Abstract:
Provided are a damping force variable valve assembly with a low-speed control valve capable of controlling an ultra-low flow rate and a low flow rate when a damping force variable valve operates in a soft mode, and a damping force variable shock absorber including the damping force variable valve assembly. The damping force variable valve assembly, which is installed in a damping force variable shock absorber for adjustment of a damping force of the shock absorber, includes: a solenoid; a spool which is movable by the magnetic force of the solenoid; a spool guide which surrounds the spool; a main valve which is installed in a main passage formed in a valve body installed in the spool guide; a back pressure chamber which is provided in the rear of the main valve; a chamber forming body which forms the back pressure chamber.

Description:
CROSS-REFERENCE(S) TO RELATED APPLICATION 
       [0001]    This application claims priority of Korean Patent Application No. 10-2013-0030691, filed on Mar. 22, 2013, in the Korean Intellectual Property Office, the contents of which are incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a damping force variable valve assembly installed in a damping force variable shock absorber, and more particularly, to a damping force variable valve assembly with a low-speed control valve capable of controlling an ultra-low flow rate and a low flow rate when a damping force variable valve operates in a soft mode, and a damping force variable shock absorber including the damping force variable valve assembly. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, a shock absorber is installed in means of transportation such as an automobile or the like, and improves a ride comfort by absorbing and damping a vibration or shock from a road surface on the drive. 
         [0006]    Such a shock absorber includes a cylinder and a piston rod installed to be compressible and extendable within the cylinder. The cylinder and the piston rod are installed in a vehicle body, wheels, or axles. 
         [0007]    A shock absorber, a damping force of which is set to be low, can improve a ride comfort by absorbing a vibration caused by uneven road surface on the drive. On the contrary, a shock absorber, a damping force of which is set to be high, can improve a steering stability by suppressing a change in a posture of a vehicle body. Therefore, in the conventional vehicles, different damping force characteristics are set to shock absorbers according to the purpose of use of the vehicles. 
         [0008]    Meanwhile, a damping force variable shock absorber has recently been developed which is mounted with a damping force variable valve at one side of the shock absorber so as to appropriately adjust a damping force characteristic, and can appropriate adjust a damping force characteristic to improve a ride comfort or a steering stability according to a road surface, a drive status, and the like. 
         [0009]      FIG. 1  is a cross-sectional view illustrating an example of a conventional damping force variable shock absorber. The conventional damping force variable shock absorber  10  includes a base shell  12  and an inner tube  14  which is movably installed inside the base shell  12  and in which a piston rod  24  is movably installed in a length direction. A rod guide  26  and a body valve  27  are installed in an upper portion and a lower portion of the inner tube  14  and the base shell  12 , respectively. In addition, a piston valve  25  is connected to one end of the piston rod  24  within the inner tube  14 , and the piston valve  25  partitions an inner space of the inner tube  14  into a rebound chamber  20  and a compression chamber  22 . A top cap  28  and a base cap  29  are installed in an upper portion and a lower portion of the base shell  12 , respectively. 
         [0010]    A reservoir chamber  30  is formed between the inner tube  14  and the base shell  12  to compensate for a change in a volume of the inner tube  14  according to a reciprocating motion of the piston rod  24 . A flow of a working fluid between the reservoir chamber  30  and the compression chamber  22  is controlled by the body valve  27 . 
         [0011]    In addition, a separator tube  16  is installed inside the base shell  12 . Due to the separator tube  16 , the inside of the base shell  12  is partitioned into a high pressure chamber PH connected to the rebound chamber  20 , and a low pressure chamber PL serving as the reservoir chamber  30 . 
         [0012]    The high pressure chamber PH is connected to the rebound chamber  20  through an inner hole  14   a  of the inner tube  14 . On the other hand, the low pressure chamber PL is connected to the compression chamber  22  through a lower passage  32 , which is formed between a body portion of the body valve  27  and the base shell  12  (or the base cap  29 ), and a passage formed in the body valve  27 . 
