US3913449A

US3913449A - Position-responsive hydraulic cylinder

Info

Publication number: US3913449A
Application number: US470133A
Authority: US
Inventors: James Allan Koch; Roger John Nelson; Donald Leroy Henderson
Original assignee: Deere and Co
Current assignee: Deere and Co
Priority date: 1974-05-15
Filing date: 1974-05-15
Publication date: 1975-10-21
Anticipated expiration: 1992-10-21
Also published as: AU7268674A; IT1035722B; AR208317A1; JPS50146793A; AU473393B2; FR2271426A1; DE2520039B2; CA1022040A; FR2271426B1; DE2520039A1; ES437680A1; GB1467932A; JPS6030841B2

Abstract

A double acting hydraulic cylinder with integral valves is described wherein rod extension is directly proportional to positioning of a control level. A change in the control lever to a certain setting causes an integral control valve to move to either side of a neutral position to selectively connect the cylinder chambers to the source or reservoir and thus to cause movement of the rod. In response to rod movement, a threaded feedback means causes movement of the valve such that, when the desired position of the rod is reached, the valve is returned to the neutral position. With the aid of an integral float valve, the control lever can be placed at a maximum or minimum setting and both chambers will be connected to the reservoir such that the position of the rod would be dependent on external forces on the rod.

Description

United States Patent 1191 Koch et al.

[451 Oct. 21, 1975 I POSITION-RESPONSIVE HYDRAULIC CYLINDER [75] Inventors: James Allan Koch, Hudson; Roger John Nelson, Cedar Falls; Donald LeRoy Henderson, Waterloo, all of Iowa [73] Assignee: Deere & Company, Moline, Ill.

[22] Filed: May 15, 1974 21 Appl. No.: 470,133

FOREIGN PATENTS OR APPLICATIONS 3/1884 United Kingdom 91/380 Primary Examiner-Paul E. Maslousky 57] ABSTRACT A double acting hydraulic cylinder with integral valves is described wherein rod extension is directly proportional to positioning of a control level. A change in the control lever to a certain setting causes an integral control valve to move to either side of a neutral position to selectively connect the cylinder chambers to the source or reservoir and thus to cause movement of the rod. In response to rod movement, a threaded feedback means causes movement of the valve such that, when the desired position of the rod is reached, the valve is returned to the neutral position. With the aid of an integral float valve, the'control lever can be placed at a maximum or minimum setting and both chambers will be connected to the reservoir such that the position of the rod would be dependent on external forces on the rod.

22 Claims, 6 Drawing Figures US. Patent Oct.21, 1975 Sheet10f4 3,913,449

58 FIG.

US. Patent Oct. 21, 1975 Sheet2of4 3,913,449

@NNN U.S. Patent Oct. 21, 1975 Sheet4of4 3,913,449

POSITION-RESPONSIVE HYDRAULIC CYLINDER BACKGROUND OF THE INVENTION The present invention relates generally to hydraulic cylinders and more specifically to a position-responsive hydraulic cylinder having an integral feed back means and integral control and float valves.

Previously position-responsive hydraulic cylinders were developed which made use of spring-type feedback means as shown in U.S. Pat. No. 2,966,891 to J. G. Williams and U.S. Pat. No. 3,51 1,134 to R. A. Wittren. These feedback means were complex in that adjustments were required for controlling spring tension versus control fluid pressure loading against a flexible diaphragm.

In addition, spring feedback means are inherently unstable under high speed operation over long rod extensions due to surging of the spring which will cause control valve flutter and may interfere with the proper operation of the cylinder.

SUMMARY OF THE INVENTION It is a general object of this invention to present a position-responsive hydraulic cylinder having an integral valve and direct mechanical feedback means not subject to flutter wherein the position of the control lever is directly proportional to the length of rod extension.

The above is accomplished by enclosing within a cylinder body a bi-directional movable piston and rod assembly and an integral three position four-way control valve for positioning the rod. By moving a control lever, the operator can move the control valve to either side of a neutral position to feed fluid to the cylinder chambers so as to cause movement of the rod in either direction. A feedback means including a member having a threaded engagement with the piston and rod assembly is directly coupled to the control valve and returns it to the neutral position when the desired rod setting is obtained.

