This invention relates to a fluid power piston device of the, differential circuit pressure operated type which exerts an extending force at a rapid or slower rate, depending upon applied load.
Hydraulic or fluid operated piston devices are commonly used to convert fluid energy into mechanical energy in many industrial applications such as clamping, press and die stamping operations. In many such applications, a relatively low resisting load is initially applied to the piston through its piston rod during the power stroke so that the pressurized fluid conducted to the cylinder housing is supplied at a constant rate with low inlet pressure to produce uniform travel of the piston until it encounters a higher resisting load near the end of the power stroke. At that point, the piston continues its travel to the end of the power stroke at the same rate under an increased inlet pressure of the fluid supplied at the same inflow rate. Accordingly, the piston device and its fluid supply system must be designed to meet maximum load conditions regardless of the relative intervals of time during which maximum load is applied to the piston. A considerable waste of fluid and energy is therefore involved.
In order to meet different load conditions, various complex arrangements have been devised, often applied to the fluid supply system to vary the inlet pressure and inflow rate of fluid to the cylinder housing enclosing the piston. Controls have also been devised to change the operational mode of the piston device by conducting uni-directional external by-pass flow passages between opposing pressure chambers of the cylinder. Complex modifications of the piston and cylinder structure have also been proposed creating a plurality of additional pressure chambers and piston pressure faces to modify the operational mode of the piston device.
It is therefore an important object of the present invention to provide a fluid operated piston device that will automatically change its operational mode to meet an increase in loading during travel in one direction, with a less complex modification of the piston and cylinder structure as compared to prior art arrangements and without complex controls in the fluid supply system associated therewith and which permits positioning of the piston device by an external force with a minimum of fluid resistance.
A further object is to provide a modified piston device which is retractable by a reversed pressurized fluid flow to permit exertion of a force in the opposite direction.