         [0013]    Meanwhile, the conventional shock absorber  10  includes a damping force variable valve assembly  40  mounted at one side of the base shell  12  so as to vary a damping force. 
         [0014]    The damping force variable valve assembly  40  is provided with oil passages communicating with the high pressure chamber PH and the low pressure chamber PL connected to the base shell  12  and the separator tube  16 , respectively. In addition, the damping force variable valve assembly  40  includes a spool  44  installed to be moved by a driving of a plunger  42 . An inner passage communicating with the high pressure chamber PH and the low pressure chamber PL is varied by movement of the spool  44 , and a damping force of the shock absorber is varied accordingly. The plunger  42  is configured to move in a horizontal direction, when viewed in  FIG. 1 , due to a magnetic force generated when an electric current flows through a solenoid. 
         [0015]    In the conventional damping force variable valve assembly, for example, when the plunger  42  moves left, the spool  44  closes the passage to generate a high damping force (hard mode). On the contrary, when the plunger  42  moves right, the spool  44  opens the passage to generate a low damping force (soft mode). 
         [0016]    In the technical field to which the invention pertains, many efforts have been made to provide a shock absorber having a good damping force variable characteristic by improving the performance of a damping force variable valve assembly. For example, Korean Patent Application Publication Nos. 10-2010-0023074 and 10-2010-0007187 disclose techniques of damping force variable valve assemblies recently developed for a shock absorber. 
         [0017]    However, in spite of many efforts to improve the performance of the damping force variable valve assembly, the conventional shock absorber has a poor damping force characteristic in a section where a moving speed of a working fluid is low. 
         [0018]    In the damping force variable valve assembly  40 , when a moving speed of a working fluid is high, that is, when a flow rate is high, a resistance is determined by a sagging amount of main disk valves stacked in a valve assembly. 
         [0019]    However, when an input (that is, shock) from a road surface is small and thus a moving speed of a working fluid is low or ultra-low, a flow rate of a working fluid flowing in a shock absorber is so extremely low that a resistance by a fixed orifice is not formed. Therefore, a damping force is not generated in a low-speed section, and a small vibration transferred from a road surface is not reduced. 
       SUMMARY OF THE INVENTION 
       [0020]    The present invention has been made in an effort to solve the above problems and is directed to provide a damping force variable valve assembly having a valve structure for a low flow rate control, which is capable of generating a damping force even in an ultra-low or low flow rate section of a working fluid when a damping force variable valve operates in a soft mode, and a damping force variable shock absorber including the damping force variable valve assembly. 
         [0021]    According to an aspect of the present invention, a damping force variable valve assembly, which is installed in a damping force variable shock absorber for adjustment of a damping force of the shock absorber, includes: a solenoid which generates a magnetic force when an electric current is applied thereto; a spool which is movable by the magnetic force of the solenoid; a spool guide which surrounds the spool to guide a movement of the spool; a valve body which is installed in the spool guide; a main valve which is installed in a main passage formed in the valve body, and generates a damping force; a back pressure chamber which is provided to have a back pressure to pressurize the main valve from the rear of the main valve; a chamber forming body which is installed outside the valve body to form the back pressure chamber; and a low-speed control valve which is installed in a low-speed passage formed in the valve body, and generates a damping force, wherein the damping force of the shock absorber is variable between a hard mode in which the back pressure of the back pressure chamber is increased and a soft mode in which the back pressure of the back pressure chamber is decreased, when an inner passage within the damping force variable valve assembly is changed by interaction of the spool and the spool guide, and the low-speed control valve generates the damping force when a flow rate of a working fluid is low in the soft mode. 
         [0022]    The valve body may be formed by sintering, and the chamber forming body may be formed by press processing. 
         [0023]    The spool may be provided by alternately forming large-diameter portions and small-diameter portions, and the large-diameter portions may be formed on both sides of the small-diameter portion so that a pressure of a working fluid passing through the small-diameter portion is equally applied to the large-diameter portions formed on both side of the small-diameter portion. 
