MULTIPLE FILTER UNIT, PARTICULARLY FOR VENTILATION AND AIR CONDITIONING SYSTEMS FOR MOTOR VEHICLES AND CLOSED ENVIRONMENTS, AND PROVIDED WITH EFFICIENCY CHECKING MEANS

Abstract: A multiple filter unit (10) in the form of a complete in­ terchangeable unit for insertion into a motor vehicle interior ventilation duct (7), or into the mouth of air conditioners or into suction-producting apparatus for closed environments, comprising a rigid casing (11) provided with retention and sealing means (12), a series of filter elements and/or chemi­ cal products (13, 15 to 18) and/or electrostatic filtering devi­ ces disposed in a predetermined order for filtering solid par­ ticulate matter, mists and air pollutant gases, and means (13a, 15a to 18a or 21, 22) for checking the degree of effi­ ciency.

Description: The present invention relates to a multiple filter unit for purifying air, in particular for motor vehicles or closed environments, and insertable into ventilation and air conditioning systems. Technical development has inevitably led to chemical, physical or biological alterations of the environment. Atmospheric pollution is itself a chemical-physical alteration of the air. The alteration is natural when it relates to bacteria, gas of vulcanic origin, marine aerosols and the like. In contrast, it is artificial if due to combustion systems, industrial plants or motorisation. Any type of combustion leads to final products which have to be dispersed and settled. These are constituted by oxygenated carbon compounds, unburnt hydrocarbons, nitrogen oxides, oxygenated sulphur compounds, water vapour and unburnt or incombustible solid particles. With regard to industrial plants, the fact that they are located in relatively small determined areas leads to a very high concentration of industrial emissions. The main industrial pollutants are oxygenated carbon compounds, nitrogen oxides, sulphur trioxide, hydrocarbons and solid particles. Motor vehicle engines themselves emit large quantities of pollutants, especially in the gaseous state, including carbon monoxide, unburnt hydrocarbons and nitrogen oxides. There are various pollutant removal methods, which can be grouped into five categories: a) conversion of the gaseous pollutant into another product and recovery of the new substance; b) decomposition of the gaseous pollutants and conversion into innocuous products; c) conversion into easily eliminated products; d) elimination of gaseous pollutants by cooling and condensation; e) elimination by absorption in liquid or adsorption on a solid. Studies carried out in Italian urban areas have demonstrated the influence which atmospheric conditions and seasonal cycles have on pollution. In this respect, particularly in winter, when wind is absent a stable system forms which tends to trap emissions, which are essentially of domestic (heating) and vehicle origin. As the day progresses, pollution high points are observed depending on the particular moment. In contrast, during summer all values decrease and are more uniform. Again, pollution is not uniform over the entire urban area, but depends on the closeness or otherwise of industries, the roads of greatest circulation, and whether tree-containing areas are present. It is however general, and extends also to roads outside the town, where is naturally proportional to the intensity of the traffic using them. In order to combat pollution, industries already use purifiers. Special foamed material is able to retain particulate matter. Filters with activated carbon are used on cooker hoods without a discharge duct. The army, the fire service and police use protective masks for high gas, fume and dust concentrations. Catalysts for application to the exhaust pipes of internal combustion engines using leadless petrol have been designed in order to prevent their very rapid deterioration. In large closed environments such as factories, cinemas, restaurants and the like, central air treatment plants are already installed, but are generally limited to solid particulate matter, so that the air which is introduced is not clean but contains pollutant substances. The air normally breathed in automobiles, offices and small closed environments is also polluted by the air originating from the outside. DE-U-7 302 084 discloses a filter unit removable as a whole, provided between the heating system and the air outlets directed towards the inside of a vehicle. GB-A-1 417 528 relates to a stand alone device which utilizes a circulation inside of the environment to be cleaned in a closed loop, without admission of external air. FR-A-1 318 259 relates to an air cleaning device for closed environments easily movable from a room to another, comprising spaced filtering elements and a fan for the emmission of air. FR-A-2 522 791 discloses a check system of the pressurizing and air conditioning systems of cabins in very toxic ambients. The pastilles of material capable of absorbing possible toxic gases are located downstream of the filtering system and are used for revealing immediately that the filter has allowed toxic gases to pass into the cabin. DE-A-2 846 036 relates to a two part filter for vehicles in which the stream of air passes through two identical tubular filtering elements with interposed a fan. JP-A-58 158 434 discloses a device for indicating the loading of an air filter, comprising a body movable inside a cylinder, moved by the pressure drop caused by the loading of the air filter. Broadly, the object of the present invention is to provide a compact, complete and easily replaceable filter unit, provided with means for monitoring the efficiency and/or