Abstract:
A damper of variable damping force adapted to be built into a vehicular suspension is disclosed. The damper has frictional force generating means for applying a frictional force to a rod. The frictional force generating means is disposed at one end of a cylinder and positioned externally of the latter.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a vehicle damper of variable damping force adapted to be built into a vehicular suspension, which utilizes friction, for varying a damping force of the damper. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a variable damping force damper of this type, for example, an orifice is formed in a piston, and a damping force is generated by the resistance that arises when oil flows through the orifice. The variation in the damping force is generally accomplished by varying the diameter of the orifice so that the flow rate of the oil flowing through the orifice is varied. 
         [0003]    However, for example, a variable damper which is devised so that the damping force of the damper is varied using an electromagnet is known from Japanese Patent Application Laying-Open Publication No. 11-2276 (JP 11-002-276 A) as another type of a damper of variable damping force. 
         [0004]    Below, the variable damping force damper disclosed in JP 11-002-276 A will be described with reference to  FIGS. 11 and 12  hereof. 
         [0005]    As is shown in  FIGS. 11 and 12 , the variable damping force damper  300  is constructed from a tubular cylinder  301 , a piston  302  that moves through this cylinder  302 , damper oil  304  that flow through the cylinder  301  via an orifice  303  formed in this piston  302 , a rod  306 , one end of which is attached to the piston  302 , and the other end of which protrudes to the outside of the cylinder  301  via a rod guide  305 , and two (upper and lower) friction generating means  308  and  309  which are accommodated inside the cylinder  301 , and which are attached to the rod  306 . 
         [0006]    The upper friction generating means  308  has an electromagnet  311  which is attached to the rod  306 , an annular plate  312  which is attracted to this electromagnet  311 , a cam surface  313  which is formed with an inclination on the electromagnet  311 , and a shoe member  316  which contacts this cam surface  313  via a plurality of balls  314 , and which has a plurality of segments  315  attached to the annular plate  312  so as to allow movement in the direction of diameter of the cylinder  301 . 
         [0007]    When the electromagnet  311  is excited and the annular plate  312  is attracted to the electromagnet  311 , the balls  314  run over the cam surface  313 , so that the segments  315  are moved outward in the radial direction of diameter of the cylinder  301  by the balls  314 , and the shoe member  316  is caused to contact the inside surface of the cylinder  301 . A frictional force is generated by the contact between this shoe member  316  and the inside surface of the cylinder  301 , and the damping force of the damper varies. The lower friction generating means  309  has the same construction as the upper friction generating means  308 . 
         [0008]    However, in the variable damping force damper  300 , the shoe members  316  are disposed in a space (inside the cylinder  301 ) in which the piston  302  is accommodated. Accordingly, the damper oil  304  is interposed between the shoe members  316  and the inside surface of the cylinder  301 . Consequently, the damper oil  304  enters the space between the shoe members  316  and the inside surface of the cylinder  301 , and it is difficult to generate a sufficient frictional force. 
         [0009]    Furthermore, the damper  300  that has a variable damping force has a structure which has two fraction generating means comprising an upper friction generating means  308  in which a frictional force is generated when a force is applied to the damper from above, and a lower friction generating means  309  in which a frictional force is generated when a force is applied to the damper from below; accordingly, the structure is complicated. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide a damper of variable damping force for use in a vehicle which can block the effects of the damper oil, and which has friction generating means of simple structure. 
         [0011]    According to a first aspect of the present invention, there is provided a damper of variable damping force for use in a vehicle, which comprises: a tubular cylinder; a piston reciprocally movable within the cylinder and demarcating an interior of the cylinder into two compartments; a rod attached to the piston and protruding to outside from one end of the cylinder via a rod guide; damper oil sealed inside the cylinder and capable of flowing through the two compartments via a plurality of orifices formed in the piston; and friction generating means for applying a frictional force to the rod, the friction generating means being disposed at one end of the cylinder and positioned externally of the cylinder. 
         [0012]    Since the friction generating means is disposed on the outside of the cylinder, this can also easily be mounted on a damper which has a conventional structure. As a result, the all-purpose use of the friction generating means can be promoted. 
         [0013]    Preferably, the friction generating means comprises: a plurality of shoe members disposed around the rod for applying a frictional force to the rod; a moving plate formed of a magnetic material; a cam member for moving the shoe members toward an outer circumferential surface of the rod; an electromagnetic coil for moving the shoe members toward an axial center of the rod by chucking the moving plate; and a compression coil spring for urging the shoe members in a direction opposite a direction of chucking of the electromagnetic coil. Owing to the spring, a single friction generating means can be used in the pushing direction of the damper and in the pulling direction of the damper. As a result, the structure is simplified compared to a case where two friction generating means are used. 
