WO1993019300A1 - Hydraulic cylinder feedback control - Google Patents

Hydraulic cylinder feedback control Download PDF

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Publication number
WO1993019300A1
WO1993019300A1 PCT/NZ1993/000018 NZ9300018W WO9319300A1 WO 1993019300 A1 WO1993019300 A1 WO 1993019300A1 NZ 9300018 W NZ9300018 W NZ 9300018W WO 9319300 A1 WO9319300 A1 WO 9319300A1
Authority
WO
WIPO (PCT)
Prior art keywords
piston
control rod
hydraulic cylinder
control
output shaft
Prior art date
Application number
PCT/NZ1993/000018
Other languages
French (fr)
Inventor
Keith Vivian Alexander
Original Assignee
C.W.F. Hamilton & Co. Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by C.W.F. Hamilton & Co. Limited filed Critical C.W.F. Hamilton & Co. Limited
Publication of WO1993019300A1 publication Critical patent/WO1993019300A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B9/00—Servomotors with follow-up action, e.g. obtained by feed-back control, i.e. in which the position of the actuated member conforms with that of the controlling member
    • F15B9/02—Servomotors with follow-up action, e.g. obtained by feed-back control, i.e. in which the position of the actuated member conforms with that of the controlling member with servomotors of the reciprocatable or oscillatable type
    • F15B9/08—Servomotors with follow-up action, e.g. obtained by feed-back control, i.e. in which the position of the actuated member conforms with that of the controlling member with servomotors of the reciprocatable or oscillatable type controlled by valves affecting the fluid feed or the fluid outlet of the servomotor
    • F15B9/10—Servomotors with follow-up action, e.g. obtained by feed-back control, i.e. in which the position of the actuated member conforms with that of the controlling member with servomotors of the reciprocatable or oscillatable type controlled by valves affecting the fluid feed or the fluid outlet of the servomotor in which the controlling element and the servomotor each controls a separate member, these members influencing different fluid passages or the same passage

Definitions

  • the invention relates to the control of hydraulic cylinders and particularly to feedback control for hydraulic cylinders to convert rotary motion of a controller to linear movement of the hydraulic cylinder.
  • the feedback control is suitable for a range of uses including operation of a hydraulic cylinder adapted to operate a reverse duct of a water jet.
  • British Patent specification number 2006991 describes a rotary to linear servo mechanism which converts mechanical rotary motion into hydraulic motion in a piston. This construction uses a spring return with a linear valve in the piston.
  • British Patent specification number 2072886 describes a servo assembly for a vehicular braking system. This assembly uses rotary porting in the piston with both spring return and porting to give true two-way actuation without the use of back pressure.
  • British Patent specification number 1467932 discloses a cylinder feedback mechanism with a rotatable piston which communicates with a valve. The mechanism uses a screw turned by the piston to operate the valve. The specification states that the screw type feedback mechanism is connected between a piston-rod and control valve so as to restore the control valve to a neutral position when the piston has moved to a position corresponding to that set by a control mechanism.
  • the valve details are axial and very complex.
  • An object of the invention is to provide a simple yet effective means for providing control of the extension of a hydraulic cylinder where the cylinder extension is a function of the position of a rotatable control lever.
  • a further object of the invention is to provide feedback and control internal to a hydraulic cylinder to thereby provide compact accurate positioning of the hydraulic cylinder.
  • a means for providing control of the extension of a hydraulic cylinder including a control rod within the cylinder, the control rod being rotated either directly by a control lever or adapted to be rotated by an output from a rotary valve, the control rod extending into a bore in the piston and an output shaft associated therewith, the output shaft extends linearly from the hydraulic cylinder, in use the piston and output shaft are moved on rotary movement of the control lever which either opens or closes porting between a hole in the piston or output shaft and a spiral groove in the control rod to create a pressure imbalance which moves the piston to a position where the force on each face of the piston is the same or opens porting in the rotary valve to move the piston which rotary movement turns an inner part of the rotary valve until the porting is closed which balances the hydraulic system.
  • a means for providing control of the extension of a hydraulic cylinder including a control rod within the hydraulic cylinder, the control rod being adapted to be rotated by an output from a hydraulically operated rotary valve, the rotary valve having a valve outer the position of which is controlled by an outer member within which is an inner member formed either integrally with or at one end of the control rod, the periphery of the control rod is twisted or formed along its length into a helical form, the control rod extending into a bore in a piston and associated output shaft of the hydraulic cylinder through a hole which is the same in cross-section as the cross-section of the twisted or helical portion of the rod, in use the piston and output shaft are moved by rotary movement of the control lever which opens porting in the rotary valve to apply pressure to one side of the piston so that it moves and as it moves forwards or backwards it rotates the control rod until the porting is closed to balance the hydraulic system.
  • a means for providing control of the extension of a hydraulic cylinder including a control rod within the hydraulic cylinder, the control rod being rotated directly by a control lever, the control rod extending into a bore in the piston and an output shaft associated therewith, the output shaft extends linearly from the hydraulic cylinder, in use the piston and output shaft are moved on rotary movement of the control lever which opens or closes porting between a hole in the piston or output shaft and a spiral groove in the control rod to thereby create a force imbalance which moves the piston to a position where the force on each side of the piston is the same.
  • Figure 1 shows a cross-section through an example which is in accordance with a second aspect of the invention
  • Figure 2 shows diagrammatically and exploded apart the internal parts of the example shown in Figure 1;
  • Figure 3 shows a section on the lines II-II through the example of the invention shown in Figures 1 and 2;
  • Figure 4 shows schematically the example shown in Figures 1 to 3;
  • Figure 5 shows a cross-section through a second example which is in accordance with a third aspect of the invention.
  • Figure 6 shows a perspective view of a control lever and control rod of the second example shown in Figure 5;
  • Figure 7 shows a plan view of a piston and control rod of the second example shown in Figure 6;
  • Figure 8 shows a plan view of the piston and control rod shown in Figure 7 after rotation of a control lever
  • Figure 9 shows a section on the lines A-A through the hydraulic cylinder shown in Figure 5;
  • Figure 10 shows a schematic hydraulic circuit diagram for the example shown in Figures 5 to 10.
  • the invention is based on a control rod extending through the centre of the hydraulic cylinder providing feedback off the piston position.
  • the first example with reference to Figures 1 to 4 is the back pressure design where the piston is one part of the valve and the control movement the other.
  • the back pressure provides two-way control.
  • the second example with reference to Figures 5 to 8 is the twisted rod design where the piston movement turns one part of the valve and the control movement turns the other.
  • the piston 1 is mounted within a hydraulic cylinder casing 2.
  • the piston 1 twists a feedback control rod 3 ( Figures 1 and 2).
  • One end 4 of the feedback rod 3 is an inner part 5 part of a rotary spool valve 6.
  • This valve could be any type of rotary valve.
  • a control lever 7 is part of or connected to the other or outer part 8 of the rotary spool valve 6.
  • the difference in angular position between the control lever 7 and the feedback rod 3 controls porting 9,10 in the outer part 8 of the spool valve 6 which causes the cylinder to either extend or contract.
  • the porting 9,10 cooperates with porting 11 on the inner part 5 of the rotary spool valve 6.
  • the feedback control rod 3 can include a twisted rod section 12 which extends through a square hole 13 in the piston 1.
  • the hole 13 is associated with a bore 14 in an output shaft 15 of the hydraulic cylinder.
  • the hydraulic power source for the hydraulic cylinder is from a pump 16 which operates in association with hydraulic liquid supply tank 17. Operation of the hydraulic circuit can be seen from Figures 1, 3 and 4 where the flow paths of the hydraulics are indicated by arrows 18,19. Rotation of the control lever 7 clockwise ( Figure 3) opens porting 9, 9 increasing pressure in the direction of arrow 19 to move cause the piston 1 to move in the direction of arrow 20. Reverse movement opening porting 10, 10 causing opposite movement.
  • the second example shown in Figures 5 to 10 is in accordance with the ⁇ e.'ond aspect of the invention and is based on a control rod 3 geing down the centre of a piston 1 in a hydraulic cylinder casing 2 and this provides feedback off the piston position.
  • Implementation in this example utilises feedback taken directly from the position of a piston 1 in relation to the rod 3.
  • a groove 21 in the control rod 3, which is directly turned by a control lever 7, acts on porting 22 in the piston 1 to provide controlled flow and pressure to both sides 23,24 of the piston 1. This provides a controlled pressure drop between both sides of the piston causing the piston to move.
  • a returning force can be by either a return spring (not shown) or a constant back pressure.
  • Closing of the restriction or port 22 by side edges 25 of the groove 21 and the cylinder extends. Opening of the port 22 and the cylinder contracts with the aid of the back pressure against the face 24 of the piston. A balance is found where the pressure drop over the restriction 22 and this provides enough force to balance the load.
  • Figure 8 is shown the positions of the edges 25 of the groove 21 after a control input from lever 7. The final position of the groove 21 and piston 1 are shown dotted.

Abstract

A hydraulic cylinder (2) having a piston (1) and a linearly extending output shaft (15) controlled by a rotary spool valve (6). The rotary spool valve (6) has a ported outer part (8) rotatable by means of a control lever (7) to pressurize the cylinder (2) and move the piston (1). Linear motion of the piston (1) is converted to rotary movement of a control rod (3) located in a bore of the piston (1) by means of twisted rod section (12). The control rod (3) is coupled to a ported inner part of the rotary spool valve (6) to provide feedback. In an alternative embodiment, the control rod (3) is directly rotated by the control lever (7) to open or close porting between a hole in the piston (1) or output shaft (15) and a spiral groove in the control rod (3) to create a force imbalance across the piston (1), which moves the piston (1) to a new position of equilibrium.

Description

HYDRAULICCYLINDERFEEDBACKCONTROL
The invention relates to the control of hydraulic cylinders and particularly to feedback control for hydraulic cylinders to convert rotary motion of a controller to linear movement of the hydraulic cylinder. The feedback control is suitable for a range of uses including operation of a hydraulic cylinder adapted to operate a reverse duct of a water jet.
A number of mechanisms for converting motion of this type have been used in the past although none of these have ever, as far as the applicants are aware, been tried for operation on a water jet. These mechanism suffer from inherent disadvantages mainly because of their size, complexity and cost which makes them unsuitable for use with a water jet. For example, British Patent specification number 1291832 describes a servo mechanism for producing an output movement dependent on two independent input movements. This mechanism utilizes back pressure dependent on a linear movement in one of the inputs. The valve is in the piston but operates linearly.
British Patent specification number 2006991 describes a rotary to linear servo mechanism which converts mechanical rotary motion into hydraulic motion in a piston. This construction uses a spring return with a linear valve in the piston.
British Patent specification number 2072886 describes a servo assembly for a vehicular braking system. This assembly uses rotary porting in the piston with both spring return and porting to give true two-way actuation without the use of back pressure. British Patent specification number 1467932 discloses a cylinder feedback mechanism with a rotatable piston which communicates with a valve. The mechanism uses a screw turned by the piston to operate the valve. The specification states that the screw type feedback mechanism is connected between a piston-rod and control valve so as to restore the control valve to a neutral position when the piston has moved to a position corresponding to that set by a control mechanism. The valve details are axial and very complex.
An object of the invention is to provide a simple yet effective means for providing control of the extension of a hydraulic cylinder where the cylinder extension is a function of the position of a rotatable control lever.
A further object of the invention is to provide feedback and control internal to a hydraulic cylinder to thereby provide compact accurate positioning of the hydraulic cylinder.
Further objects and advantages of the invention will become apparent from the following examples which are given by way of example only.
According to a broadest aspect of the invention there is provided a means for providing control of the extension of a hydraulic cylinder, the means including a control rod within the cylinder, the control rod being rotated either directly by a control lever or adapted to be rotated by an output from a rotary valve, the control rod extending into a bore in the piston and an output shaft associated therewith, the output shaft extends linearly from the hydraulic cylinder, in use the piston and output shaft are moved on rotary movement of the control lever which either opens or closes porting between a hole in the piston or output shaft and a spiral groove in the control rod to create a pressure imbalance which moves the piston to a position where the force on each face of the piston is the same or opens porting in the rotary valve to move the piston which rotary movement turns an inner part of the rotary valve until the porting is closed which balances the hydraulic system.
According to a second aspect of the invention there is provided a means for providing control of the extension of a hydraulic cylinder, the means including a control rod within the hydraulic cylinder, the control rod being adapted to be rotated by an output from a hydraulically operated rotary valve, the rotary valve having a valve outer the position of which is controlled by an outer member within which is an inner member formed either integrally with or at one end of the control rod, the periphery of the control rod is twisted or formed along its length into a helical form, the control rod extending into a bore in a piston and associated output shaft of the hydraulic cylinder through a hole which is the same in cross-section as the cross-section of the twisted or helical portion of the rod, in use the piston and output shaft are moved by rotary movement of the control lever which opens porting in the rotary valve to apply pressure to one side of the piston so that it moves and as it moves forwards or backwards it rotates the control rod until the porting is closed to balance the hydraulic system.
According to a third aspect of the invention there is provided a means for providing control of the extension of a hydraulic cylinder, the means including a control rod within the hydraulic cylinder, the control rod being rotated directly by a control lever, the control rod extending into a bore in the piston and an output shaft associated therewith, the output shaft extends linearly from the hydraulic cylinder, in use the piston and output shaft are moved on rotary movement of the control lever which opens or closes porting between a hole in the piston or output shaft and a spiral groove in the control rod to thereby create a force imbalance which moves the piston to a position where the force on each side of the piston is the same.
