthogonal to the axis LC of the cylinder 1. The second valve box 11e is cylindrical, arranged on the left side of the connecting part 11c and arranged on the cover 11a in such a manner that its axis L2 is orthogonal to the axis LC of the cylinder 1. In addition, the installation positions of the first valve casing 11d and the second valve casing 11e relative to the cover 11a are not limited to the above-mentioned positions, and the design can be changed.
第1閥箱11d形成第1閥孔h1，第2閥箱11e形成第2閥孔h2。而且，在本實施方式的後緩衝單元RCU中，由於第1閥箱11d的軸線L1和第2閥箱11e的軸線L2正交於缸1的軸線LC，因而第1閥孔h1和第2閥孔h2隔著連接部11c且以缸1的軸線LC為中心被配置成放射狀。
The first valve box 11d forms the first valve hole h1, and the second valve box 11e forms the second valve hole h2. In addition, in the rear buffer unit RCU of the present embodiment, since the axis L1 of the first valve box 11d and the axis L2 of the second valve box 11e are orthogonal to the axis LC of the cylinder 1, the first valve hole h1 and the second valve hole h2 are arranged radially with the connecting portion 11c as the center and the axis LC of the cylinder 1 as the center.
另外，在蓋11a設置埠11a1，該埠11a1係在第1閥孔h1的底部開口且連通於缸1內的壓側室R2。並且，第1閥孔h1的側部，通過缸1和外筒15之間的伸側抑振力調整通路P4而通往伸側室R1。所以，伸側室R1和壓側室R2，藉由伸側抑振力調整通路P4和第1閥孔h1而繞過設置於活塞2的第1通路P1及第2通路P2進行連通。
In addition, a port 11a1 is provided on the cover 11a, and the port 11a1 is opened at the bottom of the first valve hole h1 and connected to the pressure side chamber R2 in the cylinder 1. In addition, the side of the first valve hole h1 is connected to the extension side chamber R1 through the extension side vibration damping force adjustment passage P4 between the cylinder 1 and the outer tube 15. Therefore, the extension side chamber R1 and the pressure side chamber R2 are connected through the extension side vibration damping force adjustment passage P4 and the first valve hole h1, bypassing the first passage P1 and the second passage P2 provided in the piston 2.
如前述般，在蓋11a設置埠11a2，該埠11a2係在第2閥孔h2的底部開口且連通於缸1內的壓側室R2。並且，第2閥孔h2的側部，通過形成於連接部11c內的埠11c1而與受槽保持部11b保持的槽4內連通。如此般，在本實施方式的後緩衝單元RCU中，上部蓋11由埠11a2、埠11c1及第2閥孔h2形成且具備將壓側室R2和槽4連通的第3通路P3。
As mentioned above, the cover 11a is provided with a port 11a2, which is opened at the bottom of the second valve hole h2 and connected to the pressure side chamber R2 in the cylinder 1. In addition, the side of the second valve hole h2 is connected to the groove 4 held by the groove holding part 11b through the port 11c1 formed in the connecting part 11c. In this way, in the rear buffer unit RCU of the present embodiment, the upper cover 11 is formed by the port 11a2, the port 11c1 and the second valve hole h2 and has a third passage P3 that connects the pressure side chamber R2 and the groove 4.
上部蓋11將缸1和槽4連結，並具備：收容伸側抑振力調整閥EV的第1閥孔h1、以及在第3通路P3的途中收容閥單元V的第2閥孔h2。而且，上部蓋11，在將缸1的上端閉塞的蓋11a的側方具備形成第1閥孔h1的第1閥箱11d和形成第2閥孔h2的第2閥箱11e，具備在連接部11c的下方安裝槽4的槽保持部11b。所以，可以抑制將伸側抑振力調整閥EV及閥單元V配置於缸1的側方而後緩衝單元RCU的全長
變長的情形。此外，第1閥孔h1及第2閥孔h2，由相對於缸1沿著徑方向配置的第1閥箱11d和第2閥箱11e所形成，並且由於開口端朝向反缸側，因而伸側抑振力調整閥EV及閥單元V的拆卸也容易從後緩衝單元RCU的側方進行。
The upper cover 11 connects the cylinder 1 and the groove 4, and has a first valve hole h1 for accommodating the extension-side vibration-damping force adjustment valve EV, and a second valve hole h2 for accommodating the valve unit V in the middle of the third passage P3. In addition, the upper cover 11 has a first valve box 11d for forming the first valve hole h1 and a second valve box 11e for forming the second valve hole h2 on the side of the cover 11a that closes the upper end of the cylinder 1, and has a groove holding portion 11b for mounting the groove 4 below the connecting portion 11c. Therefore, it is possible to prevent the overall length of the buffer unit RCU from increasing when the extension-side vibration-damping force adjustment valve EV and the valve unit V are arranged on the side of the cylinder 1. In addition, the first valve hole h1 and the second valve hole h2 are formed by the first valve box 11d and the second valve box 11e arranged along the radial direction relative to the cylinder 1, and because the opening end faces the anti-cylinder side, the extension-side vibration damping force adjustment valve EV and the valve unit V can also be easily disassembled from the side of the rear buffer unit RCU.
如圖5所示般，在第1閥箱11d的開口端的內周形成螺紋部11d1，並且在比螺紋部11d1更靠軸方向，於內側朝周方向等間隔地沿著軸方向設置複數條的凹槽11d2。
As shown in FIG. 5 , a threaded portion 11d1 is formed on the inner periphery of the opening end of the first valve box 11d, and a plurality of grooves 11d2 are provided at equal intervals along the axial direction on the inner side of the threaded portion 11d1 and in the circumferential direction.
而且，在藉由第1閥箱11d形成的第1閥孔h1內，收容伸側抑振力調整閥EV。伸側抑振力調整閥EV，具備：環狀閥座50；閥體51，呈軸狀且在前端具有可遠離或接近於環狀閥座50的閥頭51b；以及筒狀的箱52，螺絲緊固於螺紋部11d1而將閥體51裝設於第1閥箱11d。閥體51，被可朝軸方向的移動地收容於第1閥箱11d。
Furthermore, the extension-side vibration damping force adjusting valve EV is accommodated in the first valve hole h1 formed by the first valve box 11d. The extension-side vibration damping force adjusting valve EV comprises: an annular valve seat 50; a valve body 51, which is axial and has a valve head 51b at the front end that can be away from or close to the annular valve seat 50; and a cylindrical box 52, which is screwed to the threaded portion 11d1 to install the valve body 51 in the first valve box 11d. The valve body 51 is accommodated in the first valve box 11d so as to be movable in the axial direction.
環狀閥座50由形成第1閥孔h1的蓋11a的埠11a1的周圍所形成。如圖5所示般，閥體51，具備：圓柱狀的胴部51a；閥頭51b，從胴部51a的前端朝軸方向突出；以及小徑部51c，從胴部51a的後端朝軸方向延伸且外徑小於胴部51a。
The annular valve seat 50 is formed around the port 11a1 of the cover 11a forming the first valve hole h1. As shown in FIG5 , the valve body 51 has: a cylindrical body 51a; a valve head 51b protruding from the front end of the body 51a in the axial direction; and a small diameter portion 51c extending from the rear end of the body 51a in the axial direction and having an outer diameter smaller than that of the body 51a.
胴部51a，具備：螺紋部51a1，設置於外周；貫穿孔51a2，將胴部51a朝徑方向貫穿；以及密封環51a4，裝設於外周且設置於比貫通孔51a2更前端側的環狀凹槽51a3。當將閥體51***由第1閥箱11d形成的第1閥孔h1內時，胴部51a嵌合於第1閥箱11d的內周，密封環51a4滑接於第1閥箱11d的內周，以將第1閥孔h1內密閉。另外，胴部51a，即使閥體51於第1閥箱11d內朝軸方向移動，仍始終配置於比相對於第1閥孔h1的伸側抑振力調整通路P4的開口部更靠成為大氣側的圖5中左方側，不將前述開口部閉塞。
閥頭51b，具備：圓柱狀的軸部51b1，從胴部51a朝軸方向延伸；圓錐形的針51b2，設置於軸部51b1的前端且可侵入環狀閥座50的內周，換言之即埠11a1內。此外，針51b2的形狀是前端尖細的形狀，而且只要是可藉由對於環狀閥座50之朝軸方向的移動來調整流路面積的話也可以是圓錐形以外的形狀。
軸部51b1的外徑，其直徑大於埠11a1的直徑，軸部51b1的端面的外周於環狀閥座50在軸方向上相對向，並且，針51b2的基端的外徑成為直徑大於埠11a1的直徑。所以，當使閥體51於第1閥箱11d內朝侵入至最深部的方向移動時，針51b2的側面就座於環狀閥座50的內緣而可以將埠11a1遮斷。另外，在針51b2的側面從環狀閥座50離開的狀態下，在針51b2和環狀閥座50的內緣之間產生間隙而開放埠11a1，藉由閥體51之朝軸方向的移動使前述間隙變大縮小而可以調整對於通過埠11a1之液體流動給予的阻力大小。此外，也可以將針51b2的基端的外徑形成為直徑小於埠11a1的直徑，使軸部51b1的右端抵接於環狀閥座50以將埠11a1遮斷。另外，小徑部51c從胴部51a的後端朝軸方向延伸，在後端設置可進行來自於外部的操作的凹槽51c1。
箱52是筒狀且大氣側的內徑成為小徑，可在內周具備階差部52a，並且分別在外周和內周的階差部52a的反大氣側具備螺紋部52b和螺紋部52c。
在箱52內***閥體51，胴部51a的螺紋部51a1螺合於箱52的內周的螺紋部52c。小徑部51c的外徑形成為可嵌合於箱52的大氣側的內徑的直徑，裝設於小徑部51c的外周的密封環51c2密合於箱52的內周而密封閥體51和箱52之間。
而且，在內周側螺合有閥體51的箱52，***第1閥箱11d內，並且將外周的螺紋部52b螺合於螺紋部11d1而固定於第1閥箱11d。當如此般將閥體51和箱52安裝於第1閥箱11d時，由於以閥體51和箱52形成進給螺絲機構，因而當使用者將螺絲起子等的工具***小徑部51c的凹槽51c1來將閥體51進行旋轉操作時，閥體51在第1閥孔h1內朝軸方向移動。由於如此般閥體51可在第1閥孔h1內朝軸方向移動，因而閥頭51b可以對於環狀閥座50遠離或接近而開閉埠11a1，並且可以藉由針51b2和環狀閥座50之間的間隙調整而調整對於通過埠11a1之液體流動給予的阻力。
此外，在設置於閥體51的胴部51a的貫穿孔51a2內，***2個的球53、54；以及配置於球53、54間的彈簧55，當將閥體51***第1閥箱11d內時，貫穿孔51a2相對向於在第1閥箱11d的內周形成的凹槽11d2。球53、54藉由彈簧55從貫穿孔51a2朝往外側突出的方向彈壓，第1閥箱11d、球53、54及彈簧55，形成掣子機構。所以，球53、54相對向於凹槽11d2而進入時只要不以掣動力矩以上的力矩使閥體51旋轉，就可以限制閥體51對於第1閥箱11d之朝周方向的旋轉。由於如此般藉由掣子機構維持閥體51和環狀閥座50的位置關係，因而可以防止在跨騎型車輛M的行走中伸側抑振力調整閥EV之流路面積任意變化的情形。
如圖1及圖7所示般，如此般構成的伸側抑振力調整閥EV，從軸方向觀看缸1和外筒15時，閥頭51b被配置於缸1和外筒15之間的範圍。所以，由於將伸側抑振力調整閥EV配置於缸1和外筒15的端部附近的同時可以配置於儘可能靠近缸1的軸線LC的位置，因而即使設置伸側抑振力調整閥EV仍可免於招致後緩衝單元RCU的全長的細長化和徑方向的大型化。
在本實施方式的後緩衝單元RCU中，設置於第3通路P3之途中的閥單元V，被收容於由第2閥箱11e形成的第2閥孔h2內。閥單元V可拆卸地收容於形成上部蓋11之第2閥孔h2的第2閥箱11e。
如圖6所示般，閥單元V，具備：壓側抑振通路PV1、壓側釋壓通路PV2、吸入通路PV3及壓側抑振力調整通路PV4，並列地連接於第3通路P3的途中；壓側抑振閥V1，設置於壓側抑振通路PV1且對於從壓側室R2朝向槽4的液體流動給予阻力；壓側釋壓閥V2，設置於壓側釋壓通路PV2且並列配置於壓側抑振閥V1，在閉閥時阻斷壓側室R2和槽4的連通，並且當壓側室R2的壓力和槽4的壓力的差壓達到開閥壓時，開閥而容許從壓側室R2朝向槽4的液體流動；伸側止回閥V3，設置於吸入通路PV3且並列配置於壓側抑振閥V1而僅容許從槽4朝向壓側室R2的液體流動；以及針閥V4，設置於壓側抑振力調整通路PV4且並列配置於壓側抑振閥V1，而對往來於槽4和壓側室R2的液體流動給予阻力，並且可藉由外部操作去調整該阻力。
具體來說，閥單元V，具備：筒狀的閥保持軸21，***於上部蓋11之第2閥孔h2內；針22，***於閥保持軸21內；閥盤23，裝設於閥保持軸21的外周；軸環24，裝設於閥保持軸21的外周；環狀的間隔件25、環狀板26及環狀板27，可軸方向移動地嵌合於軸環24的外周；盤形彈簧28，同樣配置於軸環24的外周，將間隔件25、環狀板26及環狀板27朝向閥盤23側彈壓；螺帽29，將閥盤23和軸環24固定於閥保持軸21；閥體30及彈簧31，收容於針22內；以及筒狀的套32，裝設於閥保持軸21的基端開口部的內周。
如圖6所示般，閥保持軸21為筒狀，在基端具備內外徑最大的大徑部21a，在前端具備內外徑最小的小徑部21b，在大徑部21a和小徑部21b之間具備內外徑為大徑部21a和小徑部21b的中間的中徑部21c。另外，閥保持軸21，具備：凸緣21d，係大徑部21a的外周且設置於軸方向中間；以及孔21e，將中徑部21c的內外連通。
另外，閥保持軸21，為大徑部21a的外周且在比凸緣21d更前端側具備環狀凹槽21f、螺紋部21g，將螺紋部21g與上部蓋11的第2閥箱11e的開口端內周的螺紋部11e1螺紋嚙合而固定於上部蓋11。大徑部21a的凸緣21d更基端側的外周形狀被形成為可用六角形等的工具把持的形狀，可以藉由工具的利用而容易將閥保持軸21螺紋結合於第2閥箱11e。
另外，在大徑部21a的環狀凹槽21f的外周裝設密封環21i，當將閥保持軸21***於第2閥箱11e內時，密封環21i密合於第2閥箱11e的內周而密封閥保持軸21和第2閥箱11e之間。在閥保持軸21的小徑部21b的外周，裝設有嵌合於第2閥箱11e的內周的閥盤23，當將閥保持軸21***於由上部蓋11的第2閥箱11e形成的第2閥孔h2內直到凸緣21d抵接於第2閥箱11e的端面為止時，第2閥孔h2內藉由閥盤23區隔成經由埠11a2通往壓側室R2的室A、以及經由埠11c1通往槽4的室B。閥保持軸21的內部經由第2閥孔h2內的室A及埠11a2而連通於壓側室R2，並且經由孔21e、第2閥孔h2內的室B及設置於連接部11c的埠11c1連通於槽4之液室L。
並且，閥保持軸21的大徑部21a的內周在途中前端側被縮徑，在縮徑的內周部設置螺紋部21h。階差部形成於為閥保持軸21的內周側且在中徑部21c和小徑部21b的邊境。如此般，形成於閥保持軸21的內周的前述階差部，形成針閥V4之環狀閥座33。
針22，具備頭部22a、以及連結於頭部22a的操作筒22b，可朝成為軸方向的圖6中左右方向移動地***於閥保持軸21內。
頭部22a，具備：呈筒狀且設置於圖6中成為左端的前端外周而可***環狀閥座33的內側的針部22a1、以及設置於外周的中間部且可離開或就座於環狀閥座33的凸緣22a2。針部22a1成為越朝前端越細的形狀，可***於閥保持軸21之小徑部21b內。另外，針部22a1的基端的外徑成為比環狀閥座33的內徑稍小的直徑，當針22在閥保持軸21內朝軸方向移動時，可以將以針部22a1和環狀閥座33的內緣之間的間隙所形成的流路面積的大小進行大小調整。如此般，針22和環狀閥座33在連通壓側室R2和槽4的閥保持軸21內形成針閥V4，針閥V4可以藉由調整針22相對於閥保持軸21的軸方向位置，將在閥保持軸21內形成的壓側抑振力調整通路PV4之流路面積進行大小調整。此外，針部22a1的形狀是前端尖細的形狀，而且只要是可藉由對於環狀閥座33之朝軸方向的移動來調整流路面積的話也可以是圓錐形以外的形狀。
另外，凸緣22a2於環狀閥座33在軸方向上相對向，當針22相對於閥保持軸21往成為前端側的圖6中左側移動而抵接於環狀閥座33時，可以將閥保持軸21的小徑部21b內和中徑部21c內的連通遮斷。相反地，凸緣22a2在從環狀閥座33離開的狀態下，使閥保持軸21的小徑部21b內和中徑部21c內連通。
操作筒22b，具備：凹槽22b3，為具備筒部22b1和外徑大於筒部22b1的底部22b2的有底筒狀，作為可進行來自形成於底部22b2的外部之操作的操作部；以及通孔22b4，形成於筒部22b1的側部而將筒部22b1的內外連通。而且，比頭部22a的凸緣22a2更後方側的後端22a3被壓入嵌合於操作筒22b之筒部22b1內，操作筒22b和頭部22a連結成一體。
操作筒22b的底部22b2，具備：袋孔22b5，從側方開口；以及螺紋部22b6，在外周且比袋孔22b5更前端側與形成於閥保持軸21的大徑部21a的內周的螺紋部21h螺合。另外，密封環22b7裝設於操作筒22b的筒部22b1的外周。
而且，針22***於閥保持軸21內，將螺紋部22b6與螺紋部21h螺合來裝設於閥保持軸21。當針22***於閥保持軸21內時，密封環22b7滑接於閥保持軸21的中徑部21c的內周，針22和閥保持軸21之間被密封。
另外，由於將針22的螺紋部22b6螺合於螺紋部21h，因而當將圖外的螺絲起子等的工具***操作筒22b的後端的凹槽22b3來使針22旋轉時，針22在閥保持軸21內朝成為圖6中左右方向的軸方向移動。
當在閥保持軸21內將針22如前述般收容時，在針22的操作筒22b的底部22b2的外周和閥保持軸21的大徑部21a的內周之間形成環狀的間隙。而且，將針22***於在閥保持軸21內後，當將套32壓入於閥保持軸21的大徑部21a的內周時，操作筒22b的底部22b2和閥保持軸21的大徑部21a之間的間隙閉塞。由於套32為筒狀，容許插穿操作筒22b的底部22b2的後端，因而不對螺絲起子的***於操作筒22b之凹槽22b3造成妨礙，也容許針22相對於閥保持軸21的軸方向的移動。
