PATENT ABSTRACT
A hydraulic damper ( 3 ) includes a tube ( 4 ), a piston assembly ( 5 ) disposed slidably inside the tube ( 4 ), and an additional valve assembly ( 13 ). A compression chamber ( 9 ) is defined between the piston assembly ( 5 ) and the additional valve assembly ( 13 ). An additional compensation chamber ( 14 ) is defined between the additional valve assembly ( 13 ) and one side of a slideable partition ( 10 ). A gas chamber ( 11 ) is defined at the other side of the slidable partition ( 10 ). The damper includes an additional chamber assembly ( 15 ) to retain all the advantages of a twin-tube damper while providing the single construction offered by a mono-tube damper. One end of the additional chamber assembly ( 15 ) is attached to the slidable piston chamber ( 5 ) or to said piston rod ( 6 ) at the compression side thereof and the other end of said additional chamber assembly ( 15 ) is terminated with the additional valve assembly ( 13 ).

PATENT DESCRIPTION
FIELD OF THE INVENTION 
       [0001]    The invention relates to a hydraulic damper, in particular a motor vehicle suspension damper, comprising: a tube; a piston assembly disposed slidably inside the tube and attached to a piston rod led outside the tube through a sealed piston rod guide located at the end of the tube, wherein a rebound chamber filled with working liquid is defined between said piston rod guide and said piston assembly; an additional valve assembly, wherein a compression chamber filled with working liquid is defined between said piston assembly and said additional valve assembly; a slidable partition, wherein an additional compensation chamber filled with working liquid is defined between said additional valve assembly and one side of said slidable partition; a gas chamber filled with pressurised gas and defined at the other side of said slidable partition; wherein said piston assembly is provided with rebound valve and compression valve to control the flow of working liquid passing between said compression chamber and said rebound chamber, respectively, during rebound and compression stroke of the damper, and said additional valve assembly is provided with rebound valve and compression valve to control the flow of working liquid passing between said additional compensation chamber and said compression chamber, respectively, during rebound and compression stroke of the damper. 
       BACKGROUND OF THE INVENTION 
       [0002]    Dampers of the features as above are known from the state of art as twin-tube dampers. They provide excellent tuning capabilities enabling for independent tuning both the valves of a slidable piston assembly and the valves of an additional base valve assembly that in a case of twin-tube dampers is located at the bottom end of the main tube. Twin-tube dampers also require relatively low pressure of the pressurised gas what results in relatively low internal pressure of the working liquid filling the damper, inducing relatively low friction force between a piston rod and a rod guide seal. Furthermore, the external tube is not used to guide the slidable piston assembly. Therefore possible deformations of the external tube, in particular in the bottom zone of the damper, where it is usually fixed to the steering knuckle of a vehicle suspension have no influence on the operation of the damper. Also the piston assembly is designed not to reach this bottom zone of the external tube in its sliding movement. 
         [0003]    Nonetheless, twin-tube dampers also have some disadvantages due to their complex structure, such as inter alia the necessity to provide a base valve assembly and a rod guide of a construction enabling for support of the external tube. 
         [0004]    These disadvantages of the twin tube dampers have been substantially eliminated in mono-tube dampers in which all three chambers, i.e. a rebound chamber, a compression chamber and a gas chamber, are arranged serially in a single tube. Mono-tube dampers are devoid of an additional valve assembly and an additional compensation chamber. A slidable partition is provided between the compression chamber and the gas chamber. 
         [0005]    However, other problems arise. Higher pressure is required in the chambers of the damper to eliminate free displacement of a slidable partition with no damping force generated by the valves of the piston assembly (a so called “no damping stroke effect”). This increased pressure in turn requires an improved sealing of the piston rod guide which in turn generates higher friction forces between the piston rod and the rod guide seal. Furthermore, the damper&#39;s length is increased since the gas chamber is positioned in series with the compression chamber along the longitudinal axis of the damper. Moreover, a certain dead zone exists at the end of the gas chamber where possible deformations of the main tube (which in this case is also an external tube) might lead to jamming of the slidable partition or otherwise limiting its sliding movement. Finally mono-tube dampers often provide significantly limited tuning capabilities as compared to twin-tube dampers. 
         [0006]    Yet another common disadvantage of both the above-mentioned damper types is a necessity to fill the gas chamber with a pressurised gas which process depends on the process of filing the damper with a working liquid. 
         [0007]    It has been the object of the present invention to provide a hydraulic damper that would retain all the aforementioned advantages of a twin-tube damper along with simplicity of construction as provided by a mono-tube damper. 
         [0008]    The inventors discovered that achieving these objects is possible by diverting the flow of working liquid radially inside the compression chamber (instead as radially outside as in twin-tube dampers). 
       SUMMARY OF THE INVENTION 
