FIELD OF INVENTION:

The invention relates to plausibility check for level sensing of an aqueous solution in a tank in a Selective Catalytic Reduction (SCR) system for a vehicle.

BACKGROUND OF THE INVENTION:

In today's market diesel engines are gaining momentum, by virtue of their unique characteristics such as high energy efficiency, high torque and low fuel consumptions. However, these benefits come with a trade-off. By virtue of property of the diesel fuel, the combustion happens at a very high temperature (around 600 °C). At such temperatures, the amount of Nitrogen Oxides (NOx) produced is very high.
To address the challenge of NOx emissions, Selective Catalytic Reduction (SCR) system is used. The system consists of a metering module (called Supply Module), - an AdBlue® tank, pipelines to carry AdBlue® and an electronic control unit (ECU).

A 32.5 % aqueous urea solution (AdBlue®) is injected into the exhaust gas flow as a reactant. The metering module sprays a precise quantity of AdBlue® into the exhaust, based on various parameters such as engine speed, engine torque, exhaust temperature, ambient temperature etc.

Selective Catalytic Reduction (SCR) is a proven technology to reduce nitrogen oxide emissions from combustion processes for vehicles. A reducing agent namely AdBlue® (aqueous urea) is hydrolyzed into ammonia. In the presence of the SCR catalyst the ammonia converts NO and NO2, in the exhaust, to nitrogen and water vapor. Careful control of urea injection ensures proper chemical reaction in the exhaust, thereby reducing nitrogen oxides (NOx) to the maximum possible extent.
SCR-Catalyst is a ceramic component installed in the exhaust track. It is designed to selectively reduce NOx among other emissions like CO, CO2, unburnt hydrocarbons etc. from the engine.

In an SCR system, AdBlue® is stored in a tank on the vehicle and is transported to the dosing unit. To keep the emissions below the set standards, monitoring the level of the aqueous solution in the tank is crucial. At present mainly floating resistive sensors or ultrasonic sensors are used to get required resolution of the level of the aqueous solution in the tank. These sensors are complex and expensive.

The proposed invention provides a simple device and method to monitor the level of the aqueous solution in the tank.

ADVANTAGES OF THE INVENTION:

The invention proposes a simple device and a method to determine the aqueous - solution available in the tank of an SCR system. The invention eliminates the need of complex sensors and the difficulty of placing them in a tank which has irregular shape. Using simple sensors and a simple way of placing them in the tank, the invention provides a solution to determine the level of aqueous solution available in the tank.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1: Shows the schematic of the dosing apparatus according to the invention

DESCRIPTION OF THE INVENTION:

Shown in figure 1 is a schematic of the dosing apparatus 10 according to the invention. The dosing apparatus 10 comprises a valve block 12, a tank and a dosing unit 14. The tank comprises a first compartment 16 and a second compartment 18 with a one way valve 20 in between. The valve block 12 comprises a four way valve, with two input and two outputs. The valve block 12 is connected to the first compartment 16 through the path 22 and to the second compartment through the path 24. The first compartment is connected to the dosing unit through the path 26. The dosing unit 14 is connected to the second compartment 18 through the path 28 through a second valve 48. The first compartment 16 has a sensor 30 at a predefined level L1. The second compartment 18 has two sensors 32 and 34 at two predefined levels L2 and L3.

An electronic control unit - ECU (35) is responsible to control the valve block 12 and also to monitor the sensors 30, 32 and 34.

The working of the invention is explained below.

The first compartment 16 is filled with aqueous solution. The aqueous solution is referred as solution in further parts of this document. The emission standard requires that the amount of solution injected during a predefined duration is monitored, with a given accuracy, for example, it may be required to monitor the amount of solution injected in last 48 hours, with a given accuracy. Also it may be required to monitor the actual amount of solution injected for a given quantity, for example, the actual amount of solution injected for 15 liters of assumed injection quantity.

Presently in the prior arts, the monitoring of the quantity of injection of the solution is achieved by monitoring the level of solution remaining in the tank through. By monitoring the level of the remaining solution, the prior arts compute the amount of solution injected. The sensors used in these prior arts are complex and expensive. Also the shape of the tank may cause limitations in placing the sensors at different levels to determine the level of the remaining solution.

The invention proposes a method to easily determine the volume of consumption of aqueous solution without using the complex sensors. Also the limitation caused by the shape of the tank is completely eliminated.

