Patent Publication Number: US-2006011370-A1

Title: Damping device

Description:
The invention relates to a damping device in particular for cable-supported structures such as, e.g., cable-stayed bridges, stadium roofs, guyed towers, in accordance with the preamble of claim  1 .  
      The expression “damping device” is understood to designate a hydraulic linear axis for semi-active or active damping, where essentially only control energy is introduced.  
      Cable-stayed bridges are presently considered the most economical solution for spans of about 150 m to 600 m. Most recent developments show that spans of even up to 1000 m are possible.  
      The material-saving, slim realization of large-size cable-stayed bridges does result in a construction that is attractive in terms of architecture, however the low internal damping results in structures that are extremely sensitive to vibrations. Particularly due to stimulation by wind, vibration amplitudes making it necessary to close a bridge for traffic may be reached. The strain to the components of the structure (deck and cables) is enormous, and the resulting follow-up costs are considerable.  
      The effect of known passive dampers on deck vibrations is not satisfactory. Active damping devices specifically provided in the terminating anchorages of the cable stays, on the other hand, bring about a significant reduction of the vibration amplitude. The known realizations do however—in addition to the demand of electrical actuation energy—have a considerable energy consumption.  
      It is an object of the present invention to furnish a damping device which, at minimum energy demand and a reduced size of the active element, exhibits improved response and thus damping characteristics, and permits the use of low-cost sensory equipment.  
      This object is achieved through a damping device having the features in accordance with claim  1 .  
      The damping device of the invention comprises a differential cylinder, two hydraulic units with variable pivoting angles, an electric motor associated with the hydraulic units, a hydraulic accumulator, and a tank. One hydraulic unit is arranged in the pressure medium flow path between the tank and a piston rod-side ring chamber, and the second hydraulic unit is positioned in the pressure medium flow path between the ring chamber and a cylinder chamber of the differential cylinder.  
      Instead of the adjustable hydrostatic or hydrostatic displacement machines it is also possible to employ hydrostatic displacement machines having a constant displacement volume. The variable flow required for the desired cylinder velocity is then obtained through the intermediary of a variable-speed electric motor.  
      As a result of this arrangement of the hydraulic units in accordance with the invention, these are supported against each other such that in the quasi-static condition, if the hydraulic units are designed accordingly (in accordance with the selected pressure conditions), the remaining torque is zero (when neglecting friction and other losses) and the electric motor thus determines the rotational speed nearly free from torque. One of the hydraulic units acts as a motor and drives the second hydraulic unit acting as a pump.  
      If, as a result of the vibrations, the damping device is subjected to dynamic forces, a higher pressure difference acts at the hydraulic unit operating as a motor, while the hydraulic unit operating as a pump has to deliver against a lower pressure difference. This surplus energy is—where it exceeds the frictional and other losses resulting in the power flow—absorbed by the electric motor and may be fed into the electric mains.  
      The electric motor is basically only necessary in order to activate the damping device at a low vibrational excitation, to predetermine the rotational speed, or to make the surplus power usable as electricity, or compensate for friction losses.  
      In a preferred embodiment, the differential cylinder is fixedly mounted through its piston on a terminating anchorage of a cable-stayed bridge, wherein its cylinder jacket may be shifted in the longitudinal direction of the piston. A cable stay of the cable-stayed bridge is secured to the cylinder jacket, so that through suitable actuation of the differential cylinder, the vibrations acting in the structure, or the dynamic forces accordingly acting in the cable stay, are attenuated by longitudinal movement of the cylinder jacket—in accordance with damping law—whereby it is possible to avoid uncontrolled tensions inside the structure.  
      The longitudinal movement of the cylinder jacket resulting from external loads is made possible by adjusting the pivoting angles of the hydraulic units. The pivoting angles may be adjusted such that the moving velocity of the cylinder jacket is proportional to the external loads. In other words, a high load necessitates a large pivoting angle, so that high pressure medium flows may be realized, whereas low loads necessitate small pivoting angles, so that low pressure medium flows are possible.  
      In one embodiment, the cylinder jacket of the differential cylinder is fixedly mounted, and the piston of the differential cylinder is guided in an axially displaceable manner.  
      In another embodiment, the adjustment of the pivoting angles or displacement volumes is carried out in accordance with a pressure signal from a pressure transducer arranged in the ring chamber or cylinder chamber.  
      In the static condition (stroke=0), a bias of the cable stay above the pressures prevailing in the ring chamber and cylinder chamber is set. Ideally the pressure in the cylinder chamber receiving the static cable load is designed for the maximum admissible system pressure. In the ring chamber of the differential cylinder approximately half the system pressure is desirable.  
