GB2097283A - Filter arrangements for the exhausts of IC engines - Google Patents

Abstract

A filter arrangement for the exhaust gas of an i.c. engine, for example a Diesel engine, comprises a pair of filter units (16, 17) through one of which the exhaust gas flow passes and through the other of which the engine inlet air flow passes at a given time, and ganged valves (18, 19) which periodically switch the exhaust gas flow from one filter unit to the other, and simultaneously switch the inlet air flow from the said other to the said one filter unit to flow through the latter in the opposite direction to the preceding exhaust gas flow so as to back-flush that filter unit, dislodging deposited solid particulate matter and transporting the dislodged matter into the engine air intake. The operation of valve means may be effected automatically in response to the increase in gas pressure difference across the filter element being traversed by the exhaust gas flow. In another arrangement, instead of two filter units a single rotary filter unit (101 or 120) of drum or disc type is provided, each sectional portion of whose element is traversed first by the exhaust gas flow in one direction and thereafter by the inlet air flow in the opposite direction to dislodge previously-deposited matter. <IMAGE>

Description

SPECIFICATION Filter arrangements for the exhausts of IC engines This invention relates to internal combustion engines, and is concerned with the provisions of means for reducing the amount of solid particulate material discharged from the exhaust duct of the engine into the atmosphere, by filtering out such material from the exhaust gases before they are discharged.

The invention is particularly applicable to compression-ignition engines such as Diesel engines, although it may also be applied to other kinds of l.C. engines if desired. While Diesel engines have a high thermal efficiency, i.e. a low fuel consumption, compared with petrol engines, especially at light loads, they are sometimes criticised for their dirty exhausts, which may also have a disagreable smell, particularly if badly maintained in service. Examination in the laboratory of samples of Diesel engine exhaust gases has shown that even well-adjusted Diesel engines with nonvisible exhausts operating at full load discharge a greater porportion of solid particulates, largely in the form of fine carbon, than do petrol engines over their whole load range.

It is likely that in due course the regulations controlling the exhaust emissions of l.C. engines may be tightened up, at least in certain territories, to require a substantial reduction in the quantity of particulates emitted from the exhaust ducts of all l.C. engines. Moreover it is possible that such a reduction may be found desirable from the point of view of health. In addition to such considerations a reduction in the visible smoke emitted from Diesel engines would greatly improve the public acceptability of such engines especially for use in road vehicles.

Experimental filters of the gas-permeable element type for Diesel engine exhaust gases have been made, and have been found to operate successfully in removing virtually all carbon particles at all loads, but over short periods of time only. It is found that at high engine loads virtually all the carbon retained by such a filter will be oxidised at the high exhaust gas temperature prevailing, around 800"C, and burnt off the filter element in the excess oxygen still present in the exhaust gases.However at lighter loads, whilst the exhaust gases in a petrol engine would still be at around 800"C, in the case of a Diesel engine the exhaust gas temperature can drop to as low as 250"C. This is because a Diesel engine takes in a substantially constant amount of air per cycle at all loads, the power output being varied by variation of the amount of fuel injected, so that the engine at low loads will be operating at a very high air/fuel ratio.Thus as the load is reduced and the exhaust gas temperature falls below 500"-600"C, carbon intercepted by the filter will be retained rather than being burned off, and the deposited matter will become increasingly sticky, and at really light loads almost wet, consisting probably of a variety of partially-oxidised hydrocarbons, with the result that the resistance to the flow of the exhaust gases through the filter element rapidly increases. Unfortunately in the case of Diesel engined road vehicles the road load on the engine is usually relatively low, except when accelerating or hill-climbing, so that quite long periods could occur in practice during which the exhaust gas temperature is never high enough to burn off the accumulated deposit on the element of an exhaust gas filter.

It has been suggested that a cyclone-type filter might be used to centrifuge the particulate matter out of the exhaust gases, but this has been found unsatisfactory in practice on account of the open structure and low density of the exhaust soot, requiring a very long cyclone if the separation is to be effective.

An object of the present invention is therefore to enable direct filtration of the particles of solid matter in the exhaust gases of a Diesel engine to be effective over prolonged periods of engine operation at low loads.

This can be done according to the invention by arranging for at least a part of the air flow to the engine air intake to pass through the filter element in the reverse direction to that of the exhaust gas, so as to backflush the filter and dislodge deposited solid carbonaceous matter therefrom and transport the dislodged matter into the engine air intake for combustion in the engine.

Thus according to the present invention, an l.C. engine, for example a Diesel engine, is provided with a filter means including at least one filter element through at least a part of which the engine exhaust gases are passed to filter the gases and intercept solid particulate matter being carried thereby, and with means operable during the running of the engine for periodically or progressively transferring the exhaust gas flow from the filter element, or from the said part thereof, to another filter element or to a different part of the first filter element for filtration thereby, and for then passing at least a part of the inlet air flow to the engine air intake through the first filter element, or through the said part thereof previously traversed by the exhaust gas flow, and in the direction opposite to that of the previous exhaust gas flow, so as to backflush the filter and dislodge deposited solid matter from its element and transport the dislodged matter into the air intake.

In one form of the invention, two separate filter elements are provided, through either one of which the exhaust gases can be passed in one direction to filter the exhaust gases whilst the engine inlet air flow passes through the other element before entering the engine air intake, and means is provided for switching the exhaust gas flow from the one filter element to the other and simultaneously switching the inlet air flow from the latter to the former element to pass through it in the opposite direction to that of the previous flow of exhaust gases.

It is also possible however to employ a single rotary filter having means for effecting relative rotation between the filter element and associated structure affording ducting for the exhaust gas and inlet air flows, the arrangement being such that the exhaust gas flow and the inlet air flow pass continuously in opposite directions through different portions of the filter element at a given time, the rotary drive causing each succeeding portion of the element through which the exhaust gas has passed to be then traversed in the opposite direction by the inlet air flow so as to dislodge solid matter previously deposited on it by the exhaust gas flow.

