Patent Publication Number: US-2018031070-A1

Title: Shock absorber

Description:
TECHNICAL FIELD 
     The present invention relates to a shock absorber. 
     BACKGROUND ART 
     Patent Document 1 discloses a conventional shock absorber. This shock absorber includes a cylinder, a piston, a piston rod, and a sensor. The piston is inserted into the cylinder to be axially movable therein. The piston divides an interior of the cylinder into a rod-side chamber and a piston-side chamber. The piston rod has an end connected to the piston and extends on a central axis of the cylinder, protruding out of the cylinder. The piston rod is cylindrical in shape and has a central hole extending therethrough on a central axis thereof. The piston is provided with a through hole coaxial with the central hole of the piston rod. The sensor has a body and a rod part. The body of the sensor is fixed to an end of the cylinder (the end opposed to the other end through which the piston rod protrudes). The rod part of the sensor extends in the cylinder on the central axis of the cylinder to be slidably inserted into the through hole of the piston and the central hole of the piston rod. The sensor can detect the length of the rod part inserted into the through hole of the piston and the central hole of the piston rod. 
     Thus, this shock absorber does not require any extra mounting space when to be mounted on other equipment since the sensor is built therein. Furthermore, since this shock absorber detects an expansion/contraction amount by the sensor and performs adjustment of a damping force or the like, this shock absorber can execute a feedback control or the like according to the expansion/contraction amount. 
     PRIOR ART DOCUMENT 
     Patent Documents 
     
