Abstract:
The present invention relates to a damping force control valve and a shock absorber using the same. The present invention is conceived to solve the aforementioned problems in the prior art. An object of the present invention is to provide a damping force control valve, which has an improved inner channel so that a damping force is operated in a middle mode when an electric or mechanical trouble causes a shock absorber to be out of order or malfunction, and a shock absorber using the same. According to the present invention, there is provided a damping force control valve, which includes a high pressure region in communication with a tension chamber of a cylinder and a low pressure region in communication with a reservoir chamber, and controls a damping force by adjusting pressure of a pilot chamber by first and second variable orifices, the first and second variable orifices having channels controlled to open or close by a spool. The damping force control valve comprises a main valve opened or closed according to pressure of the high pressure region, initial preload and pressure of the pilot chamber, the main valve allowing working fluid to flow from the high pressure region to the low pressure region when being opened; a first fixed orifice formed between the high pressure region and the first variable orifice; and a back pressure forming channel for making the first fixed orifice and the pilot chamber communicate with each other and controlling the pressure of the pilot chamber when the spool closes a channel connecting the high pressure region and the pilot chamber.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The present invention relates to a damping force control valve and a shock absorber using the same, and more particularly, to a damping force control valve having an orifice installed to an inlet of a pilot channel to give a high-speed damping force when a shock absorber is operated in a soft mode, and a shock absorber using the same.  
         [0003]     2. Description of the Prior Art  
         [0004]     Generally, a shock absorber of a vehicle is installed to a moving means such as a car, and thus, absorbs or buffers vibrations or shocks transferred from road wheels in contact with a road surface.  
         [0005]     This shock absorber can improve the ride comfort by lowering a damping force and thus absorbing vibrations caused by unevenness of a road surface when a vehicle is ordinarily running, and enhance the handling stability by raising a damping force and thus restraining posture change of the vehicle body when the vehicle turns, accelerates, brakes or runs at high speed.  
         [0006]     Meanwhile, in order to improve the ride comfort and handling stability, a shock absorber is recently provided with a damping force control valve mounted to one side thereof so as to suitably adjust a damping force, so that it is developed up to a damping force control shock absorber capable of suitably controlling a damping force according to a road surface state a the running state.  
         [0007]     In general, most of conventional damping force control shock absorbers control a damping force in an actuator manner, and are mainly classified into a reverse type and a normal type depending on a damping force control method.  
         [0008]     The aforementioned damping force control shock absorber is configured to increase or decrease both rebound and compressing damping forces at the same time according to an actuator current. For example, the conventional damping force control shock absorber controls a damping force in rebound and compression strokes in a soft mode by application of a certain actuator current, and also controls the damping force in a hard mode by application of a higher actuator current. Such damping force control is realized in such a manner that a spool moving according to the actuator operation controls back pressure formation in and adjustment of a pilot chamber formed in the rear of the damping force control valve.  
         [0009]      FIG. 1  is a sectional view showing a conventional damping force control valve of a shock absorber.  
         [0010]     A conventional damping force control valve  10  includes a spool rod  20  installed to an upper portion of an actuator  15  and having a plurality of channels allowing fluid communication, and a spool  25  installed to the spool rod  20  and operated by the actuator  15  to open and close each channel, as shown in  FIG. 1 .  
         [0011]     In addition, a first ring disk  32  acting as a fixed orifice is installed to the spool rod  20 , and a lower retainer  34  having a communication port  34   a  allowing fluid flow is installed to an upper portion of the first ring disk  32 .  
         [0012]     Also, a second ring disk  36  acting as a main valve is installed to an upper portion of the lower retainer  34 . The second ring disk  36  partitions a pilot chamber  45  formed in the upper portion of the lower retainer  34  from a high pressure region Ph. In addition, an upper retainer  38  having a communication port  38   a  allowing fluid flow is installed over the lower retainer  34 .  
         [0013]     Then, a nut  27  is coupled to the spool rod  20  to join the lower retainer  34  and the upper retainer  38 . Meanwhile, a spring  23  is interposed between one end of the spool rod  20  and the spool  25 , so that the spool  25  is brought into close contact with to the actuator  15 .  
