Field of the invention
This invention relates to a method of removing Diesel Exhaust Fluid (DEF) deposits in exhaust path of a vehicle and a system thereof.
Background of the invention
Packaging constraint in vehicles have led to the widespread use of compact mixing sections for mixing diesel exhaust fluid (DEF) with exhaust gas. Unfortunately, due to limited mixing length, DEF deposits of urea crystals are formed in the exhaust line at low load operating conditions. The deposits can form on the mixer, urea injector tip, pipe walls and as well as on an inlet face of a selective catalytic reduction unit (SCR). The formation of DEF crystals leads to reduced performance of SCR catalyst, incorrect dosing quantity calculation, choking of urea injector, increase in back pressure of the exhaust line, accelerated corrosion of exhaust line and so on. The crystals/deposits evaporate once the temperature is in excess of 450 degrees. In most applications due to low power density engines and high share of city driving profile, the deposits become very critical and it is of utmost importance to remove these deposits/crystals for a robust exhaust line.
A Prior art document KR890003 593 discloses A regeneration system for diesel particulate oxidizer comprises a diesel particulate oxidizer disposed in an exhaust passage for collecting the particulates from the exhaust chamber of the diesel engine, capture detecting means, operation state detecting means, indicating means for indicating the regeneration timing of the oxidizer, the first control means for producing the oxidizer regeneration signal to the indicating means, and the second control means for producing the fuel injection timing delay signal. The oxidizer regeneration signal is produced when the amount of collected particulates in the oxidizer exceeds the predetermined value.

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 a control unit in a vehicle, in accordance with an embodiment of
the invention; and
[0006] Fig.2 illustrates a flow chart of a method of removing a diesel exhaust fluid (DEF)
deposits in an exhaust path of a vehicle, according to the present invention.
Detailed description of the embodiments
[0007] Fig.1 illustrates a control unit to remove diesel exhaust fluid (DEF) deposits in an exhaust path of a vehicle, in accordance to an embodiment of the invention. The control unit 10 adapted to detect at least one vehicle operating condition for a predefined amount of time and to determine a regeneration interval of a diesel particulate filter (DPF) 14 based on the detected at least one vehicle operating condition. The control unit 10 adapted to determine formation of the DEF deposits 12 in a mixing zone 16 of the exhaust path 13 based on the detected at least one vehicle operating condition for the predefined amount of time. The control unit 10 adapted to activate at least one de-crystallization process to remove the DEF deposits 12, when the DPF 14 regeneration is not scheduled for operation.
[0008] Further the construction of an exhaust system and the components of the exhaust system in the vehicle is explained in detail. The exhaust system comprises a diesel oxidation catalyst (DOC) 18, the DPF 14 and a selective catalytic reduction unit 26 arranged in the exhaust path 13 to convert the harmful exhaust gas emitted from an engine 22 into non-harmful gas before releasing the same into the atmosphere. The dosing of the urea by a dosing module 24 into the exhaust path 13 to reduce the NOx emissions is positioned upstream to the SCR unit 26. The portion where the urea is mixed with the exhaust gas is called mixing zone 16. According to one embodiment, the mixing zone 16 is located between the DPF 14 and the SCR unit 26. According to another embodiment, the mixing zone 16 is located between the DOC 18 and the SCR unit 26. Due

to the vehicle operating conditions, the DEF deposits 12 are formed in the mixing zone 16, which reduces the efficiency of the vehicle.
[0009] At least one vehicle operating conditions is chosen from a group of operating conditions comprising a low-load condition, an increase in the engine speed, a temperature of an exhaust gas in a predefined range, distance travelled by the vehicle, a flow rate of the exhaust gas in the exhaust path 13 and the like. However, the operating conditions is not limited to the above mentioned conditions but can be other operating conditions known to a person skilled in the art. The control unit 10 activates any one of the de-crystallization process when at least one vehicle operating condition is detected for a pre-defined amount of time. For instance, the control unit 10 activates at least one de-crystallization process when the vehicle is detected operating in the low-load condition for more than 4 hours.
[0010] For another instance, the control unit 10 activates the de-crystallization process, when the temperature upstream of the SCR unit 26 is in a predefined temperature range, wherein the pre-defined temperature range is from 180degrees- 250 degrees. A temperature sensor 20 located in the exhaust path 13 measures the temperature upstream of the SCR unit 26. The control unit 10 receives the detected temperature of the exhaust gas from the temperature sensor 20.
[0011]At least one de-crystallization process is chosen from a group of de-crystallization process comprising a late post injection process, an increased rate of throttling and by delaying a main injection and the like. For example, the DEF deposits 12 in the mixing zone 16 is removed by increasing the temperature of the exhaust gas via a late post injection process. According to another embodiment of the invention, the control unit 10 is an engine control unit. The control unit 10 is chosen from a group of control units comprising a microprocessor, a microcontroller, a digital circuit, an integrated chip and the like. The DPF regeneration interval is a time period for which the regeneration of the DPF 14 is activated to remove soot particles formed in the DPF 14.