         
         Patent Document 1: Japanese Patent Application Publication No. JP 2010-12835 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Overcome by the Invention 
     In the shock absorber of Patent Document 1, however, the rod part of the sensor extends in the cylinder to be inserted into the through hole of the piston and the central hole of the piston rod. Accordingly, when a moving direction of the piston and the piston rod is shifted relative to an extending direction of the rod part of the sensor during expansion/contraction of the shock absorber, the rod part collides against the through hole of the piston and the central hole of the piston rod, with the result that the rod part would be broken, for example, would be bent. When the rod part of the sensor is broken, the shock absorber cannot accurately detect the expansion/contraction amount. 
     The present invention was made in view of the above-described circumstances in the conventional art and has an object to provide a shock absorber including a sensor accurately detecting the position of the cylinder relative to the piston rod. 
     Means for Overcoming the Problem 
     The shock absorber of the present invention includes a cylinder, a piston, a piston rod, and a sensor. The piston is inserted into the cylinder thereby to divide an interior of the cylinder into a rod-side chamber and a piston-side chamber. The piston is axially moved in the cylinder. The piston rod has an end connected to the piston and protrudes out of the cylinder. The sensor is disposed in the piston rod. The sensor detects a position of the cylinder relative to the piston rod. 
     The shock absorber of the present invention may further include a rod guide. The rod guide is provided in an open end of the cylinder and having a through hole through which the piston rod is inserted to be axially movable. The rod guide has a detected object built therein. The detected object is detected by the sensor. 
     The sensor of the shock absorber of the present invention may detect the position of the cylinder over an entire movement range of the cylinder relative to the piston rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of a shock absorber of a first embodiment; 
         FIG. 2  is a schematic sectional view of a shock absorber of a second embodiment; and 
         FIG. 3  is a schematic sectional view of a shock absorber of another embodiment. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First and second embodiments of the shock absorber of the present invention will be described with reference to the drawings. 
     First Embodiment 
     A shock absorber of the first embodiment is used in a front fork suspending a front wheel of a motor cycle or the like. The shock absorber includes a cylinder  10 , a piston  20 , a piston rod  30 , a rod guide  40 , an extended spring  50 , a bracket  60 , an inner tube  70 , an outer tube  75 , a cap  80 , a main spring  55 , and a sensor  90 . 
     The cylinder  10  is cylindrical in shape. The cylinder  10  has an end (a lower end as viewed in  FIG. 1 ) connected to a bracket  60  which will be described later. The piston  20  is columnar in shape. The piston  20  is inserted into the cylinder  10 . The piston  20  divides an interior of the cylinder  10  into a rod-side chamber  11  and a piston-side chamber  13 . The piston  20  is moved in an axial direction of the cylinder  10  while being in sliding contact with an inner peripheral surface of the cylinder  10 . The rod-side chamber  11  and the piston-side chamber  13  are filled with a hydraulic fluid. The rod-side chamber  11  and the piston-side chamber  13  communicate with each other via a flow path (not illustrated). The shock absorber generates a damping force by imparting resistance to the hydraulic fluid passing through the flow path. 
     The piston rod  30  is cylindrical in shape. The piston rod  30  is a strength member. The piston rod  30  has two ends one of which (a lower end of the piston rod  30  as viewed in  FIG. 1 ) is connected to the piston  20 . The piston rod  30  extends on a central axis of the cylinder  10 , protruding out of the other end of the cylinder  10  (an upper end of the cylinder  10  as viewed in  FIG. 1 ). The other end of the piston rod  30  (an upper end of the piston rod  30  as viewed in  FIG. 1 ) is connected to the cap  80  which will be described later, while being inserted into a connecting part  85  of the cap  80 . 
     The rod guide  40  is connected to an open end (an upper end of the cylinder  10  as viewed in  FIG. 1 ) which is the other end of the cylinder  10 . The rod guide  40  is annular in shape. The rod guide  40  has a central through hole through which the piston rod  30  is inserted to be axially movable. The rod guide  40  has a recess going around an inner peripheral surface of the through hole. An annular magnet  41  serving as a detected object is built in the recess of the rod guide  40 . The magnet  41  has an inner diameter that substantially equals an inner diameter of the through hole of the rod guide  40 . 
     The extended spring  50  is a compression coil spring. The extended spring  50  is disposed between the piston  20  and the rod guide  40  at an outer peripheral side of the piston rod  30 . The extended spring  50  has an end fixed to the rod guide  40 . When the piston rod  30  is moved in an exiting direction from the cylinder  10  with the result that the shock absorber is expanded by a predetermined amount, the extended spring  50  generates an elastic force between the piston  20  and the rod guide  40 , thereby absorbing shock. 
     The bracket  60  is provided with an attaching hole  61  to be attached to a shaft member. The bracket  60  is connected to the one end side of the cylinder  10  as described above. The bracket  60  is also connected to an end of the inner tube  70  (a lower end of the inner tube  70  as viewed in  FIG. 1 ) which will be described later. 
