US20030162451A1

US20030162451A1 - Catalytic device for watercraft engine

Info

Publication number: US20030162451A1
Application number: US10/324,622
Authority: US
Inventors: Shigeyuki Ozawa
Original assignee: Shigeyuki Ozawa
Current assignee: Yamaha Marine Co Ltd
Priority date: 2001-12-18
Filing date: 2002-12-18
Publication date: 2003-08-28
Also published as: JP2003184547A

Abstract

A watercraft is provided with an engine. An exhaust system routes exhaust gases from the engine to an external location. The exhaust system has an exhaust conduit and a catalytic device affixed to the exhaust conduit. The catalytic device has a tubular member that extends in the exhaust conduit. Two intermediate members extend in the tubular member one after another along a flow direction of the exhaust gases. The tubular member supports each intermediate member. The catalytic device has two catalysts. Each intermediate member is affixed to the tubular member at one end thereof and supports each catalyst at another end thereof.

Description

PRIORITY INFORMATION

This application is based on and claims priority to Japanese Patent Application No. 2001-384355, filed on Dec. 18, 2001, the entire contents of which is hereby expressly incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a catalytic device for an engine and, more particularly, to an improved catalytic device for an engine that incorporates a plurality of catalysts.

2. Description of Related Art

Personal watercrafts have become very popular in recent years. This type of watercraft is quite sporting in nature and carries one or more riders. A hull of the watercraft typically defines a rider's area above an engine compartment. An internal combustion engine powers a jet propulsion unit that propels the watercraft by discharging water rearward. The engine lies within the engine compartment in front of a tunnel which is formed on an underside of the hull. The jet propulsion unit is placed within the tunnel and includes an impeller that is driven by the engine.

The watercraft is provided with an exhaust system to route exhaust gases from the engine to a location outside the watercraft. In a typical arrangement, the exhaust system comprises exhaust conduits connected in series and the last conduit opens to the tunnel to discharge the exhaust gases thereto.

The exhaust system can be provided with a catalytic device that incorporates a catalyst therein to remove unburned gases such as hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) from the exhaust gases. The catalytic device is disclosed in, for example, U.S. Pat. Nos. 5,787,847, 5,797,775 and 5,983,631, and Japanese Laid-Open Patent Publications Nos. 11-303628 and 2000-130182.

FIG. 1 illustrates an exemplary catalytic device, which is shown in section along with a sectioned portion of an

exhaust conduit

20. The exhaust conduit 20 extends from an engine (not shown) to define an exhaust passage 22 that routes exhaust gases from the engine. The exhaust conduit 20 also defines a water jacket 24 around at least a section of the exhaust passage 22. A tubular member 26 extends within the exhaust passage 22 and has a circular flange 28 that is affixed to the exhaust conduit 20 with gaskets 30 disposed on both sides of the flange. An intermediate member 32 coaxially extends within the tubular member 26. The intermediate member 32 is brazed to the tubular member 26 with solder 34 at one end thereof. The intermediate member 32 holds a catalyst 36. The catalyst 36 is brazed to the intermediate member 32 with solder 38 at another end of the intermediate member 32. Retainers 40 are attached to both ends of the tubular member 26 to prevent the catalyst 36 from moving from the original position should either the catalyst 36 break from the intermediate member 32 or the intermediate member 32 break from the tubular member 26, due to vibration.

The

catalyst

36 has a length L that makes the catalyst 36 relatively large and heavy in weight. The

solders

34, 36 thus are required to be sufficiently long to support the intermediate member 32 and the catalyst 36, respectively. In addition, the retainers 40 have a width W that is necessary to keep the catalyst 36 in the original position. However, the larger the width W of the retainers 40, the smaller the effective area of the catalyst 36.

A need therefore exists for a catalytic device that can securely hold a catalyst in place while maximizing an effective area of the catalyst.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a watercraft comprises an internal combustion engine. An exhaust system is arranged to route exhaust gases from the engine to an external location. The exhaust system comprises an exhaust conduit and a catalytic device affixed to the exhaust conduit. The catalytic device comprises a support member extending in the exhaust conduit and a plurality of catalysts supported by the support member. The catalysts are disposed one after another along a flow direction of the exhaust gases.

