Patent GB-786776-A (GB)
Title: Improvements in or relating to a control apparatus
IPC: B64D31/02
Filed: 1954-11-01
Abstract: 786,776. Gas turbine plant. CHRYSLER CORPORATION. Nov. 1, 1954; No. 31492/54. Class 110 (3). [Also in Groups XXXIII and XXXV] Control apparatus for a prime mover such as a gas turbine comprises a first operating means for controlling the fuel flow to the prime mover, a second operating means for varying the load thereon and a speed governor for controlling both the means, the first means being operative to regulate the flow as a function of an operating characteristic of the prime mover when the speed governor is off-speed by less than a predetermined amount and the speed governor becoming effective above this predetermined amount to control the first operating means to make it adjust the fuel flow in accordance with its changed setting. The first means may be responsive to temperature change and the varying load that of a variable pitch propeller. Scoops 28 in the slip stream of the propeller 10 feed air to a compressor 30 whence it passes to a regenerator 34 heated by exhaust gas from the turbine 50. Conduits 38 leading from the regenerator 34 communicate through louvres 43 with an enclosed air tube 41 supplied with fuel through nozzles 39 in burners 40. Fuel is drawn from a tank 60 by a transfer pump 61 which forces it to a boost pump 63 and a fuel control 70 and also to a fuel governor 64 which by-passes the control 70 and is itself by-passed by a valve 58 and again by a cylinder priming unit 54. The fuel control responds to temperature changes in the conduits 38 as recorded by thermocouples 36. The turbine 50 drives the compressor 30 and the drive-shaft continues therethrough to drive the propeller 10 through reduction gearing with which are associated a starter relay 22, starters 23, 24 and a generator 25. A propeller speed governor 16 and an actuator 18 therefor are also provided. On a control panel 80 are a master switch 82, an auxiliary switch M.D. for manual control and also two levers, a lever 84 for setting the operational condition, e.g. "stop," "idle," " cruise " or " land " and a power lever 86 which in its right hand range controls the power and in its left hand or " B " range, beyond a detent, the propeller pitch. Control is effected on the one hand through the speed and on the other hand through the fuel as controlled by the temperature of the intakes to the burner chambers. Through a shaft 262, Fig. 14, which has two ranges of control, one for the governor and one for pitch, the power lever adjusts the setting of a speed governor, e.g. by setting the tension of the spring of a centrifugal governor 203 which acts almost instantly through an arm 206 and switches G1, G2 and more slowly through resistance connections 201, 205 either to alter the' blade pitch through solenoids 208, 209 or to open a by-pass for the fuel supply. Superimposed on the power lever control of the shaft 262 is a control exercised in general by the condition lever through a selected one of three parallel resistors SR-1, SR-L and SR-C, the control actuating a motor 260 to rotate a shaft 264, forming an extension of the shaft 262 of the motor, until movement by it of a slider 216 on a resistor 218 stops the motor. In the temperature control of the fuel for off-speed variations too small to make the speed governor operative the thermocouples 36, responding to a temperature change cause a current flow in a lead 151, Fig. 11, which bridges the two sides of a Wheatstone bridge arrangement consisting of a resistor 156 on one side and a selected one of three resistors in parallel, TR-SI, TR-L, and TR-CL on the other, selection being made by the condition lever: the current flow, acting through a carbon microphone 150, operates a transformer 155, the secondary winding of which excites the fuel control amplifier 74; the amplifier feeds a quickly responsive motor 72, Fig. 1, which operates the fuel control 70 so rapidly that burner temperature may be lowered 500‹ R in one second of time. Starting. On closing the master switch 82 and moving the condition lever 84 to " stop," the power lever is rendered inoperative and for convenience may be set at about a mid-way position. Fig. 3 shows the control circuits in their normal settings. Actuating the manual switch MD prepares a circuit for a relay R1, Fig. 3, which brings in circuits for priming and igniting the burners 40 but this can also be done automatically through a pressure-operated switch. The condition lever 84 closes a switch S-1, energizing a relay R6, maintained so until a pressure capsule P2 in the conduit 38 disconnects it at about 10,000 r.p.m., the relay preparing the idling and cruising circuits and removing a low pitch stop on the propeller to permit the blades to be set at zero pitch. The lever also closes a switch S-2, Fig. 11, in a temperature-actuated control unit including the Wheatstone bridge arrangement and causes unbalance therein with consequent substantial fuel flow. Progress