Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2001-05-11
2003-11-25
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S039281
Reexamination Certificate
active
06651442
ABSTRACT:
The invention relates to an apparatus for determining the status of a valve arrangement forming part of a fuelling system. In particular, the invention relates to an apparatus for monitoring the status of a pressure raising shut-off valve arrangement forming part of a fuelling system for an aircraft engine. The invention also relates to a method for determining the status of such a valve arrangement.
In a conventional fuelling system for an aircraft engine, a plump receives fuel at relatively low pressure through an inlet passage, the pump being driven by means of a drive shaft associated with the engine. The pump delivers fuel through a pump outlet to a metering valve arrangement and a pressure raising shut-off valve arrangement (PRSOV) which serve to regulate fuel flow to the engine. The metering valve and the pressure raising shut-off valve are responsive to signals from an electronic control circuit which, in turn, is responsive to signals from the engine and the metering valve arrangement. The provision of the pressure raising shut-off valve ensures fuel is only supplied to the engine when feel flow through the valve is of sufficiently high pressure.
Fuel flow to the engine can be modulated by moving the metering valve between a maximum flow and a minimum flow position. The pressure raising shut-off valve can be closed at any time, on demand, if it is required to shut-off the fuel supply to the engine. This may occur as a result of normal engine operation or as an emergency shut-off in the event of the occurrence of a fault, for example overspeed or fire.
For safety reasons, it is necessary to ascertain whether the pressure raising shut-off valve will close correctly upon shut-down of the engine. One step in the engine start-up procedure is therefore to check whether the pressure raising shut-off valve will close correctly during operation of the engine if normal or emergency shut-off is demanded. If a fault is detected, the subsequent engine start-up procedure is not initiated.
It is known to use microswitches to monitor the position of the shut-off valve so as to determine whether the valve will close correctly during the engine shut-down procedure and during the engine start-up procedures. When the pressure raising shut-off valve is moved to its closed position, the microswitches are closed to make an electrical connection, the absence of any resulting electrical signal indicating that closure of the shut-off valve did not occur correctly. The operation of the microswitches can, however, be unreliable. Another proposed solution is to use an inductive sensor in place of the microswitches. However, such solutions require additional wiring to be incorporated on the shut-off valve and within the electronic control unit. Furthermore, inductive sensors are relatively expensive components.
It is an object of the present invention to provide an apparatus and method for monitoring the position of a shut-off valve arrangement forming part of a fuelling system which alleviates or overcomes one or more of the aforementioned problems.
According to a first aspect of the present invention, an apparatus for determining the status of a shut-off valve arrangement forming part of a fuelling system of an engine comprises;
a metering valve arrangement comprising a metering valve member for regulating fuel flow from a pump to the engine and means for monitoring the position of the metering valve member,
the metering valve member being operable between a maximum flow position in which a maximum flow of fuel flows through the metering valve arrangement to the shut-off valve arrangement, and a minimum flow position in which a minimum flow of fuel flows through the metering valve arrangement to the shut-off valve arrangement,
means for varying fuel pressure acting on the metering valve member upon closure of the shut-off valve arrangement, and
means for monitoring the response of the metering valve arrangement to the variation in fuel pressure so as to provide an indication that the shut-off valve arrangement has closed.
The invention provides the advantage that the need for microswitches or an inductive sensor for measuring the position of a shut-off valve member forming part of the shut-off valve arrangement is removed.
Conveniently, the metering valve arrangement includes first and second control chambers associated with respective ends of the metering valve member, the position of the metering valve member being controlled by controlling fuel pressure within at least one of the first and second control chambers.
Fuel pressure within the first and second control chambers may be controlled by means of a servo-valve supplied with a current.
The current supplied to the servo-valve is conveniently controlled by means of an electronic engine controller, the current being supplied by any suitable current source.
The position sensing means conveniently takes the form of an LVDT. The LVDT enables the position of the metering valve member to be accurately measured.
In one embodiment of the invention, the apparatus comprises means for reducing fuel pressure acting on one end of the metering valve member upon closure of the shut-off valve arrangement. For examples the shut-off valve arrangement may be adapted to include a porting arrangement arranged such that, upon closure of the shut-off valve arrangement, fuel pressure within one of the first and second control chambers is caused to be reduced. In one embodiment, the shut-off valve arrangement may be provided with a port in communication with a low pressure reservoir, the port being brought into communication with one of the first or second control chambers associated with the metering valve member upon closure of the shut-off valve arrangement.
Upon closure of the shut-off valve arrangement, there is a reduction in fuel pressure acting on one end of the metering valve member which serves to urge the metering valve member towards the minimum flow position. The electronic metering valve position control loop senses the change in position of the metering valve member and increases the electrical current supplied to the servo-valve, thereby decreasing the pressure of fuel acting on the other end of the metering valve member to oppose the movement towards the minimum flow position.
The relative sizes of the additional port on the shut-off valve arrangement and a port on the servo-valve may be arranged such it either (i) the metering valve member continues to move towards the minimum flow position or (ii) the metering valve is prevented from moving towards the minimum flow position. In case (i), movement of the metering valve member is sensed by the position sensing means which generates an output signal which provides an indication that closure of the shut-off arrangement has occurred correctly. In case (ii), an increase in the current supplied to the servo-valve is detected within the electronic control loop and is used to provide an indication that closure of the shut-off valve arrangement has occurred correctly.
In an alternative embodiment of the invention, the apparatus comprises means for increasing fuel pressure acting on one end of the metering valve member upon closure of the shut-off valve arrangement. For example, the shut-off valve arrangement may be adapted to include a porting arrangement such that, upon its closure, fuel pressure acting on one end of the metering valve member is increased.
In one embodiment, the shut-off valve arrangement may be provided with a port in communication with a source of high pressure fuel, as opposed to a low pressure fuel reservoir, the port being brought into communication with one of the first or second control chambers associated with the metering valve member upon closure of the shut-off valve arrangement.
The invention may also provide the further advantage that existing fuelling systems can be adapted relatively easily by providing two additional ports on the shut-off valve arrangement without the need for additional wiring on the shut-off valve arrangement and within the electronic engine controller.
Davies Roland Douglas
Smith Trevor Stanley
Casaregola Louis J.
Goodrich Control Systems Limited
Michael & Best & Friedrich LLP
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