US2941601A

US2941601A - Fuel control

Info

Publication number: US2941601A
Application number: US476715A
Authority: US
Inventors: Stanley G Best
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1954-12-21
Filing date: 1954-12-21
Publication date: 1960-06-21
Anticipated expiration: 1977-06-21
Also published as: CH383692A

Description

June 2l, 1960 s, G, BEST FUEL CONTROL Filed Dao. 21,

PEOPLLEE C 0N 7 E 0L /NvENToR 0`gA/VLEV 6. BEST United States Patent O FUEL CONTROL Stanley G. Best, Manchester, Conn.,

Aircraft Corporation, ration of Delaware assigner to United This invention relates to controls for turbine type power'plants and more particularly to combined propeller pitch and fuel controls for turboprop power plants.

It is an object of this invention to provide a control which compensates for` the response time lag between propeller pitch change and fuel ow change during transient conditions.

It is a further object of this invention to provide a control of the type described which incorporates a droop type fuel control with a reset mechanism for the scheduled fuel flow so that the desired fuel flow is always achieved for steady-state conditons while permitting the propeller control' and fuel control to be separate and avoiding the necessity of the two controls tracking each other.

These and other objects of this invention will become readily apparentfrom the following detail description of the drawing which is a schematic illustration with some of the parts in cross section.

My copending patent application Serial No. 476,716, filed by Stanley G. Best, December 2l, 1954, now Patent 2,829,722, discloses a turboprop control system which utilizes a common r.p.m. sensing device for both the fuel control and the propeller pitch control to avoid tracking errors between the two controls. This fuel control system has similar dynamic properties as the one disclosed in the above-referred to application, however, a droop type fuel control is utilized with a resetting mechanism such that it is not necessary to have the propeller pitch control and the fuel control track each other.

Referring to the drawing, a turboprop power plant combination is generally indicated at and includes a compressor ,section 12, a combustion section 14 and a fturbine and exhaust section 16. As is usual, at least a portion of the turbine section drives a variable pitch propeller 18. The propeller 18 has the pitch of its blades regulated by a control schematically illustrated at 20. The propeller control and the pitch changing mechanism may be of the type shown and described in Caldwell et al. Patent No. 2,174,717 or Martin Patent No. 2,361,954.

A single power lever 30 is operatively connected to a group of coordinating cams for both the propeller and fuel controls. The power lever is adapted to rotate a governor setting cam 32, a fuel flow scheduling cam 34 and a propeller governor setting cam 36. The cam 36,` of course, will normally adjust a Speeder spring of a governor which in turn regulates the pitch of the blades of the propeller 18.

The cam 32 operates the rack 40 which by means of pinions `42 and 44 drives a rack 46 through a pulley and cable arrangement 48 and 5l). The rack 46 sets a Speeder spring 52 which opposes the centrifugal force provided by yweights 54 which may be rotated in proportion to the speed of rotation of the power plant by any suitable well known means. The spring 52 and the flyweights 54 comprise a governor for operating an r.p.m. pilot valve generally indicated at 56. The governing mechanism moves the valve stem 58 and the East Hartford, Conn., a

corpolands

60 and 62 so as to conduct high pressure Huid or drain pressure to the chamber 66 of an r.p.m. servo device generally indicated at 68. The r.p.m. servo has a piston 70 portions of which are of different areas. High pressure fluid is continuously supplied to the chamber 72 so that when high pressure fluid is conducted to chamber 66 the piston 70 moves downwardly, while if drain pressure is supplied to the chamber 66 the piston 70 is moved upwardly. Thus it will be seen that the fuel droop governor, in response to either a power lever movement or a speed change, positions the r.p.m. servo 68 via the r.p.m. pilot valve 56 which in turn moves the rod 76 and varies the opening of the fuel valve 78 in a manner to be described hereinafter. The r.p.m. servol piston via the rod 76 and beam 80 also moves a followup sleeve 82 which surrounds the

lands

60, 62 of the r.p.m. pilot valve' 56. As -a result the position of the r.p.m. servo piston 70 always essentially corresponds to that of the pilot valve stem 58, including the

lands

60 and 62. lhis provides the desired fuel flow droop.

Fuel flow droop can be described as a deviation of the iinal fuel flow value from the desired (set) fuel flow over the full operating range. Thus, when an olf conv dition occurs, the fuel flow does not eventually return to the exact same set conditon. This slight error or deviation provides a certain amount of stability to the control. The output of the r.p.m. servo 68, namely the motion imparted to rod 76, also moves a reset pilot valve 86 via the arm 88. In addition, the power lever can also move the reset pilot valve via the cam 34 and the` rod 90. The reset pilot valve 86 includes aland 94 which can pass high pressure uid or fluid under drain pressure via the line 96 to the chamber 98 of a reset servo 180. The reset pilot valve meters fluid into or out of the chamber 98 of the reset servo 100 so that it moves at a rate proportional to the reset pilot valve displacement. A restriction 102 may be provided in the line 96 so that the reset servo has a relatively slow response. With the reset servo having a slow response and the r.p.m. servo 68 having a relativelygrapid response the control reacts such that during dynamic transients the action is similarV to that of a permanent` droop governor control, giving good stability and high rate of response,'

the resetbeing sufficiently gradual to have little effect on response.

The reset servo 100 by means of a reset spring 162 adds or subtracts spring force to the droop governor thus changing its setting. This change in setting in turn causes the stem 58 of the r.p.m. pilot valve S6 to move thereby in turn causing motion of the piston 70 of the r.p.m. servo 68 until it has in turn recentered the land 94 of the reset pilot valve 86. The reset pilot valve being an integrating type of device will always return to its centered positon insuring that the steady-rate fuel flow is always that value which has been scheduled by the setting of the cam 34 and rod 90.

The action of the speed responsive mechanism is first to correct fuel flow in a direction to correct for an off speed condition and then to begin to reset itself in a direction to restore the fuel valve in its original position regardless of speed change. The propeller governor is finally relied upon to bring the engine back to on speed. The reset action is in a sense to restore the original fuel valve position and is a floating action` which can only reach a null when the end of link 88 is in such a position so as to close the pilot 86, and this position is fixed relative to the position of the fuel valve for any given compressor inlet pressure.

The action of the r.p.m. servo 68 on the throttle valve 78 is modified by the motion of a bellows 110 and rod 112. The bellows 110 is sealed and the outside thereof is exposed to compressor inlet pressure and temperature y such that the bellows responds to both inlet pressure and temperature. Motion of the free end of the bellows 110 and rod 112 positions a roller 114 which is interposed between the throttle valve stem 116 and a lever 118 which is engaged by the rod 76. vThe lever '118 is pivoted at 120;:

The pump feeding fuel to the throttle valve normally would have the outlet pressure thereof maintained constant; or, the pressure drop -across the throttle valve may be maintained constant by means of a by-pass type regulator 13G-so that for any given position of thc throttle valve a predetermined fuel ow will be obtained. These are well-known expedients in the art.

With a fuel control system of the type described, control functions of the following nature are obtained.

During transient conditions fuel ow is altered from the equilibrium or steady state value in a manner to aid in rapidly bringing the engine to the selected speed in a we ll damped'manner, while equilibrium or steady state fuel ow is accurately defined, independent of any tracking errors between fuel and propeller control settings.

As a result of this invention it is readily apparent that a relatively simpleyet highly accurate but dynamically stable control is provided.

Although only one embodiment of this invention has been illustrated and described herein, it will be apparent that various changes and modifications may be made in the construction and arrangement of the various parts without departing from the scope of this novel concept.

What it is desired to obtain by Letters Patent is:

1. In a fuel control for a turbine type power plant, a source of fuel under pressure, means for regulating the ow of fuel from said source to the power plant, manual means for setting said means for regulating the ow of fuel to maintain a desired fuel flow rate, a speed governor responsive to the speed of the power plant, means for setting Asaid governor including an adjustable spring, a pilot valve biased in one direction by said spring and in the other direction by centrifugal force, a servo device controlled by said pilot valve and operatively connected to said'fuel regulating means for tem,- porarily varying fuel ow upon a change in power plant speed from the set speed, mechanism responsive to the relative position of said servo device and said manuall means for resetting said governor including a second adinstable spring biasing said pilot valve in opposition to said first-mentioned spring said mechanism returning said fuel flow regulating means to its original position, and means responsive to at least one parameter of power plant operation for further varying fuel ow.

2. In a turboprop power plant including a propeller having variable pitch blades, means for regulating the pitch of said bladesvto increase the load on the engine with an increase inu speed and to decrease the load on the engine with a decrease in speed, a droop fuel governor, a fuel ow scheduling member, power control means for controlling said pitch regulating means and setting said governor and said fuel ow scheduling member, said governor including -a pilot valve, a fuel control valve for regulating the flow of fuel to the power plant, a servo device controlled by said pilot valve for varying the position of said fuel valve with variations in speed, a follow-up sleeve surrounding said pilot valve and operatively connected to said servo device to vary the effect of said pilot valve on said servo device, means for resetting said governor including a second servo device, a reset pilot valve for controlling said second servo device including operative connections to said first servo chamber, a turbine driven by device and said fuel flow scheduling member for comparing the relative positions thereof to return said fuel control valve to its original set position after a transient speed change, and means responsive to at least one parameter of power plant operation for further regulating the ow of fuel by said fuel control valve.

3. A turbine type power plant including a combustion the'v gases from said combustion chamber, a compressor driven by the turbine, a variable pitch propeller driven by the power plant, means for varying thc pitch of the propeller to control the speed of rotation thereof, a source offuel under pressure,

' means for regulating the flow of fuel from said source to said combustion chamber, power control means for manually setting a schedule of fuel ow and operatively connected to said regulating means, a speed governor including a pilot valve, means for setting the speed of said governor in accordance with the setting of said power control means, a first servo device controlled by said pilot valve for changing the fuel flow regulated by said fuel regulating means when said speed governor calls for a fuel iiow different than that called for by said power control means, a follow-up sleeve for said pilot valve, follow-up means mechanically connecting said first servo device and said Sleeve, a reset servo device connected to said power control means and said first servo for rey setting said governor to eventually return said fuel regulating means to the original fuel ow scheduled by saidpower control means including a reset pilot valve for sensing the relative positions of said first servo device and said power control means.

4. A power plant including a combustion chamber, a variable load for said power plant, means for controlling the Speed of the power plant during variations inload, sa source of fuel under pressure, means for regulating the ow of fuel from said source to said combustion chamber, power control means for setting a schedule of fuel flow and operatively connected to said regulating means, a speed governor driven by the'engine. means for setting the speed of said governor in accordance with the setting of .said power control means, a first servo device controlled by said governor for changing the fuel iiow regulated by said fuel regulating means when said speed governor is in an off-speed condition calling for a fuel iiow different than that called for by said power control means, follow-up means mechanically connecting said first servo device and said governor, and a reset servo device connected to said power control means and said first servo device for comparing the relative positions of said control means and first servo for resetting said governor to eventually return said fuel regulating means to the original fuel ow scheduled by said power control means, said means for controlling the speed of said power plant being effective to eventually return the power plant to the set speed when an off speed occurs.

References Cited in the le of thispatent UNITED STATES PATENTS