US3646754A

US3646754A - Motor operated servo pump

Info

Publication number: US3646754A
Application number: US39732A
Authority: US
Inventors: Werner G Koch; Robert H Marchell; William G Redmond
Original assignee: Ltv Electrosystems Inc
Current assignee: Ltv Electrosystems Inc
Priority date: 1970-05-22
Filing date: 1970-05-22
Publication date: 1972-03-07
Anticipated expiration: 1989-03-07
Also published as: JPS5426675B1; GB1328459A

Abstract

A power actuator in a hydraulic system is controlled in accordance with an electronic control signal energizing a variable displacement servo pump interconnected to the power actuator. In the hydraulic system, the variable displacement servo pump includes a swash plate directly coupled to and positioned by an electric motor. A transducer responds to the position of the swash plate and generates a feedback signal to balance out the effect of the electronic control signal. A pressurized reservoir supplies a base pressure to the hydraulic system when the swash plate of the variable displacement servo pump is in a neutral or null position. This reservoir is protected against an over pressure by a check valve. To compensate for unequal chamber volumes in the power actuator, a shuttle valve diverts excess fluid from the larger volume chamber to the reservoir.

Description

nited States Patent Koch et a1. Mar. 7, 1972 [541 MOTOR OPERATED SERVO PUMP 3,321,216 5/1967 Carter ..60/51 UX [72] Inventors: Weane; G.I Koch vlvlloliiiert llgzgrchell, Primary Examiner Edgar w-oeoghegan gr fifl fqgz am Attorney-Richards, Harris and Hubbard and James D. Willborn [73] Assignee: LTV Electrosystems, ]nc., Greenville, Tex.

[57] ABSTRACT [22] Filed: May 22, 1970 A power actuator in a hydraulic system is controlled in ac- [211 APPL 39,732 cordance with an electronic control signal energizing a variable displacement servo pump interconnected to the power ac- 52 u.s.c1. ..60/52 vs, 60/D1G. 2,91/411 A, the hydraulic System the variable "SPlacemfint 91/361 servo pump includes a swash plate directly coupled to and 151 1111.01 ..F15b 15/18 psifinedbyanelecmc mm-Amnsdmmslmdsmhe 1581 Field of Search ..60/D1G. 2, 52 vs; 9 1/411 A, swash Plate and genmles a feedback Signal 91/361, 244/77 R balance out the effect of the electronic control signal. A pressurized reservoir supplies a base pressure to the hydraulic [56] References Cited system when the swash plate of the variable displacement servo pump is in a neutral or null position. This reservoir is UNITED STATES NTS protected against an over pressure by a check valve. To compensate for unequal chamber volumes in the power actuator, a 2,977,765 4/1961 F11lmore ..60/52 VS Shuttle valve diverts excess fl id f the largelvolume 3,046,895 7/ 1962 Berg et a1 ..60/52 VS X chamber to the reservoir. 1,269,338 6/1918 Tourreil ..60/53 C 1,835,453 12/1931 Bahl ..60/52 VS UX 13 Claims, 2 Drawing Figures 64 is, T

SERVO PUMP MOTOR P MOTOR I I I6 I R 1. I MO 0 W I Q 24 /L 34 /42 i; 40 INVENTOR WERNER e. KOCH ROBERT H. MARCHELL F! 2 WILLIAM G. REDMOND ATTORNEYS MOTOR OPERATED SERVO PUMP This invention relates to a power actuator control system and more particularly to a hydraulic system for controlling the operation of a power actuator.

Heretofore, the swashplate of a variable displacement servo pump was positioned by a small actuator (e.g., an electrohydraulic actuator) coupled to the swashplate. This swashplate positioning actuator necessitated an auxiliary pump and a separate hydraulic system for control thereof. The auxiliary pump was also used to produce a base pressure in the main hydraulic system to insure actuator stiffness under all operating conditions. As in all hydraulic systems, the swashplate positioning system generated heat that directly resulted in a reduction of the overall system efiiciency, and also required apparatus for effective heat dissipation.

