US2922429A

US2922429A - Overspeed prevention means for turbines

Info

Publication number: US2922429A
Application number: US612603A
Authority: US
Inventors: William D Whitaker
Original assignee: Garrett Corp
Current assignee: Garrett Corp
Priority date: 1956-09-28
Filing date: 1956-09-28
Publication date: 1960-01-26
Anticipated expiration: 1977-01-26
Also published as: GB837833A; FR1183475A

Description

Jan. 26, 1960 w. n. WHITAKER 2,922,429

OVERSPEED PREVENTION MEANS FOR TURBINES Filed Sept. 28, 1956 2 sheets shaet 1 IO 22 0 20 24 as 2e h H n 38 a 2 43 b la 3 as J:

WILLIAM 0. WHITAKER,

INVENTOR.

Jan. 26, 1960 w. D. WHITAKER ovsaspmsn PREVENTION ms FOR mamas 2 Sheets-Sheet 2 Filed Sept. 28, 1956 WILLIAM D. WHITAKER,

INVENTOR.

BY #11. M,

United States Patent OVERSPEED PREVENTION MEANS FOR TURBINES William D. Whitaker, Phoenix, Ariz., assignor to The Garrett Corporation, Los Angeles, Calif., a corporation of California Application September 28, 1956, Serial No. 612,603

8 Claims. (Cl. 137-27) The present invention relates to an overspeed prevention means for turbines and, more particularly, to an overspeed prevention means for turbines operable by elastic fluids.

In the operation of turbines using an elastic motive fluid there is a tendency for the turbine to overspeed when it becomes unloaded, due to a lack of proper control or, due to breakage of mechanism which applies a load to the turbine.

Turbines motivated by elastic fluids are generally high speed, low torque machines, and usually transmit power through a power takeoff member commonly known as a quill shaft. A quill shaft is generally employed to inter-connect the turbines and a reduction gear train to which the load is connected.

These gear trains may have several power takeoff elements arranged to drive various equipment such as generators, hydraulic pumps and turbine control devices. In the event a quill shaft breaks due to fatigue or an undue load increase imposed thereon, turbine control devices driven by the reduction gear train are then incapable of sensing actual turbine speed. Under such conditions, the control devices can not correct an overspeeding condition of the turbine, whereupon it reaches run-away speed and disintegrates, thereby damaging or injuring surrounding structures or nearby personnel.

Heretofore, various attempts have been made to provide turbine overspeed prevention devices which might properly maintain control of a turbine in accordance with the speed of its supporting shaft.

Accordingly, it is an object of the invention to provide an overspeed prevention means for turbines wherein a speed responsive pneumatic valve is directly operable by a turbine and whereby the turbine supporting shaft conveniently may drive a power takeoff or quill shaft from its end which extends away from the turbine.

Another object of the invention is to provide an overspeed prevention means for turbines including a hollow turbine supporting shaft, internally of which a speed responsive pneumatic control valve is located for response to an overspeeding condition of the turbine.

Another object of the invention is to provide an overspeed prevention means for turbines which will not be disabled by the failure of a power takeoff quill shaft or reduction gear train transmitting load to the turbine.

Another object of the invention is to provide an overspeed prevention means for turbines including a novel combination of a turbine having a hollow supporting shaft containing a speed responsive control valve therein, whereby a seal disposed peripherally of the shaft is utilized to conduct control pressure to an opening in the shaft which communicates with said speed responsive control valve.

A further object of the invention is to provide an overspeed prevention means for turbines, including a pneumatic turbine driven, speed modulating governor 2,922,429 Patented Jan. 26, 1960 ICC pneumatically coupled with a pneumatic overspeed sensing valve located in a turbine shaft, whereby one speed sensing device controls flow through said turbine during normal operation thereof, and another speed sensing device, located in the turbine shaft, is arranged to cause a reduction of flow through the turbine at the inception of an overspeeding condition thereof.

A still further object of the invention is to provide a small diameter pneumatic overspeed responsive control valve which is located directly in a hollow turbine supporting shaft; the extremities of the small diameter valve being near the axis of the turbine shaft, whereby its mass and balance are not critical for high speed operation of the turbine.

Other objects and advantages of the invention will be apparent from the following specification, appended claims, and accompanying drawings, in which:

Figure 1 is a diagrammatic view of a turbine shown partially in section having an overspeed prevention means of the present invention in connection therewith;

Figure 2 is an enlarged fragmentary sectional view of a portion of Figure 1 showing the construction of the overspeed sensing valve;

Figure 3 is an enlarged sectional view taken along line 33 of Figure 2 and showing the mounting of the flyweights of the overspeed sensing valve.

