Abstract:
A gas spring ( 1 ) comprises a piston rod ( 4 ) projecting from an open end of a cylinder ( 2 ) so as to be able to elongate and contract axially, and a dust seal ( 10 ) which is in contact with the piston rod ( 4 ) to prevent dust from invading the cylinder ( 2 ). By fitting a seal protecting member ( 21 ) to the open end of the cylinder ( 2 ) to shield the dust seal ( 10 ) from exposure to the outside of the cylinder ( 2 ), protection of the dust seal ( 10 ) from deterioration and damage is enhanced.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to the protection of a dust seal of a gas spring used for assisting the opening/closing of a swing type vehicle rear window, a vehicle rear window, or a smoke scavenging window of a building. 
       BACKGROUND OF THE INVENTION 
       [0002]    JP2002-115739A, published by Japan Patent Office in 2002 proposes a gas spring comprising a piston enclosed in a cylinder filled with gas, and a piston rod connected to the piston, which projects from the cylinder in an axial direction via a bearing under the pressure of the gas acting on the piston. 
         [0003]    A retainer is fixed to the inner circumference of the cylinder between the bearing and the piston so as to limit the displacement of the piston in an elongation direction. The piston rod projects outside the cylinder through the retainer and the bearing. A dust seal is fitted onto the bearing to cause the piston rod to slide on the dust seal, thereby preventing dust from infiltrating the cylinder. The open end of the cylinder is bent inward to retain the dust seal and prevent it from dropping out of the cylinder. 
       SUMMARY OF THE INVENTION 
       [0004]    In the gas spring according to the prior art, the dust seal retained in the opening of the cylinder is exposed to outside of the cylinder in the axial direction, and the dust seal may deteriorate in a short period of time depending on the operation condition of the gas spring. Furthermore, the dust seal exposed to outside is subjected to a physical damage by foreign matter. Deterioration as well as physical damage adversely affects the sealing performance of the dust seal. However, since the dust seal is retained by the bent open end of the cylinder together with the bearing, it is difficult to replace the dust seal. 
         [0005]    It is therefore an object of this invention to protect a dust seal from deterioration and physical damage. 
         [0006]    In order to achieve the above object, this invention provides a gas spring comprising a cylinder having an open end and filled with a gas, a piston rod projecting outward from the open end of the cylinder in accordance with a pressure of the gas, which performs elongation/contraction depending on an axial load exerted thereon, a dust seal disposed in the cylinder in contact with the piston rod to prevent dust from entering the cylinder through the open end thereof, and a seal protecting member which shields the dust seal from exposure to the exterior of the cylinder. 
         [0007]    The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a longitudinal sectional view of essential parts of a gas spring according to this invention. 
           [0009]      FIG. 2  is a longitudinal sectional view of essential parts of the gas spring, illustrating an exploded state thereof. 
           [0010]      FIG. 3  is similar to  FIG. 1  but shows a second embodiment of this invention. 
           [0011]      FIG. 4  is similar to  FIG. 1  but shows a third embodiment of this invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    Referring to  FIG. 1  of the drawings, a gas spring  1  adapted to assist the opening/closing of a vertical swing door of a vehicle comprises a cylinder  2 , a piston  3  enclosed in the cylinder  2 , and a piston rod  4  connected to the piston  3  and projecting outward axially from the cylinder  2 . 
         [0013]    The cylinder  2  is filled with a pressurized gas which pushes resiliently the piston rod  4  via the piston  3  such that the piston rod  4  projects outward. Pressurized gas in chambers  30 A and  30 B delimited by the piston  3  in the cylinder  2  communicates via a through hole  31  which penetrates the piston  3  and exerts a force on the piston  3  in the elongation direction of the piston rod  4  due to a difference in the pressure receiving areas of the piston  3  in the chamber  30 A and the chamber  30 B. 
         [0014]    The piston rod  4  penetrates a bearing  9  fixed to an open end of the cylinder  2  to project outward from the cylinder  2 . It also penetrates a retainer  12  fixed in the cylinder  2  between the bearing  9  and the piston  3 . The retainer  12  limits elongation of the piston rod  4  beyond a predetermined length, by coming into contact with the piston  3 . The bearing  9  functions to support the piston rod  4  so that the piston rod  4  does not move laterally when it elongates and contracts. 
         [0015]    The retainer  12  has a fitting groove  12   c  on its outer circumference and the bearing  9  has a fitting groove  9   a  on its outer circumference. The retainer  12  and the bearing  9  are first inserted into the cylinder  2  and then fixed respectively in predetermined positions in the cylinder  2  by caulking the cylinder  2  into the fitting grooves  12   c  and  9   a  respectively. 
