Abstract:
A combined spring/damper system for the support of wheel suspensions or axles on a vehicle body, with a tubular concertina which is mounted between an outer bell and a rolling piston and the meniscus of which is guided on a cylindrical inner-wall region of the outer bell and a cylindrical outer-wall region of the rolling piston. The outer bell or the rolling piston of the displacer is supported between the vehicle body and the chassis in at least one articulated support. The concertina space is filled with a fluid and communicates with a hydraulic accumulator mounted on the chassis side or on the vehicle-body side. Thus, a combined spring/damper system is provided, which includes a low-friction and virtually maintenance-free displacer.

Description:
FIELD OF THE INVENTION 
   The invention relates to a combined spring/damper system for the support of wheel suspensions or axles on a vehicle body, with a tubular concertina which is arranged between a wheel-carrying or wheel-guiding tie-up and a tie-up located on the vehicle-body side and is mounted between an outer bell and an unrolling piston and the meniscus of which is guided on a cylindrical inner-wall region of the outer bell and a cylindrical outer-wall region of the unrolling piston. 
   BACKGROUND INFORMATION 
   German Published Patent Application No. 40 18 712 illustrates a spring/damper system with a displacer. However, with respect to a horizontal section, this displacer requires a very large construction space. 
   Furthermore, German Published Patent Application No. 297 02 927 illustrates a spring/damper system which consists of a displacer without concertina, of a hydraulic accumulator and of a hydraulic line connecting these parts. A mechanical throttle valve is arranged in the hydraulic line. As found with hydropneumatic suspension systems, the displacer connects the vehicle-wheel suspension to the vehicle body. The system is filled with a hydraulic fluid. The latter is displaced through the throttle valve into a hydraulic accumulator during the compression of a vehicle wheel. The flow resistance of the throttle valve generates a damping force, while the compression of the gas volume in the hydraulic accumulator provides a resilient force. In the displacer principle presented here, a displacer piston penetrates into a displacer cylinder. The two parts move frictionally relative to one another in a guiding and sealing gap. The friction is detrimental to the response time of the spring/damper system, so that, in use in a vehicle, there is no optimum rolling behavior of the wheels supported by this system. 
   SUMMARY 
   It is an object of the present invention to provide a combined spring/damper system which contains a low-friction displacer which is based on a tubular concertina and which has, along with a slender form of construction, an effective piston area which is invariable over the chassis stroke. 
   For this purpose, the outer bell or the rolling piston of the displacer is mounted on the vehicle body. Either the outer bell or the rolling piston is fastened on the chassis side or vehicle-body side via a joint having at least one degree of pivoting freedom. The concertina space is filled with a fluid and communicates with a hydraulic accumulator mounted on the chassis side or on the vehicle-body side. 
   The type of displacer concertina, the type of tie-up on the chassis and on the vehicle body and the filling of the concertina space with a fluid pressurized via a gas makes it possible to have a slender displacer without any mechanical frictional longitudinal guidance. Separate longitudinal guidance is unnecessary, since the pressure in the displacer concertina centers and stabilizes, via the concertina meniscus, the spring-strut parts which are moved relative to one another. 
   During loading or relieving of the displacer, a hydraulic fluid flows back and forth between the displacer and the hydraulic accumulator via a cross-sectional narrowing in the form of a hydraulic line or of a perforation. The configuration of the line or of the perforation and the nature of the throttle point arranged there influence the system damping via the size and shape of the opening cross section. In this case, the throttle point may be configured either as a nozzle or as a diaphragm or be at least one throttle non-return valve. When throttle non-return valves are used, in each case at least one valve is arranged in the line cross section or perforation cross section for each direction of flow. 
   The gas cushion of the hydraulic accumulator critically forms the system springing. 
   By using a tubular concertina, the mechanical friction of the entire system is reduced essentially to the internal friction of the concertina material or diaphragm material. The spring/damper system thereby exhibits a virtually ideal response behavior over the entire spring and damper constant range. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a spring/damper system with a tubular concertina. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a combined spring/damper system which comprises a displacer  10 , a hydraulic accumulator  30  and a fluid-carrying working line  40  arranged between these and having an integrated throttle valve  47 . 
   The displacer  10  consists, inter alia, of an outer bell  12 , of a rolling piston  22  and of a tubular concertina  11  connecting the two parts. The outer bell  12  is a bush-like hollow body which consists of a tube with a cylindrical inner wall  13  and with an outwardly curved bottom. 
   The rolling piston  22  is a hollow body having a cylindrical outer wall  23  and carrying, for example at a free outer end, the housing  34  of the hydraulic accumulator  30 . The hollow space forms a working line  40  which communicates with the fluid space  35  of the hydraulic accumulator  30 . In the exemplary embodiment, for example, a threaded bolt  25  is located at the upper end of the rolling piston  22 , by which threaded bolt the spring/damper system may be fastened to the vehicle body rigidly or flexibly via elastic intermediate elements. 
   The tubular concertina  11  is fastened between the rolling piston  22  and the outer bell  12 . For this purpose, the upper end of the tubular concertina  11  open at the tube ends is pushed with the inner wall onto the lower end of the rolling piston  22  and is fixed, for example non-positively, in a non-slip and sealing manner with the aid of a tension ring  14 . 