套32將沿著軸方向的凹槽32a在周方向等間隔設置於成為內周的前端側的圖6中左端側。當將套32壓入且固定於閥保持軸21的大徑部21a時，前述凹槽32a相對向於操作筒22b的袋孔22b5。在袋孔22b5內，***：球34、以及將球34從袋孔22b5內朝頂出方向彈壓的彈簧35。套32、球34及彈簧35形成掣子機構，只要當球34相對向進入於凹槽32a時不以掣動力矩以上的力矩使針22旋轉，就可以限制針22相對於閥保持軸21的朝周方向的旋轉。由於如此般藉由掣子機構維持針22和環狀閥座33的位置關係，因而可以防止在跨騎型車輛M的行走中針閥V4之流路面積任意變化的情形。
另外，在針22內，收容閥體30和彈簧31。詳細來說，閥體30形成為球體，將針22之頭部22a的環狀後端作為釋壓閥閥座36，藉著在操作筒22b的筒部22b1內沿軸方向移動而可離開或就座於釋壓閥閥座36。另外，在閥體30和操作筒22b的底部22b2之間，介設由線圈彈簧所成的彈簧31，將閥體30往釋壓閥閥座36彈壓。
閥體30的直徑形成為比頭部22a的後端的內周徑更大的直徑，當就座於釋壓閥閥座36時，阻斷針部22a1內和操作筒22b內的連通，當從釋壓閥閥座36離開時使針部22a1內和操作筒22b內連通。
由於在針22之操作筒22b的筒部22b1，設置有通孔22b4，因而操作筒22b內通過通孔22b4而連通於閥保持軸21的中徑部21c內。由於閥保持軸21的中徑部21c內經由孔21e及室B連通於槽4，因而操作筒22b內連通於槽4。另外，操作筒22b內，通過針22的頭部22a內而通往閥保持軸21的小徑部21b內。由於閥保持軸21的小徑部21b內經由室A及埠11a2而連通於壓側室R2，因而操作筒22b內也連通於壓側室R2。如此般，針22內，形成相對於在閥保持軸21內形成的壓側抑振力調整通路PV4而並列配置成的壓側釋壓通路PV2，在壓側釋壓通路PV2設置由閥體30、彈簧31及釋壓閥閥座36構成的壓側釋壓閥V2。
壓側釋壓閥V2，在壓側室R2內的壓力和槽4內的壓力的差壓到達開閥壓為止，被維持在閥體30藉由彈簧31繼續抵接於釋壓閥閥座36的閉閥狀態。另外，壓側釋壓閥V2，當壓側室R2內的壓力和槽4內的壓力的差壓成為開閥壓時，閥體30藉由壓側室R2內的壓力壓著，將彈簧31壓縮且從釋壓閥閥座36離開而將壓側釋壓通路PV2開放。此壓側釋壓閥V2開閥的前述開閥壓，被設定成比將活塞桿3的外周密封的密封構件8可承受的最大壓力更低的壓力。
此外，廢除針閥V4的情況下，只要以蓋取代針22而將閥保持軸21的後端閉塞，將閥體30、以及配置於閥體30和前述蓋之間的彈簧31收容於閥保持軸21內，以小徑部21b和中徑部21c之邊境的階差部作為釋壓閥閥座，構成壓側釋壓閥V2的話即可。
在閥保持軸21的小徑部21b的外周，閥盤23、與軸環24藉由小徑部21b和中徑部21c之間的外周之階差部以及螺合於小徑部21b的前端的外周的螺帽29夾住而固定。另外，環狀的間隔件25、環狀板26、環狀板27及環狀的盤形彈簧28，嵌合於軸環24的外周。
閥盤23，具備：複數個埠23a，呈環狀且將排列設置於同一圓周上而將閥盤23的厚部朝軸方向貫穿；環狀窗23b，設置於圖6中左端且由通往各埠23a的環狀凹部所形成；環狀的閥座23c，從圖6中左端朝軸方向突出而包圍各埠23a的出口端亦即環狀窗23b；以及密封環23e，裝設於在外周設置的環狀凹槽23d內。如前述般，當閥盤23安裝於閥保持軸21的小徑部21b的外周且***於第2閥孔h2內時，嵌合於第2閥箱11e的內周而將第2閥孔h2內區隔成室A和室B。設置於閥盤23的外周的密封環23e，密合於第2閥箱11e的內周而將閥盤23和第2閥箱11e之間密封，防止通過閥盤23和第2閥箱11e之間連通室A和室B。
埠23a將通往壓側室R2的室A和通往槽4的室B連通，在本實施方式的後緩衝單元RCU中，作為壓側抑振通路PV1和吸入通路PV3發揮功能。
軸環24，具備：嵌合筒部24a，呈筒狀，在外周嵌合間隔件25、環狀板26、環狀板27及環狀的盤形彈簧28；以及凸緣24b，設置於嵌合筒部24a的圖6中左端，使嵌合筒部24a的圖6中右端抵接於閥盤23的圖6中左端的內周而重疊於閥盤23。
閥盤23和軸環24，在如前述般重疊的狀態以閥保持軸21的外周的階差部和螺帽29夾住，相對於閥保持軸21固定成不動。
間隔件25是小徑的圓環狀的環狀板，可滑動地嵌合於軸環24的嵌合筒部24a的外周，可以相對於閥盤23朝軸方向移動，並可以對於閥盤23遠離或接近。此外，間隔件25的外徑，以不將埠23a閉塞的方式形成為小徑。
環狀板26是圓環狀的環狀板，可滑動地嵌合於軸環24的嵌合筒部24a的外周且重疊於間隔件25的反閥盤側，可以相對於閥盤23朝軸方向移動，並可以對於閥盤23遠離或接近。此外，環狀板26的外徑形成為直徑小於閥座23c的內徑，由於將環狀窗23b設置於閥盤23，因而容許朝外周側的閥盤23側的彎曲。
環狀板27是圓環狀的環狀板，可滑動地嵌合於軸環24的嵌合筒部24a的外周且重疊於環狀板26的反閥盤側，可以相對於閥盤23朝軸方向移動，並可以對於閥盤23遠離或接近。環狀板27的外徑，成為比閥座23c的外徑稍大的直徑以使可離開或就座於閥盤23之閥座23c。另外，環狀板27，具備排列設置於同一圓周上且將環狀板27朝軸方向貫穿的複數個孔27a。各孔27a的外接圓的直徑成為未達環狀板26的直徑，在環狀板26抵接於環狀板27的狀態下，環狀板27之孔27a被閉塞著，當環狀板26的外周朝向閥盤23側彎曲而從環狀板27離開時，孔27a被開放。所以，在環狀板26抵接於環狀板27的狀態下，當環狀板27就座於閥座23c時，將埠23a閉塞而阻斷室A和室B的連通，但由於即使當環狀板27就座於閥座23c，環狀板26仍朝閥盤23側彎曲且從環狀板27離開則孔27a開放因而室A和室B連通。並且，當環狀板27的外周朝反閥盤側彎曲，或當環狀板27在軸環24上朝從閥盤23離開的方向移動時，埠23a開放而室A和室B連通。
盤形彈簧28嵌合於軸環24的嵌合筒部24a的外周，並且在給予初期彎曲的狀態下介設於凸緣24b和環狀板27之間，始終將間隔件25、環狀板26及環狀板27朝向閥盤23側彈壓。
對於從壓側室R2朝向槽4通過埠23a的液體流動，環狀板27承受壓側室R2的壓力和盤形彈簧28的彈壓力而就座於閥座23c且將埠23a閉塞，但環狀板26通過孔27a承受壓側室R2的壓力且以間隔件25的外緣作為支點彎曲而從環狀板27離開並開放埠23a，容許從壓側室R2朝向槽4的液體流動，並且對於此液體流動給予阻力。此外，間隔件25決定環狀板26的彎曲的支點，可以藉間隔件25之外徑的設定來調整環狀板26給予液體流動的阻力大小。如此般，環狀板26作為壓側抑振閥V1之閥體發揮功能，環狀板27作為閥座發揮功能，環狀板26和環狀板27形成壓側抑振閥V1。此外，將環狀板26的內周以閥盤23直接支撐的情況下，也可以省略間隔件25，也可以複數片的環狀板積層而形成壓側抑振閥V1的閥體。
另一方面，對於從槽4朝向壓側室R2來通過埠23a的液體流動，環狀板27承受槽4的壓力而彎曲從閥座23c離開，或將盤形彈簧28壓縮而從閥盤23離開來將埠23a開放，不給予從槽4朝向壓側室R2的液體流動太大阻力地容許此液體的流動。在此情況下，環狀板26從槽4側承受壓力而抵接於環狀板27且與環狀板27一起彎曲，或在軸環24上移動而從閥盤23遠離。如此般，環狀板26、環狀板27作為伸側止回閥V3之閥體發揮功能，閥盤23作為伸側止回閥V3之閥座發揮功能，藉由閥盤23、環狀板26、環狀板27、盤形彈簧28及軸環24形成伸側止回閥V3。
另外，在本實施方式中，壓側抑振閥V1和伸側止回閥V3並列於閥盤23的埠23a，埠23a作為容許從壓側室R2朝向槽4的液體流動的壓側抑振通路PV1、以及容許從槽4朝向壓側室R2的液體流動的吸入通路PV3發揮功能。
此外，也可以於閥盤23設置相當於壓側抑振通路PV1的埠，並且設置相當於吸入通路PV3的埠，設置將相當於壓側抑振通路PV1的埠開閉的壓側抑振閥V1，設置將相當於吸入通路PV3的埠開閉的伸側止回閥V3。
另外，壓側抑振閥V1雖然如前述般構成，但只要是可對於從壓側室R2朝向槽4的液體流動給予阻力而在後緩衝單元RCU的收縮作動時產生抑振力的閥的話即可，因而可在其限度內將閥的構造做適當設計變更。
並且，伸側止回閥V3雖然如前述般構成，但只要是可以僅容許從槽4朝向壓側室R2的液體流動的閥的話即可，因而可在其限度內將閥的構造做適當設計變更。
此外，也可以將與壓側抑振閥V1和伸側止回閥V3同樣構成的閥作為活塞2之伸側抑振閥5和壓側止回閥6使用。
具體所構成的閥單元V，具備：彼此並列的壓側抑振通路PV1、壓側釋壓通路PV2、吸入通路PV3及壓側抑振力調整通路PV4，且將壓側抑振閥V1、壓側釋壓閥V2、伸側止回閥V3及針閥V4並列設置。所以，當將閥單元V***於上部蓋11的第2閥孔h2內時，可以在第3通路P3的途中，將壓側抑振閥V1、壓側釋壓閥V2、伸側止回閥V3及針閥V4彼此並列地設置。
而且，將如上述般構成的閥單元V的組裝方法的一例在以下進行說明。首先，在軸環24的嵌合筒部24a的外周，依盤形彈簧28、環狀板27、環狀板26、間隔件25的順序來將盤形彈簧28、環狀板27、環狀板26及間隔件25進行嵌合且組合。接下來，在閥保持軸21的小徑部21b的外周，將閥盤23、以及組裝有盤形彈簧28、環狀板27、環狀板26及間隔件25的軸環24依序嵌合且組合後，將螺帽29螺合於小徑部21b的前端外周。於是，在閥保持軸21的小徑部21b的外周，閥盤23、以及組裝有盤形彈簧28、環狀板27、環狀板26及間隔件25的軸環24藉由螺帽29固定。
接著，將彈簧31及閥體30依序***針22之操作筒22b內，將頭部22a的後端22a3壓入嵌合於操作筒22b的開口端，將頭部22a結合於操作筒22b，將壓側釋壓閥V2及針22組裝。接下來，將彈簧35和球34依序***於朝針22的操作筒22b之底部22b2的側方開口的袋孔22b5內後，將針22***於閥保持軸21內的同時，使底部22b2的外周的螺紋部22b6螺合於閥保持軸21的螺紋部21h。
針22螺合且收容於閥保持軸21內後，於閥保持軸21的大徑部21a的內周和操作筒22b的外周之間的環狀間隙，一邊將凹槽32a側朝向閥保持軸21內一邊將套32***，將套32壓入嵌合於大徑部21a的內周。於是，套32被固定於閥保持軸21，防止從針22的閥保持軸21脫落。
如此般，將閥盤23、軸環24、間隔件25、環狀板26、環狀板27、盤形彈簧28、收容壓側釋壓閥V2的針22及套32，組合於閥保持軸21後，即結束閥單元V的組裝。完成的閥單元V，成為具備壓側抑振閥V1、壓側釋壓閥V2、伸側止回閥V3及針閥V4的1個單元。而且，閥單元V，***於上部蓋11的第2閥箱11e內，並且藉由螺紋部11e1與閥保持軸21的大徑部21a之外周的螺紋部21g的螺合，收容於第2閥孔h2內並且固定於上部蓋11。閥單元V，由於被螺絲緊固於上部蓋11，因而可容易安裝及拆卸於上部蓋11。此外，只要是將閥單元V可拆卸於上部蓋11的緊固手段的話，也可以採用螺絲固定以外的緊固手段。
後緩衝單元RCU，如上述般構成，在以下對作動進行說明。在活塞2相對於缸1往圖1中下方移動的後緩衝單元RCU的伸長行程中，液體從藉由活塞2壓縮的伸側室R1經由第1通路P1及伸側抑振力調整通路P4往壓側室R2移動。在此伸長行程中，後緩衝單元RCU對於通過第1通路P1的液體流動藉由伸側抑振閥5給予阻力，對於通過伸側抑振力調整通路P4的液體流動藉由伸側抑振力調整閥EV給予阻力，以產生妨礙伸長的伸側的抑振力。
另外，在後緩衝單元RCU的伸長行程中，由於活塞桿3從缸1退出，因而在壓側室R2內活塞桿3從缸1退出的體積量的液體不足，但此不足量的液體，隔膜12膨漲而使氣室G擴大且從槽4的液室L經由伸側止回閥V3供給於壓側室R2。詳細來說，由於環狀板27承受槽4的壓力而從閥座23c離開且伸側止回閥V3開閥，因而液體通過埠23a而從槽4往壓側室R2移動。
在後緩衝單元RCU的伸長行程時，可藉由外部操作調整伸側抑振力調整閥EV之流路面積，由於伸側抑振力調整閥EV可使對於液體流動給予的阻力變化，因而後緩衝單元RCU可以調整伸側的抑振力。另外，伸側抑振力調整通路P4將伸側室R1和壓側室R2連通，未將伸側抑振力調整通路P4成為通過的液體直接往槽4排出的構造。所以，由於通過伸側止回閥V3的液體的流量，不超出活塞桿3從缸1內退出的體積，因而可以防止在缸1內液體不足而成為負壓的事態。
另一方面，在活塞2相對於缸1往圖1中上方移動的後緩衝單元RCU的收縮行程中，藉由活塞2壓縮的壓側室R2內的液體，使壓側止回閥6開閥而經由第2通路P2往伸側室R1移動。另外，在後緩衝單元RCU的收縮行程中，由於活塞桿3侵入缸1內，因而在缸1內活塞桿3侵入缸1內的體積量的液體過剩，但此過剩量的液體，經由壓側抑振閥V1往槽4內的液室L排出，隔膜12收縮來將氣室G縮小。在如此般後緩衝單元RCU的收縮行程中，壓側抑振閥V1及針閥V4對於從壓側室R2朝向槽4的液體流動給予阻力。如此般，在後緩衝單元RCU的收縮行程中，由於第2通路P2開放因而缸1內的伸側室R1和壓側室R2處於連通狀態，壓側抑振閥V1及針閥V4對於從壓側室R2朝向槽4的液體流動給予阻力。所以，在後緩衝單元RCU的收縮行程中，伸側室R1內和壓側室R2內的壓力皆上昇而成為大致相同壓力。在本實施方式的後緩衝單元RCU中，由於面向伸側室R1的活塞2的面積相較於面向壓側室R2的活塞2的面積僅少了活塞桿3的面積量，因而收縮作動的後緩衝單元RCU，將缸1內的壓力乘以活塞桿3的面積之值的抑振力，朝妨礙前述收縮作動的方向發揮。換言之，設定為僅在前述的活塞2的單方存在活塞桿3的單桿式的後緩衝單元RCU的情況下，產生與在收縮作動時活塞桿3的剖面積成比例的抑振力。
此外，由於在本實施方式的後緩衝單元RCU中閥單元V具備針閥V4，藉由針閥V4之流路面積的調整可使針閥V4給予液體流動的阻力變化，因而後緩衝單元RCU可調整壓側的抑振力。
另外，在後緩衝單元RCU的收縮行程中，當壓側室R2內的壓力和槽4內的壓力的差壓達到壓側釋壓閥V2的開閥壓時，由於球34從釋壓閥閥座36後退且壓側釋壓閥V2開閥，因而藉由壓側釋壓通路PV2連通壓側室R2和槽4。藉由壓側釋壓通路PV2的開放，缸1內的液體往槽4洩出，調整成為缸1內的壓力不超過壓側釋壓閥V2的開閥壓。
在此，在比較輕量的跨騎型車輛M所採用的後緩衝單元中，為了強度上無問題地謀求後緩衝單元的輕量化，所以有縮減活塞桿的外徑的情況。後緩衝單元的在收縮作動時產生的抑振力，如前述般與活塞桿剖面積成比例。因此，當欲在如此般的後緩衝單元縮減活塞桿的外徑的同時在收縮作動時發揮較大抑振力時，需要缸內的壓力成為高壓。要讓收縮作動時缸內的壓力形成高壓，壓側抑振閥V1給予液體流動的阻力加大的話即可，但當在後緩衝單元RCU的收縮作動時以高速收縮作動時，有缸內的壓力成為過大而超過將活塞桿的外周密封之密封構件的耐壓的情況。然而，在本實施方式的後緩衝單元RCU中，如上所述，閥單元V具備並列配置於壓側抑振閥V1的壓側釋壓閥V2。所以，即使在後緩衝單元RCU的收縮作動時後緩衝單元RCU的收縮速度成為高速，仍可以防止壓側釋壓閥V2開閥而缸1內的壓力成為過大的情形，可以保護將活塞桿3的外周密封的密封構件8以及防止來自於活塞桿3和密封構件8之間的液體洩漏。
另外，當從上部蓋11將閥單元V拆下，將第2閥箱11e的開口藉由未圖示的蓋閉塞時，因為壓側室R2和槽4完全不經由閥連通，所以後緩衝單元RCU僅在伸長作動時產生抑振力，在收縮作動時不產生抑振力。藉由如此般閥單元V的裝設，雖後緩衝單元RCU可以在伸長作動時和收縮作動時的雙方發揮抑振力，但將閥單元V從後緩衝單元RCU拆卸時成為僅在伸長作動時產生抑振力的後緩衝單元。
以上，本實施方式的後緩衝單元RCU，介裝於跨騎型車輛M的車體F和後輪W之間，具備：缸1；活塞2，可移動地***缸1內以將缸1內區隔成填充有液體的伸側室R1和壓側室R2；活塞桿3，可移動地***缸1內並且連結於活塞2；槽4，用於儲存液體；第1通路P1及第2通路P2，分別並列且將伸側室R1和壓側室R2連通；第3通路P3，將壓側室R2和槽4連通；伸側抑振力調整通路P4，設置於缸1的外側且將伸側室R1和壓側室R2連通；伸側抑振閥5，設置於第1通路P1並對於從伸側室R1朝向壓側室R2的液體流動給予阻力；壓側止回閥6，設置於第2通路P2並僅容許從壓側室R2朝向伸側室R1的液體流動；以及伸側抑振力調整閥EV，設置於伸側抑振力調整通路P4且可藉由來自於外側的操作而變更流路面積。
在如此般構成的後緩衝單元RCU中，在活塞2具備伸側抑振閥5，由於設置於缸1的外側的部分是可變更以緊致的構成即可的流路面積的伸側抑振力調整閥EV，因而避免後緩衝單元RCU的外形的大型化的同時可進行伸長作動時的抑振力的調整。
另外，伸側抑振力調整閥EV設置於伸側抑振力調整通路P4，該通路設置於缸1的外側，在後緩衝單元RCU安裝於跨騎型車輛M時設置於與車體F側連結的缸1側。如此般，在將後緩衝單元RCU安裝於跨騎型車輛M的狀態下，在車體F側中缸1於後輪W側配置活塞桿3，但因為伸側抑振力調整閥EV配置於缸1側，所以使用者可以容易操作伸側抑振力調整閥EV。
綜上所述，依據本實施方式的後緩衝單元RCU，即使具備伸側抑振力調整閥EV仍可避免大型化因而可以提昇對於跨騎型車輛M的後輪側的搭載性，並且也可容易調整伸長作動時的抑振力。
並且，本實施方式的後緩衝單元RCU，具備：外筒15，包覆缸1且在與缸1之間形成伸側抑振力調整通路P4；以及上部蓋11，安裝於缸1和外筒15的上端而保持槽4並且具有可連結於車體F的支架B1，伸側抑振力調整閥EV設置於上部蓋11。依據如此般構成的後緩衝單元RCU，藉著設置外筒15可以憑簡單構造將伸側抑振力調整通路P4設置於缸1的外側，由於將伸側抑振力調整閥EV設置於上部蓋11，因而可以將伸側抑振力調整閥EV配置於後緩衝單元RCU的上端。所以，依據後緩衝單元RCU，由於在上端配置伸側抑振力調整閥EV，因而使用者可以不受到跨騎型車輛M的消音器等妨礙地操作伸側抑振力調整閥EV。
而且，在本實施方式的後緩衝單元RCU中，伸側抑振力調整閥EV，具備：環狀閥座50；以及閥體51，呈軸狀且在前端具有可遠離或接近於環狀閥座50的閥頭51b，從軸方向觀看缸1和外筒15時，閥頭51b被配置於缸1和外筒15之間的範圍。依據如此般構成的後緩衝單元RCU，由於將伸側抑振力調整閥EV配置於缸1和外筒15的端部附近的同時可以配置於儘可能靠近缸1的軸線LC的位置，因而即使設置伸側抑振力調整閥EV仍可免於招致後緩衝單元RCU的全長的細長化和徑方向的大型化。
並且，本實施方式的後緩衝單元RCU具備設置於第3通路P3之途中的閥單元V，閥單元V，具備：壓側抑振閥V1，對於從壓側室R2朝向槽4的液體流動給予阻力；壓側釋壓閥V2，並列配置於壓側抑振閥V1，在閉閥時阻斷壓側室R2和槽4的連通，並且當壓側室R2的壓力和槽4的壓力的差壓達到開閥壓時，開閥而容許從壓側室R2朝向槽4的液體流動；伸側止回閥V3，並列配置於壓側抑振閥V1而僅容許從槽4朝向壓側室R2的液體流動；以及針閥V4，並列配置於壓側抑振閥V1而對於從壓側室R2朝向槽4的液體流動給予阻力並且可調整流路面積。
The body 51a has: a threaded portion 51a1 disposed on the outer periphery; a through hole 51a2 that penetrates the body 51a in the radial direction; and a sealing ring 51a4 that is installed on the outer periphery and disposed at an annular groove 51a3 that is disposed at the front end side of the through hole 51a2. When the valve body 51 is inserted into the first valve hole h1 formed by the first valve box 11d, the body 51a is engaged with the inner periphery of the first valve box 11d, and the sealing ring 51a4 is slidably connected to the inner periphery of the first valve box 11d to seal the first valve hole h1. In addition, even if the valve body 51 moves in the axial direction in the first valve box 11d, the body 51a is always arranged on the left side in FIG. 5 which is closer to the atmosphere side than the opening of the extension-side vibration-damping force adjustment passage P4 relative to the first valve hole h1, and the aforementioned opening is not closed. The valve head 51b has: a cylindrical shaft 51b1 extending in the axial direction from the body 51a; a conical needle 51b2 provided at the front end of the shaft 51b1 and capable of invading the inner periphery of the annular valve seat 50, in other words, in the port 11a1. The needle 51b2 has a tapered tip and may have a shape other than a cone as long as the flow area can be adjusted by moving in the axial direction relative to the annular valve seat 50. The outer diameter of the shaft 51b1 is larger than the diameter of the port 11a1, and the outer periphery of the end surface of the shaft 51b1 faces the annular valve seat 50 in the axial direction, and the outer diameter of the base end of the needle 51b2 is larger than the diameter of the port 11a1. Therefore, when the valve body 51 is moved in the direction of penetrating to the deepest part in the first valve box 11d, the side surface of the needle 51b2 is seated on the inner edge of the annular valve seat 50 to block the port 11a1. In addition, when the side surface of the needle 51b2 is separated from the