Power plants – Pressure fluid source and motor – Having condition responsive control in a system of...
Patent
1991-06-20
1996-01-09
Look, Edward K.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of...
91 6, 91449, 91459, F16D 3102
Patent
active
054818745
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates generally to exhaust manifolds of fluid power and control systems and to the methods of pressurization and supply of additional fluid flow to such exhaust manifolds in response to direction of displacement of the cylinder type fluid motors and to the type of loads being controlled by such motors.
BACKGROUND OF THE INVENTION
During the duty cycle of a machine the conditions at the outlet of a cylinder type fluid motor may vary widely and the very undesirable condition of cavitation may take place. As is well known to those skilled in the art, cavitation may adversely affect the life of the system components, especially the system pump, generate noise and introduce very undesirable characteristics when controlling a load. For example, when controlling a negative load, acting in the direction of the piston rod of the cylinder, the inlet flow to the cylinder has to be supplemented by flow, equivalent to the displacement of the piston rod. Such an inlet flow may have to be supplemented, when the velocity of the negative load creates an inlet flow requirement higher than the capacity of the system pump, or when the flow from the system pump is not available, which is the case either during so-called "negative load regeneration", or when the flow at negative load is not diverted to the exhaust manifold. A typical negative load regeneration system is shown in U.S. Pat. No. 4,267,860 which issued May 19, 1981 to Tadeusz Budzich.
The condition of negative load regeneration, in the embodiment described in this specification, takes place when the controlled load is of an aiding or negative load type and when the flow of fluid from the system pump is isolated from the fluid motor. The control of the position of the load is accomplished by using the potential energy of the load. Under these conditions the flow from the pump can be directed to perform useful work in the control of other resistive, or positive type loads of the system. Under these conditions additional flow can be supplied to the exhaust manifold either from an additional low pressure pump, which in a mobile type circuit may be undesirable, since it requires a separate power take-off, or from a fluid flow amplifying device, using energy derived either from the negative load, or from the system pump. Since under the above conditions some of the flow transfer may have to take place through the anticavitational controls of a mobile type valve, it is to a great advantage to supply the necessary make-up flow at a preselected pressure level, higher than atmospheric. Also by maintaining both ends of a cylinder above a certain minimum pressure level, by compressing the entrained air, which is always present in the circulating oil, the system stiffness is substantially increased, which in turn produces a number of very beneficial effects. It is also very desirable, when controlling a positive load in mobile type circuits, to completely unload the pressure of the exhaust manifold, not only in order to increase the system efficiency, but also to increase the level of the effective force, developed by the cylinder, especially when raising a load using the maximum output flow from the system pump.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention a fluid power and control system is provided comprising a cylinder type fluid motor that is subjected to a positive and a negative type load pressure and is also provided with a piston end and a piston rod end. A direction control valve means is operably connected to the fluid motor. The direction control valve means has means responsive to first and second control signals. A system pump, reservoir means, and exhaust manifold means are interposed between the direction control valve means, the fluid motor and the reservoir means. Signal generating means is operable to generate the first and second control signals. The first control signal through said direction control valve means is operable to induce displacement of the fluid motor towards the piston rod end and
REFERENCES:
patent: 3700396 (1972-10-01), Adams
patent: 4022269 (1977-05-01), Segawa
patent: 4085855 (1978-04-01), Worback
patent: 4249570 (1981-02-01), Budzich
patent: 4267860 (1981-05-01), Budzich
patent: 4610194 (1988-08-01), Budzich
patent: 4665801 (1987-05-01), Budzich
patent: 4833971 (1989-05-01), Kubik
patent: 4845948 (1989-09-01), Tha et al.
patent: 5007544 (1991-04-01), Saotome et al.
Burrows J. W.
Caterpillar Inc.
Look Edward K.
Nguyen Hoang
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