A lockable piston-cylinder unit includes a cylinder having at least one axially facing counterstop; a piston dividing the cylinder into a first working chamber and a second working chamber; a piston rod extending through the first working chamber to a free end outside the cylinder; and a fastening tube having a first end in which the free end of the piston rod is fixed, a second end which receives the cylinder coaxially, and at least one axially facing supporting stop. When the piston rod is extended to maximum extension, the fastening tube is rotatable relative to the cylinder from a release position, wherein the supporting stop is offset from a respective counterstop, to a locking position, wherein the supporting stop faces the counterstop so that the fastening tube cannot move axially relative to the cylinder.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a lockable piston-cylinder unit with a cylinder arrangement having a closed cylinder in which a piston dividing the cylinder interior into a first chamber and a second chamber is guided so as to be displaceable. The piston having a piston rod which is guided out of the cylinder interior so as to be sealed at one front side of the cylinder, the first chamber and second chamber being connected or connectable to one another.

2. Description of the Related Art

A fastening tube enclosing the cylinder arrangement and has a length greater than or equal to the move-out length of the piston rod, and is fixedly by one of its ends at the piston rod in the area of its free end and has a supporting stop. When the piston rod is moved out, the fastening tube can be moved out of its release position into a locking position in which the supporting stop contacts a counterstop of the cylinder arrangement so as to block a moving-in movement of the piston-cylinder unit.

In a gas spring of the type mentioned above, e.g., for opening hatches or doors particularly in motor vehicles, it is known that the fastening tube is mounted by its first end area in the area of the free end of the piston rod so as to be pivotable between a release position coaxial to the piston rod and a locking position which is inclined relative to the longitudinal axis of the piston rod and has the supporting stop at its second end area. When the piston rod is moved out, the fastening tube can be pivoted into the locking position and can contact one front side of the cylinder axially by the supporting stop.

This gas spring has the problem that transverse forces are generated in the system by the pivoting of the fastening tube and can cause the system to buckle when overloaded.

SUMMARY OF THE INVENTION

Therefore, it is an object of the invention to provide a piston-cylinder unit of the type mentioned above in which buckling is prevented, particularly when the piston rod is moved out.

This object is met according to the invention by arranging the cylinder arrangement and the fastening tube coaxial to one another and rotatable relative to one another with respect to their longitudinal axis between the release position and the locking position.

Transverse forces which act on the piston-cylinder unit during the pivoting of the fastening tube and, therefore, also a buckling of the piston rod caused by these transverse forces are prevented in this way.

The fastening tube can have a plurality of supporting stops and the cylinder arrangement can have a corresponding number of counterstops, and the supporting stops and the counterstops can be uniformly distributed around the circumference for a uniformly distributed support.

The counterstops can project outward radially from the cylinder arrangement, and the supporting stops can be formed so as to project radially inward from the inner wall of the fastening tube.

To prevent the cylinder arrangement from rotating relative to the fastening tube when the piston rod is not moved out fully into the locking position, means for blocking rotation can be arranged between the cylinder arrangement and the fastening tube to allow a relative rotation of the cylinder arrangement and fastening tube only when the piston rod is in the completely moved out position.

In a simple construction, the means for blocking rotation can have a rotation-blocking projection of the cylinder arrangement which projects radially outward and which engages displaceably in a longitudinal groove extending parallel to the longitudinal axis at the inner wall of the fastening tube.

Longitudinal grooves into which the supporting stops forming the rotation-blocking projections project can be formed in the inner wall of the fastening tube corresponding to the counterstop(s), wherein supporting stops are formed next to one or more ends of the longitudinal grooves which are closer to the piston rod in circumferential direction.

In another construction, the means for blocking rotation can have a guide projection of the fastening tube which projects inward radially and which engages displaceably in a longitudinal groove extending parallel to the longitudinal axis at the outer surface of the fastening tube or a structural component part enclosing the fastening tube.

An exact rotation until reaching the locking position is achieved by the cylinder arrangement and/or the fastening tube having one or more stops which are contacted by the supporting stops and/or the counterstops during the relative rotation of the cylinder arrangement and fastening tube into the locking position.

A simple arrangement of the counterstops at the cylinder arrangement results when a holding sleeve is arranged at least on the end of the cylinder arrangement on the piston rod side so as to be fixed with respect to rotation relative to it and fixed axially and which has the counterstop or counterstops, wherein the holding sleeve and the counterstops can be formed in one piece, particularly from plastic, so as to economize on parts.

The fastening tube is guided and supported, particularly when the piston rod is moved out, when the holding sleeve is displaceably guided by its radial circumferential outer surface at the inner wall of the fastening tube.