It is a subsidary object to provide a positionresponsive cylinder wherein at least at one position of the control lever, the rod can be freely moved. This is accomplished through the use of a float valve which, upon adjustment of the control lever, is moved to connect either the source or the reservoir to the control valve; the former connection allowing position responsiveness and the latter allowing the position of the rod to the dependent on external forces on the rod.

The above and additional objectives and advantages of the invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS draulic cylinder of this invention taken along line 33 of FIG. 2.

FIG. 4 is a cross-sectional view of the hydraulic cylinder of this invention taken along 4-4 of FIG. 2.

FIG. 5 is a cross-sectional view of the porting of the integral valves of this invention taken along line 55 of FIG. 3, and also illustrates a schematic hydraulic system in which the cylinder could be used.

FIG. 6 is a partial cross-sectional view similar to FIG. 3 of a portion of the hydraulic cylinder in an alternate embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS During the detailed description of the preferred embodiment, reference to the front end of the cylinder shall mean the end on the left-hand side of the views shown in FIGS. 1,2,3, and 6. Similarly, the rear end of the cylinder shall mean the end on the right-hand side of the views shown in these drawings.

Referring now to FIGS. 1 and 2, the positionresponsive hydraulic cylinder 10 of this invention is shown. The cylinder 10 includes a housing 12 having on the rear end an attaching yoke 14 for attaching the cylinder to a supporting structure such as the rear of an agricultural tractor (not shown). Slidably received within housing 12 is a piston 24 and rod 16 assembly having a yoke 18 affixed to its forward end for accepting and carrying and end member such as a tractordrawn plow (not shown). A cantilever arm 20 rigidly fastened to yoke means 18 is slidably received in a bracket 21 mounted on housing 12 in order to prevent relative rotative movement between housing 12 and rod 16. Also, by impressing on arm 20 indicia 23 a visual indication of the position of rod 16 with respect to housing 12 can be obtained.

Referring now to the cross-sectional views of FIGS. 2 through 5, the internal working components of this invention are clearly shown. Rod 16 has secured to the rear end thereof, by retaining means 22, the piston 24 which divides housing 12 into first and

second chambers

26 and 28, respectively. Appropriate sealing means 30 prevents leakage between the chambers, and the forward end of the housing 12 contains sealing O ring 32 and rod sealing means 33 to prevent leakage of the hydraulic fluid from chambe 28.

In addition to

chambers

26 and 28, housing 12 also includes a cavity 34 to the rear of chamber 26. Cavity 34 communicates with a reservoir 202 of a conventional hydraulic fluid system through a bore 35 and a reservoir connected port 36. Received within a control valve bore 37 and axially in line with rod 16 is a control valving means or three position four-way control valve 38 for selectively controlling the flow of fluid into and from

chambers

26 and 28. In the wall defining bore 37 are a plurality of spaced apart annular grooves which comprise the working ports for valve 38 and which are designated as first port 40, second port 42 and third port 44. Port is connected through a passage 48 to chamber 26, and port 44 is connected through a passageway 46 to chamber 28. Port 42 is connected through a port 50 to a remote hydraulic pressure source 200 such as a hydraulic pump.

Valve 38 includes an outer porting means 51 which is slidable in a direction parallel to the longitudinal axis of the cylinder and is stoppable by a first stop means or bore bottom 98A in the forward direction and a second stop means or cavity shoulder 98 in the rearward direction. Concentrically arranged on porting means 51 are spaced apart annular lands 54 and 56 defined on each side by

grooves

53, and 57.

Grooves

53 and 57 communicate with the reservoir through

respective slots

59 and 61 which communicate with a passageway 36A to port 36 and with cavity 34, respectively. Lands 54 and 56 are constructed to block off

ports

40 and 44 from port 42 in the neutral position. Rearward movement of porting means 51 establishes a fluid communication between

ports

42 and 44 to permit pressurized fluid to flow into chamber 28 while port 40 is connected to the reservoir through groove 52 and slot 59. Similarly, forward movement of porting means 51 establishes a fluid communication between

ports

42 and 40 to permit pressurized fluid to flow into chamber 26 while port 44 is open to the reservoir through groove 57 and slot 61.

