Arbitrary control of locking / unlocking full stroke cycle motion actuator

Abstract

The present invention discloses an actuator cylinder that can be locked and unlocked in a full-stroke cyclic motion and can be controlled arbitrarily. The actuator cylinder is simple and controllable, and can realize full-stroke free motion and active restoration of locking by active failure. The present invention is realized by the following technical scheme: during the reciprocating motion of the piston rod, the mechanical lock provides a locking force through a spring sleeve connected to a spring to realize locking or unlocking; when the hydraulic / pneumatic oil circuit system supplies pressure to the actuator cylinder cavity, the reciprocating motion of the piston rod follows the mechanical lock locking → unlocking → piston rod movement → locking → unlocking... piston rod movement to perform logical cyclic locking and unlocking. The unlocking pipeline is depressurized, and the hydraulic / pneumatic pressure supply system supplies pressure to the unlocking pipeline. The unlocking push rod moves toward the end face of the spring sleeve, pushes the spring sleeve, and pushes it away from the locked position of the mechanical lock, and is in an unlocked state, realizing the free motion of the piston rod in the full stroke of the unlocked actuator cylinder; after the unlocking pipeline is depressurized, the actuator cylinder is restored to the serial logical cyclic stroke of arbitrary locking and unlocking.

Description

Technical Field

[0001] The present invention relates to a hydraulic actuation system, an internal mechanical lock structure in a single-rod, single-piston, reciprocating motion actuation cylinder in the hydraulic and pneumatic fields, and in particular to an actuation cylinder capable of arbitrarily controlling the locking / unlocking of a full-stroke cyclic motion. Background Art

[0002] During the take-off and landing of the aircraft, as the landing gear is retracted and extended, the locking mechanism will complete the locking and positioning to ensure safe take-off and landing. However, during use, wear will gradually occur during the unlocking and locking process, which seriously affects the service life of the lock. If it is within the normal wear range, the lock can maintain a normal working state, but once a certain wear limit is exceeded, the unlocking axial force of the lock will rise sharply, causing the landing gear to retract and extend. Therefore, the normal operation of the locking mechanism is directly related to the safety of the aircraft's take-off and landing. The actuator is a typical motion drive unit that can drive the device to reciprocate. On the basis of reciprocating motion, the locked actuator can also lock the actuator at a specific position, so that the device stops at a specific position and bears a certain load.

[0003] At present, most of the actuators used in the retractable and retractable parts of aircraft hydraulic systems use hydraulic / pneumatic actuator position locking, and a mechanical locking device is installed in the actuator. A hydraulic lock is also added to the outside of the actuator. When the mechanical lock fails, the hydraulic lock does not work. The mechanical locking device of the hydraulic actuator can be roughly divided into steel ball lock, card lock, collet lock and friction lock. The steel ball lock consists of steel balls, lock rings, and conical rings. The bevel cone top angles of the conical ring and the lock ring are both 90°, and they work in conjunction with the housing, piston, piston rod and spring of the actuator. When the piston moves to the right under the action of hydraulic pressure, the piston moves to the right with the piston rod. When the steel balls (9 to 12) hit the lock ring, the piston is blocked and stops moving. The oil pressure on the cross section of the piston rod causes the piston rod to move to the right with the conical ring. The steel balls are retracted inward under the combined force of the lock ring and the piston. When the steel balls pass over the lock ring, the piston pushes the steel balls to spread outward along the conical ring under the action of the spring tension and locks. When the high-pressure oil enters in the reverse direction (retracts), the oil force pushes the piston to compress the spring to the left, causing the steel ball to shrink inward and unlock. Since the steel ball and the contact surface are in point contact, they are prone to wear.

[0004] The snap ring lock consists of a snap ring, a conical piston, a spring and a lock groove. The snap ring is open. When the piston rod is in the retracted position, the snap ring is restricted by the outer cylinder wall and is in a compressed state. The spring is compressed to make the conical piston close to the snap ring. When the actuator lowers the joint and passes the oil, the piston rod is pushed out. When the snap ring moves to the lock groove position, the snap ring diameter expands and is stuck in the lock groove. At the same time, the conical piston is inserted into the inner ring of the snap ring under the action of the spring and oil pressure, so that the snap ring cannot shrink and is locked, and the piston rod is locked in the extreme lowering position. When the actuator retracts the joint and passes the oil, the oil pushes the conical piston compression spring inward and withdraws from the snap ring. Under the action of the piston rod flange and the lock groove slope, the snap ring shrinks in diameter, disengages from the lock groove and unlocks, and the actuator piston rod is retracted (i.e., moves to the left). The snap ring lock is characterized by a large contact area, stable receiving force, and large bearing capacity (generally used for actuators that withstand large external forces).

