Hydraulic positioner with bidirectional detenting action

A hydraulic positioner for maintaining a given separation between its attachment points and having a bidirectional detenting action whereby the given separation can be altered only by application of a sufficiently large overriding force. A closed cylinder is divided into two closed fluid-filled chambers by a slidable piston. Motion of the piston requires transfer of fluid between the chambers. The transfer flow is determined by preloaded check valves in the transfer flow path. The check valves are preloaded in opposite directions to achieve the bidirectional detenting action. A reservoir supplies fluid under a small positive pressure to one of the closed fluid-filled chambers to replace fluid lost through leakage.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is in the field of hydraulics and more specifically 
relates to an hydraulic positioner for maintaining a given separation 
between its attachment points which has a bidirectional detenting action 
whereby the given separation can be altered only by application of a 
sufficiently large overriding force. 
2. The Prior Art 
Unlike shock absorbers, which are operative only when in motion, the 
present invention remains stationary between successive alterations. The 
present invention includes two attachment points whose separation is 
selectively alterable by application of a force in excess of a 
predetermined magnitude. As long as the predetermined magnitude of force 
is not exceeded, the device of the present invention provides a rigid 
connection between its two attachment points. From a first given 
separation, the attachment points can be selectively spread more widely 
apart or can be drawn more closely together, but not alteration can be 
made unless the applied force exceeds the predetermined magnitude. Thus, 
the present invention exhibits a bidirectional detenting action from any 
given separation. 
In contrast to the present invention, the invention disclosed by Ackerman 
in U.S. Pat. No. 3,236,515 exhibits a locking action rather than a 
detenting action. When Ackerman's device is locked, no amount of force 
will alter the separation between the attachement points. When Ackerman's 
device is unlocked, it will not maintain a given separation between the 
attachment points if a measurable force is applied to the attachment 
points. 
In U.S. Pat. No. 3,228,632, issued Jan. 11, 1966 to Hunth, a different form 
of lock is described. That device includes a piston movable within a 
cylinder by piston rods extending in opposite directions from the piston. 
One side of the piston is called the inlet side and the other side of it 
is called the outlet side. The device is set to transmit movements of 
varying amplitude and direction from the inlet piston rod to the outlet 
rod while preventing reaction forces applied to the outlet rod from being 
transmitted to the inlet rod. In contrast with the present invention, the 
Hunth device lacks a reservoir and employs a different system of valving. 
In U.S. Pat. No. 2,782,877 issued Feb. 26, 1957 to Crabtree, there is shown 
a shock absorber in which the rate of movement is controlled by opposed 
flapper valves. The flappers are resiliently deformable, and the 
construction of the flapper valve is such that the application of any 
measurable force will result in some fluid flow. Consequently, the 
Crabtree device is incapable of maintaining a fixed separation between its 
attachment points when forces less than a predetermined magnitude are 
applied. Crabtree shows a reservoir which is pressurized by the 
compression of air which partially fills the reservoir. Transfer of fluid 
from the reservoir to one of the working chambers is controlled by a 
preloaded ball check valve. 
In U.S. Pat. No. 2,487,472 issued Nov. 8, 1949 to Patriquin, and in 
Canadian Pat. No. 587,934, issued Dec. 1, 1951 to Whisler, Jr. there is 
shown a check valve in which an O-ring forms a seal between a surface of a 
piston and the cylinder wall. Both of these devices differ markedly in 
structure and operation from the present invention. Neither of these 
inventions will maintain a fixed separation between its attachment points 
when any measurable force is applied in one of the two directions. 
In a copending application, Ser. No. 761,908 filed Jan. 24, 1977, the 
present inventor, John Kourbetsos, has disclosed a hydraulic snubber in 
which a check valve employing an O-ring is used for limiting the rate of 
motion in one direction while alternately permitting unlimited rate of 
motion in the opposite direction. Clearly, that device cannot be used to 
maintain a fixed separation between its attachment points. 