         [0014]     The spool  25  has a hollow portion (not shown) and a plurality of vertically stepped outer diameters. Here, an upper spool slit  25   a  and a lower spool slit  25   b  are defined by the stepped outer diameters of the spool  25 . At this time, the upper spool slit  25   a  is formed to be larger than the lower spool slit  25   b , so that when the spool  25  reciprocates, the area change of the upper spool slit  25   a  with respect to the communication ports  21   a ,  21   b  and  21   c  of the spool rod  20  is greater than that of the lower spool slit  25   b  with respect to the communication port  34   a  of the spool rod  20 .  
         [0015]     Referring to  FIG. 2 , which is a schematic hydraulic circuit diagram showing a channel in the conventional damping force control valve, the operation of the conventional damping force control valve  10  so configured will be explained.  
         [0016]     As mentioned above, the damping force control valve  10  includes a first channel Qm having a main valve Km, a second channel Qr having a first variable orifice Kr, and a third channel Qc having a second variable orifice Kv and a fixed orifice Kc.  
         [0017]     In the damping force control valve  10 , the movement of the spool  25  controls the flow of the fluid that moves from a high pressure region Ph to a low pressure region Pl. When the spool  25  moves as mentioned above, open areas of the first variable orifice Kr and the second variable orifice Kv are varied.  
         [0018]     At this time, the first variable orifice Kr has an area change ratio greater than that of the second variable orifice Kv, and allows fluid to flow from the high pressure region Ph to the low pressure region Pl. Here, the area of the first variable orifice Kr is decreased as that of the second variable orifice Kv is increased, while the area of the first variable orifice Kr is increased as that of the second orifice Kv is decreased.  
         [0019]     The first channel Qm determines a valve characteristic in a middle high speed range of the soft/hard mode and has a spring preload in the form of a relief valve. Also, the pilot chamber  45  is formed in a rear surface of the valve and thus its pressure determines a valve opening pressure, thereby making the damping force control possible.  
         [0020]     In addition, the main valve Km is opened at different pressures according to a pressure Pc of the pilot chamber  45 . The pressure Pc of the pilot chamber  45  is formed by the operation of the second variable orifice Kv installed in an upstream of the third channel Qc and the fixed orifice Kc installed in a downstream. Thus, the pressure of the pilot chamber  45  increases by controlling the area of the second variable orifice Kv, whereby the damping force characteristic is converted into the hard mode.  
         [0021]     At this time, the sectional area of the second variable orifice Kv is decreased as that of the first variable orifice Kr is increased, while the sectional area of the second variable orifice Kv is increased as that of the first variable orifice Kr is decreased.  
         [0022]     In addition, the second channel Qr determines a low-speed damping force characteristic in the soft mode, and its area is changed by the first variable orifice Kr to determine a damping force.  
         [0023]     Also, the third channel Qc is configured such that the second variable orifice Kv is installed to its inlet and the fixed orifice Kc is installed to its exit so as to form a pressure of the pilot chamber  45 .  
         [0024]     In a case where the damping force characteristic formed in such a structure is the soft mode, if a predetermined current is applied to the actuator  15 , the area of the first variable orifice Kr is increased to lower a low-speed damping force, and at the same time, the channel of the second variable orifice Kv is closed to lower the pressure of the pilot chamber  45 , so that the main valve Km is opened at a low pressure.  
         [0025]     In the meantime, in a case where the damping force characteristic is the hard mode, if a high current is applied to the actuator  15 , the spool moves upward to close the first variable orifice Kr and open the second variable orifice Kv, thereby increasing the opening pressure of the main valve Km and thus increasing a damping force.  
         [0026]     Meanwhile, in the conventional damping force control valve  10  and the shock absorber using the same, when an electric or mechanical trouble causes a system malfunction to occur and thus a current is not input to the damping force control valve  10 , the damping force characteristic is fixed to the soft mode. If a steering wheel is excessively turned when the damping force control shock absorber is operated in the soft mode, the vehicle can overturn. In order to solve this problem, it is suggested in U.S. Pat. No. 6,000,508 (Dec. 4, 1999) that a restoring means such as a spring is installed to a general pilot control damping valve and a spool moves by the elasticity of the spring so that a shock absorber can be operated in a middle mode having a damping force in a middle level.  