         [0014]    According to a second aspect of the present invention, there is provided a damper of variable damping force for use in a vehicle, which comprises: a tubular cylinder; a piston reciprocally movable within the cylinder and demarcating an interior of the cylinder into two compartments; a rod attached to the piston and protruding to outside from one end of the cylinder via a rod guide; damper oil sealed inside the cylinder and capable of flowing through the two compartments via a plurality of orifices formed in the piston; friction generating means for applying a frictional force to the rod; and dividing means for dividing the interior of the cylinder, the friction generating means being disposed in a space divided and formed between the dividing means and the rod guide. 
         [0015]    Thus, the damper oil is prevented from permeating the divided spaces by the dividing means, and the effect of the damper oil can be blocked. As a result, the desired frictional force can be applied by the friction generating means. 
         [0016]    Desirably, oil having a lower viscosity than the damper oil is sealed inside the divided spaces. If the viscosity of this oil is thus low, the oil can easily spread through the entire divided space in each case; the frictional force of the friction generating means can be made uniform, and the frictional force can be kept within a specified friction range. 
         [0017]    According to a third aspect of the present invention, there is provided a damper of variable damping force for use in a vehicle, which comprises: a tubular cylinder; a piston capable of reciprocal movement within the cylinder and demarcating an interior of the cylinder into two compartments; a rod attached to the piston and protruding to outside from an interior of the cylinder; damper oil sealed inside the cylinder and capable of flowing through the two compartments via a plurality of orifices formed in the piston; and friction generating means for applying a frictional force to the rod, the friction generating means being disposed at an end of the cylinder from which the rod protrudes. 
         [0018]    Since the friction generating means is disposed on the end part of the cylinder where the rod protrudes to the outside from the inside of the cylinder, the friction generating means can also be caused to perform a rod guiding function. As a result, the variable damping force damper can be compactly constructed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Certain preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which: 
           [0020]      FIG. 1  is a sectional view showing a damper unit using a damper of variable damping force according to a first embodiment; 
           [0021]      FIG. 2  is an enlarged sectional view of a friction generating means shown in  FIG. 1 ; 
           [0022]      FIGS. 3A and 3B  are plan views showing a plurality of shoe members of the friction generating means of  FIG. 2 ; 
           [0023]      FIGS. 4A and 4B  are schematic views showing an operation of the friction generating means of  FIG. 2 ; 
           [0024]      FIG. 5  is a graph showing an example variation in the damping force characteristics of the variable damping force damper shown in  FIG. 1 ; 
           [0025]      FIG. 6  is a graph showing an example variation in the damping force characteristics in a case where a very small amplitude is excited in the variable damping force damper shown in  FIG. 1 ; 
           [0026]      FIG. 7  is a sectional view of a damper unit using a damper of variable damping force according to a second embodiment; 
           [0027]      FIG. 8  is an enlarged view of  FIG. 7 ; 
           [0028]      FIG. 9  is a sectional view of a damper unit using a damper of variable damping force according to a third embodiment; 
           [0029]      FIG. 10  is an enlarged view of  FIG. 9 ; 
           [0030]      FIG. 11  is a sectional view showing a conventional damper of variable damping force; and 
           [0031]      FIG. 12  is an enlarged view of the b region  FIG. 11 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Referring initially to  FIG. 1 , the damper unit  10  has a damper of variable damping force (shock absorber)  20  and a coil spring  12 . 
         [0033]    The damper of variable damping force  20  comprises a tubular cylinder  21 , a piston  22  which moves through this cylinder  21 , and which demarcates the interior of the cylinder  21  into two compartments, a rod  24  which is attached to this piston  22 , and which protrudes upward from one end of the cylinder  21  via a rod guide  23 , damper oil  27  which is sealed inside the cylinder  21 , and which flows through the two compartments via orifices  25  and  26  formed in the piston  22 , and friction generating means  50  which generates a frictional force between the cylinder  21  and the piston  22 . The rod  24  and cylinder  21  are covered by a tubular cover  28 . 
         [0034]    The tubular cover  28  is supported on the rod  24  via first and second damper rubbers  31  and  32 , and a damper rubber  33  inside the cover. 