In accordance with another aspect of the present invention, a watercraft comprises an internal combustion engine. An exhaust system is arranged to route exhaust gases from the engine to an external location. The exhaust system comprises an exhaust conduit and a catalytic device affixed to the exhaust conduit. The catalytic device comprises a first support member extending in the exhaust conduit. A plurality of second support members extend at least partially within the first support member and are arranged one after another along a flow direction of the exhaust gases. The first support member supports each of the second support members. A plurality of catalysts are provided. Each catalyst is supported by a respective one of the second support members.

In accordance with a further aspect of the present invention, a catalytic device is provided for an internal combustion engine. The catalytic device comprises a tubular member adapted to be disposed within an exhaust conduit of the engine. A plurality of catalysts extends in series with one another. The catalysts are spaced apart from each other and are disposed, at least in part, within the tubular member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, as noted above, is an enlarged sectional view of an exemplary catalytic device placed within an exhaust conduit. This figure is provided in order to assist the reader's understanding of problems in the related art. [0014]
FIGS. [0015] 2-10 illustrate preferred embodiments of the present catalytic device that are intended to illustrate, but not to limit, the aforementioned and other features, aspects and advantages of the present invention. The following briefly describes each of these additional figures.
FIG. 2 is a partially sectioned, side elevational view of a personal watercraft configured in accordance with a preferred embodiment of the present invention. [0016]
FIG. 3 is a cross-sectional view taken along the line [0017] 3-3 of FIG. 2.
FIG. 4 is a top plan view of an engine and a section of an exhaust system of the personal watercraft of FIG. 2. [0018]
FIG. 5 is an enlarged sectional view of an exhaust conduit of the exhaust system that incorporates a catalytic device. The catalytic device is not sectioned in this figure. [0019]
FIG. 6 is an enlarged sectional view of the exhaust conduit and the catalytic device. A portion of the exhaust conduit that defines a water jacket is shown in this figure. [0020]
FIG. 7 is another enlarged sectional view of the exhaust conduit and a catalytic device that is configured in accordance with another preferred embodiment of the present invention. Another portion of the exhaust conduit, which defines a fixing construction of the catalytic device to the exhaust conduit, also is shown in this figure. [0021]
FIG. 8 is a schematic sectional view of a catalytic device that is configured in accordance with an additional preferred embodiment of the present invention. [0022]
FIG. 9 is a schematic sectional view of a catalytic device that is configured in accordance with a further preferred embodiment of the present invention. [0023]
FIG. 10 is an enlarged sectional view of another modified catalytic device that is configured in accordance with a preferred embodiment of the present invention.[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

