GB1589966A - Fuel control system for a gas turbine engine - Google Patents

Description

(54) FUEL CONTROL SYSTEM FOR A GAS TURBINE ENGINE (71) We, LUCAS INDUSTRIES LIMITED, a British Company of Great King Street, Birmingham B19 2XF, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : This invention relates to a fuel control system for a gas turbine engine.

According to the invention a fuel control system for a gas turbine engine comprises a fuel metering valve which is responsive to a first servo pressure signal, a first pilot valve for regulating said first servo pressure signal, a control element which is movable in response to a second servo pressure signal, a second pilot valve for controlling said second servo pressure signal, means responsive to engine speed, for positioning said second pilot valve, selector means movable in response to changes in a desired speed of the engine, a member slidable relative to said control element and co-operating therewith to define a pressure regulating valve, actuating means for controlling said first pilot valve, said actuating means being responsive to the pressure controlled by said pressure regulating valve, and means for positiong said member relative to said control element in accordance with the position of said actuating means.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1, shows a block diagram of one embodiment of a gas turbine engine fuel control system, Figure 2 shows a metering and throttle arrangement forming part of Figure 1, Figure 3 shows a speed control arrangement forming part of Figure 1, and Figure 4 shows an actuator arrangement forming part of Figure 1.

In the embodiment shown generally in Figure 1 a gas turbine engine 110 is supplied with fuel from a pump ill via a metering and throttle valve arrangement 112 which is shown in more detail in Figure 2. The outlet of the pump 111 communicates with a low pressure return line 113 by way of a nonreturn valve 114. Fuel from the pump 111 is supplied via a passage 115 to a metering valve 116. Valve 116 is responsive to a first servo pressure in a chamber 117. Chamber 117 communicates with the passage 115 by means of a restrictor 118 and also with a first pilot valve 119, later to be described, by means of a passage 120.

A spill valve 121 allows fuel to be spilt from the passage 115 to the return line 113. The spill valve 121 is urged open by the pressure in passage 115 and is urged shut by a servo pressure in a chamber 122. A valve 123, later to be described supplies this servo pressure, by means of a line 124.

A throttle valve 125 is arranged in series between the metering valve 116 and an outlet passage 126 through which fuel can flow to the main burners of the engine 110. The throttle valve 125 includes a piston portion which is responsive to the pressure in a chamber 127, this pressure being derived from that in the outlet passage 126 by means of a restrictor 128, a line 129 and a control valve 130 which is operated by a torque motor 131 which is responsive to the values of engine speed and combustion chamber temperature, an unacceptable rise in these values causing valve 130 to be opened so that the throttle valve 125 moves downwardly, as shown in Figure 2 to restrict fuel flow to the outlet passage 126.

Valve 130 opens into a chamber 132 which communicates through a suitable passage (not shown) with the low pressure return line 113.

A manually-operable valve 133 permits chamber 127 to communicate, via a line 134, with the chamber 132, and thereby to move the throttle valve 125 so as completely to shut off fuel flow to the outlet passage 126.

A feed-back spring 135 co-acts with the throttle valve 125 and the control valve 130, so that movement of the valve 125 causes a change in the servo pressure in chamber 12 which opposes that movement.

In the normal operating condition (shown) of the manually operable valve 133 the outlet passage 126 communicates, via a line 136, the valve 133, a restrictor 137 and a passage 128 with the ingiter burners of the engine 110.

In the shut down condition of valve 133 the chamber 127 is connected, as previously described, to low pressure, fuel flow to the igniters is shut off and the outlet passage 126 communicates with a dump connection 139.

A solenoid valve 140 is operable at engine start up to by-pass the restrictor 137 and to supply the proper quantity of ignition fuel to the engine 110.

A sleeve 141 surrounding the throttle valve 125 is responsive to the fuel pressure immediately downstream of the controlled orifice of the throttle valve, and is biased by a spring 142 agains this downstream pressure, to provide a pressurising valve when the throttle valve 125 is open.

As shown in the speed control arrangement of Figure 3 a governor arrangement 150 is driven at the speed N of the engine 110 and includes a valve spool 151 slidable within a ported central element 152 which forms part of a piston 153. The spool 151 and element 152 co-operate to define a second pilot valve which is in series with a line 154 between the outlet of the pump 111 and a low pressure chamber 155. One side of the piston 153 is subjected to the pressure in line 154 and the other side of the piston 153 is subjected to a second servo pressure intermediate the pressure in line 154 and the pressure in the chamber 155.

