Abstract:
A piston coupled to a piston rod is fitted in a sealed cylinder in which oil is contained. During an extension stroke of the piston rod, a damping force is generated by an extension-side valve body, and at the same time, a valve-opening pressure of an extension-side main valve is adjusted by an inner pressure in an extension-side backpressure chamber. During a compression stroke of the piston rod, a damping force is generated by a compression-side valve body, and at the same time, a valve-opening pressure of a compression-side main valve is adjusted by an inner pressure in a compression-side backpressure chamber. A simple structure is realized by using a common guide bore for guiding the extension-side valve body and the compression-side valve body. Check valves are provided at both ends of the guide bore and communication passage are provided through the extension-side valve body and the compression-side valve body so that an amount of excess oil due to a movement of the extension-side valve body and the compression-side valve body can be expelled, thereby improving responsiveness of the shock absorber.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a damping force adjustable fluid pressure shock absorber in which damping force characteristics can be appropriately adjusted. 
         [0002]    As a hydraulic shock absorber mounted on a suspension apparatus of a vehicle such as an automobile, there is known a damping force adjustable hydraulic shock absorber in which damping force characteristics can be appropriately adjusted in accordance with road surface conditions, vehicle running conditions, and the like, so as to improve ride comfort and steering stability. 
         [0003]    Generally, a damping force adjustable hydraulic shock absorber comprises a sealed cylinder in which oil is contained, a piston rod, and a piston coupled to the piston rod. The piston is slidably fitted in the cylinder so as to divide the inside of the cylinder into two chambers. The piston includes a primary oil passage and a bypass passage through which the two chambers in the cylinder are in communication with each other. A damping force generating mechanism is provided at the primary oil passage. The damping force generating mechanism comprises an orifice, a disk valve and the like. A damping force adjusting valve is provided at the bypass passage. The damping force adjusting valve adjusts the passage area of the bypass passage. 
         [0004]    To reduce a damping force, the bypass passage is opened by use of the damping force adjusting valve so as to reduce resistance to an oil flow between the two chambers in the cylinder. To increase a damping force, the bypass passage is closed so as to increase resistance to an oil flow between the two chambers. In this way, damping force characteristics can be appropriately adjusted by opening or closing the damping force adjusting valve. 
         [0005]    However, a problem exists in a hydraulic shock absorber in which damping force adjustment relies, as described above, on changing only a passage area of a bypass passage; that is, although it is possible to change damping force characteristics to a large extent in a low piston speed range because in this range a damping force depends on an orifice dimension of an oil passage, it is not possible to change damping force characteristics to a large extent in middle and high piston speed ranges because in these ranges a damping force depends on an opening degree of a damping force generating mechanism (for example, disk valve) provided at a primary oil passage. 
         [0006]    With the aim of solving this problem, for example, Japanese Patent Application Public Disclosure 2003-278819 discloses a damping force adjustable hydraulic absorber provided with a pilot type damping force adjusting valve as a damping force generating mechanism on a primary oil passage. In the pilot type damping force adjusting valve, a backpressure chamber (pilot chamber) is formed at the back of a disk valve, and the backpressure chamber is in communication through a fixed orifice with a cylinder chamber of an upstream side of the disk valve, and is also in communication through a flow rate control valve (pilot control valve) with a cylinder chamber of a downstream side of the disk valve. 
         [0007]    According to this damping force adjustable hydraulic absorber, the area of the communication passage between the two chambers in the cylinder can be directly adjusted by opening or closing the flow rate control valve, and at the same time, the valve-opening pressure of the disk valve can be changed by changing the pressure in the backpressure chamber by utilizing pressure loss occurring at the flow rate control valve. In this way, it is possible to adjust not only orifice characteristics (in which a damping force is approximately proportional to the square of piston speed) but also valve characteristics (in which a damping force is approximately proportional to piston speed), thereby to widen an adjustable range of damping force. 