     The inner tube  70  is cylindrical in shape. The inner tube  70  is connected to the bracket  60  to be coaxial with the cylinder  10  and extends to cover the cylinder  10  and the rod guide  40 . The inner tube  70  is moved together with the cylinder  10  when the shock absorber is expanded/contracted. 
     The outer tube  75  is cylindrical in shape and has a larger diameter than the inner tube  70 . The outer tube  75  has two ends one of which (a lower end of the outer tube  75  as viewed in  FIG. 1 ) is located outside the inner tube  70  even when the shock absorber is most expanded. In other words, the shock absorber is expanded/contracted while the one end of the outer tube  75  always overlaps the other end of the inner tube  70 . The other end of the outer tube  75  (an upper end of the outer tube  75  as viewed in  FIG. 1 ) is connected to the cap  80  in abutment against the cap  80  so as to cover an outer peripheral surface of the cap  80 . The outer tube  75  is moved together with the cap  80 , the piston rod  30 , and the piston  20  when the shock absorber is expanded/contracted. 
     The cap  80  has a cylindrical part  81 , a flat surface part  83  spreading inward from an end of the cylindrical part  81  (a lower end of the cylindrical part  81  as viewed in  FIG. 1 ) and formed with a centrally located through hole, and a cylindrical connecting part  85  which is coaxial with the through hole and extends to the side opposite the cylindrical part  81 . The cylindrical part  81  has an outer diameter that substantially equals an inner diameter of the outer tube  75 . The connecting part  85  has an inner diameter that substantially equals the outer diameter of the piston rod  30 . 
     The main spring  55  is a compression coil spring. The main spring  55  is disposed around the piston rod  30  and interposed via a spring receiving member  55 A between the flat surface part  83  of the cap  80  and the rod guide  40 . When the shock absorber is contracted, the main spring  55  generates an elastic force between the cap  80  and the rod guide  40 , thereby absorbing shock. 
     The sensor  90  includes a sensor body  91  and a sensor probe  93  extending from the sensor body  91 . The sensor body  91  is disposed in the cap  80  to be fixed therein. The sensor probe  93  is inserted through the piston rod  30  and has a distal end inserted into the piston  20  so that the distal end is prevented from protruding from a distal end surface of the piston  20  (a lower end surface as viewed in  FIG. 1 ). The sensor  90  is a position sensor applying a magnetostriction phenomenon by magnetostriction effect. In other words, when the shock absorber is expanded/contracted, strain is generated in a magnetic field on the sensor probe  93  by the magnet  41  built in the rod guide  40  moved along the piston rod  30 . The sensor  90  measures a propagation time of the generated strain by the sensor body  91 , thereby detecting a position of the magnet  41  (a position of the rod guide  40 ). Since the sensor probe  93  extends over an entire length of the piston rod  30 , the sensor  90  can detect the position of the cylinder  10  over an entire movement range of the cylinder  10  relative to the piston rod  30 . In other words, the sensor  90  can continuously grasp expansion/contraction state of the shock absorber. 
     Thus, the shock absorber includes the cylinder  10 , the piston  20 , the piston rod  30 , and the sensor  90 . The piston  20  is inserted into the cylinder  10 , dividing the interior of the cylinder  10  into the rod-side chamber  11  and the piston-side chamber  13 . Furthermore, the piston  20  is moved in the axial direction of the cylinder  10 . The piston rod  30  has one end connected to the piston  20  and protrudes out of the cylinder  10 . The sensor  90  includes the sensor probe  93  disposed in the piston rod  30 . The sensor  90  detects the position of the cylinder  10  relative to the piston rod  30 . 
     Since the piston rod  30  of the shock absorber is the strength member, the sensor probe  93  of the sensor  90  disposed inside the piston rod of the shock absorber can be protected with the result that the sensor  90  can be prevented from being broken when the shock absorber is expanded/contracted or in another case. 
     Accordingly, the shock absorber of the first embodiment includes the sensor  90  which accurately detects the position of the cylinder  10  relative to the piston rod  30 . 
     The shock absorber of the first embodiment further includes the rod guide  40 . The rod guide  40  is provided on the open end of the cylinder  10  and has the through hole through which the piston rod  30  is inserted to be axially movable. The rod guide  40  further has the built-in magnet  41  serving as the detected object which is to be detected by the sensor  90 . Thus, since the magnet  41  is built in the rod guide  40  which is a required component, no special structure needs to be added to the shock absorber for the purpose of disposition of the magnet  41 , so that the shock absorber can be rendered simple in the structure thereby to be prevented from being increased in size. 
     Furthermore, the sensor  90  of the shock absorber of the first embodiment detects the position of the cylinder  10  over the entire movement range of the cylinder  10  relative to the piston rod  30 . As a result, since expansion/contraction state of the shock absorber can continuously be grasped, a feedback control or the like can be executed in order to perform adjustment of the damping force of the shock absorber according to the expansion/contraction state. 
     Second Embodiment 
     The shock absorber of a second embodiment is used in a rear cushion unit suspending a rear wheel of a motor cycle or the like as illustrated in  FIG. 2 . Identical or similar parts in the second embodiment are labeled by the same reference symbols as those in the first embodiment and detailed description of these parts will be eliminated. 
     The shock absorber includes a cylinder  110 , the piston  20 , the piston rod  30 , the rod guide  40 , the extended spring  50 , a bracket  160 , a main spring  155 , and the sensor  90 . The cylinder  110  is cylindrical in shape. The cylinder  110  has an end which is closed (a lower end of the cylinder  110  as viewed in  FIG. 2 ). The closed end of the cylinder  110  is provided with an attaching hole  111  to be attached to the shaft member. A flange  113  against which one end of the main spring  155  to be described later (a lower end of the main spring  155  as viewed in  FIG. 2 ) abuts is fixed to an outer peripheral surface of the cylinder  110 . The flange  113  includes a cylindrical part  113 A which is fixed to the outer peripheral surface of the cylinder  110  and an annular abutment part  113 B which spreads outward from one end of the cylindrical part  113 A (a lower end of the cylindrical part  113 A as viewed in  FIG. 2 ) and against which the one end of the main spring  155  abuts. 
     The piston rod  30  is connected to the bracket  160  with the other end thereof (an upper end of the piston rod  30  as viewed in  FIG. 2 ) being inserted into a connecting part  165  of the bracket  160 . The bracket  160  includes a housing part  161  housing the sensor body  91 , an annular flange  163  spreading outward from an outer peripheral surface of the housing part  161 , a cylindrical connecting part  165  extending in one of two directions (downward as viewed in  FIG. 2 ) from the housing part  161 , and an attaching part  167  extending in the other direction (upward as viewed in  FIG. 2 ). The housing part  161  has a cylindrical part  161 A and a flat surface part  161 B spreading inward from one end of the cylindrical part  161 A (a lower end of the cylindrical part  161 A as viewed in  FIG. 2 ) and formed with a centrally located through hole. The connecting part  165  extends coaxially with the through hole of the flat surface part  161 B of the housing part  161 . The attaching part  167  is provided with an attaching hole  167 A to be attached to a shaft member. 
     The main spring  155  is a compression coil spring. The main spring  155  is disposed around the piston rod  30  and a part of the cylinder  110  located at the side where the piston rod  30  protrudes and is interposed between the flange  113  of the cylinder  110  and the flange  163  of the bracket  160 . When the shock absorber is contracted, the main spring  155  generates an elastic force between the bracket  160  and the flange  113 , thereby absorbing shock. 
     The sensor body  91  of the sensor  90  is housed in the housing part  161  of the bracket  160 . Furthermore, the sensor probe  93  of the sensor  90  is disposed inside the piston rod  30  to extend over an entire length of the piston rod  30 . The sensor  90  is a position sensor applying a magnetostriction phenomenon by magnetostriction effect. Since the sensor probe  93  extends over the entire length of the piston rod  30 , the sensor  90  can detect the position of the cylinder  110  over an entire movement range of the cylinder  110  relative to the piston rod  30 . In other words, the sensor  90  can continuously grasp expansion/contraction state of the shock absorber. 
     Thus, the shock absorber includes the cylinder  110 , the piston  20 , the piston rod  30 , and the sensor  90 . The piston  20  is inserted into the cylinder  110 , dividing the interior of the cylinder  110  into the rod-side chamber  11  and the piston-side chamber  13 . Furthermore, the piston  20  is moved in the axial direction of the cylinder  110 . The piston rod  30  has one end connected to the piston  20  and protrudes out of the cylinder  110 . The sensor  90  includes the sensor probe  93  disposed inside the piston rod  30 . The sensor  90  detects the position of the cylinder  110  relative to the piston rod  30 . 
     Since the piston rod  30  of the shock absorber is the strength member, the sensor probe  93  of the sensor  90  disposed inside the piston rod of the shock absorber can be protected by the piston rod  30  with the result that the sensor  90  can be prevented from being broken when the shock absorber is expanded/contracted or in another case. 
     Accordingly, the shock absorber of the second embodiment includes the sensor  90  which accurately detects the position of the cylinder  110  relative to the piston rod  30 . 
     The shock absorber of the second embodiment further includes the rod guide  40 . The rod guide  40  is provided in the open end of the cylinder  110  and has the through hole through which the piston rod  30  is inserted to be axially movable. The rod guide  40  further has the built-in magnet  41  serving as the detected object which is to be detected by the sensor  90 . Thus, since the magnet  41  is built in the rod guide  40  which is a required component, no special structure needs to be added to the shock absorber for the purpose of disposition of the magnet  41 , so that the shock absorber can be rendered simple in the structure thereby to be prevented from being increased in size. 
     Furthermore, the sensor  90  of the shock absorber of the second embodiment detects the position of the cylinder  110  over the entire movement range of the cylinder  110  relative to the piston rod  30 . As a result, since expansion/contraction state of the shock absorber can continuously be grasped, a feedback control or the like can be executed in order to perform adjustment of the damping force of the shock absorber according to the expansion/contraction state. 
     OTHER EMBODIMENTS 
     The present invention should not be limited to the first and second embodiments described above with reference to the drawings, but the technical scope of the invention encompasses the following embodiments, for example. 
     (1) Although the magnet serving as the detected object is built in the rod guide in each of the first and second embodiments, a new structure may be provided to dispose the detected object around the piston rod so that the detected object is not moved relative to the cylinder.
 