         [0024]    A stepped portion coming into contact with the low-speed control valve may be formed on an outer peripheral surface of the inlet port of the spool guide, and the low-speed control valve may be assembled by interposing between the stepped portion and the valve body fitted into the spool. 
         [0025]    The main passage and the low-speed passage may form separate passages so that the main valve and the low-speed control valve are installed in parallel, and a working fluid supplied to the main valve may not pass through the low-speed control valve, and a working fluid supplied to the low-speed control valve may not pass through the main valve. 
         [0026]    According to another aspect of the present invention, a damping force variable shock absorber for adjusting a damping force of the shock absorber, includes: a base shell in which a damping force variable valve assembly is attached to an outside thereof; an inner tube which is installed inside the base shell and in which a piston rod is installed movably in a length direction; a piston valve which is connected to one end of the piston rod such that an inner space of the inner tube is partitioned into a rebound chamber and a compression chamber; and a separator tube which partitions a space between the base shell and the inner tube into a low pressure chamber and a high pressure chamber. The damping force variable valve assembly may include: a spool which is movable by a magnetic force of a solenoid; a spool guide which surrounds the spool to guide a movement of the spool; a main valve which is installed to cover a main passage formed in a valve body installed in the spool guide and generates a damping force; and a low-speed control valve which is installed to cover a low-speed passage formed in the valve body and generates a damping force. The damping force of the shock absorber may be variable between a hard mode in which a back pressure of a back pressure chamber installed at the rear of the main valve is increased and a soft mode in which the back pressure of the back pressure chamber is decreased, as an inner passage within the damping force variable valve assembly is changed by interaction of the spool and the spool guide. The low-speed control valve may generate the damping force when a flow rate of a working fluid is low in the soft mode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a cross-sectional view illustrating an example of a conventional damping force variable shock absorber. 
           [0028]      FIG. 2  is a cross-sectional view of a damping force variable valve assembly with a low-speed control valve according to the present invention. 
           [0029]      FIG. 3  is a partial enlarged cross-sectional view illustrating a spool of a damping force variable valve assembly with a low-speed control valve according to the present invention. 
           [0030]      FIG. 4  is a view for explaining an operation state of the damping force variable valve assembly according to the present invention, when a flow rate of a working fluid is low in a soft mode. 
           [0031]      FIG. 5  is a view for explaining an operation state of the damping force variable valve assembly according to the present invention, when a flow rate of a working fluid is medium or high in a soft mode. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0032]    Hereinafter, a damping force variable valve assembly of a damping force variable shock absorber according to exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description given with reference to  FIGS. 2 to 5 , like reference numerals as those of  FIG. 1  are used to refer to like elements. 
         [0033]    According to the present invention, the damping force variable valve assembly  140  is provided with oil passages communicating with a high pressure chamber PH and a low pressure chamber PL connected to a base shell  12  and a separator tube  16 , respectively. Since a structure in which the damping force variable valve assembly  140  is connected to the base shell  12  and the separator tube  16  and communicates with the high pressure chamber PH and the low pressure chamber PL is similar to that of the related art illustrated in  FIG. 1 , a structure in which the damping force variable valve assembly is connected to a side of the shock absorber is not illustrated in  FIGS. 2 to 5 . 
         [0034]    The damping force variable valve assembly  140  includes a spool  144  installed to be moved by a driving of a plunger  142 . An inner passage of the damping force variable valve assembly which communicates with the high pressure chamber PH and the low pressure chamber PL is varied by movement of the spool  144 , and a damping force of the shock absorber is varied accordingly. 
         [0035]    The damping force variable valve assembly  140  includes a main valve  150  and a back pressure chamber  160  used for varying the damping force of the shock absorber. The back pressure chamber  160  is provided to have a back pressure to pressurize the main valve  150  from the rear of the main valve  150 . The main valve  150  is installed to cover the main passage formed in a valve body from the rear of the valve body. On the other hand, the valve body is connected to the high pressure chamber PH of the above-described shock absorber through a spool guide  145  installed inside. The valve body is formed by sintering, but is not necessarily formed by a single sintered body. In the present embodiment, the valve body is provided with a first body  151  and a second body  152  formed by sintering. In addition, passages for performing various functions are formed in the first body  151  and the second body  152  constituting the valve body. 