annular valve seat 50, a gap is generated between the needle 51b2 and the inner edge of the annular valve seat 50 to open the port 11a1. By moving the valve body 51 in the axial direction, the gap is enlarged or reduced, and the resistance given to the flow of the liquid through the port 11a1 can be adjusted. In addition, the outer diameter of the base end of the needle 51b2 can be formed to be smaller than the diameter of the port 11a1, and the right end of the shaft 51b1 is made to abut against the annular valve seat 50 to block the port 11a1. In addition, the small diameter portion 51c extends in the axial direction from the rear end of the body 51a, and a groove 51c1 that can be operated from the outside is provided at the rear end. The box 52 is cylindrical and has a small diameter on the atmospheric side. It may have a step portion 52a on the inner periphery, and a threaded portion 52b and a threaded portion 52c on the outer periphery and the anti-atmospheric side of the step portion 52a on the inner periphery. The valve body 51 is inserted into the box 52, and the threaded portion 51a1 of the body 51a is screwed into the threaded portion 52c on the inner periphery of the box 52. The outer diameter of the small diameter portion 51c is formed to be a diameter that can be fitted into the inner diameter of the atmospheric side of the box 52, and the sealing ring 51c2 installed on the outer periphery of the small diameter portion 51c is tightly fitted to the inner periphery of the box 52 to seal the valve body 51 and the box 52. Furthermore, the box 52 having the valve body 51 screwed on the inner circumference is inserted into the first valve box 11d, and the threaded portion 52b on the outer circumference is screwed into the threaded portion 11d1 to be fixed to the first valve box 11d. When the valve body 51 and the box 52 are mounted on the first valve box 11d in this way, since a feed screw mechanism is formed by the valve body 51 and the box 52, when the user inserts a tool such as a screwdriver into the groove 51c1 of the small diameter portion 51c to rotate the valve body 51, the valve body 51 moves in the axial direction in the first valve hole h1. Since the valve body 51 can move in the axial direction in the first valve hole h1, the valve head 51b can open and close the port 11a1 by moving away from or approaching the annular valve seat 50, and the resistance given to the flow of the liquid through the port 11a1 can be adjusted by adjusting the gap between the needle 51b2 and the annular valve seat 50. In addition, two balls 53 and 54 are inserted into the through hole 51a2 provided in the body 51a of the valve body 51, and a spring 55 is arranged between the balls 53 and 54. When the valve body 51 is inserted into the first valve box 11d, the through hole 51a2 faces the groove 11d2 formed on the inner periphery of the first valve box 11d. The balls 53 and 54 are biased by the spring 55 in the direction of protruding outward from the through hole 51a2, and the first valve case 11d, the balls 53 and 54, and the spring 55 form a detent mechanism. Therefore, when the balls 53 and 54 enter relative to the groove 11d2, as long as the valve body 51 is not rotated with a torque greater than the detent torque, the rotation of the valve body 51 in the circumferential direction relative to the first valve case 11d can be restricted. Since the positional relationship between the valve body 51 and the annular valve seat 50 is maintained by the detent mechanism in this way, it is possible to prevent the flow area of the extension and lateral vibration suppression force adjustment valve EV from changing arbitrarily while the straddle-type vehicle M is traveling. As shown in FIG. 1 and FIG. 7 , the extension-side vibration-suppressing force adjustment valve EV thus constructed has the valve head 51b arranged in the range between the cylinder 1 and the outer tube 15 when the cylinder 1 and the outer tube 15 are viewed from the axial direction. Therefore, since the extension-side vibration-suppressing force adjustment valve EV is arranged near the ends of the cylinder 1 and the outer tube 15 and can be arranged at a position as close as possible to the axis LC of the cylinder 1, even if the extension-side vibration-suppressing force adjustment valve EV is provided, it is possible to avoid causing the entire length of the rear buffer unit RCU to be thinned and the diameter to be enlarged. In the rear buffer unit RCU of the present embodiment, the valve unit V provided in the middle of the third passage P3 is accommodated in the second valve hole h2 formed by the second valve box 11e. The valve unit V is detachably received in the second valve box 11e forming the second valve hole h2 of the upper cover 11. As shown in FIG6 , the valve unit V comprises: a pressure-side vibration suppression passage PV1, a pressure-side pressure-release passage PV2, a suction passage PV3 and a pressure-side vibration suppression force adjustment passage PV4, which are connected in parallel in the middle of the third passage P3; a pressure-side vibration suppression valve V1, which is arranged in the pressure-side vibration suppression passage PV1 and provides resistance to the flow of liquid from the pressure-side chamber R2 toward the groove 4; a pressure-side pressure-release valve V2, which is arranged in the pressure-side pressure-release passage PV2 and is arranged in parallel with the pressure-side vibration suppression valve V1, which blocks the connection between the pressure-side chamber R2 and the groove 4 when the valve is closed, and when When the differential pressure between the pressure of the pressure-side chamber R2 and the pressure of the groove 4 reaches the opening pressure, the valve is opened to allow the liquid to flow from the pressure-side chamber R2 toward the groove 4; the extension side check valve V3 is arranged in the suction passage PV3 and is arranged in parallel with the pressure-side vibration suppression valve V1 to only allow the liquid to flow from the groove 4 toward the pressure-side chamber R2; and the needle valve V4 is arranged in the pressure-side vibration suppression force adjustment passage PV4 and is arranged in parallel with the pressure-side vibration suppression valve V1, and provides resistance to the liquid flow between the groove 4 and the pressure-side chamber R2, and the resistance can be adjusted by external operation. Specifically, the valve unit V comprises: a cylindrical valve holding shaft 21 inserted into the second valve hole h2 of the upper cover 11; a needle 22 inserted into the valve holding shaft 21; a valve disc 23 mounted on the outer periphery of the valve holding shaft 21; a shaft ring 24 mounted on the outer periphery of the valve holding shaft 21; an annular spacer 25, an annular plate 26 and an annular plate 27, which are axially movable and fit into the shaft ring. 24; a disc spring 28, which is also arranged on the outer periphery of the shaft ring 24, presses the spacer 25, the annular plate 26 and the annular plate 27 toward the valve disc 23; a nut 29 fixes the valve disc 23 and the shaft ring 24 to the valve retaining shaft 21; a valve body 30 and a spring 31, which are accommodated in the needle 22; and a cylindrical sleeve 32, which is installed on the inner periphery of the base end opening of the valve retaining shaft 21. As shown in FIG6 , the valve holding shaft 21 is cylindrical, and has a large diameter portion 21a with the largest inner and outer diameters at the base end, a small diameter portion 21b with the smallest inner and outer diameters at the front end, and a middle diameter portion 21c with an inner and outer diameter that is the middle of the large diameter portion 21a and the small diameter portion 21b between the large diameter portion 21a and the small diameter portion 21b. In addition, the valve holding shaft 21 has: a flange 21d, which is the outer periphery of the large diameter portion 21a and is arranged in the middle of the axial direction; and a hole 21e, which connects the inside and the outside of the middle diameter portion 21c. In addition, the valve holding shaft 21 has an annular groove 21f and a threaded portion 21g on the outer periphery of the large diameter portion 21a and on the front end side of the flange 21d, and the threaded portion 21g is threadedly engaged with the threaded portion 11e1 on the inner periphery of the opening end of the second valve box 11e of the upper cover 11 to be fixed to the upper cover 11. The outer periphery of the flange 21d of the large diameter portion 21a on the base end side is formed into a shape that can be grasped by a tool such as a hexagonal shape, so that the valve holding shaft 21 can be easily threadedly coupled to the second valve box 11e by using a tool. In addition, a sealing ring 21i is installed on the outer periphery of the annular groove 21f of the large diameter portion 21a. When the valve retaining shaft 21 is inserted into the second valve box 11e, the sealing ring 21i is tightly fitted to the inner periphery of the second valve box 11e to seal between the valve retaining shaft 21 and the second valve box 11e. A valve disc 23 engaged with the inner circumference of the second valve box 11e is installed on the outer periphery of the small diameter portion 21b of the valve retaining shaft 21. When the valve retaining shaft 21 is inserted into the second valve hole h2 formed by the second valve box 11e of the upper cover 11 until the flange 21d abuts against the end face of the second valve box 11e, the second valve hole h2 is divided by the valve disc 23 into chamber A leading to the pressure side chamber R2 via port 11a2 and chamber B leading to the groove 4 via port 11c1. The interior of the valve retaining shaft 21 is connected to the pressure side chamber R2 via the chamber A in the second valve hole h2 and the port 11a2, and is connected to the liquid chamber L of the groove 4 via the hole 21e, the chamber B in the second valve hole h2, and the port 11c1 provided in the connecting portion 11c. In addition, the inner periphery of the large diameter portion 21a of the valve retaining shaft 21 is reduced in diameter at the front end side, and a threaded portion 21h is provided on the reduced