Patent Publication Number: US-2023144713-A1

Title: Solenoid, damping force adjustment mechanism, and damping force adjustable shock absorber

Description:
TECHNICAL FIELD 
     The present disclosure relates to a solenoid, a damping force adjustment mechanism, and a damping force adjustable shock absorber used to adjust a damping force to, for example, damp a vibration of a vehicle. 
     BACKGROUND ART 
     Generally, suspension apparatuses such as semi-active suspensions mounted on vehicles are equipped with a damping force adjustable shock absorber configured to variably adjust a damping force according to, for example, the running condition and the behavior of the vehicle. Then, one known type of the damping force adjustable shock absorber is a shock absorber using a solenoid as an electromagnetic actuator for variably adjusting the damping force. Further, a solenoid is also used for an electromagnetic valve that, for example, controls a hydraulic pressure as an electromagnetic actuator for controlling opening and closing of the valve. 
     For example, as this type of solenoid, PTL 1 discusses a solenoid including a coil that generates a magnetic force in reaction to power supply, a housing and a yoke disposed on the inner peripheral side of this coil and made from a magnetic body (first and second fixed iron cores), a connection member (a non-magnetic member) axially connecting these housing and yoke therebetween and made from a non-magnetic body, and a movable element (an armature) disposed on the inner peripheral sides of the above-described housing, yoke, and non-magnetic member and provided axially movably. 
     Further, PTL 1 discusses that a brazing method is used to join the non-magnetic member between the housing and the yoke. In this case, after the non-magnetic member is joined between the housing and the yoke by the brazing, cutting processing may be applied in such a manner that the inner peripheral surface thereof is shaped into a stepless circumferential surface. By this processing, PTL 1 allows the solenoid to improve the slidability of the movable element on the above-described inner peripheral surface. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Application Public Disclosure No. 2009-127692 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     Then, the solenoid configured as indicated in PTL 1 includes the non-magnetic member joined between the housing and the yoke (the first and second fixed iron cores), thereby achieving an increase in the magnetic flux density of the magnetic circuit with respect to the movable element due to the non-magnetic member. However, the non-magnetic member involves such a problem that applying mechanical processing (for example, the processing of cutting the inner peripheral surface) after the joining leads to a change in the magnetic characteristic due to an influence of heat, thereby facilitating the magnetization of the non-magnetic member. 
     An object of one aspect of the present invention is to provide a solenoid, a damping force adjustment mechanism, and a damping force adjustable shock absorber configured to be able to maintain a high magnetic flux density with respect to a movable element between a housing (i.e., a housing member) and a yoke and maintain an excellent thrust force characteristic, and also improve workability at the time of assembling. 
     Solution to Problem 
     According to one aspect of the present invention, a solenoid includes a coil wound annularly and configured to generate a magnetic force in reaction to power supply, and a housing member disposed on an inner periphery of the coil. The housing member extends in a direction of a winding axis of the coil. The housing member includes a housing portion opened on one end side thereof, and is made from a magnetic body. The solenoid further includes a movable element provided in the housing portion movably in the direction of the winding axis of the coil and made from a magnetic body, and a stator provided at a position facing the opening of the housing portion. The stator includes a reduced diameter portion and a side surface portion integrally made from a magnetic body. The reduced diameter portion has an outer diameter reducing as it is approaching the opening of the housing portion. The side surface portion extends from an outer periphery of the reduced diameter portion in a direction away from the opening of the housing portion. The solenoid further includes a yoke including a fixation hole having an inner peripheral surface to which a part of the side surface portion of the stator is fixed. A non-contact portion, where the yoke and the side surface portion of the stator are out of contact with each other, is formed on the housing member side of the fixation hole. 
     According to one aspect of the present invention, a damping force adjustment mechanism includes a coil wound annularly and configured to generate a magnetic force in reaction to power supply, and a housing member disposed on an inner periphery of the coil. The housing member extends in a direction of a winding axis of the coil. The housing member includes a housing portion opened on one end side thereof, and is made from a magnetic body. The damping force adjustment mechanism further includes a movable element provided in the housing portion movably in the direction of the winding axis of the coil and made from a magnetic body, a control valve configured to be controlled according to a movement of the movable element, and a stator provided at a position facing the opening of the housing portion. The stator includes a reduced diameter portion and a side surface portion integrally made from a magnetic body. The reduced diameter portion has an outer diameter reducing as it is approaching the opening of the housing portion. The side surface portion extends from an outer periphery of the reduced diameter portion in a direction away from the opening of the housing portion. The damping force adjustment mechanism further includes a yoke including a fixation hole having an inner peripheral surface to which a part of the side surface portion of the stator is fixed. A non-contact portion, where the yoke and the side surface portion of the stator are out of contact with each other, is formed on the housing member side of the fixation hole. 
     According to one aspect of the present invention, a damping force adjustable shock absorber includes a cylinder sealingly containing hydraulic fluid therein, a piston provided slidably in the cylinder, a piston rod coupled with the piston and extending out of the cylinder, and a damping force adjustment mechanism configured to generate a damping force by controlling a flow of the hydraulic fluid that is generated according to a sliding movement of the piston in the cylinder. The damping force adjustment mechanism includes a coil wound annularly and configured to generate a magnetic force in reaction to power supply, and a housing member disposed on an inner periphery of the coil. The housing member extends in a direction of a winding axis of the coil. The housing member includes a housing portion opened on one end side thereof, and is made from a magnetic body. The damping force adjustment mechanism further includes a movable element provided in the housing portion movably in the direction of the winding axis of the coil and made from a magnetic body, a control valve configured to be controlled according to a movement of the movable element, and a stator provided at a position facing the opening of the housing portion. The stator includes a reduced diameter portion and a side surface portion integrally made from a magnetic body. The reduced diameter portion has an outer diameter reducing as it is approaching the opening of the housing portion. The side surface portion extends from an outer periphery of the reduced diameter portion in a direction away from the opening of the housing portion. The damping force adjustment mechanism further includes a yoke including a fixation hole having an inner peripheral surface to which a part of the side surface portion of the stator is fixed. A non-contact portion, where the yoke and the side surface portion of the stator are out of contact with each other, is formed on the housing member side of the fixation hole. 
     Therefore, according to the aspects of the present embodiment, it becomes possible to maintain a high magnetic flux density passing through the movable element between the housing member and the yoke (the stator) and maintain an excellent thrust force characteristic, and can also improve the workability at the time of the assembling. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a vertical cross-sectional view illustrating a damping force adjustable shock absorber in which a solenoid according to a first embodiment is provided. 
         FIG.  2    is a cross-sectional view illustrating a damping force adjustment valve and the solenoid in  FIG.  1    in an enlarged manner. 
         FIG.  3    is a cross-sectional view illustrating the solenoid in an enlarged manner with the damping force adjustment valve in  FIG.  2    removed therefrom. 
         FIG.  4    is an enlarged view of main portions, which illustrates main portions of the solenoid in  FIG.  3    in an enlarged manner. 
         FIG.  5    is an enlarged view of main portions of a solenoid according to a second embodiment. 
         FIG.  6    is an enlarged view of main portions of a solenoid according to a third embodiment. 
         FIG.  7    is an enlarged view of main portions of a solenoid according to a fourth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following description, solenoids, damping force adjustment mechanisms, and damping force adjustable shock absorbers according to embodiments of the present invention will be described in detail with reference to  FIGS.  1  to  7   , citing examples in which they are applied to a damping force adjustable hydraulic shock absorber. 
     Now,  FIGS.  1  to  4    illustrate a first embodiment. In  FIG.  1   , a damping force adjustable hydraulic shock absorber  1  (hereinafter referred to as a hydraulic shock absorber  1 ) is equipped with a solenoid  33 , which will be described below. This hydraulic shock absorber  1  includes an outer tube  2 , an inner tube  4 , a piston  5 , a piston rod  8 , a rod guide  9 , a damping force adjustment mechanism  17 , and the like. In the following description, the first embodiment will be described, assuming that, for example, one axial side of the outer tube  2  and the inner tube  4  is a lower side, a lower portion side, or a lower end side, and an opposite axial side is an upper side, an upper portion side, or an upper end side. 
     The bottomed cylindrical outer tube  2 , which forms the outer shell of the hydraulic shock absorber  1 , has a lower end side closed by a bottom cap  3 , and an upper end side formed as a radially inward bent crimped portion  2 A. The rod guide  9  and a seal member  10  are provided between the crimped portion  2 A and the inner tube  4 . On the other hand, an opening  2 B is formed on the lower portion side of the outer tube  2  concentrically with a connection port  12 C of an intermediate tube  12 , which will be described below, and the damping force adjustment mechanism  17 , which will be described below, is attached so as to face this opening  2 B. Further, a mounting eye  3 A, which is attached to, for example, a wheel side of a vehicle, is provided on the bottom cap  3 . 
     The inner tube  4  is provided in the outer tube  2  coaxially with this outer tube  2 . This inner tube  4  has a lower end side fittedly attached to a bottom valve  13  and an upper end side fittedly attached to the rod guide  9 . Hydraulic liquid as hydraulic fluid is sealingly contained in the inner tube  4 , which forms a cylinder together with the outer tube  2 . The hydraulic liquid is not limited to oil liquid and oil, and may be, for example, water containing an additive mixed therein. 
     An annular reservoir chamber A is formed between the inner tube  4  and the outer tube  2 , and gas is sealingly contained in this reservoir chamber A together with the hydraulic liquid. This gas may be air in an atmospheric pressure state, or gas such as compressed nitrogen gas may be used as it. Further, the inner tube  4  is pierced to form an oil hole  4 A radially at an intermediate position of the inner tube  4  in the length direction (the axial direction) thereof. The oil hole  4 A establishes constant communication of a rod-side oil chamber B with an annular oil chamber D. 
     The piston  5  is slidably fittedly inserted in the inner tube  4 . The piston  5  divides the inside of the inner tube  4  into two chambers, a rod-side chamber (the rod-side oil chamber B) and a bottom-side chamber (a bottom-side oil chamber C). A plurality of oil passages  5 A and a plurality of oil passages  5 B are each formed on the piston  5  at circumferential intervals. The oil passages  5 A and  5 B can establish communication between the rod-side oil chamber B and the bottom-side oil chamber C. 
