CLIAMS:We claim,
1. A method for estimating a NOx value (27) in an internal combustion (IC) engine of a vehicle, said method comprising the following steps :
- determining (S1) an engine speed (11);
- determining (S2) an amount of fuel injection (13);
- determining (S3) NOx base value (16) dependent on said determined engine speed (11) and amount of fuel injection (13);
- estimating (S4) NOx Raw value (19) dependent on said determined NOx base value (16) and a predetermined lookup table (17);
- determining (S5) NOx sensor value (21) from a NOx sensor (5) located downstream catalytic converter;
- comparing (S6) the estimated NOx Raw value (19) with the NOx sensor value (21) to determine the difference value (23);
- determining (S7) correction factor (25) dependent on said difference value (23) and a predetermined correction map (30); and
- estimating (S8) the NOx value (27) depending on said estimated NOx Raw value (19) and said correction factor (25).
2. The method according to the claim 1, wherein said NOx sensor value (21) is obtained when a dosing module ( 50) is switched OFF.

3. The method according to the claim 1, wherein said estimated NOx value (27) is used for estimating dosing quantity of said dosing module (50).

4. A device (100) to estimate NOx value (27) in an internal combustion engine of a vehicle without EGR and without a NOx sensor at upstream catalytic converter, said device comprising,
- An engine speed determination means (10) to determine an engine speed (11) of said vehicle;
- A fuel determining means (12) to determine amount of fuel injection (13);
- A NOx sensor determining means (20) to determine a NOx sensor value (21) from a NOx sensor (5) located downstream catalytic converter of said vehicle,
- The NOx base value determining means (15) for determining NOx base value (16) dependent on said determined engine speed and amount of fuel injection;
- A NOx Raw value estimating means (18) for estimating NOx Raw value (19) dependent on said determined NOx base value (16) and a predetermined look up table (17);
- A dosing status determining means (26) for determining dosing status of a dosing module (50);
- a NOx comparing means (22) for comparing said estimated NOx Raw value (19) with the NOx sensor value 21 to arrive at the difference value (23);
- a correction factor determining means (24) for determining a correction factor (25) dependent on the difference value (23) and a predetermined correction map (30) ; and
- An NOx estimating means (28) for estimating NOx value (27) depending on said estimated NOx Raw value (19) and said correction factor (25). ,TagSPECI:FIELD OF THE INVENTION:
[001] This invention relates generally to a method and device to estimate NOx value in an internal combustion.
BACKGROUND OF THE INVENTION:
[002] The emission legislation is growing stricter every day. To meet the stringent emission norms various technologies are available from the engine & air system point of view including common rail systems, optimized combustion systems with improved turbochargers. In addition to these technologies exhaust gas after treatment is required to reduce the emissions further more to the required emission standards. SCR – Selective Catalytic Reduction is a one of the proven technology for reduction of oxides of Nitrogen by injecting the reducing agent called aqueous solution into the exhaust path upstream of the catalyst using a dosing valve. There are systems such as DENOXTRONIC systems for NOx after treatment in short called as DNOX systems.

