CLIAMS:We claim,
1. A device for controlling exhaust gas recirculation for an engine (100) comprising,
a first pressure sensor (101) measuring the engine intake air pressure;
a second pressure sensor (102) measuring the engine exhaust pressure; and
a control unit (103) adapted to receive said engine intake air pressure from the first pressure sensor (101) and said engine exhaust pressure from the second pressure sensor (102); said control unit (103) further adapted to compare the engine intake pressure and the engine exhaust pressure and control the amount of exhaust gas allowed to recirculate by an exhaust gas recirculation valve (104) based on said pressure comparison.
2. A device for controlling exhaust gas recirculation for an engine (100) comprising, a control unit (103) adapted to receive a pressure difference signal from differential pressure sensor (105), said differential pressure sensor (105) adapted to measure a pressure difference between engine intake air pressure and engine exhaust pressure; said control unit (103) further adapted to control the amount of exhaust gas allowed to recirculate by an exhaust gas recirculation valve (104) based on said differential pressure.
3. A device as claimed in claim (1) or (2) wherein said exhaust gas recirculation valve (104) directs a part of the exhaust gas from the engine to the engine air intake path.
4. A device as claimed in claim (1) or (2) wherein said exhaust gas recirculation valve (104) is actuated electrically or pneumatically and controlled by said control unit (103).
5. A method for controlling exhaust gas recirculation for an engine (100), said method comprising the following steps,
comparing engine intake air pressure and engine exhaust pressure; and
controlling an exhaust gas recirculation valve (104) to vary the exhaust gas recirculated to the engine (100) based on said pressure comparison.
6. A method as claimed in claim (5) wherein comparing of said engine intake air pressure measured by a first pressure sensor (101) and the engine exhaust pressure measured by a second pressure sensor (102) is done by a control unit (103).
7. A method as claimed in claim (5) wherein comparing of said engine intake air pressure and engine exhaust pressure is done by means of a differential pressure sensor (105).
8. A method as claimed in claim (5) wherein said exhaust gas recirculation valve (104) is closed progressively when the ratio of exhaust pressure to engine intake pressure increases.
9. A method as claimed in claim (5) wherein said exhaust gas recirculation valve (105) is opened progressively when the ratio of exhaust pressure to engine intake pressure decreases. ,TagSPECI:Field of the invention:
[001] The invention relates to a device and method for controlling the recirculation of exhaust gas to an engine.
Background of the invention:
[002] Exhaust Gas Recirculation (EGR) is one of the most effective techniques for reducing NOx emissions from an engine. EGR valves are positioned in the exhaust gas path such that a part of the exhaust gas is directed to the intake air path of the engine. The force to move and control the valves is either provided by a vacuum source (pneumatic EGR Valves) or by an electrical motor (electrical EGR Valves). A standard approach in modern electronic controlled Fuel Injection systems is to control the EGR Valve position and thereby the “EGR rate”, by an air mass measurement based logic. The air mass is provided by an air mass meter in the intake air path. Standard hot film air mass meters have a relative high tendency to drift in their air mass measurement over lifetime due to contamination of the measurement film.
[003] DE-10332698 discloses a method for exhaust gas recirculation wherein EGR valve is controlled based on temperature and pressure measurements at the intake of the engine when fresh air and exhaust gas is mixed together.
Brief description of the drawing:
[004] The present invention is described with reference to the following accompanying drawing,
[005] Fig. 1 illustrates a schematic of a device for controlling exhaust gas recirculation for an engine in accordance with one embodiment of the present invention where separate pressure sensors are used for measuring engine intake air pressure and engine exhaust pressure; and
[006] Fig. 2 illustrates a schematic of a device for controlling exhaust gas recirculation for an engine in accordance with one embodiment of the present invention where a differential pressure sensor is used to measure pressure difference between engine intake air pressure and engine exhaust pressure.
Detailed description of the embodiments:
[007] Fig. 1 illustrates a schematic of a device for controlling exhaust gas recirculation for an engine in accordance with one embodiment of the present invention.