     Then, an extension-side disk valve  6  is provided on the lower end surface of the piston  5 . The extension-side disk valve  6  is opened upon exceedance of the pressure in the rod-side oil chamber B over a relief setting pressure when the piston  5  is slidably displaced upward during an extension stroke of the piston rod  8 , and relieves the pressure at this time into the bottom-side oil chamber C side via each of the oil passages  5 A. This relief setting pressure is set to a higher pressure than a valve-opening pressure when the damping force adjustment mechanism  17 , which will be described below, is set to the hard side. 
     A compression-side check valve  7  is provided on the upper end surface of the piston  5 . The compression-side check valve  7  is opened when the piston  5  is slidably displaced downward during a compression stroke of the piston rod  8 , and otherwise is closed. This check valve  7  functions to permit a flow of the oil liquid in the bottom-side oil chamber C through each of the oil passages  5 B toward the rod-side oil chamber B, and prohibit a flow of the oil liquid in the opposite direction therefrom. The valve-opening pressure of this check valve  7  is set to a lower pressure than a valve-opening pressure when the damping force adjustment mechanism  17 , which will be described below, is set to the soft side, and the check valve  7  generates substantially no damping force. Generating substantially no damping force here means a force equal to or weaker than friction of the piston  5  and the seal member  10 , and not affecting a motion of the vehicle. 
     The piston rod  8  extends axially (vertically) in the inner tube  4 . The piston rod  8  is provided in such a manner that the lower end side thereof is inserted in the inner tube  4  and is fixedly attached to the piston  5  with use of a nut  8 A and the like. Further, the upper end side of the piston rod  8  protrudes so as to extend out of the outer tube  2  and the inner tube  4  via the rod guide  9 . 
     The stepped cylindrical rod guide  9  is provided on the upper end side of the inner tube  4 . The rod guide  9  positions the upper portion of the inner tube  4  at the center of the outer tube  2 , and also axially slidably guides the piston rod  8  on the inner peripheral side thereof. Further, the annular seal member  10  is provided between the rod guide  9  and the crimped portion  2 A of the outer tube  2 . The seal member  10  is a member formed by baking an elastic material such as rubber to an annular metallic plate with the piston rod  8  inserted therethrough at the center thereof, and functions to seal between the seal member  10  and the piston rod  8  due to a sliding contact of the inner periphery thereof to the outer peripheral surface of the piston rod  8 . 
     Further, a lip seal  10 A is formed on the seal member  10  on the lower surface side. The lip seal  10 A extends in contact with the rod guide  9 , and serves as a check valve. The lip seal  10 A is disposed between an oil pool chamber  11  and the reservoir chamber A, and functions to permit a flow of the oil liquid and the like in the oil pool chamber  11  toward the reservoir chamber A side via a return passage  9 A of the rod guide  9  and prohibit a flow in the opposite direction therefrom. 
     The intermediate tube  12 , which is a tubular member, is arranged between the outer tube  2  and the inner tube  4 . This intermediate tube  12  is, for example, attached to the outer peripheral side of the inner tube  4  via upper and lower tubular seals  12 A and  12 B. The intermediate tube  12  forms therein the annular oil chamber D extending so as to surround the outer peripheral side of the inner tube  4  throughout the entire circumference thereof, and the annular oil chamber D is prepared as an oil chamber independent of the reservoir chamber A. The annular oil chamber D is in constant communication with the rod-side oil chamber B via the radial oil hole  4 A formed through the inner tube  4 . The annular oil chamber D serves as a flow passage through which a flow of the hydraulic liquid is generated due to a movement of the piston rod  8 . Further, the connection port  12 C is provided on the lower end side of the intermediate tube  12 . A connection tubular member  20  of a damping force adjustment valve  18 , which will be described below, is attached to the connection port  12 C. 
     The bottom valve  13  is provided between the bottom cap  3  and the inner tube  4  while being located on the lower end side of the inner tube  4 . The bottom valve  13  includes a valve body  14 , a compression-side disk valve  15 , and an extension-side check valve  16 . The valve body  14  defines the reservoir chamber A and the bottom-side oil chamber C between the bottom cap  3  and the inner tube  4 . The compression-side disk valve  15  is provided on the lower surface side of the valve body  14 . The extension-side check valve  16  is provided on the upper surface side of the valve body  14 . Oil passages  14 A and  14 B are each formed on the valve body  14  at circumferential intervals. The oil passages  14 A and  14 B can establish communication between the reservoir chamber A and the bottom-side oil chamber C. 
     The compression-side disk valve  15  is opened upon exceedance of the pressure in the bottom-side oil chamber C over a relief setting pressure when the piston  5  is slidably displaced downward during the compression stroke of the piston rod  8 , and relieves the pressure at this time into the reservoir chamber A side via each of the oil passages  14 A. This relief setting pressure is set to a higher pressure than the valve-opening pressure when the damping force adjustment mechanism  17 , which will be described below, is set to the hard side. 
     The extension-side check valve  16  is opened when the piston  5  is slidably displaced upward during the extension stroke of the piston rod  8 , and otherwise is closed. This extension-side check valve  16  functions to permit a flow of the oil liquid in the reservoir chamber A through each of the oil passages  14 B toward the bottom-side oil chamber C, and prohibit a flow of the oil liquid in the opposite direction therefrom. The valve-opening pressure of the extension-side check valve  16  is set to a lower pressure than the valve-opening pressure when the damping force adjustment mechanism  17 , which will be described below, is set to the soft side, and the extension-side check valve  16  generates substantially no damping force. 
     Next, the damping force adjustment mechanism  17  will be described with reference to  FIGS.  1  and  2   . This damping force adjustment mechanism  17  is a mechanism that generates the damping force by controlling a flow of the hydraulic liquid generated due to the sliding movement of the piston  5  in the cylinder (the inner tube  4 ), and also variably adjusts the damping force to be generated by the hydraulic shock absorber  1 .  FIG.  2    illustrates the damping force adjustment mechanism  17  with a movable element  48  (an actuation pin  49 ) moved to the left side in  FIG.  2    (i.e., a valve-closing direction in which a pilot valve member  32  is seated on a valve seat portion  26 E of a pilot body  26 ) according to power supply from outside to a coil  34 A of a solenoid  33  (for example, control of generating a hard damping force). 
     As also illustrated in  FIG.  1   , the damping force adjustment mechanism  17  is disposed in such a manner that the proximal end side (the left end side in  FIG.  1   ) thereof is interposed between the reservoir chamber A and the annular oil chamber D, and the distal end side (the right end side in  FIG.  1   ) thereof protrudes radially outward from the lower portion side of the outer tube  2 . The damping force adjustment mechanism  17  includes the damping force adjustment valve  18  and the solenoid  33 , which will be described below. The damping force adjustment valve  18  serves as a control valve that generates a damping force having the hard or soft characteristic by variably controlling the flow of the oil liquid from the annular oil chamber D to the reservoir chamber A. The solenoid  33  adjusts valve-opening and closing operations of this damping force adjustment valve  18 . 
     In other words, the valve-opening pressure of the damping force adjustment valve  18  is adjusted by the solenoid  33  used as a damping force variable actuator, and the generated damping force is variably controlled to the hard or soft characteristic thereby. The damping force adjustment valve  18  is a valve configured in such a manner that the valve-opening and closing operations thereof are adjusted by the solenoid  33 , and is equipped with a flow passage where the flow of the hydraulic liquid is generated due to the movement of the above-described piston rod  8  (for example, between the annular oil chamber D and the reservoir chamber A). 
     Then, the damping force adjustment valve  18  includes a generally cylindrical valve case  19 , a connection tubular member  20 , a valve member  21 , and the like. The valve case  19  is provided in such a manner that the proximal end side thereof is fixedly attached around the opening  2 B of the outer tube  2  and the distal end side thereof protrudes radially outward from the outer tube  2 . The connection tubular member  20  is provided in such a manner that the proximal end side thereof is fixed to the connection port  12 C of the intermediate tube  12 , and, along therewith, the distal end side thereof includes an annular flange portion  20 A formed thereon and is arranged inside the valve case  19  with a space present therebetween. The valve member  21  is in abutment with the flange portion  20 A of this connection tubular member  20 . 
     The valve case  19  includes an annular inner flange portion  19 A formed on the proximal end side thereof and a male screw portion  19 B formed on the distal end side thereof. The inner flange portion  19 A protrudes radially inward. A lock nut  53  is threadedly attached to the male screw portion  19 B. The lock nut  53  couples this valve case  19  and a yoke  39  (a one-side tubular portion  39 D) of the solenoid  33 , which will be described below. An annular oil chamber  19 C, which is in constant communication with the reservoir chamber A, is defined between the inner peripheral surface of the valve case  19  and the outer peripheral surface of the valve member  21 , and further between the inner peripheral surface of the valve case  19  and the outer peripheral surface of the pilot body  26  and the like. 
     An oil passage  20 B is formed inside the connection tubular member  20 . The oil passage  20 B has one side in communication with the annular oil chamber D and an opposite side extending to the position of the valve member  21 . Further, an annular spacer  22  is provided in a sandwiched state between the flange portion  20 A of the connection tubular member  20  and the inner flange portion  19 A of the valve case  19 . A plurality of radially extending cutouts  22 A is provided on this spacer  22 . The cutouts  22 A serve as radial oil passages for establishing communication between the oil chamber  19 C and the reservoir chamber A. In the present embodiment, the damping force adjustment valve  18  is configured in such a manner that the cutouts  22 A for forming the oil passages are provided to the spacer  22 . However, the damping force adjustment valve  18  may be configured in such a manner that cutouts for forming the oil passages are radially provided to the inner flange portion  19 A of the valve case  19 . In the case where the damping force adjustment valve  18  is configured in this manner, the spacer  22  can be omitted and thus the number of components can be reduced. 