inner periphery. The step portion is formed on the inner periphery of the valve retaining shaft 21 and at the boundary between the middle diameter portion 21c and the small diameter portion 21b. In this way, the aforementioned step portion formed on the inner periphery of the valve retaining shaft 21 forms the annular valve seat 33 of the needle valve V4. The needle 22 has a head 22a and an operating cylinder 22b connected to the head 22a, and can be inserted into the valve holding shaft 21 in a movable manner in the left-right direction in FIG. 6 which is the axial direction. The head 22a has a needle portion 22a1 which is cylindrical and arranged on the outer periphery of the front end which is the left end in FIG. 6 and can be inserted into the inner side of the annular valve seat 33, and a flange 22a2 which is arranged in the middle part of the outer periphery and can leave or sit on the annular valve seat 33. The needle portion 22a1 is in a shape that becomes thinner toward the front end and can be inserted into the small diameter portion 21b of the valve holding shaft 21. In addition, the outer diameter of the base end of the needle portion 22a1 is slightly smaller than the inner diameter of the annular valve seat 33, and when the needle 22 moves in the axial direction in the valve holding shaft 21, the size of the flow area formed by the gap between the needle portion 22a1 and the inner edge of the annular valve seat 33 can be adjusted. In this way, the needle 22 and the annular valve seat 33 form a needle valve V4 in the valve holding shaft 21 that connects the pressure-side chamber R2 and the groove 4. The needle valve V4 can adjust the size of the flow area of the pressure-side vibration-suppressing force adjustment passage PV4 formed in the valve holding shaft 21 by adjusting the axial position of the needle 22 relative to the valve holding shaft 21. In addition, the shape of the needle portion 22a1 is a shape with a tapered front end, and may be a shape other than a cone as long as the flow surface area can be adjusted by moving in the axial direction relative to the annular valve seat 33. In addition, the flange 22a2 is opposite to the annular valve seat 33 in the axial direction, and when the needle 22 moves to the left side in FIG. 6 which becomes the front end side relative to the valve holding shaft 21 and abuts against the annular valve seat 33, the connection between the small diameter portion 21b and the middle diameter portion 21c of the valve holding shaft 21 can be blocked. On the contrary, when the flange 22a2 is separated from the annular valve seat 33, the small diameter portion 21b and the middle diameter portion 21c of the valve holding shaft 21 are connected. The operating cylinder 22b has: a groove 22b3, which is a bottomed cylinder having a cylinder 22b1 and a bottom 22b2 with an outer diameter larger than that of the cylinder 22b1, as an operating portion that can be operated from the outside formed at the bottom 22b2; and a through hole 22b4, which is formed at the side of the cylinder 22b1 and connects the inside and the outside of the cylinder 22b1. In addition, the rear end 22a3 on the rear side of the flange 22a2 of the head 22a is pressed into the cylinder 22b1 of the operating cylinder 22b, and the operating cylinder 22b and the head 22a are connected as a whole. The bottom 22b2 of the operating cylinder 22b has: a bag hole 22b5, which opens from the side; and a threaded portion 22b6, which is screwed with the threaded portion 21h formed on the inner periphery of the large diameter portion 21a of the valve retaining shaft 21 on the outer periphery and at the front end side of the bag hole 22b5. In addition, a sealing ring 22b7 is installed on the outer periphery of the barrel 22b1 of the operating cylinder 22b. Moreover, the needle 22 is inserted into the valve retaining shaft 21, and the threaded portion 22b6 is screwed with the threaded portion 21h to be installed on the valve retaining shaft 21. When the needle 22 is inserted into the valve retaining shaft 21, the sealing ring 22b7 slides on the inner periphery of the middle diameter portion 21c of the valve retaining shaft 21, and the needle 22 and the valve retaining shaft 21 are sealed. In addition, since the threaded portion 22b6 of the needle 22 is screwed into the threaded portion 21h, when a tool such as a screwdriver (not shown) is inserted into the groove 22b3 at the rear end of the operating cylinder 22b to rotate the needle 22, the needle 22 moves in the axial direction that becomes the left-right direction in FIG. 6 in the valve holding shaft 21. When the needle 22 is accommodated in the valve holding shaft 21 as described above, an annular gap is formed between the outer periphery of the bottom 22b2 of the operating cylinder 22b of the needle 22 and the inner periphery of the large diameter portion 21a of the valve holding shaft 21. Furthermore, after the needle 22 is inserted into the valve holding shaft 21, when the sleeve 32 is pressed into the inner circumference of the large diameter portion 21a of the valve holding shaft 21, the gap between the bottom 22b2 of the operating cylinder 22b and the large diameter portion 21a of the valve holding shaft 21 is closed. Since the sleeve 32 is cylindrical, it allows the rear end of the bottom 22b2 of the operating cylinder 22b to be inserted, so that the insertion of the screwdriver into the groove 22b3 of the operating cylinder 22b is not hindered, and the needle 22 is allowed to move in the axial direction relative to the valve holding shaft 21. The sleeve 32 is provided with grooves 32a along the axial direction at equal intervals in the circumferential direction on the left end side in FIG. 6 which becomes the front end side of the inner circumference. When the sleeve 32 is pressed into and fixed to the large diameter portion 21a of the valve holding shaft 21, the groove 32a is opposite to the pocket hole 22b5 of the operating cylinder 22b. In the pocket hole 22b5, a ball 34 and a spring 35 for pressing the ball 34 in the ejection direction from the pocket hole 22b5 are inserted. The sleeve 32, the ball 34 and the spring 35 form a detent mechanism, and the needle 22 can be restricted from rotating in the circumferential direction relative to the valve holding shaft 21 as long as the needle 22 is not rotated with a torque greater than the detent torque when the ball 34 is relatively inserted into the groove 32a. Since the positional relationship between the needle 22 and the annular valve seat 33 is maintained by the detent mechanism, it is possible to prevent the flow area of the needle valve V4 from changing arbitrarily while the straddle-type vehicle M is traveling. In addition, the valve body 30 and the spring 31 are housed in the needle 22. Specifically, the valve body 30 is formed into a spherical body, and the annular rear end of the head portion 22a of the needle 22 is used as a pressure relief valve seat 36. By moving in the axial direction in the cylinder portion 22b1 of the operating cylinder 22b, the valve body 30 can leave or sit on the pressure relief valve seat 36. In addition, between the valve body 30 and the bottom 22b2 of the operating cylinder 22b, a spring 31 composed of a coil spring is interposed to bias the valve body 30 toward the pressure relief valve seat 36. The valve body 30 has a diameter larger than the inner circumference of the rear end of the head 22a. When the valve body 30 is seated on the pressure relief valve seat 36, the communication between the needle 22a1 and the operating cylinder 22b is blocked. When the valve body 30 is separated from the pressure relief valve seat 36, the needle 22a1 and the operating cylinder 22b are connected. Since the through hole 22b4 is provided in the cylinder 22b1 of the operating cylinder 22b of the needle 22, the inside of the operating cylinder 22b is connected to the middle diameter part 21c of the valve holding shaft 21 through the through hole 22b4. Since the inside of the middle diameter part 21c of the valve holding shaft 21 is connected to the groove 4 via the hole 21e and the chamber B, the inside of the operating cylinder 22b is connected to the groove 4. In addition, the inside of the operating cylinder 22b leads to the inside of the small diameter portion 21b of the valve holding shaft 21 through the inside of the head portion 22a of the needle 22. Since the inside of the small diameter portion 21b of the valve holding shaft 21 is connected to the pressure side chamber R2 via the chamber A and the port 11a2, the inside of the operating cylinder 22b is also connected to the pressure side chamber R2. In this way, the inside of the needle 22 forms a pressure side pressure release passage PV2 arranged in parallel with the pressure side vibration damping force adjustment passage PV4 formed in the valve holding shaft 21, and a pressure side pressure release valve V2 composed of a valve body 30, a spring 31 and a pressure release valve seat 36 is provided in the pressure side pressure release passage PV2. The pressure-side release valve V2 is maintained in a closed state in which the valve body 30 continues to abut against the release valve seat 36 by the spring 31 until the differential pressure between the pressure in the pressure-side chamber R2 and the pressure in the groove 4 reaches the valve opening pressure. In addition, when the differential pressure between the pressure in the pressure-side chamber R2 and the pressure in the groove 4 reaches the valve opening pressure, the valve body 30 is pressed by the pressure in the pressure-side chamber R2, compresses the spring 31, and leaves the release valve seat 36 to open the pressure-side release passage PV2. The aforementioned opening pressure for opening the pressure-side pressure relief valve V2 is set to a pressure lower than the maximum pressure that the sealing member 8 that seals the outer periphery of the piston rod 3 can withstand. In addition, when the needle valve V4 is eliminated, the needle 22 is replaced by a cap, the rear end of the valve holding shaft 21 is closed, the valve body 30 and the spring 31 disposed between the valve body 30 and the aforementioned cap are accommodated in the valve holding shaft 21, and the step portion at the boundary