Patent GB-634633-A (GB)
Title: Improvements in or relating to speed control apparatus
IPC: H02P5/50
Filed: 1944-09-26
Abstract: 634,633. Automatic speed control systems. AMERICAN BRAKE SHOE CO. Sept. 26, 1944, No. 18358. Convention date, Oct. 12, 1943. [Class 38 (iv)] In a relay system a first relay when operated during the release period of the second, slowto-release relay, closes a circuit which remains closed until the second relay releases and interrupts a self-holding circuit of the first relay, operation of the first relay reducing the release time of the second relay. In Fig. 1 slave shafts 20-1, 20-2, 20-3, 20-n, driven by separate aircraft engines are each maintained in synchronism with a master shaft 20M driven from another engine 21 or from an electric motor. The master shaft drives an earthed brush 40 co-operating with a stationary commutator 36 interconnected with other stationary commutators 36, each associated with a three-brush rotor (41, 42, 43) driven by one of the slave shafts. In a typical system for controlling one of the slave shafts, 20-1, driven through gearing 25 by engine 22, speed adjusting means 26, acting on the fuel supply to engine 22 or on the pitch of the propeller 24 driven by it, is controlled by a reversible electric servomotor 27 or by a hydraulic servomotor 29, Fig. 1A, operated by a two-way solenoid valve 30, either of which is, in turn, controlled by a relay unit CU1 energized from a battery 99. At synchronism with the brushes in the position shown, a winding 61 of a master relay 60 is energized through brushes 40 and 41 and the servomotor is inoperative, but relative rotation between brushes 40 and 41 in one sense or the other on deviation from synchronism results, firstly, in the de-energization of the master relay 60, release of which is delayed by a condenser 101, and then, subsequently, if the speed deviation is above a predetermined minimum value, in the energization of a winding 71 or 72 of a balanced relay 70 through brushes 40 and 42 or brushes 40 and 43, according to the sense of deviation, to operate the servomotor in the appropriate direction to restore synchronism. The balanced relay 70 releases and the servomotor stops when the master relay 60 releases, after which the cycle of relay operation is repeated until synchronism -is restored. The duration of each operation of the servomotor is the period between operation of the relay 70 and release of the master relay 60 and is thus dependent on the magnitude of the speed deviation. The release time of the master relay 60, which is primarily dependent on the value of a resistance 102, is made large to increase sensitivity of control but is reduced on operation of the relay 70 by the energization of a winding 62 which biasses the master relay 60 toward the release position. This bias may be adjusted by a resistance in series with the winding 62 and may be arranged to differ according to the sense of servomotor operation. In modifications-: (a) an additional balanced relay is responsible both for controlling energization of the servomotor and for controlling the energization of the bias winding 62 of the master relay 60. The release of this additional relay may be delayed so that the servomotor operates continuously when the speed deviation is large ; (b) three singlewound relays only are used, the release time of the master relay being reduced by resistances introduced in parallel with its delay condenser by the other relays ; (c) an additional relay with delayed operation, energized in parallel with the servomotor, short circuits a resistance in series with the servomotor to increase the speed of servomotor operation when speed deviation is large ; (d) an additional relay with delayed release is de-energized when the servomotor commences to operate and short circuits a resistance in series with the servomotor when speed deviation is large. This relay may also have delayed operation so that the short circuit is continuous when speed deviation is large. A resistance in series with the condenser delaying release of this relay causes the release time to be dependent on the magnitude of speed deviation ; (e) as at (d) except that the resistance in series with the servomotor has a value which differs according to the sense of servomotor operation and is decreased instead of short circuited when speed deviation is large ; (f) manually adjustable valves between the solenoid valve and the hydraulic servomotor are set so that the speed of servomotor operation differs according to the sense of servomotor operation. Details of commutator units suitable for the slave shafts in which the brushes are stationary are given and relative angular adjustment of the brushes is referred to. Mechanical details of automatic and manual engine throttle control are given. Detailed wiring diagrams of single-engine and two-engine arrangements are given which include manual operation of the servomotors and indication that they have been stopped by a limit switch at the limit of travel. In the case of single-engine control the master shaft is driven by an electric motor and a single commutator unit associated with slave and master shafts is employed.