Ships – Mooring device
Reexamination Certificate
1999-07-20
2001-01-23
Sotelo, Jesus D. (Department: 3617)
Ships
Mooring device
C014S069500
Reexamination Certificate
active
06176192
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention concerns a device for adjusting ramps on ferries, floating bridges or the like, in which the bridge support and the ramps forming the connection to the bank are connected to one another pivotably via a pivot point.
In particular for the bridging of shallow bank inclines, a ramp of adequate length that connects the bridge support to the bank is required. With a bending-resistant connection of the ramp to the floating bridge support, the great supporting length of this ramp leads to bending moments, which may assume undesirably high values or even inadmissibly high values.
A device for limiting the bending moment is known from DE 31 04 361 C2. In the area of the pivot point in which the ramp is pivotably connected to the bridge support there is arranged a differential cylinder, which serves for adjusting the ramp incline. For raising the ramp, hydraulic medium is fed to the cylinder chamber on the head side and hydraulic medium is thereby displaced out of the cylinder chamber on the rod side. For lowering the ramp, hydraulic medium is displaced out of the cylinder chamber on the head side and hydraulic medium is fed to the cylinder chamber on the rod side. If the ramp resting on the bank is subjected to loading, the pressure in the cylinder chamber on the rod side increases in a way corresponding to the loading. In this case, the pressure in the cylinder chamber on the rod side is a measure of the bending moment. Flanged onto the cylinder chamber on the rod side is a pressure limiting valve, which serves as a safety valve and is connected via a first line to the cylinder chamber on the rod side of a second differential cylinder. The cylinder chamber on the head side of the second differential cylinder is connected via a second line to the cylinder chamber on the head side of the first differential cylinder. If the bending moment, and consequently the pressure in the cylinder chamber on the rod side, exceeds a predetermined value, the pressure limiting valve responds. Hydraulic medium now flows out of the cylinder chamber on the rod side of the first differential cylinder into the cylinder chamber on the rod side of the second differential cylinder and displaces the piston of the latter. The hydraulic medium thereby displaced out of the cylinder chamber on the head side of the second differential cylinder is fed to the cylinder chamber on the head side of the first differential cylinder via the second line. In order that the ramp does not lift off the bank when relieved of the load following loading, provided parallel to the pressure limiting valve is a check valve, the direction of flow of which is opposite to that of the pressure limiting valve. If the ramp is relieved of load again, its own weight causes hydraulic medium to be displaced out of the cylinder chamber on the head side of the first differential cylinder into the cylinder chamber on the head side of the second differential cylinder. The hydraulic medium thereby displaced out of the cylinder chamber on the rod side of the second differential cylinder is fed via the check valve to the cylinder chamber on the rod side of the first differential cylinder. With this device it is possible to limit the bending moment. If—as in the known device—a differential cylinder is used for adjusting the ramp, means for volume equalization of the hydraulic medium are required. In the known device, the volume equalization takes place via the second differential cylinder, which has the same dimensions as the first differential cylinder. This solution is expensive, since the additional differential cylinder is required only for the volume equalization. The additional differential cylinder needs considerable space; furthermore the free end of its piston rod must be secured in such a way that it does not constitute a hazard. In the event of leakage losses between piston and inner wall of the differential cylinder, there is also the risk that the volume equalization is not permanently ensured in spite of identical differential cylinders. The use described in DE 31 04 361 C2 of a single differential cylinder for adjusting the ramp incline cannot be simply transferred to the use of two differential cylinders arranged in parallel for adjusting the ramp incline, since the pressure limiting valve can be directly flanged only onto one of two differential cylinders for adjusting the ramp incline.
SUMMARY OF THE INVENTION
The invention is based on the object of providing a low-cost device of the type stated at the beginning.
By the invention the volume equalization container does not need to take up the entire hydraulic medium displaced out of the cylinder chamber when the safety valve responds, but only the amount corresponding to the rod volume. In this respect, it is also not necessary for the entire volume of the piston rod to be taken into account within the hydraulic cylinder, instead it suffices to take into account only the path which the piston rod can cover as a maximum when the safety valve responds. The volume equalization container can consequently be chosen to be smaller than the hydraulic cylinder serving for adjusting the ramp incline. The volume equalization container need not be adapted exactly to the dimensions of the hydraulic cylinder. It suffices if the receiving volume of the volume equalization container exceeds a minimum value, which is determined by the cross section of the piston rod and the path which the piston rod can cover as a maximum when the safety valve responds. Possible leakage losses, in particular between the piston and the inner wall of the hydraulic cylinder as well as via the adjacent valves, are equalized automatically by the hydraulic medium contained in the volume equalization container. The invention is therefore not restricted to differential cylinders but is also similarly of advantage for synchronous cylinders, which do not in themselves require any equalization of the rod volume, to make up possible leakage losses via these cylinders and adjacent valves.
Further advantageous features may also be used with the invention. A check valve arranged parallel to the safety valve prevents the ramp from lifting off the bank when relieved of load. A switching valve, which interrupts the connection between the safety valve and the volume equalization container during the desired raising and lowering of the ramp, prevents the volume equalization container from being impinged upon with the load pressure, in particular during the desired raising and lowering of the ramp. If, in the case of more than one hydraulic cylinder for adjusting the ramp incline, mutually corresponding cylinder chambers are connected to one another by a line in each case, the pressure in the interconnected cylinder chambers is equalized if there is unsymmetrical loading of the ramp in the longitudinal direction. Gas pressure accumulators are hydraulic components which are listed as available in various sizes at low cost. The pressure with which the gas pressure accumulator is pressurized can be chosen to be significantly lower than the load pressure in the cylinder chambers of the hydraulic cylinder. The pressure in the gas pressure accumulator is automatically supplemented each time it is desired to lower the ramp, that is to say also when pressing the free end of the ram against the bank. This ensures that the pressure in the gas pressure accumulator is adequately high before subjecting the ramp to loading. The maximum piston travel of the hydraulic cylinder is not used completely for the adjustment of the ramp incline, in order that a remaining path for bending-moment limitation is retained irrespective of the respective ramp incline.
REFERENCES:
patent: 5623889 (1997-04-01), Whitener
patent: 1945420 (1966-09-01), None
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patent: 3005145 (1981-08-01), None
patent: 3104361 (1982-08-01), None
patent: 3629842 (1988-03-01), None
patent: 0094108 (1985-07-01), None
patent: 0056230 (1986-07-01), None
patent: 0245227 (1987-11-01), None
patent: 0259719 (1988-03-
Farber Martin A.
Mannesmann Rexroth AG
Sotelo Jesus D.
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