US3811364A

US3811364A - Hydraulic actuator

Info

Publication number: US3811364A
Application number: US00301671A
Authority: US
Inventors: R Harkrader
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1972-10-27
Filing date: 1972-10-27
Publication date: 1974-05-21
Anticipated expiration: 1991-05-21

Abstract

A hydraulic actuator has two cylinder and piston motors of different area with the smaller piston connected to a piston rod and the larger piston capable of abutting the smaller piston. Preloaded springs bias the pistons toward each other. Servo fluid delivered between the pistons first moves both pistons a limited distance in one direction and then moves the smaller piston a larger distance in the other direction. The device may be doubleacting, in which case servo fluid may be applied to drive the pistons on the return stroke.

Description

United States Patent [191 Harkrader May 21, 1974 HYDRAULIC ACTUATOR [75] Inventor: Ronald L. Harkrader, Saginaw,

Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Oct. 27, 1972 [21] Appl. No.-: 301,671

[52] US. Cl 91/422, 91/468, 92/75, 92/130 [51] Int. C1..... F011) 7/02, F0lb 31/00 [58] Field of Search 92/75/69, 50, 130; 5 91/468, 422

[56] References Cited UNlTED STATES PATENTS 1,372,942 3/1921 Constantinesco ..92/75 1,777,293 10/1930 Curtis et a1. 92/75 2,638,289 5/1953 McKellar et al. 92/75 3,241,464 3/1966 Pierce, Jr 92/75 3,411,410 11/1968 Westbury et al 92/75 Primary ExaminerPaul E. Maslousky Attorney, Agent, or Firm-Paul Fitzpatrick 5 7] ABSTRACT A hydraulic actuator has two cylinder and piston motors of different area with the smaller piston connected to a piston rod and the larger pistoncapable of abutting the smaller pistonj Preloaded springs bias the pistons toward each other. Servo fluid delivered between the pistons first move's both pistons a limited distance in one direction and then moves the smaller piston a larger distance in the other direction. The device may be double-acting, in which case servo fluid may be applied to drive the pistons on the return stroke. e a

5 Claims, 4 Drawing Figures 1 HYDRAULIC ACTUATOR My invention relates to fluid pressure actuators and particularly to one which may be caused to execute a particular routine of movement in response to fluid pressure. While the invention may be applicable to actuators energized by gas under pressure, the preferred embodiment of the invention is directed to a device energized by substantially incompressible fluid.

The actuator was conceived in response to a requirement for a particular mode of operation of variable setting angle turbine nozzle vanes in a gas turbine engine. The system calls for an actuator which shifts the vane angle a limited amount in one direction in response to increasing pressure supplied to the actuator and then, upon still further increasing pressure, reverses the direction of movement of the vanes and moves the vanes through a rather large angle. Specifically, the small changes in angle referred to may be for improving the response and efficiency of a gas turbine engine in normal operation, whereas the long travel in the opposite direction may be for reversing the nozzle vanes to provide braking action from the turbine or to limit overspeed of the turbine.

The actuator may besingle-acting or double-acting, the provision of the double-acting characteristic involving some additions to the structure. The single-acting actuator is capable of effecting the movement desired but depends upon springs for its return movement when the fluid pressure is reduced or released. If there is substantial friction in the actuated mechanism, this may prove undesirableytherefore, the actuator in its double-acting configuration will be preferred in such cases. With a double-acting actuator and with some form of feedback of the vane angle to the control device which supplies servo fluid to the actuator, the friction can be overridden and vane angle can be precisely controlled notwithstanding friction.

The principal object of my invention is to provide a simple, reliable, and economical actuator to perform the cycle of operation described above.

A further object of the invention is to provide a hydraulic actuator which is suited to the provision of relief valves to limit the actuating force exerted in either direction.

The nature of my invention and its advantages will be more clearly apparent to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention.-

FIG. I is a plan view of an actuator embodying the invention.

FIG. 2 is a sectional view of the same taken on the plane indicated by the line 2-2 in FIG. 1.