      Another embodiment provides a pressure transducer in the cylinder chamber and/or in the range of the hydraulic accumulator for measurement and for adaptation of the hydraulic accumulator pressure and of the hydrostatic accumulator charge to the respective static load.  
      In one embodiment, the hydraulic accumulator is integrated into the differential cylinder, whereby a compact design is realized.  
      In another embodiment, the ring chamber of the differential cylinder is sealed against the environment and/or the cylinder chamber through the intermediary of a gap seal formed across an annular gap between piston-side and cylinder jacket-side surfaces.  
      In a preferred embodiment, the annular gap for sealing of the ring chamber against the external environment opens into a leakage port, wherein at least one sealing member for sealing the annular gap against the atmosphere is provided beyond the leakage port.  
      It is particularly advantageous in a like gap seal that the friction is reduced to a minimum, and cost-intense and high pressure seals that are susceptible to trouble may be omitted.  
      Other advantageous embodiments of the invention are subject matters of further subclaims.  
      Hereinafter two preferred embodiments shall be explained in more detail by referring to schematic representations, wherein: 
    
    
       FIG. 1  is a schematic view of a cable-stayed bridge,  
       FIG. 2  is a longitudinal sectional view of an embodiment in accordance with the invention which includes an external hydraulic accumulator,  
       FIG. 3  is a longitudinal sectional view of an embodiment of the invention having a hydraulic accumulator integrated into the differential cylinder, and  
       FIG. 4  is a longitudinal sectional view of a differentia cylinder having gap seals in accordance with the invention. 
    
    
       FIG. 1  shows a cable-stayed bridge  2  having one roadway  4  that is supported through the intermediary of main pylons  6 . In order to reduce the loads acting on the main pylons  6 , the roadway  4  is suspended on cable stays  8  that are supported by the main pylons  6 . The cable stays  8  are mounted via damping devices  10  on terminating anchorages  12  of the roadway  4 , so that deck vibrations may be attenuated.  
       FIG. 2  shows a longitudinal sectional view of a preferred embodiment of a damping device  10 . The damping device  10  has a differential cylinder  14 , two hydraulic units  22 ,  24 , an electric motor  26 , a hydraulic accumulator  42 , and a tank  20 .  
      The differential cylinder  14  includes a stepped piston  16  which divides the space formed by the cylinder jacket  18  into two pressure chambers—a piston rod-side ring chamber  32  and a cylinder chamber  34 .  
      The piston  16  of the differential cylinder  14  is fixedly mounted on the terminating anchorage  12  via its radially recessed part  28 —hereinafter referred to as a piston rod—so that a stroke movement is brought about by a longitudinal movement of the cylinder jacket  18 . As the piston  16  is clamped hydraulically on either side thereof, pressure medium is displaced from the one pressure chamber  32 ,  34  and replenished into the other pressure chamber  34 ,  32  during each stroke movement, wherein it is possible to compensate deficient or excessive pressure medium volumes through the tank  20 .  
      The cable stay  8  attacks on the cylinder jacket  18 , so that the bias of the cable stay  8  is predetermined by the pressures prevailing in ring chamber  32  and cylinder chamber  34 .  
      In kinematic reversal it is, however, also conceivable to fixedly mount the cylinder jacket  18  on the terminating anchorage  12  and to connect the piston rod  28  to the cable stay  8 .  
      The first hydraulic unit  22  is arranged in a first work line  36  between the low pressure-side tank  20  and the high pressure-side ring chamber  32  while being in connection with the electric motor  26 . It has a variable displacement volume and may be utilized as a pump or as a motor.  
      The second hydraulic unit  24  is arranged in a second work line  38  between the high pressure-side ring chamber  32  and the high pressure-side cylinder chamber  34 , with the second work line  38  preferably opening into the first work line  36 . Correspondingly, like the first hydraulic unit  22  the second hydraulic unit  24  also has a variable displacement volume, is furthermore in connection with the electric motor  26 , and may be utilized as a pump or as a motor.  
      Both hydrostatic or hydrostatic displacement machines  22 ,  24  convey in two directions during vibration damping, wherein the first hydraulic unit  22  is high pressure resistant only on one side, i.e., on the annular chamber side, and the other side, i.e., the tank side, is subjected to low pressure, while the second hydraulic unit  24  has to be high pressure resistant on both sides, i.e., on the annular chamber side and on the cylinder chamber side, and the direction of the pressure difference may also be reversed in accordance with a 4-quadrant operation.  
