Abstract:
In a shock absorber support arrangement including a support bearing structure, a hydraulic cylinder which includes a piston and a cylinder which is hydraulically coupled to the support bearing structure, the support bearing structure having a housing including a force transmission means having a chamber which is filled with a hydraulic medium and is in communication with the cylinder, the hydraulic cylinder being connected to the support bearing structure so as to be axially movable over a certain extent as a result of friction forces effective between the piston and the cylinder wherein the load forces of the piston are transmitted via the hydraulic fluid in the cylinder and the support bearing structure directly to the force transmission means.

Description:
[0001]     This is a Continuation-in-Part Application of International Application PCT/EP2003/012615 filed Nov. 12, 20003 and claiming the priority of German application 102 59 532.1 filed Dec. 19, 2002.  
       BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a shock absorber support arrangement including a hydraulic cylinder.  
         [0003]     In hydro-pneumatic spring-damper systems the customary spring-damper arrangement is a hydraulic cylinder. A gas spring accumulator performs the functions of the spring effect and of bearing the operating load, and the damping is provided by a throttle diaphragm in an overflow line between the hydraulic cylinder and gas spring accumulator. A damper system of such a design is known, for example from German laid-open Patent Application DE 199 32 868.  
         [0004]     Such hydro-pneumatic spring-damper arrangements may completely fulfill the tasks of conventional spring damper systems in principle, the requirements in terms of installation space being somewhat more favorable than in conventional spring damper systems. These hydro-pneumatic spring-damper arrangements also provide a very simple way of implementing active damping of the vehicle body movements or wheel movements in a vehicle by adding hydraulic fluid to the working space of the hydraulic cylinder or discharging it therefrom.  
         [0005]     However, a basic problem of such arrangements is the unavoidable friction of the hydraulic actuator in the hydraulic cylinder. Owing to the operating loads to be borne when used in a passenger car it is virtually impossible to achieve cylinder friction values below 100 to 200 N. However, this adversely affects comfort.  
         [0006]     It is known to use soft head bearings in order to improve the comfort, as illustrated in  FIG. 1 . There are however narrow configuration limits because of the basic load and the service life requirements so that it is virtually impossible to implement rigidity values of the bearings of less than 1000 N/mm.  
         [0007]     DE 196 29 959 A1 discloses a device of the generic type. A support bearing of a vibration-damping element has a hydraulic cylinder which is coupled hydraulically to the support bearing, with the support bearing having a housing which is filled completely with hydraulic medium.  
         [0008]     The object of the present invention is to provide a shock absorber support, in particular a hydropneumatic spring-damper system which increases the ride comfort of a vehicle.  
       SUMMARY OF THE INVENTION  
       [0009]     In a shock absorber support arrangement including a support bearing structure, a hydraulic cylinder which includes a piston and a cylinder which is hydraulically coupled to the support bearing structure, the support bearing structure having a housing including a force transmission means having a chamber which is filled with a hydraulic medium and is in communication with the cylinder, the hydraulic cylinder being connected to the support bearing structure so as to be axially movable over a certain extent as a result of friction forces effective between the piston and the cylinder wherein the load forces of the piston are transmitted via the hydraulic fluid in the cylinder and the support bearing structure directly to the force transmission means.  
         [0010]     The invention provides for active suspension systems which are of simple design and which are based in particular on hydropneumatic systems to be provided with a high level of comfort since a central problem of hydropneumatic systems, the disruptive influences of friction in the hydraulic cylinder, can be essentially eliminated or at least greatly reduced.  
         [0011]     When the vehicle support arrangement according to the invention is used as a head bearing it is possible to prevent or attenuate disruptive characteristics of the actual force-transmitting component.  
