Abstract:
A dust cover partially encloses a piston rod and a cylinder of a shock absorber to prevent foreign materials from being introduced into the cylinder via the piston rod. The dust cover includes at least two covers configured to be separated vertically and have ends overlapping with and sliding on each other. A gap between the two covers is defined to be directed upward.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a dust cover and a shock absorber having the same, and more particularly, to a dust cover formed to enclose a cylinder and a piston rod of a shock absorber to prevent foreign materials from being introduced into the cylinder from the outside, and a shock absorber having the same.  
         [0002]     A shock absorber, which serves to support the weight of a vehicle body and at the same time to suppress and attenuate a vibration transferred from a road to the vehicle body, is one of main components of a vehicle suspension system. Such a shock absorber absorbs and then relieves vertical vibration energy of a road wheel generated from unevenness of a road or the like, thereby preventing the vibration from being directly transferred to the vehicle body. Accordingly, the shock absorber contributes to improved ride comfort of a passenger and to protection of loaded freight and parts of the vehicle.  
         [0003]     Such a shock absorber includes a cylinder and a piston rod slidably accommodated in the cylinder. The cylinder is connected to a road wheel through a suspension arm and the like, and the piston rod is connected to a vehicle body side, wherein a piston valve is connected to a lower end of the piston rod. Accordingly, when a vehicle runs on an uneven road, the shock absorber serves to suppress and attenuate the vibrations transferred from the road to the vehicle body while compression and rebound strokes are continuously repeated.  
         [0004]     The general shock absorber further includes a dust cover partially enclosing the piston rod and the cylinder in order to prevent foreign materials from being introduced into the cylinder through the piston rod.  
         [0005]      FIG. 1  is a partial sectional view showing that a conventional dust cover is installed to a shock absorber  10 . Referring to  FIG. 1 , in the conventional shock absorber  10 , a piston rod  13  is fitted and inserted into a side of a cylinder  12 .  
         [0006]     A dust cover  11 , which is installed so as to partially enclose upper sides of the piston rod  13  and the cylinder  12  into which a side of the piston rod  13  is inserted, is configured to have an upper side fixed to the upper end of the piston rod  13  and closed and a lower side opened. When the piston rod  13  is retracted and extended, it is noted that an inner surface of the dust cover  11  slides on an outer surface of the upper side of the cylinder  12 , so that external foreign materials are prevented from contaminating the inside of the cylinder  12  and the piston rod  13 .  
         [0007]     However, during the rebound stroke, the conventional dust cover  11  slides upward relative to the cylinder  12  and thus a negative pressure is generated in the conventional dust cover  11  with the lower side opened, so that external air is introduced from below between the lower side of the dust cover  11  and the cylinder  12 . Accordingly, there is a problem in that large amounts of foreign materials are introduced from a road into the cylinder.  
         [0008]     On the other hand, although not shown, a bellows type dust cover, which is installed to fix both upper and lower ends of a cylinder, is repeatedly contracted and expanded while a piston rod repeatedly is retracted and extended, thereby causing a problem that the dust cover is worn away as well as noise is generated when the dust cover is contracted and expanded.  
       SUMMARY OF THE INVENTION  
       [0009]     An embodiment of the present invention provides a dust cover for preventing external air from being introduced into the dust cover from below during a rebound stroke, and a shock absorber having the same.  
         [0010]     In one embodiment, a dust cover is configured to partially enclose a piston rod and a cylinder of a shock absorber to prevent foreign materials from being introduced into the cylinder via the piston rod. The dust cover comprises two covers configured to be separated up and down and to have ends overlapping with and sliding on each other, wherein a gap between the two covers is defined to be directed upward.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a view showing a shock absorber according to a prior art;  
         [0012]      FIG. 2  is a view showing that a shock absorber according to the present invention is in a rebound stroke; and  
         [0013]      FIG. 3  is a view showing that the shock absorber according to the present invention is in a compression stroke. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]      FIG. 2  is a view showing that a shock absorber according to the present invention is in a rebound stroke, and  FIG. 3  is a view showing that the shock absorber according to the present invention is in a compression stroke.  
         [0015]     As shown in the figures, a shock absorber  100  according to the present invention includes a cylinder  110 , a piston rod  120 , a piston  130 , and a dust cover  140  partially enclosing upper sides of the piston rod  120  and the cylinder  110 .  