Further aspects of the invention will become apparent from the following descriptions which are given by way of example only.
Examples of the invention will become apparent from the following descriptions which are given with reference to the accompanying drawings in which:
Figure 1 shows a cross-section through an example which is in accordance with a second aspect of the invention;
Figure 2 shows diagrammatically and exploded apart the internal parts of the example shown in Figure 1;
Figure 3 shows a section on the lines II-II through the example of the invention shown in Figures 1 and 2; Figure 4 shows schematically the example shown in Figures 1 to 3;
Figure 5 shows a cross-section through a second example which is in accordance with a third aspect of the invention;
Figure 6 shows a perspective view of a control lever and control rod of the second example shown in Figure 5;
Figure 7 shows a plan view of a piston and control rod of the second example shown in Figure 6;
Figure 8 shows a plan view of the piston and control rod shown in Figure 7 after rotation of a control lever;
Figure 9 shows a section on the lines A-A through the hydraulic cylinder shown in Figure 5; and
Figure 10 shows a schematic hydraulic circuit diagram for the example shown in Figures 5 to 10.
The attached descriptions are of two implementations of the rotary valve and feedback cylinder concepts.
The invention is based on a control rod extending through the centre of the hydraulic cylinder providing feedback off the piston position.
The first example with reference to Figures 1 to 4 is the back pressure design where the piston is one part of the valve and the control movement the other. The back pressure provides two-way control.
The second example with reference to Figures 5 to 8 is the twisted rod design where the piston movement turns one part of the valve and the control movement turns the other. In the first example shown in Figures 1 to 4 the piston 1 is mounted within a hydraulic cylinder casing 2. The piston 1 twists a feedback control rod 3 (Figures 1 and 2). One end 4 of the feedback rod 3 is an inner part 5 part of a rotary spool valve 6. This valve could be any type of rotary valve. A control lever 7 is part of or connected to the other or outer part 8 of the rotary spool valve 6. The difference in angular position between the control lever 7 and the feedback rod 3 controls porting 9,10 in the outer part 8 of the spool valve 6 which causes the cylinder to either extend or contract. The porting 9,10 cooperates with porting 11 on the inner part 5 of the rotary spool valve 6. The feedback control rod 3 can include a twisted rod section 12 which extends through a square hole 13 in the piston 1. The hole 13 is associated with a bore 14 in an output shaft 15 of the hydraulic cylinder.
In use the hydraulic power source for the hydraulic cylinder is from a pump 16 which operates in association with hydraulic liquid supply tank 17. Operation of the hydraulic circuit can be seen from Figures 1, 3 and 4 where the flow paths of the hydraulics are indicated by arrows 18,19. Rotation of the control lever 7 clockwise (Figure 3) opens porting 9, 9 increasing pressure in the direction of arrow 19 to move cause the piston 1 to move in the direction of arrow 20. Reverse movement opening porting 10, 10 causing opposite movement.
In the second example similar parts to those described in the first example are reference by the same numerals. The second example shown in Figures 5 to 10 is in accordance with the øe.'ond aspect of the invention and is based on a control rod 3 geing down the centre of a piston 1 in a hydraulic cylinder casing 2 and this provides feedback off the piston position. Implementation in this example utilises feedback taken directly from the position of a piston 1 in relation to the rod 3. A groove 21 in the control rod 3, which is directly turned by a control lever 7, acts on porting 22 in the piston 1 to provide controlled flow and pressure to both sides 23,24 of the piston 1. This provides a controlled pressure drop between both sides of the piston causing the piston to move. A returning force can be by either a return spring (not shown) or a constant back pressure. Closing of the restriction or port 22 by side edges 25 of the groove 21 and the cylinder extends. Opening of the port 22 and the cylinder contracts with the aid of the back pressure against the face 24 of the piston. A balance is found where the pressure drop over the restriction 22 and this provides enough force to balance the load.
In Figure 8 is shown the positions of the edges 25 of the groove 21 after a control input from lever 7. The final position of the groove 21 and piston 1 are shown dotted.
Back pressure in this case keeps a constant pressure on face 24. If the porting 22 in the piston 1 is open, then the pressures on each side of the piston 1 will be roughly equal and the differences in area on each side of the piston 1 will cause the piston to extend. If the porting in the piston 1 closes, then the pressure on side 23 will be less than on side 24 and the piston 1 will contract.
In use the flow of hydraulic fluid is shown in Figures 5, 9 and 10. The back pressure in this example being provided by a pressure regulator 26 (Figure 10).
Thus by this invention there is provided a means for controlling extension of a hydraulic cylinder where the cylinder extension is a function of the position of a rotatable control lever.
Particular examples of the invention have been described and it is envisaged that improvements and modifications can take place without departing from the scope of the appended claims.

