Patent ID: 7083034

Claim:
A gear shift device ( 2 ) for a motor vehicle, the gear shift ( 2 ) comprising: a single gear shift cylinder ( 4 ); a single gear shift piston ( 12 ) dividing the gear shift cylinder ( 4 ) into first and second working chambers ( 22 , 24 ) and having an axial aperture ( 30 ) with an internal diameter extending between the first and the second working chambers ( 22 , 24 ); wherein a single axially fixed bolt ( 26 ) extends between the first and the second working chambers ( 22 , 24 ) through the aperture ( 30 ) and has end areas ( 32 , 34 ) with a first external diameter and a middle area having a smaller external diameter; the piston ( 12 ) is axially movable from a first end to a second end of the cylinder ( 4 ) by a pressure medium applied to one of the first and the second working chambers ( 22 or 24 ); when the piston ( 12 ) is adjacent the first end, the internal diameter of the aperture ( 30 ) forms a seal with the first external diameter of the bolt ( 26 ) to retain the pressure medium in the one of the first and the second working chambers ( 22 or 24 ); when the piston ( 12 ) is in the bolt ( 26 ) middle area, the internal diameter of the aperture ( 30 ) and the smaller external diameter of the bolt ( 26 ) form a passage between the first and the second working chambers ( 22 , 24 ) to provide a counter pressure against the piston ( 12 ) in the other of the first and the second working chambers ( 24 or 22 ); and when the piston ( 12 ) is adjacent the second end, the internal diameter of the aperture ( 30 ) forms a seal with the first external diameter of the bolt ( 26 ) to form a pressure medium buffer in the other of the first and the second working chambers ( 24 or 22 ).