An object of the present invention is to provide a more efficient hydraulic system for controlling a power actuator. Another object of this invention is to provide a hydraulic system having a static member for establishing a base pressure for actuator stiffness. A further object of this invention is to provide a hydraulic system including a direct coupled variable displacement servo pump. A still further object of this invention is to provide unequal volume actuator release in a hydraulic system.

In accordance with one aspect of this invention, a hydraulic system for controlling a power actuator includes a variable displacement servo pump interconnected to the power actuator. This variable displacement servo pump has a movable member for varying the pumping capacity thereof. A servomotor is coupled to the movable member of the servo pump to establish the pump capacity. The position of the movable member is detected by a position transducer that generates a feedback signal. This feedback signal is applied to one input of an amplifier which also receives a control signal at a second input terminal. The control signal initially controls the position of the movable member through the servomotor with the feedback signal balancing out the control signal until a zero error results at the amplifier output.

In accordance with another aspect of this invention, the hydraulic system for controlling a power actuator includes a variable displacement servo pump having fluid connections to the power actuator. The servo pump has a movable member the position of which establishes the pumping capacity. A predetermined initial pressure is maintained in the fluid connections between the servo pump and the power actuator to provide actuator stiffness. An electric torque motor is coupled to the movable member of the pump for positioning thereof in accordance with an energizing signal. The movable member of the pump is also connected to a position transducer that generates a feedback signal varying with the movable member position. This feedback signal is applied to one input of an amplifier that receives a control signal on a second input terminal. The control signal initially energizes the torque motor to position the movable member in accordance therewith. The feedback signal balances out the control signal until a zero error results at the amplifier output.

A more complete understanding of the invention and its advantages will be apparent from the specification and claims and from the accompanying drawings illustrative of the invention.

Referring to the drawings:

FIG. 1 is a block diagram of a dual redundant hydraulic system for a dual tandem power actuator; and,

FIG. 2 is a sectional view of a motor driven variable displacement servo pump.

Referring to FIG. I, there are shown two hydraulic systems in accordance with this invention, one for each half of a dual tandem power actuator. Control signals for each of the hydraulic systems may be generated in a conventional manner and applied to one input of a summing amplifier. Where the actuator is a part of an aircraft control system, the control signals may be generated by a stick transducer that converts the mechanical input from a pilots control stick into electrical signals. The control signals from the stick transducer are transmitted to one of the input terminals of the summing amplifiers by a parallel arrangement of wires which may be located along different paths in the airframe to minimize the possibility of a disruption of all the pilot generated signals. In addition to pilot generated signals, the control signals to the inputs of the amplifiers may be received from autopilot sensors, a stability augmentation system, or from other systems, such as a navigation control.

Because of the similarity of the hydraulic systems for each half of the power actuator, a detailed description of only one will be given. It will be understood, that the second system will be similar in component requirements, interconnections and in operation.

An input signal representing a desired position for the stroke member of a power actuator 10 is applied to one input terminal of a summing amplifier 12. At the output of the amplifier 12, there appears an electrical signal that is applied to a torque motor 14 for positioning the swashplate of a variable displacement servo pump 16. The pump 16 is driven by a motor 18 for pumping fluid through

conduits

20 and 22.

Referring to FIG. 2, there is shown, in section, a simplified diagram of a variable displacement servo pump with the torque motor 14 coupled to a rotatable swashplate 24 through a gear train 26.

Conduits

20 and 22 are connected to the pump housing 28 through inlet/

outlet connectors

30 and 32. These connectors have openings to a piston block 34 that contains a plurality of pistons, such as

pistons

36 and 38, arranged in a circular pattern. The piston block 34 is coupled to the drive shaft of the motor 18 through a pump shaft 40.