For example the rotary filter may have a rotating filter element and a fixed structure affording the ducts for the exhaust gas and air flows. The exhaust gases pass continuously through successive portions of the rotating filter element, which portions progressively move round into new positions in which the inlet air flow passes through them in the reverse direction to that of the exhaust gas.

The invention may be carried into practice in certain ways, but various specific embodiments thereof will now be described by way of example only and with reference to the accompanying drawings, in which Figures 1A and 1B show diagrammatically and respectively in the two operating conditions, an exhaust gas filter arrangement for a naturally-aspirated Diesel engine, with twin filters and rotary cock filter switching means; Figure 2 shows a modification of the embodiment of Figs. lA and 1 B, incorporating exhaust gas recirculation; Figures 3A and 3B are diagrams similar to Figs. 1A and 1 B of a second embodiment of the invention applied to an exhaust-gas-turbocharged Diesel engine, with spool valve switching of the twin filters;; Figures 4A and 4B are diagrams similar to Figs. 3A and 3B of a third embodiment applied to a turbocharged Diesel engine but with difference filter dispositions and switching arrangements; Figures 5A and 5B are diagrams similar to Figs. 4A and 4B of a fourth embodiment applied to a Diesel engine with pressureexchanger inlet air boosting; Figure 6 is a diagram showing a control system for operating the changeover cock in the embodiment of Figs. 1A and 1 B, or in that of Fig. 2 or for operating the spool valve or valves in the embodiment of Figs. 3A and 3B, or in that of Figs. 4A and 4B, or in that of Figs. 5A and SB, for switching the gas flows through the two filter elements in dependence on the pressure drop across one of the filter elements;; Figures 7 and 8 show alternative electronic control systems for switching over the gas flows through the two filter elements in dependence on the number of engine revolutions; Figure 9 shows diagrammatically a fifth embodiment of the invention using a single rotary filter of axial-flow type; and Figure 10 shows diagrammatically a sixth embodiment with a single rotary filter of radial-flow drum type; In the embodiment illustrated in Figs. 1A and 1 B, the invention is applied in its simplest form to a naturally-aspirated Diesel engine, i.e. one with no pressure charging of the intake air. The engine itself is shown diagrammatically at 10, with an inlet manifold 11 connected to a main inlet air duct 12, and an exhaust manifold 1 3 connected to a main exhaust gas duct 14.Two filters 1 6 and 1 7 are provided, connected as will be described.

These filters are full-flow filters each having a layer of a suitably heat-resistant filter material constituting the filter element, the materal having a sufficiently fine pore size to act as a "sieve" to intercept particles of greater size than the pore size and restrain them on the upstream side of the filter element. Diesel exhaust particulates range in size frorn about O.007 to 40 microns (micro-metres), with more than 65% less than 1 micron, so to be efficient the filters 1 6 and 1 7 must have a fine pore size. As a rough guide, a suitable pore size might be 20 micron or less. Larger pore sizes may be used but at the price of a lower filtration efficiency.

A recent development in filter design is the use of a porous ceramic matrix providing channels separated from one another by thin porous walls called divisions. Alternate channels have respectively closed and open downstream ends, and respectively open and closed upstream ends, the open upstream ends being open to the gas flow at the upstream face of the filter element, and the open downstream ends opening through the downstream face of the element. As a result, ail the gas flow enters the open upstream ends of half of the channels and passes through the porous divisions into the adjacent channels through whose open downstream ends the gas flow leaves the filter element, the porous divisions filtering the gas flow passing through their pores. The relatively fragile ceramic matrix is supported in an outer metal casing. Suitable ceramic matrix filter materials of this type are availabie from The Corning Glass Company of: Corning Glass Works, Corning, New York, United States of America. One possibly suitable example is their Type EX 47 material, having a nominal pore size of 1 2 microns, but they also supply other materials of this kind with different pore sizes. The choice of pore size will depend partly on the range of exhaust particle size to be "sieved", which may vary with different engines and fuels and with different combustion conditions; and partly on the requirements of any official regulations governing exhaust emissions which may be in force.

There is however a wide range of other heat-resisting filter materials available in suitable pore sizes, for example stainless steel wire pads compacted to the required pore sizes, and pads or felts of certain fine synthetic fibres and materials based on alumina, zirconia, etc. which can be made up as felts of suitable pore size. One example is the felt material sold under the trade name SAFFIL by Imperial Chemical Industries Limited of Mond Division, Runcorn, Cheshire, England. The filters 1 6 and 1 7 may be of any of these particular types, or other known types of suitable filter material may be used if preferred.

Two three-port two-way rotating cocks 1 8 and 1 9 have their main ports 1 8A, 1 9A connected respectively to the main inlet duct 1 2 and to the main exhaust duct 14 as shown, the two cocks having their rotating members coupled together for simultaneous operation as indicated diagrammatically at 20.

One branch port 1 8 B of the cock 1 8 is connected by a cross-connection pipe 21 to one other branch port 1 9C of cock 19; and the other branch port 1 8C of cock 1 8 is connected by a cross-connection pipe 22 to the other branch port 1 9B of cock 1 9. One filter unit 1 6 is connected at one end by a pipe 23 to the cross-connection pipe 22, the other end of the filter unit 1 6 being open either directly or through an associated silencer device to the atmosphere. The second filter unit 1 7 is connected at one end by a pipe 24 to the other cross-connection pipe 21, and once again the other end of the filter 1 7 is open either directly or through an associated silencer device to the atmosphere.By operation of the ganged cocks 1 8 and 19, each filter 1 6 and 1 7 may be operated either as an exhaust gas filter, or as an inlet air filter with the direction of flow through the filter element reversed.

Thus with the cocks 18, 1 9 in the positions shown in Fig. 1A, inlet air will be drawn into the open end of the filter 1 6 and will pass through the filter, in the direction indicated by the arrow A, and thence via pipes 23 and 22, cock 18 and pipe 1 2 to the inlet manifold 11.

