A post-treatment system includes two SCRs, a second SCR is connected to a booster in parallel, and a three-way valve is arranged before the second SCR and the booster, such that whether an exhaust gas flows through the second SCR or the booster is controlled by means of controlling the three-way valve. In the case of a low temperature, the three-way valve is controlled to close a branch of the booster, such that the exhaust gas flows through the second SCR and a first SCR that are connected in series, thereby reducing the energy loss caused by the exhaust gas flowing through the booster, and improving the NO.sub.x conversion efficiency in the case of a low temperature. In a case of a high temperature, the three-way valve is controlled to close a by-pass line, such that the exhaust gas flows through the booster and the first SCR.

An exhaust system for an internal combustion engine and having at least an exhaust duct, which originates from the internal combustion engine and has an end part, which ends with an outlet opening, through which exhaust gases are released into the atmosphere. The end part of the exhaust duct has at least one movable wall, which can be moved to different positions to vary the width of the outlet opening. There are provided a motor-driven actuator device, which is configured to move the movable wall and can be electronically controlled, and a control unit, which is configured to vary, by controlling the actuator device, the position of the movable wall depending on a rotation speed of the internal combustion engine and on an engine load of the internal combustion engine.

A replacement kit enables a user to generate a desired audible sound from an exhaust system of a motor vehicle. The kit includes a replacement catalytic converter arranged to replace the vehicle's original equipment catalytic converter. The replacement catalytic converter is connected to the vehicle's factory muffler through a replacement pipe segment to obtain a more desirable, yet muffled engine sound. The factory muffler may be removed from the motor vehicle and the replacement catalytic converter may instead be connected to a muffler bypass pipe or pipes or replacement exhaust components/segments which channels the exhaust flow directly to the atmosphere to obtain a more powerful unmuffled exciting visceral sports car engine sound.

A replacement kit for use with a motor vehicle that was originally equipped with an exhaust system including an exhaust manifold and a catalytic converter welded thereto. The replacement kit includes a replacement catalytic converter arranged for use during use of the motor vehicle on public roads. Rather than welding, the replacement catalytic converter attaches to the exhaust manifold using a clamp to form a gas-tight seal. The clamp is arranged to move from the closed position to an open position to enable disengagement of the replacement catalytic converter from the exhaust manifold and substitution of a bypass pipe in place of the replacement catalytic converter to increase performance characteristics of the vehicle during off-road use.

An aftertreatment system connected downstream an internal combustion engine arrangement for receiving exhaust gases conveyed from the internal combustion engine arrangement during operation thereof, wherein the aftertreatment system comprises first and second catalytic devices in series, wherein a gap is there between.

The dual function exhaust system attachment, which is preferably used with an all-terrain vehicle, includes a muffler, a silencing cap, and a sound-enhancing plug. In a quiet configuration, the silencing cap is mounted to conceal a primary outlet of the muffler. In a loud configuration, the sound-enhancing plug is mounted to conceal a secondary outlet of the muffler. A set of screw threads or sealing mechanism may be used to mount the silencing cap and the sound-enhancing plug. A primary perforated barrier, a solid barrier, at least one secondary perforated barrier, and a pipe section are positioned within a hollow structural body of the muffler to guide the exhaust gas flow from an inlet of the muffler to the primary outlet or the secondary outlet.

Unit for reduction of exhaust gases for an IC engine. The unit has a cylindrical housing with gas inlet and outlet openings and injector for a reducing substance. A helicoid is coaxially arranged inside the housing. A channel conveys the exhaust gases, has a substantially quadrangular cross-section, and helicoidally develops inside the unit. The helix is generated by the intersection between the inner surface of the housing and the helicoid has an inclination angle (β) relative to planes perpendicular to the generatrices of the cylindrical housing ranging from 0° to 30°. The unit includes a coaxial stiffening and stabilization sleeve located at the center of the helicoid passing axially throughout the helicoid and axially over a length at least equal to the axial length of the helicoid. The sleeve cooperates with the inner surface of the housing and with the opposite surfaces of the helicoid to define the helicoidal channel.

Various methods and arrangements for improving fuel economy in decel fuel cut-off (DFCO) operation of an internal combustion engine are described. In one aspect, a catalytic converter bypass valve diverts the pumped air in DFCO mode from flowing through a catalytic converter. The diverted, pumped air may flow through a bypass line or be returned to the engine intake manifold through an exhaust gas recirculation return line. Another aspect of the invention relates to directing the diverted pumped air through an emission control device.

An aftertreatment system (100) connected downstream an internal combustion engine arrangement (102) for receiving exhaust gases conveyed from the internal combustion engine arrangement (102) during operation thereof, wherein the aftertreatment system comprises first and second catalytic devices in series, wherein a gap is there between.

A replacement kit for use with a motor vehicle that was originally equipped with an exhaust system including an exhaust manifold and a catalytic converter welded thereto. The replacement kit includes a replacement catalytic converter arranged for use during use of the motor vehicle on public roads. Rather than welding, the replacement catalytic converter attaches to the exhaust manifold using a clamp to form a gas-tight seal. The clamp is arranged to move from the closed position to an open position to enable disengagement of the replacement catalytic converter from the exhaust manifold and substitution of a bypass pipe in place of the replacement catalytic converter to increase performance characteristics of the vehicle during off-road use.