         [0035]    The coil spring  12  is disposed between a first receiving member  35  attached to the cylinder  21 , and a second receiving member  36  positioned on the tip end part of the rod  24 . A spring-receiving washer  41 , the rod side receiving member  36 , a dish-form washer  43 , an outer damper rubber  44 , and a flat washer  45  are engaged in that order on the tip end part of the rod  24 . The tip end part of the rod  24  is formed as a screw part  46 , and a nut  47  is screwed onto this screw part  46 . 
         [0036]    The damper of variable damping force  20  is constructed from a cylinder  21 , a piston  22 , a rod  24  which protrudes via a rod guide  23 , damper oil  27  which flows through two compartments via orifices  25  and  26 , and friction generating means  50  which generates friction between cylinder  21  and the piston  22 . The friction generating means  50  is disposed on one end of the cylinder  21  on the outside of the cylinder  21 . Accordingly, this can also be easily mounted on a damper having a conventional structure, and the all-purpose use of the friction generating means  50  can be promoted. 
         [0037]    Furthermore, since an oil  58  having a lower viscosity than the damper oil  27  (see  FIG. 2 ) is sealed inside the friction generating means  50 , the low-viscosity oil can easily spread throughout; the frictional force of the friction generating means  50  can be made more uniform, and the frictional force can be kept within a specified friction range. 
         [0038]      FIG. 2  shows the friction generating means  50  shown in  FIG. 1 ,  FIG. 3A  shows a state in which the shoe members  51  is expanded in diameter, and  FIG. 3B  shows a state in which the shoe members  51  is contracted in diameter. 
         [0039]    As shown in  FIG. 2 , the friction generating means  50  has a plurality of shoe members  51  which is disposed around the rod  24 , and which applies a frictional force to the rod  24 , a moving plate  52  formed of a magnetic material which causes the shoe members  51  to move downward, a cam member  53  which causes the shoe members  51  to move in the central axial direction of the rod  24  when this moving plate  52  has moved downward, an electromagnetic coil  54  which attracts the moving plate  52  so that the moving plate  52  moves downward, a compression coil spring  56  which urges the shoe members  51  so as to provide resistance in the direction of attraction of the electromagnetic coil  54  via a washer  55 , a case  57  which accommodates the shoe members  51 , the moving plate  52 , the cam member  53 , and the electromagnetic coil  54 , and a cover  61  which seals the oil  58  having a lower viscosity than the damper oil  27  inside the case  57  via an oil seal  59 . 
         [0040]    As is shown in  FIG. 2 ,  FIG. 3A , and  FIG. 3B , the shoe members  51  is supported inside an annular recess  64  formed in the moving plate  52  via an elastic member  65 , and is supported on the cam member  53  via a plurality of balls (steel spheres)  66  so that movement is possible in the vertical direction and horizontal direction. 
         [0041]    A guide groove (not shown) is formed in the shoe members  51  or the cam member  53  so that each of the balls  66  is prevented from moving loosely. 
         [0042]    The shoe members  51  has pads  67  for each shoe member. 
         [0043]    The cam member  53  has a bobbin part  69  of a magnetic material around which the electromagnetic coil  54  is wound, and an inclined cam surface  68  which is formed on this bobbin part  69 . Each of the balls  66  is interposed between the respective shoe members  51  and the inclined cam surface  68 . 
         [0044]    The case  57  supports the rod  24  via an oil ring  71  so that sliding is possible. The cover member  61  supports the rod  24  via an oil ring  72  so that sliding is possible. 
         [0045]    Since the friction generating means  50  has a compression coil spring  56 , a single friction generating means  50  can be used in the pushing direction of the damper, and in the pulling direction of the damper. As a result, the structure can be made simpler than in a case where two friction generating means are used. 
         [0046]      FIGS. 4A and 4B  show the operating state of the friction generating means  50  shown in  FIG. 2 . 
         [0047]    As shown in  FIG. 4A , when the electromagnetic coil  54  is in a non-excited state, the shoe members  51  is lifted upward by the compression coil spring  56  as indicated by the arrows a 1 , a 1 , and the shoe members  51  is in a state of non-contact on the outer circumferential surface of the rod  24 . Specifically, if D 1  is the diameter of the rod  24 , the shoe members  51  is in a state in which gaps S 1 , S 1  are maintained with respect to the rod  24 . Accordingly, the rod  24  is in a state of non-friction with respect to the shoe members  51 . 