         [0008]    As a further improved art, for example, Japanese Patent Application Public Disclosure 2006-292092 discloses a damping force adjustable hydraulic shock absorber in which a simple structure is realized by partially sharing an oil flow passage between an extension side and a compression side, and using a single damping force adjusting valve to adjust respective damping forces of the extension and compression sides. 
         [0009]    However, the damping force adjustable hydraulic shock absorber disclosed in the above mentioned Japanese Patent Application Public Disclosure 2006-292092 has the following problem. Namely, since a valve body of the damping force adjusting valve (solenoid valve) includes pressure receiving surfaces on its end portion, it is not possible to form a passage through the valve body, through which chambers at both ends of the body could otherwise communicate with each other and thereby provide a pressure balance. Consequently, it is difficult to adequately recover a volume loss caused by a movement of the valve body, as a result of which smooth opening and closing of the valve is liable to be impeded, and responsiveness of the hydraulic shock absorber is liable to deteriorate. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention has been contrived in consideration of the above-mentioned problem, and an object thereof is to provide a damping force adjustable fluid pressure shock absorber in which a pilot type damping force valve is provided on each of an extension side and a compression side, and a simple structure and excellent responsiveness is realized. 
         [0011]    The present invention provides a damping force adjustable fluid pressure shock absorber, comprising: 
         [0012]    a cylinder in which a fluid is sealingly contained; 
         [0013]    a piston slidably fitted in the cylinder so as to divide an inside of the cylinder into two chambers; 
         [0014]    a piston rod coupled to the piston and extending to an outside of the cylinder; 
         [0015]    an extension-side flow passage and a compression-side flow passage through which the two chambers in the cylinder are in communication with each other; and 
         [0016]    a damping force generating mechanism for generating a damping force by controlling fluid flows in the extension-side flow passage and the compression-side flow passage, 
         [0017]    wherein the damping force generating mechanism comprises 
         [0018]    an extension-side main valve provided at the extension-side flow passage, 
         [0019]    an extension-side backpressure chamber for adjusting a valve-opening pressure of the extension-side main valve, 
         [0020]    an extension-side bypass flow passage through which the two chambers in the cylinder are in communication with each other, 
         [0021]    an extension-side pressure control valve provided at the extension-side bypass flow passage and adapted to be opened by receiving a pressure in the extension-side bypass flow passage, 
         [0022]    a compression-side main valve provided at the compression-side flow passage, 
         [0023]    a compression-side backpressure chamber for adjusting a valve-opening pressure of the compression-side main valve, 
         [0024]    a compression-side bypass flow passage through which the two chambers in the cylinder are in communication with each other, and 
         [0025]    a compression-side pressure control valve provided at the compression-side bypass flow passage and adapted to be opened by receiving a pressure in the compression-side bypass flow passage, 
         [0026]    the extension-side bypass flow passage introducing a pressure of an upstream side of the extension-side pressure control valve into the extension-side backpressure chamber, 
         [0027]    the compression-side bypass flow passage introducing a pressure of an upstream side of the compression-side pressure control valve into the compression-side backpressure chamber, 
         [0028]    the extension-side pressure control valve and the compression-side pressure control valve comprising 
         [0029]    a guide bore shared by the two valves, the guide bore having one end in communication with one of the two chambers in the cylinder and an opposite end in communication with the other of the two chambers in the cylinder, 
         [0030]    a first valve body slidably fitted in the guide bore, and adapted to be seated on a seat surface provided in the guide bore and to be opened by receiving a pressure in one of the extension-side bypass flow passage and the compression-side bypass flow passage, 
         [0031]    a second valve body slidably fitted in the guide bore, and adapted to be seated on a seat surface provided at the first valve body and to be opened by receiving a pressure in the other of the extension-side bypass flow passage and the compression-side bypass flow passage, 
         [0032]    a damping force adjuster for adjusting valve-opening pressures of the first valve body and the second valve body by biasing the first valve body and the second valve body in valve-closing directions thereof, 
         [0033]    a first check valve provided at the one end of the guide bore, and allowing only a fluid flow from one end side of the first valve body and the second valve body to one of the two chambers in the cylinder, and 
         [0034]    a second check valve provided at the opposite end of the guide bore, and allowing only a fluid flow from an opposite end side of the first valve body and the second valve body to the other of the two chambers in the cylinder, and 
         [0035]    an axially extending communication passage provided through the first valve body and the second valve body, the axially extending communication passage allowing communication between the one end side of the first valve body and the second valve body, and the opposite end side of the first valve body and the second valve body. 