FIG. 3 is a sectional view taken on the plane indicated by the line 3-3 in FIG. 1 illustrating a pressure relief valve.

FIG. 4 is a partial longitudinal sectional view of the relief valve illustrating a pilot valve therein.

Referring to FIGS. 1 and 2, the actuator depicted includes a body or housing 2 which may be machined casting. The body includes a flange 3 with bolt holes 4 for mounting the body on a device to be actuated such as a turbine nozzle case. The body defines an internal cavity 6 of circular cross section part of which forms a first cylinder 7. A cylindrical boss 8 extending from the inner end of the cavity 6 defines a second cylinder 10 of considerably smaller diameter than cylinder 7. The body is bored at 11 coaxially with cylinders 7 and I0 to define a bearing for a piston rod or actuating rod 12 which extends to the outside of the body and serves to connect the actuator to the mechanism to be moved by it. A stop ring or washer 14 may engage the end of the housing to limit movement of piston rod 12 into the body. This washer is impinged between the body and a nut 15 threaded on the rod which may be turned to adjust the limit position. A second nut 16 acts as a jam nut to fix the adjustment. A suitable commercial seal 18 serves to prevent leakage of hydraulic fluid from the housing along the rod 12.

The body defines two ports 19 and 20 for hydraulic actuating fluid or servo fluid. In a single-acting actuator, port 19 is the high pressure port and port 20 the low pressure. When the actuator is double-acting, however, either port may receive high pressure fluid from, or return displaced fluid to, the source of actuating fluid.

The large end of cavity 6 is closed by a cylinder head 22 retained by an expanding snap ring 23. A plug 24 threaded into the head and sealed by a gasket-26pmvides access to an adjustment to be described.

Port 19 communicates through a passage 27 (FIG. 3) with cavity 6 just to the right, as illustrated, of a shoulder 28 at the inner end of cylinder 7. It thus communicates withthe cylinders 7 and 10.

Piston rod.l2 is integral with a piston 30 reciprocable in cylinder 10 and. the rod continues beyond the piston 30 to define a rod inner end 3l. A thimble 32 which is swaged to the rod end 31 abuts a flange 33 and thus is connected to the piston rod 12. Thimble 32 includes a flange 34 which serves as one abutment for a preloaded compression spring 35, the other end of which engages the end of chamber 6'. Spring 35 thus urges the piston rod 12 into the body. A cup-shaped piston 36 having piston rings 38 is reciprocable to a limited extent in the cylinder 7. The piston 36 includes a central boss 39 which is slidable within the thimble'32. A vent 41 in the thimble prevents fluid blockage. The skirt of piston 36 is slidable within the cylinder head 22. Piston 36 is biasedinto the cylinder 7 by a preloaded compression spring 40 which engages between the cylinder head 22 and a flange 42 of the piston.

Thus, both piston 30 and piston 36 are urged into the cylinder by the

springs

35 and 40, respectively,;and are thus urged toward each other. The pistons are normally in contact, with the rod inner end 31 engaging an adjustable stop 43 having a stem 44 threaded through the boss 39. Assuming that piston 36 is normally seated against'the shoulder 28, adjustment of stem 44 determines the rest position of piston rod 12. This adjustment may be locked by a jam nut 46. It is accessible by removing plug 24. Piston 36 will separate at stop 43 from piston ,rod 12 when it travels to its stroke limit against head 22 and stop 14 engages the housing 2.

Fluid is supplied to the outer faces of the pistons; that is, the left face of piston 36 and the right face of piston 30 as illustrated, from port 20 through passages including a passage 47 extending from port 20 into cavity 6 and a passage 48 which intersects a passage 50 entering the closed end of cylinder 10. Passage 50 also provides for drainage of fluid from the seal l8. V

Passage 47 is intersected by a stepped bore 51 in the body 2, at right angles to the cylinders, which provides a housing for a relief valve 49 including a spool 52 (FIGS. 3 and 4). The passage 27 from port 19 intersects one end of the bore 51 at a port 54. The passage 47 communicates with a zone 55 of the bore between lands 56 and 58- on the relief valve spool. The valve spool is biased to the position illustrated in FIG. 3 against a shoulder in the bore by a preloaded compression spring 59 one endof which abuts a cap 60 which closes the open end of bore 51. This cap is retained by a snap ring and sealed by an G-ring. Passage 27 communicates also with the other end of valve spool 52 through a restricted passage 62 which terminates near the cap 60.