     An axially extending central hole  21 A is provided on the valve member  21  while being located at the radial center thereof. Further, a plurality of oil passage  21 B is provided on the valve member  21  at intervals in the circumferential direction around the central hole  21 A, and each of these oil passages  21 B has one end side (the left side in  FIG.  2   ) in constant communication with the oil passage  20 B of the tubular member  20 . Further, an annular recessed portion  21 C and an annular valve seat  21 D are provided on the end surface of the valve member  21  on the opposite end side thereof (the right side in  FIG.  2   ). The annular recessed portion  21 C is formed so as to surround the openings of the oil passages  21 B on the opposite side. The annular valve seat  21 D is located on the radially outer side of this annular recessed portion  21 C. A main valve  23 , which will be described below, is seated on and separated from the annular valve seat  21 D. Now, each of the oil passages  21 B of the valve member  21  serves as a flow passage through which the hydraulic oil flows between the oil passage  20 B of the connection tubular member  20  in communication with the annular oil chamber D and the oil chamber  19 C of the valve case  19  in communication with the reservoir chamber A at a flow rate according to the opening degree of the main valve  23 . 
     The main valve  23  is formed by a disk valve interposed between the valve member  21  and a large-diameter portion  24 A of a pilot pin  24  on the inner peripheral side thereof. The outer peripheral side of the main valve  23  is seated on and separated from the annular valve seat  21 D of the valve member  21 . An elastic seal member  23 A is fixedly attached to the outer peripheral portion of the main valve  23  on the back surface side thereof by a method such as baking. The main valve  23  is opened by receiving a pressure on the oil passage  21 B side (the annular chamber D side) of the valve member  21  to be separated from the annular valve seat  21 D. As a result, the oil passages  21 B (the annular oil chamber D side) of the valve member  21  is brought into communication with the oil chamber  19 C (the reservoir chamber A side) via the main valve  23 , and the amount (the flow rate) of the hydraulic oil flowing in a direction indicated by an arrow Y at this time is variably adjusted according to the opening degree of the main valve  23 . 
     The pilot pin  24  is formed into a stepped cylindrical shape, and the annular large-diameter portion  24 A is provided at an axially intermediate portion thereof. The pilot pin  24  includes an axially extending central hole  24 B on the inner peripheral side thereof, and a small-diameter hole (an orifice  24 C) is formed at one end portion of the central hole  24 B (the end portion on the connection tubular member  20  side). One end side (the left end side in  FIG.  2   ) of the pilot pin  24  is press-fitted in the central hole  21 A of the valve member  21 , and the main valve  23  is interposed between the large-diameter portion  24 A and the valve member  21 . The opposite end side (the right end side in  FIG.  2   ) of the pilot pin  24  is fitted in a central hole  26 C of the pilot body  26 . In this state, axially extending oil passages  25  are formed between the central hole  26 C of the pilot body  26  and the opposite end side of the pilot pin  24 . These oil passages  25  are in communication with a back-pressure chamber  27  formed between the main valve  23  and the pilot body  26 . In other words, the plurality of axially extending oil passages  25  is circumferentially arranged on the side surface of the pilot pin  24  on the opposite end side, and the circumferential positions other than that are press-fitted in the central hole  26 C of the pilot body  26 . 
     The pilot body  26  is formed as a generally bottomed tubular member including a cylindrical portion  26 A and a bottom portion  26 B. The cylindrical portion  26 A includes a stepped hole formed inside it. The bottom portion  26 B closes this cylindrical portion  26 A. The central hole  26 C is provided at the bottom portion  26 B of the pilot body  26 . The opposite end side of the pilot pin  24  is fitted in the central hole  26 C. A protrusion tubular portion  26 D is integrally provided on the outer peripheral side of the bottom portion  26 B of the pilot body  26 . The protrusion tubular portion  26 D extends toward the valve member  21  side (i.e., the left side in  FIG.  2   ) throughout the entire circumference thereof. The elastic seal member  23 A of the main valve  23  is liquid-tightly fitted to the inner peripheral surface of this protrusion tubular portion  26 D, and the back-pressure chamber  27  is formed between the main valve  23  and the pilot body  26  thereby. This back-pressure chamber  27  generates a pressure (a pilot pressure) that presses the main valve  23  in a valve-closing direction, i.e., in a direction causing the main valve  23  to be seated onto the annular valve seat  21 D of the valve member  21 . 
     The valve seat portion  26 E is provided on the bottom portion  26 B of the pilot body  26  so as to surround the central hole  26 C while being located on the opposite end side thereof (the right end side in  FIG.  2   ). The pilot valve member  32 , which will be described below, is seated on and separated from the valve seat portion  26 E Further, a return spring  28 , a disk valve  29 , a holding plate  30 , and the like are arranged inside the cylindrical portion  26 A of the pilot body  26 . The return spring  28  biases the pilot valve member  32  in a direction away from the valve seat portion  26 E of the pilot body  26 . The disk valve  29  forms a fail-safe valve when the solenoid  33 , which will be described below, is in a state that no power is supplied thereto (when the pilot valve member  32  is maximumly separated from the valve seat portion  26 E). The holding plate  30  includes an oil passage  30 A formed on the central side thereof. 
     A cap  31  is fitted and fixed at the opening edge of the cylindrical portion  26 A of the pilot body  26  with the return spring  28 , the disk valve  29 , the holding plate  30 , and the like arranged inside this cylindrical portion  26 A. Cutouts  31 A are formed on this cap  31  at, for example, positions of four portions circumferentially spaced apart from each other. These cutouts  31 A serve as flow passages that allow oil liquid delivered to the solenoid  33  side via the oil passage  30 A of the holding plate  30  to flow into the oil chamber  19 C (the reservoir chamber A side) in a direction indicated by an arrow X illustrated in  FIG.  2   . 
     The pilot valve member  32  forms the pilot valve together with the pilot body  26 . The pilot valve member  32  is formed into a stepped cylindrical shape, and includes a gradually narrowing taper portion at a distal end portion thereof that is seated on and separated from the valve seat portion  26 E of the pilot body  26 . The actuation pin  49  of the solenoid  33 , which will be described below, is fixed in a fitted state inside the pilot valve member  32 , and the pilot valve is configured in such a manner that the valve-opening pressure of the pilot valve member  32  is adjusted according to power supply to the solenoid  33 . A flange portion  32 A, which serves as a spring bearing, is formed on the proximal end side of the pilot valve member  32  throughout the entire circumference thereof. This flange portion  32 A functions to restrict the maximum opening degree of the pilot valve member  32  by abutting against the inner peripheral portion of the disk valve  29  when the solenoid  33  is in the state that no power is supplied thereto (i.e., when the pilot valve member  32  is displaced to a fully opened position maximumly spaced apart from the valve seat portion  26 E). 
     Next, the solenoid  33 , which forms the damping force adjustment mechanism  17  together with the damping force adjustment valve  18 , will be described with reference to  FIGS.  2 ,  3 , and  4   . 
     The solenoid  33  is used in a damping force adjustable shock absorber to adjust the valve-opening and closing operations of the damping force adjustment valve  18 . More specifically, the solenoid  33  used as the damping force variable actuator of the damping force adjustment mechanism  17  includes a molded coil  34 , a housing member  36 , a yoke  39 , a stator  41 , a non-magnetic ring  44 , the movable element  48 , the actuation pin  49 , a cover member  51 , and the like. 
     The molded coil  34  is generally cylindrically formed by winding a coil  34 A around a coil bobbin  34 B and integrally covering (molding) them with a resin member  34 C such as thermosetting resin in this state. A cable extraction portion (not illustrated) protruding axially or radially outward is provided at a circumferential part of the molded coil  34 , and an electric wire cable (not illustrated) is connected to this cable extraction portion. The coil  34 A is annularly wound around the coil bobbin  34 B, and becomes an electromagnet and generates a magnetic force in reaction to power supply (energization) from outside via the cable. 
     A seal groove  34 D is formed throughout the entire circumference on the side surface (the end surface on one axial side) of the resin member  34 C of the molded coil  34  that faces the yoke  39  (an annular portion  39 B), which will be described below. A seal member (for example, an O-ring  35 ) is attached in this seal groove  34 D. This O-ring  35  liquid-tightly seals between the molded coil  34  and the yoke  39  (the annular portion  39 B). Due to this provision, dust containing rainwater or mud water can be prevented from entering a tubular protrusion portion  39 C side of the yoke  39  via between the yoke  39  and the molded coil  34 . 
     The coil employed in the present embodiment is not limited to the molded coil  34  including the coil  34 A, the coil bobbin  34 B, and the resin member  34 C, and a coil other different from that may also be employed. For example, the employed coil may be configured in such a manner that a coil is wound around the coil bobbin  34 B made from an electrically insulating material, and the outer periphery of this coil is covered with an overmold formed by molding a resin material (not illustrated) over it (on the outer peripheral side) in this state. 
     The housing member  36  forms a first fixed iron core (a housing) provided so as to be disposed on the inner peripheral side of the molded coil  34  (i.e., the inner periphery of the coil  34 A). This housing member  36  is made as a covered cylindrical tubular member from a magnetic material (a magnetic body) such as low-carbon steel and carbon steel for machine structural use (S 10 C). The housing member  36  includes a housing tubular portion  36 A, a stepped cover portion  36 B, and a small-diameter tubular portion  36 C. The housing tubular portion  36 A is a housing portion extending in a direction of a winding axis of the molded coil  34  (the coil  34 A) and having an opening on one end side thereof. The cover portion  36 B closes the opposite end side of this housing tubular portion  36 A. The small-diameter tubular portion  36 C is formed by reducing the diameter of the outer periphery of the housing tubular portion  36 A on the opening side (the one side) thereof, and is used for joining. 
     The non-magnetic ring  44 , which will be described below, is joined to the small-diameter tubular portion  36 C of the housing member  36  via a brazed portion  45 . The housing tubular portion  36 A of the housing member  36  is formed in such a manner that the inner diameter dimension thereof is slightly larger than the outer diameter dimension of the movable element  48 , which will be described below, and the movable element  48  is axially movably housed in the housing tubular portion  36 A. 
     The cover portion  36 B of the housing member  36  (the right side in  FIGS.  2  and  3   ) is integrally formed on the housing tubular portion  36 A as a covered tubular body that closes the housing tubular portion  36 A from the opposite axial side. The cover portion  36 B has a stepped shape smaller in outer diameter than the outer diameter of the housing tubular portion  36 A, and a fitted tubular portion  51 A of the cover member  51 , which will be described below, is fittedly provided on the outer peripheral side of the cover portion  36 B. Further, a bottomed stepped hole  37  is formed in the housing member  36  while being located inside the cover portion  36 B. This stepped hole  37  includes a bush attachment hole portion  37 A and a small-diameter hole portion  37 B. The small-diameter hole portion  37 B is located at a deeper side and formed to have a smaller diameter than this bush attachment hole portion  37 A. A first bush  38  is provided in the bush attachment hole portion  37 A. The first bush  38  is used to slidably support the actuation pin  49 , which will be described below. 