         [0012]     The invention will become more readily apparent from the following embodiment thereof on the basis of the accompanying drawings 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  shows a conventional hydropneumatic spring-damper system with a soft head bearing,  
         [0014]      FIG. 2  shows the change in force as a function of the excursion/spring compression given sinusoidal excitation under the influence of a friction value of 150 N,  
         [0015]      FIG. 3  shows the spring-damper changes in force given sinusoidal excitation according to  FIG. 2 ,  
         [0016]      FIG. 4  is a basic representation of a preferred hydraulic support bearing,  
         [0017]      FIG. 5  shows schematically a preferred hydropneumatic spring-damper system with a first preferred support bearing,  
         [0018]      FIG. 6  is a schematic representation of a preferred hydropneumatic spring-damper system with a second preferred support bearing,  
         [0019]      FIG. 7  shows the change in force as a function of the excursion/spring compression given sinusoidal excitation under the influence of a friction value of 150 N with an arrangement according to the invention,  
         [0020]      FIG. 8  shows the spring-damper changes in force given sinusoidal excitation according to  FIG. 7 ,  
         [0021]      FIG. 9  shows the excursion values of the head bearing or cylinder according to  FIGS. 7 and 8 ,  
         [0022]      FIG. 10  is a basic representation of a preferred configuration of a support bearing,  
         [0023]      FIG. 11  is a basic representation of a further preferred configuration of a support bearing with extension stops and compression stops, and  
         [0024]      FIG. 12  is a basic representation of a further preferred configuration of a support bearing with longitudinal guide means. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]      FIG. 1  illustrates a known hydropneumatic spring-damper system. A hydropneumatic spring-damper system includes as a vibration-damping element a hydraulic cylinder  1  with a piston  6  which can move up to and down from in the interior of the hydraulic cylinder  1 . A gas spring accumulator  2  performs the functions of the spring effect and of bearing an operating load, said gas spring accumulator  2  being connected to the hydraulic cylinder  1  via an overflow line  4  through which a hydraulic medium can be exchanged between the hydraulic cylinder  1  and the gas spring accumulator  2 . The damping is implemented by a throttle  5  in the overflow line  4  between the hydraulic cylinder  1  and gas spring accumulator  2 . A support bearing  3  with a spring stiffness C L  is arranged at the body support end.  
         [0026]     With a spring compression by a distance Xe, a force F acts on the piston  6  which is forced upward in the direction of action of the force by a distance Xz, while the hydraulic cylinder  1  experiences excursion ΔX. Owing to the operating load to be borne, for example that of a vehicle, the unavoidable friction of the piston  6  in the hydraulic cylinder  1  leads to losses of comfort. One possibility for compensation is to reduce the spring stiffness C L  of the support bearing  7 . However, there is little room for maneuver in terms of the configuration owing to the high basic load represented by the vehicle and the existing service life requirements. For this reason, spring stiffnesses C L  with values of less than approximately C L =1000 N/mm are virtually impossible to achieve.  
         [0027]      FIG. 2  illustrates effects of the frictional forces for a sinusoidal excitation of spring compression of a conventional hydropneumatic spring-damper system with a spring stiffness of a support bearing of approximately C L =1200 N/mm and a piston friction of 150 N. In  FIG. 3 , the associated spring-damper change in force (dF_Zyl [N]) is illustrated in comparison with the spring component (dF_elast). It is apparent that when there is reversal of movement of the piston  6  jumps in force of 200 to 400 N may occur and these have a very disruptive effect which reduces comfort particularly at lower spring compression values. The force of the piston changes virtually spontaneously by up to twice the frictional force of the piston  6  especially when there is reversal of movement. The flexibility of the support bearing  7 , in this case of a head bearing, is too low to be able to effectively smooth or even out these changes in force due to friction.  
         [0028]     The principle of the solution according to the invention is outlined in  FIG. 4 . Only a support bearing  7  is represented in detail; the other arrangement (not illustrated) corresponds largely to the system illustrated in  FIG. 1 . Here, a spring-damper system is provided as a spring-damping element. The support bearing  7  has defined hydraulic, elastic and possibly damping properties and is hydraulically coupled to a hydraulic cylinder  1  (not illustrated in the figure). The body of the support bearing  7  preferably has defined stiffness properties.  
         [0029]     A hydraulic active area A L  is arranged between the support bearing  7  and hydraulic cylinder  1 . The support bearing  7  has a housing  10  with a spring stiffness C L . The housing  10  is preferably filled completely with a hydraulic medium. A pressure p is present inside the housing  10 . Since the support bearing  7  is hydraulically connected to the working space of the hollow cylinder  1 , p is also the pressure of the working space of the cylinder  1 .  
         [0030]     The hydraulic coupling of the support bearing  7  and hydraulic cylinder  1  means that the actual functions of the support bearing  7 , bearing the load and compensating lengths, can be separated. The hydraulic medium present is utilized to support the load. For a given hydraulic active area it is thus possible to ensure that the support bearing  7  fulfills its bearing function for any necessary and customary loading. The length compensation, i.e. longitudinal flexibility of the support bearing  7 , can now be implemented by means of rubber elements or steel spring elements. Since the basic load is accommodated by the hydraulic fluid, the tuning bandwidth is not limited by configuration restrictions. The spring stiffness of a support bearing according to the invention can therefore be significantly less than in a conventional support bearing  7  according to  FIG. 1 . For example, the previous limiting value with conventional support bearings of typically at least C L =1000 N/mm can be reduced to values of around 50 N/mm, preferably around 25 N/mm.  