The exhaust gas from the exhaust manifold 1 3 will travel via pipe 14, cock 19, and pipes 21 and 24 to the second filter 17, through which it will pass to atmosphere as indicated by the arrow B. Deposits of carbonaceous matter will be intercepted by the element of the filter unit 1 7 and will collect on its upstream side. As mentioned earlier, at high engine load levels the exhaust gas temperature will be high enough to cause most of the carbonaceous deposits on the element of the filter 1 7 to burn off, reacting with oxygen still present in the exhaust gases of a Diesel engine even at full load.This burn-off may be helped by the use of suitable catalysts deposited on the filter element which will simultaneously oxidise any small quantitites of unburnt hydrocarbons or carbon monoxide present in gaseous form in the exhaust gases. The use of such oxidation catalysts for gaseous emissions is well known.

However as the exhaust gas temperature drops with decreased engine load to below about 500"C the filtered carbonaceous particles cease to burn off. Indeed as the engine load drops the collected matter on the filter element becomes increasingly "wet" due to some of the fuel having been only partially burnt within the engine. As a result the gas pressure drop across the filter element rises rapidly.

At this stage, the two cocks can be turned simultaneously by the mechanism 20 into the positions shown in Fig. 1 B, interchanging the functions of the filters 1 6 and 1 7 and reversing the directions of gas flow through them.

Now the exhaust gases from the manifold 1 3 flow via the pipe 14, cock 19, pipes 22 and 23 to the filter 16, in which they will be filtered before being discharged to atmosphere in the direction of the arrow Al; and the inlet air enters the filter 1 7 in the direction shown by the arrow B1, and passes via pipes 24 and 21, cock 18 and inlet duct 12 to the inlet manifold 11.The air flow through the filter unit 1 7 is in the reverse direction to that of the previously-filtered exhaust gases, so that the partially-blocked filter element of the filter 1 7 has the inlet air drawn through it in the reverse direction, "back-flushing" the filter so as to dislodge collected material from the now-downstream face of the filter element and carrying the dislodged material along into the inlet manifold 11 and thence into the engine, where it will be at least partially burnt. In this way the filter element of the filter 1 7 will be cleared by the reversed flow of inlet air through it, whilst simultaneously the other and intially-clean filter 1 6 is in use to filter the exhaust gases and collect particulate material from them.

When the filter 1 6 becomes partially clogged, the cocks 1 8 and 1 9 will be changed over again to switch the flow direction and initiate another cycle of operation, which will be repeated when necessary.

Whilst two separate three-port two-way cocks 1 8 and 1 9 separately installed but coupled together are shown in Figs. 1 A and 1 B for clarity and simplicity, in practice the cocks can be arranged in axial alignment and with a common rotary member, or any other convenient valving arrangement may be used.

Figs. 3A and 3B show for example a spool valve arrangement having a single spool common to two valve housings as will be described. Any known arrangement of flowswitching valves and piping may be employed, including the use of electrically-operated solenoid valves.

The simplest way of triggering the operation of the change-over valves or cocks automatically is by means activated by the pressure difference across the filter element of the filter unit then in use to filter the exhaust gases.

One such means is shown in Fig. 6 and will be described below.

Fig. 2 shows a modification of the system of Figs. 1 A and 1 B, the modification being the addition of a cross-connection pipe 28 between the main inlet duct 1 2 and the main exhaust duct 14, the pipe 28 having a control valve 29 somewhere along its length. The purpose of the cross-connection pipe 28 is to enable a proportion of the exhaust gases, controlled by the valve 29, to be directly recirculated through the engine. This is a known means of reducing the formation of, and the resulting emission of, nitrogen oxides.

Various means for controlling the proportion of exhaust gases recirculated (EGR) are known.

Figs. 3A and 3B show diagrammatically an embodiment of the invention in its application to a turbocharged Diesel engine. In this embodiment parts similar to referenced parts in Figs. 1 A, 1 B and 2 are given the same reference numerals as in those Figs. The gas flow switching means is a double spool valve 30, and the turbo-compressor 31, shown diagrammatically, is positioned between the manifolds 11, 1 3 and the spool valve 30 and filters 16, 17. An EGR cross-connection pipe 28 and control valve 29 are shown for use if required, and an additional pipe 32 is shown connecting the main inlet pipe 1 2 on the intake side of the air compressor 31 A to the engine crankcase, for use in an emissioncontrolled engine.This is standard practice for ensuring that any blowback of gases past the pistons or valve stems of the engine, which will contain unburnt hydrocarbons, etc., is passed back through the engine and burnt instead of being released into the atmosphere.

The spool valve 30 has two valve chambers 35, 36 in a common valve housing 37, and a single valve spool 38 common to both chambers and having one land 39 in the valve chamber 35, for cooperation with the valve ports 35B and 35C, and a second land 40 in the valve chamber 36 for cooperation with the valve ports 36B, 36C.The portion 1 2A of the main engine inlet duct 1 2 on the intake side of the compressor 31A is connected to the main port 35A of valve chamber 35, the portion 1 4A of the main engine exhaust duct 14 on the exhaust side of the exhaust turbine 31 B is connected to the main port 36A of valve chamber 36, the pipe 21 interconnects the ports 35B and 36C, the pipe 22 interconnects the ports 35C and 36B, and the filter units 1 6 and 1 7 are connected to the pipes 22 and 21 by pipes 23 and 24 respectively, as before.

Fig. 3A shows the system with the valve spool 38 in one operative position in which the inlet air is drawn in through the filter unit 16, as indicated by the arrow A and passes via pipes 23 and 22 to port 35C, through valve chamber 35 to port 35A, and thence through the inlet pipe portion 1 2A to the intake of the compressor 31A to be compressed and delivered to the inlet manifold 11 through the duct 12; whilst the exhaust gas from the manifold 1 3 drives the exhaust gas turbine 31 B (whose rotor is connected by a shaft 42 to the compressor rotor 31A), and passes thence via pipe 14A, port 36A, chamber 36, port 36C and pipes 21 and 24 to the other filter unit 1 7 to be filtered and discharged to the atmosphere as shown by the arrow B.