     Further, the end surface of the cover portion  36 B of the housing member  36  on the opposite side thereof is disposed so as to face a cover plate  51 B of the cover member  51 , which will be described below, with an axial space present therebetween. This axial space has a function of preventing an axial force from being directly applied from the cover plate  51 B side of the cover member  51  to the housing member  36  via the cover portion  36 B. The cover portion  36 B of the housing member  36  does not necessarily have to be formed integrally with the housing tubular portion  36 A using the same material (the magnetic body). The cover portion  36 B in this case can also be made from, for example, a rigid metal material, a ceramic material, or a fiber-reinforced resin material, instead of the magnetic material. 
     The yoke  39  is a magnetic member that forms a magnetic circuit (a magnetic path) throughout the inner peripheral side and the outer peripheral side of the molded coil  34  (the coil  34 A) together with the housing member  36 . This yoke  39  includes the annular portion  39 B and a tubular protrusion portion  39 C. The annular portion  39 B is formed using a magnetic material (a magnetic body) similarly to the housing member  36 , and radially extends on one axial side of the molded coil  34  (the coil  34 A) (one side in the direction of the winding axis) and includes a stepped fixation hole  39 A on the inner peripheral side thereof. The tubular protrusion portion  39 C protrudes tubularly along the axial direction of the fixation hole  39 A from the inner peripheral side of this annular portion  39 B toward the opposite axial side (toward a connection member  44 , which will be described below). The tubular protrusion portion  39 C is used for joining. 
     Further, the yoke  39  is formed as an integrated member including a cylindrical one-side tubular portion  39 D, an opposite-side tubular portion  39 E, and a crimped portion  39 F. The one-side tubular portion  39 D extends from the outer peripheral side of the above-described annular portion  39 B toward the one axial side (the damping force adjustment valve  18  side). The opposite-side tubular portion  39 E extends from the outer peripheral side of the annular portion  39 B toward the opposite axial side (the cover member  51  side), and is formed so as to surround the molded coil  34  from the radially outer side. The crimped portion  39 F holds a flange portion  51 C of the cover member  51  provided at the distal end side of this opposite-side tubular portion  39 E in a retained state. A cutout (not illustrated) is provided at the opposite-side tubular portion  39 E of the yoke  39 . This cutout is used to expose the above-described cable extraction portion of the molded coil  34  to outside the opposite-side tubular portion  39 E. 
     An engagement recessed portion  39 G is provided between the one-side tubular portion  39 D and the opposite-side tubular portion  39 E of the yoke  39  (throughout the entire circumference or at a plurality of portions at circumferential intervals). The engagement recessed portion  39 G has a semi-circular shape in cross section so as to be opened on the outer peripheral surface of the yoke  39 . The lock nut  53 , which will be described below, is engaged with this engagement recessed portion  39 G via a retaining ring  54  (refer to  FIG.  2   ). The lock nut  53  is threadedly attached to the valve case  19  of the damping force adjustment valve  18 . Further, a seal groove  39 H is provided on the outer peripheral surface of the one-side tubular portion  39 D throughout the entire circumference. An O-ring  40  as a seal member is attached in this seal groove  39 H, and this O-ring  40  liquid-tightly seals between the yoke  39  (the one-side tubular portion  39 D) and the valve case  19  of the damping force adjustment valve  18 . 
     The stator  41  is a second fixed iron core (anchor) fixed in the fixation hole  39 A of the yoke  39  using a method such as press-fitting. The stator  41  is made from a magnetic material (a magnetic body) such as low-carbon steel and carbon steel for machine structural use (S 10 C) similarly to the housing member  36  (the first fixed iron core) and the yoke  39 , and is formed into a shape filling the fixation hole  39 A of the yoke  39  from inside. The stator  41  is formed as a short cylindrical annular member having an axially extending through-hole  41 A on the central side thereof. The surface of the stator  41  on the one axial side (the surface that axially faces the cap  31  of the damping force adjustment valve  18  illustrated in  FIG.  2   ) is formed into a flat surface similarly to the surface of the annular portion  39 B of the yoke  39  on the one side. 
     A circular recessed dented portion  41 B is provided in a recessed manner on the opposite axial side of the stator  41  (the surface on the opposite side that axially faces the movable element  48 , which will be described below) coaxially with the housing tubular portion  36 A. This recessed dented portion  41 B is formed as a circular groove slightly larger in diameter than the movable element  48  so as to allow the movable element  48 , which will be described below, to be inserted inside it advanceably and retractably according to a magnetic force. Further, a conical protrusion portion  41 C is provided on the opposite side of the stator  41  so as to surround the recessed dented portion  41 B around it (the outer periphery). This conical protrusion portion  41 C has an outer peripheral surface formed as a conical surface so as to establish a linear (linearity) magnetic characteristic between the stator  41  and the movable element  48 . 
     More specifically, the conical protrusion portion  41 C protrudes tubularly from the outer peripheral side of the stator  41  toward the opposite axial side, and the outer peripheral surface thereof is shaped like a conical surface inclined in a tapering manner so as to have an outer diameter dimension gradually reducing from the one axial side to the opposite axial side (from the radially outer side to the radially inner side of the recessed dented portion  41 B illustrated in  FIGS.  3  and  4   ). In other words, the conical protrusion portion  41 C of the stator  41  is provided at a position that faces the opening of the housing member  36  (the housing tubular portion  36 A), and is formed as a reduced diameter portion having an outer diameter reducing as it is approaching the opening of the housing tubular portion  36 A. 
     Further, aside surface portion  41 D is formed on the outer peripheral side of the stator  41 . The side surface portion  41 D extends in a direction away from the opening of the above-described housing tubular portion  36 A along the outer periphery of the conical protrusion portion  41 C (the reduced diameter portion). An annular flange portion  41 E protruding radially outward is formed at a portion of this side surface portion  41 D that is located on the one axial side of the stator  41 , and a stepped portion  41 F is formed at an axially intermediate portion of the side surface portion  41 D while being located between the conical protrusion portion  41 C (the reduced diameter portion) and the flange portion  41 E. 
     In other words, the annular flange portion  41 E is disposed at a position largely spaced apart from the opening end of the housing tubular portion  36 A to the one axial side (i.e., the end of the stator  41  opposite from the housing portion), and is fixed in the fixation hole  39 A of the yoke  39  using a method such as press-fitting. In this manner, the annular flange portion  41 E serves as a fixed portion of the stator  41  (the side surface portion  41 D) to the fixation hole  39 A of the yoke  39  and also serves as a portion where the flange portion  41 E and the fixation hole  39 A radially face each other. 
     Then, anon-contact portion  42  is formed between the side surface portion  41 D of the stator  41  and the fixation hole  39 A of the yoke  39  while being located on the opposite axial side from the flange portion  41 E (the housing member  36  side). The side surface portion  41 D of the stator  41  and the fixation hole  39 A of the yoke  39  are out of contact with each other at the non-contact portion  42 . This non-contact portion  42  is formed by an annular space defined between the fixation hole  39 A of the yoke  39  and the side surface portion  41 D (the stepped portion  41 F) of the stator  41  throughout the entire circumference. The above-described stepped portion  41 F is formed on the surface where the side surface portion  41 D of the stator  41  and the yoke  39  (the fixation hole  39 A) radially face each other. Further, in the case where the stepped portion  41 F is provided on the side surface portion  41 D of the stator  41 , this stepped portion  41 F is formed on the above-described reduced diameter portion (the conical protrusion portion  41 C) side of the side surface portion  41 D. 
     As illustrated in  FIG.  3   , a second bush  43  is fittedly provided in the above-described stepped through-hole  41 A formed on the central (inner peripheral) side of the stator  41 . The second bush  43  is used to slidably support the actuation pin  49 , which will be described below. On the other hand, as illustrated in  FIG.  2   , the pilot body  26  of the damping force adjustment valve  18 , the return spring  28 , the disk valve  29 , the holding plate  30 , the cap  31 , and the like are provided by being inserted on the inner peripheral side of the one-side tubular portion  39 D of the yoke  39 . Further, the valve case  19  of the damping force adjustment valve  18  is fitted (externally fitted) on the outer peripheral side of the one-side tubular portion  39 D. 
     The non-magnetic ring  44  is a non-magnetic connection member (a cylinder) provided on the inner peripheral side of the molded coil  34  (the coil  34 A) while being located between the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39 . The non-magnetic ring  44  is made as a stepped cylindrical member from a non-magnetic material such as austenitic stainless steel. The non-magnetic ring  44  includes an axially intermediate stepped tubular portion  44 A and first and second connection tubular portions  44 B and  44 C. The first and second connection tubular portions  44 B and  44 C protrude axially from both the ends of this stepped tubular portion  44 A, respectively. 
     Now, the non-magnetic ring  44  is formed in such a manner that the second connection tubular portion  44 C has a larger radial dimension than the first connection tubular portion  44 B by, for example, an amount corresponding to the thickness of the connection tubular portion  44 B. Then, the first and second connection tubular portions  44 B and  44 C are molded so as to each have a desired thickness (a radial thickness) using the above-described non-magnetic material so as to be able to achieve desired coaxiality together with the stepped tubular portion  44 A. The first connection tubular portion  44 B of the non-magnetic ring  44  is fitted to the small-diameter tubular portion  36 C of the housing member  36  from outside, and they are joined via the brazed portion  45 . Further, the second connection tubular portion  44 C is fitted to the outer peripheral side of the tubular protrusion portion  39 C of the yoke  39 , and they are joined via the brazed portion  46 . 
     At the brazed portions  45  and  46 , the non-magnetic ring  44  is joined to the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39 , respectively, by performing brazing processing at, for example, 1000° C. or higher using a brazing material made of pure copper brazing filler metal. Quenching processing is performed after the brazing processing. In this state, the non-magnetic ring  44  is formed in such a manner that the inner diameter thereof (i.e., the inner diameter of the stepped tubular portion  44 A) exceeds the inner diameter of the housing member  36  (the housing tubular portion  36 A) and exceeds the recessed dented portion  41 B of the stator  41  (i.e., the radial dimension of the recessed dented portion  41 B) as illustrated in  FIG.  3   . 
