US2237799A - Hydraulic governing mechanism - Google Patents

Description

April 8, 1941. N NEST 2,237,799

HYDRAULIC GOVERNING MECHANISM Filed Jul 7, 1939 Fig. I. I Fig.2.

Inventory Francis H.Van Nest,

His Attorney- Apr. 8, 1941 2,237,799 HYDRAULIC GOVERNING MECHANISM Francis H..Van Nest, Saugus, Mass., assignor to General Electric Company, a corporation of New York Application July 7, 1939, Serial No. 283,215

- The present invention relates to hydraulic gov- 4 Claims.

erning mechanisms comprising a hydraulic motor and a pilot valve for controlling the flow of operating fluid to the motor. In arrangements in which the pilot valve is connected to a speed governor, it is often subject to continuous vibrations known as bobble. This causes frequent slight movement of the pilot valve and is transmitted through the hydraulic fluid to other parts of the governing mechanism which is undesirable as it may lead to excessive wear of governor and relay parts.

The object of my invention is to provide an improved construction and arrangement of hy-,

draulic governing mechanisms whereby the bobble effect on the pilot valve is substantially reduced. This is accomplished in accordance with my invention by the provision of a pilot valve which has a valve head forming together with its housing or bushing a small dashpot. In a preferred arrangement this dashpot is supplied with operating fluid in the form of leakage from the pilot valve chamber.

For a better understanding of what I consider to be novel and my invention, attention is dirooted to the following description and the claims appended thereto in connection with the accom panying drawing.

In the drawing Fig. 1 illustrates a sectional view of a hydraulic governing mechanism embodying my invention, and Fig. 2 is a modification of a part of Fig. l.

The arrangement comprises a hydraulic motor it having a casing II with a piston l2 movably disposed therein and biased downward by a compression spring l3. The piston |2 has a stem l4 connected to a governor lever l5. Operating fluid, such as oil, is admitted to the lower portion of the cylinder and leakagefluid may be drained from the upper portion of the cylinder through a drain channel I611. The flow of operating fluid to the cylinder and the draining of fluid therefrom is controlled by a pilot valve H which has a casing l8 integrally formed with the casing II and enclosing a pilot valve bushing l9 which in turn encloses pilot valve heads 20, 2| connected to and integrally formed with a stem 22. The pilot valve bushing l9 forms ports 23 and 24 which in the present instance are covered by the pilot valve heads. Operating fluid, such as oil under pressure, is conducted to the pilot valve by a pipe 25 connected to a channel 26 in the casing II.

If the pilot valve heads are movedupwards, oil under pressure may flow from the channel 26 through the port 23 of the pilot valve and the port l6 of the hydraulic motor into the lower portion of the cylinder II. If the pilot valve heads 20, 2| are moved downward, oil may be drained from the hydraulic cylinder through its port It and the port 24 of they pilot valve.

The bushing I9 of the pilot valve is pivotally connected to the governor lever I5 and the pilot valve heads 20, 2| are connected at their lower ends to a speed governor 21 by means including a link 28 and a spring 29. The governor 2'! may be driven by the shaft of a steam turbine, not shown, and'in the present instance the governor is enclosed in an oil tank 30.

As stated before, during operation the weights of the speed governor may be subject to continuous slight movements known as bobble and.

this bobble is transmitted to the pilot valve, thereby causing continuous movement of the latter. To eliminate or dampen such movements I provide in accordance with my invention a dashpot between the pilot valve head 20 and the bushing Hi. In the present instance such dashpot is partly formed by the bushing I9 and the head 20. The space formed in the bushing l9 above the head 20 is divided by a disk or partition 3| into two chambers 32 and 33. The disk 3| is biased towards a shoulder formed by the bushing I9 by a spring 34, which latter bears at its upper end towards a plug 35 screwed into an opening in the upper end of the bushing. The disk 3| has a central opening 36 forming a small clearance with a reduced extension 31 of the valve head 20. The extension projects somewhat beyond the disk 3| into the chamber 33. The pilot valve heads 20, 2| and the extension 31 have a central bore 33 connecting at its lower end to lateral ports 33 through which fluid may be drained from the chamber 33. The chamber 32 forms a dashpot chamber. Operating fluid, such as oil, is supplied to the chamber, in the present instance in the form of leakage from the supply channel 26 along the small clearance formed between the adjacent surfaces of the valve head 20 and the bushing l8. During operation the dashpot chamber 32 fills completely with leakage fluid and the chamber 38 this with fluid up to the upper end of the extension-21, excess fluid being drained from the chamber 33 through the bore 33 and the ports 33 in the valve heads 20, 2|. The body of fluid. contamed in the dashpot chamber 32 reduces or dampens slight vibratory movements of the valve head 20. During slight upward movement of the valve head 20, fluid from the chamber I:

is forced through the small clearance formed be tween the extension 3! and the disk M, excess fluid in the chamber 33 passing through the overflow formed by the hollow extension It into the bore as. The small clearance between the extension 3'! and the disk 3! oifers a resistance to sudden changes of flow of fluid therethrough and thereby causes an increase in pressure in the chamber 33 which retards or dampens upward movement of the head it. Likewise, downward movement of the head 2t creates a vacuum in the dashpot chamber 32 because of the resistance formed by the small clearance to the flow of fluid from the chamber 33 into the chamber 82,

During normal operation of the mechanism, illcrease in speed causes downward movement of the valve head 25, thus permitting the draining fluid from the cylinder it, causing downward movement of the piston 132 by the action of the spring 83 which in turn causes turning move= ment of the governor lever 5. The governor lever 25 effects downward movement of the bushing it}, thereby restoring the latter to its original relative position 'to the pilot valve head at.

The normal operation of the mechanism is little afiected by the provision of the dashpot above the pilot valve head it. As soon as the pilot valve starts to move in either direction the response of the piston it causes the bushing to move in the same direction. Thuson a normal speed change the pilot valve only moves a few thousandths of an inch before the bushing starts to follow at the same rate. Whenever the pilot valve and bushing are moving at the same" rate, no damping of the pilot valve movement tahes place since there is no relative motion-between the pilot valve head and the bushing. During normal speed change the pilot valve head is slowed up for only the first few thousandths of an inch by the dashpot and thereafter the move" ment of the valve head is no longer aflected because of the simultaneous movement of the hushing in the same direction.

The bobble usually occurs at a frequency equal to the running speed of the governor which in many cases is about 600 R. P. M. While the piston ii of the hydraulic motor can 'follow this frequency it cannot do so exactly in phase with the pilot valve, thus causing relative motion between the pilot valve head arifd bushing and damping of the movement of the pilot valve head by the dashpot action. 4

The modification of Fig. 2 comprises a pilot valve casing 4| corresponding to the casing 58 of Fig. 1 and enclosing a bushing 42 which in turn encloses a pilot valve head 43 corresponding to the valve head 20 of Fig. l. The upper end of the bushing is pivotally connected with a governor lever 44 corresponding to 'the lever of Fig. 1. In order to dampen bobble of the head 43, the upper portion of the-bushing 42 is provided with a partition 45 dividing the space formed by the bushing and the head 48- into two chambers communicating through a. small opening 48 in the partition 45. .During operation, the

chamber 46 fills completely with leakage fluid passing along the valve head 43 and the chamber of flow of fluid ofiered by the small opening 88, I

thus dampening sudden vibratory movements of the pilot valve head til, or from another view point, reducing or dampening the transmission of bobble from a governor to the pilot valve head 33.

Having described the method 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 of the United States is:

l. Hydraulic governing mechanism comprising a hydraulic motor, a governor subject to vibration during operation, a pilot valve having a valve head connected to the governor for controlling the flow of operating fluid to the motor and a bushing connected to the motor, the bushing and the valve head defining a space, and means including a stationary disk having an opening located in the space and separating the space into two chambers communicating through the opening to form a dashpot to reduce the transmission of vibration from the governor to the pilot valve.

2. A pilot valve comprising a casing, a bushing having ports enclosed in the casing, a valve head for connection to a governor enclosed in the bushing in cooperative relation with the ports, means including the valve head and the bushing and a stationary disk with a. small opening to form a dashpot for reducing the transmission of vibration from such governor to the valve head.

'3. A pilot valve comprising a pilot valve head for connection to a governor, a bushing enclosing the head and forming a space therewith, means including a disk having a central opening located in the space and defining a dashpot chamber and a drain chamber, the head having a hollow extension projecting through an opening in the disk into the drain chamber and forming a small clearance with the opening to reduce vibration of the head due to bobble of such governor.

4. A pilot valve including a valve head, a bushing enclosing the valve head and having ports controlled by the head, the bushing having a. partition with a small opening to form two chambers, one chamber being partly defined by the head and constituting a dashpot chamber and the other chamber being completely defined by the bushing and having a drain port, a small opening in the partition restricting the displacement otiiuid between the two chambers during operation and thereby dampening vibration of the head. Y

'-' FRANCIS H. VAN NEST.

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