Axially received within porting means 51 and interconnected to an inner overtravel means 52, which will hereinafter be described, is an interconnecting means 49 comprising a helical spring 90 interposed therebetween and held by retaining means comprising the cooperation of washers 92 with

rings

94 and 94A and washer 92A with

rings

96 and 96A. The rings are positioned in grooves provided in each end of porting means 51 and overtravel means 52. Each end of spring 90 bears against one of the washers and the washers in turn bear against the retaining rings. This interconnection permits common movement of porting means 51 and overtravel means 52 to a predetermined distance in the rearward direction until porting means 51 abuts shoulder 98 and the movement of portion means 51 is abrogated, but overtravel means 52 is permitted to continue movement until a nut 76 attached to the overtravel means 52 abuts the rear wall of cavity 34. In the forward direction, portion means 51 and overtravel means 52 will both be stopped by bore bottom 98A.

Tubular overtravel means 52 which is axially received within the interconnecting means 49 includes a closed forward end 80 having therein an oblong aperture 82 and an open rearward end 84 wherein a biasing means or compression spring 86 may be interposed within the interior of overtravel means 52 to extend from closed end 80 to a positioning means 88 on the rear wall of cavity 34. Compression spring 86 serves to take up manufacturing tolerances, eliminate free play between valve 38 and a selector means 63 and the nut 76, both of which will hereinafter be described, and permit a control cable 62, included in the selector means 63, to act only in response to tensile positioning commands.

On the rear end of overtravel means 52 is an externally threaded portion which is readedly engaged with internally threaded nut 76. Nut 76 has two

slots

74A and 74B in opposite sides into which lugs 70 and 72 of a bifurcated arm member 68 slidably protrude. Member 68 is fixed to a pivot shaft 66 which is pivotally carried by housing 12 with a seal 67 and protrudes therefrom to the exterior of cylinder 10. Affixed to shaft 66 exterior to housing 12 and fixed relative to member 68 is a crank arm 64 which is a portion of the selector means 63, as shown in FIG. 1. Arm 64 is actuated by means of the control cable 62 which is operatively con,- nected with a further portion of the selector means 63 consisting of a control lever 58 and a quadrant 60 for operation by the operator.

When repositioning of rod 16 is desired, movement of control lever 58 from the old position to a new position causes pivotation of shaft 66 and movement of member 68, through cable 62 and arm 64, to cause longitudinal movement of nut 76. Since overtravel means 52 is threadedly engaged to nut 76, it will move longitudinally as will the interconnecting means 49 and porting means 51. Thus, as valve 38 moves longitudinally, lands 54 and 56 will move so as to affect communication of the source through port 42 with either

port

40 or 44 depending upon the direction of travel, while connecting the other port to the reservoir through groove 53 or groove 57 thereby causing rod 16 to either extend or retract towards the new position.

If the movement of control lever 58 is so great that port 42 will be blocked off by axial movement of porting means 51, overtravel means 52 operates to prevent this. Portingmeans 51 will be stopped by shoulder 98 before port 42 is blocked and overtravel means 52 continues to move axially rearward, and relative movement between porting means 51 and overtravel means 52 will be permitted by the compression of spring of interconnecting means 49. Overtravel means 52 in conjunction with interconnecting means 49 permits full range adjustment of control lever 58 without requiring sequential stepping through intermediate settings.

Once the desired new position of rod 16 has been obtained, the source must be disconnected, and this is done automatically by feedback means 100 rotatably carried by a journal 102 containing a sealing O-ring 99 provided in housing 12 between the chamber 26 and bore 37. Feedback means 100 has forward of journal 102, a threaded portion 104 which threadedly engages actuation means or pins 106 carried by rod 16. As rod 16 is extended or retracted, this longitudinal movement induces rotary movement of feedback means 100. Retaining means or snap ring 103 prevents forward longitudinal movement and thrust washers 101 may be added to eliminate longitudinal movement and thrust of the feedback means 100. Rearward of journal 102, feedback means 100 includes a projecting pintle 108 having a shape mating with and passing through the oblong aperture 82 in end 80 of overtravel means 52. Thus, rotary movement of feedback means 100 induces rotary movement of overtravel means 52. Since nut 76 is nonrotatably held by member 68, the threaded engagement induces longitudinal movement of valve 38 which returns to the neutral position.