Thus, it appears that none of the prior art inventions described above 
operate in the same manner as the present invention, and in addition, the 
present invention can be distinguished on the basis of its structure. 
The prior art does not disclose a hydraulic positioner for maintaining a 
given separation between its attachment points and exhibiting a 
bidirectional detenting action whereby it rigidly maintains the given 
separation until the separation is altered by application in either 
direction of an overriding force greater than some predetermined 
magnitude. The present invention further includes a pressurized reservoir 
for replacing any fluid lost by leakage. Thus, it appears that the present 
invention fills a long-standing deed for a device of its kind, and should 
prove valuable in such diverse applications as supporting the hoods of 
automobiles and trucks, positioning lamps and illuminators, and providing 
steady support for positioning apparatus used by a dentist. 
SUMMARY OF THE INVENTION 
In the present invention, a closed cylinder is divided into two closed 
fluid-filled chambers by a slidable piston. Motion of the piston within 
the cylinder requires a transfer of fluid between the chambers. This flow 
of fluid is determined by preloaded check valves, associated with the 
piston and moving with it. The check valves are preloaded in opposite 
directions to achieve a bidirectional detenting action. When a force, 
applied to the piston is less than that required to overcome the 
preloading of the appropriate check valve, the separation between the 
points of attachment remains fixed and the device provides a rigid 
connection between its attachment points. However, when the applied force 
is sufficiently great to overcome the preload on the applicable check 
valve, the valve opens, permitting transfer of fluid from one another to 
the other and resulting in movement of the piston within the cylinder, 
which in turn alters the separation between the points of attachment. 
Piston rods are attached to the piston and extend from it in opposite 
directions. Each of the piston rods passes through a seal at an end of the 
cylinder and extends beyond the cylinder. One of the rods extends into a 
reservoir of pressurized fluid. Pressurization, in a preferred embodiment 
is achieved by a compression spring which bears on a pressurizing piston. 
The rod which extends into the reservoir is provided with an internal 
passage ported to the outside surface of the rod at locations spaced 
axially along the rod so that when one of the ports opens into the 
reservoir, the port at the other end of the passage opens into one of the 
fluid-filled chambers adjacent the slidable piston. In that position, 
pressurized fluid can communicate between the reservoir and the chamber so 
as to maintain a modest overpressure in the chamber and to permit a flow 
of fluid from the reservoir into the chamber to replace fluid lost by 
leakage. 
Two check valves are associated with the piston for movement with it. In a 
preferred embodiment of the invention, one of the check valves is a 
preloaded ball check valve disposed to control the flow of fluid through a 
passage extending through the piston. In that embodiment, the other check 
valve associated with the piston includes a spring-loaded O-ring oriented 
in a plane perpendicular to the axis of the cylinder and of suitable 
diameter to slidably sealingly engage the inner surface of the cylinder. 
The O-ring is preloaded against a peripheral portion of the piston to form 
a defeatable seal with it to normally prevent the flow of fluid between 
the piston and the wall of the cylinder, between which there is a small 
space. 
In an alternative embodiment, the piston is provided with an O-ring seal 
around its periphery which maintains an undefeatable slidable sealing 
engagement between the piston and the cylinder wall. In this alternative 
embodiment, two preloaded ball check valves are associated with the piston 
and move with it. These ball check valves are preloaded in opposite 
directions and each control the flow of fluid through a passage through 
the piston. It is seen that the O-ring check valve used in the preferred 
embodiment serves a dual purpose in that it acts as a check valve and in 
addition it provides a seal between the piston and the cylinder wall, 
thereby eliminating the need for the O-ring used in the alternative 
embodiment to seal between the piston and the cylinder wall. In both of 
the embodiments described above, a small space is left intentionally 
between the metallic portion of the piston and the inner wall of the 
cylinder, and in both embodiments this space is sealed by an O-ring seal. 
In a preferred embodiment, the hydraulic positioner of the present 
invention is attached to the object whose separation it is desired to 
maintain at two points. One of the attachment points is at one end of the 
solid piston rod which extends beyond the end of the cylinder. The other 
attachment point is connected to the cylinder, and in a preferred 
embodiment is located axially at the end of the positioner opposite the 
first attachment point. 