       [0009]    Therefore, a damper of the kind mentioned in the outset, according to the present invention is characterised in that it is provided with an additional chamber assembly, wherein one end of said additional chamber assembly is attached to said slidable piston assembly or to said piston rod at the compression side thereof and the other end of said additional chamber assembly is terminated with said additional valve assembly, wherein said pressurised gas chamber and said additional compensation chamber are located inside said additional chamber assembly and are separated by said slidable partition. 
         [0010]    Preferably the damper of the present invention is a mono-tube damper. This enables for achieving simplicity of damper construction, although the additional chamber assembly may obviously also be used as an additional tuning add-on in a twin-tube damper, for example to provide additional tuning options. 
         [0011]    Preferably said additional chamber assembly comprises a uniform body, preferably screwed to the end of the piston rod. This provides a cost efficient method of manufacturing the chamber assembly in a simple stamping process. 
         [0012]    Preferably said additional chamber assembly is a separate subassembly of the damper independently assembled and filled with a pressurized gas. This further improves damper assembly process. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]    The invention shall be described and explained below in connection with the attached drawings on which: 
           [0014]      FIG. 1  is a schematic cross-sectional view of a typical mono-tube damper known from the state of art; 
           [0015]      FIG. 2  is a schematic cross-sectional view of a typical twin-tube damper known from the state of art; 
           [0016]      FIG. 3  is a schematic cross-sectional view of an embodiment of a damper according to the present invention; 
           [0017]      FIG. 4  a detailed cross-sectional view of the embodiment of an additional chamber assembly according to the present invention, and 
           [0018]      FIG. 5  is a schematic perspective view of a fragment of a typical vehicle suspension. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    A hydraulic damper  1  shown in part in  FIG. 1  is an example of a mono-tube hydraulic damper that may be employed in a vehicle suspension  200  presented in  FIG. 5 . It is shown almost fully extended in its position close to the end of the rebound stroke and comprises main cylinder tube  4  inside of which a piston assembly  5  is slidably disposed. The piston assembly  5  is attached to a piston rod  6  led outside the main tube  4  through a sealed piston rod guide  7  located at the end of the tube. The other end (not shown) of the piston rod  6  may be connected to the top mount  202  of the vehicle suspension  200 . The opposite end of the tube  4  is provided with an attachment means  16 , in a form of a bracket with two mounting holes  161 , apt to fix the damper  1  to the steering knuckle or a swing arm supporting the vehicle wheel  205 . 
         [0020]    Arched arrow lines running from the rebound chamber  8  to the sealing of the piston rod guide  7  schematically symbolize a friction force between the rod guide  6  and the sealing resulting from a reaction of the internal damper pressure to the guide sealing. 
         [0021]    A rebound chamber  8  filled with working liquid is defined between the piston rod guide  7  and the piston assembly  5 . A slidable partition  10  is disposed at the other end of the damper  1 . A compression chamber  9  filled with working liquid is defined between the piston assembly  5  and the slidable partition  10 . Pressurised gas fills the space at the other side of the slidable partition  10  defining a gas chamber  11 . 
         [0022]    The term “rebound”, as used in this specification with reference to particular elements of the damper, denotes these elements or these parts of particular elements which point toward the piston rod or—in a case of a flow direction of the working liquid—it refers to this flow direction that takes place during the rebound stroke of a damper. Similarly, the term “compression”, as used herein with reference to particular elements of the damper, denotes these elements or parts of elements which point in a direction opposite to the piston rod or—in a case of a flow direction of the working liquid—it refers to this flow direction that takes place during the compression stroke of a damper. 
         [0023]    The piston assembly  5  is provided with rebound  51  and compression  52  valves to control the flow of working liquid passing between the compression chamber  9  and the rebound chamber  8 , respectively, during rebound and compression stroke of the damper. Each valve  51  and  52  comprises a number of flow channels disposed equiangularly over the perimeter of the piston assembly  5  and a number of resilient deflectable discs covering that channels and deflecting under the pressure of working liquid. Number, shape, diameter and thickness of discs, as well as number and cross-sectional area of the channels constitute, among others, the parameters that may be utilized to influence damper characteristics. 
         [0024]    As shown, the forces or vibrations transformed to the bracket  16  may lead to deformations of the damper tube in the zone of the bracket  16 . These deformations, in turn, might lead to jamming of the slidable partition  10  or otherwise limiting its sliding movement, which must be considered while designing the damper. 
         [0025]    Above and below reference numerals of elements performing the same or similar functions remain the same, as in  FIG. 1 . 
         [0026]      FIG. 2  illustrates an exemplary twin-tube hydraulic damper  2  comprising main tube  4  and an external tube  12 . As shown the damper  2  is provided with an additional valve assembly  13 , commonly referred to as a base valve assembly and fixed at the end of the main tube  4 . A compression chamber  9  filled with working liquid is defined between the piston assembly  5  and the base valve assembly  13 , wherein an additional compensation chamber  14  filled with working liquid is defined between the base valve assembly  13  and a slidable partition  10  in a form of a ring disposed between the main tube  4  and the external tube  12 . 
