Power plants – Pressure fluid source and motor – Ram driven by fluid pumped from reservoir
Reexamination Certificate
2002-10-22
2004-06-01
Lazo, Thomas E. (Department: 3745)
Power plants
Pressure fluid source and motor
Ram driven by fluid pumped from reservoir
C060S481000, C060S482000
Reexamination Certificate
active
06742334
ABSTRACT:
BACKGROUND OF THE INVENTION
A jack is one of the commonly used tools in our daily life. It is used to reduce the force required to lift a load over a preset lift distance. Its operational principle is to force the input piston, having a smaller sectional area, to move with a smaller force. The movement of the smaller piston pushes the hydraulic oil into the output cylinder, thus driving the output piston, which has a larger sectional area to lift the load. In accordance with the Law of Conservation of Energy, the input piston travels a much larger distance than the output piston does. Thus, it is typically necessary to push the input piston repeatedly to lift the load to a certain distance. In this process, each pumping cycle against the input piston results in the same lift distance of the output piston. This is independent of the magnitude of the load. As a result, in any case of an idle load (i.e., no load), a light load, or a heavy load, it necessary to pump the jack repeatedly, with the load going up very slowly. This wastes both time and effort.
To solve this problem, hydraulic jacks have been proposed in which a blind hole is formed in the middle of the piston of the output cylinder. An oil pipe is inserted into this blind jack hole. In the case of an idle load, when the piston of the input cylinder is pumped or pressed, the hydraulic oil flows into the blind hole via the oil pipe, and pushes against the end face of the blind hole. This moves the piston up at a fast speed. In the case of a heavier load, part of the hydraulic oil goes up and opens a sequential valve leading into the output cylinder. The oil thus applies forces against the larger ring-type thrust surface of the piston, and lifts the load slowly together with the hydraulic oil that flows into the blind hole and applies forces against the end face of the blind hole. Since the blind hole has a smaller area to receive force, the lifting speed of the jack is very fast in the case of an idle load. Generally, the piston of the output cylinder reaches the weight after being pumped one or two times. On the other hand, in the case of a heavy load, since the whole sectional area of the piston of the output cylinder is taken as the thrust surface, the purpose of saving effort is also achieved, enabling the heavy load to be lifted with a low force.
However, it is found from practical application this type of hydraulic jack cannot meet the requirements as expected above. The reason is that when the hydraulic oil is pressed into the output cylinder via the oil pipe, the piston of the output cylinder goes up rapidly; the pressure in the ring-type cavity of the output cylinder goes down swiftly to suck hydraulic oil from the oil tank. However, since the piston moves relatively fast and the area of the ring-type cavity changes very quickly, the sucked hydraulic oil cannot fully fill up the ring type cavity, resulting in a phenomenon of inefficient oil suction. Since there exists some air in the ring-type cavity of the output cylinder, when the output cylinder starts to lift load, the load applies forces to the piston and makes the piston fall back a certain distance, thus reducing the speed of the load lift. Moreover, after many, repeated pumping cycles, the air held in the ring type cavity of the output cylinder flows into the input cylinder via the oil circuit, bringing about the same phenomenon of inefficient oil suction for the input cylinder. This reduces the lift distance of each pump press, and additionally, the lifting efficiency. In addition, this type of jack has also another disadvantage. Since the lifting force comes from the hydraulic oil flowing into the blind hole via the oil pipe and into the ring type cavity of the output cylinder via the one-way valve, the area of the blind hole and that of the ring type cavity changes with each pump. It is necessary to ensure a balance between the pressures from the hydraulic oil flowing into the ring type cavity and that flowing into the blind hole to achieve a steady movement of the output piston. Unfortunately, it is very difficult to accomplish such a result in a practical mass production process. As a result, when the controlled hydraulic oil enters the ring-type cavity and is locked, crack of the thin-wall oil pipe happens often due to excessively high pressure in the blind hole. This results in low yield of finished products for this type of jack and thus increases its production cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a speed regulation jack, which takes the size of the load as signal and automatically transfers between different lift speed levels, so that the lifting efficiency of the jack is increased.
It is also an object of the present invention to provide a speed regulation jack in which a limit unloading mechanism is set to prevent the piston rod from striking the cylinder top cover and possibly cracking it, so that the lifting efficiency of the jack is enhanced.
The invention concerns a speed regulation jack, which comprises at least one input cylinder and one output cylinder, and hydraulic lines connected in parallel between the input and output cylinders. A differential oil circuit is connected between the inlet cavity and the return cavity of the output cylinder, and a control valve is connected in series between the return cavity of the output cylinder and the oil tank. This control valve controls the return oil of the return cavity.
A one-way valve is set in the differential oil circuit, and the return cavity of the output cylinder is unidirectionally connected to inlet cavity via this one-way valve.
A limiting or unloading mechanism is set at the front-end of the return cavity of the output cylinder.
A return groove can be set on the mating surface between the front-end of the return cavity and the piston of the output cylinder. The return cavity is unidirectionally connected to the oil tank via a one-way valve. The core of the one-way valve is fixed to a pressure pin out of the bush of the one-way valve. One end of the pressure pin is seated in the return cavity to control the opening and closure of the one-way valve, to thereby create a limit unloading mechanism. In the case of idle operation, when the piston reaches its maximum distance, it reaches the pressure pin and opens the limit unloading mechanism—the hydraulic oil in the inlet cavity of the output cylinder returns into the oil tank via the return groove and sequential valve. This can be used to meet the requirements of inspection and test standard in the case of from idle operation to maximum oil return.
The one-way valve with a pressure pin of the limit unloading mechanism can share the same valve core with the control valve to form a composite control valve.
The control valve can be a sequential valve.
The hydraulic line can be a hydraulic speed regulation line.
Speed regulation cylinders can be set in the hydraulic speed regulation lines.
The hydraulic speed regulation lines comprise at least two hydraulic sub-lines connected in parallel. These hydraulic speed regulation lines take the load pressure of the output cylinder as its control signal to control the opening and closure of its hydraulic sub-lines or their combination at different speed levels.
Control valves are set in the hydraulic sub-lines that take the load pressure as their control signal to control the opening and closure of the hydraulic sub-lines.
The opening pressure of the control valves in the hydraulic sub-lines is set in sequence and opens in sequence with the increase of load.
Speed regulation cylinders can be set in the hydraulic sub-lines and the difference between the piston areas of the input and output cavities in the hydraulic sub-lines are set in sequence.
The hydraulic sub-line at the lowest speed level in the hydraulic speed regulation line can be directly connected to the input and output cylinders via a control valve.
A flexible restoring mechanism is set in the speed regulation cylinder, and the output cavity of the speed regulation cylinder is connected to th
Houston Eliseeva LLP
Lazo Thomas E.
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