EXHAUST SYSTEM FOR A UTILITY VEHICLE

Abstract

A utility vehicle includes an exhaust system seamlessly connected to an engine. Depending on various parameters, such as the vehicle's size and / or performance, the exhaust system is required to meet certain emissions regulations. These regulations can be met by increasing the temperature within the exhaust system; however, at particularly high temperatures, a catalytic converter can be damaged. Therefore, the exhaust system includes various cooling options to dissipate heat.

Description

EXHAUST SYSTEM FOR A UTILITY VEHICLE Field of Invention The present invention relates in general to an exhaust assembly for a vehicle and, in particular, to an exhaust assembly for a utility or off-road vehicle configured to reduce its emissions. Background of the Invention Off-road vehicles (ATVs) are typically smaller than passenger cars and are not classified according to the same standards and regulations as passenger cars. As such, ATVs may have different emissions regulations compared to passenger cars. However, if various parameters of ATVs change, such as vehicle size, performance, etc., the vehicle may be required to meet different emissions standards. Since emissions standards in the US, Europe, and other parts of the world are constantly changing, there is a need to provide ATVs configured for enhanced performance that are capable of meeting stricter emissions regulations. Summary of the Invention In one embodiment of the present description, a utility vehicle comprises a frame assembly extending to cnfrcnn / zznz / E / YiAi Ref. 333657 along a longitudinal axis and defines an operator area, a plurality of ground contact members supporting the frame assembly and including front ground contact members and rear ground contact members, a powertrain assembly supported by the frame assembly and including at least one engine and a transmission operatively coupled to the engine, and an exhaust assembly comprising an exhaust duct fluidly coupled to the engine, a catalyst fluidly coupled to the exhaust duct and configured to receive exhaust gas from the exhaust duct, and a cooling mechanism configured to provide coolant to a portion of the exhaust assembly. In another embodiment, a method for cooling a portion of an exhaust assembly for a utility vehicle engine comprises providing an exhaust duct, fluidly coupling a catalyst to the exhaust duct, directing a fluid to a portion of the exhaust assembly, and lowering the temperature of an exhaust gas flowing through the exhaust assembly after directing a fluid to the portion of the exhaust assembly. In another further embodiment, a utility vehicle comprises a frame assembly extending along a longitudinal axis and defining an operator area, a plurality of ground contact members supporting the frame assembly and including front ground contact members and rear ground contact members, a powertrain assembly supported by the frame assembly and including at least one engine and a transmission operatively coupled to the engine, and an exhaust assembly comprising an exhaust duct fluidly coupled to the engine, a first catalyst fluidly coupled to the exhaust duct and configured to receive exhaust gas from the exhaust duct, and a second catalyst positioned downstream of the first catalyst along the exhaust duct. In another embodiment, a utility vehicle comprises a frame assembly extending along a longitudinal axis and defining an operator area, a plurality of ground contact members supporting the frame assembly and including front ground contact members and rear ground contact members, a powertrain assembly supported by the frame assembly and including at least one engine and a transmission operatively coupled to the engine, and an exhaust assembly comprising an exhaust duct fluidly coupled to the engine, and a catalyst fluidly coupled to the exhaust duct and configured to receive exhaust gas from the exhaust duct, the exhaust duct, engine, and catalyst being positioned side by side along the longitudinal axis. cnfrcnn / zznz / E / YiAi Brief Description of the Figures The aforementioned and other features of this invention, and the manner of achieving them, will become more evident, and the invention itself will be better understood, with reference to the following description of embodiments of the invention taken together with the accompanying figures, where: Figure 1 is a left front perspective view of a utility vehicle of the present description; Figure 2 is a right rear perspective view of the utility vehicle in Figure 1; Figure 3 is a left side view of the utility vehicle in Figure 1; Figure 4 is a right side view of the utility vehicle in Figure 1; Figure 5 is a top view of the utility vehicle in Figure 1; Figure 6 is a front view of the utility vehicle in Figure 1; Figure 7 is a rear view of the utility vehicle in Figure 1; Figure 8A is a top schematic view of the placement of a powertrain assembly of the utility vehicle of Figure 1; Figure 8B is a top view of the utility vehicle of Figure 1 and schematically illustrates a first cnfrcnn / zznz / E / YiAi modality of the powertrain assembly and an exhaust assembly; Figure 8C is a top view of the utility vehicle in Figure 1 and schematically illustrates a second mode of the powertrain assembly and exhaust assembly; Figure 8D is a top view of the utility vehicle in Figure 1 and schematically illustrates a third modality of the powertrain assembly and exhaust assembly; Figure 9 is a left front perspective view of a continuously variable transmission of the powertrain assembly of Figures 8B and 8D; Figure 10 is a top view of the powertrain assembly and exhaust assembly of Figure 8B; Figure 11 is a top view of the powertrain assembly and exhaust assembly of Figure 8D; Figure 12 is a schematic view of the exhaust assembly of the present description, which has a first oxygen sensor; Figure 13 is a schematic view of the exhaust assembly of the present description, which has a second oxygen sensor; Figure 14 is a cross-sectional view of a silencer from the exhaust assembly of Figure 13; Figure 15 is a schematic view of the exhaust assembly of Figure 14, which has a third oxygen sensor; Figure 16 is a right rear perspective view cnfrcnn / zznz / E / YiAi of an alternative mode silencer of the exhaust assembly described herein; Figure 17 is a cross-sectional view of the silencer in Figure 16; Figure 18 is a schematic view of a first cooling mode for the exhaust assembly described herein; Figure 19 is a schematic view of a second cooling mode for the exhaust assembly described herein; Figure 20 is a schematic view of a third cooling mode for the exhaust assembly described herein; Figure 21 is a schematic view of a fourth cooling mode for the exhaust assembly described herein; Figure 22 is a schematic view of a fifth cooling mode for the exhaust assembly described herein; Figure 23 is a schematic view of a sixth cooling mode for the exhaust assembly described herein; Figure 24 is a schematic view of a seventh cooling mode for the exhaust assembly described in cnfrcnn / zznz / E / YiAi herein; Figure 25 is a schematic view of an eighth cooling mode for the exhaust assembly described herein; Figure 26 is a schematic view of a ninth cooling mode for the exhaust assembly described herein; Figure 27 is a schematic view of a tenth cooling mode for the exhaust assembly described herein; Figure 28 is a schematic view of an eleventh cooling mode for the exhaust assembly described herein; Figure 29 is a schematic view of a conventional exhaust duct length that does not use the eleventh cooling mode of Figure 28; Figure 30 is a schematic view of an extended length of the exhaust duct using the eleventh cooling mode of Figure 28; Figure 31 is an additional schematic view of an extended length of the exhaust duct using the eleventh cooling mode of Figure 28; Figure 32 is a rear perspective view of a portion of an engine and alternator from the vehicle in Figure 1; Figure 33 is a rear perspective view of the alternator in Figure 32 and a fan; cnfrcnn / zznz / E / YiAi Figure 34 is an exploded view of the alternator and a fan from Figure 33; Figure 35 is a schematic view of a cooling airflow in a rear direction through a portion of the engine and alternator of Figure 32 and at least a portion of the exhaust assembly described herein; Figure 36 is a top view of the engine and exhaust assembly described herein; Figure 37 is a partially exploded view of a part of the exhaust assembly described herein; Figure 38 is a right-side view of a muffler from the exhaust assembly described herein; Figure 39 is a view of the left side of the muffler in Figure 38; Figure 40 is a top view of the silencer in Figure 36; Figure 41 is a perspective view of the silencer described herein and showing a heat shield for an exhaust gas composition sensor; Figure 42 is a cross-sectional view of the silencer of Figure 41 taken along line 4242 of Figure 41; and Figure 43 is a partially exploded view of the silencer and heat shield of Figure 41. cnfrcnn / zznz / E / YiAi The corresponding reference characters indicate the corresponding parts in the different views. Unless otherwise stated, the figures are to scale. Detailed Description of the Invention The embodiments described below are not intended to be exhaustive, nor to limit the invention to the precise forms described in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may benefit from their teachings. While the present description relates primarily to a utility vehicle, it should be understood that the features described herein may be applicable to any vehicle with one or more ground