The present invention relates to a filter apparatus for filtering air in internal combustion engines comprising a flame-retardant filter insertable into a filter housing.
There are known filter devices arranged at the air inlet of the intake tract of an internal combustion engine for filtering the air supplied to the engine and for subjecting the combustion air drawn in to a filtering operation. These filter devices comprise a filter element in a filter housing, with the filter element being constructed, for example, as a pleated synthetic nonwoven or a paper medium through which the air that is to be cleaned flows. A filter device of this type is described in published European patent application no. EP 450,299.
In addition, it is known that the filter element in the air filter may be provided with a flame-retardant filter medium whose flame-retardant effect is achieved by using special impregnations. Such flame-retardant components are produced based on phosphorus-, antimony- or bromine-containing compounds, for example, and should prevent inadvertent ignition of the filter element, which itself is highly flammable. However, one disadvantage here is that the flame-retardant impregnation may decrease the dust storage capacity of the filter element, so the surface area of the oncoming flow surface of the filter element must be increased to achieve the required filtration capacity.
Another disadvantage is that the water stability of the filter element is reduced by using the flame-retardant impregnation. However, a high water stability is necessary because if water enters the intake tract of the engine, it is necessary to ensure that the filter element will continue to fulfill its function.