         [0027]     However, in the conventional damping force control valve and the shock absorber using the same, the installation of the restoring means for restoring the spool causes the product size to be increased. In addition, the restoring force of the restoring means is operated even in a normal operation, thereby disturbing rapid control of the damping force. Thus, there is a need for developing a shock absorber capable of controlling a damping force in a middle mode without installing any additional restoring means to the shock absorber.  
       BRIEF SUMMARY OF THE INVENTION  
       [0028]     In one embodiment of the present invention provides a damping force control valve, which has an improved inner channel so that a damping force is operated in a middle mode when an electric or mechanical trouble causes a shock absorber to be out of order or malfunction, and a shock absorber using the same.  
         [0029]     According to an aspect of the present invention, there is provided a damping force control valve, which includes a high pressure region in communication with a tension chamber of a cylinder and a low pressure region in communication with a reservoir chamber, and controls a damping force by adjusting pressure of a pilot chamber by first and second variable orifices, the first and second variable orifices having channels controlled to open or close by a spool. The damping force control valve comprises a main valve opened or closed according to pressure of the high pressure region, initial preload and pressure of the pilot chamber, the main valve allowing working fluid to flow from the high pressure region to the low pressure region when being opened; a first fixed orifice formed between the high pressure region and the first variable orifice; and a back pressure forming channel for making the first fixed orifice and the pilot chamber communicate with each other and controlling the pressure of the pilot chamber when the spool closes a channel connecting the high pressure region and the pilot chamber.  
         [0030]     Here, the back pressure forming channel preferably includes a first safe orifice formed in the spool and connected to the first fixed orifice, and a second safe orifice connected to the pilot chamber. In addition, the back pressure forming channel may be open when a current supplied to an actuator for operating the spool is intercepted, thereby generating a middle damping force in the pilot chamber.  
         [0031]     In addition, according to another aspect of the present invention, there is provided a shock absorber, to which the aforementioned damping force control valve is installed to control a damping force. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]     The above and other objects, features and advantages of the present invention will become apparent from the following description of a preferred embodiment given in conjunction with the accompanying drawings, in which:  
         [0033]      FIG. 1  is a sectional view showing a conventional damping force control valve of a shock absorber;  
         [0034]      FIG. 2  is a schematic hydraulic circuit diagram showing a channel in the conventional damping force control valve;  
         [0035]      FIG. 3  is a sectional view showing a shock absorber having a damping force control valve according to the present invention;  
         [0036]     FIGS.  4  to  6  are views showing the operating state of the damping force control valve according to the present invention;  
         [0037]      FIG. 7  is a graph showing a damping force characteristic of the damping force control valve according to the present invention; and  
         [0038]      FIG. 8  is a schematic hydraulic circuit diagram showing a channel in the damping force control valve according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0039]     Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.  
         [0040]      FIG. 3  is a sectional view showing a shock absorber having a damping force control valve according to the present invention.  
         [0041]     As shown in  FIG. 3 , a shock absorber  50  according to the present invention includes a cylinder  52  which is formed to have predetermined length and diameter and of which the lower end is connected to an axle, and a piston rod  54  which is installed to be linearly movable in the cylinder  52 .  
         [0042]     Here, the cylinder  52  is filled with working fluid such as gas or oil, and a base shell  56  is arranged in its outside. Meanwhile, a rod guide  57  and a body valve  58  are respectively installed to an upper end of the cylinder  52  and a lower end of the base shell  56 . In addition, a piston valve  55  for partitioning the inner space of the cylinder  52  into a tension chamber  60  and a compression chamber  62  is coupled to the lower end of the piston rod  54  to be capable of reciprocating. Also, an upper cap  59   a  and a base cap  59   b  are respectively installed to upper and lower portions of the base shell  56 .  
