Power plants – Combustion products used as motive fluid – Combined with starting feature
Reexamination Certificate
2002-02-06
2004-02-24
Gartenberg, Ehud (Department: 3246)
Power plants
Combustion products used as motive fluid
Combined with starting feature
C137S488000
Reexamination Certificate
active
06694746
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to actuators for controlling valves to air turbine starters and more particularly to a microvolume actuator that prevents rapid opening of the air turbine starter valve when partially frozen closed.
2. Description of the Related Art
Air turbine type starter motors operate with the energy of a compressed gas such as air and are often used for starting a turbine engine, such as that used on aircraft. The compressed air for the air turbine starter is controlled by a starter valve, such as a pressure regulating and shut-off butterfly valve, or a shut-off valve.
A source of relatively clean dry air is required to power the air turbine starter. The most common source of air for this purpose are an auxiliary power unit, bleed air from the compressor stage of another operating gas turbine engine, or a gas turbine ground cart. Upon actuation of the engine start switch, the starter valve is energized and opens at a controlled rate to permit air to flow to the air turbine starter. The air turbine starter valve output air flow engages the air turbine starter motor, which converts the energy in the air to torque. This torque is applied to the engine gearbox which is then accelerated to a predetermined cut off speed whereupon the engine can accelerate to idle. The start cycle may be terminated manually by the pilot opening the start switch or automatically by a speed sensitive switch built into the starter or by a main engine speed signal to a fully automated digital engine controller (FADEC). When the start cycle is terminated, the starter valve is closed cutting off the energy to the air turbine starter. When starting air is cut off, the air turbine starter automatically disengages from the engine accessory drive shaft and comes to a stop.
The starter valve controls the output torque of the air turbine starter by means of a controlled opening rate of the valve, a controlled closing rate, and/or a pressure regulating system which delivers substantially constant pressure to the starter regardless of the upstream air pressure. These functions in a conventional starter control valve may be implemented by mechanical-pneumatic control devices such as orifices, needle valves, springs and diaphragms. While such devices are generally acceptable, these devices are complex in design and manufacture, may be difficult to adjust, and may be sensitive to environmental changes and may have poor repeatability under certain circumstances.
The starter control valve controls the pressure of the starter air that is initially supplied to the air turbine starter to prevent destructive shock to the mechanism. As the starter responds, the rate of increase in air (fluid) pressure is typically progressive to effect a smooth, rapid acceleration of the starter's turbine mechanism. In addition, the control valve may serve to regulate air pressure.
While a control valve of this type is generally acceptable, it is difficult for the valve to simultaneously regulate pressure, limit pressure rise rate, and control the speed of the air turbine starter. It is also difficult for the valve to meet strict performance requirements over a wide range of environmental conditions.
When the valve is opened, the relatively large air volume present in the actuator that controls the valve increases in pressure and becomes a reservoir of potential energy. This pressure is usually relatively small to prevent damage to the engine being started. However, when ice is in the start control valve, the valve may initially stick until the actuator develops enough torque to break the ice and open the valve. When this occurs, the pressure behind the valve may force the air into the engine in a generally uncontrolled manner. This initial high pressure spike can damage the air turbine starter, as well as the main engine gearbox.
As shown in
FIG. 1
, an air turbine starter valve actuator
100
is shown connected to a butterfly plate
202
by a butterfly shaft
102
. Pressurized air
206
enters into the duct
204
but is held back by the closed butterfly plate
202
. A probe
110
feeds the air flow into the actuator
100
. A regulator orifice
112
controls volume and pressure flow into the actuator
100
.
To close the plate
202
, inlet pressure is ported through the butterfly shaft actuator in-bleed orifice
110
and routed to an inner chamber
116
through the regulator orifice
112
. With the solenoid valve
120
de-energized as shown, a larger diameter chamber
124
is pressurized through a transmission orifice
126
so that the larger diameter chamber
124
is generally at the same pressure as the inner chamber
116
. A second smaller diameter chamber
130
is continually vented to ambient by an associated vent
132
. The resulting pressure differential across the diaphragm
144
sealing the smaller diameter chamber
116
produces an actuator force that assists the torsion spring
142
to close the butterfly plate
202
and to keep it closed.
The transmission orifice
126
is sized to control the rate of pressure change on the larger diameter chamber
124
. This produces a controlled time for the closing of the valve.
With the solenoid de-energized as shown in
FIG. 1
, the inlet pressure is routed simultaneously to the inner chamber
116
and the larger diameter chamber
124
through the regulator orifice
112
and the transmission orifice
126
, respectively. The matching of the regulator orifice
112
and the transmission orifice
126
to the volume flow time requirements of the inner chamber
116
and the larger diameter chamber
124
prevents self-opening of the butterfly plate
202
during rapid inlet pressure rate rises.
The actuator
100
opens when the solenoid
120
is energized. The valve ball
150
seats itself in the valve seat
152
generally approximate to the transmission orifice
126
. Actuator supply pressure is then vented from the larger diameter chamber
124
to ambient through the valve vent
154
. Due to the effective area of the larger diaphragm
140
relative that to the smaller diaphragm
144
, the resulting actuator force will overcome the closing torsion spring force to open the butterfly plate
202
and keep it open. The valve vent
154
is adjustable and appropriately sized to control the rate of pressure decay in the larger perimeter chamber
124
to produce a controlled rate of downstream pressure rise during the opening of the butterfly plate
202
.
As is common with some valves, the butterfly plate
202
may be opened manually by inserting a square drive tool in the end of the butterfly shaft and rotating the shaft to open the butterfly plate
202
. Normal operation is reestablished by rotating the tool to the closed position.
Valves such as the one shown in
FIG. 1
generally serve to open, close, and control the connected butterfly plate
202
so long as conditions are not severe. However, should the butterfly plate
202
become obstructed, the energy stored in the chambers of the actuator
100
may over-power the obstruction and the butterfly plate
202
, causing the butterfly plate
202
to open too quickly and without a gentle transition from unpressurized air flow to pressurized air flow. Such pressure transitions, or transients, may damage the associated air turbine starter (ATS) and engine gearbox. Damage to the ATS may shorten its useful life and prevent its full and proper operation. In particular, once the ice fails, the butterfly valve is free to open and may do so by snapping open and quickly transmitting a pressure gradient on the order of 2000 psi/second to the air turbine starter.
Damage to an ATS can be especially inconvenient, because it may prevent the starting of an engine on the ground and delay the flight for the replacement of the turbine starter. Additionally, in those rare instances where an in-flight air turbine starting is needed, a damaged air turbine starter can impact the proper operation of the starting procedure affecting aircraft safety. As the starting of the gas turbine engine associated with t
Doak John L.
Louis Ronald J.
Reed William H.
Wiggins Jimmy D.
Desmond, Esq. Robert
Gartenberg Ehud
Honeywell International , Inc.
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