Method and Apparatus for Filtering Engine Exhaust

1. Field of the Invention

The present invention relates to a filtering apparatus for engine exhaust, and in particular, to a filtering apparatus having a reusable filter element and a heat exchanger which is particularly well-suited to filtering diesel soot. A heat override valve and back pressure valve may also be included.

2. Description of the Prior Art

As concern for the environment increases, greater attention is being given to systems for eliminating damaging discharges from internal combustion engines. In the workplace, pollution created by combustion engines threatens the health of workers, as the particulate and other compounds contained in diesel exhaust may be carcinogenic. The problem is especially troublesome in enclosed environments such as warehouses or factories wherein diesel forklifts are often utilized. Fork lifts and other diesel engines are often operated in a cycling manner, that is, at maximum power for short periods which quickly raises engine and exhaust temperatures. Prior devices have not worked effectively during cycling to filter the exhaust. In addition, prior filtering units have generally been too expensive, ineffective, or too difficult to service.

Since the most efficient pleated filter material for filtering exhaust gases may have a maximum operating temperature, there must be safeguards to prevent the filter from igniting due to the hot exhaust gases. Therefore, when a predetermined temperature is exceeded, the exhaust gases must be redirected away from the filter to prevent combustion. Preferably, the problem of overheating is avoided by keeping the exhaust temperature below the ignition temperature of the soot and/or filter element. Prior devices have had no way of cooling the exhaust to prevent excessive temperature build up.

Should the exhaust temperature exceed a predetermined level, there has not been a satisfactory valving arrangement for redirecting the exhaust gases to prevent ignition of the filter element. Prior filtering apparatuses have not included temperature override devices to prevent filter ignition.

It can be seen then, that an improved filtering apparatus is needed which provides an effective reusable and replaceable filter element and which prevents overheating of the exhaust gases and includes safeguards to prevent ignition of the filter element.

The present invention is directed to a filtering apparatus, and in particular to a filtering apparatus for removing soot from engine exhaust. The present invention is particularly well suited for cleaning exhaust from diesel engines. In addition, the device includes an apparatus for cooling the exhaust prior to filtering and for re-directing the exhaust away from the filter should the exhaust temperature exceed a predetermined level.

The present invention includes a pleated filter cartridge for removing particulates and soot from the exhaust gas. The pleated filter material of the cartridge removes up to 99.5% of the particular material from the exhaust gas and traps the particulate on the interior of a filter cartridge. When the filter cartridge becomes loaded with soot, the cartridge is sealed at the ends with the soot inside the cartridge so that workers are not exposed to the soot when the cartridge is handled. The filter cartridges are replaced when loaded with soot after extended periods of use, or, following cleaning, the filter cartridges may be repeatedly re-used without loss of efficiency.

The exhaust gas is directed to the interior of the filter cartridge through a perforated acoustic tube which functions to attenuate the sound from the engine and exhaust system. Flow may be redirected so that exhaust does not enter the cartridge by a temperature override valve. The override valve closes the flow path through the perforated tube when the exhaust temperature reaches a predetermined level. The temperature override valve uses axially deflecting washer-type discs made of two different metals that expand at different rates when heated to push a plunger to close off the exhaust flow. The discs contract when the temperature decreases to an acceptable level, thereby re-opening the valve. In this manner, the filter is protected from excessive heat which may cause combustion of the filter material and/or the soot in the filter cartridge.

When the flow through the perforated acoustic tube to the filter cartridge has been cut off, resulting from closing of the temperature override valve, exhaust backs up in the exhaust system to a back pressure valve. When a predetermined pressure is reached, the valve opens to allow the exhaust gas to escape, thereby preventing damage to the engine from excessive back pressure.