         [0036]    The spool guide  145  includes an inlet port  145   a,  one or more first inlet passages  145   b,  and first to third passages  145   c,    145   d  and  145   e.  The first inlet port  145   a  is formed along a length direction such that a working fluid is introduced from the high pressure chamber PH. The one or more first inlet passages  145   b  are formed along a width direction to communicate with the inlet port  145   a.  The first to third passages  145   c,    145   d  and  145   e  are formed to block or permit the flow of the working fluid by interaction with the spool  144  as described below. 
         [0037]    The first body  151  includes a second inlet passage  151   a  formed to communicate with the first inlet passage  145   b  of the spool guide  145 , and the second body  152  includes a third inlet passage  152   a  formed to communicate with the second inlet passage  151   a  of the first body  151 . 
         [0038]    The inlet port  145   a,  the first inlet passage  145   b,  the second inlet passage  151   a,  and the third inlet passage  152   a  form the main passage such that the working fluid from the high pressure chamber PH can flow toward the main valve  150 . 
         [0039]    On the other hand, in order to form the passage of the working fluid flowing toward a low-speed control valve  170  in a low-speed section, a first low-speed passage  152   b  is formed in the second body  152 , and a second low-speed passage  151   b  is formed in the first body  151 . 
         [0040]    In addition, in order to form the passage of the working fluid moving toward the low pressure chamber PL through the main valve  150  in a medium/high-speed section, a medium/high-speed passage  152   c  is formed in the second body  152 . 
         [0041]    The back pressure chamber  160  is provided such that the pressure thereof is varied according to a driving of a solenoid  141  (that is, movement of the spool  144  due to the driving of the solenoid  141 ). A change in the pressure inside the back pressure chamber  160 , that is, a change in the back pressure to the main valve  150 , causes the main valve  150  to vary a force against the fluid passing through the main passage, thereby providing a varied damping force to the shock absorber. 
         [0042]    According to the present invention, a chamber forming body  161  for forming the back pressure chamber  160  may be formed by press processing. Since the chamber forming body  161  is formed as a pressed product, it is possible to reduce a total weight of the damping force variable valve assembly, reduce manufacturing cost and time of the valve body formed by sintering, and reduce time and effort necessary for manufacturing. 
         [0043]    A main retainer  153  and a main spring  154  are disposed in the back pressure chamber  160  so as to pressurize disks of the main valve  150  toward the valve body, that is, the second body  152 . 
         [0044]    The damping force variable valve assembly  140  includes a plunger  142  of which a moving distance is varied according to an amount of electric current applied to the solenoid  141 . On the other hand, the damping force variable valve assembly  140  includes the spool  144  that moves along a straight line while interlocking with the plunger  142  in a state of being disposed on the same axis as the plunger  142 . The spool  144  moves along the spool guide  145 . One end of the spool  144  comes into contact with the plunger  142 , and the other end of the spool  144  is elastically supported by a spool compression spring  146 . The spool compression spring  146  is supported by a plug  147  connected to the spool guide  145 . Therefore, the spool  144  moves forward by a pressurization of the plunger  142  and moves backward by a restoring force of the spool compression spring  146 . 
         [0045]    Referring to  FIG. 3 , the spool  144  is provided by alternately forming large-diameter portions and small-diameter portions. That is, when viewed from above the drawing, a first large-diameter portion  144   a,  a first small-diameter portion  144   d,  a second large-diameter portion  144   b,  a second small-diameter portion  144   e,  and a third large-diameter portion  144   c  are sequentially formed. As the spool  144  is moved by the solenoid  141 , the first small-diameter portion  144   d  may communicate the first passage  145   c  and the second passage  145   d  formed in the spool guide  145 , and the second small-diameter portion  144   e  may communicate the third passage  145   e  and the second passage  145   d  formed in the spool guide  145 . 