To prevent an unwanted automatic rotation out of the locking position into the release position, the supporting stop has a stop plane extending at an inclination to the longitudinal axis in circumferential direction from an insertion end to a locking end, wherein the locking end defining the locking position is at a greater distance from the end of the cylinder arrangement remote of the piston rod than the insertion end.

This arrangement for preventing rotation is further improved when the counterstop has another stop plane extending at an inclination to the longitudinal axis in circumferential direction from an insertion end to a locking end, wherein the locking end defining the locking position is closer to the end of the cylinder arrangement remote of the piston rod than the insertion end.

The means for preventing buckling when the piston rod is moved out is further improved when a guide sleeve is fixed in the open end area of the fastening tube, the cylinder of the cylinder arrangement being guided in the guide tube so as to be displaceable.

To prevent damage when manual force is applied to the moved out piston rod and when the fastening tube is in the locking position, the stop or stops can be deflected in opposition to a defined spring force from the locking position radially into a run-over position in which the supporting stop or supporting stops are disengaged from the counterstops and the piston rod is movable in the push-in direction. This will automatically cancel locking in the event of overloading in the move-in direction.

In a simple construction, the stop faces of the counterstops facing the supporting stops axially can be constructed as ramps which are inclined relative to the longitudinal axis, and the additional stop faces of the supporting stops which face the counterstops axially can be constructed as ramps which are inclined relative to the longitudinal axis.

For this purpose, the counterstops can serve a dual function so as to economize on parts by arranging them at the free ends of spring arms which extend axially toward the free end of the piston rod. The spring arms are fixed by their other ends at the end area of the cylinder of the cylinder arrangement on the piston rod side.

A compulsory rotation of the fastening tube into its release position is carried out when locking is overcome by a rotation-blocking first longitudinal groove extending parallel to the longitudinal axis and a parallel second longitudinal groove of the same cross section which extends parallel to the rotation-blocking longitudinal groove and in which the rotation-blocking projection projects. The second groove opens into the rotation-blocking first longitudinal groove at the end closer to the free end of the piston rod along a connection area which is inclined in the manner of a ramp toward the first longitudinal groove. The grooves are arranged at the end area of the fastening tube opposite to the end on the piston rod side. The parallel longitudinal groove is connected to the rotation-blocking longitudinal groove at the end of the connection area opposite to that in which the parallel longitudinal grooves open into the rotation-blocking longitudinal grooves.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The piston-cylinder unit shown in the drawings which is formed as a lockable gas spring has a cylinder arrangement1with a closed cylinder2in which a piston33is guided so as to be displaceable and which divides the interior of the cylinder, which is filled with a gas under pressure, into a first chamber and a second chamber.

In a piston-cylinder unit which is not formed as a gas spring, the cylinder interior can also be filled with oil.

A piston rod3is arranged at one side of the piston33. The piston rod3is guided out of the cylinder interior at a front end4of the cylinder2so as to be sealed by a sealing and guiding element23. The two chambers of the cylinder interior are connected to one another by a choke connection, not shown. The choke connection can be formed as an axial groove in the piston or in the cylinder.

A fastening tube5enclosing the cylinder arrangement1has a first end area6at the free end of the piston rod3and a second end area7extending toward the cylinder2. The fastening tube5is arranged on the piston rod3so as to be rotatable around the longitudinal axis of the piston rod3but fixed with respect to displacement axially.

The fastening tube5has an axial through-opening8in its first end area6through which the free end of the piston rod3is guided.

A first fastening part10is screwed onto the free end of the piston rod3provided with a thread9. The front side of the fastening part10facing the fastening tube5forms a stop11which is supported axially at the outlet area12of the through-opening8. A second fastening part13is arranged at the end of the cylinder2remote of the piston rod3. The two fastening parts10and13are formed as ball sockets.

A guide sleeve14is fixedly inserted into the fastening tube5in its end area7. The cylinder2of the cylinder arrangement1is displaceable in the guide sleeve14.

Starting from the end closest to the first fastening part10, six longitudinal grooves15extending parallel to the longitudinal axis are formed at the inner wall of the fastening tube5and are arranged so as to be uniformly distributed radially at the circumference and extend axially in direction of the other end of the fastening tube5. The longitudinal grooves15are incorporated directly in the fastening tube5formed as a plastic injection molded part. The webs17separating the longitudinal grooves15from one another form supporting stops18at their front ends facing the second fastening part13.