         [0043]     In addition, a reservoir chamber  64  for compensating the volume change in the cylinder  52  according to the vertical movement of the piston rod  54  is formed between the cylinder  52  and the base shell  56 , and the reservoir chamber  64  controls the fluid communication with the compression chamber  62  by means of the body valve  58 .  
         [0044]     Meanwhile, the shock absorber  50  has a damping force control valve  70  installed to one side of the base shell  56  so as to control a damping force. In addition, the shock absorber  50  includes an intermediate tube  68  installed between the cylinder  52  and the base shell  56  to be connected to the compression chamber  62  of the cylinder  52 . Also, the damping force control valve  70  has a high pressure region Ph in communication with the tension chamber  60  of the cylinder  52  through the intermediate tube  68 , and a low pressure region PI in communication with the reservoir chamber  64 .  
         [0045]     FIGS.  4  to  6  are views showing the operating state of the damping force control valve according to the present invention, and  FIG. 7  is a graph showing a damping force characteristic of the damping force control valve according to the present invention. Referring to the figures, the damping force control valve will be described below.  
         [0046]     The above damping force control valve  70  has a plurality of channels therein and a spool  85  arranged on the same axis as a pressing rod  76  of an actuator  75  to be linearly movable in cooperation with the pressing rod  76 . The spool  85 , which is to move along a spool rod  80 , has one end in contact with the pressing rod  76  and the other end elastically supported by a compression spring  83 . Thus, the spool  85  moves forward by means of the press of the pressing rod  76 , and moves back by means of a restoring force of the compression spring  83 . According to this embodiment, the actuator  75  moves the pressing rod  76  according to an input current value. That is, the actuator  75  changes the channels to set a damping force characteristic in a soft mode when a relatively low current value (e.g., 0.6A) is applied thereto and in a hard mode when a relatively high current (e.g., 1.6A) is applied thereto.  
         [0047]     Also, the spool rod  80  is formed in its center with a hollow portion into which the spool  85  is to be inserted, and is formed with a plurality of ports  81   a ,  81   b  and  81   c  in a radial direction so that the hollow portion of the spool rod  80  is connected to the outside thereof. In addition, the spool  85  has a plurality of stepped outer diameters in a vertical direction, in the upper portion of which an upper spool slit  85   a  connected to the hollow portion of the spool rod  80  is formed, and in the lower portion of which a lower spool slit  85   b  is formed. Also, the spool  85  defines the inner channels by means of the interaction with the spool rod  80 , so that the upper spool slit  85   a  or the lower spool slit  85   b  communicates with the communication ports  81   a ,  81   b  or  81   c.    
         [0048]     As mentioned above, only one actuator  75  is sufficient to control the spool  85 , and the spool  85  is actuated by the actuator  75  to control a first variable orifice Kvr and a second variable orifice Kcr formed by the communication ports of the spool rod  80  and the spool  85 . Also, a first ring disk  82  is fitted around the spool rod  80 , and a lower retainer  84  is coupled to an upper portion of the spool rod  80  to fix the first ring disk  82 . In addition, an inflow chamber  92  controlled by the first ring disk  82  is defined in a lower portion of the lower retainer  84 , and a pilot chamber  95  is defined in an upper portion thereof. Also, a communication port  84   a  for allowing the fluid flow between the inflow chamber  92  and the pilot chamber  95  is formed in the lower retainer  84 .  
         [0049]     In addition, a plurality of slits  82   a  are formed in the circumference of the first ring disk  82 , and a second fixed orifice Kc is formed in the first ring disk  82  so as to regularly discharge the fluid of the pilot chamber  95  through the slits  82   a . Here, the first ring disk  82  may be formed of a membrane having a disk shape.  
         [0050]     The second fixed orifice Kc communicates with a first fixed orifice Kr when the second variable orifice Kcr communicating with the pilot chamber  95  is opened. The second fixed orifice Kc controls the working fluid discharged to the low pressure region Pl so that the working fluid supplied through the second variable orifice Kcr controls the pressure of the pilot chamber  95 .  