With feedback means 100 cylinder 10 is completely position repsonsive to the operators command signal. In effect the position of control lever 58 indicates and is directly proportional to the position of rod 16. In addition cylinder 10 automatically compensates for fluid seepage between the

chambers

26 and 28 or between the valve ports because such seepage results in changes in rod 16 position which rotates feedback means 100 causing valve 38 to move longitudinally and place the proper ports in communication with source or reservoir as necessary to compensate for the seepage. As the seepage is replaced rod 16 will move back to its original position causing feedback means 100 to counterrotate and bring valve 38 back into the neutral position. Further, feedback means 100 permits the cylinder 10, when used in conjunction with a pressure regulating valve 114 to provide a constant output load at rod 16; in effect the cylinder 10 becomes a constant force generator at any rod position.

With the addition of a float valving means or float valve 110, the cylinder 10 can be placed in a free float condition wherein both

chambers

26 and 28 are connected to the reservoir and hence, rod 16 can be freely extended or retracted by application of exterior force on rod 16. Float valve 110 is interposed between port 50 and port 42 as can be seen from the cross-sectional views of FIGS. 4 and 5 and is slidably received within a valve bore 112 connected by passageway 36A to the reservoir, and further is urged against member 68 for movement therewith by a biasing means or spring 122. It has an annular groove 116 bordered on its ends by lands 118 and 118a, and an internal passageway 119 establishing communication between bore 112 and cavity 34. Annular groove 116 is of sufficient longitudinal length to normally allow fluid communication between port 42 and port 50 which are offset longitudinally from each other; however, when control lever 58 is extended to a minimum rod extension position, float valve 110 moves rearward so that land 118 blocks off communication between port 50 and port 42, and port 42 connects to bore 112 and through crosshole 36A to the reservoir. Since valve means 51 would be moved rearwardly to connect port 40 to groove 53, in this position both

chambers

26 and 28 are open to the reservoir allowing rod 16 to be freely adjustable by application of exterior force on the rod 16.

The operation of this invention commences with the operator selecting a length to which he wishes rod '16 to retract or extend by positioning control lever 58. This movement of control lever 58 causes pivotation of shaft 66 and movement of member 68 through an are which causes lugs 70 and 72 to push against nut 76 which in turn moves in either a forward or rearward direction as does valve 38. This motion of valve 38 allows pressurized fluid from the source to flow to either

chamber

26 or 28, while fluid in the other chamber is exhausted to the reservoir. As rod 16 begins to extend or retract, feedback means 100 commences to rotate, causing valve 38 to rotate and threadedly engage or disengage from nut 76 and hence move longitudinally with respect thereto. When rod 16 has reached its desired position, the valving means 38 will have longitudinally moved a sufficient distance to be in the neutral position and

ports

40 and 44 will be blocked off from the source connected port 42.

When the operator desires to put the cylinder in a float position, he adjusts control lever 58 to the float position, less than a minimum rod extension position, causing member 68 to pivot fully in one direction and float valve 110 to be urged by spring 122 fully in the one direction and communication between the reservoir and port 42 to occur. Consequentially, the chamber in communication with port 42 will be connected with the reservoir and simultaneously the other chamber also will be in communication with the reservoir through either

groove

53 or 57, and rod 16 can then be freely moved by pulling or pushing on it relative to housing 12.

In another preferred embodiment, the amount of adjustment of control lever 58 is made to match exactly, the amount of travel of valve 38A as shown in FIG. 6, which would eliminate the need for the overtravel means 52 and interconnecting means 49. The same numbers as in prior figures refer to the same parts in this embodiment.

Thus, it is apparent that there has been described a position-responsive hydraulic cylinder which fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and scope of the ap- 5 pended claims.

