| 摘要 |
A hydraulic platform lift for use on trucks and truck trailers has two hydraulic cylinders, one on each side of a door. The cylinders are phasing cylinders in that one cylinder is larger than the other cylinder by a specific ratio. The crosssectional area of the fluid in the rod end of the larger cylinder minus the area of the rod is equal to the cross-sectional area of the smaller cylinder. A connecting line interconnects the rod end of the large cylinder with the cap end of the small cylinder. Hydraulic fluid can be directed by control means into the cap end of the large cylinder or the rod end of the small cylinder. For upward movement, hydraulic fluid is forced into the rod end of the small cylinder. This in turn forces hydraulic fluid through the connecting line into the rod end of the large cylinder, thereby raising both pistons. For downward movement, hydraulic fluid is forced into the cap end of the large cylinder, thereby forcing fluid out of the rod end of the large cylinder and into the cap end of the small cylinder. This causes both cylinders to move downward. The platform lift also has a selflevelling feature whereby the pistons can be made level with one another by moving the platform into an uppermost position. The operational mechanism is located entirely at the sides of the trailer. The lift platform can be made to exert a positive upward force or a positive downward force during use.
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