With reference to FIGS. [0025] 2-5, an overall construction of a personal watercraft 50 that incorporates a catalytic device 52 configured in accordance with a preferred embodiment of the present invention will be described. The catalytic device has particular utility with the personal watercraft, and thus is described in the context of the personal watercraft. The catalytic device, however, can be applied to other types of watercrafts as well, such as, for example, but without limitations, small jet boats and the like. Furthermore, certain aspects and features of the catalytic device also can be applied to land vehicle and stationary engines.
The [0026] personal watercraft 50 includes a hull 56 generally formed with a lower hull section 58 and an upper hull section or deck 60. The lower hull section 58 can include one or more inner liner sections to strengthen the hull 56 or to provide mounting platforms for various internal components of the watercraft 50. Both the lower and upper hull sections 58, 60 are made of, for example, a molded fiberglass reinforced resin or a sheet molding compound. The lower hull section 58 and the upper hull section 60 are coupled together to form an internal cavity which wholly or partially defines an engine compartment 59. An intersection 62 of the hull sections 58, 60 is defined in part along an outer surface gunwale or bulwark. The hull 56 houses an internal combustion engine 64 that powers the watercraft 50. The engine 64 is disposed within the engine compartment 59.
The [0027] lower hull section 58 is designed such that the watercraft 50 planes or rides on a minimum surface area at the aft end of the lower hull 58 in order to optimize the speed and handling of the watercraft 50 when up on plane. For this purpose, the lower hull section 58 generally has a V-shaped configuration formed by a pair of inclined sections that extend outwardly from a longitudinal center line of the hull 56 to the hull's side walls at a dead rise angle. Each inclined section desirably includes at least one strake and the strakes preferably are symmetrically disposed relative to the keel line of the watercraft 50. The inclined sections also extend longitudinally from the bow toward the transom of the lower hull 58. The side walls are generally flat and straight near the stem of the lower hull 58 and smoothly blend toward the longitudinal centerline at the bow. The lines of intersection between the inclined sections and the corresponding side walls form the outer chines of the lower hull section 58.
A [0028] steering mast 66 extends generally upwardly toward the top of the upper hull section 60 to support a handlebar 68. The handlebar 68 is provided primarily for a rider to control the steering mast 66 so that a thrust direction of the watercraft 50 is controlled. The handlebar 68 also carries control devices such as, for example, a throttle lever for operating throttle valves of the engine 64.
A [0029] seat 72 extends fore to aft along a center plane of the hull 56 at a location behind the steering mast 66. The center plane extends generally vertically with the watercraft resting in normal upright position. The seat 72 has generally a saddle shape so that the rider can straddle it. The illustrated upper hull section 60 defines a seat pedestal 73 and the seat 72 is detachably placed or hingedly affixed to the seat pedestal 73. Foot areas 74 are defined on both sides of the seat 72 and at the top surface of the upper hull section 60. An access opening 76 (FIG. 3) is defined on the top surface of the seat pedestal 73 under the seat 72. The rider thus can access the engine compartment 59 through the access opening 76.
The [0030] upper hull section 60 defines a storage recess in front of the steering mast 66 and a hutch 76 is hinged to open or is detachably affixed to the upper hull section 60 to close the storage recess. A fuel tank 78 is placed in the internal cavity under the upper hull section 60 and preferably in front of the engine 64. The fuel tank 78 is coupled with a fuel inlet port positioned at a top surface of the upper hull section 60 through a filler duct 80. A closure cap 82 closes the fuel inlet port.
Air ducts or [0031] ventilation ducts 86 are provided at appropriate locations of the upper hull section 60 so that the ambient air can enter the internal cavity through the ducts 86. Except for the air ducts 86, the engine compartment 59 is substantially sealed so as to protect the engine 64 and engine related components from water.
A [0032] jet pump assembly 88 propels the watercraft 50. The jet pump assembly 88 is mounted in a tunnel or pump housing 90 formed on the underside of the lower hull section 58. Optionally, the tunnel 90 can be further isolated from the engine compartment 59 by a bulkhead. The tunnel 90 has a downward facing inlet port 92 opening toward the body of water. A bottom plate 94 closes the lower hull section 58 except for the inlet port 92 of the tunnel 90.
The [0033] jet pump assembly 88 includes an impeller 96 that is journaled within the tunnel 90. An impeller shaft 98 extends forwardly from the impeller 96 and is coupled with an output shaft 100 that extends from the engine 64 by a coupling unit 102 to be driven by the output shaft 100.
The rear end of the [0034] pump assembly 88 defines a discharge nozzle 106. A deflector or steering nozzle 108 is affixed to the discharge nozzle 106 for pivotal movement about a steering axis that extends generally vertically. A cable connects the deflector 108 with the steering mast 66 so that the rider can move the deflector 108.
When the [0035] output shaft 100 of the engine 64 drives the impeller shaft 98 and the impeller 96 thus rotates, water is drawn from the surrounding body of water through the inlet opening 92. The pressure generated in the pump assembly 88 by the impeller 96 produces a jet of water that is discharged through the discharge nozzle 106 and the deflector 108. The water jet thus produces thrust to propel the watercraft 50.