The valve spool 151 and piston 153 thus provide a follow-up servo arrangement, to position the piston 153 in accordance with the speed N of the engine 110. The profiles of the weights of the governor 150 may be such that the piston 153 adopts a position directly proportional to the speed N of the engine.

Surrounding the element 152 of the piston 153 is a collar member 156 which co-operates with a passage 157 within the control element 152 to define a pressure regulating valve 158 for an actuator piston 159. Valve 158 is in series with a restrictor 160 between the line 154 and the low pressure chamber 155.

The collar 156 is positioned in accordance with a desired speed of the engine, by means of a link 161 one end of which pivotally engages a crank 162 which is mounted on a fixed pivot 163. The other end of the link 161 -engages an arm 164 by means of a pivot pin 173. One end of the arm 164 moves with the piston 159 and the other end 174 of the arm 164 is in the form of a cam which is engaged in a fork in the collar 156. The cam end 174 of arm 164 is such that clockwise movement of arm 164 about the pin 173 urges the collar 156 to the right and anticlockwise movement of arm 164 urges the collar 156 to the left. A cam follower 165 is movable about the fixed pivot 163 by means of a pilot's speed selection lever 166.The cam follower 165 is biased into engagement with a cam surface 167 by a spring 168, and movements of the cam follower 165 are transmitted to the collar 156 by a further link 169, the crank 162 and the link 161. The stem 152 is positioned in accordance with engine speed N and the collar 156 is positioned, inter alia in accordance with desired engine speed. The arm 164 provides a feed-back line which is responsive to movement of the piston 159 to move the collar 156 in a direction which varies the servo pressure in passage 157 in a sense to oppose movement of the piston 159. The piston 159 is thus positioned in accordance with the difference between desired and actual engine speed. The position of the cam surface 167 relative to the pivot 163 is adjustable by an electric motor 170 which can slide the cam surface 167 on adjustable supports 171, 172.A lever 180 is movable by the piston 159 about a fixed pivot 181.

Movement of the piston 159 is transmitted to lever 180 by spring-biased bushes 182. Movement of the lever 180 in response to differences between the desired and actual engine speeds is limited by bell cranks 183, 184 which are biased into engagement with respective cam profiles on the stem 152 by a spring 185. The bushes 182 allow for over travel of the piston 159 after engagement of the lever 180 with either of the cranks 183, 184. The crank 182 acts as an acceleration stop and the crank 184 acts as a deceleration stop.

Referring back to Figure 2 the lever 180 coacts with an arm 186 at the free end of which is a roller transmission member 187.

The roller 187 is engaged between a first lever 190 and a second lever 191 which provides a control element for the pilot valve 119. A spring 192 is engaged between the lever 190 and the metering valve 116 is provide a position feed-back signal from the valve 116. The lever 191 extends sealingly into a chamber 193 and is acted upon by two bellows units 194, 195. Bellows unit 194 is evacuated and bellows unit 195 is responsive to a pressure P3P derived from the delivery pressure P3 of the engine compressor. Chamber 193 contains pressure P2 from an intermediate stage of the engine compressor.The lever control element 191 of the pilot valve 119 is thus positioned in accordance with engine compressor pressures P3 and P2 and the position feed-back signal provided by the spring 192 is modified in accordance with the difference between actual engine speed N and the desired engine speed, by the roller 187.

Returning to Figure 3, the servo pressure in the line 124 provides a third servo pressure signal for positioning the spill valve 121, is as indicated above, controlled by the valve 123.

Valve 123 provides a third pilot valve and is a spool valve which is connected between the line 154 and a low pressure chamber 199.

The spool of valve 123 is positioned by a governor arrangement 196 which is driven by the governor arrangement 150. An increase in the engine speed N causes the spool of valve 123 to move in a direction to increase the pressure in line 124, and thereby to decrease spill flow. The governor arrangement 196 abuts a piston 197 which is responsive to a signal pressure in a line 198, an increase in the pressure in line 198 also acting to increase the pressure in line 124.