The operation of the pump 16 is conventional with the pump capacity and fluid direction established by the angular position of the swashplate 24. By coupling the swashplate 24 directly to the torque motor 14 through the gear 26, there is eliminated the need for the conventional hydraulic actuator heretofore used to position the swashplate of a servo controlled variable displacement pump.

An energizing signal to the torque motor 14, as received from the amplifier 12, actuates the torque motor to rotate the swashplate 24 to pump fluid from the conduit 20 into the conduit 22 or from the conduit 22 to the conduit 20. As a swashplate 24 rotates in response to the output of the torque motor 14, a potentiometer transducer 42 generates a signal related to the swashplate position. This position signal is applied to a second input terminal of the amplifier 12 in a manner to balance out the input signal. Thus, the position of the swashplate 24 is at a desired setting when the output of the amplifier l2 attains a null or zero voltage level.

In one form of the amplifier 12 and the torque motor 14, the amplifier generates a variable phase output signal; that is, the phase of the output of the amplifier l2 varies with the magnitude and polarity of the input signal. This variable phase signal is applied to one winding of a two phase servomotor which positions the swashplate 24 as described. When the swashplate has been rotated to the desired angular position, the output of the transducer 42 causes the output of the amplifier 12 to attain a null phase condition. In accordance with the standard operation of a two phase servomotor, this locks the armature thereby assuring that the swashplate 24 remains in the angular position desired. In addition to two phase servomotors, the motor 14 may also be a standard DC torque motor receiving energizing signals from a suitably selected amplifier 12.

Conduits

20 and 22 connected to the servo pump 16 also connect to

chambers

44 and 46, respectively, of the power actuator 10. Chambers 44 and 46 are formed on opposite sides of a piston 48 and comprise the first stage of the power actuator 10. The first stage of the power actuator 10 is coupled to a second stage, which includes a piston 50, by means of a piston rod 52. A piston rod (stroke member) 54 that extends from the opposite side of the piston 50 connects to a power element, e.g., an aircraft control surface, to be positioned through suitable linkage.

Extending from the piston 48 through the chamber 44 is a transformer core 56 as part of a linear voltage differential transformer 58. The differential transformer 58 generates two separate but equal outer loop position feedback signals on

lines

60 and 62. Feedback signals on the

lines

60 and 62 are respectively applied to one of three inputs of the amplifiers for each of the hydraulic systems shown. The feedback signal on the line 60 is applied to a third input terminal of the summing amplifier l2 and completes an outer feedback loop.

In the operation of the servo pump 16 of the type illustrated in F IG. 2, fluid will be pumped so long as the swashplate 24 is displaced from a neutral or balanced position. An input signal to the amplifier 12 rotates the swashplate 24 to a desired position, as explained previously. This causes fluid to be pumped into one of the chambers of the first stage of the power actuator l and from the second chamber of the first stage. As fluid is thus pumped, the piston 48 is displaced thereby causing a change in the feedback signal on the line 60. This change in the outer loop feedback signal upsets the balance of the amplifier 12 as established by the output of the transducer 42. Whereas the control input signal to the amplifier l2 resulted in the swashplate 24 being positioned from a null or neutral position, and this position was maintained by the transducer 42, the outer loop feedback signal now causes the torque motor 14 to be energized in a manner to return the swashplate to the null or neutral position. As the swashplate is now positioned in response to the outer loop feedback signal, the transducer 42 output changes to approach a null level. This null level will be reached when the swashplate 24 is in its null or neutral position. The swashplate will be in the null or neutral position when the outer feedback signal on line 60 balances the control input signal and the output of the amplifier l2 approaches and holds at a null level, thereby stopping the torque motor 14.

When the swashplate of the pump 16 is in the null or neutral position, pumping action stops and the pump acts as a valve to hold fluid in the

chambers

44 and 46. At this time, the piston rod 54 will be positioned in accordance with the magnitude of the control input signal to the amplifier 12, and also the control signal to the amplifier of the second hydraulic system for the second stage of the power actuator 10.

To provide positive positioning of the power actuator 10, a base pressure should be maintained in the hydraulic system. This base pressure is provided by a pressurized reservoir 64 connected to the conduit 22 through a check valve 66. By connecting the pressurized reservoir 64 into the hydraulic system, there will always be some minimum pressure maintained in the power actuator to provide the necessary actuator stiffness, that is, a positive position. Although a simple diaphragm-type reservoir is illustrated, a spring-loaded pistontype reservoir may also be used.

By connecting the check valve 66 in the conduit from the reservoir 64, the reservoir is isolated from the system pressure when the servo pump [6 pumps into the conduit 22 from the conduit 20. This does not inhibit the effectiveness of the reservoir 64, since it is intended to provide the base pressure to the system, that is it will set the pressure level in the actuator chamber having the lowest pressure. When the swashplate of the servo pump 16 is at the null or neutral position, and the actuator is unloaded, the pressure in the two chambers will be the base pressure.

Although the power actuator 10 is shown schematically, it does illustrate one of the inherent design features of an actual model. With reference to stage one of the actuator, it will be apparent that the volume of the chamber 44 is greater than the volume of the chamber 46 due to the difference in diameter of the piston rod 52 and the transformer core 56. As a result of this difference in volume, the chamber 44 will contain a greater amount of fluid than the chamber 46 when the actuator is in a fixed position. Because of this difference in volume, when the servo pump 16 pumps fluid from the chamber 44 into the chamber 46, the excess fluid in the chamber 44 must be dumped into the reservoir 64 for smooth operation of the power actuator 10. This dumping action is accomplished by a shuttle valve 68 having a piston 70 biased into the position shown by means ofa spring 72. The valve 68 has a port 74 that is closed off by one of the lands of the piston 70 in the position illustrated. This port connects to the conduit 20 by means of a conduit 76. Another port of the valve 68 is connected to the conduit 22 by means of a conduit 78 that includes an orifice restriction 80. The orifice restriction serves to smooth the operation of the shuttle valve 68. Two other ports of the valve 68 are interconnected to the pressurized reservoir 64 through a conduit 82. One of these ports opens into the valve chamber containing the spring 72 and the other opens into the area between the lands of the piston 70.

To dump fluid from the chamber 44 into the reservoir 64, the pressure in the conduit 78 produces a force on the piston 70 in a direction opposed by the spring 72 and a force exerted on the piston resulting from the base pressure as established by the reservoir. When the pressure in the conduit 78 produces a force greater than the base pressure force and the spring force, the piston 70 moves towards the left opening the port 74. Opening the port 74 allows fluid from the chamber 44 to be diverted through the valve 68 and the conduit 82 into the reservoir 64. As fluid is dumped from the chamber 44 the piston 48 will move toward the left thereby resulting in a reduction of the pressure in the conduit 78. When the base pressure force and the spring force exceeds the force of the pressure in the conduit 78, the piston 70 will again move to close off the port 74. Thus, excess fluid in the chamber 44 will be dumped into the reservoir 64.

When pumping fluid from the chamber 46 into the chamber 44, the excess fluid condition will not exist. In this case, fluid that was previously dumped into the reservoir 64 will be reentered into the system through the check valve 66.

The overall operation of the system can be described as follows: A control input signal is amplified by the amplifier l2 and transmitted to the torque motor 14 that is direct coupled to the servo pump 16. The torque motor 14 rotates the pump swashplate 24 through the gear train 26, as explained. The swashplate angle determines the displacement or fluid output rate of the pump 16.

Assume that the input signal to the amplifier 12 was such as to cause the flow of fluid to be into the pump via the conduit 22 and out of the pump through the conduit 20. The swashplate is rotated by the input signal until the transducer 42 generates a feedback signal that cancels the input signal. When the transducer signal and the control input signal are equal, the output of the amplifier 12 goes to a null level and the torque motor 14 stops, thereby holding the swashplate 24 at an established angle.

