US2856175A - Isochronous governing mechanism - Google Patents

Description

Oct. 14, 1958 v A. F.IMARTZ, JR 2,855,175.

. ISOCHRONOUS GOVERNING MECHANISM ,w Filed Aug. 19. 1954 MAX/MUM PERMISSIBLE 7;) HINVENTOR BY We 1 I ORNEY ISOCHRONOUS GOVERNING MECHANISM Arthur F. Martz, Jr., Grosse Pointe Woods, Mich., as-

signor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application. August 19,. 1954, Serial No. 450,861

1 Claim. (Cl. 264-3) This invention relates to a governing mechanism and more particularly to an isochrono-us. governing mechanism maintaining the speed of an engine constant for each control lever setting regardless of load or any other condition. of operation.

An object of this invention is to provide an isochronous governing mechanism for an engine including a control valve metering motive fluid to the engine and being biased in, opposite directions by forces representing the actual speed of the engine and the desired speed of the engine, with the force representing the desired speed of the engine being variable whenever the actual speed does not equal the desired speed. A further object of this invention is to provide an isochr-onous governing mechanism for an engine including a control valve metering motive fluid to the engine and being biased in opposite directions by forces representing the actual speed of the engine and the desired speed of the engine, with the force representing the desired speed of the engine being variable and regulated by mechanism responsive to the difference between the desired speed of the. engine and the actual speed of the engine.

These and other objects of this invention will be readily apparent from the following specification and drawings in which:

Figure 1 is a graph showing the operation of this governing mechanism;

Figure 2 is a schematic diagram of the isochronous governing mechanism.

In certain types of engines, particularly gas turbine engines, the purpose of a speed governor is to'maintain the engine speed constant for each: control lever position regardless of the load. or other conditions of operation. This is necessary for engine stability.

In the conventional proportional governor, the governor flyweights are opposed by a compression spring, and the compression of this spring is set by the control lever position. The governor operates the control valve metering fuel or other motive fluid to the engine.

Referring now to Figure 1 of the drawings, the governor flyweight force does not equal the spring force as the engine accelerates along curve X. Various mechanisms are used to limit the maximum flow of motive fluid or fuel to the engine during acceleration as is well known in the art. As the engine comes up to speed, the governor flyweight force begins to oppose the spring force and the flow of motive fluid or fuel to the engine is reduced as the control valve closes. The flow of motive fluid or fuel then drops along a curve S as the flyweight force comes into balance with the spring force. There is a curve S for each control lever position or compression spring setting.

On each curve S, the flyweight force equals the spring force and the fuel or motive fluid flow rate to the engine is established by the operating conditions. Curves A and A are fuel or motive fluid requirement curves corresponding to various operating conditions. These curves intersect curve S at and 0' representing the operating "Ice points for a certain control lever position and for certain operating conditions.

Assuming now that a gas turbine engine is operating at point 0 and passes through warmer and less dense air, less fuel will then be required to maintain. the eng ne speed or conversely more air is required. The engme therefore speeds up causing the flyweight force to. be increased over the pring force. The fuel flow. is reduced, and moves along curve S to point 0 which represents. a higher engine speed and a decreased fuel flow. This droop curve between points 0 and 0 describes the balance which always exists between flyweight force. and spring force. The droop curve is undesirable, for the engine does not runat a constant speed. g

A constant speed or isochronous line is shown. as line R or R in the drawing. The undesirable droop curve can be straightened and made to approximate an ism chronism line by adding a reset or compensating feature to the proportional governor. In my governor, however, the governor will exactly follow an isochronous line R, there being an exact speed line for each setting of the. control 38. Thus droop is eliminated and exactspced control is maintained regardless of changes in ambient conditions.

Referring now to Figure 2 of the. drawings, the shaft 4 of agas turbine engine 2 drives a shaft 6. A conventional fuel pump 8 for supplying pressure fuel to. the engine is driven by shaft 6 through shaft It). A pair of flyball governors 12 and 14 are also driven by shaft 6 through shafts 16. and 18-,respectively.

Flyball governor 14 operates against plate 19 securedto servo valve 20 having, valve lands 22, 24, and 26 andmountcd in cylinder 27. The action of the fiyball governor is opposed by a compression spring 28. exerting a force against both valve land 26 and: cylindrical cup 30. Constant pressure fluid is admitted to the servo valve through passages 32 and '34,, and a return passage 36 under alower pressure is also provided. A control lever, 38- operates a plunger 40 by means of links 42 and 44'. Plunger 4t) bears against cup 30 and sets compression in spring 28 in accordance with control lever position.

Flyball' governor 12. operates against plate 45 secured to rod 48 which is connected to. a tapered valve plug 46. Valve plug 46 is mounted in control valve150. and controls the flow of fuel to the engine. The action of governor 121 is opposed by a compression spring 52 bearing against boththe valve plug and a cylindrical cupv 54., A rod 56 connects cup 54 to a piston 58 mounted in cylinder 60. Passages 62 and 64 connect the servo cylinder 27 to cylinder 60.