between the small diameter portion 21b and the middle diameter portion 21c is used as a pressure relief valve seat to constitute the pressure-side pressure relief valve V2. The valve disc 23 and the shaft ring 24 are fixed to the outer periphery of the small diameter portion 21b of the valve holding shaft 21 by the step portion of the outer periphery between the small diameter portion 21b and the middle diameter portion 21c and the nut 29 screwed on the outer periphery of the front end of the small diameter portion 21b. In addition, the annular spacer 25, the annular plate 26, the annular plate 27 and the annular disc spring 28 are fitted on the outer periphery of the shaft ring 24. The valve disc 23 has: a plurality of ports 23a, which are annular and arranged on the same circumference to penetrate the thick portion of the valve disc 23 in the axial direction; an annular window 23b, which is arranged at the left end in FIG. 6 and is formed by an annular recess leading to each port 23a; an annular valve seat 23c, which protrudes from the left end in FIG. 6 in the axial direction to surround the outlet end of each port 23a, namely the annular window 23b; and a sealing ring 23e, which is installed in an annular groove 23d arranged on the outer periphery. As described above, when the valve disc 23 is mounted on the outer periphery of the small diameter portion 21b of the valve holding shaft 21 and inserted into the second valve hole h2, it is fitted into the inner periphery of the second valve case 11e to partition the second valve hole h2 into chamber A and chamber B. The sealing ring 23e provided on the outer periphery of the valve disc 23 is tightly fitted into the inner periphery of the second valve case 11e to seal the valve disc 23 and the second valve case 11e, thereby preventing the communication between chamber A and chamber B through the valve disc 23 and the second valve case 11e. The port 23a connects chamber A leading to the pressure side chamber R2 and chamber B leading to the groove 4, and functions as the pressure side vibration suppression passage PV1 and the suction passage PV3 in the rear buffer unit RCU of the present embodiment. The shaft ring 24 includes: a fitting cylindrical portion 24a, which is cylindrical and has a spacer 25, an annular plate 26, an annular plate 27 and an annular disc spring 28 fitted on the outer periphery; and a flange 24b, which is provided at the left end of the fitting cylindrical portion 24a in FIG. 6, so that the right end of the fitting cylindrical portion 24a in FIG. 6 abuts against the inner periphery of the left end of the valve disc 23 in FIG. 6 and overlaps with the valve disc 23. The valve disc 23 and the shaft ring 24 are sandwiched by the step portion of the outer periphery of the valve holding shaft 21 and the nut 29 in the overlapped state as described above, and are fixed relative to the valve holding shaft 21 so as not to move. The spacer 25 is a small-diameter annular plate, which is slidably fitted on the outer periphery of the fitting tube 24a of the shaft ring 24, and can move in the axial direction relative to the valve disc 23 and can move away from or close to the valve disc 23. In addition, the outer diameter of the spacer 25 is formed to be small in a manner not to close the port 23a. The annular plate 26 is a circular ring-shaped annular plate, which is slidably fitted on the outer periphery of the fitting tube portion 24a of the shaft ring 24 and overlaps the anti-valve disc side of the spacer 25, and can move in the axial direction relative to the valve disc 23 and can move away from or approach the valve disc 23. In addition, the outer diameter of the annular plate 26 is formed to be smaller than the inner diameter of the valve seat 23c, and since the annular window 23b is provided on the valve disc 23, the valve disc 23 side toward the outer peripheral side is allowed to bend. The annular plate 27 is a circular ring-shaped annular plate, which is slidably fitted on the outer periphery of the fitting tube 24a of the shaft ring 24 and overlaps the anti-valve disc side of the annular plate 26, and can move in the axial direction relative to the valve disc 23, and can move away from or approach the valve disc 23. The outer diameter of the annular plate 27 is slightly larger than the outer diameter of the valve seat 23c so that it can leave or sit on the valve seat 23c of the valve disc 23. In addition, the annular plate 27 has a plurality of holes 27a arranged on the same circumference and penetrating the annular plate 27 in the axial direction. The diameter of the circumscribed circle of each hole 27a is less than the diameter of the annular plate 26. When the annular plate 26 abuts against the annular plate 27, the hole 27a of the annular plate 27 is closed. When the outer periphery of the annular plate 26 bends toward the valve disc 23 and leaves the annular plate 27, the hole 27a is opened. Therefore, when the annular plate 26 is in contact with the annular plate 27 and the annular plate 27 is seated on the valve seat 23c, the port 23a is closed and the communication between the chambers A and B is blocked. However, even when the annular plate 27 is seated on the valve seat 23c, the annular plate 26 is bent toward the valve disc 23 side and separated from the annular plate 27, so that the hole 27a is opened and the chambers A and B are communicated. Furthermore, when the outer periphery of the annular plate 27 is bent toward the anti-valve disc side, or when the annular plate 27 moves on the shaft ring 24 in a direction away from the valve disc 23, the port 23a is opened and the chambers A and B are communicated. The disc spring 28 is fitted into the outer periphery of the fitting tube portion 24a of the shaft ring 24, and is interposed between the flange 24b and the annular plate 27 in a state of being given an initial bend, and always presses the spacer 25, the annular plate 26 and the annular plate 27 toward the valve disc 23 side. Regarding the flow of liquid from the pressure side chamber R2 toward the groove 4 through the port 23a, the annular plate 27 receives the pressure of the pressure side chamber R2 and the spring pressure of the disc spring 28 and sits on the valve seat 23c to close the port 23a, but the annular plate 26 receives the pressure of the pressure side chamber R2 through the hole 27a and bends with the outer edge of the spacer 25 as a fulcrum to leave the annular plate 27 and open the port 23a, allowing the liquid to flow from the pressure side chamber R2 toward the groove 4 and providing resistance to the liquid flow. In addition, the spacer 25 determines the fulcrum of the bending of the annular plate 26, and the resistance of the annular plate 26 to the flow of the liquid can be adjusted by setting the outer diameter of the spacer 25. In this way, the annular plate 26 functions as the valve body of the pressure-side vibration suppression valve V1, and the annular plate 27 functions as the valve seat. The annular plate 26 and the annular plate 27 form the pressure-side vibration suppression valve V1. In addition, when the inner periphery of the annular plate 26 is directly supported by the valve disc 23, the spacer 25 can be omitted, and a plurality of annular plates can be stacked to form the valve body of the pressure-side vibration suppression valve V1. On the other hand, for the flow of liquid from the groove 4 toward the pressure side chamber R2 through the port 23a, the annular plate 27 receives the pressure of the groove 4 and bends away from the valve seat 23c, or compresses the disc spring 28 and moves away from the valve disc 23 to open the port 23a, allowing the flow of the liquid without giving much resistance to the flow of the liquid from the groove 4 toward the pressure side chamber R2. In this case, the annular plate 26 receives the pressure from the groove 4 side and abuts against the annular plate 27 and bends together with the annular plate 27, or moves on the shaft ring 24 and moves away from the valve disc 23. In this way, the annular plate 26 and the annular plate 27 function as the valve body of the extension side check valve V3, and the valve disc 23 functions as the valve seat of the extension side check valve V3. The extension side check valve V3 is formed by the valve disc 23, the annular plate 26, the annular plate 27, the disc spring 28 and the shaft ring 24. In addition, in the present embodiment, the pressure-side vibration suppression valve V1 and the extension-side check valve V3 are arranged in parallel at the port 23a of the valve disc 23, and the port 23a functions as the pressure-side vibration suppression passage PV1 that allows the liquid to flow from the pressure-side chamber R2 to the groove 4, and the suction passage PV3 that allows the liquid to flow from the groove 4 to the pressure-side chamber R2. In addition, a port corresponding to the pressure-side vibration suppression passage PV1 and a port corresponding to the suction passage PV3 may be provided on the valve disc 23, and the pressure-side vibration suppression valve V1 that opens and closes the port corresponding to the pressure-side vibration suppression passage PV1 and the extension-side check valve V3 that opens and closes the port corresponding to the suction passage PV3 may be provided. In addition, although the pressure-side vibration suppression valve V1 is constructed as described above, any valve that can provide resistance to the flow of liquid from the pressure-side chamber R2 toward the groove 4 and generate a vibration suppression force when the rear buffer unit RCU contracts can be used, and the valve structure can be appropriately designed within its limits. In addition, although the extension-side check valve V3 is constructed as described above, any valve that can only allow the flow of liquid from the groove 4 toward the pressure-side chamber R2 can be used, and the valve structure can be appropriately designed within its limits. In addition, valves having the same structure as the pressure-side vibration suppression valve V1 and the extension-side check valve V3 may be used as the extension-side vibration suppression valve 5 and the pressure-side check valve 6 of the piston 2. Specifically, the valve unit V has: a