When the spool 38 is moved to its other operating position, as shown in Fig. 3B, the gas flow through the filters is reversed, the exhaust gas being switched to the filter unit 1 6 to be filtered thereby and to emerge in the direction of arrow Al, whilst the inlet air is drawn in through filter 17 (arrow B1) and passes through that filter to "back-flush" and clean its filter eiement, the dislodged solid matter being carried by the inlet air flow through the pipe 24 and the pipe 21, the valve chamber 35, the pipe portion 12A and the compressor 31A to the duct 12 and the inlet manifold 11 to be burnt in the engine.

In each of the illustrated embodiments described above, in which the exhaust gas flow is switched cyclically between the filters 1 6 and 1 7, it is possible to provide duplicate silencers respectively for the filters 1 6 and 1 7 to ensure adequate silencing of the exhaust gas flow whichever filter it is discharged from.

The inlet air will then be drawn in through the other silencer. Alternatively a single silencer only may be provided, in conjunction with a suitable change-over valve arrangement arranged to connect it to whichever filter is in use to filter the exhaust gas flow. This change-over valve may be operated simultaneously with the switching of the change-over cocks or spool valves, and by the same operating mechanism.

Now any resistance to gas flow on the intake side of a centrifugal or axial flow compressor tends to aggravate compressor stall.

For this reason it will normally be preferable for the filter unit through which the inlet air is passing (to clean its filter element) to be situated at the downstream side of the compressor 31A. In the case of the filter being used to filter the exhaust gases, it will normally be preferable to site it on the down stream side of the exhaust turbine 31 B, which once again may be either of the radial flow or of the axial flow type. Figs. 4A and 4B show such an arrangement, parts corresponding to those of previously-described embodiments being given the same reference numerals as before.In Figs. 4A and 4B the air inlet 50 (whose air flow is in the direction of the arrow X) leads directly into the air compressor 31A whose delivery is taken via a pipe 51 and a quardruple spool valve 52 to the selected filter 1 6 or 17, whence it is returned through the valve 52 to the main inlet duct 1 2 and inlet manifold 11. The exhaust gases from the manifold 13, after driving the exhaust gas turbine 31 B, are passed by the pipe 1 4A and valve 52 to the other filter 1 7 or 1 6 in which they are filtered and then pass once more through the valve 52 before being released (through a silencer if required) into the atmosphere.

In detail, the spool valve 52 has a common valve housing 52A with four valve chambers 55, 56, 57, 58 each with a main port 55A, 56A, 57A, 58A and with two other ports 55B, 55C; 56B, 56C; 57B, 57C and 58B, 58C; the ports of these latter pairs being selected respectively by four lands 59, 60, 61, 62 on the common valve spool 63. With the valve spool in the position shown in Fig.

4A, inlet air compressed by the compressor 31A is delivered to the port 55A and chamber 55, and passes out through the port 55C and a pipe 65 to the filter 16, to flow through the filter in the direction of the arrow A. The extension 65A of the pipe 65 is blocked by the land 62 covering the port 58B. From the filter 1 6 the compressed inlet air flow, carrying any solid matter dislodged from the filter screen, passes through pipe 23, pipe 22 and port 56C to the valve chamber 56, and thence through port 56A into pipe 1 2 and so to the inlet manifold 11. Simultaneously the exhaust gases after driving the turbine 31 B enter the chamber 57 through port 57A and leave through port 57C to pass into the pipe 21 and thence via the pipe 24 into the other filter 17, to be filtered therein.The gases flow through the filter 1 7 in the direction of the arrow B, and on leaving the filter 1 7 they pass via a pipe 66 through port 58C into the valve chamber 58, from which they escape to the atmosphere through port 58A as shown by the arrow Y. The other limb 66A of the pipe 66 is at this time blocked by the land 59.

When the valve spool 63 is moved into its other operative position shown in Fig. 4B, the compressed air in the valve chamber 55 is delivered through the port 55B into the pipe limb 66A, port 55C being closed by the land 59. Port 58C is closed by the land 62, so that the compressed air enters the filter 1 7 in the direction of the arrow B1, i.e. a reversal of the flow direction through the filter 17, and from the filter the compressed air flow passes through the pipe 24, pipe 21, valve port 56B, chamber 56, and port 56A into the main inlet duct 1 2 and thence to the inlet manifold 11.

The exhaust gases after driving the turbine 31 B enter the valve chamber 57 as before, but leave through port 57B and pass via the pipes 22 and 23 into the filter 16, through which the flow is in the direction of the arrow Al. The filtered exhaust gases leaving the filter 1 6 flow through pipe 65A and port 58B into the valve chamber 58, which they leave through port 58A as before to be discharged into the atmosphere as indicated by the arrow Y.

