Brewing unit for a coffee machine

1. A brewing unit ( 1 ) of a piston coffee machine, wherein the brewing unit ( 1 ) is designed as a spindle brewing unit having a brewing slide ( 2 ) as a brewing chamber, two piston units, one of the piston units being formed as a shower screen ( 9 ) and the other of the piston units being formed as a plunger ( 10 ), a drive motor ( 20 ) and at least one gearing mechanism ( 21 , 22 ), wherein the brewing unit ( 1 ) further comprises a double-spindle assembly having an outer spindle ( 3 ) disposed radially outside the brewing chamber and an inner spindle ( 7 ) arranged coaxial with a slide axis of the slide, wherein during a brewing operation, the brewing slide ( 2 ) is configured to be moved from a first end position into an intermediate position, then into a second end position and back again into the first end position, wherein the outer spindle ( 3 ) has a movement thread ( 3 e ) which engages with an outer spindle nut ( 15 ) axially fixed in the brewing slide ( 2 ), and wherein the movement thread ( 3 e ) of the outer spindle ( 3 ) is disengaged from the outer spindle nut ( 15 ) in the first end position and in the second end position of the brewing slide ( 2 ) and a speed of the brewing slide ( 2 ) is zero even if the outer spindle ( 3 ) continues to rotate.

2. The brewing unit ( 1 ) according to claim 1 , wherein the outer spindle ( 3 ) is connected to the brewing slide ( 2 ), the inner spindle ( 7 ) is connected to the shower screen ( 9 ) or the plunger ( 10 ), and the plunger ( 10 ) or the shower screen ( 9 ) is arranged in a fixed position, wherein the brewing slide ( 2 ) is guided in a longitudinally displaceable manner by means of the outer spindle ( 3 ) and a guide rod ( 4 ), and wherein the shower screen ( 9 ) or the plunger ( 10 ) is guided in a longitudinally displaceable manner inside the brewing slide ( 2 ), wherein the brewing slide ( 2 ) and the shower screen ( 9 ) or the plunger ( 10 ) are adjustable at different speeds in common directions of movement (BR 1 , BR 2 ).

3. The brewing unit ( 1 ) according to claim 1 , wherein said outer spindle ( 3 ) is driven by the drive motor ( 20 ) and is coupled to the inner spindle ( 7 ) via the at least one gearing mechanism ( 22 ).

4. The brewing unit ( 1 ) according to claim 1 , wherein the brewing unit ( 1 ) has at least one switchable electromagnet which fixes the brewing slide ( 2 ) in one of the end positions in a releasable manner again directly or indirectly via a mechanical locking device.

5. The brewing unit ( 1 ) according to claim 1 , wherein the brewing unit ( 1 ) comprises at least one spindle re-engagement device which causes re-engagement of the outer spindle nut ( 15 ) and the movement thread ( 3 e ) in the first end position or the second end position.

6. The brewing unit ( 1 ) according to claim 5 , wherein the at least one spindle re-engagement device comprises first and second stop units ( 18 , 19 ), each with a respective compression spring ( 18 b , 19 b ), wherein the brewing slide ( 2 ) pretensions the compression spring ( 18 b ) of the first stop unit ( 18 ) in the first end position, and wherein the brewing slide ( 2 ) pretensions the compression spring ( 19 b ) of the second stop unit ( 19 ) in the second end position.

7. The brewing unit ( 1 ) according to claim 6 , wherein the compression spring ( 18 b ) of the first stop unit ( 18 ) re-engages the movement thread ( 3 e ) of the outer spindle ( 3 ) with the outer spindle nut ( 15 ) of the brewing slide ( 2 ) when the brewing slide ( 2 ) is displaced from the first end position by means of the outer spindle ( 3 ), and wherein the compression spring ( 19 b ) of the second stop unit ( 19 ) re-engages the movement thread ( 3 e ) of the outer spindle ( 3 ) with the outer spindle nut ( 15 ) of the brewing slide ( 2 ) when the brewing slide ( 2 ) is moved from the second end position by means of the outer spindle ( 3 ).

8. The brewing unit ( 1 ) according to claim 5 , wherein the at least one spindle re-engagement device comprises at least one switchable electromagnet which exerts a movement impulse on the brewing slide ( 2 ) in one of the end positions, directly or indirectly via a mechanical device, which movement impulse causes renewed engagement of the outer spindle nut ( 15 ) and movement thread ( 3 e ) in the first end position or the second end position.

9. The brewing unit ( 1 ) according to claim 5 , wherein the at least one spindle re-engagement device comprises at least two switchable and reversible electromagnets, one of which is fixed and the other of which is attached to the brewing slide ( 2 ).

10. The brewing unit ( 1 ) according to claim 5 wherein the at least one spindle re-engagement device comprises at least one friction element directly on the inner spindle ( 7 ) or indirectly on a component mounted on the inner spindle ( 7 ) in cooperation with the brewing slide ( 2 ).

11. The brewing unit ( 1 ) according to claim 5 , wherein the at least one spindle re-engagement device comprises at least one friction element configured as a hydraulic sealing element, wherein the at least one hydraulic sealing element is a seal ( 34 ) attached to the shower screen ( 9 ) or to the plunger ( 10 ), which seal ( 34 ) is controlled by the application of a pressure.

12. The brewing unit ( 1 ) according to claim 5 , wherein the at least one spindle re-engagement device comprises a driver device having at least one driver ( 37 ), which is displaceably guided on the inner spindle ( 7 ) or a component connected to the inner spindle ( 7 ) and on a guide rod ( 4 ), wherein the driver ( 37 ) is held in a rest position with respect to the inner spindle ( 7 ) or the component connected to the inner spindle ( 7 ) with a certain retaining force which is greater in the rest position than outside the rest position.

13. The brewing unit ( 1 ) according to claim 12 , wherein the at least one driver ( 37 ) comprises a first retaining element, and wherein a second retaining element is mounted on or in the inner spindle ( 7 ) or on or in the component connected to the inner spindle ( 7 ), wherein the first retaining element and the second retaining element generate the determined retaining force in the rest position of the driver ( 37 ).

14. The brewing unit ( 1 ) according to claim 13 , wherein the first retaining element is a permanent magnet or is a springloaded ball pressure element which, in a rest position of the driver ( 37 ), is in contact with a corresponding indentation or groove in the inner spindle ( 7 ) or in the component connected to the inner spindle ( 7 ), and wherein the second retaining element is a permanent magnet.

15. The brewing unit ( 1 ) according to claim 1 , wherein the inner spindle ( 7 ) comprises a movement thread ( 7 b ) which is in engagement with a fixedly rotatably mounted inner spindle nut ( 27 a ).

16. The brewing unit ( 1 ) according to claim 1 , wherein the inner spindle nut ( 27 a ) is a component of an output gear ( 27 ) of the at least one gearing mechanism ( 22 ).

17. The brewing unit ( 1 ) according to claim 15 , wherein the inner spindle ( 7 ) is connected to a securing rod ( 7 f ) as an anti-rotation device.