      The displacement volumes of the hydraulic units  22 ,  24  may be adjusted in accordance with the signal from a load cell  40 . The load cell  40  is arranged in the area of the connection cable stay  8 —cylinder jacket  18  and associated to a control loop of the hydraulic units  22 ,  24 . It detects the loads acting on the cable stay  8  and in the process passes the detected tensile strains, or forces, on to the control loop, so that the latter adjusts the pivoting angles of the hydraulic units  22 ,  24  in accordance with these external loads.  
      A different embodiment provides, instead of the cost-intense force measurement, to utilize the pressure prevailing in the ring chamber  32  or cylinder chamber  34  as a control quantity of the control loop. This may be achieved, e.g., with the aid of a pressure transducer (not represented) arranged in the ring chamber  32  or cylinder chamber  34 .  
      Moreover a hydraulic accumulator  42  is provided which is connected with the second work line  38  and with the cylinder chamber  34  through the intermediary of a third work line  44 , so that the pressure in the cylinder chamber  34  becomes largely independent of the cylinder stroke, and the pre-set pressure prevails permanently.  
      Accumulator charging and control of the accumulator pressure of the hydraulic accumulator  42  may advantageously be achieved through mutual trimming of the displacement volumes of the hydraulic units  22 ,  24 . To this end a pressure transducer or pressure measurement transformer is provided which is preferably arranged in the hydraulic accumulator port or in the work line  38  or in the cylinder chamber  34 , respectively.  
      The electric motor  26  is in operative connection with the two hydraulic units  22 ,  24 , wherein it may both be used as a drive mechanism for the hydraulic units  22 ,  24  and may also be driven by the hydraulic units  22 ,  24  in the manner of a generator to thus act as a brake. For example by driving the hydraulic units  22 ,  24  the pre-set pressures may be adjusted in the pressure chambers  32 ,  34 , and the hydraulic accumulator  42  may be charged. It is, however, also possible in operation for damping to convert the hydraulic energy generated by the first hydraulic unit  22  or the second hydraulic unit  24  into electric energy by setting the electric motor  26  up as a generator.  
      The operation of this above described arrangement of the invention shall in the following be described in more detail:  
      In the quasi-static condition (stroke=0), the damping device  10  is balanced, or in a rest position. Here preferably a pressure twice as high as in the ring chamber  32  is set in the cylinder chamber  34 , so that, for instance, the first and second hydraulic units  22 ,  24  are subjected to a same pressure difference. As no vibration loads act on the cable stay  8 , force changes are not measured by the load cell  40 . The pivoting angles of the hydraulic units  22 ,  24  are in their basic position, i.e., pivoting angle=0.  
      In the vibrating condition (stroke≠0), dynamic forces act in the cable stay  8  due to the vibrations, whereby the balance is disturbed. Here it is necessary to make a fundamental distinction between tensile and “compressive” strains. As only deviations from the static mean value are of relevance for damping regulation (the static loads are already compensated by the pressure bias), a tensile strain hereinafter means that the tensile strain on the cylinder jacket  18  or on the cylinder housing acting in the cable stay  8  as a result of vibrations tends to bring about a pressure increase in the cylinder chamber  34 , i.e., hydraulic medium is displaced from there into the hydraulic accumulator  42 , whereas this results in a pressure reduction in the ring chamber  32 . On the other hand, this means that tensile strain acting in the cable stay  8  is covered by the pre-set tensile strain. In other words, in the case of a tension the cylinder jacket  18  moves to the left in accordance with the representation of  FIG. 1 , and in the case of “pressure” to the right.  
      The load cell  40  detects the occurring tensile strains, wherein in accordance with the signal from the load cell  40  the displacement volumes of the hydraulic units  22 ,  24  are adjusted such that a stroke of the cylinder jacket  18  is admitted. Pressure medium is displaced via the respective work line  36 ,  38  from the pressure chamber  32 ,  34  diminishing in size, with pressure medium being replenished into the enlarging pressure chamber  34 ,  32  with the aid of the one hydraulic unit  22 ,  24 (pump function). Here the hydraulic unit  22 ,  24  set up as a pump is driven by the other hydraulic unit  24 ,  22  (motor).  