[0005] The spring collet of the collet lock is an integral steel cylinder with a protrusion "D" at the end of the cylinder. 16 grooves are cut along the axial direction, and it can be opened during the locking process. There are bosses E and inclined surfaces A and C on the piston rod. Locking process: When the piston rod is pushed to the right to contact the collet, the collet opens along the inclined surface A and slides onto the boss E. Thereafter, the piston moves to the left for a distance under the action of the end face of the collet. After the flange D of the collet falls into the inclined surface C, the collet closes by itself, and the piston moves to the right under the action of the spring and returns to its original position, and presses on the collet, and the piston rod is locked. Unlocking process: When high-pressure oil enters from the right, the piston first moves to the left, pulling the piston rod out of the collet, and the lock is opened, and it can withstand a large lateral load. Its active clearance is smaller than that of the steel ball lock, and it is mostly used on the load-bearing actuator of heavy aircraft.

[0006] There are 8 to 12 inclined grooves on the piston rod of the friction lock. A steel ball is embedded in each groove and blocked by a spring sheet. The piston between the two inclined surfaces can move in a certain gap. When the piston rod stays at any position without hydraulic action, under the action of external force, if the piston rod has a tendency to move left, the steel ball on the left will be stuck with the cylinder wall, and vice versa, the steel ball on the right will be stuck with the cylinder wall, so the piston is in a locked state. When oil comes from the left side of the piston, the hydraulic pressure pushes the piston to move right, and the piston rod pushes the steel ball on the right, so that it slides down along the groove and breaks contact with the cylinder wall, while the steel ball on the left automatically slides down along the groove while the piston rod moves to the right, which is the unlocked state. The key to the design of the friction lock is the inclined groove. The slope should enable the steel ball to slide down automatically and to be stuck with the cylinder wall. At the same time, the sliding range of the steel ball should not be too large, otherwise the locking will fail. The friction lock has a simple structure and can be self-locking at any position, but it can only withstand a small external load, otherwise it will wear out the cylinder wall.

[0007] The above four types of mechanical locks are commonly used aircraft hydraulic actuator mechanical lock locking devices, and they should not be automatically unlocked after being locked.

[0008] Mechanical locks are mostly in the form of "floating piston + steel ball". When in the upper locking position, the position of the steel ball is restricted by the armature, and the piston is restricted by the steel ball and cannot pop out, thus achieving upper locking. When unlocking, the electromagnet is energized to attract the armature, loosen the steel ball, and pop out the piston. Similarly, lower locking is achieved using springs, floating piston sinks, and steel balls. The disadvantages of this locking technology are that the locking force is small; the unlocking force required is large; the steel ball and armature are easily stuck, and the reliability is not high.

[0009] Therefore, the working principle of the mechanical lock inside the actuator is generally as follows: the system oil (gas) circuit supplies pressure to one chamber of the actuator, and the pressure acts on the floating piston, driving the piston rod to move. When the piston rod moves to a specific position (generally the extension / retraction limit position), the internal mechanical lock of the actuator is triggered to lock, so that the piston rod cannot continue to move, thereby locking the actuator. When the movement is to be restarted, the internal lock must be unlocked by supplying pressure through the system oil (gas) circuit before the piston rod can start to move. According to the above working principle, the logical relationship between the locking and unlocking of the mechanical lock inside the actuator and the reciprocating motion of the piston rod is a cyclic serial, that is, piston rod movement → mechanical lock locking → mechanical lock unlocking → piston rod movement → mechanical lock locking → .... Since the mechanical lock actuator cannot move freely over the full stroke, this is both a feature and advantage of the locked actuator, but with the increasing demand for fine control of the system, it has also become a limitation and disadvantage of the locked actuator. However, if an actuator without an internal mechanical lock is used directly to meet the requirement of full-stroke free movement, the actuator cannot be locked in a specific position and bear the load. Therefore, how to design a new actuator that has the locking function of a locked actuator and can move freely throughout the stroke has become an urgent problem to be solved. Summary of the invention