In all embodiments of the present invention, the two piston rods which 
extend in opposite directions from the piston move in unison with the 
piston. Alterations in the separation are accommodated by motion of the 
piston with respect to the cylinder which surrounds it. 
The novel features which are believed to characterize the invention, both 
as to its structure and operation will be better understood from the 
following detailed description considered in connection with the 
accompanying drawings in which a preferred embodiment and an alternative 
embodiment of the invention are illustrated by way of example. It is to be 
understood, however, that the drawings are for the purpose of illustration 
and description only, and are not intended as a definition of the limits 
of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the drawings in which like parts are denoted by the same 
reference numerals, the preferred embodiment and best known mode for 
practicing the invention is shown in FIG. 1 in cross sectional view. The 
body of the hydraulic positioner has the form of a hollow cylinder 12 
extending along an axis 14 from a first end 16 to a second end 18, and 
having an inwardly-facing bore surface 20. 
A piston assembly 22 is slidable axially within the cylinder and has a 
first side 24 facing to the right in FIG. 1 and a second side 26 facing to 
the left in FIG. 1. The piston has a peripheral portion 28 which includes 
generally the portions of the piston extending both radially and axially 
which lie farthest from the axis 14. It should be noted, however, that the 
peripheral portion 28 of the piston does not extend so far outward 
radially as to contact the bore surface 20; instead, an annular space is 
left between them. 
A first rod 30 attached to the first side 24 of the piston assembly 22 
extends axially in a first direction, to the right in FIG. 1 beyond the 
first end 16 of the hollow cylinder 12. A second rod 32, attached to the 
second side 26 of the piston assembly 22 extends in a second direction, to 
the left in FIG. 1 beyond the second end 18 of the hollow cylinder 12. 
The hollow cylinder 12 is sealed at its first end 16 by the U-cup seal 34 
and at its second end 18 by the resilient O-ring 36 and the metallic glide 
ring 37, the latter preventing damage to the O-ring 36 as the port 80 
slides past the O-ring. The sealing members 34, 36, 37 remain stationary 
with respect to the hollow cylinder 12. as the piston assembly 22 and the 
piston rods 30, 32 attached to it move as a unitary structure through the 
hollow cylinder 12. Additional sealing is provided by a gland 38 at the 
first end 16 of the cylinder 12. The rods 30, 32 fit slidably through the 
bearings 40, 42, also located near the ends of the cylinder and which 
maintain the alignment of the rods 30, 32 with the axis 14 of the cylinder 
12. The piston assembly 22 divide the volume of the hollow cylinder 12 
into two sealed chambers 44, 46 which are separated by the piston assembly 
22. The first rod 30 and the second rod 32 have the same diameter in the 
preferred embodiment, and therefore the volume within the hollow cylinder 
12 occupied by the piston assembly 22 and portions of the rods 30, 32 
remains constant as the piston assembly is moved axially within the 
cylinder 12. This contrasts sharply with the situation which prevails in 
many shock absorbers in which the piston assembly is attached to the end 
of only one piston rod. In such cases, the volume displaced by the piston 
rod and piston assembly varies as the piston moves due to intromission and 
withdrawal of the piston rod so that it becomes necessary to provide for 
the transfer of some of the fluid to and from a reservoir. The provision 
of the second piston rod 32 in the preferred embodiment eliminates the 
need for a reservoir, although, as will be seen below, it is desirable to 
provide a reservoir for other reasons. 
In the preferred embodiment, all of the volume within the first sealed 
chamber 44 and second sealed chamber 46 not occupied by the piston 
assembly 22 and portions of the rods 30, 32 is filled with a fluid. In the 
preferred embodiment, the fluid is a liquid hydraulic fluid, and the word 
fluid is used in its general sense to include liquids, gases, and vapors 
in other embodiments. 