As shown in Figure l of the drawing, a turbine 10 is provided with a fluid inlet scroll 12 which communicates with a variable area nozzle 14 located at the periphery of the turbine. A pressure regulating and shutoff valve 16 communicates with the scroll 12 and is arranged to supply elastic fluid under pressure thereto. A shaft 18 supports the turbine 10 and is mounted in

bearings

20 and 22. The shaft 18 is hollow and is pro vided with an open end 24 extending away from the turbine 10.

Engaged internally in the open end 24, of the shaft 18, is a splined end 26 of a power takeoff quill shaft 28 which drives a reduction gear train in a gear case 30. Connected to the gear case 30 are accessories such as an alternator 32 and hydraulic pump 33. These accessories are driven by the gear train in connection with the power takeoff quill shaft 28. Also driven by the gear train in the gear case 30 is a pneumatic speed sensor 34 which is similar to that disclosed in a copending application of John K. Jackson, Serial No. 391,099, filed November 9, 1953, now Patent No. 2,858,839, dated November 4, 1958. and entitled Precision Pneumatic Speed Sensing Governor.

Disposed in the hollow shaft 18 is a speed respon- Sive, centrifugally operated valve 36 communicating with a control pressure conduit 38 via a conventional carbon seal 40 which is disposed peripherally of the shaft 18 and which communicates with the interior thereof, as will be hereinafter described in detail. The conduit 238 communicates with the speed sensor 34, a pressure responsive electrical switch 42, and a servo actuator 44. Actuator 44 is connected with and arranged to operate the variable area nozzle 14. Also communicating with the conduit 38 is a pressure regulator 46 which receives compressed air from a suitable supply via a tube 48 and delivers such air at regulated pressure to conduit 38. At the outlet of the pressure regulator 46 an orifice 50 restricts the flow of fluid under regu- Iated pressure to the control pressure conduit 38.

In operation, either the speed sensor 34 or the valve 36 is capable of venting fluid pressure downstream of the orifice 50, whereby a pneumatic signal is conducted to the pressure switch 42 and the servo actuator 44. During normal operation of the turbine 10, the speed sensor 34 modulates control pressure in the control pressure conduit 38 and thereby controls the variable area nozzle 14 by means of the servo actuator 44 in order to maintain a desired speed of the turbine 10.

In the event the power takeoff quill shaft 28 breaks and relieves the turbine of the load normally imposed by the alternator 32 and/or the hydraulic pump 33, the turbine tends to overspeed. Under such conditions, when the turbine 10 reaches a predetermined excessive speed, the valve 36 opens and vents fluid pressure from the control pressure conduit 38 downstream of the orifice 50.

When the valve 36 operates, it moves to a full open position, as will be hereinafter described, whereby pressure in the control pressure conduit 38 is rapidly reduced to a very low value. The pneumatic signal thus provided is suflicient to operate the pressure switch 42, which causes the valve 16 to move toward closed position and shut off motive fluid entering the turbine 10. Concurrently, the servo actuator 44 also closes the variable area nozzle 14, which also tends to reduce flow through the turbine 10.

As shown in Figure 2 of the drawing, the control pressure conduit 38 communicates through a passage 39, in the seal 40, with an opening 41 in the side wall of the shaft 18. This opening 41 communicates directly with the valve 36, which is arranged to vent pressure outwardly through an opening 43 in the side wall of shaft 18, as will be hereinafter described in detail.

Referring to Figure 2 of the drawing, it will be Seen that the valve 36 is provided with a body 52 having a poppet valve seat 54 in one end thereof, adjacent to the opening 41 in the turbine shaft 18. Engaging the seat 54 is a poppet valve member 56 having a stem 58, which is axially aligned with the turbine supporting shaft 18. Secured to the stem 58 is a spring 60, which tends to hold the poppet valve member 56 tightly engaged with the seat 54.

A plug 62 is axially screw threaded into the valve body 52; and rotatably mounted in the plug 62 is a swivelling spring supporting member 64, to which one end of the spring 60 is connected. Tension of the spring 60 may be adjusted by screw threadably adjusting the plug 62 in the valve body 52 while the swivelling spring support 64 is prevented from rotating, thereby preventing a tendency of the plug 62, when rotated, to create torsional stresses in the spring 60. Pivotally mounted in the valve body 52 on pins 66 and 68 are

flyweights

70 and 72, respectively. These

flyweights

70 and 72 are provided with arms 74 and 76, respectively, which engage a shoulder washer 78 located on a reduced diameter portion 80 of the valve stem 58. The

flyweights

70 and 72 tend to move outwardly, as indicated by arrows 83 and 84, when the shaft 18 of the turbine reaches a predetermined speed, whereby the arms 74 and 76 exert force on the shoulder washer 78 toward an opening direction of the valve element 56.