contact points, including, but not limited to, all-terrain vehicles, motorcycles, snowmobiles, scooters, three-wheeled vehicles, and golf carts. Referring to Figures 1-7, an illustrative embodiment of a utility vehicle 2 is shown. The vehicle 2 is configured for off-road operation. The vehicle 2 includes a plurality of ground contact members 4, illustratively, front wheels 6 and rear wheels 8. In one embodiment, one or more of the ground contact members 4 may be replaced by tracks, such as the Prospector II tracks available from Polaris Industries Inc., headquartered at 2100 Highway 55, Medina, Minnesota 55340, or non-pneumatic wheels, such as those shown in U.S. Patent Nos. 8,176,957 and 8,104,524, the full descriptions of which are expressly incorporated herein by reference. Vehicle 2 further includes a frame assembly 10 supported by ground contact members 4, extending along a longitudinal axis L of vehicle 2 (Figure 8B). The frame assembly 10 includes a lower frame assembly 12 and an upper frame assembly 14 coupled together. The upper frame assembly 14 generally extends above the lower frame assembly 12. The frame assembly 10 supports a rear cargo area 22 and a vehicle body 20, which includes a plurality of body panels, such as a hood. Vehicle 2 also includes an open-air operator area 16, which, for illustrative purposes, includes seats 18 for one or more passengers. As such, the operator area 16 is exposed to the ambient air and is not fully enclosed. Alternatively, Vehicle 2 may include a cab assembly (not shown), such as a roof, front windshield, rear windshield, and doors, to enclose the operator area 16. The upper frame assembly 14 may generally be positioned around the operator area 16 so that seat 18 is at least partially surrounded by the upper frame assembly 14. For illustrative purposes, seat 18 includes an operator seat and a passenger seat; however, seat 18 may also include rear seats for additional passengers or may include only a single seat for carrying the operator. Seat 18 may include a seat base 18a and a seat backrest 18b. Operator area 16 further includes a plurality of operator controls 28, such as a steering wheel, by means of which an operator can provide inputs to operate the vehicle 2. Various operator controls, including the steering assembly, are described in more detail in International Patent Application No. PCT / US13 / 64516, filed on October 11, 2013 (Attorney File No. PLR-15-25448.04P-WO), the full description of which is expressly incorporated by reference herein. With reference still to Figures 1-7, Vehicle 2 includes a rear suspension assembly 24 and a front suspension assembly 26, both supported by the lower frame assembly 12. Additional details of the suspension assemblies 24, 26 can be described in U.S. Patent No. 9,566,858, granted February 14, 2017 (Attorney File No. PLR-15-26601.01P) and in U.S. Patent Application Serial No. 16 / 226,797, filed December 20, 2018 (Attorney File No. PLR-15-28340.05P-US), the full descriptions of which are expressly incorporated by reference in this document. Referring to Figures 8A-8D, Vehicle 2 further includes a powertrain assembly 30 supported by the lower frame assembly 12 and comprising at least one main drive, illustratively an engine 32, a drivetrain that may be configurable or include a shift transmission 36, a continuously variable transmission (CVT) 34, and an air intake assembly 38. The powertrain assembly 30 may be located in different positions within Vehicle 2, as shown by the various transparency representations of the powertrain 30. Although Vehicle 2 is shown illustratively as including the powertrain components listed above, Vehicle 2 is not limited to this and may include any powertrain arrangement.The drive train assembly 30 further includes final drives or differentials, for example, a front drive 39 and a rear drive 37. The rear drive 37 is operatively coupled to the rear ground contact members 8 via half-shafts and, similarly, the front drive 39 is operatively coupled to the front ground contact members 6 via half-shafts. Engine 32 is located behind the operator area 16 and usually behind the seat 18. Although the main drive unit is described as engine 32, the main drive unit can be any type of device configured to provide power to the vehicle 2, such as an electric motor, a fuel-based engine, a hybrid engine, a generator, etc. Engine 32 can be of any size and include any number of cylinders 31, for example, one cylinder, two cylinders, three cylinders, four cylinders, six cylinders, or eight cylinders. The air intake assembly 38 is seamlessly coupled to an intake manifold of engine 32 to supply it with combustion air. Additionally, the CVT 34 and the shift transmission 36 are located at least partially behind the operator area 16 and the seat 18. The CVT 34 is operatively coupled to both the engine 32 and the shift transmission 36. More specifically, the CVT 34 is operatively coupled to the engine 32 via an unlabeled crankshaft of the engine 32 and is operatively coupled to the shift transmission 36 via an unlabeled input shaft of the shift transmission 36. In various configurations, the CVT 34 may be located longitudinally in front of the engine 32 or laterally away from at least a portion of the engine 32. The shift transmission 36 may also be located longitudinally in front of or behind the engine 32 or laterally away from at least a portion of the engine 32. cnfrcnn / zznz / E / YiAi As shown in Figure 9, the CVT 34 includes a housing 50 having an inner part or cover 52 and an outer part or cover 54 detachably coupled together. The CVT housing 50 includes a single air intake port 56 for receiving air to cool the CVT 34 and a single air exhaust port 58 for expelling warm or hot air from the CVT 34. For illustrative purposes, the outer cover 54 includes the air intake port 56, and the inner cover 52 includes the air exhaust port 58. The CVT 34 includes a drive clutch or pulley, a driven clutch or pulley, and a belt extending between them (not shown). In one embodiment of the CVT 34, the belt is a rubber belt; however, in other embodiments, the belt is a steel belt. Because vehicle 2 is configured for off-road applications, the powertrain assembly 30, including an exhaust assembly 40, may have a reduced potential heat rejection length before a catalyst (e.g., catalytic converter) of the exhaust assembly 40, as the powertrain assembly 30 is generally positioned behind at least part of the operator area 16, a higher load utilization coefficient compared to typical on-road passenger vehicle usage profiles, higher specific power (hp / L) engines that may lead to an increase in exhaust gas temperature, a greater potential for higher vibration / mechanical shock loads due to the jumps that vehicle 2 is capable of making, and / or greater exposure to debris (e.g., dust, mud, grass). As such, the exhaust assembly 40 may be configured as described herein in view of the above. Referring again to Figures 8B-8D, vehicle 2 further includes an exhaust assembly 40 seamlessly coupled to the powertrain assembly 30 and, more particularly, seamlessly coupled to the engine 32. The exhaust assembly 40 includes a muffler 42, an exhaust manifold 44, an exhaust pipe 46, and an exhaust outlet 48. For illustrative purposes, the exhaust manifold 44 is coupled to the engine 32 and the exhaust pipe 46 such that the exhaust gases from the engine 32 flow into the exhaust manifold 44 and through the exhaust pipe 46. The exhaust pipe 46 and the outlet 48 are both coupled to the muffler 42, and the exhaust gases in the exhaust pipe 46 flow into the muffler 42 and exit vehicle 2 through the outlet 48. The muffler 42 can be considered a noise damper and is configured to attenuate the sound within the exhaust assembly. 40. The drivetrain assembly 30 and the exhaust assembly 40 can have various configurations. For example, in the embodiment of Figure 8B, the engine 32 is positioned longitudinally behind the air intake assembly 38, and the cylinders 31 of the engine 32 are arranged laterally, generally perpendicular to the longitudinal axis L. In this configuration of the engine 32, the CVT 34 is positioned laterally outside the engine 32 and generally extends parallel to the longitudinal axis L. In one embodiment, the CVT 34 is generally positioned behind a portion of the driver's seat 18 and is to the left of the longitudinal axis L. In other embodiments, the air intake assembly 38 can be positioned anywhere with respect to the engine 32 (e.g., above the engine 32, in front of the engine 32, etc.). Referring again to Figure 8B, the exhaust manifold 44 is positioned longitudinally behind the cylinders 31 and can be located longitudinally between the engine 32 and the muffler 42. An inlet 60 of the muffler 42 can be positioned to the right of the longitudinal axis L, and as such, the exhaust duct 46 curves or bends to the right side of the vehicle 2 to connect with the inlet 60 of the muffler 42. An outlet 62 of the muffler 42 can be positioned on the left side of the longitudinal axis L. The muffler 42 extends laterally between the inlet 60 and the outlet 62 and intersects the longitudinal axis L. Referring now to Figures 8C and 8D, the configurations described therein place engine 32 generally behind CVT 34, such that CVT 34 is longitudinally positioned between seat 18 and engine 32. In this configuration, the cylinders 31 of engine 32 extend longitudinally, and each cylinder may intersect the longitudinal axis L. Figure 8C depicts CVT 34 as a steel-belt CVT, while Figure 8D depicts CVT 34 as a rubber-belt CVT. Additional details of at least the