         [0051]     In addition, a second ring disk  86 , which is inserted into the spool rod  80  to function as a main valve Km, is arranged in an upper portion of the lower retainer  84 , and the second ring disk  86  partitions the pilot chamber  95  from a high pressure region Ph.  
         [0052]     Here, the second ring disk  86  is integrally formed, and preferably comprises a membrane having a disk shape.  
         [0053]     Thus, the pressure of the pilot chamber  95  is controlled by means of the first ring disk  82 , the second ring disk  86  that is the main valve Km is controlled to open or close according to the pressure of the high pressure region Ph and initial preload, and the working fluid is allowed to directly flow from the high pressure region Ph to the low pressure region Pl.  
         [0054]     In addition, a plurality of slits  86   a  are formed in the inner circumference of the second ring disk  86 , and the first fixed orifice Kr for discharging the fluid introduced from the high pressure region Ph is formed therein.  
         [0055]     Meanwhile, the fluid introduced into the first fixed orifice Kr of the second ring disk  86  is introduced into the first variable orifice Kvr or the second variable orifice Kcr that is formed by means of the spool  85  actuated by the actuator  75  and the communication ports  81   a ,  81   b  and  81   c  of the spool rod  80 . At this time, the cross sectional area of the second variable orifice Kcr is decreased as that of the first variable orifice Kvr is increased, while the cross sectional area of the second variable orifice Kcr is increased as that of the first variable orifice Kvr is decreased.  
         [0056]     Also, a nut  87  is coupled to the spool rod  80 , thereby joining the lower retainer  84  and an upper retainer  88 .  
         [0057]     In addition, the upper retainer  88  formed with a communication port  88   a  allowing fluid flow is coupled to the spool rod  80 , thus fixing the second ring disk  86 . The upper retainer  88  has a bypass channel  89 , which is formed to allow the interior of the hollow spool rod  80  to communicate with the low pressure region Pl.  
         [0058]     Meanwhile, the spool  85  has a hollow portion formed therein, and its one side (an upper side in the figure) is open. In addition, the spool  85  is formed with a first safe orifice  91 , F S1 , which communicates with the hollow portion of the spool  85  and an upper one side of the upper spool slit  85   a , and a second safe orifice  92 , F S2 , which communicates with the hollow portion and the lower spool slit  85   b . As mentioned above, the channel defined by the first safe orifice  91 , F S1 , the hollow portion and the second safe orifice  92 , F S2 , forms a back pressure forming channel and controls the pressure of the pilot chamber  95 .  
         [0059]     As described above, the pilot chamber  95  is changed in inner pressure as the open areas of the first variable orifice Kvr and the second variable orifice Kcr are changed by the spool  85  that is operated by the actuator  75 , thereby forming a back pressure against the second ring disk  86  at the rear thereof. Thus, the pressure change in the pilot chamber  95 , i.e., the back pressure change against the second ring disk  86 , or the main valve Km, makes the second ring disk  86  control a drag force against the fluid passing through the first variable orifice Kvr, thereby providing a controlled damping force to the shock absorber  50 .  
         [0060]     The operation of the damping force control valve configured as mentioned above will be described below.  
         [0061]     First, when a relatively low current (e.g., 0.6 A) is applied to the actuator  75 , as shown in  FIG. 4 , the operating rod of the actuator  75  slightly moves the spool  85  forward or backward and makes the first fixed orifice Kr and the first variable orifice Kvr communicate with each other. At this time, most of the fluid introduced from the high pressure region Ph is introduced into the spool slit  85   a  of the spool rod  80  through the first fixed orifice Kr, the communication port and the first variable orifice Kvr, and then discharged to the low pressure region Pl through the bypass channel  89 .  
         [0062]     In addition, a portion of the fluid introduced to the upper spool slit  85   a  is supplied to the low spool slit  85   b  through the back pressure forming channel that connects the first safe orifice  91 , F S1 , and the second safe orifice  92 , F S2 . Also, the portion of the fluid supplied to the low spool slit  85   b  is introduced into the pilot chamber  95  to increase its inner pressure, thereby controlling an opening/closing pressure of the second ring disk  86 . In addition, the other portion of the fluid introduced through the low spool slit  85   b  is discharged to the low pressure region Pl through the second fixed orifice Kc.  