We claim:

1. A position-responsive hydraulic cylinder for use in a hydraulic system including a source of fluid pressure and a fluid reservoir, said hydraulic cylinder comprising: a cylinder body having a longitudinal bore; a piston and rod assembly slidably mounted in the bore to form an expandable pressure chamber therewith, and extending from one end of the cylinder body; valving means mounted in the cylinder body at the end thereof opposite from the one end and movable to either side of a neutral position to selectively connect the chamber with the source or reservoir; selector means operatively associated with the valving means to effect the position thereof; float valving means slidable within the cylinder body and interposed between the source and the valving means and positionable by the selector means to disconnect the source and connect the reservoir to the valve means; feedback means operatively associated with the valving means and the piston and rod assembly responsive to movement of the piston and rod assembly to a position selected by the position of the selector means to move the valving means to the neutral position; the feedback means including a member having a threaded engagement with the piston and rod assembly rotatable upon movement of the piston and rod assembly and connected to the valving means to move the valving means to a neutral position upon rotation.

2. A position-responsive hydraulic cylinder as claimed in claim 1 wherein the piston and rod assembly is provided with a longitudinal bore in the rod closed at one end and open at the other; and the member having a threaded engagement with the piston and rod assembly extends into the bore in the rod and is movable rotatably with respect to and in response to the movement of the piston and rod assembly.

3. A position-responsive hydraulic cylinder as claimed in claim 1 including biasing means for urging the valving means against the selector means.

4. A position-resonsive hydraulic cylinder as claimed in claim 1 still further including biasing means for urging the float valving means against the selector means.

5. A position-responsive hydraulic cylinder as claimed in claim 4 wherein the float valving means abuts the member movably carried by the cylinder body.

6. A position-responsive hydraulic cylinder as claimed in claim 1 wherein said selector means includes a nut threadedly engaged with the valving means and nonrotatably interconnected with a member movably carried in the cylinder body such that movement of the member induces longitudinal movement of the nut, and a control lever interconnected to said member for causing movement thereof.

7. A position-responsive hydraulic cylinder as claimed in claim 1 wherein said valving means includes porting means slidable and stoppable by first and second stop means in the cylinder body and operatively associated with overtravel means; said overtravel means being axially received within and separated from the porting means by interconnecting means for relative axial movement therebetween.

8. A position-responsive hydraulic cylinder as claimed in claim 7 wherein said interconnecting means between the porting means and overtravel means is a spring interposed therebetween with retaining means contiguous to at least one end of said spring; said retaining means having first annular stop means affixed to the overtravel means and second annular stop means affixed to the porting means and aligned with the first annular stop means; said retaining means further having an annular ring interposed between the spring and the first and second stop means.

9. A position-responsive hydraulic cylinder for use in a hydraulic system including a source of fluid pressure and a fluid reservoir, said hydraulic cylinder comprising: a cylinder body having a longitudinal bore; a piston and rod assembly slidably mounted in the bore to form an expandable pressure chamber therewith, and extending from one end of the cylinder body; valving means mounted in the cylinder body at the end thereof opposite from the one end and movable to either side of a neutral position to selectively connect the chamber with the source or reservoir; selector means operatively associated with the valving means to effect the position thereof; said selector means includes a nut threadedly engaged with the valving means and nonrotatably interconnected with a member movably carried in the cylinder body such that movement of the member induces longitudinal movement of the nut, and a control lever interconnected to said member for causing movement thereof; and feedback means operatively associated with the valving means and the piston and rod assembly responsive to movement of the piston and rod assembly to a position selected by the position of the selector means to move the valving means to the neutral position; said feedback means including a member having a threaded engagement with the piston and rod assembly rotatable upon movement of the piston and rod assembly and connected to the valving means to move the valving means to a neutral position upon rotation.

10. A position-responsive hydraulic cylinder for use in a hydraulic system including a source of fluid pressure and a fluid reservoir, said hydraulic cylinder comprising: a cylinder body having a longitudinal bore; a piston and rod assembly slidably mounted in the bore to form an expandable pressure chamber therewith, and extending from one end of the cylinder body; valving means mounted in the cylinder body at the end thereof opposite from the one end and movable to either side of a neutral position to selectively connect the chamber with the source or reservoir; said valving means includes porting means axially slidable between first and second stop means in the cylinder body and operatively associated with overtravel means; said overtravel means being axially received within and separated from the porting means by interconnecting means for axial movement greater than the distance between said first and second stop means; selector means operatively associated with the overtravel means to effect the position of the valving means; and feedback means operatively associated with the overtravel means and the piston and rod assembly responsive to movement of the piston and rod assembly to a position selected by the position of the selector means to move the valving means to the neutral position; said feedback means including a member having threaded engagement with the piston and rod assembly rotatable upon movement of the piston and rod assembly and connected to the overtravel means to move the valving means to a neutral position.