steel belt CVT of Figure 8C can be described in U.S. Patent Application Serial No. 17 / 147,937, filed January 13, 2021 (Attorney File No. PLR-06-28903.02P-US), the full description of which is expressly incorporated herein by reference.For illustrative purposes, the air intake assembly 38 is positioned laterally outside the engine 32 and, while shown on the right side of the longitudinal axis L, the air intake assembly 38 can also be positioned on the left side of the longitudinal axis L. In the configuration of Figures 8C and 8D, the exhaust manifold 44 extends from the engine 32 along the left side of the longitudinal axis L, and the exhaust duct 46 is generally parallel to the longitudinal axis L when it extends between the exhaust manifold 44 and the muffler 42. As such, the inlet 60 of the muffler 42 can be positioned on the left side of the longitudinal axis L, and the outlet 62 of the muffler 42 can be positioned on the right side of the longitudinal axis L. cnfrcnn / zznz / E / YiAi Muffler 42 is positioned behind engine 32 so that engine 32 is longitudinally between muffler 42 and CVT 34. With reference to Figure 10, the embodiment of Figure 8B is shown in greater detail. For illustrative purposes, the exhaust duct 46 may include a first coupling or joint 64 and a second coupling or joint 66. The exhaust duct 46 includes a first elbow 68, a generally linear portion 70, and a second elbow 72; however, the exhaust duct 46 may include any configuration relative to the longitudinal axis L, the exhaust manifold 44, and the muffler 42. The configuration of the exhaust duct 46 does not interfere with the rear drive 37 or any other component supported on the frame assembly 10. As shown in Figure 10, the exhaust manifold 44 may generally be positioned over a portion of the movable transmission 36 and / or the rear drive 37. With reference to Figure 11, the embodiment of Figure 8D is shown in greater detail. For illustrative purposes, the exhaust duct 46 is generally perpendicular to the longitudinal axis L along a linear portion 74, but includes a curved portion 76 to couple with the inlet 60 of the muffler 42. Unlike the embodiment in Figure 10, the exhaust duct 46 in Figure 11 is positioned along the left side of the longitudinal axis L. With reference to Figure 12, exhaust gas composition sensors are included in the exhaust assembly 40 to measure the oxygen and / or other gases within the exhaust gases flowing through the exhaust assembly 40. For illustrative purposes, the exhaust assembly 40 includes at least one exhaust gas composition sensor 78 positioned upstream of the muffler 42. As such, the exhaust gas composition sensor 78 measures the concentration and / or composition of oxygen within the exhaust gases before they flow into the muffler 42. As shown in Figure 12, the exhaust gas composition sensor 78 is positioned downstream of couplings 64 and 66, and no other couplings or gaskets are placed between the exhaust gas composition sensor 78 and at least one part of the muffler 42, such as the catalyst 80.For example, sensor 78 and catalyst 80 can be positioned immediately downstream of coupling 64 but upstream of coupling 66, downstream of both couplings 64 and 66, inside silencer 72, or downstream of silencer 42 (e.g., at the outlet or exhaust pipe 48). In this way, sensor 78 and catalyst 80 can be positioned anywhere along the length or position of the exhaust assembly 40. In the configurations described later in this document, a catalyst 80 can be placed inside the muffler 42 to change the exhaust composition of the exhaust gases before they exit the vehicle 2 through outlet 48. When the catalyst 80 is placed inside the muffler 42, there are no couplings or gaskets between the exhaust gas composition sensor 78 and the catalyst 80. In this way, the exhaust gas composition sensor 78 can function as a pre-catalytic exhaust gas composition sensor.Because gaskets or couplings can periodically leak, introducing fresh air into the exhaust assembly 40, if a gasket or coupling is placed between the exhaust gas composition sensor 78 and the catalyst 80, the control system for the engine 32 may be unable to correct for this added fresh air, potentially resulting in decreased emissions performance from the catalyst 80. Furthermore, the introduction of fresh air results in an inconsistent exhaust gas air volume, leading to inefficiencies and irregularities in the performance of the catalyst 80. Therefore, the modalities described herein do not include a gasket or coupling (e.g., couplings 64, 66) between the exhaust gas composition sensors (e.g., exhaust gas composition sensor 78) and the catalyst 80.It may be evident that the illustrative modalities do not describe any coupling or joint assembled between the cnfrcnn / zznz / E / YiAi catalyst 80 and the exhaust gas composition sensor 78 downstream of the catalyst. If the catalyst 80 is positioned outside the silencer 42, for example, along a length of the exhaust duct 46, the exhaust gas composition sensor 78 is also positioned upstream of the catalyst 80, and gaskets or couplings (e.g., couplings 64, 66) are not placed between the exhaust duct 46, the exhaust gas composition sensor 78, and the catalyst 80. Figure 12 illustrates various examples where the exhaust gas composition sensor 78 and the catalyst 80 can be positioned upstream of the silencer 42. To accommodate this configuration of the catalyst 80 along a length of the exhaust duct 46, the length of the exhaust duct 46 can be extended. In some configurations, the length of the exhaust duct 46 can be extended linearly between the exhaust manifold 44 and the outlet 48 (e.g., see Figure 28); however, in other configurations (e.g.(See Figures 30 and 31), the length of the exhaust duct 46 can be increased by wrapping the exhaust duct 46 around parts of the engine 32, the exhaust manifold 44 and / or the muffler 42. It can be seen, based on the description in this document, that the flow geometry (e.g., the elbows) allows the exhaust gas to be evenly distributed across the face of catalyst 80 to maintain the performance of catalyst 80. Additionally, since the additional catalyst 80 is moved to muffler 42, the reduced sound attenuation volume remains in muffler 42 because sound attenuation does not occur until after the exhaust gas has exited catalyst 80 due to the flow matrix / straightening configuration (e.g., honeycomb) of catalyst 80. Furthermore, at low engine speeds / loads, there may be a reverse flow of ambient air flowing upwards through outlet 48 and into muffler 42, potentially affecting the operation of catalyst 80. Therefore, the position of catalyst 80 relative to outlet 48 can be optimized. As described herein, and with reference to Figures 13 and 14, the catalyst 80 is positioned between the exhaust manifold 44 and the outlet 48. In various embodiments, the catalyst 80 may be positioned within the muffler 42. The muffler 42 may also include a plurality of crosspipes 82 configured to attenuate the sound. For illustrative purposes, the crosspipes 82 include at least a first crosspipe 82a, a second crosspipe 82b, and a third crosspipe 82c; however, any number of crosspipes 82 may be included. In one embodiment, the crosspipe 82c may be integrally formed with the outlet 48. cnfrcnn / zznz / E / YiAi The silencer 42 may include walls, such as baffles or support walls, configured to support cross tubes 82 and further attenuate the sound within the silencer 42. The exhaust gases can flow in the direction of arrows F so that they flow into muffler 42 through exhaust pipe 46 and into catalyst 80. From catalyst 80, the exhaust gases follow arrows F and flow into the first crosspipe 82a. From the first crosspipe 82a, the exhaust gases flow into the second crosspipe 82b and through a length of muffler 42 before flowing into the third crosspipe 82c. The exhaust gases within the third crosspipe 82c exit muffler 42 through outlet 48 to exit vehicle 2. This flow path and the use of crosspipes 82 provide sound attenuation with muffler 42.The exhaust gases flowing between the cross tubes 82 may have a partially turbulent flow; however, as the exhaust gases flow from the muffler 42 through the third cross tube 82c and through the outlet 48, the exhaust gases generally have a laminar or smooth flow. With reference still to Figures 13 and 14, the exhaust assembly 40 may include a second exhaust gas composition sensor 86 positioned downstream of the catalyst 80, such that the second exhaust gas composition sensor 86 is a downstream sensor. The second exhaust gas composition sensor 86 is supported on the silencer 42 and may be positioned inside or outside the silencer 42. For illustrative purposes, the second exhaust gas composition sensor 86 is positioned outside the silencer 42 and is in direct communication with outlet 48 to measure the exhaust gas composition levels of the exhaust gases exiting the catalyst 80.As noted herein, the exhaust gases flowing through outlet 48, and therefore through the second exhaust gas composition sensor 86, may have a more laminar flow relative to the exhaust gases upstream of the catalyst 80. If the exhaust gases were to have turbulent flow at the second exhaust gas composition sensor 86, the measurements from the exhaust gas composition sensor 86 might not be accurate. It can be appreciated that sensor 86 can be used in addition to or instead of sensor 78, and that any exhaust gas composition sensor, either alone or in combination with other sensors, can be positioned anywhere along the length of the exhaust assembly 40 (e.g., upstream of the catalyst 80, upstream of the silencer 