The exhaust gas is cooled so that the temperature override valve does not close in the normal range of operating conditions. According to the present invention, the exhaust gas flows from the engine through an air-to-air heat exchanger. Air from the engine's cooling fan blows over the heat exchanger as exhaust gas passes through cooling tubes of the heat exchanger. In addition, the cooling tubes have heat-dissipating fins placed thereon to aid in removing the heat from the gas. The cooled exhaust gas then flows to the temperature override valve and to the filter cartridge. It can be appreciated that the cooled exhaust does not pose a threat to ignite the filter cartridge or the soot which may be trapped on the inside of the filter cartridge.

These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.

In the drawings, wherein like reference letters and numerals indicate corresponding structure throughout the several views:

FIG. 1 shows a perspective view of a forklift having its counterweight removed and equipped with a filtering apparatus according to the principles of the present invention;

FIG. 2 shows a side elevational view of the filter housing and temperature override valve of the filtering apparatus;

FIG. 3 shows a side view of the temperature override valve in the open position;

FIG. 4 shows a side view of the temperature override valve shown in FIG. 3 in the closed position;

FIG. 5 shows a side diagrammatic view of a second embodiment of a filtering apparatus mounted on a forklift; and

FIG. 6 shows a graph of exhaust temperature for a motor in hydraulic stall without cooling and utilizing exhaust cooling according to the principles of the present invention.

Referring now to the drawings, and in particular to FIG. 1, there is shown a forklift vehicle 10, equipped with a filtering apparatus 12. The filtering apparatus 12 includes a filter unit 14 including a filter housing 16 encompassing a filter cartridge. The forklift 10 includes a heat exchanger 66 mounted proximate the radiator 64 of engine 84 and receiving exhaust from the engine 84, as shown in FIG. 5. As shown in FIG. 1, the exhaust gases pass through a series of tubes 68 contained in the air stream of an engine cooling fan 86 for cooling the exhaust. The heat exchanger 66 includes a check type back pressure valve 72 mounted thereon which provides relief from excessive pressure and from excessive heat, as explained hereinafter. The tubes 68 of the heat exchanger include heat dissipating fins 70 to aid in cooling the exhaust.

The heat exchanger connects to an exhaust pipe 74 having a heat guard (not shown). The pipe 74 leads up to the filter unit 14 through an adaptor 34. In a first embodiment, shown in FIG. 1, the filter unit 14 is mounted above the operator, while in a second embodiment, shown in FIG. 5, the filter unit is mounted behind the operator. The adaptor 34 includes a housing 42 enclosing a temperature sensitive override valve 36, as shown in FIGS. 2-4.

As shown in FIGS. 3 and 4, the override valve 36 includes a central shaft 44 on which is mounted a sliding plunger 46. The plunger 46 slides to block an entrance to a perforated acoustic tube 38 which aids in sound attenuation. The central shaft 44 includes an end bracket 48 which retains a resistance spring 50 pressing against the plunger 46 and axially aligned bi-metal discs 52. A resistance spring forces the plunger 46 away from the opening to the perforated tube 38 in the normal operating position.

As shown in FIG. 2, the housing 16 of the filter unit 14 includes a removable cover 38 which may be retained by bolts 20 or other easily removable means. In a preferred embodiment, the housing has a heat shield 22 and mounting bracket 24 to protect workers and to provide for positioning the filter unit 14 in a number of mounting configurations.

The housing 16 surrounds a removable filter cartridge 28. The filter cartridge 28 has a cylindrical annular configuration with an annular pleated filter material 30 encompassed by annular end rings 32. The filter cartridge 28 mounts over the perforated tube 38 to receive exhaust gases on its interior side. The filtered gas flows radially outward through the filter material 30 and out through openings 26 in the housing 16 or passes up a stack 82, shown in FIG. 5. The perforated tube 38 includes a large number of orifices distributed over the tube for sound attenuation.

In operation, as shown in FIG. 1, gas flows from the engine through an inlet pipe 62 to the heat exchanger 66. There, cooling air flow from the radiator cooling fan, shown in FIG. 5, is blown over the heat exchanger tubes 68 to cool the exhaust gases. The fan air is circulated over the tubes 68 which also have heat-dissipating fins 70 to help remove heat for cooling the exhaust prior to filtering. In the normal range of operating conditions, the gas will flow from the heat exchanger and be directed up the riser pipe 74.