         [0036]    The damping force adjuster may comprise a proportional solenoid actuator. 
         [0037]    The damping force adjustable fluid pressure shock absorber may further comprising a biasing unit provided between the valve bodies for biasing the first valve body and the second valve body in a direction in which the valve bodies are spaced apart from each other. 
         [0038]    The first valve body may include a small diameter portion on one end side thereof, the small diameter portion adapted to be seated on the seat surface provided in the guide bore, and a large diameter portion on an opposite end side thereof, the large diameter portion adapted to be guided by the guide bore. The second valve body may include a small diameter portion on one end side thereof, the small diameter portion adapted to be seated on the seat surface provided at the first valve body, and a large diameter portion on an opposite end side thereof, the large diameter portion adapted to be guided by the guide bore. 
         [0039]    The damping force adjustable fluid pressure shock absorber may further comprising a valve seat member provided in the guide bore so as to be axially movable, the valve seat member including a one end surface serving as the seat surface which abuts against the first valve body. 
         [0040]    One of the first check valve and the second check valve may be provided in the valve seat member. 
         [0041]    The guide bore may extend in an axial direction of the piston rod. 
         [0042]    In a preferred embodiment of the present invention which will be described later, fluid is embodied as oil. However, it will be appreciated that this embodiment does not limit the present invention, and fluid in the present invention may be any fluid such as a gas or others. The term “fluid” in the accompanying claims is used to denote a concept encompassing any kind of fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]      FIG. 1  is a vertical sectional view illustrating main parts of a damping force adjustable hydraulic shock absorber of an embodiment of the present invention; 
           [0044]      FIG. 2  illustrates an oil flow during an extension stroke of a piston rod in the damping force adjustable hydraulic shock absorber shown in  FIG. 1 ; 
           [0045]      FIG. 3  illustrates an oil flow during a compression stroke of a piston rod in the damping force adjustable hydraulic shock absorber shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0046]    Hereinbelow, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
         [0047]    As shown in  FIG. 1 , a damping force adjustable hydraulic shock absorber  1  (damping force adjustable fluid pressure shock absorber) of the present embodiment is a cylindrical hydraulic shock absorber. The damping force adjustable hydraulic shock absorber  1  comprises a cylinder  2  and a piston  3  slidably fitted in the cylinder  2 . The inside of the cylinder  2  is divided by the piston  3  into two chambers, i.e., a cylinder upper chamber  2 A and a cylinder lower chamber  2 B. A distal end of a piston bolt  4  is inserted through the piston  3 . The piston  3  is fixed to the distal end of the piston bolt  4  by a nut  5 . A case  6  having a substantially bottomed cylindrical form is attached to a proximal end of the piston bolt  4  (upper portion of the piston bolt  4  in  FIG. 1 ). One end of a piston rod  7  (lower portion of the piston rod  7  in  FIG. 1 ) is coupled to a bottom of the case  6 . The other end of the piston rod  7  is slidably and liquid-tightly inserted through a rod guide (not shown) and an oil seal (not shown) which are attached to an upper end of the cylinder  2 , and extends to the outside of the cylinder  2 . 
         [0048]    A reservoir is connected to a lower end of the cylinder  2  through a base valve (not shown). Oil is sealed inside the cylinder  2  as fluid, and oil and a gas are sealed in the reservoir. In some embodiments, a free piston may be slidably fitted in a bottom side of the cylinder  2  so as to define a gas chamber, and a high-pressure gas may be sealed in the gas chamber. 
         [0049]    The piston  3  includes an extension-side oil passage  8  open to the cylinder upper chamber  2 A side, and a compression-side oil passage  9  open to the cylinder lower chamber  2 B side. An extension-side damping valve  10  (damping force generating mechanism) for controlling an oil flow passing through the extension-side oil passage  8  is provided at a lower end of the piston  3 . A compression-side damping valve  11  (damping force generating mechanism) for controlling an oil flow passing through the compression-side oil passage  9  is provided at an upper end of the piston  3 . 
         [0050]    The extension-side damping valve  10  comprises an extension-side main valve  13  (disk valve) and an extension-side backpressure chamber  15 . The extension-side main valve  13  is seated on a seat portion  12  formed on a lower end face of the piston  3 . The extension-side backpressure chamber  15  is defined at the back of the extension-side main valve  13  by a valve member  14  which is attached to the piston bolt  4  by the nut  5 . An inner pressure in the extension-side backpressure chamber  15  acts on the extension-side main valve  13  in a valve-closing direction of the valve  13 . A disk valve  16  having an orifice  16 A (cutout) is provided at the valve member  14 . The extension-side backpressure chamber  15  is connected to the cylinder lower chamber  2 B through the disk valve  16 . The extension-side backpressure chamber  15  and the lower cylinder chamber  2 B are in constant communication with each other through the orifice  16 A of the disk valve  16 . When a pressure in the extension-side backpressure chamber  15  reaches a predetermined pressure, the disk valve  16  is opened, whereby the pressure is released into the lower cylinder chamber  2 B. 
         [0051]    The extension-side backpressure chamber  15  is connected to an oil passage  18  extending in a radial direction of the piston bolt  4  through a backpressure introducing valve  17  which is provided at the valve member  14 . The radially extending oil passage  18  is also in communication with a guide bore  19  which extends along an axis of the piston bolt  4 . The backpressure introducing valve  17  is a check valve which allows an oil flow from the radially extending oil passage  18  side to the extension-side backpressure chamber  15  side. The backpressure introducing valve  17  includes an orifice  17 A through which the radially extending oil passage  18  and the extension-side backpressure chamber  15  are in constant communication with each other. The guide bore  19  is in communication with a radially extending oil passage  20 . The radially extending oil passage  20  is connected to the extension-side oil passage  8  through an extension-side orifice  21  which is provided at the piston  3 . 
         [0052]    The compression-side damping valve  11  comprises an compression-side main valve  23  (disk valve) and a compression-side backpressure chamber  25 . The compression-side main valve  23  is seated on a seat portion  22  formed on an upper end face of the piston  3 . The compression-side backpressure-chamber  25  is defined at the back of the compression-side main valve  23  by a valve member  24  which is attached to the piston bolt  4  by the nut  5 . An inner pressure in the compression-side backpressure chamber  25  acts on the compression-side main valve  23  in a valve-closing direction of the valve  23 . A disk valve  26  having an orifice  26 A (cutout) is provided at the valve member  24 . The compression-side backpressure chamber  25  is connected to the cylinder upper chamber  2 A through the disk valve  26 . The compression-side backpressure chamber  25  and the cylinder upper chamber  2 A are in constant communication with each other through the orifice  26 A of the disk valve  26 . When a pressure in the compression-side backpressure chamber  25  reaches a predetermined pressure, the disk valve  26  is opened, whereby the pressure is released into the cylinder upper chamber  2 A. 
         [0053]    The compression-side backpressure chamber  25  is connected to an oil passage  29  extending in a radial direction of the piston bolt  4  through a backpressure introducing valve  28  which is provided at the valve member  24 . The radially extending oil passage  29  is open to the guide bore  19 . The backpressure introducing valve  28  is a check valve which allows an oil flow from the radially extending oil passage  29  side to the compression-side backpressure chamber  25  side. The backpressure introducing valve  28  includes an orifice  28 A through which the radially extending oil passage  29  and the compression-side backpressure chamber  25  are in constant communication with each other. Further, a radially extending oil passage  30  is provided through an side wall of the piston bolt  4 . The radially extending oil passage  30  is connected to the compression-side oil passage  9  through a compression-side orifice  31  which is provided at the piston  3 . 