Line 198 communicates with the outlet of the metering valve 116 via a restrictor 200 and also with the outlet passage 126 via a control port 201 which can be closed off by a part 202 of the throttle valve 125 when the latter is in its fully open position. Thus with the throttle valve wide open and the port 201 shut the pressure in line 198 is that at the outlet of the metering valve 116. In this condition the pressure in the line 124 is, for a given engine speed N, dependent on the pressure at the outlet of the metering valve 116, and the spill valve 121 is thus positioned in accordance with the pressure drop across the metering valve 116. In all other conditions of the throttle valve 125 the port 201 is at least partly open, whereby the pressure in line 198 is dependent on the pressure in the outlet passage 126.In these circumstances the spill valve 121 is responsive to the pressure drop across the series arrangement of the metering valve 116 and the throttle valve 125.

The throttle valve 125 is dimensioned so that, in its wide open condition, it imposes very little restriction in fuel flow to the engine, this flow being regulated almost entirely by the metering valve 116. Control valve 130 is opened by the torque motor 131 to reduce pressure in chamber 127 and thereby to move the throttle valve in a shutting direction, only in response to an unacceptable rise in either engine speed or combustion chamber temperature. In normal operation, therefore, the spill valve 121 remains responsive to the pressure drop across the metering valve 116 only. If the throttle valve 125 moves in a closing direction the resultant decrease in pressure in the line 198 moves the spool of valve 123 to the right, reducing the pressure in line 124 to permit increased spill flow.

A stem 203 extends from the piston 153 and controls an actuator arrangement 90 which positions the engine compressor stator vanes.

The actuator arrangement 90 is shown in detail in Figure 4 and comprises a doubleacting piston 91 whose output rod 92 is connected to the stator vanes of the engine compressor. Pressure may be applied to opposite sides of the piston 91 by means of a third pilot valve 93 which has a spool control element 94 movable by a stem 95 which is integral with the piston control element 152.

Stem 95 coacts with spool 94 by means of levers 96, 97. Lever 97 pivotally engages both the spool 94 and the rod of piston 91. A roller 98 is engaged between levers 96, 97 and can be positioned via a bell-crank 99 in accordance with the intake temperature T1 of the engine 10. The response of spool 94 to movements of the stem 95 is thus responsive to engine intake temperature T1. Spool 94 is operable to apply pump delivery pressure to a selected side of the piston 91, this pressure being obtained via a line 100. The other side of piston 91 is exposed to the pressure at the inlet of the pump, via a line 102. Connection of the lever 97 to the piston 91 and the spool 94 has the effect that movement of the piston 91 urges spool 94 in a direction opposite to that originally causing the piston movement.

In use, the metering valve 116 is positioned by means of the bellows 194, 195 and the first pilot valve 119, in accordance with the compressor pressures P2 and P3. The feed-back from the metering valve 116 to the pilot valve 119 is dependent on the position of roller 187 which acts as a multiplying element between the levers 190, 191. The response of the metering valve 116 to compressor pressures P2, P3 is thus trimmed in accordance with the difference between actual engine speed N and desired engine speed 0. The positions of the engine compressor stator vanes are adjusted, by the actuator arrangement 90, in accordance with engine speed and inlet temperature.

The fuel control system described above is also shown and described in our co-pending patent application 37114/77, (Serial No.

1589967) the claims thereof being directed to the action of the part 202 of the throttle valve 125 to cause the pressure regulation effected by the spill valve 121 to be responsive to the pressure difference across the metering valve 116 when the throttle valve 125 is fully open, and to be responsive to the pressure difference across the series arrangement of the metering valve 116 and throttle valve 125 in all other operating conditions of the throttle valve 125.

WHAT WE CLAIM IS:- 1. A fuel control system for a gas turbine engine, comprising a fuel metering valve which is responsive to a first servo pressure signal, a first pilot valve for regulating said first servo pressure signal, a control element which is movable in response to a second servo pressure signal, a second pilot valve for controlling said second servo pressure signal, means responsive to engine speed, for positioning said second pilot valve, selector means movable in response to changes in a desired speed of the engine, a member slidable relative to said control element and cooperating therewith to define a pressure regulating valve, actuating means for controlling said first pilot valve, said actuating means being responsive to the pressure con trolled by said pressure regulating valve, and means for positioning said member relative to said control element in accordance with the position of said actuating means.