Upon reaching the top of the riser pipe 74, the cooled exhaust gas will enter the adaptor housing 42 and flow through the opening to the perforated tube 38. The gas then passes through the filter cartridge 28 before being vented to the atmosphere through orifices 26.

As shown in FIG. 5, in a second embodiment of the invention, a filter unit 80 is mounted on the forklift 10 behind the operator. The filter unit 80 directs filtered exhaust up through a stack 82 and then to the atmosphere.

The flow pattern, under normal conditions, takes the gas through the temperature override valve 36 in an open position, as shown in FIGS. 2 and 3. However, when conditions are such that the engine is overworked such as when hydraulic stall occurs, the exhaust gas may reach temperatures which may come close to or exceed that needed to cause combustion of the pleated filter material 30 and trapped soot. Therefore, the hot exhaust gas must be directed away from the filter cartridge 28 so that combustion of the soot or filter material 30 does not occur.

As shown in FIGS. 3 and 4, the bi-metal discs 52 of the temperature override valve 36 contain a first metal 56 affixed to a second metal 58. When the temperature rises from hot exhaust gas, the different expansion rates of the two metals 56 and 58 on each disc 52 cause the bi-metal discs 52 to deflect axially outward. The bowing discs 52 move the plunger 46 to the opening to the perforated tube 38, as shown in FIG. 4. When this occurs, the flow path to the perforated tube 38 and filter cartridge 28 closes. In the preferred embodiment, the valve 36 closes at about 220.degree. C. Therefore, gas is not allowed to reach the filter cartridge 28 and vent to atmosphere. With the valve 36 closed, the pressure builds up back through the exhaust system to the heat exchanger 66. When the exhaust back pressure exceeds a predetermined level, the back pressure valve 72 proximate the heat exchanger 66 opens so that flow may be directed to atmosphere. Therefore, the back pressure does not damage the engine. In the preferred embodiment, the back pressure valve opens at pressures of about 6-8 cm Hg.

When the temperature of the exhaust cools down so that the bi-metal discs 52 deflect to a flattened non-bowed position, the resistance spring 50 presses the plunger 46 back to the position shown in FIG. 3. The flow path to the perforated tube 38 and filter cartridge 28 again opens. The back pressure valve 72 then closes from the reduced pressure so that the flow path again directs all of the exhaust through the filter cartridge 28. It can be appreciated that in this manner, exhaust is always filtered, except under extreme conditions when excessive heat build-up occurs. It can also be appreciated that the present invention provides for safety overrides which prevent damage to the engine and prevent the pleated filter material 30 from igniting.

The pleated filter material 30 is used in the cartridge 28 as it is proved to be very efficient at filtering diesel particulate and retaining the soot from diesel engines. The efficiency has been obtained at over 99.5%. In addition, by removing the cover 18 from the housing 16, the filter cartridge may be removed and the cartridge 28 may then be cleaned and reused repeatedly with no loss of efficiency. The cartridge 28 is easily accessed and may be easily replaced by removing the cover 18. It can also be appreciated that by utilizing the cartridge 28 and covering the ends, the soot is retained on the interior of the filter cartridge so that exposure to hazardous soot material during handling of the cartridge 28 is prevented.

In FIG. 6, there is shown a comparison of engine exhaust temperature over time for exhaust gas prior to passing through a cooling apparatus and for a exhaust gas following passing through an apparatus according to the principles of the present invention. For the graph shown, a forklift was placed in hydraulic stall, that is the engine is operating under maximum power. The temperature for the non-cooled exhaust is much higher than the cooled exhaust. The maximum temperature of the cooled exhaust remains more than 100.degree. C. cooler than the non-cooled exhaust gas. It can be appreciated that this temperature is not high enough to cause ignition of the pleated filter material, whereas non-cooled exhaust under such conditions may risk igniting the filter.

It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.