Flap devices of this type are used, for example, as exhaust back flaps or exhaust return valves in low-pressure or high-pressure exhaust circuits, or as throttle flaps in the suction duct of internal combustion engines. They serve to control an exhaust quantity to be returned to the cylinders, to control the pressure in the exhaust return duct so as to reduce the pollutant emission of the engine, or to control quantity of air sucked.
Such valves are subjected to considerable stresses depending on their installation site both with regard to the incurred quantity of pollutants and with regard to prevailing temperatures. High thermal stresses on the actuators and the bearings and a risk of jamming or damage of the bearings due to contamination in the exhaust occur particularly in valves arranged in the exhaust section.
In order to avoid such damage caused by deposits on the shaft. EP 1 426 589 A2 describes a flap device supported on one side, wherein, internally of the housing and upstream of the bearing when viewed in the flow direction, a chamber is formed which, via a bore, is connected to the flow duct on the downstream side of the flap. The bearing in this arrangement is not, however, protected from the formation of ice in the switched-off state of the internal combustion engine.
EP 2 372 136 A2 describes an exhaust flap supported on both sides, wherein the side of the exhaust flap facing away from the actuator is supported in a closed plastic sleeve, the plastic sleeve having a recess formed in it which, via a bore in the flow housing, is connected to the flow duct so as to protect the shaft from formation of ice or other deposits. Such an arrangement is not however, suited for thermally highly stressable carbon-graphite bearings due to the recess in the support itself. Such an arrangement is not provided on the opposite side facing toward the actuator because this would lead to a thermal overload of the actuator.
Known arrangements thus have the disadvantage that no reliable protection against damage caused by formation of ice exists while simultaneously achieving thermal stress resistance in a flap device comprising a shaft extending into the actuator housing.