pressure-side vibration suppression passage PV1, a pressure-side pressure release passage PV2, a suction passage PV3, and a pressure-side vibration suppression force adjustment passage PV4 arranged in parallel with each other, and the pressure-side vibration suppression valve V1, the pressure-side pressure release valve V2, the extension-side check valve V3, and the needle valve V4 are arranged in parallel. Therefore, when the valve unit V is inserted into the second valve hole h2 of the upper cover 11, the pressure-side vibration suppression valve V1, the pressure-side pressure release valve V2, the extension-side check valve V3, and the needle valve V4 can be arranged in parallel with each other in the middle of the third passage P3. In addition, an example of an assembly method of the valve unit V constructed as described above is described below. First, the disc spring 28, the annular plate 27, the annular plate 26, and the spacer 25 are fitted and assembled in the order of the disc spring 28, the annular plate 27, the annular plate 26, and the spacer 25 on the outer periphery of the fitting cylindrical portion 24a of the shaft ring 24. Next, the valve disc 23 and the shaft ring 24 assembled with the disc spring 28, the annular plate 27, the annular plate 26 and the spacer 25 are sequentially fitted and assembled on the outer periphery of the small diameter portion 21b of the valve holding shaft 21, and then the nut 29 is screwed on the outer periphery of the front end of the small diameter portion 21b. Thus, the valve disc 23 and the shaft ring 24 assembled with the disc spring 28, the annular plate 27, the annular plate 26 and the spacer 25 are fixed on the outer periphery of the small diameter portion 21b of the valve holding shaft 21 by the nut 29. Next, the spring 31 and the valve body 30 are sequentially inserted into the operating cylinder 22b of the needle 22, the rear end 22a3 of the head 22a is pressed into the open end of the operating cylinder 22b, the head 22a is coupled to the operating cylinder 22b, and the pressure-release valve V2 and the needle 22 are assembled. Next, the spring 35 and the ball 34 are sequentially inserted into the pocket hole 22b5 opened on the side of the bottom 22b2 of the operating cylinder 22b of the needle 22, and the needle 22 is inserted into the valve holding shaft 21, and the threaded portion 22b6 on the outer periphery of the bottom 22b2 is screwed into the threaded portion 21h of the valve holding shaft 21. After the needle 22 is screwed and received in the valve holding shaft 21, the sleeve 32 is inserted into the annular gap between the inner periphery of the large diameter portion 21a of the valve holding shaft 21 and the outer periphery of the operating cylinder 22b, with the groove 32a facing the inside of the valve holding shaft 21, and the sleeve 32 is pressed into the inner periphery of the large diameter portion 21a. Thus, the sleeve 32 is fixed to the valve holding shaft 21, preventing the needle 22 from falling off the valve holding shaft 21. In this way, the valve disc 23, the shaft ring 24, the spacer 25, the annular plate 26, the annular plate 27, the disc spring 28, the needle 22 accommodating the pressure-side pressure-release valve V2, and the sleeve 32 are assembled to the valve holding shaft 21, and the assembly of the valve unit V is completed. The completed valve unit V becomes a single unit having the pressure-side vibration suppression valve V1, the pressure-side pressure-release valve V2, the extension-side check valve V3, and the needle valve V4. Furthermore, the valve unit V is inserted into the second valve box 11e of the upper cover 11, and is received in the second valve hole h2 and fixed to the upper cover 11 by screwing the threaded portion 11e1 with the threaded portion 21g on the outer periphery of the large diameter portion 21a of the valve holding shaft 21. Since the valve unit V is fastened to the upper cover 11 by screws, it can be easily mounted on and removed from the upper cover 11. In addition, as long as the valve unit V can be detached from the upper cover 11 by a fastening means, a fastening means other than screwing can be adopted. The rear buffer unit RCU is constructed as described above, and the operation is described below. In the extension stroke of the rear cushion unit RCU in which the piston 2 moves downward in FIG. 1 relative to the cylinder 1, the liquid moves from the extension chamber R1 compressed by the piston 2 to the compression chamber R2 via the first passage P1 and the extension vibration suppression force adjustment passage P4. In this extension stroke, the rear cushion unit RCU applies resistance to the liquid flow through the first passage P1 through the extension vibration suppression valve 5, and applies resistance to the liquid flow through the extension vibration suppression force adjustment passage P4 through the extension vibration suppression force adjustment valve EV, thereby generating an extension vibration suppression force that hinders extension. In addition, during the extension stroke of the rear cushion unit RCU, since the piston rod 3 withdraws from the cylinder 1, the volume of liquid in the compression chamber R2 is insufficient due to the withdrawal of the piston rod 3 from the cylinder 1. However, the insufficient liquid expands the air chamber G due to the expansion of the diaphragm 12 and is supplied to the compression chamber R2 from the liquid chamber L of the groove 4 through the extension side check valve V3. Specifically, since the annular plate 27 receives the pressure of the groove 4 and leaves the valve seat 23c and the extension side check valve V3 opens, the liquid moves from the groove 4 to the compression chamber R2 through the port 23a. During the extension stroke of the rear cushion unit RCU, the flow area of the extension-side vibration suppression force adjustment valve EV can be adjusted by external operation. Since the extension-side vibration suppression force adjustment valve EV can change the resistance given to the flow of the liquid, the rear cushion unit RCU can adjust the extension-side vibration suppression force. In addition, the extension-side vibration suppression force adjustment passage P4 connects the extension-side chamber R1 and the compression-side chamber R2, and the extension-side vibration suppression force adjustment passage P4 is not configured to discharge the liquid passing through it directly into the groove 4. Therefore, since the flow rate of the liquid passing through the extension-side check valve V3 does not exceed the volume of the piston rod 3 withdrawn from the cylinder 1, it is possible to prevent the situation in which the cylinder 1 is insufficient in liquid and becomes negative pressure. On the other hand, in the contraction stroke of the rear cushion unit RCU in which the piston 2 moves upward in FIG. 1 relative to the cylinder 1, the liquid in the compression side chamber R2 compressed by the piston 2 opens the compression side check valve 6 and moves to the extension side chamber R1 through the second passage P2. In addition, in the contraction stroke of the rear cushion unit RCU, since the piston rod 3 intrudes into the cylinder 1, the volume of liquid in the cylinder 1 is excessive, but this excess liquid is discharged to the liquid chamber L in the groove 4 through the compression side damping valve V1, and the diaphragm 12 contracts to shrink the air chamber G. In the contraction stroke of the rear cushion unit RCU, the pressure-side vibration suppression valve V1 and the needle valve V4 provide resistance to the flow of liquid from the pressure-side chamber R2 toward the groove 4. In this way, in the contraction stroke of the rear cushion unit RCU, since the second passage P2 is open, the extension chamber R1 and the pressure-side chamber R2 in the cylinder 1 are in a connected state, and the pressure-side vibration suppression valve V1 and the needle valve V4 provide resistance to the flow of liquid from the pressure-side chamber R2 toward the groove 4. Therefore, in the contraction stroke of the rear cushion unit RCU, the pressure in the extension chamber R1 and the pressure chamber R2 both rise to become approximately the same pressure. In the rear cushion unit RCU of the present embodiment, since the area of the piston 2 facing the extension chamber R1 is smaller than the area of the piston 2 facing the compression chamber R2 by the area of the piston rod 3, the rear cushion unit RCU in the contraction action exerts a vibration suppression force of the value of the pressure in the cylinder 1 multiplied by the area of the piston rod 3 in the direction that hinders the aforementioned contraction action. In other words, in the case of a single-rod rear cushion unit RCU in which the piston rod 3 exists only on one side of the aforementioned piston 2, a vibration suppression force proportional to the cross-sectional area of the piston rod 3 during the contraction action is generated. In addition, since the valve unit V in the rear buffer unit RCU of the present embodiment is provided with a needle valve V4, the resistance given to the flow of the liquid by the needle valve V4 can be changed by adjusting the flow area of the needle valve V4, so that the rear buffer unit RCU can adjust the vibration damping force on the pressure side. In addition, in the contraction stroke of the rear buffer unit RCU, when the differential pressure between the pressure in the pressure-side chamber R2 and the pressure in the groove 4 reaches the opening pressure of the pressure-side pressure relief valve V2, the ball 34 retreats from the pressure relief valve seat 36 and the pressure-side pressure relief valve V2 opens, so that the pressure-side chamber R2 and the groove 4 are connected through the pressure-side pressure relief passage PV2. By opening the pressure-side relief passage PV2, the liquid in the cylinder 1 is released to the groove 4, and the pressure in the cylinder 1 is adjusted to not exceed the opening pressure of the pressure-side relief valve V2. Here, in the rear shock absorber unit adopted by the relatively lightweight straddle-type vehicle M, in order to reduce the weight of the rear shock absorber unit without any problem in terms of