BRIEF DESCRIPTION OF THE DRAWING:
[003] The present invention is described with reference to the following accompanying drawing:
[004] Figure 1 illustrates a device in accordance with one embodiment of the present invention; and
[005] Figure 2 illustrates a method for estimating the NOx value in an internal combustion engine.
DETAILED DESCRIPTION OF THE DRAWING:
[006] Figure 1 illustrates a device 100 in accordance with one embodiment of the present invention.
[007] In accordance with one embodiment of the invention, the device 100 for estimating NOx value in an Internal Combustion (IC) engine (not shown) of a vehicle without EGR and without a NOx sensor at upstream of a catalytic converter is shown. The device 100 is an electronic control unit (ECU) having standard peripherals and memory. The catalytic converter such as Selective Catalytic Reduction (SCR) is located in an exhaust path of the IC engine. A dosing module is used to dose an aqueous solution into the exhaust path to reduce NOx components from the exhaust gas of the IC engine. A NOx sensor 5 is located downstream of the catalytic converter to measure the NOx value.
[008] The device 100 comprises an engine speed determination means 10, a fuel determining means 12, a NOx base value determining means 15, a NOx sensor determining means 20, a NOx Raw value estimating means 18, a dosing status determining means 26, a NOx comparing means 22, a correction factor determining means 24 and an estimating means 28.
[009] The engine speed determination means 10 determines the engine speed 11 of the vehicle. The engine speed 11 is either directly measured using an engine speed sensor (not shown) or received from an engine management control unit via a BUS network.
[0010] The fuel determining means 12 determines the amount of fuel 13 injected into the cylinder of the IC engine based on the driver demand.
[0011] The NOx base value determining means 15 determines the NOx base value 16 based on the engine speed 11 and the amount of fuel injection 13.
[0012] The NOx Raw value estimating means 18 estimates the NOx Raw value 19 dependent on the NOx base value 16 and a predetermined look up table 17. The predetermined look up table 17 further comprises factors such as boost pressure variation during dynamic operation, injection pattern variation, EGR variation for determining the NOx raw value 19. The look up table is pre-calculated and stored in a memory.
[0013] The NOx sensor determining means 20 determines the NOx sensor value 21 from a NOx sensor 5 located downstream of the catalytic converter in the exhaust path of the vehicle. The NOx sensor value 21 may be determined using moving average method and filtered before comparison. The dosing status determining means 26 determines dosing status of the dosing module 50. The NOx sensor value 21 is determined when the dosing module 50 is switched OFF. The dosing module 50 can have a dosing status - dosing ON and dosing OFF. During dosing ON status, the dosing module 50 will inject the aqueous solution into the exhaust path. And during dosing OFF status, the dosing module 50 is switched OFF. The NOx sensor value 21 is a direct indicator of engine exhaust NOx emission under the dosing OFF status. The dosing switch OFF conditions is carefully determined so that not to exceed the emission limits and a stable operating point is reached for evaluation. Such a correction accurately determines the dosing quantity and has the advantage to control the overshoot of dosing quantity which may lead to NH3 slip.
[0014] The NOx comparing means 22 compares the NOx Raw value 19 with the NOx sensor value 21 to arrive at the difference value 23 to estimate the NOx value 27. The comparison is done to arrive at the difference value 23 of the NOx Raw Value over a predetermined time. The comparison indicates the amount of correction to be done to the NOx raw value 19. The comparison of the two values can be a simple difference logic.
[0015] The correction factor determining means 24 determines the correction factor 25 dependent on the difference value 23 and a predetermined correction map 30. The predetermined correction map 30 may include the engine speed 11 and amount of fuel injection 13 to derive the correction factor 25 in addition to the difference value 23.

[0016] The NOx estimating means 28 estimates the NOx value 27 depending on the estimated NOx Raw value 19 and the correction factor 25. The estimated NOx value 27 is used for estimating dosing quantity of the dosing module 50.
[0017] In accordance with another embodiment, a method for estimating the NOx value 27 is disclosed. The method comprising the following steps:
[0018] At step S1, determining 10 an engine speed, at step S2, determining 12 an amount of fuel injection, at step S3, determining 15 NOx base value 16 dependent on the determined engine speed 11 and amount of fuel injection 13, at step S4, estimating 18 NOx Raw value 19 dependent on the NOx base value 16 and a predetermined lookup table 17, at step S5, determining NOx sensor value 21 from a NOx sensor 5 located downstream catalytic converter. The NOx sensor value 21 is obtained when a dosing module is switched OFF. At step S6, comparing the estimated NOx Raw value 19 with the NOx sensor value 21 to determine the difference value 23, at step S7, determining correction factor 25 dependent on the difference value 23 and a predetermined correction map 30 and at step S8, estimating the NOx value 27 depending on the estimated NOx Raw value 19 and the correction factor 25. The estimated actual NOx value 27 is used for estimating dosing quantity of the dosing module 50.

[0019] The present invention is advantageous in that, the NOx value 27 is used to calculate the dosing quantity of the dosing module 50 in the absence of an upstream NOx sensor which is typically used upstream of the catalytic convertor. The additional NOx sensor will not be necessary in the vehicle because of the device 100 of the current invention. The method is used to correct various correction factors to cater for the changes arising in the NOx value during dynamic operation. The difference in concentration between the NOx sensor value and NOx raw value can be used to correct the NOx value which will ensure proper dosing quantity calculation.

[0020] It must be understood that the embodiments explained in the above detailed description in only illustrative and does not limit the scope of this invention. The scope of this invention is limited only by the scope of the claims. Many modification and changes in the embodiments aforementioned are envisaged and are within the scope of this invention.