[0012] The control unit 10 activates the regeneration of the DPF 14 for every predefined interval or for every predefined vehicle travelled distance or when at least one vehicle operating conditions is detected for a predefined amount of time or when the soot particles are detected in the DPF 14. When the DPF regeneration is activated, the temperature in the exhaust path 13 reaches approximately 600degrees, by which the soot particles are oxidized. With the increased temperature in the exhaust path 13, along with the soot particles oxidization in the DPF 14, the DEF deposits 12 in the mixing zone 16 can also be removed. The control unit 10 activates only one process (either the DPF regeneration process or de-crystallization process) at one time based on the requirement.
[0013] Figure 2 illustrates a flow chart of a method of removing Diesel Exhaust Fluid (DEF) deposits 12 in exhaust path 13 of a vehicle, in accordance to the present invention. In the first step S1 of the method, at least one vehicle operating condition is detected for a predefined amount of time. In the second step S2, a regeneration interval of a diesel particulate filter (DPF) 14 is determined based on the detected at least one vehicle operating condition. In third step S3, formation of the DEF deposits 12 in a mixing zone 16 of the exhaust path 13 is determined, based on the detected at least one vehicle operating condition for the predefined amount of time. In fourth step S4, at least one de-crystallization process to remove the DEF deposits 12 is activated, when the DPF regeneration interval is not scheduled for operation.
[0014] The above method is explained below with an example. When the vehicle is running in the low-load condition for a time period of more than four hours and based on the upstream temperature of the SCR unit 26 which ranges from 180 degrees to 250 degrees, the control unit 10 detects a low-load condition. The control unit 10 determines the DPF regeneration interval when the low-load condition is detected. If the DPF regeneration interval is not scheduled for next predefined amount of time (say two hours), then the control unit 10 determines the DEF deposits in the mixing zone of the

exhaust path 13. The control unit 10 activates the de-crystallization process of late post injection, such that, the temperature of the exhaust gas is increased to approximately 450 degrees.
[0015] With the increased temperature, the DEF deposits 12 are oxidized and the non-harmful gases are emitted into the atmosphere. The control unit 10 activates the de-crystallization process only when the DPF 14 regeneration is not in operation. If, the DPF 14 regeneration is in operation or if the control unit 10 detects that the regeneration interval overlapping with the de-crystallization process, then the control unit 10 activates the regeneration of the DPF 14. The control unit 10 provides an alert to the user of the vehicle in the dashboard regarding the active state of the de-crystallization process.
[0016] According to one embodiment, the control unit 10 alerts the user of the vehicle for a predefined amount of time, to increase the speed of the vehicle for activation of the de-crystallization process by virtue of increased temperature due to high speed driving. In case, if the above condition is not met, then the control unit 10 activates the de-crystallization process in the exhaust path 13 and alerts the user of the vehicle regarding the active state of the de-crystallization process.
[0020]With the above-disclosed method, the conversion process of the exhaust gas into the non-harmful gases will be efficient. The method provides a simple, cost-effective solution of removing the DEF deposits 12 formed in the exhaust path 13. The emission compliance is efficiently achieved during low-load conditions. Field issues due to the DEF deposits 12 in the mixing zone 16 like SCR unit performance reduction, accelerated corrosion of exhaust line, risk of exhaust line choking etc. can be prevented. Alerting the user regarding an alternate route (highway or less traffic zone) driving will also delay DPF 14 regeneration further benefiting on fuel penalty.

[0021] 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.

We Claim:
1. A control unit (10) to determine diesel exhaust fluid (DEF) deposits (12) in an
exhaust path (13) of a vehicle (11), said control unit (10) adapted to :
- detect at least one vehicle operating condition for a predefined amount of time;
- determine a regeneration interval of a diesel particulate filter (DPF) (14) based on said detected at least one vehicle operating condition; characterized in that :
- determine formation of said DEF deposits (12) in a mixing zone (16) of said exhaust path (13) based on said detected at least one vehicle operating condition for said predefined amount of time; and
- activate at least one de-crystallization process to remove said DEF deposits (12), when said DPF (14) regeneration is not scheduled for operation.

2. The control unit (10) as claimed in claim, wherein said mixing zone (16) is a urea dosing zone located in between said DPF (14) and a selective catalytic reduction (SCR) unit (26).
3. The control unit (10) as claimed in claim 1, wherein said at least one vehicle operating condition is chosen from any one operating conditions comprising a low-load condition, an increase in engine speed, a temperature of an exhaust gas in a predefined range, distance travelled by said vehicle (11), a flow rate of said exhaust gas in said exhaust path (13).
4. The control unit (10) as claimed in claim 1, wherein said at least one de-crystallization process is chosen from any one of the de-crystallization process comprising a late post injection process, an increased rate of throttling and by delaying a main injection.

5. The control unit (10) as claimed in claim 1, wherein said control unit (10) adapted to alert said user of said vehicle regarding an activation state of said de-crystallization process.
6. A method of removing Diesel Exhaust Fluid (DEF) deposits (12) in exhaust path (13) of a vehicle (11), said method comprising :

- detecting at least one vehicle operating condition for a predefined amount of time;
- determining a regeneration interval of a diesel particulate filter (DPF) (14) based on said detected at least one vehicle operating condition; characterized in that :
- determining formation of said DEF deposits (12) in a mixing zone (16) of said exhaust path (13), based on said detected at least one vehicle operating condition for said predefined amount of time;
- activating at least one de-crystallization process to remove said DEF deposits (12), when said DPF (14) regeneration interval is not scheduled for operation.
7. The method as claimed in claim 6, said method comprises a step of alerting a user
of said vehicle regarding an activation state of said de-crystallization process.