42, downstream of the silencer 42, inside outlet 48, etc.). Referring now to Figure 15, the exhaust assembly 40 may include a second exhaust gas composition sensor downstream of the catalyst, shown as sensor 88. Exhaust gas composition sensor 88 is located inside the muffler 42 and can generally be positioned along the flow path (arrows F) between the second and third crosspipes 82b and 82c. Exhaust gas composition sensor 88 may be used instead of or in addition to the upstream exhaust gas composition sensor 78 and / or the second downstream exhaust gas composition sensor 86. Exhaust gas composition sensor 88 provides additional exhaust gas measurements to improve control of engine performance and other factors in an effort to reduce emissions from outlet 48.In other configurations, the sensor 88 can be placed next to the wall 84 and upstream of the flow through the transverse tube 82a. Referring to Figures 16 and 17, an alternative embodiment of the silencer 42' is described. The silencer 42' is fluidly coupled to the exhaust duct 46 and outlet 48. Exhaust gas composition sensors 78, 86 are fluidly coupled to the silencer 42'. The silencer 42' includes the catalyst 80, alternative embodiment cross-pipes 82', and alternative embodiment wall(s) 84'. The exhaust gases are configured cnfrcnn / zznz / E / YiAi to flow into, through, and out of the silencer 42' in the direction of arrows F. The illustrative silencer 42' includes a first pitch baffle 90 and a second pitch baffle 92 positioned adjacent to the respective outer casing walls 94 and 96. At least the second exhaust gas composition sensor 86 may be supported on the silencer 42' via a welded protrusion 98 (e.g., plug welds). The welded protrusion 98 may generally be positioned parallel to an axis 99 of the catalyst 80 (e.g., within a range of approximately 0 degrees to approximately 15 degrees relative to the axis 99). The exhaust gas composition sensor 86 can extend through a portion of the passage baffle 92 and the housing wall 96. For illustrative purposes, the baffle 92 and the wall 96 can be coupled together and form muffler chambers 42' such that the sensor 86 extends through the chambers defined by the baffle 92 and the wall 96.Additionally, the curved or arc-shaped baffle 92 and wall 96 direct the exhaust gas flow to sensor 86, providing an enhanced flow distribution. In this way, the exhaust gas composition sensor 86 utilizes wall 96 and can collect measurements from within an internal chamber of the muffler 42. The pitch baffle 92 is shaped to protrude both inward and outward from wall 96. The exhaust gas composition sensor 86 can monitor the exhaust gases past the catalyst from within the muffler 42 and / or within a portion of wall 96, and more specifically, the exhaust gases can be monitored from within an internal chamber of the muffler 42. Referring now to Figures 18-31, to improve emissions from outlet 48, the temperature of the exhaust assembly 40 is reduced. By reducing the temperature of the exhaust assembly 40, extended stoichiometric operation of the engine is possible, allowing for the proper operation of the catalyst. The increased cooling of the exhaust assembly 40 also reduces its impact as a source of radiant heat during heat absorption conditions, such as engine shutdown 32 immediately after a heavy vehicle load operation. Various methods described herein can be configured to limit the temperature of at least parts of the exhaust assembly 40 and / or the exhaust gas to a temperature limit (e.g., 800-1000 °C) to reduce or prevent damage to the catalyst 80.The temperature limit may be based on exhaust gas temperature values ​​or limits with respect to other parts of the exhaust assembly 40, such as, for example, thermal degradation temperature ranges of respective components of the exhaust assembly 40. Conventional methods for reducing the exhaust assembly temperature 40 and preventing thermal damage to the engine 32 and exhaust components may include fuel enrichment. More specifically, fuel enrichment can be used to reduce exhaust gas temperatures through evaporative cooling. However, catalyst emissions may increase when the engine 32 operates with fuel enrichment, and therefore, catalyst performance may be reduced and emissions at outlet 48 may increase. As described herein with regard to Figures 18-31, fuel enrichment is avoided if exhaust gas cooling can be provided by alternative methods. In the embodiment shown in Figure 18, vehicle overflow air (i.e., air flowing over and around vehicle 2), shown as arrows A, can be used to cool the exhaust assembly 40. By redirecting vehicle overflow air A through the exhaust assembly 40, the convective heat rejection of the exhaust assembly 40 is increased, thereby reducing the exhaust gas temperatures. The overflow air can be redirected through a portion of vehicle 2 via certain body parts 20, such as body panels configured as baffles and / or ducts (shown schematically in 95), and / or parts of the frame assembly 10 that can also be configured as baffles 95. The ducts or baffles 95 can be positioned anywhere along the longitudinal length of vehicle 2.As described herein, by reducing the exhaust gas temperature, stoichiometric engine operation can occur at higher engine speeds and loads while reducing vehicle emissions 2, allowing for proper operation of the catalyst, thereby reducing emissions at outlet 48. The vehicle A passage air rate increases with engine speed and load, and therefore increased cooling of the exhaust assembly 40 occurs when cooling is most needed. In the embodiment of Figure 19, convective cooling is provided to the exhaust assembly 40 by means of the airflow (arrows 104) passing through a radiator 100 of the vehicle 2. In one embodiment, the radiator 100 is the primary radiator of the engine 32; however, in other embodiments, the radiator 100 may be a secondary radiator provided within the primary cooling assembly for the engine 32. The radiator 100 may include ducts 102 fluidly coupled to the engine 32 to carry coolant to and from the engine 32. The use of airflow through the radiator 100, which is redirected to the exhaust assembly 40, provides cooling to the exhaust assembly 40 either through the vehicle's piston effect or by means of an electric fan for the radiator 100 (located adjacent to the radiator 100). In this way, the convective heat rejection of the exhaust assembly 40 reduces the exhaust gas temperatures.In the case of radiator airflow caused by the dynamic intake effect due to vehicle speed, the airflow naturally increases with engine speed / load due to the increased vehicle speed, and therefore the increase in exhaust cooling occurs when cooling is most needed. In the embodiment shown in Figure 20, convective cooling is provided to the exhaust assembly 40 by the airflow (arrows 106) from a fan 108. The fan 108 may be an electronically controlled fan. Using the fan 108 to provide airflow through the exhaust assembly 40 provides increased convective heat rejection from the exhaust assembly 40, thus reducing exhaust gas temperatures. The fan 108 may be controlled by an engine control unit or module (not shown) and may be operated only under high engine load / speed conditions when increased cooling of the exhaust assembly 40 is desired and also when additional electrical charging capacity is available from the charging system (not shown).The cnfrcnn / zznz / E / YiAi fan 108 can also be used during low vehicle speed conditions, when the vehicle 2 is stationary and / or when the engine 32 is switched off, to extract heat from the exhaust assembly 40. In one embodiment, the fan 108 can be positioned next to the hottest sections of the exhaust assembly 40. In the embodiment shown in Figure 21, convective cooling is provided to the exhaust assembly 40 via the airflow (arrows 110) from the exhaust port / outlet 58 of the CVT 34. For example, the opening of the outlet port 58 can be oriented so that the exhaust air flows directly from the CVT 34 into portions of the exhaust assembly 40. Alternatively, ducts, baffles, or a similar mechanism can be used to further direct the exhaust air from the CVT into the exhaust assembly 40. By redirecting the airflow from the CVT 34 through portions of the exhaust assembly 40, greater convective heat rejection from the exhaust assembly 40 is achieved, thus reducing the exhaust gas temperatures of the exhaust assembly. The airflow from the CVT 34 can naturally increase with engine speed / load due to the higher clutch rotational speed (e.g.,, rotational speed of a first and / or second pulley of the CVT 34), thus providing greater cooling of the exhaust system when increased cooling is desired. cnfrcnn / zznz / E / YiAi In the embodiment of Figure 22, convective cooling is provided to the exhaust assembly 40 via airflow (arrows 112) from a cooler 114. In one embodiment, the cooler 114 may be a transmission cooler of the sliding transmission 36. By redirecting the airflow that has passed through the cooler 114 through the exhaust assembly 40, whether the airflow is due to the dynamic intake effect caused by vehicle speed or by a fan (not shown) (e.g., an electric fan), increased convective heat rejection from the exhaust assembly 40 is achieved to reduce the exhaust gas temperature. The cooler 114 may be supported on a rear portion 118 of the lower frame assembly 12 (Figure 23) and positioned so that the air exiting the cooler 114 flows directly through a portion of the exhaust assembly 40.When the airflow to cooler 114 is caused by the dynamic intake effect due to vehicle speed, the airflow can naturally increase with