     An annular space  47  is formed on the small-diameter tubular portion  36 C of the housing member  36  on the outer peripheral side thereof between the small-diameter tubular portion  36 C and the first connection tubular portion  44 B of the non-magnetic ring  44 . This space  47  is an introduction path for pouring the above-described brazing material (the pure copper brazing filler metal) in a heated and melted state into between the housing member  36  (the small-diameter tubular portion  36 C) and the non-magnetic ring  44  (the first connection tubular portion  44 B). Then, this space  47  also functions as a gap for absorbing a thermal expansion difference between the small-diameter tubular portion  36 C of the housing member  36  (the tubular protrusion portion  39 C of the yoke  39 ) and the non-magnetic ring  44 . 
     An introduction path for pouring the brazing material (the pure copper brazing filler metal) of the above-described brazed portion  46  in a heated and melted state is also formed between the tubular protrusion portion  39 C of the yoke  39  and the non-magnetic ring  44  (the second connection tubular portion  44 C) similarly to the above-described space  47 . However, on the non-magnetic ring  44 , when the above-described brazing material (the pure copper brazing filler metal) is poured while being kept in the heated and melted state to join the second connection tubular portion  44 C to the outer peripheral surface of the tubular protrusion portion  39 C of the yoke  39 , an external axial force is applied to therebetween so as to eliminate the above-described space as much as possible. However, a thermal expansion difference is generated between the small-diameter tubular portion  36 C of the housing member  36  (the tubular protrusion portion  39 C of the yoke  39 ) and the non-magnetic ring  44  due to a difference in the material (the contained substance). Therefore, the axial space  47  is formed so as to extend throughout the entire circumference between the small-diameter tubular portion  36 C of the housing member  36  and the first connection tubular portion  44 B of the non-magnetic ring  44 . 
     In this case, the non-magnetic ring  44  is a non-magnetic connection member made from austenitic stainless steel, and is configured in such a manner that the brazing is performed using the pure copper brazing filler metal (the brazing material) when this non-magnetic ring  44  is joined between the housing member  36  and the yoke  39  via the brazed portions  45  and  46 . Generally, when an austenitic stainless steel component made from a non-magnetic material is distorted by being subjected to deep-drawing or cutting processing, deformation-induced martensite is generated in this material and undesirably causes the crystal structure of a part thereof to be transformed into a body-centered cubic structure instead of a face-centered cubic structure ideal as the non-magnetic material, thereby undesirably causing the non-magnetic material to have an easily magnetizable characteristic. However, the deformation-induced martensite in austenitic stainless steel is removed by applying a thermal treatment at 1000° C. or higher, and the non-magnetic material is returned to the ideal face-centered cubic structure again. This processing is called a solution heat treatment. 
     In light thereof, the present embodiment selects the pure copper brazing filler metal as the brazing material having the brazing temperature of 1000° C. or higher and performs processing workable as both the brazing and the solution heat treatment at the brazed portions  45  and  46 , thereby making it possible to return the crystal structure to the face-centered cubic structure ideal as the non-magnetic material in the non-magnetic ring  44  joined between the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39 . In addition, the non-magnetic ring  44  is press-fitted between the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39  and is brought into abutment therewith, thereby preventing or reducing a thermal deformation thereof due to the high temperature at the time of the brazing, eliminating the necessity of performing the cutting processing intended to correct the shape after the brazing, and thus succeeding in maintaining the desired dimension and shape. The brazing material may be a brazing material different from the pure copper brazing filler metal as long as the brazing temperature thereof is 1000° C. or higher. The brazing material may be, for example, yellow brass brazing filler metal, nickel brazing filler metal, gold brazing filler metal, or palladium brazing filler metal. 
     In this manner, even when the non-magnetic ring  44  is joined to the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39  via the brazed portions  45  and  46  and a thermal expansion difference derived from the difference in the material (the contained substance) is generated between them due to the quenching processing after the brazing, the occurrence of a distortion based thereon can be suppressed with the aid of the above-described space  47 . Then, the connection member made from a non-magnetic body (for example, the non-magnetic ring  44 ) may be configured to be heated and joined between the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39  using a method different from the brazing (for example, a joining method such as laser welding). 
     The movable element  48  is an armature made from a magnetic body provided movably in the direction of the winding axis of the coil  34 A between the housing tubular portion  36 A of the housing member  36  and the recessed dented portion  41 B of the stator  41 . The movable element  48  is arranged on the inner peripheral sides of the housing tubular portion  36 A of the housing member  36 , the recessed dented portion  41 B of the stator  41 , the tubular protrusion portion  39 C of the yoke  39 , and the non-magnetic ring  44 , and is axially movable between the housing tubular portion  36 A of the housing member  36  and the recessed dented portion  41 B of the stator  41 . In other words, the movable element  48  is arranged on the inner peripheral sides of the housing tubular portion  36 A of the housing member  36  and the recessed dented portion  41 B of the stator  41 , and is axially movable via the first and second bushes  38  and  43  and the actuation pin  49  under the magnetic force generated on the coil  34 A. 
     The movable element  48  is provided fixedly (integrally) to the actuation pin  49  extending through the central side thereof, and is movable together with the actuation pin  49 . The actuation pin  49  is axially slidably supported on the cover portion  36 B of the housing member  36  and the stator  41  via the first and second bushes  38  and  43 . Now, the movable element  48  is generally cylindrically formed using a ferrous magnetic body similarly to, for example, the housing member  36 , the yoke  39 , and the stator  41 . Then, a thrust force is generated on the movable element  48  in a direction for attracting the movable element  48  toward inside the recessed dented portion  41 B of the stator  41  due to the magnetic force generated on the coil  34 A. 
     The actuation pin  49  is a shaft portion that transmits the thrust force of the movable element  48  to the pilot valve member  32  of the damping force adjustment valve  18  (a control valve), and is formed by a hollow rod. The movable element  48  is integrally fixed at an axial intermediate portion of the actuation pin  49  using a method such as press-fitting, and the movable element  48  and the actuation pin  49  are sub-assembled by that. The actuation pin  49  is axially slidably supported on the cover portion  36 B of the housing member  36  and the yoke  39  (the stator  41 ) via the first and second bushes  38  and  43 . 
     One end side (the end portion on the left side in  FIG.  2   ) of the actuation pin  49  protrudes from the stator  41  (the yoke  39 ), and, along therewith, the pilot valve member  32  of the damping force adjustment valve  18  is fixed to the protrusion end thereof. Therefore, the pilot valve member  32  is axially moved integrally together with the movable element  48  and the actuation pin  49 . In other words, the valve-opening pressure of the pilot valve member  32  is set to a pressure value corresponding to the thrust force of the movable element  48  based on power supply to the coil  34 A. The movable element  48  is configured to open and close the pilot valve of the hydraulic shock absorber  1  (i.e., open and close the pilot valve member  32  from and to the pilot body  26 ) by being axially moved under the magnetic force from the coil  34 A. 
     A back-pressure chamber  50  is an oil chamber formed between the cover portion  36 B of the housing member  36  (the small-diameter hole portion  37 B of the stepped hole  37 ) and the opposite end of the actuation pin  49  (the end portion on the right side in  FIG.  2   ). This back-pressure chamber  50  is in communication with the central hole  24 B side of the pilot pin  24  via the hollow rod (the actuation pin  49 ). Therefore, the back-pressure chamber  50  is subjected to a pressure equal to the pilot valve member  32 , which is seated on and separated from the valve seat portion  26 E of the pilot body  26 . However, regarding the pressure-receiving area to receive this pressure, the area over which the opposite end surface of the actuation pin  49  receives the pressure in the back-pressure chamber  50  is smaller than the area over which the pilot valve member  32  (the one end side of the actuation pin  49 ) receives the pressure between it and the valve seat portion  26 E. This allows the thrust force that should be transmitted from the movable element  48  to the pilot valve member  32  of the damping force adjustment valve  18  via the actuation pin  49  to be reduced by an amount corresponding the difference in the pressure-receiving area therebetween. 
     In this manner, the formation of the back-pressure chamber  50  between the actuation pin  49  and the cover portion  36 B on the opposite end side of the actuation pin  49  can contribute to reducing the thrust force that should be transmitted from the movable element  48  to the pilot valve member  32  of the damping force adjustment valve  18  via the actuation pin  49  (for example, the magnetic force that should be generated by the coil  34 A of the molded coil  34 ), thereby achieving a size reduction and a weight reduction of the solenoid  33  as a whole. 
     The cover member  51  is a magnetic-body cover that covers the molded coil  34  from outside together with the opposite-side tubular portion  39 E of the yoke  39 . This cover member  51  is made from a magnetic material (a magnetic body) as the cover member that covers the molded coil  34  from the opposite axial side, and forms a magnetic circuit (a magnetic path) outside the molded coil  34  (the coil  34 A) together with the opposite-side tubular portion  39 E of the yoke  39 . Then, the cover member  51  is formed into a covered tubular shape as a whole, and includes the cylindrical fitted tubular portion  51 A and the cover plate  51 B shaped like a circular plate, which closes the opposite end side (the end portion on the right side in  FIGS.  2  and  3   ) of this fitted tubular portion  51 A. 
     Now, the fitted tubular portion  51 A of the cover member  51  is configured to be fittedly inserted on the outer periphery of the cover portion  36 B of the housing member  36  and house the cover portion  36 B of the housing member  36  inside it in this state. On the other hand, the annular flange portion  51 C extending to the radially outer side of the fitted tubular portion  51 A is formed on the outer peripheral side of the cover plate  51 B of the cover member  51 , and the outer peripheral edge of this flange portion  51 C is fixed to the crimped portion  39 F provided on the opposite-side tubular portion  39 E of the yoke  39 . Due to this configuration, the opposite-side tubular portion  39 E of the yoke  39  and the cover plate  51 B of the cover member  51  are preliminarily assembled (sub-assembled) with the molded coil  34  built inside them as illustrated in  FIG.  3   . 