11. A position-responsive hydraulic cylinder as claimed in claim 10 wherein the interconnecting means between the porting means and overtravel means is a spring interposed therebetween with retaining means contiguous to at least one end of said spring; said retaining means having a first annular stop means affixed to the overtravel means and a second annular stop means affixed to the porting means and aligned with the first annular stop means; said retaining means further having an annular ring interposed between the spring and the first and second stop means.

12. A position-responsive hydraulic cylinder for use in a hydraulic system including a source of fluid pressure and a fluid reservoir, said hydraulic cylinder comprising: a cylinder body having a longitudinal bore; a piston and rod assembly slidably mounted in the bore to form inner and outer expandable pressure chambers therewith, and extending from one end of the cylinder body; valving means mounted in the cylinder body at the end thereof opposite from the one end and movable to either side of a neutral position to selectively connect one of the chambers to the source and the other chamber to the reservoir; selector means operatively associated with the valving means to effect the position thereof; float valving means slidable within the cylinder body and interposed between the source and the valving means and positionable by the selector means to disconnect the source and connect the reservoir to the valving means; and feedback means operatively associated with the valving means and the position and rod assembly responsive to movement of the piston and rod assembly to a position selected by the position of the selector means to move the valving means to the neutral position; said feedback means including a member having a threaded engagement with the piston and rod assembly rotatable upon movement of the piston and rod assembly'and connected to the valving means to move the valving means to the neutral position upon rotation.

13. A position-responsive hydraulic cylinder as claimed in claim 12 wherein the position and rod assembly is provided with longitudinal bore in the rod closed at one end and open at the other; the member having a threaded engagement with the piston and rod assembly extends into the bore in the rod and is movable rotatably with respect to and in response to the movement of the piston and rod assembly.

14. A position-responsive hydraulic cylinder as claimed in claim 12 including biasing means for urging the valve means against the selector means to take up tolerance accumulations and eliminate free play.

15. A position-responsive hydraulic cylinder as claimed in claim 12 still further including a biasing means for urging the float valving means against the selector means.

16. A position-responsive hydraulic cylinder as claimed in claim 15 wherein the float valving means abuts the member movably carried by the cylinder body.

17. A position-responsive cylinder as claimed in claim 12 wherein said selector means includes a nut threadedly engaged with the valving means and nonrotatably interconnected with a member carried in the cylinder body such that movement of the member thereof induces longitudinal movement of the nut, and

a control lever interconnected to said member for causing movement thereof.

18. A vposition-responsive hydraulic cylinder as claimed in claim 12 wherein said valving means includes porting means slidable and stoppable by first and second stop means in the cylinder body and operatively associated with overtravel means; said overtravel means being axially received within and separated from the porting means by interconnecting means for relative axial movement therebetween.

19. A position-responsive hydraulic 'cylinder as claimed in claim 18 wherein said interconnecting means between the porting means and overtravel means is a spring interposed therebetween with a retaining means contiguous to at least one end of said spring; said retaining means having first annular stop afiixed to the porting means and aligned with the first annular stop means, said retaining means further having annular ring interposed between the spring and the first and second stop means.

20. A position-responsive hydraulic cylinder for use in a hydraulic system including a source of fluid pressure and a fluid reservoir, said hydraulic cylinder comprising: a cylinder body having a longitudinal bore; a piston and rod assembly slidably mounted in the bore to form inner and outer expandable pressure chambers therewith, and extending from one end of the cylinder body; valving means mounted in the cylinder body at the end thereof opposite from the one end and movable to either side of a neutral position to selectively connect one of the chambers to the source and the other chamber to the reservoir; selector means operatively associated with the valving means to effect the position thereof; said selector means includes a nut threadedly engaged with the valving means and nonrotatably interconnected with a member carried in the cylinder body such that movement of the member thereof induces longitudinal movement of the nut, and a control lever interconnected to said member for causing movement thereof; and feedback means operatively associated with the valving means and the piston and rod assembly responsive to movement of the piston and rod assembly to a position selected by the position of the selector means to move the valving means to the neutral position; said feedback means including a member having a threaded engagement with the piston and rod assembly rotatable upon movement of the piston and rod assembly and connected to the valving means to move the valving means to the neutral position upon rotation.

