US2126533A - Hydraulic governing mechanism - Google Patents

Description

wig- 1938 R. J. CAUGHEY HYDRAULIC GOVERNING MECHANISM Filed April 10, 1935 Inventor" Reed J. Caughe Hi Attorney.

Patented Aug. 9, 1938 UNITED STATES HYDRAULIC GOVERNING MECHANISM Reed J. Caughey, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 10, 1935, Serial No. 15,595

Claims.

The present invention relates to hydraulic governing mechanisms for prime movers such as are used for controlling the flow of elastic fluid to turbines in response to speed changes. More specifically, the invention relates to the kind of hydraulic governing mechanism in which-a speedresponsive device includes a positive displacement pump driven by the prime mover or turbine. In arrangements of this kind, in which the positive displacement pump is connected to a pilot valve and a hydraulic cylinder to cause changes in pressure in an oil supply to the cylinder, 2. considerable time lag takes place between a change in speed and the response to such change by the hydraulic cylinder or motor for positioning the element to be controlled. This is due to the fact that a considerable change has to be effected in the displacement of oil or like actuating fluid by the positive displacement pump.

One object of my invention is to provide an improved construction and arrangement of hydraulic governing mechanism of the type above specified in which said time lag is considerably reduced. This is accomplished in accordance with my invention by the provision of means connected between the positive displacement pump and the usually provided relay or pilot valve and the hydraulic cylinder or motor whereby a slight change in the amount of oil discharged by the positive displacement pump is suflicient to cause a considerable movement. of the hydraulic cyl- I pendent of the action of the automatic controlmechanism and under other conditions prevents manual control or renders-such manual control ineifective.

Still another object of my invention is to provide an improved trip mechanism for eifecting closing of a controlled element such as a valve when the bearing pressure of a prime mover or turbine drops to a certain minimum value.

For a better understanding of what I believe to be novel and my invention, attention is directed to the following description and the claims appended thereto in connection with the accompanying drawing which forms a part of my specification.

The single figure of the drawing illustrates somewhat diagrammatically a hydraulic governing mechanism for a prime mover embodying my invention.

A prime mover, in the present instance an elastic fluid turbine, I0 has an inlet connected by a conduit II to a valve chest l2. The latter is connected toa conduit l3 with a valve I4 for conducting elastic fluid to the chest l2. The valve 'chest includes a valve or valve member i5 for controlling the flow of elastic fluid from the chest to the turbine. The valve member l5 has a stem I6 with a hand wheel l'l secured thereto. A screw-threaded portion of the stem i6 is engaged by a nut l8 which in turn ispivoted to an intermediate point of a lever I 9 connected at its righthand end to a fulcrum 20 and at its left-hand end to an automatic control mechanism as will'be described hereinafter. I

Let us assume for the moment that the lefthand end of the lever I9 is fixed. Under this condition the valve 15 may be opened and closed manually by the actuation of the hand wheel ii.

Let us'now assume the valve l5 closed and the left-hand end of the lever l9 biased in upward direction. Under such condition the valve l5 cannot be opened manually because turning of the hand wheel H to cause opening of valve l5 would be compensated by upward movement of the lefthand end of the lever Ill. The arrangement, as will be more fully described hereinafter, is such that manual control is rendered ineffective as long as the automatic control mechanism calls for complete closing of the valve.

The automatic control mechanism comprises a positive displacement pump 2!. It has an element secured to and driven by a shaft 22 forming a part of the turbine rotor. The pump has a suction conduit 23 and a discharge conduit 24, including a relief valve 24a. In the present instance the suction conduit receives oil from a conduit 25. The conduit '25 receives oil under pressure by the action of another positive displacement pump '26 which may be driven at constant speed by a motor 21. The conduit 25 is connected to the turbine bearings and includes an oil cooler 28 for cooling the oil supplied to the bearings. The flow of oil through' the positive displacement pump 2| changes in response and in proportion to speed changes. Hence, this pump constitutes a speedresponsive means. Its discharge conduit 24 is connected by a conduit 29. including a needle valve 30' to the conduit 25 ahead of the oil cooler 23 as regards the direction of flow in the conduit 25. The needle valve 30 serves for speed adjustment of the governing mechanism. The conduit 24 is also connected by a conduit 3| to a pressureresponsive device 32, which latter includes a cylinder 32a and a piston 33 movably disposed in the cylinder .and connected to a stem 34.

