CLIAMS:I claim:
1. A method to control an exhaust gas recirculation valve (20) during a transient state, said method comprising :
-detecting a transient state if a rate of change of engine speed and a quantity of fuel injected into an engine is high;
- determining a boost pressure at a compressor;
- determining an exhaust gas recirculation rate for said determined boost pressure based on said engine speed and said injected fuel quantity, when said transient state is detected;
-controlling said exhaust gas recirculation valve (20) based on said determined exhaust gas recirculation rate.
2. The method claimed in claim (1), wherein said determined exhaust gas recirculation rate is converted to a valve operator position signal to control the position of said exhaust gas recirculation valve (20).
3. The method claimed in claim (1), wherein said exhaust gas recirculation rate is chosen from an exhaust gas circulation map.
4. An electronic control unit (12) in a vehicle to control an exhaust gas recirculation valve (20) during a transient state,
said electronic control unit
- receives an engine speed from an engine speed sensor (40) and a quantity of fuel injecting into an engine from an engine control unit (42);
- detects said transient state if a rate of change of said engine speed and said quantity of fuel injected into said engine is high;
- receives a boost pressure of a compressor from a pressure sensor (18);
- determines an exhaust gas recirculation rate for said received boost pressure based on said received engine speed and said received fuel quantity injected, when said transient state is detected;
- controls an actuator (19) of said exhaust gas recirculation valve (20) based on said determined exhaust gas recirculation rate.
,TagSPECI:Field of the invention
[0001] This invention relates to a method to control an exhaust gas recirculation valve during a transient state.
Background of the invention
[0002] In most modern diesel engines, it is not sufficient to simply control the amount of exhaust gas recirculating back to the combustion chamber. An exhaust gas recirculation system recirculates a part of the exhaust gas into the intake manifold of the engine to lower the combustion speed and to reduce Nitrogen Oxide emissions in the exhaust gas. The Exhaust Gas Recirculation (EGR) system operates to control the recirculation of the exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold. The exhaust gas recirculation systems includes an exhaust gas recirculation valve for controllably introducing exhaust gas into the intake manifold. The exhaust gas recirculation method is of two types: one open loop control method and a closed loop control method. The closed loop control method depends on intake air flow whereas open loop control method depends on the engine operating conditions.
[0003] A United States patent 7281518 discloses a method to improve transient emission control in an electronically controlled heavy duty diesel engine equipped with a fuel system and an air system having an exhaust gas recirculation circuit. A final exhaust gas recirculation set point is determined by adding a transient exhaust gas recirculation and the change in an exhaust gas recirculation set point. The transient exhaust gas recirculation set point is determined from the exhaust gas recirculation model using the engine emission targets and the fuel economy targets, the engine set points during transient operation are compensated based upon a modeled system response.
Brief description of the accompanying drawings
[0004] An exemplifying embodiment of the invention is disclosed in detail in the description and illustrated in the accompanying drawings:
[0005] Figure 1 illustrates an electronic control unit in a vehicle according to one embodiment of the invention;
[0006] Figure 2 illustrates a block diagram of an internal combustion engine and an exhaust gas recirculation system according to one embodiment of the invention; and
[0007] Figure 3 illustrates a flow chart of a method to control an exhaust gas recirculation valve during a transient state according to one embodiment of this invention.
Detailed description of the invention:
[0008] Fig.1 illustrates an electronic control unit 12 in a vehicle to control an exhaust gas recirculation valve 20 during a transient state according to one embodiment of the invention. The electronic control unit 12 receives an engine speed from an engine speed sensor 40 and a quantity of fuel injecting into an engine from an engine control unit 42. The electronic control unit 12 detects the transient state if a rate of change of the engine speed and the quantity of fuel injected into the engine is high. The electronic control unit 12 receives a boost pressure of a compressor from a pressure sensor 18 and determines an exhaust gas recirculation rate for the received boost pressure based on the received engine speed and the received fuel quantity injected, when the transient state is detected. The electronic control unit 12 controls an actuator 19 of the exhaust gas recirculation valve 20 based on the determined exhaust gas recirculation rate.
[0009] The engine speed will be speed of the engine 14 received from the engine speed sensor 40 and the fuel injected quantity is an amount of fuel quantity injected by an injector into a cylinder of the engine 14, received from the engine control unit 42. The boost pressure of a compressor 24 received from the pressure sensor 18 is taken into consideration during the transient state to determine the exhaust gas recirculation rate.
[00010] Fig.2 illustrates a block diagram of an internal combustion engine 14 and an exhaust gas recirculation system 11 according to one embodiment of the invention. The air enters a compressor 24 of a turbocharger 19 that includes a turbine 22. The compressed air is cooled by an intercooler 32 and enters an intake manifold 34, before entering the cylinders 13. The exhaust gas from the cylinders 13 enters an exhaust manifold 36 and a part of the exhaust gas enters into the exhaust gas recirculation system 11 and the rest of the exhaust gas into the turbine 22. The exhaust gas that entered into the exhaust gas recirculation system 11 is cooled by an exhaust gas recirculation cooler 26. Cooled exhaust gas passes through an exhaust gas recirculation valve 20. The amount of the recirculation exhaust gas passing through the exhaust gas recirculation valve 20 is regulated by an aperture of the valve 20. Depending on the position of the exhaust gas recirculation valve, cooled exhaust gas passes through the valve into an exhaust gas recirculation outlet. The electronic control unit 12 controls the position of the exhaust gas recirculation valve 20. Cooled exhaust gas and compressed air are combined in the intake manifold 34, and the resultant stream is provided to the cylinders 13 of the engine 14.
