A method is provided for detecting a level of diesel-exhaust-fluid (DEF) in a reservoir that is operatively connected to a catalyst for a diesel engine. The method is employed in a vehicle in order to facilitate a refill of the reservoir. The method includes sensing a level of diesel fuel in a fuel tank via a sensor operatively connected to the tank. The method also includes determining whether the vehicle is on an incline using the sensed level of diesel fuel in the fuel tank. The method additionally includes determining the level of DEF in the reservoir if the vehicle is determined to be substantially not on an incline. A system is also provided for detecting a level of DEF in the reservoir.

TECHNICAL FIELD

The present invention is drawn to a system and a method for detecting a level of diesel-exhaust-fluid in a reservoir provided for a diesel engine in order to facilitate a refill of the reservoir.

BACKGROUND

A diesel-exhaust-fluid is typically an aqueous solution of urea that is used in a process called selective catalytic reduction (SCR) to reduce emissions of oxides of nitrogen (NOX) from the exhaust of diesel engines employed in motor vehicles. Although the urea solution employed for such purposes generally contains high-purity urea dissolved in de-mineralized water and is non-toxic and safe to handle, the solution can be corrosive to some metals. Accordingly, such a urea solution must be stored and transported using containers that are manufactured from appropriate inert materials.

An SCR-equipped vehicle typically carries its urea solution onboard in a specially designed reservoir. The urea solution is dosed into the SCR system during engine operation at a rate equivalent to 3-5% of consumption of the diesel fuel. Such a low dosing rate ensures significant periods between refills and minimizes the reservoir's impact on chassis space. On-highway SCR systems are currently in use throughout Europe, in Japan, Australia, Hong Kong, Taiwan, Korea, New Zealand and Singapore. The United States Environmental Protection Agency (US EPA) will limit NOXby a legislative enactment to levels that will require North American trucks to be equipped with SCR post-2010.

SUMMARY

A method is provided for detecting a level of diesel-exhaust-fluid (DEF) in a reservoir that is operatively connected to a catalyst for a diesel engine. The method is employed in a vehicle in order to facilitate a refill of the reservoir. The method includes sensing a level of diesel fuel in a fuel tank via a sensor operatively connected to the tank. The method also includes determining whether the vehicle is on an incline using the sensed level of diesel fuel in the fuel tank. The method additionally includes determining the level of DEF in the reservoir if the vehicle is determined to be substantially not on an incline. A system for detecting a level of DEF in the reservoir is also provided.

The acts of sensing a level of diesel fuel in the fuel tank, and determining the level of DEF in the reservoir may be executed by a controller operatively connected to each of the tank, the sensor, and the reservoir.

The method may also include using the controller to generate a sensory signal indicative of a required refill of the reservoir.

The act of determining whether the vehicle is on an incline may include determining a magnitude of the incline such that the vehicle is termed as being substantially not on an incline when the magnitude of the determined incline is below a predetermined value. Such a predetermined value may be equal to approximately 10 degrees.

The act of determining whether the vehicle is on an incline may include comparing a level of fuel sensed during the most recent instance in which the vehicle was not on an incline and a level of fuel sensed currently. The level of fuel sensed during the most recent instance in which the vehicle was not on an incline may be a level of fuel sensed during a fuel-fill event.

The act of sensing a level of diesel fuel in the fuel tank may be performed continuously.

A system is also provided for detecting a level of DEF in a reservoir that is operatively connected to a catalyst for a diesel engine.

DETAILED DESCRIPTION

Selective catalytic reduction (SCR) is a means of converting oxides of nitrogen, also referred to as NOXwith the aid of a catalyst into diatomic nitrogen, N2, and water, H2O. A gaseous reductant, typically anhydrous ammonia, aqueous ammonia or urea, is added to a stream of exhaust gas and is absorbed onto the catalyst. Carbon dioxide, CO2, is a reaction product when urea is used as the reductant. SCR is frequently employed to reduce NOXemissions in the exhaust of diesel engines used to power motor vehicles. When used as a reductant in diesel engines, urea is generally termed “diesel-exhaust-fluid” or DEF.

Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,FIG. 1schematically depicts a motor vehicle10. The vehicle10includes a system12configured to detect a level of DEF13contained in a reservoir14for metered supply to a stream of exhaust gas16. The system12includes an internal combustion diesel engine18. Exhaust gas16is emitted from the engine18as a by-product of combustion, and is removed to the ambient through an exhaust system20. As shown, the engine18is a compression ignition, i.e., a diesel, engine. The internal combustion in diesel engine18occurs when a specific amount of ambient air flow22is mixed with a metered amount of fuel24supplied from a fuel tank26and the resultant air-fuel mixture is compressed inside the engine's cylinders (not shown). The fuel tank26includes a sensor28configured to establish or sense a level of fuel24inside the fuel tank. The sensor28may operate to sense the level of fuel24inside the fuel tank26on a continuous basis.