2. A system as claimed in Claim 1 which includes feed-back means for applying a force to said first pilot valve dependent on the operating position of said fuel metering

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   abuts a piston 197 which is responsive to a signal pressure in a line 198, an increase in the pressure in line 198 also acting to increase the pressure in line 124.

   Line 198 communicates with the outlet of the metering valve 116 via a restrictor 200 and also with the outlet passage 126 via a control port 201 which can be closed off by a part 202 of the throttle valve 125 when the latter is in its fully open position. Thus with the throttle valve wide open and the port 201 shut the pressure in line 198 is that at the outlet of the metering valve 116. In this condition the pressure in the line 124 is, for a given engine speed N, dependent on the pressure at the outlet of the metering valve 116, and the spill valve 121 is thus positioned in accordance with the pressure drop across the metering valve 116. In all other conditions of the throttle valve 125 the port 201 is at least partly open, whereby the pressure in line 198 is dependent on the pressure in the outlet passage 126.In these circumstances the spill valve 121 is responsive to the pressure drop across the series arrangement of the metering valve 116 and the throttle valve 125.

   The throttle valve 125 is dimensioned so that, in its wide open condition, it imposes very little restriction in fuel flow to the engine, this flow being regulated almost entirely by the metering valve 116. Control valve 130 is opened by the torque motor 131 to reduce pressure in chamber 127 and thereby to move the throttle valve in a shutting direction, only in response to an unacceptable rise in either engine speed or combustion chamber temperature. In normal operation, therefore, the spill valve 121 remains responsive to the pressure drop across the metering valve 116 only. If the throttle valve 125 moves in a closing direction the resultant decrease in pressure in the line 198 moves the spool of valve 123 to the right, reducing the pressure in line 124 to permit increased spill flow.

   A stem 203 extends from the piston 153 and controls an actuator arrangement 90 which positions the engine compressor stator vanes.

   The actuator arrangement 90 is shown in detail in Figure 4 and comprises a doubleacting piston 91 whose output rod 92 is connected to the stator vanes of the engine compressor. Pressure may be applied to opposite sides of the piston 91 by means of a third pilot valve 93 which has a spool control element 94 movable by a stem 95 which is integral with the piston control element 152.

   Stem 95 coacts with spool 94 by means of levers 96, 97. Lever 97 pivotally engages both the spool 94 and the rod of piston 91. A roller 98 is engaged between levers 96, 97 and can be positioned via a bell-crank 99 in accordance with the intake temperature T1 of the engine 10. The response of spool 94 to movements of the stem 95 is thus responsive to engine intake temperature T1. Spool 94 is operable to apply pump delivery pressure to a selected side of the piston 91, this pressure being obtained via a line 100. The other side of piston 91 is exposed to the pressure at the inlet of the pump, via a line 102. Connection of the lever 97 to the piston 91 and the spool 94 has the effect that movement of the piston 91 urges spool 94 in a direction opposite to that originally causing the piston movement.

   In use, the metering valve 116 is positioned by means of the bellows 194, 195 and the first pilot valve 119, in accordance with the compressor pressures P2 and P3. The feed-back from the metering valve 116 to the pilot valve 119 is dependent on the position of roller 187 which acts as a multiplying element between the levers 190, 191. The response of the metering valve 116 to compressor pressures P2, P3 is thus trimmed in accordance with the difference between actual engine speed N and desired engine speed 0. The positions of the engine compressor stator vanes are adjusted, by the actuator arrangement 90, in accordance with engine speed and inlet temperature.

   The fuel control system described above is also shown and described in our co-pending patent application 37114/77, (Serial No.

   1589967) the claims thereof being directed to the action of the part 202 of the throttle valve 125 to cause the pressure regulation effected by the spill valve 121 to be responsive to the pressure difference across the metering valve 116 when the throttle valve 125 is fully open, and to be responsive to the pressure difference across the series arrangement of the metering valve 116 and throttle valve 125 in all other operating conditions of the throttle valve 125.