   In  FIG. 1 , the lower end of the tubular concertina  11  is fastened to an approximately cylindrical portion of an assembly-aid cap  15 . For this purpose, before installation in the outer bell  12 , the lower end of the tubular concertina  11  is pushed with the inner wall onto the outer contour of the assembly-aid cap  15  and is fixed, for example non-positively and positively, in a non-slip and sealing manner by a tension ring  24 . After the assembly-aid cap  15  has been inserted into the outer bell  12 , the outer wall of the concertina  11  bears against the inner wall  13  at least in the immediate vicinity of the cap. The assembly-aid cap  15  may be fastened in the outer bell  12 . 
   In the ready-to-install state of the spring/damper system, the rolling piston  22  is seated in the outer bell  12  in such a manner that the upper end of the tubular concertina  11  is overturned inwardly to form an upwardly oriented meniscus  18 . As a result, during each operationally induced relative movement between the parts  12  and  22 , the outer wall  19  of the concertina  11  rolls on the outer wall  23  and the inner wall  13 . 
   The meniscus  18  moves over the entire stroke range between the cylindrical walls  13  and  23 . The mean radial distance between these walls is constant in the stroke range of the meniscus  19 . The distance corresponds to a gap width which is at most five times the wall thickness of the tubular concertina  11 . This allows a slender spring-strut configuration and keeps the load on the concertina  11  in the meniscus region low. Moreover, the internal friction in the tubular concertina  11  is constant over the entire stroke. 
   The outside diameter of the rolling piston is in this case, for example, approximately equal to or smaller than the useful overall stroke of the spring strut. 
   The length of the tubular concertina corresponds, for example, to twice the concertina diameter. 
   If appropriate, the outer bell may be produced so as to be widened in the lower region, i.e. in or in the vicinity of the assembly-aid cap  15 . In this case, such a widening lies outside the meniscus stroke range. During compression, the widening prevents a major angular deviation between the center line of the outer bell  12  and the center line of the rolling piston  22 , without the concertina wall  20  which bears against the rolling piston  22  coming into contact with the concertina wall  20  supported on the outer bell  12 . 
   The rear space  7  lying outside the concertina space  5  between the outer bell  12  and the rolling piston  22  is sealed against the penetration of dirt with the aid of an anti-dirt concertina  28 . The rear space  7  is connected to the surroundings via a venting bore. 
   A pivoting joint  50  is arranged at the lower end of the outer bell  12 . The spring/damper system is mounted on the chassis in an articulated manner via the pivoting joint  50 . The pivoting joint  50 , the pivot axis of which extends perpendicularly to the center line of the outer bell, consists of two bushes  51  and  53 , between which, for example, an elastomeric body  52  is vulcanized in or glued in. The elastomeric body  52  may increase the articulation of the joint  50  by up to five degrees of freedom. 
   The outer bush  51  is welded directly to the outer body  12 . The inner bush  53  serves, in the exemplary embodiment, for the fastening to the chassis. 
   Located in the upper region of the rolling piston  22  is a delivery line  17  which, if appropriate, is capable of being shut off and which issues into the working line  40 . In use as an active spring/damper system or for leveling, fluid is supplied to or extracted from the displacer via the delivery line  17 . Additional forces may be produced in a desired manner by the supply and discharge of a defined fluid quantity. The reception or removal of these additional quantities modifies the damper forces and the spring forces in the entire system. 
   The hydraulic accumulator  30  is configured, for example, as a bladder-type or diaphragm-type accumulator. A gas cushion  32  divided off by the bladder or diaphragm  31  forms the springing of the spring/damper system. Two pressure-stage valves acting in opposition to one another and taking the form of spring-plate valves are located at the transition from the working line  40  to the housing  34  of the hydraulic accumulator  30 . Each valve  47  opens in a different direction of flow from the other. In this example, the throttle action of the individual throttle non-return valve  47  may be designed, if appropriate, to be adjustable by a controllable or regulatable drive. 
   In other configurations, the length of the working line  40  may be reduced to a perforation, for example when fluid-carrying components of the displacer project into the hydraulic accumulator or are surrounded by this. For example, the outer bell  12  may be surrounded by a, for example, annular housing. In such a configuration, the total annular space located between the housing and the outer contour of the outer bell is divided into an inner and an outer annular space by a tube-like diaphragm. The outer annular space is filled with gas, while the inner annular space, comparable to the fluid space  35  from  FIG. 1 , communicates with the concertina space  5  via at least one throttle valve. 
   Fluid  1  used in the spring/damper system is, for example, a solution of water and alcohol. All alcohols which are miscible with water in any desired ratio at room temperature are suitable for this solution. For example, a water/ethanol solution or a water/glycol solution is used. A conventional water/glycol solution, such as is also used as anti-freeze cooling fluid in internal combustion engines, has, for example, an ethylene glycol fraction of 33 to 50%. Where the 50% solution is concerned, it is possible for the spring/damper system to operate down to a temperature of −35° Celsius. Moreover, this solution does not attack the conventional elastomeric materials. Rubber swelling is also on the order of the swelling which occurs in pure water. 
   Alternatively to the example embodiment described above, a spring/damper system may be provided, in which the fluid  1  for the system is a magnetorheological fluid. If, for example, a short annular portion on the hydraulic working line  40  is surrounded by a current-excited magnet coil, the excited magnet coil, in combination with the fluid  1 , constitutes a variable throttle point. With an increasing application of current to the coil, the flow velocity decreases due to an increase in the apparent or dynamic viscosity in the working line  40 , as a result of which, inter alia, the damping behavior of the entire system may be modified in a specific manner.