The embodiment illustrated in Figs. 5A and 5B is an application of the invention to a Diesel engine with pressure charging of the inlet air by means of a pressure exchanger of the type known by the Registered Trade Mark COMPREX. This is essentially a rotating drum positively driven by the engine at a predetermined speed ratio within a surrounding casing, at each end of which are two ports spaced at about 180 apart. The two ports at one end are inlet and outlet ports for the exhaust gases discharged under pressure from the exhaust manifold, whilst those at the other end are inlet and outlet ports for the inlet air for the engine.The drum itself has a large number of open-ended axially-extending passages in it, arranged in a cylindrical disposition around its axis of rotation, the two ends of each passage being at the same radius as the ports at the ends of the casing, so that each end of each passage comes successively into alignment with the two ports at that end of the housing, which are however out of register with the two ports at the other end of the housing. Exhaust gas under pressure will enter one end (the rear end) of each passage in turn of the rotating drum as that passage (already filled with inlet air at atmospheric pressure from the air inlet port) passes the exhaust gas inlet port in the housing, setting up a positive pressure wave in that passage at an instant when its other end (the forward end) is closed by the housing end wall.A compression shock wave is set up in the passage, compressing the air already contained in that passage. In the meantime the passage has moved round so that its rear end is disconnected from the exhaust gas inlet port and is closed by the housing end wall, and its forward end opens to the compressed air delivery port leading to the engine inlet manifold. The air in the passage, compressed by the shock wave produced by the exhaust gas pressure, is forced into the engine inlet manifold, being followed by the column of compressed exhaust gas trapped in the passage.However by the time the forward end of the column of exhaust gas has reached the forward end of the passage, that end has been closed by the further rotation of the rotor, and the moving column of exhaust gas is reflected from the casing end wall to create a rarifaction wave moving in the opposite direction as the rear end of passage becomes aligned with the exhaust gas discharge port at the original end of the casing, through which port the exhaust gases escape to the atmosphere. When the flow through the exhaust gas discharge port in the casing end wall is well established, the air inlet port at the other end of the casing opens to the forward end of the passage, allowing the passage to refill with inlet air as the exhaust gas moves out.At about the time when the passage is filled with air, the exhaust gas discharge port closes due to the continued rotation of the rotor, and the cycle of events repeats. Since there is a multiplicity of passages in the rotor, whose ends follows around the circumferential path containing the various ports in the casing end walls, a continuous transfer of the exhaust gases from the exhaust gas inlet port to the exhaust gas discharge port occurs accompanied by a loss of pressure, and simultaneously a continuous transfer of inlet air from the air inlet port to the air discharge port at the other end of the casing takes place accompanied by the compression of the air by the exhaust gases. A detailed description of one particular COMPREX pressure exchanger will be found in the Transactions of the Society of Automotive Engineers (of the U.S.A.) in Paper No.

118U, 1959 presented by M. Berchtold and H. P. Gull on Oct. 27-29, 1959.

In Figs. 5A and 5B the COMPREX pressure exchanger is shown purely diagrammatically at 70. The two filter units 1 6 and 1 7 are connected selectively between the pressure exchanger 70 and the engine manifolds 11 and 1 3 by a pair of separate spool valves 72, 73 each having two valve chambers, the valve spools 74, 75 of the two valves being coupled together at 76 for operation as one. In principle the functioning of the two separate valves 72, 73 is similar to that of the single four-chamber valve 52 of Figs. 4A and 4B, in that the filter unit which at any time in filtering the exhaust gases is situated upstream of the exhaust end of the pressure exchanger, whilst the reverse-flow inlet air filter is downstream of the air delivery of the pressure exchanger.

In detail, with the valve spools in the setting shown in Fig. 5A, the pressure exchanger 70 takes in atmospheric air at its inlet port 77 (arrow X) and delivers the compressed air at the delivery port 78 to flow through a pipe 79 into the main port 80A leading into a valve chamber 80 of valve 73. Port 80B of chamber 80 is closed by a land 94 of the valve spool 73, and the compressed air leaves the valve chamber 80 through a port 80C, and flows thence through the pipe 65 into a pipe 82 and thence through the filter unit 1 6 in the direction of arrow A. The air plus dislodged particulates leaving the filter 1 6 through the pipe 23 enter a chamber 84 of the valve 72 through pipe 22 and port 84C, and leave the chamber 84 of the valve 72 through port 84A leading to the main inlet air duct 1 2 and manifold 11.At the same time, the exhaust gases from the manifold 1 3 enter the other chamber 85 of the valve 72 through a port 85A, and leave through a port 85C, pipe 21 and 24 to enter the filter unit 17, through which they flow in the direction of the arrow B. The filtered gases leaving the filter 1 7 travel via a pipe 86 and the pipe 66, and enter the second chamber 88 of the valve 73 through a port 88C. From the chamber 88 the filtered gases flow through a main port 88A and a pipe 89 to the exhaust gas inlet port 90 of the pressure exchanger 70, and leave the latter through the discharge port 91 (arrow Y) after compressing the inlet gas.

When the spools 74 and 75 are moved to their operating positions shown in Fig. 5B, the lands 92 and 93 on spool 74 respectively open the ports 84B, 85B and respectively close the ports 84C, 85C of the valve 72, whilst the lands 94 and 95 on spool 75 respectively open the ports 80B and 88B and close the ports 80C and 88C of the valve 73.

As will be apparent the effect of this spool movement is to transfer the flow of exhaust gases from the manifold 1 3 first to the filter 16, through which they flow in the direction of the arrow Al, to be filtered thereby, and thence via the chamber 88 of valve 73 to the exhaust gas end of the pressure exchanger 70 as before, to compress the inlet air. At the same time the compressed inlet air flow from the exchanger 70 is transferred to the valve 73 to the filter unit 1 7 through which it flows in the reverse direction B1, and thence flows through the pipe 24 and valve 72 to the inlet duct 1 2 and manifold 11 of the engine 10.

Thus once again, each time the spool valves 72 and 73 are switched over in unison, the compressed inlet air flows in the reverse direction through the filter unit which had previously been filtering the exhaust gases, the reverse air flow cleaning the filter element and carrying the dislodged solid material back into the engine.

Fig. 6 shows diagrammatically one possible form of changeover mechanism for operating the changeover cocks 18, 1 9 of Figs. 1 A and 1 B, and Fig. 2, or for operating the spool valves of Figs. 3A and 3B, 4A and 4B, and 5A and 5B to switch the gas flows from one filter to the other. Fig. 6 shows the changeover mechanism as applied to changeover cocks 18, 1 9 but it will be apparent that it could be readily coupled to the spool valves of the other embodiments for their operation.

This particular changeover mechanism is based on the use of pressurised fluid (liquid or compressed air) to provide the required force to move over the cocks or spools in response to the change in the pressure difference across the element of the filter being used to filter the exhaust gases, as that element becomes progressively clogged up. It will be appreciated however that many other arrangements are possible for effecting this changeover.

In Fig. 6, the canister 201 or 202 of each filter unit 1 6 and 1 7 is provided with a first pressure tapping 203 or 204 on one side of its filter element and with a second filter tapping 205 or 206 on the other side of its element. In Fig. 6 the filter unit 1 7 is shown as filtering the exhaust gas flow, and the high pressure first tapping 204 which is upstream of its filter element is connected by a pipe 207 to one end of the housing of a plunger unit 208, whilst the other, low-pressure tapping 206 is connected by a pipe 209 to the other end of the housing of plunger 208, on the opposite side of its piston 210. The piston 210 of the plunger 208 is biassed by a spring 211 in the direction tending to retract its plunger rod 21 2 which protrudes from the housing.