Fluid now flows into the chamber 44 from the chamber 46 and the piston rod 54 will be extended. In other words, the servo pump 16 takes fluid from the chamber 46 and pumps it into the chamber 44. The linear voltage differential transformer 58 on the power actuator 10 produces an outer loop feedback signal proportional to actuator position. This feedback signal is applied over the line 60 to the amplifier 12 to close the outer loop. This outer loop signal then causes the torque motor 14 to begin retracting the pump swashplate 24 until the outer loop feedback signal equals the input signal to the amplifier 12. At this time, the pump swashplate is in the neutral position and the piston rod 54 has stopped moving. The piston rod 54 is at a position corresponding to the input signals.

To reverse the operation of the power actuator a similar but opposite polarity signal is provided to the amplifier 12. This causes the torque motor 14 to stroke the pump swashplate 24 in the opposite direction to cause flow into the chamber 46 and from the chamber 44. The piston rod 54 is now retracted. The outer feedback signal on the line 60 again balances the input signal until the swashplate 24 returns to the neutral positron.

When pumping into the chamber 46, the check valve 66 isolates the reservoir 64 from the pressure of the pump l6. Also,

when pumping into the chamber 46, the shuttle valve 68 establishes a flow path into the reservoir 64 from an unequal area actuator.

As mentioned earlier, the actuator has a dual tandem arrangement that includes

chambers

84 and 86. A system similar to the one described is connected to these chambers. The chamber 84 is connected to a conduit 88 which corresponds to the conduit 20, and the chamber 86 connects to a conduit 90 which corresponds to a conduit 22. The remainder of the system for the second stage of the actuator 10 will be as described using the

conduits

88 and 90 and their corresponding conduits and 22 as a reference.

While only one embodiment of the invention, together with modifications thereof, has been described in detail herein and shown in the accompanying drawings, it will be evident that various further modifications are possible without departing from the scope of the invention.

What is claimed is:

1. In a hydraulic system for controlling a power actuator comprising:

a variable displacement pump having connections to the power actuator and including a movable member for varying the pump displacement,

a servomotor coupled to the movable member of said pump for controlling the position thereof,

a transducer also coupled to the movable member and responsive to the position thereof for generating a feedback signal,

amplifier means receiving an input signal on one terminal and the feedback signal on a second terminal and generating a control signal to said servomotor related to the difference between the two input signals, and

a shuttle valve responsive to the pressure in one connection to said pump for directing fluid from a second connection to dump excess fluid from the power actuator into a holding reservoir.

2. In a hydraulic control system for controlling a power actuator as set forth in claim 1 including an actuator position transducer for generating a second feedback signal to said amplifier means proportional to the actuator position.

3. In a hydraulic system for controlling a power actuator as set forth in claim 2 including a pressurized reservoir coupled to said pump for maintaining a base pressure in the system thereby providing power actuator stiffness.

4. In a hydraulic system for controlling a power actuator, comprising:

a variable displacement pump having fluid connections to the power actuator and including a movable member for varying the pump displacement,

means for maintaining a predetermined base pressure in the fluid connections between said pump and the power actuator,

a shuttle valve responsive to the pressure in one connection of said pump for directing fluid from a second connection into said means for maintaining a predetermined base pressure, and

a servomotor mechanically connected to the movable member of said pump for controlling the position thereof in accordance with an energizing signal.

5. In a hydraulic system for controlling a power actuator as set forth in claim 4 wherein said means for maintaining the predetermined base pressure comprises a pressurized reservoir.

6. In a hydraulic system for controlling a power actuator as set forth in claim 5 including flow control means for restricting flow into said pressurized reservoir from said pump.

7. In a hydraulic system for controlling a power actuator as set forth in claim 6 wherein said flow control means includes a check valve for restricting flow from one connection to said pump into said reservoir.