As shown inFIG. 1, exhaust system20includes a series of exhaust after-treatment devices, shown as a diesel oxidation catalyst30, a selective catalytic reduction (SCR) catalyst32, and a diesel particulate filter34. The shown series exhaust after-treatment devices30,32, and34is employed to reduce various exhaust emissions of engine18. In particular, the diesel oxidation catalyst30is adapted to receive exhaust gas16from the engine18to oxidize and burn hydrocarbon emissions present in the exhaust gas. Following the diesel oxidation catalyst30, the exhaust gas16is routed to the SCR catalyst32, which is employed to reduce the emission of NOX. The reservoir14supplies DEF13to the stream of exhaust gas16as the exhaust gas flows through SCR catalyst32to thereby facilitate the reduction of NOX. After the exhaust gas16exits the SCR catalyst32, but before it is allowed to pass to the atmosphere, the gas is routed through the diesel particulate filter34where the sooty particulate matter emitted from the engine18is collected and disposed. Although, as shown, the SCR catalyst32is positioned upstream of the diesel particulate filter30, the SCR catalyst may also be positioned downstream of the diesel particulate filter without affecting the effectiveness of the exhaust after-treatment devices30,32, and34in the after-treatment of the exhaust gas16.

As shown inFIG. 2, reservoir14includes three discrete pins that are spaced at different heights within the reservoir—a pin36that is positioned at the highest level in the reservoir, a pin38that is positioned below the pin36, and a pin40that is positioned below the pin38. The pins36,38, and40are configured to detect a presence of the DEF13within the reservoir14in order to facilitate a determination of the level of the DEF and to set an alert or indicator of when a refill of the reservoir14is required. Hence, the level of DEF13is approximated based on which of the three pins36,38,40is covered by the DEF. Such discrete pins are employed in the reservoir14instead of a level sensing arrangement that may be capable of continuous fluid level detection, for example similar to the sensor28, because of the salt deposits that are typically formed by the urea-based DEF. However, when the vehicle10is on an incline, the level approximated with the aid of pins36,38,40may include significant error. Such error may be sufficient to prevent reliable assessment as to the proper instance for the refill of DEF13, and of the volume required.

Referring back toFIG. 1, the system12also includes a controller42that is operatively connected to engine18. The controller42is operatively connected to each of the fuel tank26, the sensor28, and the reservoir14. The controller42is programmed to receive a signal from sensor28indicative of the sensed level of fuel24in the fuel tank26. The controller42is also programmed to determine whether vehicle10is positioned on an incline or driving in an inclined state using the signal indicative of the sensed level of fuel24in the fuel tank26. The controller42may be a stand-alone unit, or be part of an electronic controller that regulates the operation of engine18.

The controller42is additionally programmed to determine the level of DEF13in the reservoir14if the vehicle10is determined to be substantially not on an incline, i.e., substantially level or in a horizontal plane. Whether the vehicle10is substantially not on an incline may be established via a determination of the level of diesel fuel24in the fuel tank26during the most recent instance in which the fuel tank was replenished during a fuel-fill event. To determine whether or not the vehicle10is currently on an incline, the controller42may be programmed to compare a level of fuel24sensed during the most recent instance the vehicle was not on an incline and the level of fuel24sensed by the sensor28currently. Based upon the knowledge of the physical characteristics of the fuel tank26, the difference between the fuel level sensed during the most recent filling event and the currently sensed level may be used to infer or calculate to a reasonable certainty the magnitude of the incline that the vehicle is on at the present time.

When the vehicle10is in motion it may traverse non-flat ground, and, as such, sensor28may indicate a level of fuel24in the fuel tank26that is greater or smaller than actual. Likewise, as described above, when the vehicle10is on an incline, the level of DEF13in the reservoir14may be indicated erroneously. On the other hand, it may generally be assumed that during a fuel-fill event at a fuel filling station vehicles are positioned substantially in a horizontal plane, such as within 1-2 degrees from horizontal. The determination that currently the vehicle10is substantially not on an incline may be generated if the magnitude of the calculated incline is below a predetermined value44. In a non-limiting example, such a predetermined value may be up to approximately 10 degrees in order to provide a reasonable tolerance band for refilling reservoir14with DEF13.

The value44may be predetermined empirically during the testing and development of the vehicle10to ensure that the reading of the level in DEF13at such an incline does not generate a significant unwanted error. The value44may also be programmed into controller42. The controller42may additionally be programmed to generate a sensory signal46indicative of a required refill of the reservoir14with DEF13. Such a sensory signal46may be displayed on an instrument panel48of the vehicle10as a visual alert in order to notify the vehicle's operator of the required refill of the reservoir14.

FIG. 3depicts a method50of detecting a level of DEF13in reservoir14as described with respect toFIG. 1. Accordingly, the method commences in frame52, where it includes sensing a level of diesel fuel24in the fuel tank26via sensor28. Following frame52, the method proceeds to frame54, where it includes determining whether the vehicle10is on an incline using the sensed level of diesel fuel24in the fuel tank26.

As described with respect toFIG. 1above, the determination of whether the vehicle10is on an incline may include determining a magnitude of the incline. Accordingly, the vehicle10may be termed as being substantially not on an incline when the magnitude of the determined incline is below the predetermined value44. The determination of whether the vehicle10is on an incline may additionally include comparing a level of fuel24in the fuel tank26that was sensed during the most recent instance in which the vehicle was not on an incline, such as during a fuel-fill event, and a level of the fuel sensed currently.

After the determination of whether vehicle10is on an incline is made in frame54, the method advances to frame56. In frame56, the method includes determining the level of DEF13in reservoir14if the vehicle10is determined to be substantially not on an incline. Following frame56, the method50may proceed to frame58, where the method includes using controller42to generate the sensory signal46indicative of a required refill of the reservoir14. Following frame58, and after the refill of the reservoir14has been accomplished, the method may loop back to frame52and restart the detection of the level of DEF13in the reservoir.