In the figure1, the first compartment and second compartment are shown adjacent to each other. But it is not necessary that they are adjacent to each other. Only requirement is that there should be a possibility of flow of solution from second compartment to first compartment under certain conditions.

Also the first and second compartments need not be in a regular shape, but can be in any shape. The requirements being that the sensors are placed to indicate known levels.

The dosing apparatus works in two modes. In the first mode of operation, the solution is transported from first compartment to the dosing unit for injection. In the second mode of operation, the solution from the second compartment is transferred to the first compartment. The ECU controls the modes of operation by configuring the inlets and outlets of the valve block.

Normally the dosing apparatus operates in first mode of operation. In this mode the inlet 36 is connected to outlet 22. The valve block 12 receives the pressure from the engine which is not shown, through the inlet 36. Normally the pressure is passed to the first compartment 16 whenever the solution is to be injected into the exhaust path - which is not shown. When the pressure is applied to the first compartment 16, a predefined quantity, Q1, of solution, is transported to the dosing unit 14. The dosing unit 14 passes a predefined quantity Q2, of solution, to the injectors which are not shown, through the path 50 and also returns a part, Q3, of the solution, to the second compartment 18.

The quantity Q1 is divided into Q2 and Q3. The ratio between Q2 and Q3 is known. The ECU 35 is responsible to transport the Q1 amount of solution to the dosing unit for the purpose of injection. As the ratio of Q2 and Q3 is known, the ECU keeps computing the cumulative value of Q2 which indicates the cumulative amount of solution injected. As the Q3 amount of solution is returned to second compartment for every injection, ECU 35 also keeps computing the cumulative value of Q3 which is indicative of the amount of solution available in the second compartment.

The two sensors 32 and 34 in the second compartment indicate two levels L1 and L2 respectively. The amount of solution, Q4, available in the second compartment, when the solution is at level L2 is known based on the size of the second compartment. Whenever the level of solution in the second compartment reaches L2, the ECU 35 gets a trigger 40.

Assume that the second compartment 18 is empty and the first compartment 16 is filled with solution. The cumulative value of Q2 and Q3 are reset to zero. The ECU 35 starts injecting the solution into the exhaust channel and keeps computing the cumulative values of Q2 and Q3. Q2 indicates the quantity injected and the cumulative value of Q3 indicates the current level of solution in the second compartment. Based on the cumulative quantities of Q2 and Q3, the ECU computes the level of the solution available in the first compartment at any given time.

Under the normal operating conditions when the dosing unit is injecting expected quantity of solution, when the computed cumulative value of Q3 exceeds the quantity - Q4 which is required to reach level L2, then the sensor 34 should generate the trigger 40. If the trigger 40 is not generated when cumulative value of Q3 exceeds Q4 by a threshold, then the dosing apparatus is not working as expected, i.e. the quantity of solution flowing back is not as expected. There may be more injection into the exhaust channel and less flow back into the second compartment. This may need a correction of the dosing unit 14 by adjusting the second valve 48.

Also if the trigger 40 is generated before the cumulative value Q3 reaches the value Q4, then also the dosing apparatus is not working as expected, i.e. the quantity of solution flowing back into the second compartment 18 is not as expected. There may be less injection and more flow back. This may need a correction of the dosing unit by adjusting the second valve 48.

Thus depending upon whether the trigger 40 is generated early or the trigger is delayed, it is possible to detect whether the dosing apparatus is working as expected or not. The expected working of dosing apparatus is when the actual quantities of Q2 and Q3 follow the known ratio. If the known ratio is maintained, it is possible to know the level of solution present in the second compartment 18 at any given time. This level is indicated by the cumulative value of Q3. If the ratio between Q2 and Q3 varies, then there is a mismatch between the expected quantity of solution in the second compartment and the actual quantity of the solution available in the second compartment. This erroneous behavior of the dosing apparatus 14 is detected by the early trigger or delay in the trigger.

Once the erroneous behavior is detected by the ECU, the ECU 35 generates an error signal 42. The error signal 42 may be used to light an LED or a warning lamp or may be used to generate an audio beep.

The first compartment 16 contains the sensor 30 to indicate that the level in the first compartment 16 is below dangerous level L3. When the level in the first compartment falls below the danger level L3, the sensor 30 generates a trigger 44. The ECU 35 uses this trigger 44 to warn the user that the tank is empty.