Similarly the then high-pressure tapping 205 and low-pressure tapping 203 of the filter unit 1 6 are connected respectively by pipes 21 3 and 21 4 to opposite ends of the housing of a second plunger 215, on opposite sides of its piston 216, the protruding plunger rod 217 of the plunger 215 being biassed by a spring 218 in the direction of retraction.

The springs 211 and 218 are sufficiently powerful to keep the respective plunger rods 212 and 217 fully retracted in the housings of their respective units 208 and 215, so long as the filter elements of the respective filter units 1 7 and 1 6 are not excessively clogged.

However, as the filter element of the filter unit 1 7 becomes progressively more and more clogged by accumulated matter filtered out of the exhaust gases, the pressure difference across that element will increase correspondingly until it reaches a value sufficient to overcome the spring 211 and drive the piston 210 causing the plunger rod 212 to move outwardly, thus rotating (in the anticlockwise direction in Fig. 6) a rocker 220 whose arms are respectively associated with the two plunger rods 212 and 217. A spring-loaded detent 221 is fitted to the rocker 220 to resist angular movement thereof initially, until the pressure loading of the respective plunger rod is sufficient to overcome the detent and cause the rocker to move over rapidly to its other position.

The rocker 220 carries an operating arm 222 whose head 223 is engaged in a recess in the spool rod 224 of a hydraulic or pneumatic relay valve 225, so that the angular movement of the rocker 220 operates the relay valve 225. The relay valve 225 controls a hydraulic or pneumatic actuator 226 whose plunger rod 227 is coupled by a link 228 to the spindle or spindles of the changeover cocks 18, 1 9 (or changeover spool valves as the case may be). The spool of the relay valve 225 is movable between two limiting positions in which it delivers high-pressure fluid from a supply line 229 to one end or the other of the cylinder of the actuator 226, and connects the opposite end of the actuator to a low-pressure return line 230, in conventional manner.

In the position shown in Fig. 6, the pressure difference across the element of the filter unit 16, previously in use for filtering the exhaust gases, has just overcome the spring 218 to cause the plunger 217 to rotate the rocker 220 clockwise to the position indicated. This rotation of the rocker has caused the servo valve 225 to operate the actuator 226 to change over the settings of the cocks 18, 19, switching the exhaust gas flow through the other filter unit 1 7 and the inlet air flow in the reverse direction through the filter 1 6 to backflush that filter and dislodge deposited material from its element.This switching of the gas flow through the filter element 1 6 causes a reversal of the pressure difference across it, assisting the spring 21 8 to retract the plunger rod 21 7 to its position shown.

As engine running continues, with the mechanism in the position of Fig. 6, carbonaceous matter will be progressively deposited on the upstream side of the element of filter unit 17, causing the pressure difference across that element to rise progressively until the spring 211 and the detent 221 are both overcome and the plunger rod 212 will drive the rocker 220 rapdily anticlockwise to its other position. This will change over the relay valve 225 and will cause it to operate the actuator 226 so as to change over the cocks 18, 1 9 (or equivalent spool valves) once again and switch the exhaust gas and inlet air flows back to the respective filter units 16 and 1 7.

The reverse flow of inlet air through the filter unit 1 7 will then backflush its element as described.

The mechanism will continue to operate cyclically during the running of the engine, switching the gas flows alternately through the two filter units at a periodicity dependent on the already determined value of the triggering pressure drop across the respective filter element and the rate at which the engine operating conditions cause deposition of filterclogging carbonaceous matter.

Another possible embodiment of the present invention involves the use of a rotary changeover valve driven at a reduced speed by the engine, or by a separate electric or other motor, the rotating valve member overrunning ports in a manner arranged to connect the two filter units 1 6 and 1 7 alternately to the engine exhaust and inlet systems. The rotary valve could be arranged to effect the changeover of the gas flows at predetermined fixed time intervals or after predetermined numbers of engine revolutions. Figures 7 and 8 show two possible electronic control systems for this purpose, based on counting the engine revolutions.

Thus in Fig. 7, an electromagnetic pick-up 250 consisting of a small permanent magnet with a winding is provided, and in a known manner is fixed in close proximity to the teeth 251 of the starter ring on the engine flywheel 252. As each successive tooth 251 passes by the pick-up, an electrical pulse (a voltage) is induced in the winding surrounding the pickup magnet. Thus as the flywheel 252 of the engine 10 rotates, a train of electrical pulses is, generated, the number per engine revolution depending on the number of teeth 251 on the starter ring. Alternatively some other engine-driven source of electrical pulses produced in dependence on engine revolutions may be employed.The train of pulses is supplied to a dive-by-n counter connected to a monostable circuit 254 to trigger the latter every n pulses, causing the monostable to operate a relay 255 via a driver amplifier 256. Closure of the relay 255 every n pulses operates an electric motor 257 in conjunction with a rotary switch 258 to cause the motor to step round and operate the rotary changeover valve 259, if necessary via a gearbox 260, each time the engine completes a predetermined number of revolutions.

Fig. 8 shows an alternative arrangement in which the stream of pulses from the pick-up 250 operates the counter 253 as before, but the output signals from the counter are supplied to a bistable circuit 261 connected to the drive amplifier 256. The output signals from the drive amplifier 256 every n pulses operate a soienoid-actuated pneumatic control valve 262 to connect opposite ends of the cylinder of a pneumatic ram 263 alternately to a supply of compressed air and to an exhaust to atmosphere, the resultant movements of the ram piston operating the changeover valve 259 through a crank mechanism 264.

It would also be possible to arrange for the rotary cocks or sliding spool valves in any of the embodiments of Figs. 1 A, 1 B to 5A, 5B to be tripped by a suitable device at fixed time intervals or engine revolution intervals, instead of being tripped by the filter pressure difference as described with reference to Fig. 6.