In the ordinary hydraulic governing mechanism this pressure-responsive device 32 with its stem 34 is either directly connected to the element to be controlled, in the present instance the valve l5, or is connected thereto through the intermediary of a pilot valve and a hydraulic cylinder. A pilot valve 35 having a casing 35a. and a hydraulic cylinder 36 are also provided in the present instance. The hydraulic cylinder 36 includes a piston 31 secured to a stem 38 which stem is connected at its upper end to the left-hand end of the lever l9 and at its lower end to the right-hand end of a lever 39 having an intermediate point 40 which for the present we may consider as being fixed, and a left-hand end connected by a rod 4| to a lever 42. The lever has a right-hand end connected to a valve stem 43 of the pilot valve 35. The pilot valve casing 35a is connected by a conduit 44 to the oil supply conduit 25. v

During operation, downward movement of the pilot valve stem 43 uncovers a port connecting the pilot valve to the cylinder 36 whereby oil is forced into the cylinder and causes downward movement of the piston 31 against the biasing force of a compression spring 45 disposed in the cylinder. Downward movement of the piston 31 eifects opening movement of the valve 5 and it also causes in well known manner through the lever 39 which latter may be termed a change motion lever" and the rod 4| restoring of the pilot valve to its original position in which the pilot valve stem with its heads covers the port to the hydraulic cylinder.

An increase in speed of the turbine l0 causes an increase in pressure in the conduit 3| and in the upper part of the cylinder 32a resulting in downward movement of the piston 33. Thus, regulation of the turbine valve 5 could be efiected by connecting the piston stem 34 to the pilot valve stem 43. In such an arrangement the piston 33 of the pressure-responsive device would have to move a considerable distance, that is, a considerable additional supply of oil into the pressure-responsive device 32 would have to be effected in case of considerable speed changes to cause considerable movement of the pilot valve 35 and the hydraulic motor 36. The resulting time lag of this kind of governing mechanism is considerably reduced in accordance with my invention by the provision of auxiliary means connected between the pilot valve 35 and the pressure-responsive device 32.

The left-hand end of the lever 42 in the embodiment of my invention shown in the drawing is connected to a stem 46 carrying at its lower end a piston 41 movably disposed in an auxiliary hydraulic cylinder or motor 43. The hydraulic cylinder 49 has upper and lower portions connected by conduits 49 and 5|) to an auxiliary pilot valve 5 I. The latter has a casing integrally formed with the cylinder 32a of the pressure-responsive device 32 and a valve stem 52 secured to or forming a continuation of the stem 34. The pilot valve casing is connected by means including a conduit 53 to the oil supply conduit 25. A branch conduit 54 of the conduit 53 serves to supply oil or like actuating fluid to the space formed below .the piston 33. The upper end of the stem 34 of the pressure-responsive device 32 is connected to the left-hand end of a lever 55 which has an intermediate point secured to a fulcrum 55 and a righthand end secured to the upper end of a tension spring 51. The lower end of the tension spring 51 is' secured by a nut 53 to the stem 46 of the piston 41. Another tension spring 59 is secured at its lower end by a nut 60 to the piston stem 34 and at its upper end to a fixed support 6|. In the present instance the support 6| is securely held on to the upper end of the casing 32a of the pressure-responsive device 32 and forms'in turn a support for the fulcrum 58. It is to be noted that both springs 51 and 59 are under tension. The tension of these springs, together with the pressure exerted on the lower surface of the piston 33 constitute a force tending to move the piston 33 upward. This force is normally compensated by the force exerted on the piston in downward direction by the oil pressure from conduit 3| in the upper part of the casing 32a of the pressure-responsive device 32.