The [0036] engine 64 in the illustrated embodiment operates on a two-cycle crankcase compression principle and has three cylinders 112, 114, 116 (FIG. 4) spaced apart from one another along the longitudinal center plane. The illustrated engine, however, merely exemplifies one type of engine with which the catalytic device can be used. Other types of engines having other number of cylinders, having other cylinder arrangements, other cylinder orientations (e.g., upright cylinder banks) and operating on other combustion principles (e.g., four-cycle or rotary) can of course be applied.
The [0037] engine 64 typically comprises a cylinder block defining three cylinder bores that correspond to the three cylinders 112, 114, 116. A piston reciprocates in each cylinder bore. At least one cylinder head member is affixed to the upper end of the cylinder block to close respective upper ends of the cylinder bores and defines three combustion chambers with the cylinder bores and the pistons. A crankcase member is also affixed to the lower end of the cylinder block to close the respective lower ends of the cylinder bores and to define crankcase chambers with the cylinder block. A crankshaft is rotatably connected to the pistons through connecting rods and is journaled for rotation within the crankcase member. The foregoing output shaft 100 is coupled with the crankshaft through an appropriate transmission mechanism. The cylinder block, the cylinder head and the crankcase member preferably are made of aluminum alloy and together define an engine body.
Engine mounts [0038] 120 extend from both sides of the engine body. The engine mounts 120 preferably include resilient portions made of, for example, rubber material. The engine body is mounted on the lower hull section 58 (or possibly on the hull liner) by the engine mounts 120 so that vibration of the engine body is inhibited from transferring to the hull section 58.
The [0039] engine 64 preferably is provided with an air induction system to introduce air into the crankcase chambers from within the engine compartment 59. With reference to FIGS. 3 and 4, the illustrated air induction system includes a first intake box 124 and a second intake box 126. The first intake box 124 is located in front of the engine 64 and the second intake box 126 is located on the starboard side relative to the engine 64. A connecting conduit 128 connects both the first and second intake boxes 124, 126 together. The first and second intake boxes 124, 126 define first and second plenum chambers therein, respectively. The first intake box 124 also defines an inlet port 129 through which the air in the engine compartment 59 is drawn into the first plenum chamber. On the other hand, the second plenum chamber of the second intake box 126 is coupled with intake ports of the crankcase chambers through three carburetors 130.
Each [0040] carburetor 130 incorporates a throttle valve to measure an appropriate amount of air that is delivered to the associated combustion chamber. With the throttle valve measuring the air amount, the carburetors 130 supply fuel to the crankcase chambers to form an air/fuel charge in each crankcase chamber. An amount of the fuel also is measured by the carburetor 130. The fuel amount changes in proportion to the air amount measured by the throttle valves so that a proper air/fuel ratio can be held. Alternatively, the engine 64 can employ other charge formers such as, for example, a fuel injection system.
An intake valve such as a reed valve, for example, controls each intake of the air/fuel charge into the crankcase chamber. Each crankcase chamber is connected to each combustion chamber through a scavenge passage and a scavenge port. The air/fuel charge is pre-compressed within the crankcase chamber and then is drawn into to the combustion chamber through the scavenge passage and port. [0041]
An ignition or firing system preferably is provided to ignite the air/fuel charges in the combustion chambers. The ignition system preferably includes spark plugs that have electrodes exposed into the combustion chambers and an ignition device that supply ignition power to the spark plugs. In the illustrated embodiment, high-tension cables [0042] 134 (FIG. 4) are used to supply the ignition power to the respective spark plugs. The spark plugs fire the air/fuel charges in the combustion chambers by sparks made by the ignition devices at proper ignition timings controlled by an ECU (electronic control unit) or other control units.
The [0043] engine 64 also is provided with an exhaust system to route burnt charges, i.e., exhaust gases, from the combustion chambers to a location outside of the watercraft 50. An exhaust manifold 138 preferably is coupled with exhaust ports of the combustion chambers. More specifically, three branched portions of the manifold 138 are connected to the respective exhaust ports. A fresh air/fuel charge that enters each combustion chamber pushes the exhaust gases out the exhaust port and into the exhaust manifold 138.
In the illustrated embodiment, a [0044] first exhaust conduit 142 is coupled with a common end of the exhaust manifold 138 downstream of the branch portions. The first exhaust conduit 142 extends generally around and above the front end of the engine 64. The exhaust conduit 142 then turns generally rearward and extends along the cylinder block of the engine 64 on the starboard side and generally above the second intake box 126. The exhaust conduit 142 again turns toward the port side in the rear of the engine 64 and then is generally oriented rearwardly.
An exhaust silencer or water-[0045] lock unit 146 preferably is placed at a location generally behind the engine 64 and is secured to the lower hull 58 (or possibly to a hull linear). The exhaust silencer 146 also is positioned on the port side relative to the longitudinal center plane. The distal end of the first exhaust conduit 142 is connected to an inlet port of the exhaust silencer 146 defined at a front surface thereof.
A [0046] second exhaust conduit 150 extends generally upwardly from a top surface of the exhaust silencer 146 and further extends toward the starboard side of the watercraft 50 beyond the longitudinal center plane. The second exhaust conduit 150 ends at a discharge port that opens at the tunnel 90 and thus to the exterior of the watercraft 50. The discharge port preferably is positioned at a location that can be out of the body of water in the event the watercraft 50 capsizes.
