Patent GB-650695-A (GB)
Title: Improvement in control systems for prime movers having torque-absorbing devices
IPC: G05D13/00
Filed: 1947-07-31
Abstract: 650,695. Regulating. GENERAL MOTORS CORPORATION. July 31, 1947, No. 20787. Convention date, Dec. 3, 1945. [Class 7(vi)] [Also in Groups XXVI, XXIX and XXXIII] In a control system for a prime mover having a torque-absorbing device operated thereby, the torque-absorbing device is controlled in dependence on means sensitive to integrated speed error and the supply of operating medium to the prime mover is controlled in dependence on means sensitive to the amount of speed error both said means being displaced by fluid from a common source under the control of a valve operated by a speed responsive device. As applied to an aircraft power plant having a variable pitch propeller the engine speed is governed in both the positive thrust range and in the negative thrust range and means are provided to prevent any change from the positive range to the negative when the air speed is excessive. The blade angle is manually controlled at low blade angles where automatic control is unsatisfactory. A single manual control member is provided for both positive and negative thrust ranges and for feathering. The system may be adapted for multiengine control and in this case arrangements are provided for synchronizing the engines within limits whilst permitting independent control of the engines individually. A governor 42 driven through gearing 12, 40 from an engine driven shaft operates a control valve 45 xegulating the supply of pressure fluid from a pump P to a servomotor 70 the piston 72 of which operates through rack and pinion mechanism 75, 76 a shaft 77 controlling the pitch changing mechanism. A selsyn 78 transmits an indication of the pitch to the instrument board. The rate of fluid flow to the servomotor 70 is a measure of the speed error and hence the actual movement of the servopiston 72 is a measure of the integrated speed error. The connections between the valve 45 and the servomotor 70 are interchanged when changing from positive pitch to negative pitch by a valve 64. Relief valves 79 permit fluid to pass from one side of the servopiston 72 to the other when the latter is stopped mechanically. A further controller A arranged between the valve 45 and the servomotor 70 comprises a spring-centred piston 57 with a by-pass orifice 58 arranged so that the presure difference developed across the orifice is substantally proportional to the flow through the orifice. The movement of the piston 57 is thus proportional to the movement of the valve 45 and hence to the speed error. This piston 57 acts through' linkage 152, 153 on the control valve 149 of a servomotor 140, the piston rod 141 of which adjusts a cam 134 'through a linkage 131, 138, 139. In some cases the piston 57 may operate the cam 134 directly. The servomotor 140 is supplied from the pump P through a pipe 144. The cam 134 acts through a rod 137 with the throttle valve of a carburetter reciprocating engine or with the fuel control valve of a fuel injection engine. Fig. 18 shows a device for producing a pressure difference across an orifice proportional to the flow therethrough. The piston 57<SP>1</SP> has a plug 570 having a hole 571 the diameter of which gradually increases each way from the central section and a plug 572 the greatest diameter of which is slightly less than the least diameter of the hole. The plug has flats 573 at each end and is centred by a leaf spring 576. The fuel control, the governor loading, and the blade angle are also adjusted manually by a single lever 80 which by depression of a button 85 may pass a stop 84 to pass from the positive thrust range P into the negative thrust range N or a stop 83 to pass from the positive thrust range P to the feathering range F. The lever 80 operates in unison three cams 90, 100, 110 each having parts corresponding to the ranges N, P. F, and also to a transition range T. Thus the cam 90 has a groove 91, 92, 93, 94 which acts through a roller 95 and a link 130 on the linkage 131, 138, 139 of the fuel control. The cam 100 has a groove 101, 102, 103, 104 which acts through a roller 105 and rack and pinion mechanism 30, 28, 29, 31, 32 on the opposed govern- or loading springs 42b, 42a. The pinion 28 is carried by a lever 25 movable between stops, 25a, 25b, by the synchronizing mechanism. The groove 101, 102, 103 is suitable for turbine control whereas the modified groove 101<SP>1</SP>, 102<SP>1</SP>, 103<SP>1</SP> is for reciprocating engine control. The pitch control cam 110 has an irregular groove bounded by surfaces 111, 112, 114, 115, 116, 117, 118, and 119, 120 and also a further cam groove 122 which through a linkage 67, 68 operates to reverse the valve 64 when changing from positive to negative thrust or viceversa. The surfaces 111, 118 are such that the servomotor 70 cannot reduce either the negative pitch or the positive pitch to the degree required by the governor setting so that the controller A operates to increase the fuel control to maintain the set speed. As the air speed increases the fuel setting by the cam 90 becomes adequate to satisfy the governor setting over an increasing part of the positive thrust range and in these circumstances, the surface 116 prevents any transition from the range P to the range N until the air speed is sufficently reduced to allow the roller 121 to pass through the gate 114, 115. In the case of " dive-braking " however, the cam 90 is modified as shown at 91<SP>1</SP>, 92<SP>1</SP>, 93<SP>1</SP> so that the engine speed falls below the set speed even at high air speeds, and the surface 111 is modified as shown at 111<SP>1</SP> to prevent the 100 per cent power value in the negative range being reached before the lever 80 reaches the limit of its travel. The synchronizing mechanism comprises for each engine a three-phase synchronous motor 19 operated by a master generator 243, Fig. 6, driven at predetermined speed by an electric motor 242. Each motor 19 drives a gear 18 in opposition to a gear 13 driven by the respective engine. Any difference in speed causes a gear 17 bearing planets 14, 15 to operate through gear.20 on screw mechanism 22, 23 actuating the speed setting lever 25 any further motion after the stops 25a, 25b are reached being permitted by a friction clutch 21. A master control lever 220 operates a shaft 221 to which each of the engine control levers 80 may be coupled by spring loaded ball detents 222 engaging arms 225 on the shaft 221. Each lever 80 operates a cam 230 the followers 231 of which are connected by a bar 233 the depression of which against a spring 234 operates a lever 236 to adjust the speed control 241 of the motor 242. The bar 233 responds to the highest speed setting and thus if one of the levers 80 out of alignment with the master lever 220 calls for a higher speed than the lever 220 such higher speed will obtain as regards that particular engine and as regards the other engines so far as permitted by the stops 25a, 25b. The speed setting may be modified independently of the cam 100 by a lever 36 operating through a rack 33 on the pinion 31 and in the case of several engines such levers 36 are actuated through a link 240 by a single lever C which through a crank 237 varies the fulcrum of the motor speed control unit lever 236. The blade-adjusting mechanism Fig. 12 is the same as that described in Specification 647,722 and briefly comprises a hub 302 with an accumulator 303, blade roots 310 each with a servopiston 315 under the control of a centrifugally loaded valve 361 operated from the shaft 77 through mechanism comprising gears 342, 341, 340, screws 345, a ring 346, a shoe 347, a floating lever 350, a carriage 354 and a lever 373, and a plate cover 332 enclosing an accumulator control valve AV and a minimum pressure control valve PC. A lever 500 effects independent manual control. Specifications 544,580 and 545,520 are referred to.