         [0063]     During the above process, most of the fluid is discharged through the bypass channel  89 , whereby a damping force characteristic is controlled to be in a soft mode.  
         [0064]     Meanwhile, if a relatively high current (e.g., 1.6 A) is applied to the actuator  75 , as shown in  FIG. 5 , the operating rod of the actuator  75  moves the spool  85  forward, so that the first variable orifice Kvr is closed and the first fixed orifice Kr and the second variable orifice Kcr communicate with each other.  
         [0065]     At this time, a portion of the fluid introduced from the high pressure region Ph opens the second ring disk  86  and is discharged to the low pressure region Pl, and the other portion of the fluid is supplied to the low spool slit  85   b  of the spool rod  80  through the first fixed orifice Kr, the communication port and the second variable orifice Kcr. In addition, a portion the other partial fluid introduced through the low spool slit  85   b  is introduced to the pilot chamber  95  to increase an opening/closing pressure of the second ring disk  86 , thereby controlling an opening/closing pressure of the second ring disk  86 . Also, the remainder of the other partial fluid introduced through the low spool slit  85   b  is discharged to the low pressure region Pl through the second fixed orifice Kc formed in the first ring disk  82 .  
         [0066]     Thus, the fluid introduced from the high pressure region Ph is directly discharged to the low pressure region Pl through the main valve Km including the second ring disk  86  and the second fixed orifice Kc, and during this process, the damping force characteristic is controlled to be in a hard mode.  
         [0067]     In the meantime,  FIG. 6  shows a case where a power supplied to the actuator  75  is abruptly intercepted or malfunctions, at which the spool  85  is completely moved backward to close the first variable orifice Kvr and the second variable orifice Kcr.  
         [0068]     At this time, a portion of the fluid introduced from the high pressure region Ph opens the second ring disk  86  and is discharged to the low pressure region Pl, and the other portion of the fluid is supplied to the upper spool slit  85   a  through the first fixed orifice Kr and the communication port  81   b . In addition, the other portion of the fluid is supplied to the hollow portion of the spool  85  through the first safe orifice  91 , F S1 , formed in the spool  85 , and then supplied to the low spool slit  85   b  through the second safe orifice  92 , F S12 . Also, the fluid in the low spool slit  85   b  is partially introduced into the pilot chamber  95  through the communication port  81   a  to increase an opening/closing pressure of the second ring disk  86 , thereby controlling the pressure of the main valve Km. In addition, the remainder of the fluid introduced through the low spool slit  85   b  is discharged to the low pressure region Pl through the second fixed orifice Kc formed in the first ring disk  82 .  
         [0069]     Thus, the fluid introduced from the high pressure region Ph is directly discharged to the main valve Km including the second ring disk  86 , and increases the pressure of the pilot chamber  95  in the process of discharging the fluid to the low pressure region Pl by the back pressure formation channel, so that the damping force characteristic is controlled to be in a middle mode.  
         [0070]      FIG. 8  is a schematic hydraulic circuit diagram showing a channel in the damping force control valve according to the present invention. Referring the figure, the operation of the damping force control valve so configured according to the present invention will be explained below.  
         [0071]     The damping force control valve  70  according to the present invention includes three channels, as shown in  FIG. 8 , so that different damping force characteristics are shown by means of the fluid passing through each channel. At this time, the three channels formed in the damping force control valve  70  include a first channel Qm having the main valve Km, a second channel Qr having the first fixed orifice Kr, the first variable orifice Kvr and the back pressure forming channel that connects the first fixed orifice Kr to a position between the second variable orifice Kcr and the second fixed orifice Kc, and a third channel Qv having the first fixed orifice Kr, the second variable orifice Kcr and the second fixed orifice Kc.  
         [0072]     The first channel Qm is opened or closed by the main valve Km, and the main valve Km is controlled to open or close according to the pressure of the pilot chamber  95  and the initial preload, which is formed by the operating pressure of the high pressure region Ph, the spring  83  and the like.  