The operation of the arrangement is as follows: Let us assume that the various elements are in balanced condition in the position indicated in the drawing. If now the speed of the turbine increases, the flow of oil discharged by the positive displacement pump 2| increases directly with the speed of the turbine. This increase in flow can only be passed through the fixed area of the needle valve 30 by an increase in pressure, which pressure will increase in response to the square of the flow and, therefore, the square of the speed. Hence, an increase in turbine speed causes an increase in pressure on the upper surface of the piston 33 of the pressure-responsive device 32 in proportion to the square of the speed. Due to the fixed loadings of the tension springs 59 and 51, this increase in pressure causes a downward movement of the piston 33 and the pilot valve stem 52 attached thereto. The pilot valve heads secured to the pilot valve stem 52 then uncover their ports and permit the supply of oil through conduit 49 to the upper space in the cylinder 43, and the discharge of oil from the lower space in the cylinder through the conduit50. This causes downward movement of the piston 41 and its stem 46, which movement causes further tensioning of the spring 51, thus imposing an additional load on the piston 33 of the pressure-responsive device. If the increase in loading of the piston 33, due to the increased tensioning of the spring 51, is suflicient to balance the increased oil pressure on the piston 33, then the piston 33 will stop, leaving the oil supply connected to the top of the piston 41.

If, however, the speed and therefore the oil pressure continues to increase, then further movement of the piston 41 will cause further loading of the piston 33 through increased tensioning of the spring 51 and hold the piston 33 stationary so that a constant opening of the pilot valve 5| is maintained. It is important to note that the piston 41 can make its full stroke while piston 33 is sfiitionary and while the pressure on piston 33 is increasing. Ii now the speed, and therefore the pressure, stops increasing, a slight additional movement of the piston 41 causes loading of the piston 33 suiiicient to move said piston 33 upward to a point where the pilot valve 5| resumes its original position in which the pilot valve heads cover their respective ports. As this takes place, movement of the piston 41 stops.

Downward movement of the piston creams upward movement of the pilot valve stem 43, permitting the discharge of oil from the hydraulic cylinder 36, resulting in upward movement of the piston 31 and closing movement of the valve l5. Thus, it will be readily understood that with my hydraulic governing mechanism a movement of the piston 41 is obtained which is proportional to the speed of the turbine and which movement is effected'by a slight movement of the piston 33. The latter may be termed a governor piston. This slight movement 01' the piston 33 may be effected by a small quantity of oil from the oil Dump. This considerably reduces the time lag depending upon whether an increase or a decrease respectively of the turbine speed takes place. The device 32 is not a pressure-responsive device in the ordinary sense. It is pressure-responsive in so far as movement of the .piston 33 takes place in response to a change in pressure in the line 3|.- A further increase in pressure or,'from another viewpoint, a continued increase in pressure, however, does not cause an additional or further movement of the piston 33 but causes,

through the pilot, valve 5i and the auxiliary cylinder 43 withits piston 41, tensioning of the spring 51, that is, further loading of the piston 33. Looking at the device from another viewpoint, in an ordinary pressure-responsive device, continued increase in pressure causes continued movement of such pressure-responsive device. In this particular device 32 the initial pressure change only causes movement of the pressureresponsive device, whereas the continued or further pressure change causes tensioning or loosening of the spring or springs, that is, loadingor unloading of the device. The device depends only on increments of pressure changes due to changes in speed of the pump 2| and does not depend on changes in oil pressure due to speed changes of the other pump 26 because the lower side of the piston 33 is subject to the pressure in the conduit 25. Hence, pressure changes in this, conduit will equally affect both the upper and the lower side of the piston 33.

As stated above, under certain conditions the valve l5 may be operated manually by the wheel l1. This operation is possible only as long as there is suflicient oil pressure in the cylinder 36 to resist movement of the piston 31 by the action of the compression spring 45. The valve l5 connot be opened when it is completely closed by the action of thepiston 31,-because in this case no oil pressure is exerted on the upper face of the upper side of the piston 31 and manual opening of the valve I5 is compensateddue to upward movement of the piston 31 by the action of the spring 45.