As stated, the relief valve 52 is of a pilot-operated type which depends upon a pilot valve to unbalance the pressure on the two ends of the spool when the pressure to be limited reaches the selected maximum level. Referring to FIG. 4, valve spool 52 defines an internal chamber 63 within which is mounted a compression spring 64 which encloses an abutment 66 and bears against a shoulder on the abutment. Abutment 66 urges a ball 67, which is a movable valve member, against an annular seat 68 threaded into the outer end of the spool by too high pressure, the flow from chamber 71 causes a pressure drop through passage 62, unbalancing the pressures on the ends of spool 52. The excess of pressure from port 19 and passage 27 on the iower end, as illustrated in HO. 3, will move the spool upwardly to provide a connection between passage 27 and passage 47 toallow the servo fluid to by-pass the piston and cylinder assembly. This pressure level is adjusted by the position of'the seat 68, which is set by shims 73 between the hexagonal head of the seat and the valve spool. 52. I

The relief valve 49 is provided whether the actuator is single-acting or'double-acting, since in the singleact'ing form theport I9 is the supply or high pressure port. When the actuator is double-acting and there may be high pressure at the port 20, a second relief valve 74 is provided, preferably within the piston rod 12, 31.

Referring to FIG. 2, the piston rod has a longitudinal bore 75 entered from within cylinder by a crossbore 76 and discharging at the other face of the piston 30 into cylinder 7'through a cross-bore 78. Bore 75 de-- fines'a seat fora valve ball 79 urged against it by a preloaded compression spring 80. Spring 80 is loaded by an abutment 82 threaded into the end portion 31 of the piston rod. Shifting the abutment changes the load of spring 80 and thereby the pressure at which the relief valve-ball 79 unseats to discharge fluid fronvport through

passages

48 and 50, valve 74, and passage 27 into port 19.

Considering now the operation of the device, assuming that there is no'fluid pressure or that the pressures supplied to the portsl9 and 20 are equal, the parts wil brain the position illustrated in FIG. 2. Spring 40 has a higher preload than spring 35 and thus forces piston 36 against shoulder 28 and biases piston rod 12 to its position of rest against theopposition of spring 35. This might, for example, move the turbine nozzle vanes to their engine idle or starting position. If the pressure in function of pressure difference between inlets l9 and 4 port 19 communicated to the space between the pistons becomes higher than that at the supply to port 20, this force acting on the differential of area between pistons 36'and 30 tends to move the rod 12 inward. No

movement occurs until the pressure differential becomes great enough to overcome the springforce differential between

springs

40 and 35. As the pressure increases above this point, the balanced position of the pistons with relation to spring force gradually shifts to the left as illustrated, and the rod '12 is moved inwardly through a range of positions, perhaps to a nozzle minimal area or economy position at which the stop 14 engages the body. lt would be possible to have the stop constituted by engagement of piston 36 with the cylinder head, but the arrangement shown is preferred, particularly in view of the facility of adjustment. If the pressure between the pistons. continues to increase, this pressure acting on the area of piston 30 moves the rod 12 outwardly or'to the right as shown and it may move, for example, until the piston 30 engages the inner end of cylinder 10. This outward movement may be utilized for intermediate settings, if desired. Full outward'travel will move the turbine nozzle vanes to their reverse position. This movement may determine position by balancing pressure against the resistance of spring 35, but

it may be desired only to achieve full travel outward of rod 12 by supplying high pressure to port 19. With a single-acting actuator, if the pressure is then gradually reduced, the operation takes-place reversely, with the springs moving the rod as the pressure decreases.

