Title of Invention

INTERNAL LOCKING MECHANISM FOR HYDRAULIC ACTUATOR USING SPHERICAL ENDED CYLINDRICAL PLUNGERS

Abstract Internal locking of Hydraulic Actuator used for retraction and extension of Landing Gear doors in aircraft/helicopter is provided to keep it mechanically locked in extended position, so that the actuator acts as a rigid link capable of supporting axial load. The locking is achieved automatically when the actuator is extended by having radially moving plungers in the piston head, which are held by spring loaded locking shuttle. Lock is released when hydraulic pressure is applied to retract the actuator, which pushes the locking shuttle, allowing the locking plungers to move inwards by cam action.
Full Text

The present Invention relates to Internal Locking Mechanism for Hydraulic Actuator using spherical ended cylindrical plungers.
The hydraulic actuators which operate the Landing Gear or Landing Gear Doors need to be locked in fully extended and /or retracted position, depending upon the system design, so that they remain in that position until selected otherwise. This is to make sure that the Landing Gear or the Landing Gear Doors stay locked in fully extended and / or retracted position even when there is no hydraulic pressure in the actuator to keep the actuator in selected position.
Reference may be made to James D Helm and Walter G Gellerson, Locking Actuators Today and Beyond, published in Landing Gear Systems SAE PT-37 (1990), Society of Automotive Engineers Inc. wherein claw lock or rectangular cross section segment lock are used to achieve internal locking of hydraulically operated actuators. Claw lock works on the principle of bending of cantilever fingers of the claw for engagement of the locking finger. Segment lock uses rectangular cross section segments, which are cut from hollow circular disc with cam profile on ID and OD, moving in rectangular slots in the piston head.
The drawbacks of the above said types of locks are as follows. The claw lock is difficult to manufacture and has limitations of life due to wear of the locking tongues. The segment lock due to its rectangular shape is also difficult to manufacture. The cost of both the locking arrangement goes up due to intricate manufacturing processes involved.

The main object of the present invention is to provide easily manufacturable locking mechanism that obviates the drawbacks of earlier type of locks as detailed above. Yet another object of the present invention is to provide a locking mechanism that is not only simple in design, but also cost effective.
The foregoing aspects and the consequential advantages of the invention will become more readily appreciated, as the same becomes better understood by reference to the following description, when taken in conjunction with the accompanying drawings.
Fig. 1 is a cross sectional view of the general arrangement of the locking mechanism of hydraulic actuator in extended and locked position.
Part 1 is the Cylinder of the Hydraulic Actuator that has a tapered internal surface for operation of Locking Plungers.
Part 2 is the Piston of Hydraulic Actuator which houses the locking Shuttle Part 3, Support Part 4 and Spring Part 5. The Piston also has radial holes and accommodates the Locking Plungers Part 6.
The devise of the present invention employs four cylindrical locking plungers with spherical ends. The size and number of locking plungers can be varied for different size of hydraulic actuator.
Part 7 Piston Nut and Part 8 Blanking Plug are provided to retain other parts of locking mechanism in the piston.

It has now been found that the cylindrical plungers with spherical ends would provide an easily manufacturable locking mechanism with enhanced life.
Accordingly, the present invention provides Internal Locking Mechanism for a Hydraulic Actuator in fully extended position using spherical ended cylindrical Plungers which comprises of Cylinder with special profiled internal surface, Piston, Shuttle, Support, Spring and the locking Plungers all housed in the piston and retained by blanking Plug and piston Nut.
In an embodiment of present invention, the locking mechanism described above employ cylindrical plungers with truncated conical ends as shown in Fig. 2 in place of spherical ended cylindrical plungers provide internal locking of hydraulic actuator in fully extended position.
In another embodiment of present invention, the size and number of locking plungers are varied to achieve different load capacity in different sizes of hydraulic actuators.
When the actuator is extended to its extended position the locking shuttle moves upto blanking plug under the action of compressed spring, there by causing the locking plungers move radially outwards to rest on a tapered internal surface on the cylinder. The tapered surface of the shuttle makes this outward movement possible. Once moved out, the plungers are held by the shuttle and the actuator is locked. To unlock the actuator the shuttle is pushed back by hydraulic pressure and the locking plungers move radially inwards by cam action and actuator gets unlocked. This can be seen in Fig.3 where the actuator is shown in unlocked and