Means are provided in accordance with my invention for tripping or closing the valve l5 when the pressure in the conduit 25 drops to a certain minimum value. The conduit 25, as stated above, serves to conduct oil under pressure to. the bearings. In order to keep the bearings properly lubricated and safeguard them it is desirable to supply oil or like lubricant under a certain pressure and to stop operation of the turbine in case this pressure drops to a certain minimum value. This means, which may be termed a low oil pressure trip mechanism, comprises a lever 62 which has an intermediate point supported on a fulcrum 33 and is connected at its left-hand end to the intermediate point 40 of the lever 38 and at its right-hand portion to a steam 64 which latter is secured to a washer 65. The washer is loaded by a compression spring 66 intermediate the washer and a fixed support 61. A latching collar 68 secured to the stem 64 is engaged by a lever 69 which latter has an intermediate point connected to a fulcrum 10 and a right-hand end pivotedto a stem 1|. The lower end of the stem H is fastened to a piston 12 slidably arranged in a cylinder 13 and biased downward by a compression spring 14. The biasing force of the compression spring is normally compensated by oil pressure in the lower space of the cylinder 13, which space communicates through a. pipe 15 with the conduit 25. When the bearing oil pressure drops to a certain minimum value, the piston 12 is forced downward by the action of the spring 14. This causes unlatching of the collar 38, whereby the stem 64 with the piston 65 are moved downward by the action of the compression spring 66. This in turn causes clockwise turning movement of the fulcrum lever 62, resulting in upward movement of the-pilot valve stem 43 and consequently upward movement oi the piston 31 in the hydraulic cylinder 36, thereby effecting closing of the valve 15. Return of the bearing oil pressure will restore the piston 12 to its upper position but will not effect opening of the valve l5 until the latch collar 63 is raised by the operator. To this end, the lever 62, which may be termed a resetting lever, has

a right-hand extension or handle 16.

As stated above, the speed of the turbine may be adjusted by adjustment of the needle valve 30. In case the governing mechanism is to be used as an over-speed device, the speed-adjusting needle valve 30 is placed in wide open or high speed position. I

Having described themethod of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent 01! the United States is:

l. A prime mover including the combination of a control element for controlling the supply of fluid to the prime mover, and a governing mechanism for positioning the control element in response to speed changes of the prime mover, said governing mechanism including a cylinder having a. first piston with a stem therein, a positive displacement pump driven by the prime mover and connected to one side of said piston, an auxiliary cylinder with a second piston, means including a stem for connecting the second piston to the control element, means including another pump independent from the positive displacement pump and a pilot valve connected to the first piston for conducting actuating fluid to the auxiliary cylinder, and other means for loading the first piston to counteract further pressure changes after an initial movement of the first piston in response to movement of the second piston com- 70 prising a fulcrumed lever having one end conchange and the response thereto by the auxiliary piston.

2. A governing mechanism including the combination of a pressuresresponsive device having a movable member, a positive displacement pump for forcing fluid at variable pressure into said device, a motor, means including a source of fluid under pressure independent from the pump for actuating the motor in response to movement of the movable member, and means for reducing movement of the movable member during pressure changes in response to movement of both the pressure-responsive device and the motor, said pump having an inlet connected to said source.

3. A governing mechanism including the combination of a positive displacement pump, a pressure-responsive device having a movable element and being connected to the pump to eflect movement of the element in response to speed changes of the pump, a motor, means including a source of fluid under pressure independent from the pump for actuating the motor in response to movement of said element, means for reducing movement of said element during pressure changes in response to movement of the motor, said pump having an inlet connected to said source, and a by-pass with an adjustable valve for the pump.

4. A governing'mechanism including the combination of a positive displacement pump subject to varying speed, a pressure-responsive device having a movable element and being connected to the pump, a hydraulic motor having a piston, a source of fluid under pressure independent from the pump. a pilot valve moved by the pressure- -responsive device for controlling the flow of actuating fluid from the source to the hydraulic motor, and means for reducing the amount of fluid to be forced into the pressure-responsive device during sudden considerable load changes comprising a lever, a fulcrum supporting a central portion of the lever, means connecting one end of the lever to the movable element and a spring connecting the other end of the lever to the piston to reduce the time lag between the pump and the motor.

5. A governing mechanism including the combination of a pressure-responsive device having a movable element, pumping means responsive to speed changes of an engine to be controlled for forcing fluid into the pressure-responsive device, a motor, a source of fluid under pressure independent from the device and connected to the motor, means for controlling the flow of fluid from the source to the motor in response to move-' ment of said element, biasing means normally holding said element in a fixed position against the force exerted thereon by the fluid-pressure of the pumping means, and means increasing the biasing force on said element in response to movement of the motor to reduce the time lag between 30 the device and the motor.

REED J. CAUGHEY.

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