[00011] Initially, the exhaust gas recirculation system 11 will be operating in a closed loop control technique. In closed loop control technique, an actual air mass measured by an air mass sensor 16 is compared with a desired air mass and the difference between the actual air mass and desired air mass is given to a governor (present in the electronic control unit 12). The governor calculates the difference in the air mass using a proportional integral derivative method. The output from the governor is given to an air control monitoring means (present in the electronic control unit 12) to control the position of the exhaust gas recirculation valve 20. The position of the exhaust gas recirculation valve 20 is controlled in dependence with the exhaust gas recirculation rate determined from a control map. The exhaust gas recirculation rate is determined based on the actual air mass. The closed loop control technique will be implemented only when the vehicle is in steady state i.e., the state in which there is no variation in the engine speed over time.
[00012] When the change in the engine speed and the injected fuel quantity is high, the electronic control unit 12 switches the operating condition of the vehicle from the closed loop control technique to an open loop control technique. An open loop control technique is a state in which the vehicle will be in a transient state i.e., the state in which the rate of change of the vehicle speed and the quantity of fuel injected into a cylinder 13 is varied over time. During, the transient state, the exhaust gas recirculation valve 20 is closed due to low boost pressure and to avoid the generation of the higher NOx.
[00013] Fig.3 illustrates a flow chart of a method of to control an exhaust gas recirculation valve 20 during a transient state. In step S1, a transient state is detected if a rate of change of engine speed and an amount of fuel quantity injected into the cylinders 13 is high. The transient state of a vehicle is a state in which the engine speed will be changing over time. In step S2, an exhaust gas recirculation rate for a corresponding boost pressure is determined. The exhaust gas recirculation rate is determined based on the detected engine speed and detected amount of fuel quantity getting injected during the transient state. During the transient state due to the change in the engine speed and the amount of fuel injected, the generation of the exhaust gas will be varied. Due to the variation in the quantity of the exhaust gas generated, the turbine 22 speed changes which in turn changes the boost pressure of the compressor 24 (since the turbine 22 is coupled to the compressor 24). As the time taken to increase the rotational speed of the turbine 22 increases, the boost pressure developed by the compressor 24 decreases. Depending on the boost pressure and the speed of the engine14, the exhaust gas circulation rate is determined from an exhaust gas recirculation map by the electronic control unit 12. The exhaust gas recirculation map is a map comprising plurality of exhaust gas recirculation rates for corresponding boost pressures and for corresponding engine speeds. For instance, the egr rate will be 20mg for a 200 hpa (current boost pressure) and for 1500 RPM (engine speed). In step S3, depending on the determined exhaust gas recirculation rate the exhaust gas recirculation valve 20 is opened by the electronic control unit 12 to allow the exhaust gas to pass into the engine 14. The estimated exhaust gas recirculation rate is converted to a signal which controls the position of the exhaust gas recirculation valve 20. The electronic control unit 12 controls the position of the exhaust gas recirculation valve 20 by sending the valve position signal and thus controlling an actuator associated with the exhaust gas recirculation valve 20. For example, to completely close the exhaust gas recirculation valve 20, a position signal with value 0 may be utilized, whereas a position signal with value 1 may be utilized to fully open the exhaust gas recirculation valve. Intermediate positions between open and closed may also be utilized, e. g., 0.5 for a half-open exhaust gas recirculation valve 20.
[00014] The above disclosed method is explained with an example below:
[00015] During the steady state, let the fresh air mass of 150mg and exhaust gas of 30 mg is provided to the engine cylinders and the boost pressure at this point at the compressed side will be 1200hpa. At an intermediate point during transition i.e., when the engine speed is 1200 rpm and fuel quantity getting injected is 12mg, there will be a turbo lag at the turbine 22 leading to reduced boost pressure at the compressor side 24. The boost pressure during transient (when engine speed is 1200rpm and fuel injected is 12mg) will be 1000hpa. Due to this there will be a less intake of the actual air into the cylinder 13 which is 100mg. The less intake of fresh air mass leads to the shut off of the exhaust gas recirculation valve and results in a higher NOx peaks. To avoid this condition, during the transient state, the electronic control unit 12 shifts to open loop control technique. Since, the open loop control technique is not based on fresh air mass but on the actual boost pressure available at that instant (ie. 1000hpa instead of 1200hpa), then a minimum amount (10mg) of recirculated exhaust gas is used to avoid NOx peak. So during transient an amount of 90mg of fresh air and a 10mg of recirculated exhaust gas is passed into the engine cylinder to minimize NOx emissions.
[00016] With the method disclosed above, a minimum exhaust gas recirculation flow even during acceleration to reduce NOx emission is ensured. The amount of undesired exhaust gas constituents can be kept comparatively low, and emission peaks can be reduced.
[00017] It must be understood that the examples and embodiments of the components explained in the detailed description are only illustrative and do not limit the scope of the invention. The scope of this invention is only limited by the scope of the claims.