         [0048]    As shown in  FIG. 4B , when the electromagnetic coils  54  is excited, the moving plate  52  is attracted against the force of the compression coil spring  56  as indicated by the arrows b 1 , b 1 . As is also indicated by  FIG. 3B , the shoe members  51  is compressed in diameter by the cam member  53  as shown by arrows b 2 , b 2 , and contacts the outer circumferential surface of the rod  24 . As a result, a frictional force is generated in the in the rod  24 . By adjusting the voltage that excites the electromagnetic coil  54 , it is possible to adjust the magnitude of the frictional force that is generated in the rod  24 . 
         [0049]      FIG. 5  is a graph showing one example of the variation of the damping force characteristics of the damper of variable damping force  20  shown in  FIG. 1 . The horizontal axis shows the piston speed, and the vertical axis shows the damping force of the extension cycle and compression cycle of the damper. 
         [0050]    The broken line T 1  shows the damping force characteristics with respect to the piston speed in the extension cycle of the damper in a state in which the electromagnetic coil  54  is not excited. The broken line C 1  shows the damping force characteristics with respect to the piston speed in the compression cycle of the damper in a state in which the electromagnetic coil  54  is not excited. Specifically, the broken lines T 1  and C 1  show the damper characteristics according to only the flow of the damper oil  27  as in a conventional damper. 
         [0051]    The solid lines T 2 , T 3 , and T 4  show the damping force characteristics with respect to the piston speed in the extension cycle of the damper when the electromagnetic coil  54  is excited. The relationship P 2 &lt;P 3 &lt;P 4  is established with P 2  being the power (or voltage) of the solid line T 2 , P 3  being the power (or voltage) of the solid line T 3 , and P 4  being the power (or voltage) of the solid line T 4 . Specifically, as the voltage that excites the electromagnetic coil  54  increases, the frictional force of the rod  24  also increases. In other words, the damping force in the extension cycle of the damper increases as shown by the solid lines T 2 , T 3 , and T 4 . 
         [0052]    The solid lines C 2 , C 3 , and C 4  show the damping force characteristics with respect to the piston speed in the contraction cycle of the damper when the electromagnetic coil  54  is excited. The relationship P 2 &lt;P 3 &lt;P 4  is established with P 2  being the power (or voltage) of the solid line C 2 , P 3  being the power (or voltage) of the solid line C 3 , and P 4  being the power (or voltage) of the solid line C 4 . Specifically, as the voltage that excites the electromagnetic coil  54  increases, the frictional force of the rod  24  also increases. In other words, the damping force in the contraction cycle of the damper increases as shown by the solid lines C 2 , C 3 , and C 4 . 
         [0053]    With the variable damping force damper  20 , it is possible to effectively switch the roll rigidity and damping characteristics of the vehicle during ordinary operation by controlling the friction generating means  50 . Furthermore, a stable frictional force can be obtained using the friction generating means  50 , and the stability of damping force control can also be improved. In addition, there is no hindrance of damping force control by the friction generating means  50  in the very low speed region S of approximately 0.1 m/sec, either. 
         [0054]      FIG. 6  is a graph showing one example of the variation in the damping force characteristics in a case where a very small amplitude is excited in the damper of variable damping force for use in a vehicle shown in  FIG. 1 . The horizontal axis shows the piston speed, and the vertical axis shows the damping force in the extension cycle and compression cycle of the damper. 
         [0055]    The broken line T 5  shows the damping force characteristics with respect to the piston speed in the extension cycle of the damper in the case of a state in which the electromagnetic coil  54  in a very small excitation amplitude region of the piston  22  and a very low piston speed is not excited; characteristics which rise to the right are shown. Adjustment as shown by the solid line T 6  can be accomplished by causing the friction generating means to generate a frictional force. 
         [0056]    The broken line C 5  shows the damping force characteristics with respect to the piston speed in the contraction cycle of the damper in the case of a state in which the electromagnetic coil  54  in a very small excitation amplitude region of the piston  22  and a very low piston speed is not excited; characteristics which descend to the right are shown. Adjustment as shown by the solid line C 6  can be accomplished by causing the friction generating means to generate a frictional force. 
         [0057]      FIG. 7  shows a damper unit  110  using a damper of variable damping force  120  according to a second embodiment. Members which are the same in the damper unit  10  of the first embodiment shown in  FIGS. 1 and 2  and the variable damping force damper  120  are indicated by the same reference numbers, and a detailed description of such members is omitted. 
         [0058]    The damper unit  110  has the variable damping force damper  120  (shock absorber) and a coil spring  112 . 