         [0016]     An inner cylinder  111  is installed in the cylinder  110 . The inner cylinder  111  is filled with working fluid, i.e., hydraulic oil, and fluid for compensating an internal pressure of the inner cylinder  111  is filled outside the inner cylinder  111 , i.e., between the inner cylinder  111  and the cylinder  110 . Then, the piston  130  connected to the piston rod  120  is reciprocatingly movably installed to the inner cylinder  111  of the cylinder  110  while partitioning the interior of the inner cylinder  111  into a compression chamber CC and a rebound chamber RC.  
         [0017]     The piston rod  120  is installed such that a side thereof is inserted into the inner cylinder  111  and the other side thereof protrudes out of the cylinder  110 . A rod guide  121  is installed between the piston rod  120  and the cylinder  110 . A through hole  123  is formed in the center of the rod guide  121 , and the piston rod  120  is inserted through the through hole  123 . The rod guide  121  seals between the cylinder  110 , the inner cylinder  111 , and the piston rod  120 . A coil spring  125  is installed around the piston rod  120 . The coil spring  125  is extended and compressed when the piston rod  120  moves upward and downward.  
         [0018]     A bumper stopper  150  is installed between the cylinder  110  into which the piston rod  120  is inserted and the piston rod  120 , and thus, absorbs the shock load transferred from a road wheel to a vehicle body when the piston rod  120  is retracted and extended.  
         [0019]     The dust cover  140  comprises an upper cover  141  and a lower cover  143 . The upper cover  141  is installed to be fixed to the upper end of the piston rod  120  and to enclose the bumper stopper  150  and a portion of the piston rod  120 . The lower cover  143  is installed to be fixed to the upper end of the cylinder  110  and to partially enclose the piston rod  120  inserted into the cylinder  110 . Here, the upper cover  141  has a lower side opened, while the lower cover  143  has an upper side opened. In addition, the lower cover  143  is configured to have an inner diameter larger than that of the upper cover  141 , so that when the piston rod  120  is retracted and extended, the lower end of the upper cover  141  is inserted into the upper end of the lower cover  143  and thus the outer surface of the upper cover  141  can slide on the inner surface of the lower cover  143 .  
         [0020]     When the shock absorber  100  so configured is in the rebound stroke in which the vehicle body becomes more distant from a road in a vehicle driving state, as shown in  FIG. 2 , the fluid moves toward the compression chamber CC and thus the piston valve  130  moves upward in the cylinder  110 , so that the piston rod  120  protrudes out of the cylinder  110 . Therefore, while being maintained to be inserted in the lower cover  143 , the upper cover  141  protrudes from the lower cover  143  by the stroke of the shock absorber  100 . At this time, since the upper side of the piston rod  120  is enclosed by the upper cover  141  and the upper end of the cylinder  110  into which the piston rod  120  is inserted is enclosed by the lower cover  143 , foreign materials are prevented from being introduced into the shock absorber  100 . Particularly, such a dust cover  140  is formed so that the inner diameter of the lower cover  143  is larger than that of the upper cover  141 , and thus, is configured so that the inner surface of the upper cover  141  can slide on the outer surface of the lower cover  143 . Therefore, since air is introduced from above to between the upper cover  141  and the lower cover  143  although the upper cover  141  slides upward relative to the lower cover  143  during the rebound stroke and a negative pressure is generated in the upper cover  141  and the lower cover  143 , amounts of the foreign materials introduced into the dust cover  140  from a road will be considerably reduced.  
         [0021]     In the meantime, during the compression stroke in which the vehicle body comes up to a road in a vehicle driving state, as shown in  FIG. 3 , the fluid moves toward the rebound chamber RC and thus the piston valve  130  moves downward in the cylinder  110 , so that the piston rod  120  enters the cylinder  110 . Therefore, the distance between the upper cover  141  and the lower cover  143  is reduced, and then, the upper cover  141  is inserted into the lower cover  143 . Therefore, even though the vehicle body comes up to a road, the foreign materials can be prevented from being introduced into the cylinder  110  or the piston rod  120  of the shock absorber  100 .  
         [0022]     According to the present invention, since the dust cover is configured such that external air is prevented from being introduced into the dust cover from below during a rebound stroke, there is an advantage in that amounts of foreign materials introduced into the dust cover from a road are considerably reduced.  
         [0023]     The aforementioned embodiment is only an example for embodying the present invention. The scope of the present invention is not limited to the embodiment described and illustrated above. The true scope of the present invention should be defined to the extent that those skilled in the art can make various modifications and changes thereto without departing from the scope of the invention as defined by the appended claims.