         [0046]    According to the present invention, since the large-diameter portions are formed on both sides of the small-diameter portion, the pressure of the fluid is equally applied to both the large-diameter portions, and therefore, the position of the spool is not deviated by the pressure of the fluid. 
         [0047]    That is, as indicated by an arrow of  FIG. 3 , for example, in a case where the first large-diameter portion  144   a  is present, the pressure of the fluid is applied to only the top surface of the second large-diameter portion  144   b  when the spool  144  moves and the first small-diameter portion  144   d  communicates the first passage  145   c  and the second passage  145   d  of the spool guide  145 . Therefore, when viewing the spool  144  in the drawing, a downward force is applied to the spool  144 . 
         [0048]    However, according to the present invention, since the first large-diameter portion  144   a  is present, the pressure of the fluid is applied to both the bottom surface of the first large-diameter portion  144   a  and the top surface of the second large-diameter portion  144   b  when the spool  144  moves and the first small-diameter portion  144   d  communicates the first passage  145   c  and the second passage  145   d  of the spool guide  145 . Therefore, a force for moving the spool  144  in one direction is not applied. 
         [0049]    On the other hand, one end of the plunger  142  comes into contact with the spool  144 , and the other end of the plunger  142  is elastically supported by the spool compression spring  146 . 
         [0050]    As the plunger  142  and the spool  144  are moved by the driving of the solenoid, a variable orifice is opened/closed or a passage area is adjusted by the interaction of the spool  144  and the spool guide  145 . Therefore, the opening/closing and/or the opening degree of a back pressure adjustment passage connected from the upstream side to the back pressure chamber  160  are/is controlled. 
         [0051]    The present invention may be configured to generate a damping force even in a case where the moving speed of the working fluid is low (or ultra-low) because a low-speed control valve  170  is installed in parallel to the main valve  150 . The low-speed control valve  170  may include a low-speed disk-S  171  which is mounted on a low-speed control valve mounting surface of the valve body and in which a slit is formed, and a low-speed disk  172  which can control an opening pressure or opening degree of the low-speed disk-S  171 . Although one low-speed disk-S  171  and one low-speed disk  172  are illustrated in the drawing, the number thereof can be changed when necessary upon their designs. 
         [0052]    According to the present invention, when assembling the damping force variable valve assembly, a stepped portion is formed on an outer peripheral surface of an end portion of the inlet port  145   a  of the spool guide  145 , and the low-speed control valve  170  is fitted to come into contact with the stepped portion. Then, the first body  151 , the second body  152 , and the main valve  150  are fitted. In this manner, the damping force variable valve assembly may be formed. Therefore, according to the present invention, it is unnecessary to use a nut and it is possible to prevent a change in the damping force of the low-speed valve according to a pressure caused by connection through the nut, as compared with the conventional assembling method in which the low-speed control valve  170  is installed in the valve body (that is, the first body  151 ) and is fastened by a nut or the like. 
         [0053]    Hereinafter, an operation state of the damping force variable valve assembly in a soft mode according to the present invention will be described in detail with reference to  FIGS. 4 and 5 . 
         [0054]      FIG. 4  illustrates an operation state when a flow rate of a working fluid is low (or ultra-low), and  FIG. 5  illustrates an operation state when a flow rate of a working fluid is medium or high. As illustrated in  FIGS. 4 and 5 , when the spool  144  is moved toward an opposite side of the inlet port  145   a  by the operation of the solenoid  141 , the first passage  145   c  and the second passage  145   d  of the spool guide  145  communicate with each other. The working fluid is not supplied toward the back pressure chamber  160 . Therefore, the operation state becomes a soft mode state in which the damping force of the main valve is relatively lowered. 
         [0055]    As illustrated in  FIG. 4 , when the flow rate of the working fluid in the soft mode is low, the working fluid passing through the main passage, that is, the inlet port  145   a,  the first inlet passage  145   b,  the second inlet passage  151   a,  and the third inlet passage  152   a  flows toward the second passage  145   d  of the spool guide  145  through the slit formed on the inner peripheral side of the disks included in the main valve  150 . 