         [0027]    The additional valve assembly  13  is provided with rebound  131  and compression  132  valves to control the flow of working liquid passing between the additional compensation chamber  14  and the compression chamber  9 , respectively, during rebound and compression stroke of the damper. Similarly, as in the case of the piston assembly  5 , the valves  131  and  132  comprise a number of flow channels disposed equiangularly over the perimeter of the body of the additional valve assembly  13  and a number of resilient deflectable discs covering that channels and deflecting under the pressure of working liquid. Similarly, as in the case of valves  51  and  52  of the piston assembly  5 , the valves  131  and  132  of the additional valve  13  assembly provide additional parameters that may be used to influence damper characteristic. 
         [0028]    In a damper of this kind, a gas chamber  11  filled with pressurised gas is defined at the other side of the slidable partition  10  and is further delimited by the radially outer surface of the main tube  4 , radially inner surface of the external tube  12  and axially inner surface of the piston rod guide  7 . 
         [0029]    Arrow lines between the compression chamber  9  and the additional compensation chamber  14  schematically represent radially inward and radially outward flow of working liquid through the additional valve assembly  13  between chambers  9  and  14 , respectively, during rebound and compression stroke of the damper. In other words, in a twin-tube damper, a path of working liquid flow through the additional valve assembly  13  runs outwardly relative to the main tube  4  axis. 
         [0030]    An embodiment of a damper  3  according to the present invention is illustrated on  FIG. 3 . As shown the damper  3  comprises only a main tube  2  so in this context it is a damper of a mono-tube type. Nonetheless, the damper  3  is additionally provided with an additional chamber assembly  15  attached on one end to the end of a piston rod  6  below a slidable piston assembly  5 . The chamber assembly  15  is terminated at the other end with an additional valve assembly  13  and comprises a slidable partition  10  making a sliding fit on the radially inner surface of the assembly  15 . The partition  10  divides the interior of the chamber assembly  15  into a pressurised gas chamber  11 , at the top section of the chamber assembly  15 , and an additional compensation chamber  14  at the bottom section of the assembly  15 . The additional valve assembly  13  is provided with rebound  131  and compression  132  valves to control the flow of working liquid passing between the additional compensation chamber  14  and the compression chamber  9 , respectively, during rebound and compression stroking cycle of the damper. 
         [0031]    In comparison with the twin-tube damper  2  of  FIG. 2 , in the damper  3  the working liquid flows through the additional valve assembly  13  during compression and rebound chamber radially inward relative to the main tube  4 . 
         [0032]      FIG. 4  presents an enlarged view of the additional chamber assembly  15  of the damper  3  shown in  FIG. 3 . The body  151  of the assembly has a form of a simple, uniform cup-shaped element provided at the top with an inner, cylindrical, and threaded recess  152  to receive and be fixedly attached to a threaded end of the piston rod  6 . The body  151  is opened at the bottom and provided with an internal thread  153  on its internal surface. 
         [0033]    The body  133  of the additional valve assembly  13  is screwed into an internal thread  153 . Both the compression valve  132  and the rebound valve  131  comprise a number of through channels disposed equiangularly over the perimeter of the body  133  and a number of resilient deflectable discs covering that channels and deflecting under the pressure of working liquid. 
         [0034]    The partition  10  makes a sliding fit with the inner surface of the body  151  of the additional chamber assembly  15 . Since no external forces act on the additional chamber assembly  15  while the damper is working, no deformations will occur and the sliding movement of the partition  10  is by no means limited. 
         [0035]    In the context of the damper assembly process, the additional chamber assembly  15  according to the present invention constitutes a separate subassembly that may be preliminarily and independently assembled and filled with a pressurized gas and thereafter screwed on the threaded end of the piston rod  6 . 
         [0036]      FIG. 5  schematically illustrates a fragment of a vehicle suspension  200  attached to a vehicle chassis  201  by means of a top mount  202  and a number of screws  203  disposed on the periphery of the upper surface of the top mount  202 . The top mount  202  is connected to a coil spring  204  and a rod  6  of a damper, such as the one made according to the principles of the present invention. At the other end the attachment means  16  fixed to the damper  3  tube connects the damper  3  to the steering knuckle or a swing arm supporting the vehicle wheel  205 . 
         [0037]    In order to measure the influence of the chamber assembly of the present invention on the damper performance the inventors compared the typical mono-tube damper known from the prior art, corresponding to the one shown in  FIG. 1 , with the damper made according to the present invention, corresponding to the one shown in  FIG. 3 . 
         [0038]    Testing procedure involved measuring friction at the piston rod guide during the damper operation. Characteristic dimensions of the dampers being tested, as well as the results of the testing procedure are listed in Table 1. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Comparison of a mono-tube damper with damper according to  
               