Claims

CLAIMS :
1. A means for providing control of the extension of a hydraulic cylinder, the means including a control rod within the cylinder, the control rod being rotated either directly by a control lever or adapted to be rotated by an output from a rotary valve, the control rod extending into a bore in the piston and an output shaft associated therewith, the output shaft extends linearly from the hydraulic cylinder, in use the piston and output shaft are moved on rotary movement of the control lever which either opens or closes porting between a hole in the piston or output shaft and a spiral groove in the control rod to create a pressure imbalance which moves the piston to a position where the force on each face of the piston is the same or opens porting in the rotary valve to move the piston which rotary movement turns an inner part of the rotary- valve until the porting is closed which balances the hydraulic system.
2. A means for providing control of the extension of a hydraulic cylinder, the means including a control rod within the hydraulic cylinder, the control rod being adapted to be rotated by an output from a hydraulically operated rotary valve, the rotary valve having a valve outer the position of which is controlled by an outer member within which is an inner member formed either integrally with or at one end of the control rod, the periphery of the control rod is twisted or formed along its length into a helical form, the control rod extending into a bore in a piston and associated output shaft of the hydraulic cylinder through a hole which is the same in cross-section as the cross-section of the twisted or helical portion of the rod, in use the piston and output shaft are moved by rotary movement of the control lever which opens porting in the rotary valve to apply pressure to one side of the piston so that it moves and as it moves forwards or backwards it rotates the control rod until the porting is closed to balance the hydraulic system.
3. A means as claimed in claim 2 wherein the hydraulic cylinder is circular in cross-section and the inner member is formed integrally with the one end of the control rod.
4. A means as claimed in claim 3 wherein the twisted or helical form of the control rod is square in cross-section.
5. A means as claimed in any one of the claims 2 to 4 wherein the porting in the rotary valve operates in conjunction with recessed porting on the periphery of the inner member.
6. A means for providing control of the extension of a hydraulic cylinder substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.
7. A means for providing control of the extension of a hydraulic cylinder, the means including a control rod within - li ¬
the hydraulic cylinder, the control rod being rotated directly by a control lever, the control rod extending into a bore in the piston and an output shaft associated therewith, the output shaft extends linearly from the hydraulic cylinder, in use the piston and output shaft are moved on rotary movement of the control lever which opens or closes porting between a hole in the piston or output shaft and a spiral groove in the control rod to thereby create a force imbalance which moves the piston to a position where the force on each side of the piston is the same.
8. A means as claimed in claim 7 wherein the shaft is circular in cross-section with the spiral groove in the periphery thereof and the piston has a circular bore therein in which the shaft extends.
9. A means as claimed in claim 7 or claim 8 and substantially as hereinbefore described with reference to Figures 5 to 9 of the accompanying drawings.
10. A means for providing control of the extension of a hydraulic cylinder as claimed in any one of the preceding claims and adapted to control reversing of a water jet.
11. A means for providing control of the extension of a hydraulic cylinder substantially as hereinbefore with reference to the accompanying drawings.
PCT/NZ1993/000018 1992-03-23 1993-03-23 Hydraulic cylinder feedback control WO1993019300A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NZ241132 1992-03-23
NZ24113292 1992-03-23

