Patent GB-837908-A (GB)
Title: Improvements relating to fluid operated governors
Inventor: GREEN GEORGE WILFRID ACLAND
IPC: G05D13/00
Filed: 1957-04-29
Abstract: 837,908. Fluid-pressure servomotor control systems. GREEN, G. W. A., and FOX, G. B. March 11, 1958 [April 29, 1957], No. 13553/57. Class 135. In a fluid pressure governor for a prime mover adapted to use a flow of fluid proportional to the speed of the prime mover and having in the fluid flow-path a resiliently loaded valve B, Fig. 1, incorporating a variable orifice e.g. ports F, that sets up a variable back-pressure dependent upon the prime mover speed, the back-pressure being transmitted to a spring- loaded piston H connected to the torque-controlling member of the prime mover, not shown, the speed setting is effected by adjustment of the resilient load on the valve B. A pump A,A, Fig. 1, which is driven by the prime mover, delivers liquid via a conduit M to a cylinder C in which is the piston valve B loaded by an adjustable spring D; cylinder ports F permit the liquid to escape to an annulus O connected to the tank K. The back pressure caused by flow through the ports F is conveyed by a conduit N to the piston H. The ports F may be replaced by a parallel or tapered slot, or staggered row of ports; the valve B may have a tapered left-hand end. In a modification, a sleeve is interposed between the annulus O and ports F, which sleeve is connected by a crosshead to the adjustable spring abutment E to move therewith and may also be independently adjusted by a hand wheel. In another modification, the pump A,A, Fig. 6, is connected to cylinders V, G, the former housing a spring-loaded release valve W, which upon uncovering a port Y, enables the liquid to act upon the piston valve B as in Fig. 1; the back-pressure set up by the ports F is directed behind the piston H, the arrangement providing for " safe failure." The right-hand ends of cylinders G, C and V are connected in series with the tank. The rod L of piston H has a tapered portion 52, which as the rod moves rightwardly, permits an increasing quantity of pressure fluid to escape to the tank. In a further modification, the apparatus is arranged in casing, the pump A,A, Fig. 7, supplying the valve B via a space 2, and the outflow from the ports F passing to the tank through a space 3 and a spring-loaded valve 6. The pressure difference between spaces 2, 3 is applied across the ends of a valve L slidable in the rod 10 of a power piston 9, the rod 10 being connected by a stem 14 to a member 13 attached to the torque controlling member, the member 13 supporting a plate 12 loaded by springs 11. The valve L, which may be loaded by spring J that may be supplemented by a spring J1, controls ports 17, 18 leading to the right- and left-hand sides of the piston 9; a port 19 ensures that the left side of the piston 9 is always open to the tank. The piston 9 travels to the left when the valve L admits liquid from space 3 through ports 17, rightward piston occurs when the valve interconnects ports 17, 18, the piston movement ceasing when port 17 is again closed. Separate pumps may be used for the speed-sensing circuit and torque-controlling apparatus, respectively. The rod 10 incorporates a tapered port 54 to enable fluid to be by-passed from space 2 to the tank in greater quantities as the rod moves leftwardly. A stop is provided to hold the valve 6 partially open to ensure that the prime mover stops when required; a valve may be provided to interconnect space 3 and the tank. In another modification, isochronous governing is obtained by locating the ends of spring J in helical grooves, one set of grooves being on a pilot valve and the other set on the rod of a dash pot. A threaded or spring-loaded stop may be provided to limit the leftward motion of valve B and so prevent stalling. In a further modification, the gear pump is made larger than required and the excess fluid is by-passed through a valve under the control of a thermostat responsive to the temperature of the working fluid. In a still further modification, the adjustable abutment E, Fig. 10, comprises a hollow plunger partially closed by a diaphragm a through which slides a rod b attached to a piston c sliding in the plunger E and loaded by a spring d; the space between the piston and diaphragm opens to an annulus f via a port e which communicates through a restricted port g with the space 3, Fig. 7. The annulus f, Fig. 10, is also connected to the tank by a cock h so that with the latter closed pressure builds up and moves the piston c leftwardly until a shoulder k on the rod abuts the diaphragm whereupon the rod b and abutment E act as one. When the cock h is opened in response to prime mover lubrication failure or excessive temperature, for example, the abutment E moves to stop the prime mover or reduce its speed depending on the extent of opening of the cock. In a modification, the right end of pilot valve L, Fig. 7, is loaded by a spring J, Fig. 11, via a plate 24 and a rod 25 on a piston 21 in a ported cylinder 20 so that as the flow increases in space 3, with increasing speed, the pressure drop across the cylinder ports increases and a spring 22 is compressed so moving the piston 21 leftwardly until sufficient port area is exposed to enable the spring 22 to balance the drop across the ports whereupon the action of spring J is modified; the ports may be graded and ports may also be provided in the head of piston 21 so that no torque is exerted by the prime mover below a given speed. In another modification, the piston 21, Fig. 12, is placed elsewhere in the fluid circuit and actuates a bi-conical valve closure 44, 45 to obtain an output pressure through port 35 which is intermediate that in space 3 and the tank respectively connected to ports 42, 43, the port 35 transmitting this pressure to a piston which modifies the loading of spring J, Fig. 11. Specification 555,630 is referred to.