[008] The device for controlling exhaust gas recirculation for an engine (100) comprises a first pressure sensor (101) measuring the engine intake air pressure, a second pressure sensor (102) measuring the engine exhaust pressure; and a control unit (103) adapted to receive the engine intake air pressure from the first pressure sensor (101) and the engine exhaust pressure from the second pressure sensor (102). The control unit (103) is further adapted to compare the engine intake pressure and the engine exhaust pressure and control the amount of exhaust gas allowed to recirculate by an exhaust gas recirculation valve (104) based on the pressure comparison.
[009] Fig. 2 illustrates a schematic of a device for controlling exhaust gas recirculation for an engine (100) in accordance with one embodiment of the present invention where a differential pressure sensor (105) is used to determine pressure between engine intake air pressure and engine exhaust pressure.
[0010] In accordance with another embodiment of the invention, a device for controlling exhaust gas recirculation for an engine (100) comprises, a control unit (103) adapted to receive a pressure difference signal from differential pressure sensor (105). The differential pressure sensor (105) is adapted to measure a pressure difference between engine intake air pressure and engine exhaust. The control unit (103) is further adapted to control the amount of exhaust gas allowed to recirculate by an exhaust gas recirculation valve (104) based on the differential pressure.
[0011] In accordance with one embodiment of the invention, the exhaust gas recirculation valve (104) directs a part of the exhaust gas from the engine (100) to the engine air intake path and is actuated either electrically or pneumatically and controlled by the control unit (104).
[0012] In accordance with a method for controlling exhaust gas recirculation for an engine (100), a comparison of engine intake air pressure and engine exhaust pressure is done in a first step and an exhaust gas recirculation valve is controlled to vary the exhaust gas recirculated to the engine(100) based on said pressure comparison in the second step.
[0013] In one embodiment of the invention the comparison of the engine intake air pressure measured by the first pressure sensor (101) and engine exhaust pressure measured by the second pressure sensor (102) is done by a control unit (103). Instead of air mass meter a pressure sensor in the air inlet (P2) and in the exhaust pipe (P3) are used to determine air mass using “universal gas equation”. The required EGR rate is determined based on the pressure difference in the exhaust pipe and the air inlet pipe. At low load operation conditions, the exhaust pressure P3 is relatively low but slightly above air inlet pressure P2. Thus, during low load or part load operation the ratio P3 and P2 are comparable leading to a relatively low value for P3/P2. When the ratio P3/P2 is low, a relative high EGR rate is required for engine operation and the EGR valve (104) is opened accordingly. As the load increases the exhaust pressure P3 will increase and P3/P2-ratio will increase significantly. During such high load operation conditions the recirculation of exhaust gas is not necessary and EGR rate will be reduced or EGR valve (104) will be shut off. As the exhaust pressure P3 increases, the EGR valve (104) is progressively closed. Similarly when the exhaust pressure P3 reduces as the load reduces, the EGR valve (104) is progressively opened allowing the required amount of exhaust gas to be recirculated to the engine (100).

[0014] Using pressure sensor improves emission robustness over lifetime and has to the potential of overall system cost reduction. The present invention achieves robustness by implementing a pressure sensor measurement based EGR control. The exhaust pressure sensor (102) is positioned at the hot EGR inlet side and the engine intake air pressure sensor (101) is positioned at the EGR outlet in a simple EGR valve (104) or at the outlet of an EGR/Throttle Valve combination.

[0015] This solution can be used for natural aspirated as well as turbo charged engine layouts.

[0016] In another embodiment of the invention the comparison of the engine intake air pressure and engine exhaust pressure is done by means of a differential pressure sensor (105). The differential pressure measured by the sensor (105) between the exhaust pressure P3 and the engine intake air pressure P2 is transmitted to the control unit (103). The control unit (103) determines the amount of exhaust gas that needs to be circulated to achieve reduced NOx emissions. Accordingly the control unit (103) opens the EGR valve (104) allowing part of the exhaust gas to mix with the engine intake air. The exhaust gas recirculation valve (104) is closed progressively when the ratio of exhaust pressure to engine intake pressure increases and is opened progressively when the ratio of exhaust pressure to engine intake pressure decreases.