The exhaust gases can be discharged through the [0047] exhaust manifold 138, the first exhaust conduit 142, the exhaust silencer 146 and the second exhaust conduit 150. Because of the arrangement of these exhaust components, entry of outside water into the engine 64 is inhibited even if the watercraft 50 capsizes or floats at other positions on the body of water.
The first and [0048] second exhaust conduits 142, 150 can be formed with multiple conduit sections, respectively. The illustrated first exhaust conduit 142, for example, comprises at least four conduit sections 142 a, 142 b, 142 c, 142 d (FIG. 4). A catalytic device 154, which will be described in greater detail below, is placed between the conduit sections 142 c, 142 d. The conduit sections 142 c, 142 d preferably form a large diameter portion 153 to incorporate the catalytic device 154 therein. The illustrated large diameter portion 153 is formed next to the second and third cylinders 114, 116 so that the rider can easily access to the catalytic device 154 through the access opening 76. The respective conduit sections 142 a, 142 b, 142 c, 142 d preferably are supported by the engine body. For instance, as shown in FIG. 3, the conduit sections 142 b, 142 c, which defines the large diameter portion 153, are affixed by bolts 177 to vertical stays 155 and horizontal stays 156 both extending from the engine body.
With particular reference to FIGS. 4 and 5, the [0049] watercraft 50 preferably is provided with a typical open-loop type water cooling system for the engine 64 and the exhaust system. The cooling water is introduced into the system from the body of water.
In the illustrated embodiment, the cooling system preferably includes a water intake conduit that communicates with a water jacket defined in the [0050] exhaust manifold 138. The cooling water is delivered at least to water jackets formed within the engine body to cool engine portions which build heat therein. A water jacket 158 also is defined within the first exhaust conduit 142 and preferably is formed around an exhaust passage 160 coaxially. Water pipes 162 connect the water jackets of the engine body with the water jacket 158 of the first exhaust conduit 142. In the illustrated arrangement, flexible members 164 such as rubber tubes, for example, couple the conduit sections 142 b, 142 c so as to complete the exhaust passage 160 and the water jacket 158.
The [0051] water jacket 158 ends at an appropriate downstream location in the conduit section 142 d and opens to the exhaust passage 160. The water thus is mixed with the exhaust gases and is delivered to the exhaust silencer 146. The water finally is discharged to the body of water through the second exhaust conduit 150 with the exhaust gases.
With continued reference to FIGS. [0052] 2-5 and with additional reference to FIGS. 6 and 7, the catalytic device 154 will now be described in greater detail below.
The illustrated [0053] catalytic device 154 comprises at least two catalysts 170, 172, at least one a main tubular member or first support member 174, and at least two intermediate tubular members or second support members 176.
The [0054] catalysts 170, 172 can be oxidation catalytic converters, three-way catalytic converters or any other catalytic converters. Either the same type or different types of the catalytic converters can be selected for each catalyst 170, 172. In the illustrated arrangement, each catalyst 170 has a honeycomb configuration and is shaped cylindrically about an axis 177 that extends along a flow direction of the exhaust gases. Both the catalysts 170, 172 have a length L1 along the axis 177.
The [0055] tubular member 174 is made of metal material and is formed with a cylindrical section 179 and at least one a flange section 180 that extends from the cylindrical section 179, preferably at a mid portion thereof. The cylindrical section 179 has a center axis that preferably is generally collinear with the axis 177 when the catalysts 170, 172 are placed in a preset position. The cylindrical section 179 has a length L2 along the center axis 177. The length L2 is greater than a total amount of the lengths L1 of the catalysts 170, 172. The length L2 preferably is equal to the length L of the single catalyst 36 of FIG. 1. The flange section 180 can be formed separately from the cylindrical section 179 and welded thereto. The flange section 180 is interposed between the conduit sections 142 b, 142 c with gaskets 184 disposed on both sides. Slots 186 are formed in the illustrated flange section 180 such that the water from the water jacket 158 can flow through the flange section 180. A pair of notches 188 (FIG. 3) also is formed next to two of the slots 186 to place the tubular member 174 in a preset position. Bolts 190 are inserted into bolt holes defined between the slots 186, and nuts 191 securely fix the bolts 190 in the positions.
The [0056] intermediate members 176, 178 also are made of metal material and are thinner than the tubular member 174. Each intermediate member 176, 178 preferably has a cylindrical shape similar to that of (but smaller in diameter than) the cylindrical section 179 of the tubular member 174. The intermediate members 176, 178 are interposed between the tubular member 174 and the respective catalysts 170, 172. That is, the intermediate members 176, 178 have a diameter that is smaller than a diameter of the tubular member 174 and is larger than a diameter of the catalysts 170, 172. The illustrated intermediate members 176, 178 have generally the same length L1 as the catalysts 170, 172.