operativeness of the filter, which can be easily inserted into the air inlet duct of a vehicle or into the air inlet duct or intake port of a closed-environment ventilating or air conditioning unit, for treating the air coming from the outside and purifying it before the same is introduced into the environment. More specifically, it is the object of the invention a filtering unit as above specified provided with means for checking the state of efficiency of the filter. To this purpose, the present invention provides a multiple filter unit in the form of a complete interchangeable and entirely replaceable unit, with means for checking the state of efficiency of each individual filter element, as well as means for facilitating gripping of the filter unit for replacement purposes. According to a preferred embodiment of the invention, it is possible to insert into the air inlet duct for the internal ventilation of a motor vehicle a multiple filter unit in the form of a complete interchangeable and entirely replaceable unit, comprising a substantially rigid casing, for example of cardboard, plastics material or the like, having a cross-sectional shape corresponding to that of the duct into which it is inserted, but of slightly smaller dimensions. On the outside of said casing there is provided a covering of flexible material, for example foamed material, which tapers towards the rear end in order to facilitate insertion of the filter unit into the duct, and of dimensions such as to form a forced and retention fit in the duct. Inside the casing there is provided, according to the present invention, a series of elements of filter material and/or chemical products and possibly electrostatic devices or the like, disposed in a predetermined order so as to obtain complete filtration and purification of the indrawn air both with regard to dust and mist elimination, and with regard to the elimination of pollutant gas. In the considered embodiment, in the air flow direction a first element constituted by an inertial separating filter for retaining coarse solid particulate matter is followed by a perimetral spacer to enable the air stream to attain uniform distribution, a second element constituted by an inertial separating filter of finer type for solid particulate matter of smaller diameter, a third element constituted by a separating filter or a sieve for retaining the smallest particles present in the stream, a fourth filter element constituted by one or more of the following types in combination with each other: a bed of granular adsorbent solids and/or selective molecular sieves for the removal of most of the main pollutant gases such as SO₃, CO₂, NO, and a fifth filter element constituted by a catalyst for mainly removing CO. A filter element can also be impregnated with deodorant substances or mixed with deodorant granular particles for the elimination of bad odours from the automobile passenger compartment. According to the invention, the various filter elements forming the unit are of such thickness and/or material and/or operating conditions that their degradation and life, in relation to the filtering capacity of each individual element, are substantially the same for all. Means are also provided for facilitating gripping of the filter unit and its removal for replacement purposes, and means for checking the state of efficiency of each individual filter element. Said checking means can be constituted for example by warning strips or tapes which are either separate from each other or are joined together at that end which projects from the unit, and are disposed to the rear of each filter element, and preferably in a transverse direction, so as to be traversed by a significant air flow, and further having such dimensions and characteristics as to be put under the same conditions as the respective filter element and to indicate its effective state of efficiency. According to a further preferred embodiment, the filter unit when for closed environments or air conditioning systems comprises preferably a casing provided with a flange containing holes for screws for its fixing to a fixed structure, for example for its fixing to the inlet port of an air conditioner or to a hole in a glass pane, wall or the like, and possibly a seal gasket of known type for its application to the glass pane or wall. Said filter unit can be formed from the same filter elements as those heretofore described, or alternatively as there are no longer any overall dimensional or feed requirements, one of the inertial separating filter elements can be replaced or flanked by a fixed electrostatic precipitator connected to the electricity mains, and said filter unit can be associated with a fan for creating the air charge circulation, should said fan not already exist. According to the invention, there are also provided means for checking the state of efficiency of the individual filter elements, such as warning tapes or strips, or means to allow direct viewing through the transparency of the outer casing or through an axial slot formed in the casing. These and further characteristics will be apparent from the detailed description given hereinafter by way of non-limiting example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of the filter unit inserted into a horizontal-axis air inlet port of an automobile; Figure 2 is a diagrammatic representation of the filter unit inserted into a vertical-axis air inlet port of an automobile; Figure 3 is an axial section through the filter unit; and Figure 4 shows a filter unit for closed environments. Figures 1 and 2 are a diagrammatic representation of the front zone of a motor