     In this manner, the cover portion  36 B of the housing member  36  is fittedly attached in the fitted tubular portion  51 A of the cover member  51  in the state that the molded coil  34  is built inside the opposite-side tubular portion  39 E of the yoke  39  and the cover plate  51 B of the cover member  51 . Due to this configuration, a magnetic flux can be transferred between the fitted tubular portion  51 A and the cover plate  51 B of the cover member  51  and the yoke  39 . Further, a seal groove  51 D is formed on the fitted tubular portion  51 A of the cover member  51  throughout the entire circumference on the outer peripheral side to which the resin member  34 C of the molded coil  34  is fitted. A seal member (for example, an O-ring  52 ) is attached in this seal groove  51 D. This O-ring  52  liquid-tightly seals between the molded coil  34  and the cover member  51  (the fitted tubular portion  51 A). As a result, dust containing rainwater or mud water can be prevented from entering between the housing member  36  and the molded coil  34  via between the cover member  51  and the molded coil  34 , and thus entering, for example, between the housing member  36  and the cover member  51 . 
     The yoke  39  and the cover member  51  are fastened to the valve case  19  of the damping force adjustment valve  18  using the lock nut  53  and the retaining ring  54  as fastening members as illustrated in  FIG.  2    with the molded coil  34  built inside them as illustrated in  FIG.  3   . In this case, the retaining ring  54  is attached to the engagement recessed portion  39 G of the yoke  39  prior to the lock nut  53 . This retaining ring  54  partially protrudes radially outward from the engagement recessed portion  39 G of the yoke  39  and works to transmit the fastening force derived from the lock nut  53  to the one-side tubular portion  39 D of the yoke  39 . 
     The lock nut  53  is formed as a stepped tubular member, and includes a female screw portion  53 A and an engagement tubular portion  53 B. The female screw portion  53 A is located on one axial side of the lock nut  53 , and is threadedly engaged with the male screw portion  19 B of the valve case  19  on the inner peripheral side thereof. The engagement tubular portion  53 B is bent radially inward in such a manner that the inner diameter dimension thereof falls below the outer diameter dimension of the retaining ring  54 , and is engaged with the retaining ring  54  from outside. The lock nut  53  is a fastening member that integrally couples the damping force adjustment valve  18  and the solenoid  33  by threadedly engaging the female screw portion  53 A and the male screw portion  19 B of the valve case  19  with the inner surface of the engagement tubular portion  53 B in abutment with the retaining ring  54  attached to the engagement recessed portion  39 G of the yoke  39 . 
     The solenoid  33 , the damping force adjustment mechanism  17 , and the hydraulic shock absorber  1  according to the first embodiment is configured in the above-described manner, and the operations thereof will be described next. 
     First, when the hydraulic shock absorber  1  is mounted on the vehicle such as an automobile, for example, the protrusion end (upper end) side of the piston rod  8  is attached to the vehicle body side of the vehicle, and the mounting eye  3 A side provided on the bottom cap  3  is attached to the wheel side. Then, the solenoid  33  of the damping force adjustment mechanism  17  is connected to a control apparatus (a controller) provided on the vehicle body side of the vehicle via, for example, an electric wiring (a cable) (both are not illustrated). 
     When the vehicle runs, upon occurrence of a vertical vibration due to unevenness of a road surface or the like, the piston rod  8  is displaced so as to extend or compress from and into the outer tube  2 , and therefore the damping force can be generated by the damping force adjustment mechanism  17  and the like and the vibration of the vehicle can be damped. At this time, the above-described controller can variably control the damping force to be generated by the hydraulic shock absorber  1  by changing the current value of a control signal to be supplied to the coil  34 A of the solenoid  33  to adjust the valve-opening pressure of the pilot valve member  32 . 
     At this time, the magnetic force (the magnetic flux) generated from the coil  34 A of the solenoid  33  establishes a magnetic circuit so as to pass from the housing member  36  through the movable element  48  side so as to avoid the non-magnetic ring  44  (the non-magnetic connection member), pass from the movable element  48  through the conical protrusion portion  41 C, the stepped portion  41 F, and the flange portion  41 E of the stator  41  to reach the fixation hole  39 A, the annular portion  39 B, and the opposite-side tubular portion  39 E of the yoke  39 , and further pass from the crimped portion  39 F side of the yoke  39  through the cover plate  51 B and the fitted tubular portion  51 A of the cover member  51  to return to the housing tubular portion  36 A of the housing member  36 . 
     In the magnetic circuit in this case, all the transfers of the magnetic flux can be conducted at the abutment portions (i.e., portions where magnetic bodies are in planar contact with each other) except for the transfers of the magnetic flux between the movable element  48  and the housing member  36  that face each other via an extremely small space, and between the movable element  48  and the conical protrusion portion  41 C (the reduced diameter portion) of the stator  41  that face each other in a similar manner. Therefore, the magnetic circuit of the solenoid  33  can ensure high magnetic efficiency. 
     Then, the non-magnetic ring  44 , which is the non-magnetic connection member, is provided between the housing member  36  and the yoke  39  forming the main portions of the solenoid  33  (between the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39 ) while being located on the inner peripheral side of the molded coil  34  (the coil  34 A). This non-magnetic ring  44  is joined between the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39  via the brazed portions  45  and  46  to increase the magnetic flux density of the magnetic circuit with respect to the movable element  48 . However, the non-magnetic connection member (the non-magnetic ring  44 ) involves such a problem that applying mechanical processing (for example, processing of cutting the inner peripheral surface) thereto after the joining would lead to a change in the magnetic characteristic due to a processing distortion at this time, thereby facilitating the magnetization of the non-magnetic connection member. 
     Further, for the damping force adjustment mechanism  17  provided so as to protrude radially outward from the lower portion side of the outer tube  2  as illustrated in  FIG.  1   , there is such a demand that the axial length (the protrusion dimension) thereof is desired to be reduced. Then, the reduction in the axial length requires a reduction in the axial dimension of the movable element  48 , and the securement of the thrust force characteristic as the solenoid under this condition requires an increase in the outer diameter (the radial dimension) of the movable element  48 . 
     In light thereof, in the present embodiment, the non-magnetic ring  44 , which is made from the non-magnetic material such as austenitic stainless steel, is formed as the stepped cylindrical integrated member including the axially intermediate stepped tubular portion  44 A and the first and second connection tubular portions  44 B and  44 C protruding axially from both the ends of this stepped tubular portion  44 A, respectively. Then, the non-magnetic ring  44  (the stepped tubular portion  44 A) is formed in such a manner that the inner diameter dimension thereof exceeds the inner diameters of the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39 . 
     In other words, the non-magnetic ring  44  is formed in such a manner that the inner diameter of the non-magnetic ring  44  (i.e., the inner diameter dimension of the stepped tubular portion  44 A) exceeds the inner diameter of the housing member  36  (the housing tubular portion  36 A) and the inner diameter of the yoke  39  (i.e., the inner diameter dimension of the fixation hole  39 A and the tubular protrusion portion  39 C) as illustrated in  FIGS.  3  and  4    with the non-magnetic ring  44  joined between the housing member  36  and the yoke  39  via the brazed portions  45  and  46 . 
     Further, the solenoid  33  is configured in such a manner that the radial dimension of the recessed dented portion  41 B of the stator  41  and the inner diameter dimension of the conical protrusion portion  41 C (the reduced diameter portion), and further the inner diameter dimension of the non-magnetic ring  44  increase as the outer diameter of the movable element  48  increases. In addition, the stator  41  is provided in the fixation hole  39 A of the yoke  39  axially opposite of the movable element  48  from the housing tubular portion  36 A of the housing member  36  and coaxially therewith, and the reduced diameter portion (the conical protrusion portion  41 C), which has the outer diameter reducing as it is approaching the opening of the housing tubular portion  36 A, and the side surface portion  41 D, which extends from the outer periphery of the above-described reduced diameter portion in the direction away from the opening of the above-described housing tubular portion  36 A, are integrally formed on the stator  41  from the magnetic body. 
     Then, the annular flange portion  41 E, which protrudes radially outward, is formed at the portion of this side surface portion  41 D on the one axial side of the stator  41 , and the stepped portion  41 F is formed at the axially intermediate portion of the side surface portion  41 D while being located between the conical protrusion portion  41 C (the reduced diameter portion) and the flange portion  41 E. In this state, the flange portion  41 E of the stator  41  is disposed at the position largely spaced apart from the opening end of the housing tubular portion  36 A to the one axial side (i.e., the end of the stator  41  opposite from the housing portion), and is fixed in the fixation hole  39 A of the yoke  39  using the method such as press-fitting. 
     In other words, the flange portion  41 E of the stator  41  serves as the fixed portion of the stator  41  (the side surface portion  41 D) to the fixation hole  39 A of the yoke  39 , and also serves as the portion where the flange portion  41 E and the fixation hole  39 A radially face each other. Further, the yoke  39  includes the fixation hole  39 A with a part of the side surface portion  41 D of the stator  41  (the flange portion  41 E) fixed on the inner peripheral surface thereof, and the non-contact portion  42 , where the fixation hole  39 A and the side surface portion  41 D of the stator  41  are out of contact with each other, is formed on the housing member  36  side of this fixation hole  39 A. 
     Due to this configuration, the movable element  48  can be axially movably arranged between the housing tubular portion  36 A of the housing member  36  and the recessed dented portion  41 B of the stator  41  while being located on the inner peripheral sides of the small-diameter tubular portion  36 C of the housing member  36 , the tubular protrusion portion  39 C of the yoke  39 , and the non-magnetic ring  44  (the non-magnetic connection member). In this case, the movable element  48  can be arranged inside the non-magnetic ring  44  with a space present therebetween, and this eliminates the necessity of applying mechanical processing (for example, the processing of cutting the inner peripheral surface) to the non-magnetic ring  44  after the non-magnetic ring  44  is joined to the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39 , thereby also preventing a change in the magnetic characteristic of the non-magnetic ring  44  due to an influence of heat, a processing distortion, and/or the like. 
     Further, when the flange portion  41 E of the stator  41  is fixed by being press-fitted in the fixation hole  39 A of the yoke  39  after the non-magnetic ring  44  is joined between the housing member  36  and the yoke  39  via the brazed portions  45  and  46 , the non-contact portion  42  is formed between the fixation hole  39 A of the yoke  39  and the side surface portion  41 D of the stator  41 . Therefore, even if apart of the brazing material (the pure copper brazing filler metal) of the above-described brazed portions  45  and  46  is present between the tubular protrusion portion  39 C and the connection tubular portion  44 C of the non-magnetic ring  44 , this brazing material does not adversely affect the work of press-fitting (fixing) the stator  41 , and the conical protrusion portion  41 C (the reduced diameter portion) of the stator  41  can be prevented from being deformed, for example, radially inward under an external force when being press-fitted. 