      At an increased tensile strain in the cable stay  8 , the cylinder jacket  18  moves to the left in the representation of  FIG. 1 , so that the cylinder chamber  34  diminishes and the ring chamber  32  increases in size. At the same time the pressure in the ring chamber  32  drops below the pre-set pressure (e.g., &lt;100 bar), while the pressure in the cylinder chamber  34  remains substantially unchanged (e.g., 200 bar) due to the compensating effect of the hydraulic accumulator  42 . Pressure medium thus flows from the cylinder chamber  34  via the second hydraulic unit  24  into the ring chamber  32 , with the second hydraulic unit  24  being driven by the pressure medium flow and acting as a hydrostatic motor. The latter then drives the first hydraulic unit  22 , so that the latter conveys pressure medium from the tank  20  into the ring chamber  32 . Thus the first hydraulic unit  22  acts as a pump. As the pressure drop across the second hydraulic unit  24  is greater than the pressure drop across the first hydraulic unit  22 , the second hydraulic unit  24  (motor) can generate more power than is required for driving the first hydraulic unit  22 , so that an additional consumer may furthermore be driven apart from the first hydraulic unit  22  (pump). This additional consumer is in accordance with the invention the electric motor  26  operated in this arrangement as a generator and thus converts the surplus hydraulic energy of the second hydraulic unit  24  into electric energy, i.e., acts as a brake.  
      In the event of a tensile strain of the cable stay  8 , the first hydraulic unit  22  thus acts as a pump, the second hydraulic unit  24  acts as a motor for the first hydraulic unit  22 , and the electric motor  26  optionally acts as a generator, whereby a movement of the cylinder jacket  18  is realized that damps the bridge&#39;s vibration.  
      Upon a movement of the cable stay  8  to the right, the cylinder jacket  18  moves to the right, whereby the cylinder chamber  34  is enlarged and the ring chamber  32  is reduced in size. The pressure in the ring chamber  32  rises (e.g., &gt;100 bar), while the pressure in the cylinder chamber  34  is kept constant through the intermediary of the hydraulic accumulator  42  (e.g., 200 bar). At the same time pressure medium flows from the ring chamber  32  via the first hydraulic unit  22  into the tank  20 , so that the latter is driven by the pressure medium flow and acts as a hydrostatic motor. The latter then drives the second hydraulic unit  24 , so that it acts as a pump to convey pressure medium from the ring chamber  32  into the cylinder chamber  34 . In the process the first hydraulic unit  22  (motor) generates more power than is required for driving the second hydraulic unit  24  (pump), so that an additional consumer might be operated. This additional consumer then in accordance with the invention is the electric motor  26  which acts in this arrangement as a generator and thus converts the surplus hydraulic energy of the first hydraulic unit  22  into electric energy, i.e., acts as a brake.  
      In the event of a “compressive strain” of the cable stay  8  the first hydraulic unit  22  thus acts as a motor for the second hydraulic unit  24 , the second hydraulic unit  24  acts as a pump, and the electric motor  26  optionally acts as a generator, with a movement of the cylinder jacket  18  damping the vibration of the bridge deck being realized in the process.  
      Thus in accordance with the invention a damping device  10  is furnished that operates in the biased condition substantially without external supply of energy. All the energy necessary for obtaining or compensating the pressures may, in accordance with the realization of the damping device  10  in accordance with the invention, fundamentally be obtained from the vibration energy.  
      In a preferred embodiment of the differential cylinder  14  ( FIG. 3 ), the hydraulic accumulator  42  is not arranged externally but integrated into the differential cylinder  14  with its accumulator  64 . The cylinder jacket  18  is elongated in this embodiment and delimits the accumulator  64  which is separated from the cylinder chamber  34  by a partition  46 . In order to furnish additional gas volume, the latter is connected with external compensator reservoirs  68 . The partition  46  is subjected on the cylinder chamber side to the pressure pH in the cylinder chamber  34 , so that the latter is axially displaced in accordance with the relation between the gas pressure pG and the pressure pH, and the pressure pH in the cylinder chamber  34  is kept largely constant in accordance with the laws of the state quantities of the gas.  
      Such an arrangement of the hydraulic accumulator  42  has a particularly compact construction. Moreover tubing is simple because a pressure medium line between the hydraulic accumulator  42  and the cylinder chamber  34  is not necessary.  
       FIG. 4  shows a preferred embodiment of a differential cylinder  14  having a ring chamber  32  that is sealed in accordance with the invention against an external environment  62  and against a cylinder chamber  34 . The differential cylinder  14  includes a multi-part piston  16  and a cylinder jacket  18 . The differential cylinder  14  has at the free end portion  90  of its piston  16  a reception  72  for supporting the differential cylinder  14  at the terminating anchorage  12 , and at the cylinder jacket  18  a reception  70  for securing a cable stay  8 .  
      In order to measure the stroke of the cylinder jacket  18 , the differential cylinder  14  has a stroke measuring device  76  that is arranged on the end side of the cylinder jacket  18  and is in operative connection with the piston  16 . Moreover the piston  16  comprises an annular element  66  that is in operative connection with a rod-type element  78  arranged on the cylinder jacket  18 . In the event of strokes of the cylinder jacket  18 , the annular element  66  changes its position relative to the longitudinal axis of the rod-type element  78 , so that the stroke may be determined, and a positional regulation of the damping device  10  may be realized.  
