2 Field ofthelnvention
The invention relates to the metering valve of a' fuel metering unit
comprising of a stationary valve plate with a metering orifice and a
movable metering plate of cam profile to supply the atomized fuel to the
gas turbine starter engine as per the engine operating envelope.
3 Background of the Invention
The fuel metering valve is intended for the aero gas turbine starter engine
applications to supply the metered fuel according to the engine speeds at
various operating conditions. The opening of the metering valve orifice by
the metering cam plate mechanism driven by the stepper motor in terms of
precise angular movements is controlled by an electronic control unit
(ECU) at dynamic operating conditions. A pressurizing valve in the
downstream to the metering orifice is used to maintain the pressure
difference across the metering orifice for the continuous and uninterrupted
fuel metering to the engine. The fuel supply from the existing metering unit
was uncontrollable in crucial operating points due to its inability to _open
and close at the desired resolution and repeatability. Hence, to cater to the
wider spectrum of starter engine operation with consistent repeatability
and high resolution of fuel supply, the development of new metering valve
was taken up.
3.1 Prior Art
The patent US 3808799 is for the fuel metering valve for a gas turbine engine which includes a pair of chambers within a body, one of the chambers containing devices sensitive to pressure signals derived from the engine compressor. A control element is connected to the pressure sensitive devices apd sealingly extends into the second chamber to control the magnitude of a servo pressure signal which is used to control a variable metering orifice between an inlet and an outlet for the valve. A restricted orifice interconnects the first and second chambers
The patent US 2006/0218928 A1 is for a low energy stepper motor driven fuel metering valve (FMV) that eliminates the need for a position sensor. In
this patent, the stepper motor rotates a cam that replaces the flapper valve used in conventional systems. The cam rotation increases the gap
between the cam and nozzle on one side of the cam and decreases the
gap between the cam and nozzle on the other side. The gap differences affect the pressures on the spool piston ends, which forces the piston in
the direction that will re-equalize the cam-nozzle gaps. As a result, the relatively low energy stepper motor controls the relatively high energy
hydromechanical system via the dual cam-nozzle-orifice system. The cam is precision machined and assures stroke/degree gain accuracy. The
hydraulic systefi assures the piston tracks the cam essentially perfectly except for the effects of piston stiction forces‘
4 Brief Summary of the Invention
In the present invention, the fuel metering valve along with the cam profile
metering plate is precisely designed and manufactured to achieve the'
resolytion and repeatability at the highest level while supplying a metered
quantity of atomized fuel to the starter engine covering the entire envelope
of engine operation. The specially designed cam shaped contour of the
metering plate periphery results in a predeterminedvariations of the
opening area of the metering orifice at different positions of the metering
plate and is used to control the fuel quantity to the fuel nozzles at the combustor. The fuel metering valve is arrived after sieveral iterations ‘involving in-depth analytical calculations, precision manufacturing and extensive testing.
5 Detail Description of the Drawings
Figure 1: The two-dimensional assembly (2D) section of fuel metering
system comprising of the stationary metering valve with the orifice (1),
metering plate of cam profile (2) driven by the stepper motor (4) through
the drive arm (3) and a drive pin (8)‘ The compression spring (5) and the
spring seat (6) are used to mount the metering valve assembly with spring
load on the stepper motor which is axially located inside the body (10) by
an internal circlip (7). The split pin (11) is used to lock the drive arm to the
stepper motor. The metering valve is located inside the body cover (9)
with an ‘o’ ring (10) for covering the fuel metering assembly without any
fuel leak outside the fuel pump.
Figure Zzshows the three-dimensional (SD) exploded view of fuel metering
unit assembly comprising of the stationary metering valve with the orifice
(1), movable metering plate of cam profile (2), drive arm (3). stepper motor
(4), drive pin (8), compression spring (5), spring seat (6), body (10), split
pin (11) and pins (12) for the metering plate movement restriction‘
Figure 3zshows the details of fuel metering valve assembly of stationary
metering valve (1) with a metering orifice (21) of geometry (22) with a pilot
hole (23) and restriction pin holes (24,25) and themovablemetering plate
(2) with the cam profile (26).
Figure 4: shows theperformancecomparison at minimum and maximum operating speeds (in revolutions per minute, rpm) for the new metering valve (31,32) and old metering valve (33,34). The performance comparison is performed with the normalized percentage of stepper motor
steps in the horizontal axis versus the normalized percentage of fuel flow from the fuel metering valves in the vertical axis.
6 Detail Description of the Invention
The following description particularly describes the invention, the working
principle and operation of fuel metering valve of aero gas turbine starter
engine.
The aero gas turbine starter engines are used to start the aircraft main
power plant. As in any gas turbine engine, an aero gas turbine starter
engine requires a predetermined fuel proportional to the compressed air
mass at varying engine speeds for the smooth and continuous operation.
In addition, in some aircraft applications they also perform the dual
function as an auxiliary power unit to supply the electrical power ‘to the
aircraft systems in ground and flight modes. The fuel supplied by the fuel
metering unit is sent to the combustor through the fuel nozzles to mix with
the compressed air to form an atomized fuel. In the combustor, the
combustion process is initiated by the spark igniters. The compressed air
which is continuously supplied by the upstream compressor is driven by
the staner motor till the starter engine attains the self-sustaining speed.
‘
Once the engine reaches its self-sustaining speed, the thermal energy of
the high temperature burnt gases in the combustor is utilized by the
downstream turbine section to drive the compressor. This process of the
gas turbine aerothermodynamics is highly dynamic during its entire
operation and depends on the aircraft ambient conditions where it is
mounted. The right amount of air fuel mixing with the best resolution and
repeatability is critically required to achieve the total control of the engine.
Hence, the resolution and repeatability of fuel supply to the gas turbine
starter engine in the highest level is of paramount importance for the
smooth and efficient control its operation.
Referring to Figure 1, Figure 2 and Figure 3, the stationary fuel metering
~ valve with the metering orifice (1) is opened by the movable metering plate
of cam profile (2) in terms of precise angular steps by the stepper motor governed by the electronic control unit of the engine. The fuel metering
valve (FMV) shown in Figure 3 caters for the wider range of fuel flow over
a far lesser stepper motor steps (31,32) compared to the old fuel metering
valve (33.34) as shown in Figure 4 resulting in the fuel supply of very high
resolution to the engine at very good repeatability. The new metering valve
is tested in multiple aero gas turbine starter applications and the test results
are found to be in-line with the performance as stated.
We Claim,
'1. Fuel metering valve fér supplying metered fuel to the aero gas turbine
starter engine comprising:
5 A stationary metering valve (1) having:
A metering orifice (21) of highly precise geometry (22) along with a pilot hole (23) and pin holes (24, 25); With an associated metering plate (2) having:
A cam profile (26) contour of the metering plate periphery to create 10 variations in the opening area of the metering orifice at different positions of the metering plate governed by an electronic control unit.