[0010] The purpose of the present invention is to address the problem that a locked actuator needs to move freely throughout the entire stroke, and to provide a simple, controllable, cyclic, unlimited number of operations that can actively fail and actively recover. The internal mechanical lock of the locked actuator can be actively disabled as needed, allowing the locked actuator to be in an unlocked state, so that it can move freely throughout the entire stroke. At the same time, it can also be actively recovered as needed, allowing the locked actuator to return to a locked state, so that it can be locked at a specific position, and can actively and flexibly control the unlocking mechanism when the mechanical lock inside the hydraulic actuator fails.

[0011] The technical solution adopted by the present invention to solve the technical problem is:

[0012] An actuator cylinder capable of arbitrarily controlling locking / unlocking full-stroke cyclic motion, comprising:

[0013] A hollow piston rod reciprocating in the actuator cylinder, a hollow piston integrally connected to the hollow piston rod, springs constrained at both ends of the hollow piston cavity by spring sleeves and step spring seats at opposite ends to limit freedom, a mechanical lock assembled on the circumference of the free end of the piston, an end cover sealed at the rear end of the actuator cylinder by circumferential bolts, a two-step step hole cover cavity threadedly matched with a locking cylinder cover and an unlocking pipeline connected to the two-step step hole cover cavity, and an unlocking push rod assembled in the two-step step hole cover cavity to move freely;

[0014] During the reciprocating motion of the hollow piston rod, the mechanical lock provides locking force through a spring sleeve connected to the spring to achieve locking or unlocking;

[0015] When the hydraulic / pneumatic oil system supplies pressure to the actuator cylinder cavity, the reciprocating motion of the hollow piston rod follows the serial logic cycle of mechanical lock locking → unlocking → hollow piston rod movement → locking → unlocking… the hollow piston rod movement locks and unlocks. At this time, the unlocking pipeline is depressurized, and the unlocking push rod is retracted into the cavity of the locking cylinder cover, and no axial force is generated on the spring sleeve;

[0016] When the actuator needs to move freely in the full stroke, the liquid / gas pressure supply system supplies pressure to the unlocking pipeline, and the unlocking push rod moves toward the end surface of the spring sleeve under the action of the liquid / gas pressure, pushing the spring sleeve away from the locked position of the mechanical lock, so that the mechanical lock is always in the unlocked state, realizing the free movement of the hollow piston rod in the full stroke of the actuator without locking;

[0017] After the unlocking pipeline is depressurized, the unlocking push rod retracts into the cover cavity of the locking cylinder under the action of the hollow piston movement, and the hollow piston rod resumes the serial logic cycle of any retraction, locking and unlocking. Under the action of pressure or external load, the actuator can reciprocate in the retraction and release pipeline.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The invention constrains the springs at both ends of the hollow piston cavity, whose freedom is limited by the spring sleeve and the opposite end step spring seat, and the mechanical lock assembled on the circumference of the free end of the piston, the end cover sealed at the rear end of the actuator by circumferential bolts, the two-step step hole cover cavity of the locking cylinder cover matched with the bottom of the end cover and the unlocking pipeline connected to the step hole cover cavity, and the unlocking push rod assembled in the step hole cover cavity and freely moving; it can make the internal mechanical lock of the locked actuator actively invalid and actively restore the piston rod reciprocating motion in accordance with the serial logic cycle of mechanical lock locking → unlocking → piston rod movement → locking → unlocking... piston rod movement locking and unlocking, which is simple to operate, controllable, cyclic, and unlimited in number of times. It solves the problem that the locking function and full-stroke free movement of the locked actuator in the prior art cannot coexist.

[0020] The present invention uses a spring sleeve connected to a spring to provide a locking force during the reciprocating motion of the piston rod, thereby achieving locking or unlocking, and can achieve locking flexibility at a specific position.