         [0056]    Then, the working fluid passing through the second passage  145   d  flows toward the first passage  145   c  through a space between the spool guide  145  and the first small-diameter portion  144   d  of the spool. 
         [0057]    Then, the working fluid passing through the first passage  145   c  flows toward the first low-speed passage  152   b  and the second low-speed passage  151   b,  and a damping force is generated in a low flow rate section by the low-speed control valve  170 . As described above, according to the present invention, the damping force can be generated in a low-speed section, and a small vibration from a road surface can be effectively reduced to improve a ride comfort of a vehicle. 
         [0058]    In addition, as illustrated in  FIG. 5 , when the flow rate of the working fluid in the soft mode is medium or high, the working fluid passing through the main passage, that is, the inlet port  145   a,  the first inlet passage  145   b,  the second inlet passage  151   a,  and the third inlet passage  152   a  deforms and pushes the disks included in the main valve  150 , pass through the opened main valve  150 , and then flow toward the medium/high-speed passage  152   c.  The working fluid moving toward the medium/high-speed passage  152   c  immediately flows into the reservoir chamber  30  (that is, the low pressure chamber PL) within the shock absorber. 
         [0059]    In the structure in which the low-speed control valve is connected in series to the main valve and the working fluid passes through the low-speed control valve and is then supplied to the main valve, the effect resulting from the low-speed control valve, that is, the effect that the damping force is generated even in the section where the moving speed of the working fluid is low, and the ride comfort can be improved during a fine vibration. However, the damping force characteristic of the main valve may be affected by the low-speed control valve. That is, since the working fluid needs to pass through the low-speed control valve even in the medium/high-speed section, the damping force characteristic of the main valve may be distorted. 
         [0060]    However, in the structure of the present invention in which the low-speed control valve  170  is connected in parallel to the main valve  150 , it is possible to obtain the effect resulting from the low-speed control valve  170 , that is, the effect that improves fine vibration performance and achieve a rounded ride comfort by ensuring the degree of freedom of tuning in the low-speed section. In addition, since the damping force characteristic of the main valve  150  is not affected by the low-speed control valve  170 , the damping force characteristic of the main valve  150  is distorted. Consequently, the damping force non-interlocking is possible in the low-speed section and the medium/high-speed section, and the valve performance can be improved by ensuring the degree of freedom of tuning. 
         [0061]    According to the structure of the present invention, the damping force scattering phenomenon can be improved because the passage of the working fluid flowing to the main valve  150 , that is, the main passage, is separated from the passage of the working fluid flowing to the low-speed control valve  170 , that is, the low-speed passage (first and second low-speed passages  152   b  and  151   b ). 
         [0062]    In other words, the main passage and the low-speed passage form separate passages such that the main valve  150  and the low-speed control valve  170  can be installed in parallel. Therefore, according to the present invention, the working fluid supplied to the main valve  150  can be supplied to the main valve  150  without passing through the low-speed control valve  170 . In addition, the working fluid supplied to the low-speed control valve  170  can be supplied to the low-speed control valve  170  without passing through the main valve  150 . 
         [0063]    As described above, the present invention can provide the damping force variable valve assembly having the valve structure for the low flow rate control, and the damping force variable shock absorber including the damping force variable valve assembly. 
         [0064]    Therefore, the damping force variable valve assembly according to the present invention can improve a ride comfort of a vehicle by improve a damping force characteristic in a low-speed section (also including an ultra-low-speed section) to thereby effectively reduce a small frequent vibration from a road surface. 
         [0065]    In addition, according to the present invention, since the low-speed control valve is installed not in series but in parallel to the solenoid main valve, the damping force of the medium/high-speed section obtained by the solenoid main valve is not affected by the installation of the low-speed control valve. 
         [0066]    While the embodiments of the present invention have been described with reference to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.