Hydraulic actuator with mechanical lock and installation

• US 5,379,969 A
• Filed: 04/12/1993
• Issued: 01/10/1995
• Est. Priority Date: 01/30/1992
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Smith, Mark H., Marx, Alan D., Renzelmann, Michael E.
• Primary Examiner(s): Barefoot, Galen L.
• Application Number:
  US08/045,901
• Time in Patent Office: 638 Days
• Field of Search: 244/218, 244/49, 244/120, 244/124, 244/102.56, 292/335, 292/144, 292/302, 92/14, 92/16, 92/20, 92/23, 92/24, 92/29, 116/124, 280/419
• US Class Current: 244/49
• CPC Class Codes: B64C 3/56 Folding or collapsing to reduce overall dimensions of aircraft
• CPC Class Codes: Y10T 292/432 Sliding catch
• CPC Class Codes: Y10T 292/558 Sliding bolt, swinging detent

Abstract

A plurality of radially extendable/retractable lock bolts (LB) are carried by a piston head (PH). A cylinder body (CB) in which the piston head (PH) is located includes a lock-bolt cavity (52) or cavities. When the actuator is in a lock position (fully extended or fully retracted), the lock bolt or bolts (LB) are in radial alignment with the lock bolt cavity or cavities. A locking piston (LP) within the actuator is movable axially to place a bolt block (62) radially inwardly of the lock bolt or bolts (LB), to in such position block the lock bolt or bolts (LB) against a radial inward movement out from the lock bolt cavity (52) or cavities. The locking piston (LP) includes a piston face (60) against which hydraulic fluid pressure may be directed, to move the locking piston (LP) axially, for retracting the bolt block (62) out from its position radially inwardly of the lock bolt or bolts (LB). This frees the lock bolt or bolts (LB) so that they can move radially inwardly, out from the lock bolt cavity 52 or cavities.

Claims

1. A hydraulic actuator, comprising:

an elongated cylinder body including a sidewall and end walls together defining an interior space;

a piston including a piston head within said interior space, said piston head dividing the interior space into two working chambers, one on each side of the piston head, each working chamber adapted to communicate with a pressure source for moving the piston axially within the cylinder body; and

a releasable lock for locking the piston in position relative to the cylinder body, said releasable lock comprising;

at least one radially extendible/retractable lock bolt carried by said piston head, said lock bolt being normally freed for retraction;

a complementary lock-bolt cavity within the cylinder body, and

a locking piston including a bolt block,

wherein said actuator includes a lock position in which it is desired to lock the piston to the cylinder body, and wherein when the actuator is in such lock position, the lock bolt is extendible radially outwardly into the lock-bolt cavity, and the locking piston is movable axially of the actuator to place the bolt block radially inwardly of the lock bolt, to in such position block the lock bolt against a radial inward movement out from the lock-bolt cavity, the locking piston being axially movable by means of a pressure source separately controllable from the pressure source in communication with the two working chambers.

2. A hydraulic actuator according to claim 1, wherein said locking piston includes a piston face against which hydraulic fluid may be directed, to move the locking piston axially, for retracting the bolt block out from its position radially inwardly of the lock bolt, so that the lock bolt is free to move radially inwardly, out from the lock-bolt cavity.

3. A hydraulic actuator according to claim 1, comprising a plurality of said lock bolts distributed circumferentially about the piston head, each said lock bolt being extendible radially into and retractable radially out from a lock-bolt cavity.

4. A hydraulic actuator according to claim 1, comprising a bias spring for said locking piston, wherein when the actuator is in the lock position, the bias spring biases the locking piston into a position placing the bolt block radially inwardly of the lock bolt.

5. A hydraulic actuator according to claim 4, wherein the lock bolt includes an extend cam positioned to, in response to the locking piston and the piston head being moved relatively together, be contacted by the bolt block, and wherein said extend cam is adapted to, in response to such movement and contact, cam the lock bolt radially outwardly into the lock-bolt cavity, and wherein said camming is followed by an axial movement of the bolt block into a position radially inwardly of the lock bolt.