21. A position-responsive hydraulic cylinder for use in a hydraulic system including a source of fluid pressure and a fluid reservoir, said hydraulic cylinder comprising: a cylinder body having a longitudinal bore; a piston and rod assembly slidably mounted in the bore to form inner and outer expandable pressure chambers therewith, and extending from one end of the cylinder body; valving means mounted in the cylinder body at the end thereof opposite from the one end and movable to either side of a neutral position to selectively connect one of the chambers to the source and the other chamber to the reservoir; said valving means includes porting means axially slidable between first and second stop means in the cylinder body and operatively associated with overtravel means, said overtravel means being axially received within and separated from the porting means by interconnecting means for axial movement greater than the distance between said first and second stop means; selector means operatively associated with the overtravel means to effect the position of the valving means; and feedback means operatively associated with the overtravel means and the piston and rod assembly responsive to the movement of the piston and rod assembly to a position selected by the position of the selector means to move the valving means to the neutral position; said feedback means including a member having a threaded engagement with the piston and rod assembly rotatable upon movement of the piston and rod assembly and connected to the overtravel means to move the valving means to a neutral position upon rotation.

22. A position-responsive hydraulic cylinder as claimed in claim 21 wherein the interconnecting means between the porting means and overtravel means is a spring interposed therebetween with a retaining means contiguous to at least one end of said spring; said retaining means having a first annular stop affixed to the porting means and aligned with the first annular stop means, said retaining means further having an annular ring interposed between the spring and the first and second stop means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIN Patent No. 3,913,449 Dated 21 October 1975 Inveht0r s James Allen Koch et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 44, change "resonive" to responsive;

Column 8, line 32, change "position" to -piston; line 43, change "position" to -piston.

Signal and geaied this Tenth Day of August 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN- Auesu'nx Officer Commissioner ofPatems and Trademarks

Claims

12. A position-responsive hydraulic cylinder for use in a hydraulic system including a source of fluid pressure and a fluid reservoir, said hydraulic cylinder comprising: a cylinder body having a longitudinal bore; a piston and rod assembly slidably mounted in the bore to form inner and outer expandable pressure chambers therewith, and extending from one end of the cylinder body; valving means mounted in the cylinder body at the end thereof opposite from the one end and movable to either side of a neutral position to selectively connect one of the chambers to the source and the other chamber to the reservoir; selector means operatively associated with the valving means to effect the position thereof; float valving means slidable within the cylinder body and interposed between the source and the valving means and positionable by the selector means to disconnect the source and connect the reservoir to the valving means; and feedback means operatively associated with the valving means and the position and rod assembly responsive to movement of the piston and rod assembly to a position selected by the position of the selector means to move the valving means to the neutral position; said feedback means including a member having a threaded engagement with the piston and rod assembly rotatable upon movement of the piston and rod assembly and connected to the valving means to move the valving means to the neutral position upon rotation.

17. A position-responsive cylinder as claimed in claim 12 wherein said selector means includes a nut threadedly engaged with the valving means and nonrotatably interconnected with a member carried in the cylinder body such that movement of the member thereof induces longitudinal movement of the nut, and a control lever interconnected to said member for causing movement thereof.

18. A position-responsive hydraulic cylinder as claimed in claim 12 wherein said valving means includes porting means slidable and stoppable by first and second stop means in the cylinder body and operatively associated with overtravel means; said overtravel means being axially received within and separated from the porting means by interconnecting means for relative axial movement therebetween.

19. A position-responsive hydraulic cylinder as claimed in claim 18 wherein said interconnecting means between the porting means and overtravel means is a spring interposed therebetween with a retaining means contiguous to at least one end of said spring; said retaining means having first annular stop affixed to the porting means and aligned with the first annular stop means, said retaining means further having annular ring interposed between the spring and the first and second stop means.