Patent GB-1090571-A (GB)
Title: Improved hydraulic servo systems for the control of electric motors
Inventor: WALKER WILFRED
IPC: H02P25/26
Filed: 1963-06-20
Abstract: 1,090,571. Controllers; control of A.C. motors. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. June 3, 1964 [June 20, 1963], No. 24597/63. Headings H2B and H2J. [Also in Division F1] In a control arrangement for an electric motor having an hydraulic servo system which causes relative movement between electrodes of a liquid resistance in the rotor circuit of the motor, which drives a mine winder or hoist, the pressure supply for the main piston 2 comprises an oil pump 11 and delivery pipe 10 communicating through a main sleeve valve 9 and a torque limiting valve 7 with the cylinder 5, and the sleeve valve 9 moves to direct the pressure supply via alternative paths depending upon the distance between the electrodes. Piston 2 rotates a shaft 1 to move the electrodes, and a piston 21a, 21b of sleeve valve 9 is connected via link 23 for movement with the electrodes while the sleeve 15 of valve 9 is connected via a link 16 with a winder driver's lever (not shown) linked via a linkage 20 with piston 2. Movement of the winder driver's lever to the " on " position allows the pressure medium through ports 22a, 22b, a pipe 8 and the valve 7 to move piston 2 until the sleeve 15 of valve 9 closes ports 22a, 22b, and the pressure medium, oil, then travels in an alternative path through a pipe 27 and a restricted orifice 26 to a slug valve 24, and then either directly to valve 7 and piston 2 or through a transfer valve 30 to relief orifices 34, 35, used during power or motoring or braking control. Thus orifice 26 causes avoidance of over-shooting of the electrode movement, and appropriate energization of valves 24, 30, can bring into use the dynamic braking orifice 35 or the orifice 34 used during power or motoring control. A pressure safety or relief valve 12 is provided. All the valves 7, 24 and 30 are controlled in dependence upon the current traversing the rotor circuit (see below). A star-connected liquid resistance LR forms part of a three-phase rotor circuit RC. A rectifier RE is supplied through current transformers CT. The D.C. output of the rectifier RE supplies a coil CSR of a current slugging relay, which forms part of the control unit 25 of Fig. 1, controlling valve 24, and also supplies a coil TLR of a torque limit relay which controls valve 7. A slugging solenoid SS forming part of unit 25 is connectible through terminals T1, T2, with the D.C. source (no shown in Fig. 2b), as controlled by contacts DB of a dynamic braking contactor, contacts F of a forward contactor and contacts R of a reverse contactor, of, e.g. a mine winder drive motor circuit. Contacts CSR of the current slugging relay are in series with contacts DB (Fig. 2b). Similarly a solenoid TS controlling the transfer valve 30 is connectible to terminals T1, T2, through forward contacts F and reverse contacts R, and a solenoid TLS controlling valve 7 is connectible through contacts TLR of a torque limit relay and, if required, through a main safety switch MSS to terminals T1, T2. A modified system is described (Fig. 2c, not shown) in which connection of (SS) to (T1), (T2) is via (F) and (R) in shunt with (DB) and (CSR). (TS) is parallel connected to (SS) and (CSR).