[0021] The operation is simple and controllable. When the hydraulic / pneumatic oil system supplies pressure to the actuator chamber, the reciprocating motion of the piston rod follows the serial logic cycle of mechanical lock locking → unlocking → piston rod movement → locking → unlocking... piston rod movement locks and unlocks. At this time, the unlocking pipeline is depressurized, and the unlocking push rod is retracted into the cavity of the blocking cylinder cover, and no axial force is generated on the spring sleeve; the internal mechanical lock of the locked actuator can be actively disabled and automatically restored.

[0022] A sealing structure sealed by a sealing ring is arranged on the circumference between the end cover and the locking cylinder cover, and between the locking cylinder cover and the unlocking push rod.

[0023] The hollow piston rod moves to the locked position. Under the action of the spring, the spring sleeve pushes the mechanical lock to the locking surface of the inner cavity of the actuator. The mechanical lock is locked and the hollow piston rod cannot move further. The spring force of the spring must be overcome to push the spring sleeve away. The hollow piston rod can continue to move after the mechanical lock is unlocked.

[0024] When the actuator moves freely in the full stroke, pressure is supplied to the unlocking pipeline, and the unlocking push rod moves to the right under the action of liquid / gas pressure. The spring sleeve pushes away from the locking surface of the actuator, and the mechanical lock inside the actuator fails to lock, and the hollow piston rod moves freely in the full stroke.

[0025] The present invention sets the mechanical lock near the hollow piston inside the locked actuator cylinder, and actively supplies pressure to the unlocking pipeline to push the spring sleeve and push away the locked position of the mechanical lock, so that the mechanical lock is always in the unlocked state, and the piston rod can move freely in the full stroke of the unlocked actuator cylinder; it can make the internal mechanical lock unable to complete the locking, that is, actively fail. By actively relieving the pressure of the unlocking pipeline, the internal mechanical lock can complete the locking, that is, actively recover. Control is performed through the unlocking pipeline, and all functions can be completed by only supplying pressure or relieving pressure to the unlocking pipeline, and various parameters of the supplied energy (such as pressure, flow, flow rate, etc.) can be changed at any time according to needs, so it has the characteristics of simple operation and controllability.

[0026] The operation is cyclical and has no limit on the number of times. After the unlocking pipeline is depressurized, the unlocking push rod of the present invention retracts into the cover cavity of the locking cylinder under the action of the movement of the hollow piston, and does not generate an axial force on the spring sleeve. The piston rod is restored under the action of pressure or external load, and the actuator can reciprocate in the retracting and releasing pipeline, and can be locked and unlocked in a serial logic cycle at will. When the unlocking pipeline is depressurized, the unlocking push rod is retracted into the cavity of the locking cylinder cover, which belongs to a hydraulic (gas) pressure mechanism. Its control pipeline is reversible, and there is no damage or destruction process. Therefore, it has the characteristics of cyclic operation and no limit on the number of times.

[0027] The present invention adopts an unlocking mechanism arranged near the mechanical lock inside the locked actuator. When the locked actuator needs to move freely in the full stroke, the liquid / gas pressure supply system supplies pressure to the unlocking pipeline, and the unlocking push rod moves toward the end face of the spring sleeve under the action of the liquid / gas pressure, pushes the spring sleeve, and pushes away from the locked position of the mechanical lock, so that the mechanical lock is always in the unlocked state, and the piston rod can move freely in the full stroke of the unlocked actuator. The problem of free movement of the locked actuator in the full stroke is effectively solved.

[0028] The test results show that the internal mechanical lock of the locked actuator can be actively disabled as needed, so that the locked actuator is in an unlocked state and can move freely throughout the entire stroke. At the same time, the mechanical lock recovery function can be actively restored as needed, so that the locked actuator can be restored to the locked state after the full stroke is no longer needed, and the actuator can be locked in a specific position. The operation method is simple, controllable, cyclic, and unlimited in number, which can make the designed locked actuator meet the actual use requirements well. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a partial cross-sectional schematic diagram of the actuator cylinder of the present invention that can arbitrarily control the locking / unlocking full-stroke cyclic motion;

[0030] In the figure: 1. Locking cylinder cover; 2. Unlocking push rod; 3. End cover; 4. Mechanical lock; 5. Spring sleeve; 6. Spring; 7. Unlocking pipeline; 8. Retracting and releasing pipeline; 9. Actuating cylinder; 10. Empty piston rod;