               
                 the invention 
               
             
          
           
               
                   
                 Mono-tube damper 
               
             
          
           
               
                   
                   
                 with an additional 
               
               
                   
                 typical 
                 chamber assembly 
               
               
                   
               
             
          
           
               
                 Diameter of the piston rod (6) 
                 14 
                 mm 
                 14 
                 mm 
               
               
                 Internal diameter of the main tube (4) 
                 46 
                 mm 
                 46 
                 mm 
               
               
                 Diameter of the slidable partition (10) 
                 46 
                 mm 
                 36 
                 mm (1)   
               
               
                 Gas pressure 
                 25 
                 bar 
                 5 
                 bar 
               
             
          
           
               
                 Gas force 
                   400N 
                 100N 
               
               
                 Friction* 
                 ~110N 
                  ~60N   
               
               
                   
               
               
                   (1) partition 10 is disposed within the chamber assembly 15. 
               
             
          
         
       
     
         [0039]    As shown, the damper according to the present invention enables for a 5-fold (25 bar vs. 5 bar) decrease of pressure in the gas chamber  11  in comparison with a mono-tube damper, which yields almost 2-fold decrease in the friction force (110 N vs. 60 N) at the piston rod guide  7 , which substantially improves a vehicle ride comfort. 
         [0040]    The above embodiments of the present invention are merely exemplary. The figures are not necessarily to scale, and some features may be exaggerated or minimized. These and other factors, however, should not be considered as limiting the spirit of the invention, the intended scope of protection of which is indicated in appended claims.