         [0054]    An extension-side valve body  32  (extension-side pressure control valve, first valve body) facing the radially extending oil passages  18  and  20 , and a compression-side valve body  33  (compression-side pressure control valve, second valve body) facing the radially extending oil passages  29  and  30  are slidably fitted in the guide bore  19  of the piston bolt  4 . A valve seat member  34  is screwed in the distal end of the piston bolt  4 . A solenoid actuator  35  (damping force adjuster) is disposed inside the case  6 . A front end of the extension-side valve body  32  abuts against a seat surface  34 A of the valve seat member  34 . A front end of the compression-side valve body  33  abuts against a seat surface  32 A which is positioned at a back end of the extension-side valve body  32 . A back end of the compression-side valve body  33  abuts against a plunger  36  of the solenoid actuator  35 . 
         [0055]    The valve seat member  34  includes an oil passage  37  in communication with the guide bore  19 , and a check valve  38  (first check valve) which allows only an oil flow from the oil passage  37  to the cylinder lower chamber  2 B. The extension-side valve body  32  includes a communication passage  39  which axially extends through the extension-side valve body  32  and communicates with the oil passage  37  of the valve seat member  34 . The compression-side valve body  33  includes an oil passage  41 . The oil passage  41  extends along an axis of the compression-side valve body  33 . One end of the oil passage  41  is in communication with the communication passage  39  of the extension-side valve body  32 . The other end of the oil passage  41  is in communication with the inside of a plunger bore  40  which guides the plunger  36 . The plunger  36  includes an oil passage  43 . The oil passage  43  extends in an axial direction of the plunger  36  and through the plunger  36 . The plunger bore  40  and a chamber  42  inside the case  6  are in communication with each other through the oil passage  43 . An oil passage  44  in communication with the chamber  42 , and a check valve  45  (second check valve) which allows only an oil flow from the oil passage  44  to the cylinder upper chamber  2 A are provided at the bottom of the case  6 . 
         [0056]    While the back end side of the extension-side valve body  32  is configured to be fitted in the guide bore  19 , the front end side thereof has a smaller diameter than that of the back end side. By this configuration, an annular chamber  46  in communication with the radially extending passages  18  and  29  is defined between the front end side of the extension-side valve body  32  and a side wall of the guide bore  19 . A pressure receiving surface which receives a pressure in the annular chamber  46  is formed on the front end side of the extension-side valve body  32 . A seat surface  47  is formed at the front end of the extension-side valve body  32 . When the seat surface  47  abuts against, i.e., is seated on the seat surface  34 A of the valve seat member  34 , the communication between the annular chamber  46  and the oil passage  37  of the valve seat member  34  is cut off. On the other hand, when the extension-side valve body  32  receives a pressure in the annular chamber  46  and the seat surface  47  moves away from the valve seat member  34 , the communication between the annular chamber  46  and the oil passage  37  is established. In this way, the seat surface  47  serves as a valve. That is, the valve is closed when the seat surface  47  is seated on the seat surface  34 A, while the valve is opened when the seat surface  47  is spaced away from the seat surface  34 A. 
         [0057]    While the back end side of the compression-side valve body  33  is configured to be fitted in the guide bore  19 , the front end side thereof has a smaller diameter than that of the back end side. By this configuration, an annular chamber  48  in communication with the radially extending passages  29  and  30  is defined between the front end side of the compression-side valve body  33  and the side wall of the guide bore  19 . A pressure receiving surface which receives a pressure in the annular chamber  48  is formed on the front end side of the compression-side valve body  33 . A seat surface  49  is formed at the front end of the compression-side valve body  33 . When the seat surface  49  abuts against, i.e., is seated on the seat surface  32 A at the back end of the extension-side valve body  32 , the communication between the annular chamber  48  and the oil passage  41  of the compression-side valve body  33  is cut off. On the other hand, when the compression-side valve body  33  receives a pressure in the annular chamber  48  and the seat surface  49  moves away from the seat surface  32 A at the back end of the extension-side valve body  32 , the communication between the annular chamber  48  and the oil passage  41  is established. In this way, the seat surface  49  serves as a valve. That is, the valve is closed when the seat surface  49  is seated on the seat surface  32 A, while the valve is opened when the seat surface  49  is spaced away from the seat surface  32 A. 
