Fluid handling – Self-proportioning or correlating systems – Self-controlled branched flow systems
Reexamination Certificate
2000-07-27
2001-12-11
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Self-proportioning or correlating systems
Self-controlled branched flow systems
C137S484200, C060S039281
Reexamination Certificate
active
06328056
ABSTRACT:
SUMMARY OF THE INVENTION
The present invention relates generally to methods and apparatus for fuel flow control and more particularly to a fuel bypass valve which diverts fuel from a fuel pump outlet in an attempt to maintain a constant pressure drop across a fuel metering valve located downstream of the fuel pump. In particular, the bypass valve of the present invention compensates for imbalances caused by changes in the fuel flow rate through the bypass valve or caused by the pressure drop across the bypass valve to more closely maintain the pressure differential across the metering valve constant.
In aircraft fuel control systems, it is common to control the head or pressure differential across a fuel system metering valve by diverting part of the output from a fuel pump back to the inlet of that fuel pump. In such known systems, the pressure differential across the metering valve may, for example, be applied to a spring loaded diaphragm. That diaphragm may be coupled to a bypass valve and if the pressure differential across the metering valve becomes too large, the diaphragm moves so as to open the bypass valve and spill some of the fuel from the outlet back to the pump inlet. Similar systems employing a spring-biased piston coupled to a bypass valve arrangement are also known. The mechanism which senses the pressure differential across the metering valve may be a separate component or may be an integral part of the bypass valve. With such known bypass valves, if the bypass orifice opens further to divert greater quantities of fuel, the piston or diaphragm must move against the force of the bias spring. The spring is deformed increasing its restorative force. When the piston or diaphragm again achieves equilibrium, the forces on opposite diaphragm or piston sides are again equal, but the pressure differential is not the same as it was since one of the pressures is now being supplemented by a greater spring force. Other factors such as Bernoulli forces created by the fuel flow may also contribute to this problem.
Thus, flow unbalance on the piston of a bypass valve increases as the quantity of flow returned to the pump inlet is increased. Also, the unbalance increases as the pressure drop across the bypass valve increases. These unbalance forces act to close the valve. In order to counteract these forces, the regulated pressure drop across the metering valve must increase resulting in an inaccurate control of metering head. It is highly desirable to minimize or eliminate the variations from constant metering valve head created by changes in bypass flow or bypass orifice pressure drop. The unbalance forces and their interaction vary significantly among different fuel control systems. A bypass valve design adaptable to a wide variety of different fuel control systems would also be highly desirable.
Matched flow grinding of the bypass valve components to direct the fuel flow along certain paths in an attempt to cause the fuel flow alone to compensate for such imbalance is known. Such measures have met with some success, but add significantly to the cost of a bypass valve.
More complex bypass valve configurations, such as providing a dual piston configuration with a pair of balanced high fuel pressure fuel inlets to either side of the low or return fuel outlet have also met with some success, but contribute significantly to the weight, complexity and cost of the bypass valve.
It would also be highly desirable to minimize or eliminate the variations from constant metering valve head created by changes in bypass flow or bypass orifice pressure drop without contributing significantly to the cost or weight of the bypass valve.
The present invention overcomes the prior problems and achieves the aforementioned goals by restricting the outlet area of a bypass valve downstream of the bypass ports thus creating an intermediate fuel pressure region between the two ports. This intermediate pressure is applied against an annular area of the piston and is opposed by the pump inlet pressure. As bypassed flow increases, the counterbalancing pressure increases. Proper sizing of the piston annulus and the outlet areas provides a force on the piston essentially equal to the flow unbalance, but in the opposite direction which eliminates most head shift. The piston annular area may be part of a compensating chamber or cavity having inlet and outlet orifices either or both of which may be of variable or fixed size. These orifices may comprise a plurality of openings which may be of varying shapes and spacing providing a wide latitude in design configurations.
In accordance with one form of the invention, a fuel bypass valve selectively diverts fuel from the outlet of the fuel pump back to the inlet of the fuel pump to maintain the fuel pressure differential between the inlet and the outlet of a variable orifice metering valve substantially constant. The valve provides a variable size bypass orifice and includes a movable piston for varying the size of the bypass orifice with the movable piston being urged in a direction to open the bypass orifice by high fuel pressure from the metering valve inlet and urged in a direction to close the bypass orifice by intermediate fuel pressure from the metering valve outlet. A supplemental fuel pressure compensating cavity provides a variable additional force urging the piston in a direction to increase the bypass flow. The cavity includes an annular region of the piston and augments the effect of the high fuel pressure to aid in moving the piston in the direction to open the bypass orifice. High fuel pressure is supplied to the cavity through a variable orifice inlet and applied to the annular region of the piston. Fuel exits the cavity through a variable orifice outlet. Orifice variation is caused by piston movement.
In accordance with another aspect of the invention, a bypass valve maintains a pressure differential between a high pressure source and a monitored intermediate pressure substantially constant and includes a valve housing having an inlet port adapted to be coupled to the high pressure source, an outlet port adapted to be coupled to a low pressure return, and a sensing port adapted to receive the intermediate pressure. A bypass flow path from the inlet port to the outlet port is controlled by a movable piston disposed within the valve housing for reciprocable motion along an axis. The piston has a pair of opposed faces and a hollow interior region. The hollow piston interior is coupled to the inlet port to supply high fuel pressure to one piston face. Low return pressure is applied to the other piston face. The bypass flow path includes a pressure responsive compensating cavity for providing a variable additional force urging the piston in a direction to allow the bypass flow, an inlet orifice, an outlet orifice, and a restricted flow path along a surface of the piston interconnecting the inlet orifice, outlet orifice and compensating cavity.
The present invention comprises a bypass valve for selectively diverting fluid from a high pressure source to a low pressure return for maintaining substantially constant a pressure differential between the high pressure of the source and a monitored intermediate pressure comprising a valve housing including an inlet adapted to be coupled to the high pressure source, an outlet adapted to be coupled to the low pressure return, and a sensing inlet adapted to receive the intermediate pressure. There is a movable piston disposed within the valve housing for reciprocable motion along an axis and having a pair of opposed faces. The piston has one extreme position allowing maximum flow of fluid from the high pressure source inlet to the outlet, another minimum flow extreme position substantially blocking any fluid flow from the high pressure source inlet to the outlet, and a range of intermediate positions allowing a controlled bypassing of fluid from the source to the return for maintaining the pressure differential substantially constant. High pressure fluid from the high pressure source inlet is applied to one pis
Fisher Steven F.
Futa, Jr. Paul W.
Kumar Abhay
Hepperle Stephen M.
Honeywell International , Inc.
Palguta Larry J.
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