In the preferred embodiment in FIG. 1, an O-ring 48 is associated with the 
piston assembly 22 to form a first check valve. The O-ring 48 always 
remains oriented in a plane perpendicular to the axis 14 and is captively 
confined to the piston assembly 22 by the compression spring 50 which 
bears against the crescent ring 52 continually urging the O-ring 48 to the 
right in FIG. 1. The O-ring 48 always remains in slidable sealing 
engagement with the bore surface 20, and when the piston assembly 22 is 
stationary, the O-ring 48 sealingly engages a radially extending surface 
on the peripheral portion 28 of the piston assembly 22 to form a seal 
between the piston assembly and the bore surface 20. A force applied to 
the piston assembly 22 in the second direction, left in FIG. 1, tends to 
cause the O-ring 48 to seal more tightly against the peripheral portion 28 
of the piston assembly 22, thereby preventing fluid from flowing from the 
second sealed chamber 46 around the peripheral portion 28 of the piston 
into the first sealed chamber 44. 
On the other hand, a force applied to the piston assembly 22 in the first 
direction, to the right in FIG. 1, instantaneously causes a pressure 
differential between the portions of the O-ring 48 in contact respectively 
with the fluid in the chambers 44, 46 and this differential pressure, 
aided by the sliding friction between the O-ring 48 and the bore surface 
20, urges the O-ring away from the peripheral portion 28 of the piston. 
When the separating forces exceed the force applied by the compression 
spring 50, the O-ring separates from the periperhal portion 28 of the 
piston, defeating its sealing engagement therewith, and permitting fluid 
to flow from the first sealed chamber 44 axially around the peripheral 
portion 28 of the piston through the annular space between it and the bore 
surface 20 and into the second sealed chamber 46. 
It is noteworthy that the O-ring 48 serves both as a seal between the 
piston assembly 22 and the bore surface 20 and also serves as a check 
valve to control the flow of fluid from the first sealed chamber 44 to the 
second sealed chamber 46. 
From FIG. 1 it can be seen that withdrawal of the rod 30 from the cylinder 
is possible only when sufficient force is applied to the rod 30 in the 
first direction (to the right in FIG. 1) to overcome the preloading force 
of the compression spring 50 against the O-ring 48. In this manner, the 
separation between the attachment points 54, 56 can be increased. 
Motor of the piston assembly 22 in the second direction (to the left in 
FIG. 1) is controlled by a ball check valve which controls the flow of 
fluid from the second sealed chamber 46 through a port 58 through a 
passage 60 and through a port 62 to the first sealed chamber 44. The ball 
check valve includes a circular valve seat 64 against which a ball 66 is 
continually urged by a compression spring 68. When a force is applied to 
the piston assembly 22 in the second directior (to the left in FIG. 1) a 
differential pressure is created across the ball 66 which tends to urge it 
away from the valve seat 64. When the applied force is sufficiently great, 
the urging of the compression spring 68 is overcome and the seal between 
the ball 66 and the valve seat 64 is defeated permitting fluid to flow 
from the second sealed chamber 46 to the first sealed chamber 44 thereby 
permitting the piston assembly 22 to advance in the second direction 
relative to the cylinder 12. In this manner, the separation between the 
attachment points 54, 56 is decreased , but only when a sufficiently large 
force is applied. If a lesser force is applied, the hydraulic positioner 
remains rigid, maintaining the separation between the attachment points 
54, 56. 
In the preferred embodiment, a fluid reservoir is provided in the form of a 
cylindrical extension 72 of the hollow cylinder 12, connected to the 
hollow cylinder 12 at its second end 18 and extending in the second 
direction. The cylindrical extension 72 is closed at its left-most end 74 
by an end plug 76, to form a reservoir chamber 78 closed at its other end 
by the O-ring 36 and glide ring 37. 