strength, the outer diameter of the piston rod is sometimes reduced. The vibration damping force generated by the rear shock absorber unit during the contraction action is proportional to the cross-sectional area of the piston rod as mentioned above. Therefore, when a rear-cushion unit like this is intended to reduce the outer diameter of the piston rod and exert a greater vibration suppression force during the contraction action, the pressure in the cylinder needs to be high. To make the pressure in the cylinder high during the contraction action, the resistance to the flow of the liquid given by the pressure-side vibration suppression valve V1 can be increased. However, when the rear-cushion unit RCU contracts at a high speed, the pressure in the cylinder may become too large and exceed the pressure resistance of the sealing member that seals the outer periphery of the piston rod. However, in the rear-cushion unit RCU of the present embodiment, as described above, the valve unit V has a pressure-side pressure relief valve V2 arranged in parallel with the pressure-side vibration suppression valve V1. Therefore, even if the contraction speed of the rear cushion unit RCU becomes high during the contraction operation of the rear cushion unit RCU, the pressure in the cylinder 1 can be prevented from becoming excessively high due to the opening of the pressure-side relief valve V2, and the sealing member 8 that seals the outer periphery of the piston rod 3 can be protected, and the liquid leakage from between the piston rod 3 and the sealing member 8 can be prevented. In addition, when the valve unit V is removed from the upper cover 11 and the opening of the second valve box 11e is closed by a cover not shown, since the pressure-side chamber R2 and the groove 4 are completely connected without the valve, the rear cushion unit RCU generates a vibration-damping force only during the extension operation, and does not generate a vibration-damping force during the contraction operation. By installing the valve unit V in this way, the rear buffer unit RCU can exert a vibration suppression force in both the extension action and the contraction action. However, when the valve unit V is removed from the rear buffer unit RCU, it becomes a rear buffer unit that generates a vibration suppression force only in the extension action. As described above, the rear shock absorber unit RCU of the present embodiment is installed between the body F and the rear wheel W of the straddle-type vehicle M, and comprises: a cylinder 1; a piston 2, which is movably inserted into the cylinder 1 to divide the cylinder 1 into an extension chamber R1 and a pressure chamber R2 filled with a liquid; a piston rod 3, which is movably inserted into the cylinder 1 and connected to the piston 2; a groove 4 for storing the liquid; a first passage P1 and a second passage P2, which are respectively arranged in parallel and connect the extension chamber R1 and the pressure chamber R2; a third passage P3, which connects the pressure chamber R2 and the groove 4. connected; an extension-side vibration suppression force adjustment passage P4, which is arranged on the outer side of the cylinder 1 and connects the extension-side chamber R1 and the pressure-side chamber R2; an extension-side vibration suppression valve 5, which is arranged in the first passage P1 and provides resistance to the flow of liquid from the extension-side chamber R1 toward the pressure-side chamber R2; a pressure-side check valve 6, which is arranged in the second passage P2 and only allows the flow of liquid from the pressure-side chamber R2 toward the extension-side chamber R1; and an extension-side vibration suppression force adjustment valve EV, which is arranged in the extension-side vibration suppression force adjustment passage P4 and can change the flow area by operation from the outside. In the rear shock absorber unit RCU configured as above, the piston 2 is provided with an extension-side vibration damping valve 5. Since the portion disposed on the outer side of the cylinder 1 is an extension-side vibration damping force adjusting valve EV whose flow area can be changed with a compact structure, the vibration damping force during the extension operation can be adjusted while avoiding the enlargement of the outer shape of the rear shock absorber unit RCU. In addition, the extension-side vibration damping force adjusting valve EV is disposed in the extension-side vibration damping force adjusting passage P4 disposed on the outer side of the cylinder 1, and when the rear shock absorber unit RCU is mounted on the straddle-type vehicle M, it is disposed on the side of the cylinder 1 connected to the vehicle body F side. In this way, when the rear shock absorber unit RCU is mounted on the straddle-type vehicle M, the piston rod 3 is arranged on the rear wheel W side of the cylinder 1 on the vehicle body F side, but because the extension-side vibration-suppression force adjustment valve EV is arranged on the cylinder 1 side, the user can easily operate the extension-side vibration-suppression force adjustment valve EV. In summary, according to the rear shock absorber unit RCU of this embodiment, even if the extension-side vibration-suppression force adjustment valve EV is provided, it is possible to avoid enlargement, thereby improving the mounting performance on the rear wheel side of the straddle-type vehicle M, and it is also possible to easily adjust the vibration-suppression force during the extension operation. Furthermore, the rear shock absorber unit RCU of the present embodiment comprises: an outer cylinder 15 covering the cylinder 1 and forming an extension-side vibration suppression force adjustment passage P4 between the outer cylinder 1 and the cylinder 1; and an upper cover 11 mounted on the upper ends of the cylinder 1 and the outer cylinder 15 to hold the groove 4 and having a bracket B1 connectable to the vehicle body F, and an extension-side vibration suppression force adjustment valve EV is disposed on the upper cover 11. According to the rear shock absorber unit RCU constructed in this way, the extension-side vibration suppression force adjustment passage P4 can be disposed on the outer side of the cylinder 1 with a simple structure by disposing the outer cylinder 15, and since the extension-side vibration suppression force adjustment valve EV is disposed on the upper cover 11, the extension-side vibration suppression force adjustment valve EV can be arranged on the upper end of the rear shock absorber unit RCU. Therefore, according to the rear shock absorber unit RCU, since the extension-side vibration suppression force adjustment valve EV is arranged at the upper end, the user can operate the extension-side vibration suppression force adjustment valve EV without being hindered by the muffler of the straddle-type vehicle M. Moreover, in the rear shock absorber unit RCU of the present embodiment, the extension-side vibration suppression force adjustment valve EV has: an annular valve seat 50; and a valve body 51, which is axial and has a valve head 51b at the front end that can be separated from or approached to the annular valve seat 50, and when the cylinder 1 and the outer cylinder 15 are viewed from the axial direction, the valve head 51b is arranged in the range between the cylinder 1 and the outer cylinder 15. According to the rear cushion unit RCU constructed in this way, since the extension-side vibration suppression force adjusting valve EV is arranged near the ends of the cylinder 1 and the outer tube 15 and can be arranged as close as possible to the axis LC of the cylinder 1, even if the extension-side vibration suppression force adjusting valve EV is set, it is possible to avoid causing the overall length of the rear cushion unit RCU to be slimmed down and the diameter to be enlarged. In addition, the rear buffer unit RCU of the present embodiment has a valve unit V disposed in the middle of the third passage P3. The valve unit V has: a pressure-side vibration suppression valve V1, which provides resistance to the flow of liquid from the pressure-side chamber R2 toward the groove 4; a pressure-side release valve V2, which is arranged in parallel with the pressure-side vibration suppression valve V1, and blocks the connection between the pressure-side chamber R2 and the groove 4 when the valve is closed, and when the pressure of the pressure-side chamber R2 and the groove 4 are equal, the pressure of the pressure-side chamber R2 and the groove 4 are equal. When the differential pressure of the pressure of the groove 4 reaches the opening pressure, the valve opens to allow the liquid to flow from the pressure side chamber R2 toward the groove 4; the extension side check valve V3 is arranged in parallel with the pressure side vibration suppression valve V1 and only allows the liquid to flow from the groove 4 toward the pressure side chamber R2; and the needle valve V4 is arranged in parallel with the pressure side vibration suppression valve V1 to provide resistance to the liquid flow from the pressure side chamber R2 toward the groove 4 and can adjust the flow surface area.
依據如此般構成的後緩衝單元RCU，由於壓側抑振閥V1、並列設置壓側釋壓閥V2及伸側止回閥V3的閥單元V可拆卸地設置於將壓側室R2和槽4連通的第3通路P3的途中，因而不只伸長作動時也可在收縮作動時發揮抑振力，並且也可調整收縮作動時的抑振力。並且，依據如前述般構成的後緩衝單元RCU，由於閥單元V具備壓側釋壓閥V2，因而在後緩衝單元RCU的收縮作動時即使後緩衝單元RCU的收縮速度成為高速仍可以防止缸1內的壓力成為過大的情形。
According to the rear buffer unit RCU constructed in this way, since the valve unit V including the pressure-side vibration suppression valve V1, the parallel pressure-side pressure release valve V2 and the extension-side check valve V3 is detachably arranged in the middle of the third passage P3 connecting the pressure-side chamber R2 and the groove 4, the vibration suppression force can be exerted not only during the extension action but also during the contraction action, and the vibration suppression force during the contraction action can also be adjusted. Furthermore, according to the rear buffer unit RCU constructed as described above, since the valve unit V has a pressure-side pressure relief valve V2, when the rear buffer unit RCU contracts, even if the contraction speed of the rear buffer unit RCU becomes high, it is still possible to prevent the pressure in the cylinder 1 from becoming excessive.