vehicle in which the main air inlet for the internal ventilation is generally disposed inside the engine compartment 1, below the hood 2 in a position corresponding with substantially horizontal air inlet apertures 3 disposed for example at the base of the windscreen 4. In the arrangement shown in Figure 1, below the air inlet apertures 3, there is situated a box 5 into which the air is conveyed from the outside. Any water is discharged through the outlet 5 a . In the arrangement shown in Figure 2, below the air inlet apertures 3, there is provided a cap 6 of vertical axis for conveying away from the air inlet mouth any water which has entered from the apertures. In the box 5 or below the cap 6 there is provided a duct 7 in which there is disposed an electric fan 8 which draws the external air from the mouth end of the duct 7 in order to feed it through ducting 9 to the automobile ventilation system. The multiple filter unit of the present invention, indicated overall by 10 and shown in detail in Figure 3, is located in the initial part of the duct 7. Said filter unit 10 is inserted as a complete unit and is interchangeable and completely replaceable without requiring any particular mechanical intervention. With reference to Figure 3, the filter unit 10 is constituted by a substantially rigid casing 11, for example of cardboard, plastics material or the like, having a cross-section corresponding to that of the duct 7 into which it is inserted, but with slightly smaller dimensions. On the outside of said casing 11 there is provided a layer of flexible material 12, for example foamed plastics material, which slightly tapers towards the rear end of the casing 11 and is of such dimensions as to produce a forced fit inside the duct 7 when the unit 10 is inserted therein starting from the tapered end to facilitate its entry, and to create sufficient elastic pressure on the walls of the duct 7 to retain the filter unit 10 in position. According to the present invention, inside the casing 11 there is provided a series of elements of filter material and/or chemical products, and possibly electrostatic devices, disposed in a predetermined order in order to obtain complete filtration and purification of the indrawn air. According to the invention, the filter unit 10 comprises, disposed in the air flow direction in accordance with the arrow A, a first element 13 constituted by an inertial separating filter, for example of the labyrinth type, provided for retaining coarse solid particulate matter of diameter greater than one micron (µm), while at the same time able to offer the least possible resistance to the passage of the air, and having a high dust storage capacity. Preferably, it has been found that a filter element, for example of the polyurethane foam type, with 25 passages per cm² and an axial thickness of about 6 mm is sufficient for the purpose. A perimetral spacer 14 of known type enables the air which has passed through the first filter element 13 to regain a certain degree of uniformity for improved efficiency of the subsequent filtering layers. A second element 15 is constituted by a further inertial separating filter of smaller passages, downstream of which the particulate matter suspended in the fluid stream is of diameter less than one micron. Preferably, it has been found that a filter element, for example of the polyurethane foam type, with 40 passages per cm² and an axial thickness of about 6 mm is sufficient for the purpose. A third filter element 16 is constituted by a separating filter, for example of sintered textile fibres or woven glass fibres, with high separation power, for retaining the smaller residual particles present in the stream. A fourth filter element 17 is constituted by adsorbent solids for removing certain pollutant gases, fatty constituents of the air and bad odours. Preferably, it has been found that selective granular beds, for example of activated carbon, with an axial thickness of 20 mm are sufficient for the purpose. As an alternative to, or in combination with the adsorbent solids, the fourth element can for example be a granular mixture of ASCARITE® and lithium hydroxide on an asbestos base for adsorbing a large proportion of the acid pollutant gases such as SO₂, SO₃, CO₂, NO and, partially, CO. Preferably, it has been found that a layer of 20 mm axial thickness is sufficient for the purpose. Furthermore, as an alternative to or in combination with the preceding, the fourth filter element 17 can be constituted by a molecular sieve selective for particular chemical compounds. A fifth filter element 18 is constituted by a catalyst, the purpose of which is to fix the residual pollutant substance, particularly CO, in the form of a compound by chemical reaction. Each of the aforesaid filters can be formed from a number of layers selective for different substances. Furthermore according to the invention, one of the filter elements can be impregnated with a deodorant substance or mixed with deodorant granular particles, in order to eliminate bad odours inside the automobile. On the front end of the casing 11 there is provided, rigid therewith, a transverse bar 19 provided with a gripping ring or the like 19 a , for extracting the filter unit 10 from the duct 7 when the unit 10 is to be replaced. According to the invention, the various filter elements forming the filter unit 10 are of such thickness and/or material and/or operating conditions that both their degradation and their life in relation to the filtering capacity of each element are substantially the same for all. The life and/or the state of efficiency of each individual element or of all