In the preferred embodiment, the second rod 32 extends in the second 
direction into the reservoir chamber 78. The second rod 32 is provided 
with an axially-extending passage within it, which communicates with the 
reservoir chamber 78 through a port 80 and with the second sealed chamber 
46 through the port 58. The reservoir chamber 78 is filled with fluid and 
the fluid is maintained under a small positive pressure by the force of 
the compression spring 82 applied to the U-cup seal 84. The pressure thus 
produced on the fluid in the reservoir chamber 78 is chosen to be 
considerably less than that required to open the ball check valve 66. In 
the preferred embodiment, the passage 70 is terminated by the fill screw 
86. 
Although the positioner of the present invention would function adequately 
without the reservoir, certain advantages can be obtained through its use. 
The reservoir maintains a small positive overpressure in the chamber 46. 
This overpressure is transmitted to the sealed chamber 44 when the 
chambers are in communication and also the pressure is transmitted by the 
piston assembly 22 when the check valves are closed. The small positive 
overpressure in the sealed chambers 44, 46 prevents ambient fluids from 
entering those chambers. The overpressure also serves to drive fluid from 
the reservoir chamber 78 into the sealed chambers 46, 44 to replace the 
fluid lost from those chambers by leakage. 
Turning now to the alternative embodiment of the piston assembly shown in 
FIG. 2, it can be seen that a symmetrical arrangement of ball check valves 
66, 88 is used to control the flow of fluid through the piston assembly 
22. An O-ring seal 90 is seated on the surface of the peripheral portion 
28 of the piston assembly 22, and is always in sealing engagement with 
both the piston assembly 22 and the bore surface 20 to prevent the passage 
of fluid through the space therebetween. 
In the alternative embodiment of FIG. 2, two separate passages 92, 94 are 
provided to permit the flow of fluid through the piston assembly between 
the sealed chambers 44, 46. 
When a force is applied to the piston assembly 22 in the second direction 
(to the left in FIG. 2) a pressure differential is created across the ball 
66 tending to urge it away from its seat 64. If the applied force is of 
sufficient magnitude, the ball 66 is forced away from its seat, overcoming 
the urging of the compression spring 96 and permitting the fluid to flow 
from the second sealed chamber 46, through the port 58, through the 
passage 70, past the ball valve 66 through the passage 98, through the 
passage 92 and into the first sealed chamber 44, permitting the piston 
assembly 22 to move in the second direction relative to the cylinder 12. 
Likewise, when a sufficiently strong force is applied to the piston 
assembly 22 in the first direction (to the right in FIG. 2) the ball 88 is 
moved away from its seat 100 thereby permitting fluid to flow from the 
first sealed chamber 44 through the port 102 into the passage 104, past 
the valve 88, through the passage 106 into the passage 94 to the second 
sealed chamber 46, thereby permitting the piston assembly 22 to move in 
the first direction relative to the cylinder 12. 
Thus, the alternative embodiment shown in FIG. 2 provides the same type of 
bidirectional detenting action as the preferred embodiment of FIG. 1, in 
that the device rigidy maintains a fixed separation between the attachment 
points 54, 56 until a sufficiently strong overriding force is applied in 
either direction to overcome the preloading of the respective check 
valves. The alternative embodiment shown in FIG. 2 is provided with a 
reservoir similar to that shown in connection with the preferred 
embodiment of FIG. 1. 
Thus, there has been described a hydraulic positioner which can be adjusted 
to a given separation between its attachment points and which thereafter 
maintains indefinitely the given separation, and which has a bidirectional 
detenting action whereby the given separation can be increased or 
decreased only by application of a sufficiently overriding force in the 
desired direction. 
The hydraulic positioner is provided with a pressurized reservoir of fluid 
which prevents air or ambient fluids from entering the sealed chambers, 
which would tend to render the positioner less rigid when used to maintain 
a given separation between two objects. The reservoir supplies fluid to 
the sealed chambers to replace any fluid that may be lost by leakage. 
Althrough the present invention has been described in relation to an 
exemplary preferred embodiment and an alternative embodiment, it is 
recognized that numerous design variations are conceivable within the 
spirit of the present invention. Such design variations are therefore 
included within the present invention which is limited only by the scope 
of the appended claims.