An engine air brake device for a 4-stroke recriprocating-piston internal combustion engine that has at least one intake valve per cylinder and two exhaust valves that are connected to an exhaust train and can be actuated via a valve bridge and a rocker arm that acts on said valve bridge and can be controlled by a camshaft either directly or indirectly via a push rod, each exhaust valve being biased in a closing direction by means of a closing spring, whereby a throttling device is installed in said exhaust train and can be actuated for engine deceleration such that an exhaust back pressure builds up in accumulated exhaust gas upstream of said throttling device and becomes engine-internally active for engine deceleration in conjunction with a braking device, which comprises:
- an engine internal braking device associated with only one of said two exhaust valves for each cylinder, wherein said braking device is provided with a control piston against which a valve stem of said one exhaust valve is supported, wherein said control piston is moveably guided axially in a blind bore of said valve bridge and is adapted to be pressed in a direction of said valve stem from a control pressure chamber that is supplied with pressurized oil, and optionally from an additional control compression spring, wherein pressurized oil is supplied to said control pressure chamber via a duct that is provided in said valve bridge and communicates with a duct in said rocker arm, wherein a check valve is disposed in said duct of said valve bridge and permits flow only in a direction toward said control pressure chamber, wherein a relief duct exits said control pressure chamber and opens out on an upper side of said valve bridge, wherein a brace, which doubles as a stop for said valve bridge, is provided for closing off an outlet orifice of said relief duct and for opening said outlet orifice for relieving pressure from said control pressure chamber after raising of said valve bridge, wherein a pre-tensioning force of said closing spring that is associated with said one exhaust valve is such that during engine deceleration when said throttling device is in a throttling position, an intermediate opening of said one exhaust valve is effected due to exhaust back pressure accumulated in the exhaust gas in conjunction with pressure pulsations effective therein, wherein in such intermediate opening itis possible to intervene with said engine-internal braking device during each 4-stroke engine cycle in a control-related automatic manner so that after the intermediate opening at the beginning of a second stroke said one exhaust valve, which is about to close, is intercepted by the approaching oil-pressure-charged control piston, is prevented from closing during second and third strokes, and is kept partially open until a camshaft-controlled opening at the beginning of a 4th stroke, wherein the exhaust gas pressure is highest when said throttling device is in a closing position and can, if necessary, be lowered through a controlled and/or regulated opening of said throttling device to reduce engine brake output and/or the temperature of engine-internal components, and wherein a cross-section of the oil-supply ducts, and a pressure of the oil supply to said control pressure chamber, are coordinated with each other such that during an intermediate opening of said one exhaust valve, said control pressure chamber, which enlarges in volume due to the departing control piston, can be filed with pressurized oil at least almost completely, thus ensuring that said one exhaust valve is kept in an intercepted partial opening position towards the end of an intermediate opening stroke.