Figs. 9 and 10 show embodiments of the invention in which a single rotary filter is used, in a manner which ensures that successive portions of the rotating filter element through which the engine exhaust gases have just passed to filter the gases, are moved on immediately into positions in which the inlet air for the engine passes through them in the opposite direction to the exhaust gases, so as to clean each succeeding portion of the rotating element. Thus as the filter element rotates in use, each portion of its filter element is first used to filter the exhaust gases and is then cleaned by the inlet gases before starting the next cycle of rotation.

Thus in the embodiment of Fig. 9, a rotary filter 100 is used, having an outer casing 111 carrying two sector shaped cowls 105, 109 on one radial end face and two sector shaped cowls 104, 110 on the other radial end face.

Journalled in the casing 111 is a rotary filter element comprising a short cylinder 101 of porous ceramic material affording a multiplicity of parallel axially-extending channels 102A, 102B. The channels 102A 102B are distributed radially and circumferentially over the entire radial cross-section of the cylinder 101. Each channel is closed at one end and open at the other, adjacent ends of the adjacent channels being alternately open and blind, so that gas passing axially through a section of the cylinder from one radial face to the other will pass through the porous walls (divisions) separating the adjacent channels of the respective group of channels and will be filtered by the divisions.The filter element is mounted on a shaft 103 and is rotated within its outer structural casing 111 at slow speed by the engine 10, or by a separate electric or hydraulic motor, the speed of rotation of the filter element not being necessarily in any particular ratio to engine speed.

Engine inlet air drawn in from the atmosphere passes through exhaust gases from a pipe 108 into the casing 111 to flow through a sector of the cylinder 101 occupying approximately one half of the radial cross-sectional area of the cylinder 101, which sector is covered by the funnel-shaped cowls 109, 110 so as to be filtered by the divisions between adjacent channels 102A, 102B in that sector as the air travels from the cowl 109 to the cowl 110 in the general direction of the arrow A. From the cowl 110 the inlet air passes into the duct 1 2 and thence into the engine inlet manifold 11.

Similarly, the particulate-carrying exhaust gases travel through the manifold 1 3 and duct 14 into a cowl 104 covering a sector of the radial face area of the filter element, on the diametrically-opposite side to the sector occupying approximately the remaining half of area covered by the cowls 109, 110 and pass axially through that sector of the filter element to be filtered by the divisions between its adjacent channels 102A, 102B and be collected by a cowl 105 leading to the atmosphere, via a duct 106 and any further silencer required. It will be seen that the general direction of travel of the inlet air through the filter element, shown by the arrow A, is opposite to that of the exhaust gases shown by the arrow B.As the filter element 101 is slowly rotated in use, each sectorial portion in turn of its filter element 101 constituted by the porous divisions between adjacent channels 102A, 102B, will first be traversed by the exhaust gases to filter out solid particles which will be retained on the upstream faces of the divisions, and will then be transferred from between the cowls 104, 105 to a position between the cowls 109, 110 where it will be traversed in the opposite direction by the flow of inlet air which will dislodge deposited matter and carry it into the engine inlet for combustion.

Whilst Fig. 9 relates to a naturally-aspirated engine, the arrangement can be adapted for use with a boosted engine without difficulty.

The fact that the rotating filter performs the "valving" without the need for switching valves or cocks, simplifies the pipework.

Fig. 10 shows another arrangement employing a rotating filter, in this case having the filter bed or element incorporated in the cylindrical wall of a filter drum 120, mounted for rotation on a shaft 121. The drum 120 is slowly rotated in a housing 1 23 having an inlet 1 24 through which inlet air is drawn axially inwardly into a central region 1 25 of the housing 1 23 within the filter drum 120, where it will be deflected by a fixed oblique plate 1 26 to pass radially outwardly through a section of the cylindrical filter element to emerge into a region 1 27 in the housing 1 23 outside the drum 1 20 and pass through an outlet 1 28 in the housing leading to the main inlet duct 1 2 and inlet manifold 11.Simultaneously the exhaust gases are delivered through the exhaust duct 1 4 and an inlet 1 29 into a closed region 1 30 of the interior of the housing 1 23 outside the filter drum 1 20 and separate from and on the opposite side of the shaft 121 to the region 127, so that the exhaust gases pass radially inwardly through a portion of the cylindrical filter wall of the drum 1 20 which is diametrically-opposite to that through which the inlet air passes.The filtered exhaust gases in the drum 1 20 are delfected by the inclined plate 1 26 to leave the interior of the drum axially and escape to atmosphere or to a further silencing device through a discharge stub 1 32 of the housing.

As the drum 1 20 is slowly rotated each section of the cylindrical filter wall is first traversed in the radially-inward direction by the exhaust gases to filter them, and then moves round to a diametrically-opposite position where it will be traversed by the inlet air, this time in the radially-outward direction.

Where ceramic drum types of rotary filter element are used, as in Fig. 10, it is likely that a composite structure assembled from a multiplicity of sectorial-shaped, flat or even short cylindrical matrices could be used as an aid to manufacture. Installation and driving would be very similar to the axially-traversed cylindrical arrangement of Fig. 9.

A problem which arises from the concept of using fine filters to eleminate exhaust soot being discharged into the atmosphere, and of returning the filtered matter to the engine, is that any inorganic particles, whether derived from oil additives, wear particles from within the engine, oxidation and/or corrosion products from the exhaust system, or even particles which may have passed through the inlet air filter, will be recirculated through the engine. Although the absolute quantities are small, any failure to remove them periodically will be detrimental to engine wear. Their small size makes it difficult to separate them from the filtered carbonaceous matter by normal means.It is possible to do this, however, when operating at high engine loads when the carbonaceous matter burns off the exhaust filter due to the high temperature then existing, using either of the two rotating filter types described above.

In the case of the rotating filter with axial channels of Fig. 9, it is possible to arrange for the exhaust gas flow to be vertically upwards through the divisions of the filter element so that any particulate matter is collected on the undersides of the divisions. When, at full load, the carbonaceous matter is burnt off, the non-burnable particulate matter will be largely held against the undersides of the divisions of the filter element by the exhaust gas velocity.