         [0031]     The effective area A L  between the hydraulic cylinder  1  and the support bearing  7  is preferably constant when the hydraulic cylinder  1  and/or the support bearing  7  experiences excursion. As a result of the arrangement according to the invention, a considerable improvement in comfort can be achieved. However, even if the hydraulic active area is varied, at least an improvement in comparison with the known systems can be obtained. An essentially constant hydraulic active area A L , i.e. one which is neutral in terms of area, is favorable in order to make available sufficient excursion travel for “smoothing out” the friction in the hydraulic cylinder  1 .  
         [0032]     If, for example, during the spring compression the support bearing  7  is subject to an excursion of ΔX, this is counteracted by the spring stiffness C L  and a hydraulic opposing force acting on the hydraulic effective area A L  on the support bearing  7  a bearing force K counter to the excursion ΔX: 
 
 K=C   L   ·ΔX+A   L ·(Δ X )·P
 
         [0033]     Owing to the limited space in the support bearing  7  it is necessary at the same time for a transfer volume flow S L  of the hydraulic medium to flow into the hydraulic cylinder through the hydraulic effective area A L :  
         S   L     =       A   L     ·     (     Δ   ⁢           ⁢   X     )     ·         ⅆ   Δ     ⁢           ⁢   X       ⅆ   t             
 
         [0034]     It is particularly favorable to adapt the hydraulic effective area A L  approximately to the effective hydraulic working faces of the hydraulic cylinder. Furthermore it is favorable at the same time to make the mechanical spring stiffness C L  of the support bearing relatively small. These measures make it possible for the support bearing  7  to “smooth out” changes in the frictional force of the piston  6 .  
         [0035]     The hydraulic medium can escape from the hydraulic cylinder  1  into a gas spring accumulator  2  (see  FIG. 5 ). The support bearing  7  is preferably arranged hydraulically in parallel with the gas spring accumulator  2 .  
         [0036]      FIG. 5  illustrates a first preferred arrangement according to the invention. The support bearing  7  is embodied as an ellipsoid body. Otherwise the arrangement corresponds largely to the basic outline in  FIG. 1 . The supporting body  7  is arranged axially on the hydraulic cylinder  1 , in the longitudinal direction of the hydraulic cylinder  1 . The support bearing  1  forms a head bearing of a hydropneumatic spring-damper. It is also possible to operate such an arrangement actively and to use a hydraulic pump (not illustrated) so that additional hydraulic medium can be pumped into the arrangement or hydraulic fluid can be discharged from it.  
         [0037]      FIG. 6  illustrates a second preferred arrangement according to the invention. Here, a folding bellows is used as the support bearing  7  instead of an ellipsoid body. This arrangement has the particular advantage that the hydraulic active area A L  remains neutral in terms of area during movements of the piston  6  or spring compression and spring extension movements. An elastomer can be used as the material for the housing. A further favorable and particularly corrosion-resistant alternative is a metal bellows.  
         [0038]      FIGS. 7 and 8  clearly show the improvements in comparison with  FIGS. 2 and 3  for a conventional system according to  FIG. 1 .  
         [0039]     In  FIG. 7 , the effects of the frictional forces for sinusoidal spring compression excitation of a conventional hydropneumatic spring-damper system with a spring stiffness of a support bearing  7  according to the invention of approximately C L =25 N/mm and a piston friction of 150 N are illustrated.  FIG. 8  illustrates the associated spring-damper change in force (dF_Zyl [N]) in comparison to the spring component (dF_elast). It is apparent that when there is a reversal of movement of the piston  6  virtually no further force jumps are observed. When there is a reversal of movement, the change in force according to  FIG. 7  is continuous with a gentle transition into an opposing movement.  
         [0040]     The resulting time/force profiles in  FIG. 8  are harmonic and smooth and show that adverse effects on comfort in comparison with the conventional system can be avoided.  