the elements which overall form the filter unit 10 can be checked by inserting behind each filter element 13, 15, 16, 17 and 18 a warning strip or tape which is of such material and dimensions as to behave as the filter itself or to be influenced by it in relation to the residual degree of efficiency of the element. For example, on the rear of the first element 13 there is disposed a warning strip or tape 13 a composed of the same material as the element 13 itself, but suitably decoloured or coloured so that as the air passage pores of the inertial separating filter 13 become clogged, the warning tape or strip 13 a changes colour in relation to the retained solid particles until a limiting check colour is attained, this being predetermined by the manufacturer and suitably indicated in the instructions or in a suitable space on the casing 11. The same procedure is followed for checking the state of efficiency of the other layers 15, 16, 17, 18 by respective warning tapes or strips 15 a , 16 a , 17 a , 18 a placed on their rear. In order to put said warning strips or tapes 13 a to 18 a under the same conditions as the respective filter element 13 to 18 and thus able to indicate the effective state of efficiency of the elements themselves, the warning tapes or strips can preferably be disposed transversely through a length such as to be traversed by a significant air flow. According to the invention, the user can check the state of efficiency of the entire filter by extracting said warning tapes or strips one at a time at different times until one of them shows the limiting coloration conditions indicated by the manufacturer, this signifying, on the basis of the aforegoing, that all the other layers are also substantially in the same state of efficiency. According to the invention, it is also possible to simultaneously extract all the warning tapes or strips by connecting them together at the ends which project to the outside by means of a common grip 20, to thus be able to simultaneously check the state of efficiency of each of the filter elements. In this case, it is necessary to insert more than one set of warning tapes or strips to be extracted for checking purposes at different times during the use of the filter unit 10. With reference to Figure 4, according to a further embodiment and application of the invention, the filter unit 30 is constituted by a substantially rigid outer casing or body 31, for example of metal, plastics material or the like, having a cross-section of suitable shape for fitting into seats provided either on a wall or on a glass pane. The casing 31 is preferably provided with a flange 31 a with holes for the passage of screws or the like for its connection to the fixed structure, and seal gaskets of known type. A low-speed fan 32 for creating the suction necessary for the operation of the entire filter unit 30 is fixed in known manner inside said outer rigid casing 31 and is connected to the electricity mains. The filter unit 30 for closed environments can be formed with the same filter elements already described for the motor vehicle filter unit 10 or, as an alternative to the second filter element 15 constituted preferably by an inertial separating filter, a current-fed electrostatic precipitator can be provided if there are no dimension problems or problems regarding the collection of non-conductive dusts. In an embodiment of the filter unit 30 and with reference to Figure 4, the filter unit 30 contained in the outer casing or body 31 is formed from two parts 30' and 30" which are separated from each other by said fan 32. The first filter unit 30' comprises an internal rigid casing 33 of cardboard, plastics material or the like, surrounded by a layer of flexible material 34, for example plastics foam, of such dimensions as to create sufficient elastic pressure and form a forced fit against the walls of the outer casing 31. Said inner rigid casing 33 comprises a first element 35 constituted by a coarse inertial separating filter, a perimetral spacer 36 and a second filter element 37 constituted by a current-fed electrostatic precipitator and/or a second finer inertial separating filter. Said first filter unit 30' can be removed to allow its regeneration and thus its re-utilisation. Downstream of the fan 32 there is a second filter unit 30" comprising a second inner rigid casing 38 of cardboard, pastics material or the like, covered externally by a layer of flexible material 39, for example plastics foam, of such dimensions as to create sufficient elastic pressure and constitute a forced fit against the inner walls of the outer casing 31. Said inner rigid casing 38 comprises filter elements 40, 41, 42, which can be of the same type as the filter elements 16, 17, 18 of the motor vehicle filter unit 10. According to the invention, means are also provided for checking the state of efficiency of the filter unit 30 either of the already described warning tape or strip type, or for example by directly viewing, through apertures provided in the outer casing 31 and in the inner casings 33 and 38, or through transparent casings, the colour assumed by the various elements of the filter unit 30, or other indications suitably provided for by the manufacturer, together with their relative instructions. If the filter unit of the present invention is to be provided for fitting into the inlet mouth of an air conditioning system or air conditioners, it can be formed from the same filter elements as already described, taking into consideration the fact that the suction created by the air conditoner itself is used for its operation, so that no fan 32 will be required.