It will be noted that control pressure in the conduit 38 is normally imposed on the head 82 of the poppet valve member 56, tending to hold the same on its seat 54. In addition, the spring 60 also tends to hold the poppet valve member 56 on its seat 54. When centrifugal forces acting on the

flyweights

70 and 72, in the direction of the arrows 83 and 84, become great enough to overcome the combined force of pneumatic pressure on the head 82 of the poppet valve member 56 and tension of the spring 60, the poppet valve member 56 opens with respect to the seat 54. As the poppet valve member opens, pneumatic pressure on the poppet head 82 becomes balanced, whereby a slight opening of the valve member 56 causes it to snap to full open position. Full venting capacity of the opening 41 through the valve 36 and the opening 43 is thus provided for bleeding down pressure in the control pressure conduit 38. This function, as hereinabove described, causes a closing action of the valve 16 and the variable area nozzle 14, thereby reducing speed of the turbine 10.

When speed of the turbine 10 is thus reduced a predetermined amount, centrifugal forces acting on the

flyweights

70 and 72 are overcome by force of the spring 60, which closes the valve member 56 with respect to the seat 54, thereby automatically reseating the valve 36 for a subsequent operation, in the event an ovcrspeeding tendency of the turbine 10 again occurs.

From the foregoing, it will be apparent that the overspeed prevention means, according to the present invention, is arranged directly to sense speed of the turbine supporting shaft which, at its extending end, drives a power take-off quill shaft. It will be noted that the disposition of the speed responsive pneumatic valve 36 in the turbine supporting shaft 18 permits pneumatic control fluid to communicate with the interior of the shaft near the turbine, while the extending end of the shaft conveniently is utilized as a driving connection for the power takeofl quill shaft 28.

The small diameter and nominal mass of the pneumatic valve 36 in the turbine supporting shaft is not critical to the balance of the turbine when operating at high rotational speeds.

Various modifications of the present invention may be resorted to in a manner limited only by a just interpretation of the following claims.

I claim:

1. A speed limiting device for an elastic fluid operated turbine comprising: a hollow shaft rotatably mounted to support the rotor of the turbine; fluid operated control means for varying fluid flow through the rotor; a governor for controlling the flow of fluid to said flow control means; a source of operating fluid for said flow control means; a centrifugally operated valve completely enclosed in said hollow shaft; a first opening formed in the side wall of said shaft communicating with one side of said valve, the opposite side of said valve communicating with a second opening formed in the side wall of said shaft, said second opening communicating with the atmosphere surrounding said casing; and means for connecting said first opening to said source of fluid pressure whereby pressure from such source will tend to retain said valve in a closed position, said valve being opened by centrifugal force to vent said source to the atmosphere when said turbine exceeds a predetermined speed of rotation.

2. A valve for controlling the application of operating fluid to a fluid operated governor system adapted to control the speed of a rotating body comprising: a hollow shaft rotatably mounted to support the rotating body; a valve body completely enclosed in said hollow shaft, said body having a valve seat formed thereon adjacent one end; a valve disc mounted in said valve body for movement along the axis of said shaft and adapted to engage said seat; flyweights pivotally mounted on said valve body to move said valve disc in one direction; resilient biasing means mounted in said valve body for moving said valve disc in the opposite direction; and means for connecting the source of fluid used for operating said governor system to said valve.

3. In a fluid operated turbine of the type having a rotor, the combination of: a rotatably mounted shaft for supporting the turbine rotor, said shaft having a hollow portion and a fluid passage; a transmission; a motiontransmitting connection between said shaft and said transmission; means responsive to the application of fluid pressure to control the admission of operating fluid to the turbine rotor; governor means operatively connected with said transmission and responsive to the speed of operation thereof to regulate the application of fluid pressure to said fluid control means; valve means wholly disposed in the hollow portion of said shaft to control fluid flow through the fluid passage therein, said passage communicating with said fluid control means; means wholly disposed in the hollow portion of said shaft and responsive to centrifugal force to cause said valve means to effect a predetermined operation of said fluid control means upon excessive increase in speed of the turbine rotor due to the failure of said motion-transmitting connection, said governor or parts of said fluid control means; and means for adjusting said centrifugal force responsive means to vary the shaft speed at which said valve means is actuated.