engine speed / load due to the increased vehicle speed, thus providing greater cooling of the exhaust assembly 40 when increased cooling is desired. Cooler 114 can be an air / liquid cooler or a liquid / liquid cooler. In the embodiment of Figure 23, convective cooling is provided to the exhaust assembly 40 by the airflow (arrows 119) through the wheel wells 116 of the rear ground contact members 8 at the rear 118 of the lower frame assembly 12. More specifically, the turbulent air present in the wheel wells 116 is redirected to flow over a portion of the exhaust assembly 40. By redirecting this turbulent airflow in the wheel wells 116 through the exhaust assembly 40, increased convective heat rejection from the exhaust assembly 40 is provided to reduce the exhaust gas temperatures.The turbulent airflow through the wheel wells 116 will naturally increase with engine speed / load due to the increased rotation of the rear ground contact members 8, thus providing cooling to the exhaust assembly 40 when cooling is most needed. The air in the wheel wells 116 can be directed towards the exhaust assembly 40 by a body part 20 and / or a frame assembly part 10 configured as a baffle panel, duct, or other mechanism to direct the air inwards towards the exhaust assembly 40. In the embodiment of Figure 24, convective cooling is provided to the exhaust assembly 40 by the use of a close-coupled catalyst or pre-catalyst 122 to increase the convective heat rejection of the exhaust assembly 40 and reduce the exotherm experienced in the catalyst 80 downstream of the catalyst 122. More particularly, the catalyst 122 is positioned upstream of the catalyst 80 and may be located intermediate between an exhaust manifold 44 and a catalyst 80. As such, the catalyst 122 may be supported in the exhaust duct 46 or may be positioned upstream of the catalyst 80 within the muffler 42. The catalyst 122 creates an exothermic effect that increases the exhaust gas temperatures at the beginning of the flow path 120 through the exhaust assembly 40, thereby increasing the delta T component of the heat rejection. Delta T defines the temperature difference between the hot exhaust gas and the cooling medium or fluid (e.g., ambient air). The heat transfer rate (Q) can be expressed as Q = m * Cp * dT, where m = mass flow rate of the cooling fluid (e.g., air flowing through the exhaust assembly 40), Cp = specific heat capacity of the cooling fluid (e.g., water has a higher specific heat capacity than air, so water is more effective for cooling), and dT = the difference between the temperature difference of the surface being cooled (exhaust system surface) and the temperature of the cooling fluid. It can be seen that the catalyst 122 is generally positioned next to the engine 32 and the exhaust manifold 44, such that the exotherm produced there occurs as soon as possible in the exhaust assembly 40. However, as shown in Figure 24, the catalyst 122 also facilitates greater heat transfer from the exhaust assembly 40 upstream of the catalyst 80 when positioned along any length of the exhaust duct 46. In various embodiments, the catalyst 122 can be positioned in the muffler 42 with the catalyst 80, such that the catalysts 122, 80 are placed in series within the muffler 42, or the catalyst 80 can be a multi-chamber catalyst within the muffler 42 comprising a plurality of catalyst parts in series with each other. Additionally, catalyst 122 can partially clean the exhaust gas to reduce emissions as the exhaust gases continue to flow through the downstream portion of exhaust assembly 40. This partial cleaning of the exhaust gas leads to reduced exothermic activity in catalyst 80, and therefore catalyst 80 does not experience as much heat during the operation of exhaust assembly 40. Catalyst 122 can be configured to only partially clean the exhaust gas, so that it does not experience a full exothermic reaction. Catalyst 122 can have a honeycomb configuration with a lower cell density than catalyst 80. Furthermore, catalyst 122 can be the same size as or smaller than catalyst 80 and have a large diameter-to-length ratio to make it less likely to create exhaust flow restriction.It can be seen that the catalyst 122 not only reduces the temperature experienced by the exhaust assembly 40, but also reduces emissions more quickly after the engine 32 starts operating (e.g., compared to an exhaust system without a catalyst 122) because it reaches the appropriate operating temperature faster since it is located closer to the engine 32. In the embodiment of Figure 25, cooling is provided to the exhaust assembly 40 using a water jacket or cooling jacket 124 surrounding a portion of the exhaust assembly 40 to increase heat rejection from the exhaust gas at the beginning of the flow path (e.g., before the catalyst 80). The cooling jacket 124 includes at least one channel 126 configured to receive cold water or another coolant / fluid (e.g., glycol) to reduce the temperature of a portion of the exhaust assembly 40 (e.g., a portion of the exhaust duct 46 upstream of the catalyst 80). Providing a cooling jacket 124 around a portion of the exhaust duct 46 increases heat extraction from the exhaust gas.However, the cooling jacket 124 may provide too much heat rejection for the engine cooling assembly 32 cnfrcnn / zznz / E / YiAi to handle, and as such, an additional cooling circuit may be required to better manage the cooling of the exhaust assembly 40 and the engine 32. The use of a separate circuit may allow the cooling to be optimized with respect to coolant flow rate, temperature thresholds, etc., such that the cooling jacket 124 removes only a target amount of heat and / or is only used during high engine load / speed conditions when increased cooling is desired. In the embodiment of Figure 26, cooling is provided to the exhaust assembly 40 by means of a cooling jacket 128 that surrounds a portion of the exhaust assembly 40 to increase heat rejection of the exhaust gas at the beginning of the flow path (e.g., upstream of and / or adjacent to the exhaust manifold 44). The cooling jacket 128 includes at least one channel 129 configured to circulate cold water or another coolant / fluid to reduce the temperature of a portion of the exhaust assembly 40 (e.g., a portion of the exhaust manifold 44 adjacent to the engine 32). The cooling jacket 128 may be integrated into the exhaust manifold 44 or may be separate from it and, for example, may define an extended portion of the exhaust port of the engine 32. It can be seen that the exhaust manifold 44 is coupled to the exhaust port(s) of the engine 32.The exhaust port of engine 32 is typically flush with the cylinder block of cylinder 31; however, in the embodiment of Figure 26, the exhaust port of engine 32 can be extended to provide more surface area for the cooling jacket 128. The use of a cooling jacket 128 on the exhaust port of engine 32 and / or on the exhaust manifold 44 creates more cooling jacket area along the exhaust flow path to increase heat extraction from the exhaust gas. Additionally, the cooling jacket 128 attenuates post-cylinder oxidation exotherm, further reducing downstream exhaust gas temperatures. In the embodiment of Figure 27, cooling is provided to the exhaust assembly 40 by means of a cooling jacket 130 that surrounds a portion of the exhaust assembly 40 to increase heat rejection of the exhaust gas at the beginning of the flow path. The cooling jacket 130 includes at least one channel 132 configured to receive chilled water or another coolant / fluid to reduce the temperature of a portion of the exhaust assembly 40 (e.g., a portion of the exhaust duct 46). The cooling jacket 130 is fluidly coupled to a cooling circuit 134 that includes a heater 136 for vehicle 2. More particularly, the heater 136 can be used to heat the cab of vehicle 2 (e.g., when the operator area 16 is enclosed) by receiving the heat rejected from the exhaust assembly 40 via the water / fluid that is heated after cooling the exhaust duct 46. The use of the cooling jacket 130 may result in excessive heat rejection for the engine cooling assembly 32 (e.g., radiators 100, 138), and therefore the cooling circuit 134 may be used. The use of the separate circuit 134 allows for optimization of cooling with respect to coolant flow rate, temperature thresholds, etc., so that only a target amount of heat is extracted from the exhaust assembly 40 and / or only during high engine speeds / loads when cooling is most required. The cooling circuit 134 may be used as a heat source for the heater 136 instead of the heater 136 relying on the engine cooling assembly 32 to provide cabin heat.The cooling circuit 134 can provide improved heating of the operator area 16 at low engine speeds / loads, reduced warm-up time after the engine 32 starts operating, or both compared to a cab heating system that uses only an engine cooling assembly 32. With regard to the configurations in Figures 25-27, the engine cooling assembly may include a secondary radiator or other heat exchanger 138 (in combination with or instead of the radiator 100 of Figure 19) fluidly coupled to the water jackets 124, 128, and 130. The secondary radiator 138 may be used because the main engine radiator 32 may not provide sufficient cooling for the coolant flowing through the water jackets 124, 128, and 130. The secondary radiator 138 may be positioned anywhere on the vehicle 2. For example, the secondary radiator 138 may be positioned at the front of the vehicle 2 to experience fresh ambient air without disturbance. It can be seen that the water jackets 124, 128, and 130 may be used individually