SILENCED AIR FILTER FOR INTERNAL COMBUSTION ENGINES

Abstract: An air filter, comprising a casing (1, 6) with an inlet port (4) and an outlet port (2) and internally provided with filter means, is provided, transversely to the passage of the fil­ tered air downstream of the filter means, with a perforated diaphragm (17, 18) and a deformable valve element (19) which allows the air to pass only in the direction of the intake manifold.

Description: SILENCED AIR FILTER FOR INTERNAL COMBUSTION ENGINES This invention relates to an air filter for internal combustion engines in general, which is provided with a silencer unit for eliminating noise. Normal air filters for internal combustion engines are known to comprise a casing having an inlet port and an outlet port, and housing suitable filter means which are traversed by the air flowing towards the inlet manifold of the engine concerned. Known air filters, and particularly oil bath filters, have the serious drawback of sometimes being excessively noisy, which creates soundproofing problems for vehicle engine compartments, makes the use of self-propelled machines with a non-enclosed or only partly enclosed engine uncomfortable, and considerably increases the noise level in working environments where fixed engine systems are installed. This excessive noise is mainly due to the hammering which the intake air stream undergoes when the engine intake valves close. This is because when an intake valve closes, the mass of air flowing towards the intake manifold is instantaneously halted and remains trapped between the intake manifold and the filter means of the air filter. This halting of the mass of air subjects it to a hammering effect which transmits vibrations to the surrounding metal parts, with simultaneous generation of said excessive noise, and causes part of the air to flow backwards, so increasing the noise. Up to the present time the various attempts to reduce the noise level of such filters have been directed towards special shaping of the passages and chambers traversed by the intake air stream, but such attempts have not only not given satisfactory results but have excessively complicated the filter construction, thus considerably increasing their cost. The present patent provides and protects an air filter in which said noise is practically eliminated, by means of a simple and rational design. This is attained according to the invention by disposing immediately upstream of the discharge port of the filter casing a valve element which is arranged to alternately open when the casing is under vacuum, and close when said vacuum ceases, this latter occurring in known manner during an intake stage of the engine. According to the invention, said valve element comprises an elastically deformable flap either in the form of a single element or comprising a plurality of adjacent coplanar sectors, and is disposed transversely to the passage of the filtered air directed towards the filter discharge port, and is further associated with a perforated transverse baffle, the apertures of which are alternately closed and opened by said flexible flap as stated. Finally, to the rear of the valve element there are preferably disposed stop means arranged to limit the stroke or degree of deformation of the valve element, in order to safeguard its structure. The provision of the aforesaid silencer unit means that that portion of air located between the filter and intake valve is trapped in the filter on termination of each intake stage. By this means, the initial maximum or peak value of the hammer is considerably reduced, as are consequently its surging and transient effects on the surrounding metal parts, and prevents the air flowing back from the filter, with almost total elimination of noise. The constructional characteristics and merits of the invention will be more apparent from the description of a preferred embodiment of an oil bath air filter given hereinafter by way on non-limiting example with reference to the figures of the accompanying drawings. Figure 1 is an elevational section through the invention. Figure 2 is a section on the line II-II of Figure 1. The filter shown in the figures is not to be considered in any way limitative of the invention, as the characterising elements of the invention are perfectly adaptable with identical results to general known filters, whether of dry or of oil bath type. Figure 1 shows a casing comprising an upper half shell 1 provided at its top with a side connector 2 for its connection to the intake manifold of an internal combustion engine, and at its base with a widened mouth 3. An intake cap 4 consisting of a thin hollow structure with a blank upper wall and a perforated lower wall is centrally fixed to the top of said upper half shell 1 (see Figure 1). From this lower wall there extends a central tube 5 coaxial to the upper half shell 1, said tube 5 extending to reach the mouth 3 of this latter. Into the base of the upper half shell 1 there is inserted a removable lower half shell 6, which is provided with two diametrically opposing external clips 11 (see Figure 2) for clipping over said widened mouth 3. Said lower half shell 6 has a narrower lower portion forming a container for containing an oil bath indicated diagrammatically by 33 in Figure 1, and an upper wider portion housing a normal filter cartridge 7, consisting essentially of a hollow holder filled with metal wire mesh. The filter cartridge 7 fits practically exactly into the upper part of the lower half shell 6, but from which there emerges an outer circumferential rim 8 fitted with a gasket 9, this latter being clamped into the widened mouth 3 of the upper half shell 1 by means of an outer circumferential rim 10 provided on the mouth of the lower half shell 6. At the base of the lower half shell 6 there is provided an internal coaxial cup 12 having a depth greater than the level of the oil bath 33, and provided with a circumferential series of equidistant radial holes 13. Into said cup 12, and into the oil bath 33, there is inserted the lower end of a central tube 14 which passes through the filter cartridge 14, and its upper end is mounted over the lower end of the tube 5. The lower transverse wall of the filter cartridge 7 is provided with air inlet openings 15, and its upper transverse wall is provided with corresponding discharge openings 16 for the filtered air. A ring-shaped baffle 17 provided with a circumferential series of angularly equidistant apertures 18 is fixed in proximity to the open end of the upper half shell 1. As shown in Figure 2, each aperture 18 is shaped as an isosceles trapezium with rounded corners, with its major base facing outwards and with its height disposed radially, but said apertures 18 can obviously be of any other shape, for example circular. According to the invention, one aperture 18 is preferably provided for each discharge opening 16 of the filter cartridge. With each aperture 18 there is upperly associated a flap 19 with its upper surface of greater extension than the corresponding aperture 18 (Figure 2), said flap 19 being constituted by a suitable flexible material, for example a thin metal foil, a rubber-coated fabric or another suitable material, such as a synthetic material. In the figure the flaps 19 are separate from each other, but they could obviously derive from a common central column. Above the flaps 19 there is disposed a rigid stop nember 20 for limiting the degree of deflection of the flaps 19. The member 20 consists essentially of a central flat connection ring from which there branches a series of upwardly bent, concave profiled plates (Figure 1). The plates extend radially and are provided in the same number as the flexible flaps 19, their plan profile being approximately equal to that of these latter. The stop member 20, the flexible flaps 19 and the perforated baffle 17 are fixed together by an inner circumferential set of rivets 21. Finally, between the baffles 17 and the tube 5 of the upper half shell 1 there is a compression ring 22 provided lowerly with a shoulder which clamps a seal gasket 23 against the underlying filter cartridge 7. When under non-working conditions, the flexible flaps 19 rest against the perforated baffle 17 and close the apertures 18 (position indicated by full lines in Figure 1). When an engine intake valve opens, the filter is put under vacuum and is traversed in known manner by an air stream which causes the flaps 19 to lift or open (position shown by dashed and dotted lines). When an intake stage terminates, the mass of moving air builds up and becomes compressed in the upper or discharge part of the filter, to cause instantaneous closure of the flaps 19. As the air mass upstream of the baffle is small, the residual air hammer due to repeated closure of an intake valve and the damped oscillation of the pressure induced by said hammer are also small, as are therefore the filter vibration and noise. All the objects of the invention are therefore attained. The invention is not limited to the single embodiment heretofore described, and modifications and improvements can be made thereto but without leaving the scope of the inventive idea, the basic characteristics of which are summarised in the following claims.