         [0058]    The solenoid actuator  35  generates a thrust force acting on the plunger  36  according to a current applied to a coil  50 , and pushes the extension-side and compression-side valve bodies  32  and  33  toward the valve seat member  34  side, thereby adjusting valve-opening pressures of these valves. A spring  51  biasing the plunger  36  toward the valve seat member  34  side is provided at the solenoid actuator  35 . In addition, a spring  52  is interposed between the extension-side valve body  32  and the compression-side valve body  33 . A lead wire  53  for applying a current to the coil  50  is inserted through the hollow piston rod  7 , extending to the outside. A set load of the spring  51  can be adjusted by selecting how far the valve seat member  34  is screwed in. 
         [0059]    Next, an operation of the present embodiment configured as described above will be discussed. 
         [0060]    During an extension stroke of the piston rod  7 , until the extension-side main valve  13  is opened, oil in the cylinder upper chamber  2 A side flows into the cylinder lower chamber  2 B through the extension-side oil passage  8 , the extension-side orifice  21 , the radially extending oil passage  20 , the annular chamber  46 , the radially extending oil passage  18 , the backpressure introducing valve  17 , the extension-side backpressure chamber  15  and the orifice  16 A, as indicated by a broken line in  FIG. 2  (extension-side bypass flow passage). In addition, the extension-side valve body  32  is opened by the oil flowing through the annular chamber  46 , and therefore the oil flows from the annular chamber  46  into the cylinder lower chamber  2 B through the oil passage  37  and the check valve  38 . Once the pressure in the cylinder upper chamber  2 A side reaches the valve-opening pressure of the extension-side main valve  13 , the valve  13  is opened and then the oil starts to flow from the extension-side oil passage  8  into the cylinder lower chamber  2 B directly, as indicated by a solid line in  FIG. 2  (extension-side flow passage). It should be noted that, during the above-mentioned extension stroke, a change in volume inside the cylinder  2  due to exit of the piston rod  7  from the cylinder  2  is compensated for by expansion of the gas in the reservoir or the gas chamber. 
         [0061]    Controlling a current to be applied to the coil  50  of the solenoid actuator  35  enables adjustment of the valve-opening pressure of the extension-side valve body  32 . This adjustment enables direct control of an oil flow from the annular chamber  46  to the oil passage  37 , whereby it becomes possible to adjust the damping force. At the same time, since controlling an oil flow from the chamber  46  to the passage  37  enables adjustment of a pressure of oil introduced from the annular chamber  46  to the extension-side backpressure chamber  15 , it becomes possible to control the valve-opening pressure of the extension-side main valve  13 . 
         [0062]    When the extension-side valve body  32  is opened, the back end of the compression-side valve body  33  protrudes into the plunger bore  40  of the solenoid actuator  35 . At this time, the oil in the plunger bore  40  flows into the cylinder lower chamber  2 B, which is on the low pressure side, through the oil passage  41  of the compression-side valve body  33 , the communication passage  39  of the extension-side valve body  32 , the oil passage  37  of the valve seat member  34  and the check valve  38 . In this way, an amount of oil corresponding to the protrusion of the compression-side valve body  33  can be accommodated, whereby the extension-side valve body  32  can be smoothly opened and responsiveness of the hydraulic absorber can be enhanced. 