6. A hydraulic actuator according to claim 1, wherein the lock bolt has a retract cam positioned to cam the lock bolt radially inwardly, out from the lock-bolt cavity, in response to an axial movement of the piston head relative to the cylinder body, following a retraction of the bolt block out from its position radially inwardly of the lock bolt.

7. A hydraulic actuator according to claim 1, wherein the actuator is in its lock position when extended, and when in said lock position, the lock bolt and the lock-bolt cavity are in radial alignment and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

8. A hydraulic actuator according to claim 1, wherein the actuator is in its lock position when retracted, and when in said lock position, the lock bolt and the lock-bolt cavity are in radial alignment and the lock bolt is movable radially outwardly into the lock bolt cavity, for locking the piston to the cylinder body.

9. A hydraulic actuator according to claim 1, wherein the bolt block is an annular first end portion of the locking piston, wherein said piston head includes a complementary annular passageway confronting said bolt block, and wherein relative movement of the bolt block into said annular passageway moves the bolt block into its position radially inwardly of the lock bolt.

10. A hydraulic actuator according to claim 9, wherein the lock bolt includes an extend cam positioned to be contacted by bolt block as the locking piston and piston head are moved relatively together, and wherein said extend cam is positioned to in response to such movement and contact cam the lock bolt radially outwardly into the lock-bolt cavity.

11. A hydraulic actuator according to claim 1, comprising a bias spring for said locking piston, wherein when the actuator is in its lock position, the bias spring biases the locking piston into a position placing the bolt block radially inwardly of the lock bolt, and wherein said locking piston includes a piston face against which a motive fluid may be directed, to move the locking piston axially against the bias spring, for retracting the bolt block out from its position radially inwardly of the lock bolt, so that the lock bolt is free to move radially inwardly, out from the lock-bolt cavity.

12. A hydraulic actuator according to claim 11, wherein the bolt block is an annular first end portion of the locking piston, wherein said piston head includes a complementary annular passageway confronting said bolt block, and wherein relative movement of the bolt into said annular passageway moves the bolt block into a position radially inwardly of the lock bolt.

13. A hydraulic actuator according to claim 12, wherein the locking piston includes a generally annular second end portion, and said cylinder body includes a working chamber end wall with a complementary annular second passageway in which the annular second end portion of the locking piston is received, said actuator including a seal between said second passageway and said annular second end portion of the locking piston.

14. A hydraulic actuator according to claim 11, wherein the lock bolt has a retract cam positioned to cam the lock bolt radially inwardly into a retracted position, in response to an axial movement of the piston head relative to the bolt block following a retraction of the bolt block from its position radially inwardly of the lock bolt.

15. A hydraulic actuator according to claim 14, wherein the lock bolt includes an extend cam positioned to be contacted by the bolt block, as the locking piston and piston head are moved relatively together, and wherein said extend cam is positioned to in response to such movement and contact cam the lock bolt radially outwardly into the lock-bolt cavity.

16. A hydraulic actuator according to claim 15, wherein the actuator is in its lock position when extended, and when in said position, the lock bolt and the lock-bolt cavity are in radial alignment and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

17. A hydraulic actuator according to claim 15, wherein the actuator is in its locked position when retracted, and when in said position the lock bolt and the lock-bolt cavity are in radial alignment, and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

18. A hydraulic actuator according to claim 1, wherein said cylinder body includes a shoulder, and wherein a portion of the piston head is substantially against said shoulder when the actuator is in a lock position, and wherein the lock bolt is substantially unloaded when the piston head is against such shoulder, enabling the bolt block to be retracted out from its position radially inwardly of the lock bolt when the lock bolt is unloaded.

19. A hydraulic actuator according to claim 17, wherein said locking piston includes a piston face against which hydraulic fluid may be directed, to move the locking piston axially, for retracting the bolt block out from its position radially inwardly of the lock bolt, so that the lock bolt is free to move radially inwardly, out from the lock-bolt cavity.

20. A hydraulic actuator according to claim 19, comprising a bias spring for said locking piston, wherein when the actuator is in its lock position, the bias spring biases the blocking piston into a position placing the bolt block radially inwardly of the lock-bolt.

