Patent GB-861338-A (GB)
Title: Hydraulic control system for controlling the speed of a driven apparatus
IPC: G05D13/00
Filed: 1958-04-14
Abstract: 861,338. Fluid-pressure servomotor-control systems. SUNDSTRAND CORPORATION. April 14, 1958 [June 26, 1957], No. 11754/58. Class 135. An hydraulic servomotor-control system for controlling the speed of driven apparatus, complising a speed control movable by liquid under pressure to vary the speed of the apparatus, includes a first liquid pressure control means responsive to speed of the apparatus for regulating the liquid pressure delivered to the speed control, and a second liquid pressure control means responsive only to extremes of speed of the apparatus for reducing the liquid pressure delivered to the speed control independently of the first liquid pressure control means. As shown, a pair of pumps 20, 21, Fig. 1, deliver pressure liquid jointly through a duct 22 and filter 23 to branches 24, 25 supplying pressure liquid to an hydraulic transmission 10 and first and second piston valves 31, 65 responsive respectively to primary and secondary speed governors 26, 28 driven through gearing 37, 78 by the output of the transmission. The transmission 10 comprises a rotatable barrel, axial piston wobbler type pump, pumping liquid under pressure into a rotatable axial piston hydraulic motor. The primary governor 26 which includes centrifugal weights 30 and a speeder spring 35 adjustable by a rack and pinion 36 responds to speeds over the normal operating speed range of the transmission. An increase in speed above the desired value moves the piston valve 31 to direct pressure liquid through a line 32 into a chamber 12 of a speed control and exhaust pressure liquid from a chamber 13 thereof through a line 33a, a trip valve 40 and a line 33 to a drain line 34 so that pistons 14, 15 actuate a lever 16 to adjust the inclination of the wobbler plate to reduce pump output and hence speed of the motor. Alternatively, a decrease in speed causes the piston valve 31 to direct the pressure liquid so that the pistons 14, 15 move leftwardly to increase the pump output. The secondary governor 28 includes centrifugal weights 64, Fig. 2, pivotally connected to the piston valve 65 and a rotatable ported sleeve 61 driven by a drive shaft 62 and formed with a cup-like member 63 in which the weights are mounted. Should there be a failure of the primary governor due, e.g. to the breakage of the drive shaft causing it to slow down or stop, the valve 31 positions itself so that the pistons 14, 15 would be moved to increase pump output and motor speed which could cause destruction of the transmission. To overcome this the secondary governor 28 also slows down or stops to allow rightward movement of the piston valve 65 so that a passage 51 connected to the trip valve 40 is connected to drain through ports 69, 70 and a line 71 and the spool 43 of the valve 40 moves leftwardly, connecting the chamber 13 to drain through the line 33a and a port 46. The wobbler plate then moves to reduce pump output and hence motor speed. Should, on the other hand the primary governor fail, causing it to overspeed, the increased speed of the secondary governor moves the flyweights 64 to move the piston valve 65 to connect the branch 25 through a port 27 to a space between the piston valve and a spring-loaded valve 90 controlling drain ports 72. At the same time the passage 51 is connected to drain through port 69, slant valve passage 77 and valve passages 83, 84 so that the pistons 14, 15 again move the wobbler plate to reduce pump output. The valve 90 regulates the amount of opening of the ports 72 in accordance with the pressure in the space between it and the piston valve 65 to maintain pressure in the branch 25. On a predetermined minimum speed being reached, a pressure switch 75 connected by a line 74 to the piston valve 65 is operated to establish electrical connection to an alternator driven by the transmission.