Patent GB-644286-A (GB)
Title: Control systems and apparatus for aircraft engines
IPC: B64D31/02
Filed: 1945-10-18
Abstract: 644,286. Aircraft engine control systems. BENDIX AVIATION CORPORATION. Oct. 18, 1945, No. 27324. Convention date, Oct. 30, 1944. [Class 40 (i)] In a control system for internal-combustion engines for aircraft, a master control member actuates an automatic control system for the manifold pressure, and a variable speed supercharger maintains the manifold pressure in agreement with the selected pressure determined by the position of the master control member after a predetermined position of the throttle valve has been attained. The control system is a composite one, the engine throttle being actuated as a direct function of the position of a master control lever for a pre. determined range, e.g. up to about 30 per cent full throttle, after which the lever position control is superseded automatically and the throttle is controlled as a function of the engine manifold pressure. After the throttle has been initially opened to a position in excess of a predetermined amount, say 80 per cent, a further demand for an increase in intake manifold pressure produces operation of the supercharger. The control system also embodies means for regulating the propeller pitch, first in accordance with the extent of movement of the control lever, and afterwards in dependence on the manifold pressure. Operation of the system is effected by electromagnetic induction devices of the Selsyn type. The system includes an electromagnetic clutch 2, Fig. 2, which, when de-energized provides a mechanical connection between a link 40 connected to the engine throttle, and the pilot's operating lever 1 which transmits movement thereto over members 49-55 and 30. When the clutch is energized by the closure of a switch 60 it establishes connection between the throttle control link 40 and a link 39 operated by the automatic system, and also renders effective the movement of a link 70 connected to the pilot's lever 1 and, through gears 72, 73, driving an energized transmitter rotor 77 associated with stator windings 78-80. Throttle actuator.-The stator windings 79- 80 of the transmitter Selsyn 76 are connected in a closed circuit with the stator windings 202, 203 of a Selsyn 200, the lead to the winding 203 including a field winding 205 of an induction switch 206 with a rotor 208 which has its winding connected to an amplifier 215, whereby a voltage signal produced in the closed stator circuit by movement of the pilot's lever 1 induces in the rotor 208, when in the position shown in Fig. 2, a signal which is amplified and fed over leads 216, 217 to one stator winding 221 of a throttle-controlling servo motor 220. The rotor of motor 220 is connected by gearing 240, 244 and links 245, 39, clutch 2, and links 30, 40 to actuate the throttle. At the same time a cam 250 on one gear shaft 248 is rotated, and through a follower arm 251 and gearing 254 drives the rotor 208 from the position shown towards a position at rightangles thereto. The contour of the cam 250 and the gear train are so designed that, up to about 30 per cent throttle opening the throttle control is a " position follow-up in correspondence with movement of lever 1, and between 30 and 35 per cent throttle opening the signal to the amplifier is a combination of position follow-up and manifold pressure followup, the latter taking over when'the rotor 208 lies parallel to a coil 207 in series with the rotor 271 of a Selsyn 259. Manifold pressure control. Operation of the pilot's lever 1 also causes a voltage signal to be transmitted from the stator windings 78-80 to the stator windings 260-262 of the Selsyn 259 which has its rotor connected to the stem 266 of a bellows device 265 located within a casing 268 that is connected by a tube 280 to the manifold, the arrangement being such that when the manifold pressure is in accordance with the pilot's setting of lever 1 the rotor 271 of Selsyn 259 is in a null position and no voltage is induced in its winding. If the rotor is not in the null position a signal of strength and direction in accordance with its deviation is fed from its winding through the coil 207 of the induction switch 206, the coil 207 and rotor 208 being coupled inductively when the throttle has been moved to about 35 per cent open, as described above. At this stage the throttle control is a manifold pressure follow-up, the controlling signal fed to amplifier 215 and servo 220 being derived from coil 207. Supercharger control. An auxiliary supercharger 300, Fig. 10, driven by a turbine 301 in the waste gas outlet is connected over a conduit 304 to the carburetter 307 and through a main supercharger 4A to the engine. The speed of the auxiliary supercharger is controlled by the extent of opening of the waste gate 305, which is operated by a two-phase servo motor 310, Fig. 2, connected thereto by a gear train and a link 311. A shaft 315 driven by servo motor 310 carries a cam 380 provided with a follower 381 which drives an energized wound rotor 336, the contour of the cam being such that it effects movement of the follower first at an early stage and again at a later stage of its revolution and provides an interval during which the follower is stationary. The rotor 336 is associated with stator windings 331, 337 and 338, of which 331 and 337 are connected in a closed circuit in opposition to the stator windings of Selsyn 200, the resultant signal being amplified at 350 and applied to one stator winding 321 of motor 310. The respective rotor windings 336 and 201 are so arranged that when the throttle is less than 80 per cent open the resultant signal actuates motor 310 in a direction to hold the waste gate 305 wide open, whereas at above 80 per cent throttle a reversal in the direction of the signal tends to close the waste gate. This causes an increase in manifold pressure to which the bellows element 265 responds and operates to close the throttle slightly until a null position of about 80 per cent open is reached, at which stage the signals in the interconnected stator windings 331, 337 and 202, 204 neutralize one another. Should the pilot operate the lever 1 to select a different pressure the throttle-actuating Selsyn is moved from its null position and transmits a signal to actuate the waste gate motor 310, and the resulting change in manifold pressure subsequently resets the throttle to the null or 80 per cent reference position. In a modification, Fig. 16 (not shown), the rate at which the speed of the supercharger is changed is accelerated by feeding the voltage induced in rotor winding 271, as a result of change in manifold pressure, through the primary winding of a transformer connected in the closed circuit including the winding 207 of the induction " switch " 206, Fig. 2, and connecting the secondary winding to a further control device 400 which is described in detail in Specification 644,345, [Group XXXV]. This control device adds to the interconnected throttle and waste gate circuits a signal which is dependent on the acceleration and speed of the supercharger and is derived from the change of output voltage of a generator 401 driven by the supercharger. Propeller pitch control. The stator windings 78-80 of the Selsyn 76 operated by the pilot's control lever 1 are also connected over leads 85-87 to the stator windings 90-92 of a Selsyn 93 controlling the propeller pitch governor. The voltage induced in the rotor 94 is amplified at 110 and applied to a secondary or auxiliary winding 113 of a servo motor 114, the main winding 115 being fed from mainsconnected leads 63, 64 which supply the transmitter rotor 77 also. The amplifier 110 is arranged in known manner to ensure that the field of winding 113 is displaced 90 degrees relative to the field of 115 in both forward and reverse direction. The rotor of the motor 114 drives, through a reduction gearing, a shaft 117 to which is secured an arm 118 connected by a link 119 to a propeller pitch governor control, while a cam 131, which is also secured to shaft 117, actuates a follower 133 secured to the shaft of the Selsyn rotor 94, with the result that the pitch control is operated until the rotor 94 is in a null position corresponding to the position of the transmitter rotor 77. Cam 131 is shaped to provide a continuous, smooth, non-lineal curve of actuation for the governor. The pitch governor control may be of known type, e.g. the rod 119 may control a pinion driving a vertical rack which adjusts the vertical pressure of a spring controlling the lift of a piston valve under the action of a centrifugal governor, the piston valve being located within the upper end of a rotary shaft driven by the engine, and controlling the admission of pressure fluid through radial ports to a cylinder containing a piston which is moved to adjust the propeller pitch. Specification 644,344 also is referred to.