   WHAT WE CLAIM IS:- 1. A fuel control system for a gas turbine engine, comprising a fuel metering valve which is responsive to a first servo pressure signal, a first pilot valve for regulating said first servo pressure signal, a control element which is movable in response to a second servo pressure signal, a second pilot valve for controlling said second servo pressure signal, means responsive to engine speed, for positioning said second pilot valve, selector means movable in response to changes in a desired speed of the engine, a member slidable relative to said control element and cooperating therewith to define a pressure regulating valve, actuating means for controlling said first pilot valve, said actuating means being responsive to the pressure con trolled by said pressure regulating valve, and means for positioning said member relative to said control element in accordance with the position of said actuating means.
2. 2. A system as claimed in Claim 1 which includes feed-back means for applying a force to said first pilot valve dependent on the operating position of said fuel metering

   valve, said means for controlling the first pilot valve including means for varying the force applied by said feedback means.
3. 3. A system as claimed in Claim 2 in which said feedback means comprises a first lever resiliently coupled to said fuel metering valve, said first pilot valve comprises a second lever movable to regulate said first servo pressure signal and said force varying means comprises a transmission member engaging said first and second levers and movable to vary its point of engagement with one of said levers.
4. 4. A system as claimed in Claim 3 in which said transmission member is movable to vary its point of engagement with both of said levers.
5. 5. A system as claimed in Claim 3 or Claim 4 in which said transmission member is a roller.
6. 6. A system as claimed in any of claims 3 to 5 which includes means, responsive to the position of said control element, for limiting movement of said transmission member.
7. 7. A system as claimed in any preceding claim which includes means, responsive to changes in a pressure at the engine compressor for operating said first pilot valve.
8. 8. A system as claimed in any preceding claim in which said means responsive to engine speed includes means for causing the position of said second pilot valve and the position of said control element to be directly proportional to engine speed.
9. 9. A system as claimed in any preceding claim in which said control element comprises a piston, and said second pilot valve comprises an element slideably engaging said piston and co-operating with ports therein to regulate said second servo pressure signal.
10. 10. A system as claimed in any preceding claim which includes a spill valve responsive to a third servo pressure signal for spilling fuel from the inlet of said fuel metering valve, and a third pilot valve for generating said third servo pressure signal in response to a pressure difference between the inlet and outlet of said metering valve. -
11. 11. A system as claimed in Claim 10 which includes a throttle valve in series with said fuel metering valve, and means, responsive to operation of said throttle valve, for causing said spill valve to be responsive to the pressure difference across said metering valve alone when the throttle valve is fully open, and to the pressure difference across the series arrangement ofsaid metering valve and said throttle valve in all other states of said throttle valve.
12. 12. A system as claimed in Claim 11 in which said third pilot valve is responsive to the pressure at the inlet of said fuel metering valve and to a signal pressure dependent on the pressure at the outlet of said fuel metering valve, there being a flow restrictor and a control port connected in series between the outlets of said fuel metering valve and said throttle valve, said signal pressure being that intermediate said restrictor and said port, said means responsive to operation of said throttle valve comprising a part of said throttle valve operable to shut said port when the throttle valve is fully open.
13. 13. A system as claimed in Claim 11 or Claim 12 which includes a fourth pilot valve, responsive to an unacceptable rise in an operating condition of the engine, for controlling a fourth servo pressure signal, said throttle valve being responsive to said fourth servo pressure signal.
14. 14. A system as claimed in any preceding claim in which said means for controlling the first pilot valve is resiliently coupled to said control element.
15. 15. A system as claimed in any preceding claim in which said means for controlling the first pilot valve comprises a member slidable relative to said control element and cooperating therewith to define a pressure regulating valve, an actuator responsive to a pressure controlled by said regulating valve, and means for positioning said member relative to said control element in accordance with the position of said actuator, said first pilot valve being responsive to the position of said actuator.
16. 16. A system as claimed in Claim 15 which includes a resilient coupling between said actuator and said first pilot valve.
17. 17. A system as claimed in Claim 15 or Claim 16 which includes means for positioning said member in response to movement of said selector means.
18. 18. A system as claimed in Claim 17 which includes means for varying the response of said member to movement of said selector means.
19. 19. A system as claimed in Claim 18 in which said response varying means comprises cam means coacting with said member and said selector means for varying the relative positions thereof over their ranges of movement and means for adjusting the position of said cam means.
20. 20. A fuel control system for a gas turbine engine, substantially as hereinbefore described with reference to and as shown in Figures 1 to 4 of the accompanying drawings.