Claims:We Claim:
1. An exhaust gas system for an engine (100), comprising at least:
a first flow path (102) in flow communication with an outlet (104) of said engine 100; characterized in that:

a control valve (106) located along said first flow path (102), and

a bypass path (110) located parallel to said first flow path (102).

2. The exhaust gas system of claim 1, wherein a temperature sensor (112) is located along said first flow path 102.

3. A method for controlling flow of exhaust in an exhaust gas system, said system comprising at least , a first flow path 102 in flow communication with an outlet 104 of said engine 100, a control valve 106 located along said first flow path 102, and a bypass path 110 parallel to said first flow path 102 :

Detecting (200), by said temperature sensor 112, a temperature of exhaust;

Verifying (202), by a control unit if said detected temperature of exhaust exceeds the temperature required for NOx reduction; and

4. Actuating (204), said control valve 106 in dependence of said detected temperature, to cause said exhaust to flow through one of, said first flow path 102 and said bypass path 110.
, Description:Field of the invention
[0001]This invention relates to the field of exhaust gas system.

Background of the invention
[0002]An exhaust gas treatment system is used to deliver exhaust from engine into the atmosphere. Since, the exhaust cannot be directly let out into the atmosphere, there exists a need to treat the exhaust so as to reduce harmful particles, NOx. Hydrocarbon (HC), Carbon monoxides (CO) and other matter. An effective exhaust gas treatment system is key enabler to meet future emission regulations such as but not only BS6. The performance of an exhaust gas treatment system is strongly influenced by the temperature of the chemical active catalysts. To enable the use of an NOx storage catalyst based (NSC) for diesel engine powered low priced vehicles in India (typically 1- and 2-cylinder engines) special care needs to be taken for the temperature management of the exhaust gas treatment system. Due to thermodynamic inefficiency of the used natural aspirated and highly underpowered engine powertrain setup of these vehicles. The exhaust gas treatment temperature tends to be on a higher side, exceeding the maximum operation temperature of a typical NSC (here ~400 degree C) in large operation. Key for effective NOx reduction using an NSC-based Exhaust gas treatment system is to maintain temperature of exhaust in the range of ~180 to 400 degree Celsius.

[0003] Prior art patent application DE102008028354 discloses a device for reducing exhaust gas temperature of motor vehicle engine, has temperature sensor arranged in exhaust gas system, where temperature sensor is connected with engine control unit. The device has a temperature sensor arranged in an exhaust gas system, where the temperature sensor is connected with an engine control unit. The engine control unit is formed to determine the current load case and issue a control command, in the event that the actual temperature of the exhaust gas determined by the temperature sensor exceeds a predetermined maximum temperature for a predetermined period.
Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[0005] FIG. 1 illustrates an exhaust gas system; and

[0006] FIG. 2 illustrates a method for controlling flow of exhaust in an exhaust gas system.

Detailed description of the embodiments
[0007] FIG. 1 illustrates an exhaust gas system. The exhaust gas system comprises at least a first flow path 102 in flow communication with an outlet 104 of the engine 100. A control valve 106 is located along the first flow path 102, and a bypass path 110 is located parallel to the first flow path 102. A temperature sensor 112 is located along the first flow path 102. The construction and working of the exhaust gas system will be explained in further detail. The function of the exhaust gas system is to ensure that the exhaust from the engine 100 is let out into the atmosphere. The exhaust gas system comprises a first flow path 102. The first flow path 102 is in flow communication with the outlet 104 of the engine 100. The exhaust from the engine 100, enters the first flow path 102. The temperature sensor 112 is located along the first flow path 102. The temperature sensor 112 measures the temperature of the exhaust flowing through the first flow path 102. The control valve 106 that is located along the first flow path 102, allows the exhaust to flow through either the first flow path 102 or the bypass path 110 depending upon the temperature of the exhaust.

[0008] The working of the exhaust gas system will be explained in further detail. The exhaust is generated in the engine 100 after the completion of the combustion stroke. The exhaust from the engine 100 flows through the first flow path 102 of the exhaust gas system. The temperature sensor 112 measures the temperature of the exhaust. The exhaust flows through the first flow path 102 as long as the temperature of the exhaust is within the limit prescribed for NOx reduction. Approximately, the temperature of the exhaust for NOx reduction may be around 400 degree celsius. Once the temperature exhaust exceeds the above mentioned limit, due to increase in load on the engine 100, the ability of the exhaust system to reduce NOx decreases. The conversion efficiency of NOx is higher at lower temperatures of exhaust. In order to bring down the temperature of the exhaust, the control valve 106, based on the input from the temperature sensor 112, blocks the first flow path 102 and opens the bypass path 110. The exhaust now flows through the bypass path 110. The bypass path 110 is longer than the first flow path 102, the time taken by the exhaust to flow through the bypass path 110 will be more than the time taken by the exhaust to flow through the first flow path 102. This results in heat transfer from the exhaust thereby reducing the temperature of the exhaust, during flow of exhaust through the bypass path.

[0009] FIG. 2 illustrates a method for controlling flow of exhaust in an exhaust gas system. The exhaust gas system comprises, a first flow path 102 is in flow communication with an outlet 104 of the engine 100, a control valve 106 located along the first flow path 102, and a bypass path 110 parallel to the first flow path 102. The temperature of the exhaust is detected 200 by the temperature sensor 112. A control unit verifies 202 if the detected temperature of exhaust exceeds the temperature required for NOx reduction. The control valve 106 is actuated 204 in dependence of the detected temperature, to cause the exhaust to flow through one of, the first flow path 102 and the bypass path 110.

[0010]During flow of exhaust in the exhaust gas system, the exhaust has two paths, that is the first flow path and the bypass path. Depending upon the temperature of the exhaust the control valve is operated in a way such that the exhaust may flow through either the first flow path or the bypass path. The exhaust takes a longer path when flowing through the bypass path in comparison to the flow of exhaust through. The temperature of temperature of the exhaust is reduced due to heat exchange when flowing through the bypass path 110. Hence by using a combination of paths having two different lengths, it is possible to control the temperature of exhaust for NOx reduction.

[0010]It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.