or in any combination with each other. In the configuration shown in Figures 28-31, the length of the exhaust assembly 40 (e.g., exhaust duct 46) can be extended upstream of the catalyst 80 to increase heat rejection of the exhaust gas before it enters the catalyst 80. Extending the length of the exhaust duct 46 increases the convective heat rejection of the exhaust assembly 40 by allowing more heat transfer time and surface area. In some examples, extending the length of the exhaust duct 46 can also allow for exhaust tuning, which can aid in torque curve development. As best shown in Figures 29-31, the length of the exhaust duct 46 can be increased in a plurality of configurations, and, illustratively, the length of the exhaust duct 46 is increased by wrapping the exhaust duct 46 around various components of the powertrain assembly 30 and / or exhaust assembly 40. More particularly, due to the compact arrangement of the vehicle 2 and the many components supported on the lower frame assembly 12 next to the engine 32, it may be necessary to extend the length of the exhaust duct 46 in a position next to the engine 32 to avoid interference with other components. For illustrative purposes, as shown in Figure 30, and in comparison with the length of exhaust duct 46 shown in Figure 29, the length of exhaust duct 46 can be extended by wrapping it around the engine 32 and the muffler 42, so that the exhaust duct 46 is positioned longitudinally between the engine 32 and the muffler 42. In this way, the exhaust duct 46 can begin at the exhaust manifold 44 on one side of the longitudinal axis L and terminate at the muffler 42 along a second side of the longitudinal axis L. Additionally, as shown in Figure 31, the length of exhaust duct 46 can be extended by wrapping it around the muffler 42, so that the catalyst 80 is positioned longitudinally between the engine 32 and the exhaust duct 46.In this way, the exhaust duct 46 can start at the exhaust manifold cnfrcnn / zznz / E / YiAi on a first side of the longitudinal axis L and end at the catalyst 80 along a second side of the longitudinal axis L. The embodiments of figures 30 and 31 extend the length of the exhaust duct 46 to improve the heat rejection of the exhaust assembly 40 upstream of the catalyst 80. In the embodiment of figures 32-35, cooling of the exhaust assembly 40 is provided by a fan 150 mounted on an alternator 152 of the engine 32. The alternator 152 is operatively coupled to the engine 32 and the fan 150 is detachably coupled to the alternator 152 with fasteners 154 (figure 34). The fan 150 can be protected by a cover 156. In operation, when air flows (shown by arrows 158) through the vehicle 2 in a rearward direction, the air flows over the engine 32 and through the fan 150, which directs the air rearward toward the exhaust assembly 40. More specifically, the air flowing toward the rear of the vehicle 2 is drawn from under the intake manifold of the engine 32, by the alternator 152, through the fan 150, and directed to parts of the exhaust assembly 40 such as vibration isolators (e.g., isolator 160) and the exhaust gas composition sensor pre-catalyst 78.In this way, the airflow in the exhaust assembly 40 provides convective cooling and allows heated air to exit the vehicle 2 at its rear. This airflow is also beneficial to the alternator 152, as heat is removed from the alternator 152 when the air flows to the rear of the vehicle 2. Although Figures 32-35 include the alternator 152, it can be seen that the same cooling effect for the exhaust assembly 40 can be achieved by other components of the vehicle 2, such as any belt-driven component of the powertrain assembly 30. With respect to any of the embodiments in Figures 18-35, fins or other features (shown schematically as 140 in Figure 26) may be provided on the exhaust duct 46 to increase its surface area. By increasing the surface area of ​​the exhaust duct 46, heat transfer from the exhaust assembly 40 upstream of the catalyst 80 can be improved. It can be seen that any of the cooling modes in Figures 18-35 can be used individually or in combination with any other cooling mode, depending on the configuration and parameters of the vehicle 2, powertrain assembly 30, and exhaust assembly 40. Additionally, it may be evident from the modes in Figures 18-35 that a minimum thermal shield and / or cover is illustrated along the length of the exhaust duct 46 to allow for greater heat transfer away from the exhaust duct 46 before reaching the catalyst 80. Furthermore, with any of the modes described herein, it may be desirable to increase the flow rate of the cooling medium or fluid (e.g., air, water, coolant, etc.) to increase heat transfer from the exhaust assembly 40.The coolant can be supplied at any position along the length of the exhaust assembly 40 upstream of the catalyst 80. Thus, the descriptions in Figures 18-35 herein, in combination with minimal heat shielding / covering and methods for increasing the coolant flow rate, improve the cooling of the exhaust assembly 40. This can enhance the catalyst's performance at high engine speeds / loads, thereby reducing emissions at outlet 48 compared to exhaust assemblies without the exhaust cooling systems described above. More specifically, and as is apparent from any of the configurations in Figures 18-35, alone or in combination, exhaust temperatures are affected by the heat shield, airflow, exhaust duct length, calibration parameters, and other factors.The benefits of any cooling method in Figures 18-35 can improve cooling in various parts of the exhaust assembly by 40 to 46 degrees C. cnfrcnn / zznz / E / YiAi With reference now to Figures 36 and 37, an alternative configuration of the exhaust duct 46 as duct 46' is shown. The exhaust duct 46' includes a first duct part 170 fluidly coupled to the exhaust manifold 44 and a second duct part 172 fluidly coupled to the muffler 42. A flexible bellows element 174 also defines a portion of the exhaust duct 46' and, for illustrative purposes, is positioned between the first and second duct parts 170, 172 such that the bellows element 174 is downstream of the first duct part 170 and the engine 32, but upstream of the second duct part 172, muffler 42, and exhaust gas composition sensors 78, 86.In one embodiment, the bellows element 174 can be welded to first and / or second duct sections 170, 172; however, as shown in Figure 37, the bellows element 174 can be detachably coupled to at least the second duct section 172 with a detachable coupler, such as a clamp 176. The bellows element 174 allows flexibility along the exhaust gas flow path while also maintaining exhaust gas flow. More specifically, due to its placement and configuration, the bellows element 174 is configured to flex or move with the engine movement 32 rather than transferring forward / backward forces. In one embodiment, the bellows element 174 comprises a plurality of layers, such as an interlocking metal layer, a thin metal bellows layer, and an outer woven material, which allow the bellows element 174 to be compressed and move with the movement of the motor 32. As shown in Figure 36, bellows element 174 is positioned longitudinally behind engine 32 and longitudinally in front of muffler 42. Since engine 32 can be positioned behind seat 18 in various configurations, bellows element 174 can also be positioned behind seat 18. Depending on the orientation of engine 32 within vehicle 2, a crankshaft axis CSA can extend in a generally longitudinal direction of vehicle 2, while a flow axis of bellows element 174, shown as BEA, can generally be perpendicular to the crankshaft axis CSA. More specifically, the bellows element axis BEA can be positioned at approximately 87–93 degrees to the crankshaft axis CSA. In various configurations, the bellows element 174 is placed within the side width of the engine 32 and / or silencer 42 and can be centered along the side width of the silencer 42 and / or engine 32. With reference now to Figures 38-40, an inlet pipe 180 (which may be generally defined as part of the exhaust duct 46, 46' and may be composed of first and second duct parts 170, 172 (Figures 36 and 37)) and an outlet pipe 48 from the muffler 42 may be deflected or angled and out of plane from the centerlines of the muffler 42. Having the inlet pipe 180 and / or the outlet pipe 48 deflected from the muffler 42 allows for tighter packing of components adjacent to the muffler 42. In this way, the packing of the exhaust assembly 40 allows space available for other vehicle components 2. In one embodiment, an inlet shaft IA of the inlet pipe 180 can be angled less than 90 degrees from a silencer width or side shaft MWA which allows for tighter packing where the inlet pipe enters the silencer 42.As shown in at least Figures 13-15, the cross tubes 82 can be parallel to the width axis MWA of the muffler such that the inlet pipe 180 is also at an angle of less than 90 degrees to the axis of the cross tubes 82. As shown in Figure 40, the inlet axis IA can be angled relative to a longitudinal axis MLA of the muffler. Furthermore, the inlet axis IA is angled relative to a vertical axis V of the muffler 42 and, in one embodiment, at an angle of 45 degrees or less to the vertical axis V. Still referring to figures 38-40, an outlet axis OA of outlet pipe 48 is also angled relative to the vertical axis V and, in one embodiment, at an angle of approximately 25-65 degrees relative to the vertical axis V. Additionally, the outlet axis OA is at an angle of less than cnfrcnn / zznz / E / YiAi degrees relative to the longitudinal axis MLA of the silencer and less than 90 degrees relative to the width axis MWA of the silencer. As shown in Figures 41-43, the muffler 42 may include a heat shield 162 positioned adjacent to the exhaust gas composition sensor 86. The exhaust gas composition sensor 86 is a post-catalytic sensor and is generally positioned adjacent to the outlet pipe 48. As such, in one embodiment, the heat shield 162 may be positioned generally adjacent to the outlet pipe 48. Illustratively, the heat shield 162 is attached to a wall of the muffler 42 (e.g., wall 96 (Figure 16)); however, the heat shield 162 may be at least partially attached to a portion of the sensor 86, attached to a portion of the vehicle chassis 2, or attached to any other component of vehicle 2 in a position that protects the sensor 86 from radiant heat.For illustrative purposes, the heat shield 162 is mounted on the silencer 42 and at least part of the heat shield 162 is separated from the silencer 42 by an offset distance or air gap 164. The air gap 164 can have a distance of approximately 1-7 mm. The air gap 164 can be defined by tabs 166 of the heat shield 162 extending from a central body 168 of the heat shield 162. The tabs 166 are angled relative to the central body 168 and contact the silencer 42 such that the central body 168 is maintained at the offset distance of the air gap 164 relative to the tabs 166 and the silencer 42. During operation of the exhaust assembly 40, the heat shield 162 and the air gap 164 protect the sensor 86 from heat radiated from the silencer 42 that would otherwise be directed towards the sensor 86. Additional details of Vehicle 2 and / or the powertrain assembly may be described in U.S. Patent Application Serial No. 15 / 388,436, filed December 22, 2016 (Attorney File No. PLR-1527200.OOP); U.S. Patent Application Serial No. 15 / 388,106, filed December 22, 2016 (Attorney File No. PLR-06-27992.OOP); and U.S. Patent Application Serial No. 16 / 238,991, filed January 3, 2019 (Attorney File No. PLR-1528340.04P), the full descriptions of which are expressly incorporated herein by reference. The following clauses illustrate subject matter described in this document. Clause 1. A utility vehicle comprising a frame assembly extending along a longitudinal axis and defining an operator area; a plurality of ground contact members supporting the frame assembly and including front ground contact members and rear ground contact members; a powertrain assembly supported by the frame assembly and including at least one engine and a transmission operatively coupled to the engine; and an exhaust assembly comprising: an exhaust duct fluidly coupled to the engine; a catalyst fluidly coupled to the exhaust duct and configured to receive exhaust gas from the exhaust duct; and a cooling mechanism configured to provide coolant to a portion of the exhaust assembly. Clause 2. The utility vehicle of clause 1, wherein the cooling mechanism defines a deflection mechanism configured to direct the passage air through a portion of the utility vehicle and into the exhaust assembly Clause 3. The utility vehicle of clause 1, wherein the cooling mechanism defines a radiator configured to provide coolant to the engine. Clause 4. The utility vehicle of clause 1, where the cooling mechanism defines a fan. Clause 5. The utility vehicle of clause 1, wherein the cooling mechanism defines a transmission outlet port. Clause 6. The utility vehicle of clause 1, wherein the cooling mechanism defines a refrigerator configured to provide coolant to the transmission. Clause 7. The utility vehicle of clause 1, wherein the cooling mechanism defines a deflection mechanism placed in a recess for the wheels of the rear ground contact members. Clause 8. The utility vehicle of clause 1, where the cooling mechanism defines a water jacket. Clause 9. The utility vehicle of clause 8, wherein the water jacket is positioned along a portion of the exhaust duct. Clause 10. The utility vehicle of clause 8, wherein the water jacket is fluidly coupled to a cooling circuit, and the cooling circuit includes a heater for the operator area. Clause 11. The utility vehicle of clause 10, wherein the cooling circuit defines a first cooling circuit and the second cooling circuit is operatively coupled to the engine and separate from the first cooling circuit. Clause 12. The utility vehicle of clause 10, wherein the exhaust assembly further comprises an exhaust manifold fluidly coupled to the engine and exhaust duct, and the water jacket is positioned along a portion of the exhaust manifold. Clause 13. A method for cooling a portion of an exhaust assembly for a utility vehicle engine, comprising: providing an exhaust duct; fluidly coupling a catalyst to the exhaust duct; directing a fluid to a portion of the exhaust assembly; and lowering the temperature of an exhaust gas flowing through the exhaust assembly after directing a fluid to the portion of the exhaust assembly. Clause 14. The method of clause 13, wherein directing the fluid includes directing the airflow through a portion of the utility vehicle and into the exhaust assembly portion. Clause 15. The method of clause 13, wherein directing the fluid includes directing the air through a radiator fluidly coupled to the engine and into the exhaust assembly portion. Clause 16. The method of clause 13, wherein directing the fluid includes directing the air through a fan and towards the exhaust assembly portion. Clause 17. The method of clause 13, further comprising providing a transmission operatively coupled to the engine, and wherein directing the fluid includes expelling the air from the transmission and directing the air towards the exhaust assembly portion. Clause 18. The method of clause 13, wherein directing the fluid includes flowing the fluid through a water jacket placed in the exhaust assembly portion. Clause 19. The method of clause 18, comprising cnfrcnn / zznz / E / YiAi further placing the water jacket along a portion of the exhaust duct. Clause 20. The method of clause 18, further comprising providing an exhaust manifold fluidly coupled to the engine and exhaust duct and placing the water jacket along a portion of the exhaust manifold. Clause 21. A utility vehicle, comprising a frame assembly extending along a longitudinal axis and defining an operator area; a plurality of ground contact members supporting the frame assembly and including front ground contact members and rear ground contact members; a powertrain assembly supported by the frame assembly and including at least one engine and a transmission operatively coupled to the engine; and an exhaust assembly comprising: an exhaust duct fluidly coupled to the engine; a first catalyst fluidly coupled to the exhaust duct and configured to receive exhaust gas from the exhaust duct; and a second catalyst positioned downstream of the first catalyst along the exhaust duct. Clause 22. The utility vehicle of clause 21, wherein the second catalyst is placed inside a muffler of the exhaust assembly. Clause 23. The utility vehicle of clause 21, in cnfrcnn / zznz / E / YiAi where the first catalyst is of equal or smaller size than the second catalyst. Clause 24. A utility vehicle, comprising: a frame assembly extending along a longitudinal axis and defining an operator area; a plurality of ground contact members supporting the frame assembly and including front ground contact members and rear ground contact members; a powertrain assembly supported by the frame assembly and including at least one engine and a transmission operatively coupled to the engine; and an exhaust assembly comprising: an exhaust duct fluidly coupled to the engine; and a catalyst fluidly coupled to the exhaust duct and configured to receive exhaust gas from the exhaust duct, the exhaust duct, engine, and catalyst being positioned side by side along the longitudinal axis. Clause 25. The utility vehicle of clause 24, wherein the exhaust duct is positioned longitudinally between the engine and the catalyst. Clause 26. The utility vehicle of clause 24, wherein the catalyst is positioned longitudinally between the engine and the exhaust duct. Clause 27. The utility vehicle of clause 24, wherein the exhaust assembly further comprises an exhaust gas composition sensor supported by the exhaust duct, and the exhaust is continuous between the exhaust sensor and the catalyst. Clause 28. The utility vehicle of clause 27, wherein the sensor is located downstream of the catalyst. Clause 29. The utility vehicle of clause 28, wherein the exhaust assembly further comprises a heat shield positioned adjacent to the sensor. Clause 30. The utility vehicle of clause 29, wherein at least part of the heat shield is separated from the silencer by an air gap. Clause 31. The utility vehicle of clause 27, wherein the exhaust assembly further comprises a silencer, and the exhaust duct includes a bellows, and the bellows is positioned within the utility vehicle longitudinally between the silencer and the engine. Although this invention has been described as having an illustrative design, the present invention may be further modified within the spirit and scope of this description. Therefore, this application is intended to cover any variation, use, or adaptation of the invention using its general principles. Furthermore, this application is intended to cover deviations from the present description that fall within the known or customary practice of the art to which this invention belongs. cnfrcnn / zznz / E / YiAi It is noted that with regard to this date, the method known to the applicant to carry out the aforementioned invention is the one that is clear from the description of the invention.

Claims

1. A utility vehicle, characterized in that it comprises: a frame assembly extending along a longitudinal axis and defining an operator area; a plurality of ground contact members supporting the frame assembly and including front ground contact members and rear ground contact members; a powertrain assembly supported by the frame assembly and including at least one engine and a transmission operatively coupled to the engine; and an exhaust assembly comprising: an exhaust duct fluidly coupled to the engine; a catalyst fluidly coupled to the exhaust duct and configured to receive exhaust gas from the exhaust duct; and a cooling mechanism configured to provide coolant to a portion of the exhaust assembly.

2. The utility vehicle according to claim 1, characterized in that the cooling mechanism defines a deflection mechanism configured to direct the passage air through a part of the utility vehicle and towards the exhaust assembly.

3. The utility vehicle according to claim 1, characterized in that the cooling mechanism comprises a radiator configured to provide coolant to the engine.

4. The utility vehicle according to claim 1, characterized in that the cooling mechanism comprises a fan.

5. The utility vehicle according to claim 1, characterized in that the cooling mechanism comprises a transmission outlet port.

6. The utility vehicle according to claim 1, characterized in that the cooling mechanism comprises a refrigerator configured to provide coolant to the transmission.

7. The utility vehicle according to claim 1, characterized in that the cooling mechanism comprises a deflection mechanism placed in a recess for the wheels of the rear ground contact members.

8. The utility vehicle according to claim 1, characterized in that the cooling mechanism comprises a cooling jacket. cnfrcnn / zznz / E / YiAi 9. The utility vehicle according to claim 8, characterized in that the cooling jacket is positioned along a portion of the exhaust duct.

10. The utility vehicle according to claim 8, characterized in that the cooling jacket is fluidly coupled to a cooling circuit, and the cooling circuit includes a heater for the operator area.

11. The utility vehicle according to claim 10, characterized in that the cooling circuit comprises a first cooling circuit and the second cooling circuit is operatively coupled to the engine and different from the first cooling circuit.

12. The utility vehicle according to claim 10, characterized in that the exhaust assembly further comprises an exhaust manifold fluidly coupled to the engine and the exhaust duct, and the cooling jacket is positioned along a portion of the exhaust manifold.

13. The utility vehicle according to claim 1, characterized in that the catalyst comprises a first catalyst fluidly coupled to the exhaust duct and configured to receive exhaust gas from the exhaust duct, and the catalyst further comprises a second catalyst positioned downstream of the first catalyst along the exhaust duct.

14. The utility vehicle according to claim 13, characterized in that the second catalyst is placed inside a silencer of the exhaust assembly.

15. The utility vehicle according to claim 13, characterized in that the first catalyst is of the same size as or smaller than the second catalyst.

16. A method for cooling a portion of an exhaust assembly for a utility vehicle engine, characterized in that it comprises: providing an exhaust duct; fluidly coupling a catalyst to the exhaust duct; directing a fluid to a portion of the exhaust assembly; and lowering the temperature of an exhaust gas flowing through the exhaust assembly after directing a fluid to the portion of the exhaust assembly.

17. The method according to claim 16, characterized in that directing the fluid includes directing the airflow through a part of the utility vehicle and into the exhaust assembly.

18. The method according to claim 16, characterized in that directing the fluid includes directing the air through a radiator fluidly coupled to the engine and cnfrcnn / zznz / E / YiAi towards the exhaust assembly portion.

19. The method according to claim 16, characterized in that directing the fluid includes directing the air through a fan and towards the exhaust assembly portion.

20. The method according to claim 16, characterized in that it further comprises providing a transmission operatively coupled to the engine, and wherein directing the fluid includes expelling the air from the transmission and directing the air towards the exhaust assembly portion.

21. The method according to claim 16, characterized in that directing the fluid includes flowing the fluid through a cooling jacket located in the exhaust assembly portion.

22. The method according to claim 21, characterized in that it further comprises providing an exhaust manifold fluidly coupled to the engine and the exhaust duct and placing the water jacket along a portion of the exhaust manifold.

23. A utility vehicle, characterized in that it comprises: a frame assembly extending along a longitudinal axis and defining an operator area; a plurality of ground contact members supporting the frame assembly and including front ground contact members and rear ground contact members; a powertrain assembly supported by the frame assembly and including at least one engine and a transmission operatively coupled to the engine; and an exhaust assembly comprising: an exhaust duct fluidly coupled to the engine; and a catalyst fluidly coupled to the exhaust duct and configured to receive exhaust gas from the exhaust duct, the exhaust duct, engine, and catalyst being positioned adjacent to each other along the longitudinal axis.

24. The utility vehicle according to claim 23, characterized in that the exhaust duct is positioned longitudinally between the engine and the catalyst 25. The utility vehicle according to claim 23, characterized in that the catalyst is positioned longitudinally between the engine and the exhaust duct.

26. The utility vehicle according to claim 23, characterized in that the exhaust assembly further comprises an exhaust gas composition sensor supported by the exhaust duct, and the exhaust is continuous between the exhaust sensor and the catalyst.

27. The utility vehicle according to claim 26, characterized in that the sensor is located downstream of the catalyst.

28. The utility vehicle according to claim 27, characterized in that the exhaust assembly further comprises a heat shield positioned adjacent to the sensor 29. The utility vehicle according to claim 28, characterized in that at least a portion of the heat shield is separated from the silencer by an air gap 30. The utility vehicle according to claim 23, characterized in that the exhaust assembly further comprises a silencer, and the exhaust duct includes a bellows, and the bellows is positioned within the utility vehicle longitudinally between the silencer and the engine.

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