Once the level in the second compartment reaches L2, then the solution needs to be transferred back to the first compartment. For this the valve block is configured to pass the engine pressure to the second compartment. This is referred as second mode of operation. In the second mode of operation, the inlet 36 is connected to the outlet 24. When the pressure is applied to the second compartment, the solution flows from second compartment to the first compartment through the valve 20. The ECU 35 configures the dosing apparatus to second mode of operation at an appropriate time of the engine operation.

For better accuracy, sensor 32 is used. The cumulative value of Q3 can be initialized to zero when the sensor 32 generates a trigger 46. The plausibility check is performed when the sensor 34 generates a trigger 40.

Thus by monitoring the cumulative value of Q3 which is indicative of the level of solution in the second compartment, the level of solution available in the first compartment is computed. At regular intervals a plausibility check is carried out to determine whether the dosing apparatus is working as expected. Whenever any erroneous condition is detected, the ECU 35 generates the error signal which is used to warn the user.

WE CLAIM:

1. A dosing apparatus (10) comprising a tank to store aqueous solution, a dosing unit and a valve block (12); the said tank having at least two compartments, a first compartment (16) and a second compartment (18); the said first compartment (16) having a connection to the dosing unit (14); the said dosing unit (14) having a back flow path (28) connected to the said second compartment (18); the said dosing unit (14) adapted to inject a first quantity of the aqueous solution into an exhaust path and return a second quantity of the aqueous solution to the said second compartment (18); the second compartment having at least one sensor (34) to indicate a predefined level L2 of the aqueous solution.

2. A dosing apparatus according to claim 1 wherein the said first compartment and the said second compartment are connected with a non return valve (20)

3. A dosing apparatus according to claim 1 wherein a sensor (30) is placed in the said first compartment at a predefined level L3.

4. A dosing apparatus according to claim 1 wherein the valve block (12) passes the pressure of the engine to the first compartment (16 during a first mode of operation.

5. A dosing apparatus according to claim 1 wherein the valve block (12) passes the pressure of the engine to the second compartment (18) during a second mode of operation.

6. A dosing apparatus according to claim 1, adapted to inject the aqueous solution into the exhaust channel of a vehicle during the said first mode of operation.

7. A dosing apparatus according to claim 1, adapted to transfer the aqueous solution from second compartment to the first compartment during the said second mode of operation.

8. An electronic control unit - ECU (35) to control a dosing apparatus (10) to inject aqueous solution in an exhaust channel of a vehicle; the said ECU adapted to configure a valve block (12) to connect the inlet (36) of the valve block to either a first outlet (22) or a second outlet (24); the said ECU further configured to compute the level of the solution available in a first compartment of the said dosing apparatus depending upon the cumulative value of aqueous solution injected; the said ECU further adapted to do a plausibility check on the level of the solution available in the first compartment of the said dosing apparatus on detecting a predefined event.

9. An electronic control unit (35) adapted to connect the inlet 36 of the said valve block (12) to the said first outlet (22) in a first mode of operation.

10. An electronic control unit (35) adapted to connect the inlet 36 of the said valve block (12) to the said second outlet (24) in a second mode of operation.

11. An electronic control unit (35) wherein the said predefined event is generated by a sensor 34.

12. An electronic control unit (35) adapted to compute expected level of solution in second compartment depending upon the cumulative value of aqueous solution injected

13. An electronic control unit (35) performing plausibility check wherein the said plausibility check is success if the difference between the computed quantity of solution in second compartment and the actual quantity of solution in second compartment corresponding to sensor (34), is within a predefined threshold.

14. An electronic control unit (35) adapted to generate an error signal (42) on failure of the said plausibility check.

15. An electronic control unit (35) adapted to generate an error signal (42) when the computed quantity of solution in second compartment is greater than a predefined value and the sensor (34) has failed to generate a trigger.

16. A method to determine amount of aqueous solution injected into an exhaust path of a vehicle, the said method comprising the steps:

- activating a dosing unit to inject the said aqueous solution from first compartment of
a tank, for a predetermined duration at predetermined times

- computing the cumulative amount of aqueous solution injected

- performing a plausibility check on the cumulative amount of aqueous solution injected, on detection of predefined events