62. A hydraulic actuator according to claim 1, wherein said locking piston includes a piston face against which hydraulic fluid may be directed, to move the locking piston axially, the piston face, the locking piston, and the cylinder body defining a third working chamber sealed from the first two working chambers, the third working chamber being in fluid communication with the separate pressure source.

63. A hydraulic actuator according to claim 62, wherein the cylinder body includes a radial abutment that engages said locking piston and separates the third working chamber from the other two working chambers.

64. A hydraulic actuator according to claim 9, wherein the piston includes a piston rod extending from said piston head, and the locking piston is an annular piece surrounding the piston rod.

21. An airplane, comprising:

a fuselage and a pair of wings projecting laterally outwardly on opposite sides of the fuselage, each wing having an inboard main portion connected to the fuselage and an outboard tip portion which is movable between an in use position in which it is an outboard continuation of the inboard portion of the wing and a folded position in which it extends generally vertically upwardly from the inboard portion of the wing; and

a hydraulic actuator for moving the outboard tip portion of the wing between its spread and folded positions, comprising;

an elongated cylinder body including a sidewall and end walls together defining an interior space;

a piston including a piston head within said interior space, said piston head dividing the interior space into two working chambers, one on each side of the piston head, each working chamber adapted to communicate with a hydraulic pressure source for moving said piston axially Within the cylinder body; and

a releasable lock for locking the piston in position relative to the cylinder body, said releasable lock comprising;

at least one radially extendible/retractable lock bolt carried by said piston head, said lock bolt being normally freed for retraction;

a complementary lock-bolt cavity within the cylinder body, and

a locking piston including a bolt block,

wherein said actuator includes a lock position in which it is desired to lock the piston to the cylinder body, and wherein when the actuator is in such lock position, the lock bolt is extendible radially outwardly into the lock-bolt cavity, and the locking piston is movable axially of the actuator to place the bolt block radially inwardly of the lock bolt, to in such position block the lock bolt against a radial inward movement out from the lock-bolt cavity, the locking piston being axially movable by means of a pressure source separately controllable from the pressure source in communication with the two working chambers.

22. A hydraulic actuator according to claim 21, wherein said locking piston includes a piston face against which hydraulic fluid may be directed, to move the locking piston axially, for retracting the bolt block out from its position radially inwardly of the lock bolt, so that the lock bolt is free to move radially inwardly, out from the lock-bolt cavity.

23. A hydraulic actuator according to claim 21, comprising a plurality of said lock bolts distributed circumferentially about the piston head, each said lock bolt being extendible radially into and retractable radially out from a lock-bolt cavity.

24. A hydraulic actuator according to claim 21, comprising a bias spring for said locking piston, wherein when the actuator is in the lock position, the bias spring biases the locking piston into a position placing the bolt block radially inwardly of the lock bolt.

25. A hydraulic actuator according to claim 24, wherein the lock bolt includes an extend cam positioned to, in response to the locking piston and the piston head being moved relatively together, be contacted by the bolt block, and wherein said extend cam is adapted to, in response to such movement and contact, cam the lock bolt radially outwardly into the lock-bolt cavity, and wherein said camming is followed by an axial movement of the bolt block into a position radially inwardly of the lock bolt.

26. A hydraulic actuator according to claim 25, wherein the lock bolt has a retract cam positioned to cam the lock bolt radially inwardly, out from the lock-bolt cavity, in response to an axial movement of the piston head relative to the cylinder body, following a retraction of the bolt block out from its position radially inwardly of the lock bolt.

27. A hydraulic actuator according to claim 21, wherein the actuator is in its lock position when extended, and when in said lock position, the lock bolt and the lock-bolt cavity are in radial alignment and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

28. A hydraulic actuator according to claim 21, wherein the actuator is in its lock position when retracted, and when in said lock position, the lock bolt and the lock-bolt cavity are in radial alignment and the lock bolt is movable radially outwardly into the lock bolt cavity, for locking the piston to the cylinder body.

29. A hydraulic actuator according to claim 21, wherein the bolt block is an annular first end portion of the locking piston, wherein said piston head includes a complementary annular passageway confronting said bolt block, and wherein relative movement of the bolt block into said annular passageway moves the bolt block into its position radially inwardly of the lock bolt.