A holding sleeve19is mounted on the end4of the cylinder2facing the first fastening part10, this holding sleeve19having cam-shaped counterstops20which project out axially over the end4of the cylinder2and radially over the diameter of the cylinder2, its outer diameter corresponding to the inner diameter of the fastening tube5in the area of the longitudinal grooves15.

The counterstops20correspond to the longitudinal grooves15with respect to distribution and cross-sectional profiles. When the piston rod3is moved in, the counterstops20are pushed into the longitudinal grooves15so that it is impossible for the fastening tube to rotate relative to the cylinder arrangement. When the piston rod3is moved out, the counterstops20move in the longitudinal grooves15until they are moved out of the longitudinal grooves15shortly before the end of the maximum moved out position. In this position, the counterstops20are in the release position relative to the supporting stops18. In this release position, it is possible for the counterstops20to move into the longitudinal grooves15again.

The fastening tube5can now be rotated manually around the longitudinal axis relative to the cylinder arrangement1until the side of the counterstops20directed toward the longitudinal axis in circumferential direction contacts stops21of the fastening tube5. The counterstops20are now in the locking position axially relative to the supporting stops18and the piston rod3can now no longer move in.

In the first embodiment, shown inFIGS. 1 to 6, the stop planes22of the supporting stops18and of the counterstops20, which stop planes22face one another axially in the locked position, are inclined in circumferential direction relative to the longitudinal axis. With respect to the supporting stops18in the fastening tube5, the locking end is at a greater distance from the end of the cylinder arrangement1remote of the piston rod than the insertion end. With respect to the counterstops20on the holding sleeve19, the locking end is closer to the end of the cylinder arrangement1remote of the piston side than the insertion end. In this locking position, the piston rod3is locked in its moved out position. The piston rod5can be moved back into its moved-in position again by rotating the fastening tube5back into the release position.

In the second embodiment, shown inFIGS. 7 to 15, a spring arm basket24is fastened to the holding sleeve19at the end4of the cylinder2on the piston rod side. The spring arm basket24has six spring arms25which project freely away from the cylinder2axially and are arranged so as to be distributed corresponding to the longitudinal grooves15.

Guide projections16running in the longitudinal grooves15are arranged at the cylinder2and protect the spring arms from transverse forces. The guide projections16are located either in the rotation-blocking longitudinal grooves29or in the longitudinal grooves15.

The free ends of the spring arms25are provided with counterstops20whose stop faces26are formed at an inclination to the longitudinal axis. The stop faces27of the supporting stops18are also formed at an inclination to the longitudinal axis in a corresponding manner. When the counterstops20are in the locking position axially relative to the supporting stops18, the piston rod3is preventing from moving in up to a determined force applied to the piston rod3in the moving in direction. When this determined applied force is exceeded, the stop faces26and27slide one upon the other and bend the spring arms25radially inward against their spring force. The piston rod3can now be pushed in and the counterstops20slide on the webs17.

In order to guide the counterstops20back into the longitudinal grooves15, rotation-blocking radial projections28are arranged on the holding sleeve19and project in an axially displaceable manner into corresponding rotation-blocking longitudinal grooves29formed in the inner wall of the guide sleeve14parallel to the longitudinal axis.

Referring toFIG. 14, at the end of the rotation-blocking longitudinal groove29remote of the piston rod3, a parallel longitudinal groove30of the same cross section is formed in the guide sleeve14parallel to the rotation-blocking longitudinal groove29. The end of the parallel longitudinal groove30closer to the free end of the piston rod3opens into the rotation-blocking longitudinal groove29via a connection area31which is inclined in the manner of a ramp toward the rotation-blocking longitudinal groove29. The parallel longitudinal groove30is also connected to the rotation-blocking longitudinal groove29at the end opposite to the connection area31.

When the fastening tube5is rotated out of the releasing position into the locking position, the rotation-blocking projection28is moved out of the rotation-blocking longitudinal groove29into the parallel longitudinal groove30via the connection mentioned above. When the fastening tube5is rotated back, the rotation-blocking projection28returns to the rotation-blocking longitudinal groove29again.

However, when the piston rod3is pushed in out of the locking position, the rotation-blocking projection28moves into the parallel longitudinal groove30and into the rotation-blocking longitudinal groove29again via the connection area31. In this way, a compulsory rotation of the fastening tube5is carried out relative to the cylinder arrangement1by which the counterstops20of the spring arms25catch in the longitudinal grooves15again.

When the guide projections16are located in the longitudinal grooves15, they protect the spring arms25against transverse forces. The rotation-blocking projections28are either located in the rotation-blocking longitudinal grooves29or the guide projections16are located in the longitudinal grooves15.