      The ring chamber  32  (detail x) extends radially between a jacket section  52  and an opposed cylinder jacket portion  112  and is axially delimited by opposite end faces  92 ,  94  of a slide sleeve  96  arranged on the cylinder jacket  18  and of a spacer sleeve  100  arranged on the received end portion  98  of the piston  16 . Via radial bores  102  opening into an axial pressure passage (not represented) it is connected with a pressure port  104  for connection of the first work line  36  or of the hydraulic units  22 ,  24 , respectively. In the range of the slide sleeve  96 , a leakage port  60  is provided in the cylinder jacket  18 .  
      The cylinder chamber  34  extends radially over the entire internal diameter of the cylinder jacket  18  and is axially delimited by opposed end faces  86 ,  88  of the cylinder jacket  18  and of the piston  16 . It is connected, via a pressure sleeve  106  arranged in the piston  16 , with a pressure port  108  for the connection of the second work line  38  or of the second hydraulic unit  24 , respectively, and of the hydraulic accumulator  42 .  
      The seal in accordance with the invention of the ring chamber  32  against the external environment  62  and the cylinder chamber  34  is realized with the aid of gap seals  48 ,  82  having the form of annular gaps  58 ,  84 . The annular gap  58  for sealing of the ring chamber  32  against the external environment  62  is formed between the inner peripheral surface  54  of the slide sleeve  96  and the respective outer circumference portion  50  of the piston  16 . The annular gap  58  opens into a leakage port  60 . The annular gap  84  for sealing of the ring chamber  32  against the cylinder chamber  34  is formed between the outer circumference portion  52  of the spacer sleeve  100  and the respective opposed inner peripheral portion  112  of the cylinder jacket  18 .  
      In order to achieve sufficient tightness and a sufficiently great pressure reduction through the intermediary of the annular gaps  58 ,  84 , these must be formed to be radially correspondingly narrow and axially correspondingly long.  
      In accordance with the invention, beyond the leakage port  60  radial sealing members or stripping members  80 ,  110  are provided that seal the annular gap  58  against the external environment  62 . Owing to the low pressure gradient between the pressure of the external environment  62  and the pressure of the pressure medium, only low-pressure seals  80 ,  110  are required in the range of the leakage port  60 .  
      Besides the omission of high-pressure seals for sealing of the ring chamber  32 , what is particularly positive about the gap seals  48 ,  82  of the invention is the fact that the friction between opposed piston-side surfaces  50 ,  54  and cylinder jacket-side surfaces  52 ,  56  is reduced, so that such a differential cylinder  14  exhibits a better responsiveness than comparable differential cylinders  14  with conventional seals.  
      What is disclosed is a a damping device, in particular for cable-supported structures such as, e.g., cable-stayed bridges, stadium roofs, guyed towers, comprising a differential cylinder, two hydraulic units, and an electric motor, wherein during damping the one hydraulic unit acts as a motor, and the second hydraulic unit acts as a pump, with surplus hydraulic energy being convertible into electric energy through the intermediary of the electric motor.  
     List Of Reference Symbols  
     
         
           2  cable-stayed bridge  
           4  roadway  
           6  main pylon  
           8  cable stay  
           10  damping device  
           12  terminating anchorage  
           14  differential cylinder  
           16  piston  
           18  cylinder jacket  
           20  tank  
           22  first hydraulic unit  
           24  second hydraulic unit  
           26  electric motor  
           28  piston rod  
           32  ring chamber  
           34  cylinder chamber  
           36  first work line  
           38  second work line  
           40  load cell  
           42  hydraulic accumulator  
           44  third work line  
           46  partition  
           48  gap seal  
           50  outer circumference portion  
           52  outer circumference surface  
           54  inner circumference portion  
           56  inner circumference portion  
           58  annular gap  
           60  leakage port  
           62  external environment  
           64  accumulator  
           66  annular element  
           68  compensator reservoir  
           70  reception  
           72  reception  
           74  pressure passage  
           76  stroke measuring device  
           78  rod-type element  
           80  sealing member (low-pressure seal)  
           82  gap seal  
           84  annular gap  
           86  end face  
           88  end face  
           90  free end portion  
           92  end face  
           94  end face  
           96  slide sleeve  
           98  received end portion  
           100  spacer sleeve  
           102  bores  
           104  pressure port  
           106  pressure sleeve  
           108  pressure port  
           110  sealing member  
           112  cylinder jacket portion