30. A hydraulic actuator according to claim 29, wherein the lock bolt includes an extend cam positioned to be contacted by bolt block as the locking piston and piston head are moved relatively together, and wherein said extend cam is positioned to in response to such movement and contact cam the lock bolt radially outwardly into the lock-bolt cavity.

31. A hydraulic actuator according to claim 21, comprising a bias spring for said locking piston, wherein when the actuator is in its lock position, the bias spring biases the locking piston into a position placing the bolt block radially inwardly of the lock bolt, and wherein said locking piston includes a piston face against which a motive fluid may be directed, to move the locking piston axially against the bias spring, for retracting the bolt block out from its position radially inwardly of the lock bolt, so that the lock bolt is free to move radially inwardly, out from the lock-bolt cavity.

32. A hydraulic actuator according to claim 21, wherein the bolt block is an annular first end portion of the locking piston, wherein said piston head includes a complementary annular passageway confronting said bolt block, and wherein relative movement of the bolt into said annular passageway moves the bolt block into a position radially inwardly of the lock bolt.

33. A hydraulic actuator according to claim 32, wherein the locking piston includes a generally annular second end portion, and said cylinder body includes a working chamber end wall with a complementary annular second passageway in which the annular second end portion of the locking piston is received, said actuator including a seal between said second passageway and said annular second end portion of the locking piston.

34. A hydraulic actuator according to claim 31, wherein the lock bolt has a retract cam positioned to cam the lock bolt radially inwardly into a retracted position, in response to an axial movement of the piston head relative to the bolt block following a retraction of the bolt block from its position radially inwardly of the lock bolt.

35. A hydraulic actuator according to claim 34, wherein the lock bolt includes an extend cam positioned to be contacted by the bolt block, as the locking piston and piston head are moved relatively together, and wherein said extend cam is positioned to in response to such movement and contact cam the lock bolt radially outwardly into the lock-bolt cavity.

36. A hydraulic actuator according to claim 35, wherein the actuator is in its lock position when extended, and when in said position, the lock bolt and the lock-bolt cavity are in radial alignment and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

37. A hydraulic actuator according to claim 35, wherein the actuator is in its locked position when retracted, and when in said position the lock bolt and the lock-bolt cavity are in radial alignment, and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

38. A hydraulic actuator according to claim 21, wherein said cylinder body includes a shoulder, and wherein a portion of the piston head is substantially against said shoulder when the actuator is in a lock position, and wherein the lock bolt is substantially unloaded when the piston head is against such shoulder, enabling the bolt block to be retracted out from its position radially inwardly of the lock bolt when the lock bolt is unloaded.

39. A hydraulic actuator according to claim 37, wherein said locking piston includes a piston face against which hydraulic fluid may be directed, to move the locking piston axially, for retracting the bolt block out from its position radially inwardly of the lock bolt, so that the lock bolt is free to move radially inwardly, out from the lock-bolt cavity.

40. A hydraulic actuator according to claim 39, comprising a bias spring for said locking piston, wherein when the actuator is in its lock position, the bias spring biases the blocking piston into a position placing the bolt block radially inwardly of the lock-bolt.

65. A hydraulic actuator according to claim 21, wherein said locking piston includes a piston face against which hydraulic fluid may be directed, to move the locking piston axially, the piston face, locking piston, and cylinder body defining a third working chamber sealed from the first two working chambers, the third working chamber being in fluid communication with the separate pressure source.

66. A hydraulic actuator according to claim 65, wherein the cylinder body includes a radial abutment that engages said locking piston and separates the third working chamber from the other two working chambers.

41. A hydraulic actuator, comprising:

an elongated cylinder body including a sidewall and end walls together defining an interior space;

a piston including a piston head within said interior space, said piston head dividing the interior space into two working chambers, one on each side of the piston head; and

a releasable lock for locking the piston in position relative to the cylinder body, said releasable lock comprising;

at least one radially extendible/retractable lock bolt carried by said piston head, said lock bolt being normally freed for retraction;

a complementary lock-bolt cavity within the cylinder body, and

a locking piston including a bolt block,

wherein said actuator includes a lock position in which it is desired to lock the piston to the cylinder body, and wherein when the actuator is in such lock position, the lock bolt is extendible radially outwardly into the lock-bolt cavity, and the locking piston is movable axially of the actuator to place the bolt block radially inwardly of the lock bolt, to in such position block the lock bolt against a radial inward movement out from the lock-bolt cavity; and

wherein the bolt block is an annular first end portion of the locking piston, wherein said piston head includes a complementary annular passageway confronting said bolt block, and wherein relative movement of the bolt block into said annular passageway moves the bolt block into its position radially inwardly of the lock bolt.