Claims: PATENT CLAIMS 1. An air filter, of the type comprising a casing (1, 6) having an inlet port (4) and an outlet port (2), between which suitable filter means are interposed, characterised by providing downstream of said filter means at least one elastically deformable valve element (19) associated with a valve seat to enable the air to flow only in the direction of the filter outlet port. 2. An air filter as claimed in claim 1, characterised in that said valve element and said valve seat comprise a series of thin flexible flaps 19 situated in correspondence with apertures 18 in a baffle 17 to which they are securely fixed at one end, and having a profile which at least slightly surpasses that of said apertures 18. 3. An air filter as claimed in claim 1, characterised in that said perforated baffle (17, 18) is fixed in a sealed manner to those surfaces of the casing (1) which define the passage for the filtered air. 4. An air filter as claimed in claim 1, characterised in that to the rear of said valve element there is disposed a stop member for restraining the flexible flaps (19) during their opening, said member comprising a series of profiled elements (20), one for each flap (19), and bent towards the filtered air outlet port (2). 5. An air filter as claimed in claim 1, characterised in that said stop member (20) and said flexible valve element (19) are fixed to said perforated baffle (17, 18), to form a valve unit.

Inventors: BODO, MAURO
Applicants: LOMBARDINI FABBRICA ITALIANA MOTORI S.P.A.
Application year: 1985
Main classification: F02M35
IPC codes: F02M35