Each [0057] intermediate member 176, 178 is brazed with the tubular member 174 by solder 192 at one end 194 thereof and also is brazed with each catalyst 170, 172 by solder 196 at another end thereof 198. In this description, the one end 194 where the intermediate member 176, 178 is brazed with the tubular member 174 is called as a “first end” 194 and the another end 198 which is opposite to the first end 194 is called as a “second end” 198. In a similar manner, an end 200 of each catalyst 170, 172 where the catalyst 170, 172 is brazed with the intermediate member 176, 178 is called as a “first end” 200 and the another end 202 which is opposite to the first end 200 is called as a “second end” 202. That is, the first end 200 of the catalyst 170, 172 is affixed to the second end 198 of the intermediate member 176, 178. “First” and “second” thus are not used in relation to the direction of exhaust flow and can refer to different ends on the catalysts and/or the intermediate members. For example, in the illustrated embodiment, the first end 200 of the upstream catalyst 170 is on the downstream side of the catalyst 170, while the first end 194 of the corresponding intermediate member 176 is located on the upstream side. In other embodiments, for example the embodiment shown in FIG. 8 (which will be described later), the first end 200 of the upstream catalyst 170 is located on the downstream side of the catalyst 170 while the first end 200 of the downstream catalyst 172 is located on the upstream side of the catalyst 172.
Because of the arrangement, in the illustrated embodiment, the [0058] upstream catalyst 170 is positioned in front of the downstream catalyst 172 in the exhaust flow and the first end 200 of the catalyst 170 is spaced apart from the second end 202 of the catalyst 172 by a distance D1. Preferably, the distance D1 is between approximately 2-10% of the length L1 of the catalyst 170, 172.
Each [0059] intermediate member 176, 178 is spaced apart from the tubular member 174 by a distance D2, while each catalyst 170, 172 is spaced apart from the intermediate member 176, 178 by a distance D3. The distances D2, D3 can be generally equal to each other and preferably are less than the distance D1.
Although not shown, each [0060] intermediate member 176, 178 preferably has slits that extend in a direction of the axis 177 and that are evenly spaced about the intermediate member relative to the axis 177 (e.g., about the circumference of the intermediate member). Each slot extends from the second end 198 toward the first end 194, but stops well short of the first end 194 so as to not to provide an uninterrupted area for the solder 192. The slots, however, form cantilever sections at the second end 198 to which the solder 196 is applied. Thus, the intermediate members 176, 178 can absorb thermal expansion and shrinkage of the catalyst bodies 170, 172 and can elastically suspend the catalysts 176, 178 such that the catalysts 170, 172 can move radially (i.e., in a direction normal to the axis 177).
The exhaust gases coming from the upstream portion of the [0061] exhaust passage 160 flows first through the upstream catalyst 170 and then flows through the catalyst 172. Unburned gases such as hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) in the exhaust gases are effectively neutralized by those catalysts 170, 172.
The usage of the [0062] intermediate members 176, 178 and the cantilever type support construction of the catalysts 170, 172 and the intermediate members 176, 178 inhibit mechanical vibrations within the structure of the first exhaust conduit 142 from transferring to the catalysts 170, 172, i.e., the support structure dampens such vibrations.
Because the illustrated [0063] catalysts 170, 172 are separately provided, each catalyst 170, 172 can have less weight than a single catalyst. Thus, the solders 192, 196 do not need to bear heavy catalyst(s) and the risk that the solders 192, 196 will fail is reduced. No retainers are necessary to hold the catalysts 170, 172. The catalysts 170, 172 thus can be held in the original position and the effective areas of the catalysts 170, 172 can be preserved.
In addition, in the illustrated arrangement, the [0064] catalysts 170, 172 are spaced apart from each other with the distance D1. The catalysts 170, 172 thus do not contact each other even if the catalysts 170, 172 thermally expand. The solders 192, 196 are subjected to less stress as compared to the prior design illustrated in FIG. 1. The durability of the catalytic device 154 thus is improved while eliminating the need for the retainers in many applications; however, it is understood that the retainers can still be used with the catalyst device if desired.
In the illustrated arrangement of FIGS. 6 and 7, the [0065] first end 200 of the catalyst 170 faces the second end 202 of the catalyst 172, and the second end 198 of the intermediate member 176 faces the first end 194 of the intermediate member 178. Alternatively, with reference to FIG. 8, both the first ends 200 of the catalysts 170, 172 can face each other, and both the second ends 198 of the intermediate members 176, 178 can face each other. Also, with reference to FIG. 9, both the second ends 202 of the catalysts 170, 172 can face each other, and both the first ends 194 of the intermediate members 176, 178 can face each other.
Additionally, the [0066] intermediate members 176, 178 are not necessarily in some applications. FIG. 10 illustrates a modified catalytic device 210 that has no intermediate members. In this arrangement, the catalysts 170, 172 are directly brazed to the tubular member 174. The modified arrangement can provide a simpler catalytic device.
In any embodiments and variations, the catalytic device can incorporate three or more catalysts. The number of the intermediate members can change along with the number of the catalysts. Additionally, while the illustrated embodiments disclose each of the [0067] intermediate members 176, 178 being of the same size (both in length and in diameter) and the catalyst 170, 172 being of the same size (both in length and in diameter), the sizes and shapes of these components can vary and can be different from each other. It is preferred, however, that each catalyst of the plurality have generally the same size and shape in order to minimize the cantilevered weight and to minimize the restriction to flow through the exhaust passage. For similar reasons, it is also preferred that each intermediate member of the plurality have generally the same size and shape.
Of course, the foregoing description is that of preferred constructions having certain features, aspects and advantages in accordance with the present invention. Various changes and modifications may be made to the above-described arrangements without departing from the spirit and scope of the invention, as defined by the appended claims. [0068]