Claims: An interchangeable multiple filter unit, particularly for motor ventilation and air conditioning or small closed environments, characterised by comprising: at least a substantially rigid casing (11; 33, 38) with means (19, 19 a ) thereon for gripping and extracting said casing; an outer, rearwardly tapering covering (12; 34, 39) of elastic flexible material on said casing(s) to enable said casing(s) to be forced into and retained into an air duct; said casing(s) containing a series of filter elements (13, 15-18; 35, 37, 40-42) constituted in the air flow direction by mechanical filter elements of increasing separating capacity followed by chemical filter elements comprising gas adsorbing material and catalyst for fixing any residual pollutant substance, said filter elements being of such thickness and/or material that both their degradation and their life in relation to filtering capacity of each element are substantially the same for all; and means (13 a ; 15 a -18 a ) for checking the state of efficiency of each filter element individually. A filter unit as claimed in claim 1, characterised in that the series of filter elements includes, in the fluid flow direction: a first filter element (13; 35) constituted by a coarse inertial separating filter; a perimetral spacer (14; 36); a second filter element (15; 37) constituted by a finer inertial separating filter; the combination of these two filter elements causing the retention of suspended particulate matter of diameter greater than or equal to 1 µm; a third filter element (16; 40) constituted by a fibrous separating filter or a sieve, for retaining residual minor particles suspended in the flow; a fourth filter element (17; 41) constituted by adsorbent solids or selective molecular sieves, used either individually or in combination with each other, for eliminating pollutant gases; a fifth filter element (18; 42) constituted by a catalyst, particularly for eliminating the residual CO. A filter unit as claimed in claims 1 or 2, characterised in that one of the filter elements includes a deodorant substance. A filter unit as claimed in any one of claims 1 to 3, characterised in that the means for checking the state of efficiency of the filter unit (10; 30) includes warning strips (13 a , 15 a -18 a ) of the same material as the filters with colours or decolorations or particular signs for comparison purposes, and disposed to the rear of each individual element (13, 15 to 18; 35, 40-42), preferably in a trasverse direction, said strips having dimensions such as to be traversed by a significant air flow and being extractable individually or together for the periodical checking of the state of efficiency of the filters at successive times. A filter unit as claimed in claim 4 characterised in that the ends of the strips (13 a , 15 a -18 a ) project out of the casing (11; 31) and are joined together to enable the strips to be extracted simultaneously for the periodical checking of the state of efficiency of the filter unit (10; 30) at successive times. A filter unit assembly for closed environments, characterised by comprising: an outer rigid casing (31) comprising two filter units as claimed in claim 1; a flange (31 a ) attached to said outer casing (31), with passage holes for screws for its fixing to a fixed structure, and including seal gaskets. A filter unit assembly as claimed in claim 6, characterised in that a low-speed electric fan (32) is disposed between the two filter units (30', 30") for creating the suction necessary for the operation of the entire filter assembly. A filter unit assembly as claimed in claim 6, characterised in that the first part (30') of the filter unit assembly (30) comprises: a first inner rigid casing (33) of cardboard or plastics material, surrounded by a layer of flexible material (34) of such dimensions as to create a sufficient forced and retention fit inside the rigid outer casing (31), said first inner rigid casing (33) containing a first filter element (35) constituted by a coarse inertial separating filter, a peripheral spacer (36) and a second filter element (37) constituted by a current-fed electrostatic precipitator and/or by a second inertial separating filter, the combination of said two filter elements (35, 37) causing the retention of suspended particulate matter of diameter greater than or equal to 1 µm, said first part (30') of the filter unit assembly (30) being removable to allow regeneration and thus re-utilisation of the filter elements (35, 37), and in that the second part (30") of the filter unit assembly (30) comprises: a second inner rigid casing (38) of cardboard or plastics material, surrounded by a layer of flexible material (39) of such dimensions as to create a sufficient forced and retention fit inside the rigid outer casing (31), said second inner rigid casing (38) containing a third filter element (40) constituted by a fibrous separating filter or a sieve, for retaining residual minor particles, a fourth filter element (41) constituted by adsorbent solids or by selective molecular sieves, used either individually or in combination with each other, for eliminating pollutant gases, and a fifth filter element (42) constituted by a catalyst particularly for eliminating CO. A filter unit assembly as claimed in any one of claims 6 to 8, characterised by comprising means for checking the state of efficiency of each individual element (35, 37, 40-42) of the unit (30), and constituted by warning strips with colours or decolorations or particular signs for comparison purposes, and disposed to the rear of each individual element (35, 37, 40-42) preferably in a transverse direction, or by directly viewing the colour assumed by the various elements (35, 37, 40-42) of the filter unit (30) either through apertures provided in the outer (31) and inner (33, 38) casings, or through transparent casings. A filter unit as claimed in claim 1, characterized in that said covering (12; 34, 39) is made of foamed material. A filter unit assembly as claimed in claim 8, characterised in that said layer of flexible material (34, 39) is made of foamed plastics.

Inventors: CANTONI, MARIA CRISTINA
Applicants: ITAL IDEE S.R.L.
Application year: 1985
Main classification: B01D46
IPC codes: B01D53, F24F3, B01D46, F24F13, B60H3