Publications (1)

Publication Number Publication Date
WO1993019300A1 true WO1993019300A1 (en) 1993-09-30

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ID=19923842

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/NZ1993/000018 WO1993019300A1 (en) 1992-03-23 1993-03-23 Hydraulic cylinder feedback control

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AU (1) AU3770293A (en)
WO (1) WO1993019300A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0767310A2 (en) * 1995-10-07 1997-04-09 EUROCOPTER DEUTSCHLAND GmbH Hydraulic actuator

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB841995A (en) * 1955-10-31 1960-07-20 Boulton Aircraft Ltd Improvements in or relating to fluid-pressure servo mechanisms
US3511132A (en) * 1967-11-18 1970-05-12 Rexroth Gmbh G L Hydraulic power amplifier
US4128046A (en) * 1977-01-07 1978-12-05 Bendiberica, S. A. Power steering mechanism
US4245547A (en) * 1977-10-31 1981-01-20 Commercial Shearing, Inc. Rotary to linear servo mechanisms
GB2079693A (en) * 1980-07-18 1982-01-27 Zahnradfabrik Friedrichshafen Servo units
EP0088017A2 (en) * 1982-02-26 1983-09-07 COMPAGNIE PARISIENNE D'OUTILLAGE A AIR COMPRIME Société anonyme dite: Hydraulic directional spool valve
JPS60256603A (en) * 1984-06-01 1985-12-18 Yukio Watanabe Cylinder device

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB841995A (en) * 1955-10-31 1960-07-20 Boulton Aircraft Ltd Improvements in or relating to fluid-pressure servo mechanisms
US3511132A (en) * 1967-11-18 1970-05-12 Rexroth Gmbh G L Hydraulic power amplifier
US4128046A (en) * 1977-01-07 1978-12-05 Bendiberica, S. A. Power steering mechanism
US4245547A (en) * 1977-10-31 1981-01-20 Commercial Shearing, Inc. Rotary to linear servo mechanisms
GB2079693A (en) * 1980-07-18 1982-01-27 Zahnradfabrik Friedrichshafen Servo units
EP0088017A2 (en) * 1982-02-26 1983-09-07 COMPAGNIE PARISIENNE D'OUTILLAGE A AIR COMPRIME Société anonyme dite: Hydraulic directional spool valve
JPS60256603A (en) * 1984-06-01 1985-12-18 Yukio Watanabe Cylinder device

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, M-478, page 94; & JP,A,60 256 603 (WATANABE), 18 December 1985. *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0767310A2 (en) * 1995-10-07 1997-04-09 EUROCOPTER DEUTSCHLAND GmbH Hydraulic actuator
EP0767310A3 (en) * 1995-10-07 1999-09-01 EUROCOPTER DEUTSCHLAND GmbH Hydraulic actuator

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