to idling. The condition lever 84 is moved to the " idle " position, opening the switch S-1 and actuating switches I-1, I-2 and I-3. The first two of these mainly prepare for future operation but the switch I-2 brings in a ground idle solenoid which restricts the fuel supply during idling; the switch I-3 passes power through a normally closed switch P1-2 to a relay R4 which brings into operation the starting motors 23, 24, the heavy current drawn by these operating a series relay to close a switch R5-1 in parallel with the switch P1-2 rendering the relay R4 independent of the switch P1-2 which is actuated by a low-pressure capsule P1 in the conduit 38. This capsule allows time for any accumulation of explosive gases to be blown out of the system and when the starters have turned the engine sufficiently fast to create a desired pressure, throws a double-pole doublethrow switch comprising the switches P1-1, P1-2, opening the latter, which is still by-passed by the closed switch R5-1, and closing the former to excite the relay R1 which closes the circuits actuating the priming unit 54 and ignition of the burners and isolates the ground idle solenoid 108. With the engine rotating and reaching about 8000 r.p.m., the starters draw little current, the series relay ceases to function causing the prime and starter relays R1, R4 also to cease cutting out the burner priming and igniting devices, and the latter cannot be excited again while the switch P1-2 is held open; a switch R 1-2 returns to its normal closed condition and a switch R6-3 having already been turned to its lower position by the relay R6, the ground idle solenoid 108 restricts the fuel supply by disabling the fuel amplifier 74. In a modification, Figs. 5 and 6 (not shown), the starters are arranged in series at starting and automatically change over to the parallel arrangement at about 1500 r.p.m. in response to the capsule P1. In the priming unit 54, Fig. 10, a piston 126 substantially balanced by fluid pressure is shown at the end of the priming stroke when fuel has been delivered along a pipe 131 to the end of a valve chamber 143 and thence along a pipe 135 past a check valve 137 to the burners. At the end of the stroke a spring 139 at the remote end of the chamber 143 urges the valve 134 to the left, closing off the pipe 135 and opening the pipe 131 to a pipe 122 leading from the transfer pump 61, the pressure and a spring 128 thus restoring the piston 126 to the right-hand end of its cylinder 124 and filling the space to the left of it with priming fuel. The valve 134 forms the core of a solenoid 101 which is now excited to force the valve 134 to the right compressing the spring 139 and opening the pipe 135 for the next priming stroke of the piston 126. Once running, the burners are maintained at a predetermined temperature and the fuel supply is adjusted accordingly. Against fluctuations of temperature in the incoming air the burners are protected by the thermocouples 36. In the Wheatstone bridge arrangement for controlling the burner temperature and hence the fuel, each side comprises three resistances in series, the centre one being shunted, on one side by the resistor 156 whose sliding contact 160 constitutes an index against which the other side is contrasted, this other side having the three parallel resistors TR-SI, TR-L and TR-CL shunting the centre resistance 152. On closing the master switch 82, the switch S-2 closes and the point of contact 170 on the resistor TR-SI being at a lower potential than the contact 160, current flows along the bridge line 151 from the contact 160 to actuate the fuel metering motor to increase the fuel flow and move the contact 160 towards a balanced position. Movement of the condition lever to the idling position opens the switch S-2 and closes the switch I-4 in circuit with a switch B-2 held closed in this circuit throughout the " governor " range of the power lever, to maintain the setting of the temperature control resistors. The engine how rotates at about 9.500 r.p.m. and the burner temperature is maintained at about 1,960‹ R. Cruising. With the condition lever 84 moved to cruise, the idling switches are returned to their normal positions, i.e. those shown and switches C-1, Fig. 3, and C-3, Fig. 14, closed. The power lever 86 becomes operative and is set at " cruise idle." The switch C-1 causes excitation of a relay RC, making the temperature resistor TR-CL the operative one to control the fuel supply and at 10,000 r.p.m. the capsule P2 breaks the circuit to the relay R6 which no longer holds the ground solenoid in operation. The power lever 86 carries with it the slider 252, Fig. 14, of a speed resistor SR-C forming with two other parallelly arranged speed resistors SR-L, SR-I one side of a second Wheatstone bridge whose other side is a resistor 218 having a slider 216 connected to the slider 252 on the other side of the bridge through a polarized relay PR. The slider 216 moves in keeping with the shaft 264 of the relatively slow-acting motor 260 w