     As a result, the present configuration can facilitate smooth execution of the work of press-fitting the stator  41 , which is performed after the non-magnetic ring  44  is joined between the housing member  36  and the yoke  39  via the brazed portions  45  and  46 . In other words, the present configuration can facilitate smooth execution of the work of fixing the flange portion  41 E of the stator  41  by press-fitting it into the fixation hole  39 A of the yoke  39 . 
     In this manner, according to the present embodiment, the characteristic of the non-magnetic ring  44  (the non-magnetic connection member) can be prevented from being changed due to an influence of heat, a processing distortion, and/or the like, and the solenoid  33  can maintain a high magnetic flux density of the magnetic circuit with respect to the movable element  48  between the small-diameter tubular portion  36 C of the housing member  36  and the conical protrusion portion  41 C of the stator  41  (the tubular protrusion portion  39 C of the yoke  39 ). Then, since the magnetic circuit of the solenoid  33  allows all the transfers of the magnetic flux to be conducted with the magnetic bodies in planar contact with each other except for the transfers of the magnetic flux between the movable element  48  and the housing member  36  that face each other via the extremely small space, and between the movable element  48  and the conical protrusion portion  41 C of the stator  41  that face each other in a similar manner, the magnetic circuit of the solenoid  33  can ensure high magnetic efficiency. 
     In addition, the first connection tubular portion  44 B of the non-magnetic ring  44  is fitted to the small-diameter tubular portion  36 C of the housing member  36  from outside, and they are joined via the brazed portion  45 . Further, the second connection tubular portion  44 C is fitted to the outer peripheral side of the tubular protrusion portion  39 C of the yoke  39 , and they are joined via the brazed portion  46 . Then, at the brazed portions  45  and  46 , the non-magnetic ring  44  is joined to the small-diameter tubular portion  36 C of the housing member  36  and the tubular protrusion portion  39 C of the yoke  39 , respectively, by performing the brazing processing at, for example, 1000° C. or higher using the brazing material made of the pure copper brazing filler metal, and the quenching processing is performed after the brazing processing. 
     In this manner, according to the present embodiment, the small-diameter tubular portion  36 C of the housing member  36 , the tubular protrusion portion  39 C of the yoke  39 , and the non-magnetic ring  44  are configured in the above-described manner, and the brazing processing is performed at the brazed portions  45  and  46  at, for example, 1000° C. or higher using the pure copper brazing filler metal (the brazing material), by which the three members, the small-diameter tubular portion  36 C of the housing member  36 , the tubular protrusion portion  39 C of the yoke  39 , and the non-magnetic ring  44  can be joined to each other as a shape satisfying the coaxiality and can also ensure the pressure-resistant strength against the internal hydraulic oil. 
     Further, the annular space throughout the entire circumference is formed as the non-contact portion  42  between the fixation hole  39 A of the yoke  39  and the side surface portion  41 D of the stator  41 . This facilitates smooth execution of the work of press-fitting the stator  41  (i.e., the work of fixing the stator  41  by press-fitting the flange portion  41 E of the stator  41  into the fixation hole  39 A of the yoke  39 ), which is performed after the non-magnetic ring  44  is joined between the housing member  36  and the yoke  39  via the brazed portions  45  and  46 . 
     Therefore, in the solenoid  33  used for a semi-active damper (the damping force adjustable shock absorber) to adjust the valve-opening and closing operations of the damping force adjustment valve  18 , even when the axial length of the movable element  48  is reduced to reduce the axial length of the damping force adjustment mechanism  17  (the solenoid  33 ), the present embodiment does not lead to a reduction in the region housing the molded coil  34  (the coil  34 A) due to the increase in the outer diameter of the movable element  48 , thereby preventing an influence on the number of windings of the coil and the resistance value and thus being able to ensure the thrust force characteristic as the solenoid  33 . 
     Then, at the time of the work of assembling the solenoid  33 , the present embodiment can facilitate smooth execution of the work of press-fitting (fixing) the stator  41  to the fixation hole  39 A of the yoke  39  after joining the non-magnetic ring  44  between the housing member  36  and the yoke  39  by the brazing, and prevent the conical protrusion portion  41 C (the reduced diameter portion) of the stator  41  from being deformed, for example, radially inward under an external force when being press-fitted. 
     Therefore, according to the present embodiment, the solenoid  33  can maintain a high magnetic flux density passing through the movable element  48  between the housing member  36  and the stator  41  (the yoke  39 ) and maintain an excellent thrust force characteristic as the solenoid  33 , and can also improve the workability at the time of the assembling. In the present embodiment, the solenoid  33  is configured to include the connection member  44  made from the non-magnetic body joined by being heated between the housing member  36  and the yoke  39 . However, even when the space between the housing member  36  and the yoke  39  is sealingly closed using press-fitting, a similar problem also occurs and therefore the present invention can also be applied thereto. 
     Next,  FIG.  5    illustrates a second embodiment, and the present embodiment will be described identifying similar components to the above-described first embodiment by the same reference numerals and omitting the descriptions thereof. However, the second embodiment is characterized by being configured in such a manner that a stator  61  is fixed by being press-fitted in the fixation hole  39 A of the yoke  39  instead of the stator  41  according to the first embodiment. 
     The stator  61  employed in the second embodiment is formed into a shape filling the fixation hole  39 A of the yoke  39  from inside using a magnetic material (a magnetic body) similarly to the stator  41  described in the above-described first embodiment. The stator  61  is formed as a short cylindrical annular member having an axially extending through-hole (not illustrated) on the central side thereof similarly to the stator  41  according to the first embodiment, and includes a circular recessed dented portion  61 B, a conical protrusion portion  61 C (the reduced diameter portion), and a side surface portion  61 D. Then, an annular flange portion  61 E protruding radially outward is integrally formed at a portion of this side surface portion  61 D on one axial side of the stator  61 . 
     However, in the stator  61  employed in the second embodiment, the side surface portion  61 D thereof includes the flange portion  61 E and a cylindrical portion  61 F. Then, the cylindrical portion  61 F of the stator  61  is formed to define a flat cylindrical shape to the position of the flange portion  61 E along the outer periphery of the conical protrusion portion  61 C (the reduced diameter portion). Then, a non-contact portion  62  is formed between the cylindrical portion  61 F of the stator  61  and the fixation hole  39 A of the yoke  39  while being located on the opposite axial side with respect to the flange portion  61 E (the housing member  36  side). The cylindrical portion  61 F of the stator  61  and the fixation hole  39 A of the yoke  39  are out of contact with each other at the non-contact portion  62 . This non-contact portion  62  is formed by an annular space defined between the fixation hole  39 A of the yoke  39  and the cylindrical portion  61 F of the stator  61  throughout the entire circumference. 
     Then, in the second embodiment configured in this manner, the non-contact portion  62 , which is formed by the annular space extending throughout the entire circumference, is formed between the cylindrical portion  61 F of the stator  61  and the fixation hole  39 A of the yoke  39 . Therefore, at the time of the work of assembling the solenoid  33 , the present embodiment can facilitate smooth execution of the work of press-fitting (fixing) the stator  61  to the fixation hole  39 A of the yoke  39  after joining the non-magnetic ring  44  between the housing member  36  and the yoke  39  by the brazing, and prevent the conical protrusion portion  61 C (the reduced diameter portion) of the stator  61  from being deformed, for example, radially inward under an external force when being press-fitted. 
     Next,  FIG.  6    illustrates a third embodiment, and the present embodiment will be described identifying similar components to the above-described first embodiment by the same reference numerals and omitting the descriptions thereof. However, the third embodiment is characterized by being configured in such a manner that a stator  71  is fixed by being press-fitted in the fixation hole  39 A of the yoke  39  instead of the stator  41  according to the first embodiment. 
     The stator  71  employed in the third embodiment is formed into a shape filling the fixation hole  39 A of the yoke  39  from inside using a magnetic material (a magnetic body) similarly to the stator  41  described in the above-described first embodiment. The stator  71  includes a through-hole (not illustrated) on the central side, a circular recessed dented portion  71 B, a conical protrusion portion  71 C (the reduced diameter portion), and a side surface portion  71 D, similarly to the stator  41  according to the first embodiment. Then, an annular flange portion  71 E protruding radially outward is integrally formed at a portion of this side surface portion  71 D on one axial side of the stator  71 . 
     However, in the stator  71  employed in the third embodiment, the side surface portion  71 D thereof includes the flange portion  71 E and an inclined tubular portion  71 F. Then, the inclined tubular portion  71 F of the stator  71  is formed so as to define a tapering shape obliquely inclined to the position of the flange portion  71 E along the outer periphery of the conical protrusion portion  71 C (the reduced diameter portion). Then, a non-contact portion  72  is formed between the inclined tubular portion  71 F of the stator  71  and the fixation hole  39 A of the yoke  39  while being located on the opposite axial side with respect to the flange portion  71 E (the housing member  36  side). The inclined tubular portion  71 F of the stator  71  and the fixation hole  39 A of the yoke  39  are out of contact with each other at the non-contact portion  72 . This non-contact portion  72  is formed by an annular space V-shaped in cross section that is defined between the fixation hole  39 A of the yoke  39  and the inclined tubular portion  71 F of the stator  71  throughout the entire circumference. 
     Then, in the third embodiment configured in this manner, the non-contact portion  72 , which is formed by the annular space V-shaped in cross section that extends throughout the entire circumference, is formed between the inclined tubular portion  71 F of the stator  71  and the fixation hole  39 A of the yoke  39 . Therefore, at the time of the work of assembling the solenoid  33 , the present embodiment can facilitate smooth execution of the work of press-fitting the stator  71  to the fixation hole  39 A of the yoke  39  after joining the non-magnetic ring  44  between the housing member  36  and the yoke  39  by the brazing, and prevent the conical protrusion portion  71 C (the reduced diameter portion) of the stator  71  from being deformed, for example, radially inward under an external force when being press-fitted. 