42. A hydraulic actuator according to claim 41, wherein the lock bolt includes an extend cam positioned to be contacted by bolt block as the locking piston and piston head are moved relatively together, and wherein said extend cam is positioned to in response to such movement and contact cam the lock bolt radially outwardly into the lock-bolt cavity.

43. A hydraulic actuator according to claim 41, comprising a bias spring for said locking piston, wherein when the actuator is in its lock position, the bias spring biases the locking piston into a position placing the bolt block radially inwardly of the lock bolt, and wherein said locking piston includes a piston face against which a motive fluid may be directed, to move the locking piston axially against the bias spring, for retracting the bolt block out from its position radially inwardly of the lock bolt, so that the lock bolt is free to move radially inwardly, out from the lock-bolt cavity.

44. A hydraulic actuator according to claim 43, wherein the bolt block is an annular first end portion of the locking piston, wherein said piston head includes a complementary annular passageway confronting said bolt block, and wherein relative movement of the bolt into said annular passageway moves the bolt block into a position radially inwardly of the lock bolt.

45. A hydraulic actuator according to claim 44, wherein the locking piston includes a generally annular second end portion, and said cylinder body includes a working chamber end wall with a complementary annular second passageway in which the annular second end portion of the locking piston is received, said actuator including a seal between said second passageway and said annular second end portion of the locking piston.

46. A hydraulic actuator according to claim 43, wherein the lock bolt has a retract cam positioned to cam the lock bolt radially inwardly into a retracted position, in response to an axial movement of the piston head relative to the bolt block following a retraction of the bolt block from its position radially inwardly of the lock bolt.

47. A hydraulic actuator according to claim 46, wherein the lock bolt includes an extend cam positioned to be contacted by the bolt block, as the locking piston and piston head are moved relatively together, and wherein said extend cam is positioned to in response to such movement and contact cam the lock bolt radially outwardly into the lock-bolt cavity.

48. A hydraulic actuator according to claim 47, wherein the actuator is in its look position when extended, and when in said position, the lock bolt and the lock-bolt cavity are in radial alignment and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

49. A hydraulic actuator according to claim 47, wherein the actuator is in its locked position when retracted, and when in said position the lock bolt and the lock-bolt cavity are in radial alignment, and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

50. An airplane, comprising:

a fuselage and a pair of wings projecting laterally outwardly on opposite sides of the fuselage, each wing having an inboard main portion connected to the fuselage and an outboard tip portion which is movable between an in use position in which it is an outboard continuation of the inboard portion of the wing and a folded position in which it extends generally vertically upwardly from the inboard portion of the wing; and

a hydraulic actuator for moving the outboard tip portion of the wing between its spread and folded positions, comprising;

an elongated cylinder body including a sidewall and end walls together defining an interior space;

a piston including a piston head within said interior space, said piston head dividing the interior space into two working chambers, one on each side of the piston head; and

a releasable lock for locking the piston in position relative to the cylinder body, said releasable lock comprising;

at least one radially extendible/retractable lock bolt carried by said piston head, said lock bolt being normally freed for retraction;

a complementary lock-bolt cavity within the cylinder body, and

a locking piston including a bolt block,

wherein said actuator includes a lock position in which it is desired to lock the piston to the cylinder body, and wherein when the actuator is in such lock position, the lock bolt is extendible radially outwardly into the lock-bolt cavity, and the locking piston is movable axially of the actuator to place the bolt block radially inwardly of the lock bolt, to in such position block the lock bolt against a radial inward movement out from the lock-bolt cavity; and

wherein the bolt block is an annular first end portion of the locking piston, wherein said piston head includes a complementary annular passageway confronting said bolt block, and wherein relative movement of the bolt block into said annular passageway moves the bolt block into its position radially inwardly of the lock bolt.

