Catalytic Muffler

Abstract

Catalytic muffler containing a catalyst bed between a perforate catalyst retainer and a movable pressure plate. The pressure plate applies pressure on the catalyst bed preventing it from becoming fluidized. The required pressure can be supplied by springs or by pneumatically actuated bellows. By preventing fluidization of the catalyst bed during thermal expansion and contraction, the muffler functions to prevent catalyst attrition.

Description

BACKGROUND

Catalysts have been developed which function to reduce carbon monoxide, hydrocarbons and nitrogen oxide content of the exhaust gas of internal combustion engines. These are generally used by placing a bed of the catalyst in a container and passing the exhaust gas through the catalyst bed. These containers come in a variety of designs and are referred to collectively as "catalytic mufflers." A few examples of these devices are shown in U.S. Pat. Nos. 3,146,073; 3,149,925; 3,149,926; 3,154,389; 3,380,810; 3,495,950; 3,503,714; 3,503,715; 3,567,403 and 3,600,142.

A major problem in reducing exhaust emission using a catalytic muffler is catalyst attrition. This is the physical loss of catalyst due to the catalyst breaking up during use. The powdered catalyst is either blown out the exhaust pipe or packs into a dense bed, resulting in excessive back pressure.

One cause of catalyst break up is that the catalyst bed becomes loosely packed after being used for a short time and tends to fluidize in the pulsating exhaust gas stream. This abrades the catalyst granules, leading to premature break up.

SUMMARY

An object of this invention is to provide a catalytic muffler that will hold a catalyst bed firmly, thus preventing abrasion of the catalyst granules. A further object is to provide a catalytic muffler that will prevent fluidization of the catalyst bed during use in a pulsating exhaust stream. These and other objects are accomplished by providing a catalytic muffler comprising a muffler housing having an exhaust gas inlet and outlet. Positioned within the housing are two opposed elements between which the catalyst bed is held. One of these elements is a retainer which is generally perforated to allow exhaust gas to flow to or from the catalyst bed. The other element is a movable pressure plate which maintains a pre-set pressure on the catalyst bed even when the bed expands or contracts or suffers some attrition. Pressure is maintained on the catalyst bed by pressure means connected to the pressure plate such as spring means.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing a typical exhaust system connected to an internal combustion engine.

FIG. 2 is a cross section of the catalytic muffler housing showing the catalyst granules firmly held between the retainer and pressure plate. Coil springs located outside the muffler housing are shown applying pressure on the pressure plate.

FIG. 3 is a cross section of an embodiment which shows the catalyst contained in a closed screen package which is held between a lower shaped perforated retainer and a perforate pressure plate. The catalyst package ie replaceable. A single coil spring is shown supplying the pressure.

FIG. 4 is a cross section of a catalytic muffler housing showing the catalyst in a replaceable screen bag held between a dish-shaped perforate retainer and a perforate pressure plate. Pressure is furnished to the plate by external bellows connected to the plate by a rod extending through an opening in the muffler housing. A cover surrounds the external bellows forming a closed pressure chamber in the space outside the bellows. This pressure chamber is connected to a source of pressure which actuates the bellows and applies pressure on the pressure plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, internal combustion engine 1 is connected by exhaust pipe 2 to catalytic muffler 3. Conduit 4 connects the exit port of catalytic muffler 3 to optional conventional muffler 5. The treated exhaust is vented to the atmosphere through tail pipe 6.

FIG. 2 shows in detail the construction of one embodiment of catalytic muffler 3. The catalytic muffler is formed by housing 20 having exhaust inlet 21 and exhaust outlet 22. Baffle 23 deflects exhaust entering the inlet plenum zone of housing 20 through inlet 21. Located within housing 20 is perforated catalyst retainer 24 located in proximity to exit 22. The periphery of retainer 24 is attached to housing 20 forming an exit plenum zone between retainer 24 and the bottom surface of housing 20. Also located within housing 20 is movable pressure plate 25 arranged substantially parallel to retainer 24. Plate 25 and retainer 24 form two surfaces of catalyst compartment 26, which is filled with catalyst 27, only a portion of which is shown. Screen 28 is positioned on the top surface of the catalyst bed beneath pressure plate 25. Coil springs 29 are located outside the muffler housing in spring compartments formed by spring housing 20A mounted on muffler housing 20. Any number of springs may be used. Springs 29 are operatively connected by pushrods 21A extending through an opening in housing 20 to pressure plate 25 and tend to force pressure plate 25 toward catalyst 27 with sufficient force to hold the catalyst firmly in position.

In operation, exhaust gas enters housing 20 at inlet 21 and is deflected evenly across pressure plate 25 by baffle 23. The gas passes through the perforations in plate 25 into catalyst compartment 26 where it contacts catalyst 27. The treated exhaust gas then leaves catalyst compartment 26 through the perforations in retainer 24. It then leaves housing 20 at exit 22.

Pressure plate 25 can move toward and away from catalyst 27 in response to change in the volume of the catalyst due to temperature effects or due to attrition of a portion of the catalyst. During volumetric changes in the catalyst a substantially constant pressure is maintained on the catalyst by pressure plate 25, thus preventing it from becoming a fluidized bed which causes severe abrasion of the catalyst granules.

FIG. 3 shows the construction of another embodiment of the invention. The muffler housing is formed by pan-shaped upper housing 30 and lower housing 31 which are bolted together around their periphery. In lower housing 31 is located dish-shaped perforated retainer 32 which is attached to lower housing 31 forming an exit plenum between retainer 32 and the inner surface of housing 31. Located in the bottom of lower housing 31 is exit port 33.

In the top surface of upper housing 30 is inlet port 34. Mounted inside the housing directly below inlet port 34 is baffle 35 attached at several points to upper housing 30 by spacers 36. Coil spring 37 is attached to the lower surface of baffle 35 and the upper surface of perforated pressue plate 38.

Positioned between pressure plate 38 and retainer 32 is a replaceable screen container 39 filled with exhaust gas catalyst 30A, only a portion of which is shown. In operation, exhaust gas enters the muffler housing at inlet port 34 and is diverted throughout the upper zone above the catalyst bed by deflector 35. The exhaust gas enters catalyst container 39 through and around pressure plate 38 wherein it contacts catalyst 30A. The treated exhaust gas leaves the catalyst bed through the perforations in retainer 32 and then out through exit port 33.

As the dimensions of the muffler housing and catalyst change due to temperature or catalyst attrition, pressure plate 38, in response to spring 37, compensates by moving up and down as required to maintain a substantially constant pressure on catalyst 30A in container 39.

When catalyst 30A is no longer sufficiently active it can readily be replaced by detaching lower housing 31 from upper housing 30 and removing replaceable screen container 39. The spent catalyst can be reactivated by chemical treatment, discarded, or extracted to remove valuable constituents such as palladium, platinum, and the like. A new or reactivated screen container of catalyst appropriately shaped to fit the catalyst cavity is then inserted and lower housing 31 is re-attached to upper housing 30.

The embodiment in FIG. 4 comprises a muffler housing formed by pan-shaped upper housing 40 and lower housing 41, which are attached around their periphery to form the muffler housing. Entry port 42 is located in upper housing 40. Mounted on upper housing 40 outside of the muffler housing are pressure housings 43. Inside pressure housing 43 are bellows 44, the open end of which is sealably attached to the upper surface of upper housing 40 forming an air-tight pressure chamber 48 between bellows 44 and pressure housing 43. Bellows 44 are operatively connected by pushrods 45 extending through openings 46 in upper housing 40 to pressure plate 47. Pressure chamber 48 is connected to an air pressure source such as an air tank or an engine-mounted air pump.

Inside lower housing 41 is dish-shaped perforate retainer 49 attached at its periphery to the inner surface of lower housing 41 forming plenum 40A. Exhaust gas exit 41A is located in the bottom of lower housing 41. Fitted within the cavity formed by pressure plate 47 and retainer 49 is screen container 42A filled with exhaust gas catalyst 43A, only a portion of which is shown.

In operation, exhaust gas enters the muffler housing at inlet port 42. It then passes through and around pressure plate 47 into screen container 42A wherein it contacts exhaust gas catalyst 43A. It then passes through the openings in perforate retainer 49 into plenum 40A and then out through exit port 41A.

As the catalyst volume changes in use, pressure plate 47 moves up or down in response to such volume change. Plate 47 maintains a substantially constant pressure on the catalyst bed as a result of pneumatic pressure in pressure chamber 48 tending to compress bellows 44 which is operatively connected by push-rod 45 to pressure plate 47. The pressure within chamber 48 should be adjusted such that the pressure on the catalyst bed is sufficient to hold it firmly and prevent substantial movement within the bed.

Preferably, means are provided to adjust the pressure on the catalyst bed. For example, a screw may be placed in the top of spring housing 20A which serves to move a disk located within the spring housing on top of coil spring 29. To increase pressure on the catalyst the screw is turned down, causing the coil spring to compress, thus increasing pressure on the catalyst bed.

A large variety of exhaust gas catalysts can be used in the present catalytic muffler. Examples are supported copper oxide, copper oxide-palladium, copper oxide-chromium oxide-palladium, vanadium oxide, vanadium oxide-platinum, platinum, manganese oxide, manganese oxide-iron oxide, vanadium oxide-chromium oxide, nickel oxide, copper oxide-nickel oxide, and the like. Suitable supports include alumina, silica, silica alumina, magnesia, zirconia, kieselguhr, and the like. Some representative exhaust gas catalysts are described in detail in U.S. Pat. No. 3,226,340; 3,433,581; 3,271,324; 3,207,704; 3,447,893; 3,428,573; 3,224,981; 3,540,838; 3,224,831; 3,425,792; 3,524,721; 3,545,917 and 3,374,183.

Claims

I claim:

1. A catalytic muffler comprising a muffler housing having an inlet at one end and an outlet at the other end, a transverse perforate fixed catalyst retainer member proximate to said outlet, a transverse perforate movable pressure plate proximate to said inlet and in spaced relationship to said retainer member defining a catalyst compartment between said retainer member and said pressure plate, a particulate catalyst bed within said catalyst compartment, pressure means connected to said movable pressure plate and adapted to move said pressure plate in response to a change in the volume of said catalyst bed to continuously maintain a force on said pressure plate in line with the direction of exhaust gas flow through said catalyst compartment said pressure means comprising a substantially cylindrical spring housing mounted externally of said muffler housing on the outer surface of said muffler housing, a coil spring within said spring housing, an opening in said muffler housing at the location of said spring housing, actuating means connecting said coil spring through said opening to said pressure plate whereby said coil spring applies pressure on said pressure plate in line with the direction of exhaust gas flow through said catalyst compartment.