Fuel is supplied to pump 8 by passage 66 and is delivered under pressure to the control valve 50 through passage 68. The control valve supplies metered fuel to the engine through passage 70. The excess of fuel delivered by the pump over what is required by the engine is returned from the outlet to the inlet of the pump through passage 72, bypass valve 74, and. passage 76. The by-pass valve 74 receives a pressure input from the engine fuel supply passage 70 through passage 78. The by-pass valve is provided to maintain a substantially constant pressure drop across the control valve 50 for more accurate metering of the fuel in accordance with the position of the valve plug 46. Thus, the fuel flow t0 the engine will be a known function of the valve plug displacement.

The operation of this isochronous governing mechanism will now be described. Assuming that it is desired to increase the speed of the engine, the control lever 38 is moved counterclockwise, which compresses spring 28 and moves the servo valve 20 to the left from its equilibrium position as shown in Figure 2. Pressure fluid is then admitted from passage 32 to passage 64leading to the right side of piston 58. Passage 62 from the left side of piston 58 is connected to drain through passage 36.

Pressure fluid admitted to the right side of piston 58 compresses spring 52 and moves valve plug 46 to the left to admit more fuel to the engine to increase its speed.

Consider first the control valve unit. As the engine accelerates, governor 12 tends to close the valve plug 46 against the action of spring 52. If piston 58 has a fixed position, then proportional governing occurs. An increase in speed due to operating conditions will cause the governor to further close valve plug 46 and a decrease in speed will cause spring 52 to open the valve plug against the action of governor 12. Thus, the fuel flow will increase or decrease along a curve S and the proportional governor will have undesirable speed droop.

However, in this isochronous governing mechanism, piston 58 does not have a fixed position. As the engine accelerates, governor 14 will tend to return the servo valve to its equilibrium position wherein the force of spring 28 equals the governor force and valve lands 22, 24, and 26 close passages 32, 36, and 34, respectively. Governor 12 will also tend to close the fuel valve plug 46 against the action of spring 52, and piston 58 will continue to move until the servo valve has reached equilibrium position.

Since a constant pressure is applied to the servo valve, the rate of fiow through the valve is a function of servo valve displacement which can be called the speed error. The rate of flow from the servo valve to the piston in cubic inches per second is proportional to the flow area (orifice opening). The volumes of fluid flowing into and out of cylinder 60 through passages 62 and 64 will be equal to each other and to the velocity of the piston multiplied by its area. Assuming only moderate leakage past the piston, the velocity of the piston is directly proportional to the rate of flow past the servo valve and piston velocity is thus a function of speed error. Piston displacement, which is the time integral of velocity, is thus proportional to the time integral of a function of speed error.

The initial compression is set into spring 52 by means of piston 58 whose velocity is a function of speed error. The position of this piston and the compression of spring 52 is then determined by the time integral of the speed error. Since the piston velocity is a function of speed error, the piston will not have zero velocity until the speed error is zero or until the servo valve has returned to equilibrium.

If the engine speed increases beyond the compression set into spring 28 by the control lever, either during acceleration of the engine or due to a change in operating conditions, then servo valve 20 is unbalanced to the right by governor 14. Pressure fluid then flows from passage 34. through passage 62 to the left side of piston 58 to reduce the compression of spring 52 and reduce the fuel flow. This aids governor 12 in reducing the fuel flow and establishes a new position of piston 58 and, hence, a new compression set into spring 52. Piston 58 will continue to move until the speed error is again zero.

Damping orifices and 82 are provided in passages 62 and 64, respectively, in order to obtain stability. If desired, the damping orifices may be placed within the servo valve cylinder 27 between the inlet pressure passages and passages 62 and 64.

While a specific embodiment of this invention has been shown and described, various changes and modifications may be made within the scope and spirit of the following claim.

An isochronous governing mechanism for an engine comprising a control lever for setting the desired speed of said engine, a control valve metering motive fluid to said engine, a source of fluid under pressure, first speed responsive means biasing said valve in one direction, resilient means exerting a force opposing said first speed responsive means, hydraulically actuated means regulating the force exerted by said resilient means, a hydraulic servo valve controlling the rate of flow of fluid to and from said hydraulically actuated means to vary the rate of change of said force, second speed responsive means exerting a force on said servo valve tending to control the rate of flow to said hydraulically actuated means to decrease said force exerted by said resilient means, and resilient means exerting a force on said servo valve tending to control the rate of flow to said hydraulically actuated means to increase said force exerted by said firstmentioned resilient means, said last-mentioned resilient means being set by said control lever whereby the rate of travel of said servo valve and rate of change of force exerted by said first mentioned resilient means on said control valve is responsive to the difference between the actual speed of the engine and the desired speed of the engine.

References Cited in the file of this patent UNITED STATES PATENTS 2,583,656 Lay Jan. 29, 1952 FOREIGN PATENTS 380,107 Germany Sept. 3, 1923 1,072,570 France Mar. 17, 1954

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