[0031] The present invention is further described below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0032] See also Figure 1 In the preferred embodiment described below, an arbitrarily controlled locking / unlocking full stroke cyclic motion actuator cylinder comprises: a hollow piston rod 10 reciprocating in the actuator cylinder 9, a hollow piston integrally connected to the hollow piston rod 10, a spring 6 constrained at both ends of the hollow piston cavity by a spring sleeve 5 and a step spring seat at the opposite end to limit the degree of freedom, a mechanical lock 4 assembled on the circumference of the free end of the piston, and an end cover 3 sealed at the rear end of the actuator cylinder 9 by circumferential bolts, characterized in that: a two-step step hole cover cavity that is threadedly matched with the locking cylinder cover 1 and an unlocking pipeline 7 connected to the two-step step hole cover cavity are formed at the bottom of the end cover 3, and an unlocking push rod 2 assembled in the two-step step hole cover cavity to move freely;

[0033] During the reciprocating motion of the hollow piston rod 10, the mechanical lock 4 provides a locking force through the spring sleeve 5 connected to the spring 6 to achieve locking or unlocking; when the hydraulic / pneumatic oil system supplies pressure to the actuator cylinder cavity, the reciprocating motion of the hollow piston rod 10 follows the serial logic cycle of mechanical lock locking → unlocking → hollow piston rod 10 movement → locking → unlocking... the movement of the hollow piston rod 10 locks and unlocks. At this time, the unlocking pipeline 7 is depressurized, and the unlocking push rod 2 is retracted into the cavity of the blocking cylinder cover 1, and no axial force is generated on the spring sleeve 5;

[0034] When the actuator 9 needs to move freely in the full stroke, the liquid / gas pressure supply system supplies pressure to the unlocking pipeline 7, and the unlocking push rod 2 moves toward the end surface of the spring sleeve 5 under the action of the liquid / gas pressure, pushing the spring sleeve 5 away from the locked position of the mechanical lock 4, so that the mechanical lock 4 is always in the unlocked state, and the hollow piston rod 10 can move freely in the full stroke of the unlocked actuator;

[0035] After the unlocking pipeline 7 is depressurized, the unlocking push rod 2 retracts into the cover cavity of the locking cylinder cover 1 under the action of the hollow piston movement, and the hollow piston rod 10 resumes the serial logic cycle of any locking and unlocking. Under the action of pressure or external load, the actuator 9 can reciprocate in the retraction and release pipeline 8.

[0036] A sealing structure with a sealing ring is provided on the circumference between the end cover 3 and the locking cylinder cover 1, and between the locking cylinder cover 1 and the unlocking push rod 2.

[0037] If removed Figure 1 Except for the unlocking mechanism part of the middle unlocking pipeline 7, the locking cylinder cover 1, the unlocking push rod 2 and the two sealing structures between the locking cylinder cover 1 and the end cover 3 and the unlocking push rod 2, the solid is used for filling, that is, the internal mechanical lock of the general locking actuator.

[0038] For a general locked actuator, the system controls the reciprocating motion of the hollow piston rod 10 through the retractable pipeline 8. When the hollow piston rod 10 moves to the locked position, the spring sleeve 5 pushes the internal mechanical lock 4 to the locked position under the action of the spring 6. Since the mechanical lock 4 is locked, the hollow piston rod 10 cannot move further at this time. The spring force of the spring 6 must be overcome to push the spring sleeve 5 open. The mechanical lock 4 is pushed to the locking surface of the inner cavity of the actuator 9. The mechanical lock 4 is locked, and the hollow piston rod 10 cannot move further. The spring force of the spring 6 must be overcome to push the spring sleeve 5 open. After the mechanical lock 4 is unlocked, the hollow piston rod 10 can continue to move.

[0039] After the unlocking mechanism of the present invention is added to the locking cylinder, an additional unlocking pipeline 7 is added in addition to the retracting pipeline 8. When the locking function of the locking cylinder is required, the unlocking pipeline 7 is depressurized, and the unlocking push rod 2 can be retracted into the cavity of the locking cylinder cover 1, and there is no force on the spring sleeve 5. At this time, the cylinder is the same as a general locking cylinder, and can be locked by the internal mechanical lock 4 after the hollow piston rod 10 moves to the locking position.

