Elevator installation

1. An elevator installation, comprising:

an elevator shaft;

at least a first elevator car and a second elevator car disposed in said shaft and arranged one above the other, and separately moveable from one another in an upward and downward vertical direction;

a first travel drive assigned to and operatively engaged with said first elevator car, and configured to provide traveling movement to said first elevator car;

a second travel drive assigned to and operatively engaged with said second elevator car, and configured to provide traveling movement to said second elevator car; and

a variable-length releasable coupling device configured to:

selectively couple said first elevator car to said second elevator car,

permit one of said first or second travel drives to variably adjust a spacing between the coupled-together first and second elevator cars as long as a relative speed between said first and second elevator cars is maintained below a predefined maximum relative speed, and

prevent a further change in spacing between the coupled-together first and second elevator cars when said relative speed exceeds said predefined maximum relative speed.

2. The elevator installation of claim 1 , wherein said variable-length releasable coupling device comprises:

at least one moveable coupling member, and

an influencing member in operative communication with said at least one moveable coupling member and configured to influence a movement of said moveable coupling member with respect to said influencing member, as long as the relative speed between the coupled-together first and second elevator cars is maintained below the predefined maximum relative speed.

3. The elevator installation of claim 2 , wherein said influencing member is an equalization device, and wherein said at least one moveable coupling member comprises one of a hydraulic or pneumatic piston-cylinder assembly, said piston-cylinder assembly having:

a double-acting cylinder defining a ring shaped chamber and a piston chamber therein, and

a piston fixed to a piston rod that is moveable in said ring-shaped chamber of said double-acting cylinder, wherein said ring shaped chamber and said piston chamber may be operatively coupled together by said equalization device in a manner dependent on the relative speed between the coupled-together first and second elevator cars.

4. The elevator installation of claim 3 , wherein said equalization device comprises a throttling element configured to be controlled based on the relative speed between the coupled-together first and second elevator cars.

5. The elevator installation of claim 3 , wherein said equalization device comprises at least one pump.

6. The elevator installation of claim 2 , wherein said at least one moveable coupling member comprises a first mechanical coupling element and a second mechanical coupling element that can be engaged with, and are moveable relative to, one another,

wherein said influencing member comprises at least one controllable brake element, and

wherein a relative movement of said first and second mechanical coupling elements can be arrested by said at least one controllable brake element based on the relative speed between said first and second elevator cars.

7. The elevator installation of claim 6 , wherein said first mechanical coupling element is a threaded spindle that is rotatably mounted about its longitudinal axis on said first elevator car,

wherein said second mechanical coupling element is a threaded nut fixed onto said second elevator car and which can be engaged with said threaded spindle, and

wherein a rotational speed of said threaded spindle can be limited by way of said at least one controllable break element based on the relative speed between said first and second elevator cars.

8. The elevator installation of claim 6 , wherein said first mechanical coupling element is a toothed rack that is fixed to said first elevator car, and

wherein said second mechanical coupling element is a gearwheel that is rotatably mounted on said second elevator car and is engaged with said toothed rack, a rotational speed of said gear wheel being limited by way of said at least one controllable brake element based on the relative speed between said first and second elevator cars.

9. The elevator installation of claim 2 , wherein said at least one moveable coupling member comprises a plurality of mechanical coupling elements disposed on said first elevator car and moveably connected to one another, and which mechanical coupling elements are releasably couplable to said second elevator car,

wherein said plurality of mechanical coupling elements are moveable between a compact stowed position and a plurality of coupling positions having varying extents of deployment, said plurality of mechanical coupling elements further being arrestable by way of said influencing member based on the relative speed between said first and second elevator cars.

10. The elevator installation of claim 9 , wherein said plurality of mechanical coupling elements form a support chain, and wherein said influencing member is a gearwheel that is engaged with said support chain and can be arrested.

11. The elevator installation of claim 1 , wherein the spacing between the coupled-together elevator cars can be varied, based on the relative speed between the first and second elevator cars, with the aid of the travel drives of all of the coupled elevator cars.

12. The elevator installation of claim 1 , wherein said coupling device comprises at least one motorized coupling drive configured to couple and decouple said first and second elevator cars together.

13. The elevator installation of claim 1 , wherein said first and second elevator cars are respectively connected to said first and second travel drives by supporting means.

14. The elevator installation of claim 1 , wherein said first and second elevator cars are connected to a respective counterweight by supporting means.

15. The elevator installation of claim 2 , wherein said influencing member is configured to limit a speed of said coupling member.

16. The elevator installation of claim 2 , wherein said influencing member is configured to arrest said coupling member.

17. The elevator installation of claim 2 , wherein said coupling member is configured to transmit at least one of tensile and compressive forces between the coupled-together elevator cars.

18. The elevator installation of claim 2 , wherein said coupling device comprises a plurality of coupling members of identical design.