Motors: expansible chamber type – With motive fluid valve – To provide unequal inlet and exhaust flow rates to single...
Reexamination Certificate
2000-10-12
2002-04-30
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
With motive fluid valve
To provide unequal inlet and exhaust flow rates to single...
C092S169100, C092S11700R
Reexamination Certificate
active
06378412
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of co-pending German Patent Application No. 199 54 577.4-22 entitled “Liftzylindereinheit für eine Hebebühne”, filed on Nov. 12, 1999.
FIELD OF THE INVENTION
The present invention generally relates to a lifting cylinder unit for a lifting platform. Such a lifting cylinder unit—together with other structurally identical lifting cylinder units—allows for a lifting platform being lifted and lowered. The lifting platform includes carriers with which the lifting cylinder unit is connected such that the carriers are lifted when the lifting cylinder unit extends, and such that the carriers are lowered when the lifting cylinder unit moves in the opposite direction.
More particularly, the present invention relates to a lifting cylinder unit as it is used in lifting platforms for automobiles in garages.
BACKGROUND OF THE INVENTION
Lifting cylinder units having a piston design are known in the art.
A known lifting cylinder unit includes a stationary rod tube having a longitudinal axis. The rod tube in one of its axial end regions is fixedly and sealingly connected to a rod head. A connecting bore is arranged in the rod head. The lifting cylinder unit is supplied with oil via the connecting bore. A cylinder tube is arranged outside the rod tube to be movable with respect to the rod tube in the direction of the longitudinal axis. The cylinder tube in one of its axial end regions is fixedly and sealingly connected to a cylinder bottom. The rod tube in its axial end facing away from the rod head is fixedly and sealingly connected to a piston. The piston includes a centrally located bore allowing for the passage of the hydraulic medium. A dynamic seal and at least one guide element are arranged at the circumference of the piston, and they contact the inner surface of the cylinder tube. The outer diameter of the piston is slightly less than the inner diameter of the cylinder tube at which the running surface for the dynamic seal is located. The cylinder tube at its axial end facing away from the cylinder bottom is fixedly connected to a guide bush. The guide bush with its inner surface is located on the outer surface of the rod tube. Finally, a supporting ring is welded to the outer surface of the cylinder tube. The supporting ring includes a surface for the application of a force to engage the carriers of the lifting platform.
To lift the lifting platform with the known lifting cylinder unit, a pump pumps oil through the connecting bore into the interior of a pressure chamber being formed by the rod tube. The oil fills the pressure chamber, and it flows through the centrically located bore of the piston in the direction towards the cylinder bottom. While the rod head, the rod tube and the piston are stationary, the cylinder bottom, the cylinder tube, the guide bush and the supporting ring are fixedly interconnected, and they are commonly movable in the direction of the longitudinal axis. When the oil pressure prevailing in the pressure chamber increases, the cylinder bottom moves away from the steady piston. The pressure chamber is sealed by the dynamic seal being located at the piston. To attain a sufficient sealing effect between the dynamic seal and the running surface or the bearing surface, the inner surface of the cylinder tube has an improved surface quality being produced by a special process. For example, the inner surface of the cylinder tube is being peeled and rumbled. Consequently, the process of producing the inner surface of the cylinder tube is rather complex.
When the known lifting cylinder unit is actuated, the guide bush with its inner surface slides over the outer surface of the rod tube. Thus, it is necessary to realize a certain surface quality of the outer surface of the rod tube within defined limits.
In the known lifting cylinder unit, no oil is located in the radial region between the inner surface of the cylinder tube and the outer surface of the rod tube and in the axial region between the piston and the guide bush. This region is connected to the atmosphere by an aerating opening extending through the cylinder tube in a radial direction. Due to the fact that certain humidity is contained in the environmental air, the inner surface of the cylinder tube and the outer surface of the rod tube have to be produced with a special process to prevent corrosion. To prevent corrosion, the inner surface of the cylinder tube and the outer surface of the rod tube include chromium plating. Due to the comparatively small outer diameter of the rod tube, the known lifting cylinder unit has little stiffness with the potential danger of folding.
SUMMARY OF THE INVENTION
Briefly described, the present invention provides a lifting cylinder unit for a lifting platform. The lifting cylinder unit has a plunger design, and it includes a stationary rod tube having a longitudinal axis, two axial end regions and an outer surface. A rod head is arranged in one of the axial end regions of the rod tube, the rod head being fixedly connected to the rod tube and including a connecting bore. A cylinder tube having two axial end regions and an outer surface is arranged outside the rod tube. The cylinder tube is designed and arranged to be movable with respect to the rod tube in the direction of the longitudinal axis of the rod tube. A cylinder bottom is arranged in one of the axial end regions of the cylinder tube, and it is fixedly connected to the cylinder tube. A guide bush having an inner surface and including a surface for the application of a force is fixedly connected to the outer surface of the cylinder tube. A pressure chamber is arranged inside the rod tube, and it is designed and arranged to be supplied with a hydraulic medium via the connecting bore. A dynamic seal is arranged in the region of the inner surface of the guide bush, and it is designed and arranged to seal the pressure chamber. A running surface is arranged in the region of the outer surface of the rod tube, and it is designed and arranged to contact the dynamic seal.
With the novel lifting cylinder unit, the number of necessary structural elements are advantageously reduced. The novel lifting cylinder unit has a simple structural design at low producing costs. The novel lifting cylinder unit has a plunger design. A plunger design means that no piston is being used. Contrary to a plunger design, in piston design, a stationary or movable piston is being used, the piston on its outer diameter carrying a dynamic seal sealingly contacting a running surface being arranged on an inner diameter. In a plunger design, the dynamic seal is arranged on an inner diameter, while the running surface is arranged on an outer diameter having improved surface quality. A dynamic seal is to be understood as a seal having a dynamic side, a relative movement taking place between the dynamic side and an associated running surface. Preferably, the relative movement is a translational movement of either the dynamic seal moving with respect to the running surface or the running surface moving with respect to the dynamic seal. A dynamic seal also has a static side at which no relative movement takes place. In the plunger design, the static side of the dynamic seal is arranged at an inner diameter to be stationary, whereas the dynamic side of the dynamic seal dynamically and sealingly contacts a running surface being located on an outer diameter having improved surface quality.
With the novel lifting cylinder unit, the guide bush is designed and arranged to transmit forces onto the carriers of the lifting platform as well as to seal of the pressure chamber. The dynamic seal is integrated into the guide bush in a way that the running surface for the dynamic seal is formed by the outer surface of the rod tube.
The outer surface of the rod tube contacts the hydraulic medium, preferably oil, up to the dynamic seal. Consequently, there is no danger of corrosion in this region being covered by the hydraulic medium. The inner surface of the cylinder tube does not require a special surf
Stach Karl
Wittich Kurt
Leslie Michael
Look Edward K.
Thomas Kayden Horstemeyer & Risley LLP
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