         [0041]      FIG. 9  shows the excursion values Xz of the hydraulic cylinder  1  which are associated with the preceding  FIGS. 7 and 8 , the excursion values dX of the support bearing  7  and the spring compression Xe. The support bearing  7  which, according to the invention, is coupled hydraulically to the hydraulic cylinder  1  carries out a large number of the spring compression movement in this operating case. The transitions to the actual hydraulic cylinder excursion values Xz take place harmonically and smoothly. Uncertainties with respect to the level of frictional forces play virtually no role and fluctuations in frictional force would merely shift somewhat the times when the cylinders are moved but not disrupt the continuous transitions when there is a reversal of movement.  
         [0042]      FIG. 10  illustrates a further preferred configuration of a support bearing  7  according to the invention. With the configuration of the support bearing  7  it is particularly expedient to provide as little axial rigidity of the support bearing  7  as possible and at the same time to permit no or only slight changes in the hydraulic effective area A L  during the spring compression and extension. For this purpose, the support bearing  7  can have a housing  10  which is formed from an elastomer at least in certain areas. The housing  10  may preferably be attached directly to the hydraulic cylinder  1  and to a force absorbing means  9 . For this purpose, a clamping ring  11  may be provided with which the housing  10  is secured directly to the housing of the hydraulic cylinder  1 . Furthermore, it is possible to provide a corresponding securing means  12 , for example a clamping ring, by means of which the housing  10  is attached to the force absorbing means  9 . A perforated diaphragm  8  may be provided for the hydraulic cylinder  1 . The opening of the perforated diaphragm  8  forms the hydraulic effective area A L .  
         [0043]     The force absorbing means  9  is connected, for example, to the body of a vehicle using a bearing point  13 .  
         [0044]     The housing  10  is particularly preferably composed of a rubber cylinder which forms the actual bearing element. The rubber itself gives rise to longitudinal flexibility in the direction h of the support bearing  7 . A favorable compressive strength and sufficient radial rigidity in the direction b can be produced by means of tangential, or at least almost tangential, reinforcing fibers in or on the rubber cylinder. Given an appropriately favorable configuration is possible for the rubber cylinder itself also to perform lateral guidance functions of the support bearing  7 . If relatively high lateral forces are transmitted or relatively stringent requirements are made in terms of the precision of the lateral guidance it is possible to introduce corresponding longitudinal guide means.  
         [0045]     One favorable configuration of the support bearing  7  is illustrated in  FIG. 11 . The arrangement corresponds essentially to that in  FIG. 10 . In addition, a rod  14  is provided in the housing  10  and is oriented axially with respect to the hydraulic cylinder and can project into the hydraulic cylinder. A compression stop  15  and/or an extension stop  15  may be provided on the rod  14 . As a result, the maximum compression and/or extension of the support bearing  7  can be limited or adjusted.  
         [0046]     A further favorable configuration of the support bearing  7  is illustrated in  FIG. 12 . A longitudinal guide means  18 , which limits or prevents lateral excursion of the support bearing  7 , is provided on the rod  14 . The longitudinal guide means  17  may be a cylinder which surrounds the rod concentrically. On the underside the cylinder widens in the direction of the perforated diaphragm  8  and preferably includes a ring  18 . In the perforated diaphragm  8  overflow openings whose cross sections form in total a hydraulic effective area A L  are expediently provided. The ring  18  can also be arranged on the side of the support bearing  7  which faces the force transmission means  9 .  
         [0047]     Other configurations of a support bearing which is hydraulically coupled to a hydraulic cylinder  1  are, of course, also conceivable.  
         [0048]     The invention is defined by the fact that the support bearing  7  according to the invention is not subjected to the high static loads to be borne, but those loads are hydraulically directly transmitted to the force transmission means, that is, to the vehicle body. This permits “soft” construction and, for example, the use of elastomers.  
         [0049]     It is very particularly advantageous if the support bearing  7  forms a head bearing of a hydraulic cylinder  1 . It is particularly favorable to configure the overall rigidity of the support bearing  7  in such a way that when there is spring compression or spring extension the change in force by means of an available excursion in the support bearing  7  is greater than the frictional force, in particular the static frictional force of the piston  6  in the hydraulic cylinder  1 . This ensures that the piston  6  can tear out of a frictionally clamped position again before the support bearing  7  strikes against its excursion limits. The necessary rigidity can be provided either solely by elastic material properties of the support bearing  7  or of the housing  10  or additionally or alternatively by a change in area of the hydraulic active area A L  over the spring compression travel. Both act in a comparable fashion if the overall rigidity has been configured according to the condition mentioned above.