Hydraulic Lifting Device Shock Reduction via Dual Oil Passage

The patent divides the single oil passage into two separate oil passages (first and second oil passages) with different maximum oil passage areas. The first oil passage has a smaller maximum area to limit initial flow rate and reduce shock, while the second oil passage has a larger maximum area to enable faster flow after pressure equalization. This segmentation allows the system to achieve both shock reduction and efficient lowering operation.

The system pre-equalizes the pressure difference between the hydraulic cylinder and pump during the lifting operation by controlling the switch valve timing. When the lifting operation is completed and the switch valve is closed, the pressure difference has already been reduced through the preliminary lifting action. This allows the lowering operation to start immediately when the switch valve is opened again, eliminating the time lag that would occur if pressure equalization had to be performed separately before lowering.

The patent employs dynamic control of the switch valve to regulate the opening degree and control the flow rate of hydraulic oil through the first oil passage. During the initial phase of lowering, the switch valve is opened to a limited degree to restrict flow rate and prevent shock. As the operation progresses and pressure difference decreases, the switch valve opening is increased to allow faster flow through the second oil passage. This dynamic adjustment optimizes both shock reduction and lowering speed.