         [0063]    During a compression stroke of the piston rod  7 , until the compression-side main valve  23  is opened, oil in the cylinder lower chamber  2 B side flows into the cylinder upper chamber  2 A through the compression-side oil passage  9 , the compression-side orifice  31 , the radially extending oil passage  30 , the annular chamber  48 , the radially extending oil passage  29 , the backpressure introducing valve  28 , the compression-side backpressure chamber  25  and the orifice  26 A, as indicated by a broken line in  FIG. 3  (compression-side bypass flow passage). In addition, the compression-side valve body  33  is opened by the oil flowing through the annular chamber  48 , and therefore the Oil flows from the annular chamber  48  into the cylinder upper chamber  2 A through the oil passage  41  and the plunger bore  40 , the oil passage  43  of the plunger  36 , the oil passage  44  of the case  6  and the check valve  45 . Once the pressure in the cylinder lower chamber  2 B side reaches the valve-opening pressure of the compression-side main valve  23 , the valve  23  is opened and then the oil starts to flow from the compression-side oil passage  9  into the cylinder upper chamber  2 A directly, as indicated by a solid line in  FIG. 3  (compression-side flow passage). It should be noted that, during the above-mentioned compression stroke, a change in volume inside the cylinder  2  due to entry of the piston rod  7  into the cylinder  2  is compensated for by compression of the gas in the reservoir or the gas chamber. 
         [0064]    Controlling a current to be applied to the coil  50  of the solenoid actuator  35  enables adjustment of the valve-opening pressure of the compression-side valve body  33 . This adjustment enables direct control of an oil flow from the annular chamber  48  to the oil passage  41 , whereby it becomes possible to adjust the damping force. At the same time, since controlling the oil flow from the chamber  48  to the passage  41  enables adjustment of a pressure of oil introduced from the annular chamber  48  to the compression-side backpressure chamber  25 , it becomes possible to control the valve-opening pressure of the compression-side main valve  23 . 
         [0065]    When the compression-side valve body  33  is opened, the back end of the compression-side valve body  33  protrudes into the plunger bore  40  of the solenoid actuator  35 . At this time, the oil in the plunger bore  40  flows into the cylinder upper chamber  2 A, which is on the low pressure side, through the oil passage  43  of the plunger  36 , the oil passage  44  of the case  6  and the check valve  45 . In this way, an amount of oil corresponding to the protrusion of the compression-side valve body  33  can be accommodated, whereby the compression-side valve body  33  can be smoothly opened and responsiveness of the hydraulic absorber can be enhanced. 
         [0066]    In this way, it is possible to adjust the valve-opening pressures of the extension-side and compression-side valve bodies  32  and  33  by use of the common solenoid actuator  35 , and at the same time, it is possible to adjust the valve-opening pressures of the extension-side and compression-side main valves  13  and  23  by utilizing the inner pressures in the extension-side and compression-side backpressure chambers  15  and  25 . As a result, it becomes possible to realize a simple structure while increasing an adjustable range of damping forces. 
         [0067]    According to the damping force adjustable fluid pressure shock absorber of the present embodiment, it is possible to, by adjusting the valve-opening pressures of the extension-side and compression-side pressure control valves by use of the damping force adjuster, control flows of fluid passing through the extension-side and compression-side bypass flow passages, and thereby to adjust the damping force; at the same time, it is possible to adjust the valve-opening pressures of the extension-side and compression-side main valves by adjusting pressures of fluid introduced into the extension-side and compression-side backpressure chambers. When the first or second valve of the extension-side or compression-side pressure control valve is opened, fluid is discharged from the guide bore into either of the two chambers in the cylinder through the communication passages and the first or second check valve. Therefore, it is possible to move the first and second valve bodies smoothly, and to enhance responsiveness of the fluid pressure shock absorber. 
         [0068]    Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teaching and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. 
         [0069]    The present application claims priority under 35 U.S.C. section 119 to Japanese Patent Application No. 2007-94803, filed on Mar. 30, 2007. 
         [0070]    The entire disclosure of Japanese Patent Application No. 2007-94803 filed on Mar. 30, 2007 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.