If it is arranged for the filter to pass through a zone where no gas flow occurs, much of the loose inorganic matter will fall down and can be caught in a suitable container for disposal.

After this quiescent zone the filter passes on to the area through which the ingoing air charge for the engine passes vertically downwards through the filter divisions. Whilst this will not completely eliminate recirculation of particulate inorganic matter at light loads, the ability to dispose of the non-burnable matter during periods of full load operation should keep the amount recirculated to a minimum.

Where the rotating drum type of filter is used, as in Fig. 10, the exhaust entry can be roughly horizontal with the quiescent non-flow period arranged to occur at the underside of the rotor.

It is possible to use, instead of a filter having a rotated filter element in a housing with fixed gas and air ports, a converse arrangement comprising a filter whose filter element is fixed, e.g. a fixed drum or a fixed disc, and which is provided with a rotating structure affording exhaust gas and inlet air delivery and collection ports which traverse the surface of the filter element in a circumferential or circular path so that exhaust gas is passed between the exhaust gas delivery and collection ports in one direction through one portion of the filter element, whilst inlet air is passed between the inlet ports in the opposite direction through another portion of the element which was previously traversed by the exhaust gas ports.

It is possible to conceive of the use of a flat type filter which either oscillates backwards and forwards to provide the required reversal of flow through the filter bed or, suitably articulated, comprises a "belt" passing continuously through the filter zone over rollers at the ends and, after an idle period, passing through the active zone again.

Claims (14)

1. An internal combustion engine provided with exhaust gas filter means including at least one filter element through at least a part of which the engine exhaust gases are passed to filter the gases and intercept solid particulate matter being carried thereby, and with means operable during the running of the engine for periodically or progressively transferring the exhaust gas flow from that filter element, or from the said part thereof, to a second filter element or to a different part of the first filter element for filtration thereby, and for then passing at least a part of the inlet air flow to the engine air intake through the first filter element, or through the said part thereof previously traversed by the exhaust gas flow, and in the direction opposite to that of the previous exhaust gas flow, so as to backflash that filter and dislodge deposited solid matter from its element and transport the dislodged matter into the air intake.

2. An engine as claimed in Claim 1, whose filter means comprises two separate filter elements through either of which the exhaust gases can be passed in one direction to filter the exhaust gases whilst the inlet air flow passes through the element before entering the air intake, means being provided for switching the exhaust gas flow from one filter element to other and simultaneously switching the inlet air flow from the latter to the former filter element to pass through it in the opposite direction to that of the previous flow of exhaust gases.

3. An engine as claimed in Claim 1, provided with a filter having a single filter element with means for effecting relative displacement between the filter element and associated structure affording ducting for the exhaust gas and inlet air flows, the arrangement being such that the exhaust gas flow and the inlet air flow pass continuously in opposite directions through different portions of the filter element at a given time, the displacement means causing successive portions of the element through which the exhaust gas has passed to be then traversed in the opposite direction by the inlet air flow so as to dislodge solid matter previously deposited by the exhaust gas flow.

4. An engine as claimed in Claim 3, in which the displacement means is arranged to produce relative rotation between the filter element and the associated structure affording the ducting for the exhaust gas and inlet air flows.

5. An engine as claimed in Claim 4, whose single filter has a continuously or intermittently rotated filter element and a fixed structure affording the ducts for the exhaust gas and inlet air flows.

6. An engine as claimed in Claim 4 or Claim 5, in which the filter element is of drum shape, and in which the exhaust gas flow is arranged to pass through one portion of the element in one radial direction whilst the inlet air flow is arranged to pass in the opposite radial direction through another portion of the filter element.

7. An engine as claimed in Claim 4 or Claim 5, in which the filter element is of disc or drum type arranged for the passage of the exhaust gas and inlet air flows respectively through separate portions of the filter element in opposite axial directions from one radial face to the other radial face of the filter element.

8. An engine as claimed in Claim 2, in which the means for switching the exhaust gas and inlet air flows comprises two rotary cocks coupled together for simultaneous operation by an actuating means.

9. An engine as claimed in Claim 2, in which the means for switching the exhaust gas and inlet air flows comprises valve means having either a single valve provided with several valve chambers, or two or more valves coupled together for operation in unison by an actuating means.

10. An engine as claimed in Claim 2 or Claim 8 or Claim 9 in which the means for switching the exhaust gas and inlet air flows includes a pressure-fluid operated actuating mechanism comprising a snain actuator controlled by a device responsive to change in the pressure drop across the filter element through which the exhaust gas flow is passing.

11. An engine as claimed in Claim 2 or Claim 8 or Claim 9, in which the means for switching the exhaust gas and air flows operates automatically in response to the completion by the engine of successive predetermined numbers of revolutions.

1 2. An engine as claimed in any one of the preceding claims, having means for diverting a controlled portion of the exhaust gas flow upstream of the filter means into the inlet air flow downstream of the filter means for recirculation through the engine.

1 3. An engine as claimed in Claim 9, or in any one of Claims 10 to 1 2 when dependent on Claim 9, provided with an exhaustgas-driven turbo-charger for the inlet air, whose air compressor is located upstream of the valve means and filter elements with respect to the direction of the inlet air flow.

14. An engine as claimed in Claim 9, or in any one of Claims 10 to 12 when dependent on Claim 9, provided with a pressureexchanger for compressing the inlet air opera tively connected between the exhaust gas and inlet air flows in a position upstream in the inlet air flow and downstream in the exhaust gas flow of the valve means and respective filter elements.

1 5. An internal combustion engine provided with exhaust gas filtering means substantially as specifically described herein with reference to Figs. 1A and 1 B, or to Fig. 2, or to Figs. 3A and 3B, or to Figs. 4A and 4B, or to Figs. 5A and 5B, in each case with or without the control mechanism of any one of Figs. 6 to 8, or with reference to Fig. 9 or to Fig. 10 of the accompanying drawings.