         [0059]    The variable damping force damper  120  according to the second embodiment comprises a tubular cylinder  121 ; a piston  122  which is attached to this cylinder  121  so that sliding is possible, performs a reciprocating movement through the cylinder  121 , and demarcates the cylinder  121  into two compartments; a rod  124  which is attached to this piston  122 , and which protrudes to the outside of the cylinder  121  from one end of the cylinder  121  via a rod guide  123 ; damper oil  127  which is sealed inside the cylinder  121 , and which flows through the two compartments via a plurality of orifices  125  and  126  formed in the piston  122 ; dividing means  137  which divides the interior of the cylinder  121  in order to prevent any ingress of the damper oil  127 ; friction generating means  150  which is disposed in the space  138  divided by this dividing means  137 , and which generates a frictional force in the rod  124 ; an oil  158  which has a lower viscosity than the damper oil  127  (see  FIG. 8 ), and which is sealed inside the divided space  138 ; and a tubular cover  128  which is supported on the side of the rod  124 , and which covers the rod  124  and cylinder  121 . 
         [0060]    In the dividing means  137 , the divided space  138  is sealed by the sealing member  139  shown in  FIG. 8 . 
         [0061]    The tubular cover  128  is supported on the rod  124  by first and second damper rubbers  131  and  132 , and a damper rubbed  133  inside the cover. 
         [0062]    The coil spring  112  is disposed between a cylinder side receiving member  135  attached to the cylinder  121 , and a rod side receiving means  136  interposed on the tip end of the rod  124 . A spring receiving washer  141 , the rod side receiving member  136 , a dish-form washer  143 , an outer damper rubber  144 , and a flat washer  145  are engaged in the stated order on the tip end part of the rod  124 . A nut  147  is screwed onto a screw part  146  formed on the tip end part of the rod  124 . 
         [0063]    The friction generating means  150  shown in  FIG. 8  has a plurality of shoe parts  51  which is disposed around the rod  124 , and which applies a frictional force to the rod  124 , a moving plate  52  formed of a magnetic material, a cam member  53 , an electromagnetic coil  54  which causes the shoe members  51  to move in the direction of the axial center of the rod  124  by attracting the moving plate  52 , a spring member  56  which urges the shoe members  51  via a washer  55  in the direction opposing the direction of attraction of the electromagnetic coil  54 , a case  157  which accommodates the shoe members  5   1 , the moving plate  52 , the cam member  53 , and the electromagnetic coil  54 , and a cover  161  which covers this case  157 . 
         [0064]    The case  157  has a plurality of oil flow-through holes  163  and a plurality of oil flow-through holes  164  through which the low-viscosity oil  158  flows. The cover  161  has a plurality of oil flow-through holes  165  through which the low-viscosity oil  158  flows. 
         [0065]    In the variable damping force damper  120 , the dividing means  137  that divides the interior of the cylinder  121  is disposed in order to prevent invasion by the damper oil  127 , and the friction generating means  150  is disposed in the space  138  divided by this dividing means  137 . Accordingly, the effects of the damper oil  127  can be blocked. As a result, the desired frictional force can be applied by the friction generating means  150 . 
         [0066]    Since oil  158  having a lower viscosity than the damper oil  127  is sealed inside the divided space  138 , the frictional force of the friction generating means  150  can be made more uniform, and the frictional force can be kept within the desired friction range. 
         [0067]      FIG. 9  shows a damper unit using a damper of variable damping force according to a third embodiment. Parts which are the same as parts used in the damper unit  10  shown as the first embodiment are identified with the same symbols, and a detailed description of such part is omitted. 
         [0068]    Referring to  FIG. 9 , the damper unit  210  has a damper (shock absorber) of variable damping force  220  and a coil spring  212 . 
         [0069]    The variable damping force damper  220  according to the third embodiment comprises a tubular cylinder  221 , a piston  222  which performs a reciprocating movement through this cylinder  221 , and which demarcates the cylinder  221  into two compartments, a rod  224  which is attached to this piston  222 , and which protrudes from the end part of the cylinder  221 , damper oil  227  which is sealed inside the cylinder  221 , and which flows through the two compartments via a plurality of orifices  225  and  226  formed in the piston  222 , friction generating means  250  which is disposed on the end part inside the cylinder  221 , and which also has a guide function that guides the rod  224 , friction generating means  250  which generates a frictional force in the rod  224 , and a tubular cover  228  which is supported on the rod  224 , and which covers the rod  224  and cylinder  221 . 
         [0070]    As is shown in  FIG. 10 , the upper end  221  a of the cylinder  221  is covered by a cap  239  via an oil seal  237 . An oil seal  238  is interposed between the cap  239  and the rod  224 . 
         [0071]    The friction generating means  250  is disposed on a supporting stay  229 . 
         [0072]    The tubular cover  228  is supported on the rod  224  by first and second damper rubbers  231  and  232 , and a damper rubber  233  inside the cover. 
         [0073]    The coil spring  212  is disposed between a cylinder side receiving member  235  attached to the cylinder  221 , and a rod side receiving member  236  interposed on the tip end of the rod  224 . A spring receiving washer  241 , the rod side receiving member  236 , a dish-form washer  243 , an outer damper rubber  244 , and a flat washer  245  are engaged in that order on the tip end part of the rod  224 . A nut  247  is screwed onto a screw part  246  formed on the tip end part of the rod  224 . 
         [0074]    Referring to  FIG. 10 , the friction generating means  250  has a plurality of shoe members  251  which is disposed around the rod  224 , and which guides the rod  224 , and applies a frictional force to the rod  224 , a moving plate  252  formed of a magnetic material, a cam member  253  which causes the show members  251  to move toward the axial center of the rod  224 , an electromagnetic coil  254  which causes the shoe members  251  to move toward the axial center of the rod  224  by attracting the moving plate  252 , a spring member  256  which urges the shoe members  251  in the direction of attraction of the electromagnetic coil  254  and in the opposite direction via a washer member  255 , a case  257  which accommodates the shoe members  251 , moving plate  252 , cam member  253 , and magnetic coil  254 , and a cover  262  which covers this case  257 . 
         [0075]    The shoe members  251  has members that have substantially the same construction as the shoe members  51  shown in  FIG. 2 . This plurality of shoe members  251  has a guiding function that guides the rod  224  in a manner that allows sliding when the electromagnetic coil  254  is in a non-excited state, and has members that apply a specified frictional force to the rod  224  when the electromagnetic coil  254  is excited. 
         [0076]    The shoe members  251  is supported via an elastic member  265  inside a recess  264  formed in the moving plate  252 , and is supported on the cam member  253  so that sliding is possible in the vertical direction and the horizontal direction via a plurality of balls (steel spheres)  266 . 
         [0077]    Each of the shoe members  251  has a pad  267 . 
         [0078]    The cam member  253  has a cam surface  268  that supports the balls  266 , and a bobbin part  269  formed of a magnetic material around which the electromagnetic coil  254  is wound. 
         [0079]    The oil  258  having a lower viscosity than the damper oil  227  is sealed inside the case  257 ; this makes it possible to make the frictional force of the friction generating means  250  more uniform, and to keep the frictional force within a specified friction range. 
         [0080]    The variable damping force damper  220  is constructed from a cylinder  221 , a piston  222 , a rod  224  which protrudes to the outside from the cylinder  221 , damper oil  227  which flows through the two compartments via orifices  225  and  226 , and friction generating means  250  which generates a frictional force between the cylinder  221  and the piston  222 ; this friction generating means  250  is disposed on the upper end part of the cylinder  221  from which the rod  224  is extended. 
         [0081]    Specifically, since the friction generating means  250  is disposed on the upper end part of the cylinder  221  from which the rod  224  is extended, the friction generating means  250  can be caused to perform a rod guiding function as well. As a result, the variable damping force damper  220  can be constructed in a compact manner. 
         [0082]    In the variable damping force damper  20  according to the first embodiment, as is shown in  FIG. 2 , the oil  58  having a lower viscosity than the damper oil  27  is sealed inside the case  57 , and a cover  61  is installed via an oil seal  59 . However, the present invention is not limited to this; a construction in which this low-viscosity oil is not sealed may also be used. 
         [0083]    In the variable damping force damper  20 , as is shown in  FIG. 2 , a lip  81  may also be provided in order to improve the sealing characteristics. 
         [0084]    In the variable damping force damper  20 , as is shown in  FIG. 2 , the cam member  53  is formed of a magnetic material, and has a cam surface  68  that supports the balls  66 , and a bobbin part  69  around which the electromagnetic coil  54  is wound. However, the present invention is not limited to this; the cam surface and bobbin part may also be separately formed as separate parts. 
         [0085]    The variable damping force damper according to the present invention is suitable for use in passenger vehicles such as sedans, wagons and the like. 
         [0086]    Obviously, various minor changes and modifications of the present invention are possible in light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.