51. A hydraulic actuator according to claim 50, wherein the lock bolt includes an extend cam positioned to be contacted by bolt block as the locking piston and piston head are moved relatively together, and wherein said extend cam is positioned to in response to such movement and contact cam the lock bolt radially outwardly into the lock-bolt cavity.

52. A hydraulic actuator according to claim 50, wherein the bolt block is an annular first end portion of the locking piston, wherein said piston head includes a complementary annular passageway confronting said bolt block, and wherein relative movement of the bolt into said annular passageway moves the bolt block into a position radially inwardly of the lock bolt.

53. A hydraulic actuator according to claim 52, wherein the locking piston includes a generally annular second end portion, and said cylinder body includes a working chamber end wall with a complementary annular second passageway in which the annular second end portion of the locking piston is received, said actuator including a seal between said second passageway and said annular second end portion of the locking piston.

54. A hydraulic actuator according to claim 50, comprising a bias spring for said locking piston, wherein when the actuator is in its lock position, the bias spring biases the locking piston into a position placing the bolt block radially inwardly of the lock bolt, and wherein said locking piston includes a piston face against which a motive fluid may be directed, to move the locking piston axially against the bias spring, for retracting the bolt block out from its position radially inwardly of the lock bolt, so that the lock bolt is free to move radially inwardly, out from the lock-bolt cavity.

55. A hydraulic actuator according to claim 54, wherein the lock bolt has a retract cam positioned to cam the lock bolt radially inwardly into a retracted position, in response to an axial movement of the piston head relative to the bolt block following a retraction of the bolt block from its position radially inwardly of the lock bolt.

56. A hydraulic actuator according to claim 55, wherein the lock bolt includes an extend cam positioned to be contacted by the bolt block, as the locking piston and piston head are moved relatively together, and wherein said extend cam is positioned to in response to such movement and contact cam the lock bolt radially outwardly into the lock-bolt cavity.

57. A hydraulic actuator according to claim 56, wherein the actuator is in its lock position when extended, and when in said position, the lock bolt and the lock-bolt cavity are in radial alignment and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

58. A hydraulic actuator according to claim 56, wherein the actuator is in its locked position when retracted, and when in said position the lock bolt and the lock-bolt cavity are in radial alignment, and the lock bolt is movable radially outwardly into the lock-bolt cavity, for locking the piston to the cylinder body.

59. A hydraulic actuator, comprising:

an elongated cylinder body including a sidewall and end walls together defining an interior space;

a piston including a piston head within said interior space, said piston head dividing the interior space into two working chambers, one on each side of the piston head; and

a releasable lock for locking the piston in position relative to the cylinder body, said releasable lock comprising;

at least one radially extendible/retractable lock bolt carried by said piston head, said lock bolt being normally freed for retraction;

a complementary lock-bolt cavity within the cylinder body, and

a locking piston including a bolt block,

wherein said actuator includes a lock position in which it is desired to lock the piston to the cylinder body, and wherein when the actuator is in such lock position, the lock bolt is extendible radially outwardly into the lock-bolt cavity, and the locking piston is movable axially of the actuator to place the bolt block radially inwardly of the lock bolt, to in such position block the lock bolt against a radial inward movement out from the lock-bolt cavity; and

wherein said cylinder body includes a shoulder, wherein said cylinder body includes a shoulder and wherein a portion of the piston head is substantially against said shoulder when the actuator is in a lock position, and wherein the lock bolt is substantially unloaded when the piston head is against such shoulder, enabling the bolt block to be retracted out from its position radially inwardly of the lock bolt when the lock bolt is unloaded.

60. A hydraulic actuator according to claim 59, wherein said locking piston includes a piston face against which hydraulic fluid may be directed, to move the locking piston axially, for retracting the bolt block out from its position radially inwardly of the lock bolt, so that the lock bolt is free to move radially inwardly, out from the lock-bolt cavity.

61. A hydraulic actuator according to claim 60, comprising a bias spring for said locking piston, wherein when the actuator is in its lock position, the bias spring biases the blocking piston into a position placing the bolt block radially inwardly of the lock-bolt.