     Next,  FIG.  7    illustrates a fourth embodiment, and the present embodiment will be described identifying similar components to the above-described first embodiment by the same reference numerals and omitting the descriptions thereof. However, the fourth embodiment is characterized by being configured in such a manner that a stator  81  is fixed by being press-fitted in the fixation hole  39 A of the yoke  39  instead of the stator  41  according to the first embodiment. 
     The stator  81  employed in the fourth embodiment is formed into a shape filling the fixation hole  39 A of the yoke  39  from inside using a magnetic material (a magnetic body) similarly to the stator  41  described in the above-described first embodiment. The stator  81  includes a through-hole (not illustrated) on the central side, a circular recessed dented portion  81 B, a conical protrusion portion  81 C (the reduced diameter portion), and a side surface portion  81 D, similarly to the stator  41  according to the first embodiment. Then, an annular flange portion  81 E protruding radially outward is integrally formed at a portion of this side surface portion  81 D on one axial side of the stator  81 . 
     However, in the stator  81  employed in the fourth embodiment, the conical protrusion portion  81 C (the reduced diameter portion) and the side surface portion  81 D are formed as a circular-arc tapering surface  81 F obliquely inclined in a circular-arc manner to the position of the flange portion  81 E. In this case, the circular-arc tapering surface  81 F is a circular-arc surface obliquely inclined from the conical protrusion portion  81 C (the reduced diameter portion) of the stator  81  to the position of the flange portion  81 E, and the portion between the conical protrusion portion  81 C and the side surface portion  81 D is formed so as to define a consistent circular-arc surface. Then, a non-contact portion  82  is formed between the side surface portion  81 D of the stator  81  and the fixation hole  39 A of the yoke  39  while being located on the opposite axial side with respect to the flange portion  81 E (the housing member  36  side). The side surface portion  81 D of the stator  81  and the fixation hole  39 A of the yoke  39  are out of contact with each other at the non-contact portion  82 . This non-contact portion  82  is formed by an annular space having a curved shape that is defined between the fixation hole  39 A of the yoke  39  and the side surface portion  81 D of the stator  81  throughout the entire circumference. 
     Then, in the fourth embodiment configured in this manner, the non-contact portion  82 , which is formed by the annular space having the curved shape that extends throughout the entire circumference, is formed between the side surface portion  81 D of the stator  81  and the fixation hole  39 A of the yoke  39 . Therefore, at the time of the work of assembling the solenoid  33 , the present embodiment can facilitate smooth execution of the work of press-fitting (fixing) the stator  81  to the fixation hole  39 A of the yoke  39  after joining the non-magnetic ring  44  between the housing member  36  and the yoke  39  by the brazing, and prevent the conical protrusion portion  81 C (the reduced diameter portion) of the stator  81  and the like from being deformed, for example, radially inward under an external force when being press-fitted. 
     In the above-described first embodiment, the solenoid  33  has been described citing the example in which the stator  41  is fixed by being press-fitted in the fixation hole  39 A of the yoke  39 . However, the present invention is not limited thereto, and the solenoid  33  may be configured in such a manner that the stator  41  is fixed in the fixation hole  39 A of the yoke  39  using a threaded engagement method such as a screw, a crimping method, or the like. The same also applies to the stators  61 ,  71 , and  81  used in the second, third, and fourth embodiments, respectively. 
     Further, in each of the above-described embodiments, the solenoid  33  has been described citing the example in which the opposite-side tubular portion  39 E is provided to the yoke  39  and the distal end side (the opposite axial side) of the opposite-side tubular portion  39 E is fixed to the outer peripheral side of the cover member  51  by the crimped portion  39 F. However, the present invention is not limited thereto, and the solenoid  33  may be configured in such a manner that, for example, the annular portion  39 B and the opposite-side tubular portion  39 E of the yoke  39  are formed on different members and this opposite-side tubular portion  39 E is formed integrally with the cover member  51 . Further, in the above-described embodiments, the solenoid  33  has been described citing the example in which the solenoid  33  is configured as a proportional solenoid. However, without being limited thereto, the solenoid  33  may be configured as, for example, an ON/OFF-type solenoid. 
     Next, an invention included in the above-described embodiments will be described. That is, according to a first configuration of the present invention, a solenoid includes a coil wound annularly and configured to generate a magnetic force in reaction to power supply, and a housing member disposed on an inner periphery of the coil. The housing member extends in a direction of a winding axis of the coil. The housing member includes a housing portion opened on one end side thereof, and is made from a magnetic body. The solenoid further includes a movable element provided in the housing portion movably in the direction of the winding axis of the coil and made from a magnetic body, and a stator provided at a position facing the opening of the housing portion. The stator includes a reduced diameter portion and a side surface portion integrally made from a magnetic body. The reduced diameter portion has an outer diameter reducing as it is approaching the opening of the housing portion. The side surface portion extends from an outer periphery of the reduced diameter portion in a direction away from the opening of the housing portion. The solenoid further includes a yoke including a fixation hole having an inner peripheral surface to which a part of the side surface portion of the stator is fixed. A non-contact portion, where the yoke and the side surface portion of the stator are out of contact with each other, is formed on the housing member side of the fixation hole. 
     According to a second configuration of the present invention, the solenoid according to the first configuration further includes a connection member joined by being heated between the housing member and the yoke, and made from a non-magnetic body. According to a third configuration of the present invention, in the solenoid according to the first or second configuration, a flange portion is formed on an end of the stator opposite from the housing portion, and a fixed portion of the side surface portion is a portion where the flange portion and the fixation hole face each other. According to a fourth configuration of the present invention, in the solenoid according to any of the first to third configurations, a stepped portion is formed on a surface where the side surface portion of the stator and the yoke face each other. According to a fifth configuration of the present invention, in the stator according to the fourth configuration, the stepped portion is formed on the reduced diameter portion side. 
     According to a sixth configuration of the present invention, a damping force adjustment mechanism includes a coil wound annularly and configured to generate a magnetic force in reaction to power supply, and a housing member disposed on an inner periphery of the coil. The housing member extends in a direction of a winding axis of the coil. The housing member includes a housing portion opened on one end side thereof, and is made from a magnetic body. The damping force adjustment mechanism further includes a movable element provided in the housing portion movably in the direction of the winding axis of the coil and made from a magnetic body, a control valve configured to be controlled according to a movement of the movable element, and a stator provided at a position facing the opening of the housing portion. The stator includes a reduced diameter portion and a side surface portion integrally made from a magnetic body. The reduced diameter portion has an outer diameter reducing as it is approaching the opening of the housing portion. The side surface portion extends from an outer periphery of the reduced diameter portion in a direction away from the opening of the housing portion. The damping force adjustment mechanism further includes a yoke including a fixation hole having an inner peripheral surface to which a part of the side surface portion of the stator is fixed. A non-contact portion, where the yoke and the side surface portion of the stator are out of contact with each other, is formed on the housing member side of the fixation hole. 
     According to a seventh configuration of the present invention, a damping force adjustable shock absorber includes a cylinder sealingly containing hydraulic fluid therein, a piston provided slidably in the cylinder, a piston rod coupled with the piston and extending out of the cylinder, and a damping force adjustment mechanism configured to generate a damping force by controlling a flow of the hydraulic fluid that is generated according to a sliding movement of the piston in the cylinder. The damping force adjustment mechanism includes a coil wound annularly and configured to generate a magnetic force in reaction to power supply, and a housing member disposed on an inner periphery of the coil. The housing member extends in a direction of a winding axis of the coil. The housing member includes a housing portion opened on one end side thereof, and is made from a magnetic body. The damping force adjustment mechanism further includes a movable element provided in the housing portion movably in the direction of the winding axis of the coil and made from a magnetic body, a control valve configured to be controlled according to a movement of the movable element, and a stator provided at a position facing the opening of the housing portion. The stator includes a reduced diameter portion and a side surface portion integrally made from a magnetic body. The reduced diameter portion has an outer diameter reducing as it is approaching the opening of the housing portion. The side surface portion extends from an outer periphery of the reduced diameter portion in a direction away from the opening of the housing portion. The damping force adjustment mechanism further includes a yoke including a fixation hole having an inner peripheral surface to which a part of the side surface portion of the stator is fixed. A non-contact portion, where the yoke and the side surface portion of the stator are out of contact with each other, is formed on the housing member side of the fixation hole. 
     The present invention shall not be limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail to facilitate a better understanding of the present invention, and the present invention shall not necessarily be limited to the configuration including all of the described features. Further, a part of the configuration of some embodiment can be replaced with the configuration of another embodiment. Further, some embodiment can also be implemented with a configuration of another embodiment added to the configuration of this embodiment. Further, each embodiment can also be implemented with another configuration added, deleted, or replaced with respect to a part of the configuration of this embodiment. 
     The present application claims priority under the Paris Convention to Japanese Patent Application No. 2020-076114 filed on Apr. 22, 2020. The entire disclosure of Japanese Patent Application No. 2020-076114 filed on Apr. 22, 2020 including the specification, the claims, the drawings, and the abstract is incorporated herein by reference in its entirety. 
     REFERENCE SIGNS LIST 
     
         
           1  hydraulic shock absorber (damping force adjustable shock absorber) 
           4  inner tube (cylinder) 
           5  piston 
           8  piston rod 
           17  damping force adjustment mechanism 
           18  damping force adjustment valve (control valve) 
           32  pilot valve member (valve member) 
           33  solenoid 
           34  molded coil 
           34 A coil 
           36  housing member 
           36 A housing tubular portion (housing portion) 
           36 B cover portion 
           39  yoke 
           39 A fixation hole 
           39 B annular portion 
           41 ,  61 ,  71 ,  81  stator 
           411 B,  61 B,  71 B,  81 B recessed dented portion 
           41 C,  61 C,  71 C.  81 C conical protrusion portion (reduced diameter portion) 
           41 D,  61 D,  71 D,  81 D side surface portion 
           41 E,  61 E,  71 E,  81 E flange portion 
           41 F stepped portion 
           42 ,  62 ,  72 ,  82  non-contact portion 
           44  non-magnetic ring (connection member) 
           45 , 46  brazed portion 
           48  movable element 
           49  actuation pin (shaft portion) 
           51  cover member 
         B rod-side oil chamber (rod-side chamber) 
         C bottom-side oil chamber (bottom-side chamber) 
         D annular oil chamber (flow passage)