Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Reexamination Certificate
1999-09-21
2001-03-13
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
Reexamination Certificate
active
06199378
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to the rate of pressure rise in a fluid system and more particularly to off-setting or controlling the length of time that it takes the pressure of a fluid in the fluid system to increase beyond a predetermined level.
BACKGROUND ART
Pressure relief valves are well known in the art to control the pressure level of a fluid in a fluid system. Relief valves are normally designed to open at some predetermined level and bypass a part of or all of the fluid flow from the pump to the reservoir or to some other low pressure system. Likewise relief valves have been used to control the pressure level of pilot fluid in pilot control lines in order to control the maximum pressure level within the respective pilot control lines. U.S. Pat. No. 5,813,226 which issued Sep. 29, 1998 and assigned to the assignee hereof teaches the use of a control scheme for controlling the maximum pressure level within a fluid system without the use of separate pressure relief valves. In this pressure control scheme, a control valve is used to relieve the pressure within a conduit to control the maximum pressure level. In this control scheme, it is necessary to monitor the level of pressure within the system or conduit and when the pressure level of the fluid is predicted to reach its maximum level an electronic controller directs an electrical signal to the control valve moving it towards an open position in order to control the level of pressure therein. In order to control the pressure level within a conduit or system in which the rate of pressure rise is very rapid, the control scheme of the above noted patent functions to anticipate an increase in pressure rising beyond the predetermined maximum level and initiates movement of the control valve towards an open position prior to the maximum pressure level being reached so that the control valve would be at or very near open once the pressure raises to the maximum level. This permits the control valve to open in time to minimize any “pressure overshoot” or sometimes referred to as “pressure spike”. “Pressure overshoot” is any pressure of the fluid that exceeds the preset maximum pressure level. If the rate of pressure rise is to rapid, it cannot be anticipated quick enough and the system will still be subjected to “pressure overshoot”. Another potential limitation with the control scheme of the above noted patent, is that when the system is shut down and the electronic controller is turned off, the fluid within any of the conduits between the control valve and the actuator is trapped and any thermal expansion could cause damage or failure of the conduits.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, a control arrangement is provided for offsetting the rate of pressure rise within a fluid conduit network of a fluid system. The fluid system having a source of pressurized fluid, a reservoir, a fluid actuator, an electrically actuated control valve mechanism connected to the source of pressurized fluid, the reservoir and the fluid actuator. The fluid conduit network of the fluid system having a predetermined maximum operating pressure level. The control arrangement including an input controller connected to the electrically actuated control valve mechanism and operative to generate an electrical signal representative of the desired input and an electronic controller operative to receive the signal from the input controller and direct an output signal therefrom to the electrically actuated control valve mechanism to control movement of the actuator. The control arrangement also including a pressure sensor arrangement operative to sense the pressure within the fluid conduit network of the fluid system and deliver a signal representative thereof to the electronic controller, a control scheme operative in response to the sensed pressure signal to anticipate a pressure level that would exceed the predetermined maximum pressure level and direct an electrical signal to the electrically actuated control valve mechanism to bypass a portion of the fluid flow in the system to the reservoir to relieve the overpressure condition, and a low flow pressure relief valve disposed between the fluid conduit network and the reservoir and operative in response to the pressure level in the fluid conduit network exceeding the predetermined pressure level to bypass a small volume of pressurized fluid to trim the level of any overpressure condition.
REFERENCES:
patent: 4955461 (1990-09-01), Keir
patent: 5138838 (1992-08-01), Crosser
patent: 5396923 (1995-03-01), Allen et al.
patent: 5813226 (1998-09-01), Krone et al.
patent: 2111250 (1983-06-01), None
Aardema James A.
Hajek, Jr. Thomas J.
Koehler Douglas W.
Mate Edward W.
Triffaux Vincent
Burrows J. W.
Caterpillar Inc.
Lopez F. Daniel
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