If, however, it is desired to supplement the spring force by hydraulic pressure to overcome possible friction in the turbine nozzle, the double-acting construction is employed including the relief valve 74. In this case, if the movement of rod 12 does not follow a control input, the hydraulic pressure can be reversed through a position feedback to positively drive thepiston 30 inward initially and finally exerted through passage 47 against the outer face of piston 36 to drive it back to its shoulder 28, carrying piston 30 with it. If the overbalance of pressure becomes too great, the relief valve 74 can operate to relive it. Relief valve 74 is redundant with a single-acting system but does no harm.

The operating characteristics of the actuator; that is, its characteristic of displacement of the rod 12 as a 20, in the absence of external forces, depends upon several factors. These are the effective areas of the pistons 30 and 36 and the preloadsand spring. rates of

springs

35 and 40. These may also be expressed as ratios of these parameters. A wide variety of characteristics are available, and any particular. one may be adopted by suitable selection of the parameters.

It should be clear from the foregoing to those skilled in the art that I have devised an actuator that is of simple and reliable construction and very well adapted to operate either as a single-acting or a double-acting hydraulic piston and cylinder device and which has a highly desirable movement characteristic for application to adjustment of turbine nozzles.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

I claim:

1. A hydraulic actuator comprising, in combination, a body defining a first cylinder and a second cylinder coaxial with and communicating with the first, a first piston reciprocable in the first cylinder, a second piston reciprocable in the second cylinder, the second piston being of less area than the first, means on the pistons normally abutting, a first spring biasing the first piston toward the second piston, a second spring biasing the second piston toward the first piston, the first spring having a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder being lower than that of the second cylinder, a first servo fluid connection communicating with the confronting faces of the pistons, anda second servo fluid connection communicating with the remote faces of both pistons; and an actuating rod connected to the second piston and extending from the body.

2. A hydraulic actuator comprising, in combination, a body defining a first cylinder and a second cylinder coaxial with andcommunicating with the first, a first piston reciprocable in the first cylinder, a second piston reciprocable in the second cylinder, the second piston being of less area than the first, axially adjustable means on the pistons normally abutting, a first spring biasing the first piston toward the second piston, a second spring biasing the second piston toward the first piston, the first spring having a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder being lower than that of the second cylinder, a high pressure servo fluid connection communicating with the confronting faces of the pistons, and a low pressure servo fluid connection communicating with the remote faces of both pistons; and an actuating rod connected to the second piston and extending from the body.

first spring having a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder beinglower than that of the secondcylinder, a first servo fluid connection communicating with the confronting faces of the pistons, and a second servo fluid connection communicating with the remote faces of both pistons; and an acutating rod connected to the second piston and extending from the body.

4. A'double-acting hydraulic actuator comprising, in combination, a body defining a first cylinder and a second cylinder coaxial with and communicating with the first, a first piston reciprocable in the first cylinder, a second piston reciprocable in the second cylinder, the second piston being of less area than the first, means on the pistons normally abutting, a first spring biasing the first piston toward the second piston, a second spring biasing the second piston toward the first piston, the first spring having a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder being lower than that of the second cylinder, a first servo fluid connection communicating with the confronting faces of the pistons, and a second servo fluid connection communicating with the remote faces of both pistons, a first pressure-limiting relief valve operative to bleed servo fluid from the first connection to the second, a second pressure-limiting relief valve effective to bleed servo fluid from the second connection to the first connection; and an actuating rod connected to the second piston and extending from the body.

5. A double-acting hydraulic actuator comprising, in combination, a body defining a first cylinder and a second cylinder coaxial with and communicating with the first, a first piston reciprocable in the first cylinder, a second piston reciprocable in the second cylinder, the second piston being of less area than the first, axially adjustable means on the pistons normally abutting, a first spring biasing the first piston toward the second piston, 21 second spring biasing the second piston toward the first piston, the first spring having 'a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder being lower than that of the second cylinder, a first servo fluid connection communicating with the confronting faces of the pistons, and a second servo fluid connection communicating with the remote faces of both pistons, a first pressure-limiting relief valve operative to bleed servo fluid from the first connection to the second, a second pressure-limiting relief valve mounted in the second piston effective to bleed servo fluid from the second connection to the first connection; an actuating rod connected to the second piston and extending from the body; and

limit stop means effective to limit movement of the actuating rod at each end of its travel.