此外，在本實施方式的後緩衝單元RCU中，藉由閥單元V的有無，可以將後緩衝單元RCU，設定成在伸長作動時和收縮作動時的雙方產生抑振力的後緩衝單元、與僅在伸長作動時產生抑振力的後緩衝單元的任一個。後緩衝單元RCU的製造者，可以將閥單元V以外的後緩衝單元RCU以相同的零件在相同的生產線來組裝，且可以依據使用者的要求而決定閥單元V的有無來製造後緩衝單元RCU。因
而，製造者可以減少後緩衝單元RCU的製造成本。
In addition, in the rear buffer unit RCU of the present embodiment, the rear buffer unit RCU can be set to either a rear buffer unit that generates vibration suppression force in both extension and contraction actions, or a rear buffer unit that generates vibration suppression force only in extension action, depending on the presence or absence of the valve unit V. The manufacturer of the rear buffer unit RCU can assemble the rear buffer unit RCU other than the valve unit V with the same parts on the same production line, and can manufacture the rear buffer unit RCU by determining whether the valve unit V is present or not according to the user's requirements. Therefore, the manufacturer can reduce the manufacturing cost of the rear buffer unit RCU.
另外，在本實施方式的後緩衝單元RCU中，上部蓋11，具備：蓋部11a，裝設於缸1和外筒15的上端；槽保持部11b，用於保持槽4；以及連接部11c，從蓋部11a的側方延伸而連接於槽保持部11b並且形成第3通路P3，伸側抑振力調整閥EV和閥單元V相對於蓋部11a配置於連接部11c的兩側。
In addition, in the rear cushion unit RCU of the present embodiment, the upper cover 11 comprises: a cover 11a mounted on the upper ends of the cylinder 1 and the outer tube 15; a groove holding portion 11b for holding the groove 4; and a connecting portion 11c extending from the side of the cover 11a and connected to the groove holding portion 11b to form a third passage P3, and the extension side vibration damping force adjustment valve EV and the valve unit V are arranged on both sides of the connecting portion 11c relative to the cover 11a.
依據如此般構成的後緩衝單元RCU，伸側抑振力調整閥EV和閥單元V設置於使用者容易利用的後緩衝單元RCU之上端的上部蓋11。另外，通常，後緩衝單元RCU，將槽4以朝向跨騎型車輛M的前方或後方的任一方的姿勢來設置於跨騎型車輛M，總之，因為伸側抑振力調整閥EV和閥單元V配置於將連接於槽保持部11b的連接部11c在周方向夾住的兩側，所以免於造成如伸側抑振力調整閥EV和閥單元V的雙方面向車體F的內側般的事態。所以，依據如此般構成的後緩衝單元RCU，即使安裝於跨騎型車輛M的姿勢因跨騎型車輛M的規格改變，使用者仍容易進行伸側抑振力調整閥EV和閥單元V的操作。
According to the rear shock absorber unit RCU constructed in this way, the extension-side vibration suppression force adjustment valve EV and the valve unit V are provided on the upper cover 11 at the upper end of the rear shock absorber unit RCU which is easily accessible to the user. In addition, the rear shock absorber unit RCU is usually provided on the straddle-type vehicle M with the groove 4 facing either the front or rear of the straddle-type vehicle M. In short, since the extension-side vibration suppression force adjustment valve EV and the valve unit V are arranged on both sides of the connection portion 11c connected to the groove holding portion 11b in the circumferential direction, it is prevented from causing a situation where both sides of the extension-side vibration suppression force adjustment valve EV and the valve unit V face the inner side of the vehicle body F. Therefore, according to the rear shock absorber unit RCU configured in this way, even if the installation posture on the straddle-type vehicle M changes due to the specifications of the straddle-type vehicle M, the user can still easily operate the extension and lateral vibration suppression force adjustment valve EV and the valve unit V.
另外，伸側抑振力調整閥EV和閥單元V，只要從軸方向觀看上部蓋11被配置於與槽4在周方向上錯開的位置的話即可，即使後緩衝單元RCU在將槽4朝向跨騎型車輛M的前方或後方的任一方的姿勢下設置於跨騎型車輛M，仍可將伸側抑振力調整閥EV和閥單元V的雙方朝向車體F的外側。依據如此般構成的後緩衝單元RCU，即使安裝於跨騎型車輛M的姿勢因跨騎型車輛M的規格改變，使用者仍容易進行伸側抑振力調整閥EV和閥單元V的操作。
並且，在本實施方式的後緩衝單元RCU中，上部蓋11，具備：收容伸側抑振力調整閥EV的第1閥孔h1、以及收容閥單元V的第2閥孔h2，第1閥孔h1和第2閥孔h2以缸1的軸線LC為中心被配置成放射狀。在如此般構成的後緩衝單元RCU中，第1閥孔h1和第2閥孔h2以缸1的軸線LC為中心被配置成放射狀，因而伸側抑振力調整閥EV和閥單元V也同樣地放射狀安裝於上部蓋11。在伸側抑振力調整閥EV和閥單元V平行配置般的佈局配置中，造成伸側抑振力調整閥EV和閥單元V往上部蓋11的側方伸出，但伸側抑振力調整閥EV和閥單元V放射狀安裝於上部蓋11的話可以減少往側方的伸出量。所以，在如此般構成的後緩衝單元RCU中，由於即使具備伸側抑振力調整閥EV和閥單元V仍可以減少朝徑方向的伸出量而小型化，因而可以提昇對於跨騎型車輛M的搭載性。
此外，在本實施方式的後緩衝單元RCU中，針閥V4，具有：環狀閥座33、以及可對於環狀閥座33遠離或接近的針22，壓側釋壓閥V2收容於針22內。依據如此般構成的後緩衝單元RCU，壓側釋壓閥V2收容於針22內所以可以將閥單元V的整體小型化。此外，由於壓側釋壓閥V2收容於針22內，因而不論針22的位置都可以將壓側釋壓閥V2的開閥壓固定。
並且，在本實施方式的後緩衝單元RCU中，針22，具有：頭部22a，具有：呈筒狀且設置於前端外周且可***環狀閥座33的內側的針部22a1、以及設置於外周的中間部且可離開或就座於環狀閥座33的凸緣22a2；操作筒22b，具備：呈有底筒狀且可進行來自形成於底部22b2的外部之操作的凹槽(操作部)22b3、以及連通內外的通孔22b4，連結於頭部22a的後方，壓側釋壓閥V2，具有：閥體30，將頭部22a之環狀的後端22a3作為環狀的釋壓閥閥座36，可離開或就座於釋壓閥閥座36且收容於操作筒22b內；以及彈簧31，介設於閥體30和操作筒22b之間，並且收容於操作筒22b內而將閥體30朝向釋壓閥閥座36彈壓，當閥體30從釋壓閥閥座36離開時使頭部22a內和通孔22b4成為連通。
依據如此般構成的後緩衝單元RCU，在針22設置將閥體30和彈簧31收容於頭部22a和操作筒22b內的空間，藉著以構成針22的頭部22a作為釋壓閥閥座36使用，可以合理地將壓側釋壓閥V2收容於針22內。所以，依據如此般構成的後緩衝單元RCU，可以將壓側釋壓閥V2和針22更為小型化。
此外，本實施方式的後緩衝單元RCU，具備滑接於活塞桿3的外周而將活塞桿3的外周密封的密封構件8，壓側釋壓閥V2的開閥壓被設定為未達密封構件8可承受的最大壓力。依據如此般構成的後緩衝單元RCU，由於將密封構件8可承受的最大壓力不超過缸1內的壓力，因而可以保護密封構件8和防止來自於活塞桿3和密封構件8之間的液體洩漏。
In addition, as long as the upper cover 11 is arranged at a position offset from the groove 4 in the circumferential direction when viewed from the axial direction, the extension-side vibration-suppression force adjustment valve EV and the valve unit V can be directed toward the outside of the vehicle body F even if the rear shock absorber unit RCU is installed on the straddle-type vehicle M with the groove 4 facing either the front or rear of the straddle-type vehicle M. According to the rear shock absorber unit RCU constructed in this way, even if the installation posture on the straddle-type vehicle M changes due to the specifications of the straddle-type vehicle M, the user can still easily operate the extension-side vibration-suppression force adjustment valve EV and the valve unit V.
Furthermore, in the rear cushion unit RCU of the present embodiment, the upper cover 11 has: a first valve hole h1 for accommodating the extension-side vibration suppression force adjustment valve EV, and a second valve hole h2 for accommodating the valve unit V, and the first valve hole h1 and the second valve hole h2 are arranged radially with the axis LC of the cylinder 1 as the center. In the rear cushion unit RCU thus constructed, the first valve hole h1 and the second valve hole h2 are arranged radially with the axis LC of the cylinder 1 as the center, and thus the extension-side vibration suppression force adjustment valve EV and the valve unit V are also radially mounted on the upper cover 11. In the layout configuration where the extension-side vibration suppression force adjustment valve EV and the valve unit V are arranged in parallel, the extension-side vibration suppression force adjustment valve EV and the valve unit V extend to the side of the upper cover 11, but if the extension-side vibration suppression force adjustment valve EV and the valve unit V are radially installed on the upper cover 11, the extension amount to the side can be reduced. Therefore, in the rear shock absorber unit RCU configured in this way, even if the extension-side vibration suppression force adjustment valve EV and the valve unit V are provided, the extension amount in the radial direction can be reduced and miniaturized, thereby improving the mounting performance on the straddle-type vehicle M.
In addition, in the rear buffer unit RCU of the present embodiment, the needle valve V4 has: an annular valve seat 33, and a needle 22 that can be moved away from or close to the annular valve seat 33, and the pressure-side release valve V2 is accommodated in the needle 22. According to the rear buffer unit RCU constructed in this way, the pressure-side release valve V2 is accommodated in the needle 22, so the valve unit V can be miniaturized as a whole. In addition, since the pressure-side release valve V2 is accommodated in the needle 22, the opening pressure of the pressure-side release valve V2 can be fixed regardless of the position of the needle 22.
In the rear buffer unit RCU of the present embodiment, the needle 22 has: a head portion 22a having: a needle portion 22a1 which is cylindrical and arranged at the outer periphery of the front end and can be inserted into the inner side of the annular valve seat 33, and a flange 22a2 which is arranged at the middle part of the outer periphery and can leave or sit on the annular valve seat 33; an operating cylinder 22b having: a groove (operating portion) 22b3 which is cylindrical and can be operated from the outside formed at the bottom 22b2, and a through hole 22b4 which connects the inside and the outside, connected to the head portion; Behind the head 22a, the pressure relief valve V2 has: a valve body 30, which uses the annular rear end 22a3 of the head 22a as an annular pressure relief valve seat 36, can leave or sit on the pressure relief valve seat 36 and is accommodated in the operating cylinder 22b; and a spring 31, which is interposed between the valve body 30 and the operating cylinder 22b, and is accommodated in the operating cylinder 22b to bias the valve body 30 toward the pressure relief valve seat 36, so that when the valve body 30 leaves the pressure relief valve seat 36, the head 22a and the through hole 22b4 become connected.
According to the rear buffer unit RCU constructed in this way, a space is set in the needle 22 to accommodate the valve body 30 and the spring 31 in the head 22a and the operating cylinder 22b. By using the head 22a constituting the needle 22 as the pressure relief valve seat 36, the pressure relief valve V2 on the pressure side can be reasonably accommodated in the needle 22. Therefore, according to the rear buffer unit RCU constructed in this way, the pressure relief valve V2 on the pressure side and the needle 22 can be further miniaturized.
In addition, the rear buffer unit RCU of this embodiment has a sealing member 8 that slides on the outer periphery of the piston rod 3 and seals the outer periphery of the piston rod 3, and the opening pressure of the pressure relief valve V2 is set to be less than the maximum pressure that the sealing member 8 can withstand. According to the rear cushion unit RCU constructed in this way, since the maximum pressure that the sealing component 8 can withstand does not exceed the pressure in the cylinder 1, the sealing component 8 can be protected and the liquid leakage from between the piston rod 3 and the sealing component 8 can be prevented.
以上，雖然詳細說明本發明的較佳的實施方式，但只要不偏離專利申請的範圍，仍可進行改造、變形、及變更。
Although the preferred implementation of the present invention is described in detail above, modifications, variations, and changes can still be made as long as they do not deviate from the scope of the patent application.