Claims

What is claimed is:

1. A watercraft comprising an internal combustion engine, and an exhaust system arranged to route exhaust gases from the engine to an external location, the exhaust system comprising an exhaust conduit and a catalytic device affixed to the exhaust conduit, the catalytic device comprising a support member extending in the exhaust conduit and a plurality of catalysts supported by the support member, the catalysts being disposed one after another along a flow direction of the exhaust gases.

2. The watercraft as set forth in claim 1, wherein each one of the catalysts has first and second ends and is affixed to the support member generally at the first end.

3. The watercraft as set forth in claim 2, wherein the first end of the catalyst is positioned next to the second end of another catalyst.

4. The watercraft as set forth in claim 3, wherein the first end of the catalyst is spaced apart from the second end of the another catalyst.

5. The watercraft as set forth in claim 2, wherein the first end of the catalyst is positioned next to the first end of another catalyst.

6. The watercraft as set forth in claim 2, wherein the first end of the catalyst is brazed to the support member.

7. The watercraft as set forth in claim 1, wherein the catalysts are spaced apart from one another.

8. The watercraft as set forth in claim 1, wherein each one of the catalysts is affixed to the support member via an intermediate member that extends at least within the support member.

9. The watercraft as set forth in claim 8, wherein each one of the intermediate members has first and second ends, each one of the intermediate members supports the catalyst generally at the first end and is affixed to the support member generally at the second end.

10. A watercraft comprising an internal combustion engine, and an exhaust system arranged to route exhaust gases from the engine to an external location, the exhaust system comprising an exhaust conduit and a catalytic device affixed to the exhaust conduit, the catalytic device comprising a first support member extending in the exhaust conduit, a plurality of second support members extending at least partially within the first support member and being arranged one after another along a flow direction of the exhaust gases, the first support member supporting each of the second support members, and a plurality of catalysts each supported by one of the second support members.

11. The watercraft as set forth in claim 10, wherein the catalysts are spaced apart from each other.

12. The watercraft as set forth in claim 10, wherein each of the second support members has first and second ends and supports the catalyst generally at the second end.

13. The watercraft as set forth in claim 12, wherein each of the second support members is affixed to the first support member generally at the first end.

14. The watercraft as set forth in claim 12, wherein the second end of the second support member is positioned next to the first end of another second support member.

15. The watercraft as set forth in claim 12, wherein the second end of the second support member is positioned next to the second end of another second support member.

16. A catalytic device for an internal combustion engine comprising a tubular member adapted to be disposed within an exhaust conduit of the engine, a plurality of catalysts extending in series with one another and disposed at least partially within the tubular member, the catalysts being spaced apart from each other.

17. The catalytic device as set forth in claim 16, wherein each one of the catalysts has first and second ends and is affixed to the tubular member generally at the first end.

18. The catalytic device as set forth in claim 17, wherein the first end of the catalyst is positioned next to the second end of another catalyst.