DESCRIPTION

FILTER FOR RETAINING THE PARTICULATES CARRIED IN SUSPENSION BY THE EXHAUST GASES EMITTED BY AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present invention relates to a filter for retaining the particulates carried in suspension by the exhaust gases emitted by internal combustion engines, and in particular by automotive diesel engines. PRIOR ART

The exhaust gases emitted by diesel engines are known to generally contain large quantities of solid carbon particles deriving from imperfect combustion of the diesel fuel, these being commonly known as particulates and constituting one of the most important pollution factors of this type of engine. To reduce particulate emissions, suitable antiparticulate filters are currently used, positioned at the engine exhaust exit, downstream of the oxidizing precatalyst. Said antiparticulate filters comprise a generally tube-shaped outer casing, the ends of which are provided respectively with an inlet port for the gas to be filtered and an outlet port for the filtered gas. The exhaust flow from the engine passes through said outer casing, to be intercepted by a special filter cartridge which retains the particulates and allows the aeriform phase to pass. Various types of filter cartridge are currently available, differing substantially by their shape and by the material used in their construction. A very widespread filter cartridge has a characteristic cup shape, defined by a cylindrical side wall of porous material and a disc-like end of impermeable material, and is located inside the outer casing with its concavity facing the inlet port.

The said side wall is often pleated longitudinally, to present a star geometry offering the exhaust gases a larger passage surface, and is made of a porous metal material having an interstice dimension between 1 and 10

microns.

A drawback of this type of antiparticulate filter is the non-uniform utilization of the relative filter cartridge, which undergoes relative performance deterioration, requiring frequent regeneration or replacement, with evident increase in maintenance costs.

This drawback is due mainly to the fact that the porous material side wall extends parallel to the direction of the entering exhaust gas flow, which therefore tends to flow axially along the filter cartridge interior until it reaches the disc-like, where it is deviated to flow radially. For this reason the exhaust gases preferentially pass through those portions of the porous material side wall in proximity to the disc-like end, whereas the more distant portions, which are grazed tangentially, are hardly utilized. DISCLOSURE OF THE INVENTION The object of the present invention is to overcome the said drawback within the framework of a simple, rational and low-cost solution.

This object is attained by a filter for retaining the particulates carried in suspension by the exhaust gases emitted by an internal combustion engine, comprising an outer casing the interior of which is divided by a filtering wall of porous material into two separate chambers, of which one chamber communicates with an inlet port for a gas flow to be filtered, and one chamber communicates with an outlet port for a filtered gas flow. According to the invention, said filtering wall of porous material is oblique to the direction of the entering gas flow to be filtered, such as to be struck by this latter with a certain angle of incidence. By virtue of this solution, each individual region of said filtering wall is struck and traversed directly by at least a fraction of the gas flow to be filtered, to obtain a more uniform utilization of the porous material. According to a preferred embodiment of the invention, the filtering wall of porous material extends about a central axis in accordance with a frusto- conical geometry, and is located within the outer casing such that said central axis is parallel to the direction of the gas flow to be filtered, with its major base facing against the flow.

Preferably, said filtering wall of frusto-conical extension is pleated longitudinally, such as to present a cross-section of star geometry offering a larger passage surface for the gas to be filtered, and has its minor base closed by a disc of impermeable material. Preferably, the filtering wall is made of a metal porous material, which ensures high performance in terms of mechanical strength and accumulation capacity, and facilitates regeneration. BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will be apparent on reading the ensuing description provided by way of non-limiting example, with the aid of the figures of the accompanying drawings, in which:

- Figure 1 is the section l-l of figure 2, showing an antiparticulate filter of the invention;

- Figure 2 is the section N-Il of figure 1. BEST MODE FOR CARRYING OUT THE INVENTION

The antiparticulate filter 1 shown in said figures is intended to be associated with an automotive diesel engine, to retain the particulates carried in suspension by the exhaust gases emitted during normal operation. Said antiparticulate filter 1 comprises an outer casing 2, typically of metal material, which is shaped substantially as a tube and presents a diverging initial portion 20, a cylindrical intermediate portion 21 , and a convergent terminal portion 22.

An inlet port 3 for a flow of exhaust gas to be filtered is associated with the divergent portion 20, while an outlet port 4 for a filtered exhaust gas flow is associated with the terminal portion 22. Said inlet port 3 and outlet port 4 oppose each other, with their axes coinciding with the axis of the intermediate portion 21 of the outer casing 2, so that the exhaust gases flow therethrough by following a substantially rectilinear path. The antiparticulate filter 1 comprises a filter cartridge 5 which divides the interior of the outer casing 2 into two separate chambers, of which a chamber 23 communicates with the inlet port 3 for the gas to be filtered and a chamber 24 communicates with the outlet port 4 for the filtered gas.

Said filter cartridge 5 comprises a filtering wall 50 of porous material, which extends about a central axis A in accordance with a frusto-conical geometry, and has a disc-like end 51 which closes said filtering wall 50 of frusto-conical extension at its minor base. The filtering wall 50 is permeable to the exhaust gases and is able to retain the particulates which these carry in suspension, whereas the disc-like base 51 is totally impermeable to said exhaust gases.

Preferably, the filtering wall 50 is made of metal porous material having an interstice dimension between 1 and 10 microns. In particular, the filtering wall 50 presents a series of longitudinal pleats giving it a typical star geometry in cross-section, which effectively increases the surface offered to the passage of the exhaust gases (see figure 2). The filter cartridge 5 is located within the outer casing 2 such that the central axis A of the filtering wall 50 of frusto-conical extension coincides with the axes of the inlet port 3 and outlet port 4, with its major base facing the inlet port 3.

In this manner, the filtering wall 50 lies oblique to the direction of the exhaust gas flow which enters via the inlet port 3, to flow through the convergent channel defined thereby and, on the basis of evident hydraulic considerations, to strike and at least partially pass through each of its portions.

This characteristic results in uniform utilization of the porous material, enabling the antiparticulate filter 1 to remain efficient for a considerable time before the relative filtering wall 50 clogs with particulates, and requires regeneration or replacement.