         [0016]    A seal groove  12   a  is formed on the outer circumference of the retainer  12  and a seal groove  12   b  is formed on the inner circumference thereof. An O-ring  17  is fitted into the seal grooves  12   a,    12   b,  respectively. The retainer  12  is in close contact with the inner circumference of the cylinder  2  and the outer circumference of the piston rod  4  via the O-rings  17  so as to prevent gas leakage into the chambers  30 A,  30 B. 
         [0017]    Lubricating oil is stored in a space between the retainer  12  and the bearing  9  in the cylinder  2 . 
         [0018]    A seal member  14  is fitted to an end face of the bearing  9  facing the retainer  12  in order to prevent the lubricating oil from leaking. The seal member  14  is made of an elastic material such as rubber and is fixed to the bearing  9  via a washer  14   a  made of a flat ring-shaped plate. The seal member  14  comprises an outer lip  15  which is in contact with the inner circumference of the cylinder  2  and an inner lip  16  which is in contact with the outer circumference of the piston rod  4 . 
         [0019]    A dust seal  10  is fitted to the other end face of the bearing  9 , which is far from retainer  12  and faces outward, to prevent dust from invading the cylinder  2  as the piston rod  4  slides. The dust seal  10  is made of an elastic material such as rubber and fitted onto the bearing  9  via a washer  24  made of a flat ring-shaped plate. The end face of the bearing  9  facing outward onto which the dust seal  10  is fitted is located on a small diameter part  9   b  which has a smaller diameter than the other part of the bearing  9 . The dust seal  10  comprises an annular base portion  10   a  and a dust lip  25  that extends from the inner circumference of the base portion  10   a  and is always in contact with the outer circumference of the piston rod  4 . 
         [0020]    The gas spring  1  further comprises a cap shaped seal protecting member  21  which protects the dust seal  10 . The seal protecting member  21  comprises an engaging portion  23  formed into a cylindrical shape and inserted in an annular space formed between the small diameter part  9   b  of the bearing  9  and the inner circumference of the cylinder  2 , and a shield portion  22  which extends inward from the tip of the engaging portion  23  towards the piston rod  4 . 
         [0021]    A fitting groove  23   a  is formed on the outer circumference of the engaging portion  23 . The seal protecting member  21  is fixed to the cylinder  2  by inserting the engaging portion  23  into the annular space between the small diameter part  9   b  of the bearing  9  and the inner circumference of the cylinder  2 , and caulking the cylinder  2  into the fitting groove  23   a.    
         [0022]    The shield portion  22  inclines towards the dust seal  10  as it approaches the piston rod  4  and covers the dust seal  10 . The tip of the shield portion  22  is located close to the piston rod  24  such that only a minute gap is formed between the shield portion  22  and the prison rod  4 . 
         [0023]    As wall surfaces to delimit a space inside the seal protecting member  21 , the seal protecting member  21  comprises a large diameter part  23   b  the inner circumference of which has a substantially identical diameter to the outer diameter of the small diameter part  9   b  of the bearing  9 , an annular shape step  23   d  formed on the tip of the large diameter part  23   b  to reduce the diameter of the space in a stepwise fashion, and a tapered part  23   c  gradually reducing the diameter of the space from the inner end of the ring shaped step  23   d  towards a rear face of the shield portion  22 . 
         [0024]    The base portion  10   a  of the dust seal  10  is gripped together with the washer  24  between the annular step  23   d  of the seal protecting member  21  and the end face of the small diameter part  9   b  of the bearing  9 . The dust lip  25  of the dust seal  10  is accommodated in the space formed by the tapered part  23   c  and the rear face of the shield portion  22 . The dust seal  10  is thus covered entirely by the seal protecting member  21  so as not to be exposed to the outside of the cylinder  2 . 
         [0025]    The inner diameter of the large diameter part  23   b  of the seal protecting member  21  and the outer diameter of the base portion  10   a  of the dust seal  10  are preferably determined such that the outer circumference of the base portion  10   a  is elastically fitted into the inner circumference of the large diameter part  23   b.  This setting facilitates positioning of the dust seal  10  in the radial direction. 
         [0026]    Next, referring to  FIG. 2 , assembly process of the gas spring  1  will be described. 
         [0027]    First, the piston rod  4  to which the piston  3  has been fixed is inserted into the cylinder  2  from the open end. The retainer  12 , including the O-rings  17 , is then inserted into the cylinder  2  while letting the piston rod  4  pass through the retainer  12 , and the cylinder  2  is caulked into the fitting groove  12   c  of the retainer  12  to fix the retainer  12  in a predetermined position in the cylinder  2 . 
         [0028]    The seal member  14  and the dust seal  10  are fitted to the bearing  9  and thereafter the seal protecting member  21  is fitted to the bearing  9  as shown in the figure. As described heretofore, if the large diameter part  23   b  of the seal protecting member  21  is constructed to have a function to elastically retain the outer circumference of the dust seal  10 , the seal protecting member  21  can be fitted to the bearing  9  while retaining the dust seal  10  inside. 
         [0029]    The piston rod  4  is then caused to penetrate the bearing  9  to which the seal member  14 , the dust seal  10  and the seal protecting member  21  are fitted, as shown in the figure. Next, the bearing  9  is inserted into the cylinder  2 , and when it reaches the predetermined position, the cylinder  2  is caulked into the fitting groove  9   a  to fix the bearing  9  on the inner circumference of the cylinder  2 . Further, the cylinder  2  is caulked into the fitting groove  23   a  to fix the sealing member  21  to the open end of the cylinder  2 . 
         [0030]    In the gas spring  1  constructed as described above, since the dust seal  10  is covered by the seal protecting member  21  fixed to the end of the cylinder  2 , the dust seal  10  is not exposed to ambient air, and hence deterioration of the dust seal  10  due to the operation condition of the gas spring  1  is unlikely to occur. Further, the seal protecting member  21  prevents foreign matter from coming into contact with the dust seal  10 , and hence the dust seal  10  is also unlikely to be damaged by foreign matter. 
         [0031]    The seal protecting member  21  according to this invention is arranged to be fitted to the bearing  9  in advance when installed into the cylinder  2 . Installation of the seal protecting member  21  into the cylinder  2  is therefore performed without increasing the man-hour required for assembling the gas spring  1 . In other words, by fitting the engaging portion  23  of the seal protecting member  21  onto the small diameter part  9   b  of the bearing  9 , the dust seal  10  is fitted onto the bearing  9 . In other words, the seal protecting member  21  and the dust seal  10  can be fitted onto the bearing  9  together in one operation. This invention can therefore be implemented without increasing the assembling complexity of the gas spring  1 . 
         [0032]    The seal protecting member  21  is fixed in the cylinder  2  by caulking as in the cases of the retainer  12  and the bearing  9 . Fixing the seal protecting member  21  can therefore be performed using the same device used for fixing the retainer  12  and the bearing  9  in the cylinder  2 . 
         [0033]    As a result, increases in the manufacturing cost of the gas spring  1  for implementing this invention are suppressed. 
         [0034]    Next, referring to  FIG. 3 , a second embodiment of this invention will be described. 
         [0035]    In this embodiment, the seal protecting member  21  is fixed to the open end of the cylinder  2  to prevent it from dropping out of the cylinder  2  by bending the open end of the cylinder  2  inward instead of caulking the cylinder  2 . According to this embodiment, the fitting groove  23   a  formed on the outer circumference of the seal protecting member  21  can be omitted. 
         [0036]    It is also possible to fix the bearing  9  in the cylinder  2  by press fitting instead of caulking the cylinder  2 . In this case, the fitting groove  9   a  on the outer circumference of the bearing  9  can also be omitted. 
         [0037]    Next, referring to  FIG. 4 , a third embodiment of this invention will be described. 
         [0038]    According to this embodiment, the dust seal  10  is provided with a scraper  26  instead of the dust lip  25 . The other components of the gas spring  1  are identical to those of the second embodiment. As can be understood from this embodiment, this invention can be implemented irrespective of the construction and configuration of the dust seal  10 . 
         [0039]    With respect to the above description, the contents of Tokugan 2006-033493, with a filing date of Feb. 10, 2006 in Japan, are hereby incorporated by reference. 
         [0040]    Although the invention has been described above with reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, within the scope of the claims. 
         [0041]    For example, in the embodiments described above, the inner circumference of the large diameter part  23   b  of the seal protecting member  21  elastically retains the outer circumference of the dust seal  10 , but it is also possible to provide a clearance between the outer circumference of the dust seal  10  and the inner circumference of the large diameter part  23   b.  If this modification is applied, a slight displacement of the dust seal  10  in the radial direction will be allowed. As a result, when a load acts on the piston rod  4  in a radial direction and the piston rod  4  slightly displaces radially when the gas spring  1  operates, the dust seal  10  can also displace radially in accordance with the radial displacement of the piston rod  4 . This modification is therefore preferable in view of the dust sealing performance of the dust seal  10  relative to a radial load acting on the piston rod  4 . 
         [0042]    The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows: