Actuator for an automated or automatic transmission, and method for controlling the actuator

1. An actuator ( 1 ) for an automated or automatic transmission, the actuator comprising:

a cylinder housing ( 3 ), a piston unit ( 2 ), an end stop damping device, and a piston rod ( 13 ),

wherein the piston unit ( 2 ) is coupled to the piston rod ( 13 ) and arranged in the cylinder housing ( 3 ) to be movable in two opposite directions along a longitudinal axis ( 4 ),

wherein the piston unit ( 2 ) separates two pressure chambers ( 8 , 9 ) of variable volume in the cylinder housing ( 3 ), the pressure chambers being configured to apply pressure to the piston unit ( 2 ) with compressed air from opposite sides,

wherein the two pressure chambers ( 8 , 9 ) are configured to be connected to a valve unit ( 14 ) configured to selectively switch between a pressurization or a purge of each of the two pressure chambers ( 8 , 9 ), and

wherein the end stop damping device is arranged in the actuator ( 1 ) for damping at least one end stop of the piston unit ( 2 ) and is composed of a first pneumatically active damping stage and a second mechanically active damping stage,

wherein the first pneumatically active damping stage is configured to reduce the kinetic energy of the piston unit ( 2 ) in at least one movement direction thereof when the piston unit ( 2 ) approaches at least one of two opposite end stop faces ( 5 , 6 ),

wherein the first pneumatically active damping stage is formed on the cylinder housing ( 3 ) by a pneumatic damping element ( 19 , 20 ), wherein the pneumatic damping element ( 19 , 20 ) has an air outlet ( 34 , 35 ) with a variable cross-sectional area for compressed air, which is configured to be pneumatically connected to a respective one of the two pressure chambers ( 8 , 9 ) by switching the valve unit ( 14 ) into a purge position for the respective one of the two pressure chambers ( 8 , 9 ), wherein the cross-sectional area ( 28 , 29 ) of the air outlet ( 34 , 35 ) is adjustable by a prevailing pressure in the respective pressure chamber ( 8 , 9 ) connected thereto, and

wherein the second mechanically active damping stage is configured to dissipate a kinetic energy of the piston unit ( 2 ) remaining after braking by the pneumatic damping element ( 19 , 20 ), when the piston unit ( 2 ) reaches the at least one end stop face ( 5 , 6 ),

wherein the second mechanically active damping stage becomes active upon impact on at least one of the at least one end stop face ( 5 , 6 ) and includes at least one mechanical damping element ( 40 , 41 ) formed as a rubber buffer arranged on the piston unit at a piston end proximate to one of the at least one end stop face ( 5 , 6 ) of the cylinder housing ( 3 ).

2. The actuator as claimed in claim 1 , wherein the end stop damping device is operative for both opposite directions of movement of the piston unit ( 2 ),

wherein the first pneumatically active damping stage comprises a first pneumatic damping element ( 19 ) for a first movement direction of the two opposite directions, and a second pneumatic damping element ( 20 ) for a second movement direction of the two opposite directions, the first and second pneumatic damping elements being assigned to the valve unit ( 14 ), and

wherein the second mechanically active damping stage comprises a first mechanical damping element ( 40 ) for stopping the piston unit ( 2 ) at a first end stop face ( 5 ) of the two end stop faces and a second mechanical damping element ( 41 ) for stopping the piston unit ( 2 ) at an opposite second end stop face ( 6 ) of the two end stop faces, the first and second mechanical damping elements being arranged on the piston unit ( 2 ).

3. The actuator as claimed in claim 2 , wherein the first pneumatic damping element ( 19 ) is configured to be controlled by a first 3/2-way magnetic valve ( 15 , 17 ) of the valve unit ( 14 ), that the second pneumatic damping element ( 20 ) is configured to be controlled by second 3/2-way magnetic valve ( 15 , 17 ) of the valve unit ( 14 ) wherein the first and second pneumatic damping elements ( 19 , 20 ) each have an air outlet flap ( 21 , 22 ) formed as an elastic lip arranged on a first or second outlet opening ( 23 , 24 ) of a first or second air outlet ( 34 , 35 ) respectively connected to the first pressure space ( 8 ) or the second pressure space ( 9 ) via the first or the second 3/2-way magnetic valve,

wherein the air outlet flap ( 21 ) is attached unilaterally to an associated one of the first and second air outlet openings g ( 23 , 24 ) such that the air outlet flap ( 21 , 22 ) lies under spring preload on the associated air outlet opening ( 23 , 24 ) under atmospheric pressure and by overcoming the spring preload, lifts away from the respective air outlet opening ( 23 , 24 ) on pressurization of the air outlet flap ( 21 , 22 ) from the first or second pressure chamber ( 8 , 9 ) when a pressure threshold value is exceeded,

wherein each of the two air outlet flaps ( 21 , 22 ) includes a respective permanently open passage opening ( 26 , 27 ), the passage opening having a cross-sectional area smaller than the respective air outlet opening ( 23 , 24 ) associated with the air outlet flap ( 21 , 22 ),

wherein the air outlet openings ( 23 , 24 ) which can be opened pressure-dependently are substantially smaller than a cross-sectional area ( 32 ) of the piston unit ( 2 ).

4. The actuator as claimed in claim 2 , wherein the first and second pneumatic damping elements ( 19 , 20 ) are combined in a valve block of the valve unit ( 14 ).

5. The actuator as claimed in claim 2 , wherein the first and second pneumatic damping elements ( 19 , 20 ) are directly integrated in a respective assigned 3/2-way magnetic valve ( 15 , 17 ) of the valve unit ( 14 ).

6. The actuator as claimed claim 2 , further comprising an effective dead volume ( 39 ), which remains in an end position of the piston unit ( 2 ) and includes a free volume in the region between the piston unit ( 2 ) and the first or second end stop face ( 5 , 6 ) in the respective pressure chamber ( 8 , 9 ), with a pneumatic connection between the respective pressure chamber ( 8 , 9 ) and the assigned air outlet opening ( 23 , 24 ) of the respective pneumatic damping element ( 19 , 20 ).

7. The actuator as claimed in claim 1 , wherein the piston unit ( 2 ) has a radially inner main piston ( 10 ) fixedly connected to the piston rod ( 13 ), wherein the main piston ( 10 ) carries a first auxiliary piston ( 11 ) assigned to a first pressure chamber ( 8 ) of the two pressure chambers and a second auxiliary piston ( 12 ) assigned to a second pressure chamber ( 9 ) of the two pressure chambers, that the first and second auxiliary pistons ( 11 , 12 ) are arranged radially outward from the main piston ( 2 ) with respect to the longitudinal axis, with displaceability relative thereto and coaxial with the longitudinal axis ( 4 ), wherein the at least one mechanical damping element includes a first rubber buffer arranged on the first auxiliary piston ( 11 ) at a piston end proximate to the first end stop face ( 5 ) of the cylinder housing ( 3 ), and a second rubber buffer arranged on the second auxiliary piston ( 12 ) at a piston end proximate to the second end stop face ( 6 ) of the cylinder housing ( 3 ).

8. A method for controlling the actuator ( 1 ) as claimed in claim 1 , the method comprising the following steps:

pressurizing one of the two pressure chambers ( 8 , 9 ), with a positive pressure (p(t)_ 1 ) and simultaneously purging the other of the two pressure chambers ( 9 , 8 ) to drive a movement of the piston unit ( 2 ) coaxially to the longitudinal axis ( 4 ),

performing a two-stage damping for damping the at least one end stop of the piston unit ( 2 ) at the at least one end stop face ( 5 , 6 ) in the actuator ( 1 ), by first activating the first pneumatically active damping stage, via the pneumatic damping element ( 19 , 20 ), when the piston unit ( 2 ) approaches at least one of the at least one end stop face ( 5 , 6 ), by producing a self-regulating counter-pressure (p(t)_ 2 ) countering the piston movement in the one of the two pressure chambers ( 8 , 9 ) that is to be purged, wherein the cross-sectional area ( 28 , 29 ) of the air outlet ( 34 , 35 ) of the pneumatic damping element ( 19 , 20 ) is automatically adjusted by the prevailing pressure, and subsequently, when the piston unit reaches the end stop face ( 5 , 6 ), dissipating the remaining kinetic energy of the piston unit ( 2 ) by elastic deformation of a mechanical damping element ( 40 , 41 ) of the second mechanically active damping stage upon impact on the at least one of the at least one end stop face ( 5 , 6 ).

9. An automated or automatic transmission in a drive train of a motor vehicle, with at least one actuator ( 1 ) as claimed in claim 1 .