Hydraulical shifting device for an automatic transmission

An automatic transmission in combination with a hydraulic shifting device for engaging and disengaging a parking lock, the hydraulic shifting device comprising:

• a parking lock cylinder (203) for actuating the parking lock,
• a first parking lock valve (201) which, for hydraulic control of the parking lock cylinder (203), being connected to a working pressure source and being movable to at least first and second shift positions, and
• a second parking lock valve (202) being movable to at least first and second shift positions,
• the first and the second parking lock valves (201, 202) and the parking lock cylinder (203) being designed and connected with one another in such manner that the parking lock only being disengagable by pressurization of the parking lock cylinder (203) provided that the first and the second parking lock valves (201, 202) are each in a particular shift position,
• wherein, when the first parking lock valve (201) is in a first shift position, the parking lock cylinder is connected, via the first parking lock valve (201), to a vent (260) regardless of a shift position of the second parking lock valve (202) and the parking lock is thus engaged.

A hydraulic shifting device for an automatic transmission, for engaging and disengaging a parking lock, the hydraulic shifting device comprising:

• a parking lock cylinder (203) comprises a parking lock piston (231) that is shiftable between a first position, in which parking lock is engaged, and a second shift position in which the parking lock is disengaged;
• a first parking lock valve (201) comprising a valve slide (210) being shiftable between at least first and second shift positions, and the first parking lock valve (201) being connected to a working pressure (p_MP);
• a second parking lock valve (202) comprising a valve slide (210) being shiftable between at least first and second shift positions;
• and
• the first and the second parking lock valves (201, 202) and the parking lock cylinder (203) being connected with one another such that the parking lock cylinder (203) being shifted to the first position, in which the parking lock is disengaged, only if the first parking lock valve (201) is shifted to a particular one of the first and the second shift positions and the second parking lock valve (202) is shifted to a particular one of the first and the second shift positions;
• wherein the parking lock cylinder (203) is connected, via the first parking lock valve (201), to a vent (260) such that when the first parking lock valve (201) is in the first shift position and the second parking lock valve (202) is in either the first or the second shift positions, the parking lock piston (231) is shifted to a position in which the parking lock is engaged.