Patent GB-1225807-A (GB)
IPC: E21C29/16
Filed: 1968-06-12
Abstract: 1,225,807. Mining apparatus. EICKHOFF MASCHINENFABRIK U. EISENGIESSEREI m.b.H. GEB. 12 June, 1968 [13 June, 1967], No. 27828/68. Heading E1F. [Also in Divisions F2 and H2] A hydraulic pump 2 associated with a hydraulically driven winch of a mining machine is controlled by a pump-setting device in dependence on the load current of an electric driving motor 1 of the machine, the control being such that when the load current exceeds a value close to but not exceeding that of the breakdown torque of the motor the pump is substantially instantaneously set to its idlingposition. The motor 1 drives a coal cutting tool, the pump 2, a servo pump 3 and a further pump 4. The pump 2 is in a working circuit including a motor 5 for the winch, and the pump 3 supplies a control circuit feeding liquid to the working circuit. The working pressure acts on a piston 16 of the pump-setting device, and a pilot valve 17 which can be manually actuated only when a spring-biased piston 18, thereof is under control pressure permits the control pressure to act on a piston 19 of the device to release a control sleeve 20 so that a piston 34 may be actuated. The pump 4 supplies pressure to a piston 23 of the device through an electromagnetically operated valve 22 controlled by the load current of the motor 1. A voltage proportional to the load current is produced by a transformer 24, a rectifier 25 and a resistor 26, and a nominal voltage is produced in a resistor combination 27 and is matched to the rated current of the motor 1 by resistors 28. The difference between the actual and nominal voltage is applied to transistor amplifiers 29, 30. The valve 22 is associated with coils 31, 41 selectively supplied with current from a rectifier 32 under the control of the transistor amplifiers 29, 30. In operation the coil 31 is energised to actuate the valve 22 so as to release the sleeve 20, and a spring 33 then adjusts the pump 2 through the piston 34 to an output position pre-set by a lever 35. When the motor current reaches the nominal value, i.e. there is no difference between the actual and nominal voltages, the transistor amplifier 30 opens a contact 37. The valve 22 is spring-returned to its central position, and the piston 23 is therefore locked hydraulically. When the actual voltage exceeds the nominal voltage the transistor amplifier 29 energises the coil 41 to actuate the valve 22 so as that the piston 23 sets the pump 2 to a smaller output. A transistor amplifier 42 which controls a electro-magnetically operated valve 48 is fed with the voltage difference and has a potentiometer 46 arranged so that the transistor amplifier responds to a voltage difference corresponding to the load current of the motor 1 which is close to but does not exceed the breakdown torque of the motor. Operation is such that if the machine suddenly moves into a solid heading at high speed, the valve 48 is operated to feed fluid from the control circuit to the piston 23 which substantially instantaneously sets the pump 2 to its idling position. Fluid from the working circuit may be passed by the valve 48 in place of that from the control circuit for operating the piston 23.