[0040] When the locked actuator 9 needs to move freely in the full stroke, pressure is supplied to the unlocking pipeline 7, and the unlocking push rod 2 moves a certain distance to the right under the action of the liquid (gas) pressure, and then pushes the spring sleeve 5 away from the locking surface of the actuator 9, and the internal mechanical lock 4 of the actuator 9 cannot complete the locking. Since the internal mechanical lock 4 cannot be locked, the actuator 9 is the same as a general actuator without an internal mechanical lock, and the hollow piston rod 10 can move freely in the full stroke and will not be locked in a specific position.

[0041] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An actuator cylinder capable of arbitrarily controlling the locking / unlocking of a full-stroke cycle motion, comprising: A hollow piston rod (10) reciprocating in an actuator cylinder (9), a hollow piston integrally connected to the hollow piston rod (10), a spring (6) constrained in the hollow piston cavity and limited in freedom by spring sleeves (5) and step spring seats at opposite ends at both ends, a mechanical lock (4) mounted on the circumference of the free end of the piston, and an end cover (3) sealed at the rear end of the actuator cylinder (9) by circumferential bolts, characterized in that: a two-step step hole cover cavity that is threadedly matched with a locking cylinder cover (1) and an unlocking pipeline (7) connected to the two-step step hole cover cavity are formed at the bottom of the end cover (3), and an unlocking push rod (2) is mounted in the two-step step hole cover cavity and moves freely; A sealing structure for sealing with a sealing ring is provided on the circumference between the end cover (3) and the locking cylinder cover (1), and between the locking cylinder cover (1) and the unlocking push rod (2); During the reciprocating motion of the hollow piston rod (10), the mechanical lock (4) provides a locking force through the spring sleeve (5) connected to the spring (6) to achieve locking or unlocking; when the hydraulic / pneumatic oil system supplies pressure to the actuator cylinder cavity, the reciprocating motion of the hollow piston rod (10) follows the serial logic cycle of mechanical lock locking → unlocking → hollow piston rod (10) movement → locking → unlocking… hollow piston rod (10) movement to lock and unlock, at this time, the unlocking pipeline (7) is depressurized, and the unlocking push rod (2) is retracted into the cavity of the locking cylinder cover (1), and no axial force is generated on the spring sleeve (5); When the actuator (9) needs to move freely within the full stroke, the liquid / gas pressure supply system supplies pressure to the unlocking pipeline (7), and the unlocking push rod (2) moves toward the end surface of the spring sleeve (5) under the action of the liquid / gas pressure, pushing the spring sleeve (5) away from the locked position of the mechanical lock (4), so that the mechanical lock (4) is always in the unlocked state, realizing the free movement of the hollow piston rod (10) within the full stroke of the unlocked actuator; After the unlocking pipeline (7) is depressurized, the unlocking push rod (2) retracts into the cover cavity of the locking cylinder cover (1) under the action of the hollow piston movement. Under the action of pressure or external load, the hollow piston rod (10) restores any serial logic cycle of locking and unlocking, so that the actuator cylinder (9) can reciprocate in the retraction and release pipeline (8).

2. The fully-stroke cyclic motion actuator for arbitrary control of locking / unlocking according to claim 1, characterized in that: The hollow piston rod (10) moves to the locked position. Under the action of the spring (6), the spring sleeve (5) pushes the mechanical lock (4) to the locking surface of the inner cavity of the actuator (9). The mechanical lock (4) is locked and the hollow piston rod (10) cannot move further. The spring force of the spring (6) must be overcome to push the spring sleeve (5) away. After the mechanical lock (4) is unlocked, the hollow piston rod (10) can continue to move.

3. The fully-stroke cyclic motion actuator for arbitrary control of locking / unlocking according to claim 1, characterized in that: When the actuator (9) is required to move freely within the full stroke, pressure is supplied to the unlocking pipeline (7), and the unlocking push rod (2) moves to the right under the action of the liquid / gas pressure, pushing the spring sleeve (5) away from the locking surface of the actuator (9), causing the locking of the internal mechanical lock (4) of the actuator (9) to fail, and the hollow piston rod (10) can move freely within the full stroke.

Images