8. In a hydraulic system for controlling a power actuator, comprising:

a vana le displacement pump having fluid connections through the power actuator and including a movable member for varying the pump displacement,

means for maintaining a predetermined base pressure in the fluid connections between said pump and the power actuator to provide actuator stiffness,

a transducer also coupled to the movable member and responsive to the movement thereof for generating a position feedback signal,

amplifier means receiving an input signal on one terminal and a feedback signal on a second terminal and generating a control signal to said servomotor related to the difference between the two input signals, and

a shuttle valve responsive to the pressure in one connection of said pump for directing fluid from a second connection into said means for maintaining a predetermined base pressure.

9. In a hydraulic system for controlling a power actuator,

comprising:

a variable displacement'pump having fluid connections to the power actuator and including a movable member for varying the pump displacement,

a pressurized reservoir for maintaining a predetermined base pressure in the fluid connections between said pump and the power actuator,

a check valve for restricting flow from one connection of said pump into said pressurized reservoir, and

a servomotor coupled to the movable member of said pump for controlling the position thereof in accordance with an energizing signal.

10. In a hydraulic system for controlling a power actuator as set forth in claim 8 including an actuator position transducer for generating a second feedback signal to said amplifier means proportional to the actuator position.

11. In a hydraulic system for controlling a power actuator as set forth in claim 8 wherein said means for maintaining a predetermined base pressure comprises a pressurized reservoir.

12. In a hydraulic system for controlling a power actuator as set forth in claim 11 including flow control means for restricting flow into said pressurized reservoir from said pump.

13. In a hydraulic system for controlling a power actuator as set forth in claim 12 wherein said flow control means includes a check valve for restricting flow from one connection to said pump into said reservoir.

Claims

1. In a hydraulic system for controlling a power actuator comprising: a variable displacement pump having connections to the power actuator and including a movable member for varying the pump displacement, a servomotor coupled to the movable member of said pump for controlling the position thereof, a transducer also coupled to the movable member and responsive to the position thereof for generating a feedback signal, amplifier means receiving an input signal on one terminal and the feedback signal on a second terminal and generating a Control signal to said servomotor related to the difference between the two input signals, and a shuttle valve responsive to the pressure in one connection to said pump for directing fluid from a second connection to dump excess fluid from the power actuator into a holding reservoir.

4. In a hydraulic system for controlling a power actuator, comprising: a variable displacement pump having fluid connections to the power actuator and including a movable member for varying the pump displacement, means for maintaining a predetermined base pressure in the fluid connections between said pump and the power actuator, a shuttle valve responsive to the pressure in one connection of said pump for directing fluid from a second connection into said means for maintaining a predetermined base pressure, and a servomotor mechanically connected to the movable member of said pump for controlling the position thereof in accordance with an energizing signal.

8. In a hydraulic system for controlling a power actuator, comprising: a variable displacement pump having fluid connections through the power actuator and including a movable member for varying the pump displacement, means for maintaining a predetermined base pressure in the fluid connections between said pump and the power actuator to provide actuator stiffness, a servomotor coupled to the movable member of said pump for controlling the position thereof, a transducer also coupled to the movable member and responsive to the movement thereof for generating a position feedback signal, amplifier means receiving an input signal on one terminal and a feedback signal on a second terminal and generating a control signal to said servomotor related to the difference between the two input signals, and a shuttle valve responsive to the pressure in one connection of said pump for directing fluid from a second connection into said means for maintaining a predetermined base pressure.

9. In a hydraulic system for controlling a power actuator, comprising: a variable displacement pump having fluid connections to the power actuator and including a movable member for varying the pump displacement, a pressurized reservoir for maintaining a predetermined base pressure in the fluid connections between said pump and the power actuator, a check valve for restricting flow from one connection of said pump into said pressurized reservoir, and a servomotor coupled to the movable member of said pump for controlling the position thereof in accordance with an energizing signal.