Claims

1. A hydraulic actuator comprising, in combination, a body defining a first cylinder and a second cylinder coaxial with and communicating with the first, a first piston reciprocable in the first cylinder, a second piston reciprocable in the second cylinder, the second piston being of less area than the first, means on the pistons normally abutting, a first spring biasing the first piston toward the second piston, a second spring biasing the second piston toward the first piston, the first spring having a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder being lower than that of the second cylinder, a first servo fluid connection communicating with the confronting faces of the pistons, and a second servo fluid connection communicating with the remote faces of both pistons; and an actuating rod connected to the second piston and extending from the body.

2. A hydraulic actuator cOmprising, in combination, a body defining a first cylinder and a second cylinder coaxial with and communicating with the first, a first piston reciprocable in the first cylinder, a second piston reciprocable in the second cylinder, the second piston being of less area than the first, axially adjustable means on the pistons normally abutting, a first spring biasing the first piston toward the second piston, a second spring biasing the second piston toward the first piston, the first spring having a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder being lower than that of the second cylinder, a high pressure servo fluid connection communicating with the confronting faces of the pistons, and a low pressure servo fluid connection communicating with the remote faces of both pistons; and an actuating rod connected to the second piston and extending from the body.

3. A double-acting hydraulic actuator comprising, in combination, a body defining a first cylinder and a second cylinder coaxial with and communicating with the first, a first piston reciprocable in the first cylinder, a second piston reciprocable in the second cylinder, the second piston being of less area than the first, means on the pistons normally abutting, a first spring biasing the first piston toward the second piston, a second spring biasing the second piston toward the first piston, the first spring having a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder being lower than that of the second cylinder, a first servo fluid connection communicating with the confronting faces of the pistons, and a second servo fluid connection communicating with the remote faces of both pistons; and an acutating rod connected to the second piston and extending from the body.

4. A double-acting hydraulic actuator comprising, in combination, a body defining a first cylinder and a second cylinder coaxial with and communicating with the first, a first piston reciprocable in the first cylinder, a second piston reciprocable in the second cylinder, the second piston being of less area than the first, means on the pistons normally abutting, a first spring biasing the first piston toward the second piston, a second spring biasing the second piston toward the first piston, the first spring having a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder being lower than that of the second cylinder, a first servo fluid connection communicating with the confronting faces of the pistons, and a second servo fluid connection communicating with the remote faces of both pistons, a first pressure-limiting relief valve operative to bleed servo fluid from the first connection to the second, a second pressure-limiting relief valve effective to bleed servo fluid from the second connection to the first connection; and an actuating rod connected to the second piston and extending from the body.

5. A double-acting hydraulic actuator comprising, in combination, a body defining a first cylinder and a second cylinder coaxial with and communicating with the first, a first piston reciprocable in the first cylinder, a second piston reciprocable in the second cylinder, the second piston being of less area than the first, axially adjustable means on the pistons normally abutting, a first spring biasing the first piston toward the second piston, a second spring biasing the second piston toward the first piston, the first spring having a higher preload than the second spring, the ratio of spring force to piston area of the first cylinder being lower than that of the second cylinder, a first servo fluid connection communicating with the confronting faces of the pistons, and a second servo fluid connection communicating with the remote faces of both pistons, a first pressure-limiting relief valve operative to bleed servo fluid from the first connection to the second, a second pressure-limiting relief valve mounted in the second piston effective to bleed servo fluid from the second connection to the first connection; an actuating rod connected to the second piston and extending from the body; and limit stop means effective to limit movement of the actuating rod at each end of its travel.