closed position.
The novelty of this invention is that it employs geometrically simple parts that are easy to manufacture and at the same time is suitable for loads on the lock upto 1000 kgf.
This invention is suitable, for example, in hydraulic actuators that are connected to the closing mechanism of Landing Gear doors where the Doors are to be held locked in open position when the Landing Gears are operated. These actuators which contain internal lock in extended position encounter moderate loads of 100 kgf to 1000 kgf in the locked condition and hence this mechanism is suitable.
Main advantage of this invention is that the parts required to make the locking mechanism are easy to manufacture as it is easy to maintain close tolerances on circular holes and cylindrical parts. The life of the locking mechanism is also enhanced. This design has added advantages of cost effectiveness and higher tolerance to geometric variations in the diameter of the holes and the plungers.



and the load it is to sustain.
The novelty of this invention is that it employs geometrically simple parts that are easy to manufacture and at the same time is suitable for loads on the lock upto 500 kgf
This invention is suitable, for example, in hydraulic actuators used for closing of Landing Gear doors where the Doors are to be held locked in open position when the Landing Gears are operated. These actuators encounter moderate loads of 100 kgf to 500 kgf in the locked condition and hence this mechanism is suitable.
Main advantage of this invention is that the parts required to make the locking mechanism are easy to manufacture as it is easy to maintain close tolerances on circular holes and cylindrical parts. The life of the locking mechanism is also enhanced. This design has added advantages of cost effectiveness and higher tolerance to geometric variations in the diameter of the holes and the plungers. We claim
1. An Internal Locking system that is easy to manufacture, employing geometrically
simple parts for a variety of hydraulic actuators encountering low to moderate loads
in fully extended and/or retracted position, comprising of
- cylinder with tapered internal surface and piston that houses the shuttle,
support, spring and the locking plungers and
- retained by blanking plug and piston nut.
2. The locking plungers in the internal locking system claimed in claim 1 are
cylindrical.

3. The cylindrical plungers in the internal locking system claimed in claim 1-2 are spherical ended.
4. The cylindrical locking plungers in the internal locking system claimed in claim 1-3 have truncated conical §nds.
5. An internal locking system as claimed in claim 1 in which the size and number of locking plungers can be varied as per the size of the hydraulic actuator.
6. An internal locking system as in claim 1&5 which employs four cylindrical locking plungers with spherical ends.
7. An internal locking system for hydraulic actuator as claimed in claims 1,5&6 used for opening of landing gear doors where the doors are to be held locked in open position when the landing gears are operated.
8. An internal locking system for hydraulic actuator as claimed in claims 1, 5-7 capable of taking loads upto 500 kgf
9. An internal locking system for hydraulic actuator as claimed in claims 1, 5-8 capable of taking moderate loads from 100 kgf- 500 kgf.

10. An internal locking system for hydraulic actuator as claimed in claims 1, 5-9 with low wear and tear due to point contact between the locking plungers and the cylinder.
11. An internal locking mechanism in a system as in claims 1, 5-10 in which when the actuator is extended to its extended position

- the locking plungers move radially outwards to rest on the tapered inner surface of the cylinder under action of the spring which supports the locking shuttle
- the tapered surface making the outward movement possible
- the plungers when moved out are held by the shuttle and the actuator is locked
12. An internal locking mechanism in a system in claims .1, 5-11 in which when the
actuator is unlocked from the locked position by
- pushing the shuttle back by hydraulic pressure and
- the locking plungers moving radially inwards by cam action.
13. A design of an internal locking system for hydraulic actuator maintaining close
tolerances that is easy and cost effective to manufacture.
14. A design of an internal locking system for hydraulic actuator capable of higher
tolerance to geometric variations in the diameter of the holes and the plungers.


Documents:


Patent Number 207461
Indian Patent Application Number 4/MAS/2002
PG Journal Number 44/2007
Publication Date 02-Nov-2007
Grant Date 13-Jun-2007
Date of Filing 03-Jan-2002
Name of Patentee M/S. HINDUSTAN AERONAUTICS LTD
Applicant Address 15/1, CUBBON ROAD, BANGALORE-560 001
Inventors:
# Inventor's Name Inventor's Address
1 PALAMPALLE JAYARAMI REDDY NO.1197, 16th MAIN, 2th Stage, BTM Layout, Bnagalore-560076.
2 VAZHAKALAYIL NEELAKANTAN DIVAKARAN 46, 6th Main, 13TH Cross, BTM(NS Palya)II stage, Bangalore-560076.
PCT International Classification Number F15 B-15/26
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA