Claims:We Claim:
1. An exhaust gas recirculation system (100), comprising:
an inlet path (102) to an engine (103), and
an outlet path (104) in flow communication with exhaust of said engine 103; characterized in that
an exhaust gas recirculation valve (106) located along said outlet path 104; and a flow pipe (108) connecting said outlet path (104) from a position upstream from said exhaust gas recirculation valve (106) to said inlet path (102).

2. The exhaust gas recirculation system 100 of claim 1, wherein a flow control valve (110) is located along said flow pipe.

3. A method of controlling flow of exhaust in an exhaust gas recirculation system 100, said exhaust gas recirculation system 100 comprising:
an inlet path 102 to an engine 103, and
an outlet path 104 in flow communication with exhaust of said engine 103; said method comprising

detecting (200) by a control unit at least one engine parameter;

detecting (202) pressure at inlet and outlet of said engine 103; and

actuating (204) an exhaust gas recirculation valve 106 for increasing the pressure of exhaust at said outlet path 104 with respect to pressure of air at said inlet path 102.

4. The method of claim 3, wherein said at least one engine parameter is one of engine speed, engine load and engine temperature.
, Description:Field of the invention
[0001] This invention relates to the field of exhaust gas re-circulation system.

Background of the invention.
[0002] Exhaust gas recirculation (EGR) for engines are well known. EGR can be applied downstream of the supercharger on the high pressure part (HP EGR) or upstream of the supercharger on the low pressure part (LP EGR). The HP EGR in the market the preferred solution since it doesn't load the air charging devices with the hot and dirty exhaust gases. For a combustion engine charged by a compressor however the problem is that the intake manifold pressure is higher than the exhaust manifold. Hence gases will not flow from the exhaust to the intake manifold. So the only feasible solution is to apply LP EGR. There will be an exhaust flow to the supercharger inlet, since the inlet pressure of the supercharger is below the exhaust pressure after the exhaust filter. The drawback of this solution is the big dead volume caused by the supercharger, the piping and the intercooler. This causes sluggish behavior with long response time in transient load cycles with instantaneous load changes. The exhaust gas won't reach the combustion chamber in time and the NOx emissions won't be achieved.

Brief description of the accompanying drawings
[0003] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0004] FIG. 1 illustrates an exhaust gas recirculation system; and
[0005] FIG. 2 illustrates a method for controlling flow of exhaust in an exhaust gas recirculation system.

Detailed description of the embodiments
[0006] FIG. 1 illustrates an exhaust gas recirculation system 100. The exhaust gas recirculation system 100 comprises an inlet path 102 to an engine 103 and an outlet path 104 in flow communication with exhaust of the engine 103. An exhaust gas recirculation valve 106 is located along the outlet path 104. A flow pipe connects the outlet path 104 from a position upstream from the exhaust gas recirculation valve 106 to the inlet path 102.
[0007] To enable high pressure exhaust gas recirculation the flow pipe connects the outlet path 104 from a position upstream from the exhaust gas recirculation valve 106 to the inlet path 102. To avoid fresh air flow towards exhaust a flow control valve 110 is located along the flow pipe. To enable exhaust flow towards the inlet path 102 the exhaust back pressure has to be increased. This will be done by the exhaust gas recirculation valve 106. By closing the exhaust gas recirculation valve 106 the back pressure will increase. Let p3 be the pressure in the outlet path 104 and p2 be the pressure in the inlet path 102. In case p3 > p2 the reed valve flow control valve 110 will open and exhaust will flow towards fresh air side that is the inlet path 102. The control of the exhaust gas mass flow will happen by setting the pressure difference p3/p2. This so called high pressure EGR has the advantage of fast response during transient operating cycles which requires an instantaneous response. The dead volume for EGR flow to pass through will be short.
[0008] Furthermore by increasing the backpressure p3 the gas exchange will be not ideal. Higher exhaust back pressure will cause the inlet and outlet valve of the engine 103 to overlap and hence the exhaust gas might not be flushed out completely. This as internal EGR considered air mass is an additional advantage and has to be taken into consideration for total EGR control strategy. Thus the working principle of EGR is reversed. Fully open EGR valve will allow no EGR flow, and pressure p2 will be greater than pressure p3. Highly throttled EGR will allow EGR flow, there will be p3>p2.
[0009] FIG. 2 illustrates a method of controlling flow of exhaust in an exhaust gas recirculation system 100. The exhaust gas recirculation system 100 comprises, an inlet path 102 to an engine 103, and an outlet path 104 in flow communication with exhaust of said engine 103. The method comprises detecting 200 by a control unit at least one engine parameter, detecting 202 the pressure at inlet and outlet of the engine 103, and actuating 204 an exhaust gas recirculation valve 106 for increasing the pressure at said outlet path 104 with respect to pressure at said inlet path 102.
[0010] The working of the exhaust gas recirculation system 100 will be explained in further detail. During working of the engine 103, the supercharger sucks air and delivers the compressed air to the engine 103 through the inlet path 102. The exhaust from the engine 103, flows through the outlet path 104. A control unit monitors the parameters of the engine 103. The parameter can be at least one of engine speed, engine load and engine temperature. Based on these parameters in case the exhaust needs to recirculated back to the engine 103, the exhaust gas recirculation valve 106 will be actuated by the control unit for increasing the pressure of exhaust at the outlet path 104 with respect to pressure of air at said inlet path 102.
[0011] With the proposed system 100 it is possible to have an improved response behavior of the EGR control and to avoid exposure of supercharger with hot and dirty exhaust gas and thus to eliminate costly wear and corrosion protection of the same. Furthermore the backpressure increase will slightly increase the exhaust temperature and makes it easier to guarantee the light-off temperature of the catalyst.
[0012] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention in terms of type of supercharger. 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.