Patent GB-1249190-A (GB)
Title: Methods and apparatus for controlling machines having winding devices
IPC: F16H61/46
Filed: 1968-01-17
Abstract: 1,249,190. Mineral-mining installations. EICKHOFF MASCHINENFABRIK U. EISENGIESSEREI m.b.h. GEB. 17 Jan., 1969 [18 Jan., 1968], No. 2783/69. Addition to 1,073,358. Heading E1F. [Also in Division F2] In a hydrostatic transmission driving the winch of a coal cutting machine wherein an electric motor drives a variable displacement pump 2 in closed circuit with a hydraulic motor, the pump displacement is adjusted by control means responsive to the load current of the driving motor and the pressure in the working circuit. The pump displacement may be set to a desired value by a lever 32 which acts through a spring 31 on a control bush 14 connected by a lever 17 to a control valve 18 of a follow-up servo motor 19 which adjust the pump displacement. A pump 3 supplies pressure liquid to the servo motor- 19 and supplies make up fluid to the circuit through one way valves 5. The pump 3 also supplies pressure liquid through an over pressure valve 10 to a piston 11 which is raised against the bias of a spring 15 to release a manually controlled valve 12. In the position shown the valve 12 connects the pump 3 to a space above a piston 13 which is urged downwardly to engage a groove in the bush 14 to adjust the pump displacement to zero. On changeover of the valve 12 the space above the piston 13 is vented whilst the pump 3 is connected to a space below the piston 13 whereupon the piston 13 moves upwardly to release the bush 14 and permit control of the pump displacement by the lever 32. A shuttle valve 6 connects the high pressure line of the working circuit to a piston 16 so that on excess pressure in the working circuit the piston 16 is forced downwardly against the bias of a spring into engagement with the groove in the bush 14 to reduce pump displacement and thus the excess pressure. If the excess pressure persists for a predetermined time the excess pressure valve 10 changes over to vent the chamber below the piston 11 whereupon the spring 15 returns the piston 11 and valve 12 to the position shown wherein the valve 12 supplies pressure liquid to the space above the piston 13 which moves downwardly and reduces the pump displacement to zero. The shuttle valve 6 additionally bleeds off low pressure which is returned to a reservoir through a relief valve 7 and cooler 8. Control in response to electric motor load. A voltage proportional to the electric motor loading current is generated by a transformer 20 which voltage is applied through a rectifier 21 to a comparator circuit 23. The circuit 23 compares the generated voltage with a predetermined voltage and applies the difference between the voltages to transistor amplifiers 25, 26 controlling relays 35, 33. When the generated voltage is less than the predetermined voltage a coil 27 is energised through switches 34, 36 and moves a valve 28 to a position in which it supplies pressure liquid from a pump 4 driven by the electric motor through a valve 47 to the upper face of a piston 29 which is thus moved down against the bias of a spring 13 to release the bush 14 and permit adjustment of the pump displacement by the lever 32. When the generated voltage equals the predetermined voltage the transistor amplifier 26 is modulated and energises the relay 33 which opens the contact 34 to de-energise the coil 27 whereupon the valve 28 is returned to the position shown by spring pressure. The piston 29 is thus held stationary by a fluid lock and prevents movement of the bush 14 and thus the pump displacement beyond a value corresponding to the position of the piston 29. If the generated voltage exceeds the predetermined voltage the transistor amplifier 25 is modulated and energises the relay 35 to changeover switches 36, 37 and energise a coil 38 which moves the valve 28 to a position in which it supplies pressure liquid to the lower face of the piston 29 which is thus forced into the groove in the bush 14 to reduce pump displacement. If the generated voltage exceeds the predetermined voltage by a definite amount which corresponds to the motor breakdown torque a transistor amplifier 39 is modulated to close a switch 41 and complete the circuit to an electromagnetically operated valve 44 which changes over to supply pressure liquid from the pump 3 to the lower face of the piston 29 and reduce pump displacement more rapidly than through the valve 28.  Neutral control. An electromagnetically operated valve 47 which normally connects the valve 28 to the piston 29 is changed over to the position shown in which it interconnects the chambers on both sides of the piston 29 to allow the spring 30 to neutralize the transmission when the electric motor supply is cut off, when the lever 32 is in its neutral position, and when the piston 11 is vented. When the electric motor is energised a relay 28 is also energised to change over a valve 47 and connect the valve 28 with the chamber 46. Switches 51, 52 in series with the relay 48 are closed when the piston 11 is pressurised and when the lever 32 is out of its neutral position. If the overpressure valve 10 vents the chamber 11 the switch 51 opens to de-energise the relay 48 and similarly when the lever 32 is in neutral the switch 52 opens to de-energise the relay 48. When the relay 48 is de-energised the valve 47 interconnects the chambers on opposite sides of the piston 29 to permit the spring 30 to force the bush 14 to the zero displacement position. In Fig. 2 (not shown) a single valve (56) replaces the valves 28, 47. A single transistor amplifier (57) controls the energisation of a coil (59) to move the valve (56) between positions in which it supplies pressure fluid to the upper and lower faces of the piston 29. Switches 64, 65 are moved to a position in which the coil (59) is de-energised and a coil (69) is energised when the gear shift lever is in its neutral position or the piston 11 is vented. Energisation of the coil (69) moves the valve (56) to a position in which it interconnects the chambers on either side of the piston 29 to permit the spring 30 to force the piston 29 in the groove in the bush 14. A bleed orifice is provided in the piston 29 to permit the spring 30 to force the piston 29 into the groove in the bush 14 when the driving motor is switched off.