(2) In each of the first and second embodiments, the sensor is the position sensor applying a magnetostriction phenomenon by magnetostriction effect. However, the sensor may be a position sensor applying another principle.
 
(3) Although the sensor detects the position of the cylinder over the entire movement range of the cylinder relative to the piston rod in each of the first and second embodiments, the sensor may detect a predetermined position of the cylinder relative to the piston rod.
 
(4) The shock absorber is used in the front fork in the first embodiment and in the rear cushion unit in the second embodiment. However, the shock absorber may be used for other purposes.
 
(5) Although the extended spring is disposed between the piston and the rod guide in the first embodiment, the extended spring may be disposed between the outer tube and the inner tube.
 
(6) Although the extended spring is provided in each of the first and second embodiments, the extended spring may not be provided.
 
(7) Although the main spring is provided in each of the first and second embodiments, the main spring may not be provided.
 
(8) Although the inner tube is connected to the bracket and the outer tube is connected to the cap in the first embodiment, the inner tube  170  may be connected to or may be formed integrally with the cap  80  and the outer tube  175  may be connected to or may be formed integrally with the bracket  60 , as illustrated in  FIG. 3  (identical or similar parts in  FIG. 3  are labeled by the same reference symbols as those in the first embodiment and detailed description of these parts will be eliminated).
 
(9) Although the main spring is interposed via the spring receiving member between the cap and the rod guide in the first embodiment, the main spring may be interposed between the cap and the rod guide without provision of the spring receiving member.
 
(10) Although one of the ends of the extended spring is fixed to the rod guide in the first embodiment, the one end may not be fixed to the rod guide but the other end of the extended spring may be fixed to the piston. Furthermore, neither ends of the extended spring may be connected to the rod guide or the piston.
 
(11) In the first embodiment, the cap has the connecting part extending to the side opposite the cylindrical part and the other end of the piston rod is inserted into the connecting part to be connected. However, the connecting part may be a recess formed by recessing the flat surface part into the cylindrical part and the other end of the piston rod may be inserted into the recess to be connected.
 
(12) Although the sensor probe is inserted into the piston in the first embodiment, the sensor probe just need to have a length extending to or beyond the piston side end surface of the magnet (the detected object) built in the rod guide in a most expanded state of the shock absorber, and extending not beyond the distal end surface of the piston (such a length that the distal end of the sensor probe does not protrude from the distal end surface of the piston). Additionally, when the piston rod extends through the piston to protrude from the distal end surface of the piston, the sensor probe just need to have a length that is equal to or shorter than that of the piston rod.
 
     EXPLANATION OF REFERENCE SYMBOLS 
     
         
         
           
               10 ,  110  . . . cylinder,  11  . . . rod-side chamber,  13  . . . piston-side chamber,  20  . . . piston,  30  . . . piston rod,  40  . . . rod guide,  41  . . . magnet (detected object), and  90  . . . sensor.