4. In a flu-id operated turbine of the type having a rotor, the combination of: a rotatably mounted shaft for supporting the turbine rotor, said shaft having a hollow portion and a fluid passage; a transmission; a motion-transmitting connection between said shaft and said transmission; a first means responsive to variations in fluid pressure applied thereto to control the admission of operating fluid to the turbine rotor; a second means responsive to a predetermined change in fluid pressure applied thereto to interrupt the admission of operating fluid to the turbine rotor; governor means operatively connected with said transmission and responsive to the speed of operation thereof to vary the fluid pressure applied to said first fluid control means; valve means wholly disposed in the hollow portion of said shaft to control fluid flow through the fluid passage therein, said passage communicating with said second fluid control means; and means wholly disposed in the hollow portion of said shaft and responsive to centrifugal force to cause said valve means to eflect the operation of said second fluid control means upon excessive increase in speed of the turbine rotor due to the failure of said motion-transmitting connection, said governor or said first fluid control means.

5. A speed limiting control for rotary devices comprising: a shaft with a hollow portion and inlet and outlet ports communicating therewith, said shaft being operatively connected with a rotary element driven in response to the application of motive fluid thereto; control means responsive to fluid pressure to govern the application of motive fluid to the element connected with said shaft; a valve seat provided in the hollow portion of said shaft between said ports; a valve element disposed in said shaft for movement relative to said seat to control fluid flow between said inlet and outlet ports, said valve element being disposed between said seat and said inlet port to be urged by fluid pressure toward said seat; means in said shaft responsive to centrifugal force to move said valve element away from said seat and establish communication between said inlet and outlet ports; and fluid pressure conducting means establishing communication between the inlet port in said shaft, said control means, and a source of fluid pressure.

6. A speed limiting control for rotary devices comprising: a shaft with a hollow portion and inlet and outlet ports communicating therewith, said shaft being operatively connected with a rotary element driven in response to the application of motive fluid thereto; control means responsive to fluid pressure to govern the application of motive fluid to the element connected with said shaft; a valve seat provided in the hollow portion of said shaft between said ports; a valve element disposed in said 6 shaft for movement relative to said seat to control fluid flow between said inlet and outlet ports, said valve element being disposed between said seat and said inlet port to be urged by fluid pressure toward said seat; resilient means also tending to urge said valve element toward said seat; means in said shaft responsive to centrifugal force to move said valve element away from said seat in opposition to the forces of fluid pressure and said resilient means; and fluid pressure conducting means establishing communication between the inlet port in said shaft, said control means and a source of fluid pressure.

7. In a speed limiting control for rotary devices: a shaft with a hollow portion and inlet and outlet ports communicating therewith, said shaft being operatively connected with a rotary element driven in response to the application of motive fluid thereto; a valve seat provided in the hollow portion of said shaft between said ports, said seat being concentric with the axis of rotation of said shaft; a valve element disposed concentrically with the axis of said shaft for movement relative to said seat to control fluid flow between said inlet and outlet ports, said valve element being disposed between said seat and said inlet port to be biased toward said seat by inlet port pressure; resilient means also tending to bias said valve element toward said seat; and flyweight means pivotally mounted in said shaft and operative in response to rotary movement of said shaft at a predetermined rate to move said valve element away from said seat in opposition to the forces of fluid pressure and said resilient means.

8. In a fluid operated turbine of the type having a rotor, the combination of: a rotatably mounted shaft for supporting the turbine rotor, said shaft having a hollow portion and inlet and outlet ports communicating therewith; a first means responsive to variations in fluid pressure applied thereto to control the admission of operating fluid to the turbine rotor; a second means responsive to a predetermined change in fluid pressure applied thereto to interrupt the admission of operating fluid to the turbine rotor; governor means operatively connected with said shaft and responsive to the speed of operation thereof to vary the fluid pressure applied to said first fluid control means; a valve seat provided in the hollow portion of said shaft between said ports; a valve element disposed in said shaft for movement relative to said seat to control fluid flow between said inlet and outlet ports, said valve element being disposed between said seat and said inlet port to be biased toward said seat by inlet port pressure; means in said shaft responsive to centrifugal force to move said valve element away from said seat and establish communication between said inlet and outlet ports; and fluid pressure conducting means establishing communication between the inlet port in said shaft, said governor, said first means, said second means and a source of fluid pressure, said governor normally causing moderate pressure variations in said conducting means, the valve in said shaft serving when opened to cause a drastic reduction in the pressure in said conducting means.

References Cited in the file of this patent UNITED STATES PATENTS 1,771,720 Miller July 29, 1930 1,985,773 Faber Dec. 25, 1934 2,270,306 Kalin Jan. 20, 1942 FOREIGN PATENTS 681,348 Great Britain Oct. 22, 1952