Patent ID: 7311295

Claim:
In a cylinder apparatus for a hydraulic lift jack with a transmission device, which includes a main hydraulic cylinder for pumping the oil stored in an oil tank, so that the lift jack can be ascended by the hydraulic pressure supplied by pumping, the cylinder apparatus is characterized by comprising: lifting means including x-shaped beams for moving an upper plate pivotably engaged on an upper portion of the a beam up and down by the oil pressure in the main hydraulic cylinder; fluid pumping means including the main hydraulic cylinder located below the lifting means for in-taking the oil stored in the oil tank installed at the inside of a base frame and pumping the oil to the outside, and a piston installed to move reciprocally within the main hydraulic cylinder; and pumping transmission means including a transmission control portion installed at the outside of the fluid pumping means for controlling the pumping volume of the oil so that an ascending velocity of a lift portion can be controlled progressively, and an oil pressure removing portion for the piston for removing the pressure of the oil flowed into the piston by the transmission control portion so that the fluid pumping means then can supply a little volume of oil; and wherein the lifting means is further comprised of: a pair of arms pivotably engaged with each other by a plurality of connection members so that said arms are spaced apart from each other by a predetermined distance, in which one end of said arm is engaged pivotably with both free ends of a lift link, and the other end is pivotably engaged with each other by a boss formed with a first through-hole; a pair of sub-arms pivotably engaged with each other by the connection member to be spaced apart from each other, in which one end is pivotably engaged with a respective arm, and the other end is pivotably engaged with a second boss formed with a second through-hole; and, a securing member provided with a guide shaft inserted slidably into the first and second through-holes formed at the first and second bosses, and on which a base plate is installed.