         [0073]     In addition, the fluid introduced from the high pressure region Ph is supplied through the first fixed orifice Kr, and supplied to the second channel Qr or the third channel Qv defined when the spool  85  moves forward or backward.  
         [0074]     The second channel Qr further includes the first fixed orifice Kr communicating with the high pressure region Ph, and the first variable orifice Kvr making the first fixed orifice and the low pressure region Pl communicate with each other. The fluid supplied through the first fixed orifice Kr is introduced into the first variable orifice Kvr and then discharged to the low pressure region Pl through the bypass channel  89 .  
         [0075]     Meanwhile, the back pressure forming channel formed in the second channel Qr is connected to a position between the first fixed orifice Kr and the first variable orifice Kvr and a position between the second variable orifice and the second fixed orifice Kc of the third channel Qv, thereby supplying a portion of fluid to the pilot chamber  95 . Thus, the pressure of the pilot chamber  95  is increased, and the damping force characteristic is controlled to be in a middle mode.  
         [0076]     In the meantime, the third channel Qv has the second variable orifice Kcr making the first fixed orifice Kr and the pilot chamber  95  communicate with each other, and the second fixed orifice Kc making the pilot chamber  95  and the low pressure region Pl communicate with each other. Also, the third channel Qv communicates with the low pressure region Pl when the first fixed orifice Kr, the second variable orifice Kcr and the second fixed orifice Kc are opened, and a portion of the fluid supplied to the third channel Qv is supplied to the pilot chamber  95  to control the opening/closing of the main valve Km. At this time, in case a lot of fluid is supplied through the second variable orifice Kcr, if the amount of fluid supplied to the pilot chamber  95  is increased, the pressure of the main valve Km is increased to reduce an amount of fluid passing through the first channel Qm. Meanwhile, in a case where an amount of fluid supplied through the second variable orifice Kcr is small, if the amount of fluid supplied to the pilot chamber  95  is reduced, the pressure of the main valve Km is decreased to increase an amount of fluid passing through the first channel Qm.  
         [0077]     Thus, the first fixed orifice Kr is installed at the inlet of the second variable orifice Kcr and the first variable orifice Kvr to primarily control an amount of fluid supplied to the second channel Qr and the third channel Qc.  
         [0078]     In a case where the damping force characteristic formed in such a structure is a soft mode, the area of the first variable orifice Kvr is increased to lower a low-speed damping force, and at the same time, the channel of the second variable orifice Kcr is closed to lower the pressure of the pilot chamber  45 , thereby making the main valve Km be opened at a low pressure.  
         [0079]     In addition, when the damping force characteristic is a hard mode, the first variable orifice Kvr is closed and the second variable orifice Kcr is opened contrary to the soft mode, thereby increasing the opening pressure of the main valve Km and thus increasing a damping force.  
         [0080]     Meanwhile, when an emergency state where a current is not supplied to the actuator  75 , the first variable orifice Kvr and the second variable orifice Kcr are closed and the back pressure forming channel connected to the pilot chamber  95  is open, thereby increasing a damping force at a predetermined level. Accordingly, the damping force control valve has a damping force characteristic in a middle mode when no current is supplied.  
         [0081]     Thus, even when the damping force control valve  70  of the shock absorber  50  gets out of order, the damping force characteristic is kept in the middle mode even though a steering wheel is excessively turned, so that it is possible to prevent deterioration of handling stability when the shock absorber  50  is operated only with the soft damping force.  
         [0082]     According to the damping force control valve and the shock absorber using the same configured as mentioned above according to the present invention, the back pressure forming path in the pilot chamber is variously changed, and thus a damping force can be maintained so that the handling stability of a vehicle can be secured even though the shock absorber is out of order or malfunction due to an electric or mechanical problem of the actuator.  
         [0083]     Although the damping force control valve and the shock absorber using the same according to the present invention have been described with the accompanying drawings, the present invention is not limited to the embodiment and drawings. It will be apparent that those skilled in